Purification device and purification furnace for non-volatile impurities of graphite products

Abstract

The invention provides a purification device for non-volatile impurities of a graphite product. The purification device comprises a first filler and a second filler, wherein the first filler is filled in the surrounding space of the graphite product and can conduct heat and ventilate and absorb the impurities gasified by a resistance material at the same time; the isolation layer is used for separating the first filler and the resistance material; the gas flow pipeline is used for guiding and heating purified gas and is buried in the resistance material and the thermal insulation filler, and a gas outlet of the gas flow pipeline is formed below the resistance material. And the first filler can adsorb impurities volatilized from the resistance material and prevent the impurities from entering the graphite product. Meanwhile, abundant pores of the first filler can provide abundant channels for purified gas, so that the purified gas is in full contact with the graphite product for impurity removal. Meanwhile, the purification device for the non-volatile impurities of the graphite product can also be used in a graphitization process. And removing non-volatile impurities in the graphite product in the graphitization stage. Therefore, the graphitization process and the purification process are combined, and the energy consumption is remarkably reduced.

Description

Technical Field

[0001] This application relates to the field of graphite electrode production technology, and in particular to a method and system for purifying non-volatile impurities in graphite products. Background Technology

[0002] Graphite products, such as molds, electrodes, and graphite felts, are made from raw materials such as coke, petroleum coke, and coal tar pitch through processes including batching, crushing, mixing, isostatic pressing, calcination, impregnation, and graphitization. Associated minerals in the raw materials and process contamination during production can introduce various impurities into graphite products. During the graphitization stage, the temperature of graphite products reaches 2300–3000 degrees Celsius. Under these high temperatures, most impurity elements in graphite products appear in the form of compounds, primarily high-melting-point, non-volatile oxides such as SiO2, Al2O3, FeO, CaO, P2O5, and CuO.

[0003] Graphite products are mostly used in high-temperature environments, where non-volatile impurities can be continuously released and contaminate related products, leading to a decrease in yield, especially for products with very high purity requirements, such as semiconductors and crystalline silicon. During the high-temperature sintering of semiconductor ceramic wafers, impurities from the graphite mold encapsulating the semiconductor can volatilize and contaminate the semiconductor ceramic wafers; similarly, during the preparation of crystalline silicon materials, impurities from the graphite electrodes used in the crystalline silicon furnace can volatilize and contaminate the crystalline silicon.

[0004] Currently, the main method for purifying graphite products is chlorine roasting. This involves reacting strong oxidizing halogen gases such as chlorine with oxides in graphite at high temperatures, generating volatile halide salts that evaporate from the graphite. For example, patent number 202411193365.0, entitled "A Method for Improving the Purity and Uniformity of Graphite Products for Semiconductors," describes a method where purifying gases such as chlorine halogen gases, carbon tetrafluoride, or fluorocarbons are introduced into the graphite product through a vent pipe at the bottom of an Atcheson furnace. These gases react with impurities to generate volatile substances that escape, thus achieving purification.

[0005] However, the carbon-based resistance material used in the Atchison furnace also contains a large amount of non-volatile impurities. The resistance material is tightly packed around the graphite product for heating. Under high temperatures, these impurities vaporize and penetrate into the graphite product through surface adsorption and solid-state diffusion. The purified gas, during its ascent, struggles to reach the contact surface between the resistance material and the graphite product, resulting in locally high, or even excessive, impurity content in the graphite product. Furthermore, the resistance material cannot be preheated at high temperatures for impurity removal because the non-volatile impurities are continuously released and cannot be completely removed in a short time. Prolonged heating is not only energy-intensive but also causes graphitization of the resistance material, reducing its resistivity. Due to the high temperatures, in actual production, the resistance material can generally only be used 4-6 times. Preheating the resistance material at high temperatures significantly shortens its lifespan. Summary of the Invention

[0006] In view of this, this application proposes a purification device for non-volatile impurities in graphite products, which can prevent non-volatile impurities in resistive materials from contaminating graphite products and improve the purity of graphite products.

[0007] A purification device for non-volatile impurities in graphite products includes: A first filler that fills the space around a graphite product, the first filler being thermally conductive and breathable, while absorbing vaporized impurities; An isolation layer used to separate the first filler and the resistive material; An airflow pipe for guiding and heating purified gas is embedded in resistive material and insulating filler, and the outlet of the airflow pipe is located below the resistive material.

[0008] In order to ensure that the purified gas can evenly cover the graphite product, preferably, the purification device for non-volatile impurities in the graphite product is also provided with a uniform distribution structure.

[0009] Furthermore, the uniformly distributed structure can be a uniformly distributed plate. Alternatively, the uniformly distributed structure can be a supporting grid and a leak-proof and breathable layer.

[0010] To prevent gas in the resistive material or insulating filler from seeping into the graphite product from below, preferably, a second filler is also provided below the uniformly distributed structure.

[0011] In addition, this application also provides a purification furnace for reducing the impurity content of graphite products, which includes a purification device for non-volatile impurities in graphite products.

[0012] A purification furnace for reducing the impurity content of graphite products includes a resistive material and a heat-insulating filler. The resistive material and the heat-insulating filler are doped with an inert isolating agent, which is used to suppress the vaporization of impurities in the resistive material and the heat-insulating filler.

[0013] Furthermore, the mass percentage of the inert insulating agent doped in the resistive material or thermal insulation filler is 5% to 8%.

[0014] Preferably, the inert isolating agent is silicon carbide with a particle size of 5~20μm.

[0015] The purification device for non-volatile impurities in graphite products disclosed in this application involves the following steps during installation: First, insulating packing is laid at the bottom of the Atchison furnace, and airflow pipes are pre-embedded, with the outlet of the airflow pipes level with the insulating packing. Then, graphite products are placed with the outlet of the airflow pipes as the center. Next, an isolation layer is placed around the graphite products, and then the first packing is filled between the isolation layer and the graphite products. Finally, resistance material and insulating packing are laid. After the furnace is loaded, the graphite products are graphitized through temperature control. When the temperature rises above 2000 degrees Celsius, purification gas is introduced, causing the purified gas to flow upwards along the pores in the first packing, purifying the graphite products.

[0016] The first packing material can adsorb impurities volatilized from the resistive material, preventing them from entering the graphite product. At the same time, the abundant pores of the first packing material can provide ample channels for the purified gas, allowing the purified gas to fully contact the graphite product for impurity removal.

[0017] Furthermore, the purification device for non-volatile impurities in graphite products described in this application can also be used in the graphitization process. It removes non-volatile impurities from graphite products during the graphitization stage. Thus, by combining the graphitization and purification processes, energy consumption is significantly reduced. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of the purification device for non-volatile impurities in graphite products according to Embodiment 1 of this application; Figure 2 This is a schematic diagram of the structure of the purification device for non-volatile impurities in graphite products according to Embodiment 2 of this application; Figure 3 This is a schematic diagram of the structure of the purification device for non-volatile impurities in graphite products according to Embodiment 3 of this application; Figure 4 This is a schematic diagram of a preferred embodiment of the graphite product non-volatile impurity purification device of Embodiment 4 of this application; Figure 5 This is a schematic diagram of another preferred embodiment of the graphite product non-volatile impurity purification device of Embodiment 4 of this application; Figure 6 and 7 The diagram shows two preferred embodiments of the graphite product non-volatile impurity purification device of Embodiment 5 of this application. Explanation of reference numerals in the attached drawings: Graphite product 1, First filler 2, Inner graphite layer 201, Outer graphite layer 202, Isolation layer 3, Airflow duct 4, Uniformly distributed structure 5, Support grid 501, Uniformly distributed filler 502, Second filler 6, Resistance material 7, Thermal insulation filler 8, Upper graphite felt 9, Lower graphite felt 10, Support platform 11. Detailed Implementation

[0019] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are merely illustrative of the technical solution of this application and are therefore intended to limit the scope of protection of this application.

[0020] The first packing material 2 and the airflow duct 4 of this application are both made of high-temperature resistant and corrosion-resistant materials, such as graphite and silicon carbide.

[0021] Example 1 Please refer to Figure 1 In this embodiment, the first packing material 2 of the graphite product non-volatile impurity purification device is preferably graphite, as graphite has good thermal conductivity, low cost, and does not introduce new impurities. Specifically, the first packing material 2 of the graphite product non-volatile impurity purification device is graphite particles with a particle size of 1-8 mm and an ash content of less than 0.01% to prevent the ash of the graphite particles from vaporizing and contaminating the graphite product 1. The thickness of the first packing material 2 is determined according to the size of the graphite product 1. In a preferred embodiment, the thickness of the first packing material 2 is 5-10 cm. If the first packing material 2 is too thick, the heat transfer is slow, affecting the progress of graphitization and impurity removal, and the amount of first packing material 2 used increases, resulting in higher costs. If the first packing material 2 is too thin, it is easy for irregularly shaped parts to have hollowed-out structures, thereby affecting the heat transfer from the resistive material 7 to the graphite product 1. The bottom of the first packing material 2 is in contact with the insulation layer. The isolation layer 3 used to separate the first packing material 2 and the resistive material 7 is a graphite shell with an open bottom and only one exhaust port at the top. The graphite shell is not removed during graphitization. The outlet of the airflow duct 4 is directly opposite the axis of the graphite product 1, so that the gas can be dispersed as evenly as possible around the graphite product 1.

[0022] Compared to resistive material 7, graphite particles have better thermal conductivity, resulting in better temperature uniformity when heat is conducted to the graphite product 1. This leads to a better graphitization effect when used in the graphitization process. Through the barrier effect of the first filler 2, the non-volatile impurities of the resistive material 7 first contaminate the first filler 2, reducing the consumption of purified gas and allowing a higher concentration of purified gas to penetrate into the graphite product 1, thus improving the impurity removal effect. Depending on the impurity concentration of the first filler 2, it can be used as a disposable filler or reused multiple times by incorporating new graphite particles. Since the amount of first filler 2 used is relatively small, the cost of replacing the filler is also low.

[0023] The purified gas reacts with impurities in graphite product 1 to generate products with lower melting and boiling points, which are then vaporized and discharged at high temperatures. For example, if the purified gas is chlorine, it reacts with the non-volatile impurity alumina to form aluminum chloride. Alumina has a boiling point of 2980 degrees Celsius, while aluminum chloride has a boiling point of only 180 degrees Celsius. Thus, after the impurities are converted into more volatile products, they are more easily vaporized and discharged at high temperatures, thereby reducing the impurity content of graphite product 1.

[0024] To facilitate the placement of the graphite product 1 and the filling of the first filler 2, in a preferred embodiment, the isolation layer 3 includes a cover and a cylinder, which are interlocked. After the first filler 2 is filled into the cylinder, the cover is snapped onto the cylinder.

[0025] The purified gas entering the Atchison furnace is at a low temperature, and its temperature gradually increases as it rises. The higher the temperature, the easier it is for the purified gas to react with impurities. This results in different impurity contents at different heights of the graphite product 1 after purification, meaning the impurities in graphite product 1 are unevenly distributed, especially at the bottom, where impurities are difficult to remove at low temperatures. The gas flow duct 4 of this application can be laid in the insulating packing 8 to preheat the gas, or it can be laid in the resistive material 7 to preheat the gas. After preheating, the temperature difference between the purified gas and the surrounding environment decreases, resulting in better consistency in impurity removal from graphite product 1.

[0026] Example 2 Please refer to Figure 2 The difference between this embodiment and Embodiment 1 is that the isolation layer 3 is removed before purification. In this embodiment, the material of the isolation layer 3 can be graphite, silicon carbide, resin, plastic, etc., without introducing new impurities. During removal, the isolation layer 3 is slowly lifted upwards, allowing the surrounding resistive material 7 or the first filler 2 to replace the pores of the isolation layer 3. In this way, the heat of the resistive material 7 is directly conducted to the first filler 2, resulting in high heat transfer efficiency, and the vaporized impurities in the resistive material 7 are absorbed by the first filler 2.

[0027] In this case, in order to prevent the top of the graphite product 1 from being contaminated by gaseous impurities in the insulation filler 8, the top of the graphite product 1 is covered with graphite particles with a particle size of 3-5 mm and a thickness of 2-3 cm. The ash content of the graphite particles is less than 0.01%.

[0028] Example 3 Please refer to Figure 3The difference between this embodiment and Embodiment 1 lies in that the first packing 2 is composed of an outer layer of graphite 202 and an inner layer of graphite 201. The outer layer of graphite 202 has a thickness of 3–5 cm and a particle size of 1–3 mm; the inner layer of graphite 201 has a thickness of 5–7 cm and a particle size of 5–8 mm. The outer layer of graphite 202 is mainly used for heat conduction and absorption of gaseous impurities, while the inner layer of graphite 201 is mainly used to form upward-flowing airflow channels, guiding the airflow to be evenly distributed and prolonging the gas residence time. This scheme is also applicable to Embodiment 2 and will not be repeated. When this scheme is applied to Embodiment 2, the outer layer of graphite 202 has a smaller particle size, which can effectively block and absorb vaporized impurities from the resistive material 7. The inner layer of graphite 201 has a larger particle size, which helps the purified gas to pass through and fully contact the graphite product 1.

[0029] Example 4 The difference between this embodiment and Embodiment 1 is that a uniform distribution structure 5 is provided between the graphite product 1 and the outlet of the airflow pipe 4. Before reaching the graphite product 1, the purified gas passes through the uniform distribution structure 5, which splits the gas flow, allowing it to disperse as much as possible upon reaching the graphite product 1. The purified gas then enters the first packing 2 and flows upward along the gaps in the first packing 2. During this process, the purified gas removes impurities from the graphite product 1 on the side. This scheme is also applicable to Embodiments 2 and 3, and will not be repeated here.

[0030] Based on Example 4, the uniformly distributed structure 5 has multiple forms.

[0031] Please refer to Figure 4 In a preferred embodiment, the uniform distribution structure 5 is a uniform distribution plate, and the pores of the uniform distribution plate are smaller than the pores of the first filler 2 to prevent material leakage.

[0032] Please refer to Figure 5 In another preferred embodiment, the uniformly distributed structure 5 includes a supporting grid 501 and a uniformly distributed packing 502 located above the supporting grid 501. The uniformly distributed packing 502 is a particulate packing that guides the purified gas to disperse during its ascent. The material can be graphite or silicon carbide and other high-temperature and corrosion-resistant materials. In a preferred embodiment, the particle size of the uniformly distributed packing 502 is 5-10 mm, and the thickness of the uniformly distributed packing 502 is 3-5 cm.

[0033] Example 5 The difference between this embodiment and Embodiment 4 is that a second filler 6 is further provided below the graphite product 1. The second filler 6 is used to absorb gasified impurities entering from the bottom. In a preferred embodiment, the second filler 6 is graphite particles with a particle size of 1-3 mm and a thickness of 3-5 cm.

[0034] When a uniformly distributed structure 5 is provided above the second packing 6, a certain gap needs to be left between the second packing 6 and the uniformly distributed structure 5 to allow gas diffusion. In a preferred embodiment, please refer to... Figure 6 and Figure 7 The purification device for non-volatile impurities in graphite products also includes an upper graphite felt 9, a lower graphite felt 10, and a support platform 11. The second packing material 6 is sandwiched between the upper graphite felt 9 and the lower graphite felt 10. The support platform 11 is disposed on the upper graphite felt 9, and the uniformly distributed structure 5 is disposed on the support platform 11. The support platform 11 can take various forms, such as several spaced support blocks or a ring with a certain thickness.

[0035] Example 6 This embodiment describes an Acheson furnace equipped with a purification device for non-volatile impurities in graphite products. To reduce the vaporization of impurities in the resistive material 7 and the insulating filler 8, an inert isolating agent is added to both. The inert isolating agent is uniformly dispersed in the gaps of the resistive material 7, physically isolating impurity particles such as Fe and Ca, preventing them from agglomerating at high temperatures to form large volatile phases, such as Fe₂O₃ and CaO agglomerates. Simultaneously, the inert isolating agent fills the micron-sized pores of the resistive material 7, reducing the diffusion channels for impurity gases such as Fe vapor and CaO sublimations at high temperatures, thus lowering the volatilization rate. Furthermore, the inert isolating agent does not react with metallic impurities such as Fe and Ca at high temperatures, avoiding the formation of low-melting-point compounds, and its low saturated vapor pressure prevents the introduction of new volatile impurities. The inert isolating agent can be silicon carbide, boron nitride, etc.

[0036] In a preferred embodiment, the inert isolating agent is silicon carbide. The main component of the resistive material 7 is coke, and silicon carbide with a mass ratio of 5% to 8% is doped into the coke as an inert isolating agent, and the particle size of the silicon carbide is 5 to 20 μm.

[0037] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A device for purifying a graphite product from non-volatile impurities, characterized by The application relates to a graphite product (1) and a device for purifying volatile impurities in the graphite product (1). The device comprises: a first filler (2) filled in the space around the graphite product (1), the first filler (2) being heat-conducting, air-permeable and capable of absorbing volatile impurities; a separation layer (3) for separating the first filler (2) and resistance material (7); and a gas flow pipe (4) for guiding and heating purified gas, the gas flow pipe (4) being embedded in the resistance material (7) and heat-insulating filler (8), and the gas outlet of the gas flow pipe (4) being arranged below the resistance material (7). The first filler (2) is composed of inner-layer graphite (201) and outer-layer graphite (202). The graphite product volatile impurity purifying device is further provided with a uniform distribution structure (5).

2. The apparatus for purifying a graphite product from a hard volatile impurity according to claim 1, characterized by: The uniform distribution structure (5) is a uniform distribution plate.

3. The apparatus for purifying a graphite product from a hard volatile impurity according to claim 1, wherein: The uniform distribution structure comprises a support grid (501) and uniform distribution filler (502) arranged above the support grid (501).

4. The apparatus for purifying a graphite product from a hard volatile impurity according to claim 3, wherein: A second filler (6) is further arranged below the uniform distribution structure (5).

5. The apparatus for purifying the graphite product from a hard-to-volatilize impurity according to claim 3, wherein: The device further comprises upper-layer graphite felt (9), lower-layer graphite felt (10) and a support table (11), the second filler (6) being clamped between the upper-layer graphite felt (9) and the lower-layer graphite felt (10), the support table (11) being arranged on the upper-layer graphite felt (9), and the uniform distribution structure (5) being arranged on the support table (11).

6. The apparatus for purifying a graphite product from a hard volatile impurity according to claim 3, wherein: The device further comprises resistance material (7) and heat-insulating filler (8), the resistance material (7) and the heat-insulating filler (8) being doped with inert separation agents for inhibiting the gasification of impurities in the resistance material and the heat-insulating filler.

7. The apparatus for purifying a graphite product from a hard volatile impurity according to claim 6, wherein: The mass percentage of the inert separation agents doped in the resistance material (7) or the heat-insulating filler (8) is 5-8%.

8. A purification furnace comprising the apparatus for purifying a graphite product from a nonvolatile impurity according to any one of claims 1 to 6, characterized by: The inert separation agents are silicon carbide, and the particle size of the silicon carbide is 5-20 mu m.

9. The purification furnace of claim 8, wherein: ​ 10. The purification furnace of claim 8, wherein: ​

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