地热有机朗肯循环非共沸工质与冷热源匹配特性的研究

China is rich in medium-low temperature geothermal energy. Power generation from geothermal energy is an important trend to reduce the coal consumption and atmospheric pollution in China. The organic Rankine cycle (ORC) is preferred to convert medium-low temperature geothermal energy to electricity. The use of zeotropic mixture as working fluid can improve the ORC system thermal efficiency. This project focuses on the key issues in the match characteristics of zeotropic mixtures and heat sink and source. A crossover volume translation equation of state is carried out to accurately calculate thermodynamic properties of zeotropic mixture during phase change. The interaction mechanisms of the thermodynamic parameters between the mixture and heat transfer fluid during phase change and the temperature profiles match characteristics are studied on the basis of the theoretical analysis and experimental research, then a method to determine the pinch point is presented. The synergetic relationship between the phase change heat transfer, compression, expansion for working fluid and the transportation for heat transfer fluid is analyzed. A dynamical model for ORC using zeotropic mixture as the working fluid is carried out. The transient response characteristic of phase change is analyzed for the varying parameters. A multi-parameter optimization model is established for ORC system with zeotropic mixture. The ORC performance for all operating conditions is studied and the mole fractions for the components are optimized. A working fluid selection criteria and a performance evaluation method for zeotropic mixture are presented. This project will provide scientific foundation and support for the design, optimization and operation of ORC system using medium-low temperature geothermal energy.

我国中低温地热能资源丰富，发展地热能发电是控制煤炭消耗总量、降低大气污染物排放的重要方向。有机朗肯循环(ORC)是最适宜中低温地热能发电的技术之一，非共沸混合工质具备进一步提高ORC热效率的潜力。本课题围绕非共沸混合工质相变过程与冷热源匹配特性中的关键问题开展研究。建立非共沸工质高精度跨接状态方程以精确表征相变过程关键热力性质的变化规律。理论结合实验，揭示非共沸工质相变过程与传热流体热力参数间的相互作用机制和温度匹配特性，建立夹点确定方法，探讨相变传热、工质压缩、膨胀及传热流体输运过程的能量协同关系。构建ORC动态特性模型，揭示变工况下非共沸工质相变过程对外界参数影响的瞬态响应特性。发展非共沸工质ORC热力性能多参数优化模型，掌握全工况下非共沸工质的热力性能，探索最佳工质配比，建立非共沸工质筛选准则及性能评价方法。可为中低温地热ORC发电系统的设计、优化及运行提供科学支撑。

发展了脉冲回波叠加法以高精度测量高压液体及超临界流体的声速，研制了高精度声速实验系统，可开展100 MPa的流体声速实验，测量相对标准不确定度优于0.05%开展了立方型状态方程α函数的温度相关性研究，展示了满足热力学条件的α函数的一致性和性能，解决了立方型状态方程外推到超临界区热力学性质的计算缺陷；开展了适用于近临界区的状态方程及高阶跨接函数的研究，实现了近临界区流体热力学性质的准确计算；建立了烷烃+烷烃和CO2+烷烃非共沸混合工质的跨接状态方程。提出了一种非共沸工质双压蒸发朗肯循环发电系统，探讨了双压蒸发和内回热对ORC工质与热源温度匹配特性的影响规律，揭示了双压蒸发ORC相比单压ORC的提效潜力。针对双压ORC系统，分析了不同工质与热源温度的匹配特性，探讨了工质物性对单压和双压循环结构适用的热源温度范围。将分液冷凝引入地热源非共沸工质ORC系统，以降低冷凝器面积，改善工质与冷源的温度匹配，探讨了非共沸工质R600/R601a在分液冷凝过程中与冷源温度的匹配特性，揭示了分液器入口工质干度对系统的净输出功、冷凝换热系数和换热面积的影响规律；优化了分液级数对工质冷凝换热性能的强化效果，优化了不同工质分液器入口干度，以获取最大平均冷凝换热系数，探讨了换热管内径、工质流量和冷却水温升对分液冷凝降低冷凝器面积的影响；开展了非共沸工质双循环的㶲分析，讨论了低温循环非共沸工质与冷端温度的匹配关系，提出了确定工质最佳组分配比的关键因素。研究了蒸发器夹点温差对工质与热源温度匹配特性的影响规律，讨论了蒸发器夹点温差、汽轮机配置方案、地热井深度、回注温度等对ORC系统净输出功、热效率、单位功率换热面积、平准化发电成本、动态投资回收期的影响规律；分析了不同地热井钻井成本下，蒸发器夹点温差对ORC发电成本和投资回收期的影响。在国际学术期刊发表论文10篇，其中SCI已收录10篇，国际会议论文3篇，国内会议论文4篇。