BULK SOLIDS HANDLING An I ntroduction to the Practice and Technology
C. R. WOODCOCK, DipTech, MSc, PhD, CEng, MIMechE Formerly Chief Executive of Centre for Industrial Bulk Solids Handling, Glasgow Caledonian University and
J. S. MASON, BSc, PhD, CEng, FIMechE, FIMarE, MIMinE Principal and Vice-Chancellor. Glasaow Caledonian Universitv
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BLACKIE ACADEMIC cSt PROFESSIONAL An Imprint of Chapman & Hall
London· Glasgow· Weinheim . New York· Tokyo· Melbourne· Madras
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 B1ackie 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
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Printed on acid-free text paper, manufactured in accordance with ANSIINISO Z39.48-1992 (permanence of Paper)
Preface 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. It 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. In 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
IV
PREFACE
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. In 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 Dr David Mills and Dr Alan Reed. In 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
Contents PART 1 CHARACTERIZATION, FLOW AND STORAGE 1 The nature of bulk solids 1.1 1.2
Introduction Sampling 1.2.1 Obtaining a gross sample 1.2.2 Preparing laboratory and test samples 1.3 Voidage and bulk density 1.4 Particle density 1.5 Particle size 1.5.1 Definition of 'size' and 'size distribution' 1.5.2 Measurement of particle size 1.6 Particle shape 1.7 Surface area 1.8 Particle hardness 1.9 Cohesion and adhesion 1.9.1 Angle of repose 1.9.2 Shear strength 1.9.3 The shear cell as a means of determining shear strength 1.9.4 Wall friction 1.9.5 Measurement of wall friction 1.9.6 Arching phenomena 1.10 Moisture content 1.11 Explosiveness 1.12 Notation References and bibliography
2 Gravity flow of bulk solids 2.1 2.2
2.3
2.4
2.5
2.6
Introduction Pressure distribution in a bulk solid 2.2.1 Bulk solid at rest 2.2.2 The effect of flow on the pressure distribution Flow of bulk solids from hoppers 2.3.1 Introduction 2.3.2 Core flow 2.3.3 Mass flow 2.3.4 Obstructions to gravity flow 2.3.5 Predicting the solids discharge rate Flow of bulk solids in chutes 2.4.1 Introduction 2.4.2 Flow patterns in straight inclined chutes 2.4.3 Flow patterns in curved chutes 2.4.4 Chute design Flow of bulk solids in vertical pipes 2.5.1 Introduction 2.5.2 Mode of flow 2.5.3 Flow control-J-valves and L-valves Notation References and bibliography
1
1 3 3 4 7 9
10 10
15 25 26 28 29 31 33 35 39 40 41 43 44 45 46
47
47 49 49 52 54 54 54 55 55 56 64
64 65 68 69 74 74 76 79 81 82
vi
CONTENTS
3 Dynamics of fluid/solids systems 3.1 3.2 3.3
3.4
3.5 3.6
3.7
3.8
Introduction Flow through beds of fixed particles 3.2.1 Characteristics of flow in porous media 3.2.2 The prediction of pressure-drop across a fixed particulate bed Settling behaviour of particles 3.3.1 Motion of a spherical particle settling in a stationary fluid 3.3.2 The settling of non-spherical particles 3.3.3 The settling of concentrations of particles (hindered settling) 3.3.4 Classification and sorting of particles Fluidization 3.4.1 The fluidization process 3.4.2 The prediction of minimum fluidizing velocity 3.4.3 Entrainment of particles from a fluidized bed 3.4.4 The porous membrane, or distributor 3.4.5 The influence of particle size and density Spouted bed behaviour Gas/solids flow in pipes 3.6.1 Introduction 3.6.2 The flow of gas/solids suspensions in horizontal pipes 3.6.3 The flow of gas/solids suspensions in vertical pipes 3.6.4 Flow around 90° bends 3.6.5 The prediction of pressure-drop in flowing gas/solids suspensions Liquid/solids flow in pipes 3.7.1 Flow characteristics of liquid/solids mixtures (slurries) 3.7.2 Non-Newtonian flow models for homogeneous suspension 3.7.3 The modelling of heterogeneous suspensions Notation References and bibliography
4 The design of storage bins and hoppers 4.1 4.2
Introduction Hopper geometry 4.2.1 Shape 4.2.2 Overall dimensions 4.3 Outlet size and cone angle 4.3.1 Jenike's 'flow-no flow' criterion 4.3.2 Flow Functions and flow factors 4.3.3 Outlet dimension and cone angle 4.4 Period of storage and time consolidation effects 4.4.1 Caking 4.4.2 Testing for time consolidation 4.4.3 Practical ways of minimizing time consolidation 4.5 The effect of moisture 4.6 Overcoming space limitations 4.6.1 The use of low-friction linings 4.6.2 Changing hopper shape 4.7 Structural design 4.8 Control and measurement of discharge rate 4.9 Feeders 4.9.1 Introduction 4.9.2 Belt feeders 4.9.3 Apron feeders and rotary feeders 4.9.4 Rotary table feeders 4.9.5 Screw feeders 4.9.6 Vibratory feeders 4.1 0 Discharge aids 4.1 0.1 Introduction
84
84 84 84 85 91 91 95 98 98 99 99 104 109 109 110 113 116 116 117 122 124 125 138 138 139 148 150 152
154
154 156 156 159 162 162 165 166 168 169 170 171 171 172 173 175 176 178 180 180 181 183 184 185 187 187 187
CONTENTS
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 5.2
5.3 5.4 5.5
5.6
5.7
5.8 5.9
Introduction Dust as a hazard to health 5.2.1 Dust particle size 5.2.2 Dust concentration limits Dust suppression 5.3.1 Elimination of dust 5.3.2 Control of dust dispersion Gravity and inertial separators 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 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 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 Air cleaners-electrostatic precipitators Notation References and bibliography
6 Explosion hazards 6.1 6.2
6.3 6.4
6.5 6.6
Introduction Characteristics of dust explosions 6.2.1 Ignition 6.2.2 Explosibility limits 6.2.3 Expansion effects and explosion pressures Measurement of explosion parameters 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 Static electricity Conclusion References and bibliography
VB
188 192 198 200 201
203 203 204 204 208 208 208 209 211 213 213 215 218 218 218 218 220 222 224 224 226 227 230 232 233 233
235 235 238 238 239 240 241 246 248 249 250 253 256 258 258
PART 2 MECHANICAL HANDLING 7 Belt conveyors 7.1 7.2
Introduction Features of belt conveyors 7.2.1 Belt construction 7.2.2 Idlers 7.2.3 Drive arrangements
260
260 261 261 265 268
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 8.2
8.3
8.4
Introduction 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 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 Notation References and bibliography
9 Chain and flight conveyors 9.1 9.2 9.3
9.4 9.5 9.6 9.7
Introduction Drag conveyors En-masse conveyors 9.3.1 Design features 9.3.2 Performance calculations 9.3.3 Applications of en-masse conveying Tubular drag conveyors Apron conveyors Aerial ropeways Notation References and bibliography
10 Screw conveying 10.1 10.2 10.3 10.4
Introduction Principle of operation of screw conveyors The enclosed screw or 'auger' conveyor 10.3.1 Constructional features 10.3.2 Prediction of the performance of an auger conveyor The industrial screw conveyor or 'V-trough' conveyor 10.4.1 Constructional features 10.4.2 The conveyed product
271
272
273 274 274 275 277 281 284 284 289 289 290 291 293 295 296
298 298
300 300
301 303
304
305 305 308 309 312 315 316 317
318 318 318 321 321 323 325 327 328 331 333 334
335 335 337 338 338 340 342 342
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CONTENTS
10.5 10.6 10.7
10.4.3 Conveyor selection 10.4.4 Conveyor power 10.4.5 Inclined screw conveyors Vertical screw conveyors Conclusion Notation References and bibliography
11 Vibratory conveyors 11.1 11.2
11.3 11.4 11.5 11.6
Introduction 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 Design features 11.3.1 Drive mechanism 11.3.2 Mounting systems Applications of vibratory conveying Spiral elevators Notation References and bibliography
IX
345 349 351 354 356 356 357
358 358 361 361 365 367 369 370 370 370 374 375 376 378 379
PART 3 PNEUMATIC AND HYDRAULIC TRANSPORT 12 Basic pneumatic conveying systems 12.1 12.2 12.3
12.4
12.5
Introduction Modes of conveying-dilute-phase and dense-phase 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 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 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
13 Components of pneumatic conveying systems 13.1 13.2
Introduction 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
380
380 386 386 386 390
392 392
392
393 396 398 399 399 401 403 405 407
408 408 408 408 409 411 411 412 414 416
x
CONTENTS
13.3
13.4 13.5 13.6
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 13.3.6 Entrainment devices for vacuum systems The pipeline Disengaging and collecting devices Notation References and bibliography
14 Pneumatic conveyor design 14.1 14.2
14.3 14.4 14.5
Introduction 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 Summary of preliminary design procedure for dilute-phase systems Designing from available test data 14.4.1 Conveying characteristics 14.4.2 Scaling for pipe size and conveying distance Notation References and bibliography
15 Air-assisted gravity conveying 15.1 15.2 15.3 15.4
15.5 15.6 15.7 15.8
Introduction The flow of fluidised solids Practical air-assisted gravity conveying 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 Properties of bulk solids for air-gravity conveying Air-float conveyors for horizontal and upward transport Energy consumption of air-gravity conveyors Notation References and bibliography
16 Hydraulic conveying 16.1 16.2
16.3 16.4
Introduction 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 System design 16.3.1 General design approach 16.3.2 Flow characreristics and pressure-drop Recent development References and bibliography
17 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
472
475 476 476
478 478 481 481 485 486 487 489 489 490 491 492
494 494
CONTENTS 17.2
17.3
17.4 17.5
Index
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 and unloading stations 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 and ejection of capsules Size of capsule fleet Notation References
xi 498 498 499 501 502 503 504 504 504 505 505 508 508 510 510
513
... when you caD 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 of SCIENCE, whatever the matter 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'.)
