US3567202A - Device for injection by top-blowing into a metal bath - Google Patents

Abstract

IN REFINING A FERROUS MELT IN A METALLURGICAL FURNACE, A PRIMARY STREAM OF OXIDIZING FLUIS IS TRAINED UPON THE BATH SURFACE FROM A LANCE WHICH ALSO HAS MEANS FOR EMITTING A SECONDARY STREAM OF OXIDIZING FLUID, THE LATTER ENVELOPING THE PRIMARY STREAM AND SWIRLING AROUND IT, WITH OR WITHOUT INJECTION OF SOLID PARTICLES ENTRAINED BY THE PRIMARY STREAM.

Description

March 2, 1971 R. MERCATORIS L DEVICE FOR INJECTION BY TOP-BLOWING INTO A-METAL BATH Filed 001;. 2, 196? 2 Sheets-Sheet 1 Robert Mercaroris Joseph Nepper Attorney March 2, 1971 DEVICE FOR INJECTION BY TOP-BLOWING INTO A METAL BATH 2 Sheets-Sheet l Robert Mercaforis Joseph Nepper INVENTORS.

BY Rm Attomy United States Patent 0 Int. (1621c 7/00 US. Cl. 266-34 9 Claims ABSTRACT OF THE DISCLOSURE In refining a ferrous melt in a metallurgical furnace, a primary stream of oxidizing fluid is trained upon the bath surface from a lance which also has means for emitting a secondary stream of oxidizing fluid, the latter enveloping the primary stream and swirling around it, with or without injection of solid particles entrained by the primary stream.

Our present invention relates to a device for the treat ment of a metal bath in a metallurgical furnace (converter) by top-blowing of an oxidizing fluid, usually a gas or a gas mixture, which may entrain a suspended charge of pulverulent or granular solid material such as iron, alloying metals, lime or other reagents, e.g., as described in commonly owned US. Pat. No. 3,130,252, issued Apr. 21, 1964, to Paul Metz.

In refining by top-blowing, i.e. injection from above of an oxidizing fluid (consisting in most cases of pure oxygen) which may be charged with particulate solids, it is very important that the width of the stream should be adjustable according to changing requirements during different phases of the refining operation. In the case, for example, of a treatment of phosphorus-rich pig iron by means of oxygen blown from above, it is desirable to blow at the beginning of the operation with a widely spread stream, whereas after the initiation of sufl'lcient foaming of the bath it is convenient to continue the blowing action with a more concentrated and more penetrating flow. Toward the end of the refining operation, depending on the actual conditions, it may be advantageous to blow either with a narrow or with a broad stream.

It is known to realize such variations of jet width by the use of two or more lances having different characteristics or by the use of only one lance while modifying the pressure of the injected gas and varying the distance of the lance from the bath surface. It is also possible to combine the two measures during operation. However, these prior blowing methods are not fully satisfactory and do not allow easy and rapid variation of the spread and depth of penetration of the oxygen flow.

In the aforementioned Metz patent there is described a simpler and more efficient system designed to adjust spread in a manner suitable for a good control of the refining operation. This is accomplished with the aid of a lance including a central bore for the discharge of a primary fluid stream and an annular passage which coaxially surrounds that bore and, through an array of connecting channels at the bottom of the passage, directs a secondary fluid stream into a discharge port or nozzle where the two fluids are comingled. When the secondary stream is turned on, the spread of the overall flow is increased so that the oxidizing fluid is distributed under a relatively light pressure over a large portion of the melt surface to cause intense slag foaming and concomitant dephosphorization, along with the conversion of escaping CO into CO which 3,567,202 Patented Mar. 2, 1971 is an exothermic reaction and increases the consumption of scrap iron or grapeshot. As further explained in the above patent, however, there are instancesparticularly during the later stages of refining operations-when it is advantageous to reduce the depth of penetration of the fluid into the bath, thereby achieving more effective decarburization; for this purpose the secondary fluid stream is cut off so that the primary or central stream alone impinges upon the melt.

The general object of our present invention is to provide a blowing device representing a further advance of the art, and an improvement over the disclosure of that earlier patent.

A more particular object of our invention is to provide an easily assembled lance capable of discharging two independently controllable gas streams in peripherally interacting relationship.

The blowing device according to the present invention is constituted by a cooled double lance comprising a generally upright central conduit for the injection of a refining gas, capable of entraining suspended solids to be added to the melt, and an outer conduit concentrically surrounding the former to serve for the injection of secondary oxygen. The central conduit is formed by an elongate, preferably converging-diverging tubular member. The outer conduit terminates at its bottom part in a peripheral array of generally helical channels which interconnect the two conduits and whose axes are skew to the conduit axis. This orientation of their axes increases the path length through the channels sufficiently to give guidance and direction to the outflowing jets of secondary oxygen even after they have left the discharge part. The orientation of these jets is such that the secondary flow comes only tangentially into contact with the main or central stream and surrounds it with a more or less gyratory movement completely enveloping the main jet. The cross section of the secondary discharge channels, i.e., the section transverse to the channel axis, has approximately the form of a semicircle open toward the outside. Thus, the secondary-flow channels can be machined from the outside into a metallic collar constituting the lower extremity of the lance, with considerable simplification of the manufacture thereof.

Since the invention allows the secondary-flow channels to be machined rather than bored or drilled, their direction (e.g., as defined by the angle included between the channel axis and a plane perpendicular to the conduit axis) can be chosen in accordance with the desired length of the channel path. The aforementioned angle may range between about 35 and 60.

The cross section of the secondary-flow channels can be either constant, so that each channel will have the form of a semicylinder, or varying, e.g., to form convergentdivergent passages as described in the earlier Metz patent.

The secondary oxygen jets leaving the channels can form a dense and protective secondary-oxygen envelope along the inner nozzle wall. To this end, according to another feature of the invention, the cross section of the discharge port increases abruptly at the exit of the central or main conduit in such a fashion as to create around the main oxygen stream an annular void into whose upper part the secondary channels discharge, the width of this void decreasing in the downward direction. Thus, the secondary-oxygen jets leaving the sloping channels in the direction of the nozzle outlet combine to form within the nozzle a protective oxygen sheath free from entrained solid particles. As a result, the primary oxygen stream charged with the solid particles does not come into contact with the inner nozzle wall so that the latter will not be exposed to any wear by these solids. This means a considerable increase in the life of the nozzle as compared with conventional structures.

The inclination of the channels of the outer conduit causes the secondary-oxygen stream, on leaving the nozzle, to swirl around the main stream without interacting therewith to any substantial extent, thence, the two injection streams will keep their individual functions while the control of only one stream, i.e., the secondary oxygen stream, will be sufficient to vary the spread of the flow striking the bath surface.

The main oxygen stream, serving primarily for the decarburization of the metal bath by agitating same, can be maintained effective during almost the entire treat ment or until the desired carbon content is reached. Concurrently therewith and independently of the main stream. the secondary stream can oxidize a large surface of the bath and/or of the slag, by virtue of its wide spread. It can thus be used, through suitable adjustment of its discharge rate, to accelerate the dephosphorization at any time and for any desired period. A lance according to our invention offers, accordingly, the important technical advantage of yielding at the end of the refinement a lowphosphorus metal bath that may still retain high residual carbon content. This is necessary or at least highly desirable in the manufacture of high-carbon steels, especially if the starting material is a phosphorus-rich cast iron.

Since the novel geometry of the secondary channels greatly increases the efiiciency of the secondary oxygen stream, its discharge rate can be reduced to just a fraction of that necessary with conventional lances. It therefore becomes possible to decrease the cross section of the secondary conduit and of its oxygen-supply tubes as well as the size of associated metering and flow-control equipment.

Another advantageous aspect of the invention resides in the possibility of maintaining the lance throughout the metallurgical operation at a substantially constant distance from the bath surface. Moreover, the lance can be positioned nearer to the bath surface than heretofore inasmuch as the desired spread of the oxygen flow can be realized at any instant by adjustment of the secondary stream without the necessity of increasing the nozzle distance from the melt. This is further facilitated by the fact that the absence of substantial interaction between the two streams allows the secondary stream to retain virtually its entire kinetic energy as well as its direction of flow so as to be able to spread freely and widely across the melt.

The spreading out of the oxygen flow and the presence of an enveloping sheath of secondary oxidizing fluid lead to a considerable increase of the proportion of CO burned to CO inside the converter and therefore to the fusion of a larger quantity of grapeshot.

The efiicient spreading of the oxidizing stream further promotes, very advantageously, the formation of a fluid slag layer from the beginning of the blowing operation, such layer preventing the ejection of metallic particles and thereby reducing the loss of metal which generally occurs in the early stages in the absence of a fluid slag.

A further advantage of the invention resides in the fact that, since the lance can be lowered more deeply into the converter, the zone of the refractory furnace lining subject to attack by the oxidizing fluid is reduced.

The preferred construction of a lance according to the invention offers other important technical advantages. Its axial conduits other than the outermost tube terminate at the bottom in slidably guided ends in such a Way that all the tubes of the lance can relatively expand in the longitudinal direction. This increases the useful life of the device by suppressing any thermal stresses that might otherwise result in a deformation of the tubes or a throttling of the water passage situated at the bottom of the cooling jacket in the region of the nozzle.

The invention will be described in gerater detail with reference to the accompanying drawing in which:

FIG. 1 is a cross-sectional view of a lance embodying our invention; and

FIG. 2 is a cross-sectional view taken on the line II-II of FIG. 1.

The lance shown in the drawing comprises a central tube 1 with a cylindrical main portion 11, a downwardly converging frustoconical entrance portion 13 and a downwardly diverging exit portion 12, the latter being constituted by a separate collar threadedly or otherwise received in a recess 14 at the lower end of cylinder 11. An outer shell 2 coaxially surrounds the tube 1 and defines therewith an annular passage 15 which terminates at its bottom in a peripheral array of generally helicoidal connecting channels 3, the axes A of these channels lying skew to the common axis B of tube 1 and shell 2. Channels 3 are milled into the outer periphery of collar 12 and, as here shown, are of downwardly divergent cross section; they open at the lower face 12a of member 12 into a discharge port 4 which is bounded by the inner peripheral surface 5 of an annular nozzle 16 integral with an outer ring 6, the latter merging into an extension 17' of a cooling jacket 17 which surrounds the shell 2 to define channels 9, 10 for the circulation of a cooling fluid. Elements 17, 17' and 6 are joined together by annular welding seams 8 and 8; prior to complete assembly, the absence of extension 17' gives access to a set of screws 18 by which a skirt 19 is fixed to shell 2 through the intermediary of nuts 20 welded onto the shell. A peripheral array of spacers 21 similarly connects an annular partition 22, separating the conduits 9 and 10, to a cylindrical upward extension 2' of shell 2. Packing rings 7, 7', 7" are provided along the contact surfaces of the interfitting parts which, as shown, are all centered on the same axis B for ease of assembly and disassembly.

Although the axes A of channel 3 seem to converge in FIG. 1 toward the central axis B, a reference to FIG. 2 reveals that these axes (as particularly illustrated for axis A of channel 3') do not cross the axis B but pass it at a distance r which in FIG. 1 is seen to represent the real axis of a one-sheet hyperboloid H centered on axis B, the curvature of surface 5 substantially conforming to this hyperboloid; the aforementioned axis A is one of the asymptotes, intersecting at a point 0 below the level of the discharge end of tube '1 but within the port 4. These asymptotes include with the horizontal (thus with a plane transverse to axis B) an angle a which may range within the aforestated limits and is here shown to equal about 60. It will be seen that an extension G of any generatrix of the frustoconical inner surface of collar 12 is tangent to the hyperboloid wall surface 5 of discharge port 4 defined by the nozzle 16. Since the character of surface 5 exceeds the inner diameter of collar 12 at the level of face 12a, the port 4 forms a downwardly tapering annular space S around the central region occupied by the primary fluid stream which issues from collar 12.

Owing to this construction, a stream of gaseous oxygen or other oxidizing fluid passes substantially unhindered through outlet 4, even in the presence of a secondary flow through annular passage 15, after leaving the central tube 1 by way of collar 12; this primary fluid stream may be charged with particulate solid matter which, especially during existence of an enveloping secondary flow, will be kept out of contact with the inner wall surface 5 of the nozzle.

The use of a separate nozzle member 16, with reinforced walls, affords greater wear resistance in the region of greatest thermal and mechanical stress. If the nozzle needs replacement, the lance need to be cut and subsequently rewelded only along the seam 8'; in the same way it is also possible to extract the collar 12 for replacement or repair.

Naturally, details of the construction described and illustrated may be modified without departing from the spirit and scope of our invention.

We claim:

1. A lance for training an oxidizing fluid upon a ferrous melt, comprising a generally upright elongate tubular body forming a central passage for a primary fluid stream, a shell coaxially surrounding said tubular body and forming therewith an annular passage for a secondary fluid stream, said shell extending downwardly beyond said tubular body and forming a common discharge port for said streams, and a perforated annular member at the bottom of said annular passage forming a plurality of channels peripherally arrayed about the lower end of the common axis of said body and said shell and which include an angle between substantially 35 and 60 with a plane perpendicular to the common axis of said body and said shell, the axes of said channels substantially coinciding with generatrices of a one-sheet hyperboloid centered on said common axis and having its waist within said discharge port, the peripheral surface of said discharge port having a curvature approximating the configuration of said one-sheet hyperboloid.

2. A lance as defined in claim 1, further comprising a cooling jacket surrounding said shell.

3. A lance as defined in claim 2 wherein the inner wall surface of said tubular body at the lower end thereof is a downwardly diverging frustocone Whose extended generatrices are substantially tangent to the peripheral surface of said discharge port.

4. A lance as defined in claim 2 wherein said discharge port is formed by an annular nozzle fitted into the down wardly projecting end of said shell.

5. A lance as defined in claim 4, further comprising a cooling jacket surrounding said shell and a cylindrical partition within said jacket, said nozzle being integral with an outer ring adjoining said jacket and receiving the lower end of said partition.

6. A lance as defined in claim 4 wherein said annular member comprises a collar with peripheral indentations of substantially semicircular cross-section forming said channels, the latter being externally bounded by an inner wall surface of said nozzle.

7. A lance as defined in claim 6 wherein said collar 6 has a neck received in an inner recess of said tubular body.

8. A lance for the top-blowing of a ferrous melt, comprising a generally upright elongated tubular body forming a central passage for a primary fluid stream; a shell coaxially surrounding said tubular body and forming therewith an annular passage for a secondary fluid stream; means defining a downwardly convergent frustoconical chamber forming a common discharge port for said extremes; and a perforated annular member at the bottom of said annular passage forming a plurality of channels peripherally arrayed about the lower end of the common axis of said body and said shell, said channels being each of semicircular cross section and including an angle of 35 to with a plane perpendicular to the common axis of said body and said shell, said channels being further inclined in a common sense to respective axial planes.

9. The lance defined in claim 8 wherein said discharge port is formed by an annular nozzle fitted into an end of said shell projecting downwardly beyond said tubular body, said channels being formed in a collar with peripheral indentations of substantially semicircular cross section and being externally bounded by an inner wall surface of said nozzle, said collar having a neck received in an inner recess of said tubular body.

References Cited UNITED STATES PATENTS 3,043,577 7/1962 Berry. 3,078,084 2/1963 Foresi et al. -52X 3,202,201 8/1965 Masella et al 239-1323 3,239,205 3/1966 Metz 266-34 3,241,825 3/1966 Jilek et al. 266-34 3,317,309 5/1967 Rinesch 75-51X I. SPENCER OVERHOLSER, Primary Examiner J. S. BROWN, Assistant Examiner US. Cl. X.R. 75-51, 60; 239-497

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