JP7655848B2 - Amorphous silica manufacturing apparatus and method for manufacturing amorphous silica - Google Patents

Description

The present invention relates to a reactor, a raw material supply mechanism that supplies biomass derived from silicic acid plants as a raw material to the reactor, a gas supply mechanism that supplies water vapor and an oxygen-containing gas from below the reactor, and an amorphous silica manufacturing device and method that produce amorphous silica by heat treating the amorphous silica while contacting it with the gas supplied via the gas supply mechanism.

Patent Document 1 proposes a method and apparatus for producing amorphous silica that uses biomass derived from silicic acid plants as a raw material, efficiently recovers energy, and can produce high-purity, high-quality silica.

The method for producing the amorphous silica includes a gasification step in which biomass derived from a silicic acid plant is pyrolyzed and gasified, and a firing step in which the biomass residue generated in the gasification step is fired.

The amorphous silica manufacturing apparatus also includes a gasification furnace that pyrolyzes and gasifies biomass containing silicic acid plants, a separation mechanism that separates the biomass residue from the mixture of pyrolysis gas and biomass residue discharged from the gasification furnace, and a calcination furnace that calcines the biomass residue separated by the separation mechanism to obtain amorphous silica.

According to the above-mentioned method for producing amorphous silica, the biomass derived from silicic acid plants is pyrolyzed in the gasification step and recovered as fuel, and the remaining biomass residue is calcined to remove impurities such as carbon components remaining in the biomass residue, resulting in highly pure white amorphous silica.

JP 2020-040861 A

The method for producing amorphous silica disclosed in Patent Document 1 requires the biomass residue obtained in the gasification step to be further calcined, and it is desirable to obtain amorphous silica without carrying out the time-consuming calcination process.

In addition, the supply of water vapor is essential to activate the silica produced and to prevent the temperature from rising to the range where silica crystallizes during the heat treatment process, and it is uneconomical to require a separate heat source to obtain such water vapor.

The object of the present invention is to provide an apparatus and method for producing amorphous silica that can efficiently obtain amorphous silica using biomass derived from silicic acid plants as a raw material.

In order to achieve the above-mentioned object, a first characteristic configuration of an amorphous silica manufacturing apparatus according to the present invention is a reactor, a raw material supply mechanism for supplying biomass derived from a silicic acid plant as a raw material to the reactor, a gas supply mechanism for supplying steam and an oxygen-containing gas from the bottom of the reactor where the raw material is retained, and an amorphous silica manufacturing apparatus for producing amorphous silica by heat-treating the raw material while contacting it with the steam and the oxygen-containing gas, the apparatus comprising a temperature control mechanism for maintaining the temperature of the internal space of the reactor at or below a predetermined temperature that suppresses crystallization of the amorphous silica, the temperature control mechanism being composed of a heat exchanger that uses water as a heat medium, and an upper air supply mechanism that supplies air between the gas supply mechanism and the heat exchanger to combust the raw material , and configured to supply the steam generated in the heat exchanger to the reactor via the gas supply mechanism.

Biomass derived from silicic acid plants supplied to the reactor is heat-treated by contacting steam and oxygen-containing gas, and some of it undergoes a water-gas reaction and some undergoes a combustion reaction, producing amorphous silica. During this process, the upper air supply mechanism adjusts the amount of air supplied between the gas supply mechanism and the heat exchanger, adjusting the combustion state in the space near the upper air supply mechanism, and the amount of heat recovered by the heat recovery mechanism is adjusted to the combustion state in the space near the upper air supply mechanism, so that the temperature of the inner space of the reactor is maintained at a temperature lower than the phase transition temperature range where amorphous silica crystallizes. Furthermore, the steam generated by the heat exchanger is supplied to the furnace through the gas supply mechanism, so that amorphous silica can be efficiently produced.

The second characteristic configuration is that, in addition to the first characteristic configuration described above, it is equipped with an oxygen-containing gas ratio adjustment mechanism that adjusts the ratio of the oxygen-containing gas to the supply amount of the raw material, converted into an air ratio, to a range of 1.3 to 1.5.

The oxygen-containing gas ratio adjustment mechanism adjusts the ratio of oxygen-containing gas to the raw material, converted to an air ratio, to a range of 1.3 to 1.5, which burns the carbon components contained in the raw material and efficiently produces white amorphous silica.

The third characteristic configuration is that, in addition to the first or second characteristic configuration described above, the temperature control mechanism is provided with a temperature sensor downstream of the heat exchanger provided in the reactor and between the heat exchanger and the upper air supply mechanism .

The amount of heat exchanged by the heat exchanger can be appropriately adjusted based on the value of a temperature sensor installed downstream of the heat exchanger installed in the reactor.

The first characteristic configuration of the method for producing amorphous silica according to the present invention is a method for producing amorphous silica, which comprises a raw material supplying step of supplying a raw material made of biomass derived from a silicic acid plant to a reactor by a raw material supplying mechanism, a gas supplying step of supplying steam and an oxygen-containing gas from the bottom of the reactor where the raw material is retained by a gas supplying mechanism, and a temperature adjusting step of maintaining the temperature of the inner space of the reactor at or below a predetermined temperature that suppresses crystallization of the amorphous silica, the temperature adjusting step being performed by a heat exchanger that uses water as a heat medium and an upper air supplying mechanism that supplies air between the gas supplying mechanism and the heat exchanger to combust the raw material , and the steam generated in the heat exchanger is supplied to the reactor via the gas supplying mechanism.

The second characteristic configuration is that, in addition to the first characteristic configuration described above, it is equipped with an oxygen-containing gas ratio adjustment mechanism that adjusts the ratio of the oxygen-containing gas to the supply amount of the raw material, converted into an air ratio, to a range of 1.3 to 1.5.

The third characteristic configuration is, in addition to the first or second characteristic configuration described above, that the temperature adjustment process is executed based on the value of a temperature sensor arranged downstream of the heat exchanger provided in the reactor and between the heat exchanger and the upper air supply mechanism .

As described above, the present invention makes it possible to provide an apparatus and method for producing amorphous silica that can efficiently obtain amorphous silica using biomass derived from silicic acid plants as a raw material.

FIG. 1 is an explanatory diagram showing an example of an apparatus for producing amorphous silica according to the present invention. FIG. 2A is a plan view of a gas supply mechanism when the heat treatment is mainly a combustion reaction, and FIG. 2B is a cross-sectional view of a main part of the gas supply mechanism. FIG. 2A is a plan view of a gas supply mechanism when the heat treatment is mainly a gasification reaction, and FIG. 2B is a cross-sectional view of a main part of the gas supply mechanism. An explanatory diagram of an apparatus for producing amorphous silica when the heat treatment is mainly a combustion reaction. An explanatory diagram of an amorphous silica manufacturing apparatus in which the heat treatment is mainly a gasification reaction. An explanatory diagram of a control device provided in an amorphous silica manufacturing apparatus. 1A and 1B are explanatory diagrams of an upper air supply mechanism showing another embodiment.

An example of the amorphous silica production apparatus and method according to the present invention will be described below.
[Configuration of amorphous silica production apparatus]
One embodiment of an apparatus 1 for producing amorphous silica according to the present invention is shown in Fig. 1. The apparatus 1 for producing amorphous silica includes a cylindrical reactor 2 having a constricted portion formed in the vertical center and a diameter reduced from the top to the bottom, a raw material supply mechanism 4 for supplying biomass derived from silicic acid plants as a raw material to the reactor 2, and a gas supply mechanism 3 for supplying a mixed gas of water vapor and air, which is an example of an oxygen-containing gas, from the bottom of the reactor 2, and the bottom of the reactor 2 is filled with a predetermined amount of silica sand to form a spouted bed.

The raw material supply mechanism 4 is composed of a screw conveyor mechanism equipped with a cylindrical casing and a screw blade housed in the cylindrical casing, and the tip side of the casing is flange-connected to the side wall below the narrowing portion of the reactor 2. Although not shown, a hopper equipped with a quantitative supply mechanism is provided at the base end side of the casing.

The biomass filled in the hopper is transported compactly by a screw blade and fed into reactor 2. The biomass used is the large amount of rice husks that are generated after hulling unhulled rice produced by farmers.

The gas supply mechanism 3 is composed of a header pipe 30 arranged on the lower side of the reactor 2, and multiple aeration pipes 31 with a circular cross section that are connected to the header pipe 30 in a parallel orientation. An air supply pipe 32 and a steam supply pipe 33 are connected to the header pipe 30, and a mixture of air and steam is supplied to each aeration pipe 31 via the header pipe 30. Saturated steam or superheated steam is used as the water vapor.

A small amount of silica sand is filled at the bottom of the reactor 2, and the mixed gas supplied from the gas supply mechanism 3 forms an entrained bed 9 in which the silica sand flows at the bottom of the reactor 2. In the entrained bed 9, the raw material rice husks are agitated by the silica sand and heated by steam in the presence of air while flowing, resulting in the production of amorphous silica through heat treatment. The heat treatment involves a combustion reaction in which the carbon components contained in the rice husks combine with oxygen, and a gasification reaction in which the carbon components contained in the rice husks react with steam to produce carbon monoxide and hydrogen.

The amorphous silica that has been heat-treated and turned into fine powder at the bottom of the reactor 2, i.e., the narrowed diameter section, rises inside the furnace together with the combustion exhaust gas and is discharged from the exhaust pipe 10 connected to the top of the reactor 2. Note that because the flow rate of the combustion exhaust gas decreases at the top of the reactor 2, i.e., the expanded diameter section, rice husks that have not been sufficiently heat-treated fall downward under their own weight.

The amorphous silica discharged from the exhaust pipe 10 is guided to the cyclone 7 where it is separated from the combustion exhaust gas and collected. The combustion exhaust gas from which the amorphous silica has been separated is subjected to secondary combustion in the secondary combustion equipment 8 before being released into the atmosphere.

[Configuration of heat treatment condition adjusting mechanism]
The above-mentioned amorphous silica manufacturing apparatus 1 further includes a heat treatment condition adjusting mechanism A. The heat treatment condition adjusting mechanism A is a mechanism for adjusting the heat treatment conditions of the raw material supplied to the reaction furnace 2, and is a mechanism for adjusting the proportion of carbon contained in the generated amorphous silica by switching between mainly subjecting the raw material to a combustion reaction or a gasification reaction, even though the manufacturing apparatus 1 is the same.

By adjusting the heat treatment condition adjustment mechanism A so that the combustion reaction that sufficiently burns the carbon and other impurities contained in the raw material occurs primarily, highly pure amorphous white silica can be obtained. Also, by adjusting the heat treatment condition adjustment mechanism A so that the gasification reaction occurs primarily while the carbon and other impurities contained in the raw material remain, amorphous black silica can be obtained.

In this specification, white silica refers to amorphous silica that contains less than 5% carbon by weight and has a white or whitish appearance, and black silica refers to amorphous silica that contains more than 5% carbon by weight and has a black or blackish appearance.

White silica is effectively used in industrial materials such as white cosmetic raw materials, adsorbents, and additives for white paints and resins, and agricultural materials such as fertilizers for adding silica to crops, while black silica is effectively used in industrial materials such as black cosmetic raw materials, adsorbents, and additives for black paints and resins, and additives for tires, and agricultural materials such as fertilizers for adding silica and carbon to crops.

The heat treatment condition adjustment mechanism A includes an oxygen-containing gas ratio adjustment mechanism (in this embodiment, air is used as the oxygen-containing gas, so it is an air ratio adjustment mechanism) that adjusts the ratio of the oxygen-containing gas supplied from the gas supply mechanism 3 to the supply amount of the raw material, and a fluidization condition adjustment mechanism that adjusts the fluidization condition of the raw material in the entrained bed formed inside the reactor 2 by adjusting at least one of the total amount, supply position, and supply distribution of the gas supplied from the gas supply mechanism 3.

By increasing the total amount of gas, the flow state of the raw materials becomes more intense, and by decreasing the total amount of gas, the flow state of the raw materials becomes more gentle. By adjusting the distribution of the gas supply positions to be dense, the raw materials can be agitated so that the raw materials and the gas have a uniform contact opportunity, and by adjusting the distribution of the gas supply positions to be coarse, the raw materials can be agitated so that the raw materials and the gas have a non-uniform contact opportunity. By adjusting the gas supply distribution to be dense, the raw materials can be agitated so that the raw materials and the gas have a uniform contact opportunity, and by adjusting the gas supply distribution to be coarse, the raw materials can be agitated so that the raw materials and the gas have a non-uniform contact opportunity. For example, even if the distribution of the gas supply positions is the same, the gas supply distribution can be adjusted by individually varying the amount of gas supply sprayed from each nozzle.

2(a) and (b) show a gas supply mechanism 3 (3A) for obtaining white silica by mainly inducing a combustion reaction in the reactor 2, and FIG. 3(a) and (b) show a gas supply mechanism 3 (3B) for obtaining black silica by mainly inducing a gasification reaction in the reactor 2. As described above, the gas supply mechanism 3 (3A, 3B) includes a header pipe 30 arranged on the lower side of the reactor 2 and a plurality of diffuser pipes 31 with a circular cross section connected to the header pipe 30 in a parallel position to each other. An air supply pipe 32 and a steam supply pipe 33 are connected to the header pipe 30, and a mixture of air and steam is supplied to each diffuser pipe 31 via the header pipe 30.

Each diffuser tube 31 is supported by an attachment 31F with an arc-shaped cross section that fits along the lower peripheral wall of the reactor 2. The attachment 31F is formed in a shape that covers an arc-shaped notch formed in the lower side wall of the reactor 2, and by fixing the attachment 31F to the side wall of the reactor 2 with the tip side of each diffuser tube 31 inserted into the reactor 2, the multiple diffuser tubes 31 are fixed to the reactor 2 in a parallel position to each other.

As shown in Figures 2(a) and (b), the gas supply mechanism 3 (3A) for the combustion reaction is made up of a number of small-diameter diffuser tubes 31, so that the rice husks supplied from the raw material supply mechanism 4 are stirred and burned uniformly within any plane perpendicular to the axis of the reactor 2 without creating localized high-temperature areas.

More specifically, the diffuser tube 31 has mixed gas outlet holes 31H facing two directions inclined diagonally downward at an angle θ with respect to the horizontal. The outlet holes 31H formed in each diffuser tube 31 are set so that the pitch L2 in the axial direction and in the direction intersecting the axial direction are approximately equal, and the pitch L3 between the diffuser tubes 31 is set to L3 ≈ 2L2 so that the pitches of the outlet holes 31H in the direction intersecting the axial direction are approximately equal.

The mixed gas discharged from the nozzle 31H toward the bottom of the reactor 2 blows the silica sand upward to form a spouted bed, and uniformly stirs the rice husks supplied from the raw material supply mechanism 4. The angle θ is set in the range of 30° to 60°, preferably 40° to 50°, with 45° as the center. The diameter and number of each diffuser 31 are set according to the diameter of the lower part of the reactor 2. For example, if the diameter L1 of the lower part of the reactor 2 is in the range of 300 mm to 1800 mm, the diameter of the diffuser 31 can be selected in the range of 20A (27.2 mm) to 80A (89.1 mm), and the number can be selected in the range of 6 to 30.

As shown in Figures 3(a) and (b), the gas supply mechanism 3 (3B) for the gasification reaction is made up of a small number of diffuser tubes 31 with a large diameter, so that the rice husks supplied from the raw material supply mechanism 4 flow unevenly in any plane perpendicular to the axis of the reactor 2, resulting in a large stirring effect.

More specifically, the diffuser tube 31 has mixed gas ejection holes 31H facing in two directions inclined diagonally downward at an angle θ with respect to the horizontal direction, and ejection holes 31H facing vertically downward. The ejection holes 31H formed in each diffuser tube 31 are set so that the pitch L2 in the axial direction and in the direction intersecting the axial direction are approximately equal, and the pitch L3 between the diffuser tubes 31 is set so that L3 > L2.

The mixed gas discharged from the nozzle 31H toward the bottom of the reactor 2 blows the silica sand upward to form a spouted bed, and stirs the rice husks supplied from the raw material supply mechanism 4 by lifting them up. Because L3 is set to be greater than L2, the rice husks that are lifted upward by the mixed gas flow unevenly along a large circulation path that descends through the areas between the diffuser tubes 31 where the upward flow is weak, and are stirred significantly.

The angle θ is set in the range of 30° to 60°, preferably 40° to 50°, with 45° as the center. The diameter and number of each aeration pipe 31 are set according to the diameter of the lower part of the reactor 2. For example, if the diameter of the lower part of the reactor 2 is in the range of 300mm to 1800mm, the diameter of the aeration pipe 31 can be selected in the range of 40A (48.6mm) to 80A (89.1mm), and the number can be selected in the range of 3 to 6.

In other words, the gas supply mechanism 3 (3A, 3B) constitutes a fluidization state adjustment mechanism, and the fluidization state of the rice husks is adjusted depending on which of the gas supply mechanisms 3A and 3B is used, making it possible to adjust whether the reaction is mainly a combustion reaction or a gasification reaction. The gas supply mechanism 3 (3A, 3B) executes a fluidization state adjustment process that switches the fluidization state of the raw material through the entrained bed. Note that the values of L1, L2, and L3 mentioned above are examples and are not limited to the values shown.

In other words, the flow state adjustment mechanism is configured to be adjustable to either a first flow state in which the raw materials are stirred in a state where the distribution of the gas supply positions by the gas supply mechanism 3 is dense to mainly cause the raw materials to undergo a combustion reaction and the opportunities for contact with the gas are uniform, or a second flow state in which the distribution of the gas supply positions by the gas supply mechanism 3 is sparse to mainly cause the raw materials to undergo a gasification reaction and the raw materials are stirred in a state where the opportunities for contact with the gas are uneven.

In the first flow state, the distribution of the supply positions of the gas supplied from the gas supply mechanism 3 becomes dense, so that the gas is supplied evenly to the raw material, promoting a good combustion reaction, and in the second flow state, the distribution of the supply positions of the gas supplied from the gas supply mechanism 3 becomes sparse, so that there are regions where the raw material rises with the upward flow of gas and regions where the raw material falls without being supplied with gas, promoting a good gasification reaction.

In the first fluidization state, the distribution of the supply positions of the air supplied from the gas supply mechanism 3 in a plan view becomes dense, and the rice husks flow evenly in the fluidized bed and the space above it, providing a stable opportunity for contact with the air, promoting a good combustion reaction. In the second fluidization state, the distribution of the supply positions of the air supplied from the gas supply mechanism 3 in a plan view becomes sparse, creating areas where air is supplied and a large upward flow occurs over the rice husks, and areas where no air is supplied and a downward flow occurs over the rice husks, creating a stirring effect where the rice husks rise and fall unevenly in the fluidized bed and the space above it, promoting a good gasification reaction.

In the above explanation, an example was given of adjusting the distribution of gas supply positions to adjust the flow state, but in order to adjust the flow state, it is sufficient to adjust at least one of the total amount of gas, the supply positions, and the supply distribution, and it is also possible to adjust a combination of the total amount of gas, the supply positions, and the supply distribution.

Returning to FIG. 1, compressed air is supplied from a compressor or a blower fan to the air supply pipe 32 connected to the header pipe 30, and the amount of air supplied is adjusted by a valve 32V (which may be a damper) provided on the air supply pipe 32. In addition, superheated steam generated in a heat exchanger provided in the secondary combustion equipment 8 or superheated steam generated in the heat recovery mechanism 5, which is a heat exchanger provided in the reactor 2, is supplied to the steam supply pipe 33 connected to the header pipe 30, and the amount of air supplied is adjusted by a valve 33V (which may be a damper) provided on the steam supply pipe 33. Reference numeral 34 denotes a steam flow meter.

Valve 32V functions as an air ratio adjustment mechanism, and by adjusting the air ratio to the rice husks supplied from the raw material supply mechanism 4, it is possible to adjust the rice husks to either undergo a combustion reaction or a gasification reaction.

The air ratio adjustment mechanism adjusts the theoretical air ratio to the rice husks to either a first range where the theoretical air ratio is greater than 1 so that the rice husks are primarily subjected to a combustion reaction, or a second range where the theoretical air ratio is less than 1 so that the rice husks are primarily subjected to a gasification reaction, and the air ratio adjustment process is carried out by the air ratio adjustment mechanism.

By adjusting the air ratio to rice husks to a first range that is greater than the theoretical air ratio of 1, the rice husks can be effectively combusted, and by adjusting the air ratio to a second range that is less than the theoretical air ratio of 1, the rice husks can be effectively gasified.

The first range is preferably an air ratio of 1.3 or more and 1.5 or less. If the air ratio is less than 1.3, carbon components remain in the silica and high-quality white silica cannot be obtained, and if the air ratio is greater than 1.5, the amount of heat carried out by the excess air increases, the combustion temperature drops, and good combustion conditions cannot be maintained. In addition, the second range is preferably an air ratio of 0.2 or more and 0.5 or less. If the air ratio is less than 0.2, pyrolysis is not promoted, and if the air ratio is greater than 0.5, some of the carbon is burned and good black silica cannot be obtained.

When using oxygen-containing gas other than air, such as oxygen-enriched air, the ratio of the oxygen-containing gas to the raw material can be adjusted to a first range, in which the air ratio is converted to a value greater than the theoretical air ratio of 1, via the oxygen-containing gas ratio adjustment mechanism, to achieve a good combustion reaction of the rice husks as the raw material, and the ratio of the oxygen-containing gas to the raw material can be adjusted to a second range, in which the air ratio is converted to a value less than the theoretical air ratio of 1, to achieve a good gasification reaction of the rice husks as the raw material. When oxygen-enriched air is used, the amount of gas decreases, so the flow state of the raw material can be adjusted by adjusting the total amount of gas supplied from the gas supply mechanism.

Similarly, the first range is preferably 1.3 to 1.5, and the second range is preferably 0.2 to 0.5.

Figures 4(a) and (b) show a manufacturing apparatus 1 and a gas supply mechanism 3A that obtain white amorphous silica by adjusting the heat treatment state adjustment mechanism to mainly cause the rice husks to undergo a combustion reaction. The opening of the valve 32V is adjusted by the control device (see Figure 6) so that the air ratio is in the range of 1.3 to 1.5, and the temperature at the narrowing part of the reactor 2 is adjusted to the range of 500°C to 600°C. The amount of air supplied from the upper air supply mechanism 6 via the valve 6V and the amount of heat recovered by the heat recovery mechanism 5 via the valve 5V are adjusted so that the temperature at the expanding part is in the range of 750°C to 800°C. For this purpose, the outputs of the first and second temperature sensors TH1 and TH2 installed downstream and upstream of the heat recovery mechanism 5 are input to the control device.

The combustion reaction at this time is expressed by the following reaction formula.
C + _O2 → _CO2
CO+(1/2)・O ₂ → CO ₂

Figures 5(a) and (b) show the manufacturing device 1 and gas supply mechanism 3B, which are adjusted by the heat treatment state adjustment mechanism to mainly gasify the rice husks and obtain black amorphous silica. A control device (not shown) adjusts the opening of valve 32V so that the air ratio is in the range of 0.2 to 0.5, and adjusts the amount of air supplied from the upper air supply mechanism 6 via valve 6V so that the temperature at the narrowing part of the reactor 2 is in the range of 500°C to 600°C and the temperature at the expanding part is in the range of 700°C to 750°C. The steam supplied to the steam supply pipe 33 at this time is superheated steam generated in a heat exchanger provided in the secondary combustion equipment 8.

The gasification reaction at this time is mainly a water-gas reaction, and is represented by the following reaction formula:

The water-gas reaction is an endothermic reaction in which carbon monoxide CO and hydrogen _H2 are produced from solid carbon C (biomass) and water vapor _H2O in a high-temperature environment of 500°C or higher, as shown in the following formula. By supplying a small amount of air in addition to steam to the reactor 2, the necessary reaction heat is provided by the combustion of a portion of the rice husks, and the temperature inside the furnace is maintained in a high-temperature environment of 500°C or higher.
C+ _H2O → CO+ _H2

In this embodiment, superheated steam at a temperature of 120° C. to 160° C. is supplied from the steam supply pipe 33 at a pressure of 1 MPa or less.
The steam supplied to the reactor 2 is used for initial heating of the raw material, activation including an increase in the specific surface area of silica due to the water-gas reaction and combustion reaction, and for suppressing an abnormal increase in the atmospheric temperature in the reactor due to the subsequent combustion reaction, and the amount supplied is appropriately adjusted by the valve 33V. When the water-gas reaction is mainly performed, the ratio of water steam is increased to promote activation, and the minimum amount of oxygen-containing gas that can maintain the temperature in the reactor is supplied. When the combustion reaction is mainly performed, the ratio of oxygen-containing gas is increased to promote the combustion reaction, and the water steam has the effect of suppressing the generation of a local high-temperature field due to the combustion reaction.

In this embodiment, rice husks are used as the biomass. Rice husks are approximately 70% carbohydrates such as cellulose, hemicellulose, and lignin, approximately 15-20% silica, and the majority of the remainder is water, with a small amount of alkaline impurities. This invention is suitable for use when recycling such silica-containing biomass as a resource. Therefore, the application of this invention is not limited to rice husks, and it is also possible to use biomass derived from siliceous plants such as rice straw, wheat straw, bamboo, corn, sugar cane, thin grass, and horsetail.

That is, the above-mentioned amorphous silica manufacturing apparatus 1 realizes a raw material supplying process in which raw material is supplied to the reactor by the raw material supply mechanism, a gas supplying process in which steam and an oxygen-containing gas are supplied from the bottom of the reactor where the raw material is retained by the gas supplying mechanism, and a method for manufacturing amorphous silica in which amorphous silica is produced by heat-treating the raw material while contacting it with the steam and the oxygen-containing gas.

Then, an oxygen-containing gas ratio adjustment process (air ratio adjustment process) is carried out by an oxygen-containing gas ratio adjustment mechanism (air ratio adjustment mechanism) provided in the heat treatment condition adjustment mechanism, and the proportion of carbon contained in the amorphous silica produced is adjusted by adjusting the ratio of the oxygen-containing gas supplied in the gas supply process to the supply amount of the raw material.

In addition, a flow condition adjustment process is carried out in which the flow condition of the raw material is adjusted by adjusting at least one of the total amount, supply position, and supply distribution of gas supplied in the gas supply process using the flow condition adjustment mechanism.

Furthermore, the heat treatment state adjustment mechanism includes a temperature adjustment mechanism that maintains the combustion temperature in the internal space of the reactor 2 at a predetermined temperature or lower, specifically at approximately 800°C or lower, when the rice husks are subjected to a combustion reaction. The heat recovery mechanism 5 provided in the reactor 2 functions as the temperature adjustment mechanism. In other words, when the raw material is subjected to a combustion reaction, the heat recovery mechanism 5 executes a temperature adjustment process that maintains the combustion temperature in the internal space of the reactor 2 at a predetermined temperature or lower that inhibits the crystallization of amorphous silica.

If the temperature inside the reactor 2 exceeds the above-mentioned predetermined temperature due to the combustion reaction of rice husks, which is an exothermic reaction, there is a risk that amorphous silica will crystallize and produce cristobalite, which is carcinogenic. Even in such a case, the heat recovery mechanism 5 adjusts the combustion temperature to a predetermined temperature or lower, preventing the crystallization of amorphous silica and making it possible to obtain amorphous silica stably. When the gasification reaction of rice husks mainly occurs inside the reactor 2, it is an endothermic reaction, so the combustion temperature in the internal space of the reactor 2 may be kept below the predetermined temperature even without the heat recovery mechanism 5, but if the accompanying combustion reaction causes the temperature to exceed the above-mentioned predetermined temperature, it is possible to provide the heat recovery mechanism 5.

Figure 6 shows the configuration of the control device C that controls the amorphous silica manufacturing apparatus 1. The control device C receives inputs of sensor values such as the first temperature sensor TH1, the second temperature sensor TH2, the steam flow meter 34, and the steam temperature sensor TH3 that detects the temperature of the steam output from the boiler provided in the secondary combustion equipment 8, as well as an identification signal indicating whether the heat treatment state adjusted by the heat treatment state adjustment mechanism is one that mainly promotes a combustion reaction or one that mainly promotes a gasification reaction.

When the heat treatment state adjusted by the heat treatment state adjustment mechanism is mainly a combustion reaction, the control device C adjusts the aperture of valve 32V based on the value of the second temperature sensor TH2 so that the combustion temperature of the narrowing diameter part of the reactor 2 is between 500°C and 600°C, adjusts the aperture of valve 6V to adjust the amount of air supplied from the upper air supply mechanism 6, and also adjusts the aperture of valve 33V. Furthermore, based on the value of the first temperature sensor TH1, it adjusts the aperture of valve 5V to adjust the flow rate of boiler water supplied to the heat recovery mechanism 5 so that the combustion temperature of the expanding diameter part of the reactor 2 is between 750°C and 800°C, in other words, a temperature lower than the phase transition temperature range where amorphous silica crystallizes.

For example, the temperature of the reactor 2 can be lowered by controlling the amount of air supplied from the air supply mechanism to be reduced, and the temperature of the expanded diameter section of the reactor 2 can be lowered by controlling the flow rate of the boiler water to be increased, so that the combustion temperature can be adjusted so as not to exceed a predetermined temperature.

When the heat treatment state adjusted by the heat treatment state adjustment mechanism is mainly a gasification reaction, the control device C adjusts the aperture of valve 32V and the amount of air supplied from the upper air supply mechanism 6 so that the combustion temperature of the narrowed diameter section of the reactor 2 is between 500°C and 600°C based on the value of the second temperature sensor TH2, and so that the combustion temperature of the expanded diameter section is between 700°C and 750°C based on the value of the first temperature sensor TH1, and also adjusts the aperture of valve 33V.

As described above, the temperature of the reactor 2 can be lowered by controlling the amount of air supplied from the air supply mechanism to be reduced, and the temperature of the expanded diameter section of the reactor 2 can be lowered by controlling the flow rate of the boiler water to be increased, so that the combustion temperature can be adjusted so as not to exceed a predetermined temperature. In this case, if the combustion temperature of the expanded diameter section does not exceed 800°C, there is no need to adjust the flow rate of the boiler water supplied to the heat recovery mechanism 5. The second temperature sensor TH2 may be located in any position where the temperature of the contracted diameter section can be monitored, and may be installed in either the contracted diameter section or the expanded diameter section, as long as it is upstream of the heat recovery mechanism 5.

In Figures 1, 4, and 5, an upper air supply mechanism 6 for adjusting the combustion state in the space above the entrained bed 9 is described, in which an air supply pipe is inserted from the side wall near the narrowing portion of the reactor 2, and an air supply nozzle is provided at the tip of the air supply pipe to supply air downward from the center of the reactor 2. However, the configuration of the upper air supply mechanism 6 is not limited to this example, and can be configured appropriately depending on the size of the reactor 2, etc.

For example, as shown in FIG. 7(a), an air supply pipe with an air supply nozzle at its tip may be installed to hang down from the top of the reactor 2, or as shown in FIG. 7(b), multiple air supply nozzles may be provided near the narrowed portion of the reactor 2. For example, multiple air supply nozzles may be evenly arranged on concentric circles in a plan view.

In the above-described embodiment, an example was described in which the gas supply mechanism 3 is configured to supply a mixture of water vapor and air, which is an example of an oxygen-containing gas, but as long as it has the above-described oxygen-containing gas ratio adjustment mechanism and flow state adjustment mechanism, it may be configured to supply water vapor and oxygen-containing gas separately.

In the above embodiment, a spouted bed is formed inside the reactor 2 to heat-treat the raw materials, and the raw materials are stirred and fluidized together with the silica sand in the spouted bed. However, a fluidized bed may be formed near the bottom of the reactor 2, and the raw materials are stirred and fluidized together with the silica sand in the fluidized bed. In either case, in order to bring the raw materials into good contact with the gas in the spouted bed or fluidized bed, it is preferable that the particle size of the silica sand is in the range of 0.05 mm to 2 mm. Also, if the raw materials can be heat-treated while being in contact with the gas inside the reactor 2, it is not essential to put silica sand inside the reactor 2.

The above-mentioned embodiment merely describes one specific example of the amorphous silica manufacturing apparatus and manufacturing apparatus according to the present invention, and the scope of the present invention is not limited by the description. It goes without saying that the specific configuration of each part can be appropriately modified and designed within the scope of the effect of the present invention.

Reference Signs List 1: Amorphous silica manufacturing apparatus 2: Reactor 3: Gas supply mechanism 30: Header pipe 31: Air diffuser 32: Air supply pipe 32V: Valve 33: Steam supply pipe 33V: Valve 4: Raw material supply mechanism 5: Heat recovery mechanism 6: Upper air supply mechanism 7: Cyclone 8: Secondary combustion equipment 9: Spouted bed 10: Exhaust pipe A: Heat treatment state adjustment mechanism

Claims (6)

An apparatus for producing amorphous silica, comprising: a reactor; a raw material supply mechanism for supplying biomass derived from a silicic acid plant as a raw material to the reactor; a gas supply mechanism for supplying steam and an oxygen-containing gas from a bottom of the reactor where the raw material is retained; and a heat treatment of the raw material while contacting it with the steam and the oxygen-containing gas to produce amorphous silica,
a temperature control mechanism for maintaining the temperature of the inner space of the reactor at or below a predetermined temperature that inhibits crystallization of the amorphous silica;
The temperature control mechanism is composed of a heat exchanger that uses water as a heat medium, and an upper air supply mechanism that supplies air between the gas supply mechanism and the heat exchanger to combust the raw material , and the water vapor generated in the heat exchanger is supplied to the reaction furnace via the gas supply mechanism. The amorphous silica manufacturing apparatus according to claim 1, further comprising an oxygen-containing gas ratio adjustment mechanism that adjusts the ratio of the oxygen-containing gas to the amount of the raw material supplied to a range of 1.3 to 1.5 in terms of air ratio. 3. The apparatus for producing amorphous silica according to claim 1, wherein the temperature control mechanism includes temperature sensors downstream of the heat exchanger provided in the reactor and between the heat exchanger and the upper air supply mechanism . A method for producing amorphous silica, comprising: a raw material supplying step of supplying a raw material comprising biomass derived from a silicic acid plant to a reactor by a raw material supplying mechanism; a gas supplying step of supplying steam and an oxygen-containing gas from a bottom of the reactor where the raw material is retained by a gas supplying mechanism; and a heat treatment of the raw material while contacting it with the steam and the oxygen-containing gas to produce amorphous silica,
A temperature control step of maintaining the temperature of the inner space of the reactor at or below a predetermined temperature that inhibits crystallization of the amorphous silica,
A method for producing amorphous silica, wherein the temperature adjustment step is performed by a heat exchanger using water as a heat medium , and an upper air supply mechanism that supplies air between the gas supply mechanism and the heat exchanger to combust the raw material , and the water vapor generated in the heat exchanger is supplied to the reactor via the gas supply mechanism. The method for producing amorphous silica according to claim 4, further comprising an oxygen-containing gas ratio adjustment step for adjusting the ratio of the oxygen-containing gas to the raw material to a range of 1.3 to 1.5 in terms of air ratio. 6. The apparatus for producing amorphous silica according to claim 4 or 5, wherein the temperature adjustment process is performed based on the value of a temperature sensor disposed downstream of the heat exchanger provided in the reactor and between the heat exchanger and the upper air supply mechanism .

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