中高温烟气余热动力循环优化研究

Vast quantities of waste heat of initial temperature above 350ºC with exhaust gas as the carrying medium is generated by the industrial processes. Great benefits in economy, energy saving and environments could be realized by effectively recovering power from the waste heat. The perfectness of the existing power cycles and the techno-economics of the systems are limited by the characteristic of the heat addition process and/or the properties of the working fluids. Considering the character of heat releasing process of the waste heat sources (high initial temperature, large temperature decrease, smooth enthalpy- temperature curve, and having acid dew points), the thermal stability of the working fluids, and the general temperature range of heat sinks, we proposed extra-expansion CO2 super-critical cycle and 6 other novel power cycles of high perfectness and tech-economic feasibility. This study conducts its research in optimizing the novel power cycles with respect to the working fluid choices and operating parameters, modifying the cycle designs based on calculation results, exploring more other novel ‘triangular’ power cycle designs, and investigating the upper limit temperature of stability of the working fluids. By the study, the mechanisms and regular patterns related to the cycle optimization could be revealed, and optimal combinations of cycle -working fluid -cycle parameters could be obtained for different initial temperature ranges of exhaust gases. The results could serve as the basis of application researches.

工业过程产生着大量初温在350ºC以上的中高温烟气余热，对其作高效和经济地动力回收利用，具有重要的节能环保和经济意义。现有动力回收系统中应用的或研究中提出的动力循环，其热力学完善度、系统技术经济性受到循环吸热过程特性和/或工质性质的限制。本课题考虑中高温烟气余热源的放热过程特性(初温高、大温降，温-焓曲线光滑，存在酸露点)、工质热稳定性、一般冷源温度条件，通过选择恰当的基础循环和引入相关修正/补充措施，提出了过膨胀CO2超临界循环等7种逼近三角形的循环设计。课题拟对7种循环设计开展循环性能影响机制、工质与循环参数优化和量化考证基础上的改进研究，新的循环构建研究，工质热稳定温度上限研究。期在揭示中高温烟气余热动力循环优化中的相关机理与规律，得到不同烟气进口温度范围上优良的“循环-工质-循环参数”组合。为应用研究提供基础依据。

对工业生产中产生的大量中高温烟气余热作高效和经济地动力回收利用，具有减小化石能源消耗从而缓解能源短缺压力、减少化石燃料燃烧的环境污染和温室气体CO2排放的节能环保意义和经济意义。中高温烟气余热源具有初温高，放热过程温降大、温-焓曲线光滑、烟气换热性能差，存在酸露点等特点；实际应用中或已有研究中提出的动力循环-工质组合，存在循环吸热过程与中高温烟气余热源放热过程温度曲线匹配性不足、工质热力学性质和/或热稳定性与中高温工况匹配性不足、和/或部件效率低、造价高等问题，影响了循环的热力学完善度和系统的技术经济性。本课题尝试通过循环改进设计、工质优选和循环参数优化来改善中高温烟气余热动力系统的技术经济性。就此开展了循环改进设计研究、工质优选和循环参数优化研究，和有机工质热稳定性实验研究、有机工质超临界压力下换热特性实验研究。提出了一系列循环改进设计，并分别以烟气-工质换热温差不过小为前提的单位质量流量烟气的系统净输出功率最大和经济性最优为优化目标，开展了工质优选和循环参数优化研究。得到了不同烟气初温范围上的最优“循环-工质-循环参数”组合，探讨了系统性能优化相关规律。建立了有机工质热稳定性实验系统，以静态容器测试法对几种有机工质开展了热稳定性实验研究，得到了测量结果，分析了有机工质热稳定性影响机理。建立了有机工质超临界压力下的换热实验系统，以R134a为对象物系，实验研究了工质压力、质量流量、热流密度和流向对超临界压力下换热特性的影响，得到了相应的结果和规律，拟合了换热关联式，对实验数据关联精度良好。