Patent Application
20250043370
The disclosure relates to a smelting unit for steel production with a tap weight of between 60 t and 350 t and a method for operating the same.
Steel is usually produced from input materials such as pig iron by removing the excess carbon, adding alloying materials and refining the molten metal (metallurgical work). For this purpose, the liquid pig iron is filled into a converter and then oxygen is blown onto or into the melt by means of a top lance and/or bottom or side-wall nozzles (refining of the melt). Alternatively, DRI iron can also be melted down in an electric arc furnace and such input materials can be used as pig iron melt. The melt is subsequently adjusted to the desired final alloy using alloying agents.
In order to reduce work steps, in particular refilling processes, and the associated material losses, the melting of DRI iron and refining is increasingly being carried out in a smelting unit. A smelting unit that can perform both melting and metallurgical work is known, for example, from publication EP 0 717 115 A1. In a double-receptacle electric arc furnace, electrical energy can be introduced into one of the receptacles by means of the graphite electrodes or switched to an operating state with chemical energy/refining by changing the cover. As a result, the smelting unit is able to produce a metallic melt from solid input materials, change the energy sources required for this and perform metallurgical work.
In the operating state, with which chemical energy is used and metallurgical work is performed, oxygen is blown onto the surface of the molten bath or the hot input materials by means of a blowing lance guided through the cover. The oxygen reacts with the liquid melt or the input materials and releases energy in the process. The oxygen is usually injected at a high pressure or volume flow, in order to achieve good mixing of the reactants.
A similar method is disclosed in the publication DE 101 15 779 A1. In addition to oxygen, an inert gas is injected to improve the mixing of the melt. As a result, the efficiency of the oxygen reaction is increased and the melt is heated more evenly. The oxygen input by means of the top lance is not only used to heat up the melt, but also for targeted decarburization of the melt after completion of the melting process. For this purpose, the amount of oxygen injected into the smelting unit is adapted as a function of the carbon content of the input materials.
The disadvantage of the aforementioned processes is that the high volume flows and the associated impulse of the gas jet during injection cause steel and/or slag to splash in the smelting unit (splashing). For example, the process gas injected through the side wall injector hits the surface of the molten bath at a certain angle and creates an elliptically shaped, oscillating impact cavity. The size and depth of the impact cavity depend on the distance between the side wall injector and the surface of the molten bath, the angle of inclination of the side wall injector and the process gas quantity or the process gas volume flow. At the edges of the impact cavity, individual melt areas or droplets are torn off by shear forces between the process gas jet and the melt, transported with high momentum into the furnace environment and deposited on the furnace walls, on the furnace cover and in the furnace elbow. In doing so, most of the metal droplets are torn off the edge of the impact cavity opposite the side wall injector.
As a result, deposits of slag and metal form inside the furnace and in the furnace elbow, which reduce the cross-section of the furnace elbow, impair the function of mechanical components and reduce the yield; this so-called slagging of the furnace during operation must be avoided.
The present application teaches a smelting unit and a method for operating the smelting unit, which produces a metallic melt from solid input materials by means of chemical and electrical energy and performs metallurgical work without splashing and slagging.
The smelting unit has a top lance for injecting a process gas and/or solid material, wherein the top lance can be brought into a working position through an opening in the first cover. During operation of the smelting unit, the top lance can be rotated around the axis of the top lance, on the one hand, and around a vertical axis, on the other hand. The top lance can also be pivoted around a horizontal axis. The operation of the smelting unit comprises both the treatment of a melt in the smelting unit and the sequence of a plurality of melts.
The vertical pivot axis is parallel to the axis of rotation of the top lance and makes it possible for the top lance to move on a circular arc segment around the vertical axis. The horizontal axis lies in a plane that is perpendicular to the axis of rotation of the top lance. Pivoting the top lance around such axis makes it possible to adjust different angles of the top lance with respect to the surface of the molten bath.
The distance between the surface of the molten bath and the top lance tip can be changed. A large number of side wall injectors are arranged radially circumferentially around the upper furnace for injecting a process gas and/or solid material, wherein the side wall injectors can be pivoted horizontally and/or vertically by up to ±5°.
Process gases are gases that undergo a reaction with the input materials, the melt and/or the furnace atmosphere. For example, process gases can be oxygen, nitrogen, CxHy (for example, methane, ethane, etc.), hydrogen or inert gases. Solids are alloying materials, slag formers and/or solid energy sources. For example, fine-grained coal, lime, chrome ore or similar can be used as solids.
The first working position of the top lance is defined by the fact that a gas jet emerging from the top lance at this position enters the furnace chamber and interacts with the furnace atmosphere or the melt. The movement and/or rotation around one or more axes of the top lance is carried out by means of one or more drives, which are preferably connected to the furnace control system. These can be electric, pneumatic or hydraulic drives.
The tip of the top lance is the region of the top lance that is closest to the surface of the molten bath. In doing so, it is not necessary for an outlet opening for the gas jet to be arranged at this point. Known designs for top lances typically have between 3 and 7 Laval nozzles, wherein the individual Laval nozzle itself is inclined between 7° and 25° with respect to the top lance axis. Multi-hole top lances are also known, for example, from publication DE 20 2007 009 161 U1.
Sidewall injectors make it possible for a gas jet and/or a solid to enter the furnace chamber. These can also be gas mixtures or solid/gas mixtures. The above definitions apply to the possible gases or solids. The pivot capability of up to ±5° of the side wall injectors is based on a central installation position of the respective individual injector. As a result, the alignment of the side wall injector and thus the impact cavity it creates in the surface of the molten bath can be adapted to a small extent to different operating conditions and filling levels in the smelting unit. One possible design of a side wall injector as a burner is disclosed in the publication DE 603 05 321 T2.
Such a smelting unit in conjunction with the method of operation minimizes the shear forces of the gas jets acting on the surface of the melt and thus reduces the number of steel and/or slag droplets formed inside the furnace, on the furnace cover and in the furnace elbow. The possibility of performing metallurgical work or introducing chemical energy into the smelting unit by means of the gases and/or solids is retained.
A gas jet directed at an angle from above onto the edge area of the impact cavity induced by the side wall injector reduces the oscillation width of the impact cavity of the side wall injector and disrupts or prevents and ultimately reduces the tearing off of the metal droplets at the edge of the impact cavity of the side wall injector.
The top lance is preferably designed as a multi-hole top lance and has more than 2 outlet openings, preferably more than 5 outlet openings, for a process gas and/or a solid. An increased number of outlet openings on the top lance makes it possible to influence a larger region of the surface of the molten bath. The number, size and shape of the outlet openings and the inclination of the outlet openings are adapted to the side wall injectors. Outlet openings can, for example, be designed as simple openings in the surface of the top lance. However, a nozzle shape is preferred for the design of an outlet opening. In particular, a Laval nozzle or a Venturi nozzle is preferred for a nozzle shape.
The top lance is preferably rotatable by an angle of at least +/−15°, more preferably at least +/−30°, even more preferably +/−45° around the axis of the top lance. As a result, the point of impact of an asymmetrical gas jet emerging from the top lance on the surface of the molten bath can be adjusted as required. The axis of the top lance is defined by the tip of the top lance and the point at which the top lance passes through the furnace cover.
The top lance can be rotated by an angle of at least +/−15°, preferably at least +/−30°, more preferably +/−45° around the vertical axis. The vertical axis is an axis that is parallel to or congruent with the axis of the top lance. As a result, the top lance can be pivoted in or out with respect to the smelting unit. To a small extent, limited by the opening in the furnace cover, such a pivot movement can be used to adjust the position of the impact point of the gas jet in relation to the impact cavities induced by the side wall injectors.
The top lance is preferably pivotable around the horizontal axis by an angle of at least +/−10°, more preferably at least +/−20°, even more preferably +/−30°. Horizontal axes are axes that lie in a horizontal plane. A rotation of the top lance around such an axis increases the range of movement of the tip of the top lance in the smelting unit. The tip has a particularly large range of movement if the horizontal axes of rotation are in the region of the cover opening.
The top lance preferably has at least one supersonic nozzle. Supersonic nozzles make it possible to apply a high impulse of the gas jet to the surface of the molten bath. Preferably, the volume flow of the process gas flowing through this nozzle can be regulated separately from the volume flows of the other outlet openings. As a result, it is possible to refine the melt in a targeted manner and as required, but also to reduce or increase the impulse input into the melt.
There is preferably at least one outlet opening in the top lance for every three gas jets emerging from one or more side wall injectors. It is even more preferable if there is at least one outlet opening in the top lance for every two gas jets emerging from one or more side wall injectors. It is highly preferable if there is at least one outlet opening in the top lance for each gas jet emerging from a side wall injector. As a result, the impact cavities of one or more side wall injectors can be ideally influenced by a gas jet from the top lance.
The upper furnace preferably has more than 4, more preferably more than 5, even more preferably more than 6, side wall injectors. As the number of sidewall injectors increases, the resulting impact cavity can be better distributed on the surface of the melt and the volume flow through the individual sidewall injector decreases in relation to the total volume flow required for the process.
At least one sidewall injector can preferably be switched between injector mode and burner mode. In the injector mode of the side wall injector, a blowing mode for gases as well as a conveying mode for powdery solids can be carried out by the side wall injector. As a result, a single side wall injector can also be used as a gas burner or solid fuel burner at the start of the melting process, for example.
The top lance and the side wall injectors can preferably be operated simultaneously and with coordinated volume flows for a respective process gas. Coordinated operation comprises manual, semi-manual or automatic coordination and adjusting of all volume flows entering the smelting unit through the top lance or side wall injector. The coordination is preferably carried out by adapting the pressure and/or the volume flow of the process gas for each individual side wall injector or for interconnected side wall injectors and the top lance. In the case of a multi-hole top lance, it is preferable that the gas jets emerging through the respective outlet opening can be operated individually or in groups in a coordinated manner. For this purpose, the pressure present and the volume flow can be adjusted individually or in groups for each outlet opening.
With a total volume flow of process gas required for the process, 50% to 90% of the total volume flow can be introduced by the top lance and 10% to 50% of the total volume flow can be introduced by the side wall injectors. The required total volume flow is defined by the volume flow of process gas required at that moment. The process gas can also consist of a variety of different process gases.
The first furnace cover preferably has a furnace elbow for discharging the exhaust gas produced in the smelting unit with an exhaust gas flow velocity of VAG≤50 m/s at an exhaust gas temperature of TAG≥800° C., wherein the furnace elbow has an average diameter of 1.20 m to 3.50 m. The furnace elbow is preferably inclined with respect to the vertical in a range of up to ±30° and preferably has a flow-through length of ≥2.0 m.
Furthermore, the object of the disclosure is achieved by a method for operating a smelting unit for steel production, in which the following steps are carried out:
The core of a single impact cavity is the lowest point in the surface of the molten bath caused by the gas jet. Depending on the operating state, for example the temperature of the molten bath, the shape and size of the impact cavity changes over time. The volume flows are adjusted in a coordinated manner in such a way that the surface movement of the surface of the molten bath and the tearing off of melt droplets from the impact cavity as a result of the shear forces are reduced. As a result, the depth of a single impact cavity is reduced.
The ratio of the volume flows of the process gas from the top lance VTL to two adjacent side wall injectors VSI is preferably between {dot over (V)}TL/{dot over (V)}SI≥0.5 und {dot over (V)}TL/{dot over (V)}SI≤2.0. In this adjustment range, the undulations of the surface of the molten bath and splashing can be effectively reduced. The steps of the method are preferably carried out in the order a) to e), wherein steps d) and e) preferably are performed out several times. By means of this sequence of steps a) to e), the required top lance position can be adjusted very rapidly. Due to the adapting of the top lance several times and coordinating the volume flows, it is possible to react to different operating states of the smelting unit.
Preferably, the volume flow of the process gas through the side wall injectors (15) is adjusted as a function of the volume flow of the process gas through the top lance (12) and the addition of the volume flows results in the currently required total volume flow. The current total volume flow is the volume flow related to the process point in time or process phase that is required for the metallurgical work at such point in time or phase. In doing so, the total volume flow can also be formed by different gases. This ensures, for example, that the melt is not overoxidized or overheated in relation to the point in time.
The invention is described in detail below with reference to the figures. In all figures, the same technical elements are provided with the same reference signs.
The water-cooled upper furnace 8 is substantially designed to be cylindrical in shape and has a height hO of approximately 4.5 m and a radius rO of approximately 3 m. In this example, 6 side wall injectors 15 are arranged circumferentially around the upper furnace 8. The central alignment of the side wall injectors 15 is adjusted in such a way that six impact cavities 26 are formed on a surface 6 of the molten bath. For this purpose, the side wall injectors 15 are inclined by 40° to 50°, preferably by 45°, with respect to the horizontal on the surface 6 of the molten bath. In the lateral direction, the side wall injectors 15 can be inclined by up to 15°. As a result, a counterclockwise circumferential molten bath movement in the melt 7 is induced. Three side wall injectors 15 can be switched from injector mode to burner mode. Three further side wall injectors 15 can inject solids such as coal dust, slag formers and/or alloys by means of a conveying gas.
The cooling of the upper furnace 8 and the refractory lining of the lower furnace 2 are designed for both melting mode and metallurgical mode in relation to cooling capacity and the thickness and type of refractory bricks.
The first cover 9 has an exhaust gas nozzle 10 and an opening 11 for inserting a top lance 12 into the smelting unit 1. The exhaust gas nozzle 10 is inclined by approximately 30° with respect to the vertical. The diameter is 1.45 m and the length is 2.80 m. The second cover 13 has an opening 14 in the center with a roof block for three electrodes 27. The exhaust gas nozzle 29 is smaller in diameter with respect to the exhaust gas nozzle 10 of the first cover 9. The covers 9, 13 can be exchanged during operation of the smelting unit by means of two pivot arms to which the covers 9, 13 are fastened in each case.
A gas station 28 or process gas control 16, not shown here, is connected to the side wall injectors 15 and the top lance 12 and controls the pressure and the volume flow of the process gases. The gas station 28 or process gas control 16 itself is integrated into the control system of the smelting unit 1.
The top lance 12 is attached to a further pivot arm. This can be moved with respect to the cover by means of a variety of hydraulic drives. In this example, the top lance 12 can be rotated by ±45° around its longitudinal axis 17 of the top lance 12. The top lance 12 can be pivoted by ±30° around the horizontal axis 19, wherein the pivot point is located approximately 0.5 m above the cover opening 11. In a working position, the top lance 12 can be pivoted by approximately ±10° around the pivot point of the pivot arm. The tip of the top lance 20 can be brought as close as 0.5 m to the surface 6 of the molten bath by the hydraulic drives. By means of the pivot arm, it also possible to remove the top lance 12 completely from the cover or the smelting unit 1.
The top lance 12 itself has seven outlet openings 21 in the region of the tip 20, wherein six are attached circumferentially around the outer surface. A seventh opening is positioned at the tip of the lance 20; this is in operation when the top lance is inactive in order to prevent the lance from scorching. This seventh opening can be designed as a Venturi nozzle or supersonic nozzle 22. The six outer nozzles are controlled together by the gas station 28 in relation to the pressure and volume flow. The seventh centric nozzle 22 is adjusted separately.
In Illustration 2), the impact cavities of the top lance are larger with respect to the impact cavities of the top lance shown in Illustration 1). Furthermore, the impact cavities of the top lance are pushed outwards and cover a part of the impact cavities of the side wall injectors. A change in the positioning of the impact cavities of the top lances from Illustration 1) to 2) can be carried out, for example, by increasing the distance between the top lance and the surface of the molten bath.
In Illustration 3), the impact cavities of the top lance are positioned in such a way that one impact cavity of the top lance is in contact with in each case two impact cavities of two side wall injectors or partially covers them. Such a positioning can be achieved, for example, by rotating the top lance around the axis of the top lance from a positioning as shown in Illustration 2).
Illustration 4) shows an arrangement of impact cavities with a three-hole blowing lance. In the case shown, one impact cavity of the top lance covers partial regions of two adjacent impact cavities of the side wall injectors. In contrast, in Illustration 5) three side wall injectors are arranged or active in the smelting unit. The impact cavities of the six-hole top lance are positioned in such a way that in each case two of the impact cavities touch or overlap an impact cavity of a side wall injector.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2021 214 227.3 | Dec 2021 | DE | national |
This application is a national stage application, filed under 35 U.S.C. § 371, of International Patent Application PCT/EP2022/083424, filed on Nov. 28, 2022, which claims the benefit of German Patent Application DE 10 2021 214 227.3, filed on Dec. 13, 2021.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/083424 | 11/28/2022 | WO |
