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

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                                      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

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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

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                              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

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                            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

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                      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

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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:

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                      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
-
-
-
-
-


















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      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.

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    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.

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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%.

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                                                                      (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.

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        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

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                                                                                                                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

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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

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      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

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 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

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 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

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                                                            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

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 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

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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

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       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

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      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

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                           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

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            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

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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

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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

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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

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                 _ 	(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

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                              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

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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

-------