Cooling and Sealing Air Systems

GTG (MS-5001) COOLING AND SEALING AIR SYSTEM

Document No.

O&U-12-OM-110

Revision Date of issuance

01 02/08/2010

GENERAL Air obtained from the gas turbines axial-flow compressor is used for cooling the various parts of the turbine section and for pressurizing the bearing oil seals in the gas turbine. This cooling and sealing air provides air flow to certain internal and external turbine parts to prevent excessive temperature buildup in these parts during normal operation and for sealing the turbine bearings. The parts of the turbine section which are cooled by air consist of: the first and second-stage turbine wheel forward and aft faces, the first and second-stage nozzles, the turbine shell, and support struts. The combustion chamber liners, transition pieces, and the combustion casing, are designed to utilize compressor discharge air for effective cooling of these parts.

FUNCTIONAL DESCRIPTION Air obtained from the axial-flow compressor used in the turbine cooling and bearing sealing functions includes fourth and tenth-stage extraction air, compressor high-pressure seal leakage air, and compressor discharge air.

Fourth-Stage Extraction Air Fourth-stage air is piped externally through orifices through the turbine shell and support struts to the aft surface of the second-stage wheel. This air cools the portion of the shell surrounding the first and second-stage nozzles and turbine wheels and also cools the support struts which are in the hot gas exhaust stream.

Tenth-Stage Extraction Air Tenth-stage air is piped externally through the compressor bleed valves, VAB-1 and VAB-2, to the exhaust plenum. Limit switches 33CB-1 and -2 are provided on each valve to give an indication of valve position. Tenth-stage air is also fed through the second-stage nozzle partitions for cooling the shaft surface of the first-stage turbine wheel, and the forward surface of the second-stage turbine wheel.

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GTG (MS-5001) COOLING AND SEALING AIR SYSTEM

Document No.

O&U-12-OM-110

Revision Date of issuance

01 02/08/2010

A portion of the tenth-stage air is used at the number one and the number two bearing assemblies to provide an air pressure seal for bearing lube oil. Before the sealing air is piped to these bearing areas, it is first routed through a centrifugal dirt separator which removes foreign matter injurious to the bearings. Cleaning of the separator is accomplished by a continuous blow-down orifice.

Compressor High Pressure Seal Leakage Air Compressor high pressure seal leakage air is channeled internally to the for-ward surface of the first-stage turbine wheel. This air flow provides a source of cooling air for the first-stage wheel and is exited into the exhaust hot gas path.

Compressor Discharge Air Compressor discharge air is directed internally through the partitions of the first-stage nozzle as cooling air, and exits through bleed holes located in the trailing edge of the partitions into the exhaust hot gas path. This air is also piped externally through a filter and air control solenoid valve 20CB-1 to the actuating pistons of the bleed valves. At turbine startup valve 20CB- 1, which is de-energized, prevents the compressor discharge air from actuating the pistons of the compressor bleed valves; the bleed valves are open, and tenth-stage air is vented to the exhaust plenum (and aid in the elimination of compressor surge). When the generator breaker is closed / at 95% turbine speed (FSNL), a signal from the control system energizes valve 20CB- 1. Compressor discharge air is then routed to the bleed valve actuators to close the valves and stop compressor bleed to the exhaust plenum. Pressure transmitter provides a compressor discharge feedback signal utilized by the turbine control system.

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