Single-Reheating or Double-Reheating, Which is Better for S-CO2 Coal Fired Power Generation System?

The objective of this paper is to provide the optimal choice of single-reheating or double-reheating when considering residual flue gas heat in S-CO₂ coal fired power system. The cascade utilization of flue gas energy includes three temperature levels, with high and low temperature ranges of flue gas heat extracted by S-CO₂ cycle and air preheater, respectively. Two methods are proposed to absorb residual flue gas heat Q_re in middle temperature range. Both methods shall decrease CO₂ temperature entering the boiler T₄ and increase secondary air temperature T_{sec air}, whose maximum value is deduced based on energy conservation in air preheater. The system is analyzed incorporating thermodynamics, boiler pressure drop and energy distribution. It is shown that at a given main vapor temperature T₅, the main vapor pressure P₅ can be adjusted to a value so that Qre is completely eliminated, which is called the main vapor pressure adjustment method. For this method, single-reheating is only available for higher main vapor temperatures. The power generation efficiency for single-reheating is obviously higher than double-reheating. If residual flue gas heat does exist, a flue gas heater FGC is integrated with S-CO₂ cycle, which is called the FGC method. Both single-reheating and double-reheating share similar power generation efficiency, but single-reheating creates less residual flue gas heat. We conclude that single-reheating is preferable, and the pressure adjustment method achieves obviously higher power generation efficiency than the FGC method. [ABSTRACT FROM AUTHOR]