Method for controlling the stirring of molten metal in a steelmaking furnace and associated steel production installation

Abstract

The method for controlling the stirring within a vessel (22) of a steelmaking furnace (20), comprising a metal bath (1) comprising molten metal (3) and a layer of slag (5), the method (100) comprising: - measuring at least two parameters representative of the metal bath (1) contained within the vessel (22) during stirring; - detecting, based on the measurement of the at least two parameters, the formation of an open-eye (8) in the slag layer (5); - adapting the stirring based on the detection of the formation of an open-eye (8); wherein the at least two parameters comprise a visual parameter measured on images of the slag layer (5) captured during stirring and a mechanical parameter representative of mechanical waves generated within the vessel (22) during stirring.

Description

[0001] Method for controlling the stirring of molten metal in a steelmaking furnace and associated steel production installation

[0002] The present invention concerns a method for controlling the stirring of molten metal within a vessel of a steelmaking furnace.

[0003] Steel can be currently produced through two main manufacturing routes. Nowadays, most used production route named “BF-BOF route” consists in producing hot metal in a blast furnace (BF), by use of a reducing agent, mainly coke, to reduce iron oxides and then transform hot metal into steel into a converter process or Basic Oxygen Furnace (BOF). This route, both in the production of coke from coal in a coking plant and in the production of the hot metal, releases significant quantities of CO2.

[0004] The second main route involves so-called “direct reduction methods”. Among them are methods according to the brands MIDREX®, FINMET®, ENERGIRON® / HYL, COREX®, FINEX® etc., in which sponge iron is produced in the form of HDRI (Hot Direct Reduced Iron), CDRI (Cold Direct Reduced Iron), or HBI (Hot Briquetted Iron) from the direct reduction of iron oxide carriers. Sponge iron in the form of HDRI, CDRI, and HBI undergoes further processing in EAFs to produce steel.

[0005] One of the main options chosen by steelmakers to reduce CO2 emissions is therefore to switch from the BF-BOF route towards the DRI-EAF route. However, use of DRI products in classical electrical furnaces together with ferrous scraps has some limitations. Indeed, scraps contain a lot of impurities and resulting liquid steel will need to be further processed to produce high quality steel grades. Moreover, electric arc furnaces were up to now used for production of specific grades, mostly for long products applications, which do not have the same constraints in terms of metallurgy that the grades used notably for automotive products.

[0006] After being processed in an EAF, the molten metal is put into a ladle furnace or a stirring furnace. There, a floating slag layer covers the surface of the molten metal. Said slag accounts for a barrier between the molten metal and the ambient air.

[0007] Within such a furnace, the molten metal undergoes stirring. Said stirring enables homogenization of the molten metal and / or cleaning the molten metal by reducing the content of undesired chemicals such as phosphorus, carbon and / or sulfur. The stirring makes it possible to transfer the phosphorus, carbon and / or sulfur in the slag layer. However, too strong stirring can lead to the formation of an open-eye in the slag, that is an open area through the slag layer in which the molten metal can be in direct contact with the ambient air. This can favor nitrogen pick-up or oxidization of the molten metal, which can lead to a final nitrogen or oxygen content incompatible with requirement on the final product. For example, liquid steel produced from a basic oxygen furnace contains 20-to-90 parts per million (ppm) by weight of nitrogen, compared to 100-to-140 ppm by weight of nitrogen in liquid steel produced in an electric arc furnace. The nitrogen content of current electric arc furnace (EAF) steel is thus much higher than that of basic oxygen furnace (BOF) steel and cannot meet the requirements of high-grade steel. High nitrogen content can result in inconsistent mechanical properties in hot rolled steels, embrittlement of the heat affected zone (HAZ) of welded steels, and poor cold formability.

[0008] Nowadays, the regulation of the stirring power is made by human operators based on visual observations. However, such a regulation is not satisfactory. It requires constant attention from the operator and is subject to human misinterpretation.

[0009] One of the aims of the invention is to solve this problem by proposing a method for controlling the stirring of molten metal, which enables an optimal stirring while ensuring a low nitrogen pick-up and oxidization from the molten metal during stirring.

[0010] To this end, the invention relates to a method for controlling the stirring of molten metal within a vessel of a steelmaking furnace, the vessel comprising a metal bath comprising the molten metal and a layer of slag covering at least partially the molten metal, the method comprising the following steps:

[0011] - measuring at least two parameters representative of the metal bath contained within the vessel during stirring;

[0012] - detecting, based on the measurement of the at least two parameters, the formation of an open-eye in the slag layer;

[0013] - adapting the stirring based on the detection of the formation of an open-eye; wherein the at least two parameters comprise at least one visual parameter measured on images of the slag layer captured during stirring and at least one mechanical parameter representative of mechanical waves generated within the vessel during stirring.

[0014] Thanks to these features, the formation of an open-eye can be efficiently detected based on a visual parameter measured on images of the slag layer and on a mechanical parameter representative of mechanical waves generated within the vessel during stirring. The visual parameter enables visually detecting the formation of the open-eye. Some mechanical waves generated within the vessel are representative of the stirring. Monitoring said mechanical waves makes it possible to determine if the stirring leads to the formation of an open eye.

[0015] The method can further comprise the following features, considered alone or according to any technically feasible combination:

[0016] - the stirring of molten metal is carried out during a time period, the method being carried out at several controlling instants within the time period; - at each controlling instant, during the adapting step, a power of stirring is increased or kept constant if no open-eye formation is detected, the power of stirring being decreased if an open-eye formation is detected;

[0017] - the images of the slag layer are captured by a thermal camera, the at least one visual parameter comprising an emissivity of the slag layer;

[0018] - the mechanical waves are vibrations propagating in walls of the vessel, said vibrations depending on the stirring;

[0019] - the detecting step is further based on the value of at least one additional parameter representative of the metal bath, the at least one additional parameter comprising at least one of the following:

[0020] - at least a stirring parameter representative of the stirring power;

[0021] - at least a chemical parameter representative of the nature of the components of the slag layer;

[0022] - at least a geometric parameter representative of the width of the slag layer;

[0023] - at least a thermal parameter representative of the temperature of the metal bath;

[0024] - the method further comprises a step of measuring the at least one additional parameter to obtain the value of the at least one additional parameter;

[0025] - the detecting step is based on a machine learning model which takes into account:

[0026] - a plurality of previous values of the at least two parameters and / or the at least one additional parameter at previous instants during previous stirring of the molten metal contained within the vessel and / or during previous stirring of molten metal contained within another vessel;

[0027] - the detection of the formation of an open-eye in the corresponding slag layer as a function of the plurality of previous values;

[0028] - the stirring is carried out by blowing a stirring gas, for example argon, within the molten metal; and

[0029] - the stirring is carried out to desulfurize the molten metal.

[0030] The invention further relates to a steel production installation comprising at least:

[0031] - a steelmaking furnace comprising a vessel intended to contain a metal bath comprising molten metal and a layer of slag covering at least partially the molten metal; and

[0032] - a stirring device comprising:

[0033] - a stirring tool configured for stirring the molten metal within the vessel;

[0034] - at least two sensors configured for generating data representative of at least two parameters representative of the metal bath during stirring;

[0035] - a control module configured for:

[0036] - receiving the data representative of the at least two parameters; - detecting, based on the data representative of the at least two parameters, the formation of an open-eye in the slag layer; and

[0037] - adapting a stirring power of the stirring tool based on the detection of the formation of an open-eye, wherein the at least two sensors comprise at least one camera configured for capturing images of the slag layer and at least one accelerometer configured for measuring mechanical waves generated within the vessel during stirring.

[0038] The steel production installation can further comprise the following features, considered alone or according to any technically feasible combination:

[0039] - the stirring tool is configured for stirring the molten metal during a time period, the control module being configured for receiving the data representative of the at least two parameters, detecting the formation of an open-eye in the slag layer and adapting the stirring power of the stirring tool at several controlling instants within the time period;

[0040] - at each controlling instant, the control module is configured for :

[0041] - increasing or keeping constant the stirring power if no open-eye formation is detected; and

[0042] - decreasing the stirring power if an open-eye formation is detected;

[0043] - the at least one camera is a thermal camera configured for measuring an emissivity of the slag layer; and

[0044] - the at least one accelerometer is configured for measuring vibrations propagating in walls of the vessel, said vibrations depending on the stirring.

[0045] Other aspects and advantages of the invention will appear upon reading the following description given by way of example and made in reference to the appended drawings, wherein:

[0046] - Fig. 1 is a diagrammatical representation of a part of a steel production installation in cross-section according to an embodiment of the invention; and

[0047] - Fig. 2 is a schematic illustration of a method for controlling the stirring of molten metal within a vessel of a steelmaking furnace, according to an embodiment of the invention.

[0048] In reference to Fig. 1 , there is described a steel production installation 10 according to the invention.

[0049] The steel production installation 10 comprises at least a steelmaking furnace 20 and a stirring device 40.

[0050] The steelmaking furnace 20 is designed to receive a metal bath 1 comprising molten metal 3 and a layer of slag 5. Said metal bath 1 is for instance obtained in another steelmaking furnace (not shown) such as a Basic Oxygen Furnace (BOF) or an Electric Arc Furnace (EAF). The metal bath 1 is obtained from metallic material. Preferably, the steel production installation 10 comprises an EAF (not shown) in which the metal bath 1 is obtained.

[0051] For instance, the steelmaking furnace 20 is a ladle furnace or a stirring furnace.

[0052] The steelmaking furnace 20 comprises a vessel 22 delimiting an inner volume 24 wherein the metal bath 1 is contained. As shown on the example of Fig. 1 , the vessel 22 comprises a bottom wall 26 and lateral walls 27. For instance, the vessel 22 further comprises a removable roof (not shown) designed to cooperate with the lateral walls 27 and the bottom wall 26 to delimit the inner volume 24.

[0053] The slag layer 5 covers at least partially the molten metal 3.

[0054] For example, the metallic material comprises steel scrap. Said steel scrap can be melted together with pig iron and / or direct reduced iron (DRI). For instance, the steel scrap that can be used is referred to, in the EU-21 Steel Scrap specification, as old scraps (E1 or E3), new scraps (E8), shredded scraps (E40) or fragmentized scraps (E46). In a preferred embodiment, the material melted into the EAF comprises at least 40% in weight of DRI, preferably from 40% to 60% in weight of DRI.

[0055] The percentage of DRI and / or of pig iron in the charge is highly dependent on the quality of the steel scrap which can be used and of the steel grade to be produced. If the level of impurities, such as copper, chromium, molybdenum, nickel, tin, antimony, zinc and / or arsenic is low then the quantity of scrap to be charged may be increased and thus the quantity of DRI decreased.

[0056] The stirring device 40 comprises a stirring tool 42, at least two sensors 50 and a control module 70. Advantageously, the stirring device 40 further comprises at least one additional sensor 60.

[0057] The stirring tool 42 is configured for stirring the molten metal 3 within the vessel 22. In particular, the stirring tool 42 is configured for stirring the molten metal 3 during a time period.

[0058] For instance, the stirring tool 42 comprises a gas blower 44 configured for blowing a stirring gas 46 within the molten metal 3. As shown on the example of Fig. 1 , the gas blower 44 is arranged onto the bottom wall 26 of the vessel 22, in a bottom portion 25 of the inner volume 24, opposite the slag layer 5. For instance, the stirring gas is argon.

[0059] The at least two sensors 50 are configured for generating data representative of at least two parameters representative of the metal bath 1 during stirring.

[0060] The at least two sensors 50 comprise at least one camera 52 configured for capturing images of the slag layer 5 and at least one accelerometer 54 configured for measuring mechanical waves generated within the vessel 22 during stirring. Said accelerometer 54 may be located directly on the vessel 22 or on a structure supporting the vessel 22. For instance, the at least one camera 52 is a thermal camera configured for measuring an emissivity of the slag layer 5.

[0061] For instance, the at least one accelerometer 54 is configured for measuring vibrations propagating in the walls 26, 27.

[0062] The at least one additional sensor 60 is configured for generating data representative of at least one additional parameter representative of the metal bath 1 .

[0063] For instance, said at least one additional parameter comprises at least one among the following:

[0064] - at least a stirring parameter representative of the stirring power used to stir the molten metal 3 such as the stirring gas flow rate and / or the stirring gas back-pressure;

[0065] - at least a chemical parameter representative of the nature of the components of the slag layer 5 contained within the vessel 22 such as the oxygen activity of the slag and / or the oxide contents of the slag;

[0066] - at least a geometric parameter representative of the width W of the slag layer 5;

[0067] - at least a thermal parameter representative of the temperature of the metal bath 1 ;

[0068] Advantageously, as shown on the example of Fig. 1 , the at least one additional sensor 60 comprises at least one among the following:

[0069] - at least a sensor 60A for generating data representative of the at least one stirring parameter;

[0070] - at least a sensor 60B for generating data representative of the at least one chemical parameter, for example an analyzer and / or a device configured for determining the at least one chemical parameter by online LIBS (Laser Induced Breakdown Spectroscopy) measurement, spectroscopy or by electrochemical measurements;

[0071] - at least a sensor 60C for generating data representative of the geometric parameter;

[0072] - at least a sensor 60D for generating data representative of the thermal parameter, such as a thermal camera or a pyrometer.

[0073] The control module 70 is configured for:

[0074] - receiving the data representative of the at least two parameters;

[0075] - detecting, based on the data representative of the at least two parameters, the formation of an open-eye 8 in the slag layer 5; and

[0076] - adapting a stirring power of the stirring tool 42 based on the detection of the formation of an open-eye 8.

[0077] By open-eye 8, it is meant an open area through the slag layer 5 in which the molten metal can be in direct contact with the ambient air.

[0078] Advantageously, the control module 70 is further configured for receiving the data representative of the at least one additional parameter. For instance, the control module 70 is configured for detecting the formation of an open-eye 8 based on the data representative of the at least two parameters and / or on the data representative of the at least one additional parameter.

[0079] In particular, the control module 70 is configured for receiving the data representative of the at least two parameters, detecting the formation of an open-eye 8 in the slag layer 5 and adapting the stirring power of the stirring tool 42 at several controlling instants within the time period.

[0080] Advantageously, at each controlling instant, the control module 70 is configured for increasing or keeping constant the stirring power if no open-eye formation is detected and decreasing the stirring power if an open-eye formation is detected.

[0081] For instance, the control module 70 is configured for detecting the formation of an open-eye 8 based on a machine learning model which takes into account at least:

[0082] - a plurality of previous values of the at least two parameters and / or the at least one additional parameter at previous instants during previous stirring of the molten metal 3 contained within the vessel 22 and / or during previous stirring of molten metal contained within another vessel;

[0083] - the detection of the formation of an open-eye 8 in the corresponding slag layer 5 as a function of the plurality of previous values.

[0084] In the example shown in figure 1 , the control module 70 is made in the form of software, or a software brick, executable by a processor of an electronic device (not shown). The memory of the electronic device is then able to store the control software. The processor is then able to execute the software.

[0085] In a variant not shown, the control module is produced in the form of a programmable logic component, such as an FPGA (Field Programmable Gate Array), or an integrated circuit, such as an ASIC (Application Specific Integrated Circuit).

[0086] When the electronic device is implemented in the form of one or more software programs, i.e. in the form of a computer program, also referred to as a computer program product, it is also capable of being recorded on a computer-readable medium, not shown. The computer-readable medium is, for example, a medium capable of storing electronic instructions and of being coupled to a bus of a computer system. By way of example, the readable medium is an optical disc, a magneto-optical disc, a ROM memory, a RAM memory, any type of non-volatile memory (for example FLASH or NVRAM) or a magnetic card. A computer program containing software instructions is stored on the readable medium.

[0087] In reference to Fig. 2, there is described a method 100 for controlling the stirring of molten metal 3 within a vessel 22 of a steelmaking furnace 20. Advantageously, the method 100 is carried out at each of several controlling instants of the time period during which the molten metal 3 is stirred.

[0088] For example, the stirring is carried out by blowing the stirring gas 46 within the molten metal 3. Advantageously, the stirring is carried out to desulfurize the molten metal 3.

[0089] The method 100 comprises a step 110 of measuring the at least two parameters representative of the metal bath 1 contained within the vessel 22 during stirring. The at least two parameters comprises at least one visual parameter measured on images of the slag layer 5 captured during stirring and at least one mechanical parameter representative of mechanical waves generated within the vessel 22 during stirring. For instance, the at least one visual parameter is measured by the camera 52 and the at least one mechanical parameter is measured by the accelerometer 54.

[0090] For instance, the at least one visual parameter comprises an emissivity of the slag layer 5.

[0091] For example, the mechanical waves are vibrations propagating in the walls 26, 27 of the vessel 22, said vibrations depending on the stirring.

[0092] Advantageously, the method 100 further comprises a step 120 of measuring the at least one additional parameter representative of the metal bath 1 .

[0093] For instance, the at least one stirring parameter is measured by the sensor 60A, the at least one chemical parameter is measured by the sensor 60B, the at least one geometric parameter is measured by the sensor 60C and the at least one thermal parameter is measured by the sensor 60D.

[0094] The method 100 further comprises a step 130 of detecting, based on the measurement of the at least two parameters, advantageously based on the measurement of the at least two parameters and / or the at least one additional parameter, the formation of an open-eye 8 in the slag layer 5.

[0095] For instance, a high emissivity in some areas of the slag layer 5 is representative of the formation of an open-eye 8 in said areas of the slag layer 5. For example, typical vibration patterns in the walls 26, 27 of the vessels 22 are representative of the formation of an open-eye 8 in said areas of the slag layer 5.

[0096] Advantageously, the detecting step 130 is based on the machine learning model described above.

[0097] For instance, the formation of an open-eye 8 is detected when actual values of parameters and / or additional parameters representative of the metal bath 1 are substantially equal to values of parameters and / or additional parameters which were associated with the formation of an open-eye 8. The method 100 further comprises a step 140 of adapting the stirring, in particular the stirring power, based on the detection of the formation of an open-eye 8.

[0098] For instance, at each controlling instant, the power of stirring is increased or kept constant if no open-eye formation is detected and the power of stirring is decreased if an open-eye formation is detected.

[0099] By decreasing the power of stirring in case of detection of an open-eye formation, the invention makes it possible to avoid the further formation / expansion of said open-eye or to lead to the closing of said open-eye (that is the formation of a new slag portion into the open-eye to plug said open-eye). This makes it possible to obtain an optimal covering of the metal bath by the slag layer and reduce the direct contact of the molten metal with the air.

[0100] Thanks to the above-described invention, the formation of open-eyes 8 can be efficiently detected. The stirring power can be adapted automatically without needing the intervention of a human operator. The stirring is made optimal while reducing the risk of undesired chemical compounds pick-up by the molten metal 3, such as nitrogen or oxygen.

Claims

CLAIMS1.- Method (100) for controlling the stirring of molten metal (3) within a vessel (22) of a steelmaking furnace (20), the vessel (22) comprising a metal bath (1 ) comprising the molten metal (3) and a layer of slag (5) covering at least partially the molten metal (3), the method (100) comprising the following steps:- measuring (110) at least two parameters representative of the metal bath (1 ) contained within the vessel (22) during stirring;- detecting (130), based on the measurement of the at least two parameters, the formation of an open-eye (8) in the slag layer (5);- adapting (140) the stirring based on the detection of the formation of an open-eye (8); wherein the at least two parameters comprise at least one visual parameter measured on images of the slag layer (5) captured during stirring and at least one mechanical parameter representative of mechanical waves generated within the vessel (22) during stirring.2.- Method (100) according to claim 1 , wherein the stirring of molten metal (3) is carried out during a time period, the method (100) being carried out at several controlling instants within the time period.3.- Method (100) according to claim 2, wherein at each controlling instant, during the adapting step (140), a power of stirring is increased or kept constant if no open-eye formation is detected, the power of stirring being decreased if an open-eye formation is detected.4.- Method (100) according to any one of the preceding claims, wherein the images of the slag layer (5) are captured by a thermal camera (52), the at least one visual parameter comprising an emissivity of the slag layer (5).5.- Method (100) according to any one of the preceding claims, wherein the mechanical waves are vibrations propagating in walls (26, 27) of the vessel, said vibrations depending on the stirring.6.- Method (100) according to any one of the preceding claims, wherein the detecting step (130) is further based on the value of at least one additional parameter representativeof the metal bath (1 ), the at least one additional parameter comprising at least one of the following:- at least a stirring parameter representative of the stirring power;- at least a chemical parameter representative of the nature of the components of the slag layer (5);- at least a geometric parameter representative of the width (W) of the slag layer (5);- at least a thermal parameter representative of the temperature of the metal bath (1 ).7.- Method (100) according to claim 6, comprising a step (120) of measuring the at least one additional parameter to obtain the value of the at least one additional parameter.8.- Method (100) according to claim 6 or 7, wherein the detecting step (130) is based on a machine learning model which takes into account:- a plurality of previous values of the at least two parameters and / or the at least one additional parameter at previous instants during previous stirring of the molten metal (3) contained within the vessel (22) and / or during previous stirring of molten metal contained within another vessel;- the detection of the formation of an open-eye (8) in the corresponding slag layer (5) as a function of the plurality of previous values.9.- Method (100) according to any one of the preceding claims, wherein the stirring is carried out by blowing a stirring gas (46), for example argon, within the molten metal (3).10.- Method (100) according to any one of the preceding claims, wherein the stirring is carried out to desulfurize the molten metal (3).11 .- Steel production installation (10) comprising at least:- a steelmaking furnace (20) comprising a vessel (22) intended to contain a metal bath (1 ) comprising molten metal (3) and a layer of slag (5) covering at least partially the molten metal (3); and- a stirring device (40) comprising:- a stirring tool (42) configured for stirring the molten metal (3) within the vessel;- at least two sensors (50) configured for generating data representative of at least two parameters representative of the metal bath (1 ) during stirring;- a control module (70) configured for:- receiving the data representative of the at least two parameters;- detecting, based on the data representative of the at least two parameters, the formation of an open-eye (8) in the slag layer (5); and- adapting a stirring power of the stirring tool (42) based on the detection of the formation of an open-eye (8), wherein the at least two sensors (50) comprise at least one camera (52) configured for capturing images of the slag layer (5) and at least one accelerometer (54) configured for measuring mechanical waves generated within the vessel (22) during stirring.12.- Steel production installation (10) according to claim 1 1 , wherein the stirring tool (42) is configured for stirring the molten metal (3) during a time period, the control module (70) being configured for receiving the data representative of the at least two parameters, detecting the formation of an open-eye (8) in the slag layer (5) and adapting the stirring power of the stirring tool (42) at several controlling instants within the time period.13.- Steel production installation (10) according to claim 12, wherein, at each controlling instant, the control module (70) is configured for :- increasing or keeping constant the stirring power if no open-eye formation is detected; and- decreasing the stirring power if an open-eye formation is detected.14.- Steel production installation (10) according to any one of claims 1 1 to 13, wherein the at least one camera (52) is a thermal camera configured for measuring an emissivity of the slag layer (5).15.- Steel production installation (10) according to any one of claims 1 1 to 14, wherein the at least one accelerometer (54) is configured for measuring vibrations propagating in walls (26, 27) of the vessel (22), said vibrations depending on the stirring.

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