United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S7-83-022 June 1983
SERft Project Summary
Refinery Process Heater NOx
Reductions Using Staged
Combustion Air Lances
R. J. Tidona, W. A Carter, arrd H. J. Buening
Results of fuH scale tests to evaluate
combustion modifications for emission
control and efficiency enhancement
on petroleum process heaters are sum-
marized Test objectives were to deter-
mine MOX emission reductions, thermal
efficiency changes, long-term perfor-
mance, and cost of a staged combustion
air modification (the most promising
combustion modification m pitoi scale
tests). The test unit was a vertical,
cylindrical, natural-draft crude -oil heater,
test fuels were natural gas, refinery
gas, and a combination of No. 6 oil and
refinery gas. The unit had a 16 MW
heat input capacity and was capable of
a throughput of 108 rrrVh of crude oil.
Firing refinery gas at normal excess air
levels (4 percent stack C^) at 10.4 MW
heat input during a long-term test the
staged air modification lowered NOX
emissions by 60 percent below a base-
line of 66 ng/J while increasing ther-
mal efficiency slightly. At 2 percent
stack O2, the NOX reduction reached
71 percent and heater thermal efficien-
cy was increased by about 3 percent of
the baseline thermal efficiency. For
the combined refinery gas/No. 6 oil
fuel at normal excess air and the same
heat input rate, the NOX reduction with
the application of staged air was 34
percent below a baseline of 115 ng/J.
At 2 percent stack O2, this improved to
53 percent. Thermal efficiency in-
creases at these conditions were nom-
inally the same as observed for the
refinery gas fuel. Long-term (30-day)
evaluation of the staged air system
revealed no special operating difficul-
ties or process constraints: the system
appeared to suffer no significant degra-
dation. The cost of the modification
was determined based on a permanent
system.
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 doc-
umented in a separate report of the
same title (see Project Report ordering
information at back).
Introduction and Summary
This final report is one of four final
reports covering the pitot- and full-scale
tests of combustion modification tech-
nology for reduction of NOX emissions and
to enhance thermal efficiency on industrial
process equipment
The activities summarized herein include
field evaluations of several modification
techniques applied toa natural-draft crude-
oil heater. Test efforts focused on devel-
oping a new method of staged combus-
tion which can be retrofitted on a wide
variety of process heaters and can achieve
NOX reductions of over 50 percent from
baseline, along with modest efficiency
increases.
The modifications discussed in this re-
port had previously been applied to a pilot-
scale natural-draft heater as a part of this
program in a series of tests aimed at
determining the most promising tech-
niques for full scale application. Emphasis
was placed on developing modifications
which required relatively minor hardware
changes which could be made easily on a
wide range of existing process heater
types.
During earlier testing of full scale process
heaters under EPA Contract 68-02-2144,
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operating variables such as excess air and
load were adjusted to lower NOX emissions.
No hardware changes to the units were
made during those tests, however.
Objectives and Scope
The objective of this program was to
research combustion modification con-
cepts requiring relatively minor hardware
modifications that could be used by opera-
tors and/or manufacturers of selected
industrial process equipment to reduce
emissions and to improve thermal efficien-
cy. The effort 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 The objective was to
assess the feasibility of these modifications
to the extent that they could be readily
adopted by the fuel burning equipment
manufacturers. The path to this objective
included concept definition, economic and
technical assessment, subscale perfor-
mance evaluation tests, cost/benefit anal-
ysis, full scale equipment modification or
retrofit, full scale performance evaluation
tests, and preparation of final reports and
instructional guidelines.
Past Work
The present program is a follow-on
study, building on the results of the pro-
gram reported in Reference 1. The objec-
tive of that earlier effort was to investigate
the effectiveness and applicability of com-
bustion modifications involving only op-
erating variable changes as means of im-
provement in thermal efficiency and for
emissions control in industrial and com-
bustion equipment. In that project (EPA
Contract 68-02-2144), various kinds of
industrial equipment for energy consump-
tion and emissions were surveyed. Existing
data were collected, and equipment manu-
facturers, operators, and associations were
contacted. Industries were defined for
which emissions reduction or efficiency
increase through combustion improve-
ment would be of significance on a national
basis. These industries were petroleum
refining, minerals, paper, and metals. The
characteristics of specific combustion
equipment of most importance in those
industries were defined within the limita-
tions of available data. These characteris-
tics were used as guides in selecting test
units that would be most nearly representa-
tive of the total population.
The program scope provided for tests
on 22 industrial combustion devices repre-
senting kilns, process furnaces, boilers,
stationary engines, and gas turbines in
industrial use. Emissions measured in-
cluded NO, N02, SO2, S03, CO, C02, 02,
gaseous hydrocarbons, and (where pos-
sible) particulates, particle size distribu-
tion, smoke number, and opacity. Com-
bustion modifications evaluated, where
possible, included lowered excess air,
staged combustion, reduced air preheat,
and burner register adjustment No hard-
ware modifications were attempted, how-
ever. All experiments involved only op-
erating changes.
In general, results indicate that combus-
tion modifications may be applied to in-
dustrial combustion equipment, but re-
ductions achievable can vary significantly
for different types of devices. Reductions
in NOX of up to 69 percent were observed,
but on many devices, reductions were less
than 10 percent.
As a part of the present combustion
modification program, a pilot-scale natural-
draft process heater firing natural gas. No.
2 oil. No. 6 oil, and shale oil was tested.
These test results were reported in Ref-
erence 2.
Several combustion modifications, most
of which involved minor hardware changes,
were evaluated during these tests. They
included: Iow-N0x burners, staged com-
bustion air through floor lances, staged
combustion air through a central cylinder,
steam injection, flue gas recirculation, al-
tered fuel injection geometry, and lowered
excess air.
The results of the pilot scale tests are
summarized below.
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 emitted 1 50 ng/J (firing No.
6 oil) and 63 ng/J (firing No. 2 oil).
2. Two low-NOx burner designs had
baseline NOX emissions of 47.1 -
53.0 ng/J, firing natural gas. Thus,
the mean NOX emission level from
these burners was about 18 percent
lower than the mean value for the
two standard burners. Firing No. 6
oil, one Iow-N0x burner design pro-
duced 149 ng/J, a reduction of 7
percent below the standard burner.
The reduction of NOX due to the low-
NOx burner when firing No. 2 oil was
only 2 percent below the standard
burner baseline.
3. Combustion modification techniques
were effective in reducing NOX emis-
sions on a subscale process heater
firing either natural gas or No. 6 oil.
Staged combustion air through lances
in the heater floor and coupled wi
lowered excess air was the mo
effective technique, followed by fli
gas recirculation at either normal <
reduced excess air. When proper
adjusted and under reduced exce;
air conditions, a Iow-N0x (tertiary t
design) burner also effectively lov
ered NOX emissions firing both natur
gas and No. 6 oil fuel. Lowere
excess air alone (without other moc
fications) did not effectively reduc
the NOX concentration when firir
No. 6 oil.
4. Modifications which worked well firir
gas fuel (but which were not trie
firing oil because of time or te:
equipment limitations) included stage
combustion air using a central cylii
der above the primary air zone, steal
injection, and altered fuel injectic
geometry. Each modification reduce
NOX emissions by more than 3
percent below baseline, and sorr
may be applicable to oil firing as we
as to gas firing.
5. Staged combustion air through floe
lances reduced the NOX at a norm,
operating excess air level by 4
percent below baseline (54.6 ngA
firing natural gas fuel. At lowered 0
levels, the reduction was as much a
67 percent (natural gas fuel). /
normal 02 conditions, the NOX reduc
tion firing No. 6 oil was 35 percer
below baseline (160 ng/J); at re
duced 02, the reduction reached 5
percent.
6. Staged air through floor lances wa
also the most cost-effective techniqu
based on the data available. Cost
were predicted to be roughly $700
Mg of NOX reduction for small heater
(2.9 MWand below) firing gas, an
only $30/Mg of NOX reduction fc
large heaters (147 MW and above
firing oil. Cost calculations did nc
include annual fuel costs or saving
due to the combustion modification
because of the unrealistic efficienc
changes that were observed on th
small-scale heater.
Present Test Program Approacl
Following the work just discussed,
location was sought which would perm
the application of combustion modifica
tions and, in particular, the installation c
staged combustion air lances, on a fu
scale operating process heater. A natural
draft, vertical, cylindrical crude-oil heate
was found containing six combination
fuel John Zmk burners of the same desigi
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as those previously tested at the pilot scale
facility.
Initial tests were conducted to determine
heater performance over a range of operat-
ing variables such as excess air, load, and
air register settings for various fuels. The
tests were similartothe previous full scale
tests mentioned earlier in that no hard-
ware modifications were made to effect
combustion modifications.
Once the performance of the heater was
documented over its normal range of op-
erating parameters, staged combustion air
was implemented. A prototype system,
constructed largely of polyvinyl chloride
pipe, fittings, and valves with 24 stainless
steel lances (4 per burner) was built The
system was designed to provide maximum
flexibility and flow control for minimum
cost. The heater was then reevaluated
over the same ranges of operating param-
eters. During testing of the staged air
system, several additional parameters were
varied: burner stoichiometric ratios, staged
air insertion height and staged air lance
orientation. An optimum Iow-N0x operat-
ing condition was defined as the configura-
tion at which the lowest NOX concentra-
tions were obtained while still permitting
stable heater operation without a signifi-
cant increase in CO emissions. This condi-
tion was defined for gaseous fuel and for a
50/50 mixture of No. 6 oil and gas.
A 30-day test was then conducted with
the staged air system in continuous opera-
tion firing refinery gas at the optimum low-
NOX condition. System performance and
durability were evaluated as well as the
ability to maintain steady heater operation
at the Iow-N0x condition. After the long-
term test, a permanent system was de-
signed, suitable for a typical furnace of the
same type tested in this program.
The cost based on the permanent system
design, of the staged combustion modifica-
tion was evaluated for the gaseous fuel
and for the combination fuel, and also at
two levels of stack 02.
Table 1 summarizes significant results
obtained during the full scale test program.
Conclusions and
Recommendations
The following conclusions may be drawn
from the field testing and analyses per-
formed on this project
• Lowered excess air and staged com-
bustion air reduced NOX emissions
on a natural-draft, vertical, cylindrical
process heater firing refinery gas or
combined No. 6 oil and refinery gas.
• Steam injection did not effectively
reduce NOX emission firing refinery
gas.
Table 1. Summary of Results of Combustion Modification Tests on a Full-Scale Process
Heater
Baseline /VO,
Heat
Input
MW
10.4
10.4
9.0
13.7
13.2
13.1
13.1
Fuel Type
Ref. gas
Ref. gas
Ref. gas
Ref. gas
No. 6 oil +
ret. gas
No. 6 oil +
ref. gas
A/o. 6 oil +
ref. gas
ng/J
66
66
54
61
114
115
115
ppm
dry at
3% 02
125
125
105
120
212
214
214
NOxReduction
from Baseline
%
60
71
15
2.5
34
53
28
Change in
Fuel
Consumption, %
-0.2
-4.8
-2.8
+2.2
-0.6
-4.8
-3.0
Combustion
Modification
SCA1'1
SCA + LEA/b>
LEA
Steam in/.
SCA
SCA + LEA
LEA
131 SCA = Staged Combustion Air
= Lowered Excess Air.
• In a long-term test, combined staged
combustion air and lowered excess
air reduced NOX emissions by 71
percent below a baseline of 66 ng/J
firing refinery gas, while decreasing
fuel consumption by nearly 5 percent
• Some form of automatic stack 02
control is necessary to maintain the
desired low stack 02 content which
produced optimum low NOX operation.
• Without any such automatic system,
the staged air system (operated at
normal overall excess air levels when
firing refinery gas in a long-term test)
reduced NOX emissions by 60 per-
cent below the 66 ng/J value while
decreasing fuel consumption by
about 0.2 percent
• The staged combustion air system
can function effectively and contin-
uously with little operator attention
and little lance deterioration over a
30-day period.
• The staged combustion air system is
expected to be applicable to most
types of refinery heaters, whether
forced draft or natural draft and
whether vertical or horizontal. The
cost effectiveness is likely to be site
specific, however.
• Firebox temperatures at or below
about 1200 K (1 700° F) do not ap-
pear to be important in determining
NOX emissions.
• Pilot scale predictions for NOX reduc-
tions on a natural draft process heater
with staged combustion air are ex-
pected to be valid for 100 percent
No. 6 oil firing in a full scale heater.
• The cost of staged combustion air on
a natural draft process heater applied
at normal stack 02 is calculated as
$2636/Mg NOX reduction for a
16.1 MW heater, decreasing to
$1934/Mgat 147 MW heat input
• The cost of staged combustion air
combined with lowered excess air on
a natural draft process heater applied
at 2 percent stack 02 is calculated as
$1089/Mg for a 16.1 MW unit.
The cost becomes negative for a 14 7
MW unit indicating a savings associ-
ated with the combined modifications
Possible areas for future test work in-
volving combustion modifications for NOX
control on process heaters include:
1. Evaluating staged air for a natural-
draft air-injection system, to eliminate
the cost of installing and operating a
blower.
2. Using slower air velocities in a staged
air system to reduce the pressure
requirements of the blower, thereby
lowering costs. Larger diameter air
lances could perhaps be combined
with a lower pressure blower than
that used in the present tests.
3. Coupling the staged air system with
some type of automatic stack 02
control system, to achieve optimum
heater performance with respect to
NOX and CO emission levels, as well
as heater thermal efficiency.
4. Testing the staged air system, firing
100 percent No. 6 oil fuel.
5. Applying staged combustion lances
to forced draft units both with and
without air preheat to assess NOX
reduction potentials and cost effec-
tiveness. Presumably, a special staged
air blower would not be required on
such units, thus reducing costs (al-
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though interfacing with an existing
air supply system—particularly for
preheated units—might be more
costly than modifying a relatively
simple natural draft heater).
References
1. Hunter S. C. et al., "Application of
Combustion Modifications to Indus-
trial Combustion Equipment" EPA-
600/7-79-015a (NTIS No. PB 294
214, January 1979.
2. Hunter, & C. et al., "Application of
Advanced Combustion Modifications
to Industrial Process Equipment: Sub-
scale Test Results," EPA-600/7-82-
021 (NTISNo. PB82-239310), April
1982.
R. J. Tidona, W. A. Carter, andH. J. Bueningare withKVB, Inc., Irvine, CA 92714.
Robert E. Hall is the EPA Project Officer (see below).
The complete report, entitled "Refinery Process Heater /VOX Reductions Using
Staged Combustion Air Lances." (Order No. PB 83-193 946; Cost: $20.50,
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
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
PS 0000329
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