FR2635279A1 - CLASSIFIER OF PULVERULENT MATERIALS BY GRAVITY - Google Patents

Abstract

The present invention relates to a classifier of pulverulent materials by gravity comprising a hollow body 1 having an inclined bottom 4 perforated with holes 7 for the passage of a gas, separating elements mounted inside the body 1 one at the other. -above the other, a loading device intended to bring a starting material, located above the top edge 3 of the bottom 4, a device for the evacuation of the coarse product from the classification located near the bottom edge 6 the bottom 4, at least one pipe for the evacuation of the gas and the end product, fixed to the upper part of the body 1 through the movement of the material. According to the invention, this classifier is provided with at least one threshold 8, mounted on the bottom 4 of the body 1 across the movement of the material. The invention can be applied in the metallurgical, mining, chemical industries, in the foundry, as well as in other industrial branches.

Description

1. The present invention relates to the field of

  pneumatic classification of different materials puivéru-

  slow in a rising air flow and particularly relates to a classifier of powdery materials by gravity. The invention can be advantageously applied in the metallurgical, chemical, mining, building, foundry and other industrial branches where pulverulent materials are required to be separated into two or more parts.

  according to the size of their particles, preferably

  particle size of 5 to 0.05 mm.

  The problem of creating devices that ensures

  The highly efficient separation of pulverulent materials is important at the present time in view of the development of new technologies as well as the improvement of known technologies, for example in powder metallurgy, in the production of materials.

  molding, etc. imposing the establishment of prescrip-

  more stringent requirements for the particle size distribution of starting materials, semi-finished products and finished products. Pneumatic classification is one of the processes

  most advanced separation. In practice, a classifica-

  The gravity type of the stage type 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 chimney

  born, installed above a perforated bottom. The separation of a material in the chimneys is carried out either with the aid of the separating elements, mounted on the internal walls of the chimneys (SU, A, 787113), or with the aid of the walls

  chimneys which are made in zigzag (GB, B, 2623038).

  This embodiment of the classifiers makes it possible to obtain the following characteristics: the efficiency characterized by the Eder-Mayer index d 100: up to 70 to 75% (here d75, d25) designate the dimensions of the particles which 75% c and 25% fine products are extracted at a concentration of starting material per cubic meter cut for the classification y = 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 ton 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 gas stream passing through the perforated bottom. As a result of the fluidization, the material moves in the direction of inclination of the perforated bottom. It is then sorted into fine and coarse fractions under the action of the forces of weightlessness and aerodynamic resistance. Fine classes of particles

  are driven by the updraft in the

  where they are subject to the additional classification and are free of large particles

  who have occasionally entered these chimneys.

  Thus, in the aforementioned constructions, the classification is made repeatedly of both a fine product and a coarse product which allows to obtain a good

  efficiency. However, it should be noted that the effectiveness

  of these types of classifiers proves to be insufficient in the case where the requirements to be met by the particle size composition of the powdery materials become more severe, for example in the case of the manufacture of molding materials, grinding powders and polishing powders. , metal powders, etc ... This drawback is due to the fact that the concentration of the material following the

  length of the perforated bottom and in the class-fireplaces

  is different and decreases according to the path of the material because the largest portion of fine material is

  extracted in the first chimneys and other chimneys.

  are insufficiently loaded. It is known that the decrease in the concentration of the material leads to the increase of the relative quantity of entrained material and to the raising of the "separation limit", thus, the different chimneys separate the materials according to the different limits, which results in the pollution of fine and coarse products of the classification by small and

large particles, respectively.

  Here and then, in the description that follows,

  the term "separation limit" means the diameter

  particles that are removed in classifica-

  real contributors in equal portions in end products and gross ranking. In gravity classifiers, the "separation limit" is usually set by the

  velocity of the air flow and determines the range of

  particles of both the end product and the coarse product of the classification. Therefore, the irregular concentration along the length of the perforated bottom and along the chimneys of classification lowers the quality of the classification. Furthermore, in classifiers made according to this design, there is an uneven distribution of the concentration of the material in the transverse direction, depending on the width of the perforated bottom, which is due either to the mounting or manufacturing defects of the bottom, or the more frequently, the irregular loading of the starting material along the width of the bottom.These factors cause the movement of the material in a denser current along the bottom, along one of the side walls of the classifier, and a decrease in the concentration material near the opposite side wall on the bottom. Small particles in the dense stream of material enter the coarse product, polluting it and lowering the quality of the grading. As a result, the irregular concentration of the material along the length

  and the width of the bottom and following the class-fireplaces

  drop the quality of the ranking.

  It is known that the efficiency of the classification rises, as a rule, with the increase of the residence time of the pulverulent material in the classifier because it is subject, to a large extent, to the separation action exerted by the which reduces the possibility of

  pollutants of coarse effect by small particles.

  As for time, this stay of individuals in the classifications

  In many cases, it depends to a great extent on the angle of inclination of the bottom. The lower the angle of inclination of the bottom compared to the horizontal, the more the time

  of residence of the particles in the classifier is large.

  However, in most cases, it is impossible to mount the bottom in relation to the horizontal at an angle of inclination of less than 9 B. This difficulty is due to the fact that the majority of the materials contain particles whose dimensions vary in a given direction. wide range and the larger components of these materials are not generally subject to the working class classifier, to the fluidization and, therefore, they can accumulate during operation on the fono and I '. obstructing the fact that their movement along the fono in the direction of the device discharging the coarse product is effected only due to their rolling on an inclined surface. It follows that the angle of inclination and, consequently, the residence time of the powder material in the classifier are limited, which results in a decrease in the quality of the classification. Thus, in the designs that classifiers have just been examined, the quality d. classification is limited by two causes, in particular: an irregular concentration of the material in length and in width of the perforated bottom and a small time

  of residence of the powder material in the classifier.

  The attempt to increase the residence time of the powder material in the classifier was undertaken in a gravity classifier (SU, A, 486814). This classifier comprises a body divided by vertical partitions in chimneys, each separated by vertical partitions in channels on the walls of which

  separating elements, arranged one above the other,

  above each other. The body is provided with a perforated bottom of stepped form. This bottom is inclined in the direction of the device this loading, used to bring the starting material and fixed on the body of the classifier, to the device for discharging the coarse product resulting from the classification and attached to the body. The loading device is located above the top edge of the bottom and the coarse product discharge device is near the bottom edge of the bottom. Tubing, intended to evacuate the air and the end product of the classification, are fixed to the upper part of the body. Sufficient spacing for the passage of the powder material is provided between the bottom edges of the partitions and the perforated bottom. Each of the chimney partitions is provided with a hinged flap at the bottom edge of the partition, which faces the bottom step. This flap serves to reduce the flow of charged air

  small particles of material from one chimney to another.

  In addition, this component contributes to the slowdown in

  material in the background and thus increases the time of its stay in the classifier which improves

little quality of the ranking.

  However, this embodiment of the classifier does not result in a significant improvement in the quality of the

  classification of the pulverulent material as a result of the concentration

  unevenness of the material both along the length and the width of the perforated bottom and because of the insufficient residence time of the powder material in

the classifier.

  During operation of the contemplated classifier, the powder material is fed from a loading device into the classifier body at the top edge of the perforated bottom. By passing through the bottom holes, the rising air stream forms a fluidized bed of material on the bottom. During fluidization, the powder material moves in the direction of the inclination of the bottom to the coarse product discharge device. During this movement, the material

  powder is separated into coarse and fine fractions.

  Fine fractions are entrained by the air to classification chimneys where they are subjected to several

  the separation action of the separating elements

  as they move upwards.

  According to the method implemented in this classifier, the concentration of the material is not identical along the length, nor according to the width of the perforated bottom, nor in the classification chimneys and varies several times. For example, for the separation of potassium chloride during fertilizer production, most of the material is extracted in the first chimneys. In particular, for the yield of the fine product Yf = 35.7%, it is distributed according to the stacks in the following manner: ## EQU1 ## 1 = 24.34%, 2 = 7.08%, 4 = 4.28% As can be seen from the data cited above, the fine material yield of the first chimney is six times greater than that of the last chimney and, without doubt, the concentration of the starting material discharged per cubic meter also differs according to the length from the bottom of 6 times. As already noted, the decrease in the concentration of material in each chimney contributes to the increase of its separation limit from one chimney to another. All this reduces the efficiency of the classifier's work and lowers the quality of classification products. In addition, the known design of the classifier has the disadvantage that the powder material moves in a denser layer along one of the side walls of the classifier body and a less dense layer in another wall as a result of failure to observe the accuracy of manufacture or assembly of the bottom and, as a general rule, due to uneven loading of the material along the width of the perforated bottom. As a result, small particles are driven by the denser layer of material and get into the coarse product

  by polluting it and lowering the quality of the ranking.

  The experience of using the classifier has shown that the angle of inclination of the perforated bottom relative to the horizontal, for most powdery materials whose particle size varies over a wide range, can not be inferior. to 9. In the opposite case, the perforated bottom is engorged by large particles because they are not subject to the fluidization regime and can move only by rolling on the inclined surface of the perforated bottom. Since the angle of inclination of the perforated bottom is limited, the residence time of the material in the classifier is also limited.

  which lowers the quality of the ranking.

  It was therefore proposed to develop a classi-

  gravity indicator for a powder material in which the realization of the perforated bottom of the body would distribute regularly the concentration of the material along the length and width of the bottom, according to the classification chimneys and to ensure the increase of the residence time of the material in the classifier and thereby improve the quality of the classification of

powdery materials.

  The problem thus posed is solved by means of a gravity classifier comprising a hollow body having an inclined perforated bottom with holes for the passage of a gas, separating elements arranged inside said body, mounted one behind the other, a loading device for feeding a starting product into the classifier, located above the top edge of the bottom, a device for the disposal of the coarse product of the classification, being close to of the bottom edge of the bottom, at least one tubing for the evacuation of the gas and the fine product, fixed to the upper part of the body, said classifier being, according to the invention, characterized in that at least one threshold is mounted in across the direction of displacement

material, on the bottom of the body.

  This embodiment of the classifier contributes to the fact that, by mounting a threshold on the perforated bottom,

  the material is braked in front of him and that the concentration

  The material increases in the threshold mounting area both in the fluidized bed of material above the perforated bottom and in the body space, or in a grading stack above the sill. increasing

  The concentration is determined by the height of the threshold.

  Thus, using a threshold can influence the value of the concentration of the material along the length of the perforated bottom and following the space of each stack classification and can be obtained its regular distribution which contributes to the improvement of the quality of the classification of powdery materials. In addition, the mounting of a threshold contributes to the braking of the material during its movement along the perforated bottom inclined in the direction of the

  device for evacuating the coarse product and increasing

  the residence time of the material in the classifier,

  thereby improving the quality of the ranking.

  It is advantageous for the threshold to be constituted by a plate made in such a way that the profile of its upper edge forms teeth and gaps which alternate with each other and in such a way that the lower

  entredents is at the level of the perforated bottom.

  With this embodiment of the threshold, wholesale

  pieces of material, which are not subject to fluidisation

  tion, can move freely, rolling through the entredents, following the perforated bottom, towards the device evacuating the coarse product which suffers the obstruction

the bottom.

  In the case of mounting two or more thresholds on the bottom, it is recommended that each subsequent threshold be arranged in relation to the preceding threshold so that its teeth are arranged in front of the entredents of the preceding threshold. The teeth of the sills mounted in this manner will periodically disintegrate the dense layer of pulverulent material that is formed as a result of loading the irregular classifier according to the width of the perforated bottom or because of a manufacturing or mounting of the bottom. This ensures the equalization of the concentration of the powder material along the bottom width, eliminates the entrainment of small particles with the dense layer of material towards the coarse product and improves the

quality of the ranking.

  It is known that of the two classifiers, whose efficiencies are different, a single classifier whose efficiency is higher can operate at a higher efficiency.

  high concentration of material in the flow, conditions

  which the purity of the products must satisfy

ranking are equal.

  It is also known that the flow rate of the classifier Q1 \ kg / s is determined using the following relation: 01 = p Q2 'o: p is the concentration of the powdered starting material per cubic meter, kg / m3 Q2 is the flow of air passing through the

2 3

classifier, m3 / s.

  This relationship shows that the performance of the classi-

  The indicator increases in direct proportion with the concentration of the pulverized material. It follows that by solving certain production problems, for example the problems relating to the production of construction materials for building or fertilizer, where there is no need to ensure a high purity of the products of the classification, the classifier , according to the invention, ensures reliable operation at a high concentration of material output, which increases its efficiency.

classified products.

  The gravity classifier, made according to the present invention and intended, for example, to classify molding sands, has made it possible to obtain the following results: the classification efficiency estimated according to the Eder-Mayer index t is approximately 80%, for the concentration of the material p = 3.5 kg / m3 and a flow rate t / h, the dimensions of the classifier being 1600 mm high, 400 mm deep, 1900 mm

  length. Energy consumption, including

  for dust removal from the air, did not exceed

  then 1.5 kW per ton of powder starting material.

  The invernion will be better understood and other goals, details and benefits this one will appear better at the

  light this the explanatory description that will follow of a

  embodiment given solely by way of non-limiting example with reference to the accompanying drawings in which: - Figure 1 shows schematically, in isometry, a classifier by gravity, in accordance with

  the invention, intended for the classification of a pulverulent material

  slow; FIG. 2 schematically represents the section taken along the line II - II of FIG. 1, longitudinally relative to the path of the material; and - Figure 3 is the line along line III-III

  of Figure 2, on an enlarged scale.

  The gravity classifier made according to the present invention and intended, for example, for the classification of sands molding size, comprises a body 1 (Figure 1), a device this loading used to bring the starting sand made in the form of a chute 2 and mounted above the top edge 3 (Figure 2) of the inclined perforated bottom 4, a device for discharging the coarse product made in the form of a tubing 5 fixed near the bottom boro 6 perforated bottom 4. The perforated bottom 4 is made with holes 7 (FIG. 3) for the passage of the upward air flow and is inclined relative to the horizontal according to the path of the material,

  that is, in the direction from the charging device-

  to the device for discharging the coarse product from the classification. Thresholds 8 (FIG. 2) in the form of plates, the profile of the upper edge of which is formed of teeth 9 (FIG. 3) and of the intertwined apertures 10, are mounted on the surface of the bottom 4. the pipes 11 (FIG. 1) intended to evacuate the air and the end-of-classification product are fixed to the upper part of the body 1. The body of the classifier is divided by vertical partitions 12 (FIG. 2) into classification chimneys 13 in which are arranged

  separating elements consisting of inclined flanges 14.

  These are fixed on the vertical partitions 12 and on the side walls 15 and 16 (Figure 3) of the body 1 (Figure 2) and are mounted one above the other. To create an upward flow of air through the bottom 4, there is provided a centrifugal fan 17 (Figure 1), a suction pipe 18 is placed in communication with a pipe 19 to a manifold 20. Each pipe 11 evacuation of air and fine product is connected to a cyclone 21 made according to any design that can

  be used when separating the end product from the air.

  An outlet pipe 22 of each cyclone 21 is connected to the manifold 20 and each hopper 23 of the cyclone 21 is mounted above a belt conveyor 24 made according to any design for the evacuation of the fine product. To load the starting sand in the goulo-te 2 is used a carrier 25. The evacuation of the coarse product from the classification of sand is carried out using a carrier 26, located below a feeder 27, made according to any

  design and communicated with the tubing 5.

  The gravity classifier operates as follows. By the belt conveyor 25 (Figure 1), the starting sand is fed along the arrow "a", through the chute 2, to the top edge 3 (Figure 2) of the perforated bottom 4 of the body 1 of the classifier. Under the effect of a depression created in the body by the fan 17 (Figure 1), by the upward air flow through the holes 7 (Figure 2) of the bottom 4, the sand is conveyed to the cavity of the 13. Fluidisation occurs on the surface of the inclined bottom. A fluidized bed of sand is formed on the surface of the inclined bottom 4 and the classification of the sand in coarse and fine fractions begins under the action of resistance forces and weightlessness. Fine fractions are entrained by the upward air flow towards the classification chimneys 13 where they are subjected several times to the action of the wings 14, are cleared of the large particles of

  sand occasionally driven by the air current.

  Then, fine fractions are conveyed through the pipes 11 (Figure 1) by the air stream to the cyclones 21 o they are separated from the air, accumulated in the hoppers 23, where they are discharged in the direction

  indicated by the arrow "b" by a carrier 24.

  Cleared of the small sand particles, the air passes through the outlet pipe 22, the manifold 20, the air pipe 19 into the suction pipe 18 of the fan 17. Moving along the inclined perforated bottom 4 in the fluidized bed, the large particles are freed of small particles, then having passed through the tubing 5 and the feeder 27, open the classifier and are discharged in the indicated direction

  by the arrow "c" by the conveyor belt 26.

  - During its displacement on the inclined bottom 4 (Figure 2), the sand is braked near each threshold 8 and, as a result, the concentration of the material increases in the

  threshold assembly area both in the fluidized bed and

  above the perforated bottom 4 that in the space of the body 1 or a classification fireplace 13 which is above the threshold 8. By increasing the concentration determined by the height of the thresholds, it is possible to regularly distribute the concentration of the sand along the entire length of the perforated bottom 4 and in each column of classification what

  contributes to improving the quality of the ranking.

  In addition, the thresholds 8 slow (slow down) the displacement

  sand along the bottom 4 in the direction of the tubu-

  lure 5 which increases the residence time of the sand in the classifier and further improves the quality of the classification. Since the thresholds 8 are made with the openings 10 (FIG. 3), the large pieces of material that have not been subjected to fluidization roll freely through the openings 10 along the perforated bottom 4 towards the tubing 5 (FIG. ) which removes the obstruction of the bottom 4. During the displacement of the dense layer of sand on the perforated bottom inclined 4, near one of the side walls 15, 16 (Figure 3) of the body 1 of the classifier, the teeth 9 forming the profile of the upper edge of the thresholds 8 (Figure 2) cause the deterioration of the dense layer of sand and contribute to the regular distribution of the concentration of the powder material along the width of the bottom. It should be noted that by disposing a tooth 9 of each subsequent threshold 8 opposite an entrance 10 of the preceding threshold 8, the concentration of the material is regularly distributed along the width of the bottom 4 over its entire length and, therefore, on the entire surface thus preventing a dense layer of material from carrying with it small particles in the coarse product. The quality of the ranking is thus

significantly improved.

  The classifier, made in accordance with the present invention, operates efficiently at the high concentrations of material delivered and also ensures

  as a result, a higher yield of classified product.

Claims (3)

R E V E N D I C A T I 0 N S   1. A classifier for gravity-fed powdered materials comprising a hollow body (1) having a perforated inclined bottom and holes (7) for the passage of gas, separating elements mounted inside the body (1), one on top of the other, a loading device for feeding a starting material, located above   from the top edge (3) of the bottom (4), a device for evacuating   of the coarse product from the classification located near the bottom edge (6) of the bottom (4), at least one gas and fine product discharge pipe, fixed to the upper part of the body (1), characterized in that that at least one threshold (8) is mounted on the bottom (4) of the body (1) across the displacement of the material.   2. Classifier according to claim 1, characterized in that the threshold (8) is constituted by a plate whose profile of the upper edge is formed of teeth (9) and entredents (10), the lower level of each of entredents (10) at ground level perforated (4).   3. Classifier according to claim 2, characterized in that, in the case where two thresholds, and more, are mounted on the bottom (4), each subsequent threshold (8) is arranged relative to the preceding threshold so that its teeth (9) are arranged in front of the entredents (10) previous threshold.