United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S7-85/020 Aug. 1985
Project Summary
Field Evaluation of a Utility
Dry Scrubbing System
Gary M. Blythe, Jack M. Burke, David L Lewis, and Carol May Thompson
This program was the first indepen-
dent evaluation of a full-scale utility
spray-dryer/baghouse dry flue gas
desulfurization (FGD) system. The eval-
uated system treats flue gas from a
nominal 100 MW of coal-fired power
generation.
For the test program, two different
coals were used as boiler fuels: one, a
subbituminous coal and coke mixture
with a nominal 1.2 percent sulfur con-
tent; and the other, a 3.4 percent sulfur
Illinois bituminous coal.
The test program was conducted
from July to October 1983. SO2 re-
moval, participate emissions, sulfuric
acid removal, and extensive process
data were recorded. Low sulfur coal
tests indicated that 75 percent SO2 re-
moval was achievable in the short term
at reagent ratios of 0.6 to 0.7, and 90
percent SO2 removal was achievable at
a reagent ratio of about 0.8. An average
removal of nearly 90 percent was
achieved in short-term tests with high
sulfur coal at reagent ratios of 1.3 to 1.4.
Calcium chloride addition to the atom-
izer feed slurry was found to reduce the
lime addition requirements for high sul-
fur tests by about 25 percent.
This Project Summary was devel-
oped by EPA's Air and Energy Engineer-
ing Research Laboratory, Research Tri-
angle Pack, NC, to announce key
findings of the research project that is
fully documented in a separate report
of the same title (see Project Report or-
dering information at back).
Introduction
This Summary discusses results from
a program, the objective of which has
been to acquire performance data on an
operating, utility-scale, spray-dryer-
based, dry FGD system. The system was
evaluated primarily to determine SO-z
and particulate removal performance
and lime reagent consumption. The sys-
tem chosen for evaluation is the Joy/
Niro Demonstration Unit, at the North-
ern States Power Company (NSP) River-
side Station in Minneapolis, MN. The
Riverside system was chosen for this
program because it is the first lime-
based system in operation using a full-
size (46-ft* diameter) spray dryer mod-
ule. Testing was conducted with both
low and high sulfur boiler fuels. The
program was conducted for the Envi-
ronmental Protection Agency's Air and
Energy Engineering Research Labora-
tory and for the Electric Power Research
Institute under a cooperative funding
arrangement.
Project Description
The project description includes that
of the Riverside station and FGD sys-
tem, a summary of the test program,
and a discussion of the limitations of the
Riverside system and how they have af-
fected this evaluation.
Site Description
The Riverside generating station, op-
erated by Northern States Power Com-
pany, in northeast Minneapolis. The
two units of interest on this project,
No. 6 and No. 7, began operation in
1949. The combined generating power
of Units 6 and 7 is rated at 98 MW. How-
ever, the pulverized coal, wall-fired
units were originally designed to fire an
eastern bituminous coal. Recently, the
units have fired a western (Sarpy Creek)
subbituminous coal. A small amount
(10 to 15 percent) of high sulfur coke is
Readers more familiar with metric units may use
the conversion table at the back of this Summary.
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Flue Gas —
From Unit 7
Flue Gas
From Unit 6
U Spiral Grits
Claesifter
Unit 7
Stack
ID Fan
Unit 6
Stack
ID Fan
Slaking
Water
Lime
Slurry
Storage
Trough
Atomizer
Feed Tank
Figure 1. Flow diagram for Riverside dry FGD system.
added to the subbituminous coal to im-
prove its firing properties. The units can
still be fired with high sulfur bituminous
coal, and in fact were so fueled for
5 weeks of this test program.
In 1980, a full-scale, Joy/Niro, spray-
dryer/fabric-filter FGD system was in-
stalled to treat the combined flue gas
from the two units. The fabric filter was
actually purchased by NSP because of
limitations on the ability of existing ESP
collectors to efficiently collect the ash
from the western coal. The spray dryer
system was installed by Joy/Niro under
a cooperative agreement with the utility
to serve as a full-scale demonstration of
the capabilities of their dry FGD system.
Figure 1 is a simplified flow diagram of
the system.
The spray dryer is 46 ft in diameter,
with flue gas introduced both above the
atomized spray in a roof gas disperser
and below the atomized spray in a cen:
tral gas disperser. A rotary atomizer is
used, employing a 700 hp drive motor.
The spray dryer was sized to treat flue
gas corresponding to a 70 MW boiler
load. This reduced sizing permitted sys-
tem tests at greater than design flow
rates. Note that, because Units 6 and 7
are over 30 years old, the flue gas flow
rate at 70 MW is equivalent to the flue
gas rate from about a 100 MW new unit.
A new unit would experience much less
air inleakage and operate at a much
lower net plant heat rate than these
units. The downstream fabric filter con-
tains 12 compartments, in 2 rows of 6
compartments each. Because the fabric
filter was sized to treat hot flue gas, it is
actually oversized when the spray dryer
is in operation because of the flue gas
volume shrinkage which results from
the reduced spray dryer outlet tempera-
ture.
Pebble lime reagent is slaked in a Joy/
Denver attrition slaker. A Joy/Denver
ball mill is also available for lime slak-
ing. Milk of lime, dilution water, and re-
cycle solids are added to a mix tank at
rates determined by a Honeywell pro-
cess control computer. The mix tank ef-
fluent is pumped to a separate atomizer
feed tank. From the atomizer feed tank,
slurry is pumped to a head tank at the
top of the spray dryer. A pinch-type con-
trol valve regulates the flow of slurry to
the atomizer to maintain either a con-
stant spray dryer outlet temperature or
a constant approach to adiabatic satura-
tion. When the system is operated to
control S02 removal, the Honeywell
process control computer calculates the
amount of lime which must be added
upstream at the mix tank to achieve the
desired S02 removal. Recycle material
is added at the mix tank at a rate re-
quired to bring the mix tank solids level
up to a set point, normally 35 weight
percent solids. The recycle solids are
collected from the spray dryer bottom
dropout and largely supplemented by a
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portion of the fabric filter catch.
Testing Approach
As described in the introduction, a pri-
mary objective of the program was to
quantify SO2 removal by the system. A
continuous emission monitoring sys-
tem (CEMS) was temporarily installed
to quantify S02 removal. The CEMS in-
cluded a DuPont Model 460 two-point
extractive S02 monitor and a Thermox
02 monitor (sampling the spray dryer
inlet and outlet ducts), and a Lear
Siegler SM810 in-situ point-type S02
analyzer (installed in a short run of duct
at the fabric filter outlet). A second Ther-
mox 02 analyzer was mounted on the
duct exactly opposite the Lear Siegler
monitor.
Other than SO2 removal data, lime
consumption and other important pro-
cess parameters were recorded as
hourly averages for each test day. Lime
consumption was measured primarily
by determining the lime content of the
milk of lime slurry introduced to the at-
omizer feed mix tank. The flow rate of
this slurry was continuously measured
with a magnetic flow meter and re-
corded by the Honeywell process con-
trol system computer. Other methods of
lime consumption measurement have
included continuous quicklime weigh
belt rate measurements, recording of
daily quicklime trucklbad deliveries, and
determination of the lime content and
flow rate of the actual atomizer feed
slurry. Enthalpy balances have been
used to confirm agreement between
slurry feed rate and flue gas flow mea-
surements.
In addition to quantifying S02 re-
moval and lime consumption perfor-
mance for the spray-dryer/baghouse
system, determination of particulate re-
moval performance for the system was
also an objective. This performance was
determined by manual sampling of flue
gas streams for particulate concentra-
tions, using EPA methods. Particulate
loadings were measured at the spray
dryer inlet, spray dryer outlet, and fabric
filter outlet.
Test Plan
The test schedule is summarized in
Table 1. These tests were conducted be-
tween July 11 and October 8, 1983. The
schedule shows three sets of conditions
with low sulfur, Sarpy Creek coal/coke
blend, and two sets with high sulfur
Peabody Illinois coal. The Sarpy Creek
^coal/coke blend has a nominal sulfur
"content of 1.1 to 1.2 percent and a heat-
Table 1. Test Schedule and Desired System Operation Conditions"
Fuel
Sarpy Creek Coal/Coke
Sarpy Creek Coal/Coke
Sarpy Creek Coal/Coke
Illinois Coal
Illinois Coalb
SO2
Removal
Level,
%
75
75
90
90
90
Fabric
Filter
A/C Ratio,
cfm/ft2
2:1
2.3:1
2:1
2:1
2:1
"All tests planned to be conducted at at 18°F approach to adiabatic saturation, 35 weight
percent solids in the atomizer feed slurry, a 70 MW daytime boiler load, a once-per-hour
baghouse cleaning frequency, and an attrition-type slaker.
bCalcium chloride addition tests.
ing value of 9000 Btu/lb. New Source
Performance Standards for utility boil-
ers would require 75 to 80 percent SO2
removal for boilers firing a fuel with this
sulfur and heating value. In some locali-
ties, state or local regulations might re-
quire as high as 90 percent S02 removal
with this fuel. Consequently, low sulfur
tests were conducted at both 75 and 90
percent target S02 removal levels. Addi-
tionally, some tests were conducted at a
fabric filter air-to-cloth ratio higher than
the nominal value of 2:1.
Two sets of conditions were tested
with the high sulfur coal. The coal was
an Illinois No. 6 coal with a nominal 3.4
percent sulfur content and 10,700 Btu/lb
heating value. Current New Source Per-
formance Standards for utility boilers
require approximately 90 percent S02
removal when coal of this sulfur content
and heating value is burned. Conse-
quently, only a 90 percent target S02
removal was tested with this high sulfur
coal. The tests included baseline condi-
tions of 90 percent removal with
attrition-slaked lime and a second test
run employing calcium chloride addi-
tion for lime utilization enhancement.
Chloride addition to enhance lime uti-
lization in spray-dryer/baghouse FGD
systems has been tested previously in
bench- and pilot-scale systems, but this
is the first test of chloride addition at a
full-scale utility installation. The en-
hancement effect is thought to occur be-
cause of the deliquescent properties of
calcium chloride.
System Limitations
Several system limitations combined
to restrict the amount and the type of
data that could be collected. First, as
mentioned earlier, Riverside Units 6 and
7 are peaking units. As such, they are
rarely operated in the winter and only
operate part-time during July to Octo-
ber. This part-time operation involves
unit loads of 70 to 90 MW during week-
day daylight hours, minimum load (30
to 50 MW) overnight during the week,
and banking the boilers over the week-
end. Although the FGD system was op-
erated at desired S02 removal levels 24
hours per day, only about 12 hours per
weekday of near full-load operation
were available for evaluating FGD sys-
tem performance. At the beginning of
each 12-hour full-load period, the FGD
system generally goes through a tran-
sient period due to a large increase in
boiler load. On Mondays, the unit must
undergo a cold start-up. Although this
cycling provides a severe test of the ca-
pabilities of the system, it reduces the
period of steady state operation at the
desired S02 removal level over which
lime reagent consumption can be mea-
sured.
Additionally, the Riverside system
was the first utility-scale system de-
signed and built by Joy/Niro as a
demonstration unit. As the first unit
built, the Riverside system has provided
the opportunity to refine and modify de-
sign features for subsequent systems.
Thus, some specifics of the Riverside
system are different from what will be
found in later designs. An example of
this is the slurry feed system, which has
been modified for subsequent systems
to provide quicker response to tran-
sients such as load changes. At River-
side, the slurry feed system has a resi-
dence time of about 1.5 hours. This
means that following an abrupt process
change, such as a load change, it may
take 3 to 4 hours for the slurry feed sys-
tem to stabilize near steady-state condi-
tions.
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The impacts of the slurry feed prepa-
ration system residence time are partic-
ularly important at the Riverside station,
as the normal station operation causes
significant load changes at least twice
per day. In fact, on some days during
this test program, the unit load varied
between 70 MW and 90 MW throughout
the day. On these days, the unit never
operated at one load long enough for
the feed system to stabilize. On most
other days, even if the load was steady
all day, only 8 or 9 hours of the 12 hours
of full load operation actually repre-
sented steady-state conditions.
Other aspects of the Riverside sys-
tem's status as a demonstration unit af-
fected the results of this program. For
example, the system contains only one
spray dryer module, while most utility
systems will have multiple modules. In
a multiple-module system, equipment
problems which affect one individual
module have a smaller impact on over-
all system performance. Being a one-
module system, equipment problems
tended to cause the entire system to
have to be shut down, or operated at
conditions other than those desired.
Also, because the Riverside system is a
demonstration, rather than a commer-
cial system, some individual compo-
nents of the system have not been in-
stalled with the redundancy that the
vendor would likely install in a commer-
cial system. These considerations have
had a detrimental effect on both the
amount of system downtime and the
number of process-equipment-related
upsets during the test program.
A final consideration which has af-
fectd the test program involves the re-
cent history of the Riverside station. For
nearly the first 2 years of operation, the
FGD system was used as a full-scale
demonstration and testing unit by the
process vendors. During this time, Joy/
Nirohad responsibility for the operation
of the system, even though NSP actu-
ally provided operating personnel.
Within the year prior to the test pro-
gram, NSP had assumed responsibility
for the operation of the FGD system. Im-
mediately prior to the test program, the
Units 6 and 7 boilers and FGD system
were off-line for much of the winter and
spring, as NSP does not need power
production from these units during this
time. During this long period of down-
time, normal personnel turnover (pro-
motions, retirement, transfers, etc.) re-
sulted in a number of new operators
rotating into the FGD system operating
staff. At the start of the test program,
then, the FGD system was being oper-
ated for the first time in several months
with a staff of operators having little
previous experience with the FGD sys-
tem. Early in the program, the operators
tended to revert to conservative higher
spray dryer outlet temperatures during
any minor upset, such as soot blowing
in the boilers. This would move the op-
eration away from the desired condi-
tions and would preclude acquiring de-
sired steady state operating data. As the
program continued, these excursions
occurred much less frequently as the
operators became more comfortable
with operating at test conditions.
Considering the previous discus-
sions, it was not realistic to report avail-
ability of the system, as the availability
of the Riverside system would tell little
about that of a commercial utility, multi-
module, dry FGD system on a new base-
loaded boiler. The combined effects of
weekly cold start-ups, frequent load
changes, little redundance, and a some-
what undertrained operating staff at
Riverside do little to promote a fair as-
sessment of the potential availability of
a commercial system.
However, the general operation of the
system was closely observed during the
test program. Much of the downtime or
off-condition operating time was due to
problems specific to the Riverside sys-
tem. Others appear to be more generic
to dry FGD systems. These more
generic problems are discussed in the
report, as they are more likely to occur
in other systems.
Results
The discussion of the program results
is divided into two areas: Operational
Results, which includes a qualitative
discussion of the operation of the
system during the test program; and
System Performance, which includes
preliminary S02 removal, lime con-
sumption, particulate and sulfuric acid
removal data, and solid waste charac-
teristics.
Operational Results
In general, the equipment that com-
prises the basis of the dry FGD system,
the spray dryer and baghouse, were rel-
atively trouble-free throughout the pro-
gram. At the conditions tested, the
spray dryer did not show evidence of
potential problems (e.g., wheel nozzle
pluggage, excessive buildup of solids
on the walls, or formation of wet solids
within the dryer). Some atomizer prob-
lems were observed, but most of these |
appeared to be caused by circum-
stances specifc to the situation at River-
side rather than being generic to the
Joy/Niro system. These problems will
be discussed further later in this section.
The baghouse also operated well,
with no significant bag/fabric related
problems being observed. In this
short-term test though, long-term ef-
fects such as bag life or compartment
wall corrosion rates could not be evalu-
ated.
Some problems were observed in
four specific areas—the slurry feed sys-
tem, the ash handling system, the ball
mill slaker, and in atomizer protection.
The system vendors may have ad-
dressed these problems in system de-
signs subsequent to Riverside, but the
problems could be encountered in vir-
tually any spray-dryer-based dry FGD
system. Each of these areas is discussed
below.
Slurry Feed System
In a recycle lime system, lime slurries
containing up to 25 percent solids and
recycle/lime slurries of 30 to 40 percent
solids are commonly encountered.
When dealing with slurries with a high
solids content and high viscosity, prob-
lems (e.g., plugging of pump suction
lines, solids buildup on tank walls, plug-
ging of in-line screens used to remove
oversize material, and loss of flow when
switching pumps) are commonly en-
countered. Such problems were en-
countered often at the Riverside sys-
tem. Years of operation of wet lime/
limestone FGD systems have estab-
lished means of dealing with such prob-
lems. The quantities of these slurries
that must be dealt with in a spray dryer
system, though, are much smaller than
what would be encountered in a wet
system. At Riverside, typical atomizer
feed slurry rates are 150 to 200 gpm. In
a similarly sized limestone wet FGD sys-
tem, the slurry recirculation rate could
be as high as 40,000 gpm. While some
of the slurry handling problems of a wet
FGD system may still be encountered in
a spray dryer system, they will occur on
a greatly reduced size of equipment.
This should make both problem solving
and routine maintenance easier. An-
other important point to be noted is that
chemical scaling tendencies were not
observed at Riverside.
Ash Handling System
In comparing the wet versus dry FGD t
systems, the spray dryer system has a *
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slurry feed system that deals with much
lower flow rates for a given unit capac-
ity, but the quantities of dry ash and
FGD by-products that must be moved
around the system are substantially
greater than for a comparably sized par-
ticulate collection device/wet scrubber
system.
The problem with solids handling
which most frequently occurred at
Riverside involved the baghouse me-
chanical conveyors, blow pots, and the
recycle bin rotary valve. Failures in any
of these components could interrupt the
flow of recycle material to the slurry mix
tank, and cause the system to approach
once-through operation.
Ball Mill Slaker
During this program, the ball mill
slaker did not operate successfully for
any extended period: the feed end of
the slaker tended to plug with wet lime
solids. While there are several possible
reasons why the plugging continually
occured, the actual cause was not iden-
tified.
The ball mill slaker problems at River-
side appear to be somewhat site-
specific (ball mill slakers have operated
successfully elsewhere). In retrospect,
the slaker might have run more success-
fully at a higher water-to-lime ratio, re-
sulting in a less viscous product slurry
and less vapor release. However, in the
attempts to run the ball mill slaker dur-
ing the high sulfur tests in particular, the
slaking water piping size did not allow
operation at higher water-to-lime ratio
at the lime slaking rates required. Dur-
ing the high sulfur tests, lime slaking
rates averaged approximately four
times that required for the normal low
sulfur fuel at similar unit load and per-
cent S02 removal conditions.
Atomizer Problems
Although the atomizer motor, gear-
box, and nozzle wheel were generally
trouble-free, on several occasions prob-
lems which could result in atomizer
damage were observed.
Two scenarios for potential damage
were observed. One occurred when the
unit was forced to run from the basic, or
less sophisticated, control station of the
computer control system while the
more sophisticated supervisory station
was undergoing repair. The control
software at Riverside does not have full
interlock protection for the atomizer
when running from the basic station.
. (Interlocks are software which automat-
ically shut down the atomizer when
Table 2. SO^ Removal Results, Low Sulfur Coal
Average
SO2
Removal,
%
74
75b
89
Spray
Dryer
Removal,
%
_a
67
78
Fabric
Filter
Removal,
%
_a
8
11
Reagent
Ratio
0.7
0.6
0.8
Recycle
Ratio
13:1
14:1
11:1
"Not measured.
Increased air-to-cloth ratio at fabric filter; other tests at normal air-to-cloth ratio.
Table 3. S02 Removal Results, High Sulfur Coal
Average
S02
Removal,
%
88
89a
Spray
Dryer
Removal,
%
72
62
Fabric
Filter
Removal,
%
16
27
Reagent
Ratio
1.3
1.0
Recycle
Ratio
2:1
3:1
aHigh chloride concentration tests.
given inputs that are indicators of prob-
lems which might result in damage to
the atomizer.) While running in this
mode, a minor problem involving loose
wires to the atomizer oil circulating
pump occurred, intermittently shutting
off the pump. However, the basic sta-
tion only gave the control operator an
alarm rather than shutting down the
atomizer automatically. The atomizer
continued to run for several minutes
without oil circulation and sustained
gearbox damage.
The second scenario which could re-
sult in atomizer damage was observed
on more than one occasion: it involved
feeding slurry to the atomizer wheel
when it was not rotating. Since the non-
rotating wheel has a much lower hy-
draulic capacity than a rotating wheel,
slurry fed to the standing wheel tends to
overflow the wheel and can flow up the
spindle to which the wheel is attached
and enter the atomizer oil system. In
such instances, the oil sump can be im-
mediately emptied and flushed to avoid
damage, but if the atomizer is operated
before cleaning, the slurry in the oil can
eventually cause gearbox damage.
System Performance
The results of S02 removal and lime
consumption measurements during
this test program are summarized in
Tables 2 and 3. Table 2 summarizes the
low sulfur coal SO2 removal results;
and Table 3 summarizes those for the
high sulfur coal tests.
For several reasons, the SC>2 removal
results from the program cannot be ex-
pressed as 30-day rolling averages.
First, the unit was never operated at one
set of conditions for that long a period
during the test program. Also, due to
the operating characteristics of the
peaking boilers, only 8 to 9 hours per
day typically represent full load, steady
state operation. Thus, the S02 removal
and lime consumption results represent
averages of values measured during
steady state unit operation for a portion
of a number of successive test days.
Lime consumption in Tables 2 and 3 is
expressed as a reagent ratio, defined
as:
Reagent Ratio =
Calcium in Fresh Lime
Fed to System, Ib-mole
SO2 in Inlet Flue Gas, Ib-mole
(1)
(This definition corresponds to that of
the term "stoichiometric ratio" in many
other dry FGD papers.)
Where possible, each value in Table 2
and 3 is supported by alternate calcula-
tions. For example, lime slurry feed
rates are compared to lime weight belt
readings, essentially a calcium balance
on the lime slaker. Also, weigh belt
readings have been compared against
lime truckload delivery inventories. Flue
gas flow rates are checked against
slurry feed rates by enthalpy balance
calculations.
Table 2 shows that S02 removal lev-
els of nearly 75 percent and 90 percent
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were achieved for the low sulfur fuel
with substoichiometric amounts of
lime. This may be attributable to two
factors. First, at 35 percent feed slurry
solids in low sulfur operation, very high
recycle rates are possible. This is seen
in the recycle ratio values in Table 2,
defined in this report as:
Recycle Ratio =
Recycle Material in Atomizer
Feed Slurry, Ib/hr
Fresh Hydrated Lime
[Ca(OH)2], Ib/hr
(2)
Since a large fraction of the baghouse
catch and all of the spray dryer bottom
solids are recycled, pilot plant results
indicate that high sorbent utilization
would be promoted. Additionally, anal-
yses of the Sarpy Creek coal ash indi-
cate a nominal 30 percent alkaline earth
content (CaO, MgO, Na20, and K20), be-
lieved to have contributed to S02 re-
moval. However, the "available alkalin-
ity" in the coal ash was not directly
measured.
The results in Table 2 also show the
range of SO2 removal in the spray dryer
(S.D.) and fabric filter (F.F.). S02 re-
moval in the fabric filter is calculated
relative to the spray dryer inlet S02 con-
centration as:
S02 Removal
F.F. -
[SO2 into F.F. - SO2 out of F.F.]
[S02 into S.D.]
(3)
With this definition, spray dryer re-
moval and fabric filter removal can be
summed directly to yield overall re-
moval values. The results show that, at
75 percent overall S02 removal, fabric
filter removal contributes little to the
overall removal. This occurs because
sorbent utilization is very high in the
spray dryer itself. For 90 percent re-
moval, the fabric filter contribution in-
creases somewhat, but in an amount
roughly proportional to the increase in
overall removal level.
Table 3 summarizes the high sulfur
coal test results. For the first set of data,
corresponding to normal low chloride
operation, greater than stoichiometric
amounts of fresh lime were required.
Several factors probably contributed to
this effect. One may be that, because of
the increased lime addition rates, the re-
cycle ratio was greatly reduced relative
to low sulfur values in order to maintain
the total solids in the slurry at the de-
sired weight percent value. Also, the Illi-
nois coal ash (being nonalkaline) con-
tributed no alkalinity to the S02 removal
reactions. For the first set of high sulfur
data, the fabric filter contribution to
overall S02 removal appears to be more
important than for low sulfur operation.
Chloride addition has been reported
by others to promote increased sorbent
utilization in spray-dryer-based FGD
systems. The benefits are thought to re-
sult from the deliquescent properties of
calcium chloride, which delay complete
drying of the droplets in the spray dryer
and result in higher residual moisture
levels in the fabric filter solids. The sec-
ond set of S02 removal data in Table 3
corresponds to the addition of calcium
chloride at levels which result in a chlo-
ride content of 1 percent in the fabric
filter solids collected. This chloride level
in the fabric filter solids was recom-
mended by the system vendor, Niro At-
omizer, as being an optimum value for
lime utilization enhancement, based on
pilot-scale studies conducted at their
Copenhagen, Denmark, test facility. At
Riverside, this solids chloride level re-
quired a liquid-phase chloride concen-
tration of about 7,000 ppm in the atom-
izer feed slurry. For the recycle rates at
Riverside, fresh makeup of calcium
chloride accounted for about half of this
liquid-phase content, and the remainder
dissolved from the recycle material. The
results in Table 3 show that chloride ad-
dition significantly reduced the lime
reagent ratio requirements to achieve
nearly 90 percent removal; the lime re-
quirement was reduced by about
25 percent.
The S02 removal results for these
high chloride tests indicate increased
SO2 removal across the fabric filter rela-
tive to that for the baseline high sulfur
coal test. This indicates that the benefits
of high chloride level on residual mois-
ture level in the fabric filter have a
greater impact on S02 removal than im-
pacts within the spray dryer.
At Riverside, with chloride levels in
the fabric filter solids at 1 percent, resid-
ual moisture levels increased from
below 1 percent to nearly 2 percent.
These moisture levels are still low
enough to avoid problems which result
from handling wet solids. Also, no
buildup of wet solids on the spray dryer
walls occurred during testing, and
solids collected at the bottom of the
spray dryer contained moisture levels
below 3 percent. These tests were con-
ducted at an 18°F approach to adiabatic
saturation at the dryer outlet, just as
were all previous tests.
Material balance calculations indicate
that, for a coal such as the Illinois coal
fired in the high sulfur tests at Riverside,
a chloride content of around 0.3 percent
would provide the chloride levels of this
test. This would be an uncharacteristi-
cally high chloride level for a typical 3.4
percent sulfur coal. However, based on
published bulk prices for calcium chlo-
ride, it appears that it would be eco-
nomic in this case, disregarding capital
cost considerations, to operate at high
chloride levels even if virtually all of the
chloride must be added as calcium chlo-
ride. For a 3.4 percent sulfur coal with a
higher chloride content (0.1 percent or
better), the economics would likely be
improved. Additionally, a makeup water
source with a significant chloride con-
tent, such as some cooling tower blow-
downs, should further improve these
economics.
High chloride levels could potentially
have a negative impact on system cor-
rosion rates. Corrosion rate impacts
could not be measured in this short-
term test. No profound impacts were
observed, however.
Mass Loading Measurement
Results
Table 4 presents mass loading results
for both the high sulfur and low sulfur
coal test periods. The results show that
the spray dryer increases the grain load-
ing at the fabric filter inlet to 3 to 5 times
that of the spray dryer inlet value. The
data also show that particulate removal
levels remained high throughout the
test program. Removal efficiencies
across the fabric filter varied from 99.95
to over 99.9 percent. The emission lev-
els in Table 4 are expressed as grains
per dry standard cubic foot. In all cases,
particulate emission rates measured
were below the current NSPS level for
utility boilers (0.03 lb/106 Btu).
Flue Gas SO3 Measurement
Results
Flue gas S03 concentration was also
measured. For the low sulfur coal tests,
no measurable S03 levels were de-
tected at either the spray dryer inlet or
fabric filter outlet. The inability to
meausre SO3 at the dryer inlet is appar-
ently related to the alkaline nature of the
Sarpy Creek coal ash.
Measurable levels of SO3 were found
during the high sulfur test periods.
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Table 4. Flue Gas Mass Loading Summary
Sampling
Location
Mass Loading, gr/dscf
Low Sulfur Tests
High Sulfur Tests
Spray Dryer Inlet
Spray Dryer Outlet
Fabric Filter Outlet
3.2 to 4.1
11.0 to 13.8
0.001 to 0.003a
2.8 to 4.1
14.9 to 17.2
0.001 to 0.008b
"Equivalent to 0.002 to 0.007 lb/106 Btu.
Equivalent to 0.002 to 0.018 lb/106 Btu.
Spray dryer inlet values were measured
at 2 to 6 ppm S03. Fabric filter outlet
values varied from 0.1 to 0.5 ppm.
Based on data from a limited number of
days where the spray dryer inlet and
fabric filter outlet 863 concentrations
were measured simultaneously, re-
moval efficiencies of 90 percent or bet-
ter across the system were indicated.
Solid Waste Characteristics
Solid waste characteristics for sam-
ples collected during both low sulfur
and high sulfur test conditions were
evaluated in a laboratory-scale test pro-
gram. Characteristics of both untreated
and cured solid wastes were measured.
The cured solid wastes showed best
properties for permeability coefficients
and unconfined compressive strength
when 30 to nearly 50 percent moisture
was added to the dry solids before cur-
ing. For the 75 percent removal low sul-
fur coal tests and the high sulfur coal
baseline 90 percent removal tests, per-
meability coefficients for cured samples
were in the range of 10~5 to 10~7 cm/
sec, typical of treated FGD sludge. Un-
confined compressive strengths for
these samples were over 100 psi. For
the high sulfur coal chloride addition
test, however, the permeability coeffi-
cient of the cured wastes was increased
to the 10~4 range, and the unconfined
compressive strength was reduced to
55 psi. Both changes indicate poorer
solid waste characteristics, apparently
resulting from high chloride levels.
Summary and Conclusions
Based on results from the 3-month
test program on the NSP Riverside dry
FGD system, the following conclusions
are presented:
• In general, the Riverside system ran
quite well. None of the problems an-
ticipated for spray dryer systems
(e.g., rotary atomizer wheel plug-
gage, buildup of wet solids on dryer
vessel walls, or wetting of fabric fil-
ter bag surfaces during upset condi-
tions) were observed.
• Some problem areas at Riverside
appear to be potential sources of
problems on similar dry FGD sys-
tems. These include typical prob-
lems with mixing and pumping slur-
ries with a high solids content,
solids handling equipment which
requires continual maintenance,
and sometimes inadequate atom-
izer protection during upset condi-
tions.
• At sulfur levels up to a nominal 3.4
percent, high S02 removal efficien-
cies (nearly 90 percent) were readily
achievable in the relatively short-
term periods of this program. For
the low sulfur Sarpy Creek coal/
coke mixutre, substoichiometric
amounts of lime were required even
at 90 percent S02 removal. This was
attributed to the alkaline nature of
the Sarpy Creek coal ash. For the
high sulfur Illinois coal, 90 percent
S02 removal required reagent ratios
of about 1.3 to 1.4 moles limes per
mole of inlet SO2.
• Calcium chloride addition to the at-
omizer feed slurry to achieve chlo-
ride levels of about 1 percent in the
fabric filter solids catch appeared to
be successful in promoting lime uti-
lization. For the high sulfur tests, the
lime reagent ratio to achieve 90 per-
cent S02 removal was reduced from
1.3 to 1.4 down to a range of 0.9 to
1.1 moles lime per mole of inlet S02.
This chloride level would corre-
spond to 0.3 percent chloride in a
nominal 3.4 percent sulfur coal.
Even for a low chloride, high sulfur
coal, high chloride levels achieved
through calcium chloride addition
appear to be cost effective for re-
ducing lime consumption.
• Particulate control efficiencies were
high throughout the test program,
maintaining outlet grain loadings
well below required levels. In spite
of baghouse operation within 18°F
of the adiabatic saturation tempera-
ture and very high baghouse inlet
grain loadings, no bag-fabric-
related problems were observed
and flange-to-flange pressure drop
remained acceptably low.
• For the high sulfur test periods, a
limited number of data indicated
SO3 removal levels of 90 percent or
greater.
• Solid waste characteristics for both
the low sulfur 75 percent S02 re-
moval test and the high sulfur base-
line 90 percent S02 removal test ap-
pear to be acceptable for landfilling.
A deterioration of solid waste char-
acteristics was noted, however, for
the high sulfur chloride addition
tests.
Metric Equivalents
Nonmetric units are used, for the
most part, in this Summary because of
their customary usage in the electric
power industry. Readers more familiar
with their metric counterparts may use
the following equivalents:
Yields
Nonmetric Multiplied by Metric
Btu
°F
ft
ft2
ft3
gal.
gr
hp
in2
Ib
1.06
5/9(°F-32)
30.48
0.093
28.3
3.79
0.065
746
6.45
0.45
kJ
°C
cm
m2
L
L
g
w
cm2
kg
U. 3. GOVERNMENT PRINTING OFFICE: 1985/559-111/20637
-------
G. Blythe, J. Burke, D. Lewis, and C. Thompson are with Radian Corporation,
Austin, TX 78758.
Theodore G. Brna is the EPA Project Officer (see below).
The complete report, entitled "Field Evaluation of a Utility Dry Scrubbing System,"
(Order No. PB 85-207 488/AS; Cost: $26.50, subject to change) will be
available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
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/S7-85/020
U S ENVIR PROTECTION AGENCY
SiSTDhiiSK'lT
CHICAGO IL
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