xvEPA
Design Guidelines for
an Optimum Scrubber
System
Interagency
Energy/Environment
R&D Program Report
-------
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RESEARCH AND DEVELOPMENT series. Reports m this series result from the
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Development Program. These studies relate to EPA's mission to protect the public
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EPA-600/7-79-018
January 1979
Design Guidelines for
an Optimum Scrubber System
by
E.R. Kashdan and M.B. Ranade
Research Triangle Institute
P. O. Box 12194
Research Triangle Park, North Carolina 27709
Contract No. 68-02-2612
Task No. 52
Program Element No. EHE624A
EPA Project Officer: Dale L. Harmon
Industrial Environmental Research Laboratory
Office of Energy, Minerals, and Industry
Research Triangle Park, NC 27711
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Washington, DC 20460
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ABSTRACT
The U.S. Environmental Protection Agency, Industrial Environmental
Research Laboratory, Research Triangle Park, North Carolina, is con-
sidering a demonstration of an optimum wet scrubber system for use on a
coal-fired utility boiler. The optimum wet scrubber system has such
design goals as maximum particulate collection, low power consumption,
and low maintenance. In this study, the performance and operating
experiences of existing utility scrubber systems and the state-of-the-
art in design of scrubber components are reviewed. Based on this
review, guidelines are given for the design of the optimum wet scrubber
system.
This report was submitted in fulfillment of Contract No. 68-02-2612
by Research Triangle Institute under the sponsorship of the U.S.
Environmental Protection Agency. This report covers the period April
1, 1978, to October 1, 1978, and work was completed October 20, 1978.
ii
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CONTENTS
Abstract ii
Figures iv
Tables v
Conversion Table vi
1.0 Introduction 1
1.1 Purpose of the Report 1
1.2 Scope of the Report 1
2.0 Conclusions and Recommendations 2
3.0 The Power Plant as a Source of Pollution 5
3.1 Overall Process Description 5
3.2 Coal Characterization 7
3.3 Characterization of Flue Gas from Coal-Fired
Utility Boilers 7
3.4 Legal Aspects: The New Source Performance
Standard for Particulate Matter from Coal-Fired
Utility Boilers 14
4.0 Wet Scrubber Systems 19
4.1 Scrubber Systems in Use at Power Plants 19
4.2 Estimating Power Requirements 27
4.3 Novel Scrubbers 36
5.0 Design Considerations for Wet Scrubber Systems 41
5.1 Mist Eliminators 41
5.2 Corrosion and Materials of Construction 43
5.3 Reheaters 49
5.4 Waste Disposal 55
5.5 Scaling and Other Operating Problems 53
5.6 Sampling Considerations 59
Appendix
A Flow Diagrams of Existing Particulate and Particulate-
S02 Utility Scrubber Systems A-l
B Possible Use of Condensation Scrubbers on
Coal-Fired Utility Boilers B-l
iii
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FIGURES
Number Page
3-1 Coal-fired electric generating plant with scrubbing
system 6
3-2 Nomograph for estimating uncontrolled emissions
from coal combustion 12
3-3 Flyash size distributions from several utility boilers. . . 13
4-1 Simplified flow diagram of flyash scrubbers, Four
Corners Plant (Arizona Public Service) 21
4-2 Flow diagram of combined particulate-SCL scrubber system
at Lawrence No. 4 (Kansas Power and Lignt) 23
4-3 Simplified flow diagram for the Clay Boswell Station
particulate scrubber (Minnesota Power and Light
Company) 24
4-4 Simplified Arapahoe Station scrubber flow diagram
(Colorado Public Service) 26
4-5 Correlation of scrubber outlet dust loading with
theoretical power consumption 32
4-6 Theoretical and experimental cut diameters 35
4-7 Sampling stations for scrubber installation 62
5-2 Basic Level 1 sampling and analytical scheme for
particulates and gases 66
5-3 Basic Level 1 sampling and analytical scheme for
solids, slurries and liquids 67
IV
-------
TABLES
Number Page
3-1 Example Coal Ultimate Analyses 8
3-2 Chlorine Content of Selected American Coals 9
3-3 Comparison of Flyash from Various Utility Plants 15
4-1 Condensed Summary of Particulate and Particulate-
S02 Scrubbers in the U.S 28
4-1 Condensed Summary of Particulate and Particulate-
S02 Scrubbers in the U.S. (Cont.) 29
5-1 Materials of Construction for Full-Scale Systems 44
5-1 Key to Table 5-1 45
5-2 Recommended Materials for FGD Scrubbers 46
5-3 Survey of In-Line Reheat Systems Using Steam 50
5-4 Survey of In-Line Stack Gas Reheat Systems
Using Hot Water 51
5-5 Survey of Indirect Hot Air Stack Gas
Reheat Systems 52
5-6 Survey of Direct Combustion Stack Gas Reheat
Systems 53
5-7 Survey of Scrubbing Systems With No Stack Gas
Reheat 54
5-8 Sludge Disposal Practices 57
5-9 Operating Characteristics and Problems in Scrubber
Systems 60
5-10 A Summary of Emission Characteristics Measurement
Methods 64
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CONVERSION TABLE
To Convert From
Btu/lb
scfm (60°F)
cfm
°F
ft
gal/mcf
gpm
gr/scf
hp
in.
in. W.G.
1b
psia
1 ton (short)
To
nm3/hr (0°C)
m3/hr
m3/hr
°C
m
1/m3
1 /mi n
gm/m
kW
cm
mm Hg
gm
kilopascal
metric ton
Multiply By
2.324
1.61
1.70
(°F-32)/1.8
0.305
0.134
3.79
2.29
0.746
2.54
1.87
454
6.895
0.907
vi
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1.0 INTRODUCTION
1.1 PURPOSE OF THE REPORT
The U. S. Environmental Protection Agency has been considering
lowering its New Source Performance Standard for participate emissions
from coal-fired boilers to 0.03 Ibs of particulate/million Btu. In the
case of power plants which require a scrubber system to meet S0?
emission standards, it is economically advantageous to also collect the
particulate matter with the scrubber system. But existing utility
scrubber systems either would require relatively large power consumptions
to meet the standard, or would be incapable of meeting it at all. Hence
it is desirable to design an optimum wet scrubber system which would
have maximum collection efficiency at the lowest possible energy require-
ments .
The purpose of this report then is to summarize performance data
and operating experiences of existing scrubber systems and to provide
background information for use in the design of an optimum wet scrubber
system for coal-fired utility boilers.
1.2 SCOPE OF THE REPORT
Section 2.0 presents recommendations regarding the best materials,
component designs, and scrubber type to use in the optimum wet scrubber
system.
Section 3.0 of this report indicates the tremendous variability in
emissions among power plants. Such properties as flyash size distribution,
flyash composition, and flue gas composition are considered.
Section 4.0 summarizes the scrubber types that have been used on
utility boilers. The performance of these systems is correlated with
power consumption. Two novel scrubbers are also discussed.
Section 5.0 summarizes utility operating experiences and design
considerations for various components of a scrubber system. Particulate
removal represents only one aspect of a scrubber system: such factors
as mist elimination, reheat, and corrosion must also be considered..
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2.0 CONCLUSIONS AND RECOMMENDATIONS
Design of the optimum wet scrubber system for use on coal-fired
utility boilers is a two-step process consisting of characterizing the
inlet gas stream, and then choosing the best designs for the various
scrubber components based on operating experiences and research studies.
Characterization of the inlet flue gas stream is essential, but too
frequently, neglected. The following properties should be determined.
Flyash Size Distribution. Flyash size distributions vary greatly
among power plants, depending on boiler and coal types. For a particular
scrubber, particle collection efficiency is determined by the inlet size
distribution.
There may be some merit in using a mini-scrubber rather than an
impactor to characterize the size distribution. Whereas a mini-scrubber
does not actually determine the distribution, weight percent versus
diameter, it will generally perform with the same efficiency as the
full-scale unit. Impactor data, on the other hand, are subject to
considerable error.
Flyash Composition. The chemical composition of the flyash is
important. If the flyash contains substantial quantities of alkalis,
calcium and magnesium oxides, it will scrub some SOg from the flue gas,
leading to scale formation. Flyash may also contain chlorides which can
cause stress corrosion in stainless steels.
Flue Gas Composition. The concentration of SO^ (or HgSO^) should
be determined because of its corrosiveness. Flue gas may also contain
hydrogen chloride which poses another corrosion problem.
Once the inlet gas stream has been characterized, it is necessary
to select the best scrubber components to obtain maximum performance.
The choice of components should be based on past operating experiences
and research studies. Unfortunately, operating experiences do not
always present a consistent picture, making it difficult to formulate
hard-fast rules. It should also be borne in mind that scrubber design
technology has not advanced far enough to prevent problems from arising
after construction. Hence the best overall designs are those that are
flexible enough to permit easy replacement of damaged parts.
-------
Recommendations for the various scrubber components based on this
study are as follows.
Particulate Scrubber and SOg Absorber. Current practice suggests
the use of simpler designs for both the particulate scrubber and SOg
absorber. Hence, of the conventional particulate scrubber types, a gas-
atomized scrubber, such as a venturi or rod scrubber, is recommended.
Other types are less efficient or have more operating problems. Also,
spray towers are preferable for use as the S02 absorber.
Based on a correlation of scrubber performance against energy
requirements, a pressure drop of 17±2 in. W.G. would be necessary to
meet the proposed New Source Performance Standard of 0.03 Ibs particulate/
million Btu in a conventional scrubber. When fan losses and pressure
drops across the absorber, ductwork, and mist eliminator are taken into
account, total system pressure drop may run as high as 30 in. W.G. If
this energy requirement is deemed too high, a novel particulate scrubber
should be chosen. Of the novel scrubbers tested by EPA to date, the
electrostatically augmented scrubbers appear to be the most suitable for
use on coal-fired utility boilers. Pilot units have shown good collec-
tion efficiency of flyash, coke oven battery emissions and steel mill
electric arc furnace emissions.
Mist Eliminator. Horizontal mist eliminators have greater capacities
than vertical types, but space requirements are also greater. Vertical
mist eliminators are best designed with sharp angled baffles to promote
good drainage.
Reheaters. Operating experience with reheaters militates against
the use of in-line reheaters because of combined acid and chloride
stress corrosion. The two other types of commonly used reheaters,
direct combustion and indirect hot air reheaters, are recommended and
should be designed with Interlocks to prevent heated gas from damaging
ductwork when flue gas is not present. Adequate mixing is sometimes a
problem with these types of reheaters.
To conform with present practices, English units are used throughout this
report. See Conversion Table, pg. vi.
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Materials of Construction. The most common construction material
for scrubbers is 316 stainless steel. At points of high abrasion, wear
plates, brick linings, or high grade nickel alloys are recommended. The
higher grade alloys are also recommended in areas subject to chloride
attack.
The best material for in-line reheaters appears to be the higher
grade alloys—Inconel and Hastelloy have worked well at Col strip (Montana
Power). Carbon steel and lower grade stainless steels have worked at
some plants but have failed at others.
Plastic is the best material for mist eliminators because of low
cost, light weight, and reduced corrosion potential.
Waste Disposal. Disposal of collected flyash from a particulate
scrubber is readily controlled, typically being disposed of along with
bottom ash. With a dual-function particulate-SOg scrubber system, waste
disposal is problematic because of the thixotropic nature of the sludge.
Ponding is the most common and least expensive method of disposal, but
creates a large unreelaimable area. Landfill is a better method of
disposal, but the sludge requires greater dewatering as well as stabiliza-
tion. In some site-specific cases, it may be possible to use less
common methods, such as a dry lake (arid regions) or a mine.
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3.0 THE POWER PUNT AS A SOURCE OF POLLUTION
The purpose of this report is to summarize data and provide useful
information in the design of an optimum wet scrubber system for use on a
coal-fired utility boiler. For a complete understanding of the problem,
the source of pollutant emissions must be considered as well as the
collection device. A brief description of a coal-fired electric
generating plant and its effluents follows with emphasis on aspects
relevant to a scrubber system.
3.1 OVERALL PROCESS DESCRIPTION
Modern coal-fired, electric generating plants consist of boilers,
generators, condensers, coal handling equipment, dust collection and
disposal equipment, water handling and treatment facilities, heat
recovery systems (such as economizers and air heaters), and possibly
flue gas desulfurization systems. A flow diagram of a single unit,
emphasizing sources of pollution, is shown in Figure 3-1.
Boiler types in use include cyclone, pulverized, and stoker units,
but nearly 90 percent are pulverized coal boilers (Sitig, 1977). Pul-
verized coal boilers are commonly classified as either wet bottom or dry
bottom depending on whether the slag in the furnace is molten.
Two condensing cooling systems are used by the electric utility
industry: the once-through system and the recirculatory system. In the
once-through system, all the cooling water is discharged to a heat sink,
such as a river or lake. In recirculating systems, cooling devices,
such as cooling towers or spray ponds, permit the use of recirculated
water.
As indicated in Figure 3-1, wet scrubbing systems in coal-fired
electric generating plants may be used to collect particulate matter
and/or to scrub S02 from the flue gas. In any case, a wet scrubbing
system increases both the solid and wastewater disposal problems of the
plant.
-------
TO ATMOSPHERE
t
STEAM
FUEL
COMBUS-
TION AIR
STEAM
GENERATOR
BOTTOM
ASH
f
I
I
1-
I
FLUE
GASES
FLYASH
COLLECTION
ANDSO2
SCRUBBER
BOILER
MAKEUP
Slowdown
CONDENSATE WATER
ASH
HANDLING
SYSTEM
I
Wastewater
to Ash Hand-
ling System
GENERATOR
ONCE THROUGH
COOLING WATER
RECIRCULATING COOLING
WATER
Makeup Water
COOLING
WATER
DISCHARGE TO
WATER BODY
WASTE
WATER
Blowdown
LEGEND
LIQUID FLOW
— GAS FLOW
•*~* OPTIONAL FLOW
Figure 3-1. Coal-fired electric generating plant with scrubbing system.
(Adapted from Sugarek and Sipes, 197fl.)
-------
Combustion of coal in the furnace produces both flyash (airborne)
and bottom ash (settled). Both bottom ash and collected flyash along
with sludge from a throwaway flue gas desulfurization system (where
used) are the major sources of solid waste from coal-fired utilities.
These solid wastes, which are in a slurry form, are usually sluiced to a
solid-liquid separator; the solids settle out and clarified water is
returned to the system or discharged. Ultimate disposal of the wastes
may be either in an onsite settling pond, or, after further dewatering
and treatment, in a landfill.
Water impurities build up in the boiler, cooling tower (if used),
and scrubbing system. To prevent scale formation, blowdown operations
are performed: a portion of the high impurity concentration water is
removed and replaced by low concentration feedwater. Besides these
blowdown operations, ash sluicing water and wastes from water con-
ditioning operations are the other major sources of wastewater in power
plants (Sugarek and Sipes, 1978).
3.2 COAL CHARACTERIZATION
Coal compositions vary greatly across the U. S. Generally speaking,
Western coals have lower heating values, lower sulfur content, and
higher moisture content than Eastern coals. Table 3-1 summarizes ultimate
analyses of 21 different coals.
Of particular concern to the designer of a wet scrubber system is
the chlorine content of the coal. The chlorine content of coal (in the
form of sodium and potassium chlorides) may vary from a trace amount to
as high as 0.5 percent, as shown in Table 3-2. During combustion, some of
the chlorine is converted to hydrogen chloride or other volatile chlorides.
Most of the hydrogen chloride will be absorbed in scrubbing liquor,
thereby increasing the potential for chloride stress-corrosion.
3.3 CHARACTERIZATION OF FLUE GAS FROM COAL-FIRED UTILITY BOILERS
The successful design of a wet scrubber system on a particular
coal-fired boiler requires careful consideration of the flue gas
characteristics of that boiler. The following sections are an attempt
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TABLE 3-1. EXAMPLE COAL ULTIMATE ANALYSES
oo
No.
1
2
3
4
S
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
Type
PA
PA
VA
WV
PA
PA
PA
PA
KY
OH
IL
UT
IL
MT
WY
WY
NO
Western
Eastern
C
79.84
79.45
70.00
84.21
77.52
76.74
75.42
72.66
79.94
67.39
64.24
69.83
59.88
63.48
53.89
47.10
42.46
70.*
53.13
72.7
69.9
H2
1.78
2.21
3.24
4.47
4.16
4.15
4.48
4.62
5.14
4.75
4.39
450
4.31
4.00
3.62
3.56
2.86
4.7
3.70
5.3
4.9 •
N2
0.25
0.77
0.77
1.21
1.30
1.38
1.21
1.45
1.50
1.17
1.28
1.49
1.13
1.02
1.14
0.57
0.53
1.1
1.00
1.1
1.3
S
0.71
0.60
0.62
0.74
1.68
1.68
2.20
1.82
0.70
4.00
2.70
0.90
3.20
0.43
0.30
0.55
0.40
3.4
0.39
1.0
1.1
°2
1.96
US
2.55
2.51
2.08
2.68
2.84
4.96
6.26
6.16
7.26
10.33
7.18
9.57
12.07
11.83
12.15
10.3
14.17
9.0
7.1
Ash
9.7
11.9
20.2
5.1
10.3
10.2
10.2
11.2
3.3
9.1
11.7
6.4
9.0
7.0
3.7
4.8
4.2
7.1
4.62
8.9
13.7
H20
4.5
2.5
2.0
1.0
1.3
1.5
1.5
1.5
2.5
3.6
5.8
5.2
12.2
14.1
25.0
31.0
37.0
2.7
23.
2.0
2.0
Btu/lb
12,745
12^25
11,925
14,715
13,800
13,720
13,800
13,325
14,480
12,850
11,910
12,600
11.340
11,140
9,345
8.320
7,255
12,400
13,135
12,640
Source: Leivo(1978)
Note: Coal 1-17 are from "Steam" (1966).
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TABLE 3-2. CHLORINE CONTENT OF SELECTED AMERICAN COALS
Source of Coal
StttB
Ohio
Illinois
Illinois
West Virginia
West Virginia
West Virginia
West Virginia
Pennsylvania
Pennsylvania
Indiana
Indiana
Oklahoma
Bid
Sharon
No. 6
Central Illinois
Pittsburgh
Wyoming
Upper Freeport
Sewell
Lower Freeport
Upper Kittanning
No. 4
Lower Kittanning
Henry etta
Chlorine Content, wt pet
0.01
0.39
0.35
0.07
0.11
0.17
0.27
0.14
0.13
0.06
0.16
0.46
Source: lapalucci, et al. (1969) and Smith and Gruber (1966).
-------
to summarize the physical and chemical properties of flue gas as well as
the characteristics of the dust burden that typically would be encountered
in coal-fired utility boilers.
Physical and Chemical Properties of Flue Gas
In designing a wet scrubber system, the volume of gas handled,
inlet and outlet temperatures, humidity, and S0« concentration are all
important considerations. Typical power plant flue gas volumes range
from 3000 to 4000 acfm/MW depending on coal composition, boiler heat
rate, gas temperature, and amount of excess air. Because of economies
of scale, the utility industry has tended toward larger and larger power
stations implying that scrubber systems must be capable of handling
volumes of gas as large as 4,000,000 acfm.
The temperature of the gas entering the scrubber is determined by
the efficiency of the air heater. Most steam power plants operate in
the range of 250-300°F downstream of the air heater. Exit temperatures
from the scrubber vary with sulfur content and range from 150°F below 1
percent sulfur to 180°F above 3 percent sulfur (Mcllvaine, 1974).
Because exit temperatures are low, most scrubbing systems incorporate
reheat systems which provide greater plume buoyancy and prevent corrosive
condensation.
Flue gas contains from 5 to 15 percent moisture depending on the
amount of volatile matter and on the moisture content of the coal. The
concentration of sulfur dioxide in the flue gas depends on the sulfur
content of the coal: for an average sulfur content of 2.5 percent,
there will be approximately 1500 ppm of S02 1n the flue gas (Mcllvaine,
1974). On the average, 1-3 percent of the S02 will be converted to S03.
Sulfur oxides in the flue gas make for a corrosive environment; special
alloys, coatings, and linings must be used on scrubber internals.
Characterization of Flyash
Particulate matter in utility flue gas is composed of flyash. The
characteristics of flyash (concentration, size distribution, and chemical
composition) affect both the performance and maintenance of the scrubber.
10
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Particulate Emission Quantity —
The concentration of flyash in utility flue gas depends primarily
on the following variables: (1) amount of ash in the coal, (2) method
of burning the coal, and (3) rate at which coal is burned (Sitig, 1977).
Figure 3-2 is a nomograph for estimating particulate emissions from
uncontrolled coal combustion, or equivalently, the inlet dust loading to
the scrubber. As shown in Figure 3-2, for a given coal, pulverized coal
units produce greater quantities of dust than stoker or cyclone units.
Furthermore, for a given furnace type, the flyash emission quantity will
be approximately proportional to the ash content of the coal. Inlet
dust loadings in utility flue gas may vary from 2 to 12 gr/dscf, but 4
or 5 gr/dscf is fairly typical.
In general, the size distribution of the flyash and not the emission
quantity determines the collection efficiency of a particular scrubber.
However, the dust concentration does affect the abrasiveness of the flue
gas, and hence, the potential for eroding a scrubber system. In cases
where the inlet dust loading is very heavy, some scrubbing systems use
mechanical collectors before the scrubber.
Flyash Size Distribution —
The particle collection efficiency of a scrubber is lowest for fine
particles (<3.0 microns, aerodynamic). Hence, the collection efficiency
of a particular scrubber will depend on the amount of fine particles in
the inlet dust.
Figure 3-3 shows flyash size distributions from four utility boilers,
The fine fraction varies widely, ranging from roughly 4 percent to 45
percent of the inlet dust loading, and representing about 0.05 gr/dscf
to 0.5 gr/dscf. This variation is accounted for in part by the coal and
furnace type. Lignite, for example, appears to produce a very fine
distribution. Because of the limited amount of data, however, general-
izations are difficult to make. Further, the effect of process variables
on the size distribution is not known. Suffice it to say that if the
design of the optimum wet scrubber system is to be based on impactor
measurements of the inlet flyash size distribution, then careful measure-
ments in sufficient number must be made to accurately determine the fine
particle fraction.
11
-------
REFERENCE
HEATING ASH Linc
VALUE, CONTENT,
1,OOOBtu/lb X
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
30 -
.
.
-
20 -
',
15 -
-
•^ "
•
8 -
7 •
6 •
-
5 -
.
4 -
3 -
m
2 -
_
i -
""""——
PARTICULATE EMISSIONS
lb/106 Btu { gr/dscf
A -,
— — — u _
c -
D -
F -
ft»
F -
A. CYCLONE UNITS
I 4% 02 (in flue gas)
0.3 H
0.4 -
0.5 -
0.6 -
0.8 -
1.0 -
1.5 -j
2 -
"
3 -
4
5
V
6 -
.
8 -
10 -
B. ALL STOKERS OTHER THAN
SPREADER STOKERS
C. WET BOTTOM, PULVERIZED 15 -
OR SPREADER STOKERS
WITHOUT FLYASH REIN-
JECTION
20
(Bituminous coal)
- 0.2
0.3
0.4
.
0.6
0.8
1.0
• 1.4
• 2.0
3f*
.0
• 4.0
• 5.0
• 7.0
• 80
W»H
• 10.0
D. 4RY BOTTOM PULVERIZED
E. SPREADER STOKERS WITH
FLYASH REINJECTION
F. WET BOTTOM PULVERIZED
5 ' WITH FLYASH REINJECTION
Figure 3-2. Nomograph for estimating uncontrolled emissions from coal combustion.
(Adapted from Smith and Gruber, 1966.)
12
-------
40
20
10
8
6
4
2
u
Q.
Q
1.0
0.8
0.6
0.4
0.2
0.1
LEGEND
PC: Bituminous (1.3 gr/dscf)
Lee et al. (1975)
PC: Subbituminous (ZO gr/dscf)
Accort et al. (1974)
Stoker (0.4 gr/dscf)
Hesketh (1975)
Lignite (1.0 gr/dscf)
Fox (1978)
0.05 0.5 1 2 5 10 20 40 60 80 90 95 99
Cumulative % by Weight Less Than Op
Figure 3-3. Flyash size distributions from several utility boilers
13
-------
(Figure 3-3 shows that the flyash size distribution from the stoker
unit had a large fraction of fine particles, contrary to what one would
expect from this method of firing. The distribution was indeed biased
toward the smaller sizes by the scrubbing system sampling duct which
acted like a mechanical collector (Hesketh, 1975). Nevertheless, the
sampled flue gas did contain approximately 0.1 gr/dscf below 3.0 microns).
Chemical Composition of Flyash ~
Flyash is composed primarily of silicates, oxides, sulfates, and
unburned carbon. Flyash also contains a number of trace elements (less
than 0.1 percent). Table 3-3 shows the chemical composition of flyash
from six different utilities. Studies have shown that certain trace
elements become concentrated in the submicron flyash particles. This
concentration effect arises presumably because of volatilization and
subsequent condensation of trace elements in the furnace. Those elements
which readily condense will form fine particles or be deposited on the
surfaces of small particles (Natusch, 1974).
For purposes of designing a particulate scrubber system, the calcium
oxide content of the flyash is an important consideration: the calcium
oxide will scrub a certain amount of S02 thereby forming calcium sulfate
and increasing scaling potential. Cases where the flyash was extremely
alkaline have been used to advantage in the design of a combined
particulate-S02 scrubbing system which utilized the collected flyash as
the scrubbing reagent (Grimm et al., 1978).
3.4 LEGAL ASPECTS: THE NEW SOURCE PERFORMANCE STANDARD FOR PARTICULATE
MATTER FROM COAL-FIRED UTILITY BOILERS
At this writing, the standard for particulate matter from fossil-
fuel fired steam generations (greater than 73 megawatts heat input rate)
are for emissions not to exceed: (1) 0.10 Ibs of particulate/mi11 ion
Btu, and (2) 20 percent opacity. (Code of Federal Regulations, Sec.
60.40). The proposed revised standards are for emissions not to exceed;
(1) 0.03 Ibs of particulate/mi 11 ion Btu, and (2) 10 percent opacity.
(Draft copy, "Proposed Standards of Performance for Electric Utility
Steam Generating Units," 1977). The mass emission rate, however, is the
binding constraint; that is, if a utility meets the emission standard
14
-------
TABLE 3-3. COMPARISON OF FLY ASH FROM VARIOUS UTILITY PLANTS
Compound
or
Element
Si02,%
AI203,%
Fe203,%
CaO,%
so3.%
MgO,%
Na20,%
K20,%
P2°5>%
Tj02,%
A*, ppm
Be, ppm
Cd, ppm
Cr, ppm
Cu, ppm
Hg. ppm
Mn, ppm
Ni, ppm
Pb, ppm
Se.ppm
V.ppm
Zn, ppm
B.ppm
Co, ppm
F.ppm
Plant 1
59.
27.
3.8
3.8
0.4
036
1.88
03
0.13
0.43
12.
4.3
0.5
20.
54.
0.07
267.
10.
70.
S3
90.
63.
226.
7.
140.
Plant 2
57.
20.
5.8
5.7
0.8
1.15
1.61
1.1
0.04
1.17
8.
7.
0.5
50.
128.
0.01
150.
50.
30.
73
150.
50.
200.
20.
100.
Plant3
43.
21.
5.6
17.0
1.7
2.23
1.44
0.4
0.70
1.17
15.
3.
0.5
150.
69.
0.03
150.
70.
30.
18.0
150.
71.
300.
15.
610.
Plant 4
54.
28.
3.4
3.7
0.4
1.29
0.38
1.5
1.00
0.83
6.
7.
1.0
30.
75.
0.08
100.
20.
70.
12.0
100.
103.
700.
15.
250.
Plants
NR
NR
20.4
3.2
NR
NR
NR
NR
NR
NR
8.4
8.0
6.44
206.
68.
20.0
249.
134.
32.
26.5
341.
352.
NR
6.0
624.
PlantB
42.
17.
17.3
3.5
NR
1.76
1.36
2.4
NR
1.00
110.
NR
8.0
300.
140.
0.05
298.
207.
80.
25.
440.
740.
NR
39.
NR
Source: Ray and Parker (1977)
15
-------
but fails to meet the opacity standard i t may apply for a variance
(Personal communication with John Copeland, OAQPS, EPA, RTP, North
Carolina).
It is useful to convert the emission standard to a measurable dust
concentration. The relationship between the emission standard and a
dust concentration depends on the type of coal that is burned and the
oxygen content of the flue gas. Specifically, this relationship is
given by the following equation (Code of Federal Regulations, Sec.
60.46):
E 20.9 - %02
L " ~F 2O
C = dust concentration, gr/dscf
E = emission standard, las/million Btu
F = factor representing ratio of volume of dry flue gas
to calorific value of the coal, dscf/million Btu
The value of F is taken as 10,140 dscf/million Btu for anthracite and
9820 dscf/million Btu for subbituminous and bituminous coals.
Most coal-fired, electric generating plants operate at about 3-4
percent Og (roughly 20-25 percent excess air) in the flue gas. From the
equation, then, the proposed standard of 0.03 IDS of particulate/million
Btu would be roughly equivalent to 0.017 gr/dscf. This fjgure should be
kept in mind when comparing the performance of existing scrubbing systems.
For a typical dust loading of 4.0 gr/dscf, compliance with the
proposed emission standard would require greater than 99.5 percent
overall collection efficiency. Since a significant percent of flyash (4
to 45 percent, see Figure 3-3) is below 3.0 microns, only those collection
devices with high collection efficiencies of fine particles will be able
to meet this standard.
16
-------
REFERENCES
Accortt, J. L., A. L. Plumley, and J. R. Martin. "Fine Participate
Matter Removal and S02 Absorption with a Two-State Wet Scrubber," ERA-
APT Fine Particle Scrubber Symposium, San Diego, May 1974.
Code of Federal Regulations, Title 40, Part 60, Subpart D.
Draft of Standards Support and Environmental Impact Statement Volume I:
Proposed Standards of Performance for Electric Utility Steam Generating
Units (Particulate Matter), EPA Report, Office of Air Quality Planning
and Standards, RTP, N.C./December 1977.
Ensor, D. S., B. S. Jackson, S. Calvert, C. Lake, D. V. Wallon, R. E.
Milan, K. S. Campbell, T. A. Cahill, and R. 6. Flocchini. Evaluation of a
Particulate Scrubber on a Coal-Fired Utility Boiler, NTIS Document, PB-
249-562, November 1975.
Fox, Harvey. Personal communication, Research-Cottrell, Bound Brook,
New Jersey, July 1978.
Grimm, C., J. Z. Abrams, W. W. Leffman, I. A. Raben, and C. LaMantia.
"The Colstrip Flue Gas Cleaning System," Chemical Engineering Progress,
Vol. 74, No. 2, February 1978, pp. 51-57.
Hesketh, H. E. "Pilot Plant SO, and Particulate Removal Study, Report
of Fiscal Year 1974-1975 Operations," Sponsored by Illinois Institute
for Environmental Quality and Southern Illinois University, Project No.
10.027, August 1975.
lapalucci, T. L., R. J. Demski, and D. Brenstock. "Chlorine in Coal
Combustion," Bureau of Mines, May 1969.
Lee, R. E., H. L. Crist, A. E. Riley, and K. E. MacLeod. "Concentration
and Size of Trace Metal Emissions from a Power Plant, a Steel Plant, and
a Cotton Gin," Environmental Science & Technology, Vol. 9, No. 7, July
1975, pp. 643-647.
Leivo, C. C. Flue Gas Desulfurization Systems: Design and Operating
Considerations, Volume II, Technical Report, EPA Report, EPA-600/7-78-
030b, March 1978.
Mcllvaine, R. W. The Mcllvaine Scrubber Manual, Volume II, The Mcllvaine
Company, 1974.
Natusch, D. F.f R. L. Davison, J. R. Wallace, and C. A. Evans. "Trace
Elements in Flyash," Environmental Science & Technology, Vol. 8, No.13,
December 1974, pp. 1107-1113.
17
-------
Ray, S. S., and F. G. Parker. Characterization of Ash from Coal-Fired
Power Plants, EPA Report, EPA-600/7-77-010, January 1977.
Si tig, M. Participates and Fine Dust Removal, Processes and Equipment,
Noyes Data Corporation, Park Ridge, New Jersey, 1977.
Smith, W. S., and C. W. Gruber. Atmospheric Emissions from Coal Combustion-
An Inventory Guide, NAPCA Report, No. AP-24, April 1966.
Sugarek, R. L., and T. G. Sipes. Controlling SOg Emissions from Coal-
Fired Steam-Electric Generators: Water Pollution^ Impact (Volume II.
Technical Discussion), EPA Report, EPA-600/7-78-045b, March 1978.
18
-------
4.0 WET SCRUBBER SYSTEMS
Wet scrubber systems can be classified according to their design
function, either particulate removal, SCL removal, or combined particulate-
S02 removal. For purposes of this study, only those systems designed
for particulate removal or for combined particulate-S02 removal need be
considered.
The first major application of scrubber systems to power plants
occurred in the early 1970's in the West. Here, because of the use of
low-sulfur coal, scrubber systems were designed primarily for particulate
removal. At the time, scrubbers were considered an attractive alternative
to electrostatic precipitators in light of the high resistivity coals
found in the West. However, numerous operating problems such as scaling,
plugging, and corrosion occurred because of the newness of the application.
But experience gained at these installations did advance scrubber technology.
More recently, a number of utilities have chosen double-function
scrubber systems for both particulate and S02 removal. The reason for
this decision is clearly economic: where a scrubber system is needed to
meet S02 emission standards, and a throwaway flue gas desulfurization
system (such as lime, limestone, or alkaline flyash) is used, it is less
costly to remove the dust with a particulate scrubber than with an
electrostatic precipitator (Mcllvaine and Ardell, 1978). One disadvantage
of double-function scrubber systems is that it may not be possible to
bypass one of the functions.
4.1 SCRUBBER SYSTEMS IN USE AT POWER PLANTS
Scrubber Classes
Three classes of particulate scrubbers have been used on coal-fired
utility boilers: gas-atomized, preformed spray and mobile-bed scrubbers.
Gas-atomized spray scrubbers are by far the most common. To achieve
combined S02 and particulate removal, some systems use an S02 absorber
following the particulate scrubber; other systems use a wash tray located
inside the particulate scrubber.
19
-------
A brief description of these classes of participate scrubbers
follows with examples from specific installations. Simplified flow
diagrams from a number of power plants with particulate or combined
parti oilate-S02 scrubber systems are included in Appendix A.
Gas-Atomized Spray
Gas-atomized spray scrubbers use a moving gas stream to atomize the
liquid into droplets and then accelerate the droplets. Particle collec-
tion results primarily from inertial Impaction as the gas flows around
the droplets. High particle collection efficiency requires a substantial
pressure drop with, consequently, large power consumption. Because gas
velocities are high, gas residence times are short precluding particle
collection by diffusion. As regards operational problems, plugging is
not likely, but high throat velocities can cause excessive wear.
Various geometries have been used on coal-fired utility boilers
including venturi, annular orifice, and rod bank design. Two in-
stallations have been chosen for illustration: the Four Corners Station
(Arizona Public Service), where an adjustable venturi is used to remove
particulates, and the Lawrence No. 4 Station (Kansas Power and Light),
where a rod bank particulate scrubber followed by a spray tower absorber
are used to remove both particulates and SCL.
Figure 4-1 shows a simplified flow diagram of the particulate
scrubbers at the Four Corners Station (575 MW; Arizona Public Service).
Flue gas entering the module is scrubbed by slurry sprays in the venturi
section. The gas then passes through a mist eliminator, a water-sprayed
induced-draft fan, a second mist eliminator and reheater, and finally
exits the stack. A portion of the scrubber liquor is recycled directly
to the scrubber and (internal) mist eliminator. The other portion is
bled off to the distribution tank and thickener where suspended solids
settle out. Makeup water for the scrubber slurry comes from the liquid
transfer tank which contains lime-treated thickener overflow. Solid
wastes are pumped to an ash pond. The pond is periodically dredged and
wastes ultimately disposed of in a mine. Although primarily designed
for particulate removal, the scrubber does remove some SC^ (35-40 per-
cent with lime addition, LaMantia et a!., 1977).
20
-------
FLUE GAS FROM
AIR HEATERS
MIST ELIMINATORS
DISTRIBUTION
TANK
LIME
1
MAKEUP
WATER
LIQUID TRANSFER TANK
SLUDGE IS DREDGED AND
RETURNED TO THE MINE
Figure 4rl. Simplified flow diagram of flyash scrubbers, Four Corners Plant
(Arizona Public Service)
Source: LaMantia et al., 1977.
21
-------
Figure 4-2 depicts a flow diagram of the combined particulate-SO«
scrubbing system at Lawrence No. 4 Station (125 MW; Kansas Power and
Light). Flyash is collected in the rod scrubber section; S02 is removed
in the spray tower which uses limestone as a reagent. The gas then
passes through mist eliminators and reheaters before exiting the stack.
Slurry from the spray tower reaction tank is bled to the rod scrubber
collection tank. Effluent from the collection tank is then pumped to a
thickener and ultimately, a settling pond. Thickener overflow along
with water from the pond provide makeup water for the scrubber system.
Preformed Spray
A preformed spray scrubber collects particles or gases on liquid
droplets which have been atomized by spray nozzles. The atomized spray
is directed into a chamber through which the inlet gas passes. Horizontal
and vertical gas flowpaths have been used; spray entry can be cocurrent,
countercurrent, or crossflow to the gas.
Inertial impaction is the principal collection mechanism. Residence
times, especially with high-pressure sprays, are sufficiently short so
as to preclude collection by diffusion. Efficiency is a function of
droplet size, gas velocity, liquid-to-gas ratio, and droplet trajectories.
The properties of the droplets are determined by the configuration of
the nozzles, type of liquid, and pressure in the nozzle. Liquid-to-gas
ratios for preformed spray scrubbers are generally higher than those for
gas-atomized spray scrubbers causing heavy liquid entrainment. The pres-
sure drop of the gas is low because atomization of the liquid is done by
the nozzles and not by the gas. Plugging of the nozzles is the major
operating problem with this type of scrubber.
The only applications of preformed spray scrubbers to power plants
are at the Clay Boswell (360 MW) and Syl Laskin Stations (116 MW)
(Minnesota Power and Light Co.) where they are used for particulate
removal. Figure 4-3 shows a flow diagram of the Clay Boswell scrubber.
Flue gas passes cocurrently through a quench spray and high
pressure spray. The high pressure spray is atomized when the liquid
impinges on vertical rod baffles, the resulting turbulence causing the
22
-------
ro
CO
ONE OP TWO MODULES
BYPASS
ROD
SCRUB-
BER
ADDI-
TIVE
—*r
**-
/W-O
«
GAS REHEATER
SPRAY
TOWER
ABSORBER
ROD SECTION
&- BSS^
Mist
BLOWERS I>D' FAN STACK | MAKEUP
WATER
KANSAS POWER & LIGHT CO.
LAWRENCE No. 4 AQCS CON-
VERSION CE-RS/ST
POND RETURN
»»»)>»)»»*
//xxxxx/yxx/xx//**
I* n /* *
Sprays
iJ>
ADDITIVE
Mixer
\
t-G
Collection
JL
Strainer
REACTION
BLOWERS
«-*
To Strainer
T>-
ir
Rccirc.
Tank
Recirc.
Pump
Washers^ Wash
Pump
MAKEUP WATER
EFFLUENT BLEED
I SPRAY EFFLUENT BLEED
I PUMPS
PUMP
ABSBl
I
1
\
EED
— p* —
/
D
TANK
0 STRAINER
"
1
,
^
opr
Pu
\ *
* *
ay
mp
t
-fc
i
\
j T
F
^T-
RAKE THICKENER
WEIR
OVERFLOW
| |
THICKENER
UNDERFLOW
PUMPS
TO
SETTLING
POND
Figure 4-2. Flow diagram of combined particulate-SOo scrubber system at Lawrence No. 4
(Kansas Power and Light).
Source: Green and Martin, 1977.
-------
MAKEUP WATER
TO STACK
WET ID FANS
(2)
POST HUMIDIFICAT1ON\
SPRAY )
ELBAIR
\xv
J^^. rv» ^
SCRUBBER ] II f]
SEAL TANK
MAKEUP WATER
MIST ELIMINATOR
PUNCH PLATE
BOTTOM ASH POND
Figure 4-3. Simplified Flow Diagram for the Clay Boswell
Station Particulate Scrubber (Minnesota Power
and Light Company).
Source: LaMantia etal., 1977.
24
-------
scrubbing. The gas then passes through a bank of vertical chevron
demisters, a post humidification spray, and then exits the stack.
Scrubbing slurry is supplied to the quench spray and high pressure spray
nozzles. Fresh makeup water is used for the post humidification spray.
Sprayed liquid drains to the seal tank at the base of the scrubber.
Slurry from the seal tank is pumped to two clarifiers. Overflow from
the clarifiers along with makeup water is recycled to the sprays.
Clarifier underflow is pumped to a flyash pond.
Moving-Bed
Moving-bed scrubbers provide a region of mobile packing, such as
plastic or marble spheres, where gas and liquid mix. Gas passes upward
through the bed, while liquid is sprayed up from the bottom or passed
down from the top. Particle collection is due to inertial impaction on
atomized liquid and on mobile elements. Energy requirements are relatively
low, typically a pressure drop of 4 in. W.G. per stage. Moving-bed
scrubbers have excellent absorption capabilities and have been used as
the SOg absorber following the venturi particulate scrubber at Cholla
(Arizona Public Service) and Green River (Kentucky Utilities). Ball
wear and wear of the supporting grids are the major operating problems
with these scrubbers. At present, mobile-bed scrubbers are used for
particulate removal at the Valmont, Arapahoe, and Cherokee Stations
(Colorado Public Service) and at the EPA test facility at Shawnee (TVA).
Figure 4-4 shows a flow diagram of the scrubber at the Arapahoe
Station which is typical of the scrubbers used by the Colorado Public
Service. Flue gas entering at the base of the scrubber is presaturated
before passing upward through the mobile-bed consisting of hollow
plastic spheres. The gas is scrubbed by a countercurrent flow of
liquor. Before exiting the stack, the gas passes through a chevron mist
eliminator and steam coil reheater. Scrubber slurry supplied to the top
of the tower and makeup water supplied to the demisters drain into the
base of the tower. Most of the sump liquor is recycled to the mobile-
bed; the rest is blown down to a slurry surge tank. Slurry from the
tank is pumped to a clarifier. Clarifier overflow is discharged; under-
flow is pumped to sludge ponds. Ultimate disposal of sludge and ash is
in a landfill.
25
-------
FLUE GAS TO REHEATER
PING
PONG
BALLS
FLUE GAS FROM
ELECTROSTATIC
PRECIPITATOR
CLEAR
EFFLUENT DISCHARGE
MAKEUP WATER
MIST ELIMINATOR
ut *
^
ff^^x.
1
' 1
' \
.« L"
CO
t
>^
_JZt i~\\
FLY ASH AND
BOTTOM ASH
CONTROL)
Figure 4-4. Simplified Arapahoe Station Scrubber Flow Diagram
(Colorado Public Service).
Source: LaMantia et al., 1977.
26
-------
Summary of Existing Scrubber Systems in the U.S.
Table 4-1 is a summary of the design and operating parameters of
the various particulate and particulate-S02 scrubber systems in use at
coal-fired power plants across the U. S. As indicated previously, gas-
atomized scrubbers, and particularly, Venturis, are the most widely used
scrubber design for particulate removal.
The newer installations generally have better particulate removal
capabilities, greater availabilities (defined as the fraction of a year
that the scrubber appeared to be in operable condition), and treat
larger volumes of flue gas. Landfill and ponding are the predominant
methods of waste disposal. Few of the existing scrubber systems are now
meeting the proposed New Source Performance Standard for particulates,
0.03 Ib of particulate/mi 11 ion Btu, or about 0.017 gr/dscf. Only those
systems operating with relatively large pressure drops, greater than
15.0 in. W.G., appear to be able to meet the Standard.
4.2 ESTIMATING POWER REQUIREMENTS
Estimating the power requirements of a particulate wet scrubber is
a two-step process: first a determination of the size distribution of
the dust is made; and second, an estimate is made of the power require-
ments for the scrubber which are necessary to meet emission standards.
Two approaches, the contact-power rule and the cut-power rule, have been
developed and are discussed below.
Contacting-Power Rule
The contacting-power rule, developed by Semrau (1977), represents a
completely empirical approach to the design of particulate scrubbers.
The fundamental assumption is that, for a given dust, scrubber performance
depends only on the power consumed in gas-liquid contacting, regardless
of scrubber size or geometry.
Power consumed in gas-liquid contacting depends on the manner in
which the energy is introduced. For gas-atomized scrubbers, where the
energy comes from the gas stream, theoretical power consumption is given
by
PG = 0.158 AP, hp/1000 acfm (1)
where AP = pressure loss across unit in inches W.G.
27
-------
TABLE 4.1. CONDENSED SUMMARY OF PARTICULATE AND PARTICIPATE S02 SCRUBBERS IN THE U.S.
PARTICULATE-S02 SCRUBBERS
ro
oo
UlUly
SMkM
Onion and OpttMIni PWMWIMI:
Sun-up din
RMfMI
Vmdoi
Oraon
Numtarol equipped boiten
Numbtr ol Ktubbor modirln
Innrilod Brabbif cojutity. MW
CoMoctot pnctditif Ktubbtf
Htti.il?
BypMrt
AM»olcott.«i«i/kWh
Cool hoMino. nkii. Blu/lb
Sulhir In cool, pet
A* In cod. pet
Cofcium oiidi In nh. pel.
UG.pl/IOOOicl
aP portkuUtt cnibbii. In. W.G.
iPiYlltm.ln W.G.
Into! dun lo«lln|.|./d*l
Intel SO;, ppm
Outftl dint lotdlnf. grMtcl
SO; nrnovil. pet
WMidhpoBl
AMMItty
Rttonnc*
POMWCO.
Bract M*n$tMd
No. 1. 2
4/76
Ikn.
Chrmfco
Vinnin
2
12
1660
Vn
No
4J5
11400
47
12.6
NA
20
20
NA
6-6.6
2.200 2.600
0.007 0.017
BnUdnlon)
Lmdlill
97+
1.2.1
KMMcky
Ulilfltoi
GmnRhrti
Simon
9/76
Itoil
AAF
Vmluti/
Movfc|Btd
1
1
IBO
Mich
Yn
Yn
24
10400
1.7
11.4
NA
395
7
NA
2.2
2700
99KJdniinl
90
Pond
164
1.4
PoMiCo.
Cobliip
No 1.2
9/75
nynh/Unw
CEA
Vmiuri/
WuhTiiy
2
6
720
•
Yn
No
0.26
B.B40
OB
B
22
(Slot vtnlun
IB lot iptiy
17
25.6
/'
BOO
0.018
80
Pond
BO*
1.5.6
TMMUM
Vdln Aotkority
ShHnwf
IDA
ITnt locHily)
4/72
linw/llmntoni
UOP
MmlotBod
1
1
10
Vn
No
10,6001m.)
cool lypi votiobta
17
8 16
1.6-86
2.500 4400
0.016 0.090
60 99
Pond
7.8.9
VokrAMlwitt
ShOMMJt
IOB
ITm iKHiiyl
4/72
llmi/IUnniixM
Chmlco
Vinluh/
Spray TOMI
1
1
10
Yn
No
lO.SOOIml
cool typi nrubli
21 lor vtnlun
84 lot loMt
3 16
1.5-8.5
2.500 4400
0.001 • 0.050
80 99
Pond
7.8.9
Aril MO Pi Mk
StntoCo.
ChalllSlMlon
12/71
llmnlom
RC
Vmtutl/
Spray Towtr
1
2
116
Yn
Vn
• 2.2
10,400
as
11.6
3.5
10 lot vtntuti
49 lot lOMt
15
23.5
2.0
420
0.016
69
Pond
95
1. 10, 11
Nirdwra
iMnPwjw
Shttbuim
No 1. 2
1/78
llmnlom
CE
Vinluri/
HovUHjB«d
2
24
1400
Yn
No
0.4
8,100
0.8
B
NA
Ulomnturi
10 lot bod
11
22
2.0 4.0
400 BOO
0.015 0.044
60-55
Pond
90
2. 3, 12
KonuClly
PoMrllloki
LiCyom
No. 1
2/73
limntom
BSW
ViniutV
StmTtiy
1
8
870
Yn
No
1.4
9.000 9.700
56
20 10
6.9
12 lot vtnlun
26.6 lot lOMtt
7
22
66
4.500
0.074
80
Pond
NA
2. 1. 11
K*M«
PownlLlott
LlWTtflCt
No. 4
\m
llmnlom
CE
Rod Sctubbti/
Spray TOMI
1
2
125
Yn
Yn
NA
10.000
05
96
11.2
20 lot tctubbn
10 lot lOMt
9
24
41
425
004
BO
Pond
NA
2. 3. 14
•MOOI
PONOlCO.
Rtid Gvdfif r
No. 1.2.3
3/74
wdiorii
CEA
Vntun/
WdhTray
2
2
330
Mich
Yn
Yn
NA
11.800
06
9.4
IB
12.5
15
20
OJ 0.6
300
042
85
Pond
90
II
-------
TABLE 4.1 (coot) CONDENSED SUMMARY OF PARTICULATE AND PARTICULATE-SOj SCRUBBERS IN THE U.S.
PARTICULATE SCRUBBERS
ro
vo
UWtv
Sution
Onjfn md Opmiini Panmtttn:
Sun-up din
Vmdor
Onion
Numbtf ol tqulppad boVan
Numbtr ol Knibbw modidn
Instattad Knibbtr capacity UW
Colloclor prwtdlnf crukbtr
RthNtf
Bypaart
Annual COM. mUliAWh
CotlhMtbi|vaUii,Btu/lb
Sulfur In coil, pet
Arfiln coal, pet
dkkirnoildilnHli.pct
UO, »il/1,000 Kl
A P panluilata tcnibbtr. In. W.O.
iPiyttim.ln.W.G.
Nil dun loading, (t/dnl
Inlil SOj, ppm
OuUttduitk>»dlnt,tr/d«l
SOj ramoval. pet.
Wwidbjwul
AvtilabUiry
Rthrmct
Artuu
htlfe Santo
Four Coman
12/71
ChMiico
Vtnturi
3
6
SIR
Of 0
Vn
No
NA
8.200
0.76
22
6.3
8.6
18
28
12
660
0.01 • 0.02
30-40
Him
100
1.11
nClfK rWMf
aUkjkl
Oava Johniion
4/72
Ctwmlco
Vinturi
1
3
)3n
JJU
No
No
NA
7,430
0.6
12
20
1JJ
10
16
4
600
0.04
40
LmdNI
NA
11
Vdmont
11/71
UOP
TCA
1
2
Mtch
Yn
Yn
NA
10.800
0.8
9.0
10
60
10-16
NA
0.8
600
0.02(min.)'
40
lindhll
76
11.16
NUkStnkt
CMiMvrfCtitndt
Chtroktt
11/72-7/74
UOP
TCA
3
9
660
MKh/ESP
Yn
Yn
NA
10.100
0.6
12
4
60
10-16
NA
0.4 -as
600
O-Oflmln.)1
20
Landfill
70-90
11,16
Anpthoi
9/73
UOP
TCA
1
1
Mich/ESP
Yn
Yn
NA
10.100
0.6
12
4
60
10-16
NA
0.8
600
0.02(mln.)1
20
landfill
40-70
11.16
PMtfljlkjIrt
CHyBoKMll
6/73
Knbi
Pnfomud Spray
1
1
360
Na
No
NA
8.400
0.9
9
11
6
2.6
4
1.26
1.126
0.03
40
Pond
100
11.16
Syllatkln
6/71
Krabt
Pnlaraiad Spray
2
2
116
No
No
NA
8.400
0.9
9
11
6
2.6
4
2
1.126
0.04-0.046
40
Pond
100
11.16
Uttrfo
1Mb and Clark
12/76
R-C
Vtnluri
1
1
66
MKh
No
No
NA
6.460
0.6
8.6
NA
11
13
14.6
1
620
0.03
60
Pond
NA
11.17,16
'9nt ptrfomnnet ol unibbir it nlahui pmwn drop (16).
-------
REFERENCES FOR TABLE 4-1.
1. Private communication, P. Winkler, Chemico Air Pollution Control
Company.
2. T. Devitt eta!., 1978 (EPA-600/7-78-032b).
3. B. Laseke, 1978 (EPA-600/7-78-051a).
4. B. Laseke, 1978 (EPA-600/7-78-048e).
5. C. Grimm et al., 1978.
6. J. McCain, 1977 (EPA-600/7-78-094).
7. R. Rhudy and H. Head, 1977.
8. Bechtel Progress Report, June 1977.
9. Private communication, 6. Dallabetta, Bechtel Corporation.
10. B. Laseke, 1978 (EPA-600/7-78-048a).
11. C. LaMantia et a!., 1977 (EPRI FP-595).
12. R. Kruger and M. Dinville, 1977.
13. B. Laseke, 1978 (EPA-600/7-78-048d).
14. K. Green and J. Martin, 1977.
15. Private communication, B. Pearson, Public Service Company of Colorado.
16; Private communication, D. VanTassel, Minnesota Power and Light.
17. Private communication, D. Sadowsky, Montana-Dakota Utilities.
18. Private communication, M. Richmond and H. Fox, Research-Cottrel1,
Inc.
30
-------
For preformed spray scrubbers, where the energy comes from the liquid
stream, theoretical power consumption is given by
PL = 0.583 APL QL/QG, hp/1000 acfm (2)
2
where AP. = pressure loss in liquid, Ib/in
Q, = liquid flow rate, gal /mi n
3
Qg = gas flow rate, ft /min
When scrubber overall particle collection efficiency for a constant
inlet dust is measured over a range of power consumptions, it is often
found that the "scrubber performance curve" plots as a straight line on
log-log paper, implying a power relationship given by
NT = rf/
where NT is the dimensionless transfer unit, related to efficiency (n)
by NT = In (I/O -n)) and PT is given by
The empirical constants, a and y, depend only on the characteristics of
the particulate, but are little affected by scrubber size or geometry.
The contacting-power rule finds a useful application in the design
of particulate scrubbers: since the performance curve is independent
of scrubber size, mini -scrubbers are first used on a particular dust to
determine the pressure drop necessary to meet emission standards. The
full-scale scrubber is then designed by scaling up from the mini-
scrubber results.
The contacting-power rule further implies that scrubbers operated
at higher power consumptions will be more efficient particulate
collectors— provided the increased energy results in better gas-liquid
contact. Figure 4-5, derived from Table 4-1, is a log-log plot of
operating points, outlet dust loading at a given power consumption,
for various power plant scrubber systems. (Theoretical power con-
sumption was determined by Equations 1 and 2. Plotting outlet dust
loading against power consumption is essentially equivalent to the
31
-------
0.08
0.07
0.06
0.05
1 0.04
*
C9
5
3 0.03
O KCPL
MPL <\ O O
(SL)KPlVPL NSP
0.02
O
MPL
(CB)
MDU
KCPL • KANSAS CITY POWER AND LIGHT
MPL • MINNESOTA POWER AND LIGHT
SL • SYL LASKIN
CB • CLAY BOSWELL
KPL - KANSAS POWER AND LIGHT
PPL - PACIFIC POWER AND LIGHT
NSP • NORTHERN STATES POWER
MDU - MONTANA-DAKOTA UTILITIES
NPC • NEVADA POWER COMPANY
PSCC • PUBLIC SERVICE COMPANY OF COLORADO
APS • ARIZONA PUBLIC SERVICE
FC • FOUR CORNERS
CH • CHOLLA
PPC - PENNSYLVANIA POWER COMPANY
Y = 0.068X"1-41
(r2 = 0.86)
PSCC, NPC
MPC
\
O
APS
(CH) APS\0
(FC)
2 3 4 56789 10
THEORETICAL POWER CONSUMPTION, hp/1,000 acfm
Figure 4-5. Correlation of scrubber outlet dust loading with
theoretical power consumption.
32
-------
procedure used in the contacting-power rule, assuming that flyash size
distributions are the same for the various utility boilers.) As shown,
the operating points can be readily fitted to a straight line, implying
a power-function relationship between scrubber overall collection
efficiency and power consumption. The least-squares correlation was
Y = 0.068 X"1'41, r2 = 0.86. The good fit is quite remarkable given the
variety of coals, furnaces, process variables, and inlet particle size
distributions among the plants. Based on this correlation, to achieve
the proposed New Source Performance Standard for particulates of about
0.017 gr/dscf, approximately 2.7±0.3 hp/1000 acfm (95 percent confidence
limits) theoretical power consumption, or equivalently, 17±2 in. W.G.
pressure drop is required. Although this value is only approximate, it
does underscore the fact that conventional scrubbers require a large
power consumption to meet the proposed New Source Performance Standard.
Further, this figure represents only the theoretical power consumption
across the particulate scrubber. The actual system pressure drop will
include fan losses, and losses across the absorber, mist eliminator, and
ductwork.
Cut-Power Rule
Whereas the contacting power rule provides an empirical approach to
the design of particulate scrubbers, it lacks generality in that it is
specific to a particular dust. A more general and theoretical approach
was taken by Calvert (1972, 1977) who related scrubber fractional
efficiency to power consumption.
The cut-power rule uses the quantity called the "cut diameter,"
the diameter at which the collection efficiency of the scrubber is 50
percent. Most scrubbers that collect particles by inertial impaction
perform in accordance with the following equation:
P = exp(-A dpB) (3)
where P = particle penetration
A,B = dimension!ess constants
d = aerodynamic particle diameter
33
-------
Assuming a log-normal distribution, Equation 3 can be integrated,
yielding a plot of overall penetration against the ratio of required cut
diameter to mass median diameter. Hence, by knowing the inlet particle
size distribution and the efficiency needed to meet emission standards,
one can determine the required cut diameter. For example, for a "typical"
flyash particle size distribution of d = 17 urn, a = 4, to achieve 99%
collection efficiency would require a cut diameter of approximately 0.6
um. To determine which scrubber types can meet this cut diameter,
Calvert developed theoretical impaction models of scrubber performance
(cut diameter) versus power consumption for various scrubber types. To
achieve a cut diameter of 0.6 ym, a venturi scrubber would require a
theoretical pressure drop of 15 in. W.6., agreeing well with the figure
of 17±2 in. W.G. determined from the empirical correlation above.
Figure 4-6 is a plot of theoretical venturi scrubber performance
curves and actual performance points for scrubbers operating on coal-
fired boilers (based on published data). The performance of the actual
scrubbers suggests that, as expected, lower cut diameters (higher
collection efficiencies) are achieved at the expense of greater power
consumption. Further, the performance of the venturi scrubbers agrees
well with the theoretically predicted performance for wettable particles.
(The venturi scrubber performance model is evaluated for different
values of the dimensionless factor f. The value f = 0.50 corresponds to
wettable particles, whereas f = 0.25 corresponds to nonwettable particles
(Calvert, 1977).)
The case of the moving-bed scrubber at Cherokee Station deserves
special mention. As shown in Figure 4-6, independent measurements at
similar pressure drops resulted in radically different values for the
cut diameter. In this regard, Ensor et al., (1975) reported highly
variable outlet particle concentrations which did not correlate with
pressure drop, suggesting the presence of reentrained solids from the
mist eliminator. The authors concluded that the "evidence... weighs
against one considering the agreement between predicted and experimental
cut diameters to be anything more than coincidence (Ensor et al.,
1975)." It might also be noted that a valid model for the performance
of moving-bed scrubbers has not yet been developed (Calvert, 1978).
34
-------
5.0
4.0
3.0
2.0
Ul
0 0.8
CJ
w £2 0-6
01 —
0.4
0.2
1a, 1b VENTURI SCRUBBERS
(f = 0.25, f = 0.50)
A", A TCA [CHEROKEE, 1075,1074]
Q CHEMICO VENTURI
CEA VENTURI [COLSTRIP]
VENTURI
TCA
TCA [MO HAVE]
ITVA]
1.0 2.0 3.0
POWER, hp/1,000 acfm
4.0 5.0 6.07.0
10 15 20 25 30 40
PRESSURE DROP, in. W.G.
8 10 20 40
PRESSURE DROP, cm. W.G.
60 80 100
200
Figure 4-6. Theoretical and experimental cut diameters.
-------
In general, the limitations of the techniques for measuring flyash
size distributions (see Section 5.6) undermine the usefulness of the cut-
power approach.
4.3 NOVEL SCRUBBERS
Conventional scrubbers collect particles primarily by inertia!
impaction. However, the collection efficiency of conventional scrubbers
decreases significantly for fine particles, resulting in the need for
relatively large power consumptions to remove the fine particles. As
has been shown, flyash contains a substantial fraction of fine particles,
with the result that scrubber systems operating on utility boilers may
require pressure drops as high as 30 1n. W.G. This pressure drop
represents a large power loss to a utility.
In 1973, EPA initiated a novel device evaluation program. The
purpose of the program was to identify, evaluate, and where necessary,
develop devices which would have better collection efficiencies of fine
particles. The results of this program indicate that the most efficient
novel scrubbers are those that utilize additional collection mechanisms
other than just inertial impaction.
The most promising of these novel devices are electrostatically
augmented scrubbers and condensation scrubbers. The former increases
*
particle collection by increasing the electrostatic attraction between
particles and droplets. The latter increases particle collection by
growing particles into a size range which is easier to collect and also,
by increasing diffusiophoretic forces. Other novel scrubbers, which
either consume large amounts of power or require the use of waste heat,
are deemed inappropriate for use on utility boilers and are not discussed
below.
Condensation Scrubbers
The use of condensing water to improve scrubber particle collection
efficiency is not a new idea, but until EPA sponsored research on the
subject, only small-scale laboratory studies had been done. Calvert
1973, 1974, 1975 and 1977) developed models for particle collection in
condensation scrubbers and attempted to verify those models in bench- and
pilot-scale studies.
36
-------
Calvert's studies indicate that collection of fine particles in a
condensation scrubber depends strongly on the inlet dust concentration
and the flue gas enthalpy. In assessing the possible uses of conden-
sation scrubbing, Calvert (1975) gives an approximate minimum enthalpy
of 100 kcal/kg (about 180 Btu/lb) which would be necessary for high
efficiency particle removal in a condensation scrubber. Flue gas from
utility boilers typically contain 5 to 15 percent moisture (see Section
3.3). Even at 15 percent moisture, the enthalpy would only be about 180
Btu/lb, indicating that condensation scrubbers would have only marginal
application to power plants (see Appendix B for a more detailed evaluation)
Furthermore, the collection efficiency of condensation scrubbers decreases
with increasing dust concentration because there is less water available
to condense on each particle. Theoretical calculations by Calvert (APT,
1974) have shown, for example, that for a three-plate condensation
scrubber operating at a condensation ratio of 0.1 g vapor condensed/g
dry air, particle collection efficiency for 0.75 urn (aerodynamic)
particles decreased from 100 percent at a concentration of 2 x 10
particles/cm (about 0.01 gr/scf, assuming a density of 2.0 gm/cm ) to
about 60 percent at a concentration of 10 particles/cm (about 0.6
gr/scf). Insofar as utility flue gas may contain dust loadings as high
as 8 gr/scf, condensation scrubbing does not seem very feasible.
In short, whereas it may be possible to incorporate some conden-
sation effects in scrubbers operating on utility flue gas, a con-
densation scrubber per se would not be recommended.
Electrostatically Augmented Scruobers
A number of novel devices have been developed recently which use
electrostatic forces to enhance particle collection. The scrubber types
using electrostatic augmentation vary considerably in design, but can be
classified according to whether the particles and/or the water is charged,
and whether an external electric field is applied.
37
-------
Two of the most tested electrostatically augmented scrubbers are
the TRW Charged Droplet Scrubber and the UW Electrostatic Scrubber. The
TRW scrubber uses charged droplets and an externally applied electric
field to collect particles. It has been used successfully on emissions
from a coke oven battery. The UW scrubber charges both the water drop-
lets and the particles (charged to opposite polarity); a pilot scale
unit has been successfully used on emissions from a power plant. Both
of these devices have shown high efficiencies (over 90 percent) for
submicron particles at substantially less power consumption than would
be required for a conventional venturi.
Whereas the performance of these small scale units has been en-
couraging, several points must be borne in mind before a full-scale unit
is planned for use on a power plant. First, utility flue gas contains a
heavy dust loading, as large as 8 gr/dscf, and even greater. (The UW
scrubber, although showing good collection efficiency of flyash from a
power plant, because of the sampling arrangement, had extremely low
inlet dust loadings of 0.5 gr/dscf or less (Pilat and Raemhild, 1978).)
Heavy dust loading, for example, would probably necessitate greater
charging in a UW-type scrubber. Secondly, most utilities handle large
volumes of gas compared to the volumes handled by these small units.
i
The same cost savings may not be realized in a scaled-up version of
these smaller units; the economics would have to be worked out on an
individual basis. Finally, any novel scrubber may suffer the same
corrosion problems that conventional scrubbers have experienced at power
plants. Section 5 of this report provides a summary of operating
experience of conventional scrubbers at power plants, and hence, will be
useful in the design of any novel scrubber.
38
-------
REFERENCES
Bechtel Progress Report, "EPA Alkali Scrubbing Test Facility TVA Shawnee
Power Plant," June 1977.
Calvert, S., J. Goldshmid, D. Leith, and D. Methta. Scrubber Handbook,
NTIS Document, PB 213-016, July 1972.
Calvert, S., J. Goldshmid, D. Leith, and N. Jhaveri. Feasibility of Flux
Force/Condensation Scrubbing for Fine Particulate Collection, EPA Report,
EPA-650/2-73-036, October 1973.
Calvert, S., and N. Jhaveri. "Flux-Force Condensation Scrubbing," in
EPA Fine Particle Scrubber Symposium, EPA Report, EPA-650/2-74-112,
October 1974.
Calvert, S., N. Jhaveri, and T. Huisking. Study of Flux Force/Condensation
Scrubbing of Fine Particles. EPA Report, EPA-600/2-75-018, August 1975.
Calvert, S. "How to Choose a Particulate Scrubber," Chemical Engineering,
Vol. 18, No. 84, August 29, 1977, pp. 54-68.
Calvert, S., and S. Gandhi. Fine Particle Collection by a Flux-Force
Condensation Scrubber: Pilot Demonstration, EPA-600/2-77-238, December
1977.
Calvert, S. "Field Evaluation of Fine Particle Scrubbers," The Chemical
Engineer, June 1978, pp. 485-490.
Devitt, T., R. Gerstle, L. Gibbs, S. Hartman, and N. Klier. Flue Gas
Desulfurization System Capabilities for Coal-Fired Steam Generators,
Volume II Technical Report, EPA Report, EPA-600/7-78-032b, March 1978.
Ensor, D. et al. Evaluation of a Particulate Scrubber on a Coal-Fired
Utility Boiler, NTIS Document, PB 249-562, November 1975.
Green, K., and J. Martin. "Conversion of the Lawrence No.4 Flue Gas
Desulfurization System," Presented at the Symposium on Flue Gas Desulfurization,
Sponsored by the U. S. Environmental Protection Agency, Hollywood,
Florida, November 1977.
Grimm, C. et al. "The Col strip Flue Gas Cleaning System," Chemical
Engineering Progress, Vol. 74, No.2, February 1978, pp. 51-57.
Kruger, R., and M. Dinville. "Northern States Power Company Sherburne
County Generating Plant Limestone Scrubber Experience," Presented at the
Utilities Representative Conference on Wet Scrubbing, Las Vegas, Nevada,
February 1977.
39
-------
LaMantia, C. et al. Application of Scrubbing Systems to Low Sulfur/
Alkaline Ash Coals, EPRI Report, EPRI FP-595, December 1977.
Laseke, B. Survey of Flue Gas Desulfurization Systems: Cholla Station;
Arizona Public Service Company, EPA Report, EPA-600/7-78-048a, March
T97S:
Laseke, B. Survey of Flue Gas Desulfurization Systems: LaCygne Station,
Kansas City Power and Light Company, EPA Report, EPA-600/7-78-048d,
March 1978.
Laseke, B. Survey of Flue Gas Desulfurization Systems: Green River
Station. Kentucky Utilities. EPA Report, EPA-600/7-78-048e, March 1978.
Laseke, B. EPA Utility Flue Gas Desulfurization Survey: December
1977-January 1978, EPA Report, EPA-600/7-78-051a, March 1978.
McCain, J. D. CEA Variable-Throat Venturi Scrubber Evaluation, EPA
Report, EPA-600/7-78-094, June 1978.
Mcllvaine, R. W., and M. Ardell. Research and Development and Cost Pro-
jections for Air Pollution Control Equipment, EPA Report, EPA-600/7-78-
092, June 1978.
Pilat, M., and 6. Raemhild. "University of Washington Electrostatic
Scrubber Evaluation at the Central Coal-Fired Power Plant," Draft EPA
Report, July 1978.
Rhudy, R., and H. Head. "Results of EPA Flue Gas Characterization
Testing at the EPA Alkali Wet-Scrubbing Test Facility," Presented at the
2nd Fine Particles Symposium, New Orleans, Louisiana, May 1977.
Semrau, K. "Practical Process Design of Particulate Scrubbers," Chemical
Engineering, Vol. 84, No. 20, September 26, 1977.
Szabo, M. F., and R. W. Gerstle. Operation and Maintenance of Particulate
Control Devices on Coal-Fired Utility Boilers, EPA Report, EPA-600/2-77-
129, July 1977.
40
-------
5.0 DESIGN CONSIDERATIONS FOR WET SCRUBBER SYSTEMS
Although scrubber technology has advanced considerably since the
first applications of scrubbers to coal-fired boilers, much of this
advancement has taken the form of ad hoc solutions to operating problems
at various installations. Nevertheless, operating experience is not
without interest since it seems to militate against certain bad designs
or materials and to favor the use of particular operating or maintenance
procedures.
In the following section, various scrubber topics, such as mist
elimination or reheat, are discussed. The approach is to first summarize
the state-of-the-art, including both utility experience and any theoretical
treatments, and then to list sources of information on the topic. It is
hoped that this approach will provide a useful base from which to design
various components of the optimum wet scrubber system.
5.1 MIST ELIMINATORS
General Considerations
Mist elimination is a requisite for every scrubber system. Mist
eliminators remove scrubber-liquid droplets that are entrained in the
flue gas and return the liquid to the scrubber. Poor mist elimination,
an all too common problem, can have serious consequences, including
corrosion downstream, an increase in particle outlet loading, an increase
in power requirements for reheat, and an increase in water consumption.
The state-of-the-art of mist elimination is discussed below.
Design Considerations
In a system study for EPA, Calvert, Yung, and Leung (1975) evaluated
the performance of various mist eliminators. The results of this study
that are relevant to a utility scrubber system are as follows:
41
-------
Overall droplet collector! efficiency of a mist eliminator
depends on primary collection and reentrainment. Both overall
and primary collection increase with increasing gas velocity.
At high gas velocities (nominally, 5 m/sec and over), re-
entrainment occurs, decreasing the overall collection even
though primary collection remains high.
Higher reentrainment velocities (greater mist eliminator
capacity) are obtained with mist eliminators which have good
drainage. Thus, horizontal gas flow mist eliminators have
greater capacities than vertical gas flow types. Similarly,
vertical gas flow mist eliminators with 45° baffles had
larger capacities than those with baffles inclined at 30° or
0°.
Pressure drop across a baffle mist eliminator is reasonably
well predicted by a model based on the drag coefficient for a
single plate held at an angle to the gas flow.
Solids deposition is greater on inclined baffles than on
vertical ones because of the increase in settling rate of
suspended solids. Deposition rate decreases as the slurry
flux on the surface increases.
Designs Used in Utility Scrubber Systems
A review of commercial mist eliminator designs in use in the utility
industry revealed the following practices (Ellison, 1978):
Vertical gas flow mist eliminators are used almost exclusively.
The chevron multipass (continuous vane) construction and the
baffle construction (noncontinuous slats) are common.
Vane spacing is generally 1.5 to 3.0 inches except in the
second stage of two-stage designs which generally use 7/8 to
1 inch spacing.
Plastic is the most common material of construction due to
reduced weight, cost, and corrosion potential.
Precollection and prewashing stages are commonly used to
improve demister operation.
Demister wash systems typically operate intermittently using a
mixture of clear scrubber liquid and fresh makeup water.
Horizontal gas flow mist eliminators have only recently been used
in this country, although they are common in Japan and Germany. This
type of mist eliminator has better drainage than vertical flow types,
but space requirements are greater.
42
-------
Sources of Information
See Calvert, Yung, and Leung (1975), Calvert (1978), Conkle et al..
(1976), and Ellison (1978). See Mcllvaine (1974) for a review of pro-
prietary designs.
5.2 CORROSION AND MATERIALS OF CONSTRUCTION
General Considerations
Wet scrubber systems operating on coal-fired boilers encounter an
extremely corrosive and erosive environment. Materials of construction
are subject not only to attack from absorbed S02 and S03 but also attack
from chlorides. The chlorides enter the system from the coal, and the
makeup water. Closed-loop operation of the scrubber system tends to
build up the chloride concentration. Erosion from collected flyash
aggravates the corrosion problem by destroying the protective layer of
the material.
The general trend in selection of materials has been an increase in
the use of higher grade alloys which are resistant to corrosion and
erosion. The expense of these alloys, however, prevents extensive use
of them in scrubber systems. Instead, various linings are often used to
protect less corrosion-resistant metals. But linings are temperature
sensitive: temperature excursions can be disastrous.
Plant Experience and Recommended Practices
Table 5-1 summarizes the materials of construction at a number of
utility scrubber systems as well as some of the solutions to corrosion
problems. Table 5-2 is a list of suggested materials of construction
for an S02 absorber based on sulfuric acid and chloride concentrations
(Gleason, 1975). A more detailed discussion of the materials of con-
struction for components of a scrubber system follows.
Scrubber. Materials of construction include flake-lined steel,
rubber-lined steel, or 316L stainless steel. In venturi scrubbers,
abrasion-resistant materials such as brick-lined steel or high nickel
alloys are recommended for the venturi throat. For S02 absorption,
simple designs, such as spray towers, are recommended; moving-bed
scrubbers suffer excessive wear.
43
-------
TABLE 6.1. MATERIALS OF CONSTRUCTION FOR FULL-SCALE SYSTEMS
System
Colttrtp Station
(MPC)
Sherbuma County
Generating Plant
(NSP)
Reid Gardner Sta-
tion (NPC)
Cholla Station
(APS)
Four Cornan
Plant (APS)
Diva Johnston
Plant (PP&L)
Arapahoe Station
(PSCC)
Cherokee Station
(PSCC)
Valmont Station
(PSCC)
Aurora Station
(MPftU
Clay Bonwll
(MP&L)
Icrakber
V-FL.A-FL
V-Throel-Brick
W.T.-3I6SS
V.Rod.MJ.and
Drain Pott-316L.
H-CL
V-Throit-1825
V-RL
W.T.-31BLSS
V-316LSS.
A416SS
AwatFL
V-Throit-SCBL
Other PLL or
SSL
V-PL
G-SS
Other-RL
G-SS
Other-RL
G-SS
Other-RL
316ELC
316SS
OMtatDwt
FL
CS
ML
FL
PLL
PL
(Cracking)
MS
MS
EJ-SS&F
MS
EJSS&F
FL
FL
Mist
Eliminator
PP
FRP
316LSS
PP
NA
PVC
SS
SSO&3)
316SSI4)
SS
3I6L
3I6L
Rihuttr
Plete-1625,
H-3I6LSS,
Other-HG
CS
CS
31BL
316SS
None
CS
CS(1M)
SSI3)
CS
None
None
Fan
H-RL
DF-CS
OF-CS
OF-CS
I62S
1-1626
H-RL
DF-CS
NA
DF-CS
316L
316L
Pipes
Slurry-fa
Other-SS
RL, Hetron
endCS
RL
P
Slurry-RL
RL
RL
RL
RL
Slurry-316LSS
Other-FRPor
RL
RL
Pumps
RL
Ni-Herd
RL
RL
RL
I-HM
H-RL
(Cracking)
RL
RL
RL
316SS
RL
Valvts
RL
NA
N.A.
RL
RLorSS
RL
SIBSSor
RL
316SS
(1&3)
RL(4)
SS
Slurry-
316SS
N.A.
Ta»ks
FL
N.A.
RL
FL
NA
N.A.
N.A.
RL
RL
N.A.
N.A.
Comments
Main spray pipe URL. Venturi
rod section piping Is Hetron.
Some scrubber perts ere F L.
Some rubber linings became
loose during startup, original
rigid llake In scrubber leiled.
Future reheaters will be of
Inconel. Absorbers ware FL
SS. Problems in second ab-
sorber.
Rehaaters have been re-
moved. Original 31 6SS fan
was replaced due to stress
fatigue. Original alloy 2B
pumps have been replaced.
Need to replace R L valves at
high abrasion points. Changed
to straight through plug. New
plumbob SS due to PL failure.
1.3 and 4 refer to Units 1.
3 and 4.
Scrubber liquid discharge
pipe changed from RL to
31BLSS. FRP joints failed at
200 psi. RL on pumps failed
due to high pressure.
FRP piping replaced with RL.
See next page lor explanation of tymboli.
Source: LaMantia (1977).
-------
Kay to TABLE 5-1
A
OF
EJ
G
H
I
MB
V
W.T.
Component
- Absorber
- Dry fan
— Expansion joints
- Grid plate
- Housing
- Impeller
- Marble bed
- Vertturi
- Wash tray
CL -
CS -
F
FL -
FRP -
HG -
I62S -
I825 -
MS -
P
P4L -
PL -
PLL -
PP -
PVC -
RL -
SCBL-
SS -
SSL -
Materials Other
Ceilcote lining N.A. - Not available
Carbon steel
Fabric
Flake-lined
Fiberglass
Hastelloy G
Inconel 625
Inconel 825
Mild steel
Plastic
Plairte 4004-S epoxy -lined
Polyester-lined
Plastic-lined
Polypropylene
Polyvinyl chloride
Rubber-lined
Silicon carbide brick lining
Stainless steel
Stainless steel-lined
45
-------
TABLE 6-2. RECOMMENDED MATERIALS FOR FGD SCRUBBERS
ot
Design
Once-Through
Once-Through
Once-Through
Recycle
Recycle
Recycle
Recycle
Recycle
Recycle
Chloride
Concentration
(p.p.mj
< 150
150-3,000
>3,000
<150
<150
<150
19,000
150-1,000
1,000-5,000
Concentration
(Percent)
0.25
0.25
0.25
2
2-20
20-30
0.25
2-5
2-5
Scrubber Region
Lower Tower
(Humidifier Section)
Mild steel, lead, brick
Mild steel, lead, brick
Mild steel, rubber lining, brick
Mild steel, lead, brick
Mild steel, lead, brick
Mild steel, lead, brick
Mild steel, rubber, brick
Mild steel, rubber, brick
Mild steel, rubber, brick
•Materiel
Upper Tower
(Tray Section)
316 ELC stainless steel
Alloy • 20
Mild steel, rubber lining with
titanium or Hastelloy C
316 ELC stainless steel
Alloy - 20 or Hastelloy C
(+70° C)
Mild steel, lead or rubber,
Hastelloy C treys
Mild steel, rubber, Hastelloy C
Alloy -20
Mild steel, rubber lining,
Hastelloy C
Source: Gleason (1975).
-------
At Sherburne Station (Northern States Power) erosion has been
minimized by the use of wear plates. At Cholla Station (Arizona Public
Service) corrosion and erosion have been minimized by the use of Carpenter
20 (for stress corrosion) and Inconel alloy 625 and silicon carbide
refractory (for corrosion and erosion).
Scrubber lining failures have been observed at many systems. The
reasons for failure are not known for sure, but poor application, thermal
shock, and deterioration are possible causes. Thermal shocks could be
minimized by the use of emergency sprays regulated by temperature gauges.
Ducts. Lined steel or carbon steel have been used for ducts, the
former being used for wet gas downstream of the scrubber, the latter for
reheated gas. Here, too, linings and other materials of construction
have failed due to acid condensate with subsequent corrosion. Expansion
joints should probably be made of nonmetallic materials.
Mist Eliminators. Mist eliminators are typically made from 316L
stainless or fiber reinforced plastic. Plastic types are recommended
because of reduced weight, less solids buildup, and less corrosion
potential.
Reheaters. Reheaters have been made from carbon steel, 316 stainless,
or high grade alloys such as Inconel and Hastelloy. The reheater is a
bad problem area since it is subject to both sulfur acids and chloride
attack. The higher grade materials are recommended.
Fans. Materials of construction for fans include carbon steel, 316
stainless steel, rubber-lined steel, or Inconel. Carbon steel is used
for dry gas after reheat. Abrasion, fatigue cracking, and solids buildup
causing imbalance are the most common problems with fans.
Piping, Pumps and Valves. Rubber-lined steel is the most commonly
used material for construction of pumps. However, high pressure rubber-
lined pumps (200 psi) have failed at the Syl Laskin Station (Minnesota
Power and Light) and were replaced by pumps made of 316 stainless. By
contrast, pumps made of alloy 20 failed at Four Corners (Arizona Public
Service) and were replaced by rubber-lined pumps.
47
-------
Rubber-lined steel valves and stainless steel valves are used in
scrubber systems. At the Dave Johnston Plant (Pacific Power and Light)
rubber-lined valves have failed at high abrasion points.
Rubber-lined pipes are used most often, but stainless steel and
plastic pipes are also used. Failure of high pressure fiber-reinforced
plastic pipes occurred at the Syl Laskin Station and were changed to
rubber-lined pipes.
Stacks. Stacks are subject to mortar joint damage when operated
under wet gas conditions. Fiber-reinforced plastic has been success-
fully used as a stack liner.
Design Considerations and Maintenance Procedures
Some corrosion problems can be minimized by prudent design and
careful construction. Since corrosion attack is known to be more severe
underneath deposits, good scrubber designs incorporate provisions for
effective drainage. Crevices are the single greatest source of localized
corrosion. Hence, the actual construction must be scrutinized and any
discovered crevices either filled with a plastic or welded shut. Welding
procedures, too, must be carefully chosen since poor welds are often the
target of corrosion attack. Welding can also damage coatings.
Finally, operating and maintenance procedures can prevent serious
corrosion problems. The LaCygne Station (Kansas City Power and Light),
where both participates and S02 are scrubbed, is exemplary. Here
maintenance procedures include a weekly cleaning of each scrubber module
to remove scale. Operating procedures include regulation of the pH (in
the range of 5.5 to 5.7) to minimize scale and measurement of the slurry
chloride level to insure a low level.
Source of Information
Power plant experience is summarized by LaMantia et a!., (1977).
The state-of-the-art in corrosion and materials of construction for wet
scrubber systems was greatly advanced by a recent joint NACE, APCA, and
I6CI conference held in Atlanta, Georgia, January 1978. The proceedings
from this conference were reviewed by Javetski (1978) and Mcllvaine
(1978).
48
-------
5.3 REHEATERS
General Considerations
Although reheating of scrubbed flue gas is not required by law,
reheaters are often incorporated into flue gas wet scrubber systems.
Usually, little attention is given to the design of reheaters, yet
failure of the reheater can cause severe operational problem.
There are four major reasons for providing reheat in flue gas wet
scrubber systems:
avoid downstream condensation
avoid a visible plume
enhance plume rise and pollutant dispersion
protection of the induced-draft fan.
Reheat may also prevent acid rain and stack icing, as well as reduce
plume opacity.
There are three types of reheaters commonly used at utilities.
These are in-line reheaters, direct combustion reheaters, and indirect
hot air reheaters. In-line reheaters are heat exchangers placed within
the gas stream. Steam or water are used as the source of heat. Direct
combustion reheaters burn either oil or gas, mixing the combustion gas
with the flue gas. Combustion chambers can be located either in-line or
external to the duct. Indirect hot air reheaters inject heated ambient air
into the flue gas stream. The air is heated either in an external heat
exchanger or in the boiler preheater. Alternatively, some utilities
have chosen not to use any reheat system, operating the stack under wet
conditions.
Operational Experience and Design Considerations
Operational experiences with these types of reheaters and the
option of no reheat are summarized in Tables 5-3 through 5-7. In
general, the choice of reheater type depends on space limitations and on
the amount of power that can be expended. For the same degree of reheat,
indirect hot air reheat has the highest energy requirements, but does
provide the beneficial effect of dilution (Leivo, 1978). The character-
istics of the particular installation must be considered in the design
of any reheat system.
49
-------
TABLE S-l SURVEY OF IN-LINE REHEAT SYSTEMS USING STEAM
PmwPUni
Scrabbmg Syflom
Muting Utttun (Sim)
Prawn, prig
T«nptraturi. *F
ConiumOIKMl.ii/h.
Hut Euhmgn
Tub* tilt
Numbnoltuhtbinki
MiuriiUol conn rue
lion
Soot Mowing
RrtMM Tomptntun. f
RihulH Problinu
SahiUon/OptrMion
K*nu> Cily Poww A light Anioni Public Strvtci Montiiw Pawn
llCyiM
LtaMon
115
650
60.000
S/»"OD.b»rtlubl
4 bdiki. 4 rowi/bwk
SS3I6L
250 pi* Hum blown
ISO
Tho 304 SS nhMin
IHMbKWMol
ehlofidl tnd Kid
corrouon.
RriiMlnphiggid
withicrubbH
*my.
Rwlicid 304 SS
lulmwitfiSISl
SSlubM.
iMiMtod nhMM flut
in nmp«r«iun liom
147* F 10 l»° F
TubnpraliMidbilora
flui (a mlm.
Ckalli No 1
limatom (R C)
ISO
SJIUIIIKJ
70.000
rO.O.,b*tilubi
JbmU
SS3I61
Stum. I MOMII/
bint, onci/4hu
ISO
Moduli A rafcwlK
(with uiubbintl
Hwmonic vion-
Ilonj.
Moduk 6 rthMiw
IwthoulitrubblnB)
Hiimonic nfeiunnt
Chtondi md wllu
rout KM HIKk
MIlMlntlillKl
Duels toort ittitiw
iimibiid.
Trou»h buill nound
ducllouichnin
oH btlan II ratthid
f^im^tmf
rnwnvf.
Four COIMII No. U Coliliip No 1.2
Vtnluii (CbMikol AIMHW Flynli (CEAI
260
600
7 .MO
Flmidiiibn Plmiypt
2b*nki
SSJI8L l*coiMl«S.H*tt»llovO
Slum blown. OKI/
diy
143 170
Collation uuud Loon tcilt lofmtd on
IthMlir lo to ft iifluttr but uuud no
inoMd ilttf oiw yf- opifitlnf pfobMnii.
Pilling conouon
Ihoughllobiuutid
by tulliii
Aim nrnoMl at n-
hwlir. brick diltrioi-
•lion in Iht tuck mn
hMoul.mdlMpliww
rin wtn nalmd No
lolkMHip tolunon
Mlimpiid.
Public Swvkf Camptny ol Cotoiido
ChKOkMNo. 1 ChnokwNo 2
TCA IUOPI TCA IUOPI
300 300
420 770
33.000 19.300
5/1" 0 0 . bm lutot &/6" 00.. bm 6j Unmd
lubn
2 bwki. 3 lowt/bink 3 binki. 3 towi/bwk
Cuban UMl Ciffeon tinl
Slum blONtf. onct/Jhrt SiMm blown, onn/6hn
US ICO
RitiMtirorigiiHUvhid Aim 6 moniht In tw
3binktUp|inbMkwn via. i nuj(oi jtl w«h
nmoMddintopluggigi ing cloning job w*t
wd conouon. dom. Aim 2-1/2
yunolopouion.
nijot icid Muck wot
found Ihioughoul
linmd *nd bin lubt
UCIIoni.
RopuMnmil fitiHIff
lubn oISS 3161 will
b«u»d.
Comnoimtrflb Edoon
WiU County
Limntoni I8»W)
350
415
50.000
W O.O., bin luot
3 bintt. 9 KHOtbink
SS3l6L»c«bonll»(
Evtry 4 noun
160
Modulo A rthiuw: »•
nutti tuba liibd b»
CfunolcMoridtcouo
lion RihMiiiilto
pluggtd wilh lolidi
ModuhBriliMMr. ra
huinliiMbKMtt
ol vituilion nd chlo
ridf conouon
InilMly Moduli A wn
put bick Into unto by
onnibiluing ModuM B
Mm HMiinilion im
piend by contunl un
dmpny and innrmii
rant ovtnpny ol mitt
«imin
-------
TABLE 5-4. SURVEY OF IN-LINE STACK GAS REHEAT SYSTEMS USING HOT WATER
Power Plant
Scrubbing System
Heating Medium (Hot Water)
Inlet temperature, °F
Outlet temperature, °F
Flow rate, gpm
Heat Exchanger
Tube size
Number of tube banks
Materials of construction
Soot blowing
Reheat Temperature, °F
Reheater Problems
Solution/Operation
Kansas Power and Light
Lawrence No. 4
Limestone (CE)
250
180
200
1" 0.0. finned tubes
2 banks
Carbon steel
Compressed air blower, once/4hrs
150
Frequent plugging of the reheater
during early life of system.
Tube failure due to acid corrosion
after 6 years of operation.
Plugging was alleviated by installing
soot blowers, redesigning of mist
eliminator, and installing vanes under
marble bed to improve gas distribution.
Entire scrubber system was replaced
in 1977.
Kansas City Power and Light
Hawthorn No. 4
Limestone (CE)
325
250
600
NA
NA
Carbon steel
Steam soot blower
175
Corrosion problems have been
mild compared to pluggage
problems.
Reheater is normally cleaned
every three days when scrubber
is cleaned.
The reheat pump is started prior
to placing scrubber in service.
Northern States Power
Sherco
Limestone (CE)
350
230
2,300
1/2" O.D. finned tubes
3 banks
Carbon steel
Steam soot blowers
170
Reheater is not yet in ser-
vice. Results of pilot plant
indicate system is satisfac-
tory.
Source: Choi, et al. (1977) and Leivo (1978).
-------
TABLE 5-6. SURVEY OF INDIRECT HOT AIR STACK GAS REHEAT SYSTEMS
en
ro
Power Plant
Scrubbing System
Heating Medium (Steam)
Pressure, prig
Temperature. °F
Consumption rate, Ib/hr
Heat Exchanger
Tube size
Number of tube banks
Materials of construction
Mixing of Gas
Reheat Temperature, °F
Reheater Problems
Solution/Operation
Nevada Power Company
Reid Gardner No. 1,2
Soda Ash (CEA)
460
760
20,000 • 25,000
5/8" O.D. finned tubes
3 banks, 8 rows/bank
Carbon steel
4 nozzles
169
Leak from weak spot of heater tube.
No corrosion or mixing problems.
Reheater is placed in service after
scrubber is in full operation and
shutdown prior to scrubber shutdown
to protect lined ducts.
Public Service Company of Colorado
Cherokee No. 4
TCA (UOP)
575
483
135,000
5/8" O.D. finned tubes
2 banks
Carbon steel
175
Difficulties with steam pressure reducing
valve.
Mixing problems due to poor design of
raheater fan.
Reheater fan interlocked with scrubber
booster fan to prevent reverse flow of
flue gas to reheater.
Source: Choi, et al. (1977) and Leivo (1978).
-------
TABLE 5-6. SURVEY OF DIRECT COMBUSTION STACK GAS REHEAT SYSTEMS
en
to
Power Plant
Scrubbing System
Fuel and Combustion
Combustion Chamber
Fuel Type
Combustion rate
Gas temperature, °F
Mixing of Gas
Reheat Temperature, °F
Detroit Edison Company
St. Clair
Limestone (Peabody)
External
No. 6 fuel oil
600 gph
1,200-1,400
T connection
250 • 300
TVA
Shawnee
Lime/Limestone
External
No. 2 fuel oil
37 gph
1,500-1,800
L-tube
250
Ouquesne Light
Phillips
Lime (Chemico)
In-line
No. 2 fuel oil
440 gph
3,000
•
150
Louisville Gas & Light
Paddy's Run 6
Carbidge Sludge (CE)
In-line
Natural gas
20000 scfh
NA
165-170
Reheater Problems
Solution/Operation
Failure of a thermal con-
troller causing liner dam-
age.
Firebricks in mixing chamber
fell off due to vibration.
Poor mixing results in non-
uniform temperature distri-
bution.
Combustion chamber heated
slowly to protect refractory
material from abrupt temper-
ature changes.
No corrosion problems.
Occasional carbon buildups.
Blower failed due to
mechanical problems.
Mixing was not effec-
tive causing nonuniform
temperature distribution
downstream.
Original design had in-line
burner. This was modified
to an external chamber
became of flame insta-
bility problems.
New acid proof stack liner
installed.
Reheater is little used due
to oil shortage. Stack
operated wet.
No corrosion or other
problems encountered.
Source: Choi, et al. (1977) and Leivo (1978).
-------
TABLE 6-7. SURVEY OF SCRUBBING SYSTEMS WITH NO STACK GAS REHEAT
en
Power Plant
Scrubbing System
1.0. Fan Maintenence
Stack Maintenance
Acid Rain or Fallout
Problem!
Plume Visibility
Problems
Comments
Pacific Power and Light
Dave Johnston
Venturi (Chemico)
To prevent solid deposits on the
fan blades, wash water is sprayed
periodically.
An acid-resistant lining was in-
stalled to protect the stack.
Condensate pH = 3.5.
None
No effect to visibility.
Experience with wet stack has
been satisfactory.
The City of Key West
Stock Island"
Limestone (Zum)
Little solid deposits on fan
blades. Clean up once a year.
Wash with fresh water.
Concrete gunite-type liner
might be attacked by acid.
The stack is checked period-
ically.
NA
No effect to visibility.
Scrubber went into service
in 1972. Due to problems with
the scrubber, operation has been
limited. Based on this limited
experience, no reheat has been
satisfactory.
Boston Edison
Mystic Station"
MgO scrubbing (Chemico)
No I.D. fen.
No acid attack was found in
the brick liner and the base
of the stack.
No problems.
Dense plume that dissipated
rapidly.
During the 2-year intermittent
operation, MgO agglomeration
in the stack was more serious
than acid attack to the brick
structure.
"Both power plants bum No. 6 Fuel Oil.?
Source: Choi.etal. (1977).
-------
Experience gained with reheaters has produced some useful caveats.
In-line reheaters are subject to plugging, corrosion, and vibration.
Plugging can be minimized by good mist elimination and the use of soot
blowing, done at frequent intervals. Corrosion is a difficult problem
since neither carbon steel, 304SS, 316SS, nor Corten appear to be able
to withstand combined acid and chloride-stress corrosion. More exotic
and expensive materials, such as Inconel 625 and Hastelloy G, have been
used successfully at Col strip. Design against vibration can readily be
done by using frequency analysis. Direct combustion reheaters are best
designed with an external combustion chamber, preventing the problems
encountered with in-line reheaters. Both direct combustion reheaters
and indirect hot air reheaters require interlocks to prevent the heated
gas from damaging ductwork when the cold flue gas is not present. At
the Dave Johnston Plant, where reheat is not used, the induced draft fan
is periodically washed with water to prevent solid deposits and an acid-
resistant lining is used on the stack.
In summary, reheaters are used in wet scrubber systems to provide
greater plume buoyancy and prevent downstream condensation. Utility
experience militates against the use of in-line reheaters because of
many operational problems. Where reheaters are not used, prophylactic
measures must be taken to prevent stack deterioration and (induced
draft) fan imbalance.
Sources of Information
See Leivo (1978) and Choi et al., (1977).
5.4 WASTE DISPOSAL
Disposal of utility ash, either in ponds or landfills, has been
practiced for many years. Indeed, if a wet scrubbing system is used for
particulate removal only, disposal of the collected flyash poses no
difficulties. But if the scrubber system also consists of a throwaway
flue gas desulfurization system, disposal of wastes is problematic
because sludge is exceedingly difficult to manage.
55
-------
Disposal of sludge is complicated by several undesirable properties
of the material: (1) a large percentage of occluded water which makes
the sludge physically unstable and expensive to transport, (2) a large
number of small calcium sulfite crystals which limit the amount of
dewatering that can be done by settling only and (3) the presence of
soluble and slightly soluble materials which are potential sources of
water pollution.
A typical ponding operation consists of dewatering the raw sludge
in a thickener and then pumping it in a pipeline to an ultimate disposal
site. The disposal site may be either a man-made pond or a naturally
occurring dry lake (in arid regions). A second pipeline recirculates
clear supernatant back to the scrubbing facility. Although easier and
cheaper than using a landfill, ponding has several drawbacks: first, it
requires a large land area, which will not be reclaimable (unless measures
are taken to stabilize the sludge); and second, there 1s potential water
pollution from runoff and leaching. Leaching can be minimized in man-
made ponds by using an impervious liner.
Disposal of sludge in a landfill requires greater dewatering than
ponding, and also, further processing to increase the compressive and
shear strength of the sludge. Besides thickeners, other methods of
dewatering include filtration, centrifuging, and mixing with dry-collected
flyash and lime. The physical stability of the sludge can be increased
by addition of certain chemical additives; commercially, both the Dravo
Corporation and IUCS offer additives that have been used at utilities.
Runoff from landfills can be minimized by covering the site with earth
and revegetating (local regulations permitting).
Table 5-8 summarizes the waste disposal practices of several
utilities. No clear trends emerge, but the choice of waste disposal
methods is site-specific, depending on economics, location, and local
regulations.
56
-------
TABLE 5-8. SLUDGE DISPOSAL PRACTICES
en
Station
Particulate-S02 syitems:
Bruce Mansfield
Colrtrip
Cholla
Sherburne
LaCygna
Reid Gardner
Paniculate systemi:
Four Comers
Dave Johnston
Arapahoe6
Cherokeeb
Valmontb
Syl Latkinb
Clay Boiwell
Sbe.MW
1650
720
115
1400
870
250
575
330
100
600
166
116
350
Total Dry1
Weight, tons/hr
NA
31.5
1.9
30.4
NA
3.9
69.2
19.9
0.95
6.35
2.76
3.0
32.7
Method of
Disposal
Landfill
Pond
Pond
Pond
Pond
Pond
Mine
Landfill
Pond
Landfill
Landfill
Pond
Pond
Liner
No
NA
No
Yes
No
No
No
NA
NA
NA
NA
NA
NA
Additives or
Supplemental Alkali
Drevo
Lime
(0.3 tons/hr)
Limestone
(0.6 tons/hr)
Limestone
(3.5 tons/hr)
Wet flyash
None
Lime
(0.6 tons/hr)
Lime
(0.5 tons/hr)
NA
NA
NA
NA
NA
Estimated by adding flyash and S02 removal from the system and supplemental alkali added in the system. (C02 is excluded from supplementary alkali if limestone is added.l
Supplemental alkali added to neutralize effluent only. Quantity of alkali used is not available.
Source: LaMantia (1977) and Federal Power Commission (1977).
-------
Sources of Information
Flue gas desulfurization waste disposal has been the subject of
investigation both by EPA and EPRI. For more extensive treatments, see,
for example, Leo and Rossoff (1978), Fling et al., (1978), Corbett
et al., (1977) and also Mcllvaine (1974).
5.5 SCALING AND OTHER OPERATING PROBLEMS
Scaling is the single greatest operational problem in wet scrubbers
and one that is most difficult to control. In scrubbers used for
participate removal only, the calcium and other alkalis present in the
flyash react with SOg causing scale deposits (calcium sulfate). In lime
and limestone systems, calcium sulfite (from the reaction of absorbed
SOp and slurry alkali) and calcium sulfate (from the reaction of dissolved
sulfite and oxygen) tend to precipitate out and form scale. In lime
systems, calcium carbonate may also be precipitated when COg from the
flue gas reacts with the lime (pH is high).
Various techniques for controlling scale include:
Control of pH — If a limestone system is operated at pH's
above 5.8 to 6.0 or if a lime system is operated above 8.0 to
9.0, there is a danger of sulfite scaling (Leivo, 1978). The
pH is controlled by adjusting the feed stoichiometry. On-line
pH sensors have been successful in controlling the feed in
lime systems but not in limestone systems because the pH is
fairly insensitive to the limestone feed rate in the normal pH
range. However in the limestone system, the feed can be
controlled by varying the flue gas flow rate. In particulate
control systems, the pH is generally low, hold time in the
retention tank is short, and suspended solids concentration is
low. All these contribute to the formation of calcium sulfate
scale. Hence, it is desirable to increase the scrubber liquor
pH by addition of supplementary alkali.
Hold Tank Residence Time — By providing greater residence
times in the scrubber hold tank, the supersaturation of the
liquor can be decreased before recycle to the scrubber.
Typical retention times of 5 to 15 minutes are used.
Control of Suspended Solids Concentration — Supersaturation
can be minimized by maintaining a supply of seed crystals in
the scrubber slurry. Typical concentrations range from 5 to
15 percent suspended solids. Solids are generally controlled
by regulating slurry bleed rate.
58
-------
Regulating Oxygen Concentration ~ Since calcium sulfate
scaling depends on the presence of dissolved oxygen, control
techniques center on regulating the oxygen concentration. In
the forced oxidation method, air is bubbled into the reaction
tanks to encourage sulfate crystal formation. These crystals
have better settling characteristics than sulfite crystals.
In the co-precipitation method, magnesium sulfite is used to
depress the sulfate saturation level. Precipitation of
sulfate in the holding tank is achieved by co-precipitation of
sulfate with sulfite in a mixed crystal.
Liquid-to-Gas Ratio— High liquid-to-gas ratios reduce scaling
potential since the scrubber outlet is more dilute with respect
to absorbed S0«. Unfortunately, increasing the liquid-to-gas
ratio also increases operating costs and sludge disposal.
Additives -- Two additives, Calnox 214DN and Calgon CL-14,
when used together, have been found to effectively reduce
sulfate scaling in limestone systems (Federal Power Commission,
1977).
Alkali Utilization — Experience at the TVA test facility at
Shawnee indicated that certain mud-type solid deposits, which
tended to form particularly in the mist eliminators, could be
reduced by improving alkali utilization. Above about 85 percent
alkali utilization, these solids could be removed easily with
infrequent (once per 8 hours) washings. Control of calcium
sulfate scaling at TVA was effected by varying the operating
parameters listed above (Williams, 1977).
A summary of scaling and other operating problems at various utilities
is provided in Table 5-9. As with other aspects of wet scrubber systems,
the solutions to these problems tend to be site-specific, making generalizing
difficult.
Sources of Information
See Leivo (1978), LaMantia et al. (1977), and Slack and Hoi linden
(1975).
5.6 SAMPLING CONSIDERATIONS
Sampling and measurement of various constituents of the flue gas
stream before and after the scrubber system are needed to evaluate its
performance. It is desirable that adequate sampling ports be incorporated
during the engineering design of the scrubber system to facilitate
several sampling procedures which require a variety of probes and collection
equipment.
59
-------
TABLE 5-9. OPERATING CHARACTERISTICS AND PROBLEMS IN SCRUBBER SYSTEMS
a\
o
System
Colstrip Slitlon
(MFC)
Shirburni County
Ginirtling Flint
(NSP)
Reid Gardner Stelion
(NPC)
CholliStition
(APS)
Four Comtn Flint
(APS)
DIM Johniton Flint
(PPAU
AnpihoiStition
IPSCC)
Chirokn Stition
(PSCC)
Vilmont Stition
(PSCC)
Aurora Stition
(MP8LI
Cliy Boiwrtl Stition
(MP&L)
Chemkal Scale
•-
RihMttr
••
Pond outlet pipi.
vtniuri, cyclone
Mpmtor, raheitir
Vmturi, nhiitir
md pipe*
Gypsum Kile in
Kiubbir ind pipes
••
Scrubber ind liquid
linn-gypsum icile
Milt Eliminitor
Washing
With trey & 0.8
on demliter (FAR)
Washing elrer 3-4
diyi(R)
Wishlriy
Intermittent (R|
N.A. (R)
R
Intermittent
Mnthing(C)
Intermittent
wishing (C&F)
Intermittent
waning IF)
N.A.(R)
1.2 (R)
FM Wuktag Wit/Dry Internee
Dry 1.0. (en Venturi
Dry 1.0. fin Venturi rod
Dry F.O. len
Dry F.O. (in Venturi
Wit fen IR)
1.3 (C&F) Scrubber, lignosulnt*
it uted to ivoid buildup
Dry F.O. fin Prauturation Section
Dry F.O. fin Prauturation Section
Dry F.O. fin Prauturatlon Section
Wet fin (F)
0.2 (F) Scrubber, spray piping
Comments
Close loop operation.
Effluent discharged from the
system, sluice witir, etc.
(2-3 gpm/Mw) it combined
with scrubber system (forced
oxidation).
Close loop miintiined by
evaporation from pond.
Close loop miintiimd by
evaporation from pond.
Scale ind buildup is con-
trolled by flushing from the
system.
L/G • 7.6 is intermittently
used to avoid bufldup in
scrubber and results in
dischirge of effluent
Scale ind buildup is con-
trolled by maintaining
effluent from the system.
Selling ind plugging is
controlled by effluent
discharge.
Selling and plugging is
controlled by effluent
discharge.
Noli: All the numbers represent liquid to gat ratio, gpm/1.000 ecfm.
C- Cooling tower blowdown
F- Fresh plant supply witer
R • Recycle itremi In scrubber system
F.D.-Forced draft
I.D. Induced draft
Source: UMwtii. it al.(1977).
-------
Sampling operations for the evaluation of the scrubber system will
be aimed primarily at characterizing the gas flow, particle size dis-
tribution, mass loading, and gas composition. Secondary sampling may
also be required to determine emission characteristics for the assess-
ment of environmental effects of the installation.
To obtain a representative sample of the particulate matter, and
information regarding gas flow rate, the gas flow at the sampling points
must be stable. Bends, expansion and contraction zones, and the
presence of an obstacle in the flow path can induce secondary flows such
as vortices, rotation, and large eddies. Sufficiently long runs of a
straight uniform duct are usually recommended at the sampling location
before and after the sampling point. As a rule, the sampling location
should be separated by 8 to 10 diameters downstream and by more than two
duct diameters upstream from any disturbances in the flow.
Another factor in designing sampling locations in a scrubber
system is the ease in the operation of the sampling equipment. Proper
orientation of the sampling port and availability of a clear platform
area near the port are desirable.
In the scrubber system it is also desirable to be able to evaluate
the scrubber section as well as the demister section separately, as
shown in Figure 5-1. Three sampling locations are required for evaluating
the system performance.
Most interfaces for sampling from ducts are designed to be compatible
with 3 inch (nominal) Schedule 40 pipe nipples used as sampling ports.
Occasionally an experimental system has required a 4 or 6 inch opening.
The size of the port opening necessary to insert a probe (with the usual
bend to allow sampling parallel to the flow) also depends on the length
of the port opening. In an experimental scrubber system where a variety
of sampling procedures may be used, 1t is recommended that 6 inch ports
be made available. Other considerations include availability of dia-
metrically opposite ports so that opacity monitors may be installed if
necessary.
61
-------
SAMPLING STATION
PARTICLE LADEN
FLUE GAS
en
ro
LIQUID IN
VENTURI
SCRUBBER
SLURRY
DEMISTER
EXHAUST
Figure 6-1. Sampling Stations for Scrubber Installation
-------
Sampling Operations
A list of gas stream characteristics and measurement methods of
particular interest for a particulate scrubber on a coal-fired boiler is
given in Table 5-10. Information on the gas stream flow field, and flow
rate is necessary so that correct sampling conditions may be chosen to
obtain a representative sample. Standardized methods for determining
gas composition and particulate mass loadings have been developed and
are available in the Code of Federal Regulations under Title 40—
Protection of Environment, Chapter 1—Environmental Protection Agency,
Subchapter C—Air Programs, Part 60—Standards of Performance for New
Stationary Sources, and Appendix A—Reference Methods.
Experiences in determining particle size distributions from coal-
fired boilers have shown a number of potential sources of error. Hesketh
(1975), in studying the performance of a pilot venturi scrubber, found
as much as 70 percent weight gain on glass fiber filters due to reaction
products; other surfaces such as silver foil, fluoropore, and polyvinyl
chloride also showed some weight gain. McCain (Southern Research Institute,
1976), similarly reported weight gains on a number of glass fiber filters;
the reaction products were identified as sulfate. Preconditioned materials
showed significantly less weight gain. Hesketh (1975) reported that the
use of Dow silicone lubricant as a greased substrate on impactor surfaces
during blank runs resulted in loss of weight; presumably, the weight
loss was due to the low pH environment and not the temperature (only
135°F). Wesa (1977), in summarizing Detroit Edison's experience with
sampling trains, pointed out that metal probes produce corrosion pro-
ducts, even if heated above 250°F; an inert probe was recommended. Ensor
et al., (1975), in fractional efficiency testing of the mobile-bed
scrubber at the Cherokee station, found high and variable outlet particle
concentrations presumably due to reentrainment of solids from the entrain-
ment separator. Recently, Smith, Cushing, and McCain (1977) have developed
a manual for the evaluation of electrostatic preci pita tors. Most of the
information on sampling in this manual is also applicable in scrubber
evaluation.
63
-------
TABLE 5-10. A SUMMARY OF EMISSION CHARACTERISTICS MEASUREMENT METHODS
QUANTITY MEASURED
SAMPLING METHOD
APPARATUS
REFERENCE
Travelling points
Velocity + volumetric
flow rate
C02, excess air, dry
molecular weight
Moisture (in absence
of droplets)
Particulate emissions
mass loading
Particulate emissions
mass loading
Particulate emission
mass loading
SO,
NOX
S02.S03,andH2S04
Opacity
Opacity
Aerodynamic diameter
>O.Sfim-10fim
Aerodynamic diameter
Particle size
distribution <0.5/im
Drop size distribution
Environmental assessment
Level 1
Method 1
Method 2
Method 3
Method 4
Method 5
Method 17
ASTM
Method 6
Method 7
Method 8
Method 9
Extractive
Extractive or
In-stack
Extractive or
In-stack
Extraction
In situ probe
Effluent
collection +
analysis +
bioassays
Type S pilot tube
Orsat Analyzer, glass or
stainless steel (S.SJ probe,
particulate filter
Orsat Analyzer, glass or
S.S. probe, particulate fil-
ter, ice bath, impingers
Sampling Train Cyclone/
filter holders (>22S°F)
In-stack filter thimble
In-stack filter thimble
Pyrex Probe, impingers
Pyrex Probe, collection flask
Pyrex Probe, impingers
Visual, qualified observer
Extractive sample
Heated impactor, in-stack
impactor
Cyclones (4 in diameter port)
Probe, Oiluter Electrical Aero-
sol Analyzer, diffusion battery,
condensation nuclei counter
Hot wire droplet detector
Source Assessment Sampling
System (SASS Train)
Federal Register41, 111, 23061 (1976)
Federal Register41, 111, 23063 (1976)
Federal Register*/, 111, 23069 (1976)
Federal Register 41. \ 11,23072 (1976)
Federal Register41, 111, 23076 (1976)
Federal Register41,111,42020 (1976)
Federal Register 41,111,23083
Federal Register-*/, 111,23085
Federal Register 41,\ 11.23087
Federal Register 41,111,230
Ensor and Hooper (1977)
Calvert, Leke, and Parker (1976)
Harris (1977)
Smith, Gushing, and McCain (1977)
Ensor and Hooper (1977)
Calvert, Barfaarika, Monehan (1977)
Smith and Wilson (1978)
Smith, Gushing, and McCain (1977)
Ensor and Hooper (1977)
Calvert, Barfaarika, Monahan (1977)
Hamersma, Reynolds, and Maddalone (1976)
-------
The Environmental Protection Agency has developed a procedure for
environmental assessment (Hamersma, Reynolds, and Maddalone, 1976). The
Basic Level 1 Sampling and Analytical Scheme for particulates and gases is
shown in Figure 5-2. In a scrubber system, sampling of solid, liquid, and
slurry discharges is also required for a complete environmental assessment
of the installation. A scheme for the sampling and analysis of solids,
slurries, and liquids is given in Figure 5-3.
Information on quantities of particulate and other matters needed for
the environmental assessment is available in the procedure document referred
to above.
65
-------
ELEMENTS AND
SELECTED ANIONS
PHYSICAL SEPARATION
INTO FRACTIONS.
LC/IRMS
ATOMIC
AISORPTION
ELEMENTS AND
SELECTED ANIONS
PHYSICAL SEPARATION
INTO FRACTIONS
LC/IR/HS
SEE CHAPTER IX
SEE CHAPTER X
QUITE GAS
CHROMATOGRAPHY OR
APPROVED ALTERNATIVE
XAO-Z
ASSORtER
(AS NECESSARY!
ONSITE6AS
CHROMATOGRAPHV
PHYSICAL SEPARATION
INTO I CLASSES
SEE CHAPTER X
ALIQUOT FOR GAS
CHROMATOGRAPHIC
ANALYSIS
PHYSICAL SEPARATION
INTO FRACTIONS.
LC/IR/MS
•WEIGH INDIVIDUAL CATCHES
Figure 5-2. Basic Level 1 Sampling and Analytical
Scheme for Participates and Gases
66
-------
souos
SOLID/
LIQUID
LIQUIDS
LEACHAILE
MATERIALS
ORGANIC!
MOASSAY SEE CHAPTER X
INORGANICS
OA PHYSICAL SEPARATION
INTO FRACTIONS IC/IR/MS
ELEMENTS AND
SELECTED ANIONS
INORGANICS
ORGANICS
ELEMENH AND
SELECTED ANIONS
PHYSICAL SEPARATION
INTO FRACTIONS
IC/IR/VS
SUSPENDED
SOLIDS
INORGANICS
SIOASSAV
ORGANICS
ELEMENTS AND
SELECTED ANIONS
PHYSICAL SEPARATION
INTO FRACTIONS
LC/IR/MS
INORGANICS
SELECTED
WATER
TESTS
(AQUEOUS)
SEECHAPTERX
ELEMENTS AND
SELECTED ANIONS
SEE SECTION 7il.
CHAPTER VII
ORGANIC
EXTRACTION
OR DIRECT
ANALYSIS
ORGANICS
>C12
PHYSICAL SEPARATION
INTO FRACTIONS
IC/IR/MS
OR6AMCS
ALIQUOT FOR GAS
CHROMATOGRAPHIC
ANALYSIS
Figure 5-3.
Basic Level 1 Sampling and Analytical Scheme
for Solids, Slurries and Liquids
67
-------
REFERENCES
Calyert, S. "Guidelines for Selecting Mist Eliminators," Chemical
Engineering, Vol. 85, No. 5, February 27, 1978, pp. 109-112.
Calvert, S., H. Barbarika, and G. Monahan. American Air Filter
Kinpactor 10x56 Venturi Scrubber Evaluation. EPA Report, EPA-600/
2-77-2096, November 1977.
Calvert, S., C. Lake, and R. Parker. Cascade Impactor Calibration
Guidelines. EPA Report, EPA-600/2-76-118, April 1976.
Calvert, S., S. Yung, and J. Leung. Entrainment Separators for Scrubbers-
Final Report, NTIS Document, PB 248-050, August 1975.
Choi, P. S., S. G. Bloom, H. S. Rosenberg, and S. T. DiNovo. Stack Gas Reheat
for Wet Flue Gas Desulfurization Systems, EPRI Report, EPRI FP-361,
February 1977.
Conkle, H. N., H. S. Rosenburg, and S. T. DiNova. Guidelines for the Design of
Mist Eliminators for Lime/Limestone Scrubbing Systems, EPRI Report, EPRI
FP-327, December 1976.
Corbett, W. E., 0. W. Hargove, and R. S. Merrill. A Summary of Important Chemical
Variables Upon the Performance of Lime/Limestone Wet Scrubbing Systems,
EPRI Report, EPRI FP-639, December 1977.
Ellison, W. "Scrubber Demister Technology for Control of Solids Emissions
from SOo Absorbers," Presented at the EPA Symposium on the Transfer and
Utilization of Particulate Control Technology, Denver, Colorado, July
1978.
Ensor, D. S., and R. G. Hooper. Century Industrial Products FRP-100
Wet Scrubber Evaluation, EPA Report, EPA-600/7-77-116, October 1977.
Federal Power Commission. The Status of Flue Gas Desulfurization Applications
in the United States: A Technological Assessment, July 1977.
Fling, R. B., W. M. Graven, P. P. Leo, and J. Rossoff. Disposal of Flue Gas
Cleaning Wastes: EPA Shawnee Field Evaluation-Second Annual Report, EPA
Report, EPA-600/7-78-024, February 1978.
Gleason, T. "How to Avoid Scrubber Corrosion," Chemical Engineering
Progress, Vol. 71, No. 3, March 1975, pp. 43-47.
Hamersma, J. W., S. L. Reynolds, and R. F. Maddalone. IERL-RTP Procedures
Manual: Level 1 Environmental Assessment, EPA Report, EPA-600/2-76-169a,
June 1976.
Hesketh, H. E. "Pilot Plant S02 and Particulate Removal Study, Report of
Fiscal Year 1974-1975 Operations," Sponsored by Illinois Institute for
Environmental Quality and Sourthern Illinois University, Project No.
10.027, August 1975.
68
-------
Javetski, J. "Solving Corrosion Problems in Air Pollution Control
Equipment," Power, Vol. 122, Nos.5 & 6, May (Part I) and June (Part II),
1978, pp. 72-77, and pp. 80-87.
LaMantia, C. R. et al. Application of Scrubbing Systems to Low Sulfur/Alkaline
Ash Coals, EPRI Report, EPRI FP-595, December 1977.
Leivo, C. C. Flue Gas Desulfurization Systems; Design and Operating Con-
siderations, Volume II, Technical Report, EPA Report, EPA-600/7-78-030b,
March 1978.
Leo, P. P., and J. Rossoff. Controlling SOg Emissions from Coal-Fired Steam
Electric Generators: Solid Waste Impact (VClume II, Technical Discussion),
EPA Report, EPA-600/7-78-044b, March 1978.
McCain, J. D. "Impactors: Theory, Practical Operation Problems, and
Interferences," in Southern Research Institute. Proceedings of the
Workshop on Sampling Analysis and Monitoring of Stack Emissions, NTIS
Document, PB-252 748, April 1976.
Mcllvaine, R. W. The Mcllvaine Scrubber Manual, Volume II, The Mcllvaine
Company, 1974 (with periodic updates).
Slack, A. V., and G. A. Hoilinden. Sulfur Dioxide Removal from Wastes Gases,
Noyes Data Corporation, Park Ridge, New Jersey, 1975.
Smith, W. W., and R. R. Wilson. Development and Laboratory Evaluation
of a Five-Stage Cyclone System, EPA Report, EPA-600/7-78-008, January 1978.
Smith, W. W., K. M. Cushing, and J. D. McCain. Procedures Manual for
Electrostatic Precipitator Evaluation, EPA Report, EPA-600/7-77-059,
June 1977.
Williams, J. E. "Mist Eliminator Testing at the Shawnee Prototype Lime/
Limestone Test Facility," Presented at the 2nd US/USSR Symposium on
Particulate Control, Research Triangle Park, N.C., September 1977.
Wesa, A. W. "Study of Various Sampling Procedures for Determining
Particulate Emissions from Coal-Fired Steam Generators," Combustion,
July 1977, pp. 34-39.
69
-------
APPENDIX A
FLOW DIAGRAMS OF EXISTING UTILITY PARTICULATE AND
PARTICULATE-S02 SCRUBBER SYSTEMS
(References for this section are included in the
references for Section 4.0)
A-l
-------
Clean Gas
ro
Power
Plant
Boiler
Flue
Gases
Reheater
tack
SCRUBBING
TRAIN
SPENT SLURRY
AND FLY ASH
THICKENED SLUDGE
To Treat-
ment and
Pumping
Facility
TREATED SLUDGE-
Main
Slurry
Pump
SUCTION
BOOSTER PUMP
TO SCRUB-
BERS FOR
MAKEUP
WATER
Manifold
SUPERNATANT
RETURN DISCHARGE
Reservoir
n>
Backup Line
Backup Line
t
PIPELINES TO RESERVOIR
Figure A-l. Simplified process diagram - Bruce Mansfield No. 1
(Pennsylvania Power Co.).
Source: Devitt etal., 1078.
-------
I
CO
Electrical
Generating
Unit No. 1
Electrical
Generating
Unit No. 2
I BOILER I I BOILER I
NO. 1 I | NO. 2 |
BOILER
NO. 3
MECH. CLCTRS.
1.0.
FAN
EXIST. STACK
FAN
r^wE
SCI
J IS
WET
SCRUBBER
STACK
FAN
BYPASS DAMPERS
SCRUBBER
BOOSTER FAN
MOBILE BE
CONTRACTO
REACTANT ADDITION
MAKEUP WATER
SLAVER
MAKEUP WATER
MIX/HOLD TANK
SPARE
Figure A-2. Process flow diagram - Green River No. 1, 2, and 3
(Kentucky Utilities).
Source: Devitt ctal., 1978.
-------
FLUE GAS
STEAM
TO STACK
>
Makeup Lime
Slurry —
Pond Liquor —
Return
MAKEUP
WATER
To Disposal Ponds VENTUR|/SpRAY
SCRUBBER AND TANK
TRAY RECIRCU-
LATION TANK
DISPOSAL POND
Figure A-3. Flow diagram of combined participate - SO^ scrubber system at Colstrip
(Montana Power Co.).
Source: LaMantia etal., 1977.
-------
FLUE
GAS
BOOSTER
FAN
>
-*
S02 Scrubber
Particu-
late
Scrubber
MODULE (A)
Ash-Laden
Water
LIMESTONE SLURRY MAKEUP
WATER MAKEUP
soz
TOWER
TANK
SO2 Scrubber
DEMISTER
Particulate
Scrubber
FLUE
GAS
BOOSTER
FAN
MODULE (B)
Ash-Laden
Water
1 SURGE
TANK
TO SLUDGE POND
pH 6.5
Figure A-4. Process Flow Oianram of the FGD System at the Choi la Power Plant
(Arizona Public Service).
Source: LaMantia et al., 1977.
-------
FLUE GAS
TO SCRUBBER
PRIMARY
CONTRACTOR
3>
ot
I.D. FAN
REHEATER
DEMISTER SECTION
MARBLE BED
FLUE GAS TO STACK
RIVER
MAKEUP
WATER
D
OXIDIZER
REACTION
TANK
V V W \/
SPRAY
PUMP
ASH POND
LIMESTONE
IT
(U
^U
i
n
-^L
RECIRC. PUMP
D
-^T
SLURRY
PUMP
SLOWDOWN
Figure A-5. Simplified Flow Diagram of Sherburne County Generating Station
(Northern States Power Company).
Source: LaMantia et ^1 . , 1977.
-------
TO STACK
FLUE GAS FROM
AIR HEATER
394,300 acfm
AT 285° F
REHEATER
r>
HOT AIR FROM (NOT USED IN
AIR HEATER "D" MODULE)
„ DEMISTER
2100 gpm (INTERMITTENT)
DEM.STER
140 gpm
(CONTINUOUS)
WATER WASH STAGE
HYDROCLONE
800 gpm
SLUDGE
TO POND
WATER FROM POND
RECIRCULJmON TANK
I pH 5.8
WATER MAKEUP
9000 gpm
LIMESTONE
SLURR
Figure A-6. Flow diagram of one of the eight FGD modules -
La Cygne No. 1 (Kansas City Power and Light).
Source: Devitt etal., 1978.
A-7
-------
00
ONE OF TWO MODULES
BYPASS
ROD
SCRUB -~
BER
4
D
GAS REHEATER
Ft
KANSAS POWER & LIGHT CO.
LAWRENCE No. 4 AQCS CON-
VERSION CE-RS/ST
Mist
>r Eliminator
IS
SPRAY
TOWER
ABSORBER
. POND RETURN
BLOWERS '-D-FAN STACK | MAKEUP
WATER
\ i '
BLOWERS I .11 Recife.
( Collection
• I Tank
i ^^
! Strainer
REACTION
To Strainer
Washers^ Wash
Pump
MAKEUP WATER
J| | I Pump
Recirc. K^1"
JTank |—©~
UI..L.
EFFLUENT BLEED
SPRAY
PUMPS
EFFLUENT BLE^D
PUMP
IXBSBl
|
f
EED
— t-* —
r
D
TANK
f) STRAINER
-tf
1
I
I
.
^c
6n>
opr
Pu
1
ay
mp
i
-»
i
j T
F
•"-I—-
WEIR
OVERFLOW
THICKENER
UNDERFLOW
PUMPS
TO
SETTLING
POND
Figure A-7. Flow diagram of combined particulate-SO^ scrubber system at Lawrence No. 4
(Kansas Power and Lirjht).
Source: Green and Martin, 1977.
-------
FLUE /^ —1 *
GAS -i^J
MAKE UP
Miif*O^ fc
roa^ug p
~&r
A1
(r-
A
'///////,
r
W M/
XX
9
INI
REI
R^^^l^^
4
H*
VEI
DIRECT f
JCATCD i-^^-i
k
i;
p— — — i
. V
. .*- STEAM
^ ^_^^
Ambient
7 «1 Alr
\2J
Makeup Water
From Ash Ponds
TRAY RECIRCU-
LATION TANK
MTURI RECIRCULATION
TANK
EVAPORATION PONDS
Figure A-8. Flow diagram of SO^-particulate scrubber system at Reid Gardner
Nevada Power Co.).
Source: LaMantia et al., 1977..
A-9
-------
FLUE GAS FROM
AIR HEATERS
MIST ELIMINATORS
MIST
ELIMINATORS
DISTRIBUTION
TANK
LIME
MAKEUP
WATER
LIQUID TRANSFER TANK
SLUDGE IS DREDGED AND
RETURNED TO THE MINE
Figure A-9. Simplified flow diagram of flyash scrubbers, Four Corners Plant
(Arizona Public Service).
Source: LaMahtia et al., 1977.
A-10
-------
FLUE GAS FROM AIR HEATERS
MIST
ELIMINATORS
Figure A-10. Simplified Flow Diagram for the Dave Johnston Flyash Scrubbers
(Pacific Power and Light).
Source: LaMantia etal., 1977.
-------
FLUE GAS TO REHEATER
MAKEUP WATER
PRESATURATION
FLUE GAS FROM \
ELECTROSTATIC N
PRECIPITATOR
Surge
Tank
LIME (pH
CONTROL)
POLYMER
^5^; MAKEUP WATER
MIST ELIMINATOR
R
y i
' *
RAPID
MIX
^--^
NEUTRALIZATION
FLOCCU-
LATION
UNDERFLOW TO
ASH PONDS
CLEAR
EFFLUENT
Figure A-ll. Simplified Cherokee Station Scrubber Flow Diagram
(Public Service of Colorado Company).
Source: LaMantia et al.,'1977.
A-12
-------
FLUE GAS TO R EH EATER
FLUE GAS FROM
ELECTROSTATIC
PRECIPITATOR
MAKEUP WATER
MIST ELIMINATOR
CLEAR
EFFLUENT DISCHARGE
PING
PONG
BALLS
FLY ASH AND
-BOTTOM ASH
^^
i
r 1
r
Lir
* CO
i r
Figure A-12. Simplified Arapahoe Station Scrubber Flow Diagram
(Colorado Public Service).
Source: LaMantia et al., 1977.
A-13
-------
MAKEUP WATER
QUENCH
SPRAY
ELBAIR
SCRUBBER
TO STACK
WET ID FANS
(2)
POST HUMIDIFICAT1ONN
SPRAY )
MIST ELIMINATOR
PUNCH PLATE
MAKEUP WATER
BOTTOM ASH POND
Figure A-13. Simplified Flow Diagram for the Clay Boswell Station
Participate Scrubber (Minnesota Power and Light Company).
Source: LaMantia et al., 1977.
A-14
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TO STACK
MAKEUP WATER
WET ID FANS
(2)
POST HUMIDIFICATIO
SPRAY
MIST ELIMINATOR
PUNCH PLATE
ELBAIR
SCRUBBER
NEUTRALIZED
EFFLUENT
Figure A-14. Simplified Flow Diagram for the
Syl Laskin Station Participate Scrubber
(Minnesota Power and Liaht Company).
Source: LaMantia etal., 1977.
A-15
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o\
FLUE GAS
FROM
MECHANICAL
COLLECTOR
BOOSTER
F.D. FAN
SPRAY QUENCHING
\
FLOODED DISC
SCRUBBER
GAS FLOW
DISC FEED
STACK
I
\
MIST
ELIMINATOR
SCRUBBER
RECYCLE
SUMP
t-
LIMESTONE BIN
MAKEUP WATER
V
LIMESTONE
SLURRY
TANK
WASTE POND
Figure A-15. Simplified flow diaqram of flyash scrubber, Lewis and Clark Plant
(Montana-Dakota Utilities).
Source: Szabo and Gerstle, 1977.
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APPENDIX B
POSSIBLE USE OF CONDENSATION SCRUBBERS ON
COAL-FIRED UTILITY BOILERS
B-l
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APPENDIX B
POSSIBLE USE OF CONDENSATION SCRUBBERS ON
COAL-FIRED UTILITY BOILERS
As indicated in the text (Section 4.3), condensation scrubbers
would not be recommended for use on coal-fired boilers. Because the
enthalpy of the flue gas entering the scrubber is low (about 110-190
Btu/lb, assuming 5 to 15 percent moisture at 300°F) and because the
particle concentration is high, a condenser section placed before a
conventional scrubber (the design for an optimum flux-force condensation
scrubber given in Calvert (1977)) would probably give only a marginal
increase in collection efficiency. (Calvert's studies indicate that
collection efficiency for 0.75 ym particles would decrease from 100% at
a dust concentration of 0.01 gr/scf to 60% at a dust concentration of
0.6 gr/scf. But utility flue gas may have dust concentrations as high
as 8.0 gr/scf.)
It may be possible, however, to incorporate condensation effects
into a scrubber system for use on coal-fired utility boilers. One
conceivable design would involve a two-stage particulate scrubber. The
first stage would be a moderate energy scrubber for removing large
particles, thereby significantly reducing the mass loading, followed by a
condenser section to enhance fine particle collection, and finally, a
second stage scrubber to remove these particles. It might even be
possible to use an SOg absorber as the second stage of the scrubber.
But detailed calculations would be necessary to insure that there would be
a significant effect at reasonable cost.
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TECHNICAL REPORT DATA
(Please read Instructions on ihe reverse before completing/
. REPORT NO.
EPA-600/7-79-018
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
Design Guidelines for an Optimum Scrubber System
5. REPORT DATE
January 1979
6. PERFORMING ORGANIZATION CODE
7. AUTHORIS)
8. PERFORMING ORGANIZATION REPORT MO.
E.R. Kashdan and M.B. Ranade
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Research Triangle Institute
P.O. Box 12194
Research Triangle Park, North Carolina 27709
10. PROGRAM ELEMENT NO.
EHE624A
11. CONTRACT/GRANT NO.
68-02-2612, Task 52
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Task Final; 4/78 - 10/78
14. SPONSORING AGENCY CODE
EPA/600/13
is.SUPPLEMENTARY NOTES IERL_RTP project officer is Dale L. Harmon, Mail Drop 61, 919/
541-2925.
16. ABSTRACT
The report gives results of a review of the performance and operating ex-
perience of existing utility scrubber systems and the state-of-the-art in design of
scrubber components. It also gives guidelines for the design of the optimum wet
scrubber system, based on this review. The U.S. EPA's Industrial Environmental
Research Laboratory, Research Triangle Park, North Carolina, is considering a
demonstration of an optimum wet scrubber system for use on a coal-fired utility
boiler. The optimum wet scrubber system has such design goals as maximum parti-
culate collection, low power consumption, and low maintenance.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lOENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group
Air Pollution
Flue Gases
Coal
Combustion
Scrubbers
Gas Scrubbing
Utilities
Boilers
Design
Dust
Air Pollution Control
Stationary Sources
Particulate
13B
21B
21D
07A,13I
13H
13A
14A
11G
18. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (This Report}
Unclassified
21. NO. OF PAGES
94
20. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Tjrm 2220-1 (R«»- 4-77) PREVIOUS EDITION is OBSOLETE
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