JP7726621B2 - Biomass solid fuel manufacturing method and biomass solid fuel moisture adjustment method - Google Patents

Description

The present invention relates to a method for producing biomass solid fuel, a method for adjusting the moisture content of biomass solid fuel, and biomass solid fuel.

In recent years, biomass fuels have been considered as a way to reduce _CO2 emissions, which are believed to be a cause of global warming. In fact, construction of biomass-fired power plants is underway.
For example, Patent Document 1 discloses a method for producing solid fuel, which includes a step of mechanically compressing and dehydrating biomass materials, including wood. The method for producing solid fuel described in Patent Document 1 discloses that the weight percentage of biomass materials passing through a sieve with 6.4 mm openings increases by only 5.0% or less before and after compression, and the lower heating value of the compressed biomass is 2,100 kcal/kg or more.

Furthermore, although biomass fuel has a lower calorific value than coal, which is a representative solid fuel, it is expected to be used in the same way as coal.
For example, Patent Document 2 discloses a biomass-coal co-firing system that includes a coal pulverizer that pulverizes coal to obtain coal powder, a biomass pulverizer that pulverizes biomass to obtain biomass powder, and a boiler furnace to which the coal powder and biomass powder are supplied, and that is characterized in that, during pulverization in the biomass pulverizer, additives are added to the biomass while it is mixed and pulverized.

Japanese Patent Application Laid-Open No. 2018-095685 Japanese Patent Application Laid-Open No. 2012-132602

Biomass fuels are usually transported in solidified form such as pellets or briquettes. However, when transporting biomass fuels, dust can be generated due to mechanical impacts, etc. If this dust becomes airborne and reaches a certain concentration, and if there is an ignition source such as static electricity, and the conditions are right, it can cause a dust explosion.
On the other hand, the FIT system (electricity feed-in tariff system) and laws that require electric power companies to expand the use of renewable energy are calling for an increase in the amount of biomass fuel used in power plants. In order to meet the demand for increased use of biomass fuel, it is necessary to further improve the safety of biomass fuel.
An object of the present invention is to provide a method for producing a biomass solid fuel that is less likely to cause dust explosion, a method for adjusting the moisture content of a biomass solid fuel, and a biomass solid fuel.

One aspect of the present invention provides a method for producing biomass solid fuel by forming biomass raw materials containing biomass into aggregates, the method including a step of adding moisture to at least one of the biomass raw materials and the aggregates so that the moisture content of the biomass solid fuel is 5% by mass or more and 25% by mass or less.

In the method for producing biomass solid fuel according to one aspect of the present invention, the moisture-adding step is preferably a step of immersing the biomass raw material in water, a step of spraying water onto the biomass raw material, or a step of storing the biomass raw material in a humidified space.

In the method for producing biomass solid fuel according to one embodiment of the present invention, the step of adding moisture is preferably a step of immersing the aggregates in water, a step of spraying water onto the aggregates, or a step of storing the aggregates in a humidified space.

In the method for producing biomass solid fuel according to one embodiment of the present invention, the biomass is preferably at least one type selected from the group consisting of woody biomass, herbaceous biomass, agricultural residue biomass, and palm biomass.

In one aspect of the method for producing biomass solid fuel according to the present invention, it is preferable that the biomass is powder, and that the major axis diameter of the powder is 5 mm or less.

In one aspect of the method for producing biomass solid fuel according to the present invention, the aggregates are preferably pellets or briquettes.

In the method for producing biomass solid fuel according to one aspect of the present invention, it is preferable that the biomass raw material further contains coal.

In one aspect of the method for producing biomass solid fuel according to the present invention, the particle size of the coal is preferably 1 mm or less.

In one embodiment of the method for producing biomass solid fuel according to the present invention, the ratio of coal to biomass in the biomass feedstock (coal/biomass) is preferably 0/100 or more and 75/25 or less in mass ratio.

According to one aspect of the present invention, there is provided a method for adjusting moisture content of a biomass solid fuel obtained by forming a biomass raw material containing biomass into an aggregate, the method comprising:
There is provided a method for adjusting moisture content of biomass solid fuel, comprising a moisture adjustment step of adding moisture to the biomass solid fuel to adjust the moisture content of the biomass solid fuel to 5% by mass or more and 25% by mass or less.

In the method for adjusting moisture content of biomass solid fuel according to one aspect of the present invention, the biomass solid fuel is preferably obtained by the method for producing biomass solid fuel described in any one of claims 1 to 9.

In the method for adjusting moisture content of biomass solid fuel according to one aspect of the present invention, the moisture adjustment step preferably includes adjusting the moisture content of the biomass solid fuel to between 5% and 25% by mass when the means for detecting the moisture content of the biomass solid fuel detects that the moisture content is less than 5% by mass.

In one aspect of the method for adjusting moisture content of biomass solid fuel according to the present invention, the moisture adjustment step preferably comprises a step in which a means for detecting the moisture content of the biomass solid fuel detects the moisture content, a means for controlling the moisture content based on the detected moisture content determines whether or not to add water to the biomass solid fuel, and, based on the result of the determination, adjusts the moisture content to between 5% and 25% by mass.

One aspect of the present invention provides a pellet- or briquette-shaped biomass solid fuel containing biomass, wherein the biomass content of the biomass solid fuel is 25% by mass or more but less than 95% by mass, and the moisture content is 5% by mass or more but less than 25% by mass.

One aspect of the present invention provides a method for producing biomass solid fuel that is less likely to cause dust explosions, a method for adjusting the moisture content of biomass solid fuel, and biomass solid fuel.

FIG. 2 is a schematic diagram of a minimum ignition energy measuring device used in the evaluation of the examples. 4 is a graph showing the relationship between dust concentration and discharge energy in Example 1. 10 is a graph showing the relationship between dust concentration and discharge energy in Example 2. 10 is a graph showing the relationship between dust concentration and discharge energy in Comparative Example 1. 1 is a graph showing the relationship between the mixing ratio of hydrated biomass feedstock or biomass powder in biomass feedstock and the minimum ignition energy.

In this specification, "lumps" refers to solid materials obtained by molding biomass-containing raw materials. There are no particular limitations on the types of lumps, but examples include pellets and briquettes. The lumps need only be solidified to the extent that they can be used as fuel. Therefore, there are no particular limitations on the size, shape, density, etc. of the lumps.

First Embodiment
[Method for producing biomass solid fuel]
A method for producing a biomass solid fuel according to a first embodiment (hereinafter also referred to as "the production method of this embodiment") will be described.
The manufacturing method of this embodiment is a method for manufacturing a biomass solid fuel obtained by forming a biomass raw material containing biomass into agglomerates, and specifically includes a step of adding moisture to at least one of the biomass raw material and the agglomerates so that the moisture content of the biomass solid fuel is 5% by mass or more and 25% by mass or less.
The biomass solid fuel obtained by the manufacturing method of this embodiment is a biomass raw material containing biomass formed into agglomerates, and the moisture content is adjusted to a specific range (5% by mass or more and 25% by mass or less) by adding moisture to at least one of the biomass raw material and the agglomerates.
In this embodiment, the term "lump" is used to refer to both lumps after moisture has been added (lumps whose moisture content has been adjusted to a specific range) and lumps before moisture has been added (lumps whose moisture content has not been adjusted to a specific range).
Therefore, in the production method of this embodiment, the aggregates having a moisture content adjusted to a specific range are synonymous with the biomass solid fuel obtained by the production method of this embodiment.

It is desirable for biomass solid fuel to be as dry as possible from the viewpoint of ensuring sufficient calorific value. Therefore, when producing biomass solid fuel, a step of drying the biomass raw material is usually provided in order to reduce the moisture content of the biomass raw material.
In contrast, in the production method of this embodiment, moisture is added to at least one of the biomass raw material and the aggregates obtained during the production process, thereby adjusting the moisture content of the resulting biomass solid fuel to a specific range. In other words, the production method of this embodiment is based on the opposite idea to the conventional method of "reducing the moisture content of the biomass raw material," and deliberately adds moisture to the biomass solid fuel.
Regarding the amount of moisture to be contained, by setting the moisture content of the biomass solid fuel to 5% by mass or more, the minimum ignition energy is increased and the effect of suppressing ignition of the biomass is exerted. Furthermore, by setting the moisture content to 25% by mass or less, the calorific value as a fuel is ensured.
The moisture content of semi-carbonized pellets that have not been adjusted is usually less than 5% by mass. When semi-carbonized pellets are immersed in water, the moisture content of the semi-carbonized pellets usually saturates at about 25% by mass.

Therefore, according to the production method of this embodiment, a biomass solid fuel that is less likely to cause a dust explosion can be obtained even if dust is generated due to mechanical impact or the like during transportation or storage of the biomass solid fuel. In other words, the biomass solid fuel obtained by the production method of this embodiment is a fuel with improved safety.
Hereinafter, the effect achieved by adjusting the moisture content of biomass solid fuel to 5% by mass or more and 25% by mass or less (i.e., the effect of making dust explosions less likely to occur) may be referred to as the "hydration effect."

During transportation of biomass solid fuel "Conveyance" during transportation of biomass solid fuel includes, for example, transportation from a predetermined location to a loading port, transportation from a loading port to a discharging port, transportation from a discharging port to the premises of a power plant, steel mill, factory, etc., in various locations, transportation from the premises to a furnace, etc. Examples of transportation means include an elevator, car, ship, conveyor, unloader (coal unloader), belt feeder, etc.

- When storing biomass solid fuel "Storage" when storing biomass solid fuel includes, for example, outdoor locations, indoor covered locations (dome-type, warehouse-type, etc.), storage in ship's holds, silos, and containers (e.g., bins), etc.

Furthermore, as mentioned above, there is a demand for increased use of biomass solid fuel at power plants. The manufacturing method of this embodiment makes it possible to produce biomass solid fuel with improved safety, thereby meeting the demand for increased use of biomass solid fuel.

The moisture content of the biomass solid fuel obtained by the manufacturing method of this embodiment is 5% by mass or more and 25% by mass or less, but from the perspective of further suppressing ignition of biomass and ensuring a sufficient calorific value, it is preferably 5% by mass or more and 20% by mass or less, and more preferably 5% by mass or more and 10% by mass or less.

The moisture content of the biomass solid fuel (5% by mass or more and 25% by mass or less), i.e., the total moisture (% by mass) contained in the biomass solid fuel, is adjusted by adding moisture to at least one of the biomass raw material and the aggregates during the production process.
The moisture content of the biomass solid fuel obtained by the production method of this embodiment can be confirmed by the following method.
A 1 g sample is collected from the biomass solid fuel. The collected sample is dried by heating at 107°C ± 2°C for 1 hour. The weight loss due to heating is calculated as a percentage (%) relative to the mass of the sample before heating (JIS M8820 (2000)). The above procedure is carried out three times to determine the percentage each time, and the average value is the moisture content of the biomass solid fuel.

The minimum ignition energy of the biomass raw material used in the production method of this embodiment is preferably more than 10 mJ, more preferably more than 20 mJ, and even more preferably more than 30 mJ, from the viewpoint of obtaining a biomass solid fuel that is less likely to cause dust explosions.
The minimum ignition energy of a biomass feedstock can be measured by the method described in the Examples below.

The minimum ignition energy of the biomass solid fuel obtained by the production method of this embodiment is preferably more than 10 mJ, more preferably more than 20 mJ, and even more preferably more than 30 mJ, from the viewpoint of making dust explosions less likely to occur.
The minimum ignition energy of the biomass solid fuel can be measured by taking a sample from the biomass solid fuel and using the sample in the same manner as the minimum ignition energy of the biomass raw material.

The manufacturing method of this embodiment is described below.

<Moisture addition step>
The moisture-imparting step is a step of adding moisture to at least one of the biomass raw material and the aggregates. The moisture-imparting step is not particularly limited, but is preferably a step of immersing in water, a step of spraying water, or a step of storing in a humidified space.
That is, the process for adding moisture to the biomass raw material is preferably a process for immersing the biomass raw material in water, a process for spraying water onto the biomass raw material, or a process for storing the biomass raw material in a humidified space, and the process for adding moisture to the aggregates is preferably a process for immersing the aggregates in water, a process for spraying water onto the aggregates, or a process for storing the aggregates in a humidified space.

The water content is not particularly limited, and may be, for example, tap water, well water, natural water, industrial water, lake water, river water, spring water, distilled water, etc. Moist air may also be used as the water content.
The state of moisture may be, for example, water (liquid), water droplets, mist, water vapor, etc. The temperature of the moisture is not limited.

In the water immersion step, the type of water used, the amount of water, the temperature of the water, the immersion time in water, etc. are preferably set appropriately so as to adjust the moisture content of the biomass solid fuel to the desired level. The water immersion step can be carried out using, for example, a water tank.
In the step of spraying water, it is preferable to appropriately set the type of water used, the amount of water, the temperature of the water, the state of the water, and the time of spraying water so that the desired moisture content of the biomass solid fuel can be adjusted. The means for spraying water is not particularly limited, and examples include a spray, shower, sprinkler, and hose. Rainfall may also be used as a means for spraying water.
In the process of storing in a humidified space, it is preferable to appropriately set the conditions of the space used (e.g., humidity, temperature, moisture state, size, etc.) and the storage time in the humidified space so that the moisture content of the biomass solid fuel can be adjusted to the desired level.
The means for humidifying the space is not particularly limited, and examples thereof include steam, known humidifiers, etc. Alternatively, a humid natural environment may be used as a means for humidifying the space.

(Biomass raw materials)
Biomass Biomass raw materials include biomass.
The biomass is not particularly limited, but examples thereof include woody biomass, plant biomass, agricultural residue biomass, palm biomass, cellulose products, and pulp products.
In this specification, agricultural crop residue biomass means anything other than 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) and empty fruit bunches (EFB).
The biomass is preferably at least one selected from the group consisting of woody biomass, herbaceous biomass, agricultural residue biomass, and palm biomass.

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 plant biomass include grass, naturally grown plants, and artificially planted plants. Plant biomass may be hemp, cotton, rice straw, rice husks, wheat straw, bamboo grass, and Japanese silver grass.

Agricultural crop residue biomass includes, for example, leaves, fruit clusters, stems, roots, and other non-edible unwanted parts of agricultural crops. Examples of such crops include wheat, corn, potatoes, sugarcane (including bagasse), sugarcane, starch, bananas, and castor oil.

Examples of palm biomass include palm oil pomace (PKS), fruit bunch (EFB), and fruit peel.
The above-described biomass may be used alone or in combination of two or more kinds.

The biomass is a powder, and the major axis diameter of the powder is preferably 5 mm or less, more preferably 1 mm or less, from the viewpoint of ease of forming into a mass. The lower limit of the major axis diameter of the powder is greater than 0.
The major axis diameter of a powder refers to the maximum diameter of the powder, and specifically refers to the maximum length of a straight line connecting any two points on the outer contour of the powder.
The major axis diameter of the powder can be measured by the following method: 1 g of a sample is taken from the biomass powder or biomass solid fuel and observed under a scanning electron microscope (SEM). The major axis diameter of the biomass powder in the observed field of view is measured.

From the perspective of achieving a greater hydration effect and in response to the demand for increased biomass fuel consumption, the biomass content in the biomass feedstock is preferably 25% by mass or more and 100% by mass or less, and more preferably 50% by mass or more and 100% by mass or less, relative to the biomass feedstock.

The biomass can be pulverized into powder using a known pulverizer.
For example, when wood is used as woody biomass, large pieces of wood may be roughly crushed into chips of about several centimeters in size and then crushed into powder (preferably powder with a major axis diameter of 1 mm or less). When chips or small biomass are used, it is preferable to crush them into powder (preferably powder with a major axis diameter of 1 mm or less) using a known crusher.

The method for forming the lumps is not particularly limited, but from the viewpoint of handling such as transportability and storage, compression-molded lumps are preferred.
The shape and size of the lumps are not particularly limited.
The lumps are preferably pellets or briquettes. Pellets are usually cylindrical, with a diameter of 5 mm to 10 mm and a length of 5 mm to 50 mm. Briquettes usually have a larger diameter or length than pellets.
Pellets can be produced, for example, by extruding biomass raw material or biomass raw material with adjusted moisture content through a metal hole (e.g., diameter 5 mm to 10 mm, length 5 mm to 50 mm). Pellets can also be produced using a pelletizer such as a ring die or flat die.
Briquettes can be produced, for example, by molding the material into briquettes or cylindrical shapes using a briquetting machine.

The biomass raw material or aggregates used in the manufacturing method of this embodiment may be semi-carbonized. That is, in the manufacturing method of this embodiment, the moisture-adding step may involve semi-carbonizing the biomass raw material and adding moisture to the semi-carbonized biomass raw material, or semi-carbonizing the aggregates and adding moisture to the semi-carbonized aggregates.
The method for semi-carbonization is not particularly limited, but examples include a method in which the biomass raw material or lumps are heated for a certain period of time in an airtight container using a rotary kiln or the like to increase the degree of carbonization.

Furthermore, if the biomass raw material or aggregates have not been torrefied, the moisture addition process may involve adding moisture to the biomass raw material before it is formed into aggregates, or to the aggregates. Incidentally, aggregates that have not been torrefied are usually called white pellets.

Coal The biomass feedstock may include coal. Examples of coal include bituminous coal, sub-bituminous coal, and lignite. Bituminous coal: Coal with a gross calorific value of 8,100 kcal/kg or more and less than 8,400 kcal/kg on a dry and ash-free basis. Sub-bituminous coal: Coal with a gross calorific value of 7,300 kcal/kg or more and less than 8,100 kcal/kg on a dry and ash-free basis. Lignite: Coal with a gross calorific value of 5,800 kcal/kg or more and less than 7,300 kcal/kg on a dry and ash-free basis.

Preferably, the coal is pulverized coal.
From the viewpoint of ease of forming into agglomerates, the particle size of the coal is preferably 1 mm or less, more preferably 110 μm or less. The lower limit of the particle size of the coal is greater than 0.
The particle size of the coal can be adjusted, for example, by using a sieve.

When the biomass feedstock contains coal, from the viewpoint of further exerting the hydration effect and in light of the demand for increased use of biomass fuel, the ratio of coal to biomass in the biomass feedstock (coal/biomass) is preferably more than 0/100 and not more than 75/25, more preferably more than 0/100 and not more than 50/50, in mass ratio.
When the ratio of coal to biomass (coal/biomass) is more than 0/100 and is 75/25, the hydration effect is more easily exhibited.

The biomass content in the biomass solid fuel obtained by the production method of this embodiment is preferably 25% by mass or more and 95% by mass or less, and more preferably 50% by mass or more and 95% by mass or less, relative to the biomass solid fuel, from the perspective of further demonstrating the hydration effect and in response to the demand for increased biomass fuel consumption.

The biomass solid fuel obtained by the production method of this embodiment may contain components other than biomass and coal, as long as the effects of this embodiment are not impaired.
The other components are not particularly limited, but include binders and various additives.

[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 equipment 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 (for example, 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.

Second Embodiment
[Method for adjusting moisture content of biomass solid fuel]
The moisture adjustment method for biomass solid fuel according to the second embodiment (hereinafter also referred to as the "moisture adjustment method of this embodiment") is a method for adjusting the moisture content of biomass solid fuel obtained by forming biomass raw materials containing biomass into lumps, and includes a moisture adjustment step of adding moisture to the biomass solid fuel to adjust the moisture content of the biomass solid fuel to between 5% by mass and 25% by mass.

In the moisture adjustment method of this embodiment, examples of biomass solid fuels to be subjected to moisture adjustment include: 1) biomass solid fuels produced by the production method of the first embodiment, which have dried and had a reduced moisture content (e.g., biomass solid fuels with a moisture content of less than 5% by mass) during "transportation of the biomass solid fuel" or "storage of the biomass solid fuel" as exemplified in the first embodiment; and 2) biomass solid fuels produced by a method different from the production method of the first embodiment, i.e., biomass solid fuels whose moisture has not been adjusted.

In the moisture adjustment method of this embodiment, for example, by carrying out the moisture adjustment process on the biomass solid fuel described in 1) or 2) above, the moisture content can be adjusted to 5% by mass or more and 25% by mass or less. This makes it possible to obtain biomass solid fuel that is less likely to cause dust explosions.

The moisture adjustment process is preferably a process for adjusting the moisture content of the biomass solid fuel to between 5% and 20% by mass, and more preferably between 5% and 10% by mass.

The "adding moisture" in the moisture adjustment method of this embodiment is not particularly limited, but is preferably the step of immersing the biomass solid fuel in water, the step of spraying moisture onto the biomass solid fuel, or the step of storing the biomass solid fuel in a humidified space, as described in the first embodiment.

In the moisture adjustment method of this embodiment, the biomass solid fuel to be subjected to moisture adjustment is preferably the biomass solid fuel obtained by the manufacturing method of the first embodiment. In other words, it is preferably the biomass solid fuel described in 1) above.

The moisture content of biomass solid fuel may change over time, so even if a biomass solid fuel with an adjusted moisture content is produced by the production method of the first embodiment, the moisture content may change over time.
For example, biomass solid fuel with a moisture content of 5% by mass or more (preferably 10% by mass or more) is less likely to cause dust explosions, so by applying the moisture adjustment method of this embodiment to biomass solid fuel that has dried and has a reduced moisture content (for example, biomass solid fuel with a moisture content of less than 5% by mass) or biomass solid fuel that shows a tendency toward a reduced moisture content, it is possible to produce biomass solid fuel that is less likely to cause dust explosions.
Furthermore, biomass solid fuel with a moisture content of less than 5% by mass may be broken down and blown into dust and accumulate in immovable parts of equipment during transportation, storage, and use. Dry dust blown into immovable parts of equipment can cause dust explosions.
Therefore, the moisture adjustment method of this embodiment is also effective in that it can prevent dust from drifting to immovable parts of the device, which can be a cause of dust explosions.

In the moisture adjustment method of this embodiment, the moisture adjustment step is preferably a step of adjusting the moisture content of the biomass solid fuel to 5% by mass or more and 25% by mass or less when a means for detecting the moisture content of the biomass solid fuel (hereinafter also referred to as a "moisture content detection means") detects that the moisture content is less than 5% by mass.
The moisture content detection means is not particularly limited, and for example, an optical detector or an electrical detector can be used. An example of an optical detector is an infrared moisture meter. An example of an electrical detector is a capacitance moisture meter.

In the moisture adjustment method of this embodiment, the moisture adjustment process is preferably a process in which a means for detecting the moisture content of the biomass solid fuel detects the moisture content, a means for controlling the moisture content based on the detected moisture content (hereinafter also referred to as a "moisture content control means") determines whether or not to add water to the biomass solid fuel, and based on the determination result, adjusts the moisture content to 5% by mass or more and 25% by mass or less.
The moisture content control means is not particularly limited, but for example, a known control device can be used.
That is, in the moisture adjustment method of this embodiment, when the moisture content detection means detects that the moisture content (moisture amount) of the biomass solid fuel is less than 5 mass%, it is preferable that the moisture content control means activates a moisture spraying device or moisture spraying equipment to add moisture to the biomass solid fuel (e.g., spray water) so that the moisture content of the biomass solid fuel is 5 mass% or more and 25 mass% or less.
In other words, in the moisture adjustment method of this embodiment, when the moisture content detection means detects that the moisture content (moisture content) of the biomass solid fuel is 5 mass% or more, it is preferable that the moisture content control means does not operate the moisture spraying device or moisture spraying equipment.
This allows the moisture content of biomass solid fuel to be continuously monitored, making it safer to handle, which in turn allows for expanded use of biomass solid fuel and meets the demand for increased use of biomass solid fuel.
It is preferable to install the water spraying device or water spraying equipment in a location where dust is likely to accumulate, specifically near an immovable part of the device, or in a location that is difficult to clean.

In this embodiment, the biomass contained in the biomass feedstock can be the same as the biomass described in Embodiment 1. The coal contained in the biomass feedstock can be the same as the coal described in Embodiment 1.
In this embodiment, the "biomass content in the biomass feedstock" and the "ratio of coal to biomass in the biomass feedstock (coal/biomass)" are the same as those in the first embodiment.

Third Embodiment
[Biomass solid fuel]
The biomass solid fuel according to the third embodiment is a pellet-shaped or briquette-shaped biomass solid fuel containing biomass.
The biomass content of the biomass solid fuel is 25% by mass or more and less than 95% by mass, and the moisture content of the biomass solid fuel is 5% by mass or more and 25% by mass or less.
When the moisture content of the biomass solid fuel is 5% by mass or more, the minimum ignition energy is increased, thereby exhibiting the effect of suppressing ignition of the biomass.
When the moisture content of the biomass solid fuel is 25% by mass or less, the calorific value as a fuel is ensured.
When the biomass content of the biomass solid fuel is 25% by mass or more and less than 95% by mass, the biomass solid fuel contains moisture, which makes it easier to exhibit the effect of suppressing ignition of biomass.
Therefore, according to the biomass solid fuel of this embodiment, even if dust is generated due to mechanical impact or the like during transportation or storage, dust explosions are unlikely to occur.

The moisture content of the biomass solid fuel of this embodiment is preferably 5% by mass or more and 20% by mass or less, more preferably 5% by mass or more and 10% by mass or less, from the viewpoint of further suppressing ignition of biomass and further ensuring heat generation.
Furthermore, from the viewpoint of further suppressing ignition of biomass, the moisture content of the biomass solid fuel of this embodiment is preferably 8.0 mass % or more and 25 mass % or less, and also preferably 9.1 mass % or more and 25 mass % or less.

The ratio of coal to biomass (coal/biomass) in the biomass solid fuel of this embodiment is preferably greater than 0/100 and less than or equal to 75/25 by mass.

The biomass solid fuel of this embodiment is preferably the biomass solid fuel produced by the production method of Embodiment 1. That is, the biomass solid fuel of this embodiment is preferably the biomass solid fuel produced by the production method of Embodiment 1, obtained by compressing a biomass raw material containing powdered (powdered) biomass and pulverized coal into a pellet or briquette shape.
In this embodiment, the biomass contained in the biomass solid fuel can be the same as the biomass described in Embodiment 1. The coal contained in the biomass solid fuel can be the same as the coal described in Embodiment 1.

The biomass solid fuel of this embodiment is preferably a biomass solid fuel whose moisture content has been adjusted using the moisture adjustment method of the second embodiment.

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.

The following describes examples of the present invention. The present invention is not limited to these examples.

The properties of the coal and biomass used in the examples and comparative examples are shown in Table 1.

Explanation of Table 1 Proximate analysis values are values measured in accordance with JIS M8812 (2004).
Of the elemental analysis values, carbon, hydrogen, nitrogen, and sulfur are values measured in accordance with JIS M8819 (1997), and oxygen is a value calculated from other analytical values in accordance with JIS M8813 (2004).
The higher heating value is a value measured in accordance with JIS M8814 (2003).
The fuel ratio is "fixed carbon/volatiles."
"ar" is an abbreviation for As Received Base, which represents the arrival base and indicates the state without any modification. The same is true for Table 2.
"ad" stands for Air Dry Basis, which indicates an air-dried basis, and represents a state in which the sample is dried in the air. The same applies to Table 2.
"Daf" is an abbreviation for Dry Ash Free, which represents a water-free and ash-free basis, and represents a hypothetical state in which coal is assumed to contain no moisture or ash. It is calculated by conversion from analytical values.
"<0.01" means "less than 0.01".

The ignition and explosion tests conducted in this example were conducted under the assumption that fine powder generated from biomass solid fuel would become airborne and cause a dust explosion. Therefore, powder was used in both the ignition and explosion tests. The biomass powder and pulverized coal used as powders were prepared as follows.

Example 1
<Preparation of biomass powder>
Semi-carbonized pellet-shaped biomass (manufactured by Siambiomas, woody biomass (rubber tree)) was pulverized in a pulverizer and passed through a sieve with openings of 105 μm (140 mesh) to produce biomass powder with a particle size of 105 μm or less.

<Production of pulverized coal>
Coal (lignite produced in Indonesia) was pulverized in a pulverizer and passed through a 105 μm (140 mesh) sieve in the same manner as the biomass to produce pulverized coal with a particle size of 105 μm or less.

<Preparation of biomass raw materials>
50 parts by mass of biomass powder and 50 parts by mass of pulverized coal were mixed to obtain a mixed powder of biomass powder and pulverized coal, which was used as the biomass raw material.

<Adding water to biomass raw materials>
Using an airtight container, 5 parts by mass of water was added to 100 parts by mass of biomass raw material, the container was placed in, the lid was tightly closed to prevent spillage even when shaken, and the mixture was mixed well in a shaker for 2 hours to obtain hydrated biomass raw material with a moisture content of 12.2% by mass (hereinafter also referred to as "hydrated biomass raw material").
The moisture content of the hydrated biomass raw material was calculated as follows, taking into account the total moisture content of the biomass (4.9 wt%) and the total moisture content of the coal (10.8 wt%) shown in Table 1.
Moisture content [mass%] = (5 + 2.45 + 5.4) / 105 = 12.2

Example 2
In the "addition of moisture to biomass raw material" step of Example 1, 10 parts by mass of water was sprayed per 100 parts by mass of biomass raw material in the same manner as in Example 1, and a hydrated biomass raw material of Example 2 with a moisture content of 16.2% by mass was obtained.
The moisture content of the hydrated biomass raw material was calculated as follows, taking into account the total moisture content of the biomass (4.9 wt%) and the total moisture content of the coal (10.8 wt%) shown in Table 1.
Moisture content [mass%] = (10 + 2.45 + 5.4) / 110 = 16.2

Comparative Example 1
The biomass powder and pulverized coal used in Example 1 were mixed in the parts by mass shown in Table 2 to prepare a mixed powder, which was used as the biomass raw material for Comparative Example 1. In Comparative Example 1, "addition of water to the biomass raw material" was not performed. Similarly, in Comparative Example 2 and Reference Examples 1 to 3 described below, no water was added to the biomass raw material.
The moisture content of the biomass raw material in Comparative Example 1 was calculated from the total moisture of the biomass (4.9 wt%) and the total moisture of the coal (10.8 wt%) shown in Table 1.

Comparative Example 2
The biomass powder used in Example 1 was used as the biomass raw material in Comparative Example 2.
The moisture content of the biomass raw material of Comparative Example 2 corresponds to the total moisture of the biomass shown in Table 1 (4.9 wt %).

[Reference example 1]
The pulverized coal used in Example 1 was used as the coal raw material in Reference Example 1.
The moisture content of the coal raw material in Reference Example 1 corresponds to the total moisture content of the coal shown in Table 1 (10.8 wt %).

[Reference examples 2-3]
The biomass powder and pulverized coal used in Example 1 were mixed in the parts by mass shown in Table 2 to prepare mixed powders, which were used as the biomass raw materials for Reference Examples 2 and 3, respectively.
The moisture content of the biomass raw materials in Reference Examples 2 and 3 was calculated from the total moisture of the biomass (4.9 wt%) and the total moisture of the coal (10.8 wt%) shown in Table 1.

〔evaluation〕
The following evaluations were carried out using the hydrated biomass materials obtained in Examples 1 and 2, the biomass materials obtained in Comparative Examples 1 and 2 and Reference Examples 2 and 3, and the coal material obtained in Reference Example 1 as samples.

[Minimum ignition energy]
The minimum ignition energy was measured using a minimum ignition energy measuring device (MIKE3 model, manufactured by Adolf Kuhner AG) shown in FIG.
The minimum ignition energy measuring device (MIKE3 model, manufactured by Adolf Kuhner AG) complies with the international standard "ISO/IEC 80079-20-2 Edition 1.0 2016-02:8.3 Method for determining minimum ignition energy of dust/air mixtures."

First, the minimum ignition energy measuring device 100 will be described.
The minimum ignition energy measuring device 100 includes a cylindrical glass combustion vessel 10 (inner diameter 7 cm, internal volume 1.2 L), a first support stand 30 that supports the combustion vessel 10, and a second support stand 32. A filter paper 28 is placed on top of the combustion vessel 10.
A pair of ignition electrodes 12 are disposed opposite each other inside the combustion vessel 10. The pair of ignition electrodes 12 extend from the inside to the outside of the combustion vessel 10 and are covered with electrical insulating materials 26a, 26b outside the combustion vessel 10. The pair of ignition electrodes 12 are connected to a capacitive discharge type ignition device (not shown). When a voltage is applied from the ignition device, a discharge occurs between the ignition electrodes 12, and the generated discharge energy forms a discharge spark between the ignition electrodes 12.
The combustion vessel 10 has a dispersion dish 14 on the bottom side, and a sample (hydrated biomass feedstock, biomass feedstock, or coal feedstock) is introduced into this dispersion dish 14. In addition, a reflector plate 16 is provided on the dispersion dish 14.
The dispersion tray 14 of the combustion vessel 10 is connected to a pipe 18 for blowing compressed air into the combustion vessel 10. The pipe 18 passes through the interior of the first support stand 30 and the second support stand 32, and is connected to a piping 20 having an outer diameter smaller than that of the pipe 18. Compressed air supplied from a compressor (not shown) is stored in the compressed air reservoir 24. The compressed air is introduced into the interior from the bottom side of the combustion vessel 10. The supply and stop of compressed air to the combustion vessel 10 is controlled by an electromagnetic valve 22 provided on the piping 20.
The height H (FIG. 1) from the top of the first support stand 30 to the ignition electrode 12 is 7.6 cm.

The minimum ignition energy was determined by conducting an ignition test. The following ignition test was conducted with a 1 mH inductance connected to the discharge circuit.

<Ignition test of Example 1>
First, samples were prepared so that the dust concentrations in the combustion vessel 10 were 750 g/m ³ , 1000 g/m ³ , 1250 g/m ³ , 1500 g/m ³ , 1750 g/m ³ , and 2000 g/m ³ . The sample amounts for each dust concentration were 0.9 g, 1.2 g, 1.5 g, 1.8 g, 2.1 g, and 2.4 g, respectively.
Next, 0.9 g of sample (a sample prepared so that the dust concentration would be 750 g/ ^m3 ) was placed on the dispersion tray 14 of the combustion vessel 10. Compressed air was supplied to the combustion vessel 10 from the compressed air reservoir 24, and the sample was blown up and dispersed inside the combustion vessel 10. Using a capacitive discharge ignition device, the discharge energy was changed to seven levels: 1 mJ, 3 mJ, 10 mJ, 30 mJ, 100 mJ, 300 mJ, and 1 J, and the presence or absence of ignition at each discharge energy was observed, and if necessary, the ignition delay time was changed to observe the presence or absence of ignition.
The ignition test was performed 10 times using a sample weight of 0.9 g and each discharge energy to check for ignition. If the sample ignited even once out of the 10 times, it was judged that the ignition ability was "present" under those conditions, and if the sample did not ignite even once, it was judged that the ignition ability was "absent" under those conditions.

Next, the sample amount was changed from 0.9 g to 1.2 g, 1.5 g, 1.8 g, 2.1 g, and 2.4 g in order, and an ignition test was carried out for each sample in the same manner as above.
The results are shown in Table 2.

Explanation of Table 2 Tests under conditions not shown in Table 2 (for example, sample amount 0.9 g, discharge energy 1 mJ) were not conducted because the results were predictable. The same applies to Tables 3 and 4 described below.

Minimum Ignition Energy in Example 1 Figure 2 was created from the results in Table 2. Figure 2 is a graph showing the relationship between dust concentration and discharge energy.
From FIG. 2, the minimum ignition energy (E _min ) of the hydrated biomass feedstock of Example 1 is 10 mJ<E _min <30 mJ, and its statistical minimum ignition energy (Es) is 19 mJ.
The statistical minimum ignition energy (Es) was calculated from the probability of ignition using the following formula (1) in accordance with EN13821:2002 and SAP12-10-2010 (standards of the Japan Powder Process Industry and Engineering Association). In this test, this statistical minimum ignition energy (Es) was used as the minimum ignition energy (mJ).

Es: statistical minimum ignition energy _E1 : minimum discharge energy that ignited _E2 : maximum discharge energy that did not ignite I[ _E2 ]: number of dust concentrations that ignited in _E2 (NI+I)[ _E2 ]: total number of dust concentrations tested The units for Es, _E1 and _E2 are all (mJ).

<Ignition test of Example 2>
Samples were prepared so that the dust concentrations in the combustion vessel 10 were 750 g/m ³ , 1000 g/m ³ , 1500 g/m ³ , 2000 g/m ³ , 2250 g/m ³ , and 2500 g/m ³ . The sample amounts for each dust concentration were 0.9 g, 1.2 g, 1.8 g, 2.4 g, 2.7 g, and 3.0 g, respectively.
The ignition test was carried out in the same manner as in Example 1. The results are shown in Table 3.

Minimum Ignition Energy in Example 2 Figure 3 was created from the results in Table 3. Figure 3 is a graph showing the relationship between dust concentration and discharge energy.
3, the minimum ignition energy (E _min ) of the hydrated biomass feedstock in Example 2 is 30 mJ < E _min < 100 mJ, and the statistical minimum ignition energy (E s ) is 60 mJ. The statistical minimum ignition energy (E s ) was determined in the same manner as in Example 1.

<Ignition test of Comparative Example 1>
Samples were prepared so that the dust concentrations in the combustion vessel 10 were 1000 g/m ³ , 1500 g/m ³ , 1750 g/m ³ , 2000 g/m ³ , 2250 g/m ³ and 2500 g/m ³ . The sample amounts for each dust concentration were 1.2 g, 1.8 g, 2.1 g, 2.4 g, 2.7 g and 3.0 g, respectively.
An ignition test was carried out in the same manner as in Example 1. The results are shown in Table 4.

Minimum Ignition Energy in Comparative Example 1 Figure 4 was created from the results in Table 4. Figure 4 is a graph showing the relationship between dust concentration and discharge energy.
4, the minimum ignition energy (E _min ) of the biomass feedstock of Comparative Example 1 was 3 mJ < E _min < 10 mJ, and the statistical minimum ignition energy (E s ) was 6.0 mJ. The statistical minimum ignition energy (E s ) was determined in the same manner as in Example 1.

<Ignition test and minimum ignition energy of Comparative Example 2 and Reference Examples 1 to 3>
The hydrated biomass raw material of Example 1 was replaced with the biomass powder of Comparative Example 2, the coal powder of Reference Example 1, and the biomass raw materials of Reference Examples 2 and 3, respectively, and an ignition test was conducted for each example using the same procedure as in Example 1 to determine the statistical minimum ignition energy (Es).

<Relationship between biomass powder mixing ratio and minimum ignition energy>
FIG. 5 shows the relationship between the mixing ratio of biomass powder in the biomass raw material and the minimum ignition energy.
Regions A, B, and C shown in FIG. 5 are defined as follows based on "Countermeasures for each minimum ignition energy possessed by powder" (Countermeasures for dust explosions and fires, edited by the Dust Explosion Committee of the Japan Powder Process Industry and Technology Association, "R. Siwek and C. Cesana: Ignition behavior of dusts: Meaning and interpretation, Process Safety Progress, 14, 2, pp. 107-119 (1995)" on page 169) described in the determination diagram for the risk of ignition due to electrostatic charging.
Area A: This area can be addressed by preventing static electricity buildup by grounding the container, etc.
Area B: Area where there is a risk of explosion such as the presence of a human body and where explosion control is required. Area B is an "area requiring caution."
Area C: An area where it is necessary to take measures to inactivate the entire container, control the loading speed, etc. Area C is an area that requires extreme caution.

[Lower explosive limit concentration]
The lower explosion limit concentration was determined using a blow-up type test device specified in JIS Z8818 (2002) "Method for measuring the lower explosion limit concentration of combustible dust," which has a configuration similar to that of the minimum ignition energy measuring device 100 shown in Figure 1.

The lower explosive limit concentration was determined by performing an explosion test under the following conditions:
- Measurement conditions -
・Temperature: 20.1℃～20.3℃
Relative humidity: 13% to 14%
・Blow-up pressure: 30 kPa or more and 50 kPa or less

<Explosion test of Example 1>
The hydrated biomass material of Example 1 was used as a sample.
First, samples were prepared so ^that the dust concentrations in the combustion chamber were 65 g/m ³ , 70 g/m ³ , 75 g/m ³ , 80 g/m ³ , 85 g/m ³ , 90 g/m ³ , 95 g/m 3 , 100 g/m ³ and 110 g/m ³ .

Next, a sample (hereinafter also referred to as "sample A") prepared so as to have a dust concentration of 65 g/m ³ was placed on the dispersion tray of the combustion vessel.
Compressed air was supplied from the compressed air reservoir to the combustion chamber, and the sample was blown up and dispersed into the combustion chamber, generating a dust cloud. The ignition source was a discharge spark from a neon transformer with a secondary output of 15 kV and a capacity of 20 mA.
A discharge spark was generated at the same time as the sample was blown up into the combustion vessel (discharge start time 0.1 seconds), and it was visually determined whether or not the dust cloud exploded. This procedure was repeated by changing the air pressure, etc., as necessary. The explosion test was repeated five times under the same conditions. The explosion test under the same conditions was stopped once an explosion was confirmed out of the five times. The lowest dust concentration that showed explosiveness, i.e., the dust concentration at which an explosion was confirmed, was taken as the "lower explosive limit concentration (apparent lower explosive limit concentration)."

Next, sample A was replaced by samples prepared so that the dust concentrations were 70 g/ ^m3 , 75 g/ ^m3 , 80 g/ ^m3 , 85 g/ ^m3 , 90 g/ ^m3 , 95 g/ ^m3 , 100 g/ ^m3 , and 110 g/ ^m3 , and explosion tests were carried out on each sample in the same manner as above. The results are shown in Table 5.

Explanation of Table 5: The (65) in the dust concentration of 65 g/ ^m³ means that the measurement was made with reference to the presence or absence of an explosion of the dust cloud. The same applies to (60) in Table 6 described later.

Lower Explosive Limit Concentration in Example 1 From Table 5, the lower explosive limit concentration of the hydrated biomass raw material in Example 1 was 80 g/m ³ .

<Explosion test of Comparative Example 1>
The mixed powder of Comparative Example 1 was used as a sample.
First, samples were prepared so that the dust concentrations in the combustion vessel 10 were 60 g/ ^m3 , 65 g/ ^m3 , 70 g/ ^m3 , 75 g/ ^m3 , 80 g/ ^m3 , 85 g/ ^m3 , 90 g/ ^m3 , 95 g/ ^m3 , 100 g/ ^m3 , and 110 g/ ^m3 , and explosion tests were conducted in the same manner as in Example 1. The results are shown in Table 6.

Lower Explosive Limit Concentration of Comparative Example 1 As shown in Table 6, the lower explosive limit concentration of the mixed powder of Comparative Example 1 was 75 g/m ³ .

<Lower Explosive Limit Concentration of Example 2, Comparative Example 2, and Reference Examples 1 to 3>
The hydrated biomass raw material of Example 1 was replaced with the hydrated biomass raw material of Example 2, the biomass powder of Comparative Example 2, the coal powder of Reference Example 1, and the biomass raw materials of Reference Examples 2 and 3, respectively, and explosion tests were conducted for each example using the same procedure as in Example 1 to determine the lower explosion limit concentration.
The results are shown in Table 7.

Explanation of Table 7: "-" indicates that no measurement was performed.

As can be seen from Table 7 and FIG. 5, the hydrated biomass feedstocks of Examples 1 and 2, which were produced by adding water so that the moisture content was 5% by mass or more and 25% by mass or less, had a higher minimum ignition energy than the biomass feedstocks of Comparative Examples 1 and 2, which were produced without adding water.
Furthermore, the hydrated biomass feedstock of Example 1 also had a higher lower explosion limit concentration than the biomass feedstocks of Comparative Examples 1 and 2.
Furthermore, the hydrated biomass feedstocks of Examples 1 and 2 had a high calorific value on arrival.
Furthermore, according to this embodiment, as shown in FIG. 5, by using hydrated biomass material as the biomass material, the biomass material in region C can be shifted toward region A.
Therefore, when biomass solid fuel is produced using the hydrated biomass raw material of this embodiment, the moisture content of the resulting biomass solid fuel reflects the moisture content of the hydrated biomass raw material, so a biomass solid fuel that is less likely to cause dust explosions can be obtained.

The biomass solid fuel obtained using the production method of the present invention is less likely to cause dust explosions, allowing for safe handling of biomass. This will enable expanded use of biomass in power plants, steel mills, factories, and other places.

10...Combustion vessel, 12...Ignition electrode, 14...Dispersion dish, 16...Reflector, 18...Pipe, 20...Piping, 22...Solenoid valve, 24...Compressed air reservoir, 26a, 26b...Electrical insulating material, 28...Filter paper, 30...First support base, 32...Second support base, 100...Minimum ignition energy measuring device.

Claims (10)

A method for producing a biomass solid fuel obtained by forming a biomass raw material containing biomass into an aggregate,
adding moisture to the aggregates obtained by molding so that the moisture content of the biomass solid fuel is 5% by mass or more and 25% by mass or less;
A method for producing biomass solid fuel, wherein the moisture-adding step is a step of spraying moisture onto the lumps obtained by molding, or a step of storing the lumps obtained by molding in a humidified space . The method for producing a biomass solid fuel according to claim 1 ,
The method for producing biomass solid fuel, wherein the biomass is at least one selected from the group consisting of woody biomass, herbaceous biomass, agricultural crop residue biomass, and palm biomass. The method for producing a biomass solid fuel according to claim 1 or 2 ,
A method for producing a biomass solid fuel, wherein the biomass is a powder, and the major axis diameter of the powder is 5 mm or less. The method for producing a biomass solid fuel according to any one of claims 1 to 3 ,
The method for producing a biomass solid fuel, wherein the lumps are pellets or briquettes. The method for producing a biomass solid fuel according to any one of claims 1 to 4 ,
The method for producing a biomass solid fuel, wherein the biomass feedstock further includes coal. The method for producing a biomass solid fuel according to claim 5 ,
The method for producing biomass solid fuel, wherein the coal has a particle size of 1 mm or less. The method for producing a biomass solid fuel according to claim 5 or 6 ,
A method for producing a biomass solid fuel, wherein a ratio of the coal to the biomass in the biomass raw material (coal/biomass) is 0/100 or more and 75/25 or less in mass ratio. A method for adjusting moisture content of a biomass solid fuel obtained by forming a biomass raw material containing biomass into an aggregate, comprising:
a moisture adjusting step of adjusting the moisture content of the biomass solid fuel to 5% by mass or more and 25% by mass or less by adding moisture to the biomass solid fuel;
The moisture adjustment step is a step of adjusting the moisture content of the biomass solid fuel to 5% by mass or more and 25% by mass or less when the means for detecting the moisture content of the biomass solid fuel detects that the moisture content is less than 5% by mass. A method for adjusting moisture content of a biomass solid fuel obtained by forming a biomass raw material containing biomass into an aggregate, comprising:
a moisture adjusting step of adjusting the moisture content of the biomass solid fuel to 5% by mass or more and 25% by mass or less by adding moisture to the biomass solid fuel;
The moisture adjustment process is a process in which a means for detecting the moisture content of the biomass solid fuel detects the moisture content, a means for controlling the moisture content based on the detected moisture content determines whether or not to add water to the biomass solid fuel, and based on the determination result, adjusts the moisture content to 5% by mass or more to 25% by mass or less. The method for adjusting moisture content of biomass solid fuel according to claim 8 or 9 ,
A method for adjusting moisture content of a biomass solid fuel, wherein the biomass solid fuel to be subjected to moisture adjustment is a biomass solid fuel obtained by the method for producing a biomass solid fuel according to any one of claims 1 to 7 .