EP3118551B1 - Thermal installation for drying pasty material - Google Patents

Description

GENERAL TECHNICAL FIELD

The present invention relates to an installation for drying pasty products, more particularly sludge from biological purification.

STATE OF THE ART

Sewage sludge is the main waste produced by a wastewater treatment plant from liquid effluents. These residual sediments consist mainly of dead bacteria and mineralized organic matter.

They are now valorizable in agriculture by spreading or composting. They can also, before spreading, be digested by anaerobic bacteria to produce biogas (which will itself be used for electricity, heat, etc.) and the digestate will be spread on the land (possibly after composting). They can also be incinerated, alone or with garbage.

The recovery (and generally packaging) of wet sludge from biological purification involves their drying, which is commonly done by putting them in contact with hot walls.

Thus "indirect contact dryers" are known as pallet or screw dryers, plate dryers or disk dryers. In this technology, the energy is transferred via a conductive exchange surface.

In particular, the applicant developed the installation described in the application EP1553368 , which brings excellent results.

With reference to the figure 1a (and following), this known installation 1 comprises an airtight chamber 2 which contains a pair of parallel and side-by-side horizontal rotors 20a, 20b, which comprise each a series of arms 21a, 21b carried by respective horizontal shafts 22a, 22b and rotating between fixed heating disks 23a, 23b that the arms 21a, 21b scrape while rotating. The axes of rotation of the rotors 20a, 20b are located in the same horizontal plane.

These two rotors 20a, 20b between them determine a space located under the shafts 22a, 22b of the rotors 20a, 20b and which is housed a housing which contains a horizontal recycling screw 24 whose axis is located in the plane of symmetry of the rotors 20a, 20b.

This configuration allows the formation of thin layers of products to be dried improving the heat exchange coefficient with the heating surface. The installation provides indirect heating without air or oxygen in contact with the product to be dried. It eliminates the risk of explosion related to high temperatures of dry products, and allows adequate control of recycling conditions.

• La fiabilité mécanique est faible et nécessite une maintenance fréquente ;
• Le sécheur ne répond pas de façon satisfaisante au problème de consommation énergétique du séchage.

Despite all the technical innovations implemented, two problems remain:

• Mechanical reliability is low and requires frequent maintenance;
• The dryer does not respond satisfactorily to the energy consumption problem of drying.

It would be desirable to have a new generation drying system that is more efficient, more cost-effective, more reliable, and easier to use to maintain.

PRESENTATION OF THE INVENTION

• les moyens d'augmentation des pertes de charge comprennent un labyrinthe ;
• le labyrinthe comprend une conduite verticale ascendante suivie d'une conduite verticale descendante ;
• le circuit de vapeur s'étendant latéralement depuis ladite conduite verticale descendante du labyrinthe ;
• les moyens d'augmentation des pertes de charge comprennent un filtre ;
• ledit filtre est disposé dans la conduite verticale descendante ;
• les moyens d'augmentation des pertes de charge comprennent des moyens de pulvérisation d'eau dans les buées ;
• les moyens de pulvérisation d'eau sont disposés au-dessus du filtre ;
• le circuit de vapeur est configuré de sorte que l'eau pulvérisée dans les buées ruisselle jusque dans les moyens de traitement ;
• de l'eau est pulvérisée dans les moyens de compression, des moyens de purge étant disposés sur le circuit en sortie des moyens de compression de sorte à évacuer l'eau liquide ;
• les moyens de purge présentent une conduite verticale descendante suivie d'une conduite verticale ascendante, ladite conduite verticale descendante étant une branche du circuit ;
• la conduite verticale ascendante des moyens de purge comprend un filtre ;
• les moyens de purge présentent en bas de ladite conduite verticale descendante des moyens de vidange automatique ;
• la conduite verticale ascendante est dans sa partie haute en connexion fluidique avec les moyens de traitement.

According to a first aspect, the invention relates to a thermal plant for drying pasty material, as claimed in claim 1. The installation according to the invention is advantageously completed by the following features, taken alone or in any of their technically possible combination:

• the means for increasing the pressure drops comprise a labyrinth;
• the labyrinth comprises an ascending vertical pipe followed by a descending vertical pipe;
• the vapor circuit extending laterally from said downward vertical pipe of the labyrinth;
• the means for increasing the pressure drops comprise a filter;
• said filter is disposed in the descending vertical pipe;
• the means for increasing the pressure drops comprise means for spraying water in the steams;
• the water spraying means are arranged above the filter;
• the steam circuit is configured so that the water sprayed into the steam flows into the treatment means;
• water is sprayed into the compression means, purge means being disposed on the circuit at the outlet of the compression means so as to evacuate the liquid water;
• the purge means have a descending vertical pipe followed by an upward vertical pipe, said downward vertical pipe being a branch of the circuit;
• the upward vertical duct of the purge means comprises a filter;
• the purge means have, at the bottom of said downward vertical pipe, means for automatic emptying;
• the upward vertical duct is in its upper part in fluid connection with the processing means.

PRESENTATION OF FIGURES

• les figures 1a et 1b représentent des structures de plateau chauffants connues ;
• la figure 2 est un schéma global d'une installation thermique selon l'invention ;
• les figures 3a-3c représentent sous différentes vues un mode de réalisation préféré d'une chambre d'une installation selon l'invention ;
• les figures 4a-4b représentent sous différentes vues un mode de réalisation préféré d'un circuit de vapeur d'une installation selon l'invention ;
• la figure 5 représente un mode de réalisation préféré de moyens de purge d'une installation selon l'invention ;
• les figures 6a-6c représentent sous différentes vues un mode de réalisation préféré d'un dispositif d'introduction de matière pâteuse d'une installation selon l'invention ;
• les figures 7a-7c représentent sous différentes vues un mode de réalisation préféré de moyens de conditionnement de matière séchée d'une installation selon l'invention.

Other features, objects and advantages of the invention will emerge from the description which follows, which is purely illustrative and nonlimiting, and which should be read with reference to the appended drawings in which:

• the figures 1a and 1b represent known heating plate structures;
• the figure 2 is an overall diagram of a thermal installation according to the invention;
• the Figures 3a-3c represent in different views a preferred embodiment of a chamber of an installation according to the invention;
• the Figures 4a-4b represent in different views a preferred embodiment of a steam circuit of an installation according to the invention;
• the figure 5 represents a preferred embodiment of purge means of an installation according to the invention;
• the Figures 6a-6c represent in different views a preferred embodiment of a pasty material introduction device of an installation according to the invention;
• the Figures 7a-7c represent in different views a preferred embodiment of dried material conditioning means of an installation according to the invention.

DETAILED DESCRIPTION General Architecture

With reference to the figure 2 The invention relates to a heating installation 1 of pasty material drying.

The pasty material comprises a fraction of liquid water typically between 50 and 90%. This is usually sewage sludge, but also coffee grounds, organic waste, etc. The objective is to obtain dried material having a water fraction of less than 5% for recovery of the material.

• une chambre 2 dans laquelle la matière pâteuse est chauffée (il s'agit de la partie également appelée « séchoir ») ;
• un dispositif d'introduction sous pression 7 de ladite matière pâteuse dans la chambre 2 ;
• un circuit de vapeur 4 ; et
• des moyens de conditionnement 8 de la matière pâteuse séchée issue de la chambre 2.

Installation 1 consists of four main modules:

• a chamber 2 in which the pasty material is heated (this is the part also called "dryer");
• a pressure introduction device 7 of said pasty material in the chamber 2;
• a steam circuit 4; and
• conditioning means 8 of the dried pasty material from the chamber 2.

The present installation 1 implements what is called the "mechanical vapor compression (or recompression)" (CMV). This means that the heat supplied to the pasty material in the chamber 2 is obtained not by conventional thermal means such as electric resistance or a burner, but by increasing the pressure of a gaseous coolant, in particular water vapor.

Indeed the compression of a gas makes it possible to raise its pressure and its temperature, and thus its enthalpy. Thus, the "heating means" of the present installation is a compressor 6 arranged on the steam circuit 4.

In a particularly preferred manner (this will be discussed in detail later), the recompressed vapor is composed of steam from the heating of said pasty material, i.e. evaporated water vapor from the moisture of the pasty material to be dried.

In other words, the pasty material is heated in the chamber 2, this gives off steam, which is compressed so as to heat the pasty material, etc.

This cycle has an excellent energy efficiency in that it allows to value the latent heat of the fumes. However, it poses a technical difficulty, which is that the chamber 2 must operate completely sealed, despite continuous inputs and outputs pasty material to dry / dried.

Indeed, any leak or entry of air mechanically decreases the pressure and / or the water vapor temperature, and decreases the energy efficiency. Moreover, in the case where the dried material is for example composed of sewage sludge, it gives off odors that may have an unpleasant odor, or even be toxic, and the slightest leakage could have consequences on comfort and health staff working around the drying plant.

All the innovations of the present installation 1 of which a particularly preferred embodiment will now be described aim, inter alia, to guarantee the tightness of the chamber and the purity of the vapors so as to maximize the efficiency of the CMV.

Drying chamber

The heating plates 23a, 23b of the known installation represented by the figure 1a are hollow, and fed with hot steam, which condenses by transferring its heat to the sludge, the condensate being discharged via taps in the lower part of the plates 23a, 23b as seen in detail in the left part of the figure 1a . The two plates 23a and 23b of a pair of juxtaposed plates communicate fluidically by their median part so that a first plate 23a of the pair is a point of entry of the steam, and that the other plate 23b of the pair an outlet point of the non-condensed vapor. U-shaped "upside down" is given to the trays 23a, 23b so that the shafts 22a, 22b do not pass "inside" the trays 23a, 23b and that these funds can be removed by translation, this involving nevertheless a stop and a complete emptying of the installation to disassemble the connections of the pipes. This U-shape defines four low condensate collection points per pair of trays 23a, 23b.

• du passage de toutes les tuyauteries des condensats en partie basse de la chambre 2 en garantissant l'étanchéité ;
• de la collecte de toutes les tuyauteries des condensats à l'extérieur du sécheur.

This structural choice allows a complete purge of the condensates (and therefore maximum use of the exchange surface of the trays), but causes a certain number of significant difficulties related to the realization:

• the passage of all condensate piping in the lower part of the chamber 2 ensuring sealing;
• collection of all condensate piping outside the dryer.

Alternatively, it was proposed by the Applicant, as we see on the figure 1b , A tray structure 23a, 23b including an inner plurality of inner pipes condensate drain, in particular four tubes (one for each of four low points of a pair of plates 23a, 23b "U"), so to allow a common point of collection of condensates and non-condensed steam at an "exit box". This substantially simplifies the piping system, but the purge sometimes becomes incomplete with a preferential passage of steam through a single pipe instead of the four. The draining of the condensates then becomes random, and if some of the pipes the associated lower parts in the trays are filled with condensates, which decreases the heat exchange area by the same amount. In addition, the "output boxes" are technically complex elements with a tightness that is difficult to achieve, and the maintenance remains heavy.

It would be desirable to have a new simple, efficient architecture, allowing without fail a complete purging of the heating plates, an improved sealing to favor the CMV, and a maintenance largely facilitated.

With reference to Figures 3a-3c , there is arranged in the chamber 2 of the present installation 1 at least one pair of rotors 20a, 20b (advantageously exactly one pair: left rotor 20a and a right rotor 20b) parallel arranged side by side, each comprising a shaft 22a, 22b carrying arms 21a, 21a which rotate between heating plates 23a, 23b by scraping.

As we see on the figure 2a each rotor stage 20a, 20b advantageously comprises a series of three arms 21a, 21b. There is an alternation of rotor stages 20a, 20b rotated by the shafts 22a, 22b and trays 23a, 23b.

The shafts 22a, 22b extend in a substantially horizontal plane (although advantageously slightly oriented downwards towards the rear of the chamber 2 to promote the flow of the pasty material, as will be seen later. ), and the arms / plates 21a, 21b, 23a, 23b extend in a perpendicular plane (and therefore substantially vertical).

Each plate 23a, 23b is a hollow heat exchanger in which circulates a phase-change heat transfer fluid (typically water vapor recompressed, as explained), and has a concave shape defining a substantially radial channel C for the transverse passage of a shaft 22a, 22b, which gives it substantially a shape in "C". This channel C allows that each plate 23a, 23b can take substantially the shape of a disc coinciding with the surface swept by the arms 21a, 21, without the need to thread the plates 23a, 23b on the shaft 22a, 22b. The channel C has as such a width approximately equal to the diameter of the shaft 22a, 22b.

The preferred installation 1 differs from the prior art in that the channel C extends not downwards, as seen on the figures 1a , 1b but substantially laterally. Specifically, the channel C is oriented towards the middle of the chamber 2. In other words, the "left" trays 23a have a channel C oriented to the right, and the "right" trays have a channel C oriented towards the right. left.

In one case as in the other, this allows to define within the heating plate 23a, 23b an upper portion PS and a lower portion PI separated by said channel C (which schematically correspond to the two "halves" of the "C" form each tray 23a, 23b). The notion of "superior" and "inferior" is here relative to the altitude: the upper part PS is physically above the lower part PI. This allows coolant in the liquid phase to flow by gravity from the upper part PS to the lower part PI.

As we always see on the figures 3a , the upper part PS has an inlet for the coolant (in gaseous form), and the lower part P has a heat transfer fluid outlet (in liquid and / or gaseous form if there are incondensables), said inlet and outlet of heat transfer fluid extending substantially laterally opposite the channel C. Preferably, the inlet is at the highest point of the plate 23a, 23b, and the outlet at the lowest point.

This guarantees a complete purge of the trays 23a, 23b, and therefore maximum performance: there is only one output possible for the condensates, and no "dead zones" that can be filled. In addition the realization of the steam inlet manifolds and condensate outlet is facilitated since there are only two pipes to predict, and they are easy to access.

Even more preferably, the plate 23a, 23b is integral with a side wall 31 (which is vertical) of the chamber 2, through which said heat transfer fluid inlet and outlet of the plate 23a, 23b. In in other words, the pipes are welded to the side wall, and there is no particular sealing to be provided at this level since the wall 31 can not disassemble the plates 23a, 23b. The assembly consisting of a side wall 31 and one or more plates 23a, 23b identical side by side (each separated by a rotor stage 20a, 20b) and whose inputs / outputs through the vertical wall 31 is called a "radiator block" 32. We see six successive ones on the figure 3c . Preferably, the radiator blocks 32 are connected in parallel by a common steam input circuit disposed above the side walls 31, and by a common condensate / noncondensable output circuit arranged below the side walls 31.

The idea is that said side wall 31 is a movable wall distinct from a main wall 30 of the chamber 2, said main and side walls 30, 31 being sealingly joined when the installation 1 is in operation. Thus, the seal must only be provided at the junction between the main and side walls 30, 31 (and possibly between two side walls 31 of two adjacent blocks), which is much easier than at the level of the pipes. The quality of the sealing of the chamber 2 is improved for much lower costs.

In addition, the assembly formed by at least the plate 23a, 23b and the side wall 31 (ie a radiator block 32) is adapted to slide laterally so as to disengage the shaft 22a, 22b from the channel C, for example to maintenance, since the latter extends laterally opposite to the side wall 31. This is clearly visible on the figure 3b . It suffices for this to provide horizontal rails along which the plate 23a, 23b can slide. A single man can perform this operation, whereas before he needed a crane.

In addition, there is no need to empty the entire steam circuit 4, just close two valves at the common input and output circuits so as to isolate the heat sink while keeping the other "full". This greatly facilitates maintenance.

The chamber 2 also comprises a horizontal recycling screw 24 located under the rotors 20a, 20b, the latter moving towards the bottom of the chamber 2 the dried material for extraction.

Steam circuit

• des moyens d'aspiration 3 des buées ;
• des moyens de traitement 5 ;
• des moyens de compression 6 ; et
• au moins un échangeur thermique (typiquement les plateaux chauffants 23a, 23b) disposé au sein de ladite chambre 2

As explained, the installation 1 comprises a steam circuit 4 for the circulation of steam from the heating of said pasty material in the chamber 2 with reference to Figures 4a-4b . In the preferred embodiment for the implementation of the CMV, on this circuit 4 are successively arranged:

• extraction means 3 of the steams;
• treatment means 5;
• compression means 6; and
• at least one heat exchanger (typically the heating plates 23a, 23b) disposed within said chamber 2

The suction means 3 generally take the form of a hood above the chamber 2 (with a substantially frustoconical shape), which with the main and lateral walls 30, 31 defines the sealed envelope of the chamber 2.

Despite its position well above the pasty material, it can be seen that the suction means 3 collect at the same time as the fumes solid particles resulting from the heating of said pasty material (ie microscopic fragments of the dried pasty material), called "fine". Very light, they are driven by the flow of evaporation vapor.

The problem is that these fines are found in the compressed steam, which on the one hand damages the compression means 6 and on the other hand decreases the energy performance of the installation 1. An effective CMV requires a purest vapor possible. The treatment means 5 have traditionally this role of purification of the vapors, but we note that they consume a lot of energy and tend to this butcher often (because of the fines), which results in a sudden cessation of the compression means 6, which in addition to the degradation of the equipment a temporary shutdown of the installation 1 and operating losses.

To solve this problem and to facilitate the CMV, the steam extraction means 3 comprise means of increasing head losses 40. This may seem at first sight paradoxical, insofar as it requires an increase in the consumption of energy at the compression means 6 so as to compensate for the pressure drop, but it is found that the local increase in pressure drops at the suction means effectively traps the fines. In particular these are deposited on the walls due to the increase in friction.

And insofar as the means for increasing the pressure drops 40 are arranged above the chamber 2 (which is naturally the case, in view of the "hood" shape of the means 3, the means of increasing preferably at least a portion of said trapped solid particles fall directly into the chamber 2. In other words, the system is self-locking. The fines are no longer lost, but well valued with the rest of the dried material.

Preferably, the means for increasing the pressure drop 40 have an at least partially flexible outer wall. It is then sufficient to "tap" for example by hand this flexible area so that the fines come off and fall. In particular, the means for increasing the pressure drops 40 can even comprise means of vibration (such as a piston, or a rotational weight) of said flexible part of the outer wall, which "strike" at regular intervals the part flexible to break down the fines.

The means for increasing the pressure drops 40 advantageously comprise a labyrinth 41 and / or a filter 42, preferably both. By "labyrinth" we mean a complex and sinuous part with abrupt changes of direction so as to increase the areas on which the fines can be deposited. With reference to the figure 4a the labyrinth 41 may comprise an upward vertical duct followed by a downward vertical duct. In particular, as explained the means 40 may consist of a dome, comprising a vertical dividing wall separating the ascending pipe from the down pipe.

The steam circuit 5 extends laterally from said downward vertical pipe of the labyrinth 41 so as to generate a new bend.

Said filter 42 may be arranged in the descending vertical pipe, advantageously in combination with water spray means 43 in the steam (it is noted that these may be present without the filter 42). The idea is to moisten the remaining fines that have not been trapped by the labyrinth part so as to weigh them down and make them fall.

The water spraying means 43 are in the example disposed above the filter 42, so as to have a large wet surface to touch all the fines. The steam circuit 4 is preferably configured so that the water sprayed in the steam flows into the treatment means 5. It is imperative that the water can not reach the chamber 2, which is the case as soon as the means spraying 43 are in the downcomer. It is noted that an overflow 44 makes it possible to short-circuit the filter 42 and to discharge directly into the circuit 4 water that could accumulate above the filter 42 and overflow into the chamber 2. The circuit 4 goes down as for him in slight slope towards the means of treatment 5 which collects the liquid water laden with fines, and the quasi-pure vapors.

With reference to the figure 5 , the treatment means 5 preferably have a downward vertical duct (arrival of the circuit 4) followed by an ascending vertical duct. Specifically, upward driving surrounds the downcomer in the manner of a bottle in which is inserted a straw. The lower part is filled with water from the spraying means 43, and the water vapor "bubbles" through so as to gain the top of the ascending pipe, at which the output of the treatment means 5. The upward vertical duct of the treatment means 5 comprises a filter 52, which approximately defines the separation between the low and high parts of the means 5.

The water level is preferably controlled, and for this there is a purge means 51 at the bottom of the "bottle", i.e. at the bottom of the downward vertical pipe. The purge means 51 may be automated to maintain a substantially constant level. Slight increases and decreases in the level make it possible to clean the filter 52.

Injection of pasty material

The installation 1 comprises a device for introducing under pressure 7 of said pasty substance into the chamber 2. The pasty material is thus discharged into the chamber 2 in the upper part via injectors 74a, 74b of the pressure introduction device 7, ie nozzles that disperse the material in the chamber 2 for better drying.

As explained, this device 7 is a critical component for the sealing of the chamber 2. It must inject only the pasty material and no gas for the proper functioning of the CMV. Conversely, the chamber 2 must not leak via its entrance pasty material.

For this purpose we know high pressure injection systems that try to prevent the entry / exit of air. It is noted that the fine spray nozzles of these systems tend to clog, because the pasty material is not homogeneous (possible presence of agglomerates). This results in maintenance operations for unclogging that are long and complex.

The present optimized installation 1 has, to solve this, an innovative pressure introduction device 7, in accordance with the Figures 6a-6c .

The latter comprises a first and a second introduction set 70a, 70b, typically a left set and a straight set. They are identical.

Each comprises a pasty material circuit 71a, 71b on which are successively arranged a jack 72a, 72b, a pasture admission valve 73a, 73b and an injector 74a, 74b opening into the chamber 2.

The two cylinders 72a, 72b and the two valves 73a, 73b are actuated in a coordinated manner so that when an introduction assembly 70a, 70b receives pasty material via its valve 73a, 73b, the other introductory set 70a, 70b injects pasty material into the chamber 2 via its injector 74a, 74b.

In other words, the pasty material is continuously injected into the chamber 2 via the alternating operation of the two introducer assemblies 70a, 70b. At any time (operation), one is filling while the other is in compression, the valves 73a, 73b acting as check valves. More specifically, the high-pressure material blocked in the circuits 71a, 71b acts as plugs which permanently ensure an absolute seal.

More precisely, the valves 73a, 73b are opened and then closed periodically in a coordinated manner so that the opening of one coincides with the closure of the other. This is for example obtained by a piston 78 visible on the Figure 6c which at regular intervals simultaneously changes the state of the two valves 73a, 73b. Thus, at any moment one is open and the other is closed. Preferably the cycle is symmetrical, that is to say that each valve 73a, 73b is open as much as the other.

And the pressurized introduction device 7 comprises a compressor 75 supplying in common and continuously the two valves 73a, 73b in pasty material, for example via a "Y" pipe, so that at any time the single set of introduction 70a, 70b whose valve 73a, 73b is open receives pasty material via its valve 73a, 73b. As explained, at any time a valve 73a, 73b and only one is open, and the pasty material can be supplied continuously. The absence of intermittency at this level ensures that the Y pipe is permanently full of pasty material without the possibility of air passing.

The pressurized introduction device 7 may further comprise a pasty material storage tank 77 and an endless screw 76 disposed in said tank 77 for the transfer of the pasty substance to the compressor 75.

The cylinders 72a, 72b are pistons making trips back and forth in their circuit 71a, 71b (i.e. having a periodic oscillating moment, synchronous with that of the valves 73a, 73b). More specifically, the cylinders 72a, 72b and the valve 73a, 73b of each insertion assembly 70a, 70b are actuated in a coordinated manner so that the cylinder 72a, 72b increases the pressure in the pasty circuit 71a, 71b when the valve 73a, 73b is closed, and decreases the pressure in the pasty circuit 71a, 71b when the valve 73a, 73b is open.

• dans le premier temps, la première vanne 73a est fermée et le premier vérin 72a avance. La pression augmente fortement dans le premier circuit 70a (jusqu'à plus de 100 bar, voir 200 bar) car et la matière pâteuse est pulvérisée par le premier injecteur 74a. A ces niveaux de pression, tout agglomérat qui bloquerait l'injecteur 74a est instantanément broyé, tout bouchage est impossible. Simultanément, la deuxième vanne 73b est ouverte et le deuxième vérin 72b recule. Dans la mesure où le compresseur 75 continue d'amener de la matière pâteuse aux vannes 73a, 73b et que seulement la deuxième est ouverte, cette matière est forcée d'occuper la place libérée par le deuxième vérin 72b.
• Les vannes 73a, 73b changent de position, et les vérins 72a, 72b changent de sens de déplacement, et dans un deuxième temps on fait exactement les mêmes opérations en inversant les rôles du premier et du deuxième ensemble 70a, 70b.

We obtain a two-cycle cycle:

• in the first step, the first valve 73a is closed and the first cylinder 72a advances. The pressure increases sharply in the first circuit 70a (up to more than 100 bar, see 200 bar) because and pasty material is sprayed by the first injector 74a. At these pressure levels, any agglomerate that would block the injector 74a is instantly crushed, all clogging is impossible. Simultaneously, the second valve 73b is opened and the second cylinder 72b moves back. Insofar as the compressor 75 continues to bring pasty material to the valves 73a, 73b and only the second is open, this material is forced to occupy the place released by the second cylinder 72b.
• The valves 73a, 73b change position, and the cylinders 72a, 72b change direction of movement, and in a second step we do exactly the same operations by reversing the roles of the first and second set 70a, 70b.

As explained, the operation is continuous, with absolute tightness, and a physical impossibility of blocking.

Extraction of the dried material

The installation 1 comprises conditioning means 8 of said dried pasty material from the chamber 2. As shown in FIG. figure 7a These packaging means 8 are in the rear part of the chamber and collects the dried material pushed by the screw 24, which is facilitated by a slight slope toward the rear of the chamber 2.

As explained, these means 8 are also a critical component for the sealing of the chamber 2. They must extract only the dried pasty material and let no gas enter for the proper functioning of the CMV.

With reference to figures 7b and 7c , the conditioning means 8 comprise an extrusion cylinder 82 of substantially vertical axis and directed downwards, a feeding screw 81 feeding the extrusion cylinder 82, and a booster chamber 83 extending the end of the cylinder of the cylinder. extrusion 82.

The cylinder 82 is oriented in the direction of gravity. More specifically, it compresses the dried material by pushing it downwards, that is to say to the booster chamber 83. The latter consists of an extension of the cylinder 82 receiving compressed dried material. As for the introduction device 7 of the pasty material, the idea is to use the length of the booster chamber 83 as a plug of material preventing the entry / exit of gas.

Preferably, the booster chamber 83 comprises means for increasing the pressure drops 84 so as to facilitate the generation of the plug. The higher the losses, the more the material will be packed, and the more it holds despite gravity. As shown on the Figure 7c said means for increasing head losses 84 consist of an extrusion grid, ie a die, into which the dried material must pass forcibly. This completely compresses the dried material, which can be pelletised: at each descent of the cylinder 82 (and therefore at each step of the cap downwards), means for pelletizing the dried pasty material at the outlet of said extrusion grid 84 can slice the "carrot" that is past to obtain a pellet. These constitute an optimal packaging allowing the dried material to be transported, valorized, etc.

The feed screw 81 is a worm operating intermittently, the latter and the extrusion cylinder 82 are actuated in a coordinated manner so as to fill the cylinder 82 when in the up position.

More specifically, when the cylinder 82 goes down it advances the plug of compacted material in the booster chamber 83, which brakes its descent, the screw 81 then being stopped. Then the cylinder 82 goes up, without the plug which remains where it is under the effect of gravity and strong friction due to compaction. There is then a vacuum at the top of the cap, empty which is filled with material (still not packed), brought by the screw 81 which starts. This new material will then be compacted by the cylinder 82 so as to increase the plug, etc. This guarantees a perfect seal while facilitating the packaging of the dried material.

Note that the chamber 2 provides dried material continuously, while the feed screw 81 operates intermittently. To solve this problem, we add an auxiliary screw 85 continuously supplying the dried pasty material from the chamber 2 (more precisely from a hopper 89 at the outlet of the chamber 2) to a vertical pipe 86 above the screw of feeding 81. The auxiliary screw 85 acts as a first sealing barrier preventing air from the chamber 2 to access the vertical pipe 86, which serves as a "silo" storage for the feed screw 81

Like the means for increasing the pressure drops 40 of the steam circuit 4, said vertical pipe 86 may have an area 87 at least partially flexible. This makes it possible to add to the conditioning means 8 comprise means of vibration 88 of said flexible zone 87 of the vertical pipe 86. Indeed, since the feed screw 81 does not operate continuously, the dried material which accumulates in permanence in the vertical pipe can "vault", that is to say, to stabilize in an ogival shape that prevents it from falling, and no longer allows to feed the booster screw 81 which rotates in a vacuum. There is no risk of air entry (as the cap remains in place in the booster chamber 83), but the dried material no longer comes out. The vibration of the flexible zone 87 makes it possible to collapse any potential vault in construction so as to guarantee the arrival of the material in the screw 81, and the production of pellets steadily.

DETAILED DESCRIPTION General Architecture

With reference to the figure 2 The invention relates to a heating installation 1 of pasty material drying.

The pasty material comprises a fraction of liquid water typically between 50 and 90%. This is usually sewage sludge, but also coffee grounds, organic waste, etc. The objective is to obtain dried material having a water fraction of less than 5% for recovery of the material.

• une chambre 2 dans laquelle la matière pâteuse est chauffée (il s'agit de la partie également appelée « séchoir ») ;
• un dispositif d'introduction sous pression 7 de ladite matière pâteuse dans la chambre 2 ;
• un circuit de vapeur 4 ; et
• des moyens de conditionnement 8 de la matière pâteuse séchée issue de la chambre 2.

Installation 1 consists of four main modules:

• a chamber 2 in which the pasty material is heated (this is the part also called "dryer");
• a pressure introduction device 7 of said pasty material in the chamber 2;
• a steam circuit 4; and
• conditioning means 8 of the dried pasty material from the chamber 2.

The present installation 1 implements what is called the "mechanical vapor compression (or recompression)" (CMV). This means that the heat supplied to the pasty material in the chamber 2 is obtained not by conventional thermal means such as an electric resistance or a burner, but by increasing the pressure of a gaseous coolant, in particular a fluid phase change, in particular water vapor.

Indeed the compression of a gas makes it possible to raise its pressure and its temperature, and thus its enthalpy. Thus, the "heating means" of the present installation is at least one compressor 6 disposed on the steam circuit 4, advantageously two compressors 6 arranged successively (possibly a two-stage compressor) so as to implement two levels of compression as represented on the figure 2 .

In a particularly preferred manner (this will be discussed in detail later), the recompressed vapor is composed of steam from the heating of said pasty material, i.e. evaporated water vapor from the moisture of the pasty material to be dried.

In other words, the pasty material is heated in the chamber 2, this gives off steam, which is compressed so as to heat the pasty material, etc.

This cycle has an excellent energy efficiency in that it allows to value the latent heat of the fumes. However, it poses a technical difficulty, which is that the chamber 2 must operate completely sealed, despite continuous inputs and outputs pasty material to dry / dried.

All the innovations of the present installation 1 of which a particularly preferred embodiment will now be described aim between other to guarantee the tightness of the chamber and the purity of the fumes so as to maximize the yield of the CMV.

It will be understood that even if the CMV is particularly preferred (and in the remainder of the present description we will take the example of steam vapor), the present installation can use any heat transfer fluid, including thermal fluids. conventional (without phase change).

Drying chamber

The heating plates 23a, 23b of the known installation represented by the figure 1a are hollow, and fed with hot steam, which condenses by transferring its heat to the sludge, the condensate being discharged via taps in the lower part of the plates 23a, 23b as seen in detail in the left part of the figure 1a . The two plates 23a and 23b of a pair of juxtaposed plates communicate fluidically by their median part so that a first plate 23a of the pair is a point of entry of the steam, and that the other plate 23b of the pair an outlet point of the non-condensed vapor. U-shaped "upside down" is given to the trays 23a, 23b so that the shafts 22a, 22b do not pass "inside" the trays 23a, 23b and that these funds can be removed by translation, this involving nevertheless a stop and a complete emptying of the installation to disassemble the connections of the pipes. This U-shape defines four low condensate collection points per pair of trays 23a, 23b.

• du passage de toutes les tuyauteries des condensats en partie basse de la chambre 2 en garantissant l'étanchéité ;
• de la collecte de toutes les tuyauteries des condensats à l'extérieur du sécheur.

This structural choice allows a complete purge of the condensates (and therefore maximum use of the exchange surface of the trays), but causes a certain number of significant difficulties related to the realization:

• the passage of all condensate piping in the lower part of the chamber 2 ensuring sealing;
• collection of all condensate piping outside the dryer.

Alternatively, it was proposed by the Applicant, as we see on the figure 1b , A tray structure 23a, 23b including an inner plurality of inner pipes condensate drain, in particular four tubes (one for each of four low points of a pair of plates 23a, 23b "U"), so to allow a common point of collection of condensates and non-condensed steam at an "exit box". This substantially simplifies the piping system, but the purge sometimes becomes incomplete with a preferential passage of steam through a single pipe instead of the four. The purge of the condensates then becomes random, and if some pipes clog up the lower parts associated in the trays are filled with condensates, which correspondingly decreases the heat exchange surface. In addition, the "output boxes" are technically complex elements with a tightness that is difficult to achieve, and the maintenance remains heavy.

It would be desirable to have a new simple, efficient architecture, allowing without fail a complete purging of the heating plates, an improved sealing to favor the CMV, and a maintenance largely facilitated.

With reference to Figures 3a-3c , there is arranged in the chamber 2 of the present installation 1 at least one pair of rotors 20a, 20b (advantageously exactly one pair: left rotor 20a and a right rotor 20b) parallel arranged side by side, each comprising a shaft 22a, 22b carrying arms 21a, 21a which rotate between heating plates 23a, 23b by scraping.

As we see on the figure 2a each rotor stage 20a, 20b advantageously comprises a series of three arms 21a, 21b. There is an alternation of rotor stages 20a, 20b rotated by the shafts 22a, 22b and trays 23a, 23b.

The shafts 22a, 22b extend in a substantially horizontal plane (although advantageously slightly oriented downwards towards the rear of the chamber 2 to promote the flow of the pasty material, as will be seen later), and the arms / plates 21a, 21b, 23a, 23b extend in a perpendicular (and therefore substantially vertical) plane.

Each plate 23a, 23b is a hollow heat exchanger in which circulates a heat transfer fluid in particular with a phase change (typically water vapor recompressed, as explained), and has a concave shape defining a substantially radial channel C for the passage crosswise of a shaft 22a, 22b, which gives it substantially a shape "C". This channel C allows that each plate 23a, 23b can take substantially the shape of a disk coinciding with the surface swept by the arms 21a, 21, without the need to thread the plates 23a, 23b on the shaft 22a, 22b. The channel C has as such a width approximately equal to the diameter of the shaft 22a, 22b.

The preferred installation 1 differs from the prior art in that the channel C extends not downwards, as seen on the figures 1a , 1b but substantially laterally. Specifically, the channel C is oriented towards the middle of the chamber 2. In other words, the "left" trays 23a have a channel C oriented to the right, and the "right" trays have a channel C oriented towards the right. left.

In one case as in the other, this allows to define within the heating plate 23a, 23b an upper portion PS and a lower portion PI separated by said channel C (which schematically correspond to the two "halves" of the "C" form each tray 23a, 23b). The notion of "superior" and "inferior" is here relative to the altitude: the upper part PS is physically above the lower part PI. This possibly allows liquid phase heat transfer fluid to flow by gravity from the upper part PS to the lower part PI.

As we always see on the figures 3a , the upper part PS has an inlet for the coolant (in gaseous form), and the lower part P has a heat transfer fluid outlet (in liquid and / or gaseous form if there are incondensables), said inlet and outlet of heat transfer fluid extending substantially laterally in opposite directions at channel C. Preferably, the input is at the highest point of the plate 23a, 23b, and the output at the lowest point.

This guarantees a complete purge of the trays 23a, 23b, and therefore maximum performance: there is only one output possible for the condensates, and no "dead zones" that can be filled. In addition the realization of the steam inlet manifolds and condensate outlet is facilitated since there are only two pipes to predict, and they are easy to access.

Note that if the coolant is a thermal fluid, preferably the inputs and outputs are reversed (the upper part PS has an output of the coolant, and the lower part PI has a coolant inlet). Indeed, since there are no problems with condensates, a counter-current circulation is used to promote heat exchange.

Furthermore, even more preferably, the plate 23a, 23b is integral with a side wall 31 (which is vertical) of the chamber 2, through which said heat transfer fluid inlet and outlet of the plate 23a, 23b. In other words, the pipes are welded to the side wall, and there is no particular sealing to be provided at this level since the wall 31 can not disassemble the plates 23a, 23b. The assembly consisting of a side wall 31 and one or more plates 23a, 23b identical side by side (each separated by a rotor stage 20a, 20b) and whose inputs / outputs through the vertical wall 31 is called a "radiator block" 32. We see six successive ones on the figure 3c . Preferably, the radiator blocks 32 are connected in parallel by a common steam input circuit disposed above the side walls 31, and by a common condensate / noncondensable output circuit arranged below the side walls 31.

The idea is that said side wall 31 is a movable wall distinct from a main wall 30 of the chamber 2, said main and lateral walls 30, 31 being joined tightly when the installation 1 is Operating. Thus, the seal must only be provided at the junction between the main and side walls 30, 31 (and possibly between two side walls 31 of two adjacent blocks), which is much easier than at the level of the pipes. The quality of the sealing of the chamber 2 is improved for much lower costs.

In addition, the assembly formed by at least the plate 23a, 23b and the side wall 31 (ie a radiator block 32) is adapted to slide laterally so as to disengage the shaft 22a, 22b from the channel C, for example to maintenance, since the latter extends laterally opposite to the side wall 31. This is clearly visible on the figure 3b . It suffices for this to provide horizontal rails along which the plate 23a, 23b can slide. A single man can perform this operation, whereas before he needed a crane.

In addition, there is no need to empty the entire steam circuit 4, just close two valves at the common input and output circuits so as to isolate the heat sink while keeping the other "full". This greatly facilitates maintenance.

The chamber 2 also comprises a horizontal recycling screw 24 located under the rotors 20a, 20b, the latter moving towards the bottom of the chamber 2 the dried material for extraction.

Steam circuit

• des moyens d'aspiration 3 des buées ;
• des moyens de traitement 5 ;
• des moyens de compression 6 ; et
• au moins un échangeur thermique (typiquement les plateaux chauffants 23a, 23b) disposé au sein de ladite chambre 2

As explained, the installation 1 comprises a steam circuit 4 for the circulation of steam from the heating of said pasty material in the chamber 2 with reference to Figures 4a-4b . In the preferred embodiment for the implementation of the CMV, on this circuit 4 are successively arranged:

• extraction means 3 of the steams;
• treatment means 5;
• compression means 6; and
• at least one heat exchanger (typically the heating plates 23a, 23b) disposed within said chamber 2

The suction means 3 generally take the form of a hood above the chamber 2 (with a substantially frustoconical shape), which with the main and lateral walls 30, 31 defines the sealed envelope of the chamber 2.

Despite its position well above the pasty material, it can be seen that the suction means 3 collect at the same time as the fumes solid particles resulting from the heating of said pasty material (ie microscopic fragments of the dried pasty material), called "fine". Very light, they are driven by the flow of evaporation vapor.

The problem is that these fines are found in the compressed steam, which on the one hand damages the compression means 6 and on the other hand decreases the energy performance of the installation 1. An effective CMV requires a purest vapor possible. The treatment means 5 have traditionally this role of purification of the vapors, but it is noted that they consume a lot of energy and tend to clog this often (because of the fines), which results in a sudden cessation of the means of compression 6, which results in addition to the degradation of the equipment a temporary shutdown of the installation 1 and operating losses.

To solve this problem and to facilitate the CMV, the steam extraction means 3 comprise means of increasing head losses 40. This may seem at first sight paradoxical, insofar as it requires an increase in the consumption of energy at the compression means 6 so as to compensate for the pressure drop, but it is found that the local increase in pressure drops at the suction means effectively traps the fines. In particular these are deposited on the walls due to the increase in friction.

And insofar as the means for increasing the pressure drops 40 are arranged above the chamber 2 (which is naturally the case, in view of the "hood" shape of the means 3, the means of increasing preferably at least a portion of said trapped solid particles fall directly into the chamber 2. In other words, the system is self-locking. The fines are no longer lost, but well valued with the rest of the dried material.

Preferably, the means for increasing the pressure drops 40 have an outer wall provided with vibration means (such as a piston, or a rotary feeder), which "strike" at regular intervals this wall to peel and drop the fines.

The means for increasing the pressure drops 40 advantageously comprise a labyrinth 41 and / or a filter 42, preferably both. "Labyrinth" means a complex and sinuous part with sudden changes of direction so as to increase the areas on which the fines can be deposited. With reference to the figure 4a the labyrinth 41 may comprise an upward vertical duct followed by a downward vertical duct. In particular, as explained the means 40 may consist of a dome, comprising a vertical dividing wall separating the ascending pipe from the down pipe.

The vapor circuit 4 extends laterally from said descending vertical pipe of the labyrinth 41 so as to generate a new bend.

Said filter 42 may be arranged in the descending vertical pipe, advantageously in combination with water spray means 43 in the steam (it is noted that these may be present without the filter 42). The idea is to moisten the remaining fines that have not been trapped by the labyrinth part so as to weigh them down and make them fall.

The water spraying means 43 are in the example disposed above the filter 42, so as to have a large wet surface to touch all the fines. The steam circuit 4 is preferably configured so that the water sprayed in the steam flows into the treatment means 5. It is imperative that the water can not reach the chamber 2, which is the case as soon as the means spraying 43 are in the downcomer. It is noted that an overflow 44 makes it possible to short-circuit the filter 42 and to discharge directly into the circuit 4 water that could accumulate above the filter 42 and overflow into the chamber 2. The circuit 4 goes down as for him in slight slope towards the means of treatment 5 which collects the liquid water laden with fines, and the quasi-pure vapors.

The treatment means 5 preferably consist of a scrubber which allows the steam to be purified before it is introduced into the compressor (s) 6. As can be seen in FIG. figure 2 , water is preferably sprayed in the circuit 4 just at the inlet of each compressor 6. It is water "desuperheating", which allows to cool the compressors 6 (as explained, the CMV is accompanied by a sharp rise in heat).

With reference to the figure 5 Each compressor 6 is preferably equipped with venting means 60 for removing the water desuperheating. More precisely, at the outlet of each compressor, the circuit 4 is oriented downwards (advantageously substantially vertically) and then makes a bend. A branch 40 of the circuit 4 continues downwardly in the extension of the circuit 4 before the bend, and the purge means are arranged on this branch 40. Indeed, by gravity the liquid water flows in the branch 40 instead of continuing in the circuit 4. The purge means 60 thus constitute a local low point. The present purge means 60 are further configured to eliminate any traces of fines that would remain at this time in the circuit 4 while avoiding leaks that would harm the decompression of steam.

These means 60 preferably have a downward vertical duct (branch 40 of the circuit 4) followed by an upward vertical duct. More specifically, the ascending pipe surrounds the down pipe in the manner of a bottle into which a straw is inserted. The lower part is filled with water from the compressors 6, this water forming a gas cap, and thus acting as a sealing means. An increase in the amount of water in the means 60 causes the surface of the water to reach the top of the ascending pipe, at which there is an overflow outlet, fluidly connected to the treatment means 5 which collect the water. liquid water. The upward vertical duct of the treatment means 5 comprises a filter 52, which approximately defines the separation between the low and high parts of the means 5, and makes it possible to contain any final fines that would have managed to pass through the treatment means 5.

The level of sludge (i.e., finely mixed with water) at the bottom is preferably controlled, and for this there are draining means 51 at the bottom of the "bottle", i.e. at the bottom of the descending vertical pipe. The emptying means 51 may be automated to maintain a substantially constant level.

Injection of pasty material

The installation 1 comprises a device for introducing under pressure 7 of said pasty substance into the chamber 2. The pasty material is thus discharged into the chamber 2 in the upper part via injectors 74a, 74b of the pressure introduction device 7, ie nozzles that disperse the material in the chamber 2 for better drying.

As explained, this device 7 is a critical component for the sealing of the chamber 2. It must inject only the pasty material and no gas for the proper functioning of the CMV. Conversely, the chamber 2 must not leak via its entrance pasty material.

For this purpose we know high pressure injection systems that try to prevent the entry / exit of air. It is noted that the fine spray nozzles of these systems tend to clog, because the pasty material is not homogeneous (possible presence of agglomerates). This results in maintenance operations for unclogging that are long and complex.

The present optimized installation 1 has, to solve this, an innovative pressure introduction device 7, in accordance with the Figures 6a-6c .

The latter comprises a first and a second introduction set 70a, 70b, typically a left set and a straight set. They are identical.

Each comprises a pasty material circuit 71a, 71b on which are successively arranged a jack 72a, 72b, a pasture admission valve 73a, 73b and an injector 74a, 74b opening into the chamber 2.

The two cylinders 72a, 72b and the two valves 73a, 73b are actuated in a coordinated manner so that when an introduction assembly 70a, 70b receives pasty material via its valve 73a, 73b, the other introductory set 70a, 70b injects pasty material into the chamber 2 via its injector 74a, 74b.

In other words, the pasty material is continuously injected into the chamber 2 via the alternating operation of the two introducer assemblies 70a, 70b. At any time (operation), one is filling while the other is in compression, the valves 73a, 73b acting as check valves. More specifically, the high-pressure material blocked in the circuits 71a, 71b acts as plugs which permanently ensure an absolute seal.

More precisely, the valves 73a, 73b are opened and then closed periodically in a coordinated manner so that the opening of one coincides with the closure of the other. This is for example obtained by a piston 78 visible on the Figure 6c which at regular intervals simultaneously changes the state of the two valves 73a, 73b. Thus, at any moment one is open and the other is closed. Preferably the cycle is symmetrical, that is to say that each valve 73a, 73b is open as much as the other.

And the pressure introduction device 7 comprises a compressor 75 supplying in common and continuously the two valves 73a, 73b pasty material, for example via a pipe "Y", so that at any time the single set 70a, 70b whose valve 73a, 73b is open receives pasty material via its valve 73a, 73b. As explained, at any time a valve 73a, 73b and only one is open, and the pasty material can be supplied continuously. The absence of intermittency at this level ensures that the Y pipe is permanently full of pasty material without the possibility of air passing.

The pressurized introduction device 7 may further comprise a pasty material storage tank 77 and an endless screw 76 disposed in said tank 77 for the transfer of the pasty substance to the compressor 75.

The cylinders 72a, 72b are pistons making trips back and forth in their circuit 71a, 71b (i.e. having a periodic oscillating moment, synchronous with that of the valves 73a, 73b). More specifically, the cylinders 72a, 72b and the valve 73a, 73b of each insertion assembly 70a, 70b are actuated in a coordinated manner so that the cylinder 72a, 72b increases the pressure in the pasty circuit 71a, 71b when the valve 73a, 73b is closed, and decreases the pressure in the pasty circuit 71a, 71b when the valve 73a, 73b is open.

• dans le premier temps, la première vanne 73a est fermée et le premier vérin 72a avance. La pression augmente fortement dans le premier circuit 70a (jusqu'à plus de 100 bar, voir 200 bar) car et la matière pâteuse est pulvérisée par le premier injecteur 74a. A ces niveaux de pression, tout agglomérat qui bloquerait l'injecteur 74a est instantanément broyé, tout bouchage est impossible. Simultanément, la deuxième vanne 73b est ouverte et le deuxième vérin 72b recule. Dans la mesure où le compresseur 75 continue d'amener de la matière pâteuse aux vannes 73a, 73b et que seulement la deuxième est ouverte, cette matière est forcée d'occuper la place libérée par le deuxième vérin 72b.
• Les vannes 73a, 73b changent de position, et les vérins 72a, 72b changent de sens de déplacement, et dans un deuxième temps on fait exactement les mêmes opérations en inversant les rôles du premier et du deuxième ensemble 70a, 70b.

We obtain a two-cycle cycle:

• in the first step, the first valve 73a is closed and the first cylinder 72a advances. The pressure increases sharply in the first circuit 70a (up to more than 100 bar, see 200 bar) because and pasty material is sprayed by the first injector 74a. At these pressure levels, any agglomerate that would block the injector 74a is instantly crushed, all clogging is impossible. Simultaneously, the second valve 73b is opened and the second cylinder 72b moves back. Insofar as the compressor 75 continues to bring pasty material to the valves 73a, 73b and only the second is open, this material is forced to occupy the place released by the second cylinder 72b.
• The valves 73a, 73b change position, and the cylinders 72a, 72b change direction of movement, and in a second step we do exactly the same operations by reversing the roles of the first and second set 70a, 70b.

As explained, the operation is continuous, with absolute tightness, and a physical impossibility of blocking.

Extraction of the dried material

The installation 1 comprises conditioning means 8 of said dried pasty material from the chamber 2. As shown in FIG. figure 7a These packaging means 8 are in the rear part of the chamber and collects the dried material pushed by the screw 24, which is facilitated by a slight slope toward the rear of the chamber 2.

As explained, these means 8 are also a critical component for the sealing of the chamber 2. They must extract only the dried pasty material and let no gas enter for the proper functioning of the CMV.

With reference to figures 7b and 7c , the conditioning means 8 comprise an extrusion cylinder 82 of substantially vertical axis and directed downwards, a feeding screw 81 feeding the extrusion cylinder 82, and a booster chamber 83 extending the end of the cylinder of the cylinder. extrusion 82.

The cylinder 82 is oriented in the direction of gravity. More specifically, it compresses the dried material by pushing it downwards, that is to say to the booster chamber 83. The latter consists of an extension of the cylinder 82 receiving compressed dried material. As for the introduction device 7 pasty material, the idea is to use the length of the booster chamber 83 as a plug of material preventing the entry / exit of gas.

Preferably, the booster chamber 83 comprises means for increasing the pressure drops 84 so as to facilitate the generation of the plug. The higher the pressure losses, the more the material will be compacted, and the more it will hold despite gravity. As shown on the Figure 7c said means for increasing head losses 84 consist of an extrusion grid, ie a die, into which the dried material must pass forcibly. This completely compresses the dried material, which can be pelletised: at each descent of the cylinder 82 (and therefore at each step of the cap downwards), means for pelletizing the dried pasty material at the outlet of said extrusion grid 84 can slice the "carrot" that is past to obtain a pellet. These constitute an optimal packaging allowing the dried material to be transported, valorized, etc.

The feed screw 81 is a worm operating intermittently, the latter and the extrusion cylinder 82 are actuated in a coordinated manner so as to fill the cylinder 82 when in the up position.

More specifically, when the cylinder 82 goes down it advances the plug of compacted material in the booster chamber 83, which brakes its descent, the screw 81 then being stopped. Then the cylinder 82 goes up, without the plug which remains where it is under the effect of gravity and strong friction due to compaction. There is then a vacuum at the top of the cap, empty which is filled with material (still not packed), brought by the screw 81 which starts. This new material will then be compacted by the cylinder 82 so as to increase the plug, etc. This guarantees a perfect seal while facilitating the packaging of the dried material.

Note that the chamber 2 provides dried material continuously, while the feed screw 81 operates intermittently. To solve this problem, an auxiliary screw 85 is added bringing continuously the material pastry dried from the chamber 2 (more precisely from a hopper 89 at the outlet of the chamber 2) to a vertical pipe 86 above the booster screw 81. The auxiliary screw 85 acts as a first sealing barrier preventing the air from the chamber 2 to access the vertical pipe 86, which serves as a storage "silo" for the feed screw 81

Like the means for increasing the pressure drops 40 of the steam circuit 4, said vertical pipe 86 may have an area 87 at least partially flexible. This makes it possible to add to the conditioning means 8 comprise means of vibration 88 of said flexible zone 87 of the vertical pipe 86. Indeed, since the feed screw 81 does not operate continuously, the dried material which accumulates in permanence in the vertical pipe can "vault", that is to say, to stabilize in an ogival shape that prevents it from falling, and no longer allows to feed the booster screw 81 which rotates in a vacuum. There is no risk of air entry (as the cap remains in place in the booster chamber 83), but the dried material no longer comes out. The vibration of the flexible zone 87 makes it possible to collapse any potential vault in construction so as to guarantee the arrival of the material in the screw 81, and the production of pellets steadily.

Claims (14)

1. A thermal installation (1) for drying pasty material, comprising a chamber (2) in which said pasty material is heated and a steam circuit (4) comprising successively:

   - means (3) for aspirating mists resulting from the heating of said pasty material;

   - treatment means (5);

   - compression means (6);

   - at least one heat exchanger (23a, 23b) disposed within said chamber (2);

   the installation (1) being characterized in that the aspiration means (3) comprise means (40) for increasing head losses so as to trap solid particles resulting from the heating of said pasty material and carried by said mists,
   the means (40) for increasing head losses being disposed above the chamber (2) and comprising means for vibrating the external wall, so that at least a portion of said trapped solid particles falls back into the chamber (2).
2. The installation according to claim 1, wherein the means (40) for increasing head losses comprise a labyrinth (41).
3. The installation according to claim 2, wherein the labyrinth (41) comprises a rising vertical duct followed by a descending vertical duct.
4. The installation according to claim 3, wherein the steam circuit (4) extends laterally from said descending vertical duct of the labyrinth (41).
5. The installation according to one of claims 1 to 4, wherein the means (40) for increasing head losses comprise a filter (42).
6. The installation according to claims 4 and 5 in combination, wherein said filter (42) is disposed in the descending vertical duct.
7. The installation according to one of claims 1 to 6, wherein the means (40) for increasing head losses comprise means (43) for spraying water into the mists.
8. The installation according to claims 6 and 7 in combination, wherein the means (43) for spraying water are disposed above the filter (42).
9. The installation according to one of claims 7 and 8, wherein the steam circuit (4) is configured so that the water sprayed into the mists streams all the way to the treatment means (5).
10. The installation according to one of claims 1 to 9, wherein the water is sprayed into the compression means (6), purging means (60) being disposed on the circuit (4) at the outlet of the compression means (6) so as to discharge the liquid water.
11. The installation according to claim 10, wherein the purging means (60) have a descending vertical duct (40) followed by a rising vertical duct, said descending vertical duct (40) being a branch of the circuit (4).
12. The installation according to claim 11, wherein the rising vertical duct of the purging means (60) comprises a filter (62).
13. The installation according to one of claims 11 and 12, wherein the purging means (60) have, at the bottom of said descending vertical duct (40), automatic draining means (61).
14. The installation according to one of claims 11 to 13, wherein the rising vertical duct is, in its upper part, in fluid connection with the treatment means (5).

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