Natural gas hydrate has attracted worldwide attention due to its huge reserves and clean combustion. The depressurization method is the most economical method to extract gas from hydrate. However, the mechanisms of heat transfer affecting hydrate decomposition rate during depressurization are still unclear. In this study, the gas production flux was controlled at 0.032 mol/min during depressurization, and three heat transfer conditions of hydrate deposit were used to decompose hydrate. The results show that the T-P responses of the thermodynamic system will be eventually parallel to the phase equilibrium line of hydrate during depressurization, which is not affected by the deposit heat transfer. After the deposit temperature is controlled by the thermodynamic properties of hydrate, the extra energy will be used to improve the hydrate decomposition rate under a good deposit heat transfer condition. Furthermore, ice formation during depressurization promotes hydrate decomposition, which hinders the decrease of the pressure and temperature of the deposit. Our findings reveal that the temperature of the thermodynamic system cannot be balanced by thermal energy and provide a new insight for the rate control of hydrate decomposition during depressurization from the perspective of deposit heat transfer.
Keywords Natural gas hydrate, depressurization, deposit heat transfer, ice formation, hydrate decomposition, thermodynamic system