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AUXILIARY SYSTEMS for GAS TURBINE

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AUXILIARY SYSTEMS for GAS TURBINE Powered By Docstoc
					            UNIT (4)
AUXILIARY SYSTEMS
1-   Lube oil system
2-   Fuel oil system
3-   Fuel gas system
4-   Hydraulic trip oil system
1- Lubricating oil system




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1- Components of the system:
   a- Main lubricating oil pump:
      (V103) is the gear pump connected to the main gearbox of the unit. It works
      all time at rated speed or loading. Its pressure reaches 1,5 kg/cm2.

   b- Auxiliary lubricating oil pump:
      (2792) is the centrifugal pump driven by A. C., situated inside main unit oil
      tank. Its pressure reaches 1,5 kg/cm2. On the delivery line, a non-return
      valve (2794) and a constant pressure valve to (2791) are mounted.

   c- Emergency cooling oil pump:
      (2800) is the screw pump driven by A. C., Its pressure reaches 0.6 kg/cm2.
      On the delivery line, a non-return valve (GT 4087) and a constant pressure
      valve to (2803) are mounted.

   d- High pressure oil pump or jacking pump:
      (4085) is a piston pump driven by A. C., Its pressure reaches 300 kg/cm2.
      On the delivery line, a non-return valve is mounted.

   e- Main oil tank (GT 4001):
      It is situated underneath the unit, inside which are auxiliary oil pump (2792),
      emergency cooling pump (2800) are mounted. Minimum and maximum
      marks are put on a graduated vertical scale fixed to the tank to know oil
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      level. An extraction fan is mounted on the tank to remove vapors inside tank
      (4002) and a filter (4005)for air to pass to replace vapors. A float (4004) is
      also mounted to indicate low oil level inside the tank.

   f- Main oil cooler (c100):
      To cool oil leaving auxiliary or main oil pump, in which cooling water cools
      oil to the suitable operating degree. Cooling degree is controlled by the
      quantity entering the cooler.

   g- Thermostat:
      To have an electric signal for the alarm when the oil temperature leaving
      cooler is high mounted, or to stop the turbine at this temperature.

   h- Pressure switch (2736):
      It gives signal when oil pressure decreases under certain limit to stop the
      turbine or start the emergency cooling oil pump.

   i- High pressure oil pump filter (4012):
      To filter oil before entering high-pressure pump.

   j- Pressure switch (GT 4010)
      To give signal about the situation of the jacking pump if works or not, to be
      able running the unit by an electric signal.


2- Lubricating oil system working:
   a- Start up:
        • On preparing the unit to start, pump (2792) works to supply bearings
            by the required lube oil after passing by the principle cooler (C100)
            through line (GT4050) and line (GT 4054).
        • Before starting to drive the engine by the starting device, jacking pump
            (GT 4085) is driven to raise shaft from bearing to prevent friction by
            passing oil at 300 kg/cm2 in the bearings of compressor, turbine and
            generator. The oil from the main lube oil line reaches this pump at 1.5
            kg/cm2.
        • After rotation of the engine at sufficient speed (1600 rpm), it is
            possible to depend on the dynamic pressure to have continuous oil film
            between the shaft and bearing. At this speed, the high pressure oil
            pump is automatically separated.
        • When unit reaches rated speed auxiliary lube oil pump (2792) is
            stopped and we depend on the main lube oil (V103), driven by main
            gearbox.
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b- Stop down:
   On stopping the engine for any reason, the auxiliary lube oil pump (2792)
   immediately rotates to supply bearings by the necessary lube oil. It works
   until the temperature of the gases entering the turbine to 70 oC, at which
   lube oil is stopped completely.

c- Alternating current off:
   When the alternating current is off, known by pressure reduction of lube oil
   using pressure switch (2736). When the pressure reduces to less than 0.3
   kg/cm2, emergency cooling oil pump (2800) works automatically by D. C
   from group of batteries ..




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2- Fuel oil system




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1- General introduction:
       Fuel oil system is similar to all petroleum fuels, but differ in the way of
   connection to unit (forwarding facilities) it is fed at low pressure through the
   primary filter and stop valve. The high-pressure fuel leaving the pump is
   regulated by dozing device, which is working by the servo-valve. After this the
   needed-doze fuel pass to a high-pressure filter, then divided equally to each
   nozzle by the flow divider.
       In Brown Boveri units of single combustion chamber, a simple system is
   used to control the doze by changing the nozzle opening. This unit is fully
   discussed in the following items.

2- Components of liquid fuel of gas turbine model (BBC 11L):
   a- Main fuel tank (k100):
      The tank capacity is about 1000 tons. It supplies the daily tank through the
      electric valve (5224). Level switches control its opening and closing
      according the out flow from the daily tank.

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b- Daily tank (k101):
   It is underground tank of 30 tons capacity. It has the following:
        • Three level switches
          a- level switch (5204) controls the valve of filling the daily tank from
             the main tank, according to upper and lower thresholds.
          b- Level switch alarm (5203) to indicate in alarm signal the fuel level
             in the daily tank if valve (5224) does not work.
          c- Level switch tripping that trips the unit if fuel level is low enough to
             cause danger to the unit.

       • Manual pump (5228)
         It is a gear pump driven manually to such water and dirt at a point in
         the tank bottom.

       • Level graduation (5212)
         It is used to indicate directly fuel level inside the tank.


       • Breather valves (5227, 5226)
         They are used to get rid of fuel vapors from inside the daily tank and
         fuel line.

       • Fuel pump (5214)
         It is a centrifugal pump has a discharge pressure of 30 kg/cm2,
         equipped by a constant-pressure valve (R2643) to fix the pressure at
         the required value.

c- Pressure gauge (7165):
   It is used to indicate fuel pressure exiting the fuel pump

d- Pressure switches (R2740, R2741):
   They are used to stop if the fuel pressure falls to certain limit that causes
   danger to the unit.

e- Three-way valve (5150):
   It is a three-position valve driven by the motor 5151,which works through the
   operation panel supplied by three limit switches (5156, 5157, 5159) to
   determine the following valve positions, which are:
        • Circulation, in which the valve is completely closed in front of fuel
            leaving the fuel pump.
        • Pressure, in which the fuel returns back to the daily tank.
        • Operation, in which fuel is distributed to nozzles

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   f- Solenoid valves (5195, 5196):
      They wok electrically to open and close the fuel ways to combustion chamber
      through the nozzles, and exiting the return fuel from the nozzles back to the
      tank

   g- Return fuel cooler (5230):
      It cools the return fuel before going to the tank by cooling water entering and
      exiting through valves (5231, 5232) .

   h- Pre-ignition system :
      It is a gas bottle supplies the ignition nozzle by gas fuel at the time of spark
      coming from the spark device, to cause small flame as initiative to complete
      combustion to fuel coming from main nozzles. It may also be a liquid fuel
      delivered by a small pump (5217).

3- Fuel-oil system principle:
   On starting operation, the three-way valve should be on position “circulation”.
   Fuel pump (5214) is driven after supplying lubrication and control oil to the unit.
   At the same time motor (5151) changes the three-way valve to position
   “pressure” to return fuel to the tank.
   The starter drives the unit until the ignition speed (20% of the rated speed), at
   which the spark begins and fuel is admitted to ignition nozzle. At the same time
   motor (5151) changes the three-way valve to position operation, in which fuel is
   pumped to combustion chamber through the nozzles. The required fuel is
   admitted according nozzle opening and the excess is returned back to the tank
   through the cooler (5230). Nozzle opening changes to change the quantity of
   admitted fuel to control the required combustion temperature.




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                            3- Fuel gas system




In this type of units, the gaseous fuel is used in the same nozzles but in different way
to control the quantity of used fuel before entering the combustion chamber. Natural
gas is a clean fuel, free of impurities that may cause damage to combustion
chamber, burner and turbine blades. The fuel gas system contains the following:
     1- Stop valve (GT 8001), which works electrically by a motor to open and
         closed the fuel line.
     2- Gas main line (GT 5400), which follows the stop valve.
     3- Gas escape valve (GT 8002) to let gas to escape from the gas line after
         stopping the unit and the principal stop valve (GT 8001).

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4- Gas reducing valve (2608), which controls gas pressure in the line. It work
   either hydraulically or by speed oil coming from the governor via gas
   pressure controller (2602).
5- Gas balance tank, which makes continuous balance in the line by make up.
6- Pressure switches in gas main (2742, 2737), which give electric signal on
   increase or decrease of fuel pressure.
7- Combined ignition and gas blow off valve 2605, to supply the nozzle by
   starting ignition gas and escaping gas on stopping.
8- Gas regulating valve (2600), which regulates fuel quantity and its pressure
   on starting
9- Change over valve, which increases gradually the oil pressure in line
   (GT4411) on starting through increasing gas quantity going to the nozzle
   from valve (2600) that regulates the gas.




               4- Hydraulic trip oil system




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1- Introduction:
   The hydraulic system supplies the control oil by taking oil from main gear pump
   (2795) engaged to gearbox, or through an auxiliary pump (2799) working by A.
   C. found on main oil tank. It controls the oil pressure according to the following
   factors:
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     a- Change of turbine speed on starting by the starting valve (2679).
     b- Change of speed according the sensitivity of the governor (2675).
     c- Decreasing the maximum temperature when exceeds the permissible limit
      by the temperature transmitter (2707).
     d- Stopping the unit when over speeds by the overspeed device (2730).
     e- Emergency stop by the main volt relay (2684).

2- Hydraulic control system principals:
   a- On starting
      Stopping the starting valve (2679) gradually, according to which the escape
      oil quantity decreases and oil pressure increases to point h that cause change
      over relay (2690) to go down. This causes decrease of return oil from point c,
      and by consequence, the control oil pressures in line (4425) increases that
      goes to force amplifier. This causes descending the nozzle arm connected to
      force amplifier arm, and opens the nozzle greatly to let big fuel quantity to the
      combustion chamber. The result is increasing the temperature of the generated
      gases.

  b- During operation and loading
     The governor (2675) controls the oil pressure at h by increasing oil pressure in
     line (4404), when speed decreases and the governor balls approach. This
     caused reduction of escape oil to make up this speed reduction by increasing
     oil quantity through the nozzle. The opposite happens on increasing the speed
     and the balls get faraway, then the oil pressure in line (4404) decreases at h the
     nozzle opening decreases to reduce fuel admission.




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