Air-cooled gas turbine exhaust casing

Abstract

Cooling air passages are formed in the wall of an exhaust casing connected to a turbine casing of a gas turbine. Low pressure air extracted from the low pressure stage of an air compressor of the gas turbine is supplied to the cooling air passage from the portion near the downstream end of the exhaust casing. Cooling air flows through the cooling air passage toward the upstream end of the exhaust casing and then flows into an annular cavity formed in the turbine casing near the portion corresponding to the last turbine stage. Therefore, the metal temperature of the exhaust casing near the upstream end (near the joint between the exhaust casing and the turbine casing) is lowered by the cooling air and, as cooling air of a relatively high temperature is supplied to the cavity in the turbine casing, the metal temperature of the turbine casing near the downstream end becomes higher than that provided by a conventional cooling system. Therefore, the difference between the metal temperatures of the turbine casing and the exhaust casing becomes very small and the thermal stress exerted on the exhaust casing due to the temperature difference can be largely reduced.

Dependencies are inferred from the claim text.