Coal making method

Abstract

To provide a method for producing charcoal which can be suitably used for carbonization treatment of wood pellets.SOLUTION: A coal making method includes at least an accommodating step of accommodating, in a coal making container, a heating element that generates heat at 900 °C or higher by being irradiated with microwaves, a material to be carbonized, and a heat storage layer that encloses the material to be carbonized, a sealing step of sealing the coal making container, and a microwave irradiation step of raising the temperature of the material to be carbonized to a target carbonization temperature by irradiating the heating element with microwaves.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a charcoal production method that can be suitably used for carbonizing wood pellets and the like. [Background technology]

[0002] Biomass power generation, which involves co-firing biomass, a renewable energy source, with coal, is gaining attention in order to reduce CO2 emissions from coal-fired power generation. Biomass power generation can contribute to solving global issues such as preventing global warming and creating a recycling-oriented society, while utilizing existing coal-fired power generation facilities. Wood pellets used in biomass power generation are made by pulverizing and compressing thinnings, bark, sawdust, etc. from forests into pellets.

[0003] To produce carbonized pellets by completely carbonizing wood pellets, heat treatment at least 900°C or higher in an oxygen-free atmosphere is required. In contrast, black pellets, which are produced by semi-carbonizing wood pellets, are produced by a process called torrefaction, which involves heat treatment at 250 to 300°C in an oxygen-free atmosphere. Black pellets are becoming the mainstream solid fuel for biomass power generation because they can significantly reduce the cost of carbonization compared to carbonized pellets and have a higher calorific value and better crushability compared to regular uncarbonized wood pellets. Black pellets currently in practical use have a calorific value of 6,800 to 8,000 kcal / kg and can be co-fired with coal at a maximum of 35% (Non-Patent Document 1).

[0004] However, as the global trend of withdrawing from the coal business gains momentum, there is a desire to exclusively use biomass, and there is an urgent need to develop a charcoal production method that can produce carbonized pellets with high calorific value more efficiently and cheaply.

[0005] Conventionally, a technique for carbonizing wood pellets by microwave heating has been known as a method for carbonizing wood pellets. For example, Patent Document 1 discloses a semi-carbonization process for biomass in which the furnace walls of a heating furnace are configured from the inside to the outside with a microwave absorbing layer, a microwave transmitting layer, and a microwave reflecting layer in that order, thereby internally heating the biomass by microwave irradiation and externally heating the biomass by heat transfer from the microwave absorbing layer. However, the method of Patent Document 1 can heat the biomass until the moisture contained therein evaporates, but has the problem that once the moisture is gone, heating by microwave irradiation becomes impossible and carbonization does not proceed.

[0006] Furthermore, Patent Document 2 discloses a technology for irradiating a molded product made by mixing plant biomass with powdered coal, graphite, etc., with microwaves to heat treat the product to a desired degree, such as uncarbonized, blackened, or white carbonized. However, with the method of Patent Document 2, high-temperature gases such as tar generated from wood pellets adhere to the inner wall surface of the microwave generator housing, which is at near-room temperature, necessitating periodic cleaning and maintenance of the device, leaving room for improvement in productivity. Furthermore, it is difficult to irradiate a large amount of wood pellets with microwaves uniformly, which makes mass production difficult.

[0007] Non-Patent Document 2 discloses a carbonization technology that uses highly controlled microwaves from a semiconductor microwave oscillator to transmit microwave energy directly to the biomass without using a heat transfer medium, thereby ultra-rapidly raising the temperature of biomass raw material (rice straw) at a maximum of 330°C per second. However, semiconductor microwave oscillators are much more expensive than magnetron types, and have the drawback of only being able to carbonize small amounts at a time due to the small size of the furnace body. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 7292626 [Patent Document 2] Patent No. 5474236 [Non-patent literature]

[0009] [Non-Patent Document 1] Idemitsu Kosan Co., Ltd. news release, "Construction of a commercial manufacturing plant for black pellets (product name: 'Idemitsu Green Energy Pellets') in Vietnam, contributing to CO2 reductions for Japanese coal consumers. Expanding black pellet supply bases to reach annual production of 300,000 tons within three years," [online], October 21, 2021, [accessed March 3, 2024], Internet (URL: https: / / www.idemitsu.com. / jp / news / 2021 / 211021.html) [Non-patent document 2] Tsubaki, S., and 5 others, Green Chemistry. (English), 2020, 22, 2, p.342-351 Summary of the Invention [Problem to be solved by the invention]

[0010] In view of the above-mentioned drawbacks of conventional microwave carbonization technology, the present invention aims to provide a charcoal production method based on a new concept that can produce carbonized pellets efficiently and inexpensively. [Means for solving the problem]

[0011] In view of the above object, as a result of extensive research, the present inventors have discovered that by encapsulating wood pellets in a heat storage layer containing silicic plant biomass and then irradiating them with microwaves to create a high-temperature state, carbonized pellets that have been carbonized to a desired degree can be produced extremely simply and efficiently, and have arrived at the present invention. That is, the problems of the present invention can be solved by the following configuration.

[0012] The first invention is a charcoal production method that includes at least a storage step of storing a heating element that generates heat of 900°C or higher when irradiated with microwaves, the material to be produced, and a heat storage layer that encapsulates the material to be produced inside a charcoal production vessel; a sealing step of sealing the charcoal production vessel; and a microwave irradiation step of irradiating microwaves to cause the heating element to generate heat, thereby raising the temperature of the material to a target carbonization temperature or higher, wherein the heat storage layer contains silica plant biomass.

[0013] A second aspect of the present invention is a charcoal production method, wherein the silicic acid plant biomass is rice husk or buckwheat husk.

[0014] The third invention of the present invention is a charcoal production method, wherein the heating element is a sintered body containing a residue of incineration of a silicic acid plant.

[0015] A fourth aspect of the present invention is a charcoal production method, wherein the material to be produced into carbon is a molded product obtained by compressing and molding a powdered raw material derived from a plant.

[0016] A fifth aspect of the present invention is a charcoal production method, wherein the material to be produced into carbon is wood pellets.

[0017] A sixth aspect of the present invention is a charcoal production method, characterized in that in the microwave irradiation step, the target carbonization temperature is 1000°C or higher. [Effects of the Invention]

[0018] According to the first aspect of the present invention, carbonized pellets can be produced extremely easily by rapidly raising the internal temperature of a charcoal-making vessel using a heating element capable of rapidly raising the temperature by microwave irradiation. As the material to be produced reaches the target carbonization temperature, the oxygen in the charcoal-making vessel is rapidly consumed by combustion, creating an oxygen-free atmosphere inside the sealed charcoal-making vessel. By enveloping the material to be produced in siliceous plant biomass, it becomes possible to carbonize the wood pellets to the desired degree in a short time after microwave irradiation. Furthermore, because siliceous plant biomass adsorbs wood gas components generated from the wood pellets, the charcoal-making vessel and equipment are less likely to become dirty and are easier to maintain.

[0019] According to the second invention, by using rice husks or buckwheat husks as silicic plant biomass, which are readily available and in the form of fine particles and easy to handle, the cost of charcoal production can be reduced.

[0020] According to the third aspect of the present invention, by using a sintered body containing silicic acid plant incineration residue as a heating element, it is possible to raise the temperature to the target carbonization temperature in a short time. The sintered body containing silicic acid plant incineration residue has stable heat generation performance and can be easily removed from the heat storage layer after carbonization, so it can be used repeatedly as a heating element.

[0021] According to the fourth aspect of the present invention, it is possible to carbonize a compact obtained by compressing and molding a powdered raw material derived from a plant. A compact obtained by compressing and molding a powdered raw material derived from a plant is a carbonized material that is difficult to carbonize using conventional microwave irradiation methods, but by applying the present invention, a carbonized or semi-carbonized product can be produced easily and in a short time.

[0022] According to the fifth aspect of the present invention, by using wood pellets as the material to be carbonized, carbonized pellets or semi-carbonized pellets can be produced easily and in a short time.

[0023] According to the sixth aspect of the present invention, by raising the temperature of the material to be carbonized to 1000°C or higher in the microwave irradiation step, it is possible to obtain a high-quality carbonized material having a calorific value close to that of binchotan charcoal. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a flowchart illustrating the charcoal production method of the present invention. [Figure 2] 1 is a schematic cross-sectional view illustrating a charcoal production method according to a first embodiment of the present invention. [Figure 3] 1 is a schematic cross-sectional view of a microwave irradiation device 50 equipped with a forced ventilation device used in the charcoal production method of the present invention. [Figure 4A] 1 is a schematic cross-sectional view illustrating a storage step in a charcoal production method according to a first embodiment of the present invention. FIG. [Figure 4B] 1 is a schematic cross-sectional view illustrating a storage step in a charcoal production method according to a first embodiment of the present invention. FIG. [Figure 4C] 2 is a cross-sectional view along the line AA illustrating the accommodation step in the charcoal production method according to the first embodiment of the present invention. FIG. [Figure 4D] 1 is a schematic cross-sectional view illustrating a storage step in a charcoal production method according to a first embodiment of the present invention. FIG. [Figure 4E] FIG. 2 is a schematic cross-sectional view illustrating a sealing step in the charcoal production method according to the first embodiment of the present invention. [Figure 4F] FIG. 2 is a schematic cross-sectional view illustrating a microwave irradiation step in the charcoal production method according to the first embodiment of the present invention. [Figure 5] 1 is a graph showing the temperature change of the material to be made into carbon in the carbonization method of the present invention. [Figure 6] FIG. 2 is a schematic cross-sectional view illustrating a charcoal production method according to a second embodiment of the present invention. [Figure 7] FIG. 4 is a schematic cross-sectional view illustrating a charcoal production method according to a third embodiment of the present invention. [Figure 8] FIG. 10 is a schematic cross-sectional view of a microwave irradiation device used in a charcoal production method according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0025] The charcoal production method according to the present invention will be described in detail below with reference to the drawings. Fig. 1 shows a flowchart of the charcoal production method according to the present invention, and Fig. 2 shows a schematic cross-sectional view for explaining the charcoal production method according to a first embodiment of the present invention. In the following description of this embodiment, the same reference numerals are used for the same components, and repeated explanations will be omitted.

[0026] First, in the accommodation step, the heating element 20, the material to be made into carbon 30 such as wood pellets, and silica plant biomass as the heat storage layer 40 are accommodated inside the charcoal making vessel 10 (step S1). Next, in the sealing step, the charcoal making vessel 10 is sealed with the lid 11 or an openable door (step S2). Then, the sealed charcoal making vessel 10 is stored in a microwave irradiation device 50 equipped with a microwave oscillator 51.

[0027] In the microwave irradiation process, microwaves generated from the microwave oscillator 51 are irradiated toward the heating element 20 inside the charcoal making vessel 10 (step S3). Microwaves are irradiated from the outside of the charcoal making vessel 10 to cause the heating element 20 to generate heat, and when the temperature of the material to be made into carbon 30 reaches the target charcoal making temperature (250°C or higher and 1300°C or lower), microwave irradiation is terminated. After the microwave irradiation is stopped, in the subsequent holding process, the charcoal making vessel 10 is held inside the microwave oscillator 51 to promote carbonization of the material to be made into carbon 30, and the material to be made into carbon 30 is carbonized to the desired level (step S4).

[0028] Next, in the cooling process, the charcoal making vessel 10 is removed from the microwave irradiation device 50, and the charcoal making vessel 10 is allowed to dissipate heat (step S5). After the charcoal making vessel 10 has cooled to a temperature that allows it to be handled, the heating element 20, the carbonized material to be made into charcoal 30, and the heat storage layer 40 are removed from the charcoal making vessel 10, and these are sieved to remove the heating element 20 and the heat storage layer 40, thereby recovering the carbonized material to be made into charcoal 30 (step S6).

[0029] (charcoal making container) The charcoal making vessel 10 used in the present invention can be any known vessel, without any particular limitations, as long as it is made of a material that is microwave-transparent and heat-resistant. Earthenware, pottery, porcelain, etc. are preferably used as such a charcoal making vessel. The shape of the charcoal making vessel is not particularly limited, as long as it can accommodate a heating element and the material to be made into charcoal, and can be sealed with a lid or an openable door, etc., and a container shaped like a box, a pot, etc. can be used.

[0030] (heating element) The heating element 20 used in the present invention is a heating element that can be rapidly heated to 900° C. or higher by microwave irradiation. Any known heating element can be used without any particular limitation as long as it has such rapid temperature-raising performance.

[0031] The heating element 20 is preferably a heating element that reaches 900°C or higher within 2 minutes when irradiated with microwaves in the 2.45 GHz band. It is more preferable that the heating element 20 can be heated to 1200°C or higher, and particularly preferably to 1500°C or higher, when irradiated with microwaves.

[0032] Specific examples of microwave-absorbing heat transfer media to be used in such heating element 20 include (1) lump carbon such as black charcoal, white charcoal, and binchotan charcoal, (2) carbon powder made by crushing lump carbon, (3) carbon powder mixed with conductive metal powder or ferrite, and (4) residues of silicic acid plant incineration.

[0033] In this specification, "silicic acid plant incineration residue" refers to the incineration residue obtained by incinerating almost all of the organic combustible material by subjecting biomass from silicic acid plants, such as rice husks, buckwheat husks, rice straw, wheat straw, bamboo, bagasse, and coconut shells, to self-combustion at high temperatures of 1000°C to 2000°C for a long period of time. Silicic acid plant incineration residue is primarily composed of silicon dioxide, and contains trace amounts of carbon and metal elements, and has the property of repeatedly and rapidly increasing in temperature when irradiated with microwaves.

[0034] It is believed that the reason why silica plant incineration residues exhibit this unique heat generation phenomenon is because the small amounts of carbon and metal elements contained in the residues cause induction heating and dielectric heating when exposed to microwaves.

[0035] In the present invention, the silicic acid plant incineration residue is preferably used as the microwave-absorbing heat transfer medium for the heating element 20. Conventional carbon loses its carbon element content through combustion when exposed to temperatures exceeding 900°C for extended periods, making it difficult for its heat-generating performance to stabilize. However, the carbon element contained in silicic acid plant incineration residue reduces its carbon element content even at temperatures above 900°C, ensuring stable heat-generating performance. Furthermore, conventional conductive metal powders, particularly active metals, have variable heat-generating rates due to high-temperature oxidation. Iron, for example, undergoes structural changes around 800°C, which alter its magnetic properties, making it difficult to dielectrically heat and significantly affecting its heat-generating rate. However, the metal elements contained in silicic acid plant incineration residue are stable and undergo minimal structural changes, allowing for repeated stable heat-generating performance.

[0036] The composition ratio of silicon dioxide, carbon, and metal elements contained in silicic acid plant incineration residue varies depending on the incineration conditions, the type, variety, and origin of the silicic acid plant used as raw material, but the silicon dioxide content is essentially in the range of 50 wt% to 96 wt%. The carbon content in silicic acid plant incineration residue is in the range of 0.1 wt% to 30 wt%. Metal elements contained in silicic acid plant incineration residue include potassium, magnesium, calcium, iron, aluminum, sodium, manganese, zinc, chromium, titanium, and nickel, and it is estimated that some or all of these metals exist as metal oxides. The metal element content in silicic acid plant incineration residue is in the range of 0.1 wt% to 49 wt%.

[0037] The incineration residue of silicic acid plants is an aggregate of fine particles with an average particle size of about 10 μm to 10 mm, but since it is difficult to handle in its fine particle form, it is preferable to process it into a form that is easy to handle before use. Specifically, it is preferable to form a sintered body consisting of the incineration residue of silicic acid plants and ceramic particles, or to form a molded body by wrapping the incineration residue of silicic acid plants in ceramic, and use this as the heating element 20.

[0038] By forming the silicic acid plant incineration residue into a sintered body made of ceramic particles, the carbon elements, metal elements, and other components contained in the silicic acid plant incineration residue can be covered and protected so that they are not directly exposed to the outside world. This makes it possible to prevent the carbon elements and metal elements in the silicic acid plant incineration residue from being oxidized by oxygen and degraded when the silicic acid plant incineration residue is repeatedly heated and cooled by microwave irradiation, thereby improving the durability of the heating element 20.

[0039] A particularly preferred heating element 20, a sintered body made of silicic acid plant incineration residue and ceramic particles, will now be described. The ceramic particles in the sintered body made of silicic acid plant incineration residue and ceramic particles melt during sintering. The silicic acid plant incineration residue and the ceramic particles mix and bond to each other, resulting in a stable sintered body. Specific examples of ceramic particles that can be used include soda-lime glass, borosilicate glass, lead glass, and quartz glass. The type of ceramic particles, average particle size, and mixing ratio of the silicic acid plant incineration residue and the ceramic particles can be adjusted appropriately to ensure rapid temperature rise by microwave irradiation.

[0040] A sintered body composed of silicic acid plant incineration residue and ceramic particles preferably contains 5 wt% to 50 wt% of silicic acid plant incineration residue in the sintered body. A content of less than 5 wt% of silicic acid plant incineration residue may result in insufficient heat generation performance, while a content of more than 50 wt% is undesirable because the sintered body may become brittle. In the present invention, the content of silicic acid plant incineration residue in the sintered body is more preferably 20 wt% to 40 wt%. Two or more types of silicic acid plant incineration residue may also be used in combination.

[0041] Furthermore, the sintered body consisting of silicic acid plant incineration residue and ceramic particles preferably contains 1 wt% or more of carbon elements derived from the silicic acid plant incineration residue, and more preferably contains 2 wt% or more and 20 wt% or less of carbon elements derived from the silicic acid plant incineration residue.

[0042] Furthermore, a sintered body consisting of silica plant incineration residue and ceramic particles preferably contains 0.1 wt% or more, and more preferably 0.5 wt% or more and 3.0 wt% or less, in terms of the total weight when metal elements derived from the silica plant incineration residue are replaced with metal oxides.

[0043] The shape and size of the sintered body made of silicic acid plant incineration residue and ceramic particles are not particularly limited, but from the standpoint of ease of handling, it is preferable to mold the sintered body into a size of 10 g or more and 200 g or less.

[0044] (charcoal-making material) The material to be produced 30 used in the charcoal production method of the present invention can be any plant-derived biomass without any particular limitations. Examples of plant-derived biomass that constitute the material to be produced 30 include woody biomass such as sawmill residues, construction waste wood, and unused thinned wood, as well as agricultural waste such as grass clippings, rice husks, buckwheat husks, rice straw, wheat straw, bamboo, bagasse, and coconut shells. These biomass materials may or may not be crushed or dried. Furthermore, powdered raw materials derived from these biomass materials can be compressed and molded into wood pellets or artificial logs (ogalite).

[0045] (heat storage layer) The heat storage layer 40 contains silicic plant biomass. The silicic plant biomass is at least one type of biomass selected from rice husks, buckwheat husks, rice straw, wheat straw, bamboo, bagasse, coconut shells, and the like.

[0046] The siliceous plant biomass is preferably in the form of small pieces or particles. From the viewpoint of ease of storage in the charcoal-making container 10, particles with an average particle size of 10 mm or less are preferred, and particles with a particle size of 0.1 mm to 5 mm are more preferred. Siliceous plant biomass that is originally particulate, such as rice husks and buckwheat husks, can be used as is in the heat storage layer 40. Siliceous plant biomass that is not in the form of fine particles, such as rice straw, wheat straw, bamboo, bagasse, and coconut shells, is preferably crushed into small pieces before use. Among these, rice husks and buckwheat husks are preferred from the viewpoints of ease of handling and availability. Approximately 70 to 90% by mass of rice husks and buckwheat husks are organic components, primarily cellulose, and the remaining approximately 10 to 30% by mass is inorganic components. The inorganic components are primarily silicon dioxide (silica), with trace amounts of mineral components.

[0047] Within the charcoal making vessel 10, the heat storage layer 40 is formed so as to enclose the material to be made into carbon dioxide 30. As long as the heat storage layer 40 can sufficiently ensure heat storage capacity, it is not necessary for the entire surface of the material to be made into carbon dioxide 30 to be enclosed by the heat storage layer 40, and a portion of the surface of the material to be made into carbon dioxide 30 may not be enclosed by the heat storage layer 40. For example, as shown in Figure 2, it is not a problem if the side and top surfaces of the material to be made into carbon dioxide 30 are enclosed by the heat storage layer 40, but the bottom surface of the material to be made into carbon dioxide 30 is not enclosed by the heat storage layer 40. It is preferable that the remaining voids within the charcoal making vessel 10 are filled without any gaps with the heat storage layer 40.

[0048] In the charcoal production method of the present invention, when the heat storage layer 40 is heated by microwave irradiation, the organic combustible material in the silicic acid plant biomass contained in the heat storage layer 40 is almost entirely incinerated and carbonized. When the temperature of the heat storage layer 40 exceeds 1000°C due to microwave irradiation, the silicic acid plant biomass becomes a silicic acid plant incineration residue. This silicic acid plant incineration residue not only has excellent heat storage properties, but also functions as heat-generating fine particles when irradiated with microwaves.

[0049] When the silica plant biomass contained in the thermal storage layer 40 is carbonized or converted into silica plant incineration residue, the volume of the thermal storage layer 40 decreases significantly. The rate of change in the volume of the thermal storage layer 40 varies depending on the type of silica plant biomass and the degree of carbonization, but the volume after the charcoal production process usually decreases to 1 / 3 to 1 / 10 of the volume before the charcoal production process.

[0050] In the charcoal production method of the present invention, microwave irradiation causes wood gas components generated from the material to be produced 30 to permeate the gaps in the silica plant biomass in the heat storage layer 40, and during the cooling process, they are adsorbed onto the surface of the silica plant biomass as wood tar.

[0051] In addition to silicate plant biomass, the thermal storage layer 40 may contain additives to the extent that the object of the present invention is not impaired. Examples of additives include carbonized silicate plant biomass and silicate plant incineration residue, which are obtained as by-products of the present invention. In this case, the carbonized silicate plant biomass and silicate plant incineration residue may have wood tar adsorbed on their surfaces. Furthermore, inorganic fillers such as silica sand may be mixed in the thermal storage layer 40 to increase its bulk. When an inorganic filler is used in the thermal storage layer 40, the average particle size of the inorganic filler is preferably 10 μm or more and 5 mm or less.

[0052] In the present invention, the content of siliceous plant biomass in the thermal storage layer 40 is 10 wt% or more. The content of siliceous plant biomass is preferably 50 wt% or more, more preferably 80 wt% or more, and even more preferably 90 wt% or more. From the viewpoint of efficiently treating siliceous plant biomass, which is agricultural waste, the content of siliceous plant biomass is most preferably 100 wt%.

[0053] In the present invention, the volume ratio of the heat storage layer 40 to the carbonization material 30 is preferably in the range of 75:25 to 99:1 before being placed in the charcoal making vessel 10. By setting the volume ratio of the heat storage layer 40 to the carbonization material 30 to 75:25 to 99:1, it is possible to maintain a sufficient thickness of the heat storage layer even after the silicic acid plant biomass is carbonized. A volume ratio of the heat storage layer 40 of less than 75% is not preferable because it may not ensure sufficient heat storage performance. Furthermore, wood tar that is not completely adsorbed by the heat storage layer 40 may adhere to the charcoal making vessel 10, making cleaning the charcoal making vessel more complicated. The volume ratio of the heat storage layer 40 to the carbonization material 30 is more preferably 80:20 to 95:5, and particularly preferably 85:15 to 90:10.

[0054] (Microwave irradiation device) 2, the microwave irradiation device 50 includes a microwave oscillator 51 and a heat-resistant, casing-shaped microwave reflecting container 52. The microwave oscillator 51 can be any known microwave oscillator, such as a magnetron type, a klystron type, a gyrotron type, a traveling wave tube (TWT) type, or a semiconductor type, without any particular limitation.

[0055] The frequency band of the microwaves generated by microwave oscillator 51 is not particularly limited as long as it can apply enough energy to rapidly heat heating element 20 to 900°C or higher, but from the viewpoint of cost, it is preferable to use the 2.45 GHz band, which is used in many commercially available magnetron microwave ovens. In the example of a commercially available microwave oven shown in Figure 2, microwave irradiation port 51A of microwave oscillator 51 is arranged on the side wall of microwave reflecting container 52, and is configured to oscillate microwaves toward the center of the bottom inside reflecting container 52.

[0056] In the present invention, in order to prevent contamination of microwave radiation port 51A by wood gas, it is preferable to provide microwave radiation device 50 with forced ventilation device 53. Figure 3 shows a schematic diagram of microwave radiation device 50 equipped with forced ventilation device 53.

[0057] The forced ventilation device 53 serves to exhaust wood gas generated during the microwave irradiation process and the holding process from the internal space of the microwave reflecting container 52. The forced ventilation device 53 is composed of an inlet pipe 54, an outlet pipe 55, an exhaust gas supply blower 56, and a smoke exhaust blower 57.

[0058] Nitrogen gas is preferred as the exhaust gas supplied by the forced ventilation device 53. By using nitrogen gas, oxygen can be prevented from entering the charcoal making vessel 20, and an oxygen-free atmosphere suitable for charcoal making can be maintained inside the charcoal making vessel 20. In the present invention, in order to prevent a sudden drop in the indoor temperature of the microwave reflecting vessel 52, it is preferred to supply nitrogen gas heated to approximately the same temperature as the indoor temperature of the microwave reflecting vessel 52.

[0059] The inlet pipe 54 is a hollow pipe that supplies nitrogen gas to the internal space of the microwave reflecting container 52. As shown in Fig. 3, the inlet of the inlet pipe 54 is preferably disposed on the bottom surface of the microwave reflecting container 52 so that the nitrogen gas can be supplied from below upward, and it is particularly preferable to provide the inlet near the microwave irradiation port 51A. By ejecting high-temperature nitrogen gas from below upward near the microwave irradiation port 51A, contamination of the microwave irradiation port 51A by wood gas can be effectively prevented.

[0060] The outflow pipe 55 is a hollow pipe that discharges gas remaining in the internal space of the microwave reflecting container 52. The outlet of the outflow pipe 55 may be provided at a position where the gas remaining can be discharged. For example, an outlet extending horizontally may be provided at the upper part of the side surface of the microwave reflecting container 52.

[0061] The exhaust gas containing wood gas components discharged from the outlet pipe 55 can be used as a combustible gas fuel. Alternatively, nitrogen gas heated using the waste heat of the exhaust gas may be supplied from the inlet pipe 54 to the internal space of the microwave reflecting container 52.

[0062] First Embodiment In the first embodiment, the heating element 20 is a sintered body made of silica plant incineration residue and ceramic particles, the carbonization material 30 is made of an aggregate of wood pellets (wood pellet group), and the heat storage layer 40 is made of rice husks.

[0063] (Storage process) In the accommodation step (step S1), the heating element 20, the material to be made into carbon 30, and the heat storage layer 40 are accommodated inside the charcoal making container 10. As shown in Fig. 2, the heating element 20 is enclosed by the material to be made into carbon 30 (wood pellets), and the material to be made into carbon 30 is enclosed by the heat storage layer 40 (rice husks).

[0064] 4A to 4E show the installation procedure. First, as shown in Fig. 4A, the heating element 20 is placed at the center of the bottom of the charcoal making vessel 10, and the cylindrical partition wall 12 is placed so as to surround the heating element 20.

[0065] Next, as shown in Fig. 4B, wood pellets are poured inside the partition wall 12, and rice husks are poured outside the partition wall 12. Fig. 4C is a cross-sectional view taken along line AA in Fig. 4B. As shown in Fig. 4C, the group of wood pellets, which are the material to be made into carbon 30, encloses the heating element 20, with the heating element 20 at the center, and the heat storage layer 40 surrounds the material to be made into carbon 30 via the partition wall 12.

[0066] After removing the partition 12 from the charcoal making vessel 10, rice husks are poured into the charcoal making vessel 10 up to the opening end thereof, as shown in Figure 4D, so that the sides and top of the charcoal making material 30 are enclosed by the heat storage layer 40.

[0067] When microwave irradiation carbonizes the silicate plant biomass or converts it into silicate plant incineration residue, the volume of the heat storage layer 40 decreases significantly. To ensure sufficient heat storage capacity even after the silicate plant biomass is carbonized or converted into silicate plant incineration residue, the thickness h of the heat storage layer 40 formed on the upper surface of the carbon-making material 30 in Fig. 4D is preferably 5 cm or more, and more preferably 10 cm or more.

[0068] (Sealing process) After placing the heating element 20, the material to be made into carbon dioxide 30, and the heat storage layer 40 inside the charcoal making vessel 10, the opening of the charcoal making vessel 10 is sealed with the lid 11, as shown in FIG. 4E. The lid 11 is necessary to maintain an oxygen-free atmosphere inside the charcoal making vessel 10. In the present invention, the charcoal making vessel 10 does not require a high level of airtightness; therefore, the lid 11 need only be placed on the opening of the charcoal making vessel 10; there is no need to seal the lid 11. Conversely, if the charcoal making vessel 10 is too airtight, the charcoal making vessel 10 is prone to damage due to microwave irradiation, which is undesirable. In other words, it is preferable to seal the charcoal making vessel 10 so that the internal pressure of the charcoal making vessel 10 is always kept at approximately the same level as the ambient air pressure by allowing air inside the charcoal making vessel 10 to leak out when the inside of the charcoal making vessel 10 is under positive pressure, and allowing outside air to flow in when the inside of the charcoal making vessel 10 is under negative pressure.

[0069] (Microwave irradiation process) As shown in FIG. 2, the sealed charcoal making vessel 10 is housed in a microwave irradiation device 50, and microwaves generated from a microwave oscillator 51 are irradiated toward the heating element 20 inside the charcoal making vessel 10.

[0070] As shown in Figure 4F, microwave irradiation carbonizes the carbon material 30 into carbonized pellets. At temperatures above 1000°C, the organic combustible material in the silica plant biomass contained in the heat storage layer 40 is almost entirely incinerated, resulting in silica plant incineration residue.

[0071] FIG. 5 shows an example of the temperature change of the carbonization material 30. The thermal energy generated by the heating element 20 upon absorbing microwaves causes the temperature of the carbonization material 30 (here, an aggregate of wood pellets) to rise rapidly. Carbonization of the wood pellets begins at the portion in contact with the high-temperature heating element 20, and the reaction heat propagates and spreads rapidly to the surrounding wood pellets and the heat storage layer 40. In the present invention, the carbonization material 30 is enclosed by the heat storage layer 40, so the temperature of the carbonization material 30 rises rapidly.

[0072] 5, when a sintered body made of silicic acid plant incineration residue and ceramic particles is used as the heating element 20, the temperature of the heating element 20 easily reaches 1500°C or higher in about 10 seconds to 2 minutes after the start of microwave irradiation, and the temperature of the surrounding carbonization material 30 also reaches 1200°C or higher in about 15 minutes to 1 hour. The microwave irradiation time can be set appropriately depending on the materials, shapes, arrangements, etc. of the heating element 20 and the carbonization material 30.

[0073] Once it is confirmed that the temperature of the carbonized material 30 has reached the target carbonization temperature, microwave irradiation is stopped. The target carbonization temperature may be set appropriately depending on the purpose. For example, if the carbonized material 30 is to be semi-carbonized, the target carbonization temperature is 250°C or higher and 400°C or lower; if the carbonized material is to be blackened, the target carbonization temperature is 400°C or higher and 700°C or lower; and if the carbonized material is to be whitened, the target carbonization temperature is set to 1000°C or higher.

[0074] Whether the temperature of the material 30 to be carbonized has reached the target carbonization temperature can be confirmed with a thermometer. Alternatively, a wood gas detection means for detecting wood gas emitted by the carbonization reaction may be provided inside the microwave reflecting container 52, and the detection of wood gas by the wood gas detection means can be used to indirectly determine that the material 30 to be carbonized has reached the carbonization temperature. Examples of wood gas detection means include a semiconductor gas sensor and high-speed gas chromatography.

[0075] Furthermore, if the inside of the microwave reflecting container 52 can be visually inspected, it may be determined that the carbonization of the carbonized material 30 has been completed (the target carbonization temperature has been reached) based on the decrease in the amount of black smoke (wood gas) generated.

[0076] In the present invention, after microwave irradiation is stopped, it is preferable to hold the carbonization vessel 10 in the microwave reflecting vessel 52 to sufficiently advance the carbonization reaction of the carbonization material 30 and carbonize the carbonization material 30. The holding time is preferably 15 minutes or more, more preferably 1 hour or more.

[0077] After microwave irradiation is completed, the carbonization reaction of the material 30 to be made into carbon progresses inside the charcoal making vessel 10, and wood gas continues to be discharged. If the microwave irradiating device 50 is equipped with a forced ventilation device 53, it is preferable to operate the forced ventilation device 53 during the holding step to continue discharging wood gas.

[0078] After the holding step is completed, the charcoal making vessel 10 is removed from the microwave irradiation device 50 and allowed to cool naturally. Finally, the heating element 20, the carbonized material to be made into charcoal 30, and the heat storage layer 40 are scraped out from the cooled charcoal making vessel 10, and the carbonized material to be made into charcoal 30 can be recovered by sieving them.

[0079] Second Embodiment Next, a second embodiment of the present invention will be described. The second embodiment differs from the first embodiment in that a large number of wood pellets are dispersed in the thermal storage layer 40, so that each wood pellet (material to be made into carbon 30) is enclosed by the thermal storage layer 40. In other respects, the second embodiment has a similar configuration to the first embodiment. In this way, when the material to be made into carbon 30 consists of a large number of aggregates, the aggregate consisting of a large number of wood pellets may be treated as a single mass of material to be made into carbon 30, as in the first embodiment, or may be treated as a large number of independent material to be made into carbon 30, as in the second embodiment.

[0080] 6 shows the second embodiment in which the heating element 20, the material to be made into carbon 30 (wood pellets), and the heat storage layer 40 (rice husks) are housed in the charcoal making vessel 10. In the second embodiment, the wood pellets and rice husks are mixed uniformly, and then the mixture is poured into the charcoal making vessel 10 in which the heating element 20 is installed.

[0081] Third Embodiment Next, a third embodiment of the present invention will be described. In the third embodiment, a large amount of wood pellets is produced at one time. The third embodiment differs from the first embodiment in that, in order to produce a large amount of wood pellets, the charcoal production container 10 is enlarged and multiple heating elements 20 are arranged at regular intervals. By placing the material to be produced at a distance of less than 15 cm from the heating elements 20, uneven carbonization can be reduced and the material can be carbonized uniformly. However, if the material to be produced is large in volume or long, making it difficult to fit the entire material to be produced at a distance of less than 15 cm from the heating elements, it is recommended to use multiple heating elements.

[0082] Figure 7 shows the third embodiment in which multiple heating elements 20, carbonization material 30 (wood pellets), and heat storage layer 40 (rice husks) are housed in a charcoal production vessel 10. First, rice husks are spread to a thickness of about 3 cm on the bottom of the charcoal production vessel 10, and then multiple heating elements are placed at intervals of about 20 cm. Next, wood pellets are poured in to bury the heating elements 20, and this group of wood pellets becomes the carbonization material 30. Rice husks are spread to a thickness of about 15 cm on top of the carbonization material 30, forming a heat storage layer 40 that encloses the carbonization material 30 by sandwiching it from above and below.

[0083] 8, the microwave irradiating device 50 has a built-in transport mechanism 60 that can transport the charcoal making container 10 horizontally in one direction. The microwave irradiation port 51A is provided on the top surface of the microwave reflecting container 52, and is configured so that microwaves are irradiated near the center of the transport mechanism 60.

[0084] As the charcoal making container 10 stored in the microwave irradiation device 50 is transported by the conveying mechanism 60, microwaves are sequentially irradiated onto multiple heating elements 20 arranged at regular intervals, thereby carbonizing a large amount of wood pellets.

[0085] The present invention is not limited to the above-described embodiments, and various modifications and equivalents are included within the spirit and scope of the present invention. Furthermore, the structure, shape, number, position, size, etc. of the components shown in each drawing are for the convenience of explanation and may be changed as appropriate.

[0086] As explained above, the charcoal-making method of the present invention makes it possible to inexpensively produce carbonized pellets by utilizing an existing microwave oscillator. The charcoal-making method of the present invention is an innovative method that can easily create a high-temperature atmosphere suitable for charcoal-making by irradiating microwaves to the material to be made while it is enclosed in a heat storage layer made of silica plant biomass.

[0087] The charcoal making method of the present invention eliminates the need for nitrogen atmosphere management, empirical determination of refining, and determination of cooling timing, which have traditionally been performed by skilled charcoal makers, and makes it possible to significantly reduce charcoal making time.

[0088] Furthermore, according to the charcoal production method of the present invention, the heat storage layer made of silica plant biomass adsorbs wood gas components, suppressing the evaporation of wood gas and enabling charcoal production with as little loss of fuel components as possible. Another advantage of the present invention is that the inside of the equipment can be prevented from becoming dirty with wood gas, making the equipment easier to maintain. [Example]

[0089] (Making a heating element) First, rice husks were burned at a combustion temperature of approximately 1800°C for approximately 10 hours to create rice husk incineration residue. Analysis of the rice husk incineration residue revealed that it was composed of 77 wt% silicon dioxide and 8.5 wt% carbon. The total content of metal elements, when replaced with metal oxides, was 6.2 wt%. Metal elements included potassium, magnesium, calcium, iron, aluminum, sodium, manganese, zinc, etc. A wavelength dispersive X-ray fluorescence analyzer was used to analyze the metal elements.

[0090] 10 g of the obtained rice husk incineration residue was mixed with water glass and sintered to prepare a hemispherical sintered body with a diameter of 3 cm. The weight of the obtained sintered body was 33 g. In Example 1, this sintered body was used as a heating element.

[0091] (Charcoal processing) The sintered body was placed at the bottom of a ceramic container with a diameter of 140 mm, a height of 85 mm, and a weight of 725 g, and 100 cc of white pellets and 500 cc of rice husks were placed in the ceramic container in the arrangement shown in Figure 4D.

[0092] The container was sealed with a heat-resistant glass lid, then placed inside a microwave oven and irradiated with 2.45 GHz microwaves using a 700 W magnetron. 15 minutes after the start of microwave irradiation, wood gas was observed to be generated inside the microwave oven. Microwave irradiation was continued, but the amount of wood gas generated decreased 60 minutes after the start of irradiation, so microwave irradiation was stopped and the container was left inside the microwave oven for 60 minutes.

[0093] The container was removed from the microwave oven and cooled to room temperature, after which the contents, which had become a lump, were removed from the container. The removed lump was brittle and easily crumbled when pressed with a finger. The lump was sieved to separate the carbonized pellets, heating element, and rice husk incineration residue. By the carbonization treatment of Example 1, the white pellets were carbonized and turned black, and the rice husk incineration residue had adsorbed wood tar.

[0094] The solid carbon content of the obtained carbonized pellets was 88.7%, a value close to that of Binchotan charcoal. Furthermore, when the calorific value of the obtained carbonized pellets was analyzed in accordance with JIS Z7320-2, the higher calorific value on an anhydrous basis was 7000 (kcal / kg) or more. This confirmed that the white pellets were completely carbonized by the charcoal production method of Example 1. [Example]

[0095] 100cc of white pellets and 500cc of rice husks were mixed and poured into the same ceramic container as in Example 1, and the heating element, white pellets, and rice husks were placed in the arrangement shown in Figure 6. Charcoal production was carried out in the same manner as in Example 1, and wood gas was confirmed to be generated inside the microwave oven 15 minutes after the start of microwave irradiation. Microwave irradiation was continued, and the amount of wood gas generated decreased 60 minutes after the start of irradiation, so microwave irradiation was stopped and the container was left inside the microwave oven for 60 minutes.

[0096] The container was removed from the microwave oven and cooled to room temperature. The contents of the container were then sieved to separate the carbonized pellets, heating element, and rice husk incineration residue. The carbonization treatment in Example 1 resulted in the white pellets turning black, and the rice husk incineration residue adsorbing wood tar. This confirmed that the white pellets could be carbonized even when irradiated with microwaves while dispersed in rice husks. [Industrial Applicability]

[0097] As explained above, the charcoal production method of the present invention is an innovative method that can easily create a high-temperature atmosphere suitable for charcoal production, and can be suitably used not only for carbonized pellets and sawdust charcoal, but also for the carbonization of any type of biomass. [Explanation of symbols]

[0098] 10 Charcoal making vessel 11 Lid 12 Bulkhead 20 Heating element 30 Charcoal products 40 Heat storage layer 50 Microwave irradiation device 51 Microwave Oscillator 51A Microwave irradiation port 52 Microwave Reflection Container 53 Forced ventilation system 54 Inflow pipe 55 Outflow pipe 56 Exhaust gas supply blower 57 Smoke exhaust blower 60 Conveyor mechanism

Claims

1. a step of placing a heating element that generates heat at 900°C or higher when irradiated with microwaves, a material to be produced in a charcoal production vessel, and a heat storage layer that encloses the material to be produced in the charcoal production vessel; a sealing step of sealing the charcoal making vessel; and A charcoal production method including at least a microwave irradiation step of irradiating microwaves to heat the heating element, thereby raising the temperature of the material to be produced to a target carbonization temperature or higher, A charcoal production method, characterized in that the heat storage layer contains silica plant biomass.

2. 2. The charcoal production method according to claim 1, wherein the silica plant biomass is rice husk or buckwheat husk.

3. 2. The charcoal production method according to claim 1, wherein the heating element is a sintered body containing a silica plant incineration residue.

4. 2. The charcoal production method according to claim 1, wherein the material to be produced into carbon is a compact formed by compressing a powdered raw material derived from a plant.

5. 5. The charcoal production method according to claim 4, wherein the molded product is a wood pellet.

6. 2. The charcoal production method according to claim 1, wherein the target carbonization temperature in the microwave irradiation step is 1000°C or higher.

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