United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S7-85/018 June 1985
v>EPA Project Summary
Field Evaluation of a Low NOX
Firing System for Tangentially
Coal-Fired Utility Boilers
A. Kokkinos and R. D. Lewis
This report presents the findings of a
full-scale utility demonstration of
Combustion Engineering's Low-N0x
Concentric Firing System (LNCFS)
conducted at Utah Power and Light's
400 MWe Hunter No. 2 boiler. This
program was implemented to investi-
gate and evaluate the effectiveness of
employing concentric (offset) firing to
reduce NO* emission levels from tan-
gentially coal-fired utility boilers.
This Project Summary was developed
by EPA's Air and Energy Engineering
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
Emphasis on improved quality of the
environment has led to the design of new
and unique methods of reducing NOx
emissions from coal-firing steam gener-
ators. This study gives results of a full-
scale utility demonstration of one of these
methods. This program was conducted at
Utah Power and Light Company's 400
MWe Hunter No. 2 Generating Station.
The method demonstrated was Combus-
tion Engineering's Low-NO* Concentric
Firing System (LNCFS). The LNCFS was
designed for application to tangentially
fired boilers. The principle behind the
LNCFS is aerodynamic control of the
mixing of the fuel and the combustion air
to stage the burning process. Using this
design, control is achieved by directing a
portion of the combustion air away from
the fuel's ignition and devolatilization
zone such that this zone is fuel-rich and
conducive to the in-flame NOx reduction
phenomenon.
Results
Baseline Boiler Characterization
Normal baseline operating conditions
(full load, no overfire air (OFA), and 4.5 to
5.0% excess oxygen) produced NO* emis-
sions of 450 to 460 ppmv (adjusted to 3%
oxygen). Changing the excess oxygen (or
excess air) by 1 % changed N0< emissions
by about 45 or 55 ppmv without or with
OFA, respectively. OFA reduced NOX by
between 75 and 100 ppmv. Minor but
definite NOX effects were shown for
changes in burner tilts, OFA tilts, fuel-air
flow, and fuel elevations in service. No
effect in NO, was shown to be directly
applicable to load changes. As such, the
lowest NO, emissions achievable without
degrading boiler performance were about
300 ppmv (adjusted to 3% oxygen). The
conditions set to achieve this value were
full load, 3.0% excess oxygen, and full
OFA.
Post-Modification
Characterization
During post-modification characteriza-
tion, NO. emission levels of 200 to 220
ppmv were achieved at full load, full OFA,
and the OFA uptilted. These levels were
also achieved repeatedly for boiler loads
between 370 and 380 MWe, which ap-
pear to be the optimum boiler loads for
achieving low-NO* emissions. With hori-
zontal OFA tilts, which is recommended
for long-term operation, NO, emission
levels of 250 ppmv are more typical. The
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parametric examination revealed that
with the modifications a 1% change in
excess oxygen now changed NO, by about
65 ppmv. OFA reduced NO, by about 80
ppmv. Closer ignition front stabilization
with flame holders reduces NO, by about
50 ppmv. Finally, utilization of the offset
firing system in conjunction with OFA
appears to have a synergistic NO, reduc-
tion effect of an additional 50 ppmv
beyond the OFA levels.
With respect to boiler performance,
there appear to be no significant changes
between baseline and post-modification
operation. Reduced excess air levels have
slightly improved boiler efficiency, and
the flame holders appear to have im-
proved low load ignition stabilization. But
steam temperature control and carbon-
in-flyash levels have been unchanged for
normal operating conditions.
Thirty-Day Continuous
Emissions Monitoring Tests
The 30-day continuous emissions mon-
itoring (CEM) system was employed four
times during the low-NO, test program.
Flue gas emissions of NO,, 02, CO, and
CO2 were monitored continuously and
logged at 15-minute intervals throughout
the tests. The principal goal of these tests
was to provide an overall determination
of flue gas emissions during normal boiler
load cycling over an extended period. NO,
emissions for the four tests at this unit
averaged 0.41 lb»/106 Btu* fired for the
30-day rolling averages when firing under
normal low-NO, operations. The mean
boiler load for this result is about 70% of
the unit design rating. This result also
exhibits the difference between short-
term controlled characterization tests
(NO, levels down to below 0.3 lb/106 Btu)
and long-term normal operation.
Corrosion Tests
Low-NO, boiler operation with the
concentric firing system (LNCFS) and OFA
does not detrimentally affect furnace
waterwall material wastage rates. This
was shown with over 1000 ultrasonic
wall thickness measurements. In all
cases the loss rate was less than 2 mils*
per year (MPY); for the whole boiler
average, the loss rate was 0.75 MPY. The
use of corrosion probes yielded only
qualitative trends even after 1000 hours
of testing. The wastage rate results from
the probe tests were conservative (higher)
when compared to the actual UT results.
Therefore, because each tube has a
nominal wall thickness of about 1 /4-in.*,
the wastage rates measured under this
program, about 3/4-mils per year (0.00075
in.), would not be expected to affect the
boiler's design life of 30 years.
A. Kokkinos andR. D. Lewis are with Combustion Engineering. Inc., Windsor, CT
06095.
David G. Lachapelle is the EPA Project Officer (see below).
The complete report, entitled "Field Evaluation of a Low-NO* Firing System for
Tangent/ally Coal-Fired Utility Boilers," (Order No. PB 85-201 093/AS; Cost:
$26.50, 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 Officer can be contacted at:
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
« U.S. GOVERNMENT PRINTING OFFICE: 1985-559-016/2709
'For readers more familiar with the metric system:
1 Ib = 0.454 kg and 1 Btu = 1.055 kj.
1 mil = 0 0254 mm and 1 in. = 25.4 mm.
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
OC00329 PS
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