United States
Environmental Protection
Agency
Industrial Environmental
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S7-84-031 Apr. 1984
v>ERA Project Summary
Evaluation and Demonstration of
the Chemically Active Fluid Bed
R.E. Sommer, A.S. Werner, and Z. Kowszun
Results are reported on the operation
of a 17-MW Chemically Active Fluid Bed
(CAFB) demonstration unit, retrofitted
to a natural gas boiler. The CAFB pro-
cess gasifies high-sulfur, high-metals-
content liquid and solid fuels. Residual
oil, lignite, and bituminous coal were
gasified separately or together between
November 1979 and June 1981. Oil was
gasified for 540 hours. A maximum con-
tinuous-rating test sustained 22 MW of
electrical energy for 2 hours. Sulfur re-
moval efficiencies of up to 90 percent
were achieved during oil gasification.
Lignite and bituminous coal were gas-
ified for 42 hours: sulfur removal effi-
ciencies of up to 70 percent were
obtained. Design and operational areas
which need to be upgraded were iden-
tified. Continuous monitors were used
to measure boiler flue gas emissions of
SO,, nitrogen oxides (NOX), CO, oxy-
gen, CO,, and opacity. Periodic manual
emission tests were conducted for par-
ticulate, SO,, and NOX, using EPA
reference methods. Emissions of these
three criteria pollutants were generally
lower than New Source Performance
Standards for utility boilers, although
occasionally excessive particulate and
SO, emissions were observed. NOX
emissions were consistently lower than
those from natural gas combustion. Po-
tential multimedia impacts from the
three major discharge streams from the
CAFB (boiler flue gas, spent solids from
the gasifier bed, and sulfur recovery
system ash) were characterized using
the phased approach to environmental
assessments developed by EPA. Results
of detailed chemical analyses and bio-
logical assays are reported.
This Project Summary was developed
by EPA's Industrial Environmental Re-
search 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).
Background
The Chemically Active Fluid Bed (CAFB)
process was developed in the late 1960's by
the Esso Research Center, Abingdon
(ERCA), England, as a way to generate elec-
trical energy from high-sulfur, high-metal,
heavy fuel oil. In the CAFB process, oil or
coal is fed continuously into a fluidized bed
of lime maintained at 870 °C. Air is preheated
and fed to the gasifier in substoichiometric
proportions. The fuel entering the gasifier is
vaporized, oxidized, and cracked to produce
a low-Btu low-sulfur gas which, after pass-
ing through cyclones to remove particulate
matter, is burned in a conventional gas
boiler. Sulfur contained in the oil initially
forms various gaseous compounds which
then react with the bed lime to yield solid
calcium sulfide. Some of the fuel-bound
trace elements are also bound to the bed
stone. The sulfided lime is cycled to a
regeneration unit where it is oxidized to pro-
duce calcium oxide (which is returned to the
gasifier) and S02 (which is sent to a sulfur
recovery unit).
During the early and mid-1970's, the pro-
cess was demonstrated at a 2.9 MW pilot
plant to provide energy efficiently from both
liquid and solid fuels while simultaneously
limiting emissions of S02, NOX, vanadium,
and nickel. Based on the successful pilot
plant tests in England, the U.S. EPA and the
Texas-based Central Power and Light Com-
pany (CP&L) commissioned Foster Wheeler
Energy Corporation (FWEC) to construct a
17-MW demonstration plant in San Benito,
TX. The agreement with CP&L, signed in
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May 1975, provided for construction and
operation of the demonstration plant. The
contract with EPA (68-02-2106) covered
engineering design, labor for start-up, fuels
and feedstocks, and environmental monitor-
ing. Design of the unit, based on the ERCA
design and operating experience, was ini-
tiated in January 1975, and construction was
completed in January 1979. The plant incor-
porated FWEC's proprietary sulfur recovery
system, RESOX™. More than 130 contrac-
tors and subcontractors were employed dur-
ing construction. A test program using heavy
oil, lignite, and bituminous coal was con-
ducted between October 1979 and June
1981.
This report describes the design, opera-
tion, and environmental aspects of the San
Benito plant.
Plant Operation
Oil, lignite, and bituminous coal were
gasified separately or together in the CAFB
unit, which was retrofitted on the front end
of a natural gas boiler, between November
1979 and June 1981. Eleven test runs were
conducted during this period. Operating con-
ditions and fuels employed for the runs are
summarized in Table 1. Residual oil was
gasified during the first four runs, totaling
343.5 hours of operation. The fifth gasifica-
tion run was the longest and most suc-
cessful. All three systems, the gasifier,
regenerator, and RESOX™ reactor, were
operational during the run. During the fifth
run, oil (the primary feedstock) was gasified
for 196 hours; however, lignite was intro-
duced and gasified in combination with the
oil for the final 3 hours of operation. During
the second run, a maximum continuous-
rating test sustained 22 MW of electrical
energy on oil for 2 hours. Problems with the
transfer of bed stone between the gasifier
and regenerator limited regenerator opera-
tion during oil gasification to 213 hours. The
RESOX™ sulfur recovery system was
operated during oil gasification for 115 hours.
Sulfur removal efficiencies of up to 90 per-
cent were obtained.
West Texas lignite was gasified for 10.5
hours: problems with the coal feed system
precluded additional operation. An eastern
bituminous coal was gasified for 31.7 hours
during the final four runs: again, coal feed
problems caused premature termination of
two of the runs. Throughout the final two
runs, the boiler flames were strong and well-
defined. A sulfur removal efficiency of 70
percent was achieved during the final run.
The following alterations would improve
operation:
• More efficient cleanup of product gas
entering the boiler. The single-stage
cyclones at San Benito were, at times,
inadequate.
• A sturdier, more reliable coal feed
system. The coal feed system was very
sensitive to coal physical properties and
was prone to plugging under some con-
ditions.
• A burnup cell for the carbon on the
cyclone fines.
• More reliable rotary seals, valves,
dampers, augers, and filters, to better
withstand the severe conditions of
CAFB operation.
Environmental Aspects
The demonstration unit was evaluated to
determine its capability to control flue gas
criteria pollutant emissions and to estimate
potential multimedia pollution impacts. Con-
tinuous monitors were used by FWEC to
measure S02, NOX, CO, oxygen, C02, and
opacity. In addition, periodic manual emis-
sion tests were conducted by FWEC for par-
ticulate, S02, and NO using EPA
Table 1. Summary of the 11 Gasification Runs Between December 1979 and June 1981
Hours of Fuels Regenerator RESOX™ Boiler load
Run Dates gasification used operation operation product gas
1
2
•
3
4
5
6
7
8
9
10
11
12/19/79-
12/20/79
1/27/80-
1/31/80-
4/ 8/80-
4/14/80
7/29/80-
81 1/80
9/24/80-
101 1/80
11/20/80-
11/25/80
121 9/80-
12/12/80
2/81
3/11/83-
3/12/83
61 5-61 6/81
61 7-61 8/81
61 9-6/10/81
6/22/81-
6/23/81
32
77.5
144
90
196
79
5.5
4
10
19.5
17.5
19
16
Oil
Oil
Oil
Oil
Oil
Lignite, 2 fir
Oil
Lignite
Oil/lignite
Oil
Oil/lignite
Lignite
Lignite
Oil, 3 hr
Oil /coal, 3 hr
Coal, 4 hr
Oil
Oil, Oil/coal
Oil, Oil/coal
Oil, 3 hr
Oil/ coal, 5 hr
Coal, 8 hr
No
No
No
3hr
Yes
Yes
No
Yes
Yes
No
Yes
No
No
No
No
Yes
17 hr
Yes
No
No
No
No
No
No
4MW- 6hrs
9-10MW-28hrs
9-11 MW
14-15 MW
20-22 MW- 3hrs
7.2-15 MW
10.5 MW
72 hrs product /natural gas
8.5 MW - product gas
2-hr coal provided 30% of
8.5 MW
5- 6 MW
9 MW
7.5 MW
8.7 MW
9.0 MW
4.8 MW - product gas
5.9 MW - natural gas
Comments
Maintained 22 MW for maximum
continuous rating.
First use of /V2 for material
transfer between gasifers
and regenerator.
During this run GCA performed
environmental assessment
The gasifier bed appeared to be
releasing S02.
Run aborted.
Approximately 4.5 MW was from
product gas.
The bed from run 10 was reused
in this run.
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reference methods 5, 6, and 7, respectively.
Potential multimedia environmental impacts
were determined under a separate contract
(68-02-2695) by GCA/Technology Division.
This program, which followed protocols
developed by EPA, characterized in detail the
chemical composition of the three major
streams discharged from the CAFB: boiler
flue gas, spent lime sorbent, and ash from
the sulfur recovery system.
The major environmental conclusions of
the demonstration programs follow.
• NOX emissions from the combustion of
product gas generated by gasification of
oil, lignite, or bituminous coal were con-
sistently below 100 ng/J (0.233 lb/108
Btu) and were lower than NOX emis-
sions from natural gas combustion.
• During oil gasification, the sulfur
removal efficiency (SRE) varied from 60
to 90 percent. The SRE decreased
markedly as the gasifier bed temperature
was raised above 870°C. Recycling of
RESOX™ tail gas to the gasifier
decreased SRE, probably as a conse-
quence of steam and elemental sulfur
entrained in the tail gas.
• Particulate emissions during oil gasifica-
tion averaged 31.3 ng/J (0.073 lb/10«
Btu) based on the results of five EPA
Method 5 tests. Opacity was generally
below 20 percent. However, the higher
than anticipated elutriation rate of bed
material from the gasifier resulted in ex-
cessive paniculate buildup in the boiler.
Periodically this material would be blown
off the boiler tubes by increasing the gas
flow to the boiler, resulting in momen-
tary jumps in opacity.
• Particulate collected from the boiler flue
gas showed neither appreciable toxici-
ty nor any positive mutagenicity.
• Some mutagenicity was indicated by an
Ames test on extracts of XAD porous
polymer resin used to collect samples of
gaseous organic compounds from the
flue gas.
• Leachates collected from the spent
stone and RESOX™ ash contained low
metal and anion concentrations. Anion
concentrations in both leachates were
well below EPA Primary and Secondary
Drinking Water Regulations.
Rebecca E. Sommer and Arthur S. Werner are with GCA/Technology Division,
Chapel Hill, NC 27514; Z. Kowszun is with Esso Research Centre, Abingdon,
Oxfordshire, OX136AE. England.
Samuel L. Rakes is the EPA Project Officer (see below).
The complete report, entitled "Evaluation and Demonstration of the Chemically
Active Fluid Bed," (Order No. PB84-159 243; Cost: $ 19.00, 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:
Industrial Environmental Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
U.S GOVERNMENT PRINTING OFFICE, 1984 — 759-015/7640
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Environmental Protection
Agency
Center for Environmental Research
Information
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Official Business
Penalty for Private Use $300
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