POWER October 2014 - 38

OPERATIONS & MAINTENANCE
Ortiz explained that keeping the heat inside of plant buildings had
been troublesome. Keeping doors closed was half the battle. The plant
was built with a lot of swinging doors that were easily caught by the
wind. One big improvement was changing all exterior doors to sliding
doors (Figure 1).
The plant chose to install a model made by PS Doors. The company's
industrial sliding door is designed specifically to withstand the
abuses of industrial applications-especially the effects of positive and
negative draft or wind loads-making it a good choice for use in power
generation facilities, which require sturdy, maintenance-free doors.
" The little things that we have done have really made a difference, "
said Ortiz. " The doors have helped keep the heat in the buildings
while at the same time keeping dust out. "
According to Brad Watson, senior director for corporate communications
with Luminant, the Dallas-based utility has literally thousands
of items on its winter weather preparedness checklist too. Luminant
increases management and craft staffing on all shifts for the duration
of cold weather events, and it coordinates closely with the Electric
Reliability Council of Texas, the independent system operator for the
region that manages the flow of electric power to around 24 million
Texas customers.
" In anticipation of extreme temperatures, we stockpile fuels, erect
windbreaks, and utilize large radiant heaters to supplement existing
freeze protection and insulation, " said Watson.
Use What You've Got
In some cases, the people most familiar with a problem can help develop
a unique solution. At Basin Electric's Antelope Valley Station
(AVS), the cooling towers presented a source of recurring trouble
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during the winter. The original design included a heat trace system
around the periphery of the cooling towers to prevent ice from forming
and interfering with the blades of the cooling tower fans (Figure
2). Although the load on the fans is minimal during winter months,
they must continue to rotate to keep air flowing nonetheless.
The original heat trace was difficult to maintain and stopped
working after only a few years. Replacement was problematic due
to the location and time constraints on the work. Several employees
who had worked on the system got together and collaborated
on a solution.
The purpose of the cooling tower is to remove heat from the cooling
water used to condense steam exhausted from the plant's turbine
generator. The water is typically returned to the cooling tower at a
temperature of about 80F.
The answer was to pipe some of that relatively warm water into
a ring surrounding the fan blades. The warm water keeps ice from
building up and eliminates the need for heat trace. It's more economical
too. The new design utilizes waste heat that needs to be removed
anyway and saves energy that had been consumed by the electrical
heat trace.
At the Springerville plant, conveyors offered an opportunity for
improvement. Because some were completely exposed to weather,
ice frequently developed on walkways in the winter, creating the
potential for injuries from slips and falls. The solution was to install
elevated grating (Figure 3) to provide traction for workers, thus reducing
the hazard.
Additionally, some of the Springerville buildings were constructed
with no heating system at all. Ortiz explained that TEP's maintenance
crew installed diesel heaters in these buildings (Figure 4) to keep areas
above freezing. From December through the end of March, the
heaters are used regularly.
While heat trace offers vital freeze protection in cold weather climates,
at one of Xcel's facilities, workers found that some installation
techniques were resulting in electrical shorts. Originally, the heat tape
was doubled back on itself any time the tube trace ended at an instrument
enclosure. In time, continuous heating and cooling of the heat
trace caused the insulation to break down and short out.
Similar to Basin's experience, the people performing the repairs
came up with a solution to the problem. The electricians drilled a
hole through the wall of the enclosure and mounted the power connection
box directly to the enclosure instead of to the tube, which
eliminated the short radius turn in the cable. The jacketed cabling
was taped and sealed inside the enclosure to help prevent escaping
moisture from potentially contaminating and freezing the insulation.
Problem solved!
Every Fuel Supply Situation Is Unique
Although Basin Electric's four largest plants are all coal-fired, each
is unique in its layout. Two are lignite-based (AVS and Leland Olds)
while the other two (Dry Fork Station and Laramie River Station) use
Wyoming subbituminous coal. Dry Fork and AVS are mine mouth
plants, but Leland Olds and Laramie River rely on rail delivery for
their fuel supply, so none are alike.
Lignite coal is roughly 35% water, so during long periods of subKalenborn
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CIRCLE 17 ON READER SERVICE CARD
38
zero temperatures, coal in the railcars sent to the Leland Olds facility
will freeze along the sides and start to build up in the cars. In some
cases, the train will end up back hauling 10% to 15% of the coal delivered,
because it won't dump out of the car. Using a release agent
that can be sprayed into the cars prior to loading is an option, but even
that isn't foolproof.
" The Wyoming plants are far enough south where you don't typically
have long, extreme cold snaps. They also have less moisture in
the coal, so it's not as big of an issue for them, " said Jacobs.
www.powermag.com
POWER | October 2014
http://www.abresist.com http://www.powermag.com
POWER October 2014

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