PURPOSE:To prevent a rotor from being subjected to excessive thermal stresses by raising the vapor temperatures at the outlets of the superheater and the reheater of a waste heat recovery heat exchanger at a rate lower than a value allowable to a steam turbine during the period from the start to the rated operation. CONSTITUTION:Upon the start of a complex power plant, a temperature setting device 32 works, vapor temperatures of a superheater 12 and a reheater 13 are monitored with inlet side vapor temperature detectors 27, 29, cooling water flow rate adjusting valves 25, 26 are controlled so that the outlet vapor temperatures of the superheater 12 and the reheater 13 are below set values changed according to main vapor conditions and others, and temperature reducers 21, 22 work. As a result, the temperatures, at the outlets of the superheater 12 and the reheater 13, of superheated vapor supplied to a steam turbine 4 are controlled to rise at a rate lower than the value allowed to the steam turbine 4. This prevents the steam turbine device from being subjected to excessive thermal stresses.
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