JP2011161311A - Electrostatic sorting apparatus and electrostatic sorting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To recover plastic pieces at high purity and high recovery even though the mixing ratio of plastic pieces contained in sorted materials varies. <P>SOLUTION: The recovery box 141 of an electrostatic sorting apparatus is partitioned into three boxes, i.e., a minus electrode side recovery box 141A, a plus electrode side recovery box 141B, and a middle recovery box 141C, ABSs (polymer of acrylonitrile, butadiene, styrene) are collected to the minus electrode side recovery box 141A, and PS (polystyrene) and PP (polypropylene) are collected to the plus electrode side recovery box 141B. ABS, PS and PP that can not be sorted are mixedly collected to the middle recovery box 141C. The mixed group collected to the middle recovery box 141C is conveyed by a conveying machine 151C, and is stored in a hopper 152C. A switching valve 154 circulates the mixed group stored in the hopper 152C to an electrically charged cylinder, and the circulated mixed group is electrostatically sorted again. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to an electrostatic sorting apparatus and an electrostatic sorting method for sorting plastics by electrostatic separation, for example.

  2. Description of the Related Art Generally, a plastic electrostatic sorting apparatus that frictionally charges a material to be sorted including a plurality of types of plastic pieces and sorts each charged plastic piece with an electrostatic field is generally known.

The plastic piece is charged in accordance with a frictional charging sequence (also referred to as a charging column).
The frictional charging sequence is a sequence in which substances that are likely to be positively charged when different materials are rubbed together are arranged on the upper side and substances that are easily charged negatively are arranged on the lower side.
For example, the triboelectrification order of plastic pieces (ABS, PE, PET, PP, PS, PVC) is the order of “ABS → PS → PE → PP → PET → PVC”. “ABS” represents a polymer of acrylonitrile, butadiene and styrene, “PS” represents polystyrene, “PE” represents polyethylene, “PP” represents polypropylene, “PET” represents polyethylene terephthalate, and “PVC” represents polyvinyl chloride.

  By using the triboelectric order, waste plastic can be sorted and reused.

Patent Document 1 discloses an electrostatic sorting device that sorts two or more types of plastic pieces (sorted materials).
Generally, the electrostatic sorting apparatus is composed of an input stocker, a drying furnace, an input hopper, an input feeder, a charging cylinder, an input feeder, an electrode section, and a collection box.

The material to be sorted is transferred to the charging hopper and supplied to the charging cylinder by a charging feeder provided below the charging hopper. The feeding feeder vibrates and feeds the material to be sorted into the charging cylinder, thereby adjusting the feeding speed of the material to be sorted into the charging cylinder. A certain amount of material to be sorted is put into the charging cylinder per unit time.
In the rotating charging cylinder, a plurality of types of plastic pieces constituting the material to be sorted are rubbed with each other, and each plastic piece is charged with a polarity (plus or minus) and a charge amount corresponding to the charge train. The charged material to be sorted causes pairing in which a positively charged plastic piece and a negatively charged plastic piece stick together by electrostatic force (Coulomb force).
The material to be sorted out from the charging cylinder is transferred to a carry-in feeder. The feeder Feeder eliminates the pairing of the materials to be sorted by the vertical pushing vibration that pushes the materials to be moved forward while moving the materials to be sorted up and down.
The material to be sorted whose pairing has been eliminated is dropped between electrodes (electrostatic field) to which a high DC voltage is applied. Then, each plastic piece contained in the material to be sorted is drawn toward one of the electrodes by an electrostatic force corresponding to the polarity and the charge amount while naturally dropping. Therefore, each plastic piece falls while drawing a parabolic trajectory.
The plastic pieces that fall along the parabolic trajectory are collected in a collection box provided under the electrodes.

For this reason, if the collection box is appropriately partitioned according to the proportion of plastic pieces contained in the material to be sorted (hereinafter referred to as the mixing ratio), the plastic pieces will be collected in each part of the collection box. Can do.
For example, when ABS, PS, and PP are included in the material to be sorted, if the recovery box is divided into three parts, the negative electrode side, the positive electrode side, and the middle thereof, ABS is recovered on the negative electrode side, and the positive electrode side PS and PP can be recovered. In the middle, ABS, PS and PP are mixed and recovered.

However, the mixing ratio of the plastic pieces contained in the material to be sorted varies, and the optimum partition position of the collection box also varies.
For this reason, there is a possibility that the recovery rate and purity of the selected plastic piece may be reduced.

JP 2005-138030 A JP 2000-342998 A

  An object of the present invention is, for example, to make it possible to collect plastic pieces with high purity and high recovery rate even when the mixing ratio of the plastic pieces contained in the material to be sorted varies.

The electrostatic sorting device of the present invention is
A charging unit that is charged with a material to be sorted including a plurality of pieces to be sorted with different charging characteristics, and charges the plurality of pieces to be sorted included in the inputted material to be sorted,
An electrostatic separation unit having a pair of electrodes to which a predetermined voltage is applied, and drawing a plurality of pieces to be electrified by the charging unit and falling between the pair of electrodes to the electrode side according to the polarity of the pieces to be sorted When,
A collection box that is divided into a plurality of collection units and arranged below the pair of electrodes, and that collects a plurality of pieces to be sorted that have dropped between the pair of electrodes by the plurality of collection units,
A circulating unit that feeds a piece to be sorted collected in a predetermined collection unit among the plurality of collection units to the charging unit.

  According to the present invention, for example, even if the mixing ratio of the plastic pieces (an example of the pieces to be sorted) included in the material to be sorted varies, the plastic pieces can be collected with high purity and high recovery rate.

1 is a configuration diagram of a plastic electrostatic sorting device 100 according to Embodiment 1. FIG. FIG. 3 is a configuration diagram of a collection box 141 and a stock unit 150 in the first embodiment. 4 is a table showing a calculation example of the recovery rate and purity in the first embodiment. FIG. 5 shows a switching valve 154 in the first embodiment. FIG. 3 is a diagram showing “(1) a piece of plastic that is stochastically insufficiently charged” in the first embodiment. The figure which shows the plastic piece which could cancel pairing in Embodiment 1. FIG. The figure which shows "(2) Plastic piece which could not cancel pairing" in Embodiment 1. FIG. FIG. 3 is a diagram showing “(3) a plastic piece colliding with an electrode” in the first embodiment. FIG. 4 shows “(4) a plastic piece that is difficult to be charged” in the first embodiment. 3 is a graph showing a plastic piece recovery rate during middle circulation by the plastic electrostatic sorting apparatus 100 according to the first embodiment. The block diagram with the stock part 150 in Embodiment 2. FIG. The graph which shows the relationship between the cycle time of middle circulation in Embodiment 2, and collection | recovery rate and purity.

Embodiment 1 FIG.
A circulation type electrostatic sorting apparatus that performs electrostatic sorting again on a sorting material that could not be sorted among the sorting materials that have been subjected to electrostatic sorting will be described.

In the first embodiment, the material to be sorted includes a plurality of types of pieces to be sorted having different charging characteristics (ease of charging).
For example, plastic pieces (sorted pieces) left after specific gravity sorting of mixed plastic obtained by crushing recycled waste (for example, home appliances such as air conditioners, refrigerators, and washing machines) are materials to be sorted. . A plurality of types of plastic pieces are mixed in the material to be sorted.

FIG. 1 is a configuration diagram of a plastic electrostatic sorting apparatus 100 according to the first embodiment.
The configuration and operation of the plastic electrostatic sorting apparatus 100 according to Embodiment 1 will be described below with reference to FIG.
In FIG. 1, solid and dotted arrows indicate the path of the material 101 to be sorted.

  First, the configuration of the plastic electrostatic sorting apparatus 100 will be described.

The plastic electrostatic sorting apparatus 100 (an example of an electrostatic sorting apparatus) includes a loading stocker 111, a dryer 112, a loading hopper 113, and a loading feeder 114 as a processing unit before the material to be sorted 101 is frictionally charged.
The input stocker 111 stores the material 101 to be sorted. The material to be sorted 101 stored in the input stocker 111 is input to the dryer 112.
The dryer 112 dries the material 101 to be sorted. The material to be sorted 101 dried by the dryer 112 is transferred to the input hopper 113.
The input hopper 113 discharges the material to be sorted 101 to the input feeder 114 by a certain amount.
The feeding feeder 114 feeds the material 101 to be sorted into the charging cylinder 121 by a certain amount per unit time while vibrating. The input feeder 114 adjusts the input speed of the material 101 to be sorted by vibrating. For example, the input feeder 114 is configured by a belt conveyor.

The plastic electrostatic sorting apparatus 100 includes a charging cylinder 121 as a friction charging unit that frictionally charges the material 101 to be sorted.
By rotating the charging cylinder 121, the material to be sorted 101 in the charging cylinder 121 is stirred and rubbed, and the material to be sorted 101 is charged with a polarity (plus or minus) and a charge amount corresponding to the frictional charging sequence.
The charging cylinder 121 is made of a material having a specific charging characteristic (for example, ABS), and the charging cylinder 121 itself is charged according to the frictional charging sequence by friction with the material 101 to be sorted.

The plastic electrostatic sorting device 100 includes a carry-in feeder 122 and a feeder driving device 123 as an electrostatic separation carry-in unit for carrying the frictionally charged material 101 to be carried into the electrostatic separation unit.
The carry-in feeder 122 is vibrated and pushed forward while moving the material to be sorted 101 up and down by an electrode to which a negative voltage is applied (negative electrode 131) and an electrode to which a positive voltage is applied (plus electrode 132). The material to be sorted 101 is dropped into the electrostatic field that is created. The following vibration of the carry-in feeder 122 is referred to as “vertical push-out vibration”.
The carry-in feeder 122 cancels the pairing of the material to be sorted 101 by the vertical extrusion vibration. The pairing means that the materials to be sorted 101 charged to different polarities adhere to each other by electrostatic force.
The feeder driving device 123 operates the carry-in feeder 122 so as to push it up and down and vibrate. For example, the carry-in feeder 122 is an electromagnetic feeder or an electric feeder system.

The plastic electrostatic sorting apparatus 100 includes a negative electrode 131, a positive electrode 132, and a voltage control device 133 as an electrostatic separation unit that electrostatically separates the frictionally charged material 101 to be sorted.
The negative electrode 131 and the positive electrode 132 constitute a pair of electrodes.
The voltage control device 133 applies a high DC voltage to the negative electrode 131 and the positive electrode 132 to create an electrostatic field between the electrodes.
For example, the minus electrode 131 and the plus electrode 132 are installed at an interval of 20 cm (centimeter), and the voltage control device 133 applies 60 kV (kilovolts) between the electrodes. At this time, the electric field strength between the electrodes is “3 kV / cm”.
The minus electrode 131 and the plus electrode 132 are attracted to one electrode side by an electrostatic force corresponding to the polarity and charge amount of the material to be sorted 101 that falls between the electrodes (electrostatic field). In other words, each plastic piece constituting the material to be sorted 101 falls an electrostatic field while being scattered. This is called “electrostatic separation”.

The plastic electrostatic sorting apparatus 100 includes a collection box 141 as a collection unit that collects the material to be sorted 101 that falls while being electrostatically separated between electrodes.
The collection box 141 is divided into three, and the sorted material 101 to be sorted is collected in two of the three sections (the minus electrode side collection box 141A and the plus electrode side collection box 141B), and the remaining one The material to be sorted 101 that could not be sorted is collected in the area (middle collection box 141C). Sorting is to divide by type.
Details of the collection box 141 will be described later.

Further, the plastic electrostatic sorting apparatus 100 stores the sorted material 101 that has been sorted out of the sorted material 101 collected in the collection box 141, and the sorted material 101 that has not been sorted is stored in the friction charging unit (charging cylinder 121). The stock section 150 is provided as a circulation section that circulates to).
Details of the stock unit 150 will be described later. The middle circulation hopper 159 will be described as a configuration of the stock unit 150.

FIG. 2 is a configuration diagram of the collection box 141 and the stock unit 150 according to the first embodiment.
The configuration of the collection box 141 and the stock unit 150 in the first embodiment will be described below based on FIG.

The collection box 141 is partitioned into three areas by two partition plates 142 (142A, 142B).
Hereinafter, of the two partition plates 142, the partition plate 142 disposed on the minus electrode 131 side is referred to as “partition plate 142A”, and the partition plate 142 disposed on the plus electrode 132 side is referred to as “partition plate 142B”. Further, the area on the minus electrode 131 side partitioned by the partition plate 142A is referred to as “minus electrode side recovery box 141A”, and the area on the plus electrode 132 side partitioned by the partition plate 142B is referred to as “plus electrode side recovery box 141B”. Further, a middle area partitioned by the partition plate 142A and the partition plate 142B is referred to as a “middle recovery box 141C”.

The positions of the partition plates 142A and 142B of the collection box 141 are set based on the reference value (average value) of the mixing ratio of the material 101 to be sorted.
For example, when recycling home appliances such as an air conditioner, a refrigerator, and a washing machine, the home appliances are crushed and sorted, and the plastic pieces collected by crushing and sorting are sorted by specific gravity. Then, the plastic piece (the material to be sorted 101) that could not be sorted by specific gravity sorting is electrostatically sorted by the plastic electrostatic sorting device 100. In this case, the reference value of the mixing ratio of the material 101 to be selected is “ABS: PS: PP = 42: 50: 8”, and the positions of the partition plates 142A and 142B of the collection box 141 are based on the reference value of the mixing ratio. Is set.

  However, since the type and amount of waste to be recycled vary depending on the season (or month, day), the mixing ratio of the material to be sorted 101 varies depending on the season. In addition, since the waste to be treated varies depending on time even in the same season, the mixing ratio of the material to be sorted 101 varies depending on time.

  Hereinafter, the position of the partition plates 142A and 142B set based on the reference value of the mixing ratio is referred to as “reference position”.

When the mixing ratio of the material to be sorted 101 is close to the reference value, the plastic pieces can be recovered with high purity and high recovery rate by providing the partition plates 142A and B of the recovery box 141 at the reference position. .
When the mixing ratio of the material to be sorted 101 is a value greatly deviated from the reference value, the plastic pieces are recovered with high purity by shifting the partition plates 142A and B of the collection box 141 to the safe side (outward) from the reference position. can do. However, since the minus electrode side collection box 141A and the plus electrode side collection box 141B are narrowed, the recovery rate of the plastic piece is lowered.

FIG. 3 is a table showing a calculation example of the recovery rate and purity in the first embodiment.
A calculation example of the recovery rate and a calculation example of the purity in the first embodiment will be described below based on FIG.

The recovery rate is the ratio of the recovered amount of the target plastic piece to the amount of the target plastic piece (for example, ABS) contained in the material to be sorted 101.
The purity is the ratio of the target plastic piece contained in the plurality of plastic pieces collected as the target plastic piece.

  Hereinafter, a group of ABS plastic pieces is referred to as an “ABS group”, and a group of PS and PP plastic pieces is referred to as a “PSPP group”.

For example, it is assumed that the material to be sorted 101 of “100 kg (kilograms)” exists, and the material to be sorted 101 includes an ABS group of “40.2 kg” and a PSPP group of “59.8 kg”.
As a result of electrostatic sorting of the material 101 to be sorted by the plastic electrostatic sorting device 100, the ABS group “29.7 kg” and the PSPP group “0.3 kg” are collected in the ABS collection box (minus electrode side collection box 141A). In the PSPP collection box (plus electrode side collection box 141B), the PSPP group “49.5 kg” and the ABS group “0.5 kg” were collected. In the middle collection box 141C, the ABS group “10 kg” and the PSPP group “10 kg” were collected.

In this case, the recovery rate of the ABS group is the ratio of the amount (29.7 kg) of the ABS group recovered in the ABS recovery box to the amount (40.2 kg) contained in the material to be sorted 101, and “73. 9% (= (29.7 ÷ 40.2) × 100) ”.
The purity of the ABS group is the ratio of the ABS group (29.7 kg) contained in the plastic group (29.7 kg + 0.3 kg) collected in the ABS collection box, which is “99% (= 29.7 ÷ (29 .7 + 0.3)) ”.

  Similarly, the recovery rate of the PSPP group is “82.8% (= (49.5 ÷ 59.8) × 100)”, and the purity of the PSPP group is “99% (= 49.5 ÷ (49.5 + 0). .5)) ".

  Even if the mixing ratio of the materials to be sorted fluctuates and the position of the partition plate 142 of the collection box 141 is not appropriate, the plastic electrostatic sorting apparatus 100 can remove the plastic pieces with high purity by the middle circulation method described later. And it can be recovered at a high recovery rate.

  Returning to FIG. 2, the stock unit 150 that executes the middle circulation method will be described.

The stock unit 150 includes a transport device 151, a hopper 152, a flexible container 153 (flexible container bag), a switching valve 154, a middle circulation transport device 155, and a middle circulation hopper 159.
The conveyor 151, the hopper 152, and the flexible container 153 constitute a line for conveying the material to be sorted 101 collected in the collection box 141, and are provided for each area (141 </ b> A to C) of the collection box 141.
The switching valve 154, the middle circulation transporter 155, and the middle circulation hopper 159 are provided only in the middle recovery box 141C line, and execute the middle circulation method. The middle circulation method will be described later.

The transporters 151A to 151C transport the material to be sorted 101 collected in the collection box 141 to the hoppers 152A to 152C on the same line and put them into the hoppers 152A to 152C. For example, the conveyor 151 is a belt conveyor.
The hoppers 152 </ b> A to 152 </ b> C close the lower part that opens and closes, temporarily store the material to be sorted 101, and release the material to be sorted 101 when the lower part is opened.
The flexible containers 153A to 153C are bags for packing the material to be sorted 101 released from the hoppers 152A to 152C.

  The switching valve 154 is provided between the hopper 152C and the flexible container 153C in the line of the middle collection box 141C, and the path of the material 101 to be sorted discharged from the hopper 152C is routed to the flexible container 153C and the path to the middle circulation hopper 159. Switch to either.

  The middle circulation transporter 155 transports the material to be sorted 101 released from the hopper 152C to the middle circulation hopper 159 while the path of the material to be sorted 101 is switched to the path to the middle circulation hopper 159 by the switching valve 154. . For example, the middle circulation conveyor 155 is a belt conveyor.

  The middle circulation hopper 159 moves the material to be sorted 101 conveyed by the middle circulation conveyance machine 155 to the input feeder 114.

FIG. 4 is a diagram illustrating the switching valve 154 according to the first embodiment.
The switching valve 154 according to Embodiment 1 will be described below based on FIG.

  The switching valve 154 is a rotating body having an L-shaped cross section. The position of the switching valve 154 is below the hopper 152C and above the flexible container 153C.

The switching valve 154 closes the lower part when (a) switching the route of the material to be sorted 101 discharged from the hopper 152C to the route to the middle circulation hopper 159 (middle circulation ON). At this time, the material to be sorted 101 is conveyed to the middle circulation hopper 159 by the middle circulation conveyance machine 155.
The switching valve 154 opens the lower part when (b) switching the path of the material 101 to be sorted discharged from the hopper 152C to the path to the flexible container 153C (middle circulation OFF). At this time, the material to be sorted 101 is put into the flexible container 153C.

  For example, the switching valve 154 is switched to a state of either “(a) middle circulation ON” or “(b) middle circulation OFF” by the switch.

  Next, the flow of the material to be sorted 101 will be described based on FIG. 1 and FIG.

The waste to be recycled is manually disassembled and separated into parts before being processed by the plastic electrostatic sorter 100.
Next, each part is crushed by a machine and divided into a metal group and a plastic group by wind power. In the plastic group, a plurality of types of plastic pieces such as ABS, PS, PE, PP, PET, and PVC are mixed.
The plastic group can also be classified into those having a low specific gravity (for example, PP) and those having a high specific gravity (for example, ABS, PS, and some heavy PP) by specific gravity selection.

Hereinafter, the plastic group in which ABS, PS, and PP are mixed will be described as the material to be sorted 101.
When the order of triboelectric charging of ABS, PS, and PP is expressed in the order of those that are likely to be positively charged to those that are likely to be negatively charged, the order becomes “ABS → PS → PP”.

  In FIG. 1, the material to be sorted 101 is replenished to the input stocker 111 at any time or periodically.

  The material to be sorted 101 is input from the input stocker 111 to the dryer 112 and dried by the dryer 112.

  The material to be sorted 101 dried by the dryer 112 is transferred to the charging hopper 113 and supplied to the charging cylinder 121 by a certain amount per unit time by a charging feeder 114 provided under the charging hopper 113.

The material to be sorted 101 is stirred in the charging cylinder 121.
Then, a plurality of types of plastic pieces constituting the material to be sorted 101 rub against each other in the charging cylinder 121 and are charged with a polarity and a charge amount according to the frictional charging sequence.

The material to be sorted 101 charged in the charging cylinder 121 is transferred to the carry-in feeder 122. At this time, the material to be sorted 101 is paired by electrostatic force.
However, the material to be sorted 101 cancels the pairing by the vertical pushing vibration of the carry-in feeder 122.

The material to be sorted 101 whose pairing has been eliminated by the carry-in feeder 122 is dropped between the negative electrode 131 and the positive electrode 132 (electrostatic field). Then, each plastic piece constituting the material to be sorted 101 naturally falls while being attracted to one electrode side by an electrostatic force according to the charged polarity and the charged amount.
That is, each plastic piece draws a parabolic trajectory corresponding to the polarity and the charge amount, and falls to a different position in the collection box 141.

Each plastic piece is collected in the minus electrode side collection box 141A, the plus electrode side collection box 141B, or the middle collection box 141C according to the drop position.
Since the ABS plastic piece is easy to be positively charged, it is collected in the negative electrode side recovery box 141A, and the plastic piece of PS or PP is easy to be negatively charged and is collected in the positive electrode side recovery box 141B.

In FIG. 2, the ABS group recovered in the negative electrode side recovery box 141A and the PSPP group recovered in the positive electrode side recovery box 141B are transported to the hoppers 152A and B by the transporters 151A and B and packed in the flexible containers 153A and B. Is done.
The ABS group packed in the flexible container 153A is reused as a resource.
The PSPP group packed in the flexible container 153B is sorted into the PS group and the PP group by the next stage plastic electrostatic sorting device, and then reused as a resource. The next-stage plastic electrostatic sorter adjusts the voltage applied to the electrodes (131, 132) and the position of the partition plate 142 of the collection box 141 in order to sort the PSPP group into the PS group and the PP group. .

In the middle collection box 141C, plastic pieces (ABS pieces, PS pieces and PP pieces) that have not been collected in the minus electrode side collection box 141A or the plus electrode side collection box 141B for the following reasons are collected.
(1) Stochastic insufficiently charged plastic piece (2) Plastic piece that could not be removed from pairing (3) Plastic piece that collided with electrode (4) Plastic piece that is difficult to be charged

FIG. 5 is a diagram showing “(1) stochastic insufficiently charged plastic piece” in the first embodiment.
The “(1) stochastic insufficiently charged plastic piece” collected in the middle collection box 141C will be described below with reference to FIG.

The ABS piece, the PS piece, and the PP piece are rubbed with each other in the charging cylinder 121 and charged.
(A) In most cases, the ABS piece is positively charged by the friction between the PS piece and the PP piece, and the PS piece and the PP piece are negatively charged by the friction with the ABS piece.
(B) However, when the PS piece and the PP piece finally rub, the PS piece is positively charged. However, the charge amount of the PS piece is smaller than that of the ABS piece.

The positively charged PS piece as shown in (b) is an example of “(1) a stochastic undercharged plastic piece”.
Since the PS piece is not attracted to the plus electrode 132 and is not sufficiently attracted to the minus electrode 131, the PS piece is collected in the middle collection box 141C.

FIG. 6 is a diagram showing a plastic piece in which pairing can be eliminated in the first embodiment.
FIG. 7 is a diagram showing “(2) a plastic piece whose pairing could not be resolved” in the first embodiment.
The “(2) plastic pieces whose pairing could not be resolved” collected in the middle collection box 141C will be described below with reference to FIGS.

As shown in FIG. 6, the ABS piece is positively charged by the charging cylinder 121, and the PS piece (or PP piece) is negatively charged. For this reason, the ABS piece and the PS piece (or PP piece) stick together by an electrostatic force (pairing).
The ABS piece and the PS piece that stick together are canceled by the vertical pushing vibration of the carry-in feeder 122 and fall between the electrodes (131, 132). The ABS piece is attracted to the minus electrode 131 and collected in the minus electrode side collection box 141A, and the PS piece is drawn to the plus electrode 132 and collected in the plus electrode side collection box 141B.

  However, as shown in FIG. 7, when the ABS piece and the PS piece that stick together cannot be eliminated by the vertical pushing vibration of the carry-in feeder 122, the ABS piece and the PS piece fall between the electrodes while sticking to each other. Then, it is collected in the middle collection box 141C without being sufficiently drawn to any electrode side.

  For example, pairing is not canceled when the electrostatic force between the ABS piece and the PS piece is large (the charge amount is large) or when the vertical feeding vibration of the carry-in feeder 122 is small.

  The ABS piece and the PS piece shown in FIG. 7 are examples of “(2) a plastic piece whose pairing could not be eliminated”.

FIG. 8 is a diagram showing “(3) a plastic piece colliding with an electrode” in the first embodiment.
As shown in FIG. 8, when falling between the electrodes, the PS piece (or PP piece) colliding with the plus electrode 132 bounces back and is collected in the middle collection box 141C.
Such a PS piece (or PP piece) is an example of “(3) a plastic piece colliding with an electrode”.

FIG. 9 is a diagram showing “(4) a plastic piece that is difficult to be charged” in the first embodiment.
FIG. 9A shows a plastic piece having paper or the like pasted on its surface, and FIG. 9B shows a “rolled” plastic piece having a relatively small surface area compared to its mass.
Such a plastic piece is an example of “(4) a plastic piece that is difficult to be charged”. “(4) Plastic piece which is difficult to be charged” is not sufficiently attracted to the minus electrode 131 and the plus electrode 132 because the charge amount is not sufficient, and is collected in the middle collection box 141C.

In the middle collection box 141C, ABS pieces, PS pieces, and PP pieces are mixed and collected for the reasons (1) to (4) described above.
Hereinafter, a set of ABS pieces, PS pieces, and PP pieces collected and mixed in the middle collection box 141C is referred to as a “mixed group”.

  In FIG. 2, the mixed group recovered in the middle recovery box 141C is transported to the hopper 152C by the transporter 151C and discharged from the hopper 152C.

When the switching valve 154 is (a) in the middle circulation ON state (see FIG. 4), the mixed group discharged from the hopper 152C is transported to the middle circulation hopper 159 by the middle circulation transporter 155.
The transported mixed group is dropped from the middle circulation hopper 159 to the feeding feeder 114, mixed with the material to be sorted 101 and fed into the charging cylinder 121.

  A part (or all) of “(1) stochastic insufficiently charged plastic piece” included in the mixed group is newly charged in the charging cylinder 121 to eliminate the insufficient charging, and the negative electrode side collection box It is recovered in 141A and the positive electrode side recovery box 141B.

  In addition, a part (or all) of “(2) the plastic piece that could not be paired” included in the mixed group was newly subjected to vertical extrusion vibration by the carry-in feeder 122 to cancel the pairing, Recovered in the negative electrode side recovery box 141A and the positive electrode side recovery box 141B.

  Furthermore, a part (or all) of “(3) the plastic piece colliding with the electrode” included in the mixed group falls between the electrodes without colliding with the electrode, and the negative electrode side recovery box 141A and the positive electrode are dropped. It is collected in the side collection box 141B.

  However, there is a possibility that the “(4) plastic piece that is difficult to be charged” included in the mixed group cannot be solved even if it is newly charged in the charging cylinder 121 and is recovered again in the middle recovery box 141C. high.

As described above, the plastic group corresponding to the above (1) to (3) included in the mixed group is now removed by putting the mixed group recovered without being sorted into the middle recovery box 141C into the charging cylinder 121 again. Sorted and collected in the minus electrode side collection box 141A and the plus electrode side collection box 141B.
Thereby, the recovery rate can be improved without reducing the purity of the selected plastic piece.

  Hereinafter, putting the mixed group recovered in the middle recovery box 141C without sorting into the charging cylinder 121 again is referred to as “middle circulation”.

FIG. 10 is a graph showing the recovery rate of plastic pieces during middle circulation by the plastic electrostatic sorting apparatus 100 according to the first embodiment.
As shown in FIG. 10 (a), the recovery rate of the PSPP group was improved by the middle circulation regardless of the percentage of the ABS piece contained in the material to be sorted 101.
Furthermore, as shown in FIG. 10 (b), the recovery rate of the ABS group was also improved by the middle circulation.

  Returning to FIG. 2, the description of the flow of the material to be sorted 101 will be continued.

When the switching valve 154 is switched from (a) middle circulation ON to (b) middle circulation OFF (see FIG. 4), the mixed group discharged from the hopper 152C is packed in the flexible container 153C.
Many of the plastic pieces packed in the flexible container 153C are considered to be “(4) plastic pieces that are difficult to be charged”.

  In the first embodiment, for example, the following plastic electrostatic sorting apparatus 100 has been described.

The plastic electrostatic sorting apparatus 100 includes a friction charging device (charging cylinder 121), an electrostatic separation unit (minus electrode 131, plus electrode 132), and a collection unit (collection box 141).
The friction charging device stirs and charges the pulverized plastic pieces (the material to be sorted 101) by friction.
The electrostatic separation unit is disposed in a subsequent process of the triboelectric charging device, and electrostatically separates and sorts the charged plastic pieces according to the polarity and the charge amount.
The recovery unit separately recovers the plastic pieces separated by passing through the electrostatic separation unit.
The electrostatic separation unit has a pair of fixed electrodes and a separation space (electrostatic field). The plastic piece charged with the polarity and the charge amount according to the type by the frictional charging device passes through the separation space and is separated and recovered.
The collection unit forms three collection boxes by a partition plate.
The plastic electrostatic sorting apparatus 100 employs a middle circulation system. The middle circulation system is a system in which plastic pieces collected in the center of the collection unit (middle collection box 141C) are mixed with a plurality of types of plastic pieces before charging in a pre-process (for example, on a feeding feeder) of the friction charging device. It is.

The plastic piece collected in the middle collection box is mixed with the material to be sorted on the input feeder by the middle circulation method, proceeds to the charging cylinder of the next process, and is recharged, and the pairing is canceled again on the input feeder. The electrode portion receives the re-deflecting force and is recovered again in the recovery box.
Here, pay attention to one piece of plastic collected in the middle collection box for the first time. This plastic piece is recovered by charging, de-pairing, and deflection force different from the first step in the middle circulation process. For this reason, unlike the first time, the plastic piece may be collected not in the middle collection box but in the minus electrode side collection box or the plus electrode side collection box. Further, even if the plastic piece is collected again in the middle collection box by this middle circulation, the plastic piece may be collected in the negative electrode side collection box or the plus electrode side collection box in the next middle circulation.
The above shows that the recovery rate can be improved by the middle circulation method.

  In other words, even if the mixing ratio of plastic pieces varies from season to month, monthly, daily or hourly by the middle circulation method, plastic pieces should be collected at a high recovery rate with purity exceeding the specified value for each type. Can do.

The pair of electrodes (the negative electrode 131 and the positive electrode 132) of the electrostatic separation unit may be arranged in parallel (see FIG. 1), may be arranged in a square shape (see FIG. 6), or one ( Alternatively, both of them may be drum-type electrodes (see Patent Document 2).
Although the polarity of voltage application to the electrode has been described with the electrode 131 being negative and the electrode 132 being positive, the polarity may be reversed.

The friction charging device is not limited to the charging cylinder 121.
Furthermore, the plastic piece may be charged by a method other than friction.

The types of plastic pieces to be selected are not limited to ABS and PSPP.
For example, three types of ABS, PS, and PP may be selected, or other types (PE, PET, PVC, etc.) may be selected. Depending on the number of types to be selected, the collection box 141 may be divided into four or more areas by three or more partition plates 142. Further, the collection box 141 may be divided into two areas by one partition plate 142.

You may circulate the plastic piece collect | recovered in areas other than the center area (middle collection box 141C) of the collection box 141.
For example, the collection box 141 may be divided into two sections, and the plastic pieces collected in one of the sections may be circulated.
Further, the collection box 141 may be divided into three areas, and the plastic piece collected in the middle area and the plastic piece collected in one of the remaining two areas may be circulated.
Further, the collection box 141 may be divided into four sections, and the plastic piece collected in one of the two sections in the middle may be circulated.

Furthermore, the circulation destination of the plastic piece is not limited to the input feeder 114.
For example, a plastic piece may be circulated to the carry-in feeder 122. This makes it possible to select “(2) a plastic piece whose pairing could not be resolved” and further to select “(3) a plastic piece that collided with the electrode”.
Moreover, you may circulate a plastic piece between electrodes. Thereby, “(3) Plastic piece colliding with electrode” can be selected.

  Any material other than a plastic piece may be used as the material to be sorted 101 as long as it is charged.

Embodiment 2. FIG.
A mode for improving the recovery rate by switching between “middle circulation ON” and “middle circulation OFF” at an appropriate timing will be described.

The overall configuration of the plastic electrostatic sorting apparatus 100 is the same as that of the first embodiment (see FIG. 1).
However, the configuration of the stock unit 150 is partially different from that of the first embodiment.

FIG. 11 is a configuration diagram of the stock unit 150 according to the second embodiment.
The configuration of the stock unit 150 in the second embodiment will be described below with reference to FIG.

  The stock unit 150 includes a switching valve controller 156 in addition to the configuration of the first embodiment (see FIG. 2).

The switching valve controller 156 outputs a switching valve control signal 156A that periodically switches the state of the switching valve 154. The switching valve control signal 156A represents the middle circulation cycle time.
The switching valve 154 that has received the switching valve control signal 156A is sequentially switched to a “middle circulation ON” state or a “middle circulation OFF” state in accordance with the switching valve control signal 156A (see FIG. 4).
The plastic electrostatic sorting apparatus 100 does not continuously perform the middle circulation for a longer time than necessary, and cyclically repeats the middle circulation period (middle circulation ON) and the non-middle circulation period (middle circulation OFF).

FIG. 12 is a graph showing the relationship between the cycle time of middle circulation and the recovery rate / purity in the second embodiment.
The relationship between the middle circulation cycle time and the recovery rate / purity will be described below with reference to FIG.

  Experiments were performed by changing the middle circulation cycle time, and the relationship between the middle circulation cycle time and the recovery rate and purity of the collected ABS pieces was investigated. The plastic electrostatic sorter used in the experiment has the ability to process 180 kilograms of material 101 to be sorted per hour. FIG. 12 shows the results of this experiment.

First, the middle circulation period and the non-middle circulation period were switched every 45 minutes (cycle time: 45 minutes). As a result, the ABS piece could be recovered with high purity (99% or more) and recovery rate (about 90%).
Next, the middle circulation period and the non-middle circulation period were switched every 60 minutes (cycle time: 60 minutes). As a result, the ABS piece could be recovered with the same purity and recovery rate as the cycle time of “45 minutes”.
However, as a result of switching between the middle circulation period and the non-middle circulation period every 75 minutes (cycle time: 75 minutes), the purity and the recovery rate were lower than the cycle times “45 minutes” and “60 minutes”.

The reason why the recovery and purity are reduced is estimated as follows.
There is no problem in purity and recovery for a while after starting the middle circulation. However, if the middle circulation is continued, the “(4) plastic pieces that are difficult to be charged” described in the first embodiment will gradually increase, and after a certain period of time has passed since the middle circulation is started, on the charging feeder, in the charging cylinder and on the loading feeder. As a result, the ratio of “(4) plastic pieces that are difficult to be charged” increases. That is, it is estimated that the purity and the recovery rate are deteriorated because the number of plastic pieces that are difficult to electrostatically sort increases.

  Therefore, in the second embodiment, the middle circulation is stopped at an appropriate timing, and the plastic pieces in the middle collection box 141C are collected and removed in the flexible container 153C without being circulated.

In practical operation, it is desirable that the middle circulation cycle time is long. For example, in the case of FIG. 12, the desirable time as the cycle time of the middle circulation is “60 minutes”.
The optimum middle circulation cycle time is required for the processing capacity and structure of the plastic electrostatic sorting device, the ratio of “(4) plastic pieces that are difficult to be charged” contained in the material to be sorted 101, the partition position of the collection box 141, and the like. Varies depending on purity and recovery rate. The cycle time of the middle circulation should be determined according to a characteristic curve as shown in FIG. 12 for each plastic electrostatic sorter.

  The middle circulation period and the non-middle circulation period need not be the same time.

  In the second embodiment, for example, the following plastic electrostatic sorting apparatus 100 has been described.

A middle circulation system is adopted in which the plastic piece collected in the middle collection box is mixed with the material to be sorted in the pre-process (for example, on the charging feeder) of the charging cylinder.
However, middle circulation is not continuous, but is intermittently performed by alternately switching on and off.

  By appropriately selecting the middle circulation period and the non-middle circulation period and repeating the appropriately selected middle circulation period and the non-middle circulation period, the maximum recovery rate can be obtained while ensuring the prescribed purity.

  DESCRIPTION OF SYMBOLS 100 Plastic electrostatic sorting apparatus, 101 Material to be sorted, 111 Input stocker, 112 Dryer, 113 Input hopper, 114 Input feeder, 121 Charge cylinder, 122 Carry in feeder, 123 Feeder drive device, 131 Negative electrode, 132 Positive electrode, 133 Voltage control device, 141 collection box, 141A minus electrode side collection box, 141B plus electrode side collection box, 141C middle collection box, 142, 142A, 142B partition plate, 150 stock section, 151, 151A, 151B, 151C transport machine, 152 , 152A, 152B, 152C hopper, 153, 153A, 153B, 153C flexible container, 154 switching valve, 155 middle circulation transfer machine, 156 switching valve controller, 156A switching valve control signal, 159 Middle circulation hopper.

Claims (5)

A charging unit that is charged with a material to be sorted including a plurality of pieces to be sorted with different charging characteristics, and charges the plurality of pieces to be sorted included in the inputted material to be sorted,
An electrostatic separation unit having a pair of electrodes to which a predetermined voltage is applied, and drawing a plurality of pieces to be electrified by the charging unit and falling between the pair of electrodes to the electrode side according to the polarity of the pieces to be sorted When,
A collection box that is divided into a plurality of collection units and arranged below the pair of electrodes, and that collects a plurality of pieces to be sorted that have dropped between the pair of electrodes by the plurality of collection units,
An electrostatic sorting apparatus comprising: a circulating unit that puts a piece to be sorted collected in a predetermined collecting unit among the plurality of collecting units into the charging unit.   The circulation unit continuously executes a circulation process for putting the pieces to be sorted collected by the predetermined collection unit into the charging unit for a predetermined time, then stops the circulation process, and stops the circulation process, and then 2. The electrostatic sorting apparatus according to claim 1, wherein the sorted pieces collected in a predetermined collecting unit are removed.   The electrostatic circuit according to claim 2, wherein the circulation unit alternately repeats the circulation process and a non-circulation process of removing the pieces to be sorted collected by the predetermined collection unit after the circulation process is stopped. Sorting device. The electrostatic separation unit has a positive electrode to which a positive voltage is applied and a negative electrode to which a negative voltage is applied as the pair of electrodes,
The recovery box includes a positive electrode side recovery portion positioned on the positive electrode side, a negative electrode side recovery portion positioned on the negative electrode side, and between the positive electrode side recovery portion and the negative electrode side recovery portion. Divided into the middle collection department
The electrostatic sorting device according to any one of claims 1 to 3, wherein the circulation unit puts the pieces to be sorted collected in the middle collection unit of the collection box into the charging unit. The charging unit is charged with a material to be sorted including a plurality of pieces to be sorted with different charging characteristics, and charges a plurality of pieces to be sorted included in the inputted material to be sorted.
The electrostatic separation part has a pair of electrodes to which a predetermined voltage is applied, and a plurality of pieces to be sorted which are charged by the charging unit and fall between the pair of electrodes are arranged on the electrode side according to the polarity of the pieces to be sorted Draw to
The collection box is divided into a plurality of collection units and arranged below the pair of electrodes, and a plurality of pieces to be sorted dropped between the pair of electrodes are collected by the plurality of collection units,
The electrostatic sorting method, wherein the circulating unit puts the pieces to be sorted collected in a predetermined collection unit among the plurality of collection units into the charging unit.

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