METHOD AND DEVICE FOR GLAZING A POWDER-FORMED MATERIAL

Description

Scope of the invention

[0001] The present invention relates to a continuous vitrification process for a powdered material and to a device for implementing this process.

[0002] The process and device of the invention are essentially intended to render inert by vitrification powdery or small particle size materials containing toxic substances such as asbestos or heavy metals such as mercury or lead, and their salts. Technological background

[0003] It is known that the implementation or generation of materials in powder form can lead to the dispersion of some of these materials into the surrounding atmosphere.

[0004] This dispersion can lead to risks of poisoning or be a vector for toxic gases or liquids.

[0005] The handling and treatment of these powdery materials therefore constitute major challenges from both a health and environmental point of view.

[0006] For example, the incineration of household waste, industrial or hospital waste is known as a source of powdery materials.

[0007] In particular, the incineration of household waste produces solid effluents and gaseous effluents, or incineration fumes.

[0008] Solid effluents form the mineral fraction of waste and include, in particular, so-called "boiler ash," which is a highly toxic, powdery material. This ash contains heavy metals and their salts.

[0009] The gaseous effluents are more or less acidic due to the presence of acid gases such as HCl and HF, and gaseous acid anhydrides such as SO2 and CO2. These gaseous effluents also include toxic compounds such as heavy metals and their salts, and solid residues called fly ash.

[0010] These gaseous or fume effluents must be filtered and treated to neutralize their acidity, condense metals and their salts and retain fly ash before being released into the atmosphere.

[0011] Vitrification is considered today as the main process for inerting these hazardous materials or incineration waste, with a view to their storage, or even their recovery.

[0012] Indeed, these materials containing silica and alumina liquefy and form a melt pool when subjected to temperatures above 1300°C.

[0013] When cooled, this molten bath forms a crystalline material or a solid amorphous glass, a true matrix for retaining heavy metals, which can then be manipulated.

[0014] We know from document FR 2764877 in the name of the present applicant, a device for the vitrification of powdery materials using a non-transferred arc plasma torch to melt the powdery material to be treated.

[0015] Although it gives good results, this vitrification device is found to have some drawbacks.

[0016] First, this device for vitrifying a powdered material comprises a furnace including a melting zone for the powdered material and a pouring zone for the molten bath, these two zones being separated by a barrier stone. An extraction fan extracts the gases and fumes produced during the melting of the powdered material in the melting zone through a duct.

[0017] It is thus observed that only a fraction of the gases and fumes generated during the vitrification of the powdered material are extracted for treatment. A significant portion of these gases and fumes is therefore released into the immediate environment, with harmful effects on living organisms directly exposed to them.

[0018] Furthermore, an inappropriate pressure difference applied between the melting zone and the pouring zone can result in a loss in the flow of the molten pool to the corresponding pouring zone, or even the passage of unmelted, powdery materials, also called "unmelted".

[0019] We also observe wear on the dam stone due to its prolonged contact with the molten material, which flows from the molten pool to the pouring area.

[0020] However, the wear and tear on this dam stone leads to a loss of seal between the two chambers it separates. Fumes and gases from the melting of the powdered material in the melting zone can then pass from the melting zone to the pouring zone and be released into the surrounding atmosphere.

[0021] Furthermore, it is observed that a dam stone worn in this way is likely to allow unmelted material to pass freely into the flow zone.

[0022] Document JP 2008 249220 A describes a plasma melting furnace capable of suppressing the discharge of an exhaust gas containing harmful asbestos dust ash, emanating solely from the furnace's main chamber, which contains molten slag metal. See also document FR 2 764 877 A1. Object of the invention

[0023] The present invention aims to overcome the disadvantages of the prior art by proposing a continuous vitrification process for a powdery material, simple in its design and operating method, reliable and inexpensive, meeting the aforementioned disadvantages.

[0024] In particular, an object of the present invention is such a vitrification process making it possible to capture all the gases and fumes generated during the vitrification process in order to prevent the release of these gases and fumes into the surrounding atmosphere, and thus control the health and environmental impact of this vitrification treatment.

[0025] Another object of the present invention is such a process as to significantly reduce the deterioration of the gas and fume extraction circuit from the vitrification of a powdery material, in order to space out maintenance operations over time.

[0026] Another object of the present invention is such a process maintaining the seal, in production, between the melting and casting zones.

[0027] The present invention also aims to provide a device for implementing this process, intended to render inert by vitrification a powdery material comprising toxic compounds, in particular heavy metals and their salts.

[0028] The process and device of the invention allow in particular an effective control of the melting process of a powdery material and the obtaining of an amorphous glass, or a crystallized material, which meets all the standards applicable to the storage of inert waste or even to its recovery, for example, as a construction material. BRIEF DESCRIPTION OF THE INVENTION

[0029] For this purpose, the invention relates to a vitrification process for a powdered material, according to the invention defined in claim 1.

[0030] This powdery material is introduced through at least one inlet port into the melting zone delimited by the first enclosure.

[0031] Each barrier stone determines, or limits the amount, of molten material flowing from the molten pool in the first enclosure, or main enclosure, to the pouring area in the second enclosure and at the entrance of which this barrier stone is preferably arranged.

[0032] During the operation of the vitrification device, at least one end of this barrier stone is immersed in the molten material of the melting bath to ensure a seal, preventing gases and fumes generated by the melting of the powdered material in the melting zone from spreading to the pouring zone(s). The immersed end of this barrier stone also prevents unmelted or unspent material from entering the pouring zone(s).

[0033] Advantageously, the overflow zone of each pouring zone is located at one end of the corresponding pouring zone. For illustrative purposes only, this overflow zone comprises a ramp inclined towards an outlet port along which the molten material flows.

[0034] Advantageously, thanks to the process of the present invention, all the gases and fumes produced in the vitrification device are captured and evacuated for treatment. This prevents any dispersion of harmful fumes and / or gases, particularly during the extraction stage, into the atmosphere surrounding the vitrification device, which would otherwise necessitate the addition of a fume capture device.

[0035] According to one aspect of the process of the invention, the level of the melting bath is regulated, the extraction of gases and fumes generated by the melting of the powdered material in said melting zone and the extraction of gases and fumes in each second enclosure are regulated so as to promote the flow of the molten material from the melting bath to each casting zone.

[0036] Such an embodiment is advantageously permitted by means of the immersion in the molten material of at least the end of said at least one barrier stone separating the melting zone from the corresponding pouring zone, the sealing between these two zones being thus ensured.

[0037] We therefore control the pressures independently in each of the zones, which allows us to regulate the level of the bath and the flow of the extracted molten material.

[0038] We can try to at least balance the pressures between the first enclosure delimiting the melting zone and the second enclosure delimiting the corresponding pouring zone.

[0039] It is also possible to generate a depression in said at least one second enclosure which is greater than the depression established in the first enclosure containing the melt bath, to create a suction effect towards said at least one second enclosure.

[0040] For example, this regulation is achieved by controlling extraction fans.

[0041] According to another aspect of the process of the invention, each overflow zone having an outlet port having a side wall delimiting a channel through which said part of the extracted molten bath passes, at least a part of said side wall extending outside said corresponding second enclosure comprising at least one orifice, at least a part of said gases and fumes is captured through said orifice(s) so as to dilute said gases and fumes thus captured with outside air.

[0042] It is observed that the gases and fumes which are captured are acidic and cause rapid degradation of the metal pipes of the collection system ensuring their collection and evacuation.

[0043] Maintenance operations are then required to maintain the sealing of the extraction circuit, which requires the vitrification device to be stopped.

[0044] This results in significant operating costs.

[0045] This intake of outside air advantageously dilutes the gases and fumes thus captured, which protects the elements of the gas and fume extraction circuit located downstream.

[0046] This embodiment also aims to prevent the vitrified tongue, or molten material, flowing through the outlet port to ensure its extraction from cooling.

[0047] Each overflow zone having an outlet port through which said part of the extracted molten bath passes, at least part of said gases and fumes generated during said extraction stage are captured through one or more orifices placed near said outlet port.

[0048] These openings are therefore placed on the body of the second corresponding enclosure, close to the exit port.

[0049] According to another aspect of the method of the invention, for at least one plasma torch, at least the part of said plasma torch, placed inside said first enclosure, is surrounded by a protective gaseous screen to protect at least said part, at least one means for introducing a gaseous fluid being conformed for the introduction and generation of said gaseous screen around said at least one part.

[0050] According to yet another aspect of the process of the invention, the overflow zone of each pouring zone having a pouring spout delimiting the level of the molten bath; for each pouring zone, the height of the corresponding pouring spout is adjusted to regulate the level of the molten bath so that at least the free end of said corresponding dam stone is permanently immersed when the device is in operation, or production, to maintain the seal between the melting and corresponding pouring zones for the gases and fumes produced in each of these zones.

[0051] The present invention also relates to a device for implementing the vitrification process of a powdered material as described above, according to the invention defined in claim 6.

[0052] Advantageously, said at least one plasma torch is a non-transferred arc plasma torch.

[0053] This embodiment advantageously maintains heat within the extraction port, thus promoting the fluidity of the material to be extracted. This extraction circuit advantageously comprises interconnected pipes, the interior of which is placed under negative pressure to ensure the suction of gases and fumes and their transport to a gas and fume treatment unit.

[0054] As an example, at least one first extraction port may be placed in the lower part of the corresponding second enclosure, close to, or near, the outlet port for capturing gases and fumes produced during the extraction of molten material from the vitrification device.

[0055] In various specific embodiments of this vitrification device, each has its own particular advantages and is susceptible to numerous possible technical combinations: This first enclosure includes at least one device for injecting the powdered material into said enclosure.

[0056] Preferably, each injection device is configured to ensure that the powdered material thus introduced has a component directed downwards from said first chamber and a horizontal component directed towards said pouring zone.

[0057] Advantageously, each introduction device is placed on said first enclosure opposite a corresponding pouring zone relative to the molten bath. The overflow zone of each pouring zone includes a pouring spout delimiting the level of the molten bath, the height at least of said pouring spout being variable to adjust its position and thus vary the level of the molten bath so that at least the free end of said dam stone is immersed to ensure the sealing of the corresponding pouring zone and the melting zone, the outlet port of each second enclosure includes a side wall defining an extraction channel for said part of the molten bath, which extends outside said corresponding second enclosure including at least one extraction orifice for said gases and fumes so that during the extraction of said part, outside air is mixed with said gases and fumes thus captured for their dilution.

[0058] This embodiment advantageously allows air to be drawn in through the free end of the outlet port, so that the gases and fumes thus captured are diluted before being transported through an extraction system. This advantageously protects components such as the ducts of this extraction system.

[0059] Advantageously, at least one of these extraction ports is placed lower, or below, said overflow zone.

[0060] For illustrative purposes only, this overflow system comprises a spout extended by a ramp whose slope is inclined towards the outlet port. This outlet port may, for example, have a hollow tubular shape. said orifices are regularly distributed, for example, around the perimeter of said side wall delimiting the outlet port, each second enclosure being connected to at least one extraction circuit comprising at least one fan to draw the gases and fumes produced in the corresponding enclosure, said vitrification device includes a control means to operate said fans and regulate the level of the molten bath in said melting zone in order to promote the flow of a portion of the molten bath from said melting zone to said pouring zone, the device includes at least two second enclosures, each defining a pouring zone in fluid communication with the melting zone of said first enclosure, the device includes at least one device for drawing said molten material placed downstream of at least one outlet port, said first enclosure has a straight cross-section of circular or rectangular shape,square or oblong, this device includes at least one means for injecting a protective fluid at least at the level of the part of at least one plasma torch placed inside said first enclosure, said injection means being configured to create a gaseous shield surrounding said part in order to protect it from the extreme conditions prevailing in said first enclosure.

[0061] Preferably, this protective gas is air or any other gas such as an inert gas. For example, in the latter case, it could be Nitrogen (N2). BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Other advantages, purposes, and special features of the present invention will become apparent from the following description, given for explanatory purposes only and not as a limitation, with reference to the accompanying drawings, in which: there Figure 1is a schematic and cross-sectional representation of a vitrification device according to a first particular embodiment of the present invention; the Figure 2 is a partial, top-down, cross-sectional view of the overflow area of ​​the vitrification device of the Fig. 1 ; there Figure 3 is a schematic and cross-sectional representation of a vitrification device according to a second particular embodiment of the present invention. DETAILED DESCRIPTION OF THE METHOD OF IMPLEMENTING THE INVENTION

[0063] Firstly, it should be noted that the figures are not to scale.

[0064] THE Figures 1 and 2 schematically represent a device 10 for vitrifying a powdery material according to a particular embodiment of the present invention.

[0065] This device 10 comprises a main cylindrical melting chamber, or furnace 11, which is continuously fed upstream with a stream of powdered material by means of an injection device 12. An inlet port 13, formed by a circular opening in a recess in the side wall of the melting chamber 11, allows the material to be injected into this chamber 11. This injection device 12 is chosen for its ability to deliver a controlled flow at a pressure and temperature dictated by the pressure and temperature conditions prevailing in the melting chamber 11. For example, it is a cooled screw. Injection methods using a pusher or pneumatic conveying under pressure could also be chosen.

[0066] The charge of powdered material to be treated is injected into the melting chamber 11 in such a way as to present a horizontal injection component and a vertical injection component directed towards the bottom of the melting chamber 11. This charge thus falls by gravity into a melting bath 14 contained in a crucible.

[0067] The impact zone of this charge to be treated with the melting bath 14 constitutes a mixing zone. This is therefore a zone where the charge of powdered material to be treated mixes with the material that has already been brought to a liquid state by melting, thanks to the energy supplied by a non-transferred arc plasma torch 15, in the liquid melting bath 14.

[0068] The non-transferred arc plasma torch 15 is mounted in an opening in the roof of the melting chamber 11. It is mounted on the melting chamber 11 so that the plasma beam it emits is directed directly into the melting pool 14. Advantageously, this plasma beam could be directed at an angle towards the melting pool 14 and at a slant to agitate it.

[0069] The 15 non-transferred arc plasma torch preferably operates with pressurized air treated as the plasma gas, using compression and treatment methods applied to atmospheric air. It is also possible to use other plasma gases, for example by modifying the oxygen and nitrogen percentages relative to those of atmospheric air.

[0070] Advantageously, the tip of the non-transferred arc plasma torch 15, located inside the main enclosure 11, is surrounded by a gaseous film, such as an air film or any other gas, which forms a shield protecting the tip of the plasma torch 15 from the aggressive environment within the main enclosure 11. This gaseous film is generated by means of a gas introduction device, for example, at ambient temperature, located on the fusion enclosure 11 (not shown).

[0071] Measurement and control devices (not shown) allow for the capture of pressure and temperature within the melting chamber 11 using pressure and temperature probes, the temperature of the bath using an optical pyrometer, and the monitoring of the melting of the powdered material being processed using an endoscope (not shown). These measurements are used, for example, under the control of a processing unit, such as a microprocessor programmed for this purpose, to determine the electrical power of the plasma torch 15 and / or the flow rate of the powdered material being processed into the melting bath, with the aim of controlling and optimizing the melting process and, in particular, the necessary and sufficient plasma power for melting this material.

[0072] The side wall, crucible, and vault of the melting chamber 11 are all lined internally with high-temperature refractory materials, for example, chromium / corundum-based materials. The same applies to the internal walls of the second chamber 16.

[0073] Of course, to increase the processing capacity of the vitrification device 10, the melting chamber 11 could be equipped with at least two injection devices 12 for a charge of powdered material and at least two non-transferred arc plasma torches 15 to heat the melt pool. The dimensions of the crucible would then be increased to accommodate a larger melt pool 14. For example, the melting chamber 11 could also be elongated or elliptical in shape. To ensure satisfactory evacuation of the molten material forming the melt pool 14, this vitrification device could include at least two separate pouring zones, each preferably connected to the melting chamber 11 opposite a corresponding injection device 12.

[0074] The device also includes a second enclosure 16 defining a molten material pouring zone. This pouring zone is in fluid communication with the melting zone through an opening, the upper portion of which is delimited by the end of a barrier stone 17 placed here between the main enclosure 11 and the second enclosure 16. Part of the molten material from the melting bath 14 can thus flow through this opening into the pouring zone.

[0075] The barrier stone 17 is arranged so that its free end, which, along with the surrounding walls of the enclosures, helps to define the opening, is immersed in the molten material. This barrier stone 17, in contact with the liquid molten pool 14, thus blocks the gases and fumes generated by the melting of the powdered material in the melting zone.

[0076] These fumes and gases remain confined within the internal volume of the melting chamber 11 and are extracted by means of an exhaust duct 18 located in the vault of the melting chamber 11, which is connected to a fume extraction and treatment system. These fumes and gases contain, in particular, the vaporized fraction of the powdered material charge, which results from thermochemical reactions taking place in the high-temperature melting zone, typically between 1300°C and 1600°C, of ​​the melting chamber 11.

[0077] The second chamber 16 includes a burner 19 mounted on a side wall of this second chamber, which maintains the temperature of the molten material to allow its flow through the melting zone to the outlet port. More generally, this could refer to any means of heating the molten material to maintain the temperature of the molten material in said portion of the melt pool flowing through said melting zone above its melting point, such as a non-transferred arc torch.

[0078] The second enclosure 16 also includes several orifices 20 for the extraction of gases and fumes generated in the pouring zone, which are connected to a gas and fume extraction circuit.

[0079] These extraction ports 20 are located at an overflow zone comprising an outlet port for extracting the molten material, so as to capture the gases and fumes generated during the extraction stage of this molten material. This overflow zone is situated at the opposite end of the pouring zone from the one in which the dam stone 17 is placed.

[0080] The overflow zone includes an overflow means comprising a pouring spout 21, preferably movable for adjusting its position and whose height may be adjustable, allows control of the overflow level of the molten material and thus the level of the molten pool in said pouring zone. This pouring spout 21 is extended by an inclined ramp 22, preferably movable with said pouring spout 21, conveying the overflowing molten material to an outlet port 23 for the molten material from the molten pool 14.

[0081] As depicted on the Figure 2 , this outlet port 23 of the molten material includes a hollow conduit, external to the body of the second enclosure 16, connected to this second enclosure by a pouring orifice and defining an internal channel 24 for the extraction of the molten material, into which the latter falls by gravity through the pouring orifice from the inclined ramp 22.

[0082] The extraction ports 20 are distributed here on the side wall of the hollow duct of the outlet port 23 so that outside air is drawn in simultaneously with the gases and fumes.

[0083] These gases and fumes are thus mechanically diluted, significantly reducing their deposition and corrosive action on the pipes of the gas and fume extraction circuit 25. This extraction circuit 25 advantageously defines an enclosure surrounding the outlet port 23 to capture all the generated gases and fumes.

[0084] The extracted molten material subsequently cools in the atmosphere, transforming into a non-toxic vitrified material. It should be noted that the extraction ports 20 are located outside and below the second enclosure so as not to cool the molten material flowing into the melting zone.

[0085] It can be drawn out during extraction by means of a cooled rotary roller mill 26. This mill 26 allows the molten material overflowing from the overflow means to be drawn out of the pouring zone, outside the second enclosure 16. Passing through the mill 26 ensures the amorphous nature of the solidified vitrified material.

[0086] There Figure 3 is a schematic and cross-sectional representation of a vitrification device 30 according to a second embodiment of the present invention.

[0087] The elements of the Figure 3 bearing the same references as those of Figures 1 and 2represent the same objects, which will not be described again below.

[0088] The vitrification device 30 shown on the Fig. 3 differs from the one illustrated in Figures 1 and 2 in that it includes at least one extraction port 31, which is not located in the outlet port 23 but on the side wall of the second enclosure delimiting the pouring zone. It is, however, located close to this outlet port 23 to ensure the extraction of gases and fumes generated during the extraction of the vitrified material.

Claims

1. Method for vitrifying a pulverulent material, wherein said pulverulent material is introduced into a melting zone delimited by a first chamber (11), melted by means of at least one plasma torch (15) in a melting bath (14) for supplying said bath, said melting bath (14) being placed in said melting zone, a part of said melting bath (14) being sent from said melting zone to at least one casting zone, each of said casting zones being delimited by a corresponding second chamber (16) in fluid communication with said first chamber (11), and wherein said melting bath part is extracted in an overflow zone of each corresponding casting zone, wherein the following steps are carried out: - extracting gases and fumes generated by melting the pulverulent material in said melting zone, said gases and fumes being blocked in said first enclosure (11) by at least one dam stone (17), each dam stone (17) being placed between said melting zone and a corresponding casting zone, each dam stone (17) being arranged such that at least its free end also determines said part of the melting bath (14) flowing from the melting zone to said corresponding casting zone, characterized in that the following steps are also carried out: - extracting in each second enclosure (16) at least the gases and fumes generated during said extraction step of said part of said melting bath (14), and - each overflow zone having an outlet port through which said portion of the extracted melting bath (14) passes, at least a portion of said gases and fumes generated in said extraction step are collected through one or more orifices placed in the vicinity of said outlet port.

2. Method according to claim 1, characterized in that the level of the melting bath (14) is regulated, the extraction of the gases and fumes generated by the melting of the pulverulent material in said melting zone as well as the extraction of the gases and fumes in each second chamber (16) so as to promote the flow of the molten material from the melting bath (14) to each casting zone.

3. Method according to claim 1 or 2, characterized in that each overflow zone comprising an outlet port having a side wall delimiting a channel through which said part of the extracted melting bath (14) passes, at least part of said side wall extending outside said corresponding second chamber (16) comprising at least one orifice, at least part of said gases and fumes are collected through said orifice or said orifices, so as to dilute said gases and fumes thus collected with external air.

4. The method according to any one of claims 1 to 3, characterized in that for at least one plasma torch (15), at least the part of said plasma torch (15), placed inside said first enclosure (11), is surrounded by a protective gas shield to protect at least said part, at least one means for introducing a gaseous fluid being shaped for the introduction and generation of said gaseous shield around said at least one part.

5. The method according to any one of claims 1 to 4, characterized in that the overflow zone of each casting zone comprises a pouring spout delimiting the level of the melting bath (14); for each casting zone, the height of the corresponding pouring spout is adjusted to adjust the level of the melting bath (14) such that at least the free end of said corresponding dam stone (17) is permanently immersed in operation to maintain the seal between the corresponding melting and casting zones for the gases and fumes produced in each of these zones.

6. A device for vitrifying a pulverulent material for carrying out the method according to any one of claims 1 to 5, said device comprising a first enclosure (11) delimiting a melting zone of said pulverulent material, said first enclosure (11) comprising at least one plasma torch (15) for generating a melting bath (14) from said pulverulent material, at least one second enclosure (16) delimiting a zone for casting the molten material, said first and second enclosures being in fluid communication for the flow of a part of the melting bath (14) to each corresponding casting zone, each casting zone comprising an overflow zone comprising an outlet port for extracting said part from the melting bath (14), said device also comprising a dam stone (17) placed between the melting zone and each casting zone by being arranged such that at least its free end defines said portion of the melting bath (14) flowing from the melting zone to said corresponding casting zone, whereby said dam stone (17) is intended to be in contact with said melting bath (14) to block gases and fumes produced in said melting zone as well as the unmelted material, said first enclosure (11) comprising means for extracting gases and fumes present in said melting zone, characterized in that - each second enclosure (16) is configured to collect the gases and fumes produced at least during the extraction of said molten material, - each second enclosure (16) comprising one or more orifices for extracting said gases and fumes, connected to a circuit for extracting gases and fumes, said orifices being placed in the vicinity of said extraction port or in the extraction port.

7. Device according to claim 6, characterized in that the outlet port of each second enclosure (16) has a wall side defining an extraction channel of said part of said melting bath, which extends outside said corresponding second enclosure (16) by including at least one extraction port of said gases and fumes so that upon extraction of said portion, external air is mixed with said gases and fumes thus captured for dilution thereof.

8. Device according to any one of claims 6 or 7, characterized in that it comprises at least two second enclosures each defining a casting zone in fluid communication with the melting zone of said first enclosure (11).

9. Device according to any one of claims 6 to 8, characterized in that said first enclosure (11) has a straight cross section of circular, rectangular, square or even oblong shape.

10. Device according to any one of claims 6 to 9, characterized in that it comprises at least one means for injecting a protective fluid at the level of at least the part of at least one plasma torch (15), placed inside said first enclosure (11), said injection means being configured to create a gaseous screen surrounding said part in order to protect the latter from extreme conditions prevailing in said first enclosure (11).

11. Device according to claim 10, characterized in that said protective gas is air or an inert gas.