solid fuels

Abstract

The present invention addresses the problem of providing a solid fuel made of a molded product of crushed hardwood that has high material yield and calorific value yield, is easy to handle from the viewpoint of recycling and environmental protection, has improved transportability, and has excellent crushability by mill.　In a solid fuel made from a molded product that includes crushed hardwood, the fraction of the solid fuel molded product that passes through a sieve having 1-mm square holes in the particle size after dry shredding is 60 mass% or more.

Description

Technical Field

[0001] The present invention relates to a technique for producing solid fuel from broad-leaved trees.

Background Art

[0002] In recent years, as a countermeasure against the depletion of fossil fuels and global warming caused by CO2 emissions, the use of fuels made from biomass as raw materials has been studied. Generally, biomass refers to organisms that can be used as an energy source or industrial raw material, and typical examples include wood, construction waste, agricultural waste, and the like.

[0003] As a technique for producing solid fuel from biomass, for example, a method of carbonizing biomass to produce solid fuel is known. This involves charging biomass into a carbonization furnace and heating it for a predetermined time in an oxygen-deficient atmosphere for carbonization treatment to produce solid fuel. The solid fuel thus produced is used as fuel for combustion equipment such as power generation equipment and incineration equipment. In this case, in order to improve the combustion efficiency, the solid fuel may be finely pulverized and used as pulverized fuel.

[0004] Patent Document 1 discloses a method of thermally decomposing woody biomass such as wood waste, thinned wood, garden trees, and construction waste at 240 to 300°C for 15 to 90 minutes and then pulverizing it. Patent Document 2 also discloses a method of producing solid fuel having pulverizability equivalent to coal by carbonizing biomass containing grains, fruits, and seeds by heating at an oxygen concentration of 1 to 5% and a treatment temperature of 350 to 400°C for 30 to 90 minutes.

[0005] Furthermore, Patent Document 3 describes compressing and dehydrating wood chips for heat utilization, and Patent Document 4 describes producing solid fuel by compression and solidification of plant materials such as wood. Additionally, Non-Patent Document 1 describes compressing and dehydrating bark using a reciprocating press for heat utilization in a boiler or the like.

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] Japanese Patent Publication No. 2006-026474 [Patent Document 2] Japanese Patent Publication No. 2009-191085 [Patent Document 3] Japanese Patent Publication No. 2008-036666 [Patent Document 4] Japanese Patent Publication No. 2010-189457 [Non-patent literature]

[0007] [Non-Patent Document 1] International Journal Energy Engineering, 2014, volume 4, pages 8-16 [Disclosure of the Invention] [Problems that the invention aims to solve]

[0008] Fuels obtained by carbonizing plant-based biomass such as wood generally suffer from low material and calorific yields. Furthermore, producing solid fuels from biomass such as wood incurs transportation costs, making it more expensive than coal. Therefore, to facilitate handling and transportation, the production of solid fuels from wood pulverized into pellets or similar materials is being considered. However, this requires grinding in a mill before feeding into a boiler, and problems with grindability have sometimes arisen during this process. [Means for solving the problem]

[0009] The inventors investigated a solid fuel made from a molded product that exhibits excellent pulverability in a mill containing crushed hardwoods. They discovered that by ensuring that the fraction of the molded product containing crushed hardwoods that passes through a sieve with 1 mm square holes accounts for 60% by mass or more of the particle size after dry crushing, a solid fuel with excellent pulverability in a mill using hardwoods as raw material can be obtained, thus completing the present invention.

[0010] The present invention is not limited to the following embodiments. (1) A solid fuel comprising a molded product containing crushed hardwood, wherein the molded product of the solid fuel has a particle size of 60% by mass or more that has passed through a sieve with 1 mm square holes after dry crushing. (2) The solid fuel according to (1), wherein the solid fuel is a pellet with an average length of 22 mm or less. (3) The bulk density of the molded product of crushed hardwood is 600 kg / m³ 3 More than 680kg / m 3 The solid fuel described in either (1) or (2) below. (4) A solid fuel as described in any of (1) to (3), having a mechanical durability of 95.0 to 97.0%. (5) A solid fuel according to any one of (1) to (4), wherein the size of the pulverized material is 50 mm or less and the moisture content is 8 to 30%. (6) The solid fuel according to any one of (1) to (5), wherein the solid fuel is a pellet formed from crushed acacia chips with the bark still on. (7) A solid fuel according to any of (1) to (6), wherein the ratio B / A, which is the ratio of the percentage of fraction passing through a sieve with 1 mm square holes measured after dry crushing to the percentage of fraction passing through a sieve with 1 mm square holes measured after wet crushing in accordance with ISO17830:2016, is 0.8 to 1.2. (8) A method for producing a solid fuel according to any one of (1) to (7), comprising the step of forming a solid fuel from crushed hardwood. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a solid fuel made from molded hardwood pulverizers that have excellent pulverizability in mills. In other words, according to the present invention, molding the fuel makes it easier to handle and improves transportability. Furthermore, according to the present invention, solid fuel can be produced from woody biomass, which is the raw material, in a simple manner, resulting in high material yield and calorific value yield. Therefore, the present invention is extremely useful from the viewpoint of recycling and environmental protection. [Modes for carrying out the invention]

[0012] This invention relates to a technology for producing solid fuel from biomass containing wood. In this invention, biomass containing wood (hereinafter also referred to as woody biomass) is used as a raw material, but other materials such as herbaceous plants may also be used as long as they contain wood. Examples of wood include wood chips, bark, sawdust, sawdust, forest residues, and construction waste, and a preferred example is the use of wood chips as a raw material. In this invention, there are no particular restrictions on the type of wood used, and both broad-leaved trees and coniferous trees can be used, but coniferous trees are preferred. Furthermore, only one type of wood may be used, or multiple types may be mixed and used. In addition, in this invention, not only the wood but also the bark can be used as a raw material.

[0013] The broad-leaved trees used in this invention are not particularly limited, but examples include acacia, eucalyptus, rubber tree, beech, linden, birch, poplar, oak, Japanese maple, Japanese elm, paulownia, magnolia, willow, Japanese ash, evergreen oak, sawtooth oak, horse chestnut, zelkova, Japanese bush beetle, dogwood, and Japanese ash.

[0014] In the present invention, it is preferable to use crushed hardwoods that have been ground to a size of 50 mm or less before being molded into a product, and it is preferable to use crushed hardwoods that are between 0.1 and 50 mm in size. In the present invention, the size of the crushed material is determined by the size of the circular holes in the sieve. As the apparatus for crushing hardwoods, it is preferable to crush them using a knife-cutting type biomass fuel chipper.

[0015] In the present invention, the solid fuel used as a raw material includes broad-leaved trees as described above. The weight ratio of broad-leaved trees is preferably 50% by weight or more, and may be 70% by weight or more. In one embodiment, it is also possible to use only broad-leaved trees as a raw material.

[0016] In the present invention, the obtained pulverized product of broad-leaved trees is made into briquettes or pellet-shaped molded products. The bulk density of the molded product (measured according to 6 "Bulk density test method" of JIS K 2151) is 600 kg / m 3 or more and 680 or less kg / m 3 is preferable, 602 - 650 kg / m 3 is more preferable, and 604 - 620 kg / m 3 is even more preferable. By making it into a molded product, the handling as a solid fuel can be improved, and the transportation cost can be reduced.

[0017] In one embodiment, for the molded product of the solid fuel of the present invention, in terms of the particle size after dry crushing, it is necessary that the fraction passing through a sieve with a square hole of 1 mm is 60% by mass or more, more preferably 65 - 90% by mass, and even more preferably 70 - 80% by mass or more. Usually, the disintegrability of the molded product of solid fuel is measured for the particle size of the molded product disintegrated in hot water according to ISO17830:2016(E) Solid biofuels - Particle size distribution of disintegrated pellets. In contrast, in the present invention, the disintegration of the molded product is performed dry, but it has been found that the method of the present invention has a better correlation with the pulverizability in a mill. If the fraction passing through a sieve with a square hole of 1 mm at the particle size measured by the method of the present invention is 60% by mass or more, the pulverizability in a mill is excellent.

[0018] ​The solid fuel according to the present invention preferably has a ratio B / A of 0.8 to 1.2, more preferably 0.85 to 1.15, and even more preferably 0.9 to 1.1, which is the ratio of the percentage of the fraction that passes through a sieve with 1 mm square holes to the percentage of the fraction that passes through a sieve with 1 mm square holes measured after dry crushing, measured after wet crushing, measured according to ISO 17830:2016. Here, the percentage of the fraction that passes through a sieve with 1 mm square holes is measured according to EN 15149-2:2010.

[0019] The molded solid fuel product preferably has an average length of 21 mm or less, more preferably 10 to 20 mm, and even more preferably 15 to 19 mm. An average length of 21 mm or less ensures excellent pulverization in a mill. The diameter of the molded product is preferably in the range of 5 to 15 mm, more preferably 6 to 13 mm, and even more preferably 7 to 11 mm.

[0020] In the present invention, the molding apparatus for forming the pulverized material into a molded product is not particularly limited, but a bricketer (manufactured by Kitagawa Iron Works), a ring die type pelletizer (manufactured by CPM), a flat die type pelletizer (manufactured by Dalton), etc., are preferred.

[0021] In the present invention, when using crushed hardwood as a molded product, the moisture content of the crushed hardwood is preferably 8 to 50%, more preferably 9 to 30%, and even more preferably 10 to 20%. If the moisture content is less than 8%, clogging occurs inside the briquetter or pelletizer, making it impossible to produce a stable molded product. If the moisture content exceeds 50%, it becomes difficult to mold, and the product is discharged in powder or paste form.

[0022] The molded solid fuel product of the present invention preferably has a mechanical durability of 95% or more (according to the test method for mechanical durability of wood pellet quality standard 6.5). Mechanical durability within this range indicates sufficient hardness to prevent pulverization during transport. Mechanical durability refers to the resistance of the pellet to breakage, and is the mass percentage that does not break or pulverize when subjected to a certain amount of mechanical impact. In a more preferred embodiment, the molded solid fuel product of the present invention has a mechanical durability of 97% or more.

[0023] In this invention, 1 to 50 parts by mass of binder may be added to 100 parts by mass of crushed hardwood. The binder is not particularly limited, but organic polymers (such as lignin and starch), inorganic polymers (such as acrylamide), agricultural residues (such as bran (residue generated during wheat flour production)), etc. are preferred. From the viewpoint of efficiently and effectively utilizing woody biomass, it is preferable to add a small amount of binder, preferably 1 to 50 parts by mass, more preferably 1 to 20 parts by mass. However, it is not the case that high density is impossible even if 50 parts by mass or more are added.

[0024] The solid fuel obtained by this invention can be used as boiler fuel. In particular, it is suitable as fuel for coal boilers because it can be mixed with coal, pulverized, and then co-fired with coal. [Examples]

[0025] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples. In this specification, parts, percentages, etc., are based on weight, and numerical ranges are given including their endpoints.

[0026] [Example 1] Acacia wood chips with the bark still attached were crushed using a disc chipper. After crushing, the material that passed through a 50 mm screen was used as the raw material and dried in a dryer at 120°C for 20 minutes to adjust the moisture content to 10%. The moisture content of the resulting crushed material was adjusted to 12%, and the material was subjected to high-density processing using a ring die pelletizer (manufactured by CPM) with a die hole diameter of 8 mm and an effective die hole length of 52 mm to obtain solid fuel pellets.

[0027] The following items were measured on the obtained molded product. • Average length: Measured according to ISO 17829:2015. • Bulk density: Measured according to ISO 17829:2015. • Mechanical durability: Measured according to ISO17831:2015. • Particle size after dry crushing (B): 20 g of the dried molded material was crushed for 12 seconds using a LabMill (manufactured by Osaka Chemical Co., Ltd.), and the particle size was determined by measuring the percentage of fractions that passed through a sieve with 1 mm square pores according to EN15149-2:2010 (Solid biofuels. Determination of particle size distribution. Vibrating screen method using sieve apertures of 3.15 mm and below). In the wet crushing described later, 2000 ml of water was added to 300 g of the sample for crushing, but the dry crushing was carried out in accordance with ISO17830:2016(E), except that water was not added to the dried molded material. • Particle size after wet crushing (A): After wet crushing the dried molded material according to ISO17830:2016(E) (Solid biofuels - Particle size distribution of disintegrated pellets), the particle size was determined by measuring the percentage of fractions that passed through a sieve with 1 mm square pores according to EN15149-2:2010 (Solid biofuels. Determination of particle size distribution. Vibrating screen method using sieve apertures of 3.15 mm and below). • Biomass mill input amount: The amount of molded material input into the biomass mill (manufactured by IHI) was adjusted so that the mill differential pressure could be maintained at 5.0 kPa during operation.

[0028] [Example 2]~[Example 5] Examples 2-5 were manufactured under the same conditions as Example 1, except that they used acacia wood chips with the bark still attached, but were sourced at different times.

[0029] [Comparative Example 1]~[Comparative Example 4] Comparative Examples 1-4 were the same acacia wood chips with the bark still attached, but were sourced at different times. They were manufactured under the same conditions as Example 1, except that the cutter position was adjusted to set the effective hole length of the ring die to 72 mm.

[0030] [Table 1]

[0031] As shown in Table 1, the molded products of Examples 1 to 5 exhibited good pulverability in the biomass mill, resulting in high biomass mill input rates. On the other hand, as shown in Comparative Examples 1 to 4, even if the proportion of fractions passing through 1 mm square pores was high in the particle size measured after wet crushing, it was clear that the biomass mill input rate decreased if the fraction passing through 1 mm square pores was less than 60% in the particle size measured after dry crushing according to the present invention.

Claims

1. It consists of pellets containing crushed hardwood, with a bulk density of 600-680 kg / m³. ３ A method for producing solid fuel having a mechanical durability of 95.0% or more, The process includes forming solid fuel pellets from crushed hardwood, where the crushed hardwood is dried to a moisture content of 8-30%. The above method, wherein when solid fuel pellets are dry-crushed, the fraction that passes through a sieve with 1 mm square holes after dry-crushing accounts for 60% by mass or more.

2. The method according to claim 1, wherein the solid fuel is a pellet having an average length of 22 mm or less.

3. The method according to claim 1 or 2, wherein the fraction is 90% by mass or less.

4. The method according to any one of claims 1 to 3, wherein the mechanical durability is 95.0 to 97.0%.

5. The method according to any one of claims 1 to 4, wherein the size of the pulverized material is 50 mm or less.

6. The method according to any one of claims 1 to 5, wherein the solid fuel is a pellet formed from crushed acacia chips with the bark still on.

7. The method according to any one of claims 1 to 6, wherein the ratio B / A, which is the ratio of the percentage of fractions passing through a sieve with 1 mm square holes measured after dry crushing to the percentage of fractions passing through a sieve with 1 mm square holes measured after wet crushing in accordance with ISO 17830:2016, is 0.8 to 1.2.

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