LU87856A1 - BLOWING LANCE - Google Patents

Description

BLOWING LANCE

The present invention relates to a blowing lance, in particular a blowing lance for a gas used for refining metals in their liquid state.

During a refining process such as that of cast iron or an iron alloy in which an oxidizing gas, most often pure oxygen, is injected or rather blown from above on a metal bath in melting, it is of paramount importance to be able to modify the characteristics of the jet of oxidizing gas as well as its point of impact on the surface of the metal bath according to the state of progress of the refining process in question. This becomes all the more true as modern refining technologies use primary supersonic jets of oxidizing gases.

The design of the blowing lance used in the context of a refining process as described above is complex. Indeed, the oxidizing gas must on the one hand be able to react reciprocally with the metal bath so that the reactions, such as decarburization can take place, and on the other hand be able to ensure above the surface of the bath post-combustion of the carbon monoxide released. It must also be ensured that the quantities of oxidizing gas injected can be regulated independently of the speed of the gas jet. A displacement of the point of impact of the gas jet on the surface of the bath during the refining process is moreover desirable in order to increase the surface where the metallic reactions take place and to intensify its stirring effect in the bath. . The post-combustion oxygen must, moreover, be able to embrace the widest possible reaction zone, while ensuring that the post-combustion of carbon monoxide takes place near the surface of the bath and not in the regions where the energy released would jeopardize the lance itself.

The Luxembourg patent No. 86 322 (US 4,730,784, EU 0 235 621) describes an oxygen blowing lance nozzle for refining metals which makes it possible to vary the exit speed (the Mach number) and the flow rate of the jet of oxygen independently of each other. A further development of such a blowing lance which allows the operator to vary, depending on the different refining phases, the quantity of oxygen introduced into the bath while imposing on the oxygen jet 'the shape and the optimal speed required, is the subject of Luxembourg patent No. 87 353 (US SN 395,104). According to the device of the Luxembourg patent No. 87 353, the blowing lance has a nozzle for forming and guiding the jet of refining oxygen, comprising a duct with variable section sketching a convergent followed by a neck and a diverging , the nozzle being provided with a central part movable along the axis of the nozzle at the neck. The central part follows a shape having a substantially cylindrical body and a nose which tapers concavely towards a point. By the displacement of this central part, the section of the neck as well as the diverging part can be modified and, therefore, the characteristics of the nozzle can be changed continuously.

The blowing lance of the present invention makes use of the device described in Luxembourg patent No. 87 353 which will advantageously be incorporated in the design of this new blowing lance for refining metals.

By Luxembourg patent No. 86 321 (US 4,730,813) there is known a refining oxygen blowing lance device by means of which the oxygen jet leaving the lance head can, within certain limits, be deflected by relative to the axis of the lance and directed at different points of impact with the surface of the liquid bath. The device according to Luxembourg patent No. 86 321 comprises, before the mouth of the lance head, a chamber having substantially the shape of a truncated pear. By means of gas jets striking laterally the primary jet of refining oxygen at its exit from the nozzle, the latter is deflected unilaterally in the chamber in the shape of a truncated pear, in which it moves along the wall opposite the lateral gas jet. In this way, the supersonic jet of refining oxygen exits from the mouth of the lance head at an angle to the axis of the lance, the angle of deflection depending to a large extent on the shape of the wall of said chamber. By providing several outlets for lateral gas jets sequentially directing jets against the primary refining oxygen jet, the point of impact thereof on the surface of the metal bath can be moved along the circumference d 'a circle and directed on places determined according to the position of the side jets.

Although the supersonic refining oxygen jet can be deflected in this way, the lance is subjected to strong lateral reaction forces which stress the suspension and anchoring points of the lance so much that 'it is difficult to find a reliable solution to these fixing problems in practice. Furthermore, the device according to the Luxembourg patent only allows the deflection of the refining oxygen jet at certain points or well-defined locations.

The object of the present invention is to design a blowing lance capable of providing a jet of gas whose speed and flow can be adjusted independently of one another, and whose point of impact on the surface of the bath liquid can be moved continuously during the refining operation.

The object is achieved by the lance according to the invention as characterized in claim 1.

Preferential variant embodiments are described in the dependent claims. The invention is described in more detail using the drawings which represent a preferred embodiment of the blowing lance according to the invention and in which: FIGS. 1a and 1b show a longitudinal section of the lance according to invention, in which the rotor head is shown in two different sections offset 90 ° from one another,. - Figure 2 shows a longitudinal section through the body of the rotor head of the lance according to the invention, - Figure 3 shows a cross section through the plane A-A of Figure 2.

As shown in Figures 1a and 1b, the blowing lance (1) according to the invention comprises a lance body (2) welded to a lance head (3). The lance body (2) comprises a mantle with four walls (4, 5, 6 and 7) concentric in welded steel tubes, spaced apart by intermediate pieces and connected to the lance head (3), to form a water cooling circuit (9) between the walls (4, 5 and 6) and those of the lance head (3).

The suspension of the lance as well as its sources of supply of fluid, oxygen, nitrogen and cooling water, have not been shown in FIGS. 1a and 1b, since they are not part of the object of the present invention.

The inner wall (7) of the lance body (2) forms an annular chamber (10) crossed along its axis a-a 'by a concentric rod (11) for supporting an assembly forming a Laval nozzle (12). The support rod (11) is preferably formed by a tube which allows the installation of electrical connections (not shown in the Figures) for supplying electric current to the various control mechanisms which will be described later. According to another embodiment, the rod (11) and the inner wall (7) can themselves act as conductors for the supply of electric current to said control mechanisms. The assembly forming the Laval nozzle (12) comprises a translation body (13) attached to the support rod (11) by means of a control mechanism composed of a linear servomotor (14) and a cylindrical sheath (15) in which the translation body (13) can move in the direction of the axis aa 'of the blowing lance (1). As shown in Figure 1b, the end of the translation body (13) has the shape of a kind of needle whose profile follows a continuous aerodynamic transition curve, in order to minimize the creation of turbulence in the refining gas flow. Inside the wall (7) of the mantle of the lance body (2) a concentric conduit (16) for the refining gas, that is to say the primary oxygen, is arranged. At the location of the translation body (13), the concentric conduit (16) has a converging part and a neck, which, in cooperation with the needle of the translation body (13), form a Laval nozzle, the characteristics or parameters can be modified by moving the translation body (13) in the direction of the axis a-a '. This Laval nozzle makes it possible to control the flow rate of the refining gas independently of the supersonic speed that the jet of refining gas will take when leaving the Laval nozzle by discharging centrally in the part (17) of the conduit (16 ).

The operation of the variable Lavâl nozzle (12) is described in more detail in Luxembourg patent No. 87 353, the description of which is incorporated into that of the present patent application.

Downstream of the part (17) of the conduit (16) of the refining gas, the blowing lance (1) comprises, according to the present invention, a device (18) (see Figure 1a), arranged centrally in the flow of the supersonic jet of the refining gas, in order to separate the latter aerodynamically correct into two distinct and almost equal supersonic jets. These two supersonic refining gas jets open, at the outlet of the separating device (18), into the lance head (3) in which they undergo a deflection at a determined angle, as will be explained below. .

The separating device (18) is executed in the form of a rotor which is housed in a stationary concentric piece (40) fixed in a sealed manner to the lower part of the duct (16) and in extension thereof. In the embodiment shown, the rotor (18) is suspended from the upper support (21) and the lower support (22) which both have a ball bearing. The rotor (18) is provided in its upper part with a drive or rotation mechanism (41) which comprises drive vanes (42) in the form of turbine blades. The central jet of gas leaving the Laval nozzle (13) collides with the fins (42) and sets the rotor (18) in rotational movement. The rotational speed of the rotor (18) is controlled and adjusted by means of slots (43) (see Figures 2 and 3) arranged in the rotor (18) downstream of the drive fins (42), through which a braking gas, preferably of the same composition as the refining gas, is blown. This braking gas, called tertiary gas, is brought to the slots (43) through the annular space formed between the wall (7) and the conduit (16), and the openings (44) in the part (40). The hollow interior of the rotor (18) is divided into two chambers separated by a central ramp (45) to cause the aerodynamically correct separation of the central supersonic jet leaving the Laval nozzle (13) into two distinct but identical (or almost identical) supersonic jets identical).

In Figure 1a, the sectional view of the rotor has been made so that the left part shows the channel (46) of one of said supersonic refining jets and the right part the separation ramp (45). As illustrated in FIG. 1a, a duct (47) is arranged in the lower part (downstream) of the separation ramp (45), this duct opening into the nozzle (48) of the lance head (3) by a perforated wall (49). The duct (47) is supplied, as will be described below, by a subsonic flow of oxygen, to fill the space between the two supersonic jets of refining gas in the blowing nozzle (48) of the head lance (3). The walls (50) of the blowing nozzle (48) have a curvature such that under the so-called "Coanda" effect the supersonic jet of refining gas leaving the channel (46) of the rotor (18) is deflected at an angle determined with respect to the central axis aa 'of the lance (1). This deflection of the refining gas jet is supported by the pressurized flow of subsonic gas leaving the duct (47) which envelopes and guides the supersonic jet maintaining it in the direction deviated from the central axis aa of the lance (1). Having described the formation of one of the supersonic refining gas jets, it goes without saying that the other refining jet leaves the rotor (18) and the blowing nozzle (48) in an identical (or almost identical) manner. ) at the same angle (or almost same angle) but in a direction diametrically opposite to the first refining jet relative to the central axis (a-a ') of the lance (1). As a result, the blowing lance (1) is not subjected to radial dynamic forces (apart from the existence of a residual torque acting on the rotor), since these forces, due to supersonic jets, are compensate for each other in the device according to the present invention. The supports for fixing and guiding the refining lance (1) of the present invention are therefore not subjected to stresses due to the deflection of the supersonic refining jet relative to the axis of the lance, as such was the case for the devices of the state of the art as described in the Luxembourg patent No. 86 321.

As described above, according to another characteristic of the present invention, the rotor (18) drives the two supersonic jets of refining gas in a rotational movement, so that their points of impact on the surface of the liquid metal bath are, during the refining process, moved continuously in a circle, the radius of which is determined by the angle of deflection of the jets and the distance between the lance head and the metal bath. The deflection angle of the supersonic refining gas jets is a function of the shape of the deflection wall (50) of the blowing nozzle (48).

The design of the lance head (3) was chosen in the example of a preferred embodiment of the device according to the invention shown in Figure 1a, so as to allow its easy and quick assembly and disassembly to the body or rod. spear. Although in the drawing we do not show all the details of execution, it becomes apparent to those skilled in the art that all the parts which form the lance head (3) and the rotor are nested one in the the other.

This design therefore allows rapid exchange of all parts subject to wear, either under the influence of high temperatures prevailing at this location, or by the projection of splashes of molten metal. It also allows rapid exchange of the rotor (18) as well as of the wall (50) of the lance head (3).

As can be seen in FIG. 1a, the rotor (18) is installed slightly behind the outlet orifice (33) of the lance head (3), this to protect it against the projection of particles of , liquid metal during the refining process.

Post-combustion nozzles (34) are arranged in the lance head (3) around the central orifice (33). The nozzles (34) are eight in number in the embodiment shown, arranged uniformly around the periphery of the lance head. Preferably, these post-combustion nozzles (34) are of the "double Prandtl-Meyer" type, as described in Luxembourg patent No. 87 354. They form a practically uninterrupted screen, in the form of an umbrella. , around the two supersonic jets of refining gas. The post-combustion nozzles (34) are supplied with oxygen by a secondary flow of gas circulating in the annular space between the walls (6) and (7) of the mantle of the lance (1). This same secondary flow of gas at subsonic speed feeds, via openings (51) provided in the wall of the duct (16) and an annular chamber (52), the duct (47) of the ramp (45 ) of the rotor (18). The dimensioning of the openings (51) has been chosen, in the example shown, so as to route, in substantially equal proportions, the flow of secondary gas to the post-combustion nozzles (34) and to the conduit (47) of the ramp (45).

The present invention makes available for a method of refining a molten metal bath, a blowing lance which, by its clever design, makes it possible to modify, even during refining, the characteristics of the jet of gas d refining by means of an adjustable Laval nozzle (13) and of displacing its point of impact on the liquid bath during refining by means of a mechanism for dividing rotation and direction (18, 27).

Penetration of the supersonic jet (s) of the refining gas into the molten metal bath and sparging of the latter by the said jet (s) can therefore be ensured throughout the refining process.

The design of the lance is such that it is not subjected in service to mechanical stresses which would question its effective operational use. A secondary gas flow protects the rotating parts against destructive effects from the metal bath, and secondary gas jets provide for post-combustion of the gases escaping from the molten metal bath during the refining process.

Although the invention has been described on the basis of a preferred embodiment, it is perfectly conceivable to carry it out with a separating device which divides the supersonic jet of the refining gas not only into two parts but into an even number upper of substantially identical jets.

Claims (11)

1. Blowing lance for refining liquid metals contained in a container by blowing a gas on the metal bath, comprising an adjustable nozzle (12) for independently varying the speed and the flow rate of the refining gas characterized by separator device (18) arranged in the blowing lance (1) downstream of the adjustable nozzle (12) centrally in the flow of the refining gas in order to divide the said refining flow into two distinct substantially identical jets leaving the head ( 3) lance at angles substantially equal to the axis (a-a ') of the lance (1) but in diametrically opposite directions relative to the latter. 2. Blow lance according to claim 1, characterized by a drive mechanism (41) for imparting a rotational movement to the separating device (18) around the axis (a-a ') of the lance (1). 3. Blowing lance according to claim 1 or 2 characterized in that the adjustable nozzle (12) has the form of a Laval nozzle conferring a supersonic speed on the jet of refining gas and in that said Laval nozzle comprises control means (14) for varying the characteristics of the nozzle (12) so as to be able to control the flow rate of the refining gas independently of its speed. 4. Blowing lance according to one of claims 1, 2 or 3, characterized in that the separating device (18) follows a cylindrical shape whose interior is divided into two chambers separated by a central ramp (45). 5. blowing lance according to claim 4, characterized in that a conduit (47) is arranged in the downstream part of the central separation ramp (45) which opens into the head (3) of lance and through which a flow Subsonic gas is directed to fill the space between the two (supersonic) jets of refining gas. 6. blowing lance according to any one of claims 1 to 5, characterized in that the internal walls (50) of the blowing head (3) form a nozzle (48) and in that these walls have such a curvature that the refining gas jets leaving the central separation ramp (45) are deflected, under the so-called "Coanda" effect at substantially equal angles, in directions diametrically opposite with respect to the central axis (a -a ') of the lance (1). 7. Blowing lance according to any one of claims 1 to 6, characterized in that the separating device (18) is mounted in a removable and easily replaceable manner in the lance body. 8. Blowing lance according to any one of claims 2 to 7, characterized in that the drive mechanism (41) for the rotation of the separator device (18) comprises drive fins (42) in the form of turbine blades. 9. blowing lance according to claim 8, characterized in that the speed of rotation of the separating device (18) is controlled and adjusted by means of slots (43) arranged in said device (18) downstream of the fins (42) by which brake gas is blown. 10. Blowing lance according to any one of claims 1 to 9, characterized in that the head (3) of lance comprises post-combustion nozzles (34) supplied by a subsonic secondary flow of gas. 11. Blowing lance according to any one of claims 1 to 10, characterized by water cooling circuits (9) arranged in the mantle of the lance (1) and of the head (3) of lance.