Industrial electric heating furnaces – Arc furnace device – Charging or discharging
Patent
1995-05-31
1996-09-10
Hoang, Tu
Industrial electric heating furnaces
Arc furnace device
Charging or discharging
373 82, 373 94, 373111, F27D 1300
Patent
active
055552595
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention related relates to a process and an apparatus for melting down of scrap in a shaft furnace which is operated with direct current.
2. Description of the Prior Art
The cathodes of direct current arc furnaces are customarily supported by a support arm which is fastened on a vertically movable support column. The disadvantage of this manner of constructing electrode supporting devices for arc furnaces such as known, for instance, from DE 37 01 678, is the large free length of electrode present with only a small height of the shaft of the furnace vessel. The greater the structural height of the furnace vessel, the greater also the danger of the scrap falling against the free part of the electrode resulting in the breaking of the electrode as well as short circuits. This has the negative consequence of an interruption in the transmission of power.
SUMMARY OF THE INVENTION
In addition, such furnaces are generally charged batchwise, so that there are interruptions in operation for opening the cover and removing the electrodes. The result of this is not only a reduction in production but also an increase of the wear in the furnace parts, including wear of the refractory lining as well as of the cathode which extends into the furnace vessel.
From German Patent 22 10 468, a process is known for the continuous production of steel in a shaft furnace at the bottom of which a centrally arranged electrode which extends into the furnace vessel. The electrode melts the charge of material arranged above it with an arc. A shaft furnace of this construction which is intended for melting down ore, pellets and sinter is scarcely suitable for melting down scrap. On the one hand, the necessary power cannot be introduced into the burden, while, on the other hand, the bottom electrode, which is surrounded by a slot, entails excessive risks with the level of molten bath customary with the melting of scrap.
From EP 0 336 920, a process is known for the charging, inter alia, of scrap in a melting or reduction-melting furnace in which the burden is preheated before being introduced into the furnace and is held, using an electromagnetic field, until a predetermined temperature has been reached. In this case, the burden is subjected directly to the heat of radiation and the process heat, namely to such an extent that, for instance, the scrap loses its ferromagnetic properties (Curie point) and can no longer be held by the electromagnetic field.
This melting furnace, which is designed for a continuous process, does not permit holding the column of scrap back in the furnace shaft.
The object of the present invention is to provide an arc furnace of this type which, with structurally simple means, permits substantially continuous operation and in which the energy necessary for melting can be used as efficiently as possible and in which a cathode requiring little maintenance regardless of the height of the shaft can be employed.
Pursuant to this object, one aspect of the present invention resides in the process for melting down scrap in a closed shaft furnace operated by direct current, which process includes charging the scrap into an annular chamber at a first end of the furnace so that the scrap descends into the furnace in a column with an annular fiat cross-section that defines an inner scrap-free area, drawing off heating gases which flow through the scrap opposite to the scrap descending direction from an outer cylindrical wall of the annular column of the scrap, reducing the inner scrape-free area before the scrap reaches a melt zone, melting the scrap down in the melt zone with an arc burning between a cathode and an anode by subjecting the scrap to the arc at a center of the flat cross-section, and tapping off melted products in a bottom region of a vessel arranged at the bottom end of the shaft furnace. Another aspect of the present invention resides in an arc furnace for carrying out the inventive process, which furnace includes a shaft, of direct curre
REFERENCES:
patent: 3919454 (1975-11-01), Langhammer
patent: 4001008 (1977-01-01), Stift
patent: 4691900 (1987-09-01), Maeda
Hoang Tu
Mannesmann Aktiengesellschaft
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