Device for discharging loose material and biomass torrefaction apparatus provided with such a discharging device

Abstract

The invention relates to a discharging device configured to retain loose material while controlling the flow thereof through the discharging device. The discharging device comprises a plurality of axially elongate rotors (4), the rotors (4) being parallel and arranged side by side so as to retain the loose material placed on the rotors (4) while allowing at least some of the loose material to flow between the rotors (4) under the effect of gravity. Each rotor (4) has teeth (10) distributed along the length and around the circumference of the rotor (4) and a drive assembly for rotating the rotors.

Description

[0001] Device for unloading bulk material and biomass torrefaction plant equipped with such an unloading device

[0002] The present invention relates to the field of unloading bulk material, in particular at the base of a biomass torrefaction column.

[0003] It is possible to torrefy lignocellulosic biomass to dry it and extract some of the volatile organic compounds while retaining the most energetic compounds, in order to produce a fuel.

[0004] The biomass is, for example, supplied in the form of chips, wafers and / or sticks, and torrefied by a gravity flow of the biomass, from top to bottom, in a torrefaction column in which hot gases circulate counter-current to the biomass, i.e. from bottom to top.

[0005] The characteristics of the torrefied biomass depend in particular on the time of exposure to the hot gases in the torrefaction column. It is therefore desirable to have an unloading device to ensure a controlled flow of the biomass at the bottom of the torrefaction column.

[0006] One of the aims of the invention is to provide a device for unloading bulk material which is reliable and economical and which ensures a controlled flow of the material.

[0007] To this end, the invention provides a device for unloading a bulk material configured to retain the bulk material while controlling its flow through the unloading device, the unloading device comprising a plurality of axially elongated rotors, the rotors being parallel and arranged side by side so as to retain the bulk material placed on the rotors while allowing the gravitational flow of at least a portion of the bulk material between the rotors, wherein each rotor has teeth distributed along the length and circumference of the rotor, and a drive assembly for driving the rotors in rotation.

[0008] According to particular embodiments, the unloading device comprises one or more of the following characteristics, taken individually or in all technically possible combinations:

[0009] - the drive assembly is configured to allow rotational driving of each rotor independently of the rotation of each other rotor;

[0010] - the drive assembly comprises a respective drive motor associated with each rotor;

[0011] - the rotors are associated in groups of two rotors; - the drive assembly comprises an operating mode with the rotational drive of the two rotors of each group of rotors in opposite directions and / or at the same rotational speed;

[0012] - each tooth has symmetry with respect to a radial plane passing through the central axis of the rotor carrying this tooth;

[0013] - each rotor has several rows of teeth, the teeth of each row of teeth being located in the same transverse plane and spaced circumferentially;

[0014] - the rows of teeth of each rotor are spaced from each other along this rotor;

[0015] - each row of teeth of each rotor is located opposite a gap between two adjacent rows of teeth of each other rotor adjacent to said rotor;

[0016] - each row of teeth comprises a number N of teeth equal to or greater than 5 and / or equal to or less than 10;

[0017] - the rotors are spaced so that the teeth of each rotor do not engage between the teeth of each adjacent rotor;

[0018] - each rotor has an external diameter taken as the diameter of the imaginary cylinder passing through the tops of the rotor teeth, the external diameters of the rotors are equal, and the transverse spacing between the central axes of the rotors of each pair of adjacent rotors is strictly greater than the external diameter of the rotors;

[0019] - each rotor comprises a shaft and a plurality of toothed rings, each toothed ring being threaded onto the shaft, each toothed ring carrying several of the rotor teeth;

[0020] - each tooth widens from a base of the tooth towards a top of the tooth;

[0021] - each tooth has two lateral edges extending between a base and a top of the tooth, and has two beaks, each beak being delimited between a respective lateral edge and the top of the tooth.

[0022] The invention also relates to a biomass torrefaction installation comprising a biomass torrefaction column intended to receive bulk biomass, an unloading device as defined above, arranged at a lower end of the column to retain the biomass while allowing its unloading in a controlled manner, and a gas circuit for injecting hot gas at the bottom of the column and recovering the gases at the top of the column after passing through the biomass retained in the column by the unloading device.

[0023] The invention and its advantages will be better understood upon reading the following description, given solely as a non-limiting example, and made with reference to the appended drawings, in which:

[0024] - Figure 1 is a perspective view of an unloading device; - Figure 2 is a top view of the unloading device;

[0025] - Figure 3 is a sectional view of the unloading device, along section line lll-lll in Figure 2;

[0026] - Figure 4 is a sectional view of the unloading device, along section line IV-IV in Figure 2; and

[0027] - Figure 5 is a schematic view of a biomass torrefaction installation incorporating an unloading device arranged at the bottom of a torrefaction column.

[0028] As illustrated in Figures 1-4, the unloading device 2 is configured to support and retain a bulk material resting on the unloading device 2, while allowing a controlled flow of the bulk material through the unloading device 2.

[0029] The unloading device 2 comprises a plurality of elongated rotors 4, the rotors 4 being parallel and arranged side by side so as to define a support surface 6 for the bulk material, while defining between them gaps 8 (Figures 2 and 3) to allow the gravitational flow of at least a portion of the bulk material via the gaps 8 delimited between the rotors 4.

[0030] Each rotor 4 extends along a respective central axis A. The central axes A are parallel to each other, and preferably coplanar.

[0031] Each rotor 4 is rotatably mounted around its central axis A. The rotation of the rotors 4 allows the bulk material to pass between the rotors.

[0032] The 4 rotors are similar.

[0033] Each rotor 4 has teeth 10 distributed along the length and circumference of the rotor 4.

[0034] Preferably, as best seen in Figures 2 and 3, each rotor 4 has several rows of teeth 12, the teeth 10 of each row of teeth 12 being located in the same transverse plane perpendicular to the central axis A of this rotor 4, and spaced circumferentially. The teeth 10 of each row of teeth 12 define intermediate spaces 14 between them (Figure 3).

[0035] Preferably, the teeth 10 of each row of teeth 12 are circumferentially distributed uniformly. Each tooth 10 is spaced from the next around the central axis A by an angular pitch a. The angular pitch a is constant for each row of teeth 12. Preferably, the angular pitch a is the same for each row of teeth 12 and the same for all the rotors 4.

[0036] Preferably, the rows of teeth 12 of each rotor 4 are axially spaced from each other along the central axis A of this rotor 4. The rows of teeth 12 of each rotor 4 are preferably axially distributed uniformly. Each row of teeth 12 is spaced from the next by an axial pitch P (Figure 4). The axial pitch P is constant along each rotor 4, and preferably the same for all the rotors 4.

[0037] Preferably, each row of teeth comprises a number N of teeth equal to or greater than 5 and / or equal to or less than 10. The rows of teeth 12 of the rotors 4 preferably have the same number N of teeth.

[0038] In a particular advantageous embodiment, and as visible in Figure 3, each row of teeth 12 has 5 circumferentially uniformly distributed teeth.

[0039] Preferably, when traveling axially through each rotor 4, the teeth 10 of each row of teeth 12 are angularly offset relative to the teeth 10 of the following row of teeth 12. Each tooth 10 of the row of teeth 12 is located axially opposite an intermediate space 14 between two teeth 10 of the following row of teeth 12.

[0040] In Figure 3, on each rotor 4, one row of teeth 12 and the next are visible, the teeth 10 of the next row of teeth 12 appearing between the teeth 10 of the previous row of teeth 12.

[0041] Preferably, the teeth 10 of each row of teeth 12 being distributed circumferentially uniformly with the same number of teeth 10 and / or the same angular pitch a for all the rows of teeth 12, the teeth 10 of each row of teeth 12 are angularly offset relative to the teeth of the following row of teeth 12 by an offset angle p equal to half the angular pitch a (i.e. p = a / 2).

[0042] Each rotor 4 has intervals 16 defined between the rows of teeth 12 of the rotor 16. Each interval 16 is defined between two adjacent rows of teeth 12 of the rotor 16.

[0043] Advantageously, each row of teeth 12 located between two intervals 16 has the same axial length as each interval 16 located between two rows of teeth 12.

[0044] In an exemplary embodiment, the rotors 4 are configured in such a way that each interval 16 of each rotor 4 is located opposite a row of teeth 12 of each adjacent rotor 4.

[0045] Preferably, the rotors 4 are spaced transversely from each other in such a way that the teeth 10 of each rotor 4 do not engage between the teeth 10 of each adjacent rotor 4.

[0046] Each tooth 10 has a base 18 and a top 20. The distance from the top of each tooth 10 of a rotor 4 to the central axis A of this rotor 4 is for example the same for all the teeth 10 of the rotor 4 and the same from one rotor 4 to another.

[0047] The external diameter d of each rotor 4 is taken as the diameter of an imaginary cylinder passing through the vertices 20 of the teeth 10 of the rotor 4.

[0048] Preferably, each rotor 4 has an external diameter d, the external diameters d of the rotors 4 are equal, and the transverse spacing E between the central axes A of the adjacent rotors 4 is strictly greater than the external diameter of the rotors 4.

[0049] The distance from the top of each tooth 10 of a rotor 4 to the central axis A of this rotor 4 is strictly less than half of the transverse spacing E between the central axis A of this rotor 4 and the central axis A of each adjacent rotor 4.

[0050] As visible in Figures 3 and 4, each rotor 4 comprises for example a shaft 22 extending along the central axis A and a plurality of toothed rings 24 threaded onto the shaft 22, each toothed ring 24 carrying several teeth 10.

[0051] Each toothed ring 24 defines for example a row of teeth 12. In the example illustrated, each row of teeth 12 is formed of two toothed rings 24 pressed against each other.

[0052] In one variant, each row of teeth 12 is defined by a single toothed ring 24.

[0053] In an exemplary embodiment, each rotor 4 comprises spacer rings 26, each spacer ring 26 being interposed between two rows of teeth 12 which follow each other axially along the rotor 4 to ensure an axial spacing between these two rows of teeth 12. Each spacer ring 26 makes it possible to define all or part of an axial interval 16 between two rows of teeth 12.

[0054] In the illustrated embodiment, the spacer rings 26 are associated in pairs, the two spacer rings 26 of each pair being pressed against each other and interposed axially between two rows of adjacent teeth 12 to delimit a gap 16.

[0055] In one variant, a single spacer ring 26 is interposed between each row of teeth 12 and the next.

[0056] The toothed rings 24 and the spacer rings 26 are here distinct, which makes it possible to easily adjust the axial thickness of the teeth 10 by superimposing toothed rings 24 and / or the axial spacing between the rows of teeth 12, i.e. the length of the intervals 16, by superimposing spacer rings 26. Alternatively, it is possible to provide toothed rings 24 formed from a single piece of material with spacer rings 26 ensuring the axial spacing between the adjacent toothed rings 24 to form the intervals 16.

[0057] Each toothed ring 24 is threaded onto the shaft 22 while being rotationally connected to the shaft 22. Thus, in operation, when the shaft 22 is rotated, each toothed ring 24 rotates together with the shaft 22.

[0058] In an exemplary embodiment, as visible in Figure 3, the shaft 22 of each rotor 4 has a non-circular cross-section, each ring 24 having a non-circular central orifice 30 cooperating with the shaft 22 for the rotational connection of the ring 24 on the shaft 22. The central orifice 30 is preferably of a shape complementary to that of the cross-section of the shaft 22.

[0059] In an exemplary embodiment, the shaft 22 has a cross-section having two parallel edges connected by two arcuate edges, the central orifice 30 of each ring 24 having a complementary shape. Thus, the shaft 22 has two flats 32 making it possible to ensure the rotational connection with the rings 24. Such a cross-section makes it possible to distribute the rotational connection force over a large surface.

[0060] Other shapes allowing a rotational connection are conceivable. Alternatively, it is possible to provide a rotational connection by means of a rotational locking element such as a key or a set screw.

[0061] In an exemplary embodiment, as seen in Figure 3, each tooth 10 widens from its base 18 towards its apex 20. Each tooth 10 is wider at its apex 20 than at its base 18.

[0062] Each tooth 10 has two lateral edges 34 extending between the base 18 and the apex 20 of the tooth 10, and has two beaks 36, each beak 36 being formed at the junction between a respective lateral edge 34 and the apex 20 of the tooth 10.

[0063] Each beak 36 has the shape of a point formed at the junction between the corresponding lateral edge 34 and the apex 20.

[0064] Preferably, each tooth 10 has a symmetry with respect to a plane containing the central axis of the rotor 4 and passing through the middle of the tooth 10.

[0065] In particular, preferably, the two beaks 36 of each tooth 10 are symmetrical to each other with respect to a plane containing the central axis A of the rotor 4 and passing through the middle of the tooth 10.

[0066] This allows rotor 4 to operate in the same way in both directions of rotation around its central axis A.

[0067] Preferably, the dimensions of the rotors 4 and the relative positions of the rotors 4, in particular the height of each tooth 10 (taken between its base 18 and its top 20), the spacing between the teeth 10 of the same row of teeth 12, the axial length of the intervals 16 between the rows of teeth 12, the external diameter d of the rotors 4 and / or the transverse spacing E between the rotors 4, are such that the bulk material is retained by the rotors 4 in the absence of rotation of the rotors 4, and passes between the rotors 4 in the event of rotation of the rotors 4, for example by inserting itself into the intermediate spaces 14 between the teeth 10 of the same row of teeth 12 and / or the intervals 16 between the rows of teeth 12 to pass between the rotors 4.

[0068] Preferably, each rotor 4 is provided in such a way that an element of the bulk material can be accommodated in an intermediate space 14 of a row of teeth 12, being received between the previous row of teeth 12 and the following row of teeth 12.

[0069] In an exemplary embodiment, the bulk material is in the form of plates having a width and length of between 10 mm and 100 mm.

[0070] In such a case, the external diameter d of the rotors 4 is for example between 350 mm and 400 mm and / or the transverse spacing E between the rotors 4 is for example between 380 mm and 420 mm.

[0071] Furthermore, preferably, the intermediate spaces 14 have a width of between 130 mm and 150 mm, the teeth 10 have a height (taken between the base 18 and the top 20) of between 37 mm and 42 mm and / or the intervals 16 have an axial length of between 44 mm and 48 mm.

[0072] The unloading device 2 comprises a drive assembly 40 for driving each rotor 4 in rotation around its respective central axis A.

[0073] As indicated above, in the absence of rotation of the rotors 4, the bulk material tends to become blocked and retained by the rotors 4. The rotation of the rotors 4 allows the controlled flow of the bulk material by gravity flow between the rotors 4. The bulk material passes between the rotors 4, in the intermediate spaces 14 and / or in the gaps 16.

[0074] The drive assembly 40 comprises one or more motor(s) 42 for driving the rotors 4 in rotation. Each motor 42 is, for example, an electric motor.

[0075] The drive assembly 40 includes an electronic control unit 44 configured to control the motors 42.

[0076] Advantageously, the drive assembly 40 is configured to allow the rotational driving of each rotor 4 in one direction of rotation or, preferably, in each direction of rotation around the central axis A, in particular following a continuous rotational movement in the or each direction of rotation (as opposed to an alternating rotational movement alternating a rotation in one direction of rotation with a rotation in the other direction of rotation).

[0077] Advantageously, the drive assembly 40 is configured to allow the rotational drive of each rotor 4 independently of each other rotor 4.

[0078] This can help unblock bulk material under certain conditions where the bulk material forms an arch and no longer flows.

[0079] In an exemplary embodiment, the drive assembly 40 comprises a respective motor 42 associated with each rotor 4.

[0080] This allows each rotor 4 to be driven in rotation independently of each other rotor 4 and in both directions of rotation around the central axis A of the rotor 4.

[0081] Advantageously, at least in one operating mode, the rotors 4 are associated in groups 46 of two adjacent rotors 4, the drive assembly 40 being configured to drive the two rotors 2 of each group 46 in rotation in opposite directions and / or at the same rotation speed.

[0082] Advantageously, the electronic control unit 44 comprises a variator 48 associated with each group 46, the variator 48 being common to the motors 42 of the two rotors 4 of this group 46.

[0083] Each variator 48 controls the electric current supplying the two motors 42 and thus the simultaneous rotation and at the same rotation speed of the two rotors 4 of the associated group 46.

[0084] Each rotor 4 has a first axial end 4A and a second axial end 4B. The motor 42 associated with each rotor 4 is arranged at the first axial end 4A of this rotor 4 and coupled to the first end 4A of this rotor 4.

[0085] The rotors 4 comprise first rotors 4 and second rotors 4 arranged head to tail with respect to the first rotors 4.

[0086] This facilitates the integration of the loading device 2 into an installation and its maintenance, by distributing the motors 2 on two opposite sides of the extraction device 2.

[0087] Preferably, when the rotors 4 are associated in groups 46 of two, the two rotors 4 of each group 46 have their first ends 4A located on the same side.

[0088] In an exemplary embodiment, the groups 46 of rotors 4 are arranged with an alternating configuration, the group(s) 46 of first rotors 4 alternating with the group(s) of second rotors 4.

[0089] In the illustrated embodiment, the unloading device 2 comprises six rotors 4 distributed into three groups 46 of two adjacent rotors 4, the rotors 4 of the group 46 located between the other two groups 46 being arranged head to tail with respect to the rotors 4 of two other groups 46.

[0090] The unloading device 2 comprises, for example, a support frame 50 delimiting an opening 52 for the passage of the bulk material. The rotors 4 extend across the opening 52, to oppose the free flow of the bulk material through the opening 52.

[0091] The rotors 4 extend for example between two opposite edges of the support frame 50 between which the opening 52 is delimited.

[0092] Each rotor 4 is rotatably mounted about its central axis A on the support frame 50, for example by means of bearings 54 arranged at the ends of the rotor 4. The bearings 54 are preferably rolling bearings.

[0093] The support frame 50 has, for example, a rectangular shape. It is formed of four parallel beams in pairs, including first beams 56 opposite each other and second beams 58 opposite each other, the rotors 4 extending between the first beams 56. Each bearing 54 is mounted on one of the first beams 56.

[0094] Each motor 42 is for example supported by a support console 60 disposed on the support frame 50 and extending cantilevered outwardly from the support frame 50.

[0095] The unloading device 2 here comprises a respective support console 60 associated with each group 46 of rotors 4 and supporting the motors 42 of the two rotors 4 of this group 46.

[0096] As illustrated in Figure 4, a torrefaction plant 70 is configured for torrefying biomass BM, particularly lignocellulosic biomass, in the form of a bulk material.

[0097] BM biomass is, for example, formed of particles in the form of platelets with a width and length of between 10 and 100 mm.

[0098] Biomass is, for example, made up of wood, nut shells, bagasse, straw (rice straw, wheat straw, etc.), bark, or even residues from the use of oil palm fruit (called EFB, acronym for "Empty Fruit Branch" in English).

[0099] The torrefaction installation 70 comprises a torrefaction column 72 for the gravity flow of the biomass BM from the top of the column 72 to the bottom of the column 72, countercurrent to a flow of hot gases circulating from the bottom of the column 72 to the top in the column 72.

[0100] The column 72 is tubular and extends vertically along a substantially vertical column axis B. The column 72 preferably has a frustoconical shape widening downwards. The torrefaction installation 70 comprises a feed system 74 configured to introduce biomass BM at the top of the column 72. The feed system 74 is configured to prevent the exit of hot gases from the top of the column 72.

[0101] The torrefaction facility 70 includes an extraction system 76 configured to extract the torrefied biomass BT at the bottom of the column 72.

[0102] The extraction system 76 comprises an unloading device 2 as described previously, arranged at the bottom of the column 72 to control the gravity flow of the biomass BM at the bottom of the column 72, and therefore the progression of the biomass BM in the column 72 as a whole.

[0103] The unloading device 2 is arranged so that it extends across the lower end of the column 72.

[0104] The extraction system 76 comprises for example a conveyor 78 configured to drive the torrefied biomass BT discharged through the unloading device 2, for example towards a cooling station and a packaging station.

[0105] The conveyor 78 is, for example, a screw conveyor. Alternatively, it may be a belt conveyor.

[0106] The extraction system 76 optionally includes an unloading box 80 disposed at the bottom of the column 72 and closing the lower end of the column 72.

[0107] The unloading device 2 is then arranged inside the unloading box 80, the conveyor 78 being, if necessary, arranged in the bottom of the unloading box.

[0108] The roasting installation 70 comprises a gas circuit 82 configured for the injection of hot gases at the bottom of the column 72 and the recovery of the gases at the top of the column 72 after passage of the gases through the biomass retained in the column 72 by the unloading device 2.

[0109] Preferably, the hot gases are introduced at the bottom of the column 72 through the unloading device 2. The gas circuit 82 is for example configured for the injection of the hot gases into the unloading box 80.

[0110] The gas circuit 82 comprises a production system 84 for producing hot gases. The production system 84 may, for example, comprise a burner and / or a heat exchanger.

[0111] In an exemplary embodiment, a burner is configured to generate the hot gases. Alternatively, the heat produced by the burner is used in a heat exchanger to heat gases intended to be injected at the bottom of the column 72. The gas circuit 82 preferably comprises a recovery system 86 configured to recover the gases at the top of the column 72, and preferably to filter the gases recovered at the top of the column 72. The filtering is for example provided to remove particles. The filtering is carried out for example using a cyclone effect filter or a sleeve filter.

[0112] Optionally, the gas circuit 82 is configured to recycle at least part of the gases recovered at the top of the column 72, to reinject them at the bottom of the column.

[0113] Optionally, the gas circuit 82 is configured for heat exchange between the gases recovered at the top of the column 72 and fresh gases supplying the base of the column 72, for example using a heat exchanger.

[0114] In steady state operation of the torrefaction installation 70, biomass BM is present in the column 72 and flows by gravity from the top of the column 72 to the bottom of the column 72.

[0115] The hot gases are injected at the bottom of column 72 and circulate from the bottom of column 72 to the top of column 72 while being in contact with the BM biomass being treated, then are recovered at the top of column 72.

[0116] The gases are introduced at the bottom of the column 44 at a first temperature T 1 and exit at the top of the column 44 at a second temperature T2 lower than the first temperature T 1 .

[0117] The first temperature T1 is between 220°C and 350°C, preferably between 260°C and 300°C. The second temperature T2 is, for example, between 60°C and 80°C.

[0118] The gravity flow of the biomass BM (consequently the residence time of the biomass in the column 72) is controlled using the unloading device 2, in particular by rotating the rotors 4.

[0119] Due to the dimensions of the biomass particles in relation to the dimensions of the rotors 4 and their transverse spacing E, in the absence of rotation of the rotors 4, the biomass flows little or not at all through the rotors 4.

[0120] A rotation of the rotors 4, combined with the shape of the rotors provided with teeth 10, the relative position of the teeth 10 of each rotor 4, the relative position of the teeth 10 of the different rotors 4 and the shape of the teeth 10, allows a controlled flow of the biomass BM between the rotors 4.

[0121] The intermediate spaces 14 allow the biomass particles to be housed between teeth 10 of the same rotor 4. The axial intervals 16 allow the biomass particles to be housed between rows of teeth 12 of the same rotor 4. The angular offsets of the teeth 10 of the same rotor 4, in particular between rows of teeth 12 of the same rotor 4, and the axial offsets between the teeth 10 of adjacent rotors 4, in particular between rows of teeth 12 of adjacent rotors 4, allow the biomass particles to pass between the rotors 4 in a controlled manner. The shape of the teeth 10, in particular their shape widening from the base 18 towards the top 20, in particular again with the formation of beaks 28, makes it possible to force the entrainment and passage of biomass particles which could become stuck.

[0122] The rotors 4 associated in groups 46 of two by being counter-rotating (i.e. turning in opposite directions), and preferably turning at the same speed, makes it possible to promote the passage of biomass particles between the two rotors 4 of each group 46.

[0123] The rotors 4 each formed from a shaft 22 and toothed rings 24 threaded onto the shaft 22 are easily obtained, and allow easy maintenance, for example allowing the individual replacement of a toothed ring 24 which is damaged or worn.

Claims

DEMANDS 1. A bulk material unloading device configured to retain the bulk material while controlling its flow through the unloading device, the unloading device comprising a plurality of axially elongated rotors (4), the rotors (4) being parallel and arranged side-by-side so as to retain the bulk material resting on the rotors (4) while allowing gravity flow of at least a portion of the bulk material between the rotors (4), in which each rotor (4) has teeth (10) distributed over the length and circumference of the rotor (4), and a drive assembly for rotating the rotors.

2. Unloading device according to claim 1, wherein the drive assembly is configured to allow the rotational drive of each rotor (4) independently of the rotation of each other rotor (4).

3. Unloading device according to claim 1 or claim 2, wherein the drive assembly comprises a respective drive motor (42) associated with each rotor.

4. Unloading device according to any one of the preceding claims, in which the rotors (4) are associated in groups of two rotors (4).

5. Unloading device according to claim 4, wherein the drive assembly includes an operating mode with the rotational drive of the two rotors (4) of each group of rotors (4) in opposite directions and / or at the same rotational speed.

6. Biomass unloading device according to any one of the preceding claims, wherein each tooth (10) has symmetry with respect to a radial plane passing through the central axis of the rotor (4) carrying this tooth (10).

7. Biomass unloading device according to any one of the preceding claims, in which each rotor (4) has several rows of teeth (12), the teeth (10) of each row of teeth (12) being located in the same transverse plane and circumferentially spaced.

8. Biomass unloading device according to claim 7, wherein the rows of teeth of each rotor (4) are spaced apart from each other along this rotor (4).

9. Unloading device according to claim 7 or 8, wherein each row of teeth of each rotor (4) is located opposite a gap between two adjacent rows of teeth of each other rotor (4) adjacent to said rotor (4).

10. Unloading device according to any one of claims 7 to 9, wherein each row of teeth (12) comprises a number N of teeth (10) equal to or greater than 5 and / or equal to or less than 10.

11. Unloading device according to any one of the preceding claims, wherein the rotors (4) are spaced apart so that the teeth (10) of each rotor (4) do not engage between the teeth (10) of each adjacent rotor (4).

12. Unloading device according to any one of the preceding claims, wherein each rotor (4) has an external diameter taken as the diameter of the imaginary cylinder passing through the tops of the teeth (10) of the rotor (4), the external diameters of the rotors (4) are equal, and the transverse spacing between the central axes of the rotors (4) of each pair of adjacent rotors (4) is strictly greater than the external diameter of the rotors (4).

13. Unloading device according to any one of the preceding claims, in which each rotor (4) comprises a shaft (22) and a plurality of toothed rings (24), each toothed ring (24) being threaded onto the shaft (22), each toothed ring (24) carrying several of the teeth (10) of the rotor (4).

14. Unloading device according to any one of the preceding claims, in which each tooth (10) widens from a base of the tooth (10) to a tip of the tooth (10).

15. Unloading device according to any one of the preceding claims, in which each tooth (10) has two lateral edges extending between a base and a top of the tooth (10), and has two beaks (36), each beak being delimited between a respective lateral edge and the top of the tooth (10).

16. Biomass torrefaction installation comprising a biomass torrefaction column (72) intended to receive bulk biomass, a discharge device (2) according to any one of the preceding claims, disposed at a lower end of the column (72) to retain the biomass while allowing its discharge in a controlled manner, and a gas circuit (82) for the injection of hot gas at the bottom of the column (72) and the recovery of the gas at the top of the column (72) after passing through the biomass retained in the column (72) by the discharge device (2).

Images