METHOD FOR TREATING MOLTEN METAL AND / OR SLAG IN A METAL BATH AND METAL PLANT FOR TREATING MOLTEN METAL - Patent application

Abstract

A method for treating molten metal (4) and / or slag in a metal bath, comprising the introduction of a process gas into the molten bath, characterized in that the process gas is accelerated to supersonic speed and introduced at supersonic speed below the surface (5) of the molten bath by means of at least one supersonic nozzle (6) into the liquid phase of the molten metal (4) and / or into the slag (13) and / or into the region of the phase boundary (14) between the molten metal and the slag (13). The invention further relates to a metallurgical plant for treating molten metal.

Description

[Technical field]

[0001] The present invention relates to a method for treating molten metal and / or slag in a metallurgical bath, comprising introducing a process gas into the molten bath. The present invention further relates to a metallurgical plant for treating molten metal, comprising a melting vessel and means for gasifying the molten metal and / or slag. [Background technology]

[0002] In metallurgical plants, process gases such as air, oxygen, nitrogen, argon, hydrocarbons, hydrogen, etc. are used to treat the molten metal, for example, with the intention of oxidizing unwanted accompanying elements in the molten metal or reducing the metal and / or slag.

[0003] In the pyrometallurgical processing of metals and molten metals in electric arc furnaces, it is known to blow / inject oxygen-rich gas and / or carbon-containing particles into the slag / foamed slag layer. From EP 1 466 022 B1, for example, a method is known for the pyrometallurgical processing of metals, molten metals and / or slag, in which an oxygen-containing gas is accelerated to supersonic speed with the aid of an injector and the high-velocity jet leaving the injector is used for the pyrometallurgical processing of the molten metal. The high-velocity jet is protected by a gas jacket of hot gas that envelops it, which is fed into the high-velocity jet in such a way that the relative velocity and momentum exchange between the central high-velocity jet and the jets of the hot gas jacket is minimized. This method of covering the central oxygen-rich gas jet with hot gas with the lowest possible momentum loss maximizes the length and penetration depth of the gas jet into the slag layer above the molten metal, resulting in intensive mixing and stirring of the slag layer. In the method described in EP1466022B1, a gas jet is blown onto the slag from above, blowing into the boundary layer between the slag and the metal.

[0004] WO2019 / 158479A1 discloses a method for treating molten metal in a converter, in which pure oxygen is supplied from above to the surface of the molten bath at high pressure and supersonic speed by a water-cooled lance to form cavities in the slag.

[0005] The use of supersonic injection devices in the above mentioned context is known from many publications, for example EP 0 964 065 A1.

[0006] It is also known in the art to introduce process gases into the molten metal below the surface of the molten bath so that they can react there directly with the liquid metal or slag. The introduction of these gases can be carried out, for example, by so-called bottom or sidewall flashers. In this sub-bath gassing, the process gas is introduced in the form of gas bubbles or in the form of closed gas jets that enter the liquid phase of the melt. The injection of the gas jets in the under-bath gassing is carried out at subsonic velocities. In many applications, in the area where the process gas enters the molten metal, undesirable side effects occur, such as overgrowth of purifying agents. In addition, the refractory of the melting vessel is exposed to increased wear above the gas inlet.

[0007] In principle, it is desirable for the process gas to have a high penetration depth into the molten metal and for the gas to have a stirring effect in the molten metal. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] EP1466022B1 [Patent Document 2] WO2019 / 158479A1 Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention therefore has as its object the provision of a method of the above mentioned type which avoids the above mentioned drawbacks. [Means for solving the problem]

[0010] The problem underlying the present invention is solved by providing a method having the features of claim 1 and a metallurgical plant having the features of claim 10. Advantageous embodiments of the invention are covered by the dependent claims.

[0011] One aspect of the invention relates to a method for the treatment of molten metal and / or slag in a metal bath, comprising the introduction of a process gas into the molten bath, characterized in that the process gas is accelerated to supersonic speed and introduced at supersonic speed by at least one supersonic nozzle below the surface of the molten bath, into the liquid phase of the molten metal and / or into the slag and / or into the region of the phase boundary between the molten metal and the slag. Effect of the Invention

[0012] The term molten bath as used in the present invention includes both the molten metal and the slag droplets suspended in the molten metal, as well as the slag on the molten metal. The procedure according to the invention has the particular advantage that the acceleration of the process gas to supersonic speed significantly increases the exit impulse of the process gas into the liquid phase of the molten metal, resulting in a greater penetration depth of the process gas or the supersonic gas jet into the molten metal. Due to the high exit impulse of the process gas into the molten metal, an increase in wear of the refractory material of the metal vessel receiving the molten metal is also avoided. The higher exit impulse moves the area where the individual gas bubbles break away from the gas jet penetrating the molten metal further away from the vessel wall. This reduces the concomitant back attack of the gas jet against the vessel wall and limits the wear of the refractory. The introduction of the process gas at supersonic speed creates turbulence in the molten metal, which results in agitation of the molten metal. The high momentum of the process gas entering the molten metal or slag makes it less likely for the molten metal or slag to flow back. This reduces the risk of clogging in the supersonic nozzles used. The high shear forces between the process gas and the molten metal also lead to greater disruption of the primary bubbles, reducing the bubble size and thus increasing the total surface area of ​​the gas bubbles, which in turn leads to higher emissions of the process gas. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Process gases include air, oxygen, nitrogen, argon, and hydrocarbons (C x H y Suitably a gas selected from the group consisting of argon, argon gas, argon dioxide, and hydrogen is provided.

[0014] In a preferred variant of the method according to the invention, it is provided that the process gas is introduced at several points in the molten bath by means of several supersonic nozzles.

[0015] The process gas can be introduced into the molten metal at different heights relative to the surface of the molten bath.

[0016] In an advantageous variant of the method according to the invention, it is provided that at least one supersonic nozzle is designed as a Laval supersonic nozzle with a convergent nozzle section and a divergent nozzle section. In the convergent section of the nozzle, the diameter tapers continuously (continuously decreases), which leads to an increase in the gas velocity and a decrease in pressure until the sonic speed is reached at the narrowest cross section (Mach number equal to 1). In the divergent section of the nozzle, its diameter steadily increases, the process gas is accelerated further and the pressure further decreases. As a result, the gas is accelerated beyond the local sonic speed.

[0017] Both the converging section of the supersonic nozzle and the diverging section of the supersonic nozzle can have bell-shaped profiles, whereby the bell-shaped profiles of the converging and diverging sections of the supersonic nozzle merge continuously into one another at the throat of the nozzle. Such shapes or profiles ensure that the nozzle can be used without malfunction and with low wear, and that the jet impulse at the nozzle exit is maximized, and a large supersonic length of the gas jet is achieved.

[0018] In principle, a supersonic nozzle can be designed for only one operating point with respect to the inlet pressure of the process gas, the volumetric flow rate and the ambient pressure in the molten metal. Preferably, this gas dynamic design point of the supersonic nozzle is selected such that the gas pressure of the process gas at the exit cross section of the supersonic nozzle corresponds to the ambient pressure in the molten metal. If the gas pressure of the process gas at the entrance cross section of the supersonic nozzle is set such that the gas pressure of the process gas at the exit cross section of the supersonic nozzle corresponds to the ambient pressure in the molten metal, the supersonic nozzle will operate at the design point.

[0019] The design of the supersonic nozzle is preferably carried out according to the isentropic current thread theory or with the aid of the method of characteristics. The design objective for the method according to the invention is to make the exit area of ​​the supersonic nozzle as large as the exit area of ​​the subsonic nozzle used in the prior art. Even with the same exit cross section, a properly designed supersonic nozzle generates a higher exit impulse force. This force results from: F 出口パルス =ρu 2 A [N], where ρ is the gas density at the nozzle exit, u is the gas velocity at the nozzle exit, and A is the exit diameter of the supersonic nozzle.

[0020] The characteristic method is a mathematical method for solving the gas dynamic partial differential equations for stationary, isentropic, rotationally symmetric gas flow given by:

number

[0021] Here, on the basis of Mach lines, i.e. lines of weak pressure disturbances propagating at the speed of sound and positioned at an angle to the local velocity vector, the so-called right-hand and left-hand characteristics are captured, along which analytical solutions of the above differential equations are possible and therefore known.

[0022] A characteristic method suitable for designing a supersonic nozzle for use in the method according to the invention is disclosed, for example, in EP 2 553 127 B1.

[0023] In a variant of the method according to the invention, it can be provided that at least one supersonic nozzle is operated outside the gas dynamic design point. For example, it can be provided that the supersonic nozzle is operated in such a way that the process gas is under-expanded or over-expanded in the molten metal, which leads to the generation of expansion waves and oblique or vertical compression shocks in the molten metal. As a result, pumping movements can occur in the molten metal. Over-expansion of the process gas occurs when the process gas is supplied to the supersonic nozzle at a pressure (inlet pressure) lower than the design inlet pressure. Under-expansion of the process gas occurs when the inlet pressure of the process gas at the inlet cross section of the supersonic nozzle is higher than the design inlet pressure. In one and the other operating mode, complex disturbance patterns (diamond patterns) are formed in the molten metal in the form of expansion waves and compression shocks, which the method according to the invention takes advantage of to achieve a stirring effect in the molten metal.

[0024] In a further advantageous variant of the method according to the invention, at least one supersonic nozzle acts by varying the volumetric flow rate and / or pressure of the process gas during operation, such pulsating action of the supersonic nozzle making it possible to produce an advantageous pumping effect and thus intensive mixing in the molten metal.

[0025] If multiple supersonic nozzles are located on or in the metal vessel at different positions, different heights, relative to the molten bath surface, they can, for example, be designed to have different operating points, i.e., different diameters.

[0026] Each supersonic nozzle in the metal vessel can be individually controlled, thereby varying the volumetric flow rate and pressure. In this way, the method can take into account the different geometries of different metal vessels.

[0027] The process gas can be introduced into the metal vessel vertically from below and / or from the side at different angles.

[0028] The process gas can be introduced directly into the liquid phase of the molten metal and / or slag or alternatively or additionally into the region of the phase boundary between the molten metal and the slag. In any case, an essential feature of the method according to the invention is that the process gas is introduced below the bath.

[0029] The method according to the invention involves the use of a metal surgical vessel, for example in the form of a converter, ladle furnace, electric arc furnace, etc., having a plurality of supersonic nozzles passing through the wall and / or bottom of the vessel.

[0030] For example, a Pierce Smith converter can be used as the metal vessel. Such converters include a rotatable cylinder for holding the molten metal. By rotating the cylinder, supersonic nozzles can be positioned to introduce process gases, for example, in the region of the slag / melt phase boundary, thereby allowing enhanced gas treatment.

[0031] A further aspect of the invention relates to a metallurgical plant for the treatment of molten metal having a metal vessel with means for gasifying the molten metal and / or slag, characterized in that the means for gasifying the molten metal comprise at least one supersonic nozzle located in the bottom and / or wall of the metal vessel and arranged relative to the surface of the molten metal in such a way that a submerged introduction of a process gas into the molten metal can be performed.

[0032] Usefully, the plurality of supersonic nozzles are arranged in at least one replaceable cassette in the melting vessel. The cassette may have a nozzle array in which the plurality of supersonic nozzles are arranged in a predetermined pattern. In this way, the plurality of supersonic nozzles can be quickly and easily installed and removed. The arrangement of the supersonic nozzles in the cassette or cassettes and the number of cassettes depend on the type of application.

[0033] In an advantageous variant of the system according to the invention, the nozzles in the cassette can be designed for different volumetric flow rates of the process gas supplied to the molten metal.

[0034] The present invention will now be described with reference to the accompanying drawings. [Brief description of the drawings]

[0035] FIG. 1 is a schematic diagram showing the arrangement of supersonic nozzles provided on the side wall of a metal container according to the present invention. FIG. 2 is a schematic representation of a metal vessel in the form of a Pierce-Smith converter according to the invention; FIG. 3 is an illustration showing the velocity profile of a process gas exiting a supersonic nozzle operating at a design point in accordance with the present invention. FIG. 4 is a diagram corresponding to FIG. 2, showing a waveform generated by the process gas flowing out in the molten metal during the overexpansion operation of the supersonic nozzle. FIG. 5 is a diagram corresponding to FIG. 2, showing the waveforms generated by the process gas flowing out of the molten metal during underexpansion operation of the supersonic nozzle.

[0036] FIG. 1 shows a metal vessel 1 of a plant according to the invention, which comprises a bottom 2 and a side wall 3 lined with refractory material. The metal vessel 1 is filled with molten metal 4, into which, according to the invention, a process gas is introduced, for example in the form of pure oxygen, below the molten pool surface 5 during bathing. For this purpose, a supersonic nozzle 6 with a certain outlet diameter D is provided in the side wall 3 of the metal vessel 1. The metal vessel 1 is shown only in simplified form for exemplary reasons. It can contain several supersonic nozzles 6 that are inserted in the side wall 3 or the bottom 2 of the metal vessel 1 at different positions (sidewall rinser (Seitenwandspueler and / or bottom rinser Bodenspueler). The gas jet 7 introduced by the supersonic nozzle 6 into the metal vessel 1 emerges from the supersonic nozzle 6 with a gas pressure that corresponds to the ambient pressure prevailing in the molten metal 4. The gas jet 7 has a penetration depth J due to the supersonic speed of the gas that is significantly higher than the penetration depth of a gas jet with subsonic speed.

[0037] The supersonic nozzle 6 used according to the invention can be designed as a Laval supersonic nozzle having a bell-shaped converging nozzle section 10 and a corresponding bell-shaped diverging nozzle section 11, the converging nozzle section 10 merging into the diverging nozzle section 11 in the region of the nozzle throat 12. The maximum diameter of the converging nozzle section 10 determines the inlet cross section 9 of the supersonic nozzle 6, while the maximum diameter of the diverging nozzle section 11 determines the outlet cross section 8 of the supersonic nozzle 6.

[0038] Fig. 2 shows a variant of a metal vessel 1 for carrying out the method according to the invention, which is designed as a Pierce Smith converter. The metal vessel is designed as a cylinder rotatable about its longitudinal axis, the side wall 3 of which is pierced by at least one supersonic nozzle 6, which is arranged in the side wall 3 in such a way that a gas jet 7 can be introduced into the liquid at supersonic speed into the liquid phase of the molten metal 4, or into the slag 13, or into the region of the phase boundary 14 of the molten metal 4 and the slag 13 below the surface 5 of the molten bath. In the variant of the metal vessel 1 shown in Fig. 2, the reference signs used in Fig. 1 are used for the corresponding features, whereby, in contrast to the metal vessel 1 according to Fig. 1, the side wall does not constitute a distinct bottom, since the metal vessel is composed of a cylindrical shell surface and end faces, the shell surface being referred to above as the side wall 3.

[0039] 3 to 5 show different operating modes of the metal plant according to the invention.

[0040] Figure 3 shows the velocity profile of the gas jet 7 in the supersonic nozzle 6 operating at the design point. In this operating mode, the pressure p1 at the exit cross section 8 of the supersonic nozzle 6 corresponds to the pressure p∞ in the molten metal. The inlet pressure p0 corresponds to the design inlet pressure p0. A uniform and homogeneous velocity profile is established at the exit cross section 8 of the supersonic nozzle.

[0041] In the variant of operation of the supersonic nozzle 6 shown in Fig. 4, the inlet pressure p0 of the process gas is selected to be lower than the design inlet pressure p0. At the exit cross section 8 of the supersonic nozzle 6, there is a corresponding lower pressure p1 of the process gas, which is lower than the ambient pressure p∞ of the molten metal 4. As a result, a series of compression and expansion waves are generated in the molten metal 4, generating the illustrated modulation pattern in the form of compression shocks and expansion waves. The variant of operation of the supersonic nozzle 6 shown in Fig. 3 is called overexpansion operation.

[0042] Finally, Figure 5 shows the modulation pattern of the gas flow in the molten metal 4 in the supersonic nozzle 6 during underexpanded operation. In this mode of operation of the supersonic nozzle 6, the inlet pressure p0 of the process gas is greater than the design inlet pressure p0. As a result, the pressure p1 of the process gas at the exit cross section 8 of the supersonic nozzle is greater than the ambient pressure p∞ in the molten metal 4, which causes a post-expansion of the process gas in the molten metal 4.

[0043] List of reference numbers 1 metal container 2. Bottom of metal container 3. Side walls of metal containers 4 Metal Melting 5. Molten pool surface 6 Supersonic Nozzle 7 Gas Jet 8. Supersonic nozzle exit cross section 9 Supersonic nozzle inlet cross section 10. Supersonic nozzle convergence section 11. Supersonic nozzle divergence 12 Nozzle throat 13. Slug 14 phase boundary J Gas jet penetration depth p0 Process gas inlet pressure p1 Process gas pressure at the exit cross section of the supersonic nozzle p∞ Pressure in molten metal The present invention includes the following items. [Item 1] A method for treating molten metal (4) and / or slag in a metal bath, comprising the steps of: The method comprises the introduction of a process gas into the molten bath, characterized in that the process gas is accelerated to supersonic speed and introduced at supersonic speed below the surface (5) of the molten bath by at least one supersonic nozzle (6) into the liquid phase of the molten metal (4) and / or into the slag (13) and / or into the region of the phase boundary (14) between the molten metal and the slag (13). [Item 2] 2. The method according to claim 1, characterized in that the process gas is introduced at multiple points in the molten bath using multiple supersonic nozzles (6). [Item 3] 3. The method according to item 1 or 2, characterized in that the process gases are introduced into the molten metal (4) at different heights relative to the surface of the molten bath (5). [Item 4] 4. The method according to any one of items 1 to 3, characterized in that at least one supersonic nozzle is designed as a supersonic nozzle having a convergent nozzle section (10) and a divergent nozzle section (11). [Item 5] 5. The method according to any one of items 1 to 4, characterized in that the gas dynamic design point of the at least one supersonic nozzle (6) is selected such that the gas pressure of the process gas at the exit cross section (8) of the supersonic nozzle (6) corresponds to the ambient pressure in the molten metal (4). [Item 6] 6. The method according to any one of items 1 to 5, characterized in that at least one supersonic nozzle (6) is operated outside its gas dynamic design point. [Item 7] 7. The method according to any one of items 1 to 6, characterized in that at least one supersonic nozzle (6) acts by means of a volumetric flow rate and / or a pressure of the process gas which varies during operation. [Item 8] 8. The method according to any one of items 1 to 7, characterized in that the process gas is introduced vertically into the metal container (1) from below and / or from the side. [Item 9] 9. The method according to any one of items 1 to 8, characterized in that a metal vessel (1) is used having a plurality of supersonic nozzles (6) passing through the wall and / or bottom of the vessel. [Item 10] A metallurgical plant for treating molten metal comprising a metal vessel (1) equipped with means for introducing a gas into the molten metal (4) and / or slag, 1. The metallurgical plant according to claim 1, wherein the means for introducing a gas into the molten metal comprise at least one supersonic nozzle (6) in the bottom (2) and / or in the wall of the melting vessel, which nozzle is positioned relative to the molten bath surface (5) in such a way that a submerged introduction of the process gas into the molten metal (4) and / or into the slag (13) and / or in the region of the phase boundary (14) between the molten metal and the slag (13) is possible. [Item 11] Item 11. A metal plant according to item 10 for carrying out the method according to any one of items 1 to 9. [Item 12] 12. The metal plant according to item 10 or 11, characterized in that a plurality of supersonic nozzles (6) are respectively arranged in exchangeable cassettes in the metal container (1).

Claims

1. A method for treating molten metal (4) and / or slag in a metal bath, comprising the steps of:

1. The method of claim 1, further comprising: introducing a process gas into the molten bath, wherein the process gas is accelerated to supersonic speed and introduced at supersonic speed by at least one supersonic nozzle (6) below the surface (5) of the molten bath into the liquid phase of the molten metal (4) and / or into the slag (13) and / or into the region of the phase boundary (14) between the molten metal and the slag (13); wherein the process gas is introduced at multiple points in the molten bath using multiple supersonic nozzles (6); and wherein the at least one supersonic nozzle (6) is operated to under-expand or over-expand the process gas in the molten metal, wherein both the converging section of the supersonic nozzle and the diverging section of the supersonic nozzle have a bell-shaped profile.

2. 2. The method according to claim 1, characterized in that the process gas is introduced into the molten metal (4) at different heights relative to the surface of the molten bath (5).

3. 3. The method according to claim 1 or 2, characterized in that at least one supersonic nozzle is designed as a supersonic nozzle having a convergent nozzle section (10) and a divergent nozzle section (11).

4. A method according to any one of claims 1 to 3, characterized in that at least one supersonic nozzle (6) varies the volumetric flow rate and / or pressure of the process gas during operation.

5. 5. The method according to claim 1, wherein the process gas is introduced vertically into the metal container (1) from below and / or from the side.

6. 6. The method according to claim 1, characterized in that a metal vessel (1) is used having a number of supersonic nozzles (6) passing through the wall and / or the bottom of the vessel.

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