United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S7-85/026 Aug. 1985
v>EPA Project Summary
Testing of Wall-Fired
Furnaces to Reduce
Emissions of NOX and SOX
P. L. Case, L Ho, W. D. Clark, E. Kau, D. W. Pershing, R. Payne, and M. P. Heap
This research project is one of several
programs sponsored by the EPA to
investigate and develop simultaneous
nitrogen oxide/sulfur oxide (NOX/SOX)
emission control using limestone injec-
tion in multistage burners (LIMB). The
overall technology development pro-
grams range from small-scale funda-
mental investigations to pilot-scale
development studies. The overall EPA
program includes analysis of boiler
design aspects of LIMB technology and
a full-scale, wall-fired utility boiler
demonstration. One concept of the EPA
LIMB program is that there are three
basic facets: scientific aspects, pilot-
scale studies, and application. LIMB
application is likely to be very system-
specific, involving analysis of a partic-
ular fuel/boiler/burner system, selec-
tion of a sorbent and injection method,
and consideration of the impact of LIMB
on operation of the boiler. Thus, the
results of investigations of the funda-
mental aspects of sulfur capture, pilot-
scale studies, and the development of
models for the process are essential for
the application of LIMB technology.
This Project Summary was developed
by EPA's Air and Energy Engineering
Research Laboratory, Research Triangle
Park, NC, to announce key findings of
the research project that is fully docu-
mented in two reports of the same title
(see Project Report ordering informa-
tion at back).
Summary
The research program summarized
here provides information into the devel-
opment effort at several levels. The work
reported here involved direct investiga-
tions of the role of fuel and sorbent
properties and fuel mineral matter inter-
actions. Results of these experimental
efforts can be used to clarify the sulfate
formation process and to derive guide-
lines for determining sorbent injection
locations. In addition to the experimental
work, analytical development work was
performed, including the development of
a sulfur capture model, and the applica-
tion of heat transfer models.
The overall goal of the research pro-
gram was the clarification of means to
reduce emissions of NOX and SOX from
the pulverized-coal, wall-fired combus-
tion systems found in utility boilers. The
work was divided into four separate tasks.
Task 1 provided detailed information
about sorbent and sulfur reactions under
conditions of particular interest. Task 2
evaluated the potential of a number of
design and sorbent options. Task 3 pro-
vided some information on the effect of
scale on the performance of systems
designed to reduce NOX and SOX. Task 4
summarized the data produced, providing
recommendations on optimum systems
and potential operational problems. Tasks
1 and 2, carried out in a 1 million Btu/hr
furnace, helped to determine:
• The effect of fuel type and fuel mineral
material on sulfur.
• The effect of sorbent type on sulfur
capture.
• Detailed temperature and species
characteristics of flames which gave
significantly different sulfur captures.
• The effect on sulfur capture of opera-
tional characteristics such as fuel
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injector, burner zone stoichiometry,
peak flame temperature, and load.
• The effect of sorbent injection location.
• The effect of LIMB on various furnace
operational characteristics such as
slagging, fouling, solids loads, size
distribution, and fly ash resistivity.
Taskl
Conclusions from Task 1 include:
• A good inverse correlation between
added mineral matter alumina (A^Oa)
content and sulfur capture during gas
firing has been observed; the more
alumina in the solid, the lower the
capture, using either limestone or
dolomite
• Sulfur capture for the different coals
tested with limestone and dolomite
also showed a fairly consistent inverse
correlation with the calculated AI203
content of the ash sorbent mixture (at
a Ca/S = 2.0).
• Electron micrographs of sorbent min-
eral samples show particles composed
of a mixture of Al/Si and Ca. The
particles are spherical and have been
molten at some point in the furnace.
The mechanism of mineral deactiva-
tion and formation of these spherical
particles is not clear and should be the
subject of further investigation.
• Electron micrographs of coal/sorbent
samples also showed spherical par-
ticles composed of calcium and ash
minerals such as Al, Si, and Fe.
• Injecting the sorbent downstream from
the main flame resulted in improved
utilization in coal flames. Experiments
with natural gas flames showed that
the sorbents had somewhat higher
surface areas in the reaction zone
when injected downstream. Gas-fired
experiments using mineral matter
additives showed that mineral material
deactivation of the sorbent could be
reduced by injecting the sorbent down-
stream of the main flame.
Task 2
In Task 2, a fairly extensive data base of
sulfur capture for various fuel/sorbent
pairs was established. Six fuels and five
sorbents were tested (not all possible
combinations of fuel/sorbent pairs were
included).
• The effect of sorbent type on capture
with a given fuel was dependent on
the firing conditions—including sor-
bent injection location and thermal
conditions. The hydrated limes seemed
to be more sensitive to thermal condi-
tions and the Vicron limestone least
sensitive. The German hydroxide gave
better capture than the Colton hydrox-
ide. It was not known why the two had
different captures, but the German
hydroxide did have a generally smaller
particle size distribution than the
Colton hydroxide. Dolomite gave the
highest capture with all of the fuels
tested.
• The effect of fuel type on capture with
a given sorbent was also system
dependent (injection method, firing
characteristics, and thermal condi-
tions).
• In general, sorbent size affected cap-
ture only for large particles: at mean
sizes less than 10/i
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a high temperature (>2300°F). Down-
stream sorbent injection (at temperatures
of about 2200°F) gave higher captures
than injection with the fuel for coal fired
tests, because of decreased mineral
matter interference and some increase in
sorbent surface area. Further experi-
mental work investigating the mechanism
of mineral deactivation, the possibility of
generating high surface area (highly
reactive) sorbents, and the effect of
sorbent injection on boiler operating
characteristics (especially heat transfer
concerns such as f lame emissivity) should
clarify methods of further reducing emis-
sions.
P. L. Case, L Ho, W. D. Clark, E. Kau, D. W. Pershing, R. Payne. andM. P. Heap are
with Energy and Environmental Research Corp., Irvine, CA 92714-4190.
Dennis C. Drehmel is the EPA Project Officer (see below).
The complete report consists of two volumes, entitled "Testing of Wall-Fired
Furnaces to Reduce Emissions of NO x and SO* "
"Volume 1. Final Report," (Order No. PB 85-224 632/AS; Cost: $26.50)
"Volume 2. Appendices." (Order No. PB 85-224 640/AS; Cost: $22.00)
The above reports will be available only from: (costs subject to change)
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, NC 27711
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United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
EPA/600/S7-85/026
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•frU.S. GOVERNMENT PRINTING OFFICE; 1985—559-01b/27122
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