It is known, for example from US patent no. 5,308,368, to separate a mixture of materials, such as stone, various kinds of metals, glass, compost and paper by depositing the material onto a vibrating conveyor and supplying it to an extraction plant. On said vibrating conveyor, the material is separated into a lower layer of relatively heavy pieces and an upper layer of relatively light pieces. The light pieces are removed from the vibrating conveyor by means of a suction nozzle, whilst the heavy pieces fall from the vibrating conveyor at one end thereof under the influence of the force of gravity.

Furthermore an apparatus is known wherein heterogeneous material is deposited on a vibrating conveyor, such as a downwardly sloping vibrating chute, which material is introduced into an air duct, through a side opening therein, by means of said vibrating conveyor. Fans are used to generate an upward air flow in said air duct, which air flow carries up the light fraction of the material being supplied, which has already been separated, whilst the heavier fraction falls down against the air flow. Such an apparatus may be fitted with an adjustable venturi. This makes it possible to vary the acceleration of the air that is used for the separation process in dependence on a specific waste material.

The aforesaid apparatuses are for example used for

purifying a waste flow, which mainly consists of a heavy fraction, such as stone, glass or metal, by removing a light fraction, such as wood, paper and/or plastic, which for example makes up 10 per cent by weight of the overall waste flow, from said waste flow. In such processes the purified heavy fraction constitutes the product, whilst the light fraction constitutes the waste.

The object of the invention is to provide an apparatus of the type referred to in the introduction, by means of which heterogeneous waste, a major part of which consists of a light fraction, can be processed in an effective manner and with a large capacity.

In order to accomplish that objective, the apparatus according to the invention is characterized in that said vibrating conveyor comprises a conveyor belt.

The use of said belt prevents the relatively light material from sticking to the vibrating conveyor, as is often the case with the vibrating chute that is frequently used, and a better separation of the light fraction on the one hand and the heavy fraction on the other hand is obtained. Moreover, it is possible to control the supply of the heterogeneous waste more accurately. If in addition the speed of the conveyor belt is controllable, the separation or segregation process can be further optimized by controlling the time during which the waste is present on the conveyor belt.

Preferably, elongated, rotatable rollers are disposed under the upper part of the belt, which rollers are provided with projections, which push the belt up locally and repeatedly upon being rotated, thus producing vibrations in the belt.

Furthermore, the air duct is preferably provided with a venturi at the location of the side opening. If the constriction of the venturi is adjustable, the velocity of the air flow through the heterogeneous waste being supplied can be adjusted in dependence on the composition of said waste.

The invention furthermore relates to a method for the separation of heterogeneous waste into a relatively light fraction and a relatively heavy fraction, wherein the waste is spread and introduced into a vertical or substantially vertical air flow by means of a vibrating conveyor comprising a conveyor belt, as well as to a method for obtaining a solid fuel from heterogeneous waste.

The invention will now be explained in more detail with reference to the figures, which schematically show an embodiment of the apparatus according to the present invention.

Figure 1 is a schematic, sectional view of the main components of an apparatus according to the invention.

Figures 2 and 3 are a top plan view and a side elevation, respectively, of a vibrating conveyor for use in the apparatus of Figure 1.

Figure 4 is a cross-sectional view of a pulley as used in the vibrating conveyor according to Figures 2 and 3.

Figure 1 is a sectional view of a vertical screening unit 1, which comprises an air duct 2 having an open end 3, which air duct 2 communicates with a cyclone 4, which in turn communicates with a filtering unit 5. Filtering unit 5 comprises, for example, a cascade of two, four or six fans 6, each having a capacity of for example-4000 m3/hour, by means of which it is possible to generate a reduced pressure in filtering unit 5 and thus an air flow through cyclone 4 and air duct 2. Heterogeneous waste is introduced into the air duct 2, via a side opening 8, by means of a vibrating conveyor 7.

Said waste may be household waste and/or industrial waste, for example, and it may have been presorted and/or preshredded. Such waste may for example comprise one or more of the following components: carpet remnants, plastics such as PVC, HDPE, PE, PP, etc., textile, paper and/or wood remnants, all of which are generally considered to form part of the light fraction, as well as ferrous and non-ferrous metals, sand,

stone remnants, glass and ceramics, all of which will generally be considered to form part of the heavy fraction. The dimension of these pieces of waste will generally range between 1-300 mm, whilst the density of the pieces will usually range between 5-250 kg/m3. The light fraction may for example comprise 80- 99 per cent by weight of the heterogeneous waste, whilst the heavy fraction comprises 1-20 per cent by weight thereof.

Air duct 2 is provided with an adjustable venturi 9 at the location of side opening 8, which venturi in the main consists of a constriction 9', which is made up of two plate members 10,10'which are pivotally connected to each other and to a wall of air duct 2. Said plate members 10,10'can be moved inwards or outwards by means of a long adjustment bolt 11, by means of which constriction 9'can be reduced or enlarged. The other side of constriction 9'is made up of the right-hand (in the drawing) end 12 of vibrating conveyor 7, which end 12 extends through side opening 8. A wedge 13 is mounted below said end 12, which wedge directs the air flow to the farthest point of end 12 in order to thus prevent, or at least reduce, the occurrence of turbulence in the air duct 2.

Since venturi 9 is adjustable, it is possible to regulate the air speed accurately, in dependence on the composition of the heterogeneous waste, at the location where the actual separation takes place.

Positioned below the above-described venturi 9 is a second venturi 14, which ensures that components of the light fraction that have been dragged down by the heavy fraction can be carried up yet in the accelerated air flow that has been generated by said second venturi 14.

The air flow in air duct 2 is carried to cyclone 4 via a connecting piece 15, in which an adjustable false air valve 16 is mounted, and a transition piece 17. Said adjustable false air valve 16 helps to keep the flow with which cyclone 4 is fed at a constant level, such that said flow level is and remains

within the operating range of said cyclone 4. In addition, said false air valve 16 can be used for regulating or adjusting the flow, and thus the air speed in air duct 2. Thus it may be necessary to open venturi 9 relatively far, for example for relatively large pieces, which in principle will result in a reduced air speed in venturi 9. Such a reduction may be compensated by closing the false air valve 16 further or, as the occasion arises, altogether. Furthermore it may be necessary to increase the air speed in venturi 9 in order to thus enhance the separating efficiency. This may be the case, for example, when the heterogeneous waste consists of relatively small pieces. When the false air valve 16 is closed further, or altogether, the flow with which cyclone 4 is fed can be adapted accordingly by means of the cascade of fans 6, i. e. by setting the fans 6 to a higher mark and/or by activating a larger number of fans 6.

In cyclone 4, the light fraction is separated from the heavy fraction. At the bottom of cyclone 4 is an expansion chamber 18, in which the air strongly decelerates, so that solid pieces that are present in the air, i. e. the light fraction, fall into a rotary lock 19, which is disposed under expansion chamber 18, under the influence of the force of gravity. Rotary lock 19 comprises a number of chambers, via which the light fraction is discharged to the outside without disturbing the flow in cyclone 4. The air is displaced towards an outlet 20 at the top of cyclone 4 and carried to the aforesaid filtering unit 5 via a further duct 21.

Relatively large pieces that are still present in the air flow after having passed cyclone 4, which may be the case in particular upon temporary incorrect operation of cyclone 4, will land on the bottom of the filtering unit 5 and will be discharged by means of a chain scraper 22 comprising two parallel chains 23, which are passed over chain wheels 24.

Chains 23 include rubber strips 25, which scrape pieces that

have fallen onto the bottom of the filtering unit 5 towards a rotary lock 26. The air is carried to an outlet 28 via filter modules 27.

Figures 2 and 3 show a vibrating conveyor 29 which is suitable for use in the above-described vertical screening unit 1. Vibrating conveyor 29 comprises a frame 30, in which a pulley 31,32 is rotatably mounted at respective ends thereof.

A rubber belt 33 having a thickness of, for example, 5 mm is passed over said pulleys. One of the pulleys 31,32 can be driven by a controllable electric motor 34 which is mounted on frame 30. The belt, and thus the (bend) pulley 32, are set going by driving the (driving) pulley 31. A number of beater rollers 35 is rotatably mounted beloe the upper side of belt 33, parallel to the pulleys 31,32. Each of said rollers 35 is provided with a number of projections 36, which extend in the longitudinal direction of rollers 35, across the entire width of the belt 33 in this embodiment. The distance from the central axis of rollers 35 to the underside of the upper part of the belt 33 has been selected so that said projections 36 push up the band locally and repeatedly upon rotation of rollers 35, thus producing vibrations in belt 33.

Various constructions may be used for the rollers 35, of course, they may for example consist of two cross end discs, between which a number of bars are fitted, which bars will form projections in that case. Mounted on one of the two cross ends of both the driving pulley 31 and the beater roller 35 is a respective chain wheel 37,38, which chain wheels are interconnected by means of a chain 39. The transmission ratio between said chain wheels 37,38 has been selected so that the circumferential speed of the beater rollers 35 is higher than the carrying velocity of belt 33. Thus the belt is caused to vibrate at a relatively high frequency. The frequency can be increased, of course, by increasing said ratio and/or the number of projections. The amplitude of the vibration can be

adapted by increasing the distance from the projections to the central axis of the beater rollers.

It has become apparent that an effective transport both of the light pieces and of the heavy pieces in heterogeneous waste can be obtained by using a vibrating conveyor comprising a conveyor belt, also if the waste consists of relatively light pieces for the larger part. In addition, a high degree of separation or segregation is obtained.

It is possible with the apparatus according to the invention to purify the aforesaid light fraction thoroughly, to such a degree that said fraction can be processed into pellets by means of an extruder, without said extruder being damaged or getting clogged by, for example, metal or glass remnants.

Depending on their composition, such pellets may suitably be used as an alternative fuel for generating energy or producing electricity.

The invention is not restricted to the embodiments as described above, of course, which can be varied in several ways without departing from the scope of the invention as defined in the claims.