United States Industrial Environmental Research EPA-600/7-79-045
Environmental Protection Laboratory February 1979
Agency Research Triangle Park NC 27711
Assessment of the Use
of Fugitive Emission
Control Devices
Interagency
Energy/Environment
R&D Program Report
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, havo been grouped into nine series. These nine broad cate-
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The nine series are:
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2, Environmental Protection Technology
3. Ecological Research
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5. Socioeconomic Environmental Studies
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RESEARCH AND DEVELOPMENT series. Reports m this series result from the
effort funded under the 17-agency Federal Energy/Environment Research and
Development Program. These studies relate to EPA's mission to protect the public
health and welfare from adverse effects of pollutants associated with energy sys-
tems. The goal of the Program is to assure the rapid development of domestic
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essary environmental data and control technology. Investigations include analy-
ses of the transport of energy-related pollutants and their health and ecological
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This document is available to the public through the National Technical Informa-
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EPA-60G/7-79-C45
February 1979
of the of
Fugitive Emission Control
by
D.P. Daugherty and D.W. Coy
Research Triangle Institute
P.O. Box 12194
Research Triangle Park, North Carolina 27709
Contract No. 68-02-2612
Task No. 48
Program Element No. EHE624
EPA Project Officer: Dennis C. Drehmel
Industrial Environmental Research Laboratory
Office of Energy, Minerals, and Industry
Research Triangle Park, NC 27711
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Washington, DC 20460
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ACKNOWLEDGEMENT
This report presents the results of a study conducted under EPA Contract
68-02-2612, Task 48. The research was conducted in the Industrial Process Studies
Section of the Energy and Environmental Research Division of the Research Tri-
angle Institute (RTI).
RTI acknowledges the time and courtesy extended by St. Joe Lead Company
during a visit to their Herculaneum, Missouri smelter and, equally, the consid-
eration shown by Kennecott Copper Corporation during a vist to their Hayden,
Arizona smelter. The Ransburg Corporation and Dr. Stuart Hoenig of the University
of Arizona at Tuscon provided useful information on charged fog spray devices.
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TABLE OF CONTENTS
Page
ACKNOWLEDGMENT iv
LIST OF TABLES v1
LIST OF FIGURES • v1ji
1.0 INTRODUCTION AND SUMMARY 1
2.0 CONCLUSIONS AND RECOMMENDATIONS 5
3.0 FUGITIVE EMISSION SOURCES, RATES, AND COMPOSITIONS ' 6
Lead Smelting 6
Process Description of Lead Smelting 6
Fugitive Emission Rate Data-for Lead Smelting 14
Fugitive Emission Size and Composition Data
for Lead Smelting ' 15
Copper Smelting 22
Process Description of Copper Smelting 22
Fugitive Emission Rate Data for Copper Smelting 26
Fugitive Emission Size and Composition Data for
Copper Smelting 26
4.0 CHARGED FOG SPRAYS FOR CONTROLLING FUGITIVE EMISSIONS 33
Description of Charged Fog Spray Device 33
Collection Efficiency of Charged Fog Sprays 37
Impaction/Interception 37
Diffusion 38
Phoresis 38
Electrostatic Attraction 41
Basis of Collection Efficiency for Commerical Devices 47
Cost Data and Utility Consumption for Charged Fog Sprays 50
5.0 WATER SPRAYS WITH ADDITIVE'S FOR CONTROLLING FUGITIVE EMISSIONS 57
6.0 BUILDING EVACUATION FOR CONTROLLING FUGITIVE EMISSIONS 59
Description of Building Evacuation 59
Cost and Utility Consumption for Building Evacuation 61
7.0 COMPARISON OF CHARGED FOG SPRAYS WITH BUILDING EVACUATION 63
8.0 REFERENCES 72
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TABLES
Page
Summary of Charged Fog Spray Comparison With Building 3
Evacuation
2 Summary Table — Basis for Total Particulate and Elemental
Lead Fugitive Emission Rates: Primary Lead Smelter 7
3 Summary Table — Basis for Total Particulate and Elemental
Lead Fugitive Emission Rates: Primary Copper Smelter 9
4 Relative Contributions From Various Emission Sources to
Fence!ine Concentrations of Ambient Lead at Primary Lead
Smelters 15
5 Emission Factors for Lead Smelting as Measured by MRI 16
6 Lead Concentrate Compositions 17
7 Composition of Sintering Emissions 18
8 Lead Content of Fugitive Emissions From Lead Smelting
Operational Areas 19
9 Particle Distribution for Fugitive Particulates From
Lead Smelting 20
10 Particle Distribution for Ducted Lead Sintering Machine
Gases 21
11 Distribution of Pb, Cd, Zn, and Cu in Respirable Range Near
Primary Lead Smelter 21
12 Airborne Elemental Concentrations Near Primary Lead Smelter 22
13 Composition of Copper Concentrates Processed in the U.S. 27
14 Elemental Concentrations in Air by Copper Smelter Area,
Industry-Wide Averages 28
15 Composition of Ducted Copper Converter Dusts From Bar,
Yugoslavia 29
16 Estimated Composition of Fugitive Particulates by Copper
Smelter Area 31
17 Percent of Metal Aerosols in Respirable Range: Converter,
Furnace and Crane Aisle Employees in U.S. Copper Smelters 32
VI
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TABLES (cont'd)
Number Page
18 Particle Distribution for Ducted Copper Converter Gases 32
19 Particle Distribution for Ducted Copper Reverberatory
Furnace Gases 32
20 Summary of Total Estimated Costs for Charged Fog Spray
Device 51
22 Estimate of Installation Material Costs for Charged Fog
Spray Device 53
23 Estimate of Installation Labor Costs for Charged Fog
Spray Device 54
24 Estimate of Auxiliary Equipment Costs for Charged Fog
Spray Device 55
25 Energy Consumption for Operating a Charged Fog Spray
Device 56
26 Capital and Operating Costs for B'uilding Ventilation
System at Typical Copper Smelter 62
27 Potential Applications for Charged Fog Sprays in Lead
Smeltering 64
28 Potential Applications of Charged Fog Sprays in Copper
Smeltering 65
29 Comparison of Charged Fog SPrays With Building Evacuation 68
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FIGURES
Number Page
1 Flowsheet of Typical Lead Smelting Operations 10
2 Flowsheet of Typical Copper Smelting Operations 24
3 Means of Producing a Charged Water Spray 34
4 Particle Trajectories Around a Water Droplet. 39
5 Diffusiophoretic and Thermophoretic Forces 40
6 Limiting Charge for Water Droplets " • 42
7 Typical Charge Distribution for Micron Size Particles 43
8 Effects of Particle Size, Droplet Size, Relative Humidity,
and Electrostatic Charge on Collision Efficiency 45
9 Lifetime of Water Droplets Traveling at Their Terminal
Velocity 48
10 Schematic of "Dead Spots" in Building Evacuation System 60
11 Charged Fog Spray Application Points in Lead Smelthing 66
12 Charged Fog Spray Application Points in Copper Smelting 67
13 Push-pull Local Hooding Versus Charged Fog Spray Curtain 70
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•• 1.0 INTRODUCTION AND SUMMARY
Emissions from stacks and other so-called "point sources" have, in the
past, been the main target of pollution control efforts. Windblown losses
from storage piles, dust from material handling, fumes from hot metal transfer,
and many other sources in the metals industry are not considered point sources.
Instead, pollutants from these diffuse, non-ducted sources are termed
"fugitive emissions." This report compares three fugitive control techniques--
building evacuation, charged fog sprays, and water sprays with addi-tives--as
they might be applied in lead and copper smelters.
Fugitive emissions from lead and copper smelters have serious impacts
on more than just the total suspended part4culate levels; they may also
contain toxic metals for which separate ambient standards exist or are being
contemplated. The report estimates (from admittedly rough base-data) the
reduction of total suspended particulate emissions and the reduction of
elemental lead emissions from smelters when fugitive control is applied.
Primary lead and copper smelters are considered; secondary smelters are not.
The control techniques of charged fog water sprays are emphasized in this
report. (These sprays enhance particulate collection by putting an electro-
static charge on fine water droplets.) Building enclosure and evacuation is
used as a basis with which such water sprays are compared. Secondary hooding
is not evaluated as a control method, as it is being studied by others.
Several limitations on the scope of this project need to be mentioned,
No sampling was done to measure fugitive emission rates or compositions; values
used in' the report are cited from prior publications. Likewise, even though a
copper smelter and a lead smelter were visited to discuss'using charged fog
sprays with plant engineers, there were no field trials as part of this project.
Instead, available cost and energy consumption data was used to assess whether
charged fog sprays are competitive with other devices.
Charged fog sprays are only, beginning to be commercially applied; a
small version with a maximum spray rate of 0.25 gpm is now commercially available.
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No independent test data of charged fog spray efficiencies in industrial
applications have been presented to date. In general: (a) while for
uncharged sprays, there is a minimum in the collection efficiency for about
two micron diameter particles, there is not any such minimum for charged sprays
and some improvement in collection of respirable dust is expected from charging;
(b) the charged fog sprays are best suited to localized sources of dust,
suspended in a low velocity or stationary gas stream; (c) the combination
of high temperatures and excessive gas turbulence rules out charged fog sprays
for areas such as copper converter leakage or furnace taphole emission control;
and (d) at reasonable water application rates, the charged fog sprays are
unlikely to have efficiencies approaching 90 percent—overall collection
efficiencies on the order of 50-60 percent are more likely.
Capital costs, utility requirements, and control efficiencies were
estimated for both building evacuation and charged fog spray control techniques.
The results are summarized in Table 1. Note that the reduction of fugitive
emissions cited are on the basis of total fugitive emission including open
source emissions such as windblown dust which are outside the control of
either a building evacuation system or a charged fog spray. The efficiencies
for sources within the control of building evacuation or charged sprays were
taken as 95 percent and 60 percent, respectively.
While both capital investment and energy consumption are higher for building
evacuation, the reduction of total particulate and elemental lead emissions are
also greater for building evacuation because of the higher collection efficiency
and the larger number of sources covered by a building evacuation system. About
10 to 20 k$ are required for each percentage reduction in emissions by spray
versus 100 to 200 k$ required for each percent reduction for building evacuation.
Similarly the electrical requirement is much lower for the charged fog sprays--
15 to 30 kW for each percentage reduction versus 150 to 200 kW for the
building evacuation system.
However, in spite of the apparent attractiveness of charged fog sprays,
the authors feel that there are several practical problems which prevent them
from supplanting building evacuation or secondary hooding as fugitive control
techniques. The first and main objection is their limited applicability.
Water sprays are only suitable when the process can tolerate water, when the
L
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TABLE 1. SUMMARY OF CHARGED FOG SPRAY COMPARISON -WITH BUILDING EVACUATION .
Item Lead Smelting Copper Smelting
Reduction in fugitive total particulate
emissions
by application of charged sprays 30% 20%
by application of building evacuation 45% 40%
Reduction in fugitive elemental lead
emissions
by application of charged sprays 40% 35%
by application of building evacuation 75% 65%
Estimated capital investment
for application of charged sprays 311 k$ 366 k$
.for application of building evacuation 8,683 k$ 6,'808 k$
Electrical requirement
for application of charged sprays 417 kW 450 kW
for application of building evacuation - 9,000 kW 6,000 kW
emissions are from localized sources, when there is not a great deal of air
turbulence and when the air is not at high temperatures. These limitations
rule them out for such major sources of fugitive emissions as converter leakage,
sintering discharge, and metal tapping, pouring, and casting.
A second major limit on charged fog spray control is the collection of the
agglomerated particles. It is usually assumed that once suspended particles
collide with a water droplet, they are permanently removed from the atmosphere.
This is a valid assumption for such applications as conveyor transfer points
in moderately sill air where the agglomerated dust settles out and is returned
to the process. However, when particles from, say, a railcar unloading station
are contacted with spray droplets, they may settle out on the ground, dry
out, and be reentrained. Particle control has only been temporary. The
severity of this phenomenon is a major uncertainty for future large scale
industrial applications of charged fog sprays.
It makes more sense to consider charged sprays and building evacuation
as complementary control devices instead of mutually exclusive techniques.
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Per high temperature, large scale, turbulent emissions, either building evacuation
or secondary hooding are required to collect the fugitive emissions. Charged
fog sprays are better suited for smaller, localized emission sources. Two
applications for which charged sprays may be particularly advantageous over
other controls are: (a) mobile sources such as front-end loaders (where any
other type of control is impossible), and (b) areas such as sanders or grinding
wheels where personnel exposure must be reduced without impeding access.
Water sprays with surfactant additives can be used to reduce dust entrain-
ment from hard-to-wet solids, but have an advantage over conventional water
sprays only for reducing dust generation from dusts which have not already been
suspended. Surfactants do not substantially improve the collection of particles
which have already become airborne. Thus, they are'not substitutes for charged
fog spray applications. The addition of surfactants or other additives should
be considered for such applications as conveying and storage bins where the
product is not water sensitive and can be kept moist to reduce dust entrainment
from the solid. Additives other than surfactants may be used in some cases to
form a "crust" on storage piles, etc., and reduce windblown resuspension of
dust.
More detailed discussions of the material above, together with information
on the smelting processes and the composition and amount of fugitive emissions
are presented in the main body of this report.
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2.0 CONCLUSIONS AND RECOMMENDATIONS
For equivalent degrees of control, charged fog sprays require roughly
one-tenth the capital investment and utility requirement of building
evacuation. However, the nature of charged fog sprays limit them to a
maximum of 50-60 percent collection efficiency versus 95 percent for
building evacuation.
The charged fog sprays are not expected to perform well in high tempera-
ture, very turbulent, open areas encountered in many of the major sources of
smelter fugitive particulates: converter leakage, sintering discharge, and
hot metal tapping and handling.
There is no data currently in the public domain regarding the efficiency
of charged fog sprays in industrial environments. The device cannot be con-
sidered, at this point, established technology. The next logical step in
development of the product is independent testing done on some industrial
application of the sprays. This testing would define and document the
performance of this device outside the laboratory. Several questions
regarding its performance in evaporating conditions, cross-drafts, and rigorous
environments need to be answered. Should the initial tests prove favorable, other
applications such as spray curtains or mobile charged spray devices could be
evaluated.
It is recommended that field evaluation and sampling of the charged fog
spray device in an industrial application be conducted as a follow-up of this
study. The estimated time required for such a sampling program is one man year.
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3.0 FUGITIVE EMISSION SOURCES, RATES, AND COMPOSITIONS
Primary lead and primary copper smelting are discussed separately in this
section. The sources, rates, and compositions of fugitive particulate emissions
are discussed for both. Neither stack emissions nor fugitive gaseous emissions
such as S02 are included. The study was limited to smelter operations between
ore receipt and the casting of crude metal ingots.
The smelting processes are described briefly, emphasizing factors which
alter the amount or composition of fugitive particulates. Although no single
flowsheet can represent the variations between smelters, technology most common
to United States smelters has been depicted. After this, the best available
data for fugitive emission rates, by processing step, are discussed. Sadly,
even the best estimates for rates are just that and not very reliable—few
sources have been measured, and the measurement techniques for fugitive emissions
2
only yield rates accurate within a factor of two to five. Emission rates are
presented solely as a basis for comparing control devices; in this use, inaccuracy
in their measurement does not obviate the comparison.
Composition data for the fugitive emissions conclude the discussion of
each smelting process. This data was obtained from several sources; references
are given. This composition data was combined with source emission rates to
yield Tables 2 and 3 which show the base rates of total particulate emissions
and of elemental lead emissions. This pair of tables is later used in Section
7 to compare the emissions reduction from installing charged fog sprays with
that obtained via building evacuation.
LEAD SMELTING
Process Description of Lead Smelting
Figure 1 depicts the lead smelting process steps commonly used in the
United States to produce metallic lead from the concentrated ore. The figure
is presented to acquaint the reader with the operations in primary lead smelting.
3-7
Several sources were used to develop this flowsheet. It represents no
single smelter, but instead is a composite of the operations in several
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TABLE 2. NUMMARY TABLE-BASIS FOR TOTAL PARTICULATE AND ELEMENTAL LEAD FUGITIVE
EMISSION RATES:a'b
PRIMARY LEAD SMELTER, 100,000 METRIC TONS PER YEAR
Source of Fugitive Emission
1.
2.
3.
4.
5.
6,
7.
Railroad car and truck
unloading
Limestone
Silica sand
Lead ore concentrate
Iron ore
Coke
Btast furnace flue dust
a. Storage
b. Handling and transfer
Limestone
a. Storage
Loading onto pile
Vehicular traffic
Loading out
Wind erosion
b. Handling and transfer
Silica sand
a. Storage
b. Handling and transfer
Lead ore concentrate
a. Storage
b. Handling and transfer
Iron ore
a. Storage
h. Handling and transfer
Coke
a. Storage
Total Paniculate
Operating
Parameter
metric tons/yr
Limestone unloaded
39,700
Silica unloaded
1,800
Lead ore unloaded
158,900
Iron ore unloaded
22,600
Coke unloaded
47,200
-
-
Limestone loaded
39,700
Limestone stored
39,700
Limestone loaded out
39,700
Limestone stored
39,700
Limestone handled
39,700
Silica stored
1,800
Silica handled
1,800
Concentrate stored
168,900
Concentrate handled
158,900
Ore stored
22,500
Ore handled
22,500
Coke stored
47,200
Fugitive Emissions
Uncontrolled
Emissions
metric tons/yr
4
0.19
17
2.5
9.5
Negligible
Negligible
_
1
2.5
1
2
4
0.5
0.5
26
264
14.5
22.5
3.5
Elemental Li
Weight Fraction
Lead Contained
in Emission
0
0
0.60
0
. 0
-
-
0
0
0
0
0
0
0
0.60
0.60
0
0
0
;ad Fugitive Emissions
Uncontrolled
Lead Emissions
metric tons/yr
0
0
10.2
0
0
0
0
0
0
0
0
0
0
0
15.6
158
0
0
0
See footnotes at end of table.
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TABLE 2. (cont'd)
Source of Fugitive Emission
7, Coke {continued)
h. Handling and transfer
S. Mixing and penalizing'
9. Sinter machine
10. Sinter return handling
11. Sinter machine discharge
and screens
12. Sinter crushing0
1 3. Sinter transfer to dump
area
14. Sinter product dump
area
15. Charge car or conveyor .
loading and transfer of
sinter
16. Blast furnace— monitor
(tatal)d
17. Lead pouring to ladle
and transfer
18. Slag pouring9
19. Slag granulator and
slag piling
20. Dross kettle
21. Rflverberatory furnace
leakage
Total Paniculate
Operating
Parameter
metric tons/yr
Coke handled
47,200
Lead produced
100,000
Sinter produced
349,979
Sinter produced
175,000
Sinter produced
175,000
-
Sinter transferred
175,000
Sinter dumped
175,000
Blast furnace charge
238,600
Lead produced
100,000
Lead produced
100,000
-
-
Lead produced
100,000
Lead produced
100,000
22. Lead casting Lead produced
100.000
SUBTOTAL NOT INCLUDING RESUSPENDEO DUST
23. Resuspended djst3
TOTAL FUGITIVE EMISSIONS
Fugitive Emissions
Uncontrolled
Emissions
metric tons/yr
4
114
58
788
131
c
17.5
1
61
a
47
e
f
24
150
44
1,823
740
2,563
Elemental Lead
Weight Fraction
Lead Contained
in Emission
0
0.40
0.40
0.40
0.40
-
0.40
0.40
0.40
0.35
0.50
-
-
0.25
0.25
0.50
Fugitive Emissions
Uncontrolled
Lead Emissions
metric tons/yr
0
45.6
23.2
315
52.4
c
7
0.4
' 24.4
2.8
23.5
e
f
6
37.5
22
744
74
813
Footnotes
3 Rates are only estimates to be used as a basis for comparing alternate control devices.
b Emission rates are from Reference 2, pp. 2-130 to 2-149 prorated by K to convert from 200 Mg/yr to 100 Mg/yr.
c Emissions for sinter crushing included in emissions from sinter machine discharge and screens.
Emissions for charging, blow condition, and tapping included in total. Emission factor for upset not considered part of normal
operating conditions and is not included in emission factor for the blast furnace roof monitor.
8 Emissions for slag pouring included' in lead pouring to ladle and transfer emission.
Granulated slag is wet and, therefore, most likely not a source of fugitive emissions.
3 Resuspended dust contributes additional 10 percent to elemental lead (Reference 13), Lead content of resuspended dust assumed
to be 10 weight percent to calculate total resuspended dust.
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TABLE 3, SUMMARY TABLE-BASIS FOR TOTAL PARTICIPATE AND ELEMENTAL LEAD FUGITIVE
EMISSION RATES:3'6
PRIMARY COPPER SMELTER, 100,000 METRIC TONS PER YEAR
Source of Fugitive Emission
1. Unloading and handling of
ore concent rate1-
2. Ore concentrate storage
Loading onto pile
Vehicular traffic
Loading out
Wind erosion
3. Limestone flux unloading,
handling, and storage
4. Roaster charging
5. Roaster leakage11
6. Calcine transfer
7. Charging reverberatory
furnace
8. Tapping of reverberator/
9, Reverberator/ furnace leakage9
10. Slag tapping8
11. Converter charging
12. Converter leakage
13. Slag tapping from converter
14. Blister capper tapping
1 5. Blister copper transfer
16. Charging blister copper to
fire refining furnace
17. Copper tapping and
casting
Total Participate
Operating
Parameter
metric tons/yr
Ore concentrate
337,000
Ore concentrate loaded
337,000
Ore concentrate stored
337,000
Ore concentrate loaded out
337,000
Ore concentrate stored
Limestone flux
153,000
-
-
-
Copper produced
100,000
-
-
-
Copper produced
100,000
-
-
-
-
Capper produced
100,000
Capper produced
100,000
13. Slag tapping and handling3 -
SUBTOTAL NOT INCLUDING RESUSPENDEO DUST
19. Resuspended dust
TOTAL FUGITIVE EMISSIONS
Fugitive Emissions
Uncontrolled
Emissions
metric tons/yr
1,690
.7.0
22.1
9.0
18.1
25,4
d
d
d
_ 425
e
e
e
602
f
f
f
f
95
126
9
3,020
2,013
5,033
Elemental Lead
Weight Fraction
Lead Contained
in Emission
0.0167
0.0167
0.0167
0.0167
0.0167
0
-
-
-
0.015
0.015
0.015
0.015
0.020
0.020
0.020
0.020
0.020
0.010
0.010
0.010
Fugitive Emissions
Uncontrolled
Lead Emissions
metric tons/yr
28.2
0.11
0.37
0.15
0.31
0
0 •
0
0
6.38
e
e
e
12.0
f
f
f
f
0.95
1.26
g
49.7
1.0
50,7
Footnotes
3 Rate: are only estimate! to be used as a basis for comparing alternate control devices.
b Emission rates are from Reference 2, pp. 2-115 to 2-129.
c Also include] slag handling.
Emissions from roaster charging, leakage, and transfer ate not included because of clean natures of newer roasting processes
(e.g., Fluosolids).
1 Emissions from reverberatory tapping and leakage are included in emission factor for reverberatory charging.
f
Emissions from converter leakage and tapping, and blister copper transfer are included with converter charging emission factor.
^ Emissions from slag to tapping are included in casting building emissions.
A resuspended dust contribution of 40 percent of total emissions was assumed. Lead content of resuspended dust was assumed
to be 0.05 weight percent (Reference 27).
-------
HETUMH HAG
TRIPTEH CONVEVOK
NT'W^xWWWWx^
QRANULAItNC WA|£K
Figure 1. Flowsheet of Typical Lead Smelting Operations.
-------
smelters. The purification and transport of lead smelting byproducts such as
silver and zinc are not shown in this figure. Neither is the processing of
lead ore into concentrate. Ore processing and concentration is typically
o
handled at the mine, and has been discussed elsewhere.
Manufacturing lead metal from a concentrate of sulfide ores (mainly galena,
PbS) involves three steps. First, lead sulfide is converted into lead oxide
and lead sulfate by burning 80-90 percent of the sulfur in the ore by a process
called sintering. The oxidized lead (called sinter) is then reduced to metallic
lead by heating with coke in a blast furnace. Finally, the molten crude lead
is refined to remove any remaining metals--commonly copper, zinc, antimony,
silver, and tin.
As mined, lead ore is not concentrated enough to be processed 'in a smelter.
The ore is crushed to a fine powder which is concentrated via flotation to
between 45 to 75 weight percent lead. This concentrate is shipped to the
smelter via rail cars, trucks, or barges where it is unloaded and transferred to
storage bins. The unloading, material handling, and storage of concentrate is
a potential source of fugitive emissions with high lead content (typically 60
weight percent lead.)
The concentrate is mixed with fluxes and return slag to make a feed for
the sintering process. The sintering machine is a travelling grate on which
the sulfur in the concentrate is partially burned. To control the sulfur
content of the sinter machine feed, some of the sinter product is blended with
the fresh feed to the sintering machine to lower the sulfur content to 5-7
weight percent. About 10 percent of the total feed to the sintering machine is
laid down on the grate and ignited, with the remainder of the feed being spread
on the burning ignition layer.
On the sintering machine, the heat generated by the burning sulfur fuses
the sinter into a hard clinker. The clinker (called sinter) is crushed to less
than five inches and screened. The coarse sinter is the feed for the blast
furnace and the finer material is returned for blending with fresh feed.
Material handling, sinter crushing, and particulate escaping the sintering
machine hoods all contribute to fugitive emissions in the sintering building.
11
-------
Discussions with lead industry engineers indicated sintering and the associated
crushing as probably the largest process source of fugitive particulate in lead
g
smelting.
In the next processing step, sinter, coke, and flux are charged to a blast
furnace. The coke is consumed in the blast furnace and reduces the sinter to
molten lead. Fresh sinter and coke are periodically added to maintain the
furnace charge height. The molten mass in the furnace bottom is settled into a
layer of molten lead and a lighter slag layer. The molten material may be
tapped continuously or on an intermittent basis. Typically, the molten slag is
granulated with a water jet and then dumped in open piles.
Fugitive emissions from the blast furnace are normally low, but may become
significant during process upsets. The pressure af the top of the blast furnace
normally is sufficiently low that gases passing up through the furnace are
sucked into the central collection hood and do not enter the work space dir-
ectly above the blast furnace. If the blast furnace charge is not porous
enough, high pressures can build up across the furnace charge and in extreme
circumstances blow particulate into the working area. Another problem occurs
when a "blowhole" develops and the hot gases preferentially bypass the main
body of the furnace charge through a channel which has formed. Very little
visible fugitive particulates are seen from the slag granulation.
Most zinc originally present in the ore concentrate ends up in the blast
furnace slag. When the economics so dictate, and the smelter has the proper
equipment, the zinc can be recovered in a zinc fuming furnace. Only three of
the six U.S. lead smelters have zinc fuming furnaces, and these operate inter-
mittently, depending on the zinc market conditions. Fugitive emissions from zinc
fuming furnaces have been reviewed in another report. They are not considered
in this report because most lead smelters do not have zinc fuming furnaces.
More variation is found in the refining areas of lead smelters than in the
other two' processing steps; refining is designed around the ore source available
to the smelter. The content of copper and other trace metals varies between
ores, but in general ores can be classified as Missouri or non-Missouri lead
ores. Missouri lead ores contain traces of silver and cadmium, but little
copper or others impurities. Accordingly, their refining is not as involved
12
-------
as that for the more complex ores. Missouri lead ore accounts for over 80
1
5
percent of the ore mined in the U.S. Accordingly, the following refining
sequence is from a Missouri smelter.'
Molten lead bullion from the slag settler is moved through a series of 250
ton capacity, hemispherical refining kettles. First the bullion is transferred
to a dressing kettle where sulfur and other additives are added and the metal
is cooled. At about 430° (800°F), copper and other impurities solidify and are
skimmed off and transferred to a reverberatory dressing furnace. In the dressing
furnace, soda ash is melted with the dross and causes it to separate into (a)
matte which is solidified and may be shipped to a copper smelter for recovery
of the contained copper, and (b) lead bullion which is recycled to the dressing
kettle. Impure lead from the dressing kettle is reheated in a desi-lvering
kettle where zinc is added and a crust enriched in silver and gold is removed
as the metal cools. To remove zinc remaining in the lead, a subsequent kettle
fitted with a vacuum hood is used to vaporize zinc from the molten lead. As a
final refining step, caustic soda and niter are added in a refining kettle.
The remaining impurities rise to the surface and are skimmed off. The refined
molten lead is then cast into pigs or ingots.
Fugitive emissions from the refining process consist mainly of fumes from
molten metal handling.
There are several material handling operations in the smelter which have
not been specifically mentioned above—an in-plant rail system is typically
used to transport quantities of slag to the dump, baghouse dust to storage
bins, and make other batch materials movements; the molten lead bullion is
moved via ladle cars and overhead crane ladles; and slag, although usually
granulated, may be moved in wheeled slag pots. The operation and movement of
front-end loaders, trucks, and other vehicles can create fugitive dust emissions.
A final source of fugitive particulate, often neglected but quite im-
portant, is windblown dust resuspended from the ground, storage piles, or open
areas around the smelter. In the integrated iron and steel industry, such open
source fugitive emissions have been estimated to be roughly the same magnitude
12
as fugitive emissions from process operations.
13
-------
Fugitive Emission Rate Data for Lead Smelting •
Particulate emissions that are from fugitive (i.e., non-ducted) sources
have not received the same level of study that point sources (i.e., stack
emissions) have. Accordingly, emission rate factors for fugitive sources are
not well established; few reliable measurements have been made. Available rate
data is of questionable accuracy, but since the purpose of this report is to
compare alternate control methods, rate data is presented and used as a base
case for comparing charged fog sprays with building evacuation. Only with a
clear understanding of its limitations should the data be used for any other
purpose.
PEDCo Environmental, Inc. has prepared a list of fugitive emission factors
for a hypothetical 200k metric tons per year lead smelter. The average capacity
in 1976 of the six United States primary lead smelters was only about 100k
metric tons per year, and the PEDCo factors have been prorated by one-half to
prepare the emissions rates shown on Table 2. The smelting flowsheet used by
PEDCo to estimate fugitive emission rates is not the same as that presented in
Figure 1, but it is felt that the emission factors are not accurate enough to
justify a complete recalculation of emission rates. Some modifications of the
PedCo emission rates were made—the contribution from the silver retort building
and the contribution of the zinc fuming furnace listed in the PEDCo tabulation
are not included in Table 2. Also, a contribution from particulate resuspended
from open areas was added.
13
TRC has pointed out that there may be a large contribution from resus-
pended particulate deposited on the plant grounds. They estimated the effect
of resuspended particulate by comparing ambient lead measurements from periods
of normal smelter operation with those from times when the smelter was shut
down because of strike or holiday. Their data are summarized in Table 4 and
are the basis of the resuspended dust contribution added to the fugitive
emissions inventory. Table 4 data indicate that about an additional 10 percent
contribution to elemental lead (not total particulate) is made by resuspended
particulate. For the source inventory in Table 1, this resulted in an extra 74
metric tons per year of elemental lead. To get an estimate of the total
suspended particulate contributed by resuspension, the 74 metric tons per year
14
-------
TABLE 4. RELATIVE CONTRIBUTIONS FROM VARIOUS EMISSION SOURCES TO FENCELINE
CONCENTRATIONS OF AMBIENT LEAD AT PRIMARY LEAD SMELTERS*
Plant
Bunker Hill
ASARCO, El Paso
St. Joe
ASARCO, Glover
Automobile
3
ug/m
0.5
0.4
0.2
0.4
Resuspension
3
4.6
2.7
h
1.5/0.5°
1.5d
Stack plus
fugitive9
3
wg/m
10
27
h
8/16°
15
Total
3
15
30
h
10/17°
17
Resuspension
as a percent'
age of total
46
10
K
19/3°
10C
*Data is from Reference 13.
aThe numbers presented represent long term averages (i.e., if two. years of
data are available, the value would be a two-year average). Individual
monthly averages would range higher.
Upwind data/Downwind data.
Insufficient data were available for an accurate resuspension contribution.
The number presented is based on the assumption that the fall-off rate is
similar to that exhibited by the other plants.
of lead were converted to 740 metric tons per year of total particulate by
assuming a lead content of 10 weight percent. It is recognized that this
resuspended contribution is only a gross approximation. It is included to
give a truer picture of the total fugitive emissions from a smelter.
c
Fugitive process emission measurements done by Constant et al. are presented
in Table 5. Their data considers fugitive emissions from an entire operation,
such as from the individual processes of a sinter building, as one source.
Fugitive Emission Size and Composition Data for Lead Smelting
Several sources were used to obtain composition and size data for
fugitive emissions. The compositions were used to calculate elemental lead
emission rates from emission factors for total suspended particulates. This
section discusses the origins of the composition data used in Table 2.
Galena (PbS) is the major lead-bearing mineral in-the ore concentrate
fed to lead smelters; pure galena contains 86.6 weight percent lead. Smelter
concentrates vary from around 45 percent up to 75 percent lead and contain
15
-------
TABLE 5. EMISSION FACTORS FOR LEAD SMELTING AS MEASURED BY MRI*
Total Emission Rate of Fugitive Particulate
Glover, MO Plant East Helena, MT Plant
Operation Mg/y Mg/y
Sinter Building 19.4 10.3
Blast Furnace 19.5 ' 5.5
Dross Kettles --- „-, cb
4/ .b
Reverberatory Furnace —
Ore Storage Bins 1.3 —
Plant Total 40.2 63.4b
*Yearly emission rates were calculated from Ib/day data in Reference
6 assuming 350 d/yr of smelter operation.
aAverage of dross kettles and reverberatory furnace.
Total does not include 2.2 Mg/yr from a zinc fuming facility or 5.3 Mg/yr
from a zinc furnace which were listed in Reference 6.
varying amounts of minor impurities depending on the ore source. Table 6
shows the range of lead concentrate compositions cited in the referenced
articles. Sixty percent lead was used in Table 1 for fugitive emissions from
concentrate handling. No lead enrichment in these fugitive emissions is
expected, since the ores have not yet been exposed to temperatures which might
produce fume that is enriched in volatile metals.
The lead content of fugitive emissions around the sintering machine was
taken as 40 weight percent based on the data in Table 7. Note that the final
two columns in Table 7 given compositions of fugitive emissions from two
sintering buildings as measured in Reference 6. (There are three values men-
tioned for lead content of sintering building emissions in Reference 6: 58
percent in Table 11; 27.5 percent in Table 10; and 34.5 percent calculated
from Table 8. The mid-value has been shown.)
For lead contents in other operation areas, Table 8 of this report pre-
sents sampling data from Reference 6. As is seen, there is little consistency
in the numbers. In this report, the authors have: (a) used 35 weight per-
cent lead for fugitive emissions from the blast furnace area, since about 10
16
-------
TABLE 6. LEAD CONCENTRATE COMPOSITIONS
Weight Percent Unless Otherwise Specified
Constituent
Pb
S
Zn
Fe
Cu
CaO
As
Sb
Bi
Cd
Ag
Au
Reference 8
45-60
10-30
0-15
1-8
0-3
tr-3.0
0.1-0.4
0.01-2.0
tr-0.1
tr
0-50 oz/t
0-"few" oz/t
Reference 14
55-70
13-18.5
0-6.5
0-5
0.5-4
tr
tr
No Data
No Data
tr
tr
tr
Reference 15
70
No Data
1.5
No Data
0.5
No Data
No Data
No Data
No Data
0.2
No Data
No Data
Reference 7
72
No Data
0.8-2.9
No Data
0.9
No Data
No Data
No Data
No Data
No Data
1 oz/t
No Data
Reference 17
76.1
15.6
1.0
3.9
0.04
0.25
0.28
0.12
0.04
No Data
35 oz/t
0.48 oz/t
4
-------
TABLE 7. COMPOSITION OF SINTERING EMISSIONS
WEIGHT PERCENT UNLESS OTHERWISE SPECIFIED
CONSTITUENT
Pb
S
Zn
Fe
Cu
CaO
As
Cd
Ag
FEED3
40-46
5-7
no data
no data
no data
no data
no data
no data
no data
FEEDb
32.0
10.6
5.6
9.4
2.0
4.5
no data
0.05
30-150*
FEED0
42.2
4.2
3.6
no data
no data
no data
0.38
0.0020
no data
PRODUCT6
42.0
1.86
3.93
no data
no data
no data
0.36
0.0020
no data
PRODUCT11
35.5
1.4
10.0
9.7
2.9
10.3
no data
0.04
30-150*
PRODUCT11
28-36
0.75-1.6
9.5-12.5
12-15.5
0.6-1.5
9.0-10.5
no data
no data
10-21*
ROOF
MONITORd
34.8
no data
no data
no data
no data
no data
0.033
no data
no data
ROOF
MONITOR6
9.6
no data
no data
no data
no data
no data
0.79
no data
no data
PRODUCT1
48
1.4
no data
12
1
5
no data
no data
no data
a Reference 4, p. 3-183.
b Reference 8, p. 5-13.
c Reference 16, p. 39.
d Reference 6, p. 11.
e Reference 6, p. 20.
Reference 7.
* ounces/ton
-------
TABLE 8. LEAD CONTENT OF FUGITIVE EMISSIONS FROM
LEAD SMELTING OPERATIONAL AREAS*
Operation Lead/Total Particulate
Glover, MO, plant
Ore-storage-bin area 0.508
Blast-furnace area 0.498
Sinter building 0.275
Background at truck-to-rail ore
transfer point 0.104
East Helena, MT, plant
Background at ore loading 0.217
Dross/reverberatory building 0.222
Sinter building " 0.096
Blast furnace 0.108
*Data is from Reference 6.
percent coke is added to the sinter which is initially 40 percent lead; (b)
used 50 weight percent lead for fugitive emissions from lead transfer, ladling,
and casting since furnace tapping measurements in Table 11 of Reference 6
averaged 52 percent lead; (c) eliminated slag cooling and piling from the
emissions inventory under the assumption that all slag is granulated with
negligible fugitive emissions; (d) eliminated zinc fuming emissions from the
inventory; (e) used 25 weight percent lead for fugitive emissions from the
dressing and reverberatory furnace operations, since a measurement of this
area was 22.2 percent; and (f) eliminated silver retorting emissions from the
inventory.
Some size distribution data was found for fugitive emissions from lead
smelters. Midwest Research Institute (MRI) conducted actual plant measurements
of fugitive emissions from two ASARCO primary lead smelters: the Glover,
Missouri plant and the East Helena, Montana plant. Because of the measurement
problems associated with individual sources, fugitive emissions from an entire
operation (such as the sintering building) were measured as one fugitive
source.
MRI determined the particle size range of total particulate fugitive
emissions for four locations at the Glover plant: (1) sintering building, (2)
blast furnace tapping area, (3) blast furnace feed charging area, and (4) ore
19
-------
storage bin area. A Sierra, Model 230, HiVol cascade impactor was used. A
Sierra impactor was also used to determine the particle size range for total
fugitive emissions from the East Helena blast furnace operations. The results
are summarized in Table 9.
TABLE 9. PARTICLE DISTRIBUTION FOR FUGITIVE PARTICULATES FROM LEAD SMELTING*
'Concentration Particle size range
o
Location ug/m wt% urn
Sinter building,
Glover, Missouri
Blast furnace tapping
operations,
Glover, Missouri
Blast furnace charge-feed
area,
Glover, Missouri
Ore-storage bin
Blast furnace operations,
East Helena, Montana
1,420
207
174
112
117
116
44.1
39
32.7
24.7
40.4
75.7
1,301
79.1
82.1
81.2
190
339
372
36.6
54.4
45.1
89.5
177
652
375
242
132
102
71.1
66.18
9.64
8.11
5.2?
5.45
5.40
17.19
15.20
12.74
9.62
15.74
29.51
62.81
3.82
3.96
3.92
9.17
16.32
48.03
4.72
7.02
5.82
11.55
22.86
41.43
23.82
15.37
8.38
6.48
4.52
<0.38
0-.38-0.71
0.71-1.15
1.15-2.3
' 2.3-5.6
>5.6
<0.31
0.31-0.59
0.59-0.95
0.95-1.9
1.9-4.6
>4.6
<0.33
0.33-0.63
0.63-1.0
1.0-2.03
2.03-4.9
>4.9
<0.31
0.31-0.59
0.59-0.95
0.95-1.9
1.9-4.6
>4.6
<0.31
0.31-0.59
0.59-0.95
0.95-1.9
1.9-4.6
>4.6
'tlata is from Reference 6.
20
-------
Particle sizes as determined by Harris and Drehmel with a Brink impactor
gave the data in Table 10 for ducted emissions from a lead sintering machine.
TABLE 10. PARTICLE DISTRIBUTION FOR DUCTED LEAD SINTERING MACHINES GASES*
Particle Size Particle Loading Size Distribution
mg/nT
gr/scf
wt*
>3.1
1.8-3.1
1.25-1.8
0.62-1.25
0.38-0.62
<0.38
TOTAL
93.30
37.12
0
59.47
135.88
152.77
47.18
525.72
(0.04077)
(0.01622)
(0.02599)
(0.05938)
(0.06676).
(0.02062)
(0.22974)
17.75
7.06
11.31
25.85
29.06
8.97
100.00
*Data is from Reference 17.
Some idea of the size distribution of fugitive particulates outside the
I 0
boundary of a lead smelter can be gained from data by Dorn et al. They
measured lead, cadmium, zinc, and copper levels in suspended particulate over
winter, spring, and summer seasons at a site approximately 800 meters north of a
lead smelter. An eight-stage Andersen impactor sampler was used. While they
did not present total particulate weights versus size, a rough idea of the
particles in the respirable range can be gained from the elemental distribu-
tions in Table 11. Complete elemental distribution data is given in Table 12.
TABLE 11. DISTRIBUTION OF Pb, Cd, Zn, Cu IN RESPIRABLE RANGE NEAR A
PRIMARY LEAD SMELTER*
Particle Size
ym
Pb
Element and Percent
Cd Zn
Cu
> 4.7
< 4.7
34.29
65.71
11.69
88.31
27.09
72.91
45.68
54.32
*Data is from Reference 18.
21
-------
TABLE 12. AIRBORNE ELEMENTAL CONCENTRATIONS NFAR PRIMARY LEAD SMELTER*
Elemental Concentration
Size
ym
> n
7-11
4.7-7
3.3-4.7
2.1-3.3
1.1-2.1
0.65-1.1
0.43-0.65
Pb
3
yg/m wt%
0.1064
0.0733
0.1768
0.1655
0.0691
0.1430
0.1651
0.1372
1.0361**
10.26
7.07
17.06
15.97
6.67
13.80
15.93
13.24
Cd
3
yg/m wt%
0.0009
0.0007
0.0013
0.0014
0.0011
0.0064
0.0071
0.0059
0.0248
3.63
2.82
5.24
5.65
4.44
25.81
28.62
23.79
Zn
yg/m3 wt%
0.0194
0.0113
0.0166
0.0163
0.0140
0.0307
0.0343
0.0320
0.1746
11.11
6.47
9.51
9.34
8.02
17.58
19.64
•
18.33
Cu
3
yg/m wt%
0.0042
0.0018
0.0029
0.0026
0.0015
0.0016
0.0008
0.0040
0.0194
2l'. 65
9.28
14.95
13.40
7.73
8.25
4.12
20.62
*Data is from Reference 18.
**Numbers in this column are taken as published. Individual values add to
1.0364, not 1.0361 as is shown.
COPPER SMELTING
Process Description of Copper Smelting
United States copper smelters vary more in their processing steps than do
lead smelters. Broadly speaking, (1) part of the sulfur in the ore concentrate
is burned in the roasting process, (2) the calcine produced in roasting is
melted together with fluxes in a reverberatory furnace which produces a slag
for discard and a copper bearing "matte," (3) the matte is transferred to
converters into which air is blown and iron impurities are periodically
removed as slag, and (4) blister copper from the converter is cast into anodes
which are sent to an electrolytic refining plant. Some plants carry out the
roasting in multihearth roasters, other plants use fluidized beds, and some
feed the concentrate directly to the reverberatory furnace. Newer smelting
processes are being developed—such as continuous smelting—which differ markedly
from the general scheme described above. Reference 19 provides a good overview
of the .available and developing smelting technology. Some detailed engineering
information on the United States plants, has been compiled by Pacific Environ-
mental services, Inc.20
22
-------
Figure 2 presents a flowsheet for a copper smelter having Fluosol ids"'feed
roasting and conventional reverberatory furnaces. A brief discussion of the
processing steps as sources of fugitive emissions follows.
Concentrate from outdoor storage is fed to a Fluosolids roaster to remove
part of the.sulfur in the concentrate. Feed to this roaster is via conveyor
belt and hopper. The roaster offgases pass through primary and secondary
cyclones which remove most of the calcine and discharge it into reverberatory
furnace charging bins through a sealed system. The roaster exhaust gases are
then scrubbed to remove most of the remaining fine particulates and the clean
exhaust gas stream joins the gas stream from the converters and reports to a
sulfuric acid plant.
Fugitive particulate emissions from a Fluosolids roasting system are
generated mainly by material handling. However, the other roasting process,
multihearth roasting, is not as clean. Multihearth roasters tend to have leaks
which result in fugitive particulate emissions.
One or more reverberatory furnaces follow the roasters. Calcine from the
roasting step is fed to the reverberatory furnace from calcine bins through
sealed feeders which feed the furnace for approximately two out of every
fifteen minutes. The reverberatory furnace is typically fired with natural
gas, but fuel oil can be used. Slag and matte are tapped from the reverb
furnace into ladles. The reverb slag is transported to a slag dump where it is
poured to resolidify. The copper-containing reverb matte is transferred to the
converters for additional processing.
Furnace leakage, slag and matte tapping, and hot materials transfer are
the main sources of fugitive emissions around the reverberatory furnace.
Fugitive particulate emissions from this area are relatively small; very little
visible fugitive emissions can be seen in this area, even during the tapping
operation.
Matte from the reverberatory furnace is transferred by overhead crane and
charged to one of several converters. Air is blown through tuyeres into the
charge, flux is added, and the slag produced is skimmed into ladles. The slag
is then transferred by slag hauler to cooling pits. Water sprays in the pits
(similar to lawn sprinklers) are used to assist cooling the hot converter slag
which is finally broken by a bulldozer equipped with breaker bars. The broken
23
-------
1 RAILCAH OUMfING
ORE TO GRINDING,
CCMKINTHATIOM
AHO OEWATIfllHa
Figure 2. Flowsheet of Typical Copper Smelting Operations.
-24
-------
slag is returned to the concentrator where it is reprocessed with raw ore.
Offgases from the converter are collected by hoods and pass through a gas
cooler in which the gas stream is treated by a concurrently flowing ultra-
sonically dispersed water spray. The cooled gas stream flows through high
velocity ducts to a scrubbing tower, is blended with the roaster gas stream and
reports to an acid plant for conversion into sulfuric acid. The finished
blister copper from the converters is poured into ladles for transfer by
overhead crane to an anode furnace, where it is first oxidized by the addition
of air and then reduced with propane or natural gas. The finished anode copper
is poured into anode molds, cooled, and loaded onto rail cars for shipment to
an electrolytic refinery.
Converter operations are probably the largest single process source of
fugitive emissions in a copper smelter. Access requirements and high tempera-
tures around the converter mouth make tight hooding very difficult and there is
a good deal of fume and participate that escapes around the converter hood and
rises to the roof monitors. These gases are on the order of 350 to 500 °C
(600 to 930 °F). There is an area near the converter aisle that is used to
accumulate and recycle copper scrap; fugitive dust is generated as the crane
clam shell moves this scrap material. While there is typically no hooding over
the mouth of the anode furnace, there are no visible fugitive emissions from
this operation. Copper from the anode furnace is tapped into a circular
casting wheel to make anodes for electrolytic refining. Again, no visible
fugitive emissions are seen from this operation other than steam coming from
water that is used to cool the anodes as they circulate on the wheel. The hot
anodes are picked off the wheel and dropped into a water cooling bath, and
again, while some steam is emitted, there is no visible particulate.
In general, aside from the copious fugitive particulates from the copper
converters, the strongest sources of visible fugitive particulates in a smelter
are materials transfer and vehicular traffic around the plant. Traffic includes
front-end loaders moving material for recycle, recycle slag handling, and
general truck traffic in and out of the area. Some localized sources such as
conveyor transfer points also generate fugitive particulates on a small scale.
25
-------
Fugitive Emission Rate Data for Copper Smelting
3
The sample fugitive emissions inventory prepared by PEDCo was used as the
basis for estimating fugitive emissions from a copper smelter producing 100,000
metric tons per year of crude copper. The following adjustments in the PEDCo
table were made to obtain the emission rates shown in Table 3: (a) roaster
charging, a fairly large source was omitted because of its declining use and
the small amount of fugitive emissions from the alternatives--greenfeed
reverberatory charging and Fluosolids roasting; (b) an additional 40 percent
was added to the process fugitive emissions to account for resuspended par-
ticulates, the 40 percent being the same relative amount of total particulate
as was used for lead smelting in Table 2.
No sampling of fugitive emissions in copper smelters has been'done which
compares in scope to the MRI sampling of lead smelter fugitive emissions.
EPA is currently doing some sampling of copper smelter fugitive emissions
22
through a contract to TRW, Inc. Several operations are being sampled for
fugitive emissions with the main emphasis being on fugitive arsenic emissions.
However, total particulate levels are being measured on some of the samples.
Fugitive Emission Size and Composition Data for Copper Smelting
The composition data used to obtain the elemental lead emission rates in
Table 3 are discussed below. The lead content of fugitive particulate emissions
from copper smelting is much lower than the lead content of fugitive emissions
from lead smelting. The elemental lead emission rate is far lower for copper
smelting. However, other trace metals such as arsenic may be concentrated in
some fugitive streams from the copper smelter. Information on the concentration
of metals other than lead are presented, where available, but estimates of
overall rates for elements besides lead were not made.
Fugitive emissions from material handling of copper concentrate will have
metal contents similar to the concentrate itself. There is substantial varia-
tion in metals content depending on concentrate source. In particular, lead
varies from around 50 ppm to over 10 percent. Table 13 shows the minimum,
23
maximum, and production-weighted mean values for U.S. copper concentrates.
The production-weighted mean lead content of 1.67 weight percent was used in
the fugitive emissions inventory in Table 3. Fugitive emissions from concentrate
storage and handling are the largest single source of elemental lead in the
26
-------
Inventory. It is recognized that lead contents vary widely between smelters
and lead emissions may be orders of magnitude lower for some smelters.
TABLE 13. COMPOSITION OF COPPER CONCENTRATES PROCESSED IN THE U.S.
Metal
Minimum
Composition, Weight Percent
Mean as weighted by
Maximum - 1971 production
Cu
Pb
S
As
Sb
Bi
Zn
Sn
Ni
Se
13.8
0.005
22.8
0.0007
' 0.0002
0.005
0.02
0.0003
0.0005
0.0005
36.1
13.2
44.8
12.6
3.26
0.83
12.2
0.1 "
2.4
0.095
26.9
1.67
32.0
0.97
0.10
0.024
1.49
0.0044
0.024
0.0079
For other areas in the copper smelter, perhaps the best indication of the
relative concentrations comes from some NIOSH sampling results. Between 1965
and 1973 NIOSH collected data throughout the copper industry on trace metal
levels in smelters. Samples from many smelters were obtained and used to get
long term, industry-wide averages of exposure for the following smelter areas:
(a) reverberatory furnace charging deck; (b) reverberatory furnace operators
deck; (c) converters; and (d) anode casting. Both personnel and area samples
were collected. Membrane filters with a 0.8 micron size were used to collect
metal fumes and dusts which were then analyzed by atomic absorption. Unfor-
tunately, total particulate levels are not given for the various areas, only
ambient elemental concentrations. Table 14 summarizes the NIOSH data.
Some composition data for ducted particulate from the Bor, Yugoslavia
copper smelter is given in Table 15. The lead contents for the particulate
streams in the U.S. probably averages higher than those for Bor because of the
27
-------
TABLE 14. ELEMENTAL CONCENTRATIONS IN AIR BY COPPER SMELTER AREA. INDUSTRY-WIDE AVERAGES*
3 3
Area Area Sampling, mg/m Personnel sampling, mg/m
Pb Zn Cu As Cd Mo Pb Zn Cu As Cd Mo
i -...-- ._ • _ - * ...... _ .- ->_.^>—._.....-- i v >»—a—r 11- i - *i •.-•.>.
Reverberatory 0.07 0.07 1.1 0.04 0.005 0.014 0.07 0.12 3.4 ND** 0.005 0.003
furnace
charging deck
Reverberatory 0.06 0.12 2.3 0.02 0.012 0.015 0.07 0.07 1.3 ND 0.006 0.03
furnace
operators deck
Converter aisle 0.05 0.05 0.22 0.01 0.003 0.004 0.03 0.04 0.11 ND 0.004 ND
(M
00
Anode casting 0.01 <0.01 0.13 <0.01 0.001 ND 0.01 0.01 0.07 ND <0.001 ND
**ND = No Data
*Data from Reference 24
-------
TABLE 15. COMPOSITION OF DUCTED COPPER CONVERTER DUSTS FROM BOR. YUGOSLAVIA25
Composition, Weight Percent
El ement
Cu
Pb
Fe
S
Mo
Se
As
Typical
concentrate
16
0.1
32
42
0.005
0.003
0.5
Converter dust from
Matte slag blowing
38.50
0.2785
32.04
25.80
0.0044
0.0275
0.1907
42.0
0.5914
12.05
11.82
0.0130
0.0325
1.1173
Converter dust from
copper blowing
58.26
0.8984
5.26
14.01
0.0055
0.0334
1.0783
Reverberatory
furnace
13
0.5
17
NO*
0.02
0.003
2.0
^ *No Data
LD
-------
higher average concentrate lead content In the U.S.--1.67 versus 0.5 percent.
To convert the NIOSH data into participate composition, the copper content of
the participate from each sample would be needed. As this is not provided, it
is instead assumed, based on the Bor data, that typical copper contents are 40
percent in particulate from the converter and anode areas and 15 percent in
particulate from the reverberatory area. This was done and gave the estimated
compositions in Table 16. Based on Table 16, the following lead contents were
used to prepare Table 3: for charging and tapping of the reverberatory furnace,
1.5 weight percent lead; for converter charging and leakage, 2.0 weight percent
lead; and for charging blister copper and anode furnace tapping and casting,
1.0 weight percent lead.
Little size data is available for fugitive particulate emissions from
copper smelters. In an attempt to distinguish between "respirable" and "non-
respirable" metal concentrations, the NIOSH workers took some samples through a
cyclone before analyzing for metals collected on the filter; the range for
respirable particle size is not given. Table 17 shows the results for .23 data
points for converter furnace and crane aisle employees. Harris and Drehmel
provided the values in Table 18 for ducted particulates from a copper converter
as sampled by a Brink, Model B, five-stage impactor.
p£
Thompson and Nichols measured ducted particulates from two copper rever-
beratory furnaces with cascade inertial impactors and five-stage cyclones.
Data estimated from two figures they provided are given in Table 19.
30
-------
TABLE 16: ESTIMATED COMPOSITION OF FUGITIVE PARTICULATES BY COPPPER SMELTER AREA3
Area Area Sampling Personnel Sampling
Pb Zn Cu As Cd Mo Pb Zn Cu As Cd Mo
Reverberatory 2.5 2.5 40b 1.4 0.18 0.51 0.82 1.4 40b ND** 0.06 0.04
furnace
charging deck , .
Reverberatory 1.0 2.1 40° 0.35 0.21 0.26 2.2 2.2 40° ND 0.18 0.92
furnace
operators deck
Converter aisle 3.4 3.4 15b 0.68 0.20 0.27 1.4 1.8 15b ND 0.18 ND
Anode casting 1.2 <1.2 15b <1.2 <0.12 ND 0.71 0.71 15b ND <0.07 ND
**ND = No Data
Elemental concentration data from Reference 24 converted to weight percent by assuming forty
percent copper in particulates from reverberatory furnace areas and fifteen percent copper
in particulates from the converter and anode casting areas.
Assumed
-------
TABLE 17. PERCENT OF METAL AEROSOLS IN RESPIRABLE9 RANGE: CONVERTER, FURNACE
.AND CRANE AISLE EMPLOYEES IN U.S. COPPER SMELTERS
Metal
Pb
Zn
Cu
As
Cd
Average %c Respirable
52.1
59.5
6.1
75.2
49.5
aNo size given for "respirable." Larger aerosols were removed using a
miniature cyclone before collecting remainder on a filter.
Data adapted from Reference 24.
C23 data points each, except As only has 14.
TABLE 18. PARTICLE DISTRIBUTION FOR DUCTED COPPER CONVERTER GASES
f~T -J J - , iTlm. _JI - ------- — -" ~ -•--.— -: . -• '"•'—' -^-JTJIE-—"-•--•-"-m.—•-- nr ........... ._.. ..- ^-.
Test 1 Test 2
Particle Size
vim
mg/nf
gr/scf
wtl
mg/nT
gr/scf
wt%
>3.1
1.8 - 3.1
1.25 - 1.8
0.62 - 1.25
0.38 - 0.62
<0.38
TOTAL
3.52
13.59
57.02
222.04
16.36
12.58
325.11
(0.00154)
(0.00594)
(0.02492)
(0.09703)
(0.00715)
(0.00550)
(0.14208)
1.08
4.18
17.54
68.30
5.03
3.87
100.00
10.23
15.10
56.09
137.03
42.95
4.71
266.11
(0.00447}
(0.00660)
(0.02451)
(0.05988)
(0.01877)
(0.00206)
(0.11629)
3.84
5.68
21.08
51.49
16.14
1.77
100.00
TABLE 1-9. PARTICLE DISTRIBUTION FOR DUCTED COPPER REVERBERATORY FURNACE GASES'
PLANT A PLANT B
Particle Size
mg/acm
wt%
mg/acm
wt%
> 4
2-4
1-2
0.6-1
0:3.0.6
<0.3
10
20
31
27
24
28
7
14
22
20
17
20
80
50
40
38
65
17
28
17
14
13
22
6
32
-------
4.0 CHARGED FOG SPRAYS FOR CONTROLLING FUGITIVE EMISSIONS
This section describes charged fog spray devices, discusses theoretical
and experimental efficiencies for sprays, and"presents the efficiency and costs
used as the basis for evaluating charged fog sprays.
DESCRIPTION OF CHARGED FOG SPRAY DEVICE
The spray of fine water droplets is a well-known means of dust removal.
The various types of scrubbers rely on water droplets to sweep dust from the
inlet gases, and water sprays have often been used in mining and material
handling to reduce dust levels in the air. Charged fog sprays, as evaluated in
this report, differ from conventional water sprays in that the droplets carry a
charge of static electricity. Also, the droplets used for an electrostatic
spray may be of a finer size. Since most fine particulates carry a natural
28
electrical charge, particle collection can be improved via electrostatic
attraction if the water spray droplets are charged to the opposite polarity.
The charged water droplets then exert attractive forces on the oppositely
charged particles and each droplet collects more particles as it travels through
the dust-laden gas.
The water droplets in a spray may be electrostatically charged by several .
methods. Droplets may be charged via induction from a metal ring surrounding
the spray (Figure 3a), via a charged needle in the spray (Figure 3b), or by
direct electrical contact with the water (Figure 3c). In the third case, the
spray nozzle must be insulated in such a way as to prevent current leakage
28
through the support structure or the water feedline. Hoenig mentions isolating
up to 20kV by injecting air into a plastic tubing feedline. The injected air
breaks the continuous water column into segments and prevents electrical
29
leakage via conduction through the water column. Hassler has reported an
autogenous charging method which does not require any voltage source. Droplet
charges result from water-to-metal friction in a grounded spray nozzle (Figure
3d). While not requiring any voltage source, the method does require very
pure, deionized water. Autogenous charging will work only if the nozzle
33
-------
Water
Feedline
Insulated
Metal Ring
5-10KV.
- Charge
3a. Charge Induced Via Metal Ring.
•f Cliarged
'. \ Droplets
Water
Feedline
5-1OKV
+ Charge Electrically
Isolated
Needle
Spray
.Nozzle
3b. Charging Via Needle.
ijllli' '• "•;. + Charged
••.' >V;j Droplets
Plastic Water
Feedline
Insulated
Spray
Nozzle
Air Injected J
to Segment
Water Column
5-1 OKV
+ Charge
3c. Direct Contact Water Charging.
Feedline for
De-Ionized Water
Grounded
Spray
Nozzle
'.-.. + Charged
'j.v'. Droplets
•' •' + Charged
•;' Droplets
3d. Autogenous Charging to De-ionized Water
Figure 3. Means of Producing a Charged Water Spray.
34
-------
is grounded and the water acts as an insulator; even tap water has too many
impurities to produce a charged spray by this means.
The only known commercial version of an charged fog spray device is the
Electrostatic Fogger r^manufactured by Ransburg Electrostatic Equipment, a
division of Ransburg Corporation, Indianapolis, Indiana. The original work on
the charged fog sprays was done by Dr. Stuart Hoenig at the University of
Arizona under support provided by the American Foundry Society. Dr. Hoenig
approached Ransburg and discussed the possibility of Ransburg manufacturing the
Electrostatic Fogger. Ransburg as a company has filed application for a patent
on the electrostatic fogging principle, and this patent is now pending. Ransburg
has recently begun to commercially market the Electrostatic Fogger I. Their
prior experience has been with electrostatic paint "spraying equipmen-t.
The following information was obtained during discussions with Ransburg.
The device functions by applying a 5 to 10 kilovolt induced voltage on a
metal ring surrounding the spray nozzle. This changing technique is the subject
of a U.S. Patent*. The droplets coming out the nozzle charge either positively
or negatively as controlled by connections in the control box. The Fogger does
not permit variation of the voltage applied to the metal ring other than polarity.
The control box for the Fogger is mounted separately from the spray nozzle
itself. It contains a 40 micron filter on the water supply and a pressure
regulator to maintain constant water supply pressure to the nozzle. Likewise
on the air supply to the box there is a 10 micron filter and a pressure regulator.
The box contains an indicator light which will dim when the voltage to the
spray nozzle is not high enough for one reason or another. It also has a light
which indicates when the unit itself has power. Each spray has its own control
box, although Ransburg can arrange to put multiple boxes inside one larger
cabinet. They like the approach of individual control boxes from the standpoint
that the entire water spray network is not dependent on any single component.
Electrical requirments are SOW of 115V, 60Hz.
Ransburg said the droplet size from the Fogger I is typically 25 to 75
microns, but did not provide any further data on the droplet size distribution.
*During report preparation (12/78), it was found that Ransburg had sold all
market rights, patents, and manufacturing equipment for the Electrostatic
Fogger to Ritten Corporation Ltd., 40 Rittenhouse Place, Ardmore, Pa.
35
-------
The spray device itself is a fairly simple looking item consisting of a nozzle
surrounded by the metal ring with a plastic case about the device. Air provided
to the nozzle is used mostly to atomize the water with a small amount injected
tangentially into the ring around the spray to produce a coanda effect (that
is, a swirling airflow around the spray) and project the water droplets farther
than would otherwise be obtained. Air requirements are up to 13 SCFM at 110
psig. The Fogger I provides a water stream which is indeed a "fog" and not a
mist or a spray. Typically the water droplets evaporate 2.5-3 meters (4-6
feet) from the spray nozzle and the width of the spray is about 0.7 meters (2
feet).
The particular Fogger I which is now being marketed by Ransburg is not
approved for use in hazardous atmospheres. However, Ransburg has some patented
technology in the way of safety equipment whith can be used to make these high
voltage devices sparkproof. The company has manufactured paint sprayers approved
for NFPA Class 1, Division D uses (applications with hydrocarbon solvents used
in spray painting). This feature is provided by using a high resistance element
in the charging circuit which limits the steady state current flow and by
keeping the mass (and thus the capacitance) downstream of this resistor very
small.
Ransburg is currently developing a second electrostatic fog spray to be
called Fogger II, which will be of much larger capacity. Fogger I is rated for
O O
16cm s (0.25 gpm) of water. The Fogger II is being designed for up to 190 cm s
(3 gpm) of applied water and up to 10 meters (30 feet) spray distance. The
larger flow version of the Fogger will not have as small a droplet distribution
as the Fogger I. The water droplets in it are also charged with a metallic
ring surrounding the spray nozzle, but the Fogger II will use hydraulic atomi-
zation as opposed to air atomization used in the Fogger I. With the much
higher spray rates in the Fogger II, air usage would be excessive using air
atomization in some applications. However, it will permit an air source to
produce the coanda effect if needed to project the spray farther. In the
Fogger II, the control box will include an integral pump to provide the high
pressures of 500 psi required for hydraulic atomization of the water spray.
36
-------
COLLECTION EFFICIENCY OF CHARGED FOG SPRAYS ' •
Two areas important in evaluating sprays are collection efficiency and
droplet evaporation; several studies have been made in both areas. Some of the
more advanced treatments of single droplet collection of dusts have been in the
field of meteorology concerning the scavenging of airborne dusts by rain
31 35
drops. Droplet evaporation has- been treated by researchers in combus-
qc qy OQ on
tion ' and spray drying. ' (Spray drying is the production of dry powder
39
by spraying a solution into warm gas.) Masters discusses not only droplet
evaporation, but also types of spray nozzles, droplet trajectories, and the
effect of suspended or dissolved solids in the spray. An overview of the
theory of charged droplet collections follows; for a more detailed discussion,
see the reports by Melcher and Sachar. '
For a single water droplet and a single dust particle, there are several
forces acting simultaneously that affect the likelihood of particle capture.
Fairly good theories exist which can predict how the various forces affect the
efficiency of dust collection for well-controlled experimental conditions. In
a practical application, the theories are less useful; operating conditions
vary, and it is very hard to choose representative values for many of the
parameters in the theories—dust composition, loading, size, and charge; spray
size and charge; ambient temperature and humidity; etc.
This work approaches the problem of applying theory to practical cases by
(a) briefly discussing the different collection mechanisms and their relative
magnitudes, (b) presenting some theoretical predictions of the effect of electro-
static charge on collection efficiency, and (c) showing how droplet evaporation
and water application rate should affect efficiency of dust removal. Thus, the
emphasis is on using the theory to get directional trends rather than absolute
values.
Impacti on/Intercept! on
These collection mechanisms are closely related and are the dominant
forces in collecting larger particles with water sprays. When a droplet and a
particle approach each other on a collision path, the particle tends to follow
the fluid -streamlines and be swept around the larger droplet. Because of its
37
-------
Inertia, however, the particle does not exactly follow the fluid path, but
instead cuts across some streamlines. Depending on the initial trajectory and
velocity, it may impact directly on the droplet (Figure 4a), barely graze the
droplet (Figure 4b) or entirely miss the droplet (Figure 4c). The "direct-hit"
collection of very small particles is termed impact!on, while interception
refers to the grazing trajectory of larger particles. The collision efficiency
(i.e., the fraction of area swept clean of particles by a water droplet) is
improved by increasing the relative velocities between droplet and particle,
increasing the particle diameter, and increasing particle density.
Diffusion
Particles of submicron size, and thus low inertia, are rarely captured by
impaction/interception because they follow the gas streamlines around the
particles. However, some of the very small particles are captured as they move
past a droplet because they diffuse to the droplet surface via the random
bombardment by gas molecules. This collection mechanism is termed diffusion
and is improved with decreasing particle size. For particles one micron or
larger, this mechanism is negligible.
Phoresis
Phoresis is the process in which particles move because they are subjected
to a gradient in temperature (thermophoresis) or vapor pressure (diffusiophoresis)
If a liquid is evaporating at one surface and being absorbed at another parallel
surface (Figure 5a) and there is no temperature gradient, the particles will
experience a net force in the direction of vapor molecule movement. Similarly,
if one parallel plate is kept hotter than the other, the more frequent gas
collisions on the hotter side of the particle will force the particle toward
the cooler plate (Figure 5b).
Phoretic forces are not very strong compared to the other collection
forces for particles larger than two or three microns. For the particular case
of submicron particles around an evaporating water droplet, phoretic effects
become significant. However, their net effect depends on the ambient humidity,
the droplet temperature, and the ambient temperature, and many researchers
neglect one or both of these forces.
38
-------
Fluid Streamlines
Particle
Path
Figure 4a. Path for Direct Impaction of Pnrticie.
Particle Path -> — — — — —
Direction of
Flow -y
Figure 4b. Path for Limit of Interception of Particle.
Particle Path
Figure 4c. Path for Particle Not Collected by Droplet.
Figure 4. Particle Trajectories Around a Water Droplet.
39
-------
FiIter Paper Moistened With H2S
Temperature t I t j f t t t 'ttfft'Mtt
Particle Path
Filter Paper Moistened With Pure Water
/ Air Flow
Figure 5a. Diffusiophoresis in Isothermal System,
Plate Held at High Temperature
>l
Heat Flo
1 I \
HI
( I
, Air Flow
e <
^ — """"" Particle Path
Plate Held at Low Temperature
5b. Thermophoresis Due to Temperature Gradient.
Figure 5. Thermophoretic and Diffusiophoretic Forces.
40
-------
Electrostatic Attraction
Practically all aerosols carry an electrical charge. The presence of
charge on the particle or the droplet (or both) affects the particle trajectory
around the droplet and can improve (opposite charges) or reduce (alike charges)
the collection efficiency. The interacting forces increase as charges in-
crease.
The maximum charge a droplet can carry (termed the Rayleigh limit) is
reached when the mutual repulsion of the charges accumulated on its surface
equals the surface tension holding the droplet together. The Rayleigh limit is
typically reached for evaporating droplets. At the Rayleigh limit, evaporating
droplets eject smaller charge-carrying droplets to dispose of excess charges.
The Rayleigh limit on water droplet charging is shown in Figure 6--for 100 m
- 7 12
diameter droplets, this limit is about 5X10 e per droplet (8x10 coulomb).
For a solid particle, the maximum charge is limited by the point where
ions or electrons are spontaneously emitted from the surface. However, this
limit is rarely approached. Several workers have reported the average charge
of all the particles in a dust sample to be 5 to 20 electron units (e) positive
-19 29 42 44
per particle (8x10 coulombs). J>^»^ Not all particles are positively
charged, however. There is a distribution of both positively and negatively
charged particles within the dust sample as is schematically shown in Figure 7.
Thus far, four collection mechanisms--impaction/interception, diffusion,
phoresis, and electrostatic attraction—have been highlighted. The expected
electrical charges on droplets and particles has also been discussed. How can
this information be applied to the case of interest—reduction of large scale
emissions of fugitive particulates from smelters? In an industrial appli-
cation, the water spray droplets are charged and projected into the dusty gas
stream. As the water droplets travel through the particulate cloud, they
capture dust particles, and finally, the droplets settle out of the gas stream.
Small particles which would otherwise remain suspended will settle out because
they have either become attached to the larger water droplets or agglomerated
35
with other particles. Grover et al. determined the collision efficiency of a
droplet/particle pair for the case of water droplets falling at their terminal
velocity. They calculated several cases while varying droplet size, humidity,
41
-------
a
'5
•S
1
I09
5
2
I08
i
2
!07
5
2
10s
5
2
IOJ
F
2
I04
5
10;
i r
Rayleigh Limit
for Water
(Surface Tension
= 72 Dynes/cm)
I
I I
I I
I I I
O.I 0.2 0.5
2_ 5 10 20 50 100
Particle Diameter, Mm
500 1000
Figure 6. Limiting Charge for Water Droplets.
-------
NEUTRAL
0
POSITIVE-
CHARGE
AVERAGE CHARGE IS
TYPICALLY 5-20e
POSITIVE
a
NEUTRAL
0
Figure 7. Typical Charge Distribution for Micron Size Particles.
43
-------
electric charge, etc. Cross-plots showing the effects of several variables are
seen in Figure 8. This data can ultimately be used to calculate overall
collection efficiency of a spray.
At first glance, the data in Figure 8 appears overwhelming, but on closer
inspection several important conclusions can be abstracted.
Figure 8a shows how the collision efficiency is strongly dependent on
particle diameter, decreasing from nearly 1.0 for 100 ym particles to a minimum
value of about 0.001 for particles 2-3 ym in diameter. This minimum in the
collision efficiency curve implies particles in the 2-3 pm size range, as are
commonly found in smelters, will be much more difficult to collect than the
larger particles. Notice also that for any given size particle, water droplet
size influences the collision efficiency. Larger" droplets tend to-be more
effective for larger particles, while finer droplets are more effective for the
subtnicron particles.
Figure 8b depicts how the ambient relative humidity (or equivalently, the
tendency of the droplets to evaporate) affects the collision efficiency. For
particles larger than about 3 microns, humidity has little effect, but for
finer particles, drier environments theoretically improve the collision
efficiency. In a real situation, the shorter droplet lifetimes at higher
evaporation rates might override the collision efficiency improvements.
The most pertinent information in Figure 8 is that shown in Figure 8c—the
effect of electrostatic charge on collision efficiency.
First, some background on the assumptions used to calculate Figure 8c.
35
Grover and coworkers solved the problem in which the droplet and the particle
have equal, but opposite, charges. The total charge on a droplet (or particle)
was assumed to increase proportionately with surface area. They calculated
2
three cases: (a) no static charges present; (b) Q droplet = +0.2a , Q particle
2
= 2.Or (where Q is charge expressed in esu, a is the drop radius in centi-
meters and r is the particle radius in centimeters); and (c) Q droplet =
2 2
+2.0a , Q particle = 0.2r . A fourth efficiency curve is shown which was
45
calculated by a less rigorous method to give a rough idea of the curve for Q
2 2
droplet = 20a and Q particle = 20r . For particle sizes typical in smelting
44
-------
5
2
10-1
1; 5
|
— 2
1 10-2
3
1 5
i
i
J
io-3
5
2
io-4
X^'
/'/ft''
/
OHOPLET
DIAMETER, p;m 1
- """N
\
M
**•«. 'f
x M
212— \ \\
""NjJ/
346-,^ Y/
sis-"""
i i 1 <
i —
-
•
_
-
No tlMTrBiralic cnargt
73% ralotivt tumidity
IQ'C amei«or T
_
-
-
1 , !
O.I 0.2 O.S 1.0 2 S 10 20 50 100
Piftiele OiifiHiir, ym
Figure 8a. Effect of Droplet Diameter
on Collision Efficiency,
O.I 0,2 0.5 1.0 2 5 10 20 50 100
Particli Oiamim. ^n
Figure 8b. Effect of Relative Humidity
on Collision Efficiency.
10°
i
2
10-'
- 5
S
3 5
t 2
10
5
ELECTROSTATIC CHAHCE
212/im wottr dn?0l«1
rvlotiv* humkJtty
IO°C ombitiit T
Ql 0.2 0.5 1.0 2 5 10 20 50 100
Pirricii Oiimnif, ^n
Figure 8c. Effect of Electrostatic Charge
on Collision Efficiency.
Figure 8. Effects of Particle Size, Droplet Size, Relative Humidity,
and Electrostatic Charge on Collision Efficiency.
-------
applications (3 micron particles and 200 micron droplets) and for a particle of
g
average excess charge (lOe) and a water droplet at its Rayleigh limit (2x10 e),
it is estimated that the collision efficiency curve will lie between the Q =
2 2
2.Or and the Q = 20r curves in Figure 8c.
Disregarding the details of the assumptions made, and the variations due'
to size, there are two broad conclusions that are apparent from Figure 8c.
First, the presence of electrostatic charges increases the collision efficiency.
for all size particles and eliminates the minimum around 2 microns. Secondly,
charged sprays in industrial applications would have collision efficiencies
roughly 5-10 times higher than uncharged sprays. Caution: these collision
efficiencies are for single droplets only, they do not indicate that the
overall collection of dusts by a spray will be 5-10 times higher. The rela-
tionship between single droplet collision efficiency and overall collection
efficiency is presented next.
A relationship is needed between the collision efficiency and the other
important variables such as flow rate, spray rate, system geometry, etc. In a
46
paper on suppressing airborne coal dust, Cheng presents such a relationship
for overall efficiency of a water spray on a dust cloud:
Eo • i - ^ir1' of •
where E = overall number of dust particles
collected by the spray
= single droplet collision efficiency as
discussed above
D = droplet diameter
Qw = water flowrate
Qg = gas flowrate
L = a characteristic length which measures the length
of the spray trajectory through the gas.
46
-------
Equation 1 is obviously only an idealized version of the complex inter-
action between a spray and a moving dust cloud, but the form of the equation is
instructive. By rearranging, it is seen that log 1/(1-E ) is directly pro-
portional to n and to Q water, and inversely proportional to Q gas if the
droplet size and spray geometry are constant. These relationships together
with Figure 8 can be used to predict charged spray efficiencies from experi-
mental results for uncharged commercial sprays.
BASIS OF COLLECTION EFFICIENCY FOR COMMERCIAL DEVICES
Much of the experimental measurement of fine particulate removal by water
sprays has been done by researchers attempting to reduce the level of res-
pi rable dusts in underground coal mines. Uncharged sprays reportedly reduce
respirable dust 20 to 60 percent with 30 percent seeming to be an average
48
value. Extrapolating 30 percent efficiency assuming equivalent geometry,
water rate, and droplet sizes, a charged fog spray with a five times higher
single droplet collision efficiency would remove about 80 percent of the
respirable dust. Practically, the charged fog efficiency would not be as high
because of much lower water application rates for charged fog sprays compared
to conventional sprays. I
Lab scale experiments and limited commercial applications of charged fog
28
sprays as cited by Hoenig mostly range between 50 to 80 percent collection
efficiency. This agrees well with the above analysis.
There is an important limitation on the charged fog spray applications
cited so far—they have been in enclosed areas or on applications in moderately
still air. Spray performance would not be anticipated to be very good for
highly turbulent air streams as are often encountered in smelting. The reasoning
follows.
The critical parameter in spray performance is the ratio of the spray rate
to the volume of gas treated. For still air or confined spaces, the water
droplets settle through the gas and collect and agglomerate particles. All
together, the water from one small spray may be distributed through 2-4 m
o
of volume (30-100 ft ). In an open, highly turbulent situation, both the dust
particles and the water droplets would be dispersed outward and become more and
more diluted into larger and larger volumes of gas. The effective volume of
gas that must be treated is no longer just confined to the area around the
47
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2 5 10 20 50 100 200 500 1000
Initial Droplet Diameter, Mm
Figure 9. Lifetime of Water Droplets Traveling at Their Terminal Velocity.
48
-------
spray, but also includes the entire area of turbulence which is greater by
maybe a factor of 1,000 since volume goes up with the cube of distance. (That
is, if instead of being dispersed three feet, turbulence disperses the particles
3 3
and droplets thirty feet, the gas volume goes from 9 ft to 9000 ft .) A
second factor must also be cosidered in open, turbulent environments. When the
water droplets that do collect particles eventually settle out of the air, the
particulate will be spread over a large area and in a sense, not be "collected"
at all.
A simplifying assumption in the above analyses has been that of no droplet
evaporation. When sprayed into air, the small droplets formed by a charged fog
device will evaporate unless the ambient air is saturated with water. In most
cases of practical concern, the air is not saturated, and a droplet will
completely evaporate after a certain period. The droplet lifetime determines
the effective contact time between the spray and the dust-laden stream, and
thus strongly impacts on the overall spray efficiency- (a short lifetime droplet
will disappear before collecting very many-dust particles. Some work with
charged fog sprays in high temperature enclosed systems is being done by Dr.
Hoenig at the University of Arizona at Tucson, but at this time the under-
standing of the data is incomplete.
The temperature and humidity of the ambient air are the two main variables
affecting evaporation rate. When a droplet evaporates two simultaneous pro-
cesses occur—heat flows toward the droplet from the surrounding air and water
vapor molecules diffuse away from the droplet surface into the surrounding air.
High ambient temperature increases heat flow to the droplet and hastens evapora-
tion, while low ambient humidity increases the rate of evaporation by speeding
the diffusion of water vapor molecules away from the droplet surface.
Figure 9 depicts water droplet lifetime versus droplet diameter for three
cases of practical significance: (a) 20°C (68°F), dry air which represents a
plant compressed air supply; (b) 27°C (80.6°F) air with a relative humidity of
90 percent which represents a warm, moist environment; and (c) 179 C (388 F)",
dry air which represents the severe conditions around a copper converter or
furnace taphole. Notice how, for a 200 ym droplet, the lifetime is of the
order of 0.1 second for the high temperature (170°C) conditions. During such a
short lifetime, the droplets can neither travel very far, nor encounter very
many dust particles, and correspondingly poor dust collection would be expected
under such conditions. Indeed, a 100 ym drop falling at its terminal velocity
in dry 170°C air will only travel 7 cm (3 in.) before evaporating.
49
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Summarizing the discussions of this section: (a) while for uncharged
sprays, there is a minimum in the collection efficiency for about two micron
diameter particles, there is not any such minimum for charged sparys and some
improvement or collection of respirable dust is expected from charging; (b) the
charged fog sprays are best suited to localized sources of dust, suspended in a
low velocity or stationary gas stream; (c) the combination of high temperatures
and excessive gas turbulance rule out charged fog sprays for areas such as
copper converter leakage or furnace taphole emission control; and (d) at
reasonable water application rates, the charged fog sprays are unlikely to have
efficiencies approaching 90 percent—overall collection efficiencies on the
order of 60 percent are more likely.
COST DATA AND UTILITY CONSUMPTION FOR CHARGED FOG~SPRAYS
The total erected cost for a charged fog spray device consists of: (a)
purchased equipment cost; (b) installation materials; (c) installation labor;
(d) auxliary equipment costs; and (e) indirect costs. The estimates for each
category are further discussed below—bases, assumptions, and cost data. Table
20 summarizes the cost calculations.
The charged fog sprays themselves are the largest component of purchased
equipment cost. A small charged fog spray, having a coverage area of approxi-
mately 2 ft by 6 ft, is sold for $2,000.30 This includes 50 ft of air hose,
water hose, and shielded high voltage cable, and does not include any quantity
discount which may be available for purchasing several devices. We have
assumed a 25 percent discount for buying a large number of spray units, making
the estimated price for one unit $1 ,500.
A larger scale charged fog device under development, which has a coverage
area of approximately 6 ft by 20 ft has not been commercialized and no sales
price is available. Often, prices are extrapolated from one capacity to another
using the "0.6 power rule," but since costs for the electrical equipment and
spray nozzle for a charged fog device are fairly independent of size, a smaller
exponent is appropriate for the cost-capacity equation. An exponent of 0.1
4-Q
is typical for conventional spray nozzles in the size range of interest. An
exponent of 0.2 was used to prorate the costs of the smaller device: Cost of
2 2 02
large spray = (120 ft coverage area/12 ft coverage area) x ($1,500 cost
50
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TABLE 20. SUMMARY OF TOTAL ESTIMATED COSTS FOR CHARGED FOG SPRAY DEVICE*
Cost per charged fog spray device
Item
Purchased Equipment
Installation
Materials
Total Materials
Installation Labor
Indirect Costs
Construction
Overhead
Engineering
Taxes and Freight
Total Indirects
Direct and Indirect
Excluding Auxiliary
Equipment
15% Contingency
Auxiliary Equipment
GRAND TOTAL
Small
fog
spray
$1,535
97
1,632
318
223
228
130
581
2,531
380
1,453
$4,364
Large fog spray
(with air)
$ 2,454
97
2,551
318
223
357
204
784
3,653
548
7,380
$11,581
Large fog spray
(no air)
$ 4,400
83
4,483
292
204
628
359
1,191
5,966
895
230'
$ 7,091
Mobile
fog spray
$ 2,400
- 0
2,400
75
53
336
192
581
3,056
458
- 0 -
$ 3,514
*See Tables 12-15 and text for break down of costs and bases used.
of small spray) = $2,400, quantity discount included. For the version of the
larger charged fog spray which uses no atomizing air, an additional $2,000 is
added to account for the cost of an integral high pressure water pump needed
for hydraulic atomization. For a mobile version of the spray (no air source;
D.C. battery powered) with an intermediate coverage area, a price identical to
the large spray device was used to allow for additional complexity of con-
struction.
Since industrial plant air and water systems usually contain solids that
could rapidly plug the filters, built in sprays, additional cartridge filters
for both the air and water supply to the sprays have been included. It is
51
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assumed a bank of four sprays is attached to each filter. A prorata share of
the cost of a cartridge filter for the water and a combination coalescer/filter
for the air is charged to each spray. Costs for the systems are summarized in
Table 21.
TABLE 21 . ESTIMATE OF PURCHASED EQUIPMENT COSTS FOR CHARGED FOG SPRAY DEVICES*
Item
Cost per
Spray Device
Basis for Calculations
Small Charged Fog $1 ,500
Device
Large Charged Fog $2,400
Device with Air
Atomization
Large Charged Fog $4,4
Device with Hydraulic
Atomization
Mobile Charged Fog $2,400
Device
Share of Air
Coalescer
Small fog spray $ 19
Large fog spray $ 38
Share of 40 micron
• Water Filter
Small fog spray $ 16
Large fog spray $ 16
Current sales price less assumed 25%
discount for purchase in quantity.
Cost of small fog spray prorated by
coverage assuming 0.2 exponent
in cost-capacity equation.
Cost of large fog spray having air '„
atomization plus $2,000 for in-
tegral high-pressure water pump.**
Spray for mounting on front-end
loaders, etc. Assumed to have smaller
coverage area than large device, but
cost the same because of more complex
construction.
Assume four small fog sprays per 100
acfm filter of cost $75; two large
fog sprays per 100 acfm filter
Assume four fog sprays per 15 gpm
filter of cost $66.
*0nly a part of total costs associated with charged fog spray device installa-
tion. See Table 20 for summary of complete costs.
**Reference'50
***Reference 51
Installation materials include any water or air piping, mounting equipment,
and electrical hardware. It is assumed that the high voltage cable will be in-
stalled in 1/2 in. rigid, galvanized conduit. Fifty foot of conduit per spray
is assumed. In addition, a prorata share of electrical and water tie-ins
52
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are charged to each spray. Again, a bank of four charged fog sprays is
assumed, and 50 ft of #14 copper wire with accompanying conduit, plus two
water tight and dust tight mounting boxes and 50 ft of one-half inch carbon
steel water line are included for each bank. Calculations for installation
materials are shown in Table 22.
TABLE 22. ESTIMATE OF INSTALLATION MATERIAL COSTS FORCHARGED FOG SPRAY 'DEVICE'
Item
Cost per Fog
Spray Device
Basis for Calculations
Conduit for High Voltage
Cable
Share of Conduit for
110V Feed-line
Share of Wiring for 110V
Feed-line
Share of Mounting Boxes
for 110V Feed-line
Share of Water Supply
Line
Share of Air Supply
Line
$ 21
$ 5
$ 35
$ T3
$ 9
$ 14
50 ft of 1/2" diameter rigid
diameter rigid galvanized steel
conduit per fog spray at $0.42/ft**
50 ft of conduit as above for a bank
of four fog sprays.
50 ft of #14 copper wire for a bank
of four fog sprays at $2.80/ft.**
Two pull-boxes, water tight and dust-
tight for a bank of four fog sprays
at $36 each.**
50 ft of 1/2" diameter Schedule 40,
galvanized, steel pipe for a bank of
four fog sprays at $0.69/ft.**
50 ft of 1" diameter, Schedule 40,
galvanized, steel pipe for a bank of
four fog soravs at $1.10/ft.**
*0nly a part of total costs associated with charged fog spray device installa-
tion. See Table 20 for summary of complete costs.
**Reference 52.
52
Installation labor for electrical equipment as cited by Means is used.
An additional two hours per fog spray of electrician labor and two hours of
laborer time per fog spray are included for mounting of the fog spray control
box and the fog spray nozzle. Two hours per fogger of pipefitter time is in-
cluded for water line connections. Labor costs are tabulated in Table 23.
53
-------
J^^
Item
Cost per
Charged Fog
Spray Device
Basis for Calculations
Conduit for High $ 61
Voltage Cable
Share of Conduit for $ 15
110V Feed-line
Share of Wiring for $106
110V Feed-line
Share of Mounting $ 14
Boxes for 110V
Feed-line
Share of Water Supply $ 21
Line
Share of Air Supply $ 26
Line
Mounting of Spray $ 75
Nozzle and Control
Box
50 ft of 1/2" diameter rigid
galvanized steel conduit per fog
spray at $1.22/ft.**
50 ft of conduit as above for a
bank of four fog sprays.
50 ft of #14 cooper wire for a bank
of four fog sprays at $8.45/ft.**
Two pull-boxes, watertight and dust-
tight for a bank of four fog sprays
at $27 each.**
50 ft of 1/2" diameter Schedule 40,
galvanized, steel pipe for a bank of
four fog sprays at $l.,68/ft.**
50 ft of 1" diameter, Schedule 40,
galvanized, steel pipe for a bank
of four fog sprays at $2.10/ft.**
Per fog spray: 2 hrs. of electrician
at $13.70/hr.; 2 hrs. of pipefitter at
$14.00/hr.; and 2 hrs. of laborer at
$9.70/hr.**
*0nly part of total costs associated
See Table 20 for summary of complete
**Referenee 52
with charged fog spray device installation.
costs.
Some investment is associated with auxiliary equipment needed for the fog
sprays. A prorata share of a plant air compressor (based on air consumption)
is charged to each fog spray. A 10,000 standard cubic feet per minute centri-
fugal compressor is used for the basis. Similarly, a share based on water con-
sumption of a 1,000 gpm centrifugal pump station, discharging at 100 psig, is
charged to each spray. Costs for these auxiliary pieces of equipment are pre-
sented in Table 24. Notice that the share of air compressor costs is a large
share of the costs for air atomized systems.
54
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TABLE 24. ESTIMATE OF AUXILIARY _LQU-LPJiElL_COSTS FOR CHARGED FOG SPRAY DEVICE _
Cost per
Charged Fog
Item Spray Device Basis for Calculations
Share of Compressor
Costs for Plant Air System
Small fog spray $1,430
Large fog spray $7,150
(air atomized)
Large fog spray -0-
(hydraulically
atomized)
Mobile fog spray -0-
Share of Pump Costs
for Plant Water System
Small fog spray $ 23
Large fog spry $230
(both versions)
Mobile fog spray -0-
Proration by air consumption of the
investment for a 10,000 scfm centri-
fugal compressor delivering air at
100 psig. (Estimated total erected
cost = $1.43 x ID6) Small fog spray
air consumption of 10 scfm. Large
fog spray air consumption of 50 scfm
for air atomized version, no air for
hydraulically atomized version. No
air consumption for mobile fog spray.
Proration by water consumption of
the investment for a 1000 gpm centri-
fugal pump delivering water at 100
psig. (estimated total erected cost
of $57,400).* Small fog spray water
consumption of 0.25 gpm. Large fog
SDraywater consumption of 2.5 opm**
*Cost escalated to January 1978, 25% contingency included. Reference 51.
**'Reference 30.
Indirect costs charged to each spray device are: (a) construction overhead
costs of 0.70 x (labor costs), (b) engineering costs of 0.14 (direct equipment
costs), and (c) taxes and freight of 0.08 x (direct equipment costs).
Finally a contingency fee equal to 15 percent of total direct and indirect
costs (excluding the auxiliary equipment investment which had its contingency
added separately) is added. The indirect costs are shown on Table 20, "Summary
of Total Estimated Costs for Charged Fog Spray Devices."
In addition to the capital investment associated with operating a charged
fog spray device, there are utility requirements as well—electricity, water,
and compressed air. Table 25 summarizes the utilities requirements for operation
of a charged fog spray device all converted to an equivalent kilowatt basis. By
far the largest energy requirements are for the compressed air used to atomize
and project the spray droplets. The energy required to charge the droplets is
minor and is not representative of the total energy consumption of the charged
fog device.
55
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Energy Requirement,
Equivalent Kilowatts
per Charged Fog
Item
Pumping Energy for Water
Small fog spray
Large fog spray (air
atomized)
Large fog spray
•hydraulic-ally atomized)
Mobile fog spray
Compression Energy for Air
Smal 1 fog spray
Large fog spray
(air atomized)
Large fog spray
(hydraulically
atomized)
Mobile fog spray
Electrical requirements
n
for Charging
— • ^j ' • • j
Small fog spray
Large fog spray
(both versions)
Mobile fog spray
Total Equivalent Kilowatts
Small fog spray
Large fog spray
(air atomized)
Large fog spray
(hydraulically atomized)
Mobile fog sprav
Device
0.02
0.16
1.59
1.59
2.66
13.32
-0-
-0-
0.03
0.30
0.30
2.71
13.78
1.89
1.89
Basis for Calculations
Water from centrifugal pump
at 100 psig discharge pressure,
except hydraulically atomized
version has 600 psig recipro-
cating pump; 0.25 gpm for small
fog spray; 2.5 gpm for large fog
spray; Mobile fog spray assumed
to have same requirements as
hydraulically atomized large fog
spray.
Air from plant air compressor dis-
charging at 100 psig; 10 scfm for
small fog spray; 50 scfm for large
spray; no air required for hydrauli
cally atomized version; assumed no
air required for mobile fog spray.
Charging requirement for small fog
spray from manufacturer; require-
ment for large spray prorated by
water consumption. Mobile spray
requirement assumed equal to large
fog spray.
*Reference 30.
56
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5.0 WATER SPRAYS WITH ADDITIVES FOR CONTROLLING FUGITIVE EMISSIONS
It has been suggested that water sprays containing surface active agents
would be more effective in collecting entrained dust than pure water sprays.
The equipment for such a spray system would consist of hydraulic or air atomization
spray nozzles, a reservoir and metering pump for injecting the additive into
the water, and the appropriate connecting piping. Sprays with or without
additives have been successful in reducing dust emitted from conveyor belts and
are used in quarries and mining operations.
There are conflicting reports of whether or not additives improve particle
collection by water sprays. Much of the conflict comes from a confusion in the
mechanisms working to reduce total particulate levels. There are two ways in
which water suppresses part.iculate: (a) by wetting and immobilizing dust
before becoming airborne and (b) by removing already suspended airborne particles.
To suppress dust formation, water is sprayed onto the surface of a solid
material, for example ore concentrate on a conveyor belt. The water ideally
spreads into the interstices of the solid, and wets the surface of fine particles
thus making them adhere to the larger lumps of material. The wetted solid
material then has less tendency to generate dust as it is handled since the
small, easily entrained particles have been immobilized. However, since water
has a very high surface tension (roughly 70 dynes/cm), it often is not effective
in spreading into the solid material and forming a water film around dust
particles. Instead it stays on the surface as thick droplets with resulting
poor dust suppression. The high surface tension interferes with the wetting,
spreading, and penetrating needed for suppression. |
To improve the efficiency of suppression, various compounds known as sur-
factants, or wetting agents, are added to the water. These compounds are
composed of a hydrophobic, or water-hating, group (usually a long chain hydro-
carbon) and a hydrophilic, or water-loving, group (usually a sulfate, sulfonate,
57
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hydroxide, or ethylene oxide). When mixed with water, surfactants concentrate
at the air-water interface with the hydrophilic end aligning in the water layer
and the hydrophobia portion of the molecule extending into the air layer. By
preferentially aligning at the water-air interface, the surfactants can reduce
the surface tension to around 30 dynes/cm and improve the wetting and penetra-
tion of the water. The levels of surfactant needed to effect such a surface
tension reduction is very low--0.03 to 0.1 percent. Additives other than
surfactants may be used in some cases to form a "crust" on storage piles, etc.,
and reduce windblown resuspension of dust.
»
Water sprays are also sometimes used to try and remove particles which
have already become airborne. The droplets from a water spray collect and
coalesce the fine entrained particles and increase-their settling rate. It has
been suggested that surfactants would improve particle removal for this case
also by allowing the dust particle to penetrate the water droplet more easily,
however, there is little evidence that this, occurs. Most investigators report
surfactants do little to supress airborne respirable dust. Walton and
ro
Woolcock exposed equal size droplets to the same dust concentration; one
droplet with a wetting agent and the other without. They found no significant
difference in collection efficiency for the two drops. In a recent study,
59
Woffinden et al have reported only small effects of collection efficiency, if
any, can be attributed to surface tension changes. Indeed, the effect of
adding surfactant may be slightly unfavorable.
In summaryj water sprays with additives can be used to reduce suspension
of hard-to-wet solids, but have an advantage over conventional water sprays
only for reducing dust generation from dusts which have not already been suspended.
Additives do not substantially improve the collection of particles which have
already become airborne. Thus, they are not substitutes for charged fog spray
applications. The addition of surfactants or other additives should be con-
sidered for such applications as conveying and storage bins where the product
is not water sensitive and can be kept moist to reduce dust entrainment from
the solid.
58
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6.0 BUILDING EVACUATION FOR CONTROLLING FUGITIVE EMISSIONS
This section discusses the costs, energy consumption, and known applications
of building evacuation as a means of controlling fugitive particulate emissions.
The results of this section are used as a basis of comparison for the charged
fog spray devices.
DESCRIPTION OF BUILDING EVACUATION
One method of eliminating fugitive particulate emissions.from smelting
operations which are inside a building is to install ductwork on the building
roof and large fans which draw the particulate-laden gases from the building
and pass them through a collection device. Typically, a baghouse is the control
device selected for building evacuation. Any fugitive particulates escaping
inside the smelter building are collected by the evacuation system and overall
control efficiency for fugitive emissions is quite high for building evacuation--
from 90 to over 95 percent.
While attractive from an environmental-control viewpoint, building evacua-
tion has several serious drawbacks. By enclosing the building, the emissions
can only escape through the roof ducts and high levels of particulate, S02,
etc., may build up inside the building in the workplace requiring breathing
equipment and causing occupational health concerns. An evacuation system may
collect enough gas to sufficiently ventillate the workplace overall and yet
still have unacceptable local pollutant concentrations because of "dead spots"
in the air flow pattern. Figure 10 illustrates this effect. In smelting
operations, such dead spots may create excessive temperatures as well as high
pollutant levels in some local areas.
A second drawback to building evacuation systems is the large airflow
required and the attendant high energy consumption by the blower. As a general
rule for controlling emissions with hoods, the closer the hood to the source,
the less evacuation air is required. For the particular case of building
evacuation, the intakes are located far from the particulate sources and large
volumes of air.with low particulate loadings are collected.
59
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Dead Spot
Figure 10. Schematic of "Dead Spots" in Building Evacuation System.
60
-------
Building evacuation systems have been successfully applied to electric arc
C] CO
furnace melt shops in the iron and steel industry. ' One converter building
in the copper industry has been fitted with a building evacuation system
while there are no known large building evacuation systems in the lead smelting
industry. The evacuation system in the copper smelting plant has caused severe
heat and SO^ levels in the upper areas of the building but this may be due to
inadequate fan volumes and the difficulty in designing for good air flow patterns
in a retrofitted application.
COST AND UTILITY CONSUMPTION FOR BUILDING EVACUATION
During some test work on an electric arc furnace building evacuation
system, it was reported that a total of 1230 kW load was being drawn by the
main baghouse fans treating 499,000 acfm of air at 95°F. The reverse air fan
for this system was rated at 150HP which corresponds to roughly an additional
125 kW load for a total of 0.00272 kW/acfm. The baghouse had an air-to-cloth
ratio of 2.3:1. No investment costs were given.
The retrofitted building evacuation system at the smelter cost approxi-
mately $8.5 million for a gas volume of about 600,000 acfm.10 Three 700HP fans
are used for this system for a utilities consumption of about 0.0029 kW/acfm.
As was noted, the air is not changed frequently enough in this installation
(2.7 minutes per air change) to prevent excessive local concentrations of
CO CO
pollutants. An estimate was made by the Arizona Department of Health Services
cc
for a "typical" smelter, as defined by the U.S. Bureau of Mines, for installing
building evacuation on a 100,000 ton per year smelter for the case of 1.5 air
changes per minute. The air flow for this estimate was 2,200 kacfm. Cost
for this estimate are presented in Table 26.
For comparing building evacuation with charged fog spray devices, an
initial investment of $6,808,000, (3.09 $/acfm) and utility consumption of 6000
kW were used for a building evacuation system for a converter building on a
copper smelter. The costs and utilities for building evacuation in a lead
smelter are similar to those for a copper smelter. However, it is felt that a
larger volume of building space must be evacuated in a lead smelter. The
evacuated building volume was assumed to be 150 percent of the building volume
for copper smelting. Utility requirements were prorated directly by 1.5 to vie
9,000 kW, while capital costs were prorated using the 0.6 power rule to give
1.5°'6 x $6,808,000 = $8,683.000.
61
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TABLE 26. CAPITAL AND OPERATING COST FOR BUILDING VENTILATION
SYSTEM AT TYPICAL COPPER SMELTER*
June 1978 Prices
Direct Plant Costs:
Baghouse
Fans and Motors
Electrical
Ductwork and Piping
Alterations to Building
Equipment Supports
Indirect Costs:
Engineering (14% T.D.C.)
Field Expense (20% T.D.C.)
Contractors Fee (2.5% T.D.C.)
Start-up (3.5% T.D.C.)
Contingency (20% T.I.)
TOTAL DIRECT COST
TOTAL INVESTMENT
TOTAL CAPITAL
$2,870,000
741 ,500
178,500
179,000
40,000
60,000
$4,069,000
$ 70,000
814,000
102,000
$5,555,000
142,000
1,111 ,000
$6,808,000
Estimated Annual Operating Cost
*Table from Reference 63.
62
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7.0 COMPARISON OF CHARGED FOG SPRAYS WITH BUILDING EVACUATION
Estimates of the rough quantities of the small, large, and mobile charged
fog sprays needed to control fugitive emissions in smelters are shown in Tables
27 and 28. The corresponding points of application are shown in Figures 11 and
12. These quantities are then used to estimate the cost and energy consumption
of charged fog sprays applied throughout copper and lead smelters.
For application of charged fog sprays to a lead smelter, estimated capital
investment is (24 large sprays x $7,091 each) + (4 mobile sprays x $3,514 each) +
(29 small sprays x $4,364 each) for a total of $311,000. The utility con-
sumption for the charged fog sprays in a lead smelter would be (24 large sprays
x 13.78 kW each) + (4 mobile sprays x 1.89_each) + (29 small sprays x 2.71 kW
each) for a total of 417 kW. For building evacuation, the estimated capital
costs are $8,683,000 and the utility consumption is 9000 kW.
Capital investment (including installation and all auxiliary equipment)
for application of charged fog sprays to a copper smelter is (24 large sprays x
$7,091 each) + (6 mobile sprays x $3,514 each) + (40 small sprays x $4,364
each) for a total of $366,000. The utility consumption for the charged fog
sprays in a copper smelter would be (24 large sprays x 13.78 kW each) + (6
mobile sprays x 1.89 kW each) + (40 small sprays x 2.71 kW each) for a total
of 450 kW. For building evacuation, the corresponding costs are $6,808,000
and the utilities usage is 6,000 kW.
While both capital investment and energy consumption are higher for build-
ing evacauation, the reduction of total particulate and elemental lead emissions
are also greater for building evacuation because of the higher collection
efficiency and the larger number of sources covered by a building evacuation
system.
Table 29 shows what are, by all accounts, rough estimates of the emission
reductions expected from the application of charged fog sprays and the appli-
cation of building evacuation. Estimated reductions are shown for both total
particulate fugitive emissions and elemental lead fugitive emissions.
63
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TABLE 27. POTENTIAL APPLICATIONS OF CHARGED FOG SPRAYS IN LEAD SMELTING'
Application
Number
Large Mobile Small
Comments
A-Railcar unloading
B-Conveyor transfer
C-Conveyor transfer
D-Conveyor transfer
E-Mix tripper conveyor
F-Conveyor transfer
G-Conveyor transfer
H-Conveyor transfer
I-Crusher discharge
J-Pelletizing drum
K-Conveyor transfer
L-Conveyor transfer
M-Roll grizzly discharge
N-Conveyor transfer"
0-Conveyor transfer
P-Blast furnace tripper
conveyor
Q-Front-end loader
TOTAL
16
2
2
2
24
JL
4
3
3
3
2
2
2
4-
4
2
2
2
29
Installed as "curtain."
8 on each end of shed.
Mounted to move with
tripper.
Large sprays used to
cool sinter
Large spray used to cool
sinter
Mounted to move with
tripper.
Refer to Figure 11 for locations of applications.
""Small charged spary coverage = 2 ft x 6 ft; Mobile charged spray coverage =
3 ft x 10 ft; large charged spray coverage = 6 ft x 20 ft.
64
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' TABLE 28. POTENTIAL APPLICATIONS OF CHARGED FOG SPRAYS IN COPPERJiMELTlNG_c
Number
Application Large Mobile Small Comments
A-Railcar unloading
B-Conveyor transfer
C-Conveyor transfer
D-Conveyor points in transfer
house
E-Ore bin tripper conveyor
16
Installed as "curtain."
8 on each end of shed.
3
3
Mounted to move with
tripper.
F-Conveyor transfer
G-Conveyor transfer
H-Fine ore bin tripper con-
veyor 2
I -Drier discharge conveyor
J-Conveyor transfer
K-Concentrate stacker 2
L-Dozer and front-end loader
M-Conveyor transfer
N-Conveyor transfer
0-Tripper conveyor 2
P-Conveyor transfer
Q-Conveyor transfer
R-Conveyor transfer
TOTAL 24
2
4
Mounted to move with
tripper.
2
2
6 Medium-size} mobile units
mounted on dozer/loader
4
4
2
4
_ _i
6 40
Refer to Figure 12 for locations of applications.
Small charged spray coverage = 2 ft x 6 ft; Mobile charged spray coverage =
3 ft x 10 ft; Large charged spray coverage = 6 ft x 20 ft.
65
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- NETUHN BLAH
CTl
CTl
a-' -\. i
„„ . ruu* p-""f f. J "-»" »0 ««"« '»"»
Figure 11. Charged Fog Spray Application Points in Lead Smelting.
-------
1 RAILCAR OUMfMNG
TRIPPER CONVEYOR
CONVCHTIR SL*Q
TO COOLING P1T1
Figure 12. Charged Fog Spray Application Points in Copper Smelting.
67
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TABLE 29. COMPARISON OF CHARGED FOG SPRAYS WITH BUILDING EVACUATION
Item Lead Smelting Copper Smelting
Reduction in fugitive total particu-
late emissions
by application of charged sprays 30% 20%
by application of building evacuation 45% 40%
Reduction in fugitive elemental lead
emissions
by application of charged sprays 40% 35%
by application of building evacuation 75% 65%
Estimated capital investment
for application of charged sprays 311 k$ 366 k$
for application of building evacuation 8,683 k$_ 6,808 k$
Electrical requirement
for application of charged sprays 417 kW 450 kW
for application of building evacuation 9,000 kW 6,000 kW
Several assumptions were made in compiling Table 29. The overall collection
efficiency of the charged fog sprays was taken to be 60 weight percent; for
building evacuation, 95 weight percent was used. The charged fog sprays were
considered inapplicable for hot, turbulent areas such as molten metal transfer,
lead sintering, and copper converter leakage. Building evacuation was not
considered to be effective for reducing emissions from loading onto or out of
storage piles. From the fugitive emission estimates, presented in Tables 2
and 3, the reduction of total particulate and elemental lead emissions were
made source-by-source. Some of the emission source grouplings in Tables 2
and 3 included emissions from both inside and outside the process buildings--
for example, handling and transfer of lead ore concentrate. In such cases, it
was arbitrarily assumed that one-half of the emissions occurred in the building
and would be collected by the building evacuation system at 95 percent efficiency.
It was also assumed that an evacuation system could be put on the rail car un-
loading sheds but that it would not be as efficient as the system on the main
buildings because of incomplete enclosure. A fifty percent overall capture
and collection efficiency was used for railcar unloading emissions controlled
by an evacuation system.
68
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Superficially, the figures in Table 29 indicate charged fog sprays to be
a more cost effective means for pollution control than building evacuation--
10 to 20 k$ required for each percentage reduction in emissions by sprays
versus 100 to 200 k$ required for each percent reduction by building
evacuation. Similarly the electrical requirement is much lower for the
charged fog sprays—15 to 30 kW for each percentage reduction versus 150 to
200 kW for the building evacuation system.
However, in spite of the apparent attractiveness of charged fog sprays,
the authors feel that there are several practical problems which prevent them
from supplanting building evacuation or secondary hooding as fugitive control
techniques. The first and main objection is their limited applicability. Water
sprays are only suitable when the process can tolerate water, when, the emissions
are "from localized sources, when there is not a great deal of air turbulence
and when the air is not at high temperatures. These limitations rules them
out for such major sources of fugitive emissions as converter leakage,
sintering, and metal tapping, pouring, and casting. A second major limit
on charged fog spray control is the collection of the agglomerated particles.
Throughout this treatment, it has been assumed that once suspended particles
collide with a water droplet, they are permanently removed from the atmosphere.
This is a valid assumption for such applications as conveyor transfer points
in moderately still air where the agglomerated dust settles out and is returned
to the process. However, when particles from, say, a railcar unloading station
are contacted with spray droplets, they may settle out on the ground, dry out,
and be reentrained.
One control option not yet considered in this report is localized hooding
at fugitive emission sources. Figure 13 shows two options for controlling
emissions from a railcar unloading station—a curtain of charged fog sprays and
a push-pull collection system. This application gives a direct comparison of
charged fog sprays with another control technique on the same source. Using
recommended push-pull design procedures and assuming the same utility re-
quirements and cost per cubic foot as was used for building evacuation the
following estimates were made: (a) 5.8 kW and $6,500 per lineal foot of opening
for a push-pull system and (b) 2.3 kW and $1,900 per lineal foot for the
69
-------
View from above shed opening
I 1
Pressure
Slot
i r
Air Flow
J I
Application of push-pull local hooBjng
.Suction hood
Air and participates
to fan suction and
baghouse
Air, water, and
electrical supply
A
Bank of charged fog sprays
Application of Charged Fog Spray Curtain.
Figure 13. Push-pull Local Hooding Versus Charged Fog Spray Curtain.
70
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charged water spray curtain. Neglecting the potentially serious problem of
particle reentrainment after spray evaporation, the charged sprays could in
theory collect about half of the fugitive dust less expensively and with less
energy than local hooding. However, it is pointed out that the sprays can
only collect about half the particulate and if greater than fifty percent
efficiency is needed, some other control method must be used in spite of any
extra expense.
This report has treated building evacuation and charged fog sprays as
either/or control techniques. It makes more sense to consider them as com-
plementary control devices instead of mutually exclusive techniques. For
high temperature, large scale, turblent emissions, either building evacuation
or secondary hooding is require'd to collect the fugitive emissions; Charged
fog sprays are better suited for smaller, localized emission sources. Two
applications for which charged sprays may be particularly advantageous over
other controls are: (a) mobile sources such as front-end loaders where any
other type of control is impossible and (b) areas such as sanders or grinding
wheels where personnel exposure must be reduced without impeding access.
A final caveat concerning the evaluation of charged fog sprays made in
this report: only a screening evaluation has been made. To confirm their
predicted performance in an industrial environment—where cross-drafts, reen-
trainment, and upsets occur—requires field tests and the measurement of actual
reductions obtained with and without the device in operation.
71
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trically Charged Fog," Journal of Powder and Bulk Solids Technology, v.2,
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30. Communications with E.W. Drum, Manager of the Air Pollution Control
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Efficiency with Which Aerosol Particles are Collected by Water Drops
in Subsaturated Air," Journal of the Atmospheric Sciences, v. 34, pp.
1664-1669, (October 19777";
35. Grover, S.N., H.R. Pruppacher, and A.E. Hamielec, "A Numerical Determination
of the Efficiency with Which Spherical Aerosol Particles Collide with
Spherical Water Drops Due to Inertia! Impaction and Phoretic and Electrical
Forces," Journal of the Atmospheric Sciences, v. 34, pp. 1655-1663,
(October T977T:~~
74
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36. Ranz, W.E., "On the Evaporation of a Drop of Volatile Liquid in High-
Temperature Surroundings," Transaction of the ASME, pp. 909-913, (1956).
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Engineering Progress, v. 48, pp. 141-173, (1952).
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Gases With Special Allowance for Electric Forces," Staub-Reinhajt Luft,
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U.S. Department of the Interior, Washington, pp. 92-108, (1977).
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52. Godfrey, Robert S.s editor-in-chief, Building Construction Cost Data 1978,
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76
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TECHNICAL REPORT DATA
(Please read Innmctions on the reverse before complsting)
1. REPORT NO.
EPA-SOO/7-79-045
2.
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
Assessment of the Use of Fugitive Emission
Control Devices
5. REPORT DATE
February 1979
6. PERFORMING ORGANIZATION CODE
1. AUTHOR(S)
D.P. Daugherty and D.W. Coy
8. PERFORMING ORGANIZATION REPORT NO
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Research Triangle Institute
P.O. Box 12194
Research Triangle Park, North Carolina 27709
10. PROGRAM ELEMENT NO.
EHE624
11. CONTRACT/GRANT NO.
68-02-2612. Task 48
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Task Final: 2-12/78
14. SPONSORING AGENCY CODE
EPA/600/13
15.SUPPLEMENTARY NOTES IERL_RTP project officer is Dennis C. Drehmel, MD-61, 919/541-
2925.
is. ABSTRACT
repOrt compares the efficiencies and utility consumptions expected
from three fugitive emission control techniques — building evacuation, charged fog
sprays , and water sprays with additives — if they were applied in primary lead and
copper smelters. Estimates are provided of the reduction of total suspended parti-
culate emissions and the reduction of elemental lead emissions from smelters when
fugitive control is applied. Charged fog water sprays are emphasized: they enhance
particulate collection by putting an electrostatic charge on fine water droplets. Buil-
ding enclosure and evacuation is used as a basis with which such water sprays are
compared. Available cost and energy consumption data were used to assess the
competitiveness of charged fog sprays. Charged fog sprays were found to be less
efficient than building evacuation, but also less expensive and less energy intensive
by about a factor of 10. Charged fog sprays cannot replace conventional smelter tech-
niques (e.g. , secondary hooding or building evacuation) because they are not suitable
for the typical large-volume, high-temperature, turbulent air streams. They are
better suited for smaller scale, localized emission sources (e. g. , conveyor trans-
fer points) which contribute only a fraction of the fugitive particulate emissions.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Pollution
Dust
Aerosols
Leakage
Processing
Evacuating
Fogging
Spraying
Additives
Lead
Copper
Smelters
Electrostatics
Pollution Control
Stationary Sources
Fugitive Emissions
Particulate
Charged Fog Sprays
Water Sprays
13B
11G
07D
13H
07A
07B
11F
20C
13. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
85
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
77
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