利用LNG冷能与工业余热的有机朗肯循环复合系统优化分析

Optimization and analyses of organic Rankine cycle combined system utilizing cold energy of LNG and industrial waste heat

对中低温余热(150℃)及LNG(-162℃)冷能联合利用,设计了一种复合式有机朗肯循环,对此复合循环系统进行了详细的热力分析及经济性分析,并与相对应的单独循环系统进行了比较。结果表明,该复合循环系统的净输出功比单独循环系统提高了41.55%,热效率和效率也分别提高了18.09%和19%,单位功率所需换热面积也仅为单独循环系统的61.03%。对该复合循环系统各部件进行了可用能损失分析,同时考虑了LNG余压的利用,进一步提出了优化方案。

For the use of low-temperature waste heat （about 150℃） and cold energy of liquefied natural gas （LNG, about-162℃）, this paper presents a combined system. The thermodynamic and thermo-economy properties of the system are analyzed in detail, with comparative analysis on the proposed combined system and a separated system composed of a conventional organic Rankine cycle （ORC） and a low temperature ORC. Propane and R601a are adopted as work fluids in three cycles of the system, different temperature in internal heat exchanger and that in evaporator are selected to examine the system performance and obtain the best working condition. The results show that, for the combined system, the net work output increases 41.55%. The thermal efficiency and exergy efficiency are increased by 18.09%and 19%, while the area power ratio is only 61.03%of the separated system. The exergy lost among different components of the combined system is analyzed with the pressure exergy of LNG taken into account, and an appropriate system is proposed.