GB1593390A - Separation of solid materials - Google Patents

Description

(54) SEPARATION OF SOLID MATERIALS (71) We, BICC LIMITED, a British company, of 21 Bloomsbury Street, London, WC1B 3QN, 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: This invention relates to a method of separating mixtures, such as chopped cable scrap, that contain particles of a metal and particles of two different plastics materials differing in density and/or mass and/or shape. In such mixtures the properties of two plastics materials are likely to be only slightly different but the density of the metal is considerably different.

The method of the invention comprises introducing the mixture of particles into a first separation chamber containing a liquid medium of appropriate density, producing in the separation chamber a circulating motion including a downcurrent in a first region within the first separation chamber that is sufficient to draw all classes of particle below the surface of the liquid medium and an upcurrent in a second region located between a first baffle depending from above the surface of the medium and forming a barrier between the first and second regions at the level of the surface of the medium and a second, upstanding, baffle, the upcurrent being sufficient to carry particles of both the plastics materials but not the metal particles over the second baffle and into a second separation chamber delimited from the first separation chamber by the second baffle; producing in the second separation chamber a circulating motion including a downcurrent in a third region within the second separation chamber that is sufficient to draw particles of both the plastics materials below the surface of the liquid medium and an upcurrent in a fourth region located between a third baffle depending from above the surface of the medium and forming a barrier between the third and fourth regions at the level of the surface of the medium and a fourth, upstanding baffle, the upcurrent being sufficient to carry particles of one but not both the plastics materials over the fourth baffle and into a receiver delimited from the second separation chamber by the fourth baffle.

In most cases the upstanding baffles will be in fluid-tight relation with the base of the respective separation vessel. Preferably the two baffles overlap.

The liquid medium must of course be one that in substance neither dissolves nor deleteriously affects any of the materials that are to be separated and recovered in the way described, nor causes the particles to agglomerate. An aqueous medium of suitable density will usually be preferred if it is available and meets these requirements. For separation of copper, PVC (polyvinyl chloride) and PE (polyethylene) plain water can be used and is preferred.Wetting agents are preferably not added to aqueous media, because they incrase the formation of bubbles, which are deleterious (a) because they may stick to the surfaces of particles and so cause to float particles which should and otherwise would sink, (b) because capital cost and running costs are increased and (c) because in some cases there may be difficulties in disposing of waste medium. "Conditioning" of particles by pre-treatment with a surface-active material may be desirable for some separations.

The required circulating motion can be produced in various ways. For example it could be produced by a pump drawing off fluid medium from the downcurrent region and reinjecting it in the upcurrent region, or in some cases by injecting gas or a liquid lighter than the medium in the downcurrent region, provided that the tendency of bub bles or droplets of lighter liquids to stick to particles is slight.

Preferably however the circulating motion is produced by an impeller immersed in the fluid within the separation chamber. An impeller rotating on a vertical axis is at present preferred, but an oscillating impeller or an impeller rotating on a horizontal or other axis could be used. More than one impeller can be used.

A preferred arrangement includes an impeller located centrally in or near the base of the separation chamber, rotating on a vertical axis to entrain the fluid and impel it outwardly by centrifugal motion, thereby forming an upcurrent round the periphery of the chamber and a downcurrent in the centre of the separation chamber. A part of the periphery constitutes the second region adjacent the upstanding baffle. Suitably the baffle forms one end of a rectangular separation chamber.

One preferred impeller comprises a circular disc rotatable about its axis and having a series of round rods upstanding from its periphery. Preferably the rods upstand from the upper surface only of a disc and the disc is flush with the bottom of the separation chamber or nearly so. The dimensions and speed of the impeller need to be carefully chosen in relation to the size and shape of the vessel and the nature of the particles to ensure efficient circulation of the whole volume of the fluid.

A number of separation stages may be combined (cascaded) to refine further the separation of the metal and/or of the two plastics materials, using a corresponding number of separation chambers separated by baffles in a similar fashion. When the upstanding baffles are spaced from the bottom of the chamber, suitable shaping of the bottoms may allow particles sinking in more than one chamber to collect in one place.

The upcurrent will tend to carry the fluid medium over the upstanding baffle into the receiver, and a nct flow of the medium will result unless opposed by a countervailing hydrostatic pressure produced by a higher fluid level in the receiver. Preferably the fluid level in the receiver is either substantially the same as in the separation vessel or lower, and fluid, preferably recycled, is continuously introduced into the separation chamber to maintain a constant level.

When the level of fluid in the receiver is lower than in the separation chamber the upstanding baffle constitutes a weir influencing the fluid level in the separation chamber and the flow of fluid over it constitutes a "waterfall" that may in some cases facilitate a subsequent separation step carried out in the recciver. In a cascade separation with two adjacent stages not isolated by such a waterfall or otherwise, it is very desirable for impellers that rotate on vertical axes in the chambers of the adjacent stages to do so in opposite directions.

In some cases the impeller may be a paddlewheel, typically rotating about a horizontal axis, projecting above the level of the fluid and in some cases itself constituting the depending first baffle. This is especially useful when the density of the fluid medium is close to that of the particles to be carried over the upstanding baffle.

Separated materials can be recovered in various ways. Particles light enough to float on the surface of the liquid medium are easily accessible, and can be collected for example by floating over a weir on to a suitable filter. or by scooping from the surface of the medium. Heavier particles are more difficult to recover because they settle at the bottom of the fluid in the separation chamber; in most cases it is advisable to recover them continuously or at intervals during separation. This may be done using a suitable conveyor, arranged outside the separation chamber or adequately screened from the separation zone. to raise the particles above the liquid surface, or by discharging downwards, preferably through a fluid lock.

Preferred means are: 1. A rotary conveyor comprising a rotor having at least one aperture which communicates with an opening in the bottom of the vessel where the material collects (e.g.

in a corner in the case of a rectangular flat-bottomed vessel with a central impeller) for part of the time and with a collection duct or collection vessel below for a different part of the time; 2. An equivalent arrangement with a sliding or dropping carrier; 3. A screw conveyor arranged to raise material above fluid level through a duct either inside or outside the tank, and allowing fluid to drain back into the vessel (e.g.

through clearances between the screw and its housing); 4. Porous bucket or belt conveyors; 5. Diaphragm or other suitable pumps; and 6. A rotary valve comprising a rotatable disc, preferably forming a part of the base of the vessel and flush with the remainder of the base, having at least one opening that intermittently aligns with an aperture in a baffle below it to allow direct passage of the collected material to a chamber below that is filled with fluid in hydrostatic equilibrium with the separation vessel.

If significant quantities of the medium are removed with the separated particles a suitable solid/liquid separator will be required; preferably its liquid output is returned to the region from which the mixture was withdrawn to minimise the disturbance to hydrostatic equilibrium.

The invention will be illustrated, by way of example, by a description of a preferred apparatus in accordance with the invention for the separation of chopped cable scrap consisting mainly of copper, polyvinylchloride (PVC) and polyethylene (PE) with a maximum particle size of up to about 5 mm.

The apparatus is shown in the accompanying drawings in which Figure 1 is an elevation and Figure 2 a plan.

The apparatus provides four copper/plastics separation stages in cascade followed by two PVC/PE separation stages (if more nearly complete separation were required, more stages could be provided).

The copper/plastics separation units are structurally identical and each of them is housed in a rectangular tank 1 which is 2.67 metres long (measured at the base level), 0.46 metres wide, and 0.23 metres deep (measured to the level of the liquid medium, hereinafter called water, under static conditions). It is advisable for the walls to extend at least 150 mm above this water level. The end wall at the outlet side of each tank is formed by an upstanding baffle 2 and a depending baffle 3 each extending the full width of the side; the upstanding baffle is 0.1 metres high and the depending baffle is 100 mm nearer the centre of the tank and terminates 95 mm from the base.The walls of the tank are flat, and the base is also flat apart from a central circular recess 4 which is 5 mm deep and 240 mm in diameter which accommodates an impeller 5 formed by a solid circular disc rotatable on an axial shaft extending above the water level, 5 mm thick and 230 mm in diameter and having upstanding from it a ring of 16 cylindrical pins 106 mm long by 13 mm diameter located about 13 mm from the periphery of the disc.

The impellers are driven at an adjustable speed by motors 6.

The receiver for the fourth copper/plastics separation stage is a PVC/PE separator, and consists of a hopper-shaped tank 10 the same width as the copper separation units and tapering from a length of 1.6 metres at the water level to a length of a few centimetres about 1.5 metres below. The wall of the tank furthest from the copper/plastics separator is lower than the other three walls and so acts as a weir 7 regulating the water level. Two upstanding baffles 12 extend across the tank and reach down to a level 150 mm below the level of the weir 7, one of them 335 mm and the other 960 mm from the weir; each is level with the weir and just below the water surface. Upstream of each of these upstanding baffles is a paddlewheel impeller 15 rotatable on a horizontal axis parallel to the baffles and 185 mm above the level of the weir.Each paddlewheel has two radially-extending blades 17 made of perforated sheet metal with a length (parallel to the rotation axis) of 0.44 mm and a radius of 224 mm. Each of these radially-extending blades supports at a point about 185 mm from its axis an auxiliary blade 18 also of perforated metal upstanding normally from its corresponding surface, running the full length of the main blade and about 145 mm high. The perforated sheet metal has holes each about 3.2 mm in diameter, arranged in rows about 6.35 mm apart, the holes in each row also about 6.35 mm apart and the holes in adjacent rows staggered. Each paddlewheel serves as a depending baffle and is rotated, at a low speed, by a common motor 16 to provide a downcurrent on the side further from the weir and an upcurrent nearer the weir, so providing a stage of separation in accordance with the invention.

In this tank, because the upcurrents are less strong and despite the fact that the liquid medium is the same as in the copper/plastics separation, the PVC settles, whilst the PE continues to float and is carried over the upstanding baffles 12 and eventually over the weir 7 where it can be collected by filtration or in any appropriate way.

Separated water is returned to the first copper/plastics separation stage by a pump 19 and in addition some unseparated liquid is recycled from the PVC/PE separation vessel (preferably from the region beyond the last of the upstanding baffles 12 or another part of the vessel where the ratio of plastics material to water is low) in order to equalise hydrostatic pressures in the system and avoid substantial variations in water level; a preferred recycle path via ports 20 and ducts 21 is shown.

Particles deposited on the bottom of the separating vessels are collected on a semicontinuous basis as follows: Copper continuously collects in each corner of the copper/plastics separation vessels and rests on a rotating disc mounted flush with the floor. In most cases the disc serves adjacent corners of two of the vessels. Each disc has a slot in it, into which copper is swept by the action of the tank walls and which intermittently passes over an opening below into a system of collection ducts 32 which is kept in hydrostatic equilibrium with the separation vessel and into which the recovered copper falls to be collected by a conveyor screw 33. PVC forms a thick aqueous sludge which collects from both separation stages in the common conical base 34 from which it is drained, for example by a screw conveyor system similar to that used for the copper but acting continuously.

WHAT WE CLAIM IS: 1. A method of separating a mixture containing particles of metal and particles of

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

Claims (12)

**WARNING** start of CLMS field may overlap end of DESC **. was withdrawn to minimise the disturbance to hydrostatic equilibrium. The invention will be illustrated, by way of example, by a description of a preferred apparatus in accordance with the invention for the separation of chopped cable scrap consisting mainly of copper, polyvinylchloride (PVC) and polyethylene (PE) with a maximum particle size of up to about 5 mm. The apparatus is shown in the accompanying drawings in which Figure 1 is an elevation and Figure 2 a plan. The apparatus provides four copper/plastics separation stages in cascade followed by two PVC/PE separation stages (if more nearly complete separation were required, more stages could be provided). The copper/plastics separation units are structurally identical and each of them is housed in a rectangular tank 1 which is 2.67 metres long (measured at the base level), 0.46 metres wide, and 0.23 metres deep (measured to the level of the liquid medium, hereinafter called water, under static conditions). It is advisable for the walls to extend at least 150 mm above this water level. The end wall at the outlet side of each tank is formed by an upstanding baffle 2 and a depending baffle 3 each extending the full width of the side; the upstanding baffle is 0.1 metres high and the depending baffle is 100 mm nearer the centre of the tank and terminates 95 mm from the base.The walls of the tank are flat, and the base is also flat apart from a central circular recess 4 which is 5 mm deep and 240 mm in diameter which accommodates an impeller 5 formed by a solid circular disc rotatable on an axial shaft extending above the water level, 5 mm thick and 230 mm in diameter and having upstanding from it a ring of 16 cylindrical pins 106 mm long by 13 mm diameter located about 13 mm from the periphery of the disc. The impellers are driven at an adjustable speed by motors 6. The receiver for the fourth copper/plastics separation stage is a PVC/PE separator, and consists of a hopper-shaped tank 10 the same width as the copper separation units and tapering from a length of 1.6 metres at the water level to a length of a few centimetres about 1.5 metres below. The wall of the tank furthest from the copper/plastics separator is lower than the other three walls and so acts as a weir 7 regulating the water level. Two upstanding baffles 12 extend across the tank and reach down to a level 150 mm below the level of the weir 7, one of them 335 mm and the other 960 mm from the weir; each is level with the weir and just below the water surface. Upstream of each of these upstanding baffles is a paddlewheel impeller 15 rotatable on a horizontal axis parallel to the baffles and 185 mm above the level of the weir.Each paddlewheel has two radially-extending blades 17 made of perforated sheet metal with a length (parallel to the rotation axis) of 0.44 mm and a radius of 224 mm. Each of these radially-extending blades supports at a point about 185 mm from its axis an auxiliary blade 18 also of perforated metal upstanding normally from its corresponding surface, running the full length of the main blade and about 145 mm high. The perforated sheet metal has holes each about 3.2 mm in diameter, arranged in rows about 6.35 mm apart, the holes in each row also about 6.35 mm apart and the holes in adjacent rows staggered. Each paddlewheel serves as a depending baffle and is rotated, at a low speed, by a common motor 16 to provide a downcurrent on the side further from the weir and an upcurrent nearer the weir, so providing a stage of separation in accordance with the invention. In this tank, because the upcurrents are less strong and despite the fact that the liquid medium is the same as in the copper/plastics separation, the PVC settles, whilst the PE continues to float and is carried over the upstanding baffles 12 and eventually over the weir 7 where it can be collected by filtration or in any appropriate way. Separated water is returned to the first copper/plastics separation stage by a pump 19 and in addition some unseparated liquid is recycled from the PVC/PE separation vessel (preferably from the region beyond the last of the upstanding baffles 12 or another part of the vessel where the ratio of plastics material to water is low) in order to equalise hydrostatic pressures in the system and avoid substantial variations in water level; a preferred recycle path via ports 20 and ducts 21 is shown. Particles deposited on the bottom of the separating vessels are collected on a semicontinuous basis as follows: Copper continuously collects in each corner of the copper/plastics separation vessels and rests on a rotating disc mounted flush with the floor. In most cases the disc serves adjacent corners of two of the vessels. Each disc has a slot in it, into which copper is swept by the action of the tank walls and which intermittently passes over an opening below into a system of collection ducts 32 which is kept in hydrostatic equilibrium with the separation vessel and into which the recovered copper falls to be collected by a conveyor screw 33. PVC forms a thick aqueous sludge which collects from both separation stages in the common conical base 34 from which it is drained, for example by a screw conveyor system similar to that used for the copper but acting continuously. WHAT WE CLAIM IS:

1. A method of separating a mixture containing particles of metal and particles of

two different plastics material differing in density and/or mass and/or shape comprising introducing the mixture of particles into a first separation chamber containing a liquid medium of appropriate density, producing in the separation chamber a circulating motion including a downcurrent in a first region within the first separation chamber that is sufficient to draw all classes of particle below the surface of the liquid medium and an upcurrent in a second region located between a first baffle depending from above the surface of the medium and forming a barrier between the first and second regions at the level of the surface of the medium and a second, upstanding.

baffle, the upcurrent being sufficient to carry particles of both the plastics materials but not the metal particles over the second baffle and into a second separation chamber delimited from the first separation chamber by the second baffle; producing in the second separation chamber a circulating motion including a downcurrent in a third region within the second separation chamber that is sufficient to draw particles of both the plastics materials below the surface of the liquid medium and an upcurrent in a fourth region located between a third baffle depending from above the surface of the medium and forming a barrier between the third and fourth regions at the level of the surface of the medium and a fourth, upstanding baffle, the upcurrent being sufficient to carry particles of one but not both the plastics materials over the fourth baffle and into a receiver delimited from the second separation chamber by the fourth baffle.

2. A method as claimed in Claim 1 in which the second and/or the fourth baffle upstands from and is in fluid-tight relation with the base of its chamber.

3. A method as claimed in Claim 1 or Claim 2 in which the depending and upstanding baffles in one or both of the separation chambers overlap.

4. A method as claimed in any one of Claims 1-3 in which the circulating motion in at least one of the separation chambers is produced by an impeller immersed in the fluid in that separation chamber.

5. A method as claimed in Claim 4 in which this impeller rotates about a vertical axis.

6. A method as claimed in any one of Claims 1-3 in which the circulating motion in at least the first separation chamber is produced by an impeller located centrally in or near the base of that separation chamber rotating on a vertical axis to entrain the fluid and impel it outwardly by centrifugal mo tion, thereby forming an upcurrent round the periphery of the chamber and a downcurrent in the centre of the chamber, a part of the periphery constituting the separation region adjacent the upstanding baffle.

7. A method as claimed in Claim 5 or Claim 6 in which the impeller comprises a circular disc rotatable about its axis and having a series of round rods upstanding from its periphery.

8. A method as claimed in Claim 7 in which the rods upstand from the upper surface of the disc only and the disc is flush with the separation chamber or nearly so.

9. A method as claimed in any one of the preceding claims in which the upstanding second baffle constitutes a weir.

10. A method as claimed in any one of the preceding claims in which impellers producing the circulating motion in the first and second separation chambers rotate on vertical axes in opposite directions.

11. A method of separating cable scrap substantially as described with reference to the drawings.

12. A method as claimed in any one of the preceding claims in which the plastics materials are polyvinyl chloride and polyethylene.