US2577295A - Apparatus for separating pulverulent material - Google Patents

Description

Dec. 4, 1953 N. AHLMANN APPARATUS FOR SEPRATING PULVERULENT MATERIAL Filed OG'.. 20, 194B INVENTOR Patented Dec. 4, 1951 UNITED STATES PATENT OFFICE APPARATUS FOB' SEPARATING P'ULVEBU- LENT MATERIAL Application October 20, 1948, Serial No. 55,514 In Denmark October 29, 1947 s claims. (ci. 209-141) i This invention relates to the air separation of pulverulent materials into coarse and fine fractions and is concerned more particularly with a novel method of air separation and with apparatus, by which that method can be advantageously practiced. The method of the invention is superior to those heretofore used in that, by its use, a more accurate separation of the materials above and below a critical particle size can be made, with less of the fine particles present in the coarse fraction than has heretofore been usual.

In the air separation of pulverulent materials as now carried on, it is the common practice to introduce the material into an air stream, which is then caused to rotate, so that the coarse particles are thrown out of the stream by centrifugal action, while the fine particles are entrained and carried oli in the stream. Frequently, the coarse fractionis further cleaned in a separator by distributing it by means of rapidly rotating plates in the path of a stream of air moving upwardly, the line particles then being carried off in the air stream and the coarse particles thrown out of the stream centrifugally and left behind.

In the prior methods of air separation, in which centrifugal force is employed, it is difficult to remove the ne particles completely, because of their adherence to those of a size larger than that at which the separation is intended. As a result, only about two-thirds of the particles below the critical size are removed in prior air separating operations and, while the separation can be improved by further treatment of the coarse fraction, the additional operations require the use of separators with rotating parts and other special features.

'I'he present invention is, accordingly, directed to the provision of a method of air separation, which overcomes the objections to the methods now in use, in that it produces an improved separation of the coarse and fine particles and does not require the use of separators with moving parts. In the new method, the material to be Iseparated is introduced into an air stream to pass counter-current thereto and, below the point of introduction of the material, the stream is constricted, so that its velocity is greatly increased. Immediately above the construction, the stream is caused to expand abruptly and an eddy is formed, which lies with its axis transverse to the direction of iiow of the stream. In the eddy, the particles of the material are agitated and whipped about, so that the fine particles are freed from the coarse ones and are then carried away in the stream. The speed attained by the stream in the constriction is many times in excess of the Speed required for keeping particles of the critical size in suspension and, accordingly, when the speed of the stream above the eddy is suflicient to keep the'limit particles in suspension, the coarser particles accumulate in the eddy and it becomes possible to make an effective separation of the coarse particles from the fine ones, which have adhered thereto.

The coarse particles separated in the eddy may be carried ofi discontinuously or continuously. Il the eddy is constantly formed at the same place, the coarse particles accumulate in the eddy, until the mass of the particles is suliicient to permit them to move against the high velocity air stream. It if is desired that the coarse particles be carried away continuously, the eddy is formed above a surface, which is inclined in relation to the direction of movement of the air stream, so that the eddy moves continuously down the inclined surface in the directionvof its axis. The surface may be formed, for example, by a helical support with the air stream passing along the axis of the helix. As the eddy moves continuously in the direction of its axis, the line particles are continuously carried oil' in the air stream and the length of the surface, down whichthe eddy travels, is then selected to insure the desired degree of separation. In the treatment of some materials, the angle of inclination of the surface is about 15 to the horizontal but the angle may vary within wide limits, according to the desired velocity of the eddy moving downwardly along the surface.

In the practice of the invention, the material may be separated in a conventional air separator, the coarse fraction of which is then subjected to eddy action, from which the line particles pass in the air stream to the separator. This manner of practicing the new method is advantageous, when it is desired to insure that the coarse fraction will contain little or none of the fine particles, as, for example, in the preparation of glass sand for melting in a kiln.

The apparatus for practicing the method comprises a passage extending generally upwardly and having a constriction between its ends. Air is caused to ilow upwardly through the passage and the velocity of the air is greatly increased,

' as it passes through the constriction. Immediately above the constriction', the passage increases abruptly in cross-section and has a surface, which extends away from the upper end of the constriction and has an edge, which extends trans- 3 versely to the direction of air ow and over which the air passes. When the high velocity air traveling through the constriction ows over the edge of the surface, it forms an eddy, in which the separating action above described takes place.

For a better understanding of the invention, reference may be had to the accompanying drawing, in which Figs. 1 and 2 are schematic vertical sections of different forms of apparatus for practicing the new method;

Fig. 3 is a schematic vertical section on the line 3 3 of Fig. 4 of another form of apparatus for practicing the method;

Fig. 4 is a sectional view on the line 4 4 of Fig. 3;

Fig. 5 is a schematic vertical section of another form of apparatus for practicing the method of the invention;

Fig. 6 is a sectional view on the line 6 6 of Fig. 5;

Fig. 7 is a schematic vertical section of another form of apparatus for practicing the method of the invention; and

Figs. 8 and 9 are sectional views on the lines 8 8 and 9 9 of Fig. 1, Fig. 9 being on a somewhat enlarged scale.

The apparatus illustrated in Fig. l comprises a passage, which is made up of an upper tank I0, a lower tank II, and a duct I2 connecting the top of tank II to the bottom of tank I0. The bottom end walls I3, I4 of tank I0 are convergent toward the upper end of duct I2 and the top end walls I5, I6 of tank I I converge toward the lower end of duct I2. At its upper end, tank I0 is provided with an inlet I1 for material to be treated containing a rotating gate I8, and an outlet duct I9 leads from tank I0 near its upper end to a cyclone separator 20. A duct 2| leads from the top of the separator to the intake of a fan 22 and a duct 23 leads from the outlet of the fan to the interior of tank II. The bottom end of tank II is formed as a hopper 24 having a rotary discharge gate 25 in its spout and the lower end of the cyclone separator is also formed with a hopper bottom 26 having a spout containing a rotary gate 21.

In the operation of the apparatus shown in Fig. l, the fan causes air to be delivered into tank II and the air passes upwardly through the con- 7 necting duct I2. This duct is of much lsmaller cross-section than the tanks and, as a result, the duct acts as a constriction and the air travels through it at high velocity. As the air issues from the top of duct I2 into the lower end of tank I0, the cross-sectional area of the air stream expands abruptly with the result that, as the air passes over the lower edge of wall I3 of tank I0, an eddy 28 is formed. The material t0 be treated is fed into the upper part of tank I0 through gate I8 and drops into the upward current of air within the tank. The velocity of the air within that tank is such that the particles of the critical size or smaller are carried away in the air stream, whereas the heavier particles drop through the tank and collect in the eddy 28, since they can not pass downwardly through duct I2 because of the great velocity of the air therein. The coarse particles in the eddy are subjected to great agitation and whipping action, which frees the iine particles therefrom. The ne particles carried ou by the air enter the cyclone separator 20, where they are separated from the air and discharged through the gate 21 in the spout.

When a/suicient quantity of coarse particles has garages accumulated in the eddy 28, they will pass as a mass downwardly through duct I2 and enter the tank I I to collect in the hopper bottom thereof. The coarse particles can then be discharged through the rotary gate 25, as desired.

In the apparatus shown in Fig. 2, the air passage is formed by a tank 29 having an inlet 30 for air near its lower end and an outlet 3I for air and entrained lne particles near its upper end. The material to be treated is introduced into the tank at its upper end through an inlet 32 containing a rotary gate 33 and the tank is provided with a hopper bottom 34 having an outlet 35 containing a rotary gate 35a, through which the coarse material collecting in the bottom of the tank can be discharged. Between the ends of the tank; there is a partition 36 having a central opening of much less diameter than the y tank.

In the operation of the apparatus of Fig. 2, air from a fan similar to fan 22 is introduced into the tank through inlet 30 and the air lows upwardly in the tank. As the air passes through the small opening in partitition 36, the velocity of the air is increased and an eddy 31 develops on the upper surface of the partition around the opening. After passing through the opening, the air flows upwardly through the tank and out through outlet 3I leading to a separator, which may be of conventional cyclone type and similar to separator 20 in Fig. 1. The material to be treated is admitted through gate 33 and drops into the upper part of the tank. the iine particles being carried o in the air stream through the air outlet 3l. The coarse particles collect in the eddy and are whipped about and agitated so that the fine particles adhering thereto are freed and carried oi in the air stream. The coarse particles collect in the eddy and, from time to time, pass downward through the opening in the partition to fall into the hopper bottom 34.

In the apparatus shown in Fig. 2, the tank 29 is formed with a single partition but, if desired, a second partition 38 may be disposed below partition 36, so that the coarse particles are twice subjected to the eddy action in their travel downward through the tank. The use of the second partition produces a further cleaning of the coarse fraction.

The apparatus shown in Figs. 3 and 4 includes a passage made up of an upper tank 39, a lower tank 40, and a connecting duct 4 I The bottom of tank 39 is formed with convergent walls 42, 43, leading to the upper end of duct 4I and the top walls 44, 45 of tank 40 are convergent toward the lower end of the duct. The lower edge 43a of wall 43 extends upwardly from one side of the tank 39 to the other and the tank is provided with an inlet 46 for material to be treated, which contains a rotary gate 41 and leads into the side of the tank adjacent the higher side of wall 43. An outlet 48 leads from the opposite side of the tank below the lower edge 43a of wall 43 and is provided with a rotary gate 49.

In the operation of the apparatus shown in Figs. 3 and 4, air is introduced into tank 40 to ow upwardly and, as the air travels through the duct 4I, its velocity is greatly increased. As the air ows around the edge 43a of wall 43, an eddy 50 is formed on the upper surface of wall 43, the eddy lying with its axis parallel to the edge 43a. The eddy tends to move down the wall toward the lower end thereof. The material to be treated is introduced through the inlet 46 and the ne particles are picked up and carried away through tank 39 in the air stream, while the coarse particles remain in the eddy and are prevented by the high velocity air traveling through duct 4| from passing down through the duct. The coarse particles travel down the sloping surface of wall 43 in the eddy and are discharged through outlet 48. The length of the sloping wall 43, on which the eddy is formed, is such that the desired degree oi' removal of the fine particles is achieved as the coarse particles travel from the high end of the wall to the low end. In the apparatus shown in Figs. 3 and 4, the removal of the coarse particles is continuous.

The apparatus shown in Figs. 5 and 6 includes an upright passage 5|, which is preferably of cylindrical form. The passage is provided at its lower end with a discharge spout 52 and has an air inlet 53, which extends through the wall of the spout. Within the passage is mounted a body or plug 54, which is of the same outline as the passage and smaller insize. At its opposite ends. the body is formed with conical end sections 55, 56 and section 56 p-referably extends a short distance into the end of the air inlet 53. The inner wall oi the passage is provided with a plurality of radial vanes 51 extending from end to end of the body and terminating at the conical end sections thereof. The body carries a flat strip 58 of helical form, which extends outward from the body and engages the free inner edges of the vanes.

In the operation of the appartus shown in Figs. 5 and 6, air from a fan is introduced into the passage through inlet 53 and the material to be treated is discharged into the top of the passage above the body 54. As the air travels upwardly through the passage, it passes between the outside of the body and the inner wall of the passage and this constriction causes the velocity of air ilow to be greatly increased. As the air reaches each convolution of the helical strip 58, the air iiows outwardly and around the outer edge of the strip. The strip thus provides a further constriction with further increase in the velocity of the air, as it ows over the free edges of the convolutions of the strip. Immediately above the strip, an eddy is produced, the eddy having an axis of helical form, which lies parallel to the upper surface of the strip. The material to be treated is fed into the upper end of the passage and passes down countercurrent to the air stream, the fine particles being entrained and carried away. As the coarse particles reach the top conical end section 55, they are directed outwardly and pass downward between vanes 51. The coarse particles can not pass over the edge of the helical strip, because of the high velocity of the air flowing over that edge.

Accordingly, these particles remain in the eddy,

which is traveling down over the surface of the helical strip toward the lower end thereof. The coarse particles are thus moved downward in the eddy toward the lower end of the strip 58, whence they are discharged into the spout 52. In their travel in the helical eddy, the coarse particles are greatly agitated and fine particles adhering thereto are released to be picked up in the air stream flowing upward between vanes 51 and carried out at the top of the passage.

The apparatus shown in Fig. 7 includes a separator of known construction, which includes a conical casing 59 leading down to the top of a passage 60, which is preferably of cylindrical form. A body 6| of the same cross-sectional outline as the passage but of less diameter is mounted within the passage, the body having top and bottom conical end sections 62, 63. The body carries a plurality of radial vanes 64 extending outwardly on its outer surface between its end sections and the free edges of the vanes engage the inner freeedge of a helical strip 65, which is mounted on the inner wall of the passage. At the bottom, the passage is provided with a hopper 66 for coarse material and it has 4an air inlet 61, which extends through the wall of the hopper and terminates in slightly overlapping relation to the lower conical end section 63.

A conical partition 58 is mounted within the conical casing 59 in spaced relation thereto and an inlet 59 for the material leads through the wall of casing 59 into a cylindrical partition 59a, which encloses the lower open end of partition 58. A plurality of tangential vanes 10 are mounted on the under side of the top wall 1l of casing 59 and the wall is provided with an outlet 12, through which air and entrained fine particles may pass. A baiile 13 is mounted within the upper end of casing 59 in front of the lower end of outlet 12.

In the operation of the apparatus shown in Fig. 7, air is admitted to the lower end of passage 60 through the inlet 61 and the air stream passes upwardly between vanes 54 and over the edges of the convolutions of strip 65. In that part of the passage containing the body 6|, the velocity of the air is increased, andthe air reaches a still higher velocity as it passes over the edge of each convolution of strip 65. The material to be separated is introduced through the inlet 69 and, as it drops down into the air stream flowing upwardly through passage 60, fine particles are entrained and some pass upwardly with the air through the interior of partition 68, while others pass upwardly between the partition and the wall of casing 59. At the top of casing 59, the air flows inwardly between the tangential vanes and is given a whirling motion over the top of baille 53. Any coarse particles entrained in the air stream are thrown out of the whirling air current and the i-lne particles pass upwardly through outlet 12 with the air, While the coarse particles pass downwardly through partition 68 or between that partition and casing 59. The air stream flowing upwardly over the edge of the helical strip produces an eddy on top of the strip, which has a helical axis and moves downwardly along the strip. The coarse particles are collected in the eddy and prevented from passing over the free edge of the helical strip by the high velocity air traveling upwardly over that edge. The coarse particles, accordingly, move down along the strip with the eddy, to be discharged at the lower end of the strip and fall into the discharge spout 56.

In the apparatus of Fig. 7, the fine particles, which `are not adherent to the coarse ones, are at once separated in the separator above passage 60 and carried away. The finest particles, which adhere to the coarse particles, are separated by the eddy action in the passage 60. The apparatus thus produces an excellent separation of the fine and coarse particles in a single piece of apparatus, which includes no moving parts, such as rotary distributing blades.

Iclaim:

l. An apparatus for separating' pulverulent material into coarse and fine fractions, which comprises a passage extending generally upwardly and having a constriction between its ends.

atrasos means for causing air to flow upwardly through the passage from below the constriction, the passage increasing abruptly in cross-section above the constriction and having a surface extending away from the upper end of the constriction and having an edge, which extends transversely to the direction of air flow and at an oblique angle to the horizontal and over which the air passes, means for introducing material to be separated into the passage above the constriction to pass downwardly through the air current, an outlet for the escape of air and entrained material from the passage above the constriction, and means for withdrawing the coarse material from the passage below the level of the upper end of said oblique edge.

2. An apparatus for separating pulverulent materialinto coarse and ilne fractions, which comprises a passage extending generally upwardly and having a constriction between its ends, means for causing air to owvupwardly through the passage from below the constriction, the passage increasing abruptly in cross-section above the constriction and having a surface extending away from the upper end of the constriction and having an edge, which extends transversely to the direction of air flow and at an oblique angle to the horizontal and over which the air passes,

means for introducing material to be separated into the passage above the constriction and adjacent the higher end of the surface, an outlet for the escape of air and entrained material from the passage above the constriction, and means for withdrawing the coarse material from the passage adjacent the lower end of the surface and below the level of the upper end of said oblique edge.

3. An apparatus for separating pulverulent material into fine and coarse fractions, which comprises a passage extending generally upwardly, means for causing air to flow upwardly through the passage, means in the passage forming a constriction, through which the air flows with increased velocity, and including a member having a surface of helical form and an edge, over which the air flows to form an eddy having its axis parallel to said surface, guide means in the constriction for guiding the air along a straight path, an inlet for the admission of material into the passage above the constriction, an outlet for escape of air and entrained material from the passage above the constriction, and means for withdrawing the coarse material from the passage below the constriction.

4. An apparatus for separating pulverulent material into coarse and fine fractions, which comprises a passage extending generally upwardly, means for causing air to flow upwardly through the passage, an elongated body mounted within the passage and having an outer surface lying substantially parallel to and spaced from the wall of the passage, a plurality of vanes extending axially of the body between the outer surface of the body and the passage wall, each vane having a free vertical edge, a helical member mounted in the space between the outer surface of the body and the passage wall, the member partially closing said space and having a free edge engaging the free edges of the vanes, means for introducing material to be .separated into the passage above the body, an outlet for escape of air and entrained material from the passage above the body, an inlet for air into the passage below the body, and. means for withdrawing coarse material from the passage below the body.

5. An apparatus for separating pulverulent material into coarse and fine fractions, which comprises a passage extending generally upwardly, means for causing air to flow upwardly through the passage, an elongated body mounted within the passage and having an outer surface lying substantially parallel to and spaced from the wall of the passage, a plurality of vanes mounted on the outer surface of the body and extending axially thereof, the vanes having free outer edges, a helical member mounted on the wall of the passage and extending to the outer edges of the vanes, means for introducing material to be separated into the passage above the body, an outlet for escape of air and entrained material from the passage above the body, an inlet for air into the passage below the body, and means for withdrawing coarse material from the passage below the body.

6. An apparatus for separating pulverulent material into coarse and line fractions, which comprises a passage extending generally upwardly, means for causing air to flow upwardly through the passage, an elongated body mounted within the passage and having an outer surface lying substantially parallel to and spaced from the wall of the passage, a plurality of vanes mounted on the innerfwall of the passage and extending axially of the passage, the vanes having free inner edges, a helical member mounted on the outer surface of the body and extending to the inner edges of the vanes, means for introducing material to be separated into the passage above the body, an outlet for escape of air and entrained material from the passage above the body, an inlet for air into the passage below the body, and means for withdrawing coarse material from the passage below the body.

7. An apparatus for separating pulverulent material into coarse and ne fractions by means of an air current, which comprises a passage extending substantially vertically and having an air inlet at its lower end, an outlet at its upper end for escape of air and entrained line material, and a constriction between its ends, through which air flows at high velocity, means forming a surface extending away from the constriction and having an edge, over which the air passes and which lies at an oblique angle to the horizontal, means for introducing material to be separatetd into the passage above the constriction to pass downwardly through the air current, and means for withdrawing the coarse fraction from the passage below the level of the upper end of said oblique edge.

8. An apparatus for separating pulverulent material into coarse and fine fractions, which comprises a passage extending substantially vertically and having an air inlet at its lower end. an elongatedV body mounted within the passage between its ends and having an outer surface lying substantially parallel to and spaced from the wall of the passage, a plurality of vanes extending axially of the body between the outer surface of the body and the passage wall, each vane having a free vertical edge, a helical member mounted in the space between the outer surface of the body and the passage wall, the member partially closing said space and having a free edge engaging the free edges of the vanes, means for introducing material to be separated into the passage above the body, a conical separating ,chamber in the passage above the body, thel chamber being open at top and bottom, an outlet 10 for escape of air and ent-.rained material from the passage above the chamber, and means for with. UNITED STATES PATENTS drawing coarse material from the passage below Number Name Date the body, 10,494 Shimer Feb. 7, 1854 5 177,242 Hart May 9,1876 NIKOLAI AHLMANN 514,498 ROSS Feb. 13, 1894 I 859,194 Blasco July 9, 1907 REFERENCES CITED 940,469 Middleton Nov. 16, 1909 The following references are of record in the lo zg" me "f this Patent: 1.912.910 Neuman et a1. June 6, 1933

Images