Comparative Analysis of Field Performance Testing in Centrifugal and Reciprocating Compressors

Abstract

Field testing of centrifugal compressors is often required by the operating company to determine compressor efficiency and power consumption over its speed range. Reciprocating compressors are also routinely tested to assure that adequate driver power is available and assess the losses associated with the compressor valves and pulsation controls. The uncertainties and test methods associated with field performance testing for these two compressors differ dramatically due to the field environment, unsteady flow field, and the traditional test methods used for compressor power. The field operating conditions, station piping and gas composition can influence the performance of both types but in different ways. Performance testing of a reciprocating compressor (typically based on pressure volume cards) differs dramatically from the more standardized approach to centrifugal compressor testing (based on enthalpy rise) mainly because of the effects of pulsating flow and the necessary volume bottles and pulsation filters in the reciprocating compressor installation. It is possible, however, to apply enthalpy rise methods to reciprocating compressor performance because the thermodynamic relationships still apply. In some cases, depending upon the influence of pulsations and the nozzle tap configuration, this measure of efficiency and power will introduce less uncertainty than measurements based on PV cards. Since the field test environment is less controlled than a manufacturer/third party test laboratory, uncertainty analysis must be used to validate or characterize the level of assurance in the measured performance. The uncertainty analysis can also provide an indication of the primary contributing measurements to an acceptably high uncertainty. For both reciprocating and centrifugal compressors, the uncertainty in the measured efficiency can be unacceptably high when some basic rules for proper test procedures and standards are violated. This paper presents an analysis of the requirements for proper field testing, examples of “near-ideal” test uncertainties for the two types of compressors and the primary causes of high test uncertainty in the field site test. These best practices are based on the recent industry guidelines published by the Gas Machinery Research Council (GMRC). Comparative illustrations are provided to highlight the differences in performance testing of centrifugal compressors and reciprocating compressor in terms of instrumentation, available test methods, and non-ideal effects on test uncertainty.