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 a coal making product and a heat generating material that generates heat at 900 °C or higher by being irradiated with a microwave inside a coal making container so that the coal making product is enclosed by the heat generating material, a sealing step of sealing the coal making container, and a microwave irradiation step of raising a temperature of the coal making product to a target carbonization temperature or higher by irradiating the heat generating material with a microwave to generate heat, wherein a wood pellet or the like can be easily carbonized by using a silicate plant incineration residue as the heat generating material.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 efficiently and inexpensively produce carbonized pellets with a higher calorific value.

[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 intensive research, the present inventors discovered that by encapsulating wood pellets in a heat-generating material made of silicic acid plant incineration residue and then irradiating the encapsulated wood pellets with microwaves to create a high-temperature state, carbonized pellets that have been carbonized to a desired degree can be produced in an extremely simple and efficient manner, 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 the material to be produced and a heat-generating material that generates heat to 900°C or higher when irradiated with microwaves inside a charcoal production container so that the material to be produced is enclosed by the heat-generating material, a sealing step of sealing the charcoal production container, and a microwave irradiation step of irradiating microwaves to cause the heat-generating material to generate heat, thereby raising the temperature of the material to a target carbonization temperature or higher, wherein the heat-generating material contains silica plant incineration residue.

[0013] A second aspect of the present invention is a charcoal production method, characterized in that the content of the silicic acid plant incineration residue in the heat generating material is 30 wt % or more.

[0014] The third invention of the present invention is a charcoal production method characterized in that the heat generating material has a silicon dioxide content of 60 wt% or more and 96 wt% or less, a carbon element content of 0.1 wt% or more and 20 wt% or less, and a metal element content of 0.1 wt% or more and 3.0 wt% or less.

[0015] A fourth aspect of the present invention is a charcoal-making method, wherein the incineration residue of silicic acid plants has wood gas components adsorbed on its surface.

[0016] A fifth 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.

[0017] A sixth aspect of the present invention is a charcoal production method, wherein the molded product is a wood pellet.

[0018] The seventh aspect of the present invention is a charcoal making method, characterized in that in the accommodation step, the material to be made into carbon is enclosed in the heat-generating material having a thickness of 2 cm or more.

[0019] The eighth invention 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]

[0020] According to the first aspect of the present invention, carbonized pellets can be produced extremely easily by wrapping the material to be produced in a heat-generating material containing silica plant incineration residue, which can be rapidly heated by microwave irradiation, and rapidly heating the material to the target charcoal-making temperature. As the material to be produced reaches the target carbonization temperature, the oxygen in the charcoal-making vessel is rapidly consumed by combustion, and the sealed charcoal-making vessel is maintained at a high temperature in an oxygen-free atmosphere. This configuration makes it possible to carbonize wood pellets to the desired level in a short time after microwave irradiation. Furthermore, because the heat-generating material 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. Furthermore, by effectively utilizing silica plant incineration residue, which is agricultural waste, charcoal-making costs can be further reduced.

[0021] According to the second aspect of the present invention, by incorporating 30 wt % or more of the incineration residue of silicic acid plants into the heat generating material, it is possible to ensure heat generating properties suitable for charcoal production.

[0022] According to the third aspect of the present invention, by setting the silicon dioxide content in the heat generating material to between 60 wt% and 96 wt%, the carbon content to between 0.1 wt% and 20 wt%, and the metal content to between 0.1 wt% and 3.0 wt%, the heat generating material can be heated to the target carbonization temperature in a short time by induction heating or dielectric heating using the carbon and metal elements while ensuring sufficient heat storage capacity through the silicon dioxide. The carbon element derived from the incineration residue of silicic acid plants shows little loss of carbon element content even at temperatures above 900°C, and the metal elements contained in the incineration residue of silicic acid plants are stable with little structural change, making it possible to obtain stable heat generating properties.

[0023] According to the fourth aspect of the present invention, the cost of charcoal production can be further reduced by using the residue of incineration of silicic acid plants with wood gas components adsorbed as a heat generating material. The residue of incineration of silicic acid plants with wood gas components adsorbed is obtained as a by-product of the charcoal production method of the present invention and can be repeatedly reused as a material for heat generating materials.

[0024] According to the fifth 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.

[0025] According to the sixth 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.

[0026] According to the seventh aspect of the present invention, by wrapping the material to be made into a heat-generating material at least 2 cm thick, the temperature rise and heat storage properties can be improved, and the temperature suitable for charcoal making can be maintained for a sufficient period of time. In addition, by wrapping the material into a heat-generating material of sufficient thickness, it is possible to prevent the inside of the charcoal making container from being contaminated by wood gas components generated from the material to be made into a charcoal.

[0027] According to the eighth 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]

[0028] [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 4] 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 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 6A]FIG. 2 is a schematic cross-sectional view illustrating the accommodation step in the charcoal production method according to the second embodiment of the present invention. [Figure 6B] FIG. 2 is a schematic cross-sectional view illustrating the accommodation step in the charcoal production method according to the second embodiment of the present invention. [Figure 6C] FIG. 2 is a schematic cross-sectional view illustrating the accommodation step in the charcoal production method according to the second embodiment of the present invention. [Figure 6D] FIG. 10 is a plan view illustrating the accommodation step in the charcoal production method according to the second embodiment of the present invention. [Figure 6E] FIG. 2 is a schematic cross-sectional view illustrating the accommodation step in the charcoal production method according to the 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. DETAILED DESCRIPTION OF THE INVENTION

[0029] 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.

[0030] First, in a storage step, the material to be made into charcoal 30, such as wood pellets, and the heat generating material 40 containing the incineration residue of silica plants are stored inside the charcoal making vessel 10 (step S1). Next, in a sealing step, the charcoal making vessel 10 is sealed with a 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.

[0031] In the microwave irradiation process, microwaves generated by microwave oscillator 51 are irradiated toward charcoal making vessel 10 (step S3). By irradiating microwaves to heat heat generating material 40 containing silica plant incineration residue, the temperature of carbonization material 30 reaches the target carbonization temperature (250°C or higher and 1300°C or lower), and microwave irradiation is terminated. After microwave irradiation is stopped, in the subsequent holding process, carbonization of carbonization material 30 is promoted by holding charcoal making vessel 10 inside microwave irradiator 50, and carbonization of carbonization material 30 is advanced to the desired level (step S4).

[0032] 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 carbonized material to be made 30 and the heat generating material 40 are removed from the charcoal making vessel 10, and the carbonized material to be made 30 is recovered by sieving them to remove the heat generating material 40 (step S6).

[0033] (charcoal making container) The charcoal making vessel 10 used in the present invention can be any known vessel, without 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 the material to be made 30 and the heat-generating material 40 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.

[0034] (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 constituting the material to be produced 30 include woody biomass such as sawmill residues, construction wood, and unused thinned wood, as well as agricultural waste such as grass clippings, rice 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).

[0035] (heat generating material) The heat generating material 40 used in the present invention is characterized in that it contains silica plant incineration residue as a microwave-absorbing heat medium, and it is possible to rapidly raise the temperature of the heat generating material 40 to 900°C or more by irradiating it with microwaves.

[0036] In this specification, "silicic acid plant incineration residue" refers to the incineration residue obtained by incinerating almost all organic combustible material through prolonged self-combustion at high temperatures of 1000°C to 2000°C using biomass from silicic acid plants, such as rice husks, rice straw, wheat straw, bamboo, bagasse, and coconut shells. The incineration residue is an aggregate of fine particles with an average particle size of approximately 10 μm to 10 mm. Silicic acid plant incineration residue is primarily composed of silicon dioxide, with trace amounts of carbon and metal elements. It exhibits the property of repeatedly and rapidly increasing in temperature when irradiated with microwaves. It is believed that the reason why silicic acid plant incineration residue exhibits this unique heat-generating phenomenon is that the small amounts of carbon and conductive metal elements contained in the residue cause induction heating or dielectric heating when irradiated with microwaves.

[0037] 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, as a total weight converted into metal oxides, is in the range of 0.1 wt% to 49 wt%.

[0038] The content of silica plant incineration residue in the heat generating material 40 is preferably adjusted so that it reaches 900°C or higher within 2 minutes when irradiated with microwaves in the 2.45 GHz band. Furthermore, it is more preferable that the heat generating material 40 can be heated to 1200°C or higher, and particularly preferably to 1500°C or higher.

[0039] Normally, when carbon is exposed to high temperatures exceeding 900°C for a long period of time, the amount of carbon element decreases due to combustion, making it difficult for heat generation performance to stabilize. However, the carbon element contained in silica plant incineration residues has the characteristic that the amount of carbon element decreases little even at temperatures exceeding 900°C, ensuring stable heat generation performance.

[0040] In addition, ordinary conductive metal powders, especially active metals, have inconsistent heat generation rates due to high-temperature oxidation, and iron and other metals undergo structural changes at around 800°C, which changes their magnetic properties, making them less susceptible to dielectric heating and significantly affecting the heat generation rate.However, the metal elements contained in silica plant incineration residues are stable and undergo little structural change, allowing for repeated stable heat generation characteristics.

[0041] Conventionally, carbon powder and carbon powder blended with conductive metal powder or ferrite have been known as microwave-absorbing heat transfer media, but these have had the problem of deterioration of heat-generating properties when used continuously at high temperatures above 900°C. In contrast, the silicic acid plant incineration residue used in the present invention exhibits stable heat-generating properties even when used repeatedly at high temperatures above 900°C, making it an excellent heat transfer media.

[0042] In addition to the silica plant incineration residue, additives may be blended into the heat generating material 40 to the extent that the purpose of the present invention is not impaired. Examples of additives that can be used include fillers added to increase the bulk of the heat generating material 40 and temperature-raising auxiliary materials added to rapidly raise the temperature of the heat generating material 40.

[0043] Silica sand can be used as a filler added to increase the bulk of the heat generating material 40. Alternatively, unburned biomass of silica plants (rice husks, rice straw, wheat straw, bamboo, bagasse, coconut shells, etc.) can be blended as a filler with the incineration residue of silica plants. When the heat generating material 40 is heated to over 900°C by microwave irradiation, almost all of the organic combustible material in the unburned biomass of silica plants blended into the heat generating material 40 is incinerated, and the unburned biomass becomes an incineration residue of silica plants.

[0044] Further, examples of the temperature-raising auxiliary material added to quickly raise the temperature of the heat generating material 40 to 900° C. or higher include carbon powder and conductive metal powder.

[0045] The additive to be mixed with the silicic acid plant incineration residue is preferably in powder form, and the particle shape may be spherical, fibrous (acicular), plate-like, etc. There is no particular limitation on the particle size, and for example, particles with a diameter of 100 nm to 10 mm can be used.

[0046] In the present invention, the incineration residue of silicic acid plants with wood gas components adsorbed thereon may be used as the heat generating material 40. In the microwave irradiation process, the wood gas components generated from the carbonization material 30 permeate the gaps between the particles in the heat generating material 40, and in the cooling process, they are adsorbed as wood tar onto the surface of the particles of the incineration residue of silicic acid plants.

[0047] That is, the incineration residue of silicic acid plants with adsorbed wood gas components is obtained as a by-product of the charcoal production method of the present invention. The incineration residue of silicic acid plants with adsorbed wood gas components can be easily separated from the carbonized charcoal production material 30 by sieving, and can be reused any number of times. By repeatedly reusing the incineration residue of silicic acid plants with adsorbed wood gas components as a material for constituting the heat generating material 40, the charcoal production cost can be further reduced.

[0048] In the present invention, it is preferable to adjust the compounding ratio of the silicic acid plant incineration residue and additives so that the silicon dioxide content in the heat generating material 40 is 60 wt% or more and 96 wt% or less. If the silicon dioxide content is less than 60 wt%, it is not preferable because it may not be possible to ensure sufficient heat storage capacity for charcoal production. Also, if the silicon dioxide content is less than 96 wt%, it is not preferable because the carbon element and metal element contents are insufficient and sufficient heat generating properties for charcoal production cannot be obtained.

[0049] Furthermore, the heat generating material 40 preferably contains 1 wt% or more of carbon elements derived from the incineration residue of silicic acid plants, and more preferably 2 wt% to 20 wt% of carbon elements derived from the incineration residue of silicic acid plants.The heat generating material 40 preferably contains 0.1 wt% or more of metal elements derived from the incineration residue of silicic acid plants, and more preferably 0.5 wt% to 3.0 wt% of metal elements derived from the incineration residue of silicic acid plants, in terms of the total weight of the metal oxides.

[0050] In the present invention, the content of silicic acid plant incineration residue in the heat generating material 40 is set to 30 wt% or more. If the content of silicic acid plant incineration residue is less than 30 wt%, sufficient heat generating properties for charcoal production cannot be obtained, which is undesirable. The lower limit of the content of silicic acid plant incineration residue is preferably 50 wt% or more, more preferably 70 wt% or more, even more preferably 90 wt% or more, particularly preferably 95 wt% or more, and most preferably 100 wt%.

[0051] (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.

[0052] 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 heat-generating material 40 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 disposed 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] First Embodiment 4 shows the state in which the material to be made into carbon 30 and the heat generating material 40 are contained in the charcoal making container 10 in the first embodiment. In the first embodiment, the material to be made into carbon 30 is a large number of wood pellets, and the heat generating material 40 is made of silica plant incineration residue.

[0060] (Storage process) First, wood pellets and silica plant incineration residues are mixed uniformly, and then the mixture of wood pellets and silica plant incineration residues is poured into a charcoal making container 10, so that each wood pellet is enclosed in a heat generating material 40, as shown in Figure 4.

[0061] When a large number of carbonized materials 30 are dispersed in the heat generating material 40 as in the first embodiment, the volume ratio of the heat generating material 40 to the carbonized materials 30 is set to a range of 30:70 to 80:20 before mixing. If the heat generating material 40 is less than 30% by volume, a sufficient amount of heat cannot be generated, and the carbonization reaction may not proceed easily. Preferably, the volume ratio of the heat generating material 40 to the carbonized materials 30 is set to a range of 40:60 to 70:30 before mixing.

[0062] In the present invention, it is preferable that the inside of the charcoal making vessel 10 is filled without any gaps with the material to be made 30 and the heat generating material 40. If there is a large amount of remaining space inside the charcoal making vessel 10, the heat storage capacity may be insufficient, which is undesirable. The remaining space inside the charcoal making vessel 10 is at most 30% or less of the volume of the charcoal making vessel, and preferably 10% or less.

[0063] As long as the heat generating material 30 can ensure sufficient heat generation and heat storage capacity, it is not necessary for the entire surface of the carbonization material 30 to be enclosed by the heat generating material 40, and a portion of the surface of the carbonization material 30 may not be enclosed. For example, it is not a problem if the carbonization material 30 comes into contact with the inner wall of the charcoal making vessel 10 or with other carbonization materials 30, and therefore a portion of the surface of the carbonization material 30 is not enclosed by the heat generating material 40.

[0064] (Sealing process) As shown in FIG. 4, after the material to be made 30 and the heat-generating material 40 are placed inside the charcoal making vessel 10, the opening of the charcoal making vessel 10 is sealed with the lid 11. The lid 11 is necessary to maintain an oxygen-free atmosphere inside the charcoal making vessel 10. In the present invention, a high level of airtightness is not required for the charcoal making vessel 10; 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 airtightness is too high, 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.

[0065] (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 by a microwave oscillator 51 are irradiated onto the charcoal making vessel 10.

[0066] 5 shows an example of the temperature change of the material to be made into carbon 30. The material to be made into carbon 30 (here, wood pellets) rapidly rises in temperature due to the thermal energy generated by the heat generating material 40 upon absorbing microwaves.

[0067] 5, the temperature of the heat generating material 40 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 material, shape, arrangement, etc. of the heat generating material 40 and the carbonization material 30.

[0068] 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.

[0069] 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 may be used to indirectly determine that the material 30 to be carbonized has reached the carbonization temperature. Examples of the wood gas detection means include a semiconductor gas sensor and high-speed gas chromatography.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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 carbonized material to be made 30 and the heat generating material 40 are scraped out from the cooled charcoal making vessel 10 and sieved to recover the carbonized material to be made 30.

[0074] Second Embodiment Next, a second embodiment of the present invention will be described with reference to Figures 6A to 6E. In the second embodiment, as shown in Figure 6E, the carbonization material 30 is made up of an aggregate of wood pellets (a group of wood pellets), and the aggregate of wood pellets is contained as a single mass enclosed in a heat generating material 40 made from silicic acid plant incineration residue. The second embodiment differs from the first embodiment in that the group of wood pellets is regarded as a single carbonization material 30, but otherwise has the same configuration as the first embodiment.

[0075] In the second embodiment, in the storage step (step S1), first, as shown in Fig. 6A, silica plant incineration residue (heat-generating material 40) is poured into the bottom of the charcoal-making vessel 10. Next, as shown in Fig. 6B, a cylindrical partition wall 12 is placed in the center above the heat-generating material 40.

[0076] Next, as shown in Fig. 6C, wood pellets (material to be made into carbon 30) are poured inside the partition wall 12, and silica plant incineration residue (heat generating material 40) is poured outside the partition wall 12. Fig. 6D is a plan view of Fig. 6C. As shown in Fig. 6D, the heat generating material 40 surrounds the material to be made into carbon 30 via the partition wall 12.

[0077] After removing the partition 12 from the charcoal making vessel 10, as shown in Figure 6E, silica plant incineration residue (heat generating material 40) is poured into the charcoal making vessel 10 up to near the open end, so that the charcoal making material 30 is encapsulated in the heat generating material 40.

[0078] In the second embodiment, the thickness of the heat generating material 40 is preferably 2 cm or more, and more preferably 3 cm or more. If the thickness of the heat generating material 40 is less than 2 cm, there is a possibility that sufficient heat storage capacity cannot be ensured, and there is also a problem that wood tar that is not absorbed by the heat generating material 40 adheres to the charcoal making vessel, making cleaning the charcoal making vessel complicated.

[0079] In this way, when the carbonization material 30 consists of an aggregate of many granular materials, it can be treated as many independent carbonization materials 30 as in the first embodiment, or it can be treated as a single mass of carbonization material 30 consisting of many wood pellets as in the second embodiment.

[0080] Third Embodiment Next, a third embodiment of the present invention will be described. The third embodiment differs from the first embodiment in that hollow cylindrical artificial logs (Ogalite 30') are used as the carbonization material 30 instead of wood pellets, but has the same configuration as the first embodiment in other respects.

[0081] 7 shows the state in the third embodiment where Ogalite 30' and silicic acid plant incineration residue (heat-generating material 40) are placed in a charcoal-making vessel 10. The silicic acid plant incineration residue is poured into the bottom of the charcoal-making vessel 10 to a thickness of about 3 cm, and Ogalite 30' is placed on top of it. In this state, the silicic acid plant incineration residue is poured into the charcoal-making vessel 10 up to near the open end, so that the entire surface of the Ogalite is encapsulated by the heat-generating material 40.

[0082] 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.

[0083] 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 on the material to be charcoal-made, while the material is enclosed in a heat-generating material made of the incineration residue of silicic acid plants.

[0084] 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.

[0085] Furthermore, according to the charcoal making method of the present invention, the heat generating material 40 made from the incineration residue of silica plants adsorbs wood gas components, suppressing the evaporation of wood gas and making it possible to make charcoal 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]

[0086] (Production of silica plant incineration residue) First, rice husks were burned at a combustion temperature of approximately 1800°C for approximately 10 hours to create a silica plant incineration residue. Analysis of the silica plant incineration residue revealed that it was 77 wt% silicon dioxide and 8.5 wt% carbon element. Furthermore, 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, and others. A wavelength-dispersive X-ray fluorescence analyzer was used to analyze the metal elements.

[0087] (Confirmation of the heat generating properties of silica plant incineration residue) 50g of silica plant incineration residue was placed in a ceramic container, covered with a ceramic lid, and irradiated for approximately 5 hours using microwaves (2.45GHz) from a 700W microwave oven. After terminating the irradiation, the residue was left to stand for approximately 2 hours until its surface temperature had dropped to approximately 30°C, after which irradiation was resumed for another 5 hours. This procedure was repeated over a period of approximately 8 days. As a result, the temperature of the silica plant incineration residue was heated to approximately 1500°C in approximately 1 minute each time irradiation was performed, and this temperature was maintained during irradiation, with the surface temperature decreasing when irradiation was stopped.

[0088] (Charcoal processing) 300 cc of white pellets and 300 cc of silicic plant incineration residue were mixed and then poured into a ceramic container with a diameter of 140 mm, a height of 85 mm, and a weight of 725 g, to contain the white pellets and silicic plant incineration residue in the arrangement shown in Figure 4.

[0089] 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.

[0090] The container was removed from the microwave oven and allowed to cool to room temperature. A single large lump of the contents was removed from the container. The lump was brittle and easily crumbled when pressed with a finger. The lump was sieved to separate the carbonized pellets and the silica plant incineration residue. The carbonization treatment of Example 1 resulted in the white pellets being carbonized and turning black, and the silica plant incineration residue had absorbed wood tar, forming a portion of the lump.

[0091] The solid carbon content of the obtained carbonized pellets was 89%, 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 found to be 7000 (kcal / kg) or more. This confirmed that the white pellets were completely carbonized by the charcoal production method of Example 1. [Example]

[0092] A charcoal production process was carried out in the same manner as in Example 1, except that the wood tar-adsorbed silicic acid plant incineration residue obtained in Example 1 was used instead of the silicic acid plant incineration residue. It was confirmed that the white pellets were completely carbonized. This demonstrates that even the wood tar-adsorbed silicic acid plant incineration residue can function sufficiently as a heat generating material. [Example]

[0093] Charcoal production was carried out in the same manner as in Example 1, except that 300 cc of white pellets and 300 cc of silicic acid plant incineration residue were placed in a ceramic container in the arrangement shown in Figure 6E. It was confirmed that the white pellets were completely carbonized. This confirmed that the white pellets could be carbonized by irradiating microwaves with a mass of white pellets placed in the center of a heat-generating material made of silicic acid plant incineration residue. [Example]

[0094] In Example 4, instead of white pellets, hollow cylindrical ogalite with a diameter of 6 cm and a length of 6 cm was used as the material to be made into carbon. The charcoal making method of the present invention was carried out in the same manner as in Example 1, except that ogalite and the incineration residue of silicic plants were placed in the bottom of a ceramic container with a diameter of 140 mm, a height of 85 mm, and a weight of 725 g, in the arrangement shown in Figure 7. The ogalite removed from the charcoal making container was blackened, confirming that the ogalite had been completely carbonized. Comparative Example 1

[0095] In order to confirm the heat-generating properties of a mixture consisting of 86 wt% silica sand, 8 wt% carbon powder, and 6 wt% ferrite powder as heat-generating material 40, 50 g of the mixture was filled into a ceramic container, a ceramic lid was placed on it, and microwaves (2.45 GHz) from a 700 W microwave oven were irradiated. One minute after the start of microwave irradiation, the temperature of the mixture reached a maximum of 1000°C, but after 10 minutes the temperature gradually decreased, reaching 800°C after one hour and dropping to 400°C after five hours. This is thought to be due to the thermal decomposition of the carbon powder and a structural change in the ferrite powder, which deteriorated the heat-generating properties of the mixture.

[0096] Next, a mixture of 86 wt% silica sand, 8 wt% carbon powder, and 6 wt% ferrite powder was used as the heat generating material 40 instead of the silicic acid plant incineration residue, and charcoal production was carried out in the same manner as in Example 1. The white pellets removed from the charcoal production container had turned black.

[0097] The calorific value of the carbonized pellets obtained in Comparative Example 1 was analyzed in accordance with JIS Z7320-2, and the higher calorific value on an anhydrous basis was 4428 (kcal / kg). The reason for the lower calorific value compared to Example 1 is thought to be that in Comparative Example 1, the heat generation properties of the heat generating material deteriorated during the microwave irradiation process, and therefore carbonization did not proceed sufficiently. [Industrial Applicability]

[0098] As described 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]

[0099] 10 Charcoal making vessel 11 Lid 12 Bulkhead 30 Charcoal products 30´ Ogalight 40 Heat generating material 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

Claims

1. a step of placing the material to be carbonized and a heat-generating material that generates heat of 900°C or more when irradiated with microwaves inside a charcoal-making container so that the material to be carbonized is enclosed by the heat-generating material; 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 heat-generating material, thereby raising the temperature of the material to be produced to a target carbonization temperature or higher, A charcoal-making method characterized in that the heat-generating material contains a residue of incineration of a silica plant.

2. 2. The charcoal production method according to claim 1, wherein the content of the silica plant incineration residue in the heat generating material is 30 wt % or more.

3. 2. A charcoal production method as described in claim 1, characterized in that the heat generating material has a silicon dioxide content of 70 wt% or more and 96 wt% or less, a carbon element content of 0.1 wt% or more and 20 wt% or less, and a metal element content of 0.1 wt% or more and 3.0 wt% or less.

4. 2. The charcoal production method according to claim 1, wherein the silicic acid plant incineration residue has wood gas components adsorbed on its surface.

5. 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.

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

7. 2. The charcoal making method according to claim 1, wherein in the accommodation step, the material to be made into carbon is enclosed in the heat-generating material to a thickness of 2 cm or more.

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

Images