Method for producing solid fuel

Abstract

To provide a method for producing solid fuel in which fusion of waste plastic in furnace is suppressed and solid fuel can be produced stably and efficiently without impairing quality.SOLUTION: Provided is a method for producing solid fuel that includes a heating step in which waste plastic is heat-treated in a heating furnace having 3 or more heating zones, and in which the temperature of the heating zone nearest to the waste plastic feed port in the heating furnace is at the temperature higher than the other 2 or more heating zones.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a solid fuel. [Background technology]

[0002] Waste plastics discarded as industrial or municipal waste have traditionally been simply incinerated or landfilled. However, to reduce carbon dioxide emissions and efficiently utilize resources, efforts are underway to recover the organic components of waste plastics and reuse them as solid fuel. Such solid fuels are typically produced by heating waste plastics in a heating furnace with coal to promote their pyrolysis, creating voids on the surface and inside the plastic, which reduces its strength. However, as waste plastics melt when heated, the molten resins tend to fuse together. As a result, the fused resin particles increase in size, resulting in poor heat transfer to the interior of the particles and leaving much undecomposed resin inside. As a result, the discharge of waste plastics from the furnace after heating is hindered. Even if discharge is possible, it is difficult to separate the resins from the metals during subsequent crushing and sorting. Furthermore, the increased load caused by large particles on the crusher leads to equipment damage and frequent maintenance, resulting in high running costs.

[0003] Therefore, technologies to prevent the melting of waste plastics in furnaces have been investigated. For example, it has been reported that by heating a mixture of thermoplastic plastics and pulverized coal obtained by crushing coal in a predetermined ratio, the pulverized coal adheres to the surface of the molten thermoplastic plastic, thereby preventing the melted thermoplastic plastic from melting in the furnace (Patent Document 1). It has also been reported that by heating a mixture of chlorine-containing plastics and calcium compounds in a certain ratio in a non-oxidizing atmosphere at a relatively high temperature of 500°C to 900°C, the formation of fused lumps and tar from the chlorine-containing plastics and the generation of dioxins can be prevented (Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-68769 [Patent Document 2] Japanese Patent Application Publication No. 2019-123771 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when waste plastics are mixed with other materials to prevent fusion as in Patent Document 1, it is necessary to design the equipment to be larger than the amount of waste plastics to be processed. Furthermore, when a calcium compound is mixed as in Patent Document 2, it has been confirmed that the calcium compound is incorporated into the solid fuel after heating, increasing the ash content and reducing the calorific value of the solid fuel, thereby impairing the quality of the solid fuel. In either case, there are problems such as complicated pretreatment, difficulty in temperature control, and an increase in ash content. An object of the present invention is to provide a method for producing solid fuel stably and efficiently, while suppressing the fusion of waste plastics in a furnace and without impairing the quality. [Means for solving the problem]

[0006] The inventors conducted research to determine the causes of resins contained in waste plastics fusing together in a furnace when the waste plastics are heated to pyrolysis. They discovered that, as the temperature of the waste plastics rises from room temperature to the pyrolysis temperature, the molten resins adhere to each other in a temperature range above the melting point of the resins but below the pyrolysis temperature (hereinafter also referred to as the "fusing temperature range"). Based on this knowledge, they conducted further research and discovered that dividing the furnace in which the waste plastics are heated into three or more heating zones and setting the temperature of the heating zone closest to the waste plastic supply port higher than the other two or more heating zones not only shortens the residence time of the resins in the fusing temperature range, but also suppresses fusing between the resins. Since the amount of energy output from the produced solid fuel exceeds the amount of energy input during the waste plastic heating process, this method is extremely effective as a method for immobilizing the heat of the waste plastics in solid fuel.

[0007] That is, the present invention provides the following [1] to [5]. [1] A heating step of heat-treating waste plastics in a heating furnace having three or more heating zones, The temperature of the heating zone closest to the waste plastic supply port in the heating furnace is higher than the temperature of the other two or more heating zones. A method for producing solid fuel. [2] The heating zone includes a first heating zone, a second heating zone, and a third heating zone from a waste plastic supply port toward a waste plastic discharge port, The temperature of the first heating zone is 400°C or higher and 650°C or lower, The temperature of the second heating zone is 300°C or higher and 550°C or lower, The temperature of the third heating zone is 250°C or higher and 450°C or lower. The method for producing the solid fuel described in [1] above. [3] The method for producing a solid fuel according to [1] or [2] above, wherein the heating time in each heating zone is 5 minutes or more and 60 minutes or less. [4] A method for producing a solid fuel according to any one of [1] to [3], further comprising a cooling step of cooling the waste plastic discharged from the heating furnace under stirring and / or in an inert gas atmosphere after the heating step. [5] A heating step of heat-treating waste plastics in a heating furnace having three or more heating zones, The temperature of the heating zone closest to the waste plastic supply port in the heating furnace is higher than the temperature of the other two or more heating zones. A method for preventing waste plastic from fusing together. [Effects of the Invention]

[0008] According to the present invention, it is possible to suppress the fusion of waste plastics in a furnace and to stably and efficiently produce solid fuel without compromising its quality. Furthermore, the method for producing solid fuel of the present invention has a high energy balance ratio, making it extremely effective as a method for immobilizing the calorific value of waste plastics in solid fuel. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a flowchart showing an example of a manufacturing method of the present invention. [Figure 2] FIG. 1 is a cross-sectional view showing an example of a heating furnace applicable to the manufacturing method of the present invention. [Figure 3] FIG. 10 is a cross-sectional view showing another heating furnace applicable to the manufacturing method of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] The method for producing a solid fuel of the present invention will be described below. An example of the method for producing a solid fuel of the present invention is shown in FIG. As shown in FIG. 1, in the method for producing a solid fuel of the present invention, first, waste plastics are subjected to a heating step in which they are heat-treated in a heating furnace.

[0011] The waste plastic is not particularly limited as long as it is waste containing plastic, but examples that can be used include used plastic products, scraps and defective products generated during the production and processing of plastics in factories, etc. Such waste plastics usually include plastics such as polypropylene, polyethylene, polycarbonate, polyvinyl chloride, glass fiber reinforced plastic, and carbon fiber reinforced plastic, but may also include foreign matter other than plastic, such as soil, metal, glass, paper, and wood chips. Specific examples of waste plastics include shredder dust, construction waste plastics, agricultural waste plastics, fishing waste plastics, and marine waste plastics. In this specification, "shredder dust" refers to a mixture of fragments discarded after industrial or general waste is crushed in an industrial shredder and metals are recovered. Examples of waste include discarded automobiles, discarded home appliances, vending machines, office equipment, furniture, and building materials. Two or more types of waste plastics may be mixed.

[0012] The waste plastic may be subjected to one or more physical sorting methods selected from crushing, sieving, air sorting, magnetic sorting, eddy current sorting, and gravity sorting for the purpose of adjusting particle size and removing foreign matter, from the viewpoint of promoting thermal decomposition of the waste plastic and suppressing fusion between resins.

[0013] A crusher can be used to crush waste plastics. Examples of crushers include jaw crushers, impact crushers, hammer crushers, roll crushers, and rotary crushers. A screen with a desired mesh size can be attached to the crusher for the purpose of adjusting particle size. If a screen is not attached, the fixed teeth, rotary teeth, inner wall, etc. may be adjusted to the desired clearance. Also, a sieve separator such as a vibrating sieve or a rotary sieve can be used, and the desired mesh size may be attached. Other physical separation methods will be described later.

[0014] The particle size of the crushed waste plastics is preferably 150 mm or less, more preferably 50 mm or less, and even more preferably 30 mm or less, from the viewpoint of promoting thermal decomposition of the waste plastics and suppressing fusion between resins. Note that there is no particular lower limit to the particle size of the crushed waste plastics.

[0015] The heating furnace is not particularly limited as long as it can accommodate waste plastics and be set to the desired temperature, but examples include a fixed furnace, a stoker furnace, a rotary kiln furnace, a fluidized bed furnace, a vertical furnace, and a multi-tier furnace. The shape of the heating furnace is also not particularly limited, and it can have any appropriate shape, such as a cylindrical shape or a rectangular cross section. A conveyor for transporting waste plastics from the waste plastic inlet to the discharge outlet may be installed inside the heating furnace.

[0016] The atmosphere inside the heating furnace is preferably a low-oxygen atmosphere, since this allows the heat content of resins contained in waste plastics and animal- and plant-derived fibers such as cellulose to be fixed in the solid fuel after heating and facilitates crushing, pulverization, and physical separation after the heat treatment. Here, in this specification, "low-oxygen atmosphere" refers to an atmosphere with an oxygen concentration lower than that of the atmosphere. Considering the need for continuous heating in a low-oxygen atmosphere and the increased energy balance ratio, heat treatment under low-oxygen conditions using an externally heated rotary kiln is preferred. Methods for creating a low-oxygen furnace atmosphere include filling the furnace with an inert gas such as nitrogen or water vapor, or filling the furnace with gas components (e.g., HO, CO, lower hydrocarbons, and other combustible gases) primarily generated by the thermal decomposition of waste plastics.

[0017] In order to promote the thermal decomposition of waste plastics while suppressing fusion between resins, the heating furnace does not heat the entire furnace at a constant temperature, but divides the furnace into three or more heating zones, and sets the temperature of the heating zone closest to the waste plastic supply port at a higher temperature than the other two or more heating zones. Here, in this specification, "heating zone" refers to the space within the heating furnace that is controlled to a predetermined temperature by a heat source. If the entire furnace is heated to a constant temperature at which waste plastics can be thermally decomposed, the residence time in the fusion temperature range (e.g., 150 to 250°C) will be long as the waste plastics are heated from room temperature to the thermal decomposition temperature, causing the resins to fuse together and then form clumps. In contrast, in the present invention, by exposing the waste plastics to a temperature higher than the thermal decomposition temperature at the start of heating, not only can the thermal decomposition of the waste plastics be promoted, but the residence time of the resins in the fusion temperature range can also be shortened, thereby suppressing the fusion of the resins and the resulting clumping.

[0018] An example of a heating furnace applicable to this process is shown in Figures 2 and 3. In Figures 2 and 3, the same elements are given the same reference numerals, and for convenience of illustration, the dimensional ratios of the drawings do not necessarily coincide with those in the description. The heating furnace 10 shown in Fig. 2 has three heating zones, namely, a first heating zone, a second heating zone, and a third heating zone, arranged in sequence from the waste plastic inlet to the discharge outlet, and each heating zone is provided with one heat source. An example of the heating furnace 10 shown in Fig. 2 is a continuous furnace such as a rotary kiln. 3, three independent heating furnaces each having one heat source are connected from the waste plastic supply inlet to the discharge outlet, forming one heating furnace as a whole, and each independent heating furnace is configured as one heating zone, so that a total of three heating zones are provided in sequence. In the present invention, a desired number of heating zones may be provided within one heating furnace, or one independent heating furnace may be connected to provide the heating zones. Furthermore, for example, in the heating furnace 20 shown in FIG. 2, two or more heating sources may be installed in one or more independent heating furnaces, and the heating sources installed in the same furnace may be controlled to the same temperature, thereby forming three heating zones in total, or the heating sources installed in the same furnace may be controlled to different temperatures, thereby forming four or more heating zones in total. In this way, in the present invention, the interior of the heating furnace is divided into three or more heating zones, and one or more heat sources are installed in each heating zone, thereby achieving optimal heat transfer from each heating zone to the waste plastic.

[0019] The heat source is not particularly limited as long as it can be controlled to a desired temperature, and examples thereof include a combustion burner, a hot air heater, and an electric heater.

[0020] There are usually three or more heating zones, but from the viewpoint of promoting the thermal decomposition of waste plastics and suppressing fusion between resins, the number is preferably 3 to 6, more preferably 3 to 5, and even more preferably 3. For example, when there are three heating zones, each heating zone can exhibit the following functions.

[0021] (First heating zone) By setting the temperature highest in the area closest to the waste plastic supply port, the time that the waste plastic is exposed to the fusion temperature range where the resins are likely to fuse together and form aggregates or clumps as they are heated from room temperature to the thermal decomposition temperature is shortened. (Second heating zone) This is the area located between the waste plastic supply port and discharge port, where the waste plastic is thermally decomposed to break down the resin into smaller molecules, resulting in a decrease in mechanical strength. (Third heating zone) This is the area closest to the waste plastic discharge outlet, where the thermal decomposition of the waste plastic that began in the second heating zone is maintained slowly while the waste plastic is gradually cooled toward discharge.

[0022] The temperature of each heating zone should be set so that the temperature of the heating zone adjacent to the waste plastic supply inlet is a temperature at which the waste plastic can be thermally decomposed, and the temperature of the heating zone closest to the waste plastic supply inlet is set to a temperature higher than the other two or more heating zones.However, from the viewpoint of sufficiently thermally decomposing the waste plastic while sufficiently suppressing fusion of resins, it is preferable to set the temperatures gradually lower from the heating zone adjacent to the waste plastic supply inlet to the heating zone adjacent to the waste plastic discharge outlet.

[0023] Furthermore, when three heating zones are provided, from the viewpoint of fully utilizing the functions of each heating zone described above, fully pyrolyzing the waste plastic while sufficiently suppressing fusion between resins, it is preferable to set each heating zone to the temperature shown below, and it is even more preferable that each heating zone is set to a temperature within the temperature range shown below, with the temperature gradually decreasing from the first heating zone to the third heating zone. Note that the temperatures of each heating zone shown below can be combined in any way.

[0024] The temperature of the first heating zone is preferably 400°C or higher and 650°C or lower, more preferably 450°C or higher and 650°C or lower, and even more preferably 500°C or higher and 650°C or lower. The temperature of the second heating zone is preferably 300°C or higher and 550°C or lower, more preferably 350°C or higher and 500°C or lower, and even more preferably 375°C or higher and 500°C or lower. The temperature of the third heating zone is preferably 250°C or higher and 450°C or lower, more preferably 300°C or higher and 400°C or lower, and even more preferably 350°C or higher and 400°C or lower.

[0025] The heating time in each heating zone is preferably 5 minutes or more and 60 minutes or less, more preferably 10 minutes or more and 50 minutes or less, and even more preferably 20 minutes or more and 40 minutes or less, from the viewpoint of promoting the thermal decomposition of waste plastics and suppressing fusion of resins. In addition, the total heating time of each heating zone is preferably 30 minutes or more and 180 minutes or less, more preferably 45 minutes or more and 150 minutes or less, and even more preferably 60 minutes or more and 120 minutes or less, from the viewpoint of promoting the thermal decomposition of waste plastics and suppressing fusion of resins.

[0026] After the heating step, a cooling step can be carried out to cool the waste plastics discharged from the pyrolysis furnace. For example, the waste plastics pyrolysis product can be transported from the heating furnace to an indirect rotary cooler or a cooling screw conveyor by a screw conveyor and cooled there. In the cooling step, the waste plastic pyrolyzate may be stirred to prevent fusion of resins during cooling. Cooling the waste plastic pyrolyzate in the presence of air may result in ignition and combustion, so cooling may be performed in an inert gas atmosphere. Examples of inert gases include helium, argon, and nitrogen. Cooling under stirring and cooling under an inert gas atmosphere may be performed alone or in combination.

[0027] The cooled waste plastic pyrolysis product can be subjected to one or more processes selected from a crushing process, a pulverization process, and a physical separation process. The crushing and pulverizing processes are processes for adjusting the particle size of the waste plastic pyrolysis product to a size suitable for use as solid fuel. A crusher can be used in the crushing process. The crusher can be selected appropriately from the crushers described above, but impact crushers such as hammer crushers and impact mills are preferred. The crushing process can be carried out two or more times using a combination of crushers of the same or different types. The crushing step can be carried out using a crusher. Any known crusher may be appropriately selected, with a ball mill or roller mill being preferred. Either the crushing step or the crushing step or both may be carried out.

[0028] The physical separation process is not particularly limited, and examples thereof include an air separation process, a sieve separation process, a gravity separation process, a magnetic separation process, an eddy current separation process, and a sorter separation process (optical, electromagnetic induction, transmitted X-ray, fluorescent X-ray, etc.). Two or more physical separation processes can be combined, and in such cases, the order of each process can be selected appropriately. In the solid fuel production method shown in FIG. 1, the air separation process, the sieve separation process, and the gravity separation process are performed in this order. Note that the separation conditions may be set appropriately depending on the separation method so that the desired solid fuel can be recovered. The main physical separation processes are described below.

[0029] In the air sorting step, a known air sorter can be used, and although there is no particular limitation, examples thereof include a zigzag type and an internal circulation type. In wind sorting, for example, when an internal circulation system is used, a fan creates an airflow from bottom to top, causing heavy waste plastic fragments to move downward against the airflow, while lighter fragments move upward with the airflow. In this way, waste plastic pyrolysis products are separated into heavy and light fragments, with the lighter fragments being recovered as solid fuel. In this case, it is preferable to set the wind speed for wind sorting so that the heavy products are primarily non-combustible materials such as metal and glass. For example, the wind speed is preferably 5 m / s or higher, more preferably 7.5 m / s or higher, and even more preferably 10 m / s or higher. The upper limit of wind speed can be set appropriately depending on the type of waste plastic, but is usually 30 m / s or lower, preferably 25 m / s or lower.

[0030] The sieve sorting step can use, for example, a sieve sorter of a vibration type, an in-plane motion type, a rotary type, a fixed type, etc. The sieve mesh is preferably 5 to 30 mm, more preferably 5 to 20 mm, and even more preferably 5 to 10 mm. In sieve sorting, the material is separated into over-sieve material and under-sieve material, and the under-sieve material is usually recovered after particle size adjustment.

[0031] The gravity separation step can be carried out using a known gravity separator, which may be either a dry type or a wet type, but a dry type table type gravity separator is preferred, and an air table is more preferred. In gravity separation, for example, when an air table is used, waste plastic pyrolysis products fed onto the top surface of the vibrating table are floated off the top surface of the vibrating table by the air flow passing through the vibrating table, and the vibrations applied in the inclined direction of the vibrating table cause heavy products with a high specific gravity to move to the bottom layer and light products with a low specific gravity to move to the top layer. The heavy products in the bottom layer are subjected to frictional and vibrational forces from the top surface of the vibrating table and move up the slope, while the light products in the top layer are swept down the slope without being subjected to frictional and vibrational forces from the top surface of the vibrating table. The heavy and light products are then discharged separately from the vibrating table, and the light products are recovered as solid fuel and the heavy products as non-ferrous and steel raw materials.

[0032] In the magnetic separation step, a known magnetic separator can be used, and for example, any of a drum type, a pulley type, and a hanging type may be used, without any particular limitation. In magnetic separation, for example, a magnetic separation device having a magnetic drum in which a strong magnetic field is present, a belt conveyor (moving belt) wound around the magnetic drum, and a feeder that supplies samples onto the belt surface of the belt conveyor is used to separate magnetic materials into magnetized and non-magnetized materials, and the non-magnetized materials are recovered as solid fuel and the magnetized materials are recovered as steel raw materials. From the viewpoint of removing magnetic substances, the surface magnetic flux density of the magnetic separator is preferably 700 to 10,000 gausses, more preferably 1,000 to 7,500 gausses, and even more preferably 1,500 to 5,000 gausses.

[0033] The eddy current separator may be any known eddy current separator, and is not particularly limited, but examples thereof include a rotary magnet type, a direct belt conveyor type, and a rotary cylinder type. In eddy current sorting, for example, the interaction between the electromagnetic induction effect of the moving magnetic field of a rotating magnet body installed at the tip of the conveyor belt and the induced current generated inside the conveyor belt and the moving magnetic field applies a thrust force in the rotation direction of the rotating magnet body to the waste plastic pyrolysis product transported to the tip of the conveyor belt, causing the conductive materials to fly out from the surface of the conveyor belt in the direction of the combined force of this thrust and gravity acting on the conductive materials and be removed, and the non-conductive materials are recovered as solid fuel. From the viewpoint of removing conductive substances, the rotation speed of the rotating magnet body is preferably 1500 rpm or more, more preferably 3000 rpm or more, and even more preferably 4500 rpm or more.

[0034] As explained above, the method for producing a solid fuel of the present invention is effective in suppressing the fusion of waste plastics in a furnace, and is therefore also useful as a method for preventing the fusion of waste plastics. Note that the method for preventing the fusion of waste plastics of the present invention can employ the same configuration as described above. Furthermore, as shown in the examples below, the method for producing solid fuel of the present invention outputs a large amount of energy from the produced solid fuel, and this output energy amount is greater than the amount of energy input in the waste plastic heating process, making it extremely effective as a method for fixing the heat content of waste plastic in solid fuel. [Example]

[0035] The following examples will explain the present invention in more detail, but the present invention is not limited to the examples below.

[0036] 1. Calculation of residual heat rate The total calorific value of the raw materials and the raw materials after the heating process was measured in accordance with JIS Z 7302-2, and calculated using the following formula (1) from the input mass of the raw materials, the recovered mass of the raw materials after the heating process, and the calorific values ​​of the raw materials and the raw materials after the heating process.

[0037] Heat capacity residual rate (%)= (A×B)÷(C×D)×100 (1)

[0038] (In the formula, A represents the recovered mass (kg / h) of the raw material after the heating step, B represents the total calorific value (kJ / kg) of the raw material after the heating step, C represents the input mass of the raw material, and D represents the total calorific value (kJ / kg) of the raw material.)

[0039] 2.20mm sieve passing mass percentage The raw material after the cooling step was sieved using a JIS Z 8801 compliant sieve, and the mass of the material that passed through a 20 mm sieve was measured, and the percentage of this mass to the mass of the raw material after the heating step was calculated using the following formula (2).

[0040] Mass percentage passing through 20mm sieve (%) = E÷F×100 (2)

[0041] (In the formula, E represents the mass (kg) of the raw material after the cooling step that has passed through a 20 mm mesh sieve, and F represents the mass (kg) of the raw material after the heating step.)

[0042] 3. Energy balance ratio The energy balance ratio was calculated using the calorific value per unit time (MJ / h) of the obtained solid fuel and the calorific value per unit time (MJ / h) of the fuel added in the heating process using the following formula (3).

[0043] Energy balance ratio = G ÷ H × 100 (3)

[0044] (In the formula, G represents the calorific value per unit time (MJ / h) of the obtained solid fuel, and H represents the calorific value per unit time (MJ / h) of the fuel added in the heating step.)

[0045] Examples 1 to 3 and Comparative Examples 1 and 2 An externally heated rotary kiln was used as the heating furnace, and three burners were placed inside the heating furnace to create three heating zones as shown in Figure 1. The waste plastic used was shredder dust collected by dismantling and crushing electrical appliances, furniture, etc., and the undersized plastic was used as the raw material after sieving through a 30 mm mesh sieve. Solid fuel was produced according to the flowchart shown in Figure 1. Specifically, the process is as follows: Approximately 50 t of raw material was supplied for pyrolysis at a rate of 1000 kg / h into a heating furnace in which each heating zone was controlled to the temperature shown in Table 1. The mass (kg) of the raw material recovered in the heating process per unit time was measured, and the calorific value (kJ / kg) of the raw material recovered in the heating process and the calorific value per unit time (MJ / h) of the fuel input in the heating process were calculated. Next, the raw material after the heating process was carried out from the heating furnace and cooled under a nitrogen atmosphere using an indirect rotary cooler and a cooling screw conveyor. A portion of the raw material after the cooling process was taken and sieved using a 20 mm sieve, and the mass (kg) of the material that passed through the 20 mm sieve was measured. Next, the raw material after the cooling step was crushed by a hammer crusher. The hammer crusher was equipped with a screen with an opening diameter of 8 mm, and crushing was continued until the entire amount passed through the screen. Next, the raw material after the crushing process was sorted using a wind sorter, and the solid fuel that had been crushed into fine particles by the crushing process was collected as light material, and the metals that had not been crushed into fine particles by the crushing process were collected as heavy material. Next, the heavy materials collected by the wind sorter were sieved using a 10 mm mesh, and the under-sieve material was separated using a gravity sorter. The solid fuel mixed in with the heavy materials was collected as light products, and non-ferrous and steel raw materials with concentrated iron and non-ferrous metals were collected as heavy products. The solid fuels collected in the wind sorting and gravity sorting processes were then mixed, the mass of the solid fuel was measured, and the calorific value per unit time (MJ / h) of the obtained solid fuel was calculated.

[0046] [Table 1]

[0047] From Table 1, we can see the following: (1)Residual heat rate The residual calorific value is evaluated for the solid fuel recovered in the wind sorting process and the gravity sorting process by using the calorific value fixed in the solid fuel out of the calorific value of the raw material. It can be seen that the solid fuel produced in this example has sufficient fuel value. (2) Mass percentage passing through 20mm sieve The 20mm sieve passing mass percentage is used to evaluate whether or not the resins contained in the waste plastics melt together during the heating process and the resulting clumping occurs, using the mass that passes through the 20mm sieve as an indicator. In this example, since most of the raw material after the cooling process passes through the sieve, it can be seen that the melting of the resins during the heating process and the resulting clumping are sufficiently suppressed. (3) Energy balance ratio The energy balance ratio is evaluated using the calorific value per unit time output from the obtained solid fuel and the calorific value per unit time of the fuel input in the heating process as indicators. The energy balance ratio in this example is extremely high, which shows that solid fuel can be produced cost-effectively. Therefore, the method of the present invention suppresses the fusion and resulting clumping of waste plastics during the heating process, making it possible to stably and efficiently produce high-quality solid fuel.In addition, since the energy balance ratio is high, it is extremely effective as a method for fixing the calorific value of waste plastics into solid fuel. [Explanation of symbols]

[0048] 1. First heating source 2 Second Heat Source 3. Third Heat Source 10, 20 Furnace

Claims

1. A method for producing solid fuel, comprising a heating step of heat-treating waste plastics in a heating furnace having three heating zones, The heating zone includes a first heating zone, a second heating zone, and a third heating zone arranged from a waste plastic supply port toward a waste plastic discharge port, The temperature of the first heating zone is 400°C or higher and 650°C or lower, The temperature of the second heating zone is 300°C or higher and 550°C or lower, The temperature of the third heating zone is 250°C or higher and 450°C or lower, setting the temperature of the first heating zone to a higher temperature than the other two heating zones; A method for producing solid fuel.

2. The method for producing a solid fuel according to claim 1, wherein the heating time in each heating zone is 5 minutes or more and 60 minutes or less.

3. 3. The method for producing solid fuel according to claim 1, further comprising a cooling step of cooling the waste plastic discharged from the heating furnace under stirring and / or in an inert gas atmosphere after the heating step.

4. A method for preventing fusion of waste plastics, comprising a heating step of heat-treating waste plastics in a heating furnace having three heating zones, The heating zone includes a first heating zone, a second heating zone, and a third heating zone arranged from a waste plastic supply port toward a waste plastic discharge port, The temperature of the first heating zone is 400°C or higher and 650°C or lower, The temperature of the second heating zone is 300°C or higher and 550°C or lower, The temperature of the third heating zone is 250°C or higher and 450°C or lower, setting the temperature of the first heating zone to a higher temperature than the other two heating zones; A method for preventing waste plastic from fusing together.

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