Experimental Determination of the Compressibility Factor of Natural Gas: Methods and Results

The article discusses the applicability of the equations of state for the gas phase of natural gas at temperatures below 250 K. To tackle this problem, highly accurate experimentally obtained values of the compressibility factor of natural gas are required. For this purpose, we developed a method to experimentally determine the compressibility factor of natural gas. The proposed method is based on the fact that, in order to assess the applicability of the equation of state, it is sufficient to obtain the relative value of the compressibility factor rather than determining its absolute value. This approach, which provides high accuracy in determining the compressibility factor, does not require sophisticated equipment. The method was tested on nitrogen, argon, air, and methane. The uncertainty in determining the compressibility factor did not exceed 0.1%. Two different compositions of natural gas were experimentally investigated. The method showed that the uncertainty in calculating the compressibility factor, according to the equations of state GERG-2004 and AGA8-DC92, was no more than 0.1% at a temperature of 220–250 K and a pressure of less than 5 MPa.