Thermodynamic analysis and comparison between CO2 transcritical power cycles and R245fa organic Rankine cycles for low grade heat to power energy conversion
Thermodynamic analysis and comparison between CO2 transcritical power cycles and R245fa organic Rankine cycles for low grade heat to power energy conversion
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DOI：
10.1016/j.applthermaleng.2016.06.132
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发表时间：
2016-08
影响因子：
6.4
通讯作者：
L. Li;Y. Ge;Xiang Luo;S. Tassou
中科院分区：
文献类型：
--
作者：
L. Li;Y. Ge;Xiang Luo;S. Tassou
本文从理论上研究和比较了CO2跨临界动力循环（T-CO2）和R245 fa有机朗肯循环（ORC）利用低品位热能产生有用的轴功率或电能的性能。每个动力循环由典型的朗肯循环部件组成，例如工作流体泵、气体发生器或蒸发器、具有发电机的涡轮机、空气冷却冷凝器和同流换热器（内部热交换器）。两个循环的热力学模型已经开发，并应用于计算和比较在不同的操作条件和控制策略的循环热效率和火用效率。仿真结果表明，两种循环的系统性能随工况的不同而不同。当热源（废热）温度从120 °C增加到260 °C，散热器（冷却空气）温度从20 °C降低到0 °C时，R245 fa ORC和带同流换热器的T-CO2的热效率都可以显著提高。另一方面，R245 fa ORC和T-CO2火用效率随着散热器温度的降低而增加，并且通常随着热源温度的升高而降低。此外，在相同的运行条件和传热假设下，R245 fa ORC的热效率和火用效率均略高于T-CO2。然而，在特定的操作条件下，通过在每个系统中安装同流换热器，可以提高两个循环的效率。最终，可以预测最佳操作状态，特别关注两个循环的工作流体膨胀机入口压力。
In this paper, a theoretical study is conducted to investigate and compare the performance of CO2transcritical power cycles (T-CO2) and R245fa organic Rankine cycles (ORCs) using low-grade thermal energy to produce useful shaft or electrical power. Each power cycle consists of typical Rankine cycle components, such as a working fluid pump, gas generator or evaporator, turbine with electricity generator, air cooled condenser and recuperator (internal heat exchanger). The thermodynamic models of both cycles have been developed and are applied to calculate and compare the cycle thermal and exergy efficiencies at different operating conditions and control strategies. The simulation results show that the system performances for both cycles vary with different operating conditions. When the heat source (waste heat) temperature increases from 120 °C to 260 °C and heat sink (cooling air) temperature is reduced from 20 °C to 0 °C, both thermal efficiencies of R245fa ORC and T-CO2with recuperator can significantly increase. On the other hand, R245fa ORC and T-CO2exergy efficiencies increase with lower heat sink temperatures and generally decrease with higher heat source temperatures. In addition, with the same operating conditions and heat transfer assumptions, the thermal and exergy efficiencies of R245fa ORCs are both slightly higher than those of T-CO2. However, the efficiencies of both cycles can be enhanced by installing a recuperator in each system at specified operating conditions. Ultimately, optimal operating states can be predicted, with particular focus on the working fluid expander inlet pressure for both cycles.