JP2009293032A - Method for thermal decomposition of waste plastics - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new technology overcoming disadvantages of the conventional methods used in producing high density plastic particles from waste plastics and carbonizing them in a coke oven. <P>SOLUTION: The method for obtaining fuel gas, liquefaction products and cokes includes: blending ≤5 mass% of the plastic particles having no holes or cracks passing through from the surface to the inside, a bulk density of 0.85-1.1 g/cm<SP>3</SP>and a volume of 6,000-200,000 mm<SP>3</SP>, based on 100 mass% of coal; and then carbonizing in a coke oven. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for forming a plastic having a high density into waste plastic such as waste plastic generated in a plastic processing step or used container packaging plastic. In addition, as a method of recycling, the present invention relates to a method of obtaining a fuel gas, an oily product, and coke by performing a carbonization process in a coke oven.

  Conventionally, waste plastics and used plastics generated in the plastic processing process, hereinafter referred to as waste plastics, have been incinerated or disposed of in landfills. As a result, in the case of incineration, the incinerator was damaged due to high-temperature combustion in the furnace, and problems such as generation of dioxins were caused by the reaction of mixed chlorine and generated hydrocarbons. . Also, in the landfill treatment, the plastic does not rot and the soil does not solidify, so that there is a problem that the utility value of the land is low.

  As countermeasures, various plastic recycling processes have been implemented. For example, although plasticization or gasification of plastic is performed, there is a problem that the processing cost is high. On the other hand, carbonization of plastics in a coke oven is an economical method that can be recycled in large quantities. In coke ovens, coke can be recovered along with fuel gas and oily products. This is also an excellent method.

  The carbonization method is a method in which waste plastic is mixed with coal, placed in a coke oven, and carbonized at about 1200 ° C., for example, a method described in Patent Document 1. Depending on the type of plastic used, about 15-20% of the plastic used is coke, about 25-40% is liquefied, and about 40% is coke oven gas (a gas mainly composed of hydrogen and methane). become. Coke derived from plastic is discharged from a coke oven in a state mixed with coke derived from coal, and is used as a reducing agent or fuel in a blast furnace, an alloy iron manufacturing process, or the like.

  The method of carbonizing plastic in a coke oven is an effective means for economically recycling plastic. However, there was a problem with the quality of the coke produced because there was no precise knowledge of the relationship between the method of using plastic and the coke quality. For example, in the means for recovering a large amount of gas and tar using the technique described in Patent Document 2, there is no consideration of coke quality, and when a large amount of plastic is mixed, the strength of coke produced under these conditions decreases. Has occurred. Incidentally, since coke is used in large facilities such as blast furnaces and cupolas, it is necessary to withstand the load conditions in these furnaces, and high strength is required, and deterioration of coke strength is an important quality problem. It was.

  When recycling used plastic generated at home, etc., it is used as a recycled material by separating the garbage to be mixed. In this case, foreign matter is often mixed, and as much as 10% of ash is mixed. It was also a problem to do. As a result, there were problems due to poor moldability, poor shape of the granular material, and low apparent specific gravity.

  In order to solve this problem, as described in Patent Document 3, it is described that waste plastic particles having a predetermined size and high density are mixed with coal and the mixture is subjected to dry distillation. Has been. It is described that it is preferable to use a high-density plastic granular material having an apparent density of 0.4 to 0.95 kg / liter. Thus, the improvement by the method of making the density of the waste plastic granular material high conventionally has been performed.

JP 48-34901 A Japanese Patent Laid-Open No. 8-157734 JP 2000-372017 A Japanese Patent Laid-Open No. 05-77301

  Thus, in the recycling of plastics in a coke oven in the prior art, a method of mixing waste plastic granular material with high density as described in Patent Document 3 with coal and using it in a coke oven has been performed. It was. In this method, waste plastic is not melted and molded, so the area around the cut surface is always fuzzy, and due to the influence of this part, the bulk density (the total volume of the granular material is divided by the space volume occupied by the granular material group). Value) declined, and the problem was that the flow of particulate matter was poor. As a result, there has been a problem that the granular material is bridging and cannot be cut out from the storage tank. In addition, the fuzzy part is separated from the main body, and there is a problem that much powder is generated.

In addition, the apparent density (the value obtained by dividing the mass of a single granular material by its volume) is generally 0.6 to 0.7 g / cm ³ , and 0.8 g at maximum. / Cm ³ or so. Further, it could not be increased to 0.95 g / cm ³ or more by a special method such as by using a nozzle having a small diameter of 3 to 5 mm. As a result, there is a limit to the good effect of densification on coke production, and further densification has been demanded.

  As a result, although the advantage of densifying the waste plastic granular material was understood, the sufficient result was not necessarily obtained. Therefore, a new technique for solving these problems has been demanded. Therefore, the present invention solves the above-mentioned problems, and when a high-density plastic granular material is produced from waste plastic, and this is carbonized in a coke oven, a new technique that overcomes the disadvantages of the conventional method is required. It was.

  On the other hand, a method for producing a high-density plastic product by making a part of plastic species into a molten state and extruding it from a nozzle has been conventionally performed. For example, as in Patent Document 4, there has been a method of injecting and injecting plastic into a mold. Although this method can produce high-density plastic moldings, there are problems such as low production speed and high costs due to the need to produce molten plastic by pressing it into the mold. It was inappropriate as a means to do. Accordingly, there has been a demand for a method that is suitable for waste plastic processing, can be processed at high cost and at low cost.

  The present invention has been made to solve such problems, and the contents thereof are as described in (1) to (7).

The present invention
(1) Plastic granules that do not have holes or cracks that penetrate from the surface to the inside, have an apparent density of 0.85 to 1.1 g / cm ³ , and a volume of 6000 to 200,000 cubic mm are used as coal. Waste plastic pyrolysis method characterized by mixing and dry distillation in a coke oven,
(2) The single maximum length of pores existing inside the plastic granular material is not more than a value of 1/3 of the volume of the plastic granular material, and the single volume of pores is the volume of the plastic granular material. The waste plastic pyrolysis method according to (1), characterized in that the plastic granular material, which is 10% or less, is mixed with coal and carbonized in a coke oven,
(3) A temperature of 180 to 260 ° C. in a molding apparatus for extruding waste plastic from a nozzle, which is a mixture of a plurality of types of plastics and contains a total of 50% by mass or more of a thermoplastic resin selected from polyethylene, polypropylene, and polystyrene. And after the gas in the device is sucked, it is compressed by extrusion from the nozzle, then cut and cooled with a water-cooling device. (1) or (2), the method for pyrolyzing waste plastics,
(4) A temperature of 180 to 260 ° C. in a molding apparatus that extrudes from a nozzle a waste plastic that is a mixture of a plurality of types of plastics and contains a total of 50% or more of a thermoplastic resin selected from polyethylene, polypropylene, and polystyrene. And, after the gas in the apparatus is sucked, it is compressed by extrusion from a nozzle having a diameter of 15 to 60 mm, then cut and cooled in a water-cooling apparatus within 3 seconds to produce plastic granulation The method for pyrolyzing waste plastics according to (1) or (2), wherein the product is mixed with coal and carbonized in a coke oven,
(5) Waste plastic containing a total of 50% or more of thermoplastic resins selected from polyethylene, polypropylene, and polystyrene, and containing chlorine at a ratio of 5% or less in terms of chlorine content. The waste plastic containing the plastic is gas-sucked by an exhaust device that is depressurized to 0.1 to 0.35 atm. The method for pyrolyzing waste plastics according to (1) or (2), characterized in that a plastic granulated product produced by cooling with a water cooling device is mixed with coal and subjected to dry distillation in a coke oven,
(6) The surface temperature of 80 ° C. within 2 seconds after the water cooling of the lump of waste plastic extruded from the nozzles of (3) to (4) is melted in a water cooling device. The waste plastic pyrolysis method according to (1) or (2), wherein the plastic granulated product produced by cooling is mixed with coal and subjected to dry distillation in a coke oven,
(7) The waste plastic pyrolysis method according to any one of (1) to (6), wherein a mixing ratio of plastic particulates to coal is 5% by mass or less,
It is about.

  According to the present invention, it is possible to economically produce a plastic granule having a high density and less powdering. Moreover, since the granular material manufactured in the method demonstrated above is a thing about 1.2 to 1.5 times higher in density than the thing by a prior art, even if it is the recycle process of the same conditions, it is to a coke oven. Even when the addition ratio is 1.2 to 1.5 times, the productivity of the coke oven is not deteriorated.

It is a figure which shows the whole structure of the equipment which processes waste plastics. It is a figure which shows one example of the waste plastic molding apparatus which implements this invention. It is a figure of the water-cooling apparatus which cools the lump of the waste plastics which has the fluidity extruded from the shaping | molding apparatus used in order to implement this invention. It is a figure which shows the internal structure of the granular material manufactured by this invention. It is a figure which shows the structure and contents of the carbonization chamber of a coke oven. It is a figure which shows the result of having investigated the relationship between the intensity | strength of the coke obtained from the mixture which mixed the granular material of various volumes with coal, and a granular material mixing ratio.

  Waste plastic is a mixture of multiple types of plastic pieces. As raw materials, containers and packaging discharged from households, daily plastic waste plastics, and miscellaneous waste plastics discharged from factories are common. These waste plastics are a mixture of various plastic pieces, and the raw material contains 50% by mass of a heat-softening resin such as polyethylene, polypropylene, and polystyrene. However, if the entire amount is in a molten state, problems such as severe fusion during molding and the problem that large pores remain in the molded body occur. Therefore, the maximum ratio is preferably 90% by mass. In addition, the waste plastic has a maximum length of about 50 mm or less, which facilitates the molding process. Therefore, it is desirable to perform the molding process after the crushing process.

  Generally, since foreign matter is mixed in waste plastic, it is preferable to perform an operation for removing the foreign matter before or after crushing. In order to prevent deterioration of the extrusion characteristics at the time of molding, the amount of the inorganic substance mixed is preferably 5% by mass or less. However, it is practically difficult to set the amount of inorganic matter to 0.5% by mass or less, and it does not affect the extrusion characteristics at the time of molding. The meaning is small. Therefore, a particularly desirable inorganic range for the present invention is 0.5 to 5% by mass.

  FIG. 1 shows the configuration of a waste plastic treatment facility suitable for performing these operations. The waste plastic as a raw material is cut into a size of 10 to 50 mm or less by the crusher 3 after the inorganic substance is removed by the vibration sieve 1 and the magnetic separator 2. The cut plastic piece is supplied to the molding apparatus 4 and molded. This is cooled to room temperature by the cooling device 5 to obtain a granular material.

  An example of a suitable molding apparatus for carrying out the present invention is shown in FIG. The molding device 4 includes a supply port 6, a casing 7, a push screw 8, an end plate 9, a nozzle 10, an electric heating element 11, a motor 12, a vacuum pump 13, an exhaust pipe 14, and a cutter 15. The pushing screw 8 is rotated in the direction of extruding the plastic from the nozzle 10 by the rotational force of the motor 11. Waste plastic pieces are put into the casing 7 through the supply port 6. Inside the casing 7, the waste plastic piece is pushed and compressed by the push screw 8. Using the frictional heat generated at this time and the electric heating element 11, the temperature of the waste plastic is raised to 180 to 260 ° C. At this temperature, a heat softening resin such as polyethylene, polypropylene, and polystyrene is dissolved. Polyethylene, polypropylene, polystyrene and the like are preferably 50% by mass or more. Below this ratio, there is a problem that the melted portion is reduced and adhesion at the time of molding is deteriorated. However, if the ratio of polyethylene, polypropylene, polystyrene, etc. exceeds 90% by mass, the nozzle resistance of the molding apparatus decreases and the force to compress the plastic decreases, so 90% by mass or less is desirable.

  The temperature of the waste plastic in the molding apparatus is 180 to 260 ° C. The temperature of this waste plastic is determined according to the blending ratio of each component of the plastic. When the ratio of the heat softening resin is high, or when the blending ratio of the low melting point polyethylene is large among the heat softening resins, about 180 to 200 ° C. Keep the temperature low. Moreover, when the ratio of a heat softening resin is low, or when there are many compounding ratios, such as a high melting point polypropylene, it is set as about 200-260 degreeC high temperature.

  When the temperature is lower than the above temperature, the viscosity of the plastic is high, it is difficult to mold, and the gas component that has entered the compressed plastic is difficult to escape, so that the density after molding does not increase. That is, when the temperature is lower than 180 ° C., even if a large amount of low-melting polyethylene is present, there is a problem that the liquid portion is small and the density does not increase. Further, when the temperature exceeds 260 ° C., which is higher than the above temperature, gas is generated from a part of the plastic, and there is too much gas inside the fluidized plastic, which also causes the density not to increase. In particular, when the temperature exceeds 260 ° C., there is a problem that chlorinated resins such as polyvinyl chloride and polyvinylidene chloride actively generate hydrogen chloride gas. Due to the generation of hydrogen chloride gas, there arises a problem that the granular material swells and the apparent density does not increase. Moreover, since hydrogen chloride gas is highly corrosive, it is desirable to suppress the generation of hydrogen chloride by treating it at 260 ° C. or lower from the viewpoint of equipment maintenance.

  Under this condition, the waste plastic has a liquid part of 50 to 90% and a solid or poorly fluid part of 10 to 50%, and the plastic is in a fluid state as a whole. In this state, the mixed air is trapped, the water adhering to the waste plastic before molding evaporates, and some plastic components are vaporized, so that the waste kneaded with the push-in screw 8. Gas is mixed in plastic. If this is left as it is, it results in the presence of internal pores in the granular material after cutting and cooling. As a result, there arises a problem that the apparent density of the granular material after cooling is lowered. In order to prevent this, the gas is extracted from the fluidized plastic via the exhaust pipe 14 connected to the vacuum pump 13. As for the suction pressure of casing 7, it is desirable to make it the state decompressed from atmospheric pressure. In normal processing, the suction pressure (absolute pressure) at this time is set to 0.1 to 0.5 atm. In particular, when processing a plastic containing vinyl chloride or the like, or when the productivity per one molding apparatus is high productivity of 1 ton / hour or more, it is necessary to keep the pressure relatively low. In particular, when the chlorinated resin is mixed at a ratio of 4% by mass or less in terms of chlorine, the pressure is preferably 0.1 to 0.35 atm. Since the plastic in fluidized state has high viscosity, even if the viscosity is high and low, even if it is not below 0.5 atm, it takes too much time for gas to escape, while the plastic in fluidized state is in the molding equipment. In addition, gas does not escape. However, even if the suction pressure is too low, there may be a problem that induces excessive gas generation due to decompression. Therefore, it is best to control the suction pressure to 0.1 atm or more. Note that, under high productivity conditions, when the temperature is low, ie, 180 to 200 ° C., the viscosity of the plastic is high, so the suction pressure is preferably in the range of 0.1 to 0.2 atm. At 200 to 260 ° C., the viscosity of the plastic is relatively low, so the suction pressure is particularly preferably in the range of 0.12 to 0.35 atm. In the case of uniform pressure control for producing high-density granular materials having an apparent density of about 0.9 kg / liter or more even if there is a temperature change, a range of 0.1 to 0.2 atm is good. This condition is particularly effective when the chlorinated resin is 0.5 mass% or more in terms of chlorine.

  The plastic in a fluid state is extruded from the nozzle 10. The nozzle diameter is preferably 15 to 60 mm. In the case of a nozzle diameter of less than 15 mm, a phenomenon in which a solid or poorly fluid portion in the plastic in a fluid state increases friction with the nozzle tends to occur. As a result, nozzle clogging is likely to occur. In the case of a nozzle diameter exceeding 60 mm, the flow rate of the plastic in the fluidized state in the nozzle becomes too high, causing a problem that the density of the plastic inside the casing does not increase. As a result, the apparent density does not increase. Moreover, since the plastic in this fluid state has a large variation in viscosity, a special operation is required to extrude the plastic from each nozzle evenly when extruding from a plurality of nozzles. The cutter 15 is optimally a type that rotates with a blade having an acute angle (less than 30 degrees is preferable). This is because a sharp blade is required to cut the fluid plastic.

  Therefore, the inventors conducted an experiment using a nozzle having a diameter of 15 to 60 mm, and obtained the following results. This means that in order to properly distribute the plastic in the fluidized state, the nozzles are placed apart from each other, and this interval is influenced by the diameter of the pushing screw 8. When this relationship is quantitatively evaluated, it is found that there is an appropriate range for the diameter of the pushing screw 8 and the nozzle diameter and the number of nozzles, and the ratio of the diameter of the pushing screw 8 to the product of the number of nozzles of the nozzle diameter is If it is below a certain value, it can be molded successfully. On the other hand, in the present invention, in order to make the distribution of the plastic in a fluid state uniform, it is preferable to install eight or less nozzles. Therefore, when arranging a plurality of nozzles, that is, 2 to 8 nozzles, it is effective to design the total nozzle diameter (nozzle diameter × number) to be ¼ or less of the circumferential length of the push screw 8. . Moreover, when the pushing screw 8 is comprised by a pair (2 types), it is good that the sum total of a nozzle diameter is 1/6 or less of the sum total of a screw periphery.

  The plastic extruded from the nozzle is cut by the cutter 15 to produce a lump of plastic whose length is 1 to 3 times the diameter of the nozzle 10. The lumps are cooled immediately after cutting to produce plastic granules at room temperature. When the start of cooling is delayed or when the cooling rate is low, a phenomenon occurs in which the granular material expands due to the expansion of the gas remaining in the lump. As a result, it becomes impossible to produce a high-density granular material that is the object of the present invention. This is because the plastic immediately after cutting is still in a fluid state and gas remains inside. Therefore, it is necessary to quickly solidify the fluidized plastic. For this reason, cooling is started immediately after cutting. Moreover, the cooling method employ | adopts the water cooling method from which a high cooling rate is obtained.

  When the present inventors observed a lump of plastic in a fluidized state after cutting, the swelling due to the residual gas was observed from about 2 seconds later, and was noticeable when 6 to 8 seconds passed. Become. This is because this lump has a high viscosity, and there is a time delay in the swelling phenomenon caused by the internal gas. Under appropriate conditions, it was possible to fully solidify 2 mm of plastic from the surface within 2 seconds. When a solidified layer of 2 mm or more is formed on the surface at an early stage, it has been found that the swelling phenomenon can be suppressed. Therefore, by starting water cooling within 3 seconds after cutting, the surface is cut within 6 seconds after cutting. It is good to make a solidified layer from 2mm to 2mm. By this method, a high-density granular material without swelling can be produced. On the other hand, for example, by applying water of about 50 ° C. or less to a plastic lump that is in a fluid state, the present inventors repeat various experiments to make the surface temperature of the granular material 80 ° C. or less within 3 seconds. It was found that this condition can be achieved if possible.

  Specific methods of water cooling include a method of immersing the lump in water, a method of applying a large amount of running water, and a method of spraying spray water. Further, in order to achieve the above conditions, as the water cooling strength, if the cooling rate is 10 to 60 ° C. per minute on the average of the entire cross-sectional temperature, a sufficient surface solidified layer is formed within the time required by the present invention. Can do. For this purpose, it is preferable to immerse the plastic in a flowing state in water of 50 ° C. or lower, sprinkle water of 50 ° C. or lower, or immerse in flowing water of 1 m or more per second of 65 ° C. or lower. . For example, there is a method as shown in FIG. The water tank 16 is filled with water 17 and the granular material 18 is put therein. The temperature of the water 17 is controlled by a method such as a circulating cooling method or cold water supply. The cooled granular material 18 is pulled up by a conveyor 19 and drained to obtain a product.

  The internal structure of the granular material manufactured by the above method is shown in FIG. The surface 20 is smooth because it is cooled from the molten state. There are layered pores 21 inside, and the space occupation ratio of the pores is about 5 to 15%. In the case of a granular material having a representative length of 50 mm, which is a value defined by the 1/3 power, the pore thickness is about 2 to 5 mm. If it is the granular material of this condition, it will not decompose | disassemble or deform | transform during conveyance. The apparent density of the granular material obtained by the inventors in the production experiment was 0.85 to 1.1. According to the present invention, a granular material having such an apparent density can be produced constantly. Compared to the conventional method, the density is 1.2 to 1.5 times higher.

  This granular material is confused with coal. The mixing ratio is 5% by mass or less based on coal. This is because if the amount exceeds 5% by mass, many cracks occur in the coke lump formed after dry distillation, and the yield of higher value lump coke used in blast furnaces and cupolas is reduced. is there. This phenomenon occurs even in a low-density granular material. In this case, the same phenomenon occurs even at 5% by mass or less. Since the granular material produced by the method of the present invention is densified, there is an advantage that this phenomenon is less likely to occur.

  As the coal, a mixture of caking coal and general coal pulverized to 5 mm or less is used. As a mixing method, a predetermined amount of particulate matter and coal are mixed as uniformly as possible. The mixture is fed into a coke oven as shown in FIG. The mixture 25 supplied to the carbonization chamber 22 gradually becomes high temperature due to the heat of the heating chambers 23 on both sides. Carbonization is performed from the periphery of the carbonization chamber wall 24. The thermal decomposition reaction starts when the plastic granular material reaches about 250 ° C. or more, and the plastic becomes a volatile component of hydrogen, carbon monoxide, methane, ethane, benzene, and other hydrocarbons. It goes up and is collected by the collection tube 26. Thereafter, this volatile matter is dechlorinated, desulfurized and gas-liquid separated after cooling to become a combustible gas and an oily product. Moreover, the carbon content remaining inside the carbonization chamber 22 is heated to a maximum of 1100 to 1200 ° C., and coal-derived coke is combined. The optimum carbonization time is 18-24 hours. In addition, since carbon derived from plastic has no caking property, the coke strength at the interface portion between the plastic particles and coal is low. Therefore, the mixing ratio and properties of the granular material affect the coke quality.

  In our experiments, the granular material of the present invention has the following three characteristics. First, because of the high density, there is an advantage that the volume ratio of coal to coal is low even in the same mass. Second, since there are no pores or cracks leading from the surface to the inside, water may not penetrate inside during stockpiling or when mixed with coal. Thirdly, there is an advantage that the expansion accompanying the temperature rise is small when supplied into the coke oven. These physical properties help to improve coke production conditions.

  First, since the granular material of the present invention has a high density, there is an advantage that the interfacial area is small even when the same amount of waste plastic as the low density plastic granular material produced by the conventional method is mixed with coal. For this reason, the low intensity | strength part of the manufactured coke can be reduced. FIG. 6 shows the results of examining the relationship between the strength of coke obtained from a mixture of various volumes of granular materials mixed with coal and the mixing ratio of the granular materials. The density of the plastic granular material was 0.9 to 1.05 kg / liter. When the volume is less than 6000 cubic mm, the effect of the present invention is reduced due to the problem that the interfacial area between waste plastic and coal becomes large even for high-density granular materials. On the other hand, when the volume exceeds 200,000 cubic mm, the waste plastic is thermally decomposed, and the gap after the volatile components (combustible gas component and oily product) escape is increased. If this gap is large, there is also a problem that the strength of the produced coke is lowered. This limit is 200000 cubic mm in volume. That is, if the volume of the granular material is 6000 to 200000 cubic mm (nozzle diameter is about 15 to 60 mm), the influence on the reduction of coke strength is particularly small. The meaning of the strength index shown in FIG. 6 is that when the strength index is 1% or more lower than that of coke produced in normal operation, the effect of reduced productivity of pig iron when used in a blast furnace. Is what comes out.

  It is also an important condition that the surface and the inside of the granular material are not connected by a space, that is, there are no holes or cracks penetrating from the surface to the inside. When the internal voids are connected to the outside, the moisture in the coal enters the particulate matter when mixed with the coal. As a result, when the granular material is supplied to the high temperature part in the furnace, the water inside the granular material evaporates rapidly and the filling state of the coal around the granular material is disturbed, so that water enters the inside of the granular material. Absence is an important condition for producing high strength coke. Such an event occurs when the coal moisture is 4% by mass or more.

  Further, under the condition that the granular material is supplied into the furnace and becomes 100 to 200 ° C., the plastic is softened and the internal air expands. As a result, the volume of the granular material at this temperature increases, and the effective density of the granular material decreases. As a result, there is a problem that the effect of producing a high-density granular material, which is the gist of the present invention, is reduced. Therefore, if the size of the internal pores (closed pores) is also restricted, coke production has good results. to be born. The condition is that the single maximum length of closed pores is not more than the representative length of the granular material (value defined by the 1/3 power of the volume), and the single volume is not more than 10% of the granular material. good.

  Using the waste plastic (raw material 1) having the composition shown in Table 1, waste plastic granules were produced by the method of the present invention, and this was pyrolyzed in a coke oven. The raw material 1 was waste plastic recovered from the production process of a plastic processing factory, and contained 56% by mass of polyethylene and 13% by mass of polypropylene. Therefore, the total of polyethylene and polypropylene was 69% by mass. This waste plastic did not contain chloride resin such as vinyl chloride. In Table 1, PE means polyethylene, PP means polypropylene, and PS means polystyrene.

  This mixed plastic was crushed into pieces with a maximum length of 25 mm, and processed with a molding apparatus that was a single push screw of the type shown in FIG. 2 and provided with one nozzle with a diameter of 25 mm. The processing speed was 1.0 ton / hour, and the processing temperature was set between 180 and 260 ° C. in increments of 10 ° C. At 180 ° C., the fluidity of the plastic was low, so the suction pressure (absolute pressure) was 0.115 atm. The suction pressure was 0.14 atm at 190 ° C, 0.155 atm at 200 ° C, 0.165 atm at 210 ° C, and 0.18 atm at 260 ° C. The plastic in the fluidized state exiting from the molding apparatus nozzle was poured into running water at 45 to 55 ° C. in 1.5 to 2.8 seconds. The groove width of this water flow was 250 mm, the depth was 150 mm, and the flow rate was 1.5 m / sec. The product (granular material) obtained by this treatment had a volume of 16000-25000 cubic mm and an apparent density of 0.91-1.02 kg / liter. Detailed data is shown in Table 2. Thus, the granular material obtained by processing with the operation method of the present invention was high density.

  The granular materials (products 1 to 5) obtained by the present invention were recycled in a coke oven. These granular materials had a smooth upper surface, and there were no cracks or pores reaching the inside. The maximum length of these closed pores was 2 to 10 mm, and none of them exceeded 1/2 of the representative length. The volume of the single closed pore was also 3 to 7% of the volume of the granular material. As processing conditions in the coke oven, the mixing ratio of these granular materials to coal was 2.3% by mass, and the mixture was almost uniformly mixed and supplied to the coke oven carbonization chamber. The treatment time was 20 hours, and the treatment temperature was 1160 ° C. at the maximum temperature. As a result, the amounts of the combustible gas and oily product obtained were 440 kg and 350 kg, respectively, per ton of plastic. About 190 kg of coke was converted and mixed with coal-derived coke and integrated. The strength index of this coke was (additive-free conditions) −0.52 to −0.78%. Thus, even when the mixing ratio was a relatively large amount of 2.3%, the reduction in coke strength was small. The strength index is indicated by a rate of occurrence of 15 mm or less after rotating 150 times at a speed of 15 revolutions per minute with a rotary wear device, and compared with a value without added waste plastic particulate matter.

On the other hand, the granular material produced by the conventional method had an apparent specific gravity of 0.61 g / cm ³ . This granular material having a volume of 30000 cubic mm was mixed with coal at a mixing ratio of 2.3% and recycled. The amount of combustible gas and oily product obtained with this granular material was the same as in Example 1. On the other hand, the strength index of the obtained coke was (additive-free condition) −1.25%. As described above, even in the same mixing ratio, the granule having a low specific gravity had a large decrease in the coke strength index.

  Using the waste plastic (raw material 2) having the composition described in Table 1, waste plastic granules were produced by the method of the present invention, and this was pyrolyzed in a coke oven. The raw material 2 is waste plastics for containers and packaging collected from households and daily necessities, and contained 31% by mass of polyethylene, 18% by mass of polypropylene, and 4% by mass of polystyrene. Therefore, the total of polyethylene, polypropylene and polystyrene was 53% by mass. Moreover, the chlorine contained in chloride resins, such as polyvinyl chloride, was 2.2 mass%.

  This mixed plastic was crushed into pieces with a maximum length of 25 mm, and processed in a molding apparatus having a single push screw of the type shown in FIG. 2 and provided with two nozzles with a diameter of 40 mm. The diameter of the pushing screw 8 was 160 mm, (nozzle diameter) × (number of nozzles) = 80 mm, which was a value smaller than ¼ of the circumference of the pushing screw 8. The processing speed was 1.2 tons / hour and the processing temperature was 200 ° C. The suction pressure was 0.21 atm. The plastic in the fluidized state exiting from the nozzle of the molding apparatus was charged into still water at 40 ° C. in 1 to 1.2 seconds. The product (granular material) obtained by this treatment had a volume of 140,000 cubic mm and an apparent density of 0.97.

  The granular material having a volume of 140000 cubic mm obtained in the present invention was recycled in a coke oven. The processing conditions are the same as in Example 1. The mixing ratio with coal was 2.8% by mass, and was mixed almost uniformly and supplied to the coke oven carbonization chamber. The strength index of coke obtained by this treatment was (no additive condition) −0.68%, and there was little decrease in coke strength.

  Using the waste plastic (raw material 3) having the composition shown in Table 1, waste plastic granules were produced by the method of the present invention and thermally decomposed in a coke oven. The raw material 3 was waste plastics for containers and packaging collected from households, and contained 51% by mass of polyethylene, 19% by mass of polypropylene, and 8% by mass of polystyrene. Therefore, the total of polyethylene, polypropylene and polystyrene was 78% by mass.

  Although this mixed plastic is crushed into pieces having a maximum length of 50 mm and is of the type shown in FIG. 2, it is a pair of push screws each having a diameter of 196 mm, and four nozzles having a diameter of 38 mm are installed. Processing was performed with a molding apparatus. (Nozzle diameter) × (number of nozzles) = 152 mm, which is smaller than 1/6 of the total circumference of the pushing screw 8. The processing speed was 2.4 tons / hour and the processing temperature was 185 ° C. The suction pressure was set to minus 0.11 atm. The plastic in a fluidized state exiting from the molding apparatus nozzle was poured into still water at 40 ° C. in 1 second. The product (granular material) obtained by this treatment had a volume of 76000 cubic mm and an apparent density of 0.99.

  The granular material having a volume of 76000 cubic mm obtained by this treatment was recycled in a coke oven. The processing conditions are the same as in Example 1. The mixing ratio with coal was 2.8% by mass, and was mixed almost uniformly and supplied to the coke oven carbonization chamber. The strength index of coke obtained by this recycling treatment was (no additive condition) −0.38%, and the decrease in coke strength was particularly small due to the large particle size.

  Since the present invention makes it possible to economically produce high-density, low-pulverized plastic granules from waste plastic, the present invention is useful for recycling plastic in a coke oven.

DESCRIPTION OF SYMBOLS 1 Vibrating sieve 2 Magnetic separator 3 Crusher 4 Molding device 5 Cooling device 6 Supply port 7 Casing 8 Push screw 9 End plate 10 Nozzle 11 Electric heating element 12 Motor 13 Vacuum pump 14 Exhaust pipe 15 Cutter 16 Water tank 17 Water 18 Granules 19 conveyor 20 surface 21 pores 22 carbonization chamber 23 heating chamber 24 carbonization chamber wall 25 mixture 26 recovery pipe

Claims (7)

A plastic granule that has no holes or cracks extending from the surface to the inside, an apparent density of 0.85 to 1.1 g / cm ³ , and a volume of 6000 to 200,000 cubic mm is mixed with coal. A waste plastic pyrolysis method characterized by dry distillation in a coke oven.   The maximum length of single pores existing inside the plastic granule is not more than 1/3 of the volume of the plastic granule, and the single volume of the pore is 10% or less of the volume of the plastic granule. The waste plastic pyrolysis method according to claim 1, wherein the plastic particles are mixed with coal and dry-distilled in a coke oven.   A mixture of a plurality of types of plastics, and a temperature of 180 to 260 ° C. in a molding apparatus for extruding waste plastic containing a total of 50% by mass or more of a thermoplastic resin selected from polyethylene, polypropylene, and polystyrene from a nozzle, and After compression molding by extruding from the nozzle from the state in which the gas in the apparatus is sucked, this is cut and cooled in a water-cooling device, and the plastic granulated product is mixed with coal and dry-distilled in a coke oven The waste plastic thermal decomposition method according to claim 1 or 2, wherein   A mixture of a plurality of types of plastics and a temperature of 180 to 260 ° C. in a molding apparatus for extruding waste plastic containing a total of 50% or more of a thermoplastic resin selected from polyethylene, polypropylene, and polystyrene from a nozzle, and the apparatus A plastic granulated product produced by compression molding by extruding from a state of sucking the gas from a nozzle having a diameter of 15 to 60 mm and then cutting it with a water cooling device within 3 seconds is coal. The waste plastic pyrolysis method according to claim 1, wherein the waste plastic is subjected to dry distillation in a coke oven.   Waste plastic containing a total of 50% or more of thermoplastic resins selected from polyethylene, polypropylene, and polystyrene, and containing chlorine-containing plastics in a proportion of 5% or less in terms of chlorine content. The exhausted plastic is sucked with an exhaust device that is depressurized to 0.1 to 0.35 atm, and from this state, the waste plastic is compressed by extrusion from a nozzle, and this is cooled with water. 3. The waste plastic pyrolysis method according to claim 1 or 2, wherein the plastic granulated product produced by cooling is mixed with coal and subjected to dry distillation in a coke oven.   The surface temperature is cooled to 80 ° C. or less within 2 seconds from the start of water cooling with a water cooling device of a lump of waste plastic that has been completely or partially melted extruded from the nozzle of claim 3. The waste plastic pyrolysis method according to claim 1 or 2, wherein the produced plastic granulated material is mixed with coal and subjected to dry distillation in a coke oven.   The waste plastic pyrolysis method according to any one of claims 1 to 6, wherein the mixing ratio of the plastic particles to coal is 5 mass% or less.