EP0080403A1 - Installation for introducing gas into a bath of liquid metal - Google Patents

Abstract

1. A permeable device for introducing gas into a bath of liquid metal, comprising a case (1) in which is disposed an enclosure (3) which is open in its upper part, in which is placed at least one permeable refractory element (8) retained by a first refractory binder (10), the bottom (5) of the enclosure (3) having an orifice (6) connected to an inlet tube (2) for said gases, and the enclosure being fixed in the case by a second refractory binder (11), characterised in that the case is in the form of a box open in its upper part and having a bottom through which the gas inlet tube (2) extends in a sealed manner.

Description

- The present invention relates to a permeable device for the introduction of gas into a bath of liquid metal and more particularly for the introduction of a stirring gas in liquid steel.

Currently used to introduce stirring gases into the liquid steel, during the development or refining of the latter, nozzles or permeable bricks of rectangular section which have approximately the same format as that of the bricks which are used for briquetting the refractory lining of the bottom of the converters. These permeable bricks are made up of permeable elements, molded or enclosed within a thin sheet box, at the base of which is injected, by a tube which is welded, the stirring gas.

• - la soudure du tube, effectuée sur la tôle mince, est relativement fragile et les déplacements relatifs du briquetage du convertisseur constituant le revêtement réfractaire, par rapport à la tôle de fond du blindage de ce convertisseur peuvent provoquer une rupture de la liaison entre le tube d'alimentation du gaz et la tôle mince, ce qui provoque une fissure ou une ouverture par où s'échappent les gaz de brassage . Ceux-ci se répandent alors dans le fond du briquetage du convertisseur en y créant des surpressions qui peuvent soulever le revêtement réfractaire et amener sa destruction accidentelle;
• - les dispositifs perméables du type décrit précédemment sont normalement enchassés dans le briquetage du convertisseur qui est maçonné, très serré, autour de ces dispositifs de façon à maintenir les briques du revêtement en contact étroit avec la tôle mince constituant le caisson. Il peut se produire au cours du fonctionnement du convertisseur, que sous l'effet des contraintes thermo- mécaniques, les briques de fond se déplacent les unes par rapport aux autres provoquant ainsi le desserrage du caisson et de ce fait de la tôle mince qui constitue le caisson, de l'élément perméable sous forme de brique poreuse qu'il contient. La fissure qui peut ainsi être ouverte entre la tôle du caisson et l'élément perméable constitue une amorce dangereuse d'infiltration de métal liquide;
• - la pression appliquée au fond du dispositif perméable tend à déformer les parois métalliques de faible épaisseur constituant le caisson, qui se décollent des éléments réfractaires perméables qu'il contient, ce qui est en particulier le cas lors d'un déplacement du briquetage comme indiqué précédemment. Lors de l'injection de gaz de brassage, ce dernier chemine ainsi le long du caisson par la fente qui s'est créée et à travers laquelle il se fraye un passage jusque dans le bain d'acier liquide. La largeur de cette fente peut devenir excessive et il peut se produire alors des infiltrations de métal liquide par ce passage ouvert entre la tôle du caisson et les éléments perméables qui y sont contenus. Ces infiltrations sont dangereuses car elles peuvent atteindre la partie inférieure du dispositif perméable et le détruire, et s'introduire dans le tube d'alimentation du gaz et même trouver un passage jusque vers l'extérieur du convertisseur dans les canalisations d'amenée du gaz de brassage;
• - la dépouille (ou la conicité) des dispositifs perméables qui sont exactement du même format que les briques du revêtement réfractaire du convertisseur, est relativement faible. La pression du gaz de brassage exercée sur toute la surface du fond de l'élément perméable crée une poussée telle qu'elle peut déplacer celui-ci en dehors de son caisson et le pousser progressivement au-dessus du niveau de la surface du fond du convertisseur. Son usure s'en trouve ainsi considérablement accélérée. Ce mécanisme de destruction est très dangereux car il peut conduire à une percée de l'acier liquide à travers le fond du convertisseur lorsque la brique a été totalement usée. La présente invention vise à remédier à ces inconvénients en fournissant un élément perméable pour l'introduction de gaz dans un métal liquide qui ne présente pas ces risques de désolidarisation des éléments perméables de l'enveloppe dans laquelle ils sont contenus.

However, this type of permeable device has the following disadvantages:

• - the welding of the tube, carried out on the thin sheet, is relatively fragile and the relative movements of the brickwork of the converter constituting the refractory lining, relative to the bottom sheet of the shielding of this converter can cause a break in the connection between the tube gas supply and the thin sheet metal, causing a crack or opening through which the stirring gases escape. These then spread through the bottom of the converter's brickwork, creating overpressures there that can raise the refractory lining and cause its accidental destruction;
• - Permeable devices of the type described above are normally embedded in the brickwork of the converter which is masonry, very tight, around these devices so as to keep the bricks of the coating in close contact with the thin sheet metal constituting the box. It may occur during the operation of the converter, that under the effect of thermomechanical constraints, the bottom bricks move one by compared to the others thus causing the loosening of the box and therefore of the thin sheet which constitutes the box, of the permeable element in the form of porous brick which it contains. The crack which can thus be opened between the sheet metal of the box and the permeable element constitutes a dangerous initiation of liquid metal infiltration;
• - the pressure applied to the bottom of the permeable device tends to deform the thin metal walls constituting the box, which detach from the permeable refractory elements which it contains, which is particularly the case when the brickwork is displaced as indicated previously. During the injection of stirring gas, the latter thus travels along the box through the slot which has been created and through which it makes its way into the bath of liquid steel. The width of this slot may become excessive and there may then occur infiltration of liquid metal through this open passage between the sheet of the box and the permeable elements contained therein. These infiltrations are dangerous because they can reach the bottom of the permeable device and destroy it, and get into the gas supply tube and even find a passage to the outside of the converter in the gas supply pipes. brewing;
• - the draft (or taper) of the permeable devices which are exactly the same format as the bricks of the refractory lining of the converter, is relatively small. The pressure of the stirring gas exerted over the entire surface of the bottom of the permeable element creates a thrust such that it can move the latter out of its casing and gradually push it above the level of the bottom surface of the converter. Its wear is thus considerably accelerated. This destruction mechanism is very dangerous because it can lead to a breakthrough of the liquid steel through the bottom of the converter when the brick has been completely worn. The present invention aims to remedy these drawbacks by providing a permeable element for the introduction of gas into a liquid metal which does not present these risks of separation of the permeable elements from the envelope in which they are contained.

The invention thus relates to a permeable device for the introduction of gas into a bath of liquid metal, comprising a box open at its upper part in which is disposed a refractory element permeable to gases and the bottom of which is connected to a tube of admission of said gases, characterized in that it comprises an enclosure open at its upper part, housed in the box and in which is placed at least one element: permeable refractory nent retained by a first refractory binder, the bottom of the enclosure comprising an orifice connected to the gas inlet tube which crosses the bottom of the box, and the enclosure being fixed in the box by means of a second refractory binder.

The enclosure preferably comprises a body of revolution, substantially frustoconical, the smallest diameter of which is at the upper opening and the side wall of which is provided with retaining means protruding inwards and a curved bottom whose convexity is turned towards the bottom of the box.

The retaining means may consist of one or more circumferential grooves or of a set of lugs formed in the side wall by stamping or any other means.

The invention will be explained below in more detail with the aid of the accompanying drawings which show an embodiment of it.

• la Fig. 1 est une vue en perspective avec arrachement partiel d'un dispositif perméable pour l'introduction de gaz selon la présente invention;
• la Fig. 2 est une vue en coupe du dispositif selon la Fig. 1;
• la Fig. 3 est une vue en perspective d'un élément réfractaire perméable placé dans l'enceinte de la Fig. 1.

In these drawings:

• Fig. 1 is a perspective view with partial cutaway of a permeable device for the introduction gas according to the present invention;
• Fig. 2 is a sectional view of the device according to FIG. 1;
• Fig. 3 is a perspective view of a permeable refractory element placed in the enclosure of FIG. 1.

The permeable device according to the present invention shown in FIG. 1 comprises a box 1 of generally parallelepipedal shape open at its upper part and comprising a flat bottom, this box being made of a thin sheet. The bottom of the box 1 is crossed by a gas inlet pipe 2 which is welded in a leaktight manner to the bottom of the box.

A rigid enclosure 3, which is designed to withstand the pressure of the gas, is housed in the box 1. This enclosure comprises a body 4 of substantially frustoconical shape open at its upper part; the smallest diameter of the frustoconical body corresponding to the opening and a domed bottom 5 whose convexity is turned towards the bottom of the box. The domed bottom 5 has an orifice 6 which is connected in leaktight manner to the tube 2 by a weld.

The frustoconical body 4 has along its lateral wall two circumferential grooves 7 which project towards the inside of the enclosure 3.

According to a variant, the circumferential grooves 7 can be replaced by lugs 7a, or else an appropriate combination of these grooves 7 and lugs 7a can be used.

Refractory permeable elements 8 are placed in the enclosure 3 on a bed of granular refractory material 9 intended to distribute the brewing gas over the entire section of the permeable element (more clearly visible in FIG. 2).

The permeable elements 8 are inserted in a first refractory binder 10 which is vibrated (or in the annular space situated between these permeable elements and the enclosure 3, above said bed of granular material 9.

The refractory material 10 is compatible with the refractory material which constitutes the permeable elements 8 and adheres securely to the latter whose walls are rough and / or provided with asperities. this reduces the risk of displacement of all of the permeable elements, inside the enclosure 3, on the one hand, thanks to the frustoconical shape of the latter, and, on the other hand, thanks to the circumferential grooves located in planes parallel to the upper opening and / or to the lugs formed on the internal face of the enclosure, which prevent any movement of the refractory 10 relative to this enclosure 3. The enclosure 3 is made of a sufficiently thick sheet metal to resist the pressure of the gas and its domed bottom also contributes to increasing the resistance to the pressure of the gas.

The assembly thus consisting of the enclosure 3 in which are placed permeable elements 8 embedded in a refractory binder 10, is housed in the casing 1 and made integral with the latter by insertion of a second refractory binder 11 in the space left free between the enclosure 3 and the box 1. A rigid, one-piece assembly is thus produced between the enclosure 3 and the elements it contains, and the box 1.

This box 1 is generally substantially parallelepipedal or pyramidal in shape which is compatible with the format of the brickwork used for the bottom of the converter.

The second refractory binder 11 is for example a refractory clay compatible with both the first refractory binder 10 and the refractory material which constitutes the bricks of the refractory lining covering the bottom of the converter.

• - un défaut d'étanchéité entre la tubulure 2 et l'enceinte 3 ne peut pas provoquer de désordre dommageable au fond du convertisseur, car les gaz qui s'échapperaient par la fissure ainsi ouverte, resteraient contenus dans l'enveloppe métallique constituant le caisson 1 et ne pourraient que diffuser lentement, à travers le matériau réfractaire 11 vers le bain de métal liquide contenu dans le convertisseur. Ces gaz ne pourraient pas pénétrer à l'intérieur du massif réfractaire que constituent les briques du fond du convertisseur;
• - la pression du gaz introduit par la tubulure 2, et qui peut être par exemple un gaz de brassage, peut atteindre des valeurs élevées sans dommage, car ce gaz est contenu entièrement dans l'enceinte 3 qui est -calculée pour résister à ces pressions élevées. Le gaz de brassage ne peut en outre pas chasser ou déplacer les éléments perméables 8 et le matériau liant réfractaire 10 qui les entoure, car ceux-ci sont solidaires et solidement ancrés à l'enceinte 3 grâce aux rainures 7 et/ou ergots 7a et à la forme tronconique de cette enceinte;
• - cette structure permet en outre d'adopter la forme géométrique et la section les plus favorables à la fois pour les éléments perméables 8, et pour le caisson 1 qui doit être logé dans le briquetage de fond du convertisseur.

The structure of the permeable device for the introduction of gas according to the present invention thus produced, has the following advantages:

• - a leak between the tubing 2 and the enclosure 3 cannot cause damaging disorder at the bottom of the converter, because the gases which would escape through the crack thus opened, would remain contained in the metallic envelope constituting the box 1 and could only diffuse slowly, through the refractory material 11 towards the bath of liquid metal contained in the converter. These gases could not penetrate inside the refractory mass which constitute the bricks of the bottom of the converter;
• - The pressure of the gas introduced through the pipe 2, and which can for example be a stirring gas, can reach high values without damage, because this gas is contained entirely in the enclosure 3 which is calculated to resist these pressures high. The stirring gas can also not drive out or move the permeable elements 8 and the refractory binder material 10 which surrounds them, since these are integral and solidly anchored to the enclosure 3 thanks to the grooves 7 and / or pins 7a and to the frustoconical shape of this enclosure;
• - This structure also allows to adopt the geometric shape and the most favorable section both for the permeable elements 8, and for the box 1 which must be housed in the bottom brickwork of the converter.

By way of example, the permeable elements 8 can be in the form of a monolithic mass produced from a grainy, sintered, porous refractory mixture, for example as described in US Pat. No. 4,230,931, or under the form of a stack of plates made of a refractory material, these plates being placed side by side and arranged vertically in the enclosure 3.

The plates 8, one of which is shown in detail in FIG. 3, have in particular a parallelepipedic or preferably prismatic shape generated on a trapezoidal base and are arranged vertically according to their larger dimension, so that the large base 12 of the main faces 13 of the plates rests on the bed of granular refractory material 9.

Can be provided on the side faces 14 of the plates 8 anchoring means in the form of projecting parts 15 or recessed (not shown) relative to these faces which compete with the trapezoidal shape of the main faces of the plates solid anchoring of the latter in the refractory binder 10, thus preventing any ejection of the plates 8 by the stirring gas.

The refractory mass, constituted by the joined plates, is given the desired permeability for the passage of gases, by producing substantially vertical microchannels 16 which promote the flow of gas and ensure the permeability and the flow of gas through the permeable elements. .

To make these microchannels, one can, for example, longitudinally streak one or both main faces 13 of the plates which are then joined together, so that the grooves, when the plates are stacked, constitute these longitudinal microchannels which give the permeable element excellent permeability and allow large quantities of gas to be delivered.

It is thus possible, for example, to produce plates having a thickness of approximately 8 mm, a length of 650 to 750 mm obtained in a single piece, or possibly in two pieces and a width of 150 to 250 mm. The ridges which are made on the surface of the plates, on one or both main faces, have a depth of a few tenths of a millimeter; and at most 0.3 mm, so that the open gap between two juxtaposed plates does not in any case exceed 0.5 mm. This limitation of the size of the microchannels eliminates the risk of metal infiltration which would cause progressive loss of permeability of the permeable element constituted by the stacking of platelets.

The microchannels can also be obtained by introducing, during the pressing of these plates at the bottom of the mold, an aerated organic fabric the diameter of the wires of which will be between 1 /! Oem from millimeter to 0.3 mm. When these parts are cooked, the organic fiber fabric will burn and will therefore give the platelets the microchannels necessary for good permeability.

The refractory material constituting the permeable element 8 is chosen to withstand the thermal shocks to which it is subjected when, preheated by the atmosphere of the converter, it is suddenly cooled when the mixing gas is admitted at full flow. This material must resist the action of gases which pass through it and which can be, for example: neutral, such as nitrogen or argon; reducing agents such as carbon monoxide, hydrogen; oxidizing agents such as oxygen or water vapor; or carbonating agents such as carbonic gas; or compatible mixtures of these gases. These materials must therefore resist the corrosive action of the oxidized liquid metal as well as that of the basic slag loaded with iron oxide with which they are in contact during the brewing operations.

These materials can in particular be based on grains of magnesia, corundum, sintered and / or electrofused mullite, bonded together by clay, alumina and / or chromium oxide, then refritted to high temperature. All of these plates could be made entirely of silicon nitride or a variety of sialons.

To improve the corrosion resistance of this refractory element with superficial or porous ridges, it is also possible to add to the above compounds, graphite or boron nitride which further reduce the wettability of these elements relative to the metal molten.

The first refractory binder 10 in which the permeable elements 8 are embedded must obviously be compatible with the latter and is a material conventionally used for this purpose.

The second refractory binder material is also a conventional material such as a basic rammed earth chosen for its compatibility both with the first refractory binder and with the basic refractory material which constitutes the briquetting of the bottom of the converter.

Indeed, by contacting with the liquid metal, the metal envelopes constituting the box 1 and the envelope 3 are liquefied and eliminated at least over a certain height so that the basic refractory material constituting the brickwork of the bottom of the converter contact of the second refractory binder 11 which is itself in contact with the first refractory binder 10.

Claims (11)

, 1. Permeable device for the introduction of gas into a bath of liquid metal, comprising an envelope (1) in which is disposed an enclosure (3) open at its upper part, in which is placed at least one permeable refractory element ( 8) retained by a first refractory binder (10), the bottom (5) of the enclosure comprising an orifice (6) connected to an inlet tube (2) of said gases and the enclosure being fixed in the box by means a second refractory binder (11), characterized in that the envelope is in the form of a box open at its upper part and comprising a bottom through which the tube (2) for gas admission. 2. Device according to claim 1, characterized in that the enclosure comprises a body (4) substantially frustoconical whose smallest diameter is located at the upper opening and whose side wall is provided with retaining means (7, 7a ) projecting inwards and a curved bottom (5) whose convexity is turned towards the bottom of the box. 3. Device according to claim 2, characterized in that the retaining means consist of at least one circumferential groove and / or a set of lugs. 4. Device according to any one of the preceding claims, characterized in that the box is substantially parallelepiped. 5. Device according to any one of the preceding claims, characterized in that the refractory element consists of a monolithic mass in a grainy, sintered and porous refractory mixture. 6. Device according to any one of claims 1 to 4, characterized in that the permeable element (8) consists of a set of parallelepipedic plates or straight prismatics arranged vertically along their largest dimension, the lateral faces of which are provided with anchoring means (15) and comprising longitudinal microchannels (16), placed on a bed of granular refractory material (9). 7. Device according to claim 6, characterized in that the microchannels are produced by longitudinally striating the face of the plates so that the ridges have a depth at most equal to 0.3 mm. 8 - Device according to claim 6, characterized in that the microchannels are produced by placing between the plates (8) an aerated organic tissue whose wire diameter is between 0.1 and 0.3 mm. 9 - Device according to any one of claims 6 to 8, characterized in that the plates are made of a material based on grains of magnesia, corundum, sintered and / or electrofused mullite, bonded between by the clay, alumina, and / or chromium oxide, then refritted at high temperature. 10 - Device according to any one of claims 6 to 8, characterized in that the wafers are made of silicon nitride or a variety of sialons. 11 - Device according to claim 9 or 10, characterized in that the plates further comprise as a constituent material of graphite or boron nitride.

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