United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-84-042 Apr. 1984
c/ERA Project Summary
Evaluation of an Air Curtain
Hooding System for a Primary
Copper Converter
Chuck Bruffey, Paul Clarke, Thomas Clark, Mark Phillips, and John 0. Burckle
This report presents the results of
tests conducted to evaluate the effec-
tiveness of a full-scale air curtain cap-
ture system installed on a primary
copper smelter converter for capture of
low-level fugitive particulate, including
trace metals and sulfur dioxide. The test
work was performed onsite at
ASARCO's Tacoma Smelter on the first
domestic full-scale prototype system,
resulting in the first published
evaluation of a full-scale fugitive
capture system based upon the air
curtain approach as applied to a primary
copper converter.
The installation of the air curtain
hooding system has permitted a
quantitative approach to the direct
measurement of the fugitive emissions
from a primary copper converter for the
first time. In this program, the fugitives
captured by the air curtain were
measured at a downstream sampling
point in the exhaust side of the air
curtain system during the various
portions of the converter cycle.
Emission factors were established for
sulfur dioxide, filterable particulate
(Method 5), inhalable particulate, and
selected trace elements.
This Project Summary was developed
by EPA's Industrial Environmental
Research Laboratory. Cincinnati. OH.
to announce key findings of the
research project that is fully document-
ed in a separate report of the same title
(see Project Report ordering informa-
tion at back).
Introduction
Copper converting is a batch operation
conducted in two stages to convert
copper matte produced in a smelting
furnace into blister copper. The Peirce-
Smith converter, used in all but one U.S.
smelter, is acknowledged to be the major
source of fugitive emissions in the
smelter. These fugitive emissions first
enter the workplace and, because they
are present in relatively high
concentrations, are considered
hazardous to worker health. They are
emitted from the smelter at relatively low
elevations through roof monitors and
other openings in the building. These
emissions cause deterioration of the air
quality and are believed to pose adverse
health risks to the general population
suffering prolonged exposure. While
some dispersion and dilution of the
fugitive emissions occur upon leaving the
smelter workplace, the resulting ambient
concentrations are high relative to a well-
dispersed emission from a tall stack.
A number of approaches to controlling
these emissions have been attempted by
industry with unsatisfactory results. The
major barrier to the development of an
acceptable secondary hood has been the
inability to design a system capable of
permitting crane and ladle access while
simultaneously providing for reasonably
effective capture of fugitive emissions.
The air curtain (Figure 1) is formed by
blowing air from a supply plenum or a row
of nozzles which is especially designed to
form an air sheet, or curtain, with as little
turbulence as possible. This curtain is
directed over the open space, well above
the converter, which permits crane
access. On the opposite side of the space,
the curtain and entrained air are captured
by an exhaust system. Fumes which rise
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Figure 1. Air curtain operating concept.
from the source are directed into the
suction plenum by the curtain. Air is also
pulled into the curtain from both above
and below. Since all air flow is inward,
into the curtain, a high capture efficiency
is achievable with a properly designed
and operated curtain.
In the past it has been possible to
estimate only very approximately, the
quantity and composition of the converter
fugitives for defining control strategies
and needs, making actual design and
selection of equipment somewhat risky.
Because the fugitive emissions are
effectively captured by the air curtain and
are collected by ducting, it becomes
possible to completely characterize these
emissions with a much higher degree of
confidence in order to provide actual
engineering data for design.
The tests described in the full report
were conducted jointly by the U.S.
Environmental Protection Agency's
(EPA's) Office of Air Quality Planning and
Standards and the Office of Research and
Development in cooperation with
ASARCO, the Puget Sound Air Pollution
Control Agency, and the EPA Region X
Office.
Test Program
The test program was designed to
achieve two major objectives: to estimate
the effectiveness of capture of the
converter fugitives not controlled by the
primary hood and to characterize the
captured fugitives by the "quasi-stack"
method.
Capture Effectiveness
The effectiveness of capture was
evaluated using three techniques.
• Mass balance using hexafluoride as
a tracer
• Opacity of emissions escaping
through the slot
• Observation of visible emissions
Tracer Experiments
Sulfur hexafluoride was injected into
various points within the air curtain
control volume, defined by the top, sides
and front of the air curtain structure and
the converter and primary hood which
formed the back of the structure. The
tracer experiments were of two types,
those in which the tracer was injected
into the air curtain volume above the
converter (the upper portion of the air
curtain control volume) and those in
which the tracer was injected below the
plane of the top of the converter and near
the front of the air curtain side walls (the
lower portion of the air curtain control
volume).
The recovery efficiencies measured in
the first test for individual tracer releases
above the converter varied from 69 to 119
percent, and the overall average efficien-
cy for the 45 tests was 94 percent. The
port through which the releases of the
tracer were made did not have any effect
on the average collection efficiency. The
average collection efficiency of all
releases made through a given port
ranged from 93.0 percent for Port C-6 to
95.4 percent for Port C-1. This difference
was not statistically significant. The
variability between the average collection
efficiency of the replicates made at a
given position (between the jet side and
the exhaust side) was statistically signif-
icant. The greatest difference occurred at
Port D-1, where the average collection
efficiency ranged from 83.3 to 105.7
percent. The average collection efficien-
cies for Positions 1 and 2 (near the
exhaust side) were approximately 96.6
percent and were generally higher than
those for Positions 3 and 4 (near the jet
side) which were approximately 91.6
percent.
The tracer recovery efficiencies for the
various converter operating modes were
also measured. With the exception of cold
additions, the average recovery efficiency
was not affected by the operating mode of
the converter; averages varied from 92.8
percent during blowing to 95.0 percent
during slag skimming.
For the second experiment above the
converter, the overall average tracer
recovery efficiency was 96.0 percent.
Again, the port through which the tracer
releases were made had no effect on the
average tracer recovery efficiency of the
air curtain hood. The average efficiency
varied from 94.5 percent at Port C-6 to
98.0 percent at Port B-2 (Figure 2). For
positions within the matrix, the average
collection efficiency varied from 80.7
percent at Position 4, Port D-1, to 106
percent at Position 2, Port D-1. As in the
first test series, the recovery efficiencies
were consistently higher for positions
near the exhaust side than for positions
near the jet side (Figure 3). Again, the
operating mode had no adverse effect on
the recovery efficiency measured.
Two special tests were conducted
during slag skimming where the tracer
was injected just above the top of the
converter at the front of the jet side baffle
wall. The average collection efficiency
measured was 94.5 percent, which is
comparable to that reported for the
releases on the three-dimensional matrix
in the space above the converter.
For the third experiment, several series
of tests involving the release of the tracer
into the lower portion of the air curtain
control volume near the front of the air
curtain side walls were conducted. The
first series (three tests) involved the
release of the tracer material at a location
slightly above the ladle near the jet side of
the hood. The average recovery efficiency
was 64.3 percent.
For the second series (six tests), the
tracer was released at a location slightly
above the ladle and very close to the wall
on the exhaust side. During slag
skimming, the recovery efficiency
measured (four tests) ranged from 52 to
79 percent for an average of 63.5 percent.
During matte charging, the average
recovery was 68.5 percent.
In the third series of tests, the tracer
material was also released at a location
slightly above the ladle, but farther from
the wall on the exhaust side. The
collection efficiency measured for the
seven tests ranged from 30 to 89 percent,
with an overall average of 58.7 percent. It
should be noted that the samples for tests
conducted during the operation in the
blowing mode yielded the lowest
recovery efficiencies, i.e., 32, 33, and 33
percent. These values would be expected
because the hooding system was in the
low flow mode and there was no thermal
lift which causes air to be drawn into the
air curtain control volume from the front
and carried to the upper control volume, a
phenomenon which enhances the
collection efficiency.
In the final series of tests, the tracer
was released very near the ladle on the
exhaust side of the hooding system.
Recovery efficiencies were determined
for 53 releases of the tracer material and
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Jet
Exhaust
110
100
i 90
80
70
60'
D-7
Position
Figure 2. Effect of injection port on recovery efficiency.
ranged from 27 to 128 percent, with an
overall average of 70 percent. Recovery
varied from 38 percent for the 6 tests
performed during blowing to 84 percent
for the 28 tests performed during slag
skimming. The difference between
average collection efficiencies for the
several operating modes is statistically
significant.
Opacity Measurements
An opacity monitor was mounted on
the top of the air curtain below the crane
rail in order to obtain information on
emissions escaping capture by the air
curtain and passing through the slot. A
total of 86 discrete observations was
made with results ranging from 2 to 54
percent opacity for the major converter
operations. During slag and finish
blowing, no attenuation of the monitor's
light beam was observed resulting in zero
percent opacity. The instrument output
range was 0 to 20 milliamps which
corresponds with 0 to 98.4 percent
opacity. The relationship of the instru-
ment output to opacity was exponential,
with 5 milliamps corresponding with 50
percent opacity. Therefore, emissions
during the test program were in the lower
end of instrument response. No correla-
tion between opacity and capture
effectiveness could be made because of
emissions from the front of the air curtain
system.
Visual Emissions
Two observers visually monitored the
air curtain capture effectiveness by
noting the location, approximate opacity,
duration, and significance of visible
emissions. Their estimates of capture
efficiency were within 5 to 10 percent
with only a few exceptions. Most
variability in the estimates occurred for
those operations involving rapid
evolution of emissions over a short
period, such as roll-in, roll-out, and
pouring. The average of the observations
for the various converter operating
conditions displayed the same trends as
the tracer experiments and indicates a
reasonably effective capture of fugitives.
Conclusions
In summary, the visual observation and
tracer recovery data indicated that the
fugitive emissions capture effectiveness
of the secondary hood is greater than
90 percent, averaging about 94 percent
overall. The capture effectiveness during
converter roll-in, roll-out, and slag
skimming operations is more variable
than other converter modes, since
fugitive emissions generated during
these events are dependent upon
converter and crane operations. It is also
evident that capture efficiencies of 90
percent or better are achievable for these
events under the proper crane and
converter operating conditions to
minimize fume "spillage" into the
converter aisle.
Thermal lift plays a significant role in
increased collection efficiencies for fume
generated in the lower portion of the
control area. Also, the lower tracer
recovery efficiencies for the various
converter roll-out modes are indicative of
fume "spillage" outside of the control
area.
It is believed that no practical correla-
tion can be made between opacities
recorded by the observers and the trans-
missometer. The transmissometer was
mounted perpendicular to the longitudinal
axis of the slot, whereas the position of
the visual observers was such that their
view was parallel to the longitudinal axis
of the slot, which resulted in a consider-
ably longer path length through the
escaping emissions. The apparent opacity
increases as the path length through the
emissions increases. Also, when posi-
tioned in front of the converter, the
overhead crane interfered with visual
observations above the slot area.
Emission Characterization
The capture of the fugitive emissions by
the air curtain permitted their
characterization by the "quasi-stack"
method using standard EPA stack
sampling techniques in the exhaust duct.
The converter is a batch operation
comprised of a number of steps requiring
the roll-out, charge or pour, and roll-in of
the converter. The generation of fugitive
emissions occurs primarily during these
operations because the primary hood is
raised and the draft to the primary hood is
closed off to prevent dilution of the strong
sulfur dioxide gases processed in the acid
or liquid S02 plants. During the blowing
phase of the operation, some small
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110
100
.S
.5 90
SO
70
Exhaust
Position 2
Position 1
Position 3
Jet
.V Position 4
_L
8-2
Primary Hood
D-1 C-6
Ports
C-1
•*• Front
Figure 3. Effect of injection position on recovery.
quantities of fugitive emissions are seen
to occasionally escape the primary hood.
Because of the large number of different
operations -- i.e., roll-in and roll-out;
charging of matte, anode slag, various
reverts, and scrap; slag skims; copper
pours; and blowing and holding—we
recognized that we could not character-
ize emissions for each individual
condition. Therefore, the test was
structured to provide composite data for
selected operations.
Sulfur Dioxide Emissions
The concentration of sulfur dioxide in
the air curtain exhaust was monitored by
a continuous emission monitor. More
than 470 individual data points were
utilized to characterize the converter
emissions, resulting in an emission factor
of 3.0 kg/Mg of blister copper for the total
converter cycle and 0.1 kg/Mg when the
converter was in the blowing or standby
mode.
Paniculate Emissions
Total filterable particulate was sampled
using EPA Method 5. For each of the
three converter cycles, a sample was
taken compositing all emissions over the
total converter cycle by traversing the
exhaust duct. Single point sampling was
used to obtain a composite sample
representing the emissions during those
converter operations where the primary
hood was open, i.e., charging or discharg-
ing. The emission factor for the total cycle
was calculated as 0.45 kg/Mg of blister
copper for the total cycle and 0.43 kg/Mg
for those operations where the converter
was rolled out.
Particle Size
Particle size samples were taken by
impactors to define the particle size distri-
bution within the inhalable particulate
range of 10//m and less by aerodynamic
size. The tests were conducted at points
of average velocity simultaneously
with,but at points different from, those at
which the particulate samples were
taken. The sampling was conducted in
such a manner so as to provide a
composite over a converter cycle for each
major converter operating condition.
• Charging mode which consists of all
additions to the converter such as
matte, anode slag, and cold additions
such as scrap
• Skimming mode, which consists of
slag skimming and pouring of blister
copper
• Blowing mode, which consists of all
operating conditions during which
the primary hood is closed, including
the slag, cleanup, and finish blows
The average particle size distribution
for each mode indicates that: 1) the bulk
of the particulate (88 to 98 percent) is
above 10 /t/m during blowing; 2) the
particulate is composed of both fine and
coarse particulate (70 to 84 percent less
than 10 //m) during charging; and 3) the
particulate during skimming and pouring
is predominantly (86 to 92 percent less
than 10/um) in the inhalable range (Figure
4).
Trace Metal Emissions
Arsenic, emitted in the form of arsenic
trioxide, was measured to determine both
the filterable particulate and gaseous
emission rates (Table 1). The filterable
arsenic fraction represents material col-
lected in the sample probe and on the
filter, both of which were heated to
approximately 121°C (250°F). The
gaseous arsenic fraction represents
material that passed through the heated
filter and condensed or was trapped in the
impinger section of the sample train,
which was maintained at a temperature
of 20°C (68°F) or less. In retrospect, the
sampling train should have been
operated at the temperature of the stack
gas, i.e., 15° to 30°C, to prevent
revolatilization of arsenic trioxide and
passage through the filter. Should
revolatilization occur, the amount of
arsenic reporting as gaseous would be
increased, which, could lead to a false
conclusion regarding the amount that
could be removed by dry collectors.
During Test 2, the gaseous arsenic
concentration was considerably greater
than in the other tests. During this test,
the loss of draft in the primary hood
caused by operational problems at the
chemical plant resulted in frequent
releases of smoke and fumes from the
primary hood. Significant quantities of
heavy smoke escaped the primary hood
systems, and much of these emissions
were captured by the secondary hood.
Sampling continued throughout these
intermediate upsets, but was
finally stopped when the air curtain
control system became overwhelmed by
continuous and heavy emission
discharge from the primary hood.
Therefore, it is reasonable to conclude
4
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53.3
30.0
50.0
10.O
J.O
0.1
/ Skimming
Charging
Blowing
i i 11
i i i 111
1.0 10.O
Particle Size, micrometers
100.0
'igure 4. Average particle size distribution for converter operating modes.
hat fugitive emissions generated by the
nalfunctioning primary hood draft con-
ributed to the higher arsenic concentra-
ions observed during this second cycle
est.
Conclusions
The bulk of the fugitive sulfur dioxide
missions (over one-half) was emitted
uring those converter operations
ivolving the rolling in or out of the
onverter and the charging of cold
dditions, particularly anode slag. The
emaining operations in order of
ignificance were matte charging; slag
kimming; and copper pouring and
lowing, including standby and idle. The
results of the total paniculate sampling
indicated that the bulk of the fugitive
paniculate emissions occur during those
operations occurring when the converter
is charging or discharging. This suggest
that the primary hood system is quite
effective in preventing the escape of
emissions during blowing.
The particulate size information leads
to the conclusion that the bulk (90%+) of
the fugitive particulate emitted during
blowing is greater than 10 //m, while that
emitted during the charging or
discharging is predominately (70 to 90
percent) in the inhalable range.
Emissions which occurred during a
process upset in the blowing mode
exhibited an increase in the proportion of
emissions in the fine (less than 2.5 j/m)
particle range, in addition to the
increase in total loading.
The trace metals contained in the
particulate emissions comprise an
appreciable portion of the total, some 12
to 40 percent by weight for charging and
pouring, but only a small part (5 percent)
during blowing. The bulk of the trace
elements emitted in the fugitives tends to
occur in the inhalable range with a very
considerable contribution from the fine
(less than 2.5 fjm) range.
The trace metal emissions were
dominated by arsenic and lead that are
present in high quantities in the
concentrate and carry through to the
matte which is processed in the
converter. The potential for trace metal
fugitive emissions is then greatest during
the charging of matte followed by he
charging of reverts, scrap, matte skim-
ming, copper pouring and finally blowing.
Because of the greater variability of the
trace element content of the feed mate-
rials, the content of the emissions during
charging is the most variable, followed by
slag skimming and then copper pouring.
then copper pouring.
'able 1. Summary of Arsenic Emission Data
Converter
cycle No. Test
1 TC
SM
2 TC
SM
3 TC
SM
Mass emission
rate, kg/h (Ib/h)
Filter Gas
0. 33 f 0.73)
0.99(2.18)
0.61 (1.35)
1.97 (4.35)
0.21 (0.471
1.48 (3.26)
0.04 (0.08)
0.20 (0.44)
0.72(1.59)
0.99 (2. 18)
0.07(0.16)
0.05 (0. 1 1)
Emission factor
kg/Mg (Ib/tonl
0.03 (0.06)
0.03 (0.07)
0.09 (0.20)
0.05 (0. 12)
0.01 (0.03)
0,01 (0.02)
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This Project Summary was authored by staff of PEDCo Environmental, Inc..
Cincinnati, OH 45246.
John O. Burckle is the EPA Project Officer (see below).
The complete report consists of two volumes:
"Evaluation of an Air Curtain Hooding System for a Primary Copper Converter:
Volume I" (Order No. PB 84-160 514; Cost: $ 17.50, subject to change).
"Evaluation of an Air Curtain Hooding System for a Primary Copper Converter:
Volume II. Appendices" (Order No. PB 84-160 522; Cost: $53.50, subject to
change).
The above reports will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Industrial Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
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