APPARATUS AND METHOD FOR THE PRODUCTION OF SILICON BY CARBOREDDUCTION

Abstract

The invention relates to an apparatus for the production of silicon from quartz, the apparatus comprising: a sealed enclosure (2) defining an enclosed space in which a vacuum can be generated; an electric arc furnace (1) housed inside the enclosure (2) and including a tank for containing a mixture of reagents; notable in that the apparatus further comprises a lid (3) housed within the enclosure (2) and adapted to cover a top opening in the tank. Figure to be published with the abstract: Fig. 2

Description

Title of the invention: APPARATUS AND METHOD FOR PRODUCING SILICON BY CARBOREDUCTION FIELD OF THE INVENTION

[0001] The present invention relates to the general technical field of the production of silicon from quartz.

[0002] In particular, the invention relates to a device for producing silicon by carboreduction of quartz in an electric arc furnace.

[0003] BACKGROUND OF THE INVENTION

[0004] The production of metallic silicon is generally based on the carbo-thermal reduction of quartz at high temperature and atmospheric pressure.

[0005] This carbothermic reduction of quartz can be achieved by chemically reducing quartz in the presence of carbon-based reductants in an electric arc furnace where a high temperature arc heats the reactants (quartz and reductants).

[0006] This makes it possible to produce so-called “metallurgical grade” silicon (or “MG-Si” acronym for the Anglo-Saxon expression “Metallurgical Grade Silicon”) with a maximum purity of 98-99%.

[0007] Metallurgical grade silicon can be used: • as an alloying element – ​​for example in the aluminium and steel industry – or • as a precursor - for example in the photovoltaic industry (solar panels), for silicones and for energy storage (lithium battery).

[0008] Technological developments in the fields of photovoltaics and energy storage have led metallurgical grade silicon to become a strategic material.

[0009] Therefore, the supply of high purity metallurgical grade silicon at a reasonable cost has become a necessity.

[0010] However, conventional devices and methods for producing metallurgical silicon have numerous drawbacks such as a high content of impurities.

[0011] To overcome this drawback, it is possible to use a raw material (quartz) with high purity. However, this solution increases the production cost of the metallurgical silicon produced.

[0012] Document US 11,267,714 proposes another solution consisting of implementing the carbothermic reduction of quartz at high temperature under vacuum. Carrying out the carbothermic reduction of quartz under vacuum makes it possible to promote the evaporation of the impurities present in the reactants (quartz and reducing agents) as well as in the newly produced liquid metallurgical grade silicon.

[0013] With reference to [Fig.l], the apparatus according to US 11,267,714 comprises an electric arc furnace FA and a sealed enclosure E containing the arc furnace FA. This arrangement (sealed enclosure E containing the arc furnace FA) makes it possible to control the pressure at which the carbothermic reduction of quartz is carried out.

[0014] However, the variant embodiments of the apparatus described in US 11,267,714 have certain limitations which make it difficult to use the solution according to US 11,267,714 on an industrial scale: • a first limitation concerns the relatively low reaction rate of the reagents (quartz and reducing agents), • a second limitation concerns the quantity of electrical energy required for the production of metallurgical grade silicon.

[0015] These two limitations (low reaction yield, high electrical consumption) make the solution described in US 11,267,714 too expensive to be exploited industrially.

[0016] An aim of the present invention is to propose an apparatus for producing silicon from quartz making it possible to overcome at least one of the aforementioned drawbacks.

[0017] In particular, an aim of the present invention is to propose one (or more) improvement(s) to the apparatus according to US 11,267,714 to facilitate its use on an industrial scale.

[0018] BRIEF DESCRIPTION OF THE INVENTION

[0019] To this end, the invention provides an apparatus for producing silicon from quartz, the apparatus comprising: • a sealed enclosure defining an enclosed space, the enclosure being connected to at least one suction pump to generate a pressure difference between the inside and the outside of the enclosed space, the pressure inside the enclosed space being lower than the pressure outside the enclosed space when the suction pump is activated, • an electric arc furnace housed inside the sealed enclosure, the arc furnace including: • a tank to contain a mixture of raw materials for the production of silicon, • a set of electrodes configured to form an electric arc for heating the mixture, remarkable in that the device further comprises a movable cover housed in the enclosure, the cover being adapted to cover an upper opening of the tank.

[0020] Preferred but non-limiting aspects of the apparatus according to the invention are the following: • the cover may comprise a cover plate, and at least one support shaft fixed to the cover plate, the movable cover being able to be moved between: • a closed position in which the cover plate completely covers the upper opening of the tank, and • an open position in which the upper opening of the tank is at least partially uncovered; • the cover plate may comprise at least one through-light and at least one associated shutter component, each shutter component being movable between: • a clear position in which the through-light is unblocked to allow the circulation of a gas between: • a first region defined between the tank and the cover plate, and • a second region outside the first region, • a sealed position in which the through-light is blocked to limit the flow of gas between the first and second regions; • advantageously: • each through light can be composed of a truncated cone vent arranged in the cover plate, and • each associated sealing element can be composed of: • a plug with a shape complementary to the truncated cone vent and • a suspension rod fixed to the stopper to allow its translational movement between the released and closed positions; • the cover plate may include: • a plate including cylindrical perforations, • a rotating puck configured to rest on the plate so as to be able to rotate about an axis, the rotating puck including through perforations which can be caused, by rotation about the axis, to overlap with the through perforations of the plate; • the device may also include a control unit configured to control: • the enclosure suction pump, • a source of neutral gas supply to the enclosure, • a source of electrical energy supply to the electrodes, • a cover movement motor; The control unit can be configured to: • during a pre-treatment phase: • reduce the pressure inside the enclosed space to a value lower than atmospheric pressure, • implement resistive heating of the mixture of raw materials, • separate the cover from the edges of the upper opening, • during a carbon reduction phase: • perform an initiation step consisting of the sub-steps of: • increase the pressure inside the enclosed space to a value substantially equal to atmospheric pressure, • implement electric arc heating of the mixture of raw materials, • place the cover in contact with the edges of the upper opening, • then when the temperature of the mixture is above 2000°C, carry out a treatment step consisting of: • maintaining the pressure inside the enclosed space at a value substantially equal to atmospheric pressure, • maintain electric arc heating of the raw material mixture, • open the lid slightly, • during a post-processing phase: • reduce the pressure inside the enclosed space to a value lower than atmospheric pressure, • separate the cover from the edges of the upper opening; the waterproof enclosure may include: • a floor, • a ceiling extending parallel to the floor, and • at least one side partition extending between the floor and the ceiling; the cover may include interface elements made of an electrically insulating material: • at least one interface element being positioned between the cover plate and an electrode of the electrode assembly, • at least one interface element being positioned between the cover plate and the tank.

[0021] The invention also relates to a method for producing silicon from quartz using an apparatus as defined above, remarkable in that the method comprises the following phases: • a pre-processing phase including the steps consisting of: • reduce the pressure inside the enclosed space to a value lower than atmospheric pressure, • implement resistive heating of the mixture of raw materials, • separate the cover from the edges of the upper opening, • a carbon reduction phase including: • an initiation stage composed of sub-stages consisting of: • increase the pressure inside the enclosed space to a value substantially equal to atmospheric pressure, • implement electric arc heating of the mixture of raw materials, • place the cover in contact with the edges of the upper opening, • then when the temperature of the mixture is higher than 1500°C, a treatment step composed of the sub-steps consisting of: • maintain the pressure inside the enclosed space at a value substantially equal to atmospheric pressure, • maintain electric arc heating of the raw material mixture, • open the lid slightly, • a post-processing phase including the steps consisting of: • reduce the pressure inside the enclosed space, • separate the cover from the edges of the top opening. Brief description of the drawings

[0022] Other advantages and characteristics of the device and the method for producing silicon according to the invention will emerge more clearly from the following description of several variant embodiments, given as non-limiting examples, from the appended drawings in which: • [Fig.l] is a schematic representation of a device for producing silicon of the prior art, • [Fig.2] is a schematic diagram of the silicon production device according to the invention, • [Fig.3] is a schematic representation of a first embodiment of the silicon production device according to the invention, • [Fig.4] is a schematic representation of a second embodiment of the silicon production device according to the invention, • [Fig.5] is a schematic representation of a third embodiment of the silicon production device according to the invention • [Fig.6] is a schematic representation of a tank of the device of production of silicon according to the invention, • [Fig.7] is a partial schematic representation of an electric arc furnace, • [Fig.8] is a schematic representation of a cover of the device of production of silicon according to the invention, • [Fig.9a], [Fig.9b], [Fig.9c] are schematic representations for the purpose of above a cover according to the invention, • [Fig. 10] is a schematic representation of different phases of a silicon production process according to the invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] Various embodiments of the invention will now be described with reference to the figures. In these various figures, equivalent elements are designated by the same numerical reference.

[0024] 1. General

[0025] With reference to [Fig.2], the apparatus according to the invention comprises: • an electric arc furnace 1, • a waterproof enclosure 2, and • a cover 3 adapted to cover a tank 11 of the electric arc furnace 1, the arc furnace 1 and the cover 3 being housed in the enclosure 2.

[0026] 2. Presentation of the components of the device according to the invention

[0027] 2.1. Arc furnace

[0028] The arc furnace 1 allows: • on the one hand to contain the reagents - namely quartz and reducing agents - for the production of metallurgical grade silicon, and • on the other hand, heating said reagents to high temperature to induce the carbothermic reduction reaction of quartz.

[0029] The arc furnace 1 is of a type known per se to those skilled in the art, and its operation will not be described in detail below. It comprises in particular the tank 11 and electrodes 12.

[0030] 2.1.1. Tank

[0031] As illustrated in Figures 3 to 5, the tank 11 may consist of a graphite carcass coated externally with a refractory lining. Alternatively, the tank 11 may be made of silica, metal or silicon carbide (SiC).

[0032] The tank 11 (or crucible) is intended to contain the reagents, but also the liquid silicon resulting from the carbothermic reduction reaction of the quartz.

[0033] The tank comprises a bottom 111, one (or more) side wall(s) 112, and an upper opening 113. A-A' is a longitudinal central axis of the apparatus which is vertical when the apparatus is placed on a horizontal flat surface. A side wall of the arc furnace 1 is substantially centered on the axis A-A'.

[0034] In the following, the description is oriented by considering that the terms “upper” and “high” correspond to a direction generally parallel to the axis A-A' and going from the bottom 111 towards the opening 113, while the terms “lower” and “lower” correspond to an opposite direction.

[0035] With reference to [Fig. 6], the bottom 111 of the tank 11 may comprise a pad 1111 projecting towards the inside of the tank 11. More precisely, the pad 1111 projects from the bottom 111 and extends along the axis A-A'. The pad 1111 may be made of an electrically conductive material and constitute one of the electrodes 12.

[0036] As a variant, the bottom 111 may be devoid of a stud and comprise only a circular recess 1113 through which one of the electrodes 12 is mounted. As a further variant, the bottom 111 of the tank 11 may be devoid of a stud and of a circular recess 1113, in particular in the case where the electrode (or electrodes) of the arc furnace is (are) mounted above the tank 11, as illustrated in [Fig.7].

[0037] In certain embodiments, the tank 11 may comprise a cooling system (not shown) in its upper part. This cooling system is for example composed of one (or more) panel(s) in which a heat transfer fluid circulates. In this case, the panel(s) is (are) mounted on an upper edge of the side wall(s) 112. The integration of a cooling system into the tank 11 makes it possible to precisely control the temperature in the arc furnace 1 in order to create a vertical temperature gradient, in particular with a view to increasing the quantity of reagent consumed during the carbothermic reduction reaction of quartz, and thus improving the yield of the reaction.

[0038] In other embodiments, the tank 11 is devoid of a cooling system.

[0039] The tank 11 also comprises a casting channel (or several channels) 114 for discharging the metallurgical grade silicon produced (in the liquid state) towards a casting ladle P intended to receive it for later storage.

[0040] A closure system - such as a valve or nozzle or plug made of carbonaceous material - may be provided for closing the casting channel (or channels) 114 during the carbothermic reduction reaction of the quartz.

[0041] At the time of casting, the tank 11, which may be mounted for example on a tilting cradle, is inclined towards the casting ladle so as to gradually send the metallurgical grade silicon in the liquid state through the casting channel (or channels). The casting channel (or channels) then being open, the liquid metallurgical grade silicon can then flow out of the tank and be collected in the casting ladle.

[0042] Of course, other configurations are possible to allow the extraction of metallurgical grade silicon. For example, the bottom of the container may have a non-zero slope towards the casting channel (or channels) so as to send the metallurgical grade silicon towards the casting ladle when the sealing system is removed from the channel (a method known as “tapping” in English).

[0043] 2.1.2. Electrodes

[0044] For the formation of the electric arc allowing the heating of the reactants (quartz and reducing agent), the arc furnace 1 comprises electrodes 12 supplied either from a direct current source or from an alternating current source.

[0045] Preferably, the electrodes 12 are placed in the axis of the arc furnace 1 so as to be stressed in a relatively symmetrical manner. More precisely, each electrode 12 may consist of a cylindrical graphite bar extending vertically.

[0046] In the embodiment illustrated in figures 3 to 5, the arc furnace 1 comprises: • one (or more) movable electrode(s) 121 held by one (or more) support(s) not shown, the (or each) movable electrode 121 being able to be introduced into the arc furnace 1 by passing (each) through a hole in the cover 3 • one (or more) fixed electrode(s) 122 housed in the bottom 111 of the tank 11.

[0047] The support(s) holding the movable electrode(s) allows the distance between the ends of the fixed and movable electrode(s) to be varied to control the quantity of energy transferred to the liquid silicon.

[0048] As indicated above, each electrode 121, 122 is connected to a direct current source or to an alternating current source. One of the advantages of a direct current power supply is that the electrodes are not subject to the electromagnetic effects that the electrodes of a furnace powered from an alternating current source undergo.

[0049] In the case of a direct current power supply: • the movable electrode(s) 121 can be connected to the positive pole of the direct current source to form an anode, • the fixed electrode(s) can be connected to the negative pole of the direct current source and form a cathode.

[0050] 2.2. Enclosure

[0051] The sealed enclosure 2 makes it possible to define an enclosed space in which it is possible to generate a depression, that is to say a space in which it is possible to reduce the pressure to a value lower than atmospheric pressure.

[0052] Such an enclosure can have different shapes and be made from different materials to ensure this function.

[0053] Thus, in the context of the present invention, the term "watertight enclosure" means a box composed of at least one wall on either side of which there is a pressure difference. Thus, the watertight enclosure makes it possible to delimit two zones (i.e. an internal zone and an external zone) between which there is a pressure difference.

[0054] In the embodiments illustrated in Figures 3 to 5, the sealed enclosure 2 has a cylindrical shape, and is essentially made of steel walls.

[0055] This waterproof enclosure 2 comprises: • a horizontal floor 21, • a horizontal ceiling 22, and • one (or more) vertical lateral partition(s) 23 extending between the floor 21 and the ceiling 22.

[0056] The (or one of the) side partition(s) 23 may comprise an access (hole not shown) to allow an operator to access the interior of the enclosure 2. In operation, this access is closed by a door normally locked in a sealed manner by any technique known to those skilled in the art, for example by bolting the door to said side wall, a sealing gasket (for example made of rubber) being mounted between the peripheral edges of the access and the facing door (i.e. between the edges of the access and the edges of the door facing each other).

[0057] The sealed enclosure 2 also comprises one (or more) through orifice(s), possibly for the passage: • one (or more) channel (channels) 221 for injecting gas into the enclosure 2, each channel being able to be connected to a gas supply source (such as argon), • one (or more) suction channel(s) 222 for gas contained in the enclosure 2, each channel being able to be connected to a suction pump to enable the generation of a vacuum inside the enclosure 2, • one (or more) electrode(s) 121, 122, • one (or more) supply conduit(s) 223 of the arc furnace 1 with reagents R (quartz, reducing agents, etc.). • electrical connection means (such as an electrically conductive cable, for example for the electrical connection of a sensor contained in the enclosure, etc.), • one (or more) support shaft(s) 32 of the cover 3.

[0058] When the enclosure 2 comprises several orifices, these can be provided in only one of these walls or in several separate walls.

[0059] 2.3. Cover

[0060] The cover 3 is configured to cover the upper opening 113 of the tank 11.

[0061] The cover 3 makes it possible to contain the gases, and in particular the gaseous oxide compound silicon (SiO) - formed during the carboreduction reaction of quartz inside the tank 11 of the arc furnace 1. This limits the risks of fouling of the enclosure 2, in particular at the level of its partitions 21, 22, 23 and the suction channel (or channels) 222.

[0062] Furthermore, the cover 3 makes it possible to maintain the arc furnace 1 at a temperature (and more precisely at a temperature gradient) which promotes the consumption of the reactants. This increases the reaction rate of the device, in particular with respect to the silicon production device described in US 11,267,714.

[0063] The cover 3 comprises a cover plate 31, one (or more) support shafts 32.

[0064] The cover plate 31 may have different shapes. For example, the cover plate 31 may have a truncated cone shape ([Fig. 3]), a dome shape ([Fig. 4]), or a disc shape ([Fig. 5]). The cover plate 31 may be made of any type of refractory thermal insulation material known to those skilled in the art, such as graphite.

[0065] Advantageously, the cover 3 is movable. More precisely, the cover 3 can be moved between: • a closed position in which the cover plate 31 completely covers the upper opening 113 of the tank 11 (the edges of the cover 3 being in contact with the edges of the upper opening 113 in the closed position), and • an open position in which the cover plate 31 does not cover (or partially covers) the upper opening 113 of the tank 11.

[0066] To do this, the support shaft(s) 32 of the cover 3 can be connected to one or more motor(s).

[0067] The fact that the cover 3 is movable allows access to the interior of the tank of the arc furnace 1, for example: • for maintenance operations of arc furnace 1, and / or • to load / recharge the interior of tank 11 with reagents necessary for the carboreduction reaction, and / or • to promote the evacuation of certain gases produced during the carboreduction reaction, etc.

[0068] In the embodiments illustrated in Figures 3 to 5, the cover plate 31 of the cover 3 comprises recesses for the passage: • one (or more) of the electrode(s) 121, • the supply conduit(s) 223 of the arc furnace 1 with reagents R.

[0069] Preferably, the cover 3 is electrically (and possibly thermally) insulated from the other components of the device.

[0070] In particular in the embodiments illustrated in [Fig.3] to 5, the cover 3 is electrically insulated: • of the electrode 121 (or electrodes 121) extending above the upper opening 113 of the tank 11, • of the tank 11 on which it is configured to rest (this makes it possible to electrically insulate the cover from the electrode 122 arranged under the bottom 111 of the tank 11), and • the power supply conduit(s) 223 (this limits the risk of electrocution of an operator located outside the device.

[0071] For this purpose, the cover 3 comprises interface elements 33 made of an electrically (and possibly thermally) insulating material, such as zirconia or any other material known to those skilled in the art.

[0072] Advantageously, the cover 3 may also comprise one (or more) through-light(s) 231 capable of being blocked by one (or more) movable closure component(s) 232. These through-lights 231 form conduits exhaust of the gases confined in a region RI defined between the tank 11 and the cover plate 31 when the cover 3 is in the closed position. The component(s) can be moved between: • a clear position in which the through light(s) is (are) unblocked to allow the circulation of fluids (in particular gases) between the region RI and a region R2 outside the region RI defined between the tank 11 and the cover plate 31, • a closed position in which the through light(s) is (are) blocked to confine the fluids in the region RI defined between the tank 11 and the cover plate 31.

[0073] Of course, different configurations for the production of the through-lights and the shutter components can be envisaged.

[0074] For example, in the embodiment illustrated in [Fig. 5] the cover plate 31 is made up of a single graphite plate in which truncated cone-shaped vents - forming through-holes 231 - are provided. Plugs - forming a sealing component 232 - of a shape complementary to the truncated cone-shaped vents are provided at the vents, each plug being associated with a respective vent and being suspended from a rod to allow its translational movement between the released and sealed positions.

[0075] Alternatively, in the embodiment illustrated in [Fig.8], the cover plate 31 is of the rotary closure type. In particular, the cover plate 31 comprises a plate 311 including cylindrical perforations 313 forming through-holes. The plate 311 is intended to rest on the edges of the upper opening 113.

[0076] The cover plate 31 also comprises a rotating puck 312 configured to rest on the plate 311 so as to be able to rotate on itself around the longitudinal central axis A-A'. The rotating puck 312 also comprises through perforations 314 which can be made to superimpose, by relative rotations, with the through perforations 313 of the plate 311: • when the through perforations 313, 414 overlap (see [Fig.9c]), they define a passage for the evacuation of gases and heat contained in the RI region, • when the through perforations 313, 314 do not overlap (see [Fig.9a]), the gases and heat contained in the RI region are blocked therein.

[0077] Thus, the rotating puck 312 including through perforations forms the sealing component.

[0078] 3. Operating principle

[0079] The operating principle of the apparatus according to the invention will now be described with reference to [Fig. 10] representing the main steps of a process for the production of silicon from quartz. These steps can be executed by a control unit making it possible to control the components of the apparatus described in point 2 above.

[0080] 3.1. Control unit

[0081] The control unit is for example a computer(s), a processor(s), a microcontroller(s), a microcomputer(s), a programmable logic controller(s), an application-specific integrated circuit(s), other programmable circuits, or other devices that include a computer such as a workstation.

[0082] The control unit comprises one (or more) memory(ies) which may be a ROM / RAM memory, a CD-ROM, a USB key, a central server memory. This (or these) memory(s) allows the storage of program code instructions for the execution of the process illustrated in [Fig. 10].

[0083] 3.2. Silicon production process

[0084] It is assumed that a mixture of raw materials containing for example quartz, and a reducing agent, typically carbon, has been previously positioned in the tank 11.

[0085] 3.2.1. Pre-processing phase

[0086] A pretreatment phase allowing the initiation of the carboreduction reaction as well as the removal of impurities from the mixture of raw materials is implemented. This pretreatment phase comprises the steps: • generation of a depression in the sealed enclosure 2, • resistive heating (using the energy transferred by the electrodes 12) of the mixture of raw materials contained in the tank 11, and • opening the cover 3.

[0087] To generate a vacuum, the control unit controls the activation of the suction pump(s) to suck up the gases contained in the enclosure 2. This makes it possible to generate a pressure difference between the internal zone of the enclosure 2 and a zone external to the enclosure 2.

[0088] For the resistive heating of the mixture, the control unit controls the movement of the movable electrode (or electrodes) so that it (they) comes into contact with the fixed electrode (or electrodes). The control unit also controls the activation of the current source (alternating or direct) connected to the electrodes to supply them with electrical energy. This electrical energy is converted into thermal energy by the electrodes. This makes it possible to heat the mixture of raw materials to a high temperature (typically between 1000°C and 1500°C).

[0089] For opening the cover, the control unit commands the activation of the motor(s) coupled to the support shaft(s) 32 to move the cover 3 to the open position.

[0090] During this pretreatment phase, certain impurities are volatilized, those having a high vapor pressure. Generating a vacuum in the enclosure, and opening the cover while heating the raw materials allows the impurities to escape from the enclosure (these being sucked up by the suction pump(s)).

[0091] 3.2.2. Carboreduction phase

[0092] Once this pretreatment phase is completed (when the temperature in the enclosure reaches 1000°C to 1500°C), a carboreduction phase is implemented. This carboreduction phase comprises the steps: • return to atmospheric pressure in the sealed enclosure 2, • closing the cover 3 and heating by electric arc the mixture contained in the arc furnace 1 to a carboreduction temperature, and • half-opening of the cover 3 and maintaining heating of the mixture by electric arc.

[0093] For the return to atmospheric pressure, the control unit controls the activation of the gas supply source(s) to inject a neutral gas (such as argon) into the enclosure 2. The control unit also controls the deactivation of the suction pump(s).

[0094] For the heating of the mixture by electric arc, the control unit controls the movement of the movable electrode(s) so as to move it away from the fixed electrode(s). The activation of the current source (alternating or direct) is maintained to allow the formation of an electric arc between the fixed and movable electrode(s).

[0095] For closing the cover 3, the control unit commands the activation of the motor(s) coupled to the support shaft(s) 32 to move the cover 3 to the closed position.

[0096] To half-open the cover 3, the control unit commands: • if the cover is devoid of through-light and of shutter component, the activation of the motor(s) coupled to the support shaft(s) 32 to move it into an intermediate position between the open and closed positions, • if the cover includes one or more through-lights and one or more shutter components, activating the motor(s) associated with the shutter component(s) to move it into the released position.

[0097] Closing the cover 3 and generating an electric arc in the arc furnace allows the temperature of the mixture to be rapidly increased to 1500 to 2000°C.

[0098] Once the temperature is reached, the fact of partially opening the cover 3 while maintaining the heating by electric arc allows heat dissipation from the upper part of the reaction medium: a temperature gradient is then created in the reaction medium (high temperature at the bottom of the tank 11 and lower at the upper opening of the tank 11). The fact of forming a temperature gradient in the tank 11 of the arc furnace allows the formation of the different reaction intermediates in the different temperature zones as well as the exchanges between them for an efficient carboreduction reaction.

[0099] 3.2.3. Post-processing phase

[0100] At the end of the carboreduction reaction, when all the raw materials have reacted and liquid silicon is formed in the tank 2, the cover 3 is closed. completely raised. The depression of enclosure 2 is again carried out to allow the elimination of impurities present in the liquid silicon and which have a high vapor pressure such as Phosphorus, and resistive type heating is again implemented.

[0101] The control unit controls the activation of the suction pump(s) to suck up the gases contained in the enclosure 2 and generate the vacuum in the enclosure 2.

[0102] The control unit also controls the activation of the motor(s) coupled to the cover 3 to move it to the open position.

[0103] The control unit finally commands: • the movement of the mobile electrode(s) so that it(they) comes into contact with the fixed electrode(s) • activation of the current source (alternating or direct) connected to the electrodes to supply them with electrical energy.

[0104] 4. Conclusions

[0105] The integration of a cover 3 in a device according to the invention comprising an arc furnace and a sealed enclosure has numerous advantages compared to the apparatus according to US 11,267,714.

[0106] In particular, the presence of a cover makes it possible to increase the reaction rate of the raw materials in the mixture.

[0107] Indeed, in the process according to US 11,267,714, the reaction zone is not confined. However, as indicated previously, the carboreduction reaction involves several gaseous reaction intermediates. If these reaction intermediates are not confined to the same location, then the reaction is partial, which reduces the yield of the reaction.

[0108] Furthermore, controlling the opening and closing of the cover during the carboreduction reaction allows, on the one hand, better control of the temperature gradient inside the arc furnace tank, the regulation of the temperature gradient being an important element in the formation of the different reaction intermediates and their reactions between them for the synthesis of Silicon.

[0109] The reader will have understood that numerous modifications can be made to the invention described above without materially departing from the new teachings and advantages described here.

Claims

Claims

1. Apparatus for producing silicon from quartz, the apparatus comprising: a sealed enclosure (2) defining an enclosed space, the enclosure (2) being connected to at least one suction pump for generating a pressure difference between the inside and the outside of the enclosed space, the pressure inside the enclosed space being lower than the pressure outside the enclosed space when the suction pump is activated, an electric arc furnace (1) housed inside the sealed enclosure (2), the arc furnace (1) including: a tank (11) for containing a mixture of raw materials for the production of silicon, a set of electrodes (12) configured to form an electric arc for heating the mixture, characterized in that the apparatus further comprises: a movable cover (3) housed in the enclosure (2), the cover (3) being adapted to cover an upper opening (113) of the tank (11), and a control unit configured to drive: the enclosure suction pump (2), a source of neutral gas supply to the enclosure (2), a source of electrical energy supply to the electrodes (12), a cover movement motor (3).

2. Apparatus according to claim 1, wherein the cover (3) comprises a cover plate (31), and at least one support shaft (32) fixed to the cover plate (31), the movable cover (3) being able to be moved between: a closed position in which the cover plate (31) completely covers the upper opening (113) of the tank (H), and

3.

4.

5. of the tank (11) is at least partially uncovered. Apparatus according to claim 2, wherein the cover plate (31) comprises at least one through-light (231) and at least one associated shutter component (232), each shutter component being movable between: a clear position in which the through-light (231) is unblocked to allow the circulation of a gas between: • a first region (RI) defined between the tank (11) and the cover plate (31), and • a second region (R2) outside the first region (RI), a closed position in which the through-light is blocked to limit the flow of gas between the first and second regions (RI, R2). Apparatus according to claim 3, wherein: each through light (231) is composed of a truncated cone vent arranged in the cover plate (31), each associated closure element is composed of: of a plug of complementary shape to the truncated cone vent and of a suspension rod fixed to the stopper to allow its translational movement between the released and closed positions. Apparatus according to claim 2, wherein the cover plate (31) comprises: a plate (311) including cylindrical perforations (313), a rotating puck (312) configured to rest on the plate (311) so as to be able to rotate about an axis (A-A'), the rotating puck (312) including through perforations (314) which can be brought, by rotation about the axis (A-A'), to superimpose with the through perforations (313) of the plate (311).

6. Apparatus according to any one of claims 1 to 5, wherein the control unit is configured to: • during a pre-treatment phase: • reduce the pressure inside the enclosed space to a value lower than atmospheric pressure, • implement resistive heating of the mixture of raw materials, • separate the cover (3) from the edges of the upper opening (113), • during a carbon reduction phase: • perform an initiation step consisting of the sub-steps of: • increase the pressure inside the enclosed space to a value substantially equal to atmospheric pressure, • implement electric arc heating of the mixture of raw materials, • place the cover (3) in contact with the edges of the upper opening (113), • then when the temperature of the mixture is above 2000°C, carry out a treatment step consisting of: • maintain the pressure inside the enclosed space at a value substantially equal to atmospheric pressure, • maintain electric arc heating of the raw material mixture, • half-open the cover (3), • during a post-processing phase: • reduce the pressure inside the enclosed space to a value lower than atmospheric pressure, • separate the cover (3) from the edges of the upper opening (113).

7. Apparatus according to any one of claims 1 to 6, wherein the sealed enclosure (2) comprises: • a floor (21), • a ceiling (22) extending parallel to the floor (21), and • at least one lateral partition (23) extending between the floor (21) and the ceiling (22).

8. Apparatus according to any one of claims 2 to 7, wherein the cover (3) comprises interface elements (33) made of an electrically insulating material: • at least one interface element being positioned between the cover plate (31) and an electrode of the electrode assembly (12), • at least one interface element being positioned between the cover plate (31) and the tank (11).

9. A method for producing silicon from quartz using an apparatus according to any one of claims 1 to 8, characterized in that the method comprises the following phases: • a pretreatment phase including the steps of: • decreasing the pressure inside the enclosed space to a value lower than atmospheric pressure, • implementing resistive heating of the raw material mixture, • separating the cover from the edges of the upper opening, • a carboreduction phase including: • an initiation step consisting of the sub-steps of: • increasing the pressure inside the enclosed space to a value substantially equal to atmospheric pressure, • implementing electric arc heating of the raw material mixture, • bringing the cover into contact with the edges of the upper opening, at 1500°C, a treatment step consisting of the sub-steps of: • maintain the pressure inside the enclosed space at a value substantially equal to atmospheric pressure, • maintain electric arc heating of the raw material mixture, • half-open the cover, a post-treatment phase including the steps of: • reducing the pressure inside the enclosed space, • separate the cover from the edges of the opening on superior.

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