Energy Savings for Centrifugal Compressors

Abstract

Current design improvements of both the rotating and stationary aerodynamic components of centrifugal compressors can greatly increase the efficiency of vintage machines. A centrifugal compressor built in the 1970's or 1980's might have an external polytropic efficiency in the high 70's, whereas a newer compressor might have an efficiency over 85 percent. Centrifugal compressors are designed to operate at a best efficiency point (BEP) shown on its performance map. Whether a centrifugal compressor is operating at its BEP, near choke, near the surge point, or in recycle, the operator may be able to significantly reduce the total energy consumption by rerating the installed machine with new, higher efficiency aero components. Whether the compressor is driven by an electric motor, steam turbine or gas turbine, costs for operating these drivers is ever increasing and how much it may go up in the future is uncertain. With a greater worldwide focus on protecting the environment by reducing greenhouse gases, improving the efficiency of an installed centrifugal compressor by rerating can go a long way toward that goal. This paper will explain the reasons for rerating a compressor and provide details of the rerate process.