FR2916745A1 - CONTAINER FOR TRANSPORTING POWDER OR GRANULAR PRODUCTS AND METHOD OF UNLOADING - Google Patents

Abstract

Container for the bulk transport of cohesive powdered or granular products, comprising a rigid outer casing (1), having a rear wall and a front wall, an upper wall and a bottom wall and two side walls and, inside of the outer casing, a flexible bag (10) for containing the powdered or granular product, means (20, 14, 16a, 16b) for holding the flexible bag deployed within the rigid outer casing of the container, characterized in that it comprises at least one destructuring means (19) of the powdered or granular product contained in the bag disposed at least under the front half of the bag between the bottom wall (10b) of the container. known and the bottom wall of the outer shell rigid and capable of lifting the product of a height at least equal, and preferably greater, to the shear path of the powdered product or granular and on a surface at least equal to 10 % of total area from the bottom wall of the know.

Description

The present invention relates generally to a container for the

  transporting and unloading bulk cohesive powdered or granular products, such as cements and a method of unloading these powdered or granular products from the container.

  It is conventional to transport the powdered or granular products in containers comprising a rigid outer envelope inside which is fixed a soft bag (liner) containing the powdered or granular product. The know has at least one loading opening located at its upper part for introducing, generally pneumatically, the product in the know. The bag also has an unloading opening at its bottom which allows the powdered or granular product to be unloaded by gravity when the container is tilted. A container as generally described above is in particular the subject of European Patent EP-1 101 712. The container of this European patent which is intended for the transport of powder or granular products flowing easily comprises airbags, triangular shape, located under the know on both sides of the unloading opening so that after swelling of the cushions is obtained during unloading improved guidance of the powdered product or granular to the unloading opening of the know. EP 0 538 563 also describes a container as described above for the transport and unloading of free-flowing powder or granular products.

  Some powdered or granular products exhibit a self-consolidation phenomenon during storage and this results in a very difficult flow. This is the case with cement, in particular molten cement, which is a powder whose particles have an average diameter of 20 μm, with a maximum of 5% by weight of particles having a diameter greater than 90 μm and 100% a smaller diameter. at 100 pm. More specifically, certain powdered or granular products, and in particular cement, in particular molten cement, have a high compressibility of up to 28%. The compressibility corresponds to the difference in volume between the compacted and unpacked powdered or granular product, expressed in percent. It is measured according to the protocol of ISO EN 787/11, method USP2. This behavior is favorable to a consolidation of the powdered or granular product, and it is actually observed that the density of the product bed increases during storage and / or transport. Depending on the settling conditions during storage and / or transport, these powdered or granular products can develop a cohesion or very strong cohesion. This behavior is evaluated with an annular cell. This apparatus makes it possible to measure the internal friction (shear stress) of the powdered or granular product when it is in motion. These experiments make it possible to calculate a flowability index i, which indicates the ability of a powdered or granular product to flow. The bigger i is, the easier the product flows and vice versa. In this case, the flowability of the powdered product, in particular molten cement, changes according to the storage conditions. To simulate these conditions, the cement is stored inside the annular cell under different temperature and humidity conditions by applying a normal force to the powder. The intensity of this force is chosen to correspond to the maximum pressure experienced by the powder in the container. This maximum pressure is estimated at 7500 Pa in the case of cement. According to Jenike's notation (Storage and flow of solids, Andrew Jenike, Bulletin of the Engineering Experiment, State University of UTAH, n 123 Nov. 1964, Salt Lake City, UTAH), a free-flowing powder presents a value of i> 10. From 10 to a value greater than 4, the powder is easily flowable (easy flowing), from 4 to a value greater than 2, the powder is cohesive, and from 2 to 0 the powder is very cohesive . As the cement is not packed (no stress applied before measurement), it is easily castable. On the other hand, after packing, it becomes cohesive, even very cohesive.

  The method of use of the annular cell is also described in the article by Andrew Jenike mentioned above. Once packed, it is observed that the cohesive powder or granular products, including cement, need a certain constraint to be set in motion, that is to say to aerate the product again. Once the product is aerated, the internal friction returns to the initial values. Before settlement, the stress must be applied over a certain distance to be effective. This minimum distance is called the shear path. This destructuring constraint and this shear path are also measured with the annular cell. They define the intensity of the force and the minimum displacement that will have to be applied to the product to be able to destructure it. When unloading a cohesive product, such as cement, from the container's knowledge by tilting the container (which usually contains large masses of product, at least 20 tonnes in the case of cement), if the mass before the bed of product, that is to say the mass of product contained in half of the bag adjacent to its unloading opening begins to flow relatively easily by gravity during the gradual tilting of the container, the rear mass of the bed powder, especially in the case of cement, will not flow smoothly but move suddenly and block, deforming and tearing the knowledge. The know then makes folds that trap the powder. This is what happens in the case of containers of the documents mentioned above. US Pat. No. 6,623,233 relates to a method and an apparatus for discharging bulk material, which flows with difficulty from a container. This patent proposes for the unloading of bulk products with difficult flow an air supply device for the fluidization of the bulk material which is introduced directly into the bulk material of the container. This extraction technique by direct introduction of air by means of a lance placed in the mass of the product is very difficult to implement, if only by the introduction of the lance in the full container. Deconstructing can only be local unless you move the spear in the container. The present invention therefore aims to provide a container for the bulk transport of cohesive powder or granular products, for example cement, which overcomes the disadvantages of prior art containers, and in particular ensures regular and safe unloading. powdered or granular product by simple gravity. The present invention also aims to provide a method of unloading, by simple gravity, the cohesive powder or granular product and which ensures a regular and safe discharge of the powdered or granular product by simple gravity. The above objects are achieved according to the invention by a container for the bulk transport of a cohesive powdered or granular product, comprising a rigid outer casing, having a rear wall and a front wall, a top wall and a wall. base and two side walls and, inside the outer casing, a flexible bag for containing the powdered or granular product and having a front wall, a rear wall provided with at least one loading aperture and at least one unloading opening of the powdered or granular product, an upper wall and a bottom wall, and two side walls, means for holding the flexible bag deployed inside the rigid outer casing of the container , characterized in that it comprises at least one means of destructuring the powdered or granular product contained in the knowledge disposed at least under the front half of the knowledge between the bottom wall of the known and the paro the bottom of the rigid outer casing and capable of lifting the powdered or granular product situated above a height at least equal to, preferably greater than, the shear path of the powdered or granular product and on at least one surface equal to 10% of the total area of the bottom wall of the known. The invention also relates to a method of unloading a cohesive powdered or granular product contained in a flexible bag of a container, said bag having a front wall and a rear wall provided with at least one loading opening and an unloading opening, the unloading comprising the progressive tilting of the container so that the powdered or granular product flows by gravity through the unloading opening, characterized in that it comprises, before the tilting of the container, a step of destructuring at least a portion of the cohesive powder or granular product contained in at least one half prior to the knowledge of raising at least said portion of the powdered or granular product of at least equal height, preferably greater than shear path of the powdered or granular product, said part corresponding to a surface at least equal to 10% of the total surface of the bottom wall of the know.

  The invention also relates to a device for extracting the powdered or granular product during unloading by gravity which, in particular, ensures a transfer of the product away from any moisture, including ambient air from the knowledge to a receiving device.

  According to the invention the extraction device comprises (a) a connecting piece having an open front part that can be connected to an unloading opening of a container comprising a flexible bag containing a powder or granular product that can be unloaded simply by gravity, and a rear portion secured to the front portion and comprising at least one tubular, preferably bent; (b) a device for receiving and / or transferring the powdered or granular product; and at least one flexible tubular connection, in accordion, putting in communication the front part of the connection piece and the receiving and / or transfer device. In particular, the flexible tubular connection may be connected to a tubular connection of the receiving and / or transfer device. Preferably the extraction device comprises 3 flexible tubular connections connected by their ends 3 bent pipes and 3 flexible tubular connections connected their ends 3 bent pipes and 3 tubular connections of the receiving device and / or transfer.

  Thus, when the container is lifted to discharge the powdered or granular product, the extraction device continuously adapts to the inclination of the container and allows continuous unloading without venting. By cohesive granular or powdery product is meant a powdered or granular product which has a Jenike rating of flowability i of 4 or less, more preferably 2 or less. In general terms, the destructuring means must cause the product in powder or granular form to be lifted by a height at least equal to the shear path, preferably greater than this, and over at least 10% of the surface. preferably at least 13% and more preferably at least 15% of the total area of the bottom wall of the bag. Preferably, especially in the case of cements, the lifting height is at least 8 mm, preferably 2 to 3 cm. The destructuring means is located at least under the front half of the bag and preferably consists of an air bag.

  Obviously, the airbag must be able to withstand a pressure greater than that exerted by the bed of powder on the bottom wall of the rigid outer envelope of the container. In addition, the thickness of the inflated cushion should be equal, preferably greater than the shear path of the powdered or granular product. Thus, in the case of a bed of powder exerting on the bottom wall of the rigid outer envelope of the container a pressure of 0.1 bar (this is the case of cement in standard containers), the airbag must be able to withstand a minimum internal pressure of 0.1 bar. Ideally, it was observed in this case that a pressure of 0.2 bar was sufficient. In addition, to ensure a steady gravity flow of the powdered or granular product during unloading, the airbag must, in the inflated state, have a thickness at least equal to the shear path, preferably greater (for example 8mm or more, preferably 2 to 3 cm, especially in the case of cements) and ensure the lifting of a volume of powdered or granular product corresponding to at least 10%, preferably at least 13% and better still at least 15% of the surface of the bottom wall of the bag multiplied by at least the value of the shear path, preferably a higher value. However, the surface of the airbag should not be such that the swelling of the cushion would result in a simple uniform rise of the powdered or granular product. To achieve destructuring, it is necessary that the displaced volume induces shearing of the powdered or granular product. The distribution of displaced volume may be generally expressed as an oscillation whose wavelength must be at most equal to the length of the bottom wall of the bag, and at least equal to twice the shear path. amplitude of the wave being at least equal to the shear path. Consequently, the destructuring means preferably raises a surface of the bottom wall of the bag at most equal to 50%, better still at most equal to 25% and better still at most equal to 20% of the total surface of the wall. background of the know. For example, for a container having a bottom wall of 6m x 2.4m (and therefore a known whose bottom wall has a surface of approximately the same size), we can use a 2m airbag x 1 m and can be inflated to a thickness at least equal to the shear path (for example at least 8 mm, and preferably 2 to 3 cm, especially in the case of cements). Of course, it is possible to use several air bags arranged under the bag, and in particular an air bag under each of the front and rear halves of the bag. The airbags may be uniform or compartmentalized, especially honeycombed, so as to have a corrugated uplift surface to further improve the shear of the powdered or granular product. Although only one swelling and deflation of the airbag according to the invention is necessary to obtain the destructuration of the powdered or granular product, several successive swelling and deflation can be carried out to increase the destructuring of the powdered or granular product. When gravity unloading, the cushion is deflated so as not to prevent slipping of a portion of the powdered or granular product to the outlet. The destructuring means may also be a vibration means such as a vibrating plate located under the knowledge, in particular the front half, whose amplitude and frequency are such that the vibration leads to a displaced volume of powdered product or granular similar to that of the cushion. The vibrating plate produces a vertical or elliptical oscillation movement, the direction of rotation then being such that the plate rises when it is moved towards the front wall of the bag and goes down when it is moved towards the rear wall of the bag. By way of example, especially in the case of cements, vibrations of amplitude of 2 to 3 mm and frequency of 100 to 300 rpm will be used. Although this vibrating plate can be used alone to destructure the powdered or granular product and facilitate its displacement towards the outlet, it is preferably used in conjunction with the airbag and then essentially serves to facilitate the movement of the powdered product. or granular towards the exit. Unlike the airbag, the vibrating plate can be used throughout the unloading process.

  One or more vibration devices may also be disposed on a safety frame located at the rear of the container to develop the destructuring produced, for example by the airbag. It has been found that the use, especially in the case of cements, of vibrations of amplitude 2 to 3 mm and of frequency 100 to 300 rpm led to a destructuring of powdered or granular products. Preferably, especially in the case of cement, the destructuring means applies to the powdered or granular material to be destructured a shear stress of at least 2700 Pa over a distance of at least 6 mm, preferably at least 8 mm. . The remainder of the description refers to the appended figures which represent, respectively: FIG. 1, a schematic perspective view of a container according to the invention, with the exception of the outer rigid envelope; Figure 2 is a view of the rear portion of the container according to the invention and the extraction device; and Figure 3, an exploded view of the safety frame, the connecting frame and the extraction device located at the rear of the container; and Figures 4A and 4B, diagrams of the rear of the container and the extraction device at the beginning and end of unloading. Referring to Figures 1 and 2, there is shown a container according to the invention. The container comprises an outer casing 1, rigid, of generally parallelepipedal shape having an upper wall, a bottom wall, a front wall, a rear wall and two side walls. The rear wall is generally constituted by a door allowing access to the openings for loading and unloading of a flexible bag. Inside the rigid outer casing is a flexible bag 10, for example made of polyethylene, of generally parallelepipedal shape, comprising an upper wall 10a, a bottom wall 10b, a front wall 10c, a rear wall 10d, and two side walls 10e, 10f. The rear wall 10d of the bag 10 is provided in its upper part with one or more loading openings 11 (2 in FIG. 1), and in its lower part with an unloading opening 12, preferably extending over the entire width of the knowledge, for example of rectangular shape.

  The bag 10 is attached to a lifeline 2 of the upper wall of the rigid outer casing 1 by means of tensioners 20 disposed at the periphery of the upper wall 10a of the bag. A backdrop 14 is disposed between the front wall 10c, the bottom wall 10b and to the bottom of the loading openings 11 of the rear wall 10d of the bag and the corresponding walls of the rigid outer casing 1 and is maintained by means of connecting bars 15a, 15b, 15c attaching to the rigid outer envelope 1 of the container, for example by means of straps (not shown). The backdrop 14 also has an unloading opening similar to that of the bag 10 and facing it. The bag 10 is attached to the cloth 14 by double-sided adhesive tapes 16a, 16b. On the rear face 10d of the bag 10 is placed a safety frame 17 which is removably attached to the side walls of the rigid outer casing of the container and, in correspondence with the unloading opening 12 of the bag and that of the fabric 14, a connecting frame 18 to an extraction device 30 (FIG. 2). According to the invention, an airbag 19 is disposed between the bottom wall 10b of the bag 10, generally under the cloth 14, and the bottom wall of the rigid outer casing, close to the front wall 10c of the know. This airbag 19 is located entirely under the front half of the bottom wall 10b of the know. The airbag 19 is connected by an inflation adapter 20 to a hose 21 terminating at the rear wall 10d by a connector 22 for connection to a source of swelling gas (not shown).

  Particularly in the case of cement, the airbag 19 is capable of holding a pressure of at least 0.2 bar and lifting the powdered or granular product located above a distance of 2 to 3 cm. In order to develop the destructuration produced by the airbag 19 (or the vibrating plate) during the unloading of the pneumatic vibrators 23 are fixed on the safety frame 17 located at the rear of the container. These pneumatic vibrators make it possible to vibrate the entire structure of the container during the entire unloading. In the case of cements, the vibration has an amplitude of 2 to 3 mm and a frequency of 100 to 300 revolutions / minute.

  Referring more particularly to Figures 2 and 3, will now be described the extraction device 30 which is attached to the connecting frame 18 during unloading. The extraction device 30 comprises a connecting piece 31 comprising a front portion 31a intended to be fixed on the connecting frame 18 and whose opening corresponds to the unloading opening of the bag 10 (and the backdrop 14) and a rear portion 31b integral with the front part and consisting of 3 bent pipes (obviously the number of pipes may be smaller or greater).

  A flexible, accordion-shaped tubular connector 32 is engaged at one of its ends in each of the elbows of the connecting piece 31, and at the other end in a tubular connection 33 of a receiving hopper 34. Thus, as As shown in Figures 4A and 4B, the extraction device 30 allows gravity discharge of the powdered or granular product by tilting the container upwardly about a pivot axis 35 located at the bottom of the rear portion of the container. The extraction device 30 makes it possible to discharge the powdered or granular product in the absence of air, and therefore of the humidity of the air, which is important in the case of products sensitive to humidity, such as cements. The unloading of the powdered product is therefore carried out as follows: After opening the doors forming the rear wall of the rigid outer casing, the bag is opened and the extraction device 30 is connected to the connection frame 18. The pneumatic vibrators 23 are fixed to the safety frame and the connection of these vibrators and the airbag 19 to a supply of compressed air. The airbag is inflated to a pressure of 1 bar in 45 seconds and deflated the cushion in 60 seconds. The cushion is inflated to the pressure of 1 bar in 60 seconds and deflated in 60 seconds. The pneumatic vibrators are then started. We begin then the inclination of a container. The material begins to flow around an angle of 11. The incline is continued up to about 20 and a dwell time is marked. When nothing else flows, the inclination is increased to an angle of 30 and a dwell time is again scored. When nothing else flows, the inclination is increased again up to a maximum angle of 45. The entire emptying operation lasts no more than 45 minutes. We stop the vibration and we go down the container. The connections to the sources of compressed air are disconnected and the extraction device 30 is disconnected. If necessary, the empty container (with the knowledge and the safety frame still in place) can be moved to a container undressing zone where the security framework, the knowledge and associated equipment are removed. The product contained in the receiving hopper can be conveyed, for example pneumatically, in a storage device.

Claims (17)

  Container for the bulk transport of cohesive powdered or granular products, comprising a rigid outer casing (1), having a rear wall and a front wall, an upper wall and a bottom wall and two side walls and, at inside the outer casing, a flexible bag (10) for containing the powdered or granular product and having a front wall (10c), a rear wall (10d) provided with at least one charging port (11) and at least one unloading port (12) of the powdered or granular product, an upper wall (10a) and a bottom wall (10b), and two side walls (10e, 10f), means (20, 14), , 16a, 16b) for holding the flexible bag deployed inside the rigid outer casing of the container, characterized in that it comprises at least one destructuring means (19) of the powdered or granular product contained in the know disposed at least under the half before the know between the bottom wall (10b ) of the known and the bottom wall of the outer shell rigid and capable of lifting the product of a height at least equal, and preferably greater than, the shear path of the powdered or granular product and on a surface at least equal to 10%, preferably at least 13% and better still at least 15% of the total surface of the bottom wall of the bag.   2. Container according to claim 1, characterized in that the destructuring means comprises an airbag (19).   3. Container according to claim 1, characterized in that the destructuring means is a means of vibration.   4. Container according to any one of the preceding claims, characterized in that the means of destructuring causes a lifting of the powdered or granular product of at least 8 mm and preferably from 2 to 3 cm.   5. Container according to any one of the preceding claims, characterized in that the product surface powder or granular raised is at most equal to 50%, preferably at most equal to 25% and preferably at most equal to 20% of the total surface of the bottom wall of the know.   Container according to any one of the preceding claims, characterized in that the destructuring means applies to the powdered or granular material a shear stress of at least 2700 Pa over a distance of at least 6 mm, preferably at least 8 mm.   7. Container according to any one of the preceding claims characterized in that it further comprises a propagation means of the destructuration (23).   8. Container according to claim 7, characterized in that the propagation means (23) is a device applying a vibration to the entire structure of the container.   9. Container according to claim 8, characterized in that the device applying the vibration (23) is disposed near the rear wall (10d) of the know.   A method of discharging a cohesive powdered or granular product contained in a flexible bag (10) of a container, said bag having a front wall (10c) and a rear wall (10d) provided with at least one opening for loading (11) and an unloading opening (12), the unloading comprising the progressive tilting of the container so that the powdered or granular product flows by gravity through the unloading opening (12), characterized in that it comprises, before the tilting of the container, a step of destructuring at least a portion of the powdered or granular product contained in a half before the knowledge of which raises at least said portion of the powdered or granular product d a height at least equal to, preferably greater than, the shear path of the powdered or granular product, said portion corresponding to a surface area of at least 10%, preferably at least 13% and more preferably at least equal to e to 15% of the total surface of the bottom wall of the bag.   11. The method of claim 10, characterized in that the lifting height is at least 8mm, preferably 2 to 3 cm.   12. The method of claim 10 or 11, characterized in that the displacement is obtained by means of an airbag (19).   13. Method according to any one of claims 10 to 12, characterized in that it further comprises a propagation step of the destructuring during the progressive tilting of the container.   14. The method of claim 13, characterized in that this propagation step consists of a vibration applied to the entire structure of the container.   15. Extraction device (30) comprising (a) a connecting piece (31) having an open front portion (31a) connectable to an unloading opening (12) of a container comprising a flexible bag (10) containing a powder product or granular simply dischargeable by gravity, and a rear portion (31b) integral with the front portion and comprising at least one tubing, preferably bent; (b) a device for receiving and / or transferring (34) the powdered or granular product; and at least one flexible tubular connector (32), in accordion, putting in communication the front part of the connecting piece (31) and the receiving and / or transfer device (34).   Extraction device according to claim 15, characterized in that the (or) flexible tubular connection (s) (32) is (are) connected to the receiving device and / or transfer (34) by means of (or) tubular connection (s).   17. Extraction device according to claim 15 or 16, characterized in that it comprises at least 3 flexible tubular connections.