Test results from the Department of Energy`s Pressurized Fluidized Bed Combustion Hot Gas Cleanup Program Page: 4 of 8
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Prior to the start of test campaign IV, three system
modifications were implemented. One was the removal of the
inner ring of candle filters on all top and middle plenums of
the APF. The filter removal reduced the number of filter
elements from 384 to 288 and, consequently, increased the
operational face velocity by 25 percent. The second
modification was to install a system for spoiling (reduce in
performance) the cyclone upstream of the APF. Both of these
modifications were done to avoid filter ash bridging problems
encountered in earlier tests. The third modification was the
inclusion of several types of experimental candle filter
elements.
Test Campaign IV: 7/94 - 10/94
The first two tests 19 & 20 (7/16/94) together totaled only four
hours and, therefore will not be discussed. Test 21 (7/20-27/94)
totaled 161 hours, and was terminated to repair a vibration
problem on the gas turbine. Because of the turbine limitation,
the APF temperature was in the 607 to 621 C range during most
of this run. The APF differential pressure remained stable
during the run at approximately 13.6 kPa. Test 22 (7/28 -
8/25/94) was a hot restart from the previous run, and was the
longest run to date for the APF system at just less then 680
hours. During this test, the APF operated between 650 to 760
C, additionally, various sorbents were tested. The APF pressure
drop (DP) exhibited periods of instability during this run.
At the end of test 22, the APF had logged 844 hours of operation
since it was reconfigured with 288 candles. The objective of
this test series was to determine if removal of the inner rows
of candles from the upper and middle plenums would eliminate ash
from accumulating on the ash sheds and bridging over to the
candles. An inspection on August 29, 1994 revealed that ash
bridging, while less than before, had still occurred. The APF
hopper was clean two days following shutdown, but when inspected
again four days following shutdown, ash was found in the hopper.
During the inspection with a boroscope, 14 broken filter candles
were seen, and candle pieces were later removed from the hopper.
Nine candle bottoms were recovered in the hopper. A possible
explanation for the candle breakage would be that ash, bridged
between the ash sheds and candles, expanded slightly during
cooling and absorbed moisture from the air, thereby inducing
bending moments on the candles which all failed near the top of
the filter holding fixture. Another possible explanation is
that the metal support pipe contracted more than the ceramic
candles upon cooling, which induced bending stresses in the
candles due to ash wedged between the candle bottoms and sloping
dust shed surfaces. It was decided to continue this test series
with 14 broken candles rather than declare the system out of
service at this time in order to replace them. It was planned
to replace all of the candles in the fall of 1994.
Test 23 (9/3-10/94) was a 171-hour run. During the last 90 hours
of test, the primary cyclone was spoiled by injecting air into
the ash pickup nozzle to reduce the ash transport ability and
force the ash to build up in the dip leg of the cyclone. In
order to even out the ash discharge from the APF, the back
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Dennis, R.A. Test results from the Department of Energy`s Pressurized Fluidized Bed Combustion Hot Gas Cleanup Program, article, December 1, 1995; Morgantown, West Virginia. (https://digital.library.unt.edu/ark:/67531/metadc671628/m1/4/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.