US3907670A

US3907670A - Air classifier for municipal refuse

Info

Publication number: US3907670A
Application number: US481416A
Authority: US
Inventors: John Henry Fernandes
Original assignee: Combustion Engineering Inc
Current assignee: Combustion Engineering Inc
Priority date: 1974-06-20
Filing date: 1974-06-20
Publication date: 1975-09-23
Anticipated expiration: 1992-09-23
Also published as: CA1011289A; AU8220675A; FR2275257A1; DE2523323A1; SE7507057L; IT1038914B; ES438647A1; ZA753903B; JPS5423460B2; GB1507751A; FR2275257B1; JPS5113472A

Abstract

Apparatus comprising an elutriation column for classifying a heterogeneous mixture of particulate solids material is provided with means for improving the classification of the material fractions primarily on a density basis. The material to be classified is impacted with sweep air upstream of the elutriation column for reducing the size of any bundles of agglomerated particles admitted to the apparatus thereby reducing the affect of sail area on the classification process. Additional means are provided downstream of the elutriation column for dispersing reagglomerated particles whereby the same can be returned to the elutriation column for reprocessing.

Description

United States Patent [191 Fernandes Sept. 23, 1975 1 1 AIR CLASSIFIER FOR MUNICIPAL REFUSE John Henry Fernandes, Windsor, Conn.

[75] Inventor:

22 Filed: June 20,1974

21 App1.No.:481,416

[52] US. CL... 209/137; 209/139 R; 209/147 [51] Int. Cl. B07B 7/01; B078 1 1/06 [58] Field of Search 209/3, 136-139 R, 209/140, 141, 146, 147, 153, 149; 241/19,

1 42 lo 28 3O Gebauer 209/3 Brown 209/3 X Primary Examiner-Frank W. Lutter Assistant ExaminerRalph J. Hill [57] ABSTRACT Apparatus comprising an elutriation column for classifying a heterogeneous mixture of particulate solids material is provided with means for improving the classification of the material fractions primarily on a density basis. The material to be classified is impacted with sweep air upstream of the elutriation column for reducing the size of any bundles of agglomerated particles admitted to the apparatus thereby reducing the affect of sail area on the classification process. Additional means are provided downstream of the elutriation column for dispersing reagglomerated particles whereby the same can be returned to the elutriation column for reprocessing.

14 Claims, 4 Drawing Figures US Patent Sept. 23,1975

III/III 1 II I I FIG. 3

LIGHT MATERIAL 32 OUT AIR CLASSIFIER FOR MUNICIPAL REFUSE BACKGROUND OF THE INVENTION The present invention relates to air classification apparatus that is especially useful in solids refuse disposal systems. More particularly, it relates to an improved air classifier that is adapted to more accurately separate the various fractions of material delivered to a refuse disposal system on a density basis.

Modern municipal refuse is a heterogeneous mixture of predominantly solid material, the diposal of which presents significant problems. Systems are under development whose purpose it is to recover as much as practicable of the resources embodied in the refuse for reuse, either as energy by burning the same or for the raw material value of the reclaimed elements. The economic feasibility of such systems is dependent to a great extent upon the accuracy of the mechanical separation of the material into combustible and noncombustible fractions.

It is known that air classification provides an effective method of mechanically separating particulate solids material. Several forms of air classifying apparatus are described in ASME Publication No. 69WA/- PID-9 entitled Air Classification for Reclamation Processing of Solid Waste by R. A. Boettcher. In such apparatus the material to be classified is subjected to a high velocity air stream. The heavy material component that cannot be transported in the air stream moves counter to it and is discharged from one location in the apparatus while the lighter component is entrained in the air stream and conducted thereby to a point of discharge at another location longitudinally spaced from the first.

It will be appreciated that this manner of material classification, while desirably being based solely upon material density, is also largely dependent upon the aerodynamic characteristics or sail area of the material being processed. The affect of sail area upon the classification process can be reduced by preliminary shredding the material prior to its admission to the classifier. This remedy is not totally dispositive of the problem, however, in view of the fact that municipal refuse nor mally contains a significant amount of moisture which imparts to the shredded particles a tendency to agglomerate into bundles as they move along the material flow stream. Such bundling has a detrimental affect upon accurate separation.

Although the aforementioned condition can be somewhat improved by drying the process material, either before or after shredding but prior to classification, to reduce the moisture content below about fifteen percent creates the danger of fire by the spontaneous ignition of the particulate material. Thus the prevention of agglomeration by drying cannot, as a practical matter, be totally achieved.

It is to the solution of such problems, therefore, that the present invention is directed.

SUMMARY OF THE INVENTION According to the present invention there is provided apparatus for more accurately pneumatically classifying a heterogeneous solids mixture on a density basis. Primary classification is effected within an elutriation column by the action of a high velocity air stream upon the process material admitted thereto. Means are provided for stripping light materials from the agglomerated bundles prior to depositing the same within the elutriation column. Additional means are also provided downstream of the elutriation column for dispersing any bundles of reagglomerated particles by the imposition of turbulent eddies and the impact of the bundles on the surfaces of the duct members whereupon the particles are returned to the elutriation column for reprocessing. The inventive apparatus therefore comprises a generally laterally extensive distribution chamber; means for supplying material to be processed to one end of said distribution chamber; means for directing high velocity sweep air longitudinally of said distribution chamber in impinging relation to the material therein; a generally upstanding elutriation column communicating at its top with the other end of said distribution chamber, the bottom of said column being open for the discharge of the more dense material fraction; means for supplying high velocity elutriation air to said column for upward flow therethrough; and a duct extending obliquely upwardly from the juncture of said distribution chamber and said elutriation column, said duct communicating at one end with said juncture and its other end being open for the discharge of the less dense material fraction therefrom.

A principle object of the invention, therefore, is to provide improved pneumatic classifying apparatus that is capable of more accurately classifying a heterogeneous mixture of particulate material on a density basis.

Another object of the invention is to provide improved apparatus of the described type which is capable of use in a solid waste material reclamation and disposal system for more effectively separating the process stream into component fractions primarily on a density basis. 1

Yet another object of the invention is the provision in apparatus of the described type of means for effectively dispersing any bundles of agglomerated particles both before and after primary pneumatic classification in order to achieve a more accurate separation of the material fractions.

Still another object of the invention is to provide improved apparatus of the described type in which effec tive distribution of the waste material delivered to the apparatus is effected in order to improve the accuracy of material separation.

These and other objects, features and advantages of the invention will become more fully apparent from the following detailed description when taken together with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a flow diagram illustrating a municipal waste disposal system utilizing a pneumatic classifier of the present invention;

FIG. 2 is an enlarged somewhat schematic representation of the pneumatic classifier of FIG. 1;

FIG. 3 is a section taken along line 3-3 of FIG. 2; and

FIG. 4 is a partial view of apparatus similar to that shown in FIG. 2 but illustrating an alternate embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 of the drawing illustrates a schematic flow diagram of part of a typical municipal refuse disposal systern incorporating an air classifier, indicated as 10, constructed according to the present invention. The illustrated portion of the system includes a receiving station 12 into which truckloads of refuseare deposited. Appropriate conveying equipment, indicated as belt conveyors l4 and 16, are utilized to move the refuse first to a shredder l8where it is-reduced to a particle size convenient for the processing of the material, and thence to the inlet of the classifier 10. The shredder 18 is preferably operated to reduce the particle size of the refuse to less than a two inch maximum dimension which has been determined to be an effective size for the processing steps in the disposal system. Within the classifier the particulate process material is divided into two fractions primarily on a density basis as hereinafter more fully described. The heavy fraction is removed from the classifier for disposal or further processing by a belt conveyor 20 or the like which underlies the apparatus. The light fraction is passed to a particle separator 22 in which the solid component of the fraction is separated from the carrier air. An induced draft .fan 24 effects primary air flow through the apparatus while a forced draft fan 26 may be utilizedin conjunction with the induced draft fan to augment air flow through that portion of the classifier termed the elutria- A member defining an inlet 36 that is adapted to receive shredded material from the conveyor 16. The inlet 36 overlies one end of belt conveyor 38 that is housed in the compartment 40. The conveyor 38 operates to convey the. process material to the opposite end of the compartment where it discharged the same into the upper end of upstanding inlet chute 42. The inlet chute 42 serves .to conduct the material downwardly for deposition into the rearward end of the distribution section 30. A

-The distribution section is positioned below the inlet section 28 and comprises a generally horizontally elongated chamber, having rectangularly disposed walls and a bottom plate or deck 46 onto which the shredded process material is deposited. As shown in FIG. 2, the deck 46 may be inclined downwardly toward the forward end of the chamber in order to facilitate movement of the process material therethrough. An inclination of about 5 to 10 degrees is suitable for this purpose.

As shown best in FIG. 3, the opening, indicated as 47, that forms the juncture between inlet chute 42 and the chamber 44 is preferably coextensive with the plate which defines the rear end wall of the latter. Below the opening 47 an elongated flow nozzle 48 penetrates the rear end wall of the distribution section 30 through opening 50. The nozzle 48 is connected to a manifold 52 which supplies air under pressure to the chamber 44 from a fan 54. The nozzle 48 is positioned immediately adjacent the deck 46 and is operatively disposed to impart a relatively high velocity stream of sweep air across the length of the chamber 44. The sweep air stream operates on the material deposited in the chamber to tear off lighter high sail area pieces from the bundles of accumulated refuse material. It also serves to tumble the higher density material across the deck 46 for ultimate discharge into the elutriation column 32. Tumbling of the material in this manner tends to break up any bundles-of agglomerated material prior to its discharge into the elutriation column.

The elutriation column 32 comprises a vertically elongated conduit that communicates at its upper end through opening 56 with the forward end of the chamber 44. The column 32 is arranged to effect pneumatic classification of the materialsupplied to it in the well known manner of providing an upwardly directed air stream which is projected through the falling mass of material. The air stream is maintained at a predetermined velocity which depends upon the desired classification split andentrains the light material fraction that it conveys for ultimate discharge from the particle separator 22. Heavy material that cannot be transported in the air stream at the set velocity moves downwardly through the column, countercurrent the direction of the air stream, for discharge from the bottom thereof. Elutriating air is admitted to the column by means of an air inlet conduit 58 which, in the preferred form, connects between the column and forced draft fan 26. The conduit 58 is inclined upwardly at an angle with respect to the axis of the column and is provided with adjustable dampers 60 which operate to regulate the velocity of the elutriating air stream produced in the column.

In some applications of the classifier 10 it is contemplated that the fan 26 can be omitted. In these applications an air stream of adequate velocity is induced through the conduit 58 into the elutriation column 32 solely by operation of induced draft fan 24 shown in FIG. 1.

The exhaust section 34 of the apparatus comprises an upwardly inclined duct 64 terminating in a vertical outlet leg 66. The outlet leg v66 connects with the tangential inlet 68 of the particle separator 22. As shown, the duct 64 connects atv its lower end with the chamber 44 of distribution section 30 at the outlet, or right hand end, thereof. The point of communication of the duct with the chamber is preferably disposed closely adjacent the opening 56 from the elutriation column 32 such that the duct receives flow from both the chamber and the elutriation column. The internal dimensions of the duct 64 are such as will define a flow area sufficient to provide a velocity of fluid, flow that is at least equal to the flow velocity through the elutriation column 32 in order to prevent any adverse affect upon the flow of fluid through the system.

The duct 64 is preferably disposed at an angle of about 45 with respect to the horizontal and is therefore angularly offset from the longitudinal axisof both the chamber 44 and the outlet leg 66. It therefore cooperates with these elements to define edges, indicated as 68 and 70, along the fluid flow path about which turbulent eddies are generated. Such eddies operate on the material flowing toward the light material outlet to tumble the same thereby assisting in dispersing any reagglomerated particles which may be carried into the duct 64 due to the sail area presented by their bundled configuration. This dispersal of agglomerated material is augmented by the impact surfaces provided by the angular relationship existing between the duct 64 and the outlet leg 66 against which the bundles are thrust in undergoing the abrupt changes of direction in flowing through this region of the apparatus. Following their dispersal, the particulate material which is heavier than that intended to be carried bythe air stream falls downwardly into the elutriation column 32 for further processing through the low velocity boundary layers existing adjacent the duct surfaces.

Conventional municipal waste comprises a heterogeneous mixture, listed in order of their densities, of metals, glass, stone, concrete, bricks, plastics, rubber, dirt, cotton, leather, paper, wood, food waste and yard waste. In separating this mixture into combustible and noncombustible fractions it is desirable to effect the classification split at about 100 to 120 pounds per cubic foot. Where the hereindescribed apparatus is utilized for such purposes, its mode of operation is as follows. The refuse material delivered to the classifier is preferably dried to about percent moisture content and reduced in size in shredder 18 to a maximum 7 physical dimension of approximately two inches. The elutriating air fan 26 is operated and dampers 60 adjusted to provide a flow velocity of about 80 feet per second in the elutriation column 32. Sweep air fan 54 is operated to develop an air flow through the distribution section 30. This air flow while being considerably less in total amount than that generated in the elutriation column 32, is at a velocity of about twice that of the latter. At the same time induced draft fan 24 is operated to maintain the fluid flow through the system.

The shredded material is deposited from conveyor 16 into the inlet section 28 of classifier 10 through open ing 36 from whence conveyor 38 discharges the material through chute 42 onto the deck 46 of the chamber 44 adjacent the left hand end thereof as it is viewed in FIG. 2. Under the action of the sweep air entering the chamber 44 through nozzle opening 50 the refuse material is tumbled along the length of chamber 44 toward the opening 56 disposed at the opposite end thereof. Movement of material through the chamber is assisted by the downward inclination of the deck 46. Tumbling of the material plus the action of the sweep air thereon tends to break up any bundles of agglomerated shredded material initially entering the chamber 44. The sweep air in impacting the refuse material also tends to strip or tear pieces of light material from the bundles and carry them directly into the inclined duct 64 of exhaust section 34 for ultimate discharge with the light material fraction. The principle portion of the process material, however, is discharged through opening 56 where it is subjected to the action of the elutriating air stream which is set to convey the light material particles (i.e., those having a density less than between 100 and 120 pounds per cubic foot) upwardly into the duct 64. The heavy particles fall counter the direction of the elutriating air stream through the bottom discharge opening 61 from whence they are conducted from the apparatus by conveyor to discharge outlet 62. The material conducted into duct 64, due to the disposition of the duct and its upstanding leg 66, is here subjected to turbulent eddies in the fluid flow stream which, in conjunction with the impacting surfaces presented by the casing structure, serve to break up any reagglomerated particles that may have been conducted to the exhaust section 34 due to its aerodynamic characteristics or sail area. The dispersed fragment thereafter fall counter the air flew back into the column 32 for reprocessing. The light material fraction upon exiting the outlet leg 66 is delivered through the tangential inlet 72 of particle separator 22 where the solids particles are removed from entrainment in the air stream by centrifugal action in a manner well known in the art. The solids particles discharged from separator 22 may be deposited in a hopper (not shown) or passed directly to a furnace for burning.

The embodiment of the invention illustrated in FIG. 4 is identical to that shown in FIGS. 2 and 3 with the exception that the distribution deck indicated as 46, instead of being inclined as in the previous embodiment is formed as a plate separate from, and generally horizontally disposed with respect to, the casing structure of chamber 44. The deck plate 46 is operatively mounted upon spring mounts 68 and provided with a vibrating motor 70 for inducing vibration in the plate 48 and thereby cooperating with sweep air from nozzle opening 50 to effect movement of the deposited refuse towards the elutriation column opening 58.

It will be appreciated that within the described appa ratus construction, the shredded mixture is subjected to forces operating to improve the accuracy of classification on a material density basis. Thus, tumbling action produced in the distribution section 30 ahead of the elutriation column 32 will tend to strip any very light materials from an agglomerated mass and otherwise break up the mass in order to prevent such light material from being passed with the heavy material fraction due to its agglomerated condition. Also, the forces acting in the exhaust section 34 after the elutriation column 32, because of the provision of the eddyproducing edges and impact surfaces, reduce the possibility of heavy material being discharged from the apparatus with the light material fraction due to the sail area possessed by such pieces by dispersing the same so as to reduce the affect of sail area and enable the pieces to fall to the heavy material outlet. The result of the foregoing is a device capable of pneumatic classification of a heterogeneous mixture of solid materials on a density basis that is more accurate than apparatus heretofore known in the art.

While the preferred embodiments of the present invention have been described herein, it should be understood that the description is merely illustrative and that variations and modifications can be made therein without departing from the spirit and scope of the invention. It should be further understood that the utility of the hereindescribed apparatus is not limited to solid waste materials. Its use is equally applicable in systems for separating other heterogeneous solids mixtures, such as, for example, wood chips from pulp material or foreign matter from seeds, nuts or other similar mate rial. What is sought to be protected herein, therefore, is as recited in the appended claims:

What is claimed is:

1. Apparatus for pneumatically classifying a heterogeneous mixture of particulate solids material according to relative densities and/or aerodynamic properties including a substantially closed casing structure com prising:

a. distribution chamber having a generally horizontally disposed bottom deck for deposition thereon of the material to be processed Therein;

b. means communicating with said distribution chamber adjacent one longitudinal end thereof for sup plying material to be processed thereto;

c. a generally upstanding elutriation column communicating at its top with the other longitudinal end of said distribution chamber, the bottom of said column being open for the discharge of the more dense material fraction;

d. means for supplying elutriation air to said column at a high velocity sufficient to lift some of said material while allowing the remainder thereof to fall for upward flow therethrough;

e. means for directing higher velocity sweep air against the material contained therein longitudinally of said distribution chamber in the direction of the point of communication of said elutriation column; and

f. an obliquely upwardly extending duct communicating at one end with said distribution chamber adjacent the juncture of said elutriation column and having its other end open for the discharge of the less dense material fraction therefrom.

2. Apparatus as recited in claim 1 in which said bottom deck is slightly inclined downwardly away from said sweep air directing means.

3. Apparatus as recited in claim 2 in which said bottom deck is inclined between 5 and with respect to the horizontal.

4. Apparatus as recited in claim 3 in which said bottom deck is inclined about 8 with respect to the horizontal.

5. Apparatus as recited in claim 4 including means for vibrating said bottom deck.

6. Apparatus as recited in claim 1 including means for independently controlling the admission of sweep air and elutriation air to said casing.

7. Apparatus as recited in claim 1 including means for maintaining a flow velocity in said duct to no less than that in said elutriation column.

8. Apparatus as recited in claim 1 in which said distribution chamber and said elutriation column are generally normally disposed with respect to one anotherand said duct is inclined at about 45 with respect to the horizontal.

9. Apparatus as recited in claim 8 including a generally vertically disposed outlet leg communicating with said other end of said duct.

10. Apparatus as recited in claim 1 including an exhauster fan operatively connected to said duct for inducing fluid flow through said casing.

11. Apparatus as recited in claim 1 in which said means for supplying elutriation air includes means for supplying a greater quantity of air through said elutriation column than through said distribution chamber.

12. Apparatus as recited in claim 1 in which said distribution chamber comprises a casing having rectangularly disposed, oppositely spaced side walls and an end wall at said one longitudinal end and said sweep air directing means comprises air nozzle means operatively disposed in said end wall.

13. Apparatus as recited in claim 12 in which said air nozzle means is disposed in said end wall closely adjacent the bottom side wall.

14. Apparatus as recited in claim 13 in which said air nozzle means is operative across substantially the full width of said distribution chamber.

Claims

1. APPARATUS FOR PNEUMATICALLY CLASSIFYING A HETEROGENEOUS MIXTURE OF PARTICULATE SOLIDS MATERIAL ACCORDING TO RELATIVE DENSITIES AND/OR AERODYNAMIC PROPERTIES INCLUDING A SUBSTANTIALLY CLOSED CASING STRUCTURE COMPRISING: A. DISTRIBUTION CHAMBER HAVING A GENERALLY HORIZONTALLY DISPOSED BOTTOM DECK FOR DEPOSITION THEREON OF THE MATERIAL TO BE PROCESSED THEREIN, B. MEANS COMMUNICTING WITH SID DISTRIBUTION CHAMBER ADJACENT ONE LONGITUDINAL END THEREOF FOR SUPPLYING MATERIAL TO BE PROCESSED THERETO, C. A GENERALLY UPSTANDING ELUTRIATION COLUMN COMMUNICATING AT ITS TOP WITH THE OTHER LONGITUDINAL END OF SID DISTRIBUTION CHAMBER, THHE BOTTOM OF SAID COLUMN BEING OPEN FOR THE DISCHARGE OF THE MORE DENSE MATERIAL FRACTION, D. MEANS FOR SUPPLYING ELUTRIATION AIR TO SAID COLUMN AT A HIGH VELOCITY SUFFICIENT TO LIFT SOME OF SAID MATERIAL WHILE ALLOWING THE REMAINDER THEREOF TO FALL FOR UPWARD FLOW THERETHROUGH, E. MEANS FOR DIRECTING HIGHER VELOCITY SWEEP AIR AGAINST THE MATERIAL CONTAINED THEREIN LONGITUDINALLY OF SAID DISTRIBUTION CHAMBER IN THE DIRECTION OF THE POINT OF COMMUNICATION OF SAID ELUTRIATION CLOUMN, AND F. AN OBLIQUELY UPWARDLY EXTENDING DUCT COMMUNICTING AT ONE END WITH SAID DISTRIBUTION CHAMBER ADJACENT THE JUNCTURE OF SAID ELUTRIATION COLUMN AD HAVING ITS OTHER END OPEN FOR THE DISCHARGE OF THE LESS DENSE MATERIAL FRACTION THEREFROM.

3. Apparatus as recited in claim 2 in which said bottom deck is inclined between 5* and 15* with respect to the horizontal.

4. Apparatus as recited in claim 3 in which said bottom deck is inclined about 8* with respect to the horizontal.

8. Apparatus as recited in claim 1 in which said distribution chamber and said elutriation column are generally normally disposed with respect to one another and said duct is inclined at about 45* with respect to the horizontal.