FR2707376A1 - Installation for drying humid materials, for example the droppings of poultry - Google Patents

Abstract

This installation comprises an enclosure (1) in the form of a tunnel and means (2, 3, 4) for generating therein a current of hot air; the materials to be dehydrated are transported in the form of a layer by an endless conveyor belt (6) which exposes them to the current of hot air, this belt (6) having a sinuous trajectory consisting of a set of superposed horizontal sections (60, 60') and transfer means (7) arranged at the downstream end of each of the belt sections are adapted to scrape the materials and to pour them onto the subjacent section.

Description

INSTALLATION FOR DRYING WET MATERIAL,
FOR EXAMPLE OF POULTRY BREAKS
The present invention relates to an installation for drying wet materials, such as for example poultry droppings.

 Modern livestock buildings, and in particular industrial poultry farms, are most of the time equipped with a droppings recovery and evacuation system. It is a moving endless belt extending under each battery of cages.

 To this evacuation system is associated a drying device which generally uses air heated in ducts by the interior atmosphere of the building to then be blown on the carpet by means of another network of circulation ducts of the 'air.

 The performances of this kind of system are generally poor, the dry matter content of the final product rarely being more than 50 to 55% approximately.

 Furthermore, there is a problem when dealing with a livestock building which is not equipped with a droppings drying system.

Indeed, the installation of such a system requires a complete transformation of the equipment and in particular of the batteries accommodating the poultry, so that in general the operators prefer to give it up for reasons of cost.

 The invention aims to solve these problems by proposing an installation specially designed for drying wet materials, and in particular poultry droppings, this installation making it possible to obtain a high rate of dehydration, and being capable of equipping traditional farms which are not provided initially a drying system.

 Such an installation is placed outside the livestock building, on a concrete slab.

These results are achieved in accordance with the invention thanks to the fact that the installation comprises
- a tunnel-shaped enclosure, with thermally insulated walls
means for generating a current of hot air inside the enclosure
- a very long mobile endless belt, capable of transporting the materials in the form of a layer, alternately on each of its two faces, this belt having a sinuous trajectory composed of a set of superimposed horizontal strands passing over rolls of end gear so that the material transport faces and the direction of movement of the belt are reversed from one strand to another
transfer means arranged at the downstream end of each of the carpet strands, with the exception of the lower strand, and adapted to scrape the materials transported by this strand and to pour them onto the underlying strand
- means for distributing and discharging wet materials on the upper side of the carpet
- Means for removing dry matter from the lower strand of the carpet.

Furthermore, according to a certain number of advantageous, but not limiting, characteristics of the invention
- the air flow is produced by turbines arranged at one end of the enclosure
- the carpet is driven by a heat engine which produces heat used to heat the air flow generated in the enclosure
- The turbines are also driven by said heat engine, and heat is used from the engine cooling water and the burnt gases produced by it;
- each end deflection roller is associated with a pressure roller
- the set of deflection rollers arranged at one end of the belt is positively driven in rotation, while the other deflection rollers are insane
- the set of positively driven deflection rollers is disengageable
- Said transfer means comprise a scraping and deflecting material device adapted to move the materials towards the outside of the mat, beyond at least one of its edges
- Said transfer means comprise a transverse conveyor extending under the strand of the carpet
- Said transverse conveyor comprises an Archimedes screw rotating in a bucket having a notch for the passage of materials, and for their discharge on the underlying strand
- Said scraper and deflection member has the shape of a "V" whose tip is turned upstream of the strand, capable of transferring the materials from both sides of the belt, while the Archimedes screw comprises two sections coaxial whose steps are reversed, so as to bring the materials towards the center of the underlying strand
- the downstream end zone of each strand of the belt, in which scraping and transfer of materials takes place, rests on an openwork support plate
- the installation includes a solar air preheating device
- the installation includes an automatic belt tension adjustment system.

 Other characteristics and advantages of the invention will appear from the description and the appended drawings which represent a preferred embodiment.

On these drawings
- Figure 1 is a schematic front view, partially in section along a longitudinal vertical plane, of the entire installation;
- Figure 2 is a top view of the downstream end of a horizontal carpet strand, this view showing the transfer means arranged at this end
- Figure 3 is a front view, cut by the longitudinal vertical plane III-III of Figure 2, on a slightly enlarged scale, of Figure 2
- Figure 4 is a schematic perspective view intended to illustrate the operating mode of the transverse conveyor constituting the transfer means
- Figures 5 and 6 are partial and schematic views, respectively in cross section and from the side, of the drive means of the deflection rollers provided on one of the edges of the installation.

 The installation for drying wet materials, and in particular poultry droppings, which is shown diagrammatically in FIG. 1 comprises an enclosure 1 in the form of a tunnel of great length L. This length is for example of the order of approximately 50 m .

 The walls of the enclosure are made of a thermally insulating material, for example a sandwich material of cement fibers and of polystyrene.

 In FIG. 1, one of the front walls - called the front wall - is referenced 10 while the other front wall - called the rear wall - is referenced 11.

 The ceiling wall is referenced 12. The floor is referenced S.

 This is covered over the greater part of the length of the tunnel, rear side, with a sheet metal box 13, serving as a roof, the cross section of which has the shape of an inverted "V". This box is used for solar preheating of the air, which can enter it naturally, in order to supply the air distribution turbines, as will be explained below.

 Advantageously, the external faces of the box 13 are black in color, which promotes the absorption of solar heat.

 At the front of the tunnel, on the left of FIG. 1, is a set of turbines 2. It consists of a pair of superimposed turbines 20, 21, suitable when they are rotated to produce an air flow with a large flow. This air flow is directed horizontally, along the axis of the tunnel, towards the rear of the tunnel, as is symbolized by the arrows f.

 Inside the tunnel, a little downstream of the turbines (if we consider the direction of the air flow f) is an internal combustion engine, for example a diesel engine. This motor, referenced 3, is fixed on a base 30 in such a way that it is at a certain height inside the tunnel, above the ground S.

 The motor 3 is a motor of known type, of high power.

It is cooled by water circulating in a known type of radiator, not shown in Figure 1. This radiator is cooled by the air flow produced by the turbines.

 Between the set of turbines 2 and the motor 3 is further interposed a heat exchanger 4. This exchanger comprises one or more tubes 40, for example in the form of a coil (s), which is (or are) connected (s) to the exhaust pipe for the burnt gases from the engine 3. After passing through the exchanger 4, the gases are evacuated by means of a pipe 41 outside the enclosure 1, as is symbolized by the arrow 42. Good Of course, the tubing can be equipped with a filter 43 capturing harmful particles so that the gases evacuated by the installation do not pollute the atmosphere.

 The current of air which has been heated by the exchanger 4, then by the radiator fitted to the engine 3, is symbolized by the arrows F in FIG. 1.

 It is this flow of hot air that will dry the materials in the tunnel.

 Most of the tunnel is equipped with an endless conveyor 5, the frame of which has been symbolized by a broken broken line and is referenced 50. This frame supports a certain number of return and drive rollers of a belt 6 .

 Towards the front of the tunnel is provided a row of superposed deflection and drive rollers, referenced 52. At the other end (towards the rear) is provided a similar set of rollers 52 '. The rollers 52 'are not powered, but are mounted idly on their axis. It is the carpet that drives them.

 In order not to unnecessarily complicate the figure, a relatively small number of rollers has been shown in each set 52, 52 '. In practice, this number can be relatively large, for example eighteen for each set.

 In each set of rollers, their diameter is substantially equal to their mutual spacing, and the two sets of rollers are offset in height, so that the belt passes from a roller 52 to a roller 52 ', then from a roller 52 'to a roller 52, by substantially horizontal superimposed strands.

 Of course, due to the return by the end roller, the face of the mat which corresponds to the upper face of the go strand is found to be the underside of the return strand, and vice versa.

 From one strand to the next strand, we therefore observe a change in direction of advancement and a reversal of the faces.

 In the figures, the movement of the carpet has been symbolized by arrows i, and the strands circulating from the rear towards the front of the tunnel have been referenced 60 and by the reference 60 ′ the strands circulating in the other direction .

 Each return roller 52 or 52 'is associated with a backing roller 53, respectively 53'. Its function is to press the mat against the roller so as to ensure good adhesion and avoid relative surface slippage.

 The drive rollers 52 and return 52 'are preferably tubular rollers (drum-shaped - see Figure 3) made of metal. Their diameter is for example of the order of 160 mm. The counter rollers 53 and 53 ′ are constituted by rings 531 of flexible and elastic material (rubber type) fitted onto a central tube 530.

 The axis 520 of the rollers and the central tubes 530 are guided in rotation in suitable bearings, for example with ball bearings, provided in vertical uprights 533 disposed on each side of the belt.

 In FIG. 5, the shaft guide bearings 520 have been referenced 534.

 As an indication, the carpet 6 has a length of 900 m and a width of 950 mm. This mat 6 is made of polypropylene and has a thickness of 1 mm.

 The upper 60A and lower 60'B strands extend towards the outside of the frame 50, towards the rear of the enclosure. The belts pass over return rollers 61, 62, 63, at least one of which - in this case the roller 61 - is mobile. An automatic adjustment system of a type known per se, symbolized by a spring 64 in FIG. 1, makes it possible to control the position of the roller 61 to the value of the tension of the belt 6.

 It is indeed necessary to take account of the variations in length of the carpet 6 which result from its expansion as a function of the changes in the temperature in the enclosure, this expansion being able to cause relatively large variations in length due to the great length of the carpet. .

 Thanks to this control, the belt tension remains constant, or practically constant, within a predetermined range of values.

 At the upper part of the enclosure, for example in the central area of the frame 50, is mounted a distributor tank (or hopper) 80.

 This crosses the roof elements 12, 13 so as to overhang by its lower outlet opening the strand 60A.

 The tank 80 receives the materials to be dehydrated from a conveyor 8, for example a moving endless belt.

 In the event that the drying installation adjoins a livestock building, the conveyor 8 can feed materials directly from the batteries of breeding cages located inside this building.

 At the base of the tank is mounted a set of rotary drums 81 which serve to take and distribute the materials from the tank on the carpet strand 60A, distributing them there evenly, in the form of a layer.

 These are, for example, drums having peripheral fingers arranged in a helix and overlapping one another, from a drum to the neighboring drum. Two neighboring drums rotate in opposite directions, preferably at different speeds to avoid the accumulation of materials in the same areas between the fingers.

 At the downstream end of each of the strands 60, 60 ′ of the belt are arranged transfer means 7 whose role is to scrape this end in order to remove the materials, then to distribute them on the upper face of the other underlying strand.

 The description of these transfer means 7 will now be made with reference to FIGS. 2, 3 and 4.

 The means 7 essentially comprise a scraper member 70 disposed above the strand 60 whose materials are to be scraped, as well as a transverse conveyor disposed under this strand 60, above the strand 60 'onto which it is desired to transfer said materials.

 The transfer means 7 'located at the other end of the enclosure, which this time transfer the materials from the strand 60' to the strand 60 are completely identical.

 The scraper member 7 consists of a metal plate of low height (of the order of 5 to 10 cm for example) which is folded in the shape of a "V" whose top is directed upstream, it is that is to say against the meaning i. The angle at the top of the member 70 is preferably close to the right angle. I1 is placed symmetrically above the carpet (its top being in the axis of the latter).

 The member 70 is flush with its lower edge on the upper face of the mat 60.

 At this level, the carpet strand is supported, by its lower face, by a plate 77. The latter is largely perforated, for example by means of a set of circular holes, which prevents the adhesion of the carpet.

 The presence of the support plate 77 prevents the strand 60 from collapsing at the level of the scraper and consequently improves the effectiveness of the scraping.

 Outside these end zones, the mat is also supported over its entire length by suitable means known per se, for example by transverse rods not shown.

 As symbolized by the arrows in FIG. 2, the materials are scraped and directed symmetrically towards the lateral edges 6a and 6b of the mat by the lateral faces of the scraper 70.

 Under the strand 60 is installed a transverse conveyor comprising a bucket 71 of approximately semi-cylindrical sheet metal in which is mounted a transverse Archimedes screw. This comprises an axis 72 on which are fixed, by means of radial arms 730, two helical rods 73a and 73b. These have reversed steps, this step being such that when the Archimedes' screw is driven in a certain direction, in fact in the normal direction of rotation, it moves the materials inside the bucket, from the outside towards the center.

 The end faces (transverse faces) of the bucket 71 carry bearings 720 for guiding the axis 72 in rotation.

 The bucket 71 is located a short distance from the deflection roller 52.

 I1 is largely indented on the side opposite to this roller 52 by an opening 710. As can be seen more particularly in FIG. 4, the lower edge of this indentation is symmetrically arched on either side of the axis of the mat, so that its central part is low, and comes almost flush with the upper face of the strand 60 ', while the edge of the notch is gradually raised towards the outside.

 The shaft 520 of the roller 52 is driven positively as will be explained below, from the motor 3. In FIG. 2, this positive drive of the shaft 520 has been symbolized by an arrow M.

The drive is done on one side of the mat, which corresponds to the edge 6a.

 On the other side, the shaft 520 carries at its free end a toothed wheel 522 which meshes with a wheel 532 mounted at the corresponding end of the tube 530 of the backing roller.

 Thus, the counter-roller is also driven in rotation, this via the shaft 520.

 Of course, the diameters of the pinions 522 and 532 correspond respectively to the diameters of the roller 52 and of the support rings 531 of the counter-roller, so that the belt is driven in a regular manner and is not subjected to shearing forces. longitudinal.

 The shaft 520 also carries at its end a pinion 523, by which it drives, via a chain 75 and a pinion 74, the Archimedes screw 73.

 As seen in Figure 2, the transverse conveyor 73-71 has a length substantially greater than the width of the belt 6, so that the ends of the conveyor protrude from the edges 6a and 6b.

 The deflector member 70 is positioned so as to bring the materials into the protruding parts of the bucket. On the upstream side, additional deflector plates 76 are provided which correctly channel the materials towards the bucket.

 Of course, the transverse conveyor as well as the deflector member 70 and the support plate 77 are fixed to the frame 50 by suitable means which have not been shown so as not to unnecessarily complicate the present description or the figures.

 The diagram in FIG. 4 makes it possible to understand clearly how the transfer of materials takes place from strand 60 to strand 60 ′.

 When the materials transported by the strand 60, and flowing along i, meet the scraper member 70 in the shape of a "V", they are deflected laterally. They cross the edges 6a, 6b of the mat to fall back into the end parts of the trough 71 (arrows A). The sections of Archimedes screw 73a and 73b, on the one hand ensure mixing of the product, on the other hand bring it gradually towards the center of the trough. This movement is symbolized by the arrows B.

 However, due to the presence of the opening 710, the product gradually escapes from the trough during this transfer, and is distributed over the strand 60 ′, as symbolized by the arrows C.

 According to an important characteristic of the invention, the heat engine 3 serves both to drive the set of turbines 21, 20 and the belt 6.

 The flow produced by each turbine is for example 40,000 m3 of air per hour. The air is taken from the side of the turbines, through suitable openings provided in the side walls of the enclosure.

 The motor 3 also drives a speed reducer, for example by means of a transmission belt. It is by means of this reducer, which is referenced 31 in FIG. 6, that the motor rollers 52 are driven.

 Each shaft end 520 is provided, on the opposite side to the pinion 522 which was mentioned above, a pair of pinions 33 which are carried by a sleeve mounted idly on the shaft 520. This sleeve is also integral with a coupling member of the radial dog type disc 34.

 The end portion of the shaft 520 carries anti-rotation means, for example grooves. This portion is engaged with a disc 95 which carries dogs which are complementary to those of the coupling member 34. Each disc 95 is guided in rotation in a plate 93 which can slide axially along the axis of the shaft 520. The set of plates 93 is mounted on an upright 9 which is movable in the horizontal direction and can be brought close or distant from the upright 503 for mounting the rollers 52. Appropriate guide members facilitate this translation.

 The displacement of the upright 9 relative to the fixed upright 533 is carried out for example using one (or more) screws 90 guided in rotation in the upright 9 but immobile in translation relative to the latter. The thread 92 of the screw engages in a nut 535 secured to the part 533.

 The screw 90 carries a rotary drive member 91, manual or motorized.

 Thus, by rotating the screw 90 in a certain direction, the part 9 is brought closer to the part 533, as symbolized by the arrows in FIG. 5. By rotating the screw in the other direction, these two parts are moved aside.

 The assemblies 95, 93 are guided in translation by means of rods 940 relative to the part 9. Springs 94 tend to push them towards the part 533.

 The reduction gear 31 drives directly, by means of chains 310, two pairs of neighboring sprockets 32. Each of these drives itself by means of a chain 33 another pair of neighboring sprockets 32, and so on. Of course, from one link to the other, the chains 33 are offset as can be understood from the observation of FIG. 5.

 In the position in FIG. 5, the movable part 9 is moved away from the fixed part 533, which corresponds to a disengagement situation of the rollers 52.

 Indeed, the coupling parts 95 and 34 are spaced from one another.

 Thus, each pair of pinions 32 rotates freely on the shaft 520 without driving the latter.

 On the contrary, if part 9 is brought closer to part 533, the dogs of part 95 come to engage in those of part 34, making the coupling between these two parts.

 The pair of pinions 32 then drives the part 95, which is guided in rotation in the plate 93. The part 95 itself drives via the anti-rotation link 521 the shaft 520 and, correspondingly, the roller 52 carried by it.

 The presence of the springs 94 makes it possible to postpone the engagement of the dogs when the parts 9 and 533 are brought together, this engagement being done automatically when the male parts of the dogs arrive opposite the female parts.

 The lowest strand 60'B is equipped, in its downstream zone with a system for removing dried materials.

 This system, symbolized in FIG. 1 by a rectangle with a strong contour, and referenced 65, can consist, for example, of a scraper of known type transferring the materials on an underlying conveyor, for example on a movable belt disposed transversely and which discharges materials outside the enclosure, to an appropriate storage location.

 The heat engine 3 is supplied with fuel by means of known type, from a tank (not shown) which can be placed either inside the enclosure, or outside of the latter.

 The engine has of course a variable speed.

 As an indication, its operating speed will be 2,000 rpm, and the characteristics of the reduction gear and the transmissions are chosen so that the belt 6 advances at a speed of the order of 1.5 m / min.

 We will now explain how this installation works.

 Wet materials such as, for example, poultry droppings having a dry matter content of the order of 30% are brought into the tank 80 by means of the conveyor 8.

 The heat engine 3 being started, and the drive rollers 52 being in the engaged position, the belt 6 advances according to the arrows i.

 The materials are extracted regularly following the rotation of the rollers 81 at the bottom of the tank. Thus the materials are deposited in the form of a layer on the strand 60A of the carpet 6. Preferably the layer of materials has a fairly regular thickness, of the order of 3 centimeters for example; however, it is preferable that its surface is not too smooth, but is on the contrary embossed in order to improve its thermal contact with the flow of hot air.

 As already said, the air flow symbolized by the arrows f produced by the turbines 20, 21 is successively heated by the exchanger 4 and by the radiator of the engine 3. It is therefore hot air which circulates throughout along enclosure 1, between the different strands of carpet. As an indication, the temperature of the hot air flow F is between 40 and 50 C. Air outlet openings, not shown, are advantageously provided at the rear end of the enclosure to allow the evacuation of humidified air.

 The conveyor belt is driven by the drive rollers 52. This drive takes place regularly thanks to the presence of the support counter-rollers 53.

 At the opposite end, it is the mat which drives the roller 52 '- counter-roller 53' assemblies (which are crazy).

 When the material arrives at the downstream end of the strand 60A, it is transferred by the device 7 previously described to the underlying strand 60 ', and so on for all of the strands.

 As it travels inside the enclosure, the materials will be dehydrated under the action of hot air.

 It is important to note that the transverse conveyors, (with Archimedes) constituting the transfer members 7 ensure very beneficial mixing to homogeneous and complete drying of all the materials. Indeed, the distribution of the particles in the thickness of the layer is modified each time that one passes from one strand to the next strand.

Because of the great length of the belt 6, and its low speed of advance, the residence time of the materials in the enclosure is relatively long, for example of the order of 8 hours.

 At the end of this period, they are extracted and evacuated by the system 65.

 The dry matter content of the product obtained is approximately 80%.

 As has been explained with reference to FIG. 5, it is possible to disengage the drive rollers 52, by removing the amount 9 from the amount 533.

 The materials thus park in the enclosure, while the flow of hot air continues to act, since the engine 3 continues to operate.

 This therefore further increases the drying efficiency.

 I1 should be noted that, the carpet 6 being stopped, it is possible to obtain a natural heating of the enclosure 1 under the effect of the fermentation of the materials, which is exothermic.

 The heat is stronger at the lower part of the enclosure, because the fermentation is higher the drier the material.

 This results in a rise in the temperature of the enclosure, very beneficial for the dehydration of materials.

 Thus, it is possible for example in the middle of the cycle to temporarily stop the motor 3 in order to achieve self-drying of the materials by this fermentation effect; then the installation is restarted and drying continues.

 Such a method of course makes it possible to lower the energy consumption of the installation.

 Furthermore, if desired, or under certain specific conditions, in particular when the outside temperature is very low, it is possible to supply the turbines 20 and / or 21, for example to the upper turbine 21, with preheated air. from the roof box 13 exposed to the sun's rays.

 It would also be possible to provide additional air heating means by the Joule effect, for example in the form of electric heating resistors interposed on the path of the air current. These resistors could be supplied with electricity by a generator also driven by the heat engine 3.

 The elements located inside the enclosure are subject to relatively frequent and significant thermal variations. This results in particular in a linear amplitude of expansion of the mat which is large. However, as already said, this is absorbed by the automatic voltage regulation system 64, 61.

 Furthermore, when the rollers 52 are disengaged, in particular when it is desired to carry out a self-drying by fermentation effect - all of the rollers 52 and 52 'are free to rotate.

Thus, the carpet can adjust correctly to the temperature gradient of the enclosure, without excessive tension, although certain strands 60 or 60 ′ are at temperatures different from those of the other strands. If the deflection rollers were locked in rotation, this temperature gradient could

Claims (14)

 1. Installation for drying wet materials, such as poultry droppings for example, characterized in that it comprises  - a tunnel-shaped enclosure (1), with thermally insulated walls (10, 11, 12)  - means (2, 3, 4) for generating a current of hot air inside the enclosure (1)  - a movable endless belt (6) of great length, capable of transporting the materials in the form of a layer, alternately on each of its two faces, this belt (6) having a sinuous path composed of a set of horizontal strands superimposed (60, 60 ') passing over end deflection rollers (52, 52') so that the material transport faces and the direction of movement of the belt are reversed from one strand to another  - Transfer means (7) arranged at the downstream end of each of the carpet strands (60, 60 '), with the exception of the lower strand (60'B), and adapted to scrape the materials transported by this strand (60, 60 ') and to pour them on the underlying strand (60', 60)  - Means (8, 80, 81) for distributing and discharging the wet materials on the upper strand (60A) of the carpet (6)  - Means (65) for removing dry matter from the lower strand (60'B) of the carpet (6).  2. Installation according to claim 1, characterized in that the air flow is produced by turbines (20, 21) disposed at one end of the enclosure (1).  3. Installation according to claim 1 or 2, characterized in that the carpet (6) is driven by a heat engine (3) which produces heat used to heat the air flow generated in the enclosure (1) .  4. Installation according to claims 2 and 3 taken in combination, characterized in that the turbines (20, 21) are also driven by said heat engine (3), and that heat is used from the cooling water the engine (3) and the burnt gases produced by it.  5. Installation according to one of claims 1 to 4, characterized in that each end deflection roller (52, 52 ') is associated with a pressure roller (53).  6. Installation according to one of claims 1 to 5, characterized in that the set of deflection rollers (52) disposed at one end of the belt is positively rotated, while the other deflection rollers (52 ') are crazy.  7. Installation according to claim 6, characterized in that the set of deflection rollers (52) driven positively is disengageable.  8. Installation according to one of claims 1 to 7, characterized in that said transfer means (7) comprise a member (70) for scraping and deflecting the materials adapted to move the materials towards the outside of the carpet, beyond at least one of its edges (6a, 6b).  9. Installation according to claim 8, characterized in that said transfer means (7) comprise a transverse conveyor (71, 73) extending under the strand (60, 60 ') of the carpet.  10. Installation according to claim 9, characterized in that said transverse conveyor comprises an Archimedes screw (73) rotating in a trough (71) having a notch (710) for the passage of materials, and for their discharge on the underlying strand.  11. Installation according to claims 8 and 10 taken in combination, characterized in that said scraping and deflection member has the shape of a "V" whose tip is turned upstream of the strand, able to transfer the materials on both sides (6a, 6b) of the mat, while the Archimedes' screw (73) comprises two coaxial sections (73a, 73b) whose steps are inverted, so as to bring the materials towards the center of the sub-strand jacent.  12. Installation according to one of claims 1 to 11, characterized in that the downstream end zone of each strand of the belt, in which the scraping and the transfer of the materials takes place, rests on a support plate openwork (77).  13. Installation according to one of claims 1 to 12, characterized in that it comprises a device (13) for solar preheating of the air.  14. Installation according to one of claims 1 to 13, characterized in that it comprises a system (64, 61) for automatic adjustment of the tension of the belt (6).