Combined cycle with steam cooled gas turbine

Abstract

In a method of operating a combined cycle system including a gas turbine, a steam turbine and a multi-pressure heat recovery steam generator, an improvement includes supplying gas turbine cooling duty steam from a high pressure section of the steam turbine and from an intermediate pressure evaporator in the multi-pressure heat recovery steam generator, conducting the gas turbine cooling duty steam to the gas turbine for cooling hot gas turbine parts, and then returning the gas turbine cooling duty steam to an intermediate pressure section of the steam turbine. In a start-up procedure, steam is extracted from a first pass of a high pressure superheater in the multi-pressure heat recovery steam generator, mixed with steam discharged from the high pressure superheater and then supplied to the gas turbine cooling duty system. In this same start-up procedure, the gas turbine cooling duty steam is returned to the system condenser, bypassing the intermediate pressure section of the steam turbine. Related apparatus is also disclosed.

What is claimed is: 
     
       1. In a method of operating a combined cycle system including a gas turbine, a steam turbine and a multi-pressure heat recovery steam generator, wherein gas turbine exhaust is used in the heat recovery steam generator for reheating steam from the steam turbine, the improvement comprising supplying gas turbine cooling duty steam from a high pressure section of the steam turbine and from an intermediate pressure evaporator in the multi-pressure heat recovery steam generator, conducting the gas turbine cooling duty steam to the gas turbine for cooling hot gas turbine parts, and then returning the gas turbine cooling duty steam to an intermediate pressure section of the steam turbine. 
     
     
       2. The method of claim 1 wherein, early in start-up, prior to the availability of any cooling steam, the gas turbine hot stationary and rotating parts are cooled with filtered compressor discharge air. 
     
     
       3. The method of claim 1 wherein, during start-up, as start-up cooling steam is being established, the start-up cooling steam is bypassed around the intermediate pressure section of the steam turbine to warm the piping and valves. 
     
     
       4. The method of claim 1 wherein, during start-up, steam is extracted from a first pass of a high pressure superheater in the multi-pressure heat recovery steam generator, mixed with steam discharged from the high pressure superheater and then supplied to the gas turbine cooling duty system. 
     
     
       5. The method of claim 1 wherein, during staff-up, the gas turbine cooling duty steam is returned to a condenser, bypassing the intermediate pressure section of the steam turbine. 
     
     
       6. The method of claim 1 wherein the heat recovery steam generator includes a high pressure superheater and wherein the method includes controlling temperature in the high pressure superheater by: a) extracting superheater steam from a first pass of the superheater;   b) conducting the extracted steam outside the heat recovery steam generator; and   c) reintroducing the extracted steam at the inlet of the final superheater, which occurs first in the gas path, ahead of all other HRSG heat transfer surfaces.   
     
     
       7. The method of claim 1 wherein the gas turbine cooling duty steam is mixed with steam from a reheater in the heat recovery steam generator upstream of the intermediate pressure section of the steam turbine. 
     
     
       8. In a combined cycle system including a gas turbine, a steam turbine and a multi-pressure heat recovery steam generator, the improvement comprising means for supplying gas turbine cooling duty steam from a high pressure section of the steam turbine and from an intermediate pressure evaporator in the multi-pressure heat recovery steam generator; means for conducting the gas turbine cooling duty steam to the gas turbine for cooling hot gas turbine pans; and means for returning the gas turbine cooling duty steam to an intermediate pressure section of the steam turbine.   
     
     
       9. The improvement of claim 8 wherein a start-up circuit is provided which includes means for extracting steam from a fist pass of a high pressure superheater in the multi-pressure heat recovery steam generator; means for mixing the extracted steam with steam discharged from the high pressure superheater; and means for supplying the mixed steam to the gas turbine cooling system. 
     
     
       10. The improvement of claim 8 and including means for mixing the gas turbine cooling duty steam with steam from a reheater in the heat recovery steam generator before the gas turbine cooling duty steam is returned to the intermediate pressure section of the steam turbine. 
     
     
       11. The improvement of claim 9 wherein means are provided for returning gas turbine cooling duty steam to a condenser, bypassing the intermediate pressure section of the steam turbine. 
     
     
       12. The improvement of claim 8 wherein the heat recovery steam generator includes a multi-pass superheater and wherein means are provided for controlling temperature in the superheater by extracting steam from a first pass of the superheater, for conducting the extracted steam outside the heat recovery steam generator, and for reintroducing the extracted steam at the inlet end of the final superheater. .Iadd. 
     
     
       13.  In a method of operating a combined cycle system including a gas turbine combined with a steam cycle incorporating a steam turbine and a multi-pressure heat recovery steam generator, wherein gas turbine exhaust is used in the heat recovery steam generator for reheating steam from the steam turbine, the improvement comprising supplying gas turbine cooling duty steam from a high pressure section of the steam turbine and from an intermediate pressure evaporator in the multi-pressure heat recovery steam generator, conducting the gas turbine cooling duty steam to the gas turbine for cooling hot gas turbine parts, and then returning the gas turbine cooling duty steam to the steam cycle; and wherein, early in start-up, prior to the availability of any cooling steam, the gas turbine hot stationary and rotating parts are cooled with filtered compressor discharge air, which, after cooling the gas turbine hot stationary and rotating parts, is discharged to the gas turbine exhaust. .Iaddend..Iadd.14. In a method of operating a combined cycle system including a gas turbine combined with a steam cycle incorporating a steam turbine and a multi-pressure heat recovery steam generator, wherein gas turbine exhaust is used in the heat recovery steam generator for reheating steam from the steam turbine, the improvement comprising supplying gas turbine cooling duty steam from a high pressure section of the steam turbine and from an intermediate pressure evaporator in the multi-pressure heat recovery steam generator, conducting the gas turbine cooling duty steam to the gas turbine for cooling hot gas turbine parts, and then returning the gas turbine cooling duty steam to the steam cycle; and wherein, during start-up, as start-up cooling steam is being established, the start-up cooling steam is bypassed around an intermediate pressure section of the steam turbine to warm the piping and valves. 
     
     
        .Iaddend..Iadd.5.  In a method of operating a combined cycle system including a gas turbine combined with a steam cycle incorporating a steam turbine and a multi-pressure heat recovery steam generator, wherein gas turbine exhaust is used in the heat recovery steam generator for reheating steam from the steam turbine, the improvement comprising supplying gas turbine cooling duty steam from a high pressure section of the steam turbine and from an intermediate pressure evaporator in the multi-pressure heat recovery steam generator, conducting the gas turbine cooling duty steam to the gas turbine for cooling hot gas turbine parts, and then returning the gas turbine cooling duty steam to the steam cycle; and wherein, during start-up, steam is extracted from a first pass of a high pressure superheater in the multi-pressure heat recovery steam generator, mixed with steam discharged from the high pressure superheater and then supplied to the gas turbine cooling duty system. .Iaddend.