4. Operating phases

4.1 Start

Depending on whether or not the combined-cycle power plant is equipped with a flue gas bypass system, the start-up sequence is different, but the preparation of the equipment follows a common logic.

While the combustion turbine is designed to reach its nominal characteristics (temperature, speed, power) in a very short time (< 30 min), the same cannot be said of the steam turbine recovery boilers and the cold source. The water-steam cycle requires thermal conditioning of piping, valves, exchangers and turbine, which can only take place in the presence of steam. In addition to the thermal conditioning phase, there are other steps involved in preparing the equipment to perform its function when required.