低品位热能超临界有机朗肯循环发电特性分析

Analysis on Characteristics of a Supercritical ORC Low-grade Heat Power Generation System

利用超临界有机朗肯循环(ORC)发电系统回收温度低于150℃的低品位热能,对超临界工况的3个关键问题:工质选择、加热过程和系统性能进行了分析.结果表明:对于适合超临界ORC发电系统的工质,临界温度相对较高的工质的系统循环热效率较高,膨胀机入口压力和冷凝压力较低,临界温度相对较低的工质的循环热效率较低,但能量利用率较高,膨胀机入口压力和冷凝压力较高;超临界加热器中较高的换热压力和较低的膨胀机入口温度能使热源与工质有更好的热匹配;在热源进口温度和最小换热温差的限制下,存在最佳膨胀机入口温度和膨胀机入口压力,使得系统循环热效率最高.

An analysis was carried out to following three key issues of a supercritical organic Rankine cycle(ORC)power generation system using low-grade heat source with temperature lower than 150℃,such as the working medium selection,the heating process and the system performance,etc.Results show that among all the working mediums suitable for supercritical ORC power generation systems,the one with relatively high critical temperature has higher system thermal efficiency but lower expander inlet pressure and lower condensing pressure;whereas the one with relatively low critical temperature has lower system thermal efficiency but higher energy utilization ratio,higher expander inlet pressure and higher condensing pressure.For the supercritical heater,good heat matching can be achieved between heat source and working medium under the condition of higher heat-transfer pressure and lower expander inlet temperature.Under the restriction of heat source inlet temperature and minimum heat-transfer temperature difference,there exists an optimum expander inlet temperature and expander inlet pressure,which make the system thermal efficiency reach the highest.