【作者】 顾伟；

【导师】 翁一武；

【作者基本信息】 上海交通大学 ， 动力工程及工程热物理， 2010， 博士

【摘要】 有机物朗肯循环(Organic Rankine Cycle, ORC)系统可回收利用如工业废热、太阳能热、地热、生物质热等各种类型的中低品位热能用于发电,同时具有效率高、结构简单、环境友好等优点,因此能在节能减排中起到重要的作用。本文对低品位热能利用有机物朗肯循环系统及其关键设备进行了理论分析,并且研制了1kW低品位热能利用有机物朗肯循环实验装置,最大输出电功率达到1.1kW。本文的主要研究内容如下:1完成了有机物朗肯循环系统热力模型的分析和计算。给出了用于有机物朗肯循环的有机物工质的干湿性等各种性质,比较了有机物工质与水工质在回收低品位热能上的区别,认为有机物工质具有工质干性、工作压力合适、焓降低等优点。其次,研究了不同工作参数下有机物朗肯循环的热力性能,认为过热温度对提高有机物朗肯循环第一定律效率影响不大,而蒸发压力的影响较大。然后,本文对比研究了再热、回热以及抽气回热对有机物朗肯循环的影响,认为再热可以提高低品位热能利用有机物朗肯循环系统净输出比功。2分析研究了低品位热能利用ORC系统不可逆损失最大的设备—蒸发器的稳态与动态特性。蒸发器包括预热、沸腾及过热三个过程,本文以单级逆流型蒸发器为例,采用研究蒸发器的温度分布、熵以及火用效率的方法,给出了蒸发器的性能分析。结果认为,蒸发器不可逆损失包括内部不可逆损失和外部不可逆损失两部分。蒸发压力的增加会使得内部不可逆损失减小,而外部不可逆损失增加,从而使得蒸发器的熵增随蒸发压力的变化存在最小值,而理论分析指出此熵增最小值同时也是蒸发器火用效率的最大值。对蒸发器的动态研究,首先建立了蒸发器的偏微分方程组,对此偏微分方程空间方向采用差分人工离散,而时间方向利用MATLAB Simulink的S函数进行求解,最终得到了蒸发器动态变化规律。对涡旋式膨胀机进行了理论研究与分析。根据涡旋式膨胀机的理论分析和几何建模,给出了该种膨胀机膨胀比的计算方法,各状态参数在膨胀过程中的变化情况,以及各种不可逆损失对膨胀机的影响。3提出以热回收效率而不是循环效率来评价低品位热能利用有机物朗肯循环系统的性能。由于热源流体与有机物工质存在换热不充分的现象,热源流体在离开系统排入环境时仍有一定做功能力,因此采用热回收效率能更准确反应低品位热能利用ORC系统的性能。本文给出了理想的低品位热能利用动力循环系统所能达到的最大热回收效率,同时,还证明了热回收效率分析与熵增分析具有某种意义上的等价性。然后,本文给出了低品位热能回收ORC系统的热回收效率随工作参数的变化情况,发现热回收效率随着蒸发压力的变化存在最大值,同时在此蒸发压力下熵增最小。然后,本文以有机物朗肯循环回收熔融碳酸盐燃料电池—燃气轮机尾气排热为例说明了ORC系统在回收低品位热能方面的作用,发现ORC系统能提高复合循环系统效率3.8个百分点。4在国内首次研制成功了1 kW级低品位热能利用有机物朗肯循环发电系统实验装置,并对有机物朗肯循环系统进行了实验研究。系统以异丁烷为工质,以80℃-100℃的热水模拟为热源,采用涡旋式膨胀机,发电功率达到1.1kW,最大第一定律效率达到2.9%。实验装置的建立为以后大功率有机物朗肯循环的规模化利用奠定了良好的基础。5分析了蒸发器和膨胀机的实验数据结果。蒸发器的实验数据结果分析表明,蒸发器的火用效率受蒸发压力影响较大。而膨胀机的实验结果表明,膨胀机的转速受其入口体积流量影响较大,实验中膨胀机最高转速4828rpm,最高效率0.501。由于实验设备的限制,实验系统的效率低于理论结果,但是系统的实验结果与理论分析其变化趋势基本相符。6对整个系统的实验数据分析发现,蒸发压力和工质流量存在一个最佳值,使得系统输出功率最大,其原因是由于在较高的蒸发压力或工质流量下,膨胀机入口存在气液两相的现象。不同热源温度下的测试则发现最佳蒸发压力或工质流量随热源温度的增加而增加。第一定律效率也发现了同样的最大值现象,其原因与输出功率最大值的原因类似。更多还原

【Abstract】 Organic Rankine Cycle (ORC) is an effective technique to generate power from low and medium temperature heat source, including industrial waste heat, solar heat, geothermal and biomass etc. Advantages of ORC are high efficiency, simple system, environment friendly, and so on. This work presents the theoretical analysis of Organic Rankine Cycle, as well as experiment study. The experiment system is the first 1kW experiment ORC project in China, and the maximum power of this system achieves 1.1kW. Detail of this work is as follows:1 Performance of simple Organic Rankine Cycle was presented in this work. Properties of working fluid, including isentropic properties, were firstly presented and analyzed. The difference between organic fluids and water was showed by a sample calculation, the result shows that the advantages of organic fluids is dry expansion process, proper system pressure, low enthalpy drop. Then, performance of ORC under different working parameters was showed, one of the most important result is that first law efficiency is a weak function of superheat temperature. This work also studied the effect of reheat ORC, regenerative ORC, and the result proves that ORC with reheat can improve the output power of waste heat recovery ORC system.2 Evaporator, which generates the highest irreversibility in ORC system, is analyzed by both static and dynamic model. The process of an evaporator includes preheating, boiling and superheating. A single stage counter flow evaporator was studied by its temperature distribution, entropy generation and exergy efficiency. The result shows that irreversibility of evaporator includes both internal and external irreversibility. The increasing of evaporating pressure decreases the internal entropy generation, but increases the external entropy generation. So a minimum entropy generation exists, which is also the maximum exergy efficiency for evaporator. Partial differential equations were established to describe the dynamic model of evaporator. The equations were dispersed in the space direction manually, and solved by S function of Matlab simulink. Theoretical analysis of scroll expander was presented according to geometrical study. The expansion ratio was firstly calculated. And then the change of status parameters during the expanding process was studied. At last their irreversible loss of expander is presented.3 Heat recovery efficiency describes the performance of waste heat recovery ORC system better than cycle efficiency. The reason is that waste heat flow can not transfer its all exergy to working fluid, so it still has some exergy when leaving evaporator. This process result in external loss, and heat recover efficiency can describe both external loss and internal loss exactly. Ideal heat recovery efficiency for a waste heat recovery system was presented, and it was also proved the equilibrium between maximum heat recovery efficiency and minimum entropy generation rate. The effect of working conditions on heat recovery efficiency was presented, and one of the results shows that heat recovery has a maximum value when changing evaporating pressure. At last, a triple stage hybrid system using MCFC-GT-ORC was treated as an example of waste heat recovery system, and the result shows that an increment of 3.8% can be received by combing ORC system.4 Firstly established a 1kW waste heat recovery ORC system in China. Isobutane was selected as the working fluid of the experimental system, hot water as heat source, and scroll expander as expander. The experimental system was successfully operated, a maximum power of 1.1kW and 2.9% first law efficiency has been received.5 The experiment results were analyzed by studying the performance of evaporator, expander. The testing results of evaporator show that evaporating pressure effects exergy efficiency greatly. The testing results of expander prove that expander’s inlet volume flowrate effects rotating speed of expander greatly. Maximum rotating speed during the experiment is 4828 rpm, and maximum efficiency is 0.501.6 The testing results of whole system show that expander output power has a maximum value when changing evaporating of working fluid flowrate. The reason is the two phase flow entering expander when evaporating pressure and flowrate is high. Detail test proved that the optimum evaporating pressure or fluid flowrate increases with waste heat flow temperature. The maximum cycle efficiency of the testing system is 2.9%. Cycle efficiency also has maximum value, the reason is similar. Maximum heat recovery efficiency is 0.9%, and it also has a maximum value when changing evaporating pressure or working fluid flow rate.更多还原