EP0671116B1 - Electric melting device - Google Patents

Description

The invention relates to fusion techniques electric and relates more particularly to those in which energy is dissipated by Joule effect in the melt from plunging electrodes.

For a long time, the production facilities of glass operating on large quantities have been provided with melting furnaces powered by fossil fuel, such as fuel oil or gas. This was particularly the case for the installations high capacity continuous production providing, for example, flat glass or bottle glass. On these large ovens electrical energy, when used, was essentially used as local booster to maintain the temperature of the glass in cooler areas, or outside the oven in its journey to the place of transformation or develop certain convection movements to promote homogenization, refining or transport of the material molten.

Electric fusion proper first appeared on small units for which a large flexibility in the conditions of use seemed necessary. The fluctuations in energy costs and the gradual mastery of certain technological problems have more recently led to the development of units significant production in which the entire merger process, with the exception of commissioning, takes place using electrical energy. This development requires the solution of technological problems extremely delicate.

This is how, in particular to avoid the question of oxidation of the electrodes on the surface of the molten bath, it has been proposed to immerse them completely. It's here solution adopted, for example, in the patent application French published under number FR-A-2 552 073. In this document, the electrodes are arranged vertically in the bath from the bottom of the oven. In other realizations, there are also electrodes passing through the side walls of the oven.

Regardless of the benefits it provides corrosion problems, immersion of electrodes also allows a convenient and well uniform feeding of the surface of the bath in composition of raw materials. The constitution of a relatively thick layer of composition to melt, supernatant on the molten bath, is useful in effect for several reasons. It forms, in contact with the molten bath, the permanent reserve of necessary material in continuous operation. It also protects the bath by fusion of a high heat loss by convection in contact with the atmosphere and especially by radiation.

If the ovens of the type described in the aforementioned document find very important industrial applications, they do not necessarily make it possible to respond at best to all the requirements encountered in practice. As example it is desirable in some cases and in the obvious goal of limiting investment costs, transform facilities operating with burners keeping as much of the existing elements as possible and in particular the refractory materials constituting The Pelvis. Such a transformation is not possible when it comes to implanting electrodes in the sole or in the side walls of the oven.

Ovens with submerged electrodes provide limited possibilities for adjusting the electrodes. If they lead to entirely satisfactory performance for a certain diet, they are less suitable for frequent and / or substantial changes to this plan Operating.

By the way, even if the electrode technology submerged is now well under control and can be consider a longevity of the electrodes comparable to those refractory, the risk of premature deterioration one or more electrodes that compromise the good cannot be completely ruled out.

Another solution notably described in the request French patent published under the number 2,599,734 consists to immerse electrodes through the free surface of the bath of molten material. This technique has a certain number of advantages. First of all, it of course avoids the difficulties of passing these electrodes through refractory, and also replacement problems worn, sealing or even electrodes wear of refractories, in particular due to temperature high which favors the attack of the refractory and powerful convection currents that develop upon contact.

The plunging electrode technique locates the hottest areas at the top of the melt and thus alleviates these problems.

Furthermore, this technique makes it possible to modify the electrode immersion depth and therefore the gradient of temperature. This allows changes from the oven without changing the temperature of the hearth and therefore the temperature of the glass leaving the oven.

In addition, experience shows that this technique has a very satisfactory thermal efficiency and leads to good quality of the molten material.

These plunging electrodes are usually attached on supports that overhang the melting tank at from the sides of it. Application FR-A-2 599 734 describes such a support which consists of an arm which comprises pipes for the coolant circulation and an electric cable for the supply of the electrode, and the actual electrode holder.

In normal operating conditions, a layer of composition deposited on the surface of the molten bath, which provides protection against heat loss, avoids too high a rise in the temperature of the arm that overlooks the molten bath.

However, during a standby phase, at during which the protective layer of raw materials is either of very reduced thickness or absent, the arm temperature becomes very high and causes degradation of the power supply system.

To avoid this inconvenience, a usual solution consists of a standby phase to be noted the plunging electrodes and to maintain a temperature sufficient in the bath by immersed electrodes the more often placed on the walls. This technique is effective but we find the problems related to the electrodes submerged although in this case they work under lower voltages since they only maintain the temperature of the bath already melted. Over such submerged electrodes require investment costs additional.

Another proposed solution, notably described in the US patent 4,965,812, consists in using a support electrode consisting essentially of a cooling system "water-jacket" type driver current. The feeding system is then continuously refrigerated and therefore protected from temperature rise which intervenes during a standby phase. Through however, this type of installation requires a protection because the electrode supports are maintained permanently on.

Such a device most often consists of a wire mesh that prevents employees from accessing the oven. However certain measures that require the presence of a operator near the bath and therefore the electrode supports endanger this operator.

EP-A-0 135 473 describes an arc furnace electrode support, said support comprising a current supply system and a cooling device, in which the support has a surface protection thermal and said surface is insulated from the voltage of the conductor current.

The object of the invention is a device for fusion vitrifiable charge electric which acts either in regime normal operation, either in standby period without the intervention of submerged and safe electrodes for the operators.

This object is achieved according to the invention defined in claim 1.

The electrode holder according to claim 1 satisfies the problems posed by prior techniques. Indeed, there is more risk for operators linked to maintaining electrode supply voltage. And, during a bet in standby of the melting furnace, the rise in temperature due especially the radiation of the molten glass bath does not not the degradation of the support since it has a thermally insulated surface.

In a preferred variant of the invention, the system power supply is a cooling system, "water-jacket" type conductor of electric current. This device is then surrounded by an electrical insulator, advantageously made of a material resistant to temperatures very high.

The insulation that is chosen to withstand temperatures is advantageously cooled by traffic conductive cooling system water current.

During standby, the media temperature becoming very high due to radiation, it is necessary to choose an insulating material resistant to these temperatures and a priori very expensive.

The invention advantageously proposes to surround the electrical insulation of a second cooling system of the "water-jacket" type. It is thus possible to choose a material for electrical insulation resistant to temperatures lower. In addition, such a material generally sees its electrical insulation properties improve at low temperature.

On the other hand, the cooling of this material electrical insulation ensures its durability.

The electrode support thus proposed therefore comprises two cooling systems. Cooling systems are advantageously made by circulation of water. The internal system being current conductor invention for supplying the electrode, the invention provides two separate water circulation circuits so that the current conducting water and flowing in the cooling system supplying the electrode does not bring a tension on the level of the second system of cooling which would then no longer be useful.

According to another preferred mode of the invention, the two cooling systems are powered by the same water circuit, the water being demineralized so that it either non-conductive. The feeding device water outside the electrode holder can be limited to a single circuit.

• figure 1, une coupe d'une représentation schématique partielle d'un four comportant des électrodes immergées verticalement à partir de la surface,
• figure 2, un schéma d'une réalisation selon l'invention d'une électrode et de son support.
• figure 3, une représentation schématique d'une partie d'un support selon une autre réalisation de l'invention.

Other details and advantageous characteristics of the invention emerge below from the description of the exemplary embodiments described with reference to FIGS. 1, 2 and 3 which represent:

• FIG. 1, a section of a partial schematic representation of an oven comprising electrodes immersed vertically from the surface,
• Figure 2, a diagram of an embodiment according to the invention of an electrode and its support.
• Figure 3, a schematic representation of part of a support according to another embodiment of the invention.

The diagram in Figure 1 shows part of a melting furnace associated with plunging electrodes 1. The oven is constituted by a refractory tank composed of the sole 2 and side walls 3. Above the pool, the refractory vault 4 is suspended from a metal frame 5 partially shown, said metal frame 5 overlapping the oven.

Mobile refractory walls 6 are provided which when they are in the low position, i.e. in support on the side walls 3, allow to partially isolate the molten bath 7 of the surrounding atmosphere.

Only openings in the walls 6 are provided for the passage of the electrode supports 8.

This low position of the walls 6 is adopted when the oven is put on standby and is no longer necessary to feed it with raw materials. This allows avoid excessive heat loss, and the risk of degrading all the surrounding material.

Regarding electrode 1, it is submerged on the surface of the melt 7 under the layer 9 of materials first to melt. This layer 9 which covers the weld pool 7 in normal operating mode, isolates thermally the pelvis and avoids losses thermal.

The electrode 1 is fixed to the support 8 which includes the power supply system and cooling device of electrode 1, which are not shown in this figure 1.

The support 8 is itself connected to a non-mechanism shown which allows in particular to remove an electrode 1 bath for example for a change or a repair.

In FIG. 2, the electrode 1 and its support 8 are more precisely represented and highlight the advantages of the invention.

The electrode 1, usually made of molybdenum, is fixed via an element 10, current conductor, to the tube 11 which constitutes the cooling device electric current conductor. Element 10 is an extension which is fixed to the tube 11 by screwing. At the other end of this extension 10, the electrode 1 is fixed. construction allows the assembly to be easily dismantled extension 10 / electrode 1 because the place of screwing does not never soak in the melt. Indeed, if the tube 11 was longer and dipped directly into the bath, it would be possible to directly attach electrode 1 on it for example by screwing. However, it would become much more difficult to disassemble the electrode, the attachment point having soaked in the bath of fusion. According to our setup, the change is very easy but still needs to replace the extension 10 together with the electrode 1. This extension 10 can be surrounded, at least partially, by a refractory material thick enough to avoid direct contact with raw materials or the molten bath.

On the other hand, the extension 10 also allows the passage coolant to the electrode so so that it is cooled.

Screw fixing is interesting because it allows quick replacement. Electrode replacements can be frequent because they do not intervene only in case of wear but also allow modification the electrodes and in particular their length so as to modify the level of immersion and therefore the energy intake in the oven. The tube 11 can be made of steel of so that it has good stiffness and conduction.

Within this tube 11, a second tube 12 is placed, for example concentric. This second tube 12 is for example fixed at different points to the internal surface of the tube 11. The association of these two tubes 11 and 12 allows circulation of water and thus constitutes a cooling device water-jacket type. The cooling system being designed so as to cool the electrode 1, the tube 12 passes through the extension 10.

At the other end of the tube 11 is fixed a collar 13 supply for example of copper itself placed within an insulating formwork 14. This collar 13 makes it possible to put the tube 11 at the desired tension, and this one being electrical conductor to power electrode 1 under this same tension.

Around the tube 11 is placed an insulating material 15 electrically advantageously made of a refractory material the type of electrical insulation sold under the reference MURATHERM 500 M. Material 15 is produced under form of one or more sleeves which wrap and are supported on a part of the external surface of the tube 11. This electrical insulating material therefore allows accessibility to the electrode holder without any risk of electric shock for operators who must approach the bath of fusion. The material 15 is itself surrounded by an envelope 16 concentric in which circulates a liquid of cooling such as water. This envelope 16 of "water-jacket" type includes an internal sleeve 17 which allows the circulation of water.

This second cooling device allows a part of avoiding overheating of the insulating material even if it is chosen as being able to withstand temperatures quite high and if it is already partly cooled by the first cooling system.

On the other hand, it allows to obtain an external surface the electrode holder 8, which remains relatively cold and can allow manipulation or at least approach by an operator even when the oven is on standby and support 8 is heated mainly by radiation from the melt where layer 9 of raw material is absent.

The different elements cited 11, 12, 15, 16, 17 constitute tubes, for example, concentric, placed around each other.

In the case of FIG. 3, a cooling device "water-jacket" type, current conductor, consisting of two concentric tubes 18, 19 is surrounded one or more sleeves 20 of an electrical insulating material and having good thermal insulation and good temperature resistance.

Thermal protection of the support surface electrode is then obtained on the one hand, by nature even of the sleeve 20 and on the other hand, by the presence of the device cooling which allows to cool this sleeve 20.

Electrical protection is provided by the sleeve 20 which envelops the current conducting tube 19.

The different pipes allowing the arrival and the flow of cooling water is not shown in the figures.

The water used for cooling is advantageously demineralized water, which makes it possible to use the same circuits for both cooling systems without risk of current conduction to the system external cooling, which is also connected to the Earth.

The unnumbered arrows indicate the different circuits followed by the coolant.

The electrode associated with its support thus described according to the invention allows on the one hand a safe use in normal operating mode since no device accessible is powered up and secondly use without risk of degradation of the support when the oven is put on hold.

The device composed of the electrode and its support according to the invention therefore makes it possible to keep the different advantages linked to electric fusion by submerged electrode from the surface of the melt, which have been listed previously. These are, for example, vouchers thermal yields, good material quality melted despite changes in draw, increase life of the oven because the refractories are less attacked or because it is easy to change an electrode.

In addition, the device according to the invention allows avoid the presence of fully submerged electrodes to night light periods or full-time attendance a protection system avoiding the presence of operators near continuously energized components.

Claims (6)

1. Support (8) for a melting electrode (1) immersed starting from the surface of a melting bath, said bath being constituted by a vitrifiable charge, said support (8) comprising a current supply system and a cooling device, the support having thermal protection at the surface and said surface being insulated at least partially with respect to the voltage of the current conductor; said electrical insulation being arranged at a certain distance from the immersible end of the electrode.
2. Support for an electrode according to claim 1, wherein the current supply system is a current-conducting cooling system of the water-jacket type (11, 12, 18, 19), and wherein that cooling system is surrounded by an electrical insulator (15, 20).
3. Support for an electrode according to claim 2, wherein the electrical insulator (15, 20) is of a material that is resistant to high temperatures.
4. Support for an electrode according to either claim 2 or claim 3, wherein the electrical insulator (15) is surrounded by a cooling system of the water-jacket type (16, 17).
5. Support for an electrode according to claim 4, wherein the fluid of the cooling system (16, 17) surrounding the electrical insulator is conveyed by a circuit other than the current-conducting cooling circuit (11, 12).
6. Support for an electrode according to claim 4, wherein the fluid of the cooling system (16, 17) surrounding the electrical insulator is conveyed by the circuit which supplies the current-conducting cooling system (11, 12), and the fluid is demineralised water.

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