We are focusing on the practical use of methane hydrate. For recovery and use of it as an energy resource, it is necessary to consider the possibility of clogging in the recovery pipe due to the rehydration of bubbles. The purpose of this research was to observe experimentally and evaluate theoretically the decomposition behavior of hydrate sedimentary layer and the rising behavior of bubbles generated by hydrate decomposition. Chlorodifluoromethane was used as a low pressure model gas of methane. Hydrate sedimentary layer was produced by cooling and pressurizing water in countercurrent contact with gas using a hydrate formation recovery device. The recovered hydrate was decomposed by the heating or depressurization method, without flowing water. Two theoretical rising velocities were derived from the theoretical value with using the Navier-Stokes equation or the values in consideration of the bubble shape and hydrate film existence. The experimental rising velocities of small spherical bubbles radius agreed well with the theoretical value by the Navier-Stokes equation. The relatively large elliptical bubbles showed a behavior close to the theoretical value of bubble with hydrate film. Under the pressure and temperature conditions closer to the hydrate equilibrium line, almost no generated bubbles could be identified visually.
Hydrate-based gas separation is often investigated using batch or semi-batch operations. To increase the throughput of the gas mixture without increasing the apparatus volume, it is preferable to perform a continuous operation of hydrate-based gas separation. Therefore, we proposed a flow-type apparatus for performing continuous formation with passing gaseous mixture and subsequently decomposition with passing gas hydrate particles. Characteristics of multiple fluid and heat and mass transfer of hydrate slurry are essential for the efficient operation of the apparatus. In this study, we focused on heat transfer characteristics in the presence of bubbles in water and surfactant solution. First, an apparent overall heat transfer coefficient under pressure during steady operation of the apparatus was calculated on a simple assumption. Next, to control the hydrate amount and position of hydrate-decomposition and hydrate-formation in the apparatus, we focused on the temperature profile of the inside fluid. A heat transfer model using heat balance of defining heat of hydrate-formation and heat transfer of agitation of fluid was made for hydrate-based gas separation apparatus. To evaluate the validity of the heat transfer model, a calculation value is compared with the experimental value.
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