About this lesson
A gas turbine (Brayton topping cycle) drives a generator, and its hot exhaust is not wasted: it flows through a heat recovery steam generator (HRSG) that raises steam at one pressure level for a steam turbine (Rankine bottoming cycle). Two generators from one fuel supply give much higher efficiency than a gas turbine alone.
How it works
- Air is drawn into the compressor and compressed.
- Fuel is pumped to the combustion chamber and burned in the compressed air; the flame heats the gas.
- Hot gas expands through the gas turbine, driving the compressor and a generator.
- Exhaust gas passes through the HRSG: superheater, evaporator (with steam drum), then economiser, and leaves by the stack.
- High-pressure steam from the superheater expands in the steam turbine and drives a second generator.
- Exhaust steam is condensed, pumped back via the deaerator and boiler feed pump, and returns to the economiser.