6.1AUXILIARY SYSTEM
6.1.1 Atomizing Air System
Atomizing air systems provide sufficient pressure in the air atomizing chamber of the fuel nozzle body to maintain the ratio of atomizing air pressure to compressor discharge pressure at approximately 60% speed or greater over the full operating range of the turbine. Since the output of the main atomizing air compressor, driven by the accessory gear, is low at turbine firing speed, a starting atomizing air compressor provides a similar pressure ratio during the firing and warm-up period of the starting cycle, and during operation of the accelerating cycle.
Major system components include the main atomizing air compressor, starting atomizing air compressor and atomizing air heat exchanger. Refer to the Atomizing Air Schematic Piping Diagram in the Reference Drawings section of the Inspection and Maintenance volume as shown in Figure (6.1).
6.1.2 Functional Description
When liquid fuel oil is sprayed into the turbine combustion chambers it forms large droplets as it leaves the fuel nozzles. The droplets will not burn completely in the chambers and many could go out of the exhaust stack in this state. A low pressure atomizing air system is used to provide atomizing air through supplementary orifices in the fuel nozzle which directs the air to impinge upon the fuel jet discharging from each nozzle.
This stream of atomizing air breaks the fuel jet up into a fine mist, permitting ignition and combustion with significantly increased efficiency and a decrease of combustion particles discharging through the exhaust into the atmosphere. It is necessary, therefore, that the air atomizing system be operative from the time of ignition firing through acceleration, and through operation of the turbine.
Air taken from the atomizing air extraction manifold of the compressor discharge casing passes through the air-to water heat exchanger (pre cooler) HXl to reduce the temperature of the air sufficiently to maintain a uniform air inlet temperature to the atomizing air compressor.
The atomizing air pre cooler heat exchanger Located in the turbine base under the inlet plenum uses water from the turbine cooling water system as the cooling medium to dissipate the heat. Switch 26AA:"1 is an adjustable heat sensitive thermo switch provided to sound an alarm when the temperature of the air from the atomizing air pre cooler entering the main atomizing air compressor is excessive.
When the atomizing air reaches the temperature setting of this switch, the alarm is activated. Improper control of the temperature may be due to failure of the sensor, the pre cooler or insufficient cooling water flow. Continued operation above 275 F should not be permitted for any significant length of time since it may result in failure of the main atomizing air compressor or in insufficient atomizing air to provide proper combustion Compressor discharge air, now cleaned and cooled reaches the main atomizing air compressor. This is a single stage, flange mounted, centrifugal compressor driven by an inboard shaft of the turbine accessory gear.
It contains a single impeller mounted on the pinion shaft of the integral input speed-increasing gearbox driven directly by the accessory gear. Output of the main compressor provides sufficient air for atomizing and combustion when the turbine is at approximately 60-percent speed.
Differential pressure switch 63AD-1, located in a bypass around the compressor, monitors the air pressure and annunciates an alarm if the pressure rise across the compressor should drop to a level inadequate for proper atomization of the fuel. Air, now identified as atomizing air, valves the compressor and is piped to the atomizing air manifold with “pigtail” piping providing equal pressure distribution of atomizing air to the 10 individual fuel nozzles.
When the turbine is first fired, the accessory gear is not rotating at full speed and the main atomizing air compressor is not outputting sufficient air for proper fuel atomization. During this period, the starting (booster) atomizing air
compressor, driven by an electric motor is in operation supplying the necessary atomizing air. The starting atomizing air compressor at this time has a high-pressure ratio and is discharging through the main atomizing air compressor, which has a low-pressure ratio.
The main atomizing air compressor pressure ratio increases with increasing turbine speed and at approximately 60% speed the flow demand of the main atomizing air compressor approximates the maximum flow capability of the starting atomizing air compressor. The check valve in the air input line to the main compressor begins to open allowing air to be supplied to the main compressor simultaneously from both the main airline and the starting air compressor.
The pressure ratio of the starting atomizing air compressor decreases one, and when the turbine becomes self sustaining, the starting compressor is shut down at approximately 95 percent speed 4HS pickup. Now all of the air being supplied to the main compressor is directly from the pre cooler through the check valve, bypassing the starting air compressor completely. At this time the (20AB) solenoid is energized and the isolation valve (VA22) is closed preventing any air getting to the booster compressor.
6.1.1 Atomizing Air System
Atomizing air systems provide sufficient pressure in the air atomizing chamber of the fuel nozzle body to maintain the ratio of atomizing air pressure to compressor discharge pressure at approximately 60% speed or greater over the full operating range of the turbine. Since the output of the main atomizing air compressor, driven by the accessory gear, is low at turbine firing speed, a starting atomizing air compressor provides a similar pressure ratio during the firing and warm-up period of the starting cycle, and during operation of the accelerating cycle.
Major system components include the main atomizing air compressor, starting atomizing air compressor and atomizing air heat exchanger. Refer to the Atomizing Air Schematic Piping Diagram in the Reference Drawings section of the Inspection and Maintenance volume as shown in Figure (6.1).
6.1.2 Functional Description
When liquid fuel oil is sprayed into the turbine combustion chambers it forms large droplets as it leaves the fuel nozzles. The droplets will not burn completely in the chambers and many could go out of the exhaust stack in this state. A low pressure atomizing air system is used to provide atomizing air through supplementary orifices in the fuel nozzle which directs the air to impinge upon the fuel jet discharging from each nozzle.
This stream of atomizing air breaks the fuel jet up into a fine mist, permitting ignition and combustion with significantly increased efficiency and a decrease of combustion particles discharging through the exhaust into the atmosphere. It is necessary, therefore, that the air atomizing system be operative from the time of ignition firing through acceleration, and through operation of the turbine.
Air taken from the atomizing air extraction manifold of the compressor discharge casing passes through the air-to water heat exchanger (pre cooler) HXl to reduce the temperature of the air sufficiently to maintain a uniform air inlet temperature to the atomizing air compressor.
The atomizing air pre cooler heat exchanger Located in the turbine base under the inlet plenum uses water from the turbine cooling water system as the cooling medium to dissipate the heat. Switch 26AA:"1 is an adjustable heat sensitive thermo switch provided to sound an alarm when the temperature of the air from the atomizing air pre cooler entering the main atomizing air compressor is excessive.
When the atomizing air reaches the temperature setting of this switch, the alarm is activated. Improper control of the temperature may be due to failure of the sensor, the pre cooler or insufficient cooling water flow. Continued operation above 275 F should not be permitted for any significant length of time since it may result in failure of the main atomizing air compressor or in insufficient atomizing air to provide proper combustion Compressor discharge air, now cleaned and cooled reaches the main atomizing air compressor. This is a single stage, flange mounted, centrifugal compressor driven by an inboard shaft of the turbine accessory gear.
It contains a single impeller mounted on the pinion shaft of the integral input speed-increasing gearbox driven directly by the accessory gear. Output of the main compressor provides sufficient air for atomizing and combustion when the turbine is at approximately 60-percent speed.
Differential pressure switch 63AD-1, located in a bypass around the compressor, monitors the air pressure and annunciates an alarm if the pressure rise across the compressor should drop to a level inadequate for proper atomization of the fuel. Air, now identified as atomizing air, valves the compressor and is piped to the atomizing air manifold with “pigtail” piping providing equal pressure distribution of atomizing air to the 10 individual fuel nozzles.
When the turbine is first fired, the accessory gear is not rotating at full speed and the main atomizing air compressor is not outputting sufficient air for proper fuel atomization. During this period, the starting (booster) atomizing air
compressor, driven by an electric motor is in operation supplying the necessary atomizing air. The starting atomizing air compressor at this time has a high-pressure ratio and is discharging through the main atomizing air compressor, which has a low-pressure ratio.
The main atomizing air compressor pressure ratio increases with increasing turbine speed and at approximately 60% speed the flow demand of the main atomizing air compressor approximates the maximum flow capability of the starting atomizing air compressor. The check valve in the air input line to the main compressor begins to open allowing air to be supplied to the main compressor simultaneously from both the main airline and the starting air compressor.
The pressure ratio of the starting atomizing air compressor decreases one, and when the turbine becomes self sustaining, the starting compressor is shut down at approximately 95 percent speed 4HS pickup. Now all of the air being supplied to the main compressor is directly from the pre cooler through the check valve, bypassing the starting air compressor completely. At this time the (20AB) solenoid is energized and the isolation valve (VA22) is closed preventing any air getting to the booster compressor.
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