Accurate P−ρ−T Data and Phase Boundary Determination for a Synthetic Residual Natural Gas Mixture

Abstract

This paper reports P−ρ−T data (P is pressure, ρ is mass density, T is temperature) for a ternary mixture that resembles a residual natural gas. The measurements utilized a high-pressure, single-sinker magnetic-suspension densimeter (MSD) from (200 to 450) K up to 170 MPa and an automated isochoric apparatus to determine densities and phase boundary data up to 20 MPa. The MSD technique yielded accurate data, with better than a 0.05 % estimated error at two standard deviations up to 200 MPa. The relative uncertainties for phase-boundary temperatures and pressures were 0.45 % and 0.04 %, respectively. The isochoric densities had essentially the same estimated error as the MSD data. The GERG-2004 and AGA8-DC92 equations of state compared well to the density data. A new method provided saturation densities from isochoric data with a relative uncertainty of 0.12 %, compensating the isochoric densities for cell and transfer-line volume changes and for mass interchange between the cell and the combination of the transfer line and pressure transducer.