This invention relates to a device and a process for degassing and dosing plastic waste, in particular for the subsequent introduction of said waste into a pyrol- ysis furnace.

The degassing of plastic waste is commonly done by compression of the plastic waste which reduces the volume of the plastic waste material. Since storage and transport capacities are in general limited by the volume of the stored or transported material, the degassing of plastic waste reduces costs and increases handling of the waste material. Degassing or deaeration is further necessary in case of a subsequent pyrolysis of the plastic waste, since oxygen included in the plastic waste material may cause problems or even explosions in the pyrolysis reactor.

The compression and degassing of easily compressible material, in particular tobacco, is described by DE 34 05 182 A1 . The tobacco is introduced into a container by a feeding device. The lower part of the feeding device can be moved into said container and has a double layered housing. Between the closed outer layer of the housing and the perforated inner layer of the housing an aeration channel is formed. The aeration channel is connected to a pump, which can reduce the pressure in the container, and the material inside said container is subsequently compressed by atmospheric pressure. Consequently, the material has to be soft and compressible by low pressures, such as atmospheric pressure. This process, therefore, is not applicable for plastic waste.

US 5,282,431 (DE 41 30 416 C1 ) describes a process for rendering usable disposal products, in which unsorted pollutant-containing industrial, domestic or special refuse undergoes a high temperature treatment. The disposal products are compressed batchwise to compact packs and, while maintaining the pressure, are subsequently introduced into a channel heated to temperatures of more than 100 °C in order to evaporate initially present liquids and to eliminate mechanical restoring forces. The entrained organic constituents assume a binder function. The resulting structurally stable, lumpy solid conglomerate is introduced into a high temperature reactor, maintained at at least 1000 °C and forms therein a gas-permeable bed. At high temperatures of above 1000 °C, the monomers of the plastic waste cannot be recovered from the waste material, since the monomers will decompose at such temperatures.

Document DE 10 2005 059 856 A1 describes an extruder for introducing a plastic bulk material into a reactor. The extruder comprises a screw shaft with first and second windings. Between both windings a winding-free section is disposed in which the conveyed bulk material is compacted and thereby degasi- fied. The described extruder can only handle bulk material having a small particle size of typically 10 mm x 10 mm. Consequently, plastic waste would have to be shredded into small pieces before feeding it to the extruder. It is the object underlying the present invention to provide a device and a process for degassing and dosing of large plastic waste entities without the requirement of preceding shredding of the plastic waste.

In accordance with the present invention this object is solved by the features of claims 1 and 1 1 , respectively. A device for degassing and dosing plastic waste is provided, in particular for the subsequent introduction of said waste into a pyrolysis furnace, comprising a container for receiving said plastic waste and having a rigid bottom, an upper cover that can be opened and closed, and at least four side walls, wherein a first and a second of said side walls are located opposite of each other and are movable towards and away from each other by activating respective auxiliary pistons connected to said side walls, wherein a third side wall is movable in a direction perpendicular to the first and second side walls by activating a main piston connected to said third side wall, and a fourth side wall provided opposite said third side wall and movable to open an exit from the container. It is thus not necessary to grind the plastic waste into small pieces. Rather the waste is compacted and can be introduced into the pyrolysis furnace as a block. Thereby it is possible to handle material having a particle size of e.g. 500 x 500 mm corresponding to the particle size of the waste as it comes. The air and oxygen contained in the original bulk plastic waste is pressed out of the waste during compression of the waste material.

Preferably, the cover and/or the bottom comprise(s) a plurality of openings. This ensures a complete degassing of the plastic waste, since the expelled gases can easily leave the device through the openings. Furthermore, possible gas inclusions at pressures above atmospheric pressure inside the device can be completely avoided. In a special embodiment, the openings in said cover and/or in said bottom are exclusively distributed over the base area enclosed by the side walls. Compared to a distribution of the openings over the complete area of the cover and/or the lower bottom, the durability of said cover and/or said lower bottom is increased.

In accordance with a preferred embodiment of the invention, the first and/or second side walls each comprise a central section and lateral sections, wherein said lateral sections are bent with respect to the central section towards the interior of the container. Thereby, an undesired shifting of the plastic waste during compression and degassing is avoided and the plastic waste is fixed in the central spot of the container. This ensures an equal distribution of the compressing force. Otherwise, the degassing may be incomplete and some gas inclusions may remain inside the plastic waste. Preferably, the lateral sections of the first and/or second side wall(s) are bent by an angle a of greater than 5°, preferably between 10 to 60°, more preferably between 20 to 50°, and mostly preferred about 45° relative to the central section.

In a special embodiment, the lateral sections are pivotable with respect to the central section, e.g. by providing hinges or similar joints between the central section and the lateral sections of the first and/or side walls. Thereby the angle between the lateral sections and the central section is variable, preferably between 0 and 60°. In a preferred embodiment, the angle a decreases with the movement of the first and/or second side walls towards each other and the angle a increases with the movement of the first and/or second side walls away from each other. In another embodiment, the lateral sections extend towards the third and fourth side walls and the end sections of these lateral sections enclose the third and fourth side walls. These end sections may be guided by a channel or other suitable device during movement of the first and/or second side walls towards or away from each other. In accordance with a further embodiment of the invention the first and second walls are arranged symmetrically to a central axis A of the container. This further ensures an equal distribution of the compression force over the complete plastic waste during degassing. Preferably, the fourth wall is movable in a direction perpendicular to the moving direction of the main piston. In particular, this embodiment is suitable for the subsequent introduction of said degassed waste into a pyrolysis furnace as then the opposite third side wall can simply push the compacted block out of the container into the pyrolysis oven or a channel leading thereto. In accordance with another embodiment of the invention, the cover comprises two pivotable cover sections. Thereby, the cover can be easily opened for the introduction of the plastic waste.

In accordance with further embodiment of the invention, the third wall and/or the fourth wall have/has a rectangular shape. It is further preferred that the third wall and the fourth wall have the same shape and size.

A process for degassing and dosing plastic waste according to the invention comprises the steps of: a) introducing plastic waste into a container having a rigid bottom, an upper cover that can be opened and closed, and at least four side walls, in particular into a device according to the invention, b) first degassing by closing the cover,

c) second degassing by pushing the side walls in a direction towards each other,

d) third and final degassing by pushing the main piston in a direction towards the fourth side wall,

e) opening said fourth side wall and discharging the degassed plastic waste from the container.

In a preferred embodiment of the invention, the degassed plastic waste is directly discharged to a pyrolysis reactor. Preferably, the pyrolysis reactor is operated under oxygen-free conditions and at temperatures of between 300 °C and 900 °C in order to at least partly recover the monomers building up the polymers comprised in the plastic waste.

In a further embodiment of the invention, the cover is closed with a pressure of1 to 50 bar, preferably 5 to 30 bar, most preferred 10 to 15 bar . Preferably, the first and second side walls are pushed towards each other with a pressure of 1 to 50 bar, preferably 5 to 30 bar, most preferred 10 to 15 bar.

It is particularly preferred, that the plastic waste introduced in step a) has an average particle size of more than 100 mm x 100 mm, preferably more than 300 mm x 300 mm, more preferably between 400 mm x 400 mm and 600 mm x 600 mm and mostly preferred 500 mm x 500 mm.

The invention will subsequently be explained in detail with reference to specific embodiments shown in the drawings. All features described and/or illustrated per se or in any combination form the subject-matter of the invention, independent of their inclusion in the claims or their back-reference.

In the drawing:

Fig. 1 is a side view of the device for degassing and dosing plastic waste according to the present invention. is a top view of the device shown in Fig. 1 . is a side view of the device shown in Fig. 1 illustrating the introduction of plastic waste into the container. is a detail of the first and/or second side wall in accordance with a preferred embodiment of the invention.

In Fig. 1 , the device for degassing and dosing plastic waste is shown from one side. It includes a container 1 for receiving the plastic waste having a rigid bottom 2 and an upper cover 3, the latter to be opened and closed. In the preferred embodiment shown in Fig. 1 the cover 3 comprises two pivotable cover sections 3a and 3b. Both cover sections are pivotably attached to the container body with flexible attachment means 4, e.g. frame joints. Preferably, the pivotable cover sections 3a and 3b have contact points 5 to connect to a movable device (not shown), such as a piston. This device can contact and/or be attached to the cover sections 3a and 3b in order to apply a compressing pressure and to open or close the cover sections 3a and 3b via movement along a circular arc 6.

As can best be seen in Fig. 2, the container 1 comprises four side walls 7a, 7b, 7c and 7d. The first side wall 7a is located opposite to the second side wall 7b. Said first side wall 7a can be moved towards and away from said second side wall 7b by activating an auxiliary piston 8a as indicated by arrow 13. At the same time, second side wall 7b can be moved towards and away from said first side wall 7a by activating an auxiliary piston 8b as indicated by arrow 13. The third side wall 7c is movable in a direction perpendicular to the first 7a and second side wall 7b by activating a main piston 8c as indicated by arrow 9. According to a special embodiment of the invention, the third side wall 7c can also be used to discharge the degassed plastic waste from the container 1 . Opposite of said third side wall 7c a fourth side wall 7d is provided. Said fourth side wall 7d is movable to open an exit 10 from the container 1 , e.g. a channel leading to a pyrolysis oven (not shown). In a preferred embodiment, shown in Fig. 1 , said fourth side wall 7d can be moved in a direction perpendicular to the movement 9 of the main piston 8c as indicated by arrow 1 1 . In a specific embodiment said fourth wall 7d is guided by an extension 12. In Fig. 1 said fourth side wall 7d is in an open position, allowing plastic waste to be discharged from the container 1 through the exit 10.

As shown in Fig. 2, the first and second walls 7a and 7b are arranged symmetrically to a central axis A of the container 1 . In accordance with a preferred em- bodiment, the side walls 7a and 7b are shown in two positions 14 and 15. Posi- tion 14 corresponds to an open or retracted position with a maximum distance between side walls 7a and 7b. Position 15 corresponds to an advanced position with a lesser distance between side walls 7a and 7b. Furthermore, it is shown that the end sections 16 of the first and second side walls 7a and 7b enclose the third 7c and the forth wall 7d in the advanced-position 15, which is in accordance with a special embodiment of the invention. For these end sections 16 it is in accordance with another embodiment of the invention, to provide guiding channels 17 receiving the end sections 16 of the side walls 7a and 7b and guiding these sections 16 during movement of the side walls 7a and 7b towards or away from each other.

Another preferred embodiment of the invention includes openings 18 distributed over the cover 3 and cover sections 3a and 3b. In the special embodiment shown in Fig. 2 said openings are exclusively distributed over the base area enclosed by the side walls 7a-d in the back-position 14 of side walls 7a and 7b. It is shown in Fig. 2 that the side walls 7a and 7b comprise a central section and lateral sections, which is shown in Fig. 4 in detail. Further openings (not shown) may be provided in the bottom 2 of the container. Fig. 3 illustrates the feeding of plastic waste material 20 to the container 1 by means of a feeding device 19, e.g. a conveyer. Cover 3 is opened completely for this purpose, the first to third side walls 7a-7c are in the retracted position and the fourth side wall 7d is in a closed position. In Fig. 4, a detail of the first and/or second side wall 7a and/or 7b is shown. In this preferred embodiment of the invention, the side wall(s) 7a and/or 7b com- prise(s) a central section 21 and lateral sections 22. The lateral sections 22 are bent with respect to the central section 21 towards the interior of the container 1 . In other words, the lateral sections 22 are bent away from the auxiliary pistons 8a and/or 8b. The lateral sections are bent with respect to the central section 21 by an angle a, which is between 0 and 60°, preferably between 5 and 45°, in the position shown in Fig. 4 about 20°.

As indicated by the broken lines in Fig. 2, the angle a is variable as the lateral sections 22 are pivotally connected to the central section 21 , e.g. by suitable hinges (not shown). Upon advancing the side walls 7a, 7b along the direction of arrows 13 and compressing the waste material provided therebetween, the lateral sections 22 pivot around the central section 21 and the end sections 16 slide along the guiding channels 17. Thereby the angle a is gradually reduced so that the compacted mass of plastic material approaches the form of a parallelepiped which can be easily pushed out of the container 1 through exit 10 by the third side wall 7c.

The device according to the present invention is substantially constructed as described above. Next the operation and function of the device will be described.

In a device as shown in Fig. 1 , mixed plastic waste 20 with an average particle size of e.g. 500 mm x 500 mm is introduced into the container 1 by a belt con- veyer. The mixed plastic waste 20 drops into the container 1 and is compressed in a first stage by closing the top cover 3 as far as it goes with a pressure of 1 to 50 bar, preferably 10 to 15 bar. Subsequently, the first and second side walls 7a, 7b are pushed towards each other by activating the auxiliary pistons 8a, 8b. In this second compression stage the mixed plastic is further degassed by said side walls pushing with a pressure of preferably 1 to 50 bar. In the next compression stage the third wall 7c is pushed towards the fourth wall 7d and the mixed plastic waste is pressed against the fourth wall and further compressed. Thereby, the mixed plastic waste is degassed a third time with a pressure of preferably 1 to 50 bar. The gas, e.g. air, discharged from the plastic waste, may leave the container 1 through the openings 18 in the cover 3 and/or the rigid bottom 2. In a final step, the fourth wall 7d is opened and the degassed plastic waste is discharged from the container 1 by movement of the third wall 7c towards the exit 10 of the container 1 , preferably towards a pyrolysis oven (not shown). The fourth wall 7d closes afterwards, the side walls 7a-7c are retracted to their initial position and the cover 3 is opened in order to receive another charge of plastic waste material to be degassed.

List of Reference Numerals:

1 container

2 bottom

3 cover

3a, b cover sections

4 flexible attachment means

5 contact points

6 movement direction of cover section

7a first side wall

7b second side wall

7c third side wall

7d fourth side wall

8a first auxiliary piston

8b second auxiliary piston

8c main piston

9 movement direction of main piston

10 exit

1 1 movement direction of fourth wall

12 extension

13 movement direction of auxiliary pistons

14 retracted position of side wall(s) 7a and/or 7b

15 advanced position of side wall(s) 7a and/or 7b

16 end sections of side wall(s) 7a and/or 7b 17 guiding channels

18 openings

19 feeding device

20 plastic waste

21 central section of side wall(s) 7a and/or 7b 22 lateral section of side wall(s) 7a and/or 7b