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Effect of pressure on methane recovery from natural gas hydrates by methane-carbon dioxide replacement

Chun-Gang Xu, Jing Cai, Yi-Song Yu, Ke-Feng Yan, Xiao-Sen Li
Applied energy 2018 v.217 pp. 527-536
carbon dioxide, gas hydrate, methane, temperature
Methane recovery from natural gas hydrates via CH₄-CO₂ replacement is promising for its advantage in methane recovery and CO₂ capture in the form of CO₂ hydrates. However, up to date, it is still unclear what influence the CH₄-CO₂ replacement rate and CH₄ recovery efficiency. In this work, the effects of the pressure on the dynamic of the replacement are systematically investigated by in situ Raman. The results indicate the CH₄-CO₂ replacement rate and CH₄ recovery efficiency are related to the total operating pressure and the CH₄ partial pressure in a CH₄-CO₂ binary system. On the one hand, the CH₄-CO₂ replacement can only occur under such operating pressures that the CH₄ partial pressure is lower than the pure CH₄ hydrate formation equilibrium pressure and the CO₂ partial pressure is higher than the pure CO₂ hydrate formation equilibrium pressure. On the other hand, under a certain pressure, the lower CH₄ partial pressure leads to the higher replacement rate. Due to that the condition of temperature and pressure changes continuously in the process of the replacement, the research results are of significance for guiding the successful CH₄-CO₂ replacement.