A new ocean disposal scenario for anthropogenic CO2: CO2 hydrate formation in a submerged crystallizer and its disposal

A new ocean disposal scenario for anthropogenic CO2 was proposed. The CO2 emitted from a thermal power plant will be collected and injected into a submerged crystallizer located at a depth of 450–500 m. In the crystallizer, CO2 will react with the ambient seawater, and be completely converted into CO2 hydrate particles. The hydrate particles so formed will be released into the ocean, and descend to the ocean bottom. During the descending process, the hydrate particles will gradually decompose and release CO2 into the seawater. The remaining hydrate particles will reach the ocean bottom and sequester there. To study the feasibility of the proposed scenario, an experimental simulation on the hydrate formation process and a numerical simulation on the dissolution and descending behavior of the hydrate particles in the ocean were conducted. The experiment demonstrated that a proper agitation would be necessary to produce hydrate particles even if the thermodynamic conditions are satisfied for hydrate formation. The formed hydrate particles agglomerate to a cluster. The apparent density of the cluster increased with an increase in the agitation time, and eventually the cluster had negative buoyancy in water. The critical agitation time for the buoyancy change increased dramatically with the agitation rate, but was not influenced by the initial CO2/water ratio. The energy penalty for the crystallization process was estimated to be smaller than 7% for a 100 MW power plant. Numerical simulation on the behavior of the released hydrate particles showed that larger particles of CO2 hydrate are favorable for less impact on the marine environment due to a longer traveling distance in the ocean before being completely decomposed.