Patent ID: 6339926
Filing Date: 2002-01-22
Classification: F01K,F02C,F05D,Y02E,Y02P

Abstract:
A combined power plant, comprising:a gas turbine having at least one hot part that is to be cooled with steam; a multi-pressure heat recovery steam generator generating steam by using exhaust gas from said gas turbine; a steam turbine using, as a power source, steam generated in said multi-pressure heat recovery steam generator; and a system for supplying gas turbine cooling duty steam for cooling the hot part of said gas turbine, comprising: a line, branching off from a steam line for leading high pressure steam turbine exhaust steam from a high pressure section of said steam turbine to a reheater of said multi-pressure heat recovery steam generator, and leading at least a part of the high pressure steam turbine exhaust steam to a gas turbine cooling duty steam supply line; a line, leading intermediate pressure steam from an intermediate pressure superheater of said multi-pressure heat recovery steam generator to the gas turbine cooling duty steam supply line; and a line, branching off from a steam line for leading high pressure steam from a high pressure superheater of said multi-pressure heat recovery steam generator to said high pressure steam turbine, and leading a part of the high pressure steam to the gas turbine cooling duty steam supply line, wherein a temperature lower limit region setting means is provided for setting a lower limit region within an allowable temperature range of gas turbine cooling duty steam for each gas turbine food, said lower limit region having a predetermined range starting from a lower limit of said allowable temperature range, and a control means for controlling steam supply, when the gas turbine cooling duty steam enters the lower limit region, so that a part of the high pressure steam of high temperature is supplied to the hot part of said gas turbine to raise the gas turbine cooling duty steam temperatyre so as to be higher than the lower limit region and to fall within the allowable temperature range whereby gas turbine cooling duty steam, the temperature of which is within the allowable temperature range, is supplied to the hot part of said gas turbine.