CA1085776A - Yoke shaped separation chamber with feed and flow control means - Google Patents

Abstract

YOKE SHAPED SEPARATION CHAMBER
WITH FEED AND FLOW CONTROL MEANS

ABSTRACT
A pneumatic material separator having adjacent generally vertical primary and secondary ducts, a generally vertical discharge duct communi-cating with the tops of the primary and secondary ducts and an apparatus for creating upwardly moving columns of gas in the ducts is disclosed.
All of the ducts are of equal width and have substantially rectangular cross sections. An air foil at the junction of the primary and discharge ducts is present to minimize the turbulence of gas moving therebetween. A
star feed apparatus introduces particulate material into the primary duct where the material is separated, by the upwardly moving column of gas, in-to an upwardly moving lighter fraction discharged through the discharge duct and a downwardly moving heavy fraction discharged through the primary duct. The secondary duct may be located beneath a portion of the discharge duct where gas velocity is reduced and may be oriented to receive downwardly falling objects so that the heaviest particles of the lighter fraction fall into and are discharged through the secondary duct. The secondary duct is positioned so that a column of gas moving upwardly therethrough, moves in the same general direction as the column of gas in the discharge duct so that the columns merge at a small acute angle to minimize turbulence. A
venturi formed at the top of the secondary duct accelerates the flow of gas therethrough, which flow is adjustably controlled by a damper inside the duct.

Description

1~85776 APPARATUS AND METHOD FOR PNEUMATICALLY SEPARATING
PRACTIONS OF A PARTICULATE MATERIAL

This apparatus relates generally to particle separation and more particularly to the separation of particulate material through the usé of upwardly moving streams of air or other gas.
The classification of particulate material according to density and/or aerodynamic properties by passing the particulate mixture through zones of differing air velocity has been known and practiced for a number of years. Air classification systems have been used for removing rocks or other foreign matter from such commodities as wheat, tea, raisins, wood chips and the like. A primary separation of light from heavy materials is an exceedingly important first step in the handling of heterogeneous parti-culate material. Because of the increasing cost of energy and raw materials ~
the efficiency of this first separation step may be critical in determining , the overall cost efficiency of a materials handling system.

RJP/bc E4 7/22/76 16448 Recently, compliance with environmental restrictions has necessitated the recycling of municipal garbage and in-dustrial waste which in many cases are collected without dis-crimination and contain a diverse mixture of heavy materials such as glass, metal and stones, and of lightweight materials such as paper, leaves and plastic. It is advantageous to separate lightweight from heavyweight materials since in most instances, the lightweight material is combustible and thus usable as a source of energy if separated from the heavier materials.
A variety of different apparatuses have been pro-posed to perform particle separation. The efficiency of these prior art separators has been limited by eatures which were heretofore considered necessary for a succes~ful separation process. Some of these apparatuses include complex duct arrange-ments to create turbulences in the material-bearing gas stream and thereby to improve material separation. Such designs are expensive to con~truct. Also, because of the high turbulence they create, a relatively great amount of energy is invested in moving a gas column through the tortuous ducts.
In other devices a stream of air moves upward in an essentially uninterrupted, straight column. A plurality of outlets on one side of the column are provided for materials to fall through according to their density. If, however, materials of any density or aerodynamic property migra~e to the outlets of such a device, they fall through the outlets.
The efficiency of separation is low because particles of low density and low aerodynamic characteristics will be carried out through outlets provided for the collection of denser or more aerodynamic particles.

~-` 1085776 In still other apparatuses heterogeneous material is carried into a series of columns having upwardly moving gas in each column. Because each column in the series contains gas moving upward at a velocity lower than that of the preceding column, only those particles having the desired density or aerodynamic properties can fall through to the base of each column. Although the accuracy of separation in such devices is good, the operating costs have been relatively high since they have included numerous fans to be driven and many zones of high turbulence where particulate material and/or gas must reverse direction.
Summary of the Invention ;;
It has now been discovered that a highly efficient separation of heavy and light particles may be conducted at a relatively low energy con- -sumption by feeding the heterogeneous material into columns of air which move continuously upward in substantially vertical ducts.
The invention provides apparatus for pneumatically separating frac-tions of a heterogeneous mixture of particulate material according to relative densities and/or aerodynamic properties comprising: an unobstructed, sub-stantially straight primary duct which is not inclined from vertical by more than about ten degrees and which narrows near the top to define a region of accelerating airflow; airlock feed means for feeding material to be separated into said primary duct at a location upstream of said region of accelerating airflow and without admitting a substantial amount of air into said primary duct; a discharge duct connecting with the top of said primary duct and extending upwardly therefrom; means for producing an upwardly moving column of air in said primary and discharge ducts having a velocity operable to raise a light fraction of said material while a heavy fraction falls to the -bottom of said primary duct; a secondary duct which is displaced horizontally from said primary duct and which communicates with only said discharge duct and the surrounding atmosphere so that said secondary duct provides an inlet for admitting a column of air directly, entirely from the surrounding atmos-phere into the interior of said discharge duct at a location shortly down-` stream of said region of accelerating airflo~, to increase the volume of air : : ' : :.

-1~85776 in said upwardly moving column of air in said discharge duct; and adjustable damper means operable to ad~ustably constrict said secondary duct for regulating the velocity of air moving through said discharge duct.
Particulate material is fed into a first upward moving column of air having a velocity such that a buoyant fraction of the material is raised in the column and a dense fraction falls through the column. The first column of air is deflected toward and merged into a second upward moving column of air displaced horizontally from the first column. The combined column is caused to move upwardly at a velocity less than the velocity in the first column so that heavier particles of the buoyant fraction and any dense particles which may have been unintentionally carried into the combined column will fall down into the second column and then fall to the base of that column. Lighter materials of the buoyant fraction are carried off by the combined column to a remote point. For maximum flexibility, the apparatus for this operation is designed such that the velocity of air in each column may be ad~usted independently.
Brief Description of the Drawings In the drawings:
Figure 1 is a sectional side elevation of the material separator;
and Figure 2 is a schematic diagram showing the material separator of Figure 1 incorporated as a part of a complete material separation system.
Description of the Preferred Embodiment Referring to Figure 1, the preferred embodiment of the separator of the present invention has a generally vertical duct structure which includes a primary sorting duct 12, the base of , . . i ~

RJP~bc E4 7/22/76 16448 --` 1085776 which defines an output port 14. Opening into the primary duct 12 near the top is a material input duct 16. The primary sorting duct 12 may be substantially vertical as shown by solid lines or may be inclined at an angle ~ under the input duct 16 as shown by broken lines. Preferably the angle ~ is not more than ten degrees from vertical and more preferably not more than five degrees. Conveniently, means are provided for introducing particulate material into the input duct 16 without allowing air to enter the duct. While such means may take a variety of forms, one suitable form is a rotary star feeder 18 as shown in Fig. 1.
A secondary sorting duct 24 is positioned adjacent to the primary sorting duct 12. The width of the secondary sorting duct is reduced near it~ top to form a venturi 34. Because the -throat of this venturi is the narrowest portion of the secondary sorting duct, the column of air moving through the secondary sorting duct reaches maximum velocity as it passes through the venturi 34. This area of high velocity serves as a barrier to low density particles which might fall into the venturi 34. The gecondary sorting duct 24 is provided at its bottom with an output port for the removal of particulate material and could, optionally, be fitted with suitable discharge apparatus such as a rotary star discharge apparatus. An air inlet is provided to admit air into the secondary sorting duct 24. In the embodi~
ment of Figs. 1 and 2 and orifice 26 is provided which serves as both the output port and the air inlet. Alternatively, the secondary sorting duct 24 could include an air inlet and a separate output port such as an airlock discharge device. In either case a damper means may be provided to regulate the flow of air through the inlet. One suitable damper means is the damper 32 shown in Fig. 1.

RJP/bc F.4 7/22/76 16448 , ~

10857~6 Both the pri~ary sorting duct 12 and the secondary sorting duct 24 open into the bottom of a discharge duct 20.
An airfoil 22 is provided at the junction of the material input duct 16 and the discharge duct 20 to reduce the turbulence of air flowing up through the primary sorting duct 12 and into the discharge duct 20. In the preferred embodiment, the duct work includes a region 23 of reduced cross-sectional area near the top of the primary sorting duct so that the airflow and particulate material at that point are accelerated into the discharge duct 20. The discharge duct 20 includes a lower por-tion immediately above the sorting ducts 12, 24 which is sized so that the velocity of air moving through such lower portion is less than the velocity of air moving through the primary sorting duct 12. Because the velocity of air in the lower por-tion of the discharge duct 20 is reduced, the densest particles in the discharge duct can fall downwardly into the venturi 34 and thus be collect~d in the secondary sorting duct 24. The lower portion of the discharge duct 20 iq inclined over the secondary sorting duct 24 at a small angle o from vertical so that an outer wall 36 of the discharge duct serves as a steep ramp which empties into a funnel-shaped mouth 37 of the venturi 34. Preferably the angle o is about five to fifteen degrees .
from vertical. It is desirable, but not essential, that the discharge duct 20 narrow in its upper regions, as illustrated in Fig. 1, so that the column of air bearing the lighter par-ticles of the buoyant fraction accelerates upwardly when it enters the narrowed region.
In the illustrated embodim~nt, the side walls of the .:

various ducts are movable so that the cross-sectional area of the ducts and thus the velocity of air flowing through the .~ , ~ . .
: . -RJP/bc ~4 7/22/76 16~4~

1~85776 ~: ~

ducts may be adjusted. A plurality of hinges ~8 may be pro- '' ' "
vided for ease in moving the side walls. An adjustable means of support, such as turnbuckles 40 hold the walls in the de-sired po~ition.
Means are also provided for producing upward moving ' columns of air in each of the various ducts. The columns are preferably produced by a single suction means adapted to cause a negative pressure in the discharge duct 20. In this preferred configuration the output port 14 and orifice 26 are open to the surrounding atmosphere. Alternatively, upward moving columns of air in the various ducts may be provided by blowers which move columns of air upward through the primary and secondary ', sorting ducts 12, 24,at elevated pressures or by any other suit-able means for creating upward moving columns of air in those ducts.
Operation In operation, a heterogeneous mixture of particulate material is fed into the material input duct 16 by the rotary ~tar feeder 18. The material falls by gravity into the primary , sorting duct 12 where it encounter~ a first upward moving column of air. A dense residual fraction of the material continues to fall by gravity through the primary sorting duct 12 and eventually through the output port 14. A conveyor, bin or other suitable means (not shown) may be provided beneath the output port 14 for collecting the residual fraction. The downward acceleration due to gravity of a buoyant fraction of the material is overcome by the upwardly moving column of air. This buoyant fraction is ,-raised by the column to the point 23 and from there accelerated into the discharge duct 20.

.~ - - , .

~P/bc F~4 8/4/76 164~R

, 108577f~

The column of air carrying the buoyant fraction and a second column of a7r, moving upwardly in the secondary sort-ing duct, merge as they enter the lower portion of the discharge duct 20. Because the cross-sectional area of the lower portion of the discharge duct 20 is large by comparison to the combined :
cross-sectional areas of the duct at the point 23 and the venturi 34, the merged column of air moves through the discharge duct 20 :
at a lower velocity than the column of air moving through the duct at the point 23. In order to collect particulate material 10 in the secondary sorting duct it is necessary that the cross-sectional areas of the discharge duct be set such that air moves through lower portion of that duct at a velocity not greater than the velocity of air in the primary sorting duct 12.
In this zone of decreased velocity, heavier particles of the buoyant fraction can no longer be supported by the moving column of air and will fall downwardly. Some of the heavier particles of the buoyant fraction fall against the outer wall 36 and, because the air flow will be ~lower there, may there-after roll or slide down into the mouth 37 of the venturi 34.
20 Other of the heavier particles fall directly into the funnel shaped mouth 37. Any of the heavier particles which fall back toward the point 23 are again raised on the high velocity column of air which enters the discharge duct 20 from the pri- ~ .
mary sorting duct 12. Because the discharge duct 20 is in-clined, the high velocity column of air carries most of these heavier particles to a position from which they can fall against the wall 3~ or directly into the mouth 37. All of the particles which fall into the mouth 37 encounter a second column of air which flows upwardly through the venturi 30 34. The particles continue to fall to the bottom of the second-ary sorting duct 24 only if the downward gravitational forcs .

RJP/lkt Bl 20795 3jl2/79 ~85776 acting on the particles is sufficient to overcome the upward force of this second column of air. Those particles which succeed in falling to the bottom of the secondary sorting duct 24 are thereafter discharged through the output port formed 5 by the orifice 26. Those lighter particles of the buoyant fraction which are not accelerated downwardly by gravity when they enter the discharge duct 20 are instead carried up into the upper regions of the discharge duct 20 and thereafter through an upper output port 42.
The density and/or aerodynamic characteristics of particles which enter the secondary sorting duct 24 may be regulated by the damper 32 which is adjustable to vary the flow of air through the throat of venturi 34. In order for material to fall into the secondary sorting duct, it is neces-15 sary that the damper be adjusted so that the velocity of air moving upwardly through the venturi 34 is not substantially greater than the velocity of air moving in the primary sort-ing duct. If it is desired that the secondary sorting duct be used to collect a fraction of particulate material of a 20 lesser average density than the material collected in the primary sorting duct 12, the velocity of air moving through the venturi 34 is adjusted to be less than the velocity of air in the primary duct. To prevent lightweight particles from falling into the secondary sorting duct 24, the velocity 25 of air moving through the venturi 34 is adjusted to be not substantially less than the velocity of air moving through the lower portion of the discharge duct 20.
As previously described, the air velocities in the primary sorting duct 12 and the discharge duct 20 may be varied 30 by moving the side walls of those ducts. In the preferred ~1.,~,~., .. ,,. ~ -RJP/bc E4 7/22/76 16448 _ .
108~77ti embodiment of the invention the walls of those ducts are posi-tioned so that the desired velocity ratios are achieved by adjusting the damper 32 t~ admit, through the secondary sorting duct, about ten to twenty percent of the total amount of air -moving through the entire system.
The present invention has been successfully used for the separation of rocks from wood chips. In this application, rhe materials to l~e separated are essentially of two densities only. For this reason the velocity of air in each column is adjusted to maximize the collection of rocks in both the pri-mary and secondary sorting ducts so that wood chips carried out of the discharge duct on the combined columns of air are substantially free of rocks. Tests using the improved materials separator of the present invention demonstrated a highly ef-ficient removal of 0.25 inch diameter rocks from wood chips.
The separator used for these tests had a primary sorting duct 174 sq. in. in cross-sectional area, a discharge duct with a lower portion 234 sq. in. in cross-sectional area, and a venturi having a cross-sectional area of twentv-four sq. in. In each 20 run, the discharge duct was inclined at five degrees from ;~
vertical and air moved through the venturi at a velocity of twenty to thirty feet per second. The results of several typical runs are listed in Table I.
TABLE I

Primary sort- Air velocity Rocks Discharged (percent) ing duct in primary Primary~-S-econdary T~
Run No. inclination sorting duct sorting sorting (ft/sec.) duct duct _ 1 0 48.9 90.3 3.7 94.0

2 0 49.3 88.2 7.3 95.5

3 5 53.3 96.2 1.9 98.1

4 10 53.0 88.1 6.0 94.1 RJP/bc E~ 7/22/76 1644~
. ~
~8S7~;

The separator of the present invention is also well suited for the primary separation of shredded municipal waste.
When used for this purpose, the various ducts are preferably adjusted so that the columns of air in both the sorting ducts and the discharge duct move upward at a velocity sufficient to raise lightweight materials such as paper and plastic which are generally combustible, but insufficient to raise heavier materials. At these conditions, the only particles which are collected in the secondary sorting duct 24 are those particles of the dense residual fraction which instead of falling through the bottom of the primary sorting duct 12, are unintentionally accelerated into the bottom of discharge duct 20. As compared to single column separators of similar capacity, the capture of material in the secondary sorting duct 20 of the present invention accounts for an overall improvement in separation of approximately five to ten percent.
Fig. 2 illustrates the ~eparation apparatus of the present invention in a complete system for processing shredded waste. Except for the material separator of the pre~ent inven-tion, all of the equipment illustrated is of standard design.
Shredded refuse is fed into the rotary airlock feeddevice 18 of the present invention. The residual fraction of material discharged from a separation apparatus at the output port 14 of the primary sorting duct and/or the heavier particles of the buoyant fraction which are discharged from the orifice 26 of the secondary sorting duct are collected by any suitable means. ~he lighter particles in the buoyant fraction are carried upwardly through the discharge duct 20 into a cyclone 60 which serves as a convenient separating means where the lightweight particulate materials are separated from the column ~, , . . .
.. , , :

RJP/bc E~ 7/22/76 16~4~
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10857'76 of air. Other conventional devices for separating solid particles from a gas would serve equally well for the same purpose. The lightw~ight particles are discharged from the bottom of the cyclone via a suitable airlock discharge device 62 and thereafter collected and transported to any desired location. If the air moving through the system is contaminated by toxic gases or lightweight solids, such as dust or lint, which might be harmful to the environment, a suitable treatment apparatus, indicated at 66, may be installed in the system to scrub undesirable contaminànts from the air. A blower 68 is the sole means for moving air through this preferred system.
It draws air through the entire system by creating a negative pressure in the duct indicated at 70. Air passing through this system is discharged to the atmosphere from the outlet 72 ;;
of the blower. To achieve maximum flexibility and efficiency, the blower 68 should be adjustable to vary the flow of air through the system and be equipped with automatic controls to maintain the flow of air at a constant rate so that particles collected in the various ducts of the separation apparatus will be within a uniform range of densities.
The separating apparatus of the present invention may also be used in a closed cystem. In a closed system, environmental discharge are further reduced and/or gases other than air may be used to transport the particulate material.
The complete system described above may be modified to a sub-stantially closed system by returning gas from the outlet of the blower to the output port 14 and orifice 26 which serves as gas inlets of the sorting ducts.

~ hile I have shown and described a preferred embodi-ment of my invention, it will be apparent to those skilled in -, - - , . .. . .

RJP/hc ~4 7/22/7h 16448 -the art that changes and modifications may be made without departing from my invention in its broader aspects. I there-fore intend the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

Claims (14)

The embodiments of the invention in which an ex-clusive property or privilege is claimed are defined as fol-lows:

1. Apparatus for pneumatically separating frac-tions of a heterogeneous mixture of particulate material ac-cording to relative densities and/or aerodynamic properties comprising: an unobstructed, substantially straight primary duct which is not inclined from vertical by more than about ten degrees and which narrows near the top to define a region of accelerating airflow; airlock feed means for feeding ma-terial to be separated into said primary duct at a location upstream of said region of accelerating airflow and without admitting a substantial amount of air into said primary duct;
a discharge duct connecting with the top of said primary duct and extending upwardly therefrom; means for producing an up-wardly moving column of air in said primary and discharge ducts having a velocity operable to raise a light fraction of said material while a heavy fraction falls to the bottom of said primary duct; a secondary duct which is displaced hori-zontally from said primary duct and which communicates with only said discharge duct and the surrounding atmosphere so that said secondary duct provides an inlet for admitting a column of air directly, entirely from the surrounding at-mosphere into the interior of said discharge duct at a loca-tion shortly downstream of said region of accelerating air-flow, to increase the volume of air in said upwardly moving column of air in said discharge duct; and adjustable damper means operable to adjustably constrict said secondary duct for regulating the velocity of air moving through said dis-charge duct.

2. Apparatus of claim 1 wherein said secondary duct is positioned in relation to said discharge duct such that said column of air moving through said discharge duct moves in the same general direction as said column of air moving through said secondary duct so that said columns con-verge at a small acute angle, whereby minimum turbulence will occur at the region of convergence.

3. Apparatus of claim 1 wherein said secondary duct narrows to form a venturi adjacent the location where said discharge and secondary ducts connect so that minimum turbulence will occur at the region of convergence.

4. Apparatus of claim 1 wherein said airlock feed means comprises an airlock feeder; a material input duct which connects said feeder with said primary duct; and air-foil means located at the junction of said material input duct and said primary duct to minimize the turbulence of air flowing upwardly through said primary duct into said region of accelerating airflow.

5. Apparatus of claim 1 wherein a plurality of moveable sidewalls and two fixed, flat, parallel endwalls define said primary, secondary and discharge ducts; all of said sidewalls are of equal width; and all of said sidewalls extend normally between said endwalls.

6. Apparatus of claim 1 wherein all of said ducts are of equal width and having substantially rectangular cross sections so that air admitted through said secondary duct is distributed substantially evenly across the entire width of said discharge duct.

7. Apparatus of claim 1 wherein said damper means is adjustable to limit the flow of air through said secondary duct such that air moves through a portion of said secondary duct at a velocity not substantially less than the velocity of air moving through the lower portion of said discharge duct.

8. Apparatus of claim 1 wherein said air inlet is proportioned to admit a volume of air which is about ten to twenty percent of the total volume of air admitted into the apparatus.

9. Apparatus of claim 1 wherein said discharge duct is inclined from the top of said primary duct over said secondary duct.

10. Apparatus of claim 1 further comprising an out-put port in said secondary duct.

11. Apparatus of claim 10 wherein said output port comprises the only air inlet communicating with said secondary duct.

12. Apparatus of claim 1 wherein said primary duct is inclined under said feeding means.

13. Apparatus of claim 1 wherein said secondary duct is disposed in relation to said discharge duct such that at least some of any particulate material falling downwardly in said discharge duct will fall into said secondary duct.

14. Apparatus for pneumatically separating frac-tions of a heterogeneous mixture of particulate material ac-cording to relative densities and/or aerodynamic properties comprising: an unobstructed, substantially straight primary duct which is not inclined from vertical by more than about ten degrees and which narrows near the top to define a region of accelerating airflow and which is open to the atmosphere at the bottom thereof; a generally straight discharge duct ex-tending upwardly from the top of said primary duct, connected to said primary duct, inclined at an angle of between five and fifteen degrees from vertical and having moveable walls which are positioned such that a column of air moving through a region at the bottom of said discharge duct moves at a ve-locity less than the velocity of a column of air in said pri-mary duct; a rotary star feed device for feeding material to be separated into said primary duct, without admitting a sub-stantial amount of air, at a location shortly below said top of said primary duct and upstream of said region of acceler-ating airflow so that there is a short, unobstructed path be-tween said location and the interior of said discharge duct;
airfoil means located at the junction of said primary and dis-charge ducts to minimize the turbulence of air flowing up-wardly through the primary duct and into the discharge duct;
a generally vertical secondary duct which is displaced hori-zontally from said primary duct and which communicates with only said discharge duct and the surrounding atmosphere so that said secondary duct provides an inlet for admitting a column of air directly, entirely from the surrounding atmos-phere into the interior of said discharge duct at a region shortly downstream of said region of accelerating airflow, to increase the volume of air in said upwardly moving column of air in said discharge duct and having damper means operable to adjustably constrict said secondary duct for regulating the velocity of air moving through said discharge duct; said secondary duct being disposed in relation to said discharge duct such that at least some of any particulate material fall-ing downwardly in said discharge duct will fall into said secondary duct; said secondary duct narrowing at its top to form a venturi having an upwardly opening funnel-shaped mouth which opens into said discharge duct, said venturi being po-sitioned in relation to said discharge duct such that said column of air moving through said discharge duct moves in the same general direction as said column of air moving through said secondary duct whereby said columns converge at a small acute angle so that the entire volume of a column of air moving through said secondary duct is accelerated upwardly and merged, with a minimum of turbulence, into the column of air already moving upwardly in said discharge duct; and suction means com-municating with the top of said discharge duct for producing an upwardly moving column of air in said primary duct having a velocity operable to raise a light fraction of said material into said discharge duct while a heavy fraction falls to the bottom of said primary duct, and for producing an upwardly moving column of air in said secondary duct having a velocity such that at least a portion of the light fraction in said discharge duct can fall downwardly through said secondary duct, all of said ducts being defined by a plurality of move-able sidewalls and two fixed, flat, parallel endwalls, all of said sidewalls being of equal width and extending normally between said endwalls so that all of said ducts are of equal width and have substantially rectangular cross sections where-by air admitted through said secondary duct is distributed sub-stantially evenly across the entire width of said discharge duct.