Off-Design Analysis of a Supercritical CO₂ Brayton Cycle with Ambient Air as the Cold Source Driven by Waste Heat from Gas Turbine

Utilizing energy efficiently could greatly relieve current energy crisis. Therefore, in this article, a simple supercritical CO₂ Brayton cycle for waste heat recovery from gas turbine is presented. The system uses ambient air as its cold source, which is more convenient and economic. Considering temperature difference between heat source and turbine inlet, it is of great significance to research the effects of turbine inlet temperature on the system performance due to the high temperature range of the exhaust gas from gas turbine. For this purpose, a control strategy is proposed and a mathematical model is established on off-design conditions to predict system performance when turbine inlet temperature increases from 673.15 K to 773.15 K. Results indicate that both turbine power output and system net power output increase with the rise of turbine inlet temperature, as well as total heat transfer in heater and cooler. Furthermore, the system thermal efficiency also increases until it becomes maximum on design point. In addition, the efficiency of turbomachinery varies slightly.