Method and device for separating particles of plastic foil and particles of organic material

Abstract

A method and device are used for separating particles of plastic foil from organic material. The device includes a chamber with a perforated wall. A mixture of particles of plastic foil and organic material is fed into the chamber through a feed opening. The mixture is set into a rotating movement inside the chamber by a rotor. In the vicinity of the perforations, the centrifugal force to which a particle is subjected is at least fifty times greater than the gravitational force to which the particle is subjected. An airflow is generated in the chamber parallel to the rotational axis of the rotor. Particles of organic material leave the chamber through the perforations. Particles of plastic foil are carried along by the first airflow and then discharge through an opening in the chamber.

Claims

1. A method for mutually separating particles of plastic foil and particles of organic material, the method comprising steps of: arranging perforations in a wall of a chamber; feeding a mixture comprising particles of plastic foil and particles of organic material into the chamber through a feed opening provided for the purpose; setting the introduced mixture into a rotating movement inside the chamber by means of a rotor such that in the vicinity of the perforations the centrifugal force to which a particle is subjected is at least fifty times greater than the gravitational force to which the particle is subjected; generating a first airflow in the chamber; discharging through a first discharge opening particles of organic material which have left chamber through the perforations; and discharging through a second discharge opening particles of plastic foil carried along by: the first airflow in the direction from the feed opening to the second discharge opening; and at least partially by a second airflow generated in the chamber, wherein the first airflow and the second airflow make up the totality of airflows in the chamber.

2. The method as claimed in claim 1, wherein perforations with a cross-section smaller than the average cross-section of the particles of foil are arranged in the wall.

3. The method as claimed in claim 1, wherein a large first airflow is generated such that in the vicinity of the perforations a force to which a particle of plastic foil is subjected as a result of the first airflow is greater than a centrifugal force to which the particle of plastic foil is subjected.

4. The method as claimed in claim 1, wherein the first airflow is generated by the rotor.

5. The method as claimed in claim 1, wherein the second airflow is generated by the rotor.

6. A device for mutually separating particles of plastic foil and particles of organic material, the device comprising: a housing; a chamber which is situated inside the housing and a wall of which is provided with perforations; a feed opening for feeding a mixture comprising particles of plastic foil and particles of organic material into the chamber; a rotor placed in the chamber and suitable for setting the introduced mixture into a rotating movement such that in the vicinity of the perforations the centrifugal force to which a particle is subjected is at least fifty times greater than the gravitational force to which the particle is subjected; a plurality of first blades which form part of the rotor wherein the first blades lie obliquely to the rotation axis of the rotor so as to be suitable for generating a first airflow of air drawn in through the perforations in the chamber; a first discharge opening for discharging particles of organic material which have left the chamber through the perforations; a second discharge opening for discharging particles of plastic foil carried along by the first airflow; and a plurality of second blades forming part of the rotor wherein the second blades lie parallel to the rotation axis of the rotor so as to be suitable for generating a second airflow of air through the second discharge opening, wherein the first airflow in the chamber is in the direction from the feed opening to the second discharge opening and the first airflow and the second airflow make up the totality of airflows in the chamber.

7. The device as claimed in claim 6, wherein the cross-section of the perforations is smaller than the average cross-section of the particles of foil.

8. The device as claimed in claim 6, wherein the plurality of first blades are suitable for generating a large first airflow such that in the vicinity of the perforations the force to which a particle of plastic foil is subjected as a result of the first airflow is greater than the centrifugal force to which the particle of plastic foil is subjected.

9. The device as claimed in claim 6, wherein the device also comprises third means for removing material present on a side of the wall facing toward the chamber.

10. The device as claimed in claim 9, wherein the third means comprise a number of third blades which form part of the rotor and the outer ends of which are situated in the vicinity of the side of the wall facing toward the chamber.

11. The method of claim 1, wherein that first airflow generated in the chamber is parallel to the rotation axis of the rotor.

12. The device of claim 6, wherein that first airflow generated in the chamber is parallel to the rotation axis of the rotor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is elucidated hereinbelow on the basis of non-limitative exemplary embodiments and accompanying drawings. More or less schematically in the drawings:

(2) FIG. 1 shows a cross-section of a first embodiment of a device according to the invention; and

(3) FIG. 2 shows a cross-section of a second embodiment of a device according to the invention.

EXEMPLARY EMBODIMENTS

(4) The device (100) shown in FIG. 1 comprises a cylindrical housing (1) having therein a cylindrical chamber (2), the wall (3) of which is provided with perforations (4) with a diameter of for instance 5 mm, and a feed opening (5) for infeed (A) of a mixture of particles of organic material and particles of plastic foil to be separated. The material has earlier been pressed through a screen with openings of a diameter of for instance 8 mm (not shown). Softer organic material is comminuted here to particles of organic material. The particles of plastic foil have also passed through the screen here. In the given example the mixture for separating is introduced (A) by means of an auger or worm screw (12). Device (100) further comprises a first discharge opening (7) for discharging (C) separated particles of organic material and a second discharge opening (8) for discharging (D) separated particles of plastic foil. Placed in chamber (2) is a rotor (6) which can bring about a great centrifugal acceleration, for instance 150 to 200 times the acceleration of gravitational force, in the vicinity of the wall at a rotation speed of for instance 500 to 1000 revolutions per minute. Rotor (6) comprises a number of first blades (9) lying obliquely of the rotation axis of rotor (6) and a number of second blades (10) which are located in the vicinity of second discharge opening (8) and are parallel to the rotation axis of rotor (6). Second discharge opening (8) is placed tangentially relative to rotor (6), in this case second blades (10).

(5) In accordance with a method according to the invention the mixture of particles of plastic foil and particles of organic material to be separated is introduced (A) into chamber (2) through feed opening (5) by means of auger (12). Inside chamber (2) the mixture is set into a rapid rotating movement by rotor (6), in this case first blades (9). First blades (9) lie obliquely of the rotation axis of rotor (6) such that a first airflow (B) is generated inside chamber (2) parallel to the rotation axis of rotor (6) with a speed of for instance 15 m/s at a flow rate of for instance 4000 m.sup.3/h. The heavier particles of organic material are flung outward perpendicularly of the rotation axis of rotor (6) by the rotating movement and discharged through perforations (4) to first discharge opening (7). The particles of organic material will partially deform here during passage through perforations (4). The lighter particles of plastic foil are carried along by first airflow (B) parallel to the rotation axis of rotor (6) to second discharge opening (8) and there blown out (D). Blowing out (D) is enhanced by a second airflow which is generated by the second blades (10) and which hereby also enhances the totality of airflows (B-D). It is found in practice that the heavier particles of organic material are flung outward through perforations (4) mainly in a first part (E) of chamber (2). Air which entrains (B) the lighter particles of plastic foil is mainly drawn into the chamber through perforations (4) in a second part (F) of chamber (2).

(6) Advantageous is that rotor (6), in addition to generating the rotating movement, also generates the first airflow (B) and the second airflow (D). This makes the device less complex, less expensive, less susceptible to malfunction and requiring less maintenance, since separate fans are thus not necessary. For a good separation of a given mixture parameters such as feed flow rate, centrifugal acceleration and airflow velocities will of course have to be correctly adjusted to each other.

(7) Device (200) shown in FIG. 2 again comprises a cylindrical housing (1) having therein a cylindrical chamber (2), the wall (3) of which is again provided with perforations (4), and a rotor (6). The position of rotor (6) is now however not vertical but horizontal. This is possible because the influence of gravitational force is negligible in relation to the relatively high centrifugal accelerations and air velocities. This can be favourable for instance in respect of the space taken up and the lower height of the device.

(8) Device (200) also comprises a number of third blades (11) forming part of rotor (6) for the purpose of removing material present on the inner side (13) of wall (3) of chamber (2). The outer ends of third blades (11) are situated for this purpose in the vicinity of this inner side (13). Material possibly accumulating on this inner side (13), in particular between first blades (9), can thus be removed from this inner side.

(9) With a method and device according to the invention it is possible to realize a very good separation, with for instance a percentage of plastic foil of less than 0.1% in the remaining organic fraction, this being a considerable improvement on results achieved with known methods and devices.

(10) It will be apparent that the invention is not limited to the shown and described exemplary embodiments but that diverse variants which will be obvious to a skilled person are possible within the scope of the invention. In addition to being used for mutual separation of particles of plastic foil and particles of organic material, the invention can thus also be applied for mutual separation of other types of lighter and heavier particles. Infeed can also take place other than by means of an auger or worm screw, for instance by simply making use of gravitational force.