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.

Description

TECHNICAL FIELDThis invention relates to a combined cycle power generation system in which exhaust gases from a gas turbine are recovered in an unfired, multi-pressure, heat recovery steam generator, and in which steam from the steam turbine exhaust and from the heat recovery steam generator intermediate pressure evaporator is utilized to cool the gas turbine stage 1 and 2 nozzles and buckets.BACKGROUND PRIOR ARTIn typical combined cycle power generation systems, cooling of gas turbine high temperature components and the accompanying steam cycle are usually of the following types:(1) Air Cooled Gas Turbine--The gas turbine high temperature components are cooled by air extracted or conducted from other components in the cycle. The steam cycle and the gas turbine coolant streams are not integrated.(2) Water Cooled Gas Turbine--The gas turbine high temperature components are cooled with water in the liquid phase. The heat extracted from the high temperature gas turbine components is in...

AI Technical Summary

Benefits of technology

A start-up steam supply system is also included which extracts steam from the HP superheater after the first pass and mixes it with steam from the superheater discharge to supply steam to the cooling system at the required temperature. The steam from the IP drum is also used. When the gas turbine is operating with a start-up steam supply, the cooling steam is not admitted to the IP turbine, but instead is bypassed to the condenser through the IP bypass valve and attemperator. The IP bypass valve is modulated to maintain the pressure of the cooling steam above the gas turbine compressor discharge pressure to prevent gas leakage into the cooling steam, and hence the steam cycle.

3. Control of the HP steam temperature is accomplished by the steam attemperation system which bypasses a section of the HP superheater. This system eliminates the potential for contaminants to enter the steam as can occur with attemperation with feed water. Attemperation steam is extracted after it passes through one pass in the superheater to assure that it will be dry after the small pressure drop across the steam control valve. Once the gas turbine cooling system is operating in its normal mode, with cooling steam supply from the IP evaporator and HP steam turbine exhaust, all of the HP steam passes through the high temperature section of the superheater to limit the temperature of the gas entering the reheater.

Problems solved by technology

(1) Air Cooled Gas Turbine--The gas turbine high temperature components are cooled by air extracted or conducted from other components in the cycle. The steam cycle and the gas turbine coolant streams are not integrated.

(2) Water Cooled Gas Turbine--The gas turbine high temperature components are cooled with water in the liquid phase. The heat extracted from the high temperature gas turbine components is integrated with the combined cycle steam bottoming cycle. The energy extracted from the high temperature section of the gas turbine is transported to the low temperature portion of the steam cycle to maintain the water in the liquid phase, thus compromising thermal efficiency of the cycle.

(3) Steam Cooled Gas Turbine Integrated Into a Combined Cycle with Multiple Pressure--This cycle uses steam from the low pressure section of a multiple pressure combined cycle to cool the high temperature components of the gas turbine with energy extracted from the gas turbine returned to the low pressure section of the steam cycle. This system is described in U.S. Pat. No. 4,424,668. The thermal efficiency that can be achieved by this system is inferior to that achievable with this invention, however, because, in the '668 system, energy is transported from the high temperature part of the cycle to a low temperature section of the cycle for conversion of the heat energy to power.

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