Biomass fuel production method and biomass fuel

Abstract

This biomass fuel production method comprises: a step for obtaining a semi-carbonized product having a carbon content of less than 61% by mass by heating and semi-carbonizing a biomass; and an oxidation step for oxidizing the semi-carbonized product by heating the semi-carbonized product under an atmosphere having an oxygen concentration of 3% by volume to 13% by volume under a condition of 120°C to 220°C for 12min to 240 min.

Description

Biomass fuel manufacturing method and biomass fuel

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

[0002] In recent years, CO2, which is considered to be the cause of global warming, ２ Biomass fuels are being developed to reduce greenhouse gas emissions. To improve the pulverizability and calorific value of biomass fuels, methods for carbonizing biomass have been proposed. For example, Patent Document 1 discloses a solid fuel production method in which biomass is heated 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 solid fuel production method is characterized by producing the solid fuel 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 also discloses a carbon material production method that includes a dry distillation step for obtaining biomass charcoal with a carbon content of 61% by weight or more from biomass, and an oxidation step for heating the biomass charcoal to 200°C or higher in an atmosphere with an oxygen concentration of 2 to 13% by volume.

[0003] JP 2009-191085 A JP 2023-024260 A

[0004] While solid fuel obtained by carbonizing biomass has the advantage of improved calorific value and pulverizability, it is known that changes in the chemical structure of biomass make it more susceptible to reaction with oxygen in the air. Therefore, the solid fuel described in Patent Document 1 is thought to have a tendency to spontaneously heat up. Furthermore, the method described in Patent Document 2 aims to suppress spontaneous heat generation by performing an oxidation process after obtaining biomass charcoal with a high carbon content. However, since biomass charcoal with a high carbon content is inherently prone to spontaneous heat generation, the method described in Patent Document 2, which uses such biomass charcoal, leaves room for further study in terms of sufficiently suppressing spontaneous heat generation.

[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.

[0006] [1] A method for producing biomass fuel, comprising: a step of heating and torrefying biomass to obtain a torrefied product having a carbon content of less than 61% by mass; and an oxidation step of oxidizing the torrefied product by heating the torrefied product 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. [2] The method for producing biomass fuel according to [1] above, wherein the torrefied product is in the form of powder, pellets, briquettes, or chips. [3] The method for producing biomass fuel according to [1] above, wherein the torrefied product obtained in the torrefied product 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 torrefied biomass into pellets. [4] The method for producing biomass fuel according to [1] or [2], wherein the torrefied material obtained in the step of obtaining the torrefied material is in the form of a briquette and is obtained by heating a biomass briquette containing the biomass at 220°C or more and 320°C or less, or by molding the torrefied biomass into a briquette shape. [5] The method for producing biomass fuel according to [3] or [4], wherein 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. [6] The method for producing biomass fuel according to [1] or [2], wherein the torrefied material obtained in the step of obtaining the torrefied material is in the form of chips and is obtained by heating the biomass chips at 220°C or more and 320°C or less. [7] The method for producing biomass fuel according to [1] or [2], wherein the torrefied material obtained in the torrefied material obtaining step is in powder form and is obtained by steam explosion of the biomass, or by crushing the biomass into powder and then heating the powdered biomass at 220°C or higher and 320°C or lower. [8] The method for producing biomass fuel according to any one of [1] to [7], wherein the oxidation step is a step of heating the torrefied material in an atmosphere having an oxygen concentration of 5% by volume or higher and 10% by volume or lower, at 150°C or higher and 215°C or lower, for 30 minutes or longer and 240 minutes or shorter.[9] The method for producing biomass fuel according to any one of [1] to [7], wherein, in the oxidation step, when the semi-carbonized material is heated at 180°C or higher and 215°C or lower, the oxidation step is a step of heating the semi-carbonized material 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.

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

[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 (number of moles of hydrogen atoms / number of moles of carbon atoms) is 1.08 to 1.21.

[12] The biomass fuel according to

[11] , wherein 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.

[13] The biomass fuel according to

[11] or

[12] , wherein the biomass is at least one selected from the group consisting of woody biomass, herbaceous biomass, agricultural crop residue biomass, and palm biomass.

[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.

[0009] 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. FIG. 2 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. FIG. 3 is a graph showing the relationship between the higher heating value and the heating value measured by DSC for the biomass fuels of Examples 7, Examples 11-12 and Comparative Example 3. FIG. 4 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 heating value measured by DSC for the biomass fuels of Examples 1 to 8 and Comparative Example 3. FIG. 5 is a graph showing the relationship between the molar ratio (H / C) in the biomass fuels of Examples 1 to 8 and Comparative Example 3 and the heating value measured by DSC for the biomass fuels of Examples 7, Examples 11-12 and Comparative Example 3. FIG. 6 is a graph showing the relationship between the fuel ratio and the heating value measured by DSC for the biomass fuels of Examples 1 to 4 and Comparative Examples 1 to 3. FIG. 7 is a graph showing the relationship between the fuel ratio and the heating value measured by DSC for the biomass fuels of Examples 1 to 8 and Comparative Example 3. 1 is a graph showing the relationship between the fuel ratio of biomass fuel and the calorific value measured by DSC for Example 7, Examples 11 and 12, and Comparative Example 3. FIG. 2 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.

[0010] In this specification, a numerical range expressed using "to" means a range that includes the numerical value before "to" as the lower limit and the numerical value after "to" as the upper limit. In this specification, a mass percent concentration (unit: mass % (mass %)) and a 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 having an oxygen concentration of 3% by volume to 13% by volume.

[0012] In this embodiment, the manufacturing method involves obtaining semi-carbide with a carbon content of less than 61% by mass, and then oxidizing the semi-carbide under specified conditions to produce biomass fuel. While it is desirable for biomass fuel to contain semi-carbide with a high carbon content in order to improve its calorific value and pulverizability, simply increasing the carbon content of the semi-carbide increases its susceptibility to spontaneous heating. In the method of Patent Document 2, the carbon content of 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, the method of Patent Document 2 requires carbonization of the biomass at high temperatures to increase the carbon content of the semi-carbide to 61% by mass or more. As a result, many volatile components are released from the biomass during the carbonization process, which tends to reduce the yield of carbonized material usable as fuel. Furthermore, in the method of Patent Document 2, the carbon content of the semi-carbide is excessively high, so even if the semi-carbide is subsequently subjected to an oxidation process, spontaneous heating of the carbonized material is not sufficiently suppressed. In contrast, the manufacturing method according to the present embodiment, based on the opposite concept to that of Patent Document 2, first obtains a torrefied product by adjusting the carbon content of the torrefied product so that it is not too high, specifically, so that the carbon content of the torrefied product is less than 61% by mass. In other words, the torrefied product obtaining process of the present embodiment allows biomass to be torrefied at a moderate temperature, allowing a larger amount of volatile components to remain in the torrefied product. As a result, torrefied product with properties usable as fuel (e.g., calorific value and pulverizability) can be obtained without unnecessarily reducing the yield of torrefied product, thereby enabling the torrefied product to be effectively utilized. Furthermore, the manufacturing method according to the present embodiment further performs an oxidation process on such torrefied product (torrefied product with a larger amount of volatile components remaining), thereby suppressing spontaneous heating while maintaining its usable properties as fuel. Therefore, the manufacturing method according to the present embodiment produces a biomass fuel with suppressed spontaneous heating.

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

[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, pellet, briquette, or chip. Hereinafter, the semi-carbide obtained in the step of obtaining the semi-carbide will be described as follows: a powder-shaped semi-carbide will be referred to as a semi-carbide according to Mode 1, a chip-shaped semi-carbide will be referred to as a semi-carbide according to Mode 2, a pellet-shaped semi-carbide will be referred to as a semi-carbide according to Mode 3, and a briquette-shaped semi-carbide will be referred to as a semi-carbide according to Mode 4.

[0015] <Semi-carbide 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 powdered form. The 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, we will explain the case where a powdery semi-carbonized material is obtained by the above-mentioned method (1) (by steam explosion of biomass). Steam explosion refers to a process in which biomass is steamed for a short period of time in a sealed container such as a pressure-resistant container with high-temperature, high-pressure saturated steam, and then suddenly released to atmospheric pressure for rapid cooling, destroying the structure of the biomass (in the case of wood, the wood structure) through adiabatic expansion. The shape of the biomass used for steam explosion is not particularly limited. 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 in the as-obtained state, or biomass obtained after pulverizing the obtained biomass to any shape and size. For example, palm fruit bunches can be used as-obtained. The biomass is pulverized and semi-carbonized to powder by steam explosion. For example, when the biomass used in the steam explosion is chip-like biomass (biomass chips), the biomass chips are pulverized into powder by the steam explosion. The obtained powdery 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 of the steam explosion is preferably 0.1 MPa or higher and 9.0 MPa or lower, more preferably 1.0 MPa or higher and 6.5 MPa or lower. The time of the steam explosion is preferably 10 minutes or higher and 60 minutes or lower, more preferably 15 minutes or higher and 30 minutes or lower.

[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 the 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 for steam explosion is biomass chips, the particle size of the powdery biomass obtained by steam explosion is preferably 1000 μm or less, more preferably 500 μm or less. In this specification, particle size means the major axis diameter. The major axis diameter of the biomass means the maximum length of the line when any two points on the outer contour of the biomass are connected by a straight line.

[0020] Next, a case where a powdery semi-carbonized material is obtained by the method (2) (by crushing biomass into powder and then heating the powdery biomass at 220°C or more and 320°C or less) will be described. The method for crushing biomass into powder is not particularly limited, and crushing can be performed using a known crusher. For example, when wood is used as woody biomass, large pieces of wood may be coarsely crushed into chips of about several centimeters and then crushed into powder. The particle size of the powdery 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 the biomass and the particle size of the semi-carbonized biomass can both be adjusted by known methods (for example, using a sieve, etc.).

[0021] Examples of methods for heating powdered biomass at 220°C or higher and 320°C or lower include methods in which biomass is heated for a certain period of time (e.g., air heating, exhaust gas heating, direct heating, etc.) in a container (preferably in a container that is sealed off from air). 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 when heating powdered biomass 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 1 minute to 240 minutes, preferably 1 minute to 60 minutes. The atmosphere in which powdered biomass is heated is not particularly limited, but is preferably an air-sealed atmosphere, a dry distillation gas atmosphere, or a combustion exhaust gas atmosphere.

[0022] <Semi-carbonized Product According to Aspect 2> (Semi-carbonized Product in Chip Form) In one aspect of the manufacturing method of this embodiment, the semi-carbonized product obtained in the step of obtaining the semi-carbonized product is in chip form. The semi-carbonized product in chip form can be obtained, for example, by heating acquired chip-form biomass or chip-form biomass obtained by pulverizing biomass at 220°C or higher and 320°C or lower. The size of the semi-carbonized product in chip form is not particularly limited. 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 type, heating temperature, heating time, and atmosphere used when heating the biomass in chip form are preferably in the same ranges as the heating method, heating type, heating temperature, heating time, and atmosphere used when heating the powdery biomass described above.

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

[0024] The "biomass pellets containing biomass" in (i) above refer to, for example, biomass pellets obtained by molding powdered biomass that has not been heated or torrefied, and are usually referred to as white pellets. The "tombricate biomass" in (ii) above refers to the powdered torrefied material according to Aspect 1. That is, the pellet-shaped torrefied 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 molding the powdered torrefied 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 method (i) above are preferably in the same ranges as the heating method, heating method, heating temperature, heating time, and atmosphere used when heating the powdered biomass described above. A known pelletizer or the like can be used to mold the pellets. The pellets are produced, for example, by extruding powdered biomass or powdered torrefied material through a metal hole (for example, with a diameter of 5 mm to 10 mm and a length of 5 mm to 50 mm).

[0025] <Trimmed Product According to Aspect 4> (Briquette-Shaped Trimmed Product) In one aspect of the manufacturing method of the present embodiment, the torimmed product obtained in the step of obtaining the torimmed product is in the form of a briquette. The size and shape of the torimmed product are not particularly limited. Briquettes typically have a width and length greater than those of pellets. When the briquette is cylindrical, the torimmed product has a diameter of 10 mm to 100 mm and a length of 10 mm to 300 mm, for example. The torimmed product can be obtained, for example, by (iii) heating a biomass briquette containing biomass at 220°C to 320°C, or (iv) molding torimmed biomass into a briquette.

[0026] The "biomass briquette containing biomass" in (iii) refers to, for example, a biomass briquette obtained by molding powdered biomass that has not been heated or torrefied. The size of the "torrefied biomass" in (iv) is larger than or equal to the size of the torrefied biomass contained in the pellet-shaped torrefied product. The "torrefied torrefied biomass" in (iv) may be the powdered torrefied product according to Aspect 1. That is, the briquette-shaped torrefied product according to Aspect 4 can be obtained by heating a biomass briquette containing untorrefied biomass at 220°C or higher and 320°C or lower (method (iii) above), or by molding a torrefied product of a predetermined size (for example, the powdered torrefied product according to Aspect 1) into a briquette (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 those for 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 biomass into briquettes or cylindrical shapes using a briquetting machine.

[0027] <Oxidation Step> 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 in an atmosphere having 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 for the semi-carbide in the oxidation step are as follows:

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

[0029] In the manufacturing method of this embodiment, the heating temperature of the torrefied material 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 torrefied material in the oxidation step is 120°C or higher, the carbon and oxygen in the torrefied material react efficiently, making it easier to obtain biomass fuel with reduced calorific value. When the heating temperature of the torrefied material in the oxidation step is 220°C or lower, it is possible to suppress the thermal decomposition of the torrefied material. As a result, it is easier to obtain biomass fuel with reduced spontaneous heat generation while improving yield.

[0030] In the manufacturing method of this embodiment, the heating time of the torrefied material 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. When the heating time of the torrefied material in the oxidation step is 12 minutes or more, a minimum processing time for the carbon in the torrefied material to react with oxygen can be ensured. As a result, biomass fuel with reduced calorific value can be easily obtained. When the heating time of the torrefied material in the oxidation step is 240 minutes or less, a sufficient processing time can be ensured for the carbon in the torrefied material to react with oxygen and suppress 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 150°C to 215°C for 0.5 hours to 4.0 hours in an atmosphere having an oxygen concentration of 5% to 10% by volume. When the semi-carbide is heated at 180°C to 215°C in the oxidation step, the oxidation step is preferably a step of heating under conditions of 7% to 13% by volume in an atmosphere having an oxygen concentration of 1.0 hours to 4.0 hours. In the manufacturing method of this embodiment, the oxidation step can be performed in a known reactor.

[0032] [Second Embodiment] A biomass fuel according to a 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 (number of moles of hydrogen atoms / number of moles of carbon atoms) of 1.08 to 1.21. Hereinafter, for ease of explanation, the "calorific value of the biomass fuel according to the second embodiment when 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. A carbon content of less than 61% by mass in the biomass fuel facilitates suppression of spontaneous heat generation. A calorific value measured by DSC of 8.0 J / g or less makes spontaneous heat generation due to oxidation less likely to occur. Adjusting the molar ratio (H / C) to 1.08 or more and 1.21 or less facilitates suppression of spontaneous heat generation due to oxidation. Therefore, the biomass fuel of the second embodiment can suppress spontaneous heat generation. Furthermore, the biomass fuel of the second embodiment can ensure properties (e.g., calorific value and pulverizability) that make it usable as a fuel due to the balance between the carbon content, the calorific value measured by DSC, and the molar ratio (H / C). A biomass fuel having such properties can be obtained, for example, by carrying out the production method of the first embodiment. 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 (step of obtaining semi-carbide), and then the semi-carbide is heated under specific conditions to be oxidized (step of oxidation).

[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 the 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, more preferably 1.10 or more and 1.19 or less. In this specification, the hydrogen content in the 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 ash-free basis (daf). The molar ratio of hydrogen atoms to carbon atoms (H / C) in the biomass fuel is calculated based on the content (mass%) of carbon atoms and the content (mass%) of hydrogen atoms in the biomass fuel on a dry ash-free basis (daf). 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 is expressed in units of [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 under 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 under an oxygen atmosphere using the differential scanning calorimeter may be 3.0 J / g or more and 8.0 J / g or less, or 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) Biomass is not particularly limited, and examples thereof include woody biomass, herbaceous biomass, agricultural crop residue biomass, palm biomass, cellulose products, and pulp products. In this specification, agricultural crop residue biomass refers to parts other than edible parts. In this specification, palm biomass refers to agricultural waste from palm trees that can be used as biomass fuel. The biomass is preferably at least one type 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 also 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), palm empty fruit bunches (EFB), palm trunks, etc. The above-described biomass may be used alone or in combination of two or more.

[0042] (Other Components) The biomass fuel obtained by the production method of the first embodiment and the biomass fuel of the second embodiment may contain other components. Examples of other components include 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 the 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.

[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]

[0047]

[0048] Explanation of Tables 1 and 2: Proximate analysis values ​​are values ​​measured in accordance with JIS M8812 (2004). Of the elemental analysis values, carbon, hydrogen, nitrogen, and sulfur are values ​​measured in accordance with JIS M8819 (1997), and oxygen is a value calculated from other analytical values ​​in accordance with JIS M8813 (2004). Higher heating value is a value measured in accordance with JIS M8814 (2003). Lower heating value is a value measured in accordance with JIS M8814 (2003). The fuel ratio is "fixed carbon / volatile matter." Total sulfur is quantified in accordance with JIS M8813 (2004) "Coals and cokes - Elemental analysis method." "DB" indicates higher heating value on a dry basis. "AR" indicates arrival basis. "AD" indicates air-dried basis. "daf" indicates dry ash-free basis. The fine powder ratio is measured by a method conforming to ISO 18846. The mechanical durability (unit: %) is measured by a method conforming to ISO 17831-1. The bulk density is measured by a method conforming to ISO 17828. The HGI is measured by 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] Black pellets were crushed and sieved to obtain powdery 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 15.

[0051] [Example 16] Black pellets were crushed and sieved to obtain powdery 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 16.

[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 17.

[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, biomass fuels of Comparative Examples 1 and 2 were obtained.

[0054] Comparative Example 3 Black pellets that were not subjected to an oxidation step 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 step), thereby obtaining the biomass fuel of Comparative Example 4.

[0056] [Evaluation] <Elemental Analysis> Elemental analysis was performed on the biomass fuel obtained in each example. The analysis method was the same as the analysis method for 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 (dry ash-free basis) and indicates 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] <Calorific Value by DSC> Differential scanning calorimetry (DSC) was performed to measure the calorific value of the biomass fuel obtained in each example. The results are shown in Tables 3 and 4. The calorific value of the biomass fuel (black pellets) of Comparative Example 3 was 12.01 J / g. Samples for calorific value measurement were prepared in the following manner. 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 and 16 were further pulverized to obtain fine powder with a particle size of 0.212 mm or less. These were used as samples for calorific value measurement. The measurement conditions were as follows:

[0058] (Conditions) Apparatus: Differential scanning calorimeter (Shimadzu Corporation, Model No. DSC-60) Atmosphere: Oxygen atmosphere, 50 mL / min Heating rate and holding time: Under a nitrogen atmosphere, the temperature was raised from room temperature (25°C) to 140°C at a rate of 50°C / min, and then the atmosphere was switched to oxygen and held at 140°C for 20 minutes. Sample amount: 5 mg

[0059]

[0060]

[0061] It was confirmed that the biomass fuels of Examples 1 to 17 had a calorific value by DSC of 8.0 J / g or less 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 showed high calorific values ​​by DSC (all 9.76 J / g or more), and are therefore believed 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 heating value measured by DSC, relationship between molar ratio (H / C) and heating value measured by DSC, and relationship between fuel ratio and heating value measured by DSC) Figures 1 to 9 are graphs related to the biomass fuels of Examples 1 to 8, Examples 11 and 12, and Comparative Examples 1 to 3. Figures 1 to 3 are graphs showing the relationship between higher heating value (DB) and heating value measured by DSC. In Examples 1 to 8 and Examples 11 and 12, in which BP oxidation was performed under predetermined conditions (temperature, oxygen concentration, and time), it was possible to reduce the heating value measured by DSC while maintaining the higher heating value. Figures 4 to 6 are graphs showing the relationship between molar ratio (H / C) and heating value measured by DSC. In Examples 1 to 8 and Examples 11 and 12, in which BP oxidation was performed under predetermined conditions (temperature, oxygen concentration, and time), it was possible to reduce the heating value measured by DSC while maintaining the molar ratio (H / C) 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 Examples 11 and 12, in which BP was oxidized under predetermined conditions (temperature, oxygen concentration, and time), the calorific value measured by DSC was reduced while maintaining the fuel ratio. As shown in Figures 1 to 9, in Comparative Examples 1 and 2, in which BP was oxidized at 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] (Heat generation property of biomass fuel) A wire basket test was carried out by the following method to evaluate heat generation property 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 conducted by suspending a container containing a sample in a thermostatic chamber in accordance with the United Nations Report on the Transport of Dangerous Goods (Div. 4.2 Spontaneous Combustion Test (Wire Mesh Test)). In this test, the wire basket test was conducted using an electric furnace instead of a thermostatic chamber. (Test Method) A 100 mm square container (volume 1 L) was filled with biomass fuel (1 L of pellets) as a sample, and then the container was suspended in an electric furnace at 140°C. With the electric furnace maintained at 140°C, measurements were continuously conducted until the temperature of the sample reached 200°C, or until the temperature equilibrated or began to decrease and 11 hours had elapsed since the start of the test, whichever was shorter.

[0066] Figure 10 is a graph showing the relationship between the elapsed time after the sample was 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 oxidation was performed under predetermined conditions (temperature, oxygen concentration, and time), were able to suppress the temperature rise of the biomass fuel compared to Comparative Example 3, in which no BP oxidation step was performed, and Comparative Example 4, in which BP oxidation was performed for a short time (10 minutes).

[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 method for producing biomass fuel, comprising: a step of heating and semi-carbonizing biomass to obtain semi-carbonized material having a carbon content of less than 61% by mass; and an oxidation step of oxidizing the semi-carbonized material by heating the semi-carbonized material 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.

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

3. The method for producing biomass fuel according to claim 1 or 2, wherein the torrefied material obtained in the step of obtaining the torrefied material is in the form of pellets, and is obtained by heating biomass pellets containing the biomass at a temperature of 220°C or higher and 320°C or lower, or by molding torrefied biomass into pellets.

4. The method for producing biomass fuel according to claim 1 or 2, wherein the torrefied material obtained in the step of obtaining the torrefied material is in the form of a briquette, and is obtained by heating a biomass briquette containing the biomass at a temperature of 220°C or higher and 320°C or lower, or by molding torrefied biomass into a briquette shape.

5. The method for producing biomass fuel according to claim 3 or 4, wherein the torrefied biomass is obtained by heating the biomass at a temperature of 220°C or higher and 320°C or lower, or by steam explosion of the biomass.

6. The method for producing biomass fuel according to claim 1 or 2, wherein the semi-carbonized material obtained in the step of obtaining the semi-carbonized material is in chip form and is obtained by heating the chip-form biomass at a temperature of 220°C or higher and 320°C or lower.

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

8. A method for producing biomass fuel as described in any one of claims 1 to 7, wherein the oxidation step is a step of heating the semi-carbonized material 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.

9. A method for producing biomass fuel as described in any one of claims 1 to 7, wherein, in the oxidation step, when the semi-carbonized material is heated at 180°C or higher and 215°C or lower, the oxidation step is a step of heating in an atmosphere with 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.

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

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 (number of moles of hydrogen atoms / number of moles of carbon atoms) is 1.08 or more and 1.21 or less.

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

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

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