Pneumatic Conveying of Solids

Powder Technology Series

EDITED BYBRIAN SCARLETTDelft University of TechnologyThe Netherlands

and GENJI JIMBOChubu Powtech Plaza LabJapan

Many materials exist in the form of a disperse system, for example powders,pastes, slurries, emulsions and aerosols. The study of such systems necessarilyarises in many technologies but may alternatively be regarded as a separatesubject which isconcerned with the manufacture, characterization and manipulationof such systems . Chapman & Hall were one of the first publishers to recognizethe basic importance of the subject, going on to instigate this series of books.The series does not aspire to define and confine the subject without duplication,but rather to provide a good home for any book which has a contribution tomake to the record of both the theory and the application of the subject. Wehope that all engineers and scientists who concern themselves with dispersesystems will use these books and that those who become expert will contributefurther to the series.

Particle Size MeasurementTerence Allen5th edn, 2 vols, hardback(0412753502),552 and 272 pages

Chemistry of Powder ProductionYasuo AraiHardback (0412395401),292 pages

Particle Size AnalysisClaus BernhardtTranslated by H. FinkenHardback (0412558807),428 pages

Particle ClassificationK. HeiskanenHardback (0412493004), 330 pages

Powder Surface Area and PorosityS. Lowell and Joan E. Shields3rd edn, hardback (0412396904),256 pages

Principles of Flow in Disperse SystemsO. MolerusHardback (0412 40630 6), 314 pages

Processing of Particulate SolidsJ.P .K. Seville, U. Tiizan and R. CliftHardback (0751403768), 384 pages

PneumaticConveying of Solids

A theoretical and practicalapproach

Second edition

G.E. KlinzingProfessor of Chemical Engineering

University of Pittsburgh, USA

RD. MarcusMorgan Education Technologies (pty) Ltd, South Africa

andKey Centre for Bulk Solids and Particulate Technologies

University of Newcastle, Austra lia

F. RizkProfessor Dr Ing. and Senior Engineer

Technical Research and Development DepartmentBASF-Aktiengesellschaft, Ludwigshafen, Germany

and the lateL. S. Leung

Commonwealth Scientific and Industrial Research OrganizationAustralia

Springer-Science+Business Media, B.Y.

First edition 1990

Second edition 1997

© 1990 R.D . Marcus, L.S. Leung, G.E. Klinz ing and F. Rizk

© 1997 G .E. Klinzing, R .D . Marcus and F. RizkOriginally published by Chapman & Hall in 1997.Softcover reprint of thehardcover2ndedition 1997

Typeset in 10/12 Times by AFS Image Setters, Glasgow

ISBN 978-94-015-8983-3 ISBN 978-94-015-8981-9 (eBook)DOI 10.1007/978-94-015-8981-9

Apart from any fair dealing for the purposes ofresearch or private study , orcriticism or review, as permitted under the UK Copyright Designs and PatentsAct , 1988, this publication may not be reproduced, stored, or transmitted, inany form or by any means, without the prior permission in writing of thepublishers, or in the case of reprographic reproduction only in accordancewith the terms of the licences issued by the Copyright Licensing Agency inthe UK, or in accordance with the terms of licences issued by the appropriateReproduction Rights Organisations outside the UK. Enquiries concerningreproduction outs ide the terms stated here should be sent to the publishersat the London address printed on this page.

The publisher makes no representation, express or implied, with regard tothe accuracy of the information contained in this book and cannot accept anylegal responsibility or liability for any errors or omissions that may bemade .

A catalogue record for thi s book is available from the British Library

r§ Printed on permanent acid-free text paper, manufactured in accordancewith ANSIjNISO Z39.48-1992 and ANSIjNISO Z39.48-1984 (Permanence ofPaper).

Contents

Preface to the first edition

Preface to the second edition

Foreword

Nomenclature

xi

xiii

xv

xvi

1 An overview of pneumatic conveying systems and performance 11.1 Introduction 11.2 Why pneumatic conveying? 11.3 What can be conveyed? 21.4 What constitutes a pneumatic conveying system? 61.5 Modes of pneumatic conveying 81.6 Basic pneumatic conveying systems 101.7 Further classification techniques 161.8 Description and operation of a pneumatic conveying system 161.9 Putting it all together 201.10 An overview 261.11 Some useful conversion factors 26

References 34

2 Single phase flow in pneumatic conveying systems 352.1 Introduction 352.2 Definitions 352.3 Perfect gas laws 372.4 Drying of compressed air 372.5 The compression process 382.6 Gas flow through pipes 442.7 Illustrative examples 51

References 56

3 Fluid and particle dynamics 573.1 Introduction 57

vi Contents

3.2 Law of continuity 573.3 Drag on a particle 583.4 Equations for calculation of relevant properties 683.5 Fluidization characteristics of powders 78

References 81

4 Fundamentals 844.1 Introduction 844.2 Forces acting on a single particle in an air stream 844.3 Particle size 854.4 Shape 894.5 Dynamic equations 934.6 Terminal velocity 944.7 Single particle acceleration 944.8 Centrifugal flow 954.9 Slip velocity in a gravitational field 964.10 Multiple particle systems 964.11 Voidage and slip velocity 994.12 Frictional representations 1034.13 Acceleration and development regions 1064.14 Particle distribution in pneumatic conveying 1084.15 Compressibility effect not negligible 1094.16 Speed of sound in gas-solid transport 1124.17 Gas -solid flow with varying cross-sectional area 1144.18 Branching arrangements 1164.19 Bend analysis 1174.20 Downward sloping particle flow 1214.21 Dense phase transport 1234.22 Estimation of pressure drop in slugging dense phase

conveying 1274.23 Estimation of pressure drop in non-slugging dense phase

conveying 1294.24 Plug flows 1344.25 Inclined conveying 1424.26 Simulations 1444.27 Worked examples 145

References 158

5 Flow regimes in vertical and horizontal conveying 1625.1 Introduction 1625.2 Choking versus non-choking system in vertical flow 1665.3 Choking system in vertical flow 1755.4 Non-choking system in vertical flow 1855.5 Particle segregation in vertical pneumatic transport 186

5.65.7

Saltation and pick-up in horizontal conveyingCirculating fluid bedsReferences

Contents vii

188195196

66.16.26.36.46.56.66.76.8

77.17.27.37.47.57.67.7

88.18.28.38.48.58.68.78.8

9

9.19.29.3

Principles of pneumatic conveyingIntroduction - putting it all togetherThe state diagram revisitedMethods for scaling upUse of theoretical models and definitionsAdditional pressure drop factor {}I.z}Pressure dropSome important functional relationshipsSequence to be followed to obtain the system pressure loss(L1p)References

Feeding of pneumatic conveying systemsIntroduction and overall design philosophyClassification of feeding systemsFeeder selection criteriaLow-pressure feeding devicesMedium-pressure feeding systemsHigh-pressure feeding devicesConclusionsReferences

Flow in standpipes and gravity conveyorsIntroduction - standpipe and gravity conveyorsClassification of standpipe systemsClassification of flow modes in a standpipeEquations pertaining to each flow modeFlow through a valveStability of standpipe flowAnalysis of industrial standpipes - case studiesGravity conveyorsReferences

An overview of high-pressure systems including long-distanceand dense phase pneumatic conveying systemsIntroductionHigh-pressure systemsHigh-pressure conveying

198198198213216220222228

236243

244244245245246268279314314

317317317321326329333335340346

348348349349

viii Contents

9.4 Dense phase flow classification 3509.5 A description of plug flow and the relationships between

plug flow and material characteristics 3509.6 System selection and product characteristics 3549.7 Dense phase system design 3579.8 Long-distance pneumatic conveying and pressure loss

minimization 3609.9 Conclusions 372

References 372

10 Gas-solids separation 37510.1 Introduction 37510.2 Selection criteria 37510.3 Cyclone separators - theory of the separation of particles in

the centrifugal field 37810.4 Fabric filters 40410.5 Cleaning by sound 42110.6 Conclusions 421

References 422

11 Some comments on: the flow behaviour of solids from silos;wear in pneumatic conveying systems; ancillary equipment 423

11.1 Introduction 42311.2 The flow of solids from bins 42411.3 Flow aid devices for silos and hoppers 43411.4 Wear in pneumatic conveying systems 44311.5 Attrition of particles in pipelines 45911.6 Simulation and particle-wall interactions 46411.7 Ancillary equipment 46611.8 Conclusions 480

References 481

12 Control of pneumatic transport 48312.1 Basic material flow and control theory 48312.2 Transport lags 48612.3 Analysis of gas-solid flow by transfer functions 48612.4 Stability of pneumatic transfer systems 48812.5 Air control systems for pneumatic conveying systems 49012.6 Stability analysis with Taylor series linearization 49112.7 Linear stability analysis - Jackson approach 49212.8 Stability via the Liapunov analysis 49412.9 Artificial intelligence and solids processing 497

References 499

1313.113.213.313.413.513.613.713.813.913.1013.1113.1213.13

InstrumentationStandard instrumentationTransducersCross-correlation proceduresA Coriolis force meterDielectric meterLoad cellsParticle taggingElectrostatic based metersAcoustic measurementsScrew conveyorsLight measuring devicesOther techniques for particle velocitiesInstrumentation for industrial applicationsReferences

Contents ix

500500501502504505509510511516517519520524541

1414.114.214.314.414.514.614.714.814.914.1014.11

Index

System design and worked examplesIntroductionMoisture content in airThe design of industrial vacuum systemsDilute phase pneumatic conveying system design (method 1)Dilute phase pneumatic conveying system design (method 2)Dilute phase pneumatic conveying system design (method 3)Dense phase pneumatic conveying system designCost of pneumatic conveyingDesign considerationsGas-solid flow examplesConclusionsReferences

543543543546556565572578580583584590591

593

Preface to the first edition

When the four of us decided to collaborate to write this book on pneumaticconveying, there were two aspects which were of some concern. Firstly, howcould four people, who live on four different continents, write a book on a fairlycomplex subject with such wide lines of communications? Secondly, there wasthe problem that two of the authors are chemical engineers. It has been notedthat the majority of chemical engineers who work in the field of pneumaticconveying research have spent most of their time considering flow in verticalpipes. As such, there was some concern that the book might be biased towardsvertical pneumatic conveying and that the horizontal aspects (which are clearlythe most difficult!) would be somewhat neglected.

We hope that you, as the reader, are going to be satisfied with the fact thatyou have a truly international dissertation on pneumatic conveying and, also,that there is an even spread between the theoretical and practical aspects ofpneumatic conveying technology.

We have attempted to produce a book for which we perceived a need in themarket place. The book has been written taking into consideration ourexperiences in the pneumatic conveying industries , and also taking cognizanceof the days when we started off as a junior research workers in this field. Inthose early days, it was clear that a large amount of information pertaining topneumatic conveying system design was not documented in the literature. Also,there was a certain amount of scepticism amongst the industry as to theeffectivenessof research work carried out at universities. The fact that academicsworking in the field have been branded as 'one-inch' pipe technologists isindicative of the lack of confidence shown by journalists.

As such, we have attempted to address both problems and to cater for a widecross section of readers, including practising engineers, researchers, graduatestudents, plant operating personnel and the like. The text has been so arrangedto accommodate those researchers who wish to gain more insight into thefundamentals, or to provide a short circuit for those readers who wish to addressonly the design issues relating to pneumatic conveying.

For the systems designer, it is recommended that Chapter 1 be consultedand, thereafter, the reader should study Chapters 6, 7,9, 10 and 11. In Chapter

xii Preface to the first edition

8 issues pertaining to the design of air-activated gravity conveyors are discussed,whilst a number of practical system design problems are solved in Chapter 14.

The researcher wishing to gain more insight into the technology is advisedto consult chapters 3,4, 5, 12 and 13. In these chapters an attempt has beenmade to review the relevant literature.

Those issues which are deemed important, but peripheral to this text , arediscussed in Chapter 11 , where an attempt has been made to alert the readeron such issues as silo and hopper design, wear and attrition, and ancillaryequipment. All these topics are subjects in their own right, and the readerwishing to gain more insight into these aspects is advised to consult moredefinitive texts.

We hope you find this text both useful and stimulating, and that you willreap the rewards of entering into an exciting yet complex field of fluid mechanics.

R.D . MarcusL.S. Leung

G.E. KlinzingF. Rizk

Preface to the second edition

Since writing the first edition of this handbook on pneumatic conveying, anumber of developments have taken place. First, and very sadly, we bid farewellto our esteemed colleague Ming Leung who after a protracted illness passedaway. Ming will be remembered for some of the fundamental work which hedid on vertical flow and of course on the tremendous contribution he made tothe flow in standpipes. His unique skills endeared him to all those who werefortunate to be able to be associated with him, be it as a student, a colleagueor a recipient of his consulting services. Here was an academic who disprovedthe perception of many industrialists that university doyens, working in thefield of pneumatic conveying, have little to contribute to the real world oflong-distance and high volumetric throughputs. His greatest claim to fame washis involvement in the design of the world's largest standpipe in operation atthe SASOL plant in South Africa. In memory of this very special person, wehave dedicated this second edition.

Second, the ever increasing demands for environmentally friendlymanufacturingfacilities have placed a premium on the use of pneumatic conveying as a viableform of materials handling. There has been a world-wide move towards the useof this technology, allowing users to benefit from all the unique features of beingable to contain fine powdered and granular products in a pipe. Alongside thisgrowth in utilization, there has been a corresponding increase in the use oflow-velocity systems facilitating the ability to transport friable products withminimal degradation. It is evident that the technology is now well establishedand is here to stay.

Third, as authors, we are concerned at the diminishing number of academicsentering into the field of pneumatic conveying research . We are of the opinionthat whilst from an industrial standpoint there are positive signs that fewerpeople view the technology as a black art, there are still significant challengeswhich need to be overcome. We are still dealing with highly complex interactionsbewteen a gas and a solid which is on average some 1000 times more dense. Inthe field of measurement alone there is enough scope for more research, whilstthe development of the ultimate robust equation for dense phase is still a longway off. We wish to urge the vendors of pneumatic conveying systems and

xiv Preface to the second edition

equipment to do all in their power to encourage universities to establish researchfacilities geared towards finding solutions to the many vexing questions.

We have been overwhelmed with the positive response we have had frommany readers. We have also been fortunate in having received some constructivesuggestions for inclusion in this second edition. On the basis of feedback wehave attempted to improve on the linkages between the various chapters. Wehave also spent time ensuring an improved relationship between the theory andthe practice, and have included some additional worked examples . We hopethat you will enjoy this second edition as much as we have enjoyed putting itall together.

Roy Marcus, George Klinzing, Farid RizkFebruary 1996

Foreword

Pneumatic conveying is a most important practical operation whose applicationis a vital and integral part in the good design of many processes. Such a bookcan only be written from the basis of wide experience, in this case particularlyachieved by the contribution and cooperation of four authors. The bookcombines a complete description of all the aspects of pneumatic conveyingsystems as well as the technology of feeding the systems and of separating thetransported particles and the gas. A basically technological subject such as thiscan only be systematically explained from a basis of a good understanding offluid mechanics and fluid particle interactions. This book also includes adescription of all the necessary basic laws. It is a welcome addition to theChapman & Hall Powder Technology Series.

B. SCARLETT

Nomenclature

Symbol Description Unit

Ao Cross-sectional area of opening m2

A = nD 2/4 Cross-sectional area of pipe m2

Constant or index for accelerationA* Cro ss-sectional area of a particle m2

normal to flowa Speed of sound in a pure gas mlsas Speed of sound in a gas-solid mixture mlsAr = d3 p(p p - p)g Archimedes number

'12

C l, 2 Con stant with index 1, 2c Average particle velocity, bubble mls

velocity, slug velocityCc Particle velocity at choking mls

cond itionsC' Superficial solid velocity [ = c(1 - e)] mls

2FDrag coefficientC - - -D- pW2A*

CD 00 Drag coefficient for undisturbed andunbounded fluid

CN Discharge coefficient for a nozzleCt Volumetric concentrationCv Valve coefficientD Pipe inner diameter mmDo Diameter of orifice or valve opening mDB Bend curvature diameter mmd Spherical particle diameter mmdv Volume equivalent particle diameter mms, Volume surface mean diameter mmdvs Specific surface area diameter = 4 d mmEx Electric field N /C

Nomenclature xvii

F Fo rce NFr = V/(Dg)1 /2 Froude number related to air

velocityFr* = C/(Dg)1 /2 Froude number related to particle

velocityFr, = Wr/(Dg)1 /2 Froude number related to particle

fall velocityt-; = C/(dg)1 /2 Froude number related to particle

velocity and particle sizefL Air friction factorG, AG Bulk solid mass, element of bulk kg

solid massG Solid mass flow rate kg/s

kg/ht/h

Ga = pApg(4dY/tJ 2 Galileo numberGa' = pApgd;/tJ 2 Galileo numberG, = PV Gas flux kg/m 2s

Gs = G/A Solids flux kg/m -sg = 9.81 Acceleration due to gravity m/s 2

(gravitational constant)g Index for gravitationalH Ent halpy kcal /kgI R Relative turbulence intensityK,K 1,K2 Constantsk Effective pipe wall roughness mmL,AL Length, length of element mM Mass of gas kgM w Molecular weight kg/kgmolmp Particle mass kgn Number of particles in an element,

Number of events or as exponentP Powe r of blower W,kW

P Absolute pressure Pa,kPaPdyn = pv2/2 Dynamic pressure Pa,kPa

Po Atmospheric pressure Pa,kPa

Pstat Static pressure Pa,kPaApg Gauge pressure or static pressure Pa,kPaAp Pressure difference Pa,kPa

Pa,kPaApz = Api + Apo Additional pressure drop due to Pa,kPa

presence of solids

* * p* 2AL Pressure drop due to impact andPa,kPaApz = Az 2 C Ii

friction of solids

xviii Nomenclature

liPG = p*gliZ Pressure drop due to gravity Pa,kPaQ Gas mass flow rate kg/sq Heat joulero Radius of pipe mR Gas constant Nm /kgKR* Gas constant jjkgmol/KRB Radius of curvature of bend mRe = ols]» Reynolds number related to pipe

diameterRep = od]» Reynolds number related to particle

diameterRepf = wfodlv Reynolds number related to terminal

velocity of particleRemf = Dmfdvlv Reynolds number related to minimum

fluidization velocityS Entropy kcal/Kt Ambient temperature ·Cv= AliL Volume of pipe element m3

T Absolute temperature KV = nd3/6 Volume of particle m3

.p •

V= Qlp Gas volume flow rate m3/sm3/h

Vp = Glp* Solids volume flow rate m3/sm3/h

v = VIA Average air velocity (superficial mlsvelocity)

Vc Air velocity at choking conditions m/sVo Fluidization velocity mlsDe = vie Actual gas velocity in the voids mls

or velocity of porosity wavev* Friction velocity of mixture mlsm

vmb Minimum fluidization velocity at mlswhich bubbling occurs

Dmf Minimum fluidization velocity mlss Surface area of a particle m2

vy Fluctuating fluid velocity in the mlsdirection of mean motion

v* Friction velocity at saltation mlsspoint

Dso Friction velocity at saltation point mlsof a single particle

Vs Spin velocity mlsVth Gas velocity in the venturi throat mlsW Work J

Nomenclature xix

w=v-c Relative velocity, slip velocity m/swb Rate of rise of a single bubble or plug m/s

in a fluidized bedW s = v. - c Slip velocity in a plug m/sWro Single particle settling (or terminal) m/s

velocity in an undisturbed fluidwr Particle settling velocity in a m/s

cloudwi Separation velocity m/sws1 Slip velocity of a slug m/sXir Volume fraction of solid in feed

with terminal velocity WrOi

Xit Volume fraction of solid in tubewith terminal velocity WrOi

Z,t1Z Height, height difference m

Greek (alphabet) symbols

a. and w Indexes standing for initial andterminal states respectively

Po = wro /v Velocity ratio related to singleparticle fall velocity

13 = w.]» Velocity ratio related to particlefall velocity in a cloud

Pw = tan¢w Particle/wall friction factory Gas/cloth ratio m/minJ Exponent, internal angle of friction

P*Voidagee = 1--

Pp

emr Voidage at minimum fluidizationes Voidage at saltation velocityeo Voidage of fluidized bede p Voidage of compact bede Voidage of gas outside clusters

IJ Dynamic viscosity Ns/m!

IJB Blower, compressor efficiency

IJc Collector efficiency

IJF Fractional efficiency

IJs Separator efficiency() Angle degreeA= ).L + AzJ.l Resistance factor of air and

solids in a mixture streamAL Resistance factor for air alone

in pipe

xx Nomenclature

)"ZS

)"1

Jl = 6jQ

Jl* = !:i.Gj!:i.QJlwv

Pp* = pp(l - e)!:i.p = Pp - P

p~

PoPmPp

1"

atmBcCDdynGHIFLmf

Additional pressure drop factor ina pipe due to solids in a flowingstreamAdditional pressure drop factor dueto air flowing through a plugin a pipePressure drop due to impact andfractionPressure drop factor for slug flowSpatial macroscale between particles

{Mass flow ratio

Mass load ratioMass concentration in pipe elementCoefficient for sliding frictionKinematic viscosityAir (gas) densityApparent bulk densityDensity difference betweenparticle and fluidDust concentrationBulk densityMean density of mixtureParticle densityRelaxation timeShear stressAngle of wall frictionAngle of internal frictionExponentSphericity

Subscripts

Atmospheric conditionsBubbleParticleClusterDragDynamicGravityHorizontalImpact and frictionGasChokingConditions at atmospheric pressure

mm

m2jskg/m?

kg /m 'kg /m '

mg/m?

kg /m 'kg /m?

kg /m'sNjm 2

degreedegree

statVe

StaticVerticalVoidage

Nomencla ture xxi