电站锅炉深度余热利用系统变工况节能效果分析

Energy-saving Effect Variable Condition Analysis of the Depth Waste Heat Utilization System Under off-design Condition in Utility Boiler

通过研究燃煤电站深度余热利用系统的变工况特性,以探究深度余热利用系统在变工况条件下节能效果的变化规律和原因。以某典型超超临界机组为案例,通过热力学计算与分析,定量分析机组节能效果及其变化情况,详细分析各因素对节能效果的影响。研究结果表明:从节能效果规律上看,深度余热利用系统在各负荷下均呈现较为理想的节能效果,并且在较高负荷时节能效果更稳定,在较低负荷下,随着负荷降低,节能效果呈现缓慢下降趋势。以案例机组为例,设计工况下节能效果达到3.27 g/(kW·h),随着负荷降低至90%、75%和50%,节能效果分别降至3.26 g/(kW·h)、2.94 g/(kW·h)和2.62 g/(kW·h)。进一步分析表明产生这种变化的主要原因在于低负荷时单位燃料的回收余热量和烟气流量均出现大幅下降,导致旁路烟道内烟气流量和烟气温度出现较大下降,进而导致深度余热利用系统最终节能效果出现明显下降的趋势。

Abstract; Basing on the research of the depth waste heat utilization system under off-design condition in power plant coal-fired, the change laws and reasons of energy-saving effect of depth waste heat utilization system under variable working conditions are investigated. By the base of a typical ultra-supercritical unit, the unit energy-saving effect as well as its influence factor is studied using thermodynamics calculate and analysis method. The result shows that energy-saving effect of depth waste heat utilization system is optimal under all load condition, and more stable in highly loaded condition. It decreases gradually with the decline of the load in low load condition. By the case unit for an example, the coal consumption rate-reflecting energy-saving effect-is 3.27 g/（kW.h）, with the load decreases to 90%, 75% and 50%, coal consumption rate reduced to 3.26 g/（kW, h）, 2.94 g/（kW- h） and 2.62 g/（kW- h）. By further analysis, it is stated that the reasons of this changing. The recycled waste heat of unit fuel and flue gas flow descend dramatically in low-loaded condition, which causes great decline of flue gas flow in flue gas bypass and fuel gas temperature, leading to an apparent decreasing tendency of final energy-saving effect of depth waste heat utilization system.