United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/SR-92/242 March 1993
4Sr EPA Project Summary
Evaluation of Nitrogen Oxide
Emissions Data From TVA
Coal-Fired Boilers
Susan Stamey-Hall
Current EPA emission factors (AP-
42) for nitrogen oxides (NOX) from util-
ity coal-fired boilers do not account for
variations either in emissions as a func-
tion of generating unit load, or in de-
signs of boilers of the same general
type, particularly wall-fired boilers. TVA
has recently compiled short-term NOX
emissions data from 30 units at 11 TVA
coal-fired plants. These units include
cyclone, cell burner, single wall, op-
posed wall, single tangential, and twin
tangential boiler firing designs. In this
study, the NOX emission rates from
each boiler were calculated and com-
pared with the calculated rate for each
boiler type using AP-42. Additional re-
cent NOX data (from non-TVA boilers)
were also obtained from the literature,
along with the data used to develop
the current AP-42 emission factors.
Analysis of all these data indicates that:
(1) to varying degrees, NO emissions
increase with increasing load for all
except single- and opposed-wall-fired
boilers; (2) using the current AP-42
quality rating scheme for the six boiler
types, factoring in the TVA and recent
literature data results in improved qual-
ity ratings for all NO emission fac-
tors"A" (excellent) for those of 4 of
the 6 boiler types, "B" (good) for those
of cell burners, and "C" (fair) for those
of opposed wall-fired boilers; and (3)
there was no evident relationship be-
tween NOX emissions and fuel nitrogen
content or fuel ratio (fixed carbon to
volatile matter).
This Prefect Summary was devel-
oped by EPA's Air and Energy Engi-
neering Research Laboratory, Research
Triangle Park, NC, to announce key find-
Ings of the research project that Is fully
documented In a separate report of the
same title (see Project Report ordering
Information at back).
Background
The current EPA emission factors docu-
ment (AP-42) provides information to es-
timate nitrogen oxide (NO,) emissions from
various coal-fired utility boilers burning bi-
tuminous and subbftuminous coal. The
emission factors, expressed as pounds of
NO per ton of coal burned, relate amount
of NOp emitted to amount of fuel burned.
Emission factors are provided for three
major boiler types: cyclone, tangentially
fired, and wail-fired utility boilers (Table
1). No emission factors are given for sub-
classes of these major boiler types; i.e.,
for single- or twin-furnace tangential units;
single-wall-fired units; horizontally opposed
wall-fired units; or cell-burner wall-fired
units.
The U.S. EPA's Air and Energy Engi-
neering Research Laboratory has initiated
a study to determine whether the AP-42
document could be revised to include emis-
sion factors for each boiler subclass, and
to account for factors such as boiler de-
sign and coal type.
To this purpose, NO*, emission data and
corresponding operating conditions and
coal information were obtained from the
Tennessee Valley Authority (TVA) for 30
boilers at 10 TVA coal-fired plants in Ala-
bama, Kentucky, and Tennessee. These
units encompass all three major boiler
types, and all subclasses in the tangential
and wall categories. These data were sum-
Printed on Recycled Paper
-------
marlzed and then compared to NO emis-
sions data calculated from the AP-42 emis-
sion factor. Further analysis of the TVA
data consisted of evaluating NO emis-
sions as a function of unit load. Initially,
only NOX data from TVA units were to be
evaluated. However, TVA data were lim-
ited for several boiler types, so it was
necessary to include NOx data from non-
TVA units.
Table 1. AP-42 Emission Factors*
UtilityBoiler
Type
Emission Factor
Ib ofNOjlon of coal
CyclonB
Tangontially Fired1"
Wall-Fired'
37
15
21
a From AP-42 Section 1.1 at applicable load
range of 60-110%.
* Includes single-and twin-furnace units.
e Includes single-wall, horizontattyopposed-wall,
and cell-burner units.
The most recent NOX data were ob-
tained through a literature search and from
the seven references cited in the current
AP-42 that are the basis for the current
AP-42 emission factors. These data were
combined with the TVA data by specific
boiler category and used to: (1) determine
if the TVA data could be used to modify
the AP-42 emission factors; (2) determine
if current AP-42 emission factors are con-
sistent with measured values; (3) identify
any trends, such as NO,, as a function of
load; and (4) determine new average NOX
emission rates for each boiler subclass.
Finally, the emission factor rating was
reviewed to determine if including addi-
tional data would improve the factor rat-
Ings for each boiler type. The rating is a
measure of the quantity and quality of
data used to generate the emission fac-
tors.
Results
Cyclone Furnaces
NOX emissions from 12 cyclone furnaces
ranged from 0.79 to 1.87 Ib/mBtu,* with
an average of 1.22 Ib/mBtu (33 Ib/ton").
This average is 11% lower than the AP-
42 rate of 1.37 Ib/mBtu. However, the TVA
units averaged 1.61 Ib/mBtu, which is 18%
higher than the AP-42 rate. The non-TVA
units averaged 1.11 Ib/mBtu.
11WmBtu (m-10«) - 0.43 g/MJ
M Ib/ton
Cell-Burner Wall-Fired Units
NOX emissions from five cell-burner units
ranged from 0.71 to 1.7 Ib/mBtu, with an
overall average of 1.21 Ib/mBtu (33 Ib/
ton). This average is 55% higher than the
current AP-42 rate of 0.78 Ib/mBtu. The
TVA units averaged 1.53 Ib/mBtu, which
is approximately twice the AP-42 rate. The
non-TVA units averaged 1.02 Ib/mBtu. This
clearly indicates that the cell-burner units
should be in a separate category from
other wall-fired boilers. However, data from
more cell-burner units are needed to de-
fine the emission factor and improve the
rating.
Horizontally Opposed Wall-
Fired Units
NOX emissions from three horizontally
opposed wall-fired units ranged from 0.69
to 1.24 Ib/mBtu, with an overall average
of 0.94 Ib/mBtu (25 Ib/ton). This average
is 12% higher than the current AP-42 rate
of 0.78 Ib/mBtu. The TVA units averaged
0.76 Ib/mBtu, which compares well with
the AP-42 rate; however, the non-TVA
units averaged 1.08 Ib/mBtu. This shows
that horizontally opposed units may need
a separate category; however, more data
are needed to define the emission factor
and improve the rating.
Slngle-Wall-Fired Units
NOX emissions from 15 single-wall-fired
units ranged from 0.59 to 1.12 Ib/mBtu,
with an overall average of 0.85 Ib/mBtu
(23 Ib/ton). This average is 9% higher
than the current AP-42 rate of 0.78 Ib/
mBtu. The TVA units averaged 0.81 Ib/
mBtu, which is only 3% higher than the
AP-42 rate, while the non-TVA units aver-
aged 0.90 Ib/mBtu. Sufficient data are
available to modify the emission factor for
this category.
Single-Furnace Tangential
Units
NOX emissions from 17 single-furnace
tangentially fired units ranged from 0.38
to 0.75 Ib/mBtu, with an overall average
of 0.56 Ib/mBtu (15 Ib/ton), which corre-
sponds exactly to the current AP-42 emis-
sion rate. The TVA units averaged 0.48
Ib/mBtu, which is 16% lower than the AP-
42 rate. The average for the non-TVA
units was 0.60 Ib/mBtu.
Twin-Furnace Tangential Units
NO emissions from 12 twin-furnace tan-
gentially fired units ranged from 0.55 to
0.72 Ib/mBtu, with an overall average of
0.62 Ib/mBtu (17 Ib/ton). This average is
11% higher than the AP-42 rate of 0.56
Ib/mBtu. The TVA units averaged 0.62 Ib/
mBtu and the non-TVA units averaged
0.63 Ib/mBtu. There are sufficient data to
modify the emission factor for this cat-
egory.
Emission Factor Ratings
AP-42 rates emission factors for pulver-
ized coal-fired dry bottom units and cy-
clone furnaces. Ratings are based on the
number of units tested:
A = 10 or more units (excellent)
B = 6-9 units
C = 2-5 units
D = 1 unit (poor)
The current AP-42 shows an "A" rating
for pulverized-coal, dry-bottom boilers. This
rating is deceptive in that it includes both
tangentially fired and wall-fired boilers. The
AP-42 references indicate that only seven
tangentially fired boilers and seven wall-
fired units were tested. The current rating
for cyclone furnaces is "B."
The number of units and ratings for the
AP-42-referenced boilers, the TVA boil-
ers, and the boilers identified from the
literature are compared in Table 2, which
shows that emission factor ratings can be
generated for boiler subclasses by com-
bining all the data. By doing so, "A" rat-
ings are obtained for all subclasses except
for cell-burners ("B") and horizontally op-
posed wall-fired boilers ("C").
Conclusions
The review and analysis of the NOX
emission data from both TVA and non-
TVA units, lead to the following conclu-
sions for each boiler type.
Cyclone Furnaces
1. There is a correlation between NOX
and unit load; i.e., NOX increased with
increasing load.
2. The emission factor .rating improves
from "B" to "A" with these data.
3. There are no correlations between
NOX and fuel nitrogen or fuel ratio
(fixed carbon to volatile matter).
Cell-Burner Wall-Fired Units
1. There is a correlation between NOX
and unit load; i.e., NOx increases with
unit load.
2. There is no current emission factor
rating for cell-burner units; however,
these five units would be rated "B."
3. There are no correlations between
NO and fuel nitrogen or fuel ratio.
-------
Horizontally Opposed Wall-
Fired Units
1. There are not enough data to deter-
mine a correlation between unit load
and NOX emissions.
2. There is no current emission factor
rating for horizontally opposed units;
however, these three units would be
rated "C."
3. There are no correlations between
NOX and fuel nitrogen or fuel ratio.
Single-Wall-Fired Units
1. There is a correlation between NOx
and unit load; i.e., NOX increased with
increasing load.
2. There is no current emission factor
rating for single wall-fired units; how-
ever, these 15 units would be rated
"A."
3. There are no correlations between
NOX and fuel nitrogen or fuel ratio.
Single-Furnace Tangentlally
Fired Units
1. There is a slight increase in NO, as
unit load increases.
2. There is no current emission factor
rating for this subclass; however,
these 17 units would be rated "A."
3. There are no correlations between
NOX and fuel nitrogen or fuel ratio.
Twin-Furnace Tangentlally
Fired Units
1. There is a slight correlation between
NOX and load; i.e., NOX increased with
increasing load.
2.There is no current emission factor
rating for this subclass; however,
these 12 units would be rated "A."
3. There are no correlations between
NOX and fuel nitrogen or fuel ratio.
Table 3 summarizes the average NOX
emissions from TVA and non-TVA units
for each type of boiler.
Table 2. Comparison ofAP-42 Emission Factor Ratings
Number of Units
NOt Emission Factor Rating
Firing Configuration AP-42 "
Pulverized Coal-Fired Dry Bottom °
Cell Burner Wall-Fired
Horizontally Opposed Wall-Fired
Single Wall-Fired
Single-Furnace Tangentially Fired
Twin-furnace Tangentially Fired
Cyclone Furnace
14
2
0
5
5
2
8
TVA
28
2
1
9
7
9
2
Literature "
10
1
2
1
5
1
2
Combined
52
5
3
15
17
12
12
AP-42
A
NR>
NR
NR
NR
NR
B
TVA
A
C
D
B
B
B
C
Literature *
A
D
C
D
C
D
C
Combined
A
B
C
A
A
A
A
' AP-42 referenced boilers.
* Additional boilers from literature search.
c Includes cell-burner wall-fired; horizontally opposed wall-fired; single wall-fired; single-furnace tangentially fired; and twin-furnace tangentially fired units.
6 NR=-No rating given in AP-42. - -- .-'--- - -- ;=
Table 3. Summary of Average NOX Emissions from TVA and Non-TVA Units
Boiler Type
Cyclone Furnaces
Cell-Burner, Wall-Fired Units
Horizontally Opposed, Wall-Fired Units
Single-Wall-Fired Units
Single-Furnace, Tangentially Fired Units
Twin- Furnace, Tangentially Fired Units
TVA Units
(Ib/mBtu)
1.61
1.53
0.76
0.81
0.48
0.62
Non-TVA Units
(Ib/mBtu)
1.11
1.02
1.08
0.90
0.60
0.63
Average of TVA and
Non-TVA Units
(Ib/mBtu)
1.22
1.21
0.94
0.85
0.56
0.62
AP-42'
(Ib/mBtu)
1.37
0.78
0.78
0.78
0.56
0.56
Calculated by using 13,500 Btu/lb.
US. Government Printing Office: 1993 750-071/60201
-------
S. Stamey-Hall is with Radian Corp., Research Triangle Park, NC 27709.
Julian W. Jones is the EPA Project Officer (see below).
The complete report, entitled "Evaluation of Nitrogen Oxide Emissions Data From
TVA Coal-Fired Boilers," (Order No. PB93-138865/AS; Cost: $27.00; subject to
change) will be available only from
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Off her can be contacted at
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
Penalty for Private Use
$300
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
EPA/600/SR-92/242
------- |