300 MW一次再热亚临界燃煤 发电站系统改进研究
Novel System Design for a 300 MW Single Reheat Subcritical Coal？？Fired Power Plant

在传统300 MW一次再热亚临界燃煤发电站的空气预热器中,烟气与空气的换热温差大,导致了较大的损失,并且硫酸蒸汽易在冷端凝结使受热面产生低温腐蚀和堵灰的问题。此外,在回热系统中,汽轮机的抽汽与凝结水在换热时,回热加热器热端处的传热温差大,抽汽的过热度难以利用。针对传统电站的上述不足,提出了一种新型电站设计方案,并对其进行了热力学分析和技术经济性分析。在改进电站中,烟气凝结水预热器(flue gas？？condensate preheater,FGCP)替换了传统电站中的空气预热器,省煤器后的烟气全部被用来加热部分凝结水,空气和其余凝结水则由汽轮机的抽汽进行加热,同时,增加1股高压抽汽用于保证热空气达到设计的温度要求。研究结果表明:保持FGCP中凝结水和烟气的热容流率相等,可以消除常规电站内空气预热器中的温差夹点,锅炉排烟温度降至103℃而不会产生低温腐蚀和堵灰;将空气加热器与回热加热器串联布置,优先利用了抽汽的过热热来加热空气,减小了蒸汽和凝结水的传热温差;改进电站的发电效率和净发电效率分别达到了45.34％和44.20％,相较常规电站分别提高了1.2和1.0个百分点;改进电站的动态投资回收期约为4.27a,具有可行性。
For conventional 300 MW single reheat subcritical coal？？fired power plants, the heat transfer temperature difference between flue gas and air in the air preheater is large, resulting in a large exergy loss. Moreover, the sulfuric acid vapor easily condenses on the cold side, which causes low？？temperature corrosion and ash plugging on the heated surface. In the regenerative system, the heat transfer temperature difference between the extraction steam and the condensate water at the hot end of regenerative heater(RH) is large, and the superheat degree of the extraction steam is difficult to use. To solve these problems, a novel conceptual system design for the conventional power plants is proposed. Thermodynamic analysis and techno？？economic analysis of the proposed plant are performed. In the proposed system, air preheater in conventional power plant is completely replaced by flue gas？？condensate preheater(FGCP), all the flue gas from the economizer is used to heat partial condensate in FGCP, total air together with the rest of the condensate is preheated by extraction steam, and an extra steam bleed is added to ensure that the air temperature meets the design requirement. The results show that keeping heat？？capacity flow？？rate of the partial condensate equal to that of flue gas in FGCP can avoid the pinch point of temperature difference of conventional air preheater, and the exit temperature of flue gas from boiler can be reduced to 130℃ without cold end corrosion and clog. Steam and air heaters are arranged in series after corresponding RHs, and total air is preferentially heated by extraction steam, which reduces the heat transfer temperature difference between the steam and the condensate. The power generation efficiency and the net power generation efficiency of the novel power plant are 45.34％ and 44.20％ respectively, increasing 1.2 and 1.0 percentage points compared with that of the conventional unit at the same capacity. The dynamic investment payback period of the modified power plant is about 4.27 years, which is feasible