How Combined Cycle Power Plant work (Video)

A combined cycle power plant is defined as a plant that employs more than one thermodynamic cycle. An example is combining a gas turbine and a steam turbine in an electric generation plant. The heat lost during production of power from the gas turbine is used to drive the steam turbine.

Combined Power Plant Cycle

A combined power plant cycle integrates two different thermodynamic cycles, typically a gas turbine cycle and a steam turbine cycle, to maximize efficiency in generating electricity.

1. Gas Turbine Cycle

The gas turbine cycle operates as follows:

• Compression: Air is drawn into the compressor and compressed, increasing its pressure and temperature.
• Combustion: Fuel is injected and ignited in a combustion chamber, where it mixes with the compressed air and undergoes combustion, producing high-temperature, high-pressure gases.
• Expansion: The hot gases expand through the turbine, driving it and producing mechanical work. This work is used to drive the compressor and often an electrical generator.
• Exhaust: The exhaust gases, still at high temperature and pressure, exit the turbine.

2. Steam Turbine Cycle

The steam turbine cycle utilizes the waste heat from the gas turbine cycle to produce additional power:

• Heat Recovery: The high-temperature exhaust gases from the gas turbine are used to generate steam by heating water in a heat recovery steam generator (HRSG).
• Steam Expansion: The steam produced in the HRSG is directed to a steam turbine, where it expands, driving the turbine and generating additional mechanical work.
• Electricity Generation: The steam turbine is coupled to an electrical generator, producing more electricity from the recovered heat.
• Condensation: The steam, after expanding through the turbine, is condensed back into water and fed back into the HRSG to repeat the cycle.

By combining these cycles, a combined power plant maximizes efficiency by utilizing both the high-temperature exhaust gases from the gas turbine and the additional energy extracted from the steam turbine, resulting in higher overall electricity production compared to individual cycles.