Effects of initial pressure and gas-water ratio on the CO2 hydrate-based cold thermal energy storage under the gas-inducing agitation

CO2 hydrate is emerging as a promising material for cold energy storage. To provide the optimal conditions for operating the storage system using this technology, in this paper, the combined effects of the initial pressure and gas-water (G-W) ratio on CO2 hydrate formation kinetics was tested with the introduction of gas-inducing stirring. Furthermore, their influence on the energy and economic performance of the storage system under two working modes: static and dynamic, was investigated and compared. An economic evaluation was also conducted for the dynamic mode considering varied charging durations. The results showed the existence of three crucial GW ratios for each chosen initial pressure, emphasising the need to determine the optimal ratio to maximise hydrate production. Comparing the static and dynamic modes, the dynamic scenario demonstrated higher hydrate generation under the same condition parameters. However, operating in static mode showcased superior storage capacity at low initial pressure and also when a low formation rate was available in the dynamic mode. The economic analysis suggested that in dynamic mode, increased profit gains due to high formation rates and corresponding capital investments should be considered together to determine operational conditions, aiming to achieve superior economic benefits compared to the static mode and reduce the payback cycle. Additionally, the economic evaluation indicated that with a longer charging duration, the payback cycle among various conditions converged to a similar level, and lower investment costs led to a faster decrease in the payback duration.