4.5 Article

Study on Hydrate Phase Equilibrium Diagram of Methane Containing System Based on Thermodynamic Model

Journal

FRONTIERS IN ENERGY RESEARCH
Volume 9, Issue -, Pages -

Publisher

FRONTIERS MEDIA SA
DOI: 10.3389/fenrg.2021.743296

Keywords

hydrate; methane; thermodynamics; phase equilibrium; enthalpy; free energy

Categories

Funding

  1. 111 Project [D21025]
  2. National Key Research and Development Program [2019YFC0312300]
  3. National Natural Science Foundation Item of China [U20B600505, 51874252]
  4. Open Fund of State Key Laboratory Of Oil and Gas Reservoir Geology and Exploitation (Southwest Petroleum University) [PLN 2021-02, PLN 2021-03, PLN2018-16]

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This study investigates the phase equilibrium of natural gas hydrate using the Kvamme-Tanaka statistical thermodynamic model, revealing that the phase equilibrium curves are related to the guest molecule type and gas composition. The evolution of phase equilibrium pressure of different gases varies with temperature and composition, with the phase splitting of CO2 at the quadruple point affecting the equilibrium conditions. The model shows good performance in predicting phase equilibrium, with low mean square error values for various gas systems.
Natural gas hydrate is a potential energy source in the future, which widely occurs in nature and industrial activities, and its formation and decomposition are identified by phase equilibrium. The calculation of multicomponent gas phase equilibrium is more complex than that of single component gas, which depends on the accurate model characterized by enthalpy and free energy. Based on the Kvamme-Tanaka statistical thermodynamic model, theoretical and experimental methods were used to predict and verify the phase equilibrium of pure methane hydrate and carbon dioxide hydrate in the temperature range of 273.17-289.05 K. The phase equilibrium curves of methane-containing gases such as CH4+CO2,CH4+C2H6,CH4+H2S and CH4+CO2+H2S under different mole fractions were drawn and analyzed, and the decomposition or formation enthalpy and free energy of hydrate were calculated. The results show that, the phase equilibrium curves of the methane containing systems is mainly related to the guest molecule type and the composition of gas. The evolution law of phase equilibrium pressure of different gases varies with composition and temperature, and the phase splitting of CO2 at the quadruple point affects the phase equilibrium conditions. Due to the consideration of the interaction between the motion of guest molecules and the vibration of crystal lattice, the model exhibits a good performance, which is quantified in terms of mean square error (MSE) with respect to the experimental data. The magnitudes of MSE percent are respectively 1.2, 4.8, 15.12 and 9.20 MPa2 for CH4+CO2, CH4+C2H6, CH4+H2S and CH4+CO2+H2S systems, and the values are as low as 3.57 and 1.32 MPa2 for pure methane and carbon dioxide, respectively. This study provides engineers and researchers who want to consult the diagrams at any time with some new and accurate experimental data, calculated results and phase equilibrium curves. The research results are of great significance to the development and utilization of gas hydrate and the flow safety prediction of gas gathering and transportation.

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