Electrode system

The invention relates to an electrode system for melting and stirring and also for temperature control in metallurgical vessels. To achieve optimum energy utilization with minimal gas consumption, the electrode system comprises, according to the invention, a central electrode and an outer electrode (10, 11) which are each attached to a height adjustment (12) and are connected to a common electric power source (16), to form an electric arc between central electrode and melt below the surface of the melt bath, and an annular space (23) between central electrode and outer electrode (10, 11), which is connected to a gas source (25), with the gas system being designed in such a way that finely particulate additives can also be charged into the melt.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to an electrode system for melting and stirring and 
for temperature control in metallurgical vessels. The heat source is an 
electric arc between central electrode and melt. This can, in particular, 
also be operated under the surface of the bath. As a result of the 
immersed operating state, the flushing and heating can be achieved in a 
single step using one gas feed. 
2. Description of the Prior Art 
For electrode systems for immersion burners, as for other heating systems 
in metallurgy, a high efficiency of energy utilization is required, 
because the melting and further heating of the lumpy material requires 
high melting power. To homogenize the melt in respect of temperature and 
composition, the melt also has to be stirred. In addition, in a continuous 
mode of operation, the charging of particulate raw materials and additives 
into the melt has to be made possible. Furthermore, the melting and 
heating process should be flexible in respect of the raw materials and 
additives and also result in low emissions and small amounts of waste. 
SUMMARY OF THE INVENTION 
It is therefore an object of the invention to provide an electrode system 
for melting and stirring and also for temperature control in metallurgical 
vessels, by means of which optimum energy utilization can be achieved with 
minimal gas consumption and which also makes possible environmentally 
appropriate processing of hazardous, dust-like residue materials. 
In the electrode system of the invention, the immersed operation of the 
electric arc between central electrode and melt (metal or slag) in 
combination with suitable metering in of gas achieves a very high 
efficiency of energy utilization, because the dissipation of the electric 
arc onto the furnace lining (walls and lid) no longer occurs. The hot arc 
gases heat the feedstock and are cooled significantly while rising through 
the melt. The furnace atmosphere is therefore not too hot, so that the 
metallurgical vessels above the surface of the melt bath do not have to be 
provided with cooling. In one embodiment of the electrodes made of 
graphite, the entire immersion lance facility can be operated safely and 
reliably without additional cooling. In the case of aluminum or copper 
melts, the graphite electrode materials do not react with the metal bath. 
In the case of steel melts, the outer electrode can be provided with a 
coating of refractory material to reduce the undesired carbon enrichment 
of the steel melt. If the melt should not come into contact with graphite, 
the end of the outer electrode which dips into the melt can be coated 
externally and internally with ceramic and the electrical circuit is 
closed via central electrode--melt--bottom electrode. 
In immersed operation, a minimal gas consumption is required for melting 
and further heating of the raw materials, which, owing to the omission of 
the separate flushing gas and reduced homogenization times, is achieved by 
suitable positioning of the electrodes. The gas requirement of Ar or 
N.sub.2 or reducing gas is only 50% of that of blowing systems. Via the 
annular space between the central and outer electrodes, particulate 
materials, in particular dusts, can also be introduced together with the 
blown-in gas directly into the interior of the melt, which avoids 
uncontrolled material losses, for example into the slag or the waste gas 
system. The further charging is carried out in the hotest part of the 
melt, so that the solid materials can be melted and dissolved more 
quickly. At the same time it is ensured, in the addition of mixtures, that 
components having a low boiling point, for example Pb and Zn, are largely 
evaporated. 
The invention also makes possible environmentally appropriate processing of 
hazardous, lumpy to dust-like residue materials, such as filter dusts from 
steel production and refuse incineration or aluminum sweepings or residue 
materials from grinding operations, because the electrode space has a 
closed configuration, the residue materials are introduced not onto but 
into the melt and the hot metal bath makes the inorganic and organic 
pollutants nonhazardous. 
An example of the invention is shown in the diagram and is described in 
more detail below.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The electrode system shown in FIGS. 1 and 2 comprises a central electrode 
10 and an outer electrode 11, which are each hung on a support column 13. 
By means of the height adjustment 12, the electrode bearer arms 14, 15 can 
move together and individually and can thus be positioned independently of 
one another. The two electrodes 10, 11 are connected to an electric power 
source 16, with the supply of electricity being carried out, as a matter 
of choice, via cable or conductor-rail connections or via electrically 
conductive electrode bearer arms. 
For controlled operation of the furnance, the support column 13 and the 
bearer arms 14, 15 are provided with a sensor system 31 which detects the 
respective electrode position. The sensor system comprises a toothed rack 
which is mounted on the support column and a pinion potentiometer system 
on each bearer arm. The linear movement of the bearer arms is converted by 
the rackpinion potentiometer system into an electrical potential, with the 
potential changing in proportion to the distance travelled. In addition, 
absolute positions are detected so that a one-off calibration, for example 
on assembly, is sufficient for position determination. 
Below the electrode system there is arranged a metallurgical vessel 17. The 
metallurgical vessel 17 can be equipped with transport rollers 18, 19 by 
means of which it can be moved on rails 20, 21. In addition, it is 
possible for the support column 13 to be designed as a kingpin so that the 
components 10, 11, 12, 13, 14, 15, 23, 24, 29, 30 and 31 can be swivelled 
about the axis 1. For melting lumpy material, the system can be operated 
using the central electrode 10 alone, if a bottom electrode connected to 
the electricity supply is installed in the metallurgical vessel. If a 
bottom electrode is not provided, the electrode system is lowered into the 
metallurgical vessel 17 so that during the homogenization phase the 
electrically conducting central electrode 10 and the outer electrode 11 
dip below the surface of the melt 22 (FIG. 2). Gas, for example argon 
(Ar), nitrogen (N.sub.2) or, if desired, also reducing gases, flow through 
the annular space 23 formed between central electrode 10 and outer 
electrode 11. The gas flows from the side away from the melt 22 via the 
line 24 connected to a gas source 25 into the annular space 23 and from 
there into the electric arc burning between central electrode 10 and the 
surface of the melt bath, which arc thus heats the gases. The hot gas 26 
escapes under the outer electrode 11 through the melt 22, transfers energy 
to the latter and sets it into motion for homogenization. Particulate 
materials, in particular dusts, can also be introduced together with the 
blown-in gas directly into the interior of the melt 22, which avoids 
material losses, for example into the slag or the waste gas system. 
Environmentally appropriate processing of hazardous, dust-like residue 
materials is also achieved by a closed system being provided by means of a 
lid 28 closing the metallurgical vessel 17. The lid 28 is here in 
apposition with the outer region of the outer electrode 11. As a result of 
the very low gas consumptions, the amount of waste gas formed is small. 
Furthermore, to avoid gas losses, a seal 29 is provided, above the gas 
inlet, to close off the annular space 23 between the central electrode 10 
and the outer electrode 11. The seal 29 seals off the annular space 23 
from the atmosphere. The closed system can, for disposal of hazardous, 
dust-like or gaseous residue materials, be connected to a disposal system 
not shown in more detail. 
In addition, it is possible in principle to design the central electrode 10 
likewise in the form of a pipe, so that a further gas channel 30 can be 
utilized. This is particularly advantageous if gas mixtures are used, but 
the amount of one type of gas is, for cost reasons, to be kept as small as 
possible and nevertheless the desired gas atmosphere is to be set in the 
region of the arc. That is the case, for example, in the reduction melting 
of finely particulate materials. The material is supplied together with 
nitrogen via the annular gap 23 between the central electrode and the 
outer electrode and the reducing gas, for example hydrogen (H.sub.2) or 
methane (CH.sub.4), is fed in through the drilled hole 30 of the central 
electrode 10.