GE 7FA.05 - Atomizing Air System (Dual Fuel Units Only); General Notes; Atomizing Air Compressor; Atomizing Air Pre-Cooler

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GEK 116862 Inspection and Maintenance Instructions for 7FA.05 Gas Only and Dual Fuel Gas Turbines

XIV. ATOMIZING AIR SYSTEM (DUAL FUEL UNITS ONLY)

A. General Notes

In addition to these general guidelines, reference any detailed maintenance instructions provided by

the Liquid Fuel/Atomizing Air Module (MLI A162) vendor, including maintenance manuals for the

individual components in the system (compressor, valves, etc.)

Atomizing air system leakage may result in loss of machine performance, improper combustion and

smokey exhaust. Large leaks may cause a machine to shut down. Large leaks may cause a back flow

of combustion products or unburned fuel from the combustor particularly if near the combustion

chambers. Large leaks may cause fire or explosion if an ignition source is present.

B. Atomizing Air Compressor

The atomizing air system is required during liquid fuel operation to provide sufficient pressure in the

air atomizing chamber of the fuel nozzle body to maintain the ratio of atomizing air pressure (psia) to

compressor discharge pressure (psia). This ratio should be in accordance with the value given in the

Control Specification Settings over the full operating range of the turbine. The maximum deviation

for any steady–state operation, at 100% speed, should not exceed ±0.05 for a low pressure ratio

system (between 1.30 and 1.60).

Increasing pressure ratio trends may be caused by dirty air passages in the fuel nozzles. Decreasing

pressure ratio trends may be traced to leaks in the system or to a malfunctioning atomizing air

compressor.

When a dual fuel machine is operating on gas fuel, the atomizing air manifold pressure (psia) should

be slightly higher than the compressor discharge pressure (psia), for a ratio of approximately 1.20.

For increasing and decreasing pressure trends refer to previous paragraph.

If it is determined that overheating, low pressure ratio, excessive gear or rotor noise, failing oil seal,

cylinder discoloration, or scorched paint are caused by a malfunctioning atomizing air compressor,

remove the compressor from the turbine and replace it with a new or reconditioned unit. DO NOT

DISASSEMBLE THE COMPRESSOR IN THE FIELD. Consult the GE Field Service

Representative for the disposition of a malfunctioning compressor. Atomizing air compressors should

be returned for factory preventive maintenance on a schedule recommended by the GE Field Service

Representative; or, as determined by the user’s own operating experience. Excessive gear or rotor

noise is usually due to misalignment or foreign matter. A visual rotor inspection can be made through

the air inlet or outlet connection, or through the pipe plug in the side of the compressor.

C. Atomizing Air Pre-Cooler

Exchangers are, subject to fouling (scale, sludge deposits, etc.), and should be cleaned periodically,

depending on specific conditions. A light sludge or scale coating on either side of the tube greatly

reduces its effectiveness. A marked increase in pressure drop and/or reduction in performance usually

indicates cleaning is necessary.

Neglecting to keep tubes clean may result in random tube plugging. Consequently, overheating, or

cooling, of the plugged tubes, as compared to surrounding tubes, will cause physical damage and

leakage, due to the differential thermal expansion of the metals.

If a pre-cooler tube should develop a leak, it may be possible to plug the tube in the pre-cooler and

continue using the bundle. Consult GE for information concerning how many tubes may be plugged