中温有机朗肯循环多目标优化及工质筛选

MULTI-OBJECTIVE OPTIMIZATION AND WORKING FLUID SELECTION FOR MEDIUM TEMPERATURE ORGANIC RANKINE CYCLE

为提高有机朗肯循环整体性能,从热力性、经济性和环境性3个方面出发,以系统总投资成本、环境、系统净输出功率、烟气进出口降、系统总不可逆损失构建多目标优化模型。针对523.15 K烟气余热热源,选取戊烷、庚烷、辛烷、葵烷、环己烷、苯、甲苯7种工质为待选工质,利用非支配解排序遗传算法(NSGA2),对亚临界有机朗肯循环(ORC)的蒸发温度和冷凝温度进行优化,采用理想点辅助法从帕累托解集中选出各工质的最优解,得出各工质最优蒸发温度和冷凝温度及相对应的投资回收年限和单位发电成本。结果表明:在给定热源条件下,甲苯具有最优的综合性能。在热源温度大于500 K时,当热源温度上升时,甲苯的最优蒸发温度随之上升,最优冷凝温度几乎不变,单位输出功率的系统总投资成本、改进型可持续发展系数随之减小。

In order to improve the overall performance of the organic Rankine cycle,the multi-objective optimization model is constructed from the perspective of thermodynamic,economic and environmental character. And the total investment cost of the system,the environmental exergy,the net output power of the system,exergy drop of flue gas from inlet to outlet and the total irreversible loss of the system are selected as performance indicators. For the 523.15 K flue gas waste heat source,seven kinds of working fluids including pentane,heptane,octane,decane,cyclohexane,benzene and toluene are chosen from various organic fluids. The evaporation temperature and the condensation temperature of the subcritical organic Rankine cycle(ORC)are optimized by using the non-dominated sorting genetic algorithm(NSGA2). The optimal solution of each working fluid is selected from the Pareto solution with the aid of ideal point method,and the optimal recovery time and unit cost were obtained. The results show that toluene has the best comprehensive performance under given heat source conditions. In a certain range,the optimal evaporation temperature of toluene increases while the optimal condensation temperature almost keeps constant with the increment in heat source temperature. Both the total investment cost of the unit output word of system and th sustainable development coefficient decrease along with the rise of heat source temperature.