Industrial electric heating furnaces – Arc furnace device – Electrode
Patent
1997-08-26
1998-10-13
Hoang, Tu B.
Industrial electric heating furnaces
Arc furnace device
Electrode
373 97, 373100, H05B 709
Patent
active
058223584
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method for producing a self-baking carbon electrode for the use in electric smelting furnaces. The invention further relates to an apparatus for production of such electrodes.
BACKGROUND ART
Conventional self-baking electrodes comprise a vertical arranged electrode casing normally made from steel, extending through an opening in the furnace roof or hood. The upper end of the electrode casing is open in order to allow addition of unbaked carbonaceous electrode paste which upon heating softens and melts and is thereafter baked into a solid carbon electrode due to heat evolved in the paste in the area of supply of the electric operating current to the electrode. As the electrode is consumed in the furnace the electrode is lowered and new sections of casing are installed on the top of the electrode column and further unbaked electrode paste is added.
Conventional electrodes of this type are equipped with inner, vertical metallic ribs affixed to the inner surface of the electrode casing which ribs extend radially towards the center of the electrode. When a new section of electrode casing is installed at the top of the electrode column, the ribs are welded to the ribs in the casing below in order to obtain continuous ribs in the vertical direction. The ribs serve as a reinforcement for the baked electrode and to conduct electric current and heat radially into the electrode paste during the baking process. To compensate for the consumption of the electrode, the electrode is lowered downwardly into the furnace by means of electrode holding and slipping means.
When conventional electrodes of this type are used, the electrode casing and the inner ribs melt when the electrode is being consumed in the furnace. The metal content of the casing and the ribs is thus transferred to the product produced in the smelting furnace. As the electrode casing and the inner ribs usually are made from steel, such conventional self-baking electrodes can not be used for electric smelting furnaces for the production of silicon or for the production of ferro-silicon having a high silicon content, as the iron content in the produced product will become unacceptably high.
Through the years a number of modifications of the above described conventional self-baking electrode with casing and steel ribs have been proposed in order to avoid contamination of produced silicon with iron from the casing and the steel ribs.
Thus in Norwegian patent No. 149451 it is disclosed a self-baking electrode wherein an electrode paste with a tar-based binder contained in a casing having no inner vertical ribs is baked above the area where electric operation current is supplied to the electrode and where the casing is removed after baking of the electrode, but before the electrode reaches the area where electric operating current is supplied to the electrode. In this way a casing and rib free electrode can be produced. This kind of electrode has been used in smelting furnaces for the production of silicon, but has the disadvantage compared to conventional prebaked electrodes that it needs costly apparatuses for baking of the electrode as the electrode in the area of baking has to be heated to a temperature in the range of 700.degree.-1000.degree. C. Further, as gases containing polyaromatic hydro-carbon compounds (PAH) evolve during baking, the apparatus has to be equipped with means for collecting and destroying the PAH compounds. Finally, it has to be arranged devices for removal of the casing after the electrode has been baked.
U.S. Pat. No. 4,692,929 discloses a self-baking electrode which is useful in the production of silicon. The electrode comprises a permanent metal casing having no inner ribs and a support structure for the electrode comprising carbon fibers, where the electrode paste is baked about the support structure and where the baked electrode is held by the support structure. This electrode has the disadvantage that separate holding means have to be arranged above the top of the electrode i
REFERENCES:
patent: 4527329 (1985-07-01), Bruff et al.
patent: 4575856 (1986-03-01), Persson
patent: 4692929 (1987-09-01), Cavigli et al.
patent: 4696014 (1987-09-01), Orrling
Elkem ASA
Hoang Tu B.
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