电站低低温烟气余热利用系统熵产分析

Entropy generation analysis of the super-low temperature flue gas heat recovery system in thermal power plants

电站低低温烟气处理技术是实现电站锅炉烟气高效除尘、脱硫的有效方法之一,高效回收利用锅炉烟气降温过程中形成的烟气余热,并准确评价其节能收益,对于电站节能有重要意义。文章基于热力学第二定律,根据等效热降的分析思想,利用熵产分析法,建立了电站低低温烟气余热利用系统各环节的做功能力损失模型,结合N300-16.7/537/537-7型亚临界机组的热力参数,分析了低低温烟气余热利用系统的热经济性及各环节的能量损失。结果表明:烟气余热利用各环节中,影响系统热经济性的最主要因素是烟气余热输入损失,占总做功能力损失的85.23%;系统将锅炉排烟温度从138℃降至90℃,可降低机组标准煤耗率2.15 g/(kW·h),提高全厂效率0.66%。

Super-low temperature treatment of boiler flue gas in thermal power plants is one of high- efficient techniques in dust removal and desulfurization. In a super-low temperature flue gas waste heat recovery system （super-low FGWHRS）, the waste heat coming from flue gas cooling is reused to save energy. It is of great significance for power plant energy conservation to efficiently utilize the waste heat and accurately evaluate its energy saving effect. Based on the second law of thermodynamics, the energy loss model of each process was established using entropy generation method combined with equivalent enthalpy analysis. Based on the developed model, the heat economy and energy losses of each process of the super-low FGWHRS of a subcritical unit with the ripe of N300 -16.7/537/537 -7 were analyzed. The results show that the main influencing factor on the system thermal efficiency is the exhaust gas energy of the boiler, accounting for 85.23% of total loss of working capacity. The studied system reduces the exhaust gas temperature of the boiler from 138 to 90 ℃. As a result, the plant efficiency is improved by 0.66%, saving standard coal consumption rate of 2.15 g/（ kW h）. Emission reduction and energy saving are achieved.