Thermodynamic analysis of a modified system for a 1000 MW single reheat ultra-supercritical thermal power plant

Thermodynamics analysis is performed on the modified steam system for a 1000 MW single reheat ultra-supercritical power plant and compared to the reference one. In the modified system, all the flue gas from the economizer is used to heat the partial condensate, and total air for combustion together with the rest of condensate is preheated by extraction steam from turbine. The flowrate of the partial condensate is adjustable to ensure its heat-capacity flowrate equivalent to that of the flue gas in the modified scheme, which avoids the pinch point of temperature difference of the air preheater in reference system. Results show that the exit temperature of flue gas from boiler can be reduced to a lower value without cold end corrosion and clog. The power generation efficiency of the power plant of 48.35% is achieved, which is 1.27% points higher than that of reference unit at the same capacity. The improvement of thermal efficiency is mainly from both the low-grade heat recovery of flue gas by the flue gas-condensate preheater and the small temperature difference between the flue gas and the condensate, therefore a higher inlet water temperature of the economizer can be reached.