Recirculating Pneumatic Separator

Abstract

This invention relates to a recirculating pneumatic separator which is particularly designed for separating threshed tobacco leaves form the heavier tobacco parts. The lighter tobacco fraction is carried up by air which is recirculated through the separator and the heavier tobacco function falls to an endless belt and is separately conveyed out of the separator. Means is provided for accurately controlling the air velocity in the separation chamber and for ensuring complete separation of the tobacco fractions by means of an air jet impeller.

Description

BACKGROUND OF INVENTION

In our prior U.S. Pat. No. 3,164,548 issued Jan. 5, 1965 there is disclosed a pneumatic separator which is designed to separate heavier material from lighter material, such as, for example, the stems from fragments of tobacco leaves. In this system the material to be separated is forced into the separation chamber by an impeller. Outside air is brought into the chamber and passes upwardly through the chamber carrying with it the lighter fractions whereas the heavier particles drop downwardly in the chamber and are discharged through a separate outlet. This system functioned effectively in separating tobacco stem particles from the finer cut tobacco leaves. In the preparation of tobacco particles for use there are a plurality of stages of separation, one of the initial stages involving the separation of threshed tobacco leaves from the heavier stems. It has been found that the pneumatic separator disclosed in our prior patent could not be used efficiently in these earlier stages of tobacco treatment as the threshed leaves and stems tended to form entangled balls or mats within the separator above the outlet screen for the heavier fraction and these balls prevented efficient separation of the particles and clogged the outlet passageway.

A further drawback of the separation system disclosed in our prior patent is the large quantity of air which is continuously required for operation of the separator. It can be appreciated that in a plant where a large number of separators may be operating, large quantities of air are drawn in from the plant, this air being continuously exhausted to the outside atmosphere. Thus, there was a clear need for a pneumatic separator wherein a recirculating air system is provided thereby obviating the need for a continuous supply of outside air.

SUMMARY OF INVENTION

According to the present invention there is provided a pneumatic separator in which the air used to effect the separation of the lighter particle fraction from the heavier particle fraction is recirculated so that a minimum quantity of outside makeup air is required.

The presently disclosed pneumatic separator may be used to effect the separation of threshed tobacco leaves from the heavier stem particles by reason of the provision of a secondary stage of separation. The material to be separated is thrust into the separation chamber by an impeller in a manner similar to that disclosed in our prior U.S. Pat. No. 3,164,548. However, in the wall opposite the wall in which the impeller is mounted there is provided an air jet means which forces the particles apart, thereby preventing the formation of the entangled balls or mats characteristic of the system disclosed in our prior patent. The particles are thrust across the chamber to subject the particles again to the upflowing air in the separation chamber, thus effecting a second stage of separation.

The lighter separated particles comprising the threshed tobacco leaves pass upwardly with the air and there is provided a rotating air screen through which the conveying air passes to be recirculated through the separating chamber, with the particles passing through a separate air lock and out of the pneumatic separator through an independent air-conveying system. There is provided an endless foraminous belt extending across the lower end of the separating chamber and the heavier tobacco particles which drop down on to the belt are conveyed outwardly through a separate outlet and carried off by a separate air conveying system.

A bypass air duct is provided in the recirculating air system so that a portion of the air which would normally be recirculated up through the main separation chamber may be drawn off and recirculated to the rotating air screen where the lighter tobacco particles are separated from the conveying air. This bypass means in the air-recirculating system performs two functions. It serves to regulate the air velocity through the separating chamber so that this velocity may be accurately controlled within close tolerance and the bypass system also serves to ensure that an adequate supply of air is provided at the rotating air screen. With an inadequate supply of air at the air screen the tobacco particles tend to cling to the air screen thereby clogging the screen and preventing efficient operation of the system.

In order to obtain efficient distribution of particles across the entire cross section of the separating chamber it is essential that the velocity of the air across the chamber be uniform. According to the present invention there is provided means to ensure uniform air velocity. Beneath the endless foraminous belt which carries off the heavier tobacco particles there is provided a diffusion plate which consists of a series of spaced vanes extending across the separation chamber. These vanes form a diffuser plate creating an area of pressure differential. As the air passes upwardly between the vanes in the diffuser plate the airflow velocity tends to become more even across the chamber in that as the amount of air passing through a given area increases, the resistance to flow increases and a greater amount of air tends to pass through other areas of the diffuser plate. The air moving upwardly through the separation chamber must also pass through the lower and upper runs of the endless foraminous belt and this belt also serves to create areas of pressure differential and functions to even out the air velocity across the separation chamber.

Very fine tobacco particles which pass upwardly in the separation chamber and pass through the rotating air screen will be recirculated with the recirculating air and will be caught on the lower surface of the foraminous belt. As the foraminous belt rotates, these particles will be brought to the upper run of the belt and the airflow through the belt will again convey these fine tobacco particles upwardly through the chamber and eventually these finer particles will pass through the outlet with the lighter tobacco fraction.

Means is provided for diverting a portion of the air which serves to convey the heavy particle fraction out of the pneumatic separator. This diverted air is replaced by a portion of the main separating air which flows outwardly with the heavier particle fraction and serves to draw the heavy particle fraction out into the outlet. Makeup air from the outside atmosphere is drawn into the separating chamber to replace the main separating air which is passed out with the heavier particle fraction and it is this makeup air which provides the air jet impeller creating the secondary separating stage within the separating chamber.

A primary object of the present invention is to provide a pneumatic separator with a recirculating air system so that a minimum quantity of outside air is required for operation of the separator.

Another object of the present invention is to provide a recirculating separator which is capable of separating threshed tobacco leaves from the heavier stem particles by providing an air jet impeller which creates a secondary separating stage so that the particles to be separated are passed across the separating chamber twice.

Still another object of the present invention is to provide a bypass means in the air-recirculating system so that the air velocity in the separating chamber can be accurately controlled and so that efficient operation of the rotating air screen separating means is ensured.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the recirculating pneumatic separator,

FIG. 2 is a sectional view through the separator and

FIG. 3 is an end elevational view thereof.

DETAILED DESCRIPTION OF INVENTION

Referring now more specifically to the drawings wherein like numerals indicate like parts throughout the several views the recirculating pneumatic separator is housed within a casing structure 1 and the material to be segregated by the pneumatic separator is fed into the casing structure through an inlet 2, more clearly seen in FIG. 2. There is provided a rotary screen 3 with a mesh of sufficiently fine size that it prevents the material being brought into the separator from passing therethrough. However, the conveying air which brings the material into the separator passes through the screen and out through an open end 4 of the rotary screen. Thus, the conveying air for the material being fed into the separator forms a closed circuit, passing into the separator through the inlet 2 and out through the passageway 4. There is provided an air lock 5 comprising a plurality of rotating gates which permit the material to be segregated to pass therethrough but prevents any substantial quantity of the conveying air from passing through into the main portion of the pneumatic separator. The material to be subjected to treatment within the pneumatic separator passes downwardly where it is engaged by a rotary impeller 6 and thrust by the vanes of the impeller into the main chamber 7 of the pneumatic separator. The impeller imparts to the particles of material to be separated a substantial velocity, for example, within the range of 1,000 to 1,200 feet per minute. This prevents the heavier particles from immediately dropping to the bottom of the chamber and causes the particles to pass across the chamber and be subjected to the upwardly passing air currents within the main separating chamber 7. The lighter particle fraction is carried upwardly by the upwardly moving air currents as shown at 8 whereas the heavier particles fraction passes across the chamber as shown at 9 and may abut the wall 10 of the chamber which is opposite the impeller 6. The heavier particles may drop down on to an endless foraminous belt 11 which is supported by and driven from end rolls 12 and 13. The heavier particle fraction rests on the foraminous belt and is carried therealong to the heavier particle fraction outlet 14. The heavier particles pass out of the pneumatic separator through the outlet 14 and along the passageway 15 and are carried therealong by conveying air which forms a separate external circuit as shown by the arrows 16. The inlet for this heavier particle fraction conveying system is shown at 17 and the conveying air passes along the passageway 17 into the chamber 18 where a portion of the air is drawn off as shown at 19 for a purpose which will be explained more fully hereinafter. The main portion of the air coming in through the inlet 17 passes through chamber 18 and back through the passageway 20 to the heavier particle fraction inlet 14.

Thus it can be seen that the heavier particle fraction is drawn out of the pneumatic separator through the outlet 14 by a separate conveying air which takes this fraction out through passageway 15 where the heavier particle fraction is separated and removed by means not shown and the conveying air recirculated through the inlet 17.

The lighter particle fraction passes upwardly through the main separating chamber 7 with the air currents passing upwardly through the chamber and through a substantially tangential passageway 21 into a substantially cylindrically shaped chamber 22. Centrally disposed within the chamber 22 is a cylindrical screen 23 which is mounted for rotation within the chamber. The screen 23 is of a mesh size insufficient to permit the passage of the lighter fraction particles which are carried by the air current but permit the air to pass therethrough into the central portion 24 and thence outwardly through the open ends of the rotary screen. Referring to FIG. 3 it can be seen that the air passing through the rotary screen 23 and through the open ends of the screen passes into downwardly extending ducts 25 and 26 and into the outer ends of a fan casing 27. The fan casing 27 shown in FIG. 2 houses a rotary fan which draws the air through the ducts 25 and 26 and forces the air through the fan outlet 28 and back into the lower end portion of the separating chamber 7. Thus it can be seen there is a recirculating system for the air used to effect the separation between the lighter and heavier particle fractions. This recirculating circuit comprises the main chamber 7, the passageway 21, through the rotary screen 23, outwardly through the open ends of the screen and downwardly through ducts 25 and 26, through the open ends of the fan casing 27 and through the fan outlet 28 back through the lower end of the separating chamber 7.

The lighter particles fraction passes downwardly within the cylindrical chamber 22 and into an air lock 29, through the air lock and into the lighter particle fraction passageway 30. The conveying air for the lighter particle fraction enters on one side of the casing 1 and exits through a duct 31 (FIG. 1) on the opposite side of the casing. The conveying air forms a separate circuit for drawing off the lighter particle fraction and the lighter particle fraction is collected at a location spaced from the pneumatic separator. Additional air for this conveying system may be drawn in through an upwardly extending duct 32 which draws a portion of the air 19 from the air in the conveying circuit for the heavier particle fraction. The amount of this air which is drawn off is determined by the position of a damper 33 located in the passageway 20 of the conveying circuit for the heavier particle fraction. The portion of the heavier particle fraction conveying air which is diverted into the lighter particle fraction conveying circuit is replaced by a portion of the recirculated air passing through the main separating chamber 7. The passageway of this air out through the outlet 14 assists in drawing out the heavier particle fraction from the end portion of the endless belt 11. Thus, it can be seen that a portion of the recirculated air within the chamber 7 is continuously drawn off through the outlet passageway 14. This drawn off air is made up for by drawing in outside air through a makeup inlet 34. Air drawn in through this makeup air inlet passes into the main separating chamber 7 beneath the lower end portion of wall 10 and below an adjustable deflector blade 35. The makeup air passing between the adjustable deflector 35 and the upper end of endless belt 11 creates an air jet impeller which forces the particles of material outwardly across the chamber 7. Referring to applicant's prior U.S. Pat. No. 3,164,548 it was found that when that pneumatic separator was used to separate threshed tobacco leaves from the larger stem parts a conglomerate, ball or mass of material formed at the wall opposite to the inlet impeller and these particles would not separate satisfactorily, eventually clogging the heavier particle outlet. The air jet impeller provides a secondary stage of separation, thereby preventing the formation of the ball or mass of particles and insures effective separation of all of the tobacco particles. By adjusting the position of damper 33 the amount of air to be diverted up through passageway 32 is determined and this determines the amount of main chamber air drawn out with the heavier particle fraction and thus the amount of makeup air drawn in through inlet 34. The position of deflector 35 determines the size of the inlet through which the makeup air passes into the main chamber 7 and thus the position of damper 33 and reflector 35 determined the velocity and size of the air jet impeller creating the secondary stage of separation.

Adjacent the lower end portion of the main separating chamber 7 there is provided a diffuser 36 comprising a series of angularly extending spaced vanes which extend across the separating chamber. The air passing from the circulating fan outlet 28 passes upwardly through the diffuser and the diffuser performs the function of insuring an even flow of air up through the main separating chamber 7 with a uniform velocity across the chamber. In effect the diffuser provides an area of pressure differential and provides for evening out of the air velocity in that in the event the velocity in one area increases, the resistance to flow increases and there will be a greater flow through other portions of the diffuser. The air passing through the diffuser 36 passes upwardly through the lower run of endless belt 11 and through the upper run of this belt. Any very fine tobacco particles which may have passed through screen 23 and recirculated with the recirculating air will be caught on the lower run of endless belt 11 and when the lower run of belt 11 becomes the upper run as the belt rotates, these fine particles will again be picked up and carried through separating chamber 7.

There is provided a bypass system for the recirculating air passing through the chamber 7. This bypass means includes an upwardly extending bypass duct 37 with an inlet at the lower end adjacent the outlet 28 from the fan casing 27. The outlet for the bypass passageway 37 is shown at 38 and this outlet passes air into the cylindrical chamber 22 housing the rotating separating screen 23. An adjustable damper 39 disposed within bypass duct 37 controls the amount of air flowing through this bypass duct. Thus it can be seen that a portion of the air recirculates from the chamber 22 through the central portion 24 of the rotary separating screen 23 downwardly through ducts 25 and 26 through the fan casing 27 and back up to the chamber 22 through the bypass duct 37. The bypass system shown performs two functions. The primary purpose of the bypass system is to provide adequate control over the velocity of the air passing upwardly through the main separating chamber 27. Accurate control over the velocity of the upwardly passing air is critical to the successful operation of the system. Obviously, this velocity will vary depending upon the material to be separated. In separating threshed tobacco leaves from the heavier stem particles it is desirable that an air velocity of from 600 to 800 feet per minute be maintained. With lighter products a lower velocity range is used. Within the ducts 25 and 26 as shown in FIG. 3 there are provided boltable gates 40 and 41 which may be moved inwardly and outwardly of the ducts to set the air velocity range. Thus, with the gates in their outermost position permitting maximum velocity through separating chamber 7. This maximum velocity flow may be decreased by opening the damper 39 to permit some of the recirculated air to be bypassed. The adjustable damper 39 permits approximately 30 percent control over the air velocity passing through the main separating chamber 7.

The bypass air also provides for uniform operation of the screen separator 23. That is to say, the rotating screening separator 23 operates at a maximum efficiency when sufficient air is passing over and through the screen. If the air velocity drops to too low a value the particles of product tend to cling to the screen thereby blocking the screen and preventing the recirculating air from passing therethrough and also preventing the particles from passing through the air lock 29. It is also possible that a brush might be employed adjacent to the outer surface of the screening separator 23 to remove the lighter particles from the outer surface of the screen so that these particles can pass to the lower end portion of the chamber 22 and then out through the air lock 29.

If desired, fluorescent lights may be provided as at 42 and 43 and a viewing window 44 may be provided so that the separation taking place within the chamber 7 may be viewed and adjustments made in the air velocity or the air jet impeller by setting the gates 40, 41 dampers 33 and 39 and deflector 35. The pneumatic separator disclosed herein provides a recirculating air system utilizing a minimum of outside makeup air. The bypass system for the recirculated air permits the velocity of the air passing upwardly through the main separating chamber 7 to be controlled and maintain adequate air loading of the separator screen 23. The diffuser plate 36 ensures a uniform velocity of air across the separating chamber 7 and the endless foraminous belt 11 provides a means for removing the heavier particle fraction and for collecting and recirculating the finer particles which may pass through the screening separator 23.

The air jet impeller created by the makeup air passing beneath deflector 35 provides a secondary separation stage which is essential in separating threshed tobacco leaves from the heavier stem particles. This air jet impeller thrusts the particles across the separating chamber in much the same way as the inlet impeller 6 and prevents the formation of balls or mats of conglomerate particles. The velocity of the air jet impeller may be controlled by adjusting the damper 33 and deflector 35 in the manner previously described.

Claims

Obviously many modifications and variations of the invention are possible in light of the above teachings. What is claimed as new is desired to be secured by Letters Patent is:

1. A pneumatic separator for separating lighter particles from heavier particles comprising, a separating chamber, means for circulating air upwardly through said chamber, inlet impeller means mounted on one side of said separating chamber for thrusting particles to be separated into and across the chamber, an air jet impeller means mounted on the side of said separating chamber opposite to said inlet impeller means for thrusting the particles across the chamber in a direction opposite to the direction in which said inlet impeller means thrusts the particles, means for separating the lighter particles from the upwardly circulating air and means for collecting and carrying the heavier particles from the chamber.

2. A pneumatic separator according to claim 1 and further including means for recirculating the air from the upper end of the separating chamber to the lower end thereof and bypass means in the recirculating air means to cause a portion of the air recirculated to bypass the separating chamber.

3. A pneumatic separator according to claim 2 and further including a diffuser disposed adjacent the lower end portion of the separating chamber for equalizing the velocity of the air across the separating chamber.

4. A pneumatic separator according to claim 1 wherein the means for separating the lighter particles from the upwardly circulating air includes a rotating screen.

5. A pneumatic separator according to claim 1 wherein the means for separating the lighter particles from the upwardly circulating air includes a rotating screen and further including means for recirculating the air from the upper end of the separating chamber to the lower end thereof and bypass means in the recirculating air means to cause a portion of the air recirculated to bypass the separating chamber and pass to the rotating screen.

6. A pneumatic separator according to claim 1 and further including a diffuser in said separating chamber whereby the upwardly moving air has a substantially uniform velocity across the separating chamber.

7. A pneumatic separator according to claim 1 wherein said means for carrying the heavier particles from the chamber includes an endless foraminous belt extending across the separating chamber.

8. A pneumatic separator according to claim 7 wherein said means for carrying the heavier particles from the chamber further includes an air conveyor means and a damper in said air conveyor means for diverting a portion of the air passing therethrough.

9. A pneumatic separator according to claim 8 and further including a makeup air inlet into the separating chamber to replace the air diverted from said air conveyor means.

10. A pneumatic separator for separating lighter particles from heavier particles comprising, a separating chamber, means for circulating air upwardly through said chamber, inlet impeller means mounted on one side of said separating chamber for thrusting particles to be separated into and across the chamber, means for collecting and carrying the heavier particles from the chamber, means for recirculating the air from the upper end of the separating chamber to the lower end thereof, screen means for separating the lighter particles from the circulating air, a bypass means in the recirculating air means to supply additional recirculated air to said screen means to remove lighter particles from said screen means and means for adjusting the airflow through said bypass means to vary the velocity of the air circulating upwardly in the separating chamber.

11. A pneumatic separator according to claim 10 and further including an air jet impeller means mounted on the side of the separating chamber opposite to said inlet impeller means for thrusting the particles to be separated across the chamber in a direction opposite to the direction in which said inlet impeller means thrusts the particles.