Equation Of State Influences On Compressor Performance Determination.

Abstract

Accurate prediction of centrifugal compressor aero/thermodynamic performance is essential in establishment of new equipment acceptability and verification of compressor health during continuing operation. In many cases, this may be very dependent upon the ability to precisely calculate real gas properties through the use of an equation of state. Full load, ASME PTC-10 (1997) Type 1 hydrocarbon factory test data were used to compare equipment supplier test results against a number of different equation of state predictions across the relatively broad range of pressure and temperature conditions afforded by the test. In addition, a number of pressure-volume-temperature (PVT) databases for gas mixtures available in the open literature were used to evaluate equation of state accuracy in the prediction of compressibility factor. This included the equipment supplier’s selected equation of state that acted as the baseline for predicted compressor performance comparisons. Thermodynamic properties such as enthalpy and entropy are shown to be related to the compressibility factor, so errors incurred in its calculation will also affect the accuracy of their prediction. Results of this investigation demonstrated that some equations of state offer superior prediction of thermodynamic parameters and thus compressor performance when compared to others. Specific components of a gas mixture and operating pressure and temperature levels may affect a given equation of state’s ability to accurately predict these properties. However, for a large number of industrially significant applications one or more of the equations of state investigated will yield acceptable results. In those cases where a more custom equation of state needs to be applied to a unique gas or mixture of gases, evaluation of actual PVT data for the particular application may be warranted.