Beyond emission reduction: How carbon capture reshapes operational flexibility and energy efficiency of coal-fired CHP plants

Combined heat and power (CHP) technology can effectively improve the energy efficiency of coal-fired power plants and thus cut down their carbon emission intensity in power generation. The integration of a carbon capture system (CCS) offers a further pathway to reduce carbon emissions from such plants. However, CCS integration imposes notable constraints on the operational flexibility and complicates the energy consumption characteristics of CHP plants—a critical issue that has not yet been comprehensively investigated. To address this research gap, off-design models of the CHP plant integrated with CCS were developed. Taking a 660 MW coal-fired CHP unit as the reference case, quantitative analyses were performed to evaluate impacts of CCS integration on the unit's operational flexibility, carbon emission performance, and energy efficiency. The results demonstrate that CCS integration significantly narrows of the feasible operational domain of the CHP plant: the maximum power load decreases by 22.68%, while the maximum heating load drops by 62.50%. Meanwhile, CCS integration leads to a decline in energy efficiency of the CHP plant, with the maximum reduction in energy efficiency and exergy efficiency reaching 33.56% and 18.20%, respectively. Despite these drawbacks, CCS integration achieves a remarkable reduction in carbon emissions: the maximum total carbon emission and carbon emission intensity for power generation are cut by 90.76% and 88.75%, respectively. Finally, an analysis of the additional coal consumption rate for carbon capture, which is a new indicator defined, reveals that this can drop to as low as 43.61 g/kg at the minimum carbon capture rate.