GT3 Upgrades Boost Safety and Reliability

Unit starts the New Year with new cooling and fire suppression systems

Systems improvements to GT3 (gas turbine 3), one of the workhorse peaking units at Apache Generating Station, will start the New Year positioned to serve the G&T’s Members and customers more reliably and with lower maintenance costs.

GT3 was installed at Apache Generating Station in 1974, and the original design included a two-fan heat exchanging unit that worked by running the lube oil – the oil that lubricates the turbine and generator bearings – from the unit through finned pipes. The cooling fans blew air across the finned pipes, dissipating the heat into the air which was then blown out of the enclosure.

“The new system is basically the same design, but with greater capacity; we’ve got three fans instead of two, it’s a much better design with a much larger cooling capacity to handle the lube oil supply,” Nelson said.

The new cooling system for GT3 incorporates three larger, more efficient fans, and the spray bar cooling system has been upgraded to use purified water, which will prevent a buildup of scale on the fans.

The old system was harder to maintain and eventually, in order to control temperatures, a “spray bar” system was added to the top of the cooler, which sprayed water onto the cooling fins. However, that compounded the problem because of the scaling that built up on the cooling system fin pipes and cooling fans, which required even more maintenance.

“Additionally, we are also changing our inlet air cooling water supply from raw water to condensate water which should reduce the potential for scaling on the turbine compressor blades which in turn would decrease the units efficiency over time,” Nelson said.

The fire suppression system that was part of the original construction and installation in 1974 used Halon (bromotrifluoromethane) gas to put out any fire in the turbine/generator enclosure. Halon systems have been widely used since the 1960s for these types of applications, and work when a fire triggers a blasting cap, which releases the mechanism to release the Halon gas from pressurized tanks.

In the late 1990s Halon was discovered to be an ozone-depleting agent and production was halted, making it hard to obtain for existing systems and extremely expensive. Additionally, construction of the blasting caps used to trigger a system’s release was stopped, and they’ve been harder to locate as well.

The new fire suppression system uses compressed carbon dioxide, doesn’t require blasting caps for the triggering system, and will be much less expensive to maintain and much safer to people in the event of a fire, said Nelson.

The new fire suppression system uses a bank of cylinders that hold compressed CO2, which replaces the old system that used Halon gas. The new system is more effective, less expensive to maintain and operate, and safer to people and the environment

All in all, there has been a tremendous amount of excellent work the past few months to return GT3 back to standby service.

“The two capital projects, turbine lube oil system cooler upgrade and the new fire suppression system are completed with successful operation of the unit returning it back to its rated capacity,” Nelson said.