Turboexpanders Process Applications

v Contents Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viii CHAPTER 1 Why and How Turboexpanders Are Applied . . . . . . . . . . . . . . . . .1 Turboexpanders for Energy Conversion 2, Turboexpander Applications 3, Power Recovery Turboexpanders 4, Power Absorption Methods 8, Turboexpander Qualities 10, Summary 15, Bibliography and Additional Reading 17 CHAPTER 2 Turboexpander Fundamentals . . . . . . . . . . . . . . . . . . . . . . . . . . .19 Basic Applications 19, Gas Path Equations and Analysis 21, Specific Cryogenic Applications 30, Future Applications 33, Statistical Aspects of Turboexpander Requirements 33, Radial Reaction versus Impulse Design 35, Efficiency and Sizing Calculations 36, Summary 40, Bibliography and Additional Reading 41 CHAPTER 3 Application of Cryogenic Turboexpanders . . . . . . . . . . . . . . . . . .42 Methane (Natural Gas) Liquefaction 42, Ethylene Plant Expanders 58, Gas Treating Methods 69, Summary 77, Bibliography and Recommended Reading 82 CHAPTER 4 Application of Hot Gas Turboexpanders . . . . . . . . . . . . . . . . . . .85 Nitric Acid Plant Applications 85, Integrally Geared Process Gas Radial Turbines 129, Turboexpanders in Geothermal Applications 136, Turboexpander Applications in Catalytic Cracking Units 141, Microprocessor-based Turbomachinery Management Systems 196, Material Selection for Power Recovery Turbines 233, Turboexpander Testing 243, Solid Particle Erosion 246, Power Recovery and the Eddy Current Brake 260, Bibliography and Recommended Reading 271 3322 -Frontmatter 1/3/01 3:06 PM Page v vi CHAPTER 5 Specifying and Purchasing Turboexpanders . . . . . . . . . . . . . . . .273 Cryogenic Expanders 273, Power Recovery Expanders for FCC Units in Main Air Blower or Generator Drive Service 297 CHAPTER 6 Special Features and Controls . . . . . . . . . . . . . . . . . . . . . . . . . . .333 Active Magnetic Bearings and Dry Gas Seals 333, Squeeze Film Dampers 359, Radial Fit Bolts 370, Controls 373, Bibliography and Additional Reading 400 CHAPTER 7 Turboexpander Protection and Upgrading . . . . . . . . . . . . . . . . .401 Maintenance Strategies 401, PRT Load Shedding Concerns 403, Rotor Dynamics and Vibration Analysis 419, Optimized/Reengineered Design and Economics 428, Nomenclature 437, Bibliography and Additional Reading 439 CHAPTER 8 Specific Applications and Case Histories . . . . . . . . . . . . . . . . . .440 Case 1: Cryogenic Technology Helps Optimize Productivity 440, Case 2: Turboexpanders Installed at an Older Methanol Producing Plant Provide Major Energy Savings 442, Case 3: Manufacture of Copper and Molybdenum 444, Case 4: Nickel Smelter and Oxygen Production 447, Case 5: LNG Parallel Expanders 448, Case 6: New Gas Reservoir Production with Offshore Oil Site 450, Case 7: Natural Gas “Straddle” Pipeline Application 452, Case 8: A New H 2 O 2 Plant Design 455, Case 9: Use of Magnetic Bearings by Norske Shell in an Onshore Application 456, Case 10: Gas Separation Plant in Thailand 460, Case 11: Ethylene Plant in Kuwait 460, Case 12: MTBE Plant in Texas 462, Case 13: More Energy for a Phenol Plant 463, Case 14: Improving FCC Expander Reliability Under Off-Design Conditions 464, Case 15: Generating Electricity from Excess Energy with a Letdown Gas Compressor 471, Case 16: The Use of Magnetic Bearings for Offshore Applications 481, Bibliography and Additional Reading 483 APPENDICES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .485 INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .498 3322 -Frontmatter 1/3/01 3:06 PM Page vi vii Dedication To the Memory of Dr. Judson S. Swearingen, January 11, 1907–September 5, 1999 Those who knew him well called Dr. Swearingen a man of many tal- ents, a superb theoretician, and hands-on manager. He was one of the rarest breed of individuals: An inventor and entrepreneur with a genius- level feel for machine behavior. His pioneering works, over one hundred mechanical and natural gas and/or hydrocarbon processing patents and numerous articles, led the way to a cryogenic expander technology that has become an inseparable part of the gas processing industry. 3322 -Frontmatter 1/3/01 3:06 PM Page vii Preface We planned this book to be an up-to-date overview of turboexpanders and the processes where these machines are applied in a modern, cost- conscious plant environment. Therefore, the text addresses construction features, application criteria, functional parameters, and selection guide- lines. It is clearly intended for the widest possible spectrum of engineer- ing, technical support, maintenance, operating, and managerial personnel in process plants, refineries, air liquefaction, natural gas separation, min- ing, design contracting, and many other industries. The book covers both cryogenic turboexpanders that are used to re- cover power from extremely cold gases, and hot gas expanders that recover power from gases reaching temperatures well in excess of 1,000°F. Because energy recovery applications ranging from 75–25,000 kW exist in virtually any process that uses high-temperature and/or high- pressure gases, properly designed turboexpanders will play an increas- ingly important role in modern industry. It is our hope that we have managed to thoroughly explain why, when, and how to use these machines—in both theory and practice. We, therefore, delve into issues and guidelines, overview comments and details, procedures, and tech- niques that most turboexpander owner/operators and specifying engi- neers need to know. To the best of our knowledge, this is the first comprehensive text that elaborates on the rather skimpy treatment given to turboexpanders else- where. It is clearly the first book explaining magnetic bearing applica- tions for this machinery category. In terms of audience, this book should be of unique interest to a very wide spectrum of engineers, technicians, supervisors, operators and man- agers in virtually every user plant environment. Recent technical gradu- ates, experienced and advanced individuals from air separation facilities, chemical plants, refineries, natural gas processing plants, mining, design viii 3322 -Frontmatter 1/3/01 3:06 PM Page viii ix contracting, and other industries will benefit from this highly practical, well-illustrated text. Written and compiled with the active assistance of industry experts and experienced turboexpander users, the book covers theory to the extent nec- essary to understand operating principles and overall application criteria. The interaction of components and controls, auxiliaries, and subsystems is given extensive coverage and provides continuity and readability. The reader will find both chapter sequences and the index organized for rapid retrieval of pertinent information. Referring to this text will equip every turboexpander job level and job function with an under- standing of technical matters relating to a wide variety of processes and equipment types. It combines process and mechanical technology as it applies to these machines and presents both “overview information” and more detailed explanations for the various categories of readers and interested parties. The following are some examples of the book’s problem-solving potential. A. JOB FUNCTION: Equipment Selection Engineer RESPONSIBILITY: Bid Evaluation PROBLEM: Receives offers from bidders whose com- ponent selections differ; needs to under- stand the advantages and disadvantages of certain design features HOW SOLVED: This text will provide guidance. B. JOB FUNCTION: Plant Manager RESPONSIBILITY: P&L, Plant Profitability, Safety PROBLEM: Receives contractor’s proposal for an energy conservation project, which includes a turboexpander driving a generator. HOW SOLVED: Understands operating principles and rela- tive complexity after reviewing this text. C. JOB FUNCTION: New engineer RESPONSIBILITY: Contact person between project group and operations department. PROBLEM: Confronted with a machine he knows nothing about; has no knowledge of a par- ticular process that uses turboexpanders. HOW SOLVED: Finds a thorough explanation in this text. 3322 -Frontmatter 1/3/01 3:06 PM Page ix x Rotating machinery users seem to fall into one of two categories: those who need to conserve operational costs and those who merely want to con- serve operational costs. Either category makes sense in today’s business environment, where companies concern themselves with downsizing and restructuring on an unprecedented scale. The (occasionally dubious) logic cited for this includes competitive positioning, global profile extension, and overhead streamlining. Superimposed on these learnings are issues such as increased environmental legislation and profitability targets. Against this backdrop, the quest for more efficient processes, more reliable equipment, downtime avoidance, and maintenance cost reduc- tions is understandable. How are these pursuits structured? Better yet, how should they be structured? The answer is the real best-of-class, high profitability performers who are hard at work changing old ways of thinking. They are willing to reassess work processes and work proce- dures. Best-of-class companies also revisit the basics while, understand- ably, engaging in the search for new and advanced technologies. Interestingly, modern turboexpanders cater to all of these approaches. That’s why it is incumbent upon technical personnel engaged in process engineering or power generation to become thoroughly familiar with this sometimes under-rated equipment category. In the truly forward-looking companies, turboexpanders are being considered for an ever-increasing field of industrial fluid moving and energy conservation tasks. With these facts in mind, we have compiled and updated material pro- vided by turboexpander technology experts. Editing their work proved to be a real challenge. Although we occasionally found small differences in items concerning technical detail, we discovered that some of the oldest papers and presentations on both art and science of turboexpander technology are not only still readable, but continue to be totally relevant and applicable today. We sometimes kept certain information contained in a particular author’s work even though the same topic is given partial coverage else- where in this book. We tried to remember that we wanted to achieve tech- nical relevance, readability, and balance. Occasionally, we decided that the inclusion of a parallel text offered a different or additional perspec- tive, perhaps with new or different illustrations, or an interesting but straightforward mathematical treatment. As the reader progresses through this book, he or she will uncover in successive chapters additional layers of information that give insight into how the original, generally small and somewhat “prototypish” turboexpanders became the giant monsters of our day. They have not yet reached their full and undoubtedly massive applications potential. 3322 -Frontmatter 1/3/01 3:06 PM Page x xi Indeed, turboexpanders deserve to move into the limelight. Many of these machines are contributing to the profitability of modern process plants, while at the same time protecting the environment. They are highly reliable machines that represent mature technology. And that is why we compiled this text—to acquaint the serious manager and technical special- ist with modern turboexpanders and the processes that benefit from them. Much credit goes to the manufacturing companies and writers that have designed and produced the machines and applications. Others are to be commended for writing and explaining, and for not allowing doubters and detractors to derail their enthusiasm and drive. First and foremost among these pioneers stands Dr. Judson Swearingen, who founded the Rotoflow Company and whose name is listed numerous times in the var- ious references that other solid contributors have cited in their own work product. These pertinent references are given at the end of each chapter. Acknowledgments We are grateful to the following manufacturers and publishing com- panies for providing us with reference material: • Atlas Copco / Rotoflow (a division of Atlas Copco) • Babcock Borsig • Bearings Plus • Compressor Controls Corporation • Dresser Rand • Demag Delaval • Elliott Company • GHH-Borsig • Hydrocarbon Processing (Gulf Publishing Company) • Mafi-Trench • MAN-Gutehoffnungshuette • Nova Magnetics • Revolve Technologies • Sulzer-Roteq • S2M (Société de Mécanique Magnétique) • Turbomachinery International Heinz P. Bloch Claire Soares Note 1. Conversion factors are given in Appendix A. Note 2. Please also review Appendix B and C for additional names. 3322 -Frontmatter 1/3/01 3:06 PM Page xi xii 3322 -Frontmatter 1/3/01 3:06 PM Page xii Why and How Turboexpanders Are Applied 1 1 CHAPTER ONE Why and How Turboexpanders Are Applied Turboexpanders are expansion turbines, rotating machines similar to steam turbines. Commonly, the terms “expansion turbines” and “turboexpanders” specifically exclude steam turbines and combustion gas turbines. Turboexpanders (Figure 1-1) can also be characterized as modern rotating devices that convert the pressure energy of a gas or vapor stream into mechanical work as the gas or vapor expands through the turbine. If chilling the gas or vapor stream is the main Figure 1-1. Modern turboexpander installation. (Source: Atlas Copco.) 2 Turboexpanders and Process Applications objective, the mechanical work so produced is often considered a by- product. If pressure reduction is the main objective, then heat recovery from the expanded gas is considered a beneficial byproduct. In each case, the primary objective of turboexpanders is to conserve energy. Contemporary turboexpanders do this either by recovering energy from cold gas (cryogenic type) or from hot gases at temperatures of over 1,000 degrees. Current commercial models exist in the power range of 75 kW to 25+ MW, so many applications are possible. Changing market conditions, accentuated by growing environmental awareness on a global scale, are improving market receptivity for the turboexpander. Machinery manufacturers, quick to sense this market potential, have developed design features within their turboexpander ranges that offer user-friendly features, promoting ease of maintenance and operation, and aid design optimization. TURBOEXPANDERS FOR ENERGY CONVERSION * Substantial energy can be recovered using low-grade waste heat, process gas, or waste gas pressure letdown. Centrifugal (radial inflow) turboexpanders are well adapted to such energy conservation schemes and, with recent developments that have increased their reliability, are suitable for unattended service on a 24- hour, 7-day week operational basis. Some of the recent developments include better shaft seals, thrust bearing monitoring, and superior control devices. Turboexpanders are well qualified to meet the requirements of energy conservation. Decades of development in turboexpander tech- nology have resulted in highly efficient machines that can be applied in the profitable recovery of energy from waste heat sources and gas pressure letdown. Increasing demand and the progressive depletion of energy sources point to the need for conservation and for the recovery of energy from sources once thought unprofitable. In the past, the use of the turboexpander as an energy recovery device was limited for a number of reasons: • The return on capital investment did not justify a power recovery system unless more than several thousand horsepower was recovered. *Sources: Atlas Copco (Rotoflow) Corporation and Babcock-Borsig. [...]... bearings are used Why and How Turboexpanders Are Applied 13 Figure 1-7 Seal configurations exployed in modern turboexpanders (Source: Atlas Copco.) 14 Turboexpanders and Process Applications Gleitring atmosphärische seal ring (atmospheric side) Gleitring (Gasseite) seal ring (gas side) Gegenring mating ring Figure 1-8 Special mechanical seals (contact seals) used in hot gas turboexpanders (Source: GHH-Borsig.)... greater importance than is sometimes appreciated The success of these two processes, one requiring refrigeration at –300°F, and the other at –125°F, poses the questions: What are the preferred applications for turboexpanders? Why not use them in air conditioners or other commonly used refrigeration systems? 26 Turboexpanders and Process Applications Looking at this low temperature refrigeration as to power... reduction gear and the windage-related losses of a high-speed coupling Moreover, alignment issues and noise problems are thus addressed 10 Turboexpanders and Process Applications TURBOEXPANDER QUALITIES From the preceding applications and from many hydrocarbon applications, it is apparent that a turboexpander is a special turbine that should be designed with quality features to meet the following requirements:... therefore, 4 Turboexpanders and Process Applications absorbed by an oil brake or similar device The second type ranges from 100 hp to over 2,000 hp, where the power is used to drive electric generators or process booster compressors Hydrocarbon gas expanders range in the order of 100 hp to 8,000 and more hp The majority of these machines are usually designed for power recovery duty, with a process compressor... between the possible gain of mechanical energy and the required investment cost Typical commercial applications for turboexpanders include: • Chemical and petrochemical industries —FCC —Nitric acid —Acetic acid —Terephthalic acid, or PTA (see Figure 1-9) • Natural gas and oil industry 16 Turboexpanders and Process Applications Medium: reactor Off-Gas Inlet pressure: 21 bar/7.7 bar (304,5/11,7 psia) Temperature:... success of expanders was predicted in the 1940s More recently, processes similar to those used in air separation have been applied in other fields These new applications have progressed as a result of the parallel development of new processes and improved heavyduty turboexpanders Moreover, there have been improvements in the economics of the processes themselves The following review of turbine technology... cumbersome However, the radial reaction design is well suited to turboexpanders for the above reasons, as well as other reasons that merit brief explanation GAS PATH EQUATIONS AND ANALYSIS Successful commercial expander processes depend on the design and production of suitable high-speed turbine rotors and nozzles capable 22 Turboexpanders and Process Applications Figure 2-2 Steam turbine using reaction blading... energy decrease 24 Turboexpanders and Process Applications Figure 2-4 A low temperature application of a turboexpander in the separation of air in the turboexpander is make-up for the temperature difference at the warm end of the heat exchanger plus the heat leak (if no cold or liquid product is removed) Air separation can be performed by charging the process with air at 70–85 psia Older processes used... of process and heating applications One form of solar heat does offer interesting possibilities and is referred to as OTEC (Ocean-Thermal Energy Conversion) The OTEC power plant principle uses the solar heat of ocean surface water to vaporize ammonia as a working fluid in a Rankine cycle After the fluid is expanded in the turbine, it is condensed by the 22°C colder 8 Turboexpanders and Process Applications. .. controls the thrust by control of pressure behind the thrust-balancing drum (Figure 1-6) Because of features such as these, the reliability of turboexpanders is exceptionally good Operation for several years without repair is not uncommon 12 Turboexpanders and Process Applications Figure 1-6 Rotor thrust and metering schematic Shaft Seals and Bearings Virtually all cryogenic turboexpander seals are either . of Hot Gas Turboexpanders . . . . . . . . . . . . . . . . . . .85 Nitric Acid Plant Applications 85, Integrally Geared Process Gas Radial Turbines 129, Turboexpanders in Geothermal Applications 136,. viii CHAPTER 1 Why and How Turboexpanders Are Applied . . . . . . . . . . . . . . . . .1 Turboexpanders for Energy Conversion 2, Turboexpander Applications 3, Power Recovery Turboexpanders 4, Power. alignment issues and noise problems are thus addressed. 10 Turboexpanders and Process Applications TURBOEXPANDER QUALITIES From the preceding applications and from many hydrocarbon applica- tions,