Method for controlling and inhibiting silica crystallization, and combustion device

Abstract

To provide a control method for crystallization of silica, enabling crystallization of silica during a combustion processing to be controlled by a simple method, and a combustion apparatus, and to provide a suppression method for crystallization of silica, enabling crystallization of silica during a combustion processing to be suppressed by a simple method.SOLUTION: According to one embodiment of the present invention, there is provided a control method for controlling crystallization of silica in a combustion processing of a biomass fuel including amorphous silica. The control method comprises: a step of determining an amorphous region where the silica is in an amorphous state and a crystalline region where the silica is in a crystalline state, based on a combustion temperature between 600°C to 1150°C and a holding time of the combustion temperature; and a step of controlling the combustion temperature of the biomass fuel, total elapsed time from the start of combustion of the biomass fuel, and a temperature drop rate of ash generated by combustion of the biomass fuel, based on the amorphous region and the crystalline region.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a method for controlling and inhibiting silica crystallization, and a combustion device. [Background technology]

[0002] Biomass fuels such as rice husks are difficult to decompose and tend to become industrial waste, but by burning biomass fuels, it is possible to extract both energy and silica as an industrial raw material.

[0003] Pure silica does not crystallize unless it is at a temperature much higher than the combustion temperature of a normal boiler (cristobalite: 867℃~1470℃, tridymite: 1470℃~1727℃), but biomass fuel contains inorganic elements such as K and Na in addition to silica, and due to the eutectic point effect of these elements, the silica in rice husks crystallizes even at a relatively low temperature of 600℃~900℃. Therefore, when biomass fuel is burned, energy can be obtained, but there is a risk that the silica contained in the biomass fuel will crystallize during the combustion process. Specifically, the silica (SiO2·nH2O) contained in biomass fuel is amorphous, but when burned, it produces crystalline silica such as cristobalite and quartz. This crystalline silica is recognized as a substance that is as harmful to the human body as asbestos.

[0004] For this reason, in order to suppress the eutectic point effect, a technique has been disclosed in which inorganic elements other than silica in rice husks are washed with an acid aqueous solution to shift the crystallization temperature to a higher temperature (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6618131 Summary of the Invention [Problem to be solved by the invention]

[0006] However, this technique requires the addition of chemicals such as an acid solution, energy for drying, and equipment for the drying, making it difficult to implement. Therefore, no simple technique for controlling or suppressing the crystallization of silica during combustion treatment has yet been developed.

[0007] The present invention has been made to solve the above problems. That is, the object of the present invention is to provide a method for controlling silica crystallization, which can control the crystallization of silica during combustion treatment in a simple manner, and a combustion device. Another object of the present invention is to provide a method for suppressing silica crystallization, which can suppress the crystallization of silica during combustion treatment in a simple manner. [Means for solving the problem]

[0008] [1] A method for controlling the crystallization of amorphous silica during the combustion process of a biomass fuel containing the silica, comprising the steps of: determining an amorphous region in which the silica is in an amorphous state and a crystalline region in which the silica is in a crystalline state based on a combustion temperature of 600°C or higher and 1150°C or lower and a holding time at the combustion temperature; and controlling the combustion temperature of the biomass fuel, the total elapsed time from the start of combustion of the biomass fuel, and the cooling rate of ash generated by the combustion of the biomass fuel based on the amorphous region and the crystalline region.

[0009] [2] The determination of the amorphous region and the crystalline region includes the following steps: Step 1: Burn the biomass fuel at an arbitrary first temperature within a combustion temperature range of 600° C. to 1150° C., and hold the ash generated by the combustion of the biomass fuel at the first temperature for t1 minutes, and then check whether the silica contained in the ash is in an amorphous state; Step 2: If it is confirmed that the silica is in an amorphous state as a result of Step 1, burn the biomass fuel again at the first temperature, and hold the ash generated by the combustion of the biomass fuel at the first temperature for t2 minutes longer than the previous holding time, and then check again to see if the silica is in a crystalline state. C1Repeat this step until you find the retention time T C1 And, T C1 -t2, and the retention time T during which the silica is in an amorphous state. A1 (min), and if it is confirmed that the silica is in a crystalline state as a result of step 1, the biomass fuel is combusted again at the first temperature, and the confirmation is performed again after the holding time of the ash generated by the combustion of the biomass fuel at the first temperature is reduced by t3 minutes from the previous holding time, and the holding time T A1 Repeat this step until you find the retention time T A1 And, T A1 +t3, and the retention time T during which the silica is in a crystalline state. C1 Step 3: Burn the biomass fuel at a second temperature that is lower than the first temperature and is within a combustion temperature range of 600°C to 1150°C, and hold the ash generated by the combustion of the biomass fuel at the second temperature for t4 minutes, and then check whether the silica contained in the ash is in an amorphous state. Step 4: If it is confirmed that the silica is in an amorphous state as a result of step 3, burn the biomass fuel again at the second temperature, and hold the ash generated by the combustion of the biomass fuel at the second temperature for t5 minutes longer than the previous holding time, and then check again to see if the silica is in a crystalline state. C2 Repeat this step until you find the retention time T C2 And, T C2 -t5, and the silica is in an amorphous state. A2 (min), and if it is confirmed that the silica is in a crystalline state as a result of step 3, the biomass fuel is combusted again at the second temperature, and the confirmation is performed again after reducing the holding time of the ash generated by the combustion of the biomass fuel at the second temperature by t6 minutes from the previous holding time, and the holding time T A2 Repeat this step until you find the retention time T A2 And, T A2 +t6, and the silica is in a crystalline state.C2 Step 5: In a graph with temperature (℃) on the horizontal axis and holding time (min) on the vertical axis, find T A1 , T C1 , T A2 , T C2 Plot and calculate T A1 and T A2 Connect with a straight line and T C1 and T C2 Step 6: In a graph with temperature (℃) on the horizontal axis and holding time (min) on the vertical axis, A1 and T A2 Based on the approximate function T A and at least the retention time T C1 and T C2 Based on the approximate function T C and calculate the approximation function T A The region below the approximation function T C The control method according to [1] above, wherein the upper region of the

[0010] [3] Between the steps 5 and 6, the following steps are included: Step A:T A1 and T A2 The line connecting the two and T C1 and T C2 Based on the straight line connecting the above, a predicted retention time T' is extrapolated to an arbitrary third temperature higher than the first temperature or lower than the second temperature within the combustion temperature range of 600°C to 1150°C. A3 (min), T´ C3 (min), and step B: burning the biomass fuel at the third temperature, and calculating the retention time of the ash generated by the combustion of the biomass fuel at the third temperature, respectively, as the predicted retention time T' A3 , T´ C3 In the state where the silica contained in the ash generated by the combustion of the biomass fuel is in an amorphous state, it is confirmed whether or not it is in an amorphous state. A3 If silica is confirmed to be in an amorphous state at T´ A3 is the retention time T during which silica is in an amorphous state. A3(min), and if it is confirmed that the silica is in a crystalline state, the biomass fuel is combusted again at the third temperature, and the confirmation is repeated with the retention time of the ash generated by the combustion of the biomass fuel at the third temperature reduced by t minutes from the previous retention time, and the retention time T A3 Finding T' C3 If silica is confirmed to exist in a crystalline state at T´ C3 Hold time T C3 (min), and if it is confirmed that the silica is in an amorphous state, the biomass fuel is combusted again at the third temperature, and the holding time of the ash generated by the combustion of the biomass fuel at the third temperature is increased by t8 minutes from the previous holding time, and the confirmation is repeated. The holding time T C3 In step 6, in a graph with the horizontal axis being temperature (°C) and the vertical axis being holding time (min), A1 , T A2 , and T A3 Based on the approximate function T A and at least the retention time T C1 , T C2 , and T C3 Based on the approximate function T C and calculate the approximation function T A The region below the approximation function T C The control method according to [2] above, further comprising the step of making the upper region of said crystal region.

[0011] [4] The control method according to [2] above, wherein the first temperature and the second temperature are each within a temperature range of 750°C or more and 950°C or less.

[0012] [5] The control method according to [4] above, wherein the temperature difference between the first temperature and the second temperature is 50°C or more.

[0013] [6] The control method according to [3] above, wherein the first temperature, the second temperature, and the third temperature are each within a temperature range of 750°C or more and 950°C or less.

[0014] [7] The control method described in [6] above, wherein the temperature difference between the first temperature and the second temperature is 50°C or more, and when the third temperature is higher than the first temperature, the temperature difference between the first temperature and the third temperature is 50°C or more, and when the third temperature is lower than the second temperature, the temperature difference between the second temperature and the third temperature is 50°C or more.

[0015] [8] The control method described in any one of [1] to [7] above, wherein the biomass fuel is grain husk.

[0016] [9] A method for suppressing crystallization of amorphous silica during the combustion treatment of a biomass fuel containing amorphous silica, comprising the steps of: determining an amorphous region in which the silica is in an amorphous state and a crystalline region in which the silica is in a crystalline state based on a combustion temperature of 600°C or higher and 1150°C or lower and a holding time at the combustion temperature; and controlling the combustion temperature of the biomass fuel, the total elapsed time from the start of combustion of the biomass fuel, and the cooling rate of ash generated by the combustion of the biomass fuel based on the amorphous region and the crystalline region so that the silica does not fall outside the amorphous region.

[0017]

[10] The inhibition method described in [9] above, wherein the biomass fuel is grain husk.

[0018]

[11] A combustion device comprising: a combustor that burns a biomass fuel containing amorphous silica; a cooler that cools ash produced by the combustion of the biomass fuel; and a control unit that controls the combustion temperature of the biomass fuel, the total elapsed time from the start of combustion of the biomass fuel, and the rate of cooling of the ash produced by the combustion of the biomass fuel, based on an amorphous region in which the silica is in an amorphous state and a crystalline region in which the silica is in a crystalline state, which are determined in advance based on a combustion range of 600°C to 1150°C and a holding time at the combustion temperature.

[0019]

[12] The amorphous region and the crystalline region are determined by the following steps: Step 1: Burn the biomass fuel at an arbitrary first temperature within a combustion temperature range of 600°C to 1150°C, and hold the ash generated by the combustion of the biomass fuel at the first temperature for t1 minutes, and then check whether the silica contained in the ash is in an amorphous state; Step 2: If it is confirmed that the silica is in an amorphous state as a result of Step 1, burn the biomass fuel again at the first temperature, and hold the ash generated by the combustion of the biomass fuel at the first temperature for t2 minutes longer than the previous holding time, and check again to see if the silica is in a crystalline state. C1 Repeat this step until you find the retention time T C1 And, T C1 -t2, and the retention time T during which the silica is in an amorphous state. A1 (min), and if it is confirmed that the silica is in a crystalline state as a result of step 1, the biomass fuel is combusted again at the first temperature, and the confirmation is performed again after the holding time of the ash generated by the combustion of the biomass fuel at the first temperature is reduced by t3 minutes from the previous holding time, and the holding time T A1 Repeat this step until you find the retention time T A1 And, T A1 +t3, and the retention time T during which the silica is in a crystalline state. C1 Step 3: Burn the biomass fuel at a second temperature that is lower than the first temperature and is within a combustion temperature range of 600°C to 1150°C, and hold the ash generated by the combustion of the biomass fuel at the second temperature for t4 minutes, and then check whether the silica contained in the ash is in an amorphous state. Step 4: If it is confirmed that the silica is in an amorphous state as a result of step 3, burn the biomass fuel again at the second temperature, and hold the ash generated by the combustion of the biomass fuel at the second temperature for t5 minutes longer than the previous holding time, and then check again to see if the silica is in a crystalline state. C2 Repeat this step until you find the retention time TC2 And, T C2 -t5, and the silica is in an amorphous state. A2 (min), and if it is confirmed that the silica is in a crystalline state as a result of step 3, the biomass fuel is combusted again at the second temperature, and the confirmation is performed again after reducing the holding time of the ash generated by the combustion of the biomass fuel at the second temperature by t6 minutes from the previous holding time, and the holding time T A2 Repeat this step until you find the retention time T A2 And, T A2 +t6, and the silica is in a crystalline state. C2 Step 5: In a graph with temperature (℃) on the horizontal axis and holding time (min) on the vertical axis, find T A1 , T C1 , T A2 , T C2 Plot and calculate T A1 and T A2 Connect with a straight line and T C1 and T C2 Step 6: In a graph with temperature (℃) on the horizontal axis and holding time (min) on the vertical axis, A1 and T A2 Based on the approximate function T A and at least the retention time T C1 and T C2 Based on the approximate function T C and calculate the approximation function T A The region below the approximation function T C The combustion device according to

[11] above, wherein the upper region of the crystal region is the crystal region.

[0020]

[13] Between the step 5 and the step 6, the following steps are included: Step A:T A1 and T A2 The line connecting the two and T C1 and T C2Based on the straight line connecting the above, a predicted retention time T' is extrapolated to an arbitrary third temperature higher than the first temperature or lower than the second temperature within the combustion temperature range of 600°C to 1150°C. A3 (min), T´ C3 (min), and step B: burning the biomass fuel at the third temperature, and calculating the retention time of the ash generated by the combustion of the biomass fuel at the third temperature, respectively, as the predicted retention time T' A3 , T´ C3 In the state where the silica contained in the ash generated by the combustion of the biomass fuel is in an amorphous state, it is confirmed whether or not it is in an amorphous state. A3 If silica is confirmed to be in an amorphous state at T´ A3 is the retention time T during which silica is in an amorphous state. A3 (min), and if it is confirmed that the silica is in a crystalline state, the biomass fuel is combusted again at the third temperature, and the confirmation is repeated with the retention time of the ash generated by the combustion of the biomass fuel at the third temperature reduced by t minutes from the previous retention time, and the retention time T A3 Finding T' C3 If silica is confirmed to exist in a crystalline state at T´ C3 Hold time T C3 (min), and if it is confirmed that the silica is in an amorphous state, the biomass fuel is combusted again at the third temperature, and the holding time of the ash generated by the combustion of the biomass fuel at the third temperature is increased by t8 minutes from the previous holding time, and the confirmation is repeated. The holding time T C3 In step 6, in a graph with the horizontal axis being temperature (°C) and the vertical axis being holding time (min), A1 , T A2 , and T A3 Based on the approximate function T A and at least the retention time T C1 , T C2 , and T C3 Based on the approximate function T C and calculate the approximation function TA The region below the approximation function T C The combustion apparatus according to

[12] above, wherein the step of forming the upper region of the crystal region is performed.

[0021]

[14] The combustion device according to

[12] above, wherein the first temperature and the second temperature are each within a temperature range of 750°C or more and 950°C or less.

[0022]

[15] The combustion device according to

[14] above, wherein the temperature difference between the first temperature and the second temperature is 50°C or more.

[0023]

[16] The combustion apparatus according to

[13] above, wherein the first temperature, the second temperature, and the third temperature are each within a temperature range of 750°C or more and 950°C or less.

[0024]

[17] The combustion device described in

[16] above, wherein a temperature difference between the first temperature and the second temperature is 50°C or more, and when the third temperature is higher than the first temperature, a temperature difference between the first temperature and the third temperature is 50°C or more, and when the third temperature is lower than the second temperature, a temperature difference between the second temperature and the third temperature is 50°C or more.

[0025]

[18] The combustion apparatus according to any one of

[11] to

[17] above, wherein the biomass fuel is grain husk. Effect of the Invention

[0026] According to the method for controlling silica crystallization and the combustion device of the present invention, it is possible to control the crystallization of silica during combustion treatment. Also, according to the method for inhibiting silica crystallization, it is possible to inhibit the crystallization of silica during combustion treatment. [Brief description of the drawings]

[0027] [Figure 1] FIG. 1 is a phase diagram showing the relationship between the combustion temperature and the retention time of biomass fuel. [Diagram 2]FIG. 2 is a block diagram illustrating the steps in determining amorphous and crystalline regions. [Diagram 3] FIG. 3 is a schematic configuration diagram of the combustion device according to the embodiment. [Figure 4] FIG. 4 is a phase diagram showing the relationship between the combustion temperature of rice husks, the total elapsed time, and the temperature decreasing rate in Examples 1 to 10. [Diagram 5] FIG. 5 shows the X-ray diffraction patterns of the silica of Examples 3 and 8. [Figure 6] FIG. 6 is a scanning electron microscope photograph of the silica according to Examples 3 to 6 and 8 to 10. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] Hereinafter, the method for controlling and suppressing the crystallization of silica and the combustion device according to the embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a phase diagram showing the relationship between the combustion temperature and the retention time of biomass fuel, Fig. 2 is a block diagram showing the steps for determining the amorphous region and the crystalline region, and Fig. 3 is a schematic diagram of the combustion device according to the embodiment.

[0029] <<Method of controlling and inhibiting silica crystallization>> A biomass fuel containing amorphous silica is prepared. The biomass fuel is not particularly limited as long as it contains amorphous silica, and examples thereof include cereal husks such as rice husks, barley, wheat, rye, millet, foxtail millet, and millet.

[0030] After preparing a biomass fuel containing amorphous silica, the amorphous regions where silica is in an amorphous state and the crystalline regions where silica is in a crystalline state are determined based on the combustion temperature of 600°C to 1150°C and the holding time at the combustion temperature. Specifically, these regions can be determined from a phase diagram showing the relationship between the combustion temperature of the biomass fuel and the holding time at the combustion temperature. The phase diagram is created as follows.

[0031] First, biomass fuel is prepared, lightly washed with water to remove dust, dried, and then pulverized at a predetermined rotation speed, for example, by a planetary ball mill.

[0032] The pulverized biomass fuel is fed into a combustion device, and then heated to an arbitrary first temperature within the combustion range of 600°C to 1150°C at a heating rate of 20°C / min under an air flow of 500mL / min in the combustion device, and combusted. Ash generated by the combustion of the biomass fuel is held at the first temperature for t1 minutes, and then immediately allowed to cool naturally. In the obtained ash, it is confirmed whether silica is in an amorphous state by X-ray diffraction (step 1: S1 in FIG. 2). In the confirmation of the amorphous state of silica by X-ray diffraction, if silica is crystallized, a peak or shoulder appears, and it is possible to confirm whether silica is in a crystalline state or an amorphous state by the presence or absence of the peak or shoulder. The first temperature can be 750°C to 950°C, specifically, for example, 875°C to 925°C, and t1 can be 10 minutes to 15 minutes.

[0033] If it is confirmed that the silica is in an amorphous state as a result of step 1, the biomass fuel is burned again at the first temperature, and the holding time of the ash generated by the combustion of the biomass fuel at the first temperature is increased by t2 minutes from the previous holding time, and the above confirmation is performed again. C1 Repeat this step until you find the retention time T C1 And, T C1 -t2, and the retention time T during which the silica is in an amorphous state. A1 (min) is found (Step 2(1): S2(1) in FIG. 2). Note that in this case, T A1 (min) can be considered as the maximum time for silica to crystallize. For example, T near the boundary between the amorphous and crystalline regions A1 From the viewpoint of efficiently finding the above, it is suitable to set t2 to about 1.6 to 8.7 minutes.

[0034] If it is confirmed that the silica is in a crystalline state as a result of step 1, the biomass fuel is burned again at the first temperature, and the above confirmation is performed again after the holding time of the ash generated by the combustion of the biomass fuel at the first temperature is reduced by t3 minutes from the previous holding time, and the holding time T during which the silica is in an amorphous state is determined. A1 Repeat this step until you find the retention time T A1 And, T A1 +t3, and the retention time T C1 (min) is found (Step 2(2): S2(2) in FIG. 2). Note that in this case, T C1 (min) can be considered as the shortest time for silica to crystallize. For example, T near the boundary between the amorphous and crystalline regions C1 From the viewpoint of efficiently finding the above, it is suitable to set t3 to about 1.6 to 8.7 minutes.

[0035] Similarly, the biomass fuel is burned at a second temperature lower than the first temperature within the combustion temperature range of 600°C to 1150°C, and the ash generated by the combustion of the biomass fuel is held at the second temperature for t4 minutes, and then the obtained ash is checked by X-ray diffraction method to see whether silica is in an amorphous state or not (step 3: S3 in FIG. 2). The second temperature can be 750°C to 950°C, specifically, for example, 775°C to 825°C, and t4 may be about 480 to 800 minutes. From the viewpoint of increasing accuracy, the temperature difference between the first temperature and the second temperature is preferably 50°C or more.

[0036] If it is confirmed that the silica is in an amorphous state as a result of step 3, the biomass fuel is burned again at the second temperature, and the holding time of the ash generated by the combustion of the biomass fuel at the second temperature is increased by t5 minutes from the previous holding time, and the above confirmation is performed again. The holding time T C2 Repeat this step until you find the retention time T C2 And, T C2 -t5, and silica is in an amorphous state. A2(min) is found (Step 4(1): S4(1) in FIG. 2). Note that in this case, T A2 (min) can be considered as the maximum time for silica to crystallize. For example, T near the boundary between the amorphous and crystalline regions A2 From the viewpoint of efficiently finding the above, it is appropriate to set t5 to about 70 to 350 minutes.

[0037] If it is confirmed that the silica is in a crystalline state as a result of step 3, the biomass fuel is burned again at the second temperature, and the holding time of the ash generated by the combustion of the biomass fuel at the second temperature is reduced by t6 minutes from the previous holding time, and the above confirmation is performed again. A2 Repeat this step until you find the retention time T A2 And, T A2 +t6 and silica is in a crystalline state. C2 (min) is found (Step 4(2): S4(2) in FIG. 2). Note that in this case, T C2 (min) can be considered as the shortest time for silica to crystallize. For example, T near the boundary between the amorphous and crystalline regions C2 From the viewpoint of efficiently finding the above, it is appropriate to set t6 to about 70 to 350 minutes.

[0038] Then, on a semi-logarithmic graph (vertical axis is logarithmic) with temperature (℃) on the horizontal axis and holding time (min) on the vertical axis, T A1 , T C1 , T A2 , T C2 Plot and calculate T A1 and T A2 Connect with a straight line and T C1 and T C2 Connect them with straight lines (Step 5: S5 in Figure 2).

[0039] In this graph, the predicted holding time T' is extrapolated to an arbitrary third temperature higher than the first temperature or lower than the second temperature within the combustion temperature range of 600°C to 1150°C. A3 (min), T´ C3(min) is read (Step A: SA in FIG. 2). If the third temperature is lower than the second temperature, T´ A3 (min), T´ C3 In addition to (min), the predicted holding time T´ extrapolated to any fourth temperature higher than the first temperature within the combustion temperature range of 600°C to 1150°C A4 (min), T´ C4 If the third temperature is higher than the first temperature, it is preferable to read T´ (min). A3 (min), T´ C3 In addition to (min), the predicted holding time T' extrapolated to any fourth temperature lower than the second temperature within the combustion temperature range of 600°C to 1150°C A4 (min), T´ C4 It is preferable to read the predicted retention time T' (min). A4 (min), T´ C4 By reading (min), the highly accurate approximation function T A , T C can be obtained.

[0040] Then, the biomass fuel is burned at the third temperature, and the retention time of the ash generated by the combustion of the biomass fuel at the third temperature is estimated as a predicted retention time T´. A3 , T´ C3 After that, the resulting ashes are examined by X-ray diffraction to see if the silica is in an amorphous state (Step B: SB in FIG. 2).

[0041] The result of step B is T´ A3 If silica is confirmed to be in an amorphous state at T´ A3 is the retention time T during which silica is in an amorphous state. A3 (min), and if it is confirmed that the silica is in a crystalline state, the biomass fuel is burned again at the third temperature, and the holding time of the ash generated by the combustion of the biomass fuel at the third temperature is reduced by t7 minutes from the previous holding time, and the confirmation is repeated. The holding time T A3(Step C(1): SC(1) in FIG. 2). The third temperature can be 750° C. or more and 950° C. or less, specifically, for example, 750° C. or more and 775° C. or less, or 925° C. or more and 950° C. or less. Here, from the viewpoint of improving accuracy, when the third temperature is higher than the first temperature, it is preferable that the temperature difference between the first temperature and the third temperature is 50° C. or more, and when the third temperature is lower than the second temperature, it is preferable that the temperature difference between the second temperature and the third temperature is 50° C. or more. In addition, for example, when the T A3 From the viewpoint of efficiently finding, when the third temperature is in the range of 750°C or more and 775°C or less, t7 is suitably set to about 1550 minutes to 3100 minutes, and when the third temperature is in the range of 925°C or more and 950°C or less, t7 is suitably set to about 10 seconds to 20 seconds.

[0042] The result of step B is T´ C3 If silica is confirmed to be in a crystalline state at T´ C3 Hold time T C3 If it is confirmed that the silica is in an amorphous state, the biomass fuel is burned again at the third temperature, and the holding time of the ash generated by the combustion of the biomass fuel at the third temperature is increased by t8 minutes from the previous holding time, and the confirmation is repeated. The holding time T C3 (Step C(2): SC(2) in Fig. 2). T near the boundary between the amorphous and crystalline regions is found. C3 From the viewpoint of efficiently finding, when the third temperature is in the range of 750°C or more and 775°C or less, t8 is suitably set to about 1550 minutes to 3100 minutes, and when the third temperature is in the range of 925°C or more and 950°C or less, t8 is suitably set to about 10 seconds to 20 seconds.

[0043] In addition, the predicted retention time T A4 (min), T´ C4 If you also read (min), the biomass fuel is burned at the fourth temperature, and the retention time of the ash generated by the combustion of the biomass fuel at the fourth temperature is predicted retention time T´ A4 , T´ C4After that, the resulting ash is examined by X-ray diffraction to see if the silica is in an amorphous state. The subsequent steps are the same as steps C(1) and C(2), so the explanation is omitted.

[0044] Then, using commercially available software such as EXCEL (Microsoft Corporation), a semi-logarithmic graph (vertical axis is logarithmic) with the horizontal axis being temperature (°C) and the vertical axis being retention time (min) is plotted. A1 , T A2 , and T A3 Based on the approximate function T A (Step 6: S6 in Fig. 2). Note that in the above, T A4 If a retention time T A1 , T A2 , T A3 , and T A4 Based on the approximate function T A In this case, an approximate function T is calculated based on the retention times of the four points. A It is desirable to obtain T A4 In some cases, it may be difficult to obtain the approximate function T based on the retention times of three points. A Similarly, at least the retention time T C1 , T C2 , and T C3 Based on the approximate function T C (Step 6). At this time, an approximation function T C It is desirable to obtain T C In some cases, it may be difficult to obtain the approximate function T based on the retention times of the three points shown in Figure 1. C Then, we can calculate the approximate function T A The lower region is the amorphous region, and the approximate function T C The upper region of the approximation function T A , T C can be obtained by using, for example, the least squares approximation function of EXCEL (Microsoft Corporation). The vertical axis is preferably a logarithm. The approximation function TA and the approximation function T C The intermediate region between these two is a gray zone, and the higher the measurement accuracy, the narrower this region becomes, and the closer the two become to one, resulting in a more accurate phase diagram.

[0045] In the above, steps A to C are included, but steps A to C do not have to be included. In this case, in step 5, add T A1 and T A2 Along with the straight line connecting C1 and T C2 After drawing a line connecting the retention time T A1 and T A2 Based on the approximate function T A and the retention time T C1 and T C2 Based on the approximate function T C Then, we calculate the approximate function T A The lower region is the amorphous region, and the approximate function T C The upper region is the crystalline region.

[0046] After preparing such a phase diagram, the combustion temperature of the biomass fuel, the total time elapsed since the start of the combustion of the biomass fuel, and the temperature drop rate of the ash generated by the combustion of the biomass fuel are controlled based on the amorphous region and the crystalline region shown in this phase diagram. Here, when data on the ash are plotted on a semi-logarithmic graph (vertical axis is logarithmic) with the horizontal axis being temperature (°C) and the vertical axis being total time elapsed (min), and the plotted data is connected with a curve to draw the temperature curve of the ash (see FIG. 4 described later), if a part of the temperature curve of the ash is present in the crystalline region, the silica will be in a crystalline state even if the other part of the temperature curve of the ash is present in the amorphous region. Therefore, when suppressing the crystallization of silica, the combustion temperature, the total time elapsed, and the temperature drop rate are controlled so that all parts of the temperature curve of the ash are present in the amorphous region.

[0047] The total elapsed time is not particularly limited, but can be adjusted within a range of, for example, 0 minutes to 13 days. However, although it depends on the combustion temperature, the shorter the total elapsed time, the lower the temperature curve of the ash is, so that the ash is more likely to remain in the amorphous region.

[0048] When the temperature of ash generated by the combustion of biomass fuel is lowered, the temperature curve of the ash bends to the left (low temperature side). The higher the temperature lowering rate, the more the temperature curve of the ash bends to the left. Therefore, although it depends on the maximum temperature reached during the combustion process and the holding time, if the temperature lowering rate is high, the ash tends to remain in the amorphous region. The temperature lowering rate differs depending on the type of biomass fuel, and may be adjusted within the range of 0.05°C / min to 20°C / min, for example.

[0049] Approximation function T A , T C Since varies depending on the type of biomass fuel or even the place of origin of rice husk, an approximation function T A , T C It is necessary to ask for.

[0050] Such a method for controlling or suppressing the crystallization of silica can be realized, for example, by the following combustion device and program.

[0051] <<Combustion equipment>> The combustion device 10 shown in Fig. 3 includes a combustor 11, a cooler 12, an ash collector 13, and a control unit 14. The biomass fuel supplied to the combustor 11 is preferably one that has been pulverized in advance by a pulverizer.

[0052] The combustor 11 is for burning the biomass fuel to generate combustion gas 15 and ash 16. The combustor 11 is a burner, but may be, for example, a heater that applies heat to the biomass fuel to burn the biomass fuel instead of the burner. The combustor 11 includes a combustion chamber 11A, a supply pipe 11B that supplies the biomass fuel to the combustion chamber 11A, an air supply pipe 11C that supplies air to the combustion chamber 11A, and an ignition means such as an ignition combustor (not shown). The biomass fuel supplied from the supply pipe 11B is mixed with air supplied from the air supply pipe 11C and ignited by the ignition means, so that the biomass fuel is burned in the combustion chamber 11A. Combustion gas 15 and ash 16 generated mainly by burning the combustible gas are discharged from the outlet of the combustor 11.

[0053] The cooler 12 is for quickly cooling the ash generated in the combustor 11 to a predetermined temperature. As shown in FIG. 3, the cooler 12 includes a can body 12B in which a cooling medium 12A is stored, and a combustion gas introduction section 12C, a plurality of smoke tubes 12D, and a gas collection section 12E arranged in the can body 12B. The cooler 12 receives the ash 16 discharged from the outlet of the combustor 11 together with the combustion gas, and can cool the temperature of the ash 16 together with the combustion gas 15 to a desired temperature by heat exchange with the cooling medium 12A. A temperature sensor (not shown) is arranged near the outlet of the cooler 12, and is configured to be able to measure the temperature of the ash.

[0054] The ash collector 13 is for separating and collecting the ash 16 after the cooling process introduced through the exhaust duct 17 from the combustion gas 15. The ash collector 13 includes an outer cylinder 13A having a cylindrical upper portion and a conical lower portion tapering downward, an inner cylinder 13B inserted concentrically into the center of the outer cylinder 13A, and a collection box 13C provided below the outer cylinder 13A. In the ash collector 13, the combustion gas 15 is taken out through the inner cylinder 13B, and the ash 16 separated from the combustion gas 15 is collected in the collection box 13C.

[0055] <Control Unit> The control unit 14 is for controlling the combustion temperature, the total elapsed time from the start of the combustion of the biomass fuel, the temperature drop rate of the ash generated by the combustion of the biomass fuel, etc. The combustion temperature is a temperature measured by a temperature sensor arranged in the combustor 11, and the ash temperature is a temperature measured by a temperature sensor arranged near the outlet of the cooler 12. The control unit 14 is configured to adjust the flow rate of air input into the combustor 11 and the movement of the refrigerant in the cooler 12 based on these temperatures.

[0056] The control unit 14 is a computer. The control unit 14 is electrically connected to the combustor 11 (for example, the air supply pipe 11C) and the cooler 12, and is capable of controlling the combustion temperature, the total elapsed time, and the temperature drop rate of the ash.

[0057] The control unit 14 controls the combustion temperature of the biomass fuel, the total elapsed time from the start of the combustion of the biomass fuel, and the temperature drop rate of the ash generated by the combustion of the biomass fuel, based on the combustion temperature of 600°C to 1150°C and the amorphous region and the crystalline region determined in advance based on the holding time of the combustion temperature. The amorphous region and the crystalline region are determined by the above-mentioned steps. The holding temperature is not particularly limited, but can be controlled within a range of, for example, 0 minutes to 13 days, and the temperature drop rate can be controlled within a range of, for example, 0.05°C / min to 20°C / min, although it varies depending on the type of biomass fuel.

[0058] The above control in the control unit 14 is executed by a control program. The control program causes the computer to execute a step of accepting input of information regarding the amorphous region and the crystalline region determined in advance based on the combustion temperature of 600° C. or more and 1150° C. or less and the holding time of the combustion temperature, and to control the combustion temperature of the biomass fuel, the total elapsed time from the start of the combustion of the biomass fuel, and the temperature drop rate of the ash generated by the combustion of the biomass fuel based on the above input information.

[0059] According to this embodiment, the crystallization of silica can be controlled simply by controlling the combustion temperature of the biomass fuel, the total elapsed time from the start of combustion of the biomass fuel, and the rate of temperature drop of the ash generated by the combustion of the biomass fuel based on the amorphous region and the crystalline region, thereby enabling the crystallization of silica to be controlled in a simple manner.

[0060] According to this embodiment, based on the amorphous region and the crystalline region, crystallization of silica can be suppressed simply by controlling the combustion temperature of the biomass fuel, the total elapsed time from the start of combustion of the biomass fuel, and the rate of cooling of the ash generated by the combustion of the biomass fuel so as not to deviate from the amorphous region, thereby making it possible to suppress silica crystallization in a simple manner.

[0061] In addition, in the process of carbonizing biomass fuel, if the combustion temperature and holding time of the biomass charcoal are not maintained so that the silica is in the amorphous region, the biomass charcoal will contain silica as harmful crystalline silica. On the other hand, biomass charcoal containing amorphous silica can be used for soil improvement and organic cultivation. EXAMPLES

[0062] In order to explain the present invention in detail, the following examples are given, but the present invention is not limited to these. Fig. 4 is a phase diagram showing the relationship between the combustion temperature, total elapsed time, and temperature drop rate of silica in Examples 1 to 10, Fig. 5 is an X-ray diffraction pattern of silica in Examples 3 and 8, and Fig. 6 is a scanning electron microscope photograph of silica in Examples 3 to 6 and 8 to 10.

[0063] <Rice husk> In the following, rice husks used were those of Oryza sativa, japonica harvested in the Kyoto region, lightly washed with water to remove dust, dried, and then pulverized at 400 rpm for 30 minutes in a planetary ball mill (model number "LA-PO.1", manufactured by Ito Seisakusho Co., Ltd.).

[0064] <Combustion equipment> In the following, as a combustion device, in order to perform the combustion and subsequent cooling processes under as accurate temperature control as possible, a thermal analyzer (TG / DTA) (product name: "Thermo plus TG8120", manufactured by Rigaku Corporation) was used.

[0065] <X-ray diffractometer> In the following, as an X-ray diffractometer, a high-intensity X-ray generator (product name: "MicroMax 007HF", manufactured by Rigaku Corporation) was used. The recording of the X-ray diffraction pattern by this X-ray diffractometer was carried out by packing the ash into a soft glass capillary (manufactured by Hilgenberg) with a diameter of 1 mm, installing it in a Laue camera, and irradiating it with CuKα rays generated at 40 kV and 30 mA for 60 minutes.

[0066] <Preparation of phase diagram> 10 mg of the above-ground pulverized rice husk was placed in a platinum sample pan, and the temperature was raised to 900 °C as the first temperature at a rate of 20 °C / min under an air flow of 500 mL / min to burn the rice husk. The ash generated by the combustion of the rice husk was held at the same temperature for 9 minutes as t1. Then, it was immediately allowed to cool naturally. And in the obtained ash, it was confirmed whether silica was in an amorphous state by the X-ray diffraction method using an X-ray diffractometer.

[0067] As a result, when it was confirmed that silica was in an amorphous state, the rice husk was burned at 900 °C, and the holding time of the ash generated by the combustion of the rice husk at 900 °C was increased by 2 minutes from the previous holding time as t2, and the above confirmation was performed again until the holding time T C900℃ (min) was found. This step was repeated until the holding time T C900℃ (min) and T C900℃ -2 (min) were obtained, and the holding temperature T A900℃ (min) at which silica was in an amorphous state was found.

[0068] In addition, if it is confirmed that the silica is in a crystalline state, the rice husks are burned at 900°C, and the holding time of the ash generated by the burning of the rice husks at 900°C is reduced by 2 minutes from the previous holding time as t3, and the above confirmation is performed again. A900℃ Repeat this step until you find the retention time T A900℃ (min) and T A900℃ +2 (min) and the holding temperature T at which silica is in a crystalline state C900℃ (min) was found.

[0069] Similarly, the second temperature was raised to 800°C to combust the rice husks, and the ash generated by the combustion of the rice husks was kept at 800°C for 66 minutes as t4. Then, it was immediately allowed to cool naturally. Then, in the obtained ash, it was confirmed whether or not silica was in an amorphous state by X-ray diffraction method using an X-ray diffraction device.

[0070] If it is confirmed that the silica is in an amorphous state, the rice husks are burned at 800°C, and the holding time of the ash generated by the rice husk combustion at 800°C is increased by 150 minutes from the previous holding time, which is set as t5, and the above confirmation is performed again. C800℃ Repeat this step until you find the retention time T C800℃ And, T C800℃ -150 (min) and the holding temperature T at which silica is in a crystalline state A800℃ (min) was found.

[0071] In addition, if it is confirmed that the silica is in a crystalline state, the rice husks are burned at 800°C, and the holding time of the ash generated by the combustion of the rice husks at 800°C is reduced by 150 minutes from the previous holding time as t6, and the above confirmation is performed again. A800℃ Repeat this step until you find the retention time T A800℃ And, T A800℃ +150 and the holding temperature T at which silica is in a crystalline state C800℃ (min) was found.

[0072] Then, in a semi-logarithmic graph with temperature (℃) on the horizontal axis and retention time (min) on the vertical axis, T C900℃ , T A900℃ , T C800℃ , T A800℃ Plot the T A900℃ and T A800℃ Connect with a straight line and T C900℃ and T C800℃ The predicted holding time T' is calculated by connecting the values ​​of A750℃ (min), T´ C750℃ (min) and extrapolate the predicted holding time T´ to 950℃ A950℃ (min), T´ C950℃ (min) was read.

[0073] Then, the rice husks were burned at 750°C, and the predicted retention time T´ of the ash generated by the rice husk combustion at 750°C was measured. A750℃ , T´ C750℃ After the time had elapsed, the X-ray diffraction method was used to confirm whether the silica was in an amorphous state in each of the ashes obtained. Similarly, rice husks were burned at 950°C for the predicted retention time T' A950℃ After the time had passed, the resulting ashes were examined by X-ray diffraction using an X-ray diffractometer to confirm whether the silica was in an amorphous state.

[0074] As a result, T´ A750℃ If silica is confirmed to be in an amorphous state at T´ A750℃ is the retention time T during which silica is in an amorphous state. A750℃ If it is confirmed that silica is in a crystalline state, the rice husks are burned at 750°C, and the holding time of the ash generated by the rice husk combustion at 750°C is reduced by 790 minutes from the previous holding time, which is set as t7, and the confirmation is repeated. The holding time T A750℃ found.

[0075] Also, T´ C750℃ If silica is confirmed to be in a crystalline state at T´ C750℃ Hold time T C750℃If it is confirmed that silica is in an amorphous state, the rice husks are burned at 750°C, and the holding time of the ash generated by the rice husk combustion at 750°C is increased by 790 minutes from the previous holding time, t8, and the confirmation is repeated. The holding time T C750℃ found.

[0076] Also, T´ A950℃ If silica is confirmed to be in an amorphous state at T´ A950℃ is the retention time T during which silica is in an amorphous state. A950℃ If it is confirmed that silica is in a crystalline state, the rice husks are burned at 950°C, and the holding time of the ash generated by the rice husk combustion at 950°C is reduced by 1.5 minutes from the previous holding time, and the confirmation is repeated. The holding time T A950℃ found.

[0077] Then, using EXCEL (Microsoft Corporation), the retention time T A900℃ , T A800℃ , T A750℃ , and T A950℃ Based on the approximate function T A was calculated (see Figure 4). Similarly, the retention time T C900℃ , T C800℃ , and T C750℃ Based on the approximate function T C Then, the approximation function T A The lower region is the amorphous region, and the approximate function T C The upper region of T was considered as the crystalline region. A The function is y=4×10 15 e -0.037 x (correlation coefficient R = 0.9974), and T C The function is y=10 15 e -0.036 x (correlation coefficient R = 0.9987) (see Figure 4). Approximation function T A , T C was calculated using the least squares approximation function of EXCEL (Microsoft Corporation).

[0078] <Examples 1 to 10> 10 mg of the above-mentioned crushed rice husk was placed in a platinum sample pan and burned in a combustion apparatus. Specifically, first, under an air flow of 500 mL / min, the temperature was raised at a rate of 20 °C / min to various maximum reachable temperatures x max °C to burn the rice husk. Then, the ash generated by the combustion of the rice husk was cooled under control at a constant rate of r °C / min to x end °C and then allowed to cool naturally. x max , r, x end are shown in Table 1, and the data of the ash was plotted on the phase diagram of Figure 4.

Table 1

[0079] <Measurement by X-ray diffraction method> In Examples 1 to 10, when the powdered ash obtained after combustion was recorded for an X-ray diffraction (XRD) image using an X-ray diffractometer, in Examples 4, 5, 8 to 10, four peaks attributed to α-cristobalite and a shoulder attributed to α-quartz were observed (see Figure 5). In contrast, in Examples 1, 2, 3, 6, and 7, no peaks derived from crystals were observed (see Figure 5). Thus, it was confirmed that in Examples 4, 5, 8 to 10, silica was in a crystalline state, and in Examples 1, 2, 3, 6, and 7, silica was in an amorphous state. From this result, when controlled to exist within the amorphous region in the lower region of the approximate function T A shown in Figure 4, silica became amorphous, and when outside the amorphous region in the lower region of the approximate function T A shown in Figure 4, it was confirmed that silica became crystalline.

[0080] <Taking scanning electron microscope photographs> In Examples 3 to 6 and 8 to 10, the powdered ash obtained after combustion was mounted on a sample stage using conductive tape and observed with a scanning electron microscope (SEM) (product name "S-4800", Hitachi High-Technologies Corporation) at an accelerating voltage of 1 kV and a magnification of 30,000 times, resulting in the photograph shown in FIG. 6. It was confirmed from FIG. 6 that silica was in a crystalline state in Examples 4, 5 and 8 to 10. It was also confirmed from FIG. 6 that silica was in an amorphous state in Examples 3 and 6.

[0081] These results confirmed that, based on the amorphous and crystalline regions, the crystallization of silica can be controlled or suppressed by controlling the combustion temperature, the total elapsed time from the start of combustion, and the temperature drop rate. [Explanation of symbols]

[0082] 10...Combustion device 11...Combustor 12...Cooler 13...Ash collector 14...Control section

Claims

1. A method for controlling crystallization of amorphous silica in a combustion process of a biomass fuel containing said silica, comprising: Determining an amorphous region in which the silica is in an amorphous state and a crystalline region in which the silica is in a crystalline state based on a combustion temperature of 600° C. or more and 1150° C. or less and a retention time at the combustion temperature; and controlling the combustion temperature of the biomass fuel, the total time elapsed since the start of combustion of the biomass fuel, and the temperature drop rate of ash generated by the combustion of the biomass fuel based on the amorphous region and the crystalline region; The determination of the amorphous regions and the crystalline regions comprises the steps of: Step 1: Burning a biomass fuel at a first temperature in the range of 600° C. to 1150° C., and storing the ash generated by the combustion of the biomass fuel at the first temperature t １ After the retention time is 10 minutes, it is confirmed whether the silica contained in the ash is in an amorphous state or not. Step 2: If it is determined that the silica is in an amorphous state as a result of step 1, the biomass fuel is combusted again at the first temperature, and the retention time of the ash generated by the combustion of the biomass fuel at the first temperature is increased by t from the previous retention time. ２ The confirmation is performed again after increasing the holding time T Ｃ１ This step is repeated until a retention time T Ｃ１ And, T Ｃ１ -t ２ and the retention time T during which the silica is in an amorphous state is represented by Ａ１ (min), and if it is confirmed that the silica is in a crystalline state as a result of step 1, the biomass fuel is combusted again at the first temperature, and the retention time of the ash generated by the combustion of the biomass fuel at the first temperature is increased by t from the previous retention time. ３ The confirmation is performed again after reducing the time by 1 minute, and the retention time T Ａ１ This step is repeated until a retention time T Ａ１ And, T Ａ１ +t ３ and the retention time T during which the silica is in a crystalline state is represented by Ｃ１ (min), Step 3: Burning the biomass fuel at a second temperature lower than the first temperature within a combustion temperature range of 600° C. to 1150° C., and burning the ash generated by the combustion of the biomass fuel at the second temperature t ４ After the retention time is 10 minutes, it is confirmed whether the silica contained in the ash is in an amorphous state or not. Step 4: If it is determined that the silica is in an amorphous state as a result of step 3, the biomass fuel is combusted again at the second temperature, and the retention time of the ash generated by the combustion of the biomass fuel at the second temperature is increased by t from the previous retention time. ５ The above confirmation is performed again with the holding time T Ｃ２ This step is repeated until a retention time T Ｃ２ And, T Ｃ２ -t ５ and the silica is in an amorphous state, T Ａ２ (min), and if it is confirmed that the silica is in a crystalline state as a result of step 3, the biomass fuel is combusted again at the second temperature, and the retention time of the ash generated by the combustion of the biomass fuel at the second temperature is increased from the previous retention time by t ６ The above confirmation is performed again after reducing the time by 1 minute, and the retention time T Ａ２ This step is repeated until a retention time T Ａ２ And, T Ａ２ +t ６ and the silica is in a crystalline state, Ｃ２ (min), Step 5: In a graph with temperature (°C) on the horizontal axis and holding time (min) on the vertical axis, T Ａ１ , T Ｃ１ , T Ａ２ , T Ｃ２ Plot the Ａ１ and T Ａ２ Connect with a straight line and T Ｃ１ and T Ｃ２ Connect the lines with a straight line. Step 6: In a graph with the horizontal axis being temperature (° C.) and the vertical axis being holding time (min), at least the holding time T Ａ１ and T Ａ２ Based on the approximation function T Ａ and at least the retention time T Ｃ１ and T Ｃ２ Based on the approximation function T Ｃ is calculated, and the approximation function T Ａ The lower region of the approximation function T Ｃ The control method of claim 1, wherein the upper region of the

2. Between step 5 and step 6, the following steps are included: Step A: T Ａ１ and T Ａ２ The straight line connecting Ｃ１ and T Ｃ２ Based on the straight line connecting the above, a predicted retention time T' is extrapolated to an arbitrary third temperature higher than the first temperature or lower than the second temperature within the combustion temperature range of 600° C. to 1150° C. Ａ３ (min), T' Ｃ３ (min), Step B: Burning a biomass fuel at the third temperature, and calculating the retention time of the ash generated by the combustion of the biomass fuel at the third temperature according to the predicted retention time T' Ａ３ , T' Ｃ３ In this state, it is confirmed whether or not the silica contained in the ash generated by the combustion of the biomass fuel is in an amorphous state. Step C: The result of step B, T' Ａ３ If it is confirmed that the silica is in an amorphous state at T' Ａ３ is the retention time T during which silica is in an amorphous state. Ａ３ (min), and if it is confirmed that the silica is in a crystalline state, the biomass fuel is combusted again at the third temperature, and the retention time of the ash generated by the combustion of the biomass fuel at the third temperature is increased from the previous retention time to t ７ The above confirmation is repeated with the temperature reduced for 1 minute, and the retention time T Ａ３ Find T' Ｃ３ If it is confirmed that silica exists in a crystalline state, T' Ｃ３ Hold time T Ｃ３ (min), and if it is confirmed that the silica is in an amorphous state, the biomass fuel is combusted again at the third temperature, and the retention time of the ash generated by the combustion of the biomass fuel at the third temperature is increased by t from the previous retention time. ８ The confirmation was repeated with increasing time T for 1 minute, and the retention time T for which the silica was in a crystalline state was measured. Ｃ３ Finding In step 6, in a graph in which the horizontal axis is temperature (° C.) and the vertical axis is holding time (min), Ａ１ , T Ａ２ , and T Ａ３ Based on the approximation function T Ａ and at least the retention time T Ｃ１ , T Ｃ２ , and T Ｃ３ Based on the approximation function T Ｃ is calculated, and the approximation function T Ａ The lower region of the approximation function T Ｃ The control method according to claim 1 , further comprising the step of: making the upper region of said crystal region.

3. The control method according to claim 1 , wherein the first temperature and the second temperature are each within a temperature range of 750° C. to 950° C.

4. The control method according to claim 3 , wherein the temperature difference between the first temperature and the second temperature is 50° C. or more.

5. The control method according to claim 2 , wherein the first temperature, the second temperature, and the third temperature are each within a temperature range of 750° C. or more and 950° C. or less.

6. 6. The control method of claim 5, wherein a temperature difference between the first temperature and the second temperature is 50° C. or more, and when the third temperature is higher than the first temperature, a temperature difference between the first temperature and the third temperature is 50° C. or more, and when the third temperature is lower than the second temperature, a temperature difference between the second temperature and the third temperature is 50° C. or more.

7. A control method described in any one of claims 1 to 6, wherein the biomass fuel is grain husk.

8. A method for suppressing crystallization of silica during combustion treatment of a biomass fuel containing silica, comprising: Determining an amorphous region where silica is in an amorphous state and a crystalline region where silica is in a crystalline state based on a combustion temperature of 600° C. or more and 1150° C. or less and a retention time at the combustion temperature; and controlling, based on the amorphous region and the crystalline region, the combustion temperature of the biomass fuel, the total elapsed time from the start of combustion of the biomass fuel, and the temperature drop rate of ash generated by the combustion of the biomass fuel so that the silica is present in the amorphous region; The determination of the amorphous regions and the crystalline regions comprises the steps of: Step 1: Burning a biomass fuel at a first temperature within a range of 600° C. to 1150° C., and holding the ash generated by the combustion of the biomass fuel at the first temperature for t 1 minutes, and then confirming whether or not the silica contained in the ash is in an amorphous state; Step 2: If it is confirmed that the silica is in an amorphous state as a result of step 1, burn the biomass fuel again at the first temperature, and confirm again with the retention time of the ash generated by the combustion of the biomass fuel at the first temperature increased by t 2 minutes from the previous retention time, and repeat this step until a retention time T C1 (min) at which the silica is in a crystalline state is found, and find a retention time T C1 and a retention time T A1 (min) represented by T C1 -t 2 and at which the silica is in an amorphous state. If it is confirmed that the silica is in a crystalline state as a result of step 1, burn the biomass fuel again at the first temperature, and confirm again with the retention time of the ash generated by the combustion of the biomass fuel decreased by t 3 minutes from the previous retention time, and repeat this step until a retention time T A1 (min) at which the silica is in an amorphous state is found, and find a retention time T A1 and a retention time T A1 (min) represented by T C1 -t 2 and at which the silica is in an amorphous state. + t 3 and find the retention time T C1 (min) during which the silica is in a crystalline state; Step 3: Burning the biomass fuel at a second temperature lower than the first temperature within a combustion temperature range of 600° C. to 1150° C., and holding the ash generated by the combustion of the biomass fuel at the second temperature for t 4 minutes, and then confirming whether the silica contained in the ash is in an amorphous state; Step 4: If it is confirmed that the silica is in an amorphous state as a result of step 3, burn the biomass fuel again at the second temperature, and confirm again with the holding time of the ash generated by the combustion of the biomass fuel at the second temperature increased by t 5 minutes from the previous holding time, and repeat this step until a holding time T C2 (min) at which the silica is in a crystalline state is found, and find a holding time T C2 and a T A2 (min) represented by T C2 -t 5 and at which the silica is in an amorphous state. If it is confirmed that the silica is in a crystalline state as a result of step 3, burn the biomass fuel again at the second temperature, and confirm again with the holding time of the ash generated by the combustion of the biomass fuel decreased by t 6 minutes from the previous holding time, and repeat this step until a holding time T A2 (min) at which the silica is in an amorphous state is found, and find a holding time T A2 and a T A2 +t 6 and T C2 (min) at which the silica is in a crystalline state; Step 5: In a graph with temperature (°C) on the horizontal axis and retention time (min) on the vertical axis, T A1 , T C1 , T A2 , and T C2 are plotted, and T A1 and T A2 are connected with straight lines, and T C1 and T C2 are connected with straight lines; Step 6: In a graph with the horizontal axis representing temperature (° C.) and the vertical axis representing retention time (min), an approximation function T is calculated based on at least retention times T A1 and T A2 , and an approximation function T C is calculated based on at least retention times T C1 and T C2 , and the region below the approximation function T A is defined as the amorphous region and the region above the approximation function T C is defined as the crystalline region; The method of suppressing, wherein the biomass fuel is cereal husks.

9. A combustor for burning a biomass fuel containing amorphous silica; A cooler for cooling ash produced by the combustion of the biomass fuel; and a control unit that controls the combustion temperature of the biomass fuel, the total elapsed time from the start of combustion of the biomass fuel, and the temperature drop rate of ash generated by the combustion of the biomass fuel based on an amorphous region in which the silica is in an amorphous state and a crystalline region in which the silica is in a crystalline state, which are determined in advance based on a combustion temperature of 600° C. or more and 1150° C. or less and a holding time at the combustion temperature, The amorphous regions and the crystalline regions are determined by the following steps: Step 1: Burning a biomass fuel at a first temperature in the range of 600° C. to 1150° C., and storing the ash generated by the combustion of the biomass fuel at the first temperature t １ After the retention time is 10 minutes, it is confirmed whether the silica contained in the ash is in an amorphous state or not. Step 2: If it is determined that the silica is in an amorphous state as a result of step 1, the biomass fuel is combusted again at the first temperature, and the retention time of the ash generated by the combustion of the biomass fuel at the first temperature is increased by t from the previous retention time. ２ The confirmation is performed again after increasing the holding time T Ｃ１ Until we find (min), This step is repeated for a retention time T Ｃ１ And, T Ｃ１ -t ２ and the retention time T during which the silica is in an amorphous state is represented by Ａ１ (min), and if it is confirmed that the silica is in a crystalline state as a result of step 1, the biomass fuel is combusted again at the first temperature, and the retention time of the ash generated by the combustion of the biomass fuel at the first temperature is increased by t from the previous retention time. ３ The confirmation is performed again after reducing the time by 1 minute, and the retention time T Ａ１ This step is repeated until a retention time T Ａ１ And, T Ａ１ +t ３ and the retention time T during which the silica is in a crystalline state is represented by Ｃ１ (min), Step 3: Burning the biomass fuel at a second temperature lower than the first temperature within a combustion temperature range of 600° C. to 1150° C., and burning the ash generated by the combustion of the biomass fuel at the second temperature t ４ After the retention time is 10 minutes, it is confirmed whether the silica contained in the ash is in an amorphous state or not. Step 4: If it is determined that the silica is in an amorphous state as a result of step 3, the biomass fuel is combusted again at the second temperature, and the retention time of the ash generated by the combustion of the biomass fuel at the second temperature is increased by t from the previous retention time. ５ The above confirmation is performed again with the holding time T Ｃ２ This step is repeated until a retention time T Ｃ２ And, T Ｃ２ -t ５ and the silica is in an amorphous state, T Ａ２ (min), and if it is confirmed that the silica is in a crystalline state as a result of step 3, the biomass fuel is combusted again at the second temperature, and the retention time of the ash generated by the combustion of the biomass fuel at the second temperature is increased from the previous retention time by t ６ The above confirmation is performed again after reducing the time by 1 minute, and the retention time T Ａ２ This step is repeated until a retention time T Ａ２ And, T Ａ２ +t ６ and the silica is in a crystalline state, Ｃ２ (min), Step 5: In a graph with temperature (°C) on the horizontal axis and holding time (min) on the vertical axis, T Ａ１ , T Ｃ１ , T Ａ２ , T Ｃ２ Plot the Ａ１ and T Ａ２ Connect with a straight line and T Ｃ１ and T Ｃ２ Connect the lines with a straight line. Step 6: In a graph with the horizontal axis being temperature (° C.) and the vertical axis being holding time (min), at least the holding time T Ａ１ and T Ａ２ Based on the approximation function T Ａ and at least the retention time T Ｃ１ and T Ｃ２ Based on the approximation function T Ｃ is calculated, and the approximation function T Ａ The lower region of the approximation function T Ｃ The upper region of the combustion device is the crystal region.

10. The combustion apparatus of claim 9, wherein the biomass fuel is grain husk.

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