Compact solar reactor for recycling metals

Abstract

The invention relates to a device for melting metal by means of solar energy, the device comprising a crucible (11) able to contain a liquid metal and a gas-tight enclosure (9, 13), wherein the enclosure contains the crucible, the crucible being in mechanical contact with the enclosure, wherein the enclosure comprises a first duct (7) configured for the introduction, into the enclosure and into the crucible, of divided solid metal, a second duct (14) configured for the removal, from the crucible and the enclosure, of liquid metal, and a third, optical duct (15) configured for the entry, into the enclosure and into the crucible, of sunlight (4), wherein the first duct comprises a first isolation valve (1.b) for gases, the second duct comprises a second isolation valve (1.c) for gases, and the third duct comprises a window (6) transparent to sunlight.

Description

[0001] Compact solar reactor for metal recycling.

[0002] Description

[0003] For the purposes of the application, the following definitions apply:

[0004] "Metal": Simple body, endowed with a particular luster (metallic luster), good conductor of heat and electricity, and forming, by combination with oxygen, basic oxides.

[0005] "Alloy": A metallic product obtained by incorporating one or more elements into a main component which is a metal.

[0006] "Shade": Variety of a metal-based alloy, defined by its chemical composition.

[0007] "Steel": an alloy whose main component is iron and containing a small amount of carbon (between 0.02% and 2% by mass).

[0008] "Stainless steel": steel containing chromium (at least 10.5% by mass).

[0009] “Titanium alloy”: an alloy whose main component is titanium.

[0010] “Recycling”: recreation of a product from residues resulting from its use or production.

[0011] “Crucible”: a heat-resistant or refractory container capable of containing molten metal.

[0012] “Means of tilting a crucible”: mechanical means allowing the tilting of a crucible filled with molten metal to pour this metal into a mold or ingot mold.

[0013] "Smelting or smelting or steelmaking under controlled atmosphere": Technique consisting of enveloping a crucible and its tilting means with a fluid-tight envelope or shell making it possible to isolate the crucible and the tilting means from the atmosphere outside the shell to operate inside the shell, either under vacuum (VIM melting technique or in English

[0014] "Vacuum Induction Molding") or under an inert atmosphere (nitrogen, carbon dioxide, etc.)

[0015] "Isolation valve" or "gas isolation valve": A gas-tight valve used or usable for VIM technology.

[0016] “Refractory” means a property of resistance of a material, particularly to heat.

[0017] “Slag” means the slag on the surface of a molten metal. This application concerns the field of recycling high-quality alloys and metals such as stainless steel grades or titanium alloys.

[0018] This application relates more particularly to the recycling of scraps and chips of high-quality alloys and metals by melting these materials using solar energy supplied by a concentrator, in a solar reactor.

[0019] The art prior to the present application discloses, in the field of steelmaking or metal melting, systems for melting and forming alloys or metals into ingots, in particular under a controlled atmosphere or under vacuum, from shavings of these alloys or metals and by means of electrical energy, mainly by induction.

[0020] These systems usually include a crucible, a raw material feed chamber for the crucible, a means for heating the crucible by electrical induction and a pourer or mechanical means for tilting the crucible to pour its contents in the form of liquid phase metal into a mold or ingot mold in which the ingots are cooled in the form of solid phase metal ingots.

[0021] To operate under a controlled atmosphere or vacuum (VIM), all of these elements are enclosed in a gas-tight shell or envelope. In this configuration, a layer of vacuum or inert gas ensures optimal thermal insulation between the crucible and its contents and an ambient atmosphere surrounding the shell. The conversion efficiency of the heat energy communicated to the contents of the crucible relative to the electrical power supply is thus optimal. In particular, in the case of a vacuum layer, the heat exchanges between the crucible and the envelope are reduced to radiation between the crucible and the shell.

[0022] However, the footprint of this type of installation is significant and in practice it cannot simply be fitted with a transparent window for solar energy supply to the crucible and easily transported to the focus of an existing solar concentrator.

[0023] To reduce the bulk of steelmaking systems powered by solar energy, the prior art discloses systems in which a shell, made of a heat-refractory and low thermal conductivity material, is in mechanical contact with a crucible contained in the shell. However, it is desirable to be able to control the oxygen content of the atmosphere in contact with a molten metal in order to avoid oxidation thereof and this result is obtained by making the shell gas-tight. The art prior to the present application finally discloses less bulky solar reactors operating under a controlled atmosphere, for melting metal using solar energy, which consist of a crucible and a casing or shell, containing the crucible, in mechanical contact with the crucible and provided with a removable cover comprising a transparent window.

[0024] In these solar reactors, the compactness is optimal between the shell and the crucible, these two elements being in mechanical contact. The dimensioning of the crucible is therefore defined by the maximum volume of the quantity, that is to say the weight of metallic material to be produced per casting. As this volume of material is maximum for chips of material, the dimensioning of a crucible in a solar reactor is therefore governed by the volume of chips of a weight to be produced per casting.

[0025] The ratio between the weight of the molten material and the volume of the crucible used to melt it under a controlled atmosphere is therefore, for the prior art, a constant in the field of solar reactors operating under a controlled atmosphere. This constant is equal in the prior art to the density of the chips.

[0026] Increasing the compactness of a solar reactor, defined as the ratio between the weight of the liquid metal produced, divided by the volume of the crucible necessary to produce this weight under a controlled atmosphere, is thus a difficult problem for the prior art.

[0027] In practice, the art prior to the present application is limited to solar melting under a controlled atmosphere of aluminum at a temperature of 800°C. The melting of high melting point alloys of the order of 1600°C is thus, in practice, unimaginable in the prior art.

[0028] In this context, the invention relates to:

[0029] A device for melting a metal by means of solar energy, comprising a crucible adapted to contain a molten metal and a gas-tight envelope, wherein the envelope contains the crucible, wherein the crucible is in mechanical contact with the envelope, wherein the envelope comprises a first path configured for the entry, into the envelope and inside the crucible, of metallic material in divided solid form, a second path configured for the exit, out of the crucible and out of the envelope, of metallic material in liquid form and a third optical path configured for the entry, into the envelope and inside the crucible, of sunlight, wherein the first path comprises a first isolation valve for gases, wherein the second path comprises a second isolation valve for gases and wherein the third path comprises a transparent window for sunlight. In variants:

[0030] - the crucible is made of refractory concrete.

[0031] - the casing is made of refractory ceramic.

[0032] - the window is made of quartz.

[0033] - refractory ceramic is in the form of fibers.

[0034] - the first way and the second way are one and the same way and the first isolation valve and the second isolation valve are one and the same valve.

[0035] The present application also relates to a method for heating, under a controlled atmosphere, the interior of a crucible, using solar energy, comprising the following steps:

[0036] - create a controlled atmosphere, in a gas-tight envelope containing a crucible

[0037] - creating the controlled atmosphere in a first feed chamber containing a metallic material, in divided solid phase;

[0038] - open a first gas isolation valve, between the first chamber and the envelope;

[0039] - transport the metallic material from the first chamber to the inside of the crucible, via the first gas isolation valve;

[0040] - close the first gas isolation valve;

[0041] - melt the metallic material, by means of sunlight penetrating inside the crucible via a transparent window in the envelope.

[0042] - repeat the previous steps to gradually fill the crucible with molten metal material.

[0043] In one variant the method comprises the following additional steps:

[0044] - create the controlled atmosphere in a second feed chamber containing an ingot mold;

[0045] - open a second gas isolation valve, between the second chamber and the casing; - flow the molten metallic material, from inside the crucible to the ingot mold via the second gas isolation valve;

[0046] - close the second gas isolation valve.

[0047] The invention will be better understood by referring to the numbers indicated in the text of this application to the list of figures below, in which:

[0048] Fig. 1: Figure 1 shows a solar reactor which comprises a crucible made of refractory material or material resistant to a molten metal. The crucible is surrounded by a jacket or shell which is refractory to the heat of the crucible and gas-tight. The jacket comprises a first path or interface or passage or channel or conduit, which is a feed path for raw material. The first path is closed by a first gas-tight isolation valve, in the closed position. The first valve can be controlled to occupy an open position and to allow in this position, the passage of divided material, especially in the form of chips, through the first valve and the transport of the divided material from the outside of the jacket to the inside of the crucible, via the first path. The jacket comprises a second path or interface or passage or channel or conduit, which allows the evacuation of a molten metal. When molten metal is not evacuated, ieduring melting under controlled atmosphere of solid metallic material contained in the crucible, the second path is closed by a second isolation valve in a closed and gas-tight position. When the evacuation of the molten metal is required, the valve is retracted or put in an open position allowing the passage of the molten metal through the second path of the envelope, without damage to the second valve. In addition, the envelope comprises a third path, which is a solar energy supply path, permanently closed and gas-tight, by a transparent window for sunlight. The window is configured opposite the interior of the crucible from an optical point of view, i.e. so that sunlight passing through the window illuminates the interior of the crucible via the third path.Furthermore, a fourth way or interface of the envelope is configured to allow the connection of known means of sucking the atmosphere from the envelope or shell to create a vacuum therein and to bring an inert gas or a controlled atmosphere into contact with the interior of the crucible.

[0049] The various aspects of the present application will be better understood according to the description below of detailed embodiments, given as non-limiting examples.

[0050] In a first embodiment, with reference to Figure 1, a crucible (11) made of refractory concrete or sintered ceramic, capable of containing a molten metal (12) is used. The material chosen must be heat resistant, be chemically inert with the molten metal and be resistant to erosion due to the acidity of the molten metal and the slag.

[0051] In the crucible (11), a sample collector (10) of the casting is arranged.

[0052] The crucible is placed in a metal casing (9) containing a refractory material (13) made of brick or ceramic fibers.

[0053] The casing (9) is provided with a first supply path (7) between the exterior and the interior of the casing. Throughout the present application, the term supply path is understood to mean: a channel, a passage or a conduit provided in the casing, which allows material or energy to be conveyed, thus fulfilling the function of interface between the interior of the crucible and the casing constituted as a thermodynamic system and the exterior of the casing constituted as a thermal reservoir in the sense of thermodynamics.

[0054] The first feed path or first interface is a feed path for the crucible of metallic material (8) divided into chips and contained in a material feed chamber (2. a), for the purpose of melting these chips in the crucible after introduction into the casing.

[0055] The first channel is closed during melting by a first isolation valve (lb) in the closed position, which provides gas sealing and maintains a controlled atmosphere during the melting or melting of the metal shavings.

[0056] The material feed chamber (2. a) is connected for its material outlet to the first isolation valve (lb) and limited on the other hand by another isolation valve (la) for its material inlet.

[0057] Prior to melting, a gas-tight container (the material feed chamber) containing chips to be melted can thus be connected to the first valve in a gas-tight manner, then the uncontrolled atmosphere can be removed from the container by vacuum pumping means (3.a) and replaced with a controlled atmosphere, in particular identical to that present inside the casing.

[0058] Once the atmospheres on both sides of the first valve have been made equal or equivalent for melting metals (especially without oxygen), the first valve is opened, i.e. is placed in the open position to the extent necessary to allow the passage of chips into the casing, filling the crucible. Then, once the chips have been introduced, the first valve is closed again, and thereby made gas-tight.

[0059] The shavings are then melted and gradually fill the crucible with molten metal (12).

[0060] By repeating the introduction of chips and their melting, without losing the controlled atmosphere, it is then possible to advantageously fill the crucible with a volume of molten metal comparable to the interior volume of the crucible and no longer only equal to the volume of chips filling the crucible. In addition, in this repetition, the thermal contact between the already melted metal and the new chips introduced is advantageously more intimate at each introduction, which makes it possible to improve the heat transfer to the chips and reduce their melting time, an element favorable to the use of solar energy for the melting or casting of metallic material during the repetition.

[0061] The molten metal is finally discharged after repeating the steps mentioned above, via a second feed path (14) or second interface which is here a path for discharging the molten metal from the inside of the crucible to the outside. This second path is provided with a second isolation valve (lc), which is in the closed position during the introduction of the chips and during their melting, to maintain the composition of the controlled atmosphere in contact with the inside of the crucible, i.e. inside the envelope, invariant.

[0062] The melting of the chips is obtained by supplying solar energy (4) via a third optical path (15), most simply consisting of a window (6) made of a material transparent to sunlight (4), such as quartz or sapphire. This third path is optically configured so that sunlight, incident on the window, illuminates the chips present in the crucible or the molten liquid metal containing the chips inside the crucible. Most simply, the window is opposite the interior of the crucible, i.e. the interior of the crucible is visible to an outside observer. In order to increase the collected solar energy, a solar concentrator, for example of the parabolic mirror type, will be used to provide a convergent beam, by placing the transparent window of the envelope between the parabolic mirror and the optical focus of this mirror.

[0063] Means for mechanical handling of the crucible for the easy introduction of chips, via the first path (7), for example by gravity, into the crucible, in the sense of into the hollow or concavity of this crucible, may be provided without departing from the teaching of the present application. Similarly, means for mechanical handling of the crucible for pouring the molten metal into an ingot mold (2. b), via the second path (14), for example by gravity, from the crucible, may be provided without departing from the teaching of the present application.

[0064] Advantageously, the ingoting will be carried out under a controlled atmosphere identical to that above the contents of the crucible, by connecting a gas-tight ingot mold (2. b) connected to the second valve (lc) in the closed position and isolated from the outside by an outlet valve (ld) for the ingots (5), by pumping the internal atmosphere of the ingot mold and replacing it with a controlled atmosphere identical or equivalent to that inside the casing (9), then by opening the second valve (lc) and by flowing the molten metal into the ingot mold (2. b), via the second channel (14) and under the controlled atmosphere, made homogeneous in the casing and the ingot mold, into the molds of the ingot mold (5) to form the molten metal into ingots after cooling, by closing the second valve (lc) and sending the ingots to the outside via the outlet valve of the ingot mold (ld) placed in the open position.

[0065] For the third channel (15) of the envelope, which is optical and separated from the material inlet (7) and liquid outlet (14) channels of the envelope, it will be possible, without departing from the present application, to provide a hole forming a field diaphragm in order to limit the emission of infrared radiation from the molten metal outside the envelope. This hole may have the shape of a hole, a cone or a neck or bottleneck without departing from the teaching of the present application.

[0066] One of the advantages of this first embodiment is that it allows the use of a crucible of the size of the volume of liquid to be produced and not of the size of the volume of chips of the same weight, which makes it possible to minimize the size of the crucible, and therefore of the envelope which contains it, and thus to improve the compactness of the solar reactor designed according to the principle of the present application.

[0067] Another advantage of this increased compactness is lower thermal inertia and therefore lower heat losses, enabled by less heating of the envelope, which improves the efficiency of converting solar energy into latent heat in the molten metal.

[0068] Another advantage of this increased compactness is a more intense illumination on the slag, which approaches the focal plane of the field diaphragm as the chips are converted into liquid, whereas in the prior art, the slag moves away from the focus as the chips are converted into liquid, resulting in reduced illumination. These advantages make it possible either to reach a higher temperature in the same time, or to reach a given temperature in less time. This is particularly favorable for the use of a variable source such as the sun depending on climatic conditions and subject to alternating day and night.

[0069] Other embodiments than that presented may be mentioned without departing from the teaching of the present application.

[0070] In a second embodiment, the first and second ways are identical, the first valve and the second valve being the same valve, i.e. a single valve. To achieve this embodiment, means will be used to position the chips above the crucible, i.e. by mechanically arranging the single valve at an altitude higher than that of the crucible, so as to allow the chips to fall into the crucible, by gravity. Then, once all the chips have melted in the crucible, the single valve will be mechanically arranged at an altitude lower than that of the crucible, so as to allow the flow of the molten metal from the crucible.

[0071] In this second mode, the first and second paths are in the form of a single path, which fulfills a function of input and output of material under controlled atmosphere with fusion by means of solar energy, the material being in distinct phases at input and output (divided phase at material input, liquid phase at material output). By comparison, in the first mode, the first path is a material input path in divided solid phase and the second path a material output path in liquid phase.

[0072] Variant embodiments of the methods presented may be cited without departing from the teaching of the present application.

[0073] The third optical path can thus be adapted to a given mirror concentrator, whose average ray passing through the center of the mirror and the focus of the concentrator is horizontal, oblique or vertical. In the horizontal case, for example, a mirror at 45 degrees from the horizontal and a vertical crucible surmounted by a horizontal transparent window can be used. A person skilled in the art of optics will easily determine how to illuminate the interior of the crucible through the transparent window, depending on the optical characteristics of the convergent concentrated solar beam provided by a given solar concentrator.

[0074] The vacuum pumping and gas inlet or injection means (3. a) via the fourth channel for controlling the atmosphere inside the crucible casing can also be isolated by valves and used to define pumping and atmosphere injection in the material inlet chamber as well as in the ingot mold, so as to minimize the size and the number of additional elements necessary to carry out a complete melting from the material inlet and the ingot outlet, under a controlled atmosphere.

[0075] Alternatively, separate means (3. b) from those dedicated to the crucible (3. a) may be used to create a controlled atmosphere in the chip material inlet chamber (via 3. a) or in the outlet chamber or ingot mold (via 3. b).

[0076] The invention is susceptible to industrial application or useful or usable, in the field of solar reactors for the steel industry and especially in the recycling of shavings of metallic material with a high melting point, in particular sorted by shade.

[0077] The criterion for the devices of the present application, in all its modes, ultimately appears to be the presence of physically separate and gas-tight circuits, for the transport of material to and from a crucible on the one hand and the solar heating of the material in the crucible on the other hand.

[0078] A structure conforming to this criterion allows the material to be melted to be introduced into a crucible under a controlled atmosphere, in several times, filling the crucible each time and insulating the material circuit as much as necessary to maintain this controlled atmosphere, which ultimately allows the use of a smaller crucible for the same weight of liquid produced compared to a crucible into which all of the material to be melted by solar energy is introduced in one go.

[0079] The invention is applicable to the melting of aluminum at 800°C, with a gain in thermodynamic efficiency compared to previous solutions, the reactor being more compact, but also to the melting of alloys sorted by grade melting between 1500°C and 1600°C such as stainless steels and titanium alloys and more generally for the melting of materials with a melting temperature to which the crucible and the envelope resist.

[0080] In order to quantify the advantages of the invention, it is possible to numerically simulate the temperature as a function of time for a crucible of the prior art filled with chips in one go and a crucible according to the invention progressively filled with chips melted in a fractional manner.

[0081] For a solar flux of the same power, 1300°C will be reached in 4 hours for a crucible capacity of 2500ml without the invention, the chips corresponding to a weight of 5kg being inserted in one go, against 1 hour for a capacity of 625ml with the invention, the chips being inserted in several times, for the same weight of final steel produced of 5kg.

[0082] The steel scraps or shavings used are considered in practice to be 4 times less dense than solid steel, the gain in volume of the crucibles is thus in the same ratio (625 ml x 4 = 2500 ml), and we thus obtain a time for the vacuum reactor to reach 1300°C divided by 4 if the useful volume allows it to contain molten metal rather than shavings.

[0083] For the purposes of selecting an isolation valve and arranging such a valve in a manner suitable for the methods of the present application, a person skilled in the art may take into account the maximum operating temperature of the valve and, if necessary, cool the gases in contact with the valve to avoid damage to the valve; he may also avoid direct contact of the valve with the molten metallic material, in particular at the ingot stage. The isolation valves of a VIM installation may be preferred for all the methods of the present application. Valves used in other technical fields may also be used provided that they are gas-tight and resistant to the temperature of the casing in their position. A worm screw may thus be used for introducing the solid metallic material into the crucible.For the molten metal outlet, a guillotine valve made of a material resistant to a temperature as close as possible to the metal to be melted and using silicone seals capable of withstanding temperatures of the order of 1400°C may be used; its free internal diameter once the valve is open will generally be chosen to be larger than the diameter of the material outlet path, to prevent molten metal flowing out of this path towards the ingot mold. This general criterion must be met by the molten metal outlet valves of all embodiments of the present application, in order to avoid the risk of contact of the valve with molten metal to be ingoted.

[0084] The sample collector (10) of the molten metal (12) can be included in all the modes of the present application to determine the composition of the molten metal (12) in the crucible (ll) during its progressive filling, and to modify the material (8) introduced, via the material inlet path (7) to correct a composition, in particular to produce a shade.

Claims

Claims 1. Device for melting a metal by means of solar energy, comprising a crucible (11) capable of containing a molten metal and a gas-tight envelope (9, 13), in which the envelope contains the crucible, in which the crucible is in mechanical contact with the envelope, in which the envelope comprises a first path (7) configured for the entry, into the envelope and inside the crucible, of metallic material in divided solid form, a second path (14) configured for the exit, out of the crucible and out of the envelope, of metallic material in liquid form and a third optical path (15) configured for the entry, into the envelope and inside the crucible, of sunlight (4), in which the first path comprises a first isolation valve (lb) for the gases, in which the second path comprises a second isolation valve (lc) for the gases and in which the third path comprises a window (6) transparent for sunlight.

2. Device according to claim 1 in which the crucible (11) is made of refractory concrete.

3. Device according to claim 1 in which the casing (9, 13) is made of refractory ceramic.

4. Device according to claim 1 in which the window (6) is made of quartz.

5. Device according to claim 3 in which the refractory ceramic is in the form of fibers.

6. Device according to claim 1 in which the first way and the second way are one and the same way and the first isolation valve and the second isolation valve are one and the same valve.

7. Method for heating, under a controlled atmosphere, the interior of a crucible, using solar energy, comprising the following steps: - create a controlled atmosphere, in a gas-tight envelope containing a crucible - creating the controlled atmosphere in a first feed chamber containing a metallic material, in divided solid phase; - open a first gas isolation valve, between the first chamber and the envelope; - transport the metallic material from the first chamber to the inside of the crucible, via the first gas isolation valve; - close the first gas isolation valve; - melt the metallic material, by means of sunlight penetrating inside the crucible via a transparent window in the envelope. - repeat the previous steps to gradually fill the crucible with molten metal material.

8. Method according to claim 7 comprising the following additional steps: - create the controlled atmosphere in a second feed chamber containing an ingot mold; - open a second gas isolation valve, between the second chamber and the envelope; - flow the molten metal material from inside the crucible to the ingot mold via the second gas isolation valve; - close the second gas isolation valve.

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