Design and evaluation of a CO2 liquefaction and liquid-phase compression system for decarbonized coal-fired power plants

This study investigates the energy performance and preliminary turbomachinery design of post-combustion CO2 compression systems integrated into an ultra-supercritical coal-fired power plant with carbon capture and storage (CCS). To enable pipeline transport, CO2 must be delivered at 150 bar and 15 °C, i.e., in liquid phase. Unlike conventional configurations that compress CO2 entirely in the gaseous/supercritical phase before final cooling, two alternative layouts are proposed, introducing an intermediate liquefaction step prior to liquid-phase compression. Each layout uses a chiller system that operates at CO2 condensation temperatures of 10 °C and 20 °C. The energy performance and the system layout architecture are evaluated and compared with the conventional gaseous-phase compression configuration. An in-depth sensitivity analysis, which varies the flow coefficient, the working coefficient, and the degree of reaction, confirms that the turbomachinery preliminary design, based on input parameters related to the specific speed, is a high-efficiency design. The results indicate that the 10 °C liquefaction layout requires the least compression power (60 MW), followed by the 20 °C layout (62.5 MW) and the conventional system (67 MW). Including the consumption of the chiller, the proposed systems require an additional power of 11–12 MW, compared to just over 1 MW for the conventional layout with simple CO2 cooling. These results highlight the significant influence of the integration of the chiller on the overall power requirement of the system. Although the proposed configurations result in a larger equipment footprint, the integrated capture and compression/liquefaction system allows for very low CO2 emissions, making the power plant more sustainable.