An improved PR equation of state for CO2-containing gas compressibility factor calculation

Peng-Robinson equation of state (PR EoS) is a reliable and widely used cubic EoS to predict natural gases thermodynamic properties. However, large deviations between the calculated compressibility factor values and the realistic values are observed when it is applied to the high volume CO2-content natural gas. In order to enhance its applicability, a new correction parameter associated with three-parameters (the reduced temperature Tr, reduced pressure Pr and CO2 volume content) is introduced into the attractive term of PR EoS by fitting the deviations between 267 groups of experimental compressibility factors and corresponding calculation values. The results reveal that the average absolute deviation between experimental data and predicted compressibility factors from the improved PR EoS is 2.708% when the pressures range from 3 MPa to 15 MPa, temperatures range from 263.15 K to 313.15 K and CO2 volume contents range from 9.84% to 100%. The deviation is reduced by 9.61% when compared to that of the original PR EoS. The results also demonstrate that this improved PR EoS has better performance than PRSV, PRTwu BWRS EoSs, and is essentially comparable in predictability to PC-SAFT EoS.