United States
 Environmental Protection
 Agency
Industrial Environmental
Research Laboratory
Research Triangle Park NC 2771
 Research and Development
EPA-600/S7-84-017b Apr. 1984
 Project Summary
 Development  of  Criteria  for
 Extension  of Applicability of Low
 Emission,  High  Efficiency  Coal
 Burners:  Second Annual  Report
 A.R. Brienza, S.L Chen, M.P. Heap, J.W. Lee, W.H. Nurick, D.W. Pershing,
 and D.P. Rees
  This report  describes the second
year's effort under EPA Contract 68-
02-2667, which concerns the develop-
ment of criteria for the evaluation and
applicability of low-emission,  high-
efficiency coal burners.  The report
describes progress in three major
areas: (1) bench scale studies,  (2)
distributed mixing burner development.
and (3) comparison with  commercial
practice. The bench scale studies
concern the impact of fuel characteris-
tics on fuel NO formation during the
combustion of pulverized coal. Although
fuel NO  emissions generally increase
with increasing fuel nitrogen content,
coals with the same rank and similar
nitrogen contents may produce markedly
different fuel nitrogen levels. Prelimi-
nary results indicate that a simple
procedure, evaluating reactive volatile
nitrogen, can be used to assess the
impact of coal type on fuel NO forma-
tion. Data relating to the development
of the distributed mixing burner have
been reviewed, and data have been
obtained with both single and multiple
burners. No operability problems were
encountered with different fuel types,
but NO emissions were fuel dependent.
Several commercial burners have been
tested satisfactorily in the test facility.
One gave severe flame impingement.
Carbon  monoxide  emissions were
generally higher and  nitrogen oxide
(NO>) emissions were slightly lower
than commercial practice.
  This Project Summary was developed
by EPA's Industrial Environmental
Research Laboratory, Research Triangle
Park, NC, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title  (see Project Report  ordering
information at back).

Introduction
  NOX formation in pulverized coal flames
can be reduced by  using  the  burner to
control the rate of fuel/air  mixing to
minimize fuel nitrogen conversion.  This
report describes the second year's
progress on EPA Contract 68-02-2667.
The program is aimed to:
  • Expand the fuel capability of low NOX
    burners to include the major types of
    solid fossil fuels projected for use by
    the utility industry.
  • Explore additional burner concepts
    and configurations that show poten-
    tial for improving the emission and
    thermal performance of pulverized
    coal burners.
  • Determine  the effects of multiple
    burner configurations  that  are
    encountered in utility boilers.
  • Provide for direct comparison be-
    tween the experimental burners
    being developed here  and  the
    current state-of-the-art for commer-
    cially available  coal burners.
  • Arrange for coordination  of the
    technology development program
   with  boiler manufacturers  and
    users.
  • Provide testing in support of planned
    application of the burner technology.
Figure 1 shows the relationship of the

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  Planning/Approach
      Taskl
     Program
    Definition
   Experimental
Burner Development
                             Task 2
                            Screening
                           Experiments
/
\
Task 3
Single Burner
Experiments

Task 4
Multiburner
Experiments

TaskS
Comparison with
Commercial Practice
  Relate to      |  Technology
Practical Units       Transfer
                                                    Task?
                                                 Data Analysis
                                                     and
                                              Criteria Development
Figure 1.   Overall program logic.


various  tasks that are planned to meet
these objectives. In this, the second year
of the program, efforts were expended on
the following tasks:
  • Bench scale fuel screening studies
     to assess the impact of fuel properties
     on  fuel NO formation (Task 2).
  • Tests  with  the  distributed mixing
     burner and different fuel types
     (Tasks 3 and 4).
  • Tests  with  commercial burners to
     allow a comparison with commercial
     practice.
Bench Scale Studies
  In the first year's effort, a bench scale
reactor was constructed with a design
input firing rate ranging from 50 to 150x
103 Btu/hr.* This facility, to be used for
fuel screening  studies and  concept
development, had  several versatile
features including:
  • The ability  to  burn  the fuel with
    nitrogen-free oxidant mixtures com-
    posed of 02, COz, and Ar, to define
    fuel NO production.
  • Complete control over fuel input rate
    and fuel size distribution.
  • A modular combustion chamber to
    permit probe access and variable
    heat extraction rates.
 *To convert nonmetric units to their metric equiva-
 lents, please use the conversion factors at the back
 of this Summary:
                 Table 1 lists the 25 coals tested to date in
                 this furnace and their properties. Initially,
                 the impact of fuel properties on NO
                 formation under excess air is discussed;
                 then  data obtained  to date  on the
                 evaluation of advanced concepts for NO*
                 control will be presented.


                  The  Influence of Coal
                 Properties on Fuel NO
                 Formation
                   Pulverized  coal was burned under
                 premixed and  diffusion flame conditions
                 in nitrogen-free atmospheres to evaluate
                 fuel  nitrogen conversion.  Figure 2
                 summarizes the  data obtained with the
                 coals tested to date under premixed and
                 axial  diffusion  conditions. Fuel NO
                 emissions are shown  in pounds of NOa
                 per 10s Btu as a function of percentage
                 nitrogen in the coal on a dry ash-free
                 basis  for overall 5 percent excess oxygen
                 in the combustion  products. The  data
                 presented illustrate two major points:

                   1.  Fuel NO emissions tend to increase
                     with increasing fuel nitrogen content.
                     This is most pronounced for premixed
                      conditions. However, for any given
                      nitrogen content there is a consider-
                      able spread  in fuel NO emissions,
                      indicating that some property other
                     than total fuel nitrogen content
                      influences fuel NO formation.
                   2.  Fuel nitrogen conversion decreases
                     with decreasing  fuel/air mixing
     rates.  Since oxygen availability
     controls fuel NO formation, this is
     expected.

  Some anomalous behavior was observed
associated with  fuel/air mixing effects
and fuel nitrogen formation. Some coals
show a very strong dependence of fuel
nitrogen formation  on  fuel/air mixing
characteristics.  However, this is  not
always  the case; even for coals of the
same rank, the influence of  fuel/air
mixing appears to be also coal-dependent.
Two fuels tested to date show  very
different characteristics. The  anthracite
shows  almost  no  impact of  fuel/air
mixing rate.  Since anthracite is very low
in volatile content, it can be assumed that
most of the fuel  NO formed is produced
from solid nitrogen, and that the impact of
fuel/air mixing characteristics  is mini-
mized.  Alternatively, the Australian
lignite showed a decrease in fuel NO from
950 to 675 to 175 ppm as the combustion
conditions  changed from premixed to
radial diffusion to axial diffusion.
  It can be argued that the fraction of the
coal  fuel nitrogen that  is volatile  (i.e.,
emitted with the volatile fractions during
thermal decomposition)  has a major
impact  on the formation of fuel  NO.
Therefore, two simple experiments were
carried  out to determine if volatile  fuel
nitrogen (determined by either the ASTM
volatile matter  procedure or an inert
pyrolysis experiment developed under
EPA sponsorship) can be used to predict
fuel  NO formation  in pulverized  coal
flames.  The char residue from an ASTM
volatile  test was analyzed for  nitrogen
content to determine the fraction of the
nitrogen that had been liberated with the
coal  volatiles. The results suggest  that
this method of assessing volatile nitrogen
evolution is  not even capable of ranking
fuels, and is certainly not suitable as a
predictive tool. Under EPA sponsorship, a
pyrolysis reactor  was developed to
investigate the conversion of fuel nitrogen
to HCN under both  inert  and oxidative
pyrolysis conditions.  Gas-phase kinetics
experiments suggest  that  HCN  is a
reasonable model for volatile fuel nitrogen
compounds; therefore, the amount of fuel
nitrogen that is converted to HCN could
indicate the potential for a  particular coal
to produce fuel NO. The pyrolysis experi-
ment was  operated as  a  two-stage
system. The fuel was placed in an initial
reactor whose  temperature could be
varied,  and the pyrolysis compounds
were swept into  a  secondary reactor
(maintained at 1373 K) with an inert Ar
flow. Experiments have demonstrated

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Fuel Symbol
Fuel Source
Proximate Analysis
1% as received)
Moisture
Ash
Volatile Matter
Fixed Carton
Ultimate Analysis
l%Dry)
C
H
N
S
Ash
0
Heating Value
IBtu/lb. Wet)
CLASSIFICATION
(ASTMD388)


O
Haze/ton
PA


5.13
5.74
4.39
84.74


88.45
2.14
0.79
0.47
6.05
2.10
13. 124

Anthracite



O
Upper Cliff
AL


3.0O
9.49
20.44
67.O7


79.32
4.47
1.47
1.3O
9.78
3.66
13.254

Medium
Volatile
Bituminous

O
Rosa
AL


8.02
6.79
21.81
63.38


81.23
4.73
1.54
1.04
7.38
4.08
13.394

Medium
Volatile
Bituminous

0
Black Creek
AL


2.25
4.45
28.28
65.02


8212
5.21
1.79
0.76
4.56
5.56
14.284

Medium
Volatile
Bituminous

0
W.KY


5.43
7.53
37.79
49.25


71.58
5.43
1.55
3.21
7.96
10.27
12.082

High
Volatile
A Bitu-
minous
a
wv


7.57
12.05
29.12
51.26


74.68
4.96
1.38
0.86
13.04
5.08
12.228

High
Volatile
A Bitu-
minous
O
Elkay
WV


0.60
11.61
33.35
54.44


73.96
4.93
1.39
2.47
11.69
5.56
13.115

High
Volatile
A Bitu-
minous
0
Gauley
Eagle
WV


3.72
26.89
26.65
42.74


59.43
4.11
1.35
0.84
27.94
6.33
10.110

High
Volatile
A Bitu-
minous
O
Price
UTfl)


6.39
7.40
38.89
47.32


73.52
5.52
1.44
0.61
7.89
11.29
12.340

High
Volatile
B Bitu-
minous
k.
Price
UT(II)


7.41
8.83
38.84
44.92


72.24
5.75
1.55
0.76
9.54
10.16
11.877

High
Volatile
B Bitu-
minous
0
Utah
(Coal)


4.20
9.62
42.97
43.21


69.36
5.32
1.50
1.04
10.05
12.73
11.718

High
Volatile
B Bitu-
minous
e
Utah
(Char)


2.70
16.83
10.29
70.18


75.39
1.28
1.22
1.12
17.30
3.69
11.185

—



a
Cadiz
OH


4.29
18.05
34.87
42.79


62.08
4.44
1.07
7.40
18.86
6.15
11.038

High
Volatile
B Bitu-
minous
Fuel Symbol
Fuel Source
Proximate Analysis
/% as received)
Moisture
Ash
Volatile Matter
Fixed Carbon
Ultimate Analysis
(% Dry)
C
H
N
S
Ash
0
Heating Value
(Btu/lb. Wet)
CLASSIFICATION
(ASTMD380)

Farmington
NM


7.76
17.96
34.95
39.33


63.06
4.65
1.40
O.81
19.47
10.61
10.391

High
Volatile C
Bituminous
Four
Corners
NM


5.24
24.06
35.94
34.76


55.99
4.71
1.23
1.03
25.39
11.65
9.425

High
Volatile C
Fruit/and
NM


11.02
20.72
31.66
36.60


58.71
4.21
1.30
0.93
23.29
11.56
9.344

High
Volatile C
Bituminous Bituminous
Co/strip
MT


21.27
9.58
30.82
38.33


67.52
4.36
1.38
0.63
12.17
13.94
9.169

Sub-
Hardin
MT


22.70
11.26
31.26
34.88


65.54
4.15
0.95
0.79
14.57
14.00
8.603

Sub-
Hardin
MT


20.49
8.62
33.24
37.65


67.88
4.65
0.99
1.07
10.84
14.57
9.229

Sub-
bituminous bituminous bituminous
B
B
B
Shell
TX


25.23
10.28
35.31
29.18


60.99
4.49
1.13
1.O2
13.74
18.63
8.131

Sub-
bituminous
C
Scranton
NO


34.96
7.50
28.85
28.69


64.61
4.17
0.83
1.52
11.53
17.34
6.446

Lignite
A

Beulah
ND


33.10
7.12
28.65
31.13


65.29
3.96
0.99
1.14
10.64
17.98
7.245

Lignite
A

Beulah
ND


34.63
4.97
27.02
3338


66.15
4.20
0.96
0.37
7.60
20.72
7.245

Lignite
A

Savage
MT


36.36
4.61
28.48
30.55


64.99
4.04
1.00
0,42
7.25
22.30
6.995

Lignite
A

Morwell
Australia


9.07
3.38
48.79
38.76


66.25
5.01
0.65
0.28
3.72
24.09
10.051
(wet)
—


Saar
Germany


216
8.04
36.23
53.57


76.13
5.25
1.37
0.83
8.21
8.21
13.657
(dry)
—


almost quantitative conversion of nitrogen
in pyridine to HCN at 1373 K. Thus, in this
experiment, the fraction of fuel nitrogen
capable of conversion to HCN could  be
assessed as a function  of first-stage
pyrolysis temperature. The results shown
in Figure 3 compare the fraction of fuel
nitrogen converted to  NO for  the three
combustion conditions as a function of
the fraction of the fuel nitrogen converted
to HCN under pyrolysis  conditions at
1373 K. It can be seen that the pyrolysis
data agree qualitatively with the experi-
mental results obtained in the premixed
and radial diffusion flames. The Savage
lignite (A) gives the highest percentage
conversion of fuel nitrogen to NO under
combustion conditions, and also has the
highest fraction of volatile nitrogen yield
in the inert pyrolysis study.
Optimization of Staged
Combustion Conditions

  It is generally recognized that staged
combustion offers the most cost-effective
control technique for minimizing fuel NO
formation. The basis for staged combus-
tion as an NOX control technique involves
the competition between two reaction
paths:  one  forms N2, and the other
NO from the fuel-nitrogen species. The
path producing  N2 is favored under fuel-
rich  conditions. Thermodynamic limita-
tions indicate that the total fixed nitrogen
species (NO, NH3, HCN) are minimum at
about 65 percent of the theoretical air
requirements for complete  combustion
for most hydrocarbon fuels, and that this
minimum concentration is of the order of
10  ppm under combustion conditions.
Thus, it could be concluded that if all the
nitrogen species were in the gas phase
then  this thermodynamic  limitation
would represent the minimum NO
achievable under staged combustion
conditions, since  it is  reasonable to
assume total conversion of these small
TFN concentrations during second-stage
burnout. Gas-phase kinetics would also
indicate that the approach to thermody-
namic equilibrium is accelerated at high
temperatures, even though the minimum
TFN concentration would tend to increase.
Staged combustion also has an impact on
the formation of thermal NO because the
heat release process is extended in time
allowing enthalphy loss, thus reducing
peak temperatures.
  The primary control options in a staged
system are:

-------
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1.2
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0.2
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- Premixed ^
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- r * ° 4°
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70x/03fltu/"r
" V' 5% O2 (Stack)
Open Symbols— Bituminous
-
-
-
^
-
_
Half Shaded Symbols — Subbituminous
Solid Symbols— Lignite
, * — Anthracite
\\i\\\\l
. Axial Diffusion
.

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.

-
-
-

-

-

      0.6    0.8     1.0    1.2    1.4

          Fuel Nitrogen, lb/10e Btu

Figure 2.    Fuel NO emissions as a function
            of fuel nitrogen  content and
            mixing conditions.
  • How long and at what temperature
     must the fuel products remain under
     fuel-rich conditions?
  • What is the optimum stoichiometry
     or distribution of stoichiometries in
     fuel-rich zone?
Two series of experiments have been
carried  out: one involved three-stage
combustion; and the other, heat extrac-
tion from the primary and/or secondary
zone to assess the various options.
  Experiments were carried out in which
the fuel-rich stage was divided into two
sections: the first fuel-rich stage stoichi-
ometry was maintained constant (as was
the overall excess air  level), and the
stoichiometry of the  second fuel-rich
stage was varied. Exhaust NO emissions
were reduced by about 15 percent when
operating under three-stage conditions
compared to  two-stage operation.  In
another  experiment the bench scale
reactor was modified to allow removable
space cooling coils to be added to the fuel-
rich first stage, or the second stage of a
two-stage combustion system. Maximum
emissions were obtained without cooling,
and minimum emissions were obtained
when heat was extracted from the
primary section. This is surprising since a
reduction in temperature of the first stage
would be  expected  to increase the
concentration  of total fixed nitrogen at
                                        15  0.4
                                        .C
                                         w
                                        Q
                                        as
                                        (£>
                                        O  0.3
                                        s

                                        1
                                            0.2

                                            0.1
       -  Premixed
Radial Diffusion\
                                                                                              -tt-
                                                                                                  Axial Diffusion
                                                   0.1
                                                                                              -if-
                               -If—•	•—
                       0.2         0.1           0.2        0.1
                      Fraction of Fuel N Converted to HCN at 1373 K
                                                                                                              0.2
                                        Figure 3.
           Fuel nitrogen conversion can be correlated by HCN produced during pyrolysis for
           well mixed combustion conditions.
the exit of the first stage, thus increasing
(not decreasing) final emissions.

Commercial Burner Testing
  Since a primary goal of the program is
to demonstrate the distributed mixing
burner (DMB) technology in field operating
boilers, some assurance is required that
the DMB, which has been demonstrated
only  in  the large  watertube simulator
(LWS) research furnace, will also perform
in the field as predicted. Also, the basis
for the  prototype design is the LWS
furnace, not a steam  raising system.
Although  indirect, the  approach taken
was  to  evaluate  commercial burner
operation in  the  LWS  and compare it
against  field  experience. This approach
provides some assurance that, if the
burner operates satisfactorily in the LWS,
it will also operate satisfactorily in the
field.
  The burners selected  for testing under
this program are:
   •  Babcock  and  Wilcox dual-register
     burner.
   •  Peabody Engineering Corporation
     standard pulverized-coal burner
     with low-NOx modification.
   •  Steinmuller low-NOx burner (similar
     to  burners currently used  at the
     Weiher plant in West Germany).
  All  the burners  were designed for a
nominal  firing rate of 50 x 106 Btu/hr,
and  the installation in the LWS  was
similar to that in  the field. To date, the
B&W and  Peabody burners have been
tested with the baseline Utah bituminous
     coal. The Steinmuller burner will soon be
     tested with  a bituminous coal from
     Germany (similar to coal used in the field)
     and baseline Utah coal. In support of the
     industrial  demonstration  program (EPA
     Contract  68-02-3127),  an  80 x  106
     Btu/hr, Foster Wheeler intervane burner
     (pre-NSPS) was also evaluated;  results
     are included in this report for complete-
     ness. All of the burners  gave stable
     flames and performed satisfactorily.
     However,  the Babcock and Wilcox dual-
     register burner produced  a flame that
     was too long for the LWS firing depth and
     gave severe flame impingement on the
     back wall. Thus, it  is very difficult to
     compare  field and LWS  experience
     because impingment prevented complete
     heat release  of the input coal. Several
     general conclusions can be drawn from
     the studies with commercial burners:
        • The  flames observed  in the LWS
          were judged, by experienced engi-
          neers, to be very similar to those
          observed in the field.
        • CO levels were consistently higher
          than measured in the field.
        • NO levels were slightly lower than
          measured in field operating units.

     Conclusions
        • Bench Scale Studies.  These studies
          concerned the development of a
          data base on the effect of coal type
          on NO formation and the definition
          of optimum conditions for minimum
          NO formation under idealized fuel/
                                    4

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     air contacting. Although  fuel NO
     emissions  increased with increas-
     ing coal nitrogen content, coals with
     the same rank and similar fuel nitro-
     gen content produce markedly dif-
     ferent fuel NO levels. Preliminary re-
     sults suggest that a simple proce-
     dure (that evaluated reactive volatile
     nitrogen) could be  used to  assess
     the impact of coal type on NO pro-
     duction.  Studies on the optimization
     of the conditions in  the  fuel-rich
     stage of a staged system indicate
     that minimum gas-phase nitrogen
     species (HCN + NH3 + NO) does not
     necessarily give minimum emis-
     sions after burnout.
  • Distributed Mixing Burner Develop-
     ment.  Data relating to the develop-
     ment  of the distributed  mixing
     burner have  been reviewed and
     summarized.  Single and  multiple
     burner data have been obtained for
     two different fuels. The distributed
     mixing concept can be operated with
     different fuels, and it appears that
     emission levels are sensitive to fuel
     type. However,  no attempt was
     made to reoptimize the burner for
     different fuels.
  • Comparison with Commercial Prac-
     tice.  Several commercial burners
     have been tested in  the research
     facility. All the burners performed
     satisfactorily  and produced stable
     flames. However, one burner gave a
     flame length that  caused severe
     flame impingement on the rear wall
     of the test furnace. Since  severe
     impingement cannot be tolerated in
     the field, comparison with commercial
     practice is invalid. Carbon monoxide
     emissions produced with the com-
     mercial burners were slightly higher
     than  those usually found  in field
     operating units, and NOX emissions
     were slightly lower.

Conversion Factors
  Readers  more  familiar with  metric
units may use the following factors  to
convert the nonmetric units used in this
Summary:
Nonmetric
Btu/hr
Btu/lb
lb/106 Btu
Times   Equals Metric
                           A. ft. Brienza. S. L Chen. M. P. Heap, J. W. Lee. W. H. Nurick, D. W. Pershing, and
                            D. P. Rees. are with Energy and Environmental Research Corp., Irvine, CA 92714.
                           G. Blair Martin is the EPA Project Officer (see below).
                           The complete report,  entitled "Development of Criteria for Extension of
                            Applicability of Low Emission, High Efficiency Coal Burners: Second Annual
                            Report," (Order No. PB 84-163 898; Cost: $19.00, subject to change) will be
                            available only from:
                                  National Technical Information Service
                                  5285 Port Royal Road
                                  Springfield, V'A 22161
                                  Telephone: 703-487-4650
                           The EPA Project Officer can be contacted at:
                                  Industrial Environmental Research Laboratory
                                  U.S. Environmental Protection Agency
                                  Research Triangle Park, NC 27711
 2.93
 2.33
 430
 W,
J/0
ng/J

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Environmental Protection
Agency
                               Center for Environmental Research
                               Information
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Official Business
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