Modelling and evaluation of operational flexibility and efficiency of coal-fired power units with post-combustion carbon capture

To address climate change, post-combustion carbon capture (PCC) systems are expected to become essential for coal-fired power units. This study quantitatively evaluates the flexibility and efficiency of a 660 MW combined heat and power (CHP) unit integrated with a PCC system. Two enhancement strategies—low-pressure turbine (LPT) zero-output and solution storage—are systematically analyzed using an integrated model developed in EBSILON for the power plant and a rate-based MATLAB model for the capture process. The results demonstrate that while the PCC system narrows the load range from 198–660 MW to 298–537 MW, the LPT zero-output scheme extends it to 160–537 MW, and the solution storage scheme fully restores it to 198–660 MW. Moreover, the system achieves a load change rate of approximately 20 MW/min, exceeding the rate of units without carbon capture. A 957 m3 rich solution storage tank can provide 66 MW of additional power for 10 min, corresponding to an energy storage density of 11.5 Wh/L. These findings highlight that solution storage, combined with turbine flexibility retrofits, can effectively mitigate the operational constraints imposed by PCC, enabling coal-fired units to maintain grid stability and support high renewable energy integration.