Method for producing metals, such as molten pig iron, steel pre-material and ferroalloys

With a method for producing metals, the raw material is melted in a metallurgical vessel by at least one plasma burner directed from top to bottom. In order to be able to protect the furnace brickwork from too strong a thermal load exerted by the plasma jet, and to make available the energy supplied by the plasma burner to melting and reducing the fine ore to as large an extent as possible as well as to prevent an agglomeration of the raw material to be used, the raw material is topcharged into the metallurgical vessel in the form of fine particles directed parallel to the plasma jet so as to peripherally surround the same. Oxygen-containing gases and carbon are bottom-blown into the vessel through the melt. A foamed slag is formed in the vessel, surrounding the plasma jet over its total height and the flow of supplied raw material particles peripherally. In an arrangement for carrying out the method the plasma burner is peripherally surrounded by a jacket so as to form a supply space for the fine raw material particles which surrounds the plasma burner peripherally. Nozzles are provided in the bottom of the metallurgical vessel to supply oxygen-containing gas and carbon.

BACKGROUND OF THE INVENTION 
The invention relates to a method for producing metals, in particular 
molten pig iron, steel pre-material or ferroalloys, from 
metal-oxide-containing raw material, the raw material being melted in a 
metallurgical vessel by means of at least one plasma burner directed from 
top to bottom, as well as to an arrangement for carrying out the method. 
The processing of fine ores to liquid metal, with the reduction aggregates 
presently in use, requires pre-agglomeration. If, for instance, 
fine-grained iron ores are to be reduced and melted to liquid metal, which 
usually takes place in a blast furnace or in an electric reduction 
furnace, it is necessary, in order to achieve a yield as economical as 
possible and a good reduction performance with as low a fuel consumption 
as possible, to make the ore lumpy by sintering, pelletizing or 
briquetting. 
This also holds for the production of ferroalloys (FeCr, FeMn, FeW, FeNi, 
FeSi, . . . ), which are melted primarily in electric reduction furnaces. 
The disadvantages of these known methods are to be seen, among others, in 
the high technological and economic expenditures required for the 
treatment of the ores prior to the melting and reduction processes proper, 
and in the relatively long process time. 
From Austrian patent No. 257,964, a method of the initially defined kind 
for the reduction of metallic oxides by means of an electric arc plasma is 
known. The plasma arc is struck between a plasma burner vertically 
arranged in the lid and a bottom electrode arranged in the bottom of a 
melting vessel. 
The reduction of the metal oxides takes place in the slag layer by 
subjecting the molten oxide to the electric arc plasma jet containing a 
hydrocarbon gas, and by reducing this molten oxide by the decomposition 
products of the hydrocarbon gas. 
This known method has the disadvantage that the thermal energy radiated off 
the plasma jet constitutes a great load on the furnace lining, since the 
strongest heat radiation occurs perpendicularly to the axis of the plasma 
jet. This involves a shorter furnace campaign, i.e., the operation time of 
the furnace from one bricking up to the next bricking up of the refractory 
lining, on the one hand, and a poor utilization of the energy supplied on 
the other hand, since a large part of the heat must be absorbed by the 
furnace brickwork without participating in the melting process. 
SUMMARY OF THE INVENTION 
The invention has as its object to provide a method, as well as an 
arrangement for carrying out the method, which makes it possible to 
produce both pig iron and liquid metals similar to pig iron as well as 
ferroalloys, while not only protecting the furnace brickwork from too 
strong a thermal load exerted by the plasma jet, but also making available 
the energy supplied by the plasma burner to melting and reducing the fine 
ore to as large an extent as possible. 
Furthermore, a pre-agglomeration of the raw material to be used, i.e., of 
the fine ore to be used, is to be avoided so that the expenditures 
connected therewith will be eliminated. 
This object is achieved according to the invention by a combination of the 
following characteristic features: 
the raw material is topcharged into the metallurgical vessel in the form of 
fine particles directed parallel to the plasma jet so as to peripherally 
surround the same, 
oxygen-containing gases and carbon are bottom-blown into the vessel through 
the melt, and 
a foamed slag is formed in the vessel, surrounding the plasma jet over its 
total height and the flow of supplied raw material paricles peripherally. 
The foamed slag creates an effective protection of the furnace brickwork 
against the heat radiation coming from the plasma jet. The sheathing of 
the plasma jet by the fine raw material particles used allows for an 
optimum utilization of the heat radiation of the plasma jet. The blowing 
in of carbon through the bottom leads to preventing the escape of carbon. 
By the supply of the oxygen-containing gas through the bottom, a premature 
destruction of the cathode by oxygen is prevented. 
According to a preferred embodiment, the supply of raw material particles 
is stopped after melting of the same, with merely oxygen-containing gas 
and/or carbon being blown in from the bottom through the melt. 
An arrangement for carrying out the method according to the invention 
comprises a refractorily lined metallurgical vessel and a plasma burner 
directed from top to bottom, with a counter electrode being arranged in 
the bottom of the vessel, and is characterized in that the plasma burner 
is peripherally surrounded by a jacket so as to form a supply space for 
the fine raw material particles which surrounds the plasma burner 
peripherally, and that nozzles, preferably jacket nozzles, are provided in 
the bottom of the metallurgical vessel to supply oxygen-containing gas and 
carbon.

DESCRIPTION OF EXEMPLARY EMBODIMENT 
The metallic outer jacket 1 of a metallurgical vessel 2 is provided with a 
refractory lining 3. The vessel 2 is closed by a lid 4, which is also 
refractorily lined. To the lid 4 an offgas duct 5 is connected. The vessel 
lower part 6 upwardly is followed by a substantially vertical cylindrical 
vessel part 7. A vertical plasma burner 9 centrally arranged within the 
vessel 2 projects through the lid 4 of the vessel 2 into its interior 8. 
In the bottom 10 of the vessel 2 a bottom electrode 11 for the plasma 
burner 9 also is centrally inserted. 
The plasma burner 9 is peripherally surrounded by a jacket 12 so as to form 
an annular space 13 surrounding the plasma burner 9 and open towards the 
vessel bottom 10. This annular space 13 also may be comprised of several 
top blowing lances for the raw material particles, peripherally 
surrounding the plasma burner. In the bottom 10 of the vessel 2 bottom 
nozzles 14, preferably designed as jacket nozzles, are arranged, through 
which oxygen and/or carbon is blown into the interior 8 of the vessel 2. 
In the vessel lower part 6, a slag tap hole 15 and a metal tap hole 16 are 
provided. The slag present in the vessel is denoted by 17, the molten 
metal is denoted by 18, and the plasma jet is denoted by 19. The raw 
material sheath surrounding the plasma jet bears the reference numeral 20. 
In the following, the function of the above-described arrangement during 
the production of pig iron will be explained in more detail: 
A first charging with fine ore and slag formers is effected via the annular 
space 13 (or the top blowing lances optionally provided instead). After 
this, a plasma arc 19 is struck between the plasma burner 9 movable in the 
vertical direction (for the optimum adjustment of the length of the plasma 
arc) and the water-cooled bottom electrode 11, and the charge, if desired 
mixed with fine-particle coal, is melted by the heat radiated off the 
plasma arc 19 and is reduced by means of the reduction gas blown in 
together therewith. 
After the formation of a metal sump 18 and a slag layer 17, oxygen and/or 
carbon is jetted in both from top through the annular space 13 (or the top 
blowing lances), in addition to the charge and the reduction gas, and from 
the bottom through the bottom nozzles, in order to build up a foamed slag. 
A foaming of the slag is possible only if a sufficient FeO-content and 
carbon content in the form of elementary carbon or carbon-saturated metal 
splashes are present in the slag. In this case, the carbon and the oxygen 
of the iron oxide react by forming carbon monoxide. This gas formation 
leads to a swelling or foaming of the slag. Moreover, a sufficient slag 
height and an appropriate slag viscosity are required for the foaming of 
the slag. 
Thus, the carbon serves for reduction, heating (by burning with oxygen) and 
foaming. 
As the melting phase is over, the supply of fine ores is stopped, yet 
oxygen and/or carbon continue to be nozzled in through the bottom nozzles 
14. In the subsequent finishing reduction phase the process is conducted 
in a manner that the desired tapping temperature on the one hand and a low 
metal oxide content on account of a relatively high excess of carbon in 
the slag 17 on the other hand will be achieved. Subsequently, it is 
slagged off through the slag tap hole 15 and tapped off through the metal 
tap hole 16. 
With the method according to the invention, a difference is made between a 
melting phase and a finishing reduction phase. Accordingly, also the slag 
compositions vary. In the following, recommended data of the slag analysis 
for the melting and finishing melting phases during the production of 
liquid metal similar to pig iron with about 2% carbon in a basic-lined 
reduction reactor are indicated. 
Slag composition in the melting phase: 
30 to 35% FeO+Fe.sub.3 O.sub.4 
40 to 45% CaO+MnO 
15 to 20% SiO.sub.2 
Balance P.sub.2 O.sub.5, A1.sub.2 O.sub.3, MgO, i.a. 
Slag composition in the finishing melting phase: 
10 to 15% total iron content of the slag (the iron being bound to the 
oxygen largely in the form of FeO) 
50 to 55% CaO+MnO 
20 to 25% SiO.sub.2 
Balance P.sub.2 O.sub.5, A1.sub.2 O.sub.3, MgO, i.a. 
In addition to supplying electric energy through the plasma burner 9, a 
large part of the required energy is supplied in the form of carbon and 
oxygen (--carbon burns with oxygen, thus releasing energy--), whereby it 
is possible to produce at favorable costs also high-melting alloys, in 
particular high-melting ferroalloys. The basic considerations pointed out 
above with respect to the formation of slag also hold for the production 
of ferroalloys. However, in this case the iron oxide content decreases, 
while the contents of Mn, Cr, W oxides a.o., increase. 
The high temperature produced by the plasma burner 9 is particularly 
advantageous mainly in the melting phase. For as economical a furnace 
operation as possible it is suitable if a metal sump 18 remains in the 
melting vessel 2 after tapping; at a new charging, the blowing in of 
carbon and/or oxygen (both from bottom and from top)--as an additional 
energy supply to the plasma burner 9--may be started at once. 
In addition to the advantages of an optimum utilization of the energy 
supplied by the plasma jet 19 and the fact that the furnace lining is 
spared to a large extent, the method according to the invention also 
offers the chance of keeping the amounts of offgases as low as possible by 
a clear-cut process conduct (by an appropriate energy supply by the plasma 
burner 9 as well as a dosed blowing in of heating, reduction and foaming 
gases). The hot offgases suitably can be used to preheat and/or partially 
pre-reduce the ore used.