GB2395924A

GB2395924A - Flotation separator

Info

Publication number: GB2395924A
Application number: GB0321922A
Authority: GB
Inventors: Graham Andrew Sait
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-11-07
Filing date: 2003-09-19
Publication date: 2004-06-09
Also published as: GB0321922D0; GB2396836A; GB0225929D0

Abstract

Object sorting apparatus 201 comprises a container 301 for containing a liquid, having a liquid inlet 206, and a liquid outlet 207, such that when liquid enters said inlet and exits through said outlet a linear flow of liquid is produced through the container. The apparatus has an object delivery means 303 for delivering a plurality of objects of different material composition to the flow of liquid within the container such that the objects follow paths which depend upon their density. A low density object removal means 304 receives objects which travel on the surface of the liquid, and a second object removal means 205 is positioned to screen objects from liquid which exits through the outlet.

Description

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Object Sorting Apparatus Field of the Invention

The present invention relates to object sorting apparatus for sorting 5 objects from a mixture of objects of different materials in dependence upon their density. In particular, it relates to apparatus for sorting material such as domestic waste in order to reclaim or re-use portions of it.

Brief Summary of the Invention

0 According to an aspect of the invention there is provided object sorting apparatus for sorting objects from a mixture of objects of different materials, said apparatus comprising: a container for containing a liquid, having a liquid inlet, and a liquid outlet, such that when liquid enters said inlet and exits through said outlet a flow of liquid is produced through said container; and an object delivery means for delivering a plurality of objects of different material composition to said flow of liquid within said container such that said objects follow paths which depend upon their density, a first object removal means positioned to receive objects having a density in a relatively low density band which travel on the surface of the liquid, and a 20 second object removal means positioned to screen objects from liquid which exits through said outlet.

Brief Description of the Several Views of the Drawings

Figure 1 shows a system employing the present invention; as Figure 2 shows schematically the relative density separation system 103; Figure 3 shows the relative density separator 201 and belt screen 205;

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Figure 4 provides an illustration of the relative density separator 201 which shows further detail of the internal structure of the container 301; Figure 5 shows a cross-sectional view through the separator 201; Figure 6 shows the cross-sectional view through the separator 201 of 5 Figure 5 with arrows illustrating paths of various waste objects through the flow of water; Figure 7 shows a cross-sectional view of separator 201 through the length of conveyor belt 305; Figure 8A shows a plan view of the container 301; 0 Figure 8B shows a plan view of the container 801 of an alternative embodiment; Figure 9 shows an alternative relative density separator system 903; Figure 10 shows the relative density separator 901 of Figure 9 in detail; and Figure 11 shows the separator 901 in crosssection.

Written Description of the Best Mode for Carrying Out the Invention

Figure 1 A waste reclamation system employing the present invention is 20 illustrated in Figure 1. The first process in the system is waste collection 101. Waste collection 101 is substantially a conventional process comprising the collection of domestic waste from households in a region served by the system of Figure 1.

The household waste 111 comprises a mixture of solid objects of 25 differing material composition. For example, household waste comprises: metal objects, such as food cans; glass objects, such as bottles; putrescible material such as vegetable matter, or meat; plastic materials; batteries;

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paper; and card. Conventionally, collected household waste is deposited at a landfill site, but in the present system, the waste collection process 101 transports the household waste to a reclamation plant. The reclamation plant includes apparatus for sorting the household waste depending upon 5 its constituent materials.

The domestic waste 111 received at the reclamation plant is firstly shredded by shredding apparatus 102. A conveyor is typically used to deliver the waste material into the shredder 102, which is designed to shred the waste into objects having dimensions of typically forty millimetres. The to subsequent separating stages of the system have been designed to operate with average object sizes between thirty and fiftyfive millimetres. The separation stages could be simplified by producing smaller object sizes, for example 4mm, but this would involve much higher shredding costs.

The shredder 102 is an "Untha" dual rotating shredder manufactured by Anton Unterwurzacher Maschinenbau GmbH, of Kuchl, Austria.

Preferably, the shredder is a two stage shedder, but other shredding apparatus capable of providing the required object sizes may be used.

After shedding, the shredded waste 112 is transported via a conveyor belt to a first stage separation system, in the form of a relative density 20 separator system 103. This apparatus will be described in detail below, in reference to Figures 2 to BA. The first stage separation system 103, separates the shredded waste material 112 received from the shredder into three separate groups depending upon the relative density of the objects it contains. A fourth group of waste is also generated from a water clarification as and filtering process which will be described with reference to Figure 2.

Each of the four groups of material is then individually processed further. Thus, a first group of matter 113 which has a relative density within a

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smallest predefined range is processed by a second stage process 104. The particulate matter within this range is predominantly paper, card, lower density rubber and low density plastics materials having a relative density less than water, such as expanded polystyrene. Therefore, waste matter 113 may be further processed to separate out the plastics for the purposes of recycling. Remaining material, including the paper and card is used a fuel.

A second group of matter 114, produced by the relative density separator system 103, contains particles having a density within a range which is higher than that of matter 113. This second group of matter 114, 0 contains particles of putrescible matter, higher density rubber and high density plastics, and is further processed by second stage processes 105.

For example, the second group of matter 114 may be fed into composting apparatus which composts the putrescible material. The composted material is then screened out and used for soil improvement.

Composting waste and using the composted material for soil improvement is already known, but the system of the present embodiment increases the proportion of the degradable material which is fed to the composting apparatus and therefore increases its efficiency.

Non-composted materials such as plastics and rubber that are 20 screened from the composted material may be disposed of by landfill or preferably used as a fuel.

A third group of matter 115, produced by the relative density separator system 103, contains particles having a density within a range which is higher than that of matter in either of the other groups 113, or 114. This third group 2 of matter 115, contains particles of glass, minerals, ceramics, metals. For the purposes of this specification, both metal and metal alloys will be referred to

herein as metal.

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The third group of material 115 is further processed by second stage processes 106 which separates the group into subgroups. Thus the material 115 passes along a conveyor through a magnetic separator which separates out magnetic ferrous metal particles, such as iron and mild steel particles.

5 The remaining material then passes through an eddy current separator which removes non-magnetic metal particles, such as aluminium, brass, copper, stainless steel and zinc. Both the ferrous and non-ferrous metallic particles may then be recycled.

The fourth group of material 116, obtained by a clarification and to filtering process, may be disposed of by landfill. However, where the combustible portion of the fourth group material 116 is found to be sufficiently high, it is mixed with the first group material 113 and used as a fuel to generate electricity.

Figure 2 The relative density separation system 103 is shownschematically in Figure 2. The system 103 comprises a relative density separator 201 which will be described in detail with respect to Figure 3 to 8A, a reservoir 202 of water and associated pump 203, water cleaning apparatus 204, and a 20 screening conveyor belt 205.

The relative density separator 201 is supplied with water from the reservoir 202 via a pipe 206 by means of a pump 203 which is located within the reservoir 202. The majority of the water is returned back to the reservoir 202 via outlet pipe 207, screen belt 205 and return pipe 208. The remainder 25 of the water is returned to the reservoir via pipe 209. In the present embodiment, approximately 99% is returned via pipe 207 and 1% via pipe 209.

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The pump 203 is of the type used in the sewage industry and therefore capable of coping with small objects which remain suspended in the water received from the separator 201. The pump is typically capable of pumping water at a rate of up to 400 gallons per minute (1800 litres per 5 minute) . During operation, shredded waste 112 is supplied to the separator 201 which has means for removing the low density waste 113 and high density waste 115. The intermediate density waste 114 exits the separator 201 with the water through pipe 207 and is deposited on screen belt 205 where it is 10 separated from the water.

In order to operate efficiently, the flow of water through the separator 201 must be maintained at a substantially constant rate. Two features of the present embodiment have been provided to achieve this. Firstly, it has been found that the pump 203 cannot produce a constant flow rate if the water becomes aerated, and thus the reservoir 202 is divided into two parts, namely a feeder tank 210 and a de-aeration tank 211, hydraulically linked by pipe 212. Therefore, in operation, water received from separator 201 firstly enters de-aeration tank 211 where the majority of entrapped air escapes to atmosphere. From the de-aeration tank 211 it passes through pipe 212 to the 20 feeder tank 210 from where the pump 203 pumps it back up to the separator 201. In an alternative embodiment, the reservoir is a single tank with a perforated separator plate located between a portion which receives the pipes 208, 209 and a portion which contains the pump 203.

25 In a further alternative embodiment the reservoir is a single tank of extended length, such that there is sufficient lateral distance between a portion of the reservoir that receives the pipes 208, 209 and a portion which

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contains the pump 203 to ensure that water exiting said pipes has sufficient time to de-aerate before entering said pump.

The second feature of the present embodiment provided to maintain a constant flow of water is a water level control system, comprising an 5 ultrasonic position sensor 213, a control circuit 214 and a butterfly actuator valve 215. The water level in the separator 201 is sensed by the ultrasonic sensor 213 which supplies signals to said control circuit 214 defining said level. The control circuit 214 is designed to maintain the level at a predetermined height and therefore it drives the actuator valve to further 10 open or further close in dependence of signals received from the sensor.

As stated above, the intermediate density waste 114 is deposited on screen belt 205 where it is separated from the water and stored for second stage processing. The screen belt 205 takes the form of a conveyor belt made from inter-linked metal wires which define rectangular apertures of dimension 8mm by 25mm. Thus it will be understood that a proportion of material is screened:out of the water by the screen belt 207, but smaller particles of material may pass through and remain susperded in the water.

Thus during use, the water which is constantly re-circulated through the separator 201 and reservoir 202 becomes contaminated with small particles 20 of waste and becomes generally cloudy. In order to capture this waste, the separator system 103 contains the water cleaning apparatus 204.

The water cleaning apparatus comprises a clarifier unit 216 and a filtration unit 217. Contaminated water is extracted from the reservoir 202 and received into the clarifier unit 216 where chemicals are added to cause the 25 matter suspended within the water to flocculate. In the present embodiment the chemicals are alum and polyamyl.

Following flocculation, the contaminated water is filtered by the

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filtration unit which removes the filtered contaminants 116 from the water as cakes. In the present embodiment the filtration unit is a filter press of the type having a bank of plates with a filter membrane and as used in the sewage industry. Such a filter press may be obtained from Simon Hartley Limited, or 5 Latham International Limited, England.

In alternative embodiments the filtration unit 217 is a V-fold folding belt filter press, as produced by Simon Hartley Limited, England, or a continuous bag filter unit.

Having removed contaminants by the filtration unit 217, the cleaned 10 water is returned to the feeder portion of the reservoir 202.

Figure 3 The relative density separator 201 and belt screen 205 is illustrated in Figure 3.

The separator comprises a container 301 of width 175mm and length 1000mm which has a sloping floor such that the height of the container is 200mm at one end and 500mm at the other end. The pipe 206 supplies water 320 to the container 301 at its shallow end and water escapes under gravity from the container via pipe 207 at its deep end.

20 The pipe 206 has a circular cross-section of 100mm diameter but has a final section 302 which opens out to a square cross-section as it meets the end wall of the container 301.

The shredded waste 112 is transported to the container by a feed conveyor 303. The conveyor 303 may be a conveyor belt as shown in Figure 25 3 or other conveyor means which will provide a regular feed of material into the container 301. For example, a vibrating conveyor may be used for this purpose.

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During operation, the shredded waste is dropped into the container where it enters the water flow. Once in the water flow, the waste objects become separated in dependence of their density. The present embodiment is arranged such that waste material 114 having intermediate densities 5 remains in the flow of water all through the container 201 and exits with the water through outlet 207.

Water escaping through outlet pipe 207 passes through the wire screen belt 205, which screens out intermediate density material 114 and transports it away for second stage processing.

0 The separator 201 also includes a conveyor belt 304 which provides a means for removal of the low density waste 113. The conveyor belt 304 is positioned down stream of, and in line with, the feed conveyor 303. The end of conveyor 304 nearest to conveyor 303 is submerged into the flow of water in the container 301, so that the low density material 113 which travels along the surface of the water is lifted out by conveyor 304. At the opposite end of the conveyor 304, the light waste 113 is deposited in a storage container where it awaits transportation for second stage processing.

In order to facilitate the transportation of the low density material 113 onto the conveyor 304, the conveyor belt 304 has a structure which allows 20 water to flow through it. Thus conveyor belt 304 comprises interlinked metal wires and has a similar structure to conveyor belt 205.

The separator 201 has a conveyor belt 305 which provides a means of removal for the high density waste 115. The conveyor 305 is located in a housing 306 which extends from beneath container 302, upwards at an angle 25 of approximately 45 degrees to the horizontal to an upper end 307 to one side of the container 301. During operation the high density waste 115 within shredded waste 112 sinks through the flow of water onto the submerged

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lower end of conveyor 305. Conveyor 305 transports the waste 115 from the water in the housing 306 to the upper end of the conveyor where it is deposited to await second stage processing.

5 Figure 4 Figure 4 provides an illustration of the relative density separator 201 which shows further detail of the internal structure of the container 301.

To operate effectively, the separator 201 must drop the shredded waste into a flow of liquid that is substantially linear, i.e. not turbulent. To 10 achieve this, a baffle is located in the container spaced approximately 20mm from the water inlet 402. In the present embodiment the baffle takes the form of a metal plate which has an array of apertures 403 machined therein. The baffle plate 401 is sealed to the floor and sides of the container 301 but has a free upper edge over which water flows during use. The container 301 is generally open topped. However a blanking plate 404 is fixed to the end wall and side walls hear the inlet 402 such that it extends over the top of the baffle plate 401. The baffle plate 401 and blanking plate 404 are mutually positioned to provide a window through which water flows during use; The blanking plate 404 ensures that the volume of water directed up and over the 20 baffle plate is limited and thereby contributes to the production of a linear flow through the container.

Figure 4 also shows a passageway 405 which extends down from the floor of the container 301 to the housing 306. This passageway allows the removal of the high density material 116 from the container 301.

Figure 5 A cross-sectional view through the separator 201 is shown in Figure 5.

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As shown in Figure 5 the baffle plate 401 is substantially vertical and parallel to the end wall 501 of the container 301. The arrows 502 indicate the flow through the apertures in the baffle plate 401 and through the window formed between the upper edge of the baffle plate and the lower surface of the 5 blanking plate 404.

Figure 6 The cross-sectional view through the separator 201 of Figure 5 is shown in Figure 6 with arrows illustrating paths of various waste objects 10 through the flow of water.

On leaving the feed conveyor 303 very dense objects, such as those made of metal fall rapidly through the flow of water and are therefore relatively unaffected by said flow. The path of such an object is shown by arrow 601. Such an object may hit the floor of the container 301 upstream of the passageway 405, but the flow of water and the downward slope of the container floor 610 forces it along the floor to a position where it may fall through the passageway 405 and onto the conveyor 305.

Other objects which are not quite so dense but which still have a density in the high density range will tend to be more affected by the flow of 20 water and so may follow a path which takes it directly down through the passageway 405 without hitting the floor. An arrow 602 shows the path of the least dense of such objects. Thus if the object had been any further affected by the flow it would have gone past the passageway 405 and possibly landed on the floor of the container further downstream. From there the slope of the 25 floor and the flow of water would transport it to the outlet pipe 207 to exit the container with the flow of water. The path of such an object is indicated by arrow 603.

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Arrows 604 and 605 indicate paths of low density objects having densities in the lowest band of relative densities. The least dense objects float on the surface of the water and follow path 605 while slightly denser objects may just start to sink and follow path 604. In each case the objects 5 are lifted out of the water by conveyor 304. Objects which are slightly more dense will flow beneath the end of conveyor 304 and eventually exit through outlet pipe 207.

Therefore, the separator 201 separates the shredded waste into three groups of objects, namely: objects having a density in a relatively high band 10 of densities, which fall onto, and are removed by, conveyor 305; objects having a density in a relatively low band of densities which travel along the surface of the water and are removed by conveyor 304; and objects having a density in an intermediate band of densities which remain in the flow of water and exit through the outlet 207.

For the economic operation of the waste reclamation system, it is important that the three groups are as clearly defined as possible. For example, it is undesirable for organic matter to be received into passageway 405 and for glass, ceramics etc. to be received onto conveyor 205.

Therefore, the present embodiment has a number of adjustable components 20 which allow the functioning of the separator 201 to be optimised.

Firstly, the position of the feed conveyor 303 is adjustable in that it can move backwards and forwards (as indicated by arrow 620) to decrease or increase the lateral distance between the end 606 of conveyor 303 and the downstream edge 607 of the passageway 405.

25 Secondly, the position of the conveyor 304 is adjustable backwards and forwards (as indicated by arrow 621) to decrease or increase the lateral distance between itself and the end 606 of conveyor 303.

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Thirdly, although the majority of water escapes through outlet 207, a small portion is returned through passageway 405 and pipe 209 by opening a valve 607. The flow through passageway 405 has the effect of directing objects which come close to the passageway into said passageway. In the 5 present embodiment this flow is very small compared to the flow through outlet 207, being typically 0.5% to 1%. However, by adjusting the valve the composition of material entering passageway 405 may be affected.

Although the position between the conveyors 303 and 304 is adjustable, even at their widest separation the low density material removed to by conveyor 304 flows in the water for less than four seconds. If dry paper and card is allowed to stay in the water for longer than this, it becomes saturated, its density increases and it therefore becomes harder to separate from organic material.

Figure 7 A cross-sectional view of separator 201 through the length of conveyor belt 305 is shown in Figure 7. As shown in Figure 7 the conveyor 305 rises at an angle of approximately 45 degrees to the horizontal within housing 306. Since the housing 306 and container 301 are connected by 20 passageway 405, the level 701 of the water in the housing is substantially the same as the level 702 in the container.

It should be noted that the conveyor 305 is effectively removed from the container 301 such that it does not impede the substantially linear flow of water through the container 301.

as In an alternative embodiment, the separator is substantially the same as separator 201 except the passageway 405 and conveyor 305 is not provided. Consequently, the separator merely separates the shredded waste

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into that which travels along the surface of the water and that which sinks.

Figure 8A A plan view of the container 301 is provided in Figure 8A showing the 5 position of the outlet 207, the inlet 402 the baffle plate 401, the blanking plate 404 and the passageway 405.

Figure 8B The container 801 of an alternative embodiment is shown in plan view 10 in Figure 8B. The alternative embodiment is essentially the same as the embodiment shown in Figure 3 to 8A but the width of the container 801 is approximately three times wider than that of container 301. The outlet 807, the passageway 805, the baffle plate 801 and the blanking plate 804 are correspondingly wider, as are the feeder conveyor (not shown), and the low density material conveyor (not shown. Unlike the container 301, the container 801 has three inlets 802A, 802B and 802C. These inlets are supplied by pipe network 850 which branches from pipe 206, such that an equal pressure of water is supplied to each inlet.

By scaling up the width of the apparatus in the manner indicated by 20 Figure 8B, the rate at which waste can be separated is similarly scaled up, without changing the essence of the operation.

Figure 9 An alternative relative density separator system 903 is shown in as Figure 9. The majority of the components of the system 903 are the same as those of system 103 and so have been given similar labels. Thus, for instance, the system has a reservoir 902 comprising a feeder tank 910 and

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de-aeration tank 911, as well as a water cleaning apparatus 904 having a clarifier unit 916 and filtration unit 917. It also has a supply pipe 906 to the inlet of the separator 901, and an actuator valve 915 on said pipe controlled by control circuit 914 in response to signals received from ultrasound position 5 sensor 913.

The difference between system 903 and 103 lays in the difference between the relative density separator 901 and separator 201. Whereas separator 201 has an outlet 207 which allows water to escape freely from container 201, separator 901 has outlet pipes 902 and 909 which extend 10 down into the de-aeration tank 911 via a ball valve 907A and 907B respectively. Figure 10 The relative density separator 901 of Figure 9 is shown in detail in Figure 10. The separator 901 comprises an elongate open-topped container 1001 which has an inlet at one end, supplied with water by pipe 906. Thus during use the container contains a flow of water along its length.

Adjacent the inlet is a baffle plate 1011 and blanking plate 1014 arranged in a similar manner to those of separator 201, to facilitate a linear 20 flow of water. In the present embodiment the baffle plate 1011 has an array of circular apertures defined therein.

In an alternative embodiment, the baffle plate 1011 is replaced with a baffle plate having a series of equally spaced elongate, horizontally arranged apertures, extending across more than 90% of its width. In one embodiment, 25 a second of baffle plate is positioned downstream of the first baffle plate. The second baffle plate also has equally spaced elongate, horizontally arranged apertures, extending across more than 90% of its width, but the apertures of

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the second plate are vertically arranged to be out of phase with those in the first plate.

In a further alternative embodiment, the baffle plate 1011 is replaced by a solid baffle plate extending down from the blanking plate 1014 such that 5 water entering the inlet is forced to flow under the baffle plate. A second solid vertical plate is fixed approximately 100mm downstream of the solid blanking plate and sealed to the floor and side walls of the container 1001, such that it forms a weir over which all of the water must flow.

A feed conveyor belt 1003 is positioned above the container 1001 and 10 this is arranged to feed shredded waste into the container 1001.

A wire screen conveyor belt 1004 is positioned above the container such that in operation its end nearest to the inlet is submerged below the surface of the flow of water and catches objects having a density within the low density range.

The container 1001 is cuboid shaped with a width of 175mm, a depth of 20Qmm, and a length of 1700mm. Two passageways 1005A and 1005B extend down from the floor 1010 of the container 1001 to the lower ends of conveyor housings 1006A and 1006B respectively. The conveyor housings 1006A and 1006B extend upwards at an angle of approximately 45 degrees 20 to the horizontal and house conveyor belts 1052A and 1052B respectively.

The lower ends of the conveyors 1052A and 1052B are positioned beneath passageways 1005A and 1005B respectively such that material falling through the passageways lands on the respective belt and is transported to the upper end of the belt where it is deposited for second stage processing.

All of the water entering the container from pipe 906 exits through passageway 1005A or passageway 1005B via outlet pipes 909 and 902 respectively. The pipes 909 and 902 are connected to the lower side of the

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housings 1006A and 1006B respectively, and consequently, to escape, water must pass the lower ends of conveyors 1052A and 1052B. The conveyor belts 1052A and 1052B have a structure which allows a free flow of water through them. In the present embodiment, these conveyors have a belt 5 fabricatedfrom inter-linked wires which provides a screen to screen out solid matter falling down the passageways.

The container 1001 has an extended portion 1051 between the baffle plate 1011 and the passageway 1005A. This extended portion further assists the establishment of a linear flow in the water before it reaches the position 0 where shredded waste is dropped into it from conveyor 1003.

The container 1001 contains a wedge shaped structure 1057, fabricated from sheet metal, and located between the passageways 1005A and 1005B. The front face 1058 of structure 1057 provides a deflector which deflects a portion of the water flow downwards towards the passageway 1005A The rear surface 1059 of the structure 1057 provides a sloping false floor for the container which assists the movement of intermediate density objects into passageway 1005B...

A further deflector plate 1060 is hingedly connected to the upper edge of the wedge shaped structure and arranged to be fixed at a variety of angles 20 to the horizontal. By varying this angle, the direction of a portion of the flow can be altered, and consequently the composition of the material entering passageways 1005A and 1005B may be adjusted.

A further control of the composition of material entering passageway 1005A and 1005B is provided by the valves 607 and 907. In this 25 embodiment, the flow through pipe 909 is approximately equal to flow through pipe 902, but by further opening one valve and further closing the other valve the flow of material may be adjusted. Typically, the rate of flow

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through outlet pipe 909 is between 50% and 100% of the rate of flow through outlet pipe 902.

Figure 11 5 The separator 901 is shown in cross-section in Figure 11. In operation, water enters the container 1001 from pipe 906 by passing through or over baffle plate 1011. The water then flows along the container 1001 until it reaches deflector plates 1060 and 1059. Here a first, portion of the water flow is deflected downward and exits through passageway 1005A, screen belt to 1052A and pipe 909.

The remaining, second, portion of water continues forwards, flows over the structure 1057 and exits through passageway 1005B, the screen belt 1052B and pipe 902.

Shredded waste material is dropped into the flow of water from the 5 conveyor 1003. As is the case with the embodiment of Figure 3, the path of the waste material through the water depends upon its density. Objects having a density within a low range of densities travel along the surface of the water and are received onto wire screen conveyor belt 1004. Arrow 1101 illustrates such a path.

20 Objects in a high density range fall steeply through the flow of water and consequently fall through passageway 1005A with the first portion of the water flow. They are then screened from the water exiting outlet pipe 909 by the conveyor 1052A, and said conveyor transports them from the separator.

Arrows 1103 and 1104 illustrate the paths of two objects which have 25 densities in the high range of densities and thus fall onto conveyor 1052A.

Objects in an intermediate range of densities fall through the flow of water but less steeply. Consequently, they pass beneath the conveyor 1004,

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but over the deflector plate 1060, and subsequently fall through passageway 1005B with the second flow of water. They are then screened from the water by the conveyor 1052B which transports them away. Arrow 1102 illustrates the path of such an object.

Claims

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1. Object sorting apparatus for sorting objects from a mixture of objects of different materials, said apparatus comprising: 5 a container for containing a liquid, having a liquid inlet, and a liquid outlet, such that when liquid enters said inlet and exits through said outlet a flow of liquid is produced through said container; and an object delivery means for delivering a plurality of objects of different material composition to said flow of liquid within said container to such that said objects follow paths which depend upon their density, a first object removal means positioned to receive objects having a density in a relatively low density band which travel on the surface of the liquid, and a second object removal means positioned to screen objects from 5 liquid which exits through said outlet.

2. Object sorting apparatus according to claim 1, wherein said apparatus further comprises a third object remove, means positioned to receive objects having a density in a relatively high density band compared 20 to the density of objects removed by said second object removal means.

3. Object sorting apparatus according to claim 1 or claim 2, wherein said flow of liquid is substantially linear.

25

4. Object sorting apparatus according to any of claims 1 to 3, wherein said container comprises a baffle adjacent to said inlet which defines a substantially linear flow.

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5. Object sorting apparatus according to claim 4, wherein said baffle comprises a plate defining apertures through which the liquid flows.

5

6. Object sorting apparatus according to claim 5, wherein said apparatus comprises a blanking plate defining an upper limit for the surface of said liquid adjacent to said baffle plate.

7. Object sorting apparatus according to claim 6, wherein said to baffle plate has an upper edge spaced from said blanking plate to define a window through which a highest portion of said liquid flows.

8. Object sorting apparatus according to any of claims 1 to 7, wherein said first object removal means comprises a conveyor belt formed from a material which allows the liquid to flow through.

9. Object sorting apparatus according to claim 8, wherein the conveyor belt is constructed from inter-linked metal wires.

20

10. Object sorting apparatus according to any of claims 1 to 9, wherein said second object removal means comprises a conveyor belt formed from a material which allows liquid exiting said outlet to flow through. 25

11. Object sorting apparatus according to any of claims 1 to 9, wherein said second object removal means comprises a conveyor belt formed from inter-linked metal wires such that liquid exiting said outlet is

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allowed to flow through said conveyor belt.

12. Object sorting apparatus according to claim 10 or 11 wherein said conveyor belt is located within a housing connected to said container by a passageway through which a portion of said water flows.

13. Object sorting apparatus according to any of claims 1 to 12, wherein said apparatus further comprises a reservoir which receives liquid exiting said outlet, and a pump which pumps liquid from said reservoir to o said inlet.

14. Object sorting apparatus according to claim 13, wherein said reservoir comprises a de-aeration portion separated from a feeder portion.

5

15. Object sorting apparatus according to claim 14, wherein said deaeration portion comprises a de-aeration tank and said feeder portion comprises a separate feeder tank hydraulically linked to said de-aeration tank. no

16. Object sorting apparatus according to any of claims 1 to 15, wherein said apparatus is configured to re-circulate the liquid and said apparatus further comprises a liquid cleaning apparatus configured to filter out contaminants which become suspended in re-circulated said liquid.

s

17. Object sorting apparatus according claim 16, wherein said liquid cleaning apparatus comprises a clarifying unit configured to flocculate contaminants suspended in said liquid, and a filtering unit configured to

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filter said liquid following flocculation.

18. Object sorting apparatus according claim 16 or 17, wherein said contaminants filtered from said liquid are burnt as a fuel.

19. Object sorting apparatus according any of claims 1 to 18, wherein the speed of fluid in said container and the distance between said object delivery means and said first object removal means are arranged such that said objects having a density in a relatively low density band 10 remain in said flow for less than four seconds.

20. Object sorting apparatus according any of claims 2 to 19, wherein the position of the object delivery means is adjustable to allow adjustment of the lateral distance between said object delivery means and said third object removal means.

21. Object sorting apparatus according any of claims 1 to 20, wherein the position of the first object removal means is adjustable to allow adjustment of the lateral distance between said object delivery means and 20 said first object removal means.

22. Object sorting apparatus according any of claims 1 to 21, wherein said apparatus further comprises a sensor for sensing liquid level in said container and an actuator valve which adjusts the flow through said inlet 25 in response to signals generated by said sensor.

23. Object sorting apparatus according any of claims 2 to 22,

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wherein said third object removal means comprises a passageway extending from the floor of said container to a submerged part of a conveyor belt.

24. Object sorting apparatus according any of claims 2 to 23, 5 wherein said container contains a deflection means for deflecting a portion of said flow to a second liquid outlet such that objects are deflected towards said third object removal means.

25. Object sorting apparatus according claim 24, wherein said to deflection means includes a deflection plate.

26. Object sorting apparatus according claim 25, wherein said deflection plate is mounted such that its angle to the horizontal is adjustable, thereby providing adjustment to the volume of liquid it deflects.

27. A waste recycling system comprising apparatus according to any one of claims 1 to 25 and a shredder which is configured to shred waste to produce objects which are sorted by said apparatus.

20

28. Object sorting apparatus substantially as herein described with reference to Figures 2 to 8A, or Figures 9 to 11.