United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S7-85/015 May 1985
&ERA Project Summary
Long Term Optimum
Performance/Corrosion
Tests of Combustion
Modifications for Utility
Boilers—Host Site: Utah
Power and Light Company,
Hunter No. 2
J. M. Ferraro, P. S. Natanson, and R. M. Vaccaro
Combustion modifications (e.g., low
excess air firing, staged combustion)
can decrease NO* emissions from coal-
fired utility boilers. However, these
operating conditions may affect the rate
of tube wall corrosion by creating
chemically reducing environments in
the furnace. Therefore, this study was
designed to understand the effects of
certain combustion modification (CM)
techniques for NO, control and to
determine the impact of CM on boiler
tube wall corrosion rate. The host site
for these tests was Boiler No. 2 at Utah
Power and Light Company's Hunter
Generating Station in Castle Dale, Utah.
Initially, the boiler was characterized to
determine the short term effects of CM
on boiler emissions and performance.
Later, NO, and other emissions were
monitored continuously during several
30-day periods so that longer term
operations could be evaluated. Finally.
a study of corrosion rates inside the
furnace helped to determine the cor-
rosion effects of low-NOx operation
achievable through CM.
At Hunter No. 2, a special Low-NO*
Concentric Firing System (LNCFS) was
installed by Combustion Engineering,
Inc. The LNCFS deflects some of the
combustion air away from the fuel jets
and toward the furnace walls to de-
crease both NO, emissions and corro-
sion effects. In these tests, the LNCFS
together with other combustion con-
trols were able to decrease full-load
NO, emissions from 460 vppm (0.63
Ib/MBtu. 271 ng/J) to about 305 vppm
(0.41 Ib/MBtu. 176 ng/J) during nor-
mal long term operation, and to ISO-
ZOO vppm (0.25-0.27 Ib/MBtu, 108-
116 ng/J) during shorter, well-control-
led tests using extreme CM conditions.
The long term (2-year) corrosion rate
measured in the furnace was less than 1
mil «0.001 in.) per year.
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).
Results and Conclusions
Boiler Characterization
In the "as found" (pre-LNCFS) condi-
tion, NO, emissions were about 460 vppm
(0.63 Ib/MBtu, 270 ng/J) at typical full
load conditions (~4.5% Oz, no overfire air.
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and burner tilts ±5 degrees from hori-
zontal). During these early characteriza-
tion tests, it was found that, by using the
existing boiler controls (i.e., no hardware
changes), full load NO, emissions could
be decreased by about 30% to approxi-
mately 320 vppm (0.44 Ib/MBtu, 188
ng/J) without adversely affecting boiler
performance or operability. This was
accomplished by decreasing excess oxy-
gen (to about 3.5%), opening the overfire
air dampers, and adjusting the overfire air
nozzle tilts.
Installation of the LNCFS involved
certain hardware modifications to the
boiler and produced even greater NO,
reductions than were seen during the
baseline (pre-modification) tests. For
example, under extreme low-NO, condi-
tions (not recommended for long-term
operation because of boiler operability
problems), some tests demonstrated that
NO, emissions of 180 to 200 vppm (0.25
to 0.27 Ib/MBtu, 106 to 118 ng/J) were
possible when at slightly less than full
load. These levels fulfilled the short term,
full load, optimized performance goal of
0.30 Ib/MBtu (129 ng/J) for this boiler.
Over the entire range of boiler operations,
short term tests using manual boiler
control demonstrated the ability to achieve
average NO, levels of about 265 vppm
(0.36 Ib/MBtu, 156 ng/J).
Thirty-Day Continuous Emission
Monitoring (CEM) Tests
Four times during this program, flue
gas emissions (NO, CO, 062, and O2) at
the Hunter No. 2 Unit were monitored
continuously for 30 days using CEMs.
This work permitted an evaluation of
boiler emissions over normal load cycles
for longer periods than were possible
during the earlier characterization tests.
The results show that NO, emissions (as
N02) averaged about 176 ng/J (0.41
Ib/MBtu) (well below the 1979 NSPS
limit of 260 ng/J [0.60 Ib/MBtu] for
bituminous coal) with a maximum daily
average (for any day of the four tests) of
about 240 ng/J (-0.56 Ib/MBtu).
Corrosion Tests
To more fully evaluate the longer term
effects of low-NO, operation, corrosion
tests were performed by two different
methods so that the metal wastage rates
could be measured. In the corrosion probe
method, temperature controlled samples
of boiler wall material were inserted into
the furnace for periods of 30, 300, and
1,000 hours., After removal from the
furnace, their weight loss was indicative
of the boiler tube walls' short-term cor-
rosion rate. The other method used tc
measure fireside corrosion was an ultra
sonic pulse echo method. In this method
boiler tube wall thicknesses were meas
ured on two different occasions (afte
baseline, and after Modification 2 testing
about 2 years apart (during schedule!
outages) to determine long-term corrosior
rates at hundreds of locations inside th<
furnace. The long-term corrosion rate!
measured under this program (less than'
mil [<0.001 in.] per year on the average
would not be expected to reduce thi
boiler's useful life below the 30 or mon
years normally expected.
J. M. Ferraro, P. S. Natanson, and R. M. Vaccaro are with Exxon Research and
Engineering Co., Florham Park, NJ 07932.
David G. Lachapelle is the EPA Project Officer (see below).
The complete report, entitled "L ong Term Optimum Performance/Corrosion Tests
of Combustion Modifications for Utility Boilers—Host Site: Utah Power and
Light Company, Hunter No. 2." (Order No. PB 85-193 159/AS; Cost: $28.00,
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 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: 1985-559-016/27064
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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