Manufacturing method of solid fuel

Abstract

To provide a method for producing solid fuel that suppresses the fusion and coarsening of waste plastics when waste raw materials containing waste plastics are heated, and that can produce solid fuel with small particle size in high yield. [Solution] A method for producing solid fuel is provided, comprising a heating step of introducing waste raw materials including waste plastic and pulverized coal into a heating furnace and heating them to thermally decompose at least a portion of the waste plastic, wherein the fixed carbon of the pulverized coal is 50% or less and the volatile content is 40% or less.

Description

Technical Field

[0004] , , , , , , , , , , , , , , ,

[0003] , , , , , ,

[0005] ,

[0001] The present disclosure relates to a method for manufacturing solid fuel.

Background Art

[0002] Various techniques for producing solid fuel by heat-treating waste containing waste plastic have been studied (Patent Documents 1 to 3). In Patent Document 1, attempts have been made to produce solid fuel with reduced chlorine by heating the waste to embrittle it, pulverizing it, and then performing air classification. By the way, when waste containing waste plastic is heated, the molten plastic adheres to the furnace wall of the heating furnace, increasing the maintenance frequency of the operating equipment. For this reason, in Patent Documents 2 and 3, techniques have been proposed to mix thermoplastic plastic and fine coal before heating with a heating device to suppress the fusion of the thermoplastic plastic inside the heating device.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

[0006] In the above manufacturing method, pulverized coal containing 50% or less fixed carbon and 40% or less volatile matter is introduced along with waste raw materials including waste plastics. Such pulverized coal can suppress the coarsening of waste plastics through fusion. It can also reduce the components that gasify as volatile matter. Therefore, according to the above manufacturing method, solid fuel with small particle size can be obtained in high yield. [Effects of the Invention]

[0007] According to this disclosure, it is possible to provide a method for producing solid fuel that suppresses the fusion and coarsening of waste plastics when waste raw materials containing waste plastics are heated, and that can produce solid fuel with small particle size in high yield. [Brief explanation of the drawing]

[0008] [Figure 1] This is a cross-sectional view showing an example of a solid fuel manufacturing apparatus. [Figure 2] This graph shows the particle size distribution of the solid fuels in Examples 1 and 2 and Comparative Example 1. [Figure 3] (A) is a photograph of the solid fuel of Example 1, (B) is a photograph of the solid fuel of Example 2, and (C) is a photograph of the solid fuel of Comparative Example 1. [Figure 4] This graph shows the relationship between fixed carbon in pulverized coal and the average particle size of the heat-treated material. [Modes for carrying out the invention]

[0009] Embodiments of the present disclosure will be described below, with reference to the drawings as appropriate. However, the following embodiments are illustrative for the purpose of illustrating the present disclosure and are not intended to limit the present disclosure to the following. In the description, the same reference numerals will be used for elements that are the same or have the same function, and redundant explanations will be omitted as appropriate. Also, positional relationships such as up, down, left, and right will be based on the orientation of the reference numerals in the drawings unless otherwise specified. The dimensional ratios of each element are not limited to the ratios shown. In the description, the symbol "~" used in numerical ranges indicates a numerical range that includes the upper and lower limits. For example, "X~Y" indicates a numerical range of "X or greater and Y or less". Numerical ranges in which the upper and / or lower limits of a numerical range are replaced with the values ​​described in the examples are also included in the present disclosure. If a numerical range is illustrated with only the upper limit or only the lower limit, a numerical range combining the numerical range with only the upper limit and the numerical range with only the lower limit is also included in the present disclosure. Numerical ranges in which the upper and / or lower limits of one numerical range are replaced with the upper and / or lower limits of another numerical range are also included in the present disclosure.

[0010] A method for producing solid fuel according to one embodiment includes a heating step in which waste raw materials including waste plastic and pulverized coal are introduced into a heating furnace and heated to thermally decompose at least a portion of the waste plastic.

[0011] The waste raw materials containing waste plastics may be either industrial waste or general waste, and examples include container recycling residue, shredder dust, construction waste plastics, agricultural waste plastics, fishery waste plastics, marine waste plastics, etc. The waste raw materials may also contain foreign matter other than waste plastics. Examples of foreign matter include paper, rubber, wood scraps, metal scraps, metal wires, metal foils, glass scraps, concrete scraps, ceramic scraps, slag, rubble, etc. From the viewpoint of obtaining heat-treated material with large particle size and from the viewpoint of obtaining solid fuel with high added value, the mass percentage of waste plastics in the waste raw materials may be 40% by mass or more, 50% by mass or more, or 60% by mass or more.

[0012] The thermoplastic content in the waste raw material may be 30% by mass or more, 40% by mass or more, or more than 50% by mass. Waste raw materials with a high thermoplastic content tend to melt and fuse together when heated, resulting in larger particle size. In the above manufacturing method, by using a predetermined fine coal pulverizer, the fusion and coarsening of the thermoplastic can be suppressed.

[0013] Thermoplastic plastics are plastics manufactured using thermoplastic resins. Thermoplastic plastics may include, for example, at least one selected from the group consisting of polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyethylene terephthalate, polyamide, polycarbonate, and acrylic. Thermoplastic plastics may be in the form of fluff, foam, or granules, for example.

[0014] The waste materials may include combustible materials such as thermosetting plastics, fibers, paper, cardboard, wood, leather, elastomers, and rubber, as well as non-combustible materials such as metals, ceramics, glass, sand, and stones. However, from the viewpoint of ensuring a sufficiently high calorific value for the solid fuel, the proportion of combustible materials in the waste may be 50% by mass or more, 60% by mass or more, or 70% by mass or more.

[0015] The waste material may include rigid plastics. In this disclosure, rigid plastics have a tensile modulus of 1000 MPa or more, as measured in accordance with ASTM D638. Rigid plastics have excellent mechanical strength, heat resistance, and chemical resistance, and are used in a wide range of fields, such as electronic equipment housings, automotive parts, household goods, and building materials. For example, rigid plastics may include at least one selected from the group consisting of polycarbonate, polypropylene, polystyrene, acrylonitrile butadiene styrene, polyamide, polyethylene terephthalate, polyvinyl chloride, polymethyl methacrylate, and polyphenylene sulfide.

[0016] Since hard plastic has a higher melting point than soft plastic, it is considered more difficult to fuse than soft plastic in the heating process. From the perspective of obtaining a heat-treated product with a sufficiently small particle size, the content of hard plastic in the waste raw material may be 10% by mass or more, 20% by mass or more, 30% by mass or more, or 35% by mass or more. From the perspective of relaxing the restrictions on the selection of waste raw materials, the content of hard plastic in the waste raw material may be 60% by mass or less, or 50% by mass or less.

[0017] The waste raw material may contain a thermosetting plastic. A thermosetting plastic is a plastic manufactured using a thermosetting resin. The thermosetting plastic may contain, for example, at least one selected from the group consisting of polyurethane, melamine, unsaturated polyester, phenolic resin, urea resin, silicone resin, epoxy resin, and alkyd resin. The form of the thermosetting plastic is not particularly limited, and may be, for example, fluff-like, foamed, or granular.

[0018] The maximum particle size of the waste raw material may be less than 50 mm, less than 40 mm, or less than 30 mm. Thereby, the variation in the particle size of the heat-treated product can be made sufficiently small. In addition, the "maximum particle size" in the present disclosure is based on the size of the mesh opening of the sieve. A waste raw material having a particle size less than 50 mm can be obtained as the undersize when sieving is performed using a sieve with a mesh opening of 50 mm.

[0019] The waste raw material may contain polyurethane. Polyurethane can sufficiently suppress the fusion and coarsening of thermoplastic plastics. The content of polyurethane in the waste raw material may be 2% by mass or more, 4% by mass or more, 6% by mass or more, or 8% by mass or more. From the perspective of relaxing the restrictions on the selection of waste raw materials, the content of polyurethane in the waste raw material may be 25% by mass or less, or 18% by mass or less.

[0020] The fixed carbon of the fine powder coal may be 50% or less, 49% or less, 45% or less, or 40% or less. Fine powder coal with low fixed carbon can suppress the fusion and coarsening of waste plastics. Therefore, solid fuel with a small particle size can be smoothly produced. In addition, fine powder coal with low fixed carbon can suppress the fusion of the melt of waste plastics to the inside of the heating furnace and can continue smooth operation over a long period. The fixed carbon of the fine powder coal may be 20 - 50%, or 40 - 49%.

[0021] The volatile content of the fine powder coal may be 40% or less, 35% or less, or 32% or less. As a result, the components gasifying in the heating process are reduced, and the yield of solid fuel can be made sufficiently high. From the viewpoint of lowering the ratio of fixed carbon, the volatile content of the fine powder coal may be 25% or more, or 30% or more. From the viewpoint of lowering the ratio of fixed carbon and increasing the yield of solid fuel, the volatile content of the fine powder coal may be 25 - 40%. The moisture content of the fine powder coal may be 4% or less, or 1 - 3%. The ash content of the fine powder coal may be 22% or less, 20% or less, or 17% or less. Fine powder coal with a low ash content tends to be able to suppress the fusion and coarsening of waste plastics. The ash content of the fine powder coal may be 10 - 22%, or 13 - 20%.

[0022] The ratios of the fixed carbon, ash content, volatile content, and moisture content of the fine powder coal in the present disclosure are values on an air-dried basis by proximate analysis defined in JIS M 8812:2004.

[0023] The average particle size of the fine powder coal is preferably smaller than the maximum particle size of the waste plastics. Thereby, it is possible to sufficiently suppress the fusion and coarsening of the waste plastics. The average particle size of the fine powder coal is the particle size (median diameter) corresponding to 50% by volume of the cumulative distribution curve measured using a commercially available laser diffraction particle size distribution measuring device. From the viewpoint of sufficiently suppressing the fusion and coarsening of the waste plastics and making it easy to handle, the average particle size of the fine powder coal may be 12 - 35 μm, or 15 - 30 μm. The average particle size of the fine powder coal may be adjusted by pulverizing and sieving.

[0024] The waste material and pulverized coal may be introduced separately into the heating furnace and mixed within the furnace, or a mixing step may be performed before the heating step in which the waste material and pulverized coal are mixed to prepare a mixed material. In this case, the mixed material may be introduced into the heating furnace. Materials other than the waste material and pulverized coal may be introduced into the heating furnace individually, or materials other than the waste material and pulverized coal may be mixed with the waste material and pulverized coal in the mixing step, and the resulting mixed material may be introduced into the heating furnace. The mixing step can be carried out using, for example, a V-type mixer, a W-type mixer, a drum-type mixer, a self-rotating or revolving screw conveyor, a kiln-type dryer, etc.

[0025] The mass ratio of pulverized coal to waste raw materials may be 1.0 or less, 0.8 or less, or 0.6 or less. This can reduce the consumption of fossil fuels. The pulverized coal in this embodiment has the effect of suppressing the fusion and coarsening of waste plastics, so the above mass ratio can be made sufficiently small.

[0026] A crushing step may be performed to crush the mixed raw materials obtained in the mixing step. A mixing and crushing step may also be performed using the various equipment described above to simultaneously mix and crush the waste raw materials and pulverized coal.

[0027] In the heating process, the waste raw materials and pulverized coal (or mixed raw materials) are introduced into a continuous or batch heating furnace and heated to 250-500°C, 300-450°C, or 300-400°C. The heating time may be 0.5-3 hours or 1-2 hours. This allows for sufficient thermal decomposition and desalination of waste plastics while producing solid fuel with a high yield. The inside of the heating furnace may be an inert gas atmosphere. The heating furnace may be, for example, a rotary kiln equipped with lifter blades.

[0028] The heat-treated material obtained in the heating process has suppressed coarsening and possesses a sufficiently small particle size. For example, in the heat-treated material, the mass ratio of coarse particles with a particle size of 16 mm or larger may be 20% by mass or less, 10% by mass or less, 5% by mass or less, or 3% by mass or less. The lower limit of the mass ratio of coarse particles with a particle size of 16 mm or larger may be 0.1% by mass. The mass ratio of coarse particles with a particle size of 16 mm or larger is the mass ratio on the sieve when sieved using a sieve with a mesh size of 16 mm.

[0029] In the heat-treated material, the mass ratio of particles having a particle size of less than 1 mm may be 12% by mass or more, 15% by mass or more, or 18% by mass or more. Such a heat-treated material can be used as a solid fuel without grinding.

[0030] The average particle size (Dp50) of the heat-treated material (solid fuel) may be less than 3.0 mm or less than 2.8 mm. The average particle size (Dp50) in this disclosure can be determined by the following procedure. The heat-treated material (solid fuel) is sieved using a sieve to determine the mass ratio in each of the seven particle size ranges: less than 1.0 mm, 1.0 mm or more and less than 2.0 mm, 2.0 mm or more and less than 2.8 mm, 2.8 mm or more and less than 4.7 mm, 4.7 mm or more and less than 9.5 mm, 9.5 mm or more and less than 16 mm, and 16 mm or more. The median value of each particle size range is considered to have the mass ratio in that particle size range, and seven data points are obtained. For the particle size ranges of less than 1.0 mm and 16 mm or more, the mass ratios are considered to have particle sizes of 1.0 mm and 16 mm, respectively. A quadratic function is found using the seven data points that has a correlation coefficient (r) closest to 1. Based on the obtained quadratic function, the average particle size (Dp50) is defined as the particle size at which the cumulative mass ratio from the small particle size side reaches 50% by mass.

[0031] The heat-treated material may be used as solid fuel as is. That is, the solid fuel may have the particle size and average particle size described above. The heat-treated material obtained in the heating process may be crushed after cooling. Crushing may be carried out, for example, using a mill. The yield of the heat-treated material (solid fuel) may be 70% by mass or more, 80% by mass or more, or 85% by mass or more. The yield of the heat-treated material (solid fuel) can be determined as the ratio of the mass of the heat-treated material (solid fuel) to the total mass of waste raw materials and pulverized coal (or mixed raw materials) introduced into the heating furnace.

[0032] The above-described method for manufacturing solid fuel may be carried out using, for example, the manufacturing apparatus 100 shown in Figure 1. The manufacturing apparatus 100 in Figure 1 comprises an indirectly heated rotary kiln 10 having a kiln body 12 (inner cylinder) and an outer cylinder 14, an introduction section 50 for introducing raw materials 51 into the kiln body 12 of the rotary kiln 10, and an outlet section 30 for discharging the heated material 53 (solid fuel) from the kiln body 12 of the rotary kiln 10. The introduction section 50 only needs to be configured to transport the raw materials 51, and may be equipped with a conveyor, for example. The raw materials 51 may be a mixed raw material containing waste raw materials and pulverized coal. Upstream of the introduction section 50, a mixer may be provided for mixing the waste raw materials, pulverized coal, and other raw materials as needed. In a modified example, the introduction section 50 may introduce the waste raw materials and pulverized coal separately into the kiln body 12 and mix them within the kiln body 12. In yet another variation, the introduction section 50 may introduce raw materials other than waste materials and pulverized coal into the kiln body 12.

[0033] In the rotary kiln 10, the kiln body 12 has lifter blades inside and is rotatably supported by rollers 15 and 16. Raw material 51 is introduced into the kiln body 12 from the inlet 50. The rotation axis of the kiln body 12 is slightly inclined with respect to the horizontal, with the inlet 50 side being higher than the outlet 30 side. Therefore, the raw material 51 introduced into the kiln body 12 is agitated by the lifter blades as the kiln body 12 rotates, moving from the inlet 50 side to the outlet 30 side. In Figure 1, the raw material 51 moves from left to right inside the kiln body 12.

[0034] In addition to the raw material 51, an inert gas may be introduced into the kiln body 12 of the rotary kiln 10. Examples of inert gases include nitrogen gas and exhaust gas containing carbon dioxide. The inert gas may also move along with the raw material 51 within the kiln body 12 from the upstream side to the downstream side. The raw material 51 is heated within the kiln body 12, causing the waste plastic to melt or carbonize to become a heat-treated product 53. The heat-treated product 53 is discharged from the kiln body 12 to the outlet section 30 and introduced into the cooler 40. After being cooled in the cooler 40, the heat-treated product 53 is discharged from the manufacturing apparatus 100. The heat-treated product 53 discharged from the manufacturing apparatus 100 may be used as solid fuel as is, or it may be crushed in a pulverizer.

[0035] The pyrolysis gas G3 generated by heating the raw material 51 inside the kiln body 12 is discharged from the outlet 32 ​​of the outlet section 30. An outer cylinder 14 is provided around the outer circumference of the kiln body 12. The outer cylinder 14 forms a hot gas flow path 17 that indirectly heats the kiln body 12. Hot gas G1 is supplied to the hot gas flow path 17 formed by the outer cylinder 14 from the gas inlet 21. The hot gas G1 may be exhaust gas from combustion equipment such as a boiler. The temperature of the hot gas G1 may be, for example, 400 to 500°C. The hot gas G1 heats the kiln body 12 by flowing through the hot gas flow path 17. The hot gas G1 that has heated the kiln body 12 is discharged to the outside as exhaust gas G2 from the gas outlet 22. In the manufacturing apparatus 100, the fusion of molten thermoplastic to the inner wall 13 of the kiln body 12 can be suppressed. This allows for stable and continuous operation.

[0036] The manufacturing apparatus used in the solid fuel manufacturing method of this embodiment is not limited to that shown in Figure 1. For example, the manufacturing apparatus may be a batch furnace equipped with lifter blades. In the manufacturing method of this embodiment, the fusion and coarsening of waste plastics can be suppressed by using a predetermined pulverized coal and waste raw materials. Therefore, the load of crushing the heat-treated material can be reduced, and fine solid fuel can be efficiently manufactured with a high yield. Furthermore, the fusion of waste plastics into the heating furnace can also be suppressed.

[0037] The above-described embodiment includes the following: [1] A method for producing a solid fuel comprising a heating step of introducing waste raw materials including waste plastic and pulverized coal into a heating furnace and heating them to thermally decompose at least a portion of the waste plastic, A method for producing solid fuel, wherein the fixed carbon content of the pulverized coal is 50% or less and the volatile content is 40% or less. [2] The method for producing solid fuel according to [1], wherein the ash content of the pulverized coal is 22% or less. [3] The method for producing solid fuel according to [1] or [2], wherein the content of hard plastic in the waste raw material is 10% by mass or more. [4] Prior to the heating step, the mixture step is to prepare a mixed raw material containing the waste raw material and pulverized coal, A method for producing solid fuel according to any one of [1] to [3], wherein the heating step involves introducing the mixed raw materials into the heating furnace. [5] A method for producing solid fuel according to any one of [1] to [4], wherein the mass ratio of the pulverized coal to the waste raw material is 1.0 or less. [6] A method for producing solid fuel according to any one of [1] to [5], wherein the average particle size of the heat-treated product obtained in the heating step is 3.0 mm or less. [7] A method for producing solid fuel according to any one of [1] to [6], wherein the maximum particle size of the waste material is less than 50 mm.

[0038] This disclosure is not limited to the embodiments described above. [Examples]

[0039] The contents of this disclosure will be explained in more detail below with reference to examples and comparative examples. However, this disclosure is not limited to the following examples.

[0040] Shredder dust obtained from the market was crushed using a crusher to obtain waste material (particle size: less than 22 mm). The components of this waste material, determined by manual sorting, are shown in Table 1. Four types of crushed pulverized coal (commercial products) were prepared. Industrial analysis of each pulverized coal was performed in accordance with JIS M 8812:2004. The results are shown in Tables 2 and 3.

[0041] [Table 1]

[0042] [Table 2]

[0043] (Example 1) A mixed raw material was prepared by mixing the waste raw materials shown in Table 1 and pulverized coal A shown in Table 2 in a 1:1 mass ratio. This mixed raw material was introduced into a heating furnace equipped with a lifter blade and heated while an inert gas was circulated. The heating rate was increased from room temperature to 200°C at a rate of 6°C / min, and from 200°C to 320°C at a rate of approximately 2°C / min. The rotation speed of the heating furnace was set to 1.9 rpm. The waste plastic contained in the mixed raw material melted and was thermally decomposed, and the furnace temperature reached 350°C. After holding for 1 hour, heating was stopped and the material was allowed to cool, and the heat-treated material was removed from the heating furnace. In this way, the solid fuel (heat-treated material) of Example 1 was obtained.

[0044] The particle size distribution of the solid fuel was investigated using a sieve. As described above, the mass ratios were determined for each of the seven particle size ranges: less than 1.0 mm, 1.0 mm to less than 2.0 mm, 2.0 mm to less than 2.8 mm, 2.8 mm to less than 4.7 mm, 4.7 mm to less than 9.5 mm, 9.5 mm to less than 16 mm, and 16 mm or larger. The median value of each particle size range was assumed to represent the mass ratio within that range, and seven data points were obtained. For the particle size ranges of less than 1.0 mm and 16 mm or larger, the respective mass ratios were assumed to represent particle sizes of 1.0 mm and 16 mm, respectively. Figure 2 shows the particle size distribution created based on the seven data points. Using these seven data points, a quadratic function was found that yielded the correlation coefficient (r) closest to 1, and based on this quadratic function, the particle size at which the cumulative mass percentage from the smallest particle size side reached 50% by mass was defined as the average particle size (Dp50). The results are shown in Table 3.

[0045] (Example 2, Comparative Example 1) Solid fuel (heat-treated material) was obtained in the same manner as in Example 1, except that pulverized coal shown in Table 3 was used instead of pulverized coal A. The particle size distribution and average particle size (Dp50) were determined in the same manner as in Example 1. The results are shown in Figure 2 and Table 3.

[0046] (Comparative Example 2) As waste material (particle size: less than 50 mm), container recycling residue obtained from the market was prepared. Solid fuel (heat-treated material) was obtained in the same manner as in Example 1, except that this container recycling residue was used as waste material and the pulverized coal shown in Table 3 was used. The particle size distribution and average particle size (Dp50) were determined in the same manner as in Example 1. The results are shown in Table 3.

[0047] [Table 3]

[0048] Figure 3 shows photographs of the solid fuel from Example 1 (A), Example 2 (B), and Comparative Example 1 (C) in (A). These photographs confirm that the solid fuels from Examples 1 and 2 have a lower proportion of coarse particles than the solid fuel from Comparative Example 1. Figure 4 shows a graph plotting the results from Table 3 with the fixed carbon of pulverized coal on the horizontal axis and the average particle size (Dp50) of the solid fuel on the vertical axis. From the results shown in Table 3, Figure 3, and Figure 4, it was confirmed that using pulverized coal with a low fixed carbon content results in a solid fuel with a smaller average particle size.

[0049] The yields of the solid fuels (heat-treated products) for Examples 1 and 2 and Comparative Example 1 were calculated using the following formula. As a result, the yields were 85.1% by mass for Example 1, 86.6% by mass for Example 2, and 85.6% by mass for Comparative Example 1. Thus, it was confirmed that a lower volatile content resulted in a higher yield. Yield (mass%) = Mass of solid fuel × 100 / Mass of mixed raw materials introduced into the furnace [Explanation of symbols]

[0050] 10...Rotary kiln, 12...Kiln body, 14...Outer cylinder, 15,16...Rollers, 17...Hot gas flow path, 21...Gas inlet, 22...Gas outlet, 30...Outlet section, 32...Outlet section, 40...Cooler, 50...Inlet section, 51...Raw material, 53...Heated product, 100...Manufacturing equipment.

Claims

1. A method for producing a solid fuel, comprising a heating step of introducing waste raw materials including waste plastic and pulverized coal into a heating furnace and heating them to thermally decompose at least a portion of the waste plastic, A method for producing solid fuel, wherein the fixed carbon content of the pulverized coal is 50% or less and the volatile content is 40% or less.

2. The method for producing a solid fuel according to claim 1, wherein the ash content of the pulverized coal is 22% or less.

3. A method for producing solid fuel according to claim 1 or 2, wherein the content of hard plastic in the waste raw material is 10% by mass or more.

4. Prior to the heating step, there is a mixing step of preparing a mixed raw material containing the waste raw material and the pulverized coal, The method for producing solid fuel according to claim 1 or 2, wherein the heating step involves introducing the mixed raw materials into the heating furnace.

5. A method for producing solid fuel according to claim 1 or 2, wherein the mass ratio of the pulverized coal to the waste raw material is 1.0 or less.

6. A method for producing solid fuel according to claim 1 or 2, wherein the average particle size of the heat-treated product obtained in the heating step is 3.0 mm or less.

7. A method for producing solid fuel according to claim 1 or 2, wherein the maximum particle size of the waste material is less than 50 mm.

Images