JP5272362B2 - Waste plastic grinding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for crushing waste plastics, in which waste plastics are pulverized efficiently into particles of &le;2 mm particle size and foreign matter such as metals and glass can be separated efficiently from the waste plastics. <P>SOLUTION: The method for crushing waste plastics comprises the steps of: heating and melting waste plastics; cooling the melted waste plastics to the temperature higher than room temperature to obtain a solidified material; and starting the crushing work at the temperature higher than the room temperature and not higher than 120&deg;C. It is preferable that foreign matter is removed from the crushed solidified material, a magnetic sorter and/or an eddy current sorter are used when foreign matter is removed from the crushed solidified material, and the crushed solidified material is sorted and separated into a large-sized portion and a small-sized portion, the foreign matter other than plastics is removed from the separated large-sized portion and the foreign matter-removed large-sized portion is crushed again. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a method for pulverizing waste plastics for reclaiming waste plastics to produce an ore reducing agent or a solid fuel.

  In recent years, methods for producing ore reducing agents, solid fuels and the like from waste plastics have been studied as one solution for effective use of waste plastics. This is because recycling industrial waste plastics and general waste plastics has attracted attention for effective use of resources and reduction of carbon dioxide generation. In addition, waste plastic (container and packaging waste plastics) that has been collected separately based on the Act on the Promotion of Separate Collection and Recycling of Containers and Packaging (Act No. 112 of 1995) (Container and Packaging Recycling Law) ) And recycling by recycling waste plastic (home electrical appliance waste plastic) collected separately based on the Act on Re-commercialization of Specified Household Appliances (Act No. 97 of 1998) (Home Appliance Recycling Law) Forming a type society is considered socially important.

  One important factor in producing ore reducing agents and solid fuels from waste plastics is to make the product particle size smaller than a certain level. The general use of ore reducing agents is to use heat, carbon monoxide, and hydrogen generated by partial oxidation of the reducing agent by reacting with oxygen or air to reduce the ore. Or it reacts with air and utilizes the generated heat, but since both are reactions of solid and gas, the smaller the particle diameter of the solid, the higher the reactivity. For this reason, for example, when coal is blown from the tuyeres of a blast furnace and used as an ore reducing agent in the steel industry, it is used after being pulverized and pulverized in advance. As the degree of pulverization, for example, the ratio of the particle size of 75 μm or less is 80 mass%.

  In general, there are many examples in which the particle diameter is about 2 mm or less in the range that can be regarded as fine particles sufficient as an ore reducing agent or a solid fuel. For this reason, various methods for finely pulverizing plastic to a particle size of 2 mm or less have been studied.

  The plastic pulverization methods are roughly classified into the following three types (a) to (c).

  (A) When plastic is pulverized by a pulverizer with a screen through which the pulverized material after pulverization is passed, the opening of the screen is reduced. Alternatively, the pulverized one is sieved and particles larger than the sieve opening are pulverized repeatedly.

  (B) The plastic is cooled with liquid nitrogen or the like and then crushed (for example, see Patent Document 1). For example, polypropylene is cooled to about 20 ° C. or less under zero and then pulverized. This utilizes the property that the impact strength rapidly decreases when the plastic is below the glass transition temperature. In addition, by cooling the plastic, an effect of preventing melting of the plastic due to shear heat generation during pulverization can be expected.

  (C) A plurality of types of plastics are melted and mixed, and the plastics are embrittled and then crushed (for example, see Patent Document 2). This method is more economical than other methods.

  As a method for finely pulverizing plastic, the above-described method (a) involves considerable difficulty to implement industrially. That is, unlike solid fuels such as coal and coke, plastics have extremely low pulverization properties, so that processing speed becomes extremely low when pulverizing to 2 mm or less. When a large amount of processing is attempted, heat cannot be pulverized, and heat is generated due to friction of the pulverizer. In some cases, the plastic melts. In order to solve such a problem, for example, a method of pulverizing plastic in a liquid such as water or oil is known (for example, see Patent Document 3).

In addition, methods for increasing the calorific value of the ore reducing agent and solid fuel produced were also studied. In other words, the amount of heat generated by plastics decreases due to the presence of metals such as iron, aluminum and copper mixed with waste plastics, and inorganic substances such as glass bottles and ceramics. The amount of heat generated per unit amount is increased by sorting and removing using a sorter or the like (see, for example, Patent Document 4).
JP 2001-252585 A JP-A-11-192469 Japanese Patent Laid-Open No. 4-332792 JP-A-8-47927

  However, with regard to the method (a), the method of pulverizing plastic in a liquid such as water or oil is not economical because a step of separating the liquid and the solid is required when producing a solid fuel.

  In the above-mentioned method (b), a large refrigerator is used to cool the plastic, or a cooling material such as dry ice or liquid nitrogen is required. Inferior.

  On the other hand, the method (c) described above is more economical than the other methods. In Patent Document 2, fine plastic powder can be obtained by heat-treating plastic at a temperature of 150 ° C. or higher, removing low-boiling components, cooling and solidifying, and then grinding. For this method, further efficiency is desired.

  On the other hand, regarding the method for removing foreign matter from waste plastic, it is necessary to efficiently separate the foreign matter from the plastic. As a method for separating metal from waste plastic, a method using a magnetic separator and an eddy current separator in combination as described in Patent Document 4 is also known, but it is only a simple combination of conventional methods, It's not efficient. In the conventional separation method, for example, when the waste plastic is roughly crushed to about 10 cm as is generally done, and then magnetic separation is performed, even the plastic caught in the iron is removed, so that the removal efficiency is low. There is.

  Accordingly, an object of the present invention is to solve such problems of the prior art and to provide a method for efficiently pulverizing plastic to a particle size of 2 mm or less. A further object of the present invention is to provide a method for pulverizing waste plastic that can efficiently separate foreign substances such as metal and glass from waste plastic.

  In order to solve such problems, the present inventors have conducted intensive studies. Once waste plastic composed of various kinds of plastics is heated, melted, dechlorinated, and cooled and solidified, the grindability is remarkably improved due to the difference in thermal shrinkage of each plastic. A plastic fine powder having a diameter of 2 mm or less can be obtained. The technical point is how to put the solidified plastic into the pulverizer, and it has been found that it is most effective to perform fine pulverization after coarse pulverization. In addition, it is clear that plastic and foreign matter can be easily separated even after heat melting, dechlorination, and cooling solidification treatment due to poor compatibility of the interface between the foreign matter contained in the waste plastic and the plastic. became. Furthermore, since foreign matter is inferior in pulverization compared to plastic, it is also clear that a higher proportion of foreign matter is mixed in the mixture after pulverization larger than a predetermined particle size separated by sieving after pulverization. It was. Furthermore, it became clear that the grindability of the waste plastic subjected to the heat-melting treatment hardly changes as long as it is below the temperature at which the plastic starts to melt.

From the above, the features of the present invention, which is a method for efficiently pulverizing waste plastic, are as follows.
(1) When waste plastic is heated and melted and cooled to obtain a solidified body, when the solidified body is pulverized, the pulverization is started at a temperature exceeding room temperature and 120 ° C. or less without performing the cooling to room temperature. A method for pulverizing waste plastic.
(2) The waste plastic grinding method according to (1), wherein foreign matters are removed from the solidified body after grinding.
(3) The method for pulverizing waste plastic according to (2), wherein the removal of foreign matters from the solidified body after pulverization is performed using a magnetic separator and / or an eddy current separator.
(4) The pulverized solidified material is classified, separated into a solidified material having a large particle size and a solidified material having a small particle size, and foreign substances other than plastic are removed from the solidified material having a large particle size, and then pulverized again. The waste plastic grinding method according to (2) or (3), wherein the treatment is performed.

According to the present invention, it is possible to produce a low-cost and non-polluting solid fuel and a solid reducing agent using waste plastic as a raw material. In addition, since it is possible to convert plastic containing chlorine-containing plastic into a plastic processed product that does not substantially contain chlorine, the processed plastic product obtained by the present invention can be used in a blast furnace, boiler, kiln, cupola, coke oven, etc. When used as a solid reducing agent, solid fuel, or raw material, chemical erosion of the inner wall refractory of the furnace by chlorine or a chlorine compound can be prevented. Further, by treating the waste plastic using the waste plastic grinding method of the present invention, a large amount of waste plastic can be economically implemented.

  The present invention relates to waste plastics and container packaging materials contained in municipal waste, industrial waste, general waste, etc., and waste plastics generated in the process of dismantling electrical products, automobiles, etc. The solidified material is pulverized to produce a solid fuel or ore reducing agent. At that time, foreign substances contained in the waste plastic can also be removed. In particular, it is most suitable as a foreign matter removal method when a chlorine-containing plastic such as PVC or polyvinylidene chloride is heated and melted and simultaneously subjected to heat dechlorination.

  In the present invention, the waste plastic is cooled after being melted by heating to obtain a solidified body, and when the solidified body is pulverized, the cooling is usually performed to room temperature, and the temperature is higher than room temperature and 120 ° C. or lower. Start grinding. Here, the temperature of the solidified body is a temperature at the highest temperature portion of the solidified body (a material to be crushed) before pulverization that is a lump, and the center temperature of the solidified body is usually used. By pulverizing at a higher temperature than in the past, the waste plastic can be finely pulverized, and the waste plastic can be pulverized more efficiently. In addition, foreign matter can be removed even from plastic that has been finely pulverized at a higher temperature than before. By removing foreign matter from the above pulverized product, foreign matter is less likely to be caught in the plastic and more efficiently. Foreign matter removal can be performed. The temperature at the time of pulverization is preferably 40 ° C. or more at the center of the solidified body.

  In the present invention, by setting the temperature at which pulverization is started after cooling to be higher than before, the required heat removal amount can be reduced, and as a result, the throughput can be increased if the same cooling device is used. Can be improved. Alternatively, an inexpensive cooling device having a smaller capacity can be used. The pulverization start temperature is effective as long as it exceeds room temperature, but is preferably 80 ° C. or higher in order to sufficiently improve productivity.

  FIG. 1 shows an example of the change in the center temperature when water is used to cool the molten plastic, whereas it takes 300 seconds (indicated by Y in FIG. 1) or more to cool to room temperature (25 ° C.). If it is cooled to 80 ° C., it takes about 150 seconds (indicated by “X” in FIG. 1), and the cooling can be completed in half or less of the time for cooling to room temperature. The fact that the residence time for the cooling process is halved means that the processing amount per unit time can be doubled, and the productivity can be improved.

  The removal of the foreign matter is preferably performed using a magnetic separator and / or an eddy current separator. Foreign matter of magnetic substances can be removed with a magnetic separator, and aluminum and copper can be removed with an eddy current separator. In particular, aluminum is spheroidized in the melting process of waste plastic, and the separability by the eddy current sorter is improved, so that the separation efficiency is remarkably increased as compared with the separation from simply crushed plastic.

  Foreign matter is removed by classifying the solidified material after pulverization using a sieve or the like to separate it into a solidified material having a large particle size and a solidified material having a small particle size, and then the foreign material other than plastic from the solidified material having a large particle size. It is particularly effective to carry out the removal. This is because, as described above, foreign matters are mixed at a higher rate in the solidified body after pulverization having a large particle size. Thereby, foreign matter removal can be performed with high removal efficiency. The solidified body having a large particle diameter from which foreign substances have been removed is preferably subjected to pulverization again to produce a pulverized waste plastic. The temperature of the solidified body when the pulverization process is performed again may be room temperature.

  The pulverization of the solidified body is preferably performed by two-stage pulverization using a coarse pulverizer and a fine pulverizer, followed by fine pulverization after coarse pulverization. It is important to pulverize the solidified body with a coarse pulverizer in advance to a size that can be charged into the fine pulverizer. Alternatively, it is also efficient to produce a solidified body having a size that can be directly put into a pulverizer. When fine pulverization is performed after coarse pulverization, the coarse pulverization is preferably performed at room temperature and 120 ° C. or less, and the fine pulverization is preferably performed at room temperature.

  Therefore, the waste plastic grinding equipment is equipped with a coarse pulverizer and a fine pulverizer in the pulverization process, and further equipped with at least one of a particle size classifier, a magnetic separator, and an eddy current separator. Preferably there is. The particle size classifier is a device for separating the solidified material after pulverization by sieving or the like, and the magnetic separator and the eddy current separator are devices for removing metal foreign substances from the solidified material after pulverization.

  In the following, an embodiment of the present invention is described in I.D. This will be described in more detail in the order of plastic, II. Heating and melting step, III. Cooling and solidifying step, IV. Crushing step, and V. aluminum removing step.

  [I. Plastics] Plastics that are the subject of the present invention, that is, the raw material plastics in the present invention include waste plastics and container packaging materials contained in municipal waste, industrial waste, general waste, etc., and the process of dismantling electrical products, automobiles, etc. Waste plastics generated in the above are exemplified. Moreover, a container packaging waste plastic and a household appliance waste plastic can be used.

  Specifically, polyolefins such as polyethylene and polypropylene, polyvinyl chloride, polyvinylidene chloride, chlorinated polyethylene, polystyrene, polyethylene terephthalate, polycarbonate, nylon, and other thermoplastic resins and thermosetting resins are all applicable. Only one of the plastics can be used, or two or more can be used.

  The shape of the plastic to be heat-treated may be roughly pulverized, and a size of about 10 cm square is sufficient. For general waste plastic, it is not necessary to pulverize again, and it is processed in the recovered state. Yes, film, sheet, and fiber plastics can be processed as they are. Of course, it may be finely pulverized, but the processing cost increases accordingly.

  [II. Heat-melting step] Examples of the heat treatment step include the following steps. That is, for example, waste plastic is heated and melted in a temperature range of 200 to 400 ° C., more preferably 250 to 340 ° C. in a reactor or an extruder, and dechlorination is performed when the waste plastic contains chlorine. . The treatment may be a batch type or a continuous type. An intermediate type such as batch switching may also be used.

  The treatment time is suitably 1 minute to 30 hours. When the treatment time is less than 1 minute, it becomes difficult to control the temperature in the reactor, and the dechlorination rate of the plastic treated product is lowered. Moreover, when processing time exceeds 30 hours, processing efficiency falls and it is not economical.

  A heat medium can be allowed to coexist in the heat melting treatment.

  [III. Cooling and solidifying step] The molten plastic after the heat treatment is cooled and solidified by a suitable cooling method to a temperature sufficient to solidify (solidify). In the present invention, it is only necessary that the temperature of the solidified body can be cooled to 120 ° C. or less, and without providing a special cooling step, for example, molten plastic extruded from an extruder can be pulverized almost immediately after extrusion. is there. For example, when waste plastic including container packaging waste plastic is melted and solidified, the center temperature after cooling may be controlled to be 120 ° C. or lower.

  When using a cooling and solidifying device, the molten plastic is quantitatively supplied to the belt cooler by a molten plastic conveying device, and the cooling and solidifying method is performed. The molten plastic is extruded from a hole (die) of several mm to several tens mm, It can be carried out by a so-called hot cut method in which the material is cut in a molten state and poured into water, or by a method in which it is poured as it is into a jacketed jacket capable of flowing a cooling medium and cooled in the vessel.

  What is important here is to set the size of the solidified body after cooling to a size that can be charged into a coarse pulverizer or a fine pulverizer.

[IV. Grinding step] The solidified body that has undergone the cooling and solidifying step is pulverized so as to have a predetermined particle size. The pulverization of the processed plastic product, which is a cooled and solidified product obtained by the above-described method of the present invention, can be performed very easily as compared with the pulverization of untreated plastic. In the present invention, the solidified body is not cooled to room temperature, and pulverization is started at a temperature exceeding room temperature and 120 ° C. or less. Thus, productivity improves by grind | pulverizing before a solidified body is cooled completely.

  In general, the input port of the pulverizer is limited to some extent by the size of the pulverizer body, and when the pulverized product has a long shape like a clothes basket, the raw material may be scattered at the same time as the pulverization. Further, the smaller the size of the raw material before pulverization, the smaller the work required for fine pulverization. In general, the pulverizer has a good R / r <20 as the relationship between the average particle diameter (R) of the original raw material and the average particle diameter (r) of the product. In the above example, a plate-like crushed product is obtained when cooled and solidified with a belt cooler, and after this is roughly pulverized to about 15 to 25 mm, it can be pulverized to about 1 mm or less. It is also possible to directly obtain a solidified body of about 15 to 25 mm by a hot cut method and directly pulverize it.

Coarse pulverization and fine pulverization can be performed by any type of pulverizer. For example, a jaw crusher, a roll crusher, a jet mill, a hammer mill, a ball mill, and a centrifugal mill can be used. Examples of a fine pulverizer capable of directly pulverizing a solid of about 15 to 25 mm include an ultra rotor (manufactured by Eckering (Germany)), a new microcyclomat (manufactured by Masuno Seisakusho), and the like. A schematic diagram of the pulverization principle in these pulverizers is shown in FIG. FIG. 2 shows an example of an ultra rotor in which a vortex 12 is generated between the rotating blade 11 and the casing, and the plastic solidified body 13 is crushed by collision and self-destruction in the vortex. It is characterized by little temperature rise due to airflow crushing. The particle size after pulverization varies depending on the type of product, but it is preferably 10 mm or less as a size capable of effectively separating aluminum after pulverization.

  [V. Foreign matter removing step] Foreign matter other than plastic is removed from the solidified body after pulverization. Aluminum that is granulated in the process of heating and melting and solidifying the plastic is separated from the plastic by an eddy current sorting method. At this time, a magnetic body and other foreign matters can be effectively removed by combining magnetic force sorting and wind force sorting. Eddy current sorting is a method of separating metals such as aluminum, copper, and zinc by flipping them off by electromagnetic induction force when eddy currents are generated. Magnetic sorting is performed by using magnets such as iron. This is a method for separating materials. In addition, the wind sorting is a technique for separating a pulverized solidified plastic having a specific gravity of approximately 1 from glass / ceramics having a specific gravity of 1.2 or more by utilizing a difference in specific gravity or a difference in shape.

  It is effective for improving the sorting efficiency to classify and remove the finely pulverized product with an appropriate sieve before removing the foreign matter.

  Hereinafter, the present invention will be described more specifically based on examples.

  [Pellet production method] After pulverizing municipal waste packaging plastic collected in Sakai City, Kanagawa Prefecture to about 1 cm, 10 kg of contents with water-sealed spill tube 1, heating device 2, and stirrer 3 shown in FIG. The reactor 4 having a volume of 50 liters was charged and treated at 320 ° C. for 1 hour to carry out heat melting and dechlorination treatment. The pH of the water seal water 5 was 2 or less, and chlorine ions were detected.

  Thereafter, the contents 6 are extracted from the extraction valve 7, the contents are poured into a plurality of depressions in a commercially available iron plate for takoyaki, a thermometer is set in the center of one of the depressions, and a predetermined temperature is set while cooling by water cooling. After reaching temperature, it was removed. This hemispherical waste plastic mass is called "processed waste plastic pellet". The melting point of the waste plastic was about 115 ° C., and when the central part was cooled below the melting point, the treated waste plastic pellet was completely solidified.

[Invention Example 1]
In the above-described pellet manufacturing method, a predetermined temperature for stopping cooling (hereinafter referred to as “cooling stop temperature”) is set to 100 ° C., and “processed waste plastic pellets taken out in a state where the central portion reaches 100 ° C. Was put into a cutter mill type pulverizer manufactured by Horai Iron Works, which was fitted with a sieve having an opening of 2 mm (circular hole) at the discharge port portion, and pulverized for about 1 hour. About 3.8 kg of pulverized product having an average particle diameter of 1.02 mm was recovered. When this pulverized product was pulverized by a Hosokawa Micron pulverizer ACM pulverizer (ACM-10A type) at a hammer rotation speed of 6800 rpm and a classifier rotation speed of 750 rpm, almost the entire amount was pulverized to a particle size of 1.2 mm or less. It was 0.2 mm.

  [Comparative Example] In the above-described pellet manufacturing method, a “processed waste plastic pellet” taken out in a state where the cooling stop temperature is 5 ° C. and the central portion has reached 5 ° C. is a sieve having an opening of 2 mm (circular hole). Was put into a cutter mill type pulverizer manufactured by Horai Iron Works, which was attached to the discharge port portion, and pulverized for about 1 hour. About 3.8 kg of pulverized product having an average particle diameter of 0.98 mm was recovered.

  [Invention Example 2] The “processed waste plastic pellets” taken out in a state where the cooling stop temperature is 46 ° C. and the center portion reaches 46 ° C. in the above-described pellet manufacturing method has an opening of 2 mm (circular hole). This was put into a cutter mill type pulverizer manufactured by Horai Iron Works, which was fitted with a sieve at the discharge port, and pulverized for about 1 hour. About 3.8 kg of a pulverized product having an average particle diameter of 1.01 mm was recovered.

  [Invention Example 3] The “processed waste plastic pellets” taken out in a state where the cooling stop temperature is set to 60 ° C. and the center portion reaches 60 ° C. in the above-described pellet manufacturing method has an opening of 2 mm (circular hole). This was put into a cutter mill type pulverizer manufactured by Horai Iron Works, which was fitted with a sieve at the discharge port, and pulverized for about 1 hour. About 3.8 kg of pulverized product having an average particle diameter of 1.02 mm was recovered.

  The results of Invention Examples 1 to 3 and Comparative Example are shown together in FIG. According to FIG. 4, it is clear that the average particle diameter after pulverization hardly changes even when the temperature of the object to be pulverized (“treated waste plastic pellet”) is changed. In the graph of FIG. 4, the area indicated by the diagonal line on the right side indicates an area where pulverization is impossible because the waste plastic is fused to the pulverizer.

  The average particle size is the mass fraction of each of the following four fractions obtained by the classification test in the following formula (b) obtained by modifying the following formula (A) (Rosin-Rammler-Bennet formula). And the diameter of the sieve mesh was substituted, and the proportional constants n and b in the following equation (b) were calculated by the least square method.

  The classification test is carried out using sieves with a mesh size of 2.0 mm, 1.18 mm, and 0.6 mm. (A) 2.0 mm above sieve, (B) 2.0 mm below sieve, and 1.18 mm sieve It was divided into four fractions (A) to (D): (C) 1.18 mm below sieve and 0.6 mm above sieve, (D) 0.6 mm below sieve.

R (Dp) = 100 · exp {− (Dp / De) ⁿ } (i)
log {log [100 / R (Dp)]} = n · logDp + log (b) (b)
In the above formulas (a) and (b), R (Dp) is the mass% on the integrated sieve of the sieve mesh Dp, De is the particle size characteristic number [R (Dp) is the number corresponding to mass%], and n is an equal number ( Index for evaluating the uniformity of the particle size distribution of the granular material), b is a constant and indicates an index for evaluating the fineness of the granular material.

  From the obtained n and b, D50 (50% passing sieve diameter) was calculated, and the average particle diameter was calculated.

The graph which shows an example of the change of center temperature at the time of water-cooling a molten plastic. The schematic diagram of the grinding | pulverization principle in a grinder. Schematic of a waste plastic heating and melting apparatus. The graph which shows the relationship between cooling stop temperature and an average particle diameter.

Explanation of symbols

1 Water-sealed outflow pipe 2 Heating device 3 Stirrer 4 Reactor 5 Water-sealed water 6 Contents (waste plastic)
7 Extraction valve
11 rotating blades
12 eddy currents
13 plastic solidified body

Claims (4)

Cooling the waste plastics after heating and melting a solid material, when pulverized solid embodying, the cooling, and ends at the time less than half the time to cool down to room temperature, the milling at a temperature of 120 ° C. A method for pulverizing waste plastic, characterized by starting.   2. The method for pulverizing waste plastic according to claim 1, wherein foreign matters are removed from the pulverized solidified body.   The method for pulverizing waste plastic according to claim 2, wherein the removal of the foreign matter from the solidified body after pulverization is performed using a magnetic separator and / or an eddy current separator.   The crushed solidified material is classified, separated into a solidified material having a large particle size and a solidified material having a small particle size, and after removing foreign matters other than plastic from the solidified material having a large particle size, the pulverizing treatment is performed again. The method for pulverizing waste plastic according to claim 2 or claim 3, wherein:

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