774
Chemical Process Equipment Selection and Design Stanley M. Walas Department of Chemical and Petroleum Engineering University of Kansas
Chemical Process Equipment Selection and Design Stanley M. Walas Department of Chemical and Petroleum Engineering University of Kansas
Chemical Process Equipment
Selection and Design
Stanley M. Walas
Department of Chemical and Petroleum EngineeringUniversity of Kansas
BUTTERWORTH-HEINEMANN SERIES IN CHEMICAL ENGINEERING
SERIES EDITOR ADVISORY EDITORS
HOWARD BRENNERMassachusetts Institute of Technology
ANDREAS ACRIVOSThe City College of CUNYJAMES E. BAILEYCalifornia Institute of TechnologyMANFRED M O R A R ICalifornia Institute of Technology
E. BRUCE NAUMANRensselaer Polytechnic InstituteROBERT K. PRUDHOMMEPrinceton University
SERIES TITLES
Chemical Process Equipment Stanley M. WalasConstitutive Equations for Polymer Melts and Solutions
Ronald G. LarsonGas Separa t ion by Adsorp t ion Processes Ralph T. YangHeterogeneous Reactor Design Hong H. LeeMolecular Thermodynamics of Nonideal Fluids Lloyd L. LeePhase Equilibria in Chemical Engineering Stanley M. WalasTransport Processes in Chemically Reacting Flow Systems
Daniel E. RosnerViscous Flows: The Practical Use of Theory
Stuart Winston Churchil l
RELATED TITLES
Catalyst Supports and Supported Catalysts Alvin B. StilesEnlargement and Compaction of Particulate Solids
Nayland Stanley-WoodFundamentals of Fluidized Beds John G. YatesLiquid and Liquid Mixtures J.S. Rowlimon and F. L. SwintonMixing in the Process Indus t r ies N. Harnby, M. F . Edwards ,
and A. W. NienowShel l P rocess Cont ro l Workshop David M. Prett and
Manfred MorariSolid Liquid Separation Ladislav SvarovskySupercritical Fluid Extraction Mark A. McHugh and
Val .I. Krukonis
To the memory of my parents,Stanklaus and Apolonia,
and to my wife, Suzy Belle
Copyright 0 1990 by Butterworth-Heinemann, a division of ReedPublishing (USA) Inc. All rights reserved.
The information contained in this book is based on highly regardedsources, all of which are credited herein. A wide range of referencesis listed. Every reasonable effort was made to give reliable andup-to-date information; neither the author nor the publisher canassume responsibility for the validity of all materials or for theconsequences.of their use.
No part of this publication may be reproduced, stored in a retrievalsystem, or transmitted, in any form or by any means, electronic,mechanical, photocopying, recording, or otherwise, without theprior written permission of the publisher.
Library of Congress Cataloging-in-Publication DataWalas, Stanley M.
Chemical process equipment.(Butterworth-Heinemann series in chemicalengineering)Includes bibliographical references and index.1. Chemical engineering-Apparatus and supplies.
I. Title. II. Series.TP157.w334 1988 660.283 87-26795ISBN 0-7506-9385-l (previously ISBN o-409-90131-8)
British Library Cataloguing in Publication DataWalas, Stanley M.
Chemical process equipment.-(Butterworth-Heinemann series in chemical engineering).series in chemical engineering).1. Chemical engineering-Apparatus andsuppliesI. Title660.28 TP157ISBN 0-7506-9385-l (previously ISBN o-409-90131-8)
Butterworth-Heinemann3 13 Washington StreetNewton, MA 02158-1626
10 9 8 7
Printed in the United States of America
LIST OF EXAMPLES ix
PREFACE xi
RULES OF THUMB: SUMMARY
CHAPTER 1 INTRODUCTION
1.1.1.2.
1.3.1.4.1.5.1.6.1.7.1.8.1.9.1.10.1.11.
1.12.
Contents
CHAPTER 5 TRANSFER OF SOLIDS 69
. . .x i i i
1
Process Design IEquipment 1Vendors Questionnaires 1Specification Forms 1Categories of Engineering Practice 1Sources of Information for Process Design 2Codes, Standards, and Recommended Practices 2Material and Energy Balances 3Economic Balance 4Safety Factors 6Safety of Plant and Environment 7Steam and Power Supply 9Design Basis 12Utilities 1 2Laboratory and Pilot Plant Work 12References 1 5
CHAPTER 2 FLOWSHEETS 19
2.1. Block Flowsheets 192.2. Process Flowsheets 192.3. Mechanical (P&I) Flowsheets 192.4. Utility Flowsheets 192.5. Drawing of Flowsheets 20
References 31Appendix 2.1 Descriptions of Example Process
Flowsheets 33
CHAPTER 3 PROCESS CONTROL 39 6.9.
3.1.
3.2.
3.3.
Feedback Control 39Symbols 39Cascade (Reset) Control 42Individual Process Variables 4.2Temperature 42Pressure 42Level of Liquid 43Flow Rate 43Flow of Solids 43Flow Ratio 43Composition 43Equipment Control 43Heat Transfer Equipment 44Distillation Equipment 47Liquid-Liquid Extraction Towers 50Chemical Reactors 53Liquid Pumps 55Solids Feeders 55Compressors 55References 60
CHAPTER 4 DRIVERS FOR MOVINGEQUIPMENT 61
4.1. Motors 61Induction 61
4.2.4.3.
Synchronous 61Direct Current 61Steam Turbines and Gas Expanders 62Combustion Gas Turbines and Engines 65References 68
5.1.5.2.
5.3.
5.4.
Slurry Transport 69Pneumatic Conveying 71Equipment 72Operating Conditions 73Power Consumption and Pressure Drop 7 4Mechanical Conveyors and Elevators 76Properties of Materials Handled 76Screw Conveyors 76Belt Conveyors 76Bucket Elevators and Carriers 78Continuous Flow Conveyor Elevators 82Solids Feeders 83References 88
CHAPTER 6 FLOW OF FLUIDS 91
6.1.6.2.6.3.
6.4.6.5.6.6.
6.7.
6.8.
Properties and Units 91Energy Balance of a Flowing Fluid 92Liquids 94Fittings and Valves 95Orifices 95Power Requirements 98Pipeline Networks 98Optimum Pipe Diameter 100Non-Newtonian Liquids 100Viscosity Behavior 100Pipeline Design 106Gases 109Isentropic Flow 109Isothermal Flow in Uniform Ducts 110Adiabatic Flow 110Nonideal Gases 111Liquid-Gas Flow in Pipelines 111Homogeneous Model 113Separated Flow Models 114Other Aspects 114Granular and Packed Beds 117Single Phase Fluids 117Two-Phase Flow 118
6.10. Gas-Solid Transfer 119Choking Velocity 119Pressure Drop 119
6.11. Fluidization of Beds of Particles with Gases 120Characteristics of Fluidization 123Sizing Equipment 123References 127
CHAPTER 7 FLUID TRANSPORT EQUIPMENT 129
7.1.
7.2.
7.3.7.4.7.5.
7.6.
Piping 129Valves 129Control Valves 129Pump Theory 131Basic Relations 131Pumping Systems 133Pump Characteristics 134Criteria for Selection of Pumps 140Equipment for Gas Transport 143Fans 143Compressors 145Centrifugals 1 4 5Axial Flow Compressors 146Reciprocating Compressors 146Rotary Compressors 149Theory and Calculations of Gas Compression 153Dimensionless Groups 153Ideal Gases 153 Real Processes and Gases 156Work on Nonideal Gases 156
C O N T E N T Sv i
7.7.
Efficiency 1.59Temperature Rise, Compression Ratio, Volumetric
E f f i c i e n c y 1 5 9Ejector and Vacuum Systems 162Ejector Arrangements 162Air Leakage 164Steam Consumption 165Ejector Theory 166Glossary for Chapter 7 166References 167
CHAPTER 8 HEAT TRANSFER AND HEATEXCHANGERS 169
8.1.
8.2.
8.3.
8.4.
8.5.8.6.
8.7.
8.8.
8.9.
8.10
Conduction of Heat 169Thermal Conductivity 169Hollow Cvlinder 170Composite Walls 170Fluid Films 170Mean Temperature Difference 172Single Pass Exchanger 172Multipass Exchangers 173F-Method 173O-Method 179Selection of Shell-and-Tube Numbers of Passes 179Example 179Heat Transfer Coefficients 179Overall Coefficients 180Fouling Factors 180Individual Film Coefficients 180Metal Wall Resistance 18.2Dimensionless Groups 182Data of Heat Transfer Coefficients 182Direct Contact of Hot and Cold Streams 185Natural Convection 186Forced Convection 186Condensation 187Boiling 187Extended Surfaces 188Pressure Drop in Heat Exchangers 188Types of Heat Exchangers 188Plate-and-Frame Exchangers 189Spiral Heat Exchangers 194 Compact (Plate-Fin) Exchangers 194Air Coolers 194Double Pipes 19.5Shell-and-Tube Heat Exchangers 195Construction 195Advantages 199Tube Side or Shell Side 199Design of a Heat Exchanger 199Tentative Design 200Condensers 200Condenser Configurations 204Desien Calculation Method 205The Silver-Bell-Ghaly Method 206Reboilers 206Kettle Reboilers 207Horizontal Shell Side Thermosiphons 207Vertical Thermosiphons 207 Forced Circulation Reboilers 208Calculation Procedures 208Evaporators 208Thermal Economy 210Surface Requirements 211
8.11. Fired Heaters 211Description of Eauinment 211Heat Transfer 213Design of Fired Heaters 214
8.12. Insulation of Equipment 219Low Temperatures 221Medium Temperatures 221
8.13.Refractories 221Refrigeration 224Compression Refrigeration 224Refrigerants 226Absorption Refrigeration 229Cryogenics 229References 229
9 DRYERS AND COOLING TOWERS 231
9.1. Interaction of Air and Water 2319.2. Rate of Drying 234
9.3.Laboratory and Pilot Plant Testing 237Classification and General Characteristics of
9.4.9.5.9.6.9.7.9.8.9.9.
Dryers 237Products 240Costs 240Specification Forms 240Batch Dryers 241Continuous Tray and Conveyor Belt Dryers 242Rotary Cylindrical Dryers 247Drum Dryers for Solutions and Slurries 254Pneumatic Conveying Dryers 255Fluidized Bed Dryers 262
9.10. Spray Dryers 268Atomization 276Applications 276Thermal Efficiency 276D e s i g n 2 7 6
9.11. Theorv of Air-Water Interaction in PackedTowers 277
Tower Height 2799.12. Cooling Towers 280
Water Factors 285Testing and Acceptance 285References 285
CHAPTER 10 MIXING AND AGITATION 287
10.1. A Basic Stirred Tank Design 287The Vessel 287Baffles 287Draft Tubes 287Impeller Types 287Impeller Size 287Impeller Speed 288Impeller Location 288
10.2. Kinds of Impellers 28810.3. Characterization of Mixing Quality 29010.4. Power Consumption and Pumping Rate 29210.5. Suspension of Solids 29510.6. Gas Dispersion 296
Spargers 296Mass Transfer 297System Design 297Minimum Power 297Power Consumption of Gassed Liquids 297Superficial Liquid Velocity 297Design Procedures 297
10.7. In-Line-Blenders and Mixers 30010.8. Mixing of Powders and Pastes 301
References 304
CHAPTER 11 SOLID-LIQUID SEPARATION 305
11.1. Processes and Equipment 30511.2 Theory of Filtration 306
Compressible Cakes 31011.3. Resistance to Filtration 313
Filter Medium 313Cake Resistivity 313
Compressibility-Permeability (CP) CellMeasurements 314
Another Form of Pressure Dependence 315Pretreatment of Slurries 315
11.4. Thickening and Clarifying 31511.5. Laboratory Testing and Scale-Up 317
Compression-Permeability Cell 317The SCFT Concept 317Scale-Up 318
11.6. Illustrations of Equipment 31811.7. Applications and Performance of Equipment 320
References 334
CHAPTER 12 DISINTEGRATION,AGGLOMERATION, AND SIZE SEPARATION OFPARTICULATE SOLIDS 335
12.1. Screening 335Revolving Screens or Trommels 335Capacity of Screens 335
12.2. Classification with Streams of Air or Water 337Air Classifiers 337Wet Classifiers 339
12.3. Size Reduction 33912.4. Eauiument for Size Reduction 341
Crushers 3 4 1Roll Crushers 341
12.5. Particle Size Enlargement 351Tumblers 351Roll Compacting and Briquetting 354Tabletting 357Extrusion Processes 358Prilling 361Fluidized and Spouted Beds 362Sintering and Crushing 363References 370
CHAPTER 13 DISTILLATION AND GASABSORPTION 371
1 3 . 1 .
13.2.
13.3.
13.4.
13.5.
13.6.
13.7.
Vapor-Liquid Equilibria 371Relative Volatility 374Binary x-y Diagrams 375Single-Stage Flash Calculations 375Bubblepoint Temperature and Pressure 376Dewpoint Temperature and Pressure 377Flash at Fixed Temnerature and Pressure 377Flash at Fixed Enthalpy and Pressure 377Equilibria with KS Dependent on Composition 377Evaporation or Simple Distillation 378Mult icomponent Mixtures 379Binary Distillation 379Material and Energy Balances 380Constant Molal Overflow 380Basic Distillation Problem 382Unequal Molal Heats of Vaporization 382Material and Energy Balance Basis 382Algebraic Method 382Batch Distillation 390Material Balances 391Multicomponent Separation: Generali
Considerations 393Sequencing of Columns 393Number of Free Variables 395Estimation of Reflux and Number of Travs (Fenske-
Underwood-Gilliland Method) 395 Minimum Trays 395Distribution of Nonkeys 395Minimum Reflux 397Operating Reflux 397Actual Number of Theoretical Trays 397Feed Tray Location 397
13.8.13.9.
CONTENTS Vii
Tray Efficiencies 397Absorption Factor Shortcut Method of Edmister 398Seoarations in Packed Towers 398Miss Transfer Coefficients 399Distillation 401Absorption or Stripping 401
13.10. Basis for Computer Evaluation of MulticomponentSeparations 404
Specifications 405The MESH Equations 405The Wang-Henke Bubblepoint Method 408The SR (Sum-Rates) Method 409SC (Simultaneous Correction) Method 410
13.11. Special Kinds of Distillation Processes 410Petroleum Fractionation 411Extractive Distillation 412Azeotropic Distillation 420Molecular Distillation 425
13.12. Tray Towers 426Countercurrent Trays 426Sieve Trays 428Valve Trays 429Bubblecap Trays 431
13.13. Packed Towers 433Kinds of Packings 433Flooding and Allowable Loads 433Liquid Distribution 439Liauid Holdup 439Pressure Drop 439
13.14. Efficiencies of Trays and Packings 439Trays 439Packed Towers 442References 456
CHAPTER 14 EXTRACTION AND LEACHING 459
14.1. Equilibrium Relations 45914.2. Calculation of Stage Requirements 463
Single Staee Extraction 463Crosscurrent Extraction 464Immiscible Solvents 464
14.3. Countercurrent Operation 466Minimum Solvent/Feed Ratio 468Extract Reflux 468Minimum Reflux 469Minimum Stages 469
14.4. Leaching of Solids 47014.5. Numerical Calculation of Multicomponent
Extraction 473Initial Estimates 473Procedure 473
14.6. Equipment for Extraction 476Choice of Disperse Phase 476Mixer-Settlers 477Spray Towers 478Packed Towers 478Sieve Tray Towers 483Pulsed Packed and Sieve Tray Towers 483Reciprocating Tray Towers 485Rotating Disk Contactor (RDC) 485Other Rotary Agitated Towers 485Other Kinds of Extractors 487Leaching Equipment 488References 493
CHAPTER 15 ADSORPTION AND IONEXCHANGE 495
15.1. Adsorption Equilibria 49515.2. Ion Exchange Equilibria 49715.3. Adsorption Behavior in Packed Beds 500
Regeneration 504
V i i i C O N T E N T S
15.4. Adsorption Design and Operating Practices 50415.5. Ion Exchange Design and Operating Practices 506
Electrodialysis 50815.6. Production Scale Chromatography 51015.7. Equipment and Processes 510
Gas Adsorption 511Liquid Phase Adsorption 513Ion Exchange 517Ion Exchange Membranes and Electrodialysis 5 1 7Chromatographic Equipment 520References 522
CHAPTER 16 CRYSTALLIZATION FROM SOLUTIONS 18.1. Drums 611AND MELTS 523 18.2. Fractionator Reflux Drums 6 1 2
16.1. Solubilities and Equilibria 523Phase Diagrams 523Enthalpy Balances 524
16.2. Crvstal Size Distribution 52516.3. The Process of Crystallization 528
Conditions of Precipitation 528Supersaturation 528Growth Rates 530
16.4. The Ideal Stirred Tank 533Multiple Stirred Tanks in Series 536Applicability of the CSTC Model 536
16.5. Kinds of Crystallizers 53716.6. Melt Crystallization and Purification 543
Multistage Processing 543The Metallwerk Buchs Process 543Purification Processes 543References 548
18.3. Liquid-Liquid Separators 612Coalescence 613Other Methods 613
18.4. Gas-Liquid Separators 613Droplet Sizes 613Rate of Settling 614Empty Drums 615Wire Mesh Pad Deentrainers 6 1 5
18.5. Cyclone Separators 61618.6. Storage Tanks 61918.7. Mechanical Design of Process Vessels 6 2 1
Design Pressure and Temperature 623Shells and Heads 624Formulas for Strength Calculations 624References 629
CHAPTER 19 OTHER TOPICS 631
CHAPTER 17 CHEMICAL REACTORS 549
17.1.
17.2.17.3.17.4.
17.5.
17.6.
17.7.
17.8.
Design Basis and Space Velocity 549Design Basis 549Reaction Times 549Rate Equations and Operating Modes 549Material and Energy Balances of Reactors 555Nonideal Flow Patterns 556Residence Time Distribution 556Conversion in Segregated and Maximum Mixed
Flows 560Conversion in Segregated Flow and CSTR
Batteries 560Dispersion Model 560Laminar and Related Flow Patterns 5 6 1Selection of Catalysts 562Heterogeneous Catalysts 562Kinds of Catalysts 563Kinds of Catalvzed Organic Reactions 563Physical Characteristics of Solid Catalysts 564Catalyst Effectiveness 565Types and Examples of Reactors 567Stirred Tanks 567Tubular Flow Reactors 569Gas-Liquid Reactions 571Fixed Bed Reactors 572Moving Beds 574Kilns and Hearth Furnaces 575Fluidized Bed Reactors 579Heat Transfer in Reactors 582Stirred Tanks 586Packed Bed Thermal Conductivity 587Heat Transfer Coefficient at Walls, to Particles, and
Overall 587Fluidized Beds 589Classes of Reaction Processes and Their Equipment 592Homogeneous Gas Reactions 592
Homogeneous Liquid Reactions 595Liquid-Liquid Reactions 595Gas-Liquid Reactions 595Noncatalytic Reactions with Solids 595Fluidized Beds of Noncatalytic Solids 595Circulating Gas or Solids 596Fixed Bed Solid Catalysis 596Fluidized Bed Catalysis 601Gas-Liquid Reactions with Solid Catalysts 604References 609
CHAPTER 18 PROCESS VESSELS 611
19.1. Membrane Processes 631Membranes 632Equipment Configurations 632Applications 632Gas Permeation 633
19.2. Foam Separation and Froth Flotation 635Foam Fractionation 635Froth Flotation 636
19.3. Sublimation and Freeze Drying 638Equipment 639Freeze Drying 639
19.4. Parametric Pumping 63919.5. Seoarations bv Thermal Diffusion 64219.6. Electrochemical Syntheses 645
Electrochemical Reactions 646Fuel Cells 646Cells for Synthesis of Chemicals 648
19.7. Fermentation Processing 648Processing 650Operating Conditions 650Reactors 654References 660
CHAPTER 20 COSTS OF INDIVIDUALEQUIPMENT 663
References 669
APPENDIX A UNITS, NOTATION, ANDGENERAL DATA 671
APPENDIX B EQUIPMENT SPECIFICATIONFORMS 6 8 1
APPENDIX C QUESTIONNAIRES OF EQUIPMENTSUPPLIERS 727
INDEX 747
List of Examples
1.11.2
1.3
1.4
1.53.1
4.14 .25.15 .2
5 .35 .4
6.16 .26 .36 .46 .5
6 .6
6 .76 .8
6 .9
6 . 1 0
6 . 1 16 . 1 26 . 1 36 . 1 46 . 1 5
6 . 1 67 .17 .2
7 .3
7 .4
E717
7 . 87 .97 . 1 07 . 1 1
7 . 1 27 . 1 3
i::
8 .3
8 .4
Material Balance of a Chlorination Process with Recycle 5Data of a Steam Generator for Making 250,000 lb/hr at 450psia and 650F from Water Entering at 220F 9Steam Plant Cycle for Generation of Power and LowPressure Process Steam 11Pickup of Waste Heat by Generating and SuperheatingSteam in a Petroleum Refinery 11Recovery of Power from a Hot Gas Stream 1 2Constants of PID Controllers from Response Curves to aStep Input 42Steam Requirement of a Turbine Operation 65Performance of a Combustion Gas Turbine 67Conditions of a Coal Slurry Pipeline 70Size and Power Requirement of a Pneumatic TransferLine 77Sizing a Screw Conveyor 80Sizing a Belt Conveyor 83Comparison of Redler and Zippered Belt Conveyors 88Density of a Nonideal Gas from Its Equation of State 9 1Unsteady Flow of an Ideal Gas through a Vessel 93Units of the Energy Balance 94Pressure Drop in Nonisothermal Liquid Flow 97Comparison of Pressure Drons in a Line with Several Sets ofFittings Resistances 101 A Network of Pipelines in Series, Parallel, and Branches:the Sketch, Material Balances, and Pressure DropEquations 101Flow of Oil in a Branched Pipeline 101Economic Optimum Pine Size for Pumping Hot Oil with aMotor or Turbine Drive 1 0 2 Analysis of Data Obtained in a Capillary TubeViscometer 107Parameters of the Bingham Model from Measurements ofPressure Drops in a Line 107Pressure Drop in Power-Law and Bingham Flow 110Adiabatic and Isothermal Flow of a Gas in a Pipeline 112Isothermal Flow of a Nonideal Gas 113Pressure Drop and Void Fraction in Liquid-Gas Flow 116Pressure D r p in Flow of Nitrogen and PowderedCoal 120 Dimensions of a Fluidized Bed Vessel 125Application of Dimensionless Performance Curves 132Operating Points of Single and Double Pumps in Paralleland Series 133Check of Some Performance Curves with the Concept ofSpecific Speed 136Gas Compression, Isentropic and True FinalTemperatures 155Compression Work with Variable Heat Capacity 157Polytropic and Isentropic Efficiencies 158Finding Work of Compression with a ThermodynamicChart 160Compression Work on a Nonideal Gas 160Selection of a Centrifugal Compressor 1 6 1Polytropic and Isentropic Temperatures 162Three-Stage Compression with Intercooling and PressureLoss between Stages 164Equivalent Air Rate 165Interstage Condensers 166Conduction Throueh a Furnace Wall I70Effect of Ignoring the Radius Correction of the OverallHeat Transfer Coefficient 171A Case of a Composite Wall: Optimum InsulationThickness for a Steam Line 1 7 1Performance of a Heat Exchanger with the F-Method 180
8 .58 .68 .7
8 .8
8 .9
8 . 1 08 . 1 1
8 . 1 2
8 . 1 38 . 1 48 . 1 58 . 1 68 . 1 7
9 .19 .2
9 .3
9 .4
9 .59.69 .19 .8
3:Yo9 . 1 1
10.110.210.3
10.4
11.111.211.311.412.112.213.113.213.3
13.413.5
13.6
13.713.8
13.913.1013.11
13.12
ix
Application of the Effectiveness and the 8 Method 182Sizing an Exchanger with Radial Finned Tubes 193Pressure Drop on the Tube Side of a Vertical ThermosiphonReboiler 193Pressure Drop on the Shell Side with 25% Open SegmentalBaffles by Kerns Method 194Estimation of the Surface Requirements of an AirCooler 199Process Design of a Shell-and-Tube Heat Exchanger 204Sizing a Condenser for a Mixture by the Silver-Bell-GhatlyMethod 207Comparison of Three Kinds of Reboilers for the SameService 209Peak Temperatures 214Effect of Stock Temperature Variation 214Design of a Fired Heater 217Annlication of the Wilson-Lobo-Hottel eauation 219Two-Stages Propylene Compression Refrigeration withInterstage Recycle 225Conditions in an Adiabatic Dryer 234Drying Time over Constant and Falling Rate Periods withConstant Gas Conditions 237Drying with Changing Humidity of Air in a TunnelDryer 238Effects of Moist Air Recycle and Increase of Fresh Air Ratein Belt Conveyor Drying 239Scale-Up of a Rotary Dryer 256Design Details of a Countercurrent Rotary Dryer 256Description of a Drum Drying System 260Sizing a Pneumatic Conveying Dryer 266Sizing a Fluidized Bed Dryer 2 7 2Sizing a Spray Dryer on the Basis of Pilot Plant Data 279Sizine of a Cooling Tower: Number of Transfer Units andHeight of Packing- 281Impeller Size and Speed at a Specified Power Input 293Effects of the Ratios of impeller and Tank Diameters 294Design of the Agitation System for Maintenance of aSlurry 299HP and rpm Requirements of an Aerated AgitatedTank 301Constants of the Filtration Equation from Test Data 310Filtration Process with a Centrifugal Charge Pump 311Rotary Vacuum Fil ter Operat ion 312Filtration and Washing of a Compressible Material 314Sizing a Hydrocyclone 341Power Requirement for Grinding 342Correlation of Relative Volatility 375Vanorization and Condensation of a Ternarv Mixture 378Bubblepoint Temperature with the Virial add WilsonEquations 379 Batch Distillation of Chlorinated Phenols 383Distillation of Substances with Widely Different MolalHeats of Vaporization 385Separation of an Azeotropic Mixture by Operation at TwoPressure Levels 387Separation of a Partially Miscible Mixture 388Enthalpy-Concentration Lines of Saturated Vapor andLiquid of Mixtures of Methanol and Water at a Pressure of2 aim 390Algebraic Method for Binarv Distillation Calculation 392Shorcut Design of Multicomponent Fractionation 396Calculation of an Absorber by the Absorption FactorMethod 399Numbers of Theoretical Trays and of Transfer Units withTwo Values of k,/k, for a Distillation Process 402
X LIST OF EXAMPLES
13.1313.14
13.15
13.1613.17
14.114.2
14.3
14.414.5
14.6
14.714.8
14.9
14.1014.1115.1
Trays and Transfer Units for an Absorption Process 403Representation of a Petroleum Fraction by an EquivalentNumber of Discrete Components 413Comparison of Diameters of Sieve, Valve, and BubblecapTrays for the Same Service 4 3 1Performance of a Packed Tower by Three Methods 4 4 1Tray Efficiency for the Separation of Acetone andBenzene 451The Equations for Tieline Data 465Tabulated Tieline and Distribution Data for the SystemA = I-Hexene, B = Tetramethylene Sulfone, C = Benzene,Represented in Figure 14.1 466Single Stage and Cross Current Extraction of Acetic Acidfrom Methylisobutyl Ketone with Water 468Extraction with an Immiscible Solvent 469Countercurrent Extraction Represented on Triangular andRectangular Distribution Diagrams 470Stage Requirements for the Separation of a Type I and aType II System 471Countercurrent Extraction Employing Extract Reflux 472Leaching of an Oil-Bearing Solid in a CountercurrentBattery - 472Trial Estimates and Converged Flow Rates andCompositions in all Stages of an Extraction Batterv for aFour-Component Mixture 476
,
Sizing of Spray, Packed, or Sieve Tray Towers 486Design of a Rotating Disk Contactor 488Application of Ion Exchange Selectivity Data 503
15.2
15.316.116.216.3
16.4
16.516.6
16.7
16.818.118.2
18.318.418.518.6
19.119.2
20.120.2
Adsorption of n-hexane from a Natural Gas with SilicaGel 505Size of an Ion Exchanger for Hard Water 513Design of a Crystallizing Plant 524Using the Phase Diagrams of Figure 16.2 528Heat Effect Accompanying the Cooling of a Solution ofMgSO, 529 Deductions from a Differential Distribution Obtained at aKnown Residence Time 533Batch Crystallization with Seeded Liquor 534Analysis of Size Distribution Data Obtained in aCSTC 537Crystallization in a Continuous Stirred Tank with SpecifiedPredominant Crystal Size 538Crystallization from a Ternary Mixture 544Separation of Oil and Water . 614Ouantitv of Entrainment on the Basis of Sieve TravCorrelations 6 1 7Liquid Knockout Drum (Empty) 618Knockout Drum with Wire Mesh Deentrainer 620Size and Capacity of Cyclone Separators 6 2 1Dimensions and Weight of a Horizontal PressureDrum 628Applications of the Equation for Osmotic Pressure 633Concentration of a Water/Ethanol Mixture by ReverseOsmosis 642Installed Cost of a Distillation Tower 663Purchased and Installed Cost of Some Equipment 663
This book is intended as a guide to the selection or design of theprincipal kinds of chemical process equipment by engineers inschool and industry. The level of treatment assumes an elementaryknowledge of unit operations and transport phenomena. Access tothe many design and reference books listed in Chapter 1 isdesirable. For coherence, brief reviews of pertinent theory areprovided. Emphasis is placed on shortcuts, rules of thumb, and datafor design by analogy, often as primary design processes but also forquick evaluations of detailed work.
All answers to process design questions cannot be put into abook. Even at this late date in the development of the chemicalindustry, it is common to hear authorities on most kinds ofequipment say that their equipment can be properly fitted to aparticular task only on the basis of some direct laboratory and pilotplant work. Nevertheless, much guidance and reassurance areobtainable from general experience and specific examples ofsuccessful applications, which this book attempts to provide. Muchof the information is supplied in numerous tables and figures, whichoften deserve careful study quite apart from the text.
The general background of process design, flowsheets, andprocess control is reviewed in the introductory chapters. The majorkinds of operations and equipment are treated in individualchapters. Information about peripheral and less widely employedequipment in chemical plants is concentrated in Chapter 19 withreferences 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 andmanufacturers questionnaires.
Chemical process equipment is of two kinds: custom designedand built, or proprietary off the shelf. For example, the sizes andperformance of custom equipment such as distillation towers,drums, and heat exchangers are derived by the process engineer onthe basis of established principles and data, although somemechanical details remain in accordance with safe practice codesand individual fabrication practices.
Much proprietary equipment (such as filters, mixers, conveyors,and so on) has been developed largely without benefit of muchtheory and is fitted to job requirements also without benefit of muchtheory. From the point of view of the process engineer, suchequipment is predesigned and fabricated and made available bymanufacturers in limited numbers of types, sizes, and capacities.The process design of proprietary equipment, as considered in thisbook, establishes its required performance and is a process ofselection from the manufacturers offerings, often with theirrecommendations or on the basis of individual experience.Complete information is provided in manufacturers catalogs.Several classified lists of manufacturers of chemical processequipment are readily accessible, so no listings are given here.
Because more than one kind of equipment often is suitable forparticular applications and may be available from severalmanufacturers , comparisons of equipment and typical appl icat ionsare cited liberally. Some features of industrial equipment are largelyarbitrary and may be standardized for convenience in particularindustries or individual plants. Such aspects of equipment design arenoted when feasible.
Shortcut methods of design provide solutions to problems in ashort time and at small expense. They must be used when data arelimited or when the greater expense of a thorough method is notjustifiable. In particular cases they may be employed to obtaininformation such as:
1. an order of magnitude check of the reasonableness of a resultfound by another lengthier and presumably accurate computa-tion or computer run,
2. a quick check to find if existing equipment possibly can beadapted 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 surveyand limited space as this book. References to sources of moreaccurate design procedures are cited when available.
Another approach to engineering work is with rules of thumb,which are statements of equipment performance that may obviateall need for further calculations. Typical examples, for instance, arethat optimum reflux ratio is 20% greater than minimum, that asuitable cold oil velocity in a fired heater is 6ft/sec, or that theefficiency of a mixer-settler extraction stage is 70%. The trust thatcan be placed in a rule of thumb depends on the authority of thepropounder, the risk associated with its possible inaccuracy, and theeconomic balance between the cost of a more accurate evaluationand suitable safety factor placed on the approximation. Allexperienced engineers have acquired such knowledge. Whenapplied with discrimination, rules of thumb are a valuable asset tothe process design and operating engineer, and are scatteredthroughout this book.
Design by analogy, which is based on knowledge of what hasbeen found to work in similar areas, even though not necessarilyoptimally, is another valuable technique. Accordingly, specificapplications often are described in this book, and many examples ofspecific equipment sizes and performance are cited.
For much of my insight into chemical process design, I amindebted to many years association and friendship with the lateCharles W. Nofsinger who was a prime practitioner by analogy, ruleof thumb, and basic principles. Like Dr. Dolittle of Puddleby-on-the-Marsh, he was a proper doctor and knew a whole lot.
RULES OF THUMB: SUMMARY
Although experienced engineers know where to find informationand how to make accurate computations, they also keep a minimumbody of information in mind on the ready, made up largely ofshortcuts and rules of thumb. The present compilation may fit intosuch a minimum body of information, as a boost to the memory orextension in some instances into less often encountered areas. It isderived from the material in this book and is, in a sense, a digest ofthe book.
An Engineering Rule of Thumb is an outright statementregarding suitable sizes or performance of equipment that obviatesall need for extended calculations. Because any brief statements aresubject to varying degrees of qualification, they are most safelyapplied by engineers who are substantially familiar with the topics.Nevertheless, such rules should be of value for approximate designand cost estimation, and should provide even the inexperiencedengineer with perspective and a foundation whereby the reason-ableness of detailed and computer-aided results can be appraisedquickly, particularly on short notice such as in conference.
Everyday activities also are governed to a large extent by rulesof thumb. They serve us when we wish to take a course of actionbut are not in a position to find the best course of action. Of interestalong this line is an amusing and often useful list of some 900 suchdigests 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 aboutsome topics than about others, which accounts in part for thespottiness of the present coverage, but the spottiness also is due toignorance and oversights on the part of the author. Accordingly,every engineer undoubtedly will supplement or modify this materialin his own way.
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 higherpressures, although the blower range commonly is included inthe compressor range.
2. Vacuum pumps: reciprocating piston type decrease the pressureto 1 Torr; rotary piston down to 0.001 Torr, two-lobe rotarydown to 0.0001 Torr; steam jet ejectors, one stage down tolOOTorr, three stage down to 1 Torr, five stage down to0.05 Torr.
3. A three-stage ejector needs 1OOlb steam/lb air to maintain apressure of 1 Torr.
4. In-leakage of air to evacuated equipment depends on theabsolute pressure, Torr, and the volume of the equipment, Vcuft, according to w = kVz3 lb/hr, with k = 0.2 when P is morethan 90 Torr, 0.08 between 3 and 20 Torr, and 0.025 at less than1 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,,.
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, outlettemperature 306F.
8. Exit temperature should not exceed 350-400F; for diatomicgases (C,/C, = 1.4) this corresponds to a compression ratio ofabout 4.
9. Compression ratio should be about the same in each stage of amultistage unit, ratio = (PJPi), with n stages.
10. Efficiencies of reciprocating compressors: 65% at compressionratio of 1.5, 75% at 2.0, and 80-85% at 3-6.
11. Efficiencies of large centrifugal compressors, 6000-100,000ACFM at suction, are 76-78%.
12. Rotary compressors have efficiencies of 70%, except liquid linertype which have 50%.
CONVEYORS FOR PARTICULATE SOLIDS
1. Screw conveyors are suited to transport of even sticky andabrasive solids up inclines of 20 or so. They are limited todistances of 150ft or so because of shaft torque strength. A12in. dia conveyor can handle 100@3000cuft/hr, at speedsranging from 40 to 60 pm.
2. Belt conveyors are for high capacity and long distances (a mile ormore, but only several hundred feet in a plant), up inclines of30 maximum. A 24in. wide belt can carry 3OOOcuft/hr at aspeed of lOOft/min, but speeds up to 6OOft/min are suited tosome materials. Power consumption is relatively low.Bucker elevators are suited to vertical transport of sticky andabrasive materials. With buckets 20 x 20 in. capacity can reach1000 cuft/hr at a speed of 100 ft/min, but speeds to 300 ft/minare used.Drug-type conveyors (Redler) are suited to short distances in anydirection and are completely enclosed. Units range in size from3 in. square to 19 in. square and may travel from 30 ft/min (flyash) 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 severaldestinations. Either vacuum or low pressure (6-12psig) isemployed with a range of air velocities from 35 to 120ft/secdepending on the material and pressure, air requirements from 1to 7 cuft/cuft of solid transferred.
COOLING TOWERS
1. Water in contact with air under adiabatic conditions eventuallycools 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) 5 15 25Relative volume 2.4 1.0 0.55
4. Tower fill is of a highly open structure so as to minimize pressuredrop, which is in standard practice a maximum of 2 in. of water.
5. Water circulation rate is l-4gpm/sqft and air rates are1300-1800 lb/(hr)(sqft) or 300-400 ft/min.
6. Chimney-assisted natural draft towers are of hyperboloidalshapes because they have greater strength for a given thickness;a tower 250 ft high has concrete walls 5-6 in. thick. The enlargedcross section at the top aids in dispersion of exit humid air intothe atmosphere.
7. Countercurrent induced draft towers are the most common inprocess industries. They are able to cool water within 2F of thewet bulb.
8. Evaporation losses are 1% of the circulation for every 10F ofcooling 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 isnecessary to prevent excessive salt buildup.
CRYSTALLIZATION FROM SOLUTION
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Complete recovery of dissolved solids is obtainable byevaporation, but only to the eutectic composition by chilling.Recovery by melt crystallization also is limited by the eutecticcomposition.Growth rates and ultimate sizes of crystals are controlled bylimiting the extent of supersaturation at any time.The ratio S = C/C,,, of prevailing concentration to saturationconcentration is kept near the range of 1.02-1.05.In crystallization by chilling, the temperature of the solution iskept at most l-2F below the saturation temperature at theprevailing concentration.Growth rates of crystals under satisfactory conditions are in therange of 0.1-0.8 mm/hr. The growth rates are approximately thesame in all directions.Growth rates are influenced greatly by the presence of impuritiesand of certain specific additives that vary from case to case.
DISINTEGRATION
1. Percentages of material greater than 50% of the maximum sizeare about 50% from rolls, 15% from tumbling mills, and 5%from closed circuit ball mills.
2. Closed circuit grinding employs external size classification andreturn of oversize for regrinding. The rules of pneumaticconveying are applied to design of air classifiers. Closed circuit ismost common with ball and roller mills.
3.
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Jaw crushers take lumps of several feet in diameter down to 4 in.Stroke rates are 10@300/min. The average feed is subjected to8-10 strokes before it becomes small enough to escape.Gyratory crushers are suited to slabby feeds and make a morerounded product.Roll crushers are made either smooth or with teeth. A 24in.toothed roll can accept lumps 14in. dia. Smooth rolls effectreduction ratios up to about 4. Speeds are 50-900 rpm. Capacityis about 25% of the maximum corresponding to a continuousribbon of material passing through the rolls.Hammer mills beat the material until it is small enough to passthrough the screen at the bottom of the casing. Reduction ratiosof 40 are feasible. Large units operate at 900 rpm, smaller onesup to 16,OOOrpm. For fibrous materials the screen is providedwith cutting edges.Rod mills are capable of taking feed as large as 50 mm andreducing it to 300 mesh, but normally the product range is 8-65mesh. Rods are 25-150mm dia. Ratio of rod length to milldiameter is about 1.5. About 45% of the mill volume is occupiedby rods. Rotation is at 50-65% of critical.
7. Ball mills are better suited than rod mills to fine grinding. Thecharge is of equal weights of 1.5, 2, and 3 in. balls for the finestgrinding. Volume occupied by the balls is 50% of the millvolume. Rotation speed is 70-80% of critical. Ball mills have alength to diameter ratio in the range l-1.5. Tube mills have aratio of 4-5 and are capable of very fine grinding. Pebble millshave ceramic grinding elements, used when contamination withmetal is to be avoided.
8. Roller mills employ cylindrical or tapered surfaces that roll alongflatter surfaces and crush nipped particles. Products of 20-200mesh are made.
DISTILLATION AND GAS ABSORPTION
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Distillation usually is the most economical method of separatingliquids, superior to extraction, adsorption, crystallization, orothers.For ideal mixtures, relative volatility is the ratio of vaporpressures rri2 = P,/P,.Tower operating pressure is determined most often by thetemperature of the available condensing medium, lOO-120F ifcooling water; or by the maximum allowable reboilertemperature, 150 psig steam, 366F.Sequencing of columns for separating multicomponent mix-tures: (a) perform the easiest separation first, that is, the oneleast demanding of trays and reflux, and leave the most difficultto the last; (b) when neither relative volatility nor feedconcentration vary widely, remove the components one by oneas overhead products; (c) when the adjacent orderedcomponents 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 relativevolatilities do not, remove the components in the order ofdecreasing concentration in the feed.Economically optimum reflux ratio is about 1.2 times theminimum reflux ratio R,.The economically optimum number of trays is near twice theminimum value N,,,.The minimum number of trays is found with the Fenske-Underwood equation
Nn = W[~l(l -~)lovtdM~ - ~)ltxrns~/~~~ a.
Minimum reflux for binary or pseudobinary mixtures is given bythe 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), when feed is at the bubblepoint,(R, + l)D/F = a/((~ - l), when feed is at the dewpoint.
A safety factor of 10% of the number of trays calculated by thebest means is advisable.Reflux pumps are made at least 25% oversize.For reasons of accessibility, tray spacings are made 20-24 in.Peak efficiency of trays is at values of the vapor factorF, = ~6 in the range 1.0-1.2 (ft/sec) B. This range ofF, establishes the diameter of the tower. Roughly, linearvelocities are 2ft/sec at moderate pressures and 6ft/sec invacuum.The optimum value of the Kremser-Brown absorption factorA = K(V/L) is in the range 1.25-2.0.Pressure drop per tray is of the order of 3 in. of water or 0.1 psi.Tray efficiencies for distillation of light hydrocarbons andaqueous solutions are 60-90%; for gas absorption andstripping, lo-20%.Sieve trays have holes 0.25-0.50 in. dia, hole area being 10% ofthe active cross section.Valve trays have holes 1.5 in. dia each provided with a liftablecap, 12-14 caps/sqft of active cross section. Valve trays usuallyare cheaper than sieve trays.Bubblecap trays are used only when a liquid level must bemaintained at low turndown ratio; they can be designed forlower pressure drop than either sieve or valve trays.Weir heights are 2 in., weir lengths about 75% of tray diameter,liquid rate a maximum of about 8 gpm/in. of weir; multipassarrangements are used at high liquid rates.
20. Packings of random and structured character are suitedespecially to towers under 3 ft dia and where low pressure dropis desirable. With proper initial distribution and periodicredistribution, volumetric efficiencies can be made greater thanthose of tray towers. Packed internals are used as replacementsfor achieving greater throughput or separation in existing towershells.
21. For gas rates of 500 cfm, use 1 in. packing; for gas rates of2000 cfm or more, use 2 in.
22. The ratio of diameters of tower and packing should be at least15.
23. Because of deformability, plastic packing is limited to a lo-15 ftdepth unsupported, metal to 20-25 ft.
24. Liquid redistributors are needed every 5-10 tower diameterswith pall rings but at least every 20ft. The number of liquidstreams should be 3-5/sqft in towers larger than 3 ft dia (someexperts say 9-12/sqft), and more numerous in smaller towers.
25. Height equivalent to a theoretical plate (HETP) forvapor-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 rategiven by the correlation of Sherwood, Lobo, et al.
27. Reflux drums usually are horizontal, with a liquid holdup of 5min half full. A takeoff pot for a second liquid phase, such aswater in hydrocarbon systems, is sized for a linear velocity ofthat phase of 0.5 ft/sec, minimum diameter of 16 in.
28. For towers about 3 ft dia, add 4ft at the top for vapordisengagement and 6 ft at the bottom for liquid level andreboiler return.
29. Limit the tower height to about 175 ft max because of wind loadand foundation considerations, An additional criterion is thatL/D be less than 30.
DRIVERS AND POWER RECOVERY EQUIPMENT
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Efficiency is greater for larger machines. Motors are 85-95%;steam turbines are 42-78%; gas engines and turbines are28-38%.For under IOOHP, electric motors are used almost exclusively.They are made for up to 20,000 HP.Induction motors are most popular. Synchronous motors aremade for speeds as low as 150rpm and are thus suited forexample for low speed reciprocating compressors, but are notmade smaller than 50HP. A variety of enclosures is available,from weather-proof to explosion-proof.Steam turbines are competitive above 1OOHP. They are speedcontrollable. Frequently they are employed as spares in case ofpower failure.Combustion engines and turbines are restricted to mobile andremote locations.Gas expanders for power recovery may be justified at capacitiesof several hundred HP; otherwise any needed pressure reductionin process is effected with throttling valves.
DRYING OF SOLIDS
1. Drying times range from a few seconds in spray dryers to 1 hr orless in rotary dryers and up to several hours or even several daysin tunnel shelf or belt dryers.
2. Continuous tray and belt dryers for granular material of naturalsize or pelleted to 3-15 mm have drying times in the range oflo-200 min.
3. Rotary cylindrical dryers operate with superficial air velocities of5-lOft/sec, sometimes up to 35 ft/sec when the material iscoarse. Residence times are S-90 min. Holdup of solid is 7-8%.
RULES OF THUMB: SUMMARY xv
An 85% free cross section is taken for design purposes. Incountercurrent flow, the exit gas is lo-20C above the solid; inparallel flow, the temperature of the exit solid is 100C. Rotationspeeds of about 4rpm are used, but the product of rpm anddiameter in feet is typically between 15 and 25.
4. Drum dryers for pastes and slurries operate with contact times of3-12 set, produce flakes 1-3 mm thick with evaporation rates of15-30 kg/m2 hr. Diameters are 1.5-5.Oft; the rotation rate is2-10rpm. The greatest evaporative capacity is of the order of3000 lb/hr in commercial units.
5. Pneumatic conveying dryers normally take particles l-3 mm diabut up to 10 mm when the moisture is mostly on the surface. Airvelocities are lo-30m/sec. Single pass residence times are0.5-3.0 set but with normal recycling the average residence timeis brought up to 60 sec. Units in use range from 0.2 m dia by 1 mhigh to 0.3 m dia by 38 m long. Air requirement is severalSCFM/lb of dry product /hr .
6. Fluidized bed dryers work best on particles of a few tenths of amm dia, but up to 4 mm dia have been processed. Gas velocitiesof twice the minimum fluidization velocity are a safeprescription. In continuous operation, drying times of l-2minare enough, but batch drying of some pharmaceutical productsemploys drying times of 2-3 hr.
7. Spray dryers: Surface moisture is removed in about 5sec, andmost drying is completed in less than 60 sec. Parallel flow of airand stock is most common. Atomizing nozzles have openings0.012-0.15 in. and operate at pressures of 300-4OOOpsi.Atomizing spray wheels rotate at speeds to 20,000 rpm withperipheral speeds of 250-600 ft/sec. With nozzles, the length todiameter ratio of the dryer is 4-5; with spray wheels, the ratio is0.5-1.0. For the final design, the experts say, pilot tests in a unitof 2 m dia should be made.
EVAPORATORS
1. Long tube vertical evaporators with either natural or forcedcirculation are most popular. Tubes are 19-63 mm dia and12-30 ft long.
2. In forced circulation, linear velocities in the tubes are15-20 ft/sec.
3. Elevation of boiling point by dissolved solids results indifferences of 3-10F between solution and saturated vapor.
4. When the boiling point rise is appreciable, the economic numberof effects in series with forward feed is 4-6.
5. When the boiling point rise is small, minimum cost is obtainedwith 8-10 effects in series.
6. In backward feed the more concentrated solution is heated withthe highest temperature steam so that heating surface islessened, but the solution must be pumped between stages.
7. The steam economy of an N-stage battery is approximately0.8N lb evaporation/lb of outside steam.
8. Interstage steam pressures can be boosted with steam jetcompressors of 20-30% efficiency or with mechanical compres-sors of 70-75% efficiency.
EXTRACTION, LIQUID-LIQUID
1. The dispersed phase should be the one that has the highervolumetric rate except in equipment subject to backmixingwhere it should be the one with the smaller volumetric rate. Itshould be the phase that wets the material of construction lesswell. Since the holdup of continuous phase usually is greater,that phase should be made up of the less expensive or lesshazardous material.
Xvi RULES OF THUMB: SUMMARY
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There are no known commercial applications of reflux toextraction processes, although the theory is favorable (Treybal).Mixer-settler arrangements are limited to at most five stages.Mixing is accomplished with rotating impellers or circulatingpumps. Settlers are designed on the assumption that dropletsizes are about 150 pm dia. In open vessels, residence times of30-60 min or superficial velocities of 0.5-1.5 ft/min are providedin settlers. Extraction stage efficiencies commonly are taken as80%.Spray towers even 20-40ft high cannot be depended on tofunction as more than a single stage.Packed towers are employed when 5-10 stages suffice. Pall ringsof l-l.5 in. size are best. Dispersed phase loadings should notexceed 25 gal/(min) (sqft). HETS of 5-10 ft may be realizable.The dispersed phase must be redistributed every 5-7 ft. Packedtowers are not satisfactory when the surface tension is more than10 dyn/cm.Sieve tray towers have holes of only 3-8 mm dia. Velocitiesthrough the holes are kept below 0.8 ft/sec to avoid formation ofsmall drops. Redispersion of either phase at each tray can bedesigned for. Tray spacings are 6-24 in. Tray efficiencies are inthe range of 20-30%.Pulsed packed and sieve tray towers may operate at frequenciesof 90 cycles/min and amplitudes of 6-25 mm. In large diametertowers, HETS of about 1 m has been observed. Surface tensionsas 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, platespacing normally 2 in. but in the range l-6 in. In a 30in. diatower, 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 realizeHETS in the range 0.1-0.5 m. The especially efficient Kuhniwith perforated disks of 40% free cross section has HETS 0.2 mand a capacity of 50 m3/m2 hr.
FILTRATION
1. Processes are classified by their rate of cake buildup in alaboratory 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. cakethickness cannot be formed in less than 5 min.
3. Rapid filtering is accomplished with belts, top feed drums, orpusher-type centrifuges.
4. Medium rate filtering is accomplished with vacuum drums ordisks or peeler-type centrifuges.
5. Slow filtering slurries are handled in pressure filters orsedimenting centrifuges.
6. Clarification with negligible cake buildup is accomplished withcartridges, precoat drums, or sand filters.
7. Laboratory tests are advisable when the filtering surface isexpected to be more than a few square meters, when cakewashing is critical, when cake drying may be a problem, or whenprecoating may be needed.
8. For finely ground ores and minerals, rotary drum filtration, ratesmay be 1500 lb/(day)(sqft), at 20 rev/hr and 18-25in. Hgvacuum.
9. Coarse solids and crystals may be filtered at rates of 6000lb/(day)(sqft) at 20 rev/hr, 2-6 in. Hg vacuum.
FLUIDIZATION OF PARTICLES WITH GASES
1. Properties of particles that are conducive to smooth fluidizationinclude: rounded or smooth shape, enough toughness to resist
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attrition, sizes in the range 50-500pm dia, a spectrum of sizeswith ratio of largest to smallest in the range of 10-25.Cracking catalysts are members of a broad class characterized bydiameters of 30-150 pm, density of 1.5 g/mL or so, appreciableexpansion of the bed before fluidization sets in, minimumbubbling velocity greater than minimum fluidizing velocity, andrapid disengagement of bubbles.The other extreme of smoothly fluidizing particles is typified bycoarse sand and glass beads both of which have been the subjectof much laboratory investigation. Their sizes are in the range150-500 pm, densities 1.5-4.0 g/mL, small bed expansion, aboutthe same magnitudes of minimum bubbling and minimumfluidizing velocities, and also have rapidly disengaging bubbles.Cohesive particles and large particles of 1 mm or more do notlluidize well and usually are processed in other ways.Rough correlations have been made of minimum fluidizationvelocity, minimum bubbling velocity, bed expansion, bed levelfluctuation, 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 ofthe minimum fluidizing velocity. In reactors, the entrainedmaterial is recovered with cyclones and returned to process. Indryers, the fine particles dry most quickly so the entrainedmaterial need not be recycled.
HEAT EXCHANGERS
1. Take true countercurrent flow in a shell-and-tube exchanger asa basis.
2. Standard tubes are 3/4in. OD, 1 in. triangular spacing, 16 ftlong; 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 pressurefluids.
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.8. Heat transfer coefficients for estimating purposes,
Btu/(hr)(sqft)(F): water to liquid, 150; condensers, 150; liquidto liquid, 50; liquid to gas, 5; gas to gas, 5; reboiler, 200. Maxflux in reboilers, 10,000 Btu/(hr)(sqft).
9. Double-pipe exchanger is competitive at duties requiring
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100-200 sqft.Compact (plate and fin) exchangers have 35Osqft/cuft, andabout 4 times the heat transfer per tuft of shell-and-tube units.Plate and frame exchangers are suited to high sanitationservices, and are 25-50% cheaper in stainless construction thanshell-and-tube units.Air coolers: Tubes are 0.75-1.00 in. OD, total finned surface15-20 sqft/sqft bare surface, U = 80-100 Btu/(hr)(sqft baresurface)( fan power input 2-5 HP/(MBtu/hr), approach50F or more.Fired heaters: radiant rate, 12,000 Btu/(hr)(sqft); convectionrate, 4000; cold oil tube velocity, 6 ft/sec; approx equal transfersof heat in the two sections; thermal efficiency 70-75%; flue gastemperature 250-350F above feed inlet; stack gas temperature650-950F.
INSULATION
1. Up to 650F, 85% magnesia is most used.2. Up to 1600-19OOF, a mixture of asbestos and diatomaceous
earth is used.
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
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Mild agitation is obtained by circulating the liquid with animpeller at superficial velocities of O.l-0.2ft/sec, and intenseagitation at 0.7-1.0 ft/sec.Intensities of agitation with impellers in baffled tanks aremeasured by power input, HP/1000 gal, and impeller tip speeds:
Operation HP/1000 gal Tip speed (ft/min)Blending 0.2-0.5Homogeneous reaction 0.5-l .5 7.5-10Reaction with heat transfer 1.5-5.0 10-15Liquid- l iquid mixtures 5 15-20Liquid-gas mixtures 5-10 15-20Slurries 1 0
Proportions of a stirred tank relative to the diameter D: liquidlevel = D; turbine impeller diameter = D/3; impeller level abovebottom = D/3; impeller blade width = D/15; four vertical baffleswith width = D/10.Propellers are made a maximum of 18 in., turbine impellers to9ft.Gas bubbles sparged at the bottom of the vessel will result inmild agitation at a superficial gas velocity of 1 ft/min, severeagitation at 4 ft/min.Suspension of solids with a settling velocity of 0.03 ft/sec isaccomplished with either turbine or propeller impellers, butwhen the settling velocity is above 0.15 ft/sec intense agitationwith a propeller is needed.Power to drive a mixture of a gas and a liquid can be 25-50%less than the power to drive the liquid alone.In-line blenders are adequate when a second or two contact timeis sufficient, with power inputs of 0.1-0.2 HP/gal.
PARTICLE SIZE ENLARGEMENT
1. The chief methods of particle size enlargement are: compressioninto a mold, extrusion through a die followed by cutting orbreaking to size, globulation of molten material followed bysolidification, agglomeration under tumbling or otherwiseagitated 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 byspeed, residence time, and amount of binder; 2-5 mm dia iscommon.
3. Rotary disk granulators produce a more nearly uniform productthan drum granulators. Fertilizer is made 1.5-3.5 mm; iron orelo-25 mm dia.
4. Roll compacting and briquetting is done with rolls ranging from130mm dia by 50mm wide to 910mm dia by 550mm wide.Extrudates are made l-10 mm thick and are broken down to sizefor any needed processing such as feed to tabletting machines orto dryers.Tablets are made in rotary compression machines that convertpowders and granules into uniform sizes. Usual maximumdiameter is about 1.5 in., but special sizes up to 4in. dia arepossible. Machines operate at 1OOrpm or so and make up to10,000 tablets/min.Extruders make pellets by forcing powders, pastes, and melts
RULES OF THUMB: SUMMARY Xvii
through a die followed by cutting. An 8 in. screw has a capacityof 2000 Ib/hr of molten plastic and is able to extrude tubing at150-3OOft/min and to cut it into sizes as small as washers at8OOO/min. Ring pellet extrusion mills have hole diameters of1.6-32 mm. Production rates cover a range of 30-200Ib/(hr)(HP).Prilling towers convert molten materials into droplets and allowthem to solidify in contact with an air stream. Towers as high as60m are used. Economically the process becomes competitivewith other granulation processes when a capacity of 200-409 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 minimumfluidizing velocity, with evaporation rates of 0.005-1.0 kg/m* sec. One product has a size range 0.7-2.4 mm dia.
PIPING
1. Line velocities and pressure drops, with line diameter D ininches: 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 orgas, 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 ismost common.
PUMPS
1.
2.
3.
4.
5.6.
7.
Power for pumping liquids: HP = (gpm)(psi difference)/(l714)(fractional efficiency).Normal pump suction head (NPSH) of a pump must be in excessof a certain number, depending on the kind of pumps and theconditions, if damage is to be avoided. NPSH = (pressure at theeye of the impeller - vapor pressure)/(density). Common rangeis 4-20 ft.Specific speed N, = (rpm)(gpm)0.5/(head in ft).. Pump may bedamaged if certain limits of N, are exceeded, and efficiency isbest in some ranges.Centrifugal pumps: Single stage for 15-5000gpm, 500ft maxhead; multistage for 20-11,000 gpm, 5500 ft max head. Efficiency45% at 100 gpm, 70% at 500 gpm, 80% at 10,000 gpm.Axial pumps for 20-100,000 gpm, 40 ft head, 65-85% efficiency.Rotary pumps for l-5000 gpm, 50,OOOft head, 50-80%efficiency.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 rate of reaction in every instance must be established in thelaboratory, and the residence time or space velocity andproduct 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 withliquid level equal to the tank diameter, but at high pressuresslimmer proportions are economical.
Xviii RULES OF THUMB: SUMMARY
4. Power input to a homogeneous reaction stirred tank is 0.5-1.5HP/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 thelength of time needed to achieve homogeneity, which isaccomplished with 500-2000 revolutions of a properly designedstirrer.
6.
7.
8.
9.
10.
Batch reactions are conducted in stirred tanks for small dailyproduction rates or when the reaction times are long or whensome condition such as feed rate or temperature must beprogrammed in some way.Relatively slow reactions of liquids and slurries are conductedin continuous stirred tanks. A battery of four or five in series ismost economical.Tubular flow reactors ate suited to high production rates atshort residence times (set or min) and when substantial heattransfer is needed. Embedded tubes or shell-and-tubeconstruction then are used.In granular catalyst packed reactors, the residence timedistribution often is no better than that of a five-stage CSTRbattery.For conversions under about 95% of equilibrium, theperformance of a five-stage CSTR battery approaches plugflow.
REFRIGERATION
1.2.
3.
4.5.
6.
7.
A ton of refrigeration is the removal of 12,000 Btu/hr of heat.At various temperature levels: O-50F, chilled brine and glycolsolutions; -50-40F, ammonia, freons, butane; -150--5OF,ethane or propane.Compression refrigeration with 100F condenser requires theseHP/ton at various temperature levels: 1.24 at 20F; 1.75 at 0F;3.1 at -40F; 5.2 at -80F.Below -80F, cascades of two or three refrigerants are used.In single stage compression, the compression ratio is limited toabout 4.In multistage compression, economy is improved with interstageflashing and recycling, so-called economizer operation.Absorption refrigeration (ammonia to -3OF, lithium bromide to+45F) is economical when waste steam is available at 12 psig orso.
SIZE SEPARATION OF PARTICLES
1. Grizzlies that are constructed of parallel bars at appropriatespacings are used to remove products larger than 5 cm dia.
2. Revolving cylindrical screens rotate at 15-20 rpm and below thecritical velocity; they are suitable for wet or dry screening in therange of lo-60 mm.
3. Flat screens are vibrated or shaken or impacted with bouncingballs. Inclined screens vibrate at 600-70@0 strokes/min and areused for down to 38 pm although capacity drops off sharplybelow 200pm. Reciprocating screens operate in the range30-1000 strokes/min and handle sizes down to 0.25 mm at thehigher speeds.
4. Rotary sifters operate at 500-600 rpm and are suited to a rangeof 12 mm to 50 pm.
5. Air classification is preferred for fine sizes because screens of 150mesh 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 rangebetween 28 and 200 mesh. A rake classifier operates at about 9strokes/min when making separation at 200 mesh, and 32
strokes/min at 28 mesh. Solids content is not critical, and that ofthe overflow may be 2-20% or more.
7. Hydrocyclones handle up to 6OOcuft/min and can removeparticles in the range of 300-5 pm from dilute suspensions. Inone case, a 20in. dia unit had a capacity of 1000 gpm with apressure drop of 5 psi and a cutoff between 50 and 150 pm.
UTILITIES: COMMON SPECIFICATIONS
1.
2.
3.
4.5.6.
7.
Steam: 1.5-30 psig, 250-275F; 150 psig, 366F; 400 psig, 448F;600 psig, 488F or with lOO-150F superheat.Cooling water: Supply at 80-90F from cooling tower, return at115-125F; return seawater at llOF, return tempered water orsteam condensate above 125F.Cooling air supply at 85-95F; temperature approach to process,40F.Compressed air at 45, 150, 300, or 450 psig levels.Instrument air at 45 psig, 0F dewpoint.Fuels: gas of lOOOBtu/SCF at 5-lopsig, or up to 25psig forsome types of burners; liquid at 6 million Btu/barrel.Heat transfer fluids: petroleum oils below 600F, Dowthermsbelow 750F, fused salts below llooF, direct fire or electricityabove 450F.
8. Electricity: l-100 Hp, 220-550 V; 200-2500 Hp, 2300-4000 V.
VESSELS (DRUMS)
1.
2.3.4.
5.
6.7.
8.
9.
10.
11.
12.
13.
14.
Drums are relatively small vessels to provide surge capacity orseparation of entrained phases.Liquid drums usually are horizontal.Gas/liquid separators are vertical.Optimum length/diameter = 3, but a range of 2.5-5.0 iscommon.Holdup time is 5 min half full for reflux drums, 5-10 min for aproduct feeding another tower.In drums feeding a furnace, 30 min half full is allowed.Knockout drums ahead of compressors should hold no less than10 times the liquid volume passing through per minute.Liquid/liquid separators are designed for settling velocity of2-j in./min.Gas velocity in gas/liquid separators, V = kw ft/sec,with k = 0.35 with mesh deentrainer, k = 0.1 without meshdeentrainer.Entrainment removal of 99% is attained with mesh pads of4-12 in. thicknesses; 6 in. thickness is popular.For vertical pads, the value of the coefficient in Step 9 isreduced by a factor of 213.Good performance can be expected at velocities of 30-100% ofthose calculated with the given k; 75% is popular.Disengaging spaces of 6-18in. ahead of the pad and 12in.above the pad are suitable.Cyclone separators can be designed for 95% collection of 5 pmparticles, but usually only droplets greater than 50 pm need beremoved.
VESSELS (PRESSURE)
1. Design temperature between -20F and 650F is 50F aboveoperating temperature; higher safety margins are used outsidethe given temperature range.
2. The design pressure is 10% or 10-25 psi over the maximum oper-ating pressure, whichever is greater. The maximum operatingpressure, in turn, is taken as 25 psi above the normal operation.
3. Design pressures of vessels operating at 0-1Opsig and 600-1000F are 40 psig.
RULES OF THUMB: SUMMARY Xix
4. For vacuum operation, design pressures are 15 psig and fullvacuum.
5. Minimum wall thicknesses for rigidity: 0.25 in. for 42 in. dia andunder, 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 drumsand air receivers.
7. Allowable working stresses are one-fourth of the ultimatestrength of the material.
8. Maximum allowable stress depends sharply on temperature.
Temperature 1F) - 2 0 - 6 5 0 750 850 1000Low alloy steel SA203 (psi) 18 ,750 15,650 9550 2500Type 302 stainless (psi) 18 ,750 18,750 15,900 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 equipmentschedules.
7. Capacities of storage tanks are at least 1.5 times the size ofconnecting transportation equipment; for instance, 7500 gal tanktrucks, 34,500 gal tank cars, and virtually unlimited barge andtanker capacities.
1INTRODUCTION
A/though this book is devoted to the selection and performance is dependent on the others in terms of materialdesign of individual equipment, some mention and energy ba lances and ra te p rocesses . Th is chap te r w i l lshould be made of integration of a number of units discuss general background material relating to completeinto a process. Each piece of equipment interacts process design, and Chapter 2 will treat briefly the basic topic
- w i th seve ra l o the rs i n a p lan t , and the range o f i ts requ i red of flowsheets.
1.1. PROCESS DESIGN
Process design establishes the sequence of chemical and physicaloperations; operating conditions; the duties, major specifications,and materials of construction (where critical) of all processequipment (as distinguished from utilities and building auxiliaries);the general arrangement of equipment needed to ensure properfunctioning of the plant; line sizes; and principal instrumentation.The process design is summarized by a process flowsheet, a materialand energy balance, and a set of individual equipment specifi-cations. Varying degrees of thoroughness of a process design may berequired for different purposes. Sometimes only a preliminarydesign and cost estimate are needed to evaluate the advisability offurther research on a new process or a proposed plant expansion ordetailed design work; or a preliminary design may be needed toestablish the approximate funding for a complete design andconstruction. A particularly valuable function of preliminary designis that it may reveal lack of certain data needed for final design.Data of costs of individual equipment are supplied in this book, butthe complete economics of process design is beyond its scope.
1.2. EQUIPMENT
Two main categories of process equipment are proprietary andcustom-designed. Proprietary equipment is designed by themanufacturer to meet performance specifications made by the user;these specifications may be regarded as the process design of theequipment. This category includes equipment with moving partssuch as pumps, compressors, and drivers as well as cooling towers,dryers, filters, mixers, agitators, piping equipment, and valves, andeven the structural aspects of heat exchangers, furnaces, and otherequipment. Custom design is needed for many aspects of chemicalreactors, most vessels, multistage separators such as fractionators,and other special equipment not amenable to complete stan-dardization.
Only those characteristics of equipment are specified by processdesign that are significant from the process point of view. On apump, for instance, process design will specify the operatingconditions, capacity, pressure differential, NPSH, materials ofconstruction in contact with process liquid, and a few other items,but not such details as the wall thickness of the casing or the type ofstuffing box or the nozzle sizes and the foundation dimensions--although most of these omitted items eventually must be knownbefore a plant is ready for construction. Standard specificationforms are available for most proprietary kinds of equipment and forsummarizing the details of all kinds of equipment. By providingsuitable check lists, they simplify the work by ensuring that allneeded data have been provided. A collection of such forms is inAppendix B.
Proprietary equipment is provided off the shelf in limitedsizes and capacities. Special sizes that would fit particular appli-cations more closely often are more expensive than a larger
standard size that incidentally may provide a worthwhile safetyfactor. Even largely custom-designed equipment, such as vessels, issubject to standardization such as discrete ranges of head diameters,pressure ratings of nozzles, sizes of manways, and kinds of trays andpackings. Many codes and standards are established by governmentagencies, insurance companies, and organizations sponsored byengineering societies. Some standardizations within individualplants are arbitrary choices from comparable methods, made tosimplify construction, maintenance, and repair: for example,restriction to instrumentation of a particular manufacturer or to alimited number of sizes of heat exchanger tubing or a particularmethod of installing liquid level gage glasses. All such restrictionsmust be home in mind by the process designer.
VENDORS QUESTIONNAIRES
A manufacturers or vendors inquiry form is a questionnaire whosecompletion will give him the information on which to base a specificrecommendation of equipment and a price. General informationabout the process in which the proposed equipment is expected tofunction, amounts and appropriate properties of the streamsinvolved, and the required performance are basic. The nature ofadditional information varies from case to case; for instance, beingdifferent for filters than for pneumatic conveyors. Individualsuppliers have specific inquiry forms. A representative selection isin Appendix C.
SPECIFICATION FORMS
When completed, a specification form is a record of the salientfeatures of the equipment, the conditions under which it is tooperate, and its guaranteed performance. Usually it is the basis fora firm price quotation. Some of these forms are made up byorganizations such as TEMA or API, but all large engineeringcontractors and many large operating companies have other formsfor their own needs. A selection of specification forms is inAppendix B.
1.3. CATEGORIES OF ENGINEERING PRACTICE
Although the design of a chemical process plant is initiated bychemical engineers, its complete design and construction requiresthe inputs of other specialists: mechanical, structural, electrical, andinstrumentation engineers; vessel and piping designers; andpurchasing agents who know what may be available at attractiveprices. On large projects all these activities are correlated by a jobengineer or project manager; on individual items of equipment orsmall projects, the process engineer naturally assumes this function.A key activity is the writing of specifications for soliciting bids andultimately purchasing equipment. Specifications must be written soexplicitly that the bidders are held to a uniform standard and aclear-cut choice can be made on the basis of their offerings alone.
1
2 INTRODUCTION
% of Total Project Time
Figure 1.1. Progress of material commitment, engineeringmanhours, and construction [Matozzi, Oil Gas. J. p. 304, (23 March1953)].
% of Total Project Time
Figure 1.2. Rate of application of engineering manhours of variouscategories. The area between the curves represents accumulatedmanhours for each speciality up to a given % completion of theproject [Miller, Chem. Eng., p. 188, (July 1956)].
For a typical project, Figure 1.1 shows the distributions ofengineering, material commitment, and construction efforts. Of theengineering effort, the process engineering is a small part. Figure1.2 shows that it starts immediately and finishes early. In terms ofmoney, the cost of engineering ranges from 5 to 15% or so of thetotal plant cost; the lower value for large plants that are largelypatterned after earlier ones, and the higher for small plants or thosebased 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 islisted in the references at the end of this chapter. Items that areespecially desirable in a personal library or readily accessible areidentified. Specialized references are given throughout the book inconnection with specific topics.
The extensive chemical literature is served by the bibliographicitems cited in References, Section 1.2, Part B. The book byRasmussen and Fredenslund (1980) is addressed to chemical
~engineers and cites some literature not included in some of theother bibliographies, as well as information about proprietary databanks. The book by Leesley (References, Section 1.1, Part B) hasmuch information about proprietary data banks and designmethods. In its current and earlier editions, the book by Peters andTimmerhaus has many useful bibliographies on classified topics.
For information about chemical manufacturing processes, themain 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,
but an English version was started in 1984 and three volumes peryear are planned; this beautifully organized reference should bemost welcome.
The most comprehensive compilation of physical property datais that of Landolt-Bornstein (1950-date) (References, Section 1.2,Part C). Although most of the material is in German, recentvolumes have detailed tables of contents in English and somevolumes are largely in English. Another large compilation,somewhat venerable but still valuable, is the International CriticalTables (1926-1933). Data and methods of estimating properties ofhydrocarbons and their mixtures are in the API Data Book(1971-date) (References, Section 1.2, Part C). More generaltreatments of estimation of physical properties are listed inReferences, Section 1.1, Part C. There are many compilations ofspecial data such as solubilities, vapor pressures, phase equilibria,transport and thermal properties, and so on. A few of them arelisted in References, Section 1.2, Part D, and references to manyothers are in the References, Section 1.2, Part B.
Information about equipment sizes and configurations, andsometimes performance, of equipment is best found in manufac-turers catalogs. Items 1 and 2 of References, Section 1.1, Part D,contain some advertisements with illustrations, but perhaps theirprincipal value is in the listings of manufacturers by the kind ofequipment. Thomas Register covers all manufacturers and so is lessconvenient at least for an initial search. The other three items ofthis group of books have illustrations and descriptions of all kinds ofchemical process equipment. Although these books are old, one issurprised to note how many equipment designs have survived.
1.5. CODES, STANDARDS, ANDRECOMMENDED PRACTICES
A large body of rules has been developed over the years to ensurethe safe and economical design, fabrication and testing ofequipment, structures, and materials. Codification of these ruleshas been done by associations organized for just such purposes,by professional societies, trade groups, insurance underwritingcompanies, and government agencies. Engineering contractors andlarge manufacturing companies usually maintain individual sets ofstandards so as to maintain continuity of design and to simplifymaintenance of plant. Table 1.1 is a representative table of contentsof the mechanical standards of a large oil company.
Typical of the many thousands of items that are standardized inthe field of engineering are limitations on the sizes and wallth,icknesses of piping, specifications of the compositions of alloys,stipulation of the safety factors applied to strengths of constructionmaterials, testing procedures for many kinds of materials, and soo n .
Although the safe design practices recommended by profes-sional and trade associations have no legal standing where they havenot actually been incorporated in a body of law, many of them havethe respect and confidence of the engineering profession as a wholeand have been accepted by insurance underwriters so they arewidely observed. Even when they are only voluntary, standardsconstitute a digest of experience that represents a minimum re-quirement 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 areconcerned. National Bureau of Standards Publication 329 containsabout 25,000 titles of U.S. standards. The NBS-SIS servicemaintains a reference collection of 200,000 items accessible by letteror phone. Information about foreign standards is obtainablethrough the American National Standards Institute (ANSI).
A listing of codes and standards bearing directly on process
TABLE 1.1. Internal Engineering Standards of a LargePetroleum Refinery
1 Appropriations and mechanical orders (10)2 Buildings-architectural (15)3 Buildings-mechanical (10)4 Capacities and weights (25)5 Contracts (I 0)6 Cooling towers (10)7 Correspondence (5)8 Designation and numbering rules for equipment and facil i t ies (10)
/ 9 Drainage (25)1 0 Electrical (10)1 1 Excavat ing, grading, and paving (10)1 2 Fi re f ight ing (10)1 3 Furnaces and boilers (10)1 4 General instructions (20)1 5 Handling equipment (5)1 6 Heat exchangers (IO)1 7 Instruments and controls (45)1 8 Insulat ion (IO)1 9 Machinery (35)2 0 Material procurement and disposition (20)2 1 Material selection (5)2 2 Miscellaneous process equipment (25)2 3 Personnel protective equipment (5)2 4 P ip ing (150)2 5 Piping supports (25)2 6 Plant layout (20)2 7 Pressure vessels (25)2 8 Protective coatings (IO)2 9 Roads and railroads (25)3 0 Storage vessels (45)3 1 Structural (35)3 2 Symbols and drafting practice (15)3 3 Welding (10)
Figures in parentheses identify the numbers of distinct standards.
TABLE 1.2. Codes and Standards of Direct Bearin onChemical Process Design (a Selection
A. American Institute of Chemical Engineers, 345 E. 47th St., New York,NY 10017
1. Standard testing procedures; 21 have been published, forexample on centrifuges, filters, mixers, firer heaters
B. American Petroleum Institute, 2001 L St. NW, Washington, DC 200372. Recommended practices for refinery inspections3. Guide for inspection of refinery equipment4. Manual on disposal of refinery wastes5. Recommended practice for design and construction of large, low
pressure storage tanks6. Recommended practice for design and construction of pressure
re l iev ing dev ices7. Recommended practices for safety and fire protection
C. American Society of Mechanical Engineers, 345 W. 47th St., NewYork, NY 10017
8. ASME Boiler and Pressure Vessel Code. Sec. VIII, UnfiredPressure Vessels
9. Code for pressure piping10; Scheme for identif ication of piping systems
D. American Society for Testing Materials, 1916 Race St., Philadelphia,PA 1910311. ASTM Standards, 66 volumes in 16 sections, annual, with about
30% revision each yearE. American National Standards Institute (ANSI), 1430 Broadway, New
York, NY 1001812. Abbreviations, letter symbols, graphical symbols, drawing and
drafting room practice
1.6. MATERIAL AND ENERGY BALANCES 3
TABLE 1.2-( continued)
F. Chemical Manufacturers Association, 2501 M St. NW, Washington,D C 2 0 0 3 713. Manual of standard and recommended practices for containers,
tank cars, pollution of air and water14. Chemical safety data sheets of individual chemicals
G. Cooling Tower Institute, 19827 Highway 45 N, Spring, TX 7738815. Acceptance test procedure for water cooling towers of
mechanical draft industrial typeH. Hydraulic Institute, 712 Lakewood Center N, 14600 Detroit Ave.,
Cleveland, OH 4410716. Standards for centrifugal, reciprocating, and rotary pumps17. Pipe friction manual
I. Instrument Society of America (ISA), 67 Alexander Dr., ResearchTriangle Park, NC 2770918. Instrumentation f low plan symbols19. Specification forms for instruments20. Dynamic response testing of process control instrumentation
J. Tubular Exchangers Manufacturers Association, 25 N Broadway,Tarrytown, NY 1059121. TEMA standards
K. International Standards Organization (ISO), 1430 Broadway, NewYork, NY 1001822. Many standards
TABLE 1.3. Codes and Standards Supplementary to ProcessDesign (a Selection)
A. American Concrete Institute, 22400 W. 7 Mile Rd., Detroit, Ml 482191. Reinforced concrete design handbook2. Manual of standard practice for detail ing reinforced concrete
structuresB. American Institute of Steel Construction, 400 N. Michigan Ave.,
Chicago, IL 606113. Manual of steel construction4. Standard practice for steel buildings and bridges
C. American Iron and Steel Institute, 1000 16th St. NW, Washington, DC20036
5. AISI standard steel compositionsD. American Society of Heating, Refrigerating and Air Condit ioning
Engineers (ASHRE), 1791 Tullie Circle NE, Atlanta, GA 303296. Refrigerating data book
E. Institute of Electrical and Electronics Engineers, 345 E. 47th St., NewYork, NY 100177. Many standards
F. National Bureau of Standards, Washington, DC8. American standard building code9. National electrical code
G. National Electrical Manufacturers Association, 2101 L St. NW,Washington, DC 2003710. NEMA standards
design is in Table 1.2, and of supplementary codes and standards inTable 1.3.
1.6. MATERIAL AND ENERGY BALANCES
Material and energy balances arc based on a conservation law whichis stated generally in the form
input + source = output + sink + accumulation.
The individual terms can be plural and can be rates as well asabsolute quantities. Balances of particular entities are made arounda bounded region called a system. Input and output quantities of anentity cross the boundaries. A source is
