Threshed Tobacco Lead Separator

This invention pertains to a pneumatic or aerodynamic type separator for separation of lighter and heavier particles in a mixture. The invention particularly relates to such a separator for use in separating stems from fragments of tobacco leaves.

In general, the use of pneumatic type separators for separating stems from leaf fragments in a tobacco mixture is known. Examples of such prior art systems include those disclosed in U.S. Pat. No. 3,608,716 to Rowell, U.S. Pat. No. 2,941,667 to Hilgartner et al, U.S. Pat. No. 3,006,470 to Franken and U.S. Pat. No. 3,265,210 to Harte et al. The present invention represents an improvement over this various prior art in that higher efficiency separation of tobacco stems from leaves is achieved.

It is an object of this invention to provide a separator for separating stems from leaves in a tobacco mixture.

It is a more specific object of this invention to provide such a tobacco separator which has a very high efficiency.

It is a still more specific object of this invention to provide a tobacco separator using two co-acting winnowers combined with inertial and plural air separators.

Briefly, in accordance with one embodiment of the invention, primary and secondary separation chambers are provided. The primary chamber has two winnowers mounted on opposite sides for co-action in projecting tobacco mixture back and forth across the primary chamber. Means are provided to establish a generally upward air flow in both the primary and secondary chambers. The air flow in the primary chamber serves to entrain and carry upwards to a collection duct the lighter particles. Conveyor means are provided at the bottom of the primary chamber to collect heavier particles that fall to the bottom of the primary chamber and transport and project them into the secondary chamber. The air flow in the secondary chamber serves to entrain and carry upwards to a collection duct additional lighter particles. Means are provided in the bottom of the secondary chamber to collect heavier particles that fall to the bottom of the secondary chamber.

FIG. 1 is a diagrammatic sectional elevation of one embodiment of a separator in accordance with the present invention.

FIG. 2 is a diagrammatic sectional elevation of another embodiment of a separator in accordance with the present invention in which the air supply to the primary and secondary chambers is admitted through perforations in a conveyor belt.

Prior to providing a detailed description of the exemplary preferred embodiments of the present invention, it is instructive to briefly examine the theoretical basis on which pneumatic or aerodynamic type separators function. Of course, the purpose of such a separator is to separate leaf fragments from stems in a threshed tobacco mixture. Generally, such a threshed mixture will contain whole tobacco leaves, leaves with attached stem, pieces of leaf with no stem, and pieces of stem with no leaf.

There is basically only one definite distinction between free lamina and the other products in a threshed tobacco mixture which provides a basis for mechanical separation. This is the ratio between surface area and weight. A piece of free lamina generally has a much higher surface area to weight ratio than the other products, because of the higher density and cylindrical shape of a stem.

Consider, for example, a piece of tobacco lamina 1".times.1".times.0.01", with a density of .rho. pounds/cubic inch. ##EQU1##

Consider now a piece of clean tobacco stem 1" long, with a mean diameter of 0.1" and with a density of 2.rho. lb/in..sup.3 ##EQU2##

Therefore, comparing the surface area to weight figures for lamina and stems, it may be seen that: ##EQU3##

This considerable difference makes the effect of an airflow on the component pieces very distinctive, providing that the lamina is not curled up and the stem does not have any lamina adhering to it.

To better understand the aerodynamic effect on each particle, consider the basic formula for impulse which is:

Where

F=Force

T=Time (For which force acts)

M=Mass of particle

V.sub.1 =Initial velocity

V.sub.2 =Final velocity

Also consider the basic force of gravity, which on a particle of mass M, will be

Where g=gravitational acceleration

Applying these two principles to a particle of tobacco in equilibrium in a vertical air stream, and assuming that the maximum surface area is exposed at 90.degree. to the airstream, neglecting any negative pressure on the downstream side, the following must be true:

Where

M.sub.1 =mass of particle

M.sub.2 =mass of air

For convenience, let T=1 sec. If the surface area of the particle is 1 Ft.sup.2 and V.sub.2 is 0 ft/sec, then ##EQU4## Where P.sub.A =density of air in lb/ft.sup.3 i.e. V.varies..sqroot.M

Now, for stems and lamina of equal plane surface area, stems are 15.7 times heavier (in the case in question). ##EQU5##

Note that this is a hypothetical case to demonstrate the aerodynamic difference in principle only. In actual fact, depending on many factors, the distinction may be very little or non-existant. Thus no separator can be 100% efficient. However, by dispersing the particles well, and controlling the velocity of air within the separator chamber by means of dampers, a reasonable degree of efficiency can be attained.

The important factor in achieving a high degree of efficiency in a separating chamber is the dispersion of the various particles in such a way that each is acted upon separately by the airstream. Again, the disparity in surface area to weight ratios is an advantage. By projecting the particles horizontally across the airflow, two forces must act on each particle in the horizontal plane. These are the initial kinetic energy of the particle at the moment it enters the chamber, and the drag imposed by the air on the particle travelling through it. In the case of the lamina, the weight is low and surface area high. Thus it travels only a short distance before the drag has dissipated its kinetic energy. In the case of a stem, the opposite is true, and it travels much further. This gives a convenient basis for dispersing the tobacco.

Turning now to FIG. 1, there is shown a diagrammatic sectional view of a high efficiency separator in accordance with one embodiment of the invention. An enclosure is provided defining a primary separation chamber generally indicated by reference numeral 11 and a secondary separation chamber generally indicated by reference numeral 12. The primary and secondary chambers are adjacent to one another and are separated by a divider plate 13. As shown in FIG. 1, the primary and secondary chambers have respective hood portions 11a and 12a, with the walls defining the hood portions tapering in so as to gradually reduce the cross-sectional area of the chambers adjacent the top thereof. The hood sections 11a and 12a commonly terminate at an unloading duct 14.

An inlet 16 is provided for admitting a threshed tobacco mixture into the primary chamber. Situated adjacent the inlet is a first paddle type winnower 17. The winnower 17 is coupled to a source of power (not shown) and is adapted to rotate in the direction shown by the arrow in FIG. 1. A second paddle type winnower 18 is mounted in the primary chamber 11 at a side thereof opposite the side where the first winnower 17 is mounted. The winnower 18 is also adapted to be driven by a power source (not shown) for rotation in the direction indicated by the arrow shown on the winnower 18 in FIG. 1.

A suitably sized fan 19 is provided as a source of air for the separator. Air from fan 19 is coupled through an inlet 21 into a plenum chamber 22. A damper 23 can be provided adjacent the air inlet 21 for adjusting the amount of air admitted to the plenum chamber 22. Both a horizontal tubular diffuser 24 and an inclined tubular diffuser 26 are mounted in the side of the primary chamber underneath the first winnower 17. These two tubular diffusers are coupled to the plenum chamber 22, and air in the plenum chamber 22 is admitted to the primary chamber 11 by means of these tubular diffusers. The tubular diffusers respectively include slide plates 27 and 28 for adjustments of the volume of air admitted through the diffusers into the primary chamber 11.

A conveyor means 29, which can be a simple belt conveyor, is provided extending across the bottom of the primary chamber 11 and into the secondary chamber 12. As shown in the drawing, the conveyor 29 is inclined upwardly across the bottom of the primary chamber 11 and into the secondary chamber 12.

A portion of the air from the tubular diffuser 24 is admitted via a damper 31 into a conduit 30 underneath the conveyor 29 and exits under a head roller 45 of the conveyor 29 into the bottom of the secondary chamber 12. The secondary chamber 12 includes an additional divider plate 32 extending only part way up the secondary chamber 12, as shown in FIG. 1. As shown in FIG. 1, the divider plate 32 separates the bottom of the secondary chamber 12 into a left portion 35 and a right portion 40. The conveyor means 29 extends across the left portion 35 such that the head roller 45 is underneath divider plate 32. Thus, the air coupled by conduit 30 establishes the generally upward air flow in the right portion 40 of the bottom of the secondary chamber. The upward air flow in the left portion 35 is primarily established by air from the horizontal diffuser 24 passing underneath divider plate 13.

Coupled to the bottom of the secondary chamber 12 is a stem collection chute 33. An air lock 34 is provided in the chute 33 for rotation in the direction shown to permit collection of tobacco stems while preventing air loss through the chute 33.

Tobacco lamina which are carried upwards in the primary and secondary chambers 11 and 12 are admitted into the unloading duct 14. The unloading duct 14 is coupled to a centrifugal separator 36 which also includes an air lock 37 for permitting collection of lamina without loss of air. Air from the centrifugal separator 36 is recycled to the fan 19. A damper 38 is provided at the top of the hood section 12a of the secondary chamber where it adjoins the unloading duct 14.

As an aid in understanding the operation of the embodiment of the invention shown in FIG. 1, lamina, stem, and air currents are represented in the drawing in accordance with the legend shown in FIG. 1.

In operation, air from the fan 19 is admitted through the air inlet 21 into plenum chamber 22, and from there to the tubular diffusers 24 and 26. The tubular diffuser 24 is horizontally disposed, and the tubular diffuser 26 is inclined upwardly. In accordance with one embodiment of the invention, it has been found that inclining the tubular diffuser 26 at an angle of 55.degree. with respect to the horizontal works well in achieving desired air flows in the primary chamber 11. The velocity of the air entering through the two tubular diffusers into the primary chamber is controlled by the damper 23. The slide plate adjustments 27 and 28 on each of the two tubular diffusers serves to further control the amount of air admitted to the primary chamber, as well of course as the division of the air between the two tubular diffusers.

The air flow established by the two tubular diffusers in the primary chamber is generally shown by the arrows in FIG. 1. The air flow has both horizontal and vertical components, and the air flow is such as to establish a generally upwardly air flow in the primary chamber. The horizontal air components, particularly from the diffuser 24, also have strong horizontal components tending to establish air flow components from left to right in the lower portion of the primary chamber shown in FIG. 1.

Tobacco admitted through the inlet 16 is projected into the primary chamber 11 by the winnower 17. The tobacco thus projected into the primary chamber is acted upon by the intersecting upward air flow on the left hand side of the primary chamber, and to some extent by the upward air flow from horizontal diffuser 24, whose output is deflected by divider plate 13 upwards in the right hand portion of the primary chamber 11. A large proportion of free lamina in the thus projected tobacco mixture is carried upwards by the rising air flow in the primary chamber. The first paddle type winnower 17 and the second paddle type winnower 18 are, as shown, positioned on opposite sides of the primary chamber. Also, the second winnower 18 is positioned lower than the first winnower 17. The positioning relationship between the two winnowers 17 and 18 is such that the tobacco mixture tangentially projected by the first winnower 17 strikes the second winnower 18 positioned on the opposite side of the chamber 11. Of course, a large proportion of free lamina in the thus projected mixture is carried upwards by the rising air flow in the primary chamber 11 into the hood section 11a, and thus does not encounter the second winnower 18. The second winnower 18 projects the tobacco mixture in a slightly upward trajectory back across the primary chamber 11, where the thus projected mixture is once again acted upon by the horizontal and vertical components of the air from the diffuser 24. More separation takes place during the second pass across the primary chamber, with additional lighter particles such as lamina being carried upwardly by the air flow and the heavier particles such as stem being subject to greater inertial and gravitational forces so as to move downwardly in the primary chamber 11. Borderline particles projected by the winnower 18 are blown up the divider plate 13 by the air flow out of the diffuser 24, with the thus blown particles being picked up again by the winnower 18 and projected across the primary chamber for a second chance at separating light particles such as lamina from heavy particles such as stems. The heavy particles such as stem fall in the primary chamber to the inclined conveyor 29, and are carried by the inclined conveyor 29 underneath the divider plate 13 into the secondary chamber 12.

Thus, as has been described, in the primary chamber 11 the tobacco mixture is dispersed by the two winnowers 17 and 18 and by the turning air stream from the tubular diffusers 24 and 26 acting against the flow of tobacco from the second winnower 18. Separation of lighter particles such as lamina or leaf from heavier particles such as stem is effected all through the primary chamber 11. In the hood section 11a at the top of the primary chamber the cross-sectional area is gradually reduced, which has the effect of causing higher air velocities so that entrained lamina particles are accelerated into the loading duct 14. The loading duct 14 transports entrained lamina to a centrifugal or tangential separator 36 for separating the lamina from the air stream. The air is returned to the fan 19 and lamina exits through an air lock 37 for collection.

The secondary chamber 12 shown in FIG. 1 functions in accordance with the same separation principles as the primary chamber. However, the secondary chamber does not include any winnowers. Rather, the inclined conveyor 29 which conveys the heavier particles collected in the primary chamber into the secondary chamber also projects them into the bottom portion of the secondary chamber. In fact, the particles are projected into the air stream in the right portion 40 at the bottom of the secondary chamber. Air is admitted into the right portion 40 at the bottom of the secondary chamber via its path through the damper 31 and underneath head roller 45 of the conveyor 29. Air flow in the left portion 35 at the bottom of the secondary chamber is established by the horizontal diffuser 24 underneath the divider plate 13, all as shown by the arrows in FIG. 1.

The divider plate 32 positioned in the secondary chamber 12 near the bottom thereof provides the right portion 40 with a generally small cross-sectional area. The relatively small cross-section of the area 40 results in a relatively high velocity of air and entrained particles up from the bottom of the secondary chamber 12. However, once the entrained tobacco product reaches the top of the divider plate 32, the area of the secondary chamber suddenly increases, and the air velocity drops. This provides an area of flotation for lighter particles such as lamina where a fine control can be exercised over separation of lamina from heavier particles such as stem. Lamina is entrained by the upwardly rising air flow in the secondary chamber 12 and carried through the hood section 12a into the unloading duct 14. As shown in FIG. 1, the right bottom portion 40 is inclined to the left at the bottom of the secondary chamber. Thus, in the separation area above divider plate 32 any heavier particles such as stem are projected to the left above divider plate 32 and fall back down the secondary chamber 12, to the left of the divider plate 32 into the left portion 35 and again onto the conveyor belt 29. Thus, any lamina or lighter particles entrapped by a heavy leaf, for example, which falls back down to the left of the divider plate 32 will drop back onto the conveyor belt and will be projected back into the right portion 40 at the bottom of the secondary chamber 12 to provide another opportunity for separation.

Heavy particles such as stem fall to the bottom of the secondary chamber 12 and pass into a stem collection chute 33, which may include an air lock means 34 rotating as shown in FIG. 1 for discharging the stems and heavier particles without air leakage.

The separator as has been described in connection with FIG. 1 thus provides a total of four opportunities for separation of lighter particles such as lamina or leaf from heavier particles such as stem to take place. The separator in accordance with this invention has a far higher efficiency than previous separation machines which provided only two opportunities at most for separating lighter particles from heavier particles. The separator of this embodiment of the invention has simplified controls in that there is a main damper 23 to regulate the total circulation of air in the primary and secondary chambers, and two secondary dampers 31 and 38 which, functioning together, control the flow of air and hence separation in the secondary chamber 12. The separator in accordance with FIG. 1 may be constructed in various widths to accommodate various loads, and has an approximate air volume requirement of 2,000 SCFM per foot of width.

The use of two winnowers in accordance with the present invention enables the tobacco mixture to be projected twice across the primary chamber, thus dispersing the tobacco mixture much better than the prior art. It also enables the machine to be loaded and unloaded at opposite ends, which makes the incorporation of a secondary separation chamber 12 possible.

Turning now to FIG. 2, there is shown a diagrammatic sectional view of an additional embodiment of a high efficiency separator in accordance with the principles of the present invention. In the embodiment of the invention shown in FIG. 2 the details of the separator are similar to a large extent to the details of the separator of FIG. 1, and like reference numerals have been used in FIG. 2 to refer to portions of the separator of FIG. 2 that are unchanged over that shown and described in connection with FIG. 1. The main difference between the embodiment of the invention shown in FIG. 2 and that described in connection with FIG. 1, is the manner in which air is supplied and admitted into the primary and secondary chambers of the separator. In the embodiment of FIG. 2, air from the fan 19 is admitted via an air inlet 41 into a plenum chamber 42. A damper 43 is disposed adjacent the air inlet for regulating the volume of air admitted. As before, a conveyor means 44 is disposed across the bottom of the primary chamber 11 and extending across a portion of and into the secondary chamber 12 adjacent the bottom thereof. In accordance with this embodiment of the invention, the conveyor means 44 is a belt conveyor that has a belt 46 that is perforated for admitting air to pass therethrough. In the case of the embodiment of FIG. 2, the conveyor means 44 is inclined, but inclined downwardly across the bottom of the primary chamber 11 and extends into the secondary chamber 12 across the left portion 35 terminating generally under the divider plate 32. In the embodiment of the invention illustrated in FIG. 2, air that is used for separation in the primary and secondary chambers enters from underneath and passes through the perforated belt 46 into the primary chamber 11 and the left portion 35 at the bottom of the secondary chamber 12. For the separation in the main chamber 11, air passes through the perforations in the belt 46, with the perforations acting to diffuse the air effectively, and the air flow within the primary chamber 11 is vertical. The belt 46 in the embodiment of FIG. 2 is self-cleaning as it travels from top to bottom. In accordance with one embodiment of the invention, the conveyor means 44 is inclined at an angle of 15.degree. from the horizontal, and extending "downhill" across the bottom of the primary chamber into the secondary chamber. The reason for the incline of the conveyor means 44 is to assist in the discharge of the heavier particles. That is, due to the air rising through the perforations in the perforated belt 46 there is somewhat of an air-cushion effect, so that the heavy particles carried on the belt receive very little traction from the belt. Inclining the belt assists in the belt serving to transport heavy particles.

In the embodiment of the invention disclosed in FIG. 2, the secondary air chamber 12 functions the same as the secondary air chamber 12 described in connection with FIG. 1. The only difference is that in the embodiment of FIG. 2 air enters into the left portion 35 at the bottom of the secondary chamber 12 through perforations in the belt 46. As before, air to the right portion 40 and the bottom of secondary chamber 12 enters from under and around a head roller 45 at the bottom of the secondary chamber. As before, the total air circulation through the primary and secondary chambers is controlled by a damper 43 adjacent the air inlet 41, and an additional damper 48 is provided at the top of the hood section 12a of the secondary chamber 12 to provide a further individual control over air flow in the secondary chamber.

There has been described what at present are considered to be the preferred embodiments of the invention. It should be clear, however, that various modifications are possible to the specifics of the disclosed preferred embodiments without departing from the true spirit and scope of the invention. The scope of the invention is intended to be defined in the appended claims.