EP3803243B1 - Heat treatment device comprising a refractory envelope and use of such device - Google Patents

Description

The present invention relates to a heat treatment device.

The present invention also relates to the use of such a device for heat treating a product at a temperature above 800 degrees.

BACKGROUND OF THE INVENTION

The heat treatment devices commonly used in industry generally comprise a transfer member and a heating means performing the heat treatment.

There is thus known a heat treatment device comprising an enclosure and means for conveying the product between the inlet of the enclosure and the outlet of the enclosure which comprise a screw mounted to rotate in the enclosure along a geometric axis of rotation and means for driving the screw in rotation. The device further comprises means for heating the screw by the Joule effect.

The product to be treated is usually introduced at the inlet of the enclosure in the form of divided solids. The screw continuously pushes the product towards the outlet of the enclosure. Due to the temperature of the screw, the product is heated as it progresses, which allows its heat treatment.

However, such an arrangement does not always allow treatment at high temperatures to be envisaged.

The present applicant has thus proposed in its patent EP 2 218 300 to have an enclosure having internal walls made of refractory material, the screw constituting a means of heating the internal walls so that said internal walls themselves constitute means for heating by radiation the divided solids which progress in the enclosure.

With such an installation, the heat treatment of the solids divided by the radiation is therefore favored.

However, this is not yet sufficient to consider treating a product at very high temperatures.

In the request US2018/134963 , there is proposed a device for heat treatment of a product comprising an enclosure, a conveyor comprising a screw without axis of rotation, the screw being heated by the Joule effect. The space between the screw and the casing is not characterized.

OBJECT OF THE INVENTION

The object of the present invention is to design a heat treatment device better suited to treatments at very high temperatures.

The present invention also aims to propose a use of such a device.

GENERAL DEFINITION OF THE INVENTION

• une enceinte,
• un convoyeur du produit entre une entrée de l'enceinte et une sortie de l'enceinte qui comprend une vis montée pour tourner dans l'enceinte selon un axe géométrique de rotation et qui comprend un actionneur d'entraînement en rotation de la vis selon ledit axe,
• un chauffage par effet Joule de la vis.

With a view to achieving this object, a device for heat treatment of a product is proposed, comprising:

• a speaker,
• a conveyor of the product between an inlet of the enclosure and an outlet of the enclosure which comprises a screw mounted to rotate in the enclosure according to a geometric axis of rotation and which comprises an actuator for driving the screw in rotation according to said axis,
• heating by Joule effect of the screw.

According to the invention, the enclosure comprises a casing of refractory material through which the screw extends, said casing being shaped like a tube, an internal surface of which follows the contours of the screw.

In this way, the casing conforms to the contours of the screw. Thus, a space is limited between the screw and the casing, which makes it possible to increase the heat exchanges within the casing in which the product circulates.

The invention therefore allows a very significant rise in temperature of the product.

Thanks to the invention it is therefore possible to work at high temperatures and even at very high temperatures. The inventors were thus able to observe that it was possible to work at temperatures above 800 degrees Celsius, and even above 1000 degrees Celsius and preferably still at temperatures above 1300 degrees Celsius, 1500 degrees Celsius and even 1800 degrees Celsius ( such a temperature corresponding to the maximum temperature recorded in the enclosure; generally such a temperature is found at the level of the turn and the envelope towards the outlet of the enclosure).

Of course, the invention can also be used for heat treatments at lower temperatures (and therefore at temperatures below 800 degrees Celsius) if desired.

Optionally, the casing is made of refractory ceramic.

Optionally, the envelope is shaped as a hollow cylinder.

An internal radius of the envelope is greater than the external radius of the screw by a value between 1 and 20 millimeters.

Optionally, the internal radius of the casing is greater than the external radius of the screw by a value between 5 and 15 millimeters.

Optionally, the envelope is formed from a succession of sections.

Optionally, the different sections are shaped to be fitted into each other.

Optionally, the enclosure includes an outer casing which encloses the casing and is shaped at least internally to the shape of the casing.

Optionally, the case is shaped as a hollow cylinder.

Optionally, the enclosure comprises a cover made of thermally insulating material surrounding the envelope.

The present invention also relates to a use of such a device for thermally treating a product at a temperature above 800 degrees.

Optionally, the device is used to heat treat a product and the gas associated with its decomposition at a temperature above 800 degrees.

Other characteristics and advantages of the invention will emerge more clearly in the light of the description which follows and the appended drawings, relating to a particular embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

• la figure 1 est une vue schématique en coupe longitudinale d'un dispositif de traitement thermique selon un mode de réalisation particulier de l'invention ;
• la figure 2 est une vue en perspective de l'enveloppe du dispositif illustré à la figure 1 ;
• la figure 3 est une vue en perspective d'un tronçon de l'enveloppe illustré à la figure 2 ;
• la figure 4 est une vue en coupe transversale d'une portion du dispositif illustré à la figure 1.

Reference will be made to the figures in the appended drawings, where:

• the figure 1 is a schematic view in longitudinal section of a heat treatment device according to a particular embodiment of the invention;
• the figure 2 is a perspective view of the enclosure of the device shown in figure 1 ;
• the picture 3 is a perspective view of a section of the envelope shown in figure 2 ;
• the figure 4 is a cross-sectional view of a portion of the device shown in figure 1 .

DETAILED DESCRIPTION OF A PARTICULAR EMBODIMENT OF THE INVENTION

To the figure 1 is shown the heat treatment device according to a particular embodiment of the invention, generally designated at 1.

The device 1 is here applicable to the gasification of waste, for example plants, or else still polymeric, in order to produce a gas such as for example a methane gas or else dihydrogen. Of course, this application is not limiting and the device 1 can be used for many other applications. We can mention for example roasting, pyrolysis, gasification, devolatilization, desiccation... In the same way, the divided solids can be in the form of powders, granules, pieces, fibers, sheets... and be of vegetable, mineral, chemical nature...

The device 1 comprises an enclosure 2, of essentially horizontal general direction, which is kept at a distance from the ground by legs.

The enclosure 2 here comprises an inlet 4 arranged in the cover of the enclosure 2 substantially at the level of a first longitudinal end of the enclosure 2. According to a particular embodiment, the device comprises an inlet chimney 5 which is connected in a sealed manner to input 4 of the enclosure. The inlet chimney 5 is for example connected to a device for grinding, compacting, extruding, melting or granulating the product considered in divided solids or else to a device for pre-conditioning the product considered in the form of solids. divided. A pre-conditioning device makes it possible, for example, to heat and dry said product to prescribed values of temperature and relative humidity or even to densify the product or even to humidify the product or even to extract the interstitial air therefrom. by partial or total fusion.

The enclosure 2 further comprises a first outlet 6 arranged here in the bottom of the enclosure 2 substantially at the level of the second of the two longitudinal ends of the enclosure 2. According to a particular embodiment, the device comprises a outlet chimney 7 which is connected in a sealed manner to the first outlet 6 of the enclosure 2. The outlet chimney 7 is for example connected to a device for cooling the product.

The enclosure 2 further comprises here a second outlet 8 arranged here in the lid of the enclosure 2 substantially at the level of the second of the two longitudinal ends of the enclosure 2 but which can be located further upstream. This second outlet 8 will make it possible to recover gaseous by-products which could come from the treatment of the divided solids. The nature of the gaseous by-products concerned will depend on the type of treatment concerned: it may thus be gas, smoke, steam, heavy metal, etc. According to a particular embodiment, the device comprises an outlet chimney 9 which is connected in a sealed manner to the second outlet 8 of the enclosure 2. The outlet chimney 9 is for example connected to a device for post-treatment of gaseous by-products, for example to purify said by-products gaseous products.

Boxes (not shown here) are attached to each of the ends of enclosure 2.

The device 1 comprises a screw 10 having a longitudinal axis X and mounted to rotate around said longitudinal axis X in the enclosure 2. In this case, the screw 10 has the shape of a helical serpentine which is fixed at its two ends at the end of a shaft section 11a, 11b, but this naturally only constitutes an example, and any other geometry of the helical type may be used.

The screw 10 is thus itself devoid of a shaft strictly speaking.

Each shaft section 11a, 11b is connected at its other end to a coaxial shaft which passes through an associated box.

Each box is equipped with means serving to drive the screw 10 in rotation, as well as means ensuring the supply of electrical energy to the screw 10 so that the latter forms a means of heating by the Joule effect. The screw 10 therefore constitutes a heating transfer means.

For this purpose the screw 10 is formed in its mass of an electrically conductive material. The screw 10 is chosen here so that its melting point is high and obviously higher than the temperature at which it is desired to use the device. It is thus possible to have a metal screw with a melting point above 800 degrees but preferably above 1500 degrees Celsius, preferentially above 2000 degrees Celsius, still preferentially above 2500 degrees Celsius and even above 3000 degrees Celsius. For work at very high temperatures, it is thus possible to have a screw 10 in a refractory metal or in a refractory alloy, such as an alloy based on Tantalum (the melting point of the screw 10 then being substantially 3000 degrees Celsius).

Furthermore, if it is desired to carry out a heat treatment at high temperatures (typically above 800 degrees Celsius) or very high temperatures (typically above 1500 degrees Celsius), the boxes must be arranged and connected to the enclosure 2 in such a way so that the temperature prevailing inside said boxes is a temperature compatible with the components which are arranged therein and therefore at a temperature well below 800 degrees Celsius. To this end, provision may be made for thermal insulation of the boxes and/or ventilation of the boxes (for example by cooling fins, one or more fans, circulation of a cooling fluid, etc.). Preferably, tree stumps carrying the screw 10 are hollow so that a cooling fluid can circulate inside these shaft sections.

For more details, please refer to the document EP 2 218 300 aforementioned of the applicant, in which the drive and the heating of the screw 10 as well as the cooling of the boxes and the sections of trees are further described.

According to the invention, the enclosure comprises an envelope 12 made of refractory material through which the screw 10 extends. The screw 10 thus forms, in addition to its functions of direct heating of the products coming into contact with it and of longitudinal transfer of the said products , a heating of this casing 12 which thus itself constitutes a heating by radiation of the mass of divided solids.

Because the screw 10 is formed in its mass of an electrically conductive material, and is connected to at least one electrical power supply source, it will be necessary to provide that the casing 12 is made of a material which is both refractory and electrically insulating. It may for example be a refractory concrete or a refractory ceramic material such as those commonly used to make furnace walls. Such materials have a very high melting point and in particular above 2000 degrees Celsius. The casing 12 is for example based on alumina (Al ₂ O ₃ ). Of course, the casing 12 is chosen so that its melting point is high and obviously higher than the temperature at which it is desired to use the device.

In the present case, the chimneys 5, 7, 9 are preferably also made of refractory material of the same nature as that of the casing 12.

With reference to the various figures, the envelope 12 is shaped as a tube extending longitudinally and through which the screw 10 is arranged. The tubular casing 12 thus circumferentially surrounds the screw 10.

The screw 10 also rests here on the bottom of the casing 12.

The casing 12 is therefore shaped as a hollow cylinder.

The cross section of the casing 12 follows the contours of the screw 10. The cross section of the casing 12 is thus shaped like a ring, the inner circle of which surrounds the screw 10.

In this way, a space is limited between the screw 10 and the casing 12 surrounding it.

The gas produced by the partial or total thermal decomposition of the product is thus forced to pass through the center of the screw 10 and into the corresponding helical space through the turns where the temperature is highest, which makes it possible to be able to heat treat the gas from the product at very high temperatures, just like the solid phase of the product. In addition, the gas is forced to pass from the start through the center of the screw 10 and the helical space, which makes it possible to maximize the residence time of the gas in the center of the screw 10 during its passage through the enclosure.

The gas to escape from the casing must thus traverse the space left between the heating coils of the screw 10 due to the very close proximity between the screw 10 and the casing 12. It is this distance traveled to the heart of the screw which completes the heat treatment of the gas.

The proportion of gas leaving the top of the envelope 12 is thus limited by lengthening the duration of heat treatment of said gas accordingly.

The casing 12 is therefore shaped so that it is as adjusted as possible to the diameter of the screw 10. Preferably, the internal radius of the casing 12 is identical to the external radius of the screw 10. In this case the screw 10 also touches the rest of the casing 12 (and not only the bottom of the casing). The screw 10 and the casing 12 are thus concentric.

For reasons of ease of assembly, it may be preferred that the radius of the casing 12 be slightly greater than that of the screw. In this case, the screw resting on the bottom of the casing 12, the screw 10 and the casing 12 are not concentric but slightly offset. A sky then exists in the upper part of the envelope 12. The envelope 12 is shaped so that this sky is between 1 and 20 millimeters and preferably between 5 and 15 millimeters and more preferably between 5 and 10 millimeters .

In all cases, the casing 12 is shaped like a real sheath of the screw 10 by not only being shaped to the shape of the screw 10 but also close to the screw 10.

The casing 12 naturally surrounds the screw 10 at 360 degrees. Furthermore, the casing 12 extends at least over the entire length of the screw 10.

Preferably, the envelope 12 extends over the entire length of the enclosure 2.

The envelope 12 is for example manufactured by molding.

As more visible to figures 3 and 4 , the casing 12 is not here in one piece. The envelope 12 is thus formed of a succession of sections 13.

This notably facilitates the arrangement of the screw 10 inside the casing 12. In addition, it is thus possible to change only part of the casing 12 when one of the sections 13 is damaged.

This also facilitates the manufacture of the casing 12. It is possible in particular to manufacture each section 13 by molding.

Preferably, the different sections 13 are all identical to one another.

The casing 12 typically comprises between 3 and 7 sections.

Preferably, the different sections 13 are linked together by screwing, gluing, snap-fastening, interlocking, sealing, etc.

Preferably, the different sections 13 are shaped so that they can be fitted together one after the other.

Good continuity of the casing 12 is thus ensured. This makes it possible in particular to ensure good sealing of the casing 12, which is particularly advantageous for keeping the gaseous by-products inside the casing 12.

Furthermore, the interlocking of the different sections 13 allows self-centering of the different sections 13 between them, which facilitates the assembly of the casing 12.

Each section 13 is here in the form of a cylindrical tube, a first end of the section 13 having a circular internal groove 14 and a second end of the section 13 (opposite to the first) having a circular extension 15 capable of being inserted into the internal circular groove 14 of the adjacent section 13.

There is thus an interlocking by stairs of the different sections 13 between them which ensures good sealing of the assembly.

It is possible to provide a fixing of the different sections 13 between them once they are nested (for example by ceramic sealing).

As more visible to the figure 4 , according to a particular embodiment, the enclosure 2 comprises an outer case 16 which encloses the casing 12 and the screw 10 and is preferably shaped to the shape of the casing 12, and therefore of the screw 10.

The case 16 is therefore shaped as a tube extending longitudinally and through which the casing 12 is arranged, two side walls closing the tube. Said side walls are those through which the shaft sections 11a, 11b carrying the screw 10 extend.

The case 16 thus circumferentially surrounds the envelope 12. The case 16 naturally surrounds the envelope 12 at 360 degrees.

The case 16 is thus concentric with the envelope 12.

The cross section of the case 16 follows the contours of the envelope 12. The cross section of the case 16 is thus shaped like a ring, the inner circle of which surrounds the envelope 12.

In this way, a space is limited between the case 16 and the envelope 12.

Case 16 is here in one piece.

The case 16 has the shape of a hollow cylinder.

The case 16 is made of metallic material. Typically the case 16 is made of steel, such as stainless steel, and for example non-magnetic.

According to a preferred embodiment, the case 16 and the envelope 12 are not in contact with each other.

Thus, the enclosure 2 comprises an intermediate cover 17 of thermally insulating material extending between the casing 12 and the case 16. The cover 17 is for example made of rock wool.

Cover 17 is here arranged so that the outer surface of the envelope 12 is in contact with the inner surface of the cover 17 and that the inner surface of the case 16 is in contact with the outer surface of the cover 17.

Thus the cover 17 is also shaped to the shape of the enclosure 2 and the envelope 12.

The cover 17 is therefore shaped as a tube extending longitudinally and through which the casing 12 is arranged, the cover 17 itself extending through the case 16, two side walls closing the tube. Said side walls are those against which the casing 12 rests at its two ends and those also through which the shaft sections 11a, 11b carrying the screw 10 extend. Said side walls are themselves pressed against the corresponding side walls of the case 16. The cover 17 therefore extends over the entire length of the case 16 so as to rest at its two ends on the side walls of the case 16.

Cover 17 thus surrounds envelope 12 circumferentially. Cover 17 naturally surrounds envelope 12 at 360 degrees.

The cover 17 is thus concentric with the envelope 12.

The cross section of the cover 17 follows the contours of the case 16 and the envelope 12. The cross section of the cover 17 is thus shaped like a ring, the inner circle of which surrounds the envelope 12 and the outer circle of which is surrounded by case 16.

Cover 17 is in the shape of a hollow cylinder.

Cover 17 is here in one piece.

Due to its general tubular shape with layers (case, cover, envelope, screw) very close, even in contact for the case 16 and the cover 17 of a hand and the cover 17 and the envelope 12 on the other hand, the enclosure 2 turns out to be of small dimensions.

It has thus been possible to produce a device 1 for heat treatment at high temperatures and even very high temperatures which is at the same time simple, versatile and compact, and also consumes little energy, while allowing very varied treatments.

The invention is not limited to the embodiments which have just been described, but on the contrary encompasses any variant incorporating, with equivalent means, the essential characteristics stated above.

In particular, only the casing can be shaped to the shape of the screw. The case of the speaker may thus have another shape. It is also possible to have a case of which only the internal surface follows the shape of the envelope, the external surface being however different. The case and the cover and/or the cover and the envelope may not be in contact over the entire length of the case, the cover and/or the envelope.

The cover may not be in one piece but composed of several elements fixed together and/or fixed to the envelope and/or fixed to the case. We can get rid of a blanket.

The case may also not be in one piece.

The envelope may be in one piece. Only the inner surface of the casing can be shaped to the shape of the screw, the outer surface having another shape. The casing may thus be a tube, or an elongated and hollow member, the outer contour of which is not cylindrical.

The casing and the screw may be concentric even if the internal radius of the casing is greater than that of the screw, the screw then not resting at the bottom of the casing. Although here the product is introduced in the form of divided solids into the enclosure, the product may be introduced in another form, for example liquid or gaseous. In the same way, one or more products can be recovered at the outlet in the form of gas, liquid, oil, solid, etc. The number of entries and exits from the enclosure will vary accordingly.

Among the possible applications of the invention, it will also be noted that the treatment device can be mounted downstream of a conventional pyrolysis installation so as to treat the tank emerging from this pyrolysis in order to subject it to post-treatment.

Claims (11)

1. A device for subjecting a substance to heat treatment, the device comprising:

   an enclosure;

   a conveyor for conveying the substance between an inlet of the enclosure and an outlet of the enclosure, the conveyor comprising a screw mounted to rotate inside the enclosure about an axis of rotation and including an actuator for driving the screw in rotation about said axis, the screw itself not having a rotary shaft;

   Joule effect heating of the screw;

   wherein the enclosure comprises an envelope of refractory material having the screw extending therethrough, said envelope being shaped as a tube having a main inner surface following the outlines of the screw
   being characterized in that an inner radius of the envelope is greater than the outer radius of the screw by a value lying in the range 1 mm to 20 mm.
2. The device according to claim 1, wherein the envelope is made of refractory ceramic.
3. The device according to any preceding claims, wherein the envelope is in the shape of a hollow cylinder.
4. The device according to any preceding claims, wherein the inner radius of the envelope is greater than the outer radius of the screw by a value lying in the range 5 mm to 15 mm.
5. The device according to any preceding claims, wherein the envelope is made up of a succession of segments.
6. The device according to claim 5, wherein the various segments are shaped to engage in one another.
7. The device according to any preceding claims, wherein the enclosure includes an outer casing that encloses the envelope and that is shaped, at least on the inside, to match the shape of the envelope.
8. The device according to claim 7, wherein the casing is shaped as a hollow cylinder.
9. The device according to any preceding claims, wherein the enclosure includes a blanket made of thermally insulating material surrounding the envelope.
10. A use of the device according to any preceding claims, for heat treatment of a substance at a temperature higher than 800°C.
11. The use according to claim 10, wherein the device is used to apply heat treatment both to a substance and also to gas that is associated with the substance decomposing at a temperature higher than 800°C.

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