EP0036362B1 - Apparatus for the thermal treatment of powdery or granular materials - Google Patents

Description

The present invention relates to a device for the heat treatment of divided materials and in particular of powdered or granular materials.

Heat treatment using microwaves (MO) or ultra high frequency waves (UHF) which are between approximately 300 Megahertz and approximately 30 Gigahertz is currently spreading more and more, thanks in particular to the great availability of this energy. , its good propagation in various atmospheres, its good regulation and its satisfactory enslavement. The homogeneous heating throughout the mass of the treated product which it also provides, has enabled numerous applications of this form of energy, both domestic and industrial applications. There remained, however, a significant drawback, at least as far as industrial applications of UHF radiation are concerned: if the batch processing of the various products and materials is on the whole satisfactory and no longer poses significant problems, it does not This is not the same for the continuous treatment of large quantities of materials, and in particular of materials in the divided state, such as grains, powders or the like. In fact, for this mass heat treatment to be economically profitable, it is necessary to be able to process very large quantities of material, and this without wasting energy and it is also necessary to have robust and simple installations. None of the installations of the prior art meets these basic requirements.

It is excluded to use multimode resonant cavities: on the one hand there is not enough concentration of energy density, and on the other hand it would be necessary to build very large volumes, difficult to achieve and economically unprofitable .

It is also economically unprofitable to provide a succession of resonant cavities connected to each other (such as the construction of an incient forming a "tunnel" crossing the resonant cavities, as recommended in French Patent No. 2,428,369): in addition, significant energy leaks occur, due to the material entry and exit system.

The use of single-mode and multi-mode waveguides has also been recommended, using no longer standing waves but traveling waves. Coaxial devices have thus been produced in which the materials to be treated are located inside the waveguide or else devices with transmitting antennas, in which the materials to be treated receive M.O.

• - par exemple, un dispositif utilisant une vis sans fin (Brevet français 2 337 734)
• - ou par exemple un appareil de chauffage par haute fréquence pouvant comporter une cloison hélicoîdale et dont le pas de la partie fixe est rigoureusement égal au pas de la partie mobile (Brevet Fr. 1 471 131), et d'autres encore.

In addition to the fact that, in the devices of the prior art, the flow rate of the materials to be treated is limited, even with the installation of treadmills, there also occurs large losses of energy, because the material to be treated. process thus conveyed is not in the maximum energy concentration zone. Many other attempts to produce continuous MO energy applicators have been described, in particular:

• - for example, a device using an endless screw (French patent 2,337,734)
• - Or for example a high frequency heating device which may include a helical partition and the pitch of the fixed part of which is strictly equal to the pitch of the movable part (Patent Fr. 1,471,131), and still others.

But in all cases, the same handicap remains: insufficient flow, too high loss of energy, prohibitive installation cost.

The object of the present invention is therefore to provide a device which not only makes it possible to keep on the one hand the most satisfactory single-mode waveguide-device with the highest energy density - but also, d on the other hand, to provide a device which makes it possible to continuously advance the material to be treated at a large, constant and adjustable flow rate, while maintaining it in a maximum energy field. One of the aims of the present invention is also to be able to use low power energy sources, produced in large series, therefore economically very advantageous.

The subject of the present invention is a device for the continuous heat treatment of divided materials and in particular of powdered or granular materials, by UHF radiation, is characterized in accordance with claim 1.

According to the invention, the sheath and the partitions substantially perpendicular to the sheath, that is to say the fixed part of the waveguide, represent between 1/4 and 1/2 of the total height of the waveguide .

Indeed, if the fixed part of the waveguide, that is to say the partitions and the lining which fill the space between the partitions in non-polar material, descended to half the height of the waves, the material to be treated would of course be in the maximum field of action, but the useful volume of the treated material would be reduced; if on the other hand the propeller touched the wall of the sheath, that is to say if the fixed partitions disappeared perpendicular to the sheath, the volume of materials treated would be maximum, but also the loss of energy, because the current lines of the wall itself would be cut, the optimum effect being, according to the invention, between 1/4 and 1/2 of the total height of the waveguide.

According to an advantageous embodiment of the object of the invention and to avoid the reflection of waves on the source, the width of the excitation device or dimension according to the pitch of the propeller, exceeds the pitch of the propeller.

According to another particularly advantageous embodiment of the object of the invention, the thickness of the propeller, in particular in the vicinity of the fixed part of the waveguide constituted by the partitions, is calculated in such a way that there is never any communication between two excitation guides.

This modality of the invention, which precisely allows the use of low-power and very inexpensive commercial magnetrons, makes the device according to the present invention particularly suitable for all heat treatments using large quantities of materials.

According to another embodiment, and for the same reasons, the thickness of the fixed partitions perpendicular substantially to the sheath is also calculated so that there is no communication between two excitation guides.

According to the invention, the device is provided with means for recovering and using the magnetron cooling air to optionally remove water vapor from the treated material.

According to another embodiment of the object of the invention, the heat treatment device is pressurized by an inert gas, such as nitrogen for example.

According to the invention, the material inlet and outlet openings are square section tubes whose side is at most equal to half the wavelength used for the treatment of the material.

According to another embodiment of the subject of the invention, the material inlet and outlet openings are tubes of circular section, the diameters of which do not allow the propagation of the wave used for the treatment of the matter.

According to the invention, it may be useful, in certain cases, in particular when it is desired to increase or decrease the value of the UHF electric field, to have an Archimedes screw with variable pitch.

As the location of the partitions perpendicular to the sheath is a function of the pitch of the propeller, it is obvious that in cases where the propeller forming the Archimedes screw has a variable pitch, the distance between these partitions is not uniform , but variable.

According to another advantageous embodiment of the object of the present invention, the thickness of the sheath lining, which is made of non-polar materials such as polyethylene or polystyrene, and is housed between the partitions, represents 1 / 4 to 1/2 of the total height of the waveguide.

According to the invention, the sleeve is formed of two half-sleeves assembled by two flanges.

Also in accordance with the invention, the edge of the propeller which faces the partition is cut in a bevel.

In addition to the foregoing provisions, the invention also comprises other provisions, which will emerge from the description which follows.

The present invention relates more particularly to a new device for the heat treatment of large quantities of divided materials, as well as the overall devices and methods in which the devices according to the present invention are included.

The invention can be better understood using the additional description which follows, which refers to an embodiment of the device according to the present invention.

• - la Figure 1 représente une vue schématique du dispositif, vu de l'extérieur
• - la Figure 2 représente schématiquement la partie fixe du guide d'ondes: la Figure 2a est une vue en coupe longitudinale et la Figure 2b représente une coupe transversale de ce dispositif;
• - la Figure 3 représente schématiquement la partie mobile du guide d'ondes: la Figure 3a représente une coupe longitudinale et la Figure 3b une coupe transversale de ce dispositif, et
• -la Figure 4, représente le guide d'ondes délimité par deux spires successives de l'hélice faisant face à deux cloisons fixées sur le fourreau.

It should be understood, however, that this exemplary embodiment described below and shown in the accompanying drawings, is given solely by way of illustration of the subject of the invention, but in no way constitutes a limitation thereof. . So:

• - Figure 1 shows a schematic view of the device, seen from the outside
• - Figure 2 shows schematically the fixed part of the waveguide: Figure 2a is a longitudinal sectional view and Figure 2b shows a cross section of this device;
• - Figure 3 shows schematically the movable part of the waveguide: Figure 3a shows a longitudinal section and Figure 3b a cross section of this device, and
• FIG. 4 represents the waveguide delimited by two successive turns of the propeller facing two partitions fixed on the sheath.

The device according to the invention as shown in FIG. 1, which comprises a tube 1 for entering the divided material, a tube 4 for leaving the treated material, a sheath 6 (inside which the screw turns Archimedes driven by the drive axis 5), magnetrons 2 and excitation guides 3, in reality constitutes a module 7 which can be (by removing the flange 8) attached to other modules to constitute, if desired, and depending on the quantity of material which it is desired to process, more or less long waveguides.

The fixed part of this module 7 is shown in detail in Figure 2 (Figure 2a = longitudinal section and Figure 2b = cross section). We can clearly see the partitions 9 facing the turns 10 of the propeller. For example, such a module 7 can measure 600 mm in length. It is provided with two magnetrons 2 and two excitation guides 3 of 70 mm width for example (between two successive magnetrons there are, for example, three propeller pitches 18 of total length of 150 mm) the diameter of the material supply and output tubes is 60 mm for example. The module is particularly suitable for 2.45 GHz microwave (the power of each magnetron is 1 kW). The height 14 of the partitions 9 is 20 mm for example. The material to be treated is located between the turns 10 of the propeller, in the lower part, near the drum axis 13. Knowing the minimum value of the loss factor ε "of the material to be treated, as well as its volume , the number of turns between two sources is determined, so that all the energy emitted by one source is absorbed before the energy from the next source arrives.

pour cet exemple de réalisation.The mobile part of this waveguide is shown in Figure 3 (Figure 3a is a longitudinal sectional view and Figure 3b is a cross-sectional view). The total height of the propeller plus drum is 440 mm, the propeller alone measuring 120 mm, which gives a fixed part / total height ratio

for this exemplary embodiment.

The dimensions of this module allow the useful filling of 4.8 I, or 90 kg of material per hour. In other words, by assembling, for example, ten of these modules one in the extension of the other after the removal of the flanges 8, one arrives at a treatment of nearly a ton of materials per hour, for an apparatus the total length of which does not exceed 6 m.

The sleeve 6 can advantageously be constituted by two half-sleeves 11, assembled by the flanges 15, to facilitate the mounting of these devices.

Figure 4 shows a "section" of the waveguide bounded by the sheath 6, the two fixed partitions 9, the two turns 10, and the surface of the drum axis 13. A lining 16 made of non-polar materials c ' ie non-absorbent dielectric material, for example polystyrene, fills the space between the two partitions 9. The material divided during treatment 17 is located in the lower part of the Archimedes screw above the gasket 16 .

The thickness 12 of the turns 10 in the vicinity of the partitions 9, is calculated so that there is never any communication between two excitation guides. (It is 15 mm for the non-limiting example described in the above).

The edge 19 of the propeller which faces the partition 9 is cut in a bevel.

The width, or dimension according to the pitch of the propeller 18, of the excitation device 3 applied against the sheath 6 is such that it exceeds the pitch of the propeller 18, this to avoid the reflection of the wave on the source .

The device according to the present invention, described and shown in the drawings, can, if desired, be pressurized by an inert gas - such as nitrogen for example -. It may also include (not shown in the figures) means for using the cooling air of the magnetrons 2 to remove, if necessary, the water vapor, for example, released from the treated material.

• -l'avantage de pouvoir traiter de grandes quantités de matières en continu de façon très rentable économiquement, avec une déperdition minimale d'énergie;
• - l'avantage de disposer d'installations simples, robustes et faciles à monter et à entretenir;
• -l'avantage de pouvoir utiliser des sources d'énergie de faible puissance, produites en grande série,
• - et également un avantage non négligeable que procure ce dispositif conforme à la présente invention: du fait de la présence de la vis d'Archimède, la matière, tout en subissant le traitement thermique, est constamment brassée, ce qui assure une homogénéisation parfaite de la matière traitée.

It follows from the above description, that whatever the embodiments and application adopted, there is obtained a device for the heat treatment of divided materials, using microwaves, which have, relative to devices aimed at the same goal previously known, significant advantages, among which may be mentioned in particular:

• the advantage of being able to process large quantities of materials continuously in a very economically profitable manner, with minimal energy loss;
• - the advantage of having simple, robust installations that are easy to assemble and maintain;
• -the advantage of being able to use low power energy sources, produced in large series,
• - And also a non-negligible advantage which this device in accordance with the present invention provides: due to the presence of the Archimedes screw, the material, while undergoing the heat treatment, is constantly stirred, which ensures perfect homogenization of the material treated.

Claims (11)

1. A device for the continuous heat treatment of divided materials, and particularly powder or grain materials, by UHF radiation, comprising a fixed part having a plurality of radiation sources (2) and a mobile part (19) formed by a conveyance worm rotating about an axis (13) or archimedes screw, for transporting the divided material to be treated, characterized in that it operates with a travelling wave and in that the fixed part forms with the mobile part a two part wave guide, the fixed part being formed by a sleeve (6) made from metal or from a similar conducting material, having metal dividing walls (9) substantially perpendicular to said sleeve and comprising, in the free space between the dividing walls, a lining 16 made from a non polar material, the pitch (18) of the screw corresponding exactly to the distance which separates two successive dividing walls (9) with which the sleeve (6) is provided, increased by the thickness (12) of the turn (10) of the screw, the width of the excitation guide (3) or dimension of this guide along the pitch (18) of the screw exceeding said screw pitch (18), said device further comprising: a plurality of magnetrons (2) applied against the outer surface of the sleeve (6), the distance between two successive magnetrons depending on the pitch of the screw (18) and on the material to be treated, since all the energy emitted by a source is absorbed before the energy of the following source arrives in the low part of the wave guide charged with the material to be treated; two openings, one for the intake (1), the other for the discharge (4) of the material, said openings being dimensioned so that the wave used cannot leave the wave guide.

2. The device according to claim 1, characterized in that the fixed part of the wave guide represents between one quarter and one half of the total height of the wave guide.

3. The device according to any one of claims 1 and 2, characterized in that the thickness (12) of the screw, particularly in the vicinity of the fixed part of the wave guide formed by the dividing walls (9), is calculated so that there is never communication between two excitation guides, in the top part, not charged with materials to be treated.

4. The device according to any one of claims 1 and 2, characterized in that the thickness of the fixed dividing walls (9) substantially perpendicular to the sleeve (6) is calculated so that there is no communication between two excitation guides, in the top part, not charged with materials to be treated.

5. The device according to any one of claims 1 to 4, characterized in that the device is provided with means for recovering and using the air for cooling the magnetrons (2) for possibly removing the water vapour from the treated material (17).

6. The device according to any one of claims 1 to 5, characterized in that the heat treatment device is pressurized by an inert gas.

7. The device according to any one of claims 1 to 6, characterized in that the intake and discharge openings (1, 4) for the materials (17) are square section tubes whose side is at most equal to half the wave length used for treating the material.

8. The device according to any one of claims 1 to 6, characterized in that the material intake and discharge openings are tubes having a circular section, whose diameters do not allow propagation of the wave used for treating the material.

9. The device according to any one of claims 1 to 8, characterized in that the achimedes screw is a variable pitch screw.

10. The device according to any one of claims 1 to 9, characterized in that the sleeve is formed by two half sleeves (11) assembled together by two flanges (15).

11. The device according to any one of claims 1 to 10, characterized in that the edge (19) of the screw which faces the dividing wall (9) is bevelled.

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