Salt-free recovery of metal from scrap in a plasma furnace

Abstract

The present technology relates to a a process for recycling metal scrap in order to recover said metal. The process comprises: (a) charging a batch of the metal scrap into a furnace, (b) closing a door of the furnace equipped with a seal and on which a plasma torch is installed, to enclose a charged material; (c) starting the plasma torch, (d) heating of the charge to a temperature above a volatilization point of organic compounds present in the charge, (e) removing recoverable free metal from the furnace; (f) injecting an amount of an oxidizing gas into the furnace or starting the plasma torch while rotating or oscillating the furnace, (g) stopping an oxidation reaction by providing an inert atmosphere in the furnace by filling the furnace with inert gas; and (h) removing at least a portion of the non- metallic product.

Description

SALT-FREE RECOVERY OF METAL FROM SCRAP IN A PLASMA FURNACE FIELD

[0001] The present technology relates to a process for the recovery of metal from scrap and, to a process for recycling metal scrap in order to recover the metal therefrom. The present technology also relates to an apparatus for carrying out these processes.BACKGROUND

[0002] Post-consumer metal scrap recycling has progressed significantly over the last decades due to increased interest in preserving natural resources and minimizing energy consumption, with the additional benefit of improving profitability. This trend has also proven beneficial to climate change and global warming situation by reducing greenhouse gas emissions compared to the primary production of metal from raw natural resources.

[0003] Conventional processes for recovering metal from post-consumer scrap, particularly aluminum, generally involve the use of fossil fuel burners to melt the metal and of salt fluxes to minimize metal losses through oxidation. This is typically carried out either in a reverberatory or rotary furnace, for example as depicted in U.S. Patent No.7,655,067, incorporated herein by reference.

[0004] U.S. Patent No. 10,669,609 and U.S. Patent No. 5,057,194, both incorporated herein by reference, highlight the high salt usage typical of conventional processes which is not only costly, but also generates a hazardous residue, known as salt cake, which must be dealt with. Even though reducing salt usage is certainly an attractive advancement in aluminum recycling, other breakthrough solutions must be developed to minimize greenhouse gas emissions and environmental consequences related to the recycling activities.

[0005] Canadian Patent No. 2,178,864, incorporated herein by reference, highlights the challenges encountered in conventional processes which lose significantamounts of metal through oxidation. The proposed solution of creating an inert zone between the combustion gases and the metal charge, despite having interesting benefits, has not been implemented widely in industry and still does not address the need to eliminate fossil fuels.

[0006] Accordingly, there is a substantial need in the market for new and improved technology to recover metal from post-consumer aluminum scrap, which requires neither fossil fuels nor salt fluxes. In line with the emerging circular economy movement, such a technology would ideally generate only non-hazardous by-products that can be reused in other applications and atmospheric emissions that comply with the most stringent legislation. To ensure economic viability and competitiveness, metal oxidation, or dross yield, should be minimized.

[0007] Using plasma as a heat source instead of fossil fuel burners has been proposed in the past, as depicted in U.S. Patent No. 4,877,448 and in U.S. Patent No.4,960,460, both incorporated herein by reference. Plasma offers the advantage of using electricity to render the process carbon neutral. However, this has been mostly applied to aluminum dross and not scrap. Processing scrap adds the challenge of dealing with organic contaminants, such as coatings and lacquers, so a new technology and method of operation must be developed.

[0008] European Patent No. EP 4 00 925, incorporated herein by reference, proposes the use of plasma to melt aluminum scrap, but the process continues the use of salts, as well as inert gas to volatilize organic contaminants which are treated in a postcombustion chamber to ensure respect of atmospheric emission limits. The additional downstream equipment adds significant capital cost, operating cost, and complexity to the process. This concept is similar to U.S. Patent No. 5,846,480, incorporated herein by reference, which employs fossil fuel burners instead of plasma torches. U.S. Patent No.8,685,139, incorporated herein by reference, also uses conventional burners, but in this case the organic contaminants are volatilized prior to melting.

[0009] In view of this, there is a need in the art for new and improved technology to recover metal from post-consumer aluminum scrap, which requires neither fossil fuels nor salt fluxes.SUMMARY OF TECHNOLOGY

[0010] It would thus be desirable to provide a novel process and apparatus for recycling metal scrap.

[0011] In one embodiment, the present technology relates to a process for recycling metal scrap in order to recover said metal, the process comprising: (a) charging a batch of the metal scrap into a furnace, preheated to a temperature suitable for minimizing energy requirements during the process; (b) closing a door of the furnace equipped with a seal and on which a plasma torch is installed, to enclose the charged material; (c) starting the plasma torch or making the charge move at least intermittently within the furnace; (d) heating of the charge to a temperature above the volatilization point of organic compounds present in the charge and above the melting point of the recoverable metal, a separation thereof from a non-metallic product and from the filling material and its agglomeration at the bottom of the furnace for melting of the charge; (e) removing from the furnace recoverable free metal; (f) injecting an amount of an oxidizing gas into the furnace or starting the plasma torch while rotating or oscillating the furnace, so as to oxidize sufficient non-recoverable metal within the filling material to evenly heat and store in the furnace walls and filling material sufficient energy for treating a new batch of scrap and / or thermally decompose salts, organic and / or chemical compounds; (g) stopping the oxidation reaction by providing an inert atmosphere in the furnace by filling the furnace with inert gas; and (h) removing at least a portion of the non-metallic product.

[0012] In some instances, the furnace is a rotary or a reverberatory-type furnace.

[0013] In some instances, the furnace comprises a filling material.

[0014] In some instances, step (c) of the process further comprises rotation of the furnace.

[0015] In some instances, the rotation is performed continuously.

[0016] In some instances, the rotation ensures transfer of heat between the plasma, walls of the furnace and charge.

[0017] In some instances, in step (d) of the process, heat is provided by the plasma torch.

[0018] In some instances, in step (d) of the process, heat is provided by overheating from a previous batch. In some instances, the overheating is by at least an additional 100°C.

[0019] In some instances, removal of the recoverable free metal from the furnace is performed through a taphole or through a door. In some instances, at least a portion of a non-metallic product is also removed. In some instances, at least a portion of the filling material and at least a portion of non-recoverable metal are left in the furnace. In some instances, at least a portion of the non-metallic is removed through the door. In some instances, at step (h), at least a portion of the filling material is left into the furnace.

[0020] In some instances, the process further comprises, after step (h), charging into the furnace a new batch of scrap. In some instances, after charging the new batch into the furnace, steps (a) through (g) are repeated.

[0021] In another embodiment, the present technology relates to an apparatus for recycling metal scrap comprising: (a) a rotary or reverberatory-type furnace adapted for high-temperature treatment of scrap, said furnace comprising: (i) a chamber for accumulating and conducting heat provided by an exothermic reaction within said chamber, (ii) an opening for charging scrap into the chamber; (iii) a door for hermetically closing said opening during treatment of the scrap; and (iv) a tap-hole for tapping recovered molten metal; (b) rotating element for imparting movement of the scrap in the furnace; (c) a plasma torch system operable on the hermetic door; (d) an injection element for injecting a process gas or a fuel into the furnace; (e) an injection controller for controlling injection of an oxidizing gas into the furnace; (f) a temperature monitoring element for monitoring temperature of the scrap charged inside the furnace; and (g) anexhaust gas monitoring element for monitoring exhaust gas composition, temperature and characteristics, and for adjusting the plasma gas composition.

[0022] In some instances, the furnace further comprises a drum and the door simultaneously rotates with the drum.

[0023] In some instances, the injection element is the plasma torch. In some instances, the injection element is an injection port.

[0024] In another embodiment, the present technology relates to a process for adjusting plasma gas type, the process comprising: (a) after the scrap has been charged into the furnace and during the first stage of heating when the metal is not yet melted and organic contaminants present on the metal charge are hot enough to be volatilized, the main plasma gas used is air for the following reasons: i) it is the cheapest plasma gas available; ii) metal losses through the oxidation reaction are not a concern; iii) a source of oxygen is desirable to combust the volatilized organic compounds and respect stack emissions regulations, especially for carbon monoxide (CO), volatile organic compounds (VOC’s), and nitrogen oxides (NOx); (b) based on an analyzer reading of the exhaust gas composition, once it is determined that organic compounds have been fully volatilized and combusted, as well as once temperature measurements indicate that the charge has reached a temperature above which oxidation is more likely, the main plasma gas can be switched to another gas, including but not limited to nitrogen, for the following reasons: the oxygen present in air would react significantly with the metal, thus increasing metal losses in addition to generating excessive heat and NOx; nitrogen is the second cheapest plasma gas available, much less expensive than argon, for example, which requires much larger volumes to achieve the same level of power when used as a plasma forming gas; nitrogen reacts with the metal to a lesser extent than oxygen, forming nitrides, which can be converted to valuable products by downstream industry; (c) once the metal has been recovered, the unrecoverable metal can be burned to maximize energy efficiency of the process via three options: 1 ) stop the plasma torch and inject oxygen if available, thus not requiring any external source of energy; 2) operate the plasma torch with air as the main plasma gas so that the oxygen present in air can react with the unrecoverable metal; oroperate the plasma torch with pure oxygen to oxidize the unrecoverable metal while minimizing NOx formation and 3) operate the plasma torch with nitrogen as the main plasma gas and inject air separately to control more precisely oxidation of the unrecoverable metal; and (d) once the unrecoverable metal has been oxidized, the plasma torch can continue or resume operation using air as the main plasma gas (nitrogen could also be used as a cost-effective means of minimizing NOx formation).BRIEF DESCRIPTION OF THE DRAWINGS

[0025] For a better understanding of the embodiments described herein and to show more clearly how they may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, which show at least one example of an embodiment of the present technology, and in which:

[0026] Figure 1 is a schematic representation that illustrates the steps used in the process for recovering metal from aluminum scrap, in accordance with an embodiment;

[0027] Figure 2 is a cross-sectional view showing a tilting rotary furnace used for scrap recycling, in accordance with an embodiment;

[0028] Figure 3 is a cross-sectional view showing the tilting rotary furnace with the different layers of material present in the furnace, in accordance with an embodiment; and

[0029] Figure 4 is a perspective view showing a scraping tool used to clean residues from a furnace, in accordance with an embodiment.DETAILED DESCRIPTION OF EMBODIMENTS

[0030] The present technology is explained in greater detail below. This description is not intended to be a detailed catalog of all the different ways in which the technology may be implemented, or all the features that may be added to the instant technology. For example, features illustrated with respect to one embodiment may be incorporated into other embodiments, and features illustrated with respect to a particular embodiment may be deleted from that embodiment. In addition, numerous variations and additions to thevarious embodiments suggested herein will be apparent to those skilled in the art in light of the instant disclosure which variations and additions do not depart from the present technology. Hence, the following description is intended to illustrate some particular embodiments of the technology, and not to exhaustively specify all permutations, combinations and variations thereof.

[0031] As used herein, the singular form “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise.

[0032] The recitation herein of numerical ranges by endpoints is intended to include all numbers subsumed within that range (e.g., a recitation of 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 4.32, and 5).

[0033] The term “about” is used herein explicitly or not, every quantity given herein is meant to refer to the actual given value, and it is also meant to refer to the approximation to such given value that would reasonably be inferred based on the ordinary skill in the art, including equivalents and approximations due to the experimental and / or measurement conditions for such given value. For example, the term “about” in the context of a given value or range refers to a value or range that is within 20%, preferably within 15%, more preferably within 10%, more preferably within 9%, more preferably within 8%, more preferably within 7%, more preferably within 6%, and more preferably within 5% of the given value or range.

[0034] The expression “and / or” where used herein is to be taken as specific disclosure of each of the two specified features or components with or without the other. For example “A and / or B” is to be taken as specific disclosure of each of (i) A, (ii) B and (iii) A and B, just as if each is set out individually herein.

[0035] As used herein, the term “comprise” is used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded.

[0036] The present disclosure introduces a process and an apparatus for recycling metal scrap.

[0037] The steps presented in Figure 1 are described below with reference to the elements of a plasma rotary furnace as shown in Figure 2 and material layers of Figure 3.Step A - Idle

[0038] At the start of operation or in between batches, a preheated furnace 1 is empty or contains a filling material 7, which is leftover non-metallic product from a previous batch. At this step, actions are minimized, meaning the door is kept closed and no rotation or tilting is being done, in order to reduce power consumption and heat losses while ensuring the furnace is ready for operation. A door 2 of the furnace 1 is closed while a plasma torch system 3 is on standby, ready to operate at a low power setting to maintain a minimum temperature of a refractory walls 4, of the furnace 1 , above the volatilization temperature of the organics present in the scrap charge and above the melting point of the metal to be processed. The torch included in the plasma torch system 3 can be built with the same shape and dimensions to fit in a traditional burner port, or can be built with a customized installation port at the door of the furnace to allow for positioning at different angles and / or different penetrations.Step B - Charging

[0039] When a new batch is initiated, a furnace control system or an operator will prepare the furnace 1 to receive a scrap charge by opening the door 2 and adjusting the tilt angle of the furnace to be closer to the horizontal position. It will then wait for confirmation that the charging is complete prior to readjusting the tilt angle and closing the door 2. The door 2 is equipped with seals 5 around the perimeter and a central hole (sealed or not) for the plasma torch 3 to enclose a charged material 8 (Figure 3) and ensure control over the furnace 1 atmosphere (chemistry and pressure). The door 2 may or may not rotate with the drum of the furnace 1. The seals 5 are made of high temperature ceramic ropes containing or not metal wires and adjuvants such as graphite to help reduce friction and increase longevity. The seals 5 are compressed to prevent undesired ambient air ingression, limiting oxidation of the metal, and leaks from the furnace into the surrounding environment.

[0040] Alternatively, after charging and closing the door 2, an inert gas is injected, through the plasma torch, through a separate injection port, or through both, to allow for atmosphere control, for example to minimize dross and NOx formation, but also for quenching and / or stopping of the thermite reaction, in case material charged to the furnace 1 was hot or becomes hot at this step.Step C - Melting

[0041] The melting step is the longest phase of the batch, typically representing about 60% to about 75% of the batch duration, during which the plasma torch 3 is started and the power setpoint is automatically adjusted to allow rapid melting at a heating rate up to between 3°C / min and 5°C / min and precise temperature control of plus or minus 10°C, thus preventing overshoot which could lead to undesirable metal losses and equipment wear as it is known that the higher the metal temperature is above the melting point, the higher the intensity of the thermite reaction. A separate inert gas injection port can also be used for better control over the furnace atmosphere.

[0042] During this step, the furnace 1 is rotated and / or oscillated in a continuous or intermittent manner to ensure proper mixing and transfer of heat between the plasma, the refractory walls 4, the filling material 7 if applicable, and the charge 8. The rotation speed can be adjusted between 1 rpm and 20 rpm while the oscillation is adjustable between -15° and 0° and at a frequency between 0.001 Hz.and 1 Hz. The rotation speed can be monitored, as well as variations in torque or electrical consumption while the drum is rotating in this step C. These measurements can be used as control parameters to adjust the duration of this step.

[0043] Different plasma gases can be used to affect or control the atmosphere inside the furnace 1 during this step depending on availability including but not limited to air, nitrogen, argon, helium, hydrogen, oxygen, methane, carbon dioxide, and other mixtures of gases and / or hydrocarbons, type of scrap being processed and evolution of the melting step. For example, when contaminated scrap is processed, air or oxygen can be used in the early stages to allow full combustion of the organic contaminants from the scrap inside the furnace 1 , or for economic reasons, compressed air being cheaper thanother gases, and to profit from the energy provided by combustion of the organics. Based on measurements from an exhaust gas analyzer 6 reporting for example oxygen, carbon monoxide, carbon dioxide and volatile organic compounds concentration, and exhaust gas temperature, color and opacity, indicating the end of contaminants combustion, the plasma gas can be switched to another gas such as nitrogen or argon to minimize NOx and dross formation during the remainder of the melting step. Similarly, for additional control of the furnace atmosphere, one or more separate gas injection ports can be used to introduce additional inert or oxidizing gas, or to introduce supplemental fuel if needed. When clean scrap is processed, nitrogen, argon or another gas can be used as the plasma forming gas from the beginning of the melting step. If contaminated scrap contains a low contaminant concentration, it may be preferable to use an inert plasma gas and to inject air or oxygen separately from the plasma torch or a separate injection port to control more precisely the atmosphere inside the furnace, minimizing thermite reaction and NOx formation.

[0044] If the receiver of the melted metal, such as a holding furnace or casting machine for example, is not ready when the desired melt temperature is reached, for example about 740°C for aluminum, as indicated by temperature sensors strategically positioned at different locations in the furnace 1, this step becomes similar to the above idle step A to minimize power consumption and metal losses. If a source of affordable inert or other type of gas that will minimize oxidation of the molten metal is available including but not limited to argon, the option exists to inject this gas to further reduce the metal losses due to oxidation and the potential formation of dross inside the furnace 1.

[0045] Alternatively, this step can be executed in the same furnace 1 while keeping the plasma torch 3 in the off position (with or without filling material), by heating the furnace above the preheating temperature that would otherwise be set up for operation with the plasma torch 3 on, which in practice means overheating for instance by at least an additional 100°C of the refractory walls 4.Step D - Tapping

[0046] When the receiver is ready to be filled with liquid metal, for example aluminum, the rotation and / or oscillation of the furnace 1 and the plasma torch 3 are stopped, the door 2 is opened, and a strainer (not shown) is moved into position to prevent undesirable discharge of a non-metallic product 9 and filling material 7 when present (Figure 3). The furnace 1 is tilted in a controlled manner to ensure smooth, constant and safe transition of the molten metal 10. The system will then wait for confirmation that the tapping is complete prior to readjusting the tilt angle of the furnace 1 , removing the strainer, closing the door 2 and resuming rotation and / or oscillation of the furnace 1.

[0047] The same operation can be carried out through a taphole instead of the front door 2.

[0048] At this step D, there is also the possibility to remove a fraction or the entire non-metallic product 9 and the filling material 7 (if applicable) which contains a non-recoverable metal 11.Step E - Controlled thermite reaction

[0049] Now that the valuable recoverable aluminum 10 has been removed, it is possible to improve the energy efficiency of the process by burning the unrecoverable metal 11 trapped in the non-metallic product 9, transferring additional heat (about 8.7 kWh / kg of aluminum) to the refractory walls 4 and to the filling material 7 if applicable. In this step, a source of oxygen can be used for combustion and / or oxidation and to further minimize power consumption, otherwise the plasma torch 3 system can be activated. Further improvement in energy efficiency is possible from the burning of some of the remaining carbon in the non-metallic product from the organics originally present in the charge, as in the case of melting dirty scrap or processing black dross.Step F - Discharge

[0050] When the operator is ready to discharge a fraction or the entire non-metallic product 9 and filling material 7 if applicable, the discharge step will trigger the stopping of the plasma torch system 3 or oxygen injection, as well as the opening of the door 2. Thefurnace 1 can be tilted in a controlled manner (with precision and slowly, using for instance a pendant station or from an HMI) to ensure smooth, constant and safe discharge of the non-metallic product 9 and filling material 7. At the same time, the refractory walls 4 can be cleaned using a scraping tool (also known as scraper), such as a long metal hoe installed on a forklift truck. This scraping tool, as depicted in Figure 4, includes a metal structure 12 with large enough metal channels 13 at a trailing end of the scraping tool, that are adjustable or not, to receive the forks of a forklift or another type of lifting vehicle, and a scraping plate 14 attached at a leading end of the structure 12 made of a high-temperature resisting material such as, but not limited to, stainless steel. In the case of a rotary furnace, the scraping tool is moved forward and backward at different positions along the circumference and / or length of the drum (movements provided by the vehicle where the tool is mounted) and such action dislodges the material accumulated on the walls, which can now be discharged like the rest of the material. The system will then wait for confirmation that the discharge is complete prior to readjusting the tilt angle of the furnace 1 and closing the door 2. The sequence can now return to the initial step (i.e. , idle step). Note that this step can also be carried out prior to the thermite reaction step E.

[0051] Throughout this process, process gases and dust / fumes are exhausted from the furnace 1. These are collected by a fume hood installed above the door 2 and connected to conventional gas cleaning and dust collection equipment (such as fan, baghouse, scrubber, etc.) to comply with local environmental regulations. Composition and other characteristics (such as color) of this exhaust gas mixture can be measured and / or monitored continuously and these measurements can be fed as signals to a control system that will use this feedback to adjust other process parameters such as flow of gas injection into the furnace 1 (through the torch and / or one or more separate injection ports), type of gas or gases injected, or power on or off of the torch system 3 at certain times within the production cycle (above steps A to D).

[0052] In an alternative to the above, the plasma torch 3 is installed in a reverberatory-type furnace (tilting or not), where post-consumer scrap or other type of recycling material is melted or remelted, without the use of salts to minimize oxidation effects (fluxes for alloying may still be required). In this plasma heated system, theconcepts of operation with different plasma forming gases or mixtures of gases, separate injection points, different torch setup configurations (for example, adjustable inclination and / or penetration), atmosphere control, supplemental fuel, burning of organic content, monitoring of the exhaust gases for feedback / control, are applied as described in above steps A through C, while the concept of leaving a filling material inside the furnace 1 as well as the thermite reaction of the filling material 7 described in step E will not apply.

[0053] In another embodiment of the present technology, the material processed is metal dross, including but not limited to aluminum dross, or a combination of dross and scrap. The dross can be hot or cold, white or black, or a combination thereof. Two variations are proposed for this embodiment:

[0054] • when using hot or cold dross, white and / or black, combined or not with scrap, the process is carried out by applying steps A to F. In this case, step C is carried out in a preheated rotary furnace 1, without heating with the plasma torch 3 (or any other source of external heating, including but not limited to a fuel burner), with injection of inert gas (including but not limited to argon or nitrogen) and with rotation (as described above) to facilitate separation of the metal from the non-metallic product. In the case of non-rotary or reverberatory-type furnaces, the rotation is replaced with stirring that may be, but not limited to, from mechanical or electromagnetic action.

[0055] • when using cold dross, white and / or black, combined or not with scrap, the process is carried out by applying above steps A to F, with step E being optional. In this instance, the furnace 1 (with or without filling material 8) is preheated before starting step B. After charging and closing the door 2 in step B, heating with the plasma torch 3 (or any other source of external heating, including but not limited to a fuel burner) can start. As described above, composition or other characteristics from the exhaust process gas, dust / fumes are monitored (automatically or otherwise). In this case, a color or opacity change in the exhaust gas indicates that a thermite reaction of the charged material has started inside the furnace 1. With this information (or other information obtained from the monitoring of the exhaust), the end of this heating stage is triggered. At this point, rapid quenching and stopping of the thermite reaction is carriedout with injection of inert gas and step B is completed. Then, step C is carried out in the furnace 1 (which is still hot above the melting temperature of the metal), without heating from the plasma torch 3 (or any other source of external heating, including but not limited to a fuel burner), with injection of inert gas (including but not limited to argon or nitrogen) and with rotation (as described above) to facilitate separation of the metal from the non-metallic product. In the case of non-rotary or reverberatory-type furnaces, the rotation is replaced with stirring that may be (but not limited to) from mechanical or electromagnetic action.

[0056] In both the above-described variations, step E can be carried out with the plasma torch 3 (or any other external heating source), with or without creating an oxygen rich atmosphere, to carry out thermal decomposition and / or oxidation of chemical compounds, soluble salts, organic matter and any other compounds that may remain in the non-metallic product 9 and filling material 7 (if applicable) at this stage. The chemical compounds may include but are not limited to aluminum nitride (AIN), aluminum carbide (AI4C3), any compound that will produce toxic gases in contact with water. The soluble salts include but are not limited to sodium chloride (NaCI) and potassium chloride (KCI). The organic matter includes but is not limited to compounds such as those found in black dross, secondary black dross or residues of black dross.

[0057] While the process of the present description is described using recycling aluminum (including but not limited to post consumer scrap, excess or reject material from foundries and / or manufacturing facilities, etc.), it is to be understood that, in a variation of the present disclosure, the process can also be applied to the processing of different light metals or dross from those metals or combinations of those metals with their dross, including but not limited to titanium or magnesium scrap, as well as alloys of aluminum, titanium or magnesium.EXAMPLE

[0058] The examples below are given so as to illustrate the practice of various embodiments of the present disclosure. They are not intended to limit or define the entire scope of this disclosure. It should be appreciated that the disclosure is not limited to theparticular embodiments described and illustrated herein but includes all modifications and variations falling within the scope of the disclosure as defined in the appended embodiments.

[0059] A batch of aluminum scrap weighing 1000 kg is charged in a preheated plasma rotary furnace. Assuming 98.5% of this charge is composed of pure metallic aluminum and the balance is organic compounds such as coatings and lacquers, a theoretical net energy input of 1045 MJ is required to melt the aluminum and reach a temperature of 700°C (1000 kg x 98.5% x 1.0 kJ / kg °C x 1 MJ / 1000 kJ x (700 -25 °C) + 1000 kg x 98.5% x 398 kJ / kg x 1 MJ / 1000 kJ = 1084 MJ). If the duration of the melting step is 120 minutes out of a batch duration of 180 minutes, this is equivalent to a net power input of 150 kW.

[0060] However, this is not the only energy input required as the furnace also loses heat to the surrounding environment during the whole batch duration, which must be compensated to ensure continuity of operations. For a well-insulated furnace of this size, i.e. 1.7 m3total internal volume so that the volume of melted aluminum represents 25 %, heat losses are estimated to be around 210 MJ, or 19.5 kW.

[0061] If solely relying on a plasma torch to supply the energy required, and considering a typical plasma torch thermal efficiency of 75 % combined with a process heat transfer efficiency of 60 % for an overall efficiency of 45 %, this means that a plasma torch with a gross capacity of about 375 kW would be required for this application. This is similar to published conventional technologies burner power capacity of 400 kW for similar sized furnace capacity.

[0062] An alternative source of energy proposed in the present disclosure is obtained by oxidation of a part of the unrecoverable free aluminum left after the tapping step, which generates about 8.7 kWh / kg of aluminum. In this example and assuming conservatively that only 1% of the initial aluminum charge (9.85 kg) would be available for such exothermic reaction, this represents 85.7 kWh or 309 MJ that could be stored in the refractory walls 4 or filling material for the subsequent batch, substantially reducing the net melting energy from 1084 to 775 MJ and the gross power requirement of theplasma torch from 375 to 285 kW. When taking all these numbers into consideration, this represents a total process net energy requirement of 274 kWh / ton of aluminum melted, for a total gross consumption of 609 kWh / ton total process energy requirement, which compares favorably to published conventional technologies energy consumption of 750 kWh / ton.

[0063] As for the organic fraction of the aluminum scrap, assuming it would be entirely composed of an epoxy resin (chemical formula: C21H25CIO5) with an estimated lower heating value of 10 MJ / kg, it would require a stoichiometric combustion oxygen flow rate of 370 slpm for a period of 60 minutes (half of the melting step) or 1750 slpm if using air, and would generate 150 MJ of energy. However, the latter is not considered in the energy balance presented here as most of it would leave the furnace in the exhaust gas.

[0064] While the above description provides examples of the embodiments, it will be appreciated that some features and / or functions of the described embodiments are susceptible to modification without departing from the spirit and principles of operation of the described embodiments. Accordingly, what has been described above has been intended to be illustrative of the embodiments and non-limiting, and it will be understood by persons skilled in the art that other variants and modifications may be made without departing from the scope of the embodiments as defined in the claims appended hereto.

Claims

CLAIMS1. A process for recycling metal scrap in order to recover said metal, the process comprising:(a) charging a batch of the metal scrap into a furnace, preheated to a temperature suitable for minimizing energy requirements during the process;(b) closing a door of the furnace equipped with a seal and on which a plasma torch is installed, to enclose a charged material;(c) starting the plasma torch or making the charge move at least intermittently within the furnace;(d) heating of the charge to a temperature above a volatilization point of organic compounds present in the charge and above a melting point of a recoverable metal, a separation thereof from a non-metallic product and from a filling material and its agglomeration at a bottom of the furnace for melting of the charge;(e) removing recoverable free metal from the furnace;(f) injecting an amount of an oxidizing gas into the furnace or starting the plasma torch while rotating or oscillating the furnace, so as to oxidize sufficient non-recoverable metal within the filling material to evenly heat and store in furnace walls and filling material sufficient energy for treating a new batch of scrap and / or thermally decompose salts, organic and / or chemical compounds;(g) stopping an oxidation reaction by providing an inert atmosphere in the furnace by filling the furnace with inert gas; and(h) removing at least a portion of the non-metallic product.

2. The process of claim 1 , wherein the furnace is a rotary or a reverberatory-type furnace.

3. The process of claim 1 or 2, wherein the furnace comprises a filling material.

4. The process of any one of claims 1 to 3, wherein step (c) further comprises rotation of the furnace.

5. The process of claim 4, wherein the rotation is performed continuously.

6. The process of claim 4 or 5, wherein the rotation ensures transfer of heat between the plasma, walls of the furnace and charge.

7. The process of any one of claims 1 to 6, wherein in step (d), heat is provided by the plasma torch.

8. The process of any one of claims 1 to 6, wherein in step (d), heat is provided by overheating from a previous batch.

9. The process of claim 8, wherein the overheating is by at least an additional 100°C.

10. The process of any one of claims 1 to 9, wherein removal of the recoverable free metal from the furnace is performed through a taphole or through a door.

11. The process of claim 10, further comprising removing at least a portion of a non-metallic product.

12. The process of claim 11 , further comprising leaving in the furnace at least a portion of the filling material and at least a portion of non-recoverable metal.

13. The process of any one of claims 1 to 12, wherein the at least a portion of the non-metallic is removed through the door.

14. The process of claim 13, wherein at step (h), at least a portion of the filling material is left into the furnace.

15. The process of any one of claims 1 to 14, further comprising after step (h) charging into the furnace a new batch of scrap.

16. The process of claim 15, further comprising repeating steps (a) through (g).

17. An apparatus for recycling metal scrap comprising:(a) a rotary or reverberatory-type furnace adapted for high-temperature treatment of scrap, said furnace comprising:(i) a chamber for accumulating and conducting heat provided by an exothermic reaction within said chamber,(ii) an opening for charging scrap into the chamber;(iii) a door for hermetically closing said opening during treatment of the scrap; and (iv) a tap-hole for tapping recovered molten metal;(b) rotating element for imparting movement of the scrap in the furnace;(c) a plasma torch system operable on the hermetic door;(d) an injection element for injecting a process gas or a fuel into the furnace; (e) an injection controller for controlling injection of an oxidizing gas into the furnace;(f) a temperature monitoring element for monitoring temperature of the scrap charged inside the furnace; and(g) an exhaust gas monitoring element for monitoring exhaust gas composition, temperature and characteristics, and for adjusting the plasma gas composition.

18. The apparatus of claim 17, wherein the furnaces further comprise a drum and the door simultaneously rotates with the drum.

19. The apparatus of claim 17 or 18, wherein the injection element is the plasma torch.

20. The apparatus of claim 17 or 18, wherein the injection element is an injection port.

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