JP7762509B2 - Method for producing solid fuel - Google Patents

Description

The present invention relates to a method for producing solid fuel.

Traditionally, waste plastics discarded as industrial or general waste have been simply incinerated or landfilled. However, with the aim of reducing carbon dioxide emissions and efficiently utilizing resources, efforts are being made 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 resins increase in particle 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 feeding large particles into the crusher leads to equipment damage and frequent maintenance, resulting in high running costs.

Technologies to prevent waste plastics from fusing together in furnaces are being investigated. For example, it has been reported that by heating a mixture of thermoplastic plastic and pulverized coal obtained by crushing coal in a specified ratio, the pulverized coal adheres to the surface of the molten thermoplastic plastic, thereby preventing the molten thermoplastic plastic from fusing together in the furnace (Patent Document 1). It has also been reported that by heating a mixture of chlorine-containing plastic and calcium compound in a specified 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 plastic and the generation of dioxins can be prevented (Patent Document 2).

JP 2011-68769 A Japanese Patent Application Laid-Open No. 2019-123771

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.

The inventors conducted research to determine the factors that cause resins contained in waste plastic to fuse together in a furnace when the waste plastic is heated to pyrolyze it. They discovered that, as the temperature of the waste plastic rises from room temperature to the pyrolysis temperature, melted resins fuse together in the region above the resin's melting point but below the pyrolysis temperature (hereinafter also referred to as the "fusion temperature region"). Based on this knowledge, they conducted further research and discovered that by dividing the furnace in which the waste plastic is 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, the residence time of the resin in the fusion temperature region is shortened, thereby not only suppressing the fusion of resins but also providing an extremely effective method of immobilizing the heat of the waste plastic in solid fuel, since the amount of energy output from the produced solid fuel exceeds the amount of energy input during the waste plastic heating process.

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

The present invention makes it possible to suppress the fusion of waste plastics in the furnace and produce solid fuel stably and efficiently without compromising quality. Furthermore, because the solid fuel production method of the present invention has a high energy balance ratio, it is extremely effective as a method for immobilizing the calorific value of waste plastics into solid fuel.

1 is a flowchart showing an example of a manufacturing method of the present invention. FIG. 1 is a cross-sectional view showing an example of a heating furnace applicable to the manufacturing method of the present invention. FIG. 10 is a cross-sectional view showing another heating furnace applicable to the manufacturing method of the present invention.

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.
In the method for producing a solid fuel of the present invention, as shown in FIG. 1, first, waste plastics are subjected to a heating step in which they are heat-treated in a heating furnace.

The waste plastic is not particularly limited as long as it is waste containing plastic, and 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 contain plastics such as polypropylene, polyethylene, polycarbonate, polyvinyl chloride, glass fiber reinforced plastics, and carbon fiber reinforced plastics, but may also contain foreign matter other than plastics, 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 waste 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 automation equipment, furniture, and building materials. Two or more types of waste plastics may be mixed.

The waste plastic may have been subjected to one or more physical separations selected from crushing, sieving, air separation, magnetic separation, eddy current separation, and gravity separation for the purpose of adjusting particle size and removing foreign matter, in order to promote thermal decomposition of the waste plastic and prevent fusion between resins.

Waste plastic can be crushed using a crusher. Examples of crushers include jaw crushers, impact crushers, hammer crushers, roll crushers, and rotary crushers. Crushers can be equipped with a screen with the desired mesh size to adjust particle size. If a screen is not installed, the fixed teeth, rotating teeth, inner wall, etc. can be adjusted to the desired clearance. Sieve separators such as vibrating sieves and rotary sieves can also be used, and the desired mesh size can be installed. Other physical separation methods will be explained below.

The particle size of the crushed waste plastic is preferably 150 mm or less, more preferably 50 mm or less, and even more preferably 30 mm or less, from the perspective of promoting the thermal decomposition of the waste plastic and preventing fusion between resins. There is no particular lower limit for the particle size of the crushed waste plastic.

The heating furnace is not particularly limited as long as it can accommodate waste plastic and be set to the desired temperature, but examples include fixed furnaces, stoker furnaces, rotary kilns, fluidized bed furnaces, vertical furnaces, and multi-tier furnaces. The shape of the heating furnace is also not particularly limited, and it can be any suitable shape, such as cylindrical or rectangular in cross section. A conveyor may be installed inside the heating furnace to transport the waste plastic from the waste plastic inlet to the discharge outlet.

The atmosphere inside the heating furnace is preferably a low-oxygen atmosphere, since this fixes the calorific value of resins contained in waste plastics and fibers of plant and animal origin, such as cellulose, into solid fuel after heating and facilitates crushing, pulverization, and physical separation after heat treatment. Here, in this specification, "low-oxygen atmosphere" refers to an atmosphere with an oxygen concentration lower than that of the atmosphere. Considering continuous heating in a low-oxygen atmosphere and an increase in the energy balance ratio, heat treatment under low-oxygen conditions using an externally heated rotary kiln furnace is preferred. Methods for creating a low-oxygen furnace atmosphere include, for example, filling the furnace with an inert gas such as nitrogen or water vapor, or filling the furnace with gas components (e.g., flammable gases such as _H2O , _CO2 , and lower hydrocarbons) generated primarily by the thermal decomposition of waste plastics.

In order to promote the thermal decomposition of waste plastics while suppressing fusion of 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 waste plastics will spend a long time in the fusion temperature range (e.g., 150-250°C) as they 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.

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 denoted by 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, which are 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 desired number of 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.

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

Normally, there are three or more heating zones, but from the perspective of promoting the thermal decomposition of waste plastics and suppressing fusion between resins, there are preferably three to six, more preferably three to five, and even more preferably three. For example, when there are three heating zones, each heating zone can perform the following functions:

(First Heating Zone)
By setting the area closest to the waste plastic supply port to the highest temperature, the time that the waste plastic is exposed to the fusion temperature range where the resins are likely to fuse together and become agglomerated or clumped together during the process of heating the waste plastic 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 port, and slowly maintains the thermal decomposition of the waste plastic that began in the second heating zone, while gradually cooling it towards discharge.

The temperature of each heating zone should be set so that the heating zone adjacent to the waste plastic supply inlet is at a temperature at which the waste plastic can be thermally decomposed, and the heating zone closest to the waste plastic supply inlet is set at a temperature higher than the other two or more heating zones. However, from the perspective 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.

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, and sufficiently suppressing fusion between resins, it is preferable to set each heating zone to the temperature shown below. It is even more preferable that each heating zone is set to a temperature within the temperature range shown below, with temperatures 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.

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.

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.

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.

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 for 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 performed two or more times using a combination of the same or different types of crushers.
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.

The physical separation process is not particularly limited, but examples include air separation, sieving, gravity separation, magnetic separation, eddy current separation, and sorter separation (optical, electromagnetic induction, transmitted X-ray, fluorescent X-ray, etc.). Two or more physical separation processes can be combined, in which case the order of each process can be selected as appropriate. In the solid fuel production method shown in Figure 1, the air separation process, sieving, and gravity separation processes are performed in this order. The separation conditions can 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.

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, the waste plastic pyrolysis products are separated into heavy and light fragments, and the lighter fragments are recovered as solid fuel. In this case, it is preferable to set the wind speed for wind sorting so that the heavy products are mainly non-combustible materials such as metal and glass. For example, the wind speed is preferably 5 m/s or more, more preferably 7.5 m/s or more, and even more preferably 10 m/s or more. The upper limit of wind speed can be set appropriately depending on the type of waste plastic, but is usually 30 m/s or less, preferably 25 m/s or less.

The sieve sorting step can be carried out using a sieve sorter of, for example, a vibration type, an in-plane motion type, a rotary type, a fixed type, etc. The mesh size of the sieve 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.

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 supplied to the top surface of the vibrating table are floated from the top surface of the vibrating table by the air flow passing through the vibrating table, and vibrations applied in the tilting 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, with the heavy products in the bottom layer being subjected to frictional and vibrational forces from the top surface of the vibrating table and moving up the slope, and the light products in the top layer being swept down the slope without being subjected to frictional and vibrational forces from the top surface of the vibrating table. The heavy products and light products are then discharged separately from the vibrating table, with the light products being recovered as solid fuel and the heavy products being recovered as non-ferrous and steel raw materials.

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.

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.

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.

The following examples further illustrate embodiments of the present invention. However, the present invention is not limited to the examples below.

1. Calculation of residual heat rate The total calorific value of the raw materials and the raw materials after the heating step 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 step, and the calorific values of the raw materials and the raw materials after the heating step.

Calorie residual rate (%) = (A x B) ÷ (C x D) x 100 (1)

[In the formula, A represents the mass of raw material recovered after the heating process (kg/h), B represents the total heat generation rate of the raw material after the heating process (kJ/kg), C represents the mass of raw material input, and D represents the total heat generation rate of the raw material (kJ/kg).]

2. Mass percentage passing through 20 mm sieve The raw material after the cooling step was sieved using a JIS Z 8801 compliant sieve, and the mass passing through a 20 mm sieve was measured, and the percentage relative to the mass of the raw material after the heating step was calculated using the following formula (2).

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

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

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 step, using the following formula (3).

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

[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 process.]

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 arranged in the heating furnace to provide three heating zones as shown in FIG.
Shredder dust collected from dismantled and crushed electrical appliances, furniture, etc. was used as waste plastic, and the undersize plastic was sieved through a 30 mm mesh sieve and used as the raw material to produce solid fuel 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 1,000 kg/h into a heating furnace in which each heating zone was controlled to the temperature shown in Table 1. The mass (kg) per unit time of the raw material recovered in the heating step was measured, and the calorific value (kJ/kg) of the raw material recovered in the heating step and the calorific value per unit time (MJ/h) of the fuel input in the heating step were calculated.
The raw material after the heating step was then transported from the heating furnace and cooled in a nitrogen atmosphere using an indirect rotary cooler and a cooling screw conveyor. A portion of the raw material after the cooling step was taken and sieved through 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 recovered 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 the wind-sorted heavy materials was recovered as light products, and non-ferrous and steel raw materials in which iron and non-ferrous metals were concentrated were recovered as heavy products. The solid fuels recovered in the wind sorting process and the gravity sorting process 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.

From Table 1, the following can be seen:
(1) Calorific value retention rate The calorific value retention rate is used to evaluate the fuel value of solid fuel recovered in the wind sorting process and the gravity sorting process, using the calorific value that is 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 20 mm sieve The mass percentage passing through 20 mm sieve is used to evaluate whether or not the resins contained in the waste plastics melt together during the heating process and the resulting agglomeration occurs, using the mass that passes through a 20 mm 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 agglomeration 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 extremely high energy balance ratio in this example indicates that solid fuel can be produced at a cost-effective rate.
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.

1 First heating source 2 Second heating source 3 Third heating source 10, 20 Heating furnace

Claims (4)

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. The method for producing solid fuel described in claim 1, wherein the heating time in each heating zone is 5 minutes or more and 60 minutes or less. The method for producing solid fuel according to claim 1 or 2, further comprising a cooling step in which the waste plastic discharged from the heating furnace is cooled under agitation and/or in an inert gas atmosphere after the heating step. 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.