混合工质有机闪蒸循环热力学分析

Thermodynamic Analysis of Organic Flash Cycle With Zeotropic Mixtures

有机朗肯循环(ORC)是将中低品位能源转化为有用功的有效途径。传热过程不可逆损失大是导致ORC系统效率低的重要原因,基于混合工质的有机闪蒸循环(OFC)可以同时优化蒸发器和冷凝器换热过程的温度匹配,有望进一步提升ORC系统效率。本文选取R245ca/cyclopentane、pentane/isohexane等4种混合工质,通过热力学分析对比了200℃的饱和水为热源驱动下的混合工质ORC和OFC性能,获得了混合工质质量分数和热源出口温度对系统效率的影响。发现降低热源温度能显著提高OFC系统效率,而ORC系统存在最优热源出口温度。优化热源出口温度后,混合工质OFC系统效率能与ORC系统相当甚至在一定质量分数范围内超越ORC系统,其中,混合工质neopentane/cyclopentane质量分数为0.6时,OFC最高效率达到46.87%。

Organic Rankine cycle(ORC) is regarded as a promising technique to transform low and medium-grade energy into useful work.The irreversible loss of the heat transfer processes is the major factor leading to the low system exergy efficiency.Organic flash cycle(OFC) with zeotropic mixture working fluid has the potential to optimize the temperature match both in the evaporator and condenser.In the present work,the saturated hot water at 200℃ was used as the heat source to drive the OFC and ORC system.Mixtures such as R245ca/cyclopentane,pentane/isohexane were selected as working fluids.The effect of mixture concentration and outlet temperature of the heat source on the exergy efficiency of the system was analyzed.It is found that the exergy efficiency of the OFC system could be significantly increased by reducing the heat source outlet temperature while it has an optimum heat source outlet temperature for the ORC system.At the optimum heat source outlet temperature,the OFC system with zeotropic mixture working fluid has even higher exergy efficiency than the ORC system.In the reaserch,when the mass fraction of mixed working fluid neopentane/cyclopentane is 0.6,the highest exergy efficiency of OFC can reach 46.87%.