Energy Analysis of Precompression and Turbine Recovery for Cryogenic Carbon Capture in a Direct Air Capture System

The accumulation of carbon dioxide in the atmosphere from greenhouse gas emissions is a determinant cause of climate change. Research into CO2 sequestration techniques is an approach to reduce emissions from flue gas that would otherwise enter the atmosphere. Cryogenic direct-air CO2 capture systems are advantageous over other approaches due to the technology being technically mature and capable of being rapid-scaled up to a global capacity. Direct-air capture systems utilize the high phase-transition temperature of CO2, when compared to the other gases in flue emissions, allowing the CO2 to be solidified and captured before the other gases desublimate. Increasing the partial pressure of CO2 also increases the desublimation temperature, requiring less work from the cryogenic system. However, the required energy input to precompress the air before it enters the system may prove unfavorable when calculating the total work of the system. The purpose of this study is to determine if there is a net energy benefit of precompression of atmospheric air combined with turbine recovery in a direct air capture system when compared to a system with no precompression or energy recuperation. A thermodynamic model was created to include components such as a heat exchanger, deposition chamber, and cryogenic cooler. The system was evaluated at discrete inlet temperatures and pressures and at varying mass fractions of CO2 desublimated. The overall results show that precompression interconnected with turbine energy recovery does not yield a net energy benefit and will increase the overall work required to run the system.