自冷凝CO2跨临界动力循环机理及优化研究

For low temperature heat energy, CO2 power cycle has more long-term development prospect than organic Rankine cycle considering the environmental and safe operation characteristics. For middle and high temperature heat energy, excellent thermal stability and cycle performance give the CO2 power cycle the potential to replace the conventional Rankine cycle completely. Both the main CO2 power cycles are faced with development difficulties. For the supercritical CO2 Brayton cycle, it is difficult to compress supercritical CO2 with high pressure ratio, stably and efficiently. For the CO2 transcritical power cycle, it is difficult to condense subcritical CO2 by conventional cooling water. The applicant proposed a self-condensation CO2 transcritical power cycle which overcomes the above problems. Working fluid is compressed with high pressure ratio at liquid state. Conventional cooling water is successfully applied for the new cycle. This project aims to study on the variation of the cycle performance with the operation parameters, namely, heat absorption pressure, heat absorption final temperature, heat release pressure, heat release final temperature, condensation pressure and condensation temperature, for the self-condensation CO2 transcritical power cycle, in order to find the operation and regulation mechanism and optimal operation method for the cycle. For several heat source types, the new cycle will be optimized and compared with other main CO2 power cycles for quantitative comparative evaluation. CO2 transcritical throttling in near critical region is an important process, which will be studied on for the throttling characteristics and optimal control method.

在低温热能领域，考虑到环境特性和安全运行特性，CO2动力循环比有机朗肯循环具有更长远的发展前景；在中高温热能领域，优秀的热稳定性和循环性能使得CO2动力循环具有革命性替代传统朗肯循环的潜力。然而，两个主要CO2动力循环均遇到进一步发展的难题：在超临界CO2布雷顿循环中，超临界CO2稳定、高效、高压比压缩难度极大；在CO2跨临界动力循环中，亚临界CO2难以被常规冷却水冷凝。申请人提出的自冷凝CO2跨临界动力循环，完全克服了上述两个难题，实现了液态工质高压比增压和常规冷却水冷却。本项目拟研究自冷凝CO2跨临界动力循环性能和吸热压强、吸热终温、放热压强、放热终温、凝结压强、凝结温度等运行参数间的依变规律，获得该循环的运行调节机理和优化运行方法；基于多种热源形式，研究自冷凝CO2跨临界动力循环优化运行工况，及与其他主要CO2动力循环的定量化对比评价；研究近临界区CO2跨临界节流特性及优化控制方法。

在太阳能热发电、核能发电，以及新型储能技术领域，以CO2为循环工质的动力循环具有巨大应用潜力。针对CO2跨临界动力循环中，亚临界CO2难以被常规冷却水冷凝的问题，以及超临界CO2布雷顿循环中，超临界CO2稳定、高效、高压比压缩难度大的问题，提出了自冷凝CO2跨临界动力循环。（1）建立了自冷凝CO2跨临界动力循环理论分析模型，以太阳热能为驱动热源，开展了循环性能和运行参数间依变规律的研究，获得了循环优化方法和优化运行参数。进一步地，建立了自冷凝CO2跨临界动力循环实验系统，验证了该循环的实际可行性，研究了运行参数的影响制约规律，重点关注了跨临界节流和跨临界增压过程。在30℃常规冷却水条件下，通过跨临界节流方法，实现了泵前最低5℃的饱和液供给。建立了自冷凝CO2跨临界动力循环、常规CO2跨临界动力循环、常规超临界CO2布雷顿循环等多种动力循环理论分析模型，针对循环性能和循环优势开展了对比评价分析。（2）针对亚临界CO2难以被常规冷却水（30℃）冷凝的问题，亦提出CO2混合工质方案。采用理论分析方法，优化了CO2混合工质跨临界动力循环性能。鉴于碳氢化合物与CO2混合工质的可燃性，分别采用实验研究和理论计算分析，获得了丁烷、异丁烷、丙烷与CO2组成的混合工质的燃烧特性、临界可燃比和CO2对碳氢化合物燃烧特性的影响机理。（3）在“碳中和”背景下，进一步拓展了CO2跨临界热力循环的应用领域，提出了CO2跨临界热力循环储能系统，通过正逆两个CO2跨临界热力循环，构建基于储热的综合储能系统。建立了CO2跨临界热力循环储能系统理论分析模型，以热水为储热介质，盐水为储冷介质，研究了CO2跨临界热力循环储能系统的性能和优化方法。