Paul E. Minton
Union Carbide Corporation
South Charleston, West Virginia
NBYES PUBLICATIONS
____
Westwood, New Jersey, U.S.A.
Copyright 01986 by Paul E. Minton
No part of this book may be reproduced in any form
without permission in writing from the Publisher.
Library of Congress Catalog Card Number 86.17978
ISBN: 081551097.7
Printed in the United States
Published in the United States of America by
Noyes Publications
Mill Road, Park Ridge, New Jersey 07656
1098765432 1
Library of Congress Cataloging-in-Publication Data
Minton, Paul E.
Handbook of evaporation technology.
Bibliography: p.
Includes index.
1. Evaporation Handbooks, manuals, etc.
2. Evaporators Handbooks, manuals. etc. I. Title.
TP363.M56 1986
660.2’8426 86.17978
ISBN O-8155-1097-7
Preface
This book results from an evaporation technology course I have taught for some
time. Evaporation is one of the oldest unit operations; it is also an area in which
much has changed in the last quarter century. This book is my attempt to pre-

sent evaporation technology as it is generally practiced today. Although there
are other methods of separation which can be considered, evaporation will re-
main the best separation process for many applications. However, all factors
must be properly evaluated in order to select the best evaporator type.
Evaporation technology has often been proprietary to a few companies who de-
sign evaporation systems. This situation has benefits, but it also has drawbacks
to users of evaporation equipment. Evaporation does not need to be considered
an art; good engineering can result in efficient evaporation systems which oper-
ate reliably and easily. However, some experience in evaporator design is cer-
tainly an advantage in understanding the many problems that can and do occur
in evaporation processes.
Much of what is said in this book has been said before. There have, however,
been few attempts to combine all this information into one location. I am in-
debted to the many people who have pioneered evaporation processes and have
shared their experiences.
I would like to thank Charlie Gilmour for his mould upon my engineering
career. He encouraged me and proved that heat transfer is the most rewarding
engineering discipline. I would like to acknowledge the assistance of Howard
Freese in the area of mechanically-aided, thin-film evaporation as well as his
encouragement in the writing of this book.
South Charleston, West Virginia
October 1986
Paul E. Minton
NOTICE
To the best of the Publisher’s knowledge the
information contained in this publication is
accurate; however, the Publisher assumes no
liability for any consequences arising from
the use of the information contained herein.
Final determination of the suitability of

any information or product for use con-
templated by any user, and the manner of
that use, is the sole responsibility of the
user.
Vi
vii
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Contents
Preface v
Notice vi
1. Introduction 1
2. Evaporation 2
3. What an Evaporator Does 3
4. Evaporator Elements 5
5. Liquid Characteristics 6
Concentration 6
Foaming 6
Temperature Sensitivity 6
Salting 7
Scaling 7
Fouling 7
Corrosion 7
Product Quality 7
Other Fluid Properties 7
6. Improvements in Evaporators 8
7. Heat Transfer in Evaporators 9
Modes of Heat Transfer 10
Types of Heat Transfer Operations 10
Physical Properties 38
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8. Pressure Drop in Evaporators 39
Flow Inside Tubes 39
Flow across the Tube Banks 42
9. Flow-Induced Vibration 48
Mechanisms 49
Vortex Shedding 50
Turbulent Buffeting 51
Fluid-Elastic Whirling 52
Parallel Flow Eddy Formation 53
Acoustic Vibration 53
Recommendations 55
Design Criteria 56
Fixing Vibration Problems in the Field 58
Proprietary Designs to Reduce Vibration 59
10. Natural Circulation Calandrias 60
Operation 60
Surging 64
Flow Instabilities 65
Internal Calandrias 67
Feed Location 69
Summary 69
11. Evaporator Types and Applications 70
Jacketed Vessels 71
Coils 73
Horizontal Tube Evaporators 74
Short Tube Vertical Evaporators 77
Long Tube Vertical Evaporators 81

Forced Circulation Evaporator 84
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Plate Evaporators 87
Mechanically-Aided Evaporators 90
Submerged Combustion Evaporators 100
Flash Evaporators 103
Special Evaporator Types 106
12. Fouling 113
Cost of Fouling 114
Classification of Fouling 114
Net Rate of Fouling 115
Sequential Events in Fouling 116
Precipitation Fouling 118
Particulate Fouling 120
Chemical Reaction Fouling 121
Corrosion Fouling 123
Biofouling 124
Solidification Fouling 125
Fouling in Evaporation 125
Design Considerations 127
Fouling: Philosophy of Design 127
13. Evaporator Performance 133
Venting 133
Time/Temperature Relation 139
Pressure Versus Vacuum Operation 140
Energy Economy 140
Steam Condensate Recovery 150

14. Vapor-Liquid Separation 153
Entrainment 153
Flash Tanks 155
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Wire Mesh Separators 155
Vane Impingement Separators 157
Centrifugal Separators 159
Cyclones 159
Other Separators 162
Comparison 162
Solids Deposition 162
Falling Film Evaporators 164
Flashing 164
Splashing 164
Foaming 164
15. Multiple-Effect Evaporators 166
Forward Feed 167
Backward Feed 168
Mixed Feed 169
Parallel Feed 169
Staging 169
Heat Recovery Systems 170
Calculations 170
Optimization 170
16. Heat Pumps 172
Conventional Heat Pump 172
Overhead Vapor Compression 172

Calandria Liquid Flashing 172
17. Compression Evaporation 175
18. Thermal Compression 176
Thermocompressor Operation 177
Thermocompressor Characteristics 178
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Thermocompressor Types 179
Estimating Data 180
Control 184
Application 184
19. Mechanical Vapor Compression 186
Thermodynamics 187
Factors Affecting Costs 188
Compressor Selection 189
Factors Influencing Design 190
Drive Systems 192
Centrifugal Compressor Characteristics 192
System Characteristics 199
Reliability 203
Evaporator Design 203
Application 204
Summary 204
Economics 204
20. Desalination 206
Startup and Operability 206
Complexity 206
Maintenance 207

Energy Efficiency 207
Capital Cost 208
Operating Temperature 208
Materials of Construction 209
Pretreatment 209
Chemicals and Auxiliary Energy 209
21. Evaporator Accessories 210
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22. Condensers 211
Direct Contact Condensers 211
Surface Condensers 213
23. Vacuum Producing Equipment 222
Jet Ejectors 222
Mechanical Pumps 236
Vacuum System Reliability/Maintenance 240
Multistage Combinations 240
Sizing Information 241
Estimating Energy Requirements 246
Initial System Evacuation 251
Control of Vacuum Systems 252
Costs of Vacuum Systems 256
Comparisons 257
Energy Conservation 258
24. Condensate Removal 259
Liquid Level Control 259
Steam Traps 261
Mechanical Traps 263

Thermostatic Traps 263
Thermodynamic Traps 263
Steam Trap Specification 263
Common Trap Problems 264
Selection of Steam Traps 264
Installation 265
Effect of Carbon Dioxide 268
Steam Trap Maintenance 269
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25. Process Pumps 270
General Types of Pump Designs 270
Net Positive Suction Head (NPSH) 271
Cavitation 272
Principles of Pumps and Pumping Systems 272
Avoiding Common Errors 277
26. Process Piping 279
Designing Drain Piping 280
Compressible Fluids 281
Two-Phase Flow 281
Slurry Flow 284
Piping Layout 285
27. Thermal Insulation 288
28. Pipeline and Equipment Heat Tracing 290
29. Process Vessels 292
30. Refrigeration 294
Mechanical Refrigeration 295
Steam Jet Refrigeration 295

Absorption Refrigeration 296
31. Control 297
Manual Control 297
Evaporator Control Systems 298
Control of Evaporators 302
Auto-Select Control System 304
Product Concentration 304
Condenser Control 306
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Calandria Control 310
Evaporator Base Sections and Accumulators 312
Guidelines for Instruments 313
Process Computers 316
32. Thermal Design Considerations 318
Tube Size and Arrangement 318
Extended Surfaces 319
Shellside Impingement Protection 319
Flow Distribution 321
33. Installation 322
Venting 322
Siphons in Cooling Water Piping 322
U-Bend Exchangers 323
Equipment Layout 323
Piping 323
34. Design Practices for Maintenance 324
Standard Practices 325
Repair Features 325

Chemical Cleaning Equipment 325
Mechanical Cleaning Equipment 325
Backwashing 325
Air Injection 326
35. Mechanical Design 327
Maximum Allowable Working Pressure and Temperature 327
Upset Conditions 328
Thermal Expansion 328
Tube-to-Tubesheet Joints 329
Double Tubesheets 329
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Inspection Techniques 331
36. Safety 332
Common Errors 333
Safety Relief 334
37. Materials of Construction 336
Basic Questions 336
Selection 338
38. Testing Evaporators 339
Planning the Test 339
Causes of Poor Performance 340
39. Troubleshooting 343
Calandrias 344
Condensers 345
Vacuum Fails to Build 346
No Vacuum in Steam Chest 347
Vacuum Builds Slowly 347

Foaming 348
Inadequate Circulation 348
Sudden Loss of Vacuum 348
Vacuum Fluctuates 348
Water Surge in Tail Pipe 349
Barometric Condenser Flooding 349
40. Upgrading Existing Evaporators 350
Areas for Upgrading Existing Evaporators 351
Economic Effects of Improvements 356
Guidelines for Upgrading Program 357
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41. Energy Conservation 359
42. Specifying Evaporators 360
Comparing Vendors’ Offerings 361
43. New Technology 363
44. Nomenclature 365
Greek 371
Subscripts 371
Bibliography 372
Evaporation 372
Heat Transfer 373
Boiling 374
Heat Exchangers 374
Flow-Induced Vibration 375
Fouling 375
Direct Contact Heat Transfer 375
Energy Conservation 376

Vapor Compression Evaporation 376
Vacuum Systems 377
Steam Traps 377
Control 378
Pumps 378
Process Piping and Fluid Flow 379
Separators 379
Thermal Insulation 379
Troubleshooting 380
Venting 380
Air-Cooled Heat Exchangers 380
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Heat Transfer Fluids 381
Testing 381
Electrical Heating 381
Steam Tracing 381
Jacketed Vessels 382
Turbines 382
Mechanical Design 382
Materials of Construction 382
Desalination 382
Evaporators 383
Index 384
Introduction
The industrial society in which we live has depended during recent decades
upon the earth’s supply of oil and gas as its principal source of energy. These
resources are dwindling, and most knowledgeable observers expect them to

attain peak production on a worldwide basis during the next quarter-century.
Possibly, the most important problem we face in the years immediately ahead
is the timely development of alternate energy sources in sufficient quantity to
avert serious economic and social disruption. Efficient utilization of the energy
resources currently available will extend the time period during which new en-
ergy sources can be developed.
Approximately 25% of the cost of products is the cost of energy to operate
plants. Energy is the fastest growing element of manufacturing cost.
Proper specification, design, and operation of evaporator systems will help
to reduce the cost of producing a product by evaporation. Upgrading of existing
evaporator systems is a fruitful area for achieving reduced energy requirements.
1
2
Evaporation
Evaporation is the removal of solvent as vapor from a solution or slurry.
For the overwhelming majority of evaporation systems the solvent is water.
The objective is usually to concentrate a solution; hence, the vapor is not the
desired product and may or may not be recovered depending on its value. There-
fore, evaporation usually is achieved by vaporizing a portion of the solvent
producing a concentrated solution, thick liquor, or slurry.
Evaporation often encroaches upon the operations known as distillation,
drying, and crystallization. In evaporation, no attempt is made to separate com-
ponents of the vapor. This distinguishes evaporation from distillation. Evapora-
tion is distinguished from drying in that the residue is always a liquid. The
desired product may be a solid, but the heat must be transferred in the evapo-
rator to a solution or a suspension of the solid in a liquid. The liquid may be
highly viscous or a slurry. Evaporation differs from crystallization in that evapo-
ration is concerned with concentrating a solution rather than producing or
building crystals.
This discussion will be concerned only with evaporation. Distillation,drying,

or crystallization will not be emphasized.
2
3
What an Evaporator Does
As stated above, the object of evaporation may be to concentrate a solution
containing the desired product or to recover the solvent. Sometimes both may
be accomplished. Evaporator design consists of three principal elements: heat
transfer, vapor-liquid separation, and efficient utilization of energy.
In most cases the solvent is water, heat is supplied by condensing steam, and
the heat is transferred by indirect heat transfer across metallic surfaces. For
evaporators to be efficient, the equipment selected and used must be able to
accomplish several things:
(1)
(2)
(3)
Transfer large amounts of heat to the solution with a minimum
amount of metallic surface area. This requirement, more than all
other factors, determines the type, size, and cost of the evapo-
rator system.
Achieve the specified separation of liquid and vapor and do it with
the simplest devices available. Separation may be important for
several reasons: value of the product otherwise lost; pollution;
fouling of the equipment downstream with which the vapor is
contacted; corrosion of this same downstream equipment. Inade-
quate separation may also result in pumping problems or inefficient
operation due to unwanted recirculation.
Make efficient use of the available energy. This may take several
forms. Evaporator performance often is rated on the basis of steam
economy-pounds of solvent evaporated per pound of steam used.
Heat is required to raise the feed temperature from its initial value

to that of the boiling liquid, to provide the energy required to
separate liquid solvent from the feed, and to vaporize the solvent.
The greatest increase in energy economy is achieved by reusing the
vaporized solvent as a heating medium. This can be accomplished
in several ways to be discussed later. Energy efficiency may be
3
4 Handbook of Evaporation Technology
increased by exchanging heat between the entering feed and the
leaving residue or condensate.
(4) Meet the conditions imposed by the liquid being evaporated or by
the solution being concentrated. Factors that must be considered
include product quality, salting and scaling, corrosion, foaming,
product degradation, holdup, and the need for special types of
construction.
Today many types of evaporators are in use in a great variety of applications.
There is no set rule regarding the selection of evaporator types. In many fields
several types are used satisfactorily for identical services. The ultimate selection
and design may often result from tradition or past experience. The wide varia-
tion in solution characteristics expand evaporator operation and design from
simple heat transfer to a separate art.
4
Evaporator Elements
Three principal elements are of concern in evaporator design: heat transfer,
vapor-liquid separation, and efficient energy consumption. The units in which
heat transfer takes place are called heating units or calandrias. The vapor-liquid
separators are called bodies, vapor heads, or flash chambers. The term body is
also employed to label the basic building module of an evaporator, comprising
one heating element and one flash chamber. An effect is one or more bodies
boiling at the same pressure. A multiple-effect evaporator is an evaporator
system in which the vapor from one effect is used as the heating medium for

a subsequent effect boiling at a lower pressure. Effects can be staged when con-
centrations of the liquids in the effects permits; staging is two or more sections
operating at different concentrations in a single effect. The term evaporator
denotes the entire system of effects, not necessarily one body or one effect.
5
5
Liquid Characteristics
The practical application of evaporator technology is profoundly affected
by the properties and characteristics of the solution to be concentrated. Some of
the most important properties of evaporating liquids are discussed below.
CONCENTRATION
The properties of the feed to an evaporator may exhibit no unusual problems.
However, as the liquor is concentrated, the solution properties may drastically
change. The density and viscosity may increase with solid content until the heat
transfer performance is reduced or the solution becomes saturated. Continued
boiling of a saturated solution may cause crystals to form which often must be
removed to prevent plugging or fouling of the heat transfer surface. The boiling
point of a solution also rises considerably as it is concentrated.
FOAMING
Some materials may foam during vaporization. Stable foams may cause ex-
cessive entrainment. Foaming may be caused by dissolved gases in the liquor, by
an air leak below the liquid level, and by the presence of surface-active agents or
finely divided particles in the liquor. Many antifoaming agents can be used effec-
tively. Foams may be suppressed by operating at low liquid levels, by mechanical
methods, or by hydraulic methods.
TEMPERATURE SENSITIVITY
Many chemicals are degraded when heated to moderate temperatures for
relatively short times. When evaporating such materials special techniques are
needed to control the time/temperature characteristics of the evaporator system.
6

Liquid Characteristics 7
SALTING
Salting refers to the growth on evaporator surfaces of a material having a
solubility that increases with an increase of temperature. It can be reduced or
eliminated by keeping the evaporating liquid in close or frequent contact with
a large surface area of crystallized solid.
SCALING
Scaling is the growth or deposition on heating surfaces of a material which
is either insoluble or has a solubility that decreases with an increase in temper-
ature. It may also result from a chemical reaction in the evaporator. Both scaling
and salting liquids are usually best handled in an evaporator that does not rely
upon boiling for operation.
FOULING
Fouling is the formation of deposits other than salt or scale. They may be
due to corrosion, solid matter entering with the feed, or deposits formed on the
heating medium side.
CORROSION
Corrosion may influence the selection of evaporator type since expensive
materials of construction indicate evaporators affording high rates of heat trans-
fer. Corrosion and erosion are frequently more severe in evaporators than in
other types of equipment because of the high liquid and vapor velocities, the
frequent presence of suspended solids, and the concentrations required.
PRODUCT QUALITY
Product quality may require low holdup and low temperatures. Low-holdup-
time requirements may eliminate application of some evaporator types. Product
quality may also dictate special materials of construction.
OTHER FLUID PROPERTIES
Other fluid properties must also be considered. These include: heat of solu-
tion, toxicity, explosion hazards, radioactivity, and ease of cleaning. Salting,
scaling, and fouling result in steadily diminishing heat transfer rates, until the

evaporator must be shut down and cleaned. Some deposits may be difficult and
expensive to remove.
6
Improvements in Evaporators
Many improvements have been made in evaporator technology in the last
half-century. The improvements have taken many forms but have served to
effect the following:
(1) Greater evaporation capacity through better understanding of the
heat transfer mechanisms.
(2) Better economy through more efficient use of evaporator types
(3) Longer cycles between cleaning because of better understanding of
salting, scaling, and fouling.
(4) Cheaper unit costs by modern fabrication techniques and larger
unit size.
(5) Lower maintenance costs and improved product quality by use of
better materials of construction as a result of better understanding
of corrosion.
(6) More logical application of evaporator types to specific services.
(7) Better understanding and application of control techniques and
improved instrumentation has resulted in improved product quality
and reduced energy consumption.
(8) Greater efficiency resulting from enhanced heat transfer surfaces
and better energy economy.
(9) Compressor technology and availability has permitted the applica-
tion of mechanical vapor compression.
8
Heat Transfer in Evaporators
Whenever a temperature gradient exists within a system, or when two
systems at different temperatures are brought into contact, energy is transferred.
The process by which the energy transport takes place is known as heat transfer.

The thing in transit, called heat, cannot be measured or observed directly, but
the effects it produces are amenable to observations and measurement.
The branch of science which deals with the relation between heat and other
forms of energy is called thermodynamics. Its principles, like all laws of nature,
are based on observations and have been generalized into laws which are be-
lieved to hold for all processes occurring in nature, because no exceptions have
ever been detected. The first of these principles, the first law of thermody-
namics, states that energy can be neither created nor destroyed but only changed
from one form to another. It governs all energy transformations quantitatively
but places no restrictions on the direction of the transformation. It is known,
however, from experience that no process is possible whose sole result is the net
transfer of heat from a region of lower temperature to a region of higher tem-
perature. This statement of experimental truth is known as the second law of
thermodynamics.
All heat-transfer processes involve the transfer and conversion of energy.
They must therefore obey the first as well as the second law of thermody-
namics. From a thermodynamic viewpoint, the amount of heat transferred
during a process simply equals the difference between the energy change of the
system and the work done. It is evident that this type of analysis considers
neither the mechanism of heat flow nor the time required to transfer the heat.
From an engineering viewpoint, the determination of the rate of heat trans-
fer at a specified temperature difference is the key problem. The size and cost of
heat transfer equipment depend not only on the amount of heat to be trans-
ferred, but also on the rate at which the heat is to be transferred under given
conditions.
9