中低温热能高效利用非共沸工质朗肯循环基础研究

Low-moderate temperature thermal energy below 200℃ in renewable energy and waste heat widely and largely exits in nature and industry. However, its heat-power conversion characteristics are significantly different from the conventional systems and its utilization is insufficient. Efficient use of the low-moderate temperature thermal energy is a hot while difficult topic in the international energy utilization community. This project focuses on the efficient heat-power conversion theory for the low-moderate temperature thermal energy, and selects the organic Rankine cycle (ORC) as the most important form of energy conversion for this study. To reduce the exergy loss during the heat transfer processes in the ORC, a new organic Rankine cycle with “multi-pressure evaporation & liquid-separated condensation” using zeotropic mixtures as working fluid is proposed. The new thermodynamic cycle has significantly increased freedom for cycle design with superposed advantages of zeotropic mixtures, multi-pressure evaporation and liquid-separated condensation. Therefore, the new cycle has a great potential in efficient heat-power conversion of the low-moderate temperature thermal energy below 200℃. The project will first study the process structure design and the selection criteria of appropriate working fluids for the new cycle to reveal its heat-power conversion mechanism and develop the cycle design method. Thermal property experiments will be carried out for zeotropic mixtures, aiming to provide the high-precision data and universal models for accurate prediction. Further research will focus on the flow and heat and mass transfer mechanism of zeotropic mixtures during evaporation and condensation to reveal the intrinsic characteristics. Finally, the integrated design method and operation strategy for the new thermodynamic system will be developed. When finished, the project will develop a systematic and universal efficient heat-power conversion theory appropriate for various heat sources of low-moderate temperature below 200℃.

200℃以下中低温可再生能源和工业余热储量丰富、分布广泛，但其热功转换特点与常规动力系统差异显著，利用尚不充分，是国际能源领域的热点和难点。本项目关注中低温热能的高效热功转换理论，采用有机朗肯循环（ORC）作为载体循环和研究对象；以减少换热火用损为突破口，提出“多压蒸发、分液冷凝”非共沸工质ORC新思路，从工质物性、循环形式、换热过程多个维度拓展循环构建空间，实现非共沸工质、多压蒸发和分液冷凝的优势叠加，具有实现200℃以下中低温热能高效热功转换的巨大潜力。本项目拟研究新循环的流程结构设计及适用工质标准，揭示新循环的热功转换规律和构建方法；针对关键混合体系，获得精确完整的热物性数据，建立通用型预测模型；从相界面流动和传热的微观层面出发，揭示非共沸工质流动、相变传热的机理特性；并发展新系统的集成设计方法和全工况运行策略。最终建立适用不同特性热源、系统化且普适性的中低温热能高效热功转换理论。

200℃以下中低温可再生能源和工业余热储量丰富、分布广泛，其高效利用对于实现“双碳”目标具有重要意义；但其热源温度低，热功转换特点与常规动力系统差异显著，利用尚不充分，是国际能源领域的热点和难点。本项目针对200℃以下中低温热能的高效利用，采用有机朗肯循环（ORC）作为载体循环和研究对象，以减少换热火用损为突破口，提出“多压蒸发、分液冷凝”非共沸工质ORC新思路，围绕热功转换方案设计、最优循环构建、非共沸工质热物性表征、非共沸工质传热特性揭示和热力系统集成优化等方面开展了系统研究。获得了关键混合体系的精确完整热物性数据，建立了黏度和导热系数的高精度预测模型及二元混合体系的通用型状态方程；揭示了非共沸工质的动态湿润特性、相变传热特性和气液分离机理，构建了分液冷凝器的设计准则；揭示了最佳循环形式、工质物性与热源温度间的耦合关系，建立了双压蒸发循环的最优流程设计方案；提出了多压蒸发、分液冷凝与非共沸工质的能流耦合机制，获得了新循环的构建方法，实现了三者的优势叠加；揭示了部件结构材料、热源特性与冷热源工况变化对系统性能的影响规律，建立了新系统的多目标集成设计方法和全工况运行策略；构建了适用不同中低温热源特性、系统化且具有普适意义的中低温热能高效热功转换理论，将ORC系统的转换效率相对常规循环提高了36%~53%，单位投资成本降低了1.6%~8.8%。项目研究结果可为中低温热能高效利用、新型热力循环构建、非共沸工质应用、强化换热和热力系统设计等方面提供科学依据和理论基础，对于非共沸工质朗肯循环的发展具有重要的指导意义，为中低温可再生能源及余热资源的最大限度热功转换提供了坚实科学支撑。本项目组在国家自然科学基金的资助下，顺利完成了预定研究任务，发表相关论文137篇，其中SCI期刊论文86篇；授权发明专利5项、实用新型专利7项、软件著作权2项。项目骨干陈颖教授入选国家“百千万人才工程”；培养出站博士后5人，毕业博士研究生10人、硕士研究生24人。