JP2005169255A - Specific gravity screening method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a specific gravity screening method for performing highly precise screening of waste plastics ranging from high specific gravity material to low specific gravity material with the same method and apparatus without necessitating the use of many kinds of specific gravity liquids, and for simultaneously screening many kinds of materials. <P>SOLUTION: A screen whose opening is smaller than the size of particles to be screened is arranged in a medium whose specific gravity is larger than that of the particles to be screened, the particles to be screened are arranged under the screen, the screen is intermittently vertically operated or intermittently downward flow is caused, thereby, the particles to be screened are forcibly sedimented or floated and the particles to be screened are stratified and screened by the specific gravity under the screen. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  TECHNICAL FIELD The present invention relates to a specific gravity sorting method used for general waste, industrial waste, home appliance recycling processing, and the like, and in particular, specific gravity sorting of waste plastics, etc., for separating and recovering various mixed materials such as shredder dust. Regarding the method.

  Among the waste discharged in large quantities, plastic waste continues to increase, and it is difficult to deal with the disposal measures. In particular, OA equipment and household appliances that are discarded use various types of plastics that cannot be sufficiently separated by the dismantling process prior to the integrated crushing of the discarded products. These plastics become so-called shredder dust after the integrated crushing, Since there are few ways to reuse it, it is a major obstacle to creating a recycling-oriented society, such as incineration or landfill.

  The plastics used in OA equipment and home appliances are mainly the three major general-purpose plastics, polypropylene (PP), polystyrene (PS), and acrylonitrile-butadiene-styrene (ABS). PVC), phenol (PF), which is a functional insulating material, polybutylene terephthalate (PBT), flame retardant PS with flame retardant function, flame retardant ABS, and the like, and the shredder dust is a mixture of these plastics Contains foreign substances that were not fully recovered in the previous process, such as light materials such as urethane and small metal pieces.

  In order to select PP, PS, and ABS that can be quantitatively secured from the shredder dust and can be easily reused, their specific gravity is PP (about 0.9), PS (about 1.05), ABS (about 1.05), the specific gravity of other resins and metals often exceeds 1.1, and sorting by specific gravity is effective, and urethane (specific gravity about 0.6 to 0.7) A light material such as) can be suitably used for sorting and removing by specific gravity.

  However, when the selected plastics are separated into PP, ABS, and PS, and then re-molded and recycled, the physical properties (strength, elongation, etc.) significantly decrease when any plastic is mixed with other plastics. In many cases, such waste plastics must be sorted with a very high quality.

  Therefore, as a method for sorting out such waste plastics, for example, the float / sink sorting method shown in Patent Document 1 and the liquid cyclone (registered trademark) method shown in Patent Document 2 have been proposed and put into practical use in part. ing. Further, for example, Non-Patent Document 1 describes a jig selection method.

  The floatation / sink sorting method is a method in which a crushed plastic is dispersed in a liquid medium such as water, and a plastic having a specific gravity smaller than that of the medium and a plastic having a higher specific gravity can be easily separated. Various specific gravity can be obtained by using so-called heavy liquids with different specific gravity such as water, salt water, chlorinated organic solvents, etc., or using so-called pseudo heavy liquids in which solid materials such as fine ferrosilicon are dispersed. It is possible to easily sort the crushed plastic having a thickness (see, for example, Patent Document 1).

  In the method using the liquid cyclone (registered trademark), the crushed plastic is circumferentially flowed together with the liquid medium in a cylindrical container, and particles having a specific gravity larger than that of the liquid medium and particles having a specific gravity smaller than that of the liquid medium are obtained by the above-described floatation / sediment sorting. Can also be sorted efficiently. By selecting the specific gravity of the liquid medium appropriately in the same manner as the above-described float / sink sorting, it is possible to sort with various specific gravity (see, for example, Patent Document 2).

In addition, the jig sorting method uses mixed plastics crushed on the screen and gives vertical movement from the bottom of the screen with a medium flow, etc., and uses the initial settling velocity difference due to specific gravity to stratify each plastic type. Select by letting This method can be carried out either wet or dry, but considering the specific gravity difference and size variation of the crushed mixed plastic, high precision sorting can be achieved by using a wet method that has a small specific gravity difference with the medium. (For example, refer nonpatent literature 1).
JP-A-56-56246 International Publication WO 98/41374 "Waste / Recycling Encyclopedia" Sanken Publishing 1995

  However, in floating / sink sorting, since air affects the sorting accuracy together with a liquid medium such as water, it is difficult to increase the sorting accuracy even if a defoaming device and a stirring device are provided. In other words, plastics are inherently low in hydrophilicity, and once contacted with air, PS and ABS, which have a higher specific gravity than water due to surface tension, do not easily settle, and even in water, they easily come into contact with minute bubbles. In many cases, the ABS also exhibits a behavior such as rising or floating in the middle.

  On the other hand, in the method using the liquid cyclone (registered trademark), the specific gravity fractionation proceeds only in the medium without being exposed to the air, so that the sorting accuracy is hardly deteriorated by the air.

However, in both the floating and sinking and hydrocyclone (registered trademark) methods, it is necessary to construct a multistage apparatus using various specific gravity liquids in order to sort out different kinds of mixed and crushed plastic mixed with various kinds of materials. Even when sorting and recovering the most versatile PP and PS plastics,
(1) Removal of light matter such as urethane using light specific gravity liquid (2) Recovery of PP (3) Recovery of PS and three-stage sorting tank are required.

  When removing light substances using the light specific gravity liquid described in (1) above, light specific gravity liquids such as alcohol can be used. However, in the case of highly flammable hydrocarbons, there is a major problem in ensuring safety in actual operation. As a non-combustible light specific gravity liquid, there is no suitable medium.

  A general-purpose medium such as water can be used for (2) PP recovery, and a medium with a specific gravity of about 1.1 is sufficient for (3) PS / ABS recovery. For example, salt water can be used. However, since it is multistage, there is a change in the specific gravity of the medium due to the carry-in contamination of the medium in the previous process, the temperature of the medium, etc., and it takes a lot of labor to realize a stable sorting operation.

  On the other hand, in the jig sorter as described above, a high sorting accuracy can be realized by using a wet method. As a feature of the jig device, particles of various specific gravity can be stratified without using a specific specific gravity liquid as long as it sinks in the medium, so it is necessary to take special measures to ensure the stability of the specific gravity liquid. It is possible to realize a sorting device that is resistant to external disturbances.

  However, when recovering plastics as described in (1) to (3) above, (3) PS / ABS recovery can be easily realized, but (1) in order to realize removal of light substances. There is no suitable medium.

  Considering the combination that realizes the above selections (1) to (3) by taking advantage of the characteristics of each of the above selection methods and apparatuses, the liquid cyclone (registered trademark) using water is used for the selection in (2). , (3) can be easily realized by using a jig, but (1) cannot be selected, and there is a big problem in realizing it, such as excessive capital investment. is there.

  As a problem in actual operation other than the above-described sorting accuracy, there is an excessive increase in facilities related to wastewater treatment when wet sorting is carried out, resulting in a significant increase in operating costs.

  In the conventional specific gravity sorting method, a medium such as water is usually circulated and used to reduce the cost of wastewater treatment. However, the dirt of the particles to be sorted flows out and accumulates in the medium. Since the particles to be sorted are back-contaminated by contaminants accumulated in the medium, they can only be used as low-level materials that do not function sufficiently even if sorted by type. Not.

  The shredder dust of OA equipment and home appliances is a residue that has been crushed after being used for a long period of time, and therefore, dirt, dust, detergent, food, mold, etc. are listed as contaminants. In addition to these, some parts, such as contact metals, fusible stoppers, relays, etc., use hazardous heavy metals such as mercury and cadmium. It is contained in shredder dust.

  Therefore, considering the problem of the working environment in sorting operations, the problem of maintaining the cleanliness and characteristics of the materials to be sorted, and the impact on the environment, sufficient wastewater treatment is indispensable, and the cost of recycled materials cannot be reduced. It is a factor.

  This invention has been made to solve the above-mentioned problems, and it is not necessary to use various kinds of specific gravity liquids, and high-precision waste plastic with the same method and apparatus from high specific gravity to low specific gravity. An object of the present invention is to provide a specific gravity sorting method capable of sorting different kinds of materials and capable of simultaneously sorting various kinds of materials.

  It is another object of the present invention to provide a specific gravity sorting method in which the recycled material has high cleanliness, and in addition, the wastewater treatment cost when water is used as a medium is remarkably reduced.

  The specific gravity sorting method according to the present invention is characterized in that the particles to be sorted are stratified on the floating surface for each specific gravity and sorted by repeating the act of floating the particles to be sorted after forcibly settling in the medium. .

  In the specific gravity sorting method according to the present invention, the particles to be sorted are stratified on the floating side for each specific gravity and sorted by repeating the action of forcibly precipitating the particles to be settled in the medium and then floating. Can provide sorting.

Embodiment 1 FIG.
In the present embodiment, the floating stratification screening of the present invention was performed and verified manually. Water was used as the medium, and the particles to be sorted were mixed with PP particles 13 having a particle diameter of around 4 mm and light matter 12 (urethane particles). A SUS mesh having an opening of 1 mm was fixed to the handle unit 17 for the screen 11.

FIG. 1 is a diagram showing the first embodiment, and is a diagram showing a stratified state of particles to be sorted. The actual operation will be described with reference to FIG. Sorted particles (a mixture of PP particles 13 and light matter 12) were placed in a screen container 15 and inserted into a water tank 14 in which water 16 was stored. Hold the handle unit 17,
(1) Hold the screen container 15 in water,
(2) After being moved downward by about 50 mm, it was quickly returned to its original position and held until the particles to be sorted had floated under the screen 11. By repeating this several times,
(3) The stratified state of the particles to be sorted was observed.

Generally, gravity, buoyancy, and drag act on particles that float or sink in a medium such as water.
M (dv / dt) = Mg -Mg (ρL / ρs) -Cd (A · ρL · v 2/2) (1)
Here, M is the mass of the particle, dv / dt is the acceleration of the particle, g is the acceleration of gravity, ρL is the specific gravity of the medium, ρs is the specific gravity of the particle, Cd is the drag coefficient, and A is the projected area in the sedimentation or floating direction of the particle. , V is the sedimentation or ascent rate.

Since the velocity is 0 at the initial stage of subsidence or levitation, the drag term can be ignored. Therefore, the equation (1) can be arranged as the equation (2).
dv / dt = g (1-ρL / ρs) (2)

  In the present embodiment, since the specific gravity of the PP particles 13 and the specific gravity of the light matter 12 are both smaller than the specific gravity of water, which is the medium, the right side of the equation (2) is a negative value, and each particle has an acceleration in the flying direction. Although this acceleration varies depending on the specific gravity of the particles, a flying speed difference due to the specific gravity will occur. On the other hand, when the ascent is started, the drag term (third term) in equation (1) cannot be ignored, and the drag increases as the speed increases. In any case, the forces balance and rise at a constant speed.

  Since the drag term (third term) on the right side of the equation (1) is proportional to the projected cross-sectional area of the particle, it varies depending on the size and shape of the particle. However, since the speed is determined largely depending on the specific gravity at the start of levitation, if a large number of particles rise competitively and accumulate under the screen, if the levitation and stop are repeated, the influence of the size and shape of the particles will be reduced. A stratified state according to the specific gravity can be created.

  This concept can be similarly shown in the sedimentation phenomenon, and has been explained as the stratification principle of the jig sorting apparatus. The inventor applied the stratification phenomenon due to repeated sedimentation described in the jig to the floating side, and verified that the particles to be classified can actually be stratified for each specific gravity according to the present embodiment.

  In addition, if stratified sorting can be performed on the floating side, light particles that could not be sorted without using an unpractical light solvent or the like in the jig sorting device can be sorted, for example, the most general-purpose plastic. It is possible to separate and recycle PP, which is, from the mixed crushed particles with high accuracy and ease.

Embodiment 2. FIG.
In the second embodiment, shredding dust generated from crushed household appliances was subjected to levitation stratification using salt water as a medium. FIG. 2 is a diagram showing the second embodiment, and is a schematic diagram of a specific gravity sorting device. Hereinafter, a description will be given with reference to FIG.

  Shredder dust generated from crushed household appliances includes light articles 12 such as urethane generated from refrigerators, PP particles 13 such as exteriors of washing machines and internal parts of refrigerators, PS particles 21 such as air conditioner indoor unit bodies, and around electrical components. It includes heavy objects 22 such as heavy plastics, minute covered electric wires, aluminum foil, and copper wires. The PP particles 13 and the PS particles 21 that can be collected quantitatively from these and have a high possibility of reuse if they can be separated with high purity are taken out.

  Shredder dust was pulverized and adjusted to a 6 mm under 4 mm upper, and salt water 24 adjusted to a specific gravity of 1.1 was used as the medium. In addition, the screen 11 is moved up and down to forcibly settle and float the particles to be sorted in the medium. A screw conveyor was used for the supply port 23 in order to supply the particles to be sorted into the medium.

  Since the medium specific gravity is 1.1, the heavy material 22 settles and is discharged from the lower outlet 26 of the apparatus when the particles to be sorted are supplied into the medium. Some of the heavy materials 22 were found to float with air or the like during supply, but it was confirmed that the heavy materials 22 were stirred during vertical movement on the screen 11 and separated from the air and settled. Unlike simple floatation / sink sorting, the particles to be sorted are supplied directly into the medium and stirred up and down, so that the separation accuracy of the float / sink is also significantly improved.

  The mixture of the lighter matter 12, PP particles 13, and PS particles 21 that have risen is stratified as it repeatedly forcibly settles and floats under the screen 11, and the lighter matter 12 that forms a layer at the highest position is discharged from the upper front outlet 27. The The remaining PP particles 13 and PS particles 21 move over the weir structure and move to the second stage screen.

  In the second stage screen, the remaining particles are stratified in the same manner as described above, the PP particles 13 are discharged from the upper rear discharge port 28, and finally the PS particles 21 cross the weir structure and are discharged from the final discharge port 29.

  According to the method of the present embodiment, it is possible to sort out four types of mixed crushed materials with high accuracy using a single apparatus. Compared to the method using float and sink or liquid cyclone (registered trademark) with several kinds of specific gravity liquids, there is no need to use a dangerous flammable solvent, and only one kind of specific gravity liquid is used as a medium. Thus, it is possible to avoid fluctuations in specific gravity due to contamination from the sorting tank and to realize an easy sorting operation.

Embodiment 3 FIG.
In the third embodiment, the particles to be sorted are supplied between the upper and lower two screens 11, and the particles to be sorted are layered and sorted at the same time directly below the upper screen 11 and the lower screen 11. FIG. 3 is a diagram showing the third embodiment, and is a schematic diagram of a specific gravity sorting device.

  Two screens 11 having an opening of 1 mm are installed inside the water tank, and a vertical water flow generator 31 at the bottom of the water tank generates a vertical water flow by pumping and discharging air from an air pump 32 and an air tank 33.

  The particles to be sorted are home appliance shredder dust crushed into a 6 mm under 4 mm upper as in the second embodiment, and the medium is water 34.

  The home appliance shredder dust and the medium water 34 are mixed in advance in the particle mixing tank 35 and supplied to the sorting water tank by the supply pump 36. In the sorting water tank, the PP particles 13 and the light matter 12 having a specific gravity lower than that of the water 34 float up and are deposited immediately below the upper screen. On the other hand, the PS particles 21 and the heavy matter 22 having a specific gravity greater than that of the water 34 settle and deposit on the lower screen.

  Each particle is moved up and down by the vertical water flow generator 31, and the PP particles 13 and the light matter 12 are repeatedly stratified by forced settling and floating immediately below the upper screen. At the same time, the PS particles 21 and the heavy material 22 are repeatedly forcedly levitated and settled on the lower screen, and are stratified under the same action as a general jig sorter.

  The upper and lower deposited layers that have been layered are controlled by the specific gravity position detection device 37, and are selected with the upper and lower weirs as the boundary. As the specific gravity position detection device 37, a float type detection device used in a general jig sorter can be used.

  According to the method of the third embodiment, the four different kinds of mixed crushed materials can be sorted with high accuracy by one sorter as in the second embodiment. In addition, according to this method, water can be used as a medium, so that the specific gravity of the medium can be managed more easily, and countermeasures against salt damage in the equipment and re-washing of the selected particles are not required. Can be realized.

  In the case of carrying out this embodiment, depending on the thickness of the stratified particles, the pressure loss of the vertical water flow may become abnormally large, and a sufficient flow velocity for forced sedimentation or forced levitation may not be ensured. In this case, the thickness to be stratified can be controlled by adjusting the supply amount of the selection object, the supply water amount, and the like, and can be easily handled by providing a bypass mechanism.

Embodiment 4 FIG.
In the second embodiment and the third embodiment, since only a single specific gravity liquid is used, specific gravity fluctuations due to contamination between specific gravity liquids and the like do not occur. It is contaminated with dirt and the like, and the specific gravity fluctuation of the specific gravity liquid due to these contaminants cannot be avoided. In addition, these contaminants change the apparent specific gravity of the particles to be sorted, and thus adversely affect the sorting accuracy.

  In the fourth embodiment, the particles to be sorted are wet-cleaned in the previous step in order to eliminate the contamination of these shredder dusts and enable more specific gravity selection. Furthermore, a water circulation system was established to ensure the cleanliness of the particles to be sorted while minimizing the cost of treating wastewater generated by this system.

  FIG. 4 is a diagram showing the fourth embodiment and is a schematic diagram of a specific gravity sorting system. The specific gravity sorting system will be described with reference to FIG. The particles to be sorted are shredder dust of OA equipment and home appliances, and the specific gravity liquid for performing specific gravity sorting is water.

  Sorted particles are stored in the stocker 42 and supplied to the wet cleaning machine 41 at a constant speed. Here, in the present embodiment, a friction washer that performs cleaning by mixing and rubbing particles and water is used. The cleaning apparatus may use, for example, a wet crusher as long as sufficient particle cleaning is possible. The wet cleaning machine 41 is supplied with cleaning feed water 43 together with the particles to be sorted, the washed particles to be washed are discharged from the upper part, and the washing waste water 45 is drained from the lower part.

  The cleaned particles to be sorted are supplied to the particle mixing tank 35 and are sorted for each material by the specific gravity sorting device 47 as described in the third embodiment. When each material is discharged from the specific gravity sorter 47, water which is a specific gravity liquid is also drained as specific gravity tank drain 46 at the same time, and this water is returned to the particle mixing tank 35 by a circulation pump 48. At this time, a part of the waste water is added to the cleaning water supply 43 in the previous step as cleaning return water 50. On the other hand, fresh water 51 is added to the particle mixing tank 35, and the water in the specific gravity sorter is always kept clean.

  The cleaning waste water 45 from the wet cleaning machine 41 is concentrated by the filter unit 52, and the cleaned water becomes the cleaning water supply 43. On the contrary, the concentrated water 49 is treated as waste water containing high-concentration pollutants.

  In the fourth embodiment, a 0.1 μm microfilter was used as a filter unit 52 in a cross-flow type filtration device, so that the appearance of the treated water was colorless and transparent. The filter unit 52 was able to concentrate the washing waste water 45 to about 1/10.

  According to this method, since the particles to be sorted are washed in advance, there is no deterioration of the sorting accuracy due to fluctuations in the apparent specific gravity of the particles to be sorted, and the amount of waste water to be treated can be remarkably reduced. The specific gravity water 44 can also maintain its cleanliness, and the specific gravity liquid has a final cleaning effect on the particles to be sorted. Therefore, the cleanliness of each selected material is extremely high, and it can be recycled to materials with high required characteristics. Can also be possible.

  As described above, OA equipment and home appliance shredder dust are contaminated with mud, dust, detergent bowls, food, mold, and the like, and also contain trace amounts of harmful heavy metals. These are dissolved and dispersed in the cleaning water supply 43 by the wet cleaning machine 41, and the particles to be cleaned are cleaned, but the components dissolved in the water among the contaminants are not treated by the filter unit 52, and therefore the cleaning water supply 43 The cleaning water that has accumulated inside and dissolved this component is supplied again.

  However, due to the effect of water dispersion and the effect of finishing washing with the specific gravity liquid of the specific gravity sorting device 47, it was confirmed by the mechanical properties of the sorted matter and the analysis of harmful heavy metals that the selected material is sufficiently clean. .

  The present invention is not limited to the specific gravity selection method and specific gravity selection system described in the above-described embodiment and shown in the drawings. For example, in combination with ups and downs and hydrocyclone (registered trademark), In the range where it is not possible to deviate from the gist, such as flotation and stratification of only water floated material, washing by wet crusher in the previous process, and filter unit 52 using suction filtration system It can be implemented with deformation.

It is the stratification state of the to-be-sorted particle in Embodiment 1. FIG. 6 is a schematic diagram of a specific gravity sorting apparatus according to Embodiment 2. FIG. 6 is a schematic diagram of a specific gravity sorting apparatus according to Embodiment 3. FIG. 6 is a schematic diagram of a specific gravity sorting system according to Embodiment 4. FIG.

Explanation of symbols

  11 Screen, 12 Light product, 13 PP particles, 14 Water tank, 15 Screen container, 16 Water, 17 Handle unit, 21 PS particles, 22 Heavy material, 23 Supply port, 24 Salt water, 25 Screen drive device, 26 Lower discharge port, 27 Upper front outlet, 28 Upper rear outlet, 29 Final outlet, 31 Vertical water flow generator, 32 Air pump, 33 Air tank, 34 Water, 35 Particle mixing tank, 36 Supply pump, 37 Specific gravity position detector, 38 Particle discharging device, 41 Wet washer, 42 Stocker, 43 Washing water, 44 Specific gravity water, 45 Washing wastewater, 46 Specific gravity tank wastewater, 47 Specific gravity sorting device, 48 Circulation pump, 49 Concentrated water, 50 Washing return water, 51 New water , 52 Filter unit.

Claims (8)

  A specific gravity selection method characterized in that the particles to be sorted are stratified on the floating side for each specific gravity and sorted by repeating the action of forcibly settling the particles to be sorted in a medium and then floating.   A screen having a mesh size smaller than the size of the particles to be sorted is placed in a medium having a specific gravity larger than the particles to be sorted, the particles to be sorted are placed under the screen, and the screen is moved up and down intermittently. Alternatively, the particles to be sorted are forcedly settled and floated by intermittently generating a downward flow in the medium, and the particles to be sorted are stratified and sorted by specific gravity under the screen. The specific gravity selection method according to 1.   The particles to be sorted are a mixture of many kinds of materials, and when the particles to be sorted are supplied into the medium, the particles to be sorted having a specific gravity larger than that of the medium are first discharged from the lower part and the specific gravity is smaller than that of the medium. The floated mixture is forcedly settled under the screen and floated repeatedly to stratify to discharge the lightest particles to be sorted, and the other floated mixture is moved to the next screen. The specific gravity sorting method according to claim 2, wherein the particles are layered repeatedly to discharge the particles to be sorted in the upper layer and are sorted by repeating this.   The specific gravity sorting method according to claim 3, wherein the particles to be sorted are shredder dust, and salt water is used as the medium.   The particles to be sorted are a mixture of many kinds of materials, and two screens with a mesh opening smaller than the size of the particles to be sorted are arranged in the upper and lower sides in the medium, and the particles to be sorted are introduced between the screens and intermittently. The particles to be sorted having a specific gravity smaller than that of the medium are layered for each specific gravity directly below the upper screen by the up and down movement of the typical medium or intermittently moving the screen up and down, and the medium is formed on the lower screen. A specific gravity sorting method characterized in that particles to be sorted having a larger specific gravity than each other are stratified for each specific gravity.   6. The specific gravity sorting method according to claim 5, wherein the particles to be sorted are shredder dust, and water is used as the medium.   The specific gravity sorting method according to claim 6, further comprising a step of washing the particles to be sorted in a previous step of sorting the particles to be sorted by specific gravity.   When the specific gravity sorting medium is water and the water used in the sorting process is recycled, a certain amount of waste water is used as the washing water in the previous wet washing process, and the washing waste water in the wet washing process is filtered. The specific gravity sorting method according to claim 7, wherein the specific gravity sorting method is reused as washing water.

Images