锅炉排烟温度升高对锅炉效率及煤耗的影响

摘要

在包含暖风器功能的烟气余热回收系统中，因锅炉排烟温度发生变化，在计算汽轮机侧获得热效率增益的同时，还涉及对锅炉侧热效率变化的评估。按传统理念，锅炉排烟温度升高引起排烟热损失的增大，必定使锅炉效率发生下降，煤耗增加。但在空预器进风温度提高情况下，对于锅炉排烟温度升高是否一定引起锅炉效率下降、煤耗增加，则是一个值得探讨的问题。根据热平衡原理分析了排烟温度与锅炉效率及煤耗之间的关系，论证结果表明：排烟温度对锅炉效率的影响存在两种不同基准的表达模式；因空预器进风温度提高所导致排烟温度升高时，以燃煤发热量为基准的锅炉效率计算值增大，而以输入热量为基准的锅炉效率计算值下降，但这两种表达模式对最终煤耗变化的影响则是相同的，在应用时必须区分两种不同的效率概念。在实践中，推荐首选以燃煤发热量为基准的锅炉效率模式，并按排烟温度增幅与进风温度增幅两者的比率、而不是仅按排烟温度是否升高来评估排烟热损失、锅炉效率及煤耗三者的变化。并提出在烟气余热回收系统中，应该区分“空预器排烟温度”及“锅炉机组排烟温度”这两种不同的概念。%In flue gas waste heat recovery system which contains the air heater function ,It also involves changes to the boiler side thermal efficiency evaluation at the same time in calculating thermal heat efficiency gain of steam turbine side because of the boiler exhaust temperature changing. According to the traditional concept, the boiler exhaust gas temperature increase give rise to the heat exhaust gas loss, which will enable the boiler efficiency decline and coal consumption increase. But the problem whether boiler exhaust gas temperature increase is certainly caused by boiler efficiency decrease and coal consumption increase is worth discussing when the air preheater inlet air temperature improving. According to the heat balance principle, the relationship between exhaust gas temperature and boiler efficiency and coal consumption is analysised, the results show that: there are two different kinds of expression patterns is existed between the effect of flue gas temperature and the boiler efficiency. When the exhaust gas temperature increased which caused by air preheater inlet air temperature improve, the boiler calculation efficiency which is taking the coal calorific value as the base will increase, which is taking the input heat as the base will reduce. But the effect of these two kinds of expression pattern to the final coal consumption change is the same. Two different efficiency concepts must be distinguished in application. In practice, boiler efficiency mode based on coal calorific value is first recommended. In addition, the ratio between the exhaust temperature increase and the inlet air temperature increase, but the exhaust temperature only ,to assess the change of exhaust heat loss, boiler efficiency and coal consumption. Two different concepts should be distinguished also between“air preheater exhaust temperature” and“boilerunit exhaust temperature” in gas waste heat recovery system.