Single-layer multi-furnace melting system

Abstract

The present invention discloses a single-layer multi-furnace melting system, including at least two-stage fluidized melting furnaces, each of which includes a furnace body, a heating core, an air distribution plate and a guide tube. An air distribution plate is provided at the lower part of the vertically arranged cylindrical furnace body, and the air distribution plate is covered with wind caps or air holes; a heating core is provided above the air distribution plate, and a plurality of guide tubes are provided above the heating core, and the tube wall of the guide tube is covered with through holes; an argon outlet and an argon inlet are provided on the top and bottom surfaces of the furnace body respectively; a material inlet and a material outlet are provided at the upper and lower parts of the furnace body respectively; the material outlet of the upper melting furnace and the material inlet of the lower melting furnace are connected to each other through a material conveying pipeline. The system of the present invention can realize the continuous production process of silicon carbide and ensure the stability of the product; the reaction time can be shortened from about 15 to 25 hours in the past to 1 to 2 hours now, which greatly improves the production efficiency.

Description

Technical Field

[0001] The invention relates to a melting device for producing silicon carbide, in particular to a single-layer multi-furnace melting system for producing silicon carbide, and belongs to the field of 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 sublimate the silicon carbide charge in the carbon tube furnace in a carbon tube furnace with a vacuum of 10-30 mm Hg to synthesize and produce silicon carbide 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 degrees, 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 silicon carbide crystal growth rate and difficult temperature management in the reaction space; (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. Conventional silicon carbide preparation methods are mainly divided into melting method and sublimation method.

[0003] 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.

[0004] 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.

[0005] 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.

[0006] Disadvantages of the existing technology:

[0007] (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;

[0008] (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.

[0009] (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

[0010] The purpose of the present invention is to provide a single-layer multi-furnace melting system 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 at 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.

[0011] To achieve the above object, the technical solution adopted by the present invention includes:

[0012] A single-layer multi-furnace melting system comprises at least two-stage fluidized melting furnaces, each of which comprises a furnace body, a heating core, an air distribution plate and a guide tube. An air distribution plate is provided at the lower part of the vertically arranged cylindrical furnace body, and the air distribution plate is covered with wind hoods or wind holes; a heating core is provided above the air distribution plate, and a plurality of guide tubes arranged at intervals and axially vertical are provided above the heating core; a material inlet and a material outlet are provided at the upper and lower parts of the furnace body, respectively, and the material outlet of the upper-stage melting furnace and the material inlet of the lower-stage melting furnace are interconnected through a material conveying pipeline.

[0013] In a preferred embodiment of the present invention, an argon outlet and an argon inlet are respectively provided on the top surface and the bottom surface of the furnace body.

[0014] In a preferred embodiment of the present invention, the wall of the guide tube is covered with through holes, and the diameter of the through holes is 3 to 6 mm.

[0015] In a preferred embodiment of the present invention, the hood or the air hole on the air distribution plate is circular or hexagonal, the diameter of the hood is 30 to 80 mm, and the diameter of the air hole is 3 to 8 mm.

[0016] In a preferred embodiment of the present invention, the center distance between the wind caps or wind holes is 1.0 to 1.5 times the diameter of the wind caps or wind holes.

[0017] In a preferred embodiment of the present invention, the guide tube is fixed by a fixing member at a distance of 0.05 to 0.10 meters above the air distribution plate, and the spacing between the guide tubes is 3 to 5 times the diameter of the guide tube; the height of the guide tube (4) is preferably 0.2 to 0.6 meters, and the diameter range of each guide tube (4) is preferably 0.1 to 0.3 meters, and the shape of the guide tube (4) is generally set to be cylindrical.

[0018] In a preferred embodiment of the present invention, the shape and size of the air distribution plate are the same as the cross-section of the furnace body.

[0019] In a preferred embodiment of the present invention, the furnace body has a circular cross-section and an inner diameter of 1.0 to 8.0 meters; the heating core is evenly arranged along the circular periphery at an angle α, and the angle α is between 10 and 90 degrees; the heating core is arranged above the air distribution plate (3) at a distance of 0.03 to 0.2 meters.

[0020] In a preferred embodiment of the present invention, the furnace body has a square cross-section with a side length of 1.0 to 2.8 meters; the heating cores are parallel to one side of the square and are evenly arranged along a vertical side; each heating core is installed between the rows of the hoods or vents and is arranged 0.03 to 0.2 meters above the air distribution plate, and the spacing between the heating cores is twice the diameter of the hoods or vents.

[0021] The present invention proposes a novel silicon carbide production device based on fluidization technology, which can realize segmented reaction and segmented control in the silicon carbide preparation process, not only can realize the continuity of the silicon carbide production process, but also can improve the silicon carbide crystal conversion rate.

[0022] Compared with the commonly used melting method and sublimation method, the amorphous, pure β-SiC phase, pure α-SiC phase, and α / β-SiC mixed phase products produced by the present invention can be subjected to corresponding temperature control in the fluidized bed melting furnace according to requirements, and there is no need to separate the waste material as raw material and return it to the resistance furnace to continue melting and producing silicon carbide like the conventional melting method, which can completely realize the continuous production process and ensure the stability of silicon carbide products. The reaction time for producing qualified silicon carbide products can be shortened from about 15 to 25 hours in the past to 1 to 2 hours now, greatly improving production efficiency; in the silicon carbide production process, the waste heat of the fluidizing gas is fully used for drying the production raw materials, realizing the effective recycling of energy and reducing energy consumption and production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the structure of the present invention (an embodiment of a three-stage melting furnace);

[0024] Figure 2 It is a schematic structural diagram of a (cylindrical) melting furnace of the present invention;

[0025] Figure 3 yes Figure 2 Schematic diagram of the cross section in the middle (distribution of guide tubes);

[0026] Figure 4 yes Figure 2 Schematic diagram of the lower cross section (heating core distribution);

[0027] Figure 5 It is a schematic structural diagram of a (square cylindrical) melting furnace of the present invention;

[0028] Figure 6 yes Figure 5 Schematic diagram of the cross section in the middle (distribution of guide tubes);

[0029] Figure 7 yes Figure 5 Schematic diagram of the lower cross section (heating core distribution).

[0030] Explanation of the accompanying drawings: 1. furnace body, 2. heating core, 3. air distribution plate, 4. guide tube, 5. material inlet, 6. material outlet, 7. argon inlet, 8. argon outlet, 9. argon output pipeline, 10. argon input pipeline, 11. material surface, A. first-stage melting furnace, B. second-stage melting furnace, C. third-stage melting furnace. DETAILED DESCRIPTION

[0031] 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.

[0032] See also Figure 1-Figure 7 , an embodiment of a single-layer multi-furnace melting system of the present invention, the embodiment comprises three (can be more than two) stages of fluidized melting furnaces, namely: a first stage melting furnace A, a second stage melting furnace B and a third stage melting furnace C, the material outlet 6 of the first stage melting furnace A and the material inlet 5 of the second stage melting furnace B are connected to each other through a material conveying pipeline, and the material outlet 6 of the second stage melting furnace B and the material inlet 5 of the third stage melting furnace C are connected to each other through a material conveying pipeline (see Figure 1 ).

[0033] The structure of each melting furnace is shown in Figure 2-Figure 7 , including a furnace body 1, a heating core 2, an air distribution plate 3 and a guide tube 4, an air distribution plate 3 is provided at the lower part of the vertical cylindrical furnace body 1, and the air distribution plate 3 is covered with air caps or air holes; a heating core 2 is provided on the upper side of the air distribution plate 3, and a plurality of guide tubes 4 arranged at intervals and axially vertical are provided above the heating core 2, and the tube wall of the guide tube 4 is covered with through holes; an argon outlet 8 and an argon inlet 7 are provided on the top and bottom surfaces of the furnace body 1 respectively; a material inlet 5 and a material outlet 6 are provided on the upper and lower parts of the furnace body 1 respectively. The guide tube 4 is generally cylindrical.

[0034] The working principle and specific structure of the present invention are further described below in conjunction with the accompanying drawings:

[0035] The multi-stage series melting furnace of the present invention adopts a multi-furnace series melting method (such as Figure 1As shown), the principle is to divide the raw materials into three-stage melting furnaces A, B, and C (this embodiment), and at the same time use fluidized bed melting to achieve uniform mass and heat transfer of silicon carbide raw materials in the furnace, which fundamentally solves the phenomenon of multi-product stratification in traditional preparation methods and improves the singleness and conversion rate of products. The melting furnace of each level is controlled by a graphite electric heating core 2 to control the temperature in the circuit. An air distribution plate 3 is provided in the furnace, and the air distribution plate 3 is covered with wind caps or wind holes. The wind caps or wind holes can adopt a circular structure or a regular hexagonal structure. The diameter of the wind caps is generally 30 to 80 mm, and the diameter of the wind holes is 3 to 8 mm. The specific size depends on the size of the air distribution plate. The center spacing between the wind caps or wind holes is 1.0 to 1.5 times the diameter of the wind caps or wind holes. When producing silicon carbide, the wind caps or wind holes on the air distribution plate 3 must also ensure that the wind speed of the small holes of the inert gas outlet caps and wind holes is controlled at 25 to 55 m / s to ensure that the materials in each bed layer in the furnace are in a fluidized state. The height of each melting furnace bed 11 can be controlled at 0.3-1.0 m, and the gas flow rate on the bed can be controlled at 0.8-1.5 m / s. Figure 2 , Figure 3 , Figure 5 and Figure 6As shown. Multiple guide tubes 4 can be arranged in each melting furnace, and the height h2 of the guide tube 4 is 0.2-0.6 meters, depending on the height of each melting furnace bed layer. The guide tube 4 is fixed above the air distribution plate 3 by a fixing part, and the distance h1 from the air distribution plate 3 is 0.05-0.10 meters; the spacing s and n between adjacent guide tubes 4 are 3-5 times the diameter of the guide tube, and the diameter of each guide tube 4 ranges from 0.1 to 0.3 meters; each guide tube 4 can be opened with multiple small holes around the periphery, and the aperture of the small holes is 3-6 mm, and multiple layers of small holes can be arranged on the guide tube 4. In the fluidized molten bed in each melting furnace, after the material in the bed is fluidized in a molten state through the hood or air holes on the air distribution plate 3, the reaction material further forms an internal circulation of the material from bottom to top through the interior of the guide tube 4 (the material is formed by the Ar gas coming in from the air distribution plate in the molten bed material to form bubbles, driving the material into the interior of the guide tube, and then after exiting the guide tube 4, it circulates into the guide tube 4 through the small holes on the guide tube 4 and the lower part of the guide tube 4, and repeats itself over and over again. The function of the guide tube 4 is to promote further mixing reaction of the bed material and ensure uniform reaction temperature; the function of the small holes on the guide tube 4 is to serve as a channel for promoting circulation of the material in the molten bed), further ensuring uniform temperature and sufficient mass transfer of the reaction materials in the furnace, and achieving sufficient conversion of the material. When silicon carbide products are produced in the multi-furnace series graded melting furnace of the present invention, the type of silicon carbide product is mainly controlled based on the operating temperature. In the process flow, the raw materials after drying and crushing first enter the first-stage melting furnace A of the present invention, and gradually enter the subsequent multi-stage melting furnaces (second-stage melting furnace B, third-stage melting furnace C) after a certain residence time. The channels for materials to enter the next-stage melting furnace from the previous melting furnace all use material conveying pipes, and the material conveying pipes are made of high-temperature resistant stainless steel with amorphous refractory lining. The residence time of each stage of the melting furnace can adopt different residence times, and the residence time can be approximately estimated by the quotient of the volume of the reaction bed material that can be held in the furnace and the product volume flow rate per unit time. Finally, qualified silicon carbide products are produced. Similarly, when the temperature in the multi-stage fluidized melting furnace is controlled at 2000°C, the reaction time is controlled by controlling the number (number of stages) of melting furnaces in series to achieve the complete conversion of the raw materials into β-SiC crystalline products. When the temperature in the multi-stage melting furnace is controlled to be higher than 2000°C, α-SiC crystalline products can be finally generated. In the above process of producing silicon carbide, the raw materials in each melting furnace are in a molten state, and the raw materials are in a liquid boiling state under the fluidization effect of an inert gas (generally Ar gas).

[0036] The single furnace bed surface (i.e., the cross-sectional shape of the furnace body 1) of each stage of the melting furnace of the present invention can be circular (e.g. Figure 2-Figure 4 ) or a regular quadrilateral (as Figure 5-Figure 7As shown in the figure, for a single furnace with a circular bed, the bed diameter D is between 1.0 and 8.0 meters; and for a regular quadrilateral bed, the length L and width W of each fluidized bed layer are both between 1.0 and 2.8 meters. A layer of heating core 2 is arranged on the air distribution plate 3 of a single melting furnace. The installation method of the heating core 2 is related to the shape of the bed of a single fluidized melting furnace. When the bed is circular, the heating cores can be evenly arranged at an angle α along the circumference of the circle, and the angle α can be between 10 and 90 degrees (such as Figure 4 When the bed surface is a regular polygon, the heating core is installed as follows Figure 7 The heating cores 2 of the above two types of furnaces are installed between the rows of wind caps or wind holes, and are arranged at a height of 0.03 to 0.2 m above the air distribution plate 3. The spacing between the heating cores 2 is generally about twice the diameter of the wind caps or wind holes, in the range of 60 to 160 mm.

[0037] In order to increase the waste heat of the inert gas used for fluidization in the melting production process, it is considered to recycle the waste heat: the argon outlet 8 of each melting furnace is connected to the front pretreatment process (drying and crushing) through an argon output pipeline 9 for waste heat utilization, and then returned to the argon inlet 7 of each melting furnace through an argon input pipeline 10 (see Figure 1 ). Since some carbon monoxide gas will be produced in the process of melting and producing silicon carbide, the concentration of carbon monoxide in the high-temperature fluidizing gas should be monitored in real time, and the carbon monoxide gas in the argon gas should be burned online in time to generate carbon dioxide before being recycled to the front pretreatment process to ensure the production safety of the drying and crushing device.

[0038] In the technical solution of the present invention, the fluidized inert gas (argon) of each stage of the melting furnace generates a high-speed airflow of 25 to 55 m / s through the hood holes and air holes on the air distribution plate 3 to drive the turbulence of the reactants in the molten bed, thereby achieving uniform flow and mass transfer and heat transfer in the bed. The guide tube 4 in each melting furnace further forms an internal circulation of the reaction materials inside the molten bed. The two internal and external circulations make the mixing reaction of the reaction materials more uniform, and the conversion rate of the generated silicon carbide product is higher. At the same time, each fluidized melting furnace is provided with multiple groups of graphitized heating cores 2, and the number of opened heating cores 2 is accurately controlled according to the product type to ensure the reaction temperature.

[0039] In the present invention, the production of silicon carbide products by a multi-furnace series graded melting method can ensure the full mixing of materials and mass and heat transfer. Compared with the traditional melting method and sublimation method, the reaction time for completely producing qualified silicon carbide products can be shortened from about 15 to 25 hours in the past to the current 1 to 2 hours, which greatly improves the production efficiency. At the same time, a liquid raw material system is used in the preparation of production raw materials, and the raw materials are easy to purify and easy to achieve high purity (above 4 nanometers). At the same time, after the raw materials are purified and dried, the reaction system is fully mixed and uniform, and it is easy to sinter at a relatively low temperature to obtain nano-scale silicon carbide powder, and then the crystalline phase (amorphous, pure β phase, pure α phase, α / β mixed phase) of silicon carbide is accurately controlled by controlling the reaction temperature.

[0040] The present invention solves a series of problems in the traditional silicon carbide production process, such as intermittent production and low one-way conversion efficiency of materials in the production process. In the silicon carbide production process, a multi-furnace series graded melting furnace production method is used to improve the mass transfer and heat transfer in the silicon carbide production process, and the silicon carbide product is completely converted in one step without the need to separate and reuse the spent material; the graphitized heating core 2 is used to accurately control the temperature of each bed layer or each melting furnace in the furnace to control the product type; multiple melting furnaces are used in series to achieve the reaction time of the silicon carbide production process; inert gas is used as a fluidizing gas to generate turbulence in the bed molten material to achieve material mixing and uniform reaction, and a guide tube 4 is installed in the bed layer in the furnace to further improve the turbulence degree of the reaction process and the reaction conversion rate of silicon carbide.

Claims

1. A single-layer multi-furnace melting system for producing silicon carbide materials, characterized in that: The invention comprises a melting furnace with at least two fluidization stages, each of which comprises a furnace body (1), a graphitized heating core (2), an air distribution plate (3) and a guide tube (4); an air distribution plate (3) is arranged at the lower part of the vertically arranged cylindrical furnace body (1), and the air distribution plate (3) is covered with air caps or air holes; a graphitized heating core (2) is arranged above the air distribution plate (3), and a plurality of guide tubes (4) arranged at intervals and axially vertical are arranged above the graphitized heating core (2); a material inlet (5) and a material outlet (6) are respectively arranged at the upper and lower parts of the furnace body (1), and the material outlet (6) of the upper melting furnace and the material inlet (5) of the lower melting furnace are connected to each other through a material conveying pipeline; An argon gas outlet (8) and an argon gas inlet (7) are respectively provided on the top surface and the bottom surface of the furnace body (1); The wall of the guide tube (4) is covered with through holes, and the diameter of the through holes is 3 to 6 mm; the guide tube (4) is fixed at a distance of 0.05 to 0.10 m above the air distribution plate (3) by a fixing member, and the spacing of the guide tubes (4) is 3 to 5 times the diameter of the guide tube; The shape and size of the air distribution plate (3) are the same as the cross-section of the furnace body (1); the hoods or air holes on the air distribution plate (3) are circular or regular hexagonal, the diameter of the hoods is 30 to 80 mm, and the diameter of the air holes is 3 to 8 mm; the center spacing between the hoods or air holes is 1.0 to 1.5 times the diameter of the hoods or air holes.

2. The single-layer multi-furnace melting system according to claim 1, characterized in that: The height of the guide tube (4) is 0.2 to 0.6 meters, and the diameter of each guide tube (4) is in the range of 0.1 to 0.3 meters.

3. The single-layer multi-furnace melting system according to claim 1, characterized in that: The furnace body (1) has a circular cross section and an inner diameter of 1.0 to 8.0 meters; the graphitized heating core (2) is evenly arranged along the circular periphery at an angle α, and the angle α is between 10° and 90°; the graphitized heating core (2) is arranged above the air distribution plate (3) at a distance of 0.03 to 0.2 meters.

4. The single-layer multi-furnace melting system according to claim 1, characterized in that: The furnace body (1) has a square cross section with a side length of 1.0 to 2.8 meters; the graphitized heating core (2) is parallel to one side of the square and is evenly arranged along a vertical side; each graphitized heating core (2) is installed between the rows of the wind cap or the wind hole and is arranged 0.03 to 0.2 meters above the air distribution plate (3), and the spacing between the graphitized heating cores (2) is twice the diameter of the wind cap or the wind hole.

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