BE1030218B1 - APPARATUS FOR CONTINUOUS DRYING OF PARTICLES COMPRISING A SYSTEM FOR SEPARATION AND RECIRCULATION OF THE FINER FRACTIONS OF PARTICLES - Google Patents

Abstract

The present invention relates to a dryer for drying particles comprising, • First and second plates (1a, 1b) mounted for rotation around an axis (Z), having a perforated surface, • A hot gas blowing unit (5g) following a flow parallel to the axis (Z) passing through the second plate before passing through the first plate, • First and second particle distribution units on the first and second plates and first and second recovery units (3a , 3b) particles after one rotation of each plate, • A transfer unit (4t) for particles from the first plate to the second plate, • a particle separation unit (21) upstream of the distribution unit (2a ) configured to separate fine particles (20f)) from coarse particles (20c) • means for distributing coarse particles (20c) on the first plate and fine particles on the second plate

Description

1 BE2022/5050

CONTINUOUS PARTICLE DRYING APPARATUS COMPRISING A SYSTEM

SEPARATION AND RECIRCULATION OF FINER FRACTIONS OF PARTICLES

FIELD OF INVENTION

[0001] The invention relates to an industrial dryer for continuously drying particles, preferably organic particles, for example of agro-food origin, such as cereals, or waste serving as fuel or construction materials such as shavings or fibers of wood, or other plant material. The dryer of the present invention is of the type comprising, e a first perforated plate configured to receive particles to be dried having an initial moisture content (HOa) and transport them on a rotation tower, e a transfer unit configured to transfer the partially dried particles at an intermediate moisture content (H1a) after one revolution of rotation of the first plate towards, e a second perforated plate configured to receive the partially dried particles from the first plate at the intermediate moisture content (H1a = HOb) and transport them on a rotation tower towards an evacuation system at their final moisture content (H1b), and e a unit for blowing a hot gas following a vertical flow, passing through the second plate, followed directly by the first plate, allowing the particles to be dried as they rotate on the first and second plates.

The hot gas passing through the second plate undergoes pressure losses, before reaching the first plate with a lower pressure than upstream of the second plate. Likewise, when crossing the first plateau, the hot gas again experiences a pressure loss. These pressure losses increase when the first and second plates transport a layer of particles. Pressure losses can be reduced by increasing the diameter of the perforation openings of the first and second plates. However, increasing the diameter of the tray openings results in the loss of the finer fractions of particles that pass through the tray perforations.

[0003] The dryer of the present invention makes it possible to minimize both, on the one hand, the pressure losses of the hot gas flow during its passage through the second and first plates and, on the other hand, the loss finer fractions of the particles to be dried.

TECHNOLOGY BACKGROUND

[0004] Many industrial processes require the drying of particles before their subsequent use, whether before the packaging of granular agro-food products or industrial products, or before the combustion of crushed waste used as fuel.

Depending on the type of intended use, the particles must be dried to achieve final moisture contents within well-defined target ranges (H1t+e). For example,

2 BE2022/5050 wood chips must be dried in different target ranges depending on whether they are intended for combustion, the production of pellets, the production of litter or the production of chipboard. It is of course possible to dry the particles in batches by placing the particles on preferably perforated trays in order to let a hot gas pass through them and allow the water and water vapor to escape. In certain cases a fluidized bed is formed by suspended particles under the action of the hot gas flow. However, most industrial applications require flow rates that a batch drying process cannot achieve. For this reason, the same principle of depositing the particles to be dried on a perforated support and exposing them to a flow of hot gas has been applied to devices allowing continuous drying, with a continuous source of the particles to be dried upstream of the dryer itself and a continuous discharge of the dried particles downstream thereof.

[0005] In particular, a belt dryer comprises a continuous flexible perforated belt stretched between two motorized rollers forming a loop. Air or other hot gas is blown under the upper canvas on which the particles to be dried are continuously deposited. The length of a belt dryer depends on the type of particles to be dried, their water load and the target range (H1t+e) to be achieved. Thus, a strip can reach a length of 200 m which is very expensive and difficult to assemble/disassemble on the device. A belt dryer is therefore generally reserved for drying a single type of particle, because it would be uneconomical to change the belt to optimize the type of perforation for a new type of particle. A belt dryer is very expensive and not very efficient in terms of dimensions, since the particles are only dried over less than half the length of the belt. Alternatively, a single belt can be used to dry particles of different particle sizes by selecting small opening sizes, at the cost of increasing the pressure drop of the hot gas flow.

[0006] There are also dryers with perforated trays which resemble belt dryers, except that the belt is replaced by perforated trays coupled to one another forming a sort of caterpillar. The difference with a belt dryer is that the plates are hinged so that they have the same face whether they are on the upper or lower belt of the loop. This makes it possible to reduce the length of the dryer practically in half, since the particles are subjected twice to the flow of hot gas: a first time during their passage over the upper part of the loop and a second time during their passage in the direction reverse on the lower part. Although advantageous from this point of view compared to a belt dryer, it is clear that the mechanics necessary for the movement of the plates are delicate and therefore expensive and fragile, and must be protected when exposed to fine particles likely to seize the bearings. In addition, the openings created between two adjacent plates and, above all, the spaces opening in the plate transfer mechanism during each transfer of a plate from the upper portion to the lower portion of the track create as many passages

3 BE2022/5050 preferences of lower resistance for the flow of hot gas, which lead to a significant drop in the efficiency of this type of dryer.

[0007] EP0197171 describes a dryer comprising several perforated, circular plates, superimposed and mounted to rotate on a hollow central axis. Each tray is enclosed in an individual cylindrical chamber with a roof and a floor which separate it from the other trays. Means for transferring the powder to be dried are provided between each adjacent plate. Each chamber is provided, on the one hand, with a first opening for introducing hot air, in fluid communication with the cavity of the hollow central axis, the first opening being positioned above the plate located in the corresponding chamber and, on the other hand, a second evacuation opening on the peripheral wall of the chamber in communication with the outside, the second opening being located below the corresponding plate. Hot air is blown into the cavity of the hollow shaft and is distributed in parallel in each chamber through the first hot air introduction opening. The hot air is forced to pass through the circular perforated plate before being evacuated through the second opening located on the peripheral wall of each chamber. In reality, such a system is similar in principle to a belt dryer whose linear movement has been replaced by a circular movement distributed over several stages with means of transferring the powder from one plate to another. Certainly, such a rotary system has a considerable advantage in saving floor space compared to a linear belt dryer, but such a system lacks efficiency. Indeed, if the hot air having passed through the first plates loaded with very humid particles comes out relatively saturated in humidity, the hot air passing through the last plates loaded with particles already partially dried on the previous plates, only comes out lightly loaded with humidity. humidity, which represents a considerable waste of energy.

[0008] EP2828595 describes a dryer illustrated in Figure 1, comprising first and second (or more) perforated plates (1a, 1b), superimposed and mounted to rotate around a vertical axis (Z).

A ventilation system blows hot gas vertically, first passing through the second plate (1b), before passing directly through the first plate (1a). As it is a dryer, the hot gas, after passing through the second plate (1b) then the first plate (1a) is either evacuated or recirculated, but on condition of drying and reheating it before the — reinject through the second plate.

[0009] The wet particles are distributed along a radius of the first plate (1a) by a first distribution unit (2a) and carried away by the rotation of the first plate over an angular (or azimuthal) distance of a little less 360° before being collected by a first recovery unit (3a). During the rotation of the first plate (1a), the particles are exposed to the stream of hot gas which has previously passed through the second plate where it has lost a little of its heat energy and has taken on a little humidity. The partially dried particles are transferred from the first recovery unit to a second

4 BE2022/5050 distribution system (3a) (2b) which distributes the partially dried particles along a radius of the second plate (1b) which rotates around [vertical axis (Z) in the opposite direction of the first plate (1a ). The partially dried particles are carried away by the rotation of the second plate (1b) (in the opposite direction to the first plate) over an angular (or azimuthal) distance of a little less than 360° before being collected by a second recovery unit . (3b) and evacuated. During rotation of the second plate (1b), the particles are exposed to the hot gas stream directly from the ventilation system, where the hot gas has its maximum temperature and minimum moisture content.

[0010] As seen in Figure 1, as the trays rotate in opposite directions, the hot gas reaches the particles just after being deposited along the radius of the first tray, where they have their maximum moisture content (H0a / H0a = 100%) has the highest temperature and lowest moisture content of all the hot gas that reaches the first plateau, because it has previously passed through the practically dry particles (final moisture content H1b) just before 'be evacuated with a humidity content which can be of the order (for example) of

H1b/ H0a) = 12%, where HOa is the initial moisture content of the particles at the entrance to the first tray (1a) and H1b is the final content of the particles at the exit from the second tray (1b).

[0011] The dryer described in EP2828595 is particularly efficient in terms of energy, use and occupation of floor space. As illustrated in Figures 2(b) to 7(b), the particles to be dried have a particle size distribution centered on an average size (Dm). The — openings of the perforation of the first and second plates must make it possible to retain the particles on the corresponding plate, while allowing the hot gas to pass through the plate.

We can see in Figures 2(b) to 7(b), that unless we take very small perforation opening diameters, located at the extreme left of the particle size curve, there will always be a fine fraction particles which will have a size (DO) less than the diameter (Dha, Dhb) of the — perforation openings (see portion of hatched curve (20f) of Figures 2(b) to 7(b)). If the particles (20f) of this fine fraction are in direct contact with the perforation openings of the trays, these fine particles will pass through the trays and end up on the lower floor of the dryer. It is of course possible to recover the fine particles (20f) having percolated to the floor of the dryer and to reintroduce them onto the first plate, where they risk, however, passing through it and ending up again on the floor. Such a process impairs the drying efficiency of the dryer.

[0012] Reducing the diameter (Dha, Dhb) of the perforations certainly reduces the volume of the fraction of fine particles (20f) which can pass through the plates, but considerably increases the pressure losses of the flow of hot gas crossing the plates. To date, the person skilled in the art must make a compromise in the choice of the size of the diameter of the perforations making it possible to minimize, on the one hand, the pressure losses and, on the other hand, the volume of the fraction of fine particles ( 20f) which can pass through the perforation of the trays.

> BE2022/5050

[0013] There therefore remains a need for an industrial dryer for drying particles continuously which is effective in terms of pressure losses of the hot gas and minimizing the losses of fractions of fine particles to be dried. The dryer of the present invention makes it possible to minimize both, on the one hand, the pressure losses of the flow of hot gas during its passage through the second and first plates and, on the other hand, the loss of the fractions more fine particles to dry

SUMMARY OF THE INVENTION

[0014] The present invention is defined in the independent claims. Preferred variations are defined in the dependent claims. In particular, the present invention relates to a dryer for drying particles having an initial moisture content (H0a) until reaching a final moisture content (H1b) lower than the initial content (H1b < HOa), the dryer comprising, ( a) an enclosure comprising an essentially cylindrical wall extending along a vertical axis (Z), (b) a first circular plate mounted on the wall of said enclosure substantially normal to the vertical axis (Z) and configured to enter into rotation in a first direction around the vertical axis (Z), the surface of the first plate being perforated with openings of hydraulic diameter (Dha = 4 Aa / Pa) equal to the ratio of four times an area (Aa) on a perimeter (Pa) of the openings, making the surface permeable to gases such as air and water vapor and to water, and (c) a second circular plate (1b) mounted at a certain distance from the first plate on the wall of said enclosure substantially normal to the vertical axis (Z) and configured to rotate around the vertical axis (Z), the surface of the second plate being perforated with openings of hydraulic diameter (Dhb = 4 Ab / Pb) equal to the ratio of four times an area (Ab) to a perimeter (Pb) of the openings, making the surface permeable to gases such as air and water vapor and to water.

[0015] The first and second plates are configured to, on the one hand, support the particles to be dried and, on the other hand, allow a hot gas blowing substantially parallel to the vertical axis (Z) to pass through them. . In a preferred variant, the first plate is located below the second plate and the hot gas circulates from top to bottom and is preferably hot air.

In all cases, it is preferred that the second plate rotates in an opposite direction of rotation of the first plate. The dryer further comprises, (d) a first unit for distributing the particles to be dried configured to receive the particles to be dried from a unit supply and to distribute these particles before drying along a radius of the first plate, (e) a first unit for recovering the particles deposited on the first plate after a rotation of a given angle thereof, the first recovery unit being located downstream of, preferably adjacent to the first distribution unit,

6 BE2022/5050 (f) a unit for transferring the particles collected from the first tray by the first recovery unit to a second distribution unit configured to distribute said particles along a radius of the second tray, (g) a second unit recovery (3b) of the particles deposited on the second plate after a rotation of a given angle thereof, the second recovery unit being located downstream of the, preferably adjacent to the second distribution unit and being configured to evacuate the particles after drying outside the dryer by an evacuation unit, (h) a hot gas blowing unit following a flow substantially parallel to the vertical axis (Z), passing first through the perforated surface of the second plate before pass directly afterwards through the perforated surface of the first plate,

[0016] The present invention is distinguished in that the dryer comprises, (i) a particle separation unit located in or upstream of the supply unit, the separation unit being configured to separate fine particles of diameter less than a fine diameter (DO) of coarse particles of diameter greater than the fine diameter (DO), and () a first conduit configured to supply coarse particles to the supply unit or the first distribution unit to distribute the coarse particles before drying along the radius of the first plate, and (k) a second pipe configured to supply fine particles either to the second distribution unit or to a second fines distribution unit located downstream of the second distribution unit to distribute the fine particles before drying along the radius of the second tray, i.e. a first fines distribution unit located downstream of the first distribution unit to distribute the fine particles before drying along the radius of the first tray, i.e. e a combination of two or three of the previous options, in which the terms "upstream" and "downstream" are defined in relation to the direction of movement of the particles in the dryer.

[0017] In a variant of the invention, the separation unit comprises a screening element comprising openings of hydraulic diameter (Dhs) equal to the hydraulic diameter of the openings of the first plate within a tolerance of + 10% (i.e., Dhs = Dha + 10%), preferably equal to the hydraulic diameter of the openings of the first plate (i.e., Dhs = Dha).

In this variant, the sieving element can be configured to enter into a cyclical movement of controlled trajectory, amplitude and frequency in order to improve the separation of fine particles and coarse particles.

7 BE2022/5050

[0018] In a first embodiment, the separation unit is distinct from the supply unit, and comprises, e a volume of retentate configured to contain the coarse particles after separation by the separation unit), and e a volume of sieve configured to contain fine particles after separation by the separation unit.

[0019] The first pipe connects the volume of retentate from the separation unit to the supply unit, and the second pipe connects the volume of sieve from the separation unit either to the second distribution unit, or to the first or the second fines distribution unit, or towards a combination of the aforementioned distribution units.

[0020] In an alternative embodiment, the separation unit is included in the supply unit (9), and comprises, e a volume of retentate configured to contain the coarse particles after separation by the separation unit, and e a volume of sieve configured to contain the fine particles after separation by the separation unit

[0021] The first pipe connects the volume of retentate from the supply unit to the first distribution unit and the second pipe connects the volume of sieve from the supply unit either to the second distribution unit, or towards the first or the second distribution unit of — fines, or towards a combination of the distribution units mentioned above.

[0022] The hydraulic diameters (Dha, Dhb) of the openings of the first and second plates are preferably selected so that the fine particles represent between 5% and 20% by weight of the total weight of particles before drying, preferably between 10 and 15% by weight.

[0023] The first and second plates preferably comprise a rigid self-supporting structure with high permeability of the grating type, on which is placed a filter layer comprising openings of size and density corresponding to the desired permeability depending on the type and size of the particles to dry.

[0024] The first and second units for distributing the particles to be dried on the first and second plates respectively, as well as the supply unit can each comprise at least one Archimedes screw extending along a radius of the first and second plates, respectively, said at least one Archimedes screw being enclosed in an enclosure provided with one or more openings extending along said radius of the plates.

[0025] Similarly, the first and second recovery units can each comprise at least one Archimedes screw extending along a radius of said plate which is enclosed in an enclosure provided with one or more openings extending along the radius of the first plate, said openings being connected to a scraper or brush capable of collecting and directing the particles brought by the rotation of the plate towards the Archimedes screw.

[0026] After the gas has passed through the perforated surface of the first plate, the hot gas blowing system (5) can either be configured to evacuate the gas out of the enclosure, or include a gas dryer. air allowing the humidity present in the gas to be captured before heating and recirculating the gas thus dried through the second and the first plate, respectively.

To do this, the dryer can comprise a chimney (6) essentially hollow cylindrical centered around the vertical axis (Z) and whose wall extends at least from the first plate) to the last plate comprising one or more openings providing fluidic access to the interior of the chimney to the gas having passed through the perforated surface of the first plate. The chimney may comprise either one or more openings towards the outside of the enclosure making it possible to evacuate the gas out of the enclosure, or the dryer and one or more openings configured to recirculate the gas after its passage through the dryer, following the flow substantially parallel to the Z axis, passing first through the perforated surface of the second plate before passing directly afterwards through the perforated surface of the first plate.

[0028] In a preferred variant, the supply unit (9) is connected upstream to a source of said particles to be dried, preferably a silo, the particles preferably comprising waste wood from sawmills, waste from wood from construction materials, waste paper or cardboard, agri-food products such as cereals, and can be in the form of powder, granules, shavings, pellets, cakes, or pieces generally not exceeding 10 cm in length .

BRIEF DESCRIPTION OF THE FIGURES

[0029] For a better understanding of the nature of the present invention, reference is made to the following Figures, including;

Figure 1: illustrates a dryer according to EP2828595.

Figure 2(a): illustrates a variant of a dryer according to the present invention comprising a separation system and a unit for transferring fine particles to the second plate.

Figure 2(b): illustrates a particle size distribution of the particles to be dried, with the fraction of fine particles having a diameter < OD.

Figure 2(c): illustrates the distribution of fine particles and coarse particles over the thickness of the layers of particles deposited on the first and second plates obtained with the present variant of the invention.

Figure 3(a): illustrates an alternative variant of a dryer according to the present invention comprising a separation system and a unit for transferring fine particles to the second plate.

Figure 3(b): illustrates a particle size distribution of the particles to be dried, with the fraction of fine particles having a diameter < OD.

Figure 3(c): illustrates the distribution of fine particles and coarse particles over the thickness of the layers of particles deposited on the first and second plates obtained with the present variant of the invention.

Figure 4(a): illustrates an alternative variant of a dryer according to the present invention comprising a separation system and a unit for transferring fine particles to the second plate.

Figure 4(b): illustrates a particle size distribution of the particles to be dried, with the fraction of fine particles having a diameter < OD.

Figure 4(c): illustrates the distribution of fine particles and coarse particles over the thickness of the layers of particles deposited on the first and second plates obtained with the present variant of the invention.

Figure 5(a): illustrates an alternative variant of a dryer according to the present invention comprising a separation system and a unit for transferring fine particles to the second plate.

Figure 5(b): illustrates a particle size distribution of the particles to be dried, with the fraction of fine particles having a diameter < OD.

Figure 5(c): illustrates the distribution of fine particles and coarse particles over the thickness of the layers of particles deposited on the first and second plates obtained with the present variant of the invention.

Figure 6(a): illustrates an alternative variant of a dryer according to the present invention comprising a system for separating and transferring fine particles to the first plate downstream of the first distribution means.

Figure 6(b): illustrates a particle size distribution of the particles to be dried, with the fraction of — fine particles having a diameter < OD.

Figure 6(c): illustrates the distribution of fine particles and coarse particles over the thickness of the layers of particles deposited on the first and second plates obtained with the present variant of the invention.

Figure 7(a): illustrates an alternative variant of a dryer according to the present invention comprising a system for separating and transferring fine particles to the first plate downstream of the first distribution means.

Figure 7(b): illustrates a particle size distribution of the particles to be dried, with the fraction of fine particles having a diameter < OD.

Figure 7(c): illustrates the distribution of fine particles and coarse particles over the thickness of the layers of particles deposited on the first and second plates obtained with the present variant of the invention.

Figures 8(a) & 8(b): illustrate an example of a distribution unit adapted to the present invention, (a) perspective view, (b) top view.

Figures 9(a) & 9(c): illustrate an example of a recovery unit adapted to the present invention, (a) top view, (c) cross section.

Figures 9(b) & 9(d): illustrate an alternative example of a recovery unit adapted to the present invention, (b) top view, (d) cross section

Figure 10: graphically illustrates the relative increase in the moisture content ([(HOD)inv — (HOb)ra] / (HOb)pa) of the particles distributed on the second plate (1b) only, as a function of the intermediate content in humidity (HOb / HOa) relative to the initial content (H0a), of the particles distributed on the second plate (1b), for a fraction of f = 10% of fine particles.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

The dryer according to the present invention is preferably a dryer of the type described in

EP2828595, which is discussed in the “technological background” section above and illustrated in

Figure 1. It is not essential that the first and second plates rotate in opposite directions, but counter rotations of the two plates are preferred as this increases the energy efficiency of the dryer.

The dryer of the present invention comprises an enclosure (10) comprising an essentially cylindrical wall extending along a vertical axis (Z). The enclosure encloses a first circular plate (1a) mounted on the wall of the enclosure substantially normal to the vertical axis (Z). The first plate (1a) is mounted to rotate in a first direction around the vertical axis (Z), the rotation of which is actuated by a first motor. The surface of the first plate (1a) is perforated - by openings of hydraulic diameter (Dha) thus making it permeable to fluids such as air, steam and water.

The enclosure (10) encloses a second circular plate (1b) mounted at a certain distance from the first plate on the wall of the enclosure substantially normal to the vertical axis (Z). The second plate is mounted to rotate around the vertical axis (Z), the rotation of which is actuated by a second motor (5b). The second motor (5b) may be the first motor (5a) or may be a

11 BE2022/5050 motor different from the first motor (5a). The rotation of the second plate can be in the same direction or in the opposite direction to the rotation of the first plate, and the rotation speeds (|wa|, [wb|) (in absolute values) of the first and second plates can be equal or different and can vary over time, either independently of each other or, on the contrary, the rotation speed of one plate (= “master”) imposing the rotation speed of the other plate (= “master”). Slavic"). The surface of the second plate (1b) is perforated by openings of hydraulic diameter (Dhb) thus making it permeable to fluids such as air, steam and water. The hydraulic diameters (Dha, Dhb) of the openings of the first and second plates (1a, 1b) are preferably identical (i.e., Dha = Dhb).

[0033] A first distribution unit (2a) of the particles to be dried extends along a radius of the first plate (1a) and is configured to receive the particles to be dried from a supply unit (9) and to distribute these particles before drying along a radius of the first plate (1a). The feeding unit makes it possible to control the feeding or loading rate (dma / dt) of the particles to be dried on the first tray (1a).

[0034] A first recovery unit (3a) extends along a second radius of the first plate, located downstream of, preferably adjacent to the first distribution unit (2a), The first recovery unit (3a) is configured to recover the particles deposited on the first plate (1a) after rotating it through a given angle. The angle of rotation is preferably at least equal to 300°, preferably at least equal to 320°, more preferably at least equal to 340°, and preferably the largest angle allowing the first distribution unit to be accommodated (2a) and the first recovery unit (3a) along the respective radii of the first plate (1a). A large rotation angle allows the particles to be exposed to hot gases for a given rotation speed. An angle of almost 360° can be obtained by superimposing the first distribution unit (2a) on top of the first recovery unit (3a).

The dryer also comprises a transfer unit (4t) of particles collected from the first plate (1a) by the first recovery unit (3a) to a second distribution unit (2b). The second distribution unit (2b) extends along a radius of the second tray (1b) and is configured to distribute particles on the second tray (1b), along the radius of the second tray. A second recovery unit (3b) for particles deposited on the second plate (1b) is located downstream of the second distribution unit (2b), preferably adjacent to the second distribution unit (2b), so that the particles 'reach after a rotation of a given angle thereof. The second distribution and recovery units (2b, 3b) are similar to the first distribution and recovery units (2a, 3a) and the former are arranged in a similar manner on the second tray (1b) as the latter are on the first plate (1a). However, they differ in that the second distribution unit (2b) is coupled upstream to the transfer unit (4f) and in that the second recovery unit (3b) is configured to evacuate the particles after drying out of the dryer. by an evacuation system (40).

12 BE2022/5050

The dryer comprises a hot gas blowing system (5) configured to form a flow of hot gas substantially parallel to the vertical axis (Z), passing first through the perforated surface of the second plate (1b). before passing directly afterwards through the perforated surface of the first plate (1a). It is the hot, dry gas which, by contacting the wet particles, will (a) increase their temperature and (b) evacuate part of their humidity. It follows that the temperature of the hot gas drops and its moisture content increases a first time when it passes through the second plate (1b), then a second time when it passes through the first plate (1a). The gas leaving the first plate (1a) therefore has a moisture content that is too high to be recirculated as is. In practice, the gas thus cooled and humidified is therefore either evacuated outside the enclosure into the atmosphere or for another use such as a heat exchanger or a humidifier (see dotted arrows in Figure 1 evacuating the gases out of the dryer upwards through a chimney (6) of the dryer), or recirculated after drying and heating. The blowing system may include one or, preferably, several fans. The fan(s) can be configured to suck hot gases by creating a vacuum downstream of the plates. In this variant, the fan(s) are positioned downstream of the first plate (1a). In an alternative variant, the fan(s) can be configured to blow the hot gas by creating a positive pressure upstream of the second plate (1b). In this variant, the fan(s) are positioned upstream of the second plate (1b).

The terms “upstream” and “downstream” used to define the blowing system are defined in relation to the direction of movement of the gas through the second plate (1b) before passing through the first plate (1a).

The dryer of the present invention differs from previous dryers in that it further comprises a particle separation unit (21) located in or upstream of the supply unit (9). The separation unit (21) is configured to separate fine particles (20f) with a diameter less than a fine diameter (DO) from coarse particles (20c) with a diameter greater than the fine diameter (DO). The idea is that by sieving the particles (20) before the dryer, with a separation unit (21) separating the fine particles (20f) likely to pass through the openings of the lower plate (e.g., the first plate (1a )) and thus fall on the floor of the dryer, the coarse particles (20c) retained in a volume of retentate (21c) of the separation unit (21) can be distributed on the lower plate (e.g., the first plate ( 1a)) without them being able to pass through it, since they are larger than the openings in the lower plate.

[0038] The fine particles (20f) of diameter less than the diameter of the openings of the lower plate collected in a volume of sieve (21f) of the separation unit (21) can be - distributed to different locations of the dryer discussed in more detail lower, to prevent them from coming into direct contact with the upper surface of the lower plate (e.g., first plate (1a)). Thus the quantity of fine particles which is lost on the floor of the dryer is significantly reduced, or even practically reduced to zero.

13 BE2022/5050

[0039] To achieve this objective, a first pipe (4c) connects the separation unit (21) to the power supply unit (9) or, if the separation unit (21) is integrated into the unit power supply (9), to the first distribution unit (2a). The first pipe (4c) is configured to supply coarse particles (20c) to the first distribution unit (2a), either directly or through the supply unit (9) and the supply pipe (4), to distribute the coarse particles (20c) before drying along the radius of the first plate (1a).

[0040] A second pipe (4f) connects the separation unit to one or more of the following units, e the second distribution unit (2b) (see Figures 4(a), 5(a)), i.e. e a second fines distribution unit (2bf) located downstream of the second distribution unit (2b) to distribute the fine particles (20f) before drying along the radius of the second plate (1b) (see Figures 2(a ), 3(a)), or a first fines distribution unit (2af) located downstream of the first distribution unit (2a) to distribute the fine particles (20f) before drying along the radius of the first plate ( 1b) (see Figure 6(a)), or a combination of two or three of the previous options,

The second pipe (4f) is configured to supply fine particles (20f) to one or more of the previous units. When used to refer to particle transport, the terms “upstream” and “downstream” are defined in relation to the direction of movement of the particles in the dryer.

SEPARATION UNIT (21)

The separation unit (21) is configured to separate fine particles from coarse particles. Figures 2(b) to 7(b) show an example of particle size distribution of the particles (20) to be dried. Fine particles are particles of a fine fraction of the particle size distribution, whose diameter is less than the fine diameter (DO) (see hatched area in the

Figures 2(b) to 7(b). Coarse particles are particles of the complementary or coarse fraction whose diameter is greater than the fine diameter (DO). The value of the fine diameter (DO) actually depends on the hydraulic diameter (Dha, Dhb) of the openings of the first and second plates (1a, 1b), especially of the lower plate, ie, located below the other plate (upper) . The - fine diameter corresponds to the size of the particles which would not be retained by the plates (1a, 1b) passing through the openings thereof and, in the case of the lower plate, would fall on the floor of the dryer. For example, the hydraulic diameters (Dha, Dhb) of the openings of the first and second plates (1a, 1b) are selected so that the fine particles (20f) represent less than 20%, preferably less than 15% and even more preferably less than 10% or even 5% by weight of the total weight of particles (20) before drying. In general, it is preferred that the fine particles (20f) represent between 5% and 20%, preferably between 5 and 15% by weight

14 BE2022/5050 of the total weight of particles (20) before drying. The hydraulic diameter (Dh) of a closed, plane geometric figure is defined as the ratio, Dh = 4 A / P, where P is the perimeter of the geometric figure and A is the area of the surface included in the perimeter. In the case of an opening, the geometric figure is the cross section of the opening.

[0043] In one embodiment of the invention, the separation unit (21) may comprise a volume of retentate (21c) separated from a volume of sieve (21f) by a sieving element (215).

The volume of retentate (21 c) is connected, on the one hand, upstream to a source (20s) of particles (20) to supply the separation unit (21) with particles and, on the other hand, downstream to the first pipe (4c) in order to supply coarse particles to the first distribution unit (2a), either directly or through the supply unit (9) and the supply pipe (4). The sieve volume is connected to one or more of the second distribution unit (2b) (see Figures 4(a), 5(a)) and/or the second fines distribution unit (2bf) (see Figures 4(a), 5(a)) Figures 2(a), 3(a)), and/or a first fines distribution unit (2af) (see Figure 6(a)).

[0044] In order to reduce pressure losses, it is preferable to increase (or not decrease) the hydraulic diameters of the openings of the plates. On the other hand, to minimize the loss of particles having a size less than or equal to the hydraulic diameter (Dha, Dhb) of the openings and which can pass through the plates, it is necessary to minimize the size of the hydraulic diameters of the openings of the plates. According to the present invention, the fine fraction (21f) of particles is defined as the fraction of particles having a size less than or equal to the — fine diameter (DO). The fine fraction corresponds to the fine particles (20f) which, due to their small sizes, are most likely to pass through the first plate (1a) and M or the second plate (1b) and end up on the floor of the dryer. The values of the fine diameter (DO) and the hydraulic diameter (Dha, Dhb) of the openings of the first and second plates (1a, 1b) are therefore closely linked to each other.

[0045] For example, in the case where we do not want or cannot change the hydraulic diameter (Dha, Dhb) of the openings of the first and second plates (1a, 1b), the fine diameter (DO) is equal to or slightly greater than the hydraulic diameter of the openings. In this case, the screening element (21s) has openings of dimensions equal to or slightly greater than the hydraulic diameter (Dha, Dhb) of the openings of the lower plate (e.g., the first plate (1a)), preferably Dha = Dhb . If the fraction of fine particles (20f) thus defined forms more than 20%, preferably more than 25% of the total weight of particles (20) to be dried, then it becomes preferable to consider a reduction in the hydraulic diameter (Dha, Dhb) openings of the first and second plates (1a, 1b), to reduce to or less than 20% of the total weight of particles (20) to be dried the fraction of fine particles (20f) with a diameter less than the fine diameter (DO).

[0046] On the other hand, in the case where the hydraulic diameter (Dha, Dhb) of the openings of the first

15 BE2022/5050 and second plates (1a, 1b) can be changed at will (for example by depositing a filtering layer (1bp) on a grating), it will be selected so that the value of the fine diameter (DO) defining the terminal upper fraction of fine particles (20f) above which the coarse particles (20c) cannot pass through the lower plate (e.g., the first plate (1a)), is preferably chosen so that the fraction of fine particles (20f) form approximately 5 to 20%, preferably 7 to 10% of the total particle weight. In general, the openings of the first and second plates (1a, 1b) have a hydraulic diameter (Dha, Dhb) equal to or less than the fine diameter (DO) within a tolerance of 10% below DO (i.e., Dha = 90% DO to DO) or 5% (i.e., Dha = 95% DO to DO). Preferably, Dha = Dhb. Preferably the hydraulic diameter (Dha, Dhb) of the openings of the first and second plates (1a, 1b) is equal to the fine diameter (DO) (i.e., Dha = Dhb = DO).

[0047] The screening element (215) may comprise openings of hydraulic diameter (Dhs) equal to the hydraulic diameter of the openings of the first plate (1a) within a tolerance of + 10% (i.e., Dhs = Dha to 110% Dha ) or + 5% (i.e., Dhs = Dha to 95% Dha). Preferably the hydraulic diameter (Dhs) of the openings of the screening element is equal to the hydraulic diameter (Dha) of the openings of the first plate (1a) (i.e., Dhs = Dha). Preferably, the hydraulic diameter (Dhb) of the openings of the second plate (1b) is equal to the hydraulic diameter (Dha) of the openings of the first plate (1a) (ie, Dha = Dhb). The screening element may be in the form of a plate, a basket, a membrane, etc. In a preferred variant, the sieving element (21s) is configured to vibrate, in a cyclical movement of controlled trajectory, amplitude and frequency in order to improve the separation of fine particles (20f) and coarse particles (20c). . This allows agglomerates to be broken up and fine particles to be separated more efficiently (21f). Alternatively or jointly, a rotational movement of the sieving element (21s) makes it possible to increase the pressure by centrifugal force during sieving through the sieving element (21s). In the preceding discussion, for the sake of simplification, it has often been proposed that the lower plate was the first plate (1a) because this configuration of the dryer is preferred. However, the same discussion applies mutatis mutandis in the case where the lower plate is the second plate (1b).

[0048] In a variant of the invention, illustrated in Figures 3(a), 5(a), and 7(a), the screening element (21s) of the separation unit (21) is integrated to the power unit (9). In this variant, the retentate volume (21c) is coupled to the supply unit (9) and is configured to supply the first distribution unit (2a) with coarse particles (21c), preferably by a screw. Archimedes. In an alternative variant, illustrated in Figures 2(a), 4(a), and 6(a), the sieving element (215) of the separation unit (21) is distinct from the power supply (9).

In this variant, the volume of retentate (21c) is in direct communication with an inlet of the supply unit (9) and is configured to supply the supply unit (9) with particles

16 BE2022/5050 coarse (20c).

[0049] Thus separated into a coarse fraction of coarse particles (20c) preferably constituting 85 to 95% by weight of the particle size distribution and a fine fraction of fine particles (20f) constituting the rest of the particle size distribution having a fine diameter less than or equal to the fine diameter (DO), the first distribution unit (2a) can distribute the coarse fraction of coarse particles (20c) on the first plate (1a) without risk that the fine particles (20f) pass to through the openings of the first plate (1a). The fine particles (20f) of the fine fraction can be distributed on the first and/or second plates (1a, 1b) separately in different ways. In a variant illustrated in Figures 2(a)&2(c) to 5(a)&5(c), the fine particles are distributed on the second plate (1b) only, without passing through the first plate (1a). In an alternative (or joint) variant illustrated in the

Figures 6(a)&6(c) and 7(a)&7(c), the fine particles are distributed on the first tray (1a) but only after the coarse particles (20c) have been distributed to form on the first tray (1a) a layer of coarse particles (20c) on which the fine particles (20f) are deposited.

DISTRIBUTION OF FINE PARTICLES (20f) ON THE SECOND PLATE (1b)

UNIQUELY

[0050] Figures 2(a)&2(c) to 5(a)&5(c) illustrate a first variant of the present invention in which the fine particles are distributed on the second plate (1b) only, without passing through the first plate (1a). In this variant, the volume of retentate (21c) is coupled to the first distribution unit (2a). Thus, only the coarse particles (20c) contained in the volume of retentate (21c) are transferred into the first distribution unit (2a) which distributes the particles to form on the first plate (1a) a layer exclusively formed of coarse particles, as illustrated on the first lower plate (1a) of Figures 2(c) to 5(c).

After a turn on the first plate, the coarse particles deposited on the first plate (1a) are transferred by the transfer unit (4t) to the second plate (1b) on which the fine particles (20f) are also deposited according to different embodiments.

[0051] It is true that the fine fraction of fine particles (20f) is only dried for the duration of one rotation on the second plate (1b), to the detriment of a certain efficiency of the drying process. — However, this loss of efficiency is not significant, since the fraction of fine particles (20f) only constitutes around 10% of the total weight of the particles. Thus, reference is made to Figure 10 discussed in more detail below, representing the relative increase in moisture content according to the present variant and taking the values indicated in Figure 1 which gives purely indicative values of moisture contents relative to the initial content (HOa) of the particles before drying. Taking these values of HOb / H0a) as an example, we see that the coarse particles (20c), constituting approximately (1 — f) = 90% of the total particle weight, are

17 BE2022/5050 distributed on the first plateau (1a) with an initial HOa / HOa content = 100%. After a revolution of the first plate (1a) the coarse particles are recovered by the first recovery unit (3a), transferred to the second plate and distributed on the second plate with an intermediate moisture content e.g., H1a / H0a = H0b / H0a = 50%. Fine particles are also added which have an initial moisture content H0a / H0a = 100% and constituting approximately f = 10% of the total weight of the particles. Thus, we see in Figure 10 that for an intermediate humidity content HOb / H0a = 50% to be read on the abscissa of Figure 10, we obtain a relative increase in the relative humidity content of only approximately 10%, for a fraction f = 10% of fine particles.

[0052] Furthermore, as only 90% by weight of the particles forming the coarse fraction is deposited on the first plate (1a), drying is more effective on the first plate (1a) than if all the particles had been deposited there. The intermediate content (H1a / HOa) is therefore lower if only the coarse particles (20c) were deposited on the first plate (1a) than if all the particles had been deposited there. Finally, it was observed that fine particles dried faster than coarse particles. This can even be a disadvantage in certain cases using prior art dryers, with which finer particles can be over-dried. Shortening the drying time of fine particles therefore solves this problem. For all these reasons, the loss in efficiency is therefore low in comparison with the advantage of not losing approximately 10% of the weight of the particles, or of having to reduce the size of the openings of the trays, thus increasing the pressure losses of the flow of particles. hot gas passing through the two plates.

Fines in a Second Fines Distribution Unit (2bf)

[0053] Figures 2(a) to 2(c) and 3(a) to 3(c) illustrate a first embodiment of the present variant differing from one another only in that in Figure 2 (a), the separation unit (21) is separate from the supply unit (9), while in Figure 3(a), the separation unit is integrated into the supply unit (9). power supply (9). In this first embodiment illustrated in Figures 2(a) and 3(a), the volume of sieve (21f) containing the fine particles (20f) is coupled to a second fines distribution unit (2bf) located downstream of the second distribution unit (2b) to distribute the fine particles (20f) before drying along the radius of the second plate (1b). As the second fines distribution unit (2bf) is located downstream of the second distribution unit (2b), the fine particles (20f) are deposited on a layer of particles formed exclusively from coarse particles (20c) coming from the first plate (1a). Thus, as illustrated in Figures 2(c) and 3(c), the particles deposited on the second upper plate (1b) of these Figures form two well-marked stratigraphic layers, with an upper layer formed only of fine particles ( 20f) resting on a base layer formed exclusively of coarse particles (20c). Although the hydraulic diameter (Dhb) of the

18 BE2022/5050 openings of the second plate (1b) are of the order of the fine diameter (DO) and preferably equal to the hydraulic diameter of the openings of the first plate (1a), the fine particles (20f) cannot pass through the second tray (1b) because they are separated from the openings of the second tray by the layer of coarse particles.

[0054] Without passing through the first plate and thanks to the buffer layer formed by the coarse particles (20c) on the second plate (1b), the fine particles no longer fall through the plates, despite the fact that they have a smaller size. or equal to the hydraulic diameter of the openings of the plates. This embodiment is very effective in not losing practically any of the fine particles (20f). However, this embodiment requires installing the second fines distribution unit (2bf) which, although smaller in size than the second distribution unit (2b), increases the cost of the installation and reduces the space angular available on the second plate (1b) to dry the particles.

Fines in the Second Distribution Unit (2b)

[0055] Figures 4(a) to 4(c) and 5(a) to 5(c) illustrate an alternative embodiment of the present variant differing from one another only in that in Figure 4 (a), the separation unit (21) is separate from the power unit (9), while in Figure 5(a), the separation unit is integrated into the power unit ( 9). In this alternative embodiment illustrated in Figures 4(a) and 5(a), the volume of sieve (21f) containing the fine particles (20f) is coupled to the second distribution unit (2b) where they are mixed with the coarse particles — (210) partially dried from the first tray (1a) through the transfer unit (4t) to distribute the fine particles (20f) before drying and coarse (20c) partially dried particles along the radius of the second tray ( 1b). As the fine and coarse particles are mixed in the second distribution unit (2b), the particle size is distributed homogeneously in the thickness of the layer thus formed on the second plate (1b), as illustrated — in Figures 4(c) and 5(c).

[0056] Unlike the first embodiment illustrated in Figures 2(a) and 3(a), the fine particles (20f) deposited on the second plate (2b) according to the present embodiment of Figures 4(a) and 5(a) are not separated from it by a layer of coarse particles (20c). It is therefore possible for fine particles (20f) to pass through the openings of the second plate (1b) to fall by gravity onto the first plate (1a) (see particles falling from the second plate (1b) towards the first plate (1a). ) in Figures 4(c) and 5(c)). This is, however, not a disadvantage, because the fine particles (20f) thus falling from the second plate (1b) fall onto a layer composed solely of coarse particles (20c) deposited on the first plate (1a). Thus, these fine particles falling from the second plate (1b) never come into direct contact with the first plate (1a) and therefore cannot pass through the openings thereof. Thus, although the hydraulic diameter (Dha) of the openings of the first plate (1a) are of the order

19 BE2022/5050 of the fine diameter (DO), the fine particles (20f) cannot pass through the first plate (1a) because they are separated from the openings of the first plate (1a) by the layer of coarse particles (200).

[0057] This embodiment is simple and economical to implement in a dryer of the type described in EP2828595 and illustrated in Figure 1, since it is enough to install a separation unit and corresponding pipes (4f, 4c).

DISTRIBUTION OF FINE PARTICLES (20f) OVER A LAYER OF PARTICLES

COARSE (20c) ON THE FIRST BOARD (1a)

[0058] Figures 6(a) to 6(c) and 7(a) to 7(c) illustrate an alternative variant differing from one another only in that in Figure 6(a), the separation unit (21) is separate from the power unit (9), while in Figure 7(a), the separation unit is integrated into the power unit (9). Unlike the previous variant, in which the fine particles (20f) are distributed on the second plate only, in this variant, the fine particles are deposited on the first plate (1a), on a layer consisting only of coarse particles (20c) . In this variant illustrated in Figures 6(a) and 7(a), the volume of sieve (21f) containing the fine particles (20f) is coupled to a first fines distribution unit (2af) located downstream of the first distribution unit (2a) for distributing the fine particles (20f) before drying along the radius of the first plate (1b).

[0059] As the first fine distribution unit (2af) is located downstream of the first distribution unit (2a), the fine particles (20f) are deposited on a layer of particles formed exclusively from the coarse particles deposited on the first plate (1a) by the first distribution unit (2a) upstream of the first fines distribution unit (2af).

Thus, as illustrated in Figures 6(c) and 7(c), the particles deposited on the first lower plate (1a) of these Figures form two well-marked stratigraphic layers, with an upper layer formed only of fine particles ( 20f) resting on a base layer formed exclusively of coarse particles (20c). Although the hydraulic diameter (Dha) of the openings of the first plate (1a) are of the order of the fine diameter (DO) and preferably equal to the hydraulic diameter of the openings of the second plate (1b), the fine particles (20f) do not cannot pass through the first plate (1a) because they are separated from the openings of the second plate by the layer of coarse particles.

[0060] After a turn on the first plate (1a) the fine particles (20f) placed on the coarse particles (20c) are collected by the first recovery unit (3a) and transferred by the transfer unit (4t) to the second distribution unit (2b) for distributing the mixed fine and coarse particles. The particles in two distinct layers on the first tray (1a) are mixed in the transfer units (4t) and second distribution unit (2b) which deposits the particles homogeneously on the second tray (1b). Like fine particles and

20 BE2022/5050 coarse are mixed in the second distribution unit (2b), the particle size is distributed homogeneously in the thickness of the layer thus formed on the second plate (1b), as illustrated in the Figures 6(c) and 7(c), the fine particles (20f) deposited on the second plate (2b) according to the present variant of Figures 6(a) and 7(a) are not separated from it by a layer coarse particles (20c). It is therefore possible for fine particles (20f) to pass through the openings of the second plate (1b) to fall onto the first plate (1a) (cf. particles falling from the second plate (1b) towards the first plate (1a) in THE

Figures 6(c) and 7(c)). This is, however, not a disadvantage, because the fine particles (20f) thus falling from the second plate (1b) fall onto a layer composed only of fine particles (20f), themselves deposited on a layer composed only of coarse particles ( 20c) placed on the first plate (1a). Thus, these fine particles (20f) falling from the second plate (1b) never come into direct contact with the first plate (1a) and therefore cannot pass through the openings thereof. Thus, although the hydraulic diameter (Dha) of the openings of the first plate (1a) are of the order of the fine diameter (DO), the fine particles (20f) cannot pass through the first plate (1a) because they are separated openings of the first plate (1a) by the layer of coarse particles (20c).

[0061] In this variant, all the fine (20f) and coarse (20c) particles are dried over two consecutive rotations on the first plate (1a- then the second plate (1b), whereas in the previous variant of Figures 2 to 5, only the coarse particles make two rotations, the fine particles only making one rotation on the second plate (1b).

[0062] It is clear that it is possible to combine the variants and embodiments described above, by sending a portion of the fine particles (20f) collected in the sieve volume (21f) to the first distribution unit of fines (2af) and another part towards the second distribution unit (2b) and/or towards the second fines distribution unit (2bf)

DRYER STRUCTURE - FEED UNIT (9)

[0063] The supply unit (9) is coupled upstream either to the volume of retentate (21c) of the separation unit (21), or, in the case where the separation unit (21) is integrated in the supply unit (9) to a source of particles (20s), for example stored in a silo, a container, a skip, etc. The power supply unit (9) is coupled downstream to the first distribution unit (2a). The feed unit (9) preferably makes it possible to precisely control and vary the feed rate of coarse particles (20c) to the first distribution unit (2a) in order to be able to control the thickness (da) of the layer of particles deposited on the first plate by the first distribution unit (2a).

[0064] Any power supply unit allowing such control known to those skilled in the art can be used and the present invention is not limited to a particular type or model of power supply unit. For example, the feed unit (9) may include one or more Archimedes screws whose rotation speed controls the feed rate of coarse particles

21 BE2022/5050 (21c) supplying the first distribution unit (2a). Alternatively, the feed unit may include a treadmill whose travel speed can be controlled to control the feed rate.

[0065] A fines supply unit making it possible to control the flow of fine particles (21f) towards one or more of the second distribution unit (2b), the first and/or the second fines distribution unit ( 2af, 2bf). Like the feed unit (9), the fines feed unit can be in the form of an Archimere screw or a conveyor belt. However, as the fine particle fraction (20f) only forms about 10 to 15% of the total particle weight, the fine particles (20f) collected in the sieve volume (21f) can be transferred to the feed units. corresponding ones (2b, 2af, 2bf) as they pass through the sieving element (21f), without particular control of the flow rate.

DRYER STRUCTURE - 1°" AND 2°9 DISTRIBUTION UNITS (2a, 2b)

[0066] The supply unit (9) is coupled downstream to the first distribution unit (2a) and is configured to supply coarse particles (20c) to the first distribution unit (2a) at a feed rate controlled, for example, by a processor. The first distribution unit (2a) of the particles to be dried on the first plate (1a) aims to distribute the coarse particles to be dried homogeneously along a radius of the first plate (1a) to form a layer of thickness (da, db) controlled and substantially constant along a radius of the corresponding plate. In general, the first distribution unit (2a) comprises, e a structure extending from the outer periphery to the inner periphery of a plate, preferably following a radius thereof, e means of transporting the particles from the outer periphery to the inner periphery of the trays, and finally means for depositing said particles from the means of transport to the trays.

[0067] Several solutions are possible. For example, the transport of particles from the outer periphery to the inner periphery of the trays can be ensured by a conveyor belt, either perforated or inclined transversely so as to allow the particles to sprinkle the tray located below. To assist in the dusting, the belt can be vibrated.

In an alternative and preferred variant, the first distribution unit (2a) comprises at least one Archimedes screw extending along a radius of the first plate (1a), in order to transport the particles from the outer periphery towards the inner periphery of the first plate (1a), while distributing the particles on the plate. Said at least one Archimedes screw is enclosed in an enclosure provided with one or more openings extending downwards and along said radius of the first plate (1a) in order to allow the particles to be sprinkled homogeneously along the radius of the first plate (1a).

22 BE2022/5050

[0068] In the case of an Archimedes screw, if the particles to be dried are discharged by the supply unit (9) at a first end of the Archimedes screw of the first distribution unit (1a) , for example adjacent to the enclosure (10), the risk is great that the thickness (da) of the layer of particles decreases along the radius of the first plate (1a) as we approach from the center of the board. Such a thickness gradient (d(da) / dR) is not recommended because it results in a gradient along the radius of the first plate (1a) in intermediate moisture contents (H1a) of the particles after a turn on the first tray (1a). Worse still, if the layer becomes so thin that holes appear in the layer of particles, this creates zones of low resistance to the flow of hot gas which will preferentially pass through these zones to the detriment of the particles to be dried.

[0069] To overcome this problem, the first distribution unit (2a) extending along a radius of the first plate (1a) can comprise, as illustrated in Figures 8(a) and 8(b) , a distribution screw (22v) and a recirculation screw (23v), placed side by side and enclosed in a box (2h). The box (2h) includes a feed opening coupled to an outlet (90) of the power supply unit (9). The feed opening is configured to deliver particles from the feed unit (9) to one end of the distributor screw (22v). For example, the feed opening can be located above the distribution screw (22v) in order to allow the particles to fall by gravity into the box (2h) and to be carried away by the rotation in a first direction of the distribution screw (22v) along the radius of the first plate (18).

[0070] A distribution opening (20) extends along the length of a lower face of the box (2h), below the distribution screw (22v) so that the particles can exit the box (2h ) by gravity and fall onto the first plate (1a) along its radius. In order to prevent the particles from falling mainly into a section adjacent to the feed opening (90), the distribution screw (22v) is only partially separated from the recirculation screw (23v), allowing a surplus of particles to pass from the distribution screw (22v) towards the recirculation screw (23v), which rotates in a second direction, opposite to the first direction of rotation of the distribution screw (22v) so as to transport the particles thus transferred in the direction of the enclosure (10) (i.e., towards the outer ends of the distribution and recirculation screws (22v, 23v)). At the outer end of the recirculation screw (23v) adjacent to the enclosure, the recirculation screw (23v) is provided with a pallet (23s) which, by rotation of the recirculation screw (23v) returns the particles towards the distribution screw (22v). A similar pallet (22s) is arranged at the end of the distribution screw (22v) at the inner end of the distribution screw (22v) close to the center of the dryer in order to transfer to the recirculation screw (23v) the particles located at this end without having fallen onto the first plate (1a) through the distribution opening (20). A first distribution unit (2a) of this type allows a homogeneous distribution of the particles along the radius of the first plate (1a), thus ensuring that the thickness (da) of the layer of particles deposited on the first plate (1a) is radially substantially constant.

23 BE2022/5050

[0071] The second distribution unit (2b) fulfills the same functions for the second plate (1b) as the first distribution unit (2a) for the first plate (1a), with the difference that it is not powered upstream by a power supply unit (9) but by the transfer unit (4t) discussed below. It may be different from the first distribution unit (2a), but the first and second distribution units (2a, 2b) are preferably similar and even preferably identical. The second distribution unit (2b) is preferably of the type discussed above with reference to Figures 8(a) and 8(b). Even if similar, the first and second distribution units (2a, 2b) do not necessarily have to operate at the same flow rate, and the layers deposited on the first and second plates (1a, 1b) do not necessarily have to have the same thickness (da , db).

DRYER STRUCTURE - 1°" AND 2"9 RECOVERY UNITS (3a, 3b) AND DEVICE UNIT

TRANSFER (4t)

The first recovery unit (3a) of the first plate (1a) makes it possible to recover the particles deposited on the first plate (1a) after one revolution of rotation thereof. The first recovery unit (3a) is therefore positioned upstream of the first distribution unit, adjacent to the latter so that the particles having an initial moisture content (H0a) deposited on the first plate by the first distribution unit can rotate, preferably between 340 and 360°, or preferably between 345 and 355° before being collected and evacuated from the first tray (1a) with an intermediate moisture content (H1a) by the first recovery unit (3a). To maximize the angle of rotation of the particles on the first plate (1a) between the first distribution unit (2a) and the first recovery unit (3a), they are preferably arranged one next to the other, or even the first distribution unit (2a) can be arranged above the first recovery unit (3a).

[0073] As illustrated in Figures 9(a) and 9(c), the first recovery unit (3a) …— preferably comprises at least one Archimedes screw (32v) extending along a radius of said trays which is enclosed in a box (3h) provided with one or more recovery openings (3i) extending along said radius of the corresponding tray. The openings are connected to a scraper (3r) or brush capable of collecting and directing the particles brought by the rotation of the first plate (1a) through the recovery opening (3i) into the box (3h) of the screw Archimedes (32v). By rotating, the Archimedes screw transports the particles thus collected towards an evacuation opening (30) which is connected to the transfer unit (4. The first recovery unit (3a) is thus coupled downstream to the transfer unit (4% configured to transfer the particles thus collected by the first recovery unit (3a) to the second plate (1b).

[0074] Figures 9(b) and 9(d) illustrate another variant of first recovery unit (33), particularly adapted, but not only, to cases where the first plate (1a) comprises a raised circumferential rim imposing raise the Archimedes screw (32v) above this edge. As in the variant of Figures 9(a) and 9(c), in the present variant, the first recovery unit (3a) comprises an Archimedes screw (32v) whose rotation allows

24 BE2022/5050 to radially transport the particles collected along a radius of the first plate (1a) towards the outside thereof and to discharge them towards the evacuation opening (30) connected to the unit of transfer (4t). In the present variant, the first recovery unit (3a) further comprises a multi-blade mill (3s) arranged upstream of and parallel to the Archimedes screw (32v). The rotation of the multi-blade mill (3s) makes it possible to power the Archimedes screw (32v) even if it is raised relative to the surface of the first plate. In all cases, the multi-blade mill (3s) ensures a reproducible and reliable particle supply to the Archimedes screw (32v).

The transfer unit (4t) is coupled upstream to the first recovery unit (3a) of the first tray (1a) and downstream to the second distribution unit (2b) of the second tray (1b). The function of the transfer unit (4t) is therefore to transfer the partially dried particles from the first tray (1a) to the second tray (1b) to finalize the drying of the particles. The type of transfer unit (4t) of particles from the first tray (1a) to the second tray (1b) depends on the configuration of the dryer. If the first plate (1a) is the upper plate, the transfer means can be a simple tube connecting the first recovery unit (3a) of the first plate (1a) to the second distribution unit (2b) of the second plate, in in which the particles fall by gravity. If, on the contrary, the first plate (1a) is the lower plate, it is preferable that the transfer unit (4t) includes an Archimedes screw allowing the particles to be mounted from the first lower plate (1a) towards the second plate (1b) higher. This configuration of the lower plate forming the first plate (1a) and the upper plate forming the second plate (1b) has the advantage of reducing the suspension of the finest particles, because in this configuration, the hot gas becomes flows from top to bottom, crushing particles against the respective trays.

[0076] The second recovery unit (3b) fulfills the same functions for the second tray (1b) as the first recovery unit (3a) for the first tray (1a), with the following differences, e The particles collected by the second recovery unit (3b) have a final moisture content (H1b) which must be within the predefined target range (H1b = H1t + e), after a first turn of rotation on the first plate (1a) and a second turn rotation on the second plate (1b) exposed to a flow of hot gas passing through the second plate (1b) before passing through the first plate (1a), and the second recovery unit (3b) is not coupled downstream to the transfer unit (4t) but is coupled through the recovery opening (30) to an evacuation system (40) which evacuates the particles out of the dryer.

The second recovery unit (3b) may be different from the first recovery unit (3a), but the first and second recovery units (3a, 3b) are preferably similar and even preferably identical.

25 BE2022/5050

FIRST AND SECOND TRAYS (1a, 1b)

[0078] The dryer according to the present invention is particularly advantageous because it can be used to dry particles of very different particle sizes ranging from fine particles such as sawdust, fine grains, ceramic, polymer or metallic powders, to larger particles. coarse, such as wood waste, shavings, pellets, agricultural waste, corn husks, etc. by quickly and easily changing the diameter of the platen holes as follows. As illustrated in Figures 2(c), 4(c), 6(c) and 7(c), the first and second plates (1a, 1b) can thus comprise a rigid self-supporting structure (1ac, 1bc) with high permeability grating type, on which is placed a filter layer (lap, 1bp) comprising openings of size and density corresponding to the desired permeability depending on the type and particle size of the particles to be dried. The filter layer (1ap, 1bp) can be a perforated sheet, a sieve, a grid or a cloth. To facilitate the installation of such a filter layer, it can be cut into angular sectors, which can be placed and fixed side by side directly on the grating or other self-supporting structure (1ac, 1bc) with high permeability. This would be impossible in practice with belt or perforated tray dryers which are dedicated to drying particles of a single size type.

The sequence of superposition of the first and second plates (1a, 1b) depends on the applications and preferences. For example, the first plate (1a) can be located above the second plate (1b) and the hot gas (for example hot air) then circulates from bottom to top. An advantage of this variant is that the transfer of the partially dried particles from the first upper tray (1a) to the second lower tray (1b) by the transfer unit (4t) is done from top to bottom, assisted by gravity; thus, a simple tube connecting the first recovery unit (3a) to the second distribution unit (2b) is sufficient. On the other hand, as the hot gas flow circulates from bottom to top through the second and first plates, respectively, the particles can fly away and create a cloud of dust. A slight fluidization of the layer of particles can be advantageous for drying them, but the formation of a cloud of fine dust suspended in the air must be avoided. This configuration is therefore better suited to drying heavier particles which do not easily form a dust cloud.

[0080] For lighter or finer particles, the first plate (1a) can on the contrary be located below the second plate (1b) and the hot gas thus circulates from top to bottom, as shown in Figures 1 to 7. In this configuration, the particles are pressed against the plate on which they are located, which compacts the layer of particles and considerably reduces the suspension of dust. Compaction of the particle layer by a flow of hot gas from top to bottom risks forming temperature and humidity gradients in the thickness of the layer that are greater than in a layer slightly fluidized by a flow of hot gas from below. to the top. However, the particles having different temperatures and humidity contents are mixed during the recovery of the particles from the first tray (1a) and their transfer to the second tray (1b) by the transfer unit (4t) comprising, for example example, an Archimedes screw. The mixing carried out in the unit

26 BE2022/5050 transfer (4t) makes it possible to further increase the drying efficiency by remixing the particles, thus making it possible to deposit a layer of particles of homogeneous temperature and humidity content over the thickness of the layer.

[0081] Figures 1 and 2 illustrate dryers comprising two plates. However, to reduce the floor space occupied by the equipment, it is entirely possible to mount: e at least a third circular plate mounted substantially horizontally at a certain distance from, and separated from the first plate (1a) by, the second plate (1b), rotating around the vertical axis (Z), in the opposite direction of rotation of the second plate, the surface of said plate being perforated and permeable to fluids such as air and water vapor and water, and e means for transferring the particles collected from the second plate (1b) by the recovery means (2b) to a third distribution means capable of distributing said particles along a radius of the third plate.

[0082] It is clear that as many parallel plates can be mounted in rotation around the axis (Z) as desired and according to the needs of a particular application. However, a dryer comprising two plates (1a, 1b) is suitable for the majority of applications. The use of several superimposed trays makes it possible to reduce the external diameter of the trays, but increases the production price of the dryer.

[0083] The plates (1a, 1b) are enclosed in an external enclosure of diameter - corresponding to the diameter of the plates with enough margin to avoid friction, but as little as possible to allow the interface between the plates and the exterior wall. Sealing can be ensured for example by a flexible skirt attached to the exterior wall and resting on a raised edge of the circumference of the trays. In this way, the layer of particles resting on a rotating plate is not in contact with the static skirt, thus ensuring good sealing and integrity of the layer of particles on the plate. This is not possible to achieve on a belt dryer, in which the sealing skirt is placed between the rolling belt and the particles on the belt edges. There is therefore a fringe of particles in contact with the static skirt at each edge of the band which does not move at the same speed as the particles located in the middle of the band.

[0084] As illustrated in Figure 1, the central part of the plates is preferably hollow and included in a chimney (6) which is cylindrical, interior and centered on the axis of rotation (2).

Such a chimney (6) rising over practically the entire height of the dryer, in any case between the upper and lower plates, includes numerous advantages, which amply compensate for the loss in surface area available for drying. Indeed, if the external diameter of the trays is D1 and the diameter of the cylindrical chimney is D6 = n x D1, where n < 1, the surface loss (Ai) available on each tray for drying between a full tray and a tray

27 BE2022/5050 including a chimney is A6 / A1 = n°. For example, if the chimney has a third of the diameter of the exterior enclosure (i.e., n = 1/3), the loss in surface area available for drying is only n° = 1/9 = 11%. A chimney (6) firstly allows easy access by an operator to all the mechanical elements of the machine, such as bearings, geared motors, cylinders, etc. It also facilitates the replacement of the flexible porous layers (1ap, 1bp) to be placed and fixed on the gratings (lac, 1bc) giving the trays their mechanical integrity. The chimney can also be used to house the motors (5a, 5b) driving the rotation of the plates, as well as the fans used to generate the flow of hot gas, with the advantage of a substantial reduction in the noise generated by the dryer. In the case of a gas flow from top to bottom as shown in Figure 1, windows (6w) at the bottom of the chimney (6), located below the lower plate, make it possible to recover the hot gas and the evacuate from the top inside the enclosure. Alternatively, the hot gases can be evacuated through a space defined in a double wall of the enclosure (10).

[0085] Furthermore, the chimney (6) makes it possible to fix the first and second distribution units (2a, 2b) and recovery units (3a, 3b) at their two ends in order to avoid having to fix them door-to-door. -false on the exterior enclosure only. In addition, this frees up space at the interior ends of said means located side by side to accommodate their width. Finally, such a structure makes it possible to stiffen the surface between the chimney (6) and the external enclosure (10), making it possible to maintain good flatness of the trays. This is important for cleaning and collecting particles by a scraper or brush, which are only effective if the surface of the trays is perfectly flat.

[0086] Thanks to the separation unit (21) and the distribution of coarse particles (20c) and fine particles (20f) according to the present invention, it is possible to select hydraulic diameters (Dha, Dhb) of openings larger trays than in a prior art dryer, without losing the finest particles which would otherwise end up on the floor of the dryer after passing through the first and second trays (1a, 1b).

[0087] Fine particles can nevertheless fall onto the floor of the dryer. In order to avoid an accumulation of particles on the floor and also to recover them, it is advantageous to provide the floor with an extraction opening for the finest particles which may have been deposited on the floor. In addition, a scraper or brush fixed integrally to the lower plate and capable of following the rotational movement of the latter serves to push the particles deposited on the floor towards said evacuation opening. As the scraper or brush is attached to the lower plate, it is not necessary to motorize it individually.

DRYING PRINCIPLE

[0088] The drying of the particles deposited on the first perforated plate (1a), transferred after a given rotation from the first plate to the second perforated plate (1b) and in rotation, is

28 BE2022/5050 provided by hot gas blowing means (5g) following a flow substantially parallel to the vertical axis (Z), passing through the second plate (1b) before passing through the first plate (1a) , thus defining a counter-current drying system. It is important that the hot, dry gas flow first passes through the second plate (1b), where the particles are already partially dried by their stay on the first plate (1a), which is reached by a gas flow hot partially charged with humidity after passing through the second plate (1b).

The particles are distributed on the first plate by the first distribution unit (2a) with their initial moisture content (H0a). The particles are then carried away by the rotation of the first plate (1a) before being recovered by the first recovery unit (3a) and transferred to the second plate (1b) by the transfer unit (4t). During the rotation of the first plate (1a), the particles are exposed to the flow of hot gas exiting the second plate (1b), which is slightly cooler and more humid than the hot gas upstream of the second plate (1b). The humidity level of the particles located on the first plate (1a) decreases under the action of the flow of hot gas as the rotation of the first plate (1a) progresses, until reaching the first unit of recovery (3a) with an intermediate moisture content (H1a) lower than the initial content (HOa) but still higher than the final content (H1b) (which must be within the predefined target range) (i.e., H1b < H1a < H0a). The particles transferred by the transfer unit (4t) arrive on the second plate (1b) partially dried with the intermediate content (HOb = H1a) of humidity and begin a second rotation, preferably in the opposite direction, where the flow d The hot air finishes drying them until they reach their final humidity level (H1b). Drying remains optimal both on the first tray (1a) and on the second tray (1b) because the temperature (AT) and humidity (AH) gradients between the particles and the hot gases remain high on the two trays. Indeed, with a higher temperature and a lower humidity content of the particles located on the first plate (1a), the particles of the second plate (1b) are exposed to hotter and drier gases than those of the first plate (1a). ). However, although the particles located on the first plate (1a) are exposed to less hot and more humid gases than those on the second plate, as they are more humid and less hot than the particles located on the second plate (1b), the temperature (AT) and humidity (AH) gradients between particles and hot gases remain high.

[0090] Rotation in opposite directions of the first and second plates (1a, 1b) optimizes the drying process. The hot gas, for example hot air or any other gas resulting from a combustion process, follows a path opposite to that of the particles. As the moisture content of the particles located on the second plate depends on their angular position, it follows that the moisture content of the air having passed through the second plate (1b) and carried away part of the humidity of the particles by transferring part of its heat, it also depends on the angular position and will be higher where the particles affected by the flow have a higher humidity content, i.e. in the low angles of rotation of the second plate (1b) . hot gas

29 BE2022/5050 downstream of the second plate (1b) (i.e., the gas located between the two plates) is also the gas upstream of the first plate.

[0091] Figure 1 illustrates by way of example the moisture contents of the particles according to their position on different angular sectors of the first and second plates (1a, 1b). It can be seen that after passing through the particles of the second tray (1b) adjacent to the second recovery unit (3b) which have the lowest final moisture content (H1b), the column of hot gas reaches the freshly deposited on the first tray (1a) having the highest initial moisture content (HOa). Thus, the first contact of the particles on the first plate with a column of hot gas is very effective in quickly eliminating a large quantity of water.

As the first plate rotates and the particles lose their initial moisture content, the hot gases are moderately moisture-laden but hot and dry enough to lower the moisture content to the intermediate content (H1a) which they must reach before being transferred to the second plate (1b).

[0092] In the variant of the invention in which the fine particles (20f are distributed only on the second plate (1b) and do not remain on the first plate (1a), the fraction of fine particles (20f) is not exposed to the drying action of hot gases only half of the way of the coarse particles (20c). As discussed above, as, on the one hand, the finer particles (20f) dry more quickly than the coarse particles ( 20c) and, on the other hand, the fraction of fine particles (20f) generally only represents around 10% of the weight of particles, this does not represent a very large increase in the humidity level of the particles arriving on the second plate (1b). For example, the coarse particles which constitute (100 — f% of the weight of the particles are distributed on the second plate (1b) with an intermediate humidity content (HOb = H1a) and the fine particles, which represent f% of the weight of the particles, are distributed with an initial moisture content (H0a). The relative increase = ([(HOD)inv — (HOb)ra] / (HOb)pa) of the intermediate moisture content of the particles distributed on the second plate (1b) depending on whether the particles are distributed on the second plate only ((HOb)inv = HOb) according to this variant of the present invention and without separation of fine particles (20f) ((HOb)ra = H1a) according to the prior art is therefore, (Hob)iny - (HOb)pa _ H0b-Hia _ ((100-f)% HOb + f% H0a) - H1a _ p,Hoa - H1a (HOb)pa H1a H1a H1a 20 = m Cs Le

[0093] In which; e HOa is the initial moisture content, during distribution on the first plate (1a), e Ha is the intermediate moisture content after a turn on the first plate (1a), during the recovery of the particles from the first plate ( 1a), e HOb is the intermediate moisture content, during distribution on the second plate (1a); in the case of the prior art, without separation of fine particles (209,

30 BE2022/5050 (HOb)ra = H1a; in the case of the present invention, (HOb)inv > H1a, because of the addition of the fine particles (20f) before drying, e H1b is the final moisture content after a turn on the second plate (1b), when recovery of particles from the second tray (1b).

[0094] Figure 10 graphically represents the relative increase in the moisture content ([(HOD)inv — (HOb)pa] / (HOb)ra) of the particles distributed on the second plate (1b) as a function of the content intermediate in humidity (HOb / HOa) relative to the initial content (HOa), of the particles distributed on the second plate (1b), for a fraction of f = 10% of fine particles (20f). In practice, the intermediate relative moisture content (HOb / H0a) of the particles transferred from the first plate (1a) to the second plate (1b) is between 40 and 60% of the initial moisture content (H0a) of the particles before drying, represented by the shaded area of the

Figure 10. It can be seen that under these conditions, the increase in moisture content ([(HOD)inv — (HOb)ra] / (HOb)ra) is between 5 and 15% compared to the case where the fine particles are not separated. If necessary, the second plate (1b) can rotate at a rotation speed (wb) lower than the rotation speed (wa) of the first plate (1a), in order to increase the drying time of the particles on the second plate ( 1b).

Ree Geerse OO

31 BE2022/5050

Ua of payroll vs laughter ep oenen

EE ee

Claims (14)

32 BE2022/5050 CLAIMS 1. Dryer for drying particles (20) having an initial moisture content (H0a) until reaching a final moisture content (H1b) lower than the initial content (H1b < H0a), the dryer comprising, (a) a enclosure (10) comprising an essentially cylindrical wall extending along a vertical axis (Z), (b) a first circular plate (1a) mounted on the wall of said enclosure (10) substantially normal to the vertical axis (Z) and configured to rotate in a first direction around the vertical axis (Z), the surface of the first plate being perforated with openings of hydraulic diameter (Dha = 4 Aa / Pa) equal to the ratio of four times an area (Aa) on a perimeter (Pa) of the openings, making the surface permeable to gases such as air and water vapor and to water, and (c) a second circular plate (1b) mounted at a certain distance from the first plate on the wall of said enclosure (10) substantially normal to the vertical axis (Z) and configured to rotate around the vertical axis (Z), the surface of the second plate being perforated with openings of hydraulic diameter (Dhb = 4 Ab / Pb) equal to the ratio of four times an area (Ab) on a perimeter (Pb) of the openings, making the surface permeable to gases such as air and water vapor and to water, (d) a first distribution unit (2a) of the particles to be dried configured to receive the particles to be dried from a supply unit (9) and to distribute these particles before drying along a radius of the first plate (1a), (e) a first recovery unit (3a) of the particles deposited on the first plate (1a) after a rotation of a given angle thereof, the first recovery unit being located downstream of, preferably adjacent to the first distribution unit (2a), (ff a transfer unit (41) of the particles collected from the first tray (1a) by the first recovery unit (3a) to a second distribution unit (2b) configured to distribute said particles along a radius of the second plate (1b), (g) a second recovery unit (3b) of the particles deposited on the second plate (1b) after a rotation of a given angle thereof, the second recovery unit being located downstream of, preferably adjacent to the second distribution unit (2b) and being configured to evacuate the particles after drying out of the dryer by an evacuation unit (40), (h) a blowing unit of hot gas (5) following a flow substantially parallel to the vertical axis (Z), passing first through the perforated surface of the second plate (1b) before passing directly afterwards through the perforated surface of the first plate (1a) , characterized in that the dryer comprises (i) a particle separation unit (21) located in or upstream of the feed unit (9) the separation unit (21) being configured to separate particles 33 BE2022/5050 fine particles (20f) of diameter less than a fine diameter (DO) of coarse particles (20c) of diameter greater than the fine diameter (DO), and (j) a first pipe (4c) configured to supply coarse particles (20c) the feeding unit (9) or the first distribution unit (2a) for distributing the coarse particles (20c) before drying along the radius of the first plate (1a), and (k) a second pipe ( 4f) configured to supply fine particles (20f) either to the second distribution unit (2b), or to a second fines distribution unit (2bf) located downstream of the second distribution unit (2b) to distribute the fines fine particles (20f) before drying along the radius of the second plate (1b), i.e. a first fine distribution unit (2af) located downstream of the first distribution unit (2a) to distribute the fine particles (20f) before drying along the radius of the first plate (1b), or a combination of two or three of the previous options, in which the terms “upstream” and “downstream” are defined in relation to the direction of movement of the particles in the dryer . 2. Dryer according to claim 1, in which the separation unit (21) comprises a screening element (21s) comprising openings of hydraulic diameter (Dhs) equal to the — hydraulic diameter of the openings of the first plate (1a) in a tolerance of + 10% (ie. Dhs = Dha + 10%), preferably equal to the hydraulic diameter of the openings of the first plate (1a) (i.e., Dhs = Dha). 3. Dryer according to claim 2, in which the sieving element (21s) is configured to enter into a cyclic movement of controlled trajectory, amplitude and frequency in order to - improve the separation of fine particles (20f) and coarse particles (20c). 4. Dryer according to any one of the preceding claims, in which the separation unit (21) is distinct from the supply unit (9), and comprising, e a volume of retentate (21c) configured to contain the coarse particles (20c) after separation by the separation unit (21), and e a volume of sieve (21f) configured to contain the fine particles (20f) after separation by the separation unit (21) in which the first pipe (4c) connects the retentate volume (21c) of the separation unit (21) to the supply unit (9), and in which the second pipe (4f) connects the sieve volume (21f) of the separation unit (21) either towards the second distribution unit (2b), or towards the first or second fines distribution unit (2af, 2bf), or towards a combination of the aforementioned distribution units. 5. Dryer according to any one of claims 1 to 3, in which the separation unit (21) is included in the supply unit (9), and comprising, e a volume of retentate (21c) configured to contain the coarse particles (20c) after separation by the separation unit (21), and e a volume of sieve (21f) configured to contain the fine particles (20f) after separation by the separation unit (21) in which the first pipe (4c) connects the retentate volume (21c) of the supply unit (9) to the first distribution unit (2a), and in which the second pipe (4f) connects the sieve volume (21f ) from the supply unit (9) either to the second distribution unit (2b), or to the first or second fines distribution unit (2af, 2bf), or to a combination of the aforementioned distribution units. 6. Dryer according to any one of the preceding claims, in which the hydraulic diameters (Dha, Dhb) of the openings of the first and second plates (1a, 1b) are selected so that the fine particles (20f) represent between 5% and 20% by weight of the total weight of particles (20) before drying. 7. Dryer according to any one of the preceding claims, in which the first plate (1a) is located below the second plate (1b) and where the hot gas is preferably hot air circulating from top to bottom. 8. Dryer according to any one of the preceding claims, in which the second plate (1b) rotates in the opposite direction of rotation of the first plate (1a). 9. Dryer according to any one of the preceding claims, in which the first and second plates (1a, 1b) comprise a rigid structure (1ac, 1bc) self-supporting with high permeability of the grating type, on which is placed a layer filter (1af, 1bf) comprising openings of hydraulic diameter (Dha, Dhb) and density corresponding to the desired permeability depending on the type and size of the particles (20) to be dried. 10. Dryer according to any one of the preceding claims, in which the first and second distribution units (2a, 2b) of the particles to be dried on the first and second plates (1a, 1b), respectively, each comprise at least one screw of Archimedes extending along a radius of the first and second plates (1a, 1b), respectively, said at least one Archimedes screw being enclosed in an enclosure provided with one or more openings extending along of the radius of the plates (1a, 1b). 11. Dryer according to any one of the preceding claims, wherein the first and second recovery units (3a, 3b) each comprise at least one Archimedes screw extending along a radius of said plate which is enclosed in an enclosure provided with one or more openings extending along said radius of the first plate (1a), said openings being connected to a scraper or brush capable of collecting and directing the particles brought by the rotation of the plate towards the screw Archimedes. 12. Dryer according to any one of the preceding claims, wherein after the gas has passed through the perforated surface of the first plate (1a), the hot gas blowing unit (5) is configured to evacuate the gas outside the enclosure, or e comprises an air dryer making it possible to capture the humidity present in the gas before heating and recirculating the gas thus dried through the second and the first plate (1b, 1a), respectively . 13. Dryer according to claim 12, in which the vertical axis (Z) is centered in an essentially hollow cylindrical chimney (6) whose wall extends at least from the first plate (1a) to the second plate (1b, 1b) comprising one or more openings providing fluid access to the interior of the chimney (6) to the gas having passed through the perforated surface of the first plate (13), and in which the chimney comprises either, e one or more openings towards the outside the enclosure allowing the gas to be evacuated from the enclosure, i.e. the dryer and one or more openings configured to recirculate the gas after its passage through the dryer and after heating, following the flow substantially parallel to the the vertical axis (Z), passing first through the perforated surface of the second plate (1b) before passing directly afterwards through the perforated surface of the first plate (1a). 14. Dryer according to any one of the preceding claims, in which the supply unit (9) is connected upstream to a source (20s) of the particles (20) to be dried, preferably a silo, the particles (20 ) preferably comprising waste wood from sawmills, waste wood from construction materials, waste paper or cardboard, agri-food products, and are in the form of powder, granules, chips, pellets, — cakes , or pieces not exceeding 10 cm in length.