The gas fuel system consists of the gas fuel auxiliary stop valve, gas fuel stop/ratio valve, diffusion gas control valve, PM4 gas control valve, and PM1 gas control valve. Refer to Fig. (3.30)
The stop/ratio valve (SRV) is designed to maintain a predetermined pressure (P=18 bar) at the control valve inlet. The diffusion, PM4 and PM1 gas control valves (GCVs) regulate the desired gas fuel flow delivered to the turbine in response to the command signal FSR from the SPEEDTRONIC™ panel. The dry low NOx mode of operation will determine how the control valves stage fuel to the multi-nozzle combustion system. The stop ratio valve and gas control valves are monitored for their ability to track the command set point.
The valve command set point differs from the actual valve position by a prescribed amount for a period of time; an alarm will annunciate to warn the operator. If the condition persists for an extended amount of time, the turbine will be tripped and another alarm will annunciate the trip.
3.2.3.5 Gas Fuel Operation
There are three basic modes of distributing gas fuel to the DLN-2 combustor.
These modes are described below:
1. Diffusion Mode
In this mode, all the gas fuel directed to the 5 diffusion (D5) tips in each of the combustors. At this time, the pre-mix passages PM4 and PM1are purged with compressor discharge (CPD) air. Diffusion is in the normal mode of operation from ignition to a combustion reference temperature of 2000oF (1093 oC) loading and unloading from 1950 oF till flame out and speed of 2835 rpm (95% of speed).
2. Piloted Pre-Mix
In this mode the fuel is split between the three gas control valvesPM1, PM4and D5. To fire an even premix split, the split between PM1 GCV and PM4 GCV, which feed the PM1 and PM4 manifolds respectively should be 20/80. It is normal to run the pre-mix burners slightly off even split to optimize combustion dynamics at the expense of emissions.
Piloted premix is the combustion mode between combustion reference temperature 2000 F and 2270 oF loading and 2220 oF unloading and power reach to 140 MW loading.
3. Pre-Mix.
In pre-mix, all the fuel is directed to the PM1 and PM4GCVswhich feed the pre-mix nozzles. Pre-mix mode combustion occurs above 2270 oF loading and 2220 oF unloading but D5 is purged with air. The diagrams in Figure (3.31) and Figure (3.32) show how fuel flow is controlled while transferring between the various combustion modes.
3.2.3.6 Atomizing Air System.
The Atomizing Air system for the MS7001FA and MS9001FA gas turbine provides compressed air for atomization of liquid fuel in the combustion system. The Atomizing Air is introduced through supplementary orifices in the fuel nozzles. The discharge from these nozzles impinges directly upon the liquid fuel oil spray as it enters the combustion chambers. The high velocity Atomizing Air stream shears the droplets of fuel into very small pieces, yielding a fine mist. The fine mist of fuel burns more completely in the combustion chamber, yielding significantly higher combustion efficiency and lower levels of combustion particles discharging to atmosphere through the exhaust. In addition to supplying air for atomization of liquid fuel, the Atomizing Air system also supplies purge air to the liquid fuel and water injection nozzles when the gas turbine is operating on gas fuel to prevent fuel accumulation and combustion back-flow. Immediately following shut down, the Atomizing Air Compressor can be run to purge and cool the Atomizing Air, Water Injection and Liquid Fuel nozzles. Provisions can also be made to use the Atomizing Air module to purge the Atomizing Air and Liquid Fuel piping during off-line water washes.
3.2.3.7 Atomizing Air System Components
The major Atomizing Air System components are as follows:
1. Atomizing Air Compressor/Motor assembly.
2. Inlet Air Heat Exchanger or Pre-cooler.
3. Cooling Water Control Valve and Electro-pneumatic Temperature Controller arrangement.
4. Cooling Water Electro-pneumatic Temperature Controller Thermocouple.
5. Dual Inlet Air Temperature Switches.
6. Moisture Separators.
7. Air Filter and Air Filter Differential Pressure Switch.
8. Motor Actuated Atomizing Air Compressor Bypass Valve with Limit Switches.
9. Motor Actuated Atomizing Air D/S Throttling Valve with Limit Switches.
10. Motor Actuated Atomizing Air Scavenging Valve with Limit Switches.
11. Compressor Differential Pressure Switches.
12. Compressor Discharge Temperature Switch.
13. CDP - Atomizing Air Manifold Differential Pressure Transmitters.
14. Cooling Water Bypass Solenoid, Control Valve and Limit Switches.
Exhaust gases generated from burning fuel in the combustion chambers flows through the impingement cooled transition pieces to the turbine.
The stop/ratio valve (SRV) is designed to maintain a predetermined pressure (P=18 bar) at the control valve inlet. The diffusion, PM4 and PM1 gas control valves (GCVs) regulate the desired gas fuel flow delivered to the turbine in response to the command signal FSR from the SPEEDTRONIC™ panel. The dry low NOx mode of operation will determine how the control valves stage fuel to the multi-nozzle combustion system. The stop ratio valve and gas control valves are monitored for their ability to track the command set point.
The valve command set point differs from the actual valve position by a prescribed amount for a period of time; an alarm will annunciate to warn the operator. If the condition persists for an extended amount of time, the turbine will be tripped and another alarm will annunciate the trip.
3.2.3.5 Gas Fuel Operation
There are three basic modes of distributing gas fuel to the DLN-2 combustor.
These modes are described below:
1. Diffusion Mode
In this mode, all the gas fuel directed to the 5 diffusion (D5) tips in each of the combustors. At this time, the pre-mix passages PM4 and PM1are purged with compressor discharge (CPD) air. Diffusion is in the normal mode of operation from ignition to a combustion reference temperature of 2000oF (1093 oC) loading and unloading from 1950 oF till flame out and speed of 2835 rpm (95% of speed).
2. Piloted Pre-Mix
In this mode the fuel is split between the three gas control valvesPM1, PM4and D5. To fire an even premix split, the split between PM1 GCV and PM4 GCV, which feed the PM1 and PM4 manifolds respectively should be 20/80. It is normal to run the pre-mix burners slightly off even split to optimize combustion dynamics at the expense of emissions.
Piloted premix is the combustion mode between combustion reference temperature 2000 F and 2270 oF loading and 2220 oF unloading and power reach to 140 MW loading.
3. Pre-Mix.
In pre-mix, all the fuel is directed to the PM1 and PM4GCVswhich feed the pre-mix nozzles. Pre-mix mode combustion occurs above 2270 oF loading and 2220 oF unloading but D5 is purged with air. The diagrams in Figure (3.31) and Figure (3.32) show how fuel flow is controlled while transferring between the various combustion modes.
3.2.3.6 Atomizing Air System.
The Atomizing Air system for the MS7001FA and MS9001FA gas turbine provides compressed air for atomization of liquid fuel in the combustion system. The Atomizing Air is introduced through supplementary orifices in the fuel nozzles. The discharge from these nozzles impinges directly upon the liquid fuel oil spray as it enters the combustion chambers. The high velocity Atomizing Air stream shears the droplets of fuel into very small pieces, yielding a fine mist. The fine mist of fuel burns more completely in the combustion chamber, yielding significantly higher combustion efficiency and lower levels of combustion particles discharging to atmosphere through the exhaust. In addition to supplying air for atomization of liquid fuel, the Atomizing Air system also supplies purge air to the liquid fuel and water injection nozzles when the gas turbine is operating on gas fuel to prevent fuel accumulation and combustion back-flow. Immediately following shut down, the Atomizing Air Compressor can be run to purge and cool the Atomizing Air, Water Injection and Liquid Fuel nozzles. Provisions can also be made to use the Atomizing Air module to purge the Atomizing Air and Liquid Fuel piping during off-line water washes.
3.2.3.7 Atomizing Air System Components
The major Atomizing Air System components are as follows:
1. Atomizing Air Compressor/Motor assembly.
2. Inlet Air Heat Exchanger or Pre-cooler.
3. Cooling Water Control Valve and Electro-pneumatic Temperature Controller arrangement.
4. Cooling Water Electro-pneumatic Temperature Controller Thermocouple.
5. Dual Inlet Air Temperature Switches.
6. Moisture Separators.
7. Air Filter and Air Filter Differential Pressure Switch.
8. Motor Actuated Atomizing Air Compressor Bypass Valve with Limit Switches.
9. Motor Actuated Atomizing Air D/S Throttling Valve with Limit Switches.
10. Motor Actuated Atomizing Air Scavenging Valve with Limit Switches.
11. Compressor Differential Pressure Switches.
12. Compressor Discharge Temperature Switch.
13. CDP - Atomizing Air Manifold Differential Pressure Transmitters.
14. Cooling Water Bypass Solenoid, Control Valve and Limit Switches.
Exhaust gases generated from burning fuel in the combustion chambers flows through the impingement cooled transition pieces to the turbine.
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