Cooling and sealing air system

04/13/23 Cooling and Sealing Air System 1

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Cooling and Sealing Air SystemPower Systems University

The cooling and sealing air system provides the necessary air flow from the gas turbine compressor to other parts of the gas turbine rotor and stator to prevent excessive temperature buildup in these parts during normal operation and to prevent compressor pulsation.

The MS-7001FA has a vacuum-operated lubrication system. Therefore, the bearing sealing function is not utilized. When the gas turbine is operating, air is extracted from the 9th and 13th stages of the axial flow compressor as well as from the compressor discharge.

Atmospheric air from off-base, centrifugal-type blowers is used to cool the turbine exhaust frame and No. 2 bearing area.

Cooling and sealing functions provided by the system are as follows:

1. Compressor pulsation protection2. Cool the internal parts3. Cool the turbine exhaust frame4. Cool the No. 2 bearing area5. Provide an operating air supply for the air-operated valves.


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The cooling and sealing air system consists of specially designed air passages in the turbine casing, turbine nozzles, and rotating wheel as well as piping for the compressor extraction air and associated components.

Associated components used in the system include:

1. Turbine Exhaust Frame Cooling Blowers2. No. 2 Bearing Area Blower3. Dual Drive Motors 88TK-1, –2 and 88BN–1, -24. Compressor Bleed Valves VA2-1, -2, -3, -45. Solenoid Valve 20CB-1, -2 (for control of compressor bleed valves)6. Compressor Discharge Pressure Transducers 96CD-1, -1B, and -1C


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Compressor Bleed Subsystem For Pulsation ProtectionThe pressure, speed, and flow characteristics of the gas turbine axial flow compressor are such that special equipment and sequencing of the gas turbine components are required to prevent pulsation of the compressor when the turbine is accelerating, decelerating, shutdown or tripped. The equipment required to provide this protection is the compressor bleed valves and IGV subsystem.

Four pneumatically operated compressor bleed valves [VA2-1, -2] bleed 9th stage, [VA2-3, -4] bleed 13th stage . The valves are designed to be self-opening on the loss of air supply pressure from 20CB-1, -2.This feature is considered to be fail-safe with respect to the protection of the compressor.

During turbine startup the [VA2-1 thru -4] are open, allowing 9th and 13th-stage air to be discharged into the exhaust plenum, thereby eliminating the possibility of compressor pulsation. When the turbine accelerates to full speed [VA2-1 thru -4] close and allow normal running operation of the turbine. When a turbine shutdown signal is initiated [VA2-1 thru -4] are open and 9th and 13th-stage air is again discharged into the exhaust plenum to prevent compressor pulsation during the turbine deceleration period.

Although the bleed valves appear to be in a parallel redundant arrangement, they are not redundant. Both valves are required to function to provide adequate pulsation protection.


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Turbine Nozzle Cooling Air Supply SubsystemThe cooling circuit for the turbine components consists of both internal and external circuits. The 1st and 2nd stage buckets, the 1st stage nozzle, and the 1st stage shroud are cooled by an internal cooling air circuit, while the 2nd and third stage nozzles are cooled by an external cooling air circuit.

The internal circuit is supplied by 17th stage and by compressor discharge air, and the external circuit by 13th-stage extraction air.


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Cooling and Sealing Air System (1st-Stg Bucket)

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Cooling and Sealing Air System (Air Cooled Nozzle)

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Exhaust Frame and No. 2 Bearing Area Cooling Fan Module SubsystemA cooling fan module consisting of four centrifugal blowers driven by motors, 88TK-1, –2 and 88BN–1, -2. Cooling air is provided to the exhaust frame cooling manifold and the No. 2 bearing area. Each blower is sized to provide 100 percent of the required flow for its respective cooling requirement. The motors are controlled to operate in a lead-lag arrangement so that only one combination of blowers, exhaust frame, and bearing area is operating when the gas turbine is running.

Two of the blowers [88TK-1,2] supply air for cooling of the exhaust frame and third aft wheel space. The cooling air enters the exhaust frame through eight radial nozzles on the outer annulus of the frame. The air cools the outer diameter of the outer exhaust gas path insulation pack. Some of the cooling air exits the frame at the forward joint with the third stage bucket shroud. The remainder flows aft, then turns, flowing through and cooling the radial support struts. The air cools the inner diameter of the inner exhaust gas path insulation pack and exits the exhaust frame by being dumped into the third stage bucket aft wheel space. The cooling air also prevents exhaust gas from being aspirated into the No. 2 bearing sump.


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Exhaust Frame and No. 2 Bearing Area Cooling Fan Module Subsystem (cont)A similar arrangement of two blowers [88BN-1,2] is used to provide cooling air to the No. 2 bearing area. The discharge of each passes through a diverter type check valve VCK7–3 before entering the main supply pipe to the No. 2 bearing area. This valve is required because of the lead-lag operation; otherwise the air from the operating blower would escape through the non-operating blower, thereby bypassing the cooling circuit.

Pressure switches 63TK-1 and -2 on the exhaust frame blowers, and 63BN-1 and 63BN-2 on the No. 2 bearing area blowers are used to sense each of the blower’s discharge pressure. If either blower or motor in the operating set should fail, the loss of discharge pressure will cause contacts of the respective 63TK or 63BN pressure switch to close, sending a signal to start the idle set. If a second failure should occur, the turbine will shut down in a normal shutdown sequence.

Note:Any failed blower or motor should be repaired or replaced as soon as possible to preclude the possibility of shutting down the turbine as a result of a second failure.


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Pressurized Air SupplyCompressor discharge air is used as a source of air for operating various air-operated valves in other systems. Air for this purpose is taken at the discharge of the compressor and is then piped to the various air-operated valves. In addition, compressor discharge pressure is monitored by pressure transducers 96CD-1, 96CD-1B, and 96CD-1C for use in control of the gas turbine.


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Cooling and sealing air system