Abstract:

Organic Rankine cycle (ORC) is considered as a promising heat-to-power technology for low grade heat recovery. The thermal efficiency of ORC is low and investment cost of equipment is high as temperature of heat sources is low. Low thermal efficiency results in high investment cost of equipment. This work focuses on cutting costs and increasing power generation of ORC and proposes a liquid-separation condensation and two-stage evaporation zeotropic ORC system. Multi-objective optimization using NSGA-Ⅱ is conducted for the BORC, DSORC, STORC and TLORC using zeotropic (R245fa/pentane) or pure fluids (R245fa and pentane). The optimization results indicate that:the net power output of BZORC is 5.6% and 14.0% higher than that of R245fa and pentane when using LINMAP method optimization; LINMAP point shows that the net power output of DSORC is 1.2% and 6.3% higher than that of R245fa and pentane, respectively; Among these four cycle configurations, Pareto Front shows the SIC in TLORC using R245fa/pentane is the lowest, about lower by 5.4% than BORC, while the net power output is 4.86% higher than BZORC.

Key words: thermodynamics, algorithm, optimization, organic Rankine cycle, zeotropic mixture, liquid-separation condensation, dual-pressure evaporation

摘要：

有机朗肯循环（ORC）是一种利用低温余热进行发电的热电转换技术。由于热源温位低，导致其效率不高，设备投资成本高。因此，本文从降低系统成本和提高其热力性能角度出发，把分液冷凝技术运用于双压蒸发的非共沸ORC系统，利用NSGA-Ⅱ多目标算法对基本ORC（BORC），气液分离-双级蒸发ORC（DSORC），串联双级蒸发ORC（STORC）和分液冷凝-双级蒸发ORC（TLORC）四种系统的净输出功和比成本（SIC）进行优化对比。优化结果表明：在BORC系统中，多维偏好线性规划法（LINMAP）优化得出的点表明非共沸工质的净输出功分别要比纯R245fa和纯pentane高5.6%和14.0%。在DSORC系统中，LINMAP点表明非共沸工质的净输出功要比R245fa和pentane分别高1.2%和6.3%；在所研究的四种系统中，Pareto Front表明TLORC系统SIC最低，比BORC系统低5.4%，同时净输出功比BORC系统高4.86%。

关键词: 热力学, 算法, 优化, 有机朗肯循环, 非共沸工质, 分液冷凝, 双级蒸发