reducing hazards to acceptable limits.

Specific practices for preventing hot corrosion and preserving performance include:

• Careful study of model capacity ratings. Some manufacturers have recognized the benefits of natural gas firing by increasing their model capacity ratings by several percent for gas fuel operation. These higher ratings offer more capacity, higher thermal efficiency, and lower first cost per hp (kW) without increasing the cost per hp-h (kWh) for maintenance, increasing maintenance outages, or decreasing expected turbine life.

• For operation on distillate fuels, application of filter systems featuring coalescing stages followed by 1 to 3 micron particulate control stages for the removal of water-born alkali metals.

• Compressor water washing, which has been demonstrated in field experience to be useful in recovery of performance lost to compressor fouling. On-line water washing benefits applications where economics demand maximum on-line service time and maximum life-cycle efficiency. Alternatively, off-line water washing, which removes alkali coating and carries it out of the machine in solution through cleaning solution drains, offers superior performance recovery.

Gas turbines can operate for years without a single interruption of service. They are, however, typically shutdown every three to six months for a few hours for detailed inspection and routine maintenance. This includes inspection of fuel nozzles, thermocouples, and safety and control calibrations, as well as checking of the plenum drain valve and cleaning air/oil separator.

Monthly inspections that do not require shutdown are also required. These inspections include checking fittings and oil levels and inspecting for leaks, checking, cleaning, or replacing filters, and checking all instrumentation. Daily inspections (quick visual inspection and reading of instruments) and periodic vibration testing should also be done.

Time between overhaul (TBO) is related to the quality of the preventative maintenance program, the type and quality of fuel used, the number of starts, the percent of full power rating at which the engine is operated and the quality of the turbine components, design, and construction. The TBO may range from 15,000 hours to more than 100,000 hours.

Routine maintenance costs are very low. Repair and overhaul, however, can be costly. Typically, the life-cycle maintenance cost will range from $0.002 to $0.005 per hp-h ($0.0027 to $0.0067 per kWh). Complete service contracts, including turbine engine replacement or overhaul insurance, can limit a facility's responsibility to visual inspection and recording of control and performance data. Remote monitoring can further reduce in-house responsibilities.

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