BUTTERWORTH-HEINEMANN SERIES IN CHEMICAL ENGINEERINGSERIES EDITOR HOWARD BRENNER Massachusetts Institute of Technology ADVISORY EDITORS

ANDREAS ACRIVOS The City College of CUNY JAMES E. BAILEY California Institute of Technology MANFRED M O R A R I California Institute of Technology E. BRUCE NAUMAN Rensselaer Polytechnic Institute ROBERT K. PRUDHOMME Princeton University

SERIES TITLES Chemical Process Equipment Stanley M. Walas Constitutive Equations for Polymer Melts and SolutionsRonald G. Larson

Gas Separation by Adsorption Processes Ralph T. Yang Heterogeneous Reactor Design Hong H. Lee Molecular Thermodynamics of Nonideal Fluids Lloyd L. Lee Phase Equilibria in Chemical Engineering Stanley M. Walas Transport Processes in Chemically Reacting Flow SystemsDaniel E. Rosner

Viscous Flows: The Practical Use of TheoryStuart Winston Churchill

RELATED TITLES Catalyst Supports and Supported Catalysts Alvin B. Stiles Enlargement and Compaction of Particulate SolidsNayland Stanley-Wood

Fundamentals of Fluidized Beds John G. Yates Liquid and Liquid Mixtures J.S. Rowlimon and F. L. Swinton Mixing in the Process Industries N. Harnby, M. F. Edwards,and A. W. Nienow

Shell Process Control Workshop David M. Prett andManfred Morari

Solid Liquid Separation Ladislav Svarovsky Supercritical Fluid Extraction Mark A. McHugh andVal .I. Krukonis

Chemical Process EquipmentSelection and Design

Stanley M. WalasDepartment of Chemical and Petroleum Engineering University of Kansas

To the memory of my parents, Stanklaus and Apolonia, and to my wife, Suzy Belle

Copyright 0 1990 by Butterworth-Heinemann, a division of Reed Publishing (USA) Inc. All rights reserved. The information contained in this book is based on highly regarded sources, all of which are credited herein. A wide range of references is listed. Every reasonable effort was made to give reliable and up-to-date information; neither the author nor the publisher can assume responsibility for the validity of all materials or for the consequences.of their use. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the publisher.

Library of Congress Cataloging-in-Publication Data Walas, Stanley M. Chemical process equipment. (Butterworth-Heinemann series in chemical engineering) Includes bibliographical references and index. 1. Chemical engineering-Apparatus and supplies. I. Title. II. Series. TP157.w334 1988 660.283 87-26795 ISBN 0-7506-9385-l (previously ISBN o-409-90131-8)

British Library Cataloguing in Publication Data Walas, Stanley M. Chemical process equipment.-(ButterworthHeinemann series in chemical engineering). series in chemical engineering). 1. Chemical engineering-Apparatus and supplies I. Title TP157 660.28 ISBN 0-7506-9385-l (previously ISBN o-409-90131-8) Butterworth-Heinemann 3 13 Washington Street Newton, MA 02158-1626 10 9 8 7 Printed in the United States of America

ContentsLIST OF EXAMPLES ix PREFACE xi RULES OF THUMB: SUMMARY CHAPTER 1 INTRODUCTION... xiii

CHAPTER 5 TRANSFER OF SOLIDS 69 5.1. 5.2. Slurry Transport 69 Pneumatic Conveying 71 Equipment 72 Operating Conditions 73 Power Consumption and Pressure Drop 7 4 Mechanical Conveyors and Elevators 76 Properties of Materials Handled 76 Screw Conveyors 76 Belt Conveyors 76 Bucket Elevators and Carriers 78 Continuous Flow Conveyor Elevators 82 Solids Feeders 83 References 88

1

5.3.

1.1. Process Design I 1.2. Equipment 1 Vendors Questionnaires 1 Specification Forms 1 1.3. Categories of Engineering Practice 1 1.4. Sources of Information for Process Design 2 1.5. Codes, Standards, and Recommended Practices 1.6. Material and Energy Balances 3 1.7. Economic Balance 4 1.8. Safety Factors 6 1.9. Safety of Plant and Environment 7 1.10. Steam and Power Supply 9 1.11. Design Basis 12 Utilities 1 2 1.12. Laboratory and Pilot Plant Work 12 References 1 5 CHAPTER 2 FLOWSHEETS 19 2.1. 2.2. 2.3. 2.4. 2.5. Block Flowsheets 19 Process Flowsheets 19 Mechanical (P&I) Flowsheets 19 Utility Flowsheets 19 Drawing of Flowsheets 20 References 31 Appendix 2.1 Descriptions of Example Process Flowsheets 33

5.4. 2

CHAPTER 3 PROCESS CONTROL 39 3.1. Feedback Control 39 Symbols 39 Cascade (Reset) Control 42 3.2. Individual Process Variables 4.2 Temperature 42 Pressure 42 Level of Liquid 43 Flow Rate 43 Flow of Solids 43 Flow Ratio 43 Composition 43 3.3. Equipment Control 43 Heat Transfer Equipment 44 Distillation Equipment 47 Liquid-Liquid Extraction Towers 50 Chemical Reactors 53 Liquid Pumps 55 Solids Feeders 55 Compressors 55 References 60 CHAPTER 4 DRIVERS FOR MOVING EQUIPMENT 61 4.1. Motors 61 Induction 61 Synchronous 61 Direct Current 61 4.2. Steam Turbines and Gas Expanders 62 4.3. Combustion Gas Turbines and Engines 6 5 References 68

CHAPTER 6 FLOW OF FLUIDS 91 6.1. Properties and Units 91 6.2. Energy Balance of a Flowing Fluid 92 6.3. Liquids 94 Fittings and Valves 95 Orifices 95 Power Requirements 98 6.4. Pipeline Networks 98 6.5. Optimum Pipe Diameter 100 6.6. Non-Newtonian Liquids 100 Viscosity Behavior 100 Pipeline Design 106 6.7. Gases 109 Isentropic Flow 109 Isothermal Flow in Uniform Ducts 110 Adiabatic Flow 110 Nonideal Gases 111 6.8. Liquid-Gas Flow in Pipelines 111 Homogeneous Model 113 Separated Flow Models 114 Other Aspects 114 6.9. Granular and Packed Beds 117 Single Phase Fluids 117 Two-Phase Flow 118 6.10. Gas-Solid Transfer 119 Choking Velocity 119 Pressure Drop 119 6.11. Fluidization of Beds of Particles with Gases Characteristics of Fluidization 123 Sizing Equipment 123 References 127

120

CHAPTER 7 FLUID TRANSPORT EQUIPMENT 129 7.1. 7.2. 7.3. 7.4. 7.5. Piping 129 Valves 129 Control Valves 129 Pump Theory 131 Basic Relations 131 Pumping Systems 133 Pump Characteristics 134 Criteria for Selection of Pumps 140 Equipment for Gas Transport 143 Fans 143 Compressors 145 Centrifugals 1 4 5 Axial Flow Compressors 146 Reciprocating Compressors 146 Rotary Compressors 149 Theory and Calculations of Gas Compression 153 Dimensionless Groups 153 Ideal Gases 153 Real Processes and Gases 156 Work on Nonideal Gases 156

7.6.

vi

CONTENTS

Efficiency 1.59 Temperature Rise, Compression Ratio, Volumetric Efficiency 159 7.7. Ejector and Vacuum Systems 162 Ejector Arrangements 162 Air Leakage 164 Steam Consumption 165 Ejector Theory 166 Glossary for Chapter 7 166 References 167 CHAPTER 8 HEAT TRANSFER AND HEAT EXCHANGERS 169 8.1. Conduction of Heat 169 Thermal Conductivity 169 Hollow Cvlinder 170 Composite Walls 170 Fluid Films 170 8.2. Mean Temperature Difference 172 Single Pass Exchanger 172 Multipass Exchangers 173 F-Method 173 O-Method 179 Selection of Shell-and-Tube Numbers of Passes Example 179 8.3. Heat Transfer Coefficients 179 Overall Coefficients 180 Fouling Factors 180 Individual Film Coefficients 180 Metal Wall Resistance 18.2 Dimensionless Groups 182 8.4. Data of Heat Transfer Coefficients 182 Direct Contact of Hot and Cold Streams 185 Natural Convection 186 Forced Convection 186 Condensation 187 Boiling 187 Extended Surfaces 188 8.5. Pressure Drop in Heat Exchangers 188 8.6. Types of Heat Exchangers 188 Plate-and-Frame Exchangers 189 Spiral Heat Exchangers 194 Compact (Plate-Fin) Exchangers 194 Air Coolers 194 Double Pipes 19.5 8.7. Shell-and-Tube Heat Exchangers 195 Construction 195 Advantages 199 Tube Side or Shell Side 199 Design of a Heat Exchanger 199 Tentative Design 200 8.8. Condensers 200 Condenser Configurations 204 Desien Calculation Method 205 The Silver-Bell-Ghaly Method 206 8.9. Reboilers 206 Kettle Reboilers 207 Horizontal Shell Side Thermosiphons 207 Vertical Thermosiphons 207 Forced Circulation Reboilers 208 Calculation Procedures 208 8.10 Evaporators 208 Thermal Economy 210 Surface Requirements 211 8.11. Fired Heaters 211 Description of Eauinment 211 Heat Transfer 213 Design of Fired Heaters 214 8.12. Insulation of Equipment 219 Low Temperatures 221 Medium Temperatures 221

Refractories 221 8.13. Refrigeration 224 Compression Refrigeration 224 Refrigerants 226 Absorption Refrigeration 229 Cryogenics 229 References 229 9 DRYERS AND COOLING TOWERS 231 9.1. Interaction of Air and Water 231 9.2. Rate of Drying 234 Laboratory and Pilot Plant Testing 237 9.3. Classification and General Characteristics of Dryers 237 Products 240 Costs 240 Specification Forms 240 9.4. Batch Dryers 241 9.5. Continuous Tray and Conveyor Belt Dryers 242 9.6. Rotary Cylindrical Dryers 247 9.7. Drum Dryers for Solutions and Slurries 254 9.8. Pneumatic Conveying Dryers 255 9.9. Fluidized Bed Dryers 262 9.10. Spray Dryers 268 Atomization 276 Applications 276 Thermal Efficiency 276 Design 276 9.11. Theorv of Air-Water Interaction in Packed Towers 277 Tower Height 279 9.12. Cooling Towers 280 Water Factors 285 Testing and Acceptance 285 References 285 CHAPTER 10 MIXING AND AGITATION 287 10.1. A Basic Stirred Tank Design 287 The Vessel 287 Baffles 287 Draft Tubes 287 Impeller Types 287 Impeller Size 287 Impeller Speed 288 Impeller Location 288 10.2. Kinds of Impellers 288 10.3. Characterization of Mixing Quality 290 10.4. Power Consumption and Pumping Rate 292 10.5. Suspension of Solids 295 10.6. Gas Dispersion 296 Spargers 296 Mass Transfer 297 System Design 297 Minimum Power 297 Power Consumption of Gassed Liquids 297 Superficial Liquid Velocity 297 Design Procedures 297 10.7. In-Line-Blenders and Mixers 300 10.8. Mixing of Powders and Pastes 301 References 304 CHAPTER 11 SOLID-LIQUID SEPARATION 305 11.1. Processes and Equipment 305 11.2 Theory of Filtration 306 Compressible Cakes 310 11.3. Resistance to Filtration 313 Filter Medium 313 Cake Resistivity 313

179

CONTENTS

Vii

11.4. 11.5.

11.6. 11.7.

Compressibility-Permeability (CP) Cell Measurements 314 Another Form of Pressure Dependence 315 Pretreatment of Slurries 315 Thickening and Clarifying 315 Laboratory Testing and Scale-Up 317 Compression-Permeability Cell 317 The SCFT Concept 317 Scale-Up 318 Illustrations of Equipment 318 Applications and Performance of Equipment 320 References 334

13.8. 13.9.

13.10.

CHAPTER 12 DISINTEGRATION, AGGLOMERATION, AND SIZE SEPARATION OF PARTICULATE SOLIDS 335 12.1. Screening 335 Revolving Screens or Trommels 335 Capacity of Screens 335 12.2. Classification with Streams of Air or Water 337 Air Classifiers 337 Wet Classifiers 339 12.3. Size Reduction 339 12.4. Eauiument for Size Reduction 341 Crushers 3 4 1 Roll Crushers 341 12.5. Particle Size Enlargement 351 Tumblers 351 Roll Compacting and Briquetting 354 Tabletting 357 Extrusion Processes 358 Prilling 361 Fluidized and Spouted Beds 362 Sintering and Crushing 363 References 370 CHAPTER 13 DISTILLATION AND GAS ABSORPTION 37113.1. 13.2.

13.11.

13.12.

13.13.

13.14.

Tray Efficiencies 397 Absorption Factor Shortcut Method of Edmister 398 Seoarations in Packed Towers 398 Miss Transfer Coefficients 399 Distillation 401 Absorption or Stripping 401 Basis for Computer Evaluation of Multicomponent Separations 404 Specifications 405 The MESH Equations 405 The Wang-Henke Bubblepoint Method 408 The SR (Sum-Rates) Method 409 SC (Simultaneous Correction) Method 410 Special Kinds of Distillation Processes 410 Petroleum Fractionation 411 Extractive Distillation 412 Azeotropic Distillation 420 Molecular Distillation 425 Tray Towers 426 Countercurrent Trays 426 Sieve Trays 428 Valve Trays 429 Bubblecap Trays 431 Packed Towers 433 Kinds of Packings 433 Flooding and Allowable Loads 433 Liquid Distribution 439 Liauid Holdup 439 Pressure Drop 439 Efficiencies of Trays and Packings 439 Trays 439 Packed Towers 442 References 456

CHAPTER 14 EXTRACTION AND LEACHING 459 14.1. Equilibrium Relations 459 14.2. Calculation of Stage Requirements 463 Single Staee Extraction 463 Crosscurrent Extraction 464 Immiscible Solvents 464 14.3. Countercurrent Operation 466 Minimum Solvent/Feed Ratio 468 Extract Reflux 468 Minimum Reflux 469 Minimum Stages 469 14.4. Leaching of Solids 470 14.5. Numerical Calculation of Multicomponent Extraction 473 Initial Estimates 473 Procedure 473 14.6. Equipment for Extraction 476 Choice of Disperse Phase 476 Mixer-Settlers 477 Spray Towers 478 Packed Towers 478 Sieve Tray Towers 483 Pulsed Packed and Sieve Tray Towers 483 Reciprocating Tray Towers 485 Rotating Disk Contactor (RDC) 485 Other Rotary Agitated Towers 485 Other Kinds of Extractors 487 Leaching Equipment 488 References 493 CHAPTER 15 ADSORPTION AND ION EXCHANGE 495 15.1. Adsorption Equilibria 495 15.2. Ion Exchange Equilibria 497 15.3. Adsorption Behavior in Packed Beds 500 Regeneration 504

13.3. 13.4.

13.5. 13.6.

13.7.

Vapor-Liquid Equilibria 371 Relative Volatility 374 Binary x-y Diagrams 375 Single-Stage Flash Calculations 375 Bubblepoint Temperature and Pressure 376 Dewpoint Temperature and Pressure 377 Flash at Fixed Temnerature and Pressure 377 Flash at Fixed Enthalpy and Pressure 377 Equilibria with KS Dependent on Composition 377 Evaporation or Simple Distillation 378 Multicomponent Mixtures 379 Binary Distillation 379 Material and Energy Balances 380 Constant Molal Overflow 380 Basic Distillation Problem 382 Unequal Molal Heats of Vaporization 382 Material and Energy Balance Basis 382 Algebraic Method 382 Batch Distillation 390 Material Balances 391 Multicomponent Separation: Generali Considerations 393 Sequencing of Columns 393 Number of Free Variables 395 Estimation of Reflux and Number of Travs (FenskeUnderwood-Gilliland Method) 395 Minimum Trays 395 Distribution of Nonkeys 395 Minimum Reflux 397 Operating Reflux 397 Actual Number of Theoretical Trays 397 Feed Tray Location 397

Viii CONTENTS

15.4. Adsorption Design and Operating Practices 504 15.5. Ion Exchange Design and Operating Practices 506 Electrodialysis 508 15.6. Production Scale Chromatography 510 15.7. Equipment and Processes 510 Gas Adsorption 511 Liquid Phase Adsorption 513 Ion Exchange 517 Ion Exchange Membranes and Electrodialysis 5 1 7 Chromatographic Equipment 520 References 522 CHAPTER 16 CRYSTALLIZATION FROM SOLUTIONS AND MELTS 523 16.1. Solubilities and Equilibria 523 Phase Diagrams 523 Enthalpy Balances 524 16.2. Crvstal Size Distribution 525 16.3. The Process of Crystallization 528 Conditions of Precipitation 528 Supersaturation 528 Growth Rates 530 16.4. The Ideal Stirred Tank 533 Multiple Stirred Tanks in Series 536 Applicability of the CSTC Model 536 16.5. Kinds of Crystallizers 537 16.6. Melt Crystallization and Purification 543 Multistage Processing 543 The Metallwerk Buchs Process 543 Purification Processes 543 References 548 CHAPTER 17 CHEMICAL REACTORS 549 17.1. Design Basis and Space Velocity 549 Design Basis 549 Reaction Times 549 17.2. Rate Equations and Operating Modes 549 17.3. Material and Energy Balances of Reactors 555 17.4. Nonideal Flow Patterns 556 Residence Time Distribution 556 Conversion in Segregated and Maximum Mixed Flows 560 Conversion in Segregated Flow and CSTR Batteries 560 Dispersion Model 560 Laminar and Related Flow Patterns 5 6 1 17.5. Selection of Catalysts 562 Heterogeneous Catalysts 562 Kinds of Catalysts 563 Kinds of Catalvzed Organic Reactions 563 Physical Characteristics of Solid Catalysts 564 Catalyst Effectiveness 565 17.6. Types and Examples of Reactors 567 Stirred Tanks 567 Tubular Flow Reactors 569 Gas-Liquid Reactions 571 Fixed Bed Reactors 572 Moving Beds 574 Kilns and Hearth Furnaces 575 Fluidized Bed Reactors 579 17.7. Heat Transfer in Reactors 582 Stirred Tanks 586 Packed Bed Thermal Conductivity 587 Heat Transfer Coefficient at Walls, to Particles, and Overall 587 Fluidized Beds 589 17.8. Classes of Reaction Processes and Their Equipment 592 Homogeneous Gas Reactions 592

Homogeneous Liquid Reactions 595 Liquid-Liquid Reactions 595 Gas-Liquid Reactions 595 Noncatalytic Reactions with Solids 595 Fluidized Beds of Noncatalytic Solids 595 Circulating Gas or Solids 596 Fixed Bed Solid Catalysis 596 Fluidized Bed Catalysis 601 Gas-Liquid Reactions with Solid Catalysts 604 References 609 CHAPTER 18 PROCESS VESSELS 611 18.1. Drums 611 18.2. Fractionator Reflux Drums 6 1 2 18.3. Liquid-Liquid Separators 612 Coalescence 613 Other Methods 613 18.4. Gas-Liquid Separators 613 Droplet Sizes 613 Rate of Settling 614 Empty Drums 615 Wire Mesh Pad Deentrainers 6 1 5 18.5. Cyclone Separators 616 18.6. Storage Tanks 619 18.7. Mechanical Design of Process Vessels 6 2 1 Design Pressure and Temperature 623 Shells and Heads 624 Formulas for Strength Calculations 624 References 629 CHAPTER 19 OTHER TOPICS 631 19.1. Membrane Processes 631 Membranes 632 Equipment Configurations 632 Applications 632 Gas Permeation 633 19.2. Foam Separation and Froth Flotation 635 Foam Fractionation 635 Froth Flotation 636 19.3. Sublimation and Freeze Drying 638 Equipment 639 Freeze Drying 639 19.4. Parametric Pumping 639 19.5. Seoarations bv Thermal Diffusion 642 19.6. Electrochemical Syntheses 645 Electrochemical Reactions 646 Fuel Cells 646 Cells for Synthesis of Chemicals 648 19.7. Fermentation Processing 648 Processing 650 Operating Conditions 650 Reactors 654 References 660 CHAPTER 20 COSTS OF INDIVIDUAL EQUIPMENT 663 References 669 APPENDIX A UNITS, NOTATION, AND GENERAL DATA 671 APPENDIX B EQUIPMENT SPECIFICATION FORMS 681 APPENDIX C QUESTIONNAIRES OF EQUIPMENT SUPPLIERS 727 INDEX 747

List of Examples

1.1 1.2 1.3 1.4 1.5 3.1 4.1 5.14.2 5.2 5.3 5.4

6.16.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 6.10 6.11 6.12 6.13 6.14 6.15 6.16 7.1 7.2 7.3 7.4

E717 7.8 7.9 7.10 7.11 7.12 7.13

i::8.3 8.4

Material Balance of a Chlorination Process with Recycle 5 Data of a Steam Generator for Making 250,000 lb/hr at 450 psia and 650F from Water Entering at 220F 9 Steam Plant Cycle for Generation of Power and Low Pressure Process Steam 11 Pickup of Waste Heat by Generating and Superheating Steam in a Petroleum Refinery 11 Recovery of Power from a Hot Gas Stream 1 2 Constants of PID Controllers from Response Curves to a Step Input 42 Steam Requirement of a Turbine Operation 65 Performance of a Combustion Gas Turbine 67 Conditions of a Coal Slurry Pipeline 70 Size and Power Requirement of a Pneumatic Transfer Line 77 Sizing a Screw Conveyor 80 Sizing a Belt Conveyor 83 Comparison of Redler and Zippered Belt Conveyors 88 Density of a Nonideal Gas from Its Equation of State 9 1 Unsteady Flow of an Ideal Gas through a Vessel 93 Units of the Energy Balance 94 Pressure Drop in Nonisothermal Liquid Flow 9 7 Comparison of Pressure Drons in a Line with Several Sets of Fittings Resistances 101 A Network of Pipelines in Series, Parallel, and Branches: the Sketch, Material Balances, and Pressure Drop Equations 101 Flow of Oil in a Branched Pipeline 101 Economic Optimum Pine Size for Pumping Hot Oil with a Motor or Turbine Drive 102 Analysis of Data Obtained in a Capillary Tube Viscometer 107 Parameters of the Bingham Model from Measurements of Pressure Drops in a Line 107 Pressure Drop in Power-Law and Bingham Flow 110 Adiabatic and Isothermal Flow of a Gas in a Pipeline 112 Isothermal Flow of a Nonideal Gas 113 Pressure Drop and Void Fraction in Liquid-Gas Flow 116 Pressure D r p in Flow of Nitrogen and Powdered Coal 120 Dimensions of a Fluidized Bed Vessel 125 Application of Dimensionless Performance Curves 132 Operating Points of Single and Double Pumps in Parallel and Series 133 Check of Some Performance Curves with the Concept of Specific Speed 136 Gas Compression, Isentropic and True Final Temperatures 155 Compression Work with Variable Heat Capacity 157 Polytropic and Isentropic Efficiencies 158 Finding Work of Compression with a Thermodynamic Chart 160 Compression Work on a Nonideal Gas 160 Selection of a Centrifugal Compressor 1 6 1 Polytropic and Isentropic Temperatures 162 Three-Stage Compression with Intercooling and Pressure Loss between Stages 164 Equivalent Air Rate 165 Interstage Condensers 166 Conduction Throueh a Furnace Wall I70 Effect of Ignoring the Radius Correction of the Overall Heat Transfer Coefficient 171 A Case of a Composite Wall: Optimum Insulation Thickness for a Steam Line 1 7 1 Performance of a Heat Exchanger with the F-Method 180

8.5 8.6 8.7 8.8 8.9 8.10 8.11 8.12 8.13 8.14 8.15 8.16 8.17 9.1 9.2 9.3 9.4 9.5 9.6 9.1 9.8

3:Yo10.1 10.2 10.3 10.4 11.1 11.2 11.3 11.4 12.1 12.2 13.1 13.2 13.3 13.4 13.5 13.6 13.7 13.8

9.11

13.9 13.10 13.11 13.12

Application of the Effectiveness and the 8 Method 182 Sizing an Exchanger with Radial Finned Tubes 193 Pressure Drop on the Tube Side of a Vertical Thermosiphon Reboiler 193 Pressure Drop on the Shell Side with 25% Open Segmental Baffles by Kerns Method 194 Estimation of the Surface Requirements of an Air Cooler 199 Process Design of a Shell-and-Tube Heat Exchanger 204 Sizing a Condenser for a Mixture by the Silver-Bell-Ghatly Method 207 Comparison of Three Kinds of Reboilers for the Same Service 209 Peak Temperatures 214 Effect of Stock Temperature Variation 214 Design of a Fired Heater 217 Annlication of the Wilson-Lobo-Hottel eauation 219 Two-Stages Propylene Compression Refrigeration with Interstage Recycle 225 Conditions in an Adiabatic Dryer 234 Drying Time over Constant and Falling Rate Periods with Constant Gas Conditions 237 Drying with Changing Humidity of Air in a Tunnel Dryer 238 Effects of Moist Air Recycle and Increase of Fresh Air Rate in Belt Conveyor Drying 239 Scale-Up of a Rotary Dryer 256 Design Details of a Countercurrent Rotary Dryer 256 Description of a Drum Drying System 260 Sizing a Pneumatic Conveying Dryer 266 Sizing a Fluidized Bed Dryer 2 7 2 Sizing a Spray Dryer on the Basis of Pilot Plant Data 279 Sizine of a Cooling Tower: Number of Transfer Units and Height of Packing- 281 Impeller Size and Speed at a Specified Power Input 293 Effects of the Ratios of impeller and Tank Diameters 294 Design of the Agitation System for Maintenance of a Slurry 299 HP and rpm Requirements of an Aerated Agitated Tank 301 Constants of the Filtration Equation from Test Data 310 Filtration Process with a Centrifugal Charge Pump 311 Rotary Vacuum Filter Operation 312 Filtration and Washing of a Compressible Material 314 Sizing a Hydrocyclone 341 Power Requirement for Grinding 342 Correlation of Relative Volatility 375 Vanorization and Condensation of a Ternarv Mixture 378 Bubblepoint Temperature with the Virial add Wilson Equations 379 Batch Distillation of Chlorinated Phenols 383 Distillation of Substances with Widely Different Molal Heats of Vaporization 385 Separation of an Azeotropic Mixture by Operation at Two Pressure Levels 387 Separation of a Partially Miscible Mixture 388 Enthalpy-Concentration Lines of Saturated Vapor and Liquid of Mixtures of Methanol and Water at a Pressure of 2 aim 390 Algebraic Method for Binarv Distillation Calculation 392 Shorcut Design of Multicomponent Fractionation 396 Calculation of an Absorber by the Absorption Factor Method 399 Numbers of Theoretical Trays and of Transfer Units with Two Values of k,/k, for a Distillation Process 402

ix

X

LIST

OF

EXAMPLES

Trays and Transfer Units for an Absorption Process 403 Representation of a Petroleum Fraction by an Equivalent Number of Discrete Components 413 13.15 Comparison of Diameters of Sieve, Valve, and Bubblecap Trays for the Same Service 4 3 1 13.16 Performance of a Packed Tower by Three Methods 4 4 1 13.17 Tray Efficiency for the Separation of Acetone and Benzene 451 14.1 The Equations for Tieline Data 465 14.2 Tabulated Tieline and Distribution Data for the System A = I-Hexene, B = Tetramethylene Sulfone, C = Benzene, Represented in Figure 14.1 466 14.3 Single Stage and Cross Current Extraction of Acetic Acid from Methylisobutyl Ketone with Water 468 14.4 Extraction with an Immiscible Solvent 469 14.5 Countercurrent Extraction Represented on Triangular and Rectangular Distribution Diagrams 470 14.6 Stage Requirements for the Separation of a Type I and a Type II System 471 14.7 Countercurrent Extraction Employing Extract Reflux 472 14.8 Leaching of an Oil-Bearing Solid in a Countercurrent Battery - 472 14.9 Trial Estimates and Converged Flow Rates and Compositions in all Stages of an Extraction Batterv for a , Four-Component Mixture 476 1 4 . 1 0 Sizing of Spray, Packed, or Sieve Tray Towers 486 14.11 Design of a Rotating Disk Contactor 488 15.1 Application of Ion Exchange Selectivity Data 503

13.13 13.14

15.2 15.3 16.1

16.2 16.3 16.4 16.5 16.6 16.7 16.8 18.1 18.2 18.3 18.4 18.5 18.6 19.1 19.2

20.1 20.2

Adsorption of n-hexane from a Natural Gas with Silica Gel 505 Size of an Ion Exchanger for Hard Water 513 Design of a Crystallizing Plant 524 Using the Phase Diagrams of Figure 16.2 528 Heat Effect Accompanying the Cooling of a Solution of MgSO, 529 Deductions from a Differential Distribution Obtained at a Known Residence Time 533 Batch Crystallization with Seeded Liquor 534 Analysis of Size Distribution Data Obtained in a CSTC 537 Crystallization in a Continuous Stirred Tank with Specified Predominant Crystal Size 538 Crystallization from a Ternary Mixture 544 Separation of Oil and Water . 614 Ouantitv of Entrainment on the Basis of Sieve Trav Correlations 6 1 7 Liquid Knockout Drum (Empty) 618 Knockout Drum with Wire Mesh Deentrainer 620 Size and Capacity of Cyclone Separators 6 2 1 Dimensions and Weight of a Horizontal Pressure Drum 628 Applications of the Equation for Osmotic Pressure 633 Concentration of a Water/Ethanol Mixture by Reverse Osmosis 642 Installed Cost of a Distillation Tower 663 Purchased and Installed Cost of Some Equipment 663

This book is intended as a guide to the selection or design of the principal kinds of chemical process equipment by engineers in school and industry. The level of treatment assumes an elementary knowledge of unit operations and transport phenomena. Access to the many design and reference books listed in Chapter 1 is desirable. For coherence, brief reviews of pertinent theory are provided. Emphasis is placed on shortcuts, rules of thumb, and data for design by analogy, often as primary design processes but also for quick evaluations of detailed work. All answers to process design questions cannot be put into a book. Even at this late date in the development of the chemical industry, it is common to hear authorities on most kinds of equipment say that their equipment can be properly fitted to a particular task only on the basis of some direct laboratory and pilot plant work. Nevertheless, much guidance and reassurance are obtainable from general experience and specific examples of successful applications, which this book attempts to provide. Much of the information is supplied in numerous tables and figures, which often deserve careful study quite apart from the text. The general background of process design, flowsheets, and process control is reviewed in the introductory chapters. The major kinds of operations and equipment are treated in individual chapters. Information about peripheral and less widely employed equipment in chemical plants is concentrated in Chapter 19 with references to key works of as much practical value as possible. Because decisions often must be based on economic grounds, Chapter 20, on costs of equipment, rounds out the book. Appendixes provide examples of equipment rating forms and manufacturers questionnaires. Chemical process equipment is of two kinds: custom designed and built, or proprietary off the shelf. For example, the sizes and performance of custom equipment such as distillation towers, drums, and heat exchangers are derived by the process engineer on the basis of established principles and data, although some mechanical details remain in accordance with safe practice codes and individual fabrication practices. Much proprietary equipment (such as filters, mixers, conveyors, and so on) has been developed largely without benefit of much theory and is fitted to job requirements also without benefit of much theory. From the point of view of the process engineer, such equipment is predesigned and fabricated and made available by manufacturers in limited numbers of types, sizes, and capacities. The process design of proprietary equipment, as considered in this book, establishes its required performance and is a process of selection from the manufacturers offerings, often with their recommendations or on the basis of individual experience. Complete information is provided in manufacturers catalogs. Several classified lists of manufacturers of chemical process equipment are readily accessible, so no listings are given here.

Because more than one kind of equipment often is suitable for particular applications and may be available from several manufacturers, comparisons of equipment and typical applications are cited liberally. Some features of industrial equipment are largely arbitrary and may be standardized for convenience in particular industries or individual plants. Such aspects of equipment design are noted when feasible. Shortcut methods of design provide solutions to problems in a short time and at small expense. They must be used when data are limited or when the greater expense of a thorough method is not justifiable. In particular cases they may be employed to obtain information such as: 1. an order of magnitude check of the reasonableness of a result found by another lengthier and presumably accurate computation or computer run, 2. a quick check to find if existing equipment possibly can be adapted to a new situation, 3. a comparison of alternate processes, 4. a basis for a rough cost estimate of a process. Shortcut methods occupy a prominent place in such a broad survey and limited space as this book. References to sources of more accurate design procedures are cited when available. Another approach to engineering work is with rules of thumb, which are statements of equipment performance that may obviate all need for further calculations. Typical examples, for instance, are that optimum reflux ratio is 20% greater than minimum, that a suitable cold oil velocity in a fired heater is 6ft/sec, or that the efficiency of a mixer-settler extraction stage is 70%. The trust that can be placed in a rule of thumb depends on the authority of the propounder, the risk associated with its possible inaccuracy, and the economic balance between the cost of a more accurate evaluation and suitable safety factor placed on the approximation. All experienced engineers have acquired such knowledge. When applied with discrimination, rules of thumb are a valuable asset to the process design and operating engineer, and are scattered throughout this book. Design by analogy, which is based on knowledge of what has been found to work in similar areas, even though not necessarily optimally, is another valuable technique. Accordingly, specific applications often are described in this book, and many examples of specific equipment sizes and performance are cited. For much of my insight into chemical process design, I am indebted to many years association and friendship with the late Charles W. Nofsinger who was a prime practitioner by analogy, rule of thumb, and basic principles. Like Dr. Dolittle of Puddleby-onthe-Marsh, he was a proper doctor and knew a whole lot.

RULES OF THUMB: SUMMARYAlthough experienced engineers know where to find information and how to make accurate computations, they also keep a minimum body of information in mind on the ready, made up largely of shortcuts and rules of thumb. The present compilation may fit into such a minimum body of information, as a boost to the memory or extension in some instances into less often encountered areas. It is derived from the material in this book and is, in a sense, a digest of the book. An Engineering Rule of Thumb is an outright statement regarding suitable sizes or performance of equipment that obviates all need for extended calculations. Because any brief statements are subject to varying degrees of qualification, they are most safely applied by engineers who are substantially familiar with the topics. Nevertheless, such rules should be of value for approximate design and cost estimation, and should provide even the inexperienced engineer with perspective and a foundation whereby the reasonableness of detailed and computer-aided results can be appraised quickly, particularly on short notice such as in conference. Everyday activities also are governed to a large extent by rules of thumb. They serve us when we wish to take a course of action but are not in a position to find the best course of action. Of interest along this line is an amusing and often useful list of some 900 such digests of everyday experience that has been compiled by Parker (Rules of Thumb, Houghton Mifflin, Boston, 1983). Much more can be stated in adequate summary fashion about some topics than about others, which accounts in part for the spottiness of the present coverage, but the spottiness also is due to ignorance and oversights on the part of the author. Accordingly, every engineer undoubtedly will supplement or modify this material in his own way. 9. Compression ratio should be about the same in each stage of a multistage unit, ratio = (PJPi), with n stages. 10. Efficiencies of reciprocating compressors: 65% at compression ratio of 1.5, 75% at 2.0, and 80-85% at 3-6. 11. Efficiencies of large centrifugal compressors, 6000-100,000 ACFM at suction, are 76-78%. 12. Rotary compressors have efficiencies of 70%, except liquid liner type which have 50%.CONVEYORS FOR PARTICULATE SOLIDS

COMPRESSORS AND VACUUM PUMPS

1. Fans are used to raise the pressure about 3% (12in. water), blowers raise to less than 40 psig, and compressors to higher pressures, although the blower range commonly is included in the compressor range. 2. Vacuum pumps: reciprocating piston type decrease the pressure to 1 Torr; rotary piston down to 0.001 Torr, two-lobe rotary down to 0.0001 Torr; steam jet ejectors, one stage down to lOOTorr, three stage down to 1 Torr, five stage down to 0.05 Torr. 3. A three-stage ejector needs 1OOlb steam/lb air to maintain a pressure of 1 Torr. 4. In-leakage of air to evacuated equipment depends on the absolute pressure, Torr, and the volume of the equipment, V cuft, according to w = kVz3 lb/hr, with k = 0.2 when P is more than 90 Torr, 0.08 between 3 and 20 Torr, and 0.025 at less than 1 Torr. 5. Theoretical adiabatic horsepower (THP) = [(SCFM)T1/8130a] [(PJPJ - 11, where Tt is inlet temperature in F+ 460 anda = (k - 1)/k, k = CJC,,.

1. Screw conveyors are suited to transport of even sticky and abrasive solids up inclines of 20 or so. They are limited to distances of 150ft or so because of shaft torque strength. A 12in. dia conveyor can handle 100@3000cuft/hr, at speeds ranging from 40 to 60 pm. 2. Belt conveyors are for high capacity and long distances (a mile or more, but only several hundred feet in a plant), up inclines of 30 maximum. A 24in. wide belt can carry 3OOOcuft/hr at a speed of lOOft/min, but speeds up to 6OOft/min are suited to some materials. Power consumption is relatively low. Bucker elevators are suited to vertical transport of sticky and abrasive materials. With buckets 20 x 20 in. capacity can reach 1000 cuft/hr at a speed of 100 ft/min, but speeds to 300 ft/min are used. Drug-type conveyors (Redler) are suited to short distances in any direction and are completely enclosed. Units range in size from 3 in. square to 19 in. square and may travel from 30 ft/min (fly ash) to 250 ft/min (grains). Power requirements are high. Pneumatic conveyors are for high capacity, short distance (400 ft) transport simultaneously from several sources to several destinations. Either vacuum or low pressure (6-12psig) is employed with a range of air velocities from 35 to 120ft/sec depending on the material and pressure, air requirements from 1 to 7 cuft/cuft of solid transferred.COOLING TOWERS

1. Water in contact with air under adiabatic conditions eventually cools to the wet bulb temperature. 2. In commercial units, 90% of saturation of the air is feasible. 3. Relative cooling tower size is sensitive to the difference between the exit and wet bulb temperatures: AT('F) Relative volume5 2.4 15 1.0 25 0.55

6. Outlet temperature & = T,(P,/P,). 7. To compress air from lOOF, k = 1.4, compression ratio = 3, theoretical power required = 62 HP/million tuft/day, outlet temperature 306F. 8. Exit temperature should not exceed 350-400F; for diatomic gases (C,/C, = 1.4) this corresponds to a compression ratio of about 4.

4. Tower fill is of a highly open structure so as to minimize pressure drop, which is in standard practice a maximum of 2 in. of water. 5. Water circulation rate is l-4gpm/sqft and air rates are 1300-1800 lb/(hr)(sqft) or 300-400 ft/min. 6. Chimney-assisted natural draft towers are of hyperboloidal shapes because they have greater strength for a given thickness; a tower 250 ft high has concrete walls 5-6 in. thick. The enlarged cross section at the top aids in dispersion of exit humid air into the atmosphere. 7. Countercurrent induced draft towers are the most common in process industries. They are able to cool water within 2F of the wet bulb. 8. Evaporation losses are 1% of the circulation for every 10F of cooling range. Windage or drift losses of mechanical draft towers

Xiv R U L E S O F T H U M B : S U M M A R Y

are O.l-0.3%. Blowdown of 2.5-3.0% of the circulation is necessary to prevent excessive salt buildup.

DISTILLATION AND GAS ABSORPTION

CRYSTALLIZATION

FROM

SOLUTION

1. Complete recovery of dissolved solids is obtainable by evaporation, but only to the eutectic composition by chilling. Recovery by melt crystallization also is limited by the eutectic composition. 2. Growth rates and ultimate sizes of crystals are controlled by limiting the extent of supersaturation at any time. 3. The ratio S = C/C,,, of prevailing concentration to saturation concentration is kept near the range of 1.02-1.05. 4. In crystallization by chilling, the temperature of the solution is kept at most l-2F below the saturation temperature at the prevailing concentration. 5. Growth rates of crystals under satisfactory conditions are in the range of 0.1-0.8 mm/hr. The growth rates are approximately the same in all directions. 6. Growth rates are influenced greatly by the presence of impurities and of certain specific additives that vary from case to case.

DISINTEGRATION

1. Percentages of material greater than 50% of the maximum size are about 50% from rolls, 15% from tumbling mills, and 5% from closed circuit ball mills. 2. Closed circuit grinding employs external size classification and return of oversize for regrinding. The rules of pneumatic conveying are applied to design of air classifiers. Closed circuit is most common with ball and roller mills. 3. Jaw crushers take lumps of several feet in diameter down to 4 in. Stroke rates are 10@300/min. The average feed is subjected to 8-10 strokes before it becomes small enough to escape. Gyratory crushers are suited to slabby feeds and make a more rounded product. 4. Roll crushers are made either smooth or with teeth. A 24in. toothed roll can accept lumps 14in. dia. Smooth rolls effect reduction ratios up to about 4. Speeds are 50-900 rpm. Capacity is about 25% of the maximum corresponding to a continuous ribbon of material passing through the rolls. 5. Hammer mills beat the material until it is small enough to pass through the screen at the bottom of the casing. Reduction ratios of 40 are feasible. Large units operate at 900 rpm, smaller ones up to 16,OOOrpm. For fibrous materials the screen is provided with cutting edges. 6. Rod mills are capable of taking feed as large as 50 mm and reducing it to 300 mesh, but normally the product range is 8-65 mesh. Rods are 25-150mm dia. Ratio of rod length to mill diameter is about 1.5. About 45% of the mill volume is occupied by rods. Rotation is at 50-65% of critical. 7. Ball mills are better suited than rod mills to fine grinding. The charge is of equal weights of 1.5, 2, and 3 in. balls for the finest grinding. Volume occupied by the balls is 50% of the mill volume. Rotation speed is 70-80% of critical. Ball mills have a length to diameter ratio in the range l-1.5. Tube mills have a ratio of 4-5 and are capable of very fine grinding. Pebble mills have ceramic grinding elements, used when contamination with metal is to be avoided. 8. Roller mills employ cylindrical or tapered surfaces that roll along flatter surfaces and crush nipped particles. Products of 20-200 mesh are made.

1. Distillation usually is the most economical method of separating liquids, superior to extraction, adsorption, crystallization, or others. 2. For ideal mixtures, relative volatility is the ratio of vapor pressures rri2 = P,/P,. 3. Tower operating pressure is determined most often by the temperature of the available condensing medium, lOO-120F if cooling water; or by the maximum allowable reboiler temperature, 150 psig steam, 366F. 4. Sequencing of columns for separating multicomponent mixtures: (a) perform the easiest separation first, that is, the one least demanding of trays and reflux, and leave the most difficult to the last; (b) when neither relative volatility nor feed concentration vary widely, remove the components one by one as overhead products; (c) when the adjacent ordered components in the feed vary widely in relative volatility, sequence the splits in the order of decreasing volatility; (d) when the concentrations in the feed vary widely but the relative volatilities do not, remove the components in the order of decreasing concentration in the feed. 5. Economically optimum reflux ratio is about 1.2 times the minimum reflux ratio R,. 6. The economically optimum number of trays is near twice the minimum value N,,,. 7. The minimum number of trays is found with the FenskeUnderwood equation

Nn = W[~l(l -~)lovtdM~

- ~)ltxrns~/~~~ a.

8. Minimum reflux for binary or pseudobinary mixtures is given by the following when separation is esentially complete (xD = 1) and D/F is the ratio of overhead product and feed rates:R,D/F =

l/(cu - l),

(R, + l)D/F = a/((~ - l),

when feed is at the bubblepoint, when feed is at the dewpoint.

9. A safety factor of 10% of the number of trays calculated by the best means is advisable. 10. Reflux pumps are made at least 25% oversize. 11. For reasons of accessibility, tray spacings are made 20-24 in. 12. Peak efficiency of trays is at values of the vapor factor F, = ~6 in the range 1.0-1.2 (ft/sec) B. This range of F, establishes the diameter of the tower. Roughly, linear velocities are 2ft/sec at moderate pressures and 6ft/sec in vacuum. 13. The optimum value of the Kremser-Brown absorption factor A = K(V/L) is in the range 1.25-2.0. 14. Pressure drop per tray is of the order of 3 in. of water or 0.1 psi. 15. Tray efficiencies for distillation of light hydrocarbons and aqueous solutions are 60-90%; for gas absorption and stripping, lo-20%. 16. Sieve trays have holes 0.25-0.50 in. dia, hole area being 10% of the active cross section. 17. Valve trays have holes 1.5 in. dia each provided with a liftable cap, 12-14 caps/sqft of active cross section. Valve trays usually are cheaper than sieve trays. 18. Bubblecap trays are used only when a liquid level must be maintained at low turndown ratio; they can be designed for lower pressure drop than either sieve or valve trays. 19. Weir heights are 2 in., weir lengths about 75% of tray diameter, liquid rate a maximum of about 8 gpm/in. of weir; multipass arrangements are used at high liquid rates.

RULES OF THUMB: SUMMARY xv 20. Packings of random and structured character are suited especially to towers under 3 ft dia and where low pressure drop is desirable. With proper initial distribution and periodic redistribution, volumetric efficiencies can be made greater than those of tray towers. Packed internals are used as replacements for achieving greater throughput or separation in existing tower shells. 21. For gas rates of 500 cfm, use 1 in. packing; for gas rates of 2000 cfm or more, use 2 in. 22. The ratio of diameters of tower and packing should be at least 15. 23. Because of deformability, plastic packing is limited to a lo-15 ft depth unsupported, metal to 20-25 ft. 24. Liquid redistributors are needed every 5-10 tower diameters with pall rings but at least every 20ft. The number of liquid streams should be 3-5/sqft in towers larger than 3 ft dia (some experts say 9-12/sqft), and more numerous in smaller towers. 25. Height equivalent to a theoretical plate (HETP) for vapor-liquid contacting is 1.3-1.8ft for 1 in. pall rings, 2.5-3.0 ft for 2 in. pall rings. 26. Packed towers should operate near 70% of the flooding rate given by the correlation of Sherwood, Lobo, et al. 27. Reflux drums usually are horizontal, with a liquid holdup of 5 min half full. A takeoff pot for a second liquid phase, such as water in hydrocarbon systems, is sized for a linear velocity of that phase of 0.5 ft/sec, minimum diameter of 16 in. 28. For towers about 3 ft dia, add 4ft at the top for vapor disengagement and 6 ft at the bottom for liquid level and reboiler return. 29. Limit the tower height to about 175 ft max because of wind load and foundation considerations, An additional criterion is that L/D be less than 30.DRIVERS AND POWER RECOVERY EQUIPMENT EVAPORATORS

An 85% free cross section is taken for design purposes. In countercurrent flow, the exit gas is lo-20C above the solid; in parallel flow, the temperature of the exit solid is 100C. Rotation speeds of about 4rpm are used, but the product of rpm and diameter in feet is typically between 15 and 25. 4. Drum dryers for pastes and slurries operate with contact times of 3-12 set, produce flakes 1-3 mm thick with evaporation rates of 15-30 kg/m2 hr. Diameters are 1.5-5.Oft; the rotation rate is 2-10rpm. The greatest evaporative capacity is of the order of 3000 lb/hr in commercial units. 5. Pneumatic conveying dryers normally take particles l-3 mm dia but up to 10 mm when the moisture is mostly on the surface. Air velocities are lo-30m/sec. Single pass residence times are 0.5-3.0 set but with normal recycling the average residence time is brought up to 60 sec. Units in use range from 0.2 m dia by 1 m high to 0.3 m dia by 38 m long. Air requirement is several SCFM/lb of dry product/hr. 6. Fluidized bed dryers work best on particles of a few tenths of a mm dia, but up to 4 mm dia have been processed. Gas velocities of twice the minimum fluidization velocity are a safe prescription. In continuous operation, drying times of l-2min are enough, but batch drying of some pharmaceutical products employs drying times of 2-3 hr. 7. Spray dryers: Surface moisture is removed in about 5sec, and most drying is completed in less than 60 sec. Parallel flow of air and stock is most common. Atomizing nozzles have openings 0.012-0.15 in. and operate at pressures of 300-4OOOpsi. Atomizing spray wheels rotate at speeds to 20,000 rpm with peripheral speeds of 250-600 ft/sec. With nozzles, the length to diameter ratio of the dryer is 4-5; with spray wheels, the ratio is 0.5-1.0. For the final design, the experts say, pilot tests in a unit of 2 m dia should be made.

1 . Efficiency is greater for larger machines. Motors are 85-95%;steam turbines are 42-78%; gas engines and turbines are

28-38%. 2 . For under IOOHP, electric motors are used almost exclusively.They are made for up to 20,000 HP.

3 . Induction motors are most popular. Synchronous motors aremade for speeds as low as 150rpm and are thus suited for example for low speed reciprocating compressors, but are not made smaller than 50HP. A variety of enclosures is available, from weather-proof to explosion-proof. 4 . Steam turbines are competitive above 1OOHP. They are speed controllable. Frequently they are employed as spares in case of power failure. 5 . Combustion engines and turbines are restricted to mobile and remote locations. 6 . Gas expanders for power recovery may be justified at capacities of several hundred HP; otherwise any needed pressure reduction in process is effected with throttling valves.DRYING OF SOLIDS

1. Long tube vertical evaporators with either natural or forced circulation are most popular. Tubes are 19-63 mm dia and 12-30 ft long. 2. In forced circulation, linear velocities in the tubes are 15-20 ft/sec. 3. Elevation of boiling point by dissolved solids results in differences of 3-10F between solution and saturated vapor. 4. When the boiling point rise is appreciable, the economic number of effects in series with forward feed is 4-6. 5. When the boiling point rise is small, minimum cost is obtained with 8-10 effects in series. 6. In backward feed the more concentrated solution is heated with the highest temperature steam so that heating surface is lessened, but the solution must be pumped between stages. 7. The steam economy of an N-stage battery is approximately 0.8N lb evaporation/lb of outside steam. 8. Interstage steam pressures can be boosted with steam jet compressors of 20-30% efficiency or with mechanical compressors of 70-75% efficiency.EXTRACTION, LIQUID-LIQUID

1. Drying times range from a few seconds in spray dryers to 1 hr or less in rotary dryers and up to several hours or even several days in tunnel shelf or belt dryers. 2. Continuous tray and belt dryers for granular material of natural size or pelleted to 3-15 mm have drying times in the range of lo-200 min. 3. Rotary cylindrical dryers operate with superficial air velocities of 5-lOft/sec, sometimes up to 35 ft/sec when the material is coarse. Residence times are S-90 min. Holdup of solid is 7-8%.

1. The dispersed phase should be the one that has the higher volumetric rate except in equipment subject to backmixing where it should be the one with the smaller volumetric rate. It should be the phase that wets the material of construction less well. Since the holdup of continuous phase usually is greater, that phase should be made up of the less expensive or less hazardous material.

Xvi

RULES OF THUMB: SUMMARY

2 . There are no known commercial applications of reflux toextraction processes, although the theory is favorable (Treybal). 3 . Mixer-settler arrangements are limited to at most five stages. Mixing is accomplished with rotating impellers or circulating pumps. Settlers are designed on the assumption that droplet sizes are about 150 pm dia. In open vessels, residence times of 30-60 min or superficial velocities of 0.5-1.5 ft/min are provided in settlers. Extraction stage efficiencies commonly are taken as

2.

3.

80%. 4. Spray towers even 20-40ft high cannot be depended on tofunction as more than a single stage.

5. Packed towers are employed when 5-10 stages suffice. Pall ringsof l-l.5 in. size are best. Dispersed phase loadings should not exceed 25 gal/(min) (sqft). HETS of 5-10 ft may be realizable. The dispersed phase must be redistributed every 5-7 ft. Packed towers are not satisfactory when the surface tension is more than 10 dyn/cm. Sieve tray towers have holes of only 3-8 mm dia. Velocities through the holes are kept below 0.8 ft/sec to avoid formation of small drops. Redispersion of either phase at each tray can be designed for. Tray spacings are 6-24 in. Tray efficiencies are in the range of 20-30%. Pulsed packed and sieve tray towers may operate at frequencies of 90 cycles/min and amplitudes of 6-25 mm. In large diameter towers, HETS of about 1 m has been observed. Surface tensions as high as 30-40 dyn/cm have no adverse effect. Reciprocating tray towers can have holes 9/16in. dia, 50-60% open area, stroke length 0.75 in., 100-150 strokes/mitt, plate spacing normally 2 in. but in the range l-6 in. In a 30in. dia tower, HETS is 20-25 in. and throughput is 2000 gal/(hr)(sqft). Power requirements are much less than of pulsed towers. Rotating disk contactors or other rotary agitated towers realize HETS in the range 0.1-0.5 m. The especially efficient Kuhni with perforated disks of 40% free cross section has HETS 0.2 m and a capacity of 50 m3/m2 hr.

4. 5.

6.

6.

7.

attrition, sizes in the range 50-500pm dia, a spectrum of sizes with ratio of largest to smallest in the range of 10-25. Cracking catalysts are members of a broad class characterized by diameters of 30-150 pm, density of 1.5 g/mL or so, appreciable expansion of the bed before fluidization sets in, minimum bubbling velocity greater than minimum fluidizing velocity, and rapid disengagement of bubbles. The other extreme of smoothly fluidizing particles is typified by coarse sand and glass beads both of which have been the subject of much laboratory investigation. Their sizes are in the range 150-500 pm, densities 1.5-4.0 g/mL, small bed expansion, about the same magnitudes of minimum bubbling and minimum fluidizing velocities, and also have rapidly disengaging bubbles. Cohesive particles and large particles of 1 mm or more do not lluidize well and usually are processed in other ways. Rough correlations have been made of minimum fluidization velocity, minimum bubbling velocity, bed expansion, bed level fluctuation, and disengaging height. Experts recommend, however, that any real design be based on pilot plant work. Practical operations are conducted at two or more multiples of the minimum fluidizing velocity. In reactors, the entrained material is recovered with cyclones and returned to process. In dryers, the fine particles dry most quickly so the entrained material need not be recycled.

HEAT EXCHANGERS 1. Take true countercurrent flow in a shell-and-tube exchanger as a basis. 2. Standard tubes are 3/4in. OD, 1 in. triangular spacing, 16 ft long; a shell 1 ft dia accommodates 100 sqft; 2 ft dia, 400 sqft, 3 ft dia, 1100 sqft. 3. Tube side is for corrosive, fouling, scaling, and high pressure fluids. 4. Shell side is for viscous and condensing fluids. 5. Pressure drops are 1.5 psi for boiling and 3-9psi for other services. 6. Minimum temperature approach is 20F with normal coolants, 10F or less with refrigerants. 7. Water inlet temperature is 90F, maximum outlet 120F. for estimating purposes, 8. Heat transfer coefficients Btu/(hr)(sqft)(F): water to liquid, 150; condensers, 150; liquid to liquid, 50; liquid to gas, 5; gas to gas, 5; reboiler, 200. Max flux in reboilers, 10,000 Btu/(hr)(sqft). 9. Double-pipe exchanger is competitive at duties requiring 100-200 sqft. 10. Compact (plate and fin) exchangers have 35Osqft/cuft, and about 4 times the heat transfer per tuft of shell-and-tube units. 11. Plate and frame exchangers are suited to high sanitation services, and are 25-50% cheaper in stainless construction than shell-and-tube units. 12. Air coolers: Tubes are 0.75-1.00 in. OD, total finned surface 15-20 sqft/sqft bare surface, U = 80-100 Btu/(hr)(sqft bare surface)( fan power input 2-5 HP/(MBtu/hr), approach 50F or more. 13. Fired heaters: radiant rate, 12,000 Btu/(hr)(sqft); convection rate, 4000; cold oil tube velocity, 6 ft/sec; approx equal transfers of heat in the two sections; thermal efficiency 70-75%; flue gas temperature 250-350F above feed inlet; stack gas temperature 650-950F. INSULATION

8.

9.

FILTRATION 1. Processes are classified by their rate of cake buildup in a laboratory vacuum leaf filter: rapid, 0.1-10.0 cm/set; medium, O.l-lO.Ocm/min; slow, O.l-lO.Ocm/hr. 2. Continuous filtration should not be attempted if l/8 in. cake thickness cannot be formed in less than 5 min. 3. Rapid filtering is accomplished with belts, top feed drums, or pusher-type centrifuges. 4. Medium rate filtering is accomplished with vacuum drums or disks or peeler-type centrifuges. 5. Slow filtering slurries are handled in pressure filters or sedimenting centrifuges. 6. Clarification with negligible cake buildup is accomplished with cartridges, precoat drums, or sand filters. 7. Laboratory tests are advisable when the filtering surface is expected to be more than a few square meters, when cake washing is critical, when cake drying may be a problem, or when precoating may be needed. 8. For finely ground ores and minerals, rotary drum filtration, rates may be 1500 lb/(day)(sqft), at 20 rev/hr and 18-25in. Hg vacuum. 9. Coarse solids and crystals may be filtered at rates of 6000 lb/(day)(sqft) at 20 rev/hr, 2-6 in. Hg vacuum. FLUIDIZATION OF PARTICLES WITH GASES

1. Up to 650F, 85% magnesia is most used.2. Up to 1600-19OOF, a mixture of asbestos and diatomaceous earth is used.

1. Properties of particles that are conducive to smooth fluidization include: rounded or smooth shape, enough toughness to resist

RULES OF THUMB: SUMMARY Xvii

3. Ceramic refractories at higher temperatures. 4. Cyrogenic equipment (-200F) employs insulants with fine pores in which air is trapped. 5. Optimum thickness varies with temperature: 0.5 in. at 2OOF, l.Oin. at 400F, 1.25 in. at 600F. 6. Under windy conditions (7.5 miles/hr), lo-20% greater thickness of insulation is justified.MIXING AND AGITATION

1. Mild agitation is obtained by circulating the liquid with an impeller at superficial velocities of O.l-0.2ft/sec, and intense agitation at 0.7-1.0 ft/sec. 2. Intensities of agitation with impellers in baffled tanks are measured by power input, HP/1000 gal, and impeller tip speeds:Operation Blending Homogeneous reaction Reaction with heat transfer Liquid-liquid mixtures Liquid-gas mixtures Slurries HP/1000 gal 0.2-0.5 0.5-l .5 1.5-5.0 5 5-10 10 Tip speed (ft/min) 7.5-10 10-15 15-20 15-20

through a die followed by cutting. An 8 in. screw has a capacity of 2000 Ib/hr of molten plastic and is able to extrude tubing at 150-3OOft/min and to cut it into sizes as small as washers at 8OOO/min. Ring pellet extrusion mills have hole diameters of 1.6-32 mm. Production rates cover a range of 30-200 Ib/(hr)(HP). Prilling towers convert molten materials into droplets and allow them to solidify in contact with an air stream. Towers as high as 60m are used. Economically the process becomes competitive with other granulation processes when a capacity of 200409 tons/day is reached. Ammonium nitrate prills, for example, are 1.6-3.5 mm dia in the 5-95% range. Fluidized bed granulation is conducted in shallow beds 12-24 in. deep at air velocities of 0.1-2.5 m/s or 3-10 times the minimum fluidizing velocity, with evaporation rates of 0.0051.0 kg/m* sec. One product has a size range 0.7-2.4 mm dia.PIPING

3. Proportions of a stirred tank relative to the diameter D: liquid level = D; turbine impeller diameter = D/3; impeller level above bottom = D/3; impeller blade width = D/15; four vertical baffles with width = D/10. 4. Propellers are made a maximum of 18 in., turbine impellers to 9ft. 5. Gas bubbles sparged at the bottom of the vessel will result in mild agitation at a superficial gas velocity of 1 ft/min, severe agitation at 4 ft/min. 6. Suspension of solids with a settling velocity of 0.03 ft/sec is accomplished with either turbine or propeller impellers, but when the settling velocity is above 0.15 ft/sec intense agitation with a propeller is needed. I. Power to drive a mixture of a gas and a liquid can be 25-50% less than the power to drive the liquid alone. 8. In-line blenders are adequate when a second or two contact time is sufficient, with power inputs of 0.1-0.2 HP/gal.PARTICLE SIZE ENLARGEMENT

1. Line velocities and pressure drops, with line diameter D in inches: liquid pump discharge, (5 + D/3) ft/sec, 2.0 psi/100 ft; liquid pump suction, (1.3 + D/6) ft/sec, 0.4 psi/100 ft; steam or gas, 200 ft/sec, 0.5 psi/100 ft. 2. Control valves require at least 10 psi drop for good control. 3. Globe valves are used for gases, for control and wherever tight shutoff is required. Gate valves are for most other services. 4. Screwed fittings are used only on sizes 1.5 in. and smaller, flanges or welding otherwise. 5. Flanges and fittings are rated for 150, 300, 600, 900, 1500, or 2500 psig. 6. Pipe schedule number = lOOOP/S, approximately, where P is the internal pressure psig and S is the allowable working stress (about 10,000 psi for A120 carbon steel at 500F). Schedule 40 is most common.PUMPS

1. Power for pumping liquids: HP = (gpm)(psi difference)/(l714)(fractional efficiency). 2. Normal pump suction head (NPSH) of a pump must be in excess of a certain number, depending on the kind of pumps and the conditions, if damage is to be avoided. NPSH = (pressure at the eye of the impeller - vapor pressure)/(density). Common range is 4-20 ft. in ft).. Pump may be 3. Specific speed N, = (rpm)(gpm)0.5/(head damaged if certain limits of N, are exceeded, and efficiency is best in some ranges. 500ft max 4. Centrifugal pumps: Single stage for 15-5000gpm, head; multistage for 20-11,000 gpm, 5500 ft max head. Efficiency 45% at 100 gpm, 70% at 500 gpm, 80% at 10,000 gpm. 5. Axial pumps for 20-100,000 gpm, 40 ft head, 65-85% efficiency. head, 50-80% 6. Rotary pumps for l-5000 gpm, 50,OOOft efficiency. 7. Reciprocating pumps for lo-10,000 gpm, l,OOO,OOO ft head max. Efficiency 70% at 10 HP, 85% at 50 HP, 90% at 500 HP.REACTORS

1. The chief methods of particle size enlargement are: compression into a mold, extrusion through a die followed by cutting or breaking to size, globulation of molten material followed by solidification, agglomeration under tumbling or otherwise agitated conditions with or without binding agents. 2. Rotating drum granulators have length to diameter ratios of 2-3, speeds of lo-20 rpm, pitch as much as 10. Size is controlled by speed, residence time, and amount of binder; 2-5 mm dia is common. 3. Rotary disk granulators produce a more nearly uniform product than drum granulators. Fertilizer is made 1.5-3.5 mm; iron ore lo-25 mm dia. 4. Roll compacting and briquetting is done with rolls ranging from 130mm dia by 50mm wide to 910mm dia by 550mm wide. Extrudates are made l-10 mm thick and are broken down to size for any needed processing such as feed to tabletting machines or to dryers. Tablets are made in rotary compression machines that convert powders and granules into uniform sizes. Usual maximum diameter is about 1.5 in., but special sizes up to 4in. dia are possible. Machines operate at 1OOrpm or so and make up to 10,000 tablets/min. Extruders make pellets by forcing powders, pastes, and melts

1. The rate of reaction in every instance must be established in the laboratory, and the residence time or space velocity and product distribution eventually must be found in a pilot plant. 2. Dimensions of catalyst particles are 0.1 mm in fluidized beds, 1 mm in slurry beds, and 2-5 mm in fixed beds. 3. The optimum proportions of stirred tank reactors are with liquid level equal to the tank diameter, but at high pressures slimmer proportions are economical.

Xviii RULES OF THUMB: SUMMARY

4. Power input to a homogeneous reaction stirred tank is 0.5-1.5 HP/lOOOgal, but three times this amount when heat is to be . transferred. 5 . Ideal CSTR (continuous stirred tank reactor) behavior is approached when the mean residence time is 5-10 times the length of time needed to achieve homogeneity, which is accomplished with 500-2000 revolutions of a properly designed stirrer. 6. Batch reactions are conducted in stirred tanks for small daily production rates or when the reaction times are long or when some condition such as feed rate or temperature must be programmed in some way. 7. Relatively slow reactions of liquids and slurries are conducted in continuous stirred tanks. A battery of four or five in series is most economical. 8. Tubular flow reactors ate suited to high production rates at short residence times (set or min) and when substantial heat transfer is needed. Embedded tubes or shell-and-tube construction then are used. 9. In granular catalyst packed reactors, the residence time distribution often is no better than that of a five-stage CSTR battery. 10. For conversions under about 95% of equilibrium, the performance of a five-stage CSTR battery approaches plug flow.REFRIGERATION

strokes/min at 28 mesh. Solids content is not critical, and that of the overflow may be 2-20% or more. 7. Hydrocyclones handle up to 6OOcuft/min and can remove particles in the range of 300-5 pm from dilute suspensions. In one case, a 20in. dia unit had a capacity of 1000 gpm with a pressure drop of 5 psi and a cutoff between 50 and 150 pm.UTILITIES: COMMON SPECIFICATIONS

1. Steam: 1.5-30 psig, 250-275F; 150 psig, 366F; 400 psig, 448F; 600 psig, 488F or with lOO-150F superheat. 2. Cooling water: Supply at 80-90F from cooling tower, return at 115-125F; return seawater at llOF, return tempered water or steam condensate above 125F. 3. Cooling air supply at 85-95F; temperature approach to process, 40F. 4. Compressed air at 45, 150, 300, or 450 psig levels. 5. Instrument air at 45 psig, 0F dewpoint. 6. Fuels: gas of lOOOBtu/SCF at 5-lopsig, or up to 25psig for some types of burners; liquid at 6 million Btu/barrel. 7. Heat transfer fluids: petroleum oils below 600F, Dowtherms below 750F, fused salts below llooF, direct fire or electricity above 450F. 8. Electricity: l-100 Hp, 220-550 V; 200-2500 Hp, 2300-4000 V.VESSELS (DRUMS)

1. A ton of refrigeration is the removal of 12,000 Btu/hr of heat. 2. At various temperature levels: O-50F, chilled brine and glycol solutions; -50-40F, ammonia, freons, butane; -150--5OF, ethane or propane. 3. Compression refrigeration with 100F condenser requires these HP/ton at various temperature levels: 1.24 at 20F; 1.75 at 0F; 3.1 at -40F; 5.2 at -80F. 4. Below -80F, cascades of two or three refrigerants are used. 5. In single stage compression, the compression ratio is limited to about 4. 6. In multistage compression, economy is improved with interstage flashing and recycling, so-called economizer operation. 7. Absorption refrigeration (ammonia to -3OF, lithium bromide to +45F) is economical when waste steam is available at 12 psig or so.SIZE SEPARATION OF PARTICLES

1. Grizzlies that are constructed of parallel bars at appropriate spacings are used to remove products larger than 5 cm dia. 2. Revolving cylindrical screens rotate at 15-20 rpm and below the critical velocity; they are suitable for wet or dry screening in the range of lo-60 mm. 3. Flat screens are vibrated or shaken or impacted with bouncing balls. Inclined screens vibrate at 600-70@0 strokes/min and are used for down to 38 pm although capacity drops off sharply below 200pm. Reciprocating screens operate in the range 30-1000 strokes/min and handle sizes down to 0.25 mm at the higher speeds. 4. Rotary sifters operate at 500-600 rpm and are suited to a range of 12 mm to 50 pm. 5. Air classification is preferred for fine sizes because screens of 150 mesh and finer are fragile and slow. 6. Wet classifiers mostly are used to make two product size ranges, oversize and undersize, with a break commonly in the range between 28 and 200 mesh. A rake classifier operates at about 9 strokes/min when making separation at 200 mesh, and 32

1. Drums are relatively small vessels to provide surge capacity or separation of entrained phases. 2. Liquid drums usually are horizontal. 3. Gas/liquid separators are vertical. 4. Optimum length/diameter = 3, but a range of 2.5-5.0 is common. 5. Holdup time is 5 min half full for reflux drums, 5-10 min for a product feeding another tower. 6. In drums feeding a furnace, 30 min half full is allowed. 7. Knockout drums ahead of compressors should hold no less than 10 times the liquid volume passing through per minute. 8. Liquid/liquid separators are designed for settling velocity of 2-j in./min. 9. Gas velocity in gas/liquid separators, V = kw ft/sec, with k = 0.35 with mesh deentrainer, k = 0.1 without mesh deentrainer. 10. Entrainment removal of 99% is attained with mesh pads of 4-12 in. thicknesses; 6 in. thickness is popular. 11. For vertical pads, the value of the coefficient in Step 9 is reduced by a factor of 213. 12. Good performance can be expected at velocities of 30-100% of those calculated with the given k; 75% is popular. 13. Disengaging spaces of 6-18in. ahead of the pad and 12in. above the pad are suitable. 14. Cyclone separators can be designed for 95% collection of 5 pm particles, but usually only droplets greater than 50 pm need be removed.VESSELS (PRESSURE)

1. Design temperature between -20F and 650F is 50F above operating temperature; higher safety margins are used outside the given temperature range. 2. The design pressure is 10% or 10-25 psi over the maximum operating pressure, whichever is greater. The maximum operating pressure, in turn, is taken as 25 psi above the normal operation. 3. Design pressures of vessels operating at 0-1Opsig and 6001000F are 40 psig.

RULES OF THUMB: SUMMARY Xix

4. For vacuum operation, design pressures are 15 psig and full vacuum. 5. Minimum wall thicknesses for rigidity: 0.25 in. for 42 in. dia and under, 0.32 in. for 42-60 in. dia, and 0.38 in. for over 60 in. dia. 6. Corrosion allowance 0.35 in. for known corrosive conditions, 0.15 in. for non-corrosive streams, and 0.06 in. for steam drums and air receivers. 7. Allowable working stresses are one-fourth of the ultimate strength of the material. 8. Maximum allowable stress depends sharply on temperature.Temperature 1F) Low alloy steel SA203 (psi) Type 302 stainless (psi) -20-650 18,750 18,750 750 15,650 18,750 850 9550 15,900 1000 2500 6250

VESSELS (STORAGE TANKS) 1. For less than 1000 gal, use vertical tanks on legs. 2. Between 1000 and 10,OOOgal, use horizontal tanks on concrete supports. 3. Beyond 10,000 gal, use vertical tanks on concrete foundations. 4. Liquids subject to breathing losses may be stored in tanks with floating or expansion roofs for conservation. 5. Freeboard is 15% below 500 gal and 10% above 500 gal capacity. 6. Thirty days capacity often is specified for raw materials and products, but depends on connecting transportation equipment schedules. 7. Capacities of storage tanks are at least 1.5 times the size of connecting transportation equipment; for instance, 7500 gal tank trucks, 34,500 gal tank cars, and virtually unlimited barge and tanker capacities.

INTRODUCTION

1

-

A

/though this book is devoted to the selection and design of individual equipment, some mention should be made of integration of a number of units into a process. Each piece of equipment interacts with several others in a plant, and the range of its required

performance is dependent on the others in terms of material and energy balances and rate processes. This chapter will discuss general background material relating to complete process design, and Chapter 2 will treat briefly the basic topic of flowsheets.

1.1. PROCESS DESIGN

Process design establishes the sequence of chemical and physical operations; operating conditions; the duties, major specifications, and materials of construction (where critical) of all process equipment (as distinguished from utilities and building auxiliaries); the general arrangement of equipment needed to ensure proper functioning of the plant; line sizes; and principal instrumentation. The process design is summarized by a process flowsheet, a material and energy balance, and a set of individual equipment specifications. Varying degrees of thoroughness of a process design may be required for different purposes. Sometimes only a preliminary design and cost estimate are needed to evaluate the advisability of further research on a new process or a proposed plant expansion or detailed design work; or a preliminary design may be needed to establish the approximate funding for a complete design and construction. A particularly valuable function of preliminary design is that it may reveal lack of certain data needed for final design. Data of costs of individual equipment are supplied in this book, but the complete economics of process design is beyond its scope.1.2. EQUIPMENT

standard size that incidentally may provide a worthwhile safety factor. Even largely custom-designed equipment, such as vessels, is subject to standardization such as discrete ranges of head diameters, pressure ratings of nozzles, sizes of manways, and kinds of trays and packings. Many codes and standards are established by government agencies, insurance companies, and organizations sponsored by engineering societies. Some standardizations within individual plants are arbitrary choices from comparable methods, made to simplify construction, maintenance, and repair: for example, restriction to instrumentation of a particular manufacturer or to a limited number of sizes of heat exchanger tubing or a particular method of installing liquid level gage glasses. All such restrictions must be home in mind by the process designer.VENDORS QUESTIONNAIRES

Two main categories of process equipment are proprietary and custom-designed. Proprietary equipment is designed by the manufacturer to meet performance specifications made by the user; these specifications may be regarded as the process design of the equipment. This category includes equipment with moving parts such as pumps, compressors, and drivers as well as cooling towers, dryers, filters, mixers, agitators, piping equipment, and valves, and even the structural aspects of heat exchangers, furnaces, and other equipment. Custom design is needed for many aspects of chemical reactors, most vessels, multistage separators such as fractionators, and other special equipment not amenable to complete standardization. Only those characteristics of equipment are specified by process design that are significant from the process point of view. On a pump, for instance, process design will specify the operating conditions, capacity, pressure differential, NPSH, materials of construction in contact with process liquid, and a few other items, but not such details as the wall thickness of the casing or the type of stuffing box or the nozzle sizes and the foundation dimensions-although most of these omitted items eventually must be known before a plant is ready for construction. Standard specification forms are available for most proprietary kinds of equipment and for summarizing the details of all kinds of equipment. By providing suitable check lists, they simplify the work by ensuring that all needed data have been provided. A collection of such forms is in Appendix B. Proprietary equipment is provided off the shelf in limited sizes and capacities. Special sizes that would fit particular applications more closely often are more expensive than a larger

A manufacturers or vendors inquiry form is a questionnaire whose completion will give him the information on which to base a specific recommendation of equipment and a price. General information about the process in which the proposed equipment is expected to function, amounts and appropriate properties of the streams involved, and the required performance are basic. The nature of additional information varies from case to case; for instance, being different for filters than for pneumatic conveyors. Individual suppliers have specific inquiry forms. A representative selection is in Appendix C.SPECIFICATION FORMS

When completed, a specification form is a record of the salient features of the equipment, the conditions under which it is to operate, and its guaranteed performance. Usually it is the basis for a firm price quotation. Some of these forms are made up by organizations such as TEMA or API, but all large engineering contractors and many large operating companies have other forms for their own needs. A selection of specification forms is in Appendix B.1.3. CATEGORIES OF ENGINEERING PRACTICE

Although the design of a chemical process plant is initiated by chemical engineers, its complete design and construction requires the inputs of other specialists: mechanical, structural, electrical, and instrumentation engineers; vessel and piping designers; and purchasing agents who know what may be available at attractive prices. On large projects all these activities are correlated by a job engineer or project manager; on individual items of equipment or small projects, the process engineer naturally assumes this function. A key activity is the writing of specifications for soliciting bids and ultimately purchasing equipment. Specifications must be written so explicitly that the bidders are held to a uniform standard and a clear-cut choice can be made on the basis of their offerings alone.

1

2

INTRODUCTION

% of Total Project TimeFigure

Progress of material commitment, engineering manhours, and construction [Matozzi, Oil Gas. J. p. 304, (23 March1953)].

1.1.

but an English version was started in 1984 and three volumes per year are planned; this beautifully organized reference should be most welcome. The most comprehensive compilation of physical property data is that of Landolt-Bornstein (1950-date) (References, Section 1.2, Part C). Although most of the material is in German, recent volumes have detailed tables of contents in English and some volumes are largely in English. Another large compilation, somewhat venerable but still valuable, is the International Critical Tables (1926-1933). Data and methods of estimating properties of hydrocarbons and their mixtures are in the API Data Book (1971-date) (References, Section 1.2, Part C). More general treatments of estimation of physical properties are listed in References, Section 1.1, Part C. There are many compilations of special data such as solubilities, vapor pressures, phase equilibria, transport and thermal properties, and so on. A few of them are listed in References, Section 1.2, Part D, and references to many others are in the References, Section 1.2, Part B. Information about equipment sizes and configurations, and sometimes performance, of equipment is best found in manufacturers catalogs. Items 1 and 2 of References, Section 1.1, Part D, contain some advertisements with illustrations, but perhaps their principal value is in the listings of manufacturers by the kind of equipment. Thomas Register covers all manufacturers and so is less convenient at least for an initial search. The other three items of this group of books have illustrations and descriptions of all kinds of chemical process equipment. Although these books are old, one is surprised to note how many equipment designs have survived.1.5. CODES, STANDARDS, AND RECOMMENDED PRACTICES

% of Total Project TimeFigure 1.2.

Rate of application of engineering manhours of various categories. The area between the curves represents accumulated manhours for each speciality up to a given % completion of the project [Miller, Chem. Eng., p. 188, (July 1956)]. For a typical project, Figure 1.1 shows the distributions of engineering, material commitment, and construction efforts. Of the engineering effort, the process engineering is a small part. Figure 1.2 shows that it starts immediately and finishes early. In terms of money, the cost of engineering ranges from 5 to 15% or so of the total plant cost; the lower value for large plants that are largely patterned after earlier ones, and the higher for small plants or those based on new technology or unusual codes and specifications.1.4. SOURCES OF INFORMATION FOR PROCESS DESIGN

A selection of books relating to process design methods and data is listed in the references at the end of this chapter. Items that are especially desirable in a personal library or readily accessible are identified. Specialized references are given throughout the book in connection with specific topics. The extensive chemical literature is served by the bibliographic items cited in References, Section 1.2, Part B. The book by Rasmussen and Fredenslund (1980) is addressed to chemical ~engineers and cites some literature not included in some of the other bibliographies, as well as information about proprietary data banks. The book by Leesley (References, Section 1.1, Part B) has much information about proprietary data banks and design methods. In its current and earlier editions, the book by Peters and Timmerhaus has many useful bibliographies on classified topics. For information about chemical manufacturing processes, the main encyclopedic references are Kirk-Othmer (1978-1984), McKetta and Cunningham (1976-date) and Ullmann (1972-1983) (References, Section 1.2, Part B). The last of these is in German,

A large body of rules has been developed over the years to ensure the safe and economical design, fabrication and testing of equipment, structures, and materials. Codification of these rules has been done by associations organized for just such purposes, by professional societies, trade groups, insurance underwriting companies, and government agencies. Engineering contractors and large manufacturing companies usually maintain individual sets of standards so as to maintain continuity of design and to simplify maintenance of plant. Table 1.1 is a representative table of contents of the mechanical standards of a large oil company. Typical of the many thousands of items that are standardized in the field of engineering are limitations on the sizes and wall th,icknesses of piping, specifications of the compositions of alloys, stipulation of the safety factors applied to strengths of construction materials, testing procedures for many kinds of materials, and so on. Although the safe design practices recommended by professional and trade associations have no legal standing where they have not actually been incorporated in a body of law, many of them have the respect and confidence of the engineering profession as a whole and have been accepted by insurance underwriters so they are widely observed. Even when they are only voluntary, standards constitute a digest of experience that represents a minimum requirement of good practice. Two publications by Burklin (References, Section 1.1, Part B) are devoted to standards of importance to the chemical industry. Listed are about 50 organizations and 60 topics with which they are concerned. National Bureau of Standards Publication 329 contains about 25,000 titles of U.S. standards. The NBS-SIS service maintains a reference collection of 200,000 items accessible by letter or phone. Information about foreign standards is obtainable through the American National Standards Institute (ANSI). A listing of codes and standards bearing directly on process

1.6.

MATERIAL

AND

ENERGY

BALANCES

3

TABLE 1.1. Internal Engineering Standards of a Large Petroleum Refinery 1 2 3 4 5 6 7 8 / 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 Appropriations and mechanical orders (10) Buildings-architectural (15) Buildings-mechanical (10) Capacities and weights (25) Contracts (I 0) Cooling towers (10) Correspondence (5) Designation and numbering rules for equipment and facilities (10) Drainage (25) Electrical (10) Excavating, grading, and paving (10) Fire fighting (10) Furnaces and boilers (10) General instructions (20) Handling equipment (5) Heat exchangers (IO) Instruments and controls (45) Insulation (IO) Machinery (35) Material procurement and disposition (20) Material selection (5) Miscellaneous process equipment (25) Personnel protective equipment (5) Piping (150) Piping supports (25) Plant layout (20) Pressure vessels (25) Protective coatings (IO) Roads and railroads (25) Storage vessels (45) Structural (35) Symbols and drafting practice (15) Welding (10) Figures in parentheses identify the numbers of distinct standards.

TABLE 1.2-( continued)F. Chemical Manufacturers Association, 2501 M St. NW, Washington, DC 20037 13. Manual of standard and recommended practices for containers, tank cars, pollution of air and water 14. Chemical safety data sheets of individual chemicals G. Cooling Tower Institute, 19827 Highway 45 N, Spring, TX 77388 15. Acceptance test procedure for water cooling towers of mechanical draft industrial type H. Hydraulic Institute, 712 Lakewood Center N, 14600 Detroit Ave., Cleveland, OH 44107 16. Standards for centrifugal, reciprocating, and rotary pumps 17. Pipe friction manual I. Instrument Society of America (ISA), 67 Alexander Dr., Research Triangle Park, NC 27709 18. Instrumentation flow plan symbols 19. Specification forms for instruments 20. Dynamic response testing of process control instrumentation J. Tubular Exchangers Manufacturers Association, 25 N Broadway, Tarrytown, NY 10591 21. TEMA standards K. International Standards Organization (ISO), 1430 Broadway, New York, NY 10018 22. Many standards

TABLE 1.3. Codes and Standards Supplementary to Process Design (a Selection)A. American Concrete Institute, 22400 W. 7 Mile Rd., Detroit, Ml 48219 1. Reinforced concrete design handbook 2. Manual of standard practice for detailing reinforced concrete structures B. American Institute of Steel Construction, 400 N. Michigan Ave., Chicago, IL 60611 3. Manual of steel construction 4. Standard practice for steel buildings and bridges C. American Iron and Steel Institute, 1000 16th St. NW, Washington, DC 20036 5. AISI standard steel compositions D. American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRE), 1791 Tullie Circle NE, Atlanta, GA 30329 6. Refrigerating data book E. Institute of Electrical and Electronics Engineers, 345 E. 47th St., New York, NY 10017 7. Many standards F. National Bureau of Standards, Washington, DC 8. American standard building code 9. National electrical code G. National Electrical Manufacturers Association, 2101 L St. NW, Washington, DC 20037 10. NEMA standards

TABLE 1.2. Codes and Standards of Direct Bearin Chemical Process Design (a Selection

on

A. American Institute of Chemical Engineers, 345 E. 47th St., New York, NY 10017 1. Standard testing procedures; 21 have been published, for example on centrifuges, filters, mixers, firer heaters B. American Petroleum Institute, 2001 L St. NW, Washington, DC 20037 2. Recommended practices for refinery inspections 3. Guide for inspection of refinery equipment 4. Manual on disposal of refinery wastes 5. Recommended practice for design and construction of large, low pressure storage tanks 6. Recommended practice for design and construction of pressure relieving devices 7. Recommended practices for safety and fire protection C. American Society of Mechanical Engineers, 345 W. 47th St., New York, NY 10017 8. ASME Boiler and Pressure Vessel Code. Sec. VIII, Unfired Pressure Vessels 9. Code for pressure piping 10; Scheme for identification of piping systems D. American Society for Testing Materials, 1916 Race St., Philadelphia, PA 19103 11. ASTM Standards, 66 volumes in 16 sections, annual, with about 30% revision each year E. American National Standards Institute (ANSI), 1430 Broadway, New York, NY 10018 12. Abbreviations, letter symbols, graphical symbols, drawing and drafting room practice

design is in Table 1.2, and of supplementary codes and standards in Table 1.3.1.6. MATERIAL AND ENERGY BALANCES

Material and energy balances arc based on a conservation law which is stated generally in the form input + source = output + sink + accumulation. The individual terms can be plural and can be rates as well as absolute quantities. Balances of particular entities are made around a bounded region called a system. Input and output quantities of an entity cross the boundaries. A source is an increase in the amount

4

INTRODUCTION

of the entity that occurs without a crossing of the boundary; for example, an increase in the sensible enthalpy or in the amount of a substance as a consequence of chemical reaction. Analogously, sinks are decreases without a boundary crossing, as the disappearance of water from a fluid stream by adsorption onto a solid phase within the boundary. Accumulations are time rates of change of the amount of the entities within the boundary. For example, in the absence of sources and sinks, an accumulation occurs when the input and output rates are different. In the steady state, the accumulation is zero. Although the principle of balancing is simple, its application requires knowledge of the performance of all the kinds of equipment comprising the system and of the phase relations and physical properties of all mixtures that participate in the process. As a consequence of trying to cover a variety of equipment and processes, the books devoted to the subject of material and energy balances always run to several hundred pages. Throughout this book, material and energy balances are utilized in connection with the design of individual kinds of equipment and some processes. Cases involving individual pieces of equipment usually are relatively easy to balance, for example, the overall balance of a distillation column in Section 13.4.1 and of nonisothermal reactors of Tables 17.4-17.7. When a process is maintained isothermal, only a material balance is needed to describe the process, unless it is also required to know the net heat transfer for maintaining a constant temperature. In most plant design situations of practical interest, however, the several pieces of equipment interact with each other, the output of one unit being the input to another that in turn may recycle part of its output to the inputter. Common examples are an absorber-stripper combination in which th