EP0364722B1 - Oxygen blast pipe - Google Patents

Abstract

Lance for injecting refining oxygen from above into baths of metals or of ferrous alloys contained in metallurgical vessels. In its end part the lance comprises a Laval tuyere defining in the direction of flow of the gas firstly a converging region, then a cylindrical throat and finally a diverging region. It further comprises a substantially cylindrical movable central regulating body which can be moved forward or back axially in the neck region of the Laval tuyere. The nose of the central regulating body has a special profile which, together with the outer coaxial cylindrical wall of the Laval tuyere, defines a diverging region which causes an expansion of the gas stream. The profile of the nose of the movable central body and that of the converging portion of the Laval tuyere are at least approximately complementary. The characteristics of the gas stream are modified through changing its flow profile by axial movement of the nose of the central regulating body. <IMAGE>

Description

The invention relates to a lance for refining metals or ferroalloys contained in a metallurgical vessel by means of a jet of oxygen blown at supersonic speed from above onto the molten bath.

When designing such a refining lance, a whole series of parameters are taken into account, including essentially the speed of the jet expressed by the Mach number and the optimal gas flow rate, the latter depending on the reactions targeted, as well as the metallic mass contained in the container, which is generally a converter. To obtain a supersonic jet, the central gas discharge conduit normally comprises a converging part followed by a more or less long cylindrical neck, as well as a diverging part downstream. Such a central duct is designated by the name of 'Laval nozzle'. It is also known that the Mach number depends on the pressure of the gas supply source, while the optimal flow rate is itself a function of the inlet pressure at the nozzle and the diameter of the neck of the convergent.

As the geometrical configuration of the nozzle is decisive for the characteristics of the jet, parameters such as the Mach number and the optimal flow cannot be varied independently of each other. This means that if a lance has been designed to have a high flow rate, you cannot, for example, carry out a hard jet and reduced flow blowing, nor switch to a soft and reduced flow blowing, without 'takes away in one direction or the other the optimal sizes resulting from the geometrical configuration of the nozzle. If one tries to exceed the limits of the flow rate and the speed of exit, it is created inside the metallurgical container and near the mouth of the lance of the shock waves. The consequence is that the characteristics of the jet deteriorate and that the wear of the lance progresses rapidly.

However, the metallurgist is often confronted with situations where he would have great advantage to change the characteristics of the jet during certain phases of refining. Thus, when it comes to forming a highly oxidized slag, it is recommended to inject a soft vertical jet with a high flow rate. Just as frequently, a hard vertical oxygen jet is required for reduced total flow. This last way of operation is indicated when it is a question of reducing the total volume of oxygen in order not to oxidize the slag, but to have a hard and penetrating jet to guarantee a vigorous decarburization of the metal. Thus, in order to be able to cope with the same lance with diametrically opposite refining conditions, this lance must make it possible to deliver the oxygen just as well in hard jet with reduced flow, as in soft jet with high flow.

Such an oxygen blowing lance, which includes a Laval nozzle and which makes it possible to vary the Mach number and the optimal flow rate one independently of the other, has been described in European patent application no. 235,621. To this end, provision is made to be able to mechanically reduce the cross-section of the passage of the primary oxygen jet in the nozzle and to control the characteristics of the primary jet at the outlet of the nozzle by means of a secondary gaseous curtain which completely envelops the jet. primary. Furthermore, the pressure of each of the two gases can be adjusted one independently of the other. The passage section of the primary jet in the nozzle is reduced or enlarged by means of a very tapered needle-shaped tip which is movable along the axis of the nozzle. But this fairly sophisticated lance is not very easy to handle because the primary jet and the secondary envelope influence each other and that it is a question of modulating a large number of parameters one according to the other , which makes the operation of the lance uncertain at the limits of the regulation possibilities which must be used to obtain the extreme characteristics of the refining jet.

The object of the present invention is therefore to propose an oxygen blowing lance comprising a Laval nozzle, which, in concert with a central obturation device of specific configuration, makes it easy to reach and to vary the extreme characteristics of an oxygen jet, without resorting to an auxiliary jet peripheral. In addition, the creation of turbulence must be avoided or at least minimized, for any mode of operation of this Laval nozzle. Finally, the mechanical means used must be of reduced bulk, operate at reduced motive power and include a minimum of moving parts.

This object according to the invention is achieved by a lance according to the invention as characterized in the independent claim. Preferential variant embodiments are described in the dependent claims.

The main advantage of the new lance concept according to the invention resides in the possibility offered to the metallurgist to be able to easily adapt at each instant of refining the conditions for injecting the oxygen jet according to metallurgical requirements by varying in the desired limits the volume of the ripening oxygen, while at the same time being able to jet the desired speed.

• la fig. 1 est une coupe à travers une forme d'exécution préférée de la partie de lance comprenant la conduite d'évacuation du gaz façonnée en tuyère de Laval, ainsi que l'extrémité profilée du corps qui sert par déplacement axial à régler le profil du passage d'écoulement du gaz, et
• la fig. 2 est une coupe à travers une forme d'exécution du corps central avec ses parties mobiles et ses parties fixes logeant le mécanisme d'entraînement.

The invention is described in more detail below with reference to the drawings in which:

• fig. 1 is a section through a preferred embodiment of the lance part comprising the gas evacuation pipe shaped into a Laval nozzle, as well as the profiled end of the body which serves by axial displacement to adjust the profile of the passage gas flow, and
• fig. 2 is a section through an embodiment of the central body with its mobile parts and its fixed parts housing the drive mechanism.

• en amont de l'extrémité supérieure de la lance, normalement à proximité du point de suspension de la lance à son chariot, une vanne de régulation qui permet de faire varier la pression d'entrée du gaz avec la précision désirée et dans les limites préétablies.
• à l'extrémité inférieure, ou nez de la lance, l'embouchure (près du bord supérieur de la page) d'où émerge le jet de gaz projeté contre la surface du bain à traiter.
• dans la direction radiale et à l'extérieur de la conduite centrale 1, soit un manchon de protection en matière réfractaire, soit un assemblage de tuyaux et conduites concentriques pour véhiculer l'eau de refroidissement et éventuellement de l'oxygène de postcombustion injecté indépendamment du jet primaire central. Ces éléments qui ne rentrent pas en eux-mêmes dans l'objet de l'invention n'ont pas été illustrés.

Fig. 1 shows the Laval nozzle with its parts with variable sections, as well as the profiled nose 6 of the central adjustment body 5, both located in the lower end or head of the lance. The lance head also includes the following parts:

• upstream of the upper end of the lance, normally near the point of suspension of the lance to its carriage, a regulating valve which makes it possible to vary the gas inlet pressure with the desired precision and within the pre-established limits .
• at the lower end, or nose of the lance, the mouth (near the upper edge of the page) from which emerges the jet of gas projected against the surface of the bath to be treated.
• in the radial direction and outside of the central pipe 1, either a protective sleeve made of refractory material, or an assembly of concentric pipes and pipes to convey the cooling water and optionally afterburning oxygen injected independently of the central primary jet. These elements which do not come within themselves within the object of the invention have not been illustrated.

The Laval nozzle as illustrated comprises in the direction of gas flow first a converging part 4, then a cylindrical neck 3 and finally a diverging part. The length and the shape of the converging and diverging parts are chosen according to the profile and the position of the nose 6 of the central adjustment body 5 or vice versa. It should be noted that the length of the cylindrical neck 3 can be extremely short and can be reduced to a single plane.

The upper part of the central adjustment body 5 is received in a movable manner in the lower end of a cylindrical copper casing 7, as illustrated in FIG. 2. The housing 7 is itself rigidly connected to the oxygen evacuation pipe by means of radial spacers. The adjustment body 5 at the head of the housing 7 is exchangeable, its fixing being preferably carried out by screwing. It can be moved down or up along the axis of the lance under the action of a motive force, which can for example be provided by a linear stepping motor. To this end, the adjustment body 5 is connected to a movable rod 8 actuated by the positioning cylinder 13 secured to a motor. The engine is actuated according to instructions received from an electronic control device, which transforms entry dates, such as for example the actual gas flow rate, the desired gas flow rate and the momentary position of the rod 8, to deduce the new required position of the rod 8.

Upstream of the convergent 4 of the Laval nozzle, the cavity 9 is made tight vis-à-vis the flow of oxygen by means of O-rings. More downstream, on the other hand, there is communication between the region of the neck 3 and the cavity 9 by virtue of grooves which extend axially from the cavity 9 to the surface of the profiled part of the nose 6 of the central adjustment body 5. With this measure, the driving force for actuating the central adjustment body 5 can be significantly reduced. Indeed, along the profile of the nose 6 there is an underpressure - variable depending on the point considered and according to the operating parameters of the lance - which tends to suck the central adjustment body 5 towards the orifice of the lance . Thanks to the grooves 11, the underpressure prevailing outside is also established inside the cavity.

In the vicinity of the orifice or nose of the blowing lance, a conventional divergent zone, visible in FIG. 1 and constituted by the frustoconical flaring part 2.1 of the central oxygen pipe, extends from the lance nose up to a certain distance upstream and controls the expansion of the oxygen jet in the usual manner. Upstream of this terminal region, the new divergent zone is formed by the profiled part of the nose 6 of the central adjustment body 5 which causes the expansion of the gas and it is delimited externally by the peripheral tube 2.2, which preferably has a shape cylindrical. However, this tube has no major influence on the dynamics of gas expansion. As for the geometric shape of the tip of the nose 6 of the central adjustment body 5, it is linked to that of the converging part 4 or vice versa. The shape is determined either by calculations or by empirical tests, so that the turbulence remains minimized and the gas is gradually accelerated. It appears that with suitable profiling of the nose 6 of the central adjustment body 5, for example that illustrated in FIG. 1, the predominant part of the expansion of the gas takes place along this part. It follows that the conventional divergent zone 2.1 loses most of its importance and that, at the limit, it can be envisaged for its elimination.

The neck 3 according to the invention is constituted by an outer guide wall of cylindrical shape with constant section - just as it is used in conventional nozzles - and in addition by an inner guide wall of cylindrical shape formed by the wall lateral of the central adjustment body 5. The extension of this neck depends on the position of the central adjustment body 5 and it can be reduced in the limiting case to a simple plane separating the converging part from the diverging part.

The convergent 4 is delimited by an internal cylindrical surface, formed by the side wall of the central adjustment body 5 and by an external convergent profile 4.1, constituted by the internal wall of the nozzle. The configuration of the converging zone is a little less critical than that of the new divergent profile determined by the contour of the nose 6 of the central adjustment body 5 and one could go so far as to give it a simple conical shape. Nevertheless, the fact remains that the advantages of the invention are optimally obtained if the wall 4.1 is profiled and if this profile is complementary to that of the pointed part of the nose 6 central adjustment body 5.

According to the preferred embodiment of the invention, the intersection of the profiled part of the nose 6 of the central adjustment body 5 with a plane containing the axis of the nozzle, has parabolic parts which delimit the pointed end of the profile of the nose 6 and which are connected to the central adjustment body 5 by substantially circular traces. The purpose of this configuration is to eliminate as far as possible the discontinuities likely to create disturbances.

According to the normal manner of operation of such a lance, a given pressure is chosen for the gas source - by positioning the valve in the evacuation circuit - and the gas flow is varied by modifying the position of the nose 6 of the central adjustment body 5. In this way, the gas flow rate is effectively varied for a given Mach number without causing the jet to burst. However, it is also easy to go from the operating mode established more or less as a routine mode to limiting regulation conditions. Thus, the softest possible gas jet is obtained by choosing a low pressure for the gas source and by advancing the central adjustment body 5 as much as possible, so as to minimize the effective section left free in the duct of 'oxygen. The other limiting condition consists in an extremely hard jet, which is obtained if the pressure of the gas source is high and if the central adjustment body 5 is retracted to the maximum, that is to say that the effective free section in the neck of the main duct is as large as possible.

It should be noted that if conventional Laval nozzle lances have been designed either for a hard jet or for a soft jet, they are completely unsuitable for refining phases requiring blowing conditions other than those for which the lances have been built. Indeed, a lance designed to provide a soft jet does not make it possible to substantially increase the acceleration of the gas, while with a lance constructed to obtain a hard jet the quantities of gas ejected cannot be increased at will. In both cases the increase in the pressure at the source of the gas results in the formation of shock waves, which impede the acceleration of the gas and limit its flow.

Claims (8)

1. Gas blowing lance which is used for the refining of a molten metal or ferro-alloy bath contained in a metallurgical vessel and which comprises in its terminal part a Laval tuyere having varying sections outlining in the direction of the gas flow a convergent part (4) followed by a throat (3) and a divergent part (2) near the nose of the lance, as well as a substantially cylindrical central throttle body (5) being movable along the axis of the tuyere in the area of the throat (3), characterized in that a divergent area is delimited by a substantially cylindrical wall of the inner oxygen conveying tube (1) and by a nose part (6) projecting beyond the central throttle body (5) which has a cylindrical shape and which is profiled in such a way as to assure an expansion of the gas.
2. Lance according to the claim 1, characterized in that the contour of the nose part (6) is profiled in such a way that the curves obtained by its intersection with a plan passing through the axis of the central throttle body (5) present in their midpoints an inflexion point.
3. Lance according to one of the claims 1 or 2, characterized in that the variation of the section of the nose part (6) along the axis of the central throttle body (5) within a plan perpendicular to the axis of the body (5) is reduced at the level of the central throttle body (5), important in the middle area of the nose (6) and reduced towards the extremity of the nose (6).
4. Lance according to one of the claims 1 to 3, characterized in that the intersection of the nose part (6) with a plan comprising the axis of the central throttle body (5) shows parabolic parts linked to the cylindrical body by substantially circular curves.
5. Lance according to the claim 1, characterized in that the nose part (6) of the central throttle body (5) is exchangeable.
6. Lance according to claim 1, characterized in that the central throttle body (5) is movable in an elongated cavity (9) surrounding the lower end of the said body (5), the cavity (9) being isolated with the help of O-rings (10) in a gas-tight manner from the stream of gas flowing through the main gas duct at the level of the convergent portion 4.1.
7. Lance according to the claim 6, characterized in that the said cavity (9) is in communication with the gas stream through the intermediary of grooves (11) in the nose part (6) of the central throttle body (5).
8. Lance according to one of the claims 1 to 7, characterized in that the intersection curves of the profiled nose part (6) and of the convergent portion (4.1) with a plan passing through the axis of the lance can be inferred at least in part homothetically from one another.

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