A new concept for CO2 geological sequestration is proposed here as one of promising countermeasures against the global warming. For general geological sequestration technologies, there are still some issues we need to tackle, such as the expansion of amount of sequestrated CO2, reduction of environmental risks caused by CO2 leakage, and cost saving. In order to solve these problems, we propose CO2 sequestration system to sequestrate a large amount of CO2 in the form of gas hydrate under the seafloor safely. In this system, we inject CO2 + N2 mixed gas recovered from flue gas of a coal-thermal power plant into marine sediments at high pressure and low temperature, where CO2 forms clathrate hydrate. Besides, by using CO2 + N2 mixed gas, we can reduce the cost for its sequestration and avoid blockage in marine sediments at the same time. In this work, we assessed the potential amount of sequestrated CO2 and the cost of this system. From the results, the amount of CO2 that can be sequestrated offshore Japan by this system was estimated to be twice and the sequestration cost can be reduced by 14.3%, compared with those of the CO2 aquifer storage.

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