Gas Turbines in power generation are frequently of the single rotor type. The rotor is directly connected to the electrical generator. The rotor may be supported by two journal bearings or in some cases there is an additional journal bearing situated between the axial compressor discharge and the gas turbine intake. This third bearing serves to provide the rotor with additional support required to reduce rotor dynamic instabilities. The third bearing is, therefore, inside the machine housing and a significant amount of maintenance work is necessary to inspect it. The third bearing is also exposed to elevated temperatures by, essentially, being surrounded by compressor discharge air. A certain amount of compressor discharge air leaks through the seals into the cylindrical space around the third bearing housing and from there, due to significant pressure gradients, into the third bearing. Labyrinth seals are provided to impede air leakage from the pressurized cylindrical space into the bearing cavity. The air that leaks into the bearing housing mixes with a buffer air stream. This buffer air stream serves to cool the bearing cavity and to prevent leakage of hot, high-pressure air into the bearing cavity. Two dry air streams are then routed into the atmosphere via the coaxial space formed by two cylindrical surfaces. The portion of the buffer air stream contacting the bearing lubricating oil is de-misted in a special de-mister vessel. The de-misted air is exhausted into the atmosphere and the separated oil is returned to the gas turbine lubricating oil reservoir. This Paper discusses the introduction of brush seals into the No. 3 bearing housing as an additional element in retarding the high pressure, high temperature air infiltration into the No. 3 bearing housing.

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