Exergoeconomic analysis of a system for liquefaction and purification of captured CO₂

The most severe reason for global warming is the release of anthropogenic CO₂ emissions to the atmosphere. One way to mitigate these emissions is to capture CO₂ directly at an emitting source using carbon  capture technologies. An important process in the carbon capture value chain is to condition the captured CO2 to the following transportation. In this study, a system for liquefaction and purification of CO₂ is of focus and an exergoeconomic analysis is made. In the system, CO₂ is compressed through two-stage compression with intercooling, while water condensate is removed. The liquefaction is performed using an external two-stage refrigeration cycle. The compressors were found to be the greatest source of exergy destruction and were the greatest cost contributors. An overall exergy efficiency of 39 % was found and it was seen that 13 % of the fuel supplied was lost in external coolers. To improve the system and utilise the exergy loss, two configurations for district heat integration were investigated. It was found to increase the exergy efficiency to 45 % and 50 %, respectively, depending on the configuration. Integration of district heating in the intercoolers could be made without additional costs for the system. A cost increase of the overall system of 11 % was seen when the heat discharged in the refrigeration cycle was also utilised for district heat production. This shows that there is a potential for utilising the waste heat from the system and adding revenue from district heat sales.