US3265210A

US3265210A - Method of and apparatus for air classification

Info

Publication number: US3265210A
Application number: US216871A
Authority: US
Inventors: Harte Heinz; Iwen Johannes; Wochnowski Waldemar
Original assignee: Individual
Current assignee: Individual
Priority date: 1960-10-31
Filing date: 1962-08-14
Publication date: 1966-08-09
Anticipated expiration: 1983-08-09
Also published as: US3265209A; DE1152340B

Description

Aug. 9, 1966 H. HARTE ETAL 3,

METHOD OF AND APPARATUS FOR AIR CLASSIFICATION Filed Aug. 14, 1962 W 4 WW 3 1 0 sw M M M M W United States Patent Claims. (Cl. 209136) This application is a continuation-in-part of my copending application Serial No. 182,802 filed March 27, 1962.

The present invention relates to a method of and to an apparatus for separating lighter particles ttrom heavier particles which form a mixture with the lighter particles, and more particularly to a method of and an apparatus for separating lighter particles trom heavier particles in a plurality of consecutive stages. Still more particularly, the invention relates to a method and to an apparatus especially suited for separating tobacco leaves from tobacco stems and constituting improvements over the method and apparatus disclosed in said .copending application.

It is an important object of my invention to provide a method of separating lighter particles fro-m heavier particles according to which the separation of lighter and heavier articles is carried out in a plurality of stages so that even such lighter particles which might have been entrained by or entrapped between the heavier particles during a first stage can be separated from heavier particles in the next stage or stages of the operation.

Another object of the invention is to provide a method of the just outlined characteristics according to which the separation of lighter and heavier particles may be regulated independently in each stage of operation so that the extent of separation may be adjusted in dependency on the weight of lighter and/or heavier particles, on the percentage of lighter and/or heavier particles in the mixture, on the looseness or compactness of the mixture, and on all other factors which might have a bearing on the separating operation.

A further object of the invention is to provide a very simple and efiicient apparatus for the practice of my method.

An additional object of the invention is to provide an apparatus for separating tobacco leaves from a mixture of tobacco leaves and tobacco stems which is constructed and assembled in such a way that the leaves separated in consecutive stages of separating operation may be merged into a single stream prior to their withdrawal from the apparatus.

A concomitant object of the invention is to provide an apparatus of the just outlined characteristics wherein the steams separated in consecutive stages may be withdrawn at different points or at a single point of the apparatus, depending upon whether the stems separated in consecutive stages of operation do or do not contain tobacco leaves.

Stiil another object of the invention is to provide an apparatus or the above described type which may be rapidly and conveniently adjusted for continuous and fully automatic separation of lighter particles from mixtures wherein the percentage of lighter particles may vary within a rather wide range.

Wit-h the above objects in view, the invention resides in the provision of a method of separating lighter particles from heavier particles which form a mixture with the lighter particles, comprising the steps of introducing the mixture into an ascending and preferably inclined primary air stream which is strong enough to entrain the 3,2 6 5 ,2 10 Patented August 9, 1 966 major part or all of the lighter particles but which is too weak to entrain all of the heavier particles so that the major part of heavier particles is tree to descend by gravity .whereas the major part of lighter particles ascends with the primary air stream and the remainder of the mixture tends to accumulate above such sect-ion of the primary air stream from which the majority of heavier particles descends by gravity, and transferring the remainder of the mixture from the primary air stream into an ascending secondary air stream which is strong enough to entrain the lighter particles but which is too weak to entrain the heavier particles so that the heavier particles descend by gravity [whereas the lighter particles ascend with the secondary air stream and may be merged with lighter particles entrained by the primary air stream. The heavier particles descending trom or in the primary and secondary air stream may be mixed or they may be withdrawn separately if desired.

In one of its preferred forms, the apparatus for the practice of my method comprises a housing which defines a primary and a secondary separator chamber, supply duct means for admitting a mixture of lighter and heavier particles into the lower zone of the primary chamber together with a primary air stream which permits the major part of heavier particles to descend by gravity into the lower zone and which entrains at least the major part of lighter particles and the remainder of heavier particles toward the upper zone oi? the primary chamber, transfer means provided in the proximity of the upper zones of the chambers and .defining aperture means between the chambers through which the remainder of heavier particles and some lighter particles may enter by gravity into the secondary chamber, pneumatic means for producing in the secondary chamber a secondary air stream which entrains the lighter particles into the upper zone and which permits gravitational descent of heavier particles into the lower zone of the secondary chamber, evacuating means connected with the upper zones of the chambers for withdrawing lighter particles therefrom, and take-off means for receiving heavier particles from the lower zones of the chambers.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following detailed description of a specific embodiment with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of a separator which embodies one form of my invention, one side wall and a portion of the front wall of the separator housing being broken away; and

FIG. 2 is a smaller scale side elevational view of a slightly modified separator wherein the heavier particles are taken off by a pneumatic conveyer.

Referring now in greater detail to the drawings, and first to FIG. 1, there is shown a separator comprising a main frame 1 including a horizontal top plate 8 which is supportingly connected with a separator housing 2. The housing communicates with a supply duct 3- which serves as a means for admitting a primary stream of air and a mixture of lighter and heavier particles into the lower zone of an upwardly extending primary separator chamber 10. This lower zone of the chamber 10 has two sections including a first section 3a which communicates with the duct 3, and a second section 4 which serves as a take-off duct and through which heavier particles may be evacuated by gravity from the primary separator chamber. The duct 4 accommodates an air lock here shown as a rotary cell wheel 5 which is driven by an electric motor 6 mounted on the supporting plate 8. The

by two side walls 2a, 2b.

lower portion 7 of the take-off duct 4 discharges heavier particles onto the upper run of a horizontal take-off conveyer 80.

The chamber 10 is inclined with respect to a vertical plane and is bounded by an inclined unperforated rear or lower wall 11, by a perforated or slotted front or upper wall 12 which is spaced from the rear wall 11, and It will be noted that the inclination of the upper wall 12 with respect to a vertical plane is less pronounced than the inclination of the lower wall 11 so that the width of the chamber 10 increases in a direction upwardly and away from the lower zone 3a,

4 thereof. The upper end of the upper wall 12 is connected with an arcuate baflle plate 13 which cooperates with a spaced deflector plate 14 to reduce the width of the upper zone 15 of the chamber 10, this upper zone constituting an evacuating duct through which lighter particles are removed from the housing 2. The deflector plate 14 preferably constitutes an imaginary upward extension of the lower wall 11.

In accordance with our invention, the deflector plate 14 is spaced from the upper end of the lower wall 11 to form therewith a passage or gap which accommodates a transfer means or air lock in the form of a rotary cell wheel 75, the latter driven by the output shaft of the motor 6. The casing 75a of this air lock extends between the side walls 2a, 2b and the air lock discharges a mixture of heavier and lighter particles into a secondary separator chamber 77 which is bounded by the side walls 2a, 2b, by a third wall 76 which simultaneously constitutes the rear wall of the housing 2, and by a front wall or partition 11a which terminates at the upper end of the lower wall 11 below the casing 75a. The upper zone 77a of the chamber 77 serves as an evacuating duct through which lighter particles separated from the mixture admitted by the air lock 75 are evacuated from the housing 2. It will be noted that the air lock 75 provides a connecting aperture which permits inflow of particulate matter from the upper zone of the primary chamber 10 into the upper zone of the secondary chamber 77 but which prevents flow of particulate matter in the opposite direction.

walls 11, 76 and by the side walls 2a, 2b. Both takeoff ducts extend through the supporting plate 8.

The evacuating duct 15 normally communicates with a tubular evacuating element 18 provided at the upper end of the housing 2 through which lighter particles separated in the primary chamber 10 are withdrawn from the separator. The other evacuating duct 77a may communicate with a similar tubular element 1812 which is parallel with and is scalable from the element 18. The

elements

18, 18a form part of a pneumatic evacuating conveyer which advances lighter particles to a further processing station, not shown.

A vertical front wall 29 of the housing 2 extends from the duct 3 and all the way to the upper tubular element 18a and is formed with a horizontal opening or slot 19 which is adjacent to the underside of the element 18 and whose effective area is regulatable by a flap valve 20. A similar opening or slot 21 is provided in the top wall 16 of the housing 2 between the rear wall 76 and the tubular element 18a, and the eflective area of this slot 21 is regulatable by a flap valve 22.

The underside of the tubular element 18 is perforated or apertured as at 25, this underside extending between the baflle plate 13 and the front wall 29. The

walls

13, 29, the battle plate 13, the underside 25 of the tubular element 18, and the two side walls 2a, 2b define between themselves an upwardly expanding compartment 30 which communicates with the

pneumatic conveyer

18, 18a and with the primary chamber 10. This compartment 30 may discharge some air through the slot 19, depending on the adjustment of the valve 20.

The upper edge portion of the deflector plate 14 which separates the evacuating ducts 15, 77a from each other extends toward the intake end of the

pneumatic conveyer

18, 18a and carries a pivotable flap valve 84 which may be adjusted to seal the tubular elements 18, 1811 from each other or to provide a path for the flow of lighter particles from the element 18 to the element 18a or vice versa. In addition, the flap 84 may seal the duct 15 from the pneumatic conveyer when it is pivoted into sealing engagement with the baflle plate 13. A similar flap valve 85 is hinged to the top wall 16 and serves as a means for regulating the cross sectional area of the intake end of the tubular element 18a, i.e., the valve 85 selectively permits or prevents flow of lighter particles from the duct 77a into the element 18a. The intake ends of the

elements

18, 18a are separated from each other by a wedgeshaped intermediate wall member 18b which extends between the side walls 2a, 2b. The

valves

84, 85 serve as a means for regulating the discharge of lighter particles from the chamber 10, 77 into the

pneumatic conveyer

18, 18a.

An inverted V-shaped baflle 31, 32 is pivotable about a horizontal shaft 33 whose ends are journalled in the side walls 2a, 2b. This baflle is hinged to the upper edge of the wall portion 3b bounding the section 3a and may be adjusted to change the cross-sectional area of the section 3a.

In the separator of FIG. 1, the direction of flow of lighter and heavier particles and of a mixture of such particles is shown by full-line arrows. Broken-line arrows indicate the flow of air. The separator is based on the suction principle and operates in the following manner:

The duct 3 admits a primary air stream which contains a mixture of heavierand lighter particulate matter. It is assumed that the mixture consists of tobacco leaves (lighter particles) and tobacco stems, and the purpose of the separator is to remove from the mixture all or nearly all stems so that the material evacuated through the

pneumatic conveyer

18, 18a consists mainly or exclusively of tobacco leaves.

The strength of the air stream flowing upwardly through the upper portion 3a of the duct 3 and into the lower portion of the primary separator chamber 10 is selected in such a way that the stream entrains all tobacco leaves whereas at least some stems begin to descend by gravity and pass through the air lock 5 to be discharged through the lower portion 7 of the take-off duct 4 and onto the take-off conveyer 80.

The apertured upper wall 12 permits escape of some air from the primary air stream and such escaping air produces a pressure differential which causes flow from the chamber 10 into the compartment 30 and which tends to maintain the ascending tobacco leaves in close proximity to the right-hand side of the upper wall 12, as viewed in FIG. 1. This pressure differential causes air flow through the perforations or slots of the wall 12, through the compartment 30, through the perforated underside 25 of the tubular element 18, and into the pneumatic conveyer. If the valve 20 is at least partially open, air deflected by suction may escape to the atmosphere. The strength of the suctional force is selected in such a way that the latter can counteract the gravity of tobacco leaves and thus prevents the leaves from descending through the air lock 5. The inclined lower wall 11 guides heavier stems toward the air lock 5 and enables the latter to withdraw such stems from the chamber 10. It will be noted that the compartment 30 provides with the perforated underside 25 and/or with the slot 19 a path for the deflected air thus enabling the maintenance of the major part of ascending lighter particles away from the lower wall 11 and transfer means 75.

Certain heavier leaves and some lighter stems which have reached the baffle plate 13 and are caused to impinge against the deflector plate 14 will be slowed down sufliciently to descend into the range of the second air lock 75 so that the latter transfers the mixture of such particles into the secondary chamber 77 wherein the leaves are caused to advance into the upper zone 77a under the action of an ascending secondary air stream which is produced by suction prevailing in the

pneumatic coneveyer

18, 18a. This secondary air stream enters the lower zone of the chamber 77 through the passage 78a between the flap 78 and rear wall 7 6, and thereupon flows upwardly toward the duct 77a and into the pneumatic conveyer where it merges with the primary air stream downstream of the transfer means 75. On its way to the pneumatic conveyer, the secondary air stream entrains all or nearly all leaves but is too Weak to entrain the stems so that the stems may descend by gravity to pass through the duct 79 and onto the conveyer 81. The main portion of the secondary chamber 77 is substantially vertical because it is bounded in part by the inner side of the vertical rear wall 76 and by the substantially vertical partition 11a. If the operator desires, he may prevent mixing of tobacco leaves which ascend through the evacuating ducts 15, 77a by adjusting the

valves

84, 85 in such a way that the evacuating ducts are sealed from each other. The purpose of the

valves

20, 22, 78 and of the guide plate 32 is to regulate the strength of the primary and secondary air streams and of the cross current in such a Way that the particulate matter entering the

pneumatic conveyer

18, 18a does not contain any stems and to prevent evacuation of tobacco leaves through the take-off ducts 4 and 79. The

valves

22, 78 may adjust the strength of the secondary air stream independently of the primary air stream.

The separator of FIG. 2 comprises a housing defining two

takeoff ducts

107, 179 which respectively correspond to the take-off ducts 4, 79 of FIG. 1. The

ducts

107, 179 discharge heavier particles through a single opening 83 and into a common pneumatic take-off conveyer 82; otherwise, the construction of this apparatus is the same as that of the apparatus shown in FIG. 1.

FIG. 2 shows an adjusting arm 33a which is utilized for regulating the position of the baffle 31, 32. The side wall 2a is provided with several windows 1100 which permit observation of the separating operation in the chambers 1t), 77 and in the general area of the transfer means 75.

We have found that the quantity of lighter particle removed from the originally introduced mixture by the primary air stream with or without the help of a cross current normally approximates 25-30 percent of the original mixture. The quantity of heavier particles withdrawn through the air lock 5 is about 30 percent of the originally admitted mixture so that the second air lock 75 normally transfers between 40-45 percent of the original mixture into the secondary chamber 77. In the absence of a secondary air stream, nearly one-half of the original mixture would be withdrawn from the separator without any separation of lighter particles so that the efficiency of the separator would be extremely low. The purpose of the cross current flowing in the path defined by the apertured upper wall 12, by the compartment 30, by the perforated underside 25 and/or by the slot 19 is to assist the primary air stream in entraining the major part of lighter particles toward the upper zone of the primary chamber and to reduce the capacity of heavier particles 'to entrain lighter particles counter to the direction of flow of the primary air stream.

It will be readily understood that the separator may be modified in a number of ways without departing from. the spirit of my invention. For example, it is possible to construct the housing 2 in such a way that the mixture admitted to the secondary chamber 77 is subjected to the action of a second cross current. Also, some material advancing toward the evacuating duct 77a may be transferred into a third separator chamber if necessary so that the separating operation is then carried out in three stages. While the output of the separator chamber 77 is not exceptionally high, its eificiency is very satisfactory especially if the transfer means is provided close to or at the upper end of this chamber. Moreover, since the

valves

22 and 78 permit regulation of the secondary air stream independently of the primary air stream, the lifting force of the secondary air stream may be adjusted with utmost precision to insure that only heavy particles descend through the

duct

79 or 179.

The

pneumatic conveyor

18, 18a is preferably connected to the suction side of a fan whose pressure side produces the primary air stream in a manner as disclosed in a copending application Serial No. 182,802 of Waldeman Wochnowski et al., assigned to the same assignee.

FIG. 1 shows the valve 84 in a position in which the

elements

18, 18a are sealed from each other.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features which fairly constitute essential characteristics of the generic and specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims. v

What is claimed as new and desired to be secured by Letters Patent is:

1. An apparatus for separating lighter tobacco particles from heavier tobacco particles which form a mixture with the lighter particles, comprising a housing defining an inclined primary separator chamber and a secondary separator chamber, said housing comprising an inclined internal wall which constitutes the lower wall of said primary chamber and each of said chambers having a lower zone and an upper zone; supply duct means for admitting the mixture into said primary chamber in the proximity of said lower zone thereof together with an ascending primary air stream which permits the major part of heavier particles to descend by gravity into the lower zone and which causes lighter particles and the remainder of heavier particles to ascend toward the upper zone of said primary chamber whereby the remainder of heavier particles and some of the lighter particles tend to descend by gravity onto and advance upwardly along said inclined lower wall; transfer means comprising an air lock provided in the proximity of said upper zone and defining in said inclined lower wall a connecting aperture between said chambers through which the remainder of heavier particles and such lighter particles which advance upwardly along said wall may descend by gravity into said secondary chamber; means for producing in said secondary chamber an ascending secondary air stream which entrains lighter particles into the upper zone and which permits heavier particles to descend by gravity into the lower zone of said secondary chamber; evacuating means communicating with said upper zone for withdrawing lighter particles from said chambers; and take-off means for receiving heavier particles from the lower zones of said chambers independently of each other.

2. An apparatus as set forth in claim 1, wherein the means for producing said secondary air stream is a pneumatic conveyor which is connected with said evacuating means.

3. An apparatus for separating lighter tobacco particles from heavier tobacco particles which form a mixture with the lighter particles, comprising a housing defining a primary separator chamber and a secondary separator chamber, each of said chambers having a lower zone and an upper zone; supply duct means for admitting the mixture into said primary chamber in the proximity of said lower zone thereof together with an ascending primary air stream which permits the major part of heavier particles to descend by gravity into the lower zone and which permits lighter particles and the remainder of heavier particles to ascend toward the upper zone of said primary chamber; transfer means comprising an air lock provided in the proximity of said upper zones and defining aperture means between said chambers through which the remainder of heavier particles and some lighter particles enter by gravity into said secondary chamber; means for producing in said secondary chamber an ascending secondary air stream which entrains lighter particles into the upper zone and which permits heavier particles to descend by gravity into the lower zone of said secondary chamber; valve means provided in said housing for regulating the strength of one of said streams independently of the other stream; evacuating means connected with the upper zones of said chambers for withdrawing lighter particles therefrom; and take-off means for receiving heavier particles from the lower zones of said chambers independently of each other.

4. An apparatus for separating lighter tobacco par ticles from heavier tobacco particles which form a mixture with the lighter particles, comprising a housing defining an inclined primary separator chamber and a secondary separator chamber, said housing comprising a first inclined internal wall which constitutes the lower wall of said primary chamber and a perforated second inclined internal wall which constitutes the upper wall of said primary chamber, each of said chambers having a lower zone and an upper zone; supply duct means for admitting the mixture into said primary chamber in the proximity of said lower zone thereof together with an ascending primary air stream which permits the major part of heavier particles to descend by gravity into the lower zone and which causes lighter particles and the remainder of heavier particles to ascend toward the upper zone of said primary chamber whereby the major part of lighter particles ascends along said upper wall and the remainder of heavier particles and some of the lighter particles tend to descend by gravity onto and advance upwardly along said inclined lower wall; transfer means comprising an air lock provided in the proximity of said upper zones and defining in said inclined lower wall a connecting aperture between said chambers through which the remainder of heavier particles and such lighter particles which advance upwardly along said wall may descend by gravity into said secondary chamber;

evacuating means communicating with said upper zones for withdrawing lighter particles from said chambers; and take-off means for receiving heavier particles from the lower zones of said chambers independently of each other.

5. A method of separating lighter tobacco particles from heavier tobacco particles which form a mixture with the lighter particles, comprising the steps of introducing the mixture of lighter and heavier particles into an ascending inclined first air stream having an upper and lower surface said stream being strong enough to entrain the major part of lighter particles but too weak to entrain all heavier particles so that the major part of heavier particles descends by gravity, that the major part of lighter particles ascends with the first air stream and that the remainder of the mixture tends to accumulate above such section of said stream from which the majority of heavier particles descends by gravity deflecting a portion of said inclined first air stream from said upper surface and at an angle to the direction of its ascent so as to create a pressure differential that maintains the major part of said lighter particles in said first air stream despite the tendency of the heavier particles descending from said lower surface to entrain lighter particles counter to the direction of flow of said first air stream; transferring the remainder of the mixture from said first stream into a second ascending air stream which is stong enough to entrain the lighter particles but which is too weak to entrain the heavier particles so that the heavier particles descend by gravity whereas the lighter particles ascend with the second air stream; and separately withdrawing heavier particles from said first and second air streams.

6. An apparatus for separating lighter tobacco particles from heavier tobacco particles which form a mixture with the lighter particles, comprising a housing defining a primary separator chamber and a secondary separator chamber, each of said chambers having a lower zone and an upper zone; supply duct means for admitting the mixture into said primary chamber in the proximity of said lower zone thereof together with an ascending primary air stream which permits the major part of heavier particles to descend by gravity into the lower zone and which permits lighter particles and the remainder of heavier particles to ascend toward the upper zone of said primary chamber; transfer means provided in the proximity of said upper zones and defining aperture means between said chambers through which the remainder of heavier particles and some lighter particles enter by gravity into said secondary chamber; an air lock provided in said aperture means; means for producing said primary air stream and for simultaneously producing in said secondary chamber an ascending secondary air stream which entrains lighter particles into the upper zone and which permits heavier particles to descend by gravity into the lower zone of said secondary chamber; evacuating means connected with the upper zones of said chambers for withdrawing lighter particles therefrom; and take-off means for receiving heavier particles from the lower zones of said chambers independently of each other.

7. An apparatus for separating lighter tobacco particles from a mixture of lighter and heavier tobacco particles, comprising a housing defining an inclined primary separator chamber and a secondary separator chamber, said housing comprising an inclined internal wall which constitutes the lower wall of said primary chamber and each of said chambers having a lower zone and an upper zone; supply duct means for admitting the mixture into said primary chamber in the proximity of said lower zone thereof together with an ascending primary air stream which permits the major part of heavier particles to descend by gravity into the lower zone and which causes the lighter particles and the remainder of heavier particles to ascend toward the upper zone of said primary chamber whereby the remainder of heavier particles and some of the lighter particles tend to descend by gravity onto and advance upwardly along said inclined lower wall; transfer means comprising an air lock provided in the proximity of said upper zones and defining in said inclined lower wall a connecting aperture through which the remainder of heavier particles and such lighter particles which advance upwardly along said wall may descend by gravity into said secondary chamber; a pneumatic conveyor for producing in said secondary chamber an ascending secondary air stream which entrains lighter particles into the upper zone and which permits heavier particles to descend by gravity into the lower zone of said secondary chamber; evacuating means connected with said pneumatic conveyor and with said upper zones for withdrawing lighter particles from said chambers, said evacuating means comprising a first evacuating duct connected to and receiving lighter particles from the upper zone of said primary chamber, a second evacuating duct connected to and receiving lighter particles from the upper zone of said secondary chamber, and a first and second tubular element respectively connected to and receiving lighter particles from said first duct and second duct; and take-off means for receiving heavier particles from the lower zones of said chambers.

8. An apparatus as set forth in claim 7, further comprising valve means for regulating the effective cross sectional area and the flow of air through at least one of said ducts.

9. An apparatus as set forth in claim 7, wherein said ducts have portions which are adjacent to and communicate with each other and further comprising valve means for regulating the flow of particles and air between said portions of said ducts.

10. An apparatus for separating lighter tobacco particles from heavier tobacco particles which form a mixture with the lighter particles, comprising a housing defining an inclined primary separator chamber and a secondary separator chamber, said housing comprising a first inclined iternal wall which constitutes the lower wall of said primary chamber and a perforated second inclined internal wall which constitutes the upper wall of said primary chamber, each of said chambers having a lower zone and an upper zone; supply duct means for admitting the mixture into said primary chamber in the prox imity of said lower zone thereof together with an ascending primary air stream which permits the major part of heavier particles to descend by gravity into the lower zone and which causes the lighter particles and the remainder of heavier particles to ascend toward the upper zone of said primary chamber whereby the major part of lighter particles ascends along said upper wall and the remainder of heavier particles and some of the lighter particles tend to descend by gravity onto and advance upwardly along said inclined lower wall; transfer means comprising an air lock provided in the proximity of said upper zone and defining in said inclined lower wall, a connecting aperture between said chambers through which the remainder of heavier particles and such lighter particles which advance upwardly along said lower wall may descend by gravity into said secondary chamber; means for producing a pressure differential at the opposite sides of said perforated upper wall so that some of said primary air stream is deflected so as to pass through said upper wall and to maintain the major part of ascending lighter particles to close proximity of said upper wall and away from said transfer means whereby such lighter particles enter the upper zone of said primary chamber; evacuating means communicating with said upper zones for withdrawing lighter particles from said chambers; and take-ofl? means for receiving heavier particles from the lower zone of said chambers independently of each other.

References Cited'by the Examiner UNITED STATES PATENTS HARRY B. THORNTON, Primary Examiner.

HERBERT L. MARTIN, Examiner.

Claims

5. A METHOD OF SEPARATING LIGHTER TOBACCO PARTICLES FROM HEAVIER TOBACCO PARTICLES WHICH FORM A MIXTURE WITH THE LIGHTER PARTICLES, COMPRISING THE STEPS OF INTRODUCING THE MIXTURE OF LIGHTER AND HEAVIER PARTICLES INTO AN ASCENDING INCLINED FIRST AIR STREAM HAVING AN UPPER AND LOWER SURFACE SAID STREAM BEING STRONG ENOUGH TO ENTRAIN THE MAJOR PART OF LIGHTER PARTICLES BUT TOO WEAK TO ENTRAIN ALL HEAVIER PARTICLES SO THAT THE MAJOR PART OF HEAVIER PARTICLES DESCENDS BY GRAVITY, THAT THE MAJOR PART OF LIGHTER PARTICLES ASCENDS WITH THE FIRST AIR STREAM AND THAT THE REMAINDER OF THE MIXTURE TENDS TO ACCUMULATE ABOVE SUCH SECTION OF SAID STREAM FROM WHICH THE MAJORITY OF HEAVIER PARTICLES DESCENDS BY GRAVITY DEFLECTING A PORTION OF SAID INCLINED FIRST AIR STREAM FROM SAID UPPER SURFACE AND AT AN ANGLE TO THE DIRECTION OF