PRODUCTIVITY INCREASE IN A PEIRCE-SMITH CONVERTER
USING THE COP KIN AND OPC SYSTEM
Thomas Prietl1, Andreas Filzwieser
2 and Stefan Wallner
3
1Christian Doppler Laboratory for Secondary Metallurgy of the Non-Ferrous Metals
University of Leoben, Franz-Josef-Strasse 18, 8700 Leoben, Austria 2RHI Non-Ferrous Metals Engineering GmbH
Magnesiststrasse 2, 8700 Leoben, Austria 3RHI Refractories, Business Unit Industrial
Wienerbergstrasse 11, 1100 Vienna, Austria
Key Words: Gas stirring, COPKIN, endpoint, OPC
Abstract
The use of gas stirring systems through the furnace bottom is common for anode and holding
furnaces in the copper industry The first implementation of a gas stirring COP KIN®
system in a
Peirce-Smith converter was performed at the New Boliden smelter, Rönnskar, Sweden. In
addition to other benefits, a decrease in process time and a decrease of the oxygen content in the
blister copper were observed. To determine the effects of the gas stirring system and the process
endpoint, an optical production control ‘Semtech OPC system’ was used. The light emission of
the converter flame as an optical process parameter provides qualitative on-line process
information, and is also used for endpoint determination of the slag making process, on-line
control of iron content in white metal, quality control of slag etc. The results, benefits and risks
of using the COP KIN®
and OPC system for a Peirce-Smith converter are reported.
Introduction
In order to meet stricter product-quality criteria, increasing productivity demands, tighter
energy and environmental constraints, increasing fluctuations in raw-material composition etc.,
pyrometallurgical processes are getting more and more complex and thereby more difficult to
operate and optimize. At the same time, cost-benefit arguments cause the smelting plants and
also the individual processes to become larger with increasing throughput rates, meaning that a
modest efficiency increase in one single process step might have a significant effect on the
plant profitability. Process optimization and control are becoming increasingly important. In
most facilities the operation is guided by static models, based principally on process modeling,
operator experience and the accumulated information on material input and output. The
conversion of copper in a traditional Peirce-Smith (PS) converter might be used to illustrate the
different but complementary nature of this steady-state optimization and dynamic production
control, which can assist in maintaining stable process operation in the face of disturbances.
Examples of disturbances that might enter the conversion process are unforeseen changes in
quality and tonnage of incoming matte and silica, availability and grade of cold charge, operator
interventions, shift changes, timing of cranes etc. In the conversion of copper in a PS converter,
some of the more important entities to optimize are blister-copper quantity, sulfur, oxygen and
impurity contents of blister copper, slag composition and slag temperature. They can all be
controlled by adjustment of the input to the process.
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Converter and Fire Refining Practices
Edited by A. Ross, T. Warner, and K. ScholeyTMS (The Minerals, Metals & Materials Society), 2005
Temperature, for instance, is controlled by the adjustment of air-blow rate, oxygen enrichment
and additions of cooling material. Blister copper quantity and quality are controlled by
optimization of the endpoints of the various blowing steps and the slag quality. The latter, in
turn, is controlled via silica additions. Obviously there are many means for affecting and
controlling the process and thereby the resulting output. On the other hand, there are very few
objective means for finding out the most appropriate action at a given point in time once the
process has started. Or, to be more specific, there are very few means by which to retrieve
objective information on the instantaneous status of the process, for instance as regards to slag
quality or instantaneous oxygen stage. The highly aggressive environment in smelters has
hampered the implementation of sensors for on-line measurements, which is a necessity for true
dynamic control. Consequently, true dynamic production control has developed at a slow pace.
The RHI COP KIN system
The increasing costs of the production process lead to the development of new refining
processes. The gas treatment with different gases (inert and reactive) is one possibility of such a
technology. Removal of unwanted particles from molten melt by flotation is one of the most
useful melt cleaning techniques used by the industry. Increasing the kinetics of chemical
refining reactions between slag and metal is another effect of the gas treatment. Gas injection
through the furnace bottom has been practiced in the steel industry (ladles) for more than 30
years and also in the non-ferrous industry (e.g. anode furnaces, holding furnaces, Peirce-Smith
converter etc.). There are several reasons why the non-ferrous industry does not use stirring
systems to an adequate extent. In the past no supplier would warranty the engineering, hard
ware and start-up know-how for a completely proven gas stirring system and the risk was fully
with the smelter.
This was the primary reason that 2002 the RHI Non-Ferrous Metals GmbH based in Leoben,
Austria was founded. Today RHI provides a complete gas stirring system called the
“COP KIN (Copper Kinetics) system”. This system can be easily adapted to the needs of each
customer. The gas control station is the main part of the COP KIN system. The gas station is
equipped with a certain number of gas inlets e.g. for nitrogen, air and/or natural gas and also a
certain number of outgoing pipes to the purging plugs. To guarantee a consistent stirring action
the gas pressure must be carefully monitored in real time by the control panel. A minimum
pressure of 6 bar for the inlet gas is required to ensure the gas station has the flexibility to keep
the mass flow at a constant level.
The software controls each plug individually to achieve a constant flow rate. This software is
runs independently of the furnace computer system on site and allows a constant monitoring
and adjustment of the gas flow rates as required in the treatment phases of the process.
Depending on the particular application different gas mixes and flow rates per single plug can
be programmed. In the case of an emergency, several safety devices are installed, e.g. if an inlet
gas line is blocked for some reason the control station will immediately switch to the back-up
second incoming gas line immediately and an alarm will be given. After defining the need and
targets of a gas stirring system the right type, number and position of the plugs have to be
calculated. For this engineering work the CFD software Fluent is used. In Figure 1 the parts of
the COP KIN system are shown [1].
178
gas control stationporous plug with well block
control panel
Figure 1: COP KIN system
The purging plugs are produced in various designs as a consequence of the design and
refractory improvements over the years. The lifetime of individual plugs is governed by their
exposure to chemical, operational, mechanical and thermal conditions. The most common
purging plugs in the non-ferrous industry are fired porous plugs, which are characterized by a
high opening rate, an optimal bubble formation and a long in-service lifetime, but other plug
types are also used (Figure 2) [2]. The porous plugs are covered with stainless steel and include
thermocouples, which are connected to the gas control station, to monitor the plug wear. Today
it is known from longstanding experience that the wear of a porous plug using inert gas only
(e.g. nitrogen) is similar to the wear of the surrounding lining. It is also possible to use air or
pure oxygen as a purging gas (reaction gas), but this results in increased plug wear.
For these reasons a changeable plug arrangement was developed. To have the possibility to
change plugs in such a short time and under hot conditions leads to a higher purging
performance because it is now contingent to also use reaction gases. Non-changeable systems
are often taken when changeable systems are not required. In Peirce-Smith (PS) converters a
changeable system is not necessary because the normal tuyere zone repair could also be used to
change the plugs.
179
Figure 2: Purging plug types
Application of the COP KIN system in a Peirce-Smith converter
The dominant copper smelting technology today is the combination of flash furnace, PS
converter and anode furnace, which has been widely used in the copper smelters worldwide. In
2002 the first COP KIN system was installed in one of the PS converters at the copper plant
New Boliden, Rönnskär, Sweden. Initial trials have indicated that the use of an additional
bottom gas stirring system provides metallurgical benefits. The first test trial was carried out
with two purging plugs to determine if the wear of the plugs in the converter cause operational
problems. After a normal operating period of 12 weeks, it was evident that no specific wear had
occurred using the porous plugs. In a second trial, four plugs were installed and the operational
safety and stability was evaluated. In a third and fourth test campaign the advantages of using
the COP KIN system during a whole converter lifetime (time between relining) were carried
out. At Boliden to convert matte with a copper content of approx. 60 % into blister copper (98 –
98.5 % Cu), eight steps need to be performed:
1. Charging
2. First slag blowing
3. First slag tapping
4. Matte blowing
5. Second slag tapping
6. Copper blowing
7. Tapping of the copperoxidic slag
8. Copper tapping
The implementation of the COP KIN system in a PS converter will affect the following
benefits on the various process steps:
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Charging
When the fist ladle of matte is charged into the converter it is not used as a metallurgical reactor
because the tuyere zone is out of the blowing position. To have the possibility to blow air
through the porous plugs to start the first slag blowing, the iron slagging reaction will start
immediately and the converter will be in operation from the very beginning.
First slag blowing and matte blowing
During these two steps the COP KIN system is used to boost the stirring effect in the dead
zone opposite the tuyeres. Different tests with various flow rates of purging gas were used
during these two steps. For the endpoint determination of the two periods the Optical
Production Control (OPC) system was available.
First and second slag tapping
With the use of the COP KIN system it is possible to individually control the flow rate of each
plug. Operating the plugs near the converter endwalls at a maximum flow rate (300 l/min) and
all other plugs at a minimum flow rate (10 l/min) will create a certain slag movement to the
charging/tapping door. This will result in easier slag work combined with improved separation
of slag and white metal. To remove most of the fayalite slag after the matte blowing step is
important because the less fayalite slag remaining in the converter, the more effective the slag
work during the copper blowing will be; and the lower the amount of copperoxidic slag that
will be produced.
Copper blowing
In the copper blowing process the white metal is converted into blister copper (equation 1, 2).
Cu2S + 3/2 O2 Cu2O + SO2 (1)
2 Cu2O + Cu2S 6 Cu + SO2 (2)
While the white metal is still present in the bath, the purging gas will help to minimize the dead
zone in the converter and increase the homogenization in the bath. At the end of the copper
blow a copper oxide rich slag forms. Several effects can be seen as a result of using nitrogen as
the purging gas:
The desulfurization is initiated earlier due the decreased partial pressure of SO2 in
the bath; result of the rising gas bubbles.
The oxygen efficiency increases due to improved agitation
The surface between the slag and the blister copper increases as well as the
interaction rate between both.
The amount of copperoxidic slag decreases
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Copperoxidic slag tapping
As mentioned before with the COP KIN system it is possible to control the flow rate of each
plug separately and so a certain movement of the slag towards the tapping door can be
achieved.
Copper tapping
To discharge a PS converter with 300 tons of blister per cycle, takes at least on hour. With
nitrogen as purging gas the converter can be used as a metallurgical reactor and the sulfur
content can be reduced during the discharging period. If a COP KIN system is also installed in
the anode furnace these two purging systems can work concurrently and further optimize the
process operation.
The aims at Boliden were to achieve better slag tapping, lower sulfur and oxygen contents in
the blister copper, less copperoxidic slag and as a result in consequence a reduction in process
time. Boliden has a specific PS converter process, because there is no possibility in the anode
furnace for an oxidizing step, so the have to reach a sulfur level of less than 100 ppm has to be
reached in the converter. To reach this level it is necessary to over-blow the melt, which
subsequently produces a high amount of copperoxidic slag. To compare the data from converter
1, which was equipped with the COP KIN system, with the values from the other two
converters without a stirring system, the Optical Production Control (OPC) system was used. It
was also important for a specific converter driven by the operating teams and for the endpoint
determination of the different blowing steps at the converters. In the following paragraph the
OPC system is explained [3-7].
The Semtech OPC system
For about 15 years Semtech has developed and industrialized a remote-sensing technology,
based on optics and spectroscopy, for continuous on-line process monitoring and production
control of various pyrometallurgical processes; the Semtech OPC (Optical Production Control)
System. The light emitted by the off-gas flames of a pyrometallurgical process is composed of
heat radiation from particles and droplets and discrete radiation from atoms and molecules in
the vapor phase. The radiation from the latter shows up at well-defined wavelengths, which are
characteristic for each atom and molecule and with intensities which depend on the gas-phase
concentration (e.g., the vapor pressure) of the light-emitting atoms and molecules.
The presence and concentration of a specific atom or molecule in the off-gases is, on the other
hand, determined by the thermodynamics and kinetics inside the furnace, e.g., oxidation stage,
slag composition and temperature. Thus, by analyzing spectroscopically the light emitted by the
off-gases, it is possible to obtain information on what is occurring inside the furnace. The
interest in spectroscopic methods to control smelting processes is triggered by a number of
attractive features inherent in optical measurements:
They can be performed remote, e.g. without introducing any physical sensor into the
furnace,
They can be performed on-line, e.g. sampling is not a prerequisite for the measurement,
They facilitate the detection of short-lived constituents like radicals,
They can provide continuous real-time information,
They are insensitive to electronic noise.
182
In principle the OPC system consists of
One to four light-weight telescopes, which focus light from the off-gas flames into
Optical fibers. The fibers transmit the light to the OPC Server where it enters
A spectrometer. The dispersed light is registered by
A multichannel detector and the spectroscopic information is evaluated in terms of
optical process parameters by
A PC. The optical process parameters are displayed on-line as trend curves (Figure 3)
on color monitors in front of the.
Figure 3: Semtech OPC trend curves at the end of the copper blowing step
One server can handle the input from up to four telescopes and thereby be used for
simultaneous control of the production in four furnaces or the status at different locations in one
furnace. Figure 4 shows the general layout of the OPC system designed for use at four PS
copper converters.
Figure 4: Schematic layout of Semtech OPC system monitoring the instantaneous process status
in four PS converters
183
The small, robust telescope focuses light from the off-gas flame into an optical fiber. The focal
length of the telescope is very short as compared to the distance to the converter mouth. In this
way the light entering the fiber emanates from various parts of the flame. Thus it represents the
average composition of the gas phase that is the average status of the melt. This is in contrast to,
for instance, conventional sampling via the tuyeres of a PS converter, in which case the analysis
generally yields information on the local conditions in the neighborhood of the tuyeres. For
instance, it generally appears that close to the end of a copper-making step a blister sample via a
tuyere shows higher oxygen content than a spoon sample taken via the converter mouth.
The fiber is connected to a conventional spectrometer equipped with a CCD camera with the
output analyzed on a PC. The spectroscopic information is presented in the form of trend curves
and displayed on color monitors in front of the converter operators and exported to existing data
collection systems. Figure 5 shows an on-line recording from a full converting cycle in a PS
converter. The diagram is a xy-plot of the current values of three different Optical Process
Parameters versus real time. The graph exemplifies what can be seen on a client monitor at the
end of the cycle noting that during the cycle the graph develops gradually. Basically the optical
process parameters included in Figure 5 represent time-resolved registrations of the intensities
of selected emission bands of the PbS (yellow curve) and PbO (green curve) molecules and the
ratio between the intensities of selected emission bands of the CuOH and PbO molecules (red
curve) [8, 9].
0,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1,0
11.00 12.00 13.00 14.00 15.00 16.00 17.00
Real time
Opt
ical
Pro
cess
Par
amet
ers
(arb
itrar
y un
it)
Figure 5: On-line recording of the optical process parameters PbS, PbO and CuOH/PbO during
a copper converting cycle
The behavior of the Optical Process Parameters PbS and PbO during converting can be seen to
be in qualitative agreement with the thermodynamic prediction of their vapor pressures (Figure
3). As long as the FeS and SiO2 contents of the matte match, that is as long as a fluid slag is
being formed, PbS takes on a high and PbO a low value. When the end of a slag-forming step is
approached PbS starts to decrease and PbO increases, the reason being the increasing oxygen
potential as the matte is being depleted of iron. Thus, close to the end of a step the Optical
Process Parameters gives continuous information on the iron content of the white metal. During
the copper-making step the vapor pressure of PbS and the corresponding Optical Process
Parameter are low while the PbO vapor pressure and the optical parameter PbO are high. The
abrupt change in the value of the Optical Process Parameter CuOH/PbO close to the end of the
step reflects a phase change, namely the disappearance of the white-metal phase and the onset
of the copper-oxide production.
184
The OPC technology has been tested and also permanently implemented at a variety of
metallurgical processes. Naturally the useful spectroscopic information varies between different
processes. However, a common feature of all Optical Process Parameters is that the oxygen
potential or the oxidation stage inside the furnace determines their behavior. Consequences of
using a Semtech OPC System for process optimization are shown in Figures 6, 7 and 8. OPC ok
means that the Semtech OPC system was in operation, not ok the opposite [10, 11, 12].
0,0
0,1
0,2
0,3
0,4
0,5
0,6
0 2 4 6 8 10 12 14 16 18 20 22 24 26
%Cu in slag
Rel
ativ
e fr
eque
ncy
OPC OK OPC not OK
Figure 6: Copper losses in slag
0,00
0,05
0,10
0,15
0,20
0,25
0,30
10 15 20 25 30 35 40 45 50 55 60
% Fe3O4 in slag
Rel
ativ
e fr
eque
ncy
OPC OK OPC not OK
Figure 7: Fe3O4 in slag
185
0,00
0,05
0,10
0,15
0,20
0,25
200 220 240 260 280 300 320 340 360 380 400 420
Total blowing time / cycle (minutes)
Rel
ativ
e fr
eque
ncy
OPC OK OPC not OK
Figure 8: Total blowing time
Results of the tests using the COP KIN and OPC system at a PS converter
The aim at the New Boliden smelter was to make possible a more complete and faster tapping
process of different slags by using eight purging plugs. Special attention was paid to the second
fayalite slag. This has, when it is carried in large amounts into the blister copper blowing a
phase, a disadvantageous effect on the properties of the subsequent copperoxide rich slag.
Furthermore, a better tapping of the fayalite slag would reduce the amount of copper oxide-rich
slag. At Boliden, because of a lack of an exhaust system for the SO2-containing waste gas, it is
not possible to further lower the sulfur content by oxidation in the anode furnace. For this
reason the sulfur content in the blister copper must be adjusted to about 100 ppm in the
converters already and in order to achieve such a low sulfur content, there must be an over
oxidation of the melt. The oxygen contained in the copper, which causes problems when the
anodes are cast, must then be removed at great effort via a reduction process in the anode
furnace. The excessive oxygen content causes a high by the large number of Cu2O precipitates
in the solidified metal so that the ears of the anodes break off.
By carrying out several experiments with various rates of purging with nitrogen or air, it was
investigated whether the time needed to reach a sulfur content of 100 ppm in blister copper
could be reduced. Furthermore it was investigated whether the desired sulfur content could be
achieved with a lower oxygen demand by having the purging bubbles lower the SO2-partial
pressure in the melt. The results with the developed optimal purging program are shown in the
following Figures. In Figure 9 the position of the porous purging plugs in the PS converter is
detailed.
Figure 9: Position of the plugs in the PS converter
186
The optimal purging rates during the various process steps were carried out in several different
experiments and the result, the performed purging program, is apparent in Figure 10. The whole
purging program consists of divers sub-programs.
Figure 10: Performed purging program
With the performed purging program it was possible to lower the sulfur content and the amount
of dissolved oxygen in the blister copper by increasing oxygen efficiency (Figure 11).
51,0
70,0
67,1
40
45
50
55
60
65
70
75
sulf
ur
con
ten
t [p
pm
]
conv 1 with purging plugs conv 2 all conv 3 all
3
2
1
Figure 11: Sulfur content in the blister copper; converter one was equipped with the
purging plugs
The oxygen in the blister copper in converter one was more than 1000 ppm lower than the other
converters without the COP KIN system. Also, the time to reach the endpoint after the copper
turn (the white metal phase is gone) could be abbreviated (Figure 12).
187
22,9
27,3
29,1
20
21
22
23
24
25
26
27
28
29
30
[min
] for
300
tons
and
700
Nm
3/m
in
conv 1 with purging plugs conv 2 all conv 3 all
3
2
1
Figure 12: Time needed to reach the endpoint after copper turn
With the sub-programs used during the slag tapping steps a forced movement of the slag to the
charging/tapping door was seen. This is reflected in a better tapping of the fayalite slag and a
lower amount of copperoxidic slag at the end of the conversion process (Figure 13).
18,6
26,0
21,8
17
18
19
20
21
22
23
24
25
26
27
Konvertoren
ton
s co
pp
ero
xid
ic s
lag
conv 1 with purging plugs conv 2 all conv 3 all
2
3
1
Figure 13: Produced amounts of copperoxidic slag
It was possible to achieve good results with the use of the COP KIN and Semtech OPC system
during this pilot project. Total savings have been calculated from the theoretical and
experimental data for 350 production days. By reducing the copper-oxide rich slag by one ton,
there is a timesavings of 0.5 minutes. Furthermore, 2.6 minutes for the copper blowing can be
reduced (according to New Boliden) by an increase in the oxygen utilisation by 1%. Besides
this there is an average savings of 5 minutes during the final copper blowing period (experiment
results). By using the plugs, the copper-oxide rich slag could be reduced by approx. 5 tons, i.e.,
2.5 minutes can be saved. In total, a savings of approx. 10 minutes could be saved during one
blowing cycle. If both systems are installed in all of the three converters, at New Boliden, you
will get approximately 22 blowing cycles (6600 tons of blister in a 300 tons converter) more per
year. For 350 production days and an average price for the blister copper of € 300, a benefit of
1.98 million €/year occurs.
188
Another important factor is the oxygen content in the blister copper. The consumption of
ammonia in the anode furnace (at New Boliden) depends on that amount. With the amounts of
oxygen in the blister copper using the COP KIN and Semtech OPC system, savings in process
time in the anode furnace operation are also possible. In the future the New Boliden copper
plant is going to install the COP KIN system in all converters.
Conclusion
Using the COP KIN and Semtech OPC system in the converter production control i. e. shorter
blowing times, less copper losses in slag a.s.o. can be achieved. For both systems the working
reliability and economy were sufficiently examined.
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