Method for producing amorphous silica and apparatus for producing amorphous silica

Abstract

To provide a method for producing amorphous silica, capable of stably producing amorphous silica while maintaining heat exchange performance by a heat exchanger.SOLUTION: A method for producing amorphous silica, comprising a heat treatment step of heat-treating a biomass raw material derived from a silicate plant by bringing the biomass raw material into contact with at least an oxygen-containing gas in a reaction furnace to produce amorphous silica, a heat exchange step of passing an exhaust gas after the heat treatment step containing the amorphous silica discharged from the reaction furnace through a heat exchanger to lower a temperature of the exhaust gas, and a recovery step of separating and recovering the amorphous silica contained in the exhaust gas by a solid-gas separation device after passing through the heat exchanger.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing amorphous silica from biomass derived from silica plants, and an apparatus for producing amorphous silica. [Background technology]

[0002] Patent Document 1 discloses a method for producing amorphous silica, which uses biomass derived from silicic acid plants as a raw material to obtain amorphous silica with different purities depending on the application.

[0003] The method for producing amorphous silica includes a raw material supply step of supplying raw materials to a reactor using a raw material supply mechanism, a gas supply step of supplying water vapor and an oxygen-containing gas using a gas supply mechanism from the bottom of the reactor where the raw materials remain, and a heat treatment step of producing amorphous silica by heat-treating the raw materials while bringing them into contact with the water vapor and the oxygen-containing gas.

[0004] The system includes a recovery step in which amorphous silica is recovered from exhaust gas discharged from the reactor together with the amorphous silica using a cyclone solid-gas separator, and a secondary combustion step in which the exhaust gas that has been subjected to the recovery step is subjected to secondary combustion in a secondary combustion facility. Furthermore, the system further includes a heat exchange step in which air as an oxygen-containing gas is preheated using a heat exchanger after the secondary combustion step, and a dust removal step in which soot and dust are recovered using a bag filter solid-gas separator, and the exhaust gas is treated to be released into the atmosphere after the dust removal step. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2023-098018 Summary of the Invention [Problem to be solved by the invention]

[0006] In the conventional method for producing amorphous silica described above, the amorphous silica-containing exhaust gas produced in the heat treatment step is first recovered as a recyclable resource using a cyclone in the recovery step, and then the heat exchange step is carried out.

[0007] However, amorphous silica contained in the high-temperature exhaust gas that was not completely recovered by the cyclone adheres to and accumulates on the inner walls of the heat exchange tubes in the heat exchanger used in the heat exchange process, reducing heat exchange performance and potentially preventing sufficient heat exchange between the heated medium.

[0008] In this case, the outlet temperature of the heat exchanger does not drop sufficiently, so the oxygen-containing gas to be heated cannot be sufficiently preheated, and this also interferes with the operation of the induced draft fan installed downstream of the heat exchanger.

[0009] Furthermore, since the amorphous silica recovered by the cyclone is hot, there was a concern that it would need to be cooled for handling.

[0010] An object of the present invention is to provide a method and an apparatus for producing amorphous silica that can stably produce amorphous silica while maintaining the heat exchange performance of a heat exchanger. [Means for solving the problem]

[0011] In order to achieve the above-mentioned object, a first characteristic feature of the method for producing amorphous silica according to the present invention is that it comprises: a heat treatment step in which a biomass raw material derived from a silica plant is heat-treated by contacting it with at least an oxygen-containing gas in a reactor to produce amorphous silica; a heat exchange step in which the exhaust gas after the heat treatment step, which contains the amorphous silica and is discharged from the reactor, is passed through a heat exchanger to lower the temperature of the exhaust gas; and a recovery step in which the amorphous silica contained in the exhaust gas after passing through the heat exchanger is separated and recovered using a solid-gas separator.

[0012] The exhaust gas discharged from the reactor together with the amorphous silica produced in the heat treatment process is first introduced into a heat exchanger to carry out the heat exchange process. The amorphous silica contained in the exhaust gas introduced into the heat exchange tubes of the heat exchanger collides with the inner wall as it flows down the heat exchange tube together with the exhaust gas, causing a cleaning effect that removes deposits from the inner wall, allowing the inner wall to be kept clean and maintaining good heat exchange performance. Therefore, the temperature of the amorphous silica separated by the solid-gas separator is also reduced, and it can be easily handled in this state without taking any special thermal measures.

[0013] The second characteristic configuration is that, in addition to the first characteristic configuration described above, the heat exchange step employs a multi-tube heat exchanger as the heat exchanger, and is a step in which the exhaust gas containing the amorphous silica is passed through the tubes of the multi-tube heat exchanger to exchange heat with the medium to be heated.

[0014] The heat exchanger used in the heat exchange step is preferably a multi-tube heat exchanger, and even if the heat exchange tubes are thin tubes, amorphous silica does not adhere to and accumulate on the inner walls, allowing for efficient heat exchange.

[0015] The third characteristic configuration is that, in addition to the second characteristic configuration described above, the recovery step is a step in which a filtration-type separation device or a cyclone is used as the solid-gas separation device, and the amorphous silica contained in the exhaust gas is recovered by the filtration-type separation device or the cyclone.

[0016] The exhaust gas, whose temperature has been reduced through the heat exchange process, is then introduced into a filtration-type separator or cyclone, where the amorphous silica, whose temperature has been reduced and which is now easier to handle, is separated and recovered.

[0017] A fourth characteristic feature of the present invention is that, in addition to the third characteristic feature described above, the filtration type separation device is a bag filter.

[0018] A bag filter can be suitably used as the filtration type separation device.

[0019] The fifth characteristic configuration is that, in addition to any one of the first to fourth characteristic configurations described above, in the heat treatment step, the heat treatment temperature is controlled so that the temperature of the exhaust gas discharged from the reaction furnace is 600 to 800°C.

[0020] If the heat treatment temperature exceeds 800°C, there is a risk that amorphous silica will crystallize and produce cristobalite, which is carcinogenic. However, by controlling the heat treatment temperature in the reactor so that the temperature of the exhaust gas discharged from the reactor is 600 to 800°C, it is possible to prevent the crystallization of amorphous silica and obtain amorphous silica stably. Furthermore, the exhaust gas discharged from the reactor is quickly cooled in the heat exchange process, which prevents the crystallization of amorphous silica and allows amorphous silica to be obtained more stably.

[0021] A sixth characteristic feature of the present invention is that, in addition to the fifth characteristic feature described above, the heat treatment temperature in the heat treatment step is controlled by supplying water or steam into the reactor.

[0022] By adjusting the amount and temperature of water or steam supplied into the reactor, the heat treatment temperature in the reactor is appropriately adjusted so that the temperature of the exhaust gas discharged from the reactor is 600 to 800°C.

[0023] The characteristic configuration of the amorphous silica production apparatus according to the present invention is that it comprises a raw material supply mechanism that supplies biomass derived from a silica plant as a raw material, and a gas supply mechanism that supplies at least an oxygen-containing gas to the raw material, a reactor that produces amorphous silica by heat-treating the raw material while bringing it into contact with the oxygen-containing gas, a heat exchanger that reduces the temperature of the exhaust gas containing the amorphous silica discharged from the reactor by heat exchange with a heated medium, and a solid-gas separation device that separates and recovers the amorphous silica contained in the exhaust gas after it has passed through the heat exchanger. [Effects of the Invention]

[0024] As described above, the present invention provides a method and an apparatus for producing amorphous silica that can stably produce amorphous silica while maintaining the heat exchange performance of a heat exchanger. It is now possible to do this. [Brief explanation of the drawings]

[0025] [Figure 1] An explanatory diagram showing a method for producing amorphous silica according to the present invention. [Figure 2] An explanatory diagram showing an example of an apparatus for producing amorphous silica according to the present invention. [Figure 3] (a) is a plan view of the gas supply mechanism, and (b) is a cross-sectional view of the main part of the gas supply mechanism. [Figure 4] (a) is a longitudinal cross-sectional view of the heat exchanger, and (b) is a cross-sectional view of line BB in (a). DETAILED DESCRIPTION OF THE INVENTION

[0026] An example of a method for producing amorphous silica and an apparatus for producing amorphous silica according to the present invention will be described below. [Method for producing amorphous silica] As shown in Figure 1, the method for producing amorphous silica includes a heat treatment step in which a biomass raw material derived from a silica plant is heat-treated in a reactor by contacting it with at least an oxygen-containing gas to produce amorphous silica, a heat exchange step in which the exhaust gas containing amorphous silica discharged from the reactor after the heat treatment step is passed through a heat exchanger to lower the temperature of the exhaust gas, and a recovery step in which the amorphous silica contained in the exhaust gas after passing through the heat exchanger is separated and recovered using a solid-gas separator. In this embodiment, air is used as the oxygen-containing gas, but other gases such as oxygen-enriched gases can also be used.

[0027] The heat exchange process is carried out by introducing the exhaust gas discharged from the reactor together with the amorphous silica produced in the heat treatment process into the heat exchange tubes provided in the heat exchanger. During the heat exchange process, the amorphous silica contained in the exhaust gas may adhere to the inner wall of the heat exchange tube. Even in such cases, as other amorphous silica flows down the heat exchange tube together with the exhaust gas, it collides with the inner wall one after another, thereby working as a cleaning agent to remove the deposits from the inner wall. Therefore, by maintaining the inner wall in a clean state, good heat exchange performance is maintained and long-term maintenance-free operation can be achieved. The amorphous silica separated by the solid-gas separator after heat exchange has also cooled, making it easy to handle in that state.

[0028] In the heat exchange process, a multi-tubular heat exchanger (shell-and-tube heat exchanger) is preferably used as the heat exchanger, and the exhaust gas containing amorphous silica is preferably passed through the tubes of the multi-tubular heat exchanger to exchange heat with the medium to be heated. Even if the heat exchange tubes are thin, amorphous silica does not adhere to or accumulate on the inner walls, allowing for efficient heat exchange. In this embodiment, air compressed by a compressor or the like is used as the medium to be heated, and preheated air heated in the heat exchanger is supplied to the heat treatment process. In addition to the multi-tubular heat exchanger, it is also possible to use a type of heat exchanger that has, for example, a coiled heat exchange tube in a casing, supplies exhaust gas to the heat exchange tube, and supplies the medium to be heated to the casing to perform heat exchange. Alternatively, a non-heated medium may be passed through the tubes of the multi-tubular heat exchanger instead of exhaust gas.

[0029] In the recovery process, a filtration separator or a cyclone is used as the solid-gas separator, and the amorphous silica contained in the exhaust gas is recovered by the filtration separator or the cyclone. The exhaust gas, whose temperature has been reduced through the heat exchange process, is introduced into the filtration separator or the cyclone, whereby the amorphous silica, whose temperature has been reduced and which is now easier to handle, is separated and recovered. In particular, it is preferable to use a bag filter as the filtration separator, as this allows for reliable recovery of not only coarse amorphous silica particles but also fine amorphous silica particles.

[0030] Furthermore, it is preferable to control the heat treatment temperature so that the temperature of the exhaust gas discharged from the reactor is 600 to 800°C.

[0031] If the heat treatment temperature exceeds 800°C, there is a risk that amorphous silica will crystallize and produce cristobalite, which is carcinogenic. However, by controlling the heat treatment temperature in the reactor so that the temperature of the exhaust gas discharged from the reactor is 600 to 800°C, it is possible to prevent the crystallization of amorphous silica and obtain amorphous silica stably. Furthermore, the exhaust gas discharged from the reactor is quickly cooled in the heat exchange process, which prevents the crystallization of amorphous silica and allows amorphous silica to be obtained more stably.

[0032] The heat treatment temperature in the heat treatment step is preferably controlled by supplying water or steam into the reactor.

[0033] By adjusting the amount and temperature of water or steam supplied to the reactor, the heat treatment temperature in the reactor can be appropriately adjusted so that the temperature of the exhaust gas discharged from the reactor is 600 to 800°C.

[0034] [Configuration of amorphous silica manufacturing equipment] 2 shows one embodiment of an amorphous silica production apparatus 1. The amorphous silica production apparatus 1 includes a reactor 2, a raw material supply mechanism 6 that supplies biomass derived from silica plants as a raw material to the reactor 2, and a gas supply mechanism 3 that supplies a mixed gas of water vapor and air, which is an example of an oxygen-containing gas, from below the reactor 2.

[0035] The reactor 2 includes a first cylindrical section 2A with a bottom, a second cylindrical section 2C located above the first cylindrical section 2A and having a larger diameter than the first cylindrical section 2A, and an expanded-diameter cylindrical section 2B connecting the upper end of the first cylindrical section 2A to the lower end of the second cylindrical section 2C and gradually expanding in diameter from the first cylindrical section 2A to the second cylindrical section 2C. An exhaust port 2E is formed at the top 2D of the second cylindrical section 2C. The first cylindrical section 2A, the expanded-diameter cylindrical section 2B, and the second cylindrical section 2C have circular cross sections and are arranged concentrically in a plan view. The inner diameter of the first cylindrical section 2A is set to approximately 75% of the inner diameter of the second cylindrical section 2C. The dimensions of each section of the reactor 2, including its diameter and height, are not particularly limited and can be set appropriately based on the daily biomass processing volume, the flow rate of combustion gas within the furnace, and other factors. The cross-sectional shape of the reactor 2 is not limited to a perfect circle.

[0036] A fluidized medium layer 20 is provided below the first cylindrical portion 2A, and a gas supply mechanism 3, a gas burner 4, a lower water supply mechanism 5, and a raw material supply mechanism 6 are respectively provided in the first cylindrical portion 2A, and an upper water supply mechanism 8 is provided in the second cylindrical portion 2C. Note that the upper water supply mechanism 8 may be provided in any of the first cylindrical portion 2A, the enlarged diameter cylindrical portion 2B, or the second cylindrical portion 2C as long as its water supply portion is located above the water supply portion of the lower water supply mechanism 5. Furthermore, the provision of the lower water supply mechanism 5 is not essential, and the upper water supply mechanism 8 may also perform the function of the lower water supply mechanism 5.

[0037] The bed 20 is filled with silica sand having a small particle size, which serves as a bed material for the biomass. In this embodiment, the silica sand is filled so that the top surface of the bed 20 is stationary and located above the installation height of the air diffuser 34 provided in the gas supply mechanism 3. When the reactor 2 is started up, the silica sand is fluidized by the upward flow of air jetted from the air diffuser 34 toward the bottom, forming an entrained bed 20A in the first cylindrical section 2A. The gas burner 4, which serves as a supporting burner, is ignited, raising the temperature of the entrained bed 20A. When the temperature of the entrained bed 20A reaches the self-combustion temperature of the biomass (300 to 400°C when the biomass is rice husks), the gas burner 4 is extinguished, and the biomass is dropped and supplied from the raw material supply mechanism 6 onto the entrained bed 20A.

[0038] The raw material supply mechanism 6 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 of the first cylindrical section 2A below the expanded diameter cylindrical section 2B of the reactor 2. Although not shown, a hopper equipped with a quantitative raw material supply mechanism is provided at the base end side of the casing.

[0039] The biomass filled in the hopper is supplied in a fixed amount to a screw conveyor mechanism via a material fixed-rate supply mechanism installed at the bottom of the hopper, and then transported compactly inside the casing by screw blades before being fed into reactor 2. The biomass used is the large amount of rice husks that are generated after husking unhulled rice produced by farmers.

[0040] 3(a) and (b) show an example of a gas supply mechanism 3. The gas supply mechanism 3 includes a header pipe 32 arranged around the lower periphery of the first cylindrical portion 2A of the reactor 2, and a plurality of aeration pipes 34 with a circular cross section that are connected to the header pipe 32 in a parallel orientation. An air supply pipe 30A is connected to the header pipe 32, and compressed air is supplied from a compressor or a blower fan 30. A flow rate adjustment valve 31 is provided in the air supply pipe 30A so that the amount of air supplied can be adjusted. Although air is used as the oxygen-containing gas, it is not limited to air, and an oxygen-enriched gas or the like can also be used.

[0041] Each of the air diffuser pipes 34 is supported by an attachment 33 having an arc-shaped cross section that fits along the lower peripheral wall of the first cylindrical portion 2A. The attachment 33 is formed in a shape that covers an arc-shaped notch formed in the lower side wall of the first cylindrical portion 2A, and by fixing the attachment 33 to the side wall of the reactor 2 with the tip side of each of the air diffuser pipes 34 inserted into the reactor 2, the multiple air diffuser pipes 34 are fixed to the first cylindrical portion 2A in a parallel orientation.

[0042] A steam supply mechanism 5A that supplies water vapor may be further provided in the gas supply mechanism 3. A steam supply pipe 50A that guides water vapor is connected to the header pipe 32, and a flow rate adjustment valve 51A and a flow meter F are provided on the steam supply pipe 50A, thereby making it possible to adjust the amount of steam supplied.

[0043] The steam supplied from the steam supply pipe 50A to the reactor 2 can be used for initial heating of the raw materials, activation including increasing the specific surface area of ​​silica due to the water-gas reaction and combustion reaction, and suppressing an abnormal increase in the atmospheric temperature inside the reactor due to the subsequent combustion reaction, and the supply amount is appropriately adjusted by the valve 51A. In this embodiment, superheated steam at a temperature of 120°C to 160°C is supplied at a pressure of 1 MPa or less.

[0044] In the entrained bed 20A, the high-temperature flowing silica sand and biomass are stirred and mixed, and the temperature rises due to a combustion reaction in which the carbon components contained in the biomass are burned in the entrained bed 20A and the space above it by air supplied from the gas supply mechanism 3. C+O2→ CO2

[0045] At this time, an appropriate amount of water is sprayed toward the entrained bed 20A from the upper water supply mechanism 8 and / or the lower water supply mechanism 5, thereby adjusting the temperature of the entrained bed 20A to approximately 600 to 670°C, and the space temperature in the first cylindrical section 2A, where the biomass stirred in the entrained bed 20A is mainly gasified and burned, is adjusted to approximately 700 to 800°C, which is lower than the crystallization temperature of silica. Then, water vapor is supplied to the biomass by vaporization, causing a water-gas reaction.

[0046] As shown in the following equation, the water-gas reaction and water-gas shift reaction of biomass that occur between high-temperature steam and carbon promotes the gasification reaction of biomass. C+H2O → CO+H2 (water-gas reaction) C + 2H2O → CO2 + 2H2 (water-gas shift reaction) The water-gas reaction is an endothermic reaction, and the heat generated by the combustion reaction described above serves as the heat source for the water-gas reaction.

[0047] The biomass is heated while flowing with the bed material in the entrained bed 20A, and gasification and combustion occur in the entrained bed 20A and the space above it. Unburned biomass and combustion residues rise within the furnace along with the combustion gas. The speed of the combustion gas that rises through the enlarged-diameter tubular section 2B to the second tubular section 2C, which is larger in diameter than the first tubular section 2A, is effectively suppressed, allowing the unburned biomass to descend within the furnace under its own weight and further gasification and combustion, while ensuring sufficient reaction time for the carbon monoxide contained in the combustion gas rising through the second tubular section 2C. The temperature is adjusted to 650–720°C in the enlarged-diameter tubular section 2B and 700–730°C in the second tubular section 2C, so that the carbon monoxide concentration in the combustion exhaust gas is 100 ppm or less.

[0048] By adjusting the heat treatment conditions of the raw material supplied to reactor 2, it is possible to switch between mainly subjecting the raw material to a combustion reaction or mainly subjecting the raw material to a water-gas reaction, thereby adjusting the proportion of carbon contained in the amorphous silica produced.

[0049] For example, by adjusting the amount of air supplied from the gas supply mechanism 3, it is possible to adjust the balance between the water-gas reaction, which is an endothermic reaction, and the combustion reaction, which is an exothermic reaction.

[0050] The fluidization state of the raw material in the entrained bed 20A can be adjusted to either a static or dynamic fluidization state by varying the number and diameter of the diffuser pipes 34 constituting the gas supply mechanism 3 and the number and diameter of the diffuser holes formed in each diffuser pipe 34. If the fluidization state is steady and without local fluctuations, combustion reactions occur primarily, yielding highly pure amorphous white silica, whereas if the fluidization state is dynamic, water-gas reactions occur primarily, yielding black silica containing residual impurities such as carbon contained in the raw material.

[0051] At the same time, white silica can be obtained by adjusting the ratio of the amount of air supplied from the gas supply mechanism 3 to the amount of raw material supplied to a predetermined air ratio higher than the theoretical air ratio, and black silica can be obtained by adjusting the ratio to a predetermined air ratio lower than the theoretical air ratio.

[0052] In other words, a higher proportion of the water-gas reaction produces black silica with a high carbon content, while a higher proportion of the combustion reaction produces white silica with a low carbon content. By adjusting the amount of air and / or water supplied, the amorphous silica can be gasified and combusted at a temperature lower than the phase transition temperature at which it crystallizes, thereby avoiding the production of harmful substances such as cristobalite.

[0053] Specifically, a control unit is provided that controls the amount of steam supplied from steam supply pipe 50A, the amount of air supplied from air supply pipe 30A, the amount of water supplied from water supply mechanisms 5 and 8, etc., and the amount of steam supplied is adjusted by valve 51A based on the value of flow meter F, the air ratio is adjusted by valve 31, and water supply mechanisms 5 and 8 are controlled based on the value of temperature sensor TH1 so that the desired amorphous silica is obtained, in other words, so that the heat treatment temperature in reactor 2 falls within the range of 600 to 800°C.

[0054] When most of the carbon components contained in biomass are burned, silica, which is the main component of the combustion residue, takes on a white color, and when the carbon components contained in biomass remain, silica, which is the main component of the combustion residue, takes on a black color.

[0055] White silica is effectively used in industrial materials such as white cosmetic ingredients, adsorbents, and additives for white paints and resins, as well as agricultural materials such as fertilizers for adding silica to crops. Black silica is effectively used in industrial materials such as black cosmetic ingredients, adsorbents, and additives for black paints and resins, as well as additives for tires, as well as agricultural materials such as fertilizers for adding silica and carbon to crops.

[0056] In this specification, white silica refers to amorphous silica in which the carbon content is less than 5% by weight and which has a white or whitish appearance, and black silica refers to amorphous silica in which the carbon content is more than 5% by weight and which has a black or blackish appearance.

[0057] The exhaust gas containing amorphous silica discharged from the exhaust pipe 10 is heat exchanged with preheated air, which is a heating medium, in the heat exchanger 7, and after being cooled, is led to the solid-gas separator 11 where the amorphous silica is recovered, and the exhaust gas from which the amorphous silica has been separated is released into the atmosphere. The air preheated in the heat exchanger 7 is supplied to the gas supply mechanism 3.

[0058] 4(a) and (b) show a multi-tube heat exchanger 7 as an example of the heat exchanger 7. As shown in FIG. The heat exchanger 7 comprises a cylindrical casing 70 with a circular cross section and equipped with an air inlet section 7A and an air outlet section 7B which are the heated medium, an upper tube plate 7U and a lower tube plate 7L which are welded to the upper end side and the lower end side of the cylindrical casing 70, respectively, and a plurality of heat transfer tubes 71 which are supported by the upper tube plate 7U and the lower tube plate 7L and are arranged in a vertical position in the cylindrical casing 70, through which the exhaust gas flows.

[0059] The upper end of the heat transfer tube 71 is slidably held in a sliding portion inserted into a guide tube 72 welded to the upper tube plate 7U, and the other end of the heat transfer tube 71 is supported by welding to the lower tube plate 7L.

[0060] An exhaust gas inlet header 73 having an exhaust gas inlet 7C for allowing exhaust gas to flow into the heat transfer tubes 71 is provided at the upper end of the cylindrical casing 70, and an exhaust gas outlet header 74 having an exhaust gas outlet 7D for collecting and discharging exhaust gas that has passed through the heat transfer tubes 71 is provided at the lower end.

[0061] An upper jacket section 75, whose internal space is divided into upper and lower sections, is provided directly below the exhaust gas inlet header section 73, and a cooling air inlet 7G is formed in the space above the upper jacket section 75 to supply cooling air, and an air outlet 7F is formed in the space below the upper jacket section 75 to allow air to flow out after heat exchange. In addition, a lower jacket section 76 is provided directly above the exhaust gas outlet header section 74, and an air inlet 7E is formed in the lower jacket section 76 to supply preheating air.

[0062] A plurality of baffle plates 7P are arranged alternately inside the cylindrical casing 70 along the longitudinal direction of the heat transfer tubes 71. Air that flows into the air inlet 7E of the lower jacket portion 76 is guided into the cylindrical casing 70 from the air inlet portion 7A, rises while serpentine along the baffle plates 7P, passes through the air outlet portion 7B, and flows out from the air outlet 7F. This serpentine flow path forms the air flow path.

[0063] Exhaust gas that flows in through exhaust gas inlet 7C provided in exhaust gas inlet header 73 flows down through heat transfer tubes 71 via the sliding section and flows out through exhaust gas outlet 7D provided in exhaust gas outlet header 74. Preheating air that flows in through air inlet 7E is preheated while flowing through the air flow path described above, and flows out through air outlet 7F of upper jacket 75 located at the top of cylindrical casing 70. In other words, a counterflow type heat exchanger 7 is configured in which heat exchange occurs between exhaust gas, which is a heat release side fluid flowing down through heat transfer tubes 71, and air, which is a heat receiving side fluid flowing up through the air flow path.

[0064] In this heat exchanger 7, a partition tube plate 77 is disposed opposite and spaced from an upper tube plate 7U, a cooling space 78 is formed between the upper tube plate 7U and the partition tube plate 77, and the upper ends of the heat transfer tubes 71 are simply inserted through the upper tube plate 7U but are not joined thereto. Air supplied from a cooling air inlet 7G communicating with the cooling space 78 cools the upper tube plate 7U and its vicinity, which are heated by high-temperature exhaust gas, thereby reducing the reaction force acting on the tube plates 7U and 7L even if thermal expansion occurs in the heat transfer tubes 71. Note that the heat exchanger 7 may have a configuration in which the upper ends of the heat transfer tubes 71 are welded to the upper tube plate 7U without adopting such a configuration.

[0065] In the above-described embodiment, an example has been described in which a mixed gas of water vapor and air is supplied to the reactor from the gas supply mechanism 3, but the water vapor and air may be supplied to the reactor separately. Note that, when white silica is to be obtained, it is not necessary to supply water vapor necessary for initiating a water-gas reaction, and it is sufficient to provide an auxiliary burner for initially heating the reactor.

[0066] In this embodiment, an example has been described in which rice husks are used as biomass. Rice husks are approximately 70% carbohydrates such as cellulose, hemicellulose, and lignin, approximately 15 to 20% silica, and the majority of the remainder is water, with traces of alkaline impurities. The present invention is suitable for use in regenerating such silica-containing biomass as a resource. Biomass containing silica is not limited to rice husks; it is also possible to use biomass derived from siliceous plants such as rice straw, wheat straw, bamboo, corn, sugarcane, thin grass, and horsetail. [Example]

[0067] An experiment was conducted to compare the case where the exhaust gas obtained by carrying out the heat treatment process using the above-mentioned reactor 2 was immediately introduced into a heat exchanger to exchange heat with preheating air, and then amorphous silica was recovered using a bag filter (Example of the present invention), with the case where the exhaust gas obtained by carrying out the heat treatment process using the reactor 2 was introduced into a cyclone, a recovery process was carried out, and then the exhaust gas was introduced into a heat exchanger to exchange heat with preheating air (Comparative Example).

[0068] The operating conditions were those for obtaining white silica, and the temperature was controlled by spraying water into the reactor 2 while rice husks and air were continuously supplied into the reactor 2.

[0069] In the comparative example, as time passed after the start of the experiment, the temperature difference between the inlet temperature and the outlet temperature of the exhaust gas to the heat exchanger (approximately 600°C) gradually decreased and the outlet temperature tended to increase, meaning that the heat exchange amount tended to decrease, and the differential pressure of the heat exchanger also tended to increase and exceed 1 kPa.However, in the example of the present invention, it was confirmed that the temperature difference between the inlet temperature and the outlet temperature of the exhaust gas to the heat exchanger (approximately 600°C) was maintained constant, the outlet temperature was maintained at around 250°C, and the differential pressure of the heat exchanger was stabilized at around 0.5 kPa.

[0070] Compared to the comparative examples, the present invention showed that the heat exchange amount (preheated air) was improved by approximately 40% and the pressure loss was reduced by approximately 50%, and it was found that the heat exchange amount, overall heat transfer coefficient, and pressure loss were all significantly improved.

[0071] The above experimental results confirmed that there was no increase in pressure loss in the heat exchanger compared to the comparative example, and visual inspection of the heat exchanger confirmed that there was only slight buildup of deposits on the heat transfer tubes. In other words, it is presumed that passing heat-treated ash (amorphous silica) from rice husks through the heat exchanger removed the heat-treated ash adhering to the inner walls, resulting in a so-called self-cleaning effect. This resulted in the removal of dirt from the inner diameter of the tubes inside the heat exchanger, increasing the overall heat transfer coefficient, which in turn increased the temperature difference between the inlet and outlet of the heat exchanger and the amount of heat exchanged with the preheating air.

[0072] The above-described embodiment describes one specific example of the method and apparatus for producing amorphous silica according to the present invention, and the scope of the present invention is not limited by this description. It goes without saying that the specific configuration of each part can be appropriately modified and designed within the scope of the effects of the present invention. [Explanation of symbols]

[0073] 1: Amorphous silica manufacturing equipment 2: Reactor 3: Gas supply mechanism 20: Fluid medium 20A: Spouted bed 32: Header pipe 34: Diffuser pipe 30A: Air supply pipe 31: Valve 50A: Steam supply pipe 51A: Valve 6: Raw material supply mechanism 5: Lower water supply mechanism 8: Upper water supply mechanism 7: Heat exchanger 10:Exhaust pipe 11: Solid-gas separator

Claims

1. a heat treatment step of producing amorphous silica by contacting a biomass raw material derived from a silica plant with at least an oxygen-containing gas in a reactor; a heat exchange step of passing the exhaust gas containing the amorphous silica discharged from the reactor after the heat treatment step through a heat exchanger to lower the temperature of the exhaust gas; a recovery step of separating and recovering the amorphous silica contained in the exhaust gas after passing through the heat exchanger using a solid-gas separator; A method for producing amorphous silica comprising:

2. 2. The method for producing amorphous silica according to claim 1, wherein the heat exchange step is a step in which a multi-tubular heat exchanger is used as the heat exchanger, and the exhaust gas containing the amorphous silica is passed through the tubes of the multi-tubular heat exchanger to exchange heat with the heated medium.

3. 3. The method for producing amorphous silica according to claim 2, wherein the recovery step is a step of recovering the amorphous silica contained in the exhaust gas using a filtration-type separation device or a cyclone, the solid-gas separation device being a filtration-type separation device or a cyclone.

4. 4. The method for producing amorphous silica according to claim 3, wherein the filtration type separation device is a bag filter.

5. 5. The method for producing amorphous silica according to claim 1, wherein the heat treatment temperature is controlled so that the temperature of the exhaust gas discharged from the reaction furnace is 600 to 800°C in the heat treatment step.

6. 6. The method for producing amorphous silica according to claim 5, wherein the heat treatment temperature in the heat treatment step is controlled by supplying water or water vapor into the reactor.

7. a reactor including a raw material supply mechanism for supplying biomass derived from a silica plant as a raw material, and a gas supply mechanism for supplying at least an oxygen-containing gas to the raw material, wherein the raw material is heat-treated while being brought into contact with the oxygen-containing gas to produce amorphous silica; a heat exchanger that exchanges heat with a medium to be heated to reduce the temperature of the exhaust gas containing the amorphous silica discharged from the reactor; a solid-gas separator that separates and recovers the amorphous silica contained in the exhaust gas after the exhaust gas has passed through the heat exchanger; An apparatus for producing amorphous silica, comprising:

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