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Gas Turbine Compressor and Turbine / Gas Turbine Bearing Description of Auxiliary Systems Blowoff System

Siemens AG 3.1-1400-9070/1 Power Generation MBA/MBD 0704E-X

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Refer also to:

List of Control Settings (SREL) 3.1-0210 List of Measuring Instruments 3.1-0220 Equipment List 3.1-0240 P+I Diagram, Blowoff System 3.1-1410 Associated Systems:

Compressor Cleaning 3.1-1180 P+I Diagram, Compressor Cleaning 3.1-1190 Drainage System 3.1-1200 P+I Diagram, Drainage System 3.1-1210 Pneumatic Valves and Piping for Blowoff System 3.1-9900 P+I Diagram Pneumatic Valves and Piping for Blowoff System 3.1-9910

Settings, limits, and measuring ranges of the devices referred to here are given in the List of Measuring Instruments, Equipment List, and List of Control Settings (SREL).

Function The axial compressor of the gas turbine is designed to

run at the rated speed of the turbine-generator. In a certain speed range below rated speed, the front stages of the compressor are so highly loaded aerodynamically that flow separation occurs at the compressor airfoil surfaces due to excessive deceleration. As a result, the overloaded compressor stages are no longer capable of generating the necessary increase in pressure, the phenomenon known as compressor surging occurs and the delivery rate becomes unstable. The breakdown of flow results in periodic flow reversals, manifested outwardly by pronounced, periodic fluctuations in the compressor outlet pressure together with severe vibration of the turbine-generator and pulsating noise synchronous with these pressure fluctuations. This subjects the compressor airfoils to both high alternating bending stresses and high temperatures.

Compressor surging is prevented by bleeding air from certain locations of the compressor when the speed range that is critical in terms of surging is reached.

Functional Principle Blowoff lines are connected to the compressor casing

as follows for bleeding air: two at extraction point Ea1 and one at extraction point Ea2. The blowoff lines open into the exhaust duct downstream of the gas turbine. As a result, the exhaust silencer also functions as a silencer for the blowoff air.

Each blowoff line is equipped with a butterfly-type valve which is opened when air is to be bled from the compressor. These blowoff valves are actuated pneumatically to the positions “OPEN” and “CLOSED”. System description “Pneumatic Valves and Piping for Blowoff Equipment” covers these actuators.

Extraction Compr.

Stage Blowoff valve (butterfly type)

KKS

Ea1 5 1.1 MBA41AA051

Ea1 5 1.2 MBA42AA051

Ea2 9 2 MBA43AA051

Ea3 13 3 MBA44AA051Because the blowoff lines routed below the machine

centerline act as siphons, drain lines are attached at the lowest points of these lines. Water that may have accumulated here during compressor cleaning is drained off via these lines (cf. 3.1-1200, “Drainage System” and 3.1-1180, “Compressor Cleaning”).

Open-loop Control Opening and closing of the blowoff valves is controlled

automatically as a function of plant operating conditions.

Startup with Natural Gas All blowoff valves are open at the onset of startup. They

are closed sequentially as of about 80% rated speed. This minimizes the associated abrupt changes in temperature and output.

Startup with Fuel Oil All blowoff valves are open at the onset of startup.

Shortly before rated speed is reached they are closed in a staggered sequence with brief delays.

Operation After startup has been completed the blowoff valves

always remain closed during normal operation. They are only opened in the event of overall gas turbine trip or normal shutdown.

Speed Decline If speed drops below S.TURB.70 during power

operation the generator is disconnected from the grid (load rejection). Gas turbine trip is triggered if speed continues to decline and goes below S.TURB.122, at which time all blowoff valves are opened.

Load rejection and gas turbine trip are not the subject of this description.

Gas Turbine Compressor and Turbine / Gas Turbine Bearing Description of Auxiliary Systems Blowoff System

Siemens AG 3.1-1400-9070/2 Power Generation MBA/MBD 0704E-X

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Shutdown During normal shutdown of the gas turbine, all blowoff

valves are opened simultaneously when the emergency stop valves have been closed.

GT Trip In the event that gas turbine trip is triggered, all blowoff

valves are opened immediately as it is now inevitable that the axial compressor will pass through the unfavorable speed range.

Protection Functions − Startup is aborted if blowoff valves are not open on

startup.

− Gas turbine trip is triggered if the OPEN position of any blowoff valve is not detected in the speed range critical to compressor surging.

− The gas turbine is shut down if any of the blowoff valves are still open and cannot be closed within a short time after reaching rated speed.

Manual Actuation of Individual Blowoff Valves At speeds below turning speed S.TURB.05, it is

possible to manually actuate individual blowoff valves for maintenance purposes. Manually closed blowoff valves are automatically reopened after a brief delay.

Gas Turbine Pneumatic Control Equipment Description of Auxiliary Systems Pneumatic System

Siemens AG 3.1-9800-0592/1 Power Generation 0905E-X

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Refer also to:

List of Control Settings (SREL) 3.1-0210 List of Measuring Instruments 3.1-0220 List of Electrical Loads 3.1-0230 Equipment List 3.1-0240 P+I Diagram, Pneumatic Valves and Piping 3.1-9810

Settings, limits, and measuring ranges of the devices referred to here are given in the List of Measuring Instruments, Equipment List, and List of Control Settings (SREL). The values stated in this description are only given as examples.

Description Compressed air is the working medium used by the

pneumatic actuators of various components in the gas turbine auxiliary systems. As a rule, these pneumatically-actuated valves are relevant to safety. For safety reasons, the supply of compressed air to the gas turbine is therefore independent of the power plant compressed air network and is generated by a pneumatic station. Valves in other systems are supplied in addition to the blowoff valves.

Configuration and Function of Compressor Train

The compressed air station is equipped with two redundant trains. Each train essentially comprises a compressor, a cooler, and a filter. The system has full redundancy, i.e., the capacity of each compressor train is sufficient to ensure a reliable supply of control air to the auxiliary systems (2x100%).

The two trains have an identical configuration, for this reason only one train is described in the following.

Electrically-driven compressor MBX21AN001 compresses air. Filter MBX21AT001 prefilters the air as it is drawn into the system.

Relief valve MBX21AA191 protects the compressor against excessive pressure.

Solenoid-type pressure relief valve MBX21AA501 is installed downstream of the compressors to prevent the reciprocating compressors from having to start up against pressure (startup assistance). This solenoid valve is open when the associated compressor is at standstill and is closed after the compressor is switched on.

The escaping compressed air and any condensation that forms are fed into condensation collecting tank MBX23BB001. The condensation collecting tank is equipped with silencer MBX23BS001 to reduce noise when discharging compressed air to the atmosphere.

Condensation that accumulates in the condensation collecting tank is then fed to disposal tank MBX23BB002 that is at atmospheric pressure. Because the condensation may contain oil, its disposal must comply with requirements that apply to used oil.

Swing check valve MBX21AA201 prevents venting of the train when the compressor is shut down.

Compressed air is dried in the next step. Compressed air is cooled in chiller-type compressed air drier MBX22AT001. Moisture condenses, thereby bringing the air to the prescribed dew point pressure. The separator system in the cooler separates water and oil from the stream of compressed air. Condensation is removed via drain MBX22AT011.

Compressed air from an external source can be supplied via swing check valve MBX22AA201. Shutoff valves MBX22AA253 and MBX22AA254 must be opened when compressed air is supplied from an external source.

Any dirt particles or oil droplets still present in the compressed air are removed by filter MBX22AT003. An optical differential pressure indicator equipped with differential pressure switch MBX22CP001 is provided at the filter. A group fault alarm is annunciated if the differential pressure setting of this switch is violated (cf. subsection “Monitoring”). Then the filter element must be replaced. Condensation is removed via drain MBX22AT013.

Shutoff valve MBX22AA251 can be used to isolate the train for maintenance purposes, even during plant operation.

The two trains merge downstream of the shutoff valve. Swing check valve MBX23AA201 prevents the escape of large volumes of air from the tank if there is a leak in one of the trains.

Compressed air tank MBX24BB001 is used to store the compressed air after it has been dried and cleaned.

Pressure control valve MBX24AA151 maintains system pressure even during extended outages and in the event of minor leaks. It only opens if pressure in the tank exceeds the startup pressure of the compressors. Orifice MBX24BP001 ensures that only a very small flow or air can be returned even in the event the pressure control valve malfunctions.

Tank pressure can be read off gauge MBX24CP501.

System pressure is limited by safety valve MBX24AA191.

Shutoff valve MBX24AA401 can be used as necessary to check whether condensation has formed in the tank.

Hygrometer MBX29CM001 is used to measure the relative humidity in the terminal box of the first train. If the permissible limit is exceeded, heater MBX29AH001 is

Gas Turbine Pneumatic Control Equipment Description of Auxiliary Systems Pneumatic System

Siemens AG 3.1-9800-0592/2 Power Generation 0905E-X

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switched on. This prevents the moisture contained in the air from forming condensation inside the terminal box.

Hygrometer MBX29CM002 is used to measure the relative humidity in the terminal box of the second train. If the permissible limit is exceeded, heater MBX29AH002 is switched on. This prevents the moisture contained in the air from forming condensation inside the terminal box.

Open-loop Control The open-loop control system for the pneumatic station

constitutes a black box for the gas turbine I&C system. Once the pneumatic station has been started up by manually actuating the main power switch, no further switching actions on the part of the gas turbine I&C system are required for control of the pneumatic station.

The open-loop control equipment and power supply for the electrical components are located on a separate sub-distribution board for each compressor train (MBY40GH001 and MBY40GH002 not shown).

Each of the compressors is equipped with two pressure switches (MBX24CP003 and MBX24CP004) for startup and shutdown. These two switches have the same pressure setting. This ensures that the two compressors start up simultaneously.

Monitoring The operating status signals “Pressure LOW1”,

“Pressure LOW2”, “Pressure TOO LOW1”, “Pressure TOO

LOW2”, “Compressor 1 ON”, “Compressor 2 ON”, “Fault in train 1”, and “Fault in train 2” are generated by the pneumatic station, fed into the gas turbine I&C system, processed, and then displayed on the operation and monitoring system.

The tank pressure is monitored by pressure switches MBX24CP001, MBX24CP002, and MBX24CP008. If tank pressure drops below the setting of pressure switch MBX24CP001, the pretrip alarm "PRESSURE LOW" is annunciated. If pressure in the tank continues to decline, pressure switches MBX24CP002 and MBX24CP008 operate, gas turbine trip is triggered (2-of-3 logic gating), and the alarm message “Pressure TOO LOW” is annunciated.

The signals “Compressor 1 ON” and “Compressor 2 ON” are displayed on the operation and monitoring system. If the compressors remain in operation for extended periods, it can be assumed that the system is no longer leak-tight. The pneumatic system, including all piping, must then be checked for leaks.

The alarms “Fault in train 1” and “Fault in train 2” are group fault alarms and are displayed on the operation and monitoring system. If one of these alarms is annunciated, the affected compressor train must be shut down and serviced.

Causes of faults include, for example: response of compressor circuit breaker, dehumidifier malfunction, condensation separator malfunction, startup assistance solenoid valve NOT CLOSED, response of differential pressure switch.

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G1 81MBA10EJ220FGC FCGT81 AIR SYSTEM

Date

Index Norm.

Drawn

Modification Date

SIEMENS AG

OM650 Picture DesignCheck

YOA =+

Namepage

sh.

Dep.:PG L491

1 2 3 4 5 6 7 8

A

B

C

D

E

F

A

B

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D

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1 2 3 4 5 6 7 8

11

GT81 AIR SYSTEM

*

27.06.06

.

.VAE 267

Wendenburg2006-03-03

Boettger STATION L PHASE II

JEBEL ALI POWER AND DESAL.Wbg

.

.Upd.Vers.R1

999.9T SWA ????????F

T SWAF 99999 ????999T SWA ????F

FO

999T SWA ????F

999T SWA ????F

999T SWA ????F

T SWA ????F 99.99

T SWA ????F 999.9

T SWA ????F 99.99

T SWA ????F 99.99

SS ACCMON ACT

IGV CONTROLLER:

ACT POSN

SETPOINT

TEMP COMPR INLDP FINEFILTER

DP PREFILTER

DP COALESCER

DP FILTER

DP C-C

FO OPERATION

IGV CTRL FAULT

AIR STATION

TRIP

P<MIN1

F O

F O F O

999T SWA ????F

999.9T SWA ????????F

999.9T SWA ????????F

999T SWA ????F

F O F

999T SWA ????F

F O F

999T SWA ????F

GT PNEUMATICACTUATORS

S COMPR P RA-C ON IGV ACT

S COOL AIR LMT-C ON IGV ACT

3SEAL AIR

TEMP

999T SWA ????FFO SYS

F O F

F O F

S FLAME ON

999T SWA ????FHUM TIME

RESET

IGV CONTROLLER

IGV POWER UNIT

S ACTIVE

SEVAP COOLER

ON

F OIMPLOSION DOORS

CLOSEDS

C-C ACCEL

SS

999T SWA

????

F999

T SWA

????

F

ONOFF

AIR INLET

NG OPERATION

TURB OUTLETTEMP

TEMP EXH DUCT

COOLING AIR

AIR SYSTEM

81MBA10EJ220 TURBINE SPEED

999T SWA ????F 999T SWA ????F 99.99T SWA ????FCALC TURB OUT TEMP ACTIVE POWER

CTRL ONFAULTS

F O F O