带原煤预干燥的电站高效烟气余热利用系统热力学分析

Thermodynamic Analysis of the Efficient Flue Gas Waste Heat Utilization System With Raw Coal Pre-dried of Power Plant

在燃用较高水分煤种的系统中,将原煤预干燥系统和烟气高效余热利用系统结合,能够在提高进入锅炉热量的同时充分实现能的梯级利用,缓解换热设备的低温腐蚀,进一步提高机组的经济性和安全性。为研究高效烟气余热利用系统与原煤预干燥系统结合对系统效率的影响,文章建立了干燥机、制粉系统的热平衡模型,在此基础上以国内某典型百万千瓦超超临界燃煤机组为案例,对带原煤预干燥的高效烟气余热利用系统进行了热力学计算,详细分析了系统的能量分布及经济性能,并对原煤的干燥程度对烟气酸露点和空气预热器选型的影响进行了讨论。结果表明:该系统在锅炉最大连续蒸发量(boiler maximum continuous rating,BMCR)工况下,将原煤由18.1%水分干燥至8%水分时,能够降低发电煤耗6.56g/(k W·h),较采用低温省煤器的常规余热利用系统发电煤耗降低5.74g/(k W·h),与此同时,烟气的酸露点温度、空气预热器的空气流量及换热量均有一定程度的下降,机组经济性和运行安全性均有较大幅度提高。

In the system burning high moisture coal, the integration of raw coal pre-drying system and efficient flue gas waste heat utilization system can increase the heat entering into the boiler, at the same time, energy cascade utilization can be fully achieved. The decrease of coal moisture can reduce low temperature corrosion of heat exchange equipment. The economy and safety of the unit can be further improved. In order to study the effect of the combination of efficient flue gas waste heat utilization system and coal pre-drying system on the system efficiency, the heat balance models of dryer and the coal pulverizing system were presented in this paper. On this basis, a typical domestic 1000MW ultra-supercritical coal-fired unit was taken as the case, and the thermodynamic performance of the efficient flue gas waste heat utilization system with coal pre-drying was calculated. The energy flow, the economic performance and the impacts of dry degree on acid dew point and the air preheater selection were analyzed and discussed. Results show that, under the condition of boiler maximum continuous rating （BMCR）, the coal consumption rate decreases 6.56g/（kW？h） when the moisture of coal is dried from 18.1% to 8%. The coal consumption rate of this system is 5.74g/（kW？h） lower than that of the conventional waste heat utilization system with low-temperature economizer. At the same time, the acid dew point temperature, the air flow rate and the heat transfer amount of air preheater are decreased. And the economy and safety of unit are significantly improved.