Apparatus for the continuous drying of particles

[0001] The invention relates to an industrial dryer for drying organic particles, for example derived from food such as cereals, or waste used as fuel.

Background Art [0002] Many industrial methods require drying the particles before further use, both before packaging granulated food products or industrial products, and before burning the crushed waste used as fuel. It is of course possible to perform particle drying in batches by depositing particles on plates or in a rotating drum, preferably perforated to pass hot gases and allow water and steam to be removed. In some cases, a fluidized bed is formed by suspended particles by the action of a hot gas stream. However, most industrial applications require a flow rate that batch drying cannot provide. For this reason, the principle of depositing the particles to be dried on a porous support and exposing them to a hot gas stream has been used for continuous drying devices comprising a continuous source of particles for drying above a proper dryer and continuous removal of dried particles below.

[0003] In particular, a belt dryer is schematically shown in Fig. 1 (a) and comprises a perforated elastic band stretched between two motorized rollers to form a loop. Air or other hot gas is blown below the upper fabric on which the particles to be dried are continuously deposited. A belt dryer, for example, is shown:<a href="http://vishakanindustry.com/p_beltdryer.html">http://vishakanindustry.com/p_beltdryer.html</a> (2012). The length of the belt dryer depends on the type of particles to be dried and their water load. Usually, if the area is 120 m² is required for drying particles at the desired speeds, the belt will have an area of ​​at least twice as large, on the order of 250 m² because the particles only dry at the top of the loop connecting the two rollers. For a width of 2.5 m, a 200 m tape is needed to connect two rollers about 80 m away. The tape of these dimensions is very expensive and difficult to mount / remove on the device. A belt dryer is therefore usually reserved for drying one type of particles, since changing the belt would be uneconomical to optimize the type of perforation for a new type of particles. In the event of tape damage, the entire unit must be stopped for the long time required to change or repair the tape. To support a belt of this length, numerous support rollers are mounted on bearings, which increases the costs and also the risk of failure of such a device. The belt dryer is very expensive and inefficient in terms of size because the particles are dried on less than half the length of the belt.

[0004] There are also perforated plate dryers, as shown schematically in Fig. 1 (b), which resemble belt driers, except that the belt is replaced by perforated plates joined together, forming a kind of caterpillar. The difference between the belt dryer is that the plates are articulated to show the same side either on the top or bottom of the loop belt. This can reduce almost half the length of the dryer, because the particles are subjected twice to a stream of hot gas: the first time when passing in the upper part of the loop, and the second time when passing in the opposite direction in the lower part. Although advantageously in this respect, as well as compared to belt driers, it is obvious that the mechanism necessary for moving the plates is complex and therefore expensive and fragile, especially when exposed to fine particles that block the bearings. In addition, the openings formed between two adjacent plates and, especially the spaces opening in the tray transfer mechanism during each transfer of the plate from the upper part to the lower part of the caterpillar form many preferential passes with the least resistance to the hot gas stream, which leads to a significant decrease in the efficiency of such dryers.

[0005] EP197171 discloses the dryer shown schematically in Fig. 1 (c) (without powder spreading and receiving means, for simplification of the drawing), comprising a plurality of plates (1, 1b), perforated, round, superimposed and rotatably mounted around a hollow central axis. Each plate is enclosed in a cylindrical chamber individually equipped with a roof [18] and a bottom separating it from other plates. Transfer means (4a) for drying powder are placed between each adjacent plate (see gray arrows (4a)). Each chamber is provided, on the one hand, with a first hot air inlet in fluid communication with the cavity of the hollow central axis, the first opening being located above the plate in the respective chamber, and on the other, a second outlet in the perimeter wall of the chamber in a fluid connection from the outside (or a hot air discharge system), the second opening being below the corresponding plate. Hot air is blown into the cavity with a hollow axis as the black arrows in Fig. 1 (c) show and is distributed parallel to each chamber through the first hot air introduction hole. Hot air is forced to pass through the round perforated plates before being discharged through a second hole in the peripheral wall of each chamber. In practice, such a system is basically similar to a belt dryer (see Fig. 1 (a)), whose linear movement has been replaced by a circular movement distributed over several levels with means for transferring powder from one plate to another. Of course, such a rotary system has the significant advantage of providing space savings on a linear belt dryer, but such a system is also not efficient. In fact, the hot air after passing through the first plates loaded with very wet particles comes out relatively saturated with moisture, the hot air passing through the last plates charged with particles already partially dried out of the previous plates comes out only a little saturated with moisture, which means a significant loss of energy.

[0006] There remains therefore a need to develop an industrial dryer for drying particles continuously, which is effective, easy to use, takes up less space and is cheaper. The invention provides such industrial dryers.

Summary of the Invention [0007] The invention is defined in the independent claims. Preferred embodiments are defined in the dependent claims. The invention particularly relates to a particle drying dryer comprising, (a) a housing comprising a substantially cylindrical wall extending along a vertical axis Z, (b) a first round plate mounted in the wall of the housing, substantially perpendicular to the vertical axis Z and rotating in a first direction about the axis vertical Z, the surface of this plate is perforated and permeable to gases, such as air and steam, and to water, and (c) a second round plate mounted at a distance from the first plate in the wall of the housing, substantially perpendicular to the vertical axis Z and rotating about the vertical axis Z, in the opposite direction to the direction of rotation of the first plate, the plate surface being perforated and permeable to gases, such as air and steam, and for water, (d) first means for distributing particles to be dried, adapted to distribute the particles prior to drying along the radius of the first plate, (e) means for receiving particles deposited on the first plate after rotation of the plate by a given angle, the receiving means being positioned below, preferably adjacent to the first distribution means, (f) means for transferring the collected particles from the first plate through the receiving means to the second spreading means adapted to spread the particles along the radius of the second plate.

characterized in that the dryer further comprises, hot gas blowing means along a stream substantially parallel to the Z axis, first passing through the perforated surface of the second plate immediately before passing through the perforated surface of the first plate.

[0008] In the first example of the invention, the first plate is below the second plate and the hot gas is preferably hot air circulating from the top down, while in the second example the first plate is above the second plate and the hot gas circulates from the bottom up. The first example has, among other things, the advantage that hot gas attaches the particles to the surface of the plates, which can be advantageous due to the reduction of dust generated by fine particles. The second example has the advantage that the transfer of partially dried particles from the first upper plate to the second lower plate is facilitated by gravity, which can be particularly advantageous for high density particles.

[0009] Each panel may advantageously comprise a rigid self-supporting structure with high permeability, such as a grid, on which a filter layer comprising

-4 holes with a size and density appropriate to the desired permeability depending on the type and size of particles to be dried. This solution provides greater flexibility because it is very easy to replace a perforated sheet, sieve, mesh or even a canvas on a grid for drying successively particles of very different sizes, which is practically impossible using a belt or paddle dryer.

[0010] The first and second particle spreading means to be dried on the first and second plates suitably preferably comprise at least one Archimedes screw extending along the radius of the first and second plates, respectively. Archimedes' screws are placed in a housing equipped with one or more holes extending along the radius of the plates and allowing scattering of particles on the plate located directly below.

[0011] Similarly, the receiving means of the first plate preferably comprise at least one Archimedes screw extending along the radius of the plates that are enclosed in a housing equipped with one or more holes extending along the radius of the first plate. These holes are connected to a scraper or brush, adapted to collect and direct the particles brought in by turning the plate towards the Archimedes screw. Preferably, the second plate also comprises particle receiving means, arranged on the second plate and dried on its rotation by a given angle, said collecting means being located below, preferably adjacent to the second collecting means. The preferred receiving means of the second plate are similar to the receiving means of the first plate discussed above.

[0012] The third round plate can be mounted substantially horizontally at a distance and separated from the first plate by a second plate, rotating about a vertical axis Z, in the opposite direction to the direction of rotation of the second plate, the surface of the plate being perforated and permeable to gases, such as air and steam, and water. The transfer means enable the particles collected from the second plate to be transferred, via the second take-up means discussed above, to third distribution means adapted to distribute these particles along the radius of the third plate. This configuration allows reducing the radius of the disc and thus the surface occupied by the dryer, but it is obvious that it is higher.

[0013] For collecting fine particles that have passed through the bottom plate and accumulated at the bottom of the dryer, it preferably comprises an outlet for these particles. Furthermore, the scraper is preferably permanently attached to the bottom plate and adapted to track its rotation to push the particles deposited on the bottom towards the outlet opening.

[0014] The actual drying zone is preferably comprised between an outer cylindrical wall with a diameter corresponding to the diameter of the discs and an inner cylindrical wall coaxial with the outer wall and defining a hollow housing centered around the axis of rotation of the plate. The inner wall extends continuously from at least the top plate to the bottom plate. The housing may be suitable in an advantageous way to contain the fans necessary to create a gas stream or in a drive motor to

- rotating plates and thus reducing noise. It also allows the operator to access various mechanical components from the inside for machine maintenance and repair.

[0015] The second and third driers, as described above, can be applied to the first dryer, and thus increase the drying efficiency for the same space utilization. A source of particles to be dried, e.g. a silo, may be connected above the first means for distributing the particles to be dried on the first plate. For example, the particles to be dried may be food products such as cereals, fertilizers or tea leaves, organic ground waste for drying for use as a fuel, cosmetic or pharmaceutical products in the form of particles, pigments, polymer granules, ceramic powders, etc. Above, it may be a storage and / or packaging unit.

[0016] In the case of drying the particles to be used as fuel, the dryer can be connected to a boiler fed with the dried particles as fuel. This boiler can be connected to a steam-powered turbine at T1 temperature, through a boiler that starts the electric generator. Steam or liquid from the turbine can be brought to a temperature T2 &lt;T1, and sent to a heat exchanger to heat the air by means of blowing hot gas from a dryer and / or a second dryer.

Brief description of the figures [0017] For a better understanding of the essence of the invention, reference should be made to the following figures, which:

Fig. 1: shows (a) a belt dryer, (b) a paddle dryer as known in the art and (c) a dryer according to EP197171.

Fig. 2: schematically shows two embodiments of the invention.

Fig. 3: shows the example of Fig. 2 (a).

Fig. 4: shows the example of Fig. 2 (b).

Fig. 5: shows an embodiment of the invention.

Fig. 6: graphically depicts changes in water content (solid line) and particle temperature (broken line) as well as gas entering (AIR IN) and leaving (AIR OUT) from the plate, depending on the angular position of the first and second plates.

Fig. 7: shows an example of an installation comprising a dryer according to the invention for drying waste for its use as a fuel.

Fig. 8: shows an installation according to the invention, equipped with a supplementary plate for cooling dried particles.

Detailed description of specific embodiments [0018] In contrast to the linear motion of belt or perforated plate driers, currently available on the market for drying particles and schematically represented

In Fig. 1, the dryer according to the invention has an operation based on rotation in opposite directions of at least one first and second plates (1a, 1b) superimposed. This approach allows the design of a particle drying device that is more compact than linear motion dryers. Especially and as shown in Fig. 2 to 4, the drier according to the invention comprises a first circular plate (1a) attached substantially horizontally rotating in a first direction about a vertical axis Z, the surface of this plate being perforated and permeable to gases such as air and water vapor and to water. The motor (7a) ensures rotation of the first plate (1a). The first means for spreading (2a) the particles to be dried is mounted above the first plate in such a way as to distribute these particles before drying along the radius of the first plate (1a). The first collecting means (3a) particles deposited on the first plate (1 a), after rotation by a given angle are mounted above the first spreading means (2a). To extend the drying time of the particles deposited on the first plate (1a), the first collecting means (3a) are preferably in the vicinity of the first spreading means (2a), these means preferably extending along the two radii of the disk.

[0019] The transfer means (4a) of the particles collected from the first plate (1a) by means of the take-up means (2a) allow transfer to the second plate via second spreading means (2b) adapted to distribute these particles along the radius of the second round plate (1b) . The second round plate (1b) is similar to the first plate (1a) and is mounted substantially horizontally at a distance from the latter, rotating about a vertical axis Z, but in the opposite direction of rotation of the first plate. As with the first plate (1b), the surface of the second plate (1b) is perforated and permeable to gases such as air and water vapor, and to water. The rotation of the second plate (1b) is also driven by a motor (7b), which may be the same or different from the motor (7a) enabling the rotation of the first plate (1a).

[0020] In a preferred embodiment of the invention, the second plate (1 b) also comprises receiving means (3b) particles deposited on the second plate, rotated by a given angle, the receiving means being below, preferably in the vicinity of the second spreading means (2b ) and are preferably similar to the receiving means of the first plate.

[0021] Drying of the particles deposited on the first perforated plate (1a), transferred after a given rotation of the first plate towards the second perforated plate (1b) and rotating, is provided by means of blowing hot gas (5) along a stream substantially parallel to the Z axis, first passing through the second plate (1b) before passing through the first plate (1a), thus creating an upward drying system. It is important that the hot dry gas stream first passes through the second plate, on which the particles are already partially dried by staying on the first plate, which in turn is obtained by means of a hot gas stream partially loaded with moisture after passing through the second plate. The advantages of such an upward drying system are schematically illustrated in Figs. 3, 4 and 6. Fig. 6 schematically shows the water content (solid line) and temperature (broken line) of particles (middle "particle" graph) and gas (often air) above (upper "air in" graph) and below (bottom "air out" graph) of each plate, for positions @ to E on the first

And the second plates (1a, 1b) as shown in Figs. 3 (a) and 4 (a). The ordinate relative humidity indicates the water content of the particles during their movement to the dryer, as well as the air above (air in) and below (air out) the first and second plates, respectively, at a given angular position of 0 to B relative to the original water content, conversion (H - H0) / (H1 - H0), where H is the water content in the particles as well as in the air above the first and second plates in a given angular position, H0 means the water content before contact between the gas and the particles and H1 means the water content at the end of drying, i.e. after the particles reach the second collecting means (3b) and the air below the first plate (1a).

[0022] The particles (graph in the center of the "particles") are distributed on the first plate (1a) with the maximum initial content, H0, part visible on the left side of the graph, in position 0 of the first plate (1 a) in Fig. 6 ( solid line). In Fig. 3 (a) it corresponds to the position on the left of the distributor (2a) of the first upper plate (1a), while in Fig. 4 (a) it corresponds to the position on the right side of the distributor (2a) of the first lower plate (1a). The particles are first transferred by rotating the first plate (1a), moving towards the right side of the graph in Fig. 6 passing through the positions § and | c | before being recovered by funds (3a) and transferred to item | d | the second plate by transfer means (4a). During the rotation of the first plate and the particles therein, the moisture content of these particles decreases under the influence of the hot gas stream (continuous curve of the "particle" diagram in Fig. 6). The particles reach | d | on the second plate as partially dry and start a second rotation in the opposite direction in which the stream of hot air completes their drying until reaching the final moisture content, H1, part, in position B visible on the right side of the diagram in Fig. 6 after passing through position | E | second disc (1b).

[0023] Hot gas, for example hot air or other combustion gas, follows the reverse path to the particle path. In the graph of Fig. 6, the gas exits from the right half of the graph with the initial moisture content H0, air, solid and low above the second plate (see AIR IN, second plate (1b)). When the air passes through the second plate (1b), it transfers part of its caloric and kinetic energy to the particles of the second plate (1b) that heat up (see dashed line in the "particles" diagram on the second plate (1b)), and entrains some of the moisture of the particles ( see "air out" on the second disc (1b)). The air leaving the second plate (1b) enters the first plate (1a) air (1a) (AIR OUT (1b) = AIR IN (1a)), but because the first plate rotates in the opposite direction to the second plate, the curves are inverted. It can be seen that the air arriving at position 0, in which the particles are more humid, is drier than the air arriving at position | c |, in which the particles are already partially dried. Thus, passing through the first plate (1a), the driest air passes at 0 through the most humid particles, and therefore comes out saturated with water, and partly humid air passes into | C | partially dried particles, and thus also comes out saturated with water, thereby increasing the transfer of air energy to the particles and moisture from the particles to the air. This optimization is achieved while providing a particularly compact device that is easy to use, easy to maintain and, in particular, allows easy drying of particles of very different sizes.

[0024] Application EP197171 mentioned at the outset discloses the dryer shown schematically in Fig. 1 (c), which at first glance is similar to the dryer according to the invention. In fact, the dryer differs from the dryer according to the invention, especially in that hot gas passes through only one question before draining. Indeed, the roofs [18] separate the second plate (1b) from the first plate (1a), preventing hot air from passing from said second plate (1b) to the first plate (1a). Because the hot air rises into the cavity of the central axis of rotation, where it is separated into first, second and other plates, through which it passes individually before discharge, we can talk about a system of parallel distribution of hot air (see Fig. 1 (c)). In contrast, the hot air distribution system in the dryer according to the invention is a series system, which allows to obtain a drying optimization as described above, which is much more efficient than in the case of a parallel system like the driers according to EP197171.

[0025] The superposition sequence of the first and second discs (1a, 1b) depends on the application and the user's preferences. For example, as shown in Figs. 2 (a) and 3, the first plate (1a) can be located above the second plate (1b) and hot gas (e.g. hot air) flows from the bottom up. The advantage of this example is that the transfer of partially dried particles from the first upper plate (1a) to the second lower plate (1b) by the transfer means (4a) occurs from top to bottom, by gravity. In contrast, since the hot gas stream flows from the bottom up through the first and second plates, respectively, the particles can fly up and cause dusting. Slight fluidization of the particle bed may be beneficial for drying, but the formation of a cloud of fine dust suspended in the air should be avoided. This configuration is therefore more suitable for drying heavy particles that do not easily form a dust cloud.

[0026] For lighter or finer particles, the first plate (1a) may instead be below the second plate (1b) and hot gas flows from below upwards as shown in Figs. 2 (b) and 4. In this configuration , the particles are pressed against the plate on which they are, which significantly reduces the suspension of dust. The hot gas stream flows from the bottom up, which can create compact clusters of agglomerated particles that are difficult to dry. However, these compact clusters are displaced when receiving the particles from the first plate and transferring them to the second plate, which allows further increasing the drying efficiency by re-separating and re-mixing the particles and agglomerates. This configuration has the advantage of smaller particles that easily form a dust cloud that prevents the danger of an explosion that it can generate because hot air first flows through the second higher plate (1b) before passing through the first lower plate (1a). Because the second upper plate is loaded with particles already partially dried, fine dry fly dust can pass through the holes in the second perforated plate and generate above the cloud. However, hot air pushes this cloud into the first plate (1a) immediately below, which is loaded with moist particles. There is a gradient of particle moisture over the thickness of the layer, with the particles being below the surface of the first plate heavily loaded with moisture.

This creates a paste that acts somewhat as a filter, which prevents a cloud of fine particles from passing through the first plate (1a) and losing at the bottom of the dryer.

[0027] The dryer according to the invention is particularly advantageous because it can be used to dry particles of very different sizes, from fine particles such as sawdust, fine particles, ceramic, polymer or metal powders, to larger particles such as wood waste, wood shavings , pellets, agricultural waste, corn husks, malt, etc., by quickly and easily changing the diameter of the holes in the plates as follows. The first and second boards (1a, 1b) can therefore contain a rigid free-standing structure with high permeability of the lattice type on which the filter layer is placed having holes of a size and density appropriate for the desired permeability depending on the type and size of particles to be dried. The filter layer can be a perforated plate, sieve, mesh or canvas. To facilitate the implementation of such a filter layer, it can be divided into angular sectors, which can be placed and attached side by side directly on a truss or other self-supporting structure with high permeability. It is impossible to perform with a belt dryer or with perforated plates that are designed to dry particles of one type of size.

[0028] The first and second means (2a, 2b) for distributing particles to be dried on the first and second plates (1a, 1b), respectively, are intended to distribute the particles evenly along the radius of the respective plates. In general, the distribution means (2a, 2b) therefore contain:

• a structure extending from the outer periphery to the inner periphery of the plate, preferably along its radius, • particles transferring means from the outer periphery to the inner periphery of the plate, and finally • means depositing particles from the transfer means on the plates.

[0029] Several solutions are possible. For example, the transfer of particles from the outer periphery towards the inner periphery of the plate may be provided by a transfer or perforated belt or inclined in the transverse direction so as to allow particles to spill onto the plate below. to cause dusting, the tape may vibrate. In an alternative preferred embodiment, the spreading means (2a, 2b) comprise at least one Archimedes screw extending along the radius of the first and second plates (1a, 1b), respectively, for transferring particles from the outer periphery towards the inner periphery of the respective plate. Said at least one Archimedes screw is enclosed in a housing equipped with one or more holes extending downwards and along the radius of the plates (1a, 1b) to allow the particles to be dispersed on these plates.

[0030] The receiving means (3a) on the first plate (1 a) and, if present, the receiving means (3b) on the second plate (1b), preferably comprise at least one Archimedes screw extending along the radius of these plates which are enclosed in equipped housing

-10 in one or more holes extending along the radius of the respective board. These holes are connected to a scraper or brush designed to collect and direct the particles carried by turning the plate towards the Archimedes screw. The type of means (4a) for transferring particles from the first plate (1a) to the second plate (1b) depends on the configuration of the dryer. If the first plate (1a) is the upper plate, the transfer means may be a straight pipe connecting the collection means (3a) of the first plate with the spreading means (2b) of the second plate, the particles falling under the action of gravity. Conversely, if the first plate is a bottom plate, preferably the transfer means (4a) comprise an Archimedes screw enabling particles to be erected from the first lower plate towards the second upper plate.

[0031] The figures show a dryer comprising two plates. However, to reduce the space occupied by the device, it is quite possible to mount:

At least a third circular plate mounted essentially horizontally at a distance and separated from the first plate (1a) by the second plate (1b), rotating about a vertical axis Z, in the opposite direction to the direction of rotation of the second plate, the surface of this plate being perforated and permeable to gases, such as air and steam, and to water, and • means for transferring particles collected from the second plate (1b), by collecting means (3b) to third spreading means adapted to spread particles along the radius of the third plate.

[0032] It is clear that as many parallel plates rotating about the Z axis can be mounted as desired and depending on the needs of the particular application. However, a dryer containing two plates (1a, 1b) is preferred for most applications. The use of many stacked plates limits the outer diameter of the discs.

[0033] For a particle size distribution of the same type, it is difficult to avoid that the finest particle fraction passes through the perforations of the plates and does not fall on one or more of the lower plates and then on the bottom of the enclosure enclosing the plates. in order to avoid excessive accumulation of particles at the bottom, as well as for their reception, preferably the bottom is provided with an opening for the removal of finer particles that can be deposited on the bottom. In addition, the scraper or brush is attached to the bottom plate and adapted to imitate its rotation, it is used to push the particles deposited on the bottom towards the discharge hole. Since the scraper or brush is attached to the bottom plate, it is not necessary to supply them individually.

[0034] As shown in Fig. 5, the plates (1a, 1b) are preferably housed in an outer casing (10) with a diameter of a suitable diameter of the plates with a sufficient margin to avoid friction, but also as small as possible to allow sealing of the connecting space between the panels and the outer wall (10). Sealing can be ensured, for example, by means of a flexible sheath attached to the outer wall and resting on the raised periphery of the perimeter of the discs. In this way, the bed of particles resting on the rotating disk does not come into contact with the static shield, ensuring good sealing and integrity of the bed of particles on the plate. It is not possible to carry out

In a belt dryer, in which the sealing cover is sandwiched between the tape and the particles on the edges of the tape. There is therefore a fraction of particles in contact with a static sheath on each edge of the belt that do not move at the same speed as the particles in the center of the belt.

[0035] The central part of the plate is preferably hollow and is surrounded by an inner cylindrical housing (6) centered on the Z axis of rotation, as shown in Figs. 2 and 5. Such housing increases substantially over the entire height of the dryer, at least between the upper and lower plates , providing many benefits that more than compensate for the loss of surface area available for drying. In fact, if the outer diameter of the disks D1 and the diameter of the inner cylindrical casing (6) is nx D1, where n &lt;1, the loss of available surface on each drying board between the full disk and the disk containing the inner casing is only n². For example, if the inner casing has a third of the outer casing diameter, the loss of surface area available for drying is only 1/9 - 11%. The internal housing (6) allows, first of all, easy operator access to all mechanical components of the device, such as bearings, gearmotors, cylinders, etc. It also facilitates the exchange of flexible porous layers for seating and fastening on the truss ensuring the mechanical integrity of the panels. The inner housing (6) can also be used to include motors (7, 7A) driving plate rotation, as well as fans for generating a hot gas stream, with the benefit of significantly reducing the noise generated by the dryer. In the case of gas flow from top to bottom, as shown in Figs. 2 (b) and 4, the windows (6a) at the bottom of the inner casing (6), which are below the bottom plate, allow the hot gas to be removed and carried away upwards inside the casing. In addition, it allows the distribution of means (2a, 2b) and removal (3a, 3b) at both ends to avoid having to be attached to the brackets only on the outer wall. In addition, space is obtained at the inner ends of these adjacent means to adjust their width. Finally, this structure stiffens the surface contained between the inner (6) and outer (10) housings to maintain good flatness of the plate. This is important for cleaning and receiving particles by the scraper or brush, which are effective only when the surface of the plate is perfectly flat.

[0036] The dryer of the invention may be introduced into a particle treatment installation. For example, the first means for distributing (2a) the particles to be dried in the dryer according to the invention can be connected above to a source (11) of these particles to be dried, for example a silo. The silo can store and particles containing wood waste from sawmill, wood waste from building materials, paper and cardboard waste, food products such as cereals. These particles may be in the form of powder, granules, flakes, pellets, meal, or pieces substantially not exceeding 10 cm in length. The dryer can be connected above to a solids storage unit, such as a silo or packaging line. In the case of a waste drying plant for use as a fuel, as shown in Fig. 7, the dryer can be connected to a boiler (12) suitably for feeding it with particles of organic matter, dried by the dryer as a fuel. This boiler (12) itself can be connected to the end of the generator (14)

-12 electric current through a turbine (13) supplied by steam at a temperature, T1, from the boiler. Steam after losing some of its energy in the turbine has only a temperature T2 &lt;T1 and can be sent to a heat exchanger (5A, 5B) to heat the air from the hot air blow (5) dryer (1) and / or to heat other installations in the other dryer (15). If more than one dryer is in the same installation, it is possible to save space on the ground and put two or more dryers according to the invention on top of each other.

[0037] Fig. 8 shows an embodiment of the invention in which the dryer (1) as shown in Fig. 3 (a) is connected in series with the third rotating plate (1c) below the second plate (1b) and enclosed in a cooling chamber ( 100). At the end of the drying operation, the particles are discharged from the second plate (1b) at elevated temperature (see particle temperatures in [g] in Fig. 6). For some types of powder, especially foods, it is not possible to pack them at high temperature, for example to avoid excessive condensation. to avoid having to store the powder until it cools and to be able to pack it immediately after drying, the dry powder can be directed to the cooling chamber (100), where cold air with a temperature T0 of 0 to 20 ° C, is blown through the third plate (1c ). The air heated essentially to a temperature T1> T0 of 40-55 ° C is then collected and introduced into the system (101) for heating air for heating air to a temperature T2> T1> T0 of 100-110 ° C, which is blown into the dryer, as explained in detail above. Air collected after drying can be returned to the heating system (101), but because it is saturated with moisture, it should be determined, if appropriate, whether this is beneficial or not. It should be noted that the same installation shown in Fig. 8 can be obtained by means of a dryer (1) as shown in Fig. 4 (a), simply by placing the cooling chamber (100) above the dryer (1) in Fig. 4 (a).