Ionita Claudia, Bucsa Sorin, Serban Alexandru, Dobre Catalina, Dobrovicescu Alexandru
Department of Engineering Thermodynamics, University Politehnica of Bucharest, 060042 Bucharest, Romania.
Entropy (Basel). 2022 May 24;24(6):748. doi: 10.3390/e24060748.
The use of organic Rankine cycles (ORCs) is a viable solution for the recovery of waste heat. For an air separation unit (ASU) with a production of V˙O2=58300mN3/h operating in Romania, the value of utilization of the heat transferred to the cooling system of the compression area represents 21% of the global system electrical energy input. To recover this thermal energy and transform it into mechanical energy, an ORC system was proposed. To maximize the production of mechanical power, an exergy analysis was performed. Exergy analysis was used to choose the most suitable organic fluid and find the optimum constructive structure of the Rankine cycle. The calculation of the exergy destruction in the key apparatuses of the system allowed investigation into the optimization search procedure. The large exergy destruction in the liquid preheater suggested the decrease in the temperature difference in this part of the evaporator by increasing the inlet temperature of the liquid; and an internal recuperative heat exchanger was used for this purpose. When permitted, the overheating of the vapors also reduced the temperature difference between the heat source and the organic fluid during the heat transfer process. The analysis was comparatively performed for several organic fluids such as R-245fa, R123, n-pentane and R717. The use of ammonia, that offered the possibility of superheating the vapors at the turbine inlet, brought a gain of mechanical power corresponding to 6% economy in the electrical energy input of the global plant.
采用有机朗肯循环（ORC）是回收余热的一种可行解决方案。对于罗马尼亚一台氧气产量为V˙O2=58300mN3/h的空气分离装置（ASU），传递到压缩区冷却系统的热量利用率占整个系统电能输入的21%。为了回收该热能并将其转化为机械能，提出了一种ORC系统。为了使机械功率产量最大化，进行了火用分析。火用分析用于选择最合适的有机流体，并找到朗肯循环的最佳结构。通过计算系统关键设备中的火用损失，对优化搜索过程进行了研究。液体预热器中火用损失较大，这表明通过提高液体入口温度来减小蒸发器这一部分的温差；为此使用了一个内部回热式热交换器。在允许的情况下，蒸汽过热也减小了传热过程中热源与有机流体之间的温差。对几种有机流体，如R-245fa、R123、正戊烷和R717进行了对比分析。使用氨能够使涡轮机入口处的蒸汽过热，这使得全球工厂的电能输入节省了6%的机械功率。
