FR2602438A1 - AIR CLASSIFIER OF PULVERULENT MATERIALS - Google Patents

Abstract

THE INVENTION CONCERNS AN AIR CLASSIFIER FOR PULVERULENT MATERIALS OF THE TYPE INCLUDING A CYLINDRICAL SEPARATION CHAMBER 1 LINKED TO A DEVICE 2 INTENDED TO CREATE IN IT AN UPFLOW OF AIR, A GROUP OF FUNNELS 14 FIXED ACCORDING TO THE HEIGHT OF THE CHAMBER, A HELICOIDAL ELEMENT 15 MOUNTS BETWEEN EACH PAIR OF FUNNELS. ACCORDING TO THE INVENTION, THE DEVICE INCLUDES AT LEAST TWO PLATES 16 MOUNTED ABOVE EACH HELICOIDAL ELEMENT, VERTICALLY ARRANGED AT A DISTANCE EQUAL TO ONE FROM THE OTHER ACCORDING TO THE PERIMETER OF THE CHAMBER APPLYING TO THE WALL OF THIS, THE WIDTH OF EACH PLATE DOESN'T EXCEED THE DIFFERENCE BETWEEN THE RADIUS OF THE FUNNEL OPENINGS. THE INVENTION IS IN PARTICULAR APPLICATION IN THE MINING, CHEMICAL, METALLURGICAL, FOOD AND CONSTRUCTION INDUSTRIES.

Description

The present invention relates to devices for separation

  pulverulent materials produced while particles of a mixture fall into ascending currents of gas or air and particularly relates to an air classifier of the powdery materials. The classifier which is the subject of the invention is intended for the separation of dispersed powdery materials containing particles of up to 10 mm, which takes place in two phases with a grain size of 0.02 to 5 mm. The invention finds application in particular in the mining, chemical, metallurgical, building and other branches of industry where it is necessary to separate solid powdery materials according to the particle dimensions, for example sand. , gravel, ores. It is also possible to use it in agriculture and in the food industry, for example, for the separation of the products resulting from the refining of the particles according to their size as well as to separate the grains from the grains of the grains of the

bad grass.

  In air classifiers of pulverulent materials, the main factors that influence the

  separation are the gravitational force of the particles and the resistance they oppose to the updraft of air.

  The separation of particles in a stream of air occurs not by size, density, or shape, but by a generalized dynamic characteristic that takes into account all these factors. This characteristic of the particles is their rate of displacement in a two-phase stream. The larger the difference in particle velocities, the easier the separation. The maximum possible difference between the particle velocities is obtained at unstabilized

  of two-phase current displacement.

  It follows that, to obtain a good quality of separation of a powdery material in an air classifier, it is necessary to transfer several

  times the two-phase current under unstable conditions.

  The efficiency of the operation of the classifier

  to air or the separation quality of a powder material is characterized, for example, by the criterion of Eder-Mayer.

  The unstable regimes of the movement of the two-phase currents can be obtained by various modes such as: mechanical or dynamic braking, abrupt or progressive variation of the direction of movement of the

current, application of vibrations.

  An air classifier for pulverulent materials is already known (see USSR Serial Certificate No. 882659, Cl.Int. BO7B 4/08, 1981) having a cylindrical separating chamber mounted vertically and in communication with a device creating an updraft of air therein. An opening for evacuation of the fine fraction is made in the upper part of said chamber, an opening is made in its lower part for the discharge of the coarse fraction and an opening for the loading of the powdery material is provided in its part. median. In addition, the helical elements are fixed on the inner surface of the chamber along its height and serve to swirl the updraft of air. These helical elements consist of plates arranged along a helical line, two of the aforementioned neighboring plates being oriented in opposite directions. These helical elements swirl the current to two

  phases by giving it an unstable regime movement.

  In this case, the larger particles, ie those with the largest mass, are projected under the action of centrifugal forces towards the wall of the chamber at a higher speed, whereas the particles Thinner are projected at a slower speed. Thus, the particles of the powder material are separated under the action of the centrifugal forces in the radial direction according to their size. The finer particles, which

  remain in the central part of the chamber are driven by the updraft of air. A residual portion.

  large particles and fine particles are evacuated under the action of centrifugal forces towards the part

  peripheral, towards the wall of the separation chamber.

  Its movement slows down and falls following the helical elements. The separation efficiency of this air classifier from pulverulent materials is poor because the particles are unevenly distributed according to the cross-section of the chamber and, as a result, a large amount of fine particles is entrained.

  with large particles of the powder material.

  There is also known an air classifier (see USSR N 912302, Cl.Int.BO7B 4/08, 1982) in which a group of funnels intended for the discharge of powder material from of the wall of the chamber, is fixed on the wall of the separation chamber according to its height. A helical element is disposed between two funnels for swirling the updraft of air. The helical elements are fixed on a shaft arranged along the axis of the chamber

  and mounted so as to be rotatable.

  Rotating elements greatly complicate the design of the air classifier and increase the

  energy consumption for its operation.

  There is also known an air classifier for pulverulent materials (see USSR 30 N 1093364, Cl.Int. BO7B 7/00, 1984) characterized by a simpler design and having a cylindrical separation chamber. vertically mounted, linked to a

  device that creates an updraft of air in it.

  A group of funnels for discharging powder material from the wall of the separation chamber is mounted along the height of said chamber.

  A helical element is mounted between each pair of funnels for swirling the updraft of air. An opening for the loading of the powdery material is made in the middle part along the height of the separation chamber. An opening for the discharge of the fine fraction of the powder material is provided in the upper part and an opening for the discharge of the coarse fraction of the powder material is made in the lower part; During classification, the particles of a powdery material are distributed in a manner

  irregular following the section of the separation chamber.

  The concentration of the particles measured in the peripheral zones of the separation chamber between the funnel and the helical element, under the conical surface of the funnels, is at least two times greater than that in the central part of the chamber and the Fine particles are removed from the peripheral zone together with the coarse fraction. This phenomenon results in the "dissipation" of the separation interface and at a low classification efficiency. The separation efficiency obtained in known air classifiers, evaluated according to the Eder-Mayer criterion, does not exceed 60 to 65% of the material flow rate pu 4 kg / m3 oy = Q / Q2 'Q is the classifier yield for the initial feed in kg / h, and

Q2 is the air flow in m3 / h.

  It should be noted that the nature of the particle distribution following the section of the separation chamber is substantially influenced by the ability of the particles of the powder material to aggregate and by their density. In the peripheral zone, the fine particles stick to the large particles and form therewith condensed agglomerates having a large mass, which settle and are entrained with the coarse fraction. The separation of high density pulverulent materials requires high velocities of the air stream. The action of the centrifugal forces on the particles is then strong and, as a result, the largest portion

  of particles is thrown towards the peripheral zone.

  The subject of the present invention is therefore an air classifier for pulverulent materials in which the separation chamber is equipped with elements which ensure a more even distribution of the particles of the powder material according to its section and raise

  thus the separation efficiency of the powder material.

  The problem thus posed is solved with the aid of an air classifier for pulverulent materials comprising a separating chamber arranged vertically and connected to a device which creates therein an updraft of air, depending on the height of the which is attached a group of funnels for discharging the powder material 15 from the wall of the separation chamber, a helical member being mounted between each pair of funnels for the swirling of the air updraft, the classifier comprising also an opening in the middle portion along the height of the separation chamber for loading a powder material, an opening in the upper part for the discharge of the fine fraction of the powder material and an opening in the lower part for the evacuation of the fat fraction, characterized, according to the invention, in that at least two p The lacquers are mounted above each helical element and are arranged vertically at an equal distance from each other along the perimeter of the chamber, so that each plate is applied by an edge against the wall of the chamber. , the width of each plate not exceeding the difference between the radii of the openings

of the funnel.

  This embodiment of the air classifier of the pulverulent materials makes it possible to more evenly distribute the particles of the material along the section of the chamber and thus to increase the separation efficiency of the pulverulent material in fine and coarse fractions. in that the plates, mounted between the helicoidal element and the funnel further transfer into the peripheral part of the chamber, the two-phase eddy current in an unstable regime during which a portion of particles is discharged towards the central part. from the room. In addition, condensed agglomerates disintegrate into isolated particles, a portion of which is also discharged to the central portion of the chamber which contributes to their more even distribution along the section of the chamber. The separation efficiency obtained in this air classifier, evaluated according to the Eder-Mayer criterion, is 10 to 15% higher than that of known classifiers. The invention will be better understood and other purposes, details and advantages thereof will become more apparent in the light of

  the following explanatory description of an embodiment given only as a non-exemplary example

  FIG. 1 shows an air classifier for pulverulent materials with a longitudinal sectional view of the separation chamber, according to the invention; FIG. 2 is an isometric view of part of the separation chamber provided with two funnels; - Figure 3 is a section III-III of Figure 1, on an enlarged scale, with four radially arranged plates; FIG. 4 is a cross-sectional view of a separation chamber provided with four plates disposed at an angle to the wall of the

separation chamber.

  The air classifier of the powdery materials comprises a separation chamber 1 (FIG. 1) in the form of a round section tube mounted vertically. The separation chamber 1 is placed in communication with a device 2 intended to create therein an updraft of air, with a feeder 3, and with hoppers 4, 5 for the collection of fine and

  coarse powdery material.

  The device 2 for the creation of the updraft, is a fan placed in communication with the separation chamber 1 through an air duct 6, a cyclone 7, an air duct 8, an opening 9 made in the upper part of the chamber 1. The opening 9 is intended to evacuate the fine fraction of the

powdery material.

  The device for creating the updraft of air can also be in the form of compressors,

vacuum pumps or blowers.

  The hopper 4 for collecting the fine fraction of the powdery material is mounted at the bottom of the cyclone 7 and the hopper 5 is joined to the opening 10 through which the coarse fraction of the powder material in the lower part of the drum is discharged. the separation chamber 1. An opening 11 is provided in the lower part of the chamber 1 for the admission of air. The direction of the movement of the air is indicated

in Figure 1 by the arrows.

  An opening 12 is made in the median part along the height of the chamber 1 for the loading of the powder material and is placed in coincidence with the outlet mouth of the tubing 13

  placing the feeder 3 in communication with the chamber 1.

  Conical funnels 14 are mounted on the inner surface of the separation chamber 1 along its height at a distance from one another to discharge the powder material from the wall of the chamber, and are fixed, for example , by welding. The distance between the neighboring funnels 14 is not greater than two diameters of the chamber 1 and is not less than one diameter. In this case, the diameter of the large opening of the funnel 14 is equal to a diameter D of the chamber 1 and the diameter d of the small opening of the funnel 14 is at least 0.4 times the diameter D and is not greater than 0.8 D. The angle K between the generatrix of the funnel 14 and the wall of the chamber 1 is not greater than 45. Depending on the height of the chamber 1, the number of funnels 14 can vary from two to six. In the example described, three funnels 14 are used. A helical element 15, intended for the swirling of the air updraft, is formed in the form of a vane swirler and is mounted between two funnels 14 at an equal distance. According to the variant described,

  uses two helical elements 15.

  At least two plates 16 (FIGS. 1, 2) are mounted above each helicoidal element 15 and arranged vertically at a distance equal to each other along the perimeter of the chamber so that each plate applies an edge to the

  In the example described, the plates 16 are made in the form of a rectangle trapezium.

  However, they can have the shape of a rectangle.

  The width of each plate 16 must not be greater than the difference between the radii of the openings of the funnel 14, in other words, the width of the plate 16 must be chosen so that its free edge does not disengage in the passage section of the funnel 14 regardless of its position. The number of plates 16, mounted between the funnel 14 and the helicoidal element 15 - is a function of the diameter of the separation chamber 1, the speed of movement of the current, the physical properties of the powder material and is determined by

experimental pathway.

  It is advantageous that the number of plates 16 is chosen from two to twenty. In the mode described and

  represented in FIGS. 3, 4, four plates 16 are used.

  These plates 16 can be mounted radially as shown in FIG. 3 and as well under the angle / (FIG. 4) with respect to the wall of the chamber 1. In order to make it possible to adjust the angle mounted the plates 16 (Figure 3) so that they can be oriented relative to the vertical axis passing through the edge against the wall of the chamber 1. For this purpose, there is provided in the wall of the chamber 1, the orifices 17, the number of which corresponds to that of the plates 16, in which the shafts 18 are mounted. Each axis 18 is connected to a plate 16, for example, by a welded assembly, and to a lever 19. This lever 19 is intended for the orientation of the plate 16 when it must

  to be placed in a desired position.

  The angle / 5 is chosen as a function of the physical properties of the powder material (density, particle size), the two-phase current parameters (velocity, content of powder material) experimentally and is between 0 and 45. The optimum angle / is an angle at which the maximum amount of the particles bounce toward the central portion of the chamber 1 as a result of their collision against the plate 16. The direction of movement of the two-phase current

  phases is shown in Figure 4 in a conventional manner by the arrows "1, 11, 12".

  The air classifier for powdery materials

works in the following way.

  The plates 16 (FIGS. 2, 3, 4) are first placed by means of the levers 19 in a required position depending on the speed of the updraft and the properties of the powdery material to be separated. Then, the updraft of air is created in the chamber 1 by means of the device 2 (FIG. 1) and the pulverulent material, the particles of which form with air in the chamber 1, a two-phase current, It begins to arrive from the food 3 through the opening 12. Large particles of the powder material fall from this stream by gravity and are evacuated simultaneously by the funnel 14, disposed below the opening 12, from the wall. from room 1 to the central part. Because, in the vicinity of the smaller diameter aperture of the funnel 14, the air velocity is higher, a portion of fine particles and coarse particles are entrained by the updraft of air and go up

following bedroom 1

  Smaller particles of the pulverulent material are entrained by the upward flow of air and arrive at the helical element 15 disposed above the opening 12. The helical element 15 contributes to the swirling of the next two-phase stream. the spiral indicated by the arrow 1 (FIG. 4) and the particles are distributed under the action of the centrifugal forces in the radial direction according to their dimensions. A portion of fine particles, which remains in the central part of chamber 1 (Figure 1), is driven by the updraft and arrives in

  the funnel 14 being higher.

  Larger particles and finer particles remaining are entrained under the action of centrifugal forces towards the peripheral part of the chamber 1, towards its wall. At this moment, the two-phase current collides with the plates 16, forming complementary vortices indicated by the arrows 11 (FIG. 4).

  and 12 contributing more to a more even distribution of particles in this peripheral part.

  The particles are evacuated again from the peripheral part to the central part of the chamber 1 under the action of the centrifugal forces generated in the vortices, which contributes, in turn, to an even distribution of the particles according to the section of the chamber. 1 and thus increases the separation efficiency of the powder material. It follows that the separation of the pulverulent material in fine and coarse fractions is several times following the height of the separation chamber 1

  (figure 1). The fine fraction is discharged through the opening 9, the pipe 8, the cyclone 7 to the hopper 4.

  The coarse fraction is discharged through the opening 10 to the hopper 5.

Claims (1)

R E V E N D I C A T I 0 N   Air classifier of pulverulent materials of the type having a cylindrical separation chamber (1) mounted vertically and connected to a device (2) for creating therein an updraft of air, a group of funnels (14) fixed following the height of said chamber for discharging the powder material from the wall of the separation chamber (1), a helical element (15) being mounted between each pair of black enton10 (14) for the swirling of the current ascending air, an opening (12) formed in the median portion along the height of the separation chamber (1) for loading a powder material, an opening (9) made in the upper part of said chamber, for discharging the fine fraction of the pulverulent material and an opening (10) in the lower part for discharging the coarse fraction of the pulverulent material, characterized in that at least two plates (1 6) are mounted above each helicoidal member (15) and are arranged vertically at a distance equal to each other along the perimeter of the chamber (1) so that each plate (16) is applies to the wall of the chamber (1), the width of each plate   (16) not then exceeding the difference between the aperture radii of the funnel (14).