Waste plastic processing method

Abstract

Provided is a waste plastic processing method with which it is possible to achieve both high coke strength and a reduction in the organic chlorine concentration of gas oil and / or refined gas when chlorine-containing waste plastic is processed in a coke oven. Provided is a method for processing waste plastic by dry distillation of coal and chlorine-containing waste plastic in the presence of a Ca-containing substance in the carbonization chamber of a coke oven. The Ca-containing substance is added to a granulated product of the waste plastic to produce a composite granulated product containing the waste plastic and the Ca-containing substance, and the composite granulated product is charged into the carbonization chamber.

Description

Methods for disposing of waste plastics

[0001] This invention relates to a method for processing waste plastics.

[0002] In recent years, methods have been proposed to obtain recycled materials such as carbonized products, tar, diesel fuel, and refined gas by carbonizing waste plastics in a coke oven, from the perspective of effective resource utilization and contribution to achieving carbon neutrality. This method has advantages such as the ability to process large quantities of waste plastics and the effective use of existing coke ovens. However, knowledge of suitable carbonization conditions for processing waste plastics is still insufficient. For example, when obtaining products such as tar, diesel fuel, and refined gas from the gas generated during carbonization, there are sometimes permissible upper limits set for the chlorine concentration in the products. Chlorine can exist as inorganic chlorine (i.e., the chlorine (Cl) element that constitutes chlorinated inorganic materials) or organic chlorine (i.e., the chlorine (Cl) element that constitutes chlorinated organic materials). In this disclosure, when "chlorine" is simply referred to, it includes the above-mentioned inorganic chlorine and organic chlorine. If waste plastics contain chlorine, chlorine may remain in the recycled materials. Therefore, when processing waste plastics containing chlorine, it is desirable to construct processing conditions that can control the chlorine concentration of the products within a desired range. When waste plastics are charged into a coke oven, it is particularly desirable to reduce the concentration of organochlorines in the product from the perspective of environmental impact and equipment load.

[0003] As a method for controlling the quality of products obtained by carbonization using a coke oven, carbonization using coal with additives has been proposed. For example, Patent Document 1 describes the production of blast furnace coke in which coal is mixed with CaO or a CaO-containing substance, or MgO or a MgO-containing substance, and then charged into a coke oven for carbonization. Patent Document 2 describes the production of highly reactive small-lump coke in which one or two types of Ca compounds and Fe compounds are added to the blended coal.

[0004] On the other hand, regarding used plastics as a coke substitute, Patent Document 3 describes a method for blowing used plastics into a furnace, characterized in that, in the operation of a vertical furnace using used plastics as a furnace blowing material, a granular material is blown into the furnace, which is made by mixing used plastics with a substance that lowers the melting point of the ash produced by the combustion of used plastics, and at least a part of the substance that lowers the melting point of the ash may be a CaO source and / or an MgO source.

[0005] Japanese Patent Publication No. 2003-313561, Japanese Patent Publication No. 2010-095711, Japanese Patent Publication No. 2006-152331

[0006] The CaO and MgO described in Patent Document 1 are used to lower the melting point of ash produced by carbonization, and the CaO and MgO sources described in Patent Document 3 are used to lower the melting point of ash produced by combustion. Furthermore, the Ca and Fe compounds described in Patent Document 2 are used as catalysts in the gasification reaction of coke. However, these technologies have not contributed to reducing the chlorine concentration of products obtained by carbonization using a coke oven, particularly products such as diesel fuel and purified gas. In particular, no conventional carbonization method has yet been proposed that can achieve both high coke strength and a reduction in the organochlorine concentration of diesel fuel and / or purified gas using chlorine-containing waste plastics.

[0007] The present invention aims to solve the above problems and provide a method for processing waste plastics that can achieve both high coke strength and a reduction in the concentration of organochlorine in light oil and / or purified gas when processing chlorine-containing waste plastics in a coke oven.

[0008] The gist of the present invention is as follows: [1] A method for processing waste plastics by carbonizing coal and chlorine-containing waste plastics in the carbonization chamber of a coke oven in the presence of a Ca-containing substance, wherein a Ca-containing substance is added to the granules of the waste plastics to produce a composite granule containing the waste plastics and the Ca-containing substance, and the composite granule is charged into the carbonization chamber. [2] A method for processing waste plastics by carbonizing coal and chlorine-containing waste plastics in the carbonization chamber of a coke oven in the presence of a Ca-containing substance, wherein the relationship between the amount of Ca-containing substance added to the waste plastics and the organic chlorine concentration of the generated gas, light oil obtained from the generated gas, or purified gas obtained from the generated gas is investigated in advance, the amount of Ca-containing substance to be added is determined based on the relationship so that the organic chlorine concentration of the generated gas, light oil, and purified gas whose relationship was investigated is less than or equal to a target organic chlorine concentration, and the Ca-containing substance is added to the granules of the waste plastics in the determined amount. [3] As the relationship described above, a relationship is obtained between a variable x, which is the amount of Ca-containing substance added to the waste plastic, and a variable y, which is the degree of change in the organic chlorine concentration of the generated gas, the light oil obtained from the generated gas, or the purified gas obtained from the generated gas, from before the addition of the Ca-containing substance to after the addition of the Ca-containing substance, and the value of the variable x obtained when the target value of the rate of change in the organic chlorine concentration of the generated gas, the light oil, and the purified gas for which the relationship described above was obtained is substituted for variable y is determined as the amount of Ca-containing substance added to the waste plastic, as described in [2]. [4] A method for treating waste plastic according to any one of [1] to [3], wherein a mixture of coal and the composite granules is charged into the carbonization chamber, as described in [1] to [3].

[0009] According to the present invention, a method for processing waste plastics containing chlorine is provided that can achieve both high coke strength and a reduction in the organic chlorine concentration of light oil and / or purified gas when processing chlorine-containing waste plastics in a coke oven.

[0010] Figure 1 shows the relationship between the organic chlorine concentration of the generated gas and the organic chlorine concentration of the diesel fuel. Figure 2 shows the organic chlorine concentration of the generated gas in the examples and comparative examples.

[0011] The following describes exemplary embodiments of the present invention (which may also be referred to as "embodiments" in this disclosure), but the present invention is not limited to these embodiments.

[0012] One aspect of the present invention provides a method for processing waste plastics by carbonizing coal and chlorine-containing waste plastics in the carbonization chamber of a coke oven in the presence of a Ca-containing substance. In this method, a Ca-containing substance is added to granules of waste plastics to produce a composite granule containing waste plastics and the Ca-containing substance (hereinafter sometimes simply referred to as a composite granule), and this composite granule is charged into the carbonization chamber.

[0013] The components charged into the carbonization chamber (i.e., intentionally introduced into the carbonization chamber) may consist only of coal, waste plastics, and Ca-containing materials, or they may include components other than coal, waste plastics, and Ca-containing materials (for example, one or more of binders, surfactants, biomass, etc.). The amount of components other than coal, waste plastics, and Ca-containing materials may be an amount that does not impair the effects of the present invention, for example, 10% by mass or less out of 100% by mass of the total amount of charged material. In a typical embodiment, the components charged into the carbonization chamber consist only of coal, waste plastics, and Ca-containing materials. When components other than coal, waste plastics, and Ca-containing materials are charged into the carbonization chamber, "carbonizing coal and chlorine-containing waste plastics in the presence of Ca-containing materials" in this disclosure means carbonizing a charge that also contains components other than coal, waste plastics, and Ca-containing materials. The charging timing for components other than coal, waste plastics, and Ca-containing materials may be simultaneous with the charging timing for at least one of the coal, waste plastics, and Ca-containing materials, or it may be different from the charging timing for all of the coal, waste plastics, and Ca-containing materials. Typically, the charging timing for components other than coal, waste plastics, and Ca-containing materials is simultaneous with the charging timing for at least one of the coal, waste plastics, and Ca-containing materials.

[0014] When waste plastics are thermally decomposed in the carbonization chamber of a coke oven, they can produce carbonized products (carbon residue), hydrocarbon oil (tar or diesel fuel), and refined gas (hydrocarbon gas, hydrogen gas, etc.). In this embodiment, carbonization of coal and waste plastics can produce carbonized products (coke), tar, diesel fuel, and refined gas as useful materials. The carbonized product (coke) can be used for blast furnaces and various other applications depending on its quality. The hydrocarbon oil can be used, for example, as a raw material for various chemical products. The refined gas can be used, for example, as fuel for power generation. In a typical embodiment, the product extracted from the coke oven may have a component composition of approximately 20% by mass of coke, approximately 40% by mass of oil, and approximately 40% by mass of refined gas.

[0015] A coke oven generally has a configuration in which a carbonization chamber and a combustion chamber are alternately arranged in the direction of the furnace width above a heat storage chamber. Coal and waste plastics charged into the carbonization chamber are carbonized by heat transfer from the combustion chamber, producing carbonized material, tar, diesel fuel, and refined gas as useful products. In this disclosure, the generated gas encompasses all gases that flow out of the coke oven via a riser pipe during carbonization in the carbonization chamber of the coke oven. The carbonized material is extruded in the direction of the furnace length by an extruder. The generated gases from the coke oven flow out of the coke oven via a riser pipe from the carbonization chamber and are separated from each other to produce tar, diesel fuel, and refined gas. Each carbonization chamber usually has multiple charging holes. Coal and waste plastics may each be charged into the carbonization chamber from one or more charging holes, for example, two, three, four, or five charging holes.

[0016] There are no restrictions on the timing of charging coal and waste plastics. The order in which the carbonization of coal progresses and the carbonization of waste plastics progresses is not a concern.

[0017] When chlorine-containing waste plastics are subjected to dry distillation, chlorine may remain in both the dry product and the generated gas. The majority of the chlorine in the generated gas (usually 99% or more, based on the number of chlorine atoms) is inorganic chlorine, existing as hydrogen chloride, etc. Inorganic chlorine can be neutralized by relatively easy methods, such as flushing with ammonia to convert it to ammonium chloride. On the other hand, some of the chlorine in the generated gas (usually less than 1%, based on the number of chlorine atoms) is organic chlorine, existing as chloromethane, chlorobenzene, etc., and is difficult to remove. Residual organic chlorine in the generated gas or the products obtained from it can cause environmental burdens and equipment malfunctions (corrosion, etc.).

[0018] In this embodiment, chlorine-containing waste plastics are carbonized in a coke oven in the presence of a Ca-containing substance. This allows the chlorine in the waste plastics to be converted to CaCl2 and retained (i.e., trapped) in the coke. The coke produced in the waste plastic processing method of this embodiment may contain Ca elements derived from the Ca-containing substance, and the waste plastic processing method of this embodiment does not require additional operations to separate or recover CaCl2. If the proportion of chlorine distributed into the coke from the chlorine brought into the coke oven increases, the proportion of chlorine distributed into the generated gas from the chlorine brought into the carbonization chamber will decrease. In addition, in the generated gas, chlorine atoms brought in as inorganic chlorine may constitute organic matter (i.e., inorganic chlorine is converted to organic chlorine). If the chlorine concentration in the generated gas is reduced, the generation of organic chlorine in the generated gas will also be reduced, thus reducing the organic chlorine concentration in the generated gas, and as a result, the organic chlorine concentration in the diesel fuel and refined gas obtained from the generated gas may be reduced. Thus, according to the method of this embodiment, the organic chlorine concentration in the generated gas can be reduced by the simple operation of adding a Ca-containing substance, and as a result, the organic chlorine concentration in the diesel fuel and purified gas obtained from the generated gas can be reduced. In addition, the inventors have found that the Ca-containing substance added to the waste plastic granules does not have a significant effect on the coke strength. Therefore, according to the method of this embodiment, it is possible to achieve both high coke strength and a reduction in the organic chlorine concentration of diesel fuel and / or purified gas. The organic chlorine concentration in the generated gas is determined by combustion ion chromatography. The generated gas sample to be used for measurement may be either before or after ammonia water flushing. If the sample is generated gas before ammonia water flushing, the sample is subjected to bubbling in water to remove inorganic chlorine before being subjected to measurement. According to the inventors' studies, inorganic chlorine (especially HCl) is removed by bubbling the generated gas in water, and it has been separately confirmed that inorganic chlorine is not actually present in the gas obtained by this treatment. Furthermore, if the sample is a gas generated after ammonia water flushing, inorganic chlorine has been removed by ammonia water flushing.Therefore, the chlorine concentration obtained by combustion ion chromatography of the generated gas can be considered as the organic chlorine concentration of the generated gas. Although the method of this embodiment focuses particularly on reducing the organic chlorine concentration of diesel fuel and refined gas, the same reduction in organic chlorine concentration can be achieved in tar obtained from the generated gas.

[0019] <Coal> The coal charged into the carbonization chamber may be one or more types of coal, and may be pulverized coal, molded coal, or a combination thereof. There are no particular restrictions on the type of coal. Pulverized coal refers to crushed coal, and includes coal that has been further size-adjusted after crushing, and agglomerated coal when agglomerated coal is mixed in. In this disclosure, agglomerated coal refers to coal with an equivalent spherical radius of less than 6 mm obtained by adding a binding agent to pulverized coal (in one embodiment, pulverized coal below a 0.3 mm sieve) and press-molding. In this disclosure, molded coal refers to coal with an equivalent spherical radius of 6 mm or more obtained by adding a binding agent to pulverized coal (in one embodiment, pulverized coal below a 0.3 mm sieve) and press-molding.

[0020] In one embodiment, the moisture content of the coal charged into the carbonization chamber may be 0% by mass to 10% by mass. The moisture content may be reduced, for example, by a conventionally known coal dryer.

[0021] <Waste Plastics> Waste plastics may be general waste or industrial waste, and there are no limitations on their origin. For example, waste plastics may originate from one or more sources selected from bottles (e.g., PET bottles and non-PET bottles), bottle caps, packaging films, packaging materials (e.g., expanded polystyrene packaging materials), home appliances (e.g., home appliance casings), logistics materials (e.g., pallets and containers), agricultural plastics, automobile parts, pipes, wire insulation materials, etc. In one embodiment, waste plastics may originate from one or more sources. Waste plastics may consist of one or more polymers.

[0022] Waste plastics are plastics collected as various types of waste, which may be general waste or industrial waste. In one aspect, they are plastics that meet the sorting standards of the revised Container and Packaging Recycling Law (Law Amending Part of the Law Concerning the Promotion of Separate Collection and Recycling of Containers and Packaging (Law No. 76 of June 15, 2006)), which came into effect in April 2007 (for example, PET bottles and plastic containers and packaging). Such sorting standards-compliant materials have a relatively uniform material composition, which may be advantageous for producing high-quality recycled materials.

[0023] Waste plastics may contain thermoplastic polymers and / or thermosetting polymers. Examples of thermoplastic polymers include polyolefins (e.g., polyethylene and polypropylene), polyesters (e.g., polyethylene terephthalate, polyethylene naphthalate, and polybutylene terephthalate), acrylic resins, polyvinyl alcohol, polyvinyl chloride, polyvinylidene chloride, polystyrene, polycarbonate, polyamide, polyacetal, and fluororesins. Examples of thermosetting polymers include phenolic resins, melamine resins, urea resins, polyurethanes, epoxy resins, and unsaturated polyester resins.

[0024] The waste plastic charged into the carbonization chamber in this embodiment contains chlorine. Such waste plastic may consist solely of chlorine-containing polymers, or it may be a combination of chlorine-containing polymers and chlorine-free polymers. Examples of chlorine-containing polymers include polymers having at least chlorine-containing repeating units (e.g., polyvinyl chloride, polyvinylidene chloride, vinyl chloride-vinyl acetate copolymer, vinylidene chloride-vinyl chloride copolymer, vinylidene chloride-acrylonitrile copolymer), and chlorinated products of the thermoplastic polymers or thermosetting polymers exemplified above (e.g., chlorinated polyolefins).

[0025] In one embodiment, the chlorine (Cl) element concentration in 100% by mass of the total amount of waste plastic charged into the carbonization chamber may be between 1% by mass and 70% by mass. In one embodiment, the Cl element concentration may be 1% by mass or more, or 5% by mass or more, or 10% by mass or more, or 20% by mass or more, or 30% by mass or more, or 40% by mass or more, or 50% by mass or more, or 55% by mass or more, and in one embodiment, it may be 70% by mass or less, or 65% by mass or less. The above Cl element concentration is the arithmetic mean of the polymers if the waste plastic is a combination of two or more polymers. For example, if the waste plastic is a 1:1 (mass ratio) combination of a chlorine-containing polymer with a Cl element concentration of 50% by mass and a chlorine-free polymer, the Cl element concentration in 100% by mass of the waste plastic is 25% by mass. The Cl element concentration of the waste plastic is a value obtained using combustion ion chromatography.

[0026] From the viewpoint of carbonization efficiency, the moisture content of the waste plastic may be 30% by mass or less, 20% by mass or less, 15% by mass or less, or 10% by mass or less in one embodiment.

[0027] The waste plastics charged into the carbonization chamber are granulated (i.e., molded granules). The granulated material only needs to have a granular form, and the method of obtaining the granulated material is not limited. For example, if the recovered waste plastic is granular, the granulated material can be used as is. Alternatively, the recovered waste plastic may be crushed to a desired particle size, or the recovered waste plastic may be crushed and then molded to a desired particle size (e.g., by extrusion molding). The waste plastic may be pre-treated after recovery before being charged into the carbonization chamber. Examples of pre-treatment include crushing, removal of foreign matter, granulation, and adjustment of moisture content by drying. Removal of foreign matter may include removal of metals using a magnetic separator or removal of heavy objects using an air separator. Crushing and granulation may be carried out using, for example, compression type, shear type, cutting type, impact type, or friction type crushers.

[0028] In one embodiment, the particle size of the granules may be 10 mm to 50 mm or 25 mm to 40 mm. In the case of a shape with a base (e.g., cylinder, elliptical cylinder, etc.), the particle size refers to the major axis of the base (or the maximum value if the values ​​differ between bases), and in the case of a shape without a base (e.g., sphere, ellipsoid, irregularly shaped solid, etc.), it refers to the major axis of the shape. In one embodiment, the granules are distinguished from powders and bulk materials by having a particle size of 10 mm to 50 mm as described above.

[0029] The amount of waste plastic charged into the carbonization chamber relative to 100% by mass of coal may be set appropriately according to the properties of the desired product. From the viewpoint of obtaining the advantage of processing a large amount of waste plastic, in one embodiment it may be 0.5% by mass or more, or 1% by mass or more, or 5% by mass or more, or 10% by mass or more. From the viewpoint of keeping the organochlorine concentration of the product low and obtaining high coke strength, in one embodiment it may be 5% by mass or less, or 3% by mass or less, or 1% by mass or less. The amount may be, for example, 1% by mass to 5% by mass.

[0030] <Ca-containing substances> Useful Ca-containing substances are those that can react with chlorine-containing substances (mainly HCl) generated from waste plastics to form calcium chloride (CaCl2). Examples of Ca-containing substances include calcium hydroxide, calcium carbonate, and calcium oxide, but calcium hydroxide or calcium carbonate are preferred from the viewpoint of availability and ease of handling. Ca-containing substances may be used in any form, such as powder or dispersion in a medium (e.g., water).

[0031] The amount of Ca-containing substance added may be 0.5% to 10% by mass in one embodiment, based on the amount of Ca relative to 100% by mass of waste plastic and on a Ca element basis. From the viewpoint of reducing the organochlorine concentration, the amount of this addition may be 0.5% or more by mass, or 1% or more by mass, or 1.5% or more by mass, in one embodiment. There is no particular upper limit on the amount of Ca-containing substance, but in one embodiment, based on the Ca element, it may be 10% or less by mass, or 8% or less by mass, or 5% or less by mass, or 3% or less by mass. When Ca-containing substance is added to coal, it may be advantageous from the viewpoint of high coke strength if the amount of Ca-containing substance added is 3% or less by mass, or 2% or less by mass, or 1% or less by mass, or 0.5% or less by mass, based on the amount of Ca relative to coal.

[0032] In one embodiment, after collection, waste plastic is crushed, granulated, and then charged into a carbonization chamber. Ca-containing material is added to the granulated waste plastic. Examples of addition methods include coating the outside of the granulated waste plastic, immersion, etc. Coating is preferred from the viewpoint of uniformly distributing the Ca-containing material on the surface of the waste plastic. Addition after granulation is also preferable from an equipment standpoint as it is easy to implement even when the waste plastic is obtained as granulated material. Examples of coating methods include applying the granulated material to a mixture of water and Ca-containing material (e.g., a water-containing paste), pouring the mixture over the granulated material, flowing the mixture in a curtain-like manner and passing the granulated material through it, and immersing the granulated material in the mixture. The temperature of the Ca-containing material when added to the waste plastic may be 5°C or higher and less than 250°C. By charging the pre-prepared composite granules into the carbonization chamber, the desired reaction between the Ca-containing material and the chlorine-containing material derived from the waste plastic can proceed even in a carbonization chamber without stirring means.

[0033] When Ca-containing substances are added to waste plastics, the decrease in coke strength tends to be smaller than when they are added to coal. Although not bound by theory, it is thought that the addition of Ca-containing substances does not adversely affect coke strength because a fragile structure is easily formed in waste plastics and at the interface between waste plastics and coke. In the method of this embodiment, by adding a Ca-containing substance to the granulated waste plastic, high coke strength can be achieved while reducing the organochlorine concentration of the generated gas. Furthermore, the inventors have separately confirmed that if the organochlorine concentration in the generated gas is reduced, the organochlorine concentration in the diesel fuel and / or refined gas will also be reduced. Therefore, the method of this embodiment can reduce the organochlorine concentration of diesel fuel and / or refined gas while achieving high coke strength.

[0034] <Carbonization> In this embodiment, waste plastics can be processed using a carbonization chamber used for coal carbonization. This allows waste plastics to be processed without interrupting the process of producing coke from coal. The carbonization conditions (temperature, time, etc.) may be the same as those used when producing coke using only coal. In one embodiment, the carbonization temperature may be 700°C to 1400°C, for example, 900°C to 1200°C. For example, in polyvinyl chloride (PVC), a primary pyrolysis reaction occurs at about 250°C or higher, and a secondary pyrolysis reaction occurs at about 400°C due to main chain severance. High-temperature carbonization using a coke oven is excellent for the thermal decomposition of waste plastics. In addition, in the method of this embodiment, the concentration of organochlorines in the generated gas is reduced by using a Ca-containing substance.

[0035] <Determination of the amount of Ca-containing substance to be added> In one embodiment, the relationship between the amount of Ca-containing substance added to waste plastic and the organic chlorine concentration of the generated gas, the diesel fuel obtained from the generated gas, or the purified gas obtained from the generated gas (this may be the absolute value of the organic chlorine concentration, or an index value related to the organic chlorine concentration, for example, the degree of change after adding the Ca-containing substance compared to before adding the Ca-containing substance) may be investigated in advance. Based on the above relationship, the amount of Ca-containing substance to be added may be determined so that the organic chlorine concentration of the generated gas, diesel fuel, and purified gas for which the above relationship was investigated (this may be the absolute value of the organic chlorine concentration, or an index value related to the organic chlorine concentration, for example, the degree of change after adding the Ca-containing substance compared to before adding the Ca-containing substance) is less than or equal to the target value. The above degree of change as an index value may be selected as desired from the rate of change (i.e., ratio), the amount of change (i.e., difference), etc. The above relationship represents the effect that the addition of Ca-containing substance has on the organic chlorine concentration. Therefore, by using the above relationship, it is possible to determine the amount of Ca-containing substance to add that can eliminate the discrepancy between the target value and the current value (specifically, the value before the addition of the Ca-containing substance) of the organochlorine concentration in the generated gas, diesel fuel, or refined gas.

[0036] The target organochlorine concentration of the generated gas may be determined based on a desired value for the organochlorine concentration of the product obtained from the generated gas. In one embodiment, diesel fuel and purified gas can be produced from the generated gas. In one embodiment, the target organochlorine concentration of the diesel fuel may be 50 mg / L or less, 25 mg / L or less, 13 mg / L or less, or 10 mg / L or less. In one embodiment, the target organochlorine concentration of the purified gas may be 18 μg / L or less, 9 μg / L or less, 5 μg / L or less, or 4 μg / L or less. The inventors have separately confirmed that if the organochlorine concentration of the generated gas is reduced, the organochlorine concentrations of the diesel fuel and purified gas will also be reduced. In a preferred embodiment, the target organochlorine concentration of the generated gas is determined to be below one or two of the desired target organochlorine concentrations of the diesel fuel and the purified gas. From this perspective, in one embodiment, the target organochlorine concentration of the generated gas may be 20 μg / L or less, 10 μg / L or less, 6 μg / L or less, or 5 μg / L or less. While a lower target organochlorine concentration of the generated gas is ideal, reducing the organochlorine concentration to an even lower value requires more Ca-containing material. Considering process efficiency, the impact on coke strength when the amount of Ca-containing material is increased, etc., the target organochlorine concentration of the generated gas may, in one embodiment, be 3 μg / L or more.

[0037] The desired coke strength may be predetermined depending on the desired use of the coke, the type of coke oven, the carbonization conditions, etc.

[0038] Furthermore, the organic chlorine concentration of the generated gas, diesel fuel, or refined gas may vary depending on the type and amount of coal and waste plastic, the type of Ca-containing substance, the type of coke oven, the carbonization conditions, etc. However, by examining the relationship between the amount of Ca-containing substance added and the organic chlorine concentration of the generated gas, diesel fuel, or refined gas under the actual operating conditions used for the carbonization of coal and waste plastic (type and amount of coal and waste plastic, type of Ca-containing substance, type of coke oven, carbonization conditions, etc.), or under test conditions that simulate these operating conditions, it is possible to estimate which amount of Ca-containing substance will achieve the target organic chlorine concentration. Therefore, for example, the above relationship examined with a certain type of waste plastic should not be used when using a different type of waste plastic, and it is desirable to re-examine the above relationship with the same type of waste plastic that will actually be used. The same applies to the type of Ca-containing substance, the type of coal, the type of coke oven, the carbonization conditions, etc.

[0039] The above relationship may be determined in one embodiment as follows. First, a carbonization test is performed in the carbonization chamber of a coke oven by charging coal and waste plastic containing chlorine. In one embodiment, coal and waste plastic may be charged at the same time, or waste plastic may be charged after the carbonization of coal. The carbonization test is performed for two or more, three or more, or four or more test conditions, each with only the amount of Ca-containing substance added being changed. A larger number of test conditions is preferable, but for the convenience of the test, it may be 15 or less, or 10 or less. It is desirable that the waste plastic used in the carbonization test to determine the relationship has the same or similar material composition as the waste plastic used in actual operation. An example of waste plastic used in actual operation and waste plastic used in the carbonization test having the same or similar material composition is when these waste plastics are collected via the same waste collection route. The waste plastic used in the carbonization test may be a sample of a portion of the waste plastic used in actual operation. If the density of the granulated waste plastic differs between the waste plastic used in actual operation and the waste plastic used for the carbonization test, it is preferable to select a different type of waste plastic for the carbonization test so that the densities are similar. Density can vary depending on the material composition, but it can also vary depending on the granulation method.

[0040] In each carbonization test, the organochlorine concentration is measured for the generated gas, the light oil obtained from the generated gas, or the purified gas obtained from the generated gas. It is preferable that the coke oven used for the measurement and the carbonization conditions are the same as those for carbonization in actual operation.

[0041] In one aspect, the organochlorine concentration of the generated gas is measured by sampling a part of the generated gas during carbonization. The timing for collecting the generated gas may be 5 minutes or 20 minutes after the start of carbonization, and every 20 minutes thereafter up to 420 minutes. In one aspect, the organochlorine concentration of each of the light oil and the purified gas is measured as the chlorine concentration obtained when the light oil and the purified gas are sampled and each is measured by combustion ion chromatography.

[0042] In a preferred embodiment, it may be confirmed by measuring the coke strength that no reduction in coke strength due to the influence of Ca-containing substances has occurred, that is, that the desired coke strength has been obtained. The coke strength may be drum strength (DI) measured by a drum test in accordance with JIS K 2151. Depending on the desired properties of coke, the index of coke strength can be selected from DI 150 15 , DI 150 ₆ and the like. In one aspect, DI 150 15 may be used as an index of coke strength. DI 150 15 is the mass percentage of coke retained on a 15 mm sieve after rotating the drum 150 times in the above drum test. DI 150 ₆ is the mass percentage of coke retained on a 6 mm sieve after rotating the drum 150 times in the above drum test.

[0043] Note that the relational expression may be obtained based on the measurement results related to the performance of the immediately preceding actual operation batch, instead of the measurement results obtained from the carbonization test.

[0044] Next, a relational equation is determined based on the measured organochlorine concentration. For example, these relational equations may be determined by regression analysis with the amount of Ca-containing substance added as the explanatory variable and the organochlorine concentration of the generated gas, diesel fuel, or refined gas as the dependent variable. The regression may be linear regression or nonlinear regression (e.g., polynomial regression), and for example, the least squares method may be used.

[0045] In one embodiment, a relationship can be found between a variable x, which is the amount of Ca-containing substance added to waste plastic, and a variable y, which is the degree of change in the organochlorine concentration of the generated gas, the diesel fuel obtained from the generated gas, or the purified gas obtained from the generated gas, compared to before the addition of the Ca-containing substance. The degree of change may be a rate of change (specifically, the ratio of the value after the addition of the Ca-containing substance to the value before the addition of the Ca-containing substance) or an amount of change (specifically, the difference obtained by subtracting the value before the addition of the Ca-containing substance from the value after the addition of the Ca-containing substance).

[0046] As an example, if we use the rate of change as the degree of change in the organic chlorine concentration after the addition of the Ca-containing substance compared to before the addition of the Ca-containing substance, and use linear regression, the following relation (1) is obtained: 1 - y = ax + b (1) (In this equation, x is the amount of the Ca-containing substance added to the waste plastic (in one embodiment, the mass %) of the extra number relative to 100% by mass of the waste plastic, y is the degree of change in the organic chlorine concentration after the addition of the Ca-containing substance compared to before the addition of the Ca-containing substance, and a and b are constants.) The constant a represents the degree of change in the organic chlorine concentration per unit amount of the Ca-containing substance added. The left side of the above equation (1), "1 - y", means: 1 - (organic chlorine concentration after the addition of the Ca-containing substance) / (organic chlorine concentration before the addition of the Ca-containing substance) That is, [(organic chlorine concentration before the addition of the Ca-containing substance) - (organic chlorine concentration after the addition of the Ca-containing substance)] / (organic chlorine concentration before the addition of Ca(OH)2).

[0047] There are no particular restrictions on how to confirm whether the regression analysis was performed effectively; the test may be performed using standard methods. The significance level may be selected as desired, for example, 5% or 1%.

[0048] Furthermore, in the said relational equation, the value of the variable x obtained by substituting the target value of the rate of change (degree of change) of the organochlorine concentration of the generated gas, diesel fuel, and purified gas for which the relational equation was derived, after the addition of the Ca-containing substance compared to before the addition of the Ca-containing substance, into the variable y, may be determined as the amount of Ca-containing substance to be added to the waste plastic.

[0049] As another example, if the indicator for the degree of change in the organic chlorine concentration after adding the Ca-containing substance compared to before the addition of the Ca-containing substance is to be the amount of change rather than the rate of change described above, then the equation y = ax + b, obtained by substituting 1 - y on the left side of equation (1) above with y, may be used, and a target value of the difference obtained by subtracting the value before the addition of the Ca-containing substance from the value after the addition of the Ca-containing substance, relating to the organic chlorine concentration of the generated gas, diesel fuel, or purified gas, may be substituted for y.

[0050] For example, by following the procedure described above, the amount of Ca-containing substance to be added is determined so that the organic chlorine concentration of the generated gas, diesel fuel, or refined gas is below the target organic chlorine concentration. When processing waste plastics, the Ca-containing substance should be added to the granulated waste plastic in the amount determined above.

[0051] Furthermore, if a change in the type of waste plastic being charged is expected to cause a fluctuation in the chlorine concentration of the waste plastic, a corrected amount of Ca-containing substance to be added may be calculated by multiplying the amount of Ca-containing substance to be added using the procedure described above by the ratio of [chlorine concentration after fluctuation] / [chlorine concentration before fluctuation]. When charging waste plastic with the fluctuating chlorine concentration, the Ca-containing substance should be added using the corrected amount. With the above correction, even if the chlorine concentration of the waste plastic being charged varies, a good effect of reducing the organochlorine concentration by using Ca-containing substances can be obtained.

[0052] The following describes exemplary embodiments of the present invention with reference to examples, but the present invention is not limited to these embodiments.

[0053] ≪Example of preliminary study 1≫ As a preliminary study, the relationship between the organic chlorine concentration in the generated gas and the organic chlorine concentration in the diesel fuel and refined gas was investigated. In a coke oven in operation, tests were conducted for several days each using two types of plastic with different chlorine content in all furnace groups, and the generated gas from the furnace groups was sampled at the suction main and the chlorine concentration was measured. The samples used for measurement had undergone ammonia water flushing, which removed inorganic chlorine. Therefore, the value measured as the chlorine concentration in the generated gas was considered to be the organic chlorine concentration of the generated gas. Separately, the chlorine concentration of diesel fuel obtained through the chemical refining process from the generated gas (from which inorganic chlorine had been removed by ammonia water flushing) from all furnace groups was also measured. Therefore, the value measured as the chlorine concentration in the diesel fuel was considered to be the organic chlorine concentration of the diesel fuel.

[0054] The operating conditions were changed to the following two levels by pre-mixing coal and plastic before charging it into the coke oven: [Level 1] Waste plastic with a chlorine concentration of 8300 ppm was added at an addition rate of 1% by mass (extra amount relative to 100% by mass of coal). [Level 2] Waste plastic with a chlorine concentration of 1300 ppm was added at an addition rate of 1% by mass (extra amount relative to 100% by mass of coal).

[0055] At each level, the generated gas was collected off-take main, and two samples were taken with an interval of at least six hours between them. Diesel fuel was also sampled twice, once per day. Considering that it would be stored in a relay tank, two samples of diesel fuel were taken once per day, at least two days after switching the type of waste plastic being added. All values ​​were averaged and used for analysis. If the values ​​varied, a larger number of samples should be taken and the average value used.

[0056] The chlorine concentration was measured using the procedure described below in [Measurement Conditions for Combustion Ion Chromatography]. The results are shown in Table 1. A plot of these results is shown in Figure 1.

[0057]

[0058] FIG. 1 shows the relationship between the organochlorine concentration in the generated gas and the organochlorine concentration in light oil. As can be seen from FIG. 1, it was confirmed that the organochlorine concentration in the generated gas correlates with the organochlorine concentration in light oil. Although not evaluated in the present study, since the main chlorine-containing chemical products obtained by purifying the generated gas are light oil and purified gas, it is considered that the organochlorine concentration in purified gas also correlates with the organochlorine concentration in the generated gas. Therefore, based on the above results, it is considered that when the organochlorine concentration in the generated gas is reduced, the organochlorine concentrations in light oil and purified gas will also be reduced.

[0059] <<Example 1, Comparative Example 1 and 2>> <Test Conditions> Coal and chlorine-containing waste plastics were carbonized using a test carbonization furnace. The test conditions are as follows. Sample width: 415 mm Sample length: 490 mm Sample height: 460 mm Coal charging bulk density: approx. 0.80 dry-t / m 3 For all test levels, carbonization was carried out at a carbonization temperature of 1050°C for 21 hours. At this time, the waste plastic was mixed with coal and charged.

[0060] <Materials Used> Waste plastic: Container-recycled waste plastic (a mixture mainly composed of polypropylene, polyethylene, polystyrene, polyethylene terephthalate, polyvinyl chloride, and polyvinylidene chloride; chlorine concentration: 1.5% by mass). The above chlorine concentration was measured for a powder sample of the waste plastic by the procedure described in [Measurement Conditions for Combustion Ion Chromatography] described later. Ca-containing substance: Ca(OH)₂ reagent (available from Kishida Chemical Co., Ltd., product number 000-13605, average diameter 6.6 μm) Coal: Pulverized coal pulverized to a 3 mm sieve pass ratio of 85% by mass, moisture content 4% by mass Waste plastic was granulated by a granulator with a diameter (i.e., die pore diameter) of 35 mm at a granulation temperature of 110°C, to obtain a waste plastic granule with a diameter of 35 mm.

[0061] <Carbonization Test> [Comparative Example 1] 71.27 kg of coal and 3.56 kg of waste plastic granules were carbonized. Therefore, the addition amount of the waste plastic granules is 5% by mass on an external basis relative to 100% by mass of coal. The waste plastic granules were mixed with coal and charged.

[0062] [Example 1] A paste was obtained by mixing Ca(OH)2 / water at a ratio of 1 / 1.8 (mass ratio). The paste was used to coat 3.56 kg of waste plastic granules with 0.18 kg of Ca(OH)2 (5% by mass relative to 100% by mass of waste plastic (approximately 2.70% by mass on a Ca element basis)) to obtain a composite granule. The coating was performed by placing the plastic granules in a bag containing the paste and shaking it well. 71.27 kg of coal and the obtained composite granule were subjected to dry distillation. Therefore, the amount of waste plastic granules added was 5% by mass relative to 100% by mass of coal. The composite granule was added mixed with coal.

[0063] [Comparative Example 2] Coal and Ca(OH)2 powder were mixed so that the amount of Ca(OH)2 was 0.18 kg (0.25% by mass relative to 100% by mass of coal) for 71.27 kg of coal. The resulting mixture and 3.56 kg of waste plastic granules were carbonized. Therefore, the amount of waste plastic granules added was 5% by mass relative to 100% by mass of coal. The waste plastic granules were mixed with coal and charged.

[0064] <Chlorine Concentration Measurement> Twenty minutes after the start of carbonization, a portion of the generated gas was sampled, bubbled in water, and then collected in an aluminum gas bag (capacity 1 L). The chlorine concentration of the gas in the gas bag was measured using combustion ion chromatography under the following conditions.

[0065] [Measurement Conditions for Combustion Ion Chromatography] The test was performed using a combustion IC consisting of a Nitto Seiko Analytech Co., Ltd. / AQF-2100H combustion section and a Thermo Fisher Scientific Co., Ltd. / Integrion RFIC IC section. The IC column was Dionex IonPac AS22, and 20 mM KOH was used as the eluent. The amount of gas sample introduced was 100 ml, and the sample was burned at a temperature of 1000°C with a gas atmosphere of Ar: 200 ml / min and O2: 400 ml mixed atmosphere, and chlorine was measured.

[0066] Here, inorganic chlorine (HCl) is removed by bubbling the generated gas in water, and it has been separately confirmed that inorganic chlorine is not actually present in the gas obtained by this process. Therefore, the chlorine concentration of the gas in the gas bag was considered to be the organic chlorine concentration. The results are shown in Figure 2.

[0067] Referring to Figure 2, a comparison with Comparative Example 1 (coal and waste plastic only) shows that the addition of waste plastic significantly increases the organic chlorine concentration in the generated gas. A comparison between Comparative Example 1 (coal and waste plastic only) and Example 1 (with Ca(OH)2 added to waste plastic) and Comparative Example 2 (with Ca(OH)2 added to coal) shows that Ca(OH)2 reduces the organic chlorine concentration in the generated gas regardless of whether it is added to waste plastic or coal. It is thought that the addition of Ca(OH)2 causes the Ca(OH)2 to capture chlorine derived from waste plastic in the form of CaCl2, thereby reducing the amount of chlorine distributed to the generated gas. In Comparative Example 1 (coal and waste plastic only), Example 1 (with Ca(OH)2 added to waste plastic), and Comparative Example 2 (with Ca(OH)2 added to coal), the organic chlorine concentration decreased sharply and then increased temporarily. This is thought to be due to the mixing of zones with and without waste plastic, which caused temporal fluctuations in the component composition of the generated gas.

[0068] <Drum Strength (DI) Measurement> Drum tests were conducted on coke obtained by carbonization in accordance with JIS K 2151. Measurements were performed with N=2. The results are shown in Table 2.

[0069]

[0070] A comparison between Comparative Example 1 (no Ca(OH)2 addition) and Comparative Example 2 (with Ca(OH)2 addition to coal) showed that adding a Ca-containing substance to coal resulted in a decrease in drum strength. However, a comparison between Comparative Example 1 (no Ca(OH)2 addition) and Example 1 (with Ca(OH)2 addition to waste plastic) showed that adding a Ca-containing substance to waste plastic did not result in any difference in drum strength compared to the case without Ca-containing substance addition. It is thought that the addition of a Ca-containing substance did not have a significant adverse effect on coke strength because a fragile structure is easily formed in waste plastic granules and at the interface between waste plastic granules and coke.

[0071] From these results, it can be seen that by adding a Ca-containing substance to granulated waste plastic, the organic chlorine concentration in the generated gas can be reduced while maintaining good coke strength.

Claims

1. A method for processing waste plastics by carbonizing coal and chlorine-containing waste plastics in the carbonization chamber of a coke oven in the presence of a Ca-containing substance, wherein the Ca-containing substance is added to the granules of the waste plastics to produce a composite granule containing the waste plastics and the Ca-containing substance, and the composite granule is charged into the carbonization chamber.

2. A method for treating waste plastics by carbonizing coal and chlorine-containing waste plastics in the carbonization chamber of a coke oven in the presence of a Ca-containing substance, comprising: first investigating the relationship between the amount of Ca-containing substance added to the waste plastics and the organochlorine concentration of the generated gas, the light oil obtained from the generated gas, or the purified gas obtained from the generated gas; determining the amount of Ca-containing substance to be added based on the relationship such that the organochlorine concentration of the generated gas, the light oil, and the purified gas whose relationship was investigated is less than or equal to the target organochlorine concentration; and adding the determined amount of Ca-containing substance to the granulated waste plastics.

3. As a result of the above relationship, a relationship is obtained between a variable x, which is the amount of Ca-containing substance added to the waste plastic, and a variable y, which is the degree of change in the organic chlorine concentration of the generated gas, the light oil obtained from the generated gas, or the purified gas obtained from the generated gas, from before the addition of the Ca-containing substance after the addition of the Ca-containing substance. The value of the variable x obtained when the target value of the percentage change in the organic chlorine concentration of the generated gas, the light oil, and the purified gas for which the relationship was obtained is substituted for variable y is determined as the amount of Ca-containing substance added to the waste plastic, according to claim 2.

4. A method for treating waste plastics according to any one of claims 1 to 3, wherein a mixture of coal and the composite granules is charged into the carbonization chamber.

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