Note: Descriptions are shown in the official language in which they were submitted.
The present invention relates to an AC furnace
and a process for generation of reduction gas for use in
connection with direct reduction of metallic oxides and
materials, such as iron ore concentrate, containing such
oxides, or other gas generation, or for a chemical arc
reactor.
In known devices and methods for direct reduction
in connection with metallurgical processes, there is used a
redu~tion gas, mainly carbon monoxide, CO, or hydrogen, H2.
Recirculation gas and possibl~ caxbon or hydrocarbon are
led through a plasma burner to supply sufficient energy for
decomposition of carbon dioxide, CO2, and ~12O and hydro-
carbon, and to give the gas a sufficient temperature.
In one known process, among other things carbon
dioxide ls reformed by the use of plasma burners. A disad-
vantage in this connection is that these burners are rela-
tively sensitive apparatus having limited power (normally
not designed for higher power than about 3 MW continuously)~
The present invention is an improvement of the
above-mentioned concept and is a solution to the problems
mentioned above.
According to the present invention, there is
provided a DC furnace for generation of reduction gas for
use in connection with direct reduction of metallic oxides
and materials containing such oxides, comprising:
- a reactor provided with carbonaceous electrodes
connected to the poles of a DC source, an arc being formed
between said two electrodes;
means for supplying a gas containing carbon
dioxide into said arc whereby carbon monoxide is formed
according to C + CO2~ 2 CO; and
- a single outlet for the formed gas being
arranged in the form of a hollow channel in one of said
electrodes.
~20~p~
According to the present invention there is also
provided a process for generation of reduction gas for use
in connection wlth direct reduction of metallic oxides and
materials containing such oxides, comprlsing the steps ofO
- injecting a gas containing carbon dioxide into
an arc formed in a reactor provided with electrodes
connected to the poles oE a DC source,
- forming a carbon monoxide according to
C ~ C02~ 2 CO, and
- discharging the formed gas through a single
outlet in a hollow channel in one electrode.
The specific properties of the DC arc with
respect to the gas flow are made use of here.
The gas which is to be regenerated consists
mainly of a mixture of carbon monoxide, CO, and carbon
dioxide, C02. The regeneration implies that carbon dioxide
to the greatest possible extent is converted in-to carbon
monoxide. This is achieved by the arc heating up the gas,
the carbon dioxide thus being decomposed while forming
carbon monoxide and oxygen. By the addition of carbon
~carbonaceous material) the free oxygen is taken care of so
that further carbon monoxide is formed. Such a reactor can
advantageously replace plasma burners in the prior art
process described above.
Carbon can be supplied, either as finely-grcund
powder or combined into some form of hydrocarbon, for
exampl~ oil, natural gas, liquefied petroleum gas, propane,
butane, etc. If hydrocarbon is supplied, this is also
decomposed by the arc so that free carbon in the form of
soo~, as well as hydrogen, are released. Thus, also
hydrogen forms a useful cons$ituent in the regenerated gas.
A preferred embodiment will now be described, as
example, without limitative manner, having reference to the
single Figure which is a schematic view oE the device
~2~
according to the present invention.
Two graphite electrodes with hollow channels,
the cathode 1 and the anode 2, connected to a direct
voltage source (not shown), are introduced into a reactor
vessel having a ceramic lining 3. The electrodes are pro-
vided with water-cooled electrode seals 4, 5.
The gas to be genexated is arranged to be
supplied in several different ways, such as through hollow
channel 8 in cathode 1, through nozzles 6 close to the
electrode seal 4 of the cathode 1, or through nozzles 7 at
the bottom of the reactor ve~sel 3. Also carbon or carbon
carriers, such as oil or natural gas, can be supplied
through the same openings. However, the outlet of
2a -
! 1. ~ '~
~L2~7~
the hot, regenerated gas only takes place through one opening,
namely the hollow channel 9 in the anode 2. Instead of graphite
electrodes 9 it is of course possible to use carbon electrodes.
In use of the reactor according to the invention~ the main part
of the gas and the carbon or the carbon carrier is suitably
supplied through the bottom nozzles and will then whirl up in
the reactor vessel 3. The radiation from the arc 10 is efficiently
absorbed by the free carbon or soot particles 9 which promotes
the reaction, while at the same time the walls of the vessel are
protected from direct radiation. The gas must then pass through
the arc 10 in order to flow out of the reactor 3~ whereby the
gas is further intensely heated and the reaction completed. The
shown passageway for the gas cooperates with the natural convection
of the arc 1 n, since the arc 10 acts as a powerful gas pump which
sucks up gas from the surrounding environment immediately below
the cathode ltland drives this gas at a high velocity downwards
towards the channel ~ of the anode 2.
If there should be any oxygen residues left when the gas in the
arc 10 reaches the anode 2, these will of course be attacked.
To counteract this, additional carbon or carbon carriers may be
supplied, possibly with some addition of transport gas, directiy
into the arc 10 through the hollow channel 8 in the cathode 1.
This possibîlity to inject d~rectly into the arc makes it possible
for the process to be trimmed with high efficiency and minimum
electrode wear.
A further possibility of trimming and influencing the process
in use of the reactor is afforded by the inlet nozzles 6 close
to the lead-in of the cathode 1. What is fed in here will part-
ially be directly drawn into the arc 10 because of the suction
action of the arc, and partially mix with the whirling gas and
particle flows in the reactor vessel. Therefore, from the process
point of view, feeding via the cathode nozzles 6 constitutes an
intermediate stage between direct feeding into the arc 10 through
the hollow channel 8 of the cathode 1 and feeding via the bottom
nozzles 70
~02
To attain the best heat transfer to the gas and the least electrode
wear 7 it is assumed that a relatively long arc shall be utilized,
i.e. an arc with relatively high voltage and low current. As
a guiding value for a 6 MW reactor, a voltage of 300 V and a current
of 20 kA are proposed, which gives an arcing length of approximately
700 mm.
The invention can be varied in many ways within the scope of the
following claims~ It can be employed with other gas generators
or with chemical arc reactors.
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