| JP09038524 | WIND FORCE STATIC SELECTION DEVICE |
| JP59026156 | ELECTROSTATIC SORTING APPARATUS |
| JP10263436 | ELECTRIC DISCHARGE TYPE STATIC SEPARATOR |
HOLAPPA, Rauno (Minttukuja 4, Oulunsalo, FI-90460, FI)
LESKINEN, Kalevi (Sinkkivälkkeentie 23, Oulu, FI-90240, FI)
HOLAPPA, Rauno (Minttukuja 4, Oulunsalo, FI-90460, FI)
CLAIMS
1. Method for treatment of electric and electronic scrap, in which method: the scrap to be treated is crushed into particles of such size that each particle consists essentially or mainly of one material; the particles are charged according to their triboelectric properties by rotating them (2) in a drum for rubbing them against the inner wall (5') of the drum and each other; and thereafter the particles are sorted (4) by means of an electric field, characterised in that: the material of the inner wall (5') is selected to be a material from the upper end of the triboelectric series; and said particles are before the sorting (4) additionally charged by bombing (3) them with electrons.
2. Method according to claim 1, characterised in that acrylic plastic is selected as the said material of the inner wall (5') of the drum.
3. Apparatus for treatment of electric and electronic scrap, whereby the scrap to be treated is crushed into particles of such size that each particle consists essentially or mainly of one material, the apparatus including: a drum (5) for charging the particles according to their triboelectric properties by rotating them in the drum for rubbing them against the inner wall (5') of the drum and each other; and means (7, 8, 9, 10, 11) for sorting the particles thereafter by means of an electric field; characterised in that: the inner wall (5') of said drum is of a material at the upper end of the triboelectric series; and the apparatus includes additionally means (6) for bombing said particles with electrons before said sorting.
4. Apparatus according to claim 3, characterised in that the inner wall (5 1 ) of the drum is of acrylic plastic.
5. Apparatus according to claim 3, characterised in that the means (6) for bombing the particles with electrons include a wire with high voltage made of titanium alloy. |
METHOD AND APPARATUS FOR TREATMENT OF ELECTRIC AND ELECTRONIC SCRAP
FIELD OF THE INVENTION The invention is related to a method and apparatus for treatment of electric and electronic scrap, whereby the scrap to be treated is crushed into particles of such size that each particle is essentially or mainly of one material.
BACKGROUND OF THE INVENTION Material contents of electric and electronic scrap vary for many reasons, e.g. depending on the age of the devices included in the scrap. An example of the contents of such scrap is: metals 49 percent, plastics 33 percent, glass (e.g. cathode ray tubes) 12 percent, wood 5 percent, and other materials 1 percent. In modern devices, the proportion of plastics is remarkably larger, typically more than 50 percent. An estimate is that about 2.5 million tons of various plastic materials are presently used in Europe and the United States for manufacture of electronic products. The most widely used plastic types are approximately in this order: ABS, polystyrene, polypropylene, polyurethanes, polycarbonates, polyamides, and epoxies.
For the time being, the attention in treatment of electric and electronic scrap is drawn primarily to separation and utilisation of valuable metals. The treatment includes then normally three phases: sorting, mechanical separation steps, and burning or leaching phases. For scrap rich in valuable metals, only direct leaching or burning is often applied.
In an alternative treating method, the scrap is first crushed to obtain as pure particles as possible, i.e. particles each of which consists essentially or mainly of one material. This object is normally reached as the grain size of the crashed aggregate is of the order of 2 to 4 millimetres. The process includes often two crushing phases: crushing with a rasp mill and with a granulator mill.
After that there are normally several separating phases in which the aim is often to pick up certain metals and then sort the rest of the material. Often, the first separating phase is a magnetic separating step in which magnetic metals are picked out. Often, also eddy-current separation is used by which e.g. copper and aluminium may be picked out from crashed material and separated from each other. Moreover, separators are used which are based on certain properties of materials, e.g. on specific gravity or frictional properties, examples of that being separation of materials made to flow or vibrate on a sloped surface. In one method, charged particles are allowed to circulate on an electrostatically charged outer
surface of a rotating drum, whereby they drop down from the drum at certain points according to their specific charge and gravity
For sorting rubber and plastic waste, also an as such known solution is presented in which e.g. plastic material particles are charged according to their triboelectric properties by rotating them in a drum, and then the particles which have got different charges are sorted by means of an electric field. This kind of solutions have been presented in US patents 5289922 and 6927354 and JP patent publication 7178351.
SUMMARY QF THE INVENTION An object of the invention is to present a solution utilising triboelectric charging and being specifically applicable to treatment of electric and electronic scrap with variable material contents.
To achieve this object, a method for treatment of electric and electronic scrap, in which method the scrap to be treated is crushed into particles of such size that each particle consists essentially or mainly of one material, the particles are charged according to their triboelectric properties by rotating them in a drum for rubbing them against the inner wall of the drum and each other, and thereafter the particles are sorted by means of an electric field, is characterised in that the material of the inner wall is selected to be a material from the upper end of the triboelectric series and said particles are before the sorting additionally charged by bombing them with electrons.
In an embodiment of the method, acrylic plastic is selected as the material of the inner wall of the drum.
To achieve this object, an apparatus for treatment of electric and electronic scrap, whereby the scrap to be treated is crushed into particles of such size that each particle consists essentially or mainly of one material, the apparatus including a drum for charging the particles according to their triboelectric properties by rotating them in the drum for rubbing them against the inner wall of the drum and each other, and means for sorting the particles thereafter by means of an electric field, is characterised in that the inner wall of said drum is of a material at the upper end of the triboelectric series, and that the apparatus includes additionally means for bombing said particles with electrons before said sorting. In an embodiment, the inner wall of the drum is of acrylic plastic. In a further embodiment, the means for bombing the particles with electrons include a wire with high voltage made of titanium alloy.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is described in further detail in the following with reference to the accompanying drawings, in which:
Fig. 1 presents generally an embodiment of the method according to the invention; and Fig. 2 presents schematically a possible realisation of the apparatus according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
Fig. 1 presents generally the method of the invention. Electric and electronic scrap has been crushed by e.g. a granulator mill, and the scrap material is crushed to so called degree of liberation or close to that, i.e. into so small particles that each particle is essentially or mainly of one material. Such a particle size is e.g. from 2 to 4 millimetres.
In phase 1, certain fractions, e.g. certain metals, may be separated from the electric and electronic scrap. For example, it is also possible that essentially all metals are separated and only particles which consist essentially of plastic materials are left over for continued treatment. It is also possible that particles essentially consisted of metals and particles essentially consisted of plastic materials are both allowed to proceed forward from phase 1. In the continued treatment, the particles are first charged in phase 2 by rotating them in a drum, in which they are rubbed against the inner wall of the drum and each other and are charged according to their triboelectric properties. For the inner wall of the drum or its inner surface a material is selected e.g. experimentally so that it works well as a charger of the particles rotated in the drum. In our experiments, we have found that it is advantageous to select a suitable material at the upper end of the triboelectric series as the material of the inner wall of the drum or its inner surface. For example, acrylic plastic is a well working material.
The particles are rotated in the drum with such a velocity that they are rubbed against the inner wall of the drum and each other as efficiently as possible. Such velocity must in every case be above the so called critical velocity. The critical velocity means a velocity by which the particles are kept as a layer held essentially against the inner wall of the drum during rotation. A suitable velocity is within the range of 0.5 to 0.9 times the critical velocity and depends naturally to some extent on the properties of the particles to be treated. In the experiments, we have found that a suitable velocity for printed circuit board scrap is 0.6 to 0.7 times the critical velocity. The suitable rotating velocity depends also on the diameter of the drum, for example. If the diameter of the drum is of the order of 0.5 to 1 metres, suitable rotating velocities are of the order of 40 to 60 revolutions per minute.
The time needed to charge the particles in the rotating drum is of the order of some minutes and may be within the range of 1 to 3 minutes, for example.
In table 1 here below a triboelectric series is presented which describes charging properties of some relevant plastic materials as electronic scrap is concerned. On the other hand, table 2 presents another triboelectric series in which in addition to plastic materials some other materials are included, e.g. metals widely used in electric and electronic devices. The tables are based on the information obtained from several different sources and are only indicative because many different factors affect the charging of materials in experiments and processes.
TABLE 1 : An indicative triboelectric series for some plastic materials nylon charging most positively acrylic
ABS polycarbonate (PC) polyethylene terephthalate (PET) polystyrene (PS) polypropylene (PP) polyester polyethylene (PE) polypropylene
PVC
Teflon (PTFE) silicone charging most negatively
TABLE 2: Another indicative triboelectric series for some materials glass charging most positively nylon lead aluminium steel no essential charging polystyrene mylar copper silver gold, platinum polyester polyethylene polypropylene
PVC
PCTFE silicon
Teflon silicone rubber charging most negatively
In phase 3, the particles are charged further by bombing them with electrons. The bombing may be done by means of a high voltage wire made of titanium alloy and emitting electrons around. The voltage of the wire may be e.g. 20 kV, but it may also be much higher, e.g. 80 kV. It may be contemplated also that the particles were bombed at the same time with positrons by means of a device made for this purpose. What is essential is that further charging of the particles improves significantly for example separation of different plastic types in the static separation.
In phase 4, the particles charged according to typical properties of different plastic materials are sorted by means of an electric field. Fig. 2 presents schematically a possible realisation of the apparatus according to the invention. Electric and electronic scrap, like printed circuit board scrap, is crushed by means of e.g. a granulator mill into particles the size of which is of the order of 2 to 4 millimetres. The crushed scrap may be sorted so that particles consisted essentially of plastic materials have been separated as a fraction by means of conventional methods and devices. This fraction is fed in the way indicated by the arrow E by means of e.g. a vibration feeder (a vibrated trough) into a drum 5 rotating as indicated by the arrow R. The inner surface 5' is of material suitable for charging the particles, e.g. of acrylic plastic. The rotation velocity of the drum is set suitably so that, as the drum rotates, the particle mass is lifted suitably up with the wall and is then rolling down again, whereby the rubbing between the particles is most efficient. The drum is in a suitably tilted position in which the particles proceed through the drum in a time long enough for charging, e.g. in about 2 minutes.
Below the unloading end of the drum 5 there is a conveyor 6' which transfers the particle mass into a device 6 in which the particle mass is bombed with electrons. As mentioned above, the device 6 may be based on using a high voltage metal wire, which is advantageously made of titanium alloy, e.g. chromium-titanium, as a source of electrons. The device may be also an especially for this purpose developed device by which also positrons in addition to electrons may be produced for bombing the particles.
Inside an electrostatic sorting device 7, a generally horizontal electric field is formed by means of electrodes 9 and 10. The electrodes are at the upper end closer to each other and at the lower end farther from each other so that particles having different charges may be guided by means of the field on a suitably large area. In the case of printed circuit board scrap, for example, a suitable voltage between the electrodes may be 20 to 80 kV. Depending on the application, the voltage may be remarkably higher, e.g. within the range from 100 to 150 kV. The particles are fed from above by means of a hopper 8 from which they start to fall in the electric field from a slit approximately at the middle of the field. Compartments 11 formed by separating walls have been placed below the electrodes.
9
Positively charged particles are according to their charge guided to the side of the negative electrode and negatively charged particles to the side of the positive electrode 10. The separating walls are naturally adjusted in every case suitably according to the treated material so that as good as possible or appropriate sorting is resulted. As mentioned above when considering phase 1, certain fractions may have been separated off from the electric and electronic scrap coming to the apparatus. On the other hand, also rough separation, e.g. separation of the fractions consisted essentially of metals and of plastic materials from each other, may be made also by applying the apparatus according to the invention. Different variations of the apparatus may be made for different applications, and by adjusting the operating parameters, the operation of the apparatus may be adjusted to be suitable for a task concerned. The applicability of the method and the apparatus for different tasks in the treatment of electric and electronic scrap with variable material contents is improved in that the charging of the particles may be made more efficient and be adjusted by adjusting the operation parameters of the bombing with electrons in addition to adjusting and selecting the materials and operation parameters of the drum. Several different phases of a process for treating electric and electronic scrap may be realised by means of the apparatus of the invention.
The invention is not restricted to the embodiments described above but may vary within the scope of the accompanying claims.
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