625/2-79-022
v>EPA
United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Research Triangle Park NC 27711
Technology Transfer
Capsule Report
Bahco Flue Gas
Desulfurization and
Particulate
Removal System
,?'
•*- ,1*
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Technology Transfer EPA 625/2-79-022
Capsule Report
Bahco Flue Gas
Desulfurization and
Paniculate
Removal System
July 1979
This report was developed by the
Industrial Environmental Research Laboratory
Research Triangle Park IMC 27711
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Scrubber circulating pump and piping
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1. Introduction and
Summary
This capsule report has been
prepared as an aid in solving one
of today's vitally important
technological concerns the
selection and use of fuel for
industrial-size steam generating
units and other fuel-burning
equipment. Reduced availability
of natural gas supplies, increased
cost of low sulfur oil, and pollution
problems generally associated
with coal currently present
operators of boiler installations
with a question: What is the best
technique for compliance with
particulate and sulfur dioxide
regulations? The flue gas
desulfurization (FGD) technology
described herein permits any fuel,
including high sulfur oil or coal,
to be burned in conventional
equipment in a manner that is
both cost effective and
environmentally acceptable.
In September 1974, the U.S. Air
Force (USAF) awarded a contract
to Research-Cottrell (R-C) to erect
an SC>2 and particulate emission
control system at the central heat
plant of Rickenbacker Air Force
Base (RAFB) near Columbus, Ohio.
The equipment chosen was an
R-C/Bahco scrubber (module size
50) based on technology developed
by A B Banco in Sweden. This
unit accomplishes both S02 and
particulate removal
The R-C/Bahco system has been
used on many foreign oil-fired
industrial boilers since 1969. The
installation at the Rickenbacker
facility is the first application
of the system on a coal-fired
industrial boiler.
A second contract, sponsored by
the U.S. Environmental Protection
Agency (EPA), was awarded to
Research-Cottrell in April 1975.
The key provision of this program
was to characterize the R-C/Bahco
scrubbing system installed at
RAFB in terms of its performance,
reliability, and economics for S02
and particulate control on
industrial coal-fired plants. The
R-C/Bahco system was started up
in March 1976; the Characteriza-
tion Program was started a month
later and was completed in June
1 977. Final acceptance of the
system by the USAF followed in
September 1977, at the end of a
1-year operating cost guarantee
period.
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The Characterization Program
demonstrated that the R-C/Bahco
scrubbing system is capable of
controlling both paniculate and
sulfur dioxide emissions from the
combustion of high sulfur (2 to 4
percent) midwestern coal. The
following salient data were
obtained during the program:
• Paniculate emissions were
reduced to as low as 0.15
lb/106Btu(0.27g/106cal).
• Sulfur dioxide emissions were
reduced to as low as 0.1 lb/106
Btu (0.18 g/106 cal) with lime
reagent, and as low as 0.6
lb/106 Btu (1.1 g/106 cal)
with limestone.
• Operating costs, exclusive of
capital charges, were $5.28/ton
of coal burned when using lime,
including $0.21 maintenance
costs.
• Waste product properties relative
to dewatering, handling, and
disposal were found to be
similar to those measured for
other FGD waste products.
• Operation of the system required
less than 2,000 man-hours per
year. System availability above
95 percent is projected.
• No significant buildup of scale
or solids occurred in the
scrubbing system during the test
program.
Bin activator, feeder, and lime slaker
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2. The FGD System
The R-C/Bahco facility operating
at RAFB is a calcium-based
throwaway FGD and paniculate
removal system. Either pebble lime
(CaO) or ground limestone (CaCOs)
can be used for SC>2 removal to
produce mixtures containing
calcium sulfite (CaSOs), gypsum
(CaSCU), and fly ash. The overall
chemical reactions for the
respective reagents are shown in
Table 1.
The scrubbing system comprises
the following major components:
• Flue-gas-handling equipment
• R-C/Bahco scrubber
• Reagent-handling and -storage
equipment
• Sludge disposal equipment
The entire FGD system (Figure 1)
is served by a centrally located
control room and is operated,
part time, by heat plant personnel.
Flue-Gas-Handling Equipment
The flue-gas-handling equipment
includes a flue gas header, bypass
stack, mechanical collector, and
booster fan. Flue gas from as
many as eight stoker-fired hot
water generators—up to 108,000
actual ftVmm (51 m3/s)—passes
into the header and mechanical
collector where coarse paniculate
matter is removed before it enters
the booster fan and scrubber.
Removing paniculate minimizes
erosion of the fan and other
scrubber components and reduces
the amount of wet solids handled
by the scrubbing system. The ash
is disposed of via the existing
ash-handling system. A bypass
stack in the carbon steel flue gas
header serves two purposes: it
serves as a fail-safe emergency
bypass, and it permits air to enter
the system at low loads to
maintain gas velocity through the
mechanical collector and scrubber
to maximize collection efficiency.
Gas Flow
As shown in Figure 2, the
R-C/Bahco scrubber, which is
fabricated from 316L stainless
steel, is a two-stage inverted
venturi unit specifically designed
to operate with slurries containing
calcium sulfite, calcium sulfate
(gypsum), calcium carbonate,
calcium hydroxide, and fly ash. All
of the internal gas flow passages
are large, unobstructed, and well
irrigated with circulating slurry or
makeup water to essentially
eliminate the possibility of serious
plugging problems.
Hot flue gas from the booster fan
enters the first stage, where it
impinges on the surface of the
slurry, creating a cascade of
droplets that it carries into the
throat of the lower venturi. The
droplets, containing SC>2
scrubbing reagent, cool the gas to
its saturation temperature, absorb
sulfur dioxide, and trap paniculate
Table 1.
Chemical Reactions for Lime and Limestone in SC>2 Removal
Reagent
Reaction
Lime
Limestone
CaO + HyO
CaCOj + SOy - —•
— >- Ca{OH)2
». CaSO -j + CO'i
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Thickener
Reagent system
module
Reagent
storage
Reagent
feeder and
slaker
Lime or
limestone
conveyor
Unloading
station —
Overflow
to lime-
dissolving
tank
Bypass Flue
makeup gas
stack^ from
heat
plant
Reagent-dissolving Second stage
tank pump
Mill pump
To
fly ash
disposal
Figure 1.
R-C/Bahco Scrubber System
matter. Above the first venturi, the
gas stream is turned downward
by the bottom of the pan in the
second stage venturi causing most
of the droplets to fall out. In the
second stage, or upper venturi, the
process of impinging the gas
stream on the surface of a slurry
is repeated. Here the gas/droplet
mixture passes up through the
throat of the upper venturi where
final S02 absorption and
paniculate removal are
accomplished. A cyclonic mist
eliminator above the upper venturi
imparts a spinning motion to the
gas stream, causing the droplets
to move toward the wall where
they coalesce and drain from the
scrubber. From the mist
eliminator, clean gas, which is not
reheated, enters the surrounding
atmosphere via the stack.
Slurry Flow
Two techniques of handling slurry
flow in the system are used to
eliminate or minimize the plugging
and erosion problems often
associated with calcium-based
FGD systems: maintaining
essentially constant slurry flow
rates through the scrubber, and
eliminating turndown in slurry
bleed streams by operating in an
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Schedule
Gas flow
Slurry flow
Sludge
removal
Slowdown valve-/ v
To reagent dissolver*
Stack
Manhole
Platform
Man door
Platform
Platform
stage drop collector
Ground level
Figure 2.
R-C/Bahco Scrubber
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on-and-off mode with water
flushing after slurry flow is
interrupted.
Slurry flows by gravity from top to
bottom in the scrubber, counter-
current to the gas flow. Slurry
from the reagent dissolver (which
is also of 316L stainless steel)
contains makeup reagent—either
lime or ground limestone. The
slurry enters the pan in the upper
venturi. Slurry level in the pan
determines the upper venturi
pressure drop; the level is set by
adjusting a weir in the level tank
located outside the scrubber.
Slurry streams from the mist
eliminator and the pan are
combined in the level tank before
flowing by gravity to the mill
under the lower venturi, where
another level tank is used to set
the pressure drop in the lower
venturi. Part of the slurry collected
in the area between the upper and
lower Venturis, the part that has
contacted the gas stream twice,
flows by gravity to the sludge
disposal system. In the first-stage
level tank this slurry is combined
with overflow from the mill and is
returned to the reagent dissolver.
More reagent is added in the
dissolver before the slurry is
recycled to the upper venturi. The
fluid mill is powered by an
external pump and is used to grind
coarse limestone or other large
particles in the system.
First-stage venturi, showing gas inlets and makeup water spray
manifolds
Reagent-Handling and -Storage
Equipment
The reagent system installed at
RAFB is capable of handling both
0.75-inch (1.9-cm) pebble lime
and 200-mesh ground limestone.
Primary components include
truck-unloading equipment, a steel
silo with 3 weeks' storage capacity
at winter load conditions, a weigh
belt feeder, and a lime slaker. The
silo, feeder, slaker, and reagent-
dissolving tank are integrated into
a single module to minimize
materials handling, supports, and
space requirements. Lime or
limestone drops directly out of the
silo into the feeder-slaker and
overflows into the reagent-dissolv-
ing tank directly under the slaker.
Sludge Disposal Equipment
Calcium sulfite, gypsum, and fly
ash collected in the scrubber are
concentrated from 10 percent to
approximately 40 percent solids
(by weight) in a thickener. The
overflow from the thickener is
returned by gravity to the
reagent-dissolving tank. The
underflow from the thickener is
pumped underground to a
hypalon-lined storage pond.
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3. The Test Program
The R-C/Bahco FGD system test
program, carried out at RAFB
between March 1976 and June
1977, incorporated the following
categories:
• Material balance
• Lime reagent process variable
• Lime reagent verification
• Particulate collection efficiency
• Limestone reagent process
variable
• Sludge characterization
• Scrubber reliability monitoring
Material balance tests were
conducted to establish the range
of operating conditions over which
the R-C/Bahco scrubber could be
operated and to verify performance
at design conditions by completing
material balances. Maximum and
minimum gas flow rates, pressure
drops, and slurry circulation rates
were determined and preliminary
SOa and the paniculate
performance data at the limits of
the system's capabilities were
obtained. The system was
operated at the design gas rate of
50,000 stdftVmin (25 normal
m3/s) and complete material
balances on calcium, sulfur, and
total solids were performed.
Statistically designed lime process
variable tests helped to establish
the quantitative effect of the
following process variables on SC>2
removal: gas flow rate, first- and
second-stage pressure drops, mill
and second-stage slurry rates,
lime.SO2 stoichiometric ratio,
slurry inventory, and slurry solids
concentration.
Lime reagent verification tests
were undertaken to verify the
results obtained in the lime
process variable tests, and to
determine the effect of very dilute
scrubber slurry (2 percent solids)
on system performance.
Particulate collection efficiency
tests were a continuation of the
paniculate tests initiated during
the earlier sampling phase.
Relationships were determined
between system variables,
including particle size distribution
and paniculate removal efficiency.
Limestone process variable tests
were completed using the same
statistically designed test plan
used for lime. The effect of system
variables on SOa removal
efficiency and reagent use was
determined.
Sludge samples generated at
RAFB were tested to determine
dewatering, transport, and
disposal characteristics (sludge
characterization). Samples of
sludge from lime as well as
limestone scrubbing were tested.
The R-C/Bahco system was
monitored from March 1976 to
June 1977, to document its
operating and maintenance history
and to obtain data for a cost
analysis. Data were gathered on
reagent, coal, water, and power
consumption as well as on
operating and maintenance labor
requirements.
Throughout the test program
samples were taken of slurry, flue
gas, lime, limestone, and coal,
often in duplicate, for chemical
analyses, paniculate loading, and
particle size distribution. A
field analytical laboratory was
established, and especially
developed and highly efficient test
methods using thermogravimetric
analysis were employed
extensively.
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4. Test Results
Capacity/Material Balance Tests
Performance of the size 50
R-C/Bahco scrubber at RAFB is
measured by its ability to handle
variations in system operating
parameters while reducing S02
and particulate emissions to the
limits allowed by the applicable
regulations, without exceeding the
capacity of the system. Regulations
applicable to RAFB limit SOa
emissions to 2.2 lb/106 Btu (3.96
g/106 cal) and particulate to
0.16 lb/106 Btu (0.29 g/106 cal).
Table 2 lists maximum, minimum,
and optimum operating levels
determined for the system at
RAFB. The cost of reducing
emissions to meet requirements
will be minimized at optimum
operating levels.
Lime Tests
The SC>2 removal capabilities of
the R-C/Bahco system using
pebble lime were characterized in
two steps. First, a series of
screening tests determined the
effects of slurry rates, gas rate,
venturi pressure drops, slurry
density, system volume, and lime
stoichiometry on SC>2 removal.
Tests results indicated that lime
stoichiometry—the ratio of lime
feed in the system to 862 in the
flue gas—was the only variable
controlling SC>2 removal as long
as the system was operated within
the limits outlined in Table 2.
A second group of tests, in which
the effects of the gas flow, slurry
rates and slurry density were
determined, confirmed the initial
findings that stoichiometry alone
controlled S02 removal.
Results of these verification tests
are shown in Figure 3 The figure
also shows that lime use is
essentially 100 percent—that is,
no excess lime is needed—up to
90 percent SC>2 removal. Figure 4
illustrates system performance
when S02 removal is above
90 percent—that is, when SC>2
emissions at RAFB were reduced
below 0.6 lb/106 Btu (1.08 g/106
cal). The figure indicates that over
98 percent of the S02
corresponding to 0.1 Ib S02/106
Btu (0.18 g S02/106 cal), can be
Table 2.
R-C/Bahco Scrubber Operating Levels
Variable
Gas rate (actual ft3/mm)
Slurry circulation rate (gal/mm) . . .
Venturi pressure drop for each
stage (inches H20)
Slurry concentration (wt %
solids)
Reagent.SC>2 stoichiometry
(moles reagent moles SC>2,
based on inlet SOa levels)
Lime
Limestone
S02 removal efficiency (percent)
Lime
Limestone
S02 emission (lb/106 Btu)
Lime
Limestone
Particulate emission (lb/106
Btu)
Minimum
35,000
1,500
6
2
045
055
45
40
3.7
40
02-03
Maximum
55,000
3,000
12
25
1 05
1 2
98+
85
01
1 0
014
Optimum
40,000-50,000
2,300
7-10
10
07
075
70
70
20
20
0 16
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achieved with a stoichiometry of
1.1—that is, 10 percent excess
lime. The S02 emission rates
shown in Figure 4 are well below
the required 2.2 lb/106 Btu
(3.96 g/106 cal) and the guarantee
level of 1.0 lb/106 Btu (1 8
g/106 cal).
From the lime tests it is concluded
that lime:S02 stoichiometry is the
controlling factor in determining
S02 removal efficiency. Virtually
any desired S02 removal
efficiency can be achieved when
lime is used in the R-C/Bahco
scrubber, simply by adjusting the
lime:S02 stoichiometry. Lime use
approaches 100 percent at
stoichiometric ratios up to about
0.9. At stoichiometric ratios up
to 1.1, producing up to 99 percent
removal, lime use is above
90 percent. Because most S02
regulations for industrial boilers
permit emissions in the range of
1.0 to 2.0 lb/106 Btu (1.8 to
3.6 g/106 cal), lime, with its high
removal capabilities, can be used
to obtain offset credits in a
nonattainment area to apply
toward an expansion or new
facility. No further capital
expenditure need be made,
because the R-C/Bahco system
normally would be designed to
handle lime as well as limestone,
and switching from limestone to
lime will increase the annual
operating costs only by about
15 percent.
Limestone Tests
System performance with ground
limestone was determined in a
series of screening tests very
similar to those used for pebble
lime. These tests indicated that
slurry circulation in addition to
limestone stoichiometry controls
S02 removal efficiency.
<
>
o
100
80
60
40
20
RAFB Code requirement
r?\°
02
04
06
Oi
1 0
1 2
1 4
LIME STOICHIOMETRY (moles lime per mole (S02)
Figure 3.
S02 Removal Efficiency as a Function of Lime Stoichiometry
Hypalon-hned storage pond
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Figure 5 shows the results of the
tests and gives limestone use
data. At a stoichiometry of 1.0 and
slurry circulation of 2,300 gal/min
(0.14 m3/s), slightly over
80 percent SC>2 removal is
possible with 80 percent limestone
use. A practical limit for limestone
is 80 percent SOa removal,
because higher removals result in
substantial reductions in limestone
use.
Operation with limestone at RAFB
produced sludge that contained
much more gypsum than did
operation with lime. That is, there
was more oxidation of CaSOa to
CaSO4. Table 3 shows an average
gypsum (CaS04 • 2H20) and
calcium sulfite (CaS03-1/2H20)
content of 33 and 55 percent,
respectively, when lime was used.
The limestone slurry was almost
completely oxidized and contained
78 percent sulfate and less than
1 percent sulfite. The comparison
of average lime and limestone
slurry analyses during similar
boiler load periods listed in Table 3
indicates that the oxidation trend
is probably attributable to the
lower slurry pH encountered when
using limestone, because all other
operating conditions were
essentially the same.
Particulate Removal Efficiency
Paniculate Removal Tests. Initial
particulate removal tests on the
R-C/Bahco scrubber, performed in
March, April, and May of 1976,
revealed the presence of
substantial amounts of soot in the
stack gas. The average particulate
emission rate for these tests was
0.23 lb/106 Btu (0.42 g/106 cal).
2 5
£ 20
ID
o
£ 15
<
tr
1 0
"J 05
RAFB EPA limit
Guarantee emission rate
90% lime use
07 08 09 10 11 12 13 14
LIME STOICHIOMETRY (moles lime per mole S02)
1 5
Figure 4.
Relationship Between SOa Emission Rates and Lime:SOa Stoichiometry
Overall particulate removal
averaged 93 to 94 percent. Ohio
emission standards require an
overall removal efficiency of
96 percent at a particulate inlet
loading of 1.5 gr/stdft 3 dry
(3.4 g/normal m3 dry) to achieve
an emission rate of 0.16 lb/106
Btu (0.29 g/106 cal). Venturi
pressure drops were increased to
nearly double the design value of
7 inches (18 cm) H20 to reduce
these emissions. Below
approximately 18 inches (46 cm)
H20 total pressure drop,
particulate emissions increased
rapidly. The amount of soot
present in the flue gas at RAFB is
higher than in other stoker-fired
generators similar to the
Rickenbacker boiler.
The Air Force has undertaken an
extensive program to upgrade the
heat plant at RAFB. Data obtained
during this test program
contributed substantially to
information used to plan the
upgrading program, and so far the
following modifications have been
completed:
• Installation of a new 60-Btu/h
(18-Watt) generator to replace
the two old units
• Replacement of hot water
distribution piping
• Installation of flue gas oxygen
monitoring equipment
• Repair of firing air distribution
equipment and fire box pressure
controls in the generators
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• Rebuilding mechanical collectors
and induced draft fans on the
generators
• Replacement of burned out
ledge plates, which regulate
combustion air flow around the
grates
• Repair of traveling grates
The problem with soot at RAFB
points up a critical aspect of a
successful emission control
project—namely, that proper
operation of all equipment, boilers
as well as the scrubber, is
essential to maintain satisfactory
emission levels. Inadequate
combustion or inadequate air can
be as detrimental to emission
control as improper scrubber
operation.
Slurry Entrainment and Gas
Bypassing. During the particulate
tests, two phenomena were
observed when the system was
operated above its capacity limits.
The first, called entrainment,
occurs at very low venturi
pressure drops—that is, under
6 inches (15 cm) h^O involves
small droplets of slurry carrying
through the second-stage mist
eliminator and out the stack. The
second, called bypassing, is
characterized by pulsations in the
gas flow through the scrubber; the
result is low collection efficiency
in all particle size ranges. The
second phenomenon takes place
when relatively high pressure
drops—that is, 12 inches (30 cm)
H20 or more in either venturi—are
coupled with slurry flows under
150 gal/min (0.01 m3/s) to the
scrubber.
Conclusion. The particulate
removal efficiency of the
R-C/Bahco scrubber is comparable
to that of low energy venturi
scrubbers for particles larger than
1 Mm, and appears to be better for
particles smaller than 1/im. In an
R-C/Bahco scrubber, the second
stage is the primary collector of
fine particles. Slurry carryover and
100
90
80
c
<" in
o /U
LLJ
u
60
50
0 40
30
20
10
02 04 06 08
10
12
14 16
18
STOICHIOMETRY RATIO
Figure 5.
S02 Removal Efficiency as a Function of Limestone:S02 Stoichiometry
Table 3.
Lime and Limestone Slurry Analyses
Slurry solids
CaS04 2H20
CaSOa V2H20
CaCOs
MqCO-i .
Acid insolubles
Lime
slurry
(wt%)
334
54 5
3 7
46
Limestone
slurry
(wt%)
77 5
1 0
17 3
08
3 4
Total
962
1000
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gas bypassing limit paniculate Table 4.
collection in an R-C/Bahco ^ T
scrubber operated outside the Dewater.ng Test Results
levels shown in Table 1.
Particulate emissions from
stoker-fired coal-burning
levels required by regulatory
• .r '. ' Settling
agencies if excessive soot u
formation is prevented.
Centrifuge
Sludge Characterization
Filter leaf
A series of scrubber sludge
Slurry
type
/ Lime
\ Limestone3
I Lime
... < Lime
\ Limestone
I Lime
/ Lime
\ Limestone
Feed
solids
(wt%)
162
167
167
263
384
374
246
41 5
374
Final
solids
(wt%)
44
58
58
51
56
65
58
59
74
Rate at
35 percent
solids
22 Ib/d/ft2
1 64 Ib/d/ft2
578 Ib/d/ft2
70 Ib/h/ft2
124 Ib/h/ft2
64 Ib/h/ft2
characterization tests was carried
out at the Research-Cottrell
laboratories to:
• Determine scrubber sludge
dewatering characteristics
• Evaluate transportability of
dewatered sludge
• Determine physical/structural
properties of dewatered sludge
• Measure sludge leachate
properties
Slurry Dewatering. A series of
settling, centrifuge, and filter leaf
tests was run on lime and
limestone slurry samples. The
results are summarized in Table 4.
The settling tests showed that
limestone slurries settle more
rapidly and produce denser settled
layer than lime slurries.
Flocculation improved the settling
of limestone slurries, but not
that of lime slurries.
aWith 5 ppm flocculant
Table 5.
Sludge Leachate Analysis
Analysis
IDS (mg/l)
S04 (mg/l) . . . .
COD (mg/l)
Cl (mg/l) . . .
Pb (ppb) . .
Cd (ppb)
Cr (ppb)
Hg (ppb)
Lime
leachate
2 960
1 8106
8 4
72 52
<100
... < 1 0
.... 50
<25
Limestone
leachate
2 760
1 613 1
68
4804
<100
<10
50
<25
-------
The centrifuge tests indicated that
final cake density increased as the
solids concentration in the feed
was increased, and that limestone
slurries produced higher cake
densities than did lime slurries.
Filter leaf tests showed that
limestone slurry filtration rates
were significantly lower than lime
slurry rates. However, limestone
again produced a denser cake.
Leachate Tests. Leachate tests
were performed on samples of
lime and limestone sludges. The
results are listed in Table 5.
Leachate compositions from lime
and limestone sludges are
essentially the same. Total
dissolved solids (TDS) in the range
of 2,500 to 3,000 mg/l and sulfate
levels of 1,600 to 1,800 mg/l
indicate that the leachates were
saturated with respect to CaSC>4.
Both sulfites in the sludge and
organic matter in the fly ash
contribute to the chemical oxygen
demand (COD) levels observed.
Although the chloride level in the
lime leachate is somewhat higher
than the limestone leachate, the
other trace elements are present
in similar concentrations in both
leachates. The constituents found
in these leachates are similar in
type and concentration to those
reported in other studies. If a
disposal site is placed so as to
avoid infiltration of leachate into
ground water, and if sludge and
soil cover are placed properly to
avoid excessive contamination of
runoff, leachate from these
sludges will not present an
environmentally unacceptable
disposal problem.
First-stage level tank
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5. Operating
Experience
Since startup in March 1976, the
R-C/Bahco system has performed
well in all areas essential to
successful FGD, including:
S02 removal
Paniculate removal
Scrubber reliability
Minimal routine maintenance
Moderate operating costs
Ease of operation
During the test period of about
11,000 hours, the scrubbing
system operated for 6,194 hours.
The operation is summarized in
Figure 6. It is of interest that from
December 1976 to February 1977
(when severe winter weather was
encountered), no outages resulted
from failure of auxiliary equipment.
There were a few brief shutdowns
caused by frozen air and water
lines during this period, but
system availability was over
95 percent.
Downtime is summarized in
Table 6. This table shows the
amount of time required to obtain
parts as well as the actual time
for repair work. Spare parts were
not kept on hand during the test
period, and this resulted in
substantial unnecessary
downtime. Since completion of the
test program, a full supply of
spares has been procured. Table 6
also shows that booster fan repair
time accounted for 90 percent of
the downtime caused by repairs.
The booster fan operates on the
inlet side of the scrubber,
downstream from the mechanical
collector, and handles only hot dry
flue gas with moderate amounts
of fine fly ash. Modifications to the
fan wheel and bearings, completed
in May 1977, have eliminated the
recurring failures associated with
this piece of equipment.
Total downtime, exclusive of fan
repairs and procurement, was
1,845 hours, or 17 percent of the
test period. During routine
operation, the system availability
should be over 95 percent, based
on the factors observed during
the test program.
Scrubber inspections were an
integral part of the program to
monitor scrubber performance. A
thorough internal inspection was
made in April 1976, approximately
1 month after startup. A followup
inspection was made 2 months
later, with subsequent inspections
during outages up to the end of
the test program in June 1977.
These inspections confirmed the
effectiveness of the water makeup
system in keeping key areas of
the scrubber clean.
-------
Accumulations of solids were
detected at seven locations within
the scrubber (Figure 7).
Accumulations in four areas—1, 5,
6, and 7—had no impact on
scrubber performance. Problems
of solids buildup in Areas 2, 3,
and 4 were easily corrected, as
follows:
In the first few months after
startup, the first-stage venturi
overflowed into the inlet manifold.
Area 2, resulting in an
accumulation of dried slurry in the
bottom of that area. Subsequent
investigation revealed that
operation of the first-stage at
pressure drops above 12 inches
(30 cm) H20 coupled with a
second-stage slurry pumping rate
more than 50 percent higher than
the design rate of 2,600 gal/mm
(0.16 m3/s), caused flooding when
the gas flow was reduced below
35,000 stdftVmin (17 normal
m3/s) or the booster fan was
shut down. This problem was
eliminated by decreasing the
speed of the slurry pump to
reduce the flow to design levels,
and by adding an interlock to
stop the pump when the booster
fan is shut down. The accumulated
material was removed during
subsequent heat plant outages.
Areas 3 and 4 were affected twice
during the test by accumulations
of a coarse sandy material. The
first incident, which occurred
shortly after startup, was caused
by inadequate removal of grit from
the lime slaker. The material in
the pan was removed and the
slaker was readjusted to eliminate
the problem. The second
accumulation took place during
the winter of 1976-77 when the
air lines, which activated the
blowdown valves on the first- and
second-stage level tanks, froze and
rendered these valves inoperative.
II III I
U
t fit lnsta" 1
Scrubber Replace slurry Scrubber Replace slurry sludge 1
startup pump lining inspection pump lining thickener
rake
Mar Apr May
1976
II II
4 t
ReplaCe Correct
)orque fan vibration
limiter
July Aug Sept
1976
June
II III
Repair
sludge and
slurry lines
Oct.
I.I
Install improved J^'3,06
booster fan bearing blowdown
valves
Nov Dec Jan
1976/1977
.II , ,l
t \ ft
Replace ' Inspection Repair and Replace
water booster and grit modification slaker
pump bearing removal of fan wheel motor
Mar. Apr May
1977
Feb
Scrubber 1 1
operabihty 1 1
Boiler 1 I
shutdown 1 1
Figure 6.
Downtime Related to Auxiliary Equipment
Table 6.
Downtime Summary
Hours
Percent
Booster fan
Thickener
Slurry pump
Water booster pump
Lime slaker . .
Modifications
Routine maintenance
Loss of utilities
Miscellaneous . ....
Total
Procurement
514
471
252
190
122
56
1 605
Repairs
2 252
8
18
16
11
58
2 363
Downtime
2 766
479
270
206
133
388
139
1 16
1 14
4 61 1
period
25 1
4 4
2 5
1 9
1 2
3 5
1 3
1 1
0 9
41 9
-------
The results of this part of the test
program demonstrated that there
are situations that can result in
deterioration of scrubber
performance, including:
• Infiltration of grit into the system
through the lime slaker
• Inadequate operation of the
scrubber blowdown valves
• Slow accumulation of solids in
the straightening vanes in the
stack
The infiltration of grit can be kept
to a minimum by paying close
attention to the operation of the
lime slaker grit removal circuit.
The blowdown valves should be
operated two to four times a shift,
depending on scrubber load, to
avoid accumulations of solids in
the slurry outlets.
The straightening vanes at the
base of the stack, which serve
only to minimize spin in the gas
stream leaving the scrubber, may
accumulate some material and
should be checked twice a year.
The possibility of accumulations
taking place can be minimized by
operating the scrubber within the
limits outlined in Section 3 to
avoid slurry carryover. Obviously,
elimination of the vanes would
prevent the problem entirely, but
accurate outlet particulate
sampling would then be difficult.
The RAFB operating experience
indicates that there are no
significant problems related to
the accumulation of solids in the
R-C/Bahco system. The scrubber
can tolerate substantial
accumulations of solids resulting
from external operating problems
before performance is adversely
affected. Any deterioration in
performance that does occur is
gradual and can be rectified at a
convenient time.
Stack
Manhole
7
6
*-
J
Platform
Mist eliminator
Man door
Manhole
Ground level
Platform
Platform
stage drop collector
* Water
makeup
system
Figure 7.
R-C/Bahco Scrubber Module
-------
Lime delivery truck with R-C/Bahco scrubber and lime bin in background
-------
6. Economics
Compliance with air pollution
control regulations can be
achieved in several ways. The one
frequently chosen today is
switching to a fuel such as low
sulfur oil that does not require
emission control equipment. This
choice is often based on an
economic evaluation that proves it
cost-effective. Table 7 summarizes
data gathered on costs during the
test program at RAFBa.
During the 14-month test period,
flue gas from the combustion of
27,216 tons (24,742 Mg) of coal,
which averaged 2.5 percent sulfur,
was treated by the scrubbing
system. The total operating
cost—including utilities, chemicals,
and labor—was $5.07/ton of coal
burned. Maintenance costs were
$0.21/ton including labor and
materials.
Sludge disposal cost is $0.45/ton
of coal burned, calculated in terms
of the installed cost of the pond
and an anticipated 10-year life.
The turnkey cost of the RAFB
installation was $2.25 million,
including a new substation and
additional equipment, controls, and
instrumentation necessary for the
EPA test program. Current costs
for R-C/Bahco turnkey systems
(Figure 8) are $1.3 million to
$3.7 million. Figure 9 illustrates
the capacities of the various size
systems. The system installed at
RAFB is capable of treating flue
gas from a 180,000-lb/h (23-kg/s)
steam boiler.
Table 8, based on the cost data
collected at RAFB, summarizes the
annual operating costs including
normal overheads and capital
charges for an industrial
180,000-lb/h (23-kg/s) steam
plant operating at 75 percent of
capacity.
The 1979 cost of low sulfur oil
is approximately $20 to
$22/barrel, or about $87 to $96
for energy equivalent to that
contained in 1 ton (0.91 Mg) of
coal: 25 Btu x 106 (26.4 kJ x 106).
In the case outlined in Table 8,
there would be an annual fuel
saving of between $3,400,000 and
$4,000,000, which could be
applied to coal-handling and
emission control equipment if coal
at $30/ton were burned instead
of low sulfur oil.
The R-C/Bahco system is designed
specifically for industrial-size
fossil-fuel-burning applications
that require combined S02 and
particulate removal. The system at
RAFB handles SOa and particulate
from the combustion of
midwestern high sulfur coal,
12,200 Btu/lb (28,377 kJ/kg),
6 percent ash, 3.5 percent sulfur.
Other units, listed in Table 9, have
been operating successfully since
1969 on oil-fired boilers with S02
concentrations up to 4,000 ppm.
Basically, the R-C/Bahco system
can economically reduce 562
particulate emissions from the
combustion of coal and high sulfur
oil, or emissions from certain
other sources, to levels low
enough to satisfy applicable
environmental regulations. The
R-C/Bahco system can be used
successfully for emission control
for almost any installation, where
the SC>2 concentration does not
exceed 6,000 ppm and most of the
particulate to be collected is
above 1 ^im.
a1978 is the base year for costs unless
otherwise indicated.
-------
Table 7.
RAFB Operating Cost Summary
Item
Units
Cost (S)
Per unit
Total
Power
Booster fan 3,065,000 kWh
Auxiliary equipment 602,500 kWh
Water
Potable water 4,448,120 gal
Well watej >
Chemicals
Lime
Limestone
Labor
Operating labor
Supervision (25% of operating
labor estimate)
1,768,700 gal
721 tons
130 tons
0 024/kWh
0 024/kWh
036/1,000 gal
40 35/ton
1272/ton
1,860 man-hours 7 52/man-hour
Total .
73,560
14,460
1,601
29,092
1,654
13,987
3,497
137,851
40r-
35
30
« 25
(ft
8 20
1 5
1 0
05
0
I
J I
10 20 30 40 50 60 70 80 90 100
FLUE GAS FLOW RATE (1,000 stdftVmm)
Figure 8.
R-C/Bahco Capital Costs
-------
100
00
00
D
cc
o
in
O
o
<
CO
X
CJ
RAFB flow rate
Average Maximum
Suggested
operating range
10
20
30
40 50 60 70 80 90
FLUE GAS FLOW RATE (1,000 stdftVmin)
100
110
120
Figure 9.
R-C/Bahco Scrubber Capacities
Table 8.
Annual Operating Costs
Item
Units
Cost (S)
Per unit
Total
Power
Water
Chemical (limestone)
Sludge dewatering3
Operating labor
Supervision of labor
Maintenance labor and materials
General overhead (75% of labor
man-hour costs)
Depreciation (10-year straight
line)
Taxes and insurance
3 5 million kWh
6 million gal
4,440 tons
2,200 man-hours
500 man-hours
0 024/kWh
036/1,000 gal
1272/ton
84,000
2,160
56,480
800/man-hour 17,600
1000/man-hour 5,000
12,600
- 17,300
- 225,000
— 45,000
Total
465,140
a Included in other costs
Note —Installed cost = $2 25 million Coal consumption = 60,000 tons at 3 percent
sulfur + 70 percent S02 removal Cost per ton of coal = $7 50
-------
Table 9.
R-C/Bahco Particulate/S02 Removal Systems
Company
and
location
Rickenbacker Air Force Base . . .
Columbus OH
Kino Ura Utility
Japan
Kanegafuchi Chemical
Takasago, Japan
Stora Kopparberg .... . . .
Grycksbo, Sweden
Osaka City ...
Osaka, Japan
Central Glass Company ....
Sakai, Japan
Taio Paper Company .
lyomishima, Japan
Yahagi Iron Works
Nagoya, Japan
Hiroshima City . .
Hiroshima, Japan
Daishowa Seishi
Yoshmaga, Japan
Daishowa Seishi .
Suzukawa, Japan
Sodersjukhuset
Stockholm, Sweden
No
of
units
. . 1
1
2
1
1
1
1
1
1
1
5
1
3
Unit
capacity
(stdftVmm
at 32° F)
50,000
75,000
159,000
17,700
10,000
31,300
83,000
66,400
48,300
10,000
44,200
14,700
17,700
Service
Coal-fired boiler
Oil-fired boiler
Oil-fired boiler
Black liquor boiler
Secondary sludge incinerator
Glass furnace
Oil-fired boiler
Oil-fired boiler
Sintering plant
Secondary sludge incinerator
Oil-fired boiler
Oil-fired boiler
Oil-fired boiler
Scrubbing
reagent
CaO and CaCOs dust
NaOH
NaOH
CaO and CaCOs dust
NaOH
NaOH
NaOH
NaOH
Ca(OH)2 waste carbide sludge
NaOH
NaOH
NaOH
Ca(OH)2
Table 9.
R-C/Bahco Part:culate/S02 Removal Systems—Concluded
Company
and
location
Rickenbacker Air Force Base . . ...
Columbus OH
Kmo Ura Utility
Japan
Kanegafuchi Chemical .
Takasago, Japan
Grycksbo, Sweden
Osaka City
Osaka, Japan
Central Glass Company
Sakai, Japan
Taio Paper Company
lyomishima, Japan
Yahagi Iron Works . .
Nagoya, Japan
Hiroshima City
Hiroshima, Japan
Daishowa Seishi .... .... ...
Yoshmaga, Japan
Daishowa Seishi ....
Suzukawa, Japan
Sodersjukhuset
Stockholm, Sweden
Inlet
S02
concentration
(ppm)
.... . 400-2 000
1 500
1 400-1 530
4 000-6 000
70-80
1 200b
1 000- 1 500
1,000-1,500
2 500-4 000
900-1 000
900-1 200
800-1 500
S02
removal
efficiency
(percent)
70-90a
95-98
70a
50a
98
98
98
90-95
97 5
97-99
97-99
Date
on line
Mar 1976
Sept 1974
Apr 1973
Sept 1 972
Mar 1971
Mar 1971
Jan 1971
Jan 1971
Dec 1970
Dec 1970
Aug 3 1970
July 2, 1972
July 1970
Nov 1969
Apr 1970
Nov 1970
a Sufficient to meet local code
b25 percent S03
-------
Environmental research and
development of flue gas
desulfurization programs is the
responsibility of the Industrial
Environmental Research
Laboratory in Research Triangle
Park NC. Mr. John Williams of
the Emissions/Effluent Technology
Branch is the Project Officer.
Mr. Robert J. Ferb, of Research-
Cottr.ell, is the principal
contributor. EPA wishes to thank
officials of the Rickenbacker
Air Force Base, Columbus OH, for
their cooperation and technical
assistance.
This report has been reviewed by
the Industrial Environmental
Research Laboratory, U.S.
Environmental Protection Agency,
Research Triangle Park NC, and
approved for publication. Approval
does not signify that the contents
necessarily reflect the views and
policies of the U.S. Environmental
Protection Agency, nor does
mention of trade names or
commercial products constitute
endorsement or recommendation
for use.
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