Method for producing chlorine-reduced solid fuel

Abstract

To provide an efficient method for producing a chlorine-reduced solid fuel.SOLUTION: A method for producing a chlorine-reduced solid fuel comprises a step of washing, with water, waste plastic pyrolysis carbide having a cumulative 90% particle size of 1.0 mm or less in a volume-based particle size distribution.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing chlorine-reduced solid fuel.

Background Art

[0002] Waste plastics discarded as industrial waste or general waste were simply incinerated or directly landfilled. However, from the viewpoints of reducing carbon dioxide emissions and effectively utilizing resources, recovering the organic components in waste plastics and recycling them as solid fuel has been considered.

[0003] Solid fuel can be produced, for example, by heating waste plastics in a heating furnace for pyrolysis to convert the organic components into carbides. However, since waste plastics usually contain chlorine-containing plastics such as polyvinyl chloride and polyvinylidene chloride, high concentrations of chlorine tend to remain in the produced solid fuel. When such solid fuel is used as fuel, it causes corrosion of the heating furnace, etc., so reduction of chlorine is required.

[0004] Therefore, as a method for producing solid fuel with reduced chlorine, for example, a method of washing the carbide obtained by pyrolyzing chlorine-containing plastics with water has been proposed (Patent Document 1).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the method described in Patent Document 1, when washing with water at normal temperature, the reduction of chlorine is insufficient, so it is preferably washed with water at 50°C or higher. However, in order to use water at 50°C, the water temperature in the stirring tank has to be controlled for a long time, which makes temperature control difficult and is also disadvantageous in terms of cost. In addition, since a large amount of water is required for dechlorination by washing, it is inevitable to treat a large amount of wastewater with a high chlorine concentration and a high chemical oxygen demand (COD). Therefore, there is a need for a method that can efficiently produce a solid fuel with reduced chlorine by a simple operation. Therefore, an object of the present invention is to provide a method for producing a solid fuel that can efficiently produce a solid fuel with reduced chlorine by a simple operation.

Means for Solving the Problems

[0007] As a result of investigations in view of the above problems, the present inventors have found that by controlling the waste plastic pyrolysis carbide to a predetermined particle size, the organic components containing a large amount of chlorine are concentrated with an increase in the surface area, and by washing this, chlorine can be sufficiently reduced with a small amount of water at a low temperature, and the load of wastewater treatment is also reduced. Therefore, it has been found that a chlorine-reduced solid fuel can be efficiently produced by a simple operation.

[0008] That is, the present invention provides the following [1] to [4]. [1] A method for producing a chlorine-reduced solid fuel, including a step of washing a waste plastic pyrolysis carbide having a cumulative 90% particle diameter of 1.0 mm or less in a volume-based particle size distribution with water. [2] The method for producing a chlorine-reduced solid fuel according to [1] above, wherein the temperature of the water is 50°C or less. [3] The method for producing a chlorine-reduced solid fuel according to [1] or [2] above, wherein the mass ratio of the waste plastic pyrolysis carbide to water is 1:1.5 to 1:6. [4] The method for producing a chlorine-reduced solid fuel according to any one of [1] to [3] above, wherein the washing time is 2 minutes or more and 30 minutes or less.

Effects of the Invention

[0009] According to the present invention, a solid fuel with reduced chlorine can be efficiently produced by a simple operation.

Brief Description of the Drawings

[0010]

Figure 1

Embodiments for Carrying Out the Invention

[0011] An example of the manufacturing method of the chlorine-reduced solid fuel of the present invention is shown in FIG. 1. Hereinafter, an embodiment of the manufacturing method of the chlorine-reduced solid fuel of the present invention will be described with reference to the drawings.

[0012] 〔Waste Plastic〕 In the present invention, as shown in FIG. 1, first, waste plastic is prepared. The waste plastic is not particularly limited as long as it is waste containing plastic. For example, used plastic products, scraps and defective products generated during the manufacture and processing of plastic in factories, etc. can be used. These waste plastics usually contain chlorine-containing plastics such as polyvinyl chloride and polyvinylidene chloride. Note that two or more waste plastics may be mixed, and foreign substances other than plastic such as earth and sand, metal, glass, paper, and wood chips may be included.

[0013] Specific examples of the waste plastic include, for example, shredder dust, construction waste plastic, agricultural waste plastic, fishery waste plastic, and marine waste plastic. Here, in this specification, "shredder dust" refers to a mixture of fragments that are discarded after industrial waste or general waste is crushed by an industrial shredder and metals are recovered. Examples of the waste include waste automobiles, waste household appliances, vending machines, and OA equipment.

[0014] The size of the waste plastic is not particularly limited, but from the perspective of preventing blockage troubles during transportation and heat transfer during heating, it is preferably 50 mm or less in major axis. Here, in this specification, the "major axis of the waste plastic" means the value obtained by collecting the largest waste plastic among the waste plastics and measuring the location where the diameter of the waste plastic is the largest.

[0015] 〔Thermally decomposed carbide of waste plastic〕 Next, as shown in FIG. 1, the waste plastic is heated to produce a thermally decomposed carbide of waste plastic. Here, in this specification, the "thermally decomposed carbide of waste plastic" refers to a product obtained by thermally decomposing waste plastic to convert organic components into carbides.

[0016] The heating device is not particularly limited as long as it can accommodate the waste plastic and be set to a desired temperature. For example, a fixed furnace, a stoker furnace, a rotary kiln furnace, a fluidized bed furnace, a stationary furnace, a multi-stage furnace, etc. can be mentioned. Further, the shape of the heating furnace is not particularly limited, and it can take an appropriate shape such as a cylindrical shape or a rectangular cross-sectional shape. In addition, a conveyor for transporting the waste plastic from the supply port to the discharge port may be installed in the heating furnace. The heating temperature is not particularly limited as long as the waste plastic can be thermally decomposed and carbonized. However, considering the remaining heat quantity of the carbide, it is preferably 300 °C or higher, more preferably 350 °C or higher, and preferably 650 °C or lower, more preferably 600 °C or lower, still more preferably 550 °C or lower, and even more preferably 500 °C or lower. The heating time is not particularly limited as long as the waste plastic can be thermally decomposed and carbonized. However, it is preferably 30 minutes or longer, more preferably 45 minutes or longer, still more preferably 60 minutes or longer, and preferably 150 minutes or shorter, more preferably 120 minutes or shorter, still more preferably 90 minutes or shorter.

[0017] 〔Adjustment of particle size of thermally decomposed carbide of waste plastic〕 Next, as shown in FIG. 1, the particle size of the thermally decomposed carbide of waste plastic is adjusted. The particle size adjustment may be performed by subjecting the waste plastic pyrolysis carbide to one or more steps selected from crushing and physical separation so as to obtain a desired particle size. This makes it easier to adjust the particle size of the waste plastic pyrolysis carbide to a desired size.

[0018] (Crushing) For crushing the waste plastic pyrolysis carbide, one or more selected from crushers and grinders may be used. The crushing of the waste plastic pyrolysis carbide may be performed two or more times, or may be performed one or more times after physical separation. As the crusher, a known crusher can be appropriately selected. For example, an impact crusher, a hammer crusher, a roll crusher, and a rotary crusher can be mentioned. It is possible to attach a screen with a desired mesh for the purpose of particle size adjustment to the crusher. If the screen is not attached, the fixed teeth, rotating teeth, inner wall, etc. may be adjusted to a desired clearance. Also, screening machines such as vibrating screens and rotary screens can be used, and a desired mesh can be attached. As the grinder, a known grinder can be appropriately selected. For example, a disk mill, a wonder blender, a rod mill, a ball mill, and a roller mill can be mentioned.

[0019] (Physical separation) Since the waste plastic pyrolysis carbide contains impurities such as metals, earth and sand, and glass, the waste plastic pyrolysis carbide can be physically separated for the purpose of removing impurities and adjusting the particle size. In order to efficiently remove impurities, physical separation is preferably performed after crushing the waste plastic pyrolysis carbide.

[0020] The physical separation is not particularly limited as long as it can remove impurities. For example, magnetic separation, air separation, specific gravity separation, screening, and eddy current separation can be mentioned. The physical separation may be a combination of two or more, or one physical separation may be performed two or more times.

[0021] Magnetic separation can be performed using a known magnetic separator. For example, any of a drum type, a pulley type, and a suspension type may be used, and it is not particularly limited. In magnetic separation, for example, a magnetic separation device having a magnetic drum with a high magnetic field, a belt conveyor (mobile belt) wound around the magnetic drum, and a feeder for supplying a sample onto the belt surface of the belt conveyor is used to separate magnetic and non-magnetic substances, and the non-magnetic substances are recovered. From the viewpoint of removing magnetic substances, the surface magnetic flux density of the magnetic separator is preferably 700 to 10000 Gauss, more preferably 1000 to 7500 Gauss, and even more preferably 1500 to 5000 Gauss.

[0022] Air separation can use a known air separator and is not particularly limited. For example, a zigzag type or an internal circulation type can be mentioned. In air separation, for example, when the internal circulation type is used, if an air flow is created from the bottom upward by a fan, the heavy waste plastic pyrolysis carbides move downward against the air flow, while the light substances move upward along with the air flow. In this way, the waste plastic pyrolysis carbides are separated into heavy and light substances, and the light substances are recovered. In this case, it is preferable to set the air velocity of the air separation so that the heavy products mainly contain impurities such as metals and glass. For example, the air velocity is preferably 5 m / s or more, more preferably 7.5 m / s or more, and even more preferably 10 m / s or more. Note that the upper limit value of the air velocity can be appropriately set according to the type of waste plastic, but it is usually 30 m / s or less, preferably 25 m / s or less.

[0023] Specific gravity separation can use a known specific gravity separator, and either dry or wet separation can be used. However, a dry table type specific gravity separator is preferred, and an air table is even more preferred. In specific gravity separation, for example, when using an air table, the waste plastic pyrolysis carbide supplied onto the upper surface of the vibrating table floats from the upper surface of the vibrating table by an air flow passing through the vibrating table, and due to the vibration applied in the inclined direction of the vibrating table, the heavy product with a large specific gravity moves to the lower layer, and the light product with a small specific gravity moves to the upper layer. The heavy product in the lower layer moves obliquely upward from the upper surface of the vibrating table under the action of frictional force and vibration force, and the light product in the upper layer is washed obliquely downward without receiving frictional force and vibration force from the upper surface of the vibrating table. Then, the heavy product and the light product are discharged separately from the vibrating table, and the light product is recovered.

[0024] Screening is not particularly limited as long as the particle size can be adjusted. For example, screening machines such as vibrating screens, in-plane motion screens, rotary screens, and stationary screens can be used. In screening, separation is performed into oversize and undersize, and the undersize with adjusted particle size is recovered.

[0025] Eddy current separation can be performed using a known eddy current separator and is not particularly limited. For example, a rotating magnet type, a straight belt conveyor type, and a rotating cylinder type can be mentioned. In eddy current separation, for example, due to the interaction between the induced current generated inside and the moving magnetic field under the electromagnetic induction action of the moving magnetic field of the rotating magnet body provided on the tip side of the conveyor belt, a thrust is applied to the waste plastic crushed material conveyed to the tip side of the conveyor belt in the rotation direction of the rotating magnet body, and the conductive material is made to jump out and removed in the direction of the resultant force of this thrust and the gravity acting on the conductive material from the surface of the conveyor belt, and the non-conductive material is recovered. From the viewpoint of removing the conductive material, the rotation speed of the rotating magnet body is preferably 1500 rpm or more, more preferably 3000 rpm or more, and still more preferably 4500 rpm or more.

[0026] In the flowchart shown in FIG. 1, waste plastic pyrolysis carbide is crushed, the crushed material is subjected to magnetic separation to recover non-magnetically attached materials, the non-magnetically attached materials are subjected to air separation to recover lightweight materials, and the lightweight materials are crushed again to adjust to a desired particle size. Note that the magnetically attached materials recovered by magnetic separation can be recovered as iron scrap.

[0027] The particle diameter of the waste plastic pyrolysis carbide with adjusted particle size is such that the cumulative 90% particle diameter (d90) in the volume-based particle size distribution is 1.0 mm or less. From the viewpoint of chlorine reduction, 0.9 mm or less is preferable, and 0.8 mm or less is more preferable. Also, since the moisture content tends to increase if the particle size is too fine, the particle diameter d90 is preferably 0.1 mm or more, more preferably 0.2 mm or more, and still more preferably 0.3 mm or more. Here, in this specification, the "particle size distribution" refers to the volume-based particle size distribution measured based on the sieving method using the sieves specified in JIS Z 8801-1:2019 "Test sieves - Part 1: Metal wire cloth sieves" and JIS R 1629 "Method for measuring particle size distribution of fine ceramics raw materials by laser diffraction / scattering method". Note that the particle size distribution is represented by a distribution curve with the particle diameter (μm) on the horizontal axis and the volume-based frequency (%) on the vertical axis. As a laser diffraction / scattering method particle size measuring device, for example, Microtrac (manufactured by Nikkiso Co., Ltd.) can be used. Note that in this specification, the "cumulative 90% particle diameter in the volume-based particle size distribution" is also referred to as "particle diameter d90".

[0028] 〔Water washing〕 Next, the waste plastic pyrolysis carbide adjusted to a desired particle size is washed with water. By adjusting the particle size of the waste plastic pyrolysis carbide, the organic components containing a large amount of chlorine are concentrated along with the increase in the surface area, so chlorine can be sufficiently removed by water washing. The water washing is not particularly limited as long as the waste plastic pyrolysis carbide can be brought into contact with water. For example, there are methods such as putting the waste plastic pyrolysis carbide in a water tank and stirring it, immersing the light waste plastic pyrolysis carbide in water, and spraying water on the waste plastic pyrolysis carbide. It is also possible to use commercially available devices such as a drum washer.

[0029] The temperature of the water is preferably 50°C or lower, more preferably 45°C or lower, still more preferably 40°C or lower, even more preferably 35°C or lower, and preferably 5°C or higher, more preferably 10°C or higher, still more preferably 15°C or higher. That is, a preferred embodiment is normal temperature (20 ± 15°C). Even at such a low water temperature, chlorine can be sufficiently reduced, and moreover, water temperature management is not required. From the viewpoints of chlorine reduction and production efficiency, the amount of water used is preferably such that the mass ratio (A:B) of (A) waste plastic pyrolysis carbide to (B) water is 1:1.5 to 1:6, more preferably 1:2 to 1:5, and still more preferably 1:2 to 1:4. Chlorine can be sufficiently reduced with such a small amount of water, and moreover, the load of wastewater treatment can be reduced. The washing time can be appropriately set according to the amount of waste plastic pyrolysis carbide and water used, but is preferably 2 to 30 minutes, more preferably 2.5 to 20 minutes, and still more preferably 3 to 10 minutes. Chlorine can be sufficiently reduced even in such a short time.

[0030] 〔Solid-liquid separation〕 Next, the waste plastic pyrolysis carbide after washing is subjected to solid-liquid separation. Thereby, a solid fuel with reduced chlorine can be recovered as a solid. The solid-liquid separation is not particularly limited as long as the solid and water can be separated. For example, suction filtration and centrifugation can be mentioned. For suction filtration, it is possible to use a method generally adopted in the technical field and is not particularly limited. The operation mode of centrifugation may be continuous or batch (batch type). Examples of centrifugation include centrifugal filtration and centrifugal sedimentation. Centrifugation may be performed multiple times, or a combination of centrifugal sedimentation and centrifugal filtration may be performed.

[0031] Centrifugal filtration can be performed using a centrifugal filter. There are various types of centrifugal filters, but they are not particularly limited in this step. Among them, from the viewpoint of production efficiency, a continuous screw discharge type is preferred. Examples of the filter medium for the centrifugal filter include, for example, filter cloth and screen. However, using a screen with a pore diameter of 0.05 mm or more is preferable in terms of efficient solid-liquid separation. The centrifugal force in centrifugal filtration is usually 200 - 2000 G, but from the perspective of production efficiency, 300 - 1500 G is preferable.

[0032] Centrifugal sedimentation can be carried out using a centrifugal sedimentation machine. There are various types of centrifugal sedimentation machines, but they are not particularly limited in this process. Among them, from the perspective of production efficiency, a continuous decanter type is preferable. The centrifugal force in centrifugal sedimentation is usually 1000 - 3000 G, but from the perspective of production efficiency, 1500 - 3000 G is preferable.

[0033] In this way, the chlorine-reduced solid fuel of the present invention can be produced. The obtained solid fuel has reduced not only chlorine but also moisture, has good handleability, and excellent combustibility, so it can be directly used as a fuel in front of the kiln. Alternatively, it may be mixed with waste plastics, waste tatami mats, fine coal, waste oil, etc. and used as a fuel in front of the kiln, or it may be further put into a coal mill together with coal and dried and pulverized.

[0034] As described above, the present invention has been described in detail based on its embodiments, but the present invention is not limited to the above embodiments. The present invention can be variously modified without departing from its gist. For example, in the manufacturing method shown in FIG. 1, the heavy materials recovered in the air classification can be separated by specific gravity separation into heavy products and light products, and the heavy products can be recovered as scrap. Also, the light products separated by specific gravity separation can be separated by eddy current separation to recover valuable metals such as gold, silver, palladium, platinum, and copper. Thus, the chlorine-reduced solid fuel of the present invention is also useful as a method for recycling waste plastics.

Examples

[0035] Hereinafter, the embodiments of the present invention will be further specifically described with reference to examples. However, the present invention is not limited to the following examples.

[0036] The devices used in this example are shown in Table 1.

[0037]

Table 1

[0038] The analysis methods adopted in this example are shown in Table 2.

[0039]

Table 2

[0040] Examples 1 - 8 Using shredded dust recovered by disassembling and crushing electrical appliances, furniture, etc. as waste plastics, the undersize fraction screened with a 30 - mm mesh sieve was used as the raw material. Then, chlorine - reduced solid fuel was produced according to the flowchart shown in Figure 1. Specifically, it is as follows.

[0041] <Heating process> Waste plastics were supplied to an externally - heated rotary kiln at a rate of 1000 kg / h to a level of about 50 t and heated at 400 °C to obtain waste plastic pyrolysis carbides. The pyrolysis carbides discharged from the rotary kiln were cooled by a articulated rotary cooler and a cooling screw conveyor.

[0042] <Particle size adjustment process> (Crushing 1) The waste plastic pyrolysis carbides obtained in the heating process were crushed by a hammer crusher. After crushing, the crushed material was passed through a vibrating screen equipped with a screen with an 8 - mm opening diameter. (Air classification) The undersize fraction obtained in Crushing 1 was air - classified by an air classifier, and lightweight materials (d90 = 1.2 mm) were recovered. (Crushing 2) The lightweight material obtained by air separation was crushed to the particle size shown in Table 3 using one or more selected from a disk mill, a wonder blender, and a rod mill. Then, the chlorine content of the waste plastic pyrolysis carbide with adjusted particle size was analyzed. Table 3 shows the analysis results of the particle size (d90) and chlorine content of the waste plastic pyrolysis carbide with adjusted particle size.

[0043] <Water washing process> The waste plastic pyrolysis carbide with adjusted particle size obtained in Crushing 2 was washed with water under the conditions shown in Table 3. The washed waste plastic pyrolysis carbide was subjected to suction filtration using a Buchner funnel and a vacuum pump for solid-liquid separation. Then, the chlorine content and moisture content of the waste plastic pyrolysis carbide before water washing and the solid fuel obtained by solid-liquid separation were analyzed. The results are shown in Table 4.

[0044] Comparative Examples 1 and 2 In Comparative Example 1, solid fuel was produced by the same operation as in Example 1, except that the lightweight material obtained by air separation in Example 1 was washed with water. In Comparative Example 2, solid fuel was produced by the same operation as in Comparative Example 1, except that it was washed with water at 50°C. Then, the chlorine content and moisture content of the waste plastic pyrolysis carbide before water washing and the solid fuel obtained by solid-liquid separation were analyzed. The results are shown in Table 4.

[0045]

Table 3

[0046]

Table 4

[0047] From Table 4, it can be seen that by adjusting the particle size (d90) of the waste plastic pyrolysis carbide to a specific value or less and washing it, a solid fuel with sufficiently reduced chlorine can be efficiently produced, even though a small amount of water at a low temperature is used.

Claims

1. A method for producing chlorine-reduced solid fuel, comprising a step of washing waste plastic pyrolysis carbide having a cumulative 90% particle diameter in a volume-based particle size distribution of 0.3 to 0.5 mm with water.

2. The method for producing chlorine-reduced solid fuel according to claim 1, wherein the temperature of the water is 50°C or lower.

3. The method for producing chlorine-reduced solid fuel according to claim 1 or 2, wherein the mass ratio of the waste plastic pyrolysis carbide to water is 1:1.5 to 1:

6.

4. The method for producing chlorine-reduced solid fuel according to any one of claims 1 to 3, wherein the washing time is 2 minutes or more and 30 minutes or less.

Images