JP7252388B2 - Biomass solid fuel and its production method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a solid fuel obtained by hydrothermally carbonizing biomass and a method for producing the same.

As one of the countermeasures against global warming, the use of biomass as a fuel derived from organisms as an energy source has been carried out. For example, biomass is used as a partial substitute fuel for coal in coal-fired power plants. In order to use biomass in coal-fired power plants, pulverization of biomass is necessary to improve combustion efficiency. Since the coal-fired power plant has a coal pulverizer for pulverizing coal, biomass is pulverized together with coal by the coal pulverizer, and the pulverized biomass and pulverized coal are combusted (co-combusted).

In addition, biomass generally has a high porosity and poor energy transportability, and has a high water content and a low thermal energy density. For this reason, biomass is used after being dried, pulverized and pelletized, or biomass is carbonized.

However, it is not easy to finely pulverize biomass with a coal pulverizer, and there is a problem that biomass is less pulverized than coal and cannot be sufficiently finely pulverized. Patent Literature 1 describes a solid fuel obtained by carbonizing the husks after extracting kernel oil from the seeds of coconut fruits by dry heating in a rotary kiln or the like.

WO2012/023479

However, the solid fuel described in Patent Literature 1 has a problem of causing an increase in cost due to its high carbonization temperature.

One aspect of the present invention relates to the following matter.

1. A biomass solid fuel having an air-dried base fuel ratio (fixed carbon/volatile matter) of 0.1 to 0.5.

2. Using the husk after extracting the kernel oil from the seed of the coconut fruit as a raw material,
A biomass solid fuel according to claim 1, characterized in that the proportion of K ₂ O in the anhydrous base ash is 0.50-3.00 wt%.

3. Using the husk after extracting the kernel oil from the seed of the coconut fruit as a raw material,
3. The biomass solid fuel according to 1 or 2 above, wherein the proportion of Na ₂ O in the anhydrous base ash is 0.79 wt % or less.

4. Using the husk after extracting the kernel oil from the seed of the coconut fruit as a raw material,
3. Any one of 1 to 3 above, characterized in that the fuel ratio is 0.26 to 0.50 on an air dry basis, the higher heating value on a dry basis is 5100 to 6000 kcal/kg, and the ball mill grindability index is 30 or more. A biomass solid fuel as described.

5. A step of hydrothermally carbonizing the shell after extracting the kernel oil from the seed of the coconut fruit at a temperature of 190 to 250 ° C. and a pressure of 1.0 to 4.0 MPa (G),
A method for producing a biomass solid fuel according to any one of 2 to 4 above.

6. Made from crushed bamboo,
A biomass solid fuel according to claim 1, characterized in that the proportion of K ₂ O in the anhydrous base ash is 3.00-21.50 wt%.

7. Using EFB as raw material,
2. Biomass solid fuel according to claim 1, characterized in that the proportion of K ₂ O in the anhydrous base ash is 0.10-40.00 wt%.

According to the present invention, it is possible to provide a biomass solid fuel with excellent pulverizability, high yield, and reduced production cost.

1 is a photograph showing a portion of a device for applying stress to observe fracture surfaces of palm kernel shells (PKS). It is a SEM photograph of a fracture surface of PKS. (a) shows raw PKS before hydrothermal carbonization, and (b) shows PKS after hydrothermal carbonization. 3 is an enlarged view of the SEM photograph of FIG. 2; FIG. (a) shows raw PKS before hydrothermal carbonization, and (b) shows PKS after hydrothermal carbonization. FIG. 2 shows the composition of biomass components of PKS before and after hydrothermal carbonization. 2 shows the relationship between the heating temperature of PKS and the pressure inside the container. 4 shows the relationship between the heating temperature of PKS and the pulverizability of solid fuel. Figure 2 shows the relationship between PKS heating temperature and solid fuel solids yield (dry basis) and volatiles (ashless dry basis). Figure 2 shows the relationship between PKS heating temperature and solid fuel energy yield (dry basis).

<Biomass solid fuel>
The biomass solid fuel (hereinafter also simply referred to as “solid fuel”) of the present embodiment preferably has an air-dried base fuel ratio (fixed carbon/volatile matter) of 0.1 to 0.5. When the air-dried base fuel ratio is 0.1 to 0.5, it is possible to obtain a solid fuel that is excellent in pulverizability and has a high calorie.

The raw material for the biomass solid fuel of the present embodiment is not particularly limited. EFB (Empty Fruit Bunches: Empty Fruit Bunches of Palm Oil Processing Residue) may be mentioned, of which PKS is preferred. PKS can be made into a solid fuel by performing hydrothermal carbonization in its original shape without crushing or pulverizing. Excellent for

The biomass solid fuel of the present embodiment is obtained through a hydrothermal carbonization process in which biomass as a raw material is heated in pressurized hot water and carbonized. In the hydrothermal carbonization treatment, it is preferable to put water and raw material biomass into a closed container and heat them to a predetermined temperature. Here, the weight ratio (liquid/solid ratio) represented by (water used for hydrothermal carbonization/raw material biomass) is not particularly limited, but is preferably 1 to 50, more preferably 1 to 5. . In this specification, hydrothermal carbonization is also referred to as "wet".

Conditions for hydrothermal carbonization are not particularly limited, but for example, the temperature is preferably 150° C. or higher, more preferably 190° C. or higher, and preferably 250° C. or lower, more preferably 230° C. or lower. The heating rate is not particularly limited, but is preferably 1 to 10° C./min, more preferably 1 to 5° C./min, from the ambient temperature to the desired heating temperature.

The pressure in hydrothermal carbonization is preferably 1.3 to 4.1 MPa (G), more preferably 1.3 to 3.7 MPa (G), still more preferably 2.9 to 3.7 MPa (G). . When hydrothermal carbonization is performed in a closed vessel, the pressure is determined by the heating temperature, but since decomposition gas of biomass is also generated by heating, the pressure inside the vessel is the combination of the saturated water vapor pressure of water at the heating temperature and the decomposition gas. It becomes the sum with vapor pressure. As an example, FIG. 5 shows the relationship between heating temperature and pressure when PKS is used as a raw material in Example A described later. As shown in FIG. 5, the generation of cracked gas tends to remarkably increase as the heating temperature increases.

The hydrothermal carbonization time is preferably 10 to 40 minutes, more preferably 20 to 40 minutes, still more preferably 30 to 40 minutes after reaching the desired heating temperature. Then cool and open.

The apparatus used for the hydrothermal carbonization treatment is not limited, but an autoclave, for example, is preferably used.

In the present embodiment, by hydrothermally carbonizing the raw material, the heat transfer efficiency is higher than in the case of dry carbonization, so that a solid fuel with excellent pulverizability can be obtained by heating at a low temperature. Therefore, manufacturing costs can be reduced. Furthermore, since the solid fuel of the present embodiment is produced at a lower heating temperature than dry carbonization, the energy loss due to carbonization can be suppressed, and the yield (solid yield and energy yield) is excellent (Fig. 7 and FIG. 8).

The raw material of biomass contains components such as potassium component, sodium component, and chlorine component that cause boiler corrosion problems, but the content of these components is small in the solid fuel of the present embodiment. This is presumed to be due to the elution of the above components into water during hydrothermal carbonization.

The properties of the biomass solid fuel and the production method thereof may be determined in suitable ranges depending on the type of biomass used as a raw material. Examples are described below, but the present invention is not limited to these. Industrial analysis values, elemental analysis values, and higher heating values in this specification are based on JIS M 8812, 8813, and 8814. Details of the method for measuring the ball milling index (BMI) are described in Examples below. The air-dried base refers to the solid weight measured by the air-dried sample preparation method described in Japanese Industrial Standard JIS M8811.

<Solid fuel A: Biomass solid fuel made from PKS>
As one aspect of the present invention, a biomass solid fuel (also referred to as “solid fuel A”) using PKS as a raw material will be described. PKS as a raw material preferably has a water content of 40% by mass or less, more preferably 15% by mass or less. Preferred aspects of the properties of the solid fuel A are as follows.

The solid fuel A preferably has a fuel ratio (fixed carbon/volatile matter) of 0.26 to 0.50 on an air-dried basis. When the fuel ratio is within the above range, it is possible to obtain a solid fuel excellent in pulverizability while suppressing a decrease in volatile matter. The air-dried base fixed carbon of solid fuel A is preferably 18 to 50 wt%, more preferably 20 to 35 wt%, still more preferably 24.1 to 28 wt%. The volatile content (air dry basis) is preferably 60-70% by weight, more preferably 60-68% by weight, still more preferably 60-64.9% by weight. The volatile matter contained in the solid fuel is, for example, monocyclic aromatics.

The percentage of ash on a dry basis in Solid Fuel A is preferably 5.0 wt% or less, more preferably 4.0 wt% or less. Although the lower limit is not particularly limited, it is preferably 1.9% by weight or more, more preferably 2.2% by weight or more. The proportion of the air-dried base ash in the solid fuel A is preferably 4.5% by weight or less, more preferably 3.5% by weight or less. Although the lower limit is not particularly limited, it is preferably 1.8% by weight or more, more preferably 2.0% by weight or more.

The solid fuel A preferably has a K ₂ O ratio in the anhydrous base ash of 0.50 to 3.00 wt%, more preferably 0.50 to 2.00 wt%, and further 0.50 to 1.50 wt%. Preferably, 0.50 to 1.00 wt% is even more preferred. If the potassium content in the solid fuel is too high, problems such as corrosion of the boiler may occur when using the solid fuel as fuel. The raw material PKS contains a potassium component, and in this embodiment, it is presumed that the potassium component is eluted into the water during the hydrothermal carbonization treatment, and the potassium component contained in the solid fuel can be reduced.

In the solid fuel A, the ratio of Na ₂ O in the anhydrous base ash is preferably 0.79 wt% or less, more preferably 0.75 wt% or less, even more preferably 0.70 wt% or less. It may be 0 wt%. If the sodium content in the solid fuel is too high, problems such as corrosion of the boiler may occur when the solid fuel is used as fuel. The raw material PKS contains a sodium component, and in this embodiment, it is presumed that the sodium component dissolves in water during the hydrothermal carbonization treatment, and the sodium component contained in the solid fuel can be reduced.

The dry base higher heating value is preferably 5100 to 6000 kcal/kg, more preferably 5510 to 6000 kcal/kg.

The ball mill grindability index (BMI ₂₀ ) is preferably 30 or more, more preferably 80 or more. BMI ₂₀ can be measured by the method described in Examples below.

The solid fuel A has a particle size approximately equal to that of raw PKS, and pulverization during handling is suppressed. Therefore, when the solid fuel after hydrothermal carbonization is transported, there is no contamination of the surrounding area due to dust generation. The average particle size of raw PKS is usually about 5 mm, and the average particle size of solid fuel A is also about 5 mm. Here, the average particle size referred to in the present invention means a median size, and is determined by the particle size test method described in JIS M8801.

In the method for producing solid fuel A, the conditions for hydrothermally carbonizing PKS as a raw material are not particularly limited, but the heating temperature is preferably 190 to 250 ° C., more preferably 190 to 230 ° C., and the pressure is It is preferably 1.0 to 4.0 MPa (G), more preferably 1.3 to 3.7 MPa (G), still more preferably 2.9 to 3.7 MPa (G).

<Solid fuel B: biomass solid fuel made from bamboo>
As one aspect of the present invention, a biomass solid fuel (also referred to as “solid fuel B”) made from bamboo will be described. The bamboo is preferably crushed bamboo.

The solid fuel B preferably has a fuel ratio (fixed carbon/volatile matter) of 0.10 to 0.50 on an air-dried basis.

The percentage of ash on a dry basis in the solid fuel B is preferably 1.3 wt% or less, more preferably 1.0 wt% or less. Although the lower limit is not particularly limited, it is preferably 0.6% by weight or more. The proportion of the air-dried base ash in the solid fuel B is preferably 1.2% by weight or less, more preferably 1.0% by weight or less. Although the lower limit is not particularly limited, it is preferably 0.5% by weight or more.

The proportion of chlorine in the solid fuel B is preferably 0.15 wt% or less, more preferably 0.10 wt% or less, still more preferably 0.07 wt% or less, and may be 0 wt%. The raw bamboo, which is the raw material of the solid fuel B, contains a chlorine component, and if the chlorine component is too much, problems such as boiler corrosion occur. few. It is presumed that this is because the chlorine component is eluted into the water during the hydrothermal carbonization treatment.

The solid fuel B preferably has a K ₂ O ratio in the anhydrous base ash of 3.00 to 21.50 wt%, more preferably 3 to 20 wt%, and more preferably 4 to 19 wt%. More preferably, 5 to 18 wt% is even more preferable. If the potassium content in the solid fuel is too high, problems such as corrosion of the boiler may occur when using the solid fuel as fuel. Although the raw material bamboo contains a potassium component, it is presumed that in the present embodiment, the potassium component is eluted into the water during the hydrothermal carbonization treatment, and the potassium component contained in the solid fuel can be reduced.

The dry base higher heating value is preferably 5000 to 6000 kcal/kg.

The ball mill grindability index (BMI ₂₀ ) is preferably 30 or more, more preferably 60 or more. BMI ₂₀ can be measured by the method described in Examples below.

In the method for producing solid fuel B, the conditions for hydrothermally carbonizing raw bamboo as a raw material are not particularly limited, but the temperature is preferably 190° C. to 220° C., more preferably 190° C. to 210° C., The pressure is preferably 0.9-2.4 MPa (G).

<Solid fuel C: Biomass solid fuel made from EFB>
As one aspect of the present invention, a biomass solid fuel (also referred to as “solid fuel C”) using EFB as a raw material will be described. Properties of the solid fuel C are as follows.

The solid fuel C preferably has a fuel ratio (fixed carbon/volatile matter) of 0.1 to 0.5 on an air-dried basis.

The percentage of dry-based ash in the solid fuel C is preferably 2.3% by weight or less, more preferably 1.9% by weight or less, even more preferably 1.7% by weight or less. Although the lower limit is not particularly limited, it is preferably 0.6% by weight or more. The proportion of the air-dried base ash in the solid fuel C is preferably 2% by weight or less, more preferably 1.8% by weight or less, and even more preferably 1.5% by weight or less. Although the lower limit is not particularly limited, it is preferably 0.5% by weight or more.

The raw EFB, which is the raw material of the solid fuel C, contains a chlorine component, and if the chlorine component is too much, problems such as boiler corrosion will occur. few. It is presumed that this is because the chlorine component is eluted into the water during the hydrothermal carbonization treatment. The proportion of chlorine in the solid fuel C is preferably 0.2 wt% or less, more preferably 0.01 wt% or less, still more preferably 0.008 wt% or less, and may be 0 wt%.

The solid fuel C preferably has a K ₂ O ratio of 0.10 to 40.00 wt%, more preferably 1.0 to 25 wt%, and 1.0 to 20 wt% in the anhydrous base ash. and even more preferably 1.0 to 18 wt%. If the potassium content in the solid fuel is too high, problems such as corrosion of the boiler may occur when using the solid fuel as fuel. The raw material EFB contains a potassium component, and in this embodiment, it is presumed that the potassium component is eluted into the water during the hydrothermal carbonization treatment, and the potassium component contained in the solid fuel can be reduced.

In solid fuel C, the proportion of Na ₂ O in the anhydrous base ash is preferably 1.0 wt% or less, more preferably 0.70 wt% or less, and even more preferably 0.5 wt% or less. , 0 wt %. If the sodium content in the solid fuel is too high, problems such as corrosion of the boiler may occur when the solid fuel is used as fuel. The raw material EFB contains a sodium component, and in this embodiment, it is presumed that the sodium component dissolves in water during the hydrothermal carbonization treatment, and the sodium component contained in the solid fuel can be reduced.

The dry base higher heating value is preferably 4510 to 6500 kcal/kg, more preferably 4590 to 6500 kcal/kg.

A ball mill grindability index (BMI ₃ ) of 15 or more is preferred. BMI ₃ can be measured by the method described in Examples below.

In the method for producing solid fuel C, the conditions for hydrothermally carbonizing raw EFB as a raw material are not particularly limited, but the temperature is preferably 150 ° C. to 250 ° C., more preferably 200 ° C. to 250 ° C., and the pressure is preferably 0.3 to 4.2 MPa (G), more preferably 0.4 to 4.1 MPa (G).

The solid fuel of the present invention is used as an energy source for heat utilization equipment by being supplied to the heat utilization equipment and combusted. In particular, the solid fuel of the present invention is preferably supplied to a heat utilization facility and burned as a partial substitute fuel for coal.

The heat utilization equipment in which the solid fuel of the present invention is used is not limited, and existing heat utilization equipment can be used. Examples include calcining furnaces for manufacturing equipment, coke ovens for steelmaking equipment, and blast furnaces. Among these, pulverized coal-fired boilers, rotary kilns for cement clinker manufacturing equipment, and calcining furnaces are preferred.

In order to improve combustion efficiency, the solid fuel of the present invention may be pulverized and then supplied to the heat utilization equipment. The degree of pulverization depends on the heat utilization equipment to which the solid fuel is supplied, but it is usually preferable to pulverize it so that the average particle size is 1,000 μm or less, and it is pulverized so that the average particle size is 750 μm or less. is more preferred.

The solid fuel of the present invention has excellent pulverizability and can be easily pulverized with a vertical roller mill, tube mill, hammer mill, fan type mill, etc., and is used for coal pulverization provided in coal-fired power generation equipment. It can also be easily pulverized with coal in a machine. In addition, solid fuel can be supplied to the heat utilization facility together with coal and combusted.

EXAMPLES The present invention will be specifically described below using Examples, but the present invention is not limited to these.

The methods for measuring the properties of solid fuels in Examples and Comparative Examples are as follows.

<Solid Yield, Energy Yield>
Solid yield and energy yield were calculated by the following equations.

Solids yield (dry basis) (wt%) = 100 x weight of solids after hydrothermal carbonization (dry basis) / weight of solids before hydrothermal carbonization (dry basis)
Energy yield (anhydrous basis) (cal%) = solid higher heating value after hydrothermal carbonization (anhydrous basis) x solid yield (anhydrous basis) (% by weight) / solid higher heating value before hydrothermal carbonization ( anhydrous basis)

<XRF analysis of ash>
Using a fluorescent X-ray analyzer (EDX-720 manufactured by Shimadzu Corporation), the weight ratio of the compounds shown in Tables 2 and 4 contained in the anhydrous base ash was measured.

<Ball mill grindability (BMI ₂₀ )>
The pulverization time of each biomass solid fuel was set to 20 minutes, and the weight ratio under a 150 μm sieve after 20 minutes was used as the pulverization point. The ball mill conforms to JIS M4002, and normal grade ball bearings (Φ36.5 mm x 43, Φ30.2 mm x 67, Φ30.2 mm x 67, Φ24.4 mm×10 pieces, Φ19.1 mm×71 pieces, Φ15.9 mm×94 pieces) were inserted and measured by rotating at a speed of 70 rpm. A higher value indicates that the pulverizability is improved. It was confirmed that the hydrothermal carbonization treatment increased the pulverization point.

<Ball mill grindability (BMI ₃ )>
Measurement was performed in the same manner as for BMI ₂₀ except that the biomass solid fuel was pulverized for 3 minutes, and the weight ratio under a 150 μm sieve was taken as the pulverization point.

<Example A: PKS>
(Example A1: Wet type)
PKS was dried in the sun to have a water content of 12% by mass, a particle size of 1 to 16 mm, and an average particle size of 5 mm. 280 g of this dried PKS and 840 g of water (solid-liquid ratio 3) were put into a 1.95 L autoclave and heated from atmospheric temperature to 190° C. at a temperature rising rate of 3.6° C./min. After reaching a heating temperature of 190° C. and a pressure of 1.3 MPa (G), hydrothermal carbonization was performed by maintaining the temperature for 30 minutes, followed by cooling to room temperature to obtain a solid fuel. Tables 1 and 2 show the properties of the obtained solid fuel.

(Examples A2 to A5: wet)
A solid fuel was produced in the same manner as in Example A1, except that the hydrothermal carbonization conditions were changed as shown in Table 1. Tables 1 and 2 show the properties of the obtained solid fuel.

(Comparative Example A1)
Tables 1 and 2 show the properties of the solid fuel composed of raw PKS before hydrothermal carbonization.

(Comparative example A2: dry)
As a raw material, the same dried PKS as in Example A1 was used. 4 kg of this PKS is put into a sample case with an inner diameter of 600 mm and a length of 500 mm, and the entire sample case is mounted in an externally heated rotary kiln. Heated at 2°C/min. The heating temperature used as a reference was the temperature of the gas phase atmosphere at the central portion of the axial center of the sample case. In the rotary kiln, the temperature of the gas phase atmosphere and the temperature of the heat-treated solid are the same. After the heating temperature reached 290°C, the temperature was maintained at 290°C for 1 minute, then quickly cooled to 160°C, after which the sample case was taken out from the rotary kiln, the sample was taken out into the atmosphere, and cooled to room temperature.

(Comparative Examples A3 to A7: dry)
A solid fuel was produced in the same manner as in Comparative Example A2, except that the heating temperature was changed to the temperature shown in Table 1. Tables 1 and 2 show the properties of the obtained solid fuel.

(heating temperature and pressure)
FIG. 5 shows the relationship between PKS heating temperature and pressure. The higher the heating temperature, the greater the generation of cracked gas. The cracked gas was mainly composed of CO ₂ and contained small amounts of water gas (H ₂ , CO).

(Comparison of wet and dry)
Solid fuel obtained by wet treatment (hydrothermal carbonization treatment) of the raw material PKS as in Examples A1 to A5 and dry treatment (heat treatment in the gas phase) as in Comparative Examples A2 to A7. 6 to 8 show the results of comparing the crushability and the like of the solid fuels obtained by

FIG. 6 shows the relationship between PKS heating temperature and pulverizability. As an index of grindability, the above-mentioned BMI ₂₀ (weight ratio under a 150 μm sieve) was used. Taking BMI ₂₀ =94% as the threshold grind point, the threshold was reached at about 220° C. for the wet process and at about 310° C. for the dry process. In other words, the wet method exhibited the same pulverizability at a temperature about 90° C. lower than the dry method. Therefore, if the solid fuel is produced by hydrothermal carbonization, the heating temperature can be set low, and the production cost can be reduced.

FIG. 7 shows the relationship between PKS heating temperature and solids yield (dry basis) and volatiles (ashless dry basis). The solid yields of the solid fuels obtained by the wet process (heating temperature of 220°C) and the dry process (heating temperature of 310°C) when the grindability point BMI ₂₀ = 94% were 70% and 53%, respectively. higher solids yield. The solids yield depends on the amount of volatile matter that is thermally decomposed, and the wet method produces a solid fuel with excellent pulverizability at a lower temperature than the dry method, so the amount of volatile matter that is thermally decomposed is also suppressed. It was inferred that the solid yield also increased with increasing

FIG. 8 shows the relationship between PKS heating temperature and energy yield (dry basis). The wet-derived solid fuel maintained an energy yield of approximately 80%, while the energy yield of the dry-derived solid fuel decreased to 70% upon heating. This is considered to be because the energy yield is affected by the solid yield, and it was shown that the wet process can suppress energy loss.

<Example B: Bamboo>
(Examples B1 to B4)
A solid fuel was produced in the same manner as in Example A1 except that bamboo was used as the raw material instead of PKS and the hydrothermal carbonization treatment was performed under the conditions shown in Table 3. Tables 3 and 4 show the properties of the obtained solid fuel.

(Comparative Example B1)
Tables 3 and 4 show the properties of the solid fuel made of raw bamboo before hydrothermal carbonization.

<Example C: EFB>
(Examples C1 to C3)
A solid fuel was produced in the same manner as in Example A1 except that EFB was used instead of PKS as a raw material and the hydrothermal carbonization treatment was performed under the conditions shown in Table 3. Tables 3 and 4 show the properties of the obtained solid fuel.

(Comparative Example C1)
Tables 3 and 4 show the properties of the raw EFB solid fuel before hydrothermal carbonization in Example C1.

In the table below, AD indicates air-dried base, dry indicates anhydrous base, and Daf indicates anhydrous ashless base.

As described above, the biomass solid fuel after hydrothermal carbonization has improved pulverizability (improved BMI value) compared to raw raw materials. In order to elucidate this mechanism, the present inventors compared a solid fuel obtained by hydrothermally carbonizing PKS (solid fuel of Example A4) and raw PKS as a raw material (solid fuel of Comparative Example A1). A detailed analysis was carried out.

(Observation of surface condition of fracture surface)
In order to observe the surface condition of the fracture surface of PKS before and after hydrothermal carbonization, a jig was attached to the Kiya type hardness tester, and stress (tensile/shear) perpendicular to the fiber direction of PKS was applied (see Fig. 1). , the fracture surface perpendicular to the fiber direction was obtained. The load required for rupture (load speed: 10 mm/min) was 517 N for raw PKS before hydrothermal carbonization (Comparative Example A1), but 54 N for PKS after hydrothermal carbonization (Example A4). , had decreased to about 1/10.

Before and after the hydrothermal carbonization treatment, the fracture surface of each PKS was observed with an electron microscope (SEM). SEM photographs of the fracture surface are shown in FIG. 2 (magnified view of 200 times) and FIG. 3 (magnified view of 1000 times). FIGS. 2(a) and 3(a) are photographs of raw PKS (Comparative Example A1) before hydrothermal carbonization, and FIGS. 2(b) and 3(b) are photographs after hydrothermal carbonization. is a photograph of PKS (Example A4). In the SEM photograph of the fracture surface, the raw PKS (Comparative Example A1) was uneven, while the hydrothermally carbonized PKS (Example A4) was smooth (Fig. 3). In the raw PKS (Comparative Example A1), since the fibers are loosely bound by the binder component in the raw material, it is thought that the fibers were pulled out under load and the stress was dispersed, resulting in uneven fracture surfaces. On the other hand, in the hydrothermally carbonized PKS (Example A4), the binder component was solubilized, so that the fibers were strongly bonded, and stress was concentrated during loading, so that the fracture surface became straight.

Moreover, the unevenness in the SEM photograph is considered to be the cell wall because of its size (FIGS. 2 and 3). In general, those that are difficult to break tend to have uneven fracture surfaces, and those that are easy to break tend to have linear (smooth) fracture surfaces. That is, since the raw PKS (Comparative Example A1) has a high cell wall strength, it is difficult for the fracture to penetrate the wall, and the fracture occurs along the cell wall surface, whereas the hydrothermally carbonized PKS (Example A4 ), it is considered that the rupture through the wall occurred due to the decrease in the strength of the cell wall. The same is presumed for the other Examples A1 to A3.

(Analysis of biomass component composition)
Before and after the hydrothermal carbonization treatment, the biomass component composition of each PKS was analyzed by the method shown in Table 5. Results are shown in Table 5 and FIG. In addition, in Table 5, all "%" represent "% by weight".

In the analysis of the biomass component composition, the hemicellulose was 23.4 wt% in the raw PKS (Comparative Example A1), but decreased to 8.9 wt% in the hydrothermally carbonized PKS (Example A4). At this time, the decomposition rate of hemicellulose considering the solid yield was 73 wt%. Here, the decomposition rate of hemicellulose is expressed by the following formula:
Decomposition rate (%) = 100 - [hemicellulose composition of hydrothermally treated PKS (%) x yield (%)] ÷ [(hemicellulose composition of raw PKS (%) x 100 (%)] x 100
Calculated by The decomposition rates of other components were also calculated in the same manner.

From the above results, the pulverizability of the hydrothermally carbonized PKS including Example A4 is due to the decomposition of hemicellulose, which plays an important role in maintaining the strength of the biomass skeleton such as the cell wall during the hydrothermal carbonization. It was suggested that the

Claims (3)

Made from crushed bamboo,
The air-dried base fuel ratio (fixed carbon/volatile matter) is 0.1 to 0.5,
A method for producing a biomass solid fuel, wherein the proportion of K O in the anhydrous base ash is 3.00-21.50 wt%, comprising _:
A method for producing a biomass solid fuel, comprising a step of hydrothermally carbonizing crushed bamboo at a temperature of 190-220° C. and a pressure of 0.9-2.4 MPa (G). 2. The method for producing a biomass solid fuel according to claim 1, wherein the ratio of chlorine in said biomass solid fuel is 0.15 wt % or less. 3. The method for producing a biomass solid fuel according to claim 1 , wherein said biomass solid fuel has a dry base higher calorific value of 5000 to 6000 kcal/kg and a ball mill grindability index (BMI ₂₀ ) of 30 or more.

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