Method for preparing white carbon black by catalytic thermal conversion of biomass char

Abstract

The present application relates to the field of biomass energy utilization, and particularly relates to a device for preparing white carbon black by catalytic thermal conversion of biomass char, which comprises a driving motor, a sealed joint, a furnace body, a heat preservation sleeve, a wind distribution system and a sealed end head. The device for preparing white carbon black by catalytic thermal conversion of biomass char adopts a spiral burner to burn the material, controls the residence time of the material in the furnace, reduces the combustion temperature of the rice hull char by adding a catalyst, and combines an external molten salt heat preservation system to control the temperature, so as to realize precise temperature control of the combustion process, ensure that the rice hull char is completely burned, and protect the amorphous silicon dioxide structure in the rice hull ash. In addition, the present application also proposes a method for preparing white carbon black by catalytic thermal conversion of biomass char, that is, the residence time of the material in the furnace is mainly controlled by controlling the rotating speed of the driving motor, the combustion temperature is reduced by the catalyst, and the temperature is controlled by combining the molten salt heat preservation system, so as to realize efficient preparation of white carbon black from rice hull.

Description

Technical Field

[0001] This invention relates to the field of biomass energy utilization, specifically to a method for preparing silica by catalytic thermal conversion of biomass char. Background Technology

[0002] my country is the world's largest rice producer, with an annual output exceeding 200 million tons. Rice husks, a processing byproduct, account for approximately 20% of the rice's weight, meaning about 40 million tons of rice husks need to be processed annually. The simplest way to process rice husks is through direct combustion to provide energy, but unfortunately, this produces a large amount of ash that is difficult to utilize effectively and easily causes secondary pollution. Research shows that rice husks contain 15-20 wt% amorphous silica (also known as white carbon black). If this amorphous silica can be extracted and processed into white carbon black without destroying its structure, it can be transformed from waste into a valuable resource, significantly increasing the utilization value of rice husks.

[0003] Therefore, many scholars have conducted research on producing precipitated silica from rice husks. Currently, the main methods developed include precipitation and combustion. The precipitation method involves dissolving the silicon components of rice husks, rice husk charcoal, or rice husk ash in an alkali solution to create a water glass solution. Then, the pH of the solution is adjusted using acid to induce precipitation. Finally, the solution is filtered and dried to obtain the precipitated silica product. This method is not significantly different from traditional precipitation-based precipitated silica, except for the silicon source used. Therefore, the resulting precipitated silica product is not significantly different from that of traditional precipitation-based precipitated silica and is difficult to use directly as a high-end precipitated silica product. The combustion method involves removing impurities from rice husks or rice husk charcoal, and then removing organic components through combustion to directly obtain the precipitated silica product. Compared to the precipitation method, this method does not damage the natural amorphous silica structure of rice husks, resulting in higher quality precipitated silica. However, because high temperatures can damage the amorphous silica structure and low temperatures can lead to incomplete combustion, this method requires high-precision process parameters, and currently, there is a lack of corresponding temperature-controlled combustion devices.

[0004] In contrast, rice husks have a high volatile content, resulting in a fast and violent combustion rate, making it difficult to control low combustion temperatures. Rice husk char has a low volatile content, a slow combustion reaction rate, and is easier to control in terms of temperature. However, rice husk char has drawbacks such as low volatile content, a high ignition point, and difficulty in stable combustion. Traditional fixed-bed or grate furnace charcoal combustion devices suffer from uneven air distribution, resulting in high and uneven combustion temperatures and unstable combustion, making them unsuitable for direct use in the production of precipitated silica from rice husk char. In recent years, some scholars have proposed catalytic combustion, which uses catalysts to lower the combustion temperature of rice husk char and control the combustion reaction rate, resulting in a more uniform combustion temperature distribution. This method is well-suited for temperature-controlled combustion of rice husk char to produce high-quality precipitated silica. However, corresponding catalytic combustion devices and methods are currently lacking. Therefore, there is an urgent need to develop efficient devices and methods for the catalytic thermal conversion of biomass char to produce precipitated silica, in order to achieve the efficient production of precipitated silica from rice husks. Summary of the Invention

[0005] (a) Technical problems to be solved

[0006] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a method for preparing silica by catalytic thermal conversion of biomass char that can precisely control temperature and achieve high efficiency.

[0007] (II) Technical Solution

[0008] To achieve the above objectives, the apparatus for preparing silica by catalytic thermal conversion of biomass char according to the present invention includes: a drive motor, a sealing joint, a furnace body, an insulation sleeve, an air distribution system, and a sealing end.

[0009] The furnace body includes a cylindrical spiral sleeve and a spiral shaft with spiral conveying blades rotatably disposed inside the spiral sleeve. A material inlet is provided at the upper part of the spiral sleeve near the first end, and a material outlet is provided at the lower part of the spiral sleeve near the second end. The spiral sleeve protrudes upward from the position near the material inlet to the upper part of the second end to form a flue gas passage with the spiral conveying blades. A flue gas outlet is provided on the flue gas passage.

[0010] The heat-insulating sleeve is provided outside the spiral sleeve, and a spiral guide vane is provided in the annular space between the heat-insulating sleeve and the spiral sleeve. A molten salt inlet is formed at the second end of the annular space, and a molten salt outlet is formed at the first end of the annular space.

[0011] The insulation sleeve is also provided with the air distribution system above the flue gas passage. The air distribution system includes an air inlet pipe, an air box and an air outlet pipe. The air inlet pipe is sleeved outside the flue gas outlet and connected to the air box located above the flue gas passage. The side wall of the air box has multiple sets of parallel air outlet pipes. The lower end of the air outlet pipe is connected to the spiral sleeve.

[0012] The first end of the spiral sleeve is provided with the sealing joint and the second end of the spiral sleeve is provided with the sealing end head. The sealing joint and the sealing end head together provide rotational support for the spiral shaft.

[0013] The drive motor is connected to the helical shaft through the sealed joint to drive the helical shaft to rotate.

[0014] Optionally, the air distribution system further includes multiple sets of parallel baffles disposed inside the air box, the baffles being able to guide air to flow along an S-shaped path;

[0015] The air inlet pipe is concentrically fitted outside the flue gas outlet, and the inlet section of the S-shaped path is located in the tangential direction of the air inlet pipe;

[0016] The air outlet duct is connected to the outlet section of the S-shaped path, and the lower extension of the air outlet duct is tangentially connected to the spiral sleeve to supply air into the spiral sleeve.

[0017] Optionally, the molten salt inlet is located at the lower part of the second end of the annular space, and the extending direction of the molten salt inlet is perpendicular to the axial direction of the annular space;

[0018] The molten salt outlet is located at the upper part of the first end of the annular space, and the extension direction of the molten salt outlet is perpendicular to the axial direction of the annular space.

[0019] Optionally, the spiral shaft is provided with 1 to 2 reverse blades with a pitch near the second end. The reverse blades rotate in the opposite direction to the spiral conveying blades and have the same pitch. The material outlet is located between the spiral conveying blades and the reverse blades.

[0020] And / or, the pitch of the helical conveying blade is 0.8 to 2.0 times the diameter of the helical shaft.

[0021] Optionally, the material inlet is 3 to 6 thread pitches away from the flue gas passage;

[0022] And / or, the top of the flue gas passage is 50-100 mm higher than the top of the spiral conveyor blade.

[0023] Furthermore, the present invention also provides a method for preparing precipitated silica by catalytic thermal conversion of biomass char, the method being implemented based on the above-mentioned apparatus for preparing precipitated silica by catalytic thermal conversion of biomass char, the method comprising the following steps:

[0024] S1. Start the molten salt circulation pump and introduce molten salt at 450~550℃ into the insulation sleeve to preheat the furnace body to the first temperature;

[0025] S2. Start the drive motor, add rice husk charcoal and catalyst from the material inlet at a predetermined mass ratio, adjust the speed of the drive motor, and control the residence time of the material in the furnace;

[0026] S3. Turn on the fan and introduce air of a predetermined oxygen concentration through the air inlet pipe;

[0027] S4. Adjust the flow rate of the molten salt circulation pump to control the furnace body to maintain the second temperature, and separate the solid residue discharged from the material outlet to obtain the catalyst and rice husk ash. The obtained catalyst can be recycled, and the obtained rice husk ash is the white carbon black produced.

[0028] Optionally, the molten salt in step S1 is a ternary mixed molten salt composed of lithium carbonate, sodium carbonate and potassium carbonate, with a melting point of 380~420℃ and the first temperature of 450~550℃.

[0029] Optionally, the catalyst in step S2 is a porous particulate catalyst prepared with alumina, silica or a mixture thereof as a support and copper oxide, nickel oxide, iron oxide or a mixture thereof as active material, wherein the predetermined mass ratio is 0.5 to 2.0.

[0030] Optionally, the predetermined oxygen concentration in step S3 refers to the volume of oxygen in the air being 12-21%.

[0031] Optionally, the second temperature in step S4 is 500~550℃.

[0032] (III) Beneficial Effects

[0033] The aforementioned apparatus for preparing precipitated silica from biomass charcoal via catalytic thermal conversion employs a spiral burner for material combustion, controls the residence time of the material within the furnace, lowers the combustion temperature of the rice husk charcoal by adding a catalyst, and combines this with an external molten salt insulation system for temperature control, achieving precise temperature control during the combustion process. This ensures that the rice husk charcoal is completely burned while protecting the amorphous silica structure in the rice husk ash. Furthermore, this invention also proposes a method for preparing precipitated silica from biomass charcoal via catalytic thermal conversion, which primarily controls the residence time of the material within the furnace by controlling the speed of the drive motor, lowers the combustion temperature through a catalyst, and combines this with a molten salt insulation system to control the temperature, thereby achieving efficient preparation of precipitated silica from rice husk sources.

[0034] The above technical solution also has the following beneficial effects:

[0035] 1. Compared with conventional combustion of rice husk charcoal, the addition of catalyst can lower the combustion temperature, effectively prevent incomplete combustion of rice husk charcoal due to low-temperature combustion, increase the combustion reaction rate, reduce the combustion time, and improve the combustion disposal efficiency.

[0036] 2. A cleverly designed spiral combustion device is used to control the spiral speed by driving a motor, thereby controlling the residence time of materials in the furnace and ensuring complete combustion. The operation is simple. The combustion reaction rate is controlled by controlling the oxygen concentration to prevent overheating caused by excessively fast combustion and high heat release. The flue gas channel is designed to promptly discharge the combustion generated gases, preventing the spiral burner pressure from rising sharply due to the small internal space of the spiral and the inability of the flue gas to be discharged in time. This ensures the stable operation of the device.

[0037] 3. An external molten salt insulation system is connected through the molten salt inlet and outlet. Taking advantage of the large specific heat capacity of molten salt and the small temperature change during heat absorption / release, the temperature inside the furnace is kept uniform. This can prevent the pyrolysis of carbon from being too low and the combustion from being incomplete, and can also prevent the combustion temperature from being too high and damaging the amorphous silica structure, thus further ensuring the quality of the silica. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the apparatus for preparing silica by catalytic thermal conversion of biomass char according to the present invention.

[0039] Figure 2 This is a schematic diagram of the air distribution system of the present invention.

[0040] [Explanation of Labels in the Attached Image]

[0041] 1: Drive motor; 2: Sealing joint; 3: Furnace body; 4: Spiral sleeve; 5: Insulation sleeve; 6: Air distribution system; 7: Sealing end; 31: Spiral shaft; 32: Spiral conveying blade; 33: Reverse blade; 41: Material inlet; 42: Flue gas passage; 43: Flue gas outlet; 44: Material outlet; 51: Molten salt outlet; 52: Spiral guide vane; 53: Molten salt inlet; 61: Air inlet pipe; 62: Baffle plate; 63: Air outlet pipe. Detailed Implementation

[0042] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0043] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0044] Furthermore, in this invention, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0045] In this invention, unless otherwise explicitly specified and limited, the terms "connection," "fixed," etc., should be interpreted broadly. For example, "fixed" can mean a fixed connection, a detachable connection, or an integral part; "connection" can mean a mechanical connection or an electrical connection; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0046] See Figure 1The present invention provides an apparatus for preparing silica by catalytic thermal conversion of biomass char, which includes: a drive motor 1, a sealing joint 2, a furnace body 3, an insulation sleeve 5, an air distribution system 6, and a sealing end 7.

[0047] The furnace body 3 includes a cylindrical spiral sleeve 4 and a spiral shaft 31 with spiral conveying blades 32 rotatably disposed within the spiral sleeve 4. The spiral conveying blades 32 can be directly welded to the spiral shaft 31. A material inlet 41 is provided at the upper part near the first end of the spiral sleeve 4. The catalyst and rice husk charcoal come into contact and collide to ensure temperature control. At the same time, the catalyst and rice husk charcoal collide and grind against each other in the furnace, which can reduce the particle size of the silica and improve its quality. In addition, a material outlet 44 is provided at the lower part near the second end of the spiral sleeve 4. The spiral sleeve 4 protrudes upward from the position near the material inlet 41 to the upper part of the second end, forming a flue gas channel 42 between it and the spiral conveying blades 32. The flue gas channel 42 can be a rectangular channel so that the cross-section of the spiral sleeve 4 is approximately U-shaped. A flue gas outlet 43 for exhausting flue gas is provided on the flue gas channel 42.

[0048] Furthermore, an insulating sleeve 5 is provided outside the spiral sleeve 4, and a spiral guide vane 52 is provided in the annular space between the insulating sleeve 5 and the spiral sleeve 4. Specifically, the spiral guide vane 52 can be welded to the outer surface of the spiral sleeve 4, and the internal shape of the spiral guide vane 52 is adapted to the shape of the spiral sleeve 4. A molten salt inlet 53 is formed at the second end of the annular space, and a molten salt outlet 51 is formed at the first end of the annular space.

[0049] like Figure 2 As shown, an air distribution system 6 is also provided inside the insulation sleeve 5 above the flue gas passage 42. The air distribution system 6 includes an air inlet pipe 61, an air box, and an air outlet pipe 63. The air inlet pipe 61 is sleeved outside the flue gas outlet 43 and connected to the air box located above the flue gas passage 42. Multiple sets of parallel air outlet pipes 63 are opened on the side wall of the air box. The lower end of the air outlet pipe 63 is connected to the spiral sleeve 4.

[0050] The first end of the spiral sleeve 4 is provided with a sealing joint 2, and the second end of the spiral sleeve 4 is provided with a sealing end 7. The sealing joint 2 and the sealing end 7 together provide rotational support for the spiral shaft 31. The drive motor 1 is connected to the spiral shaft 31 through the sealing joint 2 to drive the spiral shaft 31 to rotate. The first end of the spiral sleeve 4 and the first end of the annular space are both the ends closest to the drive motor 1.

[0051] Rice husk charcoal and catalyst enter the spiral sleeve 4 through material inlet 41. Driven by the spiral conveyor blades 32, they move from left to right and are thoroughly mixed under the stirring action of the spiral conveyor blades 32. Molten salt at 450-550℃ is introduced into the insulation sleeve 5 outside the spiral sleeve 4. The molten salt heats the material and comes into contact with air supplied by the air distribution system 6, causing the rice husk charcoal to undergo a combustion reaction to obtain silica. The above-mentioned apparatus for preparing silica from biomass charcoal through catalytic thermal conversion uses a spiral burner for catalytic combustion of the material, controls the residence time of the material in the furnace, reduces the combustion temperature of the rice husk charcoal by adding a catalyst, and combines this with an external molten salt insulation system for temperature control. The molten salt provides insulation and removes combustion heat in a timely manner to prevent overheating, achieving precise temperature control during the combustion process. This ensures that the rice husk charcoal is completely burned while protecting the amorphous silica structure in the rice husk ash. Simultaneously, the material and catalyst collide and grind against each other in the furnace, reducing the particle size of the silica and improving its quality. Compared to conventional combustion of rice husk charcoal, the addition of a catalyst can lower the combustion temperature, effectively preventing incomplete combustion of rice husk charcoal due to low-temperature combustion, increasing the combustion reaction rate, reducing combustion time, and improving combustion disposal efficiency.

[0052] Furthermore, the above scheme cleverly incorporates a spiral combustion device. The spiral rotation speed is controlled by the drive motor 1 to regulate the material's residence time in the furnace, ensuring complete combustion and simplifying operation. The combustion reaction rate is controlled by regulating the oxygen concentration, preventing overheating due to excessively rapid combustion and high heat release. A flue gas channel 42 is designed to promptly exhaust the combustion-generated gases, preventing a rapid increase in spiral burner pressure due to the limited internal space of the spiral and the inability to expel flue gas in time, thus ensuring stable operation of the device. An external molten salt insulation system is connected through the molten salt inlet 53 and molten salt outlet 51. Utilizing the high specific heat capacity and small temperature fluctuation during heat absorption / release of molten salt, a uniform furnace temperature is ensured. This prevents incomplete combustion of pyrolyzed carbon due to excessively low furnace temperatures and avoids damage to the amorphous silica structure due to excessively high combustion temperatures, further guaranteeing the quality of the silica.

[0053] See you again Figure 2 The air distribution system 6 may also include multiple sets of parallel baffles 62 installed inside the air box. The baffles 62 guide air flow along an S-shaped path. The entire S-shaped path corresponds to the annular space adjacent to the insulation sleeve 5 and the spiral sleeve 4. The molten salt within the annular space preheats the air to ensure the stability of temperature control within the furnace body 3. The air inlet pipe 61 is concentrically fitted outside the flue gas outlet 43. The inlet section of the S-shaped path is located tangentially to the air inlet pipe 61, allowing air to enter the S-shaped path more smoothly. The air outlet pipe 63 is connected to the outlet section of the S-shaped path. The lower extension of the air outlet pipe 63 (in...) Figure 2 The small circles on the air outlet duct 63 are shown in the middle. Figure 1The middle section is located below the air box of the air distribution system 6 and extends close to the spiral shaft 31. It is tangentially connected to the spiral sleeve 4 to supply air into the spiral sleeve 4. The front and rear sides of the rectangular flue gas passage 42 are tangent to the spiral sleeve 4. The lower extension of the air outlet duct 63 is arranged along the front or rear side of the flue gas passage 42 so that oxygen-containing air can be directly delivered to the middle of the spiral sleeve 4, thereby improving combustion efficiency.

[0054] In a preferred embodiment, the molten salt inlet 53 is located at the lower part of the second end of the annular space, and the extension direction of the molten salt inlet 53 is perpendicular to the axial direction of the annular space; the molten salt outlet 51 is located at the upper part of the first end of the annular space, and the extension direction of the molten salt outlet 51 is perpendicular to the axial direction of the annular space. This arrangement allows the extension direction of the molten salt inlet 53 or the molten salt outlet 51 to be the same as the tangential direction of the spiral guide vane 52, thereby improving the smoothness of molten salt feeding and discharging.

[0055] Furthermore, see again Figure 1 In a more preferred embodiment, the spiral shaft 31 is provided with one to two reverse blades 33 near the second end. The reverse blades 33 rotate in the opposite direction to the spiral conveying blades 32 and have the same pitch. The material outlet 44 is located between the spiral conveying blades 32 and the reverse blades 33. That is, the spiral conveying blades 32 and the reverse blades 33 are not arranged on the spiral shaft 31 directly opposite the material outlet 44, thereby ensuring that the material can be completely discharged. And / or, the pitch of the spiral conveying blades 32 is 0.8 to 2.0 times the diameter of the spiral shaft 31 to facilitate control of the feeding speed.

[0056] In addition, the material inlet 41 is 3 to 6 screw pitches away from the flue gas passage 42 so that the flue gas can be smoothly discharged when the catalyst and rice husk charcoal begin to react after sufficient heating. And / or, the top of the flue gas passage 42 is 50 to 100 mm higher than the top of the screw conveyor blades 32, thereby forming a sufficiently large flue gas expansion space to prevent excessive flue gas pressure.

[0057] Furthermore, the present invention also provides a method for preparing precipitated silica by catalytic thermal conversion of biomass char, the method being implemented based on the aforementioned apparatus for preparing precipitated silica by catalytic thermal conversion of biomass char, and the method comprising the following steps:

[0058] S1. Start the molten salt circulation pump and introduce molten salt at 450~550℃ into the insulation sleeve 5 to preheat the furnace body 3 to the first temperature;

[0059] S2. Start drive motor 1, add rice husk charcoal and catalyst from material inlet 41 at a predetermined mass ratio, adjust the speed of drive motor 1, and control the residence time of material in the furnace.

[0060] S3. Turn on the fan and introduce air with the predetermined oxygen concentration through the air inlet pipe 61;

[0061] S4. Adjust the flow rate of the molten salt circulation pump to control the furnace body 3 to maintain the second temperature. Separate the solid residue discharged from the material outlet 44 to obtain the catalyst and rice husk ash. The obtained catalyst can be recycled, and the obtained rice husk ash is the white carbon black produced.

[0062] In step S1, molten salt at 450-550℃ is introduced into the insulation sleeve 5 outside the furnace body to prevent the furnace body from overheating or losing temperature due to excessively fast or slow combustion of rice husk charcoal. The above method mainly controls the residence time of materials in the furnace by controlling the speed of the drive motor 1, reduces the combustion temperature by using a catalyst, and controls the temperature by combining the molten salt insulation system, thereby achieving efficient preparation of rice husk-derived silica.

[0063] In a preferred embodiment, the molten salt in step S1 can be a ternary mixed molten salt composed of lithium carbonate, sodium carbonate, and potassium carbonate, with a melting point of 380-420°C and a first temperature of 450-550°C. The catalyst in step S2 is a porous particulate catalyst prepared using alumina, silica, or a mixture of both as a support, and copper oxide, nickel oxide, iron oxide, or a mixture of these as the active material, with a predetermined mass ratio of 0.5-2.0. The predetermined oxygen concentration in step S3 refers to the volume percentage of oxygen in the air being 12-21%. The second temperature in step S4 is 500-550°C.

[0064] The above method will be described below based on specific embodiments, and the method specifically includes the following steps:

[0065] S1. Start the molten salt circulation pump and introduce a ternary mixed molten salt composed of lithium carbonate, sodium carbonate and potassium carbonate at 500°C into the insulation sleeve 5 to preheat the spiral sleeve 4 to 490°C.

[0066] S2. Start drive motor 1, add a mixture of rice husk charcoal and catalyst in a weight ratio of 2:1 from material inlet 41, adjust the speed of drive motor 1, and control the residence time of the material in the furnace to 30 minutes.

[0067] S3. Turn on the fan and introduce air with an oxygen concentration of 15% through the air inlet pipe 61;

[0068] S4. Adjust the flow rate of the molten salt circulation pump to control the temperature inside the spiral sleeve 4 to maintain at 500°C. Separate the solid residue discharged from the material outlet 44 to obtain the catalyst and rice husk ash. The obtained catalyst is recycled, and the obtained rice husk ash is the white carbon black produced.

[0069] By using the above method to prepare precipitated silica through precise temperature control, the yield can reach over 95% and the purity (silicon dioxide content) can reach over 98%, achieving efficient preparation of precipitated silica from rice husks and significantly improving the utilization value of rice husks.

[0070] It should be understood that the above description of specific embodiments of the present invention is only for illustrating the technical approach and features of the present invention, and is intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. However, the present invention is not limited to the specific embodiments described above. All changes or modifications made within the scope of the claims of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for preparing precipitated silica by catalytic thermal conversion of biomass char, the method being implemented using an apparatus for preparing precipitated silica by catalytic thermal conversion of biomass char, the apparatus comprising: Drive motor (1), sealing joint (2), furnace body (3), insulation sleeve (5), air distribution system (6) and sealing end (7); The furnace body (3) includes a cylindrical spiral sleeve (4) and a spiral shaft (31) with spiral conveying blades (32) rotatably disposed inside the spiral sleeve (4). A material inlet (41) is provided at the upper part near the first end of the spiral sleeve (4), and a material outlet (44) is provided at the lower part near the second end of the spiral sleeve (4). A flue gas passage (42) is formed between the upper part of the spiral sleeve (4) near the material inlet (41) and the spiral conveying blades (32). A flue gas outlet (43) is provided on the flue gas passage (42). The heat insulation sleeve (5) is provided outside the spiral sleeve (4). A spiral guide plate (52) is provided in the annular space between the heat insulation sleeve (5) and the spiral sleeve (4). A molten salt inlet (53) is formed at the second end of the annular space, and a molten salt outlet (51) is formed at the first end of the annular space. The insulation sleeve (5) is also provided with the air distribution system (6) above the flue gas passage (42). The air distribution system (6) includes an air inlet pipe (61), a wind box and an air outlet pipe (63). The air inlet pipe (61) is sleeved outside the flue gas outlet (43) and connected to the wind box above the flue gas passage (42). The side wall of the wind box has multiple sets of parallel air outlet pipes (63). The lower end of the air outlet pipe (63) is connected to the spiral sleeve (4). The first end of the spiral sleeve (4) is provided with the sealing joint (2) and the second end of the spiral sleeve (4) is provided with the sealing end (7). The sealing joint (2) and the sealing end (7) together provide rotational support for the spiral shaft (31). The drive motor (1) is connected to the spiral shaft (31) through the sealing joint (2) to drive the spiral shaft (31) to rotate; The method is characterized by comprising the following steps: S1. Start the molten salt circulation pump and introduce molten salt at 450~550℃ into the insulation sleeve (5) to preheat the furnace body (3) to the first temperature; S2. Start the drive motor (1), add rice husk charcoal and catalyst from the material inlet (41) at a predetermined mass ratio, adjust the speed of the drive motor (1), and control the residence time of the material in the furnace; S3. Turn on the fan and introduce air of a predetermined oxygen concentration through the air inlet pipe (61); S4. Adjust the flow rate of the molten salt circulation pump, control the furnace body (3) to maintain the second temperature, and separate the solid residue discharged from the material outlet (44) to obtain the catalyst and rice husk ash. The obtained catalyst can be recycled, and the obtained rice husk ash is the white carbon black produced.

2. The method for preparing silica by catalytic thermal conversion of biomass char according to claim 1, characterized in that, The air distribution system (6) also includes multiple sets of parallel baffles (62) disposed in the air box, the baffles (62) being able to guide air to flow along an S-shaped path; The air inlet pipe (61) is concentrically fitted outside the flue gas outlet (43), and the inlet section of the S-shaped path is located in the tangential direction of the air inlet pipe (61). The air outlet pipe (63) is connected to the outlet section of the S-shaped path, and the lower extension of the air outlet pipe (63) is tangentially connected to the spiral sleeve (4) to supply air into the spiral sleeve (4).

3. The method for preparing precipitated silica by catalytic thermal conversion of biomass char according to claim 1, characterized in that, The molten salt inlet (53) is located at the lower part of the second end of the annular space, and the extension direction of the molten salt inlet (53) is perpendicular to the axial direction of the annular space. The molten salt outlet (51) is located at the upper part of the first end of the annular space, and the extension direction of the molten salt outlet (51) is perpendicular to the axial direction of the annular space.

4. The method for preparing silica by catalytic thermal conversion of biomass char according to claim 1, characterized in that, The spiral shaft (31) is provided with a reverse blade (33) with a pitch of 1 to 2 near the second end. The reverse blade (33) rotates in the opposite direction to the spiral conveying blade (32) and has the same pitch. The material outlet (44) is located between the spiral conveying blade (32) and the reverse blade (33). And / or, the pitch of the helical conveying blade (32) is 0.8 to 2.0 times the diameter of the helical shaft (31).

5. The method for preparing silica by catalytic thermal conversion of biomass char according to claim 1, characterized in that, The material inlet (41) is 3 to 6 screw pitches away from the flue gas passage (42); And / or, the top of the flue gas passage (42) is 50-100 mm higher than the top of the spiral conveying blade (32).

6. The method for preparing silica by catalytic thermal conversion of biomass char according to any one of claims 1-5, characterized in that, The molten salt in step S1 is a ternary mixed molten salt composed of lithium carbonate, sodium carbonate and potassium carbonate, with a melting point of 380~420℃ and a first temperature of 450~550℃.

7. The method for preparing silica by catalytic thermal conversion of biomass char according to any one of claims 1-5, characterized in that, The catalyst in step S2 is a porous particulate catalyst prepared with alumina, silica or a mixture of the two as the support and copper oxide, nickel oxide, iron oxide or a mixture of the three as the active material, and the predetermined mass ratio is 0.5 to 2.

0.

8. The method for preparing silica by catalytic thermal conversion of biomass char according to any one of claims 1-5, characterized in that, The predetermined oxygen concentration in step S3 refers to the volume of oxygen in the air being 12-21%.

9. The method for preparing silica by catalytic thermal conversion of biomass char according to any one of claims 1-5, characterized in that, The second temperature in step S4 is 500~550℃.

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