Biomass solid fuel manufacturing method

Abstract

A biomass solid fuel manufacturing method comprising: a step for obtaining blasted biomass by blasting biomass using steam; a step for obtaining biomass pellets by molding said blasted biomass; and a pellet heating step for heating the biomass pellets at 180°C or more for at least 5 minutes.

Description

[Technical Field]

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

[0002] Coal-fired power plants have a high CO2 emission rate per unit of emissions, placing a heavy burden on the environment. To reduce CO2 emissions from coal-fired power plants, biomass co-firing, in which biomass is mixed with coal and burned, is attracting attention. Co-firing of wood chips and wood pellets is already being carried out, but biomass is less easily crushed than coal, so the maximum biomass co-firing rate is limited to a few percent.

[0003] In order to increase the biomass co-firing ratio, methods of torrefaction or steam explosion of biomass are being considered. For example, Patent Document 1 describes a method for crushing woody biomass with a size of 5 to 60 mm to a bulk density (measured according to JIS K2151-6 "Bulk Density Test Method") of 0.5 g / cm. 3 The method for producing solid fuel is disclosed, which is characterized by carrying out the densification treatment described above, followed by roasting under conditions of an oxygen concentration of 10% or less and a temperature of 170 to 350°C. Patent Document 2 also discloses a biomass solid fuel formed from molded biomass powder, characterized by a fuel ratio (fixed carbon / volatile matter) of 0.2 to 0.8, a higher heating value on an anhydrous basis of 4800 to 7000 (kcal / kg), a molar ratio O / C of oxygen (O) to carbon (C) of 0.1 to 0.7, and a molar ratio H / C of hydrogen (H) to carbon (C) of 0.8 to 1.3. Patent Document 3 also discloses a method for producing fuel pellets, which includes the steps of introducing lignocellulosic biomass having a moisture content of less than about 30% by weight into a reactor, creating a vacuum in the reactor, injecting steam having a temperature between about 180 and about 235 degrees Celsius into the reactor, maintaining the biomass in the reactor for about 1 to about 12 minutes, and removing the treated biomass from the reactor. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-189958 [Patent Document 2] International Publication No. 2016 / 056608 [Patent Document 3] Special Publication No. 2013-538240 Summary of the Invention [Problem to be solved by the invention]

[0005] The methods described in Patent Documents 1 to 3 torrefy or steam explode biomass to obtain solid fuel with improved pulverizability and co-firing ratio with coal. Furthermore, the methods described in Patent Documents 1 to 3 torrefy or steam explode biomass to obtain hydrophobic solid fuel (hereinafter sometimes referred to as "black pellets"), which can be stored outdoors. However, there are concerns about the leaching of organic components (chemical oxygen demand (COD)) when black pellets are stored outdoors. While coal hardly leaches out any organic components, black pellets do leach out, so there are concerns about the impact on the environment when they are stored outdoors. Therefore, when storing black pellets outdoors, it is necessary to minimize the leaching of organic components. To achieve this, the manufacturing process must be examined and a method for manufacturing black pellets with a structure that makes it difficult for organic components to leach out is required. Patent Documents 1 and 3 do not consider the leaching of organic components and do not take into account the risks of outdoor storage. Furthermore, the biomass solid fuel described in Patent Document 2 exhibits a relatively high COD value because the manufacturing process has not been sufficiently considered.

[0006] An object of the present invention is to provide a method for producing a biomass solid fuel with reduced COD elution from biomass obtained through a steam explosion treatment. [Means for solving the problem]

[0007] According to one aspect of the present invention, there is provided a method for producing biomass solid fuel, comprising: a step of steam exploding biomass to obtain exploded biomass; a step of molding the exploded biomass to obtain biomass pellets; and a pellet heating step of heating the biomass pellets at 180°C or higher for 5 minutes or more.

[0008] In the method for producing a biomass solid fuel according to one aspect of the present invention, it is preferable to have a first pulverization step of pulverizing the biomass before the step of obtaining the exploded biomass.

[0009] In the method for producing a biomass solid fuel according to one aspect of the present invention, it is preferable to have a second pulverization step of pulverizing the pulverized biomass after the step of obtaining the pulverized biomass.

[0010] In the method for producing a biomass solid fuel according to one aspect of the present invention, it is preferable to have a first drying step of drying the biomass before the step of obtaining the exploded biomass.

[0011] In the method for producing a biomass solid fuel according to one aspect of the present invention, it is preferable to have a second drying step of drying the exploded biomass after the step of obtaining the exploded biomass.

[0012] In the method for producing a biomass solid fuel according to one aspect of the present invention, the 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.

[0013] In the method for producing a biomass solid fuel according to one aspect of the present invention, the pellet heating step preferably involves heating the biomass pellets at an oxygen concentration of 5% by mass or less for 5 minutes to 60 minutes.

[0014] In one embodiment of the biomass solid fuel production method of the present invention, it is preferable to carry out the pellet heating step so that the COD of the biomass pellets after the pellet heating step is 1 / 6 or less of the COD of the biomass pellets before the pellet heating step.

[0015] In the method for producing a biomass solid fuel according to one aspect of the present invention, the biomass is preferably at least one selected from the group consisting of woody biomass, herbaceous biomass, agricultural crop residue biomass, and palm biomass.

[0016] According to one aspect of the present invention, it is possible to provide a method for producing a biomass solid fuel with reduced COD elution from biomass obtained through a steam explosion treatment. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a graph showing the COD of biomass solid fuels produced in Examples and Comparative Examples. [Figure 2] 1 is a graph showing the COD of biomass solid fuels produced in Examples and Comparative Examples. [Figure 3] 1 is a graph showing the HGI of biomass solid fuels produced in Examples and Comparative Examples. [Figure 4] 1 is a graph showing the weight yields of biomass solid fuels produced in Examples and Comparative Examples. [Figure 5] 1 is a graph showing higher heating values ​​on a dry basis of biomass solid fuels produced in Examples and Comparative Examples. [Figure 6] 1 is a graph showing the bulk density of biomass solid fuels produced in Examples and Comparative Examples. [Figure 7] 1 is a graph showing the mechanical durability of biomass solid fuels produced in Examples and Comparative Examples. DETAILED DESCRIPTION OF THE INVENTION

[0018] In this specification, a numerical range expressed using "to" means a range that includes the number written before "to" as the lower limit and the number written after "to" as the upper limit.

[0019] [First embodiment] [Method for producing biomass solid fuel] The method for producing biomass solid fuel according to this embodiment (hereinafter also referred to as the "production method according to this embodiment") includes a step of steam exploding biomass to obtain exploded biomass, a step of molding the exploded biomass to obtain biomass pellets, and a pellet heating step of heating the biomass pellets at 180°C or higher for 5 minutes or more. The biomass solid fuel obtained by the manufacturing method of this embodiment is obtained by molding biomass pellets using steam-exploded biomass (exploded biomass) and then carrying out a pellet heating process in which the biomass pellets are heated at 180°C or higher for 5 minutes or more. The biomass solid fuel obtained in this manner has significantly reduced COD elution compared to biomass solid fuel that has not been subjected to the pellet heating step.

[0020] The biomass solid fuel obtained by the production method of this embodiment is resistant to degradation even when wetted when stored outdoors, and COD elution is reduced, so it can be stored outdoors, which is expected to eliminate the need for facilities such as silos. In particular, since biomass solid fuels such as wood pellets tend to disintegrate when wetted with water, it is useful to produce a biomass solid fuel with reduced COD elution by the production method of this embodiment. Furthermore, as shown in the examples below, the biomass solid fuel obtained by the production method of this embodiment has the properties required for fuel (e.g., HGI, higher heating value, bulk density, and mechanical durability). By producing biomass solid fuel by the production method of this embodiment, it is possible to expand the use of biomass solid fuel.

[0021] First, the biomass used in the production method of this embodiment will be described.

[0022] (biomass) The biomass is not particularly limited, but examples thereof include woody biomass, herbaceous biomass, agricultural residue biomass, palm biomass, cellulose products, and pulp products. As used herein, crop residue biomass means anything other than the edible parts. In this specification, palm biomass refers to agricultural waste from palm trees that can be used as biomass fuel. Specific examples of palm biomass include palm kernel shells (PKS), empty fruit bunches (EFB), and palm trunks. The biomass is preferably at least one selected from the group consisting of woody biomass, herbaceous biomass, agricultural crop residue biomass, and palm biomass.

[0023] Examples of woody biomass include conifers (e.g., cedar, pine, eucalyptus, cypress, and fir), and broad-leaved trees (e.g., birch, beech, zelkova, katsura, paulownia, rubber tree, and camphor tree). Woody biomass may also be construction waste (e.g., cut off wood, chips generated at processing plants, and sawdust), forest residues, thinned wood, and bamboo. Examples of herbaceous biomass include grasses, naturally grown plants, and artificially planted plants. Herbaceous biomass may be hemp, cotton, rice straw, rice husks, wheat straw, bamboo grass, napier grass, sorghum, and Japanese silver grass.

[0024] 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.

[0025] Examples of palm biomass include palm oil pomace (PKS), fruit bunches (EFB), and fruit peels. The above-described biomass may be used singly or in combination of two or more kinds.

[0026] Next, each step of the manufacturing method of this embodiment will be described.

[0027] (Process for obtaining exploded biomass) In the production method of this embodiment, the step of obtaining exploded biomass is a step of obtaining exploded biomass by steam explosion of biomass. Steam explosion is a process in which biomass is steamed for a short period of time in a sealed container such as a pressure vessel using saturated steam at high temperature and pressure, and then suddenly released into atmospheric pressure, where it is rapidly cooled and the structure of the biomass (or the wood structure in the case of wood) is destroyed by adiabatic expansion. The shape of the biomass used in steam explosion is not particularly limited, and examples of the shape of the biomass include the shape of the biomass itself (e.g., palm empty fruit bunches), chips, elongated shapes, powder, and irregular shapes. The biomass used for steam explosion may be biomass as obtained, or biomass obtained after being crushed into any shape and size. For example, palm empty fruit bunches can be used as they are obtained. Biomass is pulverized and torrefied by steam explosion. For example, if the biomass is in chip form (biomass chips), the biomass chips are pulverized by steam explosion to form biomass powder. The resulting biomass powder (exploded biomass) is in a torrefied state.

[0028] The temperature of the steam explosion is preferably 100°C or higher and 300°C or lower, more preferably 100°C or higher and 280°C or lower. The pressure for the steam explosion is preferably 0.1 MPa or more and 9.0 MPa or less, more preferably 1.0 MPa or more and 6.5 MPa or less. The time for steam explosion is preferably 10 minutes or more and 60 minutes or less, more preferably 15 minutes or more and 30 minutes or less.

[0029] In the step of obtaining exploded biomass, the steam explosion is preferably carried out in a sealed container under saturated steam at 100°C or higher and 300°C or lower and 0.1 MPa or higher and 9.0 MPa or lower, more preferably 100°C or higher and 280°C or lower and 1.0 MPa or higher and 6.5 MPa or lower.

[0030] The size of the biomass obtained in the step of obtaining exploded biomass varies depending on the size and shape of the biomass used for steam explosion. For example, when the biomass is in the form of chips (biomass chips), the major axis diameter of the biomass powder obtained in the step of obtaining exploded biomass is preferably 1000 μm or less, and more preferably 500 μm or less. In this specification, the term "major axis diameter" refers to the maximum diameter. For example, the major axis diameter of biomass powder refers to the maximum length of a line connecting any two points on the outer contour line of the biomass powder.

[0031] (Process for obtaining biomass pellets) In the manufacturing method of this embodiment, the step of obtaining biomass pellets is a step of molding the exploded biomass to obtain biomass pellets. In this specification, pellets include briquettes. The size and shape of the pellets are not particularly limited, but the pellets are usually cylindrical and preferably have a diameter of 5 mm to 10 mm and a length of 5 mm to 50 mm. In this embodiment, biomass pellets can be produced by extruding the exploded biomass obtained by steam explosion through a metal hole (e.g., a diameter of 5 mm to 10 mm and a length of 5 mm to 50 mm). Biomass pellets can also be produced using a pelletizer such as a ring die or flat die. Biomass pellets can also be produced by molding them into briquettes or cylindrical shapes using a briquetting machine.

[0032] (Pellet heating process) In the manufacturing method of this embodiment, the pellet heating step is a step of heating the biomass pellets at 180° C. or higher for 5 minutes or longer. From the viewpoint of insolubilizing the eluted components, the pellet heating step preferably involves heating the biomass pellets at 190°C or higher for 5 minutes or more, more preferably at 200°C or higher for 5 minutes or more, even more preferably at 205°C or higher for 5 minutes or more, and even more preferably at 210°C or higher for 5 minutes or more. The upper limit temperature in the pellet heating process is preferably not too high, from the viewpoint of reducing COD elution while ensuring a balanced balance of the properties required of the fuel (e.g., HGI, higher heating value, bulk density, and mechanical durability), and from the viewpoint of reducing COD elution with less energy. Specifically, the upper limit temperature is preferably 270°C or less, more preferably 265°C or less, and even more preferably 260°C or less. In the pellet heating process, the time (heating time) for heating the biomass pellets at 180°C or higher is preferably 240 minutes or less, more preferably 120 minutes or less, even more preferably 60 minutes or less, even more preferably 50 minutes or less, and even more preferably 40 minutes or less, from the viewpoint of reducing COD leaching in a short period of time. The heating time of the biomass pellets refers to the sum of the time required to reach the target temperature from 180°C and the time required to hold the temperature at the target temperature. For example, if biomass pellets are heated from room temperature (25°C) to 230°C (target temperature) at a heating rate of 5°C / min and held at 230°C for 0 minutes, the heating time of the biomass pellets is calculated as 10 minutes, which is the sum of the time it takes to reach 230°C from 180°C (10 minutes) and the holding time at 230°C (0 minutes). In the following explanation, the target temperature may be referred to as the target temperature. In the pellet heating step, the pellets are preferably heated to a target temperature at a rate of 3°C / min to 60°C / min (preferably 3°C / min to 30°C / min). The target temperature (achieved temperature) is preferably 270°C or lower, more preferably 265°C or lower, and even more preferably 260°C or lower. As a result, the amount of COD eluted can be reduced, and the heating time for the biomass pellets can be significantly shortened.

[0033] The atmosphere in the pellet heating step preferably has a low oxygen concentration, specifically, an oxygen concentration of preferably 5% by mass or less, and more preferably 3% by mass or less. The low-oxygen atmosphere in the pellet heating step may be, for example, an inert gas atmosphere, such as at least one inert gas atmosphere selected from nitrogen gas, argon gas, carbon dioxide gas, and combustion exhaust gas.

[0034] In the pellet heating step, the biomass pellets are preferably heated at an oxygen concentration of 5% by mass or less for 5 to 60 minutes, more preferably at an oxygen concentration of 5% by mass or less for 5 to 50 minutes, and even more preferably at an oxygen concentration of 3% by mass or less for 5 to 50 minutes.

[0035] In the manufacturing method of this embodiment, it is more preferable to carry out the pellet heating step so that the COD of the biomass pellets after the pellet heating step is 1 / 6 or less of the COD of the biomass pellets before the pellet heating step is carried out. Specifically, the ratio of the COD (unit: mg / L) of the biomass pellets after the pellet heating process to the COD (unit: mg / L) of the biomass pellets before the pellet heating process (COD of biomass pellets after the pellet heating process / COD of biomass pellets before the pellet heating process) is preferably 1 / 6 or less, more preferably 1 / 8 or less, even more preferably 1 / 10 or less, even more preferably 1 / 15 or less, even more preferably 1 / 16 or less, even more preferably 1 / 18 or less, even more preferably 1 / 20 or less, even more preferably 1 / 25 or less, and even more preferably 1 / 30 or less.

[0036] (First crushing step) In the production method of this embodiment, it is preferable to have a first pulverization step of pulverizing the biomass before the step of obtaining the exploded biomass. One embodiment of the pulverization in the first pulverization step is to pulverize the obtained biomass into a shape (for example, chips or long pieces) that can be easily introduced into a steam explosion apparatus. The pulverization method is not particularly limited, and the biomass can be pulverized into chips, long pieces, or the like using a known pulverizer. The size of the chips is not particularly limited, but for example, when woody biomass is pulverized into chips, the major axis diameter is preferably 5.0 cm or less, and more preferably 1.0 cm or less.

[0037] (Second crushing step) In the production method of this embodiment, it is also preferable to have a second pulverization step of pulverizing the exploded biomass after the step of obtaining the exploded biomass. One mode of pulverization in the second pulverization step is to steam explode relatively large-sized biomass (for example, biomass with a major axis diameter on the order of several tens of centimeters), and then further pulverize the exploded biomass.

[0038] (First drying step) In the production method of this embodiment, it is preferable to have a first drying step of drying the biomass before the step of obtaining the exploded biomass. The first drying step is a step of drying the biomass and adjusting the moisture content of the biomass. The first drying step may be natural drying or heat drying. The drying temperature and drying time of the biomass are appropriately selected depending on the type and size of the biomass. For example, the drying time of the biomass is preferably 30 minutes or more. The moisture content of the biomass obtained in the first drying step is preferably 10% by mass or more and 20% by mass or less, more preferably 10% by mass or more and 15% by mass or less. By adjusting the moisture content of the biomass to 10% by mass or more and 20% by mass or less, saturated steam is more likely to be uniformly contained in each biomass during steam explosion, and uniform steam explosion is expected. Therefore, by drying the biomass in the first drying step, it is possible to obtain exploded biomass with more uniform properties in the step of obtaining exploded biomass.

[0039] (Second drying process) In the production method of this embodiment, it is also preferable to have a second drying step of drying the exploded biomass after the step of obtaining the exploded biomass. The second drying step is a step of adjusting the moisture content of the exploded biomass by drying the moisture that has adhered to the biomass during steam explosion. The second drying step may be natural drying or heat drying. The drying temperature and drying time of the exploded biomass are appropriately selected depending on the biomass type and size of the exploded biomass. For example, the drying time of the exploded biomass is preferably 30 minutes or more. The moisture content of the exploded biomass obtained in the second drying step is preferably 10% by mass or more and 20% by mass or less, more preferably 10% by mass or more and 15% by mass or less. In the second drying step, the exploded biomass is dried so that the moisture content is 10% by mass or more and 20% by mass or less, thereby improving the moldability of the pellets in the step of obtaining biomass pellets.

[0040] In the manufacturing method of this embodiment, both the first drying step and the second drying step may be performed. By performing both the first drying step and the second drying step, biomass pellets with more uniform properties can be obtained.

[0041] The production method of this embodiment may include a washing step of washing the biomass. The washing step is preferably carried out before the first drying step. The washing process removes alkali metal components adhering to the surface of the biomass, making it a fuel that is less susceptible to ash adhesion, a concern when biomass pellets are burned in a boiler. The washing water used in the washing step may be any known washing liquid such as water or hot water. The washing time and number of washings are not particularly limited.

[0042] The manufacturing method of this embodiment includes a step of obtaining exploded biomass, a step of obtaining biomass pellets, and a pellet heating step, and may include at least one of a first crushing step, a second crushing step, a first drying step, a second drying step, and a washing step, as necessary. The order of carrying out the manufacturing method of this embodiment is not particularly limited, but it is preferable to carry out the method in the following order. (1) A process for obtaining exploded biomass, a process for obtaining biomass pellets, and a process for heating the pellets. (2) A first drying step, a step of obtaining exploded biomass, a second crushing step, a step of obtaining biomass pellets, and a pellet heating step. (3) A washing step, a first crushing step, a step of obtaining exploded biomass, a second drying step, a step of obtaining biomass pellets, and a pellet heating step. (4) A washing step, a first drying step, a first crushing step, a step of obtaining exploded biomass, a step of obtaining biomass pellets, and a pellet heating step. (5) A washing process, a first drying process, a first crushing process, a process for obtaining exploded biomass, a second drying process, a process for obtaining biomass pellets, and a pellet heating process, etc.

[0043] (Other ingredients) The biomass solid fuel obtained by the production method of this embodiment may contain components other than biomass, as long as the effects of this embodiment are not impaired. The other components are not particularly limited, but include binders and various additives. Examples of binders include lignin and acrylic acid amide. The content of the binder in the biomass solid fuel is preferably 0% by mass or more and 50% by mass or less, and more preferably 0% by mass or more and 10% by mass or less. When the biomass solid fuel contains a binder, it is preferable to mold a mixture of the exploded biomass and the binder in the step of obtaining biomass pellets.

[0044] [Use of biomass solid fuel] The biomass solid fuel obtained by the production method of this embodiment can be widely used in power plants, steel mills, factories, etc. The biomass solid fuel of this embodiment may be burned alone or may be mixed with other fuels such as coal and burned (co-combustion). For example, when biomass solid fuel is used in a thermal power plant, the biomass solid fuel may be pulverized in a pulverizer and introduced into a boiler, or depending on the size, it may be introduced into the boiler as is. It is also preferable to use a mixture of biomass solid fuel and coal. In this case, existing thermal power generation facilities may be used, for example, using a coal pulverizer to pulverize the biomass solid fuel together with coal, and then the mixture may be introduced into a boiler. Alternatively, the biomass solid fuel may be pulverized in a pulverizer (e.g., a pulverizer for biomass solid fuel) separate from the coal pulverizer, and then mixed with separately pulverized coal, and the resulting mixture may be introduced into the boiler. The manner of use of the biomass solid fuel is not limited to the above.

[0045] Second Embodiment [Biomass solid fuel] The biomass solid fuel of the second embodiment is obtained by the method for producing a biomass solid fuel of the first embodiment. The biomass solid fuel of the second embodiment has a COD of 1,000 mg / L or less, a Hardgrove Crushability Index (HGI) of 25 or more, a mechanical durability of 93% or more, a higher heating value on a dry basis of 5,000 kcal / kg or more, and a bulk density of 680 kg / m 3 That's all. According to the biomass solid fuel of the second embodiment, the elution of COD is reduced.

[0046] In the biomass solid fuel of the second embodiment, from the viewpoint of reducing COD elution while ensuring a balanced set of properties required of the fuel, the preferred ranges of COD, HGI, mechanical durability, higher heating value on a dry basis, and bulk density are as follows:

[0047] (COD) The biomass solid fuel of the second embodiment has a COD of 1,000 mg / L or less, preferably 400 mg / L or less, and more preferably 200 mg / L or less. The method for measuring COD is as described in the Examples.

[0048] (Hardgrove Crushability Index (HGI)) The biomass solid fuel of the second embodiment has an HGI of 25 or more. The HGI is preferably 27.5 or more, and more preferably 30 or more. The method for measuring HGI is as described in the Examples.

[0049] (mechanical durability) The biomass solid fuel of the second embodiment has a mechanical durability of 93% or more, preferably 95% or more, and more preferably 97% or more. The method for measuring the mechanical durability is as described in the Examples.

[0050] (Higher heating value on a dry basis) The biomass solid fuel of the second embodiment has a higher heating value of 5,000 kcal / kg or more on a dry basis, preferably 5,150 kcal / kg or more, and more preferably 5,300 kcal / kg or more. The method for measuring the higher heating value on an air-dry basis is as described in the Examples.

[0051] (bulk density) The biomass solid fuel of the second embodiment has a bulk density of 680 kg / m 3 The bulk density is preferably 700 kg / m 3 More preferably, 720 kg / m 3 That's all.

[0052] Among the biomass solid fuels of the second embodiment, a biomass solid fuel having a further reduced COD, i.e., a COD of 350 mg / L or less (preferably 200 mg / L or less), a Hardgrove Crushability Index (HGI) of 25 or more, a mechanical durability of 93% or more, a higher heating value on a dry basis of 5,000 kcal / kg or more, and a bulk density of 680 kg / m 3 The biomass solid fuel described above is produced, for example, by the following production method of Aspect A. The production method of Aspect A is one aspect of the production method of the first embodiment.

[0053] (Manufacturing Method of Aspect A) The manufacturing method of aspect A includes: A step of steam exploding biomass to obtain exploded biomass; A step of molding the exploded biomass to obtain biomass pellets; and a pellet heating step of heating the biomass pellets at 210°C or higher (preferably 230°C or higher) for 20 minutes to 60 minutes.

[0054] Other Embodiments The present invention is not limited to the above-described embodiment, and any modifications and improvements that can achieve the object of the present invention are included in the present invention. [Example]

[0055] Examples of the present invention will be described below, but the present invention is not limited to these examples.

[0056] Table 1 shows the properties of the biomass used in the examples and comparative examples.

[0057] [Table 1]

[0058] Explanation of Table 1 Proximate analysis values ​​were measured in accordance with JIS M8812 (2004). Of the elemental analysis values, carbon, hydrogen, nitrogen, and sulfur were measured in accordance with JIS M8819 (1997), and oxygen was calculated from other analytical values ​​in accordance with JIS M8813 (2004). The higher heating value is a value measured in accordance with JIS M8814 (2003). The fuel ratio is "fixed carbon / volatiles." Dry basis (DB) calorific value indicates the calorific value in a dry state. "ad" stands for Air Dry Basis, which means the state of being dried in the atmosphere. "daf" is an abbreviation for Dry Ash Free, which represents a hypothetical state where biomass is assumed to contain no moisture or ash. It is calculated by conversion from analytical values.

[0059] Example 1-1 (Process for obtaining exploded biomass) Biomass (wood type 1) was pulverized in a pulverizer to obtain biomass chips. The biomass chips were dried in a dryer so that the moisture content was 10% by mass or more and 12% by mass or less. The dried biomass chips were placed in a pressure-resistant container. Steam was introduced into the pressure-resistant container, and the biomass chips were steam-exploded with saturated steam under the following conditions. The biomass chips were then rapidly released into atmospheric pressure and cooled to obtain biomass powder. -conditions- ·Temperature: 200℃ Pressure: 2.2MPa Duration: 20 minutes

[0060] (Process for obtaining biomass pellets) The biomass powder was compression molded using a compression molding device to obtain cylindrical biomass pellets (diameter 8 mm, height 10 mm to 40 mm).

[0061] (Pellet heating process) The biomass pellets were introduced into a heating furnace, and the temperature was increased to 190°C (ultimate temperature) at a rate of 5°C / min, and then maintained at this temperature for 30 minutes. Through the above steps, the biomass solid fuel of Example 1-1 was obtained.

[0062] [Examples 1-2 to 1-4 and Comparative Examples 1-2 to 1-4] Biomass solid fuels of Examples 1-2 to 1-4 and Comparative Examples 1-2 to 1-4 were obtained in the same manner as in Example 1-1, except that the ultimate temperature and retention time in the pellet heating step were changed to those shown in Table 2.

[0063] Comparative Example 1-1 A biomass solid fuel (unheated) of Comparative Example 1-1 was obtained in the same manner as in Example 1-1, except that the pellet heating step was not carried out.

[0064] Example 2-1 (Step of obtaining biomass chips) Biomass (wood type 2) was pulverized in a pulverizer to obtain biomass chips. Thereafter, the same method as in Example 1-1 was used to obtain a biomass solid fuel of Example 2-1.

[0065] Examples 2-2 to 2-4 and Comparative Examples 2-2 to 2-4 Biomass solid fuels of Examples 2-2 to 2-4 and Comparative Examples 2-2 to 2-4 were obtained in the same manner as in Example 2-1, except that the ultimate temperature and retention time in the pellet heating step were changed to those shown in Table 2.

[0066] Comparative Example 2-1 A biomass solid fuel (unheated) of Comparative Example 2-1 was obtained in the same manner as in Example 2-1, except that the pellet heating step was not carried out.

[0067] [Table 2]

[0068] 〔evaluation〕 The biomass solid fuel obtained in each example was used to carry out the following evaluations.

[0069] (COD) The soaking water used to measure COD was prepared in accordance with the "Testing Method for Metals, etc. Contained in Industrial Waste (Environment Agency Notification No. 13 of 1973)" by conducting a 6-hour shaking test and producing wastewater. The COD concentration in the prepared soaking water was measured using a simple COD meter (COD-60A) manufactured by Toa DKK. The COD concentration in the black pellet soaking water was measured in advance using the official method (JIS K0102 (2016)), and a regression equation was calculated from the correlation with the measurement results from this device. From this regression equation, the measurement value converted to the specified measurement method was calculated. The results are shown in Figures 1 and 2. As shown in Figure 1, Examples 1-1 to 1-3, in which a pellet heating process was performed, showed a significant reduction in the leaching of COD (mg / L) compared to Comparative Example 1-1, in which a pellet heating process was not performed, and Comparative Examples 1-2 to 1-3, in which a heating process was performed under the conditions shown in Table 2. In particular, in Examples 1-2 and 1-3 in which the heating step was carried out at ultimate temperatures of 210°C and 230°C, the amount of COD elution was reduced to 1 / 10 or less compared to Comparative Example 1-1 in which the heating step was not carried out. Similar results were obtained when Examples 2-1 to 2-3 were compared with Comparative Examples 2-1 to 2-3. From Figure 1, it was confirmed that COD elution could be further reduced by increasing the ultimate temperature.

[0070] As shown in Figure 2, Example 1-1, in which the biomass pellets were heated at 180°C or higher for 32 minutes (achieved temperature 190°C, holding time 30 minutes), showed a significant reduction in COD elution compared to Comparative Example 1-4, in which the biomass pellets were heated at 180°C or higher for 2 minutes (achieved temperature 190°C, holding time 0 minutes). Furthermore, in Example 1-4, in which the biomass pellets were heated at 180°C or higher for 10 minutes (achieved temperature 230°C, holding time 0 minutes), and in Example 1-3, in which the biomass pellets were heated at 180°C or higher for 40 minutes (achieved temperature 230°C, holding time 30 minutes), the amount of COD leaching was further reduced compared to Example 1-1. Similar results were obtained when Example 2-1 (ultimate temperature 190°C, holding time 30 minutes) was compared with Comparative Example 2-4 (ultimate temperature 190°C, holding time 0 minutes). Similar results were obtained when Example 2-4 (ultimate temperature 230°C, holding time 0 minutes) and Example 2-3 (ultimate temperature 230°C, holding time 30 minutes) were compared with Example 2-1.

[0071] (Hardgrove Crushability Index (HGI)) The Hardgrove Crushability Index (HGI) of the biomass solid fuels obtained in Examples 1-1 to 1-3, Examples 2-1 to 2-3, Comparative Examples 1-1 and 2-1 was measured by a method in accordance with JIS M8801 (2008). The results are shown in Figure 3. As can be seen from FIG. 3, Examples 2-1 to 2-3 in which the pellet heating step was carried out had improved HGI compared to Comparative Example 2-1 in which the pellet heating step was not carried out. A similar tendency was observed in a comparison between Examples 1-1 to 1-3 and Comparative Example 1-1.

[0072] (weight yield) The weight yields (unit: wt%) of Examples 1-1 to 1-3 and Examples 2-1 to 2-3 were calculated using the following mathematical formula (Mathematical Formula 1). The weight yields (unit: wt%) of Comparative Examples 1-1 and 2-1 were each set to 100%. The results are shown in Figure 4.

[0073]

number

[0074] As can be seen from FIG. 4, Examples 1-1 to 1-3 in which the pellet heating step was carried out had a lower weight yield than Comparative Example 1-1 in which the pellet heating step was not carried out. Similar results were obtained when Examples 2-1 to 2-3 were compared with Comparative Example 2-1.

[0075] (Higher heating value on a dry basis (DB)) The higher heating value (unit: kcal / kg) on ​​a dry basis of the biomass solid fuels obtained in Examples 1-1 to 1-3, Examples 2-1 to 2-3, Comparative Example 1-1, and Comparative Example 2-1 was measured by a method in accordance with JIS M8814 (2003). The results are shown in Figure 5. As can be seen from FIG. 5, in Examples 1-1 to 1-3 in which the pellet heating step was carried out, the higher heating value was increased compared to Comparative Example 1-1 in which the pellet heating step was not carried out. Similar results were obtained when Examples 2-1 to 2-3 were compared with Comparative Example 2-1.

[0076] (bulk density) The bulk density (unit: kg / m) of the biomass solid fuels obtained in Examples 1-1 to 1-3, Examples 2-1 to 2-3, Comparative Example 1-1, and Comparative Example 2-1 was measured by a method conforming to ISO17828. 3 ) was measured, and the results are shown in Figure 6. As can be seen from FIG. 6, Examples 1-1 to 1-3 in which the pellet heating step was carried out had a lower bulk density than Comparative Example 1-1 in which the pellet heating step was not carried out. Similar results were obtained when Examples 2-1 to 2-3 were compared with Comparative Example 2-1.

[0077] (mechanical durability) The biomass solid fuels obtained in Examples 1-1 to 1-3, Examples 2-1 to 2-3, and Comparative Example 1-1 were measured for mechanical durability (unit: %) by a method conforming to ISO17831-1. The results are shown in Figure 7. In Figure 7, "AR" stands for "As Received," and indicates that the sample is in the state it arrived in. Note that the mechanical durability was not measured for Comparative Example 2-1. As can be seen from FIG. 7, Examples 1-1 to 1-3 in which the pellet heating step was carried out had mechanical strengths almost equal to that of Comparative Example 1-1 in which the pellet heating step was not carried out. The biomass solid fuels of Examples 1-1 to 1-3 and Examples 2-1 to 2-3 all had sufficient mechanical strength. [Industrial Applicability]

[0078] The biomass solid fuel obtained by the production method of the present invention has reduced COD elution and can therefore be stored outdoors at power plants, steel mills, factories, and the like.

Claims

1. A step of steam exploding biomass to obtain exploded biomass; A step of molding the exploded biomass to obtain biomass pellets; A pellet heating step of heating the biomass pellets at 180°C or higher and 260°C or lower for 5 minutes or longer and 40 minutes or shorter, In the pellet heating step, the heating time of 5 minutes or more and 40 minutes or less is the sum of the time required to reach a target temperature from 180°C and the time required to hold the temperature at the target temperature, and the target temperature is 180°C or more and 260°C or less, The pellet heating step is carried out by heating the biomass pellets while maintaining the target temperature after the target temperature has been reached, and is carried out so that the COD of the biomass pellets after the pellet heating step is 1 / 6 or less of the COD of the biomass pellets before the pellet heating step is carried out. A method for producing biomass solid fuel.

2. The method for producing a biomass solid fuel according to claim 1, A first crushing step of crushing the biomass is included before the step of obtaining the crushed biomass. A method for producing biomass solid fuel.

3. The method for producing a biomass solid fuel according to claim 1 or 2, After the step of obtaining the exploded biomass, a second crushing step of crushing the exploded biomass is provided. A method for producing biomass solid fuel.

4. The method for producing a biomass solid fuel according to any one of claims 1 to 3, A first drying step of drying the biomass is included before the step of obtaining the exploded biomass. A method for producing biomass solid fuel.

5. The method for producing a biomass solid fuel according to any one of claims 1 to 4, After the step of obtaining the exploded biomass, a second drying step of drying the exploded biomass. The method comprises the steps of: A method for producing biomass solid fuel.

6. The method for producing a biomass solid fuel according to any one of claims 1 to 5, The steam explosion is carried out in a sealed container under saturated steam at 100°C or higher and 300°C or lower and 0.1 MPa or higher and 9.0 MPa or lower. A method for producing biomass solid fuel.

7. The method for producing a biomass solid fuel according to any one of claims 1 to 6, The pellet heating step heats the biomass pellets at an oxygen concentration of 5% by mass or less for 5 minutes to 60 minutes. A method for producing biomass solid fuel.

8. The method for producing a biomass solid fuel according to any one of claims 1 to 7, The pellet heating step is carried out so that the COD of the biomass pellets after the pellet heating step is 1 / 10 or less of the COD of the biomass pellets before the pellet heating step is carried out. A method for producing biomass solid fuel.

9. The method for producing a biomass solid fuel according to any one of claims 1 to 8, The pellet heating step is carried out so that the COD of the biomass pellets after the pellet heating step is 1 / 20 or less of the COD of the biomass pellets before the pellet heating step is carried out. A method for producing biomass solid fuel.

10. The method for producing a biomass solid fuel according to any one of claims 1 to 9, The heating temperature in the pellet heating step is 230°C or less. A method for producing biomass solid fuel.

11. The method for producing a biomass solid fuel according to any one of claims 1 to 10, The pellet heating step involves heating the pellet to a target temperature at a temperature increase rate of 3°C / min or more and 30°C / min or less. A method for producing biomass solid fuel.

12. The method for producing a biomass solid fuel according to any one of claims 1 to 11, The heating time in the pellet heating step is 32 minutes or less. A method for producing biomass solid fuel.

13. The method for producing a biomass solid fuel according to any one of claims 1 to 12, The biomass is at least one selected from the group consisting of woody biomass, herbaceous biomass, agricultural crop residue biomass, and palm biomass. A method for producing biomass solid fuel.

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