JP2004188695A - Method for recycling waste polyolefins and system therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To recycle waste polyolefins in sorted and collected waste plastics as a regenerated processing raw material. <P>SOLUTION: Collected waste plastics are unpacked or cut to remove foreign matter and the waste plastics, from which foreign matter is removed, are crushed to separate and recover waste plastics by an air elutriation method. Waste polyolefins are sorted from the recovered waste plastics by a specific gravity sorting method and supplied to an extruder to extrude a molten strand on the surface of a belt conveyor. Water is sprinkled over the belt conveyor to solidify the surface of the strand and the solidified strand is taken over by a strand cutter to be continuously cut and pelletized. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method and a system for separating waste polyolefins from waste plastics widely separated and recovered from the general public and recycling them as raw materials for reprocessing. More specifically, a material recycling method for recycling waste polyolefins as a processing raw material for molded plastic products in order to recycle waste plastics such as containers and packaging except for PET bottles, which are mainly separated and collected from general households, and the method. About the system.
[0002]
In the present invention, the term "waste plastic" refers to a plastic excluding PET bottles belonging to "8" in the table described in Article 2 of the "Ministry Ordinance on Separated Collection of Containers and Packaging Waste" promulgated in 1995. The main object is, but not limited to, a waste plastic corresponding thereto, which means waste plastic containing waste polyolefins.
[0003]
[Prior art]
Recycling of waste plastics is broadly divided into thermal recycling, in which waste plastics are burned and recovered as an energy source, and material recycling, in which waste plastics are reused as substances. There are chemical recycling for recycling as raw materials, recycling and recycling for processing into piles and blocks by pressing and melting, and recycling for recycling as raw materials for pellets. At present, the recycling of waste plastics is mainly chemical recycling and recycling recycling. However, waste PET bottles are recycled again as processing raw material PET and are relatively economically molded as value-added products. ing.
[0004]
In addition to plastic bottles, households and other sources discard a large amount of plastics, such as polyolefins, polystyrene, polyvinyl chloride, and vinylidene chloride, and collect them as "other plastics". Since the collected waste plastic contains substances other than plastic, it cannot be used for material recycling as it is at the time of collection. However, high cost is required to separate foreign matter from waste plastics.Therefore, rough separation and washing may be performed, and high-level physical properties may not be required. In many cases, horticultural products that can be directly commercialized are reprocessed or recycled as blast furnace reducing agents.
[0005]
[Problems to be solved by the invention]
The conventional waste plastic recycling method as described above has a problem that the recycled product has a low added value and its use is limited, so that both quantity and quality cannot be expected so much in the future. However, if waste plastics are successfully economically recycled as raw materials for molding and processing, they can be advantageously reused as a wide range of products according to the demand at that time, and the prospect of full-fledged recycling will be bright .
[0006]
Incidentally, polyolefins such as polyethylene and polypropylene are all thermoplastic and have similar physical and chemical properties, are compatible, have a wide variety of uses, and are commonly used. Separating polyethylene and polypropylene contained in the waste plastic as polyolefins, and recycling them as practical molding materials as pellets of polyolefins, based on the judgment that waste plastic recycling is an important part, The present invention has been completed as a result of studying a means capable of easily, stably and economically separating waste polyolefins from collected waste plastics and pelletizing them.
[0007]
[Means for Solving the Problems]
As a means for solving the above-mentioned problems, the present invention is a method for separating and recycling waste polyolefins from waste plastic collected by separate collection, etc., wherein the collected waste plastic is unpacked or cut and mixed. The waste plastic from which the foreign matter has been removed is crushed, the waste plastic from which the foreign matter has been removed is crushed, and the waste plastic is separated and collected from the crushed waste plastic by an elutriation separation method, and the specific gravity separation method is used from the collected waste plastic. Waste polyolefins are separated, the separated waste polyolefins are supplied to an extruder, heated and melted, the molten strand is extruded onto a belt conveyor, and water is sprayed on the strands on the belt conveyor to solidify at least the surface of the strands The solidified strand is taken up by a strand cutter and continuously cut into pellets. It allows to provide a recycling method of waste polyolefins, which comprises recycling the waste polyolefins as reprocessed material.
[0008]
Further, the present invention is a system for separating and recycling waste polyolefins from waste plastic collected by separated collection and the like, wherein the A step of unpacking or cutting the collected waste plastic, unpacking and cutting are performed. B step of separating and removing foreign substances mixed in the waste plastic by hand and / or using a vibration sieve, and C step of crushing waste plastic from which foreign substances have been removed, and elutriation from the crushed waste plastic A process D for separating and collecting waste plastic by a dry gravity classifier using the principle of separation, a process E for separating polyolefins from the collected waste plastic by utilizing a specific gravity difference, and a separated waste polyolefin Are fed to an extruder, formed into a molten strand, extruded onto a belt conveyor, cooled by watering, and Providing a F solidifying the Portland surface, and G step of pelletizing by cutting the solidified strand, the recycling system of waste polyolefins, which comprises a.
[0009]
In step B of the waste polyolefin recycling system, the waste plastic mixed in the foreign matter separated under the vibrating sieve is separated, sent to the step C, and combined with the waste plastic from the step B, and crushed. can do. If necessary, in the step C, the crushing of the waste plastic may be performed in a plurality of steps. Preferably, the step B and / or the step C are provided with one or a plurality of magnetic separators / separators. , To separate the magnetic material.
[0010]
As the dry type gravity classifier used in the step D, an upflow type gravity classifier in which a U-shaped duct is connected in one or more stages, and the waste plastic is caused to fly by an ascending airflow and separate from sedimenting foreign matter, respectively, is suitable. . Further, it is preferable to provide a washing / dehydrating machine between the steps D and E to wash and remove foreign substances mixed in the waste plastic. In the E step of separating polyolefin from waste plastic by the above specific gravity difference, a continuous specific gravity separation tank using water as a medium is preferably used. Further, a washing / dehydrating machine may be provided between the steps E and F to thoroughly remove foreign substances mixed in the waste polyolefin. In order to smoothly supply the waste polyolefin to the extruder, a finishing crusher or a stock hopper may be provided between the washing / dehydrating machine and the F step.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
The basic flow of the waste polyolefin recycling method and the system according to the present invention is as follows. Except for PET bottles, waste plastic used for containers and packaging separated and recovered from the general public can be easily handled by unpacking or cutting. A process, and B process of separating and removing foreign substances such as sediment, bottles, paper bags, metal pieces, and the like mixed from the unpacked and cut waste plastics by simple means such as manual selection and / or vibration sieve. The waste plastic from which the foreign matter has been removed is crushed to a size suitable for elutriation, and the waste plastic is separated from the foreign matter by a dry gravity classifier using the principle of elutriation from the crushed waste plastic. A process D for collecting, and a process E for separating polyolefins from other waste plastics by utilizing a difference in specific gravity from the collected waste plastics. The waste polyolefins are fed to an extruder, formed into a molten strand, extruded onto a belt conveyor, cooled by watering, and solidified at least in the F step, and the solidified strand is cut and pelletized. G process.
[0012]
The present invention, in addition to the above basic steps, as appropriate according to the implementation conditions, for example, washing and dehydration step, adding a crushing step and a further separation step, rearranged before and after, by-pass route of the object, A circulation route can be provided. Further, the waste plastic that can be used as a raw material for reprocessing in the present invention is not limited to the above-mentioned waste plastic, and its generation source is not limited. Hereinafter, embodiments of the present invention will be described in detail sequentially with reference to specific examples for the above-described steps. FIG. 1 is a flowchart showing an example of a waste polyolefin recycling system according to the present invention, wherein A to G show the above-described steps. FIG. 2 to FIG. 4 are explanatory views illustrating the entire process in a divided manner.
[0013]
By the way, waste plastic excluding plastic bottles separately collected from general households and the like is usually compressed once in a bale and delivered to a recycling plant for recycling as a raw material for reprocessing. At the factory that receives the waste plastic bale 11, the waste plastic and the foreign matter are unpacked or separated using a hydraulic shear 12 or the like so as to be easily separated from the foreign matter, and then unraveled. Use a crusher if necessary.
[0014]
First, foreign materials such as earth and sand, glass, porcelain, metal, and the like that are mixed are roughly removed from the loosened collected waste plastic. Most of the waste plastics are containers and packages of a certain size, and therefore, a relatively small foreign matter such as earth and sand, glass pieces, ceramic pieces, metal pieces, etc. is separated using a vibrating sieve 13 or the like as a sieve under the sieve. The sieve is preferably about 30 to 100 mm.
[0015]
The waste plastic mixed under the sieve together with the foreign matter may be collected as required by, for example, the suction blower 14 or elutriation, and returned to an appropriate position in the process as waste plastic. In this example, the air is blown to the supply side of a secondary crusher 19 described later using the suction blower 14. Relatively large foreign matters such as glass bottles, caps, paper bags, and metals mixed into the waste plastic remain on the sieve together with the waste plastic containers and packaging. Remove by hand sorting. In addition, magnetic substances such as iron and magnetic steel mixed in may be separated and removed using a magnetic separator 16. As in the present embodiment, it is desirable to provide a plurality of stages before and after the conveyer 17 between the devices or before and after the crushers 18 and 19 in the next step, and to remove the iron and steel reliably.
[0016]
The roughly-sorted waste plastic is crushed by a crusher to a size suitable for elutriating and collecting the waste plastic in the next step, preferably about 10 to 50 mm on a side. If crushing is difficult at one stage, a plurality of crushers are used in series and crushed sequentially to a required size. In the present embodiment, a primary crusher (coarse crusher) 18 and a secondary crusher (fine crusher) 19 are used to perform crushing in two stages. As a crusher, a rotary cutter is preferred because waste plastics generally have a large ratio of film-based plastics.
[0017]
Next, the waste plastic is recovered from the crushed waste plastic so as not to contain foreign matter. For this recovery, a dry gravity classifier 20 utilizing the principle of elutriation is preferably used, and among them, an upward flow type gravity classifier of a U-shaped duct multi-stage type exemplified in FIG. 5 is preferable. A U-shaped duct type upward flow type two-stage gravity classifier will be briefly described with reference to FIG. This gravity classifier is constituted by two-stage cylindrical or rectangular ducts 51 and 52 whose trunks are curved in a U-shape. One of the upper ends of each duct is used as supply ports 53 and 54, and the supply port 53 of the preceding duct is used. Is connected to an outlet 56 for pneumatic waste plastic separated by a cyclone 55. The other upper end is connected to a suction side of a suction blower 59 as outlets 57 and 58 for separated waste plastic. Discharge ports 60 and 61 for separated heavy foreign substances are provided at the bottom of each duct, and gas intake ports 62 and 63 are further provided upstream of the foreign substance discharge ports 60 and 61, respectively. The supply port 54 is connected.
[0018]
By allowing a suitable amount of gas to flow into the ducts 51 and 52 from the gas inlets 62 and 63 by the suction blower 59, a gentle downward airflow is supplied to the supply ports 53 and 54 sides of the U-shaped ducts 51 and 52, and the suction blower 59. Create a moderate updraft on the side. The waste plastic in the ducts 51 and 52 rises by the ascending airflow, and foreign matters fall into the outlets 57 and 58 and are discharged from the outlet 61 through the outlet 60. The waste plastic is easily elutriated and collected.
[0019]
The above-mentioned upflow type gravity classifier can also be used for separating waste plastics and papers. Normally, waste plastic is discharged from the bottom outlet of the U-shaped duct and paper is discharged from the lower outlet of the cyclone via the upper outlet. The separation efficiency can be improved by assembling the U-shaped ducts in multiple stages.
[0020]
Since various types of plastics are mixed in the crushed waste plastic separated so as not to contain foreign matter, required waste polyolefins are separated from them. In this example, a continuous specific gravity separation water tank 21 using water as a separation medium is used, and a plastic whose specific gravity does not exceed 1 is separated by utilizing a specific gravity difference between plastics. Plastics separated as having a specific gravity of 1 or less are substantially polyolefins such as polyethylene and polypropylene which are thermoplastic and have similar properties such as processability and are compatible with each other and can be expected to be used as a raw material for molding. is there. Thermoplastic resins such as phenolic resin, unsaturated polyester resin and urea resin, polyvinyl chloride, PET (polyethylene terephthalate), methacrylic resin, and cellulose resin are separated and used separately as plastics having a specific gravity exceeding 1. You.
[0021]
The waste polyolefins separated by the difference in specific gravity are washed and dewatered by the washing and dehydrating machine 22 to be sent to the extruder 26, and then drained by using the centrifugal dehydrating machine 23 and the like. As the washing and dewatering machine 22, a vertical continuous washing and dewatering machine is suitable. If necessary, the waste polyolefins are crushed into small pieces by using a finishing pulverizer 24, for example, by preventing bridges and smoothing the supply to the extruder 26. It is also desirable to provide a hopper stocker 25 to stabilize the operation of the preceding and following processes and to cope with troubles. Waste plastic other than waste polyolefins having a specific gravity of more than 1 is separately processed and used.
[0022]
Next, the waste polyolefins are fed into a vented extruder 26, heated and melted, and formed into strands. Usually, waste polyolefins are often in the form of a film, have a low bulk specific gravity, and contain considerable moisture even after dehydration. Depending on the collected waste plastic and the preceding treatment method, when separated from waste plastic in containers and packaging and subjected to the treatment of the present invention, the separated polyolefin has a moisture content of about 20% by weight and a bulk specific gravity of about 20% by weight. It is often around 0.2. Therefore, for continuous molding of strands, a single- or twin-screw extruder with a high compression ratio and a vent, which can compress and melt bulky waste plastics and discharge the generated steam and decomposed vapors to the outside of the machine, can be used. Used.
[0023]
The polyolefin is heated, melted, kneaded, and defoamed while being sent to the tip in the vent type extruder 26, and is formed into a molten strand 27 through a porous die at the tip and extruded. It is preferable to mount a screen changer 27 for exchanging a clogged screen pack in the mounted state at the tip of the extruder 26 and upstream of the breaker plate. Since the supplied waste plastic contains a relatively large amount of solid foreign matter and is frequently clogged, it is effective for facilitating the replacement operation of the screen pack and continuing the continuous operation.
[0024]
In the present invention, the extruded molten strand 28 is discharged onto a net belt conveyor 29, and the strands on the belt conveyor 29 are cooled by spraying cooling water, and conveyed to a strand cutter 30 while solidifying the surface. There is no particular limitation on the method of spraying the cooling water. The cooling water is sprayed, and the cooling water is brought into contact with the strands in a shower shape or a water film shape, so that at least the strand surface is solidified. A net belt, usually a wire mesh, is used for the belt. By cooling the strands on the belt conveyor, it is possible to prevent the discharge of the strands caused by foreign matter mixing, replacement of the screen pad, mixing of multiple plastics, etc., and breakage due to rapid cooling after discharging. However, since the subsequently discharged strand is again fed on the belt, it is not necessary to stop the operation, and the operation can be performed continuously.
[0025]
Furthermore, the strand is taken up by, for example, a rotary blade type strand cutter 30 and fed onto a fixed blade, and while the cooling water is sprayed to cool the pellets and the cutting blade, the strand is continuously cut with the rotary blade, Re-pelletize. In addition, a guillotine cutter or the like can be used as the strand cutter. The strand to be cut is not solidified up to the core portion, and is advantageous in that the ratio of the strand that is not cut and crushed during cutting is smaller than that of the solidified strand.
[0026]
The cut pellets are dewatered by using a dehydrator, for example, a vertical continuous centrifugal dehydrator 31 to spray water accompanying the pellets, and further passed through a sorter loader 32 such as a continuous vibrating sieve to form a powdery plastic. Should be selected and removed to improve the commercial value of the pellets.
[0027]
【The invention's effect】
By utilizing the present invention, it is possible to separate polyolefins with extremely small amount of contaminants from the separated and collected waste plastic by continuous operation and to advantageously collect them as pellets of a raw material for reprocessing. Expected to contribute to the recycling of waste plastics economically [Brief explanation of drawings]
FIG. 1 is a flowchart showing an example of a waste polyolefin recycling system according to the present invention. FIG. 2 is an explanatory diagram (including steps A to C1) illustrating the entire process divided.
FIG. 3 is an explanatory view illustrating the entire process in a divided manner (including C2 to E processes);
FIG. 4 is an explanatory view illustrating an example in which the entire process is divided (optional process between E and F processes)
FIG. 5 is an explanatory view illustrating the entire process in a divided manner (including the F and G processes).
FIG. 6 is an explanatory view of an upward flow type gravity classifier of a U-shaped duct two-stage type
11: Bale 12: Hydraulic shear 13: Continuous vibrating sieve 14: Suction blower 15: Sorting belt conveyor 16: Magnetic separator 17: Conveying conveyor 18: Primary crusher 19: Secondary crusher 20: Dry gravity classifier 21: Continuous specific gravity separation water tank 22: Vertical continuous washing and dewatering machine 23: Centrifugal dewatering machine 24: Finishing crusher 25: Stock hopper 26: Extruder with vent 27: Screen changer 28: Melting strand 29: Net belt conveyor 30: Rotating blade type strand cutter 31: Vertical continuous centrifugal dehydrator 32: Sorter loader 33: Polyolefin pellet H: Heavy specific gravity waste plastic W: Foreign matter 51: Front U-shaped duct 52: Rear U-shaped duct 53: Front supply port 54: rear-stage supply port 55: cyclone 56: pneumatic waste plastic outlet 57: front-stage Plastic outlet 58: subsequent waste plastic outlet 59: suction blower 60: front foreign matter discharge port 61 :( below) foreign matter discharge port 62: front air intake 63: subsequent gas inlets

Claims (11)

A method of separating and recycling waste polyolefins from waste plastic collected by separated collection, etc., wherein the collected waste plastic is unpacked or cut, mixed foreign substances are removed, and the waste substances from which the foreign substances have been removed are removed. Plastics are crushed, waste plastics are separated and collected from the crushed waste plastics by elutriation, and waste polyolefins are separated from the collected waste plastics by a specific gravity separation method. Are supplied to an extruder, heated and melted, the molten strand is extruded onto a belt conveyor, water is sprayed on the strands on the belt conveyor to solidify at least the surface of the strands, and the solidified strands are drawn by a strand cutter and continuously The waste polyolefins are recycled by cutting Recycling method of waste polyolefins, characterized in that the recycling as a raw material. A system that separates and recycles waste polyolefins from waste plastic collected by separate collection, etc.
A step of unpacking or cutting the collected waste plastic;
B process of separating and removing foreign substances present in the unpacked and cut waste plastic by hand sorting and / or using a vibrating sieve;
C step of crushing waste plastic from which foreign matter has been removed;
D step of separating and collecting waste plastic from the crushed waste plastic by a dry gravity classifier using the principle of elutriation separation;
An E step of separating polyolefins from the collected waste plastic using a specific gravity difference,
An F step of supplying the separated waste polyolefins to an extruder to form a molten strand, extruding the belt onto a belt conveyor, cooling by watering, and solidifying at least the strand surface;
G step of cutting and pelletizing the solidified strand;
A recycling system for waste polyolefins, comprising: In the step (B), waste plastic mixed into the foreign matter separated under the vibrating sieve is separated, sent to the step (C), combined with the waste plastic from the step (B), and crushed. Item 4. A recycling system for waste polyolefins according to Item 2. 4. The waste polyolefin recycling system according to claim 2, wherein in the step C, the waste plastic is crushed in a plurality of stages. 5. The recycling system for waste polyolefins according to claim 2, wherein one or more magnetic separators are provided in the step B and / or the step C. As the dry type gravity classifier used in the step D, a U-shaped duct is connected in one or more stages, and an upflow type gravity classifier that separates waste particles by causing waste plastic to fly by an ascending airflow is used. The recycling system for waste polyolefins according to any one of claims 2 to 5, wherein: The waste polyolefin recycling system according to any one of claims 2 to 6, wherein a washing / dehydrating machine is provided between the steps D and E to remove foreign substances mixed in the waste plastic. . The waste polyolefins according to any one of claims 2 to 7, wherein a continuous specific gravity separation tank using water as a medium is used in the E step of separating polyolefin from waste plastic by the difference in specific gravity. Recycling system. The waste polyolefin according to any one of claims 2 to 8, wherein a washing / dehydrating machine is provided between the step E and the step F to remove foreign substances mixed in the waste polyolefin. Recycling system. The system for recycling waste polyolefins according to any one of claims 2 to 9, wherein a finishing crusher is provided between the steps E and F. The recycling system for waste polyolefins according to any one of claims 2 to 10, wherein a stock hopper is provided between the E step and the F step.

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