EPA-600/2-76-036f
February 1976
Environmental Protection Technology Series
DESIGN AND OPERATING PARAMETERS
FOR EMISSION CONTROL STUDIES:
Phelps Dodge, Ajo, Copper Smelter
Industrial Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
^search Triangle Park, North Carolina 27711
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into five series. These five broad
categories were established to facilitate "urther development and application of
environmental technology. Elimination OT traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL PROTECTION
TECHNOLOGY series. This series describes research performed to develop and
demonstrate instrumentation, equipment, and methodology to repair or prevent
environmental degradation from point and non-point sources of pollution. This
work provides the new or improved technology required for the control and
treatment of pollution sources to meet environmental quality standards.
EPA REVIEW NOTICE
This report has been reviewed by the U.S. Environmental
Protection Agency, and approved for publication. Approval
does not signify that the contents necessarily reflect the
views and policy of the Agency, nor does mention of trade
names or commercial products constitute endorsement or
recommendation for use.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/2-76-036f
February 1976
DESIGN AND OPERATING PARAMETERS
FOR EMISSION CONTROL STUDIES:
PHELPS DODGE, AJO, COPPER SMELTER
by
I. J. Weisenberg and J. C. Seme
Pacific Environmental Services, Inc.
1930 14th Street
Santa Monica, California 90404
Contract No. 68-02-1405, Task 5
ROAP No. 21ADC-061
Program Element No. 1AB013
EPA Project Officer: R. D. Rovang
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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TABLE OF CONTENTS
A. INTRODUCTION AND SUMMARY 1
B. PLANT LOCATION, ACCESS AND OVERALL GENERAL ARRANGEMENT ... 1
C. PROCESS DESCRIPTION 4
D. EMITTING EQUIPMENT ... 7
a. Reverberatory Furnace ..... 7
b. Converters 9
c. Other Emitting Equipment 11
E. EXISTING CONTROL EQUIPMENT 12
F. GAS SYSTEM DUCTWORK 16
G. SULFUR BALANCE AND GAS COMPOSITION AT SYSTEM EXIT 21
H. GAS CHARACTERISTIC VARIATION 26
I. STACK DESCRIPTION 27
J. PRESENT TECHNIQUE FOR SOLID WASTE HANDLING 27
K. FOOTING AND STRUCTURAL REQUIREMENTS 27
L. EXISTING AND POTENTIALLY AVAILABLE UTILITIES ........ 27
M. POTENTIAL NEW CONTROL EQUIPMENT INSTALLATION PROBLEMS ... 28
REFERENCES 29
APPENDIX
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TABLE OF CONTENTS (continued)
LIST OF FIGURES
FIGURE 1. PLANT LOCATION (USGS) 2
FIGURE 2. GENERAL ARRANGEMENT DRAWING (Located in Pocket
Inside Back Cover) 3
FIGURE 3. PROCESS FLOW SHEET 5
FIGURE 4. ELECTROSTATIC PRECIPITATORS - GENERAL ARRANGEMENT . . 17
(Located in Pocket Inside Back Cover).
FIGURE 5. CONVERTER .AISLE. (Located in Pocket Inside
Back Cover) 19
LIST OF TABLES
TABLE 1. AVERAGE SULFUR BALANCE SUMMARY 23
TABLE 2. GAS STREAM CHARACTERISTICS 24
ii
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A. INTRODUCTION AND SUMMARY
The purpose of this report is to present background design
data on the Phelps Dodge Corporation, New Cornelia Branch Smelter
at Ajo, Arizona in sufficient detail to allow air pollution control
system engineering studies to be conducted. These studies are primarily
concerned with lean SCL streams that are currently not being captured.
Physical layout of the smelter and surrounding area along with
existing smelter and control equipment is presented. Ductwork that
would be considered for future system tie-in is defined. Emissions
from operating equipment, gas flow rates, temperatures, sulfur balance
and process flow sheet are included. Utilities, stack dimensions,
footing requirements, and solid waste handling are defined. Available
area for new control equipment, gas characteristic variation and
potential new control equipment installation problems are discussed.
B. PLANT LOCATION, ACCESS AND OVERALL GENERAL ARRANGEMENT
The Phelps Dodge Corporation smelter is located adjacent to the
town of Ajo, Arizona. An enlargement of the USGS map, showing land
contours of the immediate area, is shown in Figure 1. Design altitude
for the plant is 1800 ft. with plant site coordinates of latitude 32°22'N
and longitude 112°52'W.
Overall plant and smelter general arrangement are shown in
Figure 2. The primary particulate emission sources are the crushing
and screening operations and the reverberatory furnaces and converters.
The primary sources of sulfur dioxide are the reverberatory furnaces
and the converters.
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CONTOUR INTERVAL 40 FEET
DOTTED LINES REPRESENT 20-FOOT CONTOURS
DATUM IS MEAN SEA LEVEL
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Figure 2. GENERAL ARRANGEMENT DRAWING
(Located in Pocket Inside Back Cover)
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The major equipment at the Phelps Dodge/Ajo smelter consists
of one reverberatory furnace with waste heat boilers, three Peirce-
Smith converters with waste heat boilers, one Great Falls oxidizing
furnace, and an anode furnace with casting wheel. Major control
equipment consists of an electrostatic precipitator for dust collec-
tion from the reverberatory furnace and converter gases along with
a 600 TPD single contact acid plant and a DMA absorption plant for
S0? control currently in the start-up phase. Reverberatory furnace
gases after dust collection in the precipitator will be treated in
the DMA absorption plant for S0« removal or discharged directly to
the main stack. After dust collection in the precipitator the conver-
ter offgases are treated in either the single contact acid plant or
the dimethylaniline (DMA) absorption plant.
C. PROCESS DESCRIPTION
Phelps Dodge Corporation operates an open pit copper ore mine,
ore crushing, grinding, and milling equipment, flotation machines for
ore concentrating, and copper smelting equipment at Ajo, Arizona.
Only the copper smelting equipment and associated control equipment
are described in this report. The process flow is shown schematically
in Figure 3.
Concentrate, which contains copper together with sulfur, iron,
and some insoluble material (primarily silica and alumina), is re-
ceived from the concentrator and is loaded into containers, which are
carried by overhead cranes to the charging stations at the reverberatory
furnace.
Concentrate is charged into the reverberatory furnace through
the sidewalls, with machines called slingers. The furnace is about
100 feet long, 30 feet wide and 11 feet high. Its main purpose is to
melt the concentrate. This is done by firing the furnace with natural
gas. In the furnace the melting concentrate makes a pool or bath
about 4 feet deep. The lighter components of the bath rise to the
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Process Flow and Sulfur Balance fl
Phelps Dodge Corp./Ajo Branch prepared Oct,1975
PACIFIC ENVIRONMENTAL SERVICES
INPUTS
Fluxed Material
64,350 TPY-S
/ Liquid SOj \
141,580 TPY
\ 20, 790 TPY-S/
_ Natural Gas
(Reverb Slag \
to Slag Dump L^
1,650 TPY-S I
Reformed Gas
t 1 Blis
- \
_ ... ,__ i . . i „
y Copper 1
-H / Oxide \
1 1 ' M Slag K
j- •" V /
/Casting\ ^
\, Wheel/ . , .„
'
^— . — -^ Converter Aisle
4 Spills-Chips-Skulls
Anode \
Copper I
0 TPY-S J
•« —
^ - r
ONE REVERB
FURNACE
Collection
Two Waste
Heat Boilers
^ Tail Gas ^ (f^
1 1,650 1'PK-S 1 *" I'j \
^ — T — ' Jill
W&USVJW
360' Stack
DMA ii
Plant 4
/ c ^
47,000 SCFMf 1 Fan j
T
Electrostatic A
•" Precipitator V
Vc^ II 70,200 SCFM
1 " "11 e 590°F
T „ II 1.5Z SO
1
(Copper \ / Converter \ / \
Matte j ( Slag j U— ( Mud U— Pug Mill
*-
r
^-1
r
Plant Watery
<
THREE CONVERTERS
(Two operating, one for
production overflow)
GREAT FALLS OXIDIZING
FURNACE
INPUTS
New Solid Charge
2,640 TPY-S
t
Reverts & Scrap
w '
/
t Three Waste Balloon Flue
Heat Boilers / Sy8t.em
>*
550°F K
, /Ground Smoke\ Single
/ to \ Absorption
^1 Atmosphere 1 Acid Plant
\3,300 TPY-S/ 600 TPD
. t . . ".
/ 2 U \ / Tail Gas 1
^1X1) ^-«0 TPV-SJ
-• 1 Dust J
"
Electrostatic
Precipitator
Plant Water
/^
/
•* V Humidifier
^ || 34,500 SCFM (average) |l|l
\l 52,000 SCFM fjj 1
] per operating l:j 1
|| converter (blowing) r'j 1
*" 6. 51 S02 (average) |Jj j
360' Stack
Figure 3.
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top making a slag which is periodically skimmed off as a waste
product. The heavier (copper-bearing) part of the bath sinks to
the bottom and is withdrawn into ladles for further treatment.
This product is composed almost entirely of copper, iron and sulfur,
and is called "matte." As slag and matte are withdrawn from the
furnace, more concentrate is added, and the melting process proceeds.
Gases from the reverberatory furnace pass through a set of boilers,
making steam for generating electricity, then through a precipitator
to the gas treatment plant.
The ladles of matte taken from the reverberatory furnace are
transported by overhead cranes to converting vessels. Air is blown
through the liquid matte in the converters. Oxygen in the air unites
with the sulfur, making sulfur dioxide gas which goes through a flue
system to the gas treament plant. The iron in the matte is also
oxidized, and when silica material is introduced into the converter,
the iron oxide and silica combine to form a component in the matte
which is lighter than the copper. This material rises to the surface
to make slag, which is skimmed off and returned to the reverberatory
furnace. This process is repeated until a charge (about 50 tons) of
blister copper is left in the converter.
The blister copper, which contains a small amount of sulfur,
is then poured into an oxidizing furnace. All the remaining sulfur
is removed by blowing more air through the liquid copper, leaving a
slight excess of oxygen. Now the copper is practically free of
impurities.
The copper is then transferred to the anode furnace, where it is
accumulated for a 24-hour period and then refined by blowing a reducing
gas (reformed mixture of natural gas and air) through the molten
charge. The carbon monoxide and hydrogen in the reducing gas unite
with the oxygen in the copper, forming carbon dioxide and water which
leave the furnace as gases. When nearly all of the oxygen has been
eliminated, the copper is cast into 750-pound slabs called anodes.
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The anodes are loaded on railroad flat cars and shipped to
the Phelps Dodge refinery at El Paso, Texas. There they are put
through the electrolytic process for further refining of the copper
and recovery of the small amount of by-product gold and silver which
has remained in the copper through the smelter.
D. EMITTING EQUIPMENT
a. Reverberatory Furnace (Reference 1).
A single reverberatory furnace, 30 feet wide and 100 feet long
(inside dimensions), fired with seven 8-inch natural gas burners,
processes concentrates from the milling and flotation plant. The
concentrates, which comprise over 90% of the furnace charge, are
received from the filter plants by conveyor and with an addition of
limerock are placed in charge cans of 259 cu.ft. or approximately
ten tons capacity. Each charge is weighed on the scales. When the
can is filled and when required at the furnace, it is carried by
overhead crane to a charge point above and to the side of the furnace.
Six charge ports are provided, three on each side of the furnace. A
concrete bin of approximately 1600 tons capacity is provided for
surge storage of concentrates. When needed the concentrates are
reclaimed by clamshell from the storage into the charge cans. The
preparation department has a crushing plant containing a 36 x 48 jaw
crusher and a 4-ft standard cone crusher.
The bath smelting furnace was designed for wet smelting. The
crucible of the furnace is of rammed periclase in sections with
water-cooled 20-ft high copper jackets on top of the crucible along
the sides of the furnace and the working bottom of the furnace is
magnetite fused in place. The bath smelting furnace requires reaction
between the added new charge and the liquid bath to cause spreading
of the new charge. In case of calcines, charging them through an
inclined pipe imparts sufficient velocity that when they strike the
liquid bath reaction starts immediately causing the necessary spreading.
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This gravity charging method cannot be used with wet concentrates
however, as they will not flow through an inclined pipe as calcines
will do. Considerable research was necessary in developing proper
charging equipment. The conditions found necessary were to be able
to place the wet concentrates within the furnace at a considerable
velocity and at a relatively flat angle so that the wet concentrates
would penetrate the liquid bath sufficiently to start the spreading
reaction, and the horizontal velocity being sufficient to prevent the
concentrates from piling up in one place. A high speed belt slinger
was developed which has been quite satisfactory. Six slingers are
provided, three on each side of the furnace; each as a port through
the sidewall, covered with a vertically movable door when not in use.
When charging is to be done, the door is raised by an air cylinder,
the slinger started, and concentrates dropped into the slinger from
the charge can overehead. The slinger is adjustable as to angle of
throw horizontally and vertically and as to speed of the belt. The
rate of charge for a single slinger is 1.5 to 2 tons/min. The handling
of the wet charge through cans transported by overhead crane, and the
spreading of the charge by mechanical slingers has worked well and has
permitted realizing the benefits of bath smelting with a raw charge.
The loading of the furnace is done by one man and is controlled by
visual inspection.
The Ajo furnace is constructed of sprung silica arch and the brick-
work is maintained by silica slurry hot patching. The silicious
material of over 90% SiO? is ground wet in a ball mill and pumped to
a storage tank above the furnace, from which it is blown and sprayed
on to the interior surface of the brickwork. A curtain damper has
been used successfully in the Ajo furnace since starting and its use
has resulted in better working conditions around the flues and boilers
and has resulted in decreased maintenance expense in the uptake and
flues to the boilers. The curtain damper sections are made of cast
refractory supported by loops of water-cooled steel tubing and main-
tained by slurry patching.
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When the doors along the side of the furnace are opened and the
slinger started the pressure in the furnace tends to increase causing
fugitive gases to leave the feed openings during the feeding process.
The furnace normally tends to be below atmospheric pressure and
operated in a reducing atmosphere. Approximately 1.0 to 1.5% S0?
gas leaves the reverberatory furnace and is cooled in the waste heat
boilers. There is one opening and launder for the slag leaving the
reverberatory furnace and three for the matte. Fugitive emissions
are generated during slag and matte tapping. The hole in the side of
the furnace is plugged with clay material that is punched clear to
open and resealed by placing a glob of clay on the end of a rod and
forcing it into the hole.
There are hoods located above the matte launders. These hoods
are some distance away from the opening to allow use of the hole
punching machine which is moved along an overhead rail for placing
in position at the three locations. Each hood can be closed off
and when in use the system will pull 40,000 to 50,000 SCFM of air.
Fugitive emissions are generated at these points but the prevailing
winds tend to move them away from operating personnel. (Ref. 2).
b. Converters (Reference 1).
The three Peirce-Smith converters have 50 tuyeres each and have
the riding rings on the ends of the shells. About one-half of the
tuyeres are one and one-half inches and the rest are two inches.
The converter flux is handled in charge cans similar to the ones used
for handling furnace charge and are transported by the converter crane
to a position above the end of the converter where the silica flux
can be discharged into the Garr gun in the end of the converter,
Blister copper is finished to only a light blister, no oxide slag
being skimmed, and is transferred to the holding furnace equipped
with tuyeres where the oxidation is completed. The use of this com-
bination holding and oxidation furnace has resulted in decided econo-
mics as it has obviated making an oxide slag in the Peirce-Smith converter
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with resulting excessive corrosion of the converter lining. The use
of this holding furnace also results in increased life of the anode
furnace lining as little or no oxidation is required in the anode
furnace.
Generally the reverberatory furnace produces more matte than one
Peirce-Smith converter can handle. The surge-storage capacity of the
bath furnace makes it possible to accumulate excess matte and then two
converters may be operated for one shift or more, getting rid of the
excess. Jackets holding the tapping plates are water cooled and three
tap holes are provided. The furnace is parallel to the conveter aisle
and very short matte launders are used.
The converter hoods consist of a radiation cooled rib stainless steel
door that is moved down over the converter opening to cover the forward
portion. Tracks are located along the sides of the converter opening
supporting the door. Below the track a very close fitting wall is
formed. This wall is also ribbed for radiation cooling. The gap between
the sides of the hood and the converter shell is approximately 2 to 3
inches. This gap is necessary because a tight seal cannot be held due
to the differential expansion of the converter and the tendency for
plugging resulting from material splash. The backside of the hood is sealed
by a flap that is pressed against the back of the converter by two pneumatic
cylinders. These cylinders allow the flap to be pulled back when the converter
is rotated. The back flap is then reset for sealing after the converter
is placed in its new position. They have also tried to put a partial
hood over the top of the converter door where there is a wide gap (2
to 3 inches) and where (as noted in other smelters) some significant
fugitive emissions are produced.
The design of this door and hood was obtained from Europe and is
a simplification compared to the water cooled hoods used in some smelters.
The rectangular rib design provides radiation cooling similar to the fins
on an aircooled reciprocating engine cylinder. They have noted a con-
siderable increase in radiation heat when ribs have been used compared to
10
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previous hoods where there were no ribs, The hood is made entirely
of stainless steel and is approximately 3/4 inches thick for both
the flat plate portion and the rib. The door and walls are made of
sections of large stainless steel castings. Steel cables are used
to pull the door up and down along the track for positioning.
There are three 13* x 30* Peirce-Smith converters. They usually
use two converters and the third is used as a production overflow.
During those times when all three converters are used they have an
additional Great Falls twelve foot diameter oxidizing furnace that is
used to provide additional capacity. From the Great Falls converter
the material is then taken to the thirteen by thirty foot anode furnace.
Operation of the converters takes approximately 8 hours total
time for each complete process cycle. The converters will generate
a peak SO- concentration of 6 to 7% and an average of 4.5 to 5% during
the slag blow. The slag blow takes approximately 45 to 60 minutes and
there are at least three sometimes four. The number of blows is judged
by eye from the color of the gases leaving the converter mouth, The
copper blow which takes two hours will peak at 14% SO- and average
8 to 9% (Ref. 2).
c. Other Emitting Equipment
In the design of the plant only one anode furnace was provided
as it was thought that the second Peirce-Smith converter would be
available to hold copper while the one anode vessel was in the re-
fining and casting parts of the cycle. However, it was soon found
that numerous delays resulted when it was necessary to blow two con-
verters and also when one converter was down for repairs. A 12-ft
Great Falls converter was transferred from the United Verde plant
and set up between the converters and anode furnace and remodeled
so that it could be used for a holding furnace and also for further
oxidation of the copper. The vessel was lined with nine inches of
basic brick, insulated from the shell. Four 2-in. tuyeres were pro-
vided and a gas burner installed in the cap which was turned 180
11
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from its original position when used as a regular copper converter.
The single anode furnace 13 x 30 ft was designed to handle the day's
production of copper, about 200 tons average, making only one pour
per day. The ends of the furnace are dished, and the lining is in-
sulated from the shell throughout. In design of the casting wheel
a great deal of attention was paid to the drive mechanism giving
smooth operations with few rolled edges and little trimming required.
Tuyeres have now been installed in the anode furnace and are used
for reduction of the copper with reformed gas. In the past, reduc-
tion of the copper has been done with green oak poles.
Particulars are generated in the mining and millings opera-
tions at Ajo. Leaks in ducts and other pieces of equipment cause
fugitive emissions of particulate and S0«.' Ladles holding matte
and slag produce visible fugitive emissions.
It is reported that 15% (ground smoke) is generated through-
out the plant (Ref. 2). This was interpreted to mean 15% of the SO
generated is fugitive emissions.
E. EXISTING CONTROL EQUIPMENT
Reverberatory furnace offgases and converter offgases are treated
in separate electrostatic precipitators.
The reverberatory furnace electrostatic precipitator consists of
two independent horizontal parallel units to handle 150,000 ACFM (600°F
and 13,8 psia). Average grain loading is in the range of 0.9 Gr/SCF
(32 F and 14.7 psia). Gas treatment time is 5.97 seconds; pressure
drop across the precipitator is 0.5 inches w.c. maximum. Collecting
surfaces are plates; the discharge electrodes are spring steel wires.
The transformer- rectifiers are silicon full wave for 45KV (DC) average;
there is an automatic voltage control system to maintain the optimum
precipitator operating efficiency (about 96% neglecting sulfates). Dust
collected is conveyed to a storage bin from which it is pneumatically
conveyed to the charge mixing area for the reverberatory furnace by a
fluidflow automatic pump. This pump can handle 20,000 pounds per
12
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hour when supplied with 280 SCFM compressed air at 30 psig.(Reference 3).
The converter electrostatic precipitator is similar to the one for
the reverberatory furnace. There are two independent horizontal parallel
units with three fields each to handle 210,000 ACFM (650°F and 13.8 psia).
Average grain loading is on the order of 1.3 Gr./SCF (32°F and 14.7 psia).
Gas treatment time is 6.4 seconds; pressure drop across the precipitator
is 0.5 inches w.c. maximum. Optimum precipitator operating efficiency
is about 97.2% neglecting sulfates. Total collecting surface area is
29,808 sq. ft. Dust collected is conveyed to a storage bin from which
it is loaded into a truck for haulage to the crushing plant receiving
hopper and used with the converter flux mix. To keep the precipitators
above the condensation point of the residual gases whenever gases are
not being treated in the gas treatment plant there are burners near the
precipitator entrance which can be fired with natural gas or diesel oil.
Combustion products are exhausted by two exhaust fans (one for each pre-
cipitator outlet duct). (Reference 3).
The gas treatment plant consists of a sulfuric acid plant and
a sulfur dioxide absorption plant. The former is designed to produce
600 tons of acid per day, and the latter can produce approximately
50 tons of liquid sulfur dioxide per day. The sulfur dioxide.from the
converters can be routed to either plant to make sulfuric acid or
liquid sulfur dioxide, but the gas from the reverberatory furnace,
which is too dilute to be treated in the sulfuric acid plant, flows
only to the absorption plant. The purpose of both plants is to eliminate
sulfur dioxide from the offgases generated by the smelting operation.
The hot sulfur dioxide gas from the converters, containing
dust particles, passes through gas coolers where its temperature
is lowered to approximately 600 F, and some of the dust particles
are removed. The heat removed from the gas generates steam for sub-
sequent uses. The gas then passes through an electrostatic precipi-
tator, where the majority of the dust is recovered, and then on to
13
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the gas scrubbing section of the sulfuric acid plant. The scrubbing
section consists of a humidifying tower, a cooling tower, and a mist
precipitator. The first two towers cool the gases further and remove
the remaining dust particles. The mist precipitator is designed to
remove the sulfuric acid mists from the gas stream to avoid corrosion
of equipment down stream. From the mist precipitator the gas passes
through a drying tower, where moisture is removed. The sulfur dioxide
gas then passes through two blowers into the shell side of a series
of heat exchangers, where it is heated by hot sulfur trioxide gas,
and then passes on to a catalyst chamber. Sulfur dioxide gas is
converted to sulfur trioxide in the catalyst chamber at an elevated
temperature. The sulfur trioxide gas passes through the tube side of
the heat exchangers and loses much of its heat before entering the
absorbing tower. The circulating acid in the absorbing tower
absorbs the incoming sulfur trioxide. Sulfuric acid is produced
during the process of absorption. Additional water is required at
times to maintain a desired acid strength. The acid is pumped to
storage, whence it is shipped by railroad cars or tank trucks to
purchasers.
The single absorption 600 ton per day Monsanto Envirochem
sulfuric acid plant can operate from approximately 1.5% to as high as
14% S09 stream. The lower value requires continuous preheat to the
SO to SO- converter and if sustained for a long time period will result
in a water balance problem, with consequent reduction in acid strength.
The higher value is limited by the cooling capacity of the gas heat
exchangers on the inner stages of the converter. Typically, a 6.5%
SO stream is treated.
Many problems have been encountered with operation of the acid
plant. It was started up in the middle of November 1972 and still has
not proven satisfactory (Ref. 2). The following problems were
encountered:
1. Insufficient mist precipitator capacity.
2. Extensive corrosion of the acid heat exchanger.
3. Erosion of the dome of the humidifier chamber. The
humidifier chamber is essentially a spray cooler.
14
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It was determined that fluorine was in the water
in sufficient quantities to cause some erosion.
4, Continuous problems with pumps, lines and coolers
in terms of corrosion and even original design
capabilities were encountered.
The sulfur dioxide absorption plant (DMA.) was built to
supplement the acid plant with additional sulfur dioxide gas. Re-
verberatory gas entering the absorption plant is first cleaned by
an electrostatic precipitator and gas scrubbers then absorbed by the
dimethylaniline (DMA) solution. The gas is then dried by sulfuric
acid, and is compressed and condensed to a liquid form. Liquid sul-
fur dioxide is stored under pressure and is vaporized to supplement
the acid plant operation whenever necessary.
The DMA plant also encountered many practical problems such as:
1. The blower motor bearing went out very rapidly.
2. The FRP main duct collapsed because it originally
did not have sufficient ring supports installed.
3. The S0_ compressor failed because of particles
entering the stream.
4. The drying tower was not designed properly to give
uniform flow of gas and liquid.
5. Extensive corrosion in the weak acid system.
6. Design of the S0« vaporizer was also not satisfactory.
Considerable corrosion was encountered and is believed
caused by not having a drain in the system.
With the DMA system collecting part of the gases of the rever-
beratory furnace and with the close fitting hoods on the converters
and the sulfuric acid plant it is believed that over 90% (92%) of the
input sulfur can be fixed with the system presently installed after
modification to eliminate the problems recently encountered,
A nearby paper plant is a potential customer to receive the
liquid SO production from this smelter.
15
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Three recently prepared papers by plant personnel describe in detail
the gas treatment facilities, the SO- absorption plant and the use
of waste heat boilers in the converter department, (Ref. 3, 4, 5).
Copies of these papers are included for reference in the Appendix.
F. GAS SYSTEM DUCTWORK
The following gas system ductwork description was taken from
Reference 3.
Gases from the reverberatory furnace are passed through two
parallel waste heat boilers to partially cool the gases and to recover
some of the heat value which can be used for the production of electric-
ity or for the production of the low pressure air required for copper
converting. The gases are then treated in an electrostatic precipitator,
Figure 4. Where the two uptake flues from the waste heat boilers joined
the balloon flue for the reverberatory furnace gases, flue modifications
were made so that the gases could continue either to enter the balloon
flue or to bypass the balloon flue and be sent to a plenum chamber for
mixing and then to a new electrostatic precipitator unit. Remotely
controlled dampers in the flues accomplish this gas path selection.
An induced draft fan was installed to draw the reverberatory gases
from the reverberatory furnace through the waste heat boilers, the flue
system and the electrostatic precipitator. This fan can handle 150,000
ACFM @ 600°F with a suction of -1.75" H20 and a discharge of 3.25"H20.
All of the gases can be discharged to the 360 foot concrete stack through
a duct which enters the breeching flue between the old Cottrell plant
and the stack, or part of the gases can go to the stack and part to the
SO absorption plant. A remotely controlled damper in the flue going
to the stack controls the total volume of gas removed from the reverbera-
tory furnace and the distribution of the gas.
Treatment of this low SO- content (1.5-2%) gas that is not sent to
the main stack is in the SO- absorption plant, described in a previous section.
16
-------
FIGURE 4
REVERB. ELECTROSTATIC PRECIPITATORS - GENERAL ARRANGEMENT
ELEVATION LOOKING WEST
(Located in Pocket Inside Back Cover)
17
-------
Formerly, gases from the two Peirce-Smith converters were diluted and
partially cooled by allowing large quantities of air to e.nter the flue system
at the converter hoods. This practice required change because the gases
must be kept above 4% S02 for efficient acid plant operations. The converter
blowing operations were reviewed to determine the best approach for the new
conditions.
A third converter was installed to improve the availability of
converters for more constant production of gases by the converters while they
are converting matte. The mode of operation was to blow one converter on "A"
shift, two converters on "B" shift, and one converter on "C" shift. The
former mechanical punchers (26 - 3" tuyeres) were replaced with Gaspe
mechanical punchers (52 - 1 3/4" tuyeres); the new converter has a Gaspe
puncher.
The hoods and the old balloon flue system behind the two old converters
were removed. In order to reduce air infiltration to no more than 100%
a hood that would fit as tightly as possible over the converter mouth was
designed, Figure 5. The hood sidewalls approach within 2 to 3 inches of the
converter apron; further approach would allow splashing material to seal the
opening and restrict movement of the converter. Since a high infiltration
of air no longer is available to cool the gases, a stainless steel hood
which provides for convection was selected. This hood starts at the con-
verter mouth and ends 13 feet from the centerline of the converter. At
that point a mild steel flue section connects the hood castings and the
waste heat boiler.
The movable roof section for the hood travels on rails; when it
reaches its bottom level of travel, there is a dip in the rails so that the
hood drops to make a tight seal along its top and sides. The lower edge is
then only a few inches from the converter apron. To seal the lower, rear
opening of the hood there is a large spark shield casting which can be posi-
tioned by air cylinders to fit against the converter apron. The movable roof
section is positioned by means of cables, a hoist and a counterweight.
18
-------
FIGURE 5
CONVERTER AISLE
SECTIONAL ELEVATIONS LOOKING NORTH
(Located in Pocket Inside Back Cover)
19
-------
In order to capture any smoke that might escape from the converter
hood an experimental exhaust hood was installed over the No, 3 converter hood.
This installation included a fixed section and a movable section. However, the
latter was eliminated after the positioning cable system caused operating
problems. Design for the No.l and No. 2 converters provides for longer
fixed hood sections (these must not be too low or they will be easily damaged
when charging matte or "pulling the converter collar"). Exhaust from the
existing hood is by two 42" diameter vane axial fans each capable of
exhausting 44,470 CFM. The fans operate at 1,640 RPM. A 50 HP motor is
used to drive the fans with V-belts. For the experimental unit the gases
are discharged to the atmosphere. Gases discharged from these fans and
from the ones for the Nos. 1 and 2 converters enter ducts which take them
to the base of the 360 foot concrete stack for mixing with other gases.
It is necessary to further cool the gases (after about 100% air in-
filtration at the converter mouth and after convertion cooling from the hood
castings) so that standard steels can be used for the flues and to permit
the use of a standard electrostatic precipitator. To do this waste heat
boilers suitable for operation with copper converters were installed.
At the exit of each waste heat boiler there is a drop gate for use
as a tight shut off for repairs and then a plug damper at the entrance
to the balloon flue. The plug damper flue section is 6'-7" I.D. The
plug damper travel is I'-Sy. This damper controls the flow of gases
from the converter and waste heat boiler to the balloon flue.
A new balloon flue was constructed to accommodate the gases as they
leave the three waste heat boilers. This flue is 175 feet long before it
turns to run another 36 feet and joins the old balloon flue which goes to
the old Cottrell plant. At the point where the old and new balloon flues
join there is a damper which is used to control flow of gases to the old
system. The balloon flue height is 19'-1" above the drag chain box
and the radius of the top section is 5'-9". There are three expansion
joints (sliding plates covered with rockwool and then with Cohr lastic
20
-------
coated fabric). The drag chain system is operated automatically.
The distance between the balloon flue openings for the No. 1 and No. 2
converters is 66'-0"; the opening for the No. 2 is 48'-3" north of that
for No. 2, Gases flow from the top of the balloon flue through two short
flues to the converter electrostatic precipitator. These flues are 10'-7"
south of and north of the centerline of the No. 2 balloon flue entrance.
After the gases leave the precipitators, they pass through 6 foot
diameter ducts and are controlled by dampers so that all of the converter
gases can go to the acid plant or all to the SO absorption plant or part
of the gases to each plant. At this point the converter gas contains some
dust, acid mist, water vapor, and other impurities. Further gas purifi-
cation steps consist of gas scrubbing, gas cooling, and acid mist removal.
Treatment of the gases in the SO- absorption plant and the acid plant is
discussed in an earlier section of the report.
G. SULFUR BALANCE AND GAS COMPOSITION AT SYSTEM EXIT
The principal sulfide minerals in the concentrates are chalcopy-
rite and bornite with a variable amount of pyrite. The grade of the
matte is always over 30% but with judicious use of high quartz ore
in the flux all reverts plus some concentrates are smelted in the
converters. Control of magnetite is done by keeping the silica
content of the converter slag 29-30% and by control of the matte and
slag temperatures. Concentrates, as received from the filter plant,
are given an addition of limerock and charged directly into the furnace
by means of the slingers. Sufficient limerock is added to the charge
to give 4.0 to 5.0% CaO in the final slag.
21
-------
A typical concentrate analysis is as follows: (Ref. 1.)
Cu S102 A12°3 Fe s Ca° H2°
30.43 8.0 2.4 27.2 31.0 0.7 7.28
Reverberatory Furnace Feed
Concentrates
Limerock
Reverts
Total
Tons Cu
Matte produced 16,704 37.71
Dry
Tons
19,638
925
196
20,804
Fe S
34.0 25.5
An average sulfur balance for the Phelps Dodge Ajo smelter is
presented in Table 1. Of the 203 tons per day of sulfur, approximately 183
tons per day are captured. The acid plant and DMA plant capture 178 tons
per day and 5 tons per day are contained in the slag and solid wastes
disposed of in the dump. With these figures as a basis, the overall
smelter control efficiency is 90.1%. An average of 10 tons per day of
sulfur (20 tons per day of S0_) are discharged from the stack and fugitive
emissions account for an additional 10 tons per day of sulfur lost to the
atmosphere.
The volumetric gas flow at the converter electrostatic preci-
pitator caries from 64,100 ACFM at 540°F to 73,100 ACFM at 515°F. The
tuyeres deliver about 26,000 SCFM of air to the converters and this is
further diluted with another 26,000 SCFM. The acid plant is capable
of handling 52,000 SCFM.
Table 2 presents typical gas stream characteristics reported by
Phelps Dodge Corporation (Ref. 6).
22
-------
Table 1. PHELPS DODGE CORPORATION AJO, ARIZONA
Average Sulfur Balance Summary
Sulfur
Input
TPD-S
203
Roaster
%so2
-
TPD-S
-
Reverb
%so2
1.5
TPD-S
68
Converter
%so2
5.4
TPD-S
120
Slag &
Solid Waste
TPD-S
5
Fugitive
Emissions
TPD-S
10
Present
Sulfur
Captured
TPD-S
183
Stack
Emissions
TPD-S
10
to
OJ
-------
TABLE 2
GAS STREAM CHARACTERISTICS
OF
PHELPS DODGE CORPORATION
AJO COPPER SMELTER
SO Source
Weak
Reverb ,
.S3
.£»
Strong
Conv.
Flow rate
Scfm @
70°F 14.7Psi
45-55,000
0-78,000
Concentration
Percent
SO,,
1-3
4-0
SO,
0.1
0.1
o.,
5
8-12
Particulate
Treatment
Electro.
Precipit.
Scrubber
Precipit.
Scrubber
Outlet
Loading
Gr/ACF
.06 gr
Nil
.09 gr
Nil
Disposition of
Gas Stream
Plant
DMA
Acid
Type
Single
Absorp
tion
Capac-
ity TPD
750
Emitted through
stack
Product
Disposition
Used
X
Sold
X
Plant
Age
1950
Difficulty
of Retro-
fitting
Control
Remarks
Control units
installed
undergoing
modifications
Note: The plant generates its own power from waste heat and direct fired boilers. Water supply is limited.
smelting charge characteristics.
Uniform
Reference 6.
-------
The following data were obtained from Reference 2.
Converter Offgas Composition
Component % b.v.
N2 8°
°2 U
S02 6.9 - 9.8
S03 .05 - .07
Dust .15 g/SCF Max
*27643 SCFM to 39,849 SCFM (32°F, 14.7 psia)
Converter Dust Composition
Component % b.v.
Cu 19.0
Fe 17.0
Pb 0.83
Bi 0.61
F Nil
Sb Nil
As 0,39
Se 0.21
Si 15.0
Mg 0.57
Mo 0.08
Al 3.60
02 21.0
Cl Nil
Converter Dust Particle Size Distribution
Mesh
-48 + 65 0.5
-65 + 100 1.5
-100 +150 2.5
25
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Mesh (cont)
-150 + 200 3.5
-200 +270 5.0
-270 + 325 5.0
-325 + 32 Micron 16.6
-32 + 25 Micron 55.6
-25 Micron 9.8
100.0
H. GAS CHARACTERISTIC VARIATION
It can be expected that S0« concentration in the offgas from
the reverberatory furnace will vary significantly with time. This
results from the variation in time required for decomposition or
reaction of the various sulfide ores charged the furnace. This
variation in SO^ content has been known to vary as much as 10 to 1
within a given charging time cycle. While no data are yet available
from this smelter concerning this point, it should be considered for
control system design.
SO concentration in converter offgases will also vary con-
siderably for an entirely different reason. The operation of the
converters includes several, usually three, slag blows and one copper
blow. Between these blows the hood above the converter is closed off
by dampers so that the gases do not pass through the collection system
to the acid plant. The attempt is always made to maintain at least
one converter blowing gases into the system at any given time. Usually
a converter will be provided with 20,000 SCFM to the tuyeres. An
additional 100% of dilution air is estimated to be added to this gas
flow resulting in a total gas flow from each converter in the range
of 30,000 SCFM.
When a converter is blowing these will usually be approximately
30,000 SCFM at an SO content in the range of 4.0 to 6.0%.
26
-------
Because of the normal fluctuation in converter feed and opera-
tion, the SO concentration can vary over a relatively wide range.
In addition, the gas volume flow from the converter line to the acid
plant can vary over a wide range from maximum to zero. Operation
of the control system must be conducted in a manner to compensate
to be typical providing satisfactory control.
I. STACK DESCRIPTION
A single 360 foot stack serves the emitting equipment at
this smelter.
Main Stack
Height 360 feet
Diameter (ID) 24 feet bottom
15 feet top
J. PRESENT TECHNIQUE FOR SOLID WASTE HANDLING
Reverberatory furnace slag is hauled in slag cars to the slag
dump. Converter slag is returned to the reverberatory furnace. Dust
collected in the precipitators is transported by a pneumatic dust
handling system to a pug mill and processed for charging to the
reverberatory furnace.
K. FOOTING AND STRUCTURAL REQUIREMENTS
No local codes apply. The National Uniform Building Code is used.
Seismic zone 2 and a wind load of 20 PSF are used for design. A snow load
design value of 4PSF is standard for this smelter. The ambient temperature
ranges from a minimum of 17 F to a maximum of 120 F. The average wet
bulb temperature is 75 F.
L. EXISTING AND POTENTIALLY AVAILABLE UTILITIES
Water supply is limited at the Ajo smelter. It is expected that
future natural gas supplies will be limited. The availability of
electricity is not known.
27
-------
M. POTENTIAL NEW CONTROL EQUIPMENT INSTALLATION PROBLEMS
Available space for new control equipment can be found north
of the existing reverberatory furnace or converters. No additional
installation problems are apparent at this time.
28
-------
REFERENCES
1. Extractive Metallurgy Joseph Newton, Wiley, New York,1959.
"Smelting Practices of Phelps Dodge in Arizona" Fowler, M.G.
Phelps Dodge Corporation, Douglas, Arizona.
2. Visit to Phelps Dodge Copper Smelter at Ajo, July 25, 1974.
3. "Gas Treatment Facilities at the New Cornelia Branch of
Phelps Dodge Corporation, Ajo, Arizona," Forrest R. Rickard,
April 26, 1974.
4. "S02 Absorption Plant at the New Cornelia Branch of Phelps
Dodge Corporation, Ajo, Arizona." W.J. Chen, April 26, 1974.
5. "Use of the Gas Coolers (Waste Heat Boilers) in the Converter
Department at the New Cornelia Branch of the Phelps Dodge
Corporation, Ajo, Arizona" James B. McBiles, April 26, 1974.
6. Letter from John H. Davis, Jr., Chief Mechanical Engineer,
Western Engineering Department, Phelps Dodge Corporation,
February 12, 1975.
29
-------
APPENDIX
-------
GAS TREATMENT FACILITIES AT THE NEW CORNELIA BRANCH
OF PHELP3 DODGE CORPORATION, AJO, ARIZONA
Forrest R. Rickard
Smelter Superintendent
The Ajo Smelter of the Phelpa Dodge Corporation was placed in operation
in 1950. Gases from the one Reverberatory furnace and from the two 13' x 30'
Peirce-Smith converters were confined to separate balloon flues up to the entrance
to the Cottrell Plant. There the gases mixed and passed through a pipe type
Cottrell unit for removal of particulate matter. The gases then entered a 3&0 foot
concrete stack for dispersal to the atmosphere.
Air quality control laws, formulated by the Federal and State governing
bodies have made it necessary to prepare to be in compliance with the standards
for particulate matter and for sulfur emissions. These have dictated changes in
modes of operation and in facilities at the Ajo Swelter.
Since there are no overall accepted standard methods from which to choose,
Ajo selected both a metallurgical gas acid plant and an S02 Absorption Plant to-
gether with gas handling and cleaning system changes. We are in compliance with
the standards for particulate matter. We expect to achieve compliance with
Arizona's sulfur emission limitations within the time limits prescribed by state
law. As yet there are no federal sulfur emission limitations.
REVERBERATORY FURNACE GASES
Gases from the Reverberatory furnace have always passed through two (2)
waste heat boilers (in parallel) to partially cool the gases and to recover some
of tho heat value vhicii can be used for the production of electricity or for the
production of the low pressure air required for copper converting. Therefore,
these gases are suitable for treatment in a modern electrostatic precipitator.
Where the two (2) uptake flues from the two (2) waste heat boilers joined the
balloon flue for the Reverberatory gases, flue modifications were made so that
the £-,ases could continue either to enter the balloon flue or to bypass the
X-l
-------
balloon flue and be sent to a plenum chamber for mixing and then to a new electro-
static precipitator unit. Remotely controlled dampers in the flues accomplish
this gas path selection.
The electrostatic precipitator consists of two (2) independent horizontal
parallel units to handle 150,000 ACFM (600°F and 13.8 psia). Average grain loading
is in the range of 0.° Gr/SCF(32°F and lU.7 psia). Gas treatment time is 5.97
secondsj pressure drop across the precipitator is 0»5 inches W.G. maximum. Col-
lecting surfaces are plates; the discharge electrodes are spring steel wires. The
transformer-rectifiers are silicon full wave for U5KV (DC) average} there is an
automatic voltage control system to maintain the optimum precipitator operating
efficiency (about 96$). Dust collected is conveyed to a storage bin from which
it is pneumatically conveyed to the charge mixing area for the Reverberatory fur-
nace by a fluidflow automatic pump. This pump can handle 20,000 pounds per hour
when supplied with 280 SCFM compressed air at 30 psig.
An induced draft fan was installed to draw the reverberatory gases from
the reverberatory furnace through the waste heat boilers, the flue system and the
electrostatic precipitator. This fan will handle 150,000 ACFM @ 600°F with a
suction of -1.75" H20 and a discharge of 3.25" H20. All of the gases can be
discharged to the 360 foot concrete stack through a duct which enters the breech-
ing flue between the old Cottrell Plant and the stack, or part of the gases can
go to the stack and part to the S02 Absorption Plant. A remotely controlled
damper in the flue fcoing to the stack controls the total volume of gas removed
from the reverberatory furnace and the distribution of the gas.
Treatment of this low S02 content (1.5-2/0 .gas that is not sent to the
stack is in the S02 Absorption Plant, discussed in another paper.
CONVERTER GASES
Formerly, gases from the two (2) Peirce-Smith converters were diluted and
partially cooled by allowing large quantities of air to enter the flue system at
X-2
-------
the converter hoods. This concept required change because the gases must be kept
above k% S02 for efficient Acid Plant operations. The converter blowing opera-
tions were reviewed to determine the best approach for the new conditions.
A third converter was installed to improve the availability of converters
for more constant production of gases by the converters while they are converting
matte. The mode of operation was to blow one converter on "A" shift, two con-
verters on "B" shift, and one converter on "C" shift. The former mechanical
punchers (26 - 3" tuyeres) were replaced with Gaspe mechanical punchers (52 - 1 3/U"
tuyeres); the new converter has a Gaspe puncher.
The hoods and the old balloon flue system behind the two old converters
were removed. In order to reduce air infiltration to no more than ]00$ a hood that
would fit as tightly as possible over the converter mouth was designed. The hood
sidewalls approach within 2 to 3 inches of the converter apron; further approach
would allow splashing material to seal the opening and restrict movement of the
converter. Since a high infiltration of air no longer is available to cool the
gases, a stainless steel hood which provides for convection cooling was selected.
This hood starts at the converter mouth and ends 13 feet from the centerline of
the converter. At that point a mild steel flue section connects the hood castings
and the waste heat boiler. Three grades of stainless steel castings are used:
Cast 28-1; Alloy (HC) for the side castings:
C 0.50 max.; Mn 1.00 max.; Si 2.00 max.; P O.Oii max.; S O.OU max.; Cr 26.0-
30.0; Ni U.OO max.; ho 0.50 max.
Cast 20-9 Alloy (HE) for roof and for movable section castings:
C o 20-60; Mn 2.00 max.; Fi 2.00 max.; P 0.04 max.; S 0.04 max.; Cr 26.0-30.0;
tf:P.0-11.0; Mo 0.50 max.
Cast 25-12 Alloy (HH) was i'ound more suitable than Hi, lor the roof and movable
section casting and will be used for replacement castings:
C 0.20-0.50; Kn 2.00 max.; Si 2.00 max.; P O.Cli max.; S O.OU max.; Cr 2k.0-28.0;
Ni lloO-lU.O; Mo 0.50 max.
X-3
-------
Multiple castints were used for the original installation. However,
casting and operating experience have shown that fewer castings are more de-
sirable. The pattern can be called "waffle". The "waffle" areas are mostly
12" x 12" center to center of walls; other areas may be 7" x 9k", 7" x 10V,
12" x 1CV> depending on their location on the casting. Interior ribs are
generally 3A" thickj exterior ribs are generally 1" thick. The castings
are 1" thick on the surface presented to the gases. The "waffles" are 7"
deep. The castings for one converter weigh about 109,?60 pounds.
The movable roof section for the hood travels on rails; when it
reaches its bottom level of travel, there is a dip in the rails so that the
hood drops to make a tight seal along its top and sides. The lower edge is
then only a few inches from the converter apron. To seal the lower, rear
opening of the hood there is a large spark shield casting which can be posi-
tioned by air cylinders to fit against the converter apron. The movable roof
section is positioned by means of cables, a hoist and a counterweight.
In order to capture any smoke that might escape from the converter
hood an experimental exhaust hood was installed over the No. 3 Converter hood.
This installation included a fixed section and a movable section. However, the
latter was eliminated after the positioning cable system caused operating pro-
blems. Design for the No. 1 and No. 2 Converters provides for longer fixed
hood sections (these must not be too low or they will be easily damaged when
chaining u.atte or "pulling the converter collar"). Exhaust from the existing
hood is by two 42" diameter vane axial fans each capable of exhausting 44,470
CFtt. The fans operate at 1,6UO RPftj a 5>0 HP motor is used to drive the fans
with V-belts. Bearing selection for the operating temperature proved to be
incorrect. For the experimental unit the gases are discharged to the atmos-
phere. Gases discharged from these fans and from the ones for the Nos. 1 and
X-4
-------
2 Converters will enter ducts which will take them to the base of the 360 foot
concrete stack for mixing with other gases.
It is necessary to further cool the gases (after about 100/» air in-
filtration at the converter mouth and after convection cooling from the hood
castings) so that standard steels can be used for the flues and to permit the
use of a standard electrostatic precipitator. To do this waste heat boilers
suitable for operation with copper converters were installed.
At the exit of each waste heat boiler (one for each converter) there
is a drop gate (for use as a tight shut off for repairs) and then a plug
damper at the entrance to the balloon flue. The plug damper flue section is
6'-7" I.D. The plug damper travel is 1'-5^" (the positioner is outside the
balloon flue; the rod for the plug damper passes through the balloon fluej a
sleeve upstream of the plug damper supports that end of the plug damper rod).
This damper controls the flow of gases from the converter and waste heat boiler
to the balloon flue.
A new balloon flue was constructed to accommodate the gases as they
leave the three waste heat boilers. This flue is 175 feet long before it
turns to run another 36 feet and joins the old balloon flue which goes to the
old Cottrell Plant. At this point (where the old and new balloon flues join)
there is a damper which is used to control flow of gases to the old system.
The balloon flue height is 19'-1" above the drag chain box; the radius of the
top section is 5'-9". There are three expansion joints (sliding plates covered
with rockwool ^r.d then v.rilh Cohr lastic coated fabric). The drag chain is a
#10U, heat treated steel drag chain with 6" pitch. The drag chain system is
operated automatically.
The distance between the balloon flue openings for the No. 1 and No. 2
Converters is 66'-O"; the opening for the No. 2 is US1^" north of that for
No. 2. Cases flow from the top of the balloon flue through two short flues to
X-5
-------
the converter electrostatic precipitator. These flues are 10'-7" south of and
north of the centerline of the No. 2 balloon flue entrance.
CONVERTER GAS CLEANING
The Converter electrostatic precipitator is similar to the one for the
Reverberatory furnace. There are two (2) independent horizontal parallel units
with three fields each to handle 210,000 ACFM (650°F and 13.8 psia). Average
grain loading is on the order of 1.3 Gr./SCF (32°F and lU.7 psia). Gas treat-
ment time is 6.U seconds; pressure drop across the precipitator is 0.5 inches
W.G. maximum. Optimum precipitator operating efficiency is about 97»2$. Total
collecting surface area is 29,808 sq. ft. Dost collected is conveyed to a
storage bin from which it is loaded into a truck for haulage to the crushing
plant receiving hopper and used with the converter flux mix. To keep the pre-
cipitators above the condensation point of the residual gases whenever gases
are not, being treated in the Gas Treatment Plant there are burners near the
precipitator entrance which can be fired with natural gas or diesel oil. Com-
bustion products are exhausted by two exhaust fans (one for each precipitator
outlet duct).
After the gases leave the precipitators, they pass through 6 foot
diameter ducts and are controlled by dampers so that all of the converter
gases can go to the Acid Plant or all to the S02 Absorption Plant or part of
the gases to each plant. Treatment of the gases in the S02 Absorption Plant
is discussed in a separate paper. This paper will discuss the treatment of
converter gases in the Acid Plant.
At this point the converter gas contains some dust, acid mist, water
vapor, and other impurities. Further gas purification steps consist of gas
scrubbing, gas cooling, and acid mist removal.
The humidifying tower is a vertical, lead and acid brick lined steel
tank 13'-11" I.D. shell by approximately 18'-0" high side walls. There is a
X-6
-------
stainless steel section containing impingement trays and weak acid sprays which
is mounted on top of the tower (this section is to be replaced because the
materials of construction are not proper for this application). The bottom of
the tower serves as a pump tank for the weak acid circulating stream. The gas
(approximately 550°F and 13«6 - 13.7 psia) flows upward through the open-type
humidifying tower through a spray of weak acid. Most of the heavy dust particles
are scrubbed from the gas which is cooled by evaporation of the water from the
weak acid. The weak acid is recirculated without cooling. A horizontal, centri-
fugal, corrosion resistant (wetted parts are of Alloy 20 or equal) pump whose
capacity is lI^OO gpm is used for this application. Approximately 13 gpm of
waste weak acid is purged from the humidifying tower system to the Concentrator
tailing launder. This purge contains about 1% solids and 1% ^SCv.
The gas then passes through a gas cooling tower. Cooling is achieved
by running cooled, weak acid over a packed tower. The weak acid is cooled by
water in shell and tube heat exchangers. Water and solid impurities removed
from the gas stream are purged from the tower as a weak, impure acid. This
effluent flows by gravity to the humidifying tower. The gas cooling tower is
a vertical, lead and acid brick lined steel tank lli'-ll" I.D. shell by approxi-
mately 31'-6" high side walls. The tower is packed with 3" polypropylene Intalox
saddlesj weak acid is distributed over these saddles. The bottom of the tower
serves as a pump tank for the weak acid stream. This pump is similar to that
for the hur'idifv'inp tower. The heat exchangers are horizontal ones with im-
pervious graphite tubes designed to cool the acid going to the gas cooling
tower to °0°F with cooling water supplied at 8l°F.
The process gas next flows through a lead and lead-lined steel electro-
static precipitator for removal of sulfuric acid mist and those solids not
previously removed. The collection system consists of 28U vertical lead tubes
X-7
-------
(all are 10" I.D., except eight which are 13" I.D.) fabricated with 10 Ib. lead.
In the center of each 10" tube there is a discharge electrode system consisting
of a steel wire covered with star shaped lead and held taut by lead weights at
the lower end. A water spray system is installed at the top of the precipitator
for cleaning the electrodes. The gases pass through the tubes; an electrical
charge is imparted on the particle of acid nist or solid; the particle is de-
posited on the electrically grounded collecting tube. The acid mist collected
serves to wash the collected solids to the bottom chamber of the precipitator.
This effluent flows to the humidifying tower system.
Main ducts in the purification system are of fiberglass reinforced
polyester about V-0" diameter. Main ducts in the Acid Plant area are of steel
about Ul-6" diameter. All weak acid piping is of fiberglass reinforced poly-
ester (FRP), PVC or CPVC. Valves are of Alloy 20 construction. Substantially
all of the 93% and 9Q% acid piping is centrifugal cast iron. Valves are Alloy
20 with teflon packing. Product acid piping is black iron.
SULFURIC ACID PLANT
The cleaned process gas enters the 600 ton per day, metallurgical type
contact sulfuric acid plant; it first passes through the packed drying tower
countercurrent to a flow of 93% H230j1 to remove the water vapor contained in
the gas. The drying tower is a vertical acid brick lined steel tank lU'-7"
I.D. brick by Ijl'-O" high. The lower section is packed with one layer of 6"
carariic cross partition rin^s and 12 feet of dumed 3" ceramic Intalox saddles.
Acid distribution across the tower diameter is by a cast iron weir trouprh. which
is above the packing and has submerged discharge through closed downspouts. The
reduced top section of the tower, approximately 9'-0" I.D., contains a teflon
pad mist eliminator. Sufficient acid is circulated over the tower so that the
water vapor removed does not significantly reduce the strength of the acid in
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a single pass over the tower. Entrained acia in the gas is removed by the mist
eliminator pad.
The clean dry ;^as and the dilution air (allowed to enter the stream of
gas from the mist precipitator) are now ready to pass through the remainder of
the plant.
From the converter mouths to this point the gases are under suction de-
veloped by two parallel operated single stage centrifugal air blowers. Each unit
is designed to handle 21,2£0 SCFM (32°F and 29.92" Hg) of dry process gas with
inlet conditions of 130°F and 12.7 psig. Discharge pressure is designed at Ili7"
W.C. Each drive motor is rated at 1,000 H.P.
l
Gases from these blowers flow through the shell sides of three gas heat
exchangers (arranged in series) to be heated. The cold heat exchanger is a
vertical, tubular heat exchanger with steel shell and steel tubes. There are
1,750 tubes that are 1 3/V O.D. by 2l|'-0" longj the shell is about ll'-9" I.D.
The tube side cools the gas leaving the fourth catalyst chamber passj the shell
side partially heats the S02 gas before it enters the intermediate heat exchanger.
This unit has f>00 tubes that are 3" O.D. by lU'-O" longj the shell is about
8'-6" I.Do The tube side cools the gas leaving the second catalyst chamber passj
the shell side partially heats the 30% gas before it enters the hot heat exchanger.
This unit has 1,290 tubes (alonized both sides) that are 2" O.D. by 20'-0" longj
the shell is about 11'-3" I.D. The tube side cools the gas leaving the first
catalyst chamber passj the sh?ll side hr;ats the SO? =;as which is to enter the
first catalyst chamber pass.
The catalyst chamber (converter) is a vertical cylindrical steel tank
which is 27'-6" I.D. by about Ul'-S" high. There are four passes or catalyst
beds. The first pass catalyst is supnorted on Meehanite grids; all other
layers of catalyst, are supported on heat resistant C.I. grids. The first pass
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has a lining of high temperature insulating fire brick and is metallized down
to the division plate. 122,006 liters of "type 210 Monsanto Enviro-Chem vanadium
pentoxide catalyst is usedj all catalyst beds have 2" layers of quartz pebbles
top and bottom.
Sulfur dioxide is partially converted (Minimum conversion rate overall
is 96$ of S02 to 803) to sulfur trioxide as the gas passes through the first
catalyst riass. This conversion uses oxygen and produces heat. The gas is
cooled in the hot heat exchanger before it enters the second catalyst mass.
More conversion and generation of heat takes place. The gas is cooled in the
intermediate heat exchanger before it enters the third catalyst mass. More
conversion of S02 to 803 takes place and generates heat. These hot gases flow
through an exterior cooling loop before entering the fourth catalyst mass for
final conversion of S0£ to 803. The gases are cooled in the cold heat exchanger
before they go to the absorbing tower.
A natural gas or diesel oil fired preheater furnace supplies hot gas to
a shell and tube heat exchanger. This system is designed to heat 15,000 SCFI-1
of process gas to the desired catalyst chamber inlet temperature. It is utilized
to bring the catalyst in the catalyst chamber up to the temperature level re-
quired for the catalytic conversion of 302 to 803, whenever catalyst tempera-
tures have decreased due to a prolonged shutdown. The preheater system nay
also be used to supplement the heat requirements of the catalyst system, if an
operating upset or low 302 £as strength reduces the heat available for the con-
version reaction.
The absorbing tower is a vortical, acid brick lined, stsel tank which
is lU'-7" I.D. the brick by approximately U2'-9" high. The tower is packed
in the lower section with one layer of 6" ceramic cross partition rings and
111 feet of dumped 3" ceramic Intalox saddles. There is a cast iron weir acid
X-10
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distributor above the packing; this weir has submerged discharge through closed
downspouts. The reduced top section of the absorbing tower is about 8'-?" I.D.j
it contains an Alloy 20 pad mist eliminator.
The 303 laden gases pass upward through the absorbing tover .counter-
current to a flow of 93$ H2SO|j which absorbs the SO^ contained in the process gas.
Enough acid is circulated over the tower so that the S0% absorbed does not signi-
ficantly increase the strength of the acid in a single pass over the tower. The
process ^as then contains nitrogen, trace amounts of unabnorbed 863, unconverted
S02, and acid mist. As the gas passes through the mist eliminator, the acid mist
particles are almost completely removed. This gas should not exceed 2,5>00 ppm
by volume of S02. The gas passes through a long mild steel duct to the base of
the 360 foot concrete stack for dispersion to the atmosphere.
The strong acid circulating systems utilized to dry the S02 gas from the
purification system (humidifying tower, gas cooling tower, and mist precipitator)
and to absorb the 803 gas from the catalyst chamber are separate systems. Each
system has a pump tank (l8'-0" I.D. by 7'-0" high; vertical, acid-brick lined,
steel closed tank), a circulating pump (vertical, centrifugal, corrosion re-
sistant pumpj 2,200 gpm for drying; 2,300 gpm for absorbing), acid coolers and
a piping system. The systems are interconnected to permit control because the
strength and the temperature of the drying acid must be maintained within certain
limits to obtain the most efficient drying of the process gas which passes through
the drying tower. To obtain the most efficient absorption of 803 from the process
gas passing through the absorbing tower the strength and temperature of the ab-
sorbing acid mast be maintained within certain limits.
Acid circulated over the drying tower is weakened by the water vapor re-
moved from the S02 gas; acid circulated over the absorbing tower is strengthened
by the absorption of the 803. Approximately 35 gpm of 98.0# acid is diverted to
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the S02 Absorption Plant. To counteract these strength changes, the absorbing
tower acid is pumped to the drying tower pump tank. If the 98$ HgSO^ transferred
to the 93/5 pump tank keeps the 93% tank acid above the range of 93.19 to 93.90$
H2SOj,, water is added to dilute the acid.
The dilution of the drying acid by the water vapor from the process gas
and the addition of about 35.5 gpra of 96.$% acid from the S02 drying tower at the
S02 Absorption Plant to the 93$ pump tank raises the temperature of the scid. To
reduce the temperature the 93$ acid is passed through twelve teflon tank type
coolers (located in the 93$ pump tank) which can cool 1,700 gpm of acid to 130°F
with the cooling water at 8l°F. The acid is then returned to the drying tower.
The absorption of the S02 and any addition of water to the 98^ pump tank
raises the temperature of the absorbing acid. To reduce the temperature the ab-
sorbing acid is passed through twelve teflon tank type coolers (located in the
98,5 pump tank) which can cool 2,200 gpm of acid to 175°F with the cooling water
at 8l°F. This acid is recirculated to the absorbing tower.
Water for these teflon heat exchangers is filtered by eight filter units
each of which is 36" diameter and contains Ui^' of filter material: llj cu. ft.
of 5/8" x 1" filter gravel at the bottom, 3^ cu. ft. of 3/16" x 3/8" filter
gravel in the middle, and 7 cu. ft. of 0.81 mm x 1.5 mm torpedo sand on top.
These units are periodically back flushed.
As the acid from the 93$ pump tank is recirculated to the drying tower,
part of the flow is diverted to the crossflcw stripping tower. This tower is
a vertical, acid brick lined, steel tank which is A'9'" I.D. the brick by 29'-3"
high. The lower section is packed with one layer of 6" ceramic cross partition
rings and twelve feet of 3" C.P. rings. The top section of the tower contains
a teflon pad mist eliminator. Air is used to strip out dissolved S02 from the
acid. SOj should be 60 ppm maximum. Part of this acid returns to the 93/S pump
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tank; part of it is cooled in teflon coolers before going to storage tanks as
product acid in the 93.19$ to 93.90$ HgSO^ range. Those teflon coolers are of
the shell and tube type capable of cooling 75 gpm of acid to 110°F. The product
acid pump is an inline, horizontal, centrifugal pump constructed of Alloy 20.
The two product acid storage tanks are each 50'-0" in diameter by 23'-9" high.
Storage can be 327,000 gallons in each. Product acid is loaded into tank trucks
or railroad tank cars for transportation to market.
WATER COOLING TOWgR
The cooling water system has been designed to supply a continuous flow
of cooled water to various equipment cooling jackets, sample coolers, and heat
exchangers throughout the Converter Gas Cooler and auxiliary systems and through-
out the Acid Plant and S02 Absorption Plant.
The cooling tower is 79 feet long, 73 feet wide and U7 feet high; it is
divided into two cells. Structural members and decking are of redwood con-
struction; the basin is concrete; the remainder is of plastic or resin con-
struction. This tower is designed for double cross flowc
Hot water from the process equipment returns to a distribution deck at
the top of the tower, flows downward through the tower fill, and is pumped back
to the process equipment. Nominally 25,000 gpm can be cooled from 101°F to 8l°F
with an ambient wet bulb temperature of 75°F (maximum).
Mechanical equipment at the tower consists of two fans and four water
circulating pumpo (each at 7500 ppm).
Three chemicals are added to the cooling tower water. One is an alkaline
solution of sodium chromste and sodium phosphorate for corrosion inhibition. The
second is an alkaline solution which keeps any solids in the water suspended so
fewer deposits will occur. The third is an amine type chemical to control
bacteria and slime. Both the pH and conductivity are monitored. As the
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conductivity increases, the cooling water pur.^e valve will open and the feed
rate of the corrosion inhibitor will increase. Water is purped to the con-
centrator tailing launder.
Specific items served in the gas cooler area are as follows:, steam con-
denser; steam jet air ejector intercondenser and aftercondenser; gas cooler feed
pumps (pump oil coolers and seal coolers); boiler feed pump oil coolers, seal
coolers and bearing coolers; sample coolers; and soot blower air compressor high
and low pressure cylinder jackets, first and second stage intercoolers and
aftercooler.
Other cooling water users are the seven S02 absorption tower tray coolers,
the DMA. cooler, the stripping tower rectifier cooler, the SOg Absorption Plant
drying acid coolers,the SOg condenser, the coolers for the gas cooling towers
at the Acid Plant and S02 Absorption Plant,' the 93/o and 98$ acid coolers in the
pump tanks, the product acid coolers, S02 Absorption Plant sample coolers, the
302 fan lube oil cooler, the S02 compressor, the Acid Plant fan, lube oil
coolers and the instrument air compressor,
SOOTBLCWER AND INSTRUMENT AIR COMPRESSORS
Sootblower air is supplied by the sootblower air compressor which is lo-
cated in a separate air compressor building. This is a three stage, two cylinder
piston type, oil lubricated, air compressor designed to deliver 8£3 cubic feet of
air per minute at a discharge pressure of 5>00 psig. The compressor is designed
to run continuously vrith the air flow bcin~ controlled by cylinder unloaders and
clearance pocket valves. The first stage discharges at 42 psig, the second stage
at l6l psi-i, and the thira stage at 500 psig. This air is discharged into an
air receiver which acts as a surge chamber for the sootblower system. Sootblower
6
air flows from the receiver through a pressure control valve which reduces the
pressure to 210 psig for use by the sootblowers.
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The instrument air compressor is of the oil- free, non- lubricated type.
It is a Y-type, 2 stage unit with a capacity of 600 CFM at 13.80 psia and 110°F
at intake and a discharge pressure of 100 psig. Air is dried in a desiccant
type air dryer before being distributed throughout the Gas Treatment, facilities
for air controlled instrumentation and for operation of air operated valves.
CONTROL ROOMS
Four: control rooms were provided:
1. Reverberatory electrostatic precipitator: Power and controls for
precipitator; power distribution for soir.e smelter auxiliaries ;
instrumentation for stack monitoring.
20 Converter electrostatic precipitator: Power and controls for pre-
cipitator <>
3. Converter waste heat boilers (gas coolers): Controls and instrumen-
tation for these facilities] controls for balloon flue drag chains
controls for dampers related to balloon flue.
Uo Acid Plant and S02 Absorption Plant: This building is 1|0 '-O11 wide
by 58'-0" long overall. Of the length about 21 feet is for a
control room; 9 feet is for toilets and mechanical facilities;
and 28 feet is for electrical power distribution equipment. The
control room has panels on which information is indicated and/or
recorded, on which are located controls for various units, and on
which alarms warn of significant changes in process conaitions.
REPAIRS
Added onto the Acid Plant and S02 Absorption Plant Control ROOM build-
ing is an instrumentation service shop. This shop is l6'-8" by UO'-O". It has
facilities for instrument maintenance and spare parts storage.
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COMKUNICATIOKS
Communications consist of (l) the public telephone system with telephones
located in the Converter Waste Heat Boiler (Gas Cooler) Control Room and in the
Acid Plant and SC>2 Absorption Plant Control Room; of (2) nine portable radio sets
which are in use as follows: 2 for the Gas Coolers, 2 for the Instrument Sub-
Foremen, and one each for the Acid Plant Operator, the S02 Absorption Plant
Operator, the Repairman, the Gas Treatment Plant Foreman, and the Gas Treatment
Plant Repair Foreman; and of (3) a. Gai-Tronics Industrial Communications System
which has stations at the follo;d.ng locations: Reverberatory electrostatic pre-
cipitator control room, operator's station for No. 1 and Mo. 2 Converters, opera-
tor's station for No. 3 Converter, Converter Waste Heat Boiler Control Room,
Powerhouse, Converter electrostatic precipitator Control Room, air compressor
building, Acid Plant and SOg Absorption Plant Control Room, at the Acid Plant
acid loading station, and on the ground floor level of the S02 Absorption Plant.
PERSONNEL
Manpower requirements are as follows:
1. Converter Waste Heat Boilers (Gas Coolers): four Waste Heat Boiler
Firemen (one each shift plus one swingman); one Boiler Repairman; one
Boiler Repairman Helper; one sub-foreman. All of these are super-
vised by the Power Plant Foreman.
2, Remainder of Gas Treatment Facilities': three Acid Plant Operators;
three S02 Absorption Plant Operators; one Acid Plant Helper; one
Trainee; one Repariman; one Repairman Helper; two Instrument Elec-
trician 3ub-ForR.-r>on (also vrorlc in Gas Cooler area); one Cottrell
Lead Operator. These men are supervised by one Gas Treatment Plant
Foreman and one Gas Treatment Plant Repair Foreman.
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PROBL^I SU.'IXATIQH
Primary problems have been (l) deterioration of done of the humidifying
tower due to wrong material selection; (2) inadequate mist precipitator capacity;
(3) deterioration of tubes in cold heat exchanger because of (2); and (it) piston
and valve problems for sootblower air compressor. Corrections for these are
underway. Compliance i^oa! is to be reached by ueoember 31, 191k •
For presentation at Sraelter Division, Arizona
Section, AIMS meeting at Ajo, Arizona, on
April 26, 197U.
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9r|
'/ — i '
^H:
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S02 ABSORPTION PLANT AT THE NEW CORNELIA BRANCH
OF PHELPS DODGE CORPORATION, AJO, ARIZONA
W. J. CHEN
Gas Treatment Plant Foreman
Introduction
The S02 Absorption Plant at Ajo is designed to treat the Reverberatory
furnace gases, or the converter gases, or a combination of both. Sulfur dioxide
gas from these gases is absorbed by an organic solvent known as dimethylaniline
(DMA) in an absorption tower. Subsequent recovery of S02 gas is achieved by
thermal stripping in a stripping tower. The gaseous S02 is then dried, com-
pressed, and condensed to a liquid form. Liquid S02 is stored under pressure.
As the Acid Plant operations dictate, liquid 303 is vaporized to supplement the
supply of gaseous S02 to the Acid Plant.
Process Description
Reverberatory gases from the reverberatory electrostatic precipitator
are discharged by an induced draft fan through a long 6-foot I.D. insulated
duct to the S02 Absorption Plant. Since the S02 Absorption Plant is not de-
signed to treat all of the gases from the reverberatory furnace, part are dis-
charged to the 360-foot stack. This gas distribution is made by a butterfly
damper between the fan and the stack. A butterfly damper is installed between
the reverberatory precipitator fan and the inlet to the S02 Absorption Plant gas
cleaning facilities. Another similar damper is installed between the converter
electrostatic precipitator outlet and the inlet to the S02 Absorption Plant gas
cleaning facilities. These two dampers allow the S02 Absorption Plant to operate
with straight reverheratory eases or the combustion of both
gases.
Prior to entering the S02 Absorption Plant, the gases are cleaned by
a series of gas cleaning equipment. The gas cleaning section consists of a
humidifying tower into which the gases enter at U00°- 500°F, a packed cooling
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tower, and a mist precipitator. At the humidifying tower, the gases are evap-
oratively cooled, and some of the remaining particulate matter is removed. The
humidifying tower, comprised of two sections, is 15 feet 7 inches in diameter.
The lower section is constructed of steel which is lined with lead and with acid-
proof brick. The upper dome is constructed entirely of 316L stainless steel with
no interior lining. Solution is pumped to the upper dome and distributed over the
tower diameter by spray nozzles made of Carpenter 20 material. The weak acid
solution is circulated through the tower without cooling. The circulating pump
for the humidifying tower is a centrifugal pump. Its impeller and casing are
made of Carpenter 20 material. The related piping material is fiberglass rein-
forced plastic. An automatic level control allows any solution level build-up
due to drain back from the cooling tower and mist precipitator to be purged to
the concentrator tailing launder. The gases from the top of the humidifying
tower enter the side of the cooling tower which is constructed of steel, lined
with lead and with acid-proof brick and packed with polypropylene Intalox sad-
dles. The dish shaped roof is made of fiberglass reinforced plastic. The
weak acid solution is pumped through a series of six shell and tube heat ex-
changers before going to the upper section of the tower. The circulating pump
for the cooling tower is identical to that of the humidifying tower. The shell
and tube exchangers are designed to operate at 75 psia on the tube side and 50
psia on the shell side. The tubes are made of impervious graphite material
whereas the shell is made of steel. The weak acid solution is distributed evenly
over the tower diameter by distribution troughs and as it runs down through the
pacVing, it cools the ascending gases to 90°F. and removes more of the particulate
matter. Make-up water is added to this tower. Excess water is drained to the
humidifying tower for disposal. The gases from the cooling tower enter the bot-
tom chamber of the mist precipitator which is designed to remove sulfuric acid
X-20
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mist from the gas stream to avoid corrosion of ensuing equipment downstream. As
the gases pass through the lead tubes, any acid mist or remaining dust particles
are positively charged and attracted to the inside wall of the grounded tubes.
Droplets of acid run down the tubes and carry particulate matter with them to the
bottom chamber where they are drained by gravity to the humidifying tower for
disposal.
The gases are drawn through the gas cleaning section by a 1000 HP blower,
whose impeller is 316L stainless steel, and discharged into the absorption tower.
The capacity of the blower is 1*9,910 ACFM. Its speed is 3500 rpm. The designed
inlet pressure is minus 28 inches of water whereas the discharge pressure is 82
inches of water. A chain operated valve ahead of the blower controls the volume
of gases into the S02 Absorption Plant. The absorption tower is 13 feet in diam-
eter by 66 feet high and consists of the absorbing section, soda scrubbing section,
and acid scrubbing section. The absorbing section at the bottom consists of 8 valve
trays, three feet apart, and a mist eliminator. The entire section is constructed
of 316L stainless steel. Dimethylaniline from a stainless steel DMA feed tank
(which is 12 feet in diameter by 16 feet high) is cooled by a heat exchanger and
fed into tray 8. DMA flows from one side of a tray to the other side and then
down into the next lower tray. As the gases flow upward, SOp is absorbed by the
MA. Most of the absorption is accomplished in the lower trays resulting in a
decreasing amount of SOp available for absorption in the higher trays. Tremen-
dous amounts of heat are released during absorption, thus the EMA and S02 ab-
sorbed are removed from a higher tray, pumped through a shell and tube heat
exchanger.for coolinp, and returned to the next lower tray. The tubes through
which the DMA-S02 stream pass are made of 316L stainless steel, whereas the shell
is constructed of mild steel. Seven heat exchangers and seven tray cooler pumps
are required in this section. Both the impellers and the casings of these pumps
are made of 316L stainless steel as is all the related piping.
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The soda scrubbing section of 316L stainless steel at the middle of the
absorption tower consists of two bubble cap trays, two feet apart, and a mist
eliminator. The main function of this section is to remove the remaining SOg
from the gas stream and to provide a solution to neutralize the acid from the
acid scrubbing section. A 6% soda ash solution (or caustic soda solution) is
prepared in a 15' x 12' mix tank and transferred to a feed tank of similar size.
Both tanks are made of mild steel. The soda ash solution is fed into the upper
tray of the section and flows by gravity into the lower tray and then into a
stainless steel collection tank which is k feet in diameter by 5^5 feet high.
The acid scrubbing section at the top of the absorption tower consists
of nine bubble cap trays and a mist eliminator. This entire section and internals
are constructed of Carpenter 20 material except the mist eliminator which is made
of polypropylene. The section is designed to remove any IMA vapor before the gas
stream is discharged to the atmosphere through the 50-foot fiberglass stack. The
gases from the stack contain 15 ppm EMA and about 500 ppm S02« 5$ sulfuric acid
is prepared in a 3l6L stainless steel feed tank which is 10 feet in diameter by
10iS feet high. This weak acid feed tank is lined with 1/U" of chlorobutyl rubber
to eliminate corrosion problems which have been experienced since the start-up of
the S02 Absorption Plant. The weak acid is pumped to the top tray and overflows to
the next lower tray. The impeller and casing of the centrifugal weak acid feed
pump are made of Carpenter 20 material. The piping material from the pump to the
weak acid scrubbing section is made of either Carpenter 20 or chlorinated poly-
vinyl chloride material. IM vapor in the exhaust gases is removed by the weak
acid solution which flows by gravity from the bottom tray to the stainless steel
collection tank where neutralization takes place. The pH of the solution is
monitored in order to adjust the soda ash solution feed rate to the absorption
tower and is maintained between 7.0 and 7.5. The solution from the collection
tank flows by gravity to a separator tank.
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The pregnant IMA (IMA loaded with SC2) from the absorbing section of the
absorption tower is heated in the tube side of the pregnant DMA heat exchanger,
made of 316L stainless steel, before entering the stripping tower.
The stripping tower, which is 7^ feet in diameter by 72% feet tall, is
entirely constructed of 316L stainless steel. This tower also consists of 3
sections: regenerating, stripping, and rectifying. The regenerating section,
which generates steam for stripping purposes, consists of 7 bubble cap trays
and a mist eliminator. Water and impurities from the stainless steel regener-
ator feed tank, which is 6 feet in diameter by 6 feet high, enters the top tray
of the section. Water flows from one side of the tray to the other side of the
tray and overflows to the next lower tray. Water from the bottom of the regen-
erating section is pumped through a regenerator heater where steam is generated
and is fed back to the regenerating section. Excess water from the system is
dumped to the concentrator tailing launder. The pH of the purge water is also
monitored for controlling the feed rate of soda ash solution to the absorption
tower.
The stripping section consists of lU valve cap trays and a collection tray.
Pregnant DMA, after taking up heat from the stripped DMA in the pregnant DM
heater, enters the top tray of the section. As the DMA flows down through the
stripping section in a split flow manner, SOg is stripped out of the DMA by the
steam from the regenerating section. In order to attain an efficient stripping
of S02 gas from the DM, a sufficiently high temperature of about 176°F must be
maintained at the lop tray of the stripping section. The stripped DM from the
bottom of the stripping section is pumped through the shell side of. the pregnant
DMA heat exchanger. This DMA loses its heat before entering the separator tank
which is 10 3A feet in diameter by 16% feet high and constructed entirely of
stainless steel. The separator tank allows the separation of DMA - water mix-
tures into a DMA phase and a water phase. DMA, being lighter, overflows from
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the top of the separator tank into the DMA feed tank for reuse. The water phase
underflows from the separator tank through a dip pipe into the regenerator feed
tank for steam generation and disposal.
The rectifying section of the stripping tower consists of five bubble cap
trays, a collection tray, and a mist eliminator. This section is designed to con-
dense both IKA vapor and steam. Make-up water is fed into the top tray and flows
downwards. The hot gas consisting of S02, steam, and some IMA vapor enters the
rectifying section through the two chimneys in the collection tray from which it
is pumped through a rectifier cooler and circulated back to the top tray. As the
cold solution flows downward, both steam and IKA vapor are condensed and flow
through a downcomer into the stripping section. This stream of condensed steam
and DMA mixes with the stripped DMA in the stripping section and flows into the
separator tank for DMA and water separation.
The SC>2 gas which is saturated with water vapor is then drawn by the S02
compressor through a fiberglass duct into the bottom of a packed drying tower
which is h% feet in diameter by 21^§ feet high and is constructed of Carpenter 20
material. The drying tower is packed with ceramic material. 98/5 sulfuric acid
from the Acid Plant is cooled by a series of four shell and tube teflon heat ex-
changers and flows into a distribution trough in the drying tower. Moisture in
the S02 gas stream is removed. The diluted sulfuric acid returns to the 93%
pump tank in the Acid Plant. The dried SOg gas then enters the SC>2 compressor
which is a two stage, reciprocating compressor with automatic volume controls.
When S0j> availability decreases, the compressor unloads into the inlet bottle
rather than the product line. The SC>2 is compressed to 120 psig and is passed
through the tube side of a condenser where cooling water on the shell side con-
denses the hot, gaseous S02 into liquid S02. The product liquid S02 then flows
to the two steel horizontal storage tanks which are 10 feet in diameter by 50
X-24
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feet long. When SOp gas from the Smelter is unavailable or is low in strength,
liquid SOp is vaporized in a vaporizer with steam to supplement the Acid Plant
operation.
Steam from the converter gas coolers is stored in a steam accumulator
in the S02 Absorption Plant for use in the regenerator heater for the stripping
tower and in the S02 vaporizer. Condensate from the steam system is returned
to the converter gas cooler area or to the Power House for reuse.
The SOp Absorption Plant is equipped with extensive instrumentation to
monitor its operation. Both electronic and pneumatic instruments are used to
control the level of various feed tanks, and various trays in the absorption
tower and stripping tower. Differential pressure transmitters in the field
transmit process variable signals to the indicator-controllers in the control
room. These enable the operators to correct any deviation from a normal set
point remotely and with minimum time delay. Audible (HIGH and LOW) alanv.s are
installed to aid the operators in regulating the process variables. Audible
alarms are also installed on every critical piece of equipment to indicate mal-
function of the equipment so that the operators can react accordingly.
Temperature, pressure, conductivity and pH instruments are installed at
strategic positions. The outlet gas temperature from the humidifying tower is
interlocked with the SOp blower operation. A high temperature at the humidifying
tower outlet will automatically shut off the SOp blower. This will stop the
gas flow from the reverberatery furnace to the SOp Absorption Plant in order
to protect the low heat resistant fiber glass reinforced plastic duct.
S02 analyzers are installed to monitor the SOp concentration of the
entrance and exit gases of the Plant. The S02 totalizers which are installed
recently reveal that the inlet gases average about 1.5$ S02 whereas the exit
gases average about 1*00 ppm S02»
X-25
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General Discussion
The S02 Absorption Plant is capable of absorbing SOg from smelter gases
ranging from 1»5% to ?.($ of sulfur dioxide. The governing factor depends on
the volume of 100$ SOg gas that the S02 compressor is capable of handling. The
Plant has not been able to operate for an extended period of time, mainly due to
mechanical failures in various pieces of equipment. The first problem of this
nature was the bearing failure on the motor of the S02 blower. This has been
corrected. Another major problem is attributed to frequent overhaul of the
S02 compressor. Corrective measures to alleviate this problem consist of the
installation of a spare compressor} installation of a weak acid scrubbing tower
between the stripping tower and the drying tower to eliminate any EMA vapor
carryover; installation of a booster pump for additional drying acid to assure
*
complete removal of moisture from tho S02 gas; and additional cooling capacity
for the drying acid to lower the inlet temperature of the S02 gas to the com-
pressor.
Operation at the designed rate in the S02 Absorption Plant has not been
attained so far, mainly due to the inadequacy of the mist precipitator. Ad-
ditional mist precipitators will be installed. Other problems in the S02 Ab-
sorption Plant are: 1. Excessive corrosion noted on the weak acid feed tank
and associated pipings; 2. Rapid deterioration of the upper 316L stainless
steel dome for the humidifying tower; 3« Extensive leakage on the partition
trays in the absorption tower causing undesirable conditions. Corrective
measures for these problems are under way. In addition, difficulty has been
experienced in obtaining supplies of DMA.
For presentation at Smelter Division,
Arizona Section, AIME meeting at
Ajo, Arizona, on April 26, 19?1|.
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Figure 5. SNELIEI; A?.CA nor PLAN.
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WATER 93?SULFURIC ACID
ATMOSPHERE
VEAK AGIO
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ABSORBING
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. 7
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ABSORBER INTERCOOLEP.
AHD PUMP
RECTTTTER
COOLER
COLLECTION
*>, TANK
DMA FEED SEPARATOR
TANK TANK
PREGNANT
DMA HEATER
AND PUMP
STRIPPER
PUMP
STRIPPING
TOWER
Figure 6. SCHEMATIC FLOW SHEET
SO2 ABSORPTION PLANT
so2
COKDENSI
2
STORAGE
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USE OF THE GAS COOLERS (WASTE HEAT BOILERS) IU_ THE CONVERTER DEPARTMENT
AT THE NEW CORNELIA BRANCH OF THE PHELPS DODGE CORPORATION, AJO, ARIZONA
By James B. McBilcs
Power Plant Foreman
Introduction:
On December 21, 1970, construction was started on a Smelter Gas System
Modification at the New Cornelia Branch, Phelps Dodge Corporation; Ajo,
Arizona. On November 20, 1973, modifications were essentially completed.
In these new gas treating facilities, cooling of the copper exhaust gases
is necessary for proper operation. The first gas cooler was placed in
operation on November 17, 1972.
Process Description:
This cooling process was accomplished by installing three identical
converter gas coolers (waste heat boilers) each serving a separate
Peirce-Smith copper converter. The main function of these converter
gas coolers are two-fold. First, and primarily, they are to cool the
converter exhaust gases; and secondly, to produce a steam supply to be
used downstream in the SO Absorption Plant. The gas cooling operation
can be broken down into four (4) systems:
A. Steam and Gas Cooling Systems.
B. Condensatc System.
C. Fecdwatcr System.
D. Miscellaneous Mechanical Systems.
X-?P
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Steam and Gas Cooling Systems; The converter exhaust gases which arc
introduced into the gas cooler cause sudden and extreme load changes.
Gases going in cause a load increase; stoppage of gas flow causes a
load decrease. In order to fully obtain stabilized circulation of
boiler water under these extreme load changes, a forced circulation
type of boiler has been adapted for this application. The forced
circulation type boiler differs in the following respects from the
conventional natural circulation boiler. All the water circulation
necessary for the boiler is done by the boiler water circulation pump.
An orifice is provided at the inlet of each boiler tube so that boiler
water is circulated according to the thermal load of each circulating
circuit. Boiler water is fed to the circulation pump from the drum
through a downcomer. From the pump it enters the boiler inlet header
through the supply pipe. Here in the inlet header the boiler water is
distributed through the orifices to give the boiler tubes their necessary
water supply. While the water is being circulated, heat is absorbed and
causes a mixture of steam and water. This mixture is collected in the
boiler outlet header and enters the steam drum.
The separation of steam from the steam-water mixture is carried
out by the turbo-separator and dry screen which are installed in the
steam drum. The boiler water which is separated from the steam is
then mixed with the boiler fcedwater that is entering the drum. The mixed
boiler water then flows from the drum through the downcomer and back
in to the circulating pump.
Each gas cooler has two 1,350 gallon-per-minute forced circulating
pumps.. One of these pumps is continously running; the other is on
X-30
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standby service, set to start immediately if the operating pump fails
to provide sufficient cooler water circulation flow.
The operation of a copper converter produces sudden surges of hot
exhaust gases when the converter rolls into operating position; this
gas flow is suddenly stopped when the converter rolls out of operating
position.
In order to prevent thermal shock to the boiler during these rapid
load changes, and to prevent the tube-wall temperature from dropping to
near the acid "dew point" (about 400° F), the temperature and pressure
of the steam drum is maintained near the operating condition even when
the converter is idle. Auxiliary steam is fed automatically to the steam
drum through a sparge line, while the gas cooler is idle. The forced
circulating pumps run continually, even during idle periods.
During the operation of the converter gas coolers, the steam produced
in the gas coolers flows in to the main steam header which is equipped
with a back-pressure regulating control valve set to keep the steam drum
pressure at operating conditions (540 psig). From the main header the
steam flows to the deaerator to maintain a constant deaeratbr pressure
and to supply steam to the steam accumulator at the SOo Absorption Plant.
When an excess of steam is produced, the main header pressure will start
rising until it reaches approximately 545 psig. At this point another
pressure control valve will open and let the excess steam into the steam
condenser. During periods when no steam is being produced in the
Converter Gas Coolers, pressure is maintained in the main steam header
by the 800 psig plant steam system (from the reverb waste heat boilers')
through a pressure control valve which is set at 535 psig. This 800 psig
plant steam system also supplies steam for the sparging steam in the three
X-31
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gas cooler drums to maintain near operating pressure and temperature,
steam for the three turbines that drive the circulating pump for each
gas cooler and steam for the jet air ejectors at the steam condenser.
When the gas cooler is in operation (converter rolled in), gases
as hot as 2500° F are produced and forced into the converter exhaust
hood. Ambient infiltration air is drawn past the hood seals into the
gas stream lowering the mixed gas temperature to approximately 1200° F.
The gas then enters the converter gas cooler where heat is given
up to water circulating through the gas cooler tubes, lowering the gas
temperature to 550° F.
When the copper converter "rolls in", a sudden volume increase,
or swell, occurs when steam bubbles are formed in the gas cooler tubes
and cause an abrupt rise in the steam drum level. Similarly, when
the converter "rolls out", steam bubbles quickly collapse, or shrink,
causing an abrupt drop in the drum level. The magnitude of this swell
and shrink has been taken into consideration in the design of these
boilers.
Design pressure for these boilers are 600 psig, operating at
540 psig. Outlet steam temperature is 478° F and feedwatcr temperature
is 248° F. Inlet gas -temperature is 1200° F, and outlet gas temperature
is 650° F, plus or minus 54° F. Boiler tube heating surface is 14,565
sq. ft., and water wall heating surface is 1,960 sq. ft. Steam drum
internal diameter is 72.44 inches, and the internal length is 18' 8.2".
The total boiler water capacity is 6,470 gallons. These boilers are
7-32
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designed to handle 47,000 poundsr-pcr-houT evaporation safely.
Condensatc System; The primary purpose of the condcnsate system
is to condense the steam that is produced by- the gas coolers, but
is not needed, and to start the resulting condensate back to the
gas cooler fcedwatcr system. The condensate system consists of a
condenser, hotwell and condensate return pump,
The condenser is a tube and shell type of heat exchanger.
Steam is condensed on the outside of the tubes in the condenser
shell and collects in the hotwell. The hotwell is a storage tank
located on the bottom of the steam condenser shell to provide surge
capacity for the condensate system and to provide the condensate
pumps with proper suction pressure. The steam is condensed in the
shell of the condenser by transferring its heat into the cooling
water flowing through the condenser tubes. The heat energy that
was initially removed from the converter exhaust gases by the gas
coolers is transferred to the cooling water system and released to
the atmosphere by the cooling tower. The condenser shell operates
under vacuum conditions. A steam jet air ejector is used to evacuate
all of the air and non--condensable gases from the steam side of the
condenser. The flow of condensate from the hotwell is through the
condensate return pumps and into the deacrator.
The condcnsate level is maintained in the hotwell by steam
being condensed in the steam condenser or by the condcnsate being
returned from the condensed steam at the S0? Absorption Plant, If this
docs not maintain the hotwell level, condcnsate from the Power Plant will
X-33
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automatically feed under low level conditions. There are two condensate
return pumps, one having enough condensate capacity for the operation of
two gas coolers.
Condensate enters the deaerator from the condensate return pumps
at a temperature ranging from 80° F to 120° F, depending on the condenser
vacuum.
This deaerator is a two-stage spray tray type combination feedwater
heater and counterflow gas/liquid scrubber. The deaerator pressure is
controlled at 15 psig. Since the deaerator contains both steam and
water in equilibrium, the vessel will operate at saturation temperature
of 248° F. This will increase the condensate temperature as it sprays
into the deaerator and will remove most of the dissolved gases.
Feedwater System: The gas cooler feedwater system consists of two
boiler feed pumps and a drum level control system. These feed pumps
are eight-stage centrifugal pumps, designed to supply enough feedwater
for two gas cooler operation. Feedwater enters the feed pump from the
deaerator storage tanks. This makes it very important to maintain proper
deaerator water level to provide the pump with adequate suction pressure.
The boiler feedwater pumps discharge into a common gas cooler feedwater
header at about 650 psi. With one pump running and the other pump on
standby service, the standby pump will start automatically if the
header pressure drops too low.
linch gas cooler has identical feedwater control systems, separate
from each other, but all connected to the common feedwater header.
The feedwater is fed to the drum through a regulating valve that is
controlled by a three-element control system. This three-element control
system receives inputs from steam flow, drum level and feedwater
X-34
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flow. Each drum level control system operates primarily to balance
feedwater flow with steam flow by modulating the feedwater control
valve. However, the steam flow signal is adjusted by a drum level
correction. This correction is developed by comparing the actual
drum level with the drum level set-point. The drum level set-point is
developed as a function of steam flow. At zero steam flow the drum
level set-point will be at the lower end of its range (-8"). Under
full steaming conditions the drum level set-point will be at or near
the top of its range (+8"). Normal drum level will be any level in
this range. To prevent any high level condition a high level dump
valve is provided, which will automatically dump water from the steam
drum into the blowdown system. This valve is operated from a level
signal that is independent of the three-element control system. This
valve will automatically close just before the normal drum level
set-point is reached.
When the gas coolers are in an idle condition, the pressure and
temperature is maintained by the sparge steam system. This sparge steam
condenses, thereby raising the water level in the drum. A separate drum
level control loop is provided to prevent this undesirable accumulation
of boiler water. This control loop consists of a controller and a
control valve. This controller attempts to maintain the minimum drum
level set-point in a low-low, or no steaming condition. As the steam
flow begins to rise, this valve will automatically close. This
blowdown water is also dumped into the blowdown system.
Miscellaneous Mechanical Systems: All blowdown condensatc from steam
traps, and other waste condensate flows to a blowdown header. This
header is connected to a blowdown tank designed to accept hot flashing
water. The water is collected in the blowdown tank and flows by gravity to
X--35
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the sewer, or to the condensate receiver in the St^ Absorption Plant.
This condensate is automatically pumped to the steam condenser or
back to the Power Plant system.
Gas Cooler Water Treatment; This water treatment system is to prevent
scale from forming in the boiler tubes; to prevent corrosion of the
boiler pressure parts; and also to keep purity of the steam. This
boiler water treatment is a low pH coordinated phosphate treatment.
The chemicals used are tri-sodium phosphate (Na^PC^) and di-sodium
phosphate (Na2HP04). These chemicals are fed into the boiler drum
at a ratio of NasPO^^HPC^ = 9.1 to obtain a control limit of 5 to
15 ppm of P04 with pH value of 9.7 to 10.2. Also added to this
chemical treatment to prevent any oxygen corrosion is sodium sulfite,
Na2S03. This is controlled at 2 to 4 ppm. The dissolved solids in
these boilers are always low because of the automatic blowdown system,
which maintains the drum level when gas coolers are in the sparging
condition. A small amount of filming amines is injected into the
condensate system to prevent corrosion. These filming amines form a
protective film on all metal surfaces.
Sootblowing: Each gas cooler is equipped with its own sootblower system.
The function of the sootblower is to remove dust and any converter ash
from the gas side surfaces of the gas cooler. These sootblowers use
210 psig, air to remove the undesirable accumulations. If the sootblowers
arc not operated regularly, the accumulation will continue to build up
until it will lower the heat transfer of the gas cooler. Each gas
cooler has eight long-retract sootblowers and six wall deslagcrs. The
long retract sootblowers are arranged to clean all the pendant tubes.
The wall dcslagers extend only a short distance into the gas cooler,
just far enough to clean the side wail tubes. The dust is removed from
X-.36
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the bottom of the gas cooler by a screw conveyor. This screw conveyor
is automatically started and stopped by a timer relay. The sootblower
system for each converter gas cooler is provided with an automatic
sequence controller and interlock system. This controller is located
in the gas cooler control room. Only one sootblower system can be
operated at a time. Each system has provisions for automatic (sequential)
operation of the sootblowers, for manual operation of any one sootblower,
and for system monitoring from the control panel. A separate air system
is provided to supply seal air to the sootblower wall boxes. This system
takes air from the Plant 15 psig air header and reduces the pressure to
3 psig before it enters the sootblower wall box seals. This air is
provided to prevent converter gas cooler gas-side pressure from blowing
hot gas out and around the sootblower lances and to cool the lances when
they are in the at-rest position.
-0-
For presentation at Smelter Division,
Arizona Section A.I.M.E. Meeting
at Ajo, Arizona, on April 26, 1974.
X-37
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,—, ^«,4c*r p*easv*.e \
\ S CeVTVtOfc t/ALVf '
-------
.'TECHNICAL REPORT DATA . .
(Please read Itiitntctions on i/ie reverse before completing)
1. REPORT NO.
2PA-600/2-76-036f
2.
3. RECIPIENT'S ACCESSION'NO.
4. TITLE AND SUBTITLE
Design and Operating Parameters for Emission
Control Studies: Phelps Dodge, Ajo, Copper Smelter
5. REPORT DATE
February 1976
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO.
I. J. Weisenberg and J. C. Serne
9. PERFORMING ORG \NIZATION NAME AND ADDRESS
Pacific Environmental Services, Inc.
1930 14th Street
Santa Monica, CA 90404
10. PROGRAM ELEMENT NO.
1AB013; ROAP 21ADC-061
1 1. CONTRACT/GRANT NO.
68-02-1405, Task5
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Task Final; 4-10/75
14. SPONSORING AGENCY CODE
EPA-ORD
IS. SUPPLEMENTARY NOTES
EPA Task Officer for this report is R.Rovang, 919/549-8411, Ext 2557.
is. ABSTRACT
gjves background design data for a specific copper smelter.
The data is sufficiently detailed to allow air pollution control system engineering
studies to be conducted. These studies will be concerned primarily with lean S02
streams that currently are not being captured. Physical layout of the smelter and
the surrounding area is presented, along with existing control equipment. Ductwork
that would be considered for future system tie-in is defined. Emissions from
operating equipment, gas flow rates, temperatures, sulfur balance, and a process
flowsheet are included. Utilities, stack dimensions , footing requirements , and
solid waste handling are defined. Available area for new control equipment, gas
characteristic variation, and potential new control equipment installation
problems are discussed.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Air Pollution
Copper
Smelters
Design
Sulfur Dioxide
Utilities
Air Pollution Control
Stationary Sources
Emission Control
Operating Data
Solid Waste Handling
Wastes
13B
07B
11F
18.. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
69
70. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
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