| According to the energy use principle of"temperature matching and cascade utilization",the application potential of medium and low temperature waste heat power generation technology is huge,and it has broad application prospects in the development and utilization of industrial waste heat and new energy sources.Organic Rankine cycle(ORC)waste heat power generation technology has attracted wide attention from scholars and manufacturers at home and abroad because of its simple structure,safety and reliability,and high thermal efficiency,and a lot of research has been carried out.However,my country’s ORC power generation technology started late and developed slowly.The optimization analysis of ORC system operating parameters and comprehensive performance have important reference significance for engineering applications.Based on the thermodynamic process of ORC,its thermodynamic model and economic model were established.After that,the exergy efficiency and net present value were selected as the objective function,and under the condition of a single variable,the influence of evaporation temperature,superheat,narrow temperature difference and condensation temperature on the objective function were calculated and analyzed.Finally,the genetic algorithm(GA)was used to optimize the objective function with a single objective,and the best parameters for the operation of each working fluid system were obtained,and the working fluids with greater potential were analyzed and compared.The results showed that:each working fluid system should use a smaller condensing temperature when running,and each has an optimal evaporation temperature;except for the working fluids R1234yf and R134a with a lower critical temperature,each working fluid system should be operated with a smaller narrow point temperature difference and superheat;among the selected working fluids,the system exergy efficiency and net present value of R1234ze,R152a and R134a were relatively high,while the exergy efficiency and net present value of the R1234yf system were relatively low.Under constant heat source parameters,when the narrow point temperature difference was 5℃,10℃,15℃,and 20℃,the effects of evaporation temperature and heat source outlet temperature on the objective function were calculated and analyzed respectively.Subsequently,using the nondominant genetic algorithm(NSGA-II),the constant temperature heat source system was optimized with dual objectives,and the results were compared with the single objective optimization results with the objective function of exergy efficiency and net present value.The results showed that the greater the evaporation temperature and the heat source outlet temperature,the smaller the narrow point temperature difference,the higher the system exergy efficiency,the better the thermal performance;the Pareto optimal solution could take into account the thermal performance and economic performance of the system,and was more suitable for practical engineering problems;according to the Pareto optimal boundary solution,the relationship between exergy efficiency and net present value could be fitted,which could be selected according to actual engineering needs.A variable temperature heat source of 120～150℃ was selected,and the effects of heat source inlet temperature,narrow point temperature difference and evaporation temperature on the objective function were calculated and analyzed under the condition that the control parameters of single or multiple variables remained unchanged.Then,the weight coefficients were determined by the Pareto boundary solution and compared with the weight coefficients determined by theαmethod.At the same time,the comprehensive objective function F_x was constructed to optimize the comprehensive performance of the ORC system.The results showed that R1234ze not only has the largest exergy efficiency and net present value,but also its comprehensive performance was much better than that of R245fa and R134a,so it had great application potential.Under the comprehensive economic analysis,when the evaporation temperature was about 88℃,the relationship between the comprehensive performance of R1234ze and R134a changes.The weight coefficients determined byαmethod and Pareto boundary solution were different,but the thermodynamic and economic performance of each working medium had the same bias,and the operating parameters of the optimized system were similar with little error.The comprehensive performance analysis and operating parameter optimization of this article for variable heat source parameters had certain reference significance for engineering applications;according to the dual-objective Pareto optimal boundary solution,the relationship between exergy efficiency and net present value fitted according to the Pareto optimal boundary solution could be selected for reference according to actual engineering needs. |
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