The Dynamic Performance Study For Low-Temperature Waste Heat ORC Power Generation Set

In order to implement the basic national policy of energy conservation and emission reduction,the recycling of industrial waste heat has broad prospects for development.As a low-grade energy recovery technology,Organic Rankine Cycle(ORC)power generation system has the advantages of wide temperature span,low system evaporation pressure,simple equipment and environment-friendly,and is an efficient low-temperature waste heat recycling technology.Based on the extensive reading of relevant literature,a multi-objective system optimization model for ORC low temperature waste heat generator with 100°C industrial flue gas waste heat was established.The optimal operating parameters were simulated by using simulated annealing algorithm.The dynamic model of ORC low temperature waste heat power plant was established and simulated.The dynamic response of the system was compared and analyzed.The main work and related conclusions are as follows:(1)ORC thermodynamic cycle parameters optimization and working fluid choice.Under the given waste heat condition,a multi-objective optimization model of the system is based on the net generation efficiency of the system,the net present value of unit power and the inverse of hourly heat emission.Taking the evaporation temperature,the condensing temperature,the superheat of the refrigerant at the outlet of the evaporator,and the subcooling degree of the condenser outlet as the decision variables,the circulating parameters are optimized and calculated with the simulated return algorithm.The results of optimization show that for the same kind of organic working medium,the result cannot simultaneously achieve thermodynamics,thermal economics and environmental performance are the best.Finally,selecting R134 a as the circulating medium can make the system have the best overall performance.After selecting the optimal working fluid,the influence of the temperature difference of the heat exchanger pinch on the system evaluation index was analyzed.(2)Establish a dynamic mathematical model of ORC power plant.After the equipment structure is reasonably simplified,the evaporator and condenser are dynamically modeled by the distributed parameter method.The heat exchanger is divided into N heat exchange micro-elements equally,and each heat-exchange micro-element adopts the lumped parameter method,and the differential term of the mass conservation equation and the energy conservation equation within each heat exchange micro-element is backward differentially solves the thermodynamic parameters of the heat exchange element.The steady-state model of the working fluid pump is established by polynomial fitting.The turbine steady-state model is established by using the single stage turbine variable working condition formula.The input and output boundaries of each model are connected in turn according to the working fluid flow direction,and the external input of the cycle is clarified so as to determine the solution flow of the dynamic model.(3)Simulation of system dynamics.Use Matlab to change the thermal system simulation.Under the condition of control variables,the change of performance parameters such as temperature difference,heat load,cooling load,superheat degree,subcooling degree,system efficiency and system power of fluid inlet and outlet in the heat exchanger were compared and analyzed when the input of the cold and heat source changed stepwise.Simulation results show that increasing the heat source temperature or reducing the cold source temperature will increase the thermal load,cooling load,and superheat of the system;the change in the heat source temperature will not have a significant effect on the degree of system subcooling;raising the heat source temperature or reducing the cold source temperature will make the system output power and efficiency increase,lowering the heat source temperature or increasing the cold source temperature will reduce the output power and efficiency of the system.Reducing the cold source temperature will have a greater effect on the output power of the system;when the heat source flow rate and the cold source flow rate change step by 20%respectively,the change of heat source flow and cold source flow has little effect on the circulating parameters of the working fluid.The research results of this paper can provide theoretical reference for system optimization design and operation strategy of industrial flue gas waste heat ORC power plant.