Method for producing biomass fuel and biomass fuel

Abstract

To provide a method for producing a biomass fuel in which spontaneous heating properties are suppressed.SOLUTION: A method for producing a biomass fuel includes the steps of: obtaining a semi-carbonized material having a carbon content of less than 61 mass% by heating biomass to semi-carbonize the same; and oxidizing the semi-carbonized material by heating the same under the conditions of an oxygen concentration of 3 vol.% or more and 13 vol.% or less, a temperature of 120°C or higher and 220°C or lower, and a time of 12 minutes or longer and 240 minutes or shorter.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing biomass fuel and to a biomass fuel. [Background technology]

[0002] In recent years, biomass fuels have been developed to reduce CO2 emissions, which are believed to be a cause of global warming. To improve the pulverizability and calorific value of biomass fuels, methods of carbonizing biomass have been proposed. For example, Patent Document 1 discloses a method for producing solid fuel by heating biomass in an oxygen-deficient atmosphere to produce a solid fuel that is mixed with coal or pulverized alone and used as a pulverized fuel. This method is characterized in that the solid fuel is produced by carbonizing hard biomass, including plant shells, fruits, and seeds, by heating it at an oxygen concentration of 1 to 5% and a treatment temperature of 350 to 400°C for 30 to 90 minutes. Patent Document 2 discloses a method for producing a carbon material, which includes a dry distillation step of obtaining biomass charcoal from biomass with a carbon content of 61% by weight or more, and an oxidation step of heating the biomass charcoal to 200°C or higher in an atmosphere with an oxygen concentration of 2 to 13% by volume. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-191085 [Patent Document 2] Japanese Patent Publication No. 2023-024260 Summary of the Invention [Problem to be solved by the invention]

[0004] While solid fuel obtained by carbonizing biomass has the advantage of improving its calorific value and pulverizability, it is known that the change in the chemical structure of the biomass makes it more susceptible to reaction with oxygen in the air. Therefore, the solid fuel described in Patent Document 1 is thought to have the property of easily generating heat spontaneously. Furthermore, in the method described in Patent Document 2, after obtaining biomass charcoal with a high carbon content, an oxidation process is carried out to suppress spontaneous heating. However, since biomass charcoal with a high carbon content is inherently prone to spontaneous heating, the method described in Patent Document 2, which uses such biomass charcoal, leaves room for further investigation in terms of sufficiently suppressing spontaneous heating.

[0005] An object of the present invention is to provide a method for producing biomass fuel with suppressed spontaneous heat generation, and a biomass fuel. [Means for solving the problem]

[0006] [1] A method for producing a semi-carbonized product having a carbon content of less than 61% by mass by heating biomass to semi-carbonize it; and an oxidation process for oxidizing the semi-carbonized product by heating the semi-carbonized product in an atmosphere having an oxygen concentration of 3% by volume or more and 13% by volume or less at a temperature of 120°C or more and 220°C or less for 12 minutes or more and 240 minutes or less. Biomass fuel production method. [2] The semi-carburized material is in the form of powder, pellets, briquettes, or chips. The method for producing biomass fuel according to [1] above. [3] The semi-carbonized material obtained in the semi-carbonized material obtaining step is in the form of pellets, and is obtained by heating biomass pellets containing the biomass at 220 ° C or more and 320 ° C or less, or by molding semi-carbonized biomass into pellets. The method for producing biomass fuel according to [1] or [2] above. [4] The semi-carbonized material obtained in the step of obtaining the semi-carbonized material is in the form of a briquette, and the semi-carbonized material is obtained by heating a biomass briquette containing the biomass at a temperature of 220°C or higher and 320°C or lower; It is obtained by molding semi-carbonized biomass into briquettes. The method for producing biomass fuel according to [1] or [2] above. [5] The torrefied biomass is obtained by heating the biomass at 220 ° C or more and 320 ° C or less, or by steam explosion of the biomass. The method for producing biomass fuel according to [3] or [4] above. [6] The semi-carbonized material obtained in the semi-carbonized material obtaining step is in chip form and is obtained by heating the chip-shaped biomass at 220 ° C or more and 320 ° C or less. The method for producing biomass fuel according to [1] or [2] above. [7] The semi-carbonized material obtained in the step of obtaining the semi-carbonized material is powdery and can be obtained by steam explosion of the biomass, or by crushing the biomass into powder and then heating the powdery biomass at 220 ° C or higher and 320 ° C or lower. The method for producing biomass fuel according to [1] or [2] above. [8] The oxidation step is a step of heating the semi-carbide in an atmosphere having an oxygen concentration of 5% by volume or more and 10% by volume or less at a temperature of 150°C or more and 215°C or less for 30 minutes or more and 240 minutes or less. The method for producing biomass fuel according to any one of [1] to [7] above. [9] In the oxidation step, when the semi-carbide is heated at 180°C or higher and 215°C or lower, the oxidation step is a step of heating in an atmosphere having an oxygen concentration of 7% by volume or higher and 13% by volume or lower for 60 minutes or longer and 240 minutes or shorter. The method for producing biomass fuel according to any one of [1] to [7] above.

[10] The biomass is at least one selected from the group consisting of woody biomass, herbaceous biomass, agricultural crop residue biomass, and palm biomass; The method for producing biomass fuel according to any one of [1] to [9] above.

[0007]

[11] A biomass fuel, wherein the carbon content in the biomass fuel is less than 61% by mass, the calorific value when held at 140°C for 20 minutes in an oxygen atmosphere using a differential scanning calorimeter is 8.0 J / g or less, and the molar ratio of hydrogen atoms to carbon atoms in the biomass fuel (moles of hydrogen atoms / moles of carbon atoms) is 1.08 or more and 1.21 or less. Biomass fuel.

[12] When measured using a differential scanning calorimeter under an oxygen atmosphere at 140°C for 20 minutes, the calorific value is greater than 5.0 J / g. The biomass fuel according to

[11] .

[13] The biomass is at least one selected from the group consisting of woody biomass, herbaceous biomass, agricultural crop residue biomass, and palm biomass. The biomass fuel according to

[11] or

[12] . [Effects of the Invention]

[0008] According to one aspect of the present invention, it is possible to provide a method for producing biomass fuel and biomass fuel that suppresses spontaneous heat generation while ensuring a calorific value. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a graph showing the relationship between the higher heating value and the heating value measured by DSC for the biomass fuels of Examples 1 to 4 and Comparative Examples 1 to 3. [Figure 2] 1 is a graph showing the relationship between the higher heating value and the heating value measured by DSC for the biomass fuels of Examples 1 to 8 and Comparative Example 3. [Figure 3] 1 is a graph showing the relationship between the higher heating value and the heating value measured by DSC for the biomass fuels of Example 7, Examples 11 and 12, and Comparative Example 3. [Figure 4] 1 is a graph showing the relationship between the molar ratio (H / C) in the biomass fuels of Examples 1 to 4 and Comparative Examples 1 to 3 and the calorific value determined by DSC. [Figure 5]1 is a graph showing the relationship between the molar ratio (H / C) in biomass fuels and the calorific value determined by DSC in Examples 1 to 8 and Comparative Example 3. [Figure 6] 1 is a graph showing the relationship between the molar ratio (H / C) in the biomass fuels of Example 7, Examples 11 and 12, and Comparative Example 3 and the calorific value determined by DSC. [Figure 7] 1 is a graph showing the relationship between the fuel ratio of biomass fuels in Examples 1 to 4 and Comparative Examples 1 to 3 and the calorific value measured by DSC. [Figure 8] 1 is a graph showing the relationship between the fuel ratio of biomass fuels in Examples 1 to 8 and Comparative Example 3 and the calorific value measured by DSC. [Figure 9] 1 is a graph showing the relationship between the fuel ratio of biomass fuels in Example 7, Examples 11 and 12, and Comparative Example 3 and the calorific value measured by DSC. [Figure 10] 1 is a graph showing the relationship between the elapsed time after the sample was placed in an electric furnace and the sample temperature for Examples 11 and 12 and Comparative Examples 3 and 4. DETAILED DESCRIPTION OF THE INVENTION

[0010] In this specification, a numerical range expressed using "to" means a range that includes the number written before "to" as the lower limit and the number written after "to" as the upper limit. In this specification, mass percent concentration (unit: mass % (mass%)) and weight percent concentration (unit: weight % (wt%)) are the same value.

[0011] [First embodiment] [Method for producing biomass fuel] The method for producing biomass fuel of this embodiment includes a step of heating and semi-carbonizing biomass to obtain a semi-carbonized product having a carbon content of less than 61% by mass, and an oxidation step of oxidizing the semi-carbonized product by heating the semi-carbonized product under conditions of 120°C to 220°C for 12 minutes to 240 minutes in an atmosphere with an oxygen concentration of 3% to 13% by volume.

[0012] In the production method of this embodiment, after obtaining semi-carbide having a carbon content of less than 61 mass %, the semi-carbide is oxidized under predetermined conditions to produce biomass fuel. From the viewpoint of improving the calorific value and pulverizability, it is desirable for biomass fuel to contain semi-carbide with a high carbon content. However, simply increasing the carbon content in semi-carbide makes it more susceptible to spontaneous heating. In the method of Patent Document 2, the carbon content in the semi-carbide is increased to 61% by mass or more, and then the semi-carbide is subjected to an oxidation process, thereby reducing the calorific value of the resulting carbonized material. However, in the method of Patent Document 2, in order to increase the carbon content in the semi-carbide to 61% by mass or more, the biomass must be carbonized at a high temperature. As a result, many volatile components are released from the biomass in the carbonization process, which tends to reduce the yield of carbonized material that can be used as fuel. Furthermore, in the method of Patent Document 2, the carbon content in the semi-carbide is excessively increased, so it is thought that even if the semi-carbide is subsequently subjected to an oxidation process, the spontaneous heating of the carbon material cannot be sufficiently suppressed. In contrast, the manufacturing method according to the present embodiment is based on the opposite concept to that of Patent Document 2. First, in the step of obtaining a semi-carbide, the carbon content in the semi-carbide is adjusted so as not to be too high, specifically, so that the carbon content in the semi-carbide is adjusted to be less than 61% by mass. That is, in the step of obtaining a semi-carbide according to the present embodiment, it is possible to semi-carbide biomass at an appropriate temperature, allowing a larger amount of volatile components to remain in the semi-carbide. As a result, semi-carbide having properties (e.g., calorific value and pulverizability) that allow it to be used as fuel can be obtained without unnecessarily reducing the semi-carbide yield, thereby enabling effective use of the semi-carbide. Furthermore, in the manufacturing method according to this embodiment, such semi-carbide (semi-carbide with a large amount of volatile components remaining) is further subjected to an oxidation process, so that it is possible to suppress spontaneous heat generation while taking advantage of its properties that allow it to be used as fuel. Therefore, according to the production method of this embodiment, a biomass fuel with suppressed spontaneous heat generation can be obtained.

[0013] <Process for obtaining semi-carbide> In the manufacturing method of this embodiment, the semi-carbonized material obtained in the semi-carbonized material obtaining step is obtained by heating biomass. Semi-carbonization refers to a state in which at least a portion of biomass is carbonized. In this specification, semi-carbonization includes a state in which a portion of biomass is carbonized and a state in which all of biomass is carbonized. In the step of obtaining the semi-carbonized product, the conditions for heating the biomass are adjusted so that the carbon content in the semi-carbonized product is less than 61% by mass. In this specification, the carbon content in the semi-carbide is an elemental analysis value measured in accordance with JIS M8819 (1997), and is the content (mass%) of carbon atoms in the semi-carbide on an anhydrous (dry) basis. The method for measuring the carbon content in the semi-carbide will be described in detail in the Examples below. From the viewpoint of making spontaneous heating less likely to occur, the carbon content in the semi-carbide may be 60% by mass or less, 59.0% by mass or less, 58.5% by mass or less, 58.0% by mass or less, or 57.5% by mass or less. From the viewpoint of ensuring the calorific value of the biomass fuel, the carbon content in the semi-carbonized material is preferably 45% by mass or more, more preferably 50% by mass or more, and even more preferably 53% by mass or more.

[0014] The shape of the semi-carbide obtained in the step of obtaining the semi-carbide is not particularly limited, but the semi-carbide is preferably in the form of powder, pellets, briquettes, or chips. Hereinafter, the semi-carbide obtained in the process of obtaining the semi-carbide will be described as follows: if it is in powder form, it will be referred to as semi-carbide according to mode 1; if it is in chip form, it will be referred to as semi-carbide according to mode 2; if it is in pellet form, it will be referred to as semi-carbide according to mode 3; and if it is in briquette form, it will be referred to as semi-carbide according to mode 4.

[0015] <Semicarbide according to aspect 1> (powdered semi-carbide) In one aspect of the manufacturing method of the present embodiment, the semi-carbide obtained in the step of obtaining the semi-carbide is in a powder form. Powdered semi-carbide can be obtained, for example, by (1) steam explosion of biomass, or (2) crushing biomass into powder and then heating the powdered biomass at 220°C or higher and 320°C or lower.

[0016] First, the case where a powdery semi-carbide is obtained by the above method (1) (by steam explosion of biomass) will be described. Steam explosion is a process in which biomass is steamed for a short period of time in a sealed container such as a pressure vessel using saturated steam at high temperature and pressure, and then suddenly released into atmospheric pressure, where it is rapidly cooled and the structure of the biomass (or the wood structure in the case of wood) is destroyed by adiabatic expansion. The shape of the biomass used in steam explosion is not particularly limited, and examples of the shape of the biomass include the shape of the biomass itself (e.g., palm fruit bunches), chips, elongated shapes, powder, and irregular shapes. The biomass used for steam explosion may be biomass as obtained, or biomass obtained after being crushed into any shape and size. For example, palm fruit bunches can be used as they are obtained. Biomass is pulverized and semi-carbonized by steam explosion into powder. For example, when the biomass used in steam explosion is chip-like biomass (biomass chips), the biomass chips are pulverized into powder by steam explosion. The resulting powdered biomass corresponds to the semi-carbonized product according to aspect 1.

[0017] The temperature of the steam explosion is preferably 100°C or higher and 300°C or lower, more preferably 100°C or higher and 280°C or lower. The pressure for the steam explosion is preferably 0.1 MPa or more and 9.0 MPa or less, more preferably 1.0 MPa or more and 6.5 MPa or less. The time for steam explosion is preferably 10 minutes or more and 60 minutes or less, more preferably 15 minutes or more and 30 minutes or less.

[0018] Steam explosion is preferably carried out in a sealed container under saturated steam at 100°C to 300°C and 0.1 MPa to 9.0 MPa, more preferably 100°C to 280°C and 1.0 MPa to 6.5 MPa.

[0019] The size of biomass obtained by steam explosion varies depending on the size and shape of the biomass used for steam explosion. For example, when the biomass used in steam explosion is biomass chips, the particle size of the powdered biomass obtained by steam explosion is preferably 1000 μm or less, more preferably 500 μm or less. In this specification, particle size refers to the major axis diameter. The major axis diameter of a biomass refers to the maximum length of a straight line connecting any two points on the outer contour of the biomass.

[0020] Next, we will explain the case where powdered semi-carbide is obtained by the method (2) above (by crushing biomass into powder and then heating the powdered biomass at 220°C or higher and 320°C or lower). The method for pulverizing the biomass into powder is not particularly limited, and the biomass can be pulverized using a known pulverizer. For example, when wood is used as woody biomass, large pieces of wood may be roughly crushed into chips of about several centimeters in size, and then crushed into powder. The particle size of the powdered biomass is preferably 3 mm or less, more preferably 1 mm or less, and even more preferably 100 μm or less. In this specification, the particle size of both the biomass and the torrefied biomass can be adjusted by a known method (for example, using a sieve).

[0021] Examples of methods for heating powdered biomass at 220°C or higher and 320°C or lower include methods in which the biomass is heated for a certain period of time in a container (preferably in a container that is sealed off from air) (e.g., air heating, exhaust gas heating, direct heating, etc.). Examples of heating methods include a rotary kiln method, a screw reaction method, a multistage reaction method, a fluidized bed (bed) reaction method, a microwave reaction method, and a moving bed reaction method. The temperature at which powdered biomass is heated is preferably 230°C or higher and 310°C or lower, more preferably 240°C or higher and 300°C or lower, from the viewpoint of improving the calorific value and pulverizability. The heating time for powdered biomass depends on the heating temperature and the size of the biomass, but is usually from 1 minute to 240 minutes, preferably from 1 minute to 60 minutes. The atmosphere in which the powdered biomass is heated is not particularly limited, but is preferably an air-shielded atmosphere, a dry distillation gas atmosphere, or a combustion exhaust gas atmosphere.

[0022] <Semicarbide according to aspect 2> (chip-shaped semi-carbide) In one aspect of the manufacturing method of this embodiment, the semi-carbide obtained in the step of obtaining semi-carbide is in the form of chips. The semi-carbonized chips can be obtained, for example, by heating obtained chip-like biomass or chip-like biomass obtained by pulverizing biomass at a temperature of 220°C or higher and 320°C or lower. The size of the semi-carbonized chips is not particularly limited, but for example, when woody biomass is pulverized into chips, the major axis diameter is preferably 5.0 cm or less, and more preferably 1.0 cm or less. The heating method, heating method, heating temperature, heating time, and atmosphere when heating chip-like biomass are preferably in the same ranges as the heating method, heating method, heating temperature, heating time, and atmosphere when heating powdery biomass described above.

[0023] <Semicarbide according to aspect 3> (Pellet-shaped semi-carbide) In one aspect of the manufacturing method of the present embodiment, the semi-carbide obtained in the semi-carbide obtaining step is in the form of pellets. The size and shape of the semi-carbide pellets are not particularly limited. The pellets are usually cylindrical, with a diameter of 5 mm to 10 mm and a length of 5 mm to 50 mm. Pellet-shaped torrefied material can be obtained, for example, by (i) heating biomass pellets containing biomass at 220°C or higher and 320°C or lower, or (ii) molding torrefied biomass into pellets.

[0024] The "biomass pellets containing biomass" in (i) above are, for example, biomass pellets obtained by molding powdered biomass that has not been heated or semi-carbonized, and are usually referred to as white pellets. The "semi-carbonized biomass" in (ii) above refers to the powdery semi-carbonized material according to the first embodiment. That is, the pellet-shaped semi-carbonized material according to aspect 3 can be obtained by heating white pellets at 220°C or higher and 320°C or lower (method (i) above), or by molding the powdered semi-carbonized material according to aspect 1 into pellets (method (ii) above). The heating method, heating method, heating temperature, heating time, and atmosphere for the biomass pellets in the method (i) are preferably in the same ranges as the heating method, heating method, heating temperature, heating time, and atmosphere for heating the powdered biomass described above. The pellets can be formed using a known pelletizer, etc. The pellets are produced, for example, by extruding powdered biomass or powdered semi-carbide through a metal hole (for example, a diameter of 5 mm to 10 mm and a length of 5 mm to 50 mm).

[0025] <Semicarbide according to aspect 4> (briquette-like semi-carbide) In one aspect of the manufacturing method of the present embodiment, the semi-carbide obtained in the step of obtaining semi-carbide is in the form of a briquette. The size and shape of the semi-carbide briquette are not particularly limited. Briquettes typically have a larger width and length than pellets. When the briquette is cylindrical, the size of the semi-carburized briquette is, for example, 10 mm or more and 100 mm or less in diameter and 10 mm or more and 300 mm or less in length. Briquette-shaped torrefied material can be obtained, for example, by (iii) heating biomass briquettes containing biomass at 220°C or higher and 320°C or lower, or by (iv) molding torrefied biomass into a briquette shape.

[0026] The "biomass briquettes containing biomass" in (iii) above refer to, for example, biomass briquettes obtained by molding powdered biomass that has not been heated or semi-carbonized. The size of the "torrefied biomass" in (iv) above is larger than or equal to the size of the torrefied biomass contained in the torrefied pellets. The "semi-carbonized biomass" in (iv) above may be the powdery semi-carbonized material according to the first aspect. That is, the briquette-shaped semi-carbonized material according to the fourth embodiment can be obtained by heating a biomass briquette containing unsemi-carbonized biomass at 220°C or higher and 320°C or lower (method (iii) above), or by molding a semi-carbonized material of a predetermined size (for example, the powdered semi-carbonized material according to the first embodiment) into a briquette shape (method (iv) above). The heating method, heating method, heating temperature, heating time, and atmosphere for the biomass briquettes in (iii) are preferably in the same ranges as the heating method, heating method, heating temperature, heating time, and atmosphere for heating the powdered biomass described above. Briquettes are produced, for example, by molding the material into briquettes or cylindrical shapes using a briquetting machine.

[0027] <Oxidation process> In the manufacturing method of this embodiment, the oxidation step is a step of oxidizing a semi-carbide having a carbon content of less than 61% by mass by heating the semi-carbide under conditions of an oxygen concentration of 3% by volume or more and 13% by volume or less at 120°C or more and 220°C or less for 12 minutes or more and 240 minutes or less. The preferred ranges of the oxygen concentration, heating temperature and heating time of the semi-carbide in the oxidation step are as follows:

[0028] In the manufacturing method of this embodiment, the oxidation step may be performed in an air atmosphere. Air usually contains about 21% by volume of oxygen. Therefore, the oxygen concentration in the oxidation step may be 21% by volume or less. In the manufacturing method of this embodiment, the oxygen concentration in the oxidation step is 3 vol% or more and 13 vol% or less, preferably 4 vol% or more and 12 vol% or less, more preferably 5 vol% or more and 11 vol% or less, and even more preferably 5 vol% or more and 10 vol% or less. When the oxygen concentration in the oxidation step is 3% by volume or more, the carbon in the semi-carbonized material reacts with oxygen efficiently, making it easier to obtain biomass fuel with a reduced calorific value. When the oxygen concentration in the oxidation step is 13% by volume or less, the thermal decomposition of the semi-carbonized material can be suppressed, which makes it easier to obtain biomass fuel with reduced spontaneous heat generation while improving the yield.

[0029] In the manufacturing method of this embodiment, the heating temperature of the semi-carbide in the oxidation step is 120°C or higher and 220°C or lower, preferably 130°C or higher and 220°C or lower, and more preferably 150°C or higher and 220°C or lower. When the heating temperature of the semi-carbonized material in the oxidation step is 120°C or higher, the carbon in the semi-carbonized material reacts with oxygen efficiently, making it easier to obtain biomass fuel with a reduced calorific value. When the heating temperature of the semi-carburized material in the oxidation step is 220°C or less, the thermal decomposition of the semi-carburized material can be suppressed. As a result, it becomes easier to obtain biomass fuel with reduced spontaneous heat generation while improving the yield.

[0030] In the manufacturing method of this embodiment, the heating time of the semi-carbide in the oxidation step is 12 minutes or more and 240 minutes or less, preferably 18 minutes or more and 180 minutes or less, more preferably 24 minutes or more and 150 minutes or less, and even more preferably 30 minutes or more and 120 minutes or less. By heating the torrefied material for 12 minutes or longer in the oxidation step, the minimum processing time required for the carbon in the torrefied material to react with oxygen can be ensured, making it easier to obtain biomass fuel with reduced calorific value. If the heating time of the semi-carbide in the oxidation step is 240 minutes or less, a sufficient treatment time can be ensured for reacting the carbon in the semi-carbide with oxygen and suppressing spontaneous heat generation.

[0031] In the manufacturing method of this embodiment, the oxidation step is preferably a step of heating the semi-carbide under conditions of an oxygen concentration of 5% by volume or more and 10% by volume or less, at 150°C or more and 215°C or less, for 0.5 hours or more and 4.0 hours or less. In the oxidation step, when the semi-carbide is heated at 180°C or more and 215°C or less, The oxidation step is preferably a step of heating in an atmosphere having an oxygen concentration of 7% by volume or more and 13% by volume or less for 1.0 hour or more and 4.0 hours or less. In the production method of this embodiment, the oxidation step can be carried out in a known reactor.

[0032] Second Embodiment The biomass fuel of the second embodiment has a carbon content of less than 61% by mass, a calorific value of 8.0 J / g or less when held at 140°C for 20 minutes in an oxygen atmosphere using a differential scanning calorimeter, and a molar ratio of hydrogen atoms to carbon atoms in the biomass fuel (moles of hydrogen atoms / moles of carbon atoms) of 1.08 or more and 1.21 or less. For ease of explanation, the "calorific value measured when the biomass fuel of the second embodiment is held at 140°C for 20 minutes in an oxygen atmosphere using a differential scanning calorimeter" will be referred to as the calorific value measured by DSC (differential scanning calorimetry), and the molar ratio of hydrogen atoms to carbon atoms in the biomass fuel (number of moles of hydrogen atoms / number of moles of carbon atoms) will be referred to as the "molar ratio (H / C)."

[0033] The biomass fuel of the second embodiment has a carbon content of less than 61% by mass, a calorific value measured by DSC of 8.0 J / g or less, and a molar ratio (H / C) adjusted to 1.08 or more and 1.21 or less. When the carbon content in the biomass fuel is less than 61 mass %, spontaneous heat generation can be easily suppressed. By keeping the calorific value measured by DSC at 8.0 J / g or less, spontaneous heat generation due to oxidation is less likely to occur. By adjusting the molar ratio (H / C) to be 1.08 or more and 1.21 or less, spontaneous heat generation due to oxidation can be easily suppressed. Therefore, with the biomass fuel of the second embodiment, spontaneous heat generation can be suppressed. Furthermore, the biomass fuel of the second embodiment can ensure properties (for example, calorific value and pulverizability) that allow it to be used as fuel, due to the balance between the carbon content, the calorific value determined by DSC, and the molar ratio (H / C). Biomass fuel with these properties can be obtained, for example, by carrying out the manufacturing method of Embodiment 1. Specifically, first, semi-carbide is obtained by adjusting the carbon content in the semi-carbide to less than 61 mass% so that the carbon content is not too high (semi-carbide obtaining step), and then the semi-carbide is heated under specific conditions to be oxidized (oxidation step).

[0034] The carbon content in the biomass fuel of the second embodiment may be 60% by mass or less, 59.0% by mass or less, or 58.5% by mass or less, from the viewpoint of making spontaneous heating less likely to occur. The carbon content in the biomass fuel of the second embodiment is preferably 45% by mass or more, more preferably 50% by mass or more, and even more preferably 55% by mass or more, from the viewpoint of ensuring the calorific value of the biomass fuel. In this specification, the carbon content in biomass fuel can be measured in the same manner as the carbon content in the semi-carbonized material described above.

[0035] In the biomass fuel of the second embodiment, the molar ratio of hydrogen atoms to carbon atoms (H / C) in the biomass fuel is preferably 1.09 or more and 1.20 or less, and more preferably 1.10 or more and 1.19 or less. In this specification, the hydrogen content in biomass fuel is an elemental analysis value measured in accordance with JIS M8819 (1997), and is the content (mass%) of hydrogen atoms in the biomass fuel on a dry and ash-free basis (daf). The molar ratio of hydrogen atoms to carbon atoms (H / C) in a biomass fuel is calculated based on the carbon atom content (mass%) and hydrogen atom content (mass%) in the biomass fuel on an anhydrous ash-free (daf) basis. The molar ratio (H / C) is the ratio of the number of moles of hydrogen atoms [mol] to the number of moles of carbon atoms [mol] in the biomass fuel, and its unit is [mol / mol]. The methods for measuring the carbon content in the biomass fuel and the molar ratio of hydrogen atoms to carbon atoms (H / C) in the biomass fuel will be described in detail in the Examples below.

[0036] In the biomass fuel of the second embodiment, the calorific value (calorific value by DSC) when held at 140°C for 20 minutes in an oxygen atmosphere using a differential scanning calorimeter is preferably 1.0 J / g or more and 8.0 J / g or less, more preferably 1.0 J / g or more and 7.5 J / g or less, even more preferably 1.0 J / g or more and 7.0 J / g or less, even more preferably 3.0 J / g or more and 7.0 J / g or less, and even more preferably more than 5.0 J / g and 7.0 J / g or less. Furthermore, the calorific value (calorific value by DSC) when held at 140°C for 20 minutes in an oxygen atmosphere using the differential scanning calorimeter may be 3.0 J / g or more and 8.0 J / g or less, or may be more than 5.0 J / g and 8.0 J / g or less. The method for measuring the calorific value by DSC will be described in detail in the Examples below.

[0037] The biomass used in the above-described embodiment will be described.

[0038] (biomass) The biomass is not particularly limited, but examples thereof include woody biomass, herbaceous biomass, agricultural residue biomass, palm biomass, cellulose products, and pulp products. As used herein, crop residue biomass means anything other than the edible parts. As used herein, palm biomass refers to agricultural waste from palm trees that can be used as biomass fuel. The biomass is preferably at least one selected from the group consisting of woody biomass, herbaceous biomass, agricultural crop residue biomass, and palm biomass.

[0039] Examples of woody biomass include conifers (e.g., cedar, pine, eucalyptus, cypress, and fir), and broad-leaved trees (e.g., birch, acacia, black locust, beech, zelkova, katsura, paulownia, rubber tree, and camphor tree). Woody biomass may also be construction waste (e.g., cut off wood, chips generated at processing plants, and sawdust), forest residues, thinned wood, and bamboo. Examples of herbaceous biomass include grasses, naturally grown plants, and artificially planted plants. Herbaceous biomass may be hemp, cotton, rice straw, rice husks, wheat straw, bamboo grass, napier grass, sorghum, and Japanese silver grass.

[0040] Crop residue biomass includes, for example, leaves, fruit clusters, stems, roots, and other non-edible parts of crops such as wheat, corn, potato, sugarcane (including bagasse), and banana.

[0041] Examples of palm biomass include palm kernel shells (PKS), empty fruit bunches (EFB), and palm trunks. The above-described biomass may be used singly or in combination of two or more kinds.

[0042] (Other ingredients) The biomass fuel obtained by the production method of the first embodiment and the biomass fuel of the second embodiment may contain other components, such as binders and various additives. The content of other components is 20% by mass or less, preferably 10% by mass or less, more preferably 5.0% by mass or less, and even more preferably 1.0% by mass or less, based on the total amount of biomass fuel.

[0043] The present invention is not limited to the above-described embodiment, and any modifications and improvements that can achieve the object of the present invention are included in the present invention. [Example]

[0044] Examples of the present invention will be described below, but the present invention is not limited to these examples.

[0045] In this example, black pellets are sometimes referred to as BP. Black pellets are semi-carbonized pellets made from biomass that are heat-treated in an oxygen-free environment. Tables 1 and 2 show the properties and physical characteristics of the BP used in each example.

[0046] [Table 1]

[0047] [Table 2]

[0048] Explanation of Tables 1 and 2 Proximate analysis values ​​were measured in accordance with JIS M8812 (2004). Of the elemental analysis values, carbon, hydrogen, nitrogen, and sulfur were measured in accordance with JIS M8819 (1997), and oxygen was calculated from other analytical values ​​in accordance with JIS M8813 (2004). The higher heating value is a value measured in accordance with JIS M8814 (2003). The lower heating value is a value measured in accordance with JIS M8814 (2003). The fuel ratio is "fixed carbon / volatiles." Total sulfur is determined in accordance with JIS M8813 (2004) "Coals and cokes - Elemental analysis method." "DB" indicates higher heating value on a dry basis. "AR" indicates arrival base. "AD" indicates air dry basis. "daf" indicates dry ash-free basis. The fines content is measured by a method conforming to ISO 18846. Mechanical durability (unit: %) is measured by a method conforming to ISO 17831-1. Bulk density is measured by a method conforming to ISO 17828. HGI is measured using a method conforming to JIS M8801 (2008).

[0049] Examples 1 to 14 The black pellets were heated and oxidized (oxidation step) under the conditions shown in Tables 3 and 4. In this way, the biomass fuels of Examples 1 to 14 were obtained.

[0050] Example 15 The black pellets were crushed and sieved to obtain powdered semi-carbide with a particle size of 1 mm to 2 mm. The semi-carbide was heated and oxidized under the conditions shown in Table 4 (oxidation step) to obtain the biomass fuel of Example 16.

[0051] Example 16 The black pellets were crushed and sieved to obtain powdered semi-carbide with a particle size of less than 1 mm. The semi-carbide was heated and oxidized under the conditions shown in Table 4 (oxidation step) to obtain the biomass fuel of Example 17.

[0052] Example 17 Black pellets (cylindrical (diameter 8 mm, length 40 mm)) made from rubber were heated and oxidized under the conditions shown in Table 4 (oxidation step) to obtain the biomass fuel of Example 18.

[0053] Comparative Examples 1 and 2 The black pellets were heated and oxidized (oxidation step) under the conditions shown in Table 3. In this way, the biomass fuels of Comparative Examples 1 and 2 were obtained.

[0054] Comparative Example 3 The black pellets without undergoing the oxidation process were used as the biomass fuel of Comparative Example 3.

[0055] [Comparative Example 4] The black pellets were heated and oxidized under the conditions shown in Table 4 (oxidation process). In this way, the biomass fuel of Comparative Example 4 was obtained.

[0056] [Evaluation] [Elemental analysis] Elemental analysis of the biomass fuel obtained in each example was performed. The analysis method was the same as the analysis method of BP described above. The results are shown in Tables 3 and 4. In Tables 3 and 4, the molar ratio (H / C) [mol / mol] is a value calculated from the elemental analysis value (anhydrous and ash-free basis), and represents the molar ratio of hydrogen atoms to carbon atoms in the biomass fuel (number of moles of hydrogen atoms / number of moles of carbon atoms). The molar ratio (H / C) [mol / mol] of the biomass fuel (black pellets) of Comparative Example 3 was 1.21.

[0057] [Heat of combustion by DSC] Differential scanning calorimetry (DSC) was performed to measure the heat of combustion of the biomass fuel obtained in each example. The results are shown in Tables 3 and 4. The heat of combustion of the biomass fuel (black pellets) of Comparative Example 3 was 12.01 J / g. The samples for heat of combustion measurement were prepared by the following method. The biomass fuel of each example was pulverized to obtain fine powder with a particle size of 0.212 mm or less. The biomass fuels of Examples 15 to 16 were further pulverized to obtain fine powder with a particle size of 0.212 mm or less. These were used as the samples for heat of combustion measurement. The measurement conditions are as follows.

[0058] (Conditions) ·Apparatus: Differential scanning calorimeter (manufactured by Shimadzu Corporation, model number DSC-60) ·Atmosphere: Oxygen atmosphere, 50 mL / min Heating rate and holding time: The temperature was raised from room temperature (25°C) to 140°C at a rate of 50°C / min under a nitrogen atmosphere, then switched to an oxygen atmosphere and held at 140°C for 20 minutes. Sample amount: 5 mg

[0059] [Table 3]

[0060] [Table 4]

[0061] It was confirmed that the biomass fuels of Examples 1 to 17 had a calorific value of 8.0 J / g or less by DSC and a molar ratio (H / C) within the specified range (1.08 to 1.21). It is believed that the biomass fuels of Examples 1 to 17 can suppress spontaneous heat generation. On the other hand, the biomass fuels of Comparative Examples 1 to 4 exhibited high values ​​of calorific value (all 9.76 J / g or more) by DSC, and are therefore considered to be prone to spontaneous heat generation.

[0062] <Higher heating value and fuel ratio> The higher heating value (DB) and fuel ratio were measured for the biomass fuels obtained in Examples 1 to 8, Examples 11 and 12, and Comparative Examples 1 to 3. The measurement method was the same as the measurement method for BP in Table 1.

[0063] (Relationship between higher heating value and DSC heating value, relationship between molar ratio (H / C) and DSC heating value, and relationship between fuel ratio and DSC heating value) 1 to 9 are graphs relating to the biomass fuels of Examples 1 to 8, Examples 11 and 12, and Comparative Examples 1 to 3. 1 to 3 are graphs showing the relationship between the higher heating value (DB) and the heating value measured by DSC. In Examples 1 to 8 and 11 to 12, in which BP was oxidized under predetermined conditions (temperature, oxygen concentration, and time), the calorific value measured by DSC could be reduced while maintaining a higher calorific value. 4 to 6 are graphs showing the relationship between the molar ratio (H / C) and the calorific value measured by DSC. In Examples 1 to 8 and 11 to 12, in which BP was oxidized under predetermined conditions (temperature, oxygen concentration, and time), the heat release measured by DSC was reduced while the molar ratio (H / C) was kept within a predetermined range (1.08 or more and 1.21 or less). 7 to 9 are graphs showing the relationship between the fuel ratio and the calorific value measured by DSC. In Examples 1 to 8 and 11 to 12, in which BP was oxidized under predetermined conditions (temperature, oxygen concentration, and time), the calorific value measured by DSC could be reduced while maintaining the fuel ratio. As shown in FIGS. 1 to 9, in Comparative Examples 1 and 2 in which BP was oxidized at temperatures above 220° C., and in Comparative Example 3 in which BP was not oxidized, the calorific value measured by DSC exceeded 8.0 J / g.

[0064] (Heating rate of biomass fuel) A wire basket test was carried out by the following method to evaluate heat generation properties using the biomass fuels of Examples 11 and 12 and Comparative Examples 3 and 4. The results are shown in FIG.

[0065] (Wire basket test) The wire basket test is carried out in accordance with the United Nations Report on the Transport of Dangerous Goods (Div. 4.2 Spontaneous Combustion Test (Wire Mesh Test)) by suspending a container containing a sample in a constant temperature bath. In this test, a wire basket test was performed using an electric furnace instead of a thermostatic bath. (Test Method) A sample of biomass fuel (1 L of pellets) was placed in a 100 mm square container (volume 1 L), and the container was then hung in an electric furnace at 140°C. With the electric furnace maintained at 140°C, measurements were continuously taken until the temperature of the sample reached 200°C, or until the temperature reached equilibrium or began to decrease and 11 hours had elapsed since the start of the test, whichever was shorter.

[0066] FIG. 10 is a graph showing the relationship between the elapsed time after the samples were placed in the electric furnace and the sample temperature for Examples 11 and 12 and Comparative Examples 3 and 4. As shown in Figure 10, Examples 11 and 12, in which BP was oxidized under specified conditions (temperature, oxygen concentration, and time), were able to suppress the temperature rise of biomass fuel compared to Comparative Example 3, in which no BP oxidation step was performed, and Comparative Example 4, in which BP was oxidized for a short time (10 minutes). [Industrial Applicability]

[0067] The biomass fuel of the present invention can be used for biomass power generation in power plants, steel mills, factories, and the like.

Claims

1. A step of heating and torrefying biomass to obtain torrefied matter having a carbon content of less than 61% by mass; an oxidation step of oxidizing the semi-carbide by heating the semi-carbide in an atmosphere having an oxygen concentration of 3% by volume or more and 13% by volume or less at a temperature of 120°C or more and 220°C or less for 12 minutes or more and 240 minutes or less, Biomass fuel production method.

2. The torrefied material is in the form of powder, pellets, briquettes, or chips. The method for producing biomass fuel according to claim 1 .

3. The semi-carbide obtained in the step of obtaining the semi-carbide is in the form of a pellet, Heating biomass pellets containing the biomass at a temperature of 220°C or higher and 320°C or lower; or It is obtained by molding semi-carbonized biomass into pellets. The method for producing biomass fuel according to claim 1 or 2.

4. the semi-carburized material obtained in the step of obtaining the semi-carburized material is in the form of a briquette, Heating the biomass briquette containing the biomass at 220°C or higher and 320°C or lower; or It is obtained by molding semi-carbonized biomass into briquettes. The method for producing biomass fuel according to claim 1 or 2.

5. The torrefied biomass is Heating the biomass to a temperature of 220°C or higher and 320°C or lower; or Obtained by steam explosion of the biomass. The method for producing biomass fuel according to claim 3 or 4.

6. The semi-carbide obtained in the step of obtaining the semi-carbide is in a chip form, The biomass chips are heated at 220°C or higher and 320°C or lower. The method for producing biomass fuel according to claim 1 or 2.

7. The semi-carbide obtained in the step of obtaining the semi-carbide is in a powder form, obtained by steam explosion of the biomass; or The biomass is crushed into powder, and then the powdered biomass is heated at 220°C or higher and 320°C or lower. The method for producing biomass fuel according to claim 1 or 2.

8. The oxidation step is a step of heating the semi-carbide in an atmosphere having an oxygen concentration of 5% by volume or more and 10% by volume or less at a temperature of 150°C or more and 215°C or less for 30 minutes or more and 240 minutes or less. The method for producing biomass fuel according to any one of claims 1 to 7.

9. When the semi-carbide is heated at a temperature of 180°C or higher and 215°C or lower in the oxidation step, The oxidation step is a step of heating in an atmosphere having an oxygen concentration of 7% by volume or more and 13% by volume or less for 60 minutes or more and 240 minutes or less. The method for producing biomass fuel according to any one of claims 1 to 7.

10. The biomass is at least one selected from the group consisting of woody biomass, herbaceous biomass, agricultural crop residue biomass, and palm biomass. The method for producing biomass fuel according to any one of claims 1 to 9.

11. A biomass fuel, The carbon content in the biomass fuel is less than 61% by mass, the calorific value when held at 140°C for 20 minutes in an oxygen atmosphere using a differential scanning calorimeter is 8.0 J / g or less; the molar ratio of hydrogen atoms to carbon atoms in the biomass fuel (number of moles of hydrogen atoms / number of moles of carbon atoms) is 1.08 or more and 1.21 or less; Biomass fuel.

12. The calorific value when held at 140°C for 20 minutes in an oxygen atmosphere using a differential scanning calorimeter is more than 5.0 J / g. The biomass fuel according to claim 11.

13. The biomass is at least one selected from the group consisting of woody biomass, herbaceous biomass, agricultural crop residue biomass, and palm biomass. The biomass fuel according to claim 11 or 12.

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