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

A method for operation of a combined-cycle power plant with cogeneration, in which method combustion air is inducted in at least one gas turbine, is compressed and is supplied to at least one combustion chamber for combustion of a fuel, and the resultant exhaust gas is expanded in at least one turbine, producing work, and in which method the exhaust gas which emerges from the at least one turbine is passed through a heat recovery steam generator in order to generate steam, wherein the heat recovery steam generator is part of a water-steam circuit with at least one steam turbine, a condenser, and a feedwater pump, wherein heat is provided by extracting steam from the at least one steam turbine, the method comprising:

• passing a portion of the inducted combustion air through the at least one turbine to the heat recovery steam generator without being involved in the combustion of the fuel in the gas turbine to restrict electricity production while heat provided by the extracting of steam from the at least one steam turbine remains constant, and
• using the portion of the combustion air that is passed through the at least one turbine without being involved in the combustion of the fuel in the gas turbine to operate at least one supplementary firing in the heat recovery steam generator;
• wherein the steam extracted is used in a desalination plant for sea-water desalination, wherein the desalination plant can optionally be operated with low-pressure steam or intermediate-pressure steam, and in that, in order to restrict the electricity production, the operation of the desalination plant is additionally converted from intermediate-pressure steam to low-pressure steam.

A combined-cycle power plant comprising:

• at least one as turbine with a compressor for compression of inducted combustion air, a first combustion chamber for combustion of a fuel using the compressed combustion air, and at least one turbine for expansion of the exhaust gases created during the combustion;
• a water-steam circuit with at least one steam turbine and a heat recovery steam generator through which the exhaust gases which emerge from the gas turbine flow, wherein a capability to extract steam is provided for the steam turbine;
• a controllable bypass provided in the at least one gas turbine, via which a portion of the compressed combustion air is introduceable into the turbine by bypassing the first combustion chamber;
• and
• a supplementary firing is provided in the heat recovery steam generator, in which fuel can be burnt in order to heat the exhaust gases introduced, using the combustion air which is passed via the bypass;
• wherein the combined-cycle power plant has an associated desalination plant, which processes the steam extracted from the steam turbine for sea-water desalination, and in that the desalination plant comprises multiple-effect distillation devices which are supplied with low-pressure steam from the steam turbine;
• and
• wherein each multiple-effect distillation device has an associated thermal vapor compression device, which is operable with intermediate-pressure steam from the steam turbine, and in that the thermal vapor compression devices are designed such that they can be switched off.