Research On Integration And Parameter Optimization Of Combined Power Generation System Based On Gas Turbine Waste Heat And Geothermal Energy

The research of geothermal high-efficiency power generation technology and the improvement of industrial flue gas waste heat utilization are significant in adjusting the energy supply and demand structure,improving the comprehensive energy utilization rate,and reducing the environmental pollution.In this paper,we integrate the geothermal double flash system with the supercritical carbon dioxide（S-CO₂）Brayton cycle system to build a co-generation system and optimize the parameters,which can not only realize the full utilization of gas turbine exhaust waste heat but also effectively solve the problem of low power generation due to the low grade of heat source in the geothermal system.Firstly,four combustion turbine waste heat utilization systems are constructed:geothermal double flash,simple reheat S-CO₂,pre-compression S-CO₂,and recompression S-CO₂.The effects of the cycle parameters such as flash pressure,S-CO₂flow rate,pre-compression pressure and shunt ratio on the thermal performance indexes of the four systems are analyzed.The parameters of the four systems are optimized by genetic algorithm to maximize the net output work.The optimization results showed that the maximum net output power of the four systems were 5.24 MW,2.47 MW,2.45 MW and 2.38 MW,respectively;the waste heat utilization efficiency was 59.3%,58.2%,54.6%and 53.3%,respectively,and the net output power and waste heat utilization efficiency of the geothermal system were the highest.To further improve the waste heat utilization of the combustion engine,the geothermal system was integrated with the S-CO₂ system,and three combined systems were constructed:simple S-CO₂+geothermal system,pre-compressed S-CO₂+geo-thermal system and recompressed S-CO₂+geothermal system.The effect of the single-cycle parameter change on the maximum net output work and waste heat utilization efficiency of the system is explored,and the combined syst em’s optimisation direction is indicated.A genetic algorithm was used to optimize the system to find the maximum net output power.The optimization results show that the maximum net output power of the three combined systems are 5.99 MW,6.08 MW and 6.45 MW,respectively,and the waste heat utilization efficiency is 69.3%,69.4%and 68.2%,respectively.The three combined systems have improved the maximum net output power and waste heat utilization efficiency compared with the single geothermal system.The maximum net output power increased by 14.3%,16%,and 23.1%,respectively,and the waste heat utilization efficiency increased by 16.86%,17.03%,and15%,respectively.Finally,the cost-investment models of the three combined systems were established to compare the investment cost,levelized cost of electricity（LCOE）and pay-back period（PBP）of the combined systems at the geothermal reservoir temperatures of 120℃,130℃ and 140℃,respectively.The investment costs of the three combined systems are,in descending order,recompression S-CO₂+geothermal system,pre-compression S-CO₂+geothermal system,and simple reheat S-CO₂+geothermal system for a specific geothermal reservoir temperature.The combined system LCOE and PBP are influenced by the investment cost and the net output work of the system,resulting in different optimal combined systems corresponding to the smallest LCOE and PBP at different geothermal reservoir temperatures.When the geothermal reservoir is 120℃,130℃,and 140℃,respectively,the systems with the smallest LCOE and PBP are simple reheat S-CO₂+geothermal system（0.0529$/kWh,4.98 years）,pre-compressed S-CO₂+geothermal system（0.0519$/kWh,4.86 years）,and recompressed S-CO₂+geothermal system（0.0483$/kWh,4.57 years）.