Coal Quality Monitoring

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Commission of the European Communities

t e c h n i c a l c o a l r e s e a r c h

COAL QUALITY MONITORING

Report

EUR 13351 EN

Blow-up from microfiche original



y

Commission of the European Communities

t e c h n i c a l c o a l r e s e a r c h

COAL QUALITY MONITORING

BRITISH COAL

Headquarters Technical Department

Ashby Road, Stanhope Bretby

UK-Burton-on-Trent, Staffs. DE15 OQD

Contract No 7220-EA/812

FINAL REPORT

Research work carried out with financial aid from

the European Coal and Steel Community.

1991

Directorate-General Energy

|Ü MJ WI v

iV nL l i î RC P . B iblio th

£UR 13351 EN

| C E.



Published by the

COMMISSION OF THE EUROPEAN COMMUN ITIES

Directorate-General

Telecommunications, Information Industries and Innovation

L 2920 LUXEMBOURG

LEGAL NOTICE

Neither the Comm ission of the European Com mun ities nor any person acting on behalf

of the Commission is responsible for the use which might be made of the following

information

Catalogue number: CD-NA-13351-EN-C

© ECSC — EEC — EAEC, Brussels - Luxemb ourg, 1991



III

FOREWORD

This work was undertaken jointly by the Coal Preparation Division

of the Mining Research and Development Establishment (now Headquarters

Technical Department) and by Scientific Control Department.

Development and laboratory work was carried out at:-

M.R.D.E., Bretby (later HQTD)

HQ Scientific Control, Harrow

Scottish Area Laboratory, Edinburgh

Yorkshire Regional Laboratory, Wath (later SCL(N))

East Midlands Region Laboratory, Mansfield (later SCL(S))

On site work was carried out at:-

Bilsthorpe Colliery

Mantón Colliery

Askem Colliery

Markham Colliery

Longannet Colliery

This report was prepared by M P Armstrong (Coal Preparation) and D Page

(Scientific Control).



SYNOPSIS

This work has been undertaken to advance the development and

application of on-line coal quality monitoring in response to the

increasing need for real-time information to improve quality and

increase operational efficiency. In particular, factors affecting the

application and performance of ash and moisture measurement have been

studied.

Laboratory studies of ash content measurement utilising low energy

gamma radiation have demonstrated that the lower limit of measurement

accuracy is mainly controlled by variations in ash composition, and

reliable estimates of potential accuracy can be made from a knowledge

of the ash composition.

On-belt trials of two commercial ash monitors have shown the potential

for significant errors arising from other sources and the need to

ensure that instruments are applied in such a way that a fully

representative portion of the coal stream is interrogated.

In some circumstances, it may be more practical to monitor a sub-stream

of coal and a presentation unit has been developed which is capable of

handling wet coal, up to 25 mm top size, and producing a continuous bed

of coal suitable for interrogation by ash or moisture meters.

A previously developed, single frequency, microwave moisture meter has

been improved and, in conjunction with a specially developed ultrasonic

bed depth meter, the feasibility of measuring moisture content of coal

directly on a conveyor belt demonstrated.

A new moisture meter, which is less sensitive to the disturbing

influences of coal type, particle size and sample geometry, and which

is based on the attenuation of continuously varying frequency

microwaves, has been developed and tested satisfactorily.

A new type of capacitance moisture meter has been designed and built.

Laboratory tests on an experimental unit have demonstrated that a

reasonable accuracy is obtainable but some technical problems remain.

Development to a commercial prototype was not considered justifiable

because of high cost estimates.

A capability study of nuclear magnetic resonance techniques for

measuring moisture in coal has been made. Although reasonable accuracy

is obtainable with small volume samples, translation of the technique

to large scale on-stream monitoring is not considered to be worthwhile

because of the necessity to develop high capital cost equipment.

A survey of the status of on-line neutron gamma analysers has been

made. Their capability to measure most of the quality parameters of

coal, to a useful degree of accuracy, has been demonstrated but

applications are restricted by the high capital cost of the equipment.



VII

CONTENTS

Page

FOREWORD III

SYNOPSIS V

1. INTRODUCTION 1

1.1 General 1

1.2

Obj ectives

1

1.3 Programme of Work 1

1.4 Allocation of Work 2

2.

MAIN-STREAM ASH MONITORING - WULTEX ASHMETER 3

2.1 Design and Operation 4

2.2 Previous Investigations and Testing by British Coal 5

2.2.1 Preliminary Laboratory Calibration 5

2.2.2 Initial Trial at Mantón Colliery 5

2.3 Theoretical Assessment of Calibration Accuracy 7

2.4 Further Laboratory Investigations 7

2.4.1 Bed Depth Effects 7

2.4.2 Calibration Tests 9

2.4.3 Appraisal of Calibration Tests 10

2.5 Trial Installation at Bilsthorpe Colliery 11

2.5.1 Consideration of Requirements for Second Trial

Installation 11

2.5.2 Description of Trial Site at Bilsthorpe Colliery 11

2.5.3 Installation of Ashmeter 12

2.5.4 On-site Calibration Tests 12

2.5.5 Shift Integration Tests 14

2.6 Re-design of Ashmeter Electronics by SCL(N) 15

2.6.1 Original Polish design 15

2.6.2 Re-designed System 15

2.6.3 Information Available From Re-designed System 16

2.7 Further Trials at Mantón Colliery 17

2.7.1 Description of Installation 17

2.7.2 Dynamic Calibration Test Procedure 17

2.7.3 Dynamic Calibration Test Results 18

2.7.4 Train-load Integration 18

2.8 Further Installations 19

2.9 Summary 19



VIII

3. MAIN-STREAM ASH MONITORING - COALSCAN 3500 ASH MONITOR 20

3.1 Principle of Ash Measurement 21

3.2 Description of Commercial Unit 21

3.3 Calibration, Operation and Standardisation 22

3.4 Laboratory Investigations 23

3.4.1 Arrangements and Objectives 23

3.4.2 Setting-up Procedure 24

3.4.3 Results 26

3.5 On-Line Trials at Askem Colliery 29

3.5.1 Purchase Agreement and Installation 29

3.5.2 Commissioning and Calibration of Coalscan 3500 30

3.5.2.1 Preparatory Investigations 30

3.5.2.2 Commissioning and Preliminary Calibration 31

3.5.2.3 On-line Dynamic Calibrations 1 to 5 31

3.5.3 Investigation of Segregation on Belt 32

3.5.4 Further Dynamic Calibrations and Investigations 33

3.5.5 Performance Test 34

3.5.6 Sampling Precision 35

3.5.7 Further Investigation of Cross-belt Segregation 35

3.5.8 Seventh Dynamic Calibration Test 36

3.5.9 Comparison of Static and Dynamic Calibrations 38

3.5.10 Shift Integration Performance and Comparison with

Phase 3A Ash Monitor 3g

3.6 Summary 42

4. SUB-STREAM ASH MONITORING

4 3

4.1 Previous UK Experience and Problems 43

4.2 Previous Development of New Presentation System 44

4.3 Design of Trial Site at Markham Colliery 46

4.4 Design and Construction of New Experimental Ram-feed Unit 47

4.5 Testing of Ram-feed Unit at Markham Test Site 47

4.6 Design and Manufacture of Pre-production Prototype Unit 50

4.7 Nucleonic Ash Measuring and Signal Processing System 51

4.7.1 Design of Ash Measuring and Control System 51

4.7.2 Operation of Ash Measuring and Control System 51

4.7.3 Radiation Safety Precautions 52

4.7.4 Manufacture and Testing 53



IX

4.8 Summary 53

5. MICROWAVE MOISTURE MONITORING 54

5.1 Review of Previous Development and Testing by British Coal 54

5.1.1 Early Investigations 54

5.1.2 Microwave Bands 54

5.1.3 Earlier Applications 55

5.1.4 Previous Development and Application of X-band System 55

5.1.5 Previous Development and Application of an S-band System 56

5.1.6 Limitations to Application of S-band System 56

5.2 Developments for On-belt Microwave Moisture Monitoring 57

5.2.1 Instrumentation Requirements 57

5.2.2 Moisture Meter Electronics 57

5.2.3 Data Logger 59

5.2.4 Ultrasonic Bed Depth Meter 59

5.2.5 Trial Installation of On-belt, S-band Moisture Monitor 60

5.2.5.1 Description of Installation 60

5.2.5.2 Results of On-site Trials at Longannet 61

5.3 Swept Frequency Microwave System 61

5.3.1 Limitations of Single Frequency Systems 61

5.3.2 Principle of 2 Frequency Measurement 62

5.3.3 Effect of Variable Geometry 63

5.3.4 Experimental Laboratory Equipment 64

5.3.5 Laboratory Test Procedure 65

5.3.6 Testing of Seams from Blindwells Opencast Site 65

5.3.7 Appraisal of Test Results 65

5.4 Summary 66

6. CAPACITANCE MOISTURE MONITORING 67

6.1 Previous Investigations, Applications and Development by

British Coal 67

6.1.1 Early Investigations 67

6.1.2 Further Development and Testing 67

6.2 Insulated Plate Capacitance Moisture Monitor 68

6.2.1 Proposed Development 68

6.2.2 Design of Experimental Laboratory System 69

6.2.3 Laboratory Tests with Experimental Cell - Series I 71

6.2.4 Laboratory Testing of Experimental Cell - Series II 72

6.2.5 Proposed Further Investigations 72



7. DETERMINATION OF MOISTURE IN COAL BY NUCLEAR MAGNETIC RESONANCE 73

7.1 Introduction 73

7.2 Principle and Measurement Techniques 73

7.3 Review of Work to Date 74

7.4 Potential For On-Line Monitoring 76

7.5 Summary 77

8. THE APPLICATION OF NEUTRON/GAMMA INTERACTIONS TO ON-LINE

COAL ANALYSIS 77

8.1 Basic Principles and Techniques 77

8.2 General Review of On-line Applications 79

8.3 Commercially Available Analysers 79

8.3.1 Science Applications International Corporation 79

8.3.2 MDH-Motherwell Inc. 81

8.3.3 Gamma-Metrics 82

8.3.4 Summary of Performance Capabilities 83

8.3.5 Installations 83

8.4 Summary 84

9. GENERAL CONCLUSIONS 85

9.1 On-stream Ash Monitoring 85

9.2 Sub-stream Ash Monitoring 86

9.3 Microwave Moisture Monitoring 86

9.4 Capacitance Moisture Monitoring 86

9.5 Nuclear Magnetic Resonance 87

9.6 Neutron/gamma Analysis of Coal 87

REFERENCES 89

APPENDICES

1. EXTRACT FROM HEADS OF AGREEMENT CONTRACT BETWEEN THE NCB AND

WULTEX MACHINE CO. LTD. FOR THE TRIAL OF A WULTEX RADIOMETRIC

ASHMETER, TYPE G-3, AT MANTÓN COLLIERY 95

2.

CALCULATION OOF CALIBRATION ACCURACY FROM COAL COMPOSITION. 97



X I

3. TECHNICAL APPENDIX TO HEADS OF AGREEMENT CONTRACT FOR

EXPERIMENTAL USE OF WULTEX RADIOMETRIC ASHMETER EQUIPMENT -

OBJECTIVES, DIRECTION AND REVIEW OF TRIAL. 99

4. WULTEX RADIOMETRIC ASHMETER - SITE REQUIREMENTS FOR PROPOSED

SECOND TRIAL INSTALLATION. 103

5. HEADS OF AGREEMENT CONTRACT BETWEEN THE NCB AND WULTEX MACHINE

CO.

LTD. FOR THE TRIAL OF A WULTEX RADIOMETRIC ASHMETER AT

BILSTHORPE COLLIERY, NORTH NOTTINGHAMSHIRE AREA - APPENDIX II

ACCEPTANCE CRITERIA FOR TRIAL. 105

6. TECHNICAL APPENDIX TO AGREEMENT FOR THE TRIAL OF A COALSCAN 3500

ASH MONITOR - OBJECTIVES, DIRECTION AND REVIEW OF TRIAL. 109

7.

EXTRACT FROM HEADS OF AGREEMENT CONTRACT BETWEEN THE NCB AND

MAGCO LTD. FOR THE TRIAL OF A COALSCAN 3500 ASH MONITOR AT

ASKERN COLLIERY, SOUTH YORKSHIRE AREA - APPENDIX II, ACCEPTANCE

CRITERIA FOR TRIAL. Ill

8. SPECIFICATION FOR THE DESIGN AND MANUFACTURE OF A PRE-PRODUCTION

PROTOTYPE RAM-FEED UNIT. 115

9. ASH MEASURING AND CONTROL SYSTEM FOR RAM-FEED ASH MONITOR -

SPECIFICATION OF MAIN PROPRIETARY COMPONENTS. 119

10.

SPECIFICATION FOR X BAND MICROWAVE MOISTURE METER. 123

11.

SPECIFICATION FOR S BAND MICROWAVE MOISTURE METER. 125

12.

TECHNICAL SPECIFICATION FOR ULTRASONIC BED-DEPTH METER. 127

13. LABORATORY SWEPT FREQUENCY MICROWAVE MOISTURE SYSTEM -

SPECIFICATION OF MEASURING EQUIPMENT. 129

14.

SOME ASPECTS OF THE THEORY OF CAPACITANCE MOISTURE MONITORING. 133

15. SPECIFICATION FOR AN ELECTRONICS PACKAGE FOR EXPERIMENTAL

CAPACITANCE MOISTURE MONITORING. 137

TABLES

1. Results of Previous Testing of Wultex Radiometric Ashmeter. 145

2.

Summary of Results of Laboratory Calibration Tests with Wultex

Ashmeters at

SCL(N).

146

3. Results of Calibrations Tests with Wultex Ashmeter on Bllsthorpe

Blended Smalls. 147

4. Laboratory Investigations with Coalscan 3500 Ash Monitor •

Results of Tests to Assess Statistical Counting Error Using

Calibration Standard. 148



XII

5. Laboratory Investigations with Coalscan 3500 Ash Monitor -

Variations in Log Ratio Values Due to Changes in Bed Thickness.

18.

Results of Second Series of Laboratory Tests with Experimental

Insulated Plate Capacitance Cell.

149


Effect of Magnetite Addition to Coal Sample. 150


Effect of Calcium Carbonate Addition to Coal Sample. 15]


Effect of Kaolin Addition to Coal Sample. 152

9. Laboratory Calibration Tests with Coalscan 3500 Ash Monitor. 153

10.

Laboratory Investigations with Coalscan 3500 Ash Monitor -

Effect of Increasing Number of Static Measurements with Prepared

Samples of 25-3 mm Askem Blended Coal. 154

11.

Coalscan 3500 Ash Monitor Trial, Askem Colliery - Summary of

On-site Calibration and Performance Tests. 155

12. Coalscan 3500 Ash Monitor Trial, Askern Colliery - Results of

Investigation of Cross-belt Segregation with Oscillating Head,

Barium Source and 2 second Counting Periods. 156

13.

Experimental Ram-feed Presentation Unit with Plutonium 238

Isotope Measuring Head and Fe Correction • Laboratory

Calibration Tests on Markham Power Station Blend and Comparison

with Telsec 350 Analyser. 157

14.

Experimental Ram-feed Presentation Unit Trial, Markham Colliery

- Typical Sizing Analyses of Power Station Blend and Crushed

Product with Different Size Crusher Grids. 158

15.

Analyses of Seams from Blindwells Opencast Site Tested with the

Laboratory Swept Frequency Microwave System. 159

16. Results of Laboratory Swept Frequency Tests on a Range of Seams

from Blindwells Opencast Site. 160

17. Results of First Series of Laboratory Tests with Experimental

Insulted Plate Capacitance Cell and Different Concentrations of

Ionic Salt Solutions. 161

162

19. Calibration Tests with the Newport Mark IIIA Analyser. 163

20.

Summary of work on Moisture Measurement by NMR Spectrometry. 164

21.

Commercially Available Multielement Analysers. 165



XIII

22. Accuracy of CONAC (+1 s

wt%).

166

23.

Precision of CONAC (+1 s

wt%).

167

24.

Accuracy of ELAN (wt

) .

168

25. Precision and Accuracy of GM Coal Analyser. 169

26. Relative Accuracy of Neutron Gamma Analysis. 170

27. Units Currently Installed or Ordered. 171

FIGURES

1. Wultex Radiometric Ashmeter, Type G3 - General Arrangement on ,,-

Belt Conveyor.

2.

Wultex Radiometric Ashmeter, Type G3 - Sectional View of Isotope

Measuring Head. 174

3. Wultex Ashmeter - Theoretical Effect of Bed Depth on Countrate

for 3 Levels of Ash Content and 2 Levels of Bulk Density. 175

4.

Wultex Ashmeter - Variable Depth Sample Presentation Box for

Laboratory Investigations. 176

5. Wultex Ashmeter * Effect of Bed Depth on Ash Measurement at Two

Levels of Bulk Density with Sample from Bilsthorpe PSF Blend. 177

6. Wultex Ashmeter - Effect of Bed Depth on Ash Measurement at Two

Levels of Bulk Density with Sample from Mantón Middlings. 178

7. Wultex Ashmeter - Effect of Bed Depth on Ash Measurement at Two

Levels of Bulk Density with Sample from Gedling Middlings. 179

8. Laboratory Calibration for Mantón 50 mm - 0 Blended Coal with

Wultex (UK) Ashmeter. 180

9. Laboratory Calibration for Mantón 50 mm - 0 Blended Coal with

Wultex (Polish) Ashmeter.

10.

Laboratory Calibration for Mantón 50 mm - 0 Untreated Coal with

Wultex (UK) Ashmeter.

11.

Laboratory Calibration for Mantón 50 mm - 0 Untreated Coal with


181

182

183

12.

Laboratory Calibration for Askem 25 mm - 0 Blended Coal with

Wultex (Polish) Ashmeter. 184

13.

Laboratory Calibration for As kem 25 mm - 0 Untreated Coal with


185



XIV

14.

Laboratory Calibration for Askem 25 mm - 0 Washed Coal with


16. Laboratory Calibration for Bilsthorpe 50 mm - 0 Blended Coal

with Wultex (Polish) Ashmeter.

20.

Laboratory Calibration for Bilsthorpe 50 mm - 0 Washed Coal with


186

15.

Laboratory Calibration for Bilsthorpe 50 mm - 0 Blended Coal

with Wultex (UK) Ashmeter. 187

188

17. Laboratory Calibration for Bilsthorpe 38 mm - 0 Untreated Coal


190

8.

Laboratory Calibration for Bilsthorpe 38 mm - 0 Untreated Coal

with Wultex (Polish) Ashmeter.

19. Laboratory Calibration for Bilsthorpe 50 mm - 0 Washed Coal with


192

21.

Laboratory Calibration for Cotgrave 50 mm - 0 Blended Coal with


22. Laboratory Calibration for Cotgrave 50 mm - 0 Blended Coal with

Wultex (Polish) Ashmeter. 194

23.

Laboratory Calibration for Lea Hall 25 mm - 0 Blended Coal with


24.

Laboratory Calibration for Daw Mill 12.5 mm - 0 Untreated Coal


25.

Laboratory Calibration for Cwm 50 mm - 0 Washed Coal with Wultex

(UK) Ashmeter. 197

26.

Laboratory Calibration for Sharlston 50 mm - 0 Washed Coal with

Wultex (UK) Ashmeter.

1 9 8

27. Laboratory Calibration for Grimethorpe 50 mm - 0 Blended Coal

with Wultex (UK) Ashmeter. I99

28.

Laboratory Calibration for Grimethorpe 50 mm - 0 Untreated Coal


29. Laboratory Calibration for Grimethorpe 50 mm - 0 Washed Coal


30.

Relationship between Standard Deviation Calculated from Full

Elemental Analysis and Measured Standard Deviation for

Laboratory Calibration Tests with Wultex Ashmeter. 202



XV

31.

Relationship between Standard Deviation derived from Iron and

Ash Analysis only and measured Standard Deviation for Laboratory

Calibration Tests with Wultex Ashmeter. 203

32. Schematic Arrangement of Wultex Ashmeter Installation at

Bilsthorpe Colliery. 204

33.

Schematic Arrangement of Wultex Ashmeter Installation at Mantón

Colliery. 205

34.

Wultex Ashmeter Installation at Mantón Colliery - Dynamic

Calibration Test 1. 206

35.

Wultex Ashmeter Installation at Mantón Colliery - Dynamic

Calibration Test 2. 207

36. Schematic Illustration of the Principle of Operation of the

Coalscan 3500 Ash Monitor. 208

37. Radiation Spectrum for Coalscan 3500 Ash Monitor with americium

and barium Sources. 209

38.

Schematic Arrangement of Commercial Design of Coalscan 3500 Ash

Monitor. 210

39.


Variation of Log Ratio Standard Deviation with Duration of

Counting Period. 211

40.


Effect of Chemical Additions on Measurement of Ash Content. 212

41.

Laboratory Calibration for Askern Blended Coal (-212 pi) with

Coalscan 3500 Ash Monitor. 213

42.

First Laboratory Calibration for Gascoigne Wood Untreated Coal

(-212 p ) with Coalscan 3500 Ash Monitor. 214

43. Second Laboratory Calibration for Gascoigne Wood Untreated Coal

(-212 um) with Coalscan 3500 Ash Monitor. 215

44.

Laboratory Calibration for South Side (Grimethorpe) Blended Coal

(-212 p ) with Coalscan 3500 Ash Monitor. 216

45.

Laboratory Calibration for Askern Blended Coal (-212 p ) , from

Fourth Dynamic Calibration, with Coalscan 3500 Ash Monitor. 217

46.

Laboratory Calibration for Askern Blended Coal (-1 mm ), from

Fourth Dynamic Calibration, with Coalscan 3500 Ash Monitor. 218

47. Laboratory Calibration for Askern Simulated Blended Coal (25 -

3.18 mm) with Coalscan 3500 Ash Monitor.

2 1 9



XVI

48.

Schematic Arrangement of Coalscan 3500 and NCB/AERE Phase 3A Ash

Monitors at Askem Colliery. 220

49. On-site Static Calibration for Askem Blended Coal (-212 pn)

with Coalscan 3500 Ash Monitor. 221

50.

First Dynamic Calibration for As kem Blended Coal (25 mm - 0)


51.

Static Calibration for Askem Blended Coal Samples (-212 p»)

from First Dynamic Calibration with Coalscan 3500 Ash Monitor. 223

52. Third Dynamic Calibration for Askem Blended Coal (25 mm - 0)


53.

Fourth Dynamic Calibration for Askem Blended Coal (25 mm - 0)


54.

Fifth Dynamic Calibration for Askem Blended Coal (25 mm - 0)


55. Sixth Dynamic Calibration for Askem Blended Coal (25 mm - 0)


56. Coalscan 3500 Ash Monitor Trial at Askem Colliery - Variation

of Barium Countrate, in 2 second Periods, during Oscillation of

Measuring Head across Product Stream with 18 second Cycle Time. 228

57.

Coalscan 3500 Ash Monitor Trial at Askem Colliery • Variation

of Mean Calculated Ash Content with Mean Barium Countrate during

Oscillation of Measuring Head for 13 minute Test Period. 229

58.

Performance Test Calibration for Askem Blended Coal (25 mm - 0)


59. Coalscan 3500 Ash Monitor Trial at Askem Colliery - Variation

of Barium Countrate and Ash Content Measurements as Measuring

Head Oscillated over Stationary Conveyor spread with Even Layer

of Well Mixed -1 mm Coal Sample. 231

60.

Coalscan 3500 Ash Monitor Trial at Askem Colliery - Variation

of Americium and Barium Countrates and Computed Ash Content as

Measuring Head, with Standardisation Radiation Absorbers 232

attached to Detector, Oscillated over Conveyor Running Empty.

61.

Seventh Dynamic Calibration for Askem Blended Coal (25 mm - 0)


62. Static Calibration for Askem Blended Coal Samples (-212 pi)

from Seventh Dynamic Calibration with Coalscan 3500 Ash Monitor.

234

63.

Coalscan 3500 Ash Monitor Trial at Askern Colliery -

Relationship between Coalscan Shift Integration and Laboratory

Shift Analysis for 99 Shifts. 235



XVII

64.

Coalscan 3500 Ash Monitor Trial at Askem Colliery -

Relationship between Coalscan Shift Integration and Laboratory


65.

Phase 3A Ash Monitor Installation at Askern Colliery -

Relationship between Phase 3A Shift Integration and Laboratory


66. Coalscan 3500 Ash Monitor Trial at Askern Colliery - Difference

between Coalscan Shift Integration and Laboratory Shift Analysis

for 99 Shifts. 238

67. Coalscan 3500 Ash Monitor Trial at Askern Colliery - Difference

between Coalscan Shift Integration and Laboratory Shift Analysis

for 108 Shifts. 239

68.

Phase 3A Ash Monitor Installation at Askern Colliery -

Difference between Phase 3A Shift Integration and Laboratory


69. NCB/AERE Phase 3A Ash Monitor for Sub-Stream Monitoring

(9612/1).

241

70.

Sketch of Original Design of Experimental Ram-feed Sample

Presentation Unit for Sub-Stream Monitoring. 242

71.

Modified Experimental Ram-feed Presentation Unit incorporating

Stainless Steel Trough and Showing Nucleonic Measuring Head

Mounted on Indpendent Supports (9398/2). 243

72.

Experimental Ram-feed Presentation Unit - Typical Relationship

between Backscatter Countrate and Material Compression. 244

73.

Experimental Ram-feed Presentation Unit - Hydraulic Pressure

required to produce increasing Material Compression at Different

Moisture Levels.

77. Trial of Experimental Ram-feed Unit at Markham Colliery - Sizing

Curves for 50 mm - 0 Blended Coal and Products from Crusher with

Different Size Crusher Grids.

245

74.

Schematic Arrangement of Colliery Sampling System and Ram-feed

Unit Trial Circuit at Markham Colliery. 246

75.

Re-designed,Experimental Ram-feed Presentation Unit, for

Installation at Colliery Trial Site, with Second Outlet for

Scrapings and Proposed Feed and Reject Screw Conveyors. 247

76. Re-designed, Experimental Ram-feed Unit Installed at Colliery

Trial Site with Feed Screw Conveyor delivering to Feed Hopper

and Compacted Material in Presentation Trough (12,056/1). 248

249



X V I I I

78. Trial of Experimental Ram-feed Presentation Unit at Colliery

Site - Surface Profile of Compacted Bed with Coarse (-25 mm)

Material

(12,056/3).

250

79.

Trial of Experimental Ram-feed Presentation Unit at Colliery

Site - Surface Profile of Compacted Bed with Fine (-6 mm)

Material

(12,056/2).

251

80.

Diagram illustrating Main Design Features of Prototype Ram-feed

Presentation Unit. 252

81. General Arrangement Drawing of Prototype Ram-feed Presentation

Unit.

253

82. General View of Prototype Ram-feed Presentation Unit with

Polypropylene Trough Section following Stainless Steel

Compression Zone (Ramsey

10958).

254

83.

Rear View of Prototype Ram-feed Presentation Unit showing

Cut-outs in Feed Chute Casing for Level Sensors and Hydraulic

Cylinder Enclosure (Ramsey

10960).

255

84.

Block Diagram of Ash Measuring and Control System for Prototype

Ram-feed Ash Monitor. 256

85.

Block Diagram of Solid State X Band Microwave Moisture Meter. 257

2 5 8

6.

NCB/AERE Phase 3A Ash Monitor incorporating X Band Microwave

Moisture Meter.

87. Colliery Computer at Longannet Mine used for Computing Tonnage

Weighted Calorific Value from Ash/Moisture Monitor and Belt

Weigher Signals.

88.

Dedicated Microprocessor System at Monktonhall Colliery for

Display and Print-out of Integrated Ash, Moisture and Computed

Calorific Values.

2 5 9

2 6 0

89.

Prototype S Band Discrete Sample, Microwave Moisture Meter. 261

90.

Schematic Diagram of Re-designed Fixed Frequency, Microwave

Moisture System with High (60 dB) Dynamic Range. 262

91. Diagram of Data Logger recording signals from Phase 3A

Ash/Moisture Monitor. 263

92. Diagram of Data Logger recording signals from Belt Weigher and

Bed Depth and Moisture Meters. 264

93.

Block Diagram showing Design of Ultrasonic Bed Depth Meter. 265



X I X

94.

Schematic Arrangement of On-belt S Band Moisture Meter,

Ultrasonic Bed-depth Meter and Phase 3A Ash/Moisture Monitor

with Data Loggers at Longannet Mine. 266

95.

Trial Installation of S Band Microwave Moisture Meter and

Ultrasonic Bed-depth Meter on 25 mm - 0 Raw Coal Conveyor at

Longannet Mine with Instrumentation and Data Logger located

alongside in Protective Cabinet

(12,399/1).

267

96. Trial Installation S Band Moisture Meter at Longannet Mine

showing Microwave Transmitting Horn and Ultrasonic Bed-depth

Meter mounted above Belt Conveyor and Microwave Receiving Horn

located below (12,399/2). 268

97. Trial of S Band, On-belt, Microwave Moisture Meter and

Ultrasonic Bed-Depth Meter at Longannet Mine - Traces of

Bed-depth, Attenuation and Belt Loading plotted at 1 Minute

Intervals on 22 January 1988. 269

98.

Trial of S Band, On-belt, Microwave Moisture Meter and

Ultrasonic Bed-depth Meter at Longannet Mine • Traces of

Bed-depth, Attenuation and Belt Loading averaged over 5 Minute

Intervals on 22 January 1988. 270

99. Trial of Ultrasonic Bed-depth Meter at Longannet Mine -

Calibration Graph of Belt Weigher Readings against Bed-depth

Meter Readings integrated over 5 Minute intervals during 5 hour

period on 22 January 1988. 271

100.

Schematic Diagram of Proposed Two Frequency Microwave Moisture

Meter. 272

101. Schematic Arrangement of Laboratory Swept Frequency Microwave

System. 273

102. Laboratory Swept Frequency Microwave System - Attenuation Scan

(5-7 GHz) and Linear Regression for Parrot Crop Seam with 14.3%

Moisture. 274



Moisture. 275



Moisture. 276



Moisture. 277



XX



Moisture. 278



Moisture. 279



Moisture. 280



Moisture. 281

110. Laboratory Swept Frequency Microwave System - Calibration Graph

of Moisture Content against Attenuation/Frequency Gradient for

Parrot Crop Seam. 282


of Moisture Content against Weighted Attenuation/Frequency

Gradient for Parrot Crop seam. 283

112.

Laboratory Swept Frequency Microwave System - Calibration Graph

of Moisture Content against Attenuation/Frequency Gradient for

Seven Seams from Blindwells Opencast Site. 284


of Moisture Content against Weighted Attenuation/Frequency

Gradient for Seven Seams from Blindwells Opencast Site. 285

114. Electronic Measurement System for Experimental Insulated Plate

Capacitance Cell. 286

115. Electronic Measurement System for Experimental Insulated Plate

Capacitance Cell with Automatic Stabilisation of Buffer

Amplifier Output Signal. 287

116.

Laboratory Tests with Experimental Insulated Plate Capacitance

Cell - Relationship between Instrument Reading and Added

Moisture with Increasing Ionic Salt Content. 288

117. Laboratory Tests with Experimental Insulated Plate Capacitance

Cell - Calibration Graph for Washed Small Coal from Markham

Colliery. 289

118.

First Derivative Absorption Spectrum for Wet Coal. 290

119. Free Induction Decay Signal for Wet Coal. 291

120.

Regression Calibration for Suites 5 and 6. 292



XXI

121. Effect of Magnetite Additions on N.M.R. Instrument Reading. 293

122. S.A.I.C. 'CONAC' - Schematic Section 294

123.

MDH - Motherwell Inc. 'ELAN' - Schematic Section. 295

124.

Gamma Metrics 'Coal Analyser' - Schematic Section. 296



1. INTRODUCTION

1.1 General

The need for rapid or continuous monitoring of coal quality

continues to increase as customer requirements become more closely

specified and as producers and users seek to increase the efficiency of

operations to meet those demands. Ash and moisture contents are key

parameters in the assessment of the quality of coal in the majority of

its uses. Other factors of growing importance to the user, both for

operational and environmental reasons, are sulphur and chlorine contents

and ash analysis. The availability of real-time information on some or

all of these parameters will assist in the control of coal preparation

processes to meet specifications and to optimise operations, in terms of

cost and quality, and allow the confirmation of consignment quality

before despatch to the customer.

The classical methods of assessing coal quality by sampling,

preparation and laboratory analysis take at least 2 hours, and often

24 hours, to complete and, consequently, are of little use for plant

control purposes or pre-dispatch quality confirmation. Continuous coal

quality monitors, particularly for ash content, have been under

development and in use for 30 years but, until recently, were mainly

designed for use on sub-streams. Consequently, they often required a

considerable amount of expensive ancilliary equipment for sample

conditioning and were prone to handlability problems with many products.

1.2 Objectives

It was considered that the above problems could be largely overcome

if it was possible to make the necessary measurements, with sufficient

accuracy, directly on the product conveyor belt. Work on the

development of suitable methods and instrumentation is ongoing in a

number of countries and some commercially produced equipment has

appeared on the market. Às yet, however, reported experience on the

application of such techniques is fairly limited or confined to specific

areas of interest. It is also realised that in some circumstances the

nature of the product, the design and layout of a plant and a possible

requirement for more accurate measurements than are obtainable from

on-belt measurements could make a sub-stream monitoring system a more

suitable option.

The main objectives of this project are to advance the development

and application of main-stream on-belt monitoring for ash and moisture

contents and to develop sub-stream monitoring equipment which will

tolerate coals of difficult handlability with little or no conditioning.

1.3 Programme of work

In the field of on-belt ash monitoring the programme of work

undertaken was designed to include the on-site calibration and

performance testing of proprietary instruments based on the

back-scattering and transmission of low energy gamma radiation. In

addition, the influence of such factors as coal bed depth, and coal



composition variability on measurement accuracy was to be assessed in

both laboratory and on-site trials. On-belt moisture measurement had

not reached a commercial stage and work to study the extension of the

application of

a

British Coal developed sub-stream monitor

to direct

on-belt measurements was planned. The development of

a

new

microwave

technique, which should overcome some shortcomings of the

existing

system, was also to be pursued.

In the field of sub-steam monitoring, a major effort was to be

aimed at the production of a presentation unit which, with a minimum of

conditioning, could accept and present for interrogation by suitable ash

and moisture monitoring transducers, coal of particle sizes up to 50 mm.

Development of an improved capacitance-based moisture monitor

and

assessment of the potential for the use of nuclear magnetic resonance

was also to be undertaken.

Growing interest in the on-line measurement of other elements in

coal has resulted in the development of multi-element analysers based on

neutron-gamma techniques. An assessment of the performance, and

potential for application, of these analysers was also included in the

programme.

1.4 Allocation of work

This project was undertaken within British Coal by the Coal

Preparation Division of HQ Technical Department and Scientific Control

Department. The main division of the work was as follows:-

Coal Preparation Division

a) On site calibration trials of the Wultex and Coalscan ash meters

(in cooperation with Scientific Control)

b) Development and on-site trial of the Ram Feed Presentation Unit

c) Development of the Insulated Plate Capacitance Moisture Meter

Staff involved included:-

Coal Preparation Engineer

Engineer/Physicist

Electrical/Electronics Engineer

Scientific Control

i) Headquarters

a) Nuclear magnetic resonance studies

b) Assessment of neutron/gamma interaction applications


Senior Scientist/Nuclear Physicist



ii) Scottish Area Laboratory

Development and on-site trials of microwave moisture measurement

systems.

(This work subsequently transferred to Scientific Control Laboratory

(South)

SCL(S)).


Senior Scientist/Control Engineer

Scientist

Electronics Engineers

Coal Analysts and Technicians.

iii) Yorkshire Regional Laboratory (later Scientific Control Laboratory

(North) SCL(N))

a) Laboratory trials of on-stream ash monitor systems

b) On-site calibration trials of Wultex and Coalscan Ash Monitors

c) Ashmeter electronics redesign


Senior Scientists

Physicist

Process Engineer

Electronics Engineer and Technicians

Coal Analysts and Technicians

iv) East Midlands Regional Laboratory (later SCL(S))

On site calibration trial of Wultex Ashmeter.


Senior Scientists

Coal Analysts and Technicians

Throughout the on-site trials assistance was also received in the

organisation and execution of the trials, in the installation of

equipment and in the collection of samples from operational engineers

and other staff located at the collieries.

2.

MAIN-STREAM ASH MONITORING - WULTEX ASH METER

Main-stream ash monitoring is the continuous measurement of the ash

content of coal, in either a raw or prepared condition, by the

continuous examination of the main production stream at some suitable

location. The first of two types of main-stream ash monitors that have

been investigated and tested both in the laboratory and in a production

situation is the Wultex Radiometric Ashmeter.



2.1.

Design and Operation

The Radiometric Ashmeter was developed In Poland by the state coal

industry Research and Development Centre for Mining Mechanisation,

Electrotechnics and Automation Systems,

(EMAG).

It was designed for the

continuous measurement of the ash content of a small coal product

directly on a belt conveyor using a nucleonic backscatter technique(l).

The nucleonic measuring head is mounted behind a profiling plough

suspended by a parallelogram system from a supporting structure which

spans the belt conveyor, see Figure 1. The parallelogram system is

counterweighted so that the pressure of the profiling plough on the coal

is sufficient to produce a smooth surface profile and the required

degree of material compaction. The plough riding on the coal bed also

fulfills the important function of maintaining the measuring head at a

fixed height above the coal surface. If the flow of coal decreases such

that the coal bed reduces below the minimum depth the suspended frame

comes to rest against buffer stops and activates a switch to discontinue

the ash measurements. Hydraulic dampers are incorporated in the

parallelogram system to absorb any shocks to the system caused by sudden

changes in belt loading which might otherwise affect or damage the

measuring head. Because of the requirement to contact the coal and

produce a smooth surface profile the application of the Ashmeter is

restricted to coals which contain sufficient fines to facilitate this

and it is therefore not applicable to graded coals of large particle

size. The depth of material on the belt after profiling must also be

sufficient to ensure total absorption or backscatter of all the

radiation at the lowest ash content to be measured.

The measuring head, Figure 2, comprises the radioactive source

holder and the scintillation detector which continuously measures the

amount of radiation backscattered from the moving coal stream. Since

the ash forming elements in the coal absorb a higher proportion of the

radiation than the combustible elements the amount of backscattered

radiation measured by the detector decreases as the ash content of the

coal increases. A sliding shutter below the measuring head serves as

both a backscatter reference and as a radiation shield. On a later

design this shutter could be operated remotely by an electric actuator.

The radiation received by the scintillation detector produces

electrical pulses which are amplified for transmission to the electronic

signal processing and display unit which can be located up to 3 km from

the measuring head. The pulses are counted over a period of either

40 seconds or 2 minutes, as selected, and the pulse count is converted

to an ash value according to a pre-determined calibration for the

particular coal being monitored. The ash value is shown on a LED

display. A separate printer unit was required with the original design

of Ashmeter to provide a print out of the ash content every 40 seconds

or 2 minutes but a later design of the processing and display unit

incorporated a printer.



Technical Data - Polish Instrument

Coal size 30 mm (maximum) - 0

Depth of profiled material 150 mm minimum

Range of ash measurement 3% - 40%

Permissible variation in

moisture content + 4% on moisture content at calibration

Radioactive source Americium -241 50 mCi

Radiation detector Scintillation detector with sodium

iodide crystal

Electrical supply Instrument 240 V AC

Power requirements Instrument 100 VA (approx)

Accuracy of Ash Measurement - Based on Polish Installations

Ash

3 -

10 -

20 -

Previous

Range

10%

20%

40%

Investigations

(Root

Accuracy

Mean Square Deviation)

+ 1% ash

±1 . 5 % ash

+2.0 % ash

and Testing by British

Coal

.2

2.2.1 Preliminary Laboratory Calibration

A licence for the manufacture and supply of the Radiometric

Ashmeter outside Poland was negotiated with EMAG by Wultex Machine Co

Ltd of Huddersfield in early 1981. In May 1981, a Polish manufactured

ashmeter was made available to British Coal by Wultex for preliminary

laboratory tests at the Scientific Control Laboratory North (SCL(N)) -

formerly Yorkshire Regional Laboratory. The tests were conducted with

50 mm -0 blended power station coal from Mantón Colliery, where

production was coming only from the Parkgate seam, and gave a

calibration standard deviation of 1.02% ash for a quadratic regression.

This result was sufficiently encouraging to proceed with a trial

installation, under a Heads of Agreement Contract, at Mantón Colliery in

August 1981. Because of the possibility of coal from the neighbouring

Steetley Colliery being treated at Mantón in the near future, this coal

was also tested in the laboratory and gave a much poorer calibration

standard deviation of 1.96% ash for a quadratic regression.

2.2.2 Initial Trial at Mantón Colliery

Following on-site calibration checks at Mantón, a series of 100

tests were conducted during October 1981 in accordance with the

procedure laid down in the Heads of Agreement Contract, Appendix 1,

which required that for 95 tests out of 100 the measured ash content

should be within +2.5% of the laboratory determined ash content. Each

test extended over a 4 minute integration period during which time

between 30 and 32 sample increments were taken by a mechanical sampler

to provide a composite sample for laboratory analysis.



In addition to these acceptance tests the Ashmeter readings were

recorded and averaged over 1000 tonne train loads, corresponding to

approximately 4 hours production, and compared with laboratory ash

determinations for each consignment.

The results of these early investigations are given in Table 1.

The 100 test acceptance trials at Mantón gave an accuracy (2s) of ash

measurement of +2.58%. Only 4 tests lay outside the specified limits of

+2.5% ash after allowing for a mean bias of 1.1% between the Ashmeter

reading and the laboratory analysis. Only a small improvement in

accuracy (2s) to +2.3% ash was obtained when increasing the integration

period from 4 minutes to approximately 4 hours for train loads.

The reduced level of accuracy of the on-site ash measurements at

Mantón, as compared with the laboratory accuracy, was attributed in part

to the insufficient and variable depth of material on the conveyor belt.

Only by building up the levels in the blending bunkers, prior to each

4 minute test period, was it possible to maintain a reasonably

consistent flow rate of power station blend of around 300 t/h, which

corresponded to a bed depth of approximately 100 mm. During the loading

of each 1000 tonne train considerable variations could have occurred in

the belt loading so that the improvement in accuracy, that would have

been expected from a longer period of integration, was only partially

achieved.

The trial at Mantón continued for a period of six months in order

to check the mechanical and electrical reliability of the instrument, in

accordance with the terms of the Heads of Agreement, and no mechanical

or electrical problems arose during that period.

It was concluded from this trial that although the equipment had

proved mechanically and electrically reliable, there may be only a few

British collieries where the Wultex Ashmeter might be applied with

advantage. There would be many collieries where the inability to ensure

a sufficient and consistent material bed depth or where the production

of coal from several seams would adversely affect the accuracy of the

instrument. It was therefore decided to resume laboratory

investigations with the objectives of:-

(i) Evaluating the effect of material bed depth and bulk density

with the aim of devising a method of material presentation

so as to optimise the accuracy of the Ashmeter where the

required bed depth could not be achieved with the existing

material handling system

(ii) Assessing the possible wider application of the Ashmeter by

examining coals from multi-seam collieries and determining

the effect of variations in ash composition, in particular

the iron content, on the accuracy of the instrument.



2.3. Theoretical Assessment of Calibration Accuracy

The Wultex Ash Meter is based on the fact that at relatively low

energies (<100 keV) the intensity of radiation backscattered from a

substance is a function of its average atomic number (Z). If coal is

considered to be a 2 component mixture of ash forming minerals (Z

a

- 12)

and combustible elements (Z

c

- 6) then Z, and hence backscattered

intensity, can be related to the concentration of mineral matter, which

itself correlates with ash content.

This relationship between backscattered intensity and ash content,

however, is subject to variations from a number of sources, not least

being the assumptions that coal is a simple 2-component mixture and that

the atomic number of the ash-forming minerals (Z

a

) is constant. Given

that the coal is presented to the detector system in a well defined

geometry which allows representative interrogation of the sample, then

variability in the composition of the coal is the major perturbing

factor, usually due to changes in iron content of the ash

minerals(2).

The magnitude of composition variations can then be regarded as

controlling the lower limits on the accuracy of the method.

By using a simple model of the backscatter method and inserting

data on the composition of the coal and relevant gamma ray attenuation

coefficients it is possible to calculate the relative backscattered

radiation intensity from any sample of coal (Appendix 2). If this

procedure is followed for a range of coal samples the correlation

between calculated relative backscattered intensity and ash content can

be assessed and an estimate of ash concentration error predicted for

that set of coals.

This procedure has been followed for all the coals used in the

Wultex laboratory trials. The theoretical values of calibration

standard deviation are given in Table 2, together with the measured

values obtained in the laboratory trials.

2.4 Further Laboratory Investigations

A further Heads of Agreement Contract, Appendix 3, was negotiated

with Wultex Machine Co Ltd for a second Ashmeter to be made available on

loan for the proposed programme of laboratory investigations at

SCL(N).

This unit would be one of the first batch to be manufactured in the UK

by Wultex. Because of problems encountered by Wultex in the manufacture

of these units, in particular the reliability of the scintillation

detector, the start of this work was delayed until 1984. To try and

reduce the delay the original Polish Ashmeter was withdrawn from Mantón

Colliery to the laboratory but it required attention and no advantage

was gained. Eventually both the Mantón Ashmeter and the new Wultex

Ashmeter were used to duplicate the laboratory investigations.

2.4.1 Bed depth effects

A theoretical study of the possible effect of material bed depth

and bulk density on the ash measurement with the Wultex Ashmeter was



8

undertaken by Headquarters Scientific Control prior to the commencement

of laboratory trials. The theoretical effect of bed depth on the ash

measurement for three levels of ash content and two levels of bulk

density is shown in Figure 3. It was decided that the laboratory

investigations into the effect of bulk density would be limited to

confirming the validity of the theoretical curves but investigations

into bed depth would continue as originally planned.

Initial tests at SCL(N) to quantify the effects of bed depth and

compaction, using samples from normal commercial grades of coal, were

unsuccessful as the magnitude of the random errors made such effects

difficult to identify. The errors were further compounded by a degree

of detector instability present in the equipment at the time. The tests

were repeated using three prepared samples, each closely sized and

within a narrow range of relative density so that the inherent variation

in the density of the sample was minimised. The samples were presented

to the Ashmeters at a range of bed depths and were either loose-filled

or hand-compacted in the presentation container to give two levels of

bulk density.

The design of the presentation container used for these tests is

shown in Figure 4. The container comprised a rectangular wooden frame,

measuring 457 mm x 305 mm, with a loose wooden base which could be

positioned at four different levels to give depths of 80, 120, 160 and

200 mm. Â series of extension frames with depths varying from 6 mm to

32 mm, could be fitted to the top of the container to allow it to be

overfilled by a pre-determined amount. The material was then compacted

to the top of the container using a compression plate fitted with

spacers, selected to correspond with the extension frame being used, and

provided with compression stops to contact the top of the extension

frame and ensure that the surface of the compacted material corresponded

with the top of the original container. The extension frame was removed

before presentation to the measuring head. The lower degrees of

compaction could be achieved by hand but for greater compaction a

vibrating table was used.

The effect of varying bed depth on the measured ash content with

the three samples is shown in Figures 5, 6 and 7. The instrument

countrate readings were converted to ash content using appropriate

calibrations for the particular type of coal sample and Ashmeter. In

all cases the test results confirm the theoretical curves and show that

as the bed depth reduces below 200 mm there is a fall in countrate which

results in an increase in the indicated ash content. The effect of

reducing bed depth is slightly less with the compacted material but in

both cases the effect on ash measurement becomes significant when the

bed depth reduces below 150 mm and quite an appreciable error arises

when the depth falls to 100 mm. The tests also showed that a much more

uniform bulk density was achieved with a compacted bed than with a loose

fill.



2.4.2 Calibration Tests

Laboratory investigations into the possible range of application

of the Wultex Ashmeter to UK coals had started in 1984, prior to the

ECSC Project, and by March 1985 a total of 9 products from 4 collieries

had been tested. The selection of collieries had to be modified from

those originally planned because of the intervention of the industrial

action in 1984/5 in British Coal and coals from the Nottinghamshire

coalfield had to be substituted for those from Yorkshire. A further 7

products had been tested by mid-1986 and a summary of all 16 laboratory

calibration tests is given in Table 2.

All tests were conducted in accordance with a standard procedure.

Initial tests to investigate the repeatability of the countrate

measurements showed that the standard deviations for the 40 and 120

second counting periods were of the same order and there was no

advantage in extending the counting period beyond 40 seconds. These

preliminary tests also showed that a minimum of 10 separate

presentations were required for each sample.

Although on-site the Ashmeter would be calibrated against the

'as-received' laboratory analysis, this was not considered possible in

the laboratory because of the progressive loss of moisture that would

occur with the preparation and repetitive handling of the samples. The

laboratory tests were therefore conducted with all the samples in an

'air dried' condition. It was initially considered necessary for all

samples to be reduced below 25 mm top size to assist laboratory handling

and avoid segregation but this size reduction was not found to be

necessary and the majority of the products were tested at the original

size,

as shown in Table 2.

A standard bed depth of 200 mm, after a compaction of

approximately 9%, was used for all tests. The presentation box was

filled 5 times for each sample, with thorough mixing between each fill,

and the box was presented twice to the measuring head at each filling,

with the box being rotated through 180° for the second presentation.

Following the countrate measurements, each sample was prepared in

accordance with the requirements of BS1017 "Methods for the sampling of

coal and coke, Part 1: Sampling of Coal

(1977)"

to produce laboratory

samples for moisture, ash and ultimate analysis in accordance with the

relevant parts of BS1016 "Methods for analysis and testing of coal and

coke". In addition, the ash from each sample was subjected to full

chemical analysis.

For the first 9 calibration tests the isotope measuring heads for

both the UK manufactured Ashmeter and for the Polish made Ashmeter were

set up on the same test rig and the samples were presented to each

instrument in turn. However, because of the failure of the detector on

the UK instrument, tests 4 and 5 were conducted using only tne Polish

Ashmeter. Tests 10 onwards were conducted using only the UK Ashmeter

because the Polish instrument was being prepared for re-installation at

Mantón Colliery.



10

Where the calibration tests were conducted with both the UK and

Polish meters the results in Table 2 show that, with the exception of

Test 3 in which the detector on the UK meter was suspect, the level of

accuracy was approximately the same for both instruments.

2.4.3 Appraisal of Calibration Tests

A summary of the coal analysis and results of all 16 laboratory

calibration tests conducted with the Wultex Ashmeter is given in Table 2

and the calibration graphs are shown in Figures 8 to 29. With the

exceptions of Test 13, Sharlston Washed Coal, Test 15, Grimethorpe

(South Side) Untreated Coal and Test 3, Askem Blended Smalls using the

UK meter, all results show a good correlation between ash content and

count rate (Corr. coeff >0.87). The poor result for Test 3 (UK meter)

is attributed to the failing detector crystal and the low correlations

(<0.8) for Tests 13 and 15 to the highly variable iron content of ash.

Comparison of the measured calibration standard deviation values

with the theoretical values calculated from the full elemental analysis

shows a reasonable correlation, as illustrated in Figure 30. The

correlation coefficient between the measured and calculated standard

deviation was 0.853 and the standard deviation of the calculated values

with respect to the measured values was 0.31% ash.

The calibration accuracy for each test and, where appropriate, for

each instrument was also related to those characteristics of the

individual coals which were considered to have the greatest influence on

the calibration accuracy. These characteristics were:-

(a) the variability of the iron content of the coal, as measured

by the standard deviation; the greater the variability of

iron the poorer the expected accuracy.

(b) the relationship between the iron content and the ash

content, as given by the correlation coefficient; the

higher the correlation the greater the expected accuracy.

(c) the mean ash content of the coal; the higher the mean

ash the poorer the accuracy in absolute terms.

A multiple regression analysis, to 7 terms, between the measured

calibration accuracy and these three characteristics gave a very high

correlation coefficient of 0.973 and a standard deviation of 0.16% ash.

The graph of calculated calibration standard deviation from the

regression analysis against the measured standard deviation is shown in

Figure 31.

For this series of laboratory calibration tests the relationship

of the measured standard deviation with the combination of ash and iron

analysis was much closer than with the theoretical standard deviation

calculated from the full elemental analysis of the coal. The

possibility of using only the ash and iron analysis of the coal rather



11

than the full elemental analysis to predict the probable calibration

accuracy for ash measurement would result In a considerable saving both

in time and money, and would justify further investigations with other

nucleonic ash measuring systems.

2.5 Trial Installation at Bilsthorpe Colliery

2.5.1 Consideration of Requirements for Second Trial Installation

The requirement of a minimum bed depth of 150 mm for the effective

application of the Wultex Ashmeter would considerably restrict its use

on existing conveyors in the UK where, to limit capital cost, most coal

preparation plants were equipped with narrower and faster belt conveyors

resulting in reduced belt loading per unit length and bed depths in the

order of 75-125 mm. The first trial installation at Mantón Colliery was

monitoring a single seam output and, therefore, it was considered that

the second trial installation should be set a more severe test of

monitoring a multi-seam output. A further problem which occurred at

Mantón after the initial acceptance testing was that variable quantities

of coal from neighbouring collieries were sent for treatment to Mantón

which impaired the accuracy of the Ashmeter that had been calibrated for

the single seam output at Mantón. This situation would be avoided, if

possible, for the second trial.

One means of overcoming the problem of material bed depth on

conveyors would be to install the Ashmeter on a belt feeder. Although a

considerable number of belt feeders are in use in British Coal coal

preparation plants, most are for regulating the tonnages of the washed

and untreated components of power station blends and are not handlingthe final blended product which it would be preferable to monitor.

Also, many of the existing belt feeders incorporate weigh sections and

they would have been affected by the Ashmeter profiling plough which

would still be required on a constant depth feeder to increase the

compaction and bulk density of the material being monitored and give

improved accuracy.

To find the most suitable site for the second trial installation

of the Ashmeter a specification, included in Appendix 4, was drawn up

and circulated to Area Coal Preparation Engineers in British Coal.

2.5.2 Description of Trial Site at Bilsthorpe Colliery

A number of proposed sites were inspected and the one which came

nearest to meeting the preferred conditions stated in Appendix 4 was at

Bilsthorpe Colliery in the Nottinghamshire Area. The output at

Bilsthorpe was produced in approximately equal proportions from two

seams, Parkgate and Low Main, and no other coal was treated at the

colliery.

The blending and bunkering system for power station fuel at

Bilsthorpe is shown schematically in Figure 32. The 50 mm - 0 power

station blend is prepared by the proportional addition of

38 mm - 0 untreated coal to 50 mm - 0 washed coal and filtered fines.

After mechanical mixing, samples are taken automatically to feed an



12

existing NCB/AERE Phase 3A Ash Monitor, although problems were being

experienced with the feed presentation system of this monitor because of

the handlability of the product particularly after crushing below 6 mm.

The total make of power station blend is delivered to an open stockpile

over a ground hopper. When the site was initially inspected the product

was discharged from the ground hopper by a vibrating feeder, but plans

were being made to replace this arrangement with a variable speed belt

feeder which would hold a bed of coal 450 mm deep and approximately 2 m

in length and 1 m wide.

The belt feeder would discharge onto a 1050 mm belt conveyor which

elevates the product to the top of a battery of rapid-loading bunkers

where it is transferred to a tripper conveyor for distribution into the

individual bunkers. At this conveyor transfer point there was a second

automatic, traversing bucket sampler which was arranged to discharge a

sample increment at each end of its traverse. The minimum cycle time

for the sampler to complete 2 traverses was originally understood to be

40 second but was later found to be 1 minute.

The existing blending facilities at Bilsthorpe would allow the ash

content of the power station product to be intentionally varied for

short periods over a wide range of values to permit the on-site

calibration. The subsequent homogenising effect of the tripper conveyor

and the rapid-loading bunkers would tend to even out these variations

and restore the consistency of the final product.

2.5.3 Installation of the Ashmeter

The Ashmeter was supplied and installed at Bilsthorpe under a

Heads of Agreement by Wultex Machine Company in March/April 1985. It

was mounted over the coal bed on the belt feeder and, to allow access

for maintenance and belt changing, the standard supporting structure was

dispensed with and the parallelogram system was supported from the roof

of the underground chamber below the ground hopper. Some modifications

were necessary to the standard profiling plough and counterweight arms

because of the restricted space above the feeder. The feeder was fitted

with coal bed level sensors which reduced the belt speed to a creep

condition and interrupted the Ashmeter integration when the coal level

fell below normal. The sensors also activated the closing mechanism for

the source radiation shield. The feeder was completely fenced round for

radiation protection and the access for maintenance was interlocked with

the source radiation shield. Illuminated signs were provided to

indicate SOURCE EXPOSED or SOURCE SHIELDED.

2.5.4 On-site Calibration Tests

Completion of the Ashmeter installation was followed by several

days of stability tests, counting backscattered radiation from a

reference surface. Work was then started on the on-site calibration

tests by British Coal Scientific Control Laboratory, South (formerly

East Midlands Regional Laboratory).



13

The calibration tests were carried out in accordance with the

procedure set out in Appendix II of the Heads of Agreement, reproduced

in Appendix 5 of this report. However, the minimum cycle time for the

automatic sampler proved to be 1 minute and the duration of each

calibration test had to be increased from 12 minutes to 19 minutes in

order to collect sufficient increments to comply with BS1017. This

extended test period provided 9 print-outs of 2 minute countrate

measurements. A total of 31 calibration tests were carried out over a 5

week period.

The results for all 31 tests, covering a range of ash content of

6.6 - 36.6% (as received), are given in Table 3, column 2 alongside the

results in column 1 of the previous laboratory calibration tests on

Bilsthorpe blended smalls. Column 3 gives the results for the

25 on-site calibration tests where the ash content lay within the same

limits as the previous laboratory tests. The quadratic regression of

ash content against Ashmeter countrate for all 31 tests gave a standard

deviation of 2.9% ash, corresponding to an accuracy for 95% confidence

limits of +5.8% ash compared with the laboratory calibration of +2.64%

ash.

The calibration accuracy of the Ashmeter was well outside the

standard of operating accuracy of +3.0% ash required by the Heads of

Agreement for the trial and it was agreed with Wultex representatives

that there was no purpose in proceeding with the trial programme until

the unsatisfactory calibration accuracy had been fully investigated.

It was considered that the poor on-site calibration accuracy must

be attributable to:

either (a) segregation on the belt feeder so that the material

being examined by the Ashmeter was not representative of the whole

product stream being sampled.

or (b) changes in the analysis of the coal being mined at

Bilsthorpe in the 12 months since the laboratory calibration tests were

conducted on the Wultex static test rig at SCL(N) and gave a calibration

accuracy (for 95% confidence limits) of +2.6% which was used as a basis

for setting the performance standards for the colliery trial.

Some size segregation was evident around the conical pile which

formed over the ground hopper but before each calibration test run a

funnel shape was allowed to form in the heap by ensuring that there was

a net withdrawal from the stockpile. This withdrawal was maintained

throughout the test so that the material being examined was mainly the

current make of blend. However, there were some reports of visual

evidence of segregation across the width of the belt feeder but the

pattern was not consistent. A quantitative investigation of the

suspected segregation on the feeder was not practicable due to the .

difficulty in obtaining properly representative samples of different

parts of the coal stream at that point. Consequently, arrangements were

made to look further at the second possible cause of the poor



14

performance and to repeat the laboratory calibration tests on a second

set of coal samples.

A suite of 24 samples was collected over a 2 week period and the

laboratory calibration tests conducted using an alternative presentation

technique in addition to the method used previously. The alternative

method involved taking count readings in a five position lattice pattern

over the surface of the sample for each of two fillings of the

presentation box, compared with the previously established method of

2 count measurements for each of 5 box fillings. The alternative method

was included as possibly giving a closer simulation to the on-site

presentation and the samples were tested in an "as received" condition.

For the established presentation method the samples were 'air dried' to

allow direct comparison with the earlier laboratory calibration test.

The results of these tests are presented in Columns 4 to 7 of Table 3.

The results were evaluated for all the samples tested and also for only

those samples falling within the range of ash content of the original

tests (Column 1 ).

The calibration accuracy of the repeat laboratory calibrations

showed an appreciable deterioration from the original calibration but

was very much better than for the on-site calibration. The alternative

method of laboratory presentation with the 'as received' materials gave

a significantly higher accuracy than the previous presentation method

with the 'air dried' sample.

The results show a much lower standard deviation, or spread, of

iron in the coal for both the on-site calibration and for the repeat

laboratory calibration and this would have been expected to correspond

to an improved calibration accuracy. However, the beneficial effect of

the decreased spread of the iron content would appear to be more than

lost by the poor correlation between the iron and the ash in the coal.

The on-site calibration, having a higher iron/ash correlation than the

second laboratory calibration, would have been expected to give a level

of accuracy between the two laboratory calibrations. However, the

on-site calibration accuracy was much worse than the repeat laboratory

calibration and it must therefore be concluded that the poor on-site

calibration is not due to the chemical composition of the coal but to

other factors peculiar to the on-site monitoring conditions.

2.5.5 Shift Integration Tests

Following the failure of the Ashmeter to give a satisfactory

calibration, with short term integration periods of 20 minutes, it was

considered that it might still fulfill a useful role if an acceptable

calibration could be obtained over a shift's integration by reducing the

effect of the variations in the proportions of the two seams being mined

at Bilsthorpe. An investigation was conducted in the early part of 1986

to relate the ash content of routine shift samples to the average of the

2 minute countrate print-outs throughout the shift. The investigation

covered 28 shifts and a range of average shift ashes of 9.4% to 17.4%

but no correlation was found between the shift ash and the mean

countrate.



15

A further investigation was conducted in July 1986 to attempt to

correlate the shift ash with the average countrate print-out. The

investigation covered 15 shifts, with the shift ash varying from 11.5%

to 19.0% but again there was no correlation with the average countrate.

It was therefore concluded that despite ensuring an adequate bed depth

the Ashmeter was incapable of measuring the ash content of the

50 mm - 0 blended smalls at Bilsthorpe with an acceptable level of

accuracy. The instrument was finally removed from Bilsthorpe in 1987 in

accordance with the terms and conditions of the Heads of Agreement.

2.6 Re-design of Ashmeter Electronics by SCL(N)

2.6.1 Original Polish Design

The nucleonic/electronic measuring system of the Polish designed

Ashmeter comprised three distinct units. These were:-

(a) The isotope measuring head, Figure 2, which consisted of the

radioactive source holder, designed to produce a vertically

collimated beam of radiation, and the sodium iodide

scintillation detector which produced electrical pulses

according to the intensity of the backscattered radiation and,

in turn, the ash content of the coal being tested.

(b) The power supply and amplifier unit which required locating

within 2.5 m of the measuring head. This contained the high

voltage (800 - 1600 V) generator for the scintillation detector

and a pulse pre-amplifier which performed a linear

amplification, by a factor of 100, of the electrical pulses

from the detector. An amplitude discriminator then selected

pulses within a defined range of amplitude for onward

transmission and processing.

(c) The signal processing and display unit which could be located

at a distance of up to 3000 m from the measuring head. This

unit had only limited pulse counting, processing and display

capabilities and was the main drawback of the original system.

After more than four years plant and laboratory service the

original Polish manufactured Ashmeter was becoming unreliable and

difficult to maintain. Furthermore, the limited information available

from the processing system, consisting of either counts per second or a

relatively crude conversion to ash content, was found to be inadequate

and a new and more reliable processing system, capable of providing

additional information, was considered necessary.

The UK version of the Ashmeter, manufactured by Wultex, closely

followed the Polish design except for the incorporation of a simple

printer and did not therefore satisfy the requirements of

SCL(N).

2.6.2 Re-designed System

The original isotope measuring head was retained unchanged except

for the addition of a small rotary shutter to blank off the source when



16

not in use. The intermediate unit, incorporating the H.T. generator,

pulse pre-amplifier and simple pulse energy discriminator was also

retained. The re-design therefore mainly concerned the signal

processing and display unit and was undertaken by

SCL(N).

The new system, comprised three IP65 cabinets containing, in turn,

an intelligent terminal, a computing system and a power supply. The

IP65 cabinets vere chosen to combat the coal preparation environment and

to ensure the exclusion of dust and moisture.

The display cabinet, which can interface with the plant sequence

control system houses a four line, LCD display with 40 characters per

line, two 4 x 4 key pads and a simple paper strip printer for local hard

copy.

The computer cabinet contains a card frame and 9 printed circuit

boards. The boards contain the necessary electronics to interface to

plant signals such as 'belt standing' and 'low coal flow'. They also

receive signals from the isotope measuring head and drive outputs to the

display cabinet.

The power supply cabinet contains the battery support mechanism and

associated charging facilities.

2.6.3 Information Available from Re-designed System

The following information is displayed by the new LCD unit:

(i) Time-of-day

(ii) The length of the current integration period, which can be

selected by the operator in hours and minutes,

(iii) The time the current integration period ends,

(iv) The measurement of backscattered radiation in counts per

second, updated every minute,

(v) The ash content, corresponding to the counts per second

measurement, as determined by any form of calibration

equation,

(vi) The average ash content over a moving time period of

selected duration,

(vii) The average ash content from the beginning of the current

integration period to the present time,

(viii) The average ash content for the previous integration period.

The printer records the time of day and the running average ash

value, in addition to the times for conveyor belt standing and low coal

flow.

The setting of system variables, such as the Time of Day,

Integration Period and the time period for Running Average, is

facilitated by the terminal and menu driven interface on the display

terminal.



17

2.7 Further Trials at Mantón Colliery

2.7.1 Description of Installation

Following the completion of the laboratory investigations at

SCL(N) the original Polish Ashmeter was re-conditioned and re-installed

at Mantón Colliery towards the end of 1986 for further on-site trials.

The Ashmeter was equipped with the new electronics package, designed by

SCL(N),

for signal processing and display.

A schematic arrangement of the blending and outloading system for

the power station fuel at Mantón Colliery is shown in Figure 33. The

blend constituents, comprising clean coal -50 mm, clean coal 25 mm - 0

and untreated coal 8 mm - 0, were held in three separate bunkers, each

being discharged by a variable speed belt feeder regulated by a blending

control system. The belt feeders delivered the constituents onto a

common conveyor and the combined product passed through a mechanical

mixer in transferring to the inclined bunker feed conveyor, with a belt

width of 1050 mm and speed of 1.65 m/s, which was housed in an enclosed

gantry. The Ashmeter was located near the tail-end of this conveyor

which delivered to the outloading bunker. The blended product was

sampled at the conveyor delivery by a chain bucket sampler which

discharged the sample increments into a small hopper from which they

were fed at a controlled rate by a belt feeder to a sample crusher and

divider to provide the final consignment sample, with the excess

returning to the product stream. The belt feeder could be reversed to

by-pass the crusher and provide occasional increments for a moisture

sample.

2.7.2 Dynamic Calibration Test Procedure

The calibration samples were collected over a period of 10 minutes

and comprised 25 increments taken at 24 second intervals using the

mechanical sampler. The samples were collected in total, after the

sample crusher and before the sample divider, and returned to SCL(N) for

preparation and analysis.

The Wultex Ashmeter was operated locally, under manual control,

and the new signal processing and display system provided a reading of

the average counts per second over the 10 minutes duration of the test.

A time lag of 11 seconds between the coal passing the Ashmeter and being

sampled had to be allowed for by starting the Ashmeter 11 seconds in

advance of the sampler and stopping 11 seconds earlier.

A minimum bed depth of approximately 90 mm had to be maintained on

the conveyor to ensure the Ashmeter continued to operate. The blend

ratio was adjusted after each test to provide a different ash level in

the product. A series of at least 20 tests was conducted to provide a

calibration between ash content and countrate.



18

2.7.3 Dynamic Calibration Test Results

Two dynamic calibration tests were conducted in December 1986 and

February 1987 with the original Polish supplied, nucleonic measuring

head. A third test was conducted in October 1987 following the

replacement of the crystal in the scintillation detector but, due to an

error in the window settings, the results were invalidated. The

calibration graphs for the first and second tests are shown respectively

in Figures 34 and 35 and the results are summarised below.

Calibration Test

Dates conducted

No.

of samples

Range of Ash % (A.R.)

Mean Ash % (A.R.)

Regression Analysis

Correlation Coefficient

Standard Deviation Ash %

1

3.4.5./12/86

21

12.6 - 24.4

17.7

Linear

0.871

1.54

2

5,6,10/2/87

24

15.1 - 24.8

21.0

Linear

0.893

1.79

Comparison of these results with the plant performance test

conducted during the initial trial at Mantón, Table 1, shows an

improvement in correlation between ash content and countrate but a

reduction in calibration accuracy, particularly in Test 2, which may

have been due, in part, to deterioration in the scintillation detector.

Following the calibration the Ashraeter was used by the plant

operators to assist in controlling the quality of the blended product.

2.7.4 Train-load Integration

The loading of trains with power station blend through a single,

small capacity bunker at Mantón, rather than through rapid-loading

bunkers, made it possible to identify and sample individual train-loads.

This was the normal procedure at Mantón and it provided information on

the quality of each train-load. Following the re-installation and

calibration of the Wultex Ashmeter it was manually controlled to

integrate the ash measurement over each train-load and to provide a

print-out for comparison with the laboratory analysis.

For 114 train-loads produced in May and June 1987, ranging in ash

content from 12.3% to 21.1% the standard deviation between the average

ash content measured by the Ashmeter and the laboratory analysis was

1.73%. The failure of the detector crystal in July and problems

associated with its replacement, resulted in unreliable measurements for

several months. Following the correction of the detector problem, a

further comparison between the Ashmeter measurement and the laboratory

analysis for 237 train-loads, ranging from 11.7% to 22.6% ash, in the

four month period December 1987 to March 1988 gave a standard deviatie

of 1.64% ash.



19

2.8 Further Installations

Following a change of ownership the Wultex Machine Company

terminated the licence agreement with EMAG and ceased manufacture and

support for the Ashmeter from mid-1986.

However, the Ashmeter which had been withdrawn from Bilsthorpe

Colliery was retained by British Coal and installed early in 1988 on a

weigh-feeder handling 50 mm - 0 untreated coal on the South Side Central

Coal Preparation Plant at Grimethorpe Colliery. It will be used for

controlling the blending of washed and untreated coal for power

stations. The instrument was undergoing calibration tests at the end of

this Project.

2.9 Summary

Earlier work with the Polish G2 Radiometric Ashmeter had shown

that the instrument was mechanically and electrically reliable and could

be applied with a reasonable degree of success to the continuous on-belt

monitoring of the ash content of a blended power station fuel produced

at a single seam colliery. This degree of success, however, was

conditional on the depth of the bed of coal being sufficient to ensure

total backscatter of the radiation and on the variations in coal

composition staying fairly constant. Since neither of those conditions

were likely to be met at many installations, laboratory work was

undertaken with the Wultex Ash Meter to assess the extent of these

effects.

Measurements confirmed that the accuracy of the instrument would

be affected when the coal bed depth was reduced below 200 mm and even

with the maximum compaction which could be expected to be applied to

coal on a conveyor, the effect would be significant at bed depths less

than 150 mm. As far as the UK coal industry, which generally uses

narrow, rapidly moving belts, is concerned this effect would severely

restrict its application to those few situations where low speed belt

feeders are in use.

The effect of coal composition on accuracy was assessed by

undertaking laboratory calibration trials on 16 suites of coals from a

range of sources. Results, in terms of standard deviation of ash

content about the calibration line, ranged from 0.19% to 2.31% ash. On

average, these results represent a relative accuracy (Is) of +5% , which

would be acceptable for many applications if it could be reproduced in

an on-belt situation.

A method for calculating the expected calibration standard

deviation from the total composition of the coal has been developed and

the results correlate with the measured values with an accuracy (+ls) of

0.31% ash absolute. The major factors, however, which affect the

accuracy of the calibration standard deviation are the level of ash

content, the variability of the iron content in the coal and the degree

of correlation between iron content and ash content. Using these three



20

factors in an empirical relationship with the measured calibration

standard deviation shows that it is possible to predict, from a

knowledge of the ash and iron contents of the coal only, the expected

calibration accuracy to +0.16% ash absolute at one standard deviation.

An on-site trial was undertaken at Bilsthorpe Colliery, a two seam

mine,

where the meter was installed on a belt feeder outloading the

power station blend. A calibration trial comparing instrument readings,

integrated over 20 minutes, with the laboratory analysis of 31

corresponding samples of coal, taken from the coal stream by an

automatic sampler, gave a standard deviation of 2.8% ash, much higher

than the value of 1.8% obtained in static laboratory tests for the same

coal. Further laboratory tests confirmed that the larger on-site

calibration error could not be attributed to variations in coal

composition. There was visual evidence of cross-belt segregation of the

coal on the belt feeder but it was not practicable to quantify this or

the size of its contribution to the total error of the on-site

calibration. Two further trials, comparing instrument values integrated

over a full shift with the corresponding laboratory analyses, showed no

significant correlation. It was concluded that in the conditions found

at this site the Wultex Ashmeter was unable to provide a measurement of

ash content of sufficient accuracy to be of practical value to the plant

operations.

Throughout these plant trials the instrument was found to be

mechanically and electrically reliable. However, the signal processing

and display facilities of the meter were very limited and new units

based on microprocessors were designed and built to provide a wider

range of output data, including time-averaged values over

operator-selected periods of time. A modified meter was installed on

the power station fuel belt at Mantón Colliery, a single seam mine,

where dynamic calibration trials gave values of standard deviation of

1.5% ash and 1.8% ash, which compared with a static laboratory

calibration of 0.76% ash for the same coal. The long term performance

of the meter was assessed at this site by comparing the instrument

values integrated over individual train loads with average ash values

found by laboratory analysis. Two trials, covering 2 month and 4 month

periods,

gave standard deviations of 1.7% ash and 1.6% ash respectively.

The results obtained at this colliery are considered to be operationally

useful and instrument data are being used to assist in the manual

control of blending operations.

3. MAIN-STREAM ASH MONITORING - COALSCAN 3500 ASH MONITOR

The Coalscan 3500 Ash Monitor is the commercial version of the

SIROASH Low Energy Transmission (LET) gaug ed ) developed in Australia by

the Commonwealth Scientific and Industrial Research Organisation

(CSIRO).

It is designed for the continuous measurement of the ash

content of coal on a belt conveyor and is manufactured under licence by

Mineral Control Instrumentation Pty Ltd (MCI) of Adelaide.



21

3.1 Principle of Ash Measurement

The ash content measurement is based on the transmission through

coal of highly collimateci beams of low and high energy gamma rays. The

absorption by the coal of the lower energy gamma rays depends on the ash

content of the coal and the weight per unit area, while the absorption

of the higher energy gamma rays depends essentially on the weight per

unit area of coal in the beam. The transmitted intensities are combined

to give ash content independent of the weight per unit area:-

Ash - Ki + K2 log(I/Io)low

log(I/Io)high

where I and Io are transmitted intensities with and without coal in the

beam and "low" and "high" refer respective to low and high energy gamma

rays. The calibration constants

K\

and K2 are found from measurements

on samples of a particular coal of known ash content. The instrument

must therefore be calibrated for each particular coal.

The low energy (60 keV) gamma radiation is provided by americium

241 and, depending on the range of coal depths being encountered, the

high energy radiation is provided at either 356 keV by barium 133 or at

660 keV by caesium 137. In practice, both the low and high energy

sources are mounted in a single source holder located below the conveyor

belt, and a single detector, with energy analysis facilities, above the

belt and resolves the transmitted intensities of the 2 different energy

levels. The arrangement of the source, collimator and detector about

the conveyor is shown in Figure 36 and the gamma radiation spectrum for

Americium and barium in Figure 37.

3.2 Description of Commercial Unit

The commercial design of the Coalscan 3500 Ashmeter, Figure 38,

comprises the following system units:-

(i) C-Frame: this houses both source and detector in precise

alignment, together with the EHT supply unit and the

pre-amplifier. The sources are housed in the lower arm of

the C-frame in a tungsten block with a fail-safe shutter.

The radiation detector, which is of the scintillation type,

is housed in the upper arm together with a thermostatically

controlled heater, the EHT supply unit and the pulse

pre-amplifier.

(ii) C-Frame Support: this is a substantial stand which is

located alongside the conveyor to provide a pivoted support

for the C-frame so that it can either be positioned over

the conveyor or swung to the side of the conveyor and

stationed on the off-belt standards holder, depending on

whether or not the belt is running.



22

iii C-Frame

Actuator:

this

drives

the

C-frame

and

is

either

a

double acting pneumatic or hydraulic cylinder or a linear

electric actuator depending on the services available on

site.

iv Frame

Cabinets:

there

are

two

cabinets

mounted

directly

on

the C-frame, the first, which is thermostatically

controlled,

contains

the

Multi-Channel

Analyser

while

the

second houses the electrical terminations.

v Main Electronics Control Cabinet: this houses the control

computer,

which

handles

and

processes

all

the

signals

from

the

measuring

system,

and

the

programmable

logic

controller

PLC which controls the physical operation of the ash

monitor. The cabinet, which can be located up to 100 ■

from

the

measuring

station,

should

preferably

be

housed

in

a

protected

environment.

vi Operator Terminal: this is an RS232 terminal with a display

and

is

the

means

of

communicating

with

the

measuring

and

control systems through the main control cabinet.

vii Output Display Cabinet: this is suitable for siting in a

plant

control

room

or

plant

office

and

may

be

located

up

to

500 m from the main control cabinet. It houses a 100 m

wide, 2-pen strip chart recorder which displays both the

instantaneous

and

average

ash

content

of

the

coal.

The

instantaneous ash corresponds to the current integration

period,

typically

of

one

minute

duration.

The

average

ash

is

the

average

for

the

current

period,

e.g.,

8

hours

or

24

hours,

commencing

from

a

reference

time

of

day

or

froa

an

operator reset. This feature allows the recording of the

average

ash

content

of

the

coal

produced

during

a

particular

period.

The

display

cabinet

also

includes

a

cluster of annunciatiors which show the status of various

components in addition to high and low ash alarms.

3.3 Calibration, Operation and Standardisation

The monitor has to be calibrated for each particular application

by

measuring

the

transmitted

intensities

of

high

and

low

energy

gamma

radiation

with

coals

of

known

ash

content.

The

manufacturer

claims

that

the

instrument

can

be

calibrated

statically

in

an

off-belt

position.

It

is recommended that a set of 20 prepared samples of known analysis,

covering

the

full

range

of

ash

variation

of

the

particular

coal,

is

used.

The

coal

samples

should

each

weigh

2

kg

and

be

less

than

1

mm

particle size. They are presented to the instrument in a special sample

container and the countrates recorded. A calibration equation is

derived

from

a

regression

analysis

of

ash

content

against

the

log

countrate

ratio

and

keyed

into

the

instrument.

The

facility

to

conduct

an off-belt calibration is claimed by the manufacturers as a particular

advantage

of

the

Coalscan

3500

system

since

it

can

be

performed

with

small

samples

of



23

more accurately known ash content and without the need to sample from

the coal stream.

Following calibration, a reference standard is placed in the

off-belt measuring position. In operation the monitor positions itself

over the conveyor only when it is running and whenever the belt stops

the monitor returns to the off-belt position and commences an internal

check and standardisation routine. After completing the routine the

source is shut off and the system awaits the re-starting of the belt.

The instrument only measures the ash content when the depth of

coal on the belt exceeds approximately 50 mm (depending on bulk

density).

It automatically determines when the coal layer is too thin

and stops recording. The instantaneous ash measurement provided by the

instrument is the average over a short time interval, normally 1 minute.

In some cases it may be necessary to integrate over longer periods to

allow for variations in the thickness of the conveyor belting. The

cumulative average ash content can be provided over any period

determined by the operator. The averaging procedure takes account of

the mass per unit area of coal in the measuring beam and therefore the

cumulative average ash is claimed to be a close approximation to a

tonnage weighted ash value.

3.4 Laboratory Investigations

3.4.1 Arrangements and Objectives

In view of a proposal for the trial installation of a Coalscan

3500 Ash Monitor at As kem Colliery, agreement was reached with Mineral

Control Instrumentation, the Australian manufacturers, for the loan of a

second Coalscan 3500 instrument for static laboratory evaluation at

British Coal's Scientific Control Laboratory (North).

The loan of the equipment was the subject of a Heads of Agreement

Contract covering the installation, maintenance and the programme of

test work to be carried out during the loan period which was initially

set at 6 months but later extended. The Technical Appendix to the

Agreement outlining the objectives, duration and review of the

laboratory trials is included as Appendix 6 of this report.

These trials had two main objectives which were:-

(a) to investigate fundamental factors, such as basic error in the

statistical count, the effect of changes in elemental

composition and the effect of bed depth.

(b) to investigate the suitability of the instrument to specific

applications by testing different coals in the laboratory and

to develop a calibration procedure to simulate the dynamic

operation of the monitor in practice.

The equipment, comprising items (i), (iv), (v) and (vi) of the

standard plant system was installed and commissioned at SCL(N)

early in 1986.



24

3.4.2 Setting-up Procedure

The commissioning of the Coalscan 3500 Ash Monitor was carried out

in accordance with the setting-up procedure laid down in the instruction

manual and comprised the following stages : -

(i) Multi Channel Analyser (MCA)

The MCA supplied had optimum default settings for most

of its variables. However, three variables are required

to be set specifically for each installation and are the

EHT voltage for the scintillation detector and the low

and high energy levels for the Americium window. The

EHT voltage is found using a peak-seeking algorithm

contained in the MCA software. The latter two variables

are found by running another MCA software routine which

produces the energy spectrum and the energy levels are

chosen to include the main americium peak.

(it) Natural Background Correction

Under normal conditions the natural background radiation

is less than 50 counts per second and the correction

factor is set to zero. Alternatively, measurements are

taken with the sources removed and the countrates

obtained in the americium and caesium windows are used

as correction factors.

(iii) Background Stripping Factor

The countrate in the americium channel is principally

from americium gamma rays, however there is a degree of

interference due to gamma rays which originated from the

caesium source but have lost energy due to the

scattering processes. The process of removing these

degraded caesium gamma rays is called "background

stripping". The procedure involves introducing a 1-2 mm

thick sheet of lead in the beam which filters out the

americium gamma rays, without significantly reducing the

caesium countrate. The background stripping factor is

the ratio of the counts in the americium window divided

by the counts in the caesium window with the lead sheet

in place.

(iv) Dead Times and Standard Countrates

When countrates are high the electrical pulses

representing each count tend to overlap due to the

nature of the electronics employed. While a count is

being measured the counting system closes down for the

duration of the count measurement and is termed to be

'dead'. Measurement of the 'dead time' allows the

computer to make a statistical correction for the counts

received during this period.



25

The Coalscan has to be set up to measure ash

independently of mass loading. To carry out this

procedure the values for the counts in the americium and

caesium windows, with no intervening samples in the

beam, are required. These values cannot be measured

directly because of the high countrates produced under

these conditions and have to be determined indirectly.

The procedure to obtain values for dead times and

standard countrate involves taking measurements of

varying attenuation using standard blocks of perspex and

glass or perspex and tin. These measurements are

processed using a computer program provided to give the

dead times and standard count rates.

(v) Log Correction Factors

The log correction factors ensure that the measured ash

is independent of mass per unit area at high and low

belt loadings.

At low mass per unit area the instrument response is

non-linear. To cater for this condition a linear

approximation is employed which is used as a sub-routine

to modify the ash estimate when the Caesium countrates

are above a predetermined value. At very low mass per

unit area, equivalent to less than about 50 mm depth of

coal,

this approximation is unsatisfactory and the

instrument is set to reject such readings.

At high belt loadings, i.e.,low caesium countrates, a

theoretically calculated factor is applied.

(vi) Sample Container Factors

During off-belt calibration and standardisation it is

necessary to measure the countrates without attenuation

due to the sample container. This value cannot be

measured directly because of the high countrates

involved and is obtained indirectly by measuring a set

of standard blocks with and without the sample

container.

(vii) Calibration Standard

A calibration standard is made from three or four

standard blocks and kept separately. The Coalscan 3500

uses the measurements it obtains from this off-belt

calibration standard to correct for source decay and any

drift in the measuring equipment.



26

3.4.3 Results

(i) Basic Data

(i)(a) Statistical Counting Error

The Coalscan 3500 calculates an ash value every

50 milliseconds which is averaged over the number of

50 millisecond periods in the sampling time. In a series

of tests using the calibration standard the log ratio was

measured over 2, 4, 8, 15, 30 and 60 second periods. Two

further series of tests were conducted over 60, 120, 300

and 600 second periods. The results of all three series,

made up of tests 1-6, 7-10 and 11-14 respectively, are

given in Table 4 and Figure 39.

The two series of tests 7-10 and 11-14 show good

repeatability in terms of standard deviation. The mean

log ratio, however, is different and arose because the

instrument had not been standardising properly due to

software errors in the program. According to the

manufacturers of Coalscan 3500 a typical coal would give

a calibration gradient of between 0.01 and 0.03 log ratio

units per 1 percent ash, depending on ash composition.

For a counting period of 300 seconds the standard

deviation of the log ratio is 0.0017 and hence the

contribution of the counting statistics to the overall

precision of the ash estimate would be less than 0.1%

(absolute).

On standardising, the computer checks that the countrates

are within an acceptable band, determined by the user.

If the readings are outside this band the standards are

not revised and the readings are assumed to be caused by

system errors, e.g., incorrect alignment of the source,

standards block and detector. However, because of the

natural decay of the sources the standards countrate

gradually reduces and on this occasion it fell below the

lower acceptable limit. Adjustment of the limit brought

the standards log ratio back to normal. On the later

version of the software the band width was set

automatically as a percentage of the last valid reading

and would therefore take account of normal decay.

(i)(b) Coal Thickness

The log correction factors, described in the setting-up

procedure (3.4.2(v)), are designed to take account of

variations at deep and shallow coal depths. Measurements

made during the initial setting-up procedure to check

that compensation occurred are given in Table 5. This

table shows that the log ratio values are practically

constant over the wide range of attenuation equivalent to



27

a 4:1 ratio in bed thickness. The variation in log ratio

values is no greater than the counting statistics error

on a 300 second counting period (equivalent to 0.1% ash).

(i)(c) Chemical Composition

To investigate the effect on the Coalscan 3500 of

variations in the chemical composition of the coal ash, a

series of tests were conducted in which increasing

amounts of chemically pure reagents were added

invididually to an air-dried coal sample crushed to minus

212 microns. The reagents used were magnetite

(Fe304),

calcium carbonate (CaC0

3

) and kaolin (AI2O32SÌO22H2O).

Two readings of 5 minutes each were taken for three fills

of the container with each level of reagent addition.

The total sample weight was approximately 800 g.

The results of the tests with each of the reagents is

given in Tables 6, 7 and 8. The percentage addition of

each reagent was converted to represent the oxides

normally present in ash, i.e. % Fe3Û4 converted to %

F6203, % Ca CO3 converted to % CaO, % AI2O32SÌO22H2O

converted to % AI2O32SÌO2. The addition of each reagent

was continued until the corresponding oxide comprised

approximately 10% of the sample. For a typical coal, an

increase on log ratio of 0.012 corresponds to an increase

in ash content of 1%. Using this relationship the

increase in the log ratio measurement above that of the

original coal sample, for each level of reagent addition,

was converted to the corresponding increase in ash

content. This content was plotted against the equivalent

oxide addition for each reagent in Figure 40.

The graph shows that the effect of AI2O32SÌO2 corresponds

closely to that of typical ash. It also shows the

considerable effect that variations in iron would have on

the Coalscan measurement. For a typical coal a 1%

increase in Fe2Û3 would give rise to a 6% increase in the

Coalscan measurement of ash content. Where the

instrument is to be used on a coal which has been cleaned

using a magnetite dense medium process, particular

attention must be paid to the rinsing of the coal leaving

the process to ensure efficient removal of adhering

magnetite. The effect of variations in calcium is

approximately half that of the iron.

(ii) Accuracy of Ash Measurement

(ii)(a) Samples - 212 Microns

Suites of coal samples were collected from several

collieries, where Coalscan applications were considered

possible, and prepared to provide air-dried test samples

with a top size of 212 microns. Each sample was

presented to the Coalscan instrument 5 times, each time



28

for 5 minutes. Samples were mixed between

presentations. The samples were then analysed for ash

content and a linear regression of ash content against

log ratio calculated. The results of these tests are

summarised in Table 9 and the calibration graphs are

shown in Figures 41 to 45.

The Askern blended small coal gave a very good

calibration over quite a wide ash range and was

confirmed by the second test over a slightly reduced ash

range. By comparison, the first test with Gascoigne

Wood untreated small coal gave a poor calibration over a

fairly limited ash range of 13% . The calibration

deteriorated considerably when the ash range was

increased to 23%. The calibration for the South Side

(Grimethorpe) blended small coal was only moderately

good considering the quite narrow ash range.

(ii)(b) Samples - 1 mm

Sub-samples of the second suite of Askern blended small

samples were also tested at the slightly coarser size of

1 mm - 0 and the results are also included in Table 9,

Test 7, and Figure 46. As was expected, the calibration

accuracy was slightly worse than with the samples

reduced below 212 microns but the coarser material was

easier to handle.

Performing calibration tests under laboratory conditions

with samples reduced to such fine sizes must be regarded

as producing the most favourable results. Testing using

coarser sizes and on a colliery site could be expected

to give poorer results. On this basis of the coals

tested the only potentially suitable application was

Askern blended smalls.

(iii)(c) Samples 25 mm - 3.18 mm

A further laboratory calibration test was conducted on

Askern coal with samples prepared from known proportions

of washed smalls and raw smalls. Gross samples of

washed smalls and raw smalls were collected and air

dried. The fines below 3.18 mm in size were removed

from both samples to give products 25 mm - 3.18 mm which

were representatively sub-sampled and analysed for ash

content. Limiting the bottom size of the samples to

3.18 mm would avoid the migration of the fine material

during handling and thereby minimise bulk density

variations. Nine samples of 25 kg were prepared,

ranging from washed coal to raw coal with progressively

reducing proportions of washed coal and increasing

proportions of raw coal. The air dried ash content

ranged from 6.2% to 41.8%. The samples filled the

sample box, which was approximately 450 mm long, 300 mm



29

wide and 160 mm deep, and was presented to the Coalscan

instrument such that 12 measurements were made at 25 mm

intervals along the centre line of the box over a

distance of 275 mm. Similar readings were also taken

along two lines at one quarter and three quarters of the

width of the presentation box to give three parallel

lines of test measurements. This procedure was repeated

for the same sample after emptying, re-mixing and

re-filling the box. The sample was then analysed for

ash content. The whole test routine was repeated for

each of the 9 samples, and a summary of the results is

given in Table 10.

The linear regression for the mean of all 72

measurements for both fillings of the presentation

container against the laboratory ash for each sample,

see Figure 47, gave a calibration standard deviation of

0.83% ash

(A.D.).

Although the upper size limit of the

material was 25 mm, the very intensive examination of

these samples gave a result which was comparable with

results from previous laboratory tests with Askem

blended coal reduced to finer sizes (Table 9 ). These

gave standard deviations of 0.64% ash (A.D.) and 0.59%

ash (A.R.) for minus 212 micron material and 0.80% ash

(A.R.) for minus 1 mm material.

The mean standard deviation for the linear regression of

each individual line of measurements from both box

fillings was 1.75% ash

(A.D.).

This pattern of

measurements, comprising a single row of closely spaced

spot measurements, could be considered to simulate the

continuous, single-line measurement made by an on-belt

Coalscan installation.

On the basis of the results of this series of laboratory

tests the standard deviation for an on-belt calibration

would be expected to be 2-1 times the standard deviation

for an off-belt, static calibration. This relationship

will be investigated further in the appraisal of the

results of the Coalscan trial at Askern Colliery.

3.5 On-Line Trials at Askern Colliery

3.5.1 Purchase Agreement and Installation

Askern Colliery, in the South Yorkshire Area of British

Coal,

was

chosen for the first on-line trial of a Coalscan 3500 ash monitor which

was purchased under a Heads of Agreement Contract from Magco Ltd., the

recently appointed UK agents for

M.C.I.,

the Australian manufacturers.

The instrument was installed by Magco Ltd. in March/April 1986 to

monitor the 25 mm - 0 blended power station fuel on the final conveyor

feeding the rapid-loading bunkers.



30

The Heads of Agreement Contract document included the acceptance

criteria for the trial, see Appendix 7, which covered both the measuring

performance and reliability of the equipment. Following satisfactory

on-site calibration of the instrument, the performance criteria required

that at least 57 out of 60 tests, each conducted over an 8 minute

sampling period, should give ash measurements within +2.5% of the

laboratory ash analysis. The criteria for reliability was that the

instrument should operate continuously for a period of 60 workings days

without operational, mechanical or electrical problems and a continuous

period of 120 working days without the replacement of mechanical or

electrical components.

A schematic arrangement of the installation at the Askero coal

preparation plant is included in Figure 48. The plant, which has a

capacity of 500 t/h, produces 200/250 t/h of power station fuel. Only

part of the 25 mm - 0 raw coal is cleaned, using dense medium Vorsyls

and froth flotation, and the remainder is kept untreated. The resulting

washed smalls and untreated smalls are blended using a system of

blending bunkers and weigh feeders to produce a 25 mm - 0 power station

fuel with an ash content around 15% . An automatic traversing bucket

sampler at the discharge of the blend conveyor provides the feed to a

NCB/AERE Phase 3A ash monitor, with regularly spaced increments being

diverted to a moisture sample. From the blend conveyor the mixture of

washed and untreated smalls falls through a vertical mixer and is

delivered sideways to the 1050 mm wide inclined belt conveyor feeding

the rapid-loading bunkers.

The Coalscan instrument was installed a short distance along the

inclined bunker feed conveyor at a position adjacent to an existing area

of open platform. Some modifications were necessary to the height and

spacing of the troughing idlers to accommodate the lower arm of the Ci

frarne below the belt. Fencing was provided around the Coalscan unit for

radiation protection. The main electronics control cabinet was sited in

the plant motor control centre and the Output Display Cabinet located in

the central control room.

3.5.2 Commissioning and Calibration of Coalscan 3500

3.5.2.1 Preparatory Investigations

A suite of 20 samples of Askem power station fuel (blended

smalls) had previously been used for laboratory calibration trials with

the Wultex Radiometric Ashmeter, Table 2, Test 3, and had been analysed

for ash composition. The calibration standard deviation attributable to

the elemental compositon had been calculated as 0.84% ash and the

performance criteria for the Heads of Agreement was based on this

evaluation.

A further suite of 20 samples of As kem 25 mm - 0 blended smalls

was collected in March 1986 and, after air drying and crushing to minus

212 microns, they were tested on the Coalscan 3500 ash monitor which had

already been set up in the laboratory at

SCL(N),

Table 9, Test 1. The

calibration standard deviation for these samples was found to be 0.64%



31

ash (A.D.). thereby tending to confirm that an accuracy of +2.5% ash

should be within the capabilities of the on-line installation at Askem.

3.5.2.2

Commissioning and Preliminary Calibration

The final installation and commissioning of the equipment at

Askem was supervised by an engineering representative from the

Australian manufacturers and was completed towards the end of April,

1986. To test the system, an off-belt calibration was performed on

26-27 April using the suite of samples of As kem blended smalls reduced

to minus 212 microns and previously tested on the laboratory Coalscan

instrument, as described above. The plant off-belt calibration,

Table 11, Test 0 and Figure 49, gave a calibration standard deviation of

0.99% ash (A.D.) compared with the laboratory result of 0.64% ash

(A.D.).

3.5.2.3 On-line Dynamic Calibrations 1 to 5

The Heads of Agreement Contract specified that the instrument

would be calibrated on-belt over a range of ash content of 10-26% and

over a minimum of 30 eight minute sampling periods. A representative

2 kg sub-sample, crushed to minus 1 mm or less, would be prepared from

each calibration sample and used to perform an off-belt calibration.

The manufacturer would then have the option of entering either the

on-belt or off-belt calibration into the instrument for the performance

testing.

The first on-belt dynamic calibration was carried out on 30th

April and 1st May 1986 with 12 acceptable samples being collected on the

first day and 17 on the second day giving a total of 29 samples for

evaluation. Regression analysis of the results gave a calibration

standard deviation of 1.51% ash (A.R.), Table 11, Figure 50. The minus

212 micron sub-samples obtained from the dynamic calibration samples

were used to perform an off-belt calibration which gave a calibration

standard deviation of 0.85% ash (A.D.), Table 11, Figure 51. The

on-belt calibration standard deviation of 1.51% ash would produce an

accuracy of ash measurement (2s) of +3.02% (A.R.) which was well outside

the required accuracy of +2.5%. The off-belt calibration accuracy of

+1.7% indicated that the errors in the on-belt calibration contained a

significant contribution due to factors other than coal composition.

After examining these results the reaction of the manufacturer was

two-fold:-

(i) the larger errors had occurred at either high or low flow

rates as indicated by the caesium countrate,

(ii) the instrument had not had sufficient time to standardise

after being switched on.

It was therefore decided that a second dynamic calibration should

be carried out after the instrument had again been set up and the

standard countrate stabilised.



32

The second dynamic calibration commenced on 16th May 1986 when 12

acceptable samples were collected. This calibration exercise had,

however, to be abandoned when the Hagco representative was unable to

attend due to illness. A regression analysis was performed on the 12

samples collected and this gave a calibration standard deviation of

0.97% ash

(A.R.).

The trial suffered a further delay when the electric actuator,

controlling the movement of the C- frame, burnt out at the end of Hay

1986 and had to be replaced in early June. At the same time, Magco

installed a new version of the computer software and, following this, a

third dynamic calibration was carried out on 4-6th June 1986 when 23

samples were collected. The regression analysis gave a calibration

standard deviation of 1.76% ash

(A.R.),

Table 11, Figure 52.

The Australian manufacturers, MCI, were sent all the available

data and information for investigation and they discovered that an error

had occurred in entering the software into the instrument such that a

variable had been wrongly signed. This variable was the slope of the

flowrate correction and the effect had been to exaggerate errors at low

material flowrates.

An MCI representative came to the UK towards the end of September

1986 to discuss the progress of the trial and it was agreed to fit new

software. The comparatively low flowrates and consequent shallow bed

depths,

which were at the lower end of the range for the caesium source,

was considered to have contributed to the poorer calibrations. It was

therefore agreed to replace the caesium source with a lower energy

barium source which would be more sensitive at low flowrates.

After again setting up the instrument a fourth dynamic calibration

was conducted from 30th September to 2nd October 1986 when a total of 21

samples were taken. A regression analysis of the results gave a

calibration standard deviation of 1.39% ash (A.R.), Table 11, Figure S3.

Although this was an improvement on the third dynamic calibration it

would still not meet the accuracy requirements of the Heads of Agreement

Contract.

A fifth dynamic calibration was therefore undertaken on the 13th

and 14th November 1986 when a total of 22 samples were taken. The

regression analysis gave a calibration standard deviation of 1.39% ash

(A.R.),

Table 11, Figure 54. Although this gave a similar outcome to

the fourth calibration, when the two sets of data were combined, the

calibration standard deviation increased to 1.87% ash (A.R.).

3.5.3 Investigation of Segregation on Belt

One possible reason for the worse than expected calibration

results was that there was substantial variation in the coal quality

across the belt. A visual examination of the material on the belt prior

to the Coalscan installation revealed some size segregation but it had

not been considered significant. A series of tests were conducted in



33

which the Coalscan measuring head moved from one position to another

across the width of the belt, remaining for a period of 96 seconds in

each position. Five separate tests were carried out on the 21st October

1986 over periods ranging from approximately 15 to 100 minutes. A

further test was conducted on 19th December 1986 with the Bretby

vertical mixer inoperative. For the purpose of these tests the fifth

calibration was entered into the instrument to provide readings directly

in terms of ash content. The results of all six tests are given below:-

Mean ash content readings at two positions across the belt

Position A Position B

Test Mean Mean

Ash % (A.R.) Ash % (A.R.)

1 20.64 16.18

2 19.94 15.60

3 20.72 16.644 16.92 15.05

5 17.40 14.83

Average 19.12 15.66

A statistical analysis showed that the difference in the mean ash

contents was significant in Test 3 and highly significant in Tests 1, 2,

4 and 5. In all five tests the mean ash content was higher at positon A

than position B. This result confirmed the presence of segregation with

respect to ash content across the belt.

Following these tests,

M.C.I,

decided that the C- frame, which had

maintained a fixed position over the belt, should be made to oscillate

across the belt with an amplitude of about 200 mm and a period of about

18 seconds. To achieve this oscillation the electric actuator would be

replaced by a hydraulic ram and power pack.

There was a further delay in implementing this modification and

the oscillating head was not installed until early April 1987.

3.5.4 Further Dynamic Calibrations and Investigations

The sixth dynamic calibration, using the oscillating C- frame, was

conducted over 4 days in mid-April 1987, and a total of 32 samples were

collected. The regression analysis gave a calibration standard

deviation of 1.56% ash

(A.R.),

Table 11, Figure 55. The oscillating C-

frame had therefore failed to produce any improvement in the calibration

accuracy.

A test was then conducted using the oscillating C- frame to

investigate further the variation of ash content across the belt. With

the measuring head oscillating over a 200 mm band over a period of about

18 seconds, countrate measurements were recorded every 2 seconds over a

period of 13 minutes. The pattern of variation of barium countrates

against time, Figure 56, follows the 18 second period of oscillation and

shows a progressive reduction in barium countrate, corresponding to an

increase in belt loading, from one side of the measuring band to the

other. The results were also grouped into ranges of decreasing barium



34

countrate and the mean ash content was calculated for each range,

Table 12. The calculated ash contents were plotted against the mean

barium countrate for each of the ranges In Figure 57, and this provides

an approximate indication of the variation of ash across that section of

the belt traversed by the measuring head.

3.5.5 Performance Test

Although the level of calibration standard deviation, which had so

far been achieved from the on-site dynamic calibrations, had not reached

the level of accuracy, for 95 confidence limits, (2s), of +2.5

required by the Heads of Agreement for the trial, it was never-the-less

decided to proceed with the performance testing during May and June

1987.

The performance testing was undertaken on two days a week,

alternating between Tuesday and Thursday one week and Wednesday and

Friday the following week. Up to 9 samples a day of the blended smalls

were taken, in the same way as for the calibration procedure, by using

the automatic sampler to collect a minimum of 35 increments over a

period of about minutes. The samples were analysed for ash content

for comparison with the Coalscan measurements. The performance tests

were carried out under normal plant operating conditions, with no

deliberate variations to the composition and ash content of the blended

smalls.

Because no satisfactory calibration equation had been obtained

for the Coalscan instrument the output was given in log ratio units

which could be converted to ash content retrospectively.

A regression analysis of the results of the 57 performance tests,

which all fell within a narrow range of ash content of 10.4 - 16.1

(A.R.),

gave a standard deviation of 1.03 ash

(A.R.),

Table 11,

Figure 58 . However, the coefficient of 0.617 showed only a poor

correlation for the tests, and the comparatively low value of standard

deviation was due to the narrow range of ash content of only 5.7

encountered during the tests. When the calibration equations derived

from the results of the sixth dynamic calibration test, in total and for

individual day s samples, were applied to the log ratio measurements

obtained from the performance tests the number of performance test

samples falling outside the acceptable limits of +2.5 ash were as given

below.

Evaluation of performance test results

6th Dynamic Calibration Performance Test

Sample Range of Std. Dev. No of samples

outside

Nos Ash (A.R.) Ash (A.R.) +2.5 ash

limits

7

2

8

23

1 ■

1 ■

1 3 •

2 4

■

■ 32

• 1 2

■ 2 3

■

32

8 . 9 ■

1 0 . 8 ■

8 . 9 ■

1 2 . 7

■

• 2 4 . 7

■ 2 1 . 1

■ 2 1 . 3

■

2 4 . 7

1 . 6 7

1 . 1 5

1 . 7 9

2 . 7 5



35

The Heads of Agreement Contract required that the calibration of

the instrument was based on a minimum of 30 samples but it is evident

from the above data that if the calibration samples were collected over

a number of days the calibration standard deviation for the individual

days could vary considerably on this application.

3.5.6 Sampling Precision

An exercise was carried out to determine the contribution of the

sampling error to the calibration standard deviation. The samples were

taken, prepared and analysed using the same procedure as for the dynamic

calibration tests except that the sample increments were placed

alternately into sub-samples A and B. The results from 14 pairs of

increments was a sampling precision (2s) of +1.02% ash which was in line

with British Coal normal sampling precision.

This result was applied to the fourth dynamic calibration test

which had given the lowest standard deviation:-

(overall precision)2 - (sampling precision)2 + (Coalscan precision)2

1.39

2

- 0.51

2

+ (Coalscan precision)

2

Coalscan precision - 1.29% ash at 1 standard deviation

Having taken into account the sampling precision the accuracy of

the Coalscan instrument was still outside the acceptance requirements.

3.5.7 Further Investigation of Cross-belt Segregation

The lack of improvement in the accuracy of the Coalscan since the

installation of the oscillating head mechanism in April 1987 suggested

that the instrument was not examining a representative proportion of the

coal on the conveyor due to cross-belt segregation and the uneven

distribution of material on the belt. The scanning range of the

measuring head across the belt had been Increased but without any

improvement in results. Finally, in January 1988, a plough was attached

to the conveyor sideplate, on the opposite side of the belt to the C-

frame support, in an attempt to produce a more uniform distribution of

coal on the belt.

A series of ten tests was conducted to investigate cross-belt

segregation and the effect this might be having on the performance of

the Coalscan instrument. Countrates were recorded every 3 seconds as

the measuring head was traversing the bed, the profile of which was

modified by alterations to the plough position and the flowrate. A

computer plot of barium countrate, indicating material bed depth, and

computed ash content against time was produced for each test and

examined for evidence of segregation. The plots showed certain

inconsistencies and two further tests were devised to examine them

further.

In the first test, Test 11, the conveyor was kept stationary and a

coal sample, crushed to minus 1 mm and well mixed, was spread evenly on

the belt. The measuring head was moved backwards and forwards across

the belt with the traversing system under manual control. The plot of

barium countrate and computed ash content against time, Figure 59,



36

showed a sudden, large reduction in ash content and a lower barium

countrate with the measuring head in the extended position, towards the

far side of the belt. The chart also showed a longer time for the

outward travel of the measuring head and a shorter return time

indicating that the instrument was traversing the belt with different

speeds for outward and return travel.

In the final test, Test 12, the radiation absorbers, used for

the off-belt standardisation procedure, were secured to the underside of

the detector and with the conveyor running empty, the measuring head

traversed the belt with a cycle time of 108 seconds. The plot of barium

and americium countrates and computed ash content is shown in Figure 60.

The chart shows sudden increases in both barium and americium countrates

corresponding to a sharp fall in the ash content with the measuring head

in the extended position, at the far side of the belt. This effect was

found to correspond with a longitudinal section of the belt where the

outer cover was badly worn.

The following conclusions were drawn from this series of tests:-

(i) the apparent low ashes were mainly due to factors other

than just cross-belt segregation,

(ii) there was a section of the transverse scan width which was

giving rise to unrepresentative results and this seemed to

correspond to a section of the belt where the plastic

cover was worn,

(iii) the effect did not seem to vary significantly with

belt loading,

(iv) the scan cycle time was varying with time and confirming

previous experience.

The results of these cross-belt segregation tests were reported in

full to the manufacturer and a representative from MCI visited the

Askem installation from 9th to 12th February 1988 to investigate the

problem. The scan width was reduced from 200 mm to approximately 140 mm

to ensure that the measuring head was confined to a section of the belt

in consistently good condition. The instrument settings were also

examined and corrected where necessary, prior to a further dynamic

calibration test.

3.5.8 Seventh Dynamic Calibration Test

This test was carried out on the 14, 16 and 17th March 1988 when

7,

15 and 8 samples and measurements, respectively were taken. The

sample increments were collected at 16 second intervals over a period of

9 minutes 36 seconds, which corresponded to six complete circuits of the

conveyor belt. The odd and even increments were kept separate to enable

the sampling precision to be determined from the subsequent analysis.

whilst the samples were being collected the tracking of the conveyor was



37

monitored by taking measurements from a datum to the edge of the belt.

The belt factors were also checked before and after the calibration

test.

The samples were prepared and analysed for moisture, ash and

elemental ash composition. The standard deviation for the 7th dynamic

calibration, Table 11, Figure 61, was found to be 1.7% ash (A.R.) and

the sampling precision was calculated at 1.2% ash at the 95% confidence

level.

A static calibration was also conducted on-site on 29 and 30 March

1988 with approximately 1 kg of each sample, reduced to minus

212 micron, and the standard deviation, Table 11, Figure 62, was found

to be 0.9% ash (A.D.).

The outcome of this calibration test was considered in relation to

the following factors : -

(i) Belt factor - representative of the attenuation due to the

belt and used by the instrument to determine the radiation

intensities at the underside of the coal bed. Measurements

of the belt factor immediately before and after the dynamic

test were very similar to those obtained by MCI when setting

up the instrument a month earlier and therefore no

significant changes had taken place.

(ii) Belt drift - the lateral movement of the belt relative to

the measuring head which may occur as the belt is running,

particularly under load. During the setting up by MCI the

mean position of the belt edge from the datum was 80 mm and

the scan width was adjusted to accommodate 25 mm movement

either way without significantly affecting the belt factor,

i.e. the belt edge to datum could vary between 55 and

105 mm. The measurements taken during the test were within

these limits.

(iii) Iron content - the iron oxide in the ash and the ash % for

this test is compared below with the available analysis from

previous dynamic tests.

Calibration Test

1st Dynamic

4th Dynamic

6th Dynamic

7th Dynamic

Ash

Mean

16.4

22.2

17.9

19.1

% (A.R.)

Std. Dev.

4.7

5.1

4.7

4.2

Fe203

Mean

11.4

10.7

11.5

13.4

in Ash

Std. :

2.4

1.7

2.2

2.4

Dev

Although the iron in ash is slightly higher than previously

encountered the standard deviation is similar to previous

dynamic calibration tests and no significant change has

occurred in elemental composition from the original analysis

submitted to the manufacturers.



38

(iv) Errors - the overall error In ash measurement for the

installation could be attributed to the following sources : -

(a) Coal composition - the error attributable to variation in

coal composition can be taken as the standard deviation from

the static calibration, i.e. 0.9% ash.

(b) Sampling - the error due to sampling can be taken as the

precision of sampling, i.e. 0.6% ash at 1 standard

deviation, which is similar to a previous estimate and in

line with operational experience.

(c) Moisture - the error due to moisture was taken as 0.5% ash

at 1 standard deviation in accordance with information

received from CIRSO, Australia.

(d) Residual - that error which remains unexplained after

accounting for all other known sources of error.

This can be calculated from the known errors as follows,

where S is the standard deviation:-

(S

overall)

2

- (S

coal)

2

+ (S

sampling)

2

+ (S

moisture)

2

+ (S residual)

2

(1.7)2 - (0.9)2 + (0.6)2 +

(0.5)

2

+ (S

residual)

2

S residual - 1.2% ash

The residual error is therefore 1.2% ash and represents half

the overall measured variance. If the residual error could

be eliminated, the best achievable error of the Coalscan at

Askem would be : -

(S best

overall)

2

- (S

coal)

2

+ (S sampling)

2

+

(S moisture)

2

- (0.9)

2

+ (0.6)

2

+ (0.5)

2

S best overall - 1.2% ash

3.5.9 Comparison of Static and Dynamic Calibrations

It was originally intended, as stated in the Heads of Agreement

Contract, that the on-belt dynamic calibration test would be followed by

an off-belt static calibration using part of the laboratory sample from

the dynamic test. However, it was not anticipated that it would be

necessary to repeat the dynamic calibration so many times and, because

of the additional work involved the original procedure, was only

followed in the case of the first and seventh calibration but, in

addition, static calibrations were conducted with the laboratory

Coalscan instrument on the samples from the fourth dynamic test at -1 mm

and -212 micron sizes. The results of the dynamic and static

calibrations for these tests are summarised below with the dynamic

calibration converted to an air dried basis to enable a comparison of

accuracy to be made on a common basis. The value of standard deviation

used for Test 4



1

4

7

1.51

1.39

1.70

1.70

1.57

1.92

0.85

0.70

0.91

Mean Ratio

3?

Is derived from the mean of the variances for the two tests conducted at

different particle sizes.

Coalscan 3500 Ash Monitor Calibrations

Dynamic Static Ratio

Test Std. Dev. Std. Dev. Std. Dev. Dynamic Std. Dev. (A.D.)

% Ash (A.R.) % Ash (A.D.) % Ash (A.D.) Static Std. Dev. (A.D.)

2.0 : 1

2.24 : 1

2.11 : 1

2.12 : 1

The mean ratio of dynamic to static calibration accuracy of

2.12 : 1 compares with the ratio of 2.1:1 given by the dynamic simulation

tests with the laboratory Coalscan instrument, Table 10, between the

calibration accuracy from the comprehensive examination of samples and

from a single row of measurements. This simulation technique warrants

further investigation as a possible means of predicting on-line

performance from laboratory testing.

3.5.10 Shift Integration Performance and Comparison with

Phase 3A Ash Monitor

Following the failure of the Coalscan 3500 to meet fully the

required level of accuracy in the performance tests conducted over short

integration periods of about 10 minutes, two series of tests were

conducted to investigate the accuracy of the instrument with full shift

integration and in the second series to compare the performance with a

Phase 3A ash monitor. The calibration derived from the performance test

was entered into the Coalscan instrument and the integration period set

to correspond to the shift sampling period.

In the first series of tests the integrated ash measurement was

compared with the laboratory shift analysis for a total of 99 shifts

during the latter part of 1987. A summary of the results is given

below:-

No of shifts

Range of ash % (A.R.)

Mean ash % (A.R.)

Standard deviation

ash % (A.R.)

Laboratory

Shift Analysis

99

10.9 - 20.3

15.1

1.72

Coalscan

Shift Integration

99

11.5 - 16.7

13.3

1.0



40

Correlation coefficient

Standard deviation % ash

Calibration

0.

1.

617

03

Shift Integration

0.71

0.71

From the above results the Coalscan instrument showed much less

variability in the ash measurement than the laboratory analysis and also

a mean bias of

-1.8%.

The correlation between the Coalscan and the

laboratory analysis was not particularly good and the limited range of

ash variation resulted in a comparatively low value of standard

deviation. The relationship is shown graphically in Figure 63.

The second series of shift integration tests, including the

integrated ash measurement from the existing NCB/AERE Phase 3A ash

monitor, was conducted over 108 shifts between January and June 1988.

The Phase 3A monitor examined the total sample taken automatically from

the production stream and crushed below 5 mm. The laboratory sample was

obtained by sample division after the Phase 3A monitor. The results of

this series of tests are summarised below:-

Laboratory

Analysis

Coalscan

Integration

Phase 3A

Integration

No.

of shifts

Minimum ash % (A.R.)

Maximum ash % (A.R.)

Mean ash % (A.R.)

Std dev ash % (A.R.)

108

11.9

19.3

15.05

104

11.9

19.3

15.04

108

11.5

21.4

16.1

104

11.5

21.4

16.15

1.53 1.55

1.66 1.66

108

10.1

21.9

16.04

1.72

104

12.0

21.3

16.05

1.36

Coalscan 3500 Ash Monitor


Standard deviation ash %

Phase 3A Ash Monitor


Standard deviation ash %

Calibration

0.892

1.70

Calibration

0.98

0.84

Shift Integration

108 shifts 104 shifts

0.266 0.290

1.61 1.59

Shift Integration

108 shifts 104 shifts

0.398 0.629

1.59 1.06

The Coalscan and the Phase 3A both showed slightly more

variability in the integrated ash measurement than the laboratory

analysis over the 108 shifts. The Coalscan gave a mean bias of -1-1.05%

and the Phase 3A a mean bias of +0.99% . The correlation between the

shift integration and the laboratory ash for both the Coalscan and the

Phase 3A for the 108 shifts was extremely poor and the standard



41

deviation for the Phase 3A was much worse than would have been expected

from past experience.

The Phase 3A results showed two very low measurements around 6-7%

below the laboratory ash and also two very high measurements between

6-8% above the laboratory ash. Although there was no record of any

special circumstances to account for these large differences it was

considered that they were the result of some abnormal condition and were

well outside the range of error normally experienced with the Phase 3A

ash monitor. Since the standard deviation was also much worse than

normally achieved with this instrument, and with the calibration value,

the performance of the Phase 3A was also assessed on the basis of 104

shifts. This gave a significant increase in the correlation coefficient

and also a substantial improvement in the standard deviation to a level

nearer to that normally associated with this instrument. The

relationship between the shift integration for each instrument and the

laboratory shift analysis is shown in Figures 64 and 65.

The difference between the Coalscan measurement and the laboratory

ash, for both series of tests, and between the Phase 3A measurement and

the laboratory ash have been plotted in Figures 66, 67 and 68. In the

first series of tests the Coalscan shows a pronounced drift away from

calibration in a negative direction from an initial bias of around -0.7%

to -2.8% after 99 shifts and suggests some instability in the

instrument. In the second series of tests the Coalscan showed a

pronounced positive drift in bias from an initial bias of -1.2% to a

final figure, after 108 shifts, of +3.2%. This drift tended to confirm

instability in the Coalscan system. The plot of the difference between

the Phase 3A measurement and the laboratory ash showed an almost

constant bias of around 1% over the period, and suggested a more stable

instrument than the Coalscan.

In order to make a strict comparison of the performances of the

Coalscan 3500 and the Phase 3A ash monitor on the basis of instrument

error (Si) only, it is necessary to take recognition of the errors which

arise in the sampling (Ss), sample preparation (Sp) and analysis (Sa) of

the laboratory samples to which they are compared. Both instruments are

compared to the same laboratory sample but since the instruments are

located at different positions in the flow scheme, Figure 48, the

actual measured standard deviations (Sm) reflect the errors which arise

in the determination of the laboratory value to different degrees.

(Sm)2 - (Si)

2

+ (Ss)

2

+ (Sp)

2

+ (Sa)

2

In the case of the Coalscan 3500 Sm includes all the errors from

the determination of the laboratory value (Ss + Sp +

Sa).

Previous

tests at As kem had shown that these errors had a combined value of

0.51% ash.

Thus (Si)

2

- (Sm)

2

- (Ss + Sp + Sa )

2

-

(1.59)

2

-

(0.51)

2

Hence Coalscan Si - 1.51 % ash



42

In the case of the Phase 3A ash monitor, which was interrogating

the whole of the primary sample (after crushing to 5 mm) but before

sample preparation and analysis, the sampling errors are not included in

the comparison. Earlier work on the development of the Phase 3A ash

monitor (4) indicated that the error due to sample preparation and

analysis (Sp+Sa) amounts to approximately 1.25% of the average ash level

and hence, for this As kem trial, can be considered to be 0.19% ash.

Thus (Si)2 - (Sm)2 - (Sp+Sa)2

- (1.06)2.(0.19)2

Hence Phase 3A Si - 1.04 % ash

On the basis of instrument error, only the Coalscan 3500 showed a

50%

greater standard deviation on shift integrated ash measurement than

the Phase 3A ash monitor in this series of 104 shift results.

3.6 Summary

One of the significant advantages claimed for a two energy

transmission system is its insensitivity to coal bed thickness and

consequent suitability for application directly to coal on a conveyor.

Laboratory tests using standard absorbers representing a wide range of

coal bed thicknesses confirmed this advantage and substantiated the

claim that the instrument could be used with coal bed thickness down to

50 mm.

The effect of some coal composition factors on accuracy was

assessed experimentally, showing that the largest effect was due to iron

where a 1% addition of Fe2Û3 was found to be equivalent to an increase

of 6% in ash content.

A limited number of coals from potential sites for a trial

installation of the Coalscan Monitor were tested in the laboratory on a

static test rig. Calibration accuracy (+ls) using coal crushed to

-212 pi ranged from 0.64% to 3.67%.

An assessment of the effect of particle size on the accuracy of

the static calibration procedure was obtained by making additional

measurements on one suite of coals at coal at 1 mm - 0 and at 25-3 mm

particle size. A calibration standard deviation value of 0.64% for

-212 pa coal compares with 0.80% for 1 mm - 0 coal and 0.83% for 25-3 mm

coal which has been intensively interrogated by multiple-pass

measurements. When the pattern of measurements is reduced to a single

pass,

simulating the dynamic, on-belt situation, the value for 25-3 mm

coal is reduced to 1.75%. This suggests that the on-belt accuracy of

measurement may be significantly less than that obtained from a static

calibration and is associated with the degree of interrogation of the

sample.

The Coalscan monitor was installed on the final power station fuel

conveyor at As kem Colliery and subjected to a series of dynamic

calibration tests giving calibration standard deviation values of 1.4 to

1.8% compared with an agreed, expected performance target of less than



43

1.25%. Static off-belt calibrations with the same coals showed that the

lower than expected accuracy must be attributed to factors other than

coal composition. Evidence of cross belt segregation of ash levels and

a significant effect due to a damaged section of the conveyor were found

but when these were avoided by rectifying the operating procedures no

significant improvement in accuracy was achieved. Taking into account

the errors due to coal composition, sampling and laboratory analysis and

moisture content variations, a residual error of 1.2% ash remained and

could not be explained.

A comparison of the accuracy of dynamic calibration tests with

static tests using the same samples gave an average ratio of 2:1, the

same as found in the earlier simulated dynamic test.

A performance test, comparing instrument readings interpreted over

10 minutes with laboratory analysis, for 57 samples and two subsequent

comparisons of shift-integrated values, each comprising about 100

samples, showed only a poor correlation (r - 0.7 or

less).

During these

longer term comparisons, a significant drift in the calibrations was

also observed resulting in a pronounced bias (3% ash) at the end of each

period.

4. SUB-STREAM ASH MONITORING

Sub-stream ash monitoring involves the examination, on a

continuous or intermittent basis, of a representative proportion of the

main production stream which has been obtained by some continuous or

intermittent sampling or diversion technique. The sub-stream material

may be conditioned in some way, i.e. crushing, drying etc. prior to

examination in order to assist the presentation to the measuring system

or to improve the accuracy of ash measurement. However, conditioning

the sample usually results in delaying the ash measurement and,

therefore, a compromise has to be made between the speed and accuracy of

the measurement, depending on the purpose of the monitoring, with

continuous quality control requiring a faster response than consignment

verification. Sub-stream monitoring can be combined with a sampling

system for quality control or commercial analysis purposes and,

therefore, does not necessarily involve additional sampling facilities.

4.1 Previous UK Experience and Problems

A sub-stream ash monitor, which had been successfully applied for

a number of years at several UK collieries, was the NCB/AERE Phase 3A

ash monitor, Figure 69. This instrument was developed jointly, in the

UK, by the National Coal Board (now British Coal Corporation) and the

Atomic Energy Research Establishment

(AERE),

Harwell, in the late I960's

and was subsequently re-designed and manufactured under licence in the

UK by Gunson's Sortex Ltd.(5), The phase 3A unit had a capacity of 1 t/h

and the feed material had to be crushed below 5 mm prior to presentation

to the nucleonic ash measuring system in a 38 mm thick layer, with a

smooth profiled surface, on a rotating table. The backscatter measuring

system employs a Plutonium 238 source with a low energy gamma radiation

level of 17 KeV which limits the depth of penetration of the coal and,

consequently, the size of material which can be examined.



44

The increase in the fines content and consequently the moisture

content of most small coal products, as a result of intensive

mechanisation, resulted in difficult handlability problems on most Phase

3A installations with the eventual withdrawal from service of many

units. The difficult handlability affected all stages of the sample

handling and crushing arrangements as well as the ash monitor

presentation unit, and the requirement to crush the samples to below

5 mm in size further aggravated these handlability problems.

Investigations conducted in 1978/79 indicated that it was possible

with some coals to increase the size of the feed to the Phase 3A ash

monitor to 12 mm or even 15 mm without adversely affecting the accuracy

of ash measurement. This modification was implemented at a number of

installations by increasing the aperture of the grids on the sample

crusher from 12.5 mm to 25 mm to give a 12 mm - 0 product and provide

some alleviation of the handleability problem.

At the same time, investigations were also being made by British

Coal into the possibility of developing other presentation techniques

which would produce a consistent degree of material compaction and a

smooth surface profile but would tolerate material of more difficult

handlability. Two alternative techniques were tested and compared with

the Phase 3A turntable system. These alternatives were a belt feeder

and a screw feeder with an extension tube, both units being provided

with vertically adjustable compression plates to vary the degree of

material compaction. With coal -5 mm the free (or surface) moisture

tolerance level of the belt feeder was around 12.5% before deformation

of the coal bed occurred, with the screw feeder this level increased to

between 12.5 and 14.5% compared with around 10.5% for the Phase 3A

turntable. Tests conducted with coarser feeds showed an increase in the

moisture tolerance level and also that a smooth surface profile could be

produced by increasing the degree of material compaction.

4.2 Previous Development of New Presentation System

To assist with the handling of more difficult material and ensure

a positive flow through a compaction system it was proposed that a

horizontal, reciprocating ram be used to displace material from the

bottom of a hopper and through a compaction zone while in contact with a

short belt feeder. The belt travel would be dependent on the forward

movement of the material. An experimental laboratory unit, Figure 70,

incorporating a hydraulic ram and power pack, demonstrated that this

technique was capable of successfully handling material with a high

fines content and up to 20% free moisture and producing a smooth surface

profile. However, with no independent drive to the belt feeder the

drive transferred through the material was Insufficient to overcome the

resistance caused by particles becoming trapped in the clearance between

the belt and the side-plates. The belt feeder was therefore replaced by

a horizontal, stainless steel open top rectangular trough. It was found

that the action of the ram was capable of moving forward the compacted

bed of material a distance of at least 600 mm while maintaining a

constant bed depth.



45

A number of calibration tests were conducted on the experimental

laboratory rig, Figure 71, using the plutonium 238 backscatter system,

with proportional counter, from the Phase 3A ash monitor. This system

was independently mounted to prevent shocks from the reversal of the

hydraulic ram affecting the measuring system. These tests included a

series conducted with a suite of 34 samples of blended power station

smalls from Markham Colliery, Central Area, British Coal. The same

samples were tested successively at 50 mm, 25 mm and 5 mm top size.

After reduction to minus 212 micron for laboratory analysis the samples

were also tested on a Telsec 350 laboratory analyser using a plutonium

238 source.

A summary of the sample analysis and calibration test results are

given in Table 13. The samples covered a wide range of ash content but

the total moisture, sulphur and chlorine contents were fairly

consistent. The calibration accuracy showed only a slight deterioration

from a standard deviation of 0.81% ash at 5 mm top size to 0.90% ash at

25 mm top size and this was attributed to the degree of compaction and

the smooth surface profile produced by the ram-feed unit. There was a

poorer correlation and a marked increase in standard deviation to 1.67%

ash with the 50 mm top size material which was too coarse to give a

smooth surface profile. The much lower standard deviation given by the

quadratic regression, compared with the linear regression, pointed to

the necessity for having a signal processing system with this new ash

monitor which, unlike the Phase 3A unit, would be capable of applying a

quadratic calibration equation to the countrate measurements. The

calibration accuracy given by the Telsec instrument probably represented

the optimum that could be achieved with that particular product due to

variations in the chemical composition of the ash.

The level of accuracy achieved by the ram-feed presentation system

handling 25 mm top size material from Markham Colliery was considered

very encouraging, particularly since the colliery output was drawn from

a number of seams with differing characteristics. Discussions were

therefore started regarding a colliery trial site at Markham for an

experimental ram-feed unit, possibly replacing the existing Phase 3A ash

monitor which had failed to operate regularly because of the difficult

handlability of the material.

Using the plutonium 238 isotope head, tests were also conducted to

determine the degree of compaction of the feed material necessary to

achieve a stable level of countrates. The tests were conducted with

four different coals, one sized 50 mm - 0, two sized 25 mm - 0 and the

fourth sized 12.5 mm - 0. The entry to the compaction zone had a depth

of 120 mm and countrate measurements were made with vertical

compressions ranging, where possible, from 0 to 21mm at intervals of

3 mm. The tests were conducted under choke-feed conditions from a

part-filled hopper, with material being recirculated as necessary to

maintain this condition. All the coals tested required a minimum

vertical compression of around 12 mm, i.e. 10%, in order to achieve a

stable countrate, as illustrated in Figure 72. Measurements of the

loose and compacted bulk densities of the samples showed that this



46

degree of vertical compression corresponded to a volumetric compaction

of around 30% . Measurements were also made of the hydraulic pressure

required for vertical compressions of up to 21 mm using coal samples

with three different levels of moisture. The results were plotted in

Figure 73 and show that the pressure required to compress the material

increases with moisture content but, more significantly, the pressure

required increases dramatically for a vertical compression in excess of

12 mm for all levels of moisture tested.

4.3 Design of Trial Site at Markham Colliery

Proposals by the former North Derbyshire Area and Scientific

Control for the reorganisation of the sampling arrangements for the

50 mm - 0 power station blend at Markham Colliery in 1983, including the

removal of the Phase 3A ash monitor because of severe handlability

problems, provided an

opportunity for the incorporation of a trial site for the ram-feed

presentation unit. The design of the new sampling system and the

arrangements for the inclusion of the ram-feed unit are shown

schematically in Figure 74.

The existing mechanical sampler would be replaced by a new linear

motor driven, traversing bucket sampler at an in-line transfer point on

the conveyor system for the 50 mm - 0 blended power station product,

which was produced at a maximum rate of 850 t/h. Because of the high

flowrate the sampler would discharge an increment at each end of its

travel,

after a single pass through the falling stream of material. The

sample increment collected on the forward travel would be used for

normal laboratory analysis. It would discharge onto a slow moving belt

feeder, or pacemaker conveyor, which would regulate the feed to a swing

hammer crusher for reduction below 5 mm. The crushed sample would be

fed to a sample divider and a representative proportion diverted into a

container for laboratory analysis. The remainder of the sample was

returned by conveyor to the main product stream. At regular intervals,

increments would be automatically diverted before the crusher to provide

a moisture sample. The increments collected on the reverse travel of

the sampler were to be returned directly to the product stream but a

manual by-pass was provided to collect increments for bias testing.

Agreement was reached with both the Area and Scientific Control

that the sample increments collected on the reverse travel of the new

sampler would be used to feed a test circuit for the ram-feed unit. A

second pacemaker conveyor would be installed to collect the increments

and provide a controlled feed to a second swing hammer crusher. Tests

with Markham blended smalls at the at the manufacturer's works had

confirmed that the top size of the crushed product could be selected at

6 mm, 12.5 mm or 25 mm by changing the crusher grid plates. A larger

top size could be obtained, if required, by removal of the grid plates.

An automatic by-pass would return the sampler discharge directly to the

product stream when the ram-feed circuit was not in operation.

The crushed material would be transferred by conveyor to the

original ash monitoring room, which previously held the Phase 3A unit,



47

where the ram-feed presentation unit would be sited. A short screw

conveyor would make the final delivery to the feed hopper on the

ram-feed unit. A second screw conveyor would collect the discharge from

the ram-feed unit and also pick up any scrapings from the ram and

deliver to the reject conveyor for return to the product stream. An

intermediate, slide operated, discharge from the screw conveyor would

provide for sampling the discharge from the ram-feed unit or for

collecting the whole throughput when conducting a calibration procedure.

The ram-feed circuit would have a separate electrical control

panel from the colliery sampling system but it would be interlocked with

the sampler and the reject conveyor. Adequate access would be provided

around the circuit for operation and maintenance, and platform areas

provided for instrumentation equipment.

The reorganisation of the colliery sampling system was completed

in 1983 but the completion of the test circuit was delayed by industrial

action until March 1985. The experimental ram-feed unit was installed

by August 1985 but was not commissioned until the end of the year

because of a fire on the coal preparation plant which necessitated

replacement of the electrical switchgear, cabling and control system.

4.4 Design and Construction of New Experimental Ram-feed Unit

A new experimental ram-feed unit, Figure 75 was designed and

constructed in-house for the site trials. The trough and the feed

hopper were constructed in stainless steel, and the trough was provided

with a second outlet in the position of the retracted ram to allow any

material to be drawn back by the ram to be discharged. A proprietory

screw conveyor was adapted to operate in conjunction with the ram-feed

unit and accept the material discharged at both outlets.

The ram, 38 mm bore hydraulic cylinder and guide rails were

transferred from the previous unit. A new proprietary hydraulic power

pack was provided, complete with the necessary valves, to allow the

speed of travel of the ram to be controlled independently in both

directions. This design would permit the slow forward travel of the ram

and the faster return travel to be adjusted more precisely than the

previous improvised arrangement. The power pack was provided with both

level and temperature sensors for connection in to the electrical

control system, as required by British Coal regulations.

The ram-feed unit and the screw feeder are shown in position at

the trial site in Figure 76.

4.5 Testing of Ram-feed Unit at Markham Test Site

The installation of the ram-feed unit at the test site at Markham

Colliery, including all electrical sequence and safety interlocks to

allow automatic running, was finally completed at the beginning of 1986.

However, some teething problems with the test circuit caused

interruptions to the operation of the system during the first few months

and regular operation was not achieved until the end of April of that

year.



48

The initial trials of the ram-feed unit were intended to determine

whether:-

(a) the unit is capable of tolerating material of difficult

handlability, resulting from excessive proportions of filter

cake or recovered fines or inadequate dispersion of these

components in the blended product.

(b) this difficult material can be handled satisfactorily when

the product is crushed below 25 mm, 12.5 mm or 6 mm.

(c) the unit is capable of producing a continuous and uniformly

compacted bed under conditions of varying increment size and,

consequently, variable fcedrate and

(d) the unit can produce a continuous, smooth surface profile to

enable the measurement of iron fluorescence as a correction

factor.

By the end of June 1986 the unit had been in operation for about

300 hours, as recorded by the elapsed time meter on the system, with

only occasional attention from the colliery sampling staff. Sample

increments were being taken at 6 minute intervals and fed into the test

circuit over a period of 3-5 minutes. Under this trickle feed condition

some malformation of the coal bed occurred, probably due partly to the

feed screw delivering to one side of the feed hopper.

During the second half of 1986 the compression plate on the

ram-feed unit was increased in length from 100 mm to 300 mm to apply a

more gradual compression to the material being advanced by the ram. The

feed screw conveyor discharge chute was also modified to centralise the

material delivery into the feed hopper on the ram-feed unit. These

changes were successful in overcoming the problem of bed malformation at

low feed rates and the unit was able to produce a smooth, continuous

surface profile under both choke-feed and trickle-feed conditions. By

the end of 1986 the ram-feed unit had completed 1000 hours of operation

with no handlability problems encountered within the unit Itself.

The hydraulic pressure required by the 38 mm bore, double acting

hydraulic cylinder to produce the necessary degree of material

compaction resulted in a severe hydraulic shock to the whole unit when

the ram was reversed. It was feared that this mechanical shock would

seriously affect any nucleonic ash measuring system mounted on or over

the unit. This problem was overcome in the first half of 1987 by two

modifications to the hydraulic system:-

(a) the hydraulic cylinder was replaced by a larger unit of

63.5 mm bore to reduce the hydraulic pressure requirement

under normal feed conditions and to increase the maximum

thrust available to deal with excessive fines in the feed

material.



49

(b) the existing AC operated reversing valves were replaced by

time-delayed DC operated valves which gave a more gradual

reversing action and cured the hydraulic shock and vibration

on the unit.

At the beginning of the trial the sample crusher was fitted with

50 mm aperture grid plates to provide a product for the ram-feed unit

with an upper size of around 25 mm. During the first 9 months of the

trial the ram-feed unit proved capable of handling this size of material

with no problems, and in January 1987 the crusher was fitted with 25 mm

aperture grid plates to reduce the upper size of the crushed product to

around 12 mm. After a further 2 months of satisfactory operation these

were in turn replaced by 12.5 mm aperture grid plates to give a product

of around 6 mm top size. The trial of the experimental ram-feed unit

continued for 11 months with this size of feed, before replacement by

the prototype unit, with no handlability problems.

The sizing analysis of the original 50 mm - 0 product and the

crushed product with each size of grid plates is given in Table 14 and

plotted in Figure 77.

Throughout the trial, regular checks were made on the condition of

the coal bed produced by the ram-feed system. The bed remained

consistently at the same level along the length of the trough and there

was no tendency for it to expand after emerging from the compression

plate. Sections taken periodically from the bed had a relative density

close to 1.0 which did not appear to be measurably affected by the size

of the feed material as a result of changing the crusher grid plates.

However, the smoothness of the surface profile improved as the top size

of the feed was reduced from 25 mm to 6 mm, Figures 78 and 79.

When operating under choke-feed conditions, each 254 mm forward

stroke of the ram of advanced the coal bed by 120 mm. With a trough

width of 180 mm and a bed depth of 108 mm the volume of material

extruded per stroke was 2.33 litres which with a coal bed of relative

density 1.0, corresponded to 2.33 kg of material per stroke. The ram

had a minimum cycle time of 12 seconds, 5 seconds forward travel,

5 seconds reverse, and 1 second reversing time at each end, which gave a

maximum rate of operation of 300 strokes per hour and a maximum capacity

of 700 kg per hour. The average weight of a sample increment was around

25 kg, so the maximum possible rate of sampling would be once every 2

minutes. In practice, the sampling frequency was limited to every six

minutes by the requirements of the colliery sampling system.

During the first fifteen months of the trial a check was kept on

the sample handling system with regard to any problems with material

handlability. The build-up of fines was found to occur at the following

locations

: -

(a) sample crusher outlet chute

(b) transfer chute from transfer conveyor to screw feeder

(c) ram-feed unit feed hopper



50

The inside surfaces of these components were treated with a

proprietary epoxy paint finish to reduce fines adhesion and build-up.

This treatment overcame the problem and no further attention was

required.

Also, in the second half of 1987, an additional control panel was

introduced into the ram-feed control system to ensure that the feed rate

from the product sampling system was within the capacity of the

presentation unit. Two capacitance-type proximity switches were mounted

in cut-outs on the rear of the feed hopper; one near the top and the

other near the bottom. If the level in the feed hopper reached the

upper switch the feed system was stopped as far back as the pacemaker

conveyor and sample increments were diverted back to the product

conveyor. The feed system was re-started when the level fell below the

bottom level switch. The capacitance proximity switches were, however,

dependent on a certain level of moisture in the feed material and an

alternative type of level switch, such as a vibrating reed, may be

necessary with drier material.

4.6 Design and Manufacture of Pre-production Prototype Unit

In December 1986, when the experimental ram-feed unit at Markham

had completed 1000 hours operation with no material handlability

problems, it was decided to proceed with the design and manufacture of a

pre-production prototype unit. The design would be based on the

experimental unit and provision would be made for the incorporation of

both ash and moisture measuring systems. A specification, included in

Appendix 8, was drawn up by British Coal for the design, manufacture and

installation by an outside firm and tenders invited.

A contract was finally placed in July 1987 with Ramsey Process

Controls of Byfleet, Surrey, a firm which already had many years

experience in the supply, installation and maintenance of

instrumentation, including nucleonic equipment, in coal preparation

plants.

Following agreement on the main design features, Figure 80, the

first pre-production prototype unit was manufactured and installed at

Markham Colliery, in place of the experimental unit, in February 1988

and was in operation by 21st March 1988.

The general arrangement of the prototype unit is shown in

Figure 81 and a photograph of the completed unit prior to installation

in Figure 82. The unit, designed for floor mounting, was constructed

mainly using stainless steel. The feed hopper, with a capacity of

approximately 35kg, was lined with high molecular weight polyethylene to

reduce fines adhesion and avoid material build-up. The rear of the feed

hopper, Figure 83, included cut-outs in the stainless steel for the

positioning of upper and lower level senors. The rear view also shows

the hydraulic cylinder which, in this design, was mounted directly

in-line with the ram, and the length of the unit to the rear of the feed

hopper was minimised by allowing the ram to retract around the cylinder.

The unit was provided with two interchangeable trough sections,

made in polypropylene, which were flange connected after the compaction

zone. The longer section, 485 mm, would accommodate both ash and



51

moisture monitors, the shorter section, 285 mm, was intended for ash

monitoring only. The width and depth of the trough section were kept at

180 mm and 120 mm respectively as in the experimental unit.

The prototype unit was fitted with the longer trough and operated

successfully under surveillance, for the 6 months to September 1988.

The hydraulic power pack for this installation, supplied by British

Coal,

had a capacity of 8.41 litres/min at a maximum pressure of

8621 kPa which, in combination with a cylinder of 63.5 mm bore was

capable of producing a maximum thrust of 27.3 kN.

A second prototype unit was ordered by British Coal early in 1988

to extend the on-site trials to a second colliery.

4.7 Nucleonic Ash Measuring and Signal Processing System

4.7.1 Design of Ash Measuring and Control System

The nucleonic ash measuring system for the Ram-fed ash monitor was

based on that currently used on the NCB/AERE Phase 3A ash monitor which

had been developed and proved over a number of years. The system

employs plutonium 238 isotopes emitting 12-17 keV gamma radiation and

the ash measurement is dependent on the radiation backscattered from the

upper layers of the coal bed. The system also detects and isolates iron

fluorescence to provide a means of correcting the ash measurement for

variations in the iron content of the coal.

The design of the system is illustrated in Figure 84, and the

specification for the principal components is given in Appendix 9. The

system comprises three functionally distinct and physically separate

sections : -

(i) The radiation emission and detection units, comprising radioactive

sources and proportional counter, were designed to be mounted

immediately above the coal bed on the ram-feed unit with the pulse

pre-amplifier in close proximity.

(ii) The pulse analysing and counting section comprised standard

Nuclear Instrumentation Modules

(NIM),

of reliable manufacture,

which plugged into a standard housing, i.e. a NIM bin, complete

with a power distribution system. This unit was, in turn, housed

within an environment-proof enclosure and located in the vicinity

of the ram-feed unit.

(iii) The computing and control section comprised a micro-computer, in

an industrial housing, for the computation and display of ash

content, and a programmable logic controller (PLC) which controls

the operation of the Ram-feed unit and co-ordinates the ash

measuring system.

4.7.2 Operation of Ash Measuring and Control System

The proportion of the radiation from the plutonium sources

absorbed by the coal bed is directly related to the ash content of the

coal and the proportion backscattered is, therefore, inversely related



52

to ash content. The backscattered radiation, together with iron

fluorescence, is detected by the proportional counter which produces a

stream of charge pulses, with the magnitude of the charge dependent on

the energy of the detected radiation. The charge pulses are converted

by the pre-amplifier into amplified voltage pulses which are transmitted

to the spectroscopy amplier where it is further amplified before passing

to the spectrum stabiliser.

The spectrum stabiliser dynamically compensates the overall gain

of the counting system for any slight variations in system gain that

occur principally in the proportional counter. The voltage pulses pass

to the energy analyser which separates them into two channels. The

lower energy channel is the iron fluorescence and the higher energy

channel the backscattered radiation.

The two channels of pulses are presented individually to the dual

scaler timer module, which is under the control of the microcomputer,

and, on the instruction to start, the scaler timer accumulates counts in

two separate registers. On the command to stop counting the scaler

timer transfers the contents of the two registers to the computer, in

addition to the duration of the actual counting period. The computer

calculates the ash content from the two countrates using a previously

determined calibration equation for the particular coal under

examination. The computer screen displays the current ash content from

the last countrate measurement, the average ash content so far for the

shift and the target ash content for the particular product.

The PLC controls the operation of the Ram-feed unit and also

passes signals to the computer to instruct the dual scaler timer to

start and stop accumulating counts corresponding to the movement of the

coal bed in the Ram-feed trough. In this timing operation an allowance

is made for the initial forward movement of the ram to compress the new

coal charge before the bed itself starts to move. By taking the count

reading only from the moving coal bed it avoids the ash measurement

being biased by any interruptions to the product flow or sampler

operation when the instrument would, as a consequence, be making

repetitive measurements on the same material. Since the measurement is

made only on moving material the shift ash will be weighted according to

the size of the sample increment and, consequently, to the flowrate of

the product.

4.7.3 Radiation Safety Precautions

It was considered possible, although highly unlikely that one or

both of the plutonium 238 radioactive sources being used in the ash

measurement system could become dislodged from the source holders and

become a radiological hazard. To avoid this possibility, two

independent protection systems were incorporated in the measuring

system:-

(i) Source Loss Detector

If the countrate of backscattered radiation should

fall below a pre-set level an electronic circuit

would operate a trip and stop the Ram-feed unit.



53

(ii) Optical Bed Level Trip

In the unlikely event of an obstruction in the Ram-feed

trough, due to a foreign object or a build-up of material,

there would be the possibility of the coal bed rising

and causing damage to the isotope measuring head which might

dislodge the sources.

To prevent this happening, a bed level sensor has been

incorporated in the system. It involves an infra-red

transmitter/receiver and uses fibre optic cable to

transmit and detect a beam of infra-red light across

the Ram-feed trough immediately below the radioactive

sources. Any interruption of this light beam will

activate a trip which will stop the ram-feed unit.

4.7.4 Manufacture and Testing

At the close of the ECSC Research Project all the proprietary

items of the ash measuring system had been obtained and the assembly of

the system had been completed. Only the provision of the necessary

supporting and guarding arrangements for the isotope measuring head over

the Ram-feed trough were required before installation of the system at

the trial site could proceed.

4.8 Summary

One of the limitations of the earlier British Coal designed

sub-stream ash monitors, the Phase 3A system, was the requirement for

coal to be crushed to less than 5 mm and its inability to handle some

wet coals. Work on an alternative presentation system, which would use

a Phase 3A backscattered radiation monitor head and could handle coals

up to 25 mm particle size, had established the basic principles upon

which an experimental system, the Ram-Feed Unit, was designed and built.

This experimental unit was installed at a colliery site where it

proved its mechanical and electrical reliability and its ability to

handle coal at 25 mm, 12.5 mm and 6 mm particle size over 1000 hours of

operating experience.

Based on this experience, a prototype presentation unit, modified

to allow the addition, at a later stage, of a moisture monitoring head,

has been built and successfully operated for a period of 6 months at the

colliery site.

A second prototype presentation unit was manufactured and fitted

with a backscattered radiation detector head linked to a specially

designed signal analysis and processing system and a microcomputer-based

computing and control unit. A microwave moisture monitoring system,

based on work described in Section 5 of this report, was also fitted and

the whole assembly installed at a colliery site for trials at the end of

this project.



54

5. MICROWAVE MOISTURE MONITORING

5.1 Review of Previous Development and Testing by British Coal

5.1.1 Early Investigations

Investigations by British Coal, Scientific Control, into the

possible application of microwave attenuation for the determination of

moisture in coal began in the former North East Region in the mid I960's

and continued in that Region into the early 1970's. This early work

included both laboratory investigations (6) and plant trials (7) with

apparatus based on the proprietary equipment available at that time.

The laboratory investigations concluded that there was a useful

relationship between microwave attenuation and moisture content for any

particular coal and this might be used to monitor the moisture content

to an accuracy of about +1% . The plant trials, using an on-belt

microwave monitor and 12.5 mm - 0 washed coking coal from up to six

seams,

confirmed that the moisture content could be determined to about

+1%

on a daily basis. These investigations demonstrated that the

relationship between moisture content and microwave attenuation was

dependent on the rank of the coal and also on the size consist, so that

it would be necessary to determine a calibration for each coal to be

monitored.

5.1.2 Microwave Bands

The early investigations covered microwaves in two wavebands; the

first waveband, term X- band, covered frequencies in the range 8 to

13 GHz and the second, termed S- band, covers frequencies between 2 and

4 GHz. The range of frequency and wavelength for each band, together

with possible applications and particle size limits, are given below:-

Microwave Frequency Wavelength Possible

Band Range Range Application

X 8 - 1 3 GHz 3.75 - 2.3 cm Sampled and part-

prepared material,

Top size 15 mm

S 2 - 4 GHz 15 - 7.5 cm Unprepared material

• direct on-belt,

Top size 50 mm

The X- band microwaves have the greater attenuation due to water

and should therefore give greater accuracy. However, since the particle

size should be kept small in relation to the radiation wavelength, to

minimise resonance effects, the X- band is restricted to a top size of

15 mm. Its application is therefore mainly limited to samples which

have been subjected to some size reduction for the purposes of sample

division or ash monitoring. The S- band would be required for larger

material, as in the case of direct measurement of the product on a

conveyor belt.



55

5.1.3 Earlier Applications

Following the early investigations, a number of MX100 microwave

moisture meters, manufactured by Rank Precision Instruments

(RPI),

were

applied in the former Scottish Area of British Coal. These meters

operated in the X- band and were used mainly with 5 mm - 0 material as

discrete sample instruments. One unit was installed for continuous

measurement of 5 mm - 0 material on a sample reject conveyor. Another

unit was incorporated into a plough assembly for monitoring a 25 mm - 0

power station fuel directly on the main product conveyor. On this

latter installation the 95% confidence limits for a single determination

were +1.2% over a range of 12-20% moisture.

Also in the Scottish Area, a system manufactured by Associated

Electrical Industries (AEI) and operating in the S- band was used with

limited success on discrete samples with a 25 mm top size.

5.1.4 Previous Development and Application of X-band System

In the late 1970's, the development of a new X-band microwave

instrument by the former Scottish Area Scientific Department was

prompted by the fact that the Rank units were becoming obsolete, with

spares difficult to obtain, and AEI were no longer producing microwave

moisture meters. In 1979, a new instrument was produced which employed

all solid state electronics and a highly stable, low power generator

which permitted the use of a simple "straight through" system without

the need for balancing or reference facilities to compensate for

instability, Figure 85.

Laboratory calibration tests of the new instrument confirmed its

ability to measure moisture to around +1% on discrete 5 mm - 0 samples,

and a number of discrete sample instruments were manufactured for plant

trials.

The manufacture was later passed to a private firm to produce

commercial units.

Attempts were made to monitor the 5 mm- 0 reject material from a

Phase 3A ash monitor on a small conveyor but difficulties were

experienced in maintaining a continuous uniform bed. It was then

realised that the profiled, constant depth bed of material on the

rotating table of the ash monitor would form an ideal presentation for

continuous moisture measurement. The steel turntable of the ash monitor

was replaced by a PVC turntable which was transparent to microwaves and

this allowed the microwave moisture meter to be incorporated as an

integral part of the Phase 3A ash monitor, Figure 86, to form a combined

ash/moisture instrument. The four Phase 3A ash monitors in the Scottish

Area were then converted to include moisture measurement, while discrete

sample instruments were used at other collieries.

The continuous moisture meters gave a linear calibration accuracy,

for 95% confidence limits, varying from +0.6% to +0.9% over a range of

moisture of 8%. Over the same range of moisture the discrete sample

moisture meter gave a calibration accuracy varying from +0.35% to +1.1%.

In operational use, however, the discrete sample unit gave greater



56

accuracy (+0.7% to +1.0%) compared with the laboratory analysis, on a

daily basis, than the continuous instrument (+1.3% to +1.4%).

With the facility to continuously measure of both ash and moisture

content using the Phase 3A ash monitor, subject to the handlability of

the coal, it became possible to compute the calorific value of the

product provided the dry ash free calorific value of the product

remained reasonably constant. This arrangement was introduced at two

collieries.

At the first colliery use was made of the existing colliery

computer system, Figure 87, which, together with an existing belt

weigher, allowed tonnage weighted values to be used. Vith no existing

computing facilities at the second colliery a microprocessor-based

integration system was developed. This system, Figure 88, was able to

produce short term integrations as well as shift and daily averages, all

of which could be displayed and printed. Also, in the absence of a belt

weigher, a coal flow detector was used to suspend integration during

periods of no coal. With a sample fed monitor, such as the Phase 3A, a

degree of weighting was achieved since the quantity of sample was

dependent on the coal flowrate.

5.1.5 Previous Development and Application of an S-band System

The increasing requirement to monitor products directly on-belt

and avoid the growing handlability problems associated with sample

preparation and presentation led to the development in the early 1980's

of a new S-band instrument to allow moisture measurements on material up

to 50 mm top size.

The prototype S-band discrete sample instrument, Figure 89,

operated with a coal bed up to 300 mm thick and used a variable

frequency microwave source with a modified version of the X-band

instrument electronics. Laboratory calibration tests with 25 mm top

size material and consistent sample presentation box filling gave an

accuracy for 95% confidence limits of +0.6% . However, site trials at a

port with shipments of blended coal gave an accuracy of +2% which was

attributed to the variability of the blend and inconsistent presentation

box filling by different operators.

5.1.6 Limitations to Application of S-band System

Three main factors limited the more widespread application of the

S-band moisture meter. These were:-

(a) the analogue electronics, designed originally by Scottish

Area Laboratory, for the X-band meter, and a considerable

improvement on the older RPI unit, was limited to a range of

attenuation of about 30 dB and then only after careful

setting up.



57

(b) single frequency moisture measurement was susceptible to

changes in the geometry of the presentation system and

required, as far as possible, constant bed depth and packing

density.

(c) single frequency moisture measurement was also affected by

variations in coal type requiring separate calibration for

each particular coal.

The work carried out by the former Scottish Area Scientific

Control under this Project was directed towards overcoming these

limitations and producing a moisture meter which could be applied

directly on a conveyor belt with the minimum of presentation

requirements and which would tolerate a wide range of coal types and

moisture levels.

5.2 Developments for On-belt Microwave Moisture Monitoring

5.2.1 Instrumentation Requirements

In order to improve the performance of the fixed frequency

microwave systems, when applied directly on-belt, it was necessary to

overcome the limitations of the inadequate dynamic range of the existing

instrumentation and the problem of the variations in the geometry of the

coal bed on the belt. It would also be necessary to provide suitable

equipment for the collection and processing of the measurement data

generated in a plant trial. To meet these requirements, a range of

equipment was either modified or designed and assembled.

5.2.2 Moisture Meter Electronics

Considerable effort went into re-designing the existing

electronics to increase the dynamic range from 30 dB to 60 dB. The new

design, shown in Figure 90, comprises the following main component

parts:-

(a) Microcomputer

The electronics are designed around a RCA 1802 central

processing unit which carries out all the control functions,

synchronisation and calculations.

(b) Microwave Generation

The design allows for two versions of the computer controlled

moisture meter, the X-band (10 Ghz) and the S-band (3 Ghz).

Depending on the version the appropriate microwave oscillator

is driven by a modulator, synchronised to the microcomputer.

To provide a high degree of electrical isolation between the

microwave source and the microwave detection the

synchronisation is effected by using an optical fibre link.

The sources generate either 10 Ghz or 3 Ghz microwaves,

modulated at approximately 1 Khz.



58

(c) Microwave Detection and Amplification

The detected microwave power is fed through the amplifier

chain Al to A4. These four amplifiers each have a precision

gain which is a multiple of ten for ease of logarithmic

conversion by the computer. The actual system gain is

controlled by the computer software selecting the required

combination of amplifiers to produce a value of the required

order.

(d) Analogue to Digital Conversion (ade)

The a/d conversion is performed by an 8 bit high speed

converter. The input signal to the ade has to be in the

range 0 - 2.55 Volts. The computer selects the correct

combinations of amplifiers so that the input to the ade is

always within the required voltage range.

The computer controls the actual instant the a/d conversion

is performed. It initiates the conversions at the peak and

troughs of the modulations and subtracts one from the other

to obtain a value. This operation is performed a number of

times and the values averaged. This technique allows more

accurate readings to be obtained for low input signals,

corresponding to higher moisture contents, since random noise

is averaged out.

(e) Logarithmic Conversion

The computer software constructs a number, the exponent of

which is determined by the computer-selected amplifiers. The

mantissa, in the range 0 - 2.55, is the output from the ade.

Within the computer memory is a series of look-up tables and

the computer uses the number it constructed to look-up the

corresponding logarithmic value from the tables.

(f) Indicators

The unit has two L.E.D. indicators, one green and one red.

Green indicates that the output reading is valid and red that

the computer is going through the process of selecting the

required amplification, averaging the a/d conversions and

making the logarithmic conversion.

(g) Outputs

The computer provides a number of outputs. A digital to

analogue (d/a) converter produces an analogue signal which

gives an indication of attenuation in dbm's on a meter. The

analogue signal also drives a 4-20 mA current source for

remote indication and control purposes. The computer also

provides a standard RS 232 signal for communication with

other computers.



59

Detailed specifications for both the X-band (3 cm) and S-band

(10 cm) microwave moisture meters are included in

Appendices 10 and 11.

5.2.3 Data Logger

The data logging units, which were designed and constructed in the

Scottish Area Laboratory to record colliery trials of microwave moisture

monitoring systems, were built around a RCA 1802 microprocessor. The

same design was used with a Phase 3A ash/moisture monitor and with an

on-belt moisture monitoring system. Figures 91 and 92 show the basic

components of the logger and the incoming signals for both applications.

The data logger has three input channels; the first channel is

stored as a 2 byte number and the other two channels are stored as

single byte numbers. The input signals are sampled at one minute

intervals, converted to digital form and stored in battery-backed RAM.

Every hour the data is transferred from RAM to a disc, together with the

time and date from a real time clock in the microprocessor. The data on

the disc is structured so that it can be easily read and analysed by a

BBC microcomputer. With a one minute sampling rate the data logger can

store up to 30 days data on one disc.

5.2.4 Ultrasonic Bed Depth Meter

In order to apply microwave moisture monitoring successfully to a

product directly on-belt it was necessary, as a first step, to overcome

the problem of varying bed depth. This could be done either by

profiling the coal bed to a constant depth or employing a method of

continuously measuring the depth of material on the belt and correcting

the attenuation measurement accordingly. Since it would not be

practical, in most cases, to produce a constant bed depth it was

necessary to develop a means of continuously measuring the depth of

material in the same line of the belt as the attenuation measurement.

This measurement was achieved using ultrasonics to measure the position

of the coal surface below a fixed point at a location where the level of

the belt itself was constant, e.g. immediately over a support roller,

thereby providing an indirect measure of the bed depth.

The bed depth meter, designed and constructed at the Scottish Area

Laboratory, used components from an Ultrasonic Ranging System Designers

Kit, manufactured by the Polaroid Corporation of the USA and marketed by

Polaroid (UK) Ltd. A technical specification for the bed depth meter is

included in Appendix 12 and the main components are shown in Figure 93.

The ranging board generates a high voltage (300 V) pulse which is

applied to the ultrasonic transducer. The resulting pulse of sound

energy from the transducer is directed at the coal surface normal to the

belt, and the returning echo detected by the transducer. The ranging

board provides a control level which allowes the pulse counter to count

the incoming oscillator pulses from the time of the transmitted pulse

until the detection of the returning echo. The number of pulses counted

is therefore proportional to the distance between the transducer and the

coal surface.



60

The digital-to-analogue converter converts this count to an

analogue voltage which is proportional to distance. The

distance-to-depth converter inverts this voltage and an offset

compensates for the distance between the transducer and the empty

conveyor belt, thus providing an output to the display which shows the

depth of coal on the belt in millimetres. The frequency of the depth

measurements was 5 per second and the display updated at 0.5 second

intervals.

The output from the distance to depth converter is further

conditioned to provide a 0 - 1.6 V signal of bed depth to the data

logger. A 0.4 - 2.0 V output is also made available, together with a

4 - 20 mA signal for remote display or control purposes.

5.2.5 Trial Installation of On-belt, S-band Moisture Monitor

5.2.5.1

Description of Installation

Early in 1987, the fixed frequency S-band moisture monitoring

equipment was installed on a conveyor designed for handling up to

980 t/h of 25 mm - 0 blended raw coal at the Longannet Mine complex in

the former Scottish Area. The installation is illustrated schematically

in Figure 94 and photographs of the installation are Included in

Figures 95 and 96.

The moisture meter was installed with the microwave transmitting

horn mounted on a framework above the conveyor belt and the receiving

horn situated immediately below the top belt. The moisture meter

electronics, together with a data logger, were housed in an

environment-proof cabinet mounted alongside the belt.

The ultrasonic bed depth meter, which had already been undergoing

site trials at another colliery which was to be closed, was transferred

to Longannet and installed in-line with and immediately before the

moisture meter and as close as possible to a troughing idler. An

existing belt weigher was located about 9 metres before the moisture and

bed depth meters and the signals from all three instruments were passed

to the same data logger.

A further 5 metres before the belt weigher was an existing Birtley

automatic sampler which swept sample increments sideways off the belt at

intervals of either 2 or 3 minutes depending on whether or not coal was

being introduced from outside sources to maintain the quality of the

power station blend. The sample increments were fed via a crusher to a

Phase 3A ash monitor which had been modified to incorporate an X-band

microwave moisture meter. A second data logger was installed in the

second half of 1987 to record the ash and moisture signals from this

monitor.



61

5.2.5.2 Results of On-site Trials at Longannet

The trials at Longannet continued under the close supervision of

Scottish Area Scientific Staff until the end of 1987 when, as part of a

general re-organisation of Scientific Services in British Coal, the

Scottish Area laboratory was closed and the staff who had been involved

in this work were either re-located at the HQ Technical Department at

Bretby or left the service of British Coal. This re-organisation caused

considerable disruption to this part of the Project, with the Longannet

trial having to be terminated early in 1988 before any on-belt

calibration could be undertaken on the moisture monitor. It also

prevented a full appraisal of the data which had been collected during

the trial.

However, prior to the closure of the Scottish Area laboratory,

software was developed to analyse some of the data from the on-belt

moisture meter data-logger. This development included a program to plot

the microwave attenuation, material bed depth and flowrate over each 24

hour period against a common time base. The data for the 22nd January

1988 is shown plotted at 1 minute intervals in Figure 97. The program

was further developed to set limits of acceptable data which eliminated

data indicating saturation of the system or transient spikes. The

facility was provided to average the remaining data over selected time

intervals ranging from 2 minutes to 60 minutes. The data for the 22nd

January was averaged over 5 minute intervals and is shown in Figure 98.

The non-valid data was replaced by a zero ordinate value and these

values would be ignored in subsequent data processing.

The traces for bed depth, microwave attenuation and belt loading

in Figure 98, all respond to the main changes in flowrate. When the

belt load and bed depth measurements fell to zero the attenuation fell

to a constant level of just below 12 dB, due to the combined effect of

the conveyor belt and, in particular, the constant air gap between the

transmitting and receiving horns. During the periods of coal flow the

traces for bed depth and belt load showed a particularly close

similarity with all the main changes, and many minor changes, in coal

flow being evident on both traces. The trace of microwave attenuation

showed differences in detail from the other two.

Consecutive values of bed depth and belt weigher readings,

integrated over 5 minutes, were taken for a period of approximately

5-6 hours from 8.00 hours on the 22 January and were plotted in

Figure 99. The correlation coefficient for the quadratic regression

between flowrate and bed depth was 0.93 and the standard deviation for

the flowrate was 43.3 t/h. The bed depth meter therefore provided only

an approximate measure of the flowrate.

5.3 Swept Frequency Microwave System

5.3.1 Limitations of Single Frequency Systems

Early experience with single frequency microwave moisture meters



62

had shown that coal samples of similar moisture content but of different

rank, ash content and size consist gave different values of

attenuation (6). For each coal the calibration between attenuation and

moisture had shown a characteristic 'dog-leg' shape with the sudden

change in the attenuation/moisture relationship corresponding to the

change from inherent to free (or surface) moisture. However, apart from

this feature, the calibration for different coals varied widely,

particularly in the free moisture range, and the single frequency

moisture meter had to be calibrated for a particular coal. This

requirement was, consequently, a severe limitation where the instrument

was required for use with a blended product of variable composition.

Microwave attenuation is also dependent on the presentation

geometry and, therefore, single frequency meters ideally prefer constant

presentation conditions such as bed depth, material compaction and

distance from source to coal surface. This preference particularly

affects on-belt applications unless some compensation could be made for

bed depth variations, as was being attempted with the ultrasonic depth

meter at Longannet.

5.3.2 Principle of 2 Frequency Measurement

To endeavour to overcome the above limitations the absorption of

microwaves by water had to be examined in more detail. The water

molecule is electrically polarised and, if an electric field is applied,

the molecule will tend to align itself with the field. In doing so,

energy is extracted from the field to overcome the small but finite

inertia of the water molecule. If an alternating field of increasing

frequency is applied the water molecule will rotate faster and absorb

more power. This rising characteristic continues from low radio

frequencies and reaches a maximum in the microwave region at about

17GHz. Thereafter, the power absorbed declines as the inertia of the

molecule is too great to follow the rapidly alternating field.

The total attenuation produced by a coal sample can be represented

as:

-

A (total) - A(water) + A(coal)

The attenuation due to the water can be predicted as described

above. The attenuation due to the dry coal itself depends on the

molecular constituents and cannot be predicted. It is this factor which

adversely affects the accuracy of microwave moisture meters when

operating with blended products of varying composition.

If attenuation measurements were made at two frequencies (1) and

(2),

two equations would result:-

Ai (total) - Ai (water) + Ai (coal)

A2 (total) - A2 (water) + A2 (coal)

The two coal terms would be approximately equal and, therefore, by

subtraction



63

A2 (total) - Ai (total) - A2 (water) - A^ (water)

The effect of the dry coal would therefore be eliminated and the

resulting value would depend only on the water in the sample. Some

preliminary experimental work was undertaken using a variable frequency

microwave source set to various frequencies and the differences in

attenuation correlated to moisture with encouraging results. Resulting

from this work, a two frequency design was proposed which mixed the two

microwave frequencies for transmission through a single microwave path

and subsequently separated them, Figure 100.

At the start of this Research Project the two frequency system was

being superseded by a swept frequency approach which, in addition to

overcoming the problem of differing coal types, also compensated for the

effect of varying geometry.

5.3.3 Effect of Variable Geometry

In a microwave measuring system the electromagnetic radiation

encounters several physical boundaries such as air/coal, coal/container

wall,

and container wall/air. At each of these boundaries some of the

incident radiation is reflected as well as transmitted.

At the first air/coal boundary there will be a large amount of

reflected energy which will set up a pattern of standing waves between

the transmitting horn and the coal surface. The effect of this pattern

is to produce local variations in microwave power density. Although the

total power delivered by the source is known the actual power density at

the coal surface is determined by the standing wave pattern which, in

turn, is critically dependent on the distance between the horn and the

coal surface.

In a single frequency system these errors can be minimised by

fixing the geometry, as far as possible, but, with the changes in

geometry inherent in an on-belt system, this would be extremely

difficult to achieve. The two frequency system would be more

susceptible to the geometry since if it were set up accurately for one

wavelength it would not be correct for another unless it were carefully

chosen.

If measurements were to be taken at a large number of intervals

over a range of frequencies then the attenuation would vary cyclically

as the position of the standing wave is shifted in space. The frequency

range would have to be wide enough to include several cycles of this

variation. Using a microprocessor, a linear regression would be applied

to the attenuation measurements and the straight line obtained would

even out the cyclic variations.

The intercept and the gradient of this linearised

attenuation/frequency relationship would both increase with the moisture

content of the coal. The intercept would also be dependent on the

attenuation of the dry coal, while the gradient would depend only on the

moisture. Therefore if the gradient of the attenuation/frequency



64

relationship were used as the measurement of moisture, an instrument,

based on this technique, would be largely independent of both coal type

and the geometry of the system.

5.3.4 Experimental Laboratory Equipment

This aspect of the Research Project commenced with the

specification and procurement of the specialised microwave equipment

required for laboratory investigations of the swept frequency technique

and its incorporation in the system illustrated in Figure 101. A

detailed specification of the system components and computer software is

given in Appendix 13.

The system was designed around the Automatic Amplitude Analyser,

manufactured by Marconi Instruments, and referred to alternatively as a

scaler analyser. This instrument is an advanced processing unit capable

of accurately analysing the inputs from broadband microwave detectors

and displaying the results on a screen. Three independent channels,

designated A, B and R (reference), are provided for the connection of

the diode detectors. Each channel has an associated data store and

memory which can hold a sweep of 422 measurements over the frequency

range being used. The detector signal undergoes a digital/log

conversion process and this value was placed in the channel data store.

The value is further corrected for square law deviations and temperature

effects in the detector head. The dynamic range of the instrument is

around 70 dB.

The display shows the channel measurements in line or histogram

form with the frequency scale horizontal and the attenuation vertical.

The front panel keyboard controls a number of functions such as display

sensitivity, frequency windowing, subtraction of reference channel,

cursor position, sweep speed etc. Any of the keyboard functions can

also be accessed through the IEEE interface bus for remote computer

control.

The operation of the experimental arrangement is explained with

reference to Figure 101. Three variable sources are used to cover the

total frequency range 2-12 GHz in band-widths 2-4, 4-8 and 8-12 GHz,

corresponding to S, Q and X bands. Each band requires different

waveguides and horns. The X band components, which are relatively

inexpensive and easily available, were purchased. The larger Q and S

band components were manufactured in the laboratory workshop together

with various coal presentation systems, with sectional containers to

provide different coal bed depths.

Having positioned the coal sample, in its container, between the

transmitting and receiving horns, each test consisted of a sweep across

the relevant frequency range while measuring the transmitted and

received power through channels R and A respectively. The value A-R

then represents the power loss through the coal sample. Because of the

large number of tests carried out, and the amount of data generated, the

instrument is controlled remotely through the IEEE bus. A BBC



65

microcomputer was programmed to set the control parameters, initiate the

scan, capture the data, perform the linear regression and store the

results on disc.

5.3.5 Laboratory Test Procedure

After some preliminary trials the following procedure was adopted

for obtaining a range of samples of progressively increasing moisture

content for a particular coal. A bulk sample of approximately 30kg of

coal was crushed below 4.5 mm and dried. After thorough mixing the bulk

sample was divided into two equal and representative parts. Each part

was subjected to a further mixing and sub-division and the procedure

repeated until a suite of 16 samples of approximately 2 kg was obtained.

These samples were weighed to determine the amount of water to be added

to each sample to produce a series of samples of increasing moisture

content within a given range. The water was added using a small, manual

spray gun while the sample was being continuously hand mixed. The

samples were then sealed in plastic bags and allowed to stand for

24 hours.

The samples were taken in turn for presentation to the microwave

measuring system. Using a standard filling technique the sample was

transferred to the sample presentation tube which comprised an aluminium

tube, 150 mm diameter and 100 mm deep, with a perspex base. The sample

was placed between the vertically arranged transmitting and receiving

horns and a scan of 100 milli-seconds' duration initiated over the range

5 GHz to 7 GHz, using the middle section of the Q band microwave source.

The sample container was emptied, the sample re-mixed, the container

re-filled and the measuring procedure repeated. The whole process was

repeated a further three times to give a total of 5 scans for each

sample. The samples were then analysed for total moisture content.

5.3.6 Testing of Seams from Blindwells Opencast Site

The foregoing test procedure was applied to coal samples from

seven different seams which occurred at the Blindwells Opencast Site in

Scotland. Typical analyses for six of the seven seams, which were all

low rank, are given in Table 15. The coal samples were prepared as

described above, with each seam sample providing a suite of 16 test

samples with total moisture contents ranging from 11% to 27% .

After being weighed, each of the test samples was presented five

times to the swept frequency measuring system. The resulting scan from

each presentation was transferred from the scaler analyser to the

computer and labelled. The linear regression analysis was performed and

the gradient of the straight line fit and the intercept at 5 GHz were

determined before transferring the data to disc storage. After the

fifth presentation the sample was resealed in a plastic bag while

awaiting analysis for total moisture content.

5.3.7 Appraisal of Test Results

The plots of 8 individual scans, representing different levels of

moisture content, for the Parrot Crop seam are included in Figures 102



66

to 109 They include the straight line fit for each scan and illustrate

the change in both gradient and intercept as the moisture content

increases. The average gradient and intercept of the straight line fit

for the five presentations was determined for each of the 16 test

samples from each seam.

The calibration graph of total moisture content plotted against

the average attenuation/frequency gradient (dB/GHz) for the Parrot Crop

seam is shown in Figure 110 The quadratic regression for this

calibration gave a correlation coefficient of 0.957 and a standard

deviation of 1.28% moisture. Taking into account the mass of the

sample, the graph of total moisture against the weighted gradient

(dB/GHz/kg) is included in Figure 111. The quadratic regression in this

case showed an improvement in correlation coefficient to

0.979

and in

standard deviation to 0.91% moisture.

The data for the remaining six seams was processed using the same

method and the results of the quadratic moisture calibrations with both

the unweighted and weighted gradient for all seven seams is given in

Table 16. In addition, the results for all seven seams, totalling 108 in

all, were aggregated and plotted against the unweighted and weighted

gradients in Figures 112 and 113 respectively. The results of the

quadratic regression, included in Table 16 showed an improvement in

correlation coefficient from

0.964

to 0.973 and in standard deviation

from 1.14 to 0.99% moisture when the mass of the sample is taken into

account in the calibration.

The calibration accuracy for the combined results of all seven

seams is of the same order as for the individual seams and confirms that

the swept frequency, microwave measuring technique has considerable

potential for providing a measure of moisture content which is largely

independent of the particular coal. However, the seams tested were all

low rank and a much wider range of seams must be investigated to

determine whether a universal calibration is feasible.

5.4 Summary

Following the earlier demonstration of a British Coal moisture

meter based on the attenuation of microwaves at a single frequency to

moisture measurement of discrete samples and to a continuous sub-stream,

work was undertaken to extend the scope of applications of this

technique for on-belt measurement and to a wide range of coal types.

A new S-band meter, with an increased dynamic range, has been

designed and built, and a unit installed on a conveyor belt at a

colliery site. An ultrasonic bed depth meter has also been installed at

this site and data on microwave attenuation, bed depth and tonnage, from

an existing belt weigher, were collected on a specially designed data

logging unit. Correlations between these signals have been

demonstrated, but a reorganisation of scientific services within British

Coal resulted in termination of work at this site before a full

calibration of the moisture meter could be carried out. Arrangements

for a continuation of these trials at another site are in hand. A

second meter of this type is also being fitted to the Ram Feed Ash

Monitor for sub-stream trials.



67

A single frequency microwave moisture meter of the above type is

limited in its application by sensitivity to variations in coal type,

particle size and coal bed geometry. A system designed to minimise

these problems, by measuring the attenuation of microwaves swept through

a range of frequencies, has been developed and an experimental

laboratory unit built. Tests with samples from a range of coal seams

have shown that it is relatively insensitive to coal type and gives a

calibration accuracy of +0.4% to +1.3% moisture at one standard

deviation.

6. CAPACITANCE MOISTURE MONITORING

6.1 Previous Investigations, Applications and Developments by British

Coal

6.1.1 Early Investigations

Initial investigations into the possible application of a

capacitance technique for the on-belt monitoring of the moisture content

of coal in the UK was undertaken in the former North Durham Area of

British Coal in the mid I960's (8).

The equipment used was developed in the United States of America

by Messrs Foxboro-Yoxall. The primary measuring element consisted of a

ski plate designed to ride on the bed of coal on a conveyor. Extending

from the underside of the ski plate was a vertical keel plate which was

insulated from the ski plate. In operation the underside of the ski and

the keel plate were in contact with the coal, the coal acting as the

dieletric. The measuring system also comprised a measuring head

assembly and a capacity Dynalog recorder.

The capacitance technique depends on the very large difference in

the dielectric constant between water, at 80, and coal, at around 6, for

excitation frequencies below 10 GHz. Laboratory tests, using the

Foxboro instrument, on eleven different coals covering the full range of

coal rank and each adjusted to a standard size grading, gave standard

deviations ranging from 0.25 to 0.75% moisture for ten of the eleven

coals tested.

The instrument was then installed at a colliery to continuously

monitor 25 mm - 0 raw coal directly on a conveyor and the trial extended

for a period of two and a half years. The main problem encountered was

wear on the primary element particularly affecting the insulation

between the ski and the keel plate. The wear was partially overcome by

the use of glass instead of epoxy resin as the insulating material.

Frequent checks were made on the instrument calibration over the

duration of the trial and a calibration standard deviation of 0.5%

moisture was regularly achieved.

6.1.2 Further Development and Testing

The Foxboro moisture meter was no longer commercially available in

the UK after about 1970 and, some time later, work was begun at the



68

former Mining Research and Development Establishment (MRDE) of British

Coal to design a replacement. Initial testing of a prototype unit by

the former North East Area of British Coal indicated that results of

similar accuracy to that achieved with the Foxboro monitors was

possible. Subsequently, up to six of the MRDE developed moisture

monitors were used by the North East Area for both laboratory and plant

trials extending over a period of two years.

The very comprehensive testing by North East Area (9) led to a

number of conclusions regarding the MRDE moisture monitor in particular

and on-belt moisture monitoring in general. These were:-

(i) In situations where the coal product was well mixed and suitably

presented to the ski sensor the MRDE instrument was capable of an

accuracy (2 s) of better than +2% based on an integration period

of 4 minutes. Over longer periods, an increased accuracy was

expected.

(ii) Tests showed that the MRDE designed ski, with the two additional

vertical earthed plates, was as accurate as the original Foxboro

type ski with its single keel plate.

(iii) The insulation of the keel plate remained a problem even with the

glass inserts bedded in silicone rubber. The problem was one of

damage to the glass due to the impact of larger material or

foreign objects rather than wear.

(iv) Apart from the problem of insulation, wear on the keel plate

limited the life of the ski to an average of 9 months, depending

on the belt speed and coal nature.

(v) The monitor would not give reliable results on plants where the

washery water had a high and variable dissolved salts content

because of the effect on the conductivity of the coal.

(vi) The monitor had to be calibrated individually for each coal and,

therefore, it would not be suitable for blended products of

highly variable composition.

(vii) Because of the many problems of on-belt monitoring, consideration

should be given to monitoring moisture with a sample fed system.

The limitations of capacitance moisture monitoring had also been

reported earlier by Hampel and Hoberg (10).

6.2 Insulated Plate Capacitance Moisture Monitor

6.2.1 Proposed Development

It was considered that a number of the above limitations might be

overcome by the development of an insulated plate capacitance system for

incorporation in a sample fed, Ram-feed presentation unit.

The complete insulation of the capacitor plates would eliminate

the effect on the capacitance measurements of variations in the



69

electrical conductivity of the coal due to variations in the presence of

ionic salt solutions. In addition to increasing the electrical

conductivity of the coal, ionic salts increase the relative interfacial

dielectric permittivity of the sample due to the accumulation of salt

ions at grain boundaries, i.e. the Maxwell-Wagner effect.

The incorporation of the insulated capacitance system in a sample

fed, Ram-feed presentation unit would considerably reduce the problems

of material presentation, wear and damage. It would also simplify the

calibration procedure, which was much more complicated for on-belt

systems.

6.2.2 Design of Experimental Laboratory System

A theoretical study, reproduced in Appendix 14, was first

undertaken to examine the factors involved in the design of an insulated

capacitance monitor. This study was followed by the design of a

discrete sample cell and an electronic measuring system to investigate

the technique further in the laboratory.

(i) Design of Insulated Plate Capacitance Cell

The test cell comprised an open wooden box of internal dimensions

185 mm wide, 300 mm long and 200 mm deep. It was provided with

two aluminium plates measuring 300 mm long by 100 mm deep and

2 mm thick which were arranged against opposite sides of the box

to form a parallel plate capacitor. The inside of the cell was

lined with plastic sheet of 0.235 mm thickness.

The final effective size of the experimental cell was 180 mm

wide, 300 mm long and 100 mm deep. These dimensions corresponded

to a 300 mm long section of the trough of the Ram-feed sample

presentation unit where the insulated capacitance plates could be

incorporated into the opposite side walls of the trough.

(ii) Measurement Electronics - Design Parameters

Before designing the electronic measurement system it was

necessary to establish the following parameters:-

(a) the operating frequency

(b) the maximum value of capacitance

The operating frequency was chosen to be in excess of 10 MHz.

The maximum value of capacitance likely to be encountered could

not, however, be accurately pre-determined.

69



70

The equation defining the capacitance (C) of a parallel plate

capacitor is:-

C - Eo Er A

where Eo - Permittivity of free space (- 10'9 F/m"l)

3671

Er - Relative permittivity of the sample

A - Capacitor plate area

D - Capacitor plate separation

The maximum capacitance value would be obtained if the

measurement cell was completely filled with water (Er - 80) and

it would be given by:-

C - 80 x 10-9

x

o.l x 0.3

367T .

0.18

.-. C - 118. 10-12

F

i.e. C - 118 pF

This value represents the upper limit of capacitance which the

system was initially designed to measure.

Subsequent tests with the measurement system showed that an

operating frequency of 12.3 MHz was the most applicable.

(iii) Measurement Electronics - Description

The electronic measurement system developed for the insulated

plate capacitance cell comprised the following components,

arranged as illustrated in Figure 114.

(a) high frequency signal generator

(b) buffer amplifier

(c) measurement amplifier

(d) oscilloscope

The high frequency generator was the source of the radio

frequency signal which was used to drive the buffer amplifier.

The output from the buffer amplifier was applied across the

measurement cell and measurement resistor network. The voltage

developed across the measurement resistor was amplified and

buffered by the measurement amplifier and displayed on the

oscilloscope. Short circuited quarter-wave filters were

connected to the measurement system at positions A, B, C and D.

In addition, a 4.7pF capacitor was connected in shunt with the

measurement cell to help stabilise the measurement system by



71

providing a small fixed value of capacitance when the cell was

empty. The effect on the measurement was to cause a small

offset.

During the first series of laboratory tests it was necessary to

manually reset the high frequency generator signal level at each

change of sample moisture because of the electrical loading of

the output stage of the buffer amplifier. Prior to the second

series of laboratory tests the electronics system was modified to

include automatic output signal level stabilisation, as shown in

Figure 115. This was achieved by comparing the output signal

level from the buffer amplifier with the input level to a

differential video amplifier which was arranged as a buffer

driven amplifier. The difference between these two signals was

used to generate a control signal which was applied to the

automatic gain control input of the differential video amplifier.

6.2.3 Laboratory Tests with Experimental Cell - Series I

The first series of tests with the experimental insulated plate

capacitance cell was conducted using a bulk sample of 12.5 • 0.5 mm

washed coal from Markham Colliery Coal Preparation Plant where the trial

site for the Ram-feed sample presentation unit was located. The bulk

sample was allowed to dry in the laboratory to a final moisture level of

1.7% and was then divided into three equal sub-samples, of approximately

6 kg, and designated 1A, IB and 1C.

The moisture content of Sample 1A was successively increased by 2%

intervals, using distilled water, up to a final level of 18% added

moisture. After each moisture addition the sample was thoroughly mixed

and presented to the capacitance cell for measurement.

A similar procedure was followed with Sample IB but, instead of

distilled water, a solution of 5g/litre of sodium chloride was used to

increase the moisture content at 2% intervals. With Sample 1C the

procedure was repeated using a log/litre solution of sodium chloride.

The results obtained are presented in Table 17 and plotted in

Figure 116.

The results show that the output signal from the measuring system

increases significantly with the increasing concentration of ionic

salts. The results also show quite a marked change in the relationship

between the added moisture content and the instrument reading which up

to about 1000 mV, corresponding approximately to 8% added moisture,

appeared approximately linear. For future testing the measuring system

gain was reduced to extend the effective range and any results in excess

of 1000 mV were discarded.

The results from this first series of tests showed that variations

in the ionic salt content of moist coal samples can appreciably affect

the measurements made with an insulated plate capacitance moisture meter

and were therefore not particularly encouraging.



72

6.2.4 Laboratory Testing of Experimental Cell - Series II

A second series of tests were conducted following modifications to

the measurement system found necessary from the initial tests. The

samples were again obtained from Markham Colliery Coal Preparation Plant

and comprised 12.5 - 0.5 mm washed coal taken from the feed to the

dewatering centrifuges and, therefore, contained a high level of free

moisture. Four separate coal samples were obtained, with a 4 month

interval between the first two and second two.

A representative sub-sample, of approximately 6 kg, was taken from

the main sample in the as-sampled condition, loaded into the

experimental cell and a measurement made. The sub-sample was emptied,

mixed and re-loaded and a second measurement made. The procedure was

repeated a third time and the measurements averaged. A representative

portion of the sub-sample was then subject to moisture analysis and the

remainder mixed back into the original sample which was then allowed to

air-dry for a short time. A second sub-sample was taken and a further

set of measurements and moisture determination were made. This

procedure was repeated until the main sample reached an air-dried

condition. The same procedure was followed with the remaining three

samples and the results reported in Table 18.

The graph of total moisture content plotted against the instrument

reading, Figure 117, shows a good linear relationship extending over a

wide range of moisture content of 4.28% to 19.17%. The linear

regression analysis of total moisture with respect to instrument reading

gave the following values : -

Correlation coefficient 0.98

Standard deviation 0.88% moisture

The samples used for this second series of tests were analysed for

chlorine as an indication of the presence of ionic salts. The chlorine

level was found to be consistently low.

Taking into account that the output from Markham Colliery is drawn

from as many as five seams and that the samples were collected four

months apart the accuracy level achieved in the second series of tests

was considered particularly encouraging. It was therefore considered

possible that an insulated plate capacitance moisture meter might be

sufficiently accurate, given a suitable material presentation system, to

be useful in some coal preparation applications.

6.2.5 Proposed Further Investigations

Laboratory investigations were conducted using a comparatively

simple measuring system. A more elaborate system, capable of measuring

both the real and imaginary components of the relative permittivity of a

sample, might enable some correction for ionic salt variability to be

made. Using this more advanced measuring equipment to examine discrete

samples, further investigations could be conducted at several



73

representative colliery sites to provide information on the variability

of ionic salts between spot samples and the possible scope of

application of the measuring technique.

It was proposed to proceed with these investigations as outlined

above. A specification for a suitable measuring system was prepared and

is included in Appendix 15. The specification was put out to tender to

a number of private companies. However, the high cost of developing the

equipment together with the introduction of two proprietry moisture

monitors, suitable for use with coal, led to the suspension of further

work in this direction until both proprietary monitors had been assessed

and evaluated.

7. DETERMINATION OF MOISTURE IN COAL BY NUCLEAR MAGNETIC RESONANCE

7.1 Introduction

The potential for the use of nuclear magnetic resonance

measurements for the determination of the moisture content of solids has

long been recognised and was reported as being applicable to coal more

than 25 years ago (11). The technique is unique among those, such as

microwave attenuation, capacitance measurement and neutron modetation,

which have been tried for this purpose in that it can be so arranged as

to give a response related directly to water. This study briefly

reviews work in this field to date, includes measurements made with a

laboratory analyser and comments on the potential for the technique to

be used for on-line analysis.

7.2 Principle and Measurement Techniques

For a full understanding of nuclear magnetic resonance, reference

should be made to some suitable text book (12); for the purpose of this

report a very general outline of the principles will suffice.

Basically, the technique exploits the interactions which occur

between the magnetic moments associated with the nuclei of many nuclides

and an external field. In particular, at a given magnetic field

intensity a resonance between the external field and the magnetic

moments of the nuclei is established at a frequency which is specific to

the nuclide involved and which has an amplitude proportional to the

number of nuclei present in the interrogated volume of material. In

addition, the characteristics of the response are modified by themolecular environment of the nuclei of interest and, consequently, it is

possible to differentiate a response originating from hydrogen in liquid

water from that due to hydrogen combined with carbon in a hydrocarbon

molecule.

Two basic approaches are available for the detection of the

resonance effect, the continuous wave method and the pulsed method:-

In the continuous wave approach the material under interrogation

is placed in a homogeneous high intensity field between the poles of a

magnet and subjected to a much weaker electromagnetic field, at right

angles,

from a radiofrequency coil around the sample. At appropriate



74

combinations of these two fields, resonant absorption of energy occurs

as a result of transitions between energy levels associated with the

nuclear dipoles. The energy change is detected in the coil and

amplified. A spectrum of the energy changes in the expected region of

the resonance may be obtained by the application of a suitably varying

current to coils around the magnet poles which produces a slow linear

sweep of the magnetic field intensity within appropriate limits.

Fig 118 shows the kind of spectrum obtainable for wet coal. The

resonance signal from hydrogen in water occurs at a closely defined

value while that from hydrogen in solid hydrocarbons is broadened over a

wide range of values. Careful choice of the signal gate excludes most

of the latter giving a signal predominately arising from water.

In the pulsed approach the material is again interrogated by two

electromagnetic fields, a steady, high intensity field from a magnet and

a pulsed, lower intensity radiofrequency field which, together, meet the

energy requirements for a resonance response from hydrogen. Application

of the rf field disturbs the magnetic moment established in the presence

of the static field. Following the application of an rf pulse of

suitable duration the nuclei re-establish the original equilibrium

Boltzmann population distribution in the static field with the emission

of a transient signal known as the Free Induction Decay

(FID).

The

time-related characteristics of this signal are a function of the

molecular environment of the hydrogen nuclei. The decay time of the

response originating with hydrogen in the coal substance is much more

rapid than that associated with water, and the resulting composite

signal, Figure 119, can be readily analysed using suitable curve fitting

functions to give a signal related only to water.

7.3 Review of Work to Date

Initial studies on the quantitative determination of the moisture

content of coal were made in the I960's using an nmr spectrometer based

on the continuous wave measurement technique. These studies indicated

that the technique could be applied to a wide range of coal ranks and

was applicable to the measurement of total moisture content, including

that portion of the water absorbed into the pores of the coal(13).

Using a derivative of the nmr signal it was shown that the moisture

content correlated well with the signal height, particularly if

variations in bulk density were corrected for by including a

mass-related factor. Low ash crushed coal, with a maximum particle size

of 1.6 mm, was tested and it was shown that values of moisture content

determined in this manner were within 1% of the standard

laboratory-determined values in a range up to 30% moisture. It was even

demonstated that similar results could be obtained from a slowly moving

(grams per second) stream of coal contained within a glass tube. The

work was further extended to show that neither ash content, up to 50% ,

nor particle size, up to 6 mm, had any significant effect on the

accuracy of measurement(14).

Although measurement of moisture content using this method was

reasonably accurate and rapid, taking only a few minutes, the equipment

was complex and expensive. In particular, the requirement for a

homogeneous, high intensity magnetic field contributed significantly to

the high cost which, together with the associated technical problems,



75

restricted the magnet size and, consequently, the available volume for

interrogation of the sample. (In the case of Ladner's work(13) the

volume of coal interrogated was approximately 15 cm^.) Development of

'low resolution' continuous wave instruments in the 1970's, using a

lower intensity magnetic field, reduced the cost of nmr spectrometers

suitable for the determination of moisture in coal and further studies

of the potential accuracy of this method for static samples were made.

Using a commercial analyser with a sample volume of 40 cm^ and

measurement times of 2 minutes, Robertson (15) obtained a calibration

standard deviation of +1.3% for a suite of coals covering a wide range

of coal ranks, with moisture contents up to 23% and at a maximum

particle size of 3.8 mm. A study by Page (16), which extended tests

using the same type of instrument to a sample volume of 100 cm^, showed

that for coals with moisture contents ranging up to 11% , calibration

standard deviations of 0.2 to 0.4% moisture were obtainable irrespective

of sample volume, Table 19. Figure 120 combines the results from suites

with different maximum particle size, indicating that particle size has

no significant effect on accuracy

(+0.26%).

The individual samples

represented in this relationship were drawn from coals of NCB Coal Rank

Code numbers 300 to 700 and ranged from 4 to 47% in ash content.

This work has shown that the nmr technique is relatively

insensitive to a number of variables which occur in coal but also draws

attention to the serious errors which can result from the presence of

magnetic materials. Naturally occurring magnetic materials are rare in

coal but the widespread use of magnetite as a medium for coal cleaning

in dense medium plants means that it is likely to be present, as a

contaminant, in many products. The extent to which magnetite

contaminates prepared coal products can vary considerably but typically

could be of the order of 0.1 to 0.2% on a cleaned coal. Results

presented by Robertson indicate that addition of magnetite to samples of

coal produced significant errors. Measurements by Page confirm this and

indicated that the addition of 0.1% magnetite is equivalent to a

reduction of 0.8% in moisture content, Figure 121. Addition of

magnetite produces a broadening of the nmr spectrum as determined by the

continuous wave method, which, at least up to 0.1% addition, is

proportional to the level of contamination. This proportionality allows

some correction of the measured value to be made by making a second

measurement to include the broadened

spectrum(15).

The first reported results of the application of pulsed nmr

spectrometry to the quantitative determination of moisture in coal are

those of King (17) in 1983. The work of King is particularly relevant

to this project in that it was specifically aimed at the development of

apparatus for the measurement, using magnetic resonance methods, of a

range of parameters, including moisture content, in flowing coal. Using

specifically designed apparatus, the nmr response from moisture was

measured in powdered (<0.1 mm) coal pneumatically conveyed through a

10 mm diameter pipe at flow rates of a few kilograms per second.

Results for a range of coal types with moisture contents up to 31%

indicated that measurements with a maximum error of 1.5% moisture were

possible under these conditions. It was suggested that such



76

measurements should be feasible on coal being transported in a different

manner (e.g., on a conveyor) but no such applications have yet been

reported.

Pulsed nmr determination of moisture in coal has also been

investigated using 5 cm

3

samples of fine coal (<1 mm) in a laboratory

spectrometer (18). Over a range of moisture contents up to 26% and for

measuring periods of 20 seconds, calibration accuracies (+ls) of 0.4 to

0.7% moisture were obtained by a measurement method which was

independent of sample density. Proposals to investigate the accuracy of

measurement obtainable in sample by-lines up to 50 mm diameter and using

lower magnetic field homogeneity were made but so far have not been

reported.

7.4 Potential For On-Line Monitoring

Table 20 summarises the results of work to date showing that with

currently available equipment it is possible to measure the moisture

content of static or moving samples of coal to an accuracy of the order

of +1-2% moisture, a level which would be acceptable for on-line control

of coal quality. These measurements are substantially independent of

coal type, ash content or particle size up to 6 mm. The problem of

magnetic contamination of the sample could restrict the accuracy of the

technique when applied to products which may contain varying amounts of

magnetite carried over from dense medium coal cleaning processes. There

does,

however, appear to be some potential for the introduction of some

degree of compensation for such errors by modification of the

measurement technique.

The major restriction to the application of nmr spectrometry to

on-line measurement of moisture in coal is the requirement for a large

volume, homogeneous magnetic field. In the reported work the largest

volume of coal interrogated was 100 cm

3

. Adaptation of such

instrumentation to accept a flowing stream of coal is possible, but

would place considerable restrictions on particle size and throughput of

samples and lead to severe handlability problems with higher moisture

content coals.

To handle wet coal, as produced at a plant, it would be necessary

to have, at least, a sample sub-stream of dimensions similar to those

obtained with the Ram-feed Ash Monitor (100 x 180

mm).

This, in turn,

would necessitate a large increase in the dimensions of the magnet

required to produce a magnetic field of sufficient volume and adequate

homogeneity to allow measurements at the same level of accuracy as those

reported with smaller instruments. No such applications to the

determination of moisture in coal have been reported, but the technology

to detect relatively small amounts (0.6% by volume) of other nuclides

displaying nuclear magnetic resonance within a sensing region having a

cross sectional area of 36 cm x 58 cm and a total volume of 0.08 ra

3

has

been developed (19).



77

7.5 Summary

Work on relatively small (up to 100 cm^) volumes of coal has shown

that it is possible to determine the moisture content of coal in a

reasonably short response time to an accuracy of +1 to 2% absolute using

the phenomenon of nuclear magnetic resonance.

This degree of accuracy is obtained for over measuring periods of

20 seconds to 2 minutes and is not significantly affected by coal type,

ash content or particle size. The technique can be applied to static or

moving coal.

Bulk density variations affect the accuracy to a degree but

compensation for such effects can be readily applied.

Magnetite contamination has a significant effect on accuracy and,

although some compensation may be possible, errors from this source

present a problem which has to be addressed.

Data so far obtained relate only to small volume samples; scaling

up the technique to accommodate the larger samples normally associated

with a product sub-stream or, indeed, to full stream monitoring would

require the application of large magnets. Such a step would be costly.

In view of the progress achieved in the field of on-line moisture

in coal measurement by other techniques (e.g., microwaves), where a

similar level of performance has already been demonstrated, it is

considered that the nmr technique does not offer any substantial

technical advantages which would warrant the considerable expense in

equipment and development costs which would be required for application

to large volume coal samples.

8. THE APPLICATION OF NEUTRON/GAMMA INTERACTIONS TO ON-LINE COAL

ANALYSIS

Interest in the application of neutron/gamma interactions to coal

analysis has grown considerably in recent years, to the extent that

on-line analysers are now commercially available and operating at a

number of locations

(20-22).

8.1 Basic Principles and Techniques

When coal is subjected to a flux of fast neutrons some

interactions with nuclei result in the production of high energy gamma

radiation, at a variety of energy levels, which are specific to the

types of nuclei involved and which, under particular conditions of

measurement, can be related quantitatively to the concentrations of the

nuclei involved. Spectroscopic analysis of this gamma flux yields

information on the elemental composition of the coal. Both the incident

neutrons and the resulting gamma radiation are highly penetrating,

allowing the interrogation of substantial volumes (0.2m3) of coal and

thus reducing or eliminating the need for crushing and preparation of

the coal before analysis. The gamma ray emissions can be classed as

prompt, occurring within 10

_1

0 seconds of the interaction, or delayed,



78

arising from the decay of induced radioactivity with a half-life

measured in seconds, minutes or even longer.

Application of techniques involving delayed gamma emissions to

on-line analysers have been studied (23-24) but only a very limited

number of interactions produce emissions suitable for coal analysis and

most effort has been made in the field of prompt gamma neutron

activation analysis

(PGNAA).

Two mechanisms predominate in the

application of PGNAA to coal: (a) neutron capture interactions, which

occur mainly with neutrons at thermal energies (~10 2eV) and (b) in

elastic scattering interactions which occur with fast neutrons at energy

levels above nuclide-specific thresholds (-1 to 6 MeV for important

elements in

coal).

A convenient isotopie source of neutrons is

californium -252 (predominately 0.5 to 4 MeV) (25). Use of a 14 MeV

neutron generator has also been suggested and tried (26) but is much

less suited for an industrial environment.

In order to utilise the thermal capture interactions, moderation

of the fast neutron flux to thermal energies is necessary and, in the

case of coal, this is conveniently achieved within the bulk sample,

mainly as a result of elastic scattering interactions with hydrogen

present in the coal substance and any associated water. With a suitable

detection system, useful signals may be obtained from the thermal

neutron interactions with H, C, N, Na, Al, Si, S, CI, K, Ca, Ti, and Fe,

i.e. most of the major and minor elements present in coal and its

associated mineral matter except 0 and Mg. The spectra obtained are

complex, including significant gamma responses at more than 50 energy

levels from the 12 elements and interpretation, in terms of elemental

concentration, has to take into account the gamma ray energy response of

the detector and the effects of variations in both neutron and gamma ray

transport within the coal, due to changes in coal composition and

density. Nevertheless, it has been possible to derive algorithms which

are relatively insensitive to the major sample-related effects for

particular detector configurations and which are capable of giving

results of an accuracy, acceptable for operational purposes, for most

elements over measurement periods of a few minutes (27, 28) .

The absence of data for oxygen and the large statistical

uncertainty on the thermal neutron gamma signal from carbon impose a

significant degree of uncertainty on the measurements for some of the

other elements in coal. It has been shown that these measurement

precisions can be considerably improved if the system is set up to

generate, in addition to the thermal neutron capture gamma events, those

capture gamma events which arise as a result of Inelastic scattering of

the neutrons (29). This may be achieved by using 241 Am/Be as the

neutron source which gives strong signals for oxygen, carbon and silicon

inelastic scatter gamma radiation.

In order to obtain adequate data for total elemental analysis it

is generally considered that a high resolution semiconductor detector is

necessary (29). These devices, however, have quite low counting

efficiencies and are subject to fast neutron damage. With present

technology it is difficult to reconcile the conflicting requirements of



79

high total count rates, necessary to allow sufficient statistical

precision on individual element measurements within the time constraints

of operational requirements, without subjecting the detector to a high

intensity neutron flux which shortens its life to an unacceptable

degree. Scintillation detectors do not have this problem but their low

resolution means that only data for a few of the elements in coal are

readily resolved from the detected spectrum. One attempt to overcome

this problem has been the development of a pair spectrometer array using

up to 19 scintillation detectors (30). This system gives much improved

resolution over a simple scintillator and has a better data rate

performance than a germanium semiconductor detector.

8.2 General review of on-line applications

The feasibility of the application of neutron gamma interactions

to the analysis of bulk coal and demonstrations of results for a limited

range of elements on experimental closed loop coalflow systems were

reported in the early I960's

(31-32).

Further development of one of

these projects (33) resulted in a prototype demonstration system,

installed at a coal preparation plant in the USA, which monitored the

sulphur content of metallurgical coal flowing through a bin 4.0 m high

and 1.0 m in diameter at a rate of 6 tonnes per hour (34). Using a

large (150 x 180 mm) sodium iodide scintillation detector and a

californium -252 neutron source this installation achieved a precision

(+ls) of 0.05% sulphur over a 2 minute measuring period.

The growing importance of coal as a primary fuel in the 1970's brought

about a resurgence of interest in on-line coal analysis and a number of

research interests undertook work aimed at the development of systems of

coal analysis based on neutron activation interactions. In particular,

the Electric Power Research Institute (EPRI) in California sponsored a

programme to develop on-line analysers in 1976 which led to the

development of a family of designs for PGNÂÂ analysers by Science

Applications International Corporation (SAIC) of California (35). At

the same time MDH - Motherwell Inc. of California began a study of the

technique and subsequently designed an analyser for bulk stream (36).

In 1983 Gamma-Metrics, also of California entered the market with a Bulk

Coal Analyser.

8.3 Commercially Available Analysers

At present, SAIC, MDH and Gamma-Metrics are the only manufacturers

who have reached the commercial stage with neutron/gamma analysers and

have units operating in the field. Table 21 compares some of the

principle features and dimensions of the three analysers.

8.3.1 Science Applications International Corporation

Assisted by EPRI sponsorship, SAIC undertook a series of

experimental and theoretical programmes to establish basic design

parameters for an on-line analysis system and the potential for

application at mines and power plants. This work is reported in a



80

series of EPRI reports under the general title of 'Nuclear Assay of

Coal(37). The main conclusions arrived at were:-

(i) Given suitable constraints on coal bed thickness and density, and

on source, sample and detector configuration it was possible to

generate prompt gamma spectra in which all the main elemental

constituents of coal (except oxygen and magnesium) can be

identified.

(ii) For full elemental analysis, a high resolution germanium detector

is preferred but for some elements a low resolution sodium iodide

scintillation detector is adequate.

(iii) The susceptibility of germanium detectors to damage by neutrons

and their low counting efficiency results in a lower measurement

precision than is acceptable within the short response times

required for plant control purposes. Sodium iodide detectors do

not have this limitation.

(iv) The most accurate way of determining total hydrogen content is by

measurement of epithermal neutron flux leakage from the coal bed

with a helium -3 detector.

(v) A full elemental analyser is best served with a hybrid detector

system containing all the above types of detector.

(vi) A separate measurement of moisture content is required and can be

obtained with adequate precision using a moisture meter based on

microwave attenuation.

(vii) Mass flow information required in the data processing can be

obtained from conventional mass/density gauges.

A prototype elemental analyser (CONAC) based on these findings is

illustrated in Fig. 122.

Coal up to 75 mm particle size from the inlet feed hopper is

transferred on a flat bed conveyor between a californium -252 neutron

source and the detector assembly containing a High Purity germanium

detector, a sodium iodide scintillation detector and a helium -3

epithermal neutron detector. The belt speed is adjusted to give a flow

rate up to 30 tonnes per hour in a bed 30 cm deep and 90 cm wide. A

microwave moisture meter and a caesium -137 density gauge are installed

between the feed hopper and the neutron analyser section. The CONAC is

fitted with adequate radiation shielding and safety interlocks,

including a level detector on the feed hopper which stops the belt in

the event of an interruption to the coal feed, to ensure that radiation

levels at external surfaces meet safety regulations.

The signals from the two gamma detectors are processed to remove

pulse pile up and other unwanted effects, and subjected to suitable

stripping routines to give spectra from which the net areas of various

peaks can be related to the elements of interest. This information,

together with the output from the other detectors, is processed in the



81

microcomputer to give elemental analysis of the major and minor elements

in coal (except Mg and 0) and moisture content, ash content and

calorific value. The ash content is inferred from the sum of the ash

elements, expressed as oxides, and including empirical values for

magnesium oxide and sulphur trioxide. The calorific value is calculated

from the heats of combustion of carbon and hydrogen (modified Dulong and

Petit formula) or from the relationship between ash, moisture and dry,

ash-free calorific value. Data for elemental analysis is integrated

separately for the Ge and Nal detectors on different time bases. Data

from the Nal detector system, which gives information on H, C, S, Cl, N

and Fe, on a short time basis, is normalised against the corresponding

values from the Ge detector system, which reports on a much longer time

base.

Initially these reporting periods were 20 minutes and 3 hours

respectively (38) but subsequent improvements to the system allowed the

same analysis precision to be reached over periods of 5 and 20 minutes

(39).

The reported values for accuracy and precision are given in

Tables 22 and 23 (40).

Prototypes of two other instruments based on the same technology

have been produced. These are the SAIC Sulfurmeter (41), which is

similar in design to the CONAC but uses only a Nal detector for prompt

gamma radiation measurement, and the SAIC Rapid Sulfurmeter (42), which

also uses a Nal detector but consists of a horizontal cylinder 1.8 m

long by 1.2 m diameter with a vertical chute 0.35 m by 0.30 m which is

fitted with a bottom door and has a capacity of 110 kg of coal. This

latter instrument operates on a 6 minute batch measurement basis over a

15 minute cycle. Calibration accuracy for the Belt Sulfurmeter is

reported as 0.08% s over a range 0.4 to 4.4%. The Batch Sulfurmeter

returned a similar initial calibration accuracy and a 6 minute precision

of measurement ranging from 0.04 to 0.09% sulphur.

8.3.2 MDH - Motherwell Inc.

With a primary interest in the rapid on line measurement of

sulphur in coal, MDH chose to develop a system centred on

californium -252 and a sodium iodide scintillation detector. Their

preferred method for coal presentation was a gravity-fed vertical,

rectangular chute through which the coal passed at a rate controlled by

a feeder at the bottom outlet. Figure 123 is a schematic representation

of the instrument(ELAN). The chute is over 2.5 m high and has a cross

section of 0.35 x 0.25 m. Enclosed within a suitable radiological

shield, the source/detection system consists of two 252 Cf sources at

one side of the chute and a large Nal detector at the other. Coal, at a

maximum particle size of 100 mm, flows between the two at any convenient

rate up to 100 tonnes per hour. The top of the chute is fitted with a

microwave moisture meter and a nucleonic level gauge which is linked to

the outlet discharge feeder to ensure that the chute remains full of

coal at all times.

The signal from the detector is stripped of pulse pile-up events

to give a spectrum which is considered to be a linear superposition of

the individual spectra of the gamma radiation from thermal neutron

capture interactions with all the detectable elements in coal, together



82

with those which arise from inelastic scatter events for carbon and

oxygen and spectra representing background and neutron/detector

interactions (43). Information on these 23 component spectra is derived

from standards measured at the factory before despatch and installation

of the unit (44). The measured spectrum is decomposed into its

components giving a factor for each element which is related to its

weight fraction by normalisation to all the contributing elemental

factors. The factor for oxygen is inferred from its known relationship

with the ash elements, carbon, hydrogen and moisture. Ash content is

inferred from the sum of the ash elements, expressed as oxides,

including a value for sulphate taken from an assumed relationship with

total sulphur content, and corrected by a scaling factor for magnesium

and other undetermined ash constituents. Moisture content is obtained

directly from the microwave moisture meter. Calorific value is

calculated from the heats of combustion of carbon and hydrogen using the

Hott-Spooner relationship. Response times were initially quoted as

8 minutes for major elements and 1 hour for minor elements (45) but

current data sheets claim accurate analysis within 2 to 5 minutes.

Table 24 indicates the reported accuracy for a limited selection of

tests (46). Ån accuracy, usually within the limits of ASTM

reproducibility by normal laboratory analysis, is claimed for a 20

minute measurement period (47).

8.3.3 Gamma-Metrics

The Gamma-Metrics Coal Analyser (Model 3612C) was introduced in

1983 and designed to be a fully self-contained, portable, weatherproof

unit requiring no special housing facilities (48). The system chosen is

based on a californium -252 neutron source and scintillation detectors.

Figure 124 is a schematic representation of the instrument. Coal

presentation is via a vertical, rectangular chute 0.9 m by 0.3 m and the

flow of coal is controlled by a belt feeder at the bottom outlet. The

source/detection system consists of three 252 Cf sources, spaced

horizontally on one of the larger faces of the chute, with two large Nal

scintillation detectors on the other face. Immediately above and below

the neutron interrogation zone a 137 Cs transmission density gauge is

fitted to provide bulk density data. An ultrasonic level sensor, in the

mouth of the chute, is linked to the discharge belt feeder to ensure

that the chute remains full at all times. Coal at a maximum particle

size of 100 mm, is fed into the top of the chute at a rate up to

500 tonnes per hour.

Signals from the detector are stripped of pile-up events and other

unwanted signals to give a spectrum in which the contributions measured

in various chosen energy channels are correlated by regression

techniques to the elemental concentrations of known standards. An

initial generic calibration is made at the factory and subsequently

refined using coals from the site. Signal conditioning and data

processing is carried out within the unit and resulting values

transmitted to a display terminal. Moisture content was originally

calculated from hydrogen content, assuming a fixed C/H ratio in coal

substance. More recently, a microwave moisture meter has been offered

as an optional extra. Ash content is inferred from the sum of the ash

elements, and calorific value is calculated from the dry ash-free value



83

for the coals being measured. Response times of one minute are claimed

for the instrument. Reported values for precision and accuracy are

listed in Table 25

(49-51).

In 1986, Gamma-Metrics introduced another version of their

analyser, with a smaller chute (0.45 m x 0.3

m),

and a maximum

throughput of 100 tonnes per hour (Model

1812C).

Precision is similar

to Model 3612C but with a response time of 2 minutes.

8.3.4 Summary of Performance Capabilities

Although reported values of accuracy and precision have been given

in Tables 22-25, it is difficult to make a comparison since the

composition of test coals used and the details of the procedures often

differ. In particular, the measurement times adopted are often

different or even not clearly defined, which has had a considerable

effect on estimates of precision. The minimum response times reported

in Table 21 do not necessarily reflect the optimum required to achieve

an acceptable value, especially for the minor constituents of ash. An

estimate of the relative accuracy at present obtainable for various

parameters has been made from the available data and is given in

Table 26.

8.3.5 Installations

At present, a total of 20 neutron gamma analysers are installed or

on order. Table 27 shows the distribution among the manufacturers and

the current status of the units. Six of the analysers are at power

plants and 14 at mines; all are situated in North America.

Of the SAIC analysers, only the Batch Sulfurmeter is in use where

it monitors the quality of the clean coal product from the coal

preparation plant, with respect to sulphur content, ash content and

calorific value to facilitate SO2 emission control, which is applied in

terms of a limit on the S02/calorific value ratio. The analyser is

integrated with the cleaning plant process control. The CONAC is also

at the same plant and linked to the same product stream but also has

facilities for the testing of imported coals on a re-cycle system (52).

Its primary role as a demonstration unit has been fulfilled and it is

now out of use and under consideration for transfer to another location.

The Belt Sulfurmeter at Monroe Power Plant has been used extensively to

control the blending operations for incoming coal with respect to

sulphur content, to ensure compliance with SO2 emission regulations. It

has been shown to accurately and rapidly track sulphur variations in the

coal stream and to show a good correlation between sulphur content of

the feed to the boiler and SO2 emissions from the stack (53). Changes

in the quality of coal supplies to the power station have rendered this

application redundant and it is now out of use.

The first of the MDH ELANS was installed on a clean coal product

line at Homer City Power Plant where it measures sulphur and ash

content, moisture and calorific value to ensure compliance with SO2

emission limits (45). As with the SAIC sulfurmeter at Monroe, control



84

of the sulphur content of the feed coal to the boiler was chosen as an

alternative to flue gas de-sulphurisation to meet regulations. Of the

other 3 MDH units, two are at power plant and one at a mine, two are

recent installations and not yet commissioned while the third is still

in manufacture.

Gamma-Metrics have installed 12 units, two of which are the larger

3612C Model, and have one more under construction. They also maintain

the original production unit which is mounted on a lorry trailer with a

recirculation rig to give a self contained mobile demonstration unit.

Most of these installations have been made within the last three years

and there is as yet little published information. One unit is not in

use due to closure of the mine. The others are all at producing mines

where they provide data on the quality of coal shipments and offer a

basis for control by blending (6 units) cleaning plant control (3

units),

sorting (2 units) and direction of mining operations (1

unit).

Sulphur is the primary product quality parameter of interest but ash and

calorific value are also measured.

The majority of the analysers have been installed within the last

three years and consequently published information on operating

experience and instrument reliability is very limited. The SAIC

sulfurmeter at Monroe was put into service at the end of 1981 and was in

use,

somewhat intermittently due to problems outside the analyser

system, until 1988. The SAIC Batch sulfurmeter at Paradise has been

running as an operational tool since late 1983. The Homer City Elan has

been operating since mid-1983 but delays in the installation of a

parallel ASTM sampling system held up its full use as a plant control

instrument until mid 1985. The first Gamma-Metrics Analyser to be put

into operational use was at the Pyramid Surface Mine in early 1986. No

major reliability problems have been reported for these instruments and

operational availability is understood to be good. Capital costs are

high, ranging from £200,000 to over £500,000. Potential economic

benefits are also high, at least in the American market, where

application of this technology can result in operational cost reductions

of millions of dollars per year (54).

8.4 Summary

The principles involved in the application of neutron/gamma

interactions to coal analysis have been studied for a long time with the

result that three manufacturers now offer, and have operational

experience with analysers based on this technique. A fourth

manufacturer is just entering the market.

The analysers are capable of accepting large volume streams of

coal, up to 500 tonnes per train, with little or no preparation. They

are capable of measuring all the major and minor elements in coal

(except oxygen and magnesium) plus ash, moisture and calorific value,

and other analysis-derived parameters like ash fusion, on a continuous

basis.

Response times are of the order of tens of minutes and accuracy

is acceptable for control purposes. Accuracy ranges from relative values



85

of less than 5% for hydrogen, carbon, ash content and calorific value to

more than 30% for sodium, calcium and titanium.

Some 20 analysers have been ordered or installed and are mainly in

use in connection with the control of coal quality to specifications

designed to meet SO2 emission standards in the USA. Their potential for

use in the operation of power station boilers is under study and an

extension of their use to other areas can be expected, provided the high

capital costs of the equipment can be justified.

9. GENERAL CONCLUSIONS

9.1 On-stream Ash Monitoring

Laboratory trials of both the backscatter and transmission low

energy (60 keV) gamma radiation techniques show that calibration

accuracies for well homogenised samples range from ±0.2% ash to +3.86%

ash with an average relative value of 5%. These values are

predominantly influenced by variations in coal composition, in

particular iron content where the effect of 1% of Fe203 on the

instrument reading is equivalent to that of 6% of ash.

Using a simple mathematical model of the backscatter system, it is

possible to calculate, from the composition of the coal, the expected

calibration standard deviation of ash content for well homogenised

samples,

with a reasonable degree of accuracy. The prime compositional

factors affecting calibration accuracy are level of ash content in the

coal, variability of iron content in the coal and the degree of

correlation between iron content and ash content. A good empirical

relationship between calibration accuracy and these factors has been

found.

The sensitivity of the Wultex backscatter system to bed depth

variations limits its use to belts where coal bed thickness exceeds

150-200 mm.

On-site calibration trials at two locations indicate that other

factors,

perhaps related to lack of homogeneity throughout the coal bed

at the point of measurement, introduce significant errors. Compared

with laboratory measurements, accuracy (+ls) is reduced by a factor of

about 2 to about +10% to 20%. Increasing the integration period to

several hours offers no improvement in accuracy.

Generally, the Wultex backscatter instrument is mechanically and

electrically reliable but, at the levels of accuracy found, offers only

data of limited value for the control of processes in the preparation of

the type of blended power station fuel commonly used in the UK.

The Coalscan two-energy transmission system is relatively

insensitive to variations in coal bed depth.

Given a reasonably thorough interrogation procedure the accuracy

of static calibrations is degraded only slightly as particle size

increases from 0.2 mm to 25 mm. Simulation of the on-belt situation,



86

however, indicates that the calibration accuracy is reduced by a factor

of two to a relative value of +10% . On-belt trials confirm this level

of accuracy and integration over longer periods offers no improvement.

Â significant proportion of the measured error is not accounted for by

coal composition variations (including moisture) or sampling and

analysis of the reference samples. Direct comparison with an existing

Phase 3A sub-stream monitor taking samples from the same production

stream indicates that the on-belt monitor is less accurate. The

equipment is generally mechanically and electrically reliable but some

evidence of long term calibration drift was seen. The level of accuracy

obtained again limits its potential for blending control purposes but

this geometry should be applicable to most belts.

Trials with both on-belt systems demonstrated the considerable

difficulties of performing dynamic on-belt calibrations.

9.2 Sub-stream Ash Monitoring

A sub-stream presentation unit (the Ram Feed Unit) has been

developed, which is capable of accepting coals of difficult handlability

and up to 25 mm particle size, to produce a continuous bed of coal, with

a smooth surface profile, suitable for radiometric examination. The

unit is also designed to accept a microwave moisture meter system and

has proved to be mechanically and electrically relaible over long

periods.

Equipped with a Phase 3A type backscatter ash monitor head, it

should be capable of measuring ash content (and with a suitable moisture

meter, moisture

content),

to a higher accuracy than can be achieved with

on-belt systems.

9.3 Microwave Moisture Monitoring

An improved, single frequency, microwave moisture meter has been

developed, together with an ultra-sonic bed depth system and their

ability to monitor appropriate parameters directly on a main product

belt demonstrated. This system should form the basis of an on-belt

moisture monitoring system. This type of moisture meter is also

suitable for application in the Ram Feed sub-stream presentation unit.

A moisture meter, based on a new measuring technique which

measures microwave attenuation over a range of frequencies, has been

developed and shown to give acceptable calibration accuracy. This Swept

Frequency System will be relatively insensitive to variations in coal

type, particle size and coal bed geometry and should be capable of

application to main-stream or sub-stream monitoring.

9.4 Capacitance Moisture Monitoring

An experimental version of a new type of capacitance moisture

meter (Insulated Plate Capacitance Monitor) has been developed and

tested in the laboratory. Calibration accuracy is similar to that of

microwave systems but some sensitivity to dissolved salts, in the water

associated with coal, remains. Quotations for the production of a

prototype instrument were much higher than expected. As a result of



87

this cost and the satisfactory progress in microwave techniques it is

not considered to be economically justifiable to continue this work at

the present time.

9.5 Nuclear Magnetic Resonance

À study of the application of this technique to moisture

monitoring shows that it has the ability to measure moisture in coal to

an accuracy similar to that obtainable for microwave and capacitance

techniques.

The present state of the development, however, is restricted to

very small (100 cm^) volumes of coal and extension of the technique to

larger volumes, either in sub-streams or main-streams, will require

substantial technical effort and, if successful, is expected to result

in equipment with high capital cost. In these circumstances, it is not

considered worthwhile to pursue this particular line of work further.

9.6 Neutron/gamma Analysis of Coal

A total of 20 analysers, based on this principle, have been

ordered or installed and significant operational experience gained,

mainly in the control of product quality to meet SO2 emission standards.

These analysers are capable of real-time measurement of most of the

important elements in coal on a continuous basis, using large volume

coal streams, to an accuracy which is acceptable for some operational

purposes. An extension of their use, particularly to the field of power

station boiler control, can be expected, provided the returns can

justify the high capital cost of the equipment.



»

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9. J. HAYNES and G. GRAY. "The Continuous Monitoring of Moisture in

Coal - evaluation of the MRDE moisture monitor type MRD 60800."

NCB, N.E. Area Scientific Department Report No. A/2730,

December 1981.

10.

M. HAMPEL and H. HOBERG. "Rapid Capacitive measurement of the

water content of small coal."

Gluckauf - Forschungshefte, Vol. 37, June 1976, ppll4-122.

11.

W. R. LADNER, and A.E. STACEY. "Measurement of moisture in a

moving coal feed."

Brit. J. Appi. Phys. Vol. 13, 1962, ppl36.



90

12. R. K. HARRIS. "Nuclear magnetic resonance spectroscopy - a

physiochemical view".

Pitman, London (UK), 1983.

13.

W. R. LADNER. "The determination of the moisture in coals and

cokes by nuclear magnetic resonance".

Instrument Practice, Vol. 18, 1964, ppl039-1043.

14.

W. R. LADNER AND R WHEATLEY. "Moisture in coal by nmr: Effect of

mineral matter and size".

J. Inst. Fuel, 1966, pp280-284.

15. S. D. ROBERTSON, F. CUNLIFFE, C. S. FOWLER AND I. J. RICHMOND.

"Rapid measurement of moisture in coal and total solids in coal

slurries by low resolution proton nmr".

Fuel, Vol. 58, 1979, pp770-774.

16.

D PAGE. NCB, N.E. Area Scientific Dept., Unpublished data 1981,

17.

J. D. KING AND W. L. ROLLWITZ. "Magnetic resonance measurement of

flowing coal".

I.S.A.

Transactions, Vol. 22, 1983, pp69-76.

18.

N. G. CUTMORE, B. D. SOWERBY, L. J. LYNCH AND D. S. WEBSTER.

"Determination of moisture in black coal using pulsed nuclear

magnetic resonance spectrometry".

Fuel,

Vol. 65, 1986, pp34-39.

19.

SOUTHWEST RESEARCH INSTITUTE. "Special NMR Instrumentation

capabilities at Southwest Research Institute".

San Antonio, Tx (USA), 1977.

20.

H. R. COOPER. "Progress in on-line coal quality measurement".

Coal Quality, Jan. 1984, ppl6-23.

21.

D. O'CONNOR. "On-line coal analysis".

EPRI Journal, Vol. 12, Dec. 1987, pp42-44.

22. Anon. "On-line coal sorting".

World Mining Equipment, Feb. 1988, pp20-22.

23. T.C. MARTIN, J. D. HALL AND I. L. MORGAN. "An on-line nuclear

analysis system".

Radiosotope Instruments in Industry and Geophysics, IAEA (Vienna),

1966,

pp411-.

24.

M. R. WORMALD, C G . CLAYTON, I.S. BOYCE AND D. MORTIMER. "A

method of measuring the ash content of coal in moving wagons

Int. J. Appi. Radiat. Isot., Vol. 30, 1979, pp297-.

25.

C. G. CLAYTON AND M. R. WORMALD. "Coal analysis by nuclear

methods".

Int. J. Appi. Radiat. Isot., Vol. 34, 1983, pp3-22.

*



91

26.

C L . HERZENBERG. "Use of small accelerators in coal analysis and

coal slurry flow measurement".

IEEE Trans. Nucl. Sci. Vol. NS-26, 1979, ppl568-1573.

27.

C. G. CLAYTON, A. M. HASSAN AND M . R. WORMALD. "Multi-element

analysis of coal during borehole logging measurement of prompt

gamma rays from thermal neutron capture".

Int. J. Appi. Radiat. Isot. Vol. 34, 1983, pp83-93.

28.

BRITISH COAL HQTD. "Nuclear methods for the measurement of coal

ash".

Final report on ECSC Project 7220-EA/810, 1986.

29.

M. R. WORMALD AND C. G. CLAYTON. "In-situ analysis of coal by

measurement of neutron-induced prompt gamma rays".


30.

M. R. WORMALD. "Pair spectrometer array for prompt gamma-ray

analysis".

Trans.

A.N.S., Vol. 56, (Supplement

3),

1988, pp43-44.

31.

T. C. MARTIN, S. C. MATHUR AND I. L. MORGAN. "Application of

nuclear techniques in coal analysis".


32.

R. F. STEWART, W. L. FARRIOR. "Feasibility of continuous ash

measurement of coal".

Symp. Mineral Matter in Coal, 148th Meeting, Amer. Chem. S o c ,

1964, ppl92-197.

33.

R. F. STEWART, A.. W. HALL, J. W. MARTIN, W. L. FARRIOR AND A. M.

P0STON. "Nuclear meter for monitoring the sulphur content of coal

streams".

Tech. Prog. Rep. 74, U.S. Bureau of Mines, 1974.

34.

A. W. HALL, J W MARTIN, R. F. STEWART, A. M. POSTON. "Precision

tests of neutron sulphur meter in coal preparation plant".

Report of Investigations RI 8038, U.S. BUREAU OF MINES, 1975.

35.

H. BERNATOWICZ, D. R. BROWN AND C. M. SPENCER. "On-line coal

analysis for control of coal preparation plants".

Proc. Coal Prep. '84, Lexington, Ky, 1984, pp347-367.

36. A. CEKORICH, H. DEICH, T. HARRINGTON, J. H. MARSHALL III.

"Development of an elemental analyser for coal, oil and similar

bulk streams".

Proc. Symp., Lexington, Ky, 1984, pp347-367.

37.

"Nuclear assay of coal".

Electric Power Research Institute RP983 (USA), 1979-1983, Vols.

1-9.

38. D. R. BROWN, T GOZANI, C. M. SPENCER. "Operation of a continuous

coal assay system".

Nuclear Assay of Coal, Vol. 10, 1983, EPRI RP983 (USA).



92

39.

F. KARLSON. "On-line coal analysis".

EPRI Journal, July/Aug 1986, pp44-45.

40.

D. A. HUMPHRIS, R. W. LYNCH, 0. J. TASSICKER, M. EPSTEIN, D. R.

BROWN AND T. GOZANI. "Laboratory and field acceptance test

performance of CONAC".

Nuclear Assay of Coal, Vol. 13, CS-989, EPRI (USA), 1984,

pp7.1-7.26.

41.

J. D. RUBY, T. R. WOOD AND D. R. BROWN. "Plant Monroe Sulfurmeter

Evaluation".

CS-2365 EPRI

(USA),

1982.

42.

R. W. LYNCH, G. B. PRAY AND D. A. HUMPHRIS. "Batch sulfurmeter

installation and testing at the Paradise Coal Preparation Plant".

Nuclear Assay of Coal, Vol. 13, CS-981, EPRI (USA), 1984,

pp4.1-4.36.

43. J. H. MARSHALL III AND J. F. ZUMBERGE. "Theory of operation of a

PGNAA Instrument".

MDH-Motherwell Inc.

(USA),

1987.

44.

"Prompt-gamma neutron activation analysis of bulk coal".

ELAN Technical Data Sheet TD-1001, MDH-Motherwell Inc.

(USA),

1987.

45.

J. TICE, R. STOESSNER AND H. DEICH. "Experience with a coal

elemental analyser at the Homer City Coal Cleaning Plant".

Nuclear Assay of Coal, Vol. 13, CS-981, EPRI

(USA),

1984,

pp5.1-5.28.

46.

R. D. STOESSNER. "Homer City Station nuclear analyser system".

Paper to ASTM Seminar, Memphis TN, October 14, 1985.

47.

J. F. ZUMBERGE. "Measurement of coal quality by prompt-gamma

neutron activation analysis".

J. Coal Qual., Oct. 1987, ppl20-123.

48.

GAMMA-METRICS. "Self-contained, on-line, real-time bulk material

analyser".

European Patent Application, EP 0 171 256 A2, 1986.

49.

"Composite results of coal analyser demonstrations in 1985,

Gamma-Metrics, San Diego USA, 1986.

50.

R. L. DeMAO AND T. H. SCHADE. "Experiences in on-line coal

analysis at a surface mine".

Coal Technology 1986, Book II, Vol. 3, 1987, ppl55-172.

51.

"On-line coal analyser - 3612C". Data sheet.

Gamma-Metrics, San Diego, USA, 1987.



93

52. J. L. COLE AND E. H. CHESTNUT. "CONAC design and installation,

Paradise Steam Plant".

Nuclear Assay of Coal, Vol. 13, CS989, EPRI

(USA),

1984,

pp6.1-6.13.

53.

R. J. BUCKLER. "Application of a sulphur/BTU meter to the Monroe

Power Plant's coal blending facility".

Nuclear Assay of Coal, Vol. 8, FP989, EPRI

(USA),

1979,

pp3.1-3.18.

54.

T. R. WOOD, J. D. RUBY, D. P. REES AND J. G. WAGNER. "Fuel

management evaluation at Utah Power and Light Company's Hunter

Plant".

Nuclear Assay of Coal, Vol. 13, CS989, EPRI

(USA),

1984,

pp8.1-8.53.



95

APPENDIX 1

EXTRACT FROM HEADS OF AGREEMENT CONTRACT BETWEEN THE NCB AND WULTEX MACHINE

CO LTD FOR THE TRIAL OF A WULTEX RADIOMETRIC ASH-METER, TYPE G-3,

AT MANTÓN COLLIERY

ACCEPTANCE CRITERIA FOR TRIAL

The Plant will be deemed to have completed the Trial satisfactorily if

the following criteria are fulfilled:-

(i) Operational Reliability

To demonstrate operational reliability the Plant must be

regularly capable of operating under all feed conditions for

continuous periods of 5 working days without requiring operator

attention. This capability is to be demonstrated over a

continuous period of 60 working days. If during any 5 day

period operational attention is required then the Trial period

so far as operational reliability is concerned will revert back

to zero time and a further attempt to demonstrate this

capability for 60 workings days will be required.

(ii) Mechanical Reliability

To demonstrate mechanical reliability the Plant must be capable

of operating for a continuous period of 60 working days without

requiring any mechanical maintenance and for a continuous period

of 120 working days without requiring any replacement mechanical

parts.

If mechanical attention or replacement mechanical parts

are required within the specified periods then the Trial period

with respect to either of these requirements will revert back to

zero time and a further attempt to demonstrate the capability

for the specified period will be required.

(iii) Electrical Reliability

To demonstrate electrical reliability the Plant must be capable


requiring electrical attention and for a continuous period of

120 working days without requiring any replacement electrical

parts. If electrical attention or replacement electrical parts


with respect to either of these requirements will be considered

to revert back to zero time and a further attempt to demonstrate

the capability for the specified period will be required.



96

(iv) Performance Standards

The Radiometrie Ash-Meter, Type G-3, having been calibrated

on-stream in accordance with the Contractors instructions

against the incinerated ash content of coal samples

representing the normal range of variation of the coal stream

being monitored, will be demonstrated to be capable of ash

measurements with the degree of accuracy specified in

paragraphs (a) and (b) below.

(a) The integrated ash measurement over a period of coal flow

of one hour shall be within +1.5% ash of the incinerated

ash content for a minimum of 95% of at least fifty such

measurements made within a period of 3 months from the

date of calibration and where the mean total moisture

content during such measurements lies within +4% of the

mean total moisture content of the coal samples on which

the calibration was based.

(b) The integrated ash measurements over a period of coal flow

of four minutes shall be within +2.5% ash of the

incinerated ash content for a minimum of 95% of at least

one hundred such measurements made within a period of 3

months from the date of calibration and where the mean

total moisture content during such measurements lies

within +4% of the mean total moisture content of the coal

samples on which the calibration was based.

A second calibration of the Radiometric Ash-Meter will be

made within 4 months of the date of the first calibration

or by agreement. If the ash measurements made in

accordance with paragraphs (à) and (b) above should show a

progressive drift away from the initial calibration and if

over the period of these measurements a change should

occur in the proportion of the seam outputs at the Mine

such that the change in the output from any seam exceeds

20%

of the Mine output then the accuracy of the ash

measurements will be assessed on the basis of the mean of

the first and second calibrations.

For the purpose of assessing the performance all sampling

will be conducted in accordance with BS 1017, Part 1, 1977

and all total moisture and incinerated ash contents will

be determined in accordance with BS 1016, Part 3, 1973.



97

APPENDIX 2

CALCULATION OF CALIBRATION ACCURACY FROM COAL COMPOSITION

The relationship between backscattered Intensity and the composition

of the coal containing i elements in concentrations r is given by:-

1

'

k I

°

/ U

i

« i

r

i

£

i

(H

+ F')i ri

where

I - intensity of backscattered radiation

k - geometrical factor

I

0

- intensity of incident radiation

0* - sum of the Compton and coherent scattering coefficients

at the incident radiation energy

p - mass attenuation coefficient at the incident energy

u' - mass attenuation coefficient at the backscattered energy

From the elemental composition of the coal and tabulated values for

the scattering and attenuation coefficients, a value for relative

backscattered intensity (I/kI

0

) is calculated for each sample in a suite of

coal covering the range of ash content required. Regression analysis of

the ash content on the relative backscattered intensity provides

information on the extent of the correlation between the two parameters and

an estimate of the accuracy of ash content determination in terms of the

standard deviation of the results about the regression line.



99

APPENDIX 3

NATIONAL COAL BOARD

HEADS OF AGREEMENT CONTRACT FOR EXPERIMENTAL USE OF WULTEX RADIOMETRIC

ASHMETER EQUIPMENT

TECHNICAL APPENDIX TO AGREEMENT

OBJECTIVES, DIRECTION AND REVIEW OF TRIAL

1. OBJECTIVES OF LABORATORY INVESTIGATIONS

Introduction

NCB experience so far with the Wultex Radiometric Ashmeter has been

restricted to a trial installation at Mantón Colliery where the output has

been drawn from a single seam, although some limited information has been

gained on the affect of introducing coal from other collieries mining

different seams. The conclusion drawn from the trial was that although

there may be collieries where the Ashmeter can be employed to advantage,

there are other collieries where inability to maintain an appropriate

material bed depth and bulk density, or where production is on a multi-seam

basis, may influence the accuracy of ash measurement.

Data originating from Poland and made available to the NCB by Wultex

has suggested that certain material presentation parameters, principally

material bed depth and bulk density, could have an appreciable effect on

the accuracy of ash measurement. Laboratory investigation with the

objective of quantifying the affect of these variables is considered

necessary. The NCB, Yorkshire Regional Laboratory, is prepared to

undertake this work; and with the further objective of assessing the

factors affecting the design of a method of presentation of the coal to the

Ashmeter in order to optimise the degree of accuracy of the Ashmeter in

circumstances where the required bed depth cannot be achieved without some

modification to the presentation-conveyor layout.

Variations in the elemental composition of the ash in different seams

affect the relationship between the ash content and the backscattered

radiation. In particular, iron is known to affect the backscattered

radiation disproportionately to its mass concentration and, therefore,

variations in iron content between different seams could have a significant

affect on the accuracy of ash measurement. The iron content of the Mantón

coal was found to be reasonably consistent during the performance tests on

the Ashmeter conducted under the initial Heads of Agreement Contract.

Therefore, to assess the possible wider application of the Ashmeter the

laboratory investigations will include the examination of coal from a

multi-seam colliery with the objective of assessing the affect of

variations in ash composition and iron content on the accuracy of the

Ashmeter.



100

Stage 1 - Laboratory Investigations using Mantón Coal

It is currently proposed to conduct tests initially using samples of

part-treated smalls from Mantón Colliery since this would assist in

deciding the direction and extent of further trials with the existing

Ashmeter installation. However, the test procedures necessary to examine

different bed depths and bulk densities would encounter problems resulting

in possible errors if these investigations were attempted on a laboratory

scale with 50 mm top size material. It is therefore proposed that all coal

samples from Mantón would be screened at 25 mm and the material above this

size would be crushed below 25 mm and mixed back into the sample.

A suite, comprising a minimum of 20 calibration samples, of Mantón

part-treated smalls, and excluding any foreign coal being treated

temporarily at Mantón, will be collected. The samples will cover the

normal range of ash variation of 11% - 21% as found with the performance

tests conducted in October 1981 under the previous Heads of Agreement

Contract trials.

The laboratory tests will be conducted using the laboratory

presentation rig, modified as necessary and loaned to the NCB by the

Contractor. The NCB will provide a variable depth sample presentation

container of suitable design and means of achieving reproducible degrees of

sample compaction. Each coal sample will be tested at bed depths of 200,

160, 120 and 80 mm after a standardised compaction procedure which will

consist either of uniform dead-weight loading or subjection to vibration

for a fixed time dependent on preliminary tests. Each sample will be

presented to the Ashmeter a minimum of 10 times at each bed depth. A

measurement of the bulk density of the compacted material will be made for

each filling of the presentation container.

Additional tests to investigate the affect of variation of the bulk

density of the material will be conducted on at least three of the

calibration samples representing the lower, middle and upper portions of

the 11 - 21% ash range. These tests will be conducted at one or more

selected bed depths and at least two additional levels of bulk density

which will be achieved by varying the degree of compaction of the material.

Following the completion of testing on each of the calibration

samples it will be subjected to laboratory analysis for moisture, ash, iron

and sulphur content. A calibration for the Ashmeter, between the radiation

count readings and the laboratory ash determinations, will be obtained for

each bed depth and will permit assessment of the calibration accuracy of

the Ashmeter reading. The radiation count readings for the bulk density

tests will be converted to ash readings, according to the calibration for

the appropriate bed depth, and the affect of bulk density variations on the

ash readings will be obtained.

Stage 2 - Laboratory Investigations with Multi-seam Coal

For the second stage of the investigations it is proposed to use coal

samples, not exceeding 25 mm top size, from a multi-seam colliery where

there is a significant difference between the levels of iron content

between the seams so as to introduce a greater variability in the iron



101

content of the samples. The procedures followed in Stage 1 will be

modified and simplified, wherever possible, to reduce the amount of test

work, according to the experience and findings of Stage 1.

2.

WULTEX PARTICIPATION IN DIRECTION OF INVESTIGATIONS

The objectives of the investigation shall be as detailed in the above

Introduction unless varied by mutual written agreement between the NCB and

the Contractor.

The NCB reserve the right to determine the laboratory procedures for

the investigations but undertake to consult fully with Wultex in order to

achieve agreement before the start of the investigations and before any

significant changes are made during the course of the investigations.

Nominated Wultex Engineers will be allowed reasonable access to

observe the progress of the investigations provided each visit is agreed in

advance with the Scientist in charge of the investigations.

3. REVIEW OF PROGRESS OF INVESTIGATIONS

The NCB will hold regular meetings with nominated representatives of

Wultex to review the progress of the investigations. The frequency of such

meetings would be dependent on the progress of the work and would normally

take place not more than once per month. The results of the investigations

would either be presented at such meetings or communicated by letter to

Wultex.



103

APPENDIX

4

WÜLTEX

RADIOMETRIC

ASHMETER

SITE REQUIREMENTS FOR PROPOSED SECOND TRIAL INSTALLATION

Preparation Plant Feed

A

multi-seam

output

drawn

from

two

or

more

seams.

Any

foreign

coal

treated

should

be

on

a

regular

basis

where

it

comprises

an

appreciable

proportion

of

the

plant

throughput

(i.e.,

greater

than

10%).

Product

to

be

Monitored

Preferred

Product

Size Range

Ash

Variation

Alternative

Product

Size

Range

Ash

Variation

Monitoring Location

Preferred

Location

■

Alternative

Location

Blended

power

station

smalls

Preferably 30 mm - 0 but maximum of

50

mm

considered

At

least

+3%,

in

shift

or

train-load

samples,

in

the

range

10-20%

ash

Untreated

smalls

Preferably

less

than

30

mm

but

maximum

of

50

mm

considered

At

least

+5%

in

ash

range

20-40%

A

belt

feeder

with

a

minimum

bed

depth

of

200 mm and at least a 2 m length of

accessible

coal

surface

either

before

or

after

any

weigh

section.

Effective

product

mixing

prior

to

feeder

and

good

access

for

either

manual

or

mechanical

sampling

at

discharge

of

feeder.

A

belt

conveyor

with

belt

speed

not

greater

than 2.5 m/s, centralised product loading and

a bed depth not normally less than 150 mm

after

profiling.

Prior mixing of product either by mixer or

multiple

transfer

points.

Mechanical

sampler

at

either

return

or

head

end

of

proposed

conveyor.

Access to both sides of conveyor at monitor

location.

Headroom of 1.8 m above centre-line of belt.



105

APPENDIX 5

HEADS OF AGREEMENT CONTRACT BETWEEN THE NCB AND WULTEX MACHINE CO. LTD.

FOR THE TRIAL OF A WULTEX RADIOMETRIC ASHMETER

AT BILSTHORPE COLLIERY, NORTH NOTTINGHAMSHIRE AREA

APPENDIX II - ACCEPTANCE CRITERIA FOR TRIAL

The Plant will be deemed to have completed the Trial satisfactorily

if the following criteria are fulfilled:-


To demonstrate operational reliability the Plant must be

regularly capable of operating under all feed conditions for

continuous periods of 5 working days without requiring operator

attention. This capability is to be demonstrated over a

continuous period of 60 working days. If during any 5 day

period operator attention is required then the Trial period so

far as operational reliability is concerned will revert back to

zero time and a further attempt to demonstrate this capability

for 60 working days will be required. An example of operator

attention would be the necessity to remove a build-up of wet

fines from the contact surface of the plough unit in order to

maintain the measuring system at the correct height above the

coal surface.


To demonstrate mechanical reliability the Plant must be capable


requiring any mechanical maintenance and for a continuous

period of 120 working days without requiring any replacement

mechanical parts. If mechanical attention or replacement

mechanical parts are required within the specified periods then

the Trial period with respect to either of these requirements

will revert back to zero time and a further attempt to

demonstrate the capability for the specified period will be

required.


To demonstrate electrical reliability the Plant must be capable


requiring electrical attention and for a continuous period of

120 working days without requiring any replacement electrical

parts.

If electrical attention or replacement electrical parts




106

with respect to either of these requirements will be considered

to revert back to zero time and a further attempt to

demonstrate the capability for the specified period will be

required.


To enable the Vultex Ashmeter to provide a direct reading of

the ash content of the coal to be monitored it will be

necessary to obtain the relationship between the countrate of

the backscattered radiation and the incinerated ash content of

the coal over the normal range of ash variation, and for this

relationship to be entered in the instrument.

The Ashmeter will therefore be calibrated on site for Bilsthorpe

50 mm - 0 Blended Power Station Fuel in accordance with the following

procedure.

(a) The calibration will be based on a minimum of 30 calibration tests

each extending over a period of approximately 12 minutes and covering

a minimum range of ash content of 10% to 27%.

(b) For each calibration test the preparation plant will be operated so

as to provide sufficient current make of Power Station Fuel to

sustain a continuous flow of coal over the belt feeder at normal

flowrates for the required period of the test.

(c) The Ashmeter will be set to print out the countrate measurement every

2 minutes for 6 consecutive 2 minute periods and the arithmetic mean

of all 6 measurements will be taken to represent all the coal which

passed over the belt feeder during these measurements.

(d) The existing automatic sampler, located at the head end of the belt

conveyor which receives the coal from the belt feeder, will be used

to collect a sample, comprising a minimum of 35 full stream

increments taken at regularly spaced time intervals, from that parcel

of the coal which passed over the belt feeder during each of the

calibration tests and with due allowance being made for the time

delay in the material travelling between the Ashmeter and the

sampler.

(e) The coal samples collected during each calibration test will be

prepared and analysed in accordance with British Standard methods to

determine the total moisture and the ash content, both of which will

be reported on an 'As Received' basis.

(f) The Contractor will provide suitably experienced staff to participate

in the calibration procedure and be responsible for the operation of

the Ashmeter and obtaining the countrate print-outs for each test.

The Contractor's representatives will also be responsible for

calibrating the Ashmeter in accordance with the relationship obtained

between the countrate and the 'As Received' ash content.



107

(g) The NCB will provide experienced staff to liaise with the

Contractor's representatives and carry out the sampling and

laboratory analysis procedures.

The Ashmeter, having been calibrated for the Bilsthorpe Power Station

Fuel in accordance with the foregoing procedure, will be tested according

to the following method and the accuracy of ash measurement determined.

(a) The accuracy of the Àshmeter will be assessed in a series of tests

conducted within 2 months of calibration by comparing the average ash

reading over a 12 minute period with the incinerated ash content of a

representative, full stream sample of the product which passed over

the belt feeder during the same time period.

(b) The performance assessment will be conducted and the samples analysed

by experienced NCB staff and the Contractor's representatives will

have access to observe the testing at all stages.

(c) For each performance test the preparation plant will be operated so


sustain a continuous flow of coal over the belt feeder at normal


(d) The Àshmeter will be set to print out the average ash content at

2 minute intervals for 6 consecutive 2 minute periods and the

arithmetic mean of all six measurements will be taken as the measured

ash content of the coal passing over the belt feeder in the 12 minute

test period.

(e) A representative sample of the coal, which has passed over the belt

feeder during the 12 minute test period, will be taken in a minimum

of 35 regularly spaced increments by the automatic sampler, at the

delivery of the belt conveyor following the belt feeder, with due

allowance for the time delay in the material travelling from the

Ashmeter to the sampler.

(f) The coal sample for each performance test will be prepared and

analysed for total moisture and ash content.

(g) The performance testing will be continued until 60 tests have been

conducted in which the total moisture during each test is within +4%

of the mean total moisture content of the samples on which the

calibration was based and the incinerated ash content is within the

range of incinerated ash contents of the calibration samples.

(h) To satisfy the requirements of the NCB the average Ashmeter

measurement for the 12 minute test period shall be within +3.0% of

the incinerated ash content for at least 95% of the 60 tests which

comply with the total moisture and ash content limitations specified

in paragraph (g) above.



108

For the purposes of calibrating the Ashmeter and assessing the

performance all the sampling will be conducted in accordance with BS 1017

Part 1, 1977 and all total moisture and incinerated ash contents will be

determined in accordance with BS 1016, Part 3,1973.



109

APPENDIX 6

TECHNICAL APPENDIX TO AGREEMENT FOR THE TRIAL OF A

COALSCAN 3500 ASH MONITOR

OBJECTIVES, DIRECTION AND REVIEW OF TRIAL

1. Objectives of Laboratory Investigations

Introduction

The Board has no experience of the Coalscan 3500 ash meter but from

information gained and a description of the principles involved there are

certain advantages to be gained which are unique to this equipment.

Notwithstanding this there are doubts as to the extent to which the

technique can be successfully and usefully applied to UK coals.

From theoretical considerations, the measuring principle should

tolerate variability in bulk density, bed depth, top size and surface

profile, particularly well and without significant loss of accuracy. Its

limitations are expected to arise mainly from variations in elemental

composition of the mineral matter which provides the basis for ash content

assessment. A further limitation affecting its resolution capability

(sensitivity) could arise from excessive attenuation of the transmitted

radiations by high ash coal or high bed depths or, more particularly, a

combination of the two.

There is a clear need to quantify these parameters thoroughly and

objectively so that the limitations and possible applications can be

broadly defined. The Yorkshire Regional Laboratory are prepared to

undertake this work on behalf of the Board making use of test facilities

sited within their Coal Sample preparation area.

2.

Test Procedure

The tests fall naturally into 2 distinct categories, those directed

to the derivation of basic data and those intended to give guidance on

which plants may be suitable for any proposed installation.

2.1 Basic data - it is required to know:-

1. The magnitude of the basic error inherent in the statistical

count.

2.

The effect of changes in "iron in ash" in terms of the error in

the reported ash value at both high and low levels of ash

content.

3. The effect of changes in "calcium in ash" in terras of the error

in the reported ash at both high and low levels of ash content.



no

4.

The effect of bed depth on both resolution capability and

accuracy at both high and low ash levels. Deterioration in

performance might be expected, for example, where there is

either very little attenuation, for example shallow beds of low

ash material, or excessive attenuation as in the case of deep

beds of high ash material.

To reduce the workload in terms of replicate testing, these

tests will be conducted under idealised conditions specifically

designed to eliminate other variables or other sources of high

random errors. The coal will be ground to below 2.8 mm and

accurately profiled. Changes in iron, calcium and "ash" will be

done by controlled weighed additions of chemically pure

materials.

2.2 Suitability of Coalscan for Potential Applications at Specific

Locations

whilst it may be possible to pre-judge to some extent a likely site

for successful operation, this will be aided considerably by the results

obtained from the basic studies. When a likely plant has been selected,

taking into account coal preparation procedure, a suite of at least

20 samples will be taken from site over a period of (say) 1 shift. Each

sample will be composed of no more than a single increment large enough to

fill the test container. Each will be scanned several times for each of

several separate filling operations with the same sample and here a

knowledge of the effective beam width and count rate times are required to

decide on a presentation method more likely to simulate the "dynamic"

system which characterises the practical use of the instrument.

The whole test will be replicated using fresh samples derived from

other shifts/days. All samples so obtained will be separately prepared for

analysis by established BS techniques and analysed for ash content and ash

composition. The results will be analysed in depth and the implications

considered. The work will be repeated, refined or extended if considered

necessary. The Board reserve the right to determine the laboratory

procedures for the investigations but undertake to consult fully with the

Contractors as the UK Agents of Coalscan, in order to achieve agreement

before tests are commenced and before any significant changes are made to

the test programme during the course.

The Contractor will be allowed reasonable access to observe progress

provided each visit is agreed in advance with the Board Scientist in charge

of the investigations.

3. Review of Progress

The Board will hold regular meetings with representatives of the

Contractor to review progress of the investigations. The frequency of such

meetings would be dependent on progress but would normally take place not

more than once per month. The results of tests would either be presented

at such meetings or communicated by letter to the Contractor.



n i

APPENDIX 7

EXTRACT FROM HEADS OF AGREEMENT CONTRACT BETWEEN THE NCB AND MAGCO LTD

FOR THE TRIAL OF A COALSCAN 3500 ASH MONITOR AT ASKERN COLLIERY.

SOUTH YORKSHIRE AREA

APPENDIX II

ACCEPTANCE CRITERIA FOR TRIAL

The Plant will be deemed to have completed the Trial satisfactorily

if the following criteria are fulfilled:-


To demonstrate operational reliability the Plant must be regularly

capable of operating under all feed conditions for continuous periods

of 5 working days without requiring operator attention. This

capability is to be demonstrated over a continuous period of

60 working days. If during any 5 day period operator attention is

required then the Trial period so far as operational reliability is

concerned will revert back to zero time and a further attempt to

demonstrate this capability for 60 working days will be required.


To demonstrate mechanical reliability the Plant must be capable of

operating for a continuous period of 60 working days without

requiring any mechanical maintenance and for a continuous period of

120 working days without requiring any replacement mechanical parts.

If mechanical attention or replacement mechanical parts are required

within the specified periods then the Trial period with respect to

either of these requirements will revert back to zero time and a

further attempt to demonstrate the capability for the specified

period will be required.


To demonstrate electrical reliability the Plant must be capable of

operating for a continuous period of 60 working days wihout requiring

electrical attention and for a continuous period of 120 working days

without requiring any replacement electrical parts. If electrical

attention or replacement electrical parts are required within the

specified periods then the trial period with respect to either of

these requirements will be considered to revert back to zero time and

a further attempt to demonstrate the capability for the specified

period will be required.



172


To enable the Coalscan ash monitor to provide a direct reading of the

ash content of the coal to be monitored it will be necessary to

obtain the relationship between the countrate of the transmitted

radiation and the incinerated ash content of the coal over the normal

range of ash variation, and for this relationship to be entered in

the instrument.

The Board will require to establish any difference between the

on-belt and off-belt calibration of the ash monitor. It will

therefore be calibrated for Askem 25 - 0 mm blended power station

fuel both on-belt in accordance with the following procedure and

off-belt in accordance with the procedure specified by the

manufacturer.

(a) The on-belt calibration will be based on a minimum of 30 calibration

tests each extending over a minimum period of 8 minutes or such time

interval as agreed with the Board's Engineer and covering the normal

range of ash content of 10% to 26%.

(b) For each calibration test the preparation plant will be operated so


sustain a continuous flow of coal along the belt conveyor at normal


(c) The ash monitor will be set to give the countrate measurement for the

test period which will be taken to represent all the coal which

passed along the belt conveyor during these measurements.

(d) The existing automatic sampler, located at the head end of the belt

conveyor which feeds to the Blended Smalls conveyor, will be used to

collect a sample, comprising a minimum of 35 full stream increments

taken at regularly spaced time intervals, from that parcel of coal

which passed along the belt conveyor during each of the calibration

tests and with due allowance being made for the time delay in the

material travelling between the sampler and the ash monitor.

(e) The coal samples collected during each calibration test will be

prepared and analysed in accordance with British Standard methods to

determine the total moisture and ash content, both of which will be

reported on an 'As Received' basis.

(f) The laboratory preparation of the on-belt calibration samples will be

designed to provide a 2 kg sub-sample, crushed below 1 mm or less,

from each calibration sample. Each sub-sample will be presented in

turn to the ash monitor in the off-belt position and count readings

will be taken in accordance with the manufacturers instructions. The

sub-samples will then be subjected to separate laboratory analysis.

The contractor will then have the option of using either the on-belt

or the off-belt data to derive the calibration equation which he will

then enter into the instrument.



113

(g) The Contractor will provide suitably experienced staff to participate

in the calibration procedure and be responsible for the operation of

the ash monitor and obtaining the countrate readings for each test.

The Contractor's representatives will also be responsible for

calibrating the ash monitor in accordance with the relationship

obtained between the countrate and the 'As Received' ash content.

(h) The NCB will provide experienced staff to liaise with the

Contractor's representatives and carry out the sampling and

laboratory analysis procedures.

The ash monitor, having been calibrated for the Askern Fuel in

accordance with the foregoing procedure, will be tested according to the

following method and the accuracy of ash measurement determined.

(a) The accuracy of the ash monitor will be assessed in a series of tests

conducted within 2 months of calibration by comparing the average

ash

reading over an 8 minute period or period agreed with the Board's

Engineer with the incinerated ash content of a representative, full

stream sample of the product which passed along the belt conveyor

during the same time period.

(b) The performance assessment will be conducted and the samples analysed

by experienced NCB staff and the Contractor's representatives will

have access to observe the testing at all stages.

(c) For each performance test the preparation plant will be operated so


sustain a continuous flow of coal along the belt conveyor at normal


(d) The ash monitor will be set to give an output signal equivalent to an

integrated ash content over the test period such that the reading at

the end of the period represents the average ash content over that

period.

(e) A representative sample of the

coal,

which has passed over the belt

during the test period, will be taken in a minimum of 35 regularly

spaced increments by the automatic sampler, at the delivery of the

belt which feeds to the Blended Smalls conveyor, with due allowance

for the time delay in the material travelling from the sampler to the

ash monitor.

(f) The coal sample for each performance test will be prepared and

analysed for total moisture and ash content.

(g) The performance testing will be continued until 60 tests have been

conducted where the incinerated ash content is within the range of

incinerated ash contents of the calibration samples.



114

(h) To satisfy the requirement of the NCB the average Coalscan ash

monitor measurement for the test period shall be within +2.5% of the

incinerated ash content for at least 95% (ie 57) of the 60 tests

which comply with the ash content limitations specified in paragraph

(g) above.

For the purposes of calibrating the ash monitor and assessing the

performance all the sampling will be conducted in accordance with BS1017,

Part 1 1977 and all total moisture and incinerated ash contents will be

determined in accordance with BS1016, Part 3, 1973.



115

APPENDIX

8

Specification for the Design and Manufacture of a

Pre-production Prototype Ram-Feed Unit (RFU)

1. INTRODUCTION

1.1 Scope

This specification covers the design, manufacture, delivery,

installation and commissioning of a pre-production prototype Ram-Feed

Ash Monitor Presentation Unit (RFU).

1.2 Delivery

The pre-production RFU is to be delivered to, and installed at

Markham Colliery Coal Preparation Plant, British Coal Central Area,

Duckmanton.

1.3 Exclusions

The following items shall be excluded from the tender,

(i) All Nucleonic and electronic equipment,

(ii) The hydraulic power pack.

( H i ) The inductive proximity switches.

1.4 Schematic Diagrams and Drawings

All schematic diagrams and other drawings which are necessary to

fully illustrate the proposed design will be made available to the

Supervising Officer on completion of the design phase.

1.5 Documentation

(i) On completion the contractor shall supply two complete sets of all

arrangement and manufacturing drawings. Two sets of maintenance and

operating manuals complete with listings of, and specifications for,

all components used will also be supplied.

(ii) Final manufacturing drawings are to be prepared on British Coal

pre-numbered Drawing Sheets, which will be provided free of charge.

All drawings shall comply with British Coal's Codes of Practice,

details of which are available through the Board's Engineer.

1.6 Standard of Workmanship

The equipment to be supplied shall be constructed to a high standard;

consistent with good engineering practice.



116

1.7 Phasing

The Contract shall comprise design, manufacturing and installation

phases. The Contractor will not proceed to the manufacturing phase

until the design has been agreed with the Board's Engineer.

2.

BACKGROUND INFORMATION

Some years ago, the NCB, in conjunction with AERE Harwell, developed

the Phase 3A Ash Monitor. This ash monitor was designed to be fed at

a rate of up to 1 tonne/hour with -5 mm material. It was equipped

with a nucleonic measuring system which enabled a correction for

variations in product iron content to be made to the measured ash

reading.

Though the accuracy of this ash monitor was acceptable, it was

susceptible to blockage by material of difficult handlability and in

some installations, required constant attention.

The Ram-Feed Unit (RFU) was conceived as being a positive feed system

which would solve the problem of blockages and provide a constant

geometry coal bed compatible with the established Phase 3A nucleonic

principle.

Development of the RFU has now progressed to point where a

pre-production prototype RFU is required. This specification defines

the modifications to the present experimental RFU that are required

to be included into the pre-production prototype.

3. TECHNICAL REQUIREMENTS

It will be assumed that the tenderer has a firm appreciation of the

existing experimental RFU installation.

References will be made to the attached schematic diagram of the

experimental RFU.

It is required that the pre-production prototype RFU will be of the

same materials and manufacture as the experimental RFU except for the

inclusion of modifications detailed below in paragraphs 3.1 to 3.7

inclusive, or where specifically stated otherwise.

3.1 The trough shall be extended in length such that the free trough

length (Dimension A) is 1 metre. The design should also allow for

the trough length (Dimension A) to be reduced to the existing length,

should that be necessary.

3.2 The bottom of the trough is to be constructed such that the section

at the reject end only (Dimension B) is made from Ultra High

Molecular Weight (UHMW) Polyethylene. It shall be of sufficient

thickness and mechanical strength to prevent distortion or breakage.



117

3.3 The compression plate is to be extended to a length of 300 mm. The

hinged pivot point of the compression plate is to be designed so as

to prevent the spillage of fines from that point.

3.4 The feed chute is to be lined with UHMW polyethylene. The rear face

of the stainless steel structure of this chute is to contain two

holes each of dimension 75 mm x 75 mm, and positioned as shown on the

attached schematic diagram. These holes are to allow level switching

transducers to be incorporated into the RFU. Angle brackets, shall be

arranged on each of the vertical sides of these windows to facilitate

installation of the level sensors.

3.5 The pre-production prototype RFU is to be designed so as to minimise,

as far as practicable, the overall length of the RFU. this may be

achieved by mounting the hydraulic cylinder underneath the RFU

trough. If this option is adopted, the design will be such as to

prevent damage, or excessive build-up due to fines being scraped back

by the ram. Facility shall be available to allow for monitoring of

the limits of travel of the hydraulic cylinder.

3.6 The hydraulic cylinder is to be uprated from the existing 38 mm bore

to a 63.5 mm bore cylinder. The existing stroke length is to be

retained.

3.7 All moving parts shall be shrouded with plain mild steel safety

guards.

4. STATUTORY REQUIREMENTS

The pre-production prototype RFU will be designed and constructed in

accordance with the requirements of the Mines and Quarries Act 1954

and subsequent amendments, the Health and Safety at Work Act, and any

relevant NCB specifications and Codes of Practice.



119

APPENDIX 9

ASH MEASURING AND CONTROL SYSTEM FOR RAM-FEED ASH MONITOR

Specification of Main Proprietary Components

(Refer Figure 84)

Radioactive Sources

Number of sources

Isotope type

Emission energy

Nominal activity

Supplier

Proportional Counter

Type

Gas filling

Window material

Supplier

Plutonium 238

12 ~ 17 KeV

370 MBq per source

Amersham International

PX425

Argon/helium

Beryllium

Centronics

Preamplifier (charge sensitive)

Type

Detector voltage (max)

Sensitivity

Output voltage (max)

Power requirements

Supplier

High Tension Supply

Type

Output voltage

Power requirements

Supplier

Spectroscopy Amplifier

Type

Input range (max)

Input impedance

Output range (max)

Output impedance

Power requirements

Supplier

N.E.5289B

2kV

0.2V/pC

+8V

+24V

Nuclear Enterprises

N.E.4660

0-2kV or 0-5kV

+12V, +24V

Nuclear Enterprises

N.E.4658

+10V

=

IK ohm

+10V

~50 ohms

+12V, +24V

Nuclear Enterprises



120

S p e c t r u m S t a b i l i z e r

Type

Input range

Output range

Correction range

Power requirements

Supplier

Energy Analyser

Type

Input range

Output lower threshold

in window

upper threshold

Threshold range

Window range

Power requirements

Supplier

Dual Scaler Timer

Type

Input range

Threshold range

Outputs

Power requirements

Supplier

Power Supply Bin

Type

Supply voltage

Output voltages

Supplier

FCL 6000 Computer

Type

Supply voltage

System

Additional facilities:

Disk drives

Supplier

(i)

(ii)

(iii)

<iv)

(v)

(vi)

2050

0-10V

0-10V

-50%

to +100%

+12V, +24V

Canberra Industries Incorporated

N.E.4664

0-10V

5v TTL

5v TTL

5v TTL

0.1V to 10V

0.01V to IV or 0.1V to 10V

+12V, +24V

Nuclear Enterprises

N.E.4681

0.2V to 10V positive

0.2V - 5V

20mA current loop and RS232

+6V, +12V

Nuclear Enterprises

N.E.4601

240V A.C., 50Hz

0V, +6V, +12V, +24V to N.I.M. foi

Nuclear Enterprises

Industrial (I.P.67) Apple H e

240V

Autoprom board

RS232 board (4 channel)

32 digital I/O board

16 Opto-isolator board

Time, day, date board

Printer board

2 x disk drives (I.P.55)

Flex Controls Limited



121

Programmable Logic Controller

Type Mitsubishi F2-40

Number of inputs 24

Input voltage 24V

Number of outputs 16

Output voltage User defined

Supply voltage 110V/240V A.C.

Supplier Radio Spares



123

APPENDIX 10

SPECIFICATION FOR X BAND MICROWAVE MOISTURE METER

Applications

Coal - size

- moisture range

Other materials

Material presentation

Basis of Measurement

Measurement system

Dynamic range

Resolution

Sample rate

Accuracy of measurement

Microwave Source

Make/type

Frequency

Power

Frequency drift

Modulation frequency

Aerial systems

General

Power requirements

Main displays

End of determination indicator

Ranging indicator

Temperature range

Warm up time

Control unit dimensions

Transmitter and

receiver dimensions

less than 15 mm

5-20 %

Most particulate material such

as grain, bran, etc.

Individually designed installation

on material handling system

or Discrete sample cell for on-site

and laboratory application.

Auto-ranging microwave attenuation

meter with microprocessor control

60 dB

0.2 dB

25 per minute (approx)

+0.5% to +2% moisture dependent on

coal and method of presentation

Mullard CL8630

10.686 GHz

8 mW

0.25 MHz/degree K

1.0 kHz

18 dB pyramidal Horns

240 V, 45-50 Hz, 1.0 A

3*i digit LCD

Green LED

Red LED

5 to 40°C

10 minutes

Height 300 mm, width 400 mm,

depth 195 mm


depth 100 mm



125

APPENDIX 11

SPECIFICATION FOR S BAND MICROWAVE MOISTURE METER

Applications

Coal - size

- moisture range

Other materials

Material presentation

Basis of Measurement

Measurement system

Dynamic range

Resplution

Sample rate

Accuracy of measurement

less than 50 mm

5 - 24 %

Most particulate material such as

grain, bran etc.

Individually designed installation

on material handling system or

Discrete sample cell for on-site

and laboratory application.

Auto-ranging microwave attenuation

meter operating with microprocessor

control

60dB

0.2 dB

25 per minute (approx)

+0.5% to +2.0% moisture dependent on

coal and method of presentation

Microwave Source

Make/type

Frequency

Power

Frequency drift

Modulation frequency

Aerial systems

General

Power requirements

Main displays

End of determination indicator

Ranging indicator

Temperature range

Warm up time

Control unit dimensions

Transmitter and

receiver dimensions

Avantek 8240

3.26 GHz

25 mW

30 MHz over operating temperature

range

1.0 kHz

13 dB pyramidal Horns

240 V, 45-50 Hz, 1.0 A

34 digit LCD display

Green LED

Red LED

5-40°C

10 minutes

Height 300 mm, width 400 mm

depth 195 mm


depth 260 mm



127

APPENDIX 12

TECHNICAL SPECIFICATION FOR ULTRASONIC BED-DEPTH METER

Proprietory Components

Electrical requirements

Supply voltage

Supply current

Range

Resolution

Temperature coefficient

Accuracy

Transducer ultrasound frequency

Transmitter output level

Acceptance angle

3 dB full angle beamwidth

Measurement frequency

Outputs

Polaroid instrument-grade

electrostatic transducer.

Polaroid ultrasonic circuit board

(modified)

240 V A.C. or 110 V A.C.

(selectable within instrument)

30 mA

26 cm to 53.6 cm

(can be increased to max of 10.7 m)

1 mm in range 26 cm or 53.6 cm

5 cm in range 26 cm to 10.7 m

- 0.175%/°C

+3.5% over range 0° to 40°C

50 KHz (approx)

118 dB SPL at 1 metre (approx)

20 degrees (approx)

15 degrees (approx)

5 per second

Liquid crystal display in mm

- updated at 0.5 second intervals

0.4 to 2V (analogue)

0 to 1.6V (analogue) for

input to data logger

4 to 20 mA (analogue)



129

APPENDIX 13

LABORATORY SWEPT FREQUENCY MICROWAVE MOISTURE SYSTEM

Specification of Measuring Equipment - refer Figure 101

Swept Frequency Microwave Source - Mainframe

Make

Type

Power requirements

Frequency range

Sweep control input

Response time

Resolution

Accuracy

Marconi Instruments Limited

6700B Sweep oscillator (mainframe)

240 V, 0.5 A

Determined by plug-in unit

10 V ramp

1 mS for full sweep

Better than 0.05% of R.F. unit bandwidth

As for R.F. unit frequency accuracy

Swept Frequency Microwave Source - R.F. Plug-in Unit

Make

Type

Frequency range

Frequency accuracy

Frequency linearity

Frequency stability

Power output

Spurius signals

3 dB Splitter

Make

Type

Frequency range

Detectors

Make/type

Frequency range

Maximum input


6754A R.F. Unit

4.0 - 8.0 GHz

+0.5%

0.25%

750 kHz/°C

lOmW

20 dB below fundamental at maximum power


Part No. 2200335

2 - 18 GHz

Marconi Instruments Limited / 6511

0.01 - 20 GHz

+26dB(m) average, +30dB(m) peak

Transmitting and Receiving Horns

Make

Centre frequency

Scaler Analyser

Make

Type

Power requirements

Frequency range

Dynamic range

Frequency resolution

Amplitude resolution

British Coal, Scottish Area Laboratory

6 GHz


6500 Automatic Amplitude Analyser

240 V, 0.5 A

0-126 GHz (dependent on detector)

66 dB

within 10 MHz

+0.01 dB(m)



130

Specification of Computer Hardware - refer Figure 101

IEEE Interface

Make Acorn Computers Limited

Type IEEE 488 Interface

Power requirements 240 V, 12.5 mA

Manufactured in accordance with BS415/79 Class 1.

Microcomputer

Make Watford Electronics

Type BBC "B" with 32K extra memory

Power requirements 240 V, 0.2 A

Monitor

Make/type Microvitec / 1456


Screen size 35.6 cm

Resolution 653 horizontal, 585 vertical

Disc Drive

Make/type Teac FD55FR 13.3 cm floppy disc drive

Power requirements 240 V, 20 mA

Disc type 13.3 cm double sided, 80 tracks/side

Printer

Make/type R. S. Components Limited / RS105 matrix printer


Computer Software Facilities

(a) Transfer of data from Scaler Analyser to Computer Memory

(i) The displayed scan information comprising, horizontally,

422 frequency intervals with a vertical resolution of 256 points

(ii) The lower and upper frequency limits of the scan, i.e. the X

axis scale.

(iii) The datum and range of attenuation, i.e. the Y axis scale.

(iv) The period over which the 422 data pairs are measured, i.e.

the sweep speed.

(v) The position and corresponding frequency of an X axis cursor

used to measure the attenuation at a single point of the

scan, i.e. the brightline frequency.



131

(b) Display, print-out and Analysis of Data

(i) Display listing of frequency/attenuation data pairs.

(ii) Provide print-out of listing of frequency/attenuation data

pairs.

(iii) Display plot of frequency scan. In this mode a replica of the

scan as displayed on the scalar analyser is reproduced on the

computer monitor. Each scan can be identified by up to 78

characters.

(iv) Print-out plot of frequency scan thereby allowing a permanent

record of the scans display on the Marconi analyser to be

obtained.

(v) Perform a linear regression on the scan data and superimpose

the straight line fit on the displayed scan.

(vi) Copy the block of data transferred from the Marconi analyser on

to disc storage.

(vii) Recall data previously stored on disc and process it in

accordance with any of the above options.



133

APPENDIX 14

SOME ASPECTS OF THE THEORY OF

CAPACITANCE MOISTURE MONITORING

1. Complex Relative Permittivity

When an electric field is applied across a capacitor formed with a

dielectric containing polar molecules they tend to align in the direction of

the applied field. The rotation of these polar molecules, whilst aligning

with the applied field, is retarded because of viscous drag between the

polar molecules and the host material. This retardation results in energy

absorption from the applied field. The alignment of the polar molecules

within the applied field causes surface charges on the capacitor plates to

be neutralised. Additional charge can thus flow onto the capacitor plates

resulting in an increase in accumulated charge per applied unit of electric

field and the capacitance thereby increases.

The energy absorbed from the applied field by the rotation of the polar

molecules within the field is observed as a power loss. The relative

permittivity of such a material can be expressed as a complex number:-

i.e., Er + E'r - j E"

r

when j - -1

E'

r

represents the relative increase in capacitance

E"

r

represents the power loss to the dielectric

2.

Model of Insulated Plate Capacitance Moisture Meter

In order to design a suitable measurement system a model of the

insulated plate capacitance moisture meter was required. There were two

basic systems which could be used to model a capacitor:-

(i) a series model in which a resistor is assumed to be

connected in series with the capacitor.

(ii) a parallel model in which a resistor is assumed to

be connected in parallel with the capacitor.

In both cases the resistor, whether in series or parallel, models the

power loss to the dielectric from the applied field. For the particular

geometry, dielectric and frequency range of the proposed measurement cell, a

parallel resistor model was appropriate.

In order to show that a measure of capacitance can be obtained from the

voltage developed across a small series resistance an analysis of a parallel

model with a series connected measuring resistance is given below.



134

With reference to the attached figure

Z(s)

™

SCi

Rl + 1

SCi

Rl + R

m

(1 +

+ R

m

(1 + SCiRi)

SCiRi)

The transfer function relating input voltage to output voltage is given by

Vo(s) - Rm - R

m

(1 + SCjRl) ....... (1)

Vi(s) "zCs3 Rl + R

m

d + SC]Ri)

-

R

m + SClRlRm

Rl + Rm d + SCiRn,) R

X

+ R„, + SCiRiR

m

Converting to Fourier Transforms gives

Vo(Jw ) - Rm + j w C j R i R m

Vi ( j w) R i + Rm + jwC iR iR

m

Rl + Rm + jwC iRiRm

now i f R i » R

m

a n d l » w C i R

m

t he n ( 2 )

Vo( jw) ~ jwC iR

m

V i ( J w )

->

Ao(jw)/

wCiRn/VKjw)/

(3)

The voltage developed across the measuring resistance Rm is therefore

proportional to the capacitance.

/

I f t h e c o n d i t i o n s ( 2 ) d o n o t a p p l y t h e n i t c a n b e sh ow n t h a t :

o ( j w y i J R¿

m

+ Ri +

w

2 c 2

1

R 2

l R

2

m

) 2 + ( w C ^ i R a T ^ y ^ i Ç J w ) / ( 4)

(Rl + R

m

)

2

+ ( wC iR iRm)

2

Numerical comparison of equations (3) and (4) show good agreement when

values of w exceed 2 x 10

7

rads/sec, R

m

- 20 ohms and other values lie

within their expected ranges.

It was therefore decided to use the voltage developed across a small

(20 ohms) series resistance as the primary measurement in determining the

capacitance.

It should be noted further that if the conditions proposed in (2) are

applied, in the Laplace domain, to (1) then we find that:-



135

Vo(s)

^

SCiR

m

Vi(s)

Taking inverse transforms gives

Vo(t)^d(Vi(t)) CiR

m

dt

assuming zero initial conditions.

Now if Vi(t) contains a component of high frequency noise

then Vi(t) -

Vi(t)*

+ n(t)

b

If the frequency spectrum of n(t) - ) n^sinw^t

a

and

Vi(t)*

- Vi sin wt

b

Then Vo (t) - d(V¿sinwt +r~n i

c

sinwj

c

t) C]R

m

d t

Thus

Vo(t) - CiR

m

(wVicoswt + w

a

n

a

cosw

a

t + w

a

+i + n

a+

icosw

a+

it+ Wbn

D

coswbt)

That is the magnitude of noise signal components are amplified by

their frequencies.

For this reason the Bandwidth of the measurement oscilloscope would be

limited to 25 mHz and quarterwave filters would need to be connected to the

measurement circuit at appropriate points.



136

i_

sc,

/¿(s)

Z(s)

m

V

o

(s)

V¿(s) - Laplace Transform of Excitation Voltage

V

0

(s) - Laplace Transform of Output Voltage

Z(s) - Laplace Transform of Input Impedance

SCi

Rl

Mn

Laplace Transform of Capacitor Impedance

Laplace Transform of "Power Loss" Resistance

Laplace Transform of Measuring Resistance

PARALLEL RESISTOR MODEL



1 3 7

A P P E N D I X 15

SPECIFICATION FOR AN ELECTRONICS PACKAGE FOR EXPERIMENTAL

CAPACITANCE MOISTURE MONITORING

INTRODUCTION

1.1 Scope

This specification covers the design, development, construction,

testing and delivery of an electronics package for use with an

experimental moisture monitoring system.

1.2 Prices

The tenderer is requested to submit a listing of the tender price as

stated in the documents accompanying this specification.

1.3 Exclusions

The following items shall be excluded from the tender:

(i) The supply of the microcomputer

(ii) The supply of any moisture monitoring transducers

1.4 Completion time

The tenderer shall supply a listing of the estimated time for the

completion of each of the design, development, construction and testing

phases of the contract as stated in the document accompanying this

specification.

1.5 Schematic diagrams

The tender shall include such schematic and other diagrams as are

necessary to fully illustrate the proposals.

1.6 Documentation

The contractor shall supply two complete sets of all necessary circuit

and other diagrams. Two sets of maintenance and operating manuals,

complete with testing procedures shall also be supplied. Complete

listings of, and specifications for, all components used will be

included within the documentation.

1.7 Standard of Workmanship

The equipment to be supplied shall be constructed to a high standard

and consistent with good engineering practice.



138

2.

BACKGROUND INFORMATION

Water has a dielectric constant of approximately 80 and a typical coal

has a dielectric constant of approximately 5. By arranging for moist

coal to form the dielectric material of a capacitor, a measurement of

the moisture content of the coal can be determined by measuring

capacitance. Further, since the loss tangent of water is large

compared to that of dry coal, a measure of loss tangent can also

provide a useful correlation. Practical experimentation has shown that

effective impedance measured in the radio frequency range will also

exhibit a useful correlation.

The subject of this specification is the design, construction, testing

and delivery of an electronics package for use with such experimental

moisture monitoring transducers. The specification is designed to

indicate the desired physical arrangement of, and the functions

associated with, the component parts of the electronics package.

Schematic diagrams designed to further explain the specification are

attached as Diagrams 1 and 2.

3. GENERAL REQUIREMENTS

The electronics package is to be used for two different types of

application. These are, an on-stream system in which the transducer is

mounted as to ride on a moving bed of coal, and a discrete sample

system. Considering the on-belt application, there is a need for a

part of the electronics package to be mounted statically, adjacent to

the transducer (Unit A). The other part is to be mounted inside a

compartment within the transducer (Unit

B).

The two parts are to be

connected by a flexible armoured multicore cable. The ambient

operating temperature for the electronics package is expected to be

-10°C to +50°C. The functions associated with each part of the

electronics package, and the specifications for each of those parts are

detailed in the following sections of this specification.

4. DETAIL REQUIREMENTS - UNIT A

4.1 Unit A - Duty

This unit will provide the dc power supplies for use by both Unit A and

Unit B. It will house such local electronics and analogue displays as

are necessary to satisfy the requirements of the specification. It

will provide sockets for connection to unit B and to a local computer.

The physical layout may be similar to that shown in Appendix 1.

4.2 Unit A - Specification

This unit will comprise three compartments; X, Y and Z. The functions

and specifications for each compartment are as detailed below.



139

(X) Power supplies compartment requirements

This compartment will house such components as are necessary for

the provision of dc supplies for use by units A and B. The

mains transformer shall be fitted with an earthed interwinding

screen and shall be supplied from a 110 V/240 V, single phase,

50 Hz supply. The compartment will be wired such that the mains

(primary) wiring is segregated from the secondary and dc supply

wiring. The mains cable entry to this compartment will be by a

brass 20 mm compression gland suitable for use with 3 core

single wire armoured pvc cable with nominal core sections of

1.5 mm'. The removable cover giving access to this compartment

shall be fitted with a securely screw mounted white traffolyte

plate bearing the legend 'CAUTION. ISOLATE ELSEWHERE BEFORE

REMOVING THIS COVER', in red letters. The 110 V/240 V, single

phase,

50 Hz supply to this unit can be expected to be

contaminated with electrical noise. Provision shall be provided

such that any electrical noise does not interfere with the

operation of the electronics package. Internal earth straps and

connections shall be provided in order to maintain efficient

earth continuity. The secondary voltages and dc supplies shall

be at a voltage no greater than 25 or + 12.5 V.

(Y) Electronics compartment requirements

(i) This compartment will house the local electronics and analogue

displays. The local electronics will comprise such circuitry as

is necessary to convert the signals transmitted from Unit B into

a form in which they can be displayed on the local analogue

displays. Four displays will be available and arranged to

simultaneously display representations of the modulus and

argument of the transducer impedance and the capacitive and

conductive components of the impedance. Four 4 - 20 mA analogue

outputs representative of the above signals will also be

available and will be wired to a socket for connection to a

local computer.

Such testpoints as are necessary for the thorough testing of the

unit shall be provided on the circuit board(s) used in the

construction of unit A.

Facility shall be provided such that the gains and offset bias

of each of the signal channels can be individually and

independantly adjusted within ranges such that calibration can

be achieved.

All outputs and supplies from the unit shall be continuously

shortcircuit protected or rated, and be tolerant to any faults

likely to occur by compressive damage to or stretching of the

multicore cable linking units A and B.



140

(ii) The analogue displays shall be formed by the generation of

suitable displays on a solid state dot matrix type display.

Facility shall be provided such that the range of each of the

displays can be individually set and displayed at suitable

points adjacent to the displays. The ranges should be retained

via battery backed memory when power is removed from the unit.

The display should be arranged such that it is clearly visible

under normal or poor lighting conditions.

Such additional space and electrical supplies shall be available

as are necessary for the retrofitment of two 127 mm x 127 mm, 5V

microprocessor boards for moisture calculation.

A red 'power on' light will be provided in order to indicate

that the electrical supply to the unit is healthy. This is to

be supplied from a low voltage dc source.

Test switches, test sockets and additional circuitry such as are

necessary for the testing of all the dc voltages and all the

datalinks to and from unit A shall be included within this

compartment. A transparent high impact plastic lockable cover

shall be provided to cover all the analogue displays, indicator

lamps, controls, test switches and test sockets. It will

provide environmental protection to at least IP 55 standard.

A removable cover will be provided giving direct access to the

interior of this compartment.

(Z) Termination Compartment

This compartment will house the main termination point and

sockets for connection to Unit B and to the local computer. A

removable cover will be provided giving access to the

compartment.

4.3 General Requirements - Unit A

A carrying handle is to be provided on top of the unit. Four

mounting points are to be provided near the rear corners of the unit

and the unit is to be stable when placed on its base.

The unit is to be environmmentally protected to at least IP 55

standard and shall be of a rugged substantial construction suitable

for direct installation in a coal prpeparation plant. Sockets

provided for connection to Unit B and the local computer shall be

environmentallly protected to at least IP 55 standard. Protection

caps shall be attached to the sockets such that the sockets can be

sealed to this standard when not in use.



141

PROPOSED EXPERIMENTAL INSULATED-PLATE CAPACITANCE

MOISTURE METER - UNIT A



1 2 7 MM

L E A D

TO

TRANSDUCER

A k

0 MM

-A

k

50 MM

LEAD

TO

TRANSDUCER

rs>

io MM

PROPOSED EXPERIMENTAL INSULATED-PLATE CAPACITANCE MOISTURE METER

-

UNIT

B



143

5. DETAIL REQUIREMENTS - UNIT B

5.1 Unit B - Duty

This unit will generate radio frequency (RF) signals for use in the

measurement of the impedance of the moisture transducer. It will house

such subsequent signal processing electronics as are necessary for the

generation of signals accurately related to the modulus and argument of

the moisture monitor complex impedance. Further subsequent signal

processing electronics will be included in order to convert these

signals into a form suitable for transmission to Unit A.

5.2 Unit B - Specification

(i) Enclosure - mechanical considerations

Unit B will comprise an RF shielded enclosure of external

dimensions 127 mm x 254 mm x 50 mm. Circuit board(s) containing

the necessary electronic components will be securely mounted and

supported within this enclosure such that their operation is

unaffected by any vibration or by likely levels of impact.

Mounting points will be provided on the unit such that the unit can

be securely fastened inside the transducer. See Diagram 2 for

further details.

(ii) Electronic considerations

The RF generator output frequency will be infinitely variable by

local adjustment within the range 10 MHz to 15 MHz, and shall be

stable to within 1% of the set frequency. The output voltage from

this generator should be sufficiently large (but less than 25 V)

and stable under conditions of loading for measurements of

capacitance within the range 5 pF to 200 pF to be made with a

resolution of at least 0.1 pF. The range of the shunt resistance

will be of interest between 20 ohms and 5 k ohms.

The circuitry should be pass bandwidth limited as necessary such

that all measurements are performed only at the set frequency.

The measurement electronics should be designed such that variation

of the signal supply frequency within the stated range

(10 • 15 MHz) does not require alteration of, or manual adjustment

to any circuitry.

Such testpoints as are necessary for the thorough testing of the

unit shall be provided on the circuitboard(s). Unit B's enclosure

should be designed and arranged such that any testing can be

performed with the circuitboards in their enclosure.

With regard to temperature effects, the design and construction of

Unit B should recognise that the unit is to be housed within a

sealed compartment of limited volume.



Ì44

Full consideration must be given to any effects likely to cause

inaccuracies or mal-operation owing to stray couplings to the unit

from the transducer whilst in both static and dynamic operation.

All outputs from the unit shall be continuously shortclrcuit

protected or rated, and tolerant to any faults likely to occur by

compressive damage to or stretching of the multicore cable linking

Units A and B.

(iii) Connections

Leads for connection to the transducer shall be attached to Unit B

at the centre of both sides of the unit - see Diagrams 2.

The leads will be 150 mm long and should be arranged to prevent any

dc bias from occurring across the transducer.

A multi-way socket will be provided for attachment to the body of

the transducer. This socket shall be of the same type as fitted to

the outputs of Unit A and will be fitted with a removable

environmentally protective cap to at least IP 55 standard.

A multi-way socket shall be fitted to Unit B from which all

connections between Unit B and unit A will be made. A set of

wanderleads of length 0.5 m, fitted with a plug for connection to

Unit B, will also be providded.

6. DETAIL REQUIREMENTS - MULTICORE CABLES

Two multicore cables shall be supplied with the unit, both complete

with appropriate mechanically strong plugs. The cable lengths shall

be 10 m and 2 m. The cables shall be suitable as regards liability

to mechanical and chemical damage, and will be of a flexible

armoured, fire resisting construction.

A screened multicore cable of length 5 m, and fitted with a plug for

attachment to the computer output socket of Unit A will be provided.

It will be capable of carrying all data links to the computer

simultaneously.

7.

STATUTORY REQUIREMENTS

Both units will be designed and constructed in accordance with the

requirements of the Mines and Quarries Act 1954 and subsequent

amendments, the Health and Safety at Work Act, and any relevant NCB

specifications and Codes of Practice.

8. CONFIDENTIALITY

No information contained in this specification or in any subequent

document or discussion shall be made public or disclosed to any third

parties without the agreement of the National Coal Board.



TABLE 1 - RESULTS OF PREVIOUS TESTING OF WULTEX RADIOMETRIC ASHMETER

Laboratory

Laboratory

Laboratory

COLLIERY/

PRODUCT

Mantón

Blended Smalls

Mantón

Blended Smalls

Steetley

Blended Smalls

Manton/Steetley

Blended Smalls

Plant Train j

(4 hr)

Mantón

Blended Smalls

Mantón

Blended Smalls

SAMPLES

/TESTS/

TRAINLOADS

NO.

11

16

15

33

100

75

TOTAL

MOISTURE %

RANGE

6.4-9.3

6.4-9.3

7.8-13.6

5.6-13.6

7.2-10.9

7.3-11.5

ASH %

(A.R.)

RANGE

3.4-38.6

3.4-38.6

3.5-29.5

3.4-38.6

11.6-21.2

12.4-19.8

CALIBRATION

REGRESSION

ANALYSIS

Linear

Quadratic

Linear

Quadratic

Linear

Quadratic

Linear

Quadratic

Linear

Linear

CORR

COEFF

0.959

0.999

0.953

0.996

0.964

0.972

0.966

0.988

0.781

0.514

STD

DEV

% ASH

3.79

1.12

3.28

1.02

2.14

1.96

2.73

1.63

1.29

1.15

% SULPHUR

(A.D.)

RANGE

% IRON |

(A.D.) |

RANGE j

2.12-2.4 | 1.17-1.51 |

( Tests 46 - 100) |

<J1

(A.R. - AS RECEIVED, A.D. - AIR DRIED)



COLLIERY

MANTON

ASKERN

BILSTHORPE

COTGRAVE

LEA HALL

DAM HILL

CWM

SHARLSTON

GRIMETHORPE

CENTRAL

NASHERY

(SOUTH SIDE)

SEAN(S)

PARKGATE

KARREN HOUSE

LON MAIN,

PARKGATE

DEEP HARD

BLACK SHALE

LOWER DEEP

DEEP. SHALLOW

THICK COAL

YARD

SIX FEET

WARREN HOUSE

LOW BARNSLEY

PARKGATE,

FENTON,

NEWHILL

PRODUCT

NON. SIZE

BLENDED

PSF

5 0 - 0

UNTREATED

SMALL COAL

5 0 - 0

BLENDED

PSF

2 5 - 0

UNTREATED

SMALL COAL

2 5 - 0

WASHED

SMALL COAL

2 5 - 0

BLENDED

PSF

5 0 - 0

UNTREATED

SMALL COAL

3 8 - 0

WASHED

SMALL COAL

5 0 - 0

BLENDED

PSF

5 0 - 0

BLENDED

PSF

2 5 - 0

UNTREATED

SMALL COAL

12.5 - 0

WASHED

SMALL COAL

5 0 - 0

WASHED

SMALL COAL

5 0 - 0

BLENDED

PSF

5 0 - 0

UNTREATED

SMALL COAL

5 0 - 0

WASHED

SMALL COAL

5 0 - 0

ASHNETER

UK METER

POLISH METER

UK METER

POLISH METER

UK METER

POLISH METER

UK METER

POLISH METER

UK METER

POLISH METER

UK METER

POLISH METER

UK METER

POLISH METER

UK METER

POLISH METER

UK METER

POLISH METER

UK METER

UK METER

UK METER

UK METER

UK METER

UK METER

UK METER

NUMBER

OF

SAMPLES

20

11

28

28

20

20

20

20

20

20

20

20

20

20

20

20

40

23

18

24

18

16

13

SIZE

TESTED

2 5 - 0

2 5 - 0

2 5 - 0

2 5 - 0

2 5 - 0

5 0 - 0

3 8 - 0

5 0 - 0

5 0 - 0

2 5 - 0

12.5 - 0

5 0 - 0

5 0 - 0

5 0 - 0

5 0 - 0

5 0 - 0

RANGE OF

MOISTURE

* (A.D.)

1.8 - 3.4

1.8 - 3.2

1.9 - 3.5

3.4 - 7.6

4.6 - 6.9

4.4 - 9.3

4.0 - 5.8

2.1 - 4.3

2.9 - 8.7

2.3 - 8.4

2.3 - 10.0

3.7 - 7.2

0.2 - 0.7

1.4 - 2.2

1.0 - 1.6

1.3 - 2.5

1.0 - 1.35

RANGE

OF ASH

% (A.D.)

7.0 - 22.3

16.1 - 22.2

30.4 - 47.0

18.1 - 28.2

32.9 - 45.6

2.8 - 11.6

10.5 - 27.7

30.2 - 48.0

3.8 - 8.8

14.6 - 30.2

13.5 - 39.8

13.0 - 23.3

4.2 - 8.4

10.6 - 17.9

4.1 - 29.2

21.4 - 34.5

2.8 - 5.6

RANGE

OF IRON

X (A.D.)

0.99 - 1.75

1.37 - 1.75

1.89 - 2.45

1.40 - 1.90

1.66 - 1.94

0.50 - 0.96

0.70 - 1.70

1.33 - 2.21

0.41 - 0.99

0.54 - 1.17

0.90 - 2.17

0.59 - 1.11

0.21 - 0.50

1.84 - 2.50

0.76 - 2.53

2.33 - 3.23

0.47 - 1.24

STD.

DEV.

OF IRON

X Fe

0.17

0.11

0.15

0.12

0.083

0.119

0.246

0.218

0.175

0.155

0.315

0.119

0.073

0.21

0.55

0.246

0.278

CORR. COEFF.

BETWEEN

X Fe C ASH X

0.946

0.877

0.697

0.527

0.520

0.955

0.941

0.695

0.829

0.588

0.868

0.783

0.904

0.490

0.959

0.027

0.978

BEST CALIBRATION

CORR.

COEFF.

0.984

0.955

0.918

0.914

0.486

0.951

0.946

0.992

0.950

0.957

0.892

0.885

0.932

0.906

0.952

0.964

0.973

0.965

0.965

0.770

0.998

0.767

0.983

STD.

DEV.

X ASH

0.76(0)

0.73(Q)

1.67U)

1.75(0)

2.34(L)

0.83(L)

1.37(L)

0.36(L)

1.32(Q)

1.23(Q)

2.15(L)

1.95U)

0.52(L)

O.flO(L)

1.24(L)

1.10(L)

1.58(Q)

0.68U)

0.28U)

1.36(g)

0.54(g)

2.31(0)

0.19(0)

CALC.

STD.

DEV.

0.46(g)

0.38(L)

1.30(L)

0.84U)

l.Ol(L)

0.28U)

0.68(L)

1.10(L)

0.49(L)

0.75(L)

1.3KL)

0.63U)

0.18U)

1.23(L)

0.94(0)

2.82(L)

0.16(0)

o i

- POWER STATION FUEL (L) LINEAR REGRESSION (0) QUADRATIC REGRESSION



TABLE 3

RESULTS

OF

CALIBRATION TESTS WITH WULTEX ASHMETER

ON

BILSTHORPE BLENDED SMALLS

TEST LOCATION

Column Number

of

Samples

of Ash

of

Moisture

of Sulphur

Fe? O3 in Ash

( )

( )

Fe in

coal

( )

( )

Fe

and Ash in

Coal

on dry

(1

- Ash

-

Corr. Coeff.

in Coal

lasis

standard

|

YRL

| 2 present-

| ations x 5

|

box

fills

| AD

|

1

| 20

110.5

- 27.7

| 4.4 - 6.1

11.32

- 1.90

| 8.53

| 0.71

|

1.08

|

0.25

|

0.943

deviation)

|

1.32

|

0.950

BILSTHORPE COLLIERY

9 x 2 minute

integration periods

AR

2

31

6.6 - 36.6

9.6 - 15.8

0.98 - 1.61

6.88

1.61

0.77

0.19

0.849

2.93

0.905

3

25

10.7 - 27.5

10.7

- 15.4

1.0 - 1.50

6.65

1.13

0.76

0.14

0.680

2.77

0.754

YRL (REPEAT LABORATORY CALIBRATION)

|

5 presentations

x

2 box

fills

AR

4

| 5

24 | 19

6.3 - 37.4|11.4 - 23.6

9.0 -

14.7|11.4

- 14.5

0.85 - 1.5310.85 - 1.5

6.57 | 6.69

1.73 | 1.53

0.79 | 0.77

0.19 | 0.12

0.773 | 0.380

1.60 | 1.79

0.982 | 0.860

2 presentations |

x

5 box

fills

|

AD

|

6

24

7.0 - 39.6

3.0 - 5.2

0.94 - 1.66

6.57

1.73

0.86

0.20

0.773

1.93

0.976

7 |

19 |

12.6

- 26.11

3.0 - 5.2|

0.94 - 1.66|

6.69 |

1.53 |

0.85 |

0.13 |

0.380 |

2.10 |

0.841 |

(AR - AS RECEIVED, AD - AIR DRIED)



148

TABLE 4 LABORATORY INVESTIGATIONS WITH COALSCAN 3500

ASH MONITOR - RESULTS OF TESTS TO ASSESS

STATISTICAL

COUNTING ERROR USING CALIBRATION

STANDARD

| TEST

| 1

1

2

1

3

1

4

| 5

1

6

|

7

1 8

1

9

1 io

1 11

1 12

1 13

1 14

COUNTING

PERIOD

SECONDS

2

4

8

15

30

60

60

120

300

600

60

120

300

600

| LOG RATIO |

MEAN

2.4700

2.4688

2.4682

2.4672

2.4672

2.4693

2.4613

2.4613

2.4616

2.4613

2.4701

2.4686

2.4693

2.4685

STANDARD |

DEVIATION |

0.0182

|

0.0134

|

0.0099

|

0.0071

|

0.0050

|

0.0014 |

0.0037 |

0.0024 |

0.0016

|

0.0012

|

0.0038 |

0.0025

|

0.0017

|

0.0012 |



149

TABLE 5 LABORATORY INVESTIGATION WITH COALSCAN 3500

ASH MONITOR - VARIATIONS IN LOG RATIO VALUES DUE

TO CHANGES IN BED THICKNESS

| EQUIVALENT

| COAL BED

| THICKNESS

1 (MM)

1 85

| 128

| 168

| 202

| 230

| 253

| 272

AMERICIUM

CHANNEL

COUNTRATE

(CPS)

79114

42149

22428

12185

6769

3877

2287

MEAN

CAESIUM

CHANNEL

COUNTRATE

(CPS)

33053

25677

19877

15416

11950

9290

7186

STANDARD DEVIATION

LOG |

RATIO |

2.6026 |

2.5986 |

2.6006 |

2.6017 |

2.6008 |

2.6027 |

2.5998 |

2.6010 |

0.0015

|



150

TABLE 6 LABORATORY INVESTIGATIONS WITH COALSCAN 3500 ASH MONITOR

- EFFECT OF MAGNETITE ADDITION TO COAL SAMPLE

I TEST

1 NÇL

| 1

1 2

1 3

1

4

| 5

1 6

| 7

1 8

1 9

1

io

1 11

1 12

1 13

1 14

1 15

1 16

% ADDITION |

Fe

3

0

4

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

6.0

7.0

| 8.0

| 9.0

10.0

Fe2Û3

0.0

0.52

1.03

1.55

2.07

2.59

3.10

3.62

4.14

4.65

5.17

| 6.20

| 7.24

| 8.27

| 9.31

10.34

LOG

RATIO

2.294

2.329

2.370

2.414

2.462

2.494

2.534

2.577

2.610

2.672

2.700

2.790

2.874

2.958

3.062

3.126

INCREASE |

IN ASH % i

0.0 |

2.96 |

6.36 |

10.04 |

14.05 |

16.71 |

19.98 |

23.63 |

26.37 |

31.53 |

33.84 |

41.36 |

48.31 |

55.31 |

| 64.01 |

69.38 |

(NOTE For a typical coal an Increase In log ratio of 0.012 corresponds

to an Increase in ash content of 1%.

Therefore Increase in ash - log ratio - 2.294 % )

0.012



151


- EFFECT OF CALCIUM CARBONATE ADDITION TO COAL SAMPLE

I TEST

1 NJL-

| 1

1 2

1 3

1

4

| 5

1 6

| 7

1 8

1 9

1 io

1 11

1 12

1 13

1 14

1 15

1 16

1 17

1 18

1 19

| 20

1 21

| 22

| 23

1 24

% ADDITION |

CACO3

0.0 |

0.5 |

1.0 |

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

6.0

7.0

8.0

9.0

10.0

11.0

12.0

13.0

14.0

15.0

| 16.0

| 17.0

18.0

CAO

0.0

0.28

0.56

0.84

1.12

1.40

1.68

1.96

2.24

2.52

2.80

3.36

3.92

4.48

5.04

5.60

6.16

6.72

7.28

7.84

8.40

8.96

9.52

10.08

LOG |

RATIO

2.289

2.301

2.313

2.325

2.337

2.348

2.360

2.372

2.384

2.396

2.408

2.431

2.455

2.479

2.502

2.526

2.550

2.573

2.597

|

2.620

|

2.644

|

2.668

| 2.691

2.715

INCREASE |

IN ASH % |

0.0 |

0.83 |

1.88 |

2.83 |

3.66 |

4.66 |

5.65 |

6.64 |

7.58 |

8.63 |

9.68 |

11.48 |

13.40 |

15.25 |

17.37 |

19.29 |

21.18 |

23.20 |

25.17 |

| 27.28 |

| 29.28 |

| 31.37 |

| 33.48 |

| 35.35 |

(NOTE For a typical coal an increase In log ratio of 0.012 corresponds

to an Increase In ash content of 1%.

Therefore Increase in ash - log ratio -

2.289

% )

0.012



152


- EFFECT OF KAOLIN ADDITION TO COAL SAMPLE

I TEST

1 N<L_

| 1

1 2

1 3

1

4

| 5

1 6

| 7

1 &

1 9

1 io

1 11

1 12

1 13

1 14

1 15

1 16

1 17

1 18

% ADDITION

AI2O32SÌO22H2O | AI2O32SÌO2

0.0 | 0.0

0.5 | 0.43

1.0 | 0.86

1.5 | 1.29

2.0 | 1.72

2.5 | 2.15

3.0 | 2.58

3.5 | 3.01

4.0 | 3.44

4.5 | 3.87

5.0 | 4.31

6.0 | 5.17

7.0 | 6.03

8.0 | 6.89

9.0 | 7.75

10.0 | 8.61

11.0 | 9.47

12.0 | 10.33

LOG

RATIO

2.290

2.294

2.298

2.302

2.306

2.310

2.314

2.318

2.322

2.326

2.331

2.339

2.347

2.355

2.363

2.371

2.379

2.387

INCREASE I

IN ASH % |

0.0 |

0.1 |

0.63 |

0.79 |

1.25 |

1.37 |

1.61 |

2.16 |

2.38 |

2.78 |

3.05 |

3.55 |

4.29 |

4.92 |

5.58 |

6.39 |

7.28 |

7.98 |

(NOTE For a typical coal an increase in log ratio of 0.012 corresponds

to an increase in ash content of 1%.

Therefore increase in ash - log ratio - 2.290 % )

0.012



TABLE 9

LABORATORY CALIBRATION TESTS WITH COALSCAN 3500 ASH MONITOR

1

2

3

4

5

6

7

COLLIERY/

COAL PREPARATION

PLANT (CPP)

Askern

Gaseoigne Wood

Cascoigne Wood

South Side CPP

(Grimethorpe)

Askern

Askern

Askern

PRODUCT

Blended Smalls

Untreated Smalls

Untreated Smalls

Blended Smalls

Blended Smalls

(From 4th Dynamic Calib)

Blended Smalls

(From 4th Dynamic

Simulated Blended

Smalls

Calib)

NO.

OF

SAMPLES

20

20

20

16

21

21

9

SIZE

RANGE

TESTED

-212 micron

-212 micron

-212 micron

-212 micron

-212 micron

-1.0 mm

25-3.18 mm

RANGE

OF ASH %

(A.D.)

11.3-40.5

10.6-23.4

10.2-33.4

22.0-30.2

14.0-32.4

14.0-32.4

6.2-41.8

CALIBRATION |

CORR

COEFF

0.997

0.844

0.827

0.895

0.993

0.988

0.998

STD.

DEV. |

% ASH (A.D.)j

0.64 |

1.69 |

3.67 |

1.15 |

0.59 |

0.80 |

0.83 |

en

co

(A.D.

- AIR DRIED)



TABLE 10 - LABORATORY INVESTIGATIONS WITH COALSCAN 3500 ASH MONITOR - EFFECT OF INCREASING

NUMBER OF STATIC MEASUREMENTS WITH PREPARED SAMPLES OF 25 - 3 mm ASKERN BLENDED COAL

I ONE BOX FILL | TWO BOX FILLS |

1 1 LINE | 2 LINES | 3 LINES | 1 LINE | 2 LINES | 3 LINES |

| EITHER FILL j EITHER FILL | EITHER FILL j EACH FILL | EACH FILL | EACH FILL |

| | CALIB. | | CALIB. | | CALIB. | | CALIB. | | CALIB. | | CALIB. |

| LINE j STD. DEV. j LINES | STD. DEV. | LINES j STD. DEV. | LINES j STD. DEV. | LINES | STD. DEV. | LINES | STD. DEV. |

1 1 % ASH | | % ASH | | % ASH | | % ASH | | % ASH | | % ASH |

| A | 2.059 | AB | 1.522 | ABC | 1.315 | AD | 1.466 | ABDE | 1.009 | ABCDEF |

0.834

|

1 B | 2.157 | AC | 1.151 | DEF | 1.284 | AE | 1.662 | ABDF |

0.936

| | |

| C | 1.308 | BC J 1.652 | | | AF | 1.427 | ABEF | 1.051 | | |

1 D 1 1.362 | DE 1 1.313 | | | BD | 0.757 | ACDE | 0.976 | | |

I E | 1.570 | DF 1 1.423 | | | BE | 1.157 | ACDF |

0.933

| | |

| F | 2.043 | EF 1 1.437 | | | BF | 1.388 | ACEF |

0.989

| | |

I I I I ¡ j | CD j 0.649 | BCDE j 0.728 | | |

I I I I I I j CE j

0.846

j BCDF |

0.865

| j |

1 1 1 I j | j CF j 1.208 j BCEF | 0.961 j | |

| MEAN | 1.750 | MEAN | 1.416 | MEAN | 1.299 | MEAN | 1.173 | MEAN |

0.939

| | |

| S.D. | 0.381 | S.D. | 0.172 | | | S.D. |

0.352

| S.D. |

0.095

| | |

BOX FILL 1

BOX FILL 2

| LINE

| LINE

| LINE

A

B

C

12

12

12

READINGS |

READINGS |

READINGS |

| LINE

| LINE

| LINE

D

E

F

12

12

12

READINGS 1

READINGS |

READINGS |

CJl



TABLE 11 - COALSCAN 3500 ASH MONITOR TRIAL. ASKERN COLLIERY - SUMMARY OF ON-SITE CALIBRATION AND PERFORMANCE TESTS

Static Calib |

| NO.

1 o

| 1

• 1

2

3

4

5

6

7 |

7 |

¡ DATE(S)

| 26-27.4.86

| 30.4.86

|

1.5.86

16.5.86

4-6.6.86

30.9.86

1.10.86

2.10.86

13.11.86

14.11.86

9.4.87

14.4.87

15.4.87

16.4.87

May/June 1987

14.3.88

16.3.88 |

17.3.88

29-30.3.88 |

| NUMBER

OF

SAMPLES

| 20

12)

17)

29

12

23

5)

7)

9)

12)

10)

5)

7)

11)

9)

57

7)

15)

8)

60

29

21

22

32

30

SIZE

| RANGE

TESTED

-212 micron

| 25 mm - 0

-212 micron

25 mm - 0

25 mm - 0

25 mm - 0

25 mm - 0

25 mm - 0

25 mm - 0

25 mm - 0

-212 micron

RANGE

| OF

| ASH %

11.3-40.5 A.D.

6.9-24.6 A.R.

7.5-27.2 A.D.

6.9-31.4 A.R.

12.9-28.7 A.R.

11.2-22.0 A.R.

8.9-24.7

A.R.

10.4-16.1 A.R.

10.0-23.6 A.R.

11.0-26.5 A.D.

CALIBRATION |

CORRELATION

COEFFICIENT

0.993

0.941

0.985

TEST ABANDONED

0.963

0.954

0.906

0.934

0.617

0.892

0.976

| STD. DEV 1

% ASH |

0.99 (A.D.) |

1.51 (A.R.) |

0.85 (A.D.) |

1.76 (A.R.) |

1.39 (A.R.) |

1.39 (A.R.) |

1.56 (A.R.) |

1.03 (A.R.) |

1.70 (A.R.) |

0.91 (A.D.) |

(A.R. - AS RECEIVED, A.D. - AIR DRIED)



156

TABLE 12 COALSCAN 3500 ASH MONITOR TRIAL, ASKERN COLLIERY -

RESULTS OF INVESTIGATION OF CROSS-BELT SEGREGATION WITH

OSCILLATING HEAD, BARIUM SOURCE AND 2 SECOND COUNTING

PERIODS

| BARIUM

| COUNTRATE

| RANGE

| C.P.S.

| >14000

| 13500-13999

| 13000-13499

| 12500-12999

| 12250-12499

| 12000-12249

| 11750-11999

| 11500-11749

NO.

OF

2 SECOND

PERIODS

98

25

40

68

41

69

25

9

BARIUM COUNTRATE

MEAN

COUNTRATE

C.P.S.

15017.9

13692.7

13257.8

12705.6

12373.1

12139.4

11897.3

11679.3

STD.

DEV.

C.P.S.

686.6

131.3

137.8

135.6

72.6

74.0

64.4

50.8

CALCULATED ASH |

MEAN

ASH

%

13.1

14.5

14.3

14.4

15.1

14.6

14.4

13.8

STD. |

DEV. |

ASH % |

1.5 |

1.6 |

1.8 |

1.7 |

1.6 |

1.7 |

1.5 |

1.5 |

(C.P.S.

- counts per second)



157

TABLE

13

EXPERIMENTAL RAM-FEED PRESENTATION UNIT WITH

PLUTONIUM

238

ISOTOPE MEASURING HEAD

AND Fe

CORRECTION

- LABORATORY CALIBRATION TESTS

ON

MARKHAM POWER

STATION BLEND

AND

COMPARISON WITH TELSEC

350

ANALYSER

Sample Analysis

Number

of

samples

Total moisture

,

range

Ash content

(A.R.) range

Sulphur content

(A.R.) range

Chlorine content %(A.R.) range

34

7.43 -

10.95

-

1.65 -

0.17 -

10.42

34.4

2.00

0.22

Calibration Results

| EQUIPMENT/

| INSTRUMENT

| Experimental

| Ram-Feed Unit

| Telsec

350

| Analyser

FEED

SIZE

50

mm - 0

25

mm - 0

5

mm - 0

212 micron

-

0

LINEAR REGRESSION

CORR.

COEFF.

0.831

0.965

0.922

0.989

STD.

DEV.

ASH

1.93

0.91

1.34

0.51

QUADRATIC

CORR.

COEFF.

0.954

0.987

0.989

0.997

REGRESSION

|

STD.

|

DEV.

|

ASH

1.67 |

0.90 |

0.81 |

0.44 |



158

TABLE 14 EXPERIMENTAL RAM-FEED PRESENTATION UNIT TRIAL.

MARKHAM COLLIERY - TYPICAL SIZING ANALYSES

OF POWER STATION BLEND AND CRUSHED PRODUCT

WITH DIFFERENT SIZE CRUSHER GRIDS

| SIZE

| FRACTION

| mm

| +16

| 1 6 - 8

| 8 - 4

| 4 - 2

1 2 - 1

| 1 - 0

| TOTAL

UN-CRUSHED

PRODUCT

WT.%

17.7

10.8

21.3

18.6

15.0

16.6

100.0

CUM

WT.%

U/S

100.0

82.3

71.5

50.2

31.6

16.6

50.1

WT.%

1.3

15.0

29.6

20.0

14.4

19.7

100.0

CRUSHER GRID APERTURE

i mm

CUM

WT.%

U/S

100.0

98.7

83.7

54.1

34.1

19.7

25

WT.%

2.1

10.8

32.1

22.3

14.4

18.3

100.0

.4 mm

CUM

WT.%

U/S

100.0

97.9

87.1

55.0

32.7

18.3

12.-

WT.%

0.9

8.5

26.3

25.2

18.2

20.9

100.0

1 mm |

| CUM |

WT.% |

U/S |

100.0 |

99.1 |

90.6 |

64.3 |

39.1 |

20.9 |

(u/s - undersize)



4 Foot Upper East Crop

3 Foot East

3 Foot Normal

TABLE 15 - ANALYSES OF SEAMS

TOTAL

MOISTURE

%

19.8

17.9

19.3

19.2

21.9

21.9

LABORATORY

ASH

CONTENT

%

6.3

13.0

18.8

7.0

10.2

10.2

FROM BLINDWELLS

SWEPT FREQUENCY

VOLATILE

MATTER

%

29.5

27.2

25.2

30.8

25.9

25.9

OPENCAST

SITE

MICROWAVE SYSTEM

SULPHUR

%

0.72

0.61

2.13

N.A.

0.96

0.96

TESTED WITH

| CALORIFIC |

j VALUE |

| KJ/KG |

24,460 |

22,620 |

19,980 |

24,840 |

21,920 |

21,920 |

THE

VOLATILE

MATTER

(D.A.F.)

%

40.0

39.4

40.8

41.7

38.1

38.1

CALORIFIC |

VALUE |

(D.A.F.) |

KJ/KG j

33,120 |

32,740 |

32,280 |

33,660 |

32,280 |

32,280 |

on

N.A. - NOT AVAILABLE

D.A.F. - DRY ASH FREE



161

TABLE 17 RESULTS OF FIRST SERIES OF LABORATORY TESTS WITH

EXPERIMENTAL INSULATED PLATE CAPACITANCE CELL AND

DIFFERENT CONCENTRATIONS OF IONIC SALT SOLUTIONS

| | | SAMPLE | SAMPLE | SAMPLE |

j TEST | ADDED j 1A | IB | IC |

I

NO. |

MOISTURE

I I I 1

I 1 * 1 INSTRUMENT READING mV |

1 1 1 1 1 1

I 1 | 0 | 107 | 107 | 107 |

1 1 1 1 1 1

| 2 | 2 | 220 | 225 j 238 |

1 1 1 1 1 1

I 3 | 4 | 450 | 517 | 570 |

1 1 1 1 1 1

I 4 | 6 | 680 | 758 | 960 |

1 1 1 1 1 1

I 5 | 8 | 900 | 970 | 1200 |

1 1 1 1 1 1

I

6 | 10 | 1050 | 1120 | 1270 |

1 1 1 1 1 1

I 7 | 12 | 1160 | 1180 | 1350 |

1 1 1 1 1 1

| 8 | 14 | 1240 | 1280 | 1400 |

1 1 1 1 1 1

I

9 | 16 | 1310 | 1390 | 1460 |

1 1 1 1 1 1

| 10 | 18 | 1350 | 1430 | 1470 |

1 1 1 1 1 1

SAMPLE 1A - moisture content increased with distilled water

SAMPLE IB - moisture content increased with 5g/l solution of sodium chloride

SAMPLE IC - moisture content increased with 16g/l solution of sodium chloride



162

TABLE 18 RESULTS OF SECOND SERIES OF LABORATORY TESTS WITH

EXPERIMENTAL INSULATED PLATE CAPACITANCE CELL

| | | TOTAL | INSTRUMENT |

| TEST | | MOISTURE | READING |

1 NO. j SAMPLE | % | mV |

| 1 | 2AA | 14.54 | 753 |

| 2 | | 13.37 | 707 |

| 3 | | 11.81 | 596 |

| 4 | | 11.81 | 553 |

| 5 | | 8.40 | 433 |

| 6 | | 8.49 | 410 |

| 7 | | 7.51 | 395 |

| 8 | | 7.42 | 284 |

| 9 | | 6.29 | 249 |

| 10 | | 5.03 | 247 |

| 11 | | 4.28 | 212 |

| 12 | 2AB | 16.75 | 791 |

| 13 | | 14.42 | 713 |

| 14 | | 11.71 | 596 |

| 15 | | 8.53 | 505 |

| 16 | | 7.25 | 417 |

| 17 | | 6.65 | 383 |

| 18 | | 5.61 | 315 |

| 19 | | 4.64 | 270 |

| 20 | 2BA | 19.17 | 903 |

| 21 | | 15.21 | 715 |

| 22 | | 11.70 | 615 |

| 23 | | 9.15 | 432 |

| 24 | 2BB | 18.24 | 953 |

| 25 | | 12.10 | 680 |

| 26 | | 9.93 | 555 |

| 27 | | 7.79 | 428 |

| 28 | | 7.14 | 365 |



163

TABLE 19 CALIBRATION TESTS WITH THE NEWPORT

MARK IIIA ANALYSER

| SAMPLE VOLUME (cm

3

) | 40 | 100 |

1 I I I

| SAMPLE WEIGHT (g) | 20 - 30 | 50 - 80 |

1 I I I

| SUITE | NO. | NO. | MAX. | MOISTURE | STANDARD DEIVATION |

| | COALS | SAMPLES | PARTICLE | RANGE | (MOISTURE %)

¡ I I I S I Z E | (%) | | |

l l l l ( n m ) J i ¡ ¡

1 1 1 1 1 1 1 1

1 1 1 1 1 1 1 1

1 1 1 6 1 17 1 0.2 1 1 - 9 1 0.42 j 0.34 j

1 1 1 1 1 1 1 1

| 2 | 7 | 16 | 3.0 | 2 - 11 | 0.42 | 0.33 |

1 1 1 1 1 1 1 1

| 3 | 4 | 16 | 0.2 | 1 - 10 | 0.40 | 0.34 |

1 1 1 1 1 1 1 1

| 4 | 4 | 15 | 3.0 | 1 - 9 | 0.34 | 0.38 |

1 1 1 1 1 1 1 1

| 5 | 5 | 19 | 0.2 | 1 - 6 | 0.18 | 0.23 |

1 1 1 1 1 1 1 1

] 6 | 12 | 20 | 3.0 | 1 - 8 | 0.17 | 0.23 |

1 1 1 1 1 1 1 1



TABLE

20

SUMMARY OF WORK ON MOISTURE MEASUREMENT BY NMR SPECTROMETRY

REFERENCE

LADNER 1964

LADNER 1966

ROBERTSON

1979

PAGE 1981

KING 1983

CUTMORE

1986

NMR

METHOD

Ctf

CU

CU

CU

PULSED

PULSED

FREQUENCY

(MHz)

16

16

2.7

2.7

10, 30

10-60

PRESENT-

ATION

STATIC

MOVING

STATIC

STATIC

STATIC

MOVING

STATIC

SAMPLE

VOLUME

(cm3)

15

15

40

40

100

0.5

PARTICLE

SIZE

(mm)

0

-

1.6

0.5 - 1.6

0

-

6.0

0.2 - 3.8

0 - 0.2

0 - 3.0

< 0.1

<1

MOISTURE

RANGE

(%)

3

3

3

4

0

1

1

1

0

- 30

- 15

- 25

- 27

- 14

-

10

- 11

-

31

-

30

ACCURACY

|

(-+

2s)

|

(%) |

1

|

1 |

1 |

2.6 |

0.6

|

0.4 - 0.8 |

0.5

-

0.7

|

1.5 |

1 - 2

|

en

■i*

(CU - CONTINUOUS UAVE)



166

TABLE 22 ACCURACY OF CONAC (ils wt% )

| YEAR

| REF

| TEST

| TEST

LOCATION

TYPE

| NO. SAMPLES

1 H

1 c

1

s

1 ci

1

N

1

Si

1 Al

1 Fe

| Ca

1 Ti

1 Ash

1 Moist

| C.V.

(kJAg)

1983

LABORATORY

CALIBRATION

17

0.08

1.4

0.13

0.005

0.18

0.14

0.11

0.05

0.008

1983

LABORATORY

ACCEPTANCE

5

0.12

2.74

0.29

0.006

0.18

0.69

0.55

644

1983

FIELD

ACCEPTANCE

5

0.04

1.8

0.05

0.006

0.16

1.7

0.52

4.30

1985 |

FIELD |

|

4 1

0.12 |

1.31 |

0.13 |

0.05 |

0.99 |

1.18 |

247 |



167

TABLE

23

PRECISION

OF

CONAC

(± Is wt )

| YEAR

|

REF.

| TEST LOCATION

| REPORTING PERIOD

1 H

1 c

1 s

1

ci

1

N

|

Ash

1 Moisture

1

C.V.

(kJAg)

1983

LABORATORY

3h

0.03

1.39

0.08

0.006

0.04

0.74

0.03

347

1983

FIELD

3h

0.02

1.27

0.06

0.002

0.02

1.22

0.01

323

1985

|

FIELD

|

20m

|

00.02

|

1.88 |

0.11 |

0.10 |

0.49 |

0.16 |

286

|



168

TABLE 24 ACCURACY OF ELAN (wt %)

| YEAR

| REF

| TEST

| NO.

| ASH

1 H

1 c

1 s

1 ci

1

N

1 Si

1 Al

1

F«

| Ca

1 Na

1 K

1

Ti

1 Ash

1 C.V.

TYPE

OF SAMPLES

RANGE

(%)

(kJAg)

1983

INITIAL

COMPARISON

2

6-7

MEAN DIFF.

0.26

1.1

0.05

0.01

0.03

0.07

0.03

0.02

0.05

0.005

0.06

0.03

0.23

1983

CALIBRATION

7

4-27

r.m.s.

0.04

| 0.20

| 214

1983

COMPARISON

35

r.m.s.

0.04

1985 |

COMPLIANCE |

DEMONSTRATION |

32 |

4-7 |

r.m.s. |

0.04 |

| 0.23 |

145 |



170

TABLE 26 RELATIVE ACCURACY OF NEUTRON/GAMMA ANALYSIS

| RELATIVE ACCURACY

1

(±is)

| < 2%

| 2 - 5 %

| 5 - 1 0 %

| 10 - 20%

| 20 - 30%

| 30 - 50%

| > 50%

PARAMETER |

Calorific value j

H, C, Ash |

S, Si |

N, CI, Fe |

Al, K 1

Na,

Ti 1

Ca j



171

TABLE 27 UNITS CURRENTLY INSTALLED OR ORDERED

|

|

SAIC

| MDH - |

GAMMA-

|

TOTAL

|

|

| |

MOTHERWELL

|

METRICS

| |

| Installed

and

Operating

j 1 j 3 j 11 | 15 j

| or Commissioning | | j j j

| Installed

not in use | 2 | j 1 | 3 |

| Ordered

| j 1 | 1 j 2 |

| TOTAL

| 3 | 4 | 13 | 20 |



ISOTOPE

MEASURING

HEAD

STATUS

CONTROL

^

< > .

CONVEYOR WIDTH

160 mm

F I G U R E

1 .

W ULTEX RAD IOMET RIC AS HME T ER, T YPE

G3 -

GENERAL ARRANGEMENT

ON B ELT CONVEYOR



174

HINGED

COVER

(LOCKABLE)

RADIATION

_

SOURCE (Am241)

SOURCE

CONTAINER

SCINTILLATION

DETECTOR

SHUTTER

4 9 0

mm

FIGURE 2. WULTEX RADIOMETRIC ASHMETER, TYPE G3 -

SECTIONAL VIEW OF ISOTOPE MEASURING HEAD



0 . 8 8 - ,

BULX DENSITY

0 . 9 0 -

0 . 9 2 -

0.94 _

O

u

w 0 . 96 .

I—I

3

w

OS

0 . 9 8 -

1.00 -

900 KG/M

3

700 KG/M

3

10

ASH

15 ASH

20 ASH

u i

1-02

50

100

-nr

150

200

BED DEPTH (MM)

" I

250

FIGU RE 3 . W ULTEX AS HMET ER

*

T H E R O T E I C A L E F F E C T O F B E D D E P T H ON C O U N T R A T E F OR

3 L E V E L S O F A S H C O N T E N T A N D 2 L E V E L S O F B U L K D E N S I T Y



176

SPACERS

1 .

T

TT-+Í

COMPRESSION STOPS

7

COMPRESSION PLATE

ADJUSTABLE BASE

=

\

EXTENSION

FRAME

BOX FRAME

SAMPLE COMPRESSION WITH POSSIBLE BED DEPTH/FRAME COMBINATIONS

BED

DEPTH

(D)

mm

80

120

160

200

FRAME DEPTH (E) mm

6

8 12 16 20

32

( E 100)

COMPRESSION ; - — - ' ;

( E + D )

7.0

4.8

3.6

2.9

9.1

6.25

4.8

3.8

13.0

9.1

7.0

5.7

16.7

11.8

9.1

7.4

20.0

14.3

11.1

9.1

-

21.1.

16.7

13.8

COMPRESSION SYSTEM SPACERS FOR EACH EXTENSION FRAME

EXTENSION

FRAME DEPTH

mm

6

8

12

16

20

32

FRAME LESS

COMPRESSION

PLATE mm

-

2

6

10

14

26

SPACERS

mm

-

2

6

10

14

10+10+6

FIGURE 4. WULTEX ASHMETER - VARIABLE DEPTH SAMPLE PRESENTATION

BOX FOR LABORATORY INVESTIGATIONS



12

-i

10 _

8

_

o

■ <

< 6 -

LOOSE FILL

BULK DENSITY 769-791 KG/M

3

LABORATORY ASH

40

1

8 0

1

1 2 0

BED DEPTH (MM)

1

16 0

1

20 0

12 - I

10 -

8

-

SB

in

6 -

4 -

COMPACTED FILL

BULK

DENSITY

8 6 5 - 8 6 7

KG/M

3

UK METER

LABORATORY ASH

40

n

1

r

80 120 160

BED

DEPTH

(MM)

1

200

»J

««4

FIGURE 5. VULTEX ASHHETER - EFFECT OF BE D DEPTH ON ASH MEASUREMENT AT TW O E ELS

OF BULK DENSITY WITH SAMPLE FROM BILSTHORPE PS F BLEND



20 -,

18

16

14

3 12

10 -

POLISH METER

LOOSE FILL ,


J

^

1 H

_ L A B O R A T O R Y ASH

40

i

1 r~

80

120 160

BED DEPTH (MM)

1

2 0 0

2 0 -i

1 8 -

1 6 -

1 4

_

o

«e

ac

v)

1 2

—

1 0 —

P O L I S H M E T E R

C O M P A C T E D F I L L

B U L K D E N S I T Y 8 1 6 - 8 2 1 K G / M

3

LABORATORY

AS H

40 80

120

160

B ED DEP T H

(MM)

200

0 0

F I G U R E 6 . W U LT EX Ä S HK E T E R - E F F E C T O F B E D D E P T H ON A S H ME A S U R E ME N T A T TWO L E V E L S O F

B U L K D E N S I T Y W I TH S A M P L E F RO M M A NT ÓN M I D D L I N G S .



28 -,

28 -,

LOOSE FILL

BULK DENSITY 826-829 KG/M3

27 _

27 _

26 _

POLISH METER

o

•<

•4

25

24

23

26 —

o

•<

25 _

24 —

40

1—

8 0

1

120

BED

DEPTH

(MM)

— T

160

"I

200

23

COMPACTED


3

POLISH METER

LABORATORY ASH

40

"I 1 1 1

80 120 160 200

BED DEPTH (MM)

FIGURE 7. WULTEX ASHMETER - EFFECT OF BED DEPT H ON ASH MEASUREME NT AT TWO LEVEL S

OF BULK DENSITY WITH SAMPLE FROM GEDLING MIDDLINGS



180

25 -

<r

<r

2

o

8

20 -

15

-

10 -

■

- •

1 . . . . 1

H ' ' M

i....R>v...

. . . . i

i • • • •

Da

iP

i i i i i

i i i i i

^ x

. . . . i

i

' ■ ' ■ i

. . . . i

i i i i

c

. . . . i

■ i—i—r-T -H

■ ■ ■ -*■ 1

1—

• -

2600 2100 2200 2300 2.4øø 25øø

ASHMETER

READING

(COUNTS/SECOND)

2600

2700

FIGURE 8. LABORATORY CALIBRATION FOR MANTÓN 50 mm - 0

BLENDED

COAL

WITH

fU T X

UK)

ASHMETER



181

■

N

5-

g

5

24

-

22

-

29

18

16

14

T

1

•

T 1 1 1 1 1 1 r

T r

: ; ;

:

^ V ^ Q .

j

\

^TrR^ü

neo

X

_L

■

1150

1200

1250

ASHMETER

READING

<COUNTS/SECOND)

1300

FIGURE

9.

LABORATORY

CALIBRATION

FOR

MANTÓN

50

nun

-

0

BLENDED

COAL

WITH

WULTEX

(POLISH)

ASHMETER



182

■

r

N

2

s

3

58

45

-

48

35

3ø

25

T — i — —

r

i i i I

^ ^ L

□

¿fvgp

p

ü

. . . . ^ s ^

b

Ía. . . . l^Í .

1609

X

_L _L _L

1630

1700

1750

1800

ASHMETER

READING

(COUNTS/SECOND)

1850

FIGURE 10. LABORATORY CALIBRATION FOR MANTÓN 50 nun - O

UNTREATED

COAL

WITH

WULTEX

(UK)

ASHMETER



183

n

m

< r

X

< r

g

i -

2

o

m

850 900 950 1000

ASHMETER READING (COUNTS/SECOND)

1050

FIGURE 11. LABORATORY CALIBRATION FOR MANTON 50 mm - O

UNTREATED COAL WITH WULTEX (POLISH) ASHMETER



184

■

fi

O

t-

r

cc

o

m

<r

30

28

26

24

22

20

18

16

—1

i . .

i i 1 i i

—r

; ;

; ;

; ;

; ;

;

j

> S

\

D

i— \

i — i — i — i — i —

d

: i :

. . i . . . . i . . . . i

\ D D

fla\ o

\ n

o

_ J ■ ■ ■ 1

1 ■ 1 I 1 1

• ;

• •

;

;

;

; ;

;

;

N.

•

N x i i ;

. . . . 1 . . . . 1

1—

-

-

-

-

m

1888 1050 1100 1150 1200

ASHMETER

READING

COUNTS/SECOND)

1250

1300

FIGURE

12.

LABORATORY

CALIBRATION

FOR

ASKERN

25

mm

-

0

BLENDED

GOAL

WITH

WULTEX

POLISH)

ASHMETER



185

50

T — r

i — r

■

< r

fi

>

o:

o

(£ .

O

m

45

40

35

30

-•

.1 „ha™ D

D \

Ö \ n

•

-L

_L

■

_L

_L

i

i

i

i

850 900

950

1000

1050

ASHMETER

READING

(COUNTS/SECOND)

lløø

FIGURE

13.

LABORATORY

CALIBRATION

FOR

ASKERN

25

mm

-

O

UNTREATED COAL WITH WULTEX (POLISH) ASHMETER



186

s

■

<r

N

12

-

10

-

8

-

ó

-

— 1

1

1— 1— 1— 1— 1— 1— 1— 1— 1— 1 — I

D

N 3

1 — i — ■ — — — 1

D\

I

r i 1 1

\ a

i

r I — I — |

— i — i — i — i — i

i

i

i

i

i

1—

-

1309

1400

1500

1600

1700

ASHMETER

READING

COUNTS/SECOND

1800

FIGURE

14.

LABORATORY

CALIBRATION

FOR

ASKERN

25

mm

-

0

WASHED COAL WITH WULTEX POLISH ASHMETER



187

■

<L

N

<E

2200

2400

2600

2800

3øøø

ASHMETER

READING

(COUNTS/SECOND)

3200

FIGURE

15.

LABORATORY

CALIBRATION

FOR

BILSTHORPE

50

mm

-

0

BLENDED COAL WITH WULTEX (UK) ASHMETER



188

■

o

3

ieeø

1180

1208

1388

1488


1588

GURE

16.

LABORATORY

CALIBRATION

FOR

BILSTHORPE

50

mm

-

0

BLENDED

COAL

WITH

WULTEX

(POLISH)

ASHMETER



189

B

<I

N

1909

i i i

2000 2100 2200 2300


2400

FIGURE 17. LABORATORY CALIBRATION FOR BILSTHORPE 38 mm - O

UNTREATED COAL WITH WULTEX (UK) ASHMETER



190

■

>

g

50

-•

45

-

4ø -

35

-

30

-

-

■

-• i

— —l— — — — I ~ I — i — i — T — r — i — r — r —

° n P

o

I — I — i i i

3

^ \ .

I

i

i

i

i

j—r—i—i—i—

i

1—

•

• -

800

_L _L

X

X

850

900

?5ø

løøø

1050

ASHMETER

READING

(COUNTS/SECOND)

Uøø

FIGURE

18.

LABORATORY

CALIBRATION

FOR

BILSTHORPE

38

mm

-

O

UNTREATED

COAL

WITH

WULTEX

(POLISH)

WULTEX



191

■

<E

M

>

o

S

O

m

<r

2800

3000 3200 3400 3600

ASHMETER READING COUNTS/SECOND

3800

FIGURE 19. LABORATORY CALIBRATION FOR BILSTHORPE 50 mm - 0

WASHED COAL WITH WULTEX UK ASHMETER



192

18

■

îi

2

O

5

4

2

— i

1380

1400

1500

1600

1700

ASHMETER

READING

(COUNTS/SECOND)

1800

FIGURE

20.

LABORATORY

CALIBRATION

FOR

BILS

THORPE

50

nun

-

0

WASHED

COAL

WITH

WULTEX

(POLISH)

ASHMETER



193

■

N

O

H

2

O

o c

2400

2Ó00

2800

3000

ASHMETER

READING

(COUNTS/SECOND)

3200

FIGURE 21.LABORATORY CALIBRATION FOR COTGRAVE 50 mm - O

BLENDED

COAL

WITH

WULTEX

(UK)

ASHMETER



194

■

■

NX

(f l

>

o

<C

OC

o

m

<r

35

-

30 -

25 -•

20

-

15

-

10

-

1100

1200

1300

1400

ASHMETER

READING

COUNTS/SECOND)

1500

FIGURE

22.

LABORATORY

CALIBRATION

FOR

COTGRAVE

50

mm

-

0

BLENDED

COAL

WITH

WULTEX

POLISH)

ASHMETER



195

■

■

<I

X

CO

<t

o

45

40

35

38

25

20

15

10

- • i s :

. ;

- j

O

1

D

D

-

.

1 I I I

, . ,

^ \ n

D

.

r *

T

■ '

< a

■

^ D :

^

ţ x D

Tü

:

i

\ b

n nnìTriL ri

i

\D

'

. ._

-

-

. ._

. ._

1

1800

2000

2200

2400

2600

ASHMETER

READING

(COUNTS/SECOND)

2800

FIGURE

23.

LABORATORY

CALIBRATION

FOR

LEA

HALL

25

mm

-

0




196

25 -■

O

■

r

N

S

28

15

10

- •

- •

- ■ i

1

1 1 1 1 1

_ . . * . .

J

.

1

: o V

. . . . i

D :

. . . . i

r-i—i i i

—t 1

1

i

i

i

i

T

-

' — i — i — • — 1 —

a n i

D > v : :

D D ^ Q :

:

-

i — i — i — i i 1 i i ■ ■ i

2400

2500

2609

27øø

2800

ASHMETER

READING

(COUNTS/SECOND)

2900

3000

FIGURE

24.

LABORATORY

CALIBRATION

FOR

DAW

MILL

12.5

mm

-

O

UNTREATED

COAL

WITH

WULTEX

(UK)

ASHMETEÄ



197

■

< r

fi

< r

>

CC

o

I

g

s

3

9 -

8 -•

7 -•

5

-

4

-■

-

_ .

- •

1

| \ c

IfflS

| I - T I I - T • « TI

;

0

> EFSJ

n

:

D

:

'

■

'

'

1

— « — « — • — « — i i —

,._

-

3208 3300 3400 35øø 36øø 37øø 38øø


3900

FIGURE 25. LABORATORY CALIBRATION FOR CWM 50 mm - 0

WASHED

COAL

WITH

WULTEX

(IJK)

ASHMETER



198

■

p

B

< r

M

X

CO

<E

>

œ

o

5

20

18

16

14

12

10 -

8 — i

2500

2550

2600

2650

2700

2750

ASHMETER

READING

<COUNTS/SECOND)

2800

FIGURE 26. LABORATORY CALIBRATION FOR SHARLSTON 50 mm - 0

WASHED COAL WITH WULTEX (UK) ASHMETER



199

3ø -

25 -

Q

M

fi

<r

cc

om

<r

20

15 -

10

-

5 -

0 -•

2200 2400 2600 28øø 3øøø 3299


3400

FIGURE 27. LABORATORY CALIBRATION FOR GRIMETHORPE 50 mm - 0




200

■

< t

s/

N

g

2

O

m

5

2ø

»

i

■ ■ ■ ■ i ■ ■ ■ ■ i ■ ■ ■ ■

■ . . .

i . . . . i . . . . i . . . . i . . . . i

2868 2850 2188 2158 2288 2258 2388 2358 2488

ASHMETER

READING

(COUNTS/SECOND)

FIGURE

28.

LABORATORY

CALAIBRATION

FOR

GRIMETHORPE

50

mm

-

0

UNTREATED

GOAL

WITH

WULTEX

(UK)

ASHMETER



201

a

<i

N

CO

O

m

<£

5 -

4 -

3008 3108 3288 3388 3488 3588


3600

3788

FIGURE 29. LABORATORY CALIBRATION FOR GRIMETHORPE 50 mm - 0

WASHED COAL WITH WULTEX (UK) ASHMETER



202

x

/>

i

U

a

e

(O

i

2 .5

2

1.5

1

0 .5

- •

- •

- •

- •

1

'

D

D

. . . .

^

n ^ D

.

. . .

i

. . . .

i

— — ■ — ■ — —

D D /

□

. . . .

i — « — « — — — i

•y/fa

. . . .

. . -

m

.._

-

0.5 1 1.5 2

CALIB

STD

DEV

-

LABORATORY

MEASUREMENTS

2.5

FIGURE

30.

RELATIONSHIP

BETWEEN

STANDARD

DEVIATION

CALCULATED

FROM

FULL ELEMENTAL ANALYSIS AND MEASURED STANDARD DEVIATION

FOR

LABORATORY

CALIBRATION

TESTS

WITH

WULTEX

ASHMETER



203

2.5 -

co

I-I

O)

5-

i

o

I

s

0)

1.5

0.5

0.5 1 1.5 2

CALIB STD DEU - LABORATORY MEASUREMENTS

2.5

FIGURE 31. RELATIONSHIP BETWEEN STANDARD DEVIATION DERIVED

FROM IRON AND ASH ANALYSIS ONLY AND MEASURED

STANDARD DEVIATION FOR LABORATORY CALIBRATION

TESTS WITH WULTEX ASHMETER.



Œ

RAW

COAL

FILTER

CAKE

CLEAN

COAL

IV J

MIXER

BELT FEEDER

\

7^

BELT WEIGHER

3D

MECH

SAMPLER

BELT

WEIGHER

SHIFT

SAMPLE

RAPID

LOADING

BUNKERS

O

■Ck

FIGURE

3 2 .

SCHEMATIC

ARRANGEMENT

OF

WULTEX

ASHMETER

INSTALLATION

AT

BILSTHORPE

COLLIERY



CLEAN

COAL

-25 mm

MECHANICAL SAMPLER

I

V

<r t»|

CRUSHER

f

STATION O*"* ^ O

Ù

CONSIGNMENT

SAMPLE

o

en

FIGURE 33. SCHEMATIC ARRANGEMENT OF WÜLTEX ASHMETER INSTALLATION AT MANTON COLLIERY



206

cc

■

<E

v

M

I

W

< r

>

o

g

m

38

25

20

15

10

~1

- •

1

. . . .

0

s

i i i . i ..J

. . . .

'û

□

\n

D ^

D

. ■ . ■

. . . .

kp

D

a

. . . . ¡ . . . .

D

m

pa >

D

: ^ \

1

1

1

1

1

1

1

1

1

L

_

I

__L

L_

1

1

1

i —

—

• -

.

1300

1350

1400

1450

1500

ASHMETER

READING

(COUNTS/SECOND)

1550

FIGURE 34. WULTEX ASHMETER INSTALLATION AT MANTÓN COLLIERY

DYNAMIC

CALIBRATION

TEST

1



207

3ø

cc

< r

M

X

CO

< c

>

cc

o

<i

25 —

20

15

—

10

— 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1

-

- •

1

c

iSkn

D

i — i — i — i — i — ; — i — i — i —i — i

n

D

D

o

i — ' — « — ' — ■ — —

D

. . Q . . ^ . ^ ^

1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — J _ _

1

1 1

-

, . -

1

1250

1300

135 14 145


1500

FIGURE

35.

WULTEX

ASHMETER

INSTALLATION

AT

MANTÓN

COLLIERY

-

DYNAMIC

ALIBRATION

TEST 2.



208

H T • — - j r-*~ Signal to

amplifier

Scintillation

detector

M l . _IJS_

Am S Bo

FIGURE 36. SCHEMATIC ILLUSTRATION OF THEpRiNCIILE OF OPERATION 01

THE COALSCAN 3500 ASH MONITOR.



209

Americium ( low )

channel

Borium ( high ) chonnel

60 keV

3 5 6

Energy , keV

FIGURE 37. RADIATION SPECTRUM FOR COALSCAN 3500 ASH MONITOR WITH

AMERICIUM AND BARIUM SOURCES.



CONVEYOR

SOURCE

HOUSING

ELECTRONICS UNIT

SIGNAL CA3LE

DETECTOR

?=n

PRE AM?

±=és

S?

LOCAL CONTROL UNIT

J ^ = q ^

RADIOISO- S H U T T E R

TOPES POSITION

LIMITS

I

POWER UNITS

1-

FRAME CONTROL

SHUTTER CONTRC

,

D

FRAME POSITION LIMITS

cq

MULTI ÇHANNEI

ANAT.VSF.R

TERMINAL

I

COMPUTER

S

INPUT/

OUTPUT

POWER

SUPPLIES

RETRACTABLE FRAME

o

FIGURE 38. SCHEMATIC ARRANGMEITT~ OF COMMERCIAL DESIGN OF COALSCAN 3500 ASH MONITOR



211

0 . 0 2 0

o 0 .01 6 _

D

o

~ 1 2

g 8

Q

O C

<r

a 4

-]—i—i—i—i—|—i—i—i—i—|—i—i—i—i—|—i—i—i—i—|—i—i i

i—|—i—i—m—

* *

: : : : : :

. . . . • . i

■ : ? i i > •

J L _ I _

_L

J L.

J

i

i_i

i

L

■ ■ ■ i i i i i__i_

1

200 300 400

COUNTING PERIOD <SECS)

■COO

6

FIGURE 39. LABORATORY INVESTIGATIONS WITH COALSCAN 3500 ASH MONITOR -

VARIATION

OF

LOG

RATIO

STANDARD

DEVIATION

WITH

DURATION

OF

COUNTING

PERIOD



212

70 - i

60

50 _

40 _

K

SC

CO

w 30

CO

¡3

OS

o

20 -

10 _

* Fe20

3

© C a O

V TYPICAL ASH

0

A

l

2

0

3

2 S i 0

2

%

A D D I TI ON

FIGURE 40. LABORATORY INVESTIGATIONS WITH COALSCAN 3500 ASH MONITOR -

EFFECT OF CHEMICAL ADDITIONS ON MEASUREMENT OF ASH CONTENT



213

A

o

<r

X

w

<c

>

<z

o

»-

< t

cc

o

m

<x

45

40

35

30

25

20

15

10

—

•

1

. . . . . . . .

| 1 1 1 1 1 1 1 1 1 1 r— i 1 1 1

_ J 1 1 1 . 1 1 1 1 1

/ : -

: -

; -

j -

2 .5 2 .ó

2 . 7 2 . 8 2 . 9

LOG.

RATIO

3.1

FIGURE 41. LABORATORY CALIBRATION FOR ASKERN BLENDED COAL (-212 pn)

WITH COALSCAN 3500 ASH MONITOR.



214

a

< z

f i

X

0 1

24

22

28

18

là

14

12 -

10 -

' ' *

T — ■ — — — ■ — 1 — ■ — • — • — — 1

p

° 0 ^ ; q

:

J

y ^

■

D

: G :

D :

D

\y ^

\ :

J I L.

2 . 3 5

J i i i i L

J

L.

j i L _ l

2.4

2.45 2.5

LOG. RATIO

2.55

2.6

FIGURE

42.

FIRST

LABAORATORY

CALIBRATION

FOR

GASCOIGNE

WOOD

UNTREATED

COAL (-212 pin) WITH COALSCAN 3500 ASH MONITOR.



215

•N

a

<r

X

CO

< c

>

oc

o

I

o

m

<c

35

-•

30

-

25

-

20

15

—

10

-

;

-

:

- :

-

•

-

:

□

- i □••

i . . . .

i

« ■ ' ' i

□.

. . . .

i i i i

0 ^ °

i i i i

D

Ai

. . . .

D

y

i . . . . ¡ . . . .

. . . .

■ i i i

■

■

.

■

D

„ u i i 1

• -

• -

-

2.5 2.6

2.7 2.8

2.9 3

LOG.

RATIO

3.1

3.2

3.3

3.4

FIGURE

43.

SECOND

LABORATORY

CALIBRATION

FOR

GASCOIGNE

WOOD

UNTREATED

COAL

(-212

pu)

WITH

COALSCAN

3500

ASH

MONITOR



276

<x

I

(O

< r

I

s

5

32

-

3ø -

28

-

26

-

24 -

22

-

2ø -

- :

■

: : D n j -

:

:

□ \s^ \ \ '.

P

o^P

0

^ i i

D

-

:

Ü

l^^

:

-

i n / r n ; i -

^ ^ : :

D

= : :

i i i 1 i i i 1 i i i 1 i i i 1 i i i.- L i i ■ 1 . . . 1 . . . 1

2.6

2.62

2.64

2.66

2.68

2.7

2.72

2.74

2.76

2.78

LOG.

RATIO

FIGURE 44. LABORATORY CALIBRATION FOR SOUTH SIDE (GRIMETHORPE)

BLENDED

COAL

(-212

pi)

WITH

COALSCAN

3500

ASH

MONITOR



217

< r

Ni »

M

I

CO

< c

>

o c

o

< r

o

m

< r

35

30

-

25

-

20

-

15 -

10

— 1

- •

-

J

1 — — I — — — 1

. . . .

0D

i . . . i

Pu

i i i i

i — i — i — i i j — ■ — ■ — i - - » i

1 i i i i

. . . .

-

™

2.55

2.6

2.65

2.7

LOG.

RATIO

2.75

2.8

2.85

FIGURE

45.

LABORATORY

CALIBRATION

FOR

ASKERN

BLENDED

COAL

(-212

pi)

FROM

FOURTH

DYNAMIC

CALIBRATION,

WITH

COALSCAN

3500

ASH

MONITOR



218

35 —

38 -

N

CO

<E

>

£.

O

I-

<£

OC

O

m

<E

25

20 —

15 -

18

...J

. . . .

1 1 1 1

D P^

3

i i i i 1

°rfJ

1 1 1 1,

D ^ Q

ÏS^

i i i i

1 i i i i 1

i —

-

2.55

2.6 2.65 2.7 2.75

LOG. RATIO

2.8

2.85

FIGURE 46. LABORATORY CALIBRATION FOR ASKERN BLENDED COAL (-1 nun),

FROM FOURTH DYNAMIC CALIBRATION, WITH COALSCAN 3500

ASH MONITOR



219

<z

X

CO

<z

>

CC

o

tr

o

m

<E

45

40

35

30

25

28

15

10

5

— i

-

- ■

- •

-

i l i 1 1 i i 1 1 — — — — — j 1 1 1

r——j

1 1 1 i j

: :

Jr

: : : > / :

S5 :

: y f : :

j y ^ •

-

_

, . -

. -

r~

i i i i . i. J i i i i i i i i i i I _ I ■ ■ ' ■ ' ■ i l

2 .4

2 .5

2 .6 2 . 7

LOG. RATIO

2 . 8 2 . 9

FIGURE 47. LABORATORY CALIBRATION FOR ASKERN SIMULATED BLENDED

COAL

25

-

3.18

mm)

WITH

COALSCAN

3500

ASH

MONITOR



RAW

COAL

CLEAN

COAL

WEIGH-

FEEDER

PHASE

3A

ASH

MONITOR

MECHANICAL

.

.

_ _

SAMPLER

Y

CRUSHER

ro

ro

o

[ J LABORATORY SAMPLE

FIGURE

4 8 .

SC HEMA TIC ARRANGEMENT

O F

C O A LS C A N 3 5 0 0

A N D

N C B / A E R E P H A S E

3 A A S H

MONITORS

A T

ASKERN C OLLIERY



221

f i

I

co

<r

>

cc

o

I

<r

ce

o

m

<r

45

40

35

30

25

20

15

10

— i

- •

-

;

•

•

C

jdß

P%

1 i—_i i i i i i i i 1

: •

¿s

''■

-

:

jr

•

'

: s S ^ :

U/\

:

-

AS

:

-

:

:

:

-

: : : -

i

i

i

i

i

i

i

i

i

i

i

■

i

■

i

i

2 .5

2 . 6

2 . 7

2 . 8

LOG.

RATIO

2 . 9

FIGURE

49.

ON-SITE

STATIC

CALIBRATION

FOR

ASKERN

BLENDED

COAL

(-212

pn)

WITH

COALSCAN

3500

ASH

MONITOR



222

c c

<E

v

M

X

CO

<E

o

I -

< c

o c

s

< r

■^s

7ñ

1 5

1 0

5

— ¡ — i — ■ ■ ■ i

-

:

i—

_

———

□

/

U j

i

■ ■ •

' —

&*L..

' a *

__t i i i i i i i i

i ■■ ■| ■■■ i

C

D 1

¿ f u

: or

¿\.JQ

D

L_i ,_ i . .1

i

1

i

i

i

i

I

.

¡ r

T

2

L_I

J

,

1 1

D y

L i i i i l

-

-

-

m

-

.

-

• -

-

-

2 .3 2 35 2 4 2 45 2 5

LOG.

RATIO

2.55

2 . 6

2.65

FIGURE

50.

FIRST

DYNAMIC

CALIBRATION

FOR

ASKERN

BLENDED

COAL

(25

mm

-

0)

WITH

COALSCAN

3500

ASH

MONITOR



223

m

a

x

co

<c

>

o

h -

< Z

CC

o

m

<r

39

25

28

15

18

5

— i

- •

i — « —

r

~ >

— « — i

□

. . . .

i — i — i — i — i — |

U

. . . .

D

J

2

®

n

:

1 1 1 1 1 1 1 L_l 1 1

D

—i—i—i—i—i—i—i—i

_I_J

- 1 — 1 — . r - ,

D

s

. . . .

,.-

■

-

2.45

5 55 6 65

LOG.

RATIO

2 . 7

2 . 7 5

2 . 8

FIGURE

51. STATIG CALIBRATION

FOR ASKERN BLENDED COAL SAMPLES

212

)iin)

FROM

FIRST

DYNAMIC

CALIBRATION

WITH

COALSCAN

3500 ASH MONITOR



224

O C

< r

N

c o

< c

< r

c e

o

m

<E

35

30

25

20

15

10

5

' '

i . .

o

Q

— y

k j . S ^ i . n

: / Q

sĂac

1

■ t i i i i i i i i i i i i i ■ i

Uy

D

. . . .

1

. . . .

1

. . .

.

:

i

-

: -

: -

: -

: -

: -

-

: -

i

. . . .

i

2.45

2 .5

2.55

2 .6

2.65

2 .7

2.75

LOG.

RATIO

2 . 8 2 . 8 5

FIGURE 52. THIRD DYNAMIC CALIBRATION FOR ASKERN BLENDED COAL

25

mm

-

0 WITH

COALSCAN

3500

ASH

MONITOR



225

3ø

Q:

<r

?£

ft

<I

>

CC

O

I

<r

cc

o

m

<r

25 —

20 -

15

10

: : : Jf

D

:

: :

^ y^ \

•

- i - n / f i -

- : °:

J

: -

I

I

p é

u

\

i I -

- ;

J ?

-

-■■

X Ş o

I

i

i

i - -

:

¿¿ □ : : : :

1.95

2 . 0 5

2 . 1

LOG.

RATIO

2 . 1 5

2 . 2

FIGURE

53.

FOURTH

DYNAMIC

CALIBRATION

FOR

ASKERN

BLENDED

COAL

(25

mm

-

0)

WITH

COALSCAN

3500

ASH

MONITOR



226

C C

m

< x

f i

X

(O

<E

>

O C

o

»

< r

o c

s

1.95

2 . 8 5

LOG.RATIO

2.1

2.15

FIGURE 54. FIFTH DYNAMIC CALIBRATION FOR ASKERN BLENDED COAL

(25 mm - 0) WITH COALSCAN 3500 ASH MONITOR



227

■

< x

n

>

cc

o

»

< t

a.

o

m

< t

25

-

29

-

15

10

i i i i i i i i

T ' ' ' ' 1 f

D

aX

3 D

D

n . .

„s

D 5 ^ :

x ^ à

D

' L I

■ i L ■ i L

j i L

1.9

1.95

2.85

2.1

LOG.

RATIO

FIGURE

55.

SIXTH

DYNAMIC

CALIBRATION

FOR

ASKERN

BLENDED

COAL

(25

mm

-

0)

WITH

COALSCAN

3500

ASH

MONITOR



228

16 -

(À

■

O.

■

o

©

<9

«-•

LU

<I

o:

i

z

g

o

s

h-l

18

27

36

45

COUNTING PERIOD <No>

54

63

FIGURE

56.

COALSCAN

3500

ASH

MONITOR

TRIAL

AT

ASKERN

COLLIERY

-

VARIATION

OF BARIUM COUNTRATE, IN 2 SECOND PERIODS, DURING OSCILLATION

OF

MEASURING

HEAD

ACROSS

PRODUCT

STREAM

WITH

18

SECOND

CYCLE TIME



229

UJ

H

Z

O

O

X

CO

< r

UJ

15 . 5

15

14 . 5

14

13 . 5

13

¡ . . . .

- •

1

-,

1

„i

J_.

i

i -

•

•

*• •

\

■

. . . .

i

. . .

.

. . . .

11.5

12

12.5

13

13.5

14

14.5

MEAN

BARIUM

COUNTRATE

(1808

C.P.S.)

15

15.5

FIGURE

57.

COALSCAN

3500

ASH

MONITOR

TRIAL

AT

ASKERN

COLLIERY

-

VARIATION

OF

MEAN

CALCULATED

ASH

CONTENT

WITH

MEAN

BARIUM

COUNTRATE

DURING

OSCILLATION

OF

MEASURING

HEAD

FOR

13

MINUTE

TEST

PERIOD.



230

cc .

m

z

g

16

-

15

-

14

13

12

11

18

T ■ » » — ţ — i ' ■» • i ■ » - • » | • ■ i J i ' i -

- •

_ .

D

: D

:

q

□

: D

O-jG D ^ -

:

s^

n

jS a?

m □

D

□

' - V

1

n i n i ¡ J B P ^

■ E L J ?

d

0

D

□ i *

D

D

I

I

J L.

■

■

1.94

1.96

1.98

2

LOG.RATIO

J

i

i

i

L

2.62

2.84

FIGURE

58.

PERFORMANCE

TEST

CALIBRATION

FOR

ASKERN

BLENDED

COAL

(25

mm

-

0)

WITH

COALSCAN

3500

ASH

MONITOR.



l/l

Q.

O

O

O

o

tu

r

^ I ■ » ■ '■ » I »■aHIII IJIIM IIHIII I I I II I I I | I IWHIIII I II I I I I I I[ IIHIII I l l l ll l l l l l l | ll l l l l l | | l| | l | | | | | |J|

l

| | | |U||| | | | | |

l

| |p||| | | | | | |ni| | ITII | l l l | l l l || l | | | | | | || | | | | | | . | || | | | |niMI^

12:1ú

1 2 : 1 /

12 :1»

1^: iy

12 :20 12:2.2

12:2.i-

12 :24 12 :2ü 12:2.7 12 : 2« 12.2Ü

TIM

f

co

FIGURE

5 9 .

COALSCAN

3 5 0 0

ASH

MONITOR

TRIAL

AT

ASKERN

COLLIERY

-

VARIATION

OF

BARIUM

COUNTRATE AND ASH CONTENT MEASUREMENTS AS MEASURING HEAD OSCILLATED OVER

STATIONARY CONVEYOR SPREAD WITH EVEN LAYER OF WELL MIXED - 1 MM COAL SAMPLE.



i/l

CL

Ü

O

O

O

c -

' \

4

CD

I

5

anin

[HIIWMIUIIII

HN|unM iiiiiiniiiii|M M iniiiniiiiiii

[iiiiii

imiiiiii

i i i[iiii i i i i

II

i i i i i i i i i|ii i iMi

II

iiiii

M I

ii|iiii

I I I

IIIIIIIMI

■

■■■■■■¡■■l|HIIIIIIUIIUIIII|IIIHMIIIUMIHmnnill

HIHI

13:04

3: b 2: 6 3:ü7

1 3:0Ü

2: 9 3: 2: 2: 2 2: 2 2: 4

12:1

5

'I IM E

ro

co

ro

FIGURE 60. COALSCAN 3500

ASH MONITOR TRIAL

AT ASKERN COLLIERY

VARIATION

OF AMERCIUM

AND BARIUM

COUNTRATES

AND

COMPUTED

ASH

CONTENT

AS

MEASURING

HEAD,

WITH

STANDARDISATION

RAnTATTON

ABSORBERS ATTACHED TO DETECTOR, OSCILLATED OVER CONVEYOR RUNNING EMPTY.



233

C E

■

M

X

V)

< r

>

oc

o

f-

o

m

<r

24 -•

21

-•

18

-■

15

-

12

—

_ .

- •

1

■

■

,

□

DJ

■ ■

i—i—i i ;— ■ i i

| — i — i — ■

; ■ ■ — i — | — i — i — i — |

: D

□

. . .S i .

O . . . - ^ T . . . . ¿ I

Jr

D

i ;

D

D

\

,

,

,

,.-

. ._

.,

1.92

1.94

1.96

1.98

2

2.82

2.84

2.86

2.88

L06. RATIO

FIGURE

61.

SEVENTH

DYNAMIC

CALIBRATION

FOR

ASKERN

BLENDED

COAL

(25

mm

-

0)

WITH

COALSCAN

3500

ASH

MONITOR.



234

■ i i

N

X

(/)

Œ

>

C C

O

H

<r

28 —

24

—

20 -

16

12

:

:

:

D

- |

1

'3P

.;

:

r D . v ï T :

i ^ Q

D

¿F

V

D

C

J^TTD

J

I

I

l_

1.98

2.82

1 1 1 , 1 1

■ ■ i ■ ■

2 . 9 6

2 . 1

LOG. RATIO

2 . 1 4 2 . 1 8

FIGURE

6 2 .

STATIC

CALIBRATION

FOR

ASKERN

BLENDED

COAL

SAMPLES

( - 2 1 2 p i ) FROM SEVENTH DYNAMIC CALIBRATION WITH COALSCAN

3 5 0 0 ASH MONITOR.



235

fi

t o

< r

(D

z

HH

Q

<Z

LU

te

K

_l

<C

O

o

22

-

20 -

18

-

16

-

14

-

12

10

i i i

T

i n n

■ j^ * * - ^£ f å -Q -Q» f

Ksr. □

D

D

a j a

JJL

B . . . .

D

1

■ ' ' ■ ■ ■ '

_i

i L

J i i_

10 12

14

16

18

LABORATORY

ANALYSIS

ASH

V.

28 22

FIGURE 63. COALSCAN 3500 ASH MONITOR TRIAL AT ASKERN COLLIERY

-

RELATIONSHIP

BETWEEN

COALSCAN

SHIFT

INTEGRATION

AND

LABORATORY

SHIFT

ANALYSIS

FOR

99

SHIFTS.



236

X

<L

(D

<r

o

CO

22 -

2ø

18

16

14

12

10

- • l

i ■ ■ ■ i ■ ■ ■ » ■ ■ » L__L

10

12

14

16

18

LABORATORY

ANALYSIS

ASH

'/.

20

22

FIGURE 64. COALSCAN 3500 ASH MONITOR TRIAL AT ASKERN COLLIERY

-

RELATIONSHIP

BETWEEN

COALSCAN

SHIFT

INTEGRATION

AND

LABORATORY

SHIFT

ANALYSIS

FOR

104

SHIFTS.



237

x

•H

22

20

18

16

—

14

12

10

—

■

•

-

- y ^ r f T

i

,

^ îBà .S f fe r r t

D

\ ^

vU

^^ rrr ^

C°Ln&;.......

L...

J. i i 1 1 1 1 1

I — I — l - 1

. ._

-

10

12

14

lé 18

LABORATORY ANALYSIS ASH V.

28

22

FIGURE 65. PHASE 3A ASH MONITOR INSTALLATION AT ASKERN COLLIERY

RELATIONSHIP

BETWEEN

PHASE

3A

SHIFT

INTEGRATION

AND

LABORATORY

SHIFT

ANALYSIS

FOR

104

SHIFTS.



X

Ol

<

>

Œ

O

<

cr

o

m

<

2

UJ

ST

lü

Œ

D

O í

<

lü

2 L

Z

<

O

0]

_l

<

o

U

8

B

-2 -

-4 -

-6

-

- a

»-

JL_L1

20

40 »

m

BO

a o

100

120

ro

cs

FIGUR E 66. COALSCA N 3500 ASH MONITOR TRIAL AT ASKERN COLLIER Y - DIFFE RENCE BET WEEN COALS CAN SHIF T

INTEGRATION AND LABORATORY SHIFT ANALYSIS FOR 99 SHIFTS.



6 r

r

en

<

ir

o

B -

<

d 4

O

tn

<

i s

Z

U J

t u

(T

D

01

<

111

* -2

Z

<

01

O

u

.^-20"^ «

40

BO

BO

¿00

ISO

co

ID

-6 r

- a »-

FIGURE 67. COALSCAN 3500 ASH MONITOR TRIAL AT ASKERN COLLI ERY - DIF FERE NCE BETWEEN COALS CAN

SHIFT INTEGRATION AND LABORATORY SHIFT ANALYSIS FOR 108 SHIFTS.



I

en

<

>

c

o

I-

<

cc

o

m

<

8

tü

r

lü

d

r>

01

<

ÜJ

<

kJ

0)

<

at a

« » ■

m »

Ü .

»

»

20

40

60

O P 100

ISO

-2

«

•te

o

-B

«

-a

S H I F T S

FIGURE

68.

PHASE

3A

ASH

MONITOR

INSTALLATION

AT

ASKERN

COLLIERY

-

DIFFERENCE

BETWEEN

PHASE

3A

SHIFT

INTEGRATION

AND

LABORATORY

SHIFT

ANALYSIS

FOR

108

SHIFTS.



1 Conveyor Unit

2 Inlet Chute

3 Clean-off Scraper

4 Scraper

5 Turntable

6 Outlet Chute

7 Drive Motor/Gearbox Unit

8 Discharge Detecting Doppler

Unit Optional)

9 Air Blower Duct

10 Compression Plate

11 Eccentric Guide

12 Peripheral Side wal I

13 Proportional Counter and

Pulse Amplifier assembly

14 Radiation Source

ţ DISCHARGE

FIGURE 6 9 . NCB/AERE PHASE 3A ASH MONITOR FOR SUB-STREAM MONITORING 9 6 1 2 / 1 )



COMPACTION CHAMBER

COMPRESSION PLATE

NUCLEONIC MEASURING'

HEAD

FEED HOPPER

BELT FEEDER

WITHOUT DRIVE UNIT

DOUBLE-ACTING HYDRAULIC CYLINDER

FIGURE 70. SKETCH FOR ORIGINAL DESIGN OF EXPERIMENTAL RAM-FEED SAMPLE PRESENTATION UNIT FOR SUB-STEAM MONITORING.



243

.•*•* ìC-

tG U R E 7 1 . M O D I F IE D E X PE R IM E N T A L RA M - FE E D PR E S E N T A T I O N U N I T I N C O R P O RA T I N G

STAINLESS STEEL TROUGH AND SHOWING NUCLEONIC M EASURING HEAD M OUNTED

ON IN D E PE N D E N T S U PPO RT S ( 9 3 9 8 / 2 ) .



244

1200H

1100—

1000-

800.

T

3

12

~r

15

18

n

21

COMPRESSION (MM)

FIGURE 72. EXPERIMENTAL RAM-FEED PRESENTATION UNIT - TYPICAL RELATIONSHIP

BETWEEN BACKSCATTER COUNTRATE AND MATERIAL COMPRESSION.



245

uu «,

9 12 15

COMPRESSION (MM)

FIGURE 73. EXPERIMENTAL RAM-FEED PRESENTATION UNIT - HYDRAULIC PRESSURE

REQUIRED TO PRODUCE INCREASING MATERIAL COMPRESSION AT DIFFERENT

MOISTURE LEVELS.



246

B L E N DE D C O A L 8 5 0 t / h

- 5 0 nun

N

C

D I V E R T E R

A U T O M A T I C

X

M A N U A L

D I V E R T E R

T R A V E R S I N G S UC KE T S A M P L E R

F E E D E R

C R U S H E R

D O

- 2 5

mm

— C A L I B R A T I O N

S A M P L E S

FEEDER

0 0

C R U S H E R

- 5

mm

M O I S T U R E I

I

S A M P L E L J

1 - 5 0

mm

A

X A U T O M A T I C

*

N

D I V E R T E R

I I M O I S T U R E

S A M P L E

P N

D

D I V I D E R

L A 3 0 R A T 0 R Y

S A M P L E

T O R A P I D

L O A D I N G B U N K E R S

FIGURE 74. SCHEMATIC ARRANGEMENT OF COLLIERY SAMPLING SYSTEM AND RAM-FEED

UNIT TRIAL CIRCUIT AT MARKHAM COLLIERY.



REJECTS

COAL

ED

["RAM HEAD (RETRACTED)

rHYDRAULIC CYLINDER

STROKE

RAM HEAD

(ADVANCED)

U.

"- GUIDE

BLOCKS

? REJECT

SCAPINGS

.SUPPORT

STRUCTURE

ffî

&

M

ro

J»

FIGURE 75.

ü^fíÜÜ™

E X P E R I M E N T A L

RAM-FEED PRESENTATION UNIT. FOR INSTALLATION AT COLLIERY TRIAL SITE

WITH SECOND OUTLET FOR SCRAPINGS AND PROPOSED FEED AND REJECT SCREW CONVEYOR.



248

FIGURE 76. RE-DESIGNED, EXPERIMENTAL RAM-FEED UNIT INSTALLED AT COLLIERY TRIAL

SITE WITH FEED SCREW CONVEYOR DELIVERYING TO FEED HOPPER AND COMPACTED

MATERIAL IN PRESENTATION TROUGH (12,056/1)



249

100 - |

iu

N

M

t/5

Oí

W

Q

z

>

H

<

80 -

60 -

40 -

20 -

SCREEN SIZE

MM

x UN-CRUSHED PRODUCT

• 50.8 MM CRUSHER GRIDS

© 2 5 . 4

MM

CRUSHER GRIDS

0

12.7 MM

CRUSHER GRIDS

FIGURE 77. TRIAL OF EXPERIMENTAL RAM-FEED UNIT AT MARKHAM COLLIERY -

SIZING CURVES FOR 50 mm - 0 BLENDED COAL AND PRODUCTS FROM

CRUSHER WITH DIFFERENT SIZE CRUSHER GRIDS.



250

FIGURE 78. TRIAL OF EXPERIMENTAL RAM-FEED PRESENTATION UNIT AT COLLIERY

SITE - SURFACE PROFILE OF COMPACTED BED WITH COARSE (-25 mm) MATERIAL

(12,056/3).



251

FIGURE 79. TRIAL OF EXPERIMENTAL RAM-FEED PRESENTATION UNIT AT COLLIERY SITE

- SURFACE PROFILE OF COMPACTED BED WITH FINE (-6 mm) MATERIAL

(12,056/2).



252

FEED

HOPPER

FUTURE NUCLEONIC

MEASURING HEAD

LEVEL

SENSORS

HYDRAULIC

CYLINDER

SCRAPINGS

MATERIAL

DISCHARGE

SECTIONAL ELEVATION

1 —

1

—

T

_ L _

—r

i _

H

■ n

i

i

: z ]

s

PUN

FIGURE

80 DIAGRAM

ILLUSTRATING

MAIN

DESIGN

FEATURES

OF

PROTOTYPE

RAM FEED PRESENTATION UNIT



L t

L.J

1 fr

J

POlTPROFnCNC

OU l f

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ititi

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REFERE

HOI

» M I - K A M

UMI

ANO

MMCSSUtC

F IA I I .

i-m

m o t - s u o i

uniti

HOI

t ] I M - M U t

ANO

OUIlt t

CHMCS

HOI

I lt lO-NtCHAMCAl

OEMS

HOI

IMOO-FIASIK

IHOUCH

f lEMSDN

AMO

CHUIf

IHHHO

H O I

m o t - s u F r o m s

AN O

O M O » .

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u

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ire

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H«

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FISE

-

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BMC

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ro a

oxe

re to ca

-

ON C F E E D E * « I O U M C D

IGUR

81. GENERAL ARRANGEMENT DRAWING OF PROTOTYPE RAM FEED PRESENTATION

UNIT.



254

*/.

,

*, ¿t

f

4

' IGURE 8 2 . GENERAL VIEW OF PROTOTYPE RAM - FEED PRESE NTA TION UN IT WITH

P O L Y P R O P Y L E N E T R O U G H S E C T I O N F O L L O W I N G S T A I N L E S S S T E E L C O M P R E S S I O N

ZON E (R A MS E Y 1 0 9 5 8 ) .



255

FIGURE 83. REAR VIEW OF PROTOTYPE RAM-FEED PRESENTATION UNIT SHOWING

CUT-OUTS IN FEED CHUTE CASING FOR LEVEL SENSORS AND

HYDRAULIC CYLINDER ENCLOSURE (RAMSEY

10960).



PLUTONIUM 238

BACKSCATTER

1

PROPORTIONAL

COUNTER

(PX 425)

y

CHARGE

SENSITIVE

PREAMPLIFIER

(NE5289/B)

H.T.

SUPPLY

(NE 4660)

SPECTROSCOPY •

AMPLIFIER

(NE 4658)

SPECTRUM

STABILISER

(CANBERRA 2050)

in

oí

ENERGY

ANALYSER

(NE 4664)

DUAL

COUNTER

TIMER

(NE 4681)

RS 232

DATA PATH *""

m

DTGTTAI.

~~ CONTROL

ASH CALCULATION

AND DISPLAY

COMPUTER

(FCL 6000)

PROGRAMMABLE

LOGIC

CONTROLLER

(MITSUBISHI F2-40)

FIGURE 84 . BLOCK DIAGRAM OF ASH MEASURING AND CONTROL SYSTEM FOR PROTOTYPE RAM-FEED ASH MO NITOR.



RECEIVING

HORN

TRANSMITTING

HORN

DETECTOR

COAL

SAMPLE

VARIABLE

ATTENUATOR

QUNN

DIODE

l \>

1<s

TUNED RECTIFIER LOO

FILTER CONVERTER

L.J

DISPLAY

MODULATED

POWER SUPPLY

FIGÖRE 8 5 . BLOCK DIAGRAM OF SOLID STATE X BAND MICROWAVE MOISTURE METER.



258

/ T r a n a m m a r

Vartteal Prof»« Plat*

SMawaH

Scraper

FIGURE 86. NCB/AERE PHASE 3A ASH MONITOR INCORPORATING X BAND

MICROWXAVE MOISTURE METER.



ASH

MONITOR

M O I S T

UftC

METER

BELT

WEIGHER

INTERFACE

OTHER

COLLIERY

SIGNALS

FERRANTI

ARGUS

COMPUTER

1 1

TELETYPE

*

no

U3

FIGURE

8 7 .

£««£?£££

i S ? T S S i s

a w a

'

1

"

0

— *

WEIGHTKD

C M

™

ÏAU

*

« -



ASM MONITOR ELECTRONICS

MONITOR

OS

O

FIGURE 88 . DEDICATED MICROPROCESSOR SYSTEM AT MOMKTONHALL COLLIERY FOR DISPLAY AND PRINT-OUT OF

INTEGRATED ASH, MOISTURE AND COMPUTED CALORIFIC VALUES.



T M N S M I T T I N S

MOWN

MOOULATCO

POWER

SUPPLY

COM.

SAMPLE

MEAO

AMPUTIER

ro

MICROPROCESSOR

20mA

SERIALLINK

FIGURE 89. PROTOTYPE S BAND DISCRETE SAMPLE, MICROWAVE MOISTURE METER.



MICROWAVE SOURCE

RCñ l 8 0 2 n i CROCOf l P UT E R

DETECTOR & AMPLIFIER

NDICATORS

M

HIGH SPEED

ANALOGUE TO

DIGITAL CONVERTER

no

OUTPUTS

FIGURE 90. SCHEMATIC DIAGRAM OF RE-DESIGNED FIXED FREQUENCY, MICROWAVE MOISTURE SYSTEM WITH H IGH

(GO dB) DYNAMIC RANGE.



263

Pj±ASE3A_ASH/MOISTURE MONITOR

ASH SIGNAL MOISTURE SIGNAL

—

ANALOGUE

INTERFACE

ANALOGUE TO DIGITAL

CONVERTER

&

MULTIPLEXER

RCA1802

MICROCOMPUTER

3.5"

DISC

DATA LOGGER

FIGURE 91. DIAGRAM OF DATA LOGGER RECORDING SIGNALS FRON PHASE 3A ASH/NOISTURE

MONITOR.



264

BELT

WEIGHER

SIGNñL

ULTRASONIC

BED DEPTH

SIGNAL

—

MOISTURE

SIGNñL

ñNñLOGUE

INTERFñCE

ANALOGUE TO DIGITAL

CONVERTER

&

MULTIPLEXER

RCñl802

MICROCOMPUTER

3,5

U

DISC

DñTñ LOGGER

FIGURE 92. DIAGRAM OF DATA LOGGER RECORDING SIGNALS FRON BELT WEIGHER

AND BED DEPTH AND MOISTURE METERS.



RANGING

BOARD

PULSE

COUNTER

DIGITAL TO

ANALOGUE

CONVERTER

DISTANCE

TO

DEPTH

CONVERTER

LIQUID

CRYSTAL

DISPLAY

AMPLIFIER

TRANSDUCER

OUTPUT

ø.ifV - 2.0V)

D

ro

in

OUTPUT

0-1.GV)

SIGNAL

PATH

VOLTAGE TO

CURRENT

CONVERTER

-a

OUTPUT

H — 20mA)

CONVEYOR

BELT

FIGURE 93. BLOCK DIAGRAM SHOWING DESIGN O F ULTRASONIC BED DEPTH METER.



BIRTELY

SAMPLER

t

c

l

SAMPLE

CRUSHER

PHASE3A

ASH MOISTURE

MONITOR

4

DATA

LOGGER

SAMPLE

REJECT

r

MICROWAVE

MOISTURE

LABORATORY

SAMPLE

n

BELT

WEIGHER

L

ULTRASONIC

t

BED

DEPTH

r^

METER

■

METER

i

5mm

-

0

BLENDED

COAL

ro

oí

DISTRIBUTING

SCRAPER

I

I

DATA

LOGGER

MICROWAVE

MOISTURE

METER

ELECTRONICS

EXCHANGE

BUNKER

A

A

Œ

TO

POWER STATION

FIGURE 94. SCHEMATIC ARRANGEMENT

OF

ON-BELT

S

BAND MOISTURE METER, ULTRASONIC BED-DEPTH METER

AND

PHASE

3A

ASH/MOISTURE

MONITOR

WITH

DATA

LOGGERS

AT

LONGANNET

NINES.



267

FIGURE 95. TRIAL INSTALLATION OF S BAND MICROWAVE MOISTURE METER AND ULTRASONIC

BED-DEPTH METER ON 25 mm - O RAW COAL CONVEYOR AT LONGANNET MINE WITH

INSTRUMENTATION AND DATA LOGGER LOCATED ALONGSIDE IN PROTECTIVE

CABINET

(12,399/1).



268

FIGURE 96. TRIAL INSTALLATION S BAND MOISTURE METER AT LONGANNET MINE SHOWING

MICROWAVE TRANSMITTING HORN AND ULTRASONIC BED-DEPTH METER MOUNTED

ABOVE BELT CONVEYOR AND MICROWAVE RECEIVING HORN LOCATED BELOW

(12,399/2).



6 38 -

u

269

2 0 - -

Q.

0)

•o

,

e

T3

tt)

OQ o

1

12 IS IB 21

24

-C 1BB8-

1 2 0 0 - -

T3

O

O

— 688-

01 8-

m i

3 E 9 12 15 IB 21 24

12 15

T i m e ( h o u r s )

FIGURE 97. TRIAL OF S BAND, ON-BELT, MICROWAVE MOISTURE METER AND

ULTRASONIC BED-DEPTH METER AT LONGANNET MINE - TRACES OF

BED-DEPTH, ATTENUATION AND BELT LOADING PLOTTED AT

1 MINUTE INTERVALS ON 22 JANUARY 1988.



270

S

M

-

-C

28

+

a

w

T3

J B - -

O

CD

e

Y ^

;

JL^

IWTy

¿¡K

f

12

15

18

21

24

m

D

e

3B j

2 4 - -

<

L

0>

1 2 - . J I — -

->

■H

<

[i

0

-C 1800 T

V .

■H

■ * •

120B

+

O

6 8 8 - •

0)

8

12

15

1B

r ^ \ p ~ ~ ^ ~

v

r

^ Y

21 24

; g 12 15 18 21 24 12 15 18

T i m e h o u r s

FIGURE

9 8 .

TRIAL

OF S

BAND,

ON-BELT,

MICROWAVE

MOISTURE

METER

AND

ULTRASONIC

BED-DEPTH METER ATIONGANNET MINE -TRACES

OF BED-DEPTH, ATTENUATION

AND

BELT

LOADING

AVERAGED

OVER

5

MINUTE

INTERVALS

ON

22

JNAUARY

1 9 8 8



271

u i

x

(9

Li

680 -

509

—

400

-

300

-

200 -•

løø

-

ø -•

, , , . , , , . , . . . , , , , , , , , , , , , j T - n - r | . . . ¡

-

1

■

'

D

D

.

.

.

h

n r f i f rP iS i r n -

ö

D

;

. . . i . . . i . . . i . . .

: -

»

™

: -

:

-

L_L

1

1

1

6

8

19

BED

DEPTH

METER

<CM>

12

14

16

FIGURE 99. TRIAL OF ULTRASONIC BED-DEPTH HETER AT LONGANNET NINE -

CALIBRATION

GRAPH

OF

BELT

WEIGHER

READINGS

AGAINST

BED

DEPTH

METER

READINGS

INTEGRATED

OVER

5

MINUTE

INTERVALS

DURING

5

HOUR

PERIOD

ON

22

JANUARY

1988.



22GHz

SOURCE

1

1200 Hz

FREQUENCY

SOURCE

MICROWAVE

r u r t o o r à i í "

LnüPrlNG

CIRCUIT

HORN .

COMBINER f V -* -4

V^LJ b^

3 8GHZ

SOURCE

2

i i r w n j w z n

9 2

H z

SSÄ

SAMPLE

U n ü r r l N ü

CIRCUIT

SEPARATOR

. H O R N

V V . . M 1

RECEIVER,

CHOPPING

FREQUENCY

SOURCE

i.

SIGNAL

k .

SIGNAL OUT

PROPORTIONAL

TO MOISTURE

SIGNAL

SUBTRACTOR

^ t r A K A J U K

INJ

««J

FIGURE 100 . SCHEMATIC DIAGRAM OF PROPOSED TWO FREQUENCY MICROWAVE MOISTURE

METER.



273

SWEPT

RF

SOURCE

3 dB

SPLITTER

DETECTOR

RAMP

6500 SCALER ANALYSER

m

A B R

o

o

IEEE

BUS

INTERFACE

t

TRANSMITTING

HORN

RECEIVING

HORN

DETECTOR

FIGURE 101. SCHEMATIC ARRANGEMENT OF LABORATORY SWEPT FREQUENCY

MICROWAVE SYSTEM.



d B

- 2 8 , 8 8 -

- 2 5 . 8 8

-î

- 3 8 . 8 8 -

■

-35.88-î

-48.88

ì

-45.88

-i

7 188fts

Sweep

ro

■Ck

' 5 8 . 8 8 I » i » 11 11 1 1 1 1 1 1 11 1 11 1 1 1 11 1 1 1 1 1 1 11 1 1 1 1 1 1 11 1 1 1 11

5.88 5.22 5.44 5.67 5.89 6.11 6.33 6.56 6.78 7.88

6 H Z

FIGURE

102.

LABORATORY

SVEPT

FREQUENCY

MI

CROWS

E

SYSTEM

-

ATTENUATION

SCAN

(5-7

GHz)

AND

LINEAR REGRESSION FOR PARROT CROP SEAM WITH 14.3% MOISTURE.



d B

0 . 6 8

- 5 . 8 8 -i

- 1 8 . 8 8 - i

- 4 8 . 8 8 -

- 4 5 . 8 8 -i

■

■

i

■

■

■

i

.

.

.

i

.

i

■

.

•

i

i

i

■

i

,

i

i

,

1 8 8 n s

S w e e p

'58.88

1 1 1

11

;

1 1

»

1 1

1 1 1

11

1 1 1

1 1 1 11

1 1 1

1 1 1

1 1

1 1 1

1 1 1 11

1 1 1 11

5 . 8 8 5 . 2 2 5.44 5 . 6 7 5.89 6.11 6.33 6.56 6.78 7.88

G H Z

ro

en

FIGURE 103. LABORATORY SWEPT FREQUENCY MICROWAVE SYSTEM - ATTENUATION SCAN (5-7 GHz) AND

LINEAR

REGRESSION

FOR

PARROT

CROP

SEAM

WITH

16.

2

MOISTURE.



e

■ ■ ■ ■ ■

■

■

•

■

1

■

■

■

.

1

.

■

■

■

1

•

i

■

l

■

I

I

I

ì

1

I

I

I

I

L

d B

4 8 . 8 8

4 5 . 0 8 J

■ 5 8 8 8

-

1 8 8 n s

S w e e p

I

I

I

I

|

I

I

I

I

|

I

I

I

I

|

I

I

I

I

|

I

M

I

|

I

I

I

|

I

I

I

I

|

I

I

I

I

|

I

I

I

5 . 8 8 5.22 5.44 5.67 5.89 6.11 6.33 6.56 6.78 7.88

6 H Z

ro

FIGURE

104.

LABORATORY

SWEPT

FREQUENCY

MICROWAVE

SYSTEM

-

ATTENUATION

SCAN

(5-7

GHz)

AND

LINEAR

REGRESSION

FOR

PARROT

CROP

SEAM

WITH

18.7 MOISTURE.



d

8,1

-5 . 88

-18 .88

-3

- 1 5 . 8 8 - ;

-28 .88 -

- 2 5 . 8 8 - i

-38 .88 -i

-35 .88 •■

- 4 8 . 8 8 - í

-45 .88 -i

- u i

J-U UL

■

■ ■ ■ ■ i i i I i i I

l i l i

-58 . 88

i

i

i

i

|

i

i

i

i

i

i

i

|

i

i

i

i

i

i

i

i

r

i

i

i

i

i

i

i

|

i

i

r

f

188ns

Sweep

ro

5.88 5 .22 5 .44 5 .67 5 .89 6 .11 6 .33 6 .56 6.78 7 .88

GHZ

105.

LABORATORY

SWEPT

FREQUENCY

MICROWAVE

SYSTEM

-

ATTENUATION

SCAN

(5-7

GHz)

AND

LINEAR

REGRESSION

FOR

PARROT

CROP

SEAM

WITH

20.0 MOISTURE.



d B

8.88

-5.88

-18.88 -3

-15.88

-28.88-i

-25.88

-,

-38.88

ì

-35.88-i

-48.88

-45.88 «i

i

i

i

i

i

i

i,

i

M i i L

i

i

i

;

i

i

i

■

I

i

i

i

i

r

188ns

Sweep

' 5 8 . 8 8 - 1 1 1 1 1 1 1 1 1 1 » ' i i [ 1 1 i i 1 1 1 1 1 1 1 1 1 ' 1 1 1 1 1 1 1 ' i i i 1 1 i

5.88

5.22

5.44

5.67

5 .89

6 .11

6 .33

6.56

6 .78

7.

G H Z

r o

00





dB

-48 .88 -i

- 4 5 . 8 8 - i

I I • I I ' I L

1 I I I I

\r 168ns

Sweep

5 8 . 8 8 i i i 1 1 i i i i i | i i i 1 1 1 1 1 i 1 1 1 1 i | i 1 1 i 1 1 1 1 i 1 1 ' i i 1 1 i i i

5.88 5 .22 5 .44 5 .67 5 .8 9 6 .11 6 .33 6 .56 6 .7 8 7 .

GHZ

1 0

FIGURE 107. LABORATORY SWEPT FREQUENCY MICROWAVE SYSTEM - ATTENUATION SCAN (5-7 GHz)

AND LINEAR REGRESSION FOR PARROT CROP SEAM WITH 23.2 % MOISTURE.



Q Q [ ■ ■ ■ t l i : ■ 1 ' I I ■■

I

I

'

I

I

I

I

i

I

I ■

I

I

II

d B

-5.88 ■;

-18.88-;

-15.88-i

-28.88

-25.88

-38.88

-35.88

-48.88

-45.88

-58.88

7

188ns

Sweep

1 1 1 1 1 1 1 1 1 1 1 1 1 i c 1 1 1 1 1 1 1 1 1 1 1 » i 'i 1 1 1 1 1 1 1 1 > i 1 1 1 1 1

5.88

5.22

5.44

5.67

5.89

6.11

6.33

6.56

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GRADIENT FOR SEVEN SEAMS FROM BLINDWELLS OPENCAST SITE.



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ELECTRONIC

MEASUREMENT

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INSULATED

PLATE

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FIGURE 115.

ELECTRONIC MEASUREMENT SYSTEM FOR EXPERIMENTAL INSULATED PLATE

CAPACITANCE

CELL

WITH

AUTOMATIC

STABILISATION

OF

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AMPLIFER

OUTPUT

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1400

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FIGURE 116. LABORATORY TESTS WITH EXPERIMENTAL INSULATED

CAPACITANCE CELL RELATIONSHIP BETWEEN INSTRUMENT

READING AND ADDED MOISTURE WITH INCREASING IONIC

SALT

CONTENT.



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CAPACITANCE CELL - CALIBRATION GRAPH FOR WASHED SMALL

COAL FROM MARKHAM COLLIERY.



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FIRST DERIVATIVE ABSORPTION SPECTRUM

FOR

WET

COAL



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FIGURE 119. FREE INDUCTION DECAY SIGNAL FOR WET COAL.



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CALIBRATION

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SUITES

5

AND

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DISPLAY/

CONSOLE

AIR

CONDITIONING

UNIT

ENVIRONMENTAL

ENCLOSURE

LEVEL

DETECTOR

COAL FEED

COAL

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FIGURE 122. S.A.I.C. 'CONAC' - SCHEMATIC SE CTION



295

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DISPLAY UNIT

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DETECTOR

COAL

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MOISTURE METER

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FIGURE 123. MDH - MOTHERWELL INC. 'ELAN' - SCHEMATIC SECTION.



2.1 m

COAL

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FEED

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LEVEL

DETECTOR

SIGNAL

PROCESSOR

H DISPLAY/

CONSOLE

NEUTRON

SOURCE

SHIELDING

7.3 m

COAL

DISCHARGE

FIGURE 124 . GAMMA METRICS 'COAL ANALYSER' - SCHEMATIC SECTION.

Coal Quality Monitoring

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