Reheating weakens the effectiveness of feedwater heat regenerative cycle. For the double-reheat power unit, the irreversible exergy loss of the regenerative heaters gets greater due to the higher superheat degree of steam extractions. Considering the parameters of steam extractions of the regenerative system, these overheats could be used by the boiler to heat the working fluid and feeding air, which will decrease the steam cycle absorption and increase the system efficiency equivalently. Therefore, with a reference case of 660 MW double-reheat power unit, the energy saving potentials of steam extractions overheat recovery were analyzed, based on the energy and exergetic balance models. The results show that, the superheat degrees of No.5 to No.10 steam extractions are very high, about 118℃ to 311℃. If the overheats of the No.5 to No.10 steam extractions could be recovered to the boiler, the standard coal consumption rate for power generation could be decreased by 3.59 g/(kW·h). Exergetic analysis show that the exergetic efficiency of No.5 to No.10 heaters were increased. Moreover, the overheat recovery system was preliminarily designed. The aim of this paper is to provide fundamentals for the optimization of double-reheat power plants.%再热对给水回热效果有削弱作用,二次再热机组的蒸汽过热度较大,造成的回热过程不可逆损失也更大.分析大过热度回热系统抽汽参数可知,这些过热能量可回收用于锅炉工质和送风加热过程,从而等效降低蒸汽循环吸热量,提高系统效率.为此,本文结合某660 MW二次再热机组,基于热平衡计算模型和(用)分析模型,对抽汽过热能量回收的节能潜力展开定量研究.结果表明:该机组第5级—第10级加热器抽汽过热度很大,达118～311℃,将这些加热器过热能量全部回收用于锅炉本体,节煤量可达3.59 g/(kW·h);通过抽汽过热能量回收,可提高第5级—第10级加热器的(用)效率.此外,对过热能量回收系统进行了初步设计,为二次再热机组的系统构型优化提供依据.
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