Determinação de Propriedades Físico-Químicas de Gás Natural com Composição Similar ao do Pré-Sal Brasileiro via Simulação Molecular

Abstract

The large reserves of natural gas present in the pre-salt fields of Brazil present high concentrations of carbon dioxide, bringing great challenges for their processing. The design of equipment for this purpose requires the knowledge of some natural gas properties such as the heat capacity at constant pressure and the Joule-Thomson coefficient under high pressure and high temperature conditions, characteristic of these reservoirs, which are beyond the limits of experimental data, passing through the liquid-vapor critical regions where the divergence of these properties occurs. In addition to the equations of state, with GERG as a reference, molecular simulation can be used to simulate these properties. In this work, comparisons of the simulated results were made in the GERG and molecular simulation with experimental data. Molecular simulation was performed in the modified MCCCS Towhee program in the present dissertation to provide the properties mentioned above. In general, the simulated properties in GERG and in the molecular simulation agreed within the uncertainty limit of the simulations, however, in some conditions, the GERG showed deviations beyond 8% in relation to the experimental data and the molecular simulation showed deviations in these same conditions higher than 13%. This work extrapolated the studied pressure range up to 100000MPa. Although these pressures were well beyond those recommended for the use of GERG, the deviations from the molecular simulation results were of a maximum of 7% in density. Regarding other properties, deviations are within the range of uncertainty. In this work the liquid-vapor critical point for carbon dioxide, methane and a mixture of these substances was also mapped by analyzing the divergence of isothermal compressibility, thermal expansivity and heat capacity at constant pressure. The critical temperature for the carbon dioxide was 309K, only 5K above the experimental critical temperature. For the methane the critical temperature is above the experimental value. and for the mixture it would be necessary more results for a better conclusion