Energy recovery and steam supply for power augmentation in a combined cycle power generation system

A combined cycle power generation system comprising:

• a steam turbine;
• a combustion turbine including a compressor, a combustion chamber and a gas turbine;
• a HRSG comprising (i) an evaporator coupled to receive condensate from the steam turbine, and (ii) a superheater coupled to receive output from the evaporator, the HRSG configured to generate steam for the steam turbine with thermal energy received from the combustion turbine;
• a flash tank positioned to (i) receive water heated in the HRSG, (ii) output a first portion of the received water as steam input to the combustion chamber of the combustion turbine, and (iii) output a second portion of the water;
• a flow line connected to pass the steam from the flash tank to the combustion chamber of the combustion turbine in order to selectively provide power augmentation;
• a water tank for receiving relatively cool replenishing water for input to the steam turbine system and thereby compensate for a deficiency in working fluid resulting from diversion of steam to the combustion chamber for power augmentation;
• and
• a heat exchanger coupled to receive the water output from the flash tank and configured to receive and heat the relatively cool replenishing water from the water tank with the water output from the flash tank, wherein the heat exchanger is coupled to provide the heated replenishing water to the steam turbine.

A method of operating a combined cycle power generation system having a combustion turbine, a steam turbine system and a HRSG for transferring sensible heat from exhaust gases of the combustion turbine to the steam turbine system, comprising:

• separating moisture from a first supply of saturated steam produced at a relatively high pressure in the HRSG to provide a source of water;
• flashing a portion of the water in a flash tank to generate a second supply of steam at a lower pressure than the first supply of steam;
• selectively providing the second supply of steam to a combustion chamber of the gas turbine to provide power augmentation in the combined cycle power generation system;
• providing an unflashed portion of the water from the flash tank, as relatively hot liquid, to a heat exchange device to transfer heat present in the water to relatively cool make-up water and inputting make-up water to the steam turbine system to compensate for a deficiency in working fluid resulting from diversion of steam to the combustion chamber for power augmentation.