PARTICLE DRYING UNIT WITH RECYCLING OF A PART OF THE HOT GAS

Description

FIELD OF THE INVENTION

[0001] The invention relates to an industrial dryer for continuously drying particles, preferably organic particles, for example of agri-food origin, such as cereals, or waste used as fuel or construction materials such as wood chips or fibers, or other plant material. TECHNOLOGICAL BACKGROUND

[0002] Many industrial processes require the drying of particles before their further use, whether before packaging granular agro-food or industrial products, or before the combustion of shredded waste used as fuel. Depending on the intended use, the particles must be dried to achieve final moisture contents within target ranges (H1t± ε) well-defined. For example, wood chips will need to be dried within different target ranges depending on whether they are intended for combustion, pellet production, bedding production or chipboard production. It is of course possible to dry the particles in batches by placing the particles on trays, preferably perforated to allow a hot gas to pass through and allow water and water vapor to escape. In some cases, a fluidized bed is formed by the particles suspended 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 placing 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 of it.

[0003] 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 belt 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± ε) of water content to be achieved. Thus, a belt 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 particles, because it would be uneconomical to change the belt to optimize the perforation type for a new type of particles. A belt dryer is very expensive and inefficient in terms of dimensions, since the particles are only dried over less than half the length of the belt.

[0004] There are also perforated tray dryers that resemble belt dryers, except that the belt is replaced by perforated trays coupled to each other to form a sort of caterpillar. The difference with a belt dryer is that the trays are articulated so that they present the same face whether they are on the upper or lower belt of the loop. This makes it possible to practically reduce the length of the dryer by half, since the particles are subjected twice to the flow of hot gas: once when they pass over the upper part of the loop and a second time when they pass in the opposite direction over the lower part. Although advantageous in this respect compared to a belt dryer, it is clear that the mechanics necessary for the movements of the trays are delicate and therefore expensive and fragile, especially when exposed to fine particles that seize the bearings.In addition, the openings created between two adjacent trays and, above all, the spaces opening in the tray transfer mechanism during each transfer of a tray from the upper portion to the lower portion of the track create as many preferential passages of least resistance for the flow of hot gas, which cause a significant drop in the efficiency of this type of dryer.

[0005] EP0197171 describes a dryer comprising several perforated, circular, superimposed trays rotatably mounted on a hollow central shaft. Each tray is enclosed in an individual cylindrical chamber provided 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 tray. Each chamber is provided, on the one hand, with a first hot air introduction opening, in fluid communication with the cavity of the hollow central shaft, the first opening being positioned above the tray located in the corresponding chamber and, on the other hand, with a second discharge opening on the peripheral wall of the chamber in communication with the outside, the second opening being located below the corresponding tray. 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 tray before being discharged 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 floors with means for transferring the powder from one tray 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 trays loaded with very humid particles comes out relatively saturated with humidity, the hot air passing through the last trays loaded with particles already partially dried on the previous trays, comes out only slightly loaded with humidity, which represents a considerable waste of energy.

[0006] EP2828595 describes a dryer illustrated in Figure 1 , comprising a first and second (or more) perforated trays (1a, 1b), superimposed and mounted to rotate about a vertical axis (Z). A ventilation system blows a hot gas vertically, first passing through the second tray (1b), before passing directly through the first tray (1a). As it is a dryer, the hot gas, after passing through the second tray (1b) and then the first tray (1a), is either evacuated or recirculated, but such recirculation is conditioned by the drying and heating of the air to be recirculated before reinjecting it through the second tray.

[0007] The wet particles are distributed along a radius of the first plate (1a) by a first distribution unit (2a) and carried by the rotation of the first plate over an angular (or azimuthal) distance of slightly less than 360° before being collected by a first recovery unit (3a). During the rotation of the first plate (1a), the particles are exposed to the hot gas stream which has previously passed through the second plate where it has lost some of its heat energy and has taken on some moisture. The partially dried particles are transferred by a transfer unit (4t) from the first recovery unit to a second distribution (2b) system (3a) which distributes the partially dried particles along a radius of the second plate (1b) which rotates around the vertical axis (Z) in the opposite direction to the first plate (1a).The partially dried particles are carried away by the rotation of the second tray (1b) (in the opposite direction to the first tray) over an angular (or azimuthal) distance of just under 360° before being collected by a second recovery unit (3b) and discharged. During the rotation of the second tray (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.

[0008] As seen on the Figure 1, as the trays rotate in opposite directions, the hot gas that 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 the lowest moisture content of all the hot gas that reaches the first tray, because it has previously passed through the practically dry particles (final moisture content H1b) just before being discharged with a moisture content that can be of the order (as an example) of H1b / H0a) = 12%, where H0a is the initial moisture content of the particles at the inlet of the first tray (1a) and H1b is the final content of the particles at the outlet of the second tray (1b).

[0009] The dryer described in EP2828595 is particularly efficient in terms of energy, floor space utilization and occupation, and throughput. The throughput of particles to be dried from a dryer can be optimized by modifying the dimensions of the trays and the enclosure. For high throughputs, the radius of the trays is increased. For very large throughputs, a third tray is even described in EP2828595. However, for more modest throughputs, the corresponding reduction in tray size is not offset by a corresponding reduction in dryer production costs, since regardless of the tray size, at least two are required, as well as two sets of distribution and recovery units, as well as a distribution unit, the prices of which are incompressible.

[0010] There therefore remains a need for an industrial dryer for drying particles continuously at more modest flow rates than those contemplated by the dryer described in EP2828595 and which is efficient and less expensive to produce. US 9,347,705 B2 discloses a dryer for drying particles comprising several trays. SUMMARY OF THE INVENTION

[0011] The present invention is defined in the independent claims. Preferred variants are defined in the dependent claims. In particular, the present invention relates to a dryer for drying particles comprising, (a) an enclosure comprising a substantially cylindrical wall extending along a vertical axis (Z), (b) a single tray which is circular and mounted in the enclosure, substantially normal to the vertical axis (Z) rotating in a direction of rotation about the vertical axis (Z), the surface of the tray being perforated and permeable to gases such as air and water vapor and to water, (c) a distribution system which is configured to distribute the particles before drying along a radius of the tray, (d) a recovery system which is configured to collect the particles deposited on the tray after rotation of the tray through an angle formed between the distribution system and the recovery system, the recovery system being located downstream of, preferably adjacent to, the distribution system.

[0012] The dryer further comprises a hot gas blowing system comprising N fans configured to generate hot gas flows along N gas columns substantially parallel to the vertical axis (Z), each gas column passing through a different angular section of the tray, with N ∈ ℕ and N > 1, in which (a) the N angular sections of the tray cover an entire area of ​​the tray between the distribution system and the recovery system, (b) a first fan configured to generate a flow of hot gas along a first gas column is positioned downstream of the distribution system, the first gas column passing through a first angular section of the tray adjacent to or including the distribution system, (c) an Nth fan configured to generate a flow of hot gas along an Nth gas column is positioned upstream of the recovery system, the Nth gas column passing through an Nth angular section of the tray adjacent to or including the recovery system, wherein the terms "upstream" and "downstream" are defined with respect to the direction of rotation of the tray, and (d) second to (N-1) th fans are angularly distributed around the vertical axis (Z) between the first and Nth fans,configured to generate hot gas flows following second to (N-1) th< gas columns passing through second to (N-1) th< angular sectors between the first and N th< angular sectors, (e) after passing through the first to (N-1) th< angular sections of the tray, the first to (N-1) th< gas columns are either extracted from the enclosure or the gas from these columns is dried and reheated before being recirculated by the second to N th< fans to pass through in a new cycle the second to N th< angular sections of the tray.

[0013] The present invention differs from prior art dryers in that after passing through the Nth angular section of the single tray, the hot gas from the Nth gas column is recirculated to form, alone or in addition to an additional hot gas, the first gas column passing through the first angular sector of the single tray.

[0014] In one embodiment, the single tray includes a chimney centered on the vertical axis (Z) and passing through the tray through a circular opening, having an internal radius less than a radius of the tray. The fans may then be arranged inside the chimney and each be associated with a vertical deflection system configured to guide the hot gas generated by each fan into the enclosure and out of the chimney and orient it substantially parallel to the vertical axis (Z) towards the corresponding angular sectors and thus form the corresponding gas columns. The vertical deflection system may preferably include at least one of a tube, a deflecting surface or an array of deflecting surfaces, which is coupled to at least one opening in a wall of the chimney.

[0015] Preferably, the dryer further comprises a recirculation deflection system configured to recirculate the gas from the Nth column to the first fan by guiding it into the interior of the chimney. The recirculation deflection system preferably comprises one or more of a tube, a deflecting surface or an array of deflecting surfaces, a fan, which is coupled to at least one opening in a wall of the chimney.

[0016] The dryer may further include a controller configured to control one or more of the following parameters, a gas flow rate from one or more of the N fans, a proportion in the first gas column consisting of gas from the Nth column recycled to the first fan, a geometry of the vertical deflection system so as to modify an extent of each angular sector and a degree of overlap between two adjacent angular sectors.

[0017] It is preferable that the dryer also includes a temperature sensor and a humidity sensor configured to measure the temperature and moisture content of the hot gas exiting the Nth angular section before being recirculated to the first gas column, and wherein the controller is configured to determine the proportion in the first gas column consisting of gas from the Nth column recycled to the first fan based on the temperature and moisture content values ​​measured by the temperature and humidity sensors.

[0018] The hot gas blowing system preferably comprises a fan, preferably N fans located upstream of the single tray and configured to blow the hot gas, preferably hot air, and a gas heating device configured to heat the hot gas thus blown upstream of the single tray, where the term "upstream" is defined relative to the direction of hot gas flow.

[0019] The hot gas blowing system may also or alternatively comprise, a fan, preferably N fans, located downstream of the single tray and configured to suck in hot gas, preferably hot air and a gas heating device configured to heat the hot gas thus sucked in, and located upstream of the single tray, wherein the gas heating device comprises at least one of a heat exchanger or a gas burner, where the terms "upstream" and "downstream" are defined relative to the direction of hot gas flow.

[0020] Hot gas can flow from top to bottom, alternatively, hot gas can flow from bottom to top. Hot gas is preferably hot air.

[0021] The tray may further comprise a self-supporting rigid 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 according to the type and size of the particles to be dried.

[0022] The system for distributing the particles to be dried on the tray may comprise at least one Archimedean screw extending along a radius of the tray, said at least one Archimedean screw being enclosed in an enclosure provided with one or more openings extending along said radius of the tray.

[0023] The tray recovery system may comprise at least one Archimedes screw extending along a radius of said tray which is enclosed in an enclosure provided with one or more openings extending along said radius of the tray, said openings being connected to a scraper or brush capable of collecting and directing the particles brought by the rotation of the tray towards the Archimedes screw.

[0024] The dryer advantageously comprises a static floor located below the tray along the vertical axis, Z, the floor comprising an evacuation opening for the finest particles which may have been deposited on the floor. The dryer may further comprise a scraper fixed integrally to the tray and capable of following the rotational movement thereof to push the particles deposited on the floor towards said evacuation opening.

[0025] The particles to be dried may preferably include sawmill wood waste, construction material wood waste, paper or cardboard waste, agri-food products and are in the form of powder, granules, chips, pellets, cakes, or pieces generally not exceeding 10 cm in length. BRIEF DESCRIPTION OF THE FIGURES

[0026] For a better understanding of the nature of the present invention, reference is made to the following Figures, including; Figure 1 : illustrates a prior art disc dryer, as described in EP197171. Figure 2 : illustrates a dryer according to the present invention. Figure 3 : illustrates an alternative dryer according to the present invention. Figure 4 : illustrates a top view of a dryer according to the present invention. Figure 5 : illustrates the recirculation of hot gas in a dryer according to the present invention. Figure 6(a) & 6(b): illustrate an example of a distribution system adapted to the present invention, (a) perspective view, (b) top view. Figure 7(a) & 7(b) : illustrate an example of a recovery system adapted to the present invention, (a) top view, (b) cross section. Figure 7(c) & 7(d) : illustrate another example of a recovery system adapted to the present invention, (c) top view, (d) cross section. Figure 8(a) : illustrates the tray (1) comprising a self-supporting rigid structure (1) comprising openings of given diameter. Figure 8(b) : illustrates the tray (1) comprising a self-supporting rigid structure (1c) with high permeability of the grating type covered by a removable flexible layer (1p) comprising openings of the desired diameter depending on the application. DETAILED DESCRIPTION

[0027] The dryer according to the present invention is preferably a variation of a dryer of the type described in EP2828595, which is discussed in the “technological background” section above and illustrated in Figure 1 with its two superimposed trays (1a, 1b) rotating in counter-direction. However, suitable for flow rates of particles to be dried that are more modest than the dryer described in EP2828595, the dryer of the present invention comprises only one tray (1).

[0028] The dryer of the present invention comprises an enclosure (10) comprising a substantially cylindrical wall extending along a vertical axis (Z). Unlike the dryer described in EP2828595, the enclosure encloses a single circular tray (1) mounted on the wall of the enclosure substantially normal to the vertical axis (Z). The single tray (1) is mounted to rotate in one direction around the vertical axis (Z), the rotation of which is actuated by a first motor. The surface of the tray (1) is perforated by openings of optimized diameter for the type of particles to be dried, thus making it both capable of retaining the particles to be dried and permeable to fluids such as air, water vapor and water. Such a dryer is illustrated in Figures 2 And 3 .

[0029] A distribution system (2) for the particles to be dried extends along a radius of the tray (1) and is configured to receive the particles to be dried from a feed unit (9) and to distribute these particles along a radius of the tray (1) before drying. The feed unit makes it possible to control the feed or loading rate of the particles to be dried onto the tray (1).

[0030] A recovery system (3) extends along a second radius of the tray, located downstream of, preferably adjacent to, the distribution system (2). The recovery system (3) is configured to recover the particles deposited on the tray (1) after rotation of the latter by a given angle. The rotation angle 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 to accommodate the distribution system (2) and the recovery system (3) along the respective radii of the tray (1). A large rotation angle allows to extend the exposure time to hot gases of the particles deposited on the tray for a given rotation speed. An angle of practically 360° can be obtained by superimposing the distribution system (2) above the recovery system (3).

[0031] The dryer comprises a hot gas blowing system comprising N fans (51-5N) configured to generate hot gas flows along N gas columns substantially parallel to the vertical axis (Z), Each gas column passes through a different angular section (1.1 -1.N) of the tray (1), with N ∈ ℕ and N > 1, It is the hot, dry gas which, in contact with the wet particles, will (a) increase their temperature and (b) evacuate part of their moisture. It follows that the temperature of the hot gas drops and its moisture content increases as it passes through the tray (1). The temperature of the hot gas downstream of the tray drops and its moisture content increases with the increase in the temperature and moisture content gradients between the hot gas upstream of the tray and the particles through which it flows. The temperature of the particles increases and their moisture content decreases with the rotation angle of the tray and therefore in a sequence of angular sections (1.1 to 1.N). For a constant temperature and moisture content of the hot gas upstream of the tray (1), the temperature of the hot gas downstream of the tray drops and its moisture content increases with the rotation angle and therefore sequentially from the first angular section (1.1) at the Nth angular section (1.N).

[0032] The gas from the gas columns exiting the angular sections (1.1 to 1.(N-1)) of the tray (1) supporting the particles with high moisture contents has too high a moisture content to be recirculated as is. It is therefore discharged from the enclosure, as shown in Figures 2 to 5 or, alternatively, dehumidified and reheated before reinjecting it along the gas columns. On the other hand, the particles located in the Nth angular section (1.N) have, after a rotation of the order of 300°, a high temperature and a low humidity content (cf. eg, Figure 2, 12% humidity). Thus, after passing through the Nth angular section (1.N), the hot gas downstream of the tray has a sufficiently high temperature and a sufficiently low humidity content so as not to simply be released into the atmosphere. The hot gas blowing system (5) of the present invention makes it possible to recover the hot gas downstream of the Nth angular section (1.N) and recirculate it into the first angular section (1.1), where the particles have the lowest temperature and the highest humidity content of the rest of the tray.

[0033] As illustrated in the Figure 2, the N angular sections (1.1 -1.N) of the tray cover an entire area of ​​the tray between the distribution system (2) and the recovery system (3). In the hot gas blowing system (5) of the present invention, a first fan (51) is configured to generate a flow of hot gas along a first gas column parallel to the vertical axis (Z). It is positioned downstream of the distribution system (2) relative to the rotation of the tray, so that the first gas column passes through the first angular section (1.1) of the tray, adjacent to or including the distribution system (2). An Nth fan (5N) is configured to generate a flow of hot gas along an Nth gas column parallel to the vertical axis (Z). It is positioned upstream of the recovery system. The Nth gas column passes through the Nth angular section (1.N) of the tray adjacent to or including the recovery system (3), wherein the terms "upstream" and "downstream" are defined relative to the direction of rotation of the tray. Second to (N-1) th< fans (52, 5(N-1)) are angularly distributed around the vertical axis (Z) between the first and N th< fans (51, 5N). They are configured to generate hot gas flows in second to (N-1) th< gas columns parallel to the vertical axis (Z). They pass through second to (N-1) th< angular sectors (1.2-1.(N-1)) between the first and N th< angular sectors (1.1, 1.N).

[0034] After passing through the first to the (N-1)th angular sections (1.1, N-1) of the plate, the first to the (N-1)th gas columns are either extracted from the enclosure (cf. Figures 2 to 5) or the gas from these columns is dried and reheated before being recirculated by the second to the Nth fans (52-5N) to pass through in a new cycle the second to the Nth angular sections (1.2, N) of the tray or evacuated from the enclosure, for example by a chimney.

[0035] Unlike the first to the (N-1) th< gas columns, after passing through the N th< angular section (1.N) of the tray, the hot gas from the N th< gas column is recirculated by the N th< fan (5N) to form alone or in addition to an additional hot gas, the first gas column passing through the first angular sector (1.1) of the tray.

[0036] With this blowing system (5), the dryer of the present invention makes it possible to make savings in heating energy of the hot gas of the order of (100 / N)%, or 20 to 25% of energy for a dryer comprising N = 5 or 4 fans (51 to 55 or 51 to 54), respectively.

[0037] As illustrated in the Figure 2 , after having crossed the Nth< = 5th< angular section (1.5) of the plate, the hot gas from the 5th< column is recirculated by the first fan (51) to form alone or in addition to an additional hot gas, the first column of gas (1.1) crossing the first angular sector (1.1) of the plate.

[0038] If Hi is the moisture content of the particles in each angular section (1.1-1.5) of the tray, it is obvious that H1>H2>H3>H4>H5. Similarly, the moisture content of each column of hot air corresponding to a section of the tray, after passing through each angular section of the tray, decreases. Therefore, the moisture content contained in the hot gas of the 5th column, after passing through the 5th angular section, is low enough to be directly recirculated to the first fan in order to dry the particles located in the first angular section, in which the moisture content H1 of the particles is the highest.

[0039] Recycling the hot air passing through the Nth angular section allows for enormous energy savings without losing efficiency, given the very low humidity content of the hot air passing through the Nth angular section.

[0040] For example, for a hot air particle dryer, comprising 4 fans with air recirculation from the 4th fan (54) to the first fan (51), an energy improvement was observed. The inventors measured a 25% reduction in air flow, 16.5% less electrical power consumed, and 25% less heating power compared to the same dryer without recirculation from the 4th fan (54) to the first fan (51).

[0041] As illustrated in Figures 3 And 4, the moisture content of the particles between each angular section of the tray decreases during the drying process. For example, the initial moisture content is 100%, after passing over the first angular section 1.1, the moisture content of the particles is 75%, after passing over the second angular section 1.2, the moisture content is 50%, after passing over the third angular section 1.3, the moisture content is 32%, after passing over the fourth angular section 1.4, the moisture content is 12%. The hot air passing through the fourth angular section is therefore very low in moisture. It can therefore be recycled and redirected to the first angular section in order to dry the incoming particles having a high moisture content, for example 100%.

[0042] The tray (1) may further comprise a chimney (6) centered on the vertical axis (Z) and passing through the tray through a circular opening, having an internal radius (R6) less than a radius (R1) of the tray.

[0043] The fans are preferably arranged inside the chimney (6) and each comprise a vertical deflection system configured to guide the hot gas generated by each fan into the enclosure and out of the chimney (6) and orient it substantially parallel to the vertical axis (Z) towards the corresponding angular sectors (1.1-1.N) and thus form the corresponding gas columns. The vertical deflection system preferably comprises at least one of a tube, a deflecting surface or an array of deflecting surfaces, which is coupled to at least one opening in a wall of the chimney.

[0044] In practice, for the first N-1 angular sections of the plate, 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 (7) or a humidifier (see dotted arrows in Figure 3 discharging the gases out of the dryer upwards through a chimney (6) of the dryer), or recirculated after drying and heating. The blowing system may comprise one or, preferably, several fans. The fan(s) may be configured to suck in the hot gases by creating a vacuum, for example, below the trays, when the gas circulates from top to bottom. In this variant, the fan(s) are positioned below the tray (1). Indeed, to limit pressure losses in the product layer, it may be preferable to suck under the tray, rather than blow on the tray. Such an embodiment is illustrated in Figure 3 . BLOWING - SUCTION

[0045] The hot gas blowing system (5) can therefore be supplied either, by a fan, called a blower, configured to blow the hot gas, preferably hot air, positioned upstream of the plate (1), as illustrated in Figure 2 , either by a fan, called an aspirator, configured to suck in the hot gas, preferably hot air, located downstream of the plate, as illustrated in Figures 3 And 5 .

[0046] In both cases, the gas is heated upstream of the tray (1) by a gas heater (7) located upstream of the tray. The gas heater (7) may be provided by a heat exchanger or a gas burner, or an electrical resistance. The terms upstream and downstream are defined here in relation to the direction of the hot gas flow.

[0047] The gas (e.g., air) heating device (7) can be integrated into an upper stage of the dryer located above the disc. Fresh gas, for example fresh air, is thus drawn in from outside above this stage. In the case of a "blower" fan, the gas (or air) drawn in by the blower fan is blown towards the tray. The heating device can be located anywhere upstream of the tray, for example upstream or downstream of the blower fan, but it is preferably integrated into the blower fan. In the case of a "suction" fan, located downstream of the tray, the heating device can neither be integrated into the suction fan nor located downstream of the suction fan. The gas heating device is therefore located upstream of the tray.The gas or air is sucked in from the outside, passes through the gas heating device (7) until it reaches temperatures of, for example, between 60 and 95° and then passes through the tray to finally enter the suction fan to be blown back to the outside of the dryer for the 1st to (N-1) th suction fans and to the first gas column for the Nth suction fan. The gas blown back by the 1st to (N-1) th suction fans is cooled and practically saturated with moisture and is discharged, for example, by rising up the chimney and is blown outside. EVACUATION - RECIRCULATION OF HOT GAS

[0048] The dryer includes systems for discharging the hot gas from the first (N-1) gas columns, having passed through the tray. When discharged, the gas is cooled and moist. The gas discharge systems are configured to discharge the cooled and moist gas from the enclosure. For comfort around the dryer, the hot gas is preferably discharged upwards, along a vertical column extending beyond the circular opening. The discharge system may be the chimney but may also be located outside the enclosure, for example around the outer circumference of the enclosure, as shown in Figure 4 .

[0049] On the Figure 3 , the gas, after having crossed the (N-1) = first 4 angular sections (1.1-1.4) of the plate, is evacuated by the chimney, with the exception of the hot gas having crossed the Nth< = 5th< angular section, which is redirected towards the first angular section (1.1). On the Figure 4, the gas, after having crossed the (N-1) = 3 first angular sections, is evacuated towards the outside of the enclosure.

[0050] There Figure 5 constitutes an enlargement of a dryer of the type shown in the Figure 3which illustrates that the gas having passed through the Nth angular sector (1.N) of the plate (1) is sucked in by the Nth fan (5N) (of the "vacuum" type) and redirected to form the first column of gas passing through the first angular sector (1.1) before being sucked in by the first fan (51). The first and Nth fans, which in this example operate in suction, are located below the plate and upstream of the recovery system (3) relative to the direction of rotation of the plate. Sucked in by the Nth fan (5N), the Nth column of gas crosses the Nth angular sector (1.N) of the plate and is redirected along the trajectory (5R1) through a window (6w) in the chimney where the Nth fan (5N) is located, which blows out the still hot and practically dry gas by a gas deflection system along a trajectory (5R2, 5R3) to form the first column of gas, sucked in by the first fan (51).The air thus deflected is sucked in by the first fan (51) in order to pass through the first angular section (1.1) of the plate to then be evacuated, outside the enclosure, for example in a tube located in the chimney (6).

[0051] The deflection system is therefore configured to recirculate the gas from the Nth gas column to the first gas column by guiding it, for example through the inside of the chimney (6) after passing through the tray. The gas will therefore circulate towards the inside of the chimney following the trajectory (5R1), to rise in the chimney following the trajectory 5R2, to then be redirected towards the first section of the tray according to the trajectory (5R3), and thus form the first column of hot gas, sucked in by the first fan (51). The recirculation deflection system can be provided for example by a tube, a deflecting surface or a network of deflecting surfaces, a fan, which is coupled to at least one opening in a wall of the chimney. The Figure 5illustrates the recirculation trajectory from the Nth column to the first gas column using “aspirator” type fans. It is clear that the same trajectory (5R1, 5R2, 5R3) can be achieved with “blower” type fans.

[0052] As illustrated in the Figure 2 , the volume included under the Nth angular section (1.N) of the plate (1) can be provided with walls (10d) separating it from the volumes included under the (N-1) angular section (1.(N-1)) and / or, especially under the first angular section (1.1) to avoid recirculating hot gas from other gas columns.

[0053] The system may include a controller (8) configured to control one or more of the following parameters, a gas flow rate of one or more of the N fans, a proportion in the first gas column consisting of gas from the Nth column recycled to the first fan (51), a geometry of the vertical deflection system so as to modify an extent of each angular sector (1.1-1.N) and a degree of overlap between two adjacent angular sectors.

[0054] The system may further comprise a temperature sensor and a humidity sensor configured to measure the temperature and moisture content of the hot gas exiting the Nth angular section (5N) before being recirculated to the first gas column. The controller is configured to determine the proportion in the first gas column consisting of gas from the Nth column recycled to the first fan (51) based on the temperature and moisture content values ​​measured by the temperature and humidity sensors. If the gas from the Nth gas column has too low a temperature or too high a humidity to sufficiently heat and dry the particles deposited in the first angular section (1.1) of the tray, it should be mixed with hot, dry gas.However, if the temperature of the hot gas is too low or its moisture content too high, it is likely that the particles in the Nth angular section of the tray crossed by the Nth column have too low a temperature and / or too high a moisture content. The drying parameters may then need to be changed accordingly.

[0055] Hot gas (e.g., hot air) can flow from the bottom up. As the hot gas flow flows from the bottom up, the particles can fly away and create a dust cloud. Slight fluidization of the particle layer can be beneficial for drying the particles, 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 that do not easily form a dust cloud.

[0056] For lighter or finer particles, the hot gas may flow preferentially from top to bottom, as shown in Figures 1 to 6 In this configuration, the particles are pressed against the tray on which they are located, which considerably reduces the suspension of dust. A flow of hot gas from top to bottom risks forming compact clusters of particles agglomerated together and difficult to dry. These compact clusters are, however, broken up when the particles are recovered from the tray (1) by the recovery system. DRYER STRUCTURE - FEED UNIT (9)

[0057] The feed unit (9) is coupled upstream to a particle source (20s), for example stored in a silo, a container, a bin, etc. The feed unit (9) is coupled downstream to the distribution system (2). The feed unit (9) preferably makes it possible to precisely control and vary the particle feed rate to the distribution system (2) in order to be able to control the thickness (da) of the layer of particles deposited on the tray by the distribution system (2).

[0058] Any feed unit allowing such control known to those skilled in the art may be used and the present invention is not limited to a particular type or model of feed unit. For example, the feed unit (9) may comprise one or more Archimedean screws whose rotational speed controls the feed rate of coarse particles feeding the distribution system (2). Alternatively, the feed unit may comprise a conveyor belt whose movement speed can be controlled in order to control the feed rate. DRYER STRUCTURE - DISTRIBUTION SYSTEM (2)

[0059] The feed unit (9) is coupled downstream to the distribution system (2) and is configured to feed the distribution system (2) at a controlled feed rate. The distribution system (2) of the particles to be dried on the tray (1) has the purpose of distributing the particles to be dried homogeneously along a radius of the tray (1). In general, the distribution system (2) comprises, a structure extending from the outer periphery to the inner periphery of a tray, preferably along a radius thereof, means for transporting particles from the outer periphery to the inner periphery of the trays, and finally means for depositing said particles from the transport means to the trays.

[0060] Several solutions are possible. For example, the transport of the particles from the outer periphery to the inner periphery of the trays can be ensured by a conveyor belt, either perforated or transversely inclined so as to allow the particles to sprinkle the tray located below. To assist the dusting, the belt can be vibrated. In an alternative and preferred variant, the distribution system (2) comprises at least one Archimedean screw extending along a radius of the tray (1), in order to transport the particles from the outer periphery to the inner periphery of the tray (1). Said at least one Archimedean screw is enclosed in an enclosure provided with one or more openings extending downwards and along said radius of the tray (1) in order to allow the dusting of the particles homogeneously along the radius of the tray (1).

[0061] In the case of an Archimedean screw, if the particles to be dried are discharged from the feed unit (9) at a first end of the Archimedean screw of the distribution system (2), for example adjacent to the enclosure (10), there is a high risk that the thickness of the particle layer will decrease along the radius of the plate (1) as one approaches the center of the plate. Such a thickness gradient is not advisable because it results in a gradient along the radius of the plate (1) in intermediate moisture contents (H1a) of the particles after one revolution on the plate (1). Worse still, if the layer becomes so thin that holes appear in the particle layer, this creates areas of low resistance to the flow of hot gas which will preferentially pass through these areas to the detriment of the particles to be dried.

[0062] To overcome this problem, the distribution system (2) extending along a radius of the plate (1) may comprise, as illustrated in the Figures 6(a) and 6(b) , a distribution screw (22v) and a recirculation screw (23v), placed side by side and enclosed in a housing (2h). The housing (2h) includes a feed opening coupled to an outlet (9o) of the feed unit (9). The feed opening is configured to deliver particles from the feed unit (9) to one end of the distribution screw (22v). For example, the feed opening may be located above the distribution screw (22v) to allow the particles to fall by gravity into the housing (2h) and be carried by the rotation in a first direction of the distribution screw (22v) along the radius of the plate (1).

[0063] A distribution opening (2o) 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 tray (1) along its radius. In order to prevent the particles from falling predominantly in a section adjacent to the feed opening (9o), 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) to 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 vane (23s) which, by rotation of the recirculation screw (23v), returns the particles to the distribution screw (22v). A similar vane (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 tray (1) through the distribution opening (2o). A distribution system (2) of this type allows a homogeneous distribution of the particles along the radius of the tray (1), thus ensuring that the thickness of the layer of particles deposited on the tray (1) is radially substantially constant.

[0064] The distribution system (2) for the particles to be dried on the tray (1) is connected upstream, preferably via a feed unit (9), to a source (20s) of the particles to be dried, preferably a silo. The particles preferably comprise sawmill wood waste, construction material wood waste, paper or cardboard waste, agri-food products such as cereals, and are in the form of powder, granules, chips, pellets, cakes, or pieces generally not exceeding 10 cm in length. DRYER STRUCTURE - RECOVERY SYSTEM (3)

[0065] The recovery system (3) of the tray (1) makes it possible to recover the particles deposited on the tray (1) after one rotation thereof. The recovery system (3) is therefore positioned upstream of the distribution system (relative to the direction of rotation of the tray), adjacent to it so that the particles having an initial moisture content (H1) deposited on the first section (1.1) of the tray by the distribution system can rotate, preferably between 340 and 360°, or preferably between 345 and 355° before being collected from the Nth angular section (1.N) and removed from the tray (1) with a final moisture content (HN) by the recovery system (3).To maximize the rotation angle of the particles on the tray (1) between the distribution system (2) and the recovery system (3), they are preferably arranged next to each other, or even the distribution system (2) can be arranged above the recovery system (3).

[0066] As illustrated in the Figures 7(a) and 7(c), the recovery system (3) preferably comprises at least one Archimedean screw (32v) extending along a radius of the tray which is enclosed in a box (3h) provided with one or more recovery openings (3i) extending along said radius of the tray. The openings are connected to a scraper (3r) or brush capable of collecting and directing the particles brought by the rotation of the tray (1) through the recovery opening (3i) into the box (3h) of the Archimedean screw (32v). By rotating, the Archimedean screw transports the particles thus collected towards a discharge opening (3o) which is connected to a discharge unit (4o) which is configured to remove the dried particles from the enclosure (10) towards a storage location or further processing. In the case where, for a given application, the particles have a moisture content (HN) that is too high after one rotation of the plate, we can, reducing the thickness of the layer of particles deposited on the tray, and / or reducing the rotation speed of the tray, and / or connecting the discharge unit (4o) to the supply unit (9) to reintroduce the particles onto the tray through the distribution system (2) for a second rotation.

[0067] THE Figures 7(b) and 7(d) illustrate another variant of the recovery system (3), particularly suitable, but not exclusively, for cases where the tray (1) includes a raised circumferential rim requiring the Archimedes screw (32v) to be raised above this rim. As in the variant of the Figures 7(a) and 7(c), in the present variant, the recovery system (3) comprises an Archimedean screw (32v) whose rotation makes it possible to transport the collected particles radially along a radius of the tray (1) towards the outside thereof and to discharge them towards the discharge opening (3o) connected to the discharge unit (4o). In the present variant, the recovery system (3) further comprises a multi-blade mill (3s) arranged upstream of and parallel to the Archimedean screw (32v). The rotation of the multi-blade mill (3s) makes it possible to feed the Archimedean screw (32v) even if it is raised relative to the surface of the tray. In all cases, the multi-blade mill (3s) ensures a reproducible and reliable supply of particles to the Archimedean screw (32v). TRAY (1)

[0068] 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 metal powders, to coarser particles, such as wood waste, shavings, pellets, agricultural waste, corn husks, etc. In a first variant illustrated in Figure 8(a) , the tray is self-supporting and includes openings of a given diameter. To facilitate quick and easy changing of the diameter of the tray holes, in a second variant shown in Figure 8(b) , the tray (1) can thus comprise a self-supporting rigid structure (1c) with high permeability of the grating type. On the Figure 8(b), a filter layer (1p) comprising openings of size and density corresponding to the desired permeability according to the type and granulometry of the particles to be dried is placed on the self-supporting structure 1c with high permeability. The filter layer (1p) can be a perforated sheet, a sieve, a grid or a cloth which can be easily changed according to the type of particles to be dried. 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 (1c) with high permeability. This would be impossible in practice with belt or perforated tray dryers which are dedicated to drying particles of a single type of granulometry.

[0069] The tray (1) is enclosed in an outer enclosure of diameter corresponding to the diameter of the tray with enough margin to avoid friction, but as little as possible to allow sealing of the interface between the trays and the outer wall. Sealing can be ensured for example by a flexible skirt fixed to the outer wall and resting on a raised edge of the circumference of the trays. In this way, the layer of particles resting on a rotating tray is not in contact with the static skirt, thus ensuring good sealing and integrity of the layer of particles on the tray. This is not possible to achieve on a belt dryer, in which the sealing skirt is placed between the rolling belt and the particles located on the edges of the belt.So there is a fringe of particles in contact with the static skirt at each edge of the strip which does not move at the same speed as the particles in the middle of the strip.

[0070] As illustrated in the Figure 3, the central part of the tray is preferably hollow and included in a chimney (6) which is cylindrical, internal and centered on the axis of rotation (Z). Such a chimney (6) rising over practically the entire height of the dryer, includes many 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 = nx D1, where n < 1, the loss in surface area (A) available on the tray for drying between a solid tray and a tray including a chimney is A6 / A1 = n 2< . For example, if the chimney has a third of the diameter of the external enclosure (i.e., n = 1 / 3), the loss in surface area available for drying is only n 2< = 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, jacks, etc.It also facilitates the replacement of the flexible porous layers (1p) to be deposited and fixed on the gratings (1c) giving the trays their mechanical integrity. The chimney can also be used to house the motors driving the rotation of the trays, as well as the fans used to generate the flow of hot gas, with the advantage of a substantial reduction in the noise pollution generated by the dryer. In the case of a gas flow from top to bottom as shown in . Figure 3 , windows at the bottom of the chimney (6), located below the lower tray, allow the hot gas to be recovered and evacuated 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).

[0071] Furthermore, the chimney (6) allows the distribution (2) and recovery (3) systems to be fixed at their two ends in order to avoid having to fix them cantilevered on the outer enclosure only. In addition, this frees up space at the inner ends of said means located side by side to accommodate their width. Finally, such a structure allows the surface between the chimney (6) and the outer enclosure (10) to be stiffened, allowing the tray to be kept flat. This is important for cleaning and recovering particles using a scraper or a brush, which are only effective if the surface of the trays is perfectly flat.

[0072] Since the particle size distribution of particles of the same type can be broad, it is difficult to prevent the finest fraction of particles from passing through the perforations of the tray and falling onto the lower tray(s), then onto the floor of the enclosure enclosing the tray.

[0073] Fine particles may nevertheless fall onto the dryer floor. In order to prevent particles from accumulating on the floor and also to collect them, it is advantageous to provide the floor with an extraction opening for the finest particles that may have settled on the floor. In addition, a scraper or brush fixed integrally to the lower plate and capable of following its rotational movement is used to push the particles deposited on the floor towards the said discharge opening. Since the scraper or brush is fixed to the lower plate, it is not necessary to motorize it individually. Ref # Characteristic 1 Plateau 1.i Angular section i 1c Rigid self-supporting structure of the high permeability tray (eg, grating) 1p Filter layer of the tray 2 Distribution system 2h Distribution system box 2o Distribution opening 3 Recovery system 3h Recovery system box 3i Opening the recovery system recovery 3o Recovery system discharge opening 5 Hot gas blowing system 5g Hot gas 5i Fan 5R(i) Path of the redirected (recycled) gas 6 Chimney 6w Opening 7 Gas heating device 9 Particle feed unit to the distribution system 9o Feed opening 10 Pregnant 10d Wall 20 Particles 20s Source of particles to be dried 22v Distribution system distribution screw 22s Palette 23v Recirculation screw of the distribution system 32v Archimedes screw of the recovery system da Thickness of the particle layer H0a Initial moisture content before drying when distributed on the 1st tray H0b Intermediate moisture content when distributed on the 2nd tray (H1a = H0b) H1a Intermediate moisture content when recovering the 1st tray (H1a = H0b) H1b Final moisture content when recovering the 2nd tray

Claims

1. Dryer for drying particles comprising: (a) an enclosure (10) comprising an essentially cylindrical wall extending along a vertical axis (Z), (b) a single tray (1) that is circular and mounted in the enclosure, substantially normal to the vertical axis (Z), in rotation in a direction of rotation about the vertical axis (Z), the surface of the tray being perforated and permeable to gases such as air and steam and to water, (c) a distribution system (2) that is configured to distribute the particles before drying along a radius of the tray (1), (d) a recovery system (3) that is configured to collect the particles deposited on the tray (1) after a rotation of the tray through an angle formed between the distribution system (2) and the recovery system (3), the recovery system being located downstream of and preferably adjacent to the distribution system (2), (e) a hot gas blowing system (5) comprising N fans (51-5N) configured to generate flows of hot gas along N gas columns that are substantially parallel to the vertical axis (Z), each gas column passing through a different angular section (1.1-1.N) of the tray (1), with N ∈ ℕ and N > 1, wherein • the N angular sections (1.1-1.N) of the tray cover the whole of an area of the tray between the distribution system (2) and the recovery system (3), • a first fan (51) configured to generate a flow of hot gas along a first gas column is positioned downstream of the distribution system (2), the first gas column passing through a first angular section (1.1) of the tray adjacent to or containing the distribution system (2), • an Nth fan (5N) configured to generate a flow of hot gas along an Nth gas column is positioned upstream of the recovery system, the Nth gas column passing through an Nth angular section (1.N) of the tray adjacent to or containing the recovery system (3), wherein the terms "upstream" and "downstream" refer to the direction of rotation of the tray, and • second to (N-1)th fans (52, 5(N-1)) are distributed angularly about the vertical axis (Z) between the first and Nth fans (51, 5N), which are configured to generate flows of hot gas along second to (N-1)th gas columns passing through second to (N-1)th angular sectors (1.2-1.(N-1)) between the first and Nth angular sectors (1.1, 1.N), • having passed through the first to the (N-1)th angular sections (1.1, 1.N-1) of the tray, the first to the (N-1)th gas columns are either extracted from the enclosure or the gas in these columns is dried and reheated before being recirculated by the second to the Nth fans (52-5N) to pass through the second to the Nth angular sections (1.2, N) of the tray in another cycle; in which dryer, having passed through the Nth angular section (1.N) of the tray, the hot gas of the Nth gas column is recirculated to form, on its own or combined with an additional hot gas, the first gas column passing through the first angular sector (1.1) of the tray.

2. Dryer according to Claim 1, wherein the tray (1) comprises a chimney (6) that is centred on the vertical axis (Z) and passes through the tray via a circular opening with an internal radius less than a radius of the tray.

3. Dryer according to Claim 2, wherein the fans are disposed inside the chimney (6) and are each associated with a vertical deflection system configured to guide the hot gas generated by each fan into the enclosure and out of the chimney (6) and to orient it substantially parallel to the vertical axis (Z) toward the corresponding angular sectors (1.1-1.N), thereby forming corresponding gas columns, wherein the vertical deflection system preferably comprises at least one of the following: a tube, a deflection surface or a network of deflection surfaces, which is coupled to at least one opening (6w) in a wall of the chimney.

4. Dryer according to Claim 2 or 3, comprising a recirculation deflection system configured to recirculate the gas from the Nth column toward the first fan (51) by guiding it toward the inside of the chimney (6), and wherein the recirculation deflection system preferably comprises one or more of the following: a tube, a deflection surface or a network of deflection surfaces, a fan, which is coupled to at least one opening in a wall of the chimney.

5. Dryer according to any one of the preceding claims, also comprising a controller configured to control one or more of the following parameters: • a gas flow rate from one or more of the N fans, • a proportion of the first gas column that is gas recycled from the Nth column toward the first fan (51), • a geometry of the vertical deflection system that modifies an extent of each angular sector (1.1-1.N) and a degree of overlap between two adjacent angular sectors.

6. Dryer (1) according to Claim 5 above, comprising a temperature sensor and a moisture sensor configured to measure the temperature and the moisture content of the hot gas coming out of the Nth angular section (5N) before being recirculated toward the first gas column, and wherein the controller is configured to determine the proportion of the first gas column that is gas recycled from the Nth column toward the first fan (51) on the basis of the temperature and moisture content values measured by the temperature and moisture sensors.

7. Dryer (1) according to any one of the preceding claims, wherein the hot gas blowing system (5) comprises: • a fan, preferably N fans located upstream of the tray (1) and configured to blow the hot gas, preferably hot air, and • a gas heating device configured to heat the hot gas thus blown upstream of the first tray (1), where the term "upstream" refers to the direction of the flow of hot gas.

8. Dryer (1) according to any one of the preceding claims, wherein the hot gas blowing system (5) comprises: • a fan, preferably N fans located downstream of the tray (1) and configured to aspirate the hot gas, preferably hot air, and • a gas heating device configured to heat the hot gas thus aspirated, located upstream of the first tray (1), wherein the gas heating device comprises at least one of the following: a heat exchanger or a gas burner, where the terms "upstream" and "downstream" refer to the direction of the flow of hot gas.

9. Dryer (1) according to any one of the preceding claims, wherein the hot gas circulates from the top downwards and is preferably hot air.

10. Dryer (1) according to any one of Claims 1 to 8, wherein the hot gas circulates from the bottom upwards and is preferably hot air.

11. Dryer (1) according to any one of the preceding claims, wherein the tray (1) comprises a highly permeable, rigid, self-supporting grating structure, on which is placed a filtering layer comprising openings of size and density corresponding to the desired permeability depending on the type and size of particles to be dried.

12. Dryer (1) according to any one of the preceding claims, wherein the system (2) for distributing the particles to be dried on the tray (1) comprises at least one Archimedes screw extending along a radius of the tray (1), said at least one Archimedes screw being enclosed in an enclosure provided with one or more openings extending along said radius of the tray (1).

13. Dryer (1) according to any one of the preceding claims, wherein the recovery system (3) of the tray (1) comprises at least one Archimedes screw extending along a radius of said tray that is enclosed in an enclosure provided with one or more openings extending along said radius of the tray (1), said openings being connected to a scraper or brush configured to collect and guide the particles conveyed by the rotation of the tray toward the Archimedes screw.

14. Dryer (1) according to any one of the preceding claims, comprising a static floor located beneath the tray (1) along the vertical axis z, the floor comprising an opening for discharging the finest particles deposited on the floor, said dryer further comprising a scraper rigidly coupled to the tray and configured to follow the rotational movement thereof to push the particles deposited on the floor toward said discharge opening.

15. Dryer (1) according to any one of the preceding claims, wherein the particles to be dried comprise wood waste from sawmills, wood waste from construction materials, paper or cardboard waste, agri-food products, and are in the form of powder, granules, chips, pellets, meals, or pieces not usually greater than 10 cm long.