Gas Turbine Fuel System

General
The gas fuel system is designed to deliver gas fuel to the turbine combustion chambers at the proper pressure and flow rates to meet all of the starting, acceleration and loading requirements of gas turbine operation. A schematic diagram of the gas fuel system is provided in Figure GF-1.

The major components of a gas fuel system are the gas stop/ratio and gas control valves located in the gas fuel module. Associated with the gas valves are the necessary inlet piping and strainer, fuel vent valve, control servo valves and the distribution piping to the 14 combustion fuel nozzles.

The fuel gas stop ratio valve and the gas control valves are independent valves, located side by side in the gas fuel piping of the module. The gas fuel flows through the gas stop ratio valve and then into the gas control valves on its way to the gas manifold and individual combustion chambers. The position of each valve is servo controlled by electrical signals from the gas turbine SPEEDTRONIC control system. Both the gas stop ratio valve and the gas control valves are actuated by single-acting, hydraulic cylinders.

The following major components comprise the gas fuel system:
  • Filters
  • Gas fuel stop solenoid valves 20 FG’s
  • Fuel gas supply pressure alarm switch
  • Gas stop ratio valve VSR
  • Gas control valve VGC’s
  • Stop ratio LVDT 96 SR
  • Gas control valve LVDT 96 GC
  • Stop ratio valve-control servovalve 90 SR-1
  • Gas control valve-control servovalve 65 GC
  • Gas fuel trip valves VH 5
  • Gas fuel vent solenoid valves 20 VG-1
  • Pressure gauges
  • Lines to the 14 combustion chambers


Part Nomenclature

20 VG-1 Gas fuel (purge) vent solenoid valve.

20 FGC-1,-2,-3 Trip solenoid valve for gas control valve VGC-1,-2,-3.

20 FGS-1 Fuel gas stop valve solenoid valve.

33 VG-11 Limit switch on solenoid valve 20 VG-1.

65 GC-1,-2,-3 Gas control valve (servo-valve).

90 SR-1 Stop/speed (pressure) ratio valve servo-valve.

96 FG-2A,-2B,-2C Fuel gas inter-valve pressure transmitter.

96 FG-4A,-4B,-4C Fuel gas inter-valve pressure transmitter.

96 FG-5A,-5B,-5C Fuel gas inter-valve pressure transmitter.

96 FG-6A,-6B,-6C Fuel gas inter-valve pressure transmitter.

96 FG-1 Fuel gas supply pressure transmitter.

96 GC-1,-2 Gas control valve L.V.D.T.

96 SR-1,-2 Stop/speed (pressure) ratio valve L.V.D.T.

AHI-3,-4 Control oil hydraulic accumulator.

FH 7-1 Gas fuel Stop Valve (VSR-1). Servo Hydraulic Oil Supply Filter.

FH 8-1,-2,-3 Gas fuel Control Valve (VGC-1,-2,-3). Servo Hydraulic Oil Supply Filter.

FT_GI-1A,-1B Fuel gas temperature sensor.

FT_GI-2A,-2B Fuel gas temperature sensor.

MG1-1 Gas fuel nozzle - primary.

MG1-2 Gas fuel nozzle - secondary.

MG1-3 Gas fuel nozzle - transfer.

VGC-1 Gas control valve - Primary.

VGC-2 Gas control valve - Secondary.

VGC-3 Gas control valve - Transfer.

VH 5-1 VSR-1 security discharge valve.

VH 5-2,-3,-4 VGC-1,-2,-3 trip valve.

VSR-1 Fuel gas stop/ratio valve.

Gas Fuel System Schematic



Functional description of the gas fuel system

General
The gas control valves and the gas stop ratio valve, although similar, each perform separate functions. The fuel gas control valves meters fuel for use by the combustion chambers. It is activated by a SPEEDTRONIC control signal to admit the proper amount of fuel required by the turbine for a given load or speed. The fuel gas stop ratio valve is a dual function valve. It serves as a stop valve to shut off fuel flow to the turbine whenever

required during either normal operation or in an emergency shut-down situation. The stop ratio valve also serves as a pressure regulating valve to hold a known fuel gas pressure ahead of the gas control valve and enable the gas control valves to control fuel flow over the wide range required under turbine starting and operating conditions. Because of these dual functions the valve is sometimes called a stop/speed ratio valve.
Gas strainer
A gas strainer is installed upstream of the turbine base fuel inlet connection point, to facilitate site maintenance requirements. Connection of the fuel gas supply is made at the purchaser’s connection in the supply line ahead of the gas strainer. Foreign particles that may be in the incoming fuel gas are removed by the strainer.

Gas stop/ratio and gas control valves
The gas control valves VGC’s regulates the required control valve area and utilizes an hydraulic cylinder controlled by an electrohydraulic servo valve. The gas control valve provides a fuel gas metering function to the turbine in accordance with its speed and load requirements. The position of the gas control valve (hence fuel gas flow to the turbine) is a linear function of a Fuel stroke reference voltage (FSR) generated by the SPEEDTRONIC control.

A dump valves VH 5-2,-3,-4 are operated by trip oil acting on the piston end of a spool. An hydraulic trip solenoid valves, 20 FGC-1,-2,-3 are located in the trip oil line to the dump valves. When the trip oil pressure is normal and the 20 FGC-1,-2,-3 solenoid valves are energized to reset, the spool of the dump valves are held in a position that allows hydraulic Oil to flow between the control servo valves and the hydraulic cylinders. In this position, normal control of the gas control valve valve is allowed.

The control voltage generated acts to shift the electrohydraulic servo valve to admit oil to, or release it from, the hydraulic cylinder to position the gas control valve so that the fuel gas flow is that which is required for a given turbine speed and load situation.

The gas control valves also provides a shut-off of the fuel gas flow when required by either normal operation or emergency conditions. The hydraulic trip relays (dump valves) VH 5-2,- 3,-4 are located between the electrohydraulic servo valves 65 GC-1,-2,-3 and the hydraulic cylinders. The operation of this dump valves is the same as the trip relays (dump valves) VH 5-2,-3,-4.

The plugs in the VGC’s are contoured to provide the proper flow area in relation to valve stroke. The VGC’s use a skirted valve plug and venturi seat to obtain adequate pressure recovery. High pressure recovery occurs at valve pressure ratios substantially less than the critical pressure ratio. The result is that the flow through the VGC’s are independent of the pressure drop across the valves and is a function of valves inlet pressure, P2 temperature and valve area only.

The combined position of the control valves is intended to be proportional to FSR, which represents called-for fuel – required by the control system to maintain either speed, load, or another set point. FSR2 is the percentage of maximum fuel flow required from the Gas Fuel System. FSR2 is further divided so that a command is sent via the servo valves (65 GC-1,- 2,-3) on VGC-1,-2,-3 so that the required split of gas fuel is achieved. Dual redundant

Linear Variable Differential Transformers (LVDT’s) – 96 GC-1,-2,-3,-4,-5,-6 are used for Control valves for position sensing.

The VSR 1 and VGC's are equipped with hydraulically actuated spring return dump valves (VH 5-1,-2,-3,-4). The dump valves are held in their normal operating state by a supply of hydraulic oil referred to as trip oil. The trip oil system is triple redundant to ensure that no single device failure can disturb the operation of the power generating unit. The gas stop/ratio valve VSR-1 is similar to the gas control valves VGC’s. The ratio function of the stop ratio/valve provides a regulated inlet pressure for the control valve as a function of turbine speed. The SPEEDTRONIC pressure control loop generates a position signal to position the stop ratio valve by means of a servo valve controlled hydraulic cylinder to provide required inter valve pressure.

The gas stop ratio valve VSR-1 functions as a stop valve in the fuel gas system to provide a positive fuel shut off when required by either normal or emergency conditions. Any emergency trip or normal shut-down will trip the valve to its closed position. This is done either by dumping hydraulic oil from the valve’s hydraulic cylinder or driving the position control closed electrically. A dump valve VH 5-1 is operated by trip oil acting on the piston

end of a spool. An hydraulic trip solenoid valve, 20 FGS-1, is located in the trip oil line to the dump valve. When the trip oil pressure is normal and the 20 FGS-1 solenoid valve is energized to reset, the spool of the dump valve is held in a position that allows hydraulic oil to flow between the control servo valve and the hydraulic cylinder. In this position, normal control of the stop ratio valve is allowed.

In event of a drop in trip oil below a predetermined limit, a spring in the dump valve shifts the spool to interrupt the flow path of oil between the control servo valve and the hydraulic cylinder. Hydraulic oil is dumped and the ratio valve closes, shutting off gas fuel flow to the turbine.



Gas fuel system protective devices

Gas pressure transmitter
A low gas pressure alarm transmitter (96 FG-1) is installed in the gas piping ahead of the gas stop/ratio valve assembly. This transmitter initiates a gas fuel pressure low alarm when gas supply pressure drops below the switch setting. It also initiates a transfer to liquid fuel if gas supply pressure drops below its set point.

Gas fuel vent valve

Solenoid-operated valve 20 VG-1 is installed in the vent piping between the gas stop/speed ratio and gas control valve. When the turbine is shut down, any gas fuel that might accumulate in the compartment between the stop/speed ratio and gas control valves, vents to atmosphere through the piping. It also ensures that no gas fuel will leak past the closed gas control valve to collect in the combustors or exhaust.

Limit switch 33 VG-11 controls the full opening of solenoid valve 20 VG-1, if not open, it activates an alarm.

Pressure transmitters
Pressure transmitters, 96 FG-2A,-2B,-2C, 96 FG-4A,-4B,-4C, 96 FG-5A,-5B,-5C and 96 FG-6A,-6B-,-6C are installed in the fuel system on the gas fuel discharge side of the stop/speed ratio valve and the gas control valves, to provide the operational pressure feedback signal to the SPEEDTRONIC control system. The DC voltage output signal is the median of the 3 transmitters readings.

Servo-hydraulic supply filters
A filter FH 7-1 and FH 8-1,-2,-3 are installed in the hydraulic supply to the speed ratio and gas control valve servo-valves 90 SR-1 and 65 GC-1,-2,-3 to provide 15 microns filtration. A high filter differential pressure indicator is included.

Fuel manifolds and nozzles
Fuel from the control valve is distributed through the manifold to the fuel nozzle Assemblies mounted in each combustion chamber. Fuel from the nozzles is mixed with air in the combustion liner where combustion takes place.

Final gas filters
The final gas filters are mounted in the lines to the primary, secondary and transfer manifolds. They are part of the final gas conditioning and are to be definitely removed after 100 hours of operation. The filters are mounted vertically on lines. The filter cartridge is of cleanable filter element type.

Temperature sensors
The K-type thermocouples sensors (FT_G1-1A,-1B; FT_G1-2A,-2B) are installed in the gas fuel supply line downstream of the SRV to confirm the gas fuel inlet temperature is within specified requirements at startup and throughout turbine operation. A median select, mismatch-alarm methodology is utilized by the control to interpret the three temperature signals. High levels will result in an indication to the operator, whereas High-high levels result in lockout of premix mode. Excessively high temperature indications result in turbine trip. Low levels result in lockout of premix mode.

In event of a drop in trip oil below a predetermined limit, a spring in the dump valve shifts the spool to interrupt the flow path of oil between the control servo valve and the hydraulic cylinder. Hydraulic oil is dumped and the ratio valve closes, shutting off gas fuel flow to the turbine.



Gas purging system


Gas fuel purge


The fuel transfer manifold must be purged.

A schematic diagram of the fuel purging system is provided in Figure GP-1.

Air is the purge medium, supply by compressor discharge air for the gas side.

Gas backflow to compressor discharge must be prevented. The gas fuel system purge valves air actuated VA 13 must be closed tightly. If it does not happen, protective measures are to be taken.

On the contrary, during fuel gas operation of the unit, solenoid valves 20 PG-3, -4 are de-energized, so shutting off the pneumatic actuation of VA 13-3 and VA 13-4.

  • There are redundant VA 13 purge valves.
  • The 20 VG-3 valve vents the line to atmosphere between the purge valves. Pressure switch 63 PG-2 will alarm if excessive pressure builds up between the valves, indicating the presence of too much gas.
  • 33 PG limit switches are used to indicate the position of the VA 13 valve: open or closed. The transfer gas purge operates the same except the VA 13 valves are normally open as the transfer system is usually not flowing gas fuel.

Gas Purging System Schematic

8 comments:

  1. The system seems great it would be interesting to know how efficient a Gas Turbine Fuel System can be?

    Thanks
    Henry Jordan

    Hydraulic Seal Kits


    ReplyDelete
  2. Dear Sir,

    Could you please sent to me the good quality fuel system P&ID? The drawing on the web cant not view clearly.

    ReplyDelete
    Replies
    1. Figures and drawings are too blur to understand anything.

      Delete
  3. Our pneumatic factory was founded in 2000,CHECK HERE. In decades of serving China pneumatic industry, we have built our reputation on product knowledge, world class suppliers, application support, and value add services. Our commitment to our employees, customers and vendors is the core of our business beliefs. In our factory, there are more than 80 front-line workers, 3000 squares working shop.Our main products are air Pneumatic Cylinder, solenoid valve and also a lot of pneumatic fittings like Air Gun.

    ReplyDelete
  4. Could you please sent to me the good quality fuel system P&ID? The drawing on the web cant not view clearly.

    ReplyDelete
  5. Dear sir,
    Is it any standard's requirement for the distance between the gas purge pipes and air inlet of gas turbine?

    ReplyDelete
  6. Dear Sir,

    Is there a high pressure TRIP on the fuel gas system? if yes where it is located

    ReplyDelete
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    ReplyDelete