Cooling and Sealing Air

Gas Turbine

Cooling and Sealing Air System GEK 110654 Cooling and Sealing Air System I. GENERAL The coolin cooling g and sealing sealing air system system provid provides es the necess necessary ary air flow flow from from the the gas turbi turbine ne compressor to other parts of the gas turbine rotor and stator to prevent excessive temperature  buildup in these parts during normal operation and for sealing of the turbine bearings. Atmospheric air from external centrifugal type blowers is used to cool the turbine exhaust frame. Cooling and sealing functions provided by the system are as follows: 1. Sealing the turbine bearings. 2. Cooling the internal turbine parts subected to high temperature. !. Cooling of the turbine outer shell and exhaust frame. ". #roviding an operating air supply for air operated valves. $. Compressor pulsation protection. The cooling and sealing air system consists of specially designed air passages in the turbine casing casing%% turbin turbinee no&&l no&&les es and rotati rotating ng wheels wheels%% piping piping for the compre compresso ssorr extrac extractio tion n air and associated components. Associated components used in the s ystem include: 1. Turbine 'xhaust (rame Cooling )lowers 2. Air (ilter *with poro+stone element, !. #ressure -auge ". irt Separator  II. FUNCTIONAL DESCRIPTION A. General The cooling and sealing air system utili&es air from the axial flow compressor% extracted from several points% for sealing the bearings% cooling turbine turbine internal parts and to provide a clean air supply for air operated control valves of other s ystems. )earing sealing air is extracted from the compressor fifth stage when the turbine is in normal runnin running g operat operation ion.. /ntern /nternal al coolin cooling g air is extract extracted ed from from the discha discharge rge of the compre compresso ssorr including the internal flow of cooling air through the center of the turbine rotor. Air used in cooli cooling ng the turbin turbinee extern external al casing casing is ambien ambientt air suppl supplied ied by motor motor driven driven blower blowers. s. The schematic flow diagram% included in the 0eference rawings section of this service manual% shows both the internal and external flow of cooling and sealing air. B. Bearing Cooling and Sealing Sealing air is provided from the fifth+stage of the turbine compressor during normal running operation of the unit and is piped externally to each of the turbine bearings. rifices in the air lines to the turbine bearings limit the flow of air and pressure to each bearing.

Cooling and Sealing Air System GEK 110654 The pressuri&ed air is used to cool the bearing and help contain the lubricating fluid within the  bearing area that otherwise might seep past the mechanical seals. The air is directed at both ends of the bearing% providing a pressure barrier to the lubricating fluid. The air flow path through the  bearing seal is described in the -as Turbine section section of this manual. manual. C. Tr!ine Cooling Cooling of the turbine exhaust casing and the exhaust frame is accomplished by two motor driven centrifugal blowers *fans,% T3+1 and T3+2% which are mounted external to the turbine. An inlet screen and inlet silencer are provided with each blower and the discharge of each passes through a chec4 valve% 5C36+1 or +2% before entering the turbine shell. There it splits% some flowing flowing forward through the turbine turbine shell and out into the turbine turbine compartme compartment% nt% while while the remainder flows aft into the bearing tunnel via the exhaust frame strut passages. (rom the bearing

tunnel some cooling air flows into the !rd stage aft wheel space after which it discharges into the exhaust% and the remainder discharges into the load tunnel and out the load compartment vent. The two blowers operating simultaneously normally provide cooling of the exhaust frame and turbine shell. A pressure switch% 7!T3+1 or +2% is provided to sense blower discharge pressure. /f one of the blowers should fail% the switch will cause an alarm to be activated. The turbine will continue to run with the other blower providing cooling air at a reduced flow rate. /f both blowers should fail% the turbine will be shut down in a normal shutdown se8uence.

NOTE /f one blower fails% it should be repaired or replaced as soon as possible to preclude the possibility of shutting down the turbine by failure of the remaining blower. 'ach blower is e8uipped with a heater% 2!T3+1 or +2% to prevent condensation when the motor is not operating. D. Plsation Prote"tion The pressure% speed and flow characteristics of the gas turbine compressor are such that air must  be extracted from the eleventh stage and vented to atmosphere to prevent pulsation of the compressor during the acceleration period of the turbine starting se8uence and during deceleration of the turbine at shutdown. #neumatically operated eleventh stage air extraction valves% controlled by a three way solenoid valve% are used to accomplish the pulsation protection function. 'leventh stage air extracted from the compressor at four flanged connections is piped through the normally open% pneumatically operated% butterfly type extraction valves% 5A2+1 and +2% to the turbine exhaust plenum% during the acceleration or deceleration periods of turbine operation. 9imit switches !!C)+1 and +2% mounted on the valves% indicate valve position and operate in the starting se8uence permissive logic circuits. Compressor discharge air% controlled by solenoid valve 2C)+1% is used to close the compressor  bleed valves when the turbine reaches full speed to allow normal operation of the turbine. Air from the compressor discharge passes through a porous air filter where dirt and water are removed% using a continuous blow down orifice% before entering solenoid valve 2C)+1. (rom the solenoid valve% the air is piped to the piston housings of the two extraction valves. #GEK 110654 Cooling and Sealing Air System uring turbine startup% 2C) is de+energi&ed and the eleventh stage extraction valves are open allowing eleventh stage air to be discharged into the exhaust plenum% thereby eliminating the  possibility of compressor pulsation. 9imit Switches !!C)+1% and +2 on the valves provide  permissive logic in the starting se8uence and ensure that the extraction valves are fully opened  before the turbine is fired. The turbine accelerates to full speed and when the generator circuit  brea4er closes% the 2C)+1 solenoid valve is energi&ed to close the extraction valves and allow normal running operation of the turbine. ;hen a turbine shutdown signal is initiated and the generator circuit brea4er is opened% 2C)+1 is de+energi&ed and eleventh stage air is again discharged into the exhaust plenum to prevent compressor pulsation during the turbine deceleration period.

CAUTION
;hen water washing the gas turbine>s compressor or turbine section% it is important to 4eep water out of the components that are actuated by compressor discharge air and out of the turbines  bearings. To prevent water from entering these components and the bearings% isolation valves are  provided in the sealing lines to the bearings% and in the 2C)+1 feed line. uring normal operation of the gas turbine% all isolation valves are to be open. )efore initiating water wash% the isolation valves must be closed and the drain and air separator blow down valves opened. At the conclusion of water wash% the isolation valves must be opened and the drain and separator blow down valves closed to allow normal operation of the turbine. III. CO)PONENT DESCRIPTION A. Air Se%arator *Bearing Seal Air+ *?anufacturer + onaldson Co. /nc., *?odel + T)1+=1, B. O%eration Any dirt particles contained in the air which enter the separator are removed by the centrifuging action of the separator and eected. C. )aintenan"e /f plugging of the air separator is suspected% remove it from the line. Ta4e off both retaining rings% the outlet tube% the +ring% and the helix vane and wash metal parts in solvent or detergent to remove contaminants. Chec4 parts for any signs of erosion or corrosion. 0eassemble the unit and reinstall. The orifice may become plugged% eroded or corroded. /t is threaded into the hole and is slotted so that a screwdriver may be used to remove it. @ever attempt to remove the orifice while the separator is under pressure. Cleaning may be done with solvent or detergent as the other parts. Should the orifice hole become enlarged due to erosion or corrosion% the performance of the air cleaner will not be degraded in any manner. The only effect will be to reduce the through flow% as more air will be passing out through the orifice. The decision to replace the orifice in this case will be dependent on the end effect of the reduced air flow% rather than any effect on the cleaner. A drawing of this separator is included in the #arts 9ists and rawings section of this manual. #eriodic inspection of the (A7+1 porostone filter and bleed orifice is re8uired. The drain valve  below the filter  orifice should be opened during routine maintenance to insure that no dirt and water will bloc4 the orifice. The vent screen on the 2C)+1 solenoid is also important to chec4 during routine maintenance. The screen should be 4ept free from debris. /f the vent screen becomes clogged% the bleed valves will operate slowly or not at all% and the turbine may experience a trip.