CA1068248A - Recovery of glass from municipal waste - Google Patents

Abstract

ABSTRACT
Process for recovery of glass from municipal waste, comprising shredd-ing the waste, subjecting the shredded waste containing the glass to treat-ment in an air classifier, recovering the overhead including glass from the air classifier, the latter being operated under conditions such that the major portion of the glass particles contained in such overhead are of a fineness smaller than about 6 mesh, and usually of a size such that a substan-tial portion of such glass particles are less than about 20 mesh, screening such overhead fraction and recovering an enriched glass fraction of the aforementioned fineness, subjecting the screened glass-enriched material to treatment on an air table, and recovering a fine glass product of substan-tially reduced organic content, and having a particle size less than about 6 mesh, with a substantial portion less than about 20 mesh. Such fine glass product containing a substantial portion of glass particles of a size less than 20 mesh, can be employed in construction applications, e.g. in admixture with asphalt to form slurry seal, for production of glass and resin binder sheets, and the like, and may be further beneficiated to sufficient purity for recycle to glass manufacture.

Description

Thisinvention relates to the recovery of glass from municipal waste and trash, and is particularly concerned with procedure for recovery of a fine glass product from municipal waste, which can be used in various in-dustrial applications; and to the novel fine glass product thus recovered in the process.
The prior art heretofore has been essentially concerned with recovery of coarse glass from municipal waste or trash. Such coarse grades of glass, and the degree of impurity thereof, have not permitted this type of glass to be employed in many industrial applications, and such CQarSe and impure grades of glass particularly are not suited for recycle to glass manufacture.
Thus, it is known to shred municipal waste containing glass, and to subject the shredded material to air classification for separation of an overhead or lighter material from the heavier material which falls in the air classifier. Such heavier materials include coarse or large pieces of glass, as well as pieces of metals, rocks and wood. The heavy materials including coarse glass comprising pieces of the order of about 1/4 inch to 1 inch in size is then fed to an air table to remove organics such as plas-tics, rags, heavy paper and the like, and to separate the heavier materials into a glass product comprised of the above-noted coarse glass pieces, the glass product recovered being of a size and degree of impurity unsuitable ~or use in many industrial applications, or for recycle to glass manufacture, without further substantial and costly processing.
As previously noted, a substantial need has now developed for the recovery of glass from municipal waste and trash in the form of fine glass of substantially reduced organic content and improved purity, for use in industrial applications such as in slurry seal, as a brick additive, in composition resin-glass panels, and the like, and particularly of a grade which by further beneficiation is of sufficient purity for recycle to glass manufacture. Accordingly, it is a particular object of the present invention to produce such ~ine and relatively higher grade glass product from municipal ~,-.`

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trash and waste.
It has been found according to the present invention that if shredded waste or trash containing glass is fed to an air classifier, and the over~
head lighter material, hereinafter referred to also as "overhead lights", from the air classifier, and including fine glass, is then screened to pro-vide a screened material enriched in such fine glass, and such glass-enriched screened overhead material is separated on an air tsble, the resulting con-centrated glass product separated on such air table, and consisting essen-tially of glass, and other inorganic components, has a degree of fineness and a purity or substantial freedom from organics permitting it to be em- ~ -ployed directly in various industrial applications, and following additional purification or beneficition, especially enabling it to be recycled to glass manuacture.
According to the present invention there is provided in a process for the recovery of glass from municipal ~aste, including the steps of shredding said waste, subjecting said shredded waste to treatment in an air : :
classifier, recovering a portion of the resulting air classified shredded waste containing glass, and subjecting said portion of shredded waste to treatment on an air table; the improvement which comprises the steps of recovering the overhead lights including glass from said air classifier, said air classifier being operated under conditions such that the glass contained in said overhead lights has a particle size smaller than about 6 mesh, screening said overhead lights obtained from said air classifier, recovering a screened material enriched in glass and containing substantially all of said glass of particle size less than about 6 mesh in said overhead lights, and subjecting said screened material to treatment on an air table and recovering as product a material consisting essentially of fine glass having a particle size less than about 6 mesh and of substantially reduced organics content.
Furthermore, the invention provides the process for the recovery of glass from municipal waste, which comprises shredding said waste to produce glass generally having a par~icle size less than about 1/2 inch, subjecting ~ - 2 -S~ ~

i8248 said shredded waste containing said glass to treatment in an air classifier, recovering the overhead lights from said air classifier including glass in the form of particles of a size less than 6 mesh, screening said overhead lights obtained from said air classifier, removing a substantial portion of organics and recovering a screened material enriched in glass, subjecting said screened material to treatment on an air table and recovering a glass product consisting essentially of fine glass.
In another aspect, the invention provides a fine glass product from waste containing glass, said product comprising a major portion of glass particles of a size less than 6 mesh, and organic waste.
Thus, the present invention has as an essential novel feature the employment of that fraction of the material following shredding and which is taken off as overhead from the air classifier and then separated by screening _ 2a -106~3Z4~3 into an enriched fine glass fraction, as the material which is subjected to separation on the air table into the above-noted fine glass product of re-du~ed organic content. This feature of the invention which involves the -~
isolation of the glass from the above screened mixture produced from the lights of the air classifier, by means of an air table, thus produces a fine glass of sufficient grade and degree of purity which can be employed for producing "Thixite"* panels, understood to be composition glsss and resin-binder sheets, slurry seal, ~hich is a mixture of tar and glass used on asphalt roads for repair or filling holes therein, and a composition formed of bovine manure which has been baked and the residue thereof mixed with glass and fused to form lightweight paneling material.
In the initial processing step or shredding operation, the var-ious components of the trash or waste are broken up into coarse pieces, the glass therein generally breaking into a size substantially finer than most of the other components. Thus, for example in a typical operation of this type, the glass will break into pieces of a size less than 1/2 inch, while a sub-stantial portion of the other components, including metals, such as non-ferrous metals, stainless steel and the like, are in the form of massive pieces ranging in size upwards from about 1/2 inch, e.g. from about 1/2 inch to 12 inches in size.
Pollowing the thredding operation, the shredded waste material in-cluding the glass is fed to an air classifier. Air classifiers are well known and are generally used in waste material recovery processes to separate light materials including combustibles, in the shredded waste, from the hcav~ materials, including non-combustibles, therein. Yertical air-column and rotary drum air classifiers are particularly suited for this purpose.
The coarsely shre~ded mixed waste enters the clas~ifier at a given location.
As a result of combined gravity and aerodynamics action, lightweight mater-ials, mostly combustibles, and a portion of the glass in the shredded waste, are discharged as overhead and are separately and pneumatically conveyed * Trade Mark out of the classifier. The heavier materials, including most of the non-combustibles and a substantial proportion of the glass in the shredded waste, drop down and are removed at the lower end of the classifier. A typical illustration of an air classifier of the above type is disclosed in "Solid Waste Disposal," Volwme 1, by B. Baum and C. Parker, Ann Arbor Science Pub-lishers Inc. 1973, page 1915.
The lightweight materials or overhead lights from the air classifier include organics such as paper, leaves, plastic, cardboard, and the like, and glass in varying proportions ranging from about 2.5 to about 8% by weight. It is noted that all percentage proportions set forth herein are by weight unless otherwise indicated. The proportion of such glass in the overhead lights typically ranges for example, from about 25 to about 40~0 of the total glass in the feed to the classifier. According to the invention, the air classifier is operated so that the glass present in the overhead lights is of fine particle size less than 6 mesh, with a substantial portion usually less than about 20 mesh size. The heavier materials which drop by gravity in the air classifier and generally including a major portion of the glass in the shredded waste, e g. ranging from about 50 to about 75%
thereof, is comprised of glass particles of large size greater than 6 mesh, and up to 1 inch, or more. Such underflow also includes other inorganics such as relatively large size particles of rock, bricks, metals and the like, massive organic materials such as wood and a minor proportion of other organics.
In one mode of operation, for example, the underflow of the air class-ifier can contain about 70% of the glass in the shredded waste, such glass being of large ~ize, and the overhead lights from the classifier can contain about 30% of the glass in the shredded waste, such glass being of fine part-icle size as noted above.
The overhead lights from the air classifier is then screened to re-move a substantial portion of organics and recover the major portion of the 106824~3 glass in the material, of a particle size less than about 6 mesh, thereby Obtaining a screened material enriched in glass. Such screened material enriched in glass can contain, for example, from about 10 to about 65% by weight of glass, other inorganics such as dust and rock, and organic matter including for example paper, cardboard, lint, grass, and the like. Thus, for example, in one mode of operation such glass-enriched screened material can contain 50% glass of a particle size less than about 28 mesh, 20~ other inorganics and 30% combustible organics, and in another typical mode of operation, such glass-enriched screened material can contain 25% glass of a particle size less than 8 mesh, 25% other inorganics such as dirt and rock, and about 50% fine organic matter of the nature noted above.
The glass-enriched screened overhead from the air classifier is then fed to an air table of a conventional type which separates the heavier mat-erials in the feed material, including the glass and inorganics, from the lighter material, particularly organics. Essentially, a typical air table, also referred to as a gravity separator, basically can comprise a perfor-ated platform which can have a series of riffles running lengthwise. The platform can be inclined in a single plane or in two planes. In operation, material is placed on the high point of the platform and the platform is vibrated in two directions. In one direction the vibrator has high accel-eration and in the other direction a lower acceleration. Air is fed through the perforations to give the feed material a slight lift. The heavier mat-erial generally follows the riffles along the length of the table and falls off one end while the lighter material jumps the riffles and falls off an-other side of the table. It will be understood that various fonms of air tables can be employed, examples of these being the Forsbergs Vacuum Gravity separator marketed by Forsbergs, Inc. and the Triple/S ~ynamics separator marketed by Sutton, Inc.
Thus, upon feeding the glass-enriched screened waste material to the air table according to the invention, the air table separates out the heavies ~8248 in the form of substantially all of the glass in the feed, other inorganics, and the lights consisting essentially of organics. Thus, in the practice of the present invention the air table produces a concentrated glass frac-tion consisting of a major portion, e.g. up to 90% or more, of glass, the amount of glass in such product usually ranging from about 40% to about 70%.
The glass in such concentrated glass product has a mesh size less than 6 mesh, with a substantial portion, e.g. about 50~0 to about 90%, having a mesh size less than about 20 mesh, a minor portion of such glass, e.g. ranging from about 5% to about 20%, having a fineness less than about 48 mesh. The remainder of such concentrated glass fraction comprises about 20% to about 50% of other inorganics including rock chips, brick, and the like, and a minor amount of about 10~ to about 20%, of organics.
Thus, the products produced or separated in the air table operation include the above-noted heavy fine glass product containing only a small amount of organics, which is the major desired product, an inorganic product including brick and rock chips, a dust product and a light organic product including paper, plastics, wood, dried corn and seeds, and the like. The heavy glass product generally comprises about 60 to about 65% by weight of the overall products obtained in the air table operation.
According to another feature of the invention, the light organics fraction obtained on the air table and containing a small amount of glass can be passed through a 48 mesh screen, to obtain organics of a particle size greater than 48 mesh,substantially free of glass and suitable for use, e.g. as a powdered fuel. The glass thus separated of a particle size less than 48 mesh and which is substantially free of organics also has utility for the purposes noted above.
The enriched glass product obtained from the air table, the glass particles of which are of fine size less than 6 mesh, preferably less than about 8 mesh, and of substantially reduced organic content, can be employed directly for construction applications or for other purposes. These include use of the glass fraction às a brick additive, for admixture with tar to form slurry seal used for repair of asphalt roads, for admixture with resin binder to produce construction sheets, and for admixture with the residue of balced cattle manure, and after further processing, for production of lightweight paneling material.
Of further significance and as a feature of the invention, such fine and relatively pure (organics-free) glass product recovered from the air table, and containing glass of a mesh si~e less than 6 mesh, alternatively can be subjected to purification operations to provide a glass of purity sufficient or recycle to glass manufacture, e.g. to produce a glass for add-ition to a container grade cullet. Thus, for example, the fine glass product recovered on the air table according to the invention, can be purified and recycled to glass manufacture accorting to the process described in the Canadian Patent No. 964,773 of Booker W. Morey, et al, titled "Flotation Separation of Glass from a Mixture of Comminuted Inorganic Materials".
As an additional feature of the invention process, there can be employed an optional drying step prior to or between air classification and screening, for drying the overhead from the air classifier before screening such overhead material. Such drying aids in retucing the size of any lamps or aggregates of material in the overhead from the air classifier, and pre-vents the glass particles from sticking to the orgsnic particles such as paper, and the likeJ to thus facilitate screening thereof.
The following are examples of practice of the invention, it being understood that such examples are illustrative and not limitative of the invention.
The examples below are described for greater clarity in conjunction ,:
~ with the accompanying drawing wherein:
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FIGURE 1 is a block diagram illustrating the essential steps of the proccss;

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FIGURE 2 is a block diagram similar to Figure 1 but including an optional step in the process; and FIGURE 3 is a schematic illustration of the distribution of the prod-ucts recovered from an air table7 according to one embodiment of the invent-ion.

Referring to Figure 1 of the drawing, municipal waste or trash, in-dicated at 10, and containing 7 to 10% glass, is fed to a shredder to shred the material as indicated at 12. In the shredding operation the glass is -~
broken into various size pieces generall~ less than about l/2 inch while -80% or more of the other components are broken into pieces ranging in size from dust to 12 inches. Such other components include rock, metals,paper, cardboàrd, wood, plastics and the like. ;-The shredded material at 14 is then fed to an air classifier, as in-dicated at 16, and an overhead material 20 is recovered. Such overhead material includes about 4-6% of fine glass particles, 2-4% other inorganics including rock chips, brick and the like, and 60-70% of combustible organics including paper, cardboard, plastics and the like. The remainder is mostl~ ~-water. The air classifier is operated so that the glass particles have a size less than 28 mesh.
The underflow or heavies from the air classifier, indicated at 18~ is composed of abaut 70% of the glass contained in the waste material 10, but such glas~ particles are of a size larger than 28 mesh. Such heavies also incIude brick and rock chips, metals, and the like.
The overhead material at 20~ including the fine glass particles com-priæing about 30~0 of the glass contained in the waste material 10 is then placed on a screen as indicated at 22, such screen being of 28 mesh size.
The screened product thus produced is essentially in the form of an enriched glass material consisting of about 50% glass of particle size less 30 than 28 mesh, 20~o other inorganics, including brick and rock chips, and 30 .

. , .. ., ... . . .. - , ~,. , -combustible organics, including paper, plastics, and the like. The material retained on the screen and of a particle size larger than 28 mesh, is essen-tially composed of organics and is separated as indicated at 24.
The enriched glass material 26 thus separated in the screening oper-ation i9 fed to an air table as indicated at 28. The heavier glass partic-les are separated on the air table into a high purity glass product of par-ticle size less than 28 mesh, as indicated at 30. There is also separated on the air table a dust product, a light inorganic product and an organic product. The high purity glass product at 30 consists of about 90% glass, the dust product containing less than 1% glass and the light inorganic prod-uct containing about 13~o glass. The recovery of glass in the glass product is about 80% of the glass in the enriched glass material fed to the air table.
The grade of glass thus produced is suffic~ent for industrial appli-cation including use ac an additive for bricks or for the production of "Thixite" panels or slurry seal.
EXAMPLE 2 ;-The procedure of Example 1 is repeated, except that as indicated in Figure 2 of the drawing, following the air classifier operation at 16, the overhead material 20 containing fine glass particles is dried as indicated at 21~ and the dried material at 23 is then fed to the screen 22.
Results similar to those of Ex~mple 1 are obtained.

A feed material was derived frcm shredding municipal trash in an Eidal 1000 Shredder. The shredded material was air classified, the overhead ; fraction was dried and then screened at 8 mesh The fine material passing through the screen had the characteristics shown in table 1 below:

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~068248 It is seen from Table 1 above that a substantial portion, about 64S~, `
of the glass-enriched screened product was of a size less than 20 mesh. ~ -The glass-enriched screened material passing through the 8 mesh screen and having the characteristics noted in Table 1 above, was fed to an air table of the above-noted Triple/S type and distributed itself among four products as illustrated in Figure 3 of the drawing. It will be noted that the major portion of the feed at 32, to the air table indicated at 34, was comprised of glass product, 64.4% of the feed, and was removed at 36 from one end of the table. The organic product in the amount of 21.4% of the feed was removed at 38 at the other end of the table. A landfill waste type prod-uct, in the amount of 11.8%, was removed at 40, inte~mediate the ends of the table, and a substantially equal amount of landfill material removed at 42 was recycled and added to the feed. 2.4% of a dust product was also re- ;
moved at 44 from the air stream passing through the table.
The characteristics of each of the products obtained from the air tab-le operation i8 shown in Table 2 below. In Table 2, the legend "LOI" desig-nates "loss on ignition", and is a measure of the organics present in each of the products from the air table.
Table 2 Fraction Weight % % LOI % Glass Dust 2.4 54 3.9 Heavy 64.4 15.6 41.5 Organic 21.4 62.4 10.3 Recycle ) 23.6 57.7 16.
Landfill) From Table 2 above, it is clearly evident that the maJor portion of the glass in the feed to tke air table is present in the heavy glass product re-10~8Z4~3 moved at 36. Such heavy fraction is suitable for the above-noted industrial uses~ namely as an additive for bricks, production of "Thixite" panels, slurry seal, and the like. Alternatively, such heavy fraction product is suitable as a feed for beneficiation to a container grade cullet, prefer-ably according to the process disclosed in above Canadian Patent No. 964,773 The dust and organic fractions are suitable as pyrolysis feed or as a powdered fuel. Alternatively, the organic fraction at 38 can be purified further by screening at an appropriate size indicated by the screen analysis of Table 3 below:

Table 3 Screen Analysis of Air Table Organic Fraction & reen Cumulative Size wt ~ % LOI wt% x LOI % Inerts ~10 9.1 78.7 11.4 2.5 -10 ~ 12 6.9 79.7 20.17 3.2 -12 ~ 20 23.7 80.0 50.46 2.9 -20 ~ 48 36.9 75.4 g4.9 8.2 -48 ~ 60 7.2 22.9 g7.5 75.3 -60 + lOO13.6 6.6 ~8.95 92.6 -100 ~ 2002.1 22.7 99.7 71.3 From Table 3 above, it is noted that with particle size less than 48 mesh, most o~ the glass passes through the screen and is separated from the . ~ .
organics. As a matter of fact, some 95%of the combustible portion of the organic fraction is large~ than 48 mesh siZe, reducing the inerts from 22%
to a~out~5~.4%. The fraction of particle size less than 48 mesh and contain-ing the major portion of ths glass has only about 22% LOI, indicating very little organics.

- 12 _ ~ .

'`' ' . . ! ' . ' ' ' . . ` ~ ' ~ ~ . . . ' 10ti8Z48 The mesh sizes set forth herein are based on Tyler standard screen scale.
From the foregoing, it is seen that the invention provides novel pro-cedure for producing an improved novel glass recovery product from municipal waste and trash, such improved glass product having particles of sufficiently -fine size and being of a grade so that the product can be employed directly ~-in valuable industrial applications without any internediate grinding or ;-purification procedure required, and when the product is of sufficiently fine size and is further purified, such glass product can be recycled dire-ctly to glass manufacture.
While I have described particular embodiments of my invention for pur-poses of illustration, it is understood that other modifications and vari-ations will occur to those skilled in the art, and the invention accordingly is not to be taken as limited except by the scope of the appended claims.

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Claims (24)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a process for the recovery of glass from municipal waste, including the steps of shredding said waste, subjecting said shredded waste to treat-ment in an air classifier, recovering a portion of the resulting air class-ified shredded waste containing glass, and subjecting said portion of shre-dded waste to treatment on an air table; the improvement which comprises the steps of recovering the overhead lights including glass from said air classifier, said air classifier being operated under conditions such that the glass contained in said overhead lights has a particle size smaller than about 6 mesh, screening said overhead lights obtained from said air classi-fier, recovering a screened material enriched in glass and containing sub-stantially all of said glass of particle size less than about 6 mesh in said overhead lights, and subjecting said screened material to treatment on an air table and recovering as product a material consisting essentially of fine glass having a particle size less than about 6 mesh and of substantially re-duced organics content.

2. A process as defined in claim 1, said overhead material from said air classifier including glass containing a substantial portion of glass partic-les of a size less than about 20 mesh, and said screened overhead material enriched in glass containing a substantial portion of said glass particles of a size less than about 20 mesh, other inorganics, and organics.

3. A process as defined in claim 1, said product from said air table being heavies consisting essentially of fine glass containing a substantial por-tion of said glass particles of a size less than about 20 mesh, and suited for construction applications.

4. A process as defined in claim 1, said overhead material from said air classifier containing about 2.5 to about 8% of glass by weight of said material.

5. A process as defined in claim 2, said overhead material from said air classifier containing about 2.5 to about 8% of glass by weight of said material.

6. A process as defined in claim 1, said screened overhead material from said classifier being enriched in glass to from about 10% to about 65% by weight of glass.

7. A method as defined in claim 4, said product from said air table con-taining about 40 to about 70% glass of a particle size less than about 6 mesh, and recovering from said air table other inorganics and organics.

8. A process as defined in claim 1, said product from said air table consisting essentially of up to about 90% glass of a particle size less than about 28 mesh, and recovering from said air table other inorganics and organics.

9. A process as defined in claim 1, the under-flow of said air classi-fier containing about 70% of the glass in said shredded waste and said over-head lights from said classifier containing about 30% of the glass in said shredded waste.

10. A process as defined in claim 7, the under-flow of said air classifier containing about 70% of the glass in said shredded waste and said over-head lights from said classifier containing about 30% of the glass in said shredded waste.

11. A process as defined in claim 1, including drying said overhead lights from said air classifier prior to screening.

12. A process as defined in claim 1, including recovering organics from the material fed to said air table, said organics containing a small amount of glass, screening said organics to separate said glass and recovering an organic product substantially free of glass, and a glass product substan-tially free of organics.

13. The process for the recovery of glass from municipal waste, which com-prises shredding said waste to produce glass generally having a particle size less than about 1/2 inch, subjecting said shredded waste containing said glass to treatment in an air classifier, recovering the overhead lights from said air classifier including glass in the form of particles of a size less than 6 mesh, screening said overhead lights obtained from said air classifier, removing a substantial portion of organics and recovering a screened material enriched in glass, subjecting said screened material to treatment on an air table and recovering a glass product consisting essen-tially of fine glass.

14. A process as defined in claim 13, said screened overhead material from said air classifier enriched in glass to about 10% to about 65% of said material, said glass product from said air table containing glass in an amount ranging from about 40% to about 70% by weight, and recovering from said air table other inorganics, and organics.

15. A process as defined in claim 13, the under-flow of said air class-ifier containing about 70% of the glass in said shredded waste and said overhead lights from said classifier containing about 30% of the glass in said shredded waste.

16. A process as defined in claim 14, including recovering organics from the material fed to said air table, said organics containing a small amount of glass, screening said organics to separate said glass and recovering an organic product substantially free of glass.

17. A fine glass product from waste containing glass, said product con-prising a major portion of glass particles of a size less than 6 mesh, and organic waste.

18. A product as defined in claim 17, said product including a major por-tion of glass particles having a mesh size less than about 20 mesh.

19. A product as defined in claim 18, the amount of glass present in said product ranging from about 40% to about 70%.

20. A product as defined in claim 19, the amount of organics in said prod-uct ranging from about 10% to about 20%.

21. A product as defined in claim 20, said glass product including about 20% to about 50% of other inorganics, including rock chips, brick, and the like.

22. A product as defined in claim 18, the amount of said glass particles of a mesh size less than about 20 mesh ranging from about 50% to about 90%
of the total glass present in said product.

23. A product as defined in claim 22, including glass particles of a mesh size less than about 48 mesh, in an amount ranging from about 5% to about 20%.

24. A product as defined in claim 17, said glass particles being of a size less than about 8 mesh.