Chemical process equipment selection and design, 3rd edition

Preface to the First EditionThis 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.. Chemica

Chemical Process Equipment

Dr Fair was a colleague at Monsanto of both Dr Roy Penney and Dr James R Couper He will be sorelymissed since we relied on his advice and counsel during the preparation of this book’s manuscript.

Chemical Process Equipment

Selection and Design

Third Edition

James R Couper

W Roy Penney James R Fair Stanley M Walas

AMSTERDAM • BOSTON • HEIDELBERG • LONDON NEW YORK • OXFORD • PARIS • SAN DIEGO SAN FRANCISCO • SINGAPORE • SYDNEY • TOKYO

First edition 1988

Second edition 2005

Revised second edition 2010

Third edition 2012

Copyright © 2012 Elsevier Inc All rights reserved

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Notices

Knowledge and best practice in this field are constantly changing As new research and experience broaden ourunderstanding, changes in research methods, professional practices, or medical treatment may become necessary.Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using anyinformation, methods, compounds, or experiments described herein In using such information or methods they should

be mindful of their own safety and the safety of others, including parties for whom they have a professionalresponsibility

To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability forany injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from anyuse or operation of any methods, products, instructions, or ideas contained in the material herein

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12 13 10 9 8 7 6 5 4 3 2 1

ContentsPREFACE TO THE THIRD EDITION ix

PREFACE TO THE SECOND EDITION x

PREFACE TO THE FIRST EDITION xi

1.3 Categories of Engineering Practice 1

1.4 Sources of Information for Process Design 2

1.5 Codes, Standards, and Recommended Practices 2

1.6 Material and Energy Balances 3

1.7 Economic Balance 4

1.8 Design Safety Factors 6

1.9 Safety of Plant and Environment 7

1.10 Steam and Power Supply 8

1.11 Design Basis 10

1.12 Laboratory and Pilot Plant Work 12

Other Sources of Information 15

CHAPTER 3 PROCESS CONTROL 31

3.1 The Feedback Control Loop 31

3.2 Control Loop Performance and Tuning Procedures 33

3.3 Single Stream Control 34

3.4 Unit Operation Control 37

Bibliography 51

CHAPTER 4 DRIVERS FOR MOVING EQUIPMENT 53

4.1 Motors 53

4.2 Steam Turbines and Gas Expanders 54

4.3 Combustion Gas Turbines and Engines 57

CHAPTER 6 FLOW OF FLUIDS 83

6.1 Properties and Units 83

6.2 Energy Balance of a Flowing Fluid 84

6.3 Liquids 86

6.4 Pipeline Networks 886.5 Optimum Pipe Diameter 926.6 Non-Newtonian Liquids 936.7 Gases 99

6.8 Liquid-Gas Flow in Pipelines 1036.9 Granular and Packed Beds 1066.10 Gas-Solid Transfer 1106.11 Fluidization of Beds of Particles with Gases 111References 118

CHAPTER 7 FLUID TRANSPORT EQUIPMENT 1217.1 Piping 121

7.2 Pump Theory 1237.3 Pump Characteristics 1267.4 Criteria for Selection of Pumps 1287.5 Equipment for Gas Transport 1307.6 Theory and Calculations of Gas Compression 1397.7 Ejector and Vacuum Systems 152

References 159

8.1 Conduction of Heat 1618.2 Mean Temperature Difference 1638.3 Heat Transfer Coefficients 1658.4 Data of Heat Transfer Coefficients 1718.5 Pressure Drop in Heat Exchangers 1838.6 Types of Heat Exchangers 1848.7 Shell-and-Tube Heat Exchangers 1878.8 Condensers 195

8.9 Reboilers 1998.10 Evaporators 2018.11 Fired Heaters 2028.12 Insulation of Equipment 2118.13 Refrigeration 214

References 220

9.1 Interaction of Air and Water 2239.2 Rate of Drying 226

9.3 Classification and General Characteristics

of Dryers 2309.4 Batch Dryers 2349.5 Continuous Tray and Conveyor Belt Dryers 2369.6 Rotary Cylindrical Dryers 239

9.7 Drum Dryers for Solutions and Slurries 2469.8 Pneumatic Conveying Dryers 247

9.9 Flash and Ring Dryers 2499.10 Fluidized Bed Dryers 2539.11 Spray Dryers 2599.12 Cooling Towers 266References 275CHAPTER 10 MIXING AND AGITATION 27710.1 A Basic Stirred Tank Design 277

10.2 Vessel Flow Patterns 27910.3 Agitator Power Requirements 28110.4 Impeller Pumping 281

10.5 Tank Blending 28110.6 Heat Transfer 287v

CHAPTER 11 SOLID-LIQUID SEPARATION 329

11.1 Processes and Equipment 329

11.2 Liquid-Particle Characteristics 330

11.3 Theory of Filtration 330

11.4 Resistance to Filtration 337

11.5 Thickening and Clarifying 341

11.6 Laboratory Testing and Scale-Up 342

11.7 Illustrations of Equipment 343

11.8 Applications and Performance of Equipment 355

References 359

CHAPTER 12 DISINTEGRATION, AGGLOMERATION,

AND SIZE SEPARATION OF PARTICULATE SOLIDS 361

12.1 Screening 361

12.2 Commercial Classification with Streams of Air or

Water 368

12.3 Size Reduction 368

12.4 Equipment for Size Reduction 370

12.5 Particle Size Enlargement (Agglomeration) 378

13.2 Single-Stage Flash Calculations 402

13.3 Evaporation or Simple Distillation 406

13.9 Separations in Packed Towers 427

13.10 Basis for Computer Evaluation of Multicomponent

Extraction 50314.7 Equipment for Extraction 50714.8 Pilot-Testing 526

References 527

CHAPTER 15 ADSORPTION AND ION EXCHANGE 52915.1 Adsorption Processes 529

15.2 Adsorbents 52915.3 Adsorption Behavior in Packed Beds 53615.4 Regeneration 537

15.5 Gas Adsorption Cycles 54315.6 Adsorption Design and Operating Practices 54415.7 Parametric Pumping 547

15.8 Ion Exchange Processes 54815.9 Production Scale Chromatography 554General References 558

CHAPTER 16 CRYSTALLIZATION FROM SOLUTIONSAND MELTS 561

16.1 Some General Crystallization Concepts 56216.2 Importance of the Solubility Curve in Crystallizer

Design 56316.3 Solubilities and Equilibria 56316.4 Crystal Size Distribution 56616.5 The Process of Crystallization 56616.6 The Ideal Stirred Tank 57416.7 Kinds of Crystallizers 57716.8 Melt Crystallization and Purification 584References 589

CHAPTER 17 CHEMICAL REACTORS 59117.1 Design Basis and Space Velocity 59117.2 Rate Equations and Operating Modes 59117.3 Material and Energy Balances of Reactions 59617.4 Nonideal Flow Patterns 597

17.5 Selection of Catalysts 60217.6 Types and Examples of Reactors 60817.7 Heat Transfer in Reactors 62317.8 Classes of Reaction Processes and Their Equipment 63017.9 Biochemical Reactors and Processes 642

References 675

19.1 Membrane Processes 67719.2 Liquid-Phase Separations 683

19.3 Gas Permeation 684

19.4 Membrane Materials and Applications 684

19.5 Membrane Cells and Equipment Configurations 686

19.6 Industrial Applications 687

19.7 Subquality Natural Gas 687

19.8 The Enhancement of Separation 690

19.9 Permeability Units 693

19.10 Derivations and Calculations for Single-Stage Membrane

Separations 697

19.11 Representation of Multistage Membrane Calculations

for a Binary System 703

19.12 Potential Large-Scale Commercialization 706

References 707

CHAPTER 20 GAS-SOLID SEPARATIONS 709

20.1 Gas-Solid Separations 709

20.2 Foam Separation and Froth Flotation 717

20.3 Sublimation and Freeze Drying 719

20.4 Separations by Thermal Diffusion 720

Preface to the Third Edition

This edition of the book contains revised and updated information

from both the second edition and the revised second edition, as

well as new material as of early 2010 The authors and

collabora-tors have included information essential to the design and

specifi-cation of equipment needed for the ultimate purchasing of

equipment The vast amount of literature has been screened so that

only time-tested practical methods that are useful in the design and

specification of equipment are included The authors and

colla-borators have used their judgment about what to include based

upon their combined industrial and academic experience The

emphasis is on design techniques and practice as well as what is

required to work with vendors in the selection and purchase of

equipment This material would be especially helpful to the young

engineer entering industry, thus bridging the gap between

aca-demia and industry.Chapters 10, 13, 14, 15, and 16 have been

extensively updated and revised compared to the second andrevised second editions of the book

Dr Wayne J Genck, President of Genck International, a owned international expert on crystallization has joined the con-tributors, replacing John H Wolf, Retired President of SwensonProcess Equipment Company

ren-Older methods and obsolete equipment for the most part havebeen removed If the reader has an interest in older material, he orshe might consult previous editions of this book

This book is not intended as a classroom text, however, withsome modifications and addition of examples and problems, itcould be used for teaching purposes

James R Couper

W Roy Penney

ix

The editors of the revised edition are in agreement with the

philo-sophy and the approach that Professor Stanley Walas presented in

the original edition In general, the subject headings and format of

each chapter have been retained but the revised edition has been

corrected to eliminate errors and insofar as possible update the

contents of each chapter Material that we consider superfluous

or beyond the scope and intent of the revised edition has been

eliminated Most of the original text has been retained, since the

methods have stood the test of time and we felt that any revision

had to be a definite improvement

Chapter 3, Process Control, andChapter 10, Mixing and

Agi-tation, have been completely revised to bring the content of these

chapters up to date Chapter 18, Process Vessels, has been

expanded to include the design of bins and hoppers.Chapter 19,

Membrane Separations, is an entirely new chapter We felt that

this topic has gained considerable attention in recent years in

che-mical processing and deserved to be a chapter devoted to this

important material.Chapter 20, Gas-Solid Separation and Other

Topics, consists of material on gas-solid handling as well as the

remainder of the topics inChapter 19of the original edition

Chap-ter 21, Costs of Individual Equipment, is a revision ofChapter 20

in the original edition and the algorithms have been updated to late

2002 Costs calculated from these algorithms have been checked with equipment suppliers and industrial sources Theyhave been found to be within 20 to 25% accurate

spot-We have removed almost all the Fortran computer programlistings, since every engineer has his or her own methods for sol-ving such problems There is one exception and that is the firedheater design Fortran listing inChapter 8, Heat Transfer and HeatExchangers Our experience is that the program provides insightinto a tedious and involved calculation procedure

Although the editors of this text have had considerable trial and academic experience in process design and equipmentselection, there are certain areas in which we have limited or noexperience It was our decision to ask experts to serve as collabora-tors We wish to express our profound appreciation to those collea-gues and they are mentioned in the List of Contributors

indus-We particularly wish to acknowledge the patience and standing of our wives, Mary Couper, Merle Fair, and AnnettePenney, during the preparation of this manuscript

under-James R CouperJames R Fair

W Roy Penney

x

Preface to the First Edition

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 inChapter 1is

desir-able 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

equip-ment say that their equipequip-ment 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

appli-cations, which this book attempts to provide Much of the

infor-mation 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

chap-ters Information about peripheral and less widely employed

equip-ment 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

Appen-dixes provide examples of equipment rating forms and

manufac-turers’ 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,

con-veyors, 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

selec-tion from the manufacturers’ offerings, often with their

recommen-dations or on the basis of individual experience Complete

information is provided in manufacturers’ catalogs Several

classi-fied lists of manufacturers of chemical process equipment are

read-ily accessible, so no listings are given here

Because more than one kind of equipment often is suitable forparticular applications and may be available from several manu-facturers, comparisons of equipment and typical applications arecited liberally Some features of industrial equipment are largelyarbitrary and may be standardized for convenience in particularindustries or individual plants Such aspects of equipment designare noted 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 broadsurvey and limited space as this book References to sources ofmore 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 obviateall need for further calculations Typical examples, for instance, arethat optimum reflux ratio is 20% greater than minimum, that a sui-table cold oil velocity in a fired heater is 6 ft/sec, or that the efficiency

of a mixer-settler extraction stage is 70% The trust that can beplaced in a rule of thumb depends on the authority of the propoun-der, the risk associated with its possible inaccuracy, and the eco-nomic balance between the cost of a more accurate evaluation andsuitable safety factor placed on the approximation All experiencedengineers have acquired such knowledge When applied with discri-mination, rules of thumb are a valuable asset to the process designand operating engineer, and are scattered throughout 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

of specific 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,rule of thumb, and basic principles Like Dr Dolittle of Puddleby-on-the-Marsh,“he was a proper doctor and knew a whole lot”

Stanley M Walas

xi

James R Couper, D.Sc (Editor), Professor Emeritus, Department

of Chemical Engineering, University of Arkansas, Fayetteville,

AR; Fellow, A.I.Ch.E., Registered Professional Engineer

(Arkan-sas and Missouri)

James R Fair, Ph.D (Distillation and Absorption, Adsorption

Extraction and Leaching) (Co-editor), McKetta Chair Emeritus

Professor, Department of Chemical Engineering, The University

of Texas, Austin, TX; Fellow, A.I.Ch.E., Registered Professional

Engineer (Missouri and Texas)

Wayne J Genck, Ph.D., MBA (Crystallization), President, Genck

International, Park Forest, IL

E J Hoffman, Ph.D (Membrane Separations), Professor

Emeri-tus, Department of Chemical Engineering, University of

Wyom-ing, Laramie, WY

W Roy Penney, Ph.D (Flow of Fluids, Fluid Transport ment, Drivers for Moving Equipment, Heat Transfer and HeatExchangers, Mixing and Agitation) (Co-editor), Professor of Che-mical Engineering, University of Arkansas, Fayetteville, AR;Registered Professional Engineer (Arkansas and Missouri)

Equip-A Frank Seibert, Ph.D (Extraction and Leaching), Professor,Department of Chemical Engineering, University of Texas, Austin,

TX, Registered Professional Engineer (Texas)Terry L Tolliver, Ph.D (Process Control), Retired, Solutia,

St Louis, Fellow, A.I.Ch.E and ISA, Registered ProfessionalEngineer (Missouri)

xii

Chapter 0 RULES OF THUMB: SUMMARY

Although experienced engineers know where to find information

and how to make accurate computations, they also keep a

mini-mum body of information readily available, made largely of

short-cuts and rules of thumb This compilation is such a body of

information from the material in this book and is, in a sense, a

digest of the book

Rules of thumb, also known as heuristics, are statements of

known facts The word heuristics is derived from Greek, to

dis-cover or to invent, so these rules are known or disdis-covered through

use and practice but may not be able to be theoretically proven In

practice, they work and are most safely applied by engineers who

are familiar with the topics Such rules are of value for

approxi-mate design and preliminary cost estimation, and should provide

even the inexperienced engineer with perspective and whereby the

reasonableness of detailed and computer-aided design can be

appraised quickly, especially on short notice, such as a conference

Everyday activities are frequently governed by rules of thumb

They serve us when we wish to take a course of action but we may

not be in a position to find the best course of action

Much more can be stated in adequate fashion about some

topics than others, which accounts, in part, for the spottiness of

the present coverage Also, the spottiness is due to the ignorance

and oversights on the part of the authors Therefore, every

engi-neer undoubtedly will supplement or modify this material (Walas,

1988)

COMPRESSORS AND VACUUM PUMPS

1 Fans are used to raise the pressure about 3% (12 in 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

pres-sure 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 100 Torr, three stage down to 1 Torr, five stage down to

0.05 Torr

3 A three-stage ejector needs 100 lb steam/lb air to maintain a

pressure of 1 Torr

4 In-leakage of air to evacuated equipment depends on the

abso-lute pressure, Torr, and the volume of the equipment, V cuft,

according to w = kV2/3lb/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 horsepowerðTHPÞ = ½ðSCFMÞT1=8130a

½ðP2=P1Þa−1, where T1is inlet temperature in°F + 460 and

a = (k− 1)/k, k = Cp/Cv

6 Outlet temperature T2= T1ðP2=P1Þa:

7 To compress air from 100°F, k = 1.4, compression ratio = 3,

theoretical power required = 62 HP/million cuft/day, outlet

temperature 306°F

8 Exit temperature should not exceed 350–400°F; for diatomic

gases (Cp/Cv = 1.4) this corresponds to a compression ratio

of about 4

9 Compression ratio should be about the same in each stage of a

multistage unit, ratio = (Pn/P1)1/n, with n stages

10 Efficiencies of fans vary from 60–80% and efficiencies of

blowers are in the range of 70–85%

11 Efficiencies of reciprocating compressors: 65–70% at sion ratio of 1.5, 75–80% at 2.0, and 80–85% at 3–6

compres-12 Efficiencies of large centrifugal compressors, 6000–100,000ACFM at suction, are 76–78%

13 Rotary compressors have efficiencies of 70–78%, except liner type which have 50%

liquid-14 Axial flow compressor efficiencies are in the range of 81–83%.CONVEYORS FOR PARTICULATE SOLIDS

1 Screw conveyors are used to transport even sticky and abrasivesolids up inclines of 20° or so They are limited to distances of

150 ft or so because of shaft torque strength A 12 in dia veyor can handle 1000–3000 cuft/hr, at speeds ranging from

con-40 to 60 rpm

2 Belt conveyors are for high capacity and long distances (a mile ormore, but only several hundred feet in a plant), up inclines of 30°maximum A 24 in wide belt can carry 3000 cuft/hr at a speed of

100 ft/min, but speeds up to 600 ft/min are suited for some rials The number of turns is limited and the maximum incline is

mate-30 degrees Power consumption is relatively low

3 Bucket elevators are used for vertical transport of sticky andabrasive materials With buckets 20× 20 in capacity can reach

1000 cuft/hr at a speed of 100 ft/min, but speeds to 300 ft/minare used

4 Drag-type conveyors (Redler) are suited for short distances in anydirection and are completely enclosed Units range in size from

3 in square to 19 in square and may travel from 30 ft/min (flyash) to 250 ft/min (grains) Power requirements are high

5 Pneumatic conveyors are for high capacity, short distance(400 ft) transport simultaneously from several sources to severaldestinations Either vacuum or low pressure (6–12 psig) isemployed with a range of air velocities from 35 to 120 ft/secdepending on the material and pressure Air requirements arefrom 1 to 7 cuft/cuft of solid transferred

COOLING TOWERS

1 Water in contact with air under adiabatic conditions tually cools to the wet bulb temperature

even-2 In commercial units, 90% of saturation of the air is feasible

3 Relative cooling tower size is sensitive to the differencebetween the exit and wet bulb temperatures:

7 Countercurrent induced draft towers are the most common inprocess industries They are able to cool water within 2°F ofthe wet bulb

xiii

cooling range Windage or drift losses of mechanical draft

towers are 0.1–0.3% Blowdown of 2.5–3.0% of the circulation

is necessary to prevent excessive salt buildup

9 Towers that circulate cooling water to several process units

and are vulnerable to process intrusion should not use film fill

due to the risk of fouling and fill failure (Huchler, 2009)

10 Sites with nearby obstructions or where there is the risk that

the tower plume or combustion exhaust may be entrained

should use a couterflow configuration, and may need special

air intake designs (Huchler, 2009)

11 If the facility, like a power plant, has very high heat loads

requiring high recirculating water rates and large cooling

loads, it may require the use of natural-draft towers with

hyperbolic concrete shells (Huchler, 2009)

12 The use of variable-frequency fan drives increase capital costs

and provide operating flexibility for towers of two or more

cells (Huchler, 2009)

CRYSTALLIZATION FROM SOLUTION

1 The feed to a crystallizer should be slightly unsaturated

2 Complete recovery of dissolved solids is obtainable by

evapora-tion, but only to the eutectic composition by chilling Recovery

by melt crystallization also is limited by the eutectic composition

3 Growth rates and ultimate sizes of crystals are controlled by

limiting the extent of supersaturation at any time

4 Crystal growth rates are higher at higher temperatures

5 The ratio S = C/Csatof prevailing concentration to saturation

concentration is kept near the range of 1.02–1.05

6 In crystallization by chilling, the temperature of the solution is

kept at most 1–2°F below the saturation temperature at the

prevailing concentration

7 Growth rates of crystals under satisfactory conditions are in

the range of 0.1–0.8 mm/hr The growth rates are

approxi-mately the same in all directions

8 Growth rates are influenced greatly by the presence of

impuri-ties and of certain specific additives that vary from case to case

9 Batch crystallizers tend to have a broader crystal size

distribu-tion than continuous crystallizers

10 To narrow the crystal size distribution, cool slowly through the

initial crystallization temperature or seed at the initial

crystal-lization temperature

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

con-veying are applied to design of air classifiers Closed circuit

is most common with ball and roller mills

3 Jaw and gyratory crushers are used for coarse grinding

4 Jaw crushers take lumps of several feet in diameter down to

4 in Stroke rates are 100–300/min The average feed is

sub-jected to 8–10 strokes before it becomes small enough to

escape Gyratory crushers are suited for slabby feeds and make

a more rounded product

5 Roll crushers are made either smooth or with teeth A 24 in

toothed roll can accept lumps 14 in dia Smooth rolls effect

reduction ratios up to about 4 Speeds are 50–900 rpm

Capa-city is about 25% of the maximum corresponding to a

contin-uous ribbon of material passing through the rolls

through the screen at the bottom of the casing Reductionratios of 40 are feasible Large units operate at 900 rpm, smal-ler ones up to 16,000 rpm For fibrous materials the screen isprovided with cutting edges

7 Rod mills are capable of taking feed as large as 50 mm andreducing it to 300 mesh, but normally the product range is

8–65 mesh Rods are 25–150 mm dia Ratio of rod length tomill diameter is about 1.5 About 45% of the mill volume isoccupied by rods Rotation is at 50–65% of critical

8 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

a length to diameter ratio in the range 1–1.5 Tube mills have

a ratio of 4–5 and are capable of very fine grinding Pebblemills have ceramic grinding elements, used when contamina-tion with metal is to be avoided

9 Roller mills employ cylindrical or tapered surfaces that rollalong flatter surfaces and crush nipped particles Products of

20–200 mesh are made

10 Fluid energy mills are used to produce fine or ultrafine cron) particles

(submi-DISTILLATION AND GAS ABSORPTION

1 Distillation usually is the most economical method of ing liquids, superior to extraction, adsorption, crystallization,

tem-5 Sequencing of columns for separating multicomponent mixtures:(a) perform the easiest separation first, that is, the one leastdemanding of trays and reflux, and leave the most difficult tothe last; (b) when neither relative volatility nor feed concentra-tion vary widely, remove the components one by one as overheadproducts; (c) when the adjacent ordered components in the feedvary widely in relative volatility, sequence the splits in the order

of decreasing volatility; (d) when the concentrations in the feedvary widely but the relative volatilities do not, remove the com-ponents in the order of decreasing concentration in the feed

6 Flashing may be more economical than conventional tion but is limited by the physical properties of the mixture

distilla-7 Economically optimum reflux ratio is about 1.25 times theminimum reflux ratio Rm

8 The economically optimum number of trays is nearly twice theminimum value Nm

9 The minimum number of trays is found with the Underwood equation

Fenske-Nm= log f½ðx=ð1−xÞovhd=½x=ð1−xÞbtmsg= log α:

10 Minimum reflux for binary or pseudobinary mixtures is given bythe following when separation is essentially completeðxD≃1Þ andD/F is the ratio of overhead product and feed rates:

RmD=F = 1=ðα−1Þ, when feed is at the bubblepoint,

ðR + 1ÞD=F = α=ðα−1Þ, when feed is at the dewpoint:

11 A safety factor of 10% of the number of trays calculated by the

best means is advisable

12 Reflux pumps are made at least 25% oversize

13 For reasons of accessibility, tray spacings are made 20–30 in

14 Peak efficiency of trays is at values of the vapor factor

Fs= u ffiffiffiffiffiρv

p

in the range 1.0–1.2 (ft/sec)pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffilb=cuft: This range

of Fs establishes the diameter of the tower Roughly, linear

velocities are 2 ft/sec at moderate pressures and 6 ft/sec in

17 Tray efficiencies for distillation of light hydrocarbons and

aqu-eous solutions are 60–90%; for gas absorption and stripping,

10–20%

18 Sieve trays have holes 0.25–0.50 in dia, hole area being 10% of

the active cross section

19 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

20 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

21 Weir heights are 2 in., weir lengths about 75% of tray

dia-meter, liquid rate a maximum of about 8 gpm/in of weir;

mul-tipass arrangements are used at high liquid rates

22 Packings of random and structured character are suited

espe-cially to towers under 3 ft dia and where low pressure drop

is desirable With proper initial distribution and periodic

redis-tribution, 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

23 For gas rates of 500 cfm, use 1 in packing; for gas rates of

2000 cfm or more, use 2 in

24 The ratio of diameters of tower and packing should be at least

15

25 Because of deformability, plastic packing is limited to a 10–15 ft

depth unsupported, metal to 20–25 ft

26 Liquid redistributors are needed every 5–10 tower diameters

with pall rings but at least every 20 ft 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

27 Height equivalent to a theoretical plate (HETP) for

vapor-liquid contacting is 1.3–1.8 ft for 1 in pall rings, 2.5–3.0 ft

for 2 in pall rings

28 Packed towers should operate near 70% of the flooding rate

given by the correlation of Sherwood, Lobo, et al

29 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

30 For towers about 3 ft dia, add 4 ft at the top for vapor

disen-gagement and 6 ft at the bottom for liquid level and reboiler

return

31 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

1 Efficiency is greater for larger machines Motors are 85–95%;

steam turbines are 42–78%; gas engines and turbines are

4 Steam turbines are competitive above 100 HP They are speedcontrollable They are used in applications where speeds anddemands are relatively constant Frequently they are employed

as spares in case of power failure

5 Combustion engines and turbines are restricted to mobile andremote locations

6 Gas expanders for power recovery may be justified at capacities

of several hundred HP; otherwise any needed pressure tion in process is effected with throttling valves

reduc-7 Axial turbines are used for power recovery where flow rates,inlet temperatures or pressure drops are high

8 Turboexpanders are used to recover power in applicationswhere inlet temperatures are less than 1000°F

DRYING OF SOLIDS

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 severaldays in 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 of

10–200 min

3 Rotary cylindrical dryers operate with superficial air velocities

of 5–10 ft/sec, sometimes up to 35 ft/sec when the material iscoarse Residence times are 5–90 min Holdup of solid is

7–8% An 85% free cross section is taken for design purposes

In countercurrent flow, the exit gas is 10–20°C above the solid;

in parallel flow, the temperature of the exit solid is 100°C.Rotation speeds of about 4 rpm are used, but the product ofrpm and diameter in feet is typically between 15 and 25

4 Drum dryers for pastes and slurries operate with contact times

of 3–12 sec, produce flakes 1–3 mm thick with evaporationrates of 15–30 kg/m2

hr Diameters are 1.5–5.0 ft; the rotationrate is 2–10 rpm The greatest evaporative capacity is of theorder of 3000 lb/hr in commercial units

5 Pneumatic conveying dryers normally take particles 1–3 mmdia but up to 10 mm when the moisture is mostly on the surface.Air velocities are 10–30 m/sec Single pass residence times are0.5–3.0 sec 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 severalSCFM/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 tion In continuous operation, drying times of 1–2 min areenough, but batch drying of some pharmaceutical productsemploys drying times of 2–3 hr

prescrip-7 Spray dryers are used for heat sensitive materials Surfacemoisture is removed in about 5 sec, and most drying is com-pleted in less than 60 sec Parallel flow of air and stock is mostcommon Atomizing nozzles have openings 0.012–0.15 in andoperate at pressures of 300–4000 psi Atomizing spray wheelsrotate at speeds to 20,000 rpm with peripheral speeds of

250–600 ft/sec With nozzles, the length to diameter ratio ofthe dryer is 4–5; with spray wheels, the ratio is 0.5–1.0 Forthe final design, the experts say, pilot tests in a unit of 2 mdia should be made

RULES OF THUMB: SUMMARY XV

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 Film-related efficiency losses can be minimized by maintaining

a suitable temperature gradient, for instance 40–45°F A

rea-sonable overall heat transfer coefficient is 250 Btu/(h)(ft2)

4 Elevation of boiling point by dissolved solids results in

differ-ences of 3–10°F between solution and saturated vapor

5 When the boiling point rise is appreciable, the economic

num-ber of effects in series with forward feed is 4–6

6 When the boiling point rise is small, minimum cost is obtained

with 8–10 effects in series

7 In countercurrent evaporator systems, a reasonable

tempera-ture approach between the inlet and outlet streams is 30°F

In multistage operation, a typical minimum is 10°F

8 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

9 The steam economy of an N-stage battery is approximately

0.8N lb evaporation/lb of outside steam

10 Interstage steam pressures can be boosted with steam jet

com-pressors of 20–30% efficiency or with mechanical compressors

of 70–75% efficiency

EXTRACTION, LIQUID-LIQUID

1 The dispersed phase should be the one that has the higher

volu-metric 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

2 Although theory is favorable for the application of reflux to

extraction columns, there are very few commercial applications

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 150μm dia In open vessels, residence times of

30–60 min or superficial velocities of 0.5–1.5 ft/min are

pro-vided in settlers Extraction stage efficiencies commonly are

taken as 80%

4 Spray towers even 20–40 ft high cannot be depended on to

func-tion as more than a single stage

5 Packed towers are employed when 5–10 stages suffice Pall rings

of 1–1.5 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

6 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 At each tray, design for the redistribution of

each phase can be provided 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%

7 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

8 Reciprocating tray towers can have holes 9/16 in dia, 50–60%

open area, stroke length 0.75 in., 100–150 strokes/min, plate

tower, HETS is 20–25 in and throughput is 2000 gal/(hr)(sqft).Power requirements are much less than of pulsed towers

9 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 HETS0.2 m and a capacity of 50 m3/m2hr

FILTRATION

1 Processes are classified by their rate of cake buildup in alaboratory vacuum leaf filter: rapid, 0.1–10.0 cm/sec; medium,0.1–10.0 cm/min; slow, 0.1–10.0 cm/hr

2 The selection of a filtration method depends partly on whichphase is the valuable one For liquid phase being the valuableone, filter presses, sand filters, and pressure filters are suitable

If the solid phase is desired, vacuum rotary vacuum filters aredesirable

3 Continuous filtration should not be attempted if 1/8 in cakethickness cannot be formed in less than 5 min

4 Rapid filtering is accomplished with belts, top feed drums, orpusher-type centrifuges

5 Medium rate filtering is accomplished with vacuum drums ordisks or peeler-type centrifuges

6 Slow filtering slurries are handled in pressure filters or menting centrifuges

sedi-7 Clarification with negligible cake buildup is accomplished withcartridges, precoat drums, or sand filters

8 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, orwhen precoating may be needed

9 For finely ground ores and minerals, rotary drum filtrationrates may be 1500 lb/(day)(sqft), at 20 rev/hr and 18–25 in

Hg vacuum

10 Coarse solids and crystals may be filtered by rotary drum filters

at rates of 6000 lb/(day)(sqft) at 20 rev/hr, 2–6 in Hg vacuum

11 Cartridge filters are used as final units to clarify a low solidconcentration stream For slurries where excellent cake wash-ing is required, horizontal filters are used Rotary disk filtersare for separations where efficient cake washing is not essen-tial Rotary drum filters are used in many liquid-solid separa-tions and precoat units capable of producing clear effluentstreams In applications where flexibility of design and opera-tion are required, plate-and-frame filters are used

FLUIDIZATION OF PARTICLES WITH GASES

1 Properties of particles that are conducive to smooth fluidizationinclude: rounded or smooth shape, enough toughness to resistattrition, sizes in the range 50–500 μm dia, a spectrum of sizeswith ratio of largest to smallest in the range of 10–25

2 Cracking catalysts are members of a broad class characterized

by diameters of 30–150 μm, density of 1.5 g/mL or so, able expansion of the bed before fluidization sets in, minimumbubbling velocity greater than minimum fluidizing velocity,and rapid disengagement of bubbles

appreci-3 The other extreme of smoothly fluidizing particles is typified bycoarse sand and glass beads both of which have been the subject

of much laboratory investigation Their sizes are in the range

150–500 μm, densities 1.5–4.0 g/mL, small bed expansion, aboutthe same magnitudes of minimum bubbling and minimum flui-dizing velocities, and also have rapidly disengaging bubbles

4 Cohesive particles and large particles of 1 mm or more do notfluidize well and usually are processed in other ways

5 Rough correlations have been made of minimum fluidization

velocity, minimum bubbling velocity, bed expansion, bed level

fluctuation, and disengaging height Experts recommend,

how-ever, that any real design be based on pilot plant work

6 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 3/4 in 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 3–9 psi for other

services

6 Minimum temperature approach is 20°F with normal

cool-ants, 10°F or less with refrigerants

7 Water inlet temperature is 90°F, maximum outlet 120°F

8 Heat transfer coefficients for estimating purposes, 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 Usually, the maximum heat transfer area for a shell-and-tube

heat exchanger is in the range of 5000 ft2

10 Double-pipe exchanger is competitive at duties requiring

100–200 sqft

11 Compact (plate and fin) exchangers have 350 sqft/cuft, and

about 4 times the heat transfer per cuft of shell-and-tube units

12 Plate and frame exchangers are suited to high sanitation

ser-vices, and are 25–50% cheaper in stainless construction than

shell-and-tube units

13 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)

(°F), fan power input 2–5 HP/(MBtu/hr), approach 50°F or more

14 Fired heaters: radiant rate, 12,000 Btu/(hr)(sqft); convection

rate, 4000; cold oil tube velocity, 6 ft/sec; approx equal

trans-fers of heat in the two sections; thermal efficiency 70–75%; flue

gas temperature 250–350°F above feed inlet; stack gas

tem-perature 650–950°F

INSULATION

1 Up to 650°F, 85% magnesia is most used

2 Up to 1600–1900°F, a mixture of asbestos and diatomaceous

earth is used

3 Ceramic refractories at higher temperatures

4 Cryogenic equipment (−200°F) employs insulants with fine

pores in which air is trapped

5 Optimum thickness varies with temperature: 0.5 in at 200°F,

1.0 in at 400°F, 1.25 in at 600°F

6 Under windy conditions (7.5 miles/hr), 10–20% greater

thick-ness of insulation is justified

MIXING AND AGITATION

1 Mild agitation is obtained by circulating the liquid with an

impeller at superficial velocities of 0.1–0.2 ft/sec, and intense

4 Propellers are made a maximum of 18 in., turbine impellers to

9 ft

5 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

6 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

7 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 contacttime is 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 otherwise agi-tated conditions with or without binding agents

2 Rotating drum granulators have length to diameter ratios of

2–3, speeds of 10–20 rpm, pitch as much as 10° Size is controlled

by speed, residence time, and amount of binder; 2–5 mm dia iscommon

3 Rotary disk granulators produce a more nearly uniform duct than drum granulators Fertilizer is made 1.5–3.5 mm; ironore 10–25 mm dia

pro-4 Roll compacting and briquetting is done with rolls rangingfrom 130 mm dia by 50 mm wide to 910 mm dia by 550 mmwide Extrudates are made 1–10 mm thick and are broken down

to size for any needed processing such as feed to tablettingmachines or to dryers

5 Tablets are made in rotary compression machines that convertpowders and granules into uniform sizes Usual maximum dia-meter is about 1.5 in., but special sizes up to 4 in dia are possi-ble Machines operate at 100 rpm or so and make up to 10,000tablets/min

6 Extruders make pellets by forcing powders, pastes, and meltsthrough a die followed by cutting An 8 in screw has a capacity

of 2000 lb/hr of molten plastic and is able to extrude tubing at

150–300 ft/min and to cut it into sizes as small as washers at8000/min Ring pellet extrusion mills have hole diameters of 1.6–

32 mm Production rates cover a range of 30–200 lb/(hr)(HP)

7 Prilling towers convert molten materials into droplets and allowthem to solidify in contact with an air stream Towers as high as

60 m are used Economically the process becomes competitivewith other granulation processes when a capacity of 200–400tons/day is reached Ammonium nitrate prills, for example,are 1.6–3.5 mm dia in the 5–95% range

RULES OF THUMB: SUMMARY XVII

deep at air velocities of 0.1–2.5 m/s or 3–10 times the minimum

fluidizing velocity, with evaporation rates of 0.005–1.0 kg/m2sec

One product has a size range 0.7–2.4 mm dia

9 Agglomerators give a loosely packed product and the operating

costs are low

PIPING

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, 20D 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 = 1000 P/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 500°F) Schedule

40 is most common

PUMPS

1 Power for pumping liquids: HP = (gpm)(psi difference)/(1714)

(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 =

(pres-sure at the eye of the impeller− vapor pressure)/(density)

Com-mon range is 4–20 ft

3 Specific speed Ns= ðrpmÞðgpmÞ0:5=ðhead in ftÞ0:75 Pump may

be damaged if certain limits of Nsare exceeded, and efficiency

is best in some ranges

4 Centrifugal pumps: Single stage for 15–5000 gpm, 500 ft max

head; multistage for 20–11,000 gpm, 5500 ft max head

Effi-ciency 45% at 100 gpm, 70% at 500 gpm, 80% at 10,000 gpm

They are used in processes where fluids are of moderate

viscos-ity and the pressure increase is modest

5 Axial pumps for 20–100,000 gpm, 40 ft head, 65–85%

effi-ciency These pumps are used in applications to move large

volumes of fluids at low differential pressure

6 Rotary pumps for 1–5000 gpm, 50,000 ft head, 50–80%

9 Positive displacement pumps are used where viscosities are

large, flow rates are low, or metered liquid rates are required

REACTORS

1 Inlet temperature, pressure and concentrations are necessary

for specification of a reactor An analysis of equilibrium

should be made to define the limits of possible conversion

and to eliminate impossible results

2 Material and energy balances are essential to determine

reac-tor size

the laboratory, and the residence time or space velocity andproduct distribution eventually must be found in a pilot plant

4 Dimensions of catalyst particles are 0.1 mm in fluidized beds,

1 mm in slurry beds, and 2–5 mm in fixed beds

5 The optimum proportions of stirred tank reactors are withliquid level equal to the tank diameter, but at high pressuresslimmer proportions are economical

6 Power input to a homogeneous reaction stirred tank is 0.5–1.5HP/1000 gal, but three times this amount when heat is to betransferred

7 Ideal CSTR (continuous stirred tank reactor) behavior isapproached when the mean residence time is 5–10 times thelength of time needed to achieve homogeneity, which is accom-plished with 500–2000 revolutions of a properly designed stirrer

8 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 be pro-grammed in some way

9 Relatively slow reactions of liquids and slurries are conducted

in continuous stirred tanks A battery of four or five in series ismost economical

10 Tubular flow reactors are suited to high production rates atshort residence times (sec or min) and when substantial heattransfer is needed Embedded tubes or shell-and-tube construc-tion then are used

11 In granular catalyst packed reactors, the residence time bution often is no better than that of a five-stage CSTR battery

distri-12 For conversions under about 95% of equilibrium, the mance of a five-stage CSTR battery approaches plug flow

perfor-REFRIGERATION

1 A ton of refrigeration is the removal of 12,000 Btu/hr of heat

2 At various temperature levels: 0 to 50°F, chilled brine andglycol solutions; −50 to 40°F, ammonia, freons, or butane;

−150 to −50°F, ethane or propane

3 Compression refrigeration with 100°F condenser requires theseHP/ton at various temperature levels: 1.24 at 20°F; 1.75 at

0°F; 3.1 at −40°F; 5.2 at −80°F

4 Below−80°F, cascades of two or three refrigerants are used

5 In single stage compression, the compression ratio is limited toabout 4

6 In multistage compression, economy is improved with stage flashing and recycling, so-called economizer operation

inter-7 Absorption refrigeration (ammonia to−30°F, lithium bromide

to +45°F) 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 appropriatespacings are used to remove products larger than 5 cm dia

2 Revolving cylindrical screens rotate at 15–20 rpm and belowthe critical velocity; they are suitable for wet or dry screening

in the range of 10–60 mm

3 Flat screens are vibrated or shaken or impacted with bouncingballs Inclined screens vibrate at 600–7000 strokes/min and areused for down to 38 μm although capacity drops off sharplybelow 200 μm Reciprocating screens operate in the range

30–1000 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 range

of 12 mm to 50μm

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 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 600 cuft/min and can remove

par-ticles in the range of 300–5 μm from dilute suspensions In one

case, a 20 in dia unit had a capacity of 1000 gpm with a

pres-sure drop of 5 psi and a cutoff between 50 and 150μm

UTILITIES: COMMON SPECIFICATIONS

1 Steam: 15–30 psig, 250–275°F; 150 psig, 366°F; 400 psig, 448°F;

600 psig, 488°F or with 100–150°F superheat

2 Cooling water: Supply at 80–90°F from cooling tower, return at

115–125°F; return seawater at 110°F, return tempered water or

steam condensate above 125°F

3 Cooling air supply at 85–95°F; temperature approach to

pro-cess, 40°F

4 Compressed air at 45, 150, 300, or 450 psig levels

5 Instrument air at 45 psig, 0°F dewpoint

6 Fuels: gas of 1000 Btu/SCF at 5–10 psig, or up to 25 psig for

some types of burners; liquid at 6 million Btu/barrel

7 Heat transfer fluids: petroleum oils below 600°F, Dowtherms,

Therminol, etc below 750°F, fused salts below 1100°F, direct

fire or electricity above 450°F

8 Electricity: 1–100 Hp, 220–660 V; 200–2500 Hp, 2300–4000 V

VESSELS (DRUMS)

1 Drums are relatively small vessels to provide surge capacity or

separation of entrained phases

2 Liquiddrums usually are horizontal

3 Gas/liquidseparators 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

2–3 in./min

9 Gas velocity in gas/liquid separators, V= kpffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiρL=ρv−1ft=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 2/3

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 6–18 in ahead of the pad and 12 in

above the pad are suitable

14 Cyclone separators can be designed for 95% collection of 5μm

particles, but usually only droplets greater than 50μm need be

removed

VESSELS (PRESSURE)

1 Design temperature between −20°F and 650°F is 50°F 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 ating pressure, whichever is greater The maximum operatingpressure, in turn, is taken as 25 psi above the normal operation

oper-3 Design pressures of vessels operating at 0–10 psig and 600–

7 Allowable working stresses are one-fourth of the ultimatestrength of the material

8 Maximum allowable stress depends sharply on temperature

Low 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 10,000 gal, use horizontal tanks on concretesupports

3 Beyond 10,000 gal, use vertical tanks on concrete foundations

4 Liquids subject to breathing losses may be stored in tanks withfloating 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 andproducts, but depends on connecting transportation equipmentschedules

7 Capacities of storage tanks are at least 1.5 times the size of necting transportation equipment; for instance, 7500 gal tanktrucks, 34,500 gal tank cars, and virtually unlimited barge andtanker capacities

con-MEMBRANE SEPARATIONS

1 When calculating mole fraction relationships (see Section19.10), respective permeabilities in mixtures tend to be less, ormuch less, than measured pure permeabilities

2 In calculating the degree of separation for mixtures betweentwo components or key components, the permeability valuesused can be approximated as 50 percent of the values of thepure components

3 In calculating membrane area, these same lower membrane meability values may be used

per-4 When in doubt, experimental data for each given mixture for aparticular membrane material must be obtained

MATERIALS OF CONSTRUCTION

1 The maximum use temperature of a metallic material is given

by TMax= 2/3 (TMelting Point)

2 The coefficient of thermal expansion is of the order of 10× 10−6.Nonmetallic coefficients vary considerably

REFERENCES.M Walas, Chemical Process Equipment: Selection and Design, Butterworth-Heinemann, Woburn, MA, 1988

RULES OF THUMB: SUMMARY XIX

The following are additional sources for rules of thumb:

C.R Branan, Rules of Thumb for Chemical Engineers, 3rd ed., Elsevier

Science, St Louis, MO, 2002

A.A Durand et al.,“Heuristics Rules for Process Equipment,” Chemical

Engineering, 44–47 (October 2006)

L Huchler,“Cooling Towers, Part 1: Siting, Selection and Sizing,”

Chemi-cal Engineering Progress, 61–54 (August 2009)

(January 1966)

M.S Peters, K.D Timmerhaus, and R.E West, Plant Design and ics for Chemical Engineers, 5th ed., McGraw-Hill, Inc., New York, 2003.G.D Ulrich, and P.T Vasudevan, “A Guide to Chemical EngineeringProcess Design and Economics,” Process Publishers, Lee, NH, 2007.D.R Woods, Process Design and Engineering Practice, PTR Prentice-Hall,Englewood Cliffs, NJ, 1995

Econom-D.R Woods et al., Albright’s Chemical Engineers’ Handbook, Sec 16.11,CRC Press, Boca Raton, Fl, 2008

1 INTRODUCTION

A lthough 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 interms of material and energy balances and rate processes

In this chapter, general background material will bepresented relating to complete process design The design

of flowsheets will be considered inChapter 2

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

equip-ment (as distinguished from utilities and building auxiliaries); the

general arrangement of equipment needed to ensure proper

func-tioning of the plant; line sizes; and principal instrumentation The

process design is summarized by a process flowsheet, material and

energy balances, 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

con-struction A particularly valuable function of preliminary design is

that it may reveal lack of certain data needed for final design Data

l of costs of individual equipment are supplied inChapter 21, but the

complete economics of process design is beyond its scope

1.2 EQUIPMENT

Two main categories of process equipment are proprietary and

custom-designed Proprietary equipment is designed by the

manu-facturer to meet performance specifications made by the user; these

specifications may be regarded as the process design of the

equip-ment 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

che-mical reactors, most vessels, multistage separators such as

fraction-ators, 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 checklists,

they simplify the work by ensuring that all needed data have been

provided A collection of such forms is inAppendix B

Proprietary equipment is provided“off the shelf’’ in limited

sizes and capacities Special sizes that would fit particular

applica-tions more closely often are more expensive than a larger standard

size that incidentally may provide a worthwhile safety factor Evenlargely custom-designed equipment, such as vessels, is subject tostandardization such as discrete ranges of head diameters, pressureratings of nozzles, sizes of manways, and kinds of trays and pack-ings Many codes and standards are established by governmentagencies, insurance companies, and organizations sponsored byengineering societies Some standardizations within individualplants are arbitrary choices made to simplify construction, mainte-nance, and repair, and to reduce inventory of spare parts: forexample, limiting the sizes of heat exchanger tubing and pipe sizes,standardization of centrifugal pumps, and restriction of processcontrol equipment to a particular manufacturer There areinstances when restrictions must be relaxed for the engineer toaccommodate a design

SPECIFICATION FORMSWhen completed, a specification form is a record of the salient fea-tures of the equipment, the conditions under which it is to operate,and its guaranteed performance Usually it is the basis for a firmprice quotation Some of these forms are made up by organizationssuch as TEMA or API, but all large engineering contractors andmany large operating companies have other forms for their ownneeds A selection of specification forms is inAppendix B

1.3 CATEGORIES OF ENGINEERING PRACTICEAlthough the design of a chemical process plant is initiated by che-mical engineers, its complete design and construction requires theinputs of other specialists: mechanical, structural, electrical, andinstrumentation engineers; vessel and piping designers; and pur-chasing agents who know what may be available at attractiveprices On large projects all these activities are correlated by a pro-ject 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 ultimatelypurchasing equipment Specifications must be written so explicitlythat the bidders are held to a uniform standard and a clear-cutchoice can be made on the basis of their offerings alone

1Copyright © 2012 Elsevier Inc All rights reserved

DOI: 10.1016/B978-0-12-396959-0.00001-X

shape of the curves Note that in Figure 1.1, engineering begins

early so that critical material (e.g., special alloys) can be

com-mitted for the project.Figure 1.2shows that, in terms of total

engi-neering effort, process engiengi-neering is a small part

In terms of total project cost, the cost of engineering is a small

part, ranging from 5 to 20% of the total plant cost The lower figure

is for large plants that are essentially copies of ones built before,

while the higher figure is for small plants or those employing new

technology, unusual processing conditions, 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 items cited in

References The book by Leesley (References, Section B) has much

information about proprietary data banks and design methods In

its current and earlier editions, the book by Peters and

Timmer-haus has many useful bibliographies on various topics

For general information about chemical manufacturing

pro-cesses, the major encyclopedic references are Kirk-Othmer (1978–

1984) (1999), McKetta (1992), McKetta and Cunningham (1976),

and Ullman (1994) in ReferenceSection 1.2, Part A, as well as

Kent (1992) in ReferenceSection 1.2, Part B

Extensive physical property and thermodynamic data are

available throughout the literature Two such compilations are

tute for Physical Property Research (DIPPR) (1985) DECHEMA

is an extensive series (11 volumes) of physical property and modynamic data Some of the earlier volumes were published inthe 1980s but there are numerous supplements to update the data.The main purpose of the DECHEMA publication is to providechemists and chemical engineers with data for process design anddevelopment DIPPR, published by AIChE, is a series of volumes

ther-on physical properties The references to these publicatither-ons arefound in References, Part C The American Petroleum Institute(API) published data and methods for estimating properties ofhydrocarbons and their mixtures, called the API Data Book Ear-lier compilations include Landolt-Bornstein work, which wasstarted in 1950 but has been updated The later editions are in Eng-lish There are many compilations of special property data, such assolubilities, vapor pressures, phase equilibria, transport, and ther-mal properties A few of these are listed in References,Section 1.2,Parts B and C Still other references of interest may be found inReferences, Part C

Information about equipment sizes, configurations, and times performance is best found in manufacturers’ catalogs andmanufacturers’ web sites, and from advertisements in the journalliterature, such as Chemical Engineering and Hydrocarbon Proces-sing In References,Section 1.1, Part D also contains informationthat may be of value Thomas Register covers all manufacturersand so is less convenient for an initial search Chemical WeekEquipment Buyer’s Guide inSection 1.1, Part D, is of value inthe listing of manufacturers by the kind of equipment Manufac-turers’ catalogs and web site information often have illustrationsand descriptions of chemical process equipment

some-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 of equip-ment, structures, and materials Codification of these rules hasbeen done by associations organized for just such purposes, byprofessional societies, trade groups, insurance underwriting com-panies, and government agencies Engineering contractors andlarge manufacturing companies usually maintain individual sets

of standards so as to maintain continuity of design and to simplifymaintenance of plant In the first edition,Walas (1984)presented atable of approximately 500 distinct internal engineering standardsthat a large petroleum refinery found useful

Typical of the many thousands of items that are standardized inthe field of engineering are limitations on the sizes and wall thick-nesses of piping, specifications of the compositions of alloys, stipula-tion of the safety factors applied to strengths of constructionmaterials, testing procedures for many kinds of materials, and so on.Although the safe design practices recommended by profes-sional and trade associations have no legal standing where theyhave not actually been incorporated in a body of law, many ofthem have the respect and confidence of the engineering profession

as a whole and have been accepted by insurance underwriters sothey are widely observed Even when they are only voluntary, stan-dards constitute a digest of experience that represents a minimumrequirement of good practice

There are several publications devoted to standards of tance to the chemical industry See Burklin (1982), References,Section 1.1, Part B The National Bureau of Standards published

impor-an extensive list of U.S stimpor-andards through the NBS-SIS service(seeTable 1.1) Information about foreign standards is availablefrom the American National Standards Institute (ANSI) (seeTable 1.1)

Figure 1.1 Typical timing of material, engineering manhours, and

construction

Figure 1.2 Rate of application of engineering manhours by

engi-neering function: process engiengi-neering, project engiengi-neering, and

design engineering

A list of codes pertinent to the chemical industry is found in

Table 1.1and supplementary codes and standards inTable 1.2

1.6 MATERIAL AND ENERGY BALANCES

Material and energy balances are 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 tities of an entity cross the boundaries A source is an increase inthe amount of the entity that occurs without crossing a boundary;for example, an increase in the sensible enthalpy or in the amount

quan-of a substance as a consequence quan-of chemical reaction gously, sinks are decreases without a boundary crossing, as the dis-appearance of water from a fluid stream by adsorption onto a solidphase within the boundary

Analo-Accumulations are time rates of change of the amount of theentities within the boundary For example, in the absence ofsources and sinks, an accumulation occurs when the input and out-put rates are different In the steady state, the accumulation is zero.Although the principle of balancing is simple, its applicationrequires knowledge of the performance of all the kinds of equipmentcomprising the system as well as the phase relations and physicalproperties of all mixtures that participate in the process As a conse-quence of trying to cover a variety of equipment and processes, thebooks devoted to the subject of material and energy balances alwaysrun to several hundred pages Throughout this book, material andenergy balances are utilized in connection with the design of indivi-dual kinds of equipment and some processes Cases involving indi-vidual items of equipment usually are relatively easy to balance,for example, the overall balance of a distillation column inSection13.4 and of nonisothermal reactors ofTables 17.4–17.7 When aprocess is maintained isothermal, only a material balance is needed

to describe the process, unless it is also required to know the net heattransfer for maintaining a constant temperature

In most plant design situations of practical interest, however,the several items 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 input equipment Common examples are anabsorber-stripper combination in which the performance of theabsorber depends on the quality of the absorbent being returnedfrom the stripper, or a catalytic cracker–catalyst regenerator sys-tem whose two parts interact closely

Because the performance of a particular item of equipmentdepends on its input, recycling of streams in a process introduces

TABLE 1.1 Codes and Standards of Direct Bearing on

Chemical Process Design

A American Chemistry Council, 1300 Wilson Blvd., Arlington, VA

22209, (703) 741-5000, Fax (703) 741-6000

B American Institute of Chemical Engineers, 3 Park Avenue,

New York, NY 10016, 1-800-242-4363,www.aiche.org

Standard testing procedures for process equipment, e.g

centrifuges, filters, mixers, fired heaters, etc

C American National Standards Institute, (ANSI), 1819 L Street, NW,

6th Floor, Washington, DC, 20036, 1-202-293-8020,www.ansi.org

Abbreviations, letter symbols, graphic symbols, drawing and

drafting practices

D American Petroleum Institute, (API), 1220 L Street, NW,

Washington, 20005 1-202-682-8000,www.api.org

Recommended practices for refinery operations, guides for

inspection of refinery equipment, manual on disposal wastes,

recommended practice for design and construction of large,

low pressure storage tanks, recommended practice for design

and construction of pressure relief devices, recommended

practices for safety and fire protection, etc

E American Society of Mechanical Engineers, (ASME), 3 Park

Avenue, New York, NY, 10016,www.asme.org

ASME Boiler and Pressure Vessel Code, Sec VIII, Unfired

Pressure Vessels, Code for pressure piping, scheme for

identifying piping systems, etc

F American Society for Testing Materials, (ASTM), 110 Bar Harbor

Drive, West Conshohocken, PA,www.astm.org

ASTM Standards for testing materials, 66 volumes in 16

sections, annual with about 30% revision each year

G Center for Chemical Process Safety, 3 Park Avenue, 19th Floor,

New York, NY 10016, 1-212-591-7237,www.ccpsonline.org

Various guidelines for the safe handling of chemicals (CCPS is

sponsored by AIChE)

H Cooling Tower Institute, P.O Box 74273, Houston, TX 77273,

1-281-583-4087,www.cti.org

Acceptance test procedures for cooling water towers of

mechanical draft industrial type

I Hydraulic Institute, 9 Sylvan Way, Parsippany, NJ 07054,

1-973-267-9700,www.hydraulicinstitute.org

Standards for centrifugal, reciprocating and rotary pumps,

pipe friction manual

J Instrumentation, Systems and Automation Society (ISA), 67

Alexander Dr., Research Triangle Park, NC 27709, 1-919-549-8411,

www.isa.org

Instrumentation flow plan symbols, specification forms for

instruments, Dynamic response testing of process control

instruments, etc

K National Fire Protection Association, 1 Batterymarch Park,

Quincy, MA 02169-7471, (617) 770-3000

L Tubular Exchangers Manufacturers’ Association (TEMA), 25 North

Broadway, Tarrytown, NY 10591, 1-914-332-0040,www.tema.org

TEMA heat exchanger standards

M International Standards Organization (ISO), 1430 Broadway,

New York, NY, 10018

Many international standards

TABLE 1.2 Codes and Standards Supplementary to

Process Design (a Selection)

A American Concrete Institute, P.O Box 9094, Farmington Hills,

MI 48333, (248) 848-3700,www.aci.org.Reinforced concrete design handbook, manual of standardpractice for detailing reinforced concrete structures

B American Institute of Steel Construction, 1 E Wacker Drive, Suite

3100, Chicago, IL, 60601, (312) 670-2400,www.aisc.org.Manual of steel construction, standard practice for steelstructures and bridges

C American Iron and Steel Institute, 1140 Connecticut Avenue,

NW, Suite 705, Washington, DC, (202) 452-7100,www.aisi.org.AISI standard steel compositions

D American Society of Heating, Refrigeration and Air ConditioningEngineers, ASHRAE, 1791 Tullie Circle, NE, Atlanta, GA 30329,(404) 636-8400,www.ashrae.org

Refrigeration data handbook

E Institute of Electrical and Electronic Engineers, 445 Hoes Lane,Piscataway, NJ, 08854, (732) 981-0600,www.ieee.org.Many standards including flowsheet symbols forinstrumentation

F National Institute of Standards and Technology (NIST), 100Bureau Drive, Stop 1070, Gaithersburg, MD 20899

Formerly the National Bureau of Standards Measurement andstandards research, standard reference materials, standardsreference data, weights and measures, materials science andengineering

1.6 MATERIAL AND ENERGY BALANCES 3

positions, and properties must be found by calculation For a plant

with dozens or hundreds of streams the resulting mathematical

problem is formidable and has led to the development of many

computer algorithms for its solution, some of them making quite

rough approximations, others more nearly exact Usually the

pro-blem is solved more easily if the performance of the equipment is

specified in advance and its size is found after the balances are

completed If the equipment is existing or must be limited in size,

the balancing process will require simultaneous evaluation of its

performance and consequently is a much more involved operation,

but one which can be handled by computer when necessary

The literature on this subject naturally is extensive An early

book (for this subject), Nagiev’s Theory of Recycle Processes in

Chemical Engineering (Macmillan, New York, 1964, Russian

edi-tion, 1958) treats many practical cases by reducing them to systems

of linear algebraic equations that are readily solvable The book by

Westerberg et al., Process Flowsheeting (Cambridge Univ Press,

Cambridge, 1977), describes some aspects of the subject and has

an extensive bibliography Benedek in Steady State Flowsheeting

of Chemical Plants (Elsevier, New York, 1980) provides a detailed

description of one simulation system Leesley in Computer-Aided

Process Design (Gulf, Houston, 1982) describes the capabilities of

some commercially available flowsheet simulation programs

Some of these incorporate economic balance with material and

energy balances

Process simulators are used as an aid in the formulation and

solution of material and energy balances The larger simulators

can handle up to 40 components and 50 or more processing units

when their outputs are specified ASPEN, PRO II, DESIGN II,

and HYSIM are examples of such process simulators

A key factor in the effective formulation of material and

energy balances is a proper notation for equipment and streams

Figure 1.3, representing a reactor and a separator, utilizes a simple

type When the pieces of equipment are numbered i and j, the

nota-tion AðkÞij signifies the flow rate of substance A in stream k

proceed-ing from unit i to unit j The total stream is designated ΓðkÞ

ij :

sources or sinks outside the system.Example 1.1adopts this tion for balancing a reactor-separator process in which the perfor-mances are specified in advance

nota-Since this book is concerned primarily with one kind of ment at a time, all that need be done here is to call attention to theexistence of the abundant literature on these topics of recycle cal-culations and flowsheet simulation

equip-1.7 ECONOMIC BALANCEEngineering enterprises are subject to monetary considerations,and the objective is to achieve a balance between fixed and vari-able costs so that optimum operating conditions are met In simpleterms, the main components of fixed expenses are depreciationand plant indirect expenses The latter consist of fire and safetyprotection, plant security, insurance premiums on plant and equip-ment, cafeteria and office building expenses, roads and docks, andthe like Variable operating expenses include utilities, labor, main-tenance, supplies, and so on Raw materials are also an operatingexpense General overhead expenses beyond the plant gate aresales, administrative, research, and engineering overhead expensesnot attributable to a specific project Generally, as the capital cost

of a processing unit increases, the operating expenses will decline.For example, an increase in the amount of automatic controlequipment results in higher capital cost, which is offset by adecline in variable operating expenses Somewhere in the summa-tion of the fixed and variable operating expenses there is an eco-nomic balance where the total operating expenses are aminimum In the absence of intangible factors, such as unusuallocal conditions or building for the future, this optimum should

be the design point

Costs of individual equipment items are summarized inter 21as of the end of the first quarter of 2009 The analysis ofcosts for complete plants is beyond the scope of this book Refer-ences are made to several economic analyses that appear in the fol-lowing publications:

Chap-1 AIChE Student Contest Problems (annual) (AIChE, NewYork)

2 Bodman, Industrial Practice of Chemical Process Engineering(MIT Press, Cambridge, MA, 1968)

3 Rase, Chemical Reactor Design for Process Plants, Vol II, CaseStudies (Wiley, New York, 1977)

4 Washington University, St Louis, Case Studies in ChemicalEngineering Design (22 cases to 1984)

Somewhat broader in scope are:

5 Couper et al., The Chemical Process Industries Infrastructure:Function and Economics (Dekker, New York, 2001)

6 Skinner et al., Manufacturing Policy in the Oil Industry (Irwin,Homewood, IL., 1970)

7 Skinner et al., Manufacturing Policy in the Plastics Industry(Irwin, Homewood, IL., 1968)

Many briefer studies of individual equipment appear in somebooks, of which a selection is as follows:

• Happel and Jordan (1975):

1 Absorption of ethanol from a gas containing CO2(p 403)

2 A reactor-separator for simultaneous chemical reactions(p 419)

3 Distillation of a binary mixture (p 385)

4 A heat exchanger and cooler system (p 370)

Figure 1.3 Notation of flow quantities in a reactor (1) and

distilla-tion column (2) AðkÞij designates the amount of component A in

stream k proceeding from unit i to unit j Subscripts 0 designates

a source or sink beyond the boundary limits.Γ designates a total

flow quantity

5 Piping of water (p 353).

6 Rotary dryer (p 414)

• Humphreys, Jelen’s Cost and Optimization Engineering, 3rd

ed., McGraw-Hill, New York, 1991)

7 Drill bit life and replacement policy (p 257)

8 Homogeneous flow reactor (p 265)

9 Batch reactor with negligible downtime (p 272)

• Peters and Timmerhaus, 4th ed (1991):

10 Shell and tube cooling of air with water (p 635)

• Rudd and Watson (1968):

11 Optimization of a three stage refrigeration system (p 172)

• Sherwood (1963):

12 Gas transmission line (p 84)

13 Fresh water from sea water by evaporation (p 138)

• Ulrich (1984):

14 Multiple effect evaporator for concentrating Kraft liquor

(p 347)

• Walas (1959):

15 Optimum number of vessels in a CSTR battery (p 98)

Capital, labor, and energy costs have not escalated at the same

rate over the years since these studies were prepared, so the

conclu-sions must be revisited However, the methodologies employed and

the patterns of study used should be informative

Since energy costs have escalated, appraisals of energy tion are necessary from the standpoints of the first and second laws

utiliza-of thermodynamics Such analyses will reveal where the greatestgeneration of entropy occurs and where the most improvement inenergy saved might be made by appropriate changes of processand equipment

Analyses of cryogenic processes, such as air separation or theseparation of helium from natural gas, have found that a combina-tion of pressure drops involving heat exchangers and compressorswas most economical from the standpoint of capital invested andoperating expenses

Details of the thermodynamic basis of availability analysis aredealt with by Moran (Availability Analysis, Prentice-Hall, Engle-wood Cliffs, NJ, 1982) He applied the method to a cooling tower,heat pump, a cryogenic process, coal gasification, and particularly

to the efficient use of fuels

An interesting conclusion reached by Linnhoff [in Seider andMah (Eds.), (1981)] is that“chemical processes which are properlydesigned for energy versus capital cost tend to operate at approxi-mately 60% efficiency.’’ A major aspect of his analysis is recogni-tion of practical constraints and inevitable losses These mayinclude material of construction limits, plant layout, operability,the need for simplicity such as limits on the number of compressorstages or refrigeration levels, and above all the recognition that, forlow grade heat, heat recovery is preferable to work recovery, thelatter being justifiable only in huge installations Unfortunately,the edge is taken off the dramatic 60% conclusion by Linnhoff’s

EXAMPLE1.1

Material Balance of a Chlorination Process with Recycle

A plant for the chlorination of benzene is shown below From pilot

plant work, with a chlorine/benzene charge weight ratio of 0.82,

the composition of the reactor effluent is

1.7 ECONOMIC BALANCE 5

plexes of interrelated equipment.

1.8 DESIGN SAFETY FACTORS

A number of factors influence the performance of equipment and

plant There are elements of uncertainty and the possibility of

error, including inaccuracy of physical data, basic correlations

of behavior such as pipe friction or column tray efficiency or

gas-liquid distribution Further, it is often necessary to use

approximations of design methods and calculations, unknown

behavior of materials of construction, uncertainty of future

mar-ket demands, and changes in operating performance with time

The solvency of the project, the safety of the operators and the

public, and the reputation and career of the design engineer are

at stake Accordingly, the experienced engineer will apply safety

factors throughout the design of a plant Just how much of a

fac-tor should be applied in a particular case cannot be stated in

gen-eral terms because circumstances vary widely The inadequate

performance of a particular piece of equipment may be

compen-sated for by the superior performance of associated equipment,

as insufficient trays in a fractionator may be compensated for

by increases in reflux and reboiling, if that equipment can take

the extra load

The safety factor practices of some 250 engineers were

ascer-tained by a questionnaire and summarized inTable 1.3; additional

figures are given by Peters and Timmerhaus (1991) Relatively

inexpensive equipment that can conceivably serve as a bottleneck,

such as pumps, always is liberally sized, perhaps as much as 50%

extra for a reflux pump

In an expanding industry, it may be the policy to deliberately

oversize critical equipment that cannot be modified for increased

capacity The safety factors inTable 1.3account for future trends;

however, considerable judgment must be exercised to provide

rea-sonable chances of equipment operating without unreasonably

increasing capital investment

Safety factors must be judiciously applied and should not be

used to mask inadequate or careless design work The design

should be the best that can be made in the time economically

jus-tifiable, and the safety factors should be estimated from a careful

consideration of all factors entering into the design and the

possi-ble future deviations from the design conditions

Sometimes it is possible to evaluate the range of validity of

measurements and correlations of physical properties, phase

equili-brium behavior, mass and heat transfer efficiencies and similar

fac-tors, as well as the fluctuations in temperature, pressure, flow, etc.,

data on the uncertainty of sizing equipment can be estimated.For example, the mass of a distillation column that is relateddirectly to its cost depends on at least these factors:

1 The vapor-liquid equilibrium data

2 The method of calculating the reflux and number of trays

3 The tray efficiency

4 Allowable vapor rate and consequently the tower diameter at agiven tray spacing and estimated operating surface tension andfluid densities

5 Corrosion allowances

Also such factors as allowable tensile strengths, weld efficiencies,and possible inaccuracies of formulas used to calculate shell andhead thicknesses may be pertinent–that is, the relative uncertainty

or error in the function is related linearly to the fractional tainties of the independent variables For example, take the case

uncer-of a steam-heated thermosyphon reboiler on a distillation columnfor which the heat transfer equation is

q= UAΔT:

The problem is to find how the heat transfer rate can vary whenthe other quantities change U is an experimental value that isknown only to a certain accuracy.ΔT may be uncertain because

of possible fluctuations in regulated steam and tower pressures

A, the effective area, may be uncertain because the submergence

is affected by the liquid level controller at the bottom of the umn Accordingly,

col-dq

q = dU

U + dA

A +dðΔTÞΔT ,that is, the fractional uncertainty of q is the sum of the fractionaluncertainties of the quantities on which it is dependent In practicalcases, of course, some uncertainties may be positive and othersnegative, so that they may cancel out in part; but the only safeviewpoint is to take the sum of the absolute values

It is not often that proper estimates can be made of ties of all the parameters that influence the performance orrequired size of particular equipment, but sometimes one particu-lar parameter is dominant All experimental data scatter to someextent, for example, heat transfer coefficients; and various correla-tions of particular phenomena disagree, for example, equations of

uncertain-TABLE 1.3 Safety Factors in Equipment Design: Results of a Questionnaire

Heat exchangers, shell and tube forliquids

a

state of liquids and gases The sensitivity of equipment sizing to

uncertainties in such data has been the subject of some published

information, of which a review article is by Zudkevich (1982);

some of the cases cited are:

1 Sizing of isopentane/pentane and propylene/propane splitters

2 Effect of volumetric properties on sizing of an ethylene

compressor

3 Effect of liquid density on metering of LNG

4 Effect of vaporization equilibrium ratios, K, and enthalpies on

cryogenic separations

5 Effects of VLE and enthalpy data on design of plants for

coal-derived liquids

Examination of such studies may lead to the conclusion that some

of the safety factors of Table 1.3 may be optimistic But long

experience in certain areas does suggest to what extent various

uncertainties do cancel out, and overall uncertainties often do fall

in the range of 10–20% as stated there Still, in major cases the

uncertainty analysis should be made whenever possible

1.9 SAFETY OF PLANT AND ENVIRONMENT

The safe practices described in the previous section are primarily

for assurance that the equipment has adequate performance over

anticipated ranges of operating conditions In addition, the design

of equipment and plant must minimize potential harm to personnel

and the public in case of accidents, of which the main causes are

a human failure,

b failure of equipment or control instruments,

c failure of supply of utilities or key process streams,

d environmental events (wind, water, and so on)

A more nearly complete list of potential hazards is inTable 1.4,

and a checklist referring particularly to chemical reactions is in

Table 1.5

An important part of the design process is safety, since it is the

requirement for a chemical manufacturer’s license to operate

Therefore, safety must be considered at the early stages of design

Lechner (2006) suggested a general guideline for designing a safe

process beginning with Basic Process Engineering (STEP 1) In this

step a preliminary process engineering flowsheet is created followed

by a preliminary safety review by the project team Next Detailed

Process Engineering (STEP 2) involves the preparation of P&IDs

(Process and Instrumentation Diagrams) A detailed hazard

analy-sis is also developed and the P&IDs and the detailed hazard analysis

are subjected to a review by the project team The next step (STEP 3)

is the Management of Change It is inevitable that there will be

changes that are documented and all personnel are informed about

any changes in Steps 1 and 2 that are required to accomplish a safe

engineered process design

Ulrich and Vasudevan (2006) pointed out that it may be too

late to consider safety once a project has reached the equipment

specification and PID stage These authors listed basic steps for

inherently safer predesign when making critical decisions in the

preliminary design phase

Examples of common safe practices are pressure relief valves,

vent systems, flare stacks, snuffing steam and fire water, escape

hatches in explosive areas, dikes around tanks storing hazardous

materials, turbine drives as spares for electrical motors in case of

power failure, and others Safety considerations are paramount in

the layout of the plant, particularly isolation of especially

hazar-dous operations and accessibility for corrective action when

necessary

TABLE 1.4 Some Potential Hazards

Energy SourceProcess chemicals, fuels, nuclear reactors, generators, batteriesSource of ignition, radio frequency energy sources, activators,radiation sources

Rotating machinery, prime movers, pulverisers, grinders,conveyors, belts, cranes

Pressure containers, moving objects, falling objectsRelease of Material

Spillage, leakage, vented materialExposure effects, toxicity, burns, bruises, biological effectsFlammability, reactivity, explosiveness, corrosivity and fire-promoting properties of chemicals

Wetted surfaces, reduced visibility, falls, noise, damageDust formation, mist formation, spray

Fire HazardFire, fire spread, fireballs, radiationExplosion, secondary explosion, domino effectsNoise, smoke, toxic fumes, exposure effectsCollapse, falling objects, fragmentationProcess State

High/low/changing temperature and pressureStress concentrations, stress reversals, vibration, noiseStructural damage or failure, falling objects, collapseElectrical shock and thermal effects, inadvertent activation, powersource failure

Radiation, internal fire, overheated vesselFailure of equipment/utility supply/flame/instrument/componentStart-up and shutdown condition

Maintenance, construction, and inspection conditionEnvironmental Effects

Effect of plant on surroundings, drainage, pollution, transport,wind and light change, source of ignition/vibration/noise/radiointerference/fire spread/explosion

Effect of surroundings on plant (as above)Climate, sun, wind, rain, snow, ice, grit, contaminants, humidity,ambient conditions

Acts of God, earthquake, arson, flood, typhoon, force majeureSite layout factors, groups of people, transport features, spacelimitations, geology, geography

ProcessesProcesses subject to explosive reaction or detonationProcesses which react energetically with water or commoncontaminants

Processes subject to spontaneous polymerisation or heatingProcesses which are exothermic

Processes containing flammables and operated at high pressure

or high temperature or bothProcesses containing flammables and operated underrefrigeration

Processes in which intrinsically unstable compounds are presentProcesses operating in or near the explosive range of materialsProcesses involving highly toxic materials

Processes subject to a dust or mist explosion hazardProcesses with a large inventory of stored pressure energyOperations

The vaporisation and diffusion of flammable or toxic liquids orgases

The dusting and dispersion of combustible or toxic solidsThe spraying, misting, or fogging of flammable combustiblematerials or strong oxidising agents and their mixingThe separation of hazardous chemicals from inerts or diluentsThe temperature and pressure increase of unstable liquids

1.9 SAFETY OF PLANT AND ENVIRONMENT 7

Continual monitoring of equipment and plant is standard

practice in chemical process plants Equipment deteriorates and

operating conditions may change Repairs are sometimes made

with materials or equipment whose ultimate effects on operations

may not have been taken into account During start-up and

shut-down, stream compositions and operating conditions are much

dif-ferent from those under normal operation, and their possible effect

on safety must be considered Sample checklists of safety questions

for these periods are inTable 1.6

Because of the importance of safety and its complexity, safety

engineering is a speciality in itself In chemical processing plants of

any significant size, loss prevention reviews are held periodically by

groups that always include a representative of the safety

depart-ment Other personnel, as needed by the particular situation, are

from manufacturing, maintenance, technical service, and possibly

research, engineering, and medical groups The review considers

any changes made since the last review in equipment, repairs,

feed-stocks and products, and operating conditions

Detailed safety checklists appear in books by Fawcett and

Wood (1982) and Wells (1980) These books and the volume by

Lees (1996) also provide entry into the vast literature of chemical

process plant safety Lees has particularly complete bibliographies

Standard references on the properties of dangerous materials are

the books by Lewis (1993, 2000)

Although the books by Fawcett and Woods, Wells and Lewis

are dated, they do contain valuable information

The Center for Chemical Process Safety sponsored by AIChE

publishes various books entitled Safety Guideline Series

1.10 STEAM AND POWER SUPPLYFor smaller plants or for supplementary purposes, steam and powercan be supplied by package plants which are shippable and ready tohook up to the process Units with capacities in the range of sizes up

to about 350,000 lb/hr steam at 750º F and 850 psi are on the marketand are obtainable on a rental/purchase basis for energy needs

Reactions

1 Define potentially hazardous reactions How are they isolated?

Prevented? (SeeChapter 17)

2 Define process variables which could, or do, approach limiting

conditions for hazard What safeguards are provided against

such variables?

3 What unwanted hazardous reactions can be developed through

unlikely flow or process conditions or through contamination?

4 What combustible mixtures can occur within equipment?

5 What precautions are taken for processes operating near or within

the flammable limits? (Reference: S&PP Design Guide No 8.)

6 What are process margins of safety for all reactants and

intermediates in the process?

7 List known reaction rate data on the normal and possible

abnormal reactions

8 How much heat must be removed for normal, or abnormally

possible, exothermic reactions? (seeChaps 7, 17, and 18of

this book)

9 How thoroughly is the chemistry of the process including

desired and undesired reactions known? (See NFPA 491 M,

Manual of Hazardous Chemical Reactions)

10 What provision is made for rapid disposal of reactants if

required by emergency?

11 What provisions are made for handling impending runaways

and for short-stopping an existing runaway?

12 Discuss the hazardous reactions which could develop as a result

of mechanical equipment (pump, agitator, etc.) failure

13 Describe the hazardous process conditions that can result from

gradual or sudden blockage in equipment including lines

14 Review provisions for blockage removal or prevention

15 What raw materials or process materials or process conditions

can be adversely affected by extreme weather conditions?

Protect against such conditions

16 Describe the process changes including plant operation that

have been made since the previous process safety review

(Fawcett and Wood, 1982, pp 725–726 Chapter references refer

to this book.)

and Shut-down

Start-up Mode (§4.1)D1 Can the start-up of plant be expedited safely? Check thefollowing:

(a) Abnormal concentrations, phases, temperatures, pressures,levels, flows, densities

(b) Abnormal quantities of raw materials, intermediates, andutilities (supply, handling, and availability)

(c) Abnormal quantities and types of effluents and emissions(§1.6.10)

(d) Different states of catalyst, regeneration, activation(e) Instruments out of range, not in service or de-activated,incorrect readings, spurious trips

(f) Manual control, wrong routing, sequencing errors, pooridentification of valves and lines in occasional use, lock-outs, human error, improper start-up of equipment(particularly prime movers)

(g) Isolation, purging(h) Removal of air, undesired process material, chemicals usedfor cleaning, inerts, water, oils, construction debris, andingress of same

(i) Recycle or disposal of off-specification process materials(j) Means for ensuring construction/maintenance completed(k) Any plant item failure on initial demand and duringoperation in this mode

(l) Lighting of flames, introduction of material, limitation ofheating rate

(m) Different modes of the start-up of plant:

Initial start-up of plantStart-up of plant section when rest of plant downStart-up of plant section when other plant on-streamStart-up of plant after maintenance

Preparation of plant for its start-up on demandShut-down Mode (§§4.1,4.2)

D2 Are the limits of operating parameters, outside which remedialaction must be taken, known and measured?

D3 To what extent should plant be shut down for any deviationbeyond the operating limits? Does this require the installation ofalarm and/or trip? Should the plant be partitioned differently?How is plant restarted? (§9.6)

D4 In an emergency, can the plant pressure and/or the inventory ofprocess materials be reduced effectively, correctly, safely? What

is the fire resistance of plant? (§§9.5,9.6)D5 Can the plant be shut down safely? Check the following:(a) See the relevant features mentioned under start-up mode(b) Fail-danger faults of protective equipment

(c) Ingress of air, other process materials, nitrogen, steam,water, lube oil (§4.3.5)

(d) Disposal or inactivation of residues, regeneration of catalyst,decoking, concentration of reactants, drainage, venting(e) Chemical, catalyst, or packing replacement, blockageremoval, delivery of materials prior to start-up of plant(f) Different modes of shutdown of plant:

Normal shutdown of plantPartial shutdown of plantPlacing of plant on hot standbyEmergency shutdown of plant(Wells, 1980) (The paragraphs are from Wells)

Modern steam plants are quite elaborate structures that can

recover 80% or more of the heat of combustion of the fuel The

sim-plified sketch ofExample 1.2identifies several zones of heat transfer

in the equipment Residual heat in the flue gas is recovered as preheat

of the water in an economizer and in an air preheater The

combus-tion chamber is lined with tubes along the floor and walls to keep

the refractory cool and usually to recover more than half the heat

of combustion The tabulations of this example are of the distribution

of heat transfer surfaces and the amount of heat transfer in each zone

More realistic sketches of the cross section of a steam

genera-tor are inFigure 1.4 Part (a) of this figure illustrates the process of

natural circulation of water between an upper steam drum and a

lower drum provided for the accumulation and eventual blowdown

of sediment In some installations, pumped circulation of the water

is advantageous

Both process steam and supplemental power are recoverable

from high pressure steam which is readily generated.Example 1.3

is of such a case The high pressure steam is charged to a

turbine-generator set, process steam is extracted at the desired process sure at an intermediate point in the turbine, and the rest of the steamexpands further and is condensed

pres-In plants such as oil refineries that have many streams at hightemperatures or high pressures, their energy can be utilized to gen-erate steam and/or to recover power The two cases ofExample 1.4are of steam generation in a kettle reboiler with heat from a frac-tionator sidestream and of steam superheating in the convectiontubes of a furnace that provides heat to fractionators

Recovery of power from the thermal energy of a high perature stream is the subject ofExample 1.5 A closed circuit ofpropane is the indirect means whereby the power is recovered with

tem-an exptem-ansion turbine Recovery of power from a high pressure gas

is a fairly common operation A classic example of power recoveryfrom a high pressure liquid is in a plant for the absorption of CO2

by water at a pressure of about 4000 psig After the absorption, the

CO2is released and power is recovered by releasing the rich liquorthrough a turbine

EXAMPLE1.2

Data of a Steam Generator for Making 250,000 lb/hr at

450 psia and 650°F from Water Entering at 220°F

Fuel oil of 18,500 Btu/lb is fired with 13% excess air at 80°F Flue

gas leaves at 410°F A simplified cross section of the boiler is

shown Heat and material balances are summarized Tube

selec-tions and arrangements for the five heat transfer zones also are

summarized The term Agis the total internal cross section of the

tubes in parallel Assure 85% recovery (Steam: Its Generation and

Use, 14.2, Babcock and Wilcox, Barberton, OH, 1972) (a) Cross

section of the generator: (b) Heat balance:

Total to water and steam 285.4 Mbtu/hr

In air heater 18.0 MBtu/hr

(c) Tube quantity, size, and grouping:

Screen

2 rows of 21-in OD tubes, approx 18 ft long

Rows in line and spaced on 6-in centers

23 tubes per row spaced on 6-in centers

S = 542 sqft

A = 129 sqft

Superheater

12 rows of 21-in OD tubes (0.165-in thick), 17.44 ft long

Rows in line and spaced on 31-in centers

23 tubes per row spaced on 6-in centers

S = 3150 sqft

Ag= 133 sqft

Boiler

25 rows of 21-in OD tubes, approx 18 ft long

Rows in line and spaced on 31-in centers

35 tubes per row spaced on 4-in centers

53 rows of 2-in OD tubes (0.083-in thick), approx 13 ft longRows in line and spaced on 21-in centers

47 tubes per row spaced on 31-in centers

S = 14,800 sqft

Ag(total internal cross section area of 2173 tubes) = 39.3 sqft

Aa(clear area between tubes for crossflow of air) = 70 sqftAir temperature entering air heater = 80°F

1.10 STEAM AND POWER SUPPLY 9

1.11 DESIGN BASIS

Before a chemical process design can be properly started, a certain

body of information must be agreed upon by all participants in

the proposed plant design (engineering, research, plant supervision,

safety and health personnel, environmental personnel, and plant

management) The design basis states what is to be made, how much

is to be made, where it is to be made, and what are the raw

materi-als Distinctions must also be clear between grass-roots facilities,

battery-limits facilities, plant expansions, and plant retrofits The

required data may be classified into basic design and specific design

data These data form the basis for the project scope that is essentialfor any design and the scope includes the following:

1 Required products: their compositions, amounts, purities, cities, temperatures, pressures, and monetary values

toxi-2 Available raw materials: their compositions, amounts, ties, temperatures, pressures, monetary values, and all pertinentphysical properties unless they are standard and can be estab-lished from correlations This information about propertiesapplies also to products of item 1

toxici-Figure 1.4 Steam boiler and furnace arrangements (a) Natural circulation of water in a two-drum boiler Upper drum is for steam gagement; the lower one for accumulation and eventual blowdown of sediment (b) A two-drum boiler Preheat tubes along the floor andwalls are connected to heaters that feed into the upper drum (c) Cross section of a Stirling-type steam boiler with provisions for superheat-ing, air preheating, and flue gas economizing; for maximum production of 550,000 lb/hr of steam at 1575 psia and 900°F [Steam, Babcockand Wilcox, Barberton, OH, 1972, pp 3.14, 12.2 (Fig 2), and 25.7 (Fig 5)]

disen-3 Daily and seasonal variations of any data of items 1 and 2 and

subsequent items of these lists

4 All available laboratory and pilot plant data on reaction and

phase equilibria, catalyst degradation, and life and corrosion

of equipment

5 Any available existing plant data of similar processes

6 Local restrictions on means of disposal of wastes

Basic engineering data include:

7 Characteristics and values of gaseous and liquid fuels that are

to be used and their unit costs

8 Characteristics of raw makeup and cooling tower waters, peratures, maximum allowable temperature, flow rates avail-able, and unit costs

tem-EXAMPLE1.3

Steam Plant Cycle for Generation of Power and Low Pressure

Process Steam

The flow diagram is for the production of 5000 kW gross and

20,000 lb/hr of saturated process steam at 20 psia The feed and

hot well pumps make the net power production 4700 kW

Conditions at key points are indicated on the enthalpy–entropydiagram The process steam is extracted from the turbine at anintermediate point, while the rest of the stream expands to 1 in

Hg and is condensed (example is corrected from Perry, 6th ed.,9.43, 1984)

EXAMPLE1.4

Pickup of Waste Heat by Generating and Superheating Steam

in a Petroleum Refinery

The two examples are generation of steam with heat from a

side-stream of a fractionator in a 9000 Bbl/day fluid cracking plant,

and superheating steam with heat from flue gases of a furnace

whose main function is to supply heat to crude topping and

vacuum service in a 20,000 Bbl/day plant (a) Recovery of heatfrom a sidestream of a fractionator in a 9000 Bbl/day fluid cataly-tic cracker by generating steam, Q = 15,950,000 Btu/hr (b) Heatrecovery by superheating steam with flue gases of a 20,000 Bbl/day crude topping and vacuum furnace

1.11 DESIGN BASIS 11

9 Steam and condensate: mean pressures and temperatures and

their fluctuations at each level, amount available, extent of

recovery of condensate, and unit costs

10 Electrical power: Voltages allowed for instruments, lighting

and various driver sizes, transformer capacities, need for

emer-gency generator, unit costs

11 Compressed air: capacities and pressures of plant and

instru-ment air, instruinstru-ment air dryer

12 Plant site elevation

13 Soil bearing value, frost depth, ground water depth, piling

requirements, available soil test data

14 Climatic data Winter and summer temperature extremes,

cooling tower drybulb temperature, air cooler design

tempera-ture, strength and direction of prevailing winds, rain and

snowfall maxima in 1 hr and in 12 hr, earthquake and

hurri-cane provision

15 Blowdown and flare: What may or may not be vented to the

atmosphere or to ponds or to natural waters, nature of

required liquid, and vapor relief systems

16 Drainage and sewers: rainwater, oil, sanitary

17 Buildings: process, pump, control instruments, special

equipment

18 Paving types required in different areas

19 Pipe racks: elevations, grouping, coding

20 Battery limit pressures and temperatures of individual feed

stocks and products

21 Codes: those governing pressure vessels, other equipment,

buildings, electrical, safety, sanitation, and others

22 Miscellaneous: includes heater stacks, winterizing, insulation,

steam or electrical tracing of lines, heat exchanger tubing size

standardization, instrument locations

23 Environmental regulations

24 Safety and health requirements

A convenient tabular questionnaire is presented inTable 1.7and it

may become part of the scope For anything not specified, for

instance, sparing of equipment, engineering standards of the

designer or constructor will be used A proper design basis at the

very beginning of a project is essential to getting a project

com-pleted and on stream expeditiously

UTILITIES

These provide motive power as well as heating and cooling of

pro-cess streams, and include electricity, steam, fuels, and various fluids

whose changes in sensible and latent heats provide the necessaryenergy transfers In every plant, the conditions of the utilities aremaintained at only a few specific levels, for instance, steam at cer-tain pressures, cooling water over certain temperature ranges, andelectricity at certain voltages If a company generates its own power,provision for standby electric power from a public or private utilityshould be made in the event of plant utility failure At some stages ofsome design work, the specifications of the utilities may not havebeen established Then, suitable data may be selected from the com-monly used values itemized inTable 1.8

1.12 LABORATORY AND PILOT PLANT WORKBasic physical and thermodynamic property data are essential forthe design and selection of equipment Further, the state-of-the-art design of many kinds of equipment may require more or lessextensive laboratory or pilot plant studies Equipment manufac-turers who are asked to provide performance guarantees requiresuch information As indicated inAppendix C, typical equipmentsuppliers’ questionnaires may require the potential purchaser tohave performed such tests

Some of the more obvious areas definitely requiring test workare filtration, sedimentation, spray, or fluidized bed or any otherkind of solids drying, extrusion pelleting, pneumatic and slurryconveying, adsorption, and others Even in such thoroughlyresearched areas as vapor-liquid and liquid-liquid separations,rates, equilibria, and efficiencies may need to be tested, particularly

of complex mixtures A great deal can be found out, for instance,

by a batch distillation of a complex mixture

In some areas, suppliers may make available small-scaleequipment, such as leaf filters, that can be used to determine suit-able operating conditions, or they may do the work themselves atsuppliers’ facilities (e.g., use of drying equipment)

Pilot plant experimentation is expensive and can be time suming, delaying the introduction of the product in the market-place There have been trends and reports of recent successeswhereby extensive pilot plant research has been bypassed Onesuch study involved the manufacture of bisphenol A in whichlaboratory work bypassed the pilot plant stage and a full-scale pro-duction unit was designed and operated successfully This is notrecommended, but using some laboratory research and simulationmay make it possible to reduce or eliminate expensive pilot plantwork However, confidence must be developed in using simulation

con-to replace pilot plant work and this is obtained only throughexperience

EXAMPLE1.5

Recovery of Power from a Hot Gas Stream

A closed circuit of propane is employed for indirect recovery of

power from the thermal energy of the hot pyrolyzate of an ethylene

plant The propane is evaporated at 500 psig, and then expanded

to 100°F and 190 psig in a turbine where the power is recovered

Then the propane is condensed and pumped back to the

evapora-tor to complete the cycle Since expansion turbines are expensive

machines even in small sizes, the process is not economical on

the scale of this example, but may be on a much larger scale

TABLE 1.7 Typical Design Basis Questionnaire

1.101 Plant Location _

1.102 Plant Capacity, lb or tons/yr

1.103 Operating Factor or Yearly Operating Hours

(For most modern chemical plants, this figure is generally 8,000 hours per year)

1.104 Provisions for Expansion _

_

1.105 Raw Material Feed (Typical of the analyses required for a liquid)

Assay, wt per cent min

Impurities, wt per cent max _

Characteristic specifications

Specific gravity _

Distillation range °F _

Initial boiling point °F _

Dry end point °F

Viscosity, centipoises _

Color APHA

Heat stability color

Reaction rate with established reagent _

Acid number _

Freezing point or set point °F

Corrosion test

End-use test

For a solid material chemical assay, level of impurities and its physical

characteristics, such as specific density, bulk density, particle size distribution and

the like are included This physical shape information is required to assure that

adequate processing and material handling operations will be provided

1.1051 Source

Plant battery limits _

Storage capacity (volume or day's inventory) _

Required delivery conditions at battery limits

Pressure _

Temperature _

Method of transfer

1.106 Product Specifications

Here again specifications would be similar to that of the raw material in equivalent

or sometimes greater detail as often trace impurities affect the marketability of the

final product

Storage requirements (volume or days of inventory)

Type of product storage _

For solid products, type of container or method of shipment and loading facilities

should be outlined _

1.107 Miscellaneous Chemicals and Catalyst Supply

In this section the operating group should outline how various miscellaneous

chemicals and catalysts are to be stored and handled for consumption within the plant

1.108 Atmospheric ConditionsBarometric pressure range Temperature

Design dry bulb temperature (°F)

% of summer season this temperature is exceeded _Design wet bulb temperature (°F)

% of summer season this temperature is exceeded _Minimum design dry bulb temperature winter condition (°F) _Level of applicable pollutants that could affect the process

Examples of these are sulfur compounds, dust and solids, chlorides and salt watermist when the plant is at a coastal location. _2.100 Utilities

2.101 Electricity

Characteristics of primary supply Voltage, phases, cycles _Preferred voltage for motors

Over 200 hp _Under 200 hp Value, c/kWh _(If available and if desired, detailed electricity pricing schedule can be included forbase load and incremental additional consumption.)

2.102 Supply Water _Cleanliness _Corrosiveness Solids content analysis

Other details

2.103 Cooling WaterWell, river, sea, cooling tower, other _Quality _Value Use for heat exchanger design

Fouling properties Design fouling factor Preferred tube material

High pressure, psig _ _

Temperature, °F _ _

Moisture, % _ _

Value per thousand lb _ _

Medium pressure, psig _ _

Temperature, °F _ _

Moisture, % _ _

Value per thousand lb _ _

Low pressure, psig _ _

Required pressure at battery limits _

Value per thousand lb or gal

2.106 Boiler Feed Water

(If the quality of the process water is different from the make-up water or boiler feed

water, separate information should be provided.)

Supply pressure _

Temperature, °F _

Value per thousand gal _

Pressure, psig _

Per cent CO2 Per cent oxygen Per cent CO Other trace impurities Quantity available Value per thousand cu ft 2.109 Plant Air

Supply SourceOffsite battery limits (OSBL) Portable compressor Process air system Special compressor Supply pressure, psig

2.110 Instrument AirSupply source (OSBL) Special compressor Supply pressure, psig Dew point, °F Oil, dirt and moisture removal requirements

In general a value of plant and instrument air is usually not given as the yearlyover-all cost is insignificant in relation to the other utilities required

3.101 Waste Disposal Requirements

In general, there are three types of waste to be considered: liquid, solid andgaseous The destination and disposal of each of these effluents is usuallydifferent Typical items are as follows:

Destination of liquid effluents _Cooling water blowdown _

OTHER SOURCES OF INFORMATIONThe books listed below are what a process engineer should have available ineither his or her home office, company library or a university librarynearby that he or she may consult The books listed and books on similarsubjects are vital tools of the process engineer.

1.1 Process Design

A Books Essential to a Private LibraryD.M Himmelblau, Basic Principles and Calculations in Chemical Engineering,6th ed., PTR Prentice Hall, Englewood Cliffs, NJ, 1996

E.E Ludwig, Applied Process Design for Chemical and PetrochemicalPlants, 3rd ed., Gulf, Houston, 1995–2000, 3 vols

W.L McCabe, J.C Smith, P Harriott, Unit Operations of ChemicalEngineering, 6th ed., McGraw-Hill, New York, 2002

R.H Perry, D.W Green, Perry’s Chemical Engineers Handbook, 6th ed.,McGraw-Hill, New York, 1984; 8th ed., 2009 Earlier editions also containvaluable information

J.M Smith, H.C Van Ness, M.M Abbott, Introduction to ChemicalEngineering Thermodynamics, 6th ed., McGraw-Hill, New York, 2001.S.M Walas, Reaction Kinetics for Chemical Engineers, McGraw-Hill, NewYork, 1959

J.R Couper, Process Engineering Economics, Dekker, New York, 2003.J.M Douglas, Conceptual Design of Chemical Processes, McGraw-Hill,New York, 1991

T.F Edgar, D.M Himmelblau, Optimization of Chemical Processes,McGraw-Hill, New York, 1988

F.L Evans, Equipment Design Handbook for Refineries and ChemicalPlants, 2 vols Gulf, Houston, 1979

R.G.E Franks, Modelling and Simulation in Chemical Engineering, Wiley,New York, 1972

J Happel, D.G Jordan, Chemical Process Economics, 2nd ed., Dekker,New York, 1975

K.E Humphries, Jelen’s Cost and Optimization Engineering, 3rd ed.,McGraw-Hill, New York, 1991

D.Q Kern, Process Heat Transfer, McGraw-Hill, New York, 1950.H.Z Kister, Distillation Design, McGraw-Hill, New York, 1992

R Landau, editor The Chemical Plant, Reinhold, New York, 1966.M.E Leesley, editor Computer-Aided Process Design, Gulf, Houston,1982

O Levenspiel, Chemical Reaction Engineering, 3rd ed., Wiley, New York, 1999.N.P Lieberman, Process Design for Reliable Operations, Gulf, Houston, 1983.R.S.H Mah, W.D Seider, Foundations of Computer-Aided ChemicalProcess Design, 2 vols Engineering Foundation, New York, 1981.M.J Moran, Availability Analysis, Prentice-Hall, Englewood Cliffs, NJ,1982

F Nagiev, Theory of Recycle Processes in Chemical Engineering, Macmillan,New York, 1964

M.S Peters, K.D Timmerhaus, Process Design and Economics for ChemicalEngineers, 4th ed., McGraw-Hill, New York, 1991 and 5th ed McGraw-Hill, New York, 2003 (The units in the fourth edition are in the EnglishSystem and in the SI System in the fifth edition.)

H.F Rase, M.H Barrows, Project Engineering for Process Plants, Wiley,New York, 1957

TABLE 1.8 Typical Utility Characteristics

SteamPressure (psig) Saturation (°F) Superheat (°F)

Above 450 direct firing and electrical heating

Refrigerants

Return at 115°F, with 125°F maximum

Return at 110°F (salt water)

Return above 125°F (tempered water or steam condensate)

Cooling AirSupply at 85–95°F

Temperature approach to process, 40°F

Power input, 20 HP/1000 sqft of bare heat transfer surface

FuelGas: 5–10 psig, up to 25 psig for some types of burners, pipeline gas

at 1000 Btu/SCF

Liquid: at 6 million Btu/barrel

Compressed AirPressure levels of 45, 150, 300, 450 psig

Hill, New York, 1981.

R.W Rousseau, editor Handbook of Separation Process Technology,

Wiley, New York, 1987

D.F Rudd, C.C Watson, Strategy of Process Engineering, Wiley, New

York, 1968

T.K Sherwood, A Course in Process Design, MIT Press, Cambridge, MA, 1963

G.D Ulrich, P.T Vasudevan, Chemical Engineering Process Design and

Economics, A Practical Guide, 2nd ed., Process Publishing, Lee, NH, 2004

G.D Ulrich, P.T Vasudevan, Predesign with Safety in Mind, CEP, July

2006 27–37

J.F Valle-Riestra, Project Evaluation on the Chemical Process Industries,

McGraw-Hill, New York, 1983

A.W Westerberg et al., Process Flowsheeting, Cambridge University Press,

Cambridge, England, 1977

D.R Woods, Process Design and Engineering Practice, PTR Prentice Hall,

Englewood Cliffs, NJ, 1995

D Zudkevitch, Separation of Ethyl Acetate from Ethanol and Water,

Encycl Chem Process Des., 14, 401–483 (1982)

C Estimation of Properties

AIChE Manual for Predicting Chemical Process Data, AIChE, New York,

1984–date

W.J Lyman, W.F Reehl, D.H Rosenblatt, Handbook of Chemical

Prop-erty Estimation Methods: Environmental Behavior of Organic Compounds,

McGraw-Hill, New York, 1982

R.C Reid, J.M Prausnitz, B.E Poling, The Properties of Gases and

Liquids, 4th ed., McGraw-Hill, New York, 1987

Z Sterbacek, B Biskup, P Tausk, Calculation of Properties Using

Corre-sponding States Methods, Elsevier, New York, 1979

S.M Walas, Phase Equilibria in Chemical Engineering, Butterworth,

Stone-ham, MA, 1984

D Equipment

Chemical Engineering Catalog, Penton/Reinhold, New York, annual

Chemical Engineering Equipment Buyers’ Guide, Chemical Week, New

H.H Fawcett, W.J Wood, editors Safety and Accident Prevention in Chemical

Operations, Wiley and Sons, New York, 1982

M Kutz, editor Mechanical Engineers’ Handbook, 2nd ed., Wiley, New

York, 1998

P Lechner, Designing for a Safe Process, Chem Eng., pp 31–33 (December 20,

1994)

F.P Lees, Loss Prevention in the Process Industries, 2nd ed.,

Butterworth-Heinemann, Woburn, MA, 1996 3 vols

R.J Lewis, Hazardous Chemicals Desk Reference, 3rd ed., Van Nostrand

Reinhold, New York, 1993

R.J Lewis, Sax’s Dangerous Properties of Industrial Materials, 8th ed., Van

Nostrand Reinhold, New York, 2000

N.P Lieberman, Troubleshooting Refinery Processes, PennWell, Tulsa, OK,

1981

Process Safety Guidelines, Center for Chemical Process Safety, American

Institute of Chemical Engineers, New York, 1992–date, 22 guidelines

Hill, New York, 1983

G.L Wells, Safety in Process Plant Design, Wiley, New York, 1980

1.2 Process Equipment

A.EncyclopediasKirk-Othmer Concise Encyclopedia of Chemical Technology, (4th ed.), Wiley,New York, 1999

Kirk-Othmer Encyclopedia of Chemical Technology, 26 vols Wiley, NewYork, 1978–1984

Hill Encyclopedia of Science and Technology, 5th ed, Hill, New York, 1982

McGraw-J.J McKetta, Chemical Processing Handbook, Dekker, New York, 1992.J.J McKetta, W Cunningham, editors Encyclopedia of Chemical Proces-sing and Design, Dekker, New York, 1976–date

D.G Ullman, Encyclopedia of Chemical Technology, English edition,Verlag Chemie, Weinheim, FRG, 1994

B General Data CollectionsAmerican Petroleum Institute, Technical Data Book-Petroleum Refining,American Petroleum Institute, Washington, DC, 1971–date

W.M Haynes, editor CRC Handbook of Chemistry and Physics, CRCPress, Washington, DC, 2010

Gas Processors Suppliers Association, Engineering Data Book, 11th ed.,(1998) Tulsa, OK

J.A Kent, Riegel’s Handbook of Industrial Chemistry, 9th ed., VanNostrand Reinhold, New York, 1992

L.M Landolt-Bornstein, Numerical Data and Functional Relationships inScience and Technology, Springer, New York, 1950–date

J.G Speight, editor Lange’s Handbook of Chemistry, 13th ed., McGraw-Hill,New York, 1984

J.C Maxwell, Data Book on Hydrocarbons, Van Nostrand Reinhold, NewYork, 1950

C.L Yaws et al., Physical and Thermodynamic Properties, McGraw-Hill,New York, 1976

C Special Data CollectionsL.H Horsley, editor Azeotropic Data, Advances in Chemistry Series #6,American Chemical Society, Washington, DC, 1953

Beilstein Handbook, Beilstein Information Systems, Frankfurt, Germany.Design Institute of Physical Properties and Data (DIPPR), AmericanInstitute of Chemical Engineers, New York, 1985–9 databases Dataare updated at frequent intervals

Dortmund Data Bank, University of Oldenburg, Germany, 1996–date.Gmelin Handbook, Gmelin Institute, Germany

J Gmehling et al., Chemistry and Chemical Engineering Data Series, 11 vols.DECHEMA, Frankfurt/Main, FRG, 1977–date

J.H Keenan et al., Thermodynamic Properties of Steam, Wiley, New York,English Units, 1969, SI Units, 1978

J.A Larkin, Selected Data on Mixtures, International Data Series B, modynamic Properties of Organic Aqueous Systems, Engineering ScienceData Unit Ltd., London, 1978–date

Ther-Thermodynamic Properties of Organic Substances, ThermodynamicResearch Center, Texas A & M University, Bryan, TX, 1977–date.D.D Wagman, The NBS Tables of Chemical Thermodynamic Properties,American Chemical Society, Washington, DC, 1982

D.R Woods, Data for Process Design and Engineering Practice, PTRPrentice Hall, Englewood Cliffs, NJ, 1995

2 FLOWSHEETS

A plant design consists of words, numbers, and

pictures An engineer thinks in terms of sketches

and drawings that are his or her“pictures” To

solve a material balance problem, the engineer

will start with a block to represent equipment, or a process

step and then will show the entering and leaving streams

with their amounts and properties When asked to describe

a process, an engineer will begin to sketch equipment, show

how it is interconnected, and show the process flows and

operating conditions

Such sketches develop into flowsheets, which are moreelaborate diagrammatic representations of the equipment,the sequence of operations, and the expected performance

of a proposed plant or the actual performance of an alreadyoperating one For clarity and to meet the needs of thevarious persons engaged in design, cost estimating,purchasing, fabrication, operation, maintenance, andmanagement, several different kinds of flowsheets arenecessary Four of the main kinds will be described andillustrated

2.1 BLOCK FLOWSHEETS

At an early stage or to provide an overview of a complex process or

plant, a drawing is made with rectangular blocks to represent

indi-vidual processes or groups of operations, together with quantities

and other pertinent properties of key streams between the blocks

and into and from the process as a whole Such block flowsheets

are made at the beginning of a process design for orientation

purposes, for discussions or later as a summary of the material

balance of the process For example, the coal carbonization process

of Figure 2.1starts with 100,000 lb/hr of coal and process air,

involves six main process units, and makes the indicated quantities

of ten different products When it is of particular interest, amounts

of utilities also may be shown; in this example the use of steam is

indicated at one point The block diagram of Figure 2.2 was

prepared in connection with a study of the modification of an ing petroleum refinery The three feed stocks are separated intomore than 20 products Another representative petroleum refineryblock diagram, inFigure 13.20, identifies the various streams butnot their amounts or conditions

exist-2.2 PROCESS FLOWSHEETSProcess flowsheets embody the material and energy balances andinclude the sizes of major equipment of the plant They includeall vessels, such as reactors, separators, and drums; special proces-sing equipment; heat exchangers; pumps; and so on Numericaldata include flow quantities, compositions, pressures, and tempera-tures Major instrumentation essential for process control and thecomplete understanding of the flowsheet without reference to other

Figure 2.1 Coal carbonization block flowsheet Quantities are in lb/hr

17Copyright © 2012 Elsevier Inc All rights reserved

DOI: 10.1016/B978-0-12-396959-0.00002-1

810 HVY GAS OIL

3970 DIESEL OIL (NEW)

6394 VASGASOIL

VACUUM FLASHING

2970 STDYE OIL DIESEL OIL

SYNTNR STMS

LT CYCLE OIL

3600 MIDDLE DIS

13426 FUEL OIL

NCTE ALL QUNATITIGS ARE IN BPSD DICAPTINERE VORSO

SCALE DATE

DRM CHR

APP.

ISSUED PRM

ISSUED FOR COMST CUST JOB NO. C.W.N FOR NO.

J 5818-H DRAWING NUMBER

1010-DI-D REV.

NEW DUPLICATE UNIT

TCC UNIT (REPAIR FRGVANID)

2611 CYCLE OIL GASOLINE LIGHTER

4315

NARUTHA DESULFURIZER

(REVAMD)

ULTRAFORMER

(REVEMP) 30,000

196⬚ API

CALIFORNIA

CRUDE

18750 REDUCED CRUDE

THE C.W NOFSINGER COMPANY

KANSAS CITY MISSOURI

ALTERNATE - D REFINERY BLOCK FLOW DIAGRAM

10,444 C43 & LIGHTER

SULFUR RECOVERY (REPAIR) (& REVAMP)

1394 FOR FUEL GAS

13.8 THILLS/DAY SULFUR

815 C

3 LPG

1394 FOR FUEL GAS

815 C3 LPG

19.8 TBNS/DAY SULFUR

TCC Cont SOLING RECOVERY (REPAIR)

&

REVEUNE)

NEW DUPLICATE UNIT

TCC GASOLINE C4*

C2 & C4 SPLITTER (NEW)

C 3 N

(NEW) TCC SPILLITER

1242 LT REF.

2464 NAT.GASO.

7731 PREMIUM GASOLINE RON 100 + 1.0 CC

7 SULFUR 0.1

7751 REGULAR GASOLINE RON 90.0 + 0.8 CC

% SULFUR 0.16

information is required, particularly in the early stages of a design,

since the process flowsheet is drawn first and is the only diagram

available that represents the process As the design develops and a

mechanical flowsheet is prepared, instrumentation may be removed

to minimize clutter A checklist of information usually included on a

process flowsheet is found inTable 2.1

Working flowsheets are necessarily elaborate and difficult to

represent on the page of a book.Figure 2.3originally was 30 in

wide In this process, ammonia is made from available hydrogen

supplemented by hydrogen from the air oxidation of natural gas

in a two-stage reactor F-3 and V-5 A large part of the plant is

devoted to the purification of the feed gases—namely, the removal

of carbon dioxide and unconverted methane before they enter the

converter CV-1 Both commercial and refrigeration grade

ammo-nia are made in this plant Compositions of 13 key streams are

summarized in the tabulation Characteristics of streams, such as

temperature, pressure, enthalpy, volumetric flow rates, and so on,

sometimes are conveniently included in the tabulation, as inFigure

2.3 In the interest of clarity, it may be preferable to have a

sepa-rate sheet if the material balance and related stream information

is voluminous

A process flowsheet of the dealkylation of toluene to benzene

is inFigure 2.4; the material and enthalpy flows as well as

tem-perature and pressures are tabulated conveniently, and basic

instrumentation is represented

2.3 PROCESS AND INSTRUMENTATION DIAGRAMS (P&ID)

Piping and instrument (P&ID) diagrams emphasize two major

characteristics They do not show operating conditions or

compo-sitions or flow quantities, but they do show all major as well as

minor equipment more realistically than on the process flowsheet

Line sizes and specifications of all lines, valves and tion as well as codes for materials of construction and insulationare shown on the diagram In fact, every mechanical aspect ofthe plant regarding the process equipment and their interconnec-tions is represented except for supporting structures and founda-tions The equipment is shown in greater detail than on theprocess flowsheet, notably with respect to external piping connec-tions, internal details, and resemblance to the actual appearance.Many chemical and petroleum companies are now using ProcessIndustry Practices (PIP) criteria for the development of P&IDs Thesecriteria include symbols and nomenclature for typical equipment,instrumentation, and piping They are compatible with industrycodes of the American National Standards Institute (ANSI), Ameri-can Society of Mechanical Engineers (ASME), Instrumentation,Systems and Automation Society of America (ISA), and TubularExchanger Manufacturers Association (TEMA) The PIP criteriacan be applied irrespective of whatever Computer Assisted Design(CAD) system is used to develop P&IDs Process Industries Practice(2003) may be obtained from the Construction Industry Institutementioned in the References

instrumenta-Catena et al (1992) showed how “intelligently” created

P&IDs prepared on a CAD system can be electronically linked

to a relational database that is helpful in meeting OSHA tions for accurate piping and instrumentation diagrams

regula-Since every detail of a plant design is recorded on electronicmedia and paper, many other kinds of flowsheets are also required:for example, electrical flow, piping isometrics, and piping tie-ins toexisting facilities, instrument lines, plans, and elevations, and indivi-dual equipment drawings in detail Models and three-dimensionalrepresentations by computer software are standard practice in designoffices

The P&ID flowsheet of the reaction section of a toluene kylation unit in Figure 2.5 shows all instrumentation, includingindicators and transmitters The clutter on the diagram is mini-mized by tabulating the design and operating conditions of themajor equipment below the diagram

deal-The P&ID of Figure 2.6 represents a gas treating plantthat consists of an amine absorber and a regenerator and theirimmediate auxiliaries Internals of the towers are shown with exactlocations of inlet and outlet connections The amount of instru-mentation for such a comparatively simple process may be surpris-ing On a completely finished diagram, every line will carry a codedesignation identifying the size, the kind of fluid handled, the pres-sure rating, and material specification Complete informationabout each line—its length, size, elevation, pressure drop, fittings,etc.—is recorded in a separate line summary OnFigure 2.6, which

is of an early stage of construction, only the sizes of the lines areshown Although instrumentation symbols are fairly well standar-dized, they are often tabulated on the P&I diagram as in thisexample

2.4 UTILITY FLOWSHEETSThere are P&IDs for individual utilities such as steam, steam con-densate, cooling water, heat transfer media in general, compressedair, fuel, refrigerants, and inert blanketing gases, and how they arepiped up to the process equipment Connections for utility streamsare shown on the mechanical flowsheet, and their conditions andflow quantities usually appear on the process flowsheet

2.5 DRAWING OF FLOWSHEETSFlowsheets may be drawn by hand at preliminary stages of a project,but with process simulators and CAD software packages, it is asimple matter to develop flowsheets with a consistent set of symbols

TABLE 2.1 Checklist of Data Normally Included on a

Process Flowsheet

1 Process lines, but including only those bypasses essential to an

understanding of the process

2 All process equipment Spares are indicated by letter symbols or

notes

3 Major instrumentation essential to process control and to

understanding of the flowsheet

4 Valves essential to an understanding of the flowsheet

5 Design basis, including stream factor

6 Temperatures, pressures, flow quantities

7 Mass and/or mol balance, showing compositions, amounts, and

other properties of the principal streams

8 Utilities requirements summary

9 Data included for particular equipment

a Compressors: SCFM (60°F, 14.7 psia); ΔP psi; HHP; number of

stages; details of stages if important

b Drives: type; connected HP; utilities such as kW, lb steam/hr,

or Btu/hr

c Drums and tanks: ID or OD, seam to seam length, important

internals

d Exchangers: Sqft, kBtu/hr, temperatures, and flow quantities

in and out; shell side and tube side indicated

e Furnaces: kBtu/hr, temperatures in and out, fuel

f Pumps: GPM (60°F), ΔP psi, HHP, type, drive

g Towers: Number and type of plates or height and type of

packing identification of all plates at which streams enter or

leave; ID or OD; seam to seam length; skirt height

h Other equipment: Sufficient data for identification of duty and

size

2.5 DRAWING OF FLOWSHEETS 19