An improved supercritical coal-fired power generation system incorporating a supplementary supercritical CO2 cycle

Large superheat degree of the steam bleeds from regenerative heaters as well as the large heat transfer temperature difference during the air preheating process is not thermodynamically satisfactory in advanced supercritical power plants with the aim of high power generation efficiency. In this study, an improved supercritical coal-fired power generation system, which integrates a supercritical CO2 (S-CO2) power cycle to utilize the superheat of the steam bleeds as well as to heat the combustion air, was proposed. In the proposed system, the heat transfer temperature difference within the steam regenerative trains and air preheating process could be reduced, leading to less exergy destructions. Moreover, less required heat for flue gas air heaters makes it possible to adopt a low-temperature economizer (LTE) between the arranged two-stage flue gas air heaters, saving part of the steam bleeds, even if the exhaust flue gas temperature is kept constant. The detailed exergy distributions within the regenerative heaters and air pre-heating process were discussed using the graphical exergy analysis. The mass and energy balance of the proposed system and the overall system performance were determined using the process simulation. The economic viability and the implementation feasibility of the proposed system was also analyzed. Results showed that the exergy destruction of the regenerative heaters and air preheating process could be reduced by 4.47 MW and 11.95 MW, respectively. The gross electric power output from the proposed system was 1007.79 MW with a satisfactory energy efficiency at 46.0%, 0.4 percentage point higher than the reference power plant. The payback period of the proposed system is slightly longer than that of the reference plant at the current market condition and it will be more profitable as the S-CO2 cycle becomes more commercially mature.