FR2959428A1 - Stone sands dry fines eliminating device for e.g. ready-mixed concrete from pulverulent materials by suction, has elimination column to which upwelling current is applied to recover large solid particles at lower end of column - Google Patents

Abstract

The device (1) has a fine elimination column (2) connected by a suction pipe (3) to a dust collector (4), where the collector is equipped with sleeve filters (19). Upwelling current (F1) is applied to the elimination column so as to suck fine solid particles (7) towards an upper end (5) of a vertical pipe of the column and to recover the large solid particles at a level of a lower end (6) of a vertical pipe of the column, where the upper end of the vertical pipe is opened on the suction pipe, and lower end of the vertical pipe is opened on a large particle recuperating hopper (10).

Description

The technical field of the present invention is that of devices for separating dry solid particles of a powder material, in particular the devices for removing fines.

There are known devices for separating solid particles by application of an updraft. Thus, patent FR-2561140 discloses a summary wind separator against the current for the purpose of reducing the dedusting air consumption and energy consumption. To achieve this purpose, the separator has in a chamber, below the arrival line of the bulk material, a wall segment which widens conically towards its mouth in the collecting tank to delimit a distance particle braking.

Patent FR-2785551 discloses a device for mechanical separation of sand grains with a large particle size distribution entrained in a turbulent gas stream at high temperature resulting from a heat regeneration process of sand. The device includes a separation chamber for removing larger particles and a plate precipitation device for removing the remaining fine particles. However, in this patent, there is no powder material and the particles to be separated are present in the gas. This device aims to eliminate any impurities and does not eliminate the fines contained in the sand contrary to the invention. FR-2544636 relates to a method and a device for sorting divided products, in particular cement. Here it is not only a matter of separating the fine particles from the coarse particles by the centrifugal force, but also of dividing the fine product into several fractions of different particle sizes by division of the upflow into several partial streams of different size and speeds. It is therefore a centrifugal force grading device with a flow of air, for grains of relatively similar size. This device is not suitable for separating the fines contained in the sand contrary to the invention.

The object of the present invention is to provide a device that allows dry fines to be removed from pulverulent materials by suction. The invention therefore relates to a device comprising a fine elimination column connected by a suction duct to a dust collector equipped with bag filters, and an updraft is applied in said column to suck up its upper end. the finer solid particles called fines and recover at its open bottom end the coarse solid particles. According to one characteristic of the invention, the fines elimination column consists of a vertical duct whose upper end is open on the suction duct, the lower end of which is open on a coarse particle recovery hopper. and having on one of these side walls at its upper end a ramp for conveying the material. According to another characteristic of the invention, the fines removal column has on its inner wall shock bars and dispersion and / or shoes of the powder material. According to yet another characteristic of the invention, the shoes are constituted by horizontal plates fixed on the inner wall of the fines removal column, said plates being arranged in a vertically offset manner and situated in the vicinity of the lower end of the the column of elimination of the fines. According to yet another characteristic of the invention, the impact bars consist of horizontal bars fixed on the inner wall of the fines removal column, said bars being disposed offset both horizontally and vertically between the ramp. and the lower end of the fines elimination column and upstream of the hooves. According to yet another characteristic of the invention, the fines removal column has on its side wall an orifice for connection to a fan, said fan being a centrifugal blowing fan. According to yet another characteristic of the invention, the fines removal column comprises access hatches 5 on its side wall. According to yet another characteristic of the invention, the lower end of the fines removal column is arranged at a distance from the hopper to constitute a means for generating an air flow inside said column. of elimination of fines. According to yet another characteristic of the invention, the suction duct ensures the transfer of the air laden with fines from the fines removal column to the dust collector. According to yet another characteristic of the invention, the dust collector has a lower opening in order to evacuate the fines removed by the filters. According to yet another characteristic of the invention, the updraft is produced by a fan connected to the dust collector, said fan being a centrifugal suction fan. According to yet another characteristic of the invention, the device comprises a flow control system acting on the fan generating the updraft. According to yet another feature of the invention, the device is applied to the removal of fines from quarry sand. An advantage of the device according to the invention is that it allows the use of quarry sand in the composition of ready-to-use concretes, hydraulic concretes intended for prefabricated structures, hydrocarbon concretes, and more generally any use of quarry sands requiring a low fines content. Another advantage of the device according to the invention lies in a low power consumption. Other features, advantages and details of the invention will be better understood on reading the additional description which follows in connection with Figure 1 which shows the device for removing fines according to the invention. Hydraulic concrete for ready-mix concretes, block prefabrication or any other destination consists of cement, gravel, sand, chemical additives and water. The alluvial or aeolian natural sands generally used are appreciated because the grains that compose it are of regular shapes, smooth and little absorbent, ensuring the concrete a good maneuverability without overdosing of cement, thus limiting the phenomena of withdrawal at the time of setting. However, in regions with low natural sand production, these sands can be partially or totally replaced by quarry sands. These quarry sands are derived from crushing massive rocks in grinding-screening plants and are a consequence of gravel production. It is a sand called "tertiary" because it comes from rocks crushed successively three times to obtain tertiary gravel. These quarry sands are laden with fines that are particles smaller than about 0.063 millimeters. In the present application, the terms "fines" or "fine particles" refer to particles having dimensions ranging from about 0 millimeters to 0.063 millimeters and "coarse particles" to particles having dimensions greater than about 0.063 millimeters. The content of fines at the level of 10 to 15% by weight in the quarry sands hinders their use in concrete because the excess of fines absorbs the water of the concrete, reduces the workability and causes microcracking. To avoid these disadvantages, the fines content must not exceed 5 to 6% by weight of the sand.

To defil dry, it is necessary to work with a perfectly dry sand. This sand can for example come directly from the gravel and sand production plant and be taken from the storage silo of these sands.

In Figure 1, the device 1 according to the invention comprises a column 2 for removing fines formed by a vertical duct 9 having at its upper end 5 a routing ramp 12 of the material. The powdery material to be defiltered is introduced in the form of aggregates 20 via the ramp 12 and descends by gravity into the column 2 through which a rising current is shown schematically by the arrows F1. The granules 20 entering the device 1 have a particle size of between about 0.2 millimeters and 0.4 millimeters. The aggregates 20 are conveyed to the delivery ramp 12 by any means, in particular by means of a belt conveyor 21. The upward flow F1 causes the finest particles 7 contained in the powder material towards the upper end 5 of column 2, while the coarser particles 8 heavier will continue to descend by gravity to the lower end 6 to be recovered in a hopper 10 recovery of the defiltered material located under column 2. The current of air Incoming is shown schematically by the arrows F2 and enters the column 2 at its lower end 6 located at a distance from the hopper 10. The opening constituted by the delivery ramp 12 is equivalent in size to the width of the conveyor belt in order to limit as much as possible the entry of air through this opening. Almost all of the suction is thus done at the end 6 of the column 2. In order to promote the separation of the coarse particles 8 and the fines 7, the column 2 for eliminating fines has on its inner wall bars 13 and / or clogs 14 shock and dispersion of the material. These bars 13 force the material to separate into several jets to maximize the specific surface of the material in contact with the updraft F1. Indeed, the impact of the material on the bars 13 or on the residual sand possibly present on said bars 13 promotes the separation of coarse particles 8 and fines 7, said fines 7 may tend to remain stuck to coarse particles 8 for example to cause of residual moisture or electrostatic forces. The bars 13 are constituted by horizontal bars forming with the inner wall of the column an angle of substantially 90 °. The shoes 14 also make it possible to break the fall of the aggregates inside the column and to deflect their trajectory. These shoes 14 are in the form of horizontal plates fixed on the inner wall of the column 2 in particular arranged vis-à-vis and offset vertically. The plate form of these shoes 14 allows in particular a natural filling material which then forms a tilted pile at a slope angle, this design avoiding abrasion problems. The shoes 14 form with the side wall an angle of substantially 90 °. The bars 13 are located midway inside the column 2 and the shoes 14 are located near the end 6. The abrasion in the device 1 is reduced because there is little contact between the powder material incoming and the elements constituting said device. As soon as it enters the device 1, the powdery material is put into quasi-suspension in the upward flow F1 and the points of contact in its fall are the bars 13 placed transversely in the column 2 and the shoes 14 which they are not in contact with. direct with the material falling as protected by the accumulated material in the form of heap. In addition, the maximum speed of the upward flow F1 in the suction duct 3 is adapted to avoid contact wear between the fine particles 7 which pass through it and the metal constituting said duct 3. These measures aim at greatly limiting the abrasion in the device can reduce the maintenance and replacement of worn plates and therefore lead to lower maintenance costs and increased utilization rates of the device by reducing downtime of the device for example for maintenance. The column 2 for eliminating fines has on its side wall an orifice 11 for connecting a fan 15 under the delivery ramp 12. This fan 15 may be a centrifugal blower to produce a pulsed air stream schematized by the arrows F3 which allows a first separation of the fine particles 7 of the coarse particles 8. The column 2 also has on its side wall one or more access hatches 16 allowing in particular the maintenance of the device.

The fines 7 are driven through a suction duct 3 by the updraft Fl to a dust collector 4 equipped with a bag filter 19. The fines 7 are collected by the filters 19 and stored in a fine hopper 22. located under the dust collector 4.

The thermal flow Fl is produced by suction of the air by means of a fan 17 connected to the dust collector 4 and which can be a centrifugal suction fan. The air flow involved in column 2 is between 10,000 and 30,000 m3 / h and depends on the tonnage to be treated.

The upward flow F1 traversing the column is adjustable through a flow control system 18 placed upstream of the fan 17 which produces the updraft F1 and to change the suction. This adjustment system 18 may be mechanical, for example in the form of a damper or diaphragm or a tilter, that is to say an obstacle present in the pipe modulating the passage of the air, or electronic such as a variable speed drive acting on the fan motor 17. This flow control system must ensure a variable air flow of 10,000 and 30,000 m3 / h. This setting of the rising current F1, controlled by the measurement of the depression in the column, makes it possible to adjust the amount of fines 7 extracted from the material. Thus, the depression in the column must be of the order of 300 daPa, this depression being measured by a pressure switch placed downstream of said column 2, for example at the suction duct 3 before the dust collector. The higher the flow F1 flowing through the column 2, the greater the amount of fine extracted and the size of the particles that compose it are important. The power consumption of the device is low. Considering in the device a belt conveyor, a centrifugal suction fan and a centrifugal blowing fan, the consumption is about 40kW for a production of 50 t / h of defiltered sand. According to a particular embodiment, the conveying ramp 12 comprises orifices through which air is pulsed, for example by means of fans, in order to separate the fines 7 from the aggregates 20 by direct blowing. The entire device according to the invention is made of steel or of any material having the same properties, in particular of resistance to abrasion.

Claims (13)

REVENDICATIONS1. Device (1) for removing dry fines from pulverulent materials by suction, characterized in that it comprises a column (2) for removing fines connected by a suction pipe (3) to a dust collector (4) equipped with bag filters (19), and an updraft (F1) being applied in said column (2) to suck towards its upper end (5) the finer solid particles (7) called fines and recover at from its lower end (6) open the coarse solid particles (8). 2. Device (1) for removing dry fines from pulverulent materials by suction according to claim 1, characterized in that the column (2) for removing fines is constituted by a conduit (9) vertical whose end upper (5) is open on the suction duct (3), whose lower end (6) is open on a hopper (10) for collecting coarse particles (8) and having on one of these side walls (11). ) at its upper end (5) a routing ramp (12) of the material. 3. Device (1) for removing dry fines of powdered materials by suction according to claim 1 or 2, characterized in that the column (2) for removing fines has on its inner wall bars (13) of shock and dispersion and / or shoes (14) of the powder material. 4. Device (1) for removing dry fines of powdered materials by suction according to claim 3, characterized in that the shoes (14) are constituted by horizontal plates fixed on the inner wall of the column (2) d elimination of the fines, said plates being disposed vertically offset and located in the vicinity of the lower end (6) of the column (2) for removing fines. 5. Device (1) for the removal of dry fines of pulverulent materials by suction according to claim 3 or 4, characterized in that the bars (13) of shocks consist of horizontal bars fixed on the inner wall of the column ( 2) for removing fines, said bars (13) being arranged offset both horizontally and vertically between the delivery ramp (12) and the lower end (6) of the elimination column (2) fines and upstream of the hooves (14). 6. Device (1) for removing dry fines of powdered materials by suction according to any one of the preceding claims, characterized in that the column (2) for removing fines has on its side wall an orifice (11). ) to be connected to a fan (15), said fan (15) being a centrifugal blower. 7. Device (1) for removing dry fines of powdered materials by suction according to any one of the preceding claims, characterized in that the column (2) for removing fines comprises access hatches (16). on its side wall (11). 8. Device (1) for removing dry fines of powdered materials by suction according to any one of claims 2 to 7, characterized in that the lower end (6) of the column (2) for eliminating fines is arranged at a distance from the hopper (10) to constitute a means for generating an air flow (F2) inside said column (2) for removing fines. 9. Device (1) for removing dry fines of pulverulent materials by suction according to any one of the preceding claims, characterized in that the suction duct (3) ensures the transfer of the charged air into fines of the column (2) for removing fines to the dust collector (4). 10. Device (1) for removing dry fines of powdered materials by suction according to any one of the preceding claims, characterized in that the dust collector (4) has a lower opening to remove the fines (7) eliminated by the filters (19). 11. Apparatus (1) for removing dry fines of pulverulent materials by suction according to any one of the preceding claims, characterized in that the updraft (Fl) is produced by a fan (17) connected to the dust collector (4). said fan (17) being a centrifugal suction fan. 12. Device (1) for removing dry fines from pulverulent materials by suction according to claim 11, characterized in that it comprises a system (18) for controlling the flow acting on the fan generating the updraft (Fl) . 13. Application of the device according to any one of the preceding claims to the removal of fines quarry sand.