Organic Rankine cycle (ORC) is widely used for the low grade geothermal power generation. However, a large amount of irreversible loss results in poor technical and economic performance due to its poor matching between the heat source/sink and the working medium in the condenser and the evaporator. The condensing temperature, cooling water temperature difference and pinch point temperature difference are often fixed according to engineering experience. In order to optimize the ORC system comprehensively, the coupling effect of evaporation and condensation process was proposed in this paper. Based on the laws of thermodynamics, the energy analysis, exergy analysis and entropy analysis were adopted to investigate the ORC performance including net output power, thermal efficiency, exergy efficiency, thermal conductivity, irreversible loss, etc., using geothermal water at a temperature of 120 °C as the heat source and isobutane as the working fluid. The results show that there exists a pair of optimal evaporating temperature and condensing temperatures to maximize the system performance. The net power output and the system comprehensive performance achieve their highest values at the same evaporating temperature, but the system comprehensive performance corresponds to a lower condensing temperature than the net power output.
有机朗肯循环(ORC)被广泛应用于低品位地热发电中, 但是由于冷凝器和蒸发器中的热源/散热 器与工质的匹配性差导致了大量的不可逆损失, 严重影响了系统的技术经济性能. 并且冷凝温度, 冷 却水温差, 窄点温差通常根据工程经验被设为固定值. 为了将ORC 系统进行全面系统的优化, 本文 提出了蒸发冷凝过程的耦合效应, 基于热力学定律, 采用能量分析, 火用分析和熵分析对温度为120 °C 的地热水作为热源, 异丁烷作为工作流体的ORC 性能各项参数进行优化研究. 结果表明, 存在一组 最佳蒸发温度和冷凝温度使系统性能得到最大限度地提高; 净功率输出和系统综合性能在相同蒸发温 度下达到最佳值, 但系统达到最佳综合性能时对应的冷凝温度要低于达到最佳净输出功率时所对应的 冷凝温度.
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Foundation item: Project(2018YFB1501805) supported by the National Key Research and Development Program of China; Project(51406130) supported by the National Natural Science Foundation of China; Project(201604-504) supported by the Key Laboratory of Efficient Utilization of Low and Medium Grade Energy (Tianjin University), China
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Yang, H., Meng, N. & Li, T. Coupling effect of evaporation and condensation processes of organic Rankine cycle for geothermal power generation improvement. J. Cent. South Univ. 26, 3372–3387 (2019) doi:10.1007/s11771-019-4260-y
- Organic Rankine cycle
- geothermal power generation
- coupling effect of evaporation and condensation
- exergy analysis