Introduction

Neither the gas turbine nor the steam turbine is the most efficient heat engine burning fossil fuels. At the time of writing, the crème-de-la-crème of either prime mover is at low 40s in thermal efficiency (as a percentage). That distinction belongs to the reciprocating, i.e., piston-and-cylinder, internal combustion engines burning natural gas. Presently, best-in-class representatives of that group can claim close to 50% in brake thermal efficiency. However, when combined through a heat recovery boiler, a gas and steam turbine power plant is by far the most efficient and cleanest technology to generate electric power from burning a fossil fuel, i.e., the natural gas. Field-proven performance of the best of the bunch is above 60%. Why this is so is going to become clear when we look at the thermodynamic principles governing the respective cycles of the two prime movers.