HK1018421B - Process and device for the separation of viscoplastic materials such as plastics from materials such as paper which can be defibrated by mechanical action - Google Patents

Description

Method and device for separating viscoelastic materials, such as plastics, from materials which are comminuted under mechanical load, such as paper

The invention relates to a method and a device for separating viscoelastic materials, such as plastics and rubber, at room temperature from other materials which are comminuted under a large mechanical load, such as paper, cardboard or other cellulose-containing materials.

The separation of plastic and paper is a considerable problem, especially in the treatment of waste and in the recycling of the material contained in the waste. Such mixed waste containing both plastics and paper or containing other cellulosic materials is present in large quantities. For example, pre-selected plastic packages collected from binary systems, in particular so-called mixed components, contain not a small amount of paper components consisting of paper labels, misclassifications at the time of classification and paper-plastic composites.

Hitherto, the separation of plastics, rubber and cellulose-containing materials, such as paper, thick paper and cardboard, has been carried out by means of wet separation with maximum disintegration of the fibre matrix and then in at least two streams, namely a cellulose-containing slurry with a high water content and water-insoluble plastics. This method requires considerable energy consumption and mechanical expenditure. The paper decomposition is carried out, for example, in a wet mill, and water is added during the milling process in an amount several times greater than the weight of the plastic and paper. Here, in particular the mass of the water to be accelerated requires a lot of energy. In order to separate the paper fibres and the resulting slurry from the loaded material, or to separate dirt or other material from the plastic, so-called friction separators are used. In any case, the fibrous material flow must be dewatered next to one another, for example, by means of a vibrating screen or an earth screen. Furthermore, the water content is often reduced with filter presses, for example chamber filter presses, wherein a high water content of more than 50% remains in the waste. If the fibrous material of the paper is not used, which is the usual case for waste disposal, high storage costs are incurred due to the high water content or considerable drying costs are incurred in the case of thermal utilization of the waste. Also plastics, especially when they are multi-film, for example from the commonly occurring polyethylene films, must be dewatered when they are combined with paper, and then first dried mechanically. For this purpose, a modified centrifuge is used. If necessary, hot (secondary) drying is also required. This leads, overall, to a considerable separation expenditure and is economically disadvantageous owing to the high energy consumption.

Numerous tests were carried out for this purpose. Mention may be made here, for example, of: "Water action in Plastic recovery and treatment technology when Using plastics" book, Louis Jie Deng, German institute of Engineers, Press, Du Saedov, 1993 and technical paper: "reuse of plastics", bibliographic, eds of plastics recovery and development company, visbaron, 1992.

Existing dry separation methods of paper and plastic are performed using electrostatic charging. Mention may be made here of the separation of gravity separators, as described, for example, in german patents DE 3227874 and DE 4225977. This approach has serious drawbacks. The added material must here meet certain prerequisites in terms of geometrical dimensions and also place high demands on the dryness of the added material. Therefore, the treatment cost is considerably high. Furthermore, force-bonded and profile-bonded composite materials cannot be separated in this way.

US4,440,635 proposes a wet separation method of paper and plastic by controlling the addition of moisture to the material to be separated to a predetermined moisture content, thereby avoiding the addition of excess moisture. However, due to the different water absorption capacity of the materials, the main problem of this method is also the different water content of the materials to be separated, as in all other wet separation systems.

US3,941,689 discloses a comminution and classification device for substantially homogeneous different waste materials. Wherein the added waste material is gradually crushed or ground in a multi-stage process according to its consistency and separated from each other by sieving.

It is therefore the object of the present invention to provide an economically advantageous, technically simple method for separating viscoelastic materials, such as plastics and rubber, from materials which are comminuted under high mechanical loads, such as paper, cardboard and cardboard. As examples of plastics, mention may be made here of: low Density Polyethylene (LDPE), High Density Polyethylene (HDPE), Polypropylene (PD), polystyrene, polyvinyl chloride (PVC), Pentaerythritol (PET), and acrylonitrile-butadiene-styrene copolymer (ABS).

It has surprisingly been found that it is possible to separate viscoelastic materials such as plastics and rubber from fibrous materials such as paper in a technically simple manner in the dry state by applying high acceleration and impact forces to the mixture of plastics and fibrous materials. Wherein the fibre-containing material is comminuted under force and flows out through suitable openings of the screen basket, while the non-comminuted plastic remains inside the housing and is discharged in the axial direction. The dry separation of paper and plastic by acceleration and impact forces or by centrifuges seems surprising, since centrifuges have hitherto always been used for separating solid-liquid or liquid-liquid phases.

The invention therefore provides a method for the dry separation of viscoelastic materials, such as plastics and rubber, from materials comminuted under mechanical load, in particular paper, in which the material to be separated is subjected to large radial, axial and tangential acceleration and impact forces and a material flow of fibrous material and a material flow of viscoelastic material are discharged separately, characterized in that the viscoelastic material and the fibrous material comminuted under mechanical load are essentially a composite material and only the fibrous material is comminuted and separated from the viscoelastic material under force, while the viscoelastic material is discharged as a material flow essentially in the uncrushed state.

The material to be separated is preferably coarsely crushed to a particle size of 50 mm or less.

The invention further relates to a device for carrying out the method according to the invention, comprising a screen basket which has a substantially cylindrical shape and has openings on its circumference or openings through which the comminuted material passes, wherein the openings on the inner side of the screen basket have sharp edges in order to increase the shredding effect, and a rotatable drive shaft is arranged coaxially within an inner region of the screen basket, to which drive shaft blades are fastened, wherein the rotational speed of the blades can be adjusted within the range of 1000 to 2000 revolutions per minute in such a way that only the fibrous material is comminuted and separated from the viscoelastic material, and the viscoelastic material is discharged in a substantially non-comminuted state as a separate material flow.

The drive shaft is driven, for example, by a flange 5 and a belt drive (not shown in the figures) with an electric motor. The blade diameter is dimensioned in such a way that a gap is left between the blade end and the housing. The particle size of the material to be separated may vary depending on the geometry.

For a better distribution of the mixture of the materials to be separated which is fed in the housing, the feed-side front blade has a smaller diameter than the rear blade.

The housing and the rotating shaft with blades located inside are arranged in a box 6 with a feed opening 7 for the material mixture to be separated and a discharge opening 8 for the plastic material which rests on the other end inside the drum and is conveyed by the rotating blades. Furthermore, the box 6 has a discharge opening 9 for the separated paper. For better separation of the paper, a rotating doctor blade (not shown in the figures) can be provided.

The housing, the same drive shaft and the blades are preferably made of a high strength and corrosion resistant material such as stainless steel.

The holes 2 or apertures on the periphery of the basket 1 preferably have sharp edges (not shown |) which contribute to a better shredding of the already shredded paper that is spun centrifugally through the holes of the casing towards the basket 1, which basket 1 is supported on the outer wall of the box 6.

In order to ensure that the forward motion of the particles in the axial direction has sufficient dwell time in the device, the blades are preferably mounted at an angle of attack of 5 to 7 degrees to suit, for example, plastic mixing components from binary systems.

The shaft and the blades located inside rotate together at a speed of 1000 to 2000 revolutions per minute, preferably 1200 to 1800 revolutions, wherein the rotational speed is adjusted depending on the material mixture fed. The residence time is 10 seconds to 2 minutes.

The discharge opening can vary between 2 and 7 mm depending on the particle size of the material to be fed and the degree of separation required.

The preferred shape of the screen basket 1 is a polygon which may have an equilateral or non-equilateral area. It has been shown that the separation effect is much better than for a cylindrical screen basket if the screen basket consists of polygonal areas.

The function of the method and the device is described below by taking the figures as examples. Wherein:

FIG. 1 shows a longitudinal section through an apparatus for carrying out the process according to the invention;

FIG. 2 shows a cross-sectional view along section line AA' of FIG. 1.

The mixture of plastic and paper is fed through the feed opening 7 and distributed inside the screen basket by the front vane, which has a smaller diameter than the rear vane 4. The rotation of the shaft 3 and the blades 4 by a transmission, not shown, generates an acceleration and an impact on the mass point, by which impact the shredded paper is finally gathered at the edge of the basket 1 and flows out through the holes 2. While the plastic continues to flow in the axial direction and out through the outlet 8. The paper collected in the space formed by the box 6 and the screen basket 1 is sucked out through the outlet openings 9 by means of a pneumatic suction device (not shown in the figures).

The device according to the invention has, for example, the following dimensions: length: 1500 mm, impeller diameter: 950 mm (variable), the width of the gap between the impeller end and the housing wall is dependent on the housing shape: maximum 25 mm, number of impellers: 4 × 11, power consumption of the apparatus: 50 ~ 80 kilowatts, the exit hole of screen basket: 5 mm, throughput: 1 ton/hr.

Examples are:

the mixed waste consists of 90.4% packaging film and 9.6% coated paper and is ground by means of a grinding mill with a screen basket. The screen basket has a diameter of 50 mm. The paper is uniformly distributed in the plastic and the mixture is dry. After the first passage of the mixture through the apparatus, the following separation results were achieved:

results of the first pass:

percentage of good (%) percent of bad (%)

Recovery 93.56.5

Paper content 6.947.9

Plastics content 93.152.1

The following separation results were obtained by adding again the good percentage of the results:

the result of the second pass:

percentage of good (%) percent of bad (%)

Recovery 96.43.6

Paper content 4.571.5

Plastics content 95.528.5

That is, overall, the recovery was 90.1% with two passes of paper added at 57.6%.

Claims (13)

1. A method for the dry separation of viscoelastic materials, such as plastics and rubber, from materials which have been comminuted under mechanical load, in particular paper, in which the material to be separated is subjected to large radial, axial and tangential acceleration and impact forces and the material flow of the fibrous material and the material flow of the viscoelastic material are discharged separately, characterized in that the viscoelastic material and the material comminuted under mechanical load are essentially composite materials and only the fibrous material is comminuted and separated from the viscoelastic material under the action of the forces, while the viscoelastic material is discharged from the material flow essentially in an uncrushed state.

2. A method according to claim 1, characterized in that the mixture to be separated is coarsely crushed to a particle size of 50 mm or less.

3. A method according to claim 1 or 2, characterized in that the fibre-containing material is comminuted in the casing (1) and the comminuted material, in particular paper, is discharged through holes or outlets (2) in the circumferential surface of the casing (1), while the viscoelastic material remains inside the casing (1) and is discharged at the end of the casing (1) as a separated material flow.

4. A method according to claim 3, characterized in that the comminution effect is intensified by making the holes or outlets (2) on the inside of the casing (1) sharp-edged.

5. A method according to claim 3, characterized in that the crushing effect is enhanced by the casing (1) being given a polygonal shape.

6. A method according to claim 3, characterized in that the flow/transport of the material in the housing (1) is caused by the direct influence of means (1, 3, 4) for applying radial, axial and tangential acceleration forces.

7. Device for dry separation of viscoelastic materials, such as plastics and rubber, from materials comminuted under mechanical load, in particular paper, consisting of a screen basket (1), the screen basket has a substantially cylindrical shape and has through holes or outlets (2) for the material to be crushed on the circumference, wherein the holes (2) on the inside of the screen basket (1) have sharp edges that enhance the crushing action, a rotatable transmission shaft (3) is coaxially arranged in the inner range of the screen basket (1), a blade (4) connected with the transmission shaft is fixed on the transmission shaft, wherein the rotating speed of the blades can be adjusted within the range of 1000-2000 revolutions per minute, that is, only the fiber-containing material is comminuted and separated from the viscoelastic material, wherein the viscoelastic material exits as a separate stream in a substantially uncrushed state.

8. The apparatus of claim 7, wherein the screen basket has a polygonal shape.

9. A device according to claim 7 or 8, characterized in that the blades (4) are rigidly connected to the drive shaft.

10. A device according to claim 7 or 8, characterized in that the blades (4) are fixed to the drive shaft preferably at an angle of attack of 5 to 7 degrees.

11. Device according to claim 7 or 8, characterized in that the diameter of the blade (4) on the feed side is smaller than the diameter of the following blade.

12. A device according to claim 7 or 8, characterized in that the blades (4) are arranged on the drive shaft in such a way that a gap is present between the blade end and the housing wall.

13. Device according to claim 7 or 8, characterized in that the housing (1) with the drive shaft (3) and the blades (4) inside is arranged in a box (6) having at the feed end a feed opening (7) for the mixture to be separated and at the other end a discharge opening (8) for the plastic material which rests inside the drum and is transported by the rotating blades.