TRANSPORTATION OF DRY FLYASH: ISSUES FOR

CONSIDERATION

By

V.K.Agarwal

 Indian Institute of Technology, Delhi

 

Figure 9 Sketch of Particulate Flow in Dilute Phase Conveying

Mode of Conveying

Dilute Phase - Suspension Flow:

Requirements None

Pick-Up Velocity 12 m/s fine powders (minimum)

16 m/s fine granules

for horizontal conveying

Figure 11 Sketch of Particulate Flow in Moving Bed Flow

Mode of ConveyingDilute Phase - Suspension Flow

Requirements NonePick-Up Velocity 12 m/s fine powders (minimum) 16 m/s fine granules

Dense Phase - Non-Suspension FlowSliding Bed Flow:

Requirements Good Air Retention

Pick-Up Velocity 3 m/s (minimum)

 

Figure 14 Sketch of Particulate Flow in Plug Type Flow

Mode of ConveyingDilute Phase - Suspension Flow

Requirements NonePick-Up Velocity 12 m/s fine powders (minimum) 16 m/s fine granules

Dense Phase - Non-Suspension FlowSliding Bed Flow:

Requirements Good Air Retention

Pick-Up Velocity 3 m/s (minimum)

  Plug Flow: 

Requirements Good PermeabilityPick-Up Velocity 3 m/s

Solids Loading Ratio

a

p

m

m

63

where ϕ = solids loading ratio

= mass flow rate of material - tonne/h

and = mass flow rate of air used - kg/s

pm

am

(dimensionless) - - (3)

Diagram to Illustrate the Wide Range of Conveying Systems Available for Conventional Systems Operating With a Single Air Source

Sketch of Typical Negative Pressure Conveying System

Ash Accumulation Points and Typical Ash Distribution of a Dry Bottom Furnace

Typical Arrangement of Electrostatic Precipitator Ash Collection Hoppers

Pneumatic Ash Removal Systems with Conveying Parameters Indicated

Typical Dry Fly Ash Handling Arrangement at a Power Station

CONVEYING CAPABILITY

In Terms of• Material Flow Rate• Conveying Distance• Minimum Conveying Air Velocity• Power Requirements

Depends Upon:• Pipeline Bore

• Pipeline Length

• Pressure Drop Available

• Material Properties

Parameters Relating Compressor Rating with Material Flow Rate

Influence of Solids Loading Ratio on Conveying Air Velocity for Fine and

Coarse Grades of Flyash

Sketch of Test Facility Pipeline at the IIT

Pipeline Details:

Bore - 63 mm Length - 133 m

Bends - 10

Conveying Characteristics for Fine Grade of Fly Ash with Conveying Line Inlet Air Velocity Data

Superimposed

Conveying Characteristics for Coarse Grade of Fly Ash with Conveying Line Inlet Air Velocity Data

Superimposed

Air Mass Flow Rate - kg/s

Fly

Ash

Flo

w R

a te

- t o

nne/

h

24

20

16

12

8

4

0

Conveying line pressure

drop - bar

Solids loading ratio

Conveying limit

0 0·04 0·08 0·12 0·16

Conveying line inlet air

velocity - m/s

152·0

14161820

0·40·8

1·2

1·6 10

5

NO

GO

AREA

Air Mass Flow Rate - kg/s

24

20

16

12

8

4

0

Conveying line pressure drop

- bar

Solids loading ratio

Conveying limit

0 0·04 0·08 0·12

Conveying line inlet air velocity - m/s

NO

GO

AREA

20

10

30

40

506080

160 120 4 6 8 10

12

1∙4

0·40·8

1·2

1·6

2·0

100

Fly

Ash

Flo

w R

a te

- t o

nne/

h

a) Coarse fly ash b) Fine fly ash

Figure 5 Comparison of Conveying Characteristics for Fine and Coarse Grades of Fly Ash in IIT Pipeline

1·8

14

Conveying Parameters for Design Cases Considered in Relation to 63 mm Bore Line

 

 

 

Reference Point

Pressure Drop(bar)

Air Flow Rate (kg/s)

Inlet Air

Velocity (m/s)

Solids Loading Ratio

Fly Ash Flow Rate (tonne/h)

Test Loop

Plant Test Loop

Plant

1 1.8 0.038 3.7 150 103 20.5 14.1

2 1.3 0.060 7.2 55 40 11.8 8.64

3 1.0 0.090 12.3 20 16 6.6 5.22

4 0.8 0.087 13.2 14 11 4.5 3.59

Fly Ashy Flow Rate in Plant Pipeline of Various Bores for Range of Conveying Line

Pressure Drops Considered

Pipeline Bore(mm)

Fly Ash Flow Rate – (tonne/h)

Conveying Line Pressure Drop – (bar)

1.8 1.3 1.0 0.8

150 80 51 33 23

200 144 91 60 41

250 226 144 95 65

300 325 209 138 94

Sketch of a Typical Vacuum Conveying System Incorporating a Stepped Pipeline for

Conveying Different Grades of Fly Ash

Conveying air Velocity Profiles for the Conveying of both Coarse and Fine Ash in a

Common Negative Pressure Conveying System

RECOMMENDED OPTIONS FOR COAL ASH HANDLING AND SAFE DISPOSAL