SEFA
United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S7-82-021 Sept. 1982
Project Summary
Application of Advanced
Combustion Modifications to
Industrial Process
Subscale Test Results
S. C. Hunter, W. A. Carter, R. J. Tidona, and H. J. Buening
Results of subscale tests to evaluate
combustion modifications for emission
control on petroleum process heaters,
cement kilns, and steel furnaces are
reported. The objective was to assess
applicability, NO> emissions reduc-
tions, and cost effectiveness of several
modifications and to select the most
promising for pilot scale tests. Sub-
scale process heater baseline NO,
emissions were about 55 ng/J firing
natural gas at 2.9 MW heat input. NO,
was reduced by 67% with staged
combustion (SC) and by 63% with flue
gas recirculation (FGR). Firing No. 6
oil, baseline NO, of 160 ng/J was re-
duced by 51% with SC and by 39%
with FGR. SC was selected for pilot
scale tests. Subscale cement kiln
baseline NO, emissions were 30-60
ng/J firing natural gas at about 80 kW
heat input. Fly ash, kiln dust water,
and sulfur were injected separately to
evaluate the NOX reduction potential.
Fly ash injection reduced NO, emis-
sions by 28%, while the other inject-
ants reduced NO, by 12-20%. Further
work on a larger scale is planned prior
to selecting modifications for pilot
scale tests. For the subscale steel fur-
nace, baseline NO, emissions of 115
ng/J firing natural gas at 0.6 MWheat
input were reduced by 88% with FGR
and by 47% with water injection. Fir-
ing No. 2 oil, baseline NO, emissions
of 160 ng/J were reduced by 77%
with FGR and by 89% with steam in-
jection.
This Project Summary was dove/oped
by SPA's Industrial Environmental
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
This report documents the subscale
activities of a program whose objective
was to develop advanced combustion
modification concepts requiring relatively
minor hardware modifications that
could be used by operators and/or
manufacturers of selected industrial
process equipment to control emissions.
The development was to be performed
for equipment in which the modifications
would be most widely applicable and of
the most significance in mitigating the
impact of stationary source emissions
on the environment. Modifications were
sought which could be readily adopted
by fuel-burning-equipment manufac-
turers. The path to this goal included
concept definitions, economic and
technical assessment, subscale per-
formance evaluation tests, cost/benefit
analysis, full scale equipment modifica-
tion or retrofit, full scale performance
evaluation tests, and preparation of
final reports and instructional guidelines.
Subscale testing is a necessity for
such process categories as petroleum
process heaters where equipment
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operators are naturally reluctant to
cooperate in a modification test program
until the principle has been demonstrated
on a smaller scale. Subscale tests of
three industrial combustion devices
were conducted following a nationwide
survey of industrial combustion equip-
ment. The survey ranked these devices
according to NOX emissions and heat
input capacity. The equipment tested in
this program was chosen based on
these rankings and the modifications
tested were determined by process
constraints and cost considerations as
well as the potential for NO*reduction.
The final report covers the test site
survey, combustion modification con-
cept definition, subscale test results,
and cost analyses. The subscale test
sites included a process heater, rotary
kiln, and a steel furnace. Cost analyses
were performed for the process heater
and the steel furnace. Because the test
results at the kiln were not deemed
representative of a full scale unit, a cost
analysis was not performed for the
device.
Past Work
The present program is a follow-on
study intended to build upon the results
of the program reported in EPA-600/7-
79-015a (Ref. 1). The objective of that
earlier effort was to investigate the
effectiveness and applicability of com-
bustion modifications involving only
operating variable changes as means of
improvement in thermal efficiency and
for emissions control in industrial
combustion equipment.
The program scope provided for tests
on 22 industrial combustion devices
representative of kilns, process furnaces,
boilers, stationary engines, and gas
turbines in industrial use. Emissions
measured included NO, NOX, S02,
SOs, CO, COz, Oz, gaseous hydrocar-
bons, and where possible, particulates,
particle size distribution, smoke number,
and opacity. Combustion modifications
evaluated, where possible, included
lowered excess air, staged combustion,
reduced air preheat, and burner register
adjustments. No hardware modifications
were attempted, however. All experi-
ments involved only operating changes.
Summary of Results of
Present Program
The initial task of the present program
was to review existing source inventories
and update them where possible to
more clearly define those processes
where controls would be of maximum
benefit. The review of source emission
data provided a relative ranking of each
candidate process.
The equipment recommended for
testing included: (1) natural draft
process heaters, (2) forced draft process
heaters, (3) cement kilns, (4) steel
soaking pits and reheat furnaces, (5)
glass container furnaces, and (6)
woodbark boilers. The NO, emissions
and other characteristics of these
industrial processes are presented in
the final report.
Subscale Process Heater
Tests were conducted to evaluate the
effect of combustion modifications on
emissions from a natural draft process
heater. The reduction in NOX emissions
and the change in efficiency were
evaluated for these modifications: (1)
lowered excess air, (2) staged combus-
tion air, (3) Iow-N0x burners (tertiary air
injection and recirculating tile designs),
(4) flue gas recirculation, (5) steam
injection, and (6) altered fuel injection
geometry. The tests were conducted
with natural gas and No. 6 oil. Only
burner baseline measurements were
made with No. 2 oil. Fuel samples were
taken for all tests and the analyses were
obtained from an independent laboratory.
Baseline measurements were made
prior to the implementation of combus-
tion modifications with the burner firing
natural gas. No. 6 oil, and No. 2 oil.
Table 1 shows that the largest
percentage reductions in NOX occurred
with staged combustion air (SCA) or flue
gas recirculation (FGR) techniques
when compared to conventional burner
designs MA-16 and DBA-16 (a conven-
tional burner differing only in tile design
from the MA-16 burner). With SCA,
these reductions seem to be a relatively
Table 1.
Summary of /VOX Reduction and Efficiency Change as a Function of Combustion Modification Technique for Natural
Gas and No. 6 Oil for Natural Draft Burners
Fuel
Natural Gas
No. 6 Oil
Average Baseline NO*
MA-16
DBA-16
ppm, dry @ 3% Oz
107
131
ng/J
54.6
66.8
ppm, dry @ 3% Oz
285
ng/J
16O
Combustion Modification Technique NO* Reduction Efficiency Change
/VOX Reduction
Efficiency Change
Lowered Excess Air
Staged Combustion Air
Floor Lances, Normal Oz
Floor Lances, Low Oz
Central Cylinder, Normal Oza
Central Cylinder, Low Oz
Tertiary Air Burner, Lowest /VOX
Configuration (relative to average
baseline NO, for the MA-16)
Flue Gas Recirculation
Normal Oz
Low Oz
Steam Injection, Normal Oz
Altered Fuel Injection Geometry
Normal O2a
Low Oz
27
46
67
31
59
30
59
63
33
31
44
+4.7
+0.7
+2.6
0.0
+3.4
•2.0
+4.7
+4.9
0.0
+3.4
10
35
51
42
31
39
+0.1
-0.7
-0.4
0.0
-2.6
+2.0
' NO* reduction is relative to average baseline NOX for the DBA-16.
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strong function of excess air; whereas,
with FGR they are a rather weak function
of excess air. With natural gas fuel, all
modifications (except the tertiary air
burner) appeared to increase furnace
efficiency. With No. 6 oil, efficiency
decreased slightly with SCA and de-
creased with FGR, but increased when
FGR was coupled with low excess air.
The cost effectiveness (CE) of the
most effective NO« reduction techniques
is graphed versus heater size in Figures
1 and 2. As with other modifications,
the CE ratio decreases as the unit size
increases. Costs are based on 1978
dollars.
Subscale Rotary Cement Kiln
KVB completed a series of tests on a
subscale cement kiln. The cement kiln,
at a major cement industry association
facility, had a 13 cm (5 in.) ID, 30 cm (12
in.) OD, and was 4.6 m (15 ft) long. The
maximum kiln feed rate was only
0.0015 kg/s (12 Ib/hr), and the unit had
no air preheat capability.
All tests were conducted with natural
gas fuel. The combustion modifications
tested were: (1) sulfur addition either
with the fuel or with the feed, (2) water
injection at the burner, (3) kiln dust
injection at the burner, and (4) fly ash
injection at the burner. The effects of
these modifications on gaseous emis-
sions, kiln operating conditions (tem-
perature), and clinker quality were
studied.
Table 2 summarizes the NO, reduc-
tions obtained with each of these
techniques. Essentially, the injection of
these materials had little effect on
clinker quality. Excess air changes had
10000 r
100O
o
is
-g
$
o
I
o
o
100
10
I I I I 1 Illl
I I I 11 ill
Flue gas recirculation
Staged combustion
air - floor lances
Staged combust/on air-
central cylinder
I III
ill
I I I I I I III
10
Heater size, mw
100
Figure 1. Estimated cost as a function of heater size for three combustion
modifications to natural draft process heaters firing natural gas only.
more significant effects on the clinker
with the clinker noticeably degraded at
oxygen contents of 0.5% or less.
It is important to note that the
baseline NOX levels observed for the
subscale kiln « 100 ppm, dry at 3% 02)
were far lower than any observed by
KVB on full-scale kilns. The most likely
explanation is that ambient air was used
in all of the subscale tests. In an actual
kiln, air preheater temperatures of 144
K (1600°F) are not uncommon. In
addition, the high surface-to-volume
ratio in the small kiln may have resulted
in greater heat losses from the flame
zone, thus lowering NO* production.
Also, the high gas-to-solids ratio limited
the effect of kiln feed nitrogen on the
NO, emissions.
Combustion Modifications to
a Steel Furnace
The average baseline NO, emission
for a steel furnace burner firing natural
gas and No. 2 oil is given in Table 3. The
maximum NO reductions obtained for
each modification are summarized in
Table 4.
The cost effectiveness of these
modifications is plotted in Figures 3 and
4 against heater size for No. 2 oil fuel
and natural gas, respectively. Flue gas
recirculation (FGR) with heat recovery
capability has the lowest cost per Mg
N0« reduction for heaters larger than
13.5 MW (46 x 106 Btu/hr). For natural
gas fuel, FGR with heat recovery
becomes less expensive than water
injection for heater sizes greater than
8.5 MW (29 x 106 Btu/hr), and it is less
expensive than steam injection at
heater sizes in excess of 60 MW (205 x
106 Btu/hr) as shown in Figure 4. Costs
for the steel furnace modifications are
in 198O dollars.
Conclusions and
Recommendations
From the data obtained and the
analyses made during this program, the
following conclusions and recommen-
dations may be made.
1. For a subscale natural draft
process heater, baseline NOX levels for
two standard burners were 54.6-67.0
ng/J firing natural gas. One standard
burner was found to emit 150 ng/J
firing No. 6 oil and 63 ng/J firing No. 2
oil.
2. Two low-NOx burner designs had
baseline NO, emissions of 47.1-53.0
ng/J firing natural gas. Thus, the mean
NOx emission level from these burners
was about 18% lower than the mean
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10000
iooo
§
1
o
O
;oo
;o
i \
i i
\ i i
Flue gas recirculation
Normal 02
Staged air -
floor lances
Tertiary air burner
Low Oz
I t I t \ IUI
i i tint
w
Heater size, mw
100
Figure 2. Estimated cost as a function of heater size for two combustion
modifications and for changeover to tertiary air burner in natural draft
process heaters firing No. 6 fuel oil only.
Table 2. Maximum NO* Reductions
for Four Combustion Mod-
ifications to a Research
Cement Kiln
Combustion
Modification
Sulfur Injection
Water Injection
Kiln Dust Injection
Fly Ash Injection
Maximum /VOX
Reduction, %
12-20
14
14
28
value for the two standard burners.
Firing No. 6 oil, one low-NOx burner
design produced 149 ng/J, a reduction
of 7% below the standard burner. The
reduction of NOX due to the low-NOx
burner when firing No. 2 oil was only 2%
below the standard burner baseline.
3. Combustion modification tech-
niques were effective in reducing NOx
emissions on a subscale process heater
firing either natural gas or No. 6 oil.
Staged combustion air (accomplished
by lances through the heater floor and
coupled with lowered excess air) was
the most effective technique, followed
by flue gas recirculation at either nor-
mal or reduced excess air. When prop-
erly adjusted and under reduced excess
air conditions, a low-NOx(tertiary air de-
sign) burner was also shown to be effec-
tive in lowering NO* emissions firing
both natural gas and No. 6 oil fuel.
Lowered excess air alone was not very
effective in reducing the NOx concentra-
tion when firing No. 6 oil.
4. Modifications which worked well
firing gas fuel but which were not tried
firing oil because of time or test
equipment limitations included staged
combustion air using a central cylinder
above the primary air zone, steam
injection, and altered fuel injection
geometry. Each of these modifications
reduced NOX emissions by more than
30% below baseline and some may be
applicable to oil firing as well as gas
firing.
5. Staged combustion air by means
of floor lances reduced the NO» at a
normal operating excess air level by
46% below baseline (54.6 ng/J) firing
natural gas fuel. At lowered 02 levels
the reduction was as much as 67%
(natural gas fuel). At normal Oa condi-
tions the NO« reduction firing No. 6 oil
was 35% below baseline (160 ng/J),
and at reduced Qz, the reduction
reached 51%. This staged air technique
was also the most cost-effective tech-
nique based on the data available. Costs
are predicted to be roughly $700/Mg of
NOx reduction for small heaters (2.9
MW and below) firing gas, dropping to
only $39/Mg of NOX reduction for large
heaters (147 MW and above) firing oil.
6. Cost calculations did not include
annual fuel costs or savings due to the
combustion modifications because of
the unrealistic efficiency changes that
were observed on the small-scale
heater. With staged combustion air,
however, no large effect on efficiency is
foreseen except in cases where excess
air can be reduced. Then, efficiency can
be expected to increase with the
application of staged air.
7. In all tests, the N0« levels
observed at the pilot kiln were well
below those previously reported for full-
scale kilns indicating that the subscate
unit was not truly representative of a
production kiln. Itisthoughtthattheuse
of ambient temperature combustion air
as well as high gas-to-solids ratio in the
small kiln were the primary factors
contributing to low-NOx emissions.
8. Although the absolute NOx levels
may not have accurately reflected those
present in a full-scale kiln, the trends in
emission levels which resulted from the
injection of sulfur, water, kiln dust, and
fly ash should still provide a basis for
determining the relative effectiveness
of each injected material in reducing
NOx. With that in mind, it was discovered
that fly ash injection was the most
effective of the above in reducing NOX
emissions. At normal operating Oa NOX
emissions were reduced by 2Q% of the
baseline value when fly ash was
injected into the flame zone. Clinker
4
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Table3. Average Baseline /VO, Emission, Subscale Steel Furnace Burner
(Including All Baseline Tests at Location 4)
Fuel
NG
No. 2
ppm*
222
277
/VOx
ng/J
114.6
153.4
Number
of Tests
11
8
Coefficient*
of Variation
0.19
0.23
"ppm corrected to 3% O& dry.
" Coefficient of variation =Std deviation
Mean
Table 4. Summary of Significant Test Results. Subscale Steel Furnace Burner
Test
Number
4/3-11
4/4-13
4/3-12
4/7-2
4/8-10
Fuel
NG
NG
NG
No. 2
No. 2
Combustion
Modification
Water Injection
FGR
FGR + Water Inj.
Steam Injection
FGR
Firing
Rate
%Cap.
100
100
100
100
100
02
%
2.2
2.0
1.8
2.1
2.0
% Reduction in NO
NO From
ppm3 Nearest Baseline
98
38
24
24
57
47
88
87
89
77
"NO corrected to 3% Oa dry.
1OOOO
5000
I
I
I
to
CO
1000-
500
10
! I 1 I Mill 1 I I MIIH 1 I MUM
Fuel: No. 2 oil
Steam injection
Q Water injection
FGR (no heat recovery)
O
FGR (with heat recovery)
ll\ll 1 \ \ \\\\
10 13.5 50 100
Furnace size, mw
500 1000
Figure 3. Cost effectiveness as a function of furnace size for No. 2 fuel oil.
quality was actually slightly improved
during those tests. Injection of the other
materials reduced the NO* levels by 12-
20% with essentially no effect on pro-
duct quality.
9. Lowered excess air « 1.5% Oa)
was not a practical NOX reduction
technique for the subscale kiln. Accom-
panying CO levels were high and clinker
quality was degraded. In general, it was
found, the industry already maintains
the lowest practical oxygen levels in
most kilns (1.5-2.0% 02).
10. For the two fuels tested at the
subscale steel furnace, natural gas and
No. 2 oil, FGR proved to be the most
effective combustion modification.
Steam injection was effective firing No.
2 oil but was not tried firing natural gas
because of constraints in the test
apparatus. Water injection was less
effective firing natural gas than steam
injection was when firing oil.
11. FGR of 20% applied to the
subscale steel furnace at normal Oa
levels reduced N0« emissions firing gas
fuel by 88% and firing No. 2 oil by 77%.
Cost analyses showed that FGR is the
most attractive combustion modification
for larger furnaces (73.3 MW and up) if
the waste heat of the recirculated flue
gas is recovered. However, FGR is not as
cost effective as steam injection firing
No. 2 oil for heaters smaller than about
13.5 MW nor is it as cost effective as
water injection firing natural gas for
heaters under 8.5 MW in size.
Based on the test results on the
subscale process heater, KVB recom-
mends testing the staged air lances on a
pilot scale process heater. The test
variables should include injection
height and pattern, the burner stoi-
chiometric ratio, the excess air level,
and system performance as a function
of load. Natural gas, refinery gas, and
residual fuel oil should be tested as
these are the fuels most commonly used
at refineries.
Because of the very low NOX concen-
trations measured in the subscale
cement kiln, KVB recommends further
subscale studies in its own laboratory. A
nonproducing nonrotating model should
be constructed and tests made in which
the level of air preheat is varied. Other
operating variables which should be
investigated include inside wall tem-
perature, primary and secondary air
velocities, and primary air vitiation
(variation of O2 in the primary air
stream). Tests should be done for coal
firing and for natural gas firing.
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Post-combustion-zone mechanisms
of NOxformation as well as near-burner
mechanisms should be considered to
ensure that N Ox destroyed at the burner
end of the kiln will not be recreated at
the opposite end of the kiln. A full-scale
kiln should be tested with the most
promising combustion modification
techniques.
Both steam injection and FGR should
be applied to a pilot-scale steel furnace
based on the results of the subscale
tests reported here. Appropriate methods
to recover the waste heat of the
recirculated flue gas stream or the
steam (such as heat exchangers or
condensation heat recovery devices)
could be used to minimize efficiency
losses due to these modifications. The
possibility of doing this should be
investigated. Application of steam
injection firing gas fuel should be
investigated to verify that the technique
is effective for that fuel as well as for No.
2 oil.
Reference
1. Hunter, S. C. et al., "Application of
Combustion Modifications to
Industrial Combustion Equipment,"
EPA-600/7-79-015a, NTIS PB 294
214, January 1979.
/OOOO
5000
c
o
7000
I
500
jj> 100
«fc
50
I I | I I 11II I I TT I 11II I I IT TTT
I III I Jill
Fuel: Natural Gas
b
Steam injection
U Water injection
t \FGR (no heat recovery)
jFGR (with heat recovery)-
III!
I I I I III
5I/O 50 100
8.5 60
Furnace size, mw
50O 1000
Figure 4. Cost effectiveness as a function of furnace size for natural gas fuel.
S. C. Hunter, W. A. Carter, R. J. Tidona, and H. J. Buening are with KVB, Inc.,
Irvine. CA 92714.
Robert E. Hall is the EPA Project Officer (see below).
The complete report, entitled "Application of Advanced Combustion Modifica-
tions to Industrial Process Equipment: Subscale Test Results," (Order No.
PB 82-239 310; Cost: $21.00, 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
OUSGPO: 1982—559-092/0507
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Environmental Protection
Agency
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Information
Cincinnati OH 45268
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