United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S7-87/003 Apr. 1987
Project Summary
Evaluation of Sulfur Capture
Capability of a Prototype Scale
Controlled-Flow/Split-Flame
Burner
J. Vatsky and E. S. Schindler
This report describes large pilot
demonstration of sulfur capture using
copulverization of limestone with a high
sulfur eastern bituminous coal and com-
bustion of the mixture using Foster
Wheeler's commercial Controlled-
Flow/Split-Flame (CF/SF) Low NOX
burner. Optimization of the sulfur
capture was attempted through the use
of overfire air and two proprietary flame
temperature control methods. Addi-
tionally, the effects of excess air
changes, load changes, and different
calcium/ sulfur mole ratios (Ca/S) were
evaluated. The CF/SF burner was
chosen because of its internal staging
and proven low IMOX capabilities; its use
in combination with two flame tem-
perature reduction methods could re-
duce the flame temperature to minimize
dead burning of limestone and thus
enhance SO2 capture. Although the use
of flame temperature reduction and
overfire air improved the SO2 capture,
the optimum SO2 capture of 29% at a
Ca/S of 2.15 was low. Operation under
optimum SO2 capture mode resulted in
measured NO, emissions of 0.19 Ib/106
Btu*; CO was less than 25 ppm at an
excess oxygen level of 3.0%. The testing
was done at a 42 x 106 Btu/hr heat
input horizontally fired pilot plant con-
figured like a conventional pulverized-
coal-fired boiler.
' Readers more familiar with metric units may use
the factors listed at the back of this Summary to
convert to that system.
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 in-
formation at back).
Introduction
This report summarizes a joint Environ-
mental Protection Agency (EPA)/Foster
Wheeler Energy Corporation (FWEC) test
program to evaluate the m-situ SO2
reduction capabilities of limestone injec-
tion with a low NOX internally staged
burner when the limestone and coal are
copulvenzed and injected through the
coal nozzle. The tests were performed
between April 13 and May 16, 1983. The
burner used is Foster Wheeler's com-
mercial Controlled-Flow/Split-Flame
(CF/SF) burner (Figure i). The test pro-
gram was based on EPA's concept that, if
the limestone is intimately mixed with
the coal during the pulverization process
and burned under low NO* conditions,
high S02 capture levels can be obtained.
When this method of limestone injection
is combined with the low flame tempera-
ture characteristics of the CF/SF burner
and FWEC's proprietary flame tempera-
ture reduction methods, the total S02
capture may be enhanced. Successful
achievement of the Limestone Injection
Multistage Burner (LIMB) process may
result in S02 reductions at a much lower
cost than with conventional wet removal
methods. Although this technique may
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Table 2. Analysis of Test Limestone
Figure 1. Controlled-flow/split-flame (CF/SF) burner
not replace wet methods of S02 reduction,
it would be appropriate for retrofits of
existing uncontrolled boilers firing high
sulfur coals.
The relatively short flame produced by
the CF/SF burner is especially favorable
for retrofits where the depth of the fur-
nace is limited. Flames do not extend into
the upper furnace which would increase
the furnace exit gas temperature (FEGT).
Increasing FEGT can cause fouling and
slagging as well as uncontrolled steam
temperatures and reduced efficiency.
The tests were run at FWEC's Japanese
licensee Ishikawajima Harima Heavy
Industries Co., Ltd. (IHI) Aioi Works in
Japan where IHI has a large coal com-
bustion test facility. The fuel used is a
high sulfur western Pennsylvania bitu-
minous coal from the Middle Kittaning
Seam with a sulfur content of about
3.1%. An analysis of the fuel is shown in
Table 1.
This fuel was chosen because it is
typical of the fuels used in older boilers
that may be susceptible to acid rain
control legislation. The limestone chosen
isVicron from California's Lucerne Valley.
It is a high calcium limestone and was
chosen because it had been used before
in other EPA test programs and would
allow more relevant comparison of S02
Table 1. Analysis of Test Fuel
Fuel Name
Origin
Middle Kittaning
Western PA
Proximate
Fixed Carbon,'
Volatiles, %
Ash.%
Moisture, %
Ultimate
Carbon, %
Hydrogen, %
Oxygen, %
Nitrogen, %
Sulfur, %
HHV. Btu/lb
Operating
Conditions
Fuel Rate
kg/hr
Heat Input
106 Btu/hr
50.1
34.6
9.5
S.8
68.7
4.6
7.1
1.2
3.1
12,818
1.500
42.3
capture among EPA test programs. An
analysis of the limestone is shown in
Table 2.
Test Facility Description
IHI's test facility is designed to evaluate
fuels and combustion systems on a
Name
Origin
CaCO3, %
MgC03. %
SiO2. %
AI2O3, %
Fe203
Moisture, %
Surface, %
Inherent, %
Vicron
Lucerne Valley, CA
98.1
0.9
0.11
0.01
0.01
0.03
0.1
prototype scale (up to 50 x 106 Btu/hr).
Functionally useful steam is not gen-
erated so that operation and design
changes do not affect the steam supply to
industrial or power generation equipment.
This provides an atmosphere conducive
to testing without interruption.
The pulverized coal system differs from
that which is in current commercial prac-
tice on pulverized coal-fired boilers. An
indirect storage system is used and allows
wide variations in air/coal ratios. The
limestone bunker supplies, via a feeder, a
Foster Wheeler vertical pulverizer. The
coal and limestone are mixed and pul-
verized in the mill to a minimum coal
fineness of 70% through 200 mesh. The
pulverized fuel is carried pneumatically
to a cyclone separator where the fuel is
separated from the carrier air and fed
into a pulverized fuel bin; a baghouse
filters the air before exhausting to the
atmosphere, and collects the fines which
are also fed into the fuel bin. A screw
feeder at the botton of the fuel bin feeds
the pulverized fuel over a weighing device
and into a fuel/primary air mixer. This
allows great flexibility in controlling the
primary air to fuel ratio.
The facility is fired by a single burner
which simplifies burner flame studies
since flame interactions do not occur.
The furnace is refractory lined to simulate
utility size furnace heat release rates.
Nine view ports along each side of the
furnace at the burner level, along with
five others at upper elevations, allow the
operator to observe the flame and take
temperature measurements at different
points along the flame's length. Overfire
air ports are available for staging tests.
The combustion air takes the following
path through the system. A forced draf'
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ifan supplies atmospheric air to the shell
side of a tubular air preheater where it is
heated up to the range of 536 to 653°F.
Hot air is mixed with cold tempering air
to obtain the desired primary air temper-
ature. The remaining hot air is then
supplied to the wmdbox. Combustion
products pass out of the furnace, through
a convection section and through the
tube side of the preheater, after which it
is cleaned of paniculate matter in a
multiclone and then a baghouse. After
the baghouse, an induced draft fan forces
the combustion products to the stack.
Ttibiu 3 summarizes basic system
parameters.
Test Methodology
The intention of the test program was
to evaluate various operating modes for
their potential to improve SO2 reduction
obtainable by copulverization of coal and
limestone. A number of variables were
evaluated:
Overfire Air
Furnace Excess Oxygen
Calcium to Sulfur Mole Ratio
Two Proprietary Flame Temperature
Reduction Methods
Load
Overfire Air Injected Higher
in the Furnace
Burner Parameters
These variables were thought to have
the greatest potential in improving S02
capture. This was especially true of the
two flame temperature reduction methods
where, in the past, peak flame temper-
ature reductions of 70 to 90°F were seen
singly and over 200°F was obtained when
these methods were combined
The in-depth evaluation consisted of a
complete full factorial matrix of tests:
testing each variable in combination with
every other combination of other vari-
ables Furnace excess oxygen was an
exception in that only a half factorial was
planned
Simultaneously with the determination
of the effect each variable has on S02
reduction, S03, NOX, CO, and total hydro-
carbons were measured. The intention
was to observe the effect each variable
had on other emission species to evaluate
the overall emission characteristics of
each combination that improved SO2
reduction.
Major Results and Conclusions
Gaseous Emission Levels
• S02 Emissions
The addition of limestone to the
fuel at a Ca/S of 2 15 resulted in an
Table 3.
System Specifications
Furnace
Burner
Coal Handling
Pulverizer
Width
Depth:
Height.
Coal
Overfire Air
Heat Liberation-
Elevator
Bunker-
Table Feeder-
Type:
Capacity.
Fineness:
Tubular Air Preheater Air Flow Rate:
Air Temp. Inlet:
Air Temp Outlet:
Paniculate Collection Type:
Equipment Gas Flow Rate •
Oust Loading
Inlet:
Outlet:
Limestone Handling Bunker.
Feeder:
3100 mm (10.2 ft)
4500 mm (148 ft>
11,000 mm (36 ft)
200 kg/h (4.400 Ib/h)
As Necessary
Max 111 x. 10ekcal/m3hx
(12.5x 103 Btu/ft3h)
1. 5 T/h (11 x 103 Ib/h)
1. 10m3 (350 ft3)
2. 15 T/h (33 x 103 Ib/h) max.
IHI-FW Ring & Roller Mill MBF-16
8 T/h (17 xlO3 Ib/h)
70% through 200 mesh
31 T/h(68x103lb/h)
20°C(70°F)
320°C(610°F)
Baghouse following a multiclone
20.000 Nrrf/mm (12440 scfm)
36. g/Nm3 (87 gr/scf)
0.1. g/Nm3 (0.242 gr/scf)
225 kg/h (500 Ib/h) Max.
20-320 kg/h (50-700 Ib/h)
optimum emission reduction of 28%.
This is an improvement over the 22-
23% found without any changes in
operation of the burner-furnace. This
optimum was found with a combi-
nation of 3% excess O2, 20% overfire
air, and with FW's proprietary flame
temperature reduction method #2
(FTRM#2). Another combination of
operating variables (5% excess O2
and FTRM #2) resulted in higher
SO2 reduction at the same Ca/S,
but it also increased NOX emissions
such that the total of acid forming
emissions of SO2 and NOX was
higher than for the optimum case.
Increasing the limestone addition
rate during otherwise normal oper-
ating conditions (i.e., optimum NOX
burner settings, 3% excess 02, no
limestone, no overfire air, full load,
and no flame temperature reduction
methods in use), to a Ca/S of 3.26
resulted in 33.4% reduction. This
increase in S02 reduction is es-
sentially linear up to Ca/S = 3.26. If
the optimum S02 control method is
extrapolated to Ca/S = 3.26, the
SO2 reduction would increase to
43%. Although it is generally con-
ceded that S02 reduction is not
linear with Ca/S, a linear relation-
ship was found up to a Ca/S of
3.26, the maximum value tested.
However, this optimum occurred
with overfire air ports open, resulting
in slagging.
• NOX Emissions
In general, adding limestone to
the fuel reduced NOX by 10%. Under
normal operating conditions, the
NOX emission rate measured for the
CF/SF burner was 0.32 lb/106 Btu.
This represents a 60% reduction
from the predicted uncontrolled NOX
emission rate of 0.8 lb/106 Btu using
this fuel and a pre-NSPS burner at
this test facility. Under the conditions
of optimum SO2 reduction, the NOX
decreased to 019 lb/106 Btu, an
additional 41% reduction from 0.32
lb/106 Btu (or a total of a 76%
reduction from the uncontrolled
level). About 25 to 30% of this addi-
tional NOX reduction can be attributed
to overfire air (OFA), 10% can be
attributed to adding limestone to the
fuel, and 1% is attributed to the use
of FWEC's proprietary FTRM #2. The
negligible NOX reduction due to the
FTRM #2 is expected since the peak
flame temperature is already sub-
stantially below 2900°F.
• CO Emissions
In general, adding limestone at a
Ca/S of 2.15 reduced CO concen-
trations at the economizer outlet to
below 35 ppm corrected to 0% excess
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02, with one exception. Under
normal operating conditions, the CO
averaged 39 ppm. Under the opti-
mum S02 reduction test conditions,
the CO concentration dropped to 24
ppm, a 38% reduction. Half of this
reduction can be attributed to lime-
stone addition; the remainder can
be attributed to FIRM #2.
• SO3 Emissions
In general, adding limestone to
the fuel at a Ca/S = 2.15 always
reduced S03 concentrations to below
20 ppm corrected to 0% excess O2
regardless of the initial concentra-
tion. Under normal operating condi-
tions S03 concentrations averaged
28 ppm. Under conditions of opti-
mum SO2 reduction the SO3 con-
centrations were reduced to 8 ppm,
a 71% reduction. About equal per-
centages of this reduction can be
attributed to OFA and limestone
addition.
• Total Hydrocarbons (THC)
Limestone addition in many cases
decreased the THC emissions, but
there were many exceptions The
only operating variable that had a
consistent effect on THC was FTRM
#1, and it increased THC. Neither
excess oxygen nor overfire air had a
consistent effect on THC. Under
normal operating conditions the THC
concentrations averaged 3 ppm cor-
rected to 0% excess O2. Under
conditions of optimal S02 reduction
the THC was reduced to 1.7 ppm, a
43% reduction The reduction is at-
tributed to a synergistic effect of the
combination of OFA, FTRM #2, and
limestone addition since none of
these (alone) consistently reduced
THC
SO2 Capture in the Baghouse
No significant S02 or SO3 reduc-
tion was measured across the bag-
house with or without limestone
addition. SO3 reduction was mea-
sured across the air heater. SO3
change across the air heater cannot
be explained; additionally, the re-
duction is virtually independent of
the presence of limestone. S03 con-
centrations dropped from an average
8 ppm to about 0.3 ppm when lime-
stone was being added; S03 was
reduced from 18.3 to 0.6 ppm when
limestone was not being added, and
was further reduced to 0 4 ppm
across the baghouse. The air heater
is tubular with an exit temperature
Table 4, Ash Fusibility Temperature
Ash Fusion Temperatures, °F
Test 42 Test 43
Ca/S
Oxidizing Atmosphere
Deformation
Softening
Hemisphere
Flow
0
2372
2408
2507
2561
2.15
2426
2453
2516
2705
Reducing Atmosphere
Deformation
Softening
Hemisphere
Flow
1940
1958
1976
2453
2156
2246
2345
2552
of about 500°F. Consequently, there
should be no S03 condensation prior
to the baghouse. At these tempera-
tures the SO3 level should remain
constant unless absorption is occur-
ring on some surface. All test results
are corrected to 0% excess oxygen.
Effect on Equipment
• Furnace and Slagging Potential
No detrimental side effects were
noted. The addition of limestone to
the fuel did not increase the slagging
potential of the coal. The coal was
considered to be of medium to high
slagging potential. During normal
combustion, both with and without
limestone, slagging was not evident;
but, when overfire air was used,
slagging was evident, both with and
without limestone This was fully
expected based on an analysis of the
ash constituents and oxidizing/
reducing fusion temperatures shown
in Table 4. These results show that
the ash fusion temperatures are
higher when limestone is being
added at a Ca/S mole ratio of 2 15.
All ash fusion temperatures in-
crease as the furnace conditions
change from reducing to oxidizing.
In this case the ash softening tem-
perature increases by 450°F without
limestone addition; and by 207°F
with limestone. Also all ash fusion
temperatures increase with the
addition of limestone The increase
is largest under reducing atmo-
sphere. The reducing ash softening
temperature increases 288°F, and
the reducing hemisphere tempera-
ture increases by 369°F when lime-
stone is added to the fuel.
• Baghouse
The baghouse operated normally
during the test program. No increase
in pressure drop was seen. The daily
start-up/shutdown cycle did not
precipitate any bag blinding.
• Burner
No detrimental side effects were
noticed on the burner, flame, or
combustion in general.
Metric Conversion
Readers more familiar with metric units
may use the following factors to convert
to that system
Nonmetnc
Times
Yields Metric
Btu/hr
Btu/lb
°F
Ib/W6 Btu
1 054
232
5/9(°F-32)
430
kJ/hr
J/g
°C
ng/J
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J. Vatsky and E. S. Schindler are with Foster Wheeler Energy Corporation,
Livingston, NJ 07039.
Charles C. Masser is the EPA Project Officer (see below).
The complete report, entitled "Evaluation of Sulfur Capture Capability of a
Prototype Scale Controlled-Flow/Split-Flame Burner," (Order No. PB 87-168
670/AS; Cost: $18.95, 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
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
EPA/600/S7-87/003
0000329 PS
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