Waste heat recovery in CO2 compression

Carbon capture and storage (CCS) is a strategically important approach for achieving significant reductions in greenhouse gas emissions from large stationary emission sources, and ensures the availability of a reliable global energy supply for the future. Carbon dioxide (CO2) compression accounts for a significant amount of the capital and operating costs, and energy penalties associated with the CCS system. In this paper, different CO2 compression strategies were reviewed, and the opportunities of recovering waste heat as an effort to reduce their energy consumption were examined. Models of an intercooling compression chain and a 2-stage shockwave compression chain were built to investigate their respective energy consumption and potential waste heat recovery. An organic Rankine cycle (ORC) model was employed to recover waste heat. An exergy analysis was applied to assess the performance of the system. The results indicated that, without waste heat recovery, the shockwave compression chain had a higher specific energy requirement than the intercooling option. With waste heat recovery, the compression energy requirement in both cases dropped as expected, and the shockwave option required a lower specific compression energy with respect to the intercooling option. Within the ORC system, thermal efficiency, exergy efficiency, and exergy destruction rates decreased as turbine inlet temperature (TIT) increased. The ORC's evaporator was found to be the largest contributor to exergy destruction. These results demonstrate opportunities to optimize the CCS configuration and improve the overall economics of the plant.