Review of the operational flexibility and emissions of gas- and coal-fired power plants in a future with growing renewables

This paper reviews operational flexibility and emissions of gas- and coal-fired power plants today and in the future with higher renewables. Six study cases were considered: heavy duty gas turbines in simple and combined cycle, aero-derivative gas turbines, large-scale supercritical coal power plants and small- and mid-scale sub-critical coal power plants. The most critical operational processes and pollutants associated with these plants were identified. Then, data was collected mainly from manufacturers, but also from academic research and grey literature. The data was compared and analyzed. Detailed comparisons of the power plant characteristics as well as the current and future flexibility and emissions are provided. Furthermore, a method to quantify the ability of conventional power plants to back-up renewables and the expected benefits from improved flexibility is proposed and evaluated. Results show that gas-fired power plants are not only more efficient, but also faster and generally less polluting than coal-fired power plants. However, at their respective minimum complaint load, gas plants are less flexible and produced more NOx and CO emissions than coal-fired power plants. Results also show that on average, an improvement of approximately 50% to 100% on power ramp rates, minimum power load, number of major power cycles and emissions for these plants is sought in the future to complement renewables.