Making the case for cascaded organic Rankine cycles for waste-heat recovery
Making the case for cascaded organic Rankine cycles for waste-heat recovery
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DOI：
10.1016/j.energy.2020.118912
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发表时间：
2020-11
期刊：
影响因子：
9
通讯作者：
M. White;M. Read;A. Sayma
中科院分区：
文献类型：
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作者：
M. White;M. Read;A. Sayma
由于较大的体积膨胀比和低于大气压的冷凝压力，单级有机朗肯循环（ORC）系统的设计可能具有挑战性。级联系统可以实现更高效的膨胀过程、更高的冷凝压力，同时引入两相膨胀以增强性能的可能性。本文的目的是将单级 ORC 系统与新型两相级联系统进行比较，该系统结合了两相膨胀顶部循环和单相底部循环，用于废热回收应用。热力循环模型与可变效率膨胀机模型和离散换热器尺寸模型集成，并完成了三种热源温度（473、523 和 573 K）的单目标和多目标优化研究。结果表明，随着热源温度和相对散热器尺寸的增加，级联系统的相对性能改善也随之增加，并且可以将功率输出和第一定律热效率分别提高高达 11.1% 和 9.5%。多目标优化表明，对于固定的总传热面积，在散热器质量流量为 1 kg/s 的情况下，在 523 K 和 573 K 情况下，级联系统分别比单级系统多产生约 3.6% 和 10.5% 的功率。对于 4 kg/s 的散热器质量流量，该值增加至 11.7% 和 14.5%。
The design of single-stage organic Rankine cycle (ORC) systems can be challenging owing to large volumetric expansion ratios and sub-atmospheric condensation pressures. Cascaded systems could lead to more efficient expansion processes, higher condensation pressures, whilst introducing the possibility of two-phase expansion to enhance performance. The aim of this paper is to compare single-stage ORC systems to a novel two-phase cascaded system that combines a two-phase expansion topping cycle and a single-phase bottoming cycle for waste-heat recovery applications. Thermodynamic cycle models are integrated with variable efficiency expander models and discretised heat-exchanger sizing models, and single- and multi-objective optimisation studies are completed for three heat-source temperatures (473, 523 and 573 K). The results indicate the relative performance improvement of cascaded systems increases as the heat-source temperature and relative heat-sink size increase, and could increase power output and first-law thermal efficiency by up to 11.1% and 9.5% respectively. The multi-objective optimisation reveals that for a fixed total heat-transfer area the cascaded systems produce approximately 3.6% and 10.5% more power than the single-stage systems for the 523 and 573 K cases respectively with a heat-sink mass-flow rate of 1 kg/s. This increases to 11.7% and 14.5% for heat-sink mass-flow rate of 4 kg/s.