United States
Environmental Protection
Agency
Industrial Environmental
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S7-84-079 Sept. 1984
&ER& Project Summary
Evaluation of Long-Term NOX
Reduction on Pulverized-Coal-
Fired Steam Generators
S.S. Cherry
Long-term NO, emission data from
eight pulverized-coal-fired steam gen-
erators were analyzed for the purpose
of quantifying the effectiveness of
various combustion modifications. All
boilers, but one, were modified to
reduce NO* emissions. These combus-
tion modifications included changing
both hardware and operating procedures.
All boilers were subject to the NO* pro-
visions of the 1971 New Source
Performance Standards (NSPS).
In several instances, when long-term
emission data for the period before the
modification were not available, the
quantification of the NO, reduction was
based on the result of the performance
test required by the 1971 NSPS. NO,
reductions of from 5.1 to 60 percent
were determined without incurring sig-
nificant adverse impacts on unit opera-
tion. NO, emission levels, determined
from the performance tests, were from
146 to 473 ng/J (0.34 to 1.10 lb/106
Btu) before control implementation and
from 148 to 281 ng/J (0.34 to 0.65
lb/106 Btu) after combustion modifica-
tions were applied.
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 infor-
mation at back).
Introduction and Summary
Previous work in this program identi-
fied pulverized-coal-fired steam genera-
tors that had been modified for the
express purpose of reducing NO, emis-
sions. These modifications included
changes of both hardware (e.g., burner
substitution) and operating procedures
(e.g., overfire air system adjustment).
The purpose of this work was to
quantify the NO reduction achieved by
comparing long-term (approximately 30
days) emission data obtained before and
after the modification. Whenever possible,
the effect of the modification on unit
efficiency was also to be quantified. The
emission data was to be obtained by
certified NO and 02 (or CO2) analyzers. In
addition, the unit load (in either gross
MWe or steam flow) and coal analyses
were requested from the participating
organizations.
Table-1 summarizes the eight steam
generators which were analyzed, the
modification(s) implemented, and the NO,
reduction achieved at high load. Also
shown are the post-modification levels.
For several of these units, emission data
before the modification were not availa-
ble, in which case the NO, reduction was
referenced to the result of the perform-
ance test required by the 1971 New
Source Performance Standards. (All units
were subject to the 1971 NSPS.) The two
NO, reduction values shown for Gentle-
man Unit 1 are due to the utility's
questioning of the initial performance
test results.
Iowa Power and Light's Council Bluffs
Unit 3 is an exception in that the excess
air level was increased in an attempt to
reduce slagging. However, the NO,
increase resulting from this operational
change was also interpreted in a bilateral
manner; i.e., as a NO, decrease due to
lower excess air when the high 02 data
was used as a "before" condition.
The NO, reduction at other than high
load was also quantified when long-term
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Table 1 . Data Base and High-Load /VO« Reduction
Utility Station Unit
Iowa Power & Light
Utah Power & Light
Proprietary
Proprietary
Proprietary
Nebraska Public
Power District
Proprietary
Council Bluffs 3
Hunter 2
A
B
C
Gentleman 1
D
E
Boiler
Mfg.1*
B&W
CE
RS
RS
RS
FW
B&W
B&W
Coal
Type™
Sub
Bit
Bit
Bit
Bit
Sub
Bit
Bit
Gross
MWe
720
425
417
360
360
680
81.9""
81.9""
Modification™
LEA
LNCFS. OFAA
RB. UFA
RB
RB
OFAA. LEA
CO
CO
NO,
Reduction, %
5.1
39
40
40
41
49, 60
15
21
Post Mod.
NO
ng/J
148
155
269
279
245
188
281
236
131 B&W=Babcock & Wilcox
CE=Combustion Engineering
RS=Riley Stoker
FW=Foster Wheeler
lb> Sub=Subbituminous
Bit=Bituminous
{cl LEA -Lower excess air
LNCFS=Low-NOi concentric firing system
OFAA -Overtire air adjustment
RB=Reburnering
UFA - Underfire air added
CO = CO-based control
"" Rated steam flow, kg/s
emission data were available both before
and after implementing combustion
modification.
Discussion
The analysis is illustrated in Figures 1
and 2 for Iowa Power and Light, Council
Bluffs Unit 3. Continuous emission
monitor (CEM) and load data were
supplied by the utility for two periods:
February 16 - May 29, 1981 low 02
operation
May 30 - July 15, 1982 high O2
operation
Figure 1 compares the NO vs. load
characteristic for both periods. This char-
acteristic was developed by sorting the
hourly averaged NO into 10 equally
spaced load increments (cells) which
ranged from the minimum to the maxi-
mum loads. (Not shown in Figure 1 are
the results for the two lowest load cells
for which insufficient data were available
to make a meaningful comparison.) The
NO* measured during the unit's perform-
ance test (as required by the 1971 NSPS)
is also shown for reference.
An analysis was conducted to deter-
mine if the NO characteristics were
statistically different with the results
shown in Figure 2. In this instance, the
higher Oa during 1982 was used as a
"before" condition in order to quantify
the NO reduction resulting from lower
excess air operation. As noted, the NO
175
150
125
100
o
75
50
25
\
- 1981 (LowOi)
-- 1982 (High OJ
Performance WO*
200
400
Load, MWe (gross)
600
500
Figure 1. NO versus load comparison—Iowa Power and Light, Council Bluffs Unit 3.
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N o OB
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Environmental Protection
Agency
Center for Environmental Research
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