JP5120063B2 - Method for producing pulverized waste plastic and method for producing pellets for producing pulverized waste plastic - Google Patents

Description

  The present invention is a waste plastic pulverization for using waste plastic, which is plastic waste as general waste or industrial waste, as a raw material blown into vertical furnaces such as blast furnaces and scrap melting furnaces, cement kiln furnaces, etc. The present invention relates to a method for manufacturing a product.

  In order to use it as an alternative raw material for coke and pulverized coal, a technique for blowing waste plastic into a vertical furnace such as a blast furnace from a tuyere is known. It is possible to effectively recycle the used plastic as a coke substitute by transporting the used plastic granular material pneumatically and blowing it from the tuyere (see, for example, Patent Document 1). According to Patent Document 1, in order to improve the combustion rate in the raceway of the furnace, it is important to control the strength and particle size of the plastic particles blown into the furnace. Manufactured and blown into the furnace.

On the other hand, in order to further improve the combustion rate of waste plastic, there is a method of pulverizing waste plastic. By pulverizing the waste plastic, it is easy to blow into the furnace, and the amount of waste plastic recycled can be increased. As a technique for pulverizing waste plastic, a method for treating waste plastic is known in which waste plastic is cooled and solidified by heating and melting with an extruder to form a solidified body, and the solidified body is pulverized (for example, (See Patent Document 2).
JP 2001-220589 A JP 2006-241442 A

  According to the method described in Patent Document 2, when waste plastic is melted using an extruder, it is possible to dechlorinate the waste plastic, and continuously produce the pulverized product with high thermal efficiency. Waste plastic can be processed and pulverized. The plastic extruded from the extruder using a die or the like is cooled and solidified using a known method such as direct water cooling or indirect cooling such as a steel belt cooler, cut into a predetermined length and pelletized. It is said that a furnace blowing raw material can be obtained by roughly pulverizing and finely pulverizing the produced pellets to obtain a pulverized product.

  However, in the above, when the waste plastic is pulverized using a method of cooling and solidifying the extruded plastic by water cooling, the moisture content of the pellets that are the solidified product produced may increase. I understood. If water adheres to the surface during water cooling, it can be dealt with by draining the pellet after water cooling using a vibrating sieve, etc., but even if the pellet is drained, the moisture content of the pellet It may be 10-20 mass%. When the pulverization process is performed using pellets having a high water content, the pulverized material charged in the hopper or the like adheres to the water and causes the hopper to be clogged, making subsequent processing difficult.

  Therefore, the object of the present invention is to solve such problems of the prior art, and after the waste plastic is heated and melted by an extruder, it is cooled and solidified by cooling with water to obtain a solidified body, and when the solidified body is pulverized, An object of the present invention is to provide a method for producing a waste plastic pulverized product capable of reducing the water content.

The present inventors have found that the outlet temperature of the extruder when heat-melting waste plastic has a great influence on the water content of the solidified product after water cooling, and completed the present invention. The present invention has been made based on such findings, and the features thereof are as follows.
(1) The waste plastic is heated and melted by an extruder, dechlorinated, and then cooled and solidified to obtain a solidified body. When the solidified body is pulverized, the temperature of the waste plastic immediately after being extruded from the extruder Is controlled to 290 ° C. or less, and immediately cooled with water to obtain a solidified product.
(2) The method for producing a pulverized waste plastic according to (1), wherein the dechlorination treatment is performed by heating to 300 ° C. or higher in an extruder.
(3) Waste plastic pulverization characterized in that waste plastic is heated and melted by an extruder to dechlorinate, the temperature of waste plastic immediately after being extruded from the extruder is controlled to 290 ° C. or less, and immediately cooled with water. Manufacturing method of pellets for manufacturing products.

  According to the present invention, a solidified plastic body having a moisture content of 5 mass% or less and a low moisture content can be obtained. For this reason, the subsequent pulverization processing of the solidified body can be performed smoothly, the productivity of the pulverized waste plastic can be improved, and the recycling of the waste plastic can be promoted.

  In the present invention, waste plastic is cooled and solidified by heating and melting using an extruder to obtain a solidified body, and the solidified body is pulverized to produce a pulverized plastic. Waste plastic can be dechlorinated by heating and melting. Waste plastics are used plastics and usually consist of a mixture of a plurality of types of plastics. The extruder is an apparatus having an extrusion screw in a cylinder and melt-kneading by transferring the plastic into the cylinder while heating. Although any number of screws can be used for the extruder, it is desirable to use an extruder having two or more screws from the viewpoint of processing efficiency. The heat-melted plastic is cooled and solidified by water cooling. The solidified body that has been cooled and solidified is pulverized using a pulverizer to obtain a pulverized product of waste plastic. An embodiment of such a waste plastic crushing system will be described with reference to FIG.

  In FIG. 1, waste plastic 1 is subjected to foreign matter removal using magnetic separation, wind separation, etc. and washed with water in advance to remove foreign matter other than plastic as much as possible, and then is put into the first extruder 2. The waste plastic 1 is desirably crushed into a predetermined shape in advance, and is preferably crushed to a die diameter or less in order to prevent clogging due to foreign matter in the die 6 described later. The waste plastic 1 is heated at about 200 ° C. by the first extruder 2 and melt kneaded while dehydrating. The moisture may be removed by providing an appropriate exhaust port in the cylinder of the first extruder 2. The molten waste plastic extruded from the first extruder 2 is subsequently heated by the second extruder 3 at 300 ° C. or higher, preferably about 350 ° C., and melt-kneaded while performing a dechlorination treatment. Generated gas such as hydrogen chloride gas generated by heating in the second extruder 3 is sent to the gas processing system 5 through the vent 4 and processed. In the gas treatment system 5, a treatment such as a combustion treatment, hydrochloric acid, tar recovery or the like can be performed. The plastic extruded from the second extruder 3 using a die 6 is cut into a predetermined length, cooled in water in a water tank 7 to be solidified, and pelletized. The produced pellets are drained using a vibrating sieve 8, coarsely pulverized by a first pulverizer 9, the pulverized product is charged into a hopper 10, and further finely pulverized by a second pulverizer 11. The pulverized material thus obtained is blown into the blast furnace 12 using an existing pulverized coal blowing device or the like to obtain a furnace blowing raw material.

  When the waste plastic is processed using the system of FIG. 1, if the pellets have a high moisture content, the pellets are roughly pulverized by the first pulverizer 9 even if the draining process is performed by the vibrating sieve 8. When an object is charged into the hopper, the coarsely pulverized product adheres to the hopper or the coarsely pulverized product adheres to the hopper due to the moisture.

  In order to reduce the moisture content of the pellets, the present inventors have studied the mechanism by which such pellets with a high moisture content are produced. When the pellets after water cooling were examined, formation of pores was observed inside, and water had entered the pores. This hole is thought to be a vacuum void formed during solidification shrinkage of the molten plastic, but the molding shrinkage of the plastic is at most several volume%, and the moisture content is as high as 10 to 20 mass%. Therefore, it is not realistic to think that the cause of moisture is only due to vacuum voids. Moreover, when it manufactures using a different extruder, the above water-containing pellets may not be manufactured, and it does not fit reason. Therefore, it was estimated that the holes in the pellet were holes due to bubbles formed without allowing the gas generated in the extruder to escape. If gas generated during the cooling process in the extruder cannot be completely removed and bubbles are formed, water stays in the water due to water cooling, and water is sucked into the negative pressure gap through a slight crack. It is thought that water will invade the water.

  Therefore, a method for controlling the generation of bubbles by changing the temperature setting in the extruder was studied. The central portion of the second extruder 3 needs to be 300 ° C. or higher in order to dechlorinate waste plastic, but the gas generated in this portion is exhausted through the vent portion 4 and discharged. If the gas is generated after the molten plastic passes through the vent portion, the gas that cannot flow back to the vent portion is not discharged but may remain to form bubbles. Therefore, the following experiment was conducted on the assumption that the generation of gas can be suppressed by lowering the temperature near the outlet of the second extruder 3 and suppressing the thermal decomposition reaction of the plastic.

  The heating temperature of the first extruder 2 is 180 ° C., the dechlorination temperature of the second extruder 3 is 335 ° C., and the portion without the vent portion 4 (cooling portion) near the outlet of the second extruder 3 is set. The temperature was varied from 160-240 ° C. The temperature of the molten plastic in the cylinder of the extruder is different between the outer wall and the center of the cylinder, and it is difficult to measure directly. Temperature.

  The molten plastic extruded from the die 6 is immediately cut into a predetermined length with a cutter, pelletized by water cooling at two cooling rates of cooling in water (10 ° C.) and cooling in hot water (70 ° C.). The proportion of pellets was measured. The ratio of the water-containing pellets was determined by arbitrarily selecting about 10 pieces from the manufactured pellets and cutting them, and determining that water outflow was recognized as water-containing pellets. Further, a thermometer was directly inserted into the center of the molten plastic immediately after being extruded from the die, and the temperature (extruded plastic temperature) was measured. The results are shown in FIGS.

  FIG. 2 shows the relationship between the cooling section set temperature and the ratio of the water-containing pellets, and the solid line in the figure represents the upper limit of variation that is important in actual operation. According to FIG. 2, when the cooling part set temperature exceeds 220 ° C., the ratio of the water-containing pellets starts to increase, and when the cooling part setting temperature is 240 ° C. (extruded plastic temperature 290 ° C.), the ratio of the water-containing pellets increases. It can be seen that when the temperature is 260 ° C. (extruded plastic temperature 295 ° C.), the ratio of the water-containing pellets increases rapidly. In addition, it is considered that water-cooled pellets have a smaller proportion of water-containing pellets than water-cooled water, and it is preferable to quickly cool and terminate the thermal decomposition reaction earlier.

  FIG. 4 shows a cross-sectional photograph of a pellet produced at a cooling part set temperature of 160 ° C. (cooling in water), and FIG. 5 shows a cross-sectional picture of a pellet produced at a cooling part set temperature of 240 ° C. (cooling in water). Although the pellet of FIG. 4 had a small hole in the center, the other part was dense and the cross-section was smooth, and water was not contained in the hole. On the other hand, the pellet of FIG. 5 had a large hole in the center, a rough cross section, and a large amount of water in the hole.

  From the above, it can be seen that the temperature of the extruded molten plastic or the temperature of the cooling section of the second extruder greatly affects the moisture content of the pellets. That is, after the dechlorination treatment in the extruder, it is preferable that the molten plastic temperature is lowered as much as possible to the extent that it can be extruded, and the generation of gas due to the thermal decomposition of the plastic is suppressed and the cooling is performed quickly. Although the temperature of the extruded plastic can be lowered to about 120 ° C., since the screw motor load of the extruder increases at this temperature, it is usually preferable to perform extrusion at an extruded plastic temperature of 250 ° C. or higher.

  As shown in FIG. 3, there is a positive correlation between the set temperature of the cooling section and the temperature of the extruded plastic immediately after being extruded, so that either temperature may be used to suppress the generation of gas due to thermal decomposition. In the present invention, since it is necessary to extrude from the extruder by setting the temperature of the extruded plastic immediately after extrusion to 290 ° C. or lower, when controlling by the cooling section set temperature, the relationship as shown in FIG. 3 is measured in advance. . The extruded plastic temperature immediately after extrusion is preferably 280 ° C. or less.

  The waste plastic was pulverized using the same equipment as in FIG. In the cylinder part of the second extruder 3 that performs the dechlorination treatment, as shown in FIG. 6, the temperature is controlled by being divided into five parts C1 to C5, and the temperature raising part (C1) and the full vent part (C2 to C2), respectively. C4) and a cooling part (C5).

  The waste plastic used was waste from ordinary households, and in the state where a plurality of types of plastic and foreign materials were mixed, it was 32 mass% polyethylene, 31 mass% polypropylene, 22 mass% polystyrene, and 15 mass% other (paper, etc.). . Foreign matter was removed and washed, and a film-like material was selected and crushed to a particle size of about 20 mm and used for processing. The chlorine content was 2.4 mass% after removing foreign matter.

  Using this, the heating temperature in the first extruder 2 is 180 ° C., the heating temperature in the second extruder is 310 ° C. for C1, 345 ° C. for C2 to C4, and 180 ° C. for C5. The melted and kneaded waste plastic was extruded from a die, cut with a hot cutter and dropped into water to produce cylindrical pellets having a diameter of about 20 mm and a length of about 20 mm. The processing amount of waste plastic was 600 kg / hour.

  The temperature of the plastic at the outlet of the extruder 3 was 268 to 270 ° C. Although 20 manufactured pellets were cut and observed internally, no water-containing pellets were generated. When the water content after coarse pulverization with a hammer mill (coarse pulverizer) with a 12 mm eye opening was measured, it was 0.5 to 1.5 mass%. The pipes were not clogged at all, and finely pulverized plastics were successfully produced.

  Next, as a comparative example, in the same manner as described above, the heating temperature (set temperature) of C5 of the second extruder was set to 220 ° C. to produce pellets.

  The temperature of the plastic at the exit of the extruder 3 was 290 ° C. When the produced pellet was cut and the inside was examined, 10 out of 20 contained water, and the water after coarse crushing was 8 to 18 mass%. Thereafter, pulverization was performed, but the hopper and piping were clogged, making it difficult to continue the processing.

1 is a schematic view of an embodiment of a waste plastic crushing system. The graph which shows the relationship between the ratio of a water-containing pellet and cooling part preset temperature. The graph which shows the relationship between extrusion plastic temperature and cooling part preset temperature. The cross-sectional photograph of the pellet manufactured at the cooling part preset temperature of 160 degreeC. The cross-sectional photograph of the pellet manufactured at the cooling part preset temperature of 240 degreeC. Schematic of the cylinder part of a 2nd extruder.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Waste plastic 2 1st extruder 3 2nd extruder 4 Vent part 5 Gas processing system 6 Dies 7 Water tank 8 Vibrating sieve 9 First crusher 10 Hopper 11 Second crusher 12 Blast furnace

Claims (2)

An inlet waste plastic is introduced, and an outlet, further, by heating to 300 ° C. or higher in an extruder having a cooling portion to said outlet, heated and melted to dechlorination of the waste plastics the line stomach,
After the dechlorination, waste plastics temperature immediately after extruded from said outlet so as to be 2 8 0 ° C. or less, and controlling the temperature of the cooling section,
Manufacturing method of waste plastics pulverized material, characterized in that water cooled immediately in water waste plastics immediately after extruded from the outlet and solid material, pulverizing the solid embodying. An inlet waste plastic is introduced, and an outlet, further, by heating to 300 ° C. or higher in an extruder having a cooling portion to said outlet, heated and melted to dechlorination of the waste plastics Do
After the dechlorination, waste plastics temperature immediately after extruded from said outlet so as to be 2 8 0 ° C. or less, and controlling the temperature of the cooling section,
A method for producing pellets for producing a pulverized waste plastic, wherein the waste plastic immediately after being extruded from the outlet is immediately cooled in water.