OCGT

Open Cycle Gas Turbine (OCGT) is a type of gas-fired power plant in which compressed air is mixed with fuel and combusted, and the high-temperature expansion of the gas through a turbine produces electricity. The exhaust is discharged directly to the atmosphere, and no heat recovery steam generator is used. Most OCGT plants burn natural gas, though some can operate on liquid fuels.

Because there is no exhaust heat recovery, OCGT plants have relatively low thermal efficiency compared with combined-cycle plants. Typical net efficiencies for simple-cycle OCGTs range roughly from 30 to 40 percent, depending on size and technology. They have simpler, lower capital costs and fewer components, which makes them well suited for fast deployment. OCGTs also offer rapid start and high ramp rates, enabling them to respond quickly to changes in demand or renewable generation. Start times can be on the order of minutes, and ramp rates may be tens of megawatts per minute for large units.

Common applications include peaking power, grid support, contingency or backup generation, and capacity markets. Developments in aeroderivative designs have improved part-load efficiency and responsiveness. Modern units are often deployed for quick response to volatility in supply and demand, and some OCGTs are designed to be used in simple-cycle configurations or integrated with additional equipment to form combined-cycle plants.

Environmental considerations focus on combustion emissions, particularly nitrogen oxides. Emissions are mitigated in many installations by advanced combustors and, where applicable, selective catalytic reduction. OCGTs remain favored for their speed, flexibility, and relatively low capital cost, despite lower efficiency compared with other gas turbine configurations.