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Title:
METHOD FOR REFINING MOLTEN METAL USING A CONVERTER
Document Type and Number:
WIPO Patent Application WO/2019/158479
Kind Code:
A1
Abstract:
A method is provided for refining molten metal using a converter comprising at least one side wall nozzle mounted to a side wall of the converter. The method comprises the following steps: forming a bath of molten metal inside of the converter; blowing a mixture of an essentially Oxygen free carrier gas and powdered material onto and into a slag formed at least partially on the surface of the bath of molten metal using the at least one side wall nozzle.

Inventors:
KHADHRAOUI, Sabrine (Hauptstraße 8, Erkrath, 40699, DE)
DAS, Satyajit (Home G41 Oriental Villa, Sushant Lok 3Sector 57 Gurgaon, Haryana 1, 122011, IN)
ODENTHAL, Hans-Jürgen (Froschkönigweg 10, Mettmann, 40822, DE)
KRAUSE, Fabian (Daimlerstraße 21, Neuss, 41462, DE)
KEMMINGER, Andreas (Bilker Straße 37, Düsseldorf, 40213, DE)
Application Number:
EP2019/053318
Publication Date:
August 22, 2019
Filing Date:
February 11, 2019
Export Citation:
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Assignee:
SMS GROUP GMBH (Eduard-Schloemann-Str. 4, Düsseldorf, 40237, DE)
International Classes:
C21C5/32; C21C5/54; C21C7/00; C21C7/064; F27D3/00; F27D3/18
Foreign References:
US4195985A1980-04-01
CN102796841B2014-05-14
US3856510A1974-12-24
GB1418488A1975-12-24
GB1276029A1972-06-01
EP0030360B21988-09-28
Attorney, Agent or Firm:
KLÜPPEL, Walter (Hammerstr.2, Siegen, 57072, DE)
Download PDF:
Claims:
Claims

1. Method for refining molten metal using a converter (100) comprising at least one side wall nozzle (150) mounted to a side wall (1 13) of the converter (100), the method comprising the following steps:

Forming a bath (501 ) of molten metal inside of the converter (100); characterized in that the method comprises:

Blowing a mixture (303) of an essentially Oxygen free carrier gas and a powdered material onto and into a slag (401 ) formed at least partially on the surface (503) of the bath (501 ) of molten metal using the at least one side wall nozzle (150).

2. The method according to claim 1 , wherein the at least one side wall nozzle (150) is mounted to the side wall (1 13) lower in a vertical direction than a horizontal pivoting axis (601 ) of the converter (100), when the converter (100) is in an upright orientation, wherein the blowing the mixture (303) of the essentially Oxygen free carrier gas and the powdered material comprises:

Blowing the mixture (303) of the essentially Oxygen free carrier gas and the powdered material downwardly into the slag (401 ). 3. The method according to any one of claims 1 or 2, wherein the blowing the mixture (303) of the essentially Oxygen free carrier gas and the powdered material comprises:

Blowing the mixture (303) of the essentially Oxygen free carrier gas and the powdered material into the slag (401 ) downwardly at an injection angle (a-i , <¾) with respect to the horizontal pivoting axis (601 ), the injection angle being in between 1 ° and 60°, preferably in between 10° and 50°, more preferably in between 15° and 35°.

Seite 14

4. The method according to any one of the preceding claims 1 to 3, wherein the converter (100) further comprises at least one upper nozzle (121 ), which is movably assigned to an upper wall (1 1 1 ) of the converter (100), and wherein the method further comprises:

Blowing Oxygen gas (301 ) onto a surface (503) of the bath (501 ) of molten metal using the at least one upper nozzle (121 ).

5. The method according to claim 4, wherein the blowing the mixture (303) of the essentially Oxygen free carrier gas and the powdered material comprises:

Blowing the mixture (303) of the essentially Oxygen free carrier gas and the powdered material along a main blowing direction (603, 605) of the at least one side wall nozzle (150) into the slag (401 ), wherein said main blowing direction (603, 605) of the at least one side wall nozzle (150) forms an angle in between 45° and 89° with a main blowing direction (607) of the upper nozzle (121 ).

6. The method according to any one of the preceding claims 1 to 5, wherein the converter (100) further comprises at least one bottom nozzle mounted to a bottom wall (115) of the converter (100), the method further comprising:

Blowing a mixture of an essentially Oxygen free carrier gas and powdered material into the bath (501 ) of molten metal from below the bath (501 ) of molten metal using the at least one bottom nozzle.

7. The method according to any one of the preceding claims 1 to 6, wherein the blowing the mixture (303) of the essentially Oxygen free carrier gas and the powdered material comprises:

Blowing the essentially Oxygen free carrier gas at subsonic speed onto and into the slag (401 ).

8. The method according to any one of the preceding claims 1 to 7, wherein an inner diameter of the side wall nozzle (150) is essentially constant along a length direction (603, 605) of the side wall nozzle (150), wherein the blowing

Seite 15 the mixture (303) of the essentially Oxygen free carrier gas and the powdered material comprises:

Blowing the essentially Oxygen free carrier gas at subsonic speed onto and into the slag (401 ).

9. The method according to any one of the preceding claims 1 to 8, wherein the powdered material comprises recycled converter dust. 10. The method according to any one of the preceding claims 1 to 9, further

comprising:

Extracting a mixture of gaseous materials and converter dust from an inner converter volume during the refining of the molten metal,

Separating the powdered material from the gaseous materials; and

Blowing the separated powdered material onto the slag (401 ) via the at least one side wall nozzle (150).

1 1. The method according to any one of the preceding claims 1 to 10, wherein the powdered material comprises a dephosphorization agent, preferably selected from a group including lime powder, CaO powder and 2Ca0.Si02. 12. The method according to any one of the preceding claims 1 to 11 , wherein the powdered material comprises dolomite powder, preferably MgO.

13. The method according to any one of the preceding claims 1 to 12, wherein the powdered material comprises iron ore.

14. The method according to any one of the preceding claims 1 to 13, wherein the powdered material further comprises pulverized fuel materials including carbon and/or aluminum containing materials.

Seite 16

15. The method according to any one of the preceding claims 1 to 14, wherein the powdered material comprises foaming or anti-foaming materials.

16. The method according to any one of the preceding claims 1 to 15, wherein the carrier gas is an inert gas.

17. The method according to any one of the preceding claims 1 to 16, wherein the carrier gas comprises Argon and/or Nitrogen. 18. The method according to any one of the preceding claims 1 to 17, wherein the at least one upper nozzle (121 ) is mounted movable in a vertical direction to the upper wall (1 1 1 ) of the converter (100) via a water cooled, vertical lance (120). 19. The method according to any one of the preceding claims 1 to 18, wherein a mean diameter of particles forming the powdered material is smaller than 2 mm, preferably smaller than 1 mm, more preferably smaller than 0,1 mm.

20. The method according to any one of the preceding claims 1 to 19, wherein the molten metal comprises molten iron.

21. Converter (100) adapted to be used for refining molten metal, comprising at least one side wall nozzle (150) mounted to a side wall (113) of the converter (100); characterized in that the at least one side wall nozzle (150) is adapted to blow a mixture (303) of an essentially Oxygen free carrier gas and a powdered material into a slag (401 ), when the slag (401 ) is formed at least partially on the surface (503) of the bath

(501 ) of molten metal.

22. The converter (100) according to claim 21 , wherein the at least one side wall nozzle (150) is mounted to the side wall (1 13) at a height in a vertical direction

Seite 17 lower than a horizontal pivoting axis (601 ) of the converter (100), when the converter (100) is in an upright orientation.

23. The converter (100) according to any one of the preceding claims 21 or 22, wherein the at least one side wall nozzle (150) comprises an inner diameter, which is essentially constant along a length direction (603, 605) of the side wall nozzle (150).

24. The converter (100) according to any one of the preceding claims 21 to 23, wherein the at least one side wall nozzle (150) is mounted to the side wall

(1 13) of the converter (100) such that a main blowing direction (603, 605) of the at least one side wall nozzle (150) forms an injection angle (a-i, <¾) with respect to the horizontal pivoting axis (601 ) in between 1 ° and 60°, preferably in between 10° and 50°, more preferably in between 15° and 35°.

25. The converter (100) according to any one of the preceding claims 21 to 24, further comprising at least one upper nozzle (121 ) movably assigned to an upper wall (11 1 ) of the converter (100) and being adapted to blow Oxygen gas (301 ) onto a surface (503) of a bath (501 ) of molten metal formed inside of the converter (100).

26. The converter (100) according to any one of the preceding claims 21 to 25, further comprising at least one bottom nozzle mounted to a bottom wall (1 15) of the converter (100), adapted to blow a mixture of an essentially Oxygen free carrier gas and powdered material into the bath (501 ) of molten metal from below the bath (501 ) of molten metal.

Seite 18

Description:
METHOD FOR REFINING MOLTEN METAL USING A CONVERTER

1. Field of the invention The present invention relates to a method for refining molten metal using a converter, e.g. a converter steelmaking method for producing steel from molten iron.

2. Technical background The Linz-Donauwitz-process (also known as basic Oxygen steelmaking or Oxygen converter process) is a steel making process in which Oxygen is blown onto the surface of carbon-rich molten pig iron (iron bath) in a converter. To start the process, molten pig iron is introduced into a steelmaking converter, e.g. from a blast furnace, to form a bath of molten metal. Suitable converters are known in the art, their design being e.g. based on a Bessemer converter. The converter may be formed as a metallurgical vessel as for example disclosed in the patent specification of GB 1 276 029. As described therein, a converter can be a metallurgical vessel, which can be held using e.g. an encircling support ring having two trunnions defining a horizontal pivoting axis about which the converter can be rotated from a vertical orientation in which the steelmaking process is carried out into a tilted orientation for pouring or discharging the steel out of the converter.

For refining the molten iron, Oxygen, usually high purity Oxygen, is blown at high pressure and at supersonic speed onto and into the surface of the iron bath usually through a water-cooled lance comprising one or more nozzles at its tip. The Oxygen ignites carbon dissolved in the molten metal to form carbon monoxide and carbon dioxide thus lowering carbon content of the molten metal. Fluxes, in particular dephosphorization agents, such as e.g. burnt lime are fed into the vessel to form slag and to absorb impurities (including phosphor) during the steelmaking process.

Magnesium oxide (MgO) containing agents may be added also for protecting an inner converter lining. Blowing the Oxygen onto and into the molten metal stirs the molten metal such that metal and fluxes may form an emulsion which facilitates the refining process.

Seite 1 During the process, however, blowing Oxygen into the molten iron also results in a formation of iron oxide in the slag. The oxidized iron is then lost for the refining process which reduces a final steel yield. Describing technology where a majority of Oxygen is blown onto the molten metal surface while remaining Oxygen is introduced into the molten metal from below, the European patent EP 0 030 360 B2 discloses a method which allows achieving steel of low carbon content while not increasing iron losses in the slag. According to this patent, Oxygen is blown onto the surface of the molten metal using a water cooled lance in combination with side wall tuyeres placed within an upper portion of the converter above the horizontal converter pivoting axis. Powder lime may be introduced with the Oxygen onto the bath surface in addition to powder lime introduced through tuyeres from below.

However, it was found that in particular the use of a nozzle arrangement within an upper portion of the converter for blowing Oxygen and powdered lime in addition to Oxygen blown from a vertical lance did not yield optimal results in terms of lime powder losses. In addition, it was found that a system using the suggested

combinations of side wall nozzles and water cooled lance required complex control mechanisms.

A drawback which may be associated with a use of powdered lime is a possibly large loss of the lime as converter dust e.g. to gas cleaning plant systems. This may be less of a problem for lime powders of larger grain size or for bulk lime. However, bulk lime can be dissolved less efficiently and it was found that bulk lime can in particular not be dissolved in a foamy slag. Although a foamy slag may be advantageous for refining processes as an amount of metal droplets residing in the slag is at maximum during foaming (which results in a high decarburisation rate), only little dephosphorization appears possible when using bulk lime.

Thus, it is one object of the present invention to provide a method for refining molten metal using a converter where in particular Carbon and/or Phosphorous is removed efficiently from molten metal, preferably iron, whereby the method enables an efficient use of solid materials, in particular of dephosphorization agents, introduced into the converter. A further object of the present invention is to avoid complex control mechanisms for introducing Oxygen and solid materials into a metallurgical converter.

Seite 2 3. Summary of the invention

These and other objects, which become apparent upon reading the following description are solved by method for refining molten metal according to claim 1 and by a converter according to claim 21.

According to the invention, a method is provided for refining molten metal, preferably molten iron, e.g. molten pig iron, using a converter, e.g. a metallurgical furnace, for example for making steel from molten pig iron.

For example, the converter can be a top blown converter including at least one upper nozzle mounted to a top lance for blowing oxygen onto a bath of molten metal. In other words, in a preferred embodiment, at least one upper nozzle is movably assigned to an upper wall of the converter. Preferably, the at least one upper nozzle is mounted movably in a vertical direction to the converter and is included in a, preferably water cooled, vertical lance. The vertical lance itself can be mounted movably to the converter and can be movable through a corresponding opening formed in the upper wall of the converter.

Further, the converter can for example also be a bottom blown converter, where oxygen may be blown into the bath of molten metal from below e.g. through bottom nozzles or bottom tuyeres. Thus, in a preferred embodiment, the converter further comprises at least one bottom nozzle, e.g. at least one bottom tuyere, mounted to a bottom wall of the converter, i.e. underneath a molten metal bath when formed in the converter.

Yet further, the converter can for example also be a combined blown converter where oxygen may be partially blown into the molten bath via bottom tuyeres, while further oxygen is blown onto the bath of molten metal from above via a top lance. Thus, in a preferred embodiment, the converter can be a combined blown converter including at least one bottom nozzle and at least one upper nozzle.

According to the invention, the converter further comprises at least one side wall nozzle mounted to a side wall of the converter and the method comprises a step of forming a bath of molten metal inside of the converter. For example, to this end,

Seite 3 molten iron may be charged into the converter directly or after a suitable pretreatment stage from a blast furnace. Further, in the case of a top blown converter, the method may comprise blowing Oxygen gas onto a surface of the bath of molten metal using the at least one upper nozzle. In addition or alternatively, in the case of a bottom blown or combined blown converter, the method may comprise blowing Oxygen gas from at least one bottom nozzle or tuyere into the bath of molten metal from below.

The Oxygen gas may be high purity Oxygen and may be blown into the bath of molten metal at high pressure (e.g. in between 200 and 2000 kilopascal) at supersonic speeds. Reacting with Carbon included in the bath of molten metal to produce carbon oxides, blowing the Oxygen gas onto the bath surface provides the effect of removing carbon from the molten metal.

An iron refining or steelmaking process using the converter in accordance with the invention involves a formation of a slag on the surface of a bath of molten metal. The slag may e.g. be formed using fluxes fed into the converter to absorb impurities during the process. In the case of the converter being a top blown converter, the slag may e.g. be formed mainly aside of a hot spot zone where the Oxygen gas from the at least one upper nozzle impinges the surface of the bath of molten metal. For example as a result of a high kinetic energy transported by the oxygen stream impinging into the surface of the metal bath in this exemplary case, slag and molten metal may be mixed forming a slag/metal emulsion possibly on top of a slag layer.

According to the invention, the method further comprises blowing a mixture of a carrier gas and powdered material onto and into the slag (and/or the slag/metal emulsion) formed at least partially on the surface of the bath of molten metal using the at least one side wall nozzle. In other words, the side wall nozzle is preferably mounted to a respective side wall of the converter such that the mixture of carrier gas and powdered material is injected mainly into the slag and/or into a slag/metal emulsion, preferably avoiding the hot spot zone in the case of a top blown or combined blown converter.

The slag being the reaction zone for the powdered material, e.g. a powdered agent, in particular for powdered lime, efficiency in using solid input materials in the converter can be thus increased. Directly injecting a powdered material into the slag or into the slag/metal emulsion by means of the side wall nozzles, a high reactivity and thus an efficient use can be achieved. Preferably, the powdered material comprises a

Seite 4 dephosphorization agent selected from a group including lime powder, Calcium Oxide (CaO), and 2Ca0.Si0 2 powder may be injected directly into the reaction zone, that is the slag, which results in a high reactivity in particular in terms of efficient continuous dissolution of the agent and efficient dephosphorization of the molten metal. In particular 2Ca0.Si0 2 powder may in a preferred embodiment have a grain or particle size equal to or smaller than 2 mm, preferably in between 20 to 50 pm. It turned out that 2Ca0.Si0 2 powder can advantageously dissolve P 2 Os in solid form and thus increase the phosphorus capacity in slag which leads to high dephosphorization efficiency. Advantageously, the use of such dephosphorization agents may allow that e.g. using high amounts of lump lime with large grain size can be avoided. In particular, avoiding a use of lump lime has been found to be advantageous for a steelmaking process, as lump lime usually dissolves only slowly and undissolved parts may remain even after the end of the process. The side wall nozzles may provide the following additional advantage. For example, when oxygen is blown through bottom tuyeres in case of a bottom or combined blown converter into the bath of molten metal, the produced slag amount is usually much lower than in the case of a top blown converter. This results in lower iron loss as compared with the case of a top blown converter, however, also to limited dissolution of solid lime und thus insufficient dephosphorization. Thus, in the case of bottom blown converters, by providing the side wall nozzles, the present invention has the potential of enhancing e.g. dephosphorization in such a bottom blown converter through efficient introduction of powdered dephosphorization agents via the at least one side wall nozzle.

In case that the converter is provided with nozzles at its bottom, e.g. in addition to a top lance with upper nozzles, the method may preferably further comprise blowing a mixture of an essentially Oxygen free carrier gas and the powdered material into the bath of molten metal from below the bath of molten metal using the at least one bottom nozzle. Blowing a gas from below into the metal bath helps stirring the bath and thus facilitates the refining process. Providing additionally powdered material from below increases the total injection rate of said powdered material without introducing further load on the at least one side wall nozzle.

Seite 5 According to the invention, the carrier gas (preferably all gas from the at least one side wall nozzle) is essentially Oxygen (O) free. In other words, the carrier gas does not comprise Oxygen up to a tolerable Oxygen pollution, e.g. a residue Oxygen

concentration e.g. below 1 %, e.g. below 0,1 %, e.g. below 0,01 % (by weight).

Preferably, the carrier gas is an inert gas, preferably free of Oxygen. The inert gas may e.g. be selected from the group of noble gases and is preferably Argon (Ar).

Alternatively or in addition, the carrier gas may comprise Nitrogen (N), being preferably free of Oxygen. It turned out that the use of an oxygen-free carrier gas is advantageous as thereby, the overall system requires less complex control. For example, in the exemplary case of a top blown converter, introducing Oxygen only (or mainly) via the at least one upper nozzle, e.g. mounted to a vertical lance, prevents a necessity to synchronize oxygen blowing rates between the at least one upper nozzle and the at least one side wall nozzle. A similar effect may be achieved by using the side wall nozzle in the cases of bottom blown or combined blown converters. In a preferred embodiment, the at least one side wall nozzle is mounted to the side wall at a height in a vertical direction, the height being lower than a horizontal pivoting axis of the converter, when the converter is in an upright orientation. Preferably, blowing the mixture of the essentially Oxygen free carrier gas and the powdered material comprises blowing the mixture of the essentially Oxygen free carrier gas and the powdered material downwardly into the slag.

In other words, when the converter is not tilted, e.g. during the steelmaking process, the at least one side wall nozzle is mounted to the converter side wall underneath the pivoting axis, defined e.g. by the trunnions about which the converter may be tilted. The at least one side wall nozzle is thus mounted in close proximity to the slag and/or to the slag/metal emulsion. Thus, preferably, the at least one side wall nozzle is not used for introducing oxygen into the converter, but to introduce the powdered material, e.g. the powdered dephosphorization agent, for example powdered lime, directly into the slag or slag/metal emulsion being carried by an essentially oxygen-free gas. By mounting the at least one side wall nozzle underneath the trunnions or a trunnion ring, the at least one side wall nozzle is located in close proximity to the reaction zone, i.e. the slag. As a result, the powder can easily reach the reaction zone with minimal gas pressure such that only a reduced amount of carrier gas is necessary which is in particular advantageous if noble gasses such as Argon are used as carrier gas. In

Seite 6 case of using Nitrogen as carrier gas, unwanted Nitrogen-pickup by the metal bath can be avoided.

Blowing powdered material onto a slag and/or the metal bath surface from above, conventionally resulted in undesirably large losses of the powdered material. Usually, due to high heat and kinetic energies inside a converter, powdered and gaseous materials cannot be fully introduced into the slag/and or the metal bath but are blown into an inner volume of the converter above the metal bath and the slag. Such gaseous and powdered materials are often extracted from the converter and fed to a gas cleaning plant (GCP) for separating the gaseous and powdered materials. In conventional converters where powdered materials were introduced from above, losses to such GCP systems have been undesirably high. It was found that by mounting the at least one side wall nozzle underneath the trunnions or a trunnion ring, i.e. in close proximity to the slag, such losses could be effectively avoided and the powdered material could be efficiently introduced into the reaction zone. In this connection, it was further found that in particular a use of small grain sizes

advantageously contributed to this effect. Thus, a mean diameter of particles forming the powdered material is smaller than 2 mm, preferably smaller than 1 mm, more preferably smaller than 0,1 mm. It was found that for example by injecting powdered lime or lime fines with grain size < 2 mm via at least one side wall nozzle located close to the slag, the typical losses to the GCP system known from using small grain sized lime are avoided or minimized.

The at least one side wall nozzle is preferably arranged on the side wall of the converter underneath the trunnion ring, such that the blown mixture of carrier gas and powdered material is directed to impinge directly into the slag and/or the slag/metal emulsion. Thus, in a preferred embodiment, a corresponding injection angle is set accordingly. Preferably, the blowing of the mixture of the essentially Oxygen free carrier gas and the powdered material comprises blowing the mixture of the

essentially Oxygen free carrier gas and the powdered material into the slag

downwardly at an injection angle with respect to the horizontal pivoting axis, the injection angle being in between 1 ° and 60°, preferably in between 10° and 50°, more preferably in between 15° and 35°. It was found that in particular within these angle ranges, beneficial results could be achieved in terms of use efficiency of the powdered material, e.g. the powdered dephosphorization agent.

Seite 7 Providing the powdered material from above the molten metal bath and the slag via the at least one side wall nozzle allows the powdered material to be injected not into a hot spot zone in case of a top blown converter but rather suitably into the slag and/or slag/metal emulsion. In a preferred embodiment, the blowing the mixture of the essentially Oxygen free carrier gas and the powdered material comprises blowing the mixture of the essentially Oxygen free carrier gas and the powdered material along a main blowing direction of the at least one side wall nozzle into the slag, wherein in the exemplary case of a top blown converter, said main blowing direction of the at least one side wall nozzle forms an angle in between 45° and 89° with a main blowing direction of the upper nozzle. Thereby, the powdered material can be suitably directed to areas aside of a hot spot zone in a case of a top blown converter in which zone oxygen from the upper nozzle impinges the metal bath surface into areas where slag and/or slag/metal emulsion is usually formed.

In a preferred embodiment, the essentially Oxygen free carrier gas is blown at subsonic speed onto and into the slag. Preferably, an inner diameter of the side wall nozzle is essentially constant along a length direction of the side wall nozzle. In other words, preferably, the use of nozzles having e.g. converging and diverging inner profiles such as Laval nozzles is avoided. It was found that a use of nozzles with such inner profile are subject to larger wear of inner surfaces by grinding of particles transported through the nozzles. In the case of Laval nozzles, such grinding may be attributed to the fact that a carrier gas may reach supersonic velocities while velocities of powder particles usually remain subsonic. Nozzles with an essentially constant inner diameter are therefore advantageous as inner surfaces are subject to less wear.

The provision of the at least one side wall nozzle turned out to be further

advantageous as the at least one side wall nozzle enables a possibility of blowing converter dust. Thus, in a preferred embodiment, the powdered material comprises converter dust. Usually, converter dust is mainly iron oxide in form of Fe 2 03 and may also contain dephosphorization agents, such as CaO. It turned advantageously out that the converter dust, if introduced through the side wall nozzles can be used as a substitute for iron ore and thus as a cooling agent for the slag or as a slag former. It turned out that the cooling effect can be beneficial for dephosphorization.

Seite 8 Thereby, converter dust may be converter dust recycled from the same converter or from a different converter. The converter dust can be recycled without briquetting.

This is advantageous as briquetting processes can be avoided and as corresponding costs can be avoided.

It turned out that the use of the inventive side wall nozzles allow for an efficient recycling of powdered material lost to the inner volume of the converter above the bath of molten metal and the slag. In other words, in a preferred embodiment, converter dust may be recycled from the converter. To this end, in a preferred embodiment, the method comprises extracting a mixture of gaseous materials and converter dust from an inner converter volume during the refining of the molten metal. Thereafter, the converter dust is separated from the gaseous materials and the separated converter dust is again blown onto and into the slag via the at least one side wall nozzle. In this way, the efficiency of the use of the powdered material is further increased as powdered material which escaped the reaction zone can be recycled from the converter dust and again injected into the reaction zone, i.e. into the slag and/or the slag/metal emulsion.

In a preferred embodiment, the powdered material comprises a slag forming material, preferably lime powder, preferably CaO powder. It was found that the use of the inventive side wall nozzles leads to a high efficiency of dephosphorization. Further materials such as iron ore can be used e.g. for cooling purposes. In a preferred embodiment, the mixture of an essentially Oxygen free carrier gas and powdered material further comprises iron ore, e.g. iron ore powder. It was found that this material further has an advantageous cooling effect on the melt. Further, even though MgO-containing agents may have a negative effect on dephosphorization, this negative effect is overcompensated by the highly efficient dephosphorization enabled by the use of the side wall nozzles. Therefore, in a preferred embodiment, the mixture of an essentially Oxygen free carrier gas and powdered material further comprises dolomite powder, preferably MgO. The addition of dolomite powder helps to protect an inner converter lining.

In a preferred embodiment, the powdered material may comprise foaming or anti foaming materials. It turned out that slag foaming may have several advantages. For example, slag foaming increases the total reaction surface of the metallic droplets in

Seite 9 the slag and thus the impurities removal rate. However, excessive foaming may lead to slopping (slag overrunning from the converter mouth). Thus, by appropriately providing foaming or anti-foaming materials, slag formation can be controlled. It turned out that the side wall nozzles can be used to either enhance or suppress the slag foaming by blowing foaming or anti-foaming agents in powdered form into or onto the slag. For example, fine powder coke was found to increase the foam height while grain coke (size 1 to 2 mm) suppresses the foaming.

In addition, preferably, the mixture of an essentially Oxygen free carrier gas and the powdered material may further comprise pulverized fuel materials including carbon and/or aluminum containing materials. Thus, as compared to conventional technology according to which such fuel materials are blown from bottom nozzles underneath a bath of molten metal, e.g. an oxygen free gas can be blown from the bottom nozzles and the carbon-containing fuels, required for the energy balance, can be blown via the side wall nozzle. It was found that thereby, a considerable reduction of a burn back rate at the bottom nozzles can be achieved.

The present invention further provides a converter adapted to be used for refining molten metal. In a preferred embodiment, the converter comprises at least one upper nozzle movably assigned to an upper wall of the converter and being adapted to blow Oxygen gas onto a surface of a bath of molten metal, preferably molten iron, formed inside of the converter. According to the invention, the converter further comprises at least one side wall nozzle, preferably with an essentially constant inner diameter along its length, mounted to a side wall of the converter. Preferably, the at least one side wall nozzle is mounted to the side wall at a height in a vertical direction lower than a horizontal pivoting axis of the converter, when the converter is in an upright orientation. According to the invention, the at least one side wall nozzle is adapted to blow a mixture of an essentially Oxygen free carrier gas and powdered material into a slag, when the slag is formed at least partially on the surface of the bath of molten metal. In other words, the at least one side wall nozzle may be mounted at a suitable injection angle so that it is adapted to inject carrier gas and powdered material efficiently into a slag and/or a slag/metal emulsion.

Seite 10 To this end, the at least one side wall nozzle is preferably mounted to the side wall of the converter such that a main blowing direction of the at least one side wall nozzle forms an injection angle with respect to the horizontal pivoting axis in between 1 ° and 60°, preferably in between 10° and 50°, more preferably in between 15° and 35°. In a preferred embodiment, the converter further comprises at least one bottom nozzle mounted to a bottom wall of the converter, adapted to blow a mixture of an essentially Oxygen free carrier gas and powdered material into the bath of molten metal from below the bath of molten metal. 4. Description of the preferred embodiments

In the following, the invention is described exemplarily with reference to the enclosed figure, where: Fig. 1 shows a schematic illustration of a converter to be used in a method for refining molten metal.

Fig. 1 schematically illustrates a converter 100, in the shown only exemplary case a top blown converter, to be used in a method for refining molten metal, e.g. molten pig iron, for producing steel. A refractory lining 1 10 forms an upper wall 1 11 , a side wall 1 13 (the side wall essentially rotationally symmetric around a vertical axis 607) and a bottom wall 1 15. Fig. 1 shows the converter 100 schematically during a refining process where a bath 501 of molten metal, e.g. molten iron, is formed inside the converter, a surface 503 of the bath 501 being partially covered by slag 401. The slag 401 is formed least partially on the surface 503 of the bath 501 , in the shown example around a hot spot zone 510 of the surface 503 which is impinged by an oxygen stream 301 from an upper nozzle 121 included in a vertical lance 120. The vertical lance is mounted movable to the converter 100 along a vertical axis 607 which coincides with a main blowing direction 607 of the upper nozzle 121. As illustrated, the vertical lance itself can be mounted movably to the converter 100 and can be movable through a corresponding opening formed in the upper wall of the converter 100. For example, by moving the upper nozzle 121 downwardly close to the surface 503 of the metal bath 501 , a splashing mode of the vertical lance 120 can be enabled where the stream of oxygen from the upper nozzle 121 is used to generate metal droplets from the bath

Seite 1 1 501 of molten metal into to the slag 401. In this way, a slag-metal interface can be increased to thereby increase the reactivity of the slag 401.

Fig. 1 further shows a trunnion ring 105 (cross sections of said ring at both sides of the converter 100) which embraces the converter 100. The trunnion ring 105 has respective trunnions 106 which define a horizontal pivoting axis 601 around which the converter 100 can be tilted to pour the liquid steel after the refining process out of the converter 100.

The figure further illustrates side wall nozzles 150 which are mounted to the side wall 1 13 underneath a plane perpendicular to the vertical axis 607 and including the horizontal axis 601. In other words, the side wall nozzles 150 are mounted lower than the trunnions 106 or the trunnion ring 105, when the converter 100 is in its upright, vertical orientation in which the steelmaking or iron refining process is carried out inside of the converter 100. The figure illustrates the possibility of using a plurality of side wall nozzles (four side wall nozzles 150 are visible) which may be arranged in a ring-like fashion around the side wall 1 13 of the converter 100. Providing the side wall nozzles 150 allows the possibility that maintenance of the powder injectors, i.e.

according to the invention the side wall nozzles 150, can be done separately from the vertical lance 120, and therefore, a malfunction/breakdown of one of the side wall nozzles 150 would not affect the blowing profile and the plant operation.

As shown, the nozzles 150 are mounted to the side wall 1 13 at respective injection angles (a-i , a 2 shown in the figure) with respect to the horizontal pivoting axis 601 such that a mixture 303 of an essentially Oxygen free carrier gas, e.g. Argon and/or Nitrogen, and powdered material, e.g. powdered lime, is injected into the slag 401 while essentially avoiding the hot spot area 510. In other words, the injection angle is chosen such that a main blowing direction 603, 605 of each side wall nozzle is essentially along an orientation of the slag 401 such that the mixture 303 is not blown into the metal bath 501 but such that most of the powdered material is injected into the volume of the slag 401 and or a slag/metal emulsion.

In addition or alternatively, it is possible to use the side wall nozzles 150 to generate metal droplets from the bath 501 of molten metal into to the slag 401 by blowing onto the metal bath surface (similar to a splashing mode of the vertical lance). In this way,

Seite 12 a slag-metal interface can be increased increasing the reactivity. Using the side wall nozzles 150 in this way, it becomes possible to keep operating the vertical lance 120 and the upper nozzle 121 at a suitable vertical distance from the metal bath to reduce wear on the vertical lance 120 thereby increasing its possible lifetime.

As shown in Fig. 1 , the powdered material, e.g. the powdered lime or CaO, is injected directly into the slag, the side wall nozzles being provided in close proximity to the slag underneath the trunnion ring 105. It turned out that in this way, it becomes possible to achieve a particularly high reactivity in terms of quick and complete dissolution. At the same time, losses e.g. to a gas cleaning plant (GCP) system usually going along with the use of small grain size are avoided. In addition, by injecting the powdered lime directly into the slag, a high reactivity in terms of quick and complete dissolution is achieved and at the same time, the losses to a GCP system associated with the use of small grain size lime are avoided. Also, due to its high reactivity, powdered lime can be dissolved well in a foamy slag also when the iron oxide content in the slag is low. Losses of powdered material to the GCP system can also be efficiently avoided by blowing of the powdered material into the slag via the side wall nozzles placed in close proximity to the slag underneath the trunnion ring. Yet a further advantage achieved by blowing the mixture of carrier gas and powdered material through the side wall nozzles 150 is that a high iron content in the slag, which conventionally may be required to dissolve e.g. lime, is no longer necessary which reduces refractory and increases iron yield. As a result of the achievable efficient use of the powdered materials, an efficient dephosphorization can be achieved leading to a high quality end product, e.g. a low P-content steel with a Phosphorous (P) content as low as 50 ppm. The inventive method thus may allow also for refining of lower-priced raw materials with high phosphorus content. When the at least one side wall nozzle is provided below the trunnion ring (pivoting axis), so that the at least one side wall nozzle is situated in short distance to the slag yet a further advantage arises. The powder can then easily reach the reaction zone with minimal gas pressure (and thus minimal total gas amount). In the case when Ar-gas is used, this would lead to costs reduction and in the case of nitrogen, to less N-pickup of the bath.

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