Combined gas and steam (COGAS)

Combined gas and steam (COGAS) is a marine combined-cycle plant in which a gas turbine drives the ship or a generator, and its hot exhaust passes through a heat-recovery steam generator to raise steam for a steam turbine that produces extra shaft or electrical power. Recovering the gas-turbine exhaust heat lifts overall thermal efficiency well above a simple-cycle gas turbine, toward 45 to 50 percent. COGAS suits LNG carriers and fast vessels where gas-turbine power density and clean distillate or boil-off gas firing are wanted. It parallels land combined-cycle practice, adapted to the space, motion, and redundancy constraints of a ship.