Parameter optimization for z-factor correlations to predict Joule-Thomson inversion curve

When a real gas undergoes a volumetric process, a temperature change is usually observed. Temperature change is experienced during production at the perforations, throughout surface and subsurface chokes, at the surface where heavier hydrocarbons are removed at the processing facilities and compression and liquefaction of natural gas. Temperature change accompanying volumetric change is known as Joule-Thomson effect. The sign and magnitude of the temperature change may be determined by using Joule-Thomson coefficient. If Joule-Thomson coefficient is positive, then the gas temperature decreases as a result of expansion. Under the condition where the coefficient is negative, expansion process increases the gas temperature. If Joule-Thomson coefficient is identically zero, no temperature change will be observed as a result of volume change. Projection of the pressure-temperature pairs at which Joule-Thomson coefficient becomes zero creates an envelop on the P-T plane. This envelop is known as Joule-Thomson inversion curve. The inversion curve separates the P-T plane into two regions where the temperature changes have opposite signs. All gases have different inversion conditions. Measurement of inversion condition for gases requires precisely controlled experimental conditions. As a result of experienced difficulties in the experimental setups, the inversion data is limited in the literature. In lack of sufficient experimental data, some correlations, equation based prediction methods and molecular simulation techniques are all used to compute the inversion characteristics of the different gases. None of these methods are able to predict the inversion conditions accurately. The aim of this study is to search the applicability of several z-factor correlations extensively used in petroleum and natural gas engineering in prediction of Joule-Thomson inversion curve. Adjustable parameters of the correlations would be optimized to improve the accuracy of the inversion curve computations. Since these equations are readily programmable, they will be valuable tool in engineering calculations.