Abstract:

Organic Rankine cycle (ORC) has been widely used as the primary choice to realize power generation from low temperature waste-heat, and the combination of zeotropic mixture and dual-pressure evaporation has been evidenced their potential to significantly improve the thermal efficiency of ORC. However, it is still unclear how the multiple stages of evaporation affect the performance. In this study, a multi-pressure evaporation ORC based on zeotropic mixture (MZORC) was proposed, a heat transfer limit model was developed based on the entransy analysis, and the processes of ORC (BORC), dual-pressure evaporation MZORC and tri-pressure evaporation MZORC were simulated with Aspen Plus. The results show that MZORC can improve the performance by reducing both the heat loss and entransy dissipation caused by the evaporation. When the heat source is 423.15 K and the ambient temperature is 298.15 K, the net output power of tri-pressure evaporation MZORC can be improved by 38.6% compared with BORC, and those of BORC, dual-pressure evaporation MZORC, and tri-pressure evaporation MZORC can reach 65.0%, 79.0% and 90.1% of the theoretical limit, respectively, i.e., increasing the number of evaporation units will result in performance enhancement, approaching the theoretical limit.

Key words: organic Rankine cycle, zeotropic mixture, multi-pressure evaporation, entransy analysis, heat transfer limit model, process simulation, theoretical limit

摘要：

作为低温余热发电的首选方案，有机朗肯循环（ORC）得到广泛的工业应用。混合工质与双压蒸发结合的策略被证实能够大幅提升ORC系统热效率，但更多级蒸发对循环性能的影响仍未知。因此，提出基于混合工质的多级蒸发ORC（MZORC）概念，通过分析构建蒸发过程的传热极限模型，结合Aspen Plus对基本ORC（BORC）、两级蒸发和三级蒸发MZORC进行过程模拟，揭示了系统循环性能的理论极限。研究结果表明：MZORC能够降低循环工质蒸发过程带来的热量损失及流耗散率；423.15 K热源、298.15 K环境温度工况下，三级蒸发MZORC的净输出功较BORC有38.6%的显著提升；增加蒸发级数能够使系统性能更接近理论极限，BORC、两级蒸发和三级蒸发MZORC系统净输出功分别能够达到理论极限值的65.0%、79.0%及90.1%。

关键词: 有机朗肯循环, 混合工质, 多级蒸发, 分析, 传热极限模型, 过程模拟, 理论极限