(Pulsed atmospheric fluidized bed combustion (PAFBC)). [Comparing PAFBC vs. AFBC] Page: 17 of 30
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line. An examination of the make-up water supply rate to the steam drum
indicated a maximum flow rate of 2 gpm. This translates to a steam rate of
1000 lb/hr. A new water level control system was installed, a manual by-pass
line (Figure 4) for supplying make-up water to the drum in case of level
controller malfunction was added, and the water line from the mains to the
steam drum was changed from 1/2-inch tube to 3/4-inch pipe. The last
modification corresponded to a maximum make-up water flow rate of 6 gpm or
3,000 lb/hr steam production rate. An additional 2-inch steam vent line was
also added to the drum to avoid pressure build-up in the steam drum at high
steaming rates (>1500 lb/hr).
During this test (PAFBC Test #4), it was also noticed that pulse
combustor start-up required more than the expected amount of natural gas feed
rate. Data collected during the test on pressure drop across the venturi in
the main air line and thrust augmentor return air line indicated that about
40 percent of the total air flowed through the pulse combustor. This is quite
different from the design split of 3 to 1 between the bed and the pulse com-
bustor. This design split had previously been verified in the earlier PAFBC
shakedown test (PAFBC Test #3). The change in air split was traced to an
increase in bed height from 25 to 35 inches and the corresponding decrease in
the pulse combustor tailpipe length. The aerovalve insert was modified from
1-1/4 to 1-inch throat diameter. The pulse combustor was test fired with gas
to verify the air split. It was found that 25 percent of the total air flowed
through the pulse combustor and 75 percent through the bed, as desired.
The other companion test run on the PAFBC (PAFBC Test #5) was conducted
with coarse coal feed to the bed and gas supply to the pulse combustor. The
objective was to determine the net bed weight loss rate for operation of the
PAFBC at 6 ft/s gas velocity and an expanded bed height of about 32 inches as
in the AFBC tests. The unit was started up differently for this test. At
start-up the slumped bed was around 20-inches deep. The steam coils in the
bed were kept open and water was circulated through the pulse combustor water
jacket. Bed depth was built-up by adding bed material as needed to maintain
bed temperature at about 1550 F.ER0W-28Q.04
13
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(Pulsed atmospheric fluidized bed combustion (PAFBC)). [Comparing PAFBC vs. AFBC], report, May 1, 1989; Columbia, Maryland. (https://digital.library.unt.edu/ark:/67531/metadc1056913/m1/17/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.