Fundamental Study for Developing the Controlling Technologies of the Phase Equilibrium Condition in the Mining Method of Methane-Carbon Dioxide Replacement in Hydrates

摘要

Methane hydrates are considered one of prospective energy resources because their estimated amount is huge, tens times as much as that of the natural gases, and their load to the environment is small. In addition, there is a possibility of solving the global warming problem simultaneously by replacing methane in hydrates with carbon dioxide. For this idea to be concrete it is crucial problem to develop controlling technologies of the phase equilibrium condition in methane-carbon dioxide mixture hydrates.To achieve this purpose, firstly, the revised prediction method of the phase equilibrium condition characterized by precise fugacity calculation and accurate henry's constant estimation is developed. After confirming the accuracy of the proposed method, the control of the phase equilibrium condition by adding other hydrate former or altering the water activity is studied. Main results are as follows.(1) In the prediction of hydrate equilibrium pressure for the methane-carbon dioxide mixture hydrates, the average absolute deviation of the pressure by the proposed method is +- 3 percent.(2) Controlling method of adding other hydrate former is appropriate for shifting the equilibrium condition toward lower-pressure and higher-temperature side.(3) Controlling method of altering the water activity is applicable for shifting the equilibrium condition toward higher-pressure and lower-temperature side.