Waste plastic processing method

Abstract

Provided is a waste plastic processing method that makes it possible to achieve, when processing chlorine-containing waste plastics in a coke oven, both high coke strength and a reduction in organic chlorine concentration of light oil and / or refined gas. Provided is a waste plastic processing method in which coal and chlorine-containing waste plastics are dry distilled in a carbonization chamber of a coke oven in a presence of a Ca-containing substance, wherein: the relationship (i) between the addition amount of the Ca-containing substance and the addition target of the Ca-containing substance selected from the coal, the waste plastics, and both, and the organic chlorine concentration of generated gas, light oil, or refined gas, and the relationship (ii) between the addition amount and the addition target of the Ca-containing substance, and the coke strength are examined in advance, and on the basis of the relationships (i) and (ii), the addition amount and the addition target of the Ca-containing substance are determined such that the organic chlorine concentration of the generated gas, the light oil, and the refined gas, the relationships of which have been examined, is less than or equal to the target organic chlorine concentration, and the coke strength is greater than or equal to the target coke strength, and the Ca-containing substance is added to the determined addition target in the determined addition amount.

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. Since inorganic chlorine can be largely neutralized by ammonia flushing, it is particularly desirable to reduce the amount of organic chlorine that remains in the product even after ammonia flushing.

[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 the ash produced by carbonization, and the CaO and MgO sources described in Patent Document 3 are used to lower the melting point of the 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 the products obtained by carbonization using a coke oven, particularly light oil and purified gas. In particular, no conventional carbonization method has yet been proposed that uses chlorine-containing waste plastics and can achieve both high coke strength and a reduction in the organochlorine concentration of light oil and / or purified gas.

[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 refined 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 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, wherein the relationship (i) between the target to which the Ca-containing substance is to be added, selected from the coal, the waste plastics, and both thereof, and the amount of the Ca-containing substance added, and 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, and the relationship (ii) between the target to which the Ca-containing substance is to be added and the coke strength, and based on the relationships (i) and (ii), the target to which the Ca-containing substance is to be added and the amount added are determined such that the organic chlorine concentration of the generated gas, the light oil, and the purified gas whose relationships were investigated is less than or equal to a target organic chlorine concentration, and the coke strength is greater than or equal to a target coke strength, and the Ca-containing substance is added to the determined target in the determined amount. [2] As the relationship (i) above, equation (1) is obtained relating to variable x1, which is the amount of Ca-containing substance added to waste plastic, variable x2, which is the amount of Ca-containing substance added to coal, and variable y1, 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. As the relationship (ii) above, equation (2) is obtained relating to variable x1, which is the amount of Ca-containing substance added to waste plastic, variable x2, which is the amount of Ca-containing substance added to coal, and variable y2, which is the degree of change in the coke strength from before the addition of the Ca-containing substance to after the addition of the Ca-containing substance. The method for treating waste plastics as described in [1], wherein in relational equation (1), the target value of the degree of change in the organochlorine concentration of the generated gas, the light oil, and the purified gas for which the relational equation was determined is substituted into variable y1, and in relational equation (2), the target value of the degree of change in the coke strength after the addition of the Ca-containing substance compared to before the addition of the Ca-containing substance is substituted into variable y2, and the values ​​of variables x1 and x2 are determined as the amount of Ca-containing substance to be added to waste plastics and the amount of Ca-containing substance to be added to coal, respectively.

[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 relationship between the target and amount of Ca-containing substances to be added and the organic chlorine concentration in the generated gas.

[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, the relationship (i) between the target and amount of Ca-containing substance to be added, selected from coal, waste plastics, and both, 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, and the relationship (ii) between the target and amount of Ca-containing substance to be added and the coke strength are investigated in advance. Based on the relationships (i) and (ii), the target and amount of Ca-containing substance to be added are determined such that the organochlorine concentration of the generated gas, light oil, and purified gas for which the above relationships were investigated is less than or equal to the target organochlorine concentration, and the coke strength is greater than or equal to the target coke strength. The Ca-containing substance is then added to the determined target in the determined amount.

[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 carbonization chambers and combustion chambers are alternately arranged in the width direction of the furnace 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. The carbonized material is extruded in the length direction of the furnace by an extruder. The gases generated from the coke oven flow out of the furnace from the carbonization chamber via a riser pipe, where they are separated to produce tar, diesel fuel, and refined gas. In this disclosure, generated gases include all gases that flow out of the furnace from the carbonization chamber via a riser pipe during carbonization in the carbonization chamber of the coke oven. 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 products obtained therefrom 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 of the diesel fuel and refined gas obtained from the generated gas can be reduced. In addition, high coke strength can also be achieved by appropriately adjusting the target and amount of the Ca-containing substance to be added. The organic chlorine concentration in the generated gas is determined by combustion ion chromatography measurement. 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. Also, if the sample is generated gas after ammonia water flushing, inorganic chlorine is removed by ammonia water flushing. Therefore, the chlorine concentration obtained by combustion ion chromatography measurement of the generated gas can be considered as the organic chlorine concentration of the generated gas.While the method of this embodiment focuses particularly on reducing the organic chlorine concentration in 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 0.1% by mass and 70% by mass. In one embodiment, the Cl element concentration may be 0.1% by mass or more, 1% by mass or more, 5% by mass or more, 10% by mass or more, 20% by mass or more, 30% by mass or more, 40% by mass or more, 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 shape of the waste plastics to be charged into the carbonization chamber is not limited; they may be in the same shape as when they were collected as waste, or they may be molded after collection. In one embodiment, the waste plastics may be charged into the carbonization chamber as pellets or the like. The waste plastics may be pre-treated after collection 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 metal removal using a magnetic separator or removal of heavy objects using an air separator. Crushing and granulation may be carried out using, for example, a compression type, shear type, cutting type, impact type, or friction type crusher.

[0028] In a preferred embodiment, the waste plastic may be in the form of granules (i.e., granular molded products). In one embodiment, the particle size of the granules may be 10 mm to 50 mm or 25 mm to 40 mm. The particle size refers to the major axis of the base (or the maximum value if the values ​​differ between bases) in the case of a shape with a base (e.g., cylinder, elliptical cylinder, etc.), and to the major axis of the shape in the case of a shape without a base (e.g., sphere, ellipsoid, irregularly shaped solid, etc.).

[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] The method of adding the Ca-containing substance may be arbitrarily selected as desired. In one preferred embodiment, the Ca-containing substance may be charged into the carbonization chamber in a compounded state with the waste plastic and / or coal. In one embodiment, the waste plastic is collected, crushed, granulated, and then charged into the carbonization chamber. When adding the Ca-containing substance to the waste plastic, the timing of the addition is not limited and may be, for example, before, during, and / or after the granulation of the waste plastic. In the case of addition after granulation, one example is coating the outside of the granulated waste plastic. Coating is preferred from the viewpoint of uniformly distributing the Ca-containing substance 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 granules. As an example of a granulation method, one may be to crush the waste plastic and then extrude it into a diameter of 25 mm to 35 mm. Examples of coating methods include immersing the granules in a mixture of water and a Ca-containing substance (e.g., a water-containing paste), pouring the mixture over the granules, and flowing the mixture in a curtain-like manner, allowing the granules to pass through it. When adding a Ca-containing substance to coal, the timing of the addition is not limited; in one embodiment, it may be added before, during, and / or after the coal is crushed. When adding a Ca-containing substance to coal, it is preferable to add the Ca-containing substance as a powder from the viewpoint of dispersibility.

[0033] Examples of variations in the method of adding Ca-containing substances include (1) the target to which the substance is added (coal, waste plastic, or both), (2) the form of the Ca-containing substance (powder, water-containing paste, etc.), (3) the form of the target to which the substance is added (crushed material, granulated material, etc.), and (4) the timing of the addition (if the target to be added is granulated, before, during, or after granulation, etc.). According to the inventors' studies, it has been found that among the methods of adding Ca-containing substances, the target to which the substance is added (1) above is the one that mainly affects the organic chlorine concentration of the generated gas, light oil, or purified gas, and the coke strength. Therefore, in the method of this embodiment, the target to which the substance is added is considered along with the amount of Ca-containing substance added. The effect of reducing organic chlorine concentration tends to be greater when Ca-containing substances are added to coal than when they are added to waste plastic. On the other hand, the decrease in coke strength tends to be smaller when Ca-containing substances are added to waste plastic than when they are added to coal. Although not bound by theory, it is thought that the addition of Ca-containing substances is unlikely to adversely affect coke strength because a fragile structure is easily formed at the interface between waste plastics and waste plastics and coke. In the method of this embodiment, the target and amount of Ca-containing substances to be added are determined so that the organochlorine concentration of the generated gas, diesel fuel, or purified gas and the coke strength are balanced in a desirable way.

[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 use of a Ca-containing substance reduces the organochlorine concentration of the generated gas, light oil, or purified gas.

[0035] <Determination of the target and amount of Ca-containing substance to be added> In the method of this embodiment, the relationship (i) between the target and amount of Ca-containing substance to be added and 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 (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), and the relationship between the target and amount of Ca-containing substance to be added and the coke strength (this may be the absolute value of the coke strength, or an index value related to the coke strength, for example, the degree of change after adding the Ca-containing substance compared to before adding the Ca-containing substance) The relationship (ii) between (i) and (ii) is investigated in advance, and based on the relationships (i) and (ii), target values ​​are determined for the organic chlorine concentration (which 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) and the coke strength (which may be the absolute value of the coke strength, or an index value related to the coke strength, for example, the degree of change after adding the Ca-containing substance compared to before adding the Ca-containing substance) of the generated gas, diesel fuel, and refined gas for which the above relationships were investigated. Based on this, the target and amount of Ca-containing substance to be added are determined so that the organic chlorine concentration is less than or equal to the target organic chlorine concentration, and the coke strength is greater than or equal to the target coke strength. 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. Relationships (i) and (ii) represent the effect that the addition of Ca-containing substance has on the organic chlorine concentration and coke strength. Therefore, by using relationships (i) and (ii), it is possible to determine the target and amount of Ca-containing substance to be added that can eliminate both the discrepancy between the target value and the current value (specifically, the value before the addition of Ca-containing substance) of the organochlorine concentration in the generated gas, diesel fuel, or refined gas, and the discrepancy between the target value and the current value (specifically, the value before the addition of Ca-containing substance) of the coke strength.

[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 target 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, and the coke strength 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 target and amount of Ca-containing substance added and the organic chlorine concentration and coke strength 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 target and amount of Ca-containing substance can achieve both the target organic chlorine concentration and the target coke strength. 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 is actually 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] In one aspect, the above relationships (i) and (ii) may be obtained as follows. First, a carbonization test is performed by charging coal and chlorine-containing waste plastic into a carbonization chamber of a coke oven. In one aspect, the waste plastic may be charged after the coal is carbonized. In the carbonization test, the Ca-containing substance is added to coal or waste plastic, and the test is performed for each of two or more, three or more, or four or more test conditions in which only the addition amount of the Ca-containing substance is changed. Although a larger number of test conditions is preferable, the number may be 15 or less, or 10 or less for convenience of testing. It is desirable that the waste plastic subjected to the carbonization test for obtaining the relational expression has the same or similar material composition as the waste plastic subjected to actual operation. An example where the waste plastic subjected to actual operation and the waste plastic for the carbonization test have the same or similar material composition is a case where these waste plastics are collected through the same waste collection route. The waste plastic for the carbonization test may be obtained by sampling a part of the waste plastic subjected to actual operation. When the density of the granulated waste plastic differs between the waste plastic subjected to actual operation and the waste plastic for the carbonization test, it is preferable to reselect the waste plastic for the carbonization test so that the densities are the same. The density can vary depending on the material composition, and can also vary depending on the granulation method.

[0040] In each carbonization test, the organochlorine concentration of the generated gas, the light oil obtained from the generated gas, or the purified gas obtained from the generated gas, and the coke strength are measured. The coke oven used for the measurement and the carbonization conditions are preferably 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 light oil and purified gas is measured as the chlorine concentration obtained when light oil and purified gas are sampled and each of them is measured by combustion ion chromatography.

[0042] In one aspect, 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 may be selected from DI 150 15 , DI 150 6, etc. In one aspect, DI 150 15 may be used as an index of coke strength. DI 150 15 is the mass percentage of coke remaining 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 remaining 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 not on measurement results from a carbonization test, but on measurement results related to the performance of the immediately preceding actual operation batch.

[0044] Next, a relational expression is obtained based on the measured organochlorine concentration and coke strength. For example, these relational expressions may be obtained by regression analysis using the addition amount of a Ca-containing substance as an explanatory variable and the organochlorine concentration in generated gas, light oil or refined gas as an objective variable. Similarly, these relational expressions may be obtained by regression analysis using the addition amount of a Ca-containing substance as an explanatory variable and coke strength as an objective 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, as a relationship (i) between the target and amount of Ca-containing substance to be added and the organochlorine concentration of the generated gas, diesel fuel, or purified gas, an equation (1) can be obtained relating to variable x1, which is the amount of Ca-containing substance added to waste plastics, variable x2, which is the amount of Ca-containing substance added to coal, and variable y1, which is the degree of change in the organochlorine concentration of the generated gas, diesel fuel, or purified gas before the addition of the Ca-containing substance. As a relationship (ii) between the target and amount of Ca-containing substance to be added and the coke strength, an equation (2) can be obtained relating to variable x1, which is the amount of Ca-containing substance added to waste plastics, variable x2, which is the amount of Ca-containing substance added to coal, and variable y2, which is the degree of change in the coke strength before the addition of the Ca-containing substance. The degree of change may be expressed as a rate of change (specifically, the ratio of the value after adding the Ca-containing substance to the value before adding the Ca-containing substance) or as an amount of change (specifically, the difference obtained by subtracting the value before adding the Ca-containing substance from the value after adding the Ca-containing substance).

[0046] As an example, if we use the rate of change as the degree of change in the organochlorine concentration after the addition of the Ca-containing substance compared to before the addition of the Ca-containing substance, and use the amount of change as the degree of change in the coke strength after the addition of the Ca-containing substance compared to before the addition of the Ca-containing substance, and apply linear regression, we obtain the following equation (1a) as relation (1) and the following equation (2a) as relation (2). 1 - y1 = ax1 + bx2 (1a) y2 = cx1 + dx2 (2a) (wherein x1 is the amount of Ca-containing substance added to waste plastic (mass% relative to 100% coal by mass (external number)), x2 is the amount of Ca-containing substance added to coal (mass% relative to 100% coal by mass (external number)), y1 is the degree of change in organic chlorine concentration after the addition of Ca-containing substance compared to before the addition of Ca-containing substance, y2 is the degree of change in coke strength after the addition of Ca-containing substance compared to before the addition of Ca-containing substance, a is a constant that represents the degree of change in organic chlorine concentration per unit amount of Ca-containing substance added to waste plastic, b is a constant that represents the degree of change in organic chlorine concentration per unit amount of Ca-containing substance added to coal, c is a constant that represents the degree of change in coke strength per unit amount of Ca-containing substance added to waste plastic, d is a constant that represents the degree of change in coke strength per unit amount of Ca-containing substance added to coal.) The left side of equation (1a) above, "1 - y1", means 1 - (organic chlorine concentration after addition of Ca-containing substance) / (organic chlorine concentration before addition of Ca-containing substance), that is, [(organic chlorine concentration before addition of Ca-containing substance) - (organic chlorine concentration after addition of Ca-containing substance)] / (organic chlorine concentration before addition of Ca(OH)2). The constants a and b may be based on the slope of the linear approximation formula obtained from the plot of the amount of Ca-containing substance added and the measured organic chlorine concentration, and the constants c and d may be based on the slope of the linear approximation formula obtained from the plot of the amount of Ca-containing substance added and the measured coke strength.

[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] By substituting the target value of the rate of change (degree of change) of the organochlorine concentration of the generated gas, diesel fuel, or purified gas after the addition of the Ca-containing substance compared to before the addition of the Ca-containing substance into y1 above, and substituting the target value of the amount of change (degree of change) of the coke strength after the addition of the Ca-containing substance compared to before the addition of the Ca-containing substance into y2 above, and solving relational equations (1) and (2), the values ​​of x1 and x2 can be obtained. The values ​​of x1 and x2 can be determined as the amount of Ca-containing substance to be added to waste plastics and the amount of Ca-containing substance to be added to coal, respectively.

[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, then the equation y1 = ax1 + bx2, obtained by replacing 1 - y1 on the left side of equation (1a) with y1, 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 y1.

[0050] For example, by following the procedure described above, the target and amount of Ca-containing substances to be added are determined so that the organic chlorine concentration of the generated gas, diesel fuel, or refined gas is below the target organic chlorine concentration, and the coke strength is above the target coke strength. If the current coke strength (specifically, before the addition of Ca-containing substances) is below the target value, a separate blending action can be taken to raise the coke strength to above the target value before performing the analysis using the above formula.

[0051] The following describes exemplary embodiments of the present invention using examples, but the present invention is not limited to these embodiments.

[0052] ≪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.

[0053] 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).

[0054] 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.

[0055] 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.

[0056]

[0057] Fig. 1 shows the relationship between the organochlorine concentration of the generated gas and the organochlorine concentration of the light oil. As can be seen from Fig. 1, it was confirmed that the organochlorine concentration of the generated gas correlates with the organochlorine concentration of the light oil. Although not evaluated in the present study, since the main chlorine-containing chemical products obtained by refining the generated gas are light oil and refined gas, it is considered that the organochlorine concentration of the refined 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 of the generated gas is reduced, the organochlorine concentrations of light oil and refined gas will also be reduced.

[0058] <<Example 1>> <Test Conditions> Using a test carbonization furnace, coal and chlorine-containing waste plastic were carbonized, and the organochlorine concentration in the generated gas was evaluated. The test conditions are as follows. Sample width: 415 mm Sample length: 490 mm Sample height: 460 mm Coal charging bulk density: about 0.80 dry-t / m 3 For all 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.

[0059] <Materials Used> Container-recycled waste plastic (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 waste plastic by the procedure described in [Measurement conditions for combustion ion chromatography] described later.

[0060] Ca-containing substance: Ca(OH)₂ reagent (available from Kishida Chemical Co., Ltd., product number 000-13605, average diameter 6.6 μm) Coal: crushed coal pulverized to a 3 mm under-sieve ratio of 80% by mass, moisture content 4% by mass These were mixed at Ca(OH)₂ / water = 1 / 1.8 (mass ratio) to obtain a paste. The amount of waste plastic added was 5% by mass on an external basis relative to 100% by mass of coal.

[0061] <Addition of Ca-containing substance> [Level 1] No Ca-containing substance was added.

[0062] [Levels 2 and 3: Pre-mixing] The waste plastic and Ca(OH)2 powder were mixed so that the amount of Ca(OH)2 added was 3% by mass (approximately 1.62% by mass on a Ca element basis) (Level 2) or 5% by mass (approximately 2.70% by mass on a Ca element basis) (Level 3) relative to 100% by mass of the waste plastic, and granulated at a granulation temperature of 250°C using a granulator with a diameter (i.e., die hole diameter) of 6 mm.

[0063] [Level 4: Post-granulation coating] Waste plastic was granulated in a granulator with a diameter (i.e., die hole diameter) of 35 mm at a granulation temperature of 110°C. The above paste was applied to the granules so that the amount of Ca(OH)2 added was 5% by mass relative to 100% by mass of the waste plastic.

[0064] [Level 5: Application to coal] Crushed coal and Ca(OH)2 powder were mixed so that the amount of Ca(OH)2 added was 5% by mass, relative to 100% by mass of waste plastic (i.e., waste plastic added at an extra percent by mass of 5% relative to 100% by mass of coal).

[0065] <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 analyzed using combustion ion chromatography. The analytical conditions were as follows:

[0066] [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.

[0067] 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 treatment. Therefore, the chlorine concentration of the gas in the gas bag was considered to be the organic chlorine concentration. The results are shown in Table 2.

[0068]

[0069] The organochlorine concentration ratios in Table 2 are relative to Level 1 (no addition of Ca(OH)2) as a control. A smaller value indicates a better reduction in organochlorine concentration. As shown in Table 2, adding Ca(OH)2 to waste plastic or coal significantly reduced the organochlorine concentration in the generated gas. Furthermore, from the results for Levels 3 and 4, no significant difference in the organochlorine concentration reduction effect was observed depending on whether Ca(OH)2 was added to the waste plastic by pre-mixing or coating after granulation.

[0070] Figure 2 plots the organochlorine concentration ratios shown in Table 2, illustrating the relationship between the amount of Ca-containing substance added and the organochlorine concentration in the generated gas. Linear approximation of the plots in Figure 2 was performed, and the slope of the resulting approximation, i.e., the rate of change in organochlorine concentration per 1% by mass of Ca(OH)2 added, was determined to be approximately -1.8421 for addition to waste plastics and approximately -2.28 for addition to coal.

[0071] <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 3.

[0072]

[0073] The DI difference in Table 3 is the difference compared to Level 1 (no Ca(OH)2 addition) as the control. A smaller value (larger absolute value of the negative value) indicates a greater decrease in DI. As shown in Table 3, the change in DI due to Ca(OH)2 addition differed depending on the material to which Ca(OH)2 was added. In Levels 3 and 4, where Ca(OH)2 was added to waste plastics, both addition methods showed a DI of 0, i.e., equivalent to the control Level 1. In Level 5, where Ca(OH)2 was added to coal, the DI was -1.1 (the change in DI per 1% by mass of Ca(OH)2 added was -4.4), indicating a decrease in DI compared to the control Level 1.

[0074] Based on the results in Tables 2 and 3, if x1 is the amount of Ca(OH)2 added to waste plastic (mass% relative to 100% coal by mass (external number)), x2 is the amount of Ca(OH)2 added to coal (mass% relative to 100% coal by mass (external number)), y1 is the rate of change in organochlorine concentration after adding the Ca-containing substance compared to before adding the Ca-containing substance, and y2 is the change in drum strength after adding the Ca-containing substance compared to before adding the Ca-containing substance, then the effects of Ca(OH)2 addition on organochlorine concentration and drum strength can be expressed by the following equations (1) and (2): 1 - y1 = 1.8421x1 + 2.28x2 (1) y2 = -4.4x2 (2)

[0075] From the above, it can be seen that by substituting the ratio Cl2 / Cl1 between the current (i.e., before the addition of Ca-containing substances) organic chlorine concentration Cl1 in the generated gas and the target (i.e., after the addition of Ca-containing substances) organic chlorine concentration Cl2 in the generated gas into y1, and substituting the difference DI2-DI1 between the current (i.e., before the addition of Ca-containing substances) drum strength DI1 and the target (i.e., after the addition of Ca-containing substances) drum strength DI2 into y2, and solving equations (1) and (2) above, the values ​​of x1 and x2, that is, the target and amount of Ca-containing substances to be added, can be determined. For example, if Cl1: 13 μg / L, Cl2: 10 μg / L, DI1: 86.0, and DI2: 85.8, then 1 - 10 / 13 = 1.8421 x 1 + 2.28 x 2 and 85.8 - 86.0 = -4.4 x 2 can be solved for x1 and x2, resulting in x1 ≈ 0.127 mass% and x2 ≈ 0.045 mass%. If the current drum strength is below the target value, a separate mixing action can be taken to raise the drum strength to above the target value before performing the above calculation.

Claims

1. 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, wherein the relationship (i) between the coal, the waste plastics, and the Ca-containing substance to be added to, selected from both, and the amount of the Ca-containing substance added, and 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, and the relationship (ii) between the Ca-containing substance to be added and the coke strength, the relationship (i) between the Ca-containing substance to be added and the amount added, the relationship (i) and (ii) respectively, the Ca-containing substance to be added and the amount added, the relationship (i) and (ii) respectively, is determined so that the organic chlorine concentration of the generated gas, the light oil, and the purified gas to which the relationship was investigated is less than or equal to a target organic chlorine concentration, and the coke strength is greater than or equal to a target coke strength, and the Ca-containing substance is added to the determined target in the determined amount.

2. As relationship (i) above, equation (1) is obtained relating to variable x1, which is the amount of Ca-containing substance added to waste plastic, variable x2, which is the amount of Ca-containing substance added to coal, and variable y1, 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. As relationship (ii) above, equation (2) is obtained relating to variable x1, which is the amount of Ca-containing substance added to waste plastic, variable x2, which is the amount of Ca-containing substance added to coal, and variable y2, which is the degree of change in the coke strength from before the addition of the Ca-containing substance to after the addition of the Ca-containing substance. A method for treating waste plastics according to claim 1, wherein in relational equation (1), 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 relational equation was determined is substituted into variable y1, and in relational equation (2), the target value of the percentage change in the coke strength after the addition of the Ca-containing substance compared to before the addition of the Ca-containing substance is substituted into variable y2, and the values ​​of variables x1 and x2 are determined as the amount of Ca-containing substance to be added to waste plastics and the amount of Ca-containing substance to be added to coal, respectively.

Images