The present invention provides an oxygen lance having a wooden casing and a process for production of silicon metal or metal alloy or melting of slag in an arc furnace by use an oxygen lance having a wooden casing.

Some of the industrially important metals or alloys, e.g.

silicon metal or ferroalloys, are produced continuously in submerged arc furnaces. The liquid metal or alloy is removed continuously or discontinuously from the furnace through tap holes .

Tap holes can be clogged by freezing metal or slag, which is a by-product from contaminants in the raw materials. To open or re-open the tap holes, several methods are known (A. Schei, J.K. Truset H.Tveit; Production of High Silicon Alloys; Tapir Forlag Trondheim; 1998, page 191) .

The easiest and mostly applied method is blowing oxygen through oxygen lances. Commercially available lances are usually made of steel or steel covered with refractories. The lance is consumed in this process, and the iron ends up in the metal or alloy . In the case of silicon for chemical use, the iron content is a crucial factor. Iron contamination usually originates from contamination of the raw materials and electrode casings. Since iron cannot be removed from silicon through refining,

additional contamination should therefore be reduced to a minimum.

Unlike iron, aluminium can be removed from silicon metal through refining. Therefore, oxygen lances made of aluminium would solve the problem of additional contamination. However, lances made of aluminium will bend when having a free span between tapping equipment and taphole. Aluminium lances easily break under mechanical forces. Aluminium lances have a short service time during use. This significantly increases

consumption, and the aluminium lances can only be used in the outer parts of the tap hole. Lances made of aluminium are unsuitable for machine operation. Manual usage of lances is high-risk work.

The present invention provides an oxygen lance having a wooden casing . The oxygen lance having a wooden casing shows a suitable operational strength. Wood retains its mechanical properties when working in excessive heat. Wood will act as thermal insulation, allowing for a longer burning time, or operation time, of the lance with wooden casing and thereby reducing consumption. The wooden casing is well suited for machine use and provides greater safety for operators.

An oxygen lance is a tool that heats and melts the lance material in the presence of oxygen, preferably pressurized to create the very high temperatures required for cutting or drilling into a substrate material. Preferably, it comprises a tube of the lance material.

The lance material burns with oxygen and is preferably a metal selected from iron, titanium, aluminium, zinc or an alloy of said metals. Steel is also preferred. Furthermore, the lance material can be ceramic or plastic. In a preferred embodiment, the lance material is aluminium. The aluminium lances are used to open tap holes in submerged arc furnaces in the production of silicon without contaminating the silicon with iron.

In a preferred embodiment, the lance tube is packed with a filling material which burns with oxygen. Preferably, the filling material is the same material as the lance material. Preferably, at least one end of the lance comprises a fitting means. Preferably, both ends of the lance comprise a fitting means. Preferably, the fitting means is a thread. Preferably, one end of the lance comprises a screw thread and the other end comprises a screw nut.

Preferably, the length of the lance is from 1 to 7 m,

particularly preferred 2.5 to 6 m.

Preferably, the diameter of the lance is from 12 to 50 mm, particularly preferred 15 to 30 mm.

The wooden casing of the oxygen lance can be made of any kind of wood, such as softwood, bamboo and hardwood, natural wood, composite wood and engineered bamboo.

The outer wall of the wooden casing is preferably rectangular, in particular quadrate or circular. The inner wall of the wooden casing is preferably circular. The wooden casing has an outer diameter of preferably 30 to 100 mm, in particular 50 to 85 mm. The inner diameter depends on the diameter of the lance. The gap between the inner wall of the wooden casing and the lance preferably is from 0 to 10 mm, in particular from 0 to 3 mm.

In a preferred embodiment, there is no gap between the inner wall of the wooden casing and the lance. The lance is locked to the wooden casing by friction. A new lance having a wooden casing is fixed at the fitting means at the end of the lance and one end of the new lance. Preferably, the wooden casing is fixed with a nailplate to the new wooden casing.

The wooden casing has an outer diameter of preferably 8 to 50 cm, in particular 10 to 25 cm. The inner diameter depends on the diameter of the lance.

The length of the wooden casing is about the length of the lance. Preferably, the length of the wooden casing differs from the length of the lance by no more than 1 m, in particular no more than 50 cm.

The wooden casing can be made from a single piece, for example a wooden tube, or can be assembled from two, three, four or more parts, which preferably have the length of the casing. The parts can be connected by glue or mechanical link, for example, screwed joints or clamped joints.

Fig. 1 shows an oxygen lance (1) having a wooden casing (3) . The oxygen lance (1) has a fitting means (2) at one end, where a new lance can be fitted. The wooden casing (3) is composed of an upper part (3a) and a lower part (3b) , which are fixed together by bolts (4) . The lance (1) is locked to the wooden casing (3a, 3b) and is consumed as the lance with the wooden casing is moved forward.

The oxygen lance having a wooden casing can for example be used for cutting and drilling into concrete, special steel, cast steel, pig iron, slag and refractory. Preferably, the substrate material is concrete, special steel, cast steel, pig iron, slag and refractory material, such as alloy, cement or brick. Preferred applications of the lance are furnace tapping, tuyeres cleaning, accretions cutting, built-ups cutting inside or outside of the furnace, furnace inspection, window cleaning, or ladles cutting. The lance can be used in any process where a flame cutter is used, preferably where high temperatures of 2000 to 5000 K, in particular 2800 to 4000 K are used.

Preferred applications of the lance are furnace tapping, tuyeres cleaning, accretions cutting, built-ups cutting inside or outside of the furnace, furnace inspection, window cleaning, or ladles cutting.

The present invention further provides a process for production of silicon metal or metal alloy in an arc furnace, wherein liquid silicon metal or metal alloy is produced and the liquid metal or metal alloy is removed from the furnace through a tap hole, wherein the tap hole is opened by an oxygen lance having a wooden casing.

The liquid silicon metal or alloy is removed continuously or discontinuously from the furnace.

In a preferred embodiment, silicon metal is produced.

The present invention further provides a process for melting of slag in an arc furnace, wherein liquid slag is removed from the furnace through a tap hole, wherein the tap hole is opened by an oxygen lance having a wooden casing.

In a preferred embodiment, one end of the lance is placed in a holder and oxygen is fed through the lance.

In a preferred embodiment, the lance material is aluminium.

The lance and the wooden casing are consumed by burning with oxygen. During operation preferably a new lance is fixed at the fitting means at the end of the lance and one end of the new lance. A new wooden casing is fixed at the fitting means at the end of the lance and one end of the new lance. Preferably, the wooden casing is fixed with a nailplate to the new wooden casing. The lances with the wooden casings are preferably consumed simultaneously as they are moved forward.