Thermodynamic Cycle Optimization Based On Comprehensive Utilization Of Hot Dry Rock Energy

With the “Carbon peaking and Carbon neutrality” target put forward,the development of clean energy and renewable energy is imminent.Hot dry rock is a clean renewable energy source with abundant reserves,so it has great potential for development.Based on the development and utilization of Hot dry rock energy,this paper constructed subcritical double-pressure Organic Rankine Cycle(SDPORC),supercritical double-pressure Organic Rankine Cycle(SSDPORC)and comprehensive utilization system;constructed thermodynamic model,economic model and multiobjective optimization model by MATLAB and REFPROP.The thermodynamic analysis,economic analysis and multi-objective optimization calculations were carried out for the constructed systems;the optimal solutions for different organic working fluids at different heat source temperatures under different optimization methods were determined.The conclusions are as follows:(1)The thermal efficiencies of R601,R601 a and R600 were improved by3.45%,2.73% and 0.79%,respectively,when the heat source temperature was increased from 130℃ to 200℃ with the maximum net output power as the target.When the heat source temperature was increased from 130℃ to 180℃,the thermal efficiency of the system slightly improved when R1234 ze was used as the working fluid,and began to decrease when the heat source temperature was greater than 180℃.(2)In the SDPORC and SSDPORC,the proportion of the system investment cost is from the highest to the lowest in the order of turbine,evaporator,condenser and pump.In the comprehensive utilization system based on SDPORC and SSDPORC,the proportion of system investment cost is from the highest to the lowest in the order of heat exchanger,turbine,compressor and pump.And the system parameters of the optimal solutions were compared and analyzed.The conclusions are as follows:(1)When the heat source temperature is 150℃ and using the LINMAP method.The investment cost of the SSDPORC is 26.95% higher than that of the SDPORC and the net present value of the SSDPORC is 13.94%higher than that of SDPORC,when R601 and R1234 ze are used in SDPORC and SSDPORC,respectively.Using the TOPSIS method,the investment cost of the SSDPORC is 33.08% higher than that of the SDPORC,and the net present value is21.98% higher than that of the SDPORC.By comparing the LINMAP method and TOPSIS method,it can be found that the investment cost required for the optimization result of LINMAP method is lower than that of TOPSIS method,but its net present value and net output power are smaller than the optimal solution obtained by TOPSIS method,and the payback period is longer.(2)The suitable cycle structure and organic work fluids differ at different heat source temperatures and different objectives.In the target of maximum net output power as an example: when the heat source temperature is lower than 137.5℃,the net output power of the combination of SDPORC +R1234ze is maximum;when the heat source temperature is between 137.5℃ and182.0℃,the net output power of the combination of SSDPORC + R1234 ze is maximum;when the heat source temperature greater than 182.0℃,the net output power of the combination of SSDPORC + R600 is the largest.(3)When the heat source temperature is less than 142.13℃,SSDPORC-CCHP with R1234 ze has an overall advantage in net output power,heating capacity and cooling capacity;when the heat source temperature is greater than 142.13℃ and less than 170.0℃,SSDPORC-CCHP with R1234 ze has an overall advantage in net output power,heating capacity and cooling capacity;When the heat source temperature is greater than 170.0℃,SSDPORC-CCHP with R600 has an overall advantage in net output power,heating capacity and cooling capacity.