低温余热双循环发电系统的设计与优化

采用螺杆膨胀机双循环系统回收低温余热用于发电,拟合有机工质R245fa的热物性参数进行热力设计计算,并提出2种确定蒸发温度的方法,对单位质量的热源,分别以系统净功率、系统效率为优化目标,结合热力学第一定律与第二定律评价2种方法的优劣性.结果表明：随着蒸发温度的升高,存在最佳蒸发温度使得系统净功率最大,而系统热效率逐渐提高;系统净功率最大时,系统对余热能量回收较大,且回收量最大,故选择以系统净功率为目标作为蒸发温度的优化方法;基于蒸发压力恒定不变,证明了余热回收热量、系统净功率和系统效率随着过热度的增加而减少,应尽量采用饱和状态蒸气动力循环.

Design and Optimization of the Low-temperature Waste-heat Dual-cycle Power Generation System

The screw expander dual--cycle system was adopted for power generation by recovering low-- temperature waste heat, for which thermal design calculation was performed by fitting the thermal physical parameters of organic working medium R245fa. Two approaches for determining evaporating temperatures were proposed and compared using first and second law of thermodynamics by taking the system net power and efficiency as the optimization objects for the heat source per unit mass. Results show that with the rise of evaporating temperature, there exists an optimal evaporating temperature, in which case the system net power achieves the highest, and the system efficiency grows gradually more waste heat and most exergy are recovered by the system when the net power of system reaches the highest, and the corresponding evaporating temperature is therefore determined as the optimal one; at a constant evaporating pressure, all the waste heat recovery, the system net power and the net efficiency reduce with rising superheat degree, so the saturated steam power cycle is recommended.