- Seminole Electric is
a 1300 MW coal-fired power plant located in Palatka, Fla.
- Seminole recently converted
its scrubber effluent from landfill material into synthetic gypsum. Many new
types of equipment were installed for this conversion process; some old equipment
was required to run in and out of the original design parameter.
- 132-M, paddle mixer,
gear reducer, was one such piece of equipment. In its new operating parameter,
it was failing on average every three to four weeks, sometimes sooner.
- The average cost per
failure was about $5,000 for the swap out and rebuild of the failed unit.
Replacement of the mixer with a different style had been considered at a cost
of around $100,000, not including labor.
- The sample was collected
from a midpoint oil level plug after the plug was pulled and fluid was flushed
and allowed to run out so that a clean sample could be collected.
- Lab performed spectrometric
analysis, FTIR, viscosity and particle count. The technician requested a ferrogram
and wear debris analysis because metal particles were detected during visual
- Rubbing wear was found
in the sample, in addition to moderate nonmetallic inorganic particles.
- Suspecting fly-ash as
the contaminant after reading the results, the Seminole technician ran a patch
test and his assumption was confirmed.
- The input gear was apparently
wearing down until no gear mesh was left, resulting in the final stripping
of the teeth. Significant damage to the bearings had also been seen from a
lapping compound formed when the fly-ash mixed with the oil.
- The first line of defense
was to select an increase in oil viscosity. This gear reducer had been running
eight to ten hours per day and was now operating up to 24 hours per day. Due
to the load and temperature changes, the ISO 150 EP gear oil was increased
to ISO 320 EP gear oil. At the same time, a 2-micron moisture-removing breather
was installed ($46).
- While the breather helped,
the shaft seals were still the main area of ingression. To correct this, bearing
isolators were installed, on all three shafts for $949. Though expensive,
these seals worked great. During the first six weeks of operation with the
bearing isolators installed, oil samples were taken at one week, two weeks
and four weeks. The samples were very clean. Compared to previous samples,
you could still see through them. There were slight traces of metal from the
gear-mesh, however, this was considered as a possible normal gear break-in
- A kidney-loop filtration
unit with 10- and 3-micron nominal filters, $2,070, was installed next. This
was temporarily wired and is run each time the mixer is in use.
- Final plans are to have
this wired in through the PLC, so it will automatically run and shut down
when the mixer is in service.
- $3,065 was the total
bill for the improvements made. The mixer gear reducer has now been in use
for more than six months, and has surpassed previous mixer gear reducer longevity.
- The oil was changed after
three months while the plant was down.
- Upon visual inspection,
the sample looks as good as new oil and will be sent to the lab for further
- This gear reducer, which
started at an ISO code of 25/22, is now running at a code of 20/17 and has
already realized eight times the initial investment in savings.