Thermodynamic Study Of Gas Turbine Waste Heat Utilization System Based On CO₂ Brayton Cycle

In the process of converting fossil energy into electric energy,a large amount of energy is often released to the environment in the form of waste heat,which needs to be utilized to reduce energy consumption.With its unique advantages,the S-CO₂Brayton cycle has the possibility to replace the steam Rankine cycle in the field of waste heat power generation technology,but it is still necessary to explore the mutual conversion of heat source utilization and degree of recovery in the process of waste heat utilization from the perspective of system heat recovery.relation.Firstly,the waste heat utilization coupling is carried out for the no-regeneration cycle in which the exhaust gas from the turbine is directly discharged to the environment,which produces less output work.Then,five common basic cycles based on compression recuperation were studied.CO₂ fluids preheated by different recuperation degrees raised the lower limit of heat absorption and restricted the release of heat energy from flue gas.Aiming at this problem,the flue gas cooling（FGC）method can be used to increase the endothermic range and improve the performance of the system slightly by using the relatively low temperature CO₂ in the system.However,the heat exchange efficiency of the regenerator cannot be increased indefinitely,and the five cycle performances eventually approach the partial heating cycle.Further,the use of low temperature turbine split flow can replace the heat recovery degree in the high temperature regenerator by the external heat source,weaken the heat recovery degree,and initially realize the efficient utilization of the flue gas heat source.Secondly,exergy economic analysis is introduced,focusing on the recompression cycle with the highest recuperation degree and the partial cooling cycle with similar structure,so as to test the feasibility of the improvement plan.The results showed that the improved scheme optimizes the exergy loss of each component inside the system and significantly reduces the cost per kilowatt-hour,but increases the heat exchange area of the system heat exchange equipment,which is not conducive to the compactness of the system.After that,the temperature and pressure sensitivity analysis of the improvement scheme was carried out.The results showed that increasing the temperature of the main gas will increase the degree of internal heat recovery in the system,and the efficiency of the improved part of the cooling cycle will be more significantly improved.The performance can exceed the improved recompression cycle at 620^oC,reflecting the better waste heat utilization potential.Increasing the pressure will enhance the heat-power conversion capacity of the system,and the efficiency of the improved recompression cycle will be more obvious at this time;at 30MPa,the performance of the two improved cycles reaches the maximum difference,reflecting a better heat-power conversion capacity.In the field of waste heat utilization,the effects of temperature and pressure are reasonably coordinated according to the structural characteristics of the bottom cycle,and the coordination of heat input,system heat recovery and thermal power conversion can achieve the purpose of efficient utilization of flue gas waste heat.Finally,starting from different flue gas heat sources to explore the relationship between heat sources and circulation,the results show that when the difference between the main gas temperature and the flue gas temperature is greater than 229^oC,the efficient utilization of flue gas heat can be achieved by FGC;When the temperature difference is less than 229^oC,the degree of recuperation brought by the temperature of the main gas will hinder the heat input of the flue gas heat source;the addition of the intercooling process can reduce the initial temperature of CO₂ heat absorption,and can slightly increase the temperature of the main gas and thus improve the thermal efficiency of the cycle.This can achieve the purpose of reducing the temperature difference boundary.