JP5965693B2 - 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 singly or mixed with coal, but woody biomass is mostly fibrous among biomass, so pulverization is poor, combustion efficiency decreases, pulverizer operability decreases, 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 bark as a raw material, torrefaction under an oxygen concentration of 10% or less and a temperature of 170 to 350 ° C. The present inventors have found that a solid fuel having pulverizability equivalent to that of coal can be produced.

  The solid fuel obtained by the production method of the present invention has high substance yield and high calorie yield, and also has the same pulverization properties as coal, so it is mixed with coal and pulverized for use as fuel for pulverized coal boilers. Can do.

  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 bark is preferably ground to a size of 0.1 to 100 mm, more preferably 0.1 to 50 mm. 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.

  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 preferably 170 to 300 ° C, more preferably 200 to 260 ° C. Hemicellulose is prone to pyrolysis around 270 ° C, while cellulose is around 355 ° C and lignin is prone to pyrolysis around 365 ° C, so the baking temperature should be 170-300 ° 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 and a vertical furnace are 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]
Using a small kiln type carbonization furnace with 20 g of cedar bark crushed to 100 mm or less as a raw material, the product was obtained by performing nitrogen purging and baking at a processing temperature of 225 ° C. and a processing time of 30 minutes.

[Example 2]
A product was obtained in the same manner as in Example 1 except that the treatment temperature was 250 ° C.

[Example 3]
A product was obtained in the same manner as in Example 1 except that beech bark pulverized to 100 mm or less was used as a raw material.

[Example 4]
A product was obtained in the same manner as in Example 3 except that the treatment temperature was 250 ° C.

[Example 5]
A product was obtained in the same manner as in Example 1 except that cypress bark crushed to 100 mm or less was used as a raw material.

[Example 6]
A product was obtained in the same manner as in Example 5 except that the treatment temperature was 250 ° C.

[Comparative Example 1]
A product was obtained in the same manner as in Example 1 except that cedar chips were used as raw materials and the treatment temperature was 250 ° C.

[Comparative Example 2]
A product was obtained in the same manner as in Example 1 except that beech chips were used as raw materials and the treatment temperature was 250 ° C.

[Comparative Example 3]
A product was obtained in the same manner as in Example 1 except that cypress chips were used as raw materials and the treatment temperature was 250 ° C.

The following items were evaluated for the products obtained in Examples 1 to 6 and Comparative Examples 1 to 3, and the results are shown in Table 1.
Material yield: calculated from the weight of the sample before and after roasting.
-Calorie yield: The sample before and after roasting was calculated from the calorific value measured by the Shimadzu Institute of Advanced Automatic Cylinder Calorimeter CA-4PJ.
・ 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 products of Examples 1 to 6 manufactured by roasting using bark as a raw material have a high substance yield and a calorie yield, and a hard glove grindability index (HGI) of 30 to 70. It was within the range and the grindability was good. In particular, Examples 1 and 2 using cedar bark as a raw material were easily pulverized. On the other hand, the products of Comparative Examples 1 to 3 using chips as raw materials had an HGI of less than 30 and were inferior in grindability.

[Example 7]
Using bark of cedar crushed to 60 mm or less as a raw material, 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. The product material yield was 73.7% and the HGI was 60.5.

Claims (1)

Cedar bark having a size of 0.1 to 100 mm is roasted under conditions of an oxygen concentration of 10% or less and a temperature of 170 to 350 ° C. A method for producing a solid fuel having an index of 30 to 70.