Method for operating a gas and steam-turbine plant and plant working according to the method

摘要

A gas and steam-turbine plant includes a waste-heat steam generator downstream of a gas turbine on the exhaust-gas side. The waste-heat steam generator has a high-pressure preheater connected into a water/steam circuit of a steam turbine having a low-pressure part. In order to achieve as high a plant efficiency as possible, a heat exchanger which is disposed outside the waste-heat steam generator has a primary-side inlet connected to an outlet of the high-pressure preheater, a primary-side outlet connected to an inlet of the high-pressure preheater and a secondary side connected into an overflow conduit opening into the low-pressure part of the steam turbine. A method for operating such a plant includes superheating low-pressure steam flowing into the steam turbine by indirect heat exchange with a part stream of preheated feed water extracted from the high-pressure preheater.