United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S7-87/022 Feb. 1 988
SERA Project Summary
Chemically Active Fluid Bed
Process for Sulfur Removal
During Gasification of
Carbonaceous Fuels
Z. Kowszun
This report covers the work done
during the final 3 years of a 9-year
program to evaluate the CAFB process
for gasification and desulfurization of
liquid and solid fuels in a fluidized bed
of hot lime. A range of alternative fuels,
including three coals and a lignite, were
gasified in a 3 MWt pilot scale gasifier,
and small scale batch tests were
conducted, all in support of the design
of a demonstration plant to be retro-
fitted to a 20 MWe natural-gas-fired
power generation plant. Direct assist-
ance was given in the start-up and
troubleshooting of the 20 MWe unit,
and a design study was completed on
the potential use of a pressurized CAFB
process to fire a high efficiency gas
turbine. The pilot plant studies demon-
strated the feasibility of simultaneous
gasification and desulfurization of a
range of coals and a low grade lignite.
Best results were obtained using a
cannel coal from New Mexico. Batch
and continuous gasification tests gave
much useful process and equipment
information for the 20 MWe design,
and the pressurized CAFB studies
indicated potential for commercial
viability once gas turbine inlet temper-
atures could be raised to 1427°C.
This Project Summary was devel-
oped by EPA's Air and Energy Engi-
neering Research Laboratory. Research
Triangle Park. NC. to announce key
findings of the research project that is
fully documented in a separate report
of the same title (see Project Report
ordering information at back).
Introduction
The fifth (and final) phase of the
experimental work on the Chemically
Active Fluid Bed (CAFB) process, under
EPA contract 68-02-2159, was carried
out between May 1976 and May 1979.
In parallel, a separate study of Pressur-
ized CAFB (PCAFB), under contract 68-
02-2115, was subcontracted to and
carried out by Esso Research and Engi-
neering Co. (since then renamed Exxon
Research and Engineering Co.). Objec-
tives for this work were reassigned at
the beginning of Phase 5 of this project
in that the major effort was directed
toward the gasification of Texas lignite
to support a demonstration plant to be
engineered by Foster Wheeler Research
Corporation for Central Power and Light
Co. (CP/L) at the La Palma power station,
San Benito, Texas. Part way through
Phase 5, a further reassignment com-
bined Phases 5 and 6 and shortened the
time interval for the experimental work.
Runs 11, 12, and 13
Most of the work described in this
report was carried out in a 3 MWt
continuous pilot plant, which was con-
structed during the previous reporting
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period and consisted principally of Runs
11, 12, and 13. Early in this reporting
period, as data collection and analysis
improved, it was found that batch unit
gasification results on lignite did not
correlate with those from the continuous
plant so that the batch unit was reserved
for equipment development and testing
(distributor nozzles, injectors, cyclone
drains, screw feeder, pressure tappings,
thermocouples, etc.) and operational
tests (hot stone fallback, agglomerate
formation, solids and gas sampling, etc.),
but not for process variable evaluation
as originally intended.
Run 11 spanned the period between
December 1976 and January 1978 and
was spent mostly on exploratory work,
with considerable plant and operational
conversions as the lignite gasification
process was "learned," culminating in
a continuous run (January 23-28, 1978)
gasifying Texas lignite: no oil was used
during that week. During these tests the
following were achieved; however, not
simultaneously: carbon gasification,
>70%; carbon utilization, >90%; desul-
furization, >60%; and regeneration of
sulphur, >50%. Carbon gasification and
desulfurization, unfortunately, moved in
opposition; i.e., best carbon gasification
results corresponded to poor desulfuri-
zation. A number of operational and
equipment problems were discovered
(flame detection, fines handling, coal
feeding problems), and some problems
were solved or alleviated sufficiently to
allow continuous operation. Most of the
operating procedures used later were
established during this period.
Between Runs 11 and 12, training
sessions were held for CP/L, and a film
of some potentially hazardous operations
was produced.
Run 12, carried out in a much modified
plant, consisted of five test periods of
about 1 week each of continuous gas-
ification. These tests covered: a compar-
ison of BCR 1359 (the usual limestone)
with Texas limestone; a gradual chan-
geover from combustion to gasification
on oil to simulate the proposed San
Benito changeover procedure; gasifica-
tion of Texas lignite; comparisons of
different limestone size ranges, wet with
dried, and with and without fines rein-
jection; operation at different tempera-
tures; and combined gasification of
lignite with simultaneous oil injection.
All were successful, but with occasional
surprising results. Also gasified was a
British coal (subbituminous, low melting
point ash) which caused several bed
fusion incidents, but the tests furnished
sufficient data to allow extrapolation to
a safe continuous operating range.
Run 13 consisted of three test periods,
used mostly to repeat in more detail and
follow up some of the more interesting
operating regimes of Run 12; viz., the San
Benito start-up and combined lignite/oil
operation which appeared to combine the
best features of both operations. The last
test in the series was used to carry out
a number of short exploratory tests:
comparison of overhead with into-bed
low level injection, gasification of <25
mm lignite, gasification of Illinois No. 6
coal and a cannel coal from New Mexico,
as well as another test on the British coal.
The best gasification results were on <12
mm Texas lignite which gave carbon
gasification over 90% with simultaneous
desulfurization of 50%. The best explor-
atory test was on the high sulfur N.M.
cannel which gave an excellent product
gas with little tar, desulfurization in
excess of 90%, with simultaneous gas-
ification of 70% and an indication of
possible improvement.
Support Items
In parallel with the continuous plant
operation, batch plant and rig work was
carried out on various supporting items:
a. Operational: agglomerate forma-
tion, solids sampling, and fluidiza-
tion tests.
b. Mechanical: distributor nozzles
(prototype San Benito, non-fallback
high turndown), screw feeders,
fines reinjectors (plain eductor,
venturi eductor, J-valve), and
rotary valves.
Conclusions
Considerable operational experience
was gained, some of which was put to
good use at San Benito as on-site
operational advice.
Z. Kowszun is with Esso Research Centre, Oxfordshire, OX136AE, England.
SamuelL. Rakes is the EPA Project Officer (see below).
The complete report, entitled "Chemically Active Fluid Bed Process for Sulfur
Removal During Gasification of Carbonaceous Fuels," (Order No. PB 88-112
222/AS; Cost: $56.95, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC27711
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