Improving operation flexibility of the gas turbine through coolant intercooling and air injection using a sub-compressor

The use of renewable energy, particularly solar and wind power, is increasing, but it is necessary to alleviate the variation of such resources, a key drawback of using renewable energy. In this context, gas turbines capable of fast startup and rapidly changing power following a load have attracted considerable attention. Nevertheless, enhancing the operational flexibility of gas turbines is crucial to ensure their stable operation under various conditions. Several studies have attempted to enhance the flexible operating capabilities, by examining the operational stability assurance under a variety of conditions and life cycle increases by changing the operating conditions. This paper proposes a new gas turbine configuration and operating strategy in which a sub-compressor is used to increase the ramp rate and mitigate the thermal load of the turbine blades. The performance and dynamic behavior of the novel gas turbine was simulated using an in-house program based on the gas path analysis. Specifically, a sub-compressor with an inter-cooler was used to cool the coolant from 398 °C to 300 °C, which increased the gas turbine power by 1.3 MW and efficiency by 0.4%p compared to the conventional gas turbine. In addition, when applying a new operating strategy during the ramp-up phase, a part of coolant air was injected into the combustor to suppress the maximum turbine inlet temperature by 15 °C compared to the conventional gas turbine. As a result, the ramp rate could be doubled (from 18.75 to 37.5 %/min) by alleviating the fluctuations of hot gas temperature in the ramp-up phase. • A novel coolant inter-cooling and injection method using a sub-compressor is proposed. • The new method increases thermodynamic performance of the gas turbine. • Air injection schedule was optimized in the ramp-up phase. • Optimal air injection reduced the maximum turbine temperature in the ramp-up phase. • Even at a high ramp rate, the temperature rise of hot parts was alleviated.