Geological CO₂ Capture and Storage with Flue Gas Hydrate Formation in Frozen and Unfrozen Sediments: Method Development, Real Time-Scale Kinetic Characteristics, Efficiency, and Clathrate Structural Transition

Abstract

The climate system is changing globally, and there is substantial evidence that subsea permafrost and gas hydrate reservoirs are melting in high-latitude regions of the Earth, resulting in large volumes of CO2 (from organic carbon deposits) and CH4 (from gas hydrate reserves) venting into the atmosphere. Here, we propose the formation of flue gas hydrates in permafrost regions and marine sediments for both the geological storage of CO2 and the secondary sealing of CH4/CO2 release in one simple process, which could greatly reduce the cost of CO2 capture and storage (CCS). The kinetics of flue gas hydrate formation inside frozen and unfrozen sediments was investigated under realistic conditions using a highly accurate method and a well-characterized system. The results are detailed over a wide range of temperatures and different pressures at in situ time scales. It has been found that more than 92 mol % of the CO2 present in the injected flue gas could be captured under certain conditions. The effect of different relevant parameters on the kinetics of hydrate formation has been discussed, and compelling evidence for crystal-structure changes at high pressures has been observed. It has also been found that temperature rise leads to the release of N2 first, with the retention of CO2 in hydrates, which provides a secondary safety factor for stored CO2 in the event of a sudden temperature increase.