PρT Behavior of a Lean Synthetic Natural Gas Mixture Using Magnetic Suspension Densimeters and an Isochoric Apparatus: Part I

Abstract

Work shown in this paper reports measurements of fluid behavior and its dependence upon concentration in natural gas-like mixtures. These systematic experiments covering phase equilibrium and densities of selected mixtures use a state-of-the art apparatus. This work presents phase envelopes and density data for a synthetic natural gas-like mixture measured with an isochoric apparatus and a magnetic suspension densimeter. The isochoric apparatus permits precise, fast measurements using an automated procedure over wide ranges of pressure and temperature encompassing the cricondentherm and the cricondenbar. A comparison of the measured phase envelopes to predictions from cubic and molecular-based equation of states (EOS’s) indicate serious deviations in both cricondentherm and cricondenbar regions. Although most design software use these models, the results obtained here indicate the EOS predictions are unacceptable. Current density measurements deviate from both the AGA8-DC92 and the GERG-2004 models.

Review on Natural Gas Thermopysical Property Measurement Techniques

“…In a recent work Acosta et al [63] developed a new computational method for the analysis of isochoric data to obtain phase envelope experimental data points, reporting that the phase boundary temperatures and pressures could be determined within 0.45% and 0.04%, respectively. Our research group has developed a systematic measurement program on selected natural gas-like mixtures using the isochoric method with the cell design reported in Figure 9 [64][65][66].…”

Density measurements on binary mixtures (nitrogen + carbon dioxide and argon + carbon dioxide) at temperatures from (298.15 to 423.15) K with pressures from (11 to 31) MPa using a single-sinker densimeter

“…It basically consisted of a high-pressure measuring cell, which was installed inside a vacuum-insulated two-stage thermostat, a magnetic-suspension coupling incorporated in the measuring cell, and an analytical balance at the top of the apparatus. Both [29], C 2 H 6 [30], N 2 [28], CH 4 [31], natural gases [8,9,15,32,33] 5.0 mK [9] 0.01% of (40 or 200) MPa [28] 0.1% [9] Chamorro (250 to 400) K [25] Up to 20 MPa [25] 0 to 2000 kg/m 3 [25] CH 4 ÀN 2 [34], CO 2 ÀN 2 [10,35], CH 4 ÀCO 2 [36], COÀN 2 [37] 3.9 mK [25] (0.007 to 0.015)% of 20 MPa [25] (0.020 to 0.155)% [25] Kuramoto (293.15 to 473.15) K [22] Designed up to 20 MPa [22] n/a iso-Octane, n-nonane, n-tridecane, water, 2,4-dichlorotoluene, 3,4-dichlorotoluene, bromobenzene [22] 3.0 mK [22] n/a (6.7 to 11.7) ppm [22] Wagner (235 to 520) K [38] Up to 30 MPa [39] (2 to 2000) kg/m 3 [39] Cyclohexane, toluene, and ethanol [39], n-heptane, n-nonane, 2,4-dichlorotoluene, and bromobenzene [40], Ethylene, ethane, and sulfur hexafluoride [38], Ar and N 2 [41], CH 4 and CO 2 [42] 8.0 mK [39] 0 a The uncertainties listed, are just for information purposes and especially those estimated before 1990 are from a current point of view possibly not reliable because (i) the confidence probability was not provided in the original paper; (ii) there was no general standard to declare the measurement uncertainty at that time; or (iii) no complete analysis on the measurement uncertainty was done for these apparatuses. The...…”

“…The commonly used reference equations of state (EOS), e.g., for nitrogen [1], argon [2], carbon dioxide [3], ethane [4], ethylene [5], propane [6], and sulfur hexafluoride [7] were all modeled with the help of data measured with SSDs. Moreover, with the increasing demand for knowledge of volumetric properties of fluid mixtures, more measurements [8][9][10][11] were carried out utilizing different SSDs. However, in this context only accurate density data of binary mixtures serve to further improve the performance of multi-parameter EOS for mixtures, especially those based on the GERG EOS (GERG-2004 of Kunz et al [12] and GERG-2008 of Kunz and Wagner [13]).…”

Evaluation of prediction models for the physical parameters in natural gas liquefaction processes

“…The Gas Research Institute (Hwang et al, 1997;Magee et al, 1997) initiated a co-operative international project to establish a set of standard reference p-V-T data for five natural gas mixtures, where a Burnett apparatus was adopted to obtain the experimental results at 225-350 K for pressures to 11 MPa. A combined effort (Atilhan et al, 2011a(Atilhan et al, , 2011bMcLinden, 2011) between Qatar University, Texas A&M University, and the National Institute of Standards and Technology on the pressure-density-temperature behavior of natural gas was conducted in 2011, where an isochoric apparatus and a magnetic suspension densimeter were used to measure the p-ρ-T data of four synthetic natural gas mixtures at 250-450 K for pressures of up to 37 MPa. In consideration of the working conditions in the natural gas liquefaction processes, we choose the precise experimental results at 225-325 K for pressures of up to 11 MPa as the reference data for the evaluation of the SRK equation, the PR equation, the LKP equation and the GERG-2008 equation.…”