Note: Descriptions are shown in the official language in which they were submitted.
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TRANSLATION (HM-687PCT):
Translation of WO 2005/022,062A1 (PCT/EP2004/006,687)
with Amended Pages Incorporated Therein
ELECTRIC REDUCING FURNACE
The invention concerns an electric arc reduction furnace
for carrying out reduction processes, especially for reducing
slag to recover metallic constituents, by means of electric
energy, which is introduced into the interior of the furnace by
at least one electrode. The reduction furnace has an opening in
the wall or roof of the furnace for charging the charge material
and an opening for exhausting the gas that forms during the
reduction process from the furnace.
The slag to be purified is charged into the furnace and
reduced. The metals charged with the slag are in the form of
oxides (e.g., Cu20), sulfides (e.g., Cu2S), and pure metals
(e.g., Cu). The oxide constituents are reduced to metals by the
addition of a reducing agent. The sulfides and the pure
metallic constituents settle on the bottom of the furnace due to
their different densities.
In reduction furnaces of this type for reducing or
purifying slags, it is well known that the process gas, such as
CO, remains partly or entirely in the furnace and is burned.
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The CO-containing process gas is burned in the furnace
above the melt or slag with air, which is drawn in through
suitable openings in the furnace shell or furnace roof, and then
cooled to a certain temperature, which is predetermined by the
type of downstream dust catcher.
This is associated with the following disadvantages.
First, in the case of partial combustion of the process gas,
there is the danger of a CO explosion or the escape of the
poisonous CO gas into the furnace house.
Second, due to the combustion of the gases and of gaseous
metal vapors in the furnace, there is increased electrode
consumption and increased consumption of the reducing agents,
such as coke, coal, etc. This in turn results in high energy
losses, which can be on the order of 3-5 metric tons of coke per
day and 0.5-0.8 kg of electrode material per metric ton of
charge. In a furnace installation that purifies about 1,000
metric tons of slag per day, these additional costs amount to
US$1,000 to US$1,500 per day.
The production of this additional waste gas by the unwanted
combustion of the electrodes and reducing agents necessitates
dust catchers designed for larger volumes of waste gas. In
addition, the lining in the gas space of the furnace, especially
the roof lining, is subjected to strong thermal loads.
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The Japanese document 2000-039,118 A discloses an electric
arc reduction furnace for reducing slag. Powdered charge
material is introduced by a charging system through a suitable
charge opening in the side wall of the furnace at the level of
the slag layer and melted down electrically. Gases that form
during the reduction, CO gas in particular, are removed by an
exhaust system through a separate exhaust line in an opening in
the furnace roof.
Proceeding from the prior art, the objective of the
invention is to modify an electric arc reduction furnace in such
a way that the aforementioned disadvantages are avoided.
The crux of the invention is the realization of a furnace
with an air-sealed design in which the charge material,
especially liquid slag, is charged through an airtight opening
in the furnace, and at the same time the furnace gas is
exhausted or drawn off through the same airtight opening in the
furnace. In this way, the furnace is provided with optimum
protection against unwanted penetration of air. Oxidation of the
electrodes and/or the reducing agents is prevented.
In a preferred embodiment of the invention, the charging
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system, which is preferably designed as a charging chute and
extends into the interior of the furnace through the common
charge and waste gas exhaust opening, has a cover. This cover
is sealed from the furnace shell and formed as a waste gas
chimney towards the top.
This embodiment allows the charging of slag with a
simultaneous airtight seal and simultaneous prevention of
unwanted consumption of electrodes and reducing agents. The
cover allows continuous charging, because it is permanently
operative. With a furnace mode of operation under a slight
positive pressure, the process gas leaves the furnace via the
charge opening in the furnace shell through the waste gas
chimney formed by the charging chute and its cover.
In principle, however, it is also possible to seal this
common opening for charging and gas exhaust by means of a slide
gate. However, this can be considered only if charging is not
being performed continuously.
The chimney shape of the cover is preferably formed in such
a way that the cover of the charging system has a chimney flue
for gas exhaust more or less close to the furnace, and that the
chimney flue is followed by a post-combustion chamber. Partial
combustion of the process gases can occur in this chimney flue,
because it is not entirely possible to prevent air from also
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being drawn into the chimney flue from the charging side through
the charging system. However, the entrance of air into the
furnace is completely prevented. Specifically, as a result of
the chimney effect, air that is drawn in is not drawn into the
furnace but rather into the flue formed by the cover. In the
combustion chamber that follows the chimney flue, the controlled
supply of additional air completes the combustion of the process
gases and cools the combusted waste gas to the lower
temperatures that are required.
The conveyance of the charge material into the furnace by
the charging system in the form of a charging chute is
preferably accomplished by gravity or fluid force. However, the
invention also includes the possibility of supporting this
conveyance by mechanical means, such as vibrators and rotating
rolls.
The slags that are used are present mostly in liquid form.
Liquid slags are charged through the common charge and waste gas
exhaust opening. Solid, lumpy slag is also charged at the same
time. In one embodiment of the reduction furnace, this charge
material is charged together with the reducing agent by means of
charging tubes that extend into the interior of the furnace
through the furnace roof.
In another embodiment, it is also possible to charge solids
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through the common charge and waste gas exhaust opening. This is
advantageous especially for the reducing agent, because the oxide
constituents of the slag are then already being intensively mixed
with the reducing agent as they are being charged to the furnace.
All together, the following additional advantages are
achieved by the invention:
-- reductions of operating expenses of US$300,000 to
US$400,000 per year;
-- lower investment costs for the dust catcher, since the
waste gas volume arising from the combustion and the cooling air
for the coke and electrodes is eliminated;
-- reduced thermal load on the furnace roof due to the
elimination of the latent heat, since no combustion occurs in the
furnace;
-- a simpler design of the electrode bar, since adjustment of
the electrodes is greatly reduced;
-- assurance of a reducing furnace chamber atmosphere, which
is advantageous for recovery of the valuable materials, which are
present in the form of oxides.
In one aspect, the present invention resides in a submerged
arc furnace for carrying out reduction processes by means of
electric energy that is introduced into a furnace interior by at
least one electrode, the furnace comprising a charging device
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and a common charging and waste gas aperture for charging
material transported by the charging device into the furnace
interior, as well as for discharging process gases produced
during the reduction process from the furnace interior, wherein
the furnace being an airtight construction and the charging
device is provided with a cover with one end of said cover
sealingly engaging the furnace, the cover comprising a chimney
pipe in proximity to the furnace which serves for discharging
the gas and is realized in the form of a waste gas chimney, the
charging device protruding into the furnace interior through the
common charging and waste gas aperture or ending at the
aperture, and wherein the charging device consists of a charging
chute and the transport of charging material into the furnace is
realized via the charging chute with the aid of gravitational
force or promoted with mechanical means, the furnace comprising
a furnace roof and at least one charging pipe that serves for
charging the furnace with at least one of reducing agents and
solid slag, wherein the charging pipe protrudes into the furnace
interior through the furnace roof, wherein a post-combustion
chamber being connected to the chimney pipe downstream thereof.
In a further aspect, the present invention resides in the
submerged arc furnace, wherein the post-combustion chamber is
connected to an air supply channel for introducing air in a
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controlled fashion and for realizing a controlled post-
combustion of the process gases.
In yet a further aspect, the present invention resides in
the submerged arc furnace, wherein the common charging and waste
gas aperture is arranged in the furnace wall or in the furnace
roof, to which the charging device with the cover is connected
in an airtight fashion on an outside of the furnace.
In still yet a further aspect, the present invention
resides in the submerged arc furnace, wherein the charging
device is operable to charge liquid slag through the common
charging and waste gas aperture.
In yet a further aspect, the present invention resides in
submerged arc furnace, wherein the charging device is operable
to charge solid matter comprising solid slag and a reducing
agent through the common charging and waste gas aperture.
In yet a further aspect, the present invention resides in
the submerged arc furnace for use in reduction of slag in order
to reclaim metallic components.
In yet a further aspect, the present invention resides in
the submerged arc furnace, wherein the mechanical means comprise
at least one of vibrators and rotating rollers.
The invention is explained in greater detail below with
reference to the specific
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embodiment of the invention illustrated in the sole drawing,
which shows a cross section of a schematically indicated
reduction furnace wall with an opening that serves
simultaneously as a charge and waste gas exhaust opening.
The electric arc reduction furnace 1 is indicated by the
furnace wall 2. An electric arc reduction furnace 1 of this
type is used, for example, to carry out recycling processes,
such as oxidic waste processes, and especially to purify slags
for the purpose of recovering metallic constituents. To this
end, at least one electrode (not shown) is inserted in the
furnace interior Oi, and the charge material is melted down or
raised to high temperatures by the electric energy introduced
into the furnace, so that the reduction processes can proceed
with the aid of the reducing agents that are introduced, such as
coal and coke.
The furnace wall 2 has a charge opening 3. A charging
system 4, here in the form of a charging chute 5 or slag feed
chute, which is supported by a frame 6, extends through the
charge opening 3. Slag is charged into the furnace by means of
the charging chute 5 (arrow I). At the same time, this opening
3 also serves as an exhaust opening for the process gases that
are formed during the reduction, which are designated here as CO
and as {Zn} to reflect the gaseous metal vapors, such as Zn
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(arrow II). This opening 3 is basically the only waste gas
exhaust opening. However, an emergency chimney for the waste
gas can be provided for emergencies.
The charging chute 5 is sealed airtight from the furnace
wall 2. For this purpose, it is provided with a cover 7 in the
form of a metal housing, which extends from the furnace wall 2
to the inlet 8 of the charging chute 5. On the side of the
inlet 8, the cover 7 is bent up somewhat to provide room for the
charge material. Close to the furnace, a chimney flue 10
extends from an opening 9 in the cover 7 upward and away from
the cover 7. In this way, the cover 7 is formed as an exhaust
gas chimney in the upward direction.
The chimney flue 10 is followed in the direction of waste
gas flow by a post-combustion chamber 11, into which an air
supply channel 12 opens for feeding air into the post-combustion
chamber 11.
The process will now be explained. Charge material, such
as liquid slag, is continuously charged into the furnace
interior by means of the charging chute 5 (arrow I). Reducing
agent is charged through separate charging tubes in the furnace
roof or possibly by the charging chute 5. At the same time,
process gases flow through the same opening 3 into the chimney-
like cover 7 in the opposite direction (arrow II) from the
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charging direction. They flow off through the chimney flue
(arrow III). Air (arrow IV) that is drawn in along with the
charge material is likewise discharged through the chimney flue
(arrow V). Partial combustion of the gases can occur in the
chimney flue 10 with this air. However, the actual post
combustion with a controlled air supply occurs in the downstream
post-combustion chamber 11, into which the controlled air supply
is fed (arrow VI).
All together, the invention creates a closed electric arc
reduction furnace for purifying liquid slags. Its closed
construction is a result of the fact that the furnace is
provided with only one gas opening, through which liquid slag is
charged and the furnace gas is simultaneously drawn off. This
prevents any secondary air from penetrating to the interior of
the furnace.
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List of Reference Symbols
1 electric arc reduction furnace
2 furnace wall
3 charge opening
4 charging system
charging chute
6 frame
7 cover
8 inlet
9 opening in the cover
chimney flue
11 post-combustion chamber
12 air supply channel
Oi furnace interior
arrow I slag and reducing agent charge direction
arrow II process gas exhaust direction
arrow III flow of the process gases through the chimney
arrow IV air drawn in from the charging side
arrow V discharge through the chimney of the air drawn in
from the charging side
arrow VI controlled air supply for post combustion
