Environmental Protection Technology Series
CONTROL OF
RECLAMATION (SINTER] PLANT EMISSIONS
USING ELECTROSTATIC PRECIPITATORS
Industrial Environmental Researun Laooratory
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
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RESEARCH REPORTING SERIES
Research reports o.f the Office of Research-and Development,
U.S. Environmental Protection "Agency, have been grouped into
five series. These five broad categories were established to
facilitate further development and application of environmental
technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in
related fields. The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL PROTECTION
TECHNOLOGY series. This series describes research performed
to develop and demonstrate instrumentation, equipment and
methodology to repair or prevent environmental degradation from
point and non-point sources of pollution. This work provides the
new or improved technology required for the control and treatment
of pollution sources to meet environmental quality standards.
EPA REVIEW NOTICE
This report has been reviewed by the U. S. Environmental Protection
Agency, and approved for publication. Approval does not signify that
the contents necessarily reflect the views and policies of the Agency, nor
does mention of trade names or commercial products constitute endorse-
ment or recommendation for use.
This document is available to the public through the National
Technical Information Service, Springfield, Virginia 22161.
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CONTROL OF
RECLAMATION (SINTER) PLANT EMISSIONS
USING ELECTROSTATIC PRE CIPITATORS
by
John Varga, Jr.
Battelle-Columbus Laboratories
505 King Avenue
Columbua, Ohio 43201
Contract No. 68-02-1323, Task 32
ROAPNo. 21AQR-042
Program Element No. 1AB015
EPA Task Officer: Robert C. McCrillis
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
January 1976
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SUMMARY
The general aspects concerning the production of sinter in the inte-
grated iron and steel industry are discussed as an introduction to the
discussion on the control of emissions from sinter-plant windboxes.
Some technical design information is presented, as are data pertain-
ing to the characteristics of emissions. A limited amount of informa-
tion is provided concerning the procedures used to develop the required
design criteria for the construction of electrostatic precipitators.
"This report was prepared in response to Item AM-1-3
of the Protocol of the First Working Meeting of the
USA/USSR Task Force on Abatement of Air Pollution
from the Iron and Steel Industry. "
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-------
TABLE OF CONTENTS
Page
I. INTRODUCTION 1
II. TRENDS OF SINTER USE IN THE U.S. INTEGRATED
IRON AND STEEL INDUSTRY 3
III. AIR POLLUTION CONTROL FOR RECLAMATION
(SINTER) PLANTS 5
IV. CHARACTERIZATION OF EMISSIONS 11
V. RECLAMATION (SINTER) PLANT ELECTROSTATIC
PRECIPITATOR DESIGN CHARACTERISTICS 21
Basic Electrostatic Precipitator Parts 21
Dry-Dust-Collection Fundamentals ...... 23
Factors Affecting Dry Electrostatic
Precipitator Operation 28
Dry Electrostatic Precipitator Design Methods . . 40
Wet Electrostatic Precipitator 50
Wet-Dust-Collection Fundamentals ...... 50
Horizontal-Flow Wet Electrostatic Precipitator ... 58
Range of Applications 60
Reclamation (Sinter) Plant Design Specifications . 61
Reclamation (Sinter) Plant Electrostatic
Precipitator Design Data 61
VI. REFERENCES . . . 71
LIST OF FIGURES
Figure 1. Trend in the use of sinter in the metallic
burden of U. S. blast furnaces 4
Figure 2. Trend in the use of limestone in blast furnace
sinter as shown by the use of limestone in
the sinter mix . 4
-------
LIST OF FIGURES
(Continued)
Page
Figure 3. Effect of temperature and sinter basicity on
resistivity of sinter-plant particulate 8
Figure 4. Effect of sinter basicity on the collection
efficiency of an electrostatic precipitator .... 9
Figure 5. Flow diagram of a typical reclamation
(sinter) plant 12
Figure 6. Size distribution of particulates entering
dust collecting systems 14
Figure 7. Size distribution of sinter plant particulates
collected by different types of dust collecting
equipment 14
Figure 8. Size distribution of particulates released to the
atmosphere after passing through sinter plant
cleaning systems 16
Figure 9. Particle-size distribution of sinter machine dust . 17
Figure 10. Two possible rectifier circuits for an
electrostatic precipitator 22
Figure 11. Typical duct electrostatic precipitator .... 23
Figure 12. Voltage waveform for unfiltered half-wave
and full-wave rectification 29
Figure 13. Waveform in electrostatic precipitator
after discharge 30
Figure 14. Dust-collection efficiency as related to peak
voltage for a typical electrostatic precipitator . . 33
Figure 15. Electrostatic precipitator efficiency
as affected by gas flow 34
iv
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LIST OF FIGURES
(Continued)
Page
Figure 16. A typical relationship between dust resistivity
and temperature, for a gas improperly conditioned
for the 93 to 204 C (200 to 400 F) range .... 39
Figure 17. Relationship between precipitation-rate
parameter w and resistivity of fly ash 42
Figure 18. Relationship between the sulfur content in
electric utility plant fuel and the precipitation-
rate parameter to at 149 C (300 F) ...... 44
Figure 19. Collection efficiency as affected by power rate
per unit gas flow 45
Figure 20. Relationship between collection efficiency and
seetionalization (number of bus sections per
unit gas flow) for utility fly-ash precipitators . . 45
Figure 21. Relationship between precipitation-rate
parameter w and power density for fly
ash precipitators 48
Figure 22. Electrical resistivity of reclamation (sinter)
plant dust as affected by gas temperature and
sinter mixture 67
Figure 23. Relationship between the sulfur content in
electric-utility-plant fuel and the precipitation
rate parameter 67
Figure 24. Collection efficiency as affected by the ratio
of collection area to gas velocity 69
LIST OF TABLES
Table 1. Reclamation (Sinter) Plants in the U. S,
Integrated Iron and Steel Industry 6
Table 2. Sinter-Mix Composition 13
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LIST OF TABLES
(Continued)
Page
Table 3. Composition of Particulate Emissions 15
Table 4. Gaseous Emissions From Reclamation
(Sinter) Plants 16
Table 5. Size Distribution of Particulates Entering
the Atmosphere From an Electrostatic-
Precipitator-Controlled Sinter Plant 18
Table 6. (Plant D) Gaseous Emissions Entering the
Atmosphere From an Electrostatic Precipitator
Controlled Sinter Plant 19
Table 7. Representative Precipitation Rates, co,
for Various Applications 42
Table 8. Number of Rappers in Electrostatic
Precipitators for Various Applications 46
Table 9, Nomenclature for Wet-Dust-Collection
Fundamentals 53
Table 10. Equipment Specifications 62
Table 11. Reclamation (Sinter) Plant Data for Figure 22 .. 68
Table 12. Reclamation (Sinter) Plant Electrostatic-
Precipitator Characteristics 70
VI
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I. INTRODUCTION
The use of sintering processes to improve the characteristics of
blast-furnace burden materials has long been an accepted practice
in the integrated iron and steel industry. In recent years, as the
need increased for recovering the metallic values from the dusts
and scrap generated by the various iron and steelmaking processes,
the plants have become known as reclamation plants, rather than as
sinter plants.
A major problem in the control of emissions from a reclamation
plant is the minimizing of emissions from the windbox of the sinter-
ing machines. The integrated iron and steel industry in the United
States has used many types of control equipment in attempts to con-
trol emissions from sinter machines, with electrostatic precipitators,
cyclones, and scrubbers being used on 93 percent of the sinter
machines.
This Protocol Report discusses the application of electrostatic pre-
cipitators for the control of sintering-machine windbox emissions,
and is based on available published information and additional
information supplied by iron and steel companies.
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II. TRENDS OF SINTER USE IN THE U.S.
INTEGRATED IRON AND STEEL INDUSTRY
The integrated iron and steel industry of the United States operates
45 reclamation plants having a total of 72 sintering strands. The
reclamation plants consist of 2,9 single-strand plants, 10 double-
strand plants, 3 plants having 3 strands, 2 plants with 4 strands,
and 1 plant with 6 strands. During 1974, the integrated iron and
steel industry produced 36, 985>, 182 metric tons (40, 769, 185 net tons)
of blast furnace sinter. (1) The greatest tonnage of sinter was pro-
duced in 1964 and amounted to 49, 518, 907 metric tons (54, 585, 251
net tons). The trend in the percentage of sinter used in the metallic
burden (iron ore + pellets + sinter) of blast furnaces is shown in
Figure 1. The year 1961 was the year of greatest percentage use of
sinter, 44 percent of the blast-furnace metallic burden. The de-
crease in use of sinter has beein caused by the increase in production
and use of pellets in the U. S. integrated iron and steel industry.
Although there has been a decline in the use of sinter in blast furnaces,
the sinter that is being made iti more and more of the self-fluxing
variety (high basicity). The trend in increased basicity is illustrated
by the increased use of limestone in the sinter mix as shown in Figure
2. Integrated iron and steel plants that are heavily committed to the
use of self-fluxing sinter are using limestone in amounts even
greater than the average illustrated in Figure 2.
-------
50
Q
CC
m
o
_i
_i
<
UJ
5
u.
O
I-
LU
1-
o
40
30
20
1960
1965
1970
1974
YEAR
Figure 1. Trend in the use of sinter in the metallic
burden of U. S. blast furnaces
20
X
I
CC £
UJ U
g I
w £
- I 10
§1
I ' ' ' ' I ' ' '
1960
1965 1970 1974
YEAR
Figure 2. Trend in the use of limestone in blast
furnace sinter as shown by the use of
limestone in the sinter mix
4
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III. AIR POLLUTION CONTROL FOR
RECLAMATION (SINTER) PLANTS
The emissions associated with reclamation-plant operation are pri-
marily particulates that become entrained in the combustion air as
it is drawn through the sinter mix into the windbox. However, sulfur
dioxide, carbon monoxide, and hydrocarbons may also occur in the
emissions, depending on the operating practice of(a particular rec-
lamation plant. Sulfur dioxide may originate from sulfur contained
in the ore and the coke that are used as part of the sinter mix and
in the fuel used to ignite the mixture, and it may also originate from
the sulfur contained in machining oils that adhere to steel turnings,
which are recycled to a reclamation plant to recover the metallic
values. Machining oils are also the principal source of hydrocarbons
in reclamation-plant windbox emissions.
Electrostatic precipitators, scrubbers, and cyclones are the princi-
pal means for controlling emissions from the windboxes of sinter
machines, while baghouses are the preferred method for control at
other reclamation-plant locations, such as sinter discharge, crush-
ing, screening, and material-transfer points. The reclamation
plants in the U. S. integrated iron and steel industry are listed in
Table 1. The distribution of air pollution control equipment used on
the windbox of sinter machines is as follows:
Type of Control Number
Electrostatic Precipitator 22
Cyclones 11
Scrubbers 9
Baghouse 1
Steam Ejector 1
Mechanical 1
Total "45
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TABLE 1. RECLAMATION (SINTER) PLANTS IN THE U. S. INTEGRATED IRON AND STEEL INDUSTRY
Company
Alan Wood Steel Co.
Bethlehem Steel'Corp.
) It I Steel Corp.
U. S. Steel Corp.
W-P Steel Corp.
Bethlehem Steel Corp.
J & I Steel Corp.
Bethlehem Steel Corp.
National Steel Corp.
W-P Steel Corp.
Armco Steel Corp.
J & L Steel Corp.
Republic Steel Corp.
U. S. Steel Corp.
Youngstown S & T Co.
Armco Steel Corp.
National Steel Corp.
Inland Steel Co.
U. S, Steel Corp.
Youngstown S & T Co.
Bethlehem Steel Corp.
Interlake Steel Corp.
National Steel Corp.
Republic Steel Corp.
U. S. Steel Corp.
I-H, Wisconsin Steel
Republic Steel Corp.
U. S. Steel Corp.
Lone Star Steel Co.
Armco Steel Corp.
CF 4 I Corp.
U. S. Sreel Corp.
Kaiser Steel Corp.
Location
Swedeland, Pa.
Bethlehem, Pa.
Johnstown, Pa
Aliquippa, Pa.
Braddock, Pa.
McKeesport. Pa.
Rankln, Pa.
Saxonburg, Pa.
Falrless Hills, Pa.
Monessen, Pa.
Lackawanna. N. Y.
Star Lake, N. Y.
Sparrows Point, Md.
Welrton, W. Va.
E. Steubenvtlle. W. Va.
Mlddletown, Ohio
Cleveland, Ohio
Cleveland, Ohio
Youngstown, Ohio
Warren, Ohio
Lorain, Ohio
Youngstown, Ohio
Campbell, Ohio
Ashland, Ky.
Ecourse, Michigan
East Chicago, Ind.
Gary, Ind.
Indiana Harbor, Ind.
Burns Harbor, Ind.
South Chicago, 111.
Granite City, 111.
South Chicago, 111.
South Chicago, 111.
South Chicago. 111.
Gadsden, Ala,
Falrfield, Ala.
Lone Star. Texas
Houston, Texas
Pueblo. Colorado
Geneva, Utah
Fontana, Cal.
No. of
Strands
3
4
2
1
1
1
1
1
1
1
2
1
2
2
6
1
2
1
1
1
1
1
1
1
1
2
1
1
1
2
3
1
1
1
1
1
3
1
1
4
1
1
2
2
2
Estimated
Annual
Capacity,
net tons
475,000
2,400,000
1, 100, 000
2,700,000
600,000
325,000
600,000
1,500,000
1, 500, 000
1.500.000
3, 000, 000
500, 000
1, 100, 000
1,400,000
3, 600. 000
4,250,000
2, 800, 000
550, 000
900, 000
900; 000
400.000
500, 000
400, 000
500,000
1. 500, 000
800,000
800, 000
2,000,000
1.200,000
1.500.000
5,200,000
1.200,000
2.000.000
750,000
1,000,000
400,000
2.200.000
500. 000
500, 000
2, 500, 000
300.000
500. 000
900.000
900. 000
1,300,000
Alt Pollution Control
Ignition
Fuel
Coke -oven gas
Natural gas
Natural gas
Coke-oven gas
Mixed gas
Natural gas
Natural gas
Natural gas
Natural gas
Natural gas
Mixed gas
Coke-oven gas
Coke -oven gas
Fuel oil
Coke -oven gas
Coke-oven gas
Coke -oven gas
Natural gas
Coke-oven gas
Coke-oven gas
Coke -oven gas
Natural gas
Natural gas
Natutal gas
Natural gas
Coke-oven gas
Coke -oven gas
Mixed gas
Natural gas
Natural gas
Coke-oven gas
Coke-oven gas
Coke-oven gas
Natural gas
Coke -oven gas
Coke -oven gas
Natural gas
Natural gas
Coke-oven gas
Coke-oven gas
Mixed gas
Coke -oven gas
Machine
Wind box
Scrubber
ESP
ESP
Cyclones
ESP
Scrubber
ESP
ESP
ESP
ESP
ESP
ESP
ESP
Cyclones
ESP
Scrubber
Cyclones
Scrubber
Scrubber
ESP
Cyclones
Cyclones
Cyclones
Cyclones
ESP
Cyclones
Mechanical
Scrubber
ESP
ESP
ESP
ESP
Scrubber
ESP
Scrubber
Cyclones
ESP
Scrubber
Cyclones
ESP
Scrubber
Steam Ejector
ESP
ESP
Baghouse
Machine
Discharge
Baghouse
Baghouse
Scrubber
Baghouse
Wet separators
Recycle
Multlcyclones
Baghouse
Baghouse
Baghouse
Cyclones
Baghouse
Baghouse
Scrubber
Crushing &
Screening
Baghouse
Scrubber
Baghouse
Scrubber
Scrubber
Baghouse
Wet separators
Baghouse
Multlcyclones
Baghouse
Baghouse
Baghouse
Baghouse
Baghouse
References
(2.3)
(4,5,6,7)
(8.9)
(10,11,12)
(13)
(14)
(15)
(16,17)
(13)
(18)
(19)
(13.20)
(13,21)
(13,22)
(13.23)
(24)
(25)
(13,26)
(13.27,28)
(13,28)
(13,28)
(13,29)
(30)
(13.31)
(32)
(33)
(34.35)
(13)
(36)
(13)
(37)
(38,39)
(40.41,42)
(13)
(43,44)
(45)
(13)
(13)
(15)
(15)
(13,46,47)
(13,15)
(48,49)
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Most sintering operations that use electrostatic precipitators as
control equipment for windbox omissions also use cyclones, or
mechanical collectors, between the windbox and the fan. In the pre-
ceding tabulation, 10 sinter machines are listed as having cyclones
for the control of windbox emissions. The cyclones are the only air
pollution control devices on these 10 machines.
With respect to the control of emissions, developments in blast-
furnace technology have created problems for the reclamation-plant
operator. The increased use of high-basicity sinter introduces
higher limestone additions to the sinter mixture. The relationship
between temperature and resistivity for six different sinter-plant
dusts is shown in Figure 3.' "' The effect of sinter basicity on the
efficiency of an electrostatic precipitator is shown in Figure 4.'-^'
The variations in resistivity and the effects of basicity are the rea-
sons that the control of sinter plant emissions is difficult. The
problem of different resistivities may result in the installation of
additional electrostatic-precipitator chambers, with one group de-
signed to collect the iron oxide particulates and another group to
collect the limestone particulates. In some instances, electrostatic
precipitators were replaced by scrubbers to overcome the problem
of different properties of the two types of emissions.
Integrated iron and steel plants that have facilities for making
finished steel products, such as threaded pipe, generate oily ma-
chine turnings which are sent to the reclamation plant for recovery
of the metallic values. The oil on the turnings creates problems in
electrostatic precipitators, and in some cases hydrocarbons will
pass through a scrubber system. Electrostatic-precipitator col-
lector plates become coated with films of oil, which makes removal
of the dusts difficult and in some cases impossible. If a steel plant
is committed to the recovery of oily turnings in its reclamation plant,
the trend is to use high-energy wet scrubbers for air pollution
control, rather than electrostatic precipitators. The three newest
reclamation plants under construction or recently placed into opera-
tion in the United States (those located at Bethlehem Steel Corpora-
tion's Sparrows Point and Burns Harbor plants, and the Armco Steel
Corporation's plant at Middletown, Ohio) all have high-energy
scrubbers as the primary air pollution control equipment on the
sinter-plant windbox. (**, 22, 25, 37)
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100
V
o
>
£
C/}
LU
OC
10
12
10
,11
10
10
109
TEMPERATURE, F
200 300
400
i i i i I i i i T | i ri ii IT i i I i i i i I i i n
PLANT A
BASICITY 4.0
CaCO, -
PLANT A
BASICITY 4.0
PLANT B
BASICITY 1.0
PLANT C
BASICITY 4.0
PLANT D
BASICITY 4.0
PLANT E
BASICITY 1.0
i . .
, . . I
50
100 150
TEMPERATURE, C
200
Figure 3. Effect of temperature and sinter basicity on
resistivity of sinter-plant particulate
8
-------
100
90
~ 85
£
0 80
o
UL
ul 75
70
65
0.5 0.7
0.9 1.1 1.3
SINTER BASICITY
1.5 1.7
Figure 4. Effect of sinter basicity on the collection
efficiency of an electrostatic precipitator
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IV. CHARACTERIZATION OF EMISSIONS
Emissions from reclamation plants usually consist of the following:
(1) minor amounts of dust generated in the handling and grinding of raw
materials, (2) particulates that are drawn down through the grate bars
of the sintering machine, (3) combustion gases from ignition and firing
of the sinter mix, and (4) dust generated during the cooling, crushing
and screening operations. Points of emission are indicated in the flow
sheet in Figure 5 for a typical reclamation plant. Circled numbers on
the flow sheet are indexes to the circled numbers in the following dis-
cussion on the characterization of emissions.
(T) Iron Ore Dust. Particles are rounded to elongated in shape and
can have a size as small as 2 microns. Larger particles are opaque,
and red-orange when viewed under top light. Individual small grains
are transparent and blood-red. (51) The particulates consist mostly of
Fe2O3 or Fe3O4, some silica, and limestone, with a Mohs hardness of
5 and a specific gravity of 5.2.
(2) Limestone Dust. Primarily the mineral calcite. It is colorless,
with light-transmitting characteristics varying from transparent to
translucent. Because of their good cleavage, particles generally occur
as rhombohedra. Fragments may also occur as prisms. (->!) The Mohs
hardness is 3 and the specific gravity 2. 7.
(3) Coke Dust. Particles are opaque, irregularly shaped, quite
porous, and rough with some straight, sharp edges. They are gray to
black in reflected light and are cibout 90 percent carbon. (^1)
(4) Combustion Products. Gases leaving the sintering strand are
the result of the combustion of coke or coal in the sinter mix and of the
fuels used to ignite the sinter mixture. Fuel for ignition is primarily
coke-oven gas or natural gas, with some use of mixed gas or fuel oil.
Hydrogen sulfide in the coke-oven gas and sulfur in the coke or coal in
11
-------
COARSE ORE
LIMESTONE COKE
i
DUST] [COLLECTED DUST
ATMOSPHERE
Figure 5. Flow diagram of a typical reclamation (sinter) plant.
12
-------
the sinter mix can lead to sijlfur dioxide emissions in the off-gas.
Even though an excess of air is drawn through the sinter mix to assure
oxidizing conditions, in most caises it is insufficient to burn the hydro-
carbons completely in the sinter mix (hydrocarbons originating from
oily turnings and volatiles in coal and coke); thus unburned hydro-
carbons may be present in the sinter-plant off-gas. Incomplete com-
bustion also produces carbon monoxide in the off-gas.
(D © (Z) Sinter Dust. Dust may contain particles of iron
oxides, calcite, iron-calcium silicates, and quartz. Iron oxide can be
opaque, black, rounded particles of magnetite (Fe^Q^) with angular
faces and/or dense, rounded, elongated, and nearly spherical agglomer-
ates of hematite (Fe2O3). Calciite occurs as smooth, rounded parti-
cles, and quartz as a transparent, rounded particle. The iron-calcium
silicates are transparent, vitreous, colorless to yellow to green, and
irregularly rounded with smooth surfaces. l-*l)
Qj) Atmospheric Emissions. Characterization of emissions to the
atmosphere are discussed below, on the basis of work reported by
plants in the U.S. integrated iron and steel industry.
Data pertaining to the sinter-mis composition from three sinter plants,
the chemical compositions of particulate emissions, and the composi-
tions of gaseous emissions are given in Tables 2, 3, and 4,
respectively. (52, 53)
TABLE 2. SINTER-MIX COMPOSITION
weight percent
Sinter-Mix Components Plant F Plant G Plant H
Iron ore
Dry blast-furnace dust
Blast-furnace filter cake
Melt-shop slag
Rolling-mill scale
Basic -oxygen-furnace dust
Miscellaneous dust
Limestone or dolomite
Coke
29.1
1.3
15.8
6.5
11.5
3.5
0.0
28.2
4. 1
82. 0
0.0
0.0
0.0
15.0
3.0
49.5
5.6
4.9
0.0
7.6
0.0
6.7
20.8
4.9
13
-------
o
111
z
ui
DC
LU
O
OC
UI
a.
a
LU
100
90
80
70
60
50
40
30
20
10
0
1
i 11ui
11 nl i i i i11nl
i i i i i in
10 100 1000
PARTICLE SIZE, microns
10000
Figure 6. Size distribution of particulates entering dust collecting
systems
100
90
80
70
60
50
40
30
20
PLANT F
MULTICYCLONES-
10
100
1000
10000
PARTICLE SIZE, microns
'Policeman is an enlarged section of the duct
containing baffles and a right-angle bend.
Figure 7. Size distribution of sinter plant particulates collected
by different types of dust collecting equipment
14
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TABLE 3. COMPOSITION OF PARTICULATE EMISSIONS
weight percent
Particulate Component
Fe2O3
CaO
MgO
K20
Si02
A1203
Na20
ZnO
MnO
Chlorides
Sulfates
Hydrocarbons
Other
Loss on Ignition
Total
Plant F
33.9
7. 1
5.3
5.2
4.8
2.6
1.6
0.4
0.2
8.5
7.5
7. 4
1.6
13.9
100.0
Plant G
11.7
10.9
0.4
0.6
2.4
4.3
0.8
0. 1
0. 1
3.0
16.5
36.9
0.0
12.3
100.0
Plant H
28.0
15.0
2.0
8. 1
4.6
2.5
0.0
0.0
0.0
8.8
2. 1
0.0
0. 0
28.9
100.0
The size distributions of participates entering the dust-collecting sys-
tems in Plants F and G are shown in Figure 6. (52) The size distribu-
tions of particulates collected by different dust-collection equipment in
Plants F and G are shown in Figure 7(52)^ an(j the size distribution of
particulates released to the atmosphere from Plants F, G, H and I
are shown in Figure 8. (52> 53> 54)
Particle-size distributions of particulates entering a mechanical col-
lector vary over a considerable range, as shown in Figure 9. ^ ' The
size range of the particulates lesaving the mechanical collector and
entering the electrostatic precipitator is of a smaller magnitude than
that of particulates entering the mechanical collector.
15
-------
TABLE 4. GASEOUS EMISSIONS FROM RECLAMATION
(SINTER) PLANTS
Gaseous Component
Sulfur dioxide
Chlorides
Fluorides
Ammonia
Milligrams per Cubic Meter
Plant F Plant G Plant H
78.0 65.0 36-65
80.0 32.0 5-44
8.0 0.5 0.00
0.0 2.6 0.00
Volume
Percent
Plant H
Carbon dioxide
Carbon monoxide or
illuminants
Oxygen
4o
3.4- 5.0
0.4- 0.9
16.5-18.1
100
90
80
70
60
50
40
30
20
10
0
PLANT G\ \
X \\
1
5 10 50 100
PARTICLE SIZE, microns
500
Figure 8. Size distribution of particulates released to the
atmosphere after passing through sinter plant
cleaning systems
16
-------
LU
N
CO
UJ
o
<
LU
OC
o
LJL
Q
01
z
<
LU
OC
LU
O
CC
LU
O.
I-
C3
LU
§
O
99.9
99.8
99.5
99.0
98.0
95.0
90.0
80.0
70.0
60.0
50.0
40.0
30.0
20.0
10.0
5.0
2.0
1.0
0.5
0.2
0.1
, SIZE RANGE OF DUST FROM MECHANICAL
COLLECTOR TO ELECTROSTATIC PRECIPITATOR
SIZE RANGE OF DUST FROM SINTER
MACHINE TO MECHANICAL COLLECTOR
I
i i
J_
i i i
1
345 10 20 30 50 100
PARTICLE SIZE, microns
200 300 500 1000
Figure 9. Particle-size distribution of sinter machine dust
During 1975, emission tests were made on a sinter plant having elec-
trostatic precipitators as the wlndbox air pollution control system.
The sinter machine has four strands with an estimated production
capacity of about 227 metric tons (250 net tons) per hour. The sinter
mix composition was as follows:
Sinter-Mix Components
Iron ore
Reclaimed oily mill scale and flue dust
Reclaimed basic oxygen furnace slag
Limestone and dolomite
Coal
Total
Weight Percent
52
8
17
16
7
100
17
-------
The sinter produced has a basicity varying between 1. 0 and 1. 5, which
is in the range of self-fluxing and superfluxing sinter, for the particular
plant operation. Windbox exhausts are controlled by multiclones, fol-
lowed by electrostatic precipitators. One electrostatic precipitator is
used to control emissions from two sinter strands, and each is de-
signed to operate at a gas flow rate of 10, 903 m^/min (385, 000 acfm)
at 118 C (245 F). The size distributions of particulates collected dur-
ing two tests are given in Table 5. (54) xhe variation in the size distri-
butions is not explained in the test report. However, this may have
been caused by the day-to-day variations in the fineness of the mate-
rials charged to the sinter mix.
TABLE 5. SIZE DISTRIBUTION OF PARTICULATES ENTERING
THE ATMOSPHERE FROM AN ELECTROSTATIC-
PRECIPITATOR-CONTROLLED SINTER PLANT
(Plant I)
Particulate Size, Cumulative Weight Percent Retained
microns Test No. 1 Test No. 2
>12.00
7.50
5. 10
3.50
2.20
1. 10
0.68
0.46
<0.46
54.36
62.56
65.05
66.62
69.22
70.49
72.50
73.56
100.00
10.43
21. 50
30.97
40.20
47.89
58.65
66.99
76.48
100.00
Note: Particle size determinations were made with an
Andersen Cascade Impactor.
Gaseous emissions obtained from the same tests are given in
Table 6. (54)
18
-------
TABLE 6. (PLANT I) GASEOUS EMISSIONS ENTERING THE
ATMOSPHERE FROM AN ELECTROSTATIC
PRECIPITATOR CONTROLLED SINTER PLANT
Gaseous Component
Condensable hydrocarbons
Noncondensable hydrocarbonsi
Fluoride
Carbon monoxide
Sulfur dioxide
Sulfur trioxide
Nitrogen oxides
Milligrams
Nm3
1.036
812. 11
3.21
'
Grains
SCFD*
0. 000453
0.3539
0.00140
-
ppm
-
230
-
8000
900
11.5
71.4
'Standard cubic foot (dry).
For Plant I, particulate contents at the electrostatic precipitators were
as follows:
Average ESP inlet
Average ESP outlet
mg/m3 (dry)
595
69
grains/ft3 (dry)
0.26
0. 0.3
This corresponds to a collection efficiency of 88. 4 percent. Total emis
sions to the atmosphere amounted to 23. 4 kg per hour (51.6 pounds per
hour). This was equivalent to 0. 214 kg per tonne (0.428 pound per net
ton) of sinter.
19
-------
V. RECLAMATION (SINTER) PLANT ELECTROSTATIC
PRECIPITATOR DESIGN CHARACTERISTICS
This section of the report concerns design fundamentals for duct-type
(i.e., those that use plates for collection), wet and dry electrostatic
precipitators. Electrostatic precipitators using tubular or pipe
collectors are not considered.
BASIC ELECTROSTATIC PRECIPITATOR PARTS*
The three basic parts of any precipitator installation are:
(1) Power supply
(2) Collection area i
(3) Dust-removal area.
. The power supply generally consists of a single-phase, hjLgh-voltage
transformer, appropriate control equipment, and a bridge rectifier
circuit. The rectifier circuit can be either a full-wave or double
half-wave circuit, as shown in Figure 10.
Rectifier design has progressed from the mechanical rectifier to the
high-voltage Kenotron vacuum tube, selenium, or silicon rectifiers.
Normal transformer ratings are between 15 and 25-kva, 440-volt
primary and 50 to 75-kv secondary. In order to limit short-circuit
current surges, the transformer primary circuit usually contains a
ballast resistance or a reactor. Manual or automatic control is used
to regulate electrical conditions in the precipitator dust-collection
area.
The collection area consists of duct collection electrodes with high-
voltage discharge electrodes uniformly spaced and of uniform length,
"Reprinted from Iron and Steel Engineer. Electrostatic Precipitator Primer. J. Katz, by permission
of the Association of Iron and Steel Engineers; pp. 21-40, May 1964.
Zl
-------
HIGH VOLT.
TRANS.
BRIDGE
RECTIFIER
PRECIPITATOR
(-) PROPER
LOW VOLTAGE
INPUT
FULL-WAVE CIRCUIT SCHEMATIC
TlGtiU
TRANS.
BRIDGE PRECIPITATOR
RECTIFIER (-) PROPER
LOW VOLTAGE
INPUT
-Hck
GRD.
RETURN^
DOUBLE HALF-WAVE CIRCUIT SCHEMATIC
Figure 10. Two possible rectifier circuits for an
electrostatic precipitator
as illustrated in Figure 11. Collecting electrodes (the metal surfaces
that collect the particles) are at ground potential and are connected
directly to the frame of the precipitator. The collecting-surface
design varies with the manufacturing company and process. The duct
collecting surface may consist of perforated or solid metal plates up
to 6. 1 x 1.4 meters (20 x 4-1/2 feet). Normally a precipitator has
three to four duct sections in series. The duct width may be 200 mm
(8 inches) although 250-mm (10-inch) ducts are sometimes employed
in cleaning gases that contain large quantities of dust. There can be
five or six discharge electrodes equally spaced in each 1.4-meter
(4. 5-foot) duct section. These discharge electrodes receive the high-
voltage rectifier output and are suspended in parallel from a frame-
work that is insulated from ground by ceramic insulators.
22
-------
THE MAIN DISCHARGE
ELECTRODE FRAME IS
SUSPENDED BY POST
INSULATORS FROM THE
PRECIPITATOR ROOF.
THUS MAINTAINING
ELECTRICAL CLEARANCE
FROM GROUNDED
COLLECTING PLATES.
USUALLY STIFFENER
BAFFLES ARE PRESENT
ON ENDS TO HELP
MINIMIZE DUST
EROSION.
DIRTY GAS FLOW
CLEAN GAS FLOW
COLLECTING PLATES ARE
TIED INTO THE TOP SHELL
OF THE PRECIPITATOR.
SPACER PLATES AT THE
BOTTOM KEEP PLATES
PROPERLY ALIGNED.
PLATES CAN BE RAPPED
SEPARATELY OR IN
SECTIONS BY A BAR
CONNECTING THE ENDS
OR BOTTOMS.
Figure 11. Typical duct electrostatic precipitator
Dust removal is accomplished either mechanically or hydraulically,
depending on the physical state of the process. Most applications
involve a dry process; the collected dust is removed by rapping or
vibrating the plates. The method used to remove material from the
collecting surfaces is most important to minimize particulate reen-
trainment and electrical disturbances. Material vibrated from the
collecting plates falls into hoppers for subsequent removal.
Dry-Dust-Collection Fundamentals
Before discussing each of the major factors affecting the collection
of particulates with electrostatic precipitators, it would be well to
understand the process fundamentals. Simply stated, the process
consists of charging dust particles with a corona discharge and then
passing them through an electric field where they are attracted to
the collecting surfaces.
23
-------
There are five basic kinds of electrical discharge through a gas
spacing between a high voltage circuit:
(1) The dark discharge is not visible although chemical
action occurs. The current increases nearly
linearly with voltage.
(2) The glow or corona is the most frequent initial
discharge and is accompanied by a hissing noise.
Current increases much faster than voltage.
(3) The brush discharge usually falls midway between
corona and a spark. It consists of a number of
small sparks ending in space and originates in
surface irregularities or abnormalities in the
conductors. Current increases with possibly a
slight drop in voltage.
(4) The spark is a common discharge that is unstable
in that the increased current lowers the voltage
appreciably. It is the sudden rush of electric
current through the gas, and is limited only by
the circuit power supply. The spark is the most
complete form of gas "breakdown".
(5) The arc is not ionization by collison as are the
preceding four categories but arises from other
discharges. Current density is very high, while
the voltage decreases to a low value. This dis-
charge is particularly unstable unless the current
is limited by an external electrical circuit
resistance.
In order for a current to flow across a gas space, ionization must
be started and sustained by electron acceleration and collision with
gas molecules causing a cumulative effect.
For the case of a negative wire in a cylinder, the following explana-
tion describes the corona current ionization principle: Electrons
are released from the wire surface by a positive-ion impact or photo-
electric emission. These accelerating electrons in short movements
near the wire surface generate new electrons and positive ions by
molecular impact. The electrons quickly move away from the wire
and attach to gas molecules to form negative ions or produce new
24
-------
collisions. Once the corona glow begins, ultraviolet radiation may
produce additional photoelectrons at the wire surface. As this
electron collision continues, the negative ions build a dense cloud
throughout the space between the active region near the wire and the
passive anode. The effect of this ion space charge is to help limit
the ionizing field near the discharge wire and also to stabilize the
corona discharge.
This ion movement has two main charging effects on dust particles
in the precipitator region between the electrodes.
(1) Suspended dust particles are bombarded toward the
anode under the force of a strong electric field.
(2) Ion diffusion causes the negative ions to attach
themselves to dust piarticles less than 0.2 micron
in size and, by this method, transport these
smaller particles to the collecting plate.
The following expresses the principles of the electron precipitator
in theory.
Migration velocity or precipitation rate of particles:
a EQ Ep
«* 2?re (1)
where
a = particle radius, microns
Ep = strength of field in which particles are charged,
statvolts/cm
EQ = strength of field in which particles are collected,
statvolts/cm (normally the field close to the
collecting plates)
9 = viscosity or frictional resistance coefficient of
the gas, poises
TT= 3.1416.
Collection efficiency of precipitator:
M
T] = 1. - e V ' (2)
25
-------
where
A = effective collecting electrode area of the precipitator,
sq m (sq ft)
V = gas flow rate through the precipitator, cu m per sec
(cu ft per sec)
e = base of natural logarithms = 2. 718
c*> = migration velocity, m per sec (ft per sec).
The equation for efficiency is known as the Deutsch-Anderson
equation.
Equation (1) shows that an increase in both particle size and electric
fields, EQ and E_, will increase precipitator performance, while
increased gas viscosity will adversely affect performance. A study
of Equation (2) shows that the precipitator efficiency increases with
increasing values of the exponent - A w/V. Therefore, as the pre-
cipitator electrode area becomes greater and the migration velocity
increases, precipitator performance improves. At the same time,
if the gas flow rate increases, the precipitator performance
decreases.
To illustrate the velocity with which a single dust particle moves to
the collecting surface under the influence of an electric force, the
following example is given for a typical steel-mill gas:
a = 1 micron particle = 10"' cm
EQ = 4. 8 kv/cm = 16 statvolts/cm
Ep = 6. 0 kv/cm = 20 statvolts/cm
9 = 2. 7 x 10~4 gas viscosity at 260 C (500 F), poises.
From Equation (1), the migration velocity is:
- IP"4 x 16 x 20
" ~ 2 x 3. 14 x 2.7 x 10-4
= 18.9 cm/sec = 0.62 ft/sec.
26
-------
If the discharging wire is 100 mm (4 inches) from the collecting plate
and the gas flow through the duct is 1. 22 m/sec (4 ft/sec), the dust
particle would reach the collecting surface in approximately 0. 6 meter
(2 feet) of duct length.
Under similar dust and precipitator conditions but with the gas cooled
to 150 C (300 F), the gas viscosity decreases to 2.3 x 10 poises:
- 10"4 x 16 x 20
" ~ 2x3. 14 x 2.3 x 10-4
co = 22. 2 cm/sec = 0. 73 ft/sec.
To determine the effect on conditions in the first example by increas-
ing the average arid peak precipitator voltages by 20 percent:
10-4 x 19.2 x 24
co =
2x3. 14 x 2.7 x 10-4
w = 27. 2 cm/sec = 0. 9 ft/sec.
The dust particle drift velocity to the collecting plate increased 50 per-
cent when the precipitator voltages increased 20 percent.
Consider the first example except that the average dust particle size
is now 5 microns:
5 x 10'4 x 16 x 20
OJ =
2x3. 14 x 2.7 x 10-4
co = 95 cm/siec =3.1 ft/sec.
27
-------
Thus, a 5-micron particle should reach the collecting plate in about
0.43 feet of duct length with the 4-fps gas flow. When this is com-
pared with the migration velocity of a 1-micron dust particle, it
points up the need for an accurate dust-radius measurement to
obtain the correct migration velocity for any gas.
To calculate a precipitator collection efficiency using an average
dust particle size of 1-micron radius, substitute the original example
migration velocity in Equation (2):
0. 189 Ac
Tl-l-e r~~T~~.
A typical precipitator duct might have the following physical
parameters:
Collecting surface A
= 6. 2 m high x 3. 6 m long x 2 sides = 44. 6 sq m
= (20 ft high x 12 ft long x 2 sides = 480 sq ft).
Dust gas flow rate V at duct conditions
= 6. 2 m high x 0. 2 m wide x 1. 22 m/sec = 1. 51 cu m/sec
= (20 ft high x 0. 667 ft [ 8-inch spacing] x 4 ft/sec =
53.4 cu ft/sec).
Substituting for A and V in Equation 2:
0. 189 x 45. 1 / 0.62 x 480 \
~ i - i 53-4 I
7) = 1 - e = \ 1 - e /
T) = 1 - 0. 0037
7) = 0. 996 or 99. 6 percent.
These equations help to explain precipitator performance scientifically.
However, other factors result in discrepancies.
Factors Affecting Dry Electrostatic
Precipitator Operation
The difficulties of dust adhering to the collecting plates, poor gas
distribution and spark-over conditions are three factors that reduce
the theoretical migration velocity. Each precipitator application will
determine the deviation of the u> factor from field data. This provides
a base for future installation calculations as well as a means for
28
-------
comparing precipitators in the same application. The succeeding
paragraphs will discuss the major factors that affect precipitation.
The migration velocity, w, is quite sensitive to the voltage since the
electric fields appear as a product in Equation 1. Therefore, the
object is to obtain maximum voltage with proper corona current
flow for maximum collection efficiency. The major factors that
determine this condition are:
(1) Applied voltage frequency and waveform
(2) Spark-over characteristics
(3) Electrode characteristics
(4) Gas flow rate
(5) Gas flow distribution
(6) Dust concentration
(7) Dust composition, including particle size and
resistivity
(8) Gas temperature, pressure and humidity.
Applied Voltage, Frequency and Waveform The rectifier input is
conventional 60-hertz power. Therefore, half-wave and full-wave
energization contains 60 and 120 pulses/sec, respectively, as shown
in Figure 12.
k1 CYCLE = 1/60 SEC ~j
EACH SECTION
OBTAINS ONE
PULSE PER CYCLE
UNFILTERED HALF-WAVE ENERGIATION AT
POINT A - FIGURE 10
0|
UNFILTERED FULL-WAVE ENERGIZATION AT
POINT B - FIGURE 10
Figure 12. Voltage waveform for unfiltered half-wave and
full-wave rectification
29
-------
Negative polarity is used. The negative wave is impressed on the
discharge electrode while the grounded collecting electrode serves
as the positive terminal. Negative polarity on the electron-emitting
discharge wire has proved superior in that it allows a higher spark-
over potential to be reached in the precipitator before a voltage
breakdown occurs between the two electrodes.
Consider the precipitator proper as a number of parallel capacitors
in which the high-voltage discharge electrode and the collecting
electrode form the plates of the capacitor while the gas serves as
the capacitor dielectric. Therefore, every voltage pulse tends to
charge this precipitator capacitance, which provides a natural
voltage filter as this capacitance discharges through the gas resis-
tance, changing the actual precipitator voltage waveform to that of
Figure 13. The maximum and minimum voltages are now simply
Ep and Em.
CYCLED 1/60SEC*|
VOLTAGE DECAY
BETWEEN PULSES
PRECIPITATOR HALF-WAVE VOLTAGE
MEASURED AT POINT C - FIGURE 10
PRECIPITATOR FULL-WAVE VOLTAGE
MEASURED AT POINT D - FIGURE 10
Figure 13. Waveform in electrostatic precipitator after discharge
The current output with half-wave energization is one-half that of
full-wave energization. Also, the voltages E_ and Em of the full-
wave waveform are closer (i.e., the full-wave Ep is slightly less
than the half-wave E ), while the full-wave Em is greater than the
half-wave Em. Half-wave energization has several advantages over
full-wave in most installations.
30
-------
Two of the major advantages are:
(1) The same rectifier output can be distributed to
smaller precipitator areas, as shown in Figure 10.
This construction necessitates additional switching
and bus connections. However, the continuity of
operation and collection efficiency will usually
benefit from this construction since localized
trouble in one section will not affect the electrical
characteristics in other sections.
(2) The half-wave, because of the time lag between
voltage pulses, is less likely to sustain a voltage
breakdown between electrodes.
If, in Equation 1, EQ is the average field voltage, then EQ = 1/2
(E + Em). These measurements can be obtained by oscilloscope
readings across appropriate voltage dividers. Typical field voltages
in duct precipitators are:
E = 3.X9 to 5. 9 kv/cm (10 to 15 kv/in.)
Em = °- 3 to 0. 5 kv/cm (7 to 12 kv/in.).
Total corona current comprises a gas ionic current and a dust cur-
rent in which electrons attach themselves to a dust particle. The
ionic current is approximately 95 percent of this total current.
Oscilloscope readings of current waveforms show that conductivity
of an electron tube rectifier is in the range of 60 to 80 percent of
each half cycle. The ratio of peak current to average current should
be 4. 0 to 5. 0 for efficiency. The current will vary from 10 to 30
ma/100 sq m (1000 sq ft) of collecting area.
Alteration of the waveform by a, pulse method of energization has
definite potential advantages, but this technique has never been used
commercially. Certainly, the adjustment of voltage, frequency, and
waveform to fit individual precipitators could benefit efficiency,
especially for high-sparking conditions between discharge wire and
collection plate.
Spark-Over Characteristics - The voltage breakdown between elec-
trodes for a given precipitator depends on many complex variables
31
-------
and is the point of maximum power input. Field measurements have
shown that under normal conditions, 50 to 100 voltage breakdowns
(spark-overs) per minute are tolerable. On the basis of half-wave
energization with a possible 3600 pulses per minute, additional power
input can be obtained with 100 sparks per minute since the voltage
collapse during the spark-over is more than offset by the higher
input during the nonsparking cycle. One must differentiate between
spark-over and a power arc in that a spark-over is 1/2-cycle dura-
tion or less while a power arc may last several cycles and is quite
detrimental to precipitator performance. Some precipitator applica-
tions will not spark within power-supply input limitations because of
dust and gas conditioning. In most cases, the quantity of water
carried by the gases and the gas temperature play an important part
in this phenomenon.
Electrode Characteristics - Electrode configuration determines
voltage and current characteristics. Diameter and shape of the
discharge electrode determines the initial voltage required to start
a corona discharge. For most practical gas applications, this
voltage varies from 16 to 26 kv. In addition to material strength,
two important factors that affect the operation of the discharge elec-
trode are the wire diameter and curvature of the corona-emitting
surface. The smaller the wire diameter, the greater is the corona
current for any given voltage. The spacing between the discharge
wire and collecting surface determines the required voltage. If the
discharge wire is not centered perfectly within the collecting area,
the spark-over voltage is reduced. Higher stress concentration
exists in the reduced clearance between the wire and collecting elec-
trode. This phenomenon of concentration points becomes very
important with some types of collecting surfaces. Surface imperfec-
tions and slight differences in collection-plate construction can reduce
spark-over voltage. Figure 14 shows the relationship between field
voltage and collection efficiency and illustrates the importance of
providing maximum field voltage. Imperfections or stress concen-
trations in electrode design should be minimized, especially with
dusts resistive to current. The solid collecting plate is a recent
design that minimizes spark-over between electrodes. Dust buildup
on the discharge electrode, by producing a change in electrode con-
figuration, can cause stress concentrations at the bottom and the top
of the dust deposit. Dust buildup on the discharge wire tends to re-
duce corona current. The close spacing between discharge wires
can also result in current reduction.
32
-------
100
95
+*
c
8
8. 90
o
5 85
o
80
75
70
NOTE EFFECT OF
SMALL INCREASE IN
VOLTAGE ON EFFICIENCY
> INCREASES IN 2-KV STEPS
TYPICAL RANGE IS 32 TO 60 KV
PRECIPITATOR PEAK VOLTAGE, kilovolts
Figure 14. Dust-collection efficiency as related to peak
voltage for a typical electrostatic
precipitator
Changing the wire-to-wire spacing alters current-voltage relation-
ships. When the discharge wires are relatively far apart, the
current per unit length of wire tends to remain constant. As the
wires are spaced closer and closer, the starting voltage increases,
which tends to lower the current. Therefore, there is an optimum
wire-to-wire spacing for which the total current is a maximum, and
practice indicates that this spacing should be 150 percent of wire-to-
plate spacing. An interesting aspect of wire-to-wire spacing is that
the field strength near the plate is less midway between wires than
it is directly opposite the wires. Therefore, the closer the discharge
wires are to each other, the higher the average field strength until
the current is suppressed.
The corona current also depends on the wire-to-plate spacing and
changes inversely as the square: of the ratio between two different
spacings. If the wire-to-plate sipacings were reduced from 100 to
75 mm (4 to 3 inches), the corona current would practically double.
33
-------
However, if the wire spacing were increased from 100 to 125 mm
(4 to 5 inches), the corona current would decrease about one third.
Gas Flow Rate Collection efficiency of the precipitator is designed
on a gas-volume basis. However, the effect of gas flow on perfor-
mance is sensitive to several factors:
(1) In a high-sparking unit where power input must be
less than required to reach the designed collection
efficiency, improved collection can be obtained
at 70 to 80 percent of precipitator gas-volume
rating. Actually, a distinct difference in perfor-
mance will be noted under these conditions, as
illustrated in Figure 15.
100
95
+-
I 90
a
>"
^ 85
o
u- 80
ui
z
O 75
o
ui
8
70
CURVE A
GOOD CONDITION
CURVE B
POOR
DISTRIBUTION
CURVE C
HEAVY SPARKING
I
I
I
I
I
80 90 100 110 120 130 140
GAS FLOW, percent of rating
150
Figure 15. Electrostatic precipitator efficiency as
affected by gas flow
34
-------
(2) With maximum voltage fields and power input, gas
volume overloads of 10 to 25 percent have little
effect on collection efficiency. In fact, the dust
size determines just how much excess volume is
possible, since reentrainment in the gas is greater
with large-dust-particle collection and is minimized
with fume and wet collection. Migration drift
velocity is greatest with maximum voltage which
can overcome gas flows of even 4.6 m/sec (15 ft/
sec) through collecting areas of some cleaning
applications.
Gas Flow Distribution - Precipitator performance may deviate from
design calculations because of poor gas distribution through the pre-
cipitator inlet. Consider an installation designed for 95 percent
collection efficiency where one-half the precipitator is treating
75 percent of the gas volume. Depending on the dust, a 5 to 20 per-
cent decrease in collection efficiency may result. This condition
is the same as overloading the one half of the precipitator with
150 percent of rated gas volume.
In an inlet cross section composed of 20 to 30 equal areas, the designer
should assure that no single area deviates more than 10 to 15 percent
from the average cross-sectional flow. It is important that minimum
gas turbulence coincide with the optimum gas pattern. Minimum gas
turbulence is a direct function of inlet flue design and gas flow direct-
ing vanes and baffles if used. Usually the gas flow from a particular
process travels at high velocities (from 9. 1 to 18. 3 m/sec (30 to 60
ft/sec) and must be reduced to 1. 5 to 3. 0 m/sec (5 to 10 ft/sec) at
the precipitator inlet. Careful study at this stage of the design can
often insure a highly efficient unit. If the size of the installation or
critical nature of the process warrants the additional cost, gas-flow
pattern can be investigated in scaled-down glass models of the pro-
posed structures. However, duplicating actual gas-flow conditions
in glass-model studies presents many problems.
To help reduce gas turbulence and poor distribution, low-pressure-
drop plates across the precipitator inlet are normally employed.
However, a low-pressure drop across these plates may not^ drastically
alter existing conditions. After the unit goes into operation, it is
wise to measure the distribution pattern across the inlet with a pitot
tube or other suitable means. Field alterations can be made on the
basis of actual measured results.
35
-------
The kind of dust collected by the precipitator influences the effect of
gas distribution on precipitator efficiency. In most cases, fumes or
fine dust have less effect than gases containing larger dust particles.
In the last analysis, poor gas distribution reduces collection efficiency
appreciably since it adversely affects the electrical characteristics.
The power input of a precipitator section is limited by the lowest
spark-over point of that section.
Dust Concentration An interesting facet of electrostatic precipitation
is the effect that the quantity of dust has on the cleaning process. The
dust concentration does not basically influence the precipitator's size
for any given efficiency. The following facts should be considered
when dust concentrations are heavy. First, the quantity of dust alters
voltage-current characteristics: more dust increases voltage and
reduces current. Second, frequent dust removal from the collecting
electrode should minimize dust reentrainment in the gas stream.
Third, if the dust quantity is great enough, the first section may re-
quire 254-mm-wide (10-inch-wide) ducts to eliminate a possible spark-
over caused by excessive voltage buildup.
If the dust is discharged to the atmosphere, the dust quantity must
meet minimum stack discharge specified by community air-pollution
ordinances. Considering two different gas concentrations of 2. 3 and
34 grams/cu m (1. 0 and 15 grains/std cu ft) flowing through a 95 per-
cent efficient precipitator, comparative outlet dust discharges would
be as follows:
(2. 3 grams/cu m) x (1. 0-0. 95) = 0. 12 gram/cu m
(34. 0 grams/cu m) x (1. 0-0. 95) = 1. 70 grams/cu m
(1. 0 grains/std cu ft) x (1. 0-0. 95) = 0. 05 grain/std cu ft
(15. 0 grains/std cu ft) x (1. 0-0. 95) = 0. 75 grain/std cu ft.
In order to obtain an outlet discharge of 0. 12 gram/cu m (0. 5 grain/
std cu ft) with an inlet concentration of 34 grams/cu m (15 grains/std
cu ft) the following precipitator efficiency is required:
/ 0. 12 gram/cu m \ . , _
(1.0- * -. 1 100 = 99. 67 percent
\ 34. 0 grams/cu m /
f, ^ 0. 05 grain/std cu ft \ . nn nn , _
1.0- s . /: 100 = 99. 67 percent .
\ 15. 0 grains/std cu ft /
This efficiency can be obtained with the electrostatic precipitator but
the process should warrant the additional cost of carefully optimizing
the design.
Typical dust concentrations in iron and steel industry waste gases are:
36
-------
Open-hearth furnace - 0. 12 to 3. 43 grams/cu m (0. 05 to
1. 5 grains/std cu ft)
Basic blast furnace after usual primary dust collection -
9 to 11 grams/cu m (4. 0 to 5. 0 grains/std cu ft)
Oxygen steelmaking furnace - 9 to 21 grams/cu m (4. 0 to
9. 0 grains/std cu ft) average
Ferromanganese blast furnace after primary dust collec-
tion - 23 to 34 grams/cu m (10. 0 to 15. 0 grains/std cu ft).
Particle Size and Resistivity - The migration velocity is directly
affected by dust-particle size as noted in the basic formula. Small
particles are more difficult to precipitate out of the gas stream than
large particles, and require higher power and voltage to remove.
Although the coarser particle is more easily collected, it may also
be more easily lost to the gas stream through reentrainment resulting
from vibration of the collection plate or erosion caused by gas eddy
currents. . .
This lack of dust adhesion is a major factor in reducing the actual
precipitator efficiency below a value predicated by the calculated mi-
gration velocity. For example, although the large particle does reach
the collecting plate in a shorter time, reentrainment in the gas stream
can take place throughout the length of the precipitator until, finally,
the particle is lost to the atmosphere. The coarse or large particle
is important in some applications in that it may keep the submicron
dust from impacting on the collecting plate.
Particle size in waste gases from open-hearth processes will generally
vary from <0. 5 to 5 microns, and from 15 to 25 microns and larger
from sintering-plant operations. The smaller particles of ferrous
oxide come from open-hearth, electric-furnace, and oxygen-vessel
fumes. Submicron particles are difficult to precipitate and have a
tendency to suppress corona current if numerous enough. This charac-
teristic is similar to the space charge around a discharge electrode.
Voltage-current relationship is marked by high precipitator voltage
and practically nil corona current. Although high-voltage fields are
desirable, the electrostatic collecting process still requires sufficient
corona current to sustain ionic movement to the collecting plates.
Another interesting effect of dust-particle size is the influence on
visual stack discharge. The finer particles cause the stack discharge
37
-------
to appear quite dense, while the actual weight of dust in a given
volume of gas could fall well within air-pollution ordinance require-
ments. This phenomenon, caused by the greater surface area of
submicron particles per unit weight, is significant not only from a
community goodwill standpoint, but more importantly because of the
fact that the emissions are respirable particles.
In previous paragraphs, maximum power input and high-voltage fields
were prerequisites for efficient performance. Although the several
factors discussed earlier will tend to lower spark-over voltages,
the optimum electrical characteristics depend primarily on the resis-
tivity of the particular dust. In other words, will the dust resist or
will it react favorably to the corona current flow?
High-resistivity dust causes severe sparking between electrodes so
the power input must be reduced to reach the desirable spark-over
rate of 50 to 100 sparks per minute. Under these conditions, precipi-
tator performance sometimes runs 5 to 20 percent below design values.
The chemical composition of the dust particle directly affects its
electrical characteristics. However, proper gas temperature and
humidity can alter the dust-resistivity range to obtain good results.
In some cases, additional water, steam, or a special conditioning
gas can be injected into the gas stream to realize optimum electrical
results.
With the wet process of removing deposits from collecting surfaces,
excessive spark-over because of dust resistivity is insignificant.
Where a highly resistive dust is deposited on dry collecting surfaces,
a voltage gradient across the dust layer can be high enough to emit
its own corona discharge. This situation can disturb electrical condi-
tions, with excessive sparking at lowered voltages or with excessive
current at greatly lowered voltages without sparking. This second
condition can produce enough positive ions to counteract the negative
space charge and significantly reduce the migration rate. The term
back-discharge or back-corona commonly describes this situation.
Low gas moisture content with the absence of certain chemical impuri-
ties in the temperature range 116 to 232 C (240 to 450 F) is likely to
cause a highly resistive dust condition.
Temperature, Pressure, and Humidity - In any particular precipitator
installation, varying temperature, pressure, or humidity will cause
some change in electrical characteristics. Since higher gas
38
-------
temperature will decrease gas density, lower precipitator voltages
and higher currents are usually obtained. Higher gas pressure will
have an opposite effect by increasing the voltage and decreasing the
corona current. This phenomenon parallels the effect that increased
dust concentration has on corona power. In addition, if a highly
resistive dust is1 encountered, the resistivity can.be varied by either
increasing or decreasing gas temperature from a maximum resistivity
operating range. This maximum resistivity will vary with the kind of
dust, but the band width will normally encompass 50 to 80 C (90 to
150 F) as illustrated in Figure 16.
E
V
CO
o
Figure 16.
10
13:
DUST TEMPERATURE, F
100 200 300 400 500
600
^12
>11
E2 10
cc
,10
109
10*
T
T
I
EACH KIND OF
DUST WILL SHOW
VARYING CURVES
DUE TO MOISTURE
AND PRESSURE
50 100 150 200 250
DUST TEMPERATURE, C
300
A typical relationship between dust resistivity and
temperature for a gas improperly conditioned for
the 93 to 204 C (200 to 400 F) range
Moisture affects the electrical conditions indirectly and directly.
Moisture indirectly decreases dust resistivity, while it directly in-
creases the spark-over voltage appreciably. In the gas-temperature
range below 260 C (500 F), the indirect and direct effects from the
addition of moisture are equally beneficial. Over 260 C (500 F), the
direct effect of raising the spark-over voltage predominates.
39
-------
Increasing the moisture content usually produces a rise in precipitator
voltage and a drop in current.
Dust Removal From Collection Plates - One factor not included in the
fundamental precipitation formula but of major practical concern is the
vibration or rapping method employed to remove dust buildup from
electrode surfaces. Various equipment and methods are available but
all should
(1) Minimize irregular dust buildup on electrode surfaces
to reduce spark-over possibilities
(2) Offer rapping cycles of short enough duration to
eliminate dust puffs through the stack
(3) Determine the type of rapping system, whether
vibrating or single blow, that provides optimum dust
removal with special dust composition, temperature,
and humidity conditions
(4) Design the collecting area controlled by each plate
rapping system as small as economically possible
(5) Provide for varying the rapping magnitude between
inlet and outlet precipitator sections
(6) Above all, the pattern of any rapping system should
be determined from internal inspection if poor pre-
cipitator performance is attributed to inefficient
rapping.
Dry Electrostatic Precipitator
Design Methods
The two methods used in the design of all electrostatic precipitators
both rely on empirical relationships developed by equipment manufac-
turers over their years of construction experience. The first method
is based on the conventional Deutsch-Anders on efficiency equation
and the second method approaches the design from the standpoint of
the electrical requirements. These methods must obviously give
compatible results. They differ mainly in the fundamental way in
which design is approached.
40
-------
Dry Electrostatic Precipitator Design Method I - A common approach
to the selection of the area of collecting plate required is to utilize
the Deutsch-Anderson equation
1 ' 7) = 1 - e
where
T) = efficiency
AC = effective electrode collecting area, sq cm (sq ft)
V = gas flow rate through the precipitator, cu cm/sec (cu ft/sec)
w = migration velocity, cm/sec (ft/sec) (precipitation-rate'
parameter)
e = base of natural logarithms = 2. 718.
The critical parameter in this equation is the precipitation rate w.
This parameter varies with each installation, depending upon resis-
tivity arid particle size of the dust, quality of gas flow, reentrainment
losses, and sectionalization, among other factors. The values of
u) are selected by the equipment manufacturers on the basis of past
experience with a particular dust, or from the composition of the dust
that can be related to past experience. Each precipitator manufacturer
therefore has a file of experience from whi.ch a precipitation rate
parameter can be selected, and this file of information is kept as
proprietary data.
The values of the precipitation-rate parameter oo vary with the applica-
tion as a result of variations in dust properties. Variations also occur
within each application area. Table 7 lists the average values of
precipitation-rate parameter for various applications, and the range
of values that might be expected within each application. From this
table, it is apparent that the spread in the values of the precipitation-
rate parameter is large in some instances, such as in fly-ash precipi-
tator s, and within a reasonably narrow range in others.
The major problem in the design of precipitators based on this
approach is the selection of the precipitation-rate parameter for the
specific application. Several techniques can be used to narrow the
uncertainty of the value of to to be used. If the in situ resistivity of
dust is known, the precipitation-rate parameter can be determined
for some applications. Figure 17 shows the variation in co with
41
-------
TABLE 7. REPRESENTATIVE PRECIPITATION RATES, w, FOR
VARIOUS APPLICATIONS
Application
Utility fly ash
Pulp and paper
Sulfur ic acid
Cement (wet)
Smelter
Open hearth
Cupola
Blast furnace
Sinter plant
n.a. - data not available.
3 20 ill
cc
LU
1-
LU - .
1 16'-
cc
0.
LU g
< i 10 -
CC o
1
g
< 5 -
o
LU
? n iti
109
Average
cm/sec ft/sec
13.1 0.43
7.6 0.25
6.3 0.24
10.7 9.35
1.8 0.06
4.9 0.16
3.1 0.10
10.9 0.36
n. a. n. a.
i i i i ij i i i i i
^
^x.
^v
>S
^
, .,..1 , . . ,,
1010
Range
cm/sec ft/sec
4.0-28.4 0.13-0.67
6.4- 9.5 0.21-0.31
6.1- 8.6 0.20-0.28
0.3-12.4 0.30-0.40
n. a. n. a.
n. a. n. a.
n. a. n. a.
6.1-14.0 0.20-0.46
2.3-11.5 0.07-0.38
. . ,j -OO"
- 0.492
|
\ - 0.328 -'
\ 4
\
\
X. - 0.164
*»*^.-i
i 1 1 1 i i i i i i i i n nnn
1011 1012
RESISTIVITY, ohm-cm
Figure 17. Relationship between precipitation-rate parameter
w and resistivity of fly ash
42
-------
resistivity for fly-ash precipitators. If the precipitator being designed
is a replacement for, or an addition to an existing unit, resistivity can
be measured, and the uncertainty in the value of w can be reduced.
Alternatively, if a similar installation is available, measurements of
resistivity can be made and the value of to selected with some confidence.
The data from Figure 17 apply only to fly ash or to a dust with similar
properties. If the particle size differs significantly, the absolute
values of to will change, although the general character of the curves
would be similar.
In situ resistivity data have not been determined to the same degree in
applications other than in fly ash precipitators, so that statistically
reliable data relating to and resistivity are not generally available.
If it is impractical to select to on the basis of resistivity, other factors
can often be used. In fly-ash precipitators, resistivity is influenced
by the sulfur content of the fuel, and relationships have been developed
between precipitation-rate parameter to and percentage of sulfur con-
tent. Figure 18 shows a curve developed for a group of fly-ash precipi-
tators burning coals with varying sulfur contents. On a statistical
basis, the precipitation rate can be predicted within reasonable accur-
acy. However, on an individual installation, the variations are too
great to predict to with acceptable precision on the basis of sulfur
content alone. In many instances, the only information available is
the sulfur content of the coal, and designs are sometimes based solely
upon this parameter.
Particle size of the dust is a very important consideration in deter-
mining the value of to for design purposes. Referring to Table 5, the
variations in to between the various application areas are due largely
to particle-size variations. In cement kilns, the alkali content of
the raw material alters the size distribution of the dust. Metallurgi-
cal operations characteristically produce smaller size dusts from
high-temperature melting operations. Size of dusts from recovery
boilers in pulp and paper mills can change with temperature. These
factors result in variations in precipitation-rate parameters between
the various applications, and within the same application area.
When the selection of precipitation-rate parameter has been made,
the area of collecting surface required to achieve a given efficiency
when handling a given gas volume can be determined.
43
-------
20
0.656
o
cc
LU
LU
5
15
0.492
Ill
DC
i
g
s
10
0.328
0.164
O
ui
cc
a.
1 2 3
SULFUR CONTENT OF COAL, percent
0.000
Figure 18. Relationship between the sulfur content in electric
utility plant fuel and the precipitation-rate
parameter u> at 149 C (300 F)
The power required for a particular application is determined on an
empirical basis. ' The power requirements for a given application are
related to the efficiency and the gas volume handled. Figure 19 is
a curve showing the power requirements per unit of gas volume for
two applications: fly-ash precipitation and pulp- and paper-mill
recovery boiler precipitation. Similar curves can be developed for
other applications. The second step in design, therefore, is to deter-
mine the total power requirements based on efficiency and gas flow.
Note that the recovery-boiler precipitators require greater power
per unit of gas flow to achieve the same efficiency as that of a fly-ash
precipitator. This is primarily due to differences in particle size of
the dust and is related to the precipitation-rate parameter.
Figure 20 shows the variation in collection efficiency with the number
of independently powered bus sections. The number of sections
required to reach a given efficiency can be determined from curves
44
-------
POWER RATE, watts/1000 cu ft/min
200 300 400 500
600
FLY ASH
PRECIPITATOR
RECOVERY BOILER
PRECIPITATOR
500 1000 1500
POWER RATE, watts/100 cu m/min
2000
Figure 19. Collection efficiency as affected by power rate per
unit gas flow
NUMBER OF BUS SECTIONS PER 100,000 cu FT/MIN
0123456
99.9
§
2L
99.0
90.0
O 80.0
UJ
_i
70.0
8
60.0
50,r
T
T
I
I
0 0.5 1.0 1.5 2.0
NUMBER OF BUS SECTIONS PER 1000 CU M/MIN
Figure 20. Relationship between collection efficiency and sectionalization
(number of bus sections per unit gas flow) for utility fly-ash
precipitators
45
-------
for the specific application. The relationship shown in Figure 21 is
for fly-ash precipitators and was developed from empirical relation-
ships from a large number of tests.
The above procedure will provide a rational basis for arriving at plate
area, total power, and degree of sectionalization required. It should
be recognized that the selection of the value of w and the curves relat-
ing power and sectionalization requirements are all interrelated.
If inadequate sectionalization is used, a lower value of u> would result,
the precipitator could not be operated at the required power level,
and the efficiency would be reduced. Consequently, curves relating
the design parameter should be internally consistent.
The type and number of rappers for the collecting and discharge
electrodes depend upon the properties of the dust, gas properties,
current densities, and the configuration of the electrodes and elec-
trode support structures. High-resistivity dust is usually harder to
remove because of the increased force holding it to the plate. L/ow-
temperature operation also tends to give a moist dust that is more
difficult to remove. Table 8 shows the number of rappers per unit
are of collecting electrode and the number per unit length of dis-
charge wire for a group of installations.
TABLE 8. NUMBER OF RAPPERS IN ELECTROSTATIC PRECIPITATORS
FOR VARIOUS APPLICATIONS
Application
Utilities
Pulp and paper
Metals
Cement
Collection
Number Rappers
100 Square Meters
0.27-0.97
0.27-1.07
0.12-0.88
0.35-0.56
Electrode
Number Rappers
1000 Square Feet
0.25-0.90
0.25-0.99
0.11-0.82
0.33-0.52
Corona
Number Rappers
100 Meters
0.03-0.22
0.07-0.10
0.09-0.16
0.06-0.11
Electrode
Number Rappers
1000 Feet
0.09-0.66
0.21-0.32
0.28-0.50
0.19-0.33
The following example will serve to illustrate this design approach.
Design an electrostatic precipitator for a pulverized fuel boiler with
the following given conditions :
46
-------
(1) Dust resistivity, 7 x 1010 ohm-cm
(2) Ga's temperature, .149 C.(30.0 F) .
(3) Gas volume,. 21, 240 actual cu m/min (750, 000 actual.
cu ft/min) . . . .
(4)' Sulfur content, 1. 8 percent
'. , r ' ' * '' ' '
(5) Efficiency, 99 percent. .
Example:
(a) Select a precipitation-rate parameter.
From Figure 17 the precipitation-rate parameter corres-
ponding to a dust resistivity of 7 x 10*0 ohm-cm is about
. 10.7 cm/sec or 6. 4 m/min (0.35 ft/sec or 21. 0 ft/min)
. . (b) From the Deutsch-Anders on equation
/AC"\
r)=l-e ' V'
or rearranging
. V 100
A,= In
_ 21,240 100 _ 750,000 1
Ac ~ A A in inn _ QQ Ac ~ ?! in inn
w 100 - r)
00
6.4 100 - 99 c 21 100 - 99
= 3319 In 100 = 35,700 In 100
= 15, 285 sq m = 164, 000 ft2.
(c) Compute total power requirements.
From Figure 19, power required for 99 percent efficiency
is 495 watts/100 cu m/min (140 watts/1000 cu ft/min).
For 21, 240 cu m/min (750, 000 cu ft/min), total power =
212.4 x 495 = 105,000 watts (750 x 140 = 105,000 watts).
(d) Determine number of bus sections.
From Figure 20, number of bus sections required is 1. 22/
1000 cu m/min (3. 5/100, 000 cu ft/min).
21. 24 cu m/min x 1. 22 = 26 bus sections (7. 5 cu ft/min x
3. 5 = 26 bus sections).
(e) Determine the number of rappers required on the basis of
past experience (see Table 8).
47
-------
Dry Electrostatic Precipitator Design Method II - A second approach
to the sizing of precipitators is to determine the electrical charac-
teristics first and then develop relationships that relate efficiency
and power requirements to the required collection-surface area. The
concept of the electrical approach is based on the theoretical factors
that influence the precipitation-rate parameter, that is, the current
required to charge the particles and provide the space charge field,
and the voltage required to establish the electrostatic collection field.
In this design method, the curves relating efficiency and corona power
density are developed on an empirical basis. The curves are the same
as that for Design Method I, and are given for fly ash and recovery
boiler precipitators in Figure 19. Figure 21 is an empirically devel-
oped curve showing relationship between precipitation-rate parameter
20
-? 18
I
3 '6
tr
£ 14
LU
1 12
cc
£ 10
i s
I 6
!r 4
POWER DENSITY, watts/sq ft
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2
I
I
I I I I
T I
I I I I I I I I I I I I
0.660
0.595
0.530
0.465
0.400 0
0.335 £
3
0.270
0.205
0.140
0.075
0.000
4 567 8 9 10 11 12 13
POWER DENSITY, watts/sq m
Figure 21. Relationship between precipitation-rate parameter
w and power density for fly ash precipitators
w and corona power density. Since the total power has been determined
previously, the collecting surface area can be computed from the data
read from Figure 21. The number of independent bus sections can be
determined in the same manner as in Method I. The following example
will serve to illustrate the design procedure based on this method.
Example:
(a) Select a precipitation-rate parameter.
From experience with this coal, the precipitation rate
parameter is selected to be 10. 7 cm/sec (0. 35 ft/sec).
48
-------
(b) Compute corona power.
From Figure 19, power per unit volume corresponding
to a collection efficiency of 99 percent is 495 watts/100 cu
m/min (140 watts/1000 cu ft/min).
The total power is then computed:
4Q(i watts
p _ y3 wattsx 21,240 cu m/min =105,000 watts.
100 cu m/min
p = i/n x 750,000 cu ft/min = 105, 000 . watts J
1000 cu ft/mm '
(c) Determine collection electrode area.
From Figure 21, for w = 10. 7 cm/sec (0. 35 ft/sec), power
density = ,6. 89 watts/sq m (0. 64 watts/sq ft).
Collection electrode area = 105, 000 watts x -. f - -
' 6. 89 watts
= 15,240 sq m
Collection electrode area = 105, 000 watts x ' * -
.
, / ~ , - 64 watts
= 164, 000 sq ft
(d) Number of electrical sections.
From Figure 20, the number of sections per 1000 cu m/
min at 99 percent efficiency = 1. 22 (sections per 100, 000
cu ft/min = 3.5). ,
Number of sections = . -.--. ' - ; x 21, 240 cu m/min
1000 cu m/min
= 26.
Number of sections = . . . nnn' - 7-7 x 750, 000 cu ft/min
100, 000 cu ft/mm '
= 26.
It should be noted that the curves relating the various factors in
Method II must also be mutually compatible. The major difference
between these two design methods is that the empirical data are used
to arrive at the collecting-surface area as opposed to the use of the
Deutsch-Anderson equation. In the examples shown, the precipitation-
rate parameter to was used in both instances. However, it is possible
to develop other relationships that would eliminate the necessity for
arriving at a value of co altogether. Such relationships would be
empirical and would be subject to the same degree of uncertainty as
the selection of the precipitation- rate parameter.
49
-------
A more fundamental approach to precipitator design would be that
based upon theoretical factors such as particle size, gas composition,
dust resistivity, precipitator dimensions, and other input conditions.
This method is discussed in the following section. However, at this
time, techniques for design based only on theoretical relationships have
not been developed to the extent that they can be used on a commercial
basis.
WET ELECTROSTATIC PRECIPITATOR
The use of wet electrostatic precipitators for control of emissions from
industrial sources was generally restricted to rather specialized appli-
cations such as on acid mist, coke-oven off-gas, blast furnaces, and
detarring applications. The method of cleaning was in most cases
intermittent and of the wetted-wall type.
As a result of much more stringent local, state, and federal emission
regulations, condensable materials were added to the total particulate
loading. The removal of organic condensables, which are very difficult
to wet and which form small droplets in the 0. 1 to 2-micron range, re-
quires scrubber pressure drops in the range from 100 to 150 cm (40 to
60 inches) of water gage. Since the wet electrostatic precipitator is
always operated at saturation temperature (100 percent relative humid-
ity), it will remove organic materials with a condensation temperature
higher than or equal to the gas saturation temperature. It will also re-
move solid dust particles in the submicron range and gaseous contami-
nants soluble in the spraying liquor. The removal of emissions is done
with very low energy consumption and a pressure drop usually less than
12. 7 mm (0. 5 inch) of water gage. The electric power input through
the high-voltage power supplies is quite low, from 1. 8 to 2. 8 kw per
100 actual cu m/min (0. 5 to 0. 8 kw per 1000 actual cu ft/min).
The recent development of a continuously sprayed, parallel plate,
frame electrode and horizontal flow design has provided industry with a
realistic alternative to high-energy scrubbers. The theory of operation,
description of the design, range of applications, limitations of the
method for performance prediction, and the energy consumption are
discussed in the following sections.
Wet-Dust-Collection Fundamentals(55)
The corona generation and the charging and discharging processes in
the wet electrostatic precipitator are, in general terms, similar to what
takes place in a conventional dry electrostatic precipitator except for
some important differences.
50
-------
Since the gas in the wet precipitator is always saturated with water
vapor, there the current and voltage relationship is somewhat different
from that in the dry precipitator. With increasing amounts of water
vapor, the spark-over voltage increases (i.e., the voltage at which the
field breaks down), but the corona current at a given voltage is lower.
When solid particles and droplets enter the electrostatic field, they will
cause a local distortion of the electrostatic field between the electrode
and the collecting plate. Some of the electric Afield lines intersect the
particles, and ions generated.by the corona discharge will tend to travel
along lines of maximum voltage gradient or along the field lines; there-
fore, some of the ions will collide with the particles and the charge
gradually builds up on the particles.
This process continues until the charge on the particles is so high that
it diverts the electric-field lines away from the charged particles, pre-
venting new ions from colliding with the dust particle. When this state
has been reached, the particles are said to be saturated with charge.
Theory shows that the saturation charge value and charging time are
dependent upon electric-field strength, size of the particle, the dielec-
tric constant of the particle, and the relative position of the particle in
the field. This charging process is said to be field dependent and is the
dominant process down to a particle size of 0. 2 |Um. For smaller
particles, the so-called diffusion charging process is the dominant
mechanism; this is governed by the random thermal motion of the ions
and is not limited to a saturation charge.
As soon as the charging process of the particle starts, the resulting
electrostatic force will pull the particle towards the collecting plate.
This force, together with the gravitational and the drag forces, and the
gas flow distribution in the field determine the particle trajectory and
its point of collection.
In a dry electrostatic precipitator, the dust buildup on the collecting
plate limits the maximum voltage at which the precipitator can operate.
For dust layers with high resistivity (greater than 2 x ICr^ ohm-cm)
the voltage drop can be from 10 to 20 kv. This condition lowers the field
strength in the space between the electrode and the dust deposit surface,
and results in a lower saturation charge, which again gives a lower
electrostatic force. If, on the other hand, the resistivity of the dust
layer is lower than 10' ohm-cm, the electrostatic force holding the dust
particle on the plates is low, and reentrainment can become a serious
problem during the electrode and plate cleaning (rapping) cycle and also
during the steady operation, having the overall effect of lowering the
precipitator collection efficiency.
51
-------
For a continuously sprayed wet electrostatic precipitator, the pre-
viously discussed problems are nonexistent. The spray liquid drops
form a film on the collecting plates which continuously washes off the
dust that is being collected; the resistivity of the liquid film is the
governing factor in the dust-discharging process and not the resistivity
of the dust layer itself. Reentrainment problems are also nonexistent,
since the collected particles are instantaneously and continuously re-
moved from the point of collection and are washed down as a light
slurry. The exit loading is, therefore, much more stable and does not
have the characteristic sharp increase that the dry electrostatic pre-
cipitator has during the collection plate and electrode rapping cycles.
Therefore, for a wet electrostatic precipitator, the operation is not
influenced by the resistivity of the dust layer. The major parameters
that must be considered are the particles' dielectric constant and size.
In order to better understand the effect of low dielectric constants on
horizontal migration distance of the particle, a mathematical model of
the particle collection mechanism was developed. The analysis was
based upon a field charging process and a particle or droplet which had
to traverse the whole net field spacing (one half of the plate-to-plate
spacing). Particles of different sizes with dielectric constants of 2,
10, and 78 were investigated.
The unit consisted of parallel collecting plates with a separation of 2r.
The velocity profile between the plates was assumed to be flat (plug flow)
and turbulent drag forces were neglected. Centered between two plates
was an electrode frame, with electrode spacing assumed sufficiently
close to provide an approximately uniform electrostatic field near the
plate surface. The field strength was approximately 70 percent of the
field that was to be produced by a solid discharge plate electrode, or
E = -0. 70 dv/dr. (3)
The nomenclature for the equations is given in Table 9.
The current density under no-load condition will be
J = i/Ac. (4)
The ionic space charge can be determined from the current density
electric field equation:
J = N0epiE (E = mean electrostatic field strength). (5)
52
-------
TABLE 9. NOMENCLATURE FOR WET-DUST-COLLECTION
FUNDAMENTALS
A = 67Taf)/m = constant
Ac = Collection area
aj = Particle diameter
d.
B = qsE/m = constant
ci = Particle inlet loading
c0 = Particle outlet loading
E = Electrostatic field strength
e = Electric charge
F = Force
g = Gravitational constant
i = Current
J = Current density
In = Natural logarithm
m = Particle mass
N0 = Number density of free ions
V = Gas flow rate
q = Charge
qs = Saturation charge
r = Net field spacing
sx = Transverse distance
sz = Horizontal distance
T = Migration time for collection
t = Time
v = Voltage
w = Velocity
wgas = Gas average velocity
wx = Transverse particle velocity
wz = Horizontal particle velocity
x = Transverse horizontal distance
y = Vertical distance
z = Horizontal axial distance
£ = Dielectric constant
eo = Permittivity of free space
9 = Viscosity of gas
T] - Collection efficiency
|Uj_ = Carrier mobility of the gas
71 - 3.1416
T = Charging time constant
w = Migration velocity parameter
53
-------
The saturation charge for a nonconductive particle is
£ 2
qs = ^^z^o^- <6>
The relative dielectric constant, e, for a conducting particle approaches
infinity and is equal to one for a perfect insulator.
The expression for the charge as a function of time is
(7)
where r is a charging time constant or
r =. 4e0/N0.e/i (8)
The particle-size range examined is larger than 0.2 /um, so the diffu-
sion charge can be omitted.
If we start with a particle entering the field halfway between two plates
and without any charge, the force balance is divided into three different
components:
x - axis, the direction of the electrostatic field
(transverse to gas flow)
y - axis, the direction of the gravitation force
(vertically down)
z - axis, the direction of the gas flow
(horizontal and axial).
The force balance is then as follows:
2FX = Fqe - Fx - Fix = 0 (9)
2Fy = Fg - Frjy - Fiy = 0 (10)
2FZ = F^ - Fiz = 0 . (11)
The electrostatic force can be expressed as
Fqe - qE . (12)
54
-------
Substituting Equations (3), (6), and (7) in Equation (12) gives
...
N0eju
which shows the influence of the dielectric constant, the particle size,
and the field strength on the electrostatic force.
The gravitational force is
Fg = mg . (14)
The viscous force, assuming Stoke 's Law applies (laminar flow), is
F^ = 67rad0w (15)
and the inertia force can be expressed as
FL = m dw/dt . (16)
If we assume that a spherical particle with a radius a is moving in this
field, it will be charged to carry an amount of g (coul) charges, and the
force balance in the transverse direction, after substituting Equations
(12), (15), and (16) in Equation (9), becomes:
qE = 67Tad7}wx - m dwx/dt = 0 . (17)
Substituting Equation (7) into Equation (17) gives
t
qs E "67Tad0Wx= m~dT;
let
A =67rade/mand B = qsE/m . (19)
Substituting this in Equation (18) and integrating gives
r> /t
-
-At
J
o
55
-------
r e-At
The term \ - dt cannot be integrated but can be approximated using
%J t"r i
a series solution:
oo
Je~adx u T V n
-g^- dx = e-*db [In (b+x) + ) [ad(b+x)J /n-n i
n=l
Then, by using this expression in Equation (20) and integrating it once
more with the following initial conditions
t = 0, wx = wxo = 0 and sx = sxo = 0 ,
the travel distance sx becomes
sx = \ wxdt = f- (t - ^-(1 - e ~Ati + re
A \ A
oo
F i
. ("in + ) [(A (t+T)]n - (AT)n)/n-n.'~| -Tin. (21)
L. T l_j J T
n=l
The migration distance is from 0 to 15 centimeters (0 to 6 inches), and
the migration time, T, needed for the particle to be collected can then
be found for sx = 15 centimeters (6 inches) by a trial-and-error solu-
tion of Equation (21).
In order to obtain the horizontal distance needed for the particles to be
collected, the force balance in the z direction must be considered, i. e. ,
Equation (10). This expression becomes
67Ta(j0 (wgas - wz) = m dwz/dt , (22)
where (wgas - wz) is the relative velocity between the particle and the
gas. Integrating Equation (22), using the constants given by Equa-
tion (\9) gives
tion (19) gives
i -Af \ -Af
I 1 .** l> I i ** l»
wz = wgas (l - e ) +wzoe
56
-------
where wzo is the initial particle velocity along the z-axis. The hori-
zontal travel distance becomes, then,
T ' . .
= Jwzdt = wgas [t + j e-At-l] -iwzo e-At-l . (24)
sz
Then, by using the travel time calculated from Equation (19), the hori-
zontal traveling distance can be calculated as a function of particle
(droplet) size and dielectric constant. With two-5 /Jm particles or con-
densed droplets, one with a dielectric constant of 2 (e. g., a. condensed
hydrocarbon droplet) and one with a dielectric constant of 78 (e. g. ,
pure water droplet), migration of these two particles across a field
spacing of 15 centimeters (6 inches) with an applied voltage of 50 kv
and a gas velocity of 0. 9 m/sec (3 ft/sec) will take a horizontal dis-
tance of 2. 2 m (7. 2 ft) and 1.2m (3. 9 ft), respectively. There-
fore, the low dielectric particle takes almost twice the horizontal
distance before being collected; this analysis points to the fact that
condensable hydrocarbons (tars) and other materials with a low
dielectric constant will be much more difficult to collect than con-
ductive particles, and this has been confirmed by measurements.
When considering the removal of condensable hydrocarbons (tar mist),
it should be remembered that the dielectric constants for petroleum
distillates are quite low'-(i.e., around 2). For example, hexane (C^H^)
has a dielectric constant of 2 and a boiling point of 69 C (156 F), toluene
(CyHg) has a dielectric constant of 2. 15 and a boiling point of 110 C
(230 F), and naphthalene (CjQHg) has a dielectric constant of 2. 54 and
a boiling point of 218 C (424 F). Other organic liquids lik-e phenol form-
aldehyde resin have a dielectric constant of 6. 6. Pure water has a
dielectric constant of 78.
The removal efficiency of the wet electrostatic precipitator on a:given
gas and dust stream is a function of six basic parameters:
Collection Area
Operating Voltage
Discharge Current
Liquid-to-Gas Ratio
Treatment Time
Local Average Velocity.
57
-------
The performance is often stated by the so-called migration velocity.
The higher the migration velocity is, the better the particulate removal
efficiency or the smaller the wet electrostatic precipitator in terms of
collection area needed to treat the gas flow. The relationship between
migration velocity and wet electrostatic precipitator performance is
given below.
u = -V/A 0. 508 In (c0/Ci) , (25)
similar to the migration Equation (1).
The efficiency of the unit is given by
T)= (l-c0/Ci) 100 , (26)
and when substituting Equation (25),
7)= (l-e(-Aw/0.508Q), 100 (27)
which is another expression for the Duets ch-Anders on Equation (2).
The migration velocity w is a performance parameter that does not in
reality relate directly to the speed at which the particles migrate to the
collecting plates. It is a "catch-all" which also includes all operating
parameters not included in Equation (25).
HORIZONTAL-FLOW WET ELECTROSTATIC
PRECIPITATOR
One of the wet electrostatic precipitators can be characterized as a con-
tinuously sprayed, horizontal-flow, parallel-plate, and solid-discharge
electrode type. In terms of gaseous absorption, it can be characterized
as a combination cocurrent and a cross-flow scrubber.
In the application of a wet electrostatic precipitator, it is very important
that the gas to be treated is saturated with water vapor to prevent the
water inside the wet electrostatic precipitator from evaporating, which
causes loss of washing water and dry zones on the internal members.
The saturation of the gas can be done in a spray tower or scrubber up-
stream of the wet electrostatic precipitator, or it can be done in the
inlet section of the wet electrostatic precipitator, or both.
58
-------
In addition, it is also necessary to obtain a uniform velocity profile
across the wet electrostatic precipitator, and the diffusion of the flow
from the inlet duct velocity down to the wet electrostatic precipitator
face velocity has to be performed in the inlet section. Furthermore,
by spraying cocurrent into the inlet section, some of the coarser parti-
cles will be removed and the gas-absorption process will be started.
To accomplish this, sections of baffles and sprays are located in the
inlet cone of the wet electrostatic precipitator.
After passing through the sections of transverse baffles, the dirty gas
stream then enters into the first electrostatic field. Water sprays
located above the electrostatic-field sections introduce the proper
amount of water droplets to the gas stream for washing of internal sur-
faces. The particulates and the water droplets in the electrostatic field
pick up a charge and migrate to the collecting plates. The collected
water droplets form a continuous downward-flowing film over all the
collecting plates and keep them clean. The water film and the collected
particulates flow down the collecting plates into the troughs below,
which are sloped to a drain.
The transverse-baffle gas-distribution system combined with the ex-
tended electrode, located upstream and downstream of each field, insures
complete gas-flow uniformity from passage to passage, and collects
particulates and droplets by impingement, and by electrostatic forces.
Also, the extended discharge electrode system improves the collection
efficiency by increasing effective collection area. At the entry of a
field, particles not captured by the transverse baffles are given an
advance charge by the forward extended electrode before they come into
proximity of the collecting plates. Thus charged, the particles start
immediately to migrate toward the leading edge of the plates. It has
been found that the downstream side of the baffles at the exit of a field
collects a considerable amount of material. The very small charged
particles escaping the parallel-plate field are pulled into the wake of the
baffles by the slight vacuum resulting from the turbulent dissipation of
energy. Since the particles have an electrostatic charge, some of them
will be collected on the back side of the baffles.
All baffles systems are arranged so that a walkway runs across the front
and the back of each of the electrostatic fields. The discharge electrode
frames are mounted on collar-type, high-voltage support insulators.
Insulator compartments are heated and pressurized to prevent moisture
and particulate leakage into the insulator compartment.
59
-------
In any particulate and/or gaseous removal process where a liquid is
used, it is important to remove the carryover liquid drops and mists
before reaching the outlet of the equipment. It has been found that doing
this electrostatically is highly efficient. Hence, the last section is
operated dry, thereby establishing an electrostatic barrier that the
liquid droplets cannot penetrate. The mist collects on the front side of
the baffles, and the downstream side is dry. However, some small
dust particles can penetrate and these will collect on the downstream
baffles. Therefore, this surface is washed intermittently to prevent
buildup of particulates.
RANGE OF APPLICATIONS
During the past 2 years, many new applications have been piloted and
units have been sold and installed following successful pilot-plant work.
The wet electrostatic precipitator can be used for applications on gas
streams containing relatively light dust loading of submicron particles
and/or condensed organic materials forming a submicron fume.
Ordinarily these applications would require very-high-pressure-drop
scrubbers. The energy consumption and operating costs are less than
what would be needed to operate scrubbers. The water-treatment
requirements for the wet electrostatic precipitator would be the same as
those for scrubbers.
In some applications, where the dust resistivity is either very high or
very low, the wet electrostatic precipitator can also be applied success-
fully in competition with dry electrostatic precipitators.
Wet electrostatic precipitators have been installed for the following
applications:
(1) On Soderberg aluminum reduction cells (pot lines),
both of the vertical and horizontal stud type, for
simultaneous removal of aluminum oxides, solid and
gaseous fluorides, tar mist (condensable hydrocar-
bons), and SO2
(2) On carbon-anode baking furnaces for removal of car-
bon particles, tar mists, and SO2
(3) On fiber-glass resin application section and forming
lines for removal of short broken glass fibers,
phenolic resins, and tars
60
-------
(4) In molybdenum sulfate roasting, downstream of a
scrubber for removing ammonium sulfite - sulfate
aerosols which form in the ammonia scrubbing
process and SC>2.
Wet electrostatic precipitators are now being manufactured and installed
(1) For upgrading of low-pressure-drop scrubbers on
phosphate rock driers for removal of the submicron
particles and SO2
(2) On coke-oven batteries when connected to a continuous
shed or hood along the push side of the battery where
the coke is pushed into the railroad car. Here the wet
electrostatic precipitator will remove the fine carbon
particles and the condensable hydrocarbons during the
push cycle. In addition, the wet electrostatic precipi-
tator will collect any emissions caused by door leakage
on the push side.
A wet electrostatic precipitator has been designed to meet the require-
ments for controlling reclamation (sinter) plant emissions.
Reclamation (Sinter) Plant Design Specifications
Table 10 provides information concerning a wet electrostatic precipitator
for controlling emissions from a sinter plant producing about 2, 300, 000
metric tons (2, 530, 000 net tons) of high-basicity sinter annually. *
Reclamation (Sinter) Plant
Electrostatic Precipitator Design Data
There is very little specific design information available in the published
literature relating to the design of reclamation (sinter) plant electro-
static precipitators. Information presented in this section is indicative
of the data that have been published.
Particulate Characteristics-The electrical resistivity of the particulates
is an important design factor, and an example of the variations in elec-
trical resistivity as affected by the temperature of the gas and the sinter
mixture is shown in Figure 22. (55)
"Used with the permission of MikroPul Corporation, November 27, 1974.
61
-------
TABLE 10. EQUIPMENT SPECIFICATIONS
Gas Conditioner (Absorber) Specifications
Operating Data
Inlet Volume
Inlet Temperature
Inlet Moisture Content:
Percent Volume
Humidity
Inlet Gas Density
Outlet Volume (Saturated)
Outlet Temperature
Outlet Humidity
Outlet Gas Density
Inlet Paniculate Loading
Inlet Condensable Loading
Total Inlet Loading
Expected Outlet Paniculate Loading
Expected Outlet Condensable
Loading
Total Expected Outlet Loading
Pressure Drop Across Absorber
Gas Velocity
Treatment Time
Number of Absorbers
Operating and Performance Data
Volume at saturated conditions
Temperature at saturated conditions
Inlet Loading
Paniculate
Condensable
Total
Guaranteed Overall (Absorber
and Precipitator) Efficiency,
percent
Guaranteed Total Outlet Loading
Pressure Drop Across Precipitator
Including Gas Distribution
Devices, but excluding losses
across dampers
Gas Velocity
Treatment Time
8,496 actual cu m/min
202-204 C
12 /
0. 3^9 kg water vapor/kg
dry gas
0. 7106 kg/cu m
6, 519 actual cu m/min
kg water vapor/kg dry
gas
0.9817 kg/cu m
0. 1961 gram/cu m
0. 2591 gram/dry cu m
0.4552 gram/dry cu m
0. 0785 gram/dry cu m
0. 1943 gram/dry cu m
0. 2728 gram/dry cu m
2. 54 cm water gage
2. 92 m/sec
+1. 88 sec
Two (2)
I Precipitator
3,260 cu m/min
60 C
0.0785 gram/dry cu m
0.1943 gram/dry cu m
0. 2728 gram/dry cu m
92.45
0. 034 gram/dry cu m
127 -mm water gage
0. 832 m/sec
8.79 sec
300, 000 actual cu ft/min
395-400 F
12
0.8464 Ib water vapor/lb dry
gas
0. 04436 Ib/cu ft
230,000 actual cu ft/min
140 F
0.153 Ib water vapor/lb dry
gas
0. 06128 Ib/cu ft
0. 0857 grain/dry std cu ft
0.1132 grain/dry std cu ft
0.1989 grain/dry std cu ft
0. 0343 grain/dry std cu ft
0. 0849 grain/dry std cu ft
0.1192 grain/dry std cu ft
1.0-inch water gage
9. 59 ft/sec
+1. 88 sec
Two (2)
115,100 cu ft/min
140 F
0. 0343 grain/dry std cu ft
0.0849 grain/dry std cu ft
0.1192 grain/dry std cu ft
92.45
0. 015 grain/dry std cu ft
0. 5-inch water gage
2. 73 ft/sec
8. 79 sec
62
-------
TABLE 10. (Continued)
Arrangement
Number of Precipitators
Chambers (Number)/Precipitator
Fields (Number and Length)/
Precipitator
Casing Material and Thickness
Casing Design Pressure - Positive
Number of Hoppers per Precipitator
Hopper Material and Thickness
Type of Hopper
Insulator Compartment Materials
and Thickness
Number of Insulator Compartments
per Precipitator
Precipitator Internal Gas
Distribution Devices
(a) Types
(b) Quantity and Location per
Precipitator
(c) Material and Thickness
Number, Type, and Size of
Access Doors per Precipitator
(a) Roof
(b) Shell
(c) Insulator Compartments
(d) Inlet
(e) Outlet
Access Walkways Internal
Precipitator
4
1
3, 183 m
6.35 mm
254-mm water gage
3
6.35 mm
Sloping
2.72 mm
Transverse baffles
Two sets - inlet nozzle
One set - inlet 1st field
Two sets - between stages
One set - mist eliminator
1.56 mm, X18H11M
5, 0. 61 m x 1.37 m
2, 0.61 m x 1.37 m
6, 0.61 m x 1.37 m
1, 0.61 m x 1.37 m
1, 0. 61 m x 1.37 m
4
1
3, 6ft
1/4-inch mild steel
10-inch water gage
3
1/4-inch mild steel
Sloping
12-gage mild steel
16-gage, Type 316
2 ft x 4. 5 ft
2 ft x 4. 5 ft
2 ft x4. 5 ft
2 ft x 4. 5 ft
2 ft x 4. 5 ft
Mild steel expanded metal grating between fields
Collecting System - per Precipitator
Number of Gas Passages
Spacing of Gas Passages
Collecting Plate Material and
Thickness
Collecting Plate Effective Length
Collecting Plate Effective Height
Active Collecting Surface Area
Plate Area
Transverse Baffle Section Area
Total
28
30.5 cm
1.95 mm, X18H11M
5. 5 m
7.6 m
2, 341 sq m
390 sq m
2,731 sq m
12 inches
14-gage, Type 316
18 feet
25 feet
25, 200 sq ft
4,200 sqft
29,400 sqft
63
-------
TABLE 10. (Continued)
Discharge Electrode - Type,
Material and Thickness
Type Transformer Rectifier
Number of Transformer Rectifiers
(a) Voltage Rating, kv (dc) avg.
(b) Current Rating, ma (dc) avg.
(for pure resistive loads)
Number of Transformer Rectifier
Control Cabinets
Construction of Transformer
Rectifier Control Cabinets
Transformer Rectifier Insulation
Fluid
Wave Form of High Voltage
Number and Type of High Voltage
Switches
Key Interlocks
Control Cabinets
Transformer Rectifiers
Access Doors
Type of Transformer Rectifier
Controls
Maximum Ambient Temperature
for Transformer Rectifier, C
Connected Load kva/Precipitator
Transformer-Rectifier
Insulator Heater and Blower
Total Connected Load KVA/
Precipitator
Power Distribution
Individual Breakers Each Control
Cabinet
Central Distribution Panel
High Voltage System
3.11mm, 1X16M13ME
High Voltage Electrical Set
Silicon
3/unit
55
1,000
3/unit
NEMA. 12
Pyranol
Full Wave
3/Grounded
Yes
Yes
Yes
Thyristor
40
235
28
263
Yes
No
11-gage, Type 316L
Operating Liquid Characteristics for Precipitator and Absorber
Absorber Feed
Liquor Rate
Liquor Pressure at Nozzles
Liquor Source
Evaporation Rate
5678 1/min 1500 gal/min
293 kg/sq m 60 Ib/sq in.
gage
pH-Controlled Recycled Treated Liquor
378 1/min 100 gal/min
Precipitator Feed
2839 1/min 750 gal/min
293 kg/sq m 60 Ib/sq in.
gage
64
-------
TABLE 10. (Continued)
Operating Liquid Characteristics for Precipitator and Absorber
Absorber Feed Precipitator Feed
Liquor Quality:
The following typical liquor quality
observed during the pilot-plant study
is required for efficient absorber and
precipitator operation.
pH 9.6 9.2
mg/1 mg/1
i
Phenophthalein Alkalinity as CaCOg 1,450 1,390
Methyl Orange Alkalinity as CaCOg 3,800 3,410
Chloride as Cl 240 194
Sulfate as SO4 3,750 3,650
Hardness as CaCOg 24 25
Calcium as CaCOg 8 8
Magnesium as CaCOg 16 17
Silica as SiO2 10. 5 10.1
Total Solids 10,652 10, 224
Dissolved Solids 10,488 10,090
Suspended Solids 164 134
Total Iron as Fe 7.9 6.4
Aluminum as Al 1.8 1.6
Zinc as Zn 0.4 0.3
Lead as Pb 6.5 3.9
Cadmium as Cd 0.18 0.10
Molybdenum as Mo 1 . 1
Fluoride as F 42 40
Oil and Grease 79 108
Total Carbon 570 300
Total Inorganic Carbon 420 200
Total Organic Carbon 150 100
65
-------
GAS TEMPERATURE, F
100 150 200 250 300 350 400
ICAL RESISTIVITY, ohm-cm
ELECTR
1 x 10'°
1 x 1014
1 x 1013
<
1 x 109
1 x 108
I I I I I
PLANT 1
^^"V^, 0.6% MOISTURE
PLANT J
6% MOISTURE - ^>--^.
> <
PLANT K
6% MOISTURE ~~^^V.
i 1 i i . . 1 i i I i 1 . i i i 1
50 100 150 200
GAS TEMPERATURE, C
Figure 22. Electrical resistivity of reclamation (sinter) plant dust
as affected by gas temperature and sinter mixture
0.656
o
I
25 °-492
UJ
0.328
< 0.164
o
HI
or
O.
TEMP - 149 C
(300 F)
I
I
20
15
10
0123
SULFUR CONTENT OF THE COAL, percent
Figure 23. Relationship between the sulfur content in electric-
utility-plant coal and the precipitation-rate parameter
66
-------
Sinter mix composition, particulate size, and gas data are listed in
Table ll.(56)
TABLE 11. RECLAMATION (SINTER) PLANT DATA
FOR FIGURE 22
Parameter
Plant J
Plant K
Sinter Mixture
Iron ore and metallics, percent
Limestone or dolomite, percent
Coke, percent
Particle Size, percent -10 microns
Gas Analysis
Sulfur oxides, ppm
Moisture content, percent
Temperature
90
9
1
60
300
15
121 C (250 F)
64
35
1
45
30
10
93 C (200 F)
It is known that the sulfur content of reclamation-plant off-gas affects
the collection of emissions. While such data are not available for
reclamation-plant off-gas, Figure 23 shows the relationship between the
sulfur content in fuel and the precipitation-rate parameter to for electric-
utility electrostatic precipitators. (55)
The effect of various reclamation (sinter)-plant electrostatic-
precipitator variables on collection efficiency is shown in Figure 24.(^ '>
The limited amount of information available on reclamation (sinter)-
plant electrostatic precipitators is given in Table 12. (34, 54, 55, 58, 59)
Reclamation (sinter) plant electrostatic precipitators are typically
single-stage, horizontal-flow units. The chambers and hoppers are
usually fabricated of'plain-carbon steel, and may or may not be thermally
insulated. (55) Plain-carbon steels have, not performed as well as desired
because of the corrosive conditions that can be generated by the reaction
of sulfur oxides with moisture to fprm acids. This acid corrosion
necessitates the replacement of electrodes, collector plates, and internal
supporting members, causing excessive maintenance costs and short
service life, as compared with other equipment used in an iron and steel
plant.
67
-------
0.0
99
98
97
*-
c
Q)
B 96
. 95
o 94
2 '
LU
g 92
t 90
O
o
o
o
80
70
60
50
40
20
Ac (COLLECTION AREA), sq ft
wgas
-------
TABLE 1Z. RECLAMATION (SINTER) PLANT ELECTROSTATIC-PRECIPITATOR CHARACTERISTICS
Plant Location
Annual Production
metric tona
net tons
Strands, number
Air Volume
cu m/sec
cu ft/min
Air Temperature
C
F
Pressure Differential
kg/sq m
inches of water
Gas Velocity
cm/sec
ft/ sec
Treatment Time, seconds
Charge Section
Number of Ducts
Width
centimeters
inches
Height
meters
feet
Length
meters
feet
Number of Electrodes
Size
mm
in.2
Type of Suspension
Power
Collection Section
Number of Plates
Height
meters
feet
Length
meters
feet
Number of Electrodes
Bethlehem Steel Corp. ,
Johnstown,
Pennsylvania
998,000
1, 100,000
2
100
213,000
115
240
762
30
37
23
9
7.3
24
2.7
9
436
6
0. 0093
Plumb Bob
76
872
Inland Steel Co. ,
East Chicago,
Indiana
1,089.000
1,200,000
1
215
457,000
191
375
889
35
195
6.4
2.3
136
2.3
7. 5
7. 3
24. 0
Plant L, Plant I
Eastern Reference
Pennsylvania (54)
454,000 2,177,000
500,000 2,400,000
1 4 (2 per ESP)
80 180
170,000 385,000
149 118
300 245
660 1070
26 42
174
5. 7
4.2
70
1.8
6.0
7.3
24.0
1600
69
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VI. REFERENCES
(1) Annual Statistical Report, American Iron and Steel Institute,
1974_, pp. 65, 72.
(2) Ess, T. J. , Alan Wood Steel Company, Iron and Steel Engineer,
39: AW4-AW22, March 1962.
(3) Annual Report, Alan Wood Steel Company, ^972.
(4) Fosdick, A. H. , Operating Features and Practices at the
Bethlehem Sintering Plant. AIME Blast Furnace, Coke Oven,
and Raw Materials Proceedings. 7:106-118, 1948.
(5) Gas Cleaning System for Bethlehem's Sintering Plant. Blast
Furnace and Steel Plant. 59:60, January 1971.
(6) The Bethlehem Plant's New $2. 4-Million Stack Gas Cleaning
System. American Metal Market, p. 6, December 9, 1970.
(7) Sinter Line Baghouse Collector Still Going Strong. Iron and Steel
Engineer. 45:124, February 1968.
(8) Ess, T. J. Bethlehem's Johnstown Plant. . . A Century of Pio-
neering. Iron and Steel Engineer. 30:J2-J20, April 1953.
(9) Air Pollution Control System Installed at Bethelehem's Johnstown
Plant. Blast Furnace and Steel Plant. 56:917, October 1963.
(10) Lassen, E. , Jones and Laughlin Steel Corporation's Aliquippa
Works. Blast Furnace and Steel Plant. 54:957-958, October 1966.
^.u.i.ii-i .1
(11) J & L Operating Largest Single Strand Iron Ore Sintering Line.
Industrial Heating. 28:1682-1690, September J96J..
70
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(12) Air Pollution Control Continues at JfyL Aliquippa Works. In-
dustrial Heating. 31:486,500, March 1964^
(13) Communication from R. C. McCrillis, Environmental Protection
Agency. April 25, 1975..
(14) Harris, E. R. , and Beiser, F. R. Cleaning Sinter Plant Gas With
a Venturi Scrubber. Journal of the Air Pollution Control Associa-
tion. 15:46-49, February 1965.
(15) Communication from B. Steiner, April 9, 1975.
(16) Air Emission Control Facility at United States Steel Corp. "s
Saxonburg, Pa. , Sintering Plant. Iron and Steel Engineer.
46:45, April 1969.
(17) Faigen, M. R. , Kyler, E. B. , and Plummer, W. S. Recent
Improvements at United States Steel Saxonburg Sinter Plant.
AIME Ironmaking Proceedings. 29:310-318, 1970.
(18) To Add Sinter Plant at Monessen Works. Iron and Steel Engineer.
41: 50, April 1964.
(19) Edwards. L. H. Equipment and Operational Changes Made to Up-
grade an Old Sinter Plant. AIME Ironmaking Proceedings. 29:328-
333, 1970.
(20) Two J&L, Sintering Machines Served by Vertical Shaft Sinter
Cooler. Industrial Heating. 28:514-516, March 1961.
(21) Kraner, H. M. , and Hauser, R. E. New Sintering Plant Facilities
at Sparrows Point. Blast Furnace and Steel Plant. 44:757-759,
July 1956.
(22) Largest in Western Hemisphere. Journal of Metals. 24:8, June
1972.
(23) Watson, G. W. Weirton No. 2 Sinter Plant. Iron and Steel
Engineer. 36:105-108, June 1959.
(24) Cleaning System Turnkey Contract. American Metal Market.
p. 14, September 3, 1971.
71
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(25) Communication from B. Steiner. June 25, 19.75., ,
(26) Loofboro, K. A. J&L's Cleveland Works Sinter Plant. Iron and
Steel Engineer. 36:101-104, June
(27) Ess, T. J. Republic Builds for D.P.C. Iron and Steel Engineer.
21:R18-R38, October 1944. .
(28) Republic Steel Plants and Facilities. Republic Steel Corporation.
28 p. February 1967.
(29) Austermiller, E. O. , and Cureton, W. A. Design and Operation
of National Tube's Sintering Plant. Iron and Steel Engineer.-
28:111-117, October 1951. . . .
(30) Slater, R. A. Construction and Design Involved in a New Sintering
Plant.- Iron and Steel Engineer. 37:114-117, December 1960.
(31) Cromwell, D. P. Operations and Practice, Campbell Sintering
Plant. AIME Blast Furnace, Coke Oven, and Raw Materials
Proceedings. 7:86-89, 1948. _. . .
(32) Armco Completes Sintering Unit at Ashland Plant. Iron and Steel
Engineer., 35:146-152, October 1958..
(33) Baranyi, J. F. Results of Design Changes in Sinter Plants. Iron
and Steel Engineer. 42:85-90, December 1965.
(34) Frame, C. P., and Els on, R. J. The Effects of Mechanical. Equip-
ment on Controlling Air Pollution at No. 3 Sintering Plant, Indiana
Harbor Works, Inland Steel Company. Journal of the Air Pollu-
tion Control Association. 13:600-603, December 1963.
(35) Inland Steel Shuts Down Two Sintering Lines at Indiana Harbor
Works. Blast Furnace and Steel Plant. 55:660, July 1967.
(36) Young, T. A. , Jr. Gary Steel Works Experience With Dust
Control at Number 3 Sinter Plant. Blast Furnace and Steel Plant.
56:1057-1063, December 1968. .
(37) Bethlehem Tells Details of Proposed Sintering Plant. American
Metal Market, p. 4, November 2 1972.
72
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(38) Bayr, R. B. , and Wachowiak, R. J. Elimination of Hydrocarbon
Emissions From the Sinter Plant. AIME Ironmaking Proceedings.
31:55-58, 1972.
(39) A New $700, 000 Baghouse. Skillings Mining Review. 64(18):28,
May 3, 1975.
(40) Corzilius, W. R. Sintering Plant Expands Blast Furnace and Open
Hearth Capacity. Blast Furnace and Steel Plant. 47:44-50,
January 1959.
(41) Sinter Plant Baghouse Cleaner for Granite City Steel. Blast
Furnace and Steel Plant. 59:241, April 1971.
(42) Scrubber System For Granite City. American Metal Market.
p. 6, December 4, 1973.
(43) Pollution Control Project. American Metal Market, p. 4,
September 4, 1970.
(44) A New Baghouse Type Dust Collecting System. American Metal
Market, p. 3, December 28, 1970.
(45) Menke, G. V. Sintering Plant Emission Control Wisconsin
SteelWorks. Preprint AIME Ironmaking Conference. 10 p. 1972.
(46) CF&I Steel Installing Electrical Precipiators To Control Iron Ore
Dust At Its Pueblo Plant. Blast Furnace and Steel Plant. 57:82,
January 1969.
(47) Egley, B. D. Selection of Gas Cleaning Equipment For an Ore
Preparation Plant. Iron and Steel Engineer. 47:111-115, November
1970.
(48) Kaiser Steel Starts Operation of New Pollution Control Unit.
American Metal Market, p. 18, August 9, 1971.
(49) Nowak, T. T. Sinter Plant Baghouse. AIME Ironmaking Proceed-
ings. 31:75-84, 1972.
(50) Communication From R. L. Bump, Research-Cottrell, Inc., to
J. Varga, Jr. July 31, 1975.
73
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(51.) McCrone, W. C. , et. al. The Particle Atlas. Ann Arbor . Science
' Publishers, Inc. Ann Arbor, Michigan. 153-236, (1967).
(52) Manning, G. E. , and Rower, F. E. A Characterization of Air
Pollutants From Sintering Plant Induced Draft Stacks. AIME
Ironmaking Proceedings. 30:452-460 (1971).
(53) Suitlas, J. R. Emission Characteristics and Pilot Plant Studies
on a Sintering Plant Windb.ox Discharge. AIME Ironmaking
Proceedings, 30:461-470 (1971).
(54) Communication from R. C. McCrillis to J. Varga, Jr.
(55) Oglesby, S. , Jr., and Nichols, G. B. A Manual of Electrostatic
Precipitator Technology, Part II Application Areas.. The
National Air Pollution Control Administration, Division of Process
Control Engineering. PB 196381. 487-502 (August 25, 1970).
(56) Bakke, E. , The Application of Wet Electrostatic Precipitators for
Control of Fine Particulate Matter, Paper presented at the
Symposium on Control of Fine Particulate Emissions From Indus-
trial Sources for the Joint U. S. -U. S. S.R. Working Group, Sta-
tionary Source Air Pollution Control Technology. San Francisco,
California. 27 pp. (January 15-18, 1974).
(57) Oglesby, S. , Jr., and Nichols, G. B. A Manual of Electrostatic
Precipitator Technology, Part I - Fundamentals. The National
Air Pollution Control Administration, Division of Process Control
Engineering. PB 196380. 203-217 (August 25, 1970).
(58) Communication from R. C. McCrillis to J. Varga, Jr. April 25,
1975.
(59) Communication from W. McShane to J. Varga, Jr. July 11, 1975.
74
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TECHNICAL REPORT
(Please read Instructions on the reverse
DATA
before completing)
1. REPORT NO.
EPA-600/2-76-002
2.
3. RECIPIENT'S ACCESSION-NO.
4. TITLJE AND SUBTITLE
Control of Reclamation (Sinter) Plant Emissions
Using Electrostatic Precipitators
5. REPORT DATE
January 1976
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
John Varga, Jr.
8. PERFORMING ORGANIZATION REPORT NO
9. PERFORMING ORdANIZATION NAME AND ADDRESS
Battelle-Columbus Laboratories
505 King Avenue
Columbus, Ohio 43201
10. PROGRAM ELEMENT NO.
1AB015; ROAP 21AQR-042
11. CONTRACT/GRANT NO.
68-02-1323, Task 32
12. SPONSORING AGENCV 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
Final; 3/15-8/15/75
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
IB. ABSTRACT Tne repOrt briefly reviews the sintering process as it applies to the U.S.
integrated iron and steel industry. The review includes data on characteristics of
the emissions, and a list of all the iron and steel reclamation (sinter) plants in the
U.S., their annual capacity, and the types of emission control equipment used. The
report contains a detailed discussion of the theoretical and practical aspects of
designing both wet and dry electrostatic precipitators (ESPs) to control the sinter
machine windbox emissions. It gives design specifications for a proposed wet ESP
installation on a large modern sinter plant.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATl Field/Group
Air Pollution
Iron and Steel
Industry
Electrostatic
Precipitators
Reclamation
Sintering
Sintering Furnaces
Design
Specifications
Air Pollution Control
Stationary Sources
Sinter Plants
Sinter Machine Windbox
13B
11F
13H
13A
8. DISTRIBUTION STATEMENT
19. SECURITY CLASS (ThisReport)
Unclassified
Unlimited
21. NO. OF PAGES
81
20. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
75
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