Page 14 - Chemical Process Equipment - Selection and Design

Preface

This book is intended as a guide to the selection or design of the Because more than one kind of equipment often is suitable for
principal kinds of chemical process equipment by engineers in particular applications and may be available from several
school and industry. The level of treatment assumes an elementary manufacturers, comparisons of equipment and typical applications
knowledge of unit operations and transport phenomena. Access to are cited liberally. Some features of industrial equipment are largely
the many design and reference books listed in Chapter 1 is arbitrary and may be standardized for convenience in particular
desirable. For coherence, brief reviews of pertinent theory are industries or individual plants. Such aspects of equipment design are
provided. Emphasis is placed on shortcuts, rules of thumb, and data noted when feasible.
for design by analogy:, often as primary design processes but also for Shortcut methods of design provide solutions bo problems in a
quick evaluations of detailed work. short time and at small expense. They must be used when data are
All answers to process design questions cannot be put into a limited or when the greater expense of a thorough method is not
book. Even at this late date in the development of the chemical justifiable. In particular cases they may be employed to obtain
industry, it is common to hear authorities on most kinds of information such as:
equipment say that their equipment can be properly fitted to a
particular task only on the basis of some direct laboratory and pilot 1. an order of magnitude check of the reasonableness of a result
plant work. Nevertheless, much guidance and reassurance are found by another lengthier and presumably accurate computa-
obtainable from general experience and specific examples of tion or computer run,
successful applications, which this book attempts to provide. Much 2. a quick check to find if existing equipment possibly can be
of the informaticin is supplied in numerous tables and figures, which adapted to a new situation,
often deserve careful study quite apart from the text. 3. a comparison of alternate processes,
The general background of process design, flowsheets, and 4. a basis for a rough cost estimate of a process.
process control is reviewed in the introductory chapters. The major
kinds of operations and equipment are treated in individual Shortcut methods occupy a prominent place in such a broad survey
chapters. Information about peripheral and less widely employed and limited space as this book. References to sources of more
equipment in chemical plants is concentrated in Chapter 19 with accurate design procedures are cited when available.
references to key works of as much practical value as possible. Another approach to engineering work is with rules of thumb,
Because decisions often must be based on economic grounds, which are statements of equipment performance that may obviate
Chapter 20, on costs of equipment, rounds out the book. all need for further calculations. Typical examples, for instance, are
Appendixes provide examples of equipment rating forms and that optimum reflux ratio is 20% greater than minimum, that a
manufacturers’ questionnaires. suitable cold oil velocity in a fired heater is 6ft/sec, or that the
Chemical process equipment is of two kinds: custom designed efficiency of a mixer-settler extraction stage is 70%. The trust that
and built, or proprietary “off the shelf.” For example, the sizes and can be placed in a rule of thumb depends on the authority of the
performance of custom equipment such as distillation towers, propounder, the risk associated with its possible inaccuracy, and the
drums, and heat exchangers are derived by the process engineer on economic balance between the cost of a more accurate evaluation
the basis of established principles and data, although some and suitable safety factor placed on the approximation. All
mechanical details remain in accordance with safe practice codes experienced engineers have acquired such knowledge. When
and individual fabrication practices. applied with discrimination, rules of thumb are a valuable asset to
Much proprietanj equipment (such as filters, mixers, conveyors, the process design and operating engineer, and are scattered
and so on) has been developed largely without benefit of much throughout this book.
theory and is fitted to job requirements also without benefit of much Design by analogy, which is based on knowledge of what has
theory. Froim the point of view of the process engineer, such been found to work in similar areas, even though not necessarily
equipment is predesigned and fabricated and made available by optimally, is another valuable technique. Accordingly, specific
manufacturers in limited numbers of types, sizes, and capacities. applications often are described in this book, and many examples of
The process design of proprietary equipment, as considered in this specific equipment sizes and performance are cited.
book, establishes its. required performance and is a process of For much of my insight into chemical process design, I am
selection frlom the manufacturers’ offerings, often with their indebted to many years’ association and friendship with the late
recommendations or on the basis of individual experience. Charles W. Nofsinger who was a prime practitioner by analogy, rule
Complete information is provided in manufacturers’ catalogs. of thumb, and basic principles. Like Dr. Dolittle of Puddleby-on-
Several classified lists of manufacturers of chemical process the-Marsh, “he was a proper doctor and knew a whole lot.”
equipment are readily accessible, SO no listings are given here.

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