Method and apparatus for treating waste plastics

Abstract

To provide a method and an apparatus for treating a waste plastic, capable of thermally decomposing a chlorine-containing waste plastic at a low cost with high safety to produce a liquid oil having a low chlorine concentration.SOLUTION: The method for treating waste plastics comprises safely thermally decomposing chlorine-containing waste plastics 30 in the presence of CaO-containing collected dust 40 in a steam atmosphere and recovering a liquid oil 50 from a decomposition product produced by the thermal decomposition of the waste plastics. The apparatus 100 for treating the waste plastics is equipped with a thermal decomposition apparatus 16 for thermally decomposing the waste plastics containing chlorine in the coexistence with collected dust containing CaO in a steam atmosphere and a condenser 18 for obtaining a liquid oil component from a decomposition product produced by the thermal decomposition of the waste plastics.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a method for treating waste plastics and an apparatus for treating waste plastics. [Background technology]

[0002] There is a need to develop an economical recycling method for waste plastics (plastic waste materials), especially for waste plastics containing polyvinyl chloride (PVC), which is difficult to separate. Since chlorine accounts for more than half of the mass of the constituent elements of PVC, chemical or thermal recycling as a hydrocarbon material is difficult. In addition, there are concerns that waste plastics containing PVC may produce dioxins when burned, so landfilling is considered a more effective disposal method than incineration. Therefore, it is important to develop permanent disposal and recycling methods that can replace landfilling.

[0003] As a method for treating waste plastics containing PVC, a method of recovering hydrocarbons by pyrolysis of the waste plastics has been proposed. For example, Patent Document 1 discloses a method for dechlorinating waste plastics, in which waste plastics containing polyvinyl chloride are melted under predetermined conditions while being stirred and mixed in a reducing atmosphere, and the polyvinyl chloride is thermally decomposed, and the generated gases such as hydrogen chloride gas are discharged, and the dechlorinated molten plastics are taken out.

[0004] Furthermore, a method has been proposed in which calcium compounds such as calcium carbonate are used when thermally decomposing chlorine-containing waste plastics. For example, Patent Document 2 discloses a method for producing calcium chloride in a filter by sucking hydrogen chloride gas, which is generated when chlorine-containing waste plastics are thermally decomposed under reduced pressure and in the absence of oxygen, into a liquid filter containing calcium carbonate or the like. Patent Document 3 discloses a method in which waste plastics containing organic chlorine compounds are mixed with alkaline solids and subjected to thermal decomposition, and the chlorine compounds generated by the thermal decomposition react with the alkaline solids to capture the chlorine in the residue and remove it from the atmosphere, while the generated pyrolysis gas is condensed to produce a product oil with a low chlorine concentration. In addition, a method has been proposed in which a calcium compound is added to chlorine-containing plastic waste material, followed by thermal decomposition, and the residue after thermal decomposition is used as flux for a refining furnace or as a secondary raw material in the iron-making process (see, for example, Patent Documents 4 and 5). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 11-90387 [Patent Document 2] Japanese Patent Application Publication No. 8-151213 [Patent Document 3] Japanese Patent Application Publication No. 11-148084 [Patent Document 4] Japanese Patent Application Publication No. 10-60452 [Patent Document 5] Japanese Patent Application Laid-Open No. 2004-267987 Summary of the Invention [Problem to be solved by the invention]

[0006] The method of recovering hydrocarbons by pyrolysis of waste plastics, including PVC, requires the cost of neutralizing hydrochloric acid, is dangerous due to the high temperature process, and the high chlorine concentration in the recovered hydrocarbons makes them difficult to reuse.

[0007] The present disclosure aims to provide a method and processing device for treating waste plastics that can thermally decompose chlorine-containing waste plastics at low cost and with high safety to produce liquid oil with a low chlorine concentration. [Means for solving the problem]

[0008] The above problems can be solved by the following means. <1> Pyrolysis of chlorine-containing waste plastics in the presence of collected dust containing CaO under a water vapor atmosphere; recovering liquid oil from decomposition products produced by thermal decomposition of the waste plastic; A method for treating waste plastics, comprising: <2> The method includes cooling the water vapor atmosphere containing the decomposition products, recovering the water vapor as a hydrochloric acid solution in which chlorine derived from the waste plastics is dissolved in condensed water from the water vapor, and recovering the gas component that is not dissolved in the water as a fuel gas. <1> The method for treating waste plastics described above. <3> and recovering the solid residue after thermal decomposition of the waste plastics as a solid fuel by washing it with water. <1> or <2> The method for treating waste plastics described above. <4> The method includes either or both of using the wastewater after washing for cleaning the inside of a treatment facility that treats the waste plastics, and heating the wastewater after washing and using it as the steam. <3> The method for treating waste plastics described above. <5> and recovering calcium chloride by evaporating the water in the wastewater after the water washing. <3> or <4> The method for treating waste plastics described above. <6> The thermal decomposition of the waste plastic is carried out in a batch manner. <1> ~ <5> 1. A method for treating waste plastic according to any one of the above. <7> a thermal decomposition device that thermally decomposes chlorine-containing waste plastics in a water vapor atmosphere together with collected dust containing CaO; a condenser for obtaining liquid oil from decomposition products produced by the thermal decomposition of the waste plastic; A waste plastic treatment device comprising: [Effects of the Invention]

[0009] According to the present disclosure, a method and a processing device for waste plastics are provided that can thermally decompose chlorine-containing waste plastics at low cost and with high safety to produce liquid oil with a low chlorine concentration. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a diagram showing an example of a schematic configuration of a processing device that implements a waste plastic processing method according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0011] The inventors of the present disclosure have conducted extensive research into a method for pyrolyzing chlorine-containing waste plastics such as PVC (sometimes simply referred to as "waste plastics" in this disclosure) at low cost and with high safety to produce liquid oil with a low chlorine concentration. As a result, the inventors of the present disclosure have discovered that pyrolyzing waste plastics in the coexistence of collected dust containing CaO (sometimes simply referred to as "collected dust" in this disclosure) in a water vapor atmosphere allows for processing at low material costs and with high safety, and also makes it possible to produce liquid oil with a chlorine concentration of, for example, 260 ppm or less, thereby completing the present disclosure.

[0012] That is, the method for treating waste plastics according to the present disclosure includes pyrolyzing chlorine-containing waste plastics in the presence of collected dust containing CaO under a water vapor atmosphere, and recovering liquid oil from the decomposition products produced by the pyrolysis of the waste plastics. The waste plastic treatment method disclosed herein uses collected dust, primarily composed of CaO, obtained from steel mills and the like, to neutralize hydrochloric acid gas, thereby reducing material costs. Furthermore, the waste plastic treatment method disclosed herein performs thermal decomposition of the waste plastic in a steam atmosphere, eliminating concerns about combustion of the generated decomposition gas. Furthermore, the chlorine contained in the waste plastic reacts with the Ca contained in the collected dust and is incorporated into the solid residue, or dissolves in the water condensed from the steam atmosphere, thereby reducing the chlorine concentration in the liquid oil.

[0013] First, the materials used in the waste plastic processing method according to the present disclosure will be described.

[0014] (Waste plastic containing chlorine) The method for treating waste plastic according to the present disclosure uses waste plastic containing chlorine. Representative examples of plastics that contain chlorine (sometimes referred to as "chlorine-containing plastics" in this disclosure) include polyvinyl chloride (PVC) and polyvinylidene chloride (PVDC). PVC in particular is used, for example, as a covering material for pipes such as water pipes, electrical cords, and wire mesh, and a large amount of it is disposed of as industrial waste. The ratio of chlorine-containing plastics in the waste plastics to be treated is not particularly limited, and in addition to chlorine-containing plastics such as PVC, chlorine-free plastics such as polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyethylene terephthalate (PET) (sometimes referred to as "chlorine-free plastics" in this disclosure) may also be mixed in.

[0015] However, if the proportion of chlorine-containing plastics in the waste plastics is too high, the chlorine concentration in the liquid oil produced by pyrolysis will be high, while if the proportion of chlorine-containing plastics is too low, the amount of calcium contained in the collected dust will be excessive relative to the chlorine produced by pyrolysis. From the perspective of suppressing the chlorine content in the liquid oil produced and improving productivity, it is preferable to process waste plastics in which chlorine-containing plastics such as PVC are mixed with chlorine-free plastics with a high carbon-to-hydrogen ratio, such as PP, PS, and PE, in a mass ratio of 1:99 to 30:70. For example, when chlorine-containing plastics such as PVC and chlorine-free plastics such as PP, PS, and PE are processed together in a mass ratio of 10:90, dechlorination of over 99.9% by mass is possible.

[0016] (Collected dust containing CaO) Conventionally, Ca compounds such as CaO have been used when pyrolyzing waste plastics. However, in the waste plastic processing method according to the present disclosure, costs can be reduced by using collected dust containing CaO. The collected dust containing CaO can be collected by a dust collector in a factory or the like where CaO is generated. For example, in a steelworks, alkaline components such as CaO that are blown up from slag in a steelmaking process such as a converter are collected by a dust collector, generating a large amount of collected dust primarily composed of CaO. This collected dust generated in a steelworks (sometimes referred to as "steelworks CaO dust" in the present disclosure) can be suitably used.

[0017] Next, an example of a waste plastic processing method and processing device according to the present disclosure will be described in detail with reference to the drawings. Figure 1 shows an example of the schematic configuration of a processing device that implements the waste plastic processing method according to the present disclosure. The processing device 100 shown in Figure 1 is mainly configured with a heater 10, a water tank 12, a superheater 14, a pyrolysis device (pyrolysis furnace) 16, a condenser 18, a water washing device 22, and a wastewater tank 24.

[0018] First, a water tank 12 containing water is heated by a heater 10 to generate steam. This steam is then superheated to a temperature exceeding 100°C by a superheater 14. The superheated steam produced by the superheater 14 may be steam at a maximum temperature of 500°C, for example.

[0019] Next, the superheated steam is introduced into the pyrolysis device 16 through the pipe 20A. The pyrolysis device 16 is purged with steam to create an oxygen-free atmosphere. The pyrolysis device 16 is also heated by the heater 10, and the temperature inside the pyrolysis device 16 is controlled to be, for example, between 200°C and 500°C. The pyrolysis device 16 does not have a rotating conveyor such as a screw or rotary kiln that stirs the waste plastic 30, and is configured to perform thermal decomposition in a batch manner without stirring the waste plastic 30.

[0020] Waste plastic 30, which has been crushed in advance to a particle size of, for example, about 10 mm, and collected dust 40, which is mainly composed of CaO and has a particle size of 1 mm or less, are placed into the pyrolysis device 16. The mixing ratio of the waste plastic 30 to the collected dust 40 depends on the ratio of chlorine-containing plastic contained in the waste plastic and the ratio of CaO contained in the collected dust, but the mass ratio of waste plastic:collected dust is, for example, 10:90 to 90:10. After being added, the waste plastic 30 begins to thermally decompose in a superheated steam atmosphere. If oxygen is present in the atmosphere during the thermal decomposition of the waste plastic 30 containing PVC, an oxidation reaction may occur, resulting in the production of harmful dioxins. In the waste plastic processing method according to the present disclosure, the waste plastic 30 is thermally decomposed in a steam atmosphere, which does not create an oxidizing atmosphere and prevents the production of dioxins.

[0021] The decomposition products (cracked gas) produced by the thermal decomposition of the waste plastics 30 are introduced into the condenser 18 through the pipe 20B and condensed, for example, by a water spray method. This makes it possible to recover liquid oil 50, hydrochloric acid solution 54, and gas (gas fuel) 52 that does not condense and does not dissolve in water. The hydrochloric acid solution 54 is produced by dissolving chlorine derived from the waste plastics 30 in water that is a mixture of water sprayed in the condenser 18 and water obtained by condensing water vapor.

[0022] When the chlorine concentration in the liquid product (liquid oil fraction 50) is on the order of several percent, it is higher than the petroleum-based fuels used in thermal power plants, etc., and is therefore unsuitable as fuel. The chlorine concentration in the liquid oil fraction 50 obtained by the waste plastic processing method according to the present disclosure can be reduced to 260 ppm or less, making it suitable for use as fuel in thermal power plants, etc.

[0023] After the generation of decomposition gas in the thermal decomposition device 16 is completed, the residue remaining in the thermal decomposition device 16 is removed and washed with water in the water washing device 22. A portion of the collected dust 40, which is mainly composed of CaO that has absorbed chlorine, is washed with water, dissolved in water, and collected in the wastewater tank 24 as an aqueous solution (wastewater). A portion of the residue does not dissolve in water and remains as a solid residue. The insoluble solid residue is, for example, a heavy organic component, and can be used as a solid fuel 62, a raw material for ironmaking, etc.

[0024] In the case of a method in which waste plastics are heated by contact heat transfer using a rotary kiln, screw, or other rotating conveyor, it is desirable to remove ester compounds that are thought to be derived from PET and metal pieces as impurities beforehand. When waste plastics are pyrolyzed in a batch-type pyrolysis device 16, the waste plastics are pyrolyzed into oil without first removing impurities such as metal pieces mixed in, and the solid residue after pyrolysis can be used as solid fuel 62 or raw material for steelmaking after being washed with water.

[0025] On the other hand, if the waste plastic 30 contains PET, the esterified terephthalic acid produced after thermal decomposition may adhere to the inside of the pipe 20B between the thermal decomposition device 16 and the condenser 18, causing blockages. The wastewater (aqueous solution) remaining after use for washing the residue with water is derived from excess CaO and is alkaline, so it can be used as equipment washing water 70 for hydrolysis washing of ester-blocked matter thought to be derived from PET. If blockages such as terephthalic acid are generated and block the inside of pipe 20B, continuous operation will be hindered. However, continuous operation is possible by continuously cleaning the blockages using alkaline cleaning wastewater as described above.

[0026] Furthermore, the wastewater after washing the residue with water may be heated as water for steam 72 and used as steam in the pyrolysis device 16. In this case, after evaporation, calcium chloride is produced from chlorine (Cl) derived from the waste plastic 30 and calcium (Ca) derived from the collected dust 40, and this may be used as a snow-melting agent 64 containing calcium chloride as its main component. The wastewater after washing the residue with water may be used as either or both of water 70 for cleaning equipment and water 72 for steam.

[0027] As described above, according to the waste plastic treatment device 100 according to one embodiment of the present disclosure, chlorine-containing waste plastic 30 can be treated in a water vapor atmosphere using collected dust 40 containing CaO, thereby safely and at low cost, producing and recovering a liquid oil component 50 and a gas component 52 for recycling as fuel, etc. Furthermore, a hydrochloric acid aqueous solution 54, a solid fuel 62, and calcium chloride 64 can also be produced and recovered. Furthermore, the wastewater remaining after washing the solid residue with water can be used to clean equipment such as piping 20B and / or to generate water vapor for thermal decomposition of the waste plastic 30. This allows for the construction of a highly efficient recycling system using the waste plastic 30 and collected dust 40.

[0028] It should be noted that the waste plastic treatment device according to the present disclosure is not limited to the configuration shown in Fig. 1. For example, if the residue after pyrolysis of waste plastic is not reused, the treatment device may be mainly composed of a pyrolysis device 16 and a condenser 18. [Example]

[0029] Examples of the method for treating waste plastic according to the present disclosure will be described below. The following examples do not limit the method for treating waste plastic and the device for treating waste plastic according to the present disclosure.

[0030] A waste plastics treatment device having the general configuration shown in FIG. 1 was prepared. The waste plastics and collected dust were fed into the pyrolysis device in a mass ratio of PVC:PS:PP:PE:steel mill CaO dust = 1:1:1.5:1.5:1.34. Purging of superheated steam was started, and the inside of the furnace of the thermal decomposition apparatus was placed under a steam atmosphere. The temperature inside the furnace was increased by an average of 2.5°C / min up to 250°C, 2.7°C / min up to 320°C, 3°C / min up to 380°C, and 3.3°C / min up to 500°C. The temperature was increased at the above average rate throughout the entire temperature range.

[0031] Gas components were collected when the furnace temperature reached about 190°C, and liquid components were collected at about 210°C. Pyrolysis continued until the furnace temperature reached 500°C. The recovered liquid oil content was 40 to 55 mass % in terms of the mass ratio of carbon to hydrogen in the input raw material (waste plastic). The chlorine content in the liquid oil was 0.001% of the input raw material, and the dechlorination rate was 99.99% by mass or more. The chlorine concentration in the liquid oil was 260 ppm or less. The weight of the residue in the pyrolysis furnace was measured, and it was found that 88 mass % or more of the chlorine in the input raw material was fixed in the solid residue. [Explanation of symbols]

[0032] 10. Heater 12 Water Tank 14 Superheating device 16 Pyrolysis equipment 18 Condenser 20A, 20B piping 22 Water cleaning device 24 Wastewater Tank 30 Waste plastic 40 Dust collection 50 liquid oils 52 gas 54 Hydrochloric acid solution 62 Solid fuel 64 Calcium Chloride 70 Equipment cleaning water 72 Steam Water 100 Waste plastic processing equipment

Claims

1. Pyrolyzing chlorine-containing waste plastics in the presence of collected dust containing CaO under a water vapor atmosphere; recovering liquid oil from decomposition products produced by thermal decomposition of the waste plastic; A method for treating waste plastics, comprising:

2. 2. The method for treating waste plastic according to claim 1, further comprising: cooling the water vapor atmosphere containing the decomposition products; recovering the water vapor condensed into water as a hydrochloric acid aqueous solution in which chlorine derived from the waste plastic is dissolved; and recovering the gas component that does not dissolve in the water as a fuel gas.

3. 2. The method for treating waste plastics according to claim 1, further comprising washing the solid residue remaining after pyrolysis of the waste plastics with water and recovering it as solid fuel.

4. 4. The method for treating waste plastics according to claim 3, further comprising either or both of using the washed wastewater to clean the interior of a treatment facility that treats the waste plastics, and heating the washed wastewater to use it as steam.

5. 4. The method for treating waste plastics according to claim 3, further comprising evaporating the water in the wastewater after the water washing to recover calcium chloride.

6. 2. The method for treating waste plastics according to claim 1, wherein the thermal decomposition of the waste plastics is carried out in a batchwise manner.

7. a thermal decomposition device for thermally decomposing chlorine-containing waste plastics in a water vapor atmosphere in the presence of collected dust containing CaO; a condenser for obtaining liquid oil from decomposition products produced by the thermal decomposition of the waste plastic; A waste plastic treatment device comprising:

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