Applied Process Design for Chemical and Petrochemical Plants: Volume 1

By Ernest E. Ludwig

This expanded edition introduces new design methods and is packed with examples, design charts, tables, and performance diagrams to add to the practical understanding of how selected equipment can be expected to perform in the process situation. A major addition is the comprehensive chapter on process safety design considerations, ranging from new devices and components to updated venting requirements for low-pressure storage tanks to the latest NFPA methods for sizing rupture disks and bursting panels, and more.


*Completely revised and updated throughout

*The definative guide for process engineers and designers

*Covers a complete range of basic day-to-day operation topics

• Language: English
• Publisher: Elsevier Science
• Release date: Feb 23, 1995
• ISBN: 9780080527369

Book preview

Emphasizes how to apply techniques of process design and interpret results into mechanical equipment details

Applied Process Design: For Chemical and Petrochemical Plants

Ernest E. Ludwig

ISSN  1874-8635

Volume 1, 3rd ed. • Suppl. (C) • 1999

Table of Contents

Cover image

Title page

Inside Front Cover

Dedication

Inside Front Cover Two

Copyright page

Preface to the Third Edition

Chapter 1: Process Planning, Scheduling and Flowsheet Design

Organizational Structure

Process Design Scope

Role of the Process Design Engineer

Flowsheets—Types

Flowsheet Presentation

General Arrangements Guide

Computer-Aided Flowsheet Design/Drafting

Flowsheet Symbols

Line Symbols and Designations

Materials of Construction for lines

Test Pressure for Lines

Working Schedules

Information Checklists

Standards and Codes

System Design Pressures

Time Planning and Scheduling

Activity Analysis

Collection and Assembly of Physical Property Data

Estimated Equipment Calculation Man-Hours

Estimated Total Process Man-Hours

Example 1-1 Man-Hour Evaluation

Typical Man-Hour Patterns

Influences

Assignment of Personnel

Plant Layout

Cost Estimates

Six-Tenths Factor

Yearly Cost Indices

Return on Investment

Example 1-2 Justifiable Investment For Annual Savings [6]

Accounting Coordination

Chapter 2: Fluid Flow

Scope

Basis

Incompressible Flow

Compressible Flow: Vapors and Gases [3]

Factors of Safety for Design Basis

Important Pressure Level References

Pipe, Fittings, and Valves

Nozzles and Orifices [3]

Friction Drop for Compressible Natural Gas in Long Pipe Lines

Complex Pipe Systems Handling Natural (or similar) Gas

Two-phase Liquid and Gas Flow

Type of Flow For Horizontal Pipes

Pressure Drop in Vacuum Systems

Pressure Drop for Flashing Liquids

Nomenclature

Greek Symbols

Subscripts

Chapter 3: Pumping of Liquids

Pump Design Standardization

Basic Parts of a Centrifugal Pump

Centrifugal Pump Selection

Hydraulic Characteristics For Centrifugal Pumps

Pumping Systems and Performance

Centrifugal Pump Specifications

Sump Design for Vertical Lift

Rotary Pumps

Nomenclature

Subscripts

Greek Symbols

Chapter 4: Mechanical Separations

Particle Size

Preliminary Separator Selection

Example 4-1 Basic Separator Type Selection [2,17]

Guide to Dust Separator Applications

Guide to Liquid-Solid Particle Separators

Gravity Settlers

REMARKS REFERRED TO IN Table 4-5

Example 4-2 Hindered Settling Velocities

API-Oil Field Separators

Liquid/Liquid, Liquid/Solid Gravity Separations, Decanters, and Sedimentation Equipment

Modified Method of Happel and Jordan [29]

Example 4-3 Horizontal Gravity Settlers

Decanter [32]

Guidelines for successful decanters [32]:

Example 4-4 Decanter, using the method of Reference [32]

B. Impingement Separators

Example 4-5 Wire Mesh Entrainment Separator

Fiber Beds/Pads Impingement Eliminators

Centrifugal Separators

Example 4-6 Cyclone System Pressure Drop

Liquid Cyclone-Type Separator

Liquid Cyclone Design (Based on air-water at atmospheric pressure) Figure 4-49

Liquid-Solids Cyclone (Hydrocyclones) Separators

Solid Particles in Gas/Vapor or Liquid Streams

Inertial Centrifugal Separators

Scrubbers

Cloth or Fabric Bag Separators or Filters

Specifications

Electrical Precipitators

Nomenclature

Subscripts

Greek Symbols

Chapter 5: Mixing of Liquids

Mechanical Components

Process Results

In-line, Static or Motionless Mixing

Nomenclature

Subscripts

Greek Symbols

Chapter 6: Ejectors and Mechanical Vacuum Systems

Ejectors

Performance Factors

Types of Loads

Air Inleakage into System

Total Capacity at Ejector Suction

Ejector Selection Procedure

Barometric Condensers

Water Jet Ejectors

Steam Jet Thermocompressors

Ejector Control

Time Required For System Evacuation

Mechanical Vacuum Pumps

Nomenclature

Greek Symbols

Subscripts

Chapter 7: Process Safety and Pressure-Relieving Devices

Types of Positive Pressure Relieving Devices (see manufacturers’ catalogs for design details)

General Code Requirements [1]

Pressure Settings and Design Basis

Establishing Relieving or Set Pressures

Selection and Application

Emergency Pressure Relief: Fires and Explosions Rupture Disks

Rupture Disk Sizing Design and Specification

Emergency Vent Equipment

Flame Arrestors

Explosions

Confined Explosions

Flammability

Blast Pressures

Liquid Mist Explosions

Dust Explosions

Runaway Reactions: DIERS

Flares/Flare Stacks

Flares

Purging of Flare Stacks and Vessels/Piping

Static Electricity

Nomenclature

Subscripts

Greek Symbols

Listing of Final Reports from the Diers Research Program (Design Institute of Emergency Relief Systems)

Appendix

A-1 Alphabetical Conversion Factors

A-2 Physical Property Conversion Factors

A-3 Synchronous Speeds

A-4 Conversion Factors

A-5 Temperature Conversion

A-6 Altitude and Atmospheric Pressures

A-7 Vapor Pressure Curves. (Courtesy Ingersoll-Rand Co.)

A-8 Pressure Conversion Chart

A-9 Vacuum Conversion

A-10 Decimal and Millimeter Equivalents of Fractions

A-11 Particle Size Measurement

A-12 Viscosity Conversions. (By permission, Tube Turns Div., Chemetron Corp., Bull. TT 725.)

A-13 Viscosity Conversions. (Courtesy Kinney Vacuum Div., The New York Air Brake Co.)

A-14 Commercial Wrought Steel Pipe Data (Based on ANSI B36.10 wall thicknesses)

A-15 Stainless Steel Pipe Data (Based on ANSI B36.19 wall thicknesses)

A-16 Properties of Pipe

A-17 Equation of Pipes

A-18 Circumferences and Areas of Circles (Advancing by eighths)

A-19 Capacities of Cylinders and Spheres

A-20 Tank Capacities, Horizontal Cylindrical—Contents of Tanks with Flat Ends When Filled to Various Depths

A-21 Tank Capacities, Horizontal Cylindrical—Contents of Standard Dished Heads When Filled to Various Depths

A-22 Miscellaneous Formulas (Courtesy of Chicago Bridge and Iron Co.)

A-23 Decimal Equivalents in Inches, Feet and Millimeters

A-24 (By permission of Buffalo Tank Div., Bethlehem Steel Corp.)

A-25 Wind Chill Equivalent Temperatures on Exposed Flesh at Varying Velocity

A-26 Impurities in Water

A-27 Water Analysis Conversions for Units Employed: Equivalents

A-28 Parts Per Million to Grains Per U. S. Gallon

A-29 Formulas, Molecular and Equivalent Weights, and Conversion Factors to CaCO3 of Substances Frequently Appearing in the Chemistry of Water Softening

A-30 Grains Per U.S. Gallons—Pounds Per 1000 Gallons

A-31 Parts Per Million—Pounds Per 1000 Gallons

A-32 Coagulant, Acid, and Sulfate—1 ppm Equivalents

A-33 Alkali and Lime—1 ppm Equivalents

A-34 Sulfuric, Hydrochloric Acid Equivalent

A-35 Asme Flanged and Dished Heads IDD Chart

Index

Inside Front Cover

Gulf Professional Publishing

An Imprint of Elsevier

Dedication

To my wife, Sue, for her

patient encouragement and help

Inside Front Cover Two

Disclaimer

The material in this book was prepared in good faith and carefully reviewed and edited. The author and publisher, however, cannot be held liable for errors of any sort in these chapters. Furthermore, because the author has no means of checking the reliability of some of the data presented in the public literature, but can only examine it for suitability for the intended purpose herein, this information cannot be warranted. Also because the author cannot vouch for the experience or technical capability of the user of the information and the suitability of the information for the user’s purpose, the use of the contents must be at the best judgment of the user.

Copyright page

Applied Process Design for Chemical and Petrochemical Plants

Volume 1, Third Edition

Copyright © 1999 by Butterworth-Heinemann. All rights reserved. Printed in the United States of America. This book, or parts thereof, may not be reproduced in any form without permission of the publisher.

Permissions may be sought directly from Elsevier’s Science and Technology Rights Department in Oxford, UK. Phone: [phone], Fax: [phone], e-mail: [e-mail]. You may also complete your request on-line via the Elsevier homepage: http://www.elsevier.com by selecting Customer Support and then Obtaining Permissions.

Library of Congress Cataloging-in-Publication Data

Ludwig, Ernest E.

Applied process design for chemical and petrochemical plants / Ernest E. Ludwig. — 3rd ed.

p. cm.

Includes bibliographical references and index.

ISBN-13: 978-0-88415-025-1 ISBN-10: 0-88415-025-9 (v. 1)

1. Chemical plants—Equipment and supplies. 2. Petroleum industry and trade—Equipment and supplies. I. Title.

TP 155.5.L8 1994

660′ .283—dc20 94-13383

CIP

Originally published by Gulf Publishing Company,

Houston, TX.

ISBN-13: 978-0-88415-025-1 ISBN-10: 0-88415-025-9 (v. 1)

10 9 8 7 6 5

For information, please contact:

Manager of Special Sales

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Preface to the Third Edition

Ernest E. Ludwig and P.E.

This volume of Applied Process Design is intended to be a chemical engineering process design manual of methods and proven fundamentals with supplemental mechanical and related data and charts (some in the expanded Appendix). It will assist the engineer in examining and analyzing a problem and finding a design method and mechanical specifications to secure the proper mechanical hardware to accomplish a particular process objective. An expanded chapter on safety requirements for chemical plants and equipment design and application stresses the applicable Codes, design methods, and the sources of important new data.

This manual is not intended to be a handbook filled with equations and various data with no explanation of application. Rather, it is a guide for the engineer in applying chemical processes to the properly detailed hardware (equipment), because without properly sized and internally detailed hardware, the process very likely will not accomplish its unique objective. This book does not develop or derive theoretical equations; instead, it provides direct application of sound theory to applied equations useful in the immediate design effort. Most of the recommended equations have been used in actual plant equipment design and are considered to be some of the most reasonable available (excluding proprietary data and design methods) that can be handled by both the inexperienced as well as the experienced engineer. A conscious effort has been made to offer guidelines of judgment, decisions, and selections, and some of this will also be found in the illustrative problems. My experience has shown that this approach at presentation of design information serves well for troubleshooting plant operation problems and equipment/systems performance analysis. This book also can serve as a classroom text for senior and graduate level chemical plant design courses at the university level.

The text material assumes that the reader is an undergraduate engineer with one or two years of engineering fundamentals or a graduate engineer with a sound knowledge of the fundamentals of the profession. This book will provide the reader with design techniques to actually design as well as mechanically detail and specify. It is the author’s philosophy that the process engineer has not adequately performed his or her function unless the results of a process calculation for equipment are specified in terms of something that can be economically built or selected from the special designs of manufacturers and can by visual or mental techniques be mechanically interpreted to actually perform the process function for which it was designed. Considerable emphasis in this book is placed on the mechanical Codes and some of the requirements that can be so important in the specifications as well as the actual specific design details. Many of the mechanical and metallurgical specifics that are important to good design practice are not usually found in standard mechanical engineering texts.

The chapters are developed by design function and not in accordance with previously suggested standards for unit operations. In fact, some of the chapters use the same principles, but require different interpretations that take into account the process and the function the equipment performs in the process.

Because of the magnitude of the task of preparing the material for this new edition in proper detail, it has been necessary to omit several important topics that were covered in the previous edition. Topics such as corrosion and metallurgy, cost estimating, and economics are now left to the more specialized works of several fine authors. The topic of static electricity, however, is treated in the chapter on process safety, and the topic of mechanical drivers, which includes electric motors, is covered in a separate chapter because many specific items of process equipment require some type of electrical or mechanical driver. Even though some topics cannot be covered here, the author hopes that the designer will find design techniques adaptable to 75 percent to 85+ percent of required applications and problems.

The techniques of applied chemical plant process design continue to improve as the science of chemical engineering develops new and better interpretations of the fundamentals of chemistry, physics, metallurgical, mechanical, and polymer/plastic sciences. Accordingly, this third edition presents additional reliable design methods based on proven techniques developed by individuals and groups considered competent in their subjects and who are supported by pertinent data. Since the first and second editions, much progress has been made in standardizing (which implies a certain amount of improvement) the hardware components that are used in designing process equipment. Much of the important and basic standardization has been incorporated in this latest edition. Every chapter has been expanded and updated with new material.

All of the chapters have been carefully reviewed and older (not necessarily obsolete) material removed and replaced by newer design techniques. It is important to appreciate that not all of the material has been replaced because much of the so-called older material is still the best there is today, and still yields good designs. Additional charts and tables have been included to aid in the design methods or explaining the design techniques.

The author is indebted to the many industrial firms that have so generously made available certain valuable design data and information. Thus, credit is acknowledged at the appropriate locations in the text, except for the few cases where a specific request was made to omit this credit.

The author was encouraged to undertake this work by Dr. James Villbrandt and the late Dr. W. A. Cunningham and Dr. John J. McKetta. The latter two as well as the late Dr. K. A. Kobe offered many suggestions to help establish the usefulness of the material to the broadest group of engineers and as a teaching text.

In addition, the author is deeply appreciative of the courtesy of The Dow Chemical Co. for the use of certain noncredited materials and their release for publication. In this regard, particular thanks is given to the late N. D. Griswold and Mr. J. E. Ross. The valuable contribution of associates in checking material and making suggestions is gratefully acknowledged to H. F. Hasenbeck, L. T. McBeth, E. R. Ketchum, J. D. Hajek, W.J. Evers, and D. A. Gibson. The courtesy of the Rexall Chemical Co. to encourage completion of the work is also gratefully appreciated.

Chapter 1

Process Planning, Scheduling and Flowsheet Design

Process engineering design is the application of chemical, mechanical, petroleum, gas and other engineering talents to the process-related development, planning, designs and decisions required for economical and effective completion of a process project [7]. Although process design engineers are organizationally located in research, technical service, economic evaluation, as well as other specific departments, the usual arrangement is to have them available to the engineering groups concerned with developing the engineering details of a project. This is in order to provide process details as well as to evaluate bids for the various items of equipment. Process design is usually a much more specific group responsibility in engineering contractor organizations than in a chemical or petrochemical production company, and the degree of distinction varies with the size of the organization.

The average process engineer has the following responsibilities:

1. Prepares studies of process cycles and systems for various product production or improvements or changes in existing production units; prepares material and heat balances.

2. Prepares economic studies associated with process performance.

3. Designs and/or specifies items of equipment required to define the process flowsheet or flow system; specifies corrosion resistant materials of construction.

4. Evaluates competitive bids for equipment.

5. Evaluates operating data for existing or test equipment.

6. Guides flowsheet draftsmen in detailed flowsheet preparation.

The process engineer also develops tests and interprets data and information from the research pilot plant. He aids in scaling-up the research type flow cycle to one of commercial feasibility.

The process engineer must understand the interrelationship between the various research, engineering, purchasing, expediting, construction and operational functions of a project. He must appreciate that each function may and often does affect or influence the process design decisions. For example, it is foolish to waste time designing or calculating in detail, when the basic components of the design cannot be economically fabricated, or if capable of being fabricated, cannot possibly be delivered by the construction schedule for the project. Some specific phases of a project that require process understanding include plant layout, materials of construction for corrosion as well as strength, start-up operations, trouble-shooting, maintenance, performance testing and the like.

Organizational Structure

The process design function may be placed in any one of several workable locations in an organization. These locations will be influenced by the primary function of the overall company, i.e., chemical production, engineering, engineering sales, design and manufacture of packaged or specific equipment manufacture, etc. For best efficiency, regardless of the business nature of the company, the process design being a specialty type operation, works best when specifically identified and given the necessary freedom of contact within and without the company to maintain a high level of practical, yet thorough direction.

A typical working arrangement is shown in Figure 1-1 [7].

Figure 1-1 A process engineering section supervision chart. By permission, E. E. Ludwig [7].

In a consulting or engineering contractor organization, process design and/or process engineering is usually a separate group responsible for developing the process with the customer, or presenting the customer with a turnkey proposed process.

In an operating or producing chemical or petrochemical company the process engineering and design may be situated in a research, technical service, or engineering department. In most cases it is associated with an engineering department if new projects and processes are being planned for the company. If located elsewhere, the designs and planning must be closely coordinated with the engineering activity.

Most current thinking establishes a project team headed by a project engineer or manager to oversee the accomplishment of a given plant development for a process company. If the projects or jobs are small, then the scope of activity is limited and may often be consolidated in a single individual for project and process responsibility. For projects larger than $500,000, the project and process responsibility usually are best kept separate in order to expedite the specific accomplishment of the process design phase. When the process design engineer is required to interrupt calculations and specification development and to follow some electrical, structural or even expediting delivery question or problem, the design work cannot be completed at best efficiency and often the quality of process design suffers, assuming there is a fixed target date for completion of the various phases as well as the overall project.

Figure 1-2 diagrammatically suggests a team arrangement for accomplishing the planning of a process project. The arrows indicate directions of flow of communications and also the tie-in relationship of the process design function in the accomplishment of an assignment. The planning team in the box works to place the proper perspective on all phases of the engineering functions by developing a working atmosphere of understanding for accomplishing the engineering design. This is physically represented by mechanical vessels, piping, structures, electrical, instrumentation, civil and any other specialized functions. In many projects, the Lead Process Engineer and the Project Lead Engineer are the only individuals who see the details of the overall scope of the project.

Figure 1-2 Typical organization of ‘engineering planning team.’ By permission, E. E. Ludwig [7].

Process Design Scope

The term process design is used here to include what is sometimes referred to as process engineering. Yet in some process engineering operations, all process design functions may not be carried out in detail. As discussed, process design is intended to include:

1. Process material and heat balances.

2. Process cycle development, correlation of pilot or research data, and correlation of physical data.

3. Auxiliary services material and heat balances.

4. Flowsheet development and detailed completion.

5. Chemical engineering performance design for specific items of equipment required for a flowsheet, and mechanical interpretation of this to a practical and reasonable specification. Here the process requirements are converted into hardware details to accomplish the process end results at each step in the product production process.

6. Instrumentation as related to process performance, presentation and interpretation of requirements to instrument specialists.

7. Process interpretation for proper mechanical, structural, civil, electrical, instrument, etc., handling of the respective individual phases of the project.

8. Preparation of specifications in proper form and/or detail for use by the project team as well as for the purchasing function.

9. Evaluation of bids and recommendation of qualified vendor.

Most of the functions are fairly self explanatory; therefore, emphasis will be placed only on those requiring detailed explanation.

Role of the Process Design Engineer

Although the working role of the process design engineer may include all of the technical requirements listed above, it is very important to recognize what this entails in some detail. The process design engineer, in addition to being capable of participating in evaluation of research and pilot plant data and the conversion of this data into a proposed commercial process scheme, must also:

1. Prepare heat and material balance studies for a proposed process, both by hand and by use of computer programs.

2. Prepare rough cost economics, including preliminary sizing and important details of equipment, factor to an order of magnitude capital cost estimate [34] (see also [19]), prepare a production cost estimate, and work with economic evaluation representatives to establish a payout and the financial economics of the proposed process.

3. Participate in layout planning for the proposed plant (see [46] [47]).

4. Prepare final detailed heat and material balances.

5. Prepare detailed sizing of all process equipment and possibly some utility systems. It is important that the process engineer visualize the flow and processing of the fluids through the system and inside the various items of equipment in order to adequately recognize what will take place during the process.

6. Prepare/supervise preparation of draft of process flowsheets for review by others.

7. Prepare/supervise preparation of piping or mechanical flow diagram (or P and ID), with necessary preliminary sizing of all pipe lines, distillation equipment, pumps, compressors, etc., and representation of all instrumentation for detailing by instrument engineers.

8. Prepare mechanical and process specifications for all equipment, tanks, pumps, compressors, separators, drying systems, refrigeration systems. This must include the selection of materials of construction and safety systems and the coordination of specifications with instrumentation and electrical requirements.

9. Determine size and specifications for all safety relief valves and/or rupture disks for process safety relief (including run-a-way reactions) and relief in case of external fire.

10. Prepare valve code specifications for incorporation on item 6 above, or select from existing company standards for the fluids and their operating conditions (see Figures 1-25 and 1-26).

Figure 1-25 Typical valve codes and specifications. By permission, Borden Chemicals and Plastics Operating Limited Partnership.

Figure 1-26 Partial presentation of piping materials specifications for a specific process service. By permission, Borden Chemicals and Plastics, Operating Limited Partnership.

11. Select from company insulation standards (or prepare, if necessary) the insulation codes to be applied to each hot or cold pipe or equipment. Note that insulation must be applied in some cases only to prevent operating personnel from contacting the base equipment. See Table 1-1 for typical insulation thickness from which code numbers can be established.

Table 1-1

Typical Thickness Chart—Insulation for Services 70°F through 1200°F Piping, Vessels & Equipment 36″ Diameter & Smaller

Temperatures in chart are maximum operating temperatures in degrees Fahrenheit for given thickness.

Note: All hot insulated piping shall be coded, including piping insulated for personnel protection. Thickness is a function of insulation composition.

12. Establish field construction hydraulic test pressures for each process equipment. Sometimes the equipment is blanked or blocked off, and no test pressure is applied in the field, because all pressure equipment must be tested in the fabricators’ or manufacturers’ shop per ASME Code.

13. Prepare drafts of line schedule and/or summary sheets (Figures 1-24A–D), and equipment summary schedules (Figures 1-27, 1-28, 1-29, 1-30), plus summary schedules for safety relief valves and rupture disks, compressors and other major equipment.

Figure 1-27 Centrifugal pumps summary.

Figure 1-28 Centrifugal pump schedule.

Figure 1-29 Vessel and tank summary sheet.

Figure 1-30 Vessel and tank schedule.

14. Prepare detailed process and mechanical specifications for developing proposals for purchase by the purchasing department.

The process design engineer actually interprets the process into appropriate hardware (equipment) to accomplish the process requirements. Therefore, the engineer must be interested in and conversant with the layout of the plant; the relationship of equipment for maintenance; the safety relationships of equipment in the plant; the possibilities for fire and/or explosion; the possibilities for external fire on the equipment areas of the plant; the existence of hazardous conditions, including toxic materials and pollution, that could arise; and, in general, the overall picture.

The engineer’s ability to recognize the interrelationships of the various engineering disciplines with the process requirements is essential to thorough design. For example, the recognition of metallurgy and certain metallurgical testing requirements as they relate to the corrosion in the process environment is absolutely necessary to obtain a reliable process design and equipment specification. An example of the importance of this is hydrogen brittlement (see latest charts [54]). Another important area is water service (see [49]). The engineer selecting the materials of construction should recognize the importance of plastics and plastic composites in the design of industrial equipment and appreciate that plastics often serve as better corrosive resistant materials than do metals.

Flowsheets—Types

The flowsheet is the road-map of a process, and serves to identify and focus the scope of the process for all interested and associated functions of the project. As a project progresses, the various engineering disciplines read their portions of responsibility from the flowsheet, although they may not understand the process or other details relative to some of the other phases of engineering. Here is where the process and/or project engineer serves to tie together these necessary segments of work. This often involves explanations sufficiently clear to enable these other groups to obtain a good picture of the objective and the problems associated with attaining it.

The flowsheet also describes the process to management as well as those concerned with preparing economic studies for process evaluation.

A good process flowsheet pictorially and graphically identifies the chemical process steps in proper sequence. It is done in such a manner and with sufficient detail to present to others a proper mechanical interpretation of the chemical requirements.

There are several types of flowsheets:

1 Block Diagram, Figure 1-3

Usually used to set forth a preliminary or basic processing concept without details. The blocks do not describe how a given step will be achieved, but rather what is to be done. These are often used in survey studies to management, research summaries, process proposals for packaged steps, and to talk-out a processing idea. For management presentations the diagrams of Figures 1-4, 1-5A and B and 1-6A and B are pictorial and help illustrate the basic flow cycle.

Figure 1-3 Block flow diagram.

Figure 1-4 Pictorial flow diagram establishes key processing steps: Cement manufacture. By permission, E-M Synchronizer, Electric Machinery Mfg. Co.

Figure 1-5A Pictorial sections flow diagram for principal operations: phosphate recovery. By permission, Deco Trefoil, 1958, Denver Equipment Co.

Figure 1-5B Isometric pictorial flow diagram. By permission, J. W. Keating and R. D. Geckler, Aerojet General Corp.

Figure 1-6A Typical flow scheme for separation and purification of vent streams.

Figure 1-6B This low pressure cycle is used for production of oxygen in steady state conditions. By permission, Air Products and Chemicals Inc.

2 Process Flowsheet or Flow Diagram, Figure 1-7

Used to present the heat and material balance of a process. This may be in broad block form with specific key points delineated, or in more detailed form identifying essentially every flow, temperature and pressure for each basic piece of process equipment or processing step. This may and usually does include auxiliary services to the process, such as steam, water, air, fuel gas, refrigeration, circulating oil, etc. This type of sheet is not necessarily distributed to the same groups as would receive and need the piping flowsheet described next, because it may contain detailed confidential process data.

Figure 1-7 Heat and material balance establishes material and thermal requirements. By permission, J. P. O’Donnell [9].

3 Piping Flowsheet or Mechanical Flow Diagram, Figures 1-8, 1-9, or Piping and Instrumentation Diagram

Used to present mechanical-type details to piping and mechanical vessel designers, electrical engineers, instrument engineers, and other engineers not directly in need of process details. This sheet contains pipe sizes, all valves (sizes and types), temperature points, and special details needed to insure a common working basis for all persons on a project. In some engineering systems, detailed specifications cannot be completed until this flowsheet is basically complete.

Figure 1-8 Mechanical detail flow diagram. By permission, Fluor Corp. Ltd.

Figure 1-9 Typical process and piping flow diagram. By permission, E. E. Ludwig [56].

4 Combined Process and Piping Flowsheet or Diagram, Figures 1-10 and 1-11

Used to serve the same purpose as both the process and the piping flow diagram combined. This necessarily results in a drawing with considerably more detail than either of types 2 and 3 just discussed. However, the advantage is in concentrating the complete data and information for a project at one point. It does require close attention in proper reading and often opens data to larger groups of persons who might misinterpret or misuse it.

Figure 1-10 Piping detail isometric flow diagram.

Figure 1-11 Typical material balance process flowsheet.

Some companies do not allow the use of this sheet in their work primarily because of the confidential nature of some of the process data. Where it is used, it presents a concise summary of the complete process and key mechanical data for assembly. This type of sheet requires more time for complete preparation, but like all engineering developments preliminary issues are made as information is available. Often the sheet is not complete until the piping and other detailed drawings are finished. This then is an excellent record of the process as well as a work sheet for training operators of the plant.

5 Utility Flowsheets or Diagrams, Figures 1-12 and 1-13

Used to summarize and detail the interrelationship of utilities such as air, water (various types), steam (various types), heat transfer mediums such as Dowtherm, process vents and purges, safety relief blow-down, etc., to the basic process. The amount of detail is often too great to combine on other sheets, so separate sheets are prepared.

Figure 1-12 Standard type layout for service piping diagram.

Figure 1-13 Typical utility flow diagram. By permission, Stearns-Roger Mfg. Co.

These are quite valuable and time saving during the engineering of the project. They also identify the exact flow direction and sequence of tie-in relationships for the operating and maintenance personnel.

6 Special Flowsheets or Diagrams

From the basic process-containing flowsheet other engineering specialties develop their own details. For example, the instrument engineer often takes the requirements of the process and prepares a completely detailed flowsheet which defines every action of the instruments, control valves, switches, alarm horns, signal lights, etc. This is his detailed working tool.

The electrical engineer likewise takes basic process and plant layout requirements and translates them into details for the entire electrical performance of the plant. This will include the electrical requirements of the instrumentation in many cases, but if not, they must be coordinated.

O’Donnell [9] has described the engineering aspects of these special flowsheets.

7 Special or Supplemental Aids

(a) Plot Plans, Figure 1-14

Plot plans are necessary for the proper development of a final and finished process, piping or utility flowsheet. After broad or overall layout decisions are made, the detailed layout of each processing area is not only helpful but necessary in determining the first realistic estimate of the routing, lengths and sequence of piping. This is important in such specifications as pipe sizing, and pump head and compressor discharge pressures. The nature of the fluids—whether hazardous, toxic, etc.,—as well as the direction or location or availability for entrance to the area, definitely influences decisions regarding the equipment layout on the ground, in the structures, and in relation to buildings. Prevailing wind direction and any other unusual conditions should also be considered.

Figure 1-14 Typical process area plot plan and study elevations. By permission, Fluor Corp. Ltd.

The use of pictorial isometric or oblique views of plot areas as shown in Figure 1-15 is very helpful for equipment location evaluation. With talented personnel, this type of layout study can replace model studies. These layouts are also useful for management presentations.

Figure 1-15 Pictorial plot plan layout. Courtesy of Prengle, Dukler and Crump, Houston, Texas.

(b) Models, Figure 1-16A and 16B

Scale models are a real asset in the effective and efficient layout and sometimes process development of a plant. Although any reasonable scale can be used, the degree of detail varies considerably with the type of process, plant site, and overall size of the project. In some instances cardboard, wooden, or plastic blocks cut to a scale and placed on a cross-section scale board will serve the purpose. Other more elaborate units include realistic scale models of the individual items of equipment. These are an additional aid in visualizing clearances, orientation, etc.

Figure 1-16A Simple block model plant layout. Courtesy of Socony Mobil Oil Co. Inc.

Figure 1-16B Detailed layout and piping model for a refinery unit. Courtesy of Socony Mobil Oil Co. Inc.

A complete model usually includes piping, valves, ladders, floor grating, etc. This essentially completes the visualization of the condition of the layout. In fact, many engineering offices use models to varying degrees and often make direct space-clearance measurements from them. Others photograph the models, or sections, for use by the piping engineers at their desks. In some few instances, dimensioned photographs have been issued directly to construction forces in place of drawings.

The models are even more helpful to the process engineer than simple plot plans. The advantages are multiplied, as with models the process engineer can study as well as solicit the advice of other engineers in visualizing a processing condition.

Plant model costs vary depending upon the degree of detail included. Considerable decision making information can be obtained from a set-up of block layout only, and these costs would be extremely small. For a reasonably complete scale piping detail model the costs are reported⁵ as 0.1 to 0.6 percent of the cost of the plant. The large plants over $20 million cost in the lower 0.1 percent range while small plant models cost in the 0.6 to 1.0 percent range. Even these costs can be reduced if all minute detail is avoided, and only basic decision making piping is included. The necessary model structure and rough block outline equipment for a $1 million hydrocarbon compression and processing plant costs around $1,000 to $2,000.

Paton [15] reports total model costs of 0.4 to 1.0 percent of erected plant costs for a $1 million plant. These are actual costs and do not reflect profits. Material costs are less than 10 percent of total model costs, and usually less than 5 percent. For a $30 million plant model costs run as low as 0.1 percent. These are for models which include plant layout, piping layout, and piping details. If simpler models are used the costs should be less.

Flowsheet Presentation

Experienced flowsheet layout personnel all emphasize the importance of breaking processes into systems and logical parts of systems such as reaction, compression, separating, finishing, refrigeration, storage, etc., for detailed drafting. This point cannot be overemphasized, since considerably more space is needed for final completion of all details than is usually visualized at first. The initial layout of the key equipment should be spread farther than looks good to the eye. In fact, it probably looks wasteful of drawing space.

Later as process and sometimes service lines, valves, controls and miscellaneous small accessories are added this extra space will be needed to maintain an easily readable sheet. As this develops, attention should be given to the relative weights and styles of lines to aid in the readability of the sheets.

Figure 1-11 suggests an approach to standardization of form for general use. It can be rearranged in several ways to provide a format suitable for any one of several purposes. Of particular importance is the flexibility of adding or deleting data without changing other details. Some companies prefer to place the process data on a separate sheet, although the same basic form for the table can be retained as shown in Figure 1-11. The layout principles of Figure 1-8 are also standardized by some companies.

General Arrangements Guide

Each phase of the process is best represented on individual flowsheets. Electric power, fuel gas, drainage and the many other auxiliary system requirements are also best defined by separate individual flowsheets. These should be complete including all headers, branch takeoffs, tie-ins to existing or known points, etc. Only in this way can all the decisions as well as specifications be delineated for the various parts contributing to the entire project. The master process or mechanical flowsheet must contain specific references to the other sheets for continuation of the details and complete coordination.

Flowsheet size may vary depending upon the preferences of the individuals using them. The most popular system uses one size sheet about 24 × 36 inches for all flowsheets. The use of miscellaneous large and small sizes to represent the entire project is often awkward when collected, and increases the possibilities of sheets becoming misplaced. Some groups use sheets from a roll and these are sized to length by systems, becoming 24 × 60 inches, 24 × 72 inches or longer. These are fine for initial study but become tedious to handle on the usual desk. These sheets can be reduce to 11 × 36 inches or 11 by 48 inches both of which are more convenient to work with. These strip-type sheets allow large portions of the process to be grouped together, and are adaptable for folding into reports, etc.

Since the flowsheet is the primary reference for all engineers working on a project, it must contain all of the decisions, data, flow connections, vents, drains etc., which can reasonably be included without becoming confusing and difficult to read.

It is important that the various items of equipment and valves be spaced, pictorially represented and sized as to be easy to read, recognized and followed. On the surface this may sound easy, while in reality it takes an experienced flowsheet detailer to arrange the various items in an eye-pleasing and efficient arrangement. Suggestive outline figures plus shading often yields the best looking flowsheet (Figure 1-10); however, the extra time for detail costs time and money. Some compromise is often indicated. Reference to the various flowsheets illustrated here indicates that the equipment can be arranged by (1) working from a base line and keeping all heights relative and (2) by placing the various items in a straight-through flow pattern without relative heights. The first scheme is usually preferred for working flowsheets. Whenever possible, all auxiliary as well as spare equipment is shown. This facilitates the full and proper interpretation of all the details.

Figure 1-17 [2] can be used as a guide in establishing relative sizes of equipment as represented on a flowsheet. This chart is based on approximate relative proportions pictured by the mind’s eye [2]. For example, the 10-foot diameter × 33-foot high tank would scale to 1.5 inches high. By using the height-developed scale factor, the diameter would be (1.5″/33′) (10′) = 0.45″ or say 0.5″ diameter on the flowsheet.

Figure 1-17 Flowsheet scale reference diagram. By permission, R. H. Berg [2].

For some purposes the addition of equipment specification and performance data on the flowsheets adjacent to the item is of value. In many cases though, this additional information makes the sheets difficult to read. The use of equipment summary tables similar to flow and pipe data tables can avoid this objection and yet keep the information on the sheets. Some flowsheets include relief valve set pressures adjacent to the valves, volume capacities of storage tanks, etc.

Computer-Aided Flowsheet Design/Drafting

Current technology allows the use of computer programs and data bases to construct an accurate and detailed flowsheet. This may be a process type diagram or a piping and mechanical/instrument diagram, depending on the input. See Figures 1-9, 1-10, 1-18A and 1-18B.

Figure 1-18A Computer generated P. and I D. flowsheet. Courtesy of Intergraph Corp., Bul. DP016A0.

Figure 1-18B Computer generated instrumentation detail for P. and I D. flowsheet. Courtesy of Integraph Corp., Bul. DP016A0.

Flowsheet Symbols

To reduce detailed written descriptions on flowsheets, it is usual practice to develop or adopt a set of symbols and codes which suit the purpose. Flowsheet symbol standardization has been developed by various professional and technical organizations for their particular fields. Most of these have also been adopted by the American National Standards Institute (ANSI). The following symbol references are related and useful for many chemical and mechanical processes:

1. American Institute of Chemical Engineers

(a) Letter Symbols for Chemical Engineering, ANSI Y10.12

2. American Society of Mechanical Engineers

(a) Graphic Symbols for Plumbing, ANSI or ASA Y32.4

(b) Graphic Symbols for Railroad Maps and Profiles, ANSI or ASA Y32.7

(c) Graphic Symbols for Fluid Power Diagrams, ANSI or ASA Y32.10

(d) Graphic Symbols for Process Flow, ANSI or ASA Y32.11

(e) Graphic Symbols for Mechanical and Acoustical Elements as Used in Schematic Diagrams, ANSI or ASA Y32.18

(f) Graphic Symbols for Pipe Fittings, Valves and Piping, ANSI or ASA Z32.2.3

(g) Graphic Symbols for Heating, Ventilating and Air Conditioning, ANSI or ASA Z32.2.4

(h) Graphic Symbols for Heat-Power Apparatus, ANSI or ASA Z32.2.6

3. Instrument Society of America

(a) Instrumentation Symbols and Identification, ISA-S5.1, also see Reference 27

Other symbols are established for specialized purposes.

The physical equipment symbols established in some of these standards are often not as descriptive as those the chemical, petrochemical, and petroleum industry is accustomed to using. The bare symbolic outlines given in some of the standards do not adequately illustrate the detail needed to make them useful. Accordingly, many process engineers develop additional detail to include on flowsheets, such as Figures 1-19 A-E and 1-20 A-B-C which enhance the detail in many of these standards. Various types of processing suggest unique, yet understandable, symbols, which do not fit the generalized forms.

Figure 1-19A Process vessels.

Figure 1-19B Pumps and solids.

Figure 1-19C Storage equipment.

Figure 1-19D Flow and instruments.

Figure 1-19E Filters, evaporators and driers.

Figure 1-20A Special types of descriptive flowsheet symbols.

Figure 1-20B Commonly used instruments for process instrumentation flowsheets. Adapted by permission, ISA Std. ANSI Y32.20—1975, ISA S5.1—1973, Instrumentation Symbols and Identification, Latest edition, 1984.

Many symbols are pictorial which is helpful in representing process as well as control and mechanical operations. In general, experience indicates that the better the representation including relative locating of connections, key controls and even utility connections, and service systems, the more useful will be the flowsheets for detailed project engineering and plant design.

To aid in readability by plant management as well as engineering and operating personnel, it is important that a set of symbols be developed as somewhat standard for a particular plant or company. Of course, these can be improved and modified with time and as needed, but with the basic forms and letters established, the sheets can be quite valuable. Many companies consider their flowsheets quite confidential since they contain the majority of key processing information, even if in summary form.

Line Symbols and Designations

The two types of lines on a flowsheet are (1) those representing outlines and details of equipment, instruments, etc., and (2) those representing pipe carrying process or utility liquids, solids, or vapors and electrical or instrument connections. The latter must be distinguished among themselves as suggested by Figure 1-21.

Figure 1-21 Line Symbols. By permission, ISA Std. S5.1—1973 and 1984.

In order to represent the basic type of solution flowing in a line, designations or codes to assign to the lines can be developed for each process. Some typical codes are:

RW — River Water

TW — Treated Water

SW — Sea Water

BW — Brackish Water

CW — Chilled Water

S — Low Pressure Steam

S150 — 150 psi Steam

S400 — 400 psi Steam

V — Vent or Vacuum

C — Condensate (pressure may be indicated)

D — Drain to sewer or pit

EX — Exhaust

M — Methane

A — Air (or PA for Plant Air)

F — Freon

G — Glycol

SA — Sulfuric Acid

B — Brinez

CL — Chlorine

P — Process mixture (use for in-process lines not definitely designated by other symbols)

Sometimes it is convenient to prefix these symbols by L to indicate that the designation is for a line and not a vessel or instrument.

Materials of Construction for lines

The process designer must also consider the corrosive nature of the fluids involved when selecting construction materials for the various process and utility service lines. Some designers attach these materials designations to the line designation on the flowsheets, while others identify them on the Line Summary Table (Figure 1-24D). Some typical pipe materials designations are:

Figure 1-24D Line summary table.

CS40 — Carbon steel, Sch. 40

CS80 — Carbon steel, Sch. 80

SS316/10 — Stainless steel 316m Sch. 10

GL/BE — Glass bevel ends

N40 — Nickel, Sch. 40

TL/CS — Teflon-lined carbon steel

PVC/CS Polyvinyl chloride — lined CS

PP — Solid polypropylene (designate weight sch)

Test Pressure for Lines

The process designer also needs to designate the hydraulic test pressures for each line. This testing is performed after construction is essentially complete and often is conducted by testing sections of pipe systems, blanking off parts of the pipe or equipment, if necessary. Extreme care must be taken to avoid over pressuring any portion of pipe not suitable for a specific pressure, as well as extending test pressure through equipment not designed for that level. Vacuum systems must always be designed for full vacuum, regardless of the actual internal process absolute vacuum expected. This absolute zero design basis will prevent the collapse of pipe and equipment should internal conditions vary. Some line design systems include the test pressure in the line code, but this often becomes too unwieldly for drafting purposes.

The usual complete line designation contains the following: (1) line size (nominal); (2) material code; (3) sequence number; and (4) materials of construction.

Examples:

2″—CL6—CS40

3″—CL6a—CS40

4″—RW1—CS40

16″—S150—CS40

3″—P—TL/CS

See Figures 1-23 and 1-24A through D.

Figure 1-23 Examples of line numbering.

Figure 1-24A Line Schedule.

Some engineers rearrange the sequence of the code although the information remains essentially the same. The line number sequence is conveniently arranged to start with one (1) or 100 for each of the fluid designations (CL, P, etc.). Since the sequence numbers are for coordination purposes and will appear on piping drawings, Line Schedule (Figure 1-24A through D), the number has no significance in itself. It is convenient to start numbering with the first process flow sheet and carry on sequentially to each succeeding sheet. Sometimes, however, this is not possible when several detailers are preparing different sheets, so each sheet can be given arbitrary beginning numbers such as 100, 300, 1000, etc. Although the sequential number may be changed as the line connects from equipment to equipment, it is often convenient to use the system concept and apply alphabetical suffixes to the sequence number as shown in Figures 1-22 and 1-23.

Figure 1-22 Use of alphabetical suffixes with line symbols.

This contributes materially to the readability of the flowsheets. Each line on the flowsheet must represent an actual section or run of piping in the final plant and on the piping drawings.

Suggested guides for line identification for any one principal fluid composition:

1. Main headers should keep one sequence number (Figure 1-23).

2. New sequence numbers should be assigned:

(a) Upon entering and leaving an item of equipment

(b) To take-off or branch lines from main headers

(c) To structural material composition of line changes

3. Alphabetical suffixes should be used in the following situations as long as clarity of requirements is clear, otherwise add new sequence numbers.

(a) For secondary branches from headers or header-branches

(b) For by-pass lines around equipment, control valves, etc. Keep same sequence number as the inlet or upstream line (Figure 1-23).

(c) For identical multiple systems, piping corresponding identical service items, and lines.

In order to coordinate the process flowsheet requirements with the mechanical piping specifications, Line Schedules are prepared as shown in Figure 1-24A through D. The complete pipe system specifications are summarized by codes on these schedules; refer to paragraph on Working Schedules.

Equipment code designations can be developed to suit the particular process, or as is customary a master coding can be established and followed for all projects. A suggested designation list (not all inclusive for all processes) for the usual process plant equipment is given in Table 1-2 and process functions in Table 1-3.

Table 1-2

A System of Equipment Designations

AD — Air Drier

AF — Air Filter

Ag — Agitator

B — Blower

BR — Barometric Refrigeration Unit

C — Compressor

CP — Car Puller

CT — Cooling Tower

CV — Conveyor

D — Drum or tank

DS — Desuperheater

E — Heat Exchanger, condenser, reboiler, etc.

Ej — Jet Ejector

Ex — Expansion Joint

F — Fan

FA — Flame Arrestor

Fi — Filter (line type, tank, centrifugal)

GT — Gas Turbine

MB — Motor for Blower

MC — Motor for Compressor

MF — Motor for Fan

MP — Motor for Pump

P — Pump

PH — Process Heater or Furnace

R — Reactor

S — Separator

St — Strainer

ST — Steam Turbine

Str — Steam trap

SV — Safety Valve

Tr — Trap

V — Valve

VRV — Vacuum Relief Valve

Table 1-3

Typical Identification for Flowsheet Process Functions

AS—Air Supply

BD—Blowdown

BF—Blind Flange

CBD—Continuous Blowdown

CD—Closed Drain

CH-O—Chain Operated

CSO—Car Seal Open

CSC—Car Seal Closed

DC—Drain Connection

EBD—Emerg. Blowdown Valve

ESD—Emerg. Shutdown

FC—Fail Closed

FO—Fail Open

HC—Hose Connection

IBD—Intermittent Blowdown

LO—Lock Open

ML—Manual Loading

NC—Normally Closed

NO—Normally Open

OD—Open Drain

P—Personnel Protection

QO—Quick Opening

SC—Sample Protection

SO—Steam Out

TSO—Tight Shut Off

VB—Vacuum Breaker

The various items are usually numbered by type and in process flow order as set forth on the flowsheets. For example:

Some equipment code systems number all items on first process flowsheet with 100 series, as C-101, C-102, P-106 to represent compressors number 101 and 102 in different services and pump 106 as the sixth pump on the sheet. The second sheet uses the 200 series, etc. This has some engineering convenience but is not always clear from the process view.

To keep process continuity clear, it is usually best to number all like items sequentially throughout the process, with no concern for which flowsheet they appear on. Also, another popular numbering arrangement is to identify a system such as reaction, drying, separation, purification, incineration, vent, and cooling tower waters and number all like process items within that system, for example:

Reactor System, R: Reactor is RD-1

Reactor vent cooler is RE-1

Reactor vent condenser is RE-2

Reactor recycle pump is RP-1

Level control valve is RLC-1

Relief valve is RSV-1

Then, establish the same concept for all other unit or block processing systems. This is often helpful for large projects, such as refinery or grass roots chemical processes.

Valve identification codes are usually used in preference to placing each valve specification on the flowsheet. This latter method is feasible for small systems, and is most workable when a given manufacturer (not necessarily the same manufacturer for all valves) can be selected and his valve catalog figure number used on the flowsheet. For large jobs, or where many projects are in progress at one time, it is common practice to establish valve specifications for the various process and utility services (see Figures 1-25 and 1-26) by manufacturers’ catalog figure numbers. These are coded as V-11, V-12, V-13, etc., and such code numbers are used on the flowsheets wherever these valves are required. (Also see Figures 1-8 and 1-9.) By completely defining the valve specification in a separate specification book the various valves—gate, globe, butterfly, plug, flanged end, screwed end, welding end—can be identified for all persons involved on a project, including piping engineers and field erection contractors.

Figure 1-20C summarizes a system for representing piping components on the flow sheets.

Figure 1-20C Flow diagram symbols: valves, fittings and miscellaneous piping. (Compiled from several sources, and in particular, Fluor Corp, Ltd.)

The instrument symbols of Table 1-4 and Figures 1-23B and C are representative of the types developed by the Instrument Society of America and some companies.

Table 1-4

Instrumentation Nomenclature—Complete General Identification*

Some other designation systems indicate the recording or indicating function in front of rather than behind the instrument function. For example:

Control valves carry the same designation as the instrument to which they are connected.

Thermocouples carry the same designation as the recorder or indicator to