Limitations of ASME PTC 10 in Accurately Evaluation Centrifugal Compressor Thermodynamic Performance

Abstract

The American Society of Mechanical Engineers (ASME) “Performance Test Code on Compressors and Exhausters,” ASME PTC 10-1997, has served worldwide as the standard for determining centrifugal compressor thermodynamic performance during factory acceptance and field performance testing. The methodology applied in PTC 10 is based upon the original work of Schultz (1962) which utilizes a polytropic model of the compression process. Recent efforts associated with the selection and testing of compressors for high pressure carbon dioxide/hydrocarbon mixture reinjection compression services have revealed that the application of PTC 10 can result in significant errors in the estimation of compressor polytropic head and efficiency. The defined evaluation procedures use compressor suction and discharge pressures and temperatures along with gas composition to determine the thermodynamic properties necessary to derive the estimated head and efficiency. While it is recognized that these properties vary continuously from suction to discharge, average properties are used along with a correction factor proposed by Schultz (1962) to correct for variations in these properties along the actual compression path followed. Previous investigations by Mallen and Saville (1977), Huntington (1985), and Hundseid, Bakken and Helde (2006) have identified errors in some compressor applications and have proposed methods to address these issues, however, they have not fully identified the root cause nor the conditions under which these errors become significant. The results of this effort will: 1. Illustrate those portions of the test code procedures that are subject to errors caused by unique process conditions. 2. Identify those gas conditions where the errors incurred in the application of the code are significant. 3. Propose an alternate evaluation method of test results and predictions that will reduce errors in the calculation of derived properties relevant to determination of compressor performance parameters. Actual factory and field test data have been utilized where appropriate and available to support the theoretical principles developed in this study.