EP0055956A1 - Blowing lance for injecting an oxidising gas, especially oxygen, for treating metal melts - Google Patents

Abstract

A lance for blowing an oxydizing gas onto a bath of molten metal, especially for blowing oxygen on a bath of molten pig iron for transforming the same into steel. The lance is provided in an end wall of its nose with at least one central aperture for blowing gas jets at great impulsion onto the bath and a plurality of auxiliary apertures for blowing gas streams of considerably smaller impulsion onto the bath. The auxiliary apertures are constituted by elongated slots through the end wall arranged spaced from each other along a circle at a distance of adjacent edges of the slots and that at least one main aperture of about 2-20 cm. This construction permits to improve the amount of secondary combustion of the reaction gas while prolonging the useful life of the nose of the lance. The lance is advantageously used in conjunction with blowing a stirring gas through the bath of molten metal through refractory gas permeable elements provided in the bottom of a crucible containing the bath.

Description

The present invention relates to a lance for blowing oxidizing gas, in particular oxygen, intended to be placed above a bath of molten metal in J _J - crucible for metallurgical treatment, in particular above of a cast iron bath for refining it into steel.

More specifically, the invention relates to lances the nose of which comprises, in addition to the usual main openings opening onto the front face of the nozzle and serving for blowing oxygen in the form of jets with strong impulse for refining properly said (oxidation of the impurities in the metal bath), additional (or secondary) openings for blowing a stream of oxygen at low speed intended to improve the secondary combustion rate of the refining gases.

It is recalled that the "nose" of the lance constitutes the end through which the refining oxygen exits in the direction of the bath. In general, the "nose" is a hollow piece of copper, attached to the end of the lance body.

It is also recalled that the term "front face" means the part of the nose turned opposite the metal bath contained in the crucible.

It is also recalled that the secondary combustion rate reflects the proportion of C0 ₂ in the reaction gases, this C0 ₂ being obtained by oxidation of the CO which is released from the metal bath following decarburization of the latter by oxygen d refining.

Multipurpose lances of this type already exist. However, progress is still possible, both in terms of increasing the secondary combustion of the reaction gases and the durability of the lance noses. These are the aims of the present invention.

To this end, the subject of the invention is a lance for blowing oxidizing gas, in particular oxygen, for refining molten metals, in particular a cast iron bath, the lance nose of which comprises two categories of '' openings: main openings opening onto the front face of the nose and serving for the blowing of oxygen with high impulse and at least one additional opening for blowing a current of oxygen at low speed, lance characterized in that the annex opening consists of several slots placed at a distance in the extension of the others in an annular assembly configuration surrounding at a distance, counted edge to edge, between 2 and 20 cm approximately, the main opening or the group formed by the main openings, and in that said slots open onto the front face of the nose.

The original idea at the base of the invention, as it will probably already understand, create straight from launch, or at least most _t o _t possible after release, a continuous sheet of oxygen which flourishes in the form of an "umbrella" around the main jets on its way to the metal bath.

For this, it is advisable that the secondary openings are not in the form of circular orifices, but on the contrary in the form of more or less elongated slots, arranged annularly around the main openings, one after the other.

The invention results from the following essential considerations:

To obtain a high secondary combustion rate, the oxygen stream (s) which create the necessary oxidizing atmosphere must be, from the outset, that is to say as soon as possible after leaving the lance. , not confined in jets located on the axis of the openings, but on the contrary diffused laterally as widely as possible. The jets then meet at a short distance from the lance to quickly form a conical gas layer, centered on the nose of the lance and which encircles the main jets by covering the metal bath from a distance. Under these conditions, an oxygen screen is formed above it that the CO emerging from the bath must pass through.

Furthermore, it has been found that practically all known lance noses wear out preferentially between the main openings and this despite the efforts made to improve the efficiency of their cooling by circulation of internal water. Thanks to their research work, the inventors were able to establish that this wear, responsible for an early scrapping of the lance noses, was mainly due to suction phenomena causing gas recirculations around the high-oxygen jets. impulse. Thus, the very hot gases present in the atmosphere above the bath and loaded with solid particles are locally sucked towards the lance and come to erode the surface of the nose around the main oxygen orifices and in particular, the zones located between these orifices, since this is where the effects of recirculation specific to several neighboring main jets add up.

Thanks to the presence of auxiliary orifices in the form of slots, in accordance with the invention, the gas flows favorably are modified against the lance nose, so that the phenomena of wear by recirculation of the hot gases are considerably reduced.

In accordance with the invention, such a result is achieved when the slots are spaced from the main openings by a distance comprised between 2 and 20 cm approximately, this distance being counted from edge to edge, because the section of the orifices concerned does not intervene much.

If the slots are located too close (less than 2 cm approximately), the gas recirculation around the main jets is certainly suppressed, but the oxygen currents at the outlet of the slots are accelerated by the entrainment effect of the main jets, so that ultimately this amounts to moving the problem of wear around the secondary slots. In addition, this acceleration is opposed to the lateral diffusion of the secondary currents, so that, in the best of cases, the formation of a homogeneous conical sheet of oxygen above the bath is delayed and the secondary combustion reduced .

On the other hand, if the slits are placed too far, that is to say more than 20 cm approximately, they have practically no more influence on the aerodynamics in the vicinity of the main jets of oxygen. However, the secondary slits should not however be placed on the lateral flank of the nose because otherwise, the desired effect is not obtained.

We will now illustrate what has just been said with the aid of the attached drawing plates in which FIGS. 1 and 2 schematically represent a lance nose according to the invention seen from below, that is to say seen of the metal bath to be treated, and FIG. 3 is a view in vertical section along the axial plane AA of FIG. 2.

In the figures, we see at 1 the front face of the lance nose 2. This face, of substantially planar shape, has in its central part three main orifices 3 for blowing jets of oxygen with strong impulse (refining oxygen ).

At a distance denoted "d" comprised, as has been said, between approximately 2 and 20 cm from the edge of the orifices 3, openings are provided for the outlet of the oxygen pulse streams, intended to form a conical sheet continuous surrounding the main jets and covering the surface of the metal bath to be refined.

In accordance with the invention, these additional openings can have numerous design variants, going from a configuration in small multiple slots 6 (FIG. 2) practically rectilinear, passing through configurations with slots in a more or less elongated arc, such as 5 (Figure 1).

It should be emphasized in fact that the gaseous screen of conical shape sought can be produced from a succession of spaced apart slots (Figures 1 and 2). The advantage of this embodiment is to be able to provide between the slots, small bridges 7 which facilitate, in terms of technological development of a cooling water circuit inside the lance nose. In this case, however, it is advantageous to provide slots with a divergent profile in the direction of blowing to allow better lateral diffusion of the different oxygen streams; secondary which can then join quickly as soon as they exit the slots, to form as soon as possible the uniform gas screen sought. For this purpose, the short sides of the slots have been chamfered. These chamfers are clearly visible at 18 in FIG. 2.

Figure 3 shows the lance nose 2 in vertical section as mounted at the lower end of the lance body, which is constituted in the usual way by three concentric tubes 8, 9 and 10. As can be seen account, the nose 2 is a hollow piece of copper, molded so as to provide central passages 11 which open on the front face 1 through the openings 3 already mentioned. This part is then drilled by machining and copper barrels 12 are placed in the holes thus produced. These guns have a passage section 13 of oblong shape in the direction perpendicular to the plane of the figure and open on the front face 1 through the slots 6.

An internal partition 14, which can be attached or molded from the original with the nose, divides the interior volume of the nose into two compartments, interior 15 and exterior 16, communicating with each other by annular passages 17 formed around the main passages 11. In this way, a sealed cooling water circuit is created inside the nose which effectively irrigates the entire front face 1. The water circulation is indicated by arrows.

Of course, the invention is not limited to the examples described, but extends to multiple variants or equivalents insofar as the technical characteristics set out in the appended claims are respected.

Furthermore, it is clear that the practical implementation of the invention supposes that means are provided which make it possible to differentiate the oxygen blowing speeds between the main jets with high impulses intended for refining, and the jets secondary to lower momentum intended to form the gas screen.

These means can be purely constructive, the relative caliber of the passages 13 ensuring the distribution of the flow rates (FIG. 3), or more elaborate to allow dynamic and independent adjustments of the gas flows from, for example, two separate oxygen supplies and a double flow lance body.

à l'oxygène de bains métalliques carburés contenus dans un récipient métallurgique. De préférence, elle s'applique conjointement avec une opération de brassage du bain obtenu par une insufflation de gaz de brassage (gaz neutre ou éventuellement oxydant) au travers de tuyères ou d'éléments réfractaires aéroperméables incorporés en paroi du récipient, à un niveau inférieur à celui du bain, et plus généralement, dans le fond du récipient. C'est en effet dans les conditions opératoires précitées que les meilleurs résultats sur le plan de la combustion secondaire ont pu être enregistrés à ce jour par les inventeurs, notamment en raison du fait, semble-t-il, que le brassage pneumatique du bain'par insufflation d'un gaz par le fond est de nature à stabiliser la hauteur de couche du laitier, donc également, la distance séparant l'extrémité de la lance de la surface de laitier.On the other hand, the invention is of general application to

oxygen from metal fuel baths contained in a metallurgical vessel. Preferably, it is applied in conjunction with an operation for stirring the bath obtained by blowing in stirring gas (neutral or possibly oxidizing gas) through nozzles or air-tight refractory elements incorporated into the wall of the container, at a lower level. to that of the bath, and more generally, in the bottom of the container. It is indeed under the aforementioned operating conditions that the best results in terms of secondary combustion have been recorded to date by the inventors, in particular due to the fact, it seems, that the pneumatic mixing of the bath 'by blowing a gas from the bottom is likely to stabilize the height of the slag layer, therefore also the distance between the end of the lance and the slag surface.

Claims (6)

1) Lance for blowing oxidizing gas, in particular oxygen, for the treatment of molten metals, in particular for refining a steel melt bath, and comprising a lance nose provided with two categories of openings : at least one main opening for blowing gaseous jets with high impulse and opening onto the central region of the front face of the lance nose, and at least one additional opening for blowing gas streams with substantially weaker impulse, characterized in that the additional opening is constituted by several slots placed at a distance in the extension of the others in an annular overall configuration surrounding at a distance, counted edge to edge, between 2 and 20 cm approximately, the main opening or the group formed by the main openings, and in that said slots open onto the front face of the nose. 2) blowing lance according to claim 1, characterized in that the slots have a divergent profile in the direction of the gas blowing. 3) blowing lance according to claim 2, characterized in that the short sides of the slots are chamfered. 4) Application of the lance according to claims 1, 2 or 3, to a steel plant for refining with oxygen a bath of cast iron contained in a container, characterized in that the wall of the container has at one level lower than that of the bath, means for blowing a stirring gas into the bath. 5) Application according to claim 4, characterized in that the means for blowing a stirring gas into the bath are air-tight refractory elements. 6) Application according to claim 4, characterized in that the means for blowing a stirring gas into the bath are nozzles.

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