Preliminary Chemical Engineering Plant Design PDF

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Preliminary Chemical Engineering Plant Design WilliamD.Baasel Professor of Chemical Engineering Ohio University ELSEVIER New York/Oxford/Amsterdam Contents Preface xi 1. INTRODUCTION TO PROCESS DESIGN 1 Research, 2. Other Sources of Innovations, 3. Process Engineering, 4. Professional Responsibiliti...

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Preliminary Chemical Engineering Plant Design WilliamD.Baasel Professor of Chemical Engineering Ohio University

ELSEVIER New

York/Oxford/Amsterdam

Contents xi

Preface 1.

INTRODUCTION TO PROCESS DESIGN

1

Other Sources of Innovations, 3. Research, 2. Process Engineering, 4. Professional Responsibilities, 7. Competing Processes, 8. Typical Problems a Process Engineer Tackles, 9. Comparison with Alternatives, 14. Completing the Project, 16. Units, 17. References, 18. Bibliography, 18. 2.

23

SITE SELECTION Other Site Location Factors, 34. Major Site Location Factors, 25. Study: Site Selection, 48. References, 54.

3.

Case

THE SCOPE

57

The Product, 60. Capacity, 60. Quality, 66. Raw Material Storage, 67. Product Storage, 68. The Process, 69. Waste Disposal, Utilities, Shipping and Laboratory Requirements, 70. Plans for Future Expansion, 70. Hours of Operation, 71. Completion Date, 71. Safety, 71. Case Study: Scope, 72. Scope Summary, 75. References, 78. 4.

PROCESS DESIGN AND SAFETY

79

Chemistry, 79. Separations, 80. Unit Ratio Material Balance, 84. Detailed Flow Sheet, 85. Safety, 89. Case Study: Process Design, 97. Change of Scope, 103. References, 103. 5.

EQUIPMENT LIST Sizing 111. 113. 114. 117.

105

Planning for Future Expansion, of Equipment, 106. Materials of Construction, 113. Temperature and Pressure, Laboratory Equipment, 114. Completion of Equipment List, Rules of Thumb, 114. Case Study: Major Equipment Required, References, 133. Change of Scope, 132. 141

6. LAYOUT New Plant Layout, 141. Expansion and Improvements of Existing Facilities, 152. Case Study: Layout and Warehouse Requirements, 153. References, 158. vii

Contents

viii

7.

159

PROCESS CONTROL AND INSTRUMENTATION Plant Safety, Product Quality 160. Product Quantity, 160. Control System, 161. Manual or Automatic Control, 161. Final Control Element, 162. Variables to be Measured, 162. Averaging versus Set 163. Control and Instrumentation Symbols, 164. Tempered Heat Point Control, 166. Material Balance Control, 167. Cascade Control, 170. Feedforward Control, Transfer, 168. Pneumatic versus Elec171. Blending, 172. Digital Control, 172. Case Study: Instrumentation and Control, tronic Equipment, 173. 174. References, 180.

8.

ENERGY AND UTILITY BALANCES AND MANPOWER NEEDS

181

Energy Balances, 183. Sizing Energy Conservation of Energy, 182. Equipment, 191. Planning for Expansion, 204. Lighting, 205. Ventilation, Space Heating and Cooling, and Personal Water Requirements, 207. Utility Requirements, 209. Manpower RequireCase Study: Energy Balance and ments, 210. Rules of Thumb, 2 11. References, 232. Utility Assessment, 213. Change of Scope, 231. 9.

COST

ESTIMATION

237

Cost Indexes, 237. How Capacity Affects Costs, 239. Factored Cost Estimate, 246. Improvements on the Factored Estimate, 249. Module Cost Estimation, 254. Unit Operations Estimate, 258. Detailed Cost Estimate, 263. Accuracy of Estimates, 264. Case Study: Capital Cost Estimation, 264. References, 2 7 5 . 10.

279

ECONOMICS Capital, 284. Elementary ProfitaCost of Producing a Chemical, 28 1. Compound Interest, bility Measures, 285. Time Value of Money, 293. Rate of 295. Net Present Value-A Good Profitability Measure, 307. Comparison of Net Return-Another Good Profitability Measure, 311. Present Value and Rate of Return Methods, 316. Proper Interest Rates, Case Study: Economic 317. Expected Return on the Investment, 323. Evaluation, 324. Problems, 330. References, 338.

11.

DEPRECIATION, AMORTIZATION, DEPLETION AND INVESTMENT CREDIT

339

Depreciation, 339. Amortization, 348. Depletion 348. Special Tax Rules, 350. Investment Credit, 349. The Net Present Value and Rate of Return, 350. 351. References, 352. 12.

Allowance, Case Study: Problems.

DETAILED ENGINEERING, CONSTRUCTION, AND STARTUP Detailed Engineering, 363. References. 367.

353.

353 Construction

361.

Startup,

Contents 13.

PLANNING TOOLS-CPM AND PERT

ix 369

CPM, 370. Manpower and Equipment Leveling, 376. Cost and Schedule Control, 380. Time for Completing Activity, 380. References, 390. Computers, 381. PERT, 382. Problems, 386. 14.

OPTIMIZATION TECHNIQUES

391

Single Variable Starting Point, 392. One-at-a-Time Procedure, 393. End Game, Gptimizations, 396. Multivariable Optimizations, 396. Optimizing Optimizations , 409. Algebraic Objective Functions, 409. 409. Optimization and Process Design, 410. References, 412. 15.

DIGITAL COMPUTERS AND PROCESS ENGINEERING

415

Program Sources, Computer Programs, 416. Sensitivity, 420. References, 422. 420. Evaluation of Computer Programs, 421. 16.

POLLUTION AND ITS ABATEMENT

423

Determining Pollution Standards, What is Pollution?, 424. Air Pollution Abatement 425. Meeting Pollution Standards, 428. BOD and Methods, 431. Water Pollution Abatement Methods, 437. COD, 447. Concentrated Liquid and Solid Waste Treatment Procedures, 452. References, 454. Appendices

459

Index

479

Preface The idea for this book was conceived while I was on a Ford Foundation residency at the Dow Chemical Company in Midland, Michigan. I was assigned to the process engineering department, where I was exposed to all areas of process engineering, project engineering, and plant construction. My previous industrial experiences had been in pilot plants and research laboratories. Much to my surprise, I found that what was emphasized in the standard plant design texts was only a part of preliminary process design. Such areas as writing a scope, site selection, equipment lists, layout, instrumentation, and cost engineering were quickly glossed over. After I returned to Ohio University and began to teach plant design, I decided a book that emphasized preliminary process engineering was needed. This is the result. It takes the reader step by step through the process engineering of a chemical plant, from the choosing of a site through the preliminary economic evaluation. So that the reader may fully understand the design process, chapters dealing with planning techniques, optimization, and sophisticated computer programs are in. cluded. These are meant merely to give the reader an introduction to the topics. TO discuss them thoroughly would require more space than is warranted in an introductory design text. They (and other sophisticated techniques, like linear programming) are not emphasized more because before these techniques can be applied a large amount of information about the process must be known. When it is not available, as is often the case, the engineer must go through the preliminary process design manually before these newer techniques can be used. It is to this initial phase of design that this book is directed. Three types of design problems fit this situation. One is the design of a plant for a totally new product. The second is the design of a new process for a product that currently is being produced. The last is the preliminary design of a competitor’s plant, to determine what his costs are. In each of these, little is known about the process, so that a large amount of educated guessing must occur. As time goes on, more and more people are being involved in these types of plant design. Most chemical companies estimate that 50% of their profits 10 years hence will come from products not currently known to their research laboratories. Since these will compete with other products now on the market, there will be a great need for improving present processes and estimating a rival’s financial status. This book deals mainly with chemical plant design, as distinct from the design of petroleum refineries. For the latter, large amounts of data have been accumulated, and the procedures are very sophisticated. It is assumed that the reader has some xi

xii

PREFACE

familiarity with material and energy balances. A background in unit operations and thermodynamics would also be helpful, although it is not necessary. No attempt is made to repeat the material presented in these courses. This book applies a systems philosophy to the preliminary process design and cost estimation of a plant. In doing so, it tries to keep in perspective all aspects of the design. There is always a tendency on the part of designers to get involved in specific details, and forget that their job is to produce a product of the desired quality and quantity, at the lowest price, in a safe facility. What is not needed is a technological masterpiece that is difficult to operate or costly to build. For those using this book as a text, I suggest that a specific process be chosen. Then, each week, one chapter should be read, and the principles applied to the specific process selected. The energy balance and economic chapters may each require two weeks. The pollution abatement chapter may be included after Chapter 8, or it can be studied as a separate topic unrelated to the over-all plant design. Each student or group of students may work on a different process, or the whole class may work on the same process. The advantage of the latter method is that the whole class can meet weekly to discuss their results. This has worked very successfully at Ohio University. In the discussion sections, the various groups present their conclusions, and everyone, especially the instructor, benefits from the multitude of varied and imaginative ideas. Initially, this procedure poses a problem, since in most college courses there is a right and a wrong answer, and the professor recognizes and rewards a correct response. In designing a plant, many different answers may each be right. Which is best often can be determined only by physically building more than one plant, and evaluating each of them. Of course, no company would ever do this. It would build the plant that appears to contain fewer risks, the one that seems to be best economically, or some combination of these. Since the student will build neither, and since the professor probably cannot answer certain questions because of secrecy agreements or lack of knowledge, the student must learn to live with uncertainty. He will also learn how to defend his own views, and how to present material so as to obtain a favorable response from others. These learning experiences, coupled with exposure to the process of design as distinct from that of analysis and synthesis, are the major purposes of an introductory design course. Besides students, this book should be useful to those in industry who are not intimately familiar with process engineering. Researchers should be interested in process design because their projects are often killed on the basis of a process engineering study. Administrators need to have an understanding of this because they must decide whether to build a multi-million-dollar plant designed by a process engineering team. Operating personnel should know this because they must run plants designed by process engineers. Similarly, project engineers and contractors need to understand process engineering because they must take the resultant plans and implement them. Finally, pilot plant and semi-plant managers and operators need to know the problems that can arise during process design because they often

Preface

...

xiii

must determine whether the various schemes devised by process designers are feasible. The importance of preliminary design cannot be underestimated. For every plant built, 10 partially engineered plants are rejected. For some of these, over $100,000 worth of engineering will have been completed before the plant is rejected. Often this loss could have been avoided if there had been a greater understanding of preliminary chemical engineering process design by all concerned. I wish to express my deep thanks to the Dow Chemical Company, particularly to my preceptors Dr. Harold Graves and James Scovic, and everyone in the Process Engineering Department. They were completely open with me, and showed me how chemical engineering plant design is done. Also, I would like to thank all those others at Dow who spent a lot of time educating me. I would also like to acknowledge the support of the Chemical Engineering Department at Ohio University, and especially its chairman, Dr. Calvin Baloun. However, the group that had the greatest influence on the final form of this book was the Ohio University Chemical Engineering seniors of 1970, 1971, 1972, 1973, and 1974. They evaluated the material and suggested many improvements that were incorporated into this book. To them I am deeply indebted. I would also like to thank the following people who assisted me in the preparation of the manuscript: Linda Miller, Carolyn Bartels, Audrey Hart, Joan Losh, Cindy Maggied, and Judy Covert. William D. Baasel March 18, 1974

CHAPTER1

Introduction to Process Design Design is a creative process whereby an innovative solution for a problem is conceived. A fashion designer creates clothes that will enhance the appeal of an individual. An automobile designer creates a car model that will provide transportation and a certain appeal to the consumer. The car’s appeal may be because of its power, beauty, convenience, economy, size, operability, low maintenance, uniqueness, or gimmicks. A process engineer designs a plant to produce a given chemical. In each of these instances a new thing is created or an old thing is created in a new way. Design occurs when a possible answer for a present or projected need or desire by people or industry has been found. If a product were not expected to meet a need or desire, there would be no reason to produce it and hence no reason for design. A company or person is not going to manufacture something that cannot be sold at a profit. The needs may be basic items like substances with which to clean ourselves, coverings to keep our bodies warm, dishes upon which to place our food, or cures for our diseases. The desires may be created by the advertising firms, as in the case of vaginal deodorants and large sexy cars. Often the need or desire can be satisfied by a substance that is presently on the market, but it is projected that a new product will either do a betterjob, cost less, or require less time and effort. The toothpastes produced before 1960 did a respectable job of cleaning teeth, but the addition of fluoride made them better cavity preventatives, and those toothpastes that added fluorides became the best sellers. Orange juice could be shipped in its natural form to northern markets, but frozen concentrated orange juice occupies one-fourth the volume and costs less to the consumer. TV dinners and ready-to-eat breakfast cereals cost more than the same foods in their natural state, but they reduce the time spent in the kitchen. All of these items resulted from research followed by design. Most companies in the consumer products industries realize that their products and processes must be continually changed to compete with other items that are attempting to replace them. Sometimes almost a complete replacement occurs within a short time and a company may be forced to close plants unless an alternate use of its products is found. As an example, consider the case of petroleum waxes. In the late 1950s the dairy industry consumed 220,000 tons per year of petroleum waxes for coating paperboard cartons and milk bottle tops. This was 35% of the total U.S. wax production. By 1966 this market had dropped to 14% of its former level (25,000 tons / yr) because polyethylene and other coatings had replaced it.l

2

INTRODUCTION TO PROCESS DESIGN

One reason for conducting research is to prevent such a change from completely destroying a product’s markets. This may be done by improving the product, finding new uses for it, or reducing its costs. Cost reduction is usually accomplished by improving the method of producing the product. Research is also conducted to find new substances to meet industry’s and people’s needs and desires. Once a new product that looks salable or an appealing new way for making a present product is discovered, a preliminary process design for producing the item is developed. From it the cost of building and operating the plant is estimated. This preliminary process design is then compared with all possible alternatives. Only if it appears to be the best of all the alternatives, if it has potential for making a good profit, and if money is available, will the go-ahead for planning the construction of a facility be given. Since the goal of a chemical company is to produce the products that will make the most money for its stockholders, each of these phases is important; each will be discussed in greater detail. RESEARCH

Most large chemical companies spend around 5% of their total gross sales on some type of research. In 1967 the Gulf Research and Development Company, a wholly owned subsidiary of the Gulf Oil Corp., spent $30,000,000 on research and . development.2 Of this, 58% was for processes and 42% was for products. This means most of their sizeable research budget went into developing new processes or improving old ones. A company sells its products because either they are better than, or they cost less than, a competitive product. If a company does not keep reducing its processing costs and improving quality it can easily lose its markets. An example of how technological improvements in the production of fertilizers have forced many older plants out of business is given in Chapter 3. If Gulf’s research budget is broken down another way, basic research received 8% of $30,000,000, applied research got 41%, development projects received 22%, and technical service ended up with 2%. Basic research consists of exploratory studies into things for which an end use cannot be specified. It might include a study to determine the effect of chlorine molecules on the diffusivity of hydrocarbons or a study of the dissolution of single spheres in a flowing stream. The prospective dollar value of this research cannot be estimated. Applied research has a definite goal. One company might seek a new agricultural pesticide to replace DDT. Another might be testing a new approach to manufacturing polystyrene. Development projects are related to the improvement of current production methods or to determining the best way of producing a new product. They could involve anything from designing a new waste recovery system to studying the feasibility of replacing conventional controllers in an existing plant with direct digital control.

Research and Other Sources of Innovations

3

Technical service is devoted to making the company’s products more acceptable to the user. Its people try to convince prospective users of the advantages of using their company’s chemicals. This cannot be done in the manner of a television commercial by using gimmicks or sex appeal, but must rely on cold, hard facts. Why should a manufacturer switch from a familiar, adequate product to a new one? Since no chemical is completely pure and since each manufacturer uses at least a slightly different process and often different raw materials, the impurities present in products from several suppliers will be different. How these impurities will affect products, processes, catalysts, and so on is often unknown. It is the job of technical service representatives to find out. For instance, caustic soda produced as a by-product of chlorine production in a mercury cell cannot be used in the food or photographic industries because trace amounts of mercury might be present. One case where technical service representatives were called in oc...