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 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. SITE SELECTION 23 Major Site Location Factors, 25. Other Site Location Factors, 34. Case Study: Site Selection, 48. References, 54. 3. THE SCOPE 57 The Product, 60. Capacity, 60. Quality, 66. Raw Material Stor- age, 67. Product Storage, 68. The Process, 69. Waste Disposal, Utilities, Shipping and Laboratory Requirements, 70. Plans for Future Ex- pansion, 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. CaseStudy: Process De- sign, 97. Change of Scope, 103. References, 103. 5. EQUIPMENT LIST 105 Sizing of Equipment, 106. Planning for Future Expansion, 111. Materials of Construction, 113. Temperature and Pressure, 113. Laboratory Equipment, 114. Completion of Equipment List, 114. Rules of Thumb, 114. Case Study: Major Equipment Required, 117. Change of Scope, 132. References, 133. 6. LAYOUT 141 New Plant Layout, 141. Expansion and Improvements of Existing Facilities, 152. Case Study: Layout and Warehouse Requirements, 153. References, 158. vii Contents viii 7. PROCESS CONTROL AND INSTRUMENTATION 159 Product Quality 160. Product Quantity, 160. Plant Safety, 161. Manual or Automatic Control, 161. Control System, 162. Variables to be Measured, 162. Final Control Element, 163. Control and Instrumentation Symbols, 164. Averaging versus Set Point Control, 166. Material Balance Control, 167. Tempered Heat Transfer, 168. Cascade Control, 170. Feedforward Control, 171. Blending, 172. Digital Control, 172. Pneumatic versus Elec- tronic Equipment, 173. Case Study: Instrumentation and Control, 174. References, 180. 8. ENERGY AND UTILITY BALANCES AND MANPOWER NEEDS 181 Conservation of Energy, 182. Energy Balances, 183. Sizing Energy Equipment, 191. Planning for Expansion, 204. Lighting, 205. Ventilation, Space Heating and Cooling, and Personal Water Re- quirements, 207. Utility Requirements, 209. Manpower Require- ments, 210. Rules of Thumb, 2 11. Case Study: Energy Balance and Utility Assessment, 213. Change of Scope, 231. References, 232. 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, 275. 10. ECONOMICS 279 Cost of Producing a Chemical, 28 1. Capital, 284. Elementary Profita- bility Measures, 285. Time Value of Money, 293. Compound Interest, 295. Net Present Value-A Good Profitability Measure, 307. Rate of Return-Another Good Profitability Measure, 311. Comparison of Net Present Value and Rate of Return Methods, 316. Proper Interest Rates, 317. Expected Return on the Investment, 323. Case Study: Economic Evaluation, 324. Problems, 330. References, 338. 11. DEPRECIATION, AMORTIZATION, DEPLETION AND INVESTMENT CREDIT 339 Depreciation, 339. Amortization, 348. Depletion Allowance, 348. Investment Credit, 349. Special Tax Rules, 350. Case Study: The Net Present Value and Rate of Return, 350. Problems. 351. References, 352. 12. DETAILED ENGINEERING, CONSTRUCTION, AND STARTUP 353 Detailed Engineering, 353. Construction 361. Startup, 363. References. 367. Contents ix 13. PLANNING TOOLS-CPM AND PERT 369 CPM, 370. Manpower and Equipment Leveling, 376. Cost and Schedule Control, 380. Time for Completing Activity, 380. Computers, 381. PERT, 382. Problems, 386. References, 390. 14. OPTIMIZATION TECHNIQUES 391 Starting Point, 392. One-at-a-Time Procedure, 393. Single Variable Gptimizations, 396. Multivariable Optimizations, 396. End Game, 409. Algebraic Objective Functions, 409. Optimizing Optimizations , 409. Optimization and Process Design, 410. References, 412. 15. DIGITAL COMPUTERS AND PROCESS ENGINEERING 415 Computer Programs, 416. Sensitivity, 420. Program Sources, 420. Evaluation of Computer Programs, 421. References, 422. 16. POLLUTION AND ITS ABATEMENT 423 What is Pollution?, 424. Determining Pollution Standards, 425. Meeting Pollution Standards, 428. Air Pollution Abatement Methods, 431. Water Pollution Abatement Methods, 437. BOD and 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 prelimi- nary 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 introduc- tory design text. They (and other sophisticated techniques, like linear program- ming) 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 success- fully 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 introduc- tory 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