Thermodynamic performance analysis and optimization of a double-reheat coal-fired units coupled with carbon capture system

To mitigate carbon emissions from coal-fired units, a thermal model of a 1000 MW double-reheat coal-fired unit coupled with a carbon capture system was developed using Ebsilon software. The thermal performance of the unit under off-designs conditions was analyzed. When the CO 2 regeneration energy consumption is 4.0 GJ/t, the power output of the coal-fired unit decreases by 221.25 MW to 80 MW under different working conditions. In response, three optimization approaches were proposed: Scheme I incorporates flue gas waste heat recovery into the regenerative system, Scheme II integrates the solar energy system with the No. 1 high-pressure regenerative heater, and Scheme III couples the solar energy system with the carbon capture system’s reboiler. Thermal efficiency and exergy efficiency were analyzed for each scheme. The results show that all three optimization schemes can effectively improve the unit’s standard coal consumption rate, heat rate, and cycle thermal efficiency, with the improvement effect being more pronounced at lower loads. Under off-design conditions, the average cycle thermal efficiency of Schemes I, II, and III increased by 0.03 %, 2.8 %, and 2.0 %, respectively, while the standard coal consumption rate decreased by an average of 0.29 g/(kWh), 22.46 g/(kWh), and 16.99 g/(kWh). Under off-design conditions, the exergy efficiency trends of the heaters were consistent across all three schemes. The low-pressure heater exergy efficiency in each scheme outperformed that of the standalone carbon capture system. Additionally, Scheme II demonstrated superior boiler exergy efficiency compared to the other two schemes.