Multi-objective Optimization Of Organic Rankine Cycle Based On Genetic Algorithm

Organic Rankine Cycle(ORC),as a new type of low-temperature waste heat recovery technology,has the advantages of simple structure,high efficiency,and environmental friendliness.It is of great significance to energy conservation,emission reduction,and environmental protection.The ORC system needs to take the thermal performance,economic performance,and environmental performance into comprehensive consideration in actual operation.In this paper,the multi-objective optimization of organic Rankine cycle has been studied by genetic algorithm,and the influence of the temperature of the heat source and the properties of the working substance on the overall performance of the system and optimum operating parameters have been analyzed,which has provided a theoretical basis for the application of organic Rankine cycle.The main work and conclusions of the paper are as follows:1)With the goal of thermal efficiency,payback period and the annual reduction of equivalent carbon dioxide,a multi-objective optimization model of the basic organic Rankine cycle has been established.The evaporation pressure,pinch temperature difference and superheat degree of the system have been optimized by the genetic algorithm.The entropy weight method and grey correlation method have been used to make the decision on the Pareto obtained by the optimization and determine the optimal operating parameters of the system.The results show that when the temperature of heat source is 450K,the optimal evaporation pressure of R245ca is 1500.00kPa,the pinch temperature difference is 5.09K,and the superheat degree is 5.01 K,and the corresponding thermal efficiency is 14.00%,the payback period is 2.77 years,and the annual reduction of equivalent carbon dioxide is 2.98 x 106 kg.The thermal efficiency increases with the increase of the evaporation pressure,the payback period decreases with the increase of the evaporation pressure,and the annual emission reduction increases with the increase of the evaporation pressure.The pinch temperature difference and superheat have great effect on the objective function,and the change of it is small.The pinch temperature difference is about 5K,and the superheat is about 5.5K.2)Based on the multi-objective optimization model,the effects of heat source temperature and working fluids substance properties on the comprehensive performance of the BORC system have been studied.The results show that twelve kinds of working fluids are selected,the R142b has the best overall performance when the heat source temperature is 420K～440K,and the overall performance of R114、R245fa、R1233zd、RE245fa2 is best when the heat source temperature is 450K～480K.Thermal efficiency and the annual reduction of equivalent carbon dioxide increases with the increase of heat source temperatures,and the payback period decreases with the increase of heat source temperature.There is heat source temperature that most closely matches for different working fluids,and the optimal heat source temperature depends on the boiling point of the working fluids.3)Firstly,a multi-objective optimization model of dual loop organic Rankine cycle(DORC)has been established.And then multi-objective optimization studies have been carried out.Finally,the working fluids of the system have been screened.The research results show that the thermal efficiency of DORC system increases by 5.4%,the payback period increases by 21.18%,and the annual the annual reduction of equivalent carbon dioxide increases by 15.36%when compared with BORC system.Comparing the comprehensive performance of the twelve kinds of working fluids,the comprehensive performance of R114 is optimal.The optimal evaporation pressure of the system is inversely proportional to the boiling point of the working fluids.When different working fluids are used is better than used same working fluids in the high and low temperature cycle in the DORC system,the thermal efficiency increases by 8.8%,the payback period decreases 11.8%,and the annual reduction of equivalent carbon dioxide increases by 15.36%.R114 and R21 are used in low temperature cycle,and the comprehensive performance of the DORC system is the best when RE245fa2 is selected at the high temperature cycle.