EPA-R2-73-292a
July 1973
Environmental Protection Technology Series
EXPERIMENTAL COMBUSTOR
FOR DEVELOPMENT OF PACKAGE
EMISSION CON'-ROl
I
fi Stceti. NW
wt;SiiSH«iiS^Si
)006
-------
EPA-R2-73-292a
EXPERIMENTAL COMBUSTOR
FOR DEVELOPMENT
OF PACKAGE BOILER
EMISSION CONTROL TECHNIQUES
PHASE I OF
by
L.J. Muzio and R .P . Wilson, Jr.
Environmental and Applied Science Division
Ultrasystems, Inc.
2400 Michelson Dr.
Irvine, California 92664
Contract No. 68-02-0222
Program Element No. 1A2014
EPA Project Officer: G .B . Martin
Control Systems Laboratory
National Environmental Research Center
Research Triangle Park, North Carolina 27711
Prepared for
AMERICAN PETROLEUM INSTITUTE
1801 K STREET, N.W.
WASHINGTON, D.C. 20006
and
OFFICE OF RESEARCH AND MONITORING
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
July 1973
-------
This report has been reviewed by the Environmental Protection Agency and
approved for publication. Approval does not signify that the contents
necessarily reflect the views and policies of the Agency, nor does
mention of trade names or commercial products constitute endorsement
or recommendation for use.
11
-------
ABSTRACT
Harmful emissions from commercial (3-30 x 10 Btu/hr) and industrial
(30-500 x 10 Btu/hr) package boilers are a significant factor in our air pollu-
tion problem, contributing 26% of the nitric oxide produced by stationary
combustion sources . Evidence indicates that these NO emissions are
x
most readily controlled by flame modification, such as flue gas recirculation
and staged combustion, rather than attempting to process the stack gases.
In Phase I of the three-phase program, a unique 3.7 x 10 Btu/hr oil
combustion facility was designed and built to develop NO control techniques
J\.
for small boilers. The facility duplicates the key aspects of the oil flames
c n
of representative boilers in the 10 -10 Btu/hr range, and is capable of
recycling and injecting any given amount of flue gas or air at unconventional
sites on the combustor boundary. The facility is also fully instrumented to
measure all flows (air, fuel, flue gas), temperatures along the combustor,
and NO , CO, O_, and smoke emissions.
5C £
Preliminary tests indicate that emissions from the test combustor
(approximately 300 ppm of NO or 4.4 gm NO/Kg fuel), while operating on
No. 6 oil, are consistent with emissions from field-tested package boilers
operating on No. 6 oil.
111
-------
TABLE OF CONTENTS
Section
Abstract iii
Summary of Phase I Activities vi
1. INTRODUCTION
A. Package Boilers as Emissions Sources 1
B. Some Fundamentals of NOx Formation in Flames 1
C. Control of NOx by Flame Modification 5
D. Side Effects of NOx Control 6
E. Rationale of the 3-Phase Program 8
II. COMBUSTOR FACILITY
A. Summary of Overall Features of the Combustor 10
B. Burner Furnace and Cooling System 12
1. Combustor 12
2. Burner 13
3. Fuel Supply 13
4. Convective Section 16
5. Coolant System 17
C. Instrumentation and Flame Modification Provisions 18
1. Air and Flue Gas Distribution System 18
2. Instrumentation 20
III. PRELIMINARY SHAKEDOWN AND EMISSIONS TESTING
A. System Performance 25
B. Preliminary Test Results 26
1. Flame Sampling 26
2. Emissions Testing with No. 6 Oil 32
IV. TEST PROGRAM
A. General Approach 37
B. Pollutant Minimization Tests 38
C. Versatility Tests 42
D. Plans for Field Testing 43
V. REFERENCES 44
VI. TABLE OF CONVERSION FACTORS 45
-------
SUMMARY OF PHASE I ACTIVITIES
c
Harmful emissions from commercial (3-30 x 10 Btu/hr) and industrial
(30-500 x 10 Btu/hr) package boilers are a significant factor in our air pollution
problem, contributing 13% of the nitric oxide produced by all combustion sources
and 26% of stationary sources . Typical package units firing heavy oil release
nitric oxide in the 100-400 ppm range and particulates in the range 1-4 gpm/kg
(2 3)
fuel ' . Yet unlike the mammoth utility boilers which are popular watersheds of
public environmental concern, comparatively little attention has been directed to
the commercial or industrial size units.
The evidence continues to mount that NO is most readily controlled by
X
flame modification rather than attempting to process the stack gases. External
flue gas recirculation (adding flue gas to the fresh charge at the burner) and
staged combustion (controlling the air/fuel mixing and thus heat release along
the combustor) can significantly reduce NO in practical combustion systems;
X
on the order of 50% reductions in NO have been realized. It is the long range
5C
goal of our program to uncover some of the best ways of applying these NO
3\
reduction techniques to the flames of package boilers: best in the sense of
emissions/ practical economy of burner/furnace hardware changes, and
functional goals such as steam generation and flame stability.
In Phase I of the three phase program a unique oil combustion facility
was designed and built especially to serve as a test bed for developing NOX
control techniques for package boilers. Not only does the facility duplicate
6 8
key aspects of the oil flames representative of boilers in 10 - 10 Btu/hr range,
but unlike these boilers the facility also can perform unusual functions at the
experimenter s command. Foremost is the capability of recycling any given
amount of flue gas and injecting either this flue gas or a portion of air at
unconventional sites on the combustor boundary. The facility is also fully
instrumented to measure all flows (air, fuel, flue gas), temperatures along the
combustor, and NO , CO, O9 and smoke emissions. All signals are electrical
x £
and are collected, scaled, digitized and recorded on magnetic tape by a specially
designed data acquisition system. Further, a calorimetric probe has been
designed and built which can simultaneously determine the temperature at any
vi
-------
point in the combustor and extract a sample for chemical analysis.
Shakedown tests were completed and the flame related hardware is
readily variable over a wide range with excellent control. The following
systems are operating as designed:
• modified burner
• combustor thermal and flow instrumentation
• flame probe
• emission sampling and analysis system
• fuel supply systems (No. 6 oil, No. 2 oil, natural gas)
• Dowtherm coolant system
• flue gas recirculation system
• staged air system including rear injection boom
Preliminary tests indicate that the emissions from the combustor (approximately
300 ppm of NO or 4.4 gm NO/Kg fuel) while operating on No. 6 oil are consistent
with emissions from field tested package boilers operating on No. 6 oil.
The combustor is presently ready for rigorous testing in Phase II to
uncover the optimum techniques of flue gas recirculation and staged combustion
to control NOV emissions. The techniques uncovered during Phase II will then
X
be applied to actual field package boilers during Phase III.
vii
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I. INTRODUCTION
A. PACKAGE BOILERS AS EMISSION SOURCES
Harmful emissions from package boilers are a significant factor in our
national air-pollution problem, contributing 13% of the nitric oxide produced
by all combustion sources, 26% of moving and stationary sources . Package
boilers are boilers which can be manufactured at the manufacturer's facility
and transported as a package via train to the operating site. The range of
operating load is from 3 million to 500 million Btu/hr and these units are used
wherever a source of steam is needed; hospitals, schools, industrial plants,
large apartment buildings, etc. Typical package units firing heavy oil release
nitric oxide in the 1.0- 15,0 gm NO/kg fuel range, and particulates in the range
(7 "^
1-4 gm/kg fuelv ' . In Table 1 we present a survey of available results.
Yet unlike the mammoth utility boilers which are popular watersheds of public
environmental concern, comparatively little attention has been directed to the
commercial (3 - 30 x 106 Btu/hr} and industrial (30-500x10 BtuAr) size units.
This uneven distribution of expressed concern has little rational basis. For
although these emission rates and the total fuel consumption by commercial
and industrial units seem low compared to those of large stationary sources
and motor vehicles, these emissions are delivered unavoidably and directly to
the near vicinity of schools, small businesses, and hotels with comparatively
little chance to disperse before human contact.
B. SOME FUNDAMENTALS OF NO FORMATION IN FLAMES
.X.
While the exact mechanism for producing NO over the entire range of
X
combustion conditions has not been completely defined, the general flame
conditions which must exist to form NO are reasonably well understood. As
X
most practical combustion systems utilize turbulent diffusion flames, the
discussion of NO formation will be focused on the processes in this type of
X
flame. Two mechanisms are possible: Thermal Fixation and Fuel-Nitrogen
conversion
(a) Thermal Mechanism
The sequence:
-------
TABLE 1
SUMMARY OF EMISSIONS FROM OIL FIRED PACKAGE BOILERS
Ref.
4
4
4
4
5
5
S
3
6
6
6
6
6
6
6
•6
6
6
6
6
6
6
6
7
7
7
7
7
7
7
7
7
7
7
Boiler Type
Scotch Marine 125 HP
Scotch Marine 150 HP
Scotch Marine 150 HP
Scotch Marino 150 HP
Scotch Marine ISO HP
Scotch Marine 60 HP
Scotch Marine 350 HP
Scotch Marine COO HP
Scotch Marine 80 HP
Cleaver Brooks
Foster Wheeler
(water tubo)
Scotch Marine
(Kewance>
Keeler-V.'ater Tube
Water Tube
Water Tube
Scotch Marine
Cleaver Brocks
Locomotive Type
120 HP
Scotch Marine 125 HP
Water Tube 460 HP
Water Tube 500 HP
Water Tubo 580 HP
Water Tube 2-15 HP
Water Tube 425 HP
Water Tube 870 HP
Fire Tube 60 HP
Water Tube 100 HP
Scotch Marine 200 HP
Water Tube 200 HP
Water Tube 300 HP
Fire Tube 300 H?
Scotch Marine 350 HP
Scotch Marine 40 HP
Scotch Marine 90 HP
Scotch Marine 90 HP
Scotch Marine 300 HP
Scotch Marine 300 HP
Scotch Marine 80 HP
Scotch Marine 80 HP
Scotch Marine 100 HP
Scotch Marine 100 HP
Scotch Marine 600 H?
Scotch Marine 500 HP
Burner Type
Rjtary Cup
Air Atomized
Pressure Atomized
Air Atonized
Air Atomized
Air Atonized
Air Atoraized
Steam Atomized
Rotary Cup
Pressure Atomized
Steam Atomized
Steam Atomized
Air Atomized
Air Atomized
Steam Atomized
Pressure Atomized
Pressure Atomized
Steara Atomized
Steam Atomized
MCL 7-23
Pressure Atomized
Stpam Atomized
Pressure Atomized
Pressure Atomized
Centrifugal Atomized
Pressure Atomized
Centrifuqal Atomized
Stcdra Atomized
Centrifugal Atomized
-
-
-
-
-
-
_
-
-
-
-
Rated Output
10» Btu/hr
5
6.2
6.2
6.2
6.2
2.8
14.6
8.1
3.3
15
21
14.2
21
23
30
4.2
1.5
4.8
5
18.5
20
23
9.8
17
35
2.8
4
3.1
3.1
12
12
14.6
1.6
3.7
3.7
12
12
3.3
3.3
4
4
28
28
Test Load
10b Btu/hr
4
S
S
5
5
2.2
11.7
7
2.7
10
12
9
14
21 .
14.4
0.7
l.S
5.3
3.4
11.8
36
8.5
14.7
23.6
25
1.3
0.9
3.1
1.4
3.4
5.8
12.5
-
-
-
-
-
-
-
-
-
-
-
Fuel
#6
#5
#5
#5
#6
#2
*4
#4
#S
#6
#6
*6
#6
#2
16
#1
*6
PS300
PS300
PS300
PS300
PS300
PS400
PE400
PS400
PS200
PS200
Diesel
Diesel
PS200
PS200
Diesel
S2
#2
#4
#2
#6
*2
*5
#2
#6
#2
*6
Fuel N
'i wt
0.44
0.33
0.16
0.25
0.39
0.03
0.22
0.22
0.21
-
_
-
-
-
-
-
-
-
_
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Excess
Air %
27
36
26
19
36
29
23
27
31
22
30
22
48
58
130
72
10-38
68
180
107
92
95
43
110
73
65
290 .
210
370
115
220
94
26
30
25
27
30
26
30
26
31
25
27 .
NO,,
qm/Kg Fuel
14.2
8.8
5.7
6.0
10.8
1.4
15.2
7.4
3.1
6.2
3.1
2.3
1.5
-
6.0
-
3-6
9.2
5.3
6.1
7.3
6.0
8.3
8.6
6.5
1.2
2.1
1
4
1.1
0.7
2.1
1.2
1.5
4.8
1.4
4.9
2
5.7
2.4
5.7
2.4
5.1
Particulars
gm/Kci Fuel
3.8
4.7
6.0
2.2
9.5
1.5-4.8
6.9
4.6
2.7
5.0
-
CO
qm/K.-: Fuel
0.4
0.55
0.44
0.43
0.53
0.04
0.34
0.28
0.07
1.1
["very 1
-
_
-
.
-
-
_
_
-
_
-
-
-
_
-
.
HC
gm/Ka ~»f*l
0.0?
0.04
0.04
0.04
0.04
O.li
0.04
0.13
o.o:
o.os
ow"]
-
-
_
_
-
-
-
-
-
_
-
-
_
.
-
-
SUMMARY OF EMISSIONS FROM GAS FIRED PACKAGE BOILERS
Ref.
S
5
8
6
6
6
6
6
6
6
6
6
6
6
6
6
6
1
7
7
7
7
7
7
Boiler Type
Fire Tube
Scotch Marino
Superior
Tubeless 30 HP
Fire Tube 60 H?
Scotch Marine 150 HP
Scotch Marine 200 HP
Water Tube 200 HP
Water Tube 245 IIP
Water Tube 300 HP
Fire Tubo 300 HP
Scotch M.irinc 350 HP
Water Tube 42 S HP
Water Tube 460 HP
Water Tubo 500 HP
Water Tube 5dO HP
Water Tube 870 HP
Scotch Mortne 60 UP
Scotch M.irinc 40 HP
Scotch Marine 90 HP
Scotch Marine 300 HP
Scotch Marine HO HP
Scotch Marine 100 IIP
Scotch Marine GOO HP
Burner Type
Premix
Premix
Slit
Premix
N'ozzlc Mix
Multijot Ri.-.g
Multiset King
Multijet Ring
4 Segment
Sing
Multliet
MultijGt Ring
Multijot Nozzle Mix
Multliet Ring
Multijot Nozzle Mix
Multijet Ring
Multljct Ring
Rated Output
1Q6 Btu/hr
7.2
4.2
6
1.4
2.8
6.2
8.1
8.1
9.8
12
12
14.6
17
18.5
20
23
35
2.8
1.6
3.7
12
3.3
4
28
Test Load
106 Btu/hr
9.3
0.98
6
0.88
2.14
7.6
4.5
2.6
14. 8(?>
S.I
6.4
11.3
25.8
16.2
30
11.6
25
1.9
-
-
-
-
-
-
Excess
Air %
»100
85
22
98
93
13
94
135
16
13
124
72
48
85
84
0
73
17
27
16
16
17
16
15
•'•'Ox
gm/Kg Fuel
3.2
3.7
2.0
1.04
1.1
0.5
0.4
0.6
0.23
0.68
1.2
1.5
2.6
1.2
3.6
1.45
3.5
0.7
1.6
1.7
2.1
8.8
1.2
1.8
Participate
gm/Kg Fuel
O.S
0.8
-
-
CO
gm/Kg Fu?l
0.3
70
-
.
-
-
-
HC
gm 'Kg T.?!
0.07
1.9
-
-
-
-
-
-------
O + M <*O + O + M (1)
£*
0+N2 slow NO+N »)
N + 02 -»NO + O (3)
which produces thermal NO is painfully sensitive to temperature excursions
2C
above the 3000 F mark. The adiabatic flame temperature for oil/air flames
at 8% excess air is 3600 F; natural gas flames fall in the same general range.
For every additional 100°F, the NO production jumps about a factor of 3 . It
is this thermal on/off switch, caused by the large activation energy of
reaction (2), which controls the overall sequence. These thermo-chemical
facts of life amount to one thing — an NO disaster occurs whenever near-
5C
adiabatic conditions are produced unless very rapid quenching follows.
In addition, typical combustor residence times are short compared to
the time to reach equilibrium and therefore the absolute values of NO measured
x
in combustors are about an order of magnitude below equilibrium values (see
Figure 1) at flame temperature.
(b) Fuel-Nitrogen Mechanism
This mechanism occurs during oil combustion where nitrogen atoms
can become available by liberation of nitrogen organically bound in the fuel
molecules. Even though the amount of chemically bound nitrogen in oil is
small, on the order of 0.05% for a distillate No. 2 fuel oil and 0.4% for a
No. 6 residual oil, it is comparable to the concentration of NO formed and
can be the controlling factor in some oil-fired units. This effect is clearly
shown in Figure 2 where sampling by Battelle of the NO emissions from a
commercial boiler operating at 80% load are plotted as a function of fuel
nitrogen content . At present little is known about the detailed mechanism
of fuel bound nitrogen conversion to NO. Limited experimental studies have
shown that approximately 40% of th
in package boiler type combustors .
shown that approximately 40% of the fuel bound nitrogen is converted to NO
*
*The actual conversion fraction depends on the operating conditions of the
combustor, load, excess air, etc.
-------
10000
1000
i
d
•z.
100
0.6 0.7
Air Rich
0.8 0.9 1.0
Equlvalance Ratio, J
Figure 1.
Fuel Rich
Equilibrium NO
1.1
1.2
/uu
•600
500
E
a 400
0*
•D
i
I 300
s
200
100
0
Logond
O Commercial Boiler with four fuels
O Other boilers
-
0
O
-
,
0/X
/ 0
O /
_ ^- ""
0 0
O
1 1 1 1
0 0.1 0.2 0.3 0.4 0
Nitrogen In Fuel, weight percent
Figure 2.
-------
C . CONTROL OF NOX BY FLAME MODIFICATION
Both pollutants can be kept low if (1) peak temperatures which otherwise
enhance (NO) production are avoided and if (2) hot fuel-rich zones are
X
avoided to minimize smoke particle production. Two stage combustion (SC) may be
used to delay heat release, dissolve spatial temperature peaks and reduce
oxygen availability, thus reducing NOX- Recirculated flue gas (ER), acts as a
thermal ballast to dilute reactants and thereby hold temperatures down, with a
subsequent suppression of NO .
J\
Some experience has been gained in applying flue gas recirculation and
staged combustion to practical combustion systems. In practice, flue gas
recirculation cuts nitric oxide emissions significantly. Por example, in tests
conducted by Martin and Berkau, approximately 22% NO reduction was obtained
J^.
on a laboratory combustor fired with a distillate fuel doped with 1% pyridine,
(9)
while 85% reductions were realized with the distillate fuel alonev . Turner and
Siegmund obtained approximately 33% reduction in NO in a 50 hp Cleaver
/ 1 /\ \ "^
Brooks boiler fired with a residual fuel oil . A theoretical predicting assum-
ing a perfectly homogeneous distribution of flue gas into the reacting gases
indicate an NO reduction of 99%. The difference is attributed to mixing effects
x
and fuel nitrogen which were omitted from the theoretical prediction. In order
for ER to be effective, the flue gas must be intimately mixed with the incoming air.
The effects of staged combustion on the NO emissions cannot be pre-
X
dieted without a rigorous theory for air entrainment into the oil-spray combustion
zone. However, empirical results have been gathered for oil-fired boilers in the
10 Btu/hr range ' ' , and for a coal-fired test furnace . In the former
case, a corner fired unit was operated with one burner tier supplied with air only
(25% of stoichiometric requirement) thus forcing the other burner tiers to operate
fuel rich (85% of stoichiometric air requirement). In this manner, NO reductions
J\.
of 30-40% were observed at 10% excess air.
Barnhard's results are similar : with 95% of stoichiometric air through
the burners and 15% through auxiliary "overfire" ports, NO was reduced 27%.
J\.
When these fractions were shifted to 90%-20%, the reduction increased to 47%.
-------
(12)
Selective secondary-air distribution was used by Bienstock, et al.
to reduce NO by 62% on pulverized-coal fired tests. It was found essential
X
to preheat the downstream air to 1940 F in order to avoid quenching the flame
in such a small furnace (rating ^ 04 x 10 BTU/hr).
D. SIDE EFFECTS OF NO CONTROL
X
Controlling NO with flue gas recirculation or staged comes not without
X
a penalty. There are a number of factors which must be considered in the
application of a particular control technique. Exhaust gas recirculation may
result in condensation in the lines with associated corrosion problems; flame
stability problems may arise.
When staged combustion is employed to control NO problems of heat
^t
distribution throughout the combustor may prove itself to be a culprit. Another
potential problem source may be the complexity of the system required to meter
the air to the required points within the combustor.
In addition, reducing NO must not result in unacceptable increases in
X
the emissions of carbon monoxide, hydrocarbons or particulates. Due to the
reduced temperatures encountered during ER applications, smoke and CO may
appear due to the retardation of the oxidation reactions which are exponentially
dependent on temperature. During staged combustion one must be certain that
the smoke formed in the fuel-rich primary zone is oxidized durther downstream
in the combustor. The real challenge then is to exploit these two techniques
without interrupting the necessary fuel/air oxidation sequence. To reduce NO
X
the flame must be cooled and the oxygen availability reduced without trigger-
ing soot-forming reactions which produce slow-burning solid carbon.
Thus, oil combustion with minimum air pollution inevitably is a tradeoff
in design and operating configurations. This dichotomy was clear from the
work of Wasser, et al., on oil-fired furnace emissions. Particulate, CO,
and NOV emissions are superimposed in Figure 3 to illustrate the tradeoff
X
involved.
-------
109
10
Emissions
Level
1.0
0.1
.01
1 » I
CO
I I
1.0 l.S 2.0
(&lr)/(stotch. olr)
2.5
Figure 3.
Emissions Tradeoff
-------
E. RATIONALE OF THE 3-PHASE PROGRAM
The evidence continues to mount that external flue gas recirculation (ER)
and staged combustion (SC) can reduce NO significantly in practical combustioi
X
equipment. It is the long-range goal of our program to uncover some of the
best ways of applying these NO -reduction techniques to the flames of
X
packaged boilers . . . best in the sense of emissions, best in the sense of
practical economy of burner/furnace hardware changes, and best in the
sense of functional goals such as steam generation and flame stability.
Unlike abatement of emissions from motor vehicles and utility source? ,
which may require modifications amounting to 10-20% of capital costs, with
package boilers the opportunity exists to make marked abatement progress
without severe sacrifice. Some 800 water-tube and 11,000 fire-tube boilers are
(13)
installed yearly in the United States and many others are refitted with
components intended to improve air/fuel mixing. The mixing hardware
represents a small fraction of the total cost of package boilers; the major
share going to the furnace, water/steam handling system, air blower, fuel
pump, and associated controls. Furthermore, the initial capital cost of a
package boiler is only about 5% of the operating costs (primarily for fuel)
(14)
over the boiler lifetime . i'hus , modifications to the mixing hardware
which cost a fraction of 1% of the total boiler costs (capital plus operating)
ov.'ir the years are reasonable.
Let us define more carefully the scope of the program. In seeking
hardware changes which minimize emissions, there is considerably more
latitude in developing a fresh redesign intended for new units, than in
searching for a simple modification that can be made in the field to convert
existing boilers. The larger, expensive water-tube units with high output
and high NO level are suitable for field modification. The smaller fire-tube
J\
units could be practically modified only if the changes were quite simple;
and, since some 11-12,000 are sold each year, they invite a complete redesign.
To the extent that increasing hardware changes may lead to ever lower emissions,
it makes sense to find both:
-------
(i) a simple modification suitable for field conversion, and
(ii) an exhaustive redesign to guide the manufacture of new units
The range of improvement sought is 50-80%.
Essentially, there are two sequential activities in developing a new
hardware concept to where it is acceptable to industry - an exploratory activity
to uncover promising concepts, and a rigorous field-testing activity to establish
the long-term operating validity of the concept. The former calls for experi-
mental inventiveness and disciplined mathematical modeling; the latter calls
for engineering and manufacturing experience with problems encountered in the
field.
To make the search for optimum ER and SC configurations easier,
an experimental facility was needed, and the activities of Phase I were
directed to satisfy this need. The goal was a versatile simulated package
boiler which provides the experimenter with a selection of air/flue-gas
injection options, and allows him to exercise each of these options (or
combinations thereof) over a continuous range while the burner is firing.
Furthermore, sensors or monitors were to be provided so that the experi-
menter can keep close quantitative track of operational parameters and of
how well the injection scheme is working to reduce emissions. This
document describes an experimental facility which meets these goals.
-------
II. COMBUSTOR FACILITY
A. SUMMARY OF OVERALL FEATURES OF THE COMBUSTOR
The objective of Phase I was to bring into existence a unique oil-
combustion facility. In order to generate applicable NO -control techniques
X
for package boilers, a rather schizophrenic combustor was conceived and
built: To the boiler manufacturer, the flame had to be of authentic shape and
simulate the heat transfer characteristics found in package boilers. To the
combustion experimentalist, the flame had to be a highly controlled and
instrumented system with options for modifying the flame at will. Foremost
was the capability of recycling any given amount of flue gas and injecting
either this flue gas or a portion of air at unconventional sites on the combustor
boundary. No existing package boiler in the 20 gal/hr range was nearly
versatile enough without overwhelming modifications; a specially designed
furnace combustor was built to meet these specifications. All of the flame-
related hardware is readily variable over a wide range and with good control, fuel
flow, air flow and distribution, staged air, flue gas recirculation. Both the flame
and emissions are measurable at any point. Furthermore, the combustion system
gives a reproducible and stable flame with consistent emissions behavior.
Given the wide assortment of oil-fired package boilers scattered around
the United States, pollutant minimization is best carried out on a single
representative unit. In selecting the size of this unit, it makes sense to
work on as small a scale as practicable. Although full-scale testing on units
o
in the 10 BTU/hr range will ultimately be necessary to demonstrate the effective-
ness of ER/SC modification, these modifications are most quickly located and
efficiently developed in subscale combustor tests. Lab-scale devices give the
opportunity for relatively straightforward experiments, encouraging inventiveness
and discovery.
In designing the test facility , attention was paid to providing three
commodities: authenticity, versatility, and data-gathering efficiency.
Without moving the design away from that of a typical package boiler, an
effort has been made to include as many options as possible to the experimenter,
both in standard parameters (e.g. , fuel type, atomization type, load) and
especially in the modes of external flue-gas recirculation and staged combustion.
10
-------
Port tor inokB dttarmination
Modiilv oonitnicUon
lot cMtxlno conbmtlan
for in«ly«l» tor HOj. CO
rlu« O«i RvclrcuUtlon
OrgAnle coolant to allow w«ll
temperature of 430-60CTT
without htgh pr*l*ur«f
•onttorad c*lcrUmtk»Ur
ProvUlon (or >t*gxl >lr
SmodUUd lo control \
r «nd MCOndiry mta }
HI J
No. «, No. 2 ml, NM.
Figure 4.
Diagram of Experimental Combustor
-------
NOMINAL SPECIFICATION
Load: 3.7 x 10 Btu/hr
r o
Combustion Intensity: 1.7 x 10 Btu/hr ft
Combustor L/D: 3.9
Wall Temperatures: 450°F
Fuel: No. 6 Oil, No. 2 Oil or Natural Gas
Tho overall combustor system is shown in Figure 4.
B. BURNER FURNACE AND COOLING SYSTEM
1. Combustor
The basic furnace is a cylinder of inside diameter 23 "and length 90",
o
giving a volume of 21.6 ft and L/D « 4. A sketch of the furnace is shown in
Figure 5 . The reader may wish to refer to complete engineering drawings of
the combustor and convective section (Appendix A) of the reference report " .
The furnace is composed of three cylindrical modules each of 30:! length;
this presents the option of changing both volume and L/D merely by removing
one furnace module. In addition, an 11" throat module connects burner to
furnace and provides a portion of the refractory burner cone.
Downstream of the throat, the walls of the three furnace modules are to
be cooled to 400-450°F, and are constructed of steel. Refractory may be added
to the furnace as a cylindrical insert.
STD. Pipe 24" O.D. x 3/a" Wall
One (1\H" Throat Section
Three (3) 30" Modular Furnace Sections
Annular Coolant
Jacket
Figure 5.
12
-------
2. Burner
A commercial 90 HP, dual-fired burner was selected as the skeleton for
a research burner. Designed for application in multi-pass scotch marine,
water tube, or firebox boilers, the burner is set up for low-pressure atomi-
zation of oil and forced-draft operation. Extensive shopping was done before
selection of the burner as the burner is significantly more critical to NO
.A.
formation than the combustor section. The specifications are as follows:
Manufacturer Ray
Model AECR-144
Size 90 HP
Nominal load 3.7 x 106 Btu/hr (25.1 gph or 3766 CFH)
Fuel Heavy oil or natural gas
Fuel gas pressure 1.5'1 w.c. at burner inlet
2.7" w.c. at valve inlet
Atomization Air, low pressure (15-20 psi)
Oil viscosity 200 SSF at pump
20 SSF at nozzle
Oil heaters 3 KW plus tailpiece
Stock blower 3 HP, 800 scfm
Oil pump Two stage, gear driven
The adaptation of this burner to a configuration amenable for research
included the following changes:
(i) Physical separation of primary and secondary air supplies for
independent metering.
(ii) Provision for variable swirl rate.
(iii) Provision for variable fuel/air ratio independent of load.
(iv) Replacing the stock blower with a higher pressure unit
capable of distributing air to downstream injectors.
(v) Insertion of precision flow metering devices for fuel and
air.
A sketch of the modified burner is shown in Figure 6 .
3 . Fuel Supply Systems
The fuel supply design was based on burner specifications and manu-
facturer recommendations for the Ray Burner Model AECR-144. Separate
13
-------
Secondary air Chamber
Primary Air Tube
Gas Tubes
Primary Air Manifold
Oil Inlet
Gas Supply Duct
Ray Air Control Valve
• Secondary Air Inlet Duct
Oil Noztf
Natural
Gas
Manifol
Figure 6.
Modified Burner
14
-------
systems have been developed for natural gas and No. 6 oil and No. 2 oil.
(15)
Details are given in the reference report.
No. 6 Oil
The supply system for No. 6 fuel oil is designed to preheat the oil to
120°F at the inlet to the burner pump. The burner itself is equipped with an
additional oil heater to raise the oil temperature up to 200 F prior to
atomization.
Two underground storage tanks, each of 9940-gallon capacity, were
installed. Either tank can be tapped, and a "hot well" is set up within the
tank by returning hot oil to the vicinity of the suction inlet.
A uniform supply of oil to be used for the test program was carefully
selected by the API representatives. Characteristics of this oil are given
below:
Gravity, °API 16.7
Flash Point, PMCC, F 265
Pour Point, F 80
Viscosity, SSF at 122°F, sec 97
Heat of Combustion, gross, Btu/lb 17,740
Water and Sediment, % 0.08
Ash, % 0.02
Sulfur, % 0.42
Nitrogen, Kjeldahl, % 0.36
Carbon, % 87.68
Hydrogen, % 11.61
Composition is as reported by Schwarzkopf Microanalytical; the margin of
error is + .02%. Other properties are taken from Union Oil test results.
No. 2 Oil
In addition to operation on No. 6 oil the burner may also operate on a No. 2
distillate oil. During operation on No. 2 oil the No. 6 fuel supply system is
bypassed and the No. 2 oil is fed to the burner from 55-gallon drums.
15
-------
An adequate supply of No. 2 oil from the same base stock as the
No. 6 oil was obtained for use throughout the test program. An analysis
of the oil is given below:
Carbon, % 86.21
Hydrogen, % 12.68
Sulfur, % 0.24
Nitrogen, Kjeldahl % 0.05
4 * Convective Section
The convective section is shown schematically in Figure 7. It is
designed to cool up to 40% of the combustion gases at full load from the 1800 F
combustor exit temperature to a flue temperature of approximately 400 F. Based
on overall design criteria which included heat transfer characteristics, econo-
mics and ease of operation and maintenance, a shell-and-tube heat exchanger
with one tube pass was selected as the final heat exchanger design configura-
tion. The flue gas enters the tube side of the heat exchanger and is cooled by
count erf lowing Dowtherm "G" coolant. The liquid Dowtherm is circulated
around the tubes by baffles on the shell side of the heat exchanger.
Transition Duct
to Reclrculatlon
Stack (6" Diameter)
To Main Stack
Flue Gs •
Reclrcu-
la t Ion
(400°F)
Dow
too
1
Vent 100 gpm 330^ /
1 -7 Flow Baffles j
[
L
" -'- "..' "
X
=====
_J
I [
1
f- \
/^Shell Std. Pipe 16" Dla x 91- 1/4" Ig. /
103 Straight Tubes-/
gpm, 300°F Std. Pipe 1" OD x 0.109" Wall x 9' Ig,
From Combustor
Figure 7. Convective Section
16
-------
5 Coolant System
During burner operation the coolant distribution system provides a
continuous flow of liquid coolant to the flue gas convective section and to
the combustor wall cooling jacket. Dowtherm was selected as the working
fluid to avoid the high pressures associated with 400-500 F wall temperature
when water is used. The heat exchanger components of the cooling system are
connected in series with a bypass around the heat sink to control fluid
temperature. Dowtherm G, a new liquid phase heat transfer fluid* designed
for use between 0-650°F is particularly suited to the present application. It
is the most stable low pressure, liquid phase heat transfer fluid available.
This stability minimizes the problems resulting from accidental overheating
caused by flame impingement, improper firing of the heater, and inadequate
circulation. Start-up and shut-down problems are minimized by this fluid's
excellent flow characteristics at low temperatures. Dowtherm G remains a
liquid and is easily pumped at temperatures down to 0°F. This solves many of
the problems of start-up and shut-down and eliminates the need for steam
tracing.
The nominal coolant flow rate is approximately 100 gpm. Resistance
temperature detectors (RTD's) are located at nine key points in the system to
continuously monitor the heat load. At design conditions, the heated Dowtherm
is cooled from 390°F at the cooling jacket exit to 300°F by a standard forced-
air heat exchanger.
* Patent Pending
17
-------
C. INSTRUMENTATION AND FLAME MODIFICATION PROVISIONS
1. Air and Flue Gas Distribution System
The overall distribution system is presented in schematic form in
Figure 8. Basically, eight supply points are fed from two reservoirs of air
and flue gas which are at elevated pressure (1 psi) due to centrifugal
blowers.
Theeight supply points include seveninjection points for air, and
five for flue gas:
Provision Provision Symbol
for flue for air
gas
(j) Burner primary x x P
(ii) Burner gas-ports x ^
(iii) Burner secondary x x S
(iv) Throat injectors x x T
(v)-(vii)Sidewall injectors xxx Wi'W2/W3
(viii)Axial injection from rear x ^
The air distribution manifold is designed to deliver combustion air (flow
rate controlled) from the blower outlet to the burner/furnace inlets described
in the above options. The original blower supplied air at ^ 6-7" HgO. Because
of the extensive piping and valve/flowmeter requirements, the blower size was
increased to supply approximately 1000 cfm of air at 1-lb pressure.
The flue gas manifold will recirculate exhaust gases to various supply
points. The flue gas fan will circulate up to 500 cfm of gas and compensate for
a 1 Ib pressure drop through the supply lines.
18
-------
Wall
i.'i Convootivc
Section (6" diara)
Oil Atorniziuo Air
Flue
Gar,
Blower
Boost Blower
Flexible Hose to
Ir.jection Boom
Figure 8 . Air and Flue Gas Distribution System.
19
-------
2. Instrumentation
Summary of instrumentation
Basically there arc four classes of sensors used in the experimental
facility:
(i) Air, fuel, and coolant flow rates sensed by differential
pressure or turbines
(ii) Temperature sensors for air, flue gas, oil, and coolant
(ili) Emissions analyzers for 09, CO, NO , and smoke
L* X
(iv) Calorimctric sensors for aspirating probe
These sensors constitute some 25 channels of data to be recorded for each
run. A data logger has been designed to collect, condition, digitize, and
store all data upon command from the experimenter, or at preprogrammed
intervals. A complete scan is possible within 30 seconds, liberating the
test engineer from tedious and time consuming interpolations and chart
readings . A second benefit accrues later when the data is to be displayed
or manipulated, because the computer can digest the data stored on 1/2" tape.
The ranges and accuracy of all sensors is jiven in table 2.
In addition to monitoring the combustor input-output variable, a double-
jacketed calorimetric probe has been developed specifically for boiler flame
..ampling and manufactured by the Calprobe Company. The probe is shown
schematically in Figure B.
The cooled probe is inserted through the end wall and traverses the
flame through various axial and radial positions. This can be done in the
flame environment which is characterized by turbulent, low speed, oxidizing
flow at 1-atm pressure and up to 3500°F mean temperature. The heat flux to
2
an exposed surface is approximately 0.3 Btu/in -sec for an oil flame.
Obviously, in the near field of the burner, where heavy concentration of oil
droplets exist, the probe may be expected to aspirate droplets.
20
-------
Chan.
No.
TABLE 2
SUMMARY OF INSTRUMENTATION
Display
Range
Description of Sensor
0 to 1 PSID
2 0 to 1000 PPM
3 0 to .100 Ib/min
4 0 to 1000 PPM
5-11 0 to 1000°F
12 0 to 1000°F
13 0 to 100°F
14 0 to 1000°F
15 0 to 1000°F
16 0 to 2000°F
17 0 to 100°F AT
18 0 to 10%
19 0 to 10 ft
20 0 to 1000° angle
o
21 0 to lOOOmg/m
22 0 to . 1 GPM
23 0 to 0.5 GPM
24 0 to 100 GPM
25-30 Spare
0-9
Gas flow rates: full scale signal of interest = 0.6PSID
supplied by Dyna science* P90D diff. press,, transducer
and CD10 Signal Conditioner in con junction, with a dif-
ferential pressure scanning valve; 12 points.
CO level, Beckman* 315B on. 0-500 PPM Range.
Probe gas flow (Thermosystem Mass Fldwmeter Model 1352-3G)
NO level, Spectra Systems* on 0-300 PPM Range.
Coolant temp, (platinum RTD, repeatable to 2.5°F).
(Measures 100-500°F).
Oil temp, (platinum RTD), +1°F repeatability.
(Measures 190-230°F).
Air temp, (platinum RTD), +2°F ace. (Measures 50-100°F)
Flue temp, (platinum RTD), +5°F ace. (300-500°F).
Probe gas temp. (CU-CO thermocouple), +5°F ace.
(200-400°F).
Exit gas temp. , (chrome alumuel thermocouple) .
(Measures 1000-2000°F).
Probe water AT (CU-CO thermocouples)
(Measures 10-60°F).
O2 Level (Beckman* 715 on 0-25% range and Taylor
Servomex OA256 on 0-10% range).
Potentiometer, boom position z. (0-10 ft).
Potentiometer, boom orientation 0. (0-160°).
2
Smoke meter (+.5% or lOmg/m Resolution ok) . Typical
range 50-500 mg/m .
Probe Water Flow. (Cox LFG-0 turbine flowmeter).
Oil Flow (Cox LFG-0 turbine flowmeter) .
Coolant Flow. (Potter 2-5426 turbine flowmeter) .
Smoke (Bacharach smoke tester) .
*Mention of specific manufacturer does not constitute endorsement by Ultrasystems
or by the program sponsors.
21
-------
The temperature of the gas as it enters the probe is deduced from how
much the gas heats up the coolant before leaving the probe.
_ A _ . . Cylindrical -v
Outer Jacket "\ Spacer \.
Inner Jacket
Hot Gas
Cooled
Thermocouples
Gas Sample
Exhaust
Air Gap Insulation
Figure 9. Calprobe Double-Jacketed Probe (3/8" diameter)
The spatial resolution of the temperature measurement is on the order
of 10-probe diameters. The time response of the system is set by the flow
rates of coolant and aspirated gas, and is about 5 sec. Clearly the
fluctuations in temperature will be averaged out, giving the mean
temperature T. Accuracy is + 2% or about + 60 F .
Emissions Measuring System
Samples taken from the flame through the flame probe as well as
from the downstream exhaust gas will be analyzed for CO, NO , and O
X.
the profiles of mean concentration, Y. (r,z) (where i = CO, NO, and Og
Thus
are
established for the same spatial locations as the flame temperature measure-
ments . In particular, it will be of interest to correlate local temperature with
local Y-T_,, and to probe large eddy structures for unusual pollution-formation
JNIU
behavior.
22
-------
As shown in Figure 10, sample conditioning includes water separation,
filters, dryers, flow meters, and a diaphragm pump which produces the
desired flow.
The following instruments are used to analyze for specific gases:
NO : Chemiluminescent, modified EPA design
rfV
CO: NDIR, Beckman #3ISA
O~: Polarographic, Beckman #715
Paramagnetic, Taylor Servomex OA250
Particulates: Beta filter
Smoke: Bacharach smoke tester
The response time is in all cases dependent on the sampling system,
so that with a reasonably short sampling time the response times will be
from 20 to 40 seconds.
The accuracy of all instruments is normally ± 1% of full scale and the
sensitivity as high as ±0.5% of full scale. With a Beckman NDIR 315A,
sensitized to 500 ppm CO full scale it is thus possible to determine 100 ppm
of CO with an accuracy of + 5% of that value (+ 5 ppm).
The determination of possibly low NO levels (10-50 ppm) will be quite
feasible using a chemiluminescent detector. It appears to be the best of
all continuous read-out methods and it should at least provide for a good
indication of the low pollutant levels achieved.
23
-------
Filter
Diaphragm
Pump
N5
Dilution
Gas
3-way Valv
Trap
Smoke Meter
Rotameter
20 LPM
Bypass
Pump
Beta Filter
Pressure
Relief
Velve
-X3—jj
Rotameter
Filter
I _
Rotameter
Filter
Rotameter
NO Analyzer
x
(Chemilum)
0 - 100 ppm
0-300 ppm
0 - 1000ppm
CO Analyzer
(NDIR)
0 - 100 ppm
0 - 500 ppm
O2 Analyzer
(Paramagnetic)
0 - 5 %
0 - 10%
0 - 25%
-M-
n
t i
Span Zero
Gas Gas
D
A
T
A
A
C
Q
u
I
s
I
T
I
O
N
S
Y
S
T
1
Figure 10.
Emissions Measuring System
-------
III. PRELIMINARY SHAKEDOWN AND EMISSIONS TESTING
A. System Performance
The combustor, air distribution, burner, fuel supply, coolant and flue
gas recirculation systems were inspected and operated in a series of
shakedown tests. All systems were found to be operating satisfactorily and
within the design specifications. Specific details of the shakedown and
performance tests are given in the reference report and the results of the
system performance is tabulated below:
Load: 20 - 150% rated
Performance at Full Load (3.7 x 106 Btu/hr)
Excess Air Up to 75%
Primary Air/Total Air 20-80%
Oil Temperature Up to 200°F
Atomization Air Pressure 10-20 psi
Flue Gas Recirculation* 0-40%
Rear Injection Staged Air/ 0-50% @ 17% excess Air
Total Air
Sidwall Injector Air/Total 0-50% @ 17% excess Air
Air
Coolant Temperature Rise «50°F
Along Combustor
*Amount of recirculation is defined as
R = faiass rate of recirculated
(mass rate of fuel + air)
25
-------
B. Preliminary Test Results
1. Preliminary Flame Sampling
The flame sampling probe has been successfully operated in the combustor
with both gas and oil firing. During these tests, observations were made of
probe coolant flowrates, probe clogging, coolant leaks, excessive probe
vibration, and excessive probe heating. It should be noted that during these
tests the burner was in an interim stage of development with a swirl vane in
the primary air flow passage and the secondary air introduced tangentially
and radially. Hence, the sampling was performed in order to test the probe
in the hot combustor environment and not to obtain data on the.combustor
performance.
Tests were performed with the combustor gas fired at 2.6 x 10 Btu/hr
with 73% excess air. Radial profiles were obtained for nitric oxide and
temperature at two axial locations in the combustor, 88 inches from the
burner surface and 32 inches from the burner surface. The results of these
tests are shown in Figure 11 and 12 . As can be seen in Figure 11, at 88 inches
from the burner, the temperature is fairly uniform across the combustor. It should
be noted that due to a large uncertainty in the sample flowrate through the probe
the absolute temperature levels are uncertain. Due to this uncertainty, the
temperatures are presented on an arbitrary scale. Spacial range of the probe
in the radial direction is from the combustor axis out to 86% of the combustor
radius. Similarly, the nitric oxide profile 88 inches from the'burner surface
is uniform across the cross section as seen in Figure 12.
The probe was then moved to a position 32 inches from tl>e burner surface.
At this location definite variations in nitric oxide and temperature are observed
over the cross section. As is seen in Figure 11 , the temperature gradually
increases from the centerline out to a distance of r/R =0.5 (r/R is the ratio of
probe radial position to combustor radius). At r/R = 0.5 there is a rather abrupt
increase in temperature after which the temperature is fairly uniform. The
nitric oxide profile at a distance of 32 inches from the burner surface shows
that the NO concentration gradually decreases from a centerline value of
55 ppm (corrected to stoichiom'etric with the local oxygen concentration) to
a value of 48 ppm at r/R = 0.6. Between r/R of 0.6 and 0.86 there is a
26
-------
m
cc
UJ
o:
a:
tu
Q.
8
0,2
Fuel: Gas
Load: 2.6x 106 Btu/hr
Excess Air: 73%
P/S/NS: 20/38/42%
L = Distance From Burner
(Interim Burner Configuration)
0.4
0.6
0.8
1.0
Figure 11 . Radial and Axial Variations in Temperature with
Gas Firing
27
-------
•a
8
£
40
L = 32"
O.
a.
a
7*'
'x
O
a
30
20
10
NO
_.-, - Q2
Fuel: Gas
Load: 2.6 x 105 Btu/hr
Excess Air: 73%
P/S/NS: 20/38/42%
L= Distance From Burner
[Interim Burner Configuration)
.6
.8
1.0
r/R
Figure 12. Radial and Axial Variations in Nitric Oxide
with Gas Firing
28
-------
rather abrupt decrease in nitric oxide to a value of 42 ppm. Further, from
Figure 12, it is observed that approximately 70%of the NO is formed within
a distance of 32 inches of the burner. During sampling with the combustor
gas fired no overheating or clogging problems were encountered and the
probe could be operated in the flame for extended periods of time.
Following the gas flame sampling, the probe was used to sample an oil
flame. During these tests the combustor was oil fired at 2.5 x 10 Btu/hr
with 70% excess air. Radial profiles of nitric oxide and temperature were
measured at three axial positions; 88 inches, 57 inches, and 32 inches from
the oil nozzle. The results of these tests are presented in Figures 13 and 14..
The results presented in Figure 13 show a somewhat uniform temperature 32
inches from the burner which extends from the centerline out to about 0.6
of the combustor radius, after which the temperature rises. Farther
downstream the temperature profile flattens out as shown in the profiles
taken 57 and 88 inches from the oil nozzle. The nitric oxide results for this
flame are shown in Figure 14.
During sample of the oil flame, there was significant soot accumulation
in the probe and line. At 32 inches from the burner the sample flowrate
decreased by 40% after 10 minutes of operation. The sample line and probe
were then purged with air after which the sample flowrate increased to its
original value. This procedure was then repeated every 10 minutes during
sampling. Since the probe was purged and the sample flowrate returned to
its initial value it appears that the aspiration and accumulation of oil within
the probe is not a problem.
29
-------
QL
LJ
K
LI
Q.
2
LU
H
Fuel: Oil
Load: 2.5x 10° Btu/hr
P/S/NS: 27/36/35%
Excess Air: 70%
(Interim Burner Configuration)
0.2
0.4 0.6
r/R
0.8
1.0
Figure 13 . Radial end Axial Variations in Temperature
with OL1 Firing
30
-------
300
200
It
2
•o
u
s
ou
Q.
cf 100
O
a
L = 32"
10
L = 88"
8
L= Distance from burner
NO
02
Fuel: Oil
Load: 2.5 x 106 Btu/hr
Excess Air: 70%
P/S/NS: 27/38/35%
_ (Interim Burner Configuration)
0.2
0.4 „. 0.6
r/R
0.8
1.0
Figure I4. Radial and Axial Variations in Nitric Oxide
with Oil Firing
31
-------
2. Preliminary Emissions Testing with No. 6 Oil
Following completion of the combustor shakedown tests, preliminary
emissions tests were conducted. In order to establish an understanding of the
emissions behavior of the combustor, tests were performed with No. 6 oil firing
at variable load, excess air, primary/secondary ratio. The results of these
tests are presented in Figures 15, 16 and 17 with a brief discussion below.
In Figure 15, results are presented of the effect of excess air on nitric
oxide and smoke emissions while operating on No. 6 oil. In these tests, the
excess air was varied by holding the load constant and varying the total air
flow. The results show that varying the excess air from 7% to 50% results in
a 12% increase in NO. In terms of mass emissions the combustor is emitting,
on the average, 4.4 grams NO/kg fuel which is within the range of typical opera-
tion of oil fired package boilers as shown in Table 1.
For comparison purposes, the NO and smoke emissions from an identical
combustor operated by the EPA are also shown in Figure 15. The only difference
in the two units is that the EPA facility utilizes an unmodified Ray burner. The
higher NO emissions obtained from the Ultrasystems facility may be due to the
differences in the nitrogen content of the fuels. This may also account for the
differences in smoke emissions from the two units: Smoke emissions from the
Ultrasystems unit are approximately one bacharach smoke number higher than the
EPA combustor.
Next, the effect of the primary to secondary air ratio on NO and smoke
emissions was investigated. These results are shown in Figure 16 with the
burner operating at 17% excess air and at two loads, 3.5 x 10 Btu/hr and
2.8 x 106 Btu/hr.
The effect of swirl on NO and smoke emissions was investigated and the
results are shown in Figure 17. During these tests the burner was operated at a
load of 3.5 x 10 Btu/hr, 17% excess air and an air distribution of 50% primary,
50% secondary. The amount of swirl is controlled by varying the inlet velocity
of the secondary air. As shown in Figure 6, the secondary air enters the burner
tangentially; hence, varying the inlet velocity will vary the inlet angular momen-
tum. Thus the amount of swirl, which is characterized as
32
-------
300 r
8
tj
•fi
E
8
I
*
100
Fuel: No. 6 oil
O Ultras/stems Combustor
(modified Ray burner)
Load: 3.5x106 Btu/hr
Primary/Secondary Air: 50/50, %
A EPA Combustor
(unmodified Ray burner)
High Fire
0,A NO
•A Smoke
10
8
6
4
2
u
2
u
D
CD
10
20
30
40
50
Excess Air, %
Figure 15. Effect of Excess Air on NO and Smoke Emissions.
33
-------
300 r
200
0)
(ft
.a
o
Q.
Q.
100
Fuel: No. 6 oil
Excess Air: 17%
Load:
A 2.8xlO§ Btu/hr
O 3.5xl06 Btu/hr
O,A NO
O,A Smoke
10
8
•5
2
u
o
CD
o
z
o
J*
o
40
50
60
70
% Primary Air
Figure 16. Effect of Primary Air on NO and Smoke Emissions,
34
-------
_ (Angular momentum)
(Axial momentum) (burner radius)
can be varied.
The combustor is presently ready for rigorous pollutant minimization
testing.
35
-------
300
Fuel: No. 6 Oil
Load: 3.5 x 106 Btu/hr
Excess Air: 17%
Primary/ Secondary Air:
50/50%
CO
CD
200
cu-
O
ss
CO
I
a.
100
10
8
o
a
o
o
6 £
Q
O
4 z
0)
±i
o
2 E
in
OJ
0.2
0.4
0.6 0,8 KO 2.0
Swirl Parameter
4.0 6.0 8,0 10.0
4.54.0 3.0 2.0 1.0
Air Control Valve Opening, in,
0.5
-------
W. TEST PROGRAM
TEST PROGRAM TO UNCOVER OPTIMUM CONFIGURATIONS
A. General Approach
Package boilers are fired under such widely varying conditions (load,
fuel type, atomization, L/D) that a technique which controls emissions at
condition A may give excessive smoke or NO at condition B. Furthermore,
j\.
there are so many promising ER and SC injection techniques that it is irrational
to attempt to test each control technique under each boiler operating variation.
This dilemma is portrayed in Figure 18 where the spectre of fifty thousand
conceivable tests arises.
Pollution-Minimization Tests
f Scheme E
At least 250
distinct injection Scheme D
schemes for ER
orSC, and burner Scheme C
aerodynamic Scheme B
changes
Scheme A
f 1
(*
•X
(*
X
X
X
X
X
X
X
X X
X
X
X X
X
X
X
X
X
X
X
X
X
X X
X
X
X X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
— \ f —
3 excess
air
levels
Versatility
Tests for
Promising Schemes
At Least 200 Distinct Combustor Settings
(Excess air, load, atomization, fuel type, oil temperature,
wall temperature, duty cycle)
Figure 18 . Conceivable Test Matrix Showing 50,000
Possible Tests
The basic approach of the proposed test program is to screen all ER/SC
injection schemes at the same restricted representative combustor settings,
then expose the most promising ER/SC control schemes to a wide range of
combustor settings. These two test series are represented by vertical and
horizontal bars in Figure IB . In total, approximately lOOOtests are indicated ,
distributed as follows:
37
-------
Pollutant Minimization Tests: approximately 800
Versatility Tests: approximately 200
The test facility has been designed with enough versatility to permit
not only 3 burner changes but also testing of 5 injection concepts with about
5 distinct parametric variations of each. While the combustor is fired up,
a given ER or SC technique may be run through 10 variations in 4 or 5 hours,
allowing each run to reach steady state before recording flame and omissions
data. Another 3 or 4 hours is allotted for furnace preparation, instrument
calibration and clean-up. Thus, tests are executed in sots of about 10 at an
average overall rate of 45 minutes per test.
The dual approach described above guarantees a comprehensive treatment
of the possibilities in exhaust recirculation and staged combustion. The number
of tests is reduced to 1COO from at least 50,000, without severe danger of over-
looking a promising technique. Since a control technique should not be considered
unless it functions under "standard" operating conditions, the efficient reduction
of the test matrix as described in Figure 18 is justified.
The value of the wealth of emissions data to be produced is magnified
by a consistent framework of understanding. For this reason, Phase II is
composed of acquiring data and explaining it by model development,
computerized predictions, and critical interpretation.
B. Pollutant Minimization Tests
All tests to seek air or flue-gas injection schemes giving minimum
pollution are to be run on No. 6 fuel oil under standard conditions of
firing rate, atomization mode, combustion-chamber L/D. (Versatility tests
are run later)
38
-------
The first tests are run just making simple burner changes with cursory
flame sampling to indicate pollutant levels at several areas within the firing
tube. Variations will include:
Swirl
Primary/secondary ratio
Oil temperature
Atomization air pressure
In summary, four relatively simple burner modifications will be
investigated as means to reduce emissions. In general, these "front-end"
modifications call for much less severe hardware changes than the furnace
modifications to be described, and therefore are logical candidates for
quick field modification. The effectiveness of these burner-oriented techniques
relies on the well-known sensitivity of emissions to near-burner mixing
patterns. They are so simple, we should try them first. This initial data
will be compared with the test results taken during the baseline tests. A
simple model will also be composed to explain the baseline emission results.
The baseline results establish control data for comparison with combustion
modification, and will be repeated periodically throughout the test program to
verify standardization of the furnace. Any systematic trends such as soot
accumulation will be detected.
The next combustion modification series will utilize exhaust recirculation.
Three injection schemes will be used, listed in order of estimated promptness
of flame dilution and cooling:
1. Conventional annular injection
2. Injection through fuel gas ports
3. Throat exit injection
The percent of flue gas recirculated and the excess air will be varied for each
injection scheme, while monitoring NO. CO, O9, and smoke in the flue gas
X £t
and recording furnace exit temperature. The range in recirculation will be
limited by excessive smoke production and/or combustion instability; and
similar extremes will be determined for all injection configurations. Flame
sampling will be carried out extensively enough to characterize all the
significant changes occurring within the combustion chamber with each
39
-------
injection profile. When the test series is complete and the data displayed
by computer-drawn graphics, the model for pollutant formation will be
upgraded to explain the new results.
Tests of staged combustion ("SC") will follow the ER testing. Variations
in injection schemes will include the following five locations of introducing
air for delayed combustion:
1. Throat exit injection
2-4. Downstream wall jets w, , w?, w_
5. Downstream axial countershower
These concepts arc to be tested singly and in combination, so that at least
30 possibilities are there. Five air distribution profiles (e.g., primary vs.
secondary, upstream vs. downstream) will be tested for each injection scheme
Throughout the pollutant minimization tests, a few points will be made
using a low nitrogen No. 2 oil. This will allow the assessment of the nitric
oxide arising from nitrogen fixation and from fuel nitrogen.
A test program of 828 tests is shown in Table 3.
After the tests of staged combustion and combined ER/SC, the model will
be modified to account for axisymmetric mixing. The upgraded model will then
be exercised to explain the SC results.
A parametric study will be conducted with the model to indicate the most
promising designs for combustion modification. In a parallel effort, other
promising designs will be derived from direct correlations and analysis of the
test data. These two sources for test planning will be combined with an
engineering and economics analysis to determine a final set of tests demonstrating
the designs for minimum practical emissions.
40
-------
Baseline Conditions:
TABLE 3
POLLUTANT MINIMIZATION TESTS
Load (Full - 3.7 x 106 Btu/hr, Part - 2 x 106 BtuAr
Excess Air (17%, 35%)
Air Distribution (Primary/Secondary - 50/50)
Oil Temperature (200°F)
Atomization (air, 18 psi)
Combustor (L/D = 4)
Coolant Inlet Temperature (350 F)
No. 6 Oil
Focus of Test
Burner Variations
External
Recirculation
Staged Combustion
Combined Stage
and Recirculation
Interspersed
Standardization
Final Tests of
Test Conditions
Primary/secondary - 30/70, 40/60, 50/50,
60/40, 70/30*
Secondary swirl - primary = 40%: low swirl,
intermediate, high swirl**
primary = 50%: low swirl,
intermediate, high swirl
primary = 60%: low swirl,
intermediate , high swirl
Oil temperature: Full load: 170, 180, 190,
200°F
Part load: 180, 190, 200,
210, 220 F
Atomization Air Pressure: 14, 16, 18, 20 psi
3 recycle ratios - 10%, 20%, 30%
Baseline: 3.7x10 Btu/hr, 17% excess air
I. Injection schemes
2 - burner equivalence ratios (£=0.7,1.0)
3 - air distribution a) single modification vary
vary primary /secondary
40/60, 50/50, 60/40
b) multiple injection vary
staged/burner air ratios
20/80,50/50,80/20
II. Side wall Injector Orientation
3 injectors
4 orientations (upstream, downstream .toward
and against swirl)
1 load 3.7x10 Btu/hr, 1 excess air, 17%
1 burner equivalence ratio
2 types of external recirculation, combined
with 4 types of staged combustion,
2 levels of ER (10%, 30%)
2 levels of staging (Burner $=0.7,1.0)
Performed at random to monitor any systematic
trends in combustor behavior and for tests with
No. 2 oil
1 ER@ 6 levels of ER (5,10,15,20,25,35%)
2 SC @ 2x(% staged, burner $=0.8,1.0)
@ 2 distribution profiles
2 combinations ER/SC @ 3 ER levels (10,20
30%) @ 3 % staged (burner $=0.8,0.9,1.0)
41 Total
No. Tests
88
168
230
12
150
50
66
64
828
**For these tests the baseline primary/secondary will be varied.
-------
C. Versatility Tests
Package boilers operate over a considerable range of conditions. In order
to evaluate combustion modification techniques for emission control, this
entire range must be traversed with the control technique in force. After all,
what good is an NO -reduction technique if it billows smoke at low load .
s*i
A distinct series of the test program is planned to do this. For discussion,
let us assume there will bo three optimum configurations developed in the
pollutant minimization work, for example
(i) One each configuration applicad e for simple in-the-field
modifications for fire-tube boilers ,
(ii) a similar configuration for water-tube package boilers,
(iii) one configuration which is an extensive departure from current
package boiler design.
The three designs (which will have performed with minimum pollutant
emission at the standard test condition) will be tested in a versatility test
series where firing rate, fuel, chamber shape, duty cycle, and atomization
mode will be varied. The parameters and number of variations to be tested are
proposed in Table 4.
TABLE 4
VERSATILITY TESTS
1
* Parameter
Load
Excess air
Fuel (gas, #6 oil, #2 oil)
Atomization mode (steam vs. air
vs. sonic)
! #6 oil variations (e.g. Nitrogen
j content)
1
1 Total number of combinations tested
Desired Variations
3
I
3
3
i
3 (#6 oil only)
2 (oil only)
126 oil :
18 gas
The versatility testing will provide additional empirical data to correlate
with the mathematical model.
\2
-------
D Plans for Field Testing
As part of the concluding work in Phase II, the plans for the Phase III
field testing are to be formulated. The ER and SC injection schemes to be
tested under practical field conditions are now determined. In coordination
with FW, we will plan modifications to fire-tube and water-tube units which
are operating in the field. Particularly sensitive repercussions noticed in
using SC and ER techniques will be carefully noted to be duly observed in
Phase III trial runs.
Some of the aspects of field testing which will be taken into account
are:
1. Which emissions must be monitored and what boiler points
are best to monitor.
2. Opportunity to shut down and modify existing units.
3. Test plans for comprehensive series of one-hour runs.
Competence of the boiler operators at a given location
to handle additional controls or monitors in connection
with long term field testing.
4. Type and uniformity of fuel available.
5. Type of boiler service such as load level, degree of transient
operation, continuity of operation.
43
-------
V. REFERENCES
1. Levy, A. , et al, "A Field Investigation of Emissions 'Prom Fuel Oil
Combustion for Space Heating," API Publication 4099, 1 November 1971.
2. Bartok, W., Crawford, A. R., and Piageri, G. J., "Systematic
Investigation of Nitrogen Oxides Emissions and Combustion Control
Methods for Power Plant Boilers," Paper 38c, AIChE Meeting, 70th
National (1971).
3. Eahn, G. S., and Burkland, C. V., "Chemical Kinetics in Low Emission
External Combustion, " Preprint 37a, presented at the 70th AIChE National
Meeting, Atlantic City, 24 August-1 September (1971).
4. Tornaras, Z. G. and Reckner, L., "Tests on Burner-Boiler Units, No. 6
Oil", Scott Research Laboratories, Inc., SRL Project 1077, Contract
PH 27-00154 NCAPL (1968).
5. Hungobrauck, R. P0? Von Lehuden, D= J., and Meeker, J. E., "Emissions
of Polynuclear Hydrocarbons and Other Pollutants from Heat Generation and
Incineration Processes", ]APCA 14 267 (1964).
6. Chass, R. L., George, R. E., "Contaminant Emissions from the
Combustion of Fuels, " Paper 59-52 presented at the Air Pollution Control
Association 52nd Annual Meeting, June 1959.
7. API SS5 Task Force, Progress Report, 1972.
8. Sommerlad, R. E., Private Communication, March (1971).
9. Martin, G.B., Berkau, E. E., "Preliminary Evaluation of rlue Gas Recir-
culation as a Control Method for Thermal and Fuel Related Nitric Oxide
Emissions," presented at WSSCI Meeting, University of California Irvine,
October 1971.
10. Turner, D. W. , and Siegmund C. W., "Staged Combustion and Flue Gas
Recycle: Potential for Minimizing NO from Fuel Oil Combustion," presented
at The American Flame Research Committee Flame Days, Chicago, Illinois,
September 6-7, 1972.
11. Barnhard, D. H., and Diehl, E. K., "Control of Nitrogen Oxides in Boiler
Flue Gases by Two Stage Combustion," J.APCA, 10, 397 (1960).
12. Bienstock, D., Amsler, R. L., and Bauer, E. R.,Jr., "Formation of Oxides
of Nitrogen in Pulverized Coal Combustion," J.APCA, 16, 442 (1966).
13. Downham, A.F., "Trends in Small Boiler Design," presented at the American
Power Conference (1964).
14. Andrews, R. L., Siegmund, C. W., and Levine, D. G., "Effect of Flue Gas
Recirculation on Emissions from Heating-Oil Combustion," APCA 61st Annual
Meeting (1968).
15. "A Versatile Combustor for Developing Emission Control Techniques,"
Reference Report of Phase I activities for API Task Force SS4.
44
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VI. TABLE OF CONVERSION FACTORS
To
LENGTH
AREA
VOLUME
MASS
PRESSURE
ENERGY
POWER
TEMPERATURE
Convert
inches
feet
meters
square inches
square feet
square meters
cubic inches
cubic feet
liters
gallons
cubic centimeters
pounds
grains
2
pounds/in
pounds/in
Btu
Btu/hr
kilowatts
horsepower
horsepower{boiler)
horsepower (boiler)
degrees Faronheit
(°F)
degrees Rankine
<°R>
Into
meters
meters
centimeters
square meters
square meters
square centimeters
cubic centimeters
cubic meters
cubic meters
liters
cubic meters
grams
kilograms
2
dynes/cm
feet of water
gram-calories
gram-calories/second
gram-caloriesAour
kilowatts
BtuAr
kilowatts
degrees Celsius(°C)
degrees Kelvin (°K)
Multiply By
2.54x 10"2
3.048 x 10"1
1.0 x 102
6.452
9.29 x 10~2
1.0 x 104
1.639 x 101
2.832 x 10~2
1.0 x 10"3
3.785
1.0 x 10~6
4.54x 102
1.0 x 103
6.9 x 104
1.60x 10~2
2.52x 102
7. Ox 10"2
8.6 x 105
7.46 x 10"1
3.35 x 101
9.803
(°F - 32)
x 5.56 x 10
5.56 x 10"1
45
-------
BIBLIOGRAPHIC DATA '• Deport No. 2.
SHEET EPA-R2-73-292a
4. Title and Subtitle'
Experimental Combustor for Development of Package
Boiler Emission Control Techniques --Phase I of III
7. Authorfs )
L. J. Muzio and R. P.Wilson, Jr.
9- Performing Organization Njrnc and Address
Ultrasystems , Inc.
2400 Michelson Drive
Irvine, California 92664
1Z Sponsoring Organization Name .ind Address (S66 BlOCk 15)
EPA, Office of Research and Monitoring
NERC-RTP, Control Systems Laboratory
Research Triangle Park, North Carolina 27711
3. Recipient's Accession No.
5. Report Oate
July 1973
6.
8- Performing Organization kept.
No.
10, Project/Task/Work Unit No
11. Contract/ Gram No. ;
68-02-0222
13. Type of Report & Period
Covered
Phase I of HI
14.
is. supplementary Notes This study was co-sponsored by: The American Petroleum
Institute, 1801 K Street, NW, Washington, D. C. 20006.
16. Abstracts Tne rep0rt describes Phase I of a program during which a unique 3. 7
million Btu/hr oil combustor was designed and built to develop NOx control
techniques for small boilers. The facility duplicates key aspects of oil flames of
representative boilers in the 1 million to 1 billion Btu/hr range, and can recycle
and inject any amount of flue gas or air at unconventional sites on the combustion
boundary. The facility can also measure all flows (air, fuel, and flue gas),
temperatures along the combustor, and NOx, CO, O2, and smoke emissions.
Preliminary tests indicate that emissions from the combustor (approximately 300
ppm of NO or 4. 4 gm NO/Kg fuel), operating on No. 6 oil, are consistent with
emissions from field-tested package boilers. In Phase II, the combustor will be
used to screen many different applications of combustion modification techniques for
controlling pollutant emissions. Phase III will include long-term testing of
] the optimum configurations.
17. Key Words and Document Analysis. 17o. Prscripiurs
Air Pollution
Boilers
Combustion
Emission
Nitrogen Oxides
Nitrogen Oxide (NO)
Fuel Oil
Carbon Monoxide
Oxygen
l7b. Identifiers,'Open-landed Terms
Air Pollution Control
Stationary Sources
Industrial Boilers
Commercial Boilers
package Boilers
Smoke
Test Equipment
Flame Modification
Flue Gas Recirculation
Staged Combustion
No. 6 Oil
!7c. COSATI Field/Group 21B 21D 13B
10. Availability Statement
Unlimited
19. Security Class (This
Report)
UNCLASSIFIED
20. Security Class (This
UNCLASSIFIED
21- No. ot Pages
46
22. Price
NTIS-35 (REV. 3-7Z)
46
USCOMM-DC H9S2-P72
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