Industrial electric heating furnaces – Arc furnace device – Electrode
Patent
1995-07-26
1997-01-21
Hoang, Tu
Industrial electric heating furnaces
Arc furnace device
Electrode
373 37, 373 52, 373 94, H05B 706
Patent
active
055965989
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to electric melting techniques, and more specifically those in which energy is dissipated in the molten mass by Joule effect, by means of plunging electrodes.
2. Discussion of the Background
For a long time, glass production installations which operate on large quantities have been provided with melting furnaces which are supplied with fossil fuel, such as fuel oil or gas. This is the case in particular for large capacity continuous production installations which for example provide flat glass or bottle glass. When electrical energy is in these large furnaces, it is essentially as a local booster, in order to maintain the temperature of the glass in the least hot areas, or outside the furnace along the path of the glass towards its place of transformation, or in order to develop specific convection movements, to assist homogenization, refining or transport of the molten material.
True electric melting was used firstly in small units in which considerable flexibility in the conditions of use appeared to be necessary. Fluctuations of energy costs and gradual mastery of certain technological problems have led more recently to the development of major production units in which all of the melting process, with the exception of commissioning, takes place using electric energy. This development requires the solution of extremely delicate technological problems.
Thus, in particular, in order to avoid oxidation of the electrodes at the surface of the melting bath, it has been proposed to immerse the electrodes completely. This is the solution used for example in French patent application FR-A-2 552 073. In this document, the electrodes are disposed vertically in the bath, such that they project from the hearth of the furnace. In other embodiments, electrodes also pass through the lateral walls of the furnace.
Irrespective of the advantages it provides relative to corrosion problems, immersion of the electrodes also permits convenient, regular supply of the surface of the bath with a composition of raw-materials. Formation of a relatively thick layer of composition to be melted, floating on the molten bath, is in fact advantageous for several reasons. In contact with the melting bath, it provides the permanent reserve of material necessary for continuous operation. It also protects the melting bath against substantial loss of heat by convection in contact with the atmosphere, and in particular by radiation.
Although furnaces of the type described in the aforementioned document have very important industrial applications, they do not necessarily provide the best solution to all requirements encountered in practice. For example, in some cases, and with the obvious purpose of limiting investment costs, it is desirable to transform installations which operate with burners by maintaining as many as possible of the existing components, and in particular the refractory materials which constitute the pouring basin. Transformation of this type is not possible when the electrodes are to be installed in the hearth or in the lateral walls of the furnace.
Furnaces of which the electrodes are immersed, have limited possibilities for adjusting the electrodes. Although they provide entirely satisfactory performance for specific operating conditions, they are less suitable for frequent and/or substantial modifications of these operating conditions.
In addition, even though the technology of immersed electrodes has now been well-mastered, and a long service life of the electrodes which is comparable with that of the refractory units can be envisaged, the risk of premature deterioration of one of a plurality of electrodes, thus affecting satisfactory operation, cannot be altogether eliminated.
Another solution which is described in particular in French patent application 2 599 734, consists of plunging electrodes through the free surface of the bath of molten material. This technique has a given number of advantages. Firstly, it obviously prevents the difficu
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patent: 3327040 (1967-06-01), Molstedt et al.
patent: 4477911 (1984-10-01), Racki
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patent: 4710607 (1987-12-01), Wilhelmi et al.
patent: 4965812 (1990-10-01), Sorg et al.
Caillaud Thierry
Delahalle Gerard
Maugendre Stephane
Peigne Pierre
Szalata Francois
Hoang Tu
Isover Saint Gobain
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