变工况下热泵供热及膨胀机供热的热力性能对比分析

通过对各设备进行建模，以某300 MW热电联产机组为例，对热泵供热及利用小型膨胀机发电后排汽供热两种方案进行变工况分析。结果表明，对于热泵供热方案，在不同的主蒸汽流量下，都存在一个最佳出口热网水温，使系统煤耗最低；采用热泵最佳参数与膨胀机方案进行变工况对比，发现在采暖抽汽参数较低时，热泵方案的煤耗高于膨胀机方案，随着采暖抽汽参数的增大，当热泵出口最佳热网水温超过70℃时，热泵方案的煤耗开始低于膨胀机方案；同样，在采暖抽汽参数较低时，热泵供热效率比膨胀机方案低，当热泵出口最佳热网水温超过64℃时，热泵方案供热效率开始超过膨胀机方案；提出等效节能量指标，并通过计算表明该指标可用于对比两方案的节能效益。

COMPARATIVE ANALYSIS OF THERMODYNAMIC PERFORMANCES OF EAT PUMP HEATING AND EXPANDER HEATING UNDER VARIABLE WORKING CONDITIONS

Heat pump heating and back-pressure expander heating are two common schemes for cascade utilization of extraction steam for heating. However, the off-design characteristics of the two schemes are not clear, and there are few comparative studies between the two schemes. Through modeling for each equipment, taking a 300 MW cogeneration unit as an example, the thermodynamic performances of the two schemes under variable working conditions are analyzed. The results show that for the heat pump heating scheme, there is an optimal outlet temperature under different main steam flow rates corresponding to the lowest coal consumption rate of the system. The heat pump heating scheme with the optimal parameters is compared with the expander heating scheme, it is found that when the extraction steam parameters are low, the coal consumption rate of the heat pump heating scheme is higher than that of the expander heating scheme. With the increase of extraction steam parameters, when the optimal outlet temperature of the heat pump is higher than 70 ℃, the coal consumption of the heat pump heating scheme is lower than that of the expander heating scheme. Similarly, when the extraction steam parameters are low, the heating process exergy efficiency of heat pump heating scheme is lower than that of expander heating scheme. When the optimal outlet temperature of the heat pump exceeds 64 ℃, the heating process exergy efficiency of the heat pump heating scheme begins to exceed that of expander heating scheme. The equivalent energy saving index is proposed, and the calculation results show that the index can be used to compare the energy-saving benefits of the two schemes.