Plasma torch and method for operating a metallurgical furnace

Abstract

The invention relates to a plasma torch (1) and a method for operating a metallurgical furnace.

Description

[0001] The invention relates to a plasma torch and a method for operating a metallurgical furnace.

[0002] Plasma torches are used for the efficient heating of gaseous media, particularly in metallurgical processes. These torches generate an extremely hot plasma jet, primarily produced by the ionization of a gas. An electric arc is passed through a gas such as argon or nitrogen, causing the gas to transition into a plasma state. The plasma can reach temperatures of up to 30,000 °C, which is extremely hot and energetic. An electrode (cathode) located inside the plasma torch is subject to intensive wear and tear and must be replaced at regular intervals, usually every few hundred to a thousand hours.

[0003] There are two different designs of plasma torches: Plasma torches with an integrated anode, wherein an electric arc is generated within a nozzle tip located at the plasma outlet, allowing plasma to exit freely from the nozzle tip; plasma torches with a metallic counterpart as the anode, wherein an electric arc forms between the cathode, acting as the electrode in the nozzle, and the metallic counterpart. An example of an application is the plasma cutter.

[0004] A nozzle positioned at the outlet of the plasma torch focuses the plasma jet to concentrate energy onto a small area or section. This high energy can be used to melt and / or vaporize materials, or to cut them. Plasma torches are also used in processes such as plasma spraying, where material is applied to surfaces, or in plasma chemistry, where reactions are initiated by a plasma.

[0005] Plasma torches can be controlled via precise control systems to regulate temperature and gas flow. Therefore, a plasma torch is a versatile tool used in many industrial and scientific applications.

[0006] A plasma torch works by generating an extremely hot plasma jet through the ionization of a gas. An electric arc is created within a nozzle of the plasma torch, ionizing the gas flowing through the torch and thus through the nozzle. The gas, often argon, nitrogen, or air, is heated so intensely by the arc that it transitions into a plasma state. This process ionizes the gas atoms, creating an electrically conductive plasma. The nozzle and other components of the plasma torch are often cooled, particularly with water, to manage the high temperatures and prevent overheating.

[0007] Conventional plasma torches generate an electric arc by applying a high voltage between a cathode and an anode, which heats the gas and produces plasma. This technology has the disadvantage that the extremely high temperatures severely limit the lifespan of the cathode and anode.

[0008] Furthermore, a method and a device for automatically replacing electrodes (cathodes) in plasma torches is known from US 2022 / 0256683 A1 in order to maintain almost continuous operation, but the plasma torch is not in operation during the cathode change.

[0009] Also known as "hot-wire," this technique in plasma cutting technology involves using an auxiliary anode in the form of an external wire, which is fed in front of the nozzle and thus directly into the plasma jet. Furthermore, a plasma cutting system with water injection is also known, in which the water is directed so that it hits and touches the plasma arc between the constricting nozzle bore and the front part of the nozzle. The force of the water promotes a (further) constriction of the plasma arc, thereby enabling higher cutting speeds and improved cut quality.

[0010] Furthermore, the use of plasma torches in metallurgical furnaces is known from US 9 752 206 B2.

[0011] The object of the present invention is to provide a plasma torch that is subject to lower thermal stress compared to the prior art, as well as a method for operating a metallurgical furnace with a corresponding plasma torch.

[0012] This problem is solved with respect to a plasma torch having the features of claim 1 and with respect to a method having the features of claim 10. Further embodiments are set out in the dependent claims.

[0013] The first teaching of the invention relates to a plasma torch with a nozzle arranged at the outlet of the plasma torch for directing a plasma jet, which can be generated with a plasma gas flowing through the nozzle in conjunction with an arc generated inside the nozzle, wherein the arc can be generated by applying a voltage between a cathode arranged inside the plasma torch and an anode arranged inside the nozzle, wherein the cathode is designed as a hollow electrode for passing a cooling medium through it.

[0014] The inventors have discovered that by using a hollow electrode as the cathode, through which a cooling medium can be passed, improved cooling is provided, and the heat inevitably generated during the operation of the plasma torch can be dissipated more quickly and effectively, thereby delaying thermal fatigue of the cathode and thus increasing the service life of the cathode.

[0015] Besides gases, liquids are preferably suitable as cooling media, especially water.

[0016] Suitable plasma gases include nitrogen, argon, or air. However, other gases such as carbon monoxide, carbon dioxide, hydrogen, steam, coke oven gas, blast furnace gas, natural gas, or a mixture of these gases can also be used.

[0017] According to one embodiment, the cathode can be arranged to be tracked within the plasma torch. This allows both a trackable anode and a trackable cathode to result in a stable and uninterrupted process.

[0018] According to one embodiment, additional cathodes can be inserted laterally from the plasma torch or from the rear on the opposite side of the outlet into the plasma torch and thus be advanced within the plasma torch. Preferably, these additional cathodes can be advanced from the rear on the opposite side of the outlet into the plasma torch and connected to the remaining cathode within the plasma torch, preferably by a material bond, so that a quasi-extension of the cathode can be achieved and thus the cathode can be extended virtually indefinitely.

[0019] The cathode can be a highly electrically conductive metal, such as copper or a copper alloy, and / or a wear-resistant metal, such as hafnium or a hafnium alloy. In particular, the anode can be made of a composite material that is both highly electrically conductive and wear-resistant, preferably comprising or consisting of a composite of copper or a copper alloy and hafnium or a hafnium alloy. The cathode can, for example, have a diameter between 5 and 100 mm, in particular at least 8, 10, or 15 mm, and in particular at most 90, 70, or 60 mm, depending on the dimensions of the plasma torch. The wall thickness of the cathode can be between 1 and 10 mm.

[0020] For example, the anode is located in the area of ​​the plasma torch exit inside the nozzle, preferably in the area of ​​the narrowest cross-section inside the nozzle.

[0021] According to a preferred embodiment, the anode can be arranged in a helical shape within the nozzle. "Helix shape" within the meaning of the invention means that, preferably, an anode consisting of an elongated wire electrode corresponds to a ring in a top view. The helical shape can, for example, have a number of turns between at least 1 and n, where n can, for example, be a maximum of 10. The turns do not necessarily have to be complete to result in a natural number as the number of turns, but can also be non-integers (positive numbers), such as 1.4, 2.3, or 3.7. Thus, any number, including any non-integer, where only one decimal place is considered, between 1.0, 1.1, 1.2, ... 9.8, 9.9, 10.0 is conceivable as a number of turns and is hereby explicitly disclosed.

[0022] The anode can be a highly electrically conductive metal, such as copper or a copper alloy, and / or a wear-resistant metal, such as hafnium or a hafnium alloy. In particular, the anode can be made of a composite material that is both highly electrically conductive and wear-resistant, preferably comprising or consisting of a composite of copper or a copper alloy and hafnium or a hafnium alloy. The anode can, for example, have a diameter between 0.5 and 10 mm, in particular at least 1, 2, or 5 mm, and in particular at most 9, 8, or 7 mm.

[0023] According to one embodiment, the anode can be arranged as a wire electrode and be guided within the nozzle. Preferably, the anode can be arranged in a channel and be guided. This allows, for example, a trouble-free feeding of the anode into or to the nozzle. For instance, the channel can be located outside the plasma torch, and the anode can be inserted and / or guided into the interior of the nozzle via a feed opening. Preferably, the anode, functioning as a wire electrode, can be withdrawn from a coil. This allows for the provision of a virtually endless long product.

[0024] According to one embodiment, the nozzle can include a section with a helical contour on its inner wall, in which the anode can be received and / or tracked. This can facilitate and / or support the tracking of the anode, and in particular ensure that, preferably during targeted tracking of the cathode, especially into a defined operating position, a constant distance between the anode and cathode is always maintained, thus guaranteeing a stable process. The helical contour preferably ensures precise and / or defined positioning of the tracked anode. The helical contour can be cylindrical or conical.

[0025] The second teaching of the invention relates to a method for operating a metallurgical furnace, comprising at least one plasma torch with a nozzle arranged at the outlet of the plasma torch for directing a plasma jet, which is generated with a plasma gas flowing through the nozzle in conjunction with an electric arc generated inside the nozzle, wherein the electric arc is generated by applying a voltage between a cathode arranged inside the plasma torch and an anode arranged inside the nozzle, wherein the cathode is designed as a hollow electrode through which a cooling medium is passed.

[0026] According to one embodiment, the cooling medium can be continuously passed through the cathode, thus enabling targeted cooling of the cathode and reducing cathode wear.

[0027] According to one embodiment, water or a gas can be used as the cooling medium. Preferably, a gas is used that is inert and does not participate in the metallurgical process, such as argon or nitrogen, or a gas that is selected to actively support the metallurgical process, such as air, carbon monoxide, carbon dioxide, hydrogen, steam, natural gas, coke oven gas, blast furnace gas, or a mixture of the aforementioned gases. If the metallurgical furnace is particularly preferably a blast furnace, a direct reduction furnace, or a furnace in the non-ferrous (NF) industry, the gases that actively support the process can be used as reducing agents in the metallurgical process. For example, the water is heated as it flows through the hollow cathode, changes its state of matter, and decomposes into hydrogen and oxygen.The released hydrogen serves as a reducing agent, particularly in blast furnaces or direct reduction furnaces, for reducing iron ore. The released oxygen can react with a carbon carrier, for example by blowing in carbon particles, to form carbon monoxide, which can then be used for further reduction.

[0028] The use of at least one plasma torch on the blast furnace or several plasma torches distributed around the circumference of the blast furnace can, for example, replace the classic introduction of hot blast at least partially or even completely.

[0029] A direct reduction furnace, as defined in the invention, is a direct reduction reactor in which iron ore (10) is reduced to sponge iron (DRI) using hot reducing gases, which can have a temperature between 700 and 1200 °C. This standard process can be replaced by using at least one plasma torch and a suitable plasma gas, such as hydrogen, carbon monoxide, or carbon dioxide, since the required temperature is generated by the plasma and, for example, at least part of the required reducing gas can be provided, in particular by the cooling medium, preferably by the gas from the plasma torch.

[0030] A furnace in the non-ferrous metals industry is a furnace that can reach a temperature between 700 and 1500 °C and in which metallurgical treatment is carried out using a gas phase and / or by producing metal / slag. In this standard process, the use of at least one plasma torch and a suitable plasma gas, such as argon, nitrogen, air, hydrogen, carbon monoxide, or carbon dioxide, can be replaced, since the required temperature is generated by the plasma and, for example, at least part of the required furnace atmosphere can be provided, in particular by the cooling medium, preferably by the gas from the plasma torch.

[0031] To avoid repetition, reference is made to the details of the first teaching. Corresponding features of the first teaching are therefore also applicable and / or implementable in the second teaching and thus comprehensible to a person skilled in the art. Consequently, all combinations of individual features of the first teaching with the second teaching are also disclosed.

[0032] The invention is explained in more detail with reference to the following exemplary embodiments in conjunction with the drawing. Identical parts are provided with the same reference numerals. They show Figure 1 shows a schematic longitudinal section of a first embodiment of a plasma torch according to the invention, and Figure 2 shows a schematic longitudinal section of a second embodiment of a plasma torch according to the invention.

[0033] In Figure 1Figure 1 shows a schematic longitudinal section of a plasma torch (1) according to a first embodiment. The plasma torch (1) comprises a nozzle (3) arranged at its outlet for directing a plasma jet (12), which can be generated by a plasma gas (10) flowing through the nozzle (3) in conjunction with an electric arc (13) generated within the nozzle (3). The electric arc (13) can be generated by applying a voltage, for example, by means of a voltage source (5), between a cathode (4) arranged inside the plasma torch (1) and an anode (6) arranged inside the nozzle (3). The cathode (4) is designed as a hollow electrode for passing a cooling medium (11) through it.

[0034] Both the cathode (4) within the plasma torch (1) and the anode (6), as a wire electrode within the nozzle (3), can be arranged in a tracking manner. The tracking of the cathode (4) is indicated by the arrow in conjunction with the reference numeral (4.1). The tracking of the anode (6) is indicated by the arrow in conjunction with the reference numeral (6.1). The anode (6) can be arranged in a helical form (6.2) within the nozzle (3). In this embodiment, the helical form (6.2) has a minimum number of turns, in particular 1.5. The nozzle (3) can include a section with a helical contour (3.2) on its inner wall (3.1) in which the anode (6) can be received and / or tracked. The anode (6) can be removed from a coil (6.4).The anode (6) can be arranged to be tracked in a channel (2), wherein the channel (2) is located outside the plasma torch (1) and the anode (6) can be inserted and / or tracked into the interior of the nozzle (3) via a feed opening (not shown) in the nozzle (3). Further cathodes (4) can be inserted laterally to the plasma torch (1) or from the rear on the opposite side of the outlet into the plasma torch (1), preferably connected to the (residual) cathode (4) still present in the plasma torch (1), and thus tracked within the plasma torch (1).

[0035] If the anode (6) is damaged in the arc generation area (13), the anode (6) is pushed forward, for example by at least one turn. This creates a temporary protrusion (6.3) at the nozzle exit (3), which gradually melts, burns off, or evaporates over time. If the cathode (4) is damaged in the arc generation area (13), particularly in the front section of the cathode (4), the cathode (4) is pushed forward, for example by a few millimeters or centimeters, towards the nozzle exit (3) or the anode (6), so that the front section is brought closer to the anode (6) or the nozzle exit (3) and gradually melts, burns off, or evaporates over time.

[0036] Figure 2Figure 1 shows a schematic longitudinal section of a plasma torch (1) according to a second embodiment. The construction is almost identical to the first embodiment, with the difference that in this embodiment the helical shape (6.2) has a number of turns of at least 4.0, in particular 4.5. Although not shown, the nozzle in the second embodiment can nevertheless include a section with a helical contour on its inner wall in which the anode can be received and / or guided. The helical contour and thus also the helical shape (6.2) can be cylindrical or conical (not shown here) in both embodiments.

[0037] In both illustrations, the use of the respective plasma torch (1) is indicated by a reference line (B), which symbolizes a wall of an exemplary blast furnace, a direct reduction furnace, or a furnace in the non-ferrous metals industry. Thus, the plasma (12) radiates into the interior (A) of a blast furnace, a furnace in the non-ferrous metals industry, or a direct reduction furnace. The loading of additional cathodes (4) and the provision of coils (6.4) therefore take place outside the reference line (B). The arrangement of the plasma torch (1) on / in a wall is only exemplary, as, of course, depending on the application, the plasma torch (1) can extend further into the furnace chamber than shown, or be set back in / on the wall. The nozzle (3) and, optionally, other parts of a plasma torch (1) connected to the nozzle (3) are generally cooled by means of a cooling system (7) due to the high heat generation by the plasma (12).

[0038] Essential is the passage (11) of a cooling medium through the cathode (4), which is designed as a hollow electrode. Preferably, water or, more preferably, gas is passed through as the cooling medium. Corresponding embodiments (not shown) for connecting water- or gas-carrying lines to the plasma torch or to the hollow electrode are, of course, unproblematic for those skilled in the art.

Claims

1. Plasma torch (1) with a nozzle (3) arranged at the outlet of the plasma torch (1) for directing a plasma jet (12), which can be generated with a plasma gas (10) flowing through the nozzle (3) in conjunction with an electric arc (13) generated inside the nozzle (3), wherein the electric arc (13) can be generated by applying a voltage between a cathode (4) arranged inside the plasma torch (1) and an anode (6) arranged inside the nozzle (3), characterized by the fact that the cathode (4) is designed as a hollow electrode for passing a cooling medium (11) through it.

2. Plasma torch according to claim 1, wherein the cathode (4) is arranged to be tracked within the plasma torch (1).

3. Plasma torch according to claim 2, wherein further cathodes (4) can be inserted laterally of the plasma torch (1) or from the rear on the opposite side of the outlet into the plasma torch (1) and can thus be advanced within the plasma torch (1).

4. Plasma torch according to claim 3, wherein further cathodes (4) are arranged to be guided from the rear on the opposite side of the exit into the plasma torch (1) and are connectable to the (residual) cathode (4) still present in the plasma torch (1).

5. Plasma torch according to one of the preceding claims, wherein the anode (6) is arranged in a helical shape inside the nozzle (3).

6. Plasma torch according to one of the preceding claims, wherein the anode (6) is arranged as a wire electrode within the nozzle (3) in a manner that allows it to be tracked.

7. Plasma torch according to claim 6, wherein the anode (6) is arranged to be tracked in a channel (2).

8. Plasma torch according to claim 6 or 7, wherein the anode (6) is removable from a coil (6.4).

9. Plasma torch according to one of claims 6 to 8, wherein the nozzle (3) comprises on its inner wall (3.1) a section with a helical contour (3.2) in which the anode (6) can be received and / or tracked.

10. Method for operating a metallurgical furnace comprising at least one plasma torch (1) with a nozzle (3) arranged at the outlet of the plasma torch (1) for directing a plasma jet (12) which is generated by a plasma gas (10) flowing through the nozzle (3) in conjunction with an electric arc (13) generated inside the nozzle (3), wherein the electric arc (13) is generated by applying a voltage between a cathode (4) arranged inside the plasma torch (1) and an anode (6) arranged inside the nozzle (3), characterized by the fact that the cathode (4) is designed as a hollow electrode through which a cooling medium (11) is passed.

11. Method according to claim 10, wherein the cooling medium (11) is continuously passed through.

12. Method according to claim 10 or 11, wherein the cooling medium (11) is argon, nitrogen, air, carbon monoxide, carbon dioxide, hydrogen, steam, natural gas or water.

13. Method according to one of claims 10 to 12, wherein further cathodes (4) are introduced laterally to the plasma torch (1) or from the rear on the opposite side of the outlet into the plasma torch (1) and are thus guided within the plasma torch (1).

14. Method according to one of claims 10 to 13, wherein the anode (6) is arranged as a wire electrode in a helical shape inside the nozzle (3).

15. Method according to any one of claims 10 to 14, wherein the metallurgical furnace is a blast furnace, a non-ferrous metals furnace or a direct reduction furnace.

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