United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S7-81-151 Oct. 1981
Project Summary
Fuel NOx Control by
Catalytic Combustion
E. K. Chu, K. D. Seifert, R. M. Kendall, and J. P. Kesselring
This report describes the results of
an experimental study to define
operating conditions for catalytic
combustors that give low levels of
NOx emissions for fuel-bound nitrogen
compounds, and to quantitatively
determine the fate of fuel nitrogen
during catalytic combustion. Tests
were conducted with platinum and
nickel oxide catalysts over a range of
test conditions, using ammonia and
methylamine as model fuel nitrogen
compounds. Fuel NO > emissions were
found to be strongly dependent on
catalyst type, but varying mass through-
put, bed temperature, fuel, and fuel
nitrogen type had virtually no effect on
fuel NO,. The dominant nitrogenous
products resulting from the catalytic
combustion of a nitrogen-containing
fuel were NO, N2, NH3, and HCN.
This Project Summary was devel-
oped by EPA's Industrial Environ-
mental 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}.
As a result of this experimental study,
an improved understanding of fuel NO,
formation during catalytic combustion
has been gained. Knowledge gained in
this report may lead to further develop-
ment of catalytic burners which control
both thermal and fuel NO,. One feasible
concept which was demonstrated in
previous work and further verified by
the present study is the two-stage
catalytic combustion system. Also, data
obtained under the present study
indicate that the design of a lean low
NO, combustor may be possible. This
summarizes the conclusions reached
and the concepts formulated under this
study, and makes recommendations for
further study.
Based on results of screening tests,
the bed operating temperature was
shown to have only a slight effect on
fuel NO, emissions. Under fuel-lean
conditions, the bed operating tempera-
ture affected fuel NO, emissions in-
directly, depending on the CO emissions
and the stoichiometry. High CO emis-
sions tended to suppress fuel NO,
emissions, and this effect became less
significant as the test condition became
leaner. Under fuel-rich conditions, an
increase in the.bed operating tempera-
ture tended to shift the fuel NO.
minimum slightly toward stoichiometric
conditions.
The mass throughput was found to
have no significant effect on fuel NO,
emissions under fuel-lean conditions.
Under fuel-rich conditions, however, an
increase in the mass throughput ap-
peared to broaden the fuel NO, minimum.
In addition, a second fuel NO, minimum
was observed for cases where both the
mass throughput and the bed operating
temperature were low.
No significant effects on fuel NO,
emissions due to the difference in fuel
type were observed. Under fuel-lean
conditions with natural gas, fuel NO,
emissions maximized at 130 percent
theoretical air and declined slightly a;
theoretical air was further increased
With propane, fuel NO, emissions alsc
maximized at the same stoichiometn
but remained relatively constant a:
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theoretical air was further increased.
Under fuel-rich conditions, the fuel NO,
minimum for propane appeared to be
somewhat broader and slightly deeper
than that for natural gas.
Fuel NO, emissions were found to be
strongly dependent on the catalyst
type—a more active catalyst results in
higher fuel NOX emissions with other
operating parameters held constant.
Under fuel-rich conditions, the less
active NiO/Pt catalyst achieved a
conversion of NH3 of only 25 percent,
while the more active Pt catalyst had a
conversion of 80 percent.
Fuel NOx formation was found to be
insensitive to the molecular structure of
the chemically bound nitrogen com-
pounds tested. This indicates that the
pyrolysis process was not the controlling
step for fuel NOX formation, if the
chemically bound nitrogen content is
highly volatile.
The percentage of NH3 conversion to
fuel N0« was found to be inversely
proportional to the chemically bound
nitrogen content. This phenomenon
was probably due to the destruction
reaction prompted by the excess NHs.
Based on results of detailed tests, it
was verified that NO, N2, NH3, and HCN
are the dominant products of the
chemically bound nitrogen conversion
process. fs^O was not detected for any
condition tested. With the addition of
HzS to the reactive mixture, NO emis-
sions were slightly increased under
fuel-rich conditions and inhibited at
stoichiometric conditions. A nitrogen
balance within reasonable accuracy
was not obtained with H2S addition. The
error may be due to the interference of
sulfide with the specific ion electrode
measurements for HCN and NH3.
To obtain further understanding of
fuel NOx formation during catalytic
combusiton, as well as to develop low
NOx combustors, the following studies
are recommended:
• A study of CO-NO-catalyst reactions
under fuel-lean conditions.
• Test of fuels which contain chemi-
Fuel/Air
cally bound nitrogen—especially
those which contain refractory
chemically bound nitrogen.
• A study of NOx-SOx interactions
during catalytic combustion for
both fuel-rich and fuel-lean condi-
tions.
• Development of a fuel-lean low
NO« combustor; e.g..
Secondary
Fuel
CO Generating
Catalyst
Reduction
Catalyst
CO + NO - Nz
Cleanup
Catalyst
£ K. Chu, K. D. Seifert, R. M. Kendall, and J. P. Kesselring are with Acurex
Corporation, 485 Clyde Avenue. Mountain View, CA 94042.
G. Blair Martin is the EPA Project Officer (see below).
The complete report, entitled "Fuel NO* Control by Catalytic Combustion,"
(Order No. PB 82-102 351; Cost: $11.00, 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 Protect/on Agency
Research Triangle Park. NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Postage and
Fees Paid
Environmental
Protection
Agency
EPA 335
Official Business
Penalty for Private Use $300
U S
00005*19
AGENCY
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