What role does natural gas play in the combined cycle process?

In the combined cycle process, natural gas plays a critical role as a fuel source that is burned in a combustion turbine to generate electricity. When natural gas is burned, it produces high-temperature gases that expand and spin a turbine, which then drives a generator to produce electricity. This is the primary function of natural gas in this system.

Additionally, the waste heat generated from this initial combustion is captured and used to produce steam in a heat recovery steam generator (HRSG). The steam produced then spins a steam turbine, further increasing the overall efficiency of the power generation process. This dual use of energy—first as combustion gas and then in steam form—highlights the effectiveness of the combined cycle system, which can reach efficiency rates significantly higher than simple cycle systems.

In contrast to heating or acting as a coolant, the role of natural gas in this context is integral to directly generating electrical energy through mechanical movement in turbines. Thus, the correct answer directly reflects how natural gas contributes to the conversion of thermal energy into mechanical and subsequently electrical energy in the combined cycle power generation process.