DEVICE FOR MELTING METALS

Abstract

The invention relates to a device for melting metals, the melting temperature of which is below 1000 °C. In this respect, equipment (2) for the formation of a plasma (8) is arranged in a melting furnace (1). The equipment (2) is connected to an electrical power supply and to at least one first feed pipe for a plasma-generating gas with which the plasma (8) can be formed. The equipment (2) is configured, dimensioned, arranged, and / or oriented such that the formed plasma (8) is positioned at a distance from the metal mass to be melted (9). A hot gas stream can be formed from the plasma (8) and is directed towards the mass to be melted (9). A melting basin or crucible (5) is arranged in the melting furnace (1) to receive the molten metal. (Figure 1).

Description

The invention relates to a device for melting metals, particularly non-ferrous metals. In this respect, the term "metals" also includes their alloys, the melting point of which should ideally be below 1000 °C. The invention is particularly suitable for melting aluminum and its alloys. Until now, melting these metals has typically involved using oil or gas burners in variously configured melting furnaces, where the hot flames melt the metal into a liquid state. The combustion of the respective hydrocarbon releases relatively large quantities of CO2 into the Earth's atmosphere through chemical oxidation, which is extremely harmful from a climate change perspective. Furthermore, inductive heating of the metal as a melt is also known. However, due to the alternating electric fields produced, a strong stirring effect occurs in the resulting molten mass. This leads to a high degree of oxide inclusions in the metal, severely compromising the quality of components manufactured from the melt. Induction-heated melting furnaces are also generally unsuitable for melting recycled material with coarse lumps or foundry scrap due to unfavorable coupling conditions. Electric resistance furnaces are also known. These generally have only reduced power, so as a rule they are only suitable for keeping molten metal warm. There had also been attempts to use plasma to melt metal. In this regard, an electric arc was used to generate plasma. For this purpose, an electrode was brought into contact with the unmelted mass to be melted. However, this led to contamination of the metal to be melted, and it was impossible to prevent or selectively influence this contamination. A loss of contact leads to the immediate interruption of the electric arc during complete melting and must therefore be avoided through very complex process control. Therefore, the invention aims to indicate possibilities for melting metal, in which the costs for the installation technique are kept within limits, the release of CO2 in situ is avoided as much as possible, as well as contamination of the molten mass obtained. According to the invention, this objective is achieved with a device having the characteristics of claim 1. Advantageous configurations and improvements of the invention can be realized with characteristics indicated in the dependent claims. In the device according to the invention for melting metals, particularly non-ferrous metals with a melting point preferably below 1000 °C, a melting furnace includes equipment for generating a plasma in the form of a free-gas torch and transferring heat by radiation to the mass to be melted. This can be a melting furnace of any other type, configured without modification. Preferably, shaft furnaces or open-hearth furnaces are used, but crucible furnaces are also acceptable. The equipment is connected to an electrical power supply and also to at least one first feed pipe for a plasma-forming gas with which the plasma can be formed. The equipment is configured, sized, arranged, and / or oriented such that the plasma generated is positioned at a distance from the metal mass to be melted. A hot gas stream may be formed from the plasma, directed towards the mass to be melted. Therefore, the plasma never comes into direct contact with the unmelted or molten mass. Consequently, the use of an electrode that would make contact with the mass to be melted or the molten mass can also be avoided, as such an electrode should not be present. The plasma formed should act solely as a heat source in this respect. This allows the metal mass to be heated exclusively by the thermal energy of the hot gas stream and the thermal radiation emitted by the plasma. The generated plasma should be configured and arranged in the device so that free electrically charged particles (particularly ions and electrons) cannot, or at least almost cannot, come into contact with the metal to be melted. To achieve this, the volumetric flow rate and flow velocity of at least one other feed gas, which essentially forms the hot gas stream, can also be adjusted or regulated. Plasma can also be mixed with another gas (secondary gas) to form a plasma torch or a stable gas torch, which also emits radiant energy towards the material to be melted. The material to be melted can then be heated with the hot gas from the plasma or gas torch, along with the radiant energy, to melt the material in the furnace chamber of the melting furnace. For receiving the molten metal, a melting basin or crucible is arranged in the melting furnace. In an alternative according to the invention, the equipment may be configured with a microwave generator and a resonator connected to it with at least one reflection plate for the generated microwaves, which is configured as a waveguide. Furthermore, the equipment should include an electrical ignition unit with an ignition electrode electrically isolated from a housing. The ignition unit serves exclusively for the ignition of a plasma and can be connected once a sufficiently large quantity of plasma has formed after the formation of free charge carriers from the plasma gas used, which has been effected by the generated microwaves. The plasma should form in the stationary microwave region inside the resonator, in front of at least one reflecting plate with plasma gas flowing there. Translational movement of the formed plasma can be largely prevented, allowing it to act as a stationary heat source and generate a hot gas stream. In this alternative, the plasma should be formed within the equipment housing, and the hot gas stream should be directed by at least one flow control element toward the mass to be melted inside the melting furnace. The flow control element(s) may be tubes or channels through which the hot gas flows toward the mass to be melted. The flow control elements may be made of glass, glass ceramic, or a purely ceramic material. There may also be at least two flow control elements. In this regard, a flow control element may be arranged in at least one area within the flow control element with a larger inner diameter or larger free cross-sectional area, and may form a heat shield there. The flow control elements should not be in direct contact with each other. Alternatively, the equipment may consist of two electrodes positioned at a distance from each other, between which a plasma gas flows toward the material to be melted, and an electric arc discharge occurs. In this respect, the equipment can be configured similarly to a standard plasma burner, such as those used for cutting and welding materials. One electrode is typically made of tungsten, hafnium, or an alloy thereof. The counter electrode may form a housing through which the plasma gas flows. Only the dimensions and operating parameters would need to be adapted to the metal melting application. However, even in this case, the plasma generated should not come into direct contact with the material to be melted and should serve only as a heat source for heating a gas, which can then be used as a hot gas stream or a free-gas torch for melting. The housing may be connected to at least one other supply pipe for plasma-forming gas or another gas (secondary gas). This other supply pipe may be located at a distance from the first supply pipe. Preferably, the other supply pipe may be located in the area of ​​the formed plasma or behind it as viewed in the flow direction. Advantageously, the electrical power of the equipment's microwave generator or electric arc discharge, the volumetric flow rate of the plasma gas, and / or the volumetric flow rate of the other gas can be regulated. In this respect, a measured temperature can represent, for example, the regulated quantity. This could be the temperature of the hot gas stream, the plasma, the mass to be melted, or the molten mass. The temperature should preferably be determined without contact, for example, by thermography or a pyrometer. However, the temperature can also be regulated. This can be done according to process control requirements, for example, to melt or maintain the temperature of a molten mass. It is also possible to regulate the microwave generator in such a way that the length of the gas torch formed with the plasma or the length of the plasma torch formed is adapted in the direction of the mass to be melted, so that the useful radiation energy part can be influenced in particular. Advantageously, the plasma gas can be introduced tangentially with a spin into the casing before coming under the influence of the microwaves. This prolongs the contact time, and the free charge carriers (ions, electrons) can be more effectively raised to a higher energy level, thus increasing efficiency. However, another gas can also enter the housing tangentially, either alone or in addition to the other. In this regard, it is possible to introduce plasma gas into the housing parallel to the longitudinal axis of the equipment housing or in the direction of the hot gas flow. This can be done by entering the equipment housing through an inlet opening that may be located directly next to the ignition equipment. Plasma gas inlets may be arranged in a distributed manner along the circumference of the housing, allowing plasma gas to enter the housing from the feed pipe. Argon can be advantageously used as the plasma gas, or another gas for that matter, since it is completely inert with respect to both the material being melted and the molten mass. However, when melting aluminum or its alloys, nitrogen or another gas should be avoided as the plasma gas. Oxygen or air promote oxidation and are therefore undesirable in this regard. However, a mixture of gases such as plasma gas or another gas can also be used. In this regard, the respective gas proportions of the mixture can be adjusted to the specific metal being melted. For example, argon can be mixed with air, and it is desirable that the air proportion be smaller than the argon proportion. There may also be a return line for the hot gas extracted from the melting furnace, allowing for its reuse as a plasma gas and / or another gas in the circuit, or for other uses of the waste heat. Operation with recirculation reduces the amount of plasma gas or other gas required, thus lowering costs, particularly for argon. rnbn ιη / ζζηζ / Β / γίΛΐ However, the residual heat from the extracted hot gas can also be used, for example to keep the molten mass hot or for preheating, in particular, the other gas. In the invention, microwaves with a frequency in the range of 500 MHz to 5000 MHz can be used, with an electrical power in the range of 5 kW to 3000 kW. The total volumetric flow rate of plasma gas and / or the other gas should be chosen at least so large that the stream of hot gas entering the melting furnace reaches the unmelted mass to be melted, or at least comes close to it, so that the mass to be melted is melted by thermal radiation. Furthermore, it is advantageous to place the ignition electrode of a plasma ignition system, which generates plasma via microwaves, within a beam trap. For this purpose, the ignition electrode can be housed in a tube or channel-shaped element whose inner diameter or free internal cross-sectional area is smaller than that of the housing of the equipment in which the plasma is generated. In this respect, it is particularly advantageous for the tip of this electrode to be located at the rear of the tube or channel-shaped element, i.e., inside the beam trap. This embodiment can increase the service life of the ignition electrode and completely prevent contamination of the molten mass with the electrode material. The plasma-generating equipment can be advantageously mounted on a pivoting device within the furnace body, enabling selective and variable guidance of the gas torch, plasma torch, or hot gas stream within the furnace chamber. This allows for changes in the direction of a gas or plasma torch and enables selective local heating of the respective mass to be melted within the furnace chamber. For example, the outer edges or the center of the mass to be melted in the furnace chamber can be heated more or less intensely, depending on the immediate requirements. In the invention, the housing can be cooled at least in zones. Temperature regulation, particularly in the flow control element(s), can also be advantageous to reduce the effect of sharp temperature changes in this zone. Large temperature differences occurring for short periods should be particularly avoided. As explained above, the invention significantly reduces the amount of CO2 released. Existing melting furnaces can be retrofitted or retrofitted with minimal effort. The quality of the molten metal is at least comparable to that achievable with conventional gas or oil burners. Contamination and oxidation of the molten metal can be largely avoided or even completely eliminated. The invention will now be explained in more detail by way of example. In this regard, features may be combined independently of the respective example or corresponding representation in a figure. Individual features are not limited to the respective example or representation. In this regard, they show: Figure 1 is a schematic representation of an example of a device according to the invention and Figure 2 is a cross-sectional representation of a partial area of ​​an example of equipment for forming a plasma by microwaves. Figure 1 schematically shows an example of a device according to the invention with a melting furnace 1. A door (not shown) is provided on one side of the melting furnace 1, through which it is possible to charge the melting furnace 1 with unmelted material 9. The unmelted material 9 can be placed on a pouring platform 4, which is inclined obliquely at an angle, in the example shown an angle of 10°, so that the molten metal can drip from the pouring platform 4 into the crucible 5 or into a melting basin (not shown). A plasma-forming device 2 is flanged to the housing 6 of the melting furnace 1. At least one flow control element (not shown here) passes through the housing wall of the melting furnace 1 into the furnace 1, allowing at least one hot gas stream to be directed to the unmelted mass 9. The housing is pivotally mounted, enabling the tracking of the gas torch, plasma torch, or hot gas stream formed with the plasma 8 during melting. Through a window embedded in the casing wall 6 of the rnbn ιη / ζζηζ / Β / γίΛΐ melting furnace 1, the melting process can be observed from the outside or a determination of the temperature inside the melting furnace 1 can also be made from there. Figure 1 also shows an extraction 7 for hot exhaust gas in the melting furnace 1, by means of which the hot exhaust gas can be extracted from the melting furnace 1. The hot exhaust gas can be recirculated and can be returned for example as plasma or another gas. The hot exhaust gas extracted can also be used to keep the molten mass warm or for other purposes where thermal energy can be harnessed. The hot exhaust gas can also be passed through a heat exchanger. Figure 2 shows essential elements of equipment 2 for plasma formation. The microwave generator, which is a common product on the market, has been omitted. It is flanged to resonator 10. The microwaves 11 generated by the microwave generator can be obtained in the resonator 10 as standing waves. For this purpose, a reflection plate 10.1 is also arranged on a flange of the housing 13 of equipment 2, facing a second flange 21. The microwave generator is connected to the second flange 21. The reflection plate 10.1 may be made of glass. Near the microwave reflection plate 10.1, a supply pipe 17 for a refrigerant gas is provided in the housing 13 of the equipment 2. The refrigerant gas may flow additionally for a cooling effect along the surface of the reflection plate 10.1 inside the housing 13 and may clean it or keep it free of particles. In Figure 2, to the left of the housing 13 of equipment 2, an ignition unit with a rod-shaped ignition electrode 12 can be seen. This is connected to one pole of an electrical voltage source (not shown). Applying an electrical voltage to this ignition electrode 12 for a short time can result in a further increase in the energy of the fed plasma gas, leading to the ignition of a plasma 8 in the resonator 10 area and the stationary microwaves 11 generated there. Once the plasma 8 has been ignited, the ignition unit can be disconnected. As explained in the general part of the description, the housing 13 can be configured in the ignition equipment area with the ignition electrode 12 as a lightning trap. The plasma gas can enter only through the beam trap or only through inlets 18 arranged in a distributed manner along the circumference of the housing 13. However, a combination of the two forms is also possible. A spin effect can be achieved and exploited by means of a tangential entry, preferably through several entries 18. In the example shown, another gas supply line has been omitted. However, at least one other gas can be introduced into the housing 13 of equipment 2, preferably in the plasma zone 8. Then, at least one other gas can be used primarily for the hot gas stream. The hot gas stream exits equipment 2 in the direction of the drawn arrow. For this purpose, three flow control elements 14, 15, and 16 in the form of tubes are provided in this example. The quartz glass tube 14, with the smallest diameter, encloses the plasma 8. In its area facing the melting furnace 1, which is positioned opposite the ignition equipment, it is enclosed by another flow control element 15 in the form of a tube, which can also act as a shield against thermal radiation. In the area of ​​the flange of the casing 13, which faces the melting furnace 1, a third flow control element 16 in the form of a tube is arranged, having the largest diameter. The third flow control element 16 can extend at least to the wall of the casing 6 of the melting furnace 1, so that the hot gas stream can be directed through a perforation in the wall of the casing 6 to the material to be melted 9 arranged in the melting furnace 1. However, its length can also be chosen so that it protrudes into the interior of the melting furnace 1. The third tube-shaped flow control element 16 can be guided and secured in a flange 19 of the housing 13 of equipment 2. The flow control elements 14, 15, and 16 are fitted into one another. However, they must not come into contact with each other. In addition to the supply pipe 17 for a refrigerant gas, other areas of the housing 13 of equipment 2 may also be configured for cooling and can be used for this purpose. A refrigerant (gas or liquid) can flow through these areas. These areas should be located at least close to the plasma 8 that has formed. In the example shown, flange-shaped cooling 20 is provided in an area of ​​the housing 13 of equipment 2.

Claims

1. Device for melting metals, in particular non-ferrous metals, comprising equipment (2) for the formation of a plasma (8) in a melting furnace (1), the equipment (2) being connected to an electrical power supply and at least one first feed pipe for a plasma-generating gas with which the plasma (8) can be formed being connected to the equipment (2), and the equipment (2) being configured, dimensioned, arranged and / or oriented such that the plasma (8) formed is disposed at a distance from the metal mass to be melted (9), and a hot gas stream being formed with the plasma (8) in this respect, which is oriented in the direction of the mass to be melted (9), and a melting basin or crucible (5) being arranged in the melting furnace (1) for receiving the molten metal.

2. Device according to claim 1, characterized in that the equipment (2) is configured such that the plasma-generating gas of the plasma (8) and another gas form a gas torch or a free plasma torch in the furnace chamber of the melting furnace (1) that can utilize the hot gases and the radiation energy thereof for heat transmission and for melting a respective metal.

3. Device according to claim 1, characterized in that the equipment (2) is configured with a microwave generator and a resonator (10) connected thereto which is configured as a waveguide and with at least one reflection plate (10.1) for generated microwaves (11).

4. Device according to the preceding claim, characterized in that the equipment (2) is configured with an electrical ignition equipment, having an ignition electrode (12) electrically isolated from a housing (13), the plasma (8) being formed in the stationary microwave zone inside the resonator (10) in front of at least one reflection plate (10.1) with plasma-generating gas flowing there and the plasma (8) in the housing (13). rnbn ιη / ζζηζ / Β / γίΛΐ 5. Device according to one of the two preceding claims, characterized in that the hot gas stream is directed by means of at least one flow control element (14, 15, 16) in the direction of the mass to be melted (9).

6. Device according to one of the three preceding claims, characterized in that the ignition electrode (12) of the electric ignition equipment for plasma is arranged in a ray trap.

7. Device according to any of the preceding claims, characterized in that the power, length, temperature and / or length of the gas torch or free plasma torch can be changed with an adjustable microwave generator.

8. Device according to one of the preceding claims, characterized in that the equipment (2) is formed with two electrodes arranged at a distance from each other, between which a plasma gas flows in the direction of the mass to be melted (9) and an electric discharge by voltaic arc takes place.

9. Device according to one of the preceding claims, characterized in that at least one other supply pipe for plasma gas or other gas is connected to the housing (13) of the equipment (2).

10. Device according to any one of claims 3 to 6, characterized in that the electrical power of the microwave generator of the equipment or of the electric arc discharge of the equipment (2), the volumetric flow of the plasmagen gas and / or the volumetric flow of the other gas can be regulated.

11. Device according to one of the preceding claims, characterized in that at least the plasma gas and / or other gas enters tangentially with a spin into the housing (13).

12. Device according to any of the preceding claims, characterized in that argon is used as the plasma gas and / or another gas. rnbn ιη / ζζηζ / Β / γίΛΐ 13. Device according to any one of claims 3 to 10, characterized in that microwaves are used with a frequency in the range of 500 MHz to 5000 MHz, with an electrical power in the range of 5 kW to 3000 kW.

14. Device according to one of the preceding claims, characterized in that a mixture of gases is used as plasma gas and / or another gas.

15. Device according to one of the preceding claims, characterized in that a return pipe is provided for the hot gas extracted from the melting furnace (1), with which a new use of this gas can be achieved as plasma-generating gas and / or another gas in the circuit or another use of the residual heat.

16. Device according to any of the preceding claims, characterized in that the equipment (2) is fixed to a pivoting device on the body of the furnace, so that selective and variable guidance of the gas torch, 15 plasma torch or hot gas stream in the furnace chamber is possible.

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