EP0086694B1 - Top-blown lance for a metallurgical converter - Google Patents

Abstract

A gas-injection lance has a main tube centered on an axis and having a lower end formed adjacent the axis with a plurality of throughgoing inner orifices and an upper end to which is fed a treatment gas under pressure that pressurizes the interior of the tube therewith sufficiently that the gas exits from the lower end through the inner orifices at supersonic speed. An annular array of nozzles traversing the lower tube end around the inner orifices each have an outer end opening outside of the tube and an inner end inside the tube. Respective pressure-reducers each have one side open at the lower tube end inside the tube and another side connected to the inner end of a respective nozzle for passing gas from the interior of the tube into the nozzles with a substantial pressure reduction so that the gas exits from the outer ends of the nozzles at subsonic speed. The pressure-reducers each comprise a body forming a chamber of predetermined flow cross section into which the respective inner nozzle end opens and an inlet on the body having an opening of flow cross section much smaller than that of the chamber and of the respective nozzle.

Description

The present invention relates to a gas injection lance specially designed for metallurgical converters with oxygen blowing from above, by the fact that it makes it possible to produce two concentric gas flows under different generating pressures.

Lances are commonly used in metallurgical converters which inject oxygen to the surface of a liquid metal to be refined, such as cast iron or steel. It is known that it is often advantageous, in this kind of operation, to complete the refining reaction of the molten metal by a secondary combustion of the gases which are released from the metal bath, this secondary combustion requiring a pressure which generates oxygen. lower and an annular distribution of the injection around the, or, more generally, the central primary jets with strong impulse ensuring the conversion of the bath. For this, we use - as shown for example in document LU-A-78906 - so-called "double flow" lances, supplied by two separate oxygen circuits at different generating pressures from outside the converter. However, it is known that it is not always easy to implement such dual-flow lances, with two separate feeds, and difficulties may arise with regard to the individual controls of each flow.

Similar difficulties are generally encountered with lances with a single supply source and the separation of the gas stream into two separate outlet streams is carried out by simple withdrawal of the secondary stream outside the internal chamber of the body of the lance and serving to the admission of the main flow to the blowing orifices of primary jets (DE-A-1 408 783).

The present invention makes it possible to avoid these drawbacks thanks to a lance specially designed to produce, from a single supply source of the lance, two different generating pressures, that generating the secondary flow being insensitive to the fluctuations of the other , which generates the main flow. The lance according to the invention also has the advantage of being able to be easily mounted on existing installations using single-flow lances, often even by replacing only the nose of the lance, that is to say the extreme part. the closest, to the liquid metal bath and from which the gas flows come out.

The invention thus relates to a gas injection lance comprising an internal chamber for admitting a main gas flow to a first series of injection orifices and, inside said chamber, means for formation of a secondary flow delivered to a second series of outlet orifices, said means taking a fraction of the main flow in the internal chamber, lance characterized in that said means are constituted by necks at speed of sonic flow followed by expansion pots and connected to the second series of outlet orifices and in that said second series of outlet orifices is arranged annularly around the first series of injection orifices.

Advantageously, the necks with a sonic flow speed, which open in the inlet chamber of the main flow, each at the inlet of a pressure reducing valve, individually supply only one of the orifices of injection of the second series. This solution, where the secondary flow is taken separately for each of the orifices to which it is brought, is most often preferable. However, in some cases, it is also possible, as a variant, for one or more necks followed by expansion pots, a common collector distributing the secondary flow thus withdrawn and expanded towards the various outlet orifices.

The lance according to the invention is particularly suitable for being mounted on a metallurgical converter with top-refining oxygen blowing (type LD), so as to allow the injection of oxygen in the direction of the surface of a metal bath during refining. The lance can then include all the ancillary equipment known in this kind of application, for example means for cooling by circulation of water in a jacket surrounding the wall of the inlet chamber of the main gas flow. On the other hand, the secondary blowing orifices are advantageously oriented, as in conventional double-flow lances, at an inclination, relative to the axis, greater than for the main flow injection orifices. This arrangement, combined with the reduced speed of the secondary flow, ensures the best secondary combustion in a converter, because this secondary flow occupies a conical annular space which widens and widens around the central cone formed by the main flow.

To bring the operation of the lance according to the invention even closer to that of a conventional dual-flow oxygen lance with two separate supplies, it may be useful to provide a possibility of adjusting the gas flow rate through the orifices of the second series, corresponding to the secondary flow. To this end, in a preferred embodiment of the lance according to the invention, the latter comprises means for adjusting the sampling of secondary flow in the internal chamber of the lance which may advantageously be constituted by means for adjusting the pass section of the necks through which this sampling is carried out at sonic flow speed. The more or less great restriction of the passage section has an effect on the quantity of gas withdrawn and therefore on the generating pressure obtained, after the expansion waves, at the outlet orifices of the series corresponding to the secondary flow. For obvious reasons of convenience, it is desirable that the adjustment can be carried out by the end of the lance opposite to that of the nose which comprises the outlet orifices. Any device known per se can be used to modify the internal section of the necks according to the needs of this adjustment. In all cases, the section of the necks is chosen to be strictly less than the section of the outlet openings of the secondary flow, which is sufficient to ensure a sonic speed of the flow in the necks under the pressure conditions usually prevailing in the internal chamber. of the lance (the pressure there always being greater than 10 bars, while the lower pressure limit not to be exceeded is close to 2 bars).

• la figure 1 est une vue schématique d'une lance selon l'invention, montée dans un convertisseur métallurgique ;
• la figure 2 représente, en coupe longitudinale 5 le nez d'une lance selon l'invention ;
• la figure 3 représente de même un détail d'une telle lance dans une variante de réalisation ;
• la figure 4 illustre schématiquement un autre mode de réalisation en variante de celui de la figure 3 et
• la figure 5 illustre schématiquement la répartition des orifices d'injection dans une vue de l'extrémité de la lance.

The invention will now be more fully described with reference to particular, in no way limiting, embodiments of the lance according to the invention. Their description is illustrated by the figures of the accompanying drawings, in which:

• Figure 1 is a schematic view of a lance according to the invention, mounted in a metallurgical converter;
• 2 shows, in longitudinal section 5 the nose of a lance according to the invention;
• Figure 3 also shows a detail of such a lance in an alternative embodiment;
• FIG. 4 schematically illustrates another embodiment as an alternative to that of FIG. 3 and
• FIG. 5 schematically illustrates the distribution of the injection orifices in a view of the end of the lance.

In Figure 1, there is shown a converter 1 containing a liquid metal 2 being refined. The refining reaction is carried out by blowing oxygen onto the surface of the metal. The converter is equipped for this with a lance 3, arranged vertically in the axis of the converter.

The lance 3 is essentially constituted by a tubular wall 4, closed at the lower end by a nose through which are pierced the blowing orifices designated under the general reference 6.

At the upper end of the lance, the interior of the tubular wall 4 is connected to a pipe 7 which supplies it with pressurized oxygen from an external source. During its operation, the lance is continuously cooled thanks to a circulation of water which takes place in a double jacket enveloping the wall 4. FIG. 1 therefore shows the two coaxial walls 8 and 9 which surround the lance, as well as the nozzles 10 and 11 for the inlet and outlet of the cooling water respectively.

Figures 1 and 5 show how are distributed and arranged the orifices 6 through which the oxygen supplied under pressure in the lance leaves at the lower end thereof. Figure 2 shows more precisely how these holes are made. These are in fact blowing pipes (12, 13) open at their two ends and passing through the wall of the lance and its double water circulation jacket. They are divided into two concentric series or crowns. All are inclined relative to the axis of the lance, deviating from this axis from the inside towards the outside of the lance. Thanks to this arrangement, a primary blowing cone 14, or main in the axis of the lance, is formed in operation, at the outlet of the orifices 47 of the pipes 12 of the internal series, while the pipes 13 of the series external ensure, through their orifices 48, a secondary oxygen blowing 15 which widens annularly around the main cone 14.

The efficiency of this operation also requires that oxygen be admitted under a lower generating pressure to the pipes 13 of the outer ring than to the pipes 12 of the inside ring. For this purpose, the nose of the lance is produced as shown in FIG. 2. It shows an internal chamber 16 delimited by the tubular wall 4, which is completed by an end piece 17 which constitutes its bottom. The seal between the wall 4 itself and the bottom 17 is produced by a fitting assembly with interposition of seals 18 to compensate for the effects of differential expansion with the rest of the lance body. We also see, around the end piece 17, two coaxial skirts 20 and 21 which are connected to the tubular casings 8 and 9 respectively of the double cooling jacket. The external skirt 21 is welded to the end of the external envelope 9. Its bottom 22 is closed and only crossed by the blowing pipes 12 and 13. The intermediate skirt 20 fits freely in the end of the envelope 8, intermediate between the wall 4 and the outer envelope 9. Its bottom 23 only consists of radial lugs which pass around the tubes 12 and 13 and leave an opening 24 in the axis of the lance. The circulation of the cooling water is thus ensured as illustrated by the arrows in FIG. 2, the water descending along the tubular wall 4 and rising in the annular space between the intermediate casing 8 and the outer casing 9.

Among other details of embodiment which emerge from FIG. 2, it will be noted that the tubes of the internal crown are of larger diameter than the tubes of the external crown and that they are slightly conical, whereas the tubes of the crown external are cylindrical. However, these details, which are advantageous in the particular case represented, are in general by no means imperative.

In the internal chamber 16 receiving the oxygen under pressure are arranged expansion pots 26, in a number equal to that of the blowing tubes 13 of the outer ring. Each pot 26 forms an elongated vertical cylindrical enclosure which conducts oxygen taken from the chamber 16 individually to one of the outlet orifices 48 of the blowing pipes 13 of the external crown. Its lower end is connected to a bent extension 28 of the corresponding pipes 13, inside the chamber 16. In the particular case shown. this end is constituted by a tip 27 welded to the pot 26 and screwed onto a socket 30 itself welded to the end of the extension 28. It is noted that the internal section of the pipes 13 is smaller than that of the pots 26, which leads to having the connector ends 27 with a profile converging in the direction of blowing to speed up the gas in the pipes 13.

At its upper end the pot 26 opens in the chamber 16 by a neck of reduced section 29. This neck is formed with a converging entry in a nozzle 31 attached to the end of the cylindrical chamber of the pot 26. Its section is lower than that of the corresponding outlet orifice 48.

It is understood that thanks to this arrangement, when the oxygen is introduced into the chamber 16 under a pressure which is generally of the order of 10 to 15 bars, the main flow is formed directly under this pressure at the level of the blowing tubes. 12 of the internal crown, while a fraction of this main flow is taken by the necks 29. The circulation is sonic through these necks and the oxygen taken relaxes in the pots 26 before reaching the blowing tubes 13 of the outer crown.

If one wishes to be able to intervene in addition to the oxygen flow rate taken to constitute the secondary flow, one can add to the expansion pot an adjustment system making it possible to vary the section of passage of the necks 29, and therefore to adjust the gas flow that they take, which leads to modify the pressure generating the secondary flow at the outlet of the expansion pots.

FIG. 3 illustrates a possibility of making such a system. There is schematically shown a blowing tube 13, with its internal extension 28, the corresponding cylindrical expansion pot 26, terminated by the neck 29. The passage section of the neck 29 can be partially closed off with a needle 33 which can be moved above this neck, parallel to its axis. In the particular case shown, the displacement of the needle 33 is ensured by a jack 34 mounted on a support 35 fixed on the upper end of the pot 26. It was assumed here that the jack was hydraulically or pneumatically operated (using of a fluid, such as water or a compressed gas inert with respect to oxygen), provided from outside the lance. An inlet pipe 36 and a return pipe 37 for this fluid are arranged vertically in the axis of the lance and connected respectively to two O-ring collectors 38 and 39, common to the different expansion pots and which are connected by flexible pipes various cylinders. But of course, one could just as easily, to move the needles 33 in an adjustable manner, use other control means, for example mechanical jacks. For the passage of conduits 36 and 37, or of any other tube or rod for controlling the movement of the needles, the conduit 7 which supplies oxygen to the upper end of the lance (FIG. 1), has a vertical passage 40, in the axis of the lance, provided with sealing means not shown. FIG. 4 illustrates another embodiment of a lance according to the invention, which differs from that of FIG. 3 by the means which make it possible to adjust the cross-section for the passage of the necks at the entry into each trigger pot 26. In this case, the neck itself is defined by a flexible deformable membrane 42, mounted in leaktight manner between the upper end of the pot 26 and a rigid annular ring 43. An annular chamber 44 is formed around the flexible membrane 42 by an enclosure 45 fixed in a sealed manner, on the one hand on the upper end of the pot 26, on the other hand on the ring 43. A pipe 46 makes it possible to admit into this chamber a control fluid under an adjustable pressure from the outside of the spear. According to this pressure, the membrane 42 is more or less deformed and swollen towards the axis of the neck where the oxygen circulates, which gives the latter a more or less narrowed passage section.

Naturally, the variant embodiments which have just been described are in no way limitative of the invention, but their description clearly shows how the means provided make it possible to drop the generating pressure at the injection orifices of the secondary flow by ascent. in supersonic regime in the necks 26, then passage from this supersonic regime to a subsonic flow through expansion waves in pots 29 which are sufficiently long.

Claims (9)

1. A gas injection lance comprising an inside chamber for admitting a main stream of gas to a first series of injection openings and, in the interior of said chamber, means for forming a secondary stream fed to a second series of outlet openings, said means effecting the removal of a fraction of the main stream in the inside chamber, characterized in that said means consist of sonic flow rate necks (29), followed by expansion cylinders (26) connected to the second series of outlet openings, and in that said second series of outlet openings (48) is disposed annularly around the first series of injection openings (47).

2. A gas injection lance according to claim 1, characterized in that said open sonic flow rate necks (29) in the chamber for admitting the main stream, each at the entrance to one expansion cylinder (26), individually ensure the feeding of one of the injection openings of the second series.

3. A lance according to claim 1 or 2, characterized in that it comprises means for regulating the throughput of gas removed from the main stream for admission to the injection openings of the second series.

4. A lance according to claim 2, characterized in that it comprises means for regulating the open cross-sections of said necks (29).

5. A lance according to claim 4, characterized in that said regulating means comprise nozzle pins (33) respectively disposed at the entrance of each of the necks (29) and displaceable by actuators (34) controlled from outside the lance.

6. A lance according to claim 4, characterized in that said necks are formed by a flexible tubular membrane (42) and in that said regulating means comprise an adjustable-pressure chamber (44) formed around said membrane.

7. A lance according to any of claims 1 to 6, characterized in that it comprises means for cooling by circulation of air around the wall of the inside admission chamber.

8. A lance according to any of claims 2 to 7, characterized in that the openings (47) of said first series are prolonged in the interior of the lance by tubes (12) formed across a bottom belonging to an adaptable lance nose which supports said expansion cylinders (26).

9. The use of the lance according to any of claims 1 to 8, for refining liquid metals in an oxygen top blowing metallurgical converter.

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