Gas Turbine Training Manual
GAS FUEL SYSTEM 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. The major component of a gas fuel system is the gas stop/ratio and control valves assembly located in the gas fuel module. Associated with this gas valve is the necessary inlet piping and strainers, fuel vent valve, control servo valves, pressure gauges and the distribution piping to the combustion fuel nozzles. The major component of a gas fuel system is the gas stop/ratio and control valves located in the gas fuel module. Associated with this gas valve is the necessary inlet piping and strainers, fuel vent valve, control servo valves, pressure gauges and the distribution piping to the combustion fuel nozzles.
The following major components comprise the gas fuel system. a. Gas fuel strainer. b. Gas stop ratio valve and control valve (VSR-1, VGC-1). c. Fuel gas low-pressure alarm switch (63FG-3). d. Pressure Gauges. e. Gaseous fuel vent valve (20VG-1). f. Gas fuel trip valve (VH5-1) g. Stop ratio valve servo & Control valve servo (65GC-1 & 65SR-1) h. Gas control valve LVDTs (96GC-1,-2) i . Pressure transducers (96FG-2A-2B,-2C) j. Stop ratio LVDTs (96SR-1,-2) k. Gas fuel servo-hydraulic supply filter (FH7-1) l. Gas fuel manifold and nozzles (MG1-1)
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Gas Turbine Training Manual
FUNCTIONAL DESCRIPTION Gas fuel is first cleaned by passing through a strainer as it comes from the supply piping prior to flowing through the gas valve and into the gas manifold piping. The gas fuel is metered and controlled by the gas valve (gas stop ratio and control valve) to supply the required flow to the gas turbine combustion system. The fuel gas stop ratio and control valve consists of two independent valves(a stop ratio valve and a control valve) combined into one housing assembly. For higher rating Gas Turbines are provided with two separate valves in place of a single assembly. Both the gas stop ratio valve and the gas control valve are stroked by Electro-hydraulic servo actuators. These actuators are single acting type. The fuel gas control valve 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 used to shut off fuel flow to the turbine whenever required. It also controls the pressure ahead of the fuel gas control valve. This enables the gas control valve to control fuel flow over the wide range required under turbine starting and operating conditions. GAS STOP/RATIO AND CONTROL VALVE. The gas control valve part of the gas stop/ratio and 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. The control voltage generated acts to shift the electro-hydraulic 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 stop ratio valve is similar to the gas control valve. Its plug, however, has a steeper taper to provide the high gain necessary to maintain good pressure control. 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 functions in the fuel gas system to provide a positive fuel shutoff when required by either normal or emergency conditions. A gas fuel trip is operated by trip oil pressure acting/removal on the piston end of a spool. When the trip oil flows 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 pressure below predetermined limit, a spring in the trip 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 stop ratio valve closes, shutting off fuel gas flow to the turbine.
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Scheme For Hazardous Gas Detectors System
Gas Turbine Training Manual
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Scheme For Fuel Gas System
Gas Turbine Training Manual
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Gas Turbine Training Manual 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 strainers. Foreign particles that may be in the incoming fuel gas are removed by the strainer. A blow down connection on the bottom of the gas strainer body provides for periodic cleaning of the strainer screen. Frequency of cleaning will depend on the quality of the fuel gas being used. The strainer should be cleaned shortly after full turbine load has been attained for the first time and after any disassembly of the purchaser’s fuel gas lines. PROTECTIVE DEVICES Low Gas Pressure Switch A low gas pressure switch 63FG-3, installed in the gas piping ahead of the gas stop/speed ratio and control valve assembly provides alarm protection should the gas pressure drop below the switch setting. An alarm will be indicated on the annuniciator in the control center. Fuel Gas Vent Valve Solenoid-operated valve 20VG-1, is installed in the vent piping from the casing of the combination gas stop/speed ratio and gas control valve. When the turbine is shutdown, any fuel gas that might accumulate in the compartment between the stop/speed ratio and control valve, vents to atmosphere through the piping. Pressure Transducer Three pressure transducers, 96FG-2A, 2B and 2C, are installed in the fuel line on the gas fuel discharge side of the stop/speed ratio valve; the intermediate gauge measures the pressure as it leaves the valve; and the downstream gauge measures pressure of the gas leaving the gas control valve and flowing to the gas manifold. SERVO-HYDRAULIC SUPPLY FILTER A filter (FH7-1) is installed in the hydraulic supply to the speed ratio and tag control valve servo valves 90SR-1 and 65GC-1 to provide 15 microns filtration. A high filter differential pressure indicator is included. FUEL MANIFOLD 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.
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