Method for determining extrusion timing of coke oven, method for estimating time required for dry distillation, method for estimating amount of plastic that can be charged, and method for producing coke

Abstract

Provided, with regard to the dry distillation of plastic in a coke oven, is a method for determining the extrusion timing of the coke oven, which method makes it possible to directly and accurately confirm the timing at which extrusion can be carried out without the problem of dust generation. One embodiment of the present invention provides a method for determining the extrusion timing of a dry-distilled product when plastic is dry distilled in a carbonization chamber of a coke oven into which coal is not charged, wherein: the methane concentration in an 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; in this control of the internal pressure, gas flow between the carbonization chamber and a dry main branched from an ascending pipe connected to the carbonization chamber is blocked, or the internal pressure of the carbonization chamber is set to a pressure higher than the pressure of the dry main; and the extrusion starting time point is determined to be a time point delayed by a predetermined extrusion delay time from a time point at which this methane concentration has decreased to a predetermined methane concentration threshold.

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 perspective of effective utilization of resources and contribution to the realization of carbon neutrality, the recycling of plastics (that is, converting plastics into recycled products, 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 facilities. However, the knowledge about the carbonization conditions suitable for the recycling of plastics is not yet sufficient. In particular, when the carbonized product is extruded from the coke oven by an extruder, if the carbonization of the plastic has not proceeded sufficiently, 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 producing fuel gas by blending plastics with raw coal or carbonizing them alone.

[0004] Japanese Patent Laid-Open No. 48-032902, Japanese Patent Laid-Open No. 2023-34503

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

[0006] Patent Document 1 mentions that plastic waste can be carbonized alone, but it does not focus on a method for directly confirming the progress of carbonization when carbonizing plastic waste, and there is room for improvement in accurately determining the extrusion timing. One aspect of the present invention aims to solve the above problems and provide a method for determining the extrusion timing of a coke oven that can directly and accurately confirm the timing at which extrusion without the problem of dust generation becomes possible when carbonizing plastics in a coke oven.

[0007] The gist of the present invention is as follows: [1] A method for determining the timing of extrusion of a carbonized product when carbonizing a plastic in a carbonization chamber of a coke oven that is not charged with coal, comprising: controlling the internal pressure of the carbonization chamber to be equal to or greater than a predetermined positive pressure value, measuring the methane concentration in the exhaust gas from the carbonization chamber; in the control of the internal pressure, blocking the gas flow between the carbonization chamber and a dry main branching from a 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 start of extrusion to be a time 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 at or below a predetermined carbon monoxide 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 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 at or below a predetermined carbon dioxide 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 a predetermined methane concentration threshold until the point in time when the methane concentration decreases to a 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 predetermined retrospective time earlier than the time when the methane concentration decreases to a predetermined methane concentration threshold until the time when the methane concentration decreases to a predetermined methane concentration threshold, wherein one or more of the above conditions are met. [5] A method for estimating the carbonization time required when carbonizing plastic in a carbonization chamber of a coke oven that is not charged with coal, the time from the time plastic is charged to the time when the carbonized material is extruded, 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. 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, based on the carbonization time, which is the time from the time the plastic is charged to the time the carbonized material is extruded, when carbonizing plastic in a carbonization chamber of a coke oven that is not charged with coal, 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 plastic into a carbonization chamber of a coke oven that is not charged with coal, thereby producing coke derived from 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 that 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 to be charged, into the relational expression for the amount of plastic to be charged into the carbonization chamber of the coke oven, to calculate the first time, which is the carbonization time required; or (2B) Substituting a second time, which is a desired carbonization time required, into the relational expression for the second charge amount, which is the amount of plastic to be charged into the carbonization chamber of the coke oven; (3) (3A) Charging the first charge amount of plastic into the carbonization chamber of a coke oven where no coal is charged, 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 into the carbonization chamber of a coke oven where no coal is charged, 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 0.8% + 1 hour, against the maximum charging height of the plastics in Examples 1 and 2. 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 a carbonized product when carbonizing plastic in a carbonization chamber of a coke oven that is not charged with coal, 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 controlling 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. 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 term "extrusion time of the carbonized product" means the time when the extrusion of the carbonized product begins.

[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 plastics can produce carbonized products (coke), tar, diesel fuel, and gas as useful materials. Depending on its quality, the coke can be used for blast furnaces and various other applications. 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. 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. The plastic may 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. In this embodiment, the time when extrusion without dusting becomes possible can be defined as the extrusion time. In the carbonization of plastics, 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 is almost complete, 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 and is therefore 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 usually flow back into the carbonization chamber from the riser pipe. However, our investigations have shown that, especially at the end of carbonization, despite a decrease in the amount of gas generated in the carbonization chamber, gas continues to be drawn out of the carbonization chamber into the riser pipe, causing the internal pressure of the carbonization chamber to decrease. Furthermore, our investigations have shown that this decrease in internal pressure can cause combustion gases 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, and gas to flow back into the carbonization chamber from the dry main (i.e., the main coke oven gas recovery pipe). The inflow 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 flammable 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 for accurately measuring methane concentration even at the end of carbonization, in order to make the methane concentration in the exhaust gas a useful 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 that in controlling the internal pressure, blocking the gas flow between the carbonization chamber and the dry main, or setting the internal pressure of the carbonization chamber to a pressure 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 through the furnace walls, etc. Therefore, the upper limit of the internal pressure of the carbonization chamber is a pressure that can ensure the sealing performance 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 considered 100%, the volume of the carbonized product is typically around 80-90% for coal, whereas for plastics (for example, polyethylene (PE) 28%, polypropylene (PP) 31%, polystyrene (PS) 23%, polyethylene terephthalate (PET) 17%, polyvinyl chloride (PVC) 1%), it is typically around 20%. In addition, since plastics tend to generate more gas in the initial stages of carbonization than coal, the charge amount is often less than the maximum capacity of the carbonization chamber in order to suppress gas eruption from the carbonization chamber. For these reasons, in the carbonization of plastics, even when the maximum amount of plastic considered in relation to the internal volume of the carbonization chamber is charged, a large furnace top space is created at the top of the carbonization chamber in the latter half of the carbonization process. If the amount of gas generated is the same, a larger furnace top space results in lower internal pressure in the carbonization chamber. Furthermore, experiments have shown that the gas generation rate per unit mass of plastic tends to be slower than that of coal. Therefore, our investigations revealed that, despite the fact that the amount of gas generated per unit mass tends to be higher in plastic than in coal, the decrease in internal pressure of the carbonization chamber may be more pronounced in plastic than in coal.

[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, plastic is carbonized in a carbonization chamber that is not charged with coal. Note that "not charged with coal" means that coal is not intentionally added. Therefore, carbonization chambers where coal exists as a residue (e.g., deposits on the furnace wall) are also included in the category of carbonization chambers that are not charged with coal. In a typical embodiment, the only component charged into the carbonization chamber (i.e., intentionally introduced into the carbonization chamber) is plastic. In this embodiment, it is important to remove the carbonized coke without generating dust. Therefore, the quality of the resulting coke is not particularly limited. The coke may be used for appropriate applications depending on its quality, such as for blast furnaces or casting.

[0018] <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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] <Carbonization> The carbonization conditions (temperature, time, etc.) may be the same as those used when producing coke using 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 thermal decomposition below 500°C. 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 higher, 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.

[0024] 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 operational performance when charging plastics into the coke oven used. For example, if the total carbonization period is approximately 19 hours and the amount of plastic charged is such that the first 9.5 hours are performed without internal pressure control and the last 9.5 hours are performed with internal pressure control, based on those 19 hours.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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 later by a predetermined extrusion grace period than the time when the methane concentration decreases to a predetermined methane concentration threshold. 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. 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, when carbonization is progressing, the exhaust gas is mainly composed of hydrogen and water vapor, so no visible smoke is generated even if coke is extruded at this stage. In this embodiment, the extrusion timing is determined to be the time when no visible smoke is generated when coke is extruded. The presence or absence of visible smoke can be distinguished, for example, by imaging the situation during coke extrusion and analyzing the image using the method described in Japanese Patent Application Publication No. 2023-34503. In this method, the difference in brightness between the inside and outside of the visible smoke detection area in the image can be defined as an index value. More specifically, if the index value exceeds a standard value, and the duration of the index value exceeding the standard value is less than a predetermined threshold, it can be determined that visible smoke is present. The methane concentration can be used as is based on the measured value, or a correction value as described below may be used. That is, the exhaust gas passing through the riser pipe may contain not only the gas generated by carbonization but also atmospheric components present in the carbonization chamber. As carbonization progresses and the amount of gas generated decreases, the proportion of atmospheric components in the exhaust gas passing through the riser pipe may increase. Therefore, using the gas analyzer described above, in addition to the methane concentration, the concentration of, for example, nitrogen (i.e., a substance that is abundant and inert among atmospheric components) may be measured, and the measured value of methane concentration may be corrected according to the following formula. Correction using nitrogen concentration may be particularly useful when the plastic is not nitrogen-containing plastic. The nitrogen concentration in the atmosphere is approximately 78%. Therefore, for example, the correction value calculated using the following formula: Methane concentration correction value (%) = Measured methane concentration (%) / (100 (%) - Nitrogen concentration (%) / 0.78) × 100 may be treated as the methane concentration in the exhaust gas.The nitrogen concentration in the exhaust gas may be an actual measured value, or it may be a calculated value obtained by subtracting, for example, the total measured concentration of carbon monoxide, oxygen, carbon dioxide, and hydrogen (as components other than nitrogen in the atmosphere) in the exhaust gas from 100%.

[0031] 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. This determination may be performed by a calculation mechanism (for example, a computer) calculating a numerical value representing the extrusion timing from the "predetermined methane concentration threshold" and the "predetermined extrusion grace period". The "predetermined methane concentration threshold" and the "predetermined extrusion grace period" for the methane concentration can be obtained as follows. According to the inventors' studies, it was found that when charging and carbonizing plastics under arbitrarily selected specific coke ovens and specific carbonization conditions (for example, the conditions described in Example 1 below, i.e., the carbonization chamber having a height of 7.1 m, a length of 16.7 m, and a width of 460 mm, with each carbonization chamber (oven) having four charging holes, and using granulated plastic with a particle size of several 30 mm as the plastic), visible smoke is not generated during extrusion if the methane concentration one hour before extrusion of the carbonized material is 0.8% or less. In this disclosure, methane concentration refers to volume fraction. Furthermore, in the carbonization of coal, it was found that under specific coke ovens and specific carbonization conditions (for example, the conditions described in Reference Example 1 below, namely, 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, with 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, where coal with a moisture content of 2 mass%, a 3 mm sieve filtering ratio of 10 mass%, and a volatile content of 27 mass%), extrusion without visible smoke generation becomes possible one hour after the methane concentration in the exhaust gas decreases to 4%. In actual operation, the procedure of measuring the methane concentration immediately before extrusion is inconvenient for operational reasons.In the above-mentioned 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 0.8% or less or 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 0.8% or less or 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.

[0032] The methane concentration in the exhaust gas can vary depending on the operating conditions (type of coke oven, type of 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 plastics (type of coke oven, type of 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 much time must pass after charging the plastic 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.

[0033] [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 material 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.

[0034] 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% or 0.8%. 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 0.8% 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 0.8%, etc.

[0035] In one embodiment, in addition to the methane concentration in the exhaust gas from the carbonization chamber, the concentration of one or more gases 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 measured correctly. As mentioned above, at the stage where carbonization is progressing, the emission of hydrocarbon gases is almost complete, and the exhaust gas consists mainly of hydrogen and water vapor. According to the inventors' studies, at this stage, the concentrations of carbon monoxide, carbon dioxide, and hydrogen in the exhaust gas are almost constant. However, if gas is flowing into the carbonization chamber, a decrease in the relative proportion of hydrogen in the exhaust gas (and therefore a decrease in hydrogen concentration), an increase in the concentration of carbon monoxide or carbon dioxide due to the combustion of gas in the carbonization chamber, etc. may occur. In other words, fluctuations in the concentrations of carbon monoxide, carbon dioxide, or hydrogen at the end of carbonization may indicate the inflow of gas into the carbonization chamber. In this embodiment, the extrusion timing can be determined based on the methane concentration in the exhaust gas by appropriately controlling the internal pressure of the carbonization chamber. Furthermore, when there is little fluctuation in the concentrations of carbon monoxide, carbon dioxide, or hydrogen, it is further confirmed that the methane concentration can be measured accurately.

[0036] 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.

[0037] 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.

[0038] Each of the "predetermined carbon monoxide concentration threshold," "predetermined carbon dioxide concentration threshold," and "predetermined hydrogen concentration threshold" can be predetermined based on the variability of the measured values. In one embodiment, the predetermined carbon monoxide concentration threshold, predetermined carbon dioxide concentration threshold, and predetermined hydrogen concentration threshold can be determined based on the variability (standard deviation) σ obtained from the measured values. For example, in light of the fact that the variability of the three gas components decreases after a certain period of time has elapsed since the start of carbonization, the concentration values ​​of the average value minus 3σ (in one embodiment, for hydrogen) or the average value plus 3σ (in one embodiment, for carbon monoxide and carbon dioxide) can be set as thresholds based on the measured values ​​of each gas component after a certain period of time has elapsed.

[0039] Measurements of carbon monoxide concentration, carbon dioxide concentration, or hydrogen concentration from a predetermined time interval earlier than the time when the methane concentration decreases to a predetermined methane concentration threshold until the time when the methane concentration decreases to a predetermined methane concentration threshold may be performed continuously or at predetermined time intervals. The time interval is not limited to this, but examples include 5 to 15 minutes. The determination of whether the carbon monoxide concentration, carbon dioxide concentration, or hydrogen concentration is below (or above) a predetermined threshold from a predetermined time interval earlier than the time when the methane concentration decreases to a predetermined methane concentration threshold until the time when the methane concentration decreases to a predetermined methane concentration threshold may be made based on the measured values ​​of each gas themselves, or based on an approximation formula derived from the plot of measured values. The approximation formula may be linear or nonlinear (e.g., polynomial, exponential).

[0040] [Method for estimating carbonization time required] One aspect of the present invention also provides a method for estimating the carbonization time required, which is the time from the point of charging plastic to the start point of extrusion of the carbonized product when dry-distilling plastic in a coke oven's carbonization chamber without coal charged. The method includes measuring the methane concentration in the exhaust gas from the carbonization chamber while controlling the internal pressure of the carbonization chamber to be not less than a predetermined positive pressure value. However, in this control of the internal pressure, the gas flow between the carbonization chamber and the dry main separated from the riser pipe connected to the carbonization chamber is blocked, or the internal pressure of the carbonization chamber is set higher than the pressure of the dry main. A relational expression between the amount of plastic charged into the carbonization chamber of the coke oven and the carbonization time required is obtained. However, the start point of extrusion is a point that is delayed by a predetermined extrusion allowance time from the point when the methane concentration has decreased to a predetermined methane concentration threshold value. In the relational expression, an estimated value of the carbonization time required is obtained, which is the carbonization time required when the value of the amount of plastic charged is substituted into the amount of plastic charged into the carbonization chamber of the coke oven, thus providing a method for estimating the carbonization time required. In this embodiment, attention is paid to the point when the methane concentration in the exhaust gas has decreased to a predetermined methane concentration threshold value. For example, the carbonization time required can be estimated by the following procedure.

[0041] <Measurement of Methane Concentration in Exhaust Gas> First, a carbonization test is performed by charging plastic into the carbonization chamber of a coke oven that is not charged with 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. It is preferable to have a large number of test conditions, 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 is preferably the same as or similar in material composition as the plastic used in actual operation. An example of plastics used in actual operation and plastics used in 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 in 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 in 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.

[0042] 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.

[0043] <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 may be the charged mass, and in another embodiment, it may be the charging height (i.e., the height from the bottom of the carbonization chamber to the top surface of the charged plastic). Note that the charging height for each charging hole usually takes its highest value directly below the charging hole, so this highest value may be defined as the charging height for each charging hole. 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 charging of the entire amount of plastic is completed. Also, in one embodiment, the amount charged is the maximum value of the amount charged per single charging hole (e.g., charged mass or charging height) through charging at multiple charging holes and multiple timings. In this case, the time of plastic loading is the point at which the maximum amount of plastic in question is loaded (or the latest point in time if there are multiple amounts).

[0044] For example, a relational expression between variable x, which is the amount of plastic charged into the carbonization chamber, and variable y, which is the required time for carbonization, may be obtained by regression analysis with variable x as an explanatory variable and variable y as an objective variable. The regression may be linear regression or non-linear regression (for example, polynomial regression, exponential regression), and for example, the least squares method may be used. In one aspect, the following formula (1a) is obtained as the relational expression in the case of a cubic equation. y = ax 3 + bx 2 + cx + d (1a) (In the formula, y is the required time for carbonization (hours), x is the amount of plastic charged per charging hole (kg), and a, b, c, and d are constants.) Also, in one aspect, the following formula (1b) is obtained as the relational expression in the case of a quadratic equation. y = ex 2 + fx + g (1b) (In the formula, y is the required time for carbonization (hours), x is the amount of plastic charged per charging hole (kg), and e, f, and g are constants.)

[0045] The method for confirming whether the regression analysis has been effectively performed is not particularly limited, and a test may be performed by a normal method. The significance level may be selected as desired, for example, 5% or 1%.

[0046] <Calculation of Estimated Value of Required Carbonization Time> In the relational expression derived by the procedure exemplified above, when the value of the amount of plastic charged is substituted for variable x, the value of variable y can be obtained as the estimated value of the required carbonization time of the plastic. And in actual operation, it can be handled that the extrusion time has been reached when the required carbonization time corresponding to this estimated value has elapsed.

[0047] [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, based on the carbonization time, which is the time from the time the plastic is charged to the time the carbonized material is extruded, when carbonizing plastic in a carbonization chamber of a coke oven that is not charged with coal, the method comprising: controlling the internal pressure of the carbonization chamber to a predetermined positive pressure value or higher, measuring the methane concentration in the exhaust gas from the carbonization chamber, 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; determining a relationship between the amount of plastic charged into the carbonization chamber of the coke oven and the carbonization time, 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.

[0048] [Coke Production Method] This embodiment also provides a coke production method in which plastic is charged into a carbonization chamber of a coke oven that is not charged with coal, thereby producing coke derived from plastic. In one embodiment, coke production can be carried out by the following procedure: While controlling the internal pressure of the carbonization chamber to be above a predetermined positive pressure value, the methane concentration in the exhaust gas from the carbonization chamber is measured, 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 first charging amount of plastic into the carbonization chamber of the coke oven, which is not charged with coal, and perform carbonization for a time of the first time or longer, or (3B) Plastic is charged into the carbonization chamber of the coke oven, which is not charged with coal, in an amount equal to or less than the second charge amount, and after carbonization for the second hour, coke is extruded using an extruder.

[0049] The following describes exemplary embodiments of the present invention with reference to examples, but the present invention is not limited to these embodiments.

[0050] <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.

[0051] 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 riser tube. Referring to Figure 4, the dynamic pressure was positive immediately after the plastic was charged, but turned negative 30 minutes after charging, 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 riser tube. 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.

[0052] 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.

[0053] <Example 1: Determination of Completion of Carbonization> A carbonization chamber of a coke oven that was not charged with coal was used. The carbonization chamber had a height of 7.1 m, a length of 16.7 m, and a width of 460 mm, and each carbonization chamber (furnace) was equipped with four charging holes. Granulated plastic with a particle size of several 30 mm was used as the plastic.

[0054] 1.5 tons / hole, or a total of 6.0 tons, of plastic was charged into the carbonization chamber through its four charging holes. Carbonization was performed while maintaining the internal pressure (specifically, the pressure inside the pressure adjustment mechanism installed on the top of the riser pipe) at a positive pressure of +10 mmAq relative to the dry main pressure. The internal pressure was measured using a differential pressure gauge. The internal pressure was adjusted by opening and closing a cock 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, oxygen, carbon dioxide, and hydrogen in the exhaust gas that passed through the riser pipe of the carbonization chamber were measured using an infrared gas analyzer (Fuji Electric Co., Ltd., model ZSVS). In this study, the measured methane concentration was corrected according to the following formula, and the calculated corrected value was treated as the methane concentration in the exhaust gas. Methane concentration correction value (unit: %) = Measured methane concentration (unit: %) / (100 - Calculated nitrogen concentration (unit: %) / 0.78) The calculated nitrogen concentration in the above formula was calculated according to the following formula: Calculated nitrogen concentration (%) = 100 - (Total measured concentration of carbon monoxide, oxygen, carbon dioxide, and hydrogen (%))

[0055] Figure 5 is a graph plotting the methane concentration in the exhaust gas against the carbonization time (i.e., 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. In Example 1, the methane concentration decreased to 0.8% by 22.7 hours after the time T was charged with the plastic. When the carbonized plastic was extruded 23.7 hours after the time T was charged with the plastic, no visible smoke was generated, and the completion of carbonization was confirmed. Specifically, coke was extruded 23.7 hours after the time T was charged with the plastic, the situation at that time 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 was quantified by image analysis. The range that does not cause problems 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.

[0056] From the above results, it can be seen that in the coke oven used in Example 1, the completion of carbonization can be determined by the combination of a "predetermined methane concentration threshold" of 0.8% and a "predetermined extrusion grace period" of 1 hour. In Example 1, due to the setting of the measurement conditions, the time when the presence or absence of visible smoke was confirmed (23.7 hours after plastic charging) was 1 hour after the time when the methane concentration in the exhaust gas decreased to 0.8% (22.7 hours after plastic charging). Note that the methane concentration threshold is not limited to the above 0.8%. 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 the following Example 2, the above 1 hour was defined as a "predetermined extrusion grace period," and the completion time of carbonization was determined to be the time after the methane concentration in the exhaust gas reached a threshold of 0.8% by the "predetermined extrusion grace period" (1 hour).

[0057] <Example 2: Estimation of Carbonization Time> The carbonization chambers were 7.1 m high, 16.7 m long, and 460 mm wide, and each carbonization chamber (furnace) had four charging holes. Hereafter, the charging holes will be referred to as charging hole 1, charging hole 2, charging hole 3, and charging hole 4, in order of distance from the riser pipe. Granulated plastic with a particle size of several 30 mm was used as the plastic. The carbonization time was investigated when the amount of plastic charged was changed to condition 1 (0.05 ton in charging hole 3), condition 2 (0.5 ton in the same), condition 3 (0.6 ton each in charging holes 2 and 3), condition 4 (0.6 ton, 1.0 ton, and 0.9 ton each in charging holes 2, 3, and 4), or condition 5 (0.7 ton, 1.3 ton, and 2.1 ton each in charging holes 2, 3, and 4). Except for the type of plastic used and the amount charged, the procedure was the same as in Example 1. The plastic was charged into different carbonization chambers of the coke oven at the respective charging amounts for conditions 1 to 5. Figure 6 is a graph plotting the carbonization time, which is the time from the time the plastic was charged to the point when the methane concentration decreased to 0.8% plus 1 hour, against the maximum charging height of the plastic in Examples 1 and 2. In the graph of Figure 6, the horizontal axis is the maximum charging height of the plastic (as the charging amount), and the vertical axis is the carbonization time obtained by adding 1 hour (i.e., the "predetermined extrusion grace period" obtained in Example 1) to the time from the time the plastic was charged to the point when the methane concentration decreased to 0.8%. The results of Example 1 are also plotted in Figure 6. The maximum loading height for plastic refers to the loading height into the loading hole at the largest loading height for plastic under each condition. In Example 1, this is 4.0 m, and in Example 2, conditions 1 to 5 are 0.6 m, 1.9 m, 2.0 m, 2.6 m, and 4.1 m, respectively.

[0058] When the plots for Examples 1 and 2 in Figure 6 were subjected to polynomial regression, the following relation (1) was obtained. The coefficient of determination of the following equation is R 2 The value was 0.9991. y = 0.5946x 2 +4.0637x - 1.8218 (1) In the formula, x is the maximum plastic loading height (in m) and y is the carbonization time (in h).

[0059] As the results above show, the absolute value of the carbonization time changes when the amount of plastic charged into the carbonization chamber changes, but the carbonization time estimated based on the methane concentration in the exhaust gas showed a good correlation with the amount of plastic charged. From this, it can be seen that estimating the carbonization time by adding a certain amount of time from the point when the methane concentration in the exhaust gas decreases to a threshold is possible regardless of the amount of plastic charged.

[0060] <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.

[0061] 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.

[0062] [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).

[0063] [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.

[0064] [Results of Reference Example 1 and Comparative Reference Example 1] Figure 7 is a plot of the methane 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 plot of the carbon monoxide 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 plot of the carbon dioxide 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 plot of the hydrogen 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 are the measurement points in Reference Example 1, the white circles are 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. The graph in Figure 8 has the elapsed time since coal charging on the horizontal axis and the carbon monoxide concentration in the exhaust gas on the vertical axis. 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 lines connect the plots in Figure 7, and the dashed line is the threshold for carbon monoxide concentration. The graph in Figure 9 has the elapsed time since coal charging on the horizontal axis and the carbon dioxide concentration in the exhaust gas on the vertical axis. 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 lines connect 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 since 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 connect the plots in Figure 7, and the dashed line is the threshold for hydrogen concentration.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] Furthermore, preliminary measurements of carbon monoxide concentration in five different furnaces showed no significant change after 15.5 hours, with the average value from 15 hours 33 minutes to 18 hours 35 minutes being 4.6%, and σ being 0.9%. Considering that carbon monoxide concentration increases with the inflow of air or other gases, +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 remained below 7.3% from 15.5 hours (3 hours earlier than the point at which the methane concentration decreased to 4%, 18.5 hours after coal charging) until that point. Similarly, preliminary measurements of carbon dioxide concentration showed no significant change after 15.5 hours, with the average value from 15 hours 33 minutes to 18 hours 35 minutes being 0.193%, and σ being 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, the hydrogen concentration was measured in advance and did not change significantly after 15.5 hours. 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.

[0069] 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.

[0070] 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.

[0071] <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.

[0072] 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 of the tests except for 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.

[0073]

[0074] As described above, in the carbonization of plastics in Example 1 and 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 plastics may contain methane, carbon monoxide, carbon dioxide, or hydrogen, similar to coal, it is presumed that even when the material being carbonized is plastic instead of 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 a carbonized product when carbonizing plastic in a carbonization chamber of a coke oven that is not charged with coal, 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; in the control of the internal pressure, blocking the gas flow between the carbonization chamber and a dry main branching from a 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 start of extrusion to be a time 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 a predetermined carbon monoxide 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 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 in time 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) 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 a predetermined methane concentration threshold until the point in time when the methane concentration decreases to a predetermined methane concentration threshold.

5. A method for estimating the carbonization time required when carbonizing plastic in a carbonization chamber of a coke oven that is not charged with coal, the time from the time plastic is charged to the time when the carbonized material is extruded, 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. 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, based on the carbonization time, which is the time from the time the plastic is charged to the time the carbonized material is extruded, when carbonizing plastic in a carbonization chamber of a coke oven that is not charged with coal, 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 plastic into a carbonization chamber of a coke oven that is not charged with coal, thereby producing coke derived from 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 that 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 to be charged, into the relational expression for the amount of plastic to be charged into the carbonization chamber of the coke oven, to calculate the first time, which is the carbonization time required; or (2B) Substituting a second time, which is a desired carbonization time required, into the relational expression for the second charge amount, which is the amount of plastic to be charged into the carbonization chamber of the coke oven; (3) (3A) Charging the first charge amount of plastic into the carbonization chamber of a coke oven where no coal is charged, 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 into the carbonization chamber of a coke oven where no coal is charged, and performing carbonization for a period of time of the second time, and then extruding coke using an extruder.

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