JP2006281506A - Treatment method of waste plastic - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a treatment method of a waste plastic constituted so as not to produce a large amount of a polluted medium liquid required for water purification treatment when the waste plastic is separated into a chlorine-free plastic and a chlorine-containing plastic by a wet centrifugal separation method and reduced in the load of water treatment. <P>SOLUTION: In the treatment method of the waste plastic for separating and recovering the chlorine-free plastic from the waste plastic containing the chlorine-containing plastic, the waste plastic is separated into a high specific gravity plastic and a low specific gravity plastic on the basis of specific gravity difference using the wet centrifugal separation method and the separated low specific gravity plastic is washed with water. The wet centrifugal separation method is performed using a centrifugal separator which uses circulating water and the circulating water is preferably subjected to incineration treatment. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a waste plastic treatment method for separating chlorine-containing plastic from waste plastic such as general waste and industrial waste and recovering non-chlorine-containing plastic.

  Plastic waste, generally called waste plastic, is a mixed state of a plurality of types of plastics. In addition to polyethylene (PE), polypropylene (PP), polystyrene (PS), polyethylene terephthalate (PET), PVC (polychlorinated). Also included are chlorine-containing plastics such as vinyl) and PVDC (polyvinylidene chloride) (hereinafter, PVC and / or PVDC are referred to as “chlorine-containing plastics”). When such mixed waste plastic is reused, for example, as a furnace fuel or a reducing material for iron sources, the generation of chlorine-containing gas becomes a problem, and therefore, a process for separating chlorine-containing plastic from waste plastic is performed. ing. In addition, when using waste plastic as a material recycling raw material for producing a recycled product, it is necessary to perform sufficient washing in addition to separation of the chlorine-containing plastic in order to obtain a high-quality recycled product.

  As a method of removing chlorine-containing plastic from waste plastic and recycling it, waste plastic is sorted into solid plastic and lightweight plastic using a rocking repulsive sorter, and then crushed and processed by wet specific gravity differential sorting. Is known (see, for example, Patent Document 1). The specific gravity difference sorting method pays attention to the fact that the specific gravity of chlorine-containing plastics is larger than that of non-chlorine-containing plastics such as PE, PP and PS. In this method, the specific gravity component is divided into the low specific gravity component, the high specific gravity component is removed as a chlorine-containing plastic, and the low specific gravity component is recovered as a non-chlorine-containing plastic.

  Specific gravity difference selection methods include liquid cyclones, wet vertical separators (separators that float low specific gravity and settle high specific gravity), wet processing methods such as wet centrifugation, and no liquid. There is a processing method by a dry method, and separation processing of waste plastics by a wet centrifugal method is said to have particularly high separation accuracy. The wet centrifugation method is performed as follows.

  The waste plastic dispersed in the medium liquid is charged into the rotating cylinder where water or the medium liquid whose specific gravity is adjusted stays. In the rotating drum, plastic pieces having a large specific gravity gather near the inner wall of the rotating drum, and plastic pieces having a small specific gravity gather on the inner side of the rotating drum. Then, by removing the two separated plastics from the respective outlets, the charged waste plastic is separated into a high specific gravity component made of chlorine-containing plastic and a low specific gravity component made of non-chlorine-containing plastic. The

  On the other hand, waste plastic is waste and contains a large amount of pollutants. When such contaminated waste plastic is put into a wet centrifuge, the waste plastic is agitated in the medium liquid, so that the medium liquid is easily contaminated and bubbles are generated. It is difficult to achieve good separation. In addition, the specific gravity of the medium liquid may change due to the elution of contaminants, which may cause a deterioration in separation accuracy.

The above-mentioned wet centrifuge is developed for waste plastics with relatively high cleanliness such as industrial waste, and is not suitable for the specific gravity separation of waste plastics containing a large amount of contaminants. ing. Therefore, when waste plastic such as household waste, which is general waste, is subjected to specific gravity separation using a centrifugal separator, it is washed in advance and then put into the centrifugal separator for separation. The cleaning method is a screw type that sprinkles waste plastic from the top while conveying the waste plastic with a screw, a sieve type that sprinkles waste plastic from the top while sieving on the sieve, and a rotating blade is installed near the water surface in the pool to dispose of the waste plastic. A pool type for cleaning while transporting is known.
JP 2001-219427 A

  However, if a pre-washing process for washing waste plastic is performed before the separation process by the wet centrifugation method, a large amount of sewage is generated in this pre-washing process, and it becomes necessary to install a large-scale water treatment facility. There is a problem that the processing load becomes high.

  Accordingly, an object of the present invention is to solve such problems of the prior art and to contaminate a medium that requires water purification treatment when separating waste plastic into non-chlorine-containing plastic and chlorine-containing plastic by wet centrifugation. It is an object of the present invention to provide a method for treating waste plastic with a low water treatment load without generating a large amount of liquid.

The features of the present invention for solving such problems are as follows.
(1) A waste plastic treatment method for separating and recovering non-chlorine-containing plastic from waste plastic containing chlorine-containing plastic, wherein the waste plastic is divided into a high specific gravity plastic and a low specific gravity plastic by a specific gravity difference using a wet centrifugal method. A method for treating waste plastic, characterized in that the separated low specific gravity plastic is subjected to a water washing treatment.
(2) The method for treating waste plastics according to (1), wherein the wet centrifugation is performed using a centrifugal separator using circulating water.

  ADVANTAGE OF THE INVENTION According to this invention, the quantity of the waste liquid required for the water quality purification process generate | occur | produced when separating a waste plastic into a non-chlorine containing plastic and a chlorine containing plastic can be decreased. Therefore, waste plastic can be processed at low cost, and recycling of waste plastic can be promoted.

  The present inventors have conceived the present invention by finding out that the wet centrifugation method has an excellent waste plastic cleaning effect.

  That is, in the wet centrifugation method, in addition to the cleaning action by water in the conventional cleaning method (for example, the above-described screw type, sieve type, pool type method, etc.), a rotating drum (for example, an inner diameter) that rotates at a high speed of about 700 to 1500 rpm. It has been found that there is a powerful cleaning effect of removing contaminants adhering to the waste plastic by impact force by jetting and colliding the medium liquid mixed with waste plastic within about 500-600 mm). . For this reason, even if the medium liquid is contaminated to some extent, it is possible to maintain a large cleaning effect due to the impact force as described above.

  In addition, as a result of the study by the present inventors, the change in specific gravity of the medium liquid due to the elution of contaminants attached to the waste plastic is not so large, and the influence on the separation accuracy of chlorine-containing plastic and non-chlorine-containing plastic is small, It has been found that generation of bubbles due to contamination of the medium liquid can be prevented by adding an antifoaming agent to the medium liquid. Therefore, under conditions where the change in specific gravity of the medium liquid does not significantly affect the separation accuracy of the chlorine-containing plastic, the medium liquid can be recycled multiple times, and the amount of waste liquid discharged in the process by the wet centrifugation method can be reduced. It is possible to reduce. The load of water treatment is reduced by reducing the amount of waste liquid that requires water purification treatment by using the medium liquid multiple times. Furthermore, it is possible to eliminate the wastewater treatment by incinerating the medium liquid used a plurality of times.

  As described above, washing is performed simultaneously with the separation of chlorine-containing plastic and non-chlorine-containing plastic using a wet centrifugation method, and the waste plastic separated after the treatment by the wet centrifugation method is washed with water. In the present invention, it is not necessary to perform a water washing treatment before the treatment by the wet centrifugation method. When waste plastics before the treatment by the wet centrifugation method are washed with water, the waste water contains a large amount of pollutants, and thus waste water treatment is necessary. In addition, since ordinary water washing treatment does not provide a strong washing effect as in the case of the wet centrifugal separation method, it is difficult to circulate waste water or perform combustion treatment.

  The waste plastic after the treatment using the wet centrifugation method is attached with a medium liquid contaminated by multiple use. Therefore, in order to obtain a cleaner waste plastic, the remaining adhering medium liquid is washed and removed. In this case, light washing that allows water to pass through is sufficient. The waste water generated from the cleaning water does not need to be subjected to water purification. Since the wastewater generated in the water washing process has relatively good water quality, the medium liquid in the process using the wet centrifuge method can be used to discharge plastic when the medium liquid is circulated and used in a wet centrifuge, for example. It may be used as a replenishing water for the medium liquid that decreases with the increase. In this case, naturally, no water treatment facility is required.

  In this way, when the waste plastic is separated by using the wet centrifugation method and then washed with water, since the waste plastic is already washed to a considerable extent when separated by the wet centrifugation method, it is discharged in the washing process. The degree of pollution of the wastewater is low, and almost no water purification treatment is required. In many cases, it can be discharged directly into sewage. Therefore, if the above method is used, a sufficiently cleaned non-chlorine-containing plastic can be obtained without providing a water purification treatment step.

  Based on the above knowledge, when separating and recovering non-chlorine-containing plastics from waste plastics containing chlorine-containing plastics, the waste plastics are separated into high specific gravity plastics and low specific gravity plastics by the specific gravity difference using the wet centrifugal method. It was found that waste plastic can be treated without generating a large amount of contaminated wastewater that requires water purification treatment by washing with low specific gravity plastic. At this time, the wet centrifugation method is performed using a centrifugal separator using circulating water, and the circulating water is incinerated when the degree of contamination exceeds a predetermined level, so that waste water treatment is almost unnecessary. can do.

  Further, if the chlorine-containing plastic separated by the wet centrifugation method is similarly washed with water, a chlorine-containing plastic having a high degree of cleaning can be easily obtained. This processing may be appropriately performed as necessary.

  The plastic to be separated as the chlorine-containing plastic is preferably polyvinyl chloride and / or polyvinylidene chloride. These plastics can be easily separated using water as a medium liquid.

  FIG. 1 is an explanatory view of a method for treating waste plastic. An embodiment of the present invention will be described with reference to FIG.

  In FIG. 1, reference numeral 100 denotes a mixed waste plastic containing chlorine-containing plastic, which is a collected waste. The mixed waste plastic crushed to a size of about 10 to 50 mm square in the crushing step 11 is a wet centrifuge step 12. Sent to. In the wet centrifugal separation step 12, a wet centrifugal separation device shown in FIG. 2 to be described later is used, and a sorting process based on a specific gravity difference using water is performed to obtain a high specific gravity 103 (PVC or the like) and a low specific gravity 102. The waste plastic is washed at the same time as the separation process. Among the bisected plastics, the high specific gravity 103 is a high chlorine concentration plastic, and the low specific gravity 102 is mainly a non-chlorine-containing plastic such as PE, PP and PS. An appropriate amount of an antifoaming agent is added to the medium liquid (water) used in the wet centrifugation step 12, and the medium liquid is circulated while adding clean water as appropriate. When the medium liquid is contaminated or the amount of suspended solids exceeds a predetermined standard due to recycling, the medium liquid is incinerated and disposed of.

  Since the non-chlorine-containing plastic, which has a low specific gravity of 102, from which the chlorine-containing plastic is separated and removed from the mixed waste plastic, has sewage adhering to the surface, it is washed by a water washing treatment step 13 using a water washing apparatus shown in FIG. Then, the dirty water is removed, and the washing water adhering in the dehydration step 14 is removed to obtain the washed plastic 104. The treated water used in the rinsing process 13 has a high cleanliness with a low content of pollutants, and can be discharged as it is or with a small amount of diluted water.

  Next, a wet centrifuge used in the wet centrifuge process will be described. FIG. 2 is an explanatory diagram of an embodiment of a wet centrifuge. The wet centrifuge 20 has a truncated cone-shaped portion formed on both sides, a rotating cylinder 21 that rotates while retaining water or a medium liquid whose specific gravity is adjusted, and a slightly different speed from the rotating cylinder 21. The main part is composed of a rotating shaft to be rotated and screw conveyors 22a and 22b made of screws provided on the shaft. In the figure, reference numeral 102 denotes a low specific gravity plastic, and 103 denotes a high specific gravity plastic.

  Separation of plastic by this apparatus is performed as follows. An amount of medium liquid that allows a space to be formed in the upper portion of the rotating drum 21 is retained and rotated, and a waste plastic crushed product dispersed in the medium liquid is charged from the waste plastic charging pipe 23. In the rotary cylinder 21, among the plastic pieces inserted from the waste plastic charging tube 23 into the central portion of the rotary cylinder 21, those having a specific gravity smaller than the medium liquid float up and have a specific gravity larger than the medium liquid. Settles. At this time, the settling of the plastic having a specific gravity larger than that of the medium liquid is promoted by the action of the centrifugal force generated as the rotating drum 21 rotates. Also, the effect of removing dirt on the plastic surface is generated by the impact force when the plastic is struck against the water surface. The plastic piece having a high specific gravity (high specific gravity) gathers in the vicinity of the inner wall of the rotary drum 21, and the plastic piece having a low specific gravity (low specific gravity) is near the liquid surface of the medium liquid (on the center side of the rotary drum 21). get together. The high specific gravity portion 103 is scraped out by the screw conveyor 22a having a large diameter, discharged from the high specific gravity portion outlet 24, and processed as a chlorine-containing plastic portion. The low specific gravity 102 is scraped out by a screw conveyor 22b having a small diameter, discharged from the low specific gravity outlet 25, and recovered as non-chlorine-containing plastic.

  Next, the rinsing apparatus used in the rinsing process 13 will be described. FIG. 3 is an explanatory view of an embodiment of the water washing apparatus. The low specific gravity 102 of the waste plastic separated and washed in the wet centrifugation step 12 is introduced from the upper surface of the water tank 1 containing water. The plastic that has entered the water tank 1 advances while being pushed forward (rightward toward the paper surface) by the rotary paddle 2 installed on the upper surface of the water tank, and dirty adhered water is rinsed out before being discharged. The water tank 1 keeps the water surface 4 constant by the makeup water 3. In the case where the low specific gravity component 102 contains foreign matters such as metal or the high specific gravity plastic 105, the low specific gravity component 102 settles in the water tank 1 and is separated. The plastic discharged from the water tank 1 is dehydrated by the centrifugal dehydrator 5 to obtain a washed plastic 104. The dehydrated water is discharged as drainage 6. Since the degree of contamination of the waste water 6 is mild, it is treated as sewage waste water without providing a water treatment facility.

  The clean non-chlorine-containing plastic obtained by removing chlorine-containing plastic and contamination from waste plastic by the above treatment method is suitable as a recycled material, particularly a material recycled material.

  Waste plastic collected by local governments and used for containers and packaging, whose chlorine content is about 1.5 mass%, is washed and the chlorine-containing plastic is separated and removed to obtain waste plastic with low chlorine concentration Processed. The main non-chlorine-containing plastic contained in the waste plastic was PE.

  The treatment for separating and washing the chlorine-containing plastic was performed as follows. A container-packaged plastic bale product was loosened with a crusher and then crushed with a crusher to obtain a screen passing material of about 10 to 50 mm.

The crushed material was charged into a wet centrifuge having an internal volume of about 5 m ³ having the same configuration as that shown in FIG. 2, and a specific gravity difference sorting process for separating the crushed material into a high specific gravity component and a low specific gravity component was performed. Water was used as the medium liquid for dispersing the plastic crushed material. The water was recirculated and used for an average of about one week while supplying the shortage, and then incinerated. The ratio of the low specific gravity recovered as a non-chlorine-containing plastic by this treatment was 72 mass% with respect to the charged crushed material, and the chlorine content was 0.65 mass%. The proportion of the high specific gravity was 28 mass%, and the chlorine content was 3.8 mass%.

  Next, the low specific gravity was put into a washing apparatus having the same configuration as that shown in FIG. When the quality of the used water was examined, the degree of contamination was mild and the wastewater was discharged without any special treatment. The plastic recovered as a non-chlorine-containing plastic has a cleaner appearance and lower odor than after the wet centrifugation process, and the non-chlorine-containing plastic suitable for material recycling could be recovered.

It is explanatory drawing of one Embodiment which concerns on the waste plastic processing method of this invention. It is a figure which shows an example which concerns on the structure of the wet centrifuge used in a specific gravity difference selection process. It is a figure which shows an example of the apparatus used at a water-washing process process.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Water tank 2 Rotating paddle 3 Supply water 4 Water surface 5 Centrifugal dehydrator 6 Drainage 11 Crushing process 12 Wet centrifugal separation process 13 Water washing process 14 Dehydration process 20 Wet centrifuge 21 Rotating drum 22a Screw conveyor 22b Screw conveyor 23 Waste plastic equipment Inlet pipe 24 High specific gravity outlet 25 Low specific gravity outlet 100 Mixed waste plastic 102 Low specific gravity 103 High specific gravity 104 Washed plastic 105 Foreign materials such as metal and high specific gravity plastic

Claims (2)

  A waste plastic treatment method for separating and recovering non-chlorine-containing plastic from waste plastic containing chlorine-containing plastic, wherein the waste plastic is separated into high specific gravity plastic and low specific gravity plastic by a specific gravity difference using a wet centrifugal method. A method for treating waste plastic, wherein the separated low specific gravity plastic is washed with water.   2. The method for treating waste plastic according to claim 1, wherein the wet centrifugation is performed using a centrifugal separator using circulating water.

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