Combined cycle electric power plant having a control system which

Abstract

A combined cycle electric power plant includes gas and steam turbines and a steam generator for recovering the heat in the exhaust gases exited from the gas turbine and for using the recovered heat to produce and supply steam to the steam turbine. A condenser is associated with the steam turbine for converting the spent steam from the steam turbine into condensate to be supplied to the steam generator. The steam generator includes a low pressure storage tank, a first heat exchange tube, a boiler feedwater pump for directing fluid from the low pressure storage tank through the first heat exchange tube, a main storage drum, a second heat exchange tube, and a high pressure recirculation pump for directing water from the main storage drum through the second heat exchange tube. An afterburner further heats the exhaust gas turbine gases passed to the first and second heat exchange tubes. Method and apparatus are provided for controlling the transfer of the operation of the steam generator from a WET mode of operation to a DRY mode of operation. In particular, the heat supplied to the gas turbine exhaust gases is reduced, the fluid introduced into the steam generator is cut off, a blowdown valve for directing fluid from the steam generator is opened to further drain fluid therefrom, heat is continued to be supplied to the first and second heat exchange tubes whereby steam is continued to be generated within said generator and directed to the steam turbine, and finally the outlets associated with the steam generator are closed and the steam generator is filled with a suitable non-corrosive fluid such as nitrogen gas.