Chemical Process Equipment 3rd Edition Selection and Design
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Chemical Process Equipment 3rd Edition Selection and Design

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Preface to Chemical Process Equipment Selection and Design

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 designs and reference books listed in Chapter 1 is desirable.

For coherence, brief reviews of the pertinent theories are provided. Emphasis is placed on shortcuts, rules of thumb, and data for design by analogy, often as primary design processes but also for quick evaluations of detailed work.

All answers to process design questions cannot be put into a book. Even at this late date in the development of the chemical industry, it is common to hear authorities on most kinds of equipment say that their equipment can be properly fitted to a particular task only on the basis of some direct laboratory and pilot plant work.

Nevertheless, much guidance and reassurance are obtainable from general experience and specific examples of successful applications, which this book attempts to provide.

Much of the information is supplied in numerous tables and figures, which often deserve careful study quite apart from the text.

The general background of process design, flowsheets, and process control is reviewed in the introductory chapters. The major kinds of operations and equipment are treated in individual chapters.

Information about peripheral and less widely employed equipment in chemical plants is concentrated in Chapter 19 with references to key works of as much practical value as possible.

Because decisions often must be based on economic grounds, Chapter 20, on costs of equipment, rounds out the book. Appendixes provide examples of equipment rating forms and manufacturers’ questionnaires.

Chemical process equipment is of two kinds: custom designed and built, or proprietary ‘‘off the shelf.’’ For example,

the sizes and performance of custom equipment such as distillation towers, drums, and heat exchangers are derived by the process engineer on the basis of established principles and data, although some mechanical details remain in accordance with safe practice codes and individual fabrication practices.

Much proprietary equipment (such as filters, mixers, conveyors, and so on) has been developed largely without the benefit of much theory and is fitted to job requirements also without the benefit of much theory.

From the point of view of the process engineer, such equipment is predesigned and fabricated and made available by manufacturers in limited numbers of types, sizes, and capacities.

The process design of proprietary equipment, as considered in this book, establishes its required performance and is a process of selection from the manufacturers’ offerings, often with their recommendations or on the basis of individual experience.

Complete information is provided in manufacturers’ catalogs. Several classified lists of manufacturers of chemical process equipment are readily accessible, so no listings are given here.

Because more than one kind of equipment often is suitable for particular applications and may be available from several manufacturers, comparisons of equipment and typical applications are cited liberally.

Some features of industrial equipment are largely arbitrary and may be standardized for convenience in particular industries or individual plants. Such aspects of equipment design are noted when feasible. Shortcut methods of design provide solutions to problems in a short time and at a small expense.

They must be used when data are limited or when the greater expense of a thorough method is not justifiable. In particular cases, they may be employed to obtain information such as:

  1.  an order of magnitude check of the reasonableness of a result found by another lengthier and presumably accurate computation or computer run,
  2. a quick check to find if existing equipment possibly can be adapted to a new situation,
  3.  a comparison of alternate processes,
  4. a basis for a rough cost estimate of a process.

Shortcut methods occupy a prominent place in such a broad survey and limited space as this book. References to sources of more accurate design procedures are cited when available.

Another approach to engineering work is with rules of thumb, which are statements of equipment performance that may obviate all need for further calculations.

Typical examples, for instance, are that optimum reflux ratio is 20% greater than the minimum, that a suitable 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 be placed in a rule of thumb depends on the authority of the propounder, the risk associated with its possible inaccuracy, and the economic balance between the cost of a more accurate evaluation and suitable safety factor placed on the approximation.

All experienced engineers have acquired such knowledge. When applied with discrimination, rules of thumb are a valuable asset to the process design and operating engineer and are scattered throughout this book.

Design by analogy, which is based on knowledge of what has been found to work in similar areas, even though not necessarily optimally, is another valuable technique.

Accordingly, specific applications often are described in this book, and many examples of specific equipment sizes and performance are cited.

For much of my insight into chemical process design, I am indebted to many years’ association and friendship with the late Charles W. Nofsinger, who was a prime practitioner by analogy, rule of thumb, and basic principles. Like Dr. Dolittle of Puddleby-on-the-Marsh, ‘‘he was a proper doctor and knew a whole lot.’’ 

The editors of the revised edition are in agreement with the philosophy 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, and Chapter 10 Mixing and Agitation 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 chemical 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 in Chapter 19 of the original edition.

Chapter 21, Costs of Individual Equipment, is a revision of Chapter 20 in the original edition and the algorithms have been updated to late 2002. Costs calculated from these algorithms have been spot-checked with equipment suppliers and industrial sources.

They have been found to be within 20 to 25% accurate. We have removed almost all the Fortran computer program listings since every engineer has his or her own methods for solving such problems.

There is one exception and that is the fired heater design Fortran listing in Chapter 8, Heat Transfer and Heat Exchangers.

Our experience is that the program provides insight into a tedious and involved calculation procedure. Although the editors of this text have had considerable industrial and academic experience in process design and equipment selection, there are certain areas in which we have limited or no experience.

It was our decision to ask experts to serve as collaborators. We wish to express our profound appreciation to those colleagues and they are mentioned in the List of Contributors.

We particularly wish to acknowledge the patience and understanding of our wives, Mary Couper, Merle Fair, and Annette Penney, during the preparation of this manuscript.

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