Performance Analysis on a Coupled System of Gas Turbine and Air Cycle Driven by the Waste Heat of Flue Gas

In this work, a novel gas-air combined cycle of power generation system is proposed to enhance the generation capability of gas turbines, which uses the Ericsson cycle to transform gas turbine waste energy into a more useful form of energy. In this paper, the temperature-entropy diagram of the combined system is given, and the gas-air combined cycle system is built and simulated. After validation of the simulation, the effects of air flow, ambient temperature, pressure ratio and gas turbine load on the power generation capability and energy utilization efficiency are investigated. The results show that the air circle greatly improves the overall power generation efficiency with the same gas supply. The maximum power generation efficiency of the gas-air combined cycle is 31.95% at the rated load of the gas turbine with an optimized air flow of 14 kg/s, in which the power generation efficiency of the air cycle is 4.47%. The increase of air flow rate can improve the net output power, while the power generation efficiency of air circle and combined circle all increases first and then decreases. As the increase of pressure ratio of compressors, the power generation efficiency increases first and then decreases, while the energy utilization efficiency increases significantly with the decreasing of outlet temperature of smoke from the high-pressure heater and low-pressure heater. The ambient temperature effects on the power generation of the air circle and the combined circle are almost linear. The generation efficiency of the air circle and combined circle are all increased with the increase of gas turbine load. Therefore, under the selection of suitable working conditions, the gas-air combined cycle power generation system can effectively improve the total power generation efficiency and has great potential in waste heat utilization.