Furnace assembly for a metal production process

Abstract

A furnace assembly (1; 1-1; 1-2; 1-3; 1-4) for a metal production process, comprising: an electric arc furnace (3) configured for flat bath operation and having a bottom (3a), and an electromagnetic stirrer (5) configured to be disposed below the bottom (3a) of the electric arc furnace (3) to activate stirring of the molten metal (M) in the electric arc furnace (3), wherein a metal charging region (11) is located off-center with respect to a central point of the bottom (3a) of the electric arc furnace (3), and wherein the electromagnetic stirrer (5) comprises coils configured to generate a progressive magnetic wave in a first direction along a stirring direction axis, wherein the electromagnetic stirrer (5) is configured to be arranged with respect to a central plane (7) extending through the center of the electric arc furnace (3) and through a draw-out bore (3b) or tuyere (3b) of the electric arc furnace (3), such that the stirring direction axis is at an angle (α) with respect to the central plane (7), wherein the stirring direction axis intersects the central plane.

Description

Furnace assembly for a metal production process TECHNICAL FIELD This description generally refers to metal production and, in particular, to a furnace assembly for a metal production process. BACKGROUND The flat bath operation (FBO) is a continuous feeding or small-batch charging process of metallic materials, such as scrap, pig iron, direct reduced iron (DRI), hot metal, or hot briquetted iron (HBI), into the furnace bath of an electric arc furnace (EAF) without opening the furnace roof. During metal charging, the electric arc is continuously fed with current, and the metallic materials are continuously melted in the bath. This process provides high energy efficiency and reduces electrode consumption. A problem with flat bath melting processes is homogenizing the furnace bath temperature, especially in the metal charging area, which is always a cold zone. Incomplete metal melting in the cold zone creates potential problems such as concentration gradients, unreliable measurements, unsafe process control, overheated bath, and excessive drawdown temperature. To address this issue of uneven temperature, stirring the bath to improve convection is recommended. For this purpose, gas agitation at the bottom of porous plugs has been implemented in some of these furnaces. For bottom gas agitation, porous plugs with direct or indirect gas purging are installed in the lower refractory lining. Typically, 3 to 5 porous plugs are required, depending on the furnace size. The agitation intensity is controlled by the gas, typically nitrogen or argon, and by the flow rate and pressure. Document EP2751510 is an example of a furnace assembly from the technical field. SUMMARY There are some challenges with bottom gas agitation. For example, incomplete bath mixing can occur, with dead zones far from the plugs, resulting in limited homogenization of the furnace bath. Furthermore, agitation patterns and direction are determined by the plug positions, which limit horizontal flow velocity. Additionally, refractory wear around the porous plug is more severe, and the plugs at the bottom are risk points for casting breakage. Finally, the porous plug's lifespan is often shorter than that of the bottom lining campaign, and online maintenance of porous plugs is a difficult and complex task. In light of the above, one object of the present description is to provide a furnace assembly for a metal production process that solves, or at least mitigates, the problems of the prior art. Therefore, a furnace assembly for a metal production process is provided, according to claim 1. Other embodiments of said furnace assembly are described in dependent claims 2-11. One effect that can be achieved in this way is that agitation can be provided throughout the entire casting bath, with virtually no dead zone. Therefore, more efficient metal production can be achieved using an electric arc furnace configured for flat bath operation. Furthermore, there is no negative effect on the refractory lining and no risk of molten metal breakage, as is the case with porous plugs. Additionally, the long lifespan of the electromagnetic stirrer coil requires virtually no maintenance. Electromagnetic stirring reduces overheating of the casting surface, and the heat from the arc zone is rapidly transferred to the casting volume. The reduction in the temperature of the overheated surface minimizes heat losses in the furnace wall and roof during power-on, thereby reducing electricity consumption. Another advantage of reduced overheating during power-on is less wear on the refractory lining in the slag line area of ​​the electric arc furnace. Another effect of the electromagnetic stirrer on the electric arc furnace with a flat bath operation process is a significant improvement in process reliability. Rapid melting, for example of scrap metal and ferrochrome, provides rapid homogenization of the molten bath in terms of both chemical composition and temperature. The homogeneous temperature throughout the bath allows for faster extraction and reduces extraction delays. Eliminating thermal stratification in the molten bath also reduces the extraction temperature. The high eccentric lower free-drain opening frequency is a significant benefit for operational safety and productivity. According to the invention, the electric arc furnace has a metal charging region, where the electromagnetic stirrer is configured to be arranged to provide stirring of molten metal in the metal charging region. The metal charging region is a region inside the electric arc furnace that receives the charged metal. It includes a portion of the bottom of the electric arc furnace, where the metal initially accumulates before being melted by the heat and mixed with the rest of the molten metal by the electromagnetic stirrer. According to the invention, the metal charging region is located off-center with respect to a central point at the bottom of the electric arc. According to the invention, the electromagnetic stirrer comprises coils configured to generate a progressive magnetic valve in a first direction along a stirring direction axis, wherein the electromagnetic stirrer is configured to be arranged relative to a central plane extending through the center of the electric arc furnace and through a flue or extraction nozzle of the electric arc furnace, such that the stirring direction axis is at an angle relative to the central plane. The first direction, which defines the axis of the stirring direction along a molten metal stirring direction in the electric arc furnace, intersects the central plane. This plane is a central plane when the arc furnace is in operation, that is, when it is in a draw-to-draw melting cycle. In this way, the stirring force will be directed straight towards the metal-charging region, thus achieving more efficient stirring in the consistently cool metal-charging area. "Cool" here refers to the temperature relative to the rest of the casting. According to an aspect that is not part of the claimed invention, the angle is in the range of 0° and 90°. According to one realization, the angle is 90°. According to one embodiment, the angle is greater than 0° and less than 90°. The stirring force created by the electromagnetic stirrer will be directed toward the cold scrap zone of the metal charging region at a selectable angle in the range of 0 to 90 degrees. This electromagnetic stirrer configuration will create a flow of molten metal from the cold metal charging region in the furnace, which greatly improves molten metal homogenization and furnace temperature. According to one embodiment, the electromagnetic stirrer is arranged centered below the electric arc furnace. According to one embodiment, the electromagnetic aggregator is arranged off-center below the electric arc furnace. One embodiment comprises an electromagnetic stirrer position controller configured to control the orientation of the electromagnetic stirrer relative to the electric arc furnace, thereby adjusting the angle. More flexible control of the stirring direction can be provided. For example, the electromagnetic stirrer can be oriented at a certain angle relative to the sufficiently flat central stirring of the melt, i.e., also in the metal-loading region, while the stirring can reduce turbulence formation above the draw hole, as described in EP2751510. One embodiment comprises a frequency converter configured to control the current in the electromagnetic stirrer and a system control configured to control the frequency converter. According to one embodiment, the electric arc furnace is configured to receive metallic material charge from one side of the electric arc furnace. According to one embodiment, the electric arc furnace is configured to receive metallic material loading from above the electric arc furnace. According to one embodiment, the electric arc furnace is configured to receive a continuous load of metallic material. The electric arc furnace can be configured, for example, to receive a continuous charge of metallic material via a conveyor belt or slide. Alternatively, or additionally, the electric arc furnace can be configured to receive a continuous charge of metallic material from a hole in the furnace roof. In this case, the furnace roof can be provided with a through-hole or opening to allow the top feeding of the metallic material into the electric arc furnace. According to one embodiment, the electric arc furnace is configured to receive tray charge of the metallic material through a channel. Generally, all terms used in the claims should be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to an element, apparatus, component, means, etc., should be interpreted broadly as referring to at least one instance of the element, apparatus, component, means, etc., unless explicitly stated otherwise. BRIEF DESCRIPTION OF THE DRAWINGS The specific embodiments of the inventive concept will now be described by way of example, with reference to the accompanying drawings, in which: Figure 1 schematically shows a partially transparent top view of an electric arc furnace and an electromagnetic stirrer provided below the electric arc furnace; and Figures 2a-5b schematically show several examples of furnace assemblies in a partially transparent top view and in cross-section. DETAILED DESCRIPTION The inventive concept will now be described more fully below with reference to the accompanying drawings, which show exemplary embodiments. However, the inventive concept can be embodied in many different forms and should not be interpreted as limited to the embodiments shown here; rather, these embodiments are provided by way of example so that this description will be thorough and complete and will convey the scope of the inventive concept to those skilled in the art. The same numbers refer to the same elements throughout the description. This description refers to a furnace assembly for a metal production process. The metal production process could be, for example, a steel production process, an aluminum production process, or a lead production process. The furnace assembly comprises an electric arc furnace and an electromagnetic stirrer configured to be positioned beneath the electric arc furnace to enable the stirring of molten metal within the furnace. The electromagnetic stirrer may be configured, for example, to be mounted on oscillators of the electric arc furnace and rotated in conjunction with a tilting system of the electric arc furnace, or it may be configured, for example, to be mounted beneath the electric arc furnace on a separate support structure, such as a trolley, which is configured to be stationary or to rotate synchronously with the bottom of the electric arc furnace following a draw operation. The electric arc furnace presented here is configured for flat bath operation. Here, the electric arc furnace is configured to receive metal continuously during a draw-to-draw cycle. To this end, the electric arc furnace is configured to be continuously charged with metal during a draw-to-draw cycle. The charging assembly and the electric arc furnace can be configured, for example, for a Consteel®, Quantum®, or EcoArc® process / assembly, or for continuous DRI feeding from the roof of the electric arc furnace. Therefore, the electric arc furnace can be configured, for example, to be charged with metal from the side of the furnace, in which case the electric arc furnace is configured as a shaft furnace. Alternatively, the electric arc furnace can be configured to be charged with metal from the roof.The metallic material can be either pre-heated, hot, or cold. Figure 1 schematically shows a partially transparent top view of an example of a furnace assembly 1 for metal production. The furnace assembly 1 comprises an electric arc furnace 3 having a furnace body or shell configured to receive and retain metallic material during a draw-to-draw cycle. The furnace body or casing is further configured to receive a plurality of electrodes arranged to be lowered into the furnace body or casing to melt any metallic material contained therein. The electric arc furnace 3 comprises a bottom 3a having a drawhole 3b or, alternatively or additionally, a nozzle 3c, in order to permit the extraction of heat from the metal from the furnace body or casing. In the case of a variation that includes a drawhole 3b, the drawhole 3b is arranged offset, or off-center, with respect to the center point of the bottom 3a of the furnace casing. The furnace assembly 1 further comprises an electromagnetic stirrer 5. The bottom 3a of the electric arc furnace 3 comprises a non-magnetic window, below which the electromagnetic stirrer 5 is configured for installation. The non-magnetic window may comprise, for example, austenitic stainless steel or any other type of non-magnetic metallic material. The electromagnetic stirrer 5 comprises a magnetic core and coils arranged around the magnetic core, not shown. The coils can be configured to be connected to a respective electrical phase of an AC power supply, so that the electromagnetic stirrer 5 can be powered by a low-frequency, multi-phase AC current. Therefore, the coils are configured such that when properly supplied with a respective AC current, a progressive magnetic field is generated along an axis of the stirring direction 9. In operation, the low-frequency AC current flowing through the coils generates a progressive magnetic field, which penetrates the bottom of the electric arc and thus generates forces in the molten metal or casting. Since the magnetic field penetrates the entire depth of the casting, the casting will flow in the same direction, along the stirring direction axis 9, through the entire diameter / width of the electric arc furnace and downward through the entire depth of the bath. After reaching the wall of the electric arc furnace, the casting will flow backward along the sides of the furnace. Furthermore, Figure 1 shows a central plane 7, which extends through the center point of the bottom 3a and through the center of the extraction hole 3b, or in the case of the presence of a nozzle 3c, through the center of the nozzle 3c. This plane is typically a vertical plane when the furnace assembly 1 has been installed in a metal workshop or metal mill, for example, a steel rolling mill or an aluminum rolling mill. The electromagnetic stirrer 5 is configured so that there is an angle α between the central plane 7 and the stirring direction axis 9 that intersects the central plane 7. In the example shown in Figure 1, the angle α is 90°. According to one variation, the angle α between the central plane 7 and the stirring direction axis 9 can range from 0° to 90°. For example, angle α can be 0°, or it can be greater than 0° but less than 90°. In the latter case, the electromagnetic stirrer 5 would be inclined or positioned obliquely with respect to the central plane 7. The electromagnetic stirrer 5 can be positioned centered beneath the electric arc furnace with respect to the center of the electric arc furnace, or it can be positioned off-center. The orientation of the electromagnetic stirrer relative to the central plane 7 can be adjusted either manually or automatically. For example, the furnace assembly may include an electromagnetic stirrer position controller to adjust the orientation of the electromagnetic stirrer 5 relative to the electric arc furnace 3, and specifically relative to the central plane 7, thereby adjusting angle α. Angle α can be adjusted or controlled, for example, based on the instantaneous amount of overall stirring required for the melt or based on the need to reduce turbulence above the draft hole 3a, if the electric arc furnace 3 has a draft hole. The orientation of the electromagnetic stirrer 5 can be a compromise between optimal overall stirring and turbulence reduction. The electric arc furnace 3 also has a metal charging region 11, which is a region of the bottom 3a of the furnace body or shell, where the metallic material continuously charged in the furnace shell initially accumulates in the electric arc furnace 3. The metal charging region 11 may be arranged off-center with respect to the center of the bottom 3a, as shown in the example in Figure 1. Alternatively, the metal charging region 11 may be arranged at the center or essentially at the center of the bottom 3a. If the electric arc furnace is configured to be charged with metallic material through the through-hole or drill in the furnace roof, the metal charging region 11 will not typically be at the bottom of the furnace shell, but rather on the surface or meniscus of the casting. In this case, the metal charging region may be centered or off-center within a horizontal section of the electric arc furnace. The electromagnetic stirrer 5 is arranged so that the stirring force it creates is directed towards the cold zone formed by the metal charging region 11, or at an angle of up to 90° depending on the stirrer's orientation relative to the central plane 7. This allows for the creation of a flow of molten metal to or from the metal charging region 11 in the electric arc furnace 3, which greatly improves molten metal homogenization and temperature compared to the use of, or without, porous plugs in combination with gas. As mentioned above, the electromagnetic stirrer 5 can be arranged centrally below the electric arc furnace or outside of it.In the latter case, the electromagnetic stirrer can be arranged, for example, below the metal loading area 11, with the angle α anywhere from 0° to 90° with respect to the central plane 7. The furnace assembly may include a power converter, typically a frequency converter (not shown), configured to control the current in the coils of the electromagnetic stirrer, thereby controlling the stirring of the molten metal or casting contained in the furnace shell. In this case, the furnace assembly may also include a control system configured to control the frequency converter, thereby controlling the current in the electromagnetic stirrer. Several examples of an oven assembly will now be shown with reference to Figures 2a-5b. Figure 2a shows a partially transparent bottom view of an example of a furnace assembly 1 with flat bath operation. The exemplified furnace assembly 1-1 is continuously fed with metallic material from the side of the furnace shell by means of a conveyor belt 4. The electromagnetic stirrer 5 is arranged below the bottom of the electric arc furnace 3. The electromagnetic stirrer 5, shown with solid lines, is illustrated with an angle α that is 90° with respect to the central plane 7 shown in Figure 1. The electromagnetic stirrer 5 is also shown with another orientation, with dashed lines, where the angle α is 0° with respect to the central plane 7. The electromagnetic stirrer 5 can be configured to be oriented with any angle α between 0° and 90° or with essentially any angle α between 0° and 90°.For example, if the electromagnetic stirrer is motor-driven, not all angles are achievable, and the actual orientation may depend on the resolution provided by the electromagnetic stirrer position controller. Figure 2b shows a cross-sectional view of assembly 1-1, with the cross-section taken along lines AA in Figure 2a. Also shown here are the electrodes 13 immersed in the molten metal M and the metal charging region 11. According to this example, the metallic material can be continuously charged into the furnace shell or body by means of a conveyor belt 4 moving from the side towards the electric arc furnace 3. Figure 3a shows a partially transparent top view of another example of a furnace assembly 1 with flat bath operation. The exemplified furnace assembly 1-2 is fed with metallic material from the top to, for example, an off-center location in the electric arc furnace 3, via a vessel 15 arranged above the electric arc furnace 3. The electromagnetic stirrer 5 can again be oriented within 0° and 90° with respect to the central plane 7 shown in Figure 1. Figure 3b shows the furnace assembly 1-2 through the cross-section taken along lines BB. Figure 4a shows a partially transparent top view of another example of a furnace assembly 1 with flat bath operation. The furnace assembly 1-3 shown is continuously fed with metal from one side via a conveyor belt 4, and is also charged from the top via a trough 15 positioned above the electric arc furnace 3. The feed can be provided alternatively by means of the conveyor belt and the trough, or simultaneously. In this example, the electric arc furnace has a nozzle for removing the molten metal, but it could alternatively be provided with a withdrawal hole. The electromagnetic stirrer 5 can also be configured in this case to be oriented within 0° and 90° with respect to the central plane 7 shown in Figure 1. Figure 4b shows the furnace assembly 1-3 through the cross section taken on lines CC. Figure 5a shows a partially transparent top view of another example of a furnace assembly 1 with flat bath operation. The furnace assembly 1-4 exemplified is continuously fed with metallic material from above the metal arc furnace 3 by means of a conveyor belt or slide. The roof of the electric arc furnace 3 is provided with a through-hole 16, i.e., a feed hole, for example, the "5th hole," for feeding metallic material into the electric arc furnace 3 by means of a conveyor belt or slide. The metallic material may comprise or be, for example, directly reduced iron. The electromagnetic stirrer 5, as described above, may be able to be oriented within 0° and 90° with respect to the central plane 7 shown in Figure 1. Figure 5b shows the furnace assembly 1-3 through the cross section taken on lines DD. The metallic material used for continuous feeding can be, for example, scrap metal, iron alloys, direct reduced iron, hot briquetted iron, pig iron, hot metal, or a mixture of materials and metallic oxides. The inventive concept has been described primarily above with reference to some examples. However, as will be readily apparent to a person skilled in the art, other embodiments than those described above are equally possible within the scope of the inventive concept, as defined by the appended claims.

Claims

1. A furnace assembly (1; 1-1; 1-2; 1-3; 1-4) for a metal production process, comprising: an electric arc furnace (3) configured for flat bath operation and having a bottom (3a), and an electromagnetic stirrer (5) configured to be disposed below the bottom (3a) of the electric arc furnace (3) to activate the stirring of the molten metal (M) in the electric arc furnace (3), wherein a metal charging region (11) is located off-center with respect to a central point of the bottom (3a) of the electric arc furnace (3), and wherein the electromagnetic stirrer (5) comprises coils configured to generate a progressive magnetic wave in a first direction along an axis of stirring direction,wherein the electromagnetic stirrer (5) is configured to be arranged with respect to a central plane (7) extending through the center of the electric arc furnace (3) and through a draw-out bore (3b) or nozzle (3b) of the electric arc furnace (3), such that the stirring direction axis is at an angle (a) with respect to the central plane (7), wherein the stirring direction axis intersects the central plane.

2. The furnace assembly (1; 1-1; 1-2; 1-3; 1-4) according to claim 1, wherein the angle (a) is 90°.

3. The furnace assembly (1; 1-1; 1-2; 1-3; 1-4) according to claim 1, wherein the angle (a) is greater than 0° and less than 90°.

4. The furnace assembly (1) according to any of the preceding claims, wherein the electromagnetic stirrer (5) is arranged centrally below the electric arc furnace (3).

5. The furnace assembly (1) according to any of the preceding claims,wherein the electromagnetic stirrer (5) is arranged off-center below the electric arc furnace.

6. The furnace assembly (1; 1-1; 1-2; 1-3; 1-4) according to any of the preceding claims, comprising an electromagnetic stirrer position controller configured to control the orientation of the electromagnetic stirrer (5) relative to the electric arc furnace (3) to thereby adjust the angle (a).

7. The furnace assembly (1; 1-1; 1-2; 1-3; 1-4) according to any of the preceding claims, comprising a frequency converter configured to control the current in the electromagnetic stirrer (5), and a control system configured to control the frequency converter.

8. The furnace assembly (1; 1-1; 1-3) according to any of the preceding claims,wherein the electric arc furnace is configured to receive a charge of metallic material from one side of the electric arc furnace.

9. The furnace assembly (1; 1-2; 1-3; 1-4) according to any of the preceding claims, wherein the electric arc furnace is configured to receive a charge of metallic material from above the electric arc furnace.

10. The furnace assembly (1; 1-1; 1-3; 1-4) according to claims 8 or 9, wherein the electric arc furnace is configured to receive a continuous charge of metallic material.

11. The furnace assembly (1; 1-2; 1-3) according to claims 8 or 9, wherein the electric arc furnace is configured to receive a ladle charge of metallic material through a channel.

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