The experiment of CO2 hydrate conversion from microscopic ice particle under low temperature and low pressure was performed in fluidized bed. The ice particle was generated by ultrasonic mist generator, and its diameter was about 5 μm. The experimental condition was 253 K and 0.7 MPa for temperature and pressure respectively. In the previous work, conversion rate of CO2 hydrate from ice particle after sufficient time up to 90 hours was no greater than 60 to 80%. This stoppage was presumed to happen because of narrowing flow channel of the gas due to hydrate growth. To prevent this stoppage, fluidized bed was introduced. During reaction process, CO2 gas flows through the reactor, and the flow rate is adjusted with air compressor and piston attached to the reactor with pipe. The ice-to-hydrate conversion rate was measured with different flow rate and the result was compared with that of the fixed bed.
Clathrate hydrate is a clathrate compound that has guest molecule trapped within a crystal structure of water and it is stable under high pressure and low temperature. CCS (Carbon Dioxide Capture and Storage) is a technology to prevent increase of CO2 concentration in ice due to the fossil fuel combustion. In the process of CCS technology, CO2 capture and separation is known to be the most cost-consuming process. Most of the methods require high pressure, and pressurization accounts for a large percentage of cost. Methods like using chemical absorption solution are widely used, and improvement of the solution is studied by many researchers. The idea to capture CO2 by hydrate was developed. By using tetrahydrofuran (THF) as a surfactant, hydrate formation experiment in 1 atm, 273 K is conducted. (Jae Woo Choi, et al. 2014) Tetra-n-butyl ammonium bromide (TBAB) is also considered to form hydrates in low pressure. (Li et al. 2010)
To form CO2 hydrates in low pressure, one idea is to conduct formation in low temperature. Usually, this idea is not favored because low temperature also requires enormous energy. In most of the liquefied natural gas (LNG) power station or other power plants, however, practically all the cold energy is wasted. If we combine CO2 hydrate formation in low pressure and the use of cold energy which makes low temperature condition, we can get rid of concerns about costs.
