Combined cycle electric power plant and a heat recovery steam generator

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 receives the spent steam from the steam turbine for converting it into condensate. The steam generator includes a deaerator for receiving the condensate flow from the condenser and for storing it in a storage portion, a feedwater pump for directing the stored condensate through a first heat exchange tube whereby heat is transferred from the gas turbine exhaust gases to the fluid, a main drum for receiving and storing the heated fluid and a second heat exchange tube for heating the fluid by the gas turbine exhaust gases into superheated steam to be supplied to the steam turbine. A water make-up system is associated with the condenser and includes a water make-up storage tank, a return valve for extracting condensate from that supplied to the deaerator for storage in the water make-up storage tank, and a make-up valve for returning water from the water make-up storage tank into the condenser. Fluid level control is provided for maintaining the fluid level within a hotwell storage portion of the condenser, and within the storage portion of the deaerator, by controlling the position of the condensate valve. In particular, the fluid level control is responsive primarily to a measurement of the superheated steam as supplied to said steam turbine and in particular to a difference signal between the flow of superheated steam to said steam turbine and the condensate flow to said deaerator for the control of the position of the condensate valve, and secondarily, to measurements of the fluid level within the deaerator storage portion and the hotwell storage portion to trim the effect of the aforementioned difference signal upon the position of the condensate valve.