Method for operating a combined-cycle power plant, and combined-cycle power plant useful for carrying out the method

A method for operating a combined-cycle power plant, the plant including a gas turbine with a compressor and a turbine, a heat recovery steam generator connected downstream to the gas turbine and configured and arranged to produce steam in a water/steam cycle, and at least one once-through cooler through which flows compressed air when compressed in the compressor and for cooling the gas turbine, and, converts feed water supplied from the heat recovery steam generator into steam, and discharges the steam to the heat recovery steam generator, the method comprising:

• switching the combined-cycle power plant between a single-cycle operating mode, in which only a gas turbine cycle is used for power generation, and a combined-cycle operating mode, in which the gas turbine cycle and the water/steam cycle are used for power generation, without lowering the load of the gas turbine;
• wherein switching to the single-cycle operating mode comprises diverting hot exhaust gases from the gas turbine away from the heat recovery steam generator into a secondary exhaust stack, and simultaneously reducing a feed of feed-water from the heat recovery steam generator and substituting feed-water from another source of feed water;
• and
• wherein switching to the combined-cycle operating mode comprises directing hot exhaust gases from the gas turbine to the heat recovery steam generator, and simultaneously reducing the feed of feed-water from said another source of feed water and substituting feed-water from the heat recovery steam generator;
• and
• wherein said another source of feed-water comprises a separate single-cycle feed-water system.