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BULK SOLIDS H ND L ING n I ntroduction to the Practice and echnology C R WOODCOCK, DipTech, MSc, PhD, CEng, MIMechE Formerly Chief Executive o Centre or Industrial Bulk Solids Handling, Glasgow Caledonian University and J S MASON, BSc, PhD, CEng, FIMechE, FIMarE, MIMinE Principal and Vice-Chancel lor. Glasa ow Caledoni an Universitv t1l BL CKI E C DEMIC c t PROFESSION L An Imprint o Chapman Hall London· Glasgow· Weinheim . New York· Tokyo· Melbourne· Madras

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BULK SOLIDS H NDLING

n I ntroduction to the Practice and

echnology

C R

WOODCOCK, DipTech, MSc, PhD, CEng, MIMechE

Formerly Chief Executive

o

Centre or Industrial Bulk Solids Handling,

Glasgow Caledonian University

and

J

S MASON, BSc, PhD, CEng, FIMechE, FIMarE, MIMinE

Principal and Vice-Chancellor. Glasaow Caledonian Universitv

t1l

BL CKIE C DEMIC

c t

PROFESSION L

An

Imprint

o

Chapman Hall

London· Glasgow· Weinheim . New York· Tokyo· Melbourne· Madras

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Published by

Blackie Academic Professional, an

imprint

of Chapman Hall,

Wester Cleddens Road, Bishopbriggs, Glasgow G64 2NZ

Chapman HalI,

2 6

Boundary Row, London SEI 8HN,

UK

B ackie Academic Professional, Wester Cleddens Road, Bishopbriggs,

Glasgow G64

2NZ

UK

Chapman HaII GmbH, Pappelallee 3 69469 Weinheim, Germany

Chapman HaII USA,

liS

Fifth Avenue, Fourth Floor, New York,

NY 10003, USA

Chapman HaII Japan, ITP-Japan, Kyowa Building, 3F, 2-2-1 Hirakawacho,

Chiyoda-ku, Tokyo 102, Japan

DA Book Aust.) Pty Ltd, 648 Whitehorse Road, Mitcham 3132, Victoria,

Australia

Chapman Hall India, R. Seshadri, 32 Second Main Road, CIT East,

Madras 600 035, India

First edition 1987

Reprinted 1993, 1995

© 1987 Chapman Hall

Softcover reprint

of

the hardcover 1st edition 1987

Typeset in 101l2pt Times by Thomson Press India) Ltd., New Delhi

ISBN-13: 978-94-010-7689-0

DOl: 10.1007/978-94-009-2635-6

e-ISBN-13: 978-94-009-2635-6

Apart from any fair dealing for the purposes of research or private study, or

criticism or review as permitted under the UK Copyright Designs and Patents

Act, 1988, this publication may not be reproduced, stored, or transmitted, in

any form

or

by any means, without the prior permission in writing

of

the

publishers, or in the case of reprographic reproduction only in accordance with

the terms of the licences issued by the Copyright Licensing Agency in the UK,

or in accordance with the tenns of licences issued by the appropriate

Reproduction Rights Organization outside the UK. Enquiries concerning

reproduction outside the terms stated here should be sent to the publishers at the

Glasgow address printed on this page.

The publisher makes no representation, express or implied, with regard to the

accuracy of the information contained in this book and cannot accept any legal

responsibility or liability for any errors or omissions that may be made.

A catalogue record for this book

is

available from the British Library

Library of Congress Catalog Card Number: 85-29147

00

Printed

on

acid-free text paper, manufactured in accordance with

ANSIINISO Z39.48-1992 permanence of Paper)

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  reface

An understanding ofthe properties and the handling characteristics of liquids

and gases has long been regarded as an essential requirement for most

practising engineers. It

is therefore

not

surprising that over the years there has

been a regular appearance of books dealing with the fundamentals of fluid

mechanics fluid flow

hydraulics and related topics. What is surprising is that

there has been no parallel development of the related discipline of Bulk Solids

Handling despite its increasing importance in modern industry across the

world. t is only very recently that a structured approach to the teaching and

learning of the subject has begun to evolve.

A reason for the slow emergence of Bulk Solids Handling as an accepted

topic of study in academic courses on mechanical agricultural chemical

mining and civil engineering is perhaps that the practice

is

so often taken for

granted. Certainly the variety of materials being handled in bulk is almost

endless ranging in size from fine dust to rocks in value from refuse to gold and

in temperature from deep-frozen peas to near-molten metal. Almost everyone

has seen a belt conveyor in operation perhaps carrying grain on the local

farm or stone and rock from a nearby

quarry but

how many would know

that belt conveyors are now being developed to transport bulk solids at rates

in excess of 30 000 tonnes per hour? The domestic vacuum cleaner is a familiar

machine in which dust particles are conveyed through a pipe in a stream of air

but few people would appreciate that large lumps of coal and rock and even

fish can be transported in a similar way. Examples of bulk solids handling can

be found in almost every kind of industry and the problems associated with the

design installation and operation of plant for the storage and transport of

materials in bulk are many and varied.

No

book can be a substitute for the

technical skill acquired through long experience in the industry. Nevertheless

we have attempted to present here a foundation of knowledge generally with a

practical rather than an academic emphasis upon which expertise in various

specialized aspects of bulk solids handling can be developed subsequently.

Governments of many nations are now recognizing that the education and

training of engineers in many fields should include some study of the

technology of bulk solids covering the properties storage flow and transport

of a wide range of materials in particulate or granular form. n the United

Kingdom for example recent initiatives emanating from the Department of

Industry have led to conferences courses and various publications aimed at

promoting a greater awareness of the unique features of bulk solids. The

School of Engineering at Thames Polytechnic and in particular the staff of its

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IV

PREF CE

Bulk Solids Handling Unit, have been deeply involved in these initiatives from

the outset and this book

is

the result of a clearly perceived need for an

introduction to the subject that would identify and set out a structure for the

area of study that

is

becoming known by the convenient, if not entirely

accurate, title Bulk Solids Handling . Many specialist treatments are already

available: works

on

particle technology, hopper design, fluidization, dust

control, pneumatic conveying, and others, can be found on library shelves and

in most cases these are excellent and valuable works of reference for the

experienced engineer. However, for the student and for the engineer who

requires an overview of the emerging discipline of bulk solids handling,

supported by an adequate coverage of fundamentals, this book should

provide essential reading.

n

common with most books of similar size and scope, this one should really

be regarded as the product of a team effort. We as authors and editors, would

unhesitatingly acknowledge the contributions, both direct and indirect, of our

colleagues in the Bulk Solids Handling Unit at Thames Polytechnic, notably

r David Mills and r Alan Reed. n their various ways the academic and

technician staff of the School of Engineering, together with many of our

postgraduate and undergraduate students, have played some part in the

events leading up to the conception, preparation and, ultimately, the

production of this book. Although it

is

perhaps a little unfair to mention

individuals by name,

we

do gratefully acknowledge the patient and tolerant

efforts of Mrs Pam Colley in undertaking the massive task of typing the

manuscript. Finally, our sincere thanks and appreciation goes to our

respective families, especially to our wives Angela and Fran, for the patience,

understanding and considerable fortitude that they have shown during the

months that this book has been in preparation, and indeed during the many

years that we have both been so deeply involved in the multitude of activities

arising out of our interest in the fascinating subject of Bulk Solids Handling.

CRW

JSM

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  ontents

PART 1 CHARACTERIZATION, FLOW AND STORAGE

1

The nature o bulk solids

1

1 1 Introduction

1

1 2

Sampling

3

1 2 1 Obtaining a gross sample

3

1 2 2

Preparing laboratory and test samples

4

1 3

Voidage and bulk density

7

1 4 Particle density

9

1 5 Particle size

10

1 5 1 Definition of size and size distribution

10

1 5 2 Measurement of particle size

15

1 6

Particle shape

25

1 7

Surface area

26

1 8

Particle hardness

28

1 9 Cohesion and adhesion

29

1 9 1

Angle of repose

31

1 9 2 Shear strength

33

1 9 3

The shear cell as a means of determining shear strength

35

1 9 4

Wall friction 39

1 9 5 Measurement of wall friction

40

1 9 6

Arching phenomena

41

1 10 Moisture content

43

1 11 Explosiveness

44

1 12 Notation

45

References and bibliography

46

2 ravity flow o

bulk

solids

7

2 1

Introduction 47

2 2 Pressure distribution in a bulk solid

49

2 2 1 Bulk solid

at

rest 49

2 2 2

The effect of flow on the pressure distribution

52

2 3 Flow of bulk solids from hoppers

54

2 3 1

Introduction

54

2 3 2

Core flow

54

2 3 3

Mass flow

55

2 3 4 Obstructions to gravity flow

55

2 3 5 Predicting the solids discharge rate

56

2 4 Flow of bulk solids in chutes

64

2 4 1 Introduction

64

2 4 2

Flow patterns in straight inclined chutes

65

2 4 3 Flow patterns in curved chutes

68

2 4 4 Chute design

69

2 5 Flow of bulk solids in vertical pipes

74

2 5 1 Introduction 74

2 5 2

Mode of flow 76

2 5 3

Flow control J valves and L-valves

79

2 6

Notation

81

References and bibliography

82

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vi

CONTENTS

3 Dynamics

o

fluid solids systems 84

3 1

Introduction 84

3 2

Flow through beds of fixed particles 84

3 2 1 Characteristics of

flow in

porous media 84

3.2.2 The prediction of pressure-drop across a fixed particula te bed

85

3 3 Settling behaviour of particles 91

3 3 1 Motion of a spherical particle settling in a stationary fluid 91

3.3.2 The settling of non-spherical particles

95

3 3 3 The settling of concentrations of particles (hindered settling) 98

3.3.4 Classification and sorting of particles

98

3 4 Fluidization 99

3 4 1

The fluidization process 99

3.4.2 The prediction of minimum fluidizing velocity

104

3 4 3 Entrainment of particles from a fluidized bed 109

3.4.4 The porous membrane, or distributor 109

3 4 5 The influence of particle size and density

110

3 5

Spouted bed behaviour

113

3 6 Gas/solids

flow in

pipes 116

3 6 1 Introduction

116

3.6.2 The

flow

of gas/solids suspensions in horizontal pipes 117

3 6 3 The flow of gas/solids suspensions in vertical pipes 122

3.6.4 Flow around 90° bends 124

3 6 5 The prediction o pressure-drop in flowing gas/solids suspensions 125

3 7 Liquid/solids flow in pipes 138

3 7 1 Flow characteristics of liquid/solids mixtures (slurries) 138

3.7.2 Non-Newtonian

flow

models for homogeneous suspension 139

3 7 3 The modelling of heterogeneous suspensions

148

3 8 Notation

150

References and bibliography 152

4 he design of storage

bins

and hoppers 154

4 1 Introduction 154

4 2 Hopper geometry 156

4 2 1 Shape 156

4.2.2 Overall dimensions 159

4 3 Outlet size and cone angle 162

4 3 1

Jenike s flow-no flow criterion

162

4.3.2 Flow Functions and

flow

factors 165

4.3.3 Outlet dimension and cone angle 166

4.4 Period of storage and time consolidation effects 168

4 4 1

Caking

169

4.4.2 Testing for time consolidation 170

4 4 3

Practical ways of minimizing time consolidation 171

4 5 The effect of moisture 171

4.6 Overcoming space limitations 172

4 6 1 The use of low-friction linings 173

4.6.2 Changing hopper shape

175

4.7 Structural design 176

4 8 Control and measurement o discharge rate 178

4 9 Feeders 180

4 9 1

Introduction

180

4.9.2 Belt feeders 181

4 9 3

Apron feeders and rotary feeders

183

4.9.4 Rotary table feeders

184

4 9 5 Screw feeders 185

4.9.6 Vibratory feeders 187

4 1

0 Discharge aids 187

4 1 0 1

Introduction 187

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4.10.2 Pneumatic methods

4 10 3 Vibrational methods

4.10.4 Mechanical methods

4 11

Notation

References and bibliography

5 Dust control

5 1 Introduction

5 2 Dust as a hazard to health

5 2 1 Dust particle size

CONTENTS

5 2 2 Dust concentration limits

5 3 Dust suppression

5 3 1

Elimination of dust

5 3 2 Control of dust dispersion

5 4 Gravity and inertial separators

5 5 Air cleaners cyclones

5 5 1

Principle of operation

5 5 2 Prediction of collecting efficiency

5 5 3 Prediction of pressure drop

5 5 4 Cyclone selection

5 6 Air

cleaners wet

washers or scrubbers

5 6 1 Principle of operation

5 6 2 Low pressure drop wet washers

5 6 3 High pressure drop wet washers

5 7 Air

cleaners filters

5 7 1 Mechanism of filtration

5 7 2 Filter media

5 7 3 Bag filters design and selection

5 7 4 Filter cleaning

5 8

Air cleaners electrostatic precipitators

5 9

Notation

References and bibliography

6 Explosion hazards

6 1

Introduction

6 2 Characteristics of dust explosions

6 2 1 Ignition

6 2 2 Explosibility limits

6 2 3

Expansion effects and explosion pressures

6 3 Measurement of explosion parameters

6 4

Explosion risks and system design

6 4 1 Minimizing sources of ignition and prevention of ignition

6 4 2 Containment

6 4 3 Explosion relief venting

6.4.4 Detection and suppression

6 5 Static electricity

6 6 Conclusion

References and bibliography

PART MECHANICAL H NDLING

7 Belt conveyors

7 1 Introduction

7 2 Features of belt conveyors

7 2 1 Belt construction

7.2.2 Idlers

7 2 3

Drive arrangements

V

188

192

198

200

201

2 3

203

204

204

208

208

208

209

211

213

213

215

218

218

218

218

220

222

224

224

226

227

230

232

233

233

235

235

238

238

239

240

241

246

248

249

250

253

256

258

258

26

260

261

261

265

268

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viii

CONTENTS

7 2 4

The power unit

7 2 5 Loading and discharge arrangements

7 2 6

Belt cleaners

7 3

Belt conveyor design

7 3 1 The bulk solid to

be

transported

7 3 2 Belt speed

7 3 3 Belt width

7 3 4

Belt tension

7 3 5

Idler spacing

7 3 6 Power requirements

7 4 Belt conveyor variants

7 4 1

The cable belt conveyor

7 4 2

Belt conveyors without idlers

7 4 3 Closed-belt or pipe conveyors

7 4 4 Sand wich belts

7.5. Notation

References and bibliography

8 Bucket elevators

8 1 Introduction

8 2

Principal types of bucket elevator

8 2 1 Centrifugal discharge elevators

8 2 2

Continuous bucket elevators

8 2 3

Pivoted buckets

8.2.4 Profiled-belt elevators

8 3

Design and selection of bucket elevators

8 3 1 Design features

8 3 2

Loading

8 3 3

Discharge

8.3.4 Capacity

8 3 5

Driving power

8 4 Notation

References and bibliography

9 Chain and flight conveyors

9 1

Introduction

9 2 rag conveyors

9 3 En-masse conveyors

9 3 1

Design features

9.3.2 Performance calculations

9 3 3

Applications of en-masse conveying

9.4 Tubular drag conveyors

9 5

Apron conveyors

9 6 Aerial ropeways

9 7 Notation

References and bibliography

1 Screw conveying

10 1

Introduction

10 2 Principle of operation of screw conveyors

10 3 The enclosed screw or auger conveyor

10 3 1

Constructional features

10 3 2

Prediction of the performance of an auger conveyor

10 4 The industrial screw conveyor or V-trough conveyor

10 4 1 Constructional features

10 4 2 The conveyed product

271

7

273

274

274

275

277

281

284

284

289

289

290

291

293

295

296

98

298

300

300

301

303

304

305

305

308

309

312

315

316

317

3 8

318

318

321

321

323

325

327

328

331

333

334

335

335

337

338

338

340

342

342

344

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10.4.3 Conveyor selection

10.4.4 Conveyor power

CONTENTS

10.4.5 Inclined screw conveyors

10.5

Vertical screw conveyors

10.6 Conclusion

10.7

Notation

References and bibliography

11 Vibratory conveyors

11.1 Introduction

11.2 Movement of a bulk solid in a vibrating trough

11 .2.1

The motion of the trough

11.2.2 The motion of bulk material in the trough

11.2.3 Average conveying velocity

11.2.4 The influence of the design parameters

11.2.5

Two-phase trough motion

11.3

Design features

11.3.1 Drive mechanism

11.3.2 Mounting systems

11.4 Applications of vibratory conveying

11.5 Spiral elevators

11.6 Notation

References and bibliography

P RT

3 PNEUM TIC ND

HYDR ULIC

TR NSPORT

2 Basic pneumatic conveying systems

12.1 Introduction

12.2 Modes of conveying-dilute-phase and dense-phase

12.3 Low-pressure pneumatic conveying systems

12.3.1 Positive-pressure systems

12.3.2

Negative-pressure vacuum) systems

12.3.3

Combined negative/positive pressure systems

12.4 High-pressure systems

12.4.1 General features

12.4.2 Single blow tank systems

12.4.3

Twin blow tanks and continuously operating systems

12.4.4 Long-distance conveying

12.5

Low-velocity conveying and the use of supplementary air

feeds

12.5.1 General features

12.5.2 Plug-forming systems

12.5.3

Plug-limiting systems

12.5.4 Air-injection and booster systems

References and bibliography

3 Components

o

pneumatic conveying systems

13.1 Introduction

13.2 The air supply

13.2.1 General requirements

13.2.2 Fans and turbo-blowers

13.2.3 Roots-type blowers

13.2.4 Sliding-vane rotary compressors

13.2.5 Screw compressors

13.2.6 Reciprocating compressors

13.2.7 Vacuum pumps

IX

345

349

351

354

356

356

357

358

358

361

361

365

367

369

370

370

370

374

375

376

378

379

38

380

386

386

386

390

392

392

392

393

396

398

399

399

401

403

405

407

4 8

408

408

408

409

411

411

412

414

416

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x

13 3 Feeding devices

13 3 1

Rotary valves

13 3 2 Screw feeders

13 3 3 Venturi feeders

13 3 4 Gate lock valves

13 3 5 Blow tanks

CONTENTS

13 3 6 Entrainment devices for vacuum systems

13 4 The pipeline

13 5 Disengaging and collecting devices

13 6 Notation

References and bibliography

4 Pneumatic conveyor design

14 1 Introduction

14 2 General design procedure

14 2 1 Conveying velocity and volumetric air flow rate

14 2 2 Solids mass flowrate and solids loading ratio

14 2 3

Pipeline diameter

14.2.4 Pressure drop

14 2 5 Stepped pipelines

14 2 6 Selection of the air mover

14 3 Summary of preliminary design procedure for dilute phase systems

14 4

Designing from available test data

14 4 1 Conveying characteristics

14 4 2 Scaling for pipe size and conveying distance

14 5

Notation

References and bibliography

5

Air assisted

gravity

conveying

15 1 Introduction

15 2 The flow of fluidised solids

15 3 Practical air assisted gravity conveying

15 4 Design parameters for air gravity conveyors

15 4 1 Slope of channel

15 4 2

Conveying distance

15 4 3

Width of conveying channel

15 4 4 Air requirement

15 5 Properties of bulk solids for air gravity conveying

15 6

Air float conveyors for horizontal and upward transport

15 7 Energy consumption of air gravity conveyors

15 8 Notation

References and bibliography

6 Hydraulic

conveying

16 1 Introduction

16 2 Components of a hydraulic conveying system

16 2 1 Pumps

16 2 2 Slurry preparation plant

16 2 3 The pipeline

16 2 4 De watering equipment

16 3 System design

16 3 1 General design approach

16 3 2 Flow characreristics and pressure drop

16 4

Recent development

References and bibliography

7 Capsule transport

17 1

Introduction

417

417

425

426

427

428

431

433

436

436

436

438

438

439

439

441

442

443

446

446

447

448

448

449

454

454

456

456

458

461

465

465

466

466

468

470

47

475

476

476

478

478

481

481

485

486

487

489

489

490

491

492

494

494

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CONTENTS

17 2

Capsule transport in a pneumatic pipeline

17 2 1 General features of a pneumo capsule system

17 2 2

The capsules

17 2 3

The pipeline

17.2.4 The air supply

17 2 5 Loading nd unloading stations

17 3

Capsule transport in a hydraulic pipeline

17 3 1 General features of a hydro capsule system

17 3 2

The capsules

17 3 3 The pipeline

17 3 4

The water supply and pump system

17 3 5 Injection nd ejection of capsules

17 4

Size of capsule fleet

17 5

Notation

References

ndex

xi

498

498

499

501

502

503

504

504

504

505

505

508

508

510

510

5 3

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when you ca meaS\lfe what you are speaking about, and express it in numbers, you know

something

about

it;

but

when you cannot measure it, when you cannot express it in numbers, your

knowledge

is of

a meagre

and

unsatisfactory kind: it may be the beginning

of

knowledge,

but

you

have scarcely, in your thoughts, advanced to the state o SCIENCE, whatever the matte r may be.

(Lord Kelvin, as Sir William Thomson, speaking on Electrical Units

of

Measurement

at

the

Institution

of

Civil Engineers, London, 3 May 1883.)

(Arab proverb, freely translated as Experience without learning

is

better than learning without

experience .)