Single furnace multi-layer fluidized melting furnace

Abstract

The present invention discloses a single-furnace multi-layer fluidized melting furnace, comprising a furnace body arranged vertically, a plurality of bed layers arranged at intervals from top to bottom in the furnace body, one end of each bed layer connected to one side of the inner wall of the furnace body, a guide port arranged between the other end and the other side of the inner wall of the furnace body, and the guide ports of adjacent bed layers are arranged alternately relative to each other; the bed layer comprises an air distribution plate, a graphite heating core and an overflow weir, the air distribution plate is arranged horizontally, the air distribution plate is covered with wind caps or air holes, an overflow weir extending upward is arranged at one end of the air distribution plate adjacent to the guide port, and a graphite heating core is arranged above the air distribution plate; an argon outlet and a product outlet are respectively arranged on the top and bottom surfaces of the furnace body; a raw material inlet and an argon inlet are respectively arranged on the top and bottom of the furnace body. The single-furnace multi-layer fluidized melting furnace of the present invention adopts a multi-layer bed reaction, with uniform temperature and uniform material mixing, and the product can be directly processed without separation to obtain a finished silicon carbide product, and there is no problem of recycling the recycled materials.

Description

Technical Field

[0001] The invention relates to a melting furnace, in particular to a single-furnace multi-layer fluidized melting furnace for producing silicon carbide, and belongs to the field of fluidized melting furnace equipment for producing silicon carbide. Background Art

[0002] Silicon carbide materials are widely used, mainly in the solar photovoltaic industry, semiconductor industry, and piezoelectric crystal industry. At present, the preparation of conventional silicon carbide mainly comes from artificial synthesis, and its preparation methods mainly include sublimation method and melting method. Among them, the sublimation method is to produce silicon carbide by sublimating the silicon carbide charge in the carbon tube furnace in a carbon tube furnace with a vacuum of 10-30 mm Hg on the inner wall; the melting method is to bury a closed graphite dry crucible in an electric furnace with a strictly controlled temperature of 2600°C, and place the bonded and formed silicon carbide ingredients in a closed graphite dry crucible in advance to melt and produce silicon carbide. However, the above methods have the following disadvantages in the production process: (1) Both the melting method and the sublimation method are intermittent production, and the products are manually graded and sorted out of the furnace; (2) The material reaction of the melting method is incomplete. After the preparation is completed, the materials in the furnace only form silicon carbide products in the center, and other materials are not completely reacted, such as existing as insulation layers, silicon carbide oxide layers, adhesive layers and amorphous layers; the sublimation method has a low growth rate of silicon carbide crystals, and the temperature in the reaction space is difficult to effectively manage; (3) In the process of preparing silicon carbide by the melting method and the sublimation method, the raw materials are bonded together, and the mass transfer and heat transfer efficiency are low. However, the application of the fluidization method can effectively improve the mixing uniformity of the raw materials for preparing silicon carbide, improve the mass transfer and heat transfer efficiency, avoid the defects of slow silicon carbide crystal generation rate and difficult to control operating temperature in the sublimation method, and also overcome the problem that different furnace material layers are formed from the inside to the outside of the conventional melting method resistance furnace, resulting in the secondary melting furnace reuse of unreacted raw materials.

[0003] Conventional silicon carbide preparation methods are mainly divided into melting method and sublimation method.

[0004] Characteristics of the melting method: The main equipment for preparing silicon carbide by the melting method is a resistance furnace. Among them, the two ends of the resistance furnace are end walls, graphite electrodes are set near the center, and the furnace core is connected between the two electrodes; the furnace core is filled with the charge participating in the reaction (mainly quartz and carbonaceous raw materials), and the outside is insulation. When the charge is melted to produce silicon carbide, the temperature of the furnace core is usually guaranteed to rise to 2600-2700℃ by power supply. At this time, the electrically heated furnace core will transfer heat to the charge, so that it will gradually heat up to above 1450℃ to generate silicon carbide and emit carbon monoxide. With the extension of heating time, the high temperature range of the charge will continue to expand, and more and more silicon carbide will be generated at the same time, which will eventually cause silicon carbide to evaporate, move and crystallize in the furnace to form a cylindrical crystal tube. When the temperature in the crystal tube exceeds 2600℃, part of the silicon carbide product will begin to decompose again, and the decomposed silicon will combine with the carbon in the charge to become new silicon carbide.

[0005] Commonly used melting method silicon carbide production equipment mainly includes raw material mixing device, melting production device (resistance furnace) and product processing device. The silicon raw material, carbon raw material and auxiliary materials crushed into a certain particle size are mixed and formed evenly in the mixing device and then sent to the melting production device; the mixed material and the recycled waste material generated by the previous operation are together in the melting production unit to produce high-purity silicon carbide products at a high temperature of about 2600°C. However, in the melting production unit, not all raw materials and recycled waste materials are converted into silicon carbide products in the resistance furnace. Therefore, in the subsequent product processing unit, the recycled waste materials that have not generated qualified products are processed and then enter the melting production unit again to continue to produce silicon carbide. At the same time, the high-temperature silicon carbide heat generated by the melting production process in this process is not recycled.

[0006] Characteristics of the sublimation method: The sublimation method is currently the most commonly used method for commercial production of silicon carbide crystals. It is to place the pre-treated silicon carbide powder between a graphite crucible and a porous graphite tube, and to sublimate and grow the generated silicon carbide in an inert atmosphere (usually argon) at a temperature of 2500°C. However, this method has a slow silicon carbide generation rate during the production process, and it is difficult to control the crystal size of the grown silicon carbide crystals; at the same time, the operating temperature during production is also difficult to control.

[0007] Disadvantages of the existing technology:

[0008] (1) Both the melting method and the sublimation method are intermittent production, and the products are manually graded and sorted after they are taken out of the furnace;

[0009] (2) The melting method causes incomplete reaction of materials. After the preparation is completed, the materials in the furnace only form silicon carbide products in the center, and other materials do not react completely, such as the existence of insulation layer, silicon carbide layer, adhesive layer and amorphous layer. The sublimation method has the problem of low growth rate of silicon carbide crystals and difficulty in temperature management in the reaction space.

[0010] (3) In the process of preparing silicon carbide by melting and sublimation methods, the raw materials are bonded together, resulting in low mass transfer and heat transfer efficiency. Summary of the invention

[0011] The purpose of the present invention is to provide a single-furnace multi-layer fluidized melting furnace to solve the problem of uneven mass and heat transfer in the traditional silicon carbide production process, realize the continuous production process of silicon carbide and temperature control in each stage, and overcome the disadvantages of low one-way material conversion efficiency and continued separation and reuse of product waste materials in the traditional silicon carbide production process.

[0012] To achieve the above object, the technical solution adopted by the present invention is:

[0013] A single-furnace multi-layer fluidized melting furnace comprises a vertically arranged furnace body, wherein a plurality of bed layers are arranged at intervals from top to bottom in the furnace body, one end of each bed layer is connected to one side of the inner wall of the furnace body, and a guide port for downward flow of materials is provided between the other end and the other side of the inner wall of the furnace body, and the guide ports of adjacent bed layers are relatively alternately arranged; the bed layer comprises an air distribution plate, a graphite heating core and an overflow weir, the air distribution plate is horizontally arranged, and the air distribution plate is covered with wind hoods or wind holes, an overflow weir extending upward is provided at one end of the air distribution plate adjacent to the guide port, and a graphite heating core is provided on the air distribution plate; an argon outlet and a product outlet are respectively provided on the top and bottom surfaces of the furnace body; a raw material inlet and an argon inlet are respectively provided on the top and bottom of the furnace body.

[0014] As a preferred specific embodiment of the present invention, the cross-section of the furnace body can be circular or square, and its inner diameter or side length is 1.0 to 8.0 meters; wherein, for the furnace body with a circular cross-section, the air distribution plate is in the shape of a circular segment with a diameter the same as the inner diameter of the furnace body, the missing part of the circular segment serves as the guide port, and the overflow weir is arranged on the straight edge of the circular segment; the distance between the midpoint of the straight edge of the circular segment and the inner wall of the furnace body across the guide port is 1 / 8 to 1 / 16 of the diameter of the air distribution plate; for the furnace body with a square cross-section, the length of the air distribution plate is equal to the side length of the furnace body cross-section, and the width of the guide port is 1 / 8 to 1 / 16 of the length of the air distribution plate.

[0015] As a preferred specific embodiment of the present invention, the graphite heating core is installed between the rows of the hood or the vents, and is located 0.03 to 0.2 m above the air distribution plate. The installation distance of the graphite heating core is preferably twice the distance of the hood or the vent diameter: the reaction temperature of each layer of the bed in the furnace is controlled by controlling the charging intensity of the graphite heating core to achieve the temperature control requirements of different silicon carbide products. The reaction temperature of each layer of the bed can be controlled separately.

[0016] As a preferred specific implementation scheme of the present invention, the diameter of the hood is 30 to 80 mm, and the diameter of the air hole is 3 to 8 mm.

[0017] As a preferred specific embodiment of the present invention, the center distance between the wind caps or wind holes (10) is 1.0 to 1.5 times the diameter of the wind caps or wind holes.

[0018] As a preferred specific implementation scheme of the present invention, the spacing between each layer of air distribution plates is 0.1 to 0.8 meters. The present invention proposes a novel method and device for preparing silicon carbide based on fluidization technology, which can realize segmented reaction and segmented control in the silicon carbide preparation process, not only realizing the continuity of the silicon carbide production process, but also improving the silicon carbide crystal conversion rate.

[0019] The present invention adopts a single-furnace multi-layer fluidized melting method to produce silicon carbide products, which can ensure sufficient mixing of materials and mass and heat transfer. Compared with traditional melting and sublimation methods, the reaction time for completely producing qualified silicon carbide products can be shortened from about 15 to 25 hours in the past to 1 to 2 hours at present, greatly improving production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a cross-sectional structural schematic diagram of the present invention;

[0021] Figure 2 yes Figure 1 AA cross-sectional view (circular furnace body);

[0022] Figure 3 yes Figure 1 AA cross-sectional view (rectangular furnace body);

[0023] Figure 4 yes Figure 2 Dimensional drawing (excluding graphite heating core);

[0024] Figure 5 yes Figure 3 Dimensional drawing (without graphite heating element).

[0025] Explanation of the reference numerals: 1. furnace body, 2. overflow weir, 3. guide port, 4. air distribution plate, 5. product outlet, 6. argon gas inlet, 7. graphite heating core, 8. raw material inlet, 9. argon gas outlet, 10. wind hood or wind hole, 11. material surface. DETAILED DESCRIPTION

[0026] The present invention is described below in conjunction with specific embodiments and accompanying drawings, and the advantages and features of the present invention will become clearer as the description proceeds. However, it should be understood that these embodiments are exemplary only and do not constitute any limitation to the scope of the present invention. It should be understood by those skilled in the art that the details and forms of the technical solution of the present invention may be modified or replaced without departing from the spirit and scope of the present invention, but these modifications or replacements all fall within the protection scope of the present invention.

[0027] See also Figure 1-Figure 5An embodiment of a single-furnace multi-layer fluidized melting furnace of the present invention comprises a vertically arranged furnace body 1, in which multiple layers of beds are arranged from top to bottom at intervals, one end of each bed is connected to one side of the inner wall of the furnace body 1, and a guide port 3 for downward flow of materials is arranged between the other end and the other side of the inner wall of the furnace body 1, and the guide ports 3 of adjacent beds are arranged alternately relative to each other; the bed comprises an air distribution plate 4, a graphite heating core 7 and an overflow weir 2, the air distribution plate 4 is horizontally arranged, and the air distribution plate 4 is covered with wind caps or air holes 10, an overflow weir 2 extending upward is arranged at one end of the air distribution plate 4 adjacent to the guide port 3, and a graphite heating core 7 is arranged above the air distribution plate 4; an argon outlet 9 and a product outlet 5 are respectively arranged on the top and bottom surfaces of the furnace body 1; a raw material inlet 8 and an argon inlet 6 are respectively arranged on the top and bottom of the furnace body 1.

[0028] The air distribution plate 4 is covered with hoods or air holes 10, the diameter of the hood is generally 30 to 80 mm, and the diameter of the air hole is 3 to 8 mm, and the specific size depends on the size of the air distribution plate 4. The hood or air hole 10 generally adopts a circular structure, and the center spacing between the hoods or air holes 10 is 1.0 to 1.5 times the diameter of the hood or air hole. The hood or air hole 10 on the bed layer must ensure that the wind speed of the inert gas outlet hood and the small hole of the air hole is controlled at 25 to 55 m / s when producing silicon carbide, ensuring that the materials in each bed layer in the furnace are in a fluidized state. The height of the material surface 11 (i.e. the height of the material in the bed layer) of each bed layer of the melting furnace can be controlled at 0.1 to 0.8 meters, depending on the number of beds in the furnace, and the gas flow rate of the material surface 11 is controlled at 0.6 to 1.2 m / s. The reaction temperature of each bed layer in the furnace is controlled by controlling the current intensity of the graphite heating core 7 to achieve the temperature control requirements for producing different silicon carbide products. For example, when the temperature of each fluidized bed layer in the furnace is controlled at 2000℃, all the raw materials can be converted into β-SiC crystal products. When the temperature of each layer in the furnace is controlled to be higher than 2600℃, α-SiC crystal products can be finally generated.

[0029] The cross section of the furnace body 1 is circular or regular quadrilateral, and its inner diameter or side length is 1.0 to 8.0 meters. The shape of the bed of the single-furnace multi-layer fluidized melting furnace is the same as the cross-sectional shape of the furnace body 1. The bed is formed by high-temperature resistant stainless steel or special-shaped high-temperature refractory materials, and the bed is fixed by furnace body refractory bricks and high-temperature resistant stainless steel ribs. For a circular bed (see Figure 2 and Figure 4 ), the air distribution plate 4 is in the shape of a circular segment with the same diameter as the inner diameter of the furnace body 1, and the missing part of the circular segment serves as the guide port 3. The bed diameter D of each fluidized bed layer is 1.0 to 8.0 meters, and an overflow weir is arranged on the air distribution plate 4 of each bed layer. The distance L1 between the overflow weir and the inner wall of the furnace is 1 / 8 to 1 / 16 of the bed diameter D. For a regular quadrilateral bed surface (see Figure 3 and Figure 5), the side length L of the cross section of the furnace body 1 is between 1.0 and 2.8 meters, the length of the air distribution plate 4 of each fluidized bed layer is L, and the width is W. An overflow weir 2 is arranged on one side of the air distribution plate 4 of each bed layer, and the distance L1 between the overflow weir 2 and the inner wall of the furnace body (i.e., the width of the guide port 3) is 1 / 8 to 1 / 16 of the bed length L, and the width of the bed layer W = L-L1. The spacing H between each layer of the air distribution plates 4 of the single-furnace multi-layer fluidized melting furnace is between 0.1 and 0.8 meters, depending on the number of beds in the furnace. Due to the multi-layer fluidization, one layer of graphite heating core 7 is arranged in each bed layer, and the arrangement method is as follows Figure 2 and Figure 3 The graphite heating core 7 is installed between the rows of wind caps or wind holes, and is arranged at a height of 0.03 to 0.2 m above the air distribution plate 4. The installation distance of the graphite heating core 7 is generally about twice the diameter of the wind cap or wind hole, which is 60 to 160 mm.

[0030] The working process and structure of the present invention are further described below:

[0031] The pre-treated production raw materials with a certain particle size enter the first bed layer in the furnace body 1 from the raw material inlet 8. The molten reaction materials at a certain temperature enter the last bed layer through the guide port 3 in turn. The finished silicon carbide products are collected, cooled and transported out from the product outlet 5 at the bottom of the furnace. The Ar gas (fluidizing gas) in the furnace enters the furnace body 1 from the argon inlet 6 at the bottom of the furnace and flows out from the argon outlet 9 at the top of the furnace body 1. The materials in each bed layer are connected to each other through the guide port 3 to realize the flow of materials in the upper and lower beds. The Ar gas flowing out from the argon outlet 9 at the top of the furnace body 1 can be reused in the pretreatment device.

[0032] The present invention adopts a single furnace multi-layer fluidized melting method to produce silicon carbide in a furnace body 1. The multi-layer fluidized melting temperature can be controlled separately in the furnace body 1. The temperature of each bed layer can be different, so that the mixed raw materials can be continuously heated and heated after entering the furnace. When the pretreated production raw materials enter the top bed layer of the furnace body 1, the furnace with the heating core turned on will gradually melt the production raw materials from solid to liquid on the bed layer, and then participate in the melting reaction of each bed layer through the overflow weir and the guide pipe of each bed layer in turn. The molten production raw materials of each bed layer are in a liquid boiling state under the fluidization of an inert gas (generally Ar gas). Finally, the complete reaction conversion of different crystalline silicon carbide products will be achieved by controlling the reaction temperature in a certain number of beds, so as to achieve continuous production process and stable products.

[0033] When the present invention is used to produce silicon carbide, the type of silicon carbide product is mainly controlled based on the operating temperature. Generally, the temperature of the heating cores of several bottom layers is controlled at about 2600°C for the production of pure α-SiC phase products, the temperature of the heating cores is controlled at about 2000°C for β-SiC phase products, and the temperature of the heating cores is controlled at 2000-2600°C for α / β-SiC mixed phases. When the single-furnace multi-layer fluidized melting furnace of the present invention is working, the fluidized inert gas (argon) generates a high-speed airflow of 25-55 m / s through the hood holes and the air holes 10 to drive the turbulence of the raw materials in the molten bed layer, thereby achieving uniform flow and mass transfer and heat transfer in the bed layer. At the same time, each layer of the fluidized bed layer is provided with multiple groups of graphite heating cores 7, and the number of opened heating cores is accurately controlled according to the product type to ensure the reaction temperature.

[0034] The present invention adopts a single-furnace multi-layer fluidized melting method to produce silicon carbide products, which can ensure sufficient mixing of materials and mass transfer and heat transfer. Compared with traditional melting and sublimation methods, the reaction time for completely producing qualified silicon carbide products can be shortened from about 15 to 25 hours in the past to 1 to 2 hours at present, greatly improving production efficiency.

[0035] The single-furnace multi-layer fluidized melting furnace of the present invention adopts a multi-layer bed reaction, with uniform temperature and uniform material mixing. Therefore, the product obtained after the reaction does not need to be separated, and the silicon carbide finished product can be obtained directly after being processed by the product processing device, and there is no problem of recycling the return material. However, the traditional silicon carbide production process is a fixed bed reaction, and the heat is transferred from the center of the furnace to the outside of the furnace for heat reaction. Therefore, the final product produced contains a considerable portion of silicon raw materials and carbonaceous raw materials that do not participate in the reaction, which need to be separated and further reused as return materials. Only after the above separation can a qualified silicon carbide product be obtained.

Claims

1. A single-furnace multi-layer fluidized melting furnace, comprising a furnace body (1) arranged vertically, It is characterized in that Multiple layers of beds are arranged in intervals from top to bottom in the furnace body (1), one end of each bed is connected to one side of the inner wall of the furnace body (1), and a guide port (3) for downward flow of materials is arranged between the other end and the other side of the inner wall of the furnace body (1), and the guide ports (3) of adjacent beds are arranged alternately relative to each other; the bed comprises an air distribution plate (4), a graphite heating core (7) and an overflow weir (2), the air distribution plate (4) is arranged horizontally, and the air distribution plate (4) is covered with wind caps or wind holes (10), an overflow weir (2) extending upward is arranged at one end of the air distribution plate (4) adjacent to the guide port (3), and a graphite heating core (7) is arranged on the upper surface of the air distribution plate (4); The graphite heating core (7) is installed between the rows of wind hoods or wind holes (10), and is located 0.03 to 0.2 m above the air distribution plate (4). The installation distance of the graphite heating core (7) is twice the diameter of the wind hood or wind hole (10); the diameter of the wind hood is 30 to 80 mm, and the diameter of the wind hole (10) is 3 to 8 mm; the center distance between the wind hoods or wind holes (10) is 1.0 to 1.5 times the diameter of the wind hood or wind hole.

2. The single-furnace multi-layer fluidized melting furnace according to claim 1, It is characterized in that An argon gas outlet (9) and a product outlet (5) are respectively provided on the top surface and the bottom surface of the furnace body (1).

3. The single-furnace multi-layer fluidized melting furnace according to claim 1, It is characterized in that A raw material inlet (8) and an argon gas inlet (6) are respectively provided at the top and the bottom of the furnace body (1).

4. The single-furnace multi-layer fluidized melting furnace according to claim 1, It is characterized in that The cross section of the furnace body (1) is circular or square, and its inner diameter or side length is 1.0 to 8.0 meters.

5. The single-furnace multi-layer fluidized melting furnace according to claim 4, It is characterized in that For a furnace body (1) having a circular cross section, the air distribution plate (4) is in the shape of a circular segment with a diameter the same as the inner diameter of the furnace body (1), the missing portion of the circular segment serves as the guide port (3), and the overflow weir (2) is arranged on the straight edge of the circular segment; the distance between the midpoint of the straight edge of the circular segment and the inner wall of the furnace body (1) on the opposite side of the guide port (3) is 1 / 8 to 1 / 16 of the diameter of the air distribution plate (4).

6. The single-furnace multi-layer fluidized melting furnace according to claim 4, It is characterized in that For a furnace body (1) with a square cross section, the length of the air distribution plate (4) is equal to the side length of the cross section of the furnace body (1), and the width of the air guide port (3) is 1 / 8 to 1 / 16 of the length of the air distribution plate (4).

7. The single-furnace multi-layer fluidized melting furnace according to claim 1, It is characterized in that The spacing between each layer of the air distribution plates (4) is 0.1 to 0.8 meters.

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