Conventional Natural Gas Combined Cycle Power Plant

The process under analysis comprises two thermodynamic cycles: (1) Brayton Cycle; and (2) Rankine Cycle.

Braxton Cycle. In the first cycle, occurred in a combustion turbine, compressed air then runs through a mixing chamber where natural gas is added. The pressurized air and natural gas mixture is then ignited in an expansion cylinder and energy is released. High pressure hot gas from combustion expands through the turbine, spinning rotating blades. The rotating blades then spin a shaft. This cycle is known as Brayton cycle. In the case of the process approached in this report, the shaft is, in fact, a generator that produces electricity.

Rankine Cycle. The waste heat from the gas turbine exhaust is used in a boiler to evaporate high pressure water, forming high pressure dry saturated steam, which expands through a steam turbine, generating electricity. The steam expansion decreases its temperature and pressure, which may cause some condensation. The wet low pressure steam is then condensed at a constant pressure to become saturated water that will be reused in the cycle. This thermodynamic cycle is called Rankine Cycle.

The use of the heat released in the Brayton Cycle as energy to generate the high pressure steam in the Rankine Cycle increases the total energy extracted from the natural gas. This entire process is also called Brayton-Rankine combined cycle.