Exergetic comparison of CO2 capture techniques from solid fossil fuel power plants

• Exergy analysis in a coal fired power plant with amine scrubbing, calcium looping and oxyfuel for CCS.
• MEA case: 7.7% of the exergy input is lost in the capture unit and 1.0% during CO2 compression.
• CaL process: the capture option with the lowest exergy penalty (−9.0% compared to reference case).
• Oxy-fuel: most of the exergy losses (5.1% of exergy input) are observed in the ASU.
• High quality heat from fuel combustion is the best exergy medium for CCS in thermal plants.

There are several carbon capture and storage concepts for the reduction of CO2 emissions of power plants that are promising and have been under development recently. In this study, three carbon capture technologies, the amine scrubbing, the calcium looping, and the oxyfuel combustion were evaluated in terms of exergy losses when applied in fossil fuel power plants. Although both first two options are post combustion capture technologies, they affect the power plant differently: the amine system consumes steam for stripping (reboiler), whilst calcium sorbents regeneration process consumes fuel. On the other hand, oxyfuel technology suffers due to the power consumption penalties for the oxygen production in an Air Separation Unit. The exergy analysis revealed that in the amine scrubbing case, 7.7% of the total exergy input to the power plant is destroyed in the capture unit and 1.0% during CO2 compression. Although a considerable amount of the total exergy input (22.3%) is dissipated in the calcium looping process, the overall scheme is the most efficient with the lowest exergy penalty of −9.0%, whereas in the amine and oxyfuel case this penalty amounts to −10.0% and −9.5% respectively. In the oxy-combustion case, the ASU is the main unit where most of the exergy losses for CO2 capture are observed (5.1% of the total exergy input in the system).

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