Waste plastic processing method

Abstract

According to the present invention, coal for producing coke or mixed coal for producing coke that includes coal and waste plastic for mixing is charged into a carbonization chamber (2) of a coke oven (1) and dry distilled to produce coke (13). When the dry distillation is complete, a portion or all of a plurality of charging ports (4 (4a–4d)) that are provided in the carbonization chamber of the coke oven are used to charge waste plastic (14 (14b–14d)) into an upper space (5) that is above the coke inside the carbonization chamber in order from the charging port closest to an ascension pipe (3) to the charging port farthest from the ascension pipe. The present invention thereby provides a waste plastic processing method that makes it possible to keep pyrolysis gas from waste plastic from leaking or erupting from charging ports.

Description

How to dispose of waste plastic

[0001] The present invention relates to a method for treating waste plastics, and more particularly to a method for treating waste plastics using a coke oven.

[0002] Large quantities of waste plastics, both industrial and general waste, have traditionally been disposed of by landfilling or partial incineration. Even in landfills, waste plastics are not decomposed by bacteria in the soil, and when incinerated, they generate a large amount of heat, adversely affecting incinerators. Furthermore, when waste plastics contain chlorine, the disposal of the chlorine in the exhaust gases during incineration presents a problem. Given the expected future shortage of landfill sites and growing awareness of environmental issues, there is a desire to promote the recycling of waste plastics. Possible recycling methods include reuse as plastic, utilization of the heat generated during combustion, and the use of gases and oils obtained through thermal decomposition during heating as fuels or chemical raw materials.

[0003] For example, Patent Document 1 discloses a method for recycling waste plastics by mixing plastic granules molded at 100 to 160°C with coal and carbonizing the mixture in a coke oven (hereinafter referred to as the "coal mixed charging method"). On the other hand, Patent Document 2 describes that mixing a large amount of plastic in the coal mixed charging method reduces the strength of the produced coke, and that in order to limit the reduction in coke strength to a few percent, the mass ratio of plastic to coal needs to be 1% or less, and that the amount that can be recycled is limited depending on the target coke strength level.

[0004] Another known method for treating waste plastics while suppressing a decrease in coke strength is a method (hereinafter referred to as "top space charging") in which waste plastics are charged into the space above the coal or a mixture of coal and waste plastics (hereinafter, the mixture of coal and waste plastics is also referred to as "mixed coal") charged into the carbonization chamber (the upper (top-side) space in the carbonization furnace where coal or mixed coal is not charged). Patent Document 3 discloses that this top space charging method allows most of the waste plastics to be pyrolyzed in a high-temperature coke oven, resulting in the production of high-calorie pyrolysis gases containing hydrogen, methane, ethane, propane, and the like. These pyrolysis gases are recovered as part of the coke oven gas generated in the coke oven chamber by the pyrolysis of coal and reused as raw materials for various products. The following technologies have been disclosed regarding the top space charging method.

[0005] Patent Document 4 discloses a method for treating waste plastics, which involves preparing a coke oven charge coal or a coke oven charge coal containing 0.1 to 1.0 wt% of waste plastics, charging the prepared coal into a coke oven, and then charging waste plastics into the top space above the charged coal. The waste plastics are then pyrolyzed during carbonization to recover tar, diesel, gas, and coke (residue). Two methods for treating waste plastics are disclosed: charging waste plastics into the top space above the charged coal through a charging port after the coal is charged, and supplying waste plastics from a supply device connected to the top space of the coke oven from after the coal is charged until the end of carbonization. These methods are said to enable the treatment of the same amount of waste plastic as when approximately 5 wt% of waste plastic is blended into the top space. In the method described in Patent Document 4, the raw material charging lid is opened and waste plastic is charged while coal is being carbonized in the carbonization chamber of the coke oven, and therefore it is necessary to ensure that the amount of gas generated in the carbonization chamber does not exceed the gas recovery capacity of the riser pipe.

[0006] Patent Document 5 discloses a method for producing coke by carbonizing coal in a coke oven and then charging waste plastics into the upper space of the coke oven. The document describes a method for charging polymer waste into the coke oven in an atmosphere-shielded environment, in which a hopper is attached to a charging car and a cylindrical chute is attached to the coke oven's coal inlet (see Figure 5 of the document). It states that the preferred charging time is during the coke maturation period (approximately 2 hours) between the end of the fire (completion of carbonization) and the coke extrusion, which is usually referred to as the "restoration time." This is because during this time, the amount of coke oven gas generated is small and the heat dissipated from the coke oven is large and can be utilized as heat for gas decomposition.

[0007] Patent Document 6 discloses a method for treating waste plastics in a coke oven carbonization chamber equipped with a leveler, in which waste plastics or a mixture of waste plastics and returned coal is supplied to the leveler at the end of coal charging into the carbonization chamber or after coal has been charged, and the waste plastics are treated. The method described in Patent Document 4 requires the installation of a new dedicated waste plastic supply device for each charging port. The method described in Patent Document 5 requires the modification of a coal charging car to create a facility that charges waste plastics while shielding it from the atmosphere. In contrast, the method described in Patent Document 6 claims to solve these problems.

[0008] JP 2001-49261 A JP 2019-135278 A JP 2002-47494 A JP 8-157834 A JP 4-41588 A JP 2002-371285 A

[0009] As mentioned above, the headspace charging method can process a larger amount of waste plastic than the coal mixed charging method. Therefore, in the current situation where the promotion of waste plastic recycling is desired, the headspace charging method is more effective. Furthermore, in the headspace charging method, the form of waste plastic to be charged is not limited to molded plastic granules, and it is also possible to charge and pyrolyze waste plastic in its crushed state.

[0010] Proposed headspace charging methods include a method of charging waste plastics before the start of (or during) the carbonization of charged coal or mixed coal (Patent Documents 4 and 6, hereinafter also referred to as the headspace pre-charging method), and a method of charging waste plastics after the carbonization of coal or mixed coal (hereinafter also referred to as coal, etc.) is completed (Patent Document 5, hereinafter also referred to as the headspace post-charging method). The headspace post-charging method makes it possible to process a larger amount of waste plastics because it can utilize the upper space (furnace top side space) of the coke chamber that has expanded due to the compaction (burn-down) of the carbonized coal, etc.

[0011] In the front-space charging method, pyrolysis gas derived from coal or mixed coal (coal, etc.) and pyrolysis gas derived from waste plastics are generated at the same time during carbonization. In contrast, in the rear-space charging method, pyrolysis gas derived from coal, etc. is generated during carbonization, and pyrolysis gas derived from waste plastics is generated after carbonization is completed when the amount of pyrolysis gas derived from coal, etc. has decreased. This makes it possible to disperse the generation of pyrolysis gas and increase the amount of waste plastics that can be processed.

[0012] In the upper space rear charging method, waste plastics can be charged using a coal car through multiple charging ports installed at the furnace top. Currently, coal cars are equipped with mechanisms (such as auxiliary hoppers, described below) for charging (injecting) through the charging ports to prevent coal from scattering, allowing waste plastics to be charged while being largely isolated from the atmosphere. However, in the upper space front charging method and upper space rear charging method, it is difficult to supply waste plastics using a leveler (leveling device) for waste plastic supply. This is because many types of waste plastics soften and melt at relatively low temperatures (below approximately 200°C), so there is a concern that the waste plastics will adhere to the leveler, which could result in the waste plastic being pulled out of the kiln or the leveler malfunctioning.

[0013] When waste plastics are charged through multiple charging ports at the top of the furnace, multiple piles of waste plastics (hereinafter referred to as waste plastic piles) form on top of the carbonized coal in the coke chamber. If waste plastics are charged through all charging ports simultaneously, the amount of pyrolysis gas from the waste plastics increases rapidly, exceeding the gas recovery capacity of the riser pipe. This increases the gas pressure in the coke chamber, leading to the risk of pyrolysis gas leaking through the charging ports or gaps in the furnace cover (hereinafter referred to as charging ports). This could lead to ignition and damage to the coke oven body hardware and coal-loading cars. Furthermore, if pyrolysis gas leaks outside the coke oven, the amount of pyrolysis gas recovered by the riser pipe decreases. While it is possible to prevent the increase in gas pressure and pyrolysis gas leakage by reducing the amount of waste plastic charged, this would also reduce the amount of waste plastic processed. Furthermore, taking a long time to charge waste plastics leads to a decrease in the coke oven's operating rate.

[0014] The present invention aims to provide a method for processing waste plastics that can ensure work safety when the waste plastics are charged into the upper space inside the carbonization chamber through a charging port at the top of the carbonization chamber after the carbonization of coal or mixed coal.

[0015] (1) A method for treating waste plastics, comprising charging coal for cokemaking or mixed coal for cokemaking containing coal and mixed waste plastics into a carbonization chamber of a coke oven and carbonizing it to produce coke, and after carbonization is completed, using some or all of a plurality of charging ports provided in the carbonization chamber of the coke oven, charging waste plastics into an upper space in the carbonization chamber above the coke in order from the port closest to the riser pipe to the port furthest from the riser pipe. (2) The method for treating waste plastics described in (1), wherein, of all the charging ports for charging the waste plastics, two or more consecutive ports but less than the total number of ports are grouped, and the waste plastics are charged simultaneously into each port in the group instead of being charged in the order. (3) The method for treating waste plastics described in (2), wherein a plurality of the groups are provided and the waste plastics are charged into the groups.

[0016] According to the present invention, the order in which waste plastics are charged from the charging port can be specified, thereby ensuring the safety of the work.

[0017] 1 is a cross-sectional view showing an example of a state in which the carbonization of coal charged in the carbonization chamber is completed. ３ 1 is a graph showing the relationship between the total amount of generated gas (m / h) and the charging time interval, where the charging time interval is β seconds. ３ 1 is a graph showing the relationship between the charging time interval (times) ( / h) and the charging time interval, where the charging time interval is γ seconds. FIG. 1 is an explanatory diagram illustrating a charging method in which waste plastics are charged into the riser pipe sequentially from the side farthest from the side closest to the riser pipe using multiple charging ports. FIG. 1 is an explanatory diagram illustrating a charging method in which waste plastics are charged into the riser pipe sequentially from the side nearer to the side farthest from the riser pipe using multiple charging ports. FIG. 1 is a graph showing the measurement results of the space temperature in the auxiliary hopper in Comparative Example 1 of Example 1. FIG. 2 is a graph showing the measurement results of the space temperature in the auxiliary hopper in Inventive Example 1 of Example 1. FIG. 3 is a graph showing the measurement results of the space temperature in the auxiliary hopper in Inventive Example 3 of Example 3. FIG. 4 is a graph showing the measurement results of the space temperature in the auxiliary hopper in Comparative Example 3 of Example 3.

[0018] The present invention relates to a method for treating waste plastics, which comprises charging coal for cokemaking or a mixed coal for cokemaking containing coal and waste plastics to be mixed with coal into a carbonization chamber of a coke oven, carbonizing the coal to produce coke, and, after carbonization, using some or all of a plurality of charging ports provided in the carbonization chamber of the coke oven to charge waste plastics into an upper space in the carbonization chamber above the coke, in order from the charging port closest to the riser pipe to the charging port furthest from the riser pipe. The present invention will be described below with reference to the drawings.

[0019] Fig. 1 is a cross-sectional view showing an example of a state in which carbonization of coal for coke production (hereinafter also referred to as charged coal) charged into a coke chamber is completed. While Fig. 1 illustrates a coke chamber 2 having four charging ports 4, the number of charging ports 4 is not limited to this example and may be any number. For example, the number of charging ports 4 may be five or six. Furthermore, instead of the charged coal 11, mixed coal for coke production containing coal and mixed waste plastics (hereinafter also referred to as mixed coal 12) may be charged and carbonized. The charging of the mixed coal 12 is similar to the charged coal 11, and therefore, for convenience, only the charged coal 11 will be described below.

[0020] Coal 11 is charged into the coke oven chamber 2 of the coke oven 1 by a coal car 31 through multiple charging ports 4 (shown by the two-dot chain line in FIG. 1 ) provided at the top of the coke oven in the furnace longitudinal direction (horizontal direction in FIG. 1 ). As carbonization progresses, the charged coal 11 thermally decomposes, generating coke oven gas (COG). The generated coke oven gas passes through the upper space 5 (furnace top side space) in the coke oven chamber and is recovered by a riser pipe 3 provided at the top of the furnace on the pusher side (PS) side (left side of FIG. 1 ). In FIG. 1 , the two-dot chain line indicates the top surface of the charged coal 11 before carbonization, and the solid line indicates the top surface of the coke 13 (the charged coal 11 after carbonization is completed). After carbonization is completed, the charged coal 11 has a smaller volume due to densification, and the upper space 5 is wider. The upper space 5 is the space above the top end (top surface) of the charged coal in the coke oven chamber.

[0021] In the present invention, waste plastics 14 are charged on top of the coke 13 (charged coal 11 after carbonization has been completed) through the charging port 4 and are thermally decomposed in the upper space 5 of the carbonization chamber 2. The waste plastics 14 are charged in an environment where the temperature inside the furnace has increased due to the carbonization of the charged coal 11, and the thermal decomposition of the waste plastics 14 is promoted using the time (standing time) from the completion of the carbonization of the charged coal 11 (fire-out) until it is extruded by the extruder. Pyrolysis gas produced by the thermal decomposition of the waste plastics 14 flows toward the riser 3 and is recovered by the riser 3.

[0022] In the present invention, waste plastics 14 are charged sequentially from the charging port closest to the riser pipe 3 to the charging port furthest from the riser pipe 3 using some or all of the multiple charging ports 4 provided in the carbonization chamber of the coke oven. As a result of conducting charging experiments in a coke oven, it was found that charging sequentially from the side closest to the riser pipe to the side furthest from the riser pipe can prevent fires and accidents caused by leakage or ejection of pyrolysis gas from the charging ports. The presumed reason for this will be explained below with reference to the drawings.

[0023] 3 and 4, which will be described later, are diagrams illustrating a method for charging waste plastics using multiple charging ports provided at the furnace top. In these figures, the four charging ports 4 are labeled 4a, 4b, 4c, and 4d in order from the farthest from the riser 3 (the coke side (CS) side). The mountain-shaped waste plastics formed when the waste plastics are charged through the charging ports 4a, 4b, 4c, and 4d are labeled 14a, 14b, 14c, and 14d, respectively. Furthermore, the pyrolysis gases generated from the waste plastics 14a, 14b, 14c, and 14d (the waste plastic piles 14a, 14b, 14c, and 14d) are labeled 24a, 24b, 24c, and 24d, respectively.

[0024] Here, the amount of waste plastics charged from each charging port and the total amount can be set to satisfy, for example, the following conditions. Specifically, when waste plastics are charged into each charging port, the amount charged must be such that the waste plastics do not rise to the top of the kiln (less than the allowable waste plastic charging amount α described below), and the total amount of gas generated when the waste plastics are charged must be within the allowable range of the high-pressure ammonia suction capacity of the riser pipe 3 inside the kiln (hereinafter referred to as the riser pipe gas suction capacity). These two conditions are explained below.

[0025] The upper limit value α (kg) of the allowable amount of waste plastics to be charged at each charging port 4 (allowable waste plastics charging amount) can be estimated, for example, based on the following formula (1). Formula (1) shows the relationship between the amount of waste plastics charged x (kg) and the stack height of the waste plastics (hot plastics stack height) y' (m) when the waste plastics are charged into the high-temperature space (hot) inside the carbonization chamber. In formula (1), y (m) represents the stack height of the waste plastics at room temperature (room-temperature plastics stack height), and a (-) represents the vertical sinking rate of the waste plastics in the high-temperature space immediately after charging. In addition, θ (°) represents the angle of repose of the waste plastics, and ρ (kg / m ３ ) is the bulk density of the waste plastic, d (m) is the distance in the furnace width direction of the inner space of the carbonization chamber, and x (kg) is the amount of waste plastic charged (amount of waste plastic charged). The pile of waste plastic 14 charged in the upper space 5 has a triangular cross section with height = y and base = 2y / tan θ, and has a plate-like shape with a width of d. Based on the equation for calculating the volume of this plate-like shape, the following equation (1) is derived: y' = a x y = a x ((x x tan θ) / (ρ x d)) １／２ …(1)

[0026] In the above formula (1), the height h (m) of the upper space 5 after the charging coal 11 is burned is substituted for the hot plastic loading height y' to obtain the waste plastic charging amount x ｈ (kg) and calculate the amount of waste plastic charged x ｈ is estimated as the upper limit value α (kg) of the allowable waste plastic charging amount. By charging an amount of waste plastic at each charging port 4 so as not to exceed the allowable waste plastic charging amount α and close to the allowable waste plastic charging amount α, it is possible to prevent the waste plastic from overflowing from the charging port while ensuring the amount of waste plastic to be processed.

[0027] The amount of waste plastics charged at each charging port 4 is determined based on the riser gas suction capacity, i.e., the amount of gas that can be sucked into the riser gas, i.e., the allowable gas generation amount δ (m ３ / h) is also taken into consideration. Specifically, by making sure that the total amount of gas (pyrolysis gas) generated when waste plastics are charged from the charging port 4 into the high-temperature space after carbonization of coal or the like (coal or mixed coal), i.e., the total amount of pyrolysis gas generated from the coal or the like after carbonization and the pyrolysis gas generated from the waste plastics, does not exceed the allowable amount of gas generated δ, it is possible to prevent leakage of pyrolysis gas from the waste plastics, ensure work safety, and also ensure the amount of pyrolysis gas recovered. Note that the allowable amount of gas generated δ (m ３ / h) can be increased or decreased by adjusting the suction power of the suction blower.

[0028] Here, the total amount of generated gas (pyrolysis gas) (m ３ 2A and 2B show the time change of the total amount of generated gas (m / h) when there are two charging ports for the sake of simplicity, that is, when waste plastics are charged once from each port (two times in total). ３ 2A and 2B show the relationship between the time interval (seconds) between the first and second chargings of waste plastics and the time interval (seconds) between the charging of waste plastics from the charging port. The graph in FIG. 2A shows the case where the time interval between the first and second chargings is β seconds, while the graph in FIG. 2B shows the case where the time interval is γ seconds. In FIGS. 2A and 2B, the dashed line indicates the amount of gas generated from coal, etc. after carbonization. The dashed line indicates the amount of gas generated when the first waste plastics are charged. The dashed line indicates the amount of gas generated from the first waste plastics, even after the second waste plastics are charged. The dashed line indicates the amount of gas generated from the first waste plastics, even after the second waste plastics are charged. The dashed line indicates the total amount of gas generated from the first and second waste plastics when the second waste plastics are charged. A stacked line graph is used to show the total amount of gas generated over time. The same amount of waste plastic, α kg, was charged in both cases. Since the amount of waste plastic charged in the first and second runs is the same, it is assumed that the amount of gas generated over time in the first and second runs is approximately the same, and both graphs (the dashed line alone and the difference between the two-dot dashed line and the dashed dotted line) have the same shape. ３ / h) is shown by a thick solid line. It can be seen that the time change in the gas generation rate after the first and second waste plastic charging respectively shows that the gas generation rate increases rapidly immediately after charging, reaches a maximum value, and then decreases with the passage of time. Compared to the charging time interval β in Figure 2A, the charging time interval γ in Figure 2B is longer. As shown in Figure 2A, when the charging time interval is β seconds, the gas generation rate due to the first charging is still close to the maximum after the time β from the first charging, so that the elapsed time t １ ~t ２ Since the total amount of generated gas exceeds the allowable amount of generated gas δ at (minutes), there is a risk of leakage of generated gas (pyrolysis gas). On the other hand, as shown in Figure 2B, when the charging time interval is set to γ ​​seconds, the amount of gas generated by the first charging decreases after the time γ from the first charging, and the total amount of generated gas does not exceed the allowable amount of generated gas δ. The charging time interval is set so that the total amount of generated gas does not exceed the allowable amount of generated gas δ, as shown in Figure 2B.

[0029] As described above, FIGS. 2A and 2B illustrate a case in which the same amount of waste plastic is charged sequentially from each of the two charging ports with a charging time interval. However, if the carbonization chamber is equipped with four charging ports, each port is used for charging four times (or two or more times, but less than four times, if grouped). The charging time intervals may be set so that the total amount of generated gas does not exceed the allowable gas generation rate δ from the first charging of the waste plastic to the time when the peak of the generated gas rate due to the last charging of the waste plastic is exceeded. Here, the charging time intervals may be the same or different. For example, the time interval between the first and second charging and the time interval between the second and third charging may be the same or different. Furthermore, the amount of waste plastic charged from each charging port may be set so that the total amount of generated gas does not exceed the allowable gas generation rate δ from the first charging of the waste plastic to the time when the peak of the generated gas rate due to the last charging of the waste plastic is exceeded. The charging times may be the same or different.

[0030] It is preferable that the amount of waste plastics charged from each charging port and the total amount of waste plastics charged be an amount that will allow the thermal decomposition of the waste plastics to be completed sufficiently within the time it takes for the coke to be discharged from the kiln, and that the allowable range of the extrusion load at the time of discharge from the kiln and the amount of chlorine contained in the waste plastic decomposition gas that will be emitted are also taken into consideration.

[0031] Even when waste plastics 14 are sequentially charged into a plurality of charging ports 4 under conditions taking into consideration the above-mentioned upper limit value α of the allowable waste plastic charging amount and the allowable amount of gas generated δ, pyrolysis gas may leak from the charging port 4 or the like depending on the charging order. As a result of conducting charging experiments in a coke oven, the present inventors have found that by charging in order from the side closest to the riser pipe to the side furthest from the riser pipe, it is possible to prevent fires and accidents caused by leakage or eruptions of pyrolysis gas from the charging port. The presumed reason for this will be explained below with reference to the drawings.

[0032] FIG. 3 is an explanatory diagram for explaining the case where waste plastic 14 is charged in order (4a → 4b → 4c → 4d) from the side farthest from the riser pipe 3 (the side opposite the riser pipe) to the side closest to the riser pipe 3 (the side close to the riser pipe). It shows the state where waste plastic 14a has been charged from the charger 4a, waste plastic 14b from the charger 4b, and waste plastic 14c has been charged from the charger 4c.

[0033] In the thermal decomposition reaction of waste plastic 14, the amount of pyrolysis gas generated is greatest immediately after loading when the waste plastic is placed under high temperature, and then decreases to a nearly constant amount (see the dashed-dotted lines in Figures 2A and 2B). The volume of waste plastics 14a and 14b decreases as time passes as the thermal decomposition progresses. In Figure 3, for waste plastics 14a and 14b, the dashed-dotted lines represent the time of loading, and the solid lines represent the time after loading (when waste plastic 14c is loaded). The solid line for waste plastic 14c represents the time of loading. As shown for waste plastics 14a and 14b in this figure, the volume of the waste plastic decreases over time after loading. However, because thermal decomposition is not complete even after the time has passed since loading, pyrolysis gases 24a and 24b continue to be generated from waste plastics 14a and 14b, as indicated by the arrows in Figure 3. When waste plastics 14c are charged through the charging port 4c, the waste plastics 14c narrow the flow path (space) of pyrolysis gases 24a and 24b toward the riser pipe. Furthermore, the pyrolysis gas 24c generated from the waste plastics 14c is mixed with the waste plastics 14c, resulting in an excessive amount of gas near the charging port 4c. As a result, the gas pressure increases, and as shown by the dashed arrows, the pyrolysis gases 24a and 24b leak or erupt from the charging port 4c during the charging of the waste plastics 14c. Although not shown, depending on the situation (the degree of narrowing of the flow path and the cumulative amount of gas generated), not only the pyrolysis gases 24a and 24b but also the pyrolysis gas 24c may leak from the charging port 4c, or the pyrolysis gases 24a and 24b may leak not only from the charging port 4c but also from the charging ports 4b and 4a.

[0034] FIG. 4 is an explanatory diagram for explaining the case where the waste plastic 14 is charged in order from the side closest to the riser pipe 3 (the riser pipe side) to the side furthest from the riser pipe 3 (the side opposite to the riser pipe) among the four charging ports 4 (4d → 4c → 4b → 4a), and shows the state at the time when the waste plastic 14d has been charged from the charging port 4d and the waste plastic 14c has been charged from the charging port 4c, and the waste plastic 14b has been charged from the charging port 4b.

[0035] As time passes, the waste plastics 14d and 14c undergo thermal decomposition, and their volumes decrease as shown by the two-dot chain lines (when the waste plastics 14d and 14c are charged) and the solid line (when the waste plastic 14b is charged) in Figure 4. However, because the thermal decomposition is not complete, pyrolysis gases 24d and 24c continue to be generated from the waste plastics 14d and 14c, as shown by the arrows. When the waste plastic 14b is charged through the charging port 4b, the waste plastic 14a has not yet been charged through the charging port 4a, so no pyrolysis gas is generated from the waste plastic on the side opposite the riser pipe from the waste plastic 14b. Therefore, unlike the waste plastic 14c in Figure 3, the charging of the waste plastic 14b does not narrow the flow path (space) to the riser pipe. Furthermore, when the waste plastic 14b is charged, as shown in FIG. 4, the volume of the waste plastics 14d and 14c and the amount of pyrolysis gas 24d and 24c generated are reduced, so that a flow path (space) for the pyrolysis gas 24b generated from the waste plastic 14b to the riser pipe side is secured, and therefore the gas pressure does not increase, and leakage or eruptions of the pyrolysis gas 24 can be suppressed.

[0036] In this way, by charging the waste plastics 14 in order from the charging port closest to the riser pipe 3 (the riser pipe side) to the charging port farthest from the riser pipe (the anti-riser pipe side), it is possible to prevent the flow path (space) toward the riser pipe from narrowing, and suppress leakage and spouting of the pyrolysis gas 24. In the above-mentioned Fig. 4, an example is shown in which the waste plastics 14 are charged one by one into all four charging ports 4 in order from the side closest to the riser pipe 3 to the side farthest from the riser pipe 3, but it is also possible not to charge waste plastics into some of the charging ports. Even if there are charging ports 4 into which waste plastics are not charged, as long as the charging ports are charged in order from the side closest to the riser pipe 3 to the side farthest from the riser pipe 3, it is possible to prevent leakage and spouting of the pyrolysis gas 24.

[0037] The following cases are possible examples of charging ports 4 into which waste plastics should not be charged. For example, if a portion of the upper part of the furnace wall inside the coke oven carbonization chamber is damaged, waste plastics may not be charged to avoid placing a burden on that portion. Also, if the top surface level of a portion of the coke that was previously charged and carbonized with coal is higher than a specified position, waste plastics may not be charged into that portion.

[0038] Furthermore, when it is necessary to shorten the waste plastic charging time, the above-mentioned allowable gas generation amount δ (m ３ / h), the following method can be adopted. That is, of all the charging ports for charging waste plastics, two or more but less than the total number of charging ports that are consecutive in order from the side closest to the riser pipe to the side farthest from the riser pipe are grouped together, and instead of charging waste plastics sequentially, the charging ports belonging to the same group can be charged with waste plastics simultaneously. The number of groups to be set may be two or more but less than the total number of charging ports, but from the viewpoint of operability, a smaller number is preferable; for example, the number of groups can be two or three. Here, "simultaneously" means that there is a period of time when the waste plastics are being charged simultaneously. For example, in the coking chamber 2 having four charging ports 4 in Fig. 4, the charging port 4d and the charging port 4c are grouped together, and the waste plastics 14d and 14c are simultaneously charged from the charging port 4d and the charging port 4c of one group in order from the side closer to the riser pipe 3 (the riser pipe side) to the side farther from the riser pipe 3 (the anti-riser pipe side), and then the waste plastics 14b are charged from the charging port 4b, and then the waste plastics 14a are charged from the charging port 4a. Note that the charging ports belonging to different groups are not charged simultaneously.

[0039] The waste plastics may be charged by providing a plurality of groups of charging ports into which the waste plastics are charged simultaneously. For example, in the carbonization chamber 2 having four charging ports 4 as shown in Fig. 4, the charging ports 4d and 4c may be grouped as a first group, and the charging ports 4b and 4a may be grouped as a second group. After the waste plastics 14d and 14c are charged simultaneously through the charging ports 4d and 4c, the waste plastics 14b and 14a may be charged simultaneously through the charging ports 4b and 4a. Alternatively, the charging ports 4c, 4b, and 4a may be grouped as one group. After the waste plastic 14d is charged through the charging port 4d, the waste plastics 14c, 14b, and 14a may be charged simultaneously through the charging ports 4c, 4b, and 4a.

[0040] In the case shown in Figure 3, if waste plastic 14c is charged after the generation of pyrolysis gases 24a and 24b has sufficiently decreased, leakage or eruptions of pyrolysis gases 24a and 24b will not occur. However, the total charging time of waste plastics per kiln is limited by the operating rate of the coke oven. If it takes a long time to charge waste plastics into one kiln, the original pace of coke discharge will also be delayed, resulting in a decrease in coke production and a decrease in the total amount of waste plastics processed.

[0041] Furthermore, as described above, when groups of two or more but less than the total number of charging ports are formed in succession from the side closest to the riser pipe to the side furthest from the riser pipe, and waste plastics are charged simultaneously into each charging port of this group, an upper limit is set on the amount of waste plastics charged except for the charging port that is the furthest from the riser pipe in this group. Specifically, for example, for the charging port other than the furthest from the riser pipe, based on the waste plastics stacking height (hot plastics stacking height) y' (m) in the above-mentioned formula (1), the vertical cross-sectional area (cross-section perpendicular to the kiln length direction (m ２ )) is calculated, and the cross-sectional area is the cross-sectional area C of the riser pipe 3 (cross-sectional area perpendicular to the central axis (m ２Therefore, the number of charging ports to be grouped is determined by predicting the total amount of generated gas from the properties of the waste plastics to be charged, the temperature inside the kiln, the amount of waste plastics to be charged into each charging port, and the charging time intervals, and determining whether the total amount of generated gas is greater than the allowable amount of generated gas δ (m ３ / h) or less, and the longitudinal cross-sectional area (m ２ ) is the cross-sectional area C (m ２ ) or more. From the viewpoint of efficiency, it is preferable to minimize the number of times that waste plastic is charged into the charging port provided in one kiln, but as mentioned above, since an upper limit is set on the amount of waste plastic that can be charged, the amount of waste plastic that can be processed may decrease. It is preferable to determine the operating conditions by determining productivity for each case where the number of times of charging, charging time interval, and total charging amount are different.

[0042] A typical chamber-type coke oven has four or five charging ports, and the present invention can be applied to these. Furthermore, among unique furnace types, stamping furnaces with multiple gas suction ports on the furnace top can also be used with the present invention. On the other hand, furnaces with jumper pipes or standpipes installed at the charging port on the opposite end of the riser pipe on the furnace top have significantly different gas flow rates inside the coke chamber, making it difficult to obtain sufficient benefits from the present invention.

[0043] (Example 1) In a carbonization chamber with five charging ports, an experiment (Invention Example 1, Comparative Example 1) was conducted in which waste plastic was charged after the completion of carbonization of coal for coke production. The dimensions of the carbonization chamber were furnace height: 5.0 m, furnace length: 14.62 m, and furnace width: 0.45 m. The waste plastic was a volume-reduced molded product made from recycled plastic container packaging collected and manufactured in accordance with the Container and Packaging Recycling Law (Law Concerning Promotion of Separate Collection and Recycling of Containers and Packaging). The dimensions of the waste plastic were a diameter of approximately 26 mm, a height of approximately 50 mm, and a bulk density of approximately 0.29 t / m ３In this Example 1 and Example 2 described later, the total amount of waste plastics charged and the amount charged at each charging port are set to the above-mentioned upper limit value α (kg) of the allowable waste plastic charging amount, and the time interval between charging from each charging port (charging time interval) is set to the amount of gas (m ３ / h) is the allowable gas generation amount δ (m ３ The time is set to the shortest time that does not exceed 1 / h.

[0044] A coal car was used to charge the waste plastic. The coal car had a hopper that received coal from the coal tower, a feeder (table feeder) installed at the bottom of the hopper, and an auxiliary hopper for charging the coal supplied from the feeder into the charging port. Like the coal, the waste plastic was supplied to the hopper of the coal car and charged through the charging port. The total amount of waste plastic charged was 300 kg, and 60 kg of waste plastic was charged through each charging port in turn by opening the charging lid, and the charging lid was closed immediately after the waste plastic charging was completed.

[0045] In Example 1, the waste plastics were charged in order from the side closest to the riser pipe to the side furthest from the five charging ports, and in Comparative Example 1, the waste plastics were charged in order from the side furthest from the riser pipe to the side closest to the five charging ports. The first waste plastics were charged when COG gas generation by coal carbonization had ceased or was sufficiently reduced (for example, when COG gas generation was 200 Nm in the case of a coke oven with a furnace height of 6 m). ３ After charging the waste plastic for 5 seconds, the process moved to the next charging port, and charging was repeated for five charging ports. In order to shorten the total charging time, the lid of the next charging port was opened at the same time as the lid of the previous charging port was closed.

[0046] To assess the risk of fire spreading to the waste plastic in the hopper of a coal car due to gas leakage from the charging port, a thermocouple was installed in the auxiliary hopper of the coal car (a hole was drilled in the side of the auxiliary hopper, and the thermocouple was inserted and fixed) and evaluated by temperature measurement. The presence or absence of pyrolysis gas leakage from the charging port was also confirmed visually. Visual observation using an offline uniform temperature heating furnace and thermoviewer revealed that waste plastic from recycled containers and packaging products may soften and ignite at temperatures above approximately 300°C, depending on the properties of the various plastics that make up the waste plastic. Therefore, the upper limit for waste plastic combustion risk management was set at 300°C. Furthermore, because the fire must be quickly extinguished by water spraying if the waste plastic in the auxiliary hopper were to ignite, safety was taken into consideration when conducting the test.

[0047] Figure 5 shows the temperature measurement results using thermocouples for Comparative Example 1, and Figure 6 shows the results for Example 1. The vertical axis shows the space temperature (°C) in the auxiliary hopper, and the horizontal axis shows the elapsed (carbonization) time (hours:minutes) from the time of coal charging. The legends #1 to #5 in Figures 5 and 6 indicate charging ports #1 to #5, and are numbered in ascending order from the farthest to the closest from the riser pipe, with port #5 being the closest charging port. In Comparative Example 1 (Figure 5), waste plastic charging began at 20 hours 45 minutes 48 seconds, 20 hours 47 minutes 54 seconds, 20 hours 49 minutes 00 seconds, 20 hours 51 minutes 06 seconds, and 20 hours 53 minutes 12 seconds, starting from port #1 and then port #5, respectively (waste plastic charging start times #1 to #5). In Example 1 (Figure 6), waste plastic charging began at 20 hours, 54 minutes, and 34 seconds, 20 hours, 55 minutes, and 53 seconds, 20 hours, 58 minutes, and 20 seconds, 20 hours, 59 minutes, and 49 seconds, and 21 hours, 6 minutes, and 26 seconds, respectively, from charging entrance No. 5 to No. 1 (waste plastic charging start times #1 to #5). It took approximately 5 seconds from the start to completion of waste plastic charging. As shown in Figures 5 and 6, the temperature in the auxiliary hopper space before the start of waste plastic charging was 10 to 15°C, which was approximately the same as the outside air temperature above the coke oven.

[0048] In Example 1, as shown in Figure 6, the temperature in the space inside each auxiliary hopper of the coal car above the charging port did not rise by more than 15°C throughout the entire measurement. Furthermore, only minor gas leakage was confirmed by visual inspection. As mentioned above, the coke oven is provided with a riser pipe 3 in the coke chamber 2, and gas is suctioned through the riser pipe 3, creating a negative pressure inside the coke chamber 2. In Example 1, the temperature did not rise after the waste plastic was charged because the negative pressure created by the gas suction through the riser pipe 3 was maintained, and outside air was sucked into each auxiliary hopper, even when the waste plastic was charged through the charging ports No. 1 to No. 5.

[0049] In Comparative Example 1, as shown in Figure 5, waste plastics were charged in order from the first port, which was the furthest from the riser pipe, and as a result, a rise in temperature inside the auxiliary hopper was confirmed at ports 4 and 5. A large amount of gas was also confirmed to be blown out from ports 4 and 5 by visual inspection. The reason why the temperature rose after the waste plastics were charged at ports 4 and 5 in Comparative Example 1 is that when the waste plastics were charged from ports 4 and 5, the negative pressure caused by the gas suction in the riser pipe 3 could not be maintained, and the pyrolysis gas from the waste plastics was blown up into the auxiliary hopper directly above ports 4 and 5.

[0050] Note that, although conditions such as atmospheric temperature varied between Example 1 and Comparative Example 1 due to differences in weather, etc., a difference of a few degrees Celsius is not a problem because the test was conducted to examine the effect of pyrolysis gas generated in the carbonization chamber at the high temperatures at which waste plastics melt. Furthermore, since the amount of waste plastic charged was constant at each charging port, it is thought that the pressure distribution due to pyrolysis gas would not fluctuate significantly even with slight variations in the charging intervals. Furthermore, when waste plastics are charged into all charging ports simultaneously, gas is generated more rapidly than when the charging timing of each port is varied, making it difficult to secure a flow path to the riser pipe. Furthermore, it is thought that it becomes difficult to maintain negative pressure due to gas suction in the riser pipe 3, resulting in gas ejection from each charging port.

[0051] (Example 2) In a carbonization chamber with four charging ports, an experiment was conducted to charge waste plastic after the completion of carbonization of coal for coke production. The dimensions of the carbonization chamber were furnace height: 4.0 m, furnace length: 13.40 m, and furnace width: 0.40 m. The waste plastic used was a volume-reduced molded product of recycled plastic container packaging, with dimensions of approximately 29 mm in diameter, approximately 60 mm in height, and a bulk density of approximately 0.3 t / m ３ The waste plastics were charged in a cylindrical pellet form. The coal charging car had the same configuration as in Example 1. The total amount of waste plastics charged was 80 kg, and 20 kg of waste plastics was charged from each charging port.

[0052] In Example 2, the four charging ports were numbered No. 1 through No. 4, arranged from the farthest to the nearest from the riser pipe, with No. 1 and No. 2 designated as Group A and No. 3 and No. 4 designated as Group B. In this experiment, 20 kg of waste plastic was charged into each of the four charging ports (80 kg in total) from a coal car using a two-part charging method, first into Group B, which was closest to the riser pipe, and then into Group A, which was farthest from the riser pipe (charging ports in the same group were charged simultaneously). After charging was completed, the charging lids of all charging ports were closed, the coal car was moved, and then the charging lids of the charging ports of Group A and Group B were opened. The pressure directly below each charging port was measured by inserting a long-handled probe into the charging port to confirm the retention of generated gas (pressure distribution), and the flame ejection was visually confirmed.

[0053] As described above, when waste plastics were charged into the coal car, with Group B (closer to the riser pipe) first and Group A (farther from the riser pipe) second, all waste plastics were successfully charged without any pyrolysis gas or flame emissions at any of the charging ports. When the charging ports of Group A (ports 1 and 2) were simultaneously opened after the waste plastics were charged, almost no flames were observed from either port, and the pressure directly below both ports was confirmed to be nearly negative. On the other hand, when the charging ports of Group B (ports 3 and 4) were simultaneously opened, significant flames were observed from port 3. The pressure directly below the port 3 was also high. The pressure directly below the port 4 was a stable negative pressure, and no flames were observed.

[0054] In Example 2, the pressure directly below the No. 3 charging port was the highest, which is thought to be due to the cumulative effect of the gas generated from the waste plastics charged at No. 1, No. 2, and No. 3 ports, which are located farthest from the riser pipe. The negative pressure directly below the No. 4 port is thought to be due to the fact that a flow path for the generated gas was secured because the port is closest to the riser pipe. Conversely to the above test example, if Group A, which is farther from the riser pipe, was charged first and Group B, which is closer to the riser pipe, was charged last, during the operation of opening the No. 3 port charging cover and charging the waste plastics, the cumulative effect of the gas generated from the waste plastics charged at No. 1, No. 2, and No. 3 ports could have caused the pyrolysis gas from the waste plastics to rise into the auxiliary hopper of the coal car, potentially causing a fire. Furthermore, in the waste plastics charging operation, group B, which was closest to the riser pipe, was charged first, followed by group A, which was farthest from the riser pipe, and after the charging lid of port 3 was closed and in a closed state, waste plastics were charged from ports 1 and 2, so it is thought that no pyrolysis gases or the like were emitted during the entire charging operation process.

[0055] (Example 3) As in Example 2, an experiment was conducted on charging waste plastics into a coke chamber having four charging ports after completion of carbonization of coal for coke production. The size of the coke chamber, the shape of the waste plastics used, and the shape of the coal charging car were also the same as in Example 2. In Example 3, the four charging ports were numbered No. 1 to No. 4, from the side farthest from the riser pipe to the side nearest, with No. 1 and No. 2 ports grouped as Group A and No. 3 and No. 4 ports grouped as Group B.

[0056] In Example 3, waste plastics were charged using a coal car, with Group B (Nos. 3 and 4) closest to the riser pipe first, followed by Group A (Nos. 1 and 2) farthest from the riser pipe. Because Nos. 3 and 4 of Group B were charged simultaneously, the height of the waste plastics at No. 4, which is closer to the riser pipe, was not fully contracted compared to charging each port individually, narrowing the waste plastic gas path at No. 3 charging port. As a result, as shown in Figure 7, a small amount of high-temperature gas was emitted from No. 3 port, compared to Figures 5 and 6, and the auxiliary hopper temperature rose slightly. However, this temperature was below the 300°C upper limit for waste plastic combustion risk management and was at a level that did not interfere with actual operation. Note that the gas collected at No. 3 port was only the waste plastic gas from No. 3 port.

[0057] In Example 3, two groups were charged, and because ports 1 and 2 were charged simultaneously, the height of the waste plastic at port 2, which was closer to the riser pipe, was not fully shrunk compared to port-by-port charging, narrowing the waste plastic gas path at port 1. Similarly, a small amount of high-temperature gas was ejected from the port farther from the riser pipe, causing the auxiliary hopper temperature to rise slightly, but this was lower than the upper limit of 300°C for managing the risk of waste plastic combustion, and was at a level that did not interfere with actual operation. The gas that collected at port 1 was only the waste plastic gas from port 1.

[0058] In Comparative Example 3, charging was performed with Group A (ports 1 and 2), which was far from the riser pipe, first, followed by Group B (ports 3 and 4), which was closer to the riser pipe. If charging from the side opposite the riser pipe, the situation when charging Group A (ports 1 and 2) would be similar to that shown in Figure 7. This is because the gas that gathers at port 1 is only the waste plastic gas from port 1. On the other hand, when charging Group B (ports 3 and 4), the generated gas from ports 1, 2, and 3 concentrates at port 3, causing a large-scale ejection of high-temperature gas, as shown in Figure 8, and causing the auxiliary hopper temperature to rise sharply, exceeding the upper limit of 300°C, the upper limit for managing the risk of waste plastic combustion.

[0059] From the above results, in order to avoid the risk of pyrolysis gas escaping when waste plastics are charged, it is preferable to charge the waste plastics starting from the port closest to the riser pipe to the port furthest from the riser pipe. Specifically, when forming groups to charge waste plastics simultaneously and shortening the waste plastic charging time, it is preferable to charge the waste plastics simultaneously into ports 3 and 4 and then into ports 1 and 2 (Group B → Group A) rather than charging the waste plastics simultaneously into ports 1 and 2 and then into ports 3 and 4 (Group A → Group B).

[0060] 1: Coke oven 2: Carbonization chamber 3: Riser pipe 4: Charging port (4a, 4b, 4c, 4d) 5: Upper (furnace top side) space 11: Coal (coal for coke production) 12: Mixed coal (mixed coal for coke production: mixture containing coal and mixed waste plastic) 13: Coke 14: Waste plastic (14a, 14b, 14c, 14d) 24: Pyrolysis gas (24a, 24b, 24c, 24d) 31: Coal charging car

Claims

1. A method for treating waste plastics, characterized in that coal for coke production, or mixed coal for coke production containing coal and mixed waste plastics, is charged into the carbonization chamber of a coke oven and carbonized to produce coke, and after carbonization is completed, waste plastics are charged into the upper space inside the carbonization chamber, which is the space above the top of the coke (the charged coal after carbonization is completed), from some or all of the multiple charging ports provided in the carbonization chamber of the coke oven, in order from the charging port closest to the riser pipe to the charging port furthest from the riser pipe.

2. A method for processing waste plastic as described in claim 1, characterized in that one or more groups of loading ports are set, each group consisting of any number of loading ports that are two or more but less than the total number of loading ports and that have consecutive loading orders for the waste plastic, and the waste plastic is loaded into all of the loading ports belonging to the same group at the same time.

3. The method for treating waste plastics according to claim 2, wherein two or more groups are provided and the waste plastics are charged into the groups.

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