Characterization of a biomethane-like synthetic gas mixture through accurate density measurements from (240 to 350) K and pressures up to 14 MPa

Abstract

In this work the thermodynamic behavior of a synthetic four-component biomethane-like mixture, composed mainly of methane (96.48%), with small amounts of carbon dioxide (2.00%), nitrogen (1.50%), and traces of oxygen (0.02%), is studied using accurate (p,ρ,T) experimental data. Two mixtures of identical nominal compositions were prepared by the gravimetric method at the Spanish National Metrology Institute (Centro Español de Metrología, CEM) and at the Slovak National Metrology Institute (Slovenský Metrologický Ústav, SMÚ). The composition was double checked by Gas Chromatography, at both NMI and at the beginning and end of the measurements. An additional test of the consistency of the given compositions was performed by measuring the density of both mixtures at selected points, with two different techniques, in two different laboratories. Accurate density measurements have been taken over a wide temperature range, from (240 to 350) K, and pressures up to 14 MPa, using a single-sinker densimeter with magnetic suspension coupling. Experimental data are compared with the densities calculated with the GERG-2008 and AGA8-DC92 equations of state. Deviations between experimental and GERG-2008-estimated densities are within a ±0.03% band at all temperatures, which shows the outstanding performance of the current reference equation for natural gases when describing a biomethane-like mixture. Deviations between experimental and AGA-8-estimated densities are higher than 0.04% at 250 K for pressures greater than 10 MPa and also at 240 K for pressures higher than 9 MPa. This work is part of the research project 'Metrology for Biogas' supported by the European Metrology Research Program.

Accurate experimental (p, ρ, T) data of the (CO2 + O2) binary system for the development of models for CCS processes

“…The residence time of the mixture in the cell is never longer than 40 hours. Specific sorption tests for this particular mixture were performed in the same way as they were done in previous investigations [11], [25]- [35]. Continuous density measurements on the same state point were recorded over 48 hours.…”

Thermodynamic characterization of the (CO2 + O2) binary system for the development of models for CCS processes: Accurate experimental (p, ρ, T) data and virial coefficients

“…The residence time of the mixture in the cell never exceeded 40 hours. In this study, specific sorption tests for this particular mixture were performed in the same way as in previous works [12], [17]- [27]. Continuous density measurements on the same state point were recorded over 48 hours to detect any drifting.…”

Determination of the force transmission error in a single-sinker magnetic suspension densimeter due to the fluid-specific effect and its correction for use with gas mixtures containing oxygen

“…The uncertainty of each single value of ερ obtained for a selected temperature and pressure from density measurements on pure oxygen can be obtained by applying the law of propagation of uncertainty [38] to equation (17). For this purpose, the contributions from the uncertainty of the experimental density, corrected for the apparatus-specific effect but not for the fluid-specific effect, U(ρΦ=Φ0), the uncertainty of the reference EoS from Span and Wagner, U(ρEoS), the uncertainty of the specific magnetic susceptibility of O2, U(χs), and the uncertainty of the density of the silicon sinker, U(ρs), must be considered.…”

“…The fluidspecific term of the FTE, as well as the apparatus-specific effect, are unique for each SSMSD, and therefore, must be determined independently for each densimeter. The SSMSD at the University of Valladolid (UVa) [8] [9] has been used during the last few years to measure the density of different binary mixtures [8,[10][11][12][13][14][15][16] and multicomponent mixtures [17][18][19][20]. As no significant amount of any paramagnetic component was present in those mixtures, only the apparatus-specific correction was considered.…”