Biomass solid fuel and method for producing biomass solid fuel

Abstract

This biomass solid fuel contains semi-carbonized pellets containing a semi-carbonized biomass in which biomass is semi-carbonized, and a hydrophobic substance covering at least part of the surfaces of the semi-carbonized pellets, wherein the content of the hydrophobic substance with respect to the total mass of the biomass solid fuel is 1.0 mass% to 30.0 mass%.

Description

Biomass solid fuel and method for producing biomass solid fuel

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

[0002] In recent years, CO2, which is considered to be the cause of global warming, ２ Biomass fuels are being considered to reduce CO emissions. ２ However, plants produce CO ２ As a result, the use of biomass fuels made from wood and other materials reduces atmospheric CO2 emissions overall. ２ If this biomass fuel is used as fuel for a power plant, CO emissions will be significantly reduced compared to power plants that use conventional fossil fuels such as coal. ２ It is expected to reduce CO2 emissions. While other renewable energy sources, such as solar and wind power, are becoming more widespread, biomass fuels can be stored in silos and thus flexibly generate electricity in line with demand (supply-demand adjustment function), unlike other sources that rely on natural resources (such as sunlight and weather). This makes them an excellent renewable energy source, as they can be operated in a similar manner to conventional fossil-fuel thermal power plants. As biomass power generation has become more widespread in Japan in recent years, various studies have been conducted on the characteristics of biomass fuels. For example, Patent Document 1 discloses a method for producing solid fuel, including a spraying step in which heated oil is sprayed onto solid biomass pieces to permeate the solid biomass pieces, and a molding step in which the oil-permeated solid biomass pieces are compressed and molded to produce solid fuel. Patent Document 2 discloses wood fuel pellets composed of a mixture of wood flour with a particle size of 0.2 mm or less, dried to a water content of 2 to 7% by weight, and rosin in an amount of 0.1 to 5% by weight. Furthermore, Non-Patent Document 1 discloses a technique for semi-carbonizing biomass in biomass fuel in order to improve the calorific value.

[0003] International Publication No. 2018 / 135660 Japanese Patent Application Laid-Open No. 2014-185304

[0004] Manufacturing Technology and Evaluation Method of Heat-Treated Biomass Pellet Fuel, Takahiro Yoshida, Experimental Mechanics, Vol. 19 (2019) No. 3

[0005] However, as biomass power generation becomes more widespread, issues surrounding biomass fuels are becoming more apparent. One of these is the phenomenon of spontaneous combustion due to the spontaneous heat generated by the biomass fuel itself. In recent years, fires caused by spontaneous heat generation of biomass fuels (e.g., wood pellets) have frequently occurred at biomass power plants and other facilities. When large quantities of biomass fuel are stored for long periods of time, the temperature gradually rises due to spontaneous heat generation, which can eventually lead to fire. Spraying water to cool the fuel can actually further promote spontaneous heat generation due to (1) promotion of biomass fermentation and oxidation, (2) heat generation in biomass due to the heat of moisture, and (3) heat generation in biomass due to the heat of condensation of water vapor. Water is also sometimes sprayed to suppress dust generated during handling, but for the same reason, this increases the risk of spontaneous combustion.

[0006] An object of the present invention is to provide a biomass solid fuel capable of suppressing spontaneous combustion, and a method for producing the biomass solid fuel.

[0007] [1] A biomass solid fuel comprising torrefied pellets containing torrefied biomass obtained by torrefying biomass, and a hydrophobic substance coating at least a portion of the surface of the torrefied pellets, wherein the content of the hydrophobic substance is 1.0 mass% to 30.0 mass% relative to the total mass of the biomass solid fuel. [2] The biomass solid fuel according to [1], wherein the proportion of fixed carbon in the biomass solid fuel is 20% or more by mass. [3] The biomass solid fuel according to [1] or [2], wherein the hydrophobic substance is one or more selected from the group consisting of heavy oil, light oil, petroleum-based residual oil, vegetable oil, waste plastic oil, waste tire oil, and biotar. [4] The biomass solid fuel according to any one of [1] to [3], wherein the hydrophobic substance is vegetable oil. [5] The biomass solid fuel according to any one of [1] to [4], wherein the hydrophobic substance is one or more selected from the group consisting of oleic acid, stearic acid, linoleic acid, palmitic acid, and lauric acid. [6] The biomass solid fuel according to [1] or [2], wherein the hydrophobic substance is vegetable oil, the vegetable oil contains a triglyceride in which three fatty acids are ester-bonded to glycerin, and the combined mass percentage of saturated fatty acids having no carbon-carbon double bond and unsaturated fatty acids having one carbon-carbon double bond is 70% or more relative to the total mass of the fatty acids constituting the triglyceride. [7] The biomass solid fuel according to [6], wherein the saturated fatty acid having no carbon-carbon double bond is one or more selected from the group consisting of caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, hepcadecanoic acid, stearic acid, arachidic acid, behenic acid, and lignoceric acid, and the unsaturated fatty acid having one carbon-carbon double bond is one or more selected from the group consisting of palmitoleic acid, heptadecenoic acid, oleic acid, eicosenoic acid, and tetracosenoic acid. [8] The biomass solid fuel according to [6] or [7], wherein the vegetable oil is one or more selected from the group consisting of olive oil, rapeseed oil, palm oil, sunflower oil, safflower oil, coconut oil, and pongamia oil.[9] The biomass solid fuel according to any one of [6] to [8], wherein the content of the vegetable oil is 2.5 mass% or more and 15.0 mass% or less relative to the total mass of the biomass solid fuel.

[10] The biomass solid 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.

[0008]

[11] A method for producing a biomass solid fuel, comprising the steps of obtaining torrefied pellets containing torrefied biomass obtained by torrefying biomass, and coating at least a portion of the surface of the torrefied pellets with a hydrophobic substance so that the content of the hydrophobic substance is 1.0% by mass or more and 30.0% by mass or less relative to the total mass of the biomass solid fuel.

[12] The method for producing a biomass solid fuel according to

[11] , wherein the coating step is carried out by spraying, sprinkling, applying, or depositing a coating liquid containing the hydrophobic substance onto the surface of the torrefied pellets, or by immersing the torrefied pellets in a coating liquid containing the hydrophobic substance.

[13] The method for producing a biomass solid fuel according to

[11] or

[12] , wherein the proportion of fixed carbon in the biomass solid fuel is 20% by mass or more.

[14] The method for producing a biomass solid fuel according to any one of

[11] to

[13] , wherein the hydrophobic substance is one or more selected from the group consisting of heavy oil, light oil, petroleum-based residual oil, vegetable oil, waste plastic oil, waste tire oil, and biotar.

[15] The method for producing a biomass solid fuel according to any one of

[11] to

[13] , wherein the hydrophobic substance is vegetable oil, the vegetable oil contains a triglyceride in which three fatty acids are ester-bonded to glycerin, and the combined mass percentage of saturated fatty acids having no carbon-carbon double bond and unsaturated fatty acids having one carbon-carbon double bond is 70% or more relative to the total mass of the fatty acids constituting the triglyceride.

[16] The method for producing a biomass solid fuel according to

[15] , wherein the saturated fatty acid having no carbon-carbon double bond is one or more selected from the group consisting of caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, hepcadecanoic acid, stearic acid, arachidic acid, behenic acid, and lignoceric acid, and the unsaturated fatty acid having one carbon-carbon double bond is one or more selected from the group consisting of palmitoleic acid, heptadecenoic acid, oleic acid, eicosenoic acid, and tetracosenoic acid.

[17] The method for producing a biomass solid fuel according to

[15] or

[16] , wherein the vegetable oil is one or more selected from the group consisting of olive oil, rapeseed oil, palm oil, sunflower oil, safflower oil, coconut oil, and pongamia oil.

[18] The method for producing a biomass solid fuel according to any one of

[15] to

[17] , wherein in the coating step, the content of the vegetable oil is 2.5 mass% or more and 15.0 mass% or less relative to the total mass of the biomass solid fuel.

[19] The method for producing a biomass solid fuel according to any one of

[11] to

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

[20] The method for producing a biomass solid fuel according to any one of

[11] to

[19] , wherein in the coating step, the coating liquid is a hydrophobic solution containing the hydrophobic substance and a solvent, an emulsion containing the hydrophobic substance, water, and an emulsifier, a molten liquid containing a melted hydrophobic substance, or a spreading-agent-containing molten liquid containing the melted hydrophobic substance and a spreading agent.

[21] The method for producing a biomass solid fuel according to

[20] , wherein when the molten liquid or the spreading-agent-containing molten liquid is used to coat the surfaces of the torrefied pellets, the viscosity of the molten liquid or the spreading-agent-containing molten liquid is 8 mPa·s or more and 200 mPa·s or less.

[22] The method for producing a biomass solid fuel according to any one of

[11] to

[21] , wherein the step of obtaining torrefied pellets comprises a step of molding the biomass to obtain biomass pellets, and a step of heating the biomass pellets at 240°C or more and 350°C or less.

[0009] According to one aspect of the present invention, it is possible to provide a biomass solid fuel capable of suppressing spontaneous combustion, and a method for producing the biomass solid fuel.

[0010] Graph showing the results of a wire basket test for Examples 1 to 4 and Comparative Example 1. Graph showing the results of a wire basket test for Examples 5 to 10 and Comparative Example 1. Graph showing the results of a wire basket test for Example 11 and Comparative Example 1. Graph showing the results of a wire basket test for Examples 1A to 8A, Reference Examples 1A to 4A, and Comparative Example 1A. Graph showing the relationship between the mass percentage of the total content (also referred to as "C:0+C:1") of saturated fatty acids having no carbon-carbon double bond (also referred to as C:0) and unsaturated fatty acids having one carbon-carbon double bond (also referred to as C:1) relative to the total mass of fatty acids constituting the triglyceride, and the time to reach 200°C. Graph showing the results of a spontaneous heat generation test for Example 8A and Comparative Example 1A.

[0011] 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.

[0012] [First embodiment] [Biomass solid fuel] The biomass solid fuel of this embodiment contains torrefied pellets containing torrefied biomass obtained by torrefying biomass, and a hydrophobic substance that coats at least a portion of the surface of the torrefied pellets. The content of the hydrophobic substance is 1.0 mass % or more and 30.0 mass % or less relative to the total mass of the biomass solid fuel.

[0013] The biomass contained in the biomass solid fuel of this embodiment is heated and semi-carbonized biomass (semi-carbonized biomass). Semi-carbonization refers to a state in which at least a portion of the biomass is carbonized. In this specification, "semi-carbonization" encompasses a state in which a portion of the biomass is carbonized and a state in which all of the biomass is carbonized.

[0014] Biomass pellets, including wood pellets, are fuels made by compressing various biomass materials into pellets for improved handling. They have been used for environmentally friendly home heating and biomass power generation. Semi-carbonizing these biomass pellets increases their energy density and improves their crushability and water resistance, making them suitable for use in existing coal-fired power plants. Semi-carbonization, also known as torrection, is a process that involves heating biomass at temperatures between 200°C and 350°C to decompose volatile components (low-boiling components) and increase the carbon ratio. When biomass is gradually heated above 200°C, carbonization progresses while generating pyrolysis gas (see Figure 2 in Non-Patent Document 1). Although the weight of biomass decreases, the calorific value increases due to carbonization, improving the energy density per unit weight. Furthermore, the pyrolysis gas generated during "torrefaction" can be used as fuel for heat treatment of biomass, so "torrefaction" can be carried out without adding new fuel from outside, which is environmentally friendly. In this specification, "torrefied" biomass pellets are referred to as "torrefied pellets," and biomass pellets that have not been "torrefied" are sometimes referred to as "general biomass pellets."

[0015] Torrefied pellets have superior hydrophobicity compared to general biomass pellets. The biomass solid fuel of this embodiment has a structure in which at least a portion of the surface of the hydrophobic torrefied pellets is further coated with a hydrophobic substance, making it difficult for oxygen and moisture in the air to penetrate into the interior. For example, in the biomass solid fuel of this embodiment, more than half of the surface of the torrefied pellets is coated with a hydrophobic substance (see Table 3 in the Examples section below). This biomass solid fuel of this embodiment is obtained by obtaining torrefied pellets and then applying a hydrophobic substance to the surface of the torrefied pellets. Therefore, it is believed that the coverage rate (area %) of the torrefied pellet surface with the hydrophobic substance is higher than that of solid fuels obtained by adding oil to untorrefied biomass and then pelletizing it, as in Patent Documents 1 and 2. As a result, the structure makes it difficult for oxygen and moisture in the air to come into contact with the biomass inside the pellets. Furthermore, the hydrophobic substance used as a coating material also has the effect of adhering fine particles together, which reduces the generation of dust that normally occurs during handling and eliminates the need for excessive watering. Therefore, the biomass solid fuel of this embodiment can suppress spontaneous combustion caused by the phenomenon of spontaneous heating.

[0016] Furthermore, according to the biomass solid fuel of this embodiment, the surface of the torrefied pellets is covered with a hydrophobic material, so that even if the torrefied pellets are watered or exposed to rain during storage, the elution of organic matter can be suppressed, thereby reducing the COD (chemical oxygen demand) and BOD (biochemical oxygen demand) in the wastewater.

[0017] <Torocarbonized pellets> Torocarbonized pellets contain components of torocarbonized biomass and have a high fixed carbon content. The fixed carbon content is the fixed carbon value determined by proximate analysis. Proximate analysis values ​​are measured in accordance with JIS M8812 (2004). According to JIS M8812 (2004), fixed carbon is the value calculated using the following formula. The unit is mass %. Here, the volatile content is the weight percentage that evaporates when a sample is heated to 900°C in the absence of oxygen. Fixed carbon (%) = 100 - [moisture (%) + ash (%) + volatile content (%)]

[0018] There are two methods for producing torrefied pellets: one is torrefying general biomass pellets, and the other is torrefy biomass first and then pelletize it. Generally, torrefying increases the fixed carbon content. The fixed carbon content (by mass) of the biomass solid fuel of this embodiment is preferably 20% or more, more preferably 20% to 40%, and even more preferably 20% to 35%. The size of the primary particles contained in the torrefied pellets varies depending on the size and shape of the pellets to be formed. The major axis diameter of the primary particles is, for example, 1000 μm or less, preferably 500 μm or less. In this specification, the major axis diameter refers to the maximum diameter. For example, the major axis diameter of a primary particle refers to the maximum length of a line connecting any two points on the outer contour of the primary particle. In this specification, the major axis diameter of the primary particles can be adjusted by known methods (e.g., using a sieve).

[0019] <Hydrophobic Substance> In this embodiment, at least a portion of the surface of the torrefied pellets is coated with a hydrophobic substance. The hydrophobic substance is not particularly limited, but examples thereof include heavy oil, light oil, petroleum-based residual oil, vegetable oil, biotar, waste plastic oil, waste tire oil, kerosene, and mineral oil. The hydrophobic substances may be used alone or in combination of two or more. Examples of heavy oils include asphalt, coal tar, atmospheric residue (AR), and vacuum residue (VR). Examples of light oils include naphtha, heavy cracked gas oil (HCO), undesulfurized vacuum gas oil (VGO), light gas oil (LGO), desulfurized vacuum gas oil (VHHGO), and heavy gas oil (HGO). Examples of petroleum residual oils include cracked residual oil (CLO), atmospheric residual oil (RC), desulfurized residual oil (DSRC), undesulfurized vacuum residual oil (VC), and ethylene bottom oil. CLO is a cracked residual oil produced when heavy oil is cracked, specifically a vacuum cracked residual oil obtained at an oil refinery. Examples of vegetable oils include olive oil, corn oil, sesame oil, rice bran oil, soybean oil, rapeseed oil, palm oil, coconut oil, sunflower oil, safflower oil, cottonseed oil, coconut oil, jatropha oil, pongamia oil, and vegetable oil. Biotar is a distillate obtained by heating wood or the like at 300°C or higher in an oxygen-free environment.

[0020] Preferred embodiments of the hydrophobic substance include the following embodiments 1 and 2.

[0021] (Aspect 1) In Aspect 1 of this embodiment, the hydrophobic substance is preferably one or more selected from the group consisting of heavy oil, light oil, petroleum-based residual oil, vegetable oil, waste plastic oil, waste tire oil, and biotar. In Aspect 1 of this embodiment, the hydrophobic substance is preferably vegetable oil. In Aspect 1 of this embodiment, the hydrophobic substance is more preferably one or more selected from the group consisting of asphalt, coal tar, CLO, rapeseed oil, palm oil, coconut oil, and biotar.

[0022] In aspect 1 of this embodiment, the content of the hydrophobic substance relative to the total mass of the biomass solid fuel is 1.0 mass% or more and 30.0 mass% or less, preferably 1.0 mass% or more and 20.0 mass% or less, more preferably 1.0 mass% or more and 15 mass% or less, even more preferably 3.0 mass% or more and 10 mass% or less, and even more preferably 3.0 mass% or more and 5.0 mass% or less. In aspect 1 of this embodiment, when the content of the hydrophobic substance is 1.0 mass% or more, the hydrophobic component penetrates into the pores of the torrefied pellets, and a spontaneous heating suppression effect is observed under normal usage conditions. In aspect 1 of this embodiment, when the content of the hydrophobic substance is 30.0 mass% or less, the entire surface of the torrefied pellets is sufficiently coated, and no excess coating remains on the surface of the torrefied pellets.

[0023] In aspect 1 of this embodiment, the hydrophobic substance is preferably one or more selected from the group consisting of oleic acid, stearic acid, linoleic acid, palmitic acid, and lauric acid (hereinafter also referred to as fatty acid group). In aspect 1 of this embodiment, when the hydrophobic substance is vegetable oil, the content of fatty acid groups constituting triglycerides contained in the vegetable oil is preferably 40% by mass or more and 90% by mass or less, more preferably 50% by mass or more and 80% by mass or less, and even more preferably 60% by mass or more and 80% by mass or less, relative to the total mass of the vegetable oil. In aspect 1 of this embodiment, the vegetable oil as the hydrophobic substance is preferably one or more selected from the group consisting of rapeseed oil, palm oil, and coconut oil.

[0024] (Aspect 2) In Aspect 2 of this embodiment, the hydrophobic substance is vegetable oil, and the vegetable oil contains a triglyceride in which three fatty acids are ester-bonded to glycerin. Preferably, the total mass percentage of the saturated fatty acid (C:0) with no carbon-carbon double bond and the unsaturated fatty acid (C:1) with one carbon-carbon double bond (C:1) is 70% or more. Here, unsaturated fatty acids are easily oxidized, and the greater the number of double bonds in their structure, the more easily they are oxidized. The biomass solid fuel according to Aspect 2 of this embodiment uses vegetable oil as the hydrophobic substance, and the total mass percentage of the vegetable oil (C:0+C:1) is 70% or more. Therefore, the surface of the torrefied pellets is coated with vegetable oil containing a higher amount of fatty acids that are less susceptible to oxidation. According to Aspect 2 of this embodiment, it is believed that the "vegetable oil (hydrophobic substance) containing a higher amount of fatty acids that are resistant to oxidation" covers the active sites on the surface of the torrefied pellets, thereby suppressing the reaction between the active sites and oxygen. It is not necessary for the active sites on the surface of the torrefied pellets to be 100% covered by the hydrophobic substance; it is sufficient that the hydrophobic substance covers the active sites so that the number of active sites exposed on the surface is reduced. According to Aspect 2 of this embodiment, a hydrophobic substance having a structure that makes it resistant to destruction (i.e., oxidation) even when the temperature rises, i.e., a "vegetable oil containing a higher amount of fatty acids that are resistant to oxidation," is believed to maintain its effect of suppressing the reaction between the active sites and oxygen. The biomass solid fuel according to Aspect 2 of this embodiment can effectively suppress spontaneous combustion, as shown in Examples 1A to 8A described below.

[0025] In Aspect 2 of this embodiment, the vegetable oil is not particularly limited, and may be selected so that the mass percentage of the total content (C:0 + C:1) of fatty acids constituting the triglycerides in the vegetable oil is 70% or more. The selected vegetable oil may be used alone, or two or more may be used in combination. In Aspect 2 of this embodiment, the vegetable oil is preferably one or more selected from the group consisting of olive oil, rapeseed oil, palm oil, sunflower oil, safflower oil, coconut oil, and pongamia oil, more preferably one or more selected from the group consisting of olive oil, palm oil, sunflower oil, safflower oil, coconut oil, and pongamia oil, and even more preferably one or more selected from the group consisting of palm oil, sunflower oil, safflower oil, coconut oil, and pongamia oil. In aspect 2 of this embodiment, the mass percentage of the total content (C:0 + C:1) relative to the total mass of fatty acids constituting the triglycerides in the vegetable oil is more preferably 75% or more, and even more preferably 79% or more. In aspect 2 of this embodiment, the saturated fatty acid without a carbon-carbon double bond is, for example, one or more selected from the group consisting of caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, hepcadecanoic acid, stearic acid, arachidic acid, behenic acid, and lignoceric acid. In aspect 2 of this embodiment, the unsaturated fatty acid with one carbon-carbon double bond is, for example, one or more selected from the group consisting of palmitoleic acid, heptadecenoic acid, oleic acid, eicosenoic acid, and tetracosenoic acid.

[0026] In aspect 2 of this embodiment, the content of the vegetable oil is preferably 2.5% by mass or more and 15.0% by mass or less, more preferably 3.0% by mass or more and 12.0% by mass or less, and even more preferably 4.0% by mass or more and 11% by mass or less, relative to the total mass of the biomass solid fuel. In particular, when the vegetable oil is pongamia oil, the content of the pongamia oil is preferably 2.5% by mass or more and 10.0% by mass or less, more preferably 2.5% by mass or more and 8.0% by mass or less, and even more preferably 2.5% by mass or more and 6.0% by mass or less, relative to the total mass of the biomass solid fuel. In aspect 2 of this embodiment, when the vegetable oil content is 2.5% by mass or more, the hydrophobic component penetrates most of the pores of the torrefied pellets, making it difficult for the active sites to come into contact with air, which makes it easier to achieve the spontaneous heating suppression effect under normal usage conditions. In aspect 2 of this embodiment, when the vegetable oil content is 15.0 mass% or less, excess coating is less likely to remain on the surface of the torrefied pellets, which not only reduces the amount used (cost reduction) but also makes it easier to clean biomass solid fuel production equipment and consumption equipment (boilers, etc.) during regular repairs, etc.

[0027] In the biomass solid fuel, the amount of fatty acids constituting triglycerides in vegetable oil is measured by gas chromatography (GC). A specific measurement method will be described in the Examples section.

[0028] In aspect 1 or 2 of this embodiment, the coverage rate (area %) of the torrefied pellet surface with the hydrophobic substance is preferably 50 area % or more, more preferably 60 area % or more, even more preferably 70 area % or more, and even more preferably 80 area % or more. The coverage rate (area %) of the torrefied pellet surface with the hydrophobic substance is preferably 95 area % or less, more preferably 90 area % or more, and even more preferably 85 area % or more. The upper limit of the coverage rate (area %) is 100 area %. The coverage rate of the torrefied pellet surface with the hydrophobic substance is calculated by measuring the specific surface area of ​​nitrogen gas using a gas / vapor adsorption analyzer (manufactured by Microtrac-Bell). The specific surface area of ​​nitrogen gas is measured using a value obtained by the BET method. It is believed that nitrogen gas is mainly adsorbed into the pores of the torrefied biomass. Therefore, the coverage rate (area %) of the torrefied pellet surface with the hydrophobic substance is calculated by dividing the specific surface area S of the torrefied pellet surface before coating with the hydrophobic substance by the specific surface area S of the torrefied pellet surface. ０ (m ２ / g), and the specific surface area S of the torrefied pellet surface after coating with a hydrophobic substance １ (m ２ / g) is used to calculate the coverage (area %) of the torrefied pellet surface with the hydrophobic substance (S ０ -S １ ) / S ０ ) x 100 (Equation 1)

[0029] The raw material of torrefied biomass (biomass before torrefaction) will be explained.

[0030] <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.

[0031] Examples of woody biomass include conifers (e.g., cedar, pine, cypress, and fir), and broad-leaved trees (e.g., acacia, eucalyptus, birch, 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.

[0032] 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.

[0033] 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.

[0034] In the biomass solid fuel of this embodiment, the biomass (raw material for the semi-carbonized biomass) is preferably at least one selected from the group consisting of woody biomass, herbaceous biomass, agricultural crop residue biomass, and palm biomass. The shape of the biomass is not particularly limited. Examples of the shape of the biomass include chips, elongated shapes, powder, and irregular shapes. In this embodiment, the semi-carbonized pellets of Aspect 1 or Aspect 2 before being coated with the hydrophobic substance can be obtained, for example, by molding semi-carbonized biomass into pellets, or by obtaining general biomass pellets and then subjecting them to heat treatment.

[0035] (Form of Biomass Solid Fuel) The form of the biomass solid fuel in this embodiment includes pellets and briquettes and may be any form. For example, pellets are typically cylindrical, preferably having a diameter of 5 mm to 10 mm and a length of 5 mm to 50 mm. Briquettes are generally cylindrical, tablet-shaped, briquette-shaped, cubic, or rectangular, and a volume of 1 mL to 1 L is convenient.

[0036] (Other Components) The biomass solid fuel of this embodiment may contain other components to the extent that the effects of this embodiment are not impaired. Examples of other components include emulsifiers, spreading agents, binders, and various additives. The content of other components is preferably 10% by mass or less, more preferably 8% by mass or less, even more preferably 5% by mass or less, even more preferably 3% by mass or less, and even more preferably 1% by mass or less, based on the total amount of the biomass solid fuel.

[0037] [Use of Biomass Solid Fuel] The biomass solid fuel of this embodiment can be widely used in power plants, steel mills, factories, etc. For example, when using the biomass solid fuel in a thermal power generation facility, the biomass solid fuel may be pulverized using a coal pulverizer and introduced into a boiler using an existing thermal power generation facility. The use of the biomass solid fuel is not limited to the above.

[0038] Second Embodiment Biomass Solid Fuel Manufacturing Method The second embodiment of the biomass solid fuel manufacturing method includes the steps of obtaining torrefied pellets containing torrefied biomass obtained by torrefying biomass, and coating at least a portion of the surface of the torrefied pellets with a hydrophobic substance (hereinafter also referred to as the coating step) so that the content of the hydrophobic substance is 1.0% by mass or more and 30.0% by mass or less (preferably 1.0% by mass or more and 20.0% by mass or less) relative to the total mass of the biomass solid fuel. The second embodiment provides a method for manufacturing a biomass solid fuel that can suppress spontaneous combustion. The biomass solid fuel of the first embodiment is obtained by the manufacturing method of the second embodiment. Therefore, the biomass solid fuel obtained by the manufacturing method of the second embodiment exhibits the same effects as the first embodiment. Examples of the hydrophobic substance used in the manufacturing method of the second embodiment include the hydrophobic substance of Aspect 1 and the hydrophobic substance of Aspect 2 described in the first embodiment.

[0039] Each step will be described below.

[0040] <Step of Obtaining Semi-Carbonized Pellets> One aspect of the step of obtaining semi-carbonized pellets includes a step of molding semi-carbonized biomass at a predetermined pressure (hereinafter also referred to as a semi-carbonized biomass molding step).

[0041] (Molding process of semi-carbonized biomass) The semi-carbonized biomass used in the molding process of semi-carbonized biomass is obtained by heating (steaming) biomass of any size (unsemi-carbonized biomass) at, for example, 200°C to 350°C or by steam explosion. The semi-carbonized biomass obtained in this manner is crushed as necessary and then molded into semi-carbonized pellets. Known conditions (time, pressure, atmosphere, etc.) can be applied as heating conditions and steam explosion conditions. Semi-carbonized pellets can be obtained, for example, by extruding semi-carbonized biomass through a metal hole (e.g., diameter 5 mm to 10 mm, length 5 mm to 200 mm) or by using a known pelletizer. The pressure during molding is preferably 50 MPa to 150 MPa.

[0042] Another aspect of the process for obtaining semi-carbonized pellets includes a process for molding non-semi-carbonized biomass to obtain general biomass pellets, and a process for heating the general biomass pellets (hereinafter also referred to as a process for heating the general biomass pellets).

[0043] (Step of Obtaining General Biomass Pellets) General biomass pellets are usually obtained by molding powdered biomass (biomass that has not been semi-carbonized) in the same manner as for the semi-carbonized pellets described above.

[0044] (Heating process of general biomass pellets) The heating temperature in the heating process of general biomass pellets is preferably 240° C. or higher and 350° C. or lower, more preferably 250° C. or higher and 350° C. or lower, and even more preferably 270° C. or higher and 330° C. The heating time in the heating process of general biomass pellets depends on the heating temperature, but is preferably 10 minutes or higher and 240 minutes or lower, more preferably 20 minutes or higher and 180 minutes or lower, and even more preferably 30 minutes or higher and 150 minutes or lower.

[0045] The heating atmosphere in the heating process of general biomass pellets must be low in oxygen, and is preferably an inert atmosphere or a reducing atmosphere. A dry distillation gas atmosphere or a combustion exhaust gas atmosphere is also possible. The oxygen concentration in the heating process of general biomass pellets is preferably 5% by mass or less, and more preferably 3% by mass or less.

[0046] <Coating Step> In the coating step of the second embodiment, when the hydrophobic substance of Aspect 1 described in the first embodiment is used, the coating step is a step of coating at least a portion of the surface of the torrefied pellets with the hydrophobic substance so that the content of the hydrophobic substance is 1.0 mass% to 30.0 mass% (preferably 1.0 mass% to 20.0 mass%) relative to the total mass of the biomass solid fuel. In the coating step of the second embodiment, when the hydrophobic substance of Aspect 2 described in the first embodiment is used, the coating step is a step of coating at least a portion of the surface of the torrefied pellets with the hydrophobic substance so that the content of the hydrophobic substance is 2.5 mass% to 15.0 mass% (preferably 3.0 mass% to 12.0 mass%) relative to the total mass of the biomass solid fuel. The configuration of the coating step described below is common to both the case where the hydrophobic substance of Aspect 1 is used and the case where the hydrophobic substance of Aspect 2 is used.

[0047] The coating step is preferably carried out by spraying, sprinkling, coating, or depositing the coating liquid containing the hydrophobic substance onto the surface of the torrefied pellets, or by immersing the torrefied pellets in the coating liquid containing the hydrophobic substance.

[0048] In the coating step, the form of the coating liquid is not particularly limited. In the coating step, the coating liquid is preferably a hydrophobic solution containing a hydrophobic substance and a solvent, an emulsion containing a hydrophobic substance, water, and an emulsifier, a molten liquid containing a melted hydrophobic substance, or a "spreader-containing molten liquid" containing a melted hydrophobic substance and a spreading agent.

[0049] The hydrophobic substance in the biomass solid fuel preferably penetrates the surface or interior of the torrefied pellets and is integrated with the torrefied biomass. Specifically, it is preferable that the hydrophobic substance not be present independently, for example, in a solid state, on the surface or interior of the torrefied pellets as much as possible. Therefore, in the coating process, it is preferable to spread a coating liquid (a coating liquid in which the hydrophobic substance is brought into a liquid state and its viscosity is reduced) obtained by, for example, the following methods (i) to (iv) on the torrefied pellets as the substrate. The coating liquid obtained by method (i) is an example of a hydrophobic solution. The coating liquid obtained by method (ii) is an example of an emulsion. The coating liquid obtained by method (iii) is an example of a molten liquid. The coating liquid obtained by method (iv) is an example of a molten liquid containing a spreading agent. (i) Dissolve or disperse the hydrophobic substance in a solvent. (ii) Use an emulsifier to emulsify the hydrophobic substance in a solvent (e.g., water) to form an emulsion. (iii) Melt the hydrophobic substance itself. (iv) Melting the hydrophobic substance together with the spreading agent, or melting the hydrophobic substance and then adding the spreading agent.

[0050] When using a coating liquid in which a hydrophobic substance is diluted with a solvent, as in method (i), the hydrophobic substance must be easily soluble in the solvent. Examples of solvents include organic solvents (e.g., aromatics (e.g., toluene), alcohols (e.g., ethanol), ethers, n-hexane, and cyclohexane). The higher the solubility of the hydrophobic substance, the easier it is to adjust the concentration (viscosity) to a desired level, making it more user-friendly. When the coating liquid is a hydrophobic solution, the content of the hydrophobic substance relative to 100% by mass of the solvent is typically 1.0% by mass or more and 95% by mass or less, preferably 5.0% by mass or more and 75% by mass or less, and more preferably 10% by mass or more and 70% by mass or less. When the content of the hydrophobic substance relative to 100% by mass of the solvent is 1.0% by mass or more, the hydrophobic substance can be easily added, thereby shortening the processing time. On the other hand, when the content of the hydrophobic substance relative to 100% by mass of the solvent is 95% by mass or less, the viscosity of the solution can be reduced, making it easier to spread the hydrophobic substance on the substrate.

[0051] When the coating liquid is an emulsion, as in the method (ii) above, a known emulsifier can be used. Examples of emulsifiers include glycerin fatty acid esters, glyceride derivatives in which an organic acid is ester-bonded to a monoglyceride, polyglycerin fatty acid esters, and sucrose fatty acid esters. Emulsifiers can be used alone or in combination. Known emulsification methods can be used. For example, an emulsion can be obtained by mixing a hydrophobic substance, water, and an emulsifier and stirring the mixture with a homogenizer. Heating may be performed as needed when mixing the hydrophobic substance, water, and emulsifier, and when stirring the mixture. When the coating liquid is a water emulsion, a high concentration of the hydrophobic substance in the coating liquid is preferred, since drying takes longer when the amount of water is large. On the other hand, emulsification may be difficult if the concentration of the hydrophobic substance is too high. Therefore, when the coating liquid is an emulsion of water, the concentration of the hydrophobic substance in the coating liquid is preferably 28% by mass or more and 50% by mass or less, and more preferably 30% by mass or more and 45% by mass or less.

[0052] When using a coating liquid in which a hydrophobic substance is heated and melted (hereinafter referred to as the melting method), as in the above-mentioned methods (iii) or (iv), the melting point of the hydrophobic substance is preferably low, specifically, 50°C or lower. The lower limit of the melting point of the hydrophobic substance is not particularly limited, but is, for example, -10°C or higher. In the melting method, if the melting point of the hydrophobic substance is -10°C or higher, it becomes difficult to evaporate at room temperature (25°C). Furthermore, if the melting point of the hydrophobic substance is 50°C or lower, the thermal energy required to melt the hydrophobic substance can be reduced, and solidification on the surface of the torrefied pellets can be easily suppressed. This may save the effort of preheating the object to be coated when spreading the hydrophobic substance on the object.

[0053] When the coating liquid is a molten liquid obtained by melting the hydrophobic substance itself, this is preferable from the viewpoint of simplifying the process and reducing solvent costs. When the coating liquid used for the molten liquid is a molten liquid, the hydrophobic substance is preferably vegetable oil, more preferably palm oil. When the coating liquid is a molten liquid, the content of the hydrophobic substance in the coating liquid is 90% by mass or more, more preferably 95% by mass or more. The upper limit of the content of the hydrophobic substance in the coating liquid is 100% by mass.

[0054] When the coating liquid is a spreading agent-containing melt, a known spreading agent can be used as the spreading agent contained in the spreading agent-containing melt. Examples of spreading agents include polyoxyethylene fatty acid esters, polyoxyethylene alkyl phenyl ethers, and polyoxyethylene alkyl ethers. Spreaders can be used alone or in combination. When the coating liquid is a spreading agent-containing melt, the content of the hydrophobic substance in the coating liquid is, for example, 90% by mass or more and 99.5% by mass or less, and the content of the spreading agent in the coating liquid is, for example, 0.5% by mass or more and 10% by mass or less.

[0055] When a melting-type coating liquid is used, the "molten hydrophobic substance" is obtained by heating the hydrophobic substance, for example, at a temperature of 40°C to 100°C. The spreading-agent-containing melted liquid is obtained by adding a spreading agent to the melted hydrophobic substance, or by heating the spreading agent together with the hydrophobic substance. Adding a spreading agent reduces the viscosity of the spreading-agent-containing melted liquid or prevents the spreading-agent-containing melted liquid from solidifying.

[0056] When using a coating liquid for the melting method, from the viewpoint of lowering the viscosity and making it easier to spread the coating liquid, the viscosity of the coating liquid (melt liquid or melt liquid containing a spreading agent) when coating the surface of the semi-carbonized pellets with the coating liquid (melt liquid or melt liquid containing a spreading agent) is preferably 8 mPa·s or more and 200 mPa·s or less, more preferably 10 mPa·s or more and 100 mPa·s or less, even more preferably 10 mPa·s or more and 80 mPa·s or less, even more preferably 10 mPa·s or more and 60 mPa·s or less, even more preferably 10 mPa·s or more and 40 mPa·s or less, and even more preferably 10 mPa·s or more and 30 mPa·s or less. When a melting-type coating liquid is used, the temperature of the coating liquid (melt liquid or spreader-containing melt liquid) is preferably 40°C or higher and 100°C or lower, more preferably 40°C or higher and 80°C or lower, even more preferably 40°C or higher and 70°C or lower, and even more preferably 40°C or higher and 60°C or lower. The spreader-containing melt liquid preferably contains melted vegetable oil and a spreader, and more preferably contains melted palm oil and a spreader. The viscosity is measured using a Brookfield rotational viscometer (B-type viscometer, model number: DV-II+pro).

[0057] In the coating step, methods for spraying and scattering the coating liquid can be applied using, for example, known nozzles (e.g., spray nozzles and ultrasonic nozzles). As a coating method, a method for using a known coater (e.g., a rotary coater) can be applied. As an immersion method in the coating step, for example, a method for immersing the semi-carbonized pellets in a container containing a hydrophobic substance, the hydrophobic solution, the emulsion, the melt, or the spreader-containing melt can be used. As a vapor deposition method in the coating step, known vapor deposition methods (e.g., atmospheric vapor deposition and vacuum vapor deposition) can be used.

[0058] The biomass described in the first embodiment can be used as the raw material for the torrefied biomass (biomass before torrefaction) used in the production method of the second embodiment. In the second embodiment, the fixed carbon ratio of the biomass solid fuel is preferably in the same range as in the first embodiment. In the second embodiment, the content of other components relative to the total mass of the biomass solid fuel is preferably in the same range as in the first embodiment. In the second embodiment, the coverage rate (area %) of the torrefied pellet surface with the hydrophobic substance is preferably in the same range as in the first embodiment.

[0059] (Hydrophobic substance of aspect 1) In the second embodiment, when the hydrophobic substance of aspect 1 is used, the hydrophobic substance preferably satisfies the following requirements: The content of the hydrophobic substance relative to the total mass of the biomass solid fuel is preferably in the same range as that described in the first embodiment. In the second embodiment, the total content of the fatty acid group relative to the total mass of the biomass solid fuel is preferably in the same range as that described in the first embodiment.

[0060] (Hydrophobic Substance of Aspect 2) When the hydrophobic substance of Aspect 2 is used in the second embodiment, the hydrophobic substance preferably satisfies the following requirements. The content of the hydrophobic substance relative to the total mass of the biomass solid fuel is preferably within the same range as that described in the first embodiment. The hydrophobic substance of Aspect 2 is a vegetable oil, and in the vegetable oil, the mass percentage of the total content (C:0 + C:1) relative to the total mass of fatty acids constituting triglycerides is preferably 70% or more, more preferably 75% or more, and even more preferably 79% or more. Examples of saturated fatty acids (C:0) having no carbon-carbon double bond and unsaturated fatty acids (C:1) having one carbon-carbon double bond include the saturated fatty acids (C:0) and unsaturated fatty acids (C:1) described in the first embodiment. The hydrophobic substance (vegetable oil) of Aspect 2 is preferably one or more selected from the group consisting of olive oil, rapeseed oil, palm oil, sunflower oil, safflower oil, coconut oil, and pongamia oil. In the second embodiment, by using the hydrophobic substance (vegetable oil) of aspect 2, at least a portion of the surface of the torrefied pellets is coated with vegetable oil containing a large amount of fatty acids that are resistant to oxidation. As a result, for the same reason as in the first embodiment, a biomass solid fuel that can effectively suppress spontaneous combustion is obtained.

[0061] Other Embodiments The present invention is not limited to the above-described embodiments, and any modifications, improvements, etc. that can achieve the object of the present invention are included in the present invention.

[0062] Examples of the present invention will be described below, but the present invention is not limited to these examples.

[0063] <Production of Biomass Solid Fuel (1)> Biomass solid fuels were produced in Examples 1 to 11. The torrefied pellets used in Examples 1 to 11 and Comparative Example 1 were obtained by heat treating ordinary biomass pellets made from acacia trees in an oxygen-blocked state. Table 1 shows the properties of the torrefied pellets. Table 1 also shows the properties of the biomass solid fuel obtained in Example 8.

[0064]

[0065] Explanation of Table 1: Proximate analysis values ​​are values ​​measured in accordance with JIS M8812 (2004). Of the elemental analysis values, carbon, hydrogen, and nitrogen are values ​​measured in accordance with JIS M8819 (1997). Higher heating value is a value measured in accordance with JIS M8814 (2003). Total sulfur is quantified in accordance with JIS M8813 (2004) "Coals and cokes - Elemental analysis method." The fuel ratio is "fixed carbon / volatile matter." "AR" indicates arrival basis. "AD" indicates air-dry basis, representing the state after drying in the atmosphere. "DB" indicates higher heating value on an anhydrous basis. "DAF" indicates an anhydrous ash-free basis. "ash" indicates ash-based. Ash fusion temperature (oxidation) is a value measured in accordance with JIS M8801 (2004) "Test method for ash fusion properties." Ash composition is a value measured by X-ray fluorescence (XRF) in accordance with ASTM D4326-13 "Standard Test Method for Major and Minor Elements in Coal and Coke Ash By X-Ray Fluorescence." The fine powder ratio is calculated from the total amount of product, with fine powder being defined as material that passes through a metal sieve with a circular hole diameter (nominal opening) of 3.15 mm as specified in JIS Z 8801-2 (Test sieves - Part 2: Metal sieves). 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 by a method conforming to JIS M8801 (2008).

[0066] Example 1 Asphalt was used as the hydrophobic substance. Asphalt emulsion (emulsion, Toa Road Co., Ltd., trade name Tackfine, PKM-T) was used as the coating liquid. Semi-carbonized pellets (1,000 g) were uniformly spread on a metal pad. The semi-carbonized pellets were stirred while spraying asphalt emulsion (200 g). Spraying of the asphalt emulsion was repeated several times so that the ratio of asphalt (hydrophobic substance) added to the semi-carbonized pellets became the value shown in Table 2 (coating process). Thereafter, the semi-carbonized pellets sprayed with the asphalt emulsion were dried in an electric furnace at 90°C for 4 hours. In this way, the biomass solid fuel of Example 1 was obtained.

[0067] Example 2 Coal tar was used as the hydrophobic substance. Coal tar (100 g) was added to n-hexane (152 mL, 100 g) to obtain a coating liquid (n-hexane solution). Then, torrefied pellets (1,000 g) were uniformly spread on a metal pad. The torrefied pellets were stirred while being sprayed with the n-hexane solution. Spraying of the n-hexane solution was repeated several times (coating process) so that the ratio of coal tar (hydrophobic substance) added to the torrefied pellets reached the values ​​shown in Table 2. In this way, the biomass solid fuel of Example 2 was obtained.

[0068] Example 3 CLO (petroleum residual oil) was used as the hydrophobic substance. CLO (100 g) was placed in n-hexane (152 mL) to obtain a coating liquid (n-hexane solution). Thereafter, the biomass solid fuel of Example 3 was obtained in the same manner as in Example 2. In the coating process, spraying of the n-hexane solution was repeated several times so that the ratio of CLO (hydrophobic substance) added to the torrefied pellets reached the value shown in Table 2.

[0069] Example 4: Rapeseed oil was used as the hydrophobic substance. Rapeseed oil (200 g) was added to toluene (100 mL) to obtain a coating liquid (toluene solution). The biomass solid fuel of Example 4 was then obtained in the same manner as in Example 2. In the coating process, the toluene solution was sprayed several times so that the ratio of rapeseed oil (hydrophobic substance) added to the semi-carbonized pellets reached the values ​​shown in Table 2.

[0070] Example 5 Biotar was used as the hydrophobic substance. 200 g of "Kiktar" (biotar) manufactured by Mokubokuki Co., Ltd. was used. 200 g of biotar was added to 152 mL of n-hexane (100 g) to obtain a coating liquid (n-hexane solution). The same method as in Example 2 was then used to obtain the biomass solid fuel of Example 5. In the coating process, spraying of the n-hexane solution was repeated several times so that the ratio of biotar (hydrophobic substance) added to the torrefied pellets reached the values ​​shown in Table 2.

[0071] Example 6 Palm oil was used as the hydrophobic substance. Palm oil (200 g) was added to n-hexane (152 mL, 100 g) to obtain a coating liquid (n-hexane solution). The biomass solid fuel of Example 6 was then obtained in the same manner as in Example 2. In the coating process, the n-hexane solution was sprayed several times so that the ratio of palm oil (hydrophobic substance) added to the torrefied pellets reached the values ​​shown in Table 2.

[0072] Example 7 A biomass solid fuel of Example 7 was obtained in the same manner as in Example 6, except that palm oil (100 g) was used.

[0073] Example 8 A biomass solid fuel of Example 8 was obtained in the same manner as in Example 6, except that palm oil (50 g) was used.

[0074] Example 9: Palm oil was used as the hydrophobic substance. A palm oil emulsion (palm oil emulsified in water) was used as the coating liquid. Palm oil (35 g) was mixed with an emulsifier (1.75 g, decaglycerol monostearate) and distilled water (200 g) and emulsified for 3 minutes using an ultrasonic homogenizer to obtain a palm oil emulsion. Semi-carbonized pellets (700 g) were uniformly spread on a metal pad. The semi-carbonized pellets were stirred while spraying the palm oil emulsion. Spraying of the palm oil emulsion was repeated several times so that the palm oil (hydrophobic substance) content relative to the semi-carbonized pellets was the value shown in Table 2. The semi-carbonized pellets sprayed with the palm oil emulsion were then dried in a thermostatic chamber at 70°C for 4 hours. In this way, the biomass solid fuel of Example 9 was obtained.

[0075] Example 10 Palm oil was used as the hydrophobic substance. A palm oil melt containing heated and melted palm oil and a spreading agent (spreader-containing melt) was used as the coating liquid. The palm oil melt was obtained by heating palm oil (100 g) and a spreading agent (1.9 g, Betalin-A, manufactured by Sankei Chemical Co., Ltd., main component: 80% by mass of polyoxyethylene alkylphenyl ether) in a water bath at 60°C to achieve a viscosity suitable for spraying. The viscosity of the resulting palm oil melt was measured using the method described above and found to be 18.5 Pa·s at 60°C. Semi-carbonized pellets (1,000 g) were spread on a metal pad and heated in a thermostatic bath at 107°C for 120 minutes. After removing the metal pad from the thermostatic bath, the palm oil melt heated to 60°C was quickly sprayed onto the semi-carbonized pellets. The metal pad was then returned to the thermostatic bath at 107°C and heated for 15 minutes. The following steps were then repeated several times (coating step): removing the metal pad from the thermostatic bath at 107°C, spraying the torrefied pellets with molten palm oil heated to 60°C (hereinafter also referred to as the spraying operation), and returning the metal pad to the thermostatic bath at 107°C, to obtain the biomass solid fuel of Example 10. The spraying operation was repeated several times so that the ratio of palm oil (hydrophobic substance) added to the torrefied pellets reached the value shown in Table 2.

[0076] [Example 11] Coconut oil was used as the hydrophobic substance. Coconut oil (70 g) was added to ethanol (100 g = 127 mL) to obtain a coating liquid (ethanol solution). The biomass solid fuel of Example 11 was then obtained in the same manner as in Example 2. In the coating process, the ethanol solution was sprayed several times so that the ratio of coconut oil (hydrophobic substance) added to the semi-carbonized pellets reached the values ​​shown in Table 2.

[0077] Comparative Example 1 The semi-carbonized pellets were used as the biomass solid fuel in Comparative Example 1.

[0078] [Evaluation (1)] [Spontaneous Heat Generation] A wire basket test was carried out by the following method using the biomass solid fuels of Examples 1 to 11 and Comparative Example 1 to evaluate spontaneous heat generation. The results are shown in Figures 1 to 3 and Table 2.

[0079] (Wire Basket Test) The wire basket test was conducted 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 thermostatic chamber. In this test, the wire basket test was conducted using an electric furnace instead of a thermostatic chamber, and the spontaneous heat generation property was evaluated as A, B, or C based on the evaluation criteria described below. (Test Method) The biomass solid fuel (approximately 520 g, equivalent to 1 L) of each example was placed as a sample in a 100 mm square container (volume 1 L), and then the container was suspended in the electric furnace. The electric furnace was heated, and after the temperature of the electric furnace reached 140°C, the temperature of the sample was continuously measured while the electric furnace was maintained at 140°C. The test was conducted continuously until the shorter of the following (1) and (2) times: (1) The temperature of the sample reached 200°C while the electric furnace was maintained at 140°C. (2) With the electric furnace kept at 140°C, the temperature of the sample is equilibrated without reaching 200°C, or begins to drop, and 12 hours have passed since the start of the test (start of heating the electric furnace).

[0080] (Evaluation criteria) A: The maximum temperature of the sample is less than 200°C, and then the temperature gradually decreases. B: After the temperature of the sample reaches 140°C, it reaches 200°C 5.0 hours or later (including 5.0 hours). C: After the temperature inside the furnace reaches 140°C, it reaches 200°C 5.0 hours earlier (excluding 5.0 hours).

[0081]

[0082] Figures 1 to 3 show the results of the wire basket test for Examples 1 to 11 and Comparative Example 1. Figures 1 to 3 and Table 2 show that the biomass solid fuels of Examples 1 to 3 and Examples 5 to 11, in which at least a portion of the surface was coated with a hydrophobic substance, did not reach a maximum temperature of 200°C. Furthermore, the biomass solid fuel of Example 4, in which at least a portion of the surface was coated with a hydrophobic substance, gradually reached 200°C over 5.0 hours after the furnace temperature reached 140°C. On the other hand, the biomass solid fuel of Comparative Example 1, in which the surface was not coated with a hydrophobic substance, rose linearly to 200°C over time. From the above, it is believed that the biomass solid fuels of Examples 1 to 11 can suppress spontaneous combustion.

[0083] [Coverage (area %) of the surface of the semi-carbonized pellets by the hydrophobic substance] The coverage (area %) of the surface of the semi-carbonized pellets by the hydrophobic substance was measured by the method described above using evaluation samples 1 to 4 prepared by the following method. The results are shown in Table 3.

[0084] (Evaluation Samples 1 to 4) Biomass solid fuels for evaluation samples 1 to 4 were obtained in the same manner as in Example 6, except for the following procedure: The amount of palm oil added to n-hexane was adjusted, and spraying of the n-hexane solution was repeated several times so that the ratio of palm oil added to the semi-carbonized pellets reached the values ​​shown in Table 3 (coating step).

[0085] (Comparative Sample 1) The semi-carbonized pellets shown in Table 1 were used as comparative sample 1.

[0086]

[0087] As shown in Table 3, it can be seen that 63.2 area % or more of the surface of the semi-carbonized pellets was covered with palm oil in evaluation samples 1 to 4. Among them, evaluation samples 1 and 2 had a small amount of palm oil added to the semi-carbonized pellets (2.83 mass % to 3.57 mass %), but the surface of the semi-carbonized pellets was covered with palm oil by 63.2 area % or more.

[0088] <Production of Biomass Solid Fuel (2)> The torrefied pellets used in Examples 1A to 8A, Reference Examples 1A to 4A, and Comparative Example 1A were obtained by heat treating ordinary biomass pellets made from acacia trees in an oxygen-blocked state. The properties of the torrefied pellets used in Examples 1A to 8A, Reference Examples 1A to 4A, and Comparative Example 1A were the same as those shown in Table 1.

[0089] (Analysis of Fatty Acids) The fatty acids constituting the triglycerides contained in vegetable oils were analyzed. Table 4 shows the components of 12 types of vegetable oils (fats and oils). The vegetable oil components were analyzed by gas chromatography (GC). The analytical method was a GC-FID (flame ionization detector), and reference was made to "AOCS Official Method Ce-1b-89" and the "Food Labeling Standards (March 30, 2015, Food Labeling Standards No. 139)" provided by the Consumer Affairs Agency, "Attachment: Nutritional Labeling (Attachment: Analytical Methods for Nutritional Components, etc., pages 20-26)." The test solution injected into the gas chromatograph (with a flame ionization detector and split / splitless inlet) was the test solution prepared according to the "Preparation of Fatty Acid Methyl Esters" procedure described on pages 23-24 of the "Attachment: Analytical Methods for Nutritional Components, etc."

[0090]

[0091] (Explanation of Table 4) CX:0 indicates that the fatty acid has X carbon atoms and 0 carbon-carbon double bonds (saturated fatty acid). X is an integer. For example, C16:0 indicates that the fatty acid has 16 carbon atoms and 0 carbon-carbon double bonds. Similarly, CX:1 indicates that the fatty acid has 1 carbon-carbon double bond. For example, C16:1 indicates that the fatty acid has 16 carbon atoms and 1 carbon-carbon double bond. Total content (C:0 + C:1) indicates the total content [mass%] of saturated fatty acids (C:0) with 0 carbon-carbon double bonds and fatty acids (C:1) with 1 carbon-carbon double bond.

[0092] Example 1A The biomass solid fuel obtained in Example 10 was used as the biomass solid fuel in Example 1A.

[0093] Example 2A: Safflower oil was used as the hydrophobic substance. Safflower oil (104 g) was added to n-hexane (152 mL, 100 g) to obtain a coating liquid (n-hexane solution). Then, semi-carbonized pellets (1,000 g) were uniformly spread on a metal pad. The semi-carbonized pellets were stirred while being sprayed with the n-hexane solution. Spraying of the n-hexane solution was repeated several times (coating process) so that the ratio of safflower oil (hydrophobic substance) added to the semi-carbonized pellets reached the values ​​shown in Table 5. In this way, the biomass solid fuel of Example 2A was obtained.

[0094] Example 3A A biomass solid fuel of Example 3A was obtained in the same manner as in Example 2A, except that pongamia oil (50 g) was used instead of safflower oil.

[0095] Example 4A A biomass solid fuel of Example 4A was obtained in the same manner as in Example 2A, except that sunflower oil (100 g) was used instead of safflower oil.

[0096] [Example 5A] As the biomass solid fuel in Example 5A, the biomass solid fuel obtained in Example 11 was used.

[0097] Example 6A A biomass solid fuel of Example 6A was obtained in the same manner as in Example 2A, except that rapeseed oil (103 g) was used instead of safflower oil.

[0098] Example 7A A biomass solid fuel of Example 7A was obtained in the same manner as in Example 3A, except that pongamia oil (29.9 g) was used.

[0099] Example 8A A biomass solid fuel of Example 8A was obtained in the same manner as in Example 2A, except that palm oil (50 g) was used instead of safflower oil.

[0100] Reference Example 1A A biomass solid fuel of Reference Example 1A was obtained in the same manner as in Example 2A, except that soybean oil (100 g) was used instead of safflower oil.

[0101] Reference Example 2A A biomass solid fuel of Reference Example 2A was obtained in the same manner as in Example 2A, except that cottonseed oil (102 g) was used instead of safflower oil.

[0102] Reference Example 3A A biomass solid fuel of Reference Example 3A was obtained in the same manner as in Example 2A, except that corn oil (105 g) was used instead of safflower oil.

[0103] Reference Example 4A A biomass solid fuel of Reference Example 4A was obtained in the same manner as in Example 2A, except that rice bran oil (99 g) was used instead of safflower oil.

[0104] Comparative Example 1A The torrefied pellets were used as the biomass solid fuel of Comparative Example 1A.

[0105] [Evaluation (2)] [Spontaneous Heat Generation] Using the biomass solid fuels of Examples 1A to 8A, Reference Examples 1A to 4A, and Comparative Example 1A, a wire basket test was conducted in the same manner as in Example 1, and the time required for the temperature to reach 200°C was measured. The test time was 12 hours. The results are shown in Figures 4 and 5 and Table 5. In Figures 4 and 5, the percentages in parentheses indicate "mass %."

[0106]

[0107] Figure 4 shows the results of the wire basket test for Examples 1A to 8A, Reference Examples 1A to 4A, and Comparative Example 1A. Figure 5 shows the relationship between the "mass percentage of the total content of saturated fatty acids and unsaturated fatty acids with one double bond (C:0 + C:1)" relative to the total mass of fatty acids and the time to reach 200°C for the fatty acids constituting the triglycerides contained in the vegetable oil. The vegetable oils used in Examples 1A to 8A had a "mass percentage of the total content of saturated fatty acids and unsaturated fatty acids with one double bond (C:0 + C:1)" relative to the total mass of fatty acids of 70% or more, while the vegetable oils used in Reference Examples 1A to 4A had a mass percentage of the total content (C:0 + C:1) less than 70%. Figures 4 to 5 and Table 5 show that the biomass solid fuels of Examples 1A to 5A and Examples 7A to 8A did not reach a maximum temperature of 200°C. The biomass solid fuel of Example 6A gradually reached 200°C over 4.5 hours after the furnace temperature reached 140°C. The biomass solid fuels of Reference Examples 1A to 4A reached 200°C at a faster rate than Example 6A. The biomass solid fuel (semi-carbonized pellets) of Comparative Example 1A reached 200°C in 6.4 hours. Therefore, the biomass solid fuels of Examples 1A to 8A can effectively suppress spontaneous combustion.

[0108] [Temperature-Rise Test in an Oxygen and Water Vapor Atmosphere] Using the biomass solid fuels of Example 8A and Comparative Example 1A, a temperature-rise test was conducted by introducing saturated water vapor into an atmosphere of 21% oxygen and 79% nitrogen, similar to air. This atmosphere is similar to an actual outdoor storage site, but the pseudo-insulated condition allows for easier heat generation than solid fuels stored in an actual storage site, allowing for a relatively short heat generation evaluation. First, the biomass solid fuels of Example 8A and Comparative Example 1A were dried at 70°C under vacuum for three days to remove almost all moisture (referred to as "bone-dry state"). The bone-dry sample (biomass solid fuel of Example 8A or Comparative Example 1A) was loaded into a reactor (300 L). Nitrogen gas was flowed through the reactor (50 mL / min). When the sample temperature reached 50°C, the nitrogen gas was switched to "oxygen gas (50 mL / min, 21% oxygen by volume) and nitrogen gas (same, 79% by volume) containing saturated water vapor," and sample temperature measurement was initiated. Measurement was terminated when the sample temperature reached 150°C.

[0109] Figure 6 shows the results of the spontaneous combustion test for Example 8A and Comparative Example 1A. The weight of the biomass solid fuel at this time was 153.1 g for Example 8A and 144.5 g for Comparative Example 1A. From a kinetic perspective, the heating rate is proportional to the calorific value (the greater the amount of sample), but is inversely proportional to the heat capacity (specific heat x weight). Therefore, slight weight differences are considered to cancel each other out and not affect the heating rate. As shown in Figure 6, the biomass solid fuel of Example 8A took more than two days longer to heat up to 150°C than the biomass solid fuel of Comparative Example 1A. Therefore, the biomass solid fuel of Example 8A can effectively suppress spontaneous combustion.

[0110] The biomass solid fuel of the present invention can be used for biomass power generation in power plants, steel mills, factories, and the like.

Claims

1. A biomass solid fuel comprising: torrefied pellets containing torrefied biomass obtained by torrefying biomass; and a hydrophobic substance that coats at least a portion of the surface of the torrefied pellets, wherein the content of the hydrophobic substance is 1.0 mass% or more and 30.0 mass% or less relative to the total mass of the biomass solid fuel.

2. The biomass solid fuel according to claim 1, wherein the proportion of fixed carbon in the biomass solid fuel is 20% or more by mass.

3. The biomass solid fuel according to claim 1 or 2, wherein the hydrophobic substance is one or more selected from the group consisting of heavy oil, light oil, petroleum residual oil, vegetable oil, waste plastic oil, waste tire oil, and biotar.

4. The biomass solid fuel according to any one of claims 1 to 3, wherein the hydrophobic substance is vegetable oil.

5. The biomass solid fuel according to any one of claims 1 to 4, wherein the hydrophobic substance is one or more selected from the group consisting of oleic acid, stearic acid, linoleic acid, palmitic acid, and lauric acid.

6. The biomass solid fuel according to claim 1 or claim 2, wherein the hydrophobic substance is vegetable oil, the vegetable oil contains a triglyceride in which three fatty acids are ester-bonded to glycerin, and the combined mass percentage of saturated fatty acids with no carbon-carbon double bond and unsaturated fatty acids with one carbon-carbon double bond is 70% or more relative to the total mass of the fatty acids constituting the triglyceride.

7. The biomass solid fuel according to claim 6, wherein the saturated fatty acid having no carbon-carbon double bond is one or more selected from the group consisting of caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, hepcadecanoic acid, stearic acid, arachidic acid, behenic acid, and lignoceric acid, and the unsaturated fatty acid having one carbon-carbon double bond is one or more selected from the group consisting of palmitoleic acid, heptadecenoic acid, oleic acid, eicosenoic acid, and tetracosenoic acid.

8. The biomass solid fuel according to claim 6 or 7, wherein the vegetable oil is one or more selected from the group consisting of olive oil, rapeseed oil, palm oil, sunflower oil, safflower oil, coconut oil, and pongamia oil.

9. The biomass solid fuel according to any one of claims 6 to 8, wherein the content of the vegetable oil is 2.5 mass % or more and 15.0 mass % or less relative to the total mass of the biomass solid fuel.

10. The biomass solid 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 method for producing biomass solid fuel, comprising: a step of obtaining torrefied pellets containing torrefied biomass obtained by torrefying biomass; and a step of coating at least a portion of the surface of the torrefied pellets with a hydrophobic substance so that the content of the hydrophobic substance is 1.0 mass% or more and 30.0 mass% or less relative to the total mass of the biomass solid fuel.

12. The method for producing a biomass solid fuel according to claim 11, wherein the coating step is carried out by spraying, sprinkling, applying or depositing the coating liquid containing the hydrophobic substance onto the surface of the torrefied pellets, or by immersing the torrefied pellets in the coating liquid containing the hydrophobic substance.

13. The method for producing a biomass solid fuel according to claim 11 or 12, wherein the proportion of fixed carbon in the biomass solid fuel is 20% or more by mass.

14. A method for producing biomass solid fuel according to any one of claims 11 to 13, wherein the hydrophobic substance is one or more selected from the group consisting of heavy oil, light oil, petroleum residual oil, vegetable oil, waste plastic oil, waste tire oil, and biotar.

15. A method for producing biomass solid fuel as described in any one of claims 11 to 13, wherein the hydrophobic substance is vegetable oil, the vegetable oil contains a triglyceride in which three fatty acids are ester-bonded to glycerin, and the mass percentage of the total content of saturated fatty acids with no carbon-carbon double bond and unsaturated fatty acids with one carbon-carbon double bond relative to the total mass of the fatty acids constituting the triglyceride is 70% or more.

16. The method for producing a biomass solid fuel according to claim 15, wherein the saturated fatty acid having no carbon-carbon double bond is one or more selected from the group consisting of caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, hepcadecanoic acid, stearic acid, arachidic acid, behenic acid, and lignoceric acid, and the unsaturated fatty acid having one carbon-carbon double bond is one or more selected from the group consisting of palmitoleic acid, heptadecenoic acid, oleic acid, eicosenoic acid, and tetracosenoic acid.

17. The method for producing a biomass solid fuel according to claim 15 or 16, wherein the vegetable oil is one or more selected from the group consisting of olive oil, rapeseed oil, palm oil, sunflower oil, safflower oil, coconut oil, and pongamia oil.

18. A method for producing a biomass solid fuel according to any one of claims 15 to 17, wherein in the coating step, the content of the vegetable oil is 2.5 mass% or more and 15.0 mass% or less relative to the total mass of the biomass solid fuel.

19. A method for producing biomass solid fuel according to any one of claims 11 to 18, wherein the biomass is at least one selected from the group consisting of woody biomass, herbaceous biomass, agricultural crop residue biomass, and palm biomass.

20. A method for producing a biomass solid fuel as described in any one of claims 12 to 19, wherein in the coating step, the coating liquid is a hydrophobic solution containing the hydrophobic substance and a solvent, an emulsion containing the hydrophobic substance, water, and an emulsifier, a molten liquid containing the melted hydrophobic substance, or a spreading agent-containing molten liquid containing the melted hydrophobic substance and a spreading agent.

21. A method for producing biomass solid fuel as described in claim 20, wherein the viscosity of the melting liquid or the melting liquid containing a spreading agent when coating the surface of the torrefied pellets with the melting liquid or the melting liquid containing a spreading agent is 8 mPa·s or more and 200 mPa·s or less.

22. A method for producing biomass solid fuel according to any one of claims 11 to 21, wherein the step of obtaining the semi-carbonized pellets comprises: a step of molding the biomass to obtain biomass pellets; and a step of heating the biomass pellets at a temperature of 240°C or higher and 350°C or lower.

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