Centrifugal Compressor Surge and Surge Control

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Practical Aspects of Centrifugal Compressor Surge and Surge Control

Transcript of Centrifugal Compressor Surge and Surge Control

PRACTICAL ASPECTS OF CENTRIFUGAL COMPRESSOR SURGE AND SURGE CONTROL

j'jMeherwan P . Boyce is President of Boyce Engineering International, Inc., a major Houston-based consulting and en gineering Jinn. His past experience in corporates many academic and profes sional positions, including Director of the Gas Turbine Laboratories and Pro fessor of Mechanical Engineering at Tex as A&'A-1 University, where he organized and was chairman of the Turbomachin- ery Symposium. Dr. Boyce has authoredmore than fift y significant pa pers and technical reports on fluid mechanics and turbo1nachinery, and he is a member of SAE , ASM E , and several other professional and honorary societies. He is also a registered professional engineer in the State of Texas.Dr , Boyce received B .S. and li.1.S . degrees in M echanical Engineering from the South Dakota School of M ines and Technology and the State University of New York, respective ly, and his Ph .D . in M echanical Engineering from the Univer sity of Oklahoma.

William R. Bohannan is Chief M e chanical Engineer and Technology Coor dinatorfor the San Francisco Division of Bechtel Petroleum, lnc. He heads a group of engineering specialists engaged in the selection studies, specification, evaluation , ap plication engineering , testing, and commissioning of mechani cal equipment associated with projects handled by this division. He also guides the Division's involvement in technicalsocieties and committees. M uch of his thirty years' experience has been involved in compressor and turbine ap plications. His previous assignments include seven years with a compressor manufacturer and five years with petroleum refining com panies."A1r . Bohannan holds a B .S . degree in M echanical Engineer ingfrom South Dakota School of M ines and Technology. He is a registered professional engineer in the State of California and a member of AS A1E and the Vibration institute, and he participates in the mechanical equipment activities of API .

Royce N . Brown is a Consulting Engi neer with Dow Chemical U.S.A., Engi neering and C onstruction S ervices, Houston, Texas. His responsibilities in clude specifications, consulting and field assistance in the area of large rotating equipment for Dotv world wide . To gether with his responsibilities as Con sulting Engineer, he heads the Rotating Equipment and Critical Equipment In strumentation Group. He holds a B .S .degree in Mechanical Engineering /ram the University of Texas and a M .S. degree in Mechanical Engineering from .the Univer sity of Wisconsin. He is a fellow me1nber of I SA; a member of ASM E, SM E, and API; and an associate member of SAE . He is active in the M echanical Equipment subcommittee of the CRE, where he is the chairman of the API 617 Task Force. M r. Brown is a registered professional engineer in Texas, Louisi ana, Wisconsin, and California.

john R. Gaston is a Senior Controls Design Engineer for Dresser Industries, Inc., Clark Division, Olean, NY . He joined Dresser Clark in 1956 and has held various positions in Field Service. Since 1967, he has been responsible for application and design engineering of control systems for turbo (centrifugal and axialflow) compressors. He has pre sented papers on compressor control at various ISA and other conferences. Hereceived the Chemical-Petroleum Division of ISA 's Dick Pond award in recognition of the best technical pa per at the annual Syniposium held at San Francisco in 1974. M r. Gaston is a member of the National 31anagement Association, a Senior Member of the Instrument S ociety of America and n registered professional engineer (control systems ) in the State of California .

Cyrus Meher-Homji is Engineering Consultant M anager with Boyce Engi neering International, where he is in valved with various consulting work in the turbomachinery and engineering management areas.His counsulting activities include de sign, vibration and peiforrnance analy sis, economic analysis and reliabilit y en gineering .ln the past, he was a develop- 1nent engineer with Boyce Engineeringand was involved in the design and development of a protot y pe externall y fired steam injected gas turbinefor the U .S . Depart ment of Energy. His areas of interest are rotor dynamics, turbomachinery prognosis and diagnosis, engineering manage ment, and reliabilit y and maintainabilit y.M r. Meher-Homji has a B .S . degree in M echanical Engi neering and an M .E. degree in Industrial Engineering from Texas A&A1 University, and a "/.1 .B A. degreefrom the Univer sity of Houston.

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HSPROCEEDINGS OF THE T\VELFTH TURB011ACHINERY SYMPOSIUM

Robert H . ll-1eier joined Cooper Ener g y Services Company in 1966 and has had a long association with centriftLgal compressor design and development . Presentl y, he is f..f anager of Design and Development for Rotating Products. His abilit y to read and speak German and French is especiall y valuable in pre sentations and specifications review . He holds a degree fro1n the Swiss Federal Institute of Technology.

Norbert E . Pobanz graduated from UCLA. with a B .S. degree in General Engineering in Januar y, 1958. In June, 1981, he received a Af BA, Af anagement, from Golden Gate Uni1;ersity in San Francisco. During the past twenty-four years, he has been closely associated with the use of computer simulation to evaluate engineering designs in many technical fields. During the past eight years, he has been in charge of a simulation and advanced control specialt y group for Bechtel Petro leum, Inc . Recentl y, his responsibilities have expanded to include nwnagement of a dedicated simulation facility to per form studies and to analyze distributed control systems. Prior to his years with Bechtel, he was employed by Electronic Associates, Inc. for fourteen years. His responsibilities in eluded dynamic analysis, technical support for marketing, and management of computer simulation facilities.M r . Pobanz is a registered professional engineer (control systems) in the State of California . He has Senior Member status in the Instrument Society of America and the S ociety for Cmnputer Simulation ( SGS ), Presentl y, he is Senior Vice Presi dent of SGS . He has published numerous articles in thefield of simulation.

ABSTRACTThis paper addresses the area of compressor stability, surge and surge control and relates to the practical aspects involved. An emphasis is placed on the physical understanding of surge phenomena and on the practical limitations of surge control systems. Topics discussed are physical interpretation of instability, causative factors, types of stall, machine and process design factors, surge effects and characteristics, control system types and practical application aspects. Some case studies also are presented. The discussion primarily relates to centrifugal compressors, but several aspects pertain to axial flow compressors as \veil. The paper is split into three sections: Section A consists of an introduction to surge and a discussion of centrifugal compressor design and process factors that affect operating stability. Section B discusses the various types of control schemes and surge protection devices. Several exam ples and common pitfalls are addressed. Section C addresses the importan t design tool, surge system simulation. Several references are provided to enable the reader to pursue this topic in greater detail.

A. INTRODUCTION TOCENTRIFUGAL COMPRESSOR SURGECentrifugal compressor systems at numerous installations have suffered serious mechanical damage to compressor inter nals or to other parts of the piping systems as a result of

operation in the surge condition. In other cases, compressors, usually smaller machines, have operated for long periods \Vith intermittent or even continuous light surge \Vithout mechani cal harm, although'vith significant impairment of aerodynamic performance. These conditions generally are the product of one or more of the foIIo,ving deficiencies:1. Poor matching of the compressor to the system's re- quirements.2. Inappropriate compressor design.3. Inadequate antisurge control system.4. Unfavorable arrangement of piping and process com ponents of the system. (This often can magnify surge.)Because of the shape of their performance curves, the application of centrifugal compressors frequently is consider ably more complex than that of reciprocating machines. A centrifugal compressor driven by an electric motor offers an imposing challenge to the controls engineer ,..,hen this con stant-speed machine must accommodate a 'vide range of vari ables in its operating conditions. Centrifugal compressor appli cations continue to become more complicated \Vith increases in the numbers of stages per casing, casings in tandem \Vith a single driver, and sidestream nozzles; higher pressures and speeds; and more operating conditions for a given machine involving \Vider ranges of flo,vs, molecular ,..,eights, and pres sures. This everincreasing complexity requires a better under standing of the causes of surge and its detrimental effects in order that adequate control systems may be applied. It also creates the need for surge control system simulation studies, which must be conducted at the design phase. This topic is addressed in Section C.A typical performance map for a centrifugal compressor is sho,vn in Figure 1. The operating line is the surge line modified by a safety margin to ensure trouble-free operation. Note that the total pressure ratio changes \vith flo\v, speed, molecular \veight, suction pressure and temperature. Also, note that operating at higher efficiency implies operation closer to surge. It should be noted here that total pressure increases occur only in the impeller. To make the curve general, the concept of aerodynamic speeds and corrected mass flow rates has been used.The su