Method for melting and thermally treating solids

Abstract

According to the method, at least one hot process gas flow is provided by inductively heating at least one body, through which and / or past which process gas to be heated is directed in the direction of solids to be thermally treated or melted, and the at least one body is heated using an electric coil which surrounds the body and is connected to an electric alternating voltage source or an electric direct voltage source that is operated in pulses. At least one chemical element and / or at least one chemical compound is / are introduced into the hot process gas flow, ions from said at least one chemical element and / or chemical compound being converted to an excited state by the heat of the process gas flow or at least one chemical reaction being initiated such that the proportion of electromagnetic radiation which is directed onto the thermally treated or melted product, having a wavelength of ≥ 575 nm, is increased by at least 10% of the total spectrum of the electromagnetic radiation.

Description

[0001] Process for melting and heat treating solids

[0002] The invention relates to a method for melting and heat treating solids in a melting furnace or melting tank as well as batch and continuous furnaces.

[0003] Until now, it has been common practice to use oil or gas burners for melting and heat-treating these solids in variously configured furnaces. Their hot flames heat the material and convert it into the liquid phase. During the combustion of the respective hydrocarbon compounds, which originate from fossil sources, relatively large amounts of CO2 formed through chemical oxidation are released into the Earth's atmosphere with the flue gas, which is particularly detrimental from the perspective of climate change and the consumption of natural fossil resources.

[0004] Furthermore, it is also known to perform inductive heating and inductive melting of conductive solids, particularly metal, as the melt or treatment material. However, the resulting alternating electric fields cause a strong stirring effect of the resulting melt. This leads to a significant amount of oxide inclusions in the metal, which has a severe adverse effect on the quality of the components manufactured with the resulting melt. Furthermore, due to unfavorable coupling conditions, inductively heated melting furnaces are generally poorly suited for melting coarse recycled material or cast scrap.

[0005] Electrically resistance-heated furnaces are also common. These usually have low power and are therefore generally only suitable for keeping already molten metal hot by suppressing heat loss.

[0006] In recent times, however, technical possibilities have been developed that allow heat treatment and melting of solids by using electrical energy, in which a hot process gas stream can be used for melting by indirect inductive heating.

[0007] Such a technical solution, which concerns the indirect inductive heating of a process gas stream, is disclosed in DE 10 2022 207 481 A1. Reference is made to its contents below.

[0008] However, the disadvantage is that the heating of the melt can only be achieved with the thermal energy of the process gas stream and with electromagnetic radiation. The wavelength spectrum of the electromagnetic radiation also plays a role, as different wavelengths are known to be absorbed differently by a correspondingly irradiated material and thus contribute to its heating to varying degrees.

[0009] Depending on the type of process gas, a process gas stream emits predominantly short-wave electromagnetic radiation, which impinges on the respective melting material or a melting tank for melting. This radiation, which predominantly contains discrete (blue or green) radiation components, is absorbed with relatively low efficiency by the solids (metals, glasses) being melted or heat-treated or by the melting tank, so that the overall efficiency is correspondingly reduced.

[0010] It is therefore an object of the invention to provide possibilities by which the efficiency in the heat treatment and / or melting of solids such as metals and glasses can be easily increased if a hot process gas stream which has been heated by indirect inductive heating is used to generate the required process heat.

[0011] According to the invention, this object is achieved by a method having the features of claim 1. Advantageous embodiments and further developments of the invention can be realized with features defined in the dependent claims.

[0012] The invention involves at least one hot process gas stream, which is directed by inductive heating of at least one body through and / or past the process gas to be heated, toward the solid (metal, glass) to be heat-treated or melted, or a melting tank, or at a distance from its surface. The heating of the at least one body is achieved by an electrical coil enclosing the body, which is connected to an electrical AC voltage source or a pulsed electrical DC voltage source. Only the thermal energy of the process gas stream and the emitted electromagnetic radiation are used to provide process heat.

[0013] According to the invention, at least one chemical element and / or at least one chemical compound is / are introduced into the hot process gas stream, and ions from the chemical element or chemical compound are converted into an excited state using the heat of the process gas stream. In combination with the conversion into an excited state, photons are released. Alone or in addition to the excitation of the ions, at least one exothermic chemical reaction can be initiated, the energy of which can additionally heat the process gas stream. During a chemical reaction, as far as possible, no H2 or CO2 should be released and allowed to enter the sphere of influence of the solid or molten material to be heat-treated or melted.

[0014] In any case, the proportion of electromagnetic radiation directed at the melt with wavelengths > 575 nm is increased by at least 10%, preferably by at least 30% of the total spectrum of electromagnetic radiation, with a transition from a discrete to a continuous radiation spectrum (solid-state radiation of carbon) being sought. The transition to a continuous spectrum enables the long-wave portion of the electromagnetic radiation to penetrate the surface of the heat-treated material or the melt, thereby enabling highly efficient heat input. With short-wave, discrete electromagnetic radiation, on the other hand, reflection from the surface (solid or melt) dominates, so that a large proportion of the radiation energy heats the furnace walls and is dissipated unused with the flowing gases by convection.

[0015] Preferably, the process gas flow should be directed at an angle between 0° and 20° relative to the surface of the solid being heat-treated or melted, or to the already molten melt material or the melting tank. However, it can also be directed directly at the solid being heat-treated or melted.

[0016] The solid thus melted with the process gas stream can then be transferred to a melting tank or crucible in the melting furnace. Melted solid (metal or glass) in a melting tank can be removed or discharged from it.

[0017] The chemical element used can be Na, Ca, Sr, Li, Rb, Mg, or carbon, or the chemical compound used can be at least one chemical compound containing at least one of these chemical elements. Of the alkali metals, their salts, in particular, can be used as chemical compounds. For example, the use of sodium or a sodium compound results in yellow electromagnetic radiation; Ca or a calcium compound results in orange-red; Sr or a strontium compound results in red; Li or a lithium compound results in red; and Rb or a rubidium compound also results in red due to the well-known flame coloration effect. The use of carbon-containing compounds results in a continuous spectrum with a maximum in the yellow radiation range.

[0018] The at least one chemical element and / or the at least one chemical compound should be supplied in a proportion of greater than 15 vol.%, preferably at least 0.2 vol.% up to a maximum of 10 vol.% in relation to the supplied process gas stream.

[0019] As already indicated, C or a hydrocarbon compound can also be used as a chemical element.

[0020] In principle, the feed can be in any possible state of matter—solid, liquid, or gaseous. It is also possible to feed a chemical element or compound in a solvent, i.e., in dissolved form.

[0021] The at least one chemical element or at least one chemical compound should be introduced into a region of the process gas stream where a minimum temperature of 750 °C is maintained. This is particularly important if the proportion of long-wave electromagnetic radiation with wavelengths of 575 nm and greater is to be achieved by introducing chemical compounds that require a chemical reaction. This is particularly advantageous when introducing hydrocarbon compounds.

[0022] In addition to oils, hydrocarbon-containing process gases such as pyrolysis gases, gasification gases, or flare gases, or other gaseous hydrocarbons such as propane or butane, can also be used to advantageously influence the spectrum of electromagnetic radiation used for heat treatment and melting. Other gases with sufficiently broad absorption bands can also be used, especially carbon-free gases (e.g., NH3) or gas mixtures ("Radiation of gases and vapors").

[0023] If contaminated or toxic hydrocarbon compounds are introduced, they should be introduced into the process gas stream in such a way that these chemical compounds are broken down due to the prevailing temperatures and gas composition. Contaminated or toxic hydrocarbon compounds can include, for example, oils used for cooling in transformers. These can also include spent thermal oils for heating or cooling high-temperature processes, oil or tar condensates from pyrolysis processes (biogenic residues), solvent waste, biogenic or mineral oils, or waste oils.

[0024] Thus, the process according to the invention can also be used for safe disposal, since the hazardous components can be chemically converted into non-hazardous or significantly less hazardous components and at the same time can be used to increase the efficiency during heat treatment and melting.

[0025] Hydrocarbon compounds, in particular, can be introduced directly into the hot process gas stream, providing sufficiently high temperatures for decomposition through chemical reaction(s). This leads to the complete decomposition and oxidation of the hydrocarbons. For example, aromatics such as toluene, benzene, phenol, xylene, or furan.

[0026] (e.g. toluene: C7H S + W24H2O + 7CO2) and polycyclic aromatic hydrocarbons such as naphthalene, fluorene or pyrene

[0027] (Example: Naphthalene: C W H S + 1202— 4H2O + 10CCU) can be rendered harmless.

[0028] The concentration of CO2 released in the flue gas when using these additives is extremely low due to the very low dosage / admixture. However, chemical elements and chemical compounds added according to the invention can also be added directly or at a distance of preferably no more than 50 mm after the process gas stream exits the device.

[0029] The method according to the invention can be carried out using a device as described in DE 10 2022 207 481 A1. Reference is made to the entire disclosure of this document.

[0030] In this device, a process gas flows through a first internally hollow body at a predeterminable volume flow from an inlet to an outlet. The first internally hollow body is enclosed or surrounded by at least one electrical coil which is connected to an electrical voltage source with which alternating voltage or a pulsed direct voltage is applied to the electrical coil. With the at least one electrical coil, heating by electrical induction of the first internally hollow body or at least one metal body which is / are arranged inside the first internally hollow body can be achieved. In this case, the process gas flows along the inner wall of the first internally hollow body and / or the surface, preferably the outer surface of the at least one metal body, for its heating.The first internally hollow body and the at least one metal body are each formed from a material whose melting temperature is greater than the maximum temperature of the heated process gas.

[0031] The first internally hollow body and / or the at least one metal body can be formed from a steel and / or a refractory metal and / or its alloys—in particular a tantalum-, tungsten-, niobium-, or molybdenum-based alloy. In a base alloy, the aforementioned metals are contained at a level of at least 50% by mass. However, the first internally hollow body can also be formed from a refractory material, in particular quartz glass, Al2O3, ZrO2, or MgO, which cannot be heated inductively. This is particularly the case if the at least one metal body is arranged in its interior and is heated inductively. Several metal bodies can also be arranged as loose beds and / or composite bodies inside the internally hollow body, around which the process gas flows, and the process gas is heated along the flow path from the inlet to the outlet.

[0032] The process gas can be air, but also any other gas or gas mixture that may be beneficial for the respective heating process. This particularly includes inert gases that can prevent any influence on the elements, materials, and objects to be heated.

[0033] The metal body can be designed in the form of a screw, in which the process gas to be heated flows through the turns of the screw, or in the form of a spiral. The enlarged surface area of ​​the at least one metal body can be advantageously utilized for heat transfer to the process gas. However, it is also possible to use metal bodies with contoured elements (elevations, depressions) to enlarge the total surface area of ​​the at least one metal body.

[0034] It is also possible for the at least one electrical coil to enclose a second internally hollow body made of a metal, in addition to the first internally hollow body made of a non-metallic material, and the at least one metal body. The second internally hollow body can be made of a suitable metal or a suitable ceramic, and the first internally hollow body can be made of a non-metallic material, in particular a ceramic material. Both internally hollow bodies should have a sufficiently high melting point.

[0035] A fireproof closure element can be arranged at the inlet to the process gas device to prevent backflow of the heated process gas. This reduces energy and, in particular, heat losses, and ensures that the process gas enters exclusively through the appropriately dimensioned inlet. The first internally hollow body and the Meta II body, as well as any second internally hollow body, should be tubular. The body(s) could also have other geometries of their internal free cross-sectional areas and / or their surfaces. However, the tubular shape offers advantages in terms of flow and due to the relatively large surface area, which contributes to heating the process gas.

[0036] The first internally hollow body can be enclosed by a second and / or a third internally hollow body, so that process gas flows through a gap between the first internally hollow body and the second internally hollow body and / or through a gap between the second internally hollow body and the third internally hollow body, in countercurrent or cocurrent to the process gas flow, to heat the process gas. This enables effective preheating of process gas and utilization of waste heat.

[0037] In the invention, the temperature of the process gas exiting the outlet can be controlled by adjusting the process gas volume flow and / or the electrical power with which the at least one electrical coil is operated. For this purpose, the temperature of the process gas at the outlet can be determined.

[0038] Process gas flows through the device, exits as hot gas and can be used as a hot gas flare.

[0039] A key factor for efficiency is the good heat transfer from the metal body(s) to the flowing process gas. A tube-in-tube solution with several hollow bodies can achieve thermal insulation and preheating of the process gas, thus improving efficiency.

[0040] The at least one chemical element or the at least one chemical compound can be introduced into the interior of an internally hollow body or into the hot process gas stream after the hot process gas stream has exited the device in order to achieve the desired influence according to the invention on the radiation spectrum of the electromagnetic radiation used to heat melting material or a melting tank.

Claims

Patent claims Method for the heat treatment and melting of solids, in particular metal or glass, in which at least one hot process gas stream, which is directed by inductive heating of at least one body, through and / or past the process gas to be heated in the direction of the solid to be heat treated or melted or at a distance along or directly onto the surface of the solid to be heat treated or melted or a melting tank, and the heating of the at least one body is achieved by an electrical coil enclosing the latter, which is connected to an electrical AC voltage source or a pulsed electrical DC voltage source, wherein at least one chemical element and / or at least one chemical compound is / are introduced into the hot process gas stream,by which the ion(s) are converted into an excited state with the heat of the process gas stream, or at least one chemical reaction is initiated, so that the proportion of electromagnetic radiation directed at the heat-treatment or melting material with wavelengths of > 575 nm is increased by at least 10% of the total spectrum of electromagnetic radiation. A method according to claim 1, characterized in that the process gas stream is directed at an angle between 0° and 20° relative to the surface of the solid, heat-treatment or melting material, or the surface of a melting tank.

3. Method according to one of the preceding claims, characterized in that Na, Ca, Sr, Li, Rb, Mg or carbon is used as the chemical element or as the chemical compound in which at least one of these chemical elements is contained.

4. Method according to one of the preceding claims, characterized in that the at least one chemical element and / or the at least one chemical compound is supplied in a proportion of greater than 0 to 15 vol.% in relation to the supplied process gas stream.

5. Method according to one of the preceding claims, characterized in that the at least one chemical element or the at least one chemical compound is fed into a region of the process gas stream in which a minimum temperature of 750 °C is maintained.

6. Method according to one of the preceding claims, characterized in that a salt or a hydrocarbon compound is used as at least one chemical compound.

7. Method according to one of the preceding claims, characterized in that the proportion of electromagnetic radiation with wavelengths > 575 nm is increased by at least 30%.

8. Method according to one of the preceding claims, characterized in that contaminated or toxic hydrocarbon compounds are introduced into the sphere of influence of the process gas stream in such a way that, due to the high temperatures and the prevailing gas composition, chemical compounds are broken down and thus the proportions of contaminated or toxic compounds contained in the process gas stream are substantially reduced.

9. A process according to any one of the preceding claims, characterized in that solid, gaseous or liquid products from the thermal cracking or gasification of biomass, residues, waste precipitation or fossil fuels as chemical compound(s).