Method for determining extrusion timing for coke oven, method for estimating time required for dry distillation, method for estimating chargeable plastic amount, and method for producing coke

Abstract

Provided is a method for determining extrusion timing for a coke oven, the method enabling direct and highly accurate confirmation on timing at which extrusion without accompanying a dust emission problem becomes possible when dry-distilling plastic in the coke oven. One embodiment of the present invention provides a method for determining extrusion timing when charging plastic after charging coal and dry-distilling the coal and the plastic in a carbonization chamber of a coke oven. In the method for determining extrusion timing: the methane concentration in exhaust gas from the carbonization chamber is measured while the internal pressure of the carbonization chamber is controlled to a predetermined positive pressure value or higher; during the control of the internal pressure, the gas flow between the carbonization chamber and a dry main branched from a riser pipe connected to the carbonization chamber is blocked, or the internal pressure of the carbonization chamber is set to be higher than the pressure of the dry main; and a time point which is later, by a predetermined extrusion postponement duration, than a time point when the methane concentration was decreased to a predetermined methane concentration threshold is determined as an extrusion start time point.

Description

Method for Determining Extrusion Timing of Coke Oven, Method for Estimating Carbonization Time Required, Method for Estimating Amount of Plastic That Can Be Charged, and Coke Production Method

[0001] The present invention relates to a method for determining the extrusion timing of a coke oven.

[0002] In recent years, from the viewpoints of effective utilization of resources and contribution to achieving carbon neutrality, recycling of plastics (that is, converting plastics into recycled materials, which are useful substances that can be used as resources) has been demanded. Among them, the method of carbonizing plastics in a coke oven to obtain useful substances such as carbonized products, tar, light oil, and gas is advantageous in that a large amount of plastics can be processed by effectively using existing equipment. However, the knowledge about the carbonization conditions suitable for plastic recycling is not yet sufficient. In particular, if the carbonization of plastics has not sufficiently progressed when the carbonized product is extruded from the coke oven by an extruder, an inconvenience such as the generation of visible smoke (hereinafter also referred to as dust generation) may occur. Therefore, it is desired to construct carbonization conditions that can more reliably avoid the problem of dust generation during extrusion.

[0003] Patent Document 1 describes a method for manufacturing coke for a blast furnace, which is characterized in that, in a method of charging a coke raw material into the carbonization chamber of a coke oven first and then charging waste plastics into the top space of the oven, a correlation between the type and amount of waste plastics and the thermal decomposition time of the waste plastics is obtained in advance, and the type, charging amount, charging timing, and residence time of the waste plastics to be charged are set so that the thermal decomposition of the waste plastics charged before the coke extrusion is completed.

[0004] Japanese Patent Application Laid-Open No. 2002-047494, Japanese Patent Application Laid-Open No. 2023-34503

[0005] S. Honus et al., Fuel 221 (2018) pp.346-360

[0006] The method described in Patent Document 1 is a method for producing coke by charging plastic into the upper space of a carbonization chamber, and aims to suppress dust generation during extrusion and reduce extrusion resistance. However, the method described in Patent Document 1 does not directly confirm the progress of the carbonization of the plastic, and there was room for improvement in determining the extrusion timing with high accuracy. One aspect of the present invention aims to solve the above problems and provide a method for determining the extrusion timing in a coke oven that can directly and accurately confirm the timing at which extrusion without the problem of dust generation becomes possible when carbonizing plastic in a coke oven.

[0007] The gist of the present invention is as follows: [1] A method for determining the timing of extrusion of carbonized material when carbonizing coal and plastic in the carbonization chamber of a coke oven, wherein the internal pressure of the carbonization chamber is controlled to be above a predetermined positive pressure value, the methane concentration in the exhaust gas from the carbonization chamber is measured, in the control of the internal pressure, the gas flow between the carbonization chamber and a dry main branching from a riser pipe connected to the carbonization chamber is blocked, or the internal pressure of the carbonization chamber is made higher than the pressure of the dry main, and the extrusion start time is determined to be later by a predetermined extrusion grace period than the time when the methane concentration decreases to a predetermined methane concentration threshold. [2] The method for determining the timing of extrusion according to [1], wherein in the control of the internal pressure, the gas flow is blocked by closing the gas passage between the carbonization chamber and the dry main, and the amount of gas flowing out of the carbonization chamber to the riser pipe is adjusted according to the internal pressure of the carbonization chamber. [3] The extrusion timing determination method according to [2], wherein, in the control of the internal pressure, when the internal pressure of the carbonization chamber decreases, the gas flow path of the riser pipe is narrowed to reduce the amount of gas flowing out of the carbonization chamber to the riser pipe.[4] The following (1) to (3): (1) Further measure the carbon monoxide concentration in the exhaust gas and maintain the carbon monoxide concentration below a predetermined carbon monoxide concentration threshold from a predetermined retrospective time earlier than the time when the methane concentration decreases to the predetermined methane concentration threshold until the time when the methane concentration decreases to the predetermined methane concentration threshold; (2) Further measure the carbon dioxide concentration in the exhaust gas and maintain the carbon dioxide concentration below a predetermined carbon dioxide concentration threshold from a predetermined retrospective time earlier than the time when the methane concentration decreases to the predetermined methane concentration threshold until the time when the methane concentration decreases to the predetermined methane concentration threshold; and (3) The method for determining the extrusion timing according to any one of [1] to [3], which further measures the hydrogen concentration in the exhaust gas and maintains the hydrogen concentration at or above a predetermined hydrogen concentration threshold from a point in time that is at least a predetermined retrospective time earlier than the point in time when the methane concentration decreases to the predetermined methane concentration threshold until the point in time when the methane concentration decreases to the predetermined methane concentration threshold. [5] A method for estimating the carbonization time required in the carbonization chamber of a coke oven, which is the time from the time when plastic is charged after coal is charged to the time when the carbonized product is extruded when the coal and plastic are carbonized, wherein the internal pressure of the carbonization chamber is controlled to be above a predetermined positive pressure value, and the methane concentration in the exhaust gas from the carbonization chamber is measured, provided that in the control of the internal pressure, the gas flow between the carbonization chamber and the dry main branching from the riser pipe connected to the carbonization chamber is blocked, or the internal pressure of the carbonization chamber is made higher than the pressure of the dry main, and a relationship formula between the amount of plastic charged into the carbonization chamber of the coke oven and the carbonization time is determined, provided that the extrusion start time is later by a predetermined extrusion grace period than the time when the methane concentration decreases to a predetermined methane concentration threshold. A method for estimating the carbonization time, which is the carbonization time obtained when the amount of plastic to be charged is substituted into the carbonization chamber of the coke oven in the aforementioned relational equation.[6] A method for estimating the amount of plastic that can be charged into the carbonization chamber of a coke oven, based on the carbonization time, which is the time from the time when plastic is charged after coal is charged into the carbonization chamber to the time when the carbonized product is extruded when the coal and plastic are carbonized, wherein the internal pressure of the carbonization chamber is controlled to be above a predetermined positive pressure value, and the methane concentration in the exhaust gas from the carbonization chamber is measured, provided that in the control of the internal pressure, the gas flow between the carbonization chamber and the dry main branching from the riser pipe connected to the carbonization chamber is blocked, or the internal pressure of the carbonization chamber is made higher than the pressure of the dry main, and a relationship formula between the amount of plastic charged into the carbonization chamber of the coke oven and the carbonization time is determined, provided that the extrusion start time is later by a predetermined extrusion grace period than the time when the methane concentration decreases to a predetermined methane concentration threshold. A method for estimating the amount of plastic that can be charged into the carbonization chamber of the coke oven, which is the amount of plastic that can be charged into the carbonization chamber of the coke oven when the desired carbonization time is substituted into the carbonization time in the aforementioned relational equation.[7] A coke production method comprising charging a plastic after charging coal in the carbonization chamber of a coke oven to produce coke derived from the coal and the plastic, wherein the internal pressure of the carbonization chamber is controlled to be above a predetermined positive pressure value, and the methane concentration in the exhaust gas from the carbonization chamber is measured, provided that in the control of the internal pressure, the gas flow between the carbonization chamber and the dry main branching from the riser pipe connected to the carbonization chamber is blocked, or the internal pressure of the carbonization chamber is made higher than the pressure of the dry main, (1) a relationship formula is determined between the amount of plastic charged into the carbonization chamber of the coke oven and the carbonization time, which is the time from the time of charging the plastic to the time of starting the extrusion of the carbonized product, provided that the time of starting the extrusion is later by a predetermined extrusion grace period than the time when the methane concentration decreases to a predetermined methane concentration threshold, (2) A method for producing coke, comprising: (2A) substituting a first charge amount, which is a desired amount of plastic charged, into the relational formula for the first time required for carbonization, which is the carbonization time, or (2B) substituting a second time, which is a desired carbonization time, into the relational formula for the second charge amount, which is the amount of plastic charged into the carbonization chamber of the coke oven; (3) (3A) charging the first charge amount of plastic and performing carbonization for a period of time of the first time or longer, or (3B) charging the second charge amount or less of plastic and performing carbonization for a period of time of the second time, and then extruding coke using an extruder.

[0008] According to one aspect of the present invention, a method for determining the extrusion timing in a coke oven can be provided, which allows for direct and highly accurate confirmation of the timing at which extrusion of plastics during carbonization in a coke oven becomes possible without the problem of dust generation.

[0009] This is a schematic diagram showing an example of the general configuration of a coke oven. This is a diagram illustrating an example of a method for controlling the internal pressure of the carbonization chamber. This is a diagram showing the change over time of the static pressure near the base of the riser pipe in the carbonization chamber during the carbonization of plastics in the preliminary study. This is a diagram showing the change over time of the dynamic pressure near the base of the riser pipe in the carbonization chamber during the carbonization of plastics in the preliminary study. This is a diagram plotting the methane concentration in the exhaust gas against the elapsed time from the time the plastics were charged in Example 1. This is a diagram plotting the carbonization time, which is the time from the time the plastics were charged to the point when the methane concentration decreased to 4% + 1 hour, against the amount of plastics charged. This is a diagram plotting the methane (CH4) concentration in the exhaust gas against the elapsed time from the time the coals were charged in Reference Example 1 and Comparative Reference Example 1. This is a diagram plotting the carbon monoxide (CO) concentration in the exhaust gas against the elapsed time from the time the coals were charged in Reference Example 1 and Comparative Reference Example 1. Reference Example 1 and Comparative Reference Example 1 are plots showing the carbon dioxide (CO2) concentration in the exhaust gas against the elapsed time from the time of coal charging. Reference Example 1 and Comparative Reference Example 1 are plots showing the hydrogen (H2) concentration in the exhaust gas against the elapsed time from the time of coal charging.

[0010] 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.

[0011] [Extrusion Timing Determination Method] One aspect of the present invention provides a method for determining the extrusion timing of carbonized materials when carbonizing coal and plastic in the carbonization chamber of a coke oven after charging coal, the method comprising: controlling the internal pressure of the carbonization chamber to be above a predetermined positive pressure value, measuring the methane concentration in the exhaust gas from the carbonization chamber, blocking the gas flow between the carbonization chamber and the dry main branching from the riser pipe connected to the carbonization chamber, or making the internal pressure of the carbonization chamber higher than the pressure of the dry main, and determining the extrusion start time to be later by a predetermined extrusion grace period than the time when the methane concentration decreases to a predetermined methane concentration threshold. The methane concentration in the exhaust gas can be used as an indicator that directly represents the progress of carbonization. Furthermore, according to this embodiment, the methane concentration in the exhaust gas can be measured with high accuracy by controlling the internal pressure of the carbonization chamber.Therefore, according to the extrusion timing determination method of this embodiment, the time when extrusion without the problem of dust generation becomes possible can be directly and accurately confirmed. In this disclosure, the extrusion time of the carbonized product means the start time of extrusion of the carbonized product. While embodiments in which components other than coal and plastic are charged into the carbonization chamber are not excluded as long as they do not impair the effects of the present invention, in a typical embodiment, the only components charged into the carbonization chamber (i.e., intentionally introduced into the carbonization chamber) are coal and plastic.

[0012] When plastics are pyrolyzed in the carbonization chamber of a coke oven, they can produce carbonized products (carbon residue), hydrocarbon oil (as tar or diesel fuel), gas (hydrocarbon gas, hydrogen gas, etc.), and by-products. In this embodiment, carbonization of coal and plastics can produce carbonized products (coke), tar, diesel fuel, and 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 gas can be recovered from the top of the coke oven and used, for example, as fuel for power generation. In a typical embodiment, the product removed 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 gas.

[0013] Figure 1 is a schematic diagram showing an example of the general configuration of a coke oven. Referring to Figure 1, the coke oven 100 generally has a configuration in which a carbonization chamber 30 (having a furnace width W, furnace height H, and furnace length L) and a combustion chamber 40 are alternately arranged in the direction of the furnace width W via the furnace wall 20 above the heat storage chamber 10. Coal and plastics charged into the carbonization chamber 30 are carbonized by heat transfer from the combustion chamber 40, producing carbonized material, tar, diesel fuel, and gas as useful products. The carbonized material is extruded in the direction of the furnace length L by an extruder (not shown). The tar, diesel fuel, and gas flow out of the furnace from the carbonization chamber 30 via a riser pipe (not shown) connected to the carbonization chamber 30, and are separated from each other. At this time, the coke oven gas branches off from the riser pipe and is led to the dry main (i.e., the main coke oven gas recovery pipe). In a typical configuration, the riser pipe and the dry main are connected by a bend pipe. Each carbonization chamber 30 typically has a plurality of charging holes (not shown) at its top. Coal and plastic may each be charged into the carbonization chamber through one or more charging holes, for example, two, three, four, or five charging holes.

[0014] In carbonization using a coke oven, extrusion that does not involve the generation of visible smoke (dusting) is desirable from the viewpoint of the working environment and dust collection costs. The inventors have found that if the methane concentration in the exhaust gas from the carbonization chamber can be accurately measured, especially at the end of carbonization, the time when extrusion without dusting becomes possible can be predicted based on the decrease in the methane concentration over time. The inventors have also found that this behavior applies to both coal and plastic carbonization. In this embodiment, the time when extrusion without dusting becomes possible can be defined as the extrusion time. In both coal and plastic carbonization, the composition of the exhaust gas from the carbonization chamber (i.e., the gas discharged via the riser pipe) changes according to the progress of carbonization. That is, at the stage when carbonization is not progressing, hydrocarbon gases are discharged along with carbonization, while at the stage when carbonization is progressing, the discharge of hydrocarbon gases has almost finished, so the exhaust gas consists mainly of hydrogen and water vapor. Among the hydrocarbon gases in the exhaust gas, methane is usually present in the largest amount, making it easy to measure. Therefore, the methane concentration in the exhaust gas is a suitable indicator that directly represents the progress of carbonization. Normally, in a coke oven, the carbonization chamber is constantly drafted towards the riser pipe due to the chimney effect of the riser pipe and the ejector effect of ammonia water injected at the bend connecting the riser pipe and the dry main. Therefore, regardless of the internal pressure of the carbonization chamber, gas does not normally flow back into the carbonization chamber from the riser pipe. However, according to the inventors' investigation, it was found that, especially in the final stages of carbonization, the internal pressure of the carbonization chamber decreases because gas continues to be drawn out of the carbonization chamber into the riser pipe despite a decrease in the amount of gas generated in the carbonization chamber. Furthermore, according to the inventors' investigation, it was found that this decrease in internal pressure causes combustion gas from the combustion chamber to flow into the carbonization chamber from the joints in the furnace wall, outside air to flow into the carbonization chamber from gaps in the furnace lid, and gas to flow back into the carbonization chamber from the dry main (i.e., the main pipe for recovering coke oven gas). The influx of gas into the carbonization chamber interferes with the accurate measurement of methane concentration.For example, factors that cause fluctuations in methane concentration include the inflow of combustion gases into the carbonization chamber, combustion of combustible gases in the carbonization chamber due to the intrusion of outside air, and backflow of gas from the dry main into the carbonization chamber. Factors that cause a decrease in methane concentration include the inflow of outside air into the carbonization chamber. The inventors investigated a method to accurately measure the methane concentration even at the end of carbonization in order to make the methane concentration in the exhaust gas useful as an indicator for determining the progress of carbonization. As a result, they found that measuring the methane concentration while controlling the internal pressure of the carbonization chamber to be above a predetermined positive pressure value, and blocking the gas flow between the carbonization chamber and the dry main, or making the internal pressure of the carbonization chamber higher than the dry main pressure, is useful for accurate measurement of methane concentration. Here, positive pressure means a pressure higher than the atmospheric pressure at the location where the coke oven is installed. Note that if the internal pressure of the carbonization chamber is excessively high, the gas inside the carbonization chamber will leak out of the carbonization chamber from the furnace walls, etc. Therefore, the upper limit of the internal pressure in the carbonization chamber is the pressure that can ensure the sealing of the carbonization chamber.

[0015] For example, Non-Patent Document 1 (S. Honus et al., Fuel 221 (2018) pp.346-360) describes that the exhaust gas generated during the carbonization of coal and plastics (e.g., polyethylene terephthalate, polyethylene, polypropylene, polyvinyl chloride, or polystyrene) contains hydrocarbons (e.g., methane, ethylene), hydrogen, carbon monoxide, or carbon dioxide. In other words, the composition of the exhaust gas from plastics and coal is generally similar. During carbonization, the volume of the carbonized product decreases compared to the charge material in both plastics and coal. According to the inventors' studies, the rate of this volume reduction (bulk loss) tends to be significantly larger in plastics compared to coal. For example, when the volume of the charge is taken as 100%, the volume of the carbonized product can typically be about 80-90% for coal, whereas for plastic (for example, 28% polyethylene (PE), 31% polypropylene (PP), 23% polystyrene (PS), 17% polyethylene terephthalate (PET), and 1% polyvinyl chloride (PVC)), it can typically be about 20%. Therefore, in the carbonization of plastic, even when the maximum amount of plastic is charged considering the internal volume of the carbonization chamber, a large space at the top of the furnace is created in the latter half of the carbonization process. Furthermore, according to the inventors' studies, considering that the main purpose of a coke oven is usually the production of coke, even taking into account that the amount of gas generated per unit mass is greater for plastic than for coal, the amount of gas generated from plastic remains at only a few percent to over 20 percent of that generated from coal. Therefore, it was found that the decrease in internal pressure of the carbonization chamber can be more pronounced when carbonizing coal and plastic than when carbonizing coal alone.

[0016] In the method of this embodiment, the internal pressure of the carbonization chamber is appropriately controlled, which suppresses the inflow of combustion gases and outside air into the carbonization chamber, as well as the backflow of gas from the dry main into the carbonization chamber, even in the carbonization of plastics where a decrease in internal pressure in the carbonization chamber is likely to occur. As a result, accurate measurement of the methane concentration in the exhaust gas derived from plastics is possible even at the end of carbonization when the amount of gas generated is low.

[0017] In this embodiment, the plastic is charged into the carbonization chamber after the coal has been charged. In one embodiment, the plastic is charged at a time when at least a portion of the coal has already been converted to coke by carbonization. In this case, the plastic may be charged into the furnace top space above the coke through the charging hole. The order in which the carbonization of coal progresses and the carbonization of plastic progresses is not important. In a typical embodiment, the methane concentration in the exhaust gas decreases over time even after it falls below the methane concentration threshold of this disclosure. According to the inventors' studies, even if the timing of the carbonization of coal and the carbonization of plastic differs, the point in time when extrusion without dust generation becomes possible can be estimated by examining the change in the overall methane concentration of the exhaust gas. Since the amount of gas generated decreases towards the end of carbonization for both coal and plastic, the components of the exhaust gas will be strongly influenced by the components of the exhaust gas generated from the substance whose carbonization has not progressed as much. Therefore, even in cases where the carbonization of coal and plastic progresses at different rates, if the methane concentration in the exhaust gas can be measured with high accuracy, the extrusion timing can be correctly estimated. In other words, because the method of this embodiment has excellent accuracy in measuring methane concentration, it may be possible to determine the extrusion timing with high accuracy regardless of the ratio of the amount of plastic charged to the amount of coal charged.

[0018] In this embodiment, it is sufficient that the coke, which is the carbonized product, can be extracted without generating dust. Therefore, the quality of the obtained coke is not particularly limited. The coke may be used for appropriate purposes according to its quality, such as for blast furnaces or casting.

[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] <Plastics> Plastics can be recycled (i.e., made into useful materials usable as resources) by carbonization in a coke oven. In one embodiment, the plastic may be waste plastic. Waste plastic may be general waste or industrial waste, and there are no limitations on its origin. The plastic may originate from one or more of the following: 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, the plastic may originate from a single source, for example, a plastic substantially derived solely from PET bottles, a plastic substantially derived solely from expanded polystyrene packaging materials, etc. The plastic may be composed of two or more polymer materials. The plastic may originate from two or more sources. According to this embodiment, even if the properties of the material to be processed are diverse, the recycled material can be extruded without causing dust generation problems.

[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 amended Container and Packaging Recycling Law (Law No. 76 of June 15, 2006), which was enacted by the Japanese government in April 2007 and came into effect (e.g., PET bottles and plastic containers and packaging). Such sorting standards-compliant materials have a relatively uniform material composition, which can be advantageous for producing high-quality recycled materials.

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

[0024] From the viewpoint of carbonization efficiency, the moisture content of the plastic may, in one embodiment, be 30% by mass or less, 20% by mass or less, 15% by mass or less, or 10% by mass or less.

[0025] The shape of the plastic charged into the carbonization chamber is not limited; it may be in the same shape as when it was collected as waste, or it may be molded after collection. In one embodiment, the plastic may be charged into the carbonization chamber as pellets or the like. The plastic 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, removal of heavy objects using an air separator, etc. Crushing and granulation may be carried out using, for example, a compression type, shear type, cutting type, impact type, or friction type crusher.

[0026] The amount of 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 recycling plastic, in one embodiment, the amount may be 1% by mass or more, 5% by mass or more, or 10% by mass or more.

[0027] <Carbonization> In this embodiment, plastics can be recycled using a carbonization chamber that has already been charged with coal. This allows plastics to be processed without interrupting the process of producing coke from coal. The carbonization conditions (temperature, time, etc.) may be the same as 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. Generally, polymer materials are largely decomposed by heat at 500°C or below. For example, in polyethylene (PE), polystyrene (PS), polyethylene terephthalate (PET), and polypropylene (PP), which make up the majority of recovered plastics, thermal decomposition begins at approximately 300°C and is completed at approximately 420°C to 470°C. In addition, in polyvinyl chloride (PVC), which may be contained in plastics and can generate harmful gases when burned, a primary thermal decomposition reaction occurs at approximately 250°C or above, and a secondary thermal decomposition reaction occurs at approximately 400°C due to main chain severance. High-temperature carbonization using a coke oven is excellent for the thermal decomposition of plastics. Therefore, even if the plastic contains recalcitrant organic substances that can be an environmental burden, it is possible to produce clean recycled materials containing various useful components without the undesirability of releasing harmful substances into the environment. In particular, according to the method of this embodiment, it is possible to extrude the carbonized material without generating dust, even when processing large quantities of plastic.

[0028] In this embodiment, the methane concentration in the exhaust gas from the carbonization chamber is measured while controlling the internal pressure of the carbonization chamber to be above a predetermined positive pressure value. This measurement may be performed by a measuring mechanism (for example, a gas analyzer described later). If the internal pressure is not controlled, the decrease in internal pressure at the end of carbonization will cause combustion gas from the combustion chamber to flow into the carbonization chamber through joints in the furnace wall, outside air to flow into the carbonization chamber through gaps in the furnace lid, or gas to flow back into the carbonization chamber from the dry main (i.e., the main pipe for recovering coke oven gas). The inflow of gas into the carbonization chamber hinders the accurate measurement of the methane concentration. In this embodiment, the inflow of such gases is prevented by controlling the internal pressure to be above a predetermined positive pressure value, thereby enabling accurate measurement of the methane concentration. Typically, the internal pressure of the carbonization chamber is controlled to be above a predetermined positive pressure value throughout the entire period of carbonization. However, since accuracy in measuring methane concentration is particularly required at the end of carbonization, internal pressure control may be omitted during the first half of carbonization (in one embodiment, from the start of carbonization to the halfway point of the total period) and only implemented during the second half of carbonization (in one embodiment, from the halfway point of the total period to the start of extrusion). In one embodiment, the entire carbonization period may be estimated based on values ​​related to the operating history of the coke oven used. For example, if a coke oven is used in which the entire carbonization period is approximately 19 hours, the first 9.5 hours may be carried out without internal pressure control, and the last 9.5 hours with internal pressure control, based on that 19 hours.

[0029] The internal pressure of the carbonization chamber is measured, in one embodiment, as the pressure in the space above the carbonization chamber, and in another embodiment, as the pressure inside the pressure adjustment mechanism installed on the lid of the riser pipe. By controlling the internal pressure of the carbonization chamber to a positive pressure, it is possible to prevent gas from flowing into the carbonization chamber through joints in the furnace wall, gaps in the furnace lid, etc. However, even if the internal pressure of the carbonization chamber is positive, if the pressure of the dry main is higher than the internal pressure of the carbonization chamber, gas may flow back from the dry main into the carbonization chamber. In this embodiment, in controlling the internal pressure of the carbonization chamber, (1) the gas flow between the carbonization chamber and the dry main is blocked, or (2) the internal pressure of the carbonization chamber is made higher than the pressure of the dry main. In this embodiment, the carbonization chamber is not only controlled to a positive pressure, but the inflow of gas into the carbonization chamber is controlled to substantially prevent it. This makes it possible to accurately measure the methane concentration. In one embodiment, when the internal pressure of the carbonization chamber decreases, the gas flow path of the riser pipe may be narrowed to reduce the amount of gas flowing from the carbonization chamber to the riser pipe. Reducing the gas outflow rate contributes to preventing an increase in the internal pressure of the carbonization chamber, and therefore to preventing gas from entering the carbonization chamber, thus enabling accurate measurement of the methane concentration. In one embodiment, "when the internal pressure of the carbonization chamber decreases" may be selected from (i) when the internal pressure of the carbonization chamber decreases from a pressure higher than the dry main pressure to a pressure lower than or equal to the dry main pressure, (ii) when the internal pressure of the carbonization chamber decreases from above +10 mmAq relative to atmospheric pressure to below +10 mmAq relative to atmospheric pressure, or (iii) when the time derivative of the internal pressure of the carbonization chamber becomes negative.

[0030] Figure 2 illustrates an example of a method for controlling the internal pressure of the carbonization chamber. Referring to Figures 1 and 2, in this embodiment, a gas flow G1 from the outside or the combustion chamber 40 into the carbonization chamber 30 of the coke oven 100, a gas flow G2 released from the carbonization chamber 30 to the outside via the riser pipe 31, and a gas flow G3 reaching the dry main 33 via the bend pipe 32 branching off from the riser pipe 31 can occur. The internal pressure may be controlled by blocking the gas flow between the carbonization chamber 30 and the dry main 33 (for example, by closing the gas flow path with a valve 34, etc.) and then controlling the amount of gas flowing out of the carbonization chamber 30 to the riser pipe 31 (for example, by providing a cock 35B on the piping 35A attached to the lid 35 for restricting the gas flow, and adjusting the opening of the cock 35B according to the internal pressure of the carbonization chamber 30), or by making the internal pressure of the carbonization chamber 30 higher than the pressure of the dry main 33 (for example, by adjusting the internal pressure of the carbonization chamber 30 to be higher than the pressure of the dry main 33 using a furnace internal pressure adjustment mechanism (not shown)). For example, the internal pressure of the carbonization chamber may be maintained within a desired range by blocking the gas flow between the carbonization chamber 30 and the dry main 33 (for example, by closing the gas flow path with a valve 34, etc.), then fully opening the cock 35B, and then changing the opening of the cock 35B as needed between fully open and fully closed. The opening of the gas passage in the riser pipe 31 can be adjusted manually or automatically based on measurement data of the internal pressure in the carbonization chamber. The specific method for controlling the internal pressure is not limited and can be appropriately selected according to the type of coke oven, etc. The dry main pressure can be measured with a pressure gauge.

[0031] In one embodiment, the coke oven may not be equipped with a furnace pressure adjustment mechanism. In this case, in controlling the internal pressure of the carbonization chamber, the gas flow between the carbonization chamber and the dry main may be blocked by closing the gas passage between them, and the amount of gas flowing from the carbonization chamber to the riser pipe may be adjusted according to the internal pressure of the carbonization chamber. The internal pressure of the carbonization chamber tends to decrease as the amount of exhaust gas generated decreases as carbonization progresses; however, in this embodiment, the gas flow between the carbonization chamber and the dry main is blocked. By doing so, it is possible to control the internal pressure of the carbonization chamber to a desired positive pressure value or higher even at the end of carbonization by adjusting the amount of gas flowing from the carbonization chamber to the riser pipe.

[0032] The "predetermined" internal pressure of the carbonization chamber is a value predetermined according to the type of coke oven, carbonization conditions, etc., so that accurate measurement of methane concentration is possible even at the end of carbonization. In one embodiment, the internal pressure of the carbonization chamber is predetermined to be above a pressure that prevents combustion gas from the combustion chamber from flowing into the carbonization chamber from the joints in the furnace wall, prevents outside air from flowing into the carbonization chamber from the gaps in the furnace lid, and, if the connection between the carbonization chamber and the dry main is not blocked, prevents gas from flowing back into the carbonization chamber from the dry main (i.e., the main coke oven gas recovery pipe). The predetermined value is assumed to be positive pressure, and in one embodiment, it is a value greater than +0 mmAq relative to atmospheric pressure, with a preferred example considering the pressure distribution inside the carbonization chamber being +10 mmAq. On the other hand, from the viewpoint of preventing ignition due to gas leakage from the furnace lid, charging hole, etc., it is preferable that the internal pressure is not extremely high. In this regard, in one embodiment, the internal pressure may be controlled to be less than or equal to +70 mmAq, or less than or equal to +50 mmAq, or less than or equal to +20 mmAq relative to atmospheric pressure.

[0033] Referring to Figure 2, the methane concentration in the exhaust gas may be measured by introducing the exhaust gas WG, which passes through the pipeline 35A attached to the canopy 35, into the gas analyzer 36 via the introduction pipe 35C. In one embodiment, the gas analyzer 36 is an infrared gas analyzer. The methane concentration may be measured continuously or at predetermined time intervals.

[0034] In this embodiment, the extrusion timing is determined based on the methane concentration measured as described above. Specifically, the extrusion timing is determined to be the point in time later by a predetermined extrusion grace period than the point in time when the methane concentration decreases to a predetermined methane concentration threshold. This determination may be performed by a calculation mechanism (e.g., a computer) calculating a numerical value for the extrusion timing from the predetermined methane concentration threshold and the predetermined extrusion grace period. The inventors investigated the relationship between the methane concentration in the exhaust gas and the progress of carbonization during the extrusion of the carbonized material in the carbonization of plastics. At the stage when carbonization is not progressing, the exhaust gas contains a large amount of hydrocarbon gases, so if coke is extruded at this stage, visible smoke is generated due to the incomplete combustion of hydrocarbon gases. On the other hand, at the stage when carbonization is progressing, the exhaust gas is mainly composed of hydrogen and water vapor, so even if coke is extruded at this stage, no visible smoke is generated. In this embodiment, the extrusion timing is defined as the point in time when no visible smoke is generated when extruding coke. The presence or absence of visible smoke can be distinguished, for example, by imaging the conditions during coke extrusion and analyzing the image using the method described in Japanese Patent Publication No. 2023-34503. In this method, the difference in brightness inside and outside the visible smoke determination area in the image can be defined as an index value. More specifically, if the index value exceeds a standard value, and the time during which the index value exceeds the standard value is less than a predetermined threshold, it can be determined that visible smoke is present.

[0035] In this embodiment, the timing of extrusion of the carbonized product is determined by a combination of (1) a "predetermined methane concentration threshold" for the methane concentration in the exhaust gas, and (2) a "predetermined extrusion grace period" (measurement time), which is the time lag from the point when the methane concentration decreases to the said methane concentration threshold until the point when it is confirmed by measurements to check the progress of carbonization that extrusion without dust generation is possible. The "predetermined methane concentration threshold" and the "predetermined extrusion grace period" can be obtained as follows. According to the inventors' studies, in the charging and carbonization of plastics under arbitrarily selected specific coke ovens and specific carbonization conditions (for example, the conditions described in Example 1 below, i.e., a coke oven operating with a carbonization chamber having a height of 4 m, a length of 13.4 m, and a width of 400 mm, each carbonization chamber (furnace) having four charging holes, a coal charging amount of 13.6 t per carbonization chamber (furnace), an average fall time of 16 hours, and a settling time of 4 hours, in which coal with a moisture content of 2 mass%, a 3 mm sieve filtering ratio of 10 mass%, and a volatile content of 27 mass%), it was found that when the methane concentration one hour before the extrusion of the carbonized material is 4% or less, no visible smoke is generated during extrusion. Note that the methane concentration in this disclosure refers to the volume fraction. Furthermore, it was found that in the carbonization of coal, extrusion without the generation of visible smoke becomes possible one hour after the methane concentration in the exhaust gas has decreased to 4%. In actual operation, the procedure of measuring the methane concentration immediately before extrusion is inconvenient for operational reasons. In the above study of the carbonization of plastics or coal under specific coke ovens and carbonization conditions, the fact that the interval between the point at which the methane concentration decreased to 4% or less and the point at which it was found that extrusion without visible smoke generation became possible was "1 hour" means that if the start time of extrusion is set to "1 hour" after the point at which the methane concentration decreases to 4% or less, extrusion without dust generation problems can be achieved, that is, it is possible to determine the timing of extrusion of the carbonized material based on the methane concentration evaluated "1 hour" before extrusion.

[0036] The methane concentration in the exhaust gas can vary depending on the operating conditions (type of coke oven, type of coal and plastic, carbonization conditions, etc.). However, by examining the relationship between the methane concentration in the exhaust gas and the progress of carbonization during extrusion (in one embodiment, the state of visible smoke generation) under the actual operating conditions used for the carbonization of coal and plastic (type of coke oven, type of coal and plastic, carbonization conditions, etc.), or under test conditions that simulate these operating conditions, it is possible to estimate to what extent the methane concentration in the exhaust gas must decrease before extrusion without dust generation becomes possible (in other words, how long after charging the plastics before extrusion without dust generation becomes possible). By setting the methane concentration value obtained in this way as a threshold, the timing of extrusion can be determined based on this threshold. Ideally, the methane concentration in the exhaust gas measured to examine the relationship with the progress of carbonization during extrusion (in one embodiment, the state of visible smoke generation) should be the value immediately before extrusion. In this case, the "predetermined extrusion grace period" (measurement time) can be set to zero, so the extrusion time can be determined to be the point at which the methane concentration decreases to a predetermined methane concentration threshold. However, as mentioned above, in actual operation, the procedure of measuring the methane concentration immediately before extrusion is inconvenient for operational reasons. Therefore, the methane concentration measured to investigate the relationship with the carbonization progress during extrusion may be a value obtained a predetermined time before extrusion. In one embodiment, the threshold may be set to the methane concentration in the exhaust gas at a predetermined time before the extrusion point at which it is confirmed that no visible smoke is generated (in one embodiment, one hour before as mentioned above). In this case, the above predetermined time (in one embodiment, one hour) is set to a non-zero "predetermined extrusion grace period," and the extrusion time may be determined to be the point at which the methane concentration decreases to a predetermined methane concentration threshold, and is delayed by the "predetermined extrusion grace period." Note that when the methane concentration measurement and the measurement to investigate the carbonization progress can be carried out is determined by operational reasons and is not affected by the amount of plastic charged. In other words, the "predetermined extrusion grace period" does not depend on the amount of plastic loaded.

[0037] [Example of procedure for determining "predetermined methane concentration threshold" and "predetermined extrusion grace period"] As an example, the following procedure may be used: (i) Determine the "predetermined methane concentration threshold" for the methane concentration in the exhaust gas based on (a) the relationship between the elapsed time from the time the plastic was charged and the methane concentration in the exhaust gas, and (b) the relationship between the elapsed time from the time the plastic was charged and whether or not visible smoke was generated during extrusion. For example, based on the above relationships (a) and (b), a person skilled in the art can predict that if the methane concentration in the exhaust gas is α% or less, the carbonization has progressed sufficiently and no visible smoke will be generated even if the carbonized product is extruded after a certain period of time, and can set the value of α% as the methane concentration threshold. The above prediction may be carried out by a person skilled in the art based on ordinary trial and error. The above trial and error may be an experimental trial and error in which the measurement of methane concentration and the confirmation of whether or not visible smoke is generated during extrusion are repeated, but computer simulation may be used instead of experimental repetition. (ii) Next, the point in time when the methane concentration in the exhaust gas reaches a predetermined methane concentration threshold is determined from the above relationship (a). The time lag between this point in time and the point in time when the progress of carbonization during extrusion is investigated in order to examine the above relationship (b) is defined as the predetermined extrusion grace period.

[0038] The "predetermined methane concentration threshold" for the methane concentration in the exhaust gas is not limited to this, but may be a value selected in the range of 0% to 20%, for example, 4%, 5%, 6%, etc. In this embodiment, the combination of the "predetermined methane concentration threshold" and the "predetermined extrusion grace time" for a particular coke oven and a particular carbonization condition is not limited to one. For example, if it is confirmed that extrusion without dust generation is possible when the "predetermined methane concentration threshold" is 4% and the "predetermined extrusion grace time" is 1 hour for a particular coke oven and a particular carbonization condition, it is possible to change the "predetermined extrusion grace time" to a time longer than 1 hour, or change the "predetermined methane concentration threshold" to a value lower than 4%, etc.

[0039] In one aspect, in addition to the methane concentration in the exhaust gas from the carbonization chamber, the concentration of one or more selected from carbon monoxide, carbon dioxide, and hydrogen in the exhaust gas is measured. The concentrations of these gases can be used as auxiliary indicators to confirm whether the methane concentration is being accurately measured. As described above, at the stage where carbonization is progressing, the emission of hydrocarbon-based gases has almost ended, and the exhaust gas is mainly composed of hydrogen and water vapor. According to the study by the present inventors, at such a stage, the concentrations of carbon monoxide, carbon dioxide, and hydrogen in the exhaust gas are almost constant. However, if gas inflow into the carbonization chamber occurs, a decrease in the relative proportion of hydrogen in the exhaust gas (and thus a decrease in the hydrogen concentration), an increase in the concentration of carbon monoxide or carbon dioxide due to combustion of the gas in the carbonization chamber, etc. may occur. That is, at the end of carbonization, fluctuations in the concentration of carbon monoxide, carbon dioxide, or hydrogen may suggest gas inflow into the carbonization chamber. In this embodiment, by appropriately controlling the internal pressure of the carbonization chamber, the extrusion timing can be determined based on the methane concentration in the exhaust gas. However, when there are few fluctuations in the concentration of carbon monoxide, carbon dioxide, or hydrogen, it is further confirmed that the methane concentration is being accurately measured.

[0040] In particular, when the ratio of plastic to coal is low, the absolute amount of exhaust gas derived from plastic is small. Therefore, the advantage of measuring the concentration of one or more selected from carbon monoxide, carbon dioxide, and hydrogen as an indicator to confirm whether the methane concentration is being accurately measured is more prominent in such a case.

[0041] In one embodiment, the method for determining the extrusion timing is as follows (1) to (3): (1) Further measure the carbon monoxide concentration in the exhaust gas and maintain the carbon monoxide concentration below a predetermined carbon monoxide concentration threshold from a point that is at least a predetermined retrospective time earlier than the point in time when the methane concentration decreases to a predetermined methane concentration threshold until the point in time when the methane concentration decreases to a predetermined methane concentration threshold; (2) Further measure the carbon dioxide concentration in the exhaust gas and maintain the carbon dioxide concentration below a predetermined carbon dioxide concentration threshold from a point that is at least a predetermined retrospective time earlier than the point in time when the methane concentration decreases to a predetermined methane concentration threshold until the point in time when the methane concentration decreases to a predetermined methane concentration threshold; and (3) It is preferable to satisfy one or more of the following conditions: (1) the hydrogen concentration in the exhaust gas is further measured and at least one of the following conditions is met: the hydrogen concentration is maintained at or above a predetermined hydrogen concentration threshold from a point in time that is a predetermined retrospective time earlier than the point in time when the methane concentration decreases to a predetermined methane concentration threshold until the point in time when the methane concentration decreases to a predetermined methane concentration threshold. If the exhaust gas does not satisfy any of the above (1) to (3), examples of methods to make the exhaust gas satisfy one or more of the above (1) to (3) include closing the gas flow path between the carbonization chamber and the dry main if it is not closed, and narrowing the gas flow path of the riser pipe to reduce the amount of gas flowing from the carbonization chamber to the riser pipe.

[0042] The "predetermined retrospective time" in the above-mentioned "time earlier by a predetermined retrospective time than the time when the methane concentration decreases to a predetermined methane concentration threshold" can be predetermined according to the convenience of measuring the gas concentration, etc. In one embodiment, this "predetermined retrospective time" may be a value selected within the range of 420 minutes to 10 minutes, or 420 minutes to 40 minutes, for example, 60 minutes, 180 minutes, etc.

[0043] Each of the "predetermined carbon monoxide concentration threshold value", "predetermined carbon dioxide concentration threshold value", and "predetermined hydrogen concentration threshold value" can be determined in advance based on the variation of the measured values. In one aspect, the predetermined carbon monoxide concentration threshold value, the predetermined carbon dioxide concentration threshold value, and the predetermined hydrogen concentration threshold value can be determined based on the variation (standard deviation σ) obtained from the measured values. For example, in view of the fact that the variation of the three types of gas components becomes smaller after a certain period of time has elapsed since the start of carbonization, based on the measured values of each gas component after the elapse of a certain period of time, the concentration value of the average value - 3σ (for hydrogen in one aspect) or the average value + 3σ (for carbon monoxide and carbon dioxide in one aspect) can be set as the threshold value.

[0044] The measurement of the carbon monoxide concentration, carbon dioxide concentration, or hydrogen concentration from a point earlier than the point when the methane concentration has decreased to the predetermined methane concentration threshold value by the predetermined retrospective time until the point when the methane concentration has decreased to the predetermined methane concentration threshold value may be carried out continuously or at a predetermined time interval. The time interval, although not limited thereto, can be exemplified by 5 minutes to 15 minutes. From a point earlier than the point when the methane concentration has decreased to the predetermined methane concentration threshold value by the predetermined retrospective time until the point when the methane concentration has decreased to the predetermined methane concentration threshold value, the determination of whether the carbon monoxide concentration, carbon dioxide concentration, or hydrogen concentration is below (or above) the predetermined threshold value may be made based on the measured value of the concentration of each gas itself, or may be made based on an approximate formula derived from the plot of the measured values. The approximate formula may be linear or non-linear (for example, polynomial, exponential).

[0045] [Method for Estimating Carbonization Time] Another aspect of the present invention is a method for estimating the carbonization time, which is the time from the time when plastic is charged after coal is charged into the carbonization chamber of a coke oven to the time when the carbonized material is extruded when the coal and plastic are carbonized, wherein the internal pressure of the carbonization chamber is controlled to be above a predetermined positive pressure value, and the methane concentration in the exhaust gas from the carbonization chamber is measured, provided that in the control of the internal pressure, the gas flow between the carbonization chamber and the dry main branching from the riser pipe connected to the carbonization chamber is blocked, or the internal pressure of the carbonization chamber is made higher than the pressure of the dry main, and a relationship formula between the amount of plastic charged into the carbonization chamber of the coke oven and the carbonization time is determined, provided that the extrusion start time is later by a predetermined extrusion grace period than the time when the methane concentration decreases to a predetermined methane concentration threshold. The present invention provides a method for estimating the carbonization time, which is obtained by substituting the amount of plastic to be charged into the carbonization chamber of the coke oven into the given relational expression, and thereby obtaining an estimated carbonization time. In this embodiment, the focus is on the point in time when the methane concentration in the exhaust gas decreases to a predetermined methane concentration threshold. For example, the carbonization time can be estimated by following the procedure below.

[0046] <Measurement of Methane Concentration in Exhaust Gas> First, in the carbonization chamber of the coke oven, a carbonization test is performed by charging plastic after charging coal. For improved estimation accuracy, it is preferable to charge the plastic after the carbonization of the coal. The carbonization test is performed for each of two or more, three or more, or four or more test conditions, in which only the amount of plastic charged is 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. The plastic used in the carbonization test to determine the relationship between the amount of plastic charged into the carbonization chamber of the coke oven and the carbonization time required should preferably have the same or similar material composition as the plastic used in actual operation. An example of plastics used in actual operation and plastics used for the carbonization test having the same or similar material composition is when these plastics are collected via the same waste collection route. The plastic used for the carbonization test may be a portion of the plastic used in actual operation. If the density of the granulated plastic differs between the plastic used in actual operation and the plastic used for the carbonization test, it is preferable to select a different plastic for the carbonization test so that the density is similar. Density can vary depending on the material composition, but it can also vary depending on the granulation method.

[0047] In each carbonization test, the flow path between the carbonization chamber and the dry main is blocked, and the methane concentration in the exhaust gas from the carbonization chamber is measured while controlling the internal pressure of the carbonization chamber to a predetermined positive pressure value or higher. The internal pressure of the carbonization chamber, the method of controlling it, and the procedure for measuring the methane concentration may be the same as those exemplified in the [Extrusion Timing Determination Method] section, and will not be repeated here. The methane concentration may be measured continuously or at predetermined time intervals, as exemplified in the [Extrusion Timing Determination Method] section. Note that the relational formula may be derived based on the methane concentration measurement results from the most recent operational batch, rather than the measurement results from the carbonization test.

[0048] <Derivation of the Relationship Formula> Next, based on the methane concentration measured in <Measurement of Methane Concentration in Exhaust Gas> above (i.e., the change in methane concentration over time measured for each amount of plastic charged), a relationship formula is derived between the amount of plastic charged per charging hole and the carbonization time required. The carbonization time required is the time from the time of charging the plastic to the time of the start of extrusion of the carbonized material. The start of extrusion is a time that is later than the time when the methane concentration has decreased to a predetermined methane concentration threshold by a predetermined extrusion grace period. The methane concentration threshold may be a value predetermined based on a prior study on the relationship between the methane concentration in the exhaust gas and the progress of carbonization during extrusion (in one embodiment, the visible smoke generation situation), and the value itself is not limited. For example, the procedure described in the section [Example of Procedure for Determining "Predetermined Methane Concentration Threshold" and "Predetermined Extrusion Grace Period"] may be used as the prior study. It is preferable that the coke oven and carbonization conditions used in the prior study are the same as those used in the carbonization test to determine the above relationship formula. The amount of plastic charged as variable x may be set according to the purpose. For example, in one embodiment, the amount charged is the total amount charged (i.e., the sum of the amounts charged from multiple charging holes and charging at multiple timings). In this case, the time of plastic charging, in the time from the time of plastic charging to the time of carbonization extrusion (start of extrusion), is the time when the entire amount of plastic has been charged. In another embodiment, the amount charged is the maximum amount charged per single charging hole, through charging at multiple charging holes and multiple timings. In this case, the time of plastic charging is the time when the amount of plastic equal to the maximum value has been charged (the latest time if there are multiple times).

[0049] For example, a relationship between variables x and y can be obtained by regression analysis, where variable x is the amount of plastic charged into the carbonization chamber and variable y is the carbonization time. The regression can be linear or nonlinear (e.g., polynomial regression, exponential regression), and for example, the least squares method can be used. In one embodiment, the following equation (1a) is obtained as the relationship when it is a cubic equation: y = ax 3 +bx 2+ cx + d (1a) (wherein y is the carbonization time (hours), x is the amount of plastic charged per charging hole (kg), and a, b, c, and d are constants.) In one embodiment, the following equation (1b) is obtained as the relationship when it is a quadratic equation. y = ex 2 +fx+g (1b) (wherein y is the carbonization time (hours), x is the amount of plastic charged per charging hole (kg), and e, f, and g are constants.)

[0050] 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%.

[0051] <Calculation of Estimated Carbonization Time> In the relational equation derived using the procedure exemplified above, the value of variable y obtained by substituting the amount of plastic to be charged into variable x can be obtained as an estimated carbonization time for the plastic. Then, in actual operation, the time for extrusion can be treated as having reached the point where the carbonization time related to this estimated value has elapsed. In the carbonization test to derive the relational equation between variables x and y, the timing of adding the plastic can be after charging the coal, but from the viewpoint of obtaining a more precise estimate, it is preferable to add it after the carbonization of the coal. In actual operation, the estimated carbonization time based on the relational equation between variables x and y can be usefully utilized regardless of whether the plastic is charged during or after the carbonization of the coal.

[0052] [Method for Estimating the Amount of Plastic Charged] Another aspect of the present invention is a method for estimating the amount of plastic that can be charged into the carbonization chamber of a coke oven, based on the carbonization time, which is the time from the time when plastic is charged after coal is charged to the time when the carbonized product is extruded when the coal and plastic are carbonized, wherein the internal pressure of the carbonization chamber is controlled to be above a predetermined positive pressure value, the methane concentration in the exhaust gas from the carbonization chamber is measured, provided that in the control of the internal pressure, the gas flow between the carbonization chamber and the dry main branching from the riser pipe connected to the carbonization chamber is blocked, or the internal pressure of the carbonization chamber is made higher than the pressure of the dry main, and a relationship formula between the amount of plastic charged into the carbonization chamber of the coke oven and the carbonization time is determined, provided that the extrusion start time is later by a predetermined extrusion grace period than the time when the methane concentration decreases to a predetermined methane concentration threshold. This invention provides a method for estimating the amount of plastic that can be charged into the carbonization chamber of a coke oven, by substituting the desired carbonization time into the given relational equation. This method derives a relational equation using the same procedure as in the [Method for Estimating Carbonization Time], and then, by substituting the carbonization time required in actual operation into the carbonization time in the given relational equation, it is possible to estimate the maximum amount of plastic that can be extruded within the given carbonization time without generating dust. This allows for the maximum processing of plastic while maintaining the operational efficiency of the coke oven.

[0053] [Coke Production Method] This embodiment also provides a coke production method in which, after charging coal in the carbonization chamber of a coke oven, plastic is charged to produce coke derived from coal and plastic. In one embodiment, coke production can be carried out by the following procedure. The methane concentration in the exhaust gas from the carbonization chamber is measured while controlling the internal pressure of the carbonization chamber to be above a predetermined positive pressure value, however, in this control of the internal pressure, the gas flow between the carbonization chamber and the dry main branching from the riser pipe connected to the carbonization chamber is blocked, or the internal pressure of the carbonization chamber is made higher than the pressure of the dry main. (1) Determine a relationship between the amount of plastic charged into the carbonization chamber of the coke oven and the carbonization time, which is the time from the time of plastic charging to the time of extrusion of the carbonized product, provided that the time of extrusion start is later than the time when the methane concentration decreases to a predetermined methane concentration threshold by a predetermined extrusion grace period, (2) (2A) Substitute the desired amount of plastic charged, the first charging amount, into the relationship with the amount of plastic charged into the carbonization chamber of the coke oven to calculate the carbonization time, the first time, or (2B) Substitute the desired carbonization time, the second time, into the relationship with the carbonization time to calculate the second charging amount, which is the amount of plastic charged into the carbonization chamber of the coke oven, (3) (3A) Charge the plastic with the first charging amount and perform carbonization for a time of the first time or longer, or (3B) Charge the plastic in an amount equal to or less than the second charge amount, perform carbonization for the second time, and then extrude the coke using an extruder. Note that in (1) above, the timing of adding the plastic may be after the coal has been charged, but it is preferable that it be after the coal has been carbonized. In (3) above, the timing of adding the plastic may be during or after the coal has been carbonized, and may be set arbitrarily according to important items such as the total process time from the coal charge to the start of coke extrusion, the quality of the coke, and the amount of plastic processed.

[0054] The following describes exemplary embodiments of the present invention with reference to examples, but the present invention is not limited to these embodiments.

[0055] <Preliminary Study: Changes in Internal Pressure of the Carbonization Chamber over Time during the Carbonization of Plastics> A carbonization chamber of a coke oven that was not charged with coal was used. The carbonization chamber was 7.1 m high, 16.7 m long, and 460 mm wide, and each carbonization chamber (furnace) had four charging holes. Granulated material with a diameter of several 30 mm was used as the plastic.

[0056] 0.6 tons / hole, or a total of 1.2 tons, of plastic was charged through two of the four charging holes in the carbonization chamber. The pressure was measured using a Pitot tube installed near the base of the riser tube. Static and dynamic pressures were recorded from the time of plastic charging until approximately 5 hours later. The internal pressure of the carbonization chamber is the sum of the static and dynamic pressures, i.e., the total pressure. Figure 3 shows the change in static pressure near the base of the riser tube in the carbonization chamber over time during the carbonization of plastics in the preliminary study. Figure 4 shows the change in dynamic pressure near the base of the riser tube in the carbonization chamber over time during the carbonization of plastics in the preliminary study. In the graph of Figure 3, the horizontal axis is time from plastic charging, and the vertical axis is static pressure. In the graph of Figure 4, the horizontal axis is time from plastic charging, and the vertical axis is dynamic pressure. The dashed line in Figure 4 indicates a dynamic pressure of 0 Pa. Referring to Figure 3, the static pressure shifted from atmospheric pressure + approximately 100 Pa (approximately 10.20 mmAq) to atmospheric pressure + approximately 80 Pa (approximately 8.16 mmAq). Note that in Figure 3, there are times when the static pressure temporarily exceeded approximately 100 Pa and times when it temporarily fell significantly below approximately 50 Pa. These are due to the circulation of nitrogen gas to prevent blockage of the gas flow path involved in the measurement. Referring to Figure 4, the dynamic pressure was positive immediately after the plastic was inserted, but turned negative 30 minutes after insertion, and thereafter remained generally negative (minimum of approximately -6 Pa). Note that in Figure 4, there is a time when the dynamic pressure temporarily fell significantly below approximately -3 Pa. This is due to the circulation of nitrogen gas to prevent blockage of the gas flow path involved in the measurement. The total pressure (static pressure + dynamic pressure) was maintained at positive pressure throughout the study. Furthermore, the pressure measured by the Pitot tube tends to be about 4 to 5 mmAq higher than the pressure inside the pressure regulating mechanism installed in the roof of the ascent tube.

[0057] Traditionally, in the normal operation of a coke oven, it was assumed that the gas flow would be from the carbonization chamber towards the dry main. However, in this preliminary study using plastics, the dynamic pressure became negative, as described above. This suggests that gas flowed back from the dry main into the carbonization chamber during carbonization. In the carbonization of plastics, the internal pressure of the carbonization chamber tends to decrease, and therefore it is presumed that this internal pressure tends to be lower than the dry main pressure. From the results of this preliminary study, it was found that if the internal pressure of the carbonization chamber is not specifically controlled during the carbonization of plastics, gas backflow from the dry main to the carbonization chamber occurs even in the early stages of carbonization, 30 minutes after charging, that is, when the amount of gas generated is still high. Therefore, in the following examples, we attempted to carbonize plastics while controlling the internal pressure of the carbonization chamber.

[0058] <Example 1: Determination of Extrusion Timing> An operational coke oven was used. This coke oven had a carbonization chamber with a height of 4 m, a length of 13.4 m, and a width of 400 mm. It was operating with a coal charging amount of 13.6 t per carbonization chamber, an average ignition time of 16 hours, and a settling time of 4 hours. Each carbonization chamber (furnace) was equipped with four charging holes. The coal charged had a moisture content of 2 mass%, a 3 mm sieve content of 10 mass%, and a volatile content of 27 mass%. Granulated material with a particle size of over 30 mm was used as the plastic.

[0059] The methane concentration in the exhaust gas passing through the riser pipe of the carbonization chamber was measured every 20 minutes using an infrared gas analyzer (Fuji Electric Co., Ltd., model ZSVS). First, preliminary studies confirmed that in coal carbonization, the methane concentration should fall below 4% one hour before extrusion without dust generation becomes possible. Therefore, for coal carbonization, it was assumed that extrusion without dust generation would be possible within the following hour once the methane concentration fell to approximately 4% or less. A total of 160 kg of plastic was charged into the furnace top space above the coal-derived coke, 40 kg per hole. The internal pressure (specifically, the pressure inside the pressure adjustment mechanism installed on the riser pipe lid) was maintained at +10 mmAq relative to atmospheric pressure, and carbonization was further carried out. The internal pressure was measured using a differential pressure gauge. The internal pressure was controlled by separating the carbonization chamber from the dry main (i.e., blocking the gas flow between them by closing the valve between them) and then opening and closing a cock in the gas passage of the riser tube according to the internal pressure.

[0060] Figure 5 is a graph plotting the methane concentration in the exhaust gas against the elapsed time from the time T when the plastic was charged in Example 1. In the graph of Figure 5, the horizontal axis is the elapsed time from the time T when the plastic was charged, and the vertical axis is the methane concentration in the exhaust gas. The curve in Figure 5 is an approximation curve of the plot, and the dashed line represents a methane concentration of 4%. In Example 1, the methane concentration continued to decrease until 2.8 hours after the plastic was charged. After 2.8 hours, the methane concentration decreased to 4% (dashed line in the figure). It was then estimated that extrusion without dust generation problems became possible after 3.8 hours from the time the plastic was charged. Specifically, when the presence or absence of visible smoke was checked when the carbonized material was extruded 3.8 hours after the plastic was charged, there was no visible smoke generation. Specifically, the situation when the carbonized material was extruded 3.8 hours after the plastic was charged was imaged, and the presence or absence of visible smoke was identified using the image analysis method described in Japanese Patent Application Publication No. 2023-34503. The analysis conditions were as follows. First, the level of visible smoke during extrusion in normal operation is quantified using image analysis. Multiple extrusions and analyses are performed to determine the acceptable range. Based on this range, it is determined whether the smoke emission in subsequent extrusions is within an acceptable range.

[0061] From the above results, it can be seen that in the coke oven used in Example 1, the time at which extrusion without dust generation becomes possible can be determined by a combination of a "predetermined methane concentration threshold" of 4% and a "predetermined extrusion grace period" of 1 hour. In Example 1, due to the setting of the measurement conditions, the time at which the presence or absence of visible smoke was confirmed (3.8 hours after plastic charging) was 1 hour after the time at which the methane concentration in the exhaust gas reached 4% (2.8 hours after plastic charging). Note that the methane concentration threshold is not limited to the above 4%. In other words, the combination of a "predetermined methane concentration threshold" and a "predetermined extrusion grace period" is not limited to one for a particular coke oven and a particular carbonization condition. In Example 2 below, the above 1 hour was set as the "predetermined extrusion grace period," and the extrusion time was determined to be the time after the time at which the methane concentration in the exhaust gas reached the threshold of 4% by the "predetermined extrusion grace period" (1 hour).

[0062] <Example 2: Estimation of Carbonization Time> The carbonization time was investigated when the amount of plastic charged was changed to condition 1 (20 kg in each of the four charging holes), condition 2 (30 kg), condition 3 (40 kg) (already implemented as Example 1), or condition 4 (50 kg). The procedure was the same as in Example 1, except for the amount of plastic charged. Plastic was charged into the furnace top space of the upper layer of coke in different carbonization chambers of the coke oven, according to the respective amounts for conditions 1, 2, and 4. Figure 6 is a graph plotting the carbonization time in Example 2, which is the time from the time of plastic charging to the time when the methane concentration decreased to 4% + 1 hour, against the amount of plastic charged. In the graph of Figure 6, the horizontal axis is the amount of plastic charged, and the vertical axis is the carbonization time obtained by adding 1 hour (i.e., the "predetermined extrusion grace period" defined in Example 1) to the time from the time of plastic charging to the time when the methane concentration decreased to 4%. Condition 3 involved plotting the values ​​obtained in Example 1.

[0063] When the plot in Figure 6 was subjected to polynomial (cubic) regression, the following relationship was obtained: y = -0.0000656x 3 +0.0086987x 2-0.2757121x + 5.0953206 [y: carbonization time (hours), x: amount of plastic charged per charging hole (kg)]

[0064] By using the above relational equation, it is possible to estimate the carbonization time required for a given amount of plastic charged.

[0065] <Reference Example 1, Comparative Reference Example 1: Measurement of Methane, Carbon Monoxide, Carbon Dioxide, and Hydrogen Concentrations in Exhaust Gas During Coal Carbonization> Next, we examined the advantages of evaluating the concentrations of carbon monoxide, carbon dioxide, and hydrogen in addition to the methane concentration in the exhaust gas. In this example, for the convenience of the experiment, coal alone was subjected to carbonization. In Reference Example 1 and Comparative Reference Example 1, coal was carbonized, and the concentrations of methane, carbon monoxide, carbon dioxide, and hydrogen in the exhaust gas from the carbonization chamber were measured.

[0066] An operational coke oven was used. This coke oven had a carbonization chamber that was 4 m high, 13.4 m long, and 400 mm wide. It was operating with a coal charging capacity of 13.6 tons per carbonization chamber, an average burn-down time of 16 hours, and a resting time of 4 hours. Each carbonization chamber (furnace) had four charging holes. The coal charged had a moisture content of 2% by mass, a 3 mm sieve content of 90% by mass, and a volatile content of 27% by mass.

[0067] [Reference Example 1] A total of 13.6 tons of coal were charged in at 3.4 tons per hole from four charging holes. Carbonization was performed while maintaining the internal pressure (specifically, the pressure inside the pressure adjustment mechanism installed on the roof of the riser pipe) at +10 mmAq relative to atmospheric pressure. The internal pressure was measured using a differential pressure gauge. The internal pressure was adjusted by opening and closing a cock installed in the gas flow path of the riser pipe according to the internal pressure, after disconnecting the carbonization chamber from the dry main (i.e., blocking the gas flow between them by closing the valve between them). The concentrations of methane, carbon monoxide, carbon dioxide, and hydrogen in the exhaust gas that passed through the riser pipe were measured approximately every 20 minutes using an infrared gas analyzer (Fuji Electric Co., Ltd., model ZSVS).

[0068] [Comparative Reference Example 1] In Comparative Reference Example 1, coal carbonization was performed using the same procedure as in Reference Example 1, except that the internal pressure of the carbonization chamber was not controlled, and the concentrations of methane, carbon monoxide, carbon dioxide, and hydrogen were measured. Specifically, the connection between the carbonization chamber and the dry main was severed, while the cock of the gas flow path in the riser pipe was opened, and the methane concentration was measured under negative pressure inside the carbonization chamber. In Comparative Reference Example 1, the internal pressure of the carbonization chamber 17.3 hours after coal charging was -5 mmAq relative to atmospheric pressure.

[0069] [Results of Reference Example 1 and Comparative Reference Example 1] Figure 7 is a graph plotting the methane (CH4) concentration in the exhaust gas against the elapsed time from the time of coal charging in Reference Example 1 and Comparative Reference Example 1. Figure 8 is a graph plotting the carbon monoxide (CO) concentration in the exhaust gas against the elapsed time from the time of coal charging in Reference Example 1 and Comparative Reference Example 1. Figure 9 is a graph plotting the carbon dioxide (CO2) concentration in the exhaust gas against the elapsed time from the time of coal charging in Reference Example 1 and Comparative Reference Example 1. Figure 10 is a graph plotting the hydrogen (H2) concentration in the exhaust gas against the elapsed time from the time of coal charging in Reference Example 1 and Comparative Reference Example 1. In the graph of Figure 7, the horizontal axis is the elapsed time from the time of coal charging, and the vertical axis is the methane concentration in the exhaust gas. In Figure 7, the black circles represent the measurement points in Reference Example 1, the white circles represent the measurement points in Comparative Reference Example 1, the curve is the approximation curve of the plots in Figure 7, the dashed line is the threshold for methane concentration, and the dashed line is the point at which the methane concentration reached the threshold on the approximation curve. In the graph of Figure 8, the horizontal axis is the elapsed time from the time of coal charging, and the vertical axis is the carbon monoxide concentration in the exhaust gas. In Figure 8, the black circles represent the measurement points in Reference Example 1, the white circles represent the measurement points in Comparative Reference Example 1, the straight line is the line connecting the plots in Figure 7, and the dashed line is the threshold for carbon monoxide concentration. In the graph of Figure 9, the horizontal axis is the elapsed time from the time of coal charging, and the vertical axis is the carbon dioxide concentration in the exhaust gas. In Figure 9, the black circles represent the measurement points in Reference Example 1, the white circles represent the measurement points in Comparative Reference Example 1, the straight line is the line connecting the plots in Figure 7, and the dashed line is the threshold for carbon dioxide concentration. The graph in Figure 10 has the elapsed time from the time of coal charging on the horizontal axis and the hydrogen concentration in the exhaust gas on the vertical axis. In Figure 10, the black circles represent the measurement points in Reference Example 1, the white circles represent the measurement points in Comparative Reference Example 1, the straight lines are the lines connecting the plots in Figure 7, and the dashed lines are the hydrogen concentration thresholds.

[0070] Referring to Reference Example 1, Figure 7 shows that the methane concentration decreased monotonically over time from the time of coal charging. Referring to Figures 8-10, the concentrations of carbon monoxide, carbon dioxide, and hydrogen remained almost constant over time from the time of coal charging.

[0071] When the plot of Reference Example 1 shown in Figure 7 was approximated by a curve, the following equation was obtained. The coefficient of determination of the following equation is R 2 The value was 0.9993. y = 5.081 × 10 3 ×e -0.387x (In the formula, x is the elapsed time since coal charging (hours), and y is the methane concentration (%).) When a methane concentration of 4% was substituted for y in the above formula, x (elapsed time since coal charging) was 18.5 hours. Furthermore, one hour later, at 19.5 hours, the coke was extruded to check for the presence or absence of visible smoke during extrusion, and no visible smoke was generated. Specifically, the situation during extrusion was imaged, and the presence or absence of visible smoke was identified using the image analysis method described in Japanese Patent Publication No. 2023-34503. The analysis conditions were as follows: First, the level of visible smoke during extrusion in normal operation was quantified by image analysis. The acceptable range was determined by multiple extrusions and analyses. Based on the obtained range, it was determined whether the smoke generation situation of subsequent extrusions was within an acceptable range.

[0072] From the above results, it can be seen that in the coke oven used in Reference Example 1, the threshold for methane concentration in the exhaust gas can be set to 4%, and the time after one hour has elapsed since the methane concentration fell below this threshold can be determined as the extrusion time. In Reference Example 1, due to the setting of the measurement conditions, the time at which the presence or absence of visible smoke was confirmed (19.5 hours after coal charging) was one hour after the time when the methane concentration decreased to 4% (18.5 hours after coal charging). Therefore, this one hour can be set as the "predetermined extrusion grace period," and the time after the methane concentration in the exhaust gas reached the threshold of 4% can be determined as the extrusion time. Note that the threshold for methane concentration is not limited to the above 4%. For example, in Reference Example 1, when a methane concentration of 5% is substituted for y in the above formula, x (elapsed time since coal charging) is approximately 17.9 hours. In the study of Reference Example 1, as mentioned above, it was confirmed that no visible smoke was generated during extrusion 19.5 hours after coal charging. Therefore, instead of setting the "predetermined methane concentration threshold" to 4% and the "predetermined extrusion grace period" to 1 hour, it is also possible to set the "predetermined methane concentration threshold" to 5% and the "predetermined extrusion grace period" to 1.6 (= 19.5 - 17.9) hours.

[0073] Furthermore, measurements of carbon monoxide concentration were taken for five different furnaces. The results showed that there was no significant change after 15.5 hours, and the average value from the measured value at 15 hours and 33 minutes to the measured value at 18 hours and 35 minutes was 4.6%, with a σ of 0.9%. Considering that the carbon monoxide concentration shows high values ​​when air or other gases flow in, +3σ was used, and the carbon monoxide concentration threshold was set at 7.3% (dashed line in the figure) based on 4.6 + 0.9 × 3. As shown in Figure 8, the carbon monoxide concentration was maintained at 7.3% or less from 15.5 hours after the time when the methane concentration decreased to 4% (18.5 hours after coal charging) until 18.5 hours later. Similarly, measurements of carbon dioxide concentration showed that there was no significant change after 15.5 hours, and the average value from the measured value at 15 hours and 33 minutes to the measured value at 18 hours and 35 minutes was 0.193%, with a σ of 0.135%. Considering that carbon dioxide concentrations are high when air or other gases are inflowing, the carbon dioxide concentration threshold was set to 0.6% (dashed line in the figure) based on 0.193 + 0.135 × 3, using +3σ. As shown in Figure 9, the carbon dioxide concentration remained below 0.6% from 15.5 hours after the start of coal charging (3 hours earlier than when the methane concentration decreased to 4%) until 18.5 hours after the start of coal charging. Similarly, when the hydrogen concentration was measured, it did not change significantly after 15.5 hours, and the average value from the measured value at 15 hours and 33 minutes to the measured value at 18 hours and 35 minutes was 86.3%, with a σ of 2.5%. Considering that hydrogen concentrations are low when air or other gases are inflowing, the hydrogen concentration threshold was set to 78.8% (dashed line in the figure) based on 86.3 - 2.5 × 3, using -3σ. As shown in Figure 10, the hydrogen concentration remained above 78.8% from 15.5 hours after the start of coal charging (3 hours earlier than the point when the methane concentration decreased to 4%, which was 18.5 hours after coal charging) until 18.5 hours later. These results suggest that in Reference Example 1, no gas inflow into the carbonization chamber occurred, and the methane concentration could be accurately measured.

[0074] Referring to Figure 7, in Reference Example 1, the methane concentration decreased monotonically with the passage of time from coal charging. On the other hand, in Comparative Reference Example 1, no clear trend was observed in the change of methane concentration in the exhaust gas with the passage of time from coal charging. From the above, it is thought that in Comparative Reference Example 1, the carbonization chamber was under negative pressure, which caused gas to flow into the carbonization chamber, making it impossible to accurately measure the methane concentration.

[0075] Furthermore, referring to Figure 8, from 15.5 hours after coal charging (3 hours earlier than the point when the methane concentration decreased to 4%, 18.5 hours after coal charging) to 18.5 hours after coal charging, in Reference Example 1, the carbon monoxide concentration was maintained at 7.3% or less, whereas in Comparative Reference Example 1, the carbon monoxide concentration exceeded 7.3%, and showed a more rapid change compared to Reference Example 1, suggesting the intrusion of external air or other gases. In addition, referring to Figure 9, from 15.5 hours after coal charging (3 hours earlier than the point when the methane concentration decreased to 4%, 18.5 hours after coal charging) to 18.5 hours after coal charging, in Reference Example 1, the carbon dioxide concentration was maintained at 0.6% or less, whereas in Comparative Reference Example 1, it exceeded 0.6%, and showed a more rapid change compared to Reference Example 1, suggesting the intrusion of external air or other gases. In addition, referring to Figure 10, from 15.5 hours after coal charging (3 hours earlier than the point when the methane concentration decreased to 4% (18.5 hours after coal charging)) until 18.5 hours after coal charging, the hydrogen concentration in Reference Example 1 was maintained at 78.8% or higher, whereas in Comparative Reference Example 1, it fell below 78.8% and showed a more rapid change compared to Reference Example 1, suggesting the intrusion of external air or other gases. From the above, it can be concluded that in Comparative Reference Example 1, the negative pressure in the carbonization chamber caused gas to flow into the carbonization chamber, making it impossible to accurately measure the methane concentration.

[0076] <Comparative Reference Example 2: Measurement of Methane Concentration in Exhaust Gas> In Comparative Reference Example 2, coal carbonization was performed using the same procedure as in Reference Example 1, except that the internal pressure of the carbonization chamber was not controlled, and the methane concentration was measured. Specifically, the methane concentration was measured with the furnace pressure at +2 mmAq relative to atmospheric pressure, which is positive pressure but lower than the dry main pressure of +6 mmAq, with the gas flow between them not interrupted by opening the valve between them and the furnace. In Comparative Reference Example 2, tests 1 to 5 were conducted under the same conditions except that the furnaces were different.

[0077] Table 1 shows the relationship between the elapsed time from the time of coal charging and the methane concentration in the exhaust gas in Comparative Reference Example 2. As shown in Table 1, in Comparative Reference Example 2, the methane concentration tended to increase significantly with time, particularly at the end of carbonization, approximately 16 hours after coal charging. In Tests 1 to 5, which were conducted under identical conditions except for the different furnaces, in four tests excluding Test 4, the measurement range of the infrared gas analyzer was exceeded after approximately 17.5 hours from coal charging, making concentration measurement impossible. In Comparative Reference Example 2, the methane concentration in the exhaust gas decreased as carbonization progressed, but it is thought that the methane concentration began to increase at the end of carbonization due to a decrease in the internal pressure of the carbonization chamber and subsequent backflow of gas from the dry main into the carbonization chamber.

[0078]

[0079] As described above, in the carbonization of coal and plastic in Example 1, and in the carbonization of coal in Reference Example 1, the methane concentration in the exhaust gas at the end of carbonization was low, below 4%, but because the internal pressure of the carbonization chamber was appropriately controlled, the concentration could be accurately measured. Furthermore, from the results of Reference Example 1, it can be seen that in the carbonization of coal, the concentrations of carbon monoxide, carbon dioxide, and hydrogen in the exhaust gas can serve as auxiliary indicators to confirm whether the methane concentration is being measured correctly. Since the exhaust gas generated in the carbonization of plastic may contain methane, carbon monoxide, carbon dioxide, or hydrogen, similar to coal, it is presumed that even when the carbonization target is a combination of coal and plastic rather than coal, the concentrations of carbon monoxide, carbon dioxide, or hydrogen in the exhaust gas can serve as auxiliary indicators to confirm whether the methane concentration is being measured correctly.

Claims

1. A method for determining the timing of extrusion of carbonized materials when carbonizing coal and plastic in the carbonization chamber of a coke oven, wherein the internal pressure of the carbonization chamber is controlled to be above a predetermined positive pressure value, the methane concentration in the exhaust gas from the carbonization chamber is measured, and in the control of the internal pressure, the gas flow between the carbonization chamber and the dry main branching from the riser pipe connected to the carbonization chamber is blocked, or the internal pressure of the carbonization chamber is made higher than the pressure of the dry main, and the extrusion start time is determined to be later by a predetermined extrusion grace period than the time when the methane concentration decreases to a predetermined methane concentration threshold.

2. The extrusion timing determination method according to claim 1, wherein, in the control of the internal pressure, the gas flow is blocked by closing the gas passage between the carbonization chamber and the dry main, and the amount of gas flowing out from the carbonization chamber to the riser pipe is adjusted according to the internal pressure of the carbonization chamber.

3. The extrusion timing determination method according to claim 2, wherein, in the control of the internal pressure, when the internal pressure of the carbonization chamber decreases, the gas flow path of the riser pipe is narrowed to reduce the amount of gas flowing from the carbonization chamber to the riser pipe.

4. The following (1) to (3): (1) Further measure the carbon monoxide concentration in the exhaust gas and maintain the carbon monoxide concentration below the predetermined carbon monoxide concentration threshold from a predetermined retrospective time earlier than the time when the methane concentration decreases to the predetermined methane concentration threshold until the time when the methane concentration decreases to the predetermined methane concentration threshold; (2) Further measure the carbon dioxide concentration in the exhaust gas and maintain the carbon dioxide concentration below the predetermined carbon dioxide concentration threshold from a predetermined retrospective time earlier than the time when the methane concentration decreases to the predetermined methane concentration threshold until the time when the methane concentration decreases to the predetermined methane concentration threshold; and (3) The method for determining the extrusion timing according to any one of claims 1 to 3, which satisfies one or more of the following conditions: (3) Further measuring the hydrogen concentration in the exhaust gas, and maintaining the hydrogen concentration at or above a predetermined hydrogen concentration threshold from a point in time that is at least a predetermined retrospective time earlier than the point in time when the methane concentration decreases to the predetermined methane concentration threshold until the point in time when the methane concentration decreases to the predetermined methane concentration threshold.

5. A method for estimating the carbonization time required in the carbonization chamber of a coke oven, which is the time from the time when plastic is charged after coal is charged to the time when the carbonized product is extruded when the coal and plastic are carbonized, wherein the internal pressure of the carbonization chamber is controlled to be above a predetermined positive pressure value, and the methane concentration in the exhaust gas from the carbonization chamber is measured, provided that in the control of the internal pressure, the gas flow between the carbonization chamber and the dry main branching from the riser pipe connected to the carbonization chamber is blocked, or the internal pressure of the carbonization chamber is made higher than the pressure of the dry main, and a relationship formula between the amount of plastic charged into the carbonization chamber of the coke oven and the carbonization time is determined, provided that the extrusion start time is later by a predetermined extrusion grace period than the time when the methane concentration decreases to a predetermined methane concentration threshold. A method for estimating the carbonization time, wherein the carbonization time is estimated when the amount of plastic to be charged is substituted into the carbonization chamber of the coke oven in the aforementioned relational equation.

6. A method for estimating the amount of plastic that can be charged into the carbonization chamber of a coke oven, based on the carbonization time, which is the time from the time when plastic is charged after coal is charged to the time when the carbonized product is extruded when the coal and plastic are carbonized, wherein the internal pressure of the carbonization chamber is controlled to be above a predetermined positive pressure value, and the methane concentration in the exhaust gas from the carbonization chamber is measured, provided that in the control of the internal pressure, the gas flow between the carbonization chamber and the dry main branching from the riser pipe connected to the carbonization chamber is blocked, or the internal pressure of the carbonization chamber is made higher than the pressure of the dry main, and a relationship formula between the amount of plastic charged into the carbonization chamber of the coke oven and the carbonization time is determined, provided that the extrusion start time is later by a predetermined extrusion grace period than the time when the methane concentration decreases to a predetermined methane concentration threshold. A method for estimating the amount of plastic that can be charged into the carbonization chamber of the coke oven, which is the amount of plastic that can be charged into the carbonization chamber of the coke oven when the desired carbonization time is substituted into the carbonization time in the aforementioned relational equation.

7. A coke production method comprising charging coal and then plastic into the carbonization chamber of a coke oven to produce coke derived from the coal and the plastic, wherein the internal pressure of the carbonization chamber is controlled to be above a predetermined positive pressure value, and the methane concentration in the exhaust gas from the carbonization chamber is measured, provided that in the control of the internal pressure, the gas flow between the carbonization chamber and the dry main branching from the riser pipe connected to the carbonization chamber is blocked, or the internal pressure of the carbonization chamber is made higher than the pressure of the dry main, (1) a relationship formula is determined between the amount of plastic charged into the carbonization chamber of the coke oven and the carbonization time, which is the time from the time of plastic charging to the time of the start of carbonization extrusion, provided that the start of extrusion is a time later by a predetermined extrusion grace period than the time when the methane concentration decreases to a predetermined methane concentration threshold, (2) A method for producing coke, comprising: (2A) substituting a first charge amount, which is a desired amount of plastic charged, into the relational formula for the first time required for carbonization, which is the carbonization time, or (2B) substituting a second time, which is a desired carbonization time, into the relational formula for the second charge amount, which is the amount of plastic charged into the carbonization chamber of the coke oven; (3) (3A) charging the first charge amount of plastic and performing carbonization for a period of time of the first time or longer, or (3B) charging the second charge amount or less of plastic and performing carbonization for a period of time of the second time, and then extruding coke using an extruder.

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