FR2635278A1 - GRAVITY CLASSIFIER - Google Patents

Abstract

The invention relates to the pneumatic classification of different powdery materials by an ascending air stream. According to the invention, the gravity classifier comprises a hollow body 1 having a perforated inclined bottom 5, separating elements being mounted inside the body 1 one above the other; a loading device is arranged above the top edge 8 of the bottom 5; a coarse product discharge device is attached to the lower part of the body 1; at least one pipe 12 is mounted at the upper part of the body 1 for the discharge of the gas stream with the end product; at least one grid 13 is mounted above the bottom 5, across the displacement of the updraft, and which covers the cross section of the body 1. The invention is applicable to the chemical, mining, foundry and other industries industrial branches.

Description

The present invention relates to the field of pneumatic classification

  different pulverulent materials by an updraft and has

  especially for object a classifier by gravity.

  The invention can advantageously be applied in the chemical, mining, building, foundry and industrial industries, where it is necessary to use pulverulent materials to be separated into two or more products according to the size of their particles, which

  Preferably, it is in the range of 0.05 to 1 mm.

  The problem of creating devices for highly efficient classification is important at present, because the creation of new technological processes and the improvement of those already known, for example in powder metallurgy, in the production of molding materials etc ..., impose increasingly stringent requirements to meet the particle size composition of starting materials, semi-products and products. Pneumatic classification is one of the most advanced separation processes. In practice, a graded gravity classifier has shown its good qualities in the implementation of the method of pneumatic classification of pulverulent materials. This classifier is in the form of a three-dimensional body, shared by vertical partitions in a row of chimneys, installed above a perforated bottom. The separation of a material in the chimneys is carried out either by means of separating elements, mounted on the internal walls of the chimneys (SU, A, 787113), or thanks to the fact that the walls of the chimneys are in zigzag (GB, B, 262038). This embodiment of the classifiers makes it possible to obtain the following characteristics: an efficiency characterized by the EderMayer index x = d 5. 100 Up to 70 to 75% (in the present case, d75, d25 denote the dimensions of the particles extracted in 75% and 25% fine products respectively for a concentration of the starting material, per cubic meter cut for classification, u = 2.0 to 2.5 kg / m3 and a flow rate of up to 60 to 100 t / h The energy consumption does not exceed 2.5 kW per tonne of starting material In the described types of classifiers, the method of classifying pulverulent materials is to create a fluidized bed using, for this purpose, An upward flow of gas passing through a perforated bottom As a result of the fluidization, the material moves in the direction of the inclination of the perforated bottom and is then sorted into fine and coarse fractions under the action of the forces of gravity and resistance aerodynamic classes Fine particle classes are driven by the upward air flow in the chimneys where they are further classified and are

  large particles that enter occasionally.

  Thus, in the constructions mentioned above, the classification is made repeatedly, both of a fine product than of a coarse product, which allows

to obtain a good efficiency.

  However, it should be noted that the effectiveness of these types of classifiers is insufficient in the case where the requirements to be met by the particle size distribution of the powdery materials become more severe, for example in the case of the manufacture of molding materials. , grinding powders and polishing powders and the like. This disadvantage is due to the fact that the distribution of the material along the length of the perforated bottom is not regular: a substantially large quantity of the material accumulates near the loading device, especially in the case where problems have to be solved. at a high concentration of the starting material dispensed per meter, that is, with the increase in the concentration of the starting material delivered per cubic meter, the graded product yield of the classifier increases in direct proportion, and at the same time, the higher the product yield, the lower the efficiency of the ranking. These disadvantages are due to the efficient operation of the feed assembly consisting of classification chemistries and a perforated bottom. The duration of the classification of a starting material, on the perforated bottom. Fine fractions and coarse fractions depend on the height of the fluidized bed of the material on this bottom. The higher the height of this bed is. the more the classification in coarse and fine fractions is bad, the longer the time required for blowing the small fractions of this bed is important. Since the direction of gas jets between the particles of the material in a fluidized bed is occasional and constantly changing, small particles are evidently retained by large particles in a high fluidized bed, that is, the thicker the material layer on the perforated bottom, the greater the likelihood of a small particle escaping out of

of the layer is small.

  A gravity classifier (SU, A, 1015935) is known which comprises a hollow body having an inclined bottom pierced with holes for the circulation of a stream of gas. The bottom is inclined in the direction of the loading device, intended to bring a starting material, and on the body of the classifier is fixed a

  device for discharging the product in large particles.

  The body is equipped with vertical partitions that form filing chimneys. Separating elements are fixed inside the chimneys, on the side walls and on the partitions, one above the other. The loading device, intended to introduce the starting material into the classifier, is disposed above the upper edge of the bottom of the body. The device for discharging the product in large particles is provided

  in the body and is arranged near the bottom edge of the bottom.

  Evacuation pipes of the gas stream and the product in small particles are attached to the part

upper body.

  The classifier works as follows. The starting material is conveyed by the loading device on the perforated bottom, through which air is blown into the stackers. A fluidized bed of the starting material is then formed on the perforated bottom and moves thereon to the unloading device. During the fluidization, the fine fractions are progressively entrained in the classification chimneys where they are subjected several times to the action of the separating elements and are freed of the large particles. While moving on the perforated bottom, the large particles of the starting material reach its bottom part and arrive in the unloading device. However, the classifier of this known design is characterized by a poor efficiency of the classification during the increase of the flow, since all the volume of the starting material is distributed on a single perforated bottom and when this rate of the classifier

  increases, the height of the fluidized bed also increases.

  In this design of the classifier, the time during which small fractions are entrained out of the fluidized bed is large enough and that is why one can not evacuate all the fine fractions during the passage of the material through the perforated bottom and consequently, a portion of these pollutes the coarse product. As the flow rate of the classifier increases, the height of the fluidized bed on the perforated bottom increases, and consequently the amount of small fractions entrained out of the fluidized bed decreases, ie the pollution, by the fine fractions, coarse product,

increases.

  It has therefore been proposed to develop a gravity classifier for powdery materials,

  the design of which would make it possible to regulate

  the height of the fluidized bed of the powder material and the increase of the residence time of the material in the classifier and thus to increase the efficiency of the

classification of the starting product.

  The problem thus posed is solved by the fact that the gravity classifier for pulverulent materials, comprising a hollow body, the inclined bottom of which is pierced with holes for the passage of a stream of gas, separating elements, fixed to the inside the body and installed on top of each other, a loading device used to bring a starting material into the classifier, located above the upper edge of the bottom of the body, a device for discharging the coarse product, fixed in the lower part of the body, at least one tubing, intended for the evacuation of the stream of gas charged with particles of fine product, mounted on the upper part of the body and connected to it, is characterized, according to the invention, by that at least one grid is mounted above the perforated bottom, across the direction of upward flow, which covers the cross-sectional area of the body and

is attached to it.

  This embodiment of the classifier makes it possible, thanks to the assembly of grids above the perforated bottom, to distribute the starting material according to the grids and the bottom, by forming a fluidized bed of the material on each grid and on the bottom. At the feed of the starting material on the perforated bottom, or on any grid, there is a mutual exchange of masses and the formation of fluidized beds on all the grids and on the bottom, which translates by a noticeable increase in the residence time of the material in the classifier. Practice has shown that the yield of fine fractions of the material increases with the increase of its time of

stay in the separator.

  In addition, the efficiency of the classification depends only very slightly on the increase of the flow in a separator provided with grids mounted above the perforated bottom, which is due to a regular distribution of the starting material according to all the grids, allowing form thin fluidized beds on all grids. It is advantageous that the passage section of each subsequent gate of the separator, in the direction of the displacement of the gas updraft, is greater than or equal to the passage section of the previous gate. Thanks to this embodiment of the passage sections of the grids, the accumulation of the smaller fractions on the upper grids is ensured, because the flow-current of the gas through the upper grids is lower than the

  passage of the current through the lower grids and, -

  therefore, the separation limit is shifted in the direction of the small fractions. In the

  this description, the term "separation limit"

  indicates the average diameter of the particles extracted from the starting material in the separator and present in equal amounts in the fine and coarse products resulting from the classification. In gravity classifiers, the "separation limit" is usually set by means of the variation of the speed of the

air flow.

  In addition, the increase of the product yield classified at the output of the classifier to a determined value of the efficiency of the classification is obtained by increasing the concentration of the material discharged per unit of volume thanks to the design mentioned above. classifier which ensures a regular distribution of the concentration between the chimneys of classification, as well as on the surface of the grids and on the perforated bottom. For concentrations of 2 to 6 kg / m, the value of the efficiency of the classification remains practically constant and is about 80 to 85% according to

the Eder-Mayer index. -

  The classifier according to the present invention, used for example for the classification of molding sands, made it possible to obtain the following results: efficiency of the classification estimated according to the Eder-Mayer index x = 85% for a material concentration i = 2 kg / m3 and a flow rate of 30 t / h, and x = 80% for

= 6 kg / m $ - and the same flow rate.

  The invention will be better understood and other purposes, features, details and advantages thereof

  will become clearer during the description

  explanatory text which will follow with reference to the accompanying schematic drawings given solely by way of example illustrating an embodiment of the invention and in which: FIG. 1 schematically shows a gravity classifier according to the invention, intended for classifying a powder material according to the size of its particles, in vertical section made in the direction of movement of the material, with partial tearing; and FIG. 2 shows the same classifier according to the invention, in isometry, with partial tearing of the lower part, following the perforated bottom

and the grids.

  The gravity classifier according to the present invention is intended, for example, for the classification of particle size molding sand, comprises a hollow body i (FIG. 1), shared by vertical partitions 2 in a row of classification stacks. in which separating elements are mounted one above the other. The separating elements are in the form of inclined plates 4 which are fixed on the vertical partitions 2 and on the side walls of the body. At its lower part, the body 1 is closed by an inclined perforated bottom 5 through the holes 6 of which a stream of gas reaches the classifier. A loading device having the shape of an inclined trough 9 is fixed to the wall 7 of the body, to the upper edge 8 of the inclined bottom 5. An unloading device, constituted of a hollow pipe 11, is

  attached to the bottom edge 10 of the perforated bottom 5.

  Tubing 12, intended to evacuate the gas stream, is fixed to the upper body i of the gravity classifier. The number of tubes 12 may be equal to the number of classification stacks 3 but it is also possible to evacuate the fines and the gas stream through a single manifold 12. In addition; it is possible to combine the classification fireplaces 3 two by two, using the

tubing 12.

  Grids 13 (Figure 2) are mounted and fixed in the body 1 above the perforated bottom 5, across the direction of movement of the updraft. The passage section of each grid 13 following, in the direction of movement of the gas updraft, is greater than or equal to the passage section of the grid 13 previous. This embodiment provides a regular distribution of the speed of the air flow along the height. The displacement of the gas stream through the perforated bottom 5 and the classification chimneys 3 is provided by a fan (not shown). The gas-dust mixture is separated in special and suitable devices,

  for example, in cyclones (not shown).

  The feed of the starting material and the disposal of the classified product are effused, for example, with the aid of

carriers (ncn represented).

  The classifier works as follows. The starting material is introduced through the inclined trough 9 on the top edge of the perforated bottom 5 of the body 1. The gas stream is created by a fan. Under the effect of the depression, created in the body by the fan, the sand is conveyed into the cavities of the chimneys 3 by the updraft through the

holes 6 of the bottom 5.

  There is the formation of a fluidized bed and a distribution of the material between the grids 13. Under the action of the forces of resistance and gravity, the sand is classified in coarse and fine fractions. The fine fractions are evacuated by the upward air flow to the classification chimneys 3, where they are subjected several times to the action of the inclined plates 4 and are cleaned of large particles occasionally driven by the air current. Then, the fine fractions are evacuated by the current of air, towards the cyclones then

  are separated from the air and evacuated by a carrier.

  Due to the fact that the starting material is distributed in fluidized bed on all the grids 13, there is an intense evacuation of the fine fractions and an intense exchange of the masses between the fluidized beds on the grids 13. stay of the material in the classifier increases, as well as the efficiency of the ranking. During the fluidization, the material moves in the direction of the inclination of the perforated bottom 5. Moving along the perforated bottom in the fluidized bed, large particles are freed of small particles and exit the

  classifier and then evacuated by a carrier.

  Due to the fact that the fine fractions are evacuated in a more intense manner, fluidized beds distributed on the grids, we obtain, with the gravity classifier according to the invention, a higher classification efficiency than with a classifier

  known as the closest prior art.

Claims (2)

  1. Gravity classifier for powdery materials, of the type comprising a hollow body having a perforated inclined bottom with holes for the passage of a stream of gas, separating elements, fixed inside the body and installed at each above the others, a loading device for introducing a starting material into the classifier, located above the upper edge of the bottom of the body, a device for discharging the product consisting of coarse particles, attached to the lower part of the a body, at least one tubing, for evacuating the flow of gas charged with the fine product, mounted on the upper part of the body and connected thereto, characterized in that at least one grid (13) is mounted above the perforated bottom (5), across the direction of movement of the updraft, which covers the cross-section   passage of the body (1) and is attached thereto.   2. Classifier according to claim 1, characterized in that the passage section of each grid (13) next, in the path of the gas updraft, is greater than or equal to the passage section of the grid (13) above.