GB1587636A

GB1587636A - Method and apparatus for sorting waste material

Info

Publication number: GB1587636A
Application number: GB19434/77A
Authority: GB
Original assignee: Newell Dunford Engineering Ltd
Current assignee: Newell Dunford Engineering Ltd
Priority date: 1977-05-09
Filing date: 1977-05-09
Publication date: 1981-04-08
Also published as: SE430951B; FR2390208A1; IT1109190B; SE7805222L; NL7804867A; IT7823141A0; DE2820206A1; FR2390208B1

Description

(54) METHOD AND APPARATUS FOR SORTING WASTE MATERIAL (71) We, NEWELL DUNFORD ENGINEERING LIMITED, a British Company of Newell Dunford House, Portsmouth Road, Surbiton, Surrey KT6 5QF, England do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a method and apparatus for sorting waste material.

Municipal solid waste, as collected from dustbins etc., is composed of mixtures in all proportions of waste from domestic and trade sources. Typically, the raw material contains 30% by weight of cellulosic fibres in the form of board or paper fragments.

It would be desirable to be able to sort the parts of the material containing cellulosic fibres and the plastics from the remainder of the material and then to sort the cellulosic fibre containing waste from the plastics material waste.

Various methods have been proposed for doing this, but none of these have proved to be entirely satisfactory.

It is now proposed, according to the present invention, to provide a method of sorting rubbish comprising taking the raw rubbish, subjecting it to a primary air classification to separate a primary light fraction, which contains a concentrate of plastics, paper and board fragments, and a primary heavy fraction composed of other materials, subjecting the primary light fraction to a conditioning step in which the primary light fraction is wetted and formed into pellets, and subjecting the pellets to a secondary air classification, whereby the wetted, absorbent pellets are separated into a secondary heavy fraction and the non-absorbent pellets are separated into a secondary light fraction.

With this method, the primary light fraction is, as indicated made damp and an intimate mixture is made between the water and the cellulosic fibre containing portion of the primary light fraction. The cellulosic fibre absorbs the water, but the plastics material does not. Then, when the dampened light fraction is formed into pellets and is fed to the secondary air classification stage, the plastics material will be relatively lighter than the wet cellulosic fibres, and will thereby be separated therefrom. The action of wetting and pelletizing the primary light fraction is that it produces a nodular product containing the partially defibred cellulosic material and a laminar product consisting of unwetted plastics, waxed papers and plastic paper laminates.These products are then fed to the secondary air classifier and the cellulosic content is now denser and more streamlined than the non-wetted materials, having a higher wetability in the pelletizing and wetting stage. The result of these differences is to cause the cellulosic fibre containing pellets to pass to the secondary heavy fraction discharge of the secondary air classifier and the non-wetted largely plastic, content, to be emitted as the light fraction discharge.

The resulting secondary heavy fraction is a material which can be further treated and refined by means of traditional cellulosic pulp treatment equipment to produce an acceptable cellulosic pulp for paper and board making.

In a preferred arrangement, either one or preferably both of the primary and second air classifying operations will be carried out in a classifier comprising a vessel which is open at both ends, the axis of the vessel, in a direction transverse to the open end, being inclined to the horizontal, means being provided to feed material to be classified into the upper end and means being provided to introduce air into the vessel, so as to cause the air to flow spirally within the vessel and axially out of the upper end. In one particular embodiment, the vessel is of frustoconical formation.It will be appreciated that in the primary classification step, according to the present invention, the lighter fraction including the cellulosic fibre containing material and plastic will proceed upwardly out of the classifier and the heavier fraction will proceed downwardly out of the lower end of the classifier. Similarly, in the secondary classification step, the plastics pellets, which are effectively undampened because they have no absorbent powers, will proceed out of the upper end of the vessel and the wet fraction containing the cellulosic fibre will proceed out of the lower end.

The effect of the rotation of the classifier is to cause agglomeration of the paper and board fragments to particles which are, for example, approximately 1 cm in diameter.

The invention also provides apparatus for sorting rubbish, such apparatus comprising a primary air classifier, for separating the rubbish into a primary light fraction and a primary heavy fraction, wetting and pelletizing means, means to feed the primary light fraction to said wetting and pelletizing means, a secondary air classifier and means to feed the pellets formed in the wetting and pelletizing means to the secondary air classifier.

In the method and apparatus of the present invention, the primary light fraction may be wetted in a horizontal ribbon or screw mixer, or in a wet hammer mill, for example.

The primary light fraction may be formed into pellets in a rotary drum pelletizer, a disc pelletizer or a contrarotating pelletizer, for example.

In order that the invention may more readily be understood, the following description is given, merely by way of example, reference being made to the accompanying drawing which illustrates schematically the flow of material through apparatus according to the invention, which is only shown diagrammatically, to carry out the method of the invention.

In the drawing, rubbish to be treated is unloaded, for example from a lorry 10 in a reception area 11 onto a feeder 12 by which it is fed into a pulverizer 13. This pulverizer may be of the type having a conical top portion in which is rotatable a set of flails, which rotate about a vertical axis, and these have the effect of sorting some of the more resilient material out of the rubbish and throwing it out, and the material is drawn downwardly by air and is pulverized in the lower portion 13a of the pulverizer. The material which has been pulverized is then fed under a magnetic separation device 14 and the ferrous materials are drawn off and taken to the ferrous metal collector 15. The remaining material, which will be the majority, leaving the pulverizer 13, 13a, is fed on to a rotary screen 16 and this consists of a fine screen portion 1 6a and a coarse screen portion 16b.The fine material is removed in the portion 16a and collected at 17 from which it is sent to an incinerator or to a pit or for compost and the remaining material is passed into the portion 16b. The really coarse material can then be fed back via line 18 to the pulverizer 13 for retreatment.

The remaining material leaves the coarse screen 16h via line 19 and is sent to a primary classifier 20. This classifier is in the form of a frustoconical vessel which is rotatable about an axis 21 which is transverse to the upper open end. It will be noted that this axis is inclined to the horizontal by an amount which ensures that the lower surface of the vessel 20 is also inclined downwardly towards the lefthand end. Air is blown in at 22 in such a way as to be caused to spiral within the vessel 20 and leave via the righthand or wider upper end.

The effect of this is to classify the material entering the vessel 20 into a lighter fraction which is taken up by the air at 22 and a heavier fraction which falls down by gravity and is taken out at 23 for collection at 24 prior to tipping. Some of the material leaving as the heavier primary fraction will be ferrous material and a second magnetic separator 25 is provided, the ferrous metal being collected at 26.

The light fraction leaving at 22 is fed through a further rotary screen 27 and thence on to a conditioner 28. This conditioner includes a mixer 29 which may be of the horizontal ribbon or screw type or be a wet hammer mill, and also a pelletizer or nodulizer 30 which may, for example, be of the rotating drum, disc, or contrarotating belt type. Water is fed in at 31 and this may include a biocide, bleaching agent and/or wetting agent.

The resulting pelletized wetted material leaves the conditioner 28 at 32 and passes on to a second classifier 33 which is similar to the classifier 20 in its construction and is rotatable about an axis 34, air being introduced at 35.

The pellets entering the vessel 33 will be classified into a heavy fraction which will include those portions of the pellets which are absorbent and will flow out at the bottom lefthand end and be discharged at 36 and may be fed into a pulp treatment plant indicated schematically at 7.

The lighter fraction leaving the secondary classifier 33 will contain those materials which do not absorb water, such as plastics, waxed paper and paper based laminates.

These are removed at 38 and collected at 39 for further processing for disposal.

WHAT WE CLAIM IS:- 1. A method of sorting rubbish comprising taking the raw rubbish, subjecting it to a primary air classification to separate a primary light fraction, which contains a concentrate of plastics, paper and board fragments, and a primary heavy fraction composed of other materials, subjecting the primary light fraction to a conditioning step in which the primary light fraction is wetted and formed into pellets, and subjecting the pellets to a secondary air classification. whereby the wetted, absorbent pellets are separated into

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. which are effectively undampened because they have no absorbent powers, will proceed out of the upper end of the vessel and the wet fraction containing the cellulosic fibre will proceed out of the lower end. The effect of the rotation of the classifier is to cause agglomeration of the paper and board fragments to particles which are, for example, approximately 1 cm in diameter. The invention also provides apparatus for sorting rubbish, such apparatus comprising a primary air classifier, for separating the rubbish into a primary light fraction and a primary heavy fraction, wetting and pelletizing means, means to feed the primary light fraction to said wetting and pelletizing means, a secondary air classifier and means to feed the pellets formed in the wetting and pelletizing means to the secondary air classifier. In the method and apparatus of the present invention, the primary light fraction may be wetted in a horizontal ribbon or screw mixer, or in a wet hammer mill, for example. The primary light fraction may be formed into pellets in a rotary drum pelletizer, a disc pelletizer or a contrarotating pelletizer, for example. In order that the invention may more readily be understood, the following description is given, merely by way of example, reference being made to the accompanying drawing which illustrates schematically the flow of material through apparatus according to the invention, which is only shown diagrammatically, to carry out the method of the invention. In the drawing, rubbish to be treated is unloaded, for example from a lorry 10 in a reception area 11 onto a feeder 12 by which it is fed into a pulverizer 13. This pulverizer may be of the type having a conical top portion in which is rotatable a set of flails, which rotate about a vertical axis, and these have the effect of sorting some of the more resilient material out of the rubbish and throwing it out, and the material is drawn downwardly by air and is pulverized in the lower portion 13a of the pulverizer. The material which has been pulverized is then fed under a magnetic separation device 14 and the ferrous materials are drawn off and taken to the ferrous metal collector 15. The remaining material, which will be the majority, leaving the pulverizer 13, 13a, is fed on to a rotary screen 16 and this consists of a fine screen portion 1 6a and a coarse screen portion 16b.The fine material is removed in the portion 16a and collected at 17 from which it is sent to an incinerator or to a pit or for compost and the remaining material is passed into the portion 16b. The really coarse material can then be fed back via line 18 to the pulverizer 13 for retreatment. The remaining material leaves the coarse screen 16h via line 19 and is sent to a primary classifier 20. This classifier is in the form of a frustoconical vessel which is rotatable about an axis 21 which is transverse to the upper open end. It will be noted that this axis is inclined to the horizontal by an amount which ensures that the lower surface of the vessel 20 is also inclined downwardly towards the lefthand end. Air is blown in at 22 in such a way as to be caused to spiral within the vessel 20 and leave via the righthand or wider upper end. The effect of this is to classify the material entering the vessel 20 into a lighter fraction which is taken up by the air at 22 and a heavier fraction which falls down by gravity and is taken out at 23 for collection at 24 prior to tipping. Some of the material leaving as the heavier primary fraction will be ferrous material and a second magnetic separator 25 is provided, the ferrous metal being collected at 26. The light fraction leaving at 22 is fed through a further rotary screen 27 and thence on to a conditioner 28. This conditioner includes a mixer 29 which may be of the horizontal ribbon or screw type or be a wet hammer mill, and also a pelletizer or nodulizer 30 which may, for example, be of the rotating drum, disc, or contrarotating belt type. Water is fed in at 31 and this may include a biocide, bleaching agent and/or wetting agent. The resulting pelletized wetted material leaves the conditioner 28 at 32 and passes on to a second classifier 33 which is similar to the classifier 20 in its construction and is rotatable about an axis 34, air being introduced at 35. The pellets entering the vessel 33 will be classified into a heavy fraction which will include those portions of the pellets which are absorbent and will flow out at the bottom lefthand end and be discharged at 36 and may be fed into a pulp treatment plant indicated schematically at 7. The lighter fraction leaving the secondary classifier 33 will contain those materials which do not absorb water, such as plastics, waxed paper and paper based laminates. These are removed at 38 and collected at 39 for further processing for disposal. WHAT WE CLAIM IS:-

1. A method of sorting rubbish comprising taking the raw rubbish, subjecting it to a primary air classification to separate a primary light fraction, which contains a concentrate of plastics, paper and board fragments, and a primary heavy fraction composed of other materials, subjecting the primary light fraction to a conditioning step in which the primary light fraction is wetted and formed into pellets, and subjecting the pellets to a secondary air classification. whereby the wetted, absorbent pellets are separated into

a secondary heavy fraction and the nonabsorbent pellets are separated into a secondary light fraction.

2. A method according to claim 1, wherein the primary light fraction is wetted in a horizontal ribbon or screw mixer.

3. A method according to claim 1, wherein the primary light fraction is wetted in a wet hammer mill.

4. A method according to claim 1, 2 or 3, wherein the primary light fraction is formed into pellets in a rotary drum pelletizer, a disc pelletizer or a contrarotating belt pelletizer.

5. A method according to any preceding claim, wherein the wetting is carried out using an aqueous solution containing a biocide, a wetting agent and/or a bleaching agent.

6. A method according to any preceding claim, wherein at least one of the primary and secondary air classification steps is carried in a classifier comprising a vessel which is open at both ends, the axis of the vessel, in a direction transverse to the open end, being inclined to the horizontal, and the material to be classified is fed into the upper end and means are provided to introduce air into the vessel so as to cause the air to flow spirally within the vessel and axially out of the upper end.

7. Apparatus for sorting rubbish, such apparatus comprising a primary air classifier, for separating the rubbish into a primary light fraction and a primary heavy fraction, wetting and pelletizing means, means to feed the primary light fraction to said wetting and pelletizing means, a secondary air classifier and means to feed the pellets formed in the wetting and pelletizing means to the secondary air classifier.

8. Apparatus according to claim 7, wherein the wetting means comprises a horizontal ribbon mixer, or a screw mixer.

9. Apparatus according to claim 7, wherein the wetting means comprises a wet hammer mill.

10. Apparatus according to claim 7, 8 or 9, wherein the pelletizing means comprises a rotary drum pelletizer, a disc pelletizer or a contrarotating belt pelletizer.

11. Apparatus according to any one of claims 7 to 10, wherein at least one of the primary and secondary air classifiers comprises a vessel which is open at both ends, the axis of the vessel, in a direction transverse to the open end, being inclined to the horizontal, means being provided to feed material to be classified into the upper end and means being provided to introduce air into the vessel so as to cause the air to flow spirally within the vessel and axially out of the upper end.

12. A method of sorting rubbish substantially as hereinbefore described, with reference to and as illustrated in the accompanying drawings.

13. Apparatus for sorting rubbish substantially as hereinbefore decribed with reference to and as illustrated in the accompanying drawing.