Steam attemperation circuit for a combined cycle steam cooled gas turbine

A reheat steam cycle configuration for a steam turbine and gas turbine combined cycle system comprising:

• a steam turbine connected to a load;
• a condenser for receiving exhaust steam from the steam turbine and for condensing said exhaust steam to water;
• at least one heat recovery steam generator for receiving water from said condenser and for converting said water to steam for return to said steam turbine;
• at least one gas turbine for supplying heat to said heat recovery steam generator in the form of exhaust gases;
• wherein said at least one heat recovery steam generator includes a reheater of receiving cold reheat steam from the steam turbine and superheater for receiving high pressure steam from a high pressure evaporator within said heat recovery steam generator, said superheater having first and final passes at opposite ends with one or more intermediate passes therebetween, and wherein said cold reheat steam and said high pressure steam flow in a direction opposite to that of said exhaust gases from said gas turbine, said final pass of said superheater being located within said heat recovery steam generator where gas turbine exhaust gas temperatures are highest, and wherein an attemperating conduit extends outside said heat recovery steam generator and connects said opposite ends of said superheater so as to introduce cooler superheated steam from said first pass into said final pass of said superheater.

A method of controlling temperature of superheated steam in a heat recovery steam generator which includes at least one evaporator and a superheater having first and second opposite ends thereof and one or more intermediate passes therebetween, the method comprising the steps of:

• a) extracting superheater steam from the first end of the superheater in the heat recovery steam generator adjacent said at least one evaporator;
• b) conducting the extracted steam outside the heat recovery steam generator;
• and
• c) reintroducing the extracted steam into the heat recovery steam generator at the second end of said superheater.