LU85300A1 - IMPROVEMENTS IN ELECTRODES FOR PLASMA OVENS - Google Patents

Description

ί i * Λ -ΙΟ 2243/8304.

METALLURGICAL RESEARCH CENTER -CENTRUM V00R RESEARCH IN DE METALLURGIE »

Non-profit association -Vereniging zonder winstoogmerk, BRUXELLES, (Belgium).

Improvements to electrodes for plasma ovens.

The present invention relates to an improved electrode for an arc plasma oven.

In recent years, there has been an incessant development of the technique of injection into the blast furnace of hot reducing gases produced, or at least brought to the desired temperature, by means of an arc plasma oven.

In this technique, an electric arc is blown between two electrodes between which the gaseous fluid to be heated is circulated. This gaseous fluid contains a certain amount of oxidizing gas, for example air.

At present, the electrodes used in arc plasma ovens are generally made of copper, due to the excellent thermal and electrical conductivity of this metal. They generally come in the form of two. tubes of the same axis, placed in the extension of each other i ί V Λ - 2 -

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and separated by a space through which the gas to be heated circulates.

However, these copper electrodes have a significant drawback when the plasma furnace is supplied with direct current. Indeed, the anode is attacked by the oxygen present in the gaseous fluid; there is rapid oxidation in the region where the anode foot of the arc acts, and the anode undergoes rapid erosion thereby greatly limiting its life.

It is therefore necessary to replace it frequently, which significantly disrupts the use of the oven.

An attempt has been made to remedy this drawback by rotating the arc at high speed inside the electrodes. In this way, we have succeeded in extending the life of the electrodes to a certain extent, but this improvement remains limited, because the cause of the degradation, namely the oxidation of the anode, has not been eliminated.

The present invention relates to an electrode for an arc plasma oven, which does not have the drawback mentioned above.

In particular, the electrode which is the subject of the present invention is practically insensitive to oxidation, when it is used as an anode in a plasma furnace supplied with direct current, or with rectified alternating current.

For this purpose, the tubular electrode for plasma arc furnace, which is the subject of. present invention, is essentially characterized in that at least the part on which the arc of the * said plasma oven acts is silver.

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According to a first variant of the device of the invention, the electrode is in the form of a composite tube, comprising an outer tube made of a material allowing its cooling, for example made of copper, and an inner tubular element made of silver, housed in a coaxial position in this outer tube.

According to a particular embodiment of this first variant, the inner tubular element in silver extends only over a part of the length of the electrode. In this case, it is advantageously housed in an annular recess made in the inner wall of the outer tube.

Still according to the invention, the inner tubular element is advantageously crimped into the outer tube.

The attached figures illustrate, by way of example, the two embodiments which have just been described.

FIG. 1 shows a tubular electrode consisting of a copper tube 1 in which a tubular silver element 2 is crimped, extending over the entire length of the tube 1.

FIG. 2 represents an electrode analogous to that of the? FIG. 1, in which the silver tubular element 2 extends only over part of the length of the electrode and is housed in a recess 3 made in the inner wall of the outer tube 1.

According to another variant of the device of the invention, the tubular electrode consists of an outer tube made of a material allowing its cooling, for example copper, the inner surface of which is coated with a layer of deposited silver Γ ™ "" ---------------- - 4 - '»a

It would obviously not go beyond the scope of the invention for the so-called 'silver layer to be deposited by another method / such as by vapor deposition under vacuum or by projection.

The silver electrode according to the invention has proved to be particularly advantageous when it is used as an anode of an arc plasma oven. It has a lifespan at least ten times longer than that of copper-plated electrodes, this / i more than makes up for the difference in price it entails.

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Claims (7)

1. Tubular electrode for plasma arc furnace, characterized in that at least the part on which the arc of said plasma furnace acts is silver. 2. Electrode according to claim 1, characterized in that it comprises an outer tube made of a material allowing the cooling of the electrode and of a tu- element. silver inner ring, housed in a coaxial position in said outer tube. 3. Electrode according to claim 2, characterized in that said inner tubular element extends only over a part of the length of said outer tube and in that it is housed in an annular recess formed in the inner wall of the says outer tube. 4. Electrode according to either of Claims 2 and 3, characterized in that the said inner tubular element is crimped into the said outer tube. 5. Electrode according to claim 1, characterized in that it consists of an outer tube, made of a material * allowing the cooling of the electrode, the inner surface r of which is coated with a layer of silver. 6. Electrode according to either of Claims 2 to 5, characterized in that the said outer tube is made of copper. 7. Use of an electrode according to either of claims 1 to 6, as anode of an arc plasma oven. AT -