JP6169323B2 - Method for producing solid fuel and solid fuel - Google Patents

Description

  The present invention relates to a method for producing a solid fuel obtained by torrefaction of bark.

In recent years, as a countermeasure against global warming due to depletion of fossil fuels and CO ₂ emissions, the use of fuels made from biomass has been studied. In general, biomass refers to a living organism that can be used as an energy source or an industrial raw material, and representative examples are wood, building waste, agricultural waste, and the like. Various methods for effectively utilizing biomass have been proposed. Among them, as a useful method capable of converting biomass into a high value-added product at a low cost, there is a method for producing a solid fuel by carbonizing biomass. In this method, biomass is put into a carbonization furnace and heated for a predetermined time in an oxygen-deficient atmosphere to be carbonized to produce a solid fuel.

  The solid fuel thus produced is used as a fuel for combustion facilities such as power generation facilities and incineration facilities. In this case, the solid fuel may be finely pulverized and used as a finely divided fuel in order to improve combustion efficiency. is there. Solid fuel is pulverized by itself or mixed with coal, but most of wood biomass is fibrous, so the pulverization is poor, the combustion efficiency is lowered, the operability of the pulverizer is reduced, etc. There was a problem.

  Patent Document 1 discloses a method of pulverizing woody biomass such as waste wood, thinned wood, garden wood, construction waste, etc. at a temperature of 240 ° C or higher and 300 ° C or lower for 15 to 90 minutes. Has been. If the heating temperature is lower than 240 ° C, crushability and pulverization will not be improved. If the heating temperature is higher than 300 ° C, the amount of fine powder on the order of submicron will increase during crushing and pulverization, and powder trouble will easily occur. Therefore, it is not preferable.

  Patent Document 2 discloses that biomass containing cereals, berries and seeds is carbonized by heating for 30 to 90 minutes at an oxygen concentration of 1 to 5% and a treatment temperature of 350 to 400 ° C. A method for producing a solid fuel having the same is disclosed.

JP 2006-26474 A JP 2009-191085

  However, the carbide produced by the above method has a low material yield and a calorie yield, and is not sufficiently pulverizable compared to coal. It is mixed with coal and pulverized for use as a fuel for pulverized coal boilers. Is difficult.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have used woody biomass containing bark that has a size of 60 mm or less and a fraction of a size of less than 0.5 mm as less than 10% by mass. As a result, it was found that a solid fuel having pulverizability equivalent to that of coal can be produced by torrefaction under conditions of an oxygen concentration of 10% or less and a temperature of 170 to 350 ° C.

  The bark prepared in the present invention has a high bulk density and a small amount of fines. Therefore, there are problems of transportability due to clogging of the rotary valve at the inlet of the carbonization furnace, and excessive rejection of the cyclone after the dryer. This prevents clogging and the like from occurring. In addition, the solid fuel obtained by the production method of the present invention has a high substance yield and calorie yield, and also has the same pulverization properties as coal, so it is mixed with coal and pulverized to produce fuel for pulverized coal boilers. Can be used as

  In the present invention, bark is used as a raw material. Bark is not used much and is often discarded. As a result of studying the effective use of bark, the present inventors have found that solid fuel having good properties can be obtained when roasted using bark as a raw material, compared to chips of xylem. Since the bark has less hemicellulose content than the xylem, the substance yield after roasting is increased. The tree species can be either hardwood or softwood, but cedar bark is preferred. The water content is preferably 10% or less, and more preferably 5% or less.

  However, when bark pulverized material is used as a raw material, problems such as clogging of the rotary valve at the carbonization furnace inlet and clogging due to excessive rejection in the cyclone after the dryer occur. There was a thing. This was thought to be due to the low bulk density of the bark pulverized material and the large amount of fines.

  In the present invention, it is necessary to use a bark having a size of 60 mm or less and a fraction having a size of less than 0.5 mm of less than 10% by mass. In the present invention, the size of the bark is sieved according to the size of the circular hole of the sieve. That is, a wood chip having a size of less than 0.5 mm passes through a hole having a diameter of 0.5 mm. When the fraction with a size of less than 0.5 mm is 10% by mass or more, the transportability is reduced due to clogging due to the bridge at the rotary valve at the inlet of the carbonization furnace due to the decrease in bulk density, and after the dryer due to the increase in fines. There will be no clogging due to excessive rejection in the cyclone. As an apparatus for pulverizing the bark, it is preferable to pulverize with a knife cutting type biomass fuel chipper.

  The torrefaction in the present invention is a process of heating in a low oxygen atmosphere at a temperature lower than a so-called carbonization process. The normal carbonization temperature of wood is 400-700 ° C, but roasting is performed at a lower temperature. By performing the roasting, a solid fuel having an energy density higher than that of the starting material can be obtained.

  The roasting treatment conditions in the present invention are an oxygen concentration of 10% or less and a temperature of 170 to 350 ° C. When the oxygen concentration exceeds 10%, the substance yield and the calorie yield decrease. Further, if the temperature is less than 170 ° C., the grindability described later is insufficient, and if it exceeds 350 ° C., the substance yield and the calorie yield decrease. The temperature is more preferably 200 to 320 ° C. Hemicellulose is prone to pyrolysis around 270 ° C, while cellulose is prone to pyrolysis around 355 ° C and lignin is around 365 ° C, so the processing temperature during roasting is 170-350 ° C. Thus, it is speculated that hemicellulose can be preferentially pyrolyzed to produce a solid fuel that can achieve both material yield and pulverization.

  In the present invention, the apparatus for performing the roasting treatment is not particularly limited, but a rotary kiln or vertical furnace usually used as a carbonization furnace is preferable. In order to adjust the oxygen concentration to 10% or less, the inside of the apparatus is preferably replaced with an inert gas such as nitrogen. The treatment time is preferably 15 to 180 minutes.

  The solid fuel obtained in the present invention has a material yield of 60 to 90% and a calorific yield of 70 to 95% with respect to the raw bark. The hard glove grindability index (HGI) defined in JIS M 8801: 2004, which is an index of grindability, is preferably 30 to 70, more preferably 40 to 60. It shows that it becomes easy to grind, so that HGI becomes high. If HGI is in the range of 30 to 70, it can be mixed with coal and pulverized. Since the HGI of coal is usually 40 to 70, the solid fuel obtained in the present invention has the same pulverization properties as coal.

  EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[Example 1]
The cedar bark was pulverized with a knife cutting type biomass fuel chipper (manufactured by Green Products Co., Ltd., Wood Hacker MEGA360DL). After pulverization, the bark that passed through the 70 mm screen was further classified into fractions of> 2 mm, 2 mm to 0.5 mm, and 0.5 mm>, and each mass ratio was measured. (Please describe the classification method and equipment.)
Table 1 shows the distribution of bulk density and size of the obtained bark. Using this bark as a raw material, a drying treatment was performed at 120 ° C. for 10 minutes with a dryer. Subsequently, using a large kiln type carbonization furnace, a nitrogen purge was performed, and the product was obtained by baking at a carbonization furnace inlet temperature of 310 ° C., a carbonization furnace outlet temperature of 310 ° C., and a residence time of 30 minutes. Neither clogging of the rotary valve at the inlet of the carbonization furnace nor clogging of the cyclone after the dryer occurred.

[Comparative Example 1]
Cedar bark was pulverized with a hammer mill (PROGRIND 1500T, manufactured by Prrsident Husky Corporetion), and a product was obtained in the same manner as in Example 1 except that bark that passed through a 100 mm screen was used as a raw material after pulverization. .

The following items were evaluated for the products obtained in Example 1 and Comparative Example 1, and the results are shown in Table 1. Comparative Example 2 is untreated cedar bark.
Material yield: calculated from the weight of the sample before and after roasting.
・ Crushability: The sample was pulverized with a ball mill at 200 rpm for 4 minutes, the weight of what passed 200 mesh was measured, and converted from the value of the hard glove grindability index (HGI), which is an indicator of coal pulverization, HGI.

  As shown in Table 1, the product of Example 1 produced by roasting bark having a size of 60 mm or less and a fraction of a size of less than 0.5 mm less than 10% by mass as a raw material has a substance yield. In addition, the heat yield was high, the hard glove grindability index (HGI) was in the range of 30 to 70, and the grindability was good. On the other hand, in Comparative Example 1 using a raw material having a fraction of less than 0.5 mm in size of 10% by mass or more, the rotary valve at the inlet of the carbonization furnace was clogged or the cyclone after drying was clogged, and could not be manufactured. . In Comparative Example 1, the bulk density is lower than that in Example 1, which is considered to be a cause of deterioration in operability. The untreated bark of Comparative Example 2 had an HGI of less than 30 and was inferior in grindability.

Claims (1)

A woody biomass containing bark that has been pulverized so that a fraction with a size of 60 mm or less and a size of less than 0.5 mm is less than 10% by mass is screened, and has an oxygen concentration of 10% or less and a temperature of 170- A method for producing a solid fuel, characterized by roasting in a rotary kiln having a rotary valve at an inlet at 350 ° C.