A double-layer composite reduction device for magnesium smelting

Abstract

This invention discloses a double-layer composite reduction device for magnesium smelting, comprising a reduction reaction unit, a slag discharge unit, and a crystallization unit. The reduction reaction unit includes a heat-resistant steel outer tank, a ceramic inner tank, and a central cylinder. The ceramic inner tank is mounted on a support device inside the heat-resistant steel outer tank. The outer diameter of the ceramic inner tank is smaller than the inner diameter of the heat-resistant steel outer tank, with a gap between them to avoid direct contact and damage to the device due to differences in thermal expansion coefficients, thereby improving the efficiency of the reduction device and extending its service life. Furthermore, a pressure adjustment device is provided at the top of the ceramic inner tank. By adjusting the pressure adjustment device, the pressure applied to the ceramic inner tank can be adjusted to maintain the stability of the ceramic inner tank and prevent damage to the inner ceramic tank due to the cooling and shrinkage of the metal tank, thus extending the service life of the ceramic inner tank.

Description

Technical Field

[0001] This invention relates to the field of vacuum pyrometallurgical smelting of metallic magnesium, and more particularly to a double-layer composite reduction apparatus for magnesium smelting. Background Technology

[0002] The Pidgeon process accounts for over 80% of the world's primary magnesium production and is currently the mainstream magnesium smelting technology globally. The externally heated vertical tank silicon process is developed from the traditional horizontal tank Pidgeon process, aiming to utilize the gravity of the raw materials and reducing slag for feeding and slag removal, thereby increasing the mechanization and automation of production. Currently, heat-resistant steel reducing tanks are commonly used in silicon magnesium smelting, but "tank adhesion and glazing" occurs during actual production. "Tank adhesion and glazing" is essentially a molten adhesion phenomenon after the furnace charge or reducing slag melts and softens. It not only forms a glaze layer of a certain thickness on the tank wall, affecting the heat transfer rate and reduction efficiency, but also causes slag balls to stick together, resulting in difficulty in slag removal and even tank stagnation. Therefore, "tank adhesion and glazing" is a major challenge restricting the development of externally heated silicon magnesium smelting technology.

[0003] Currently, no detailed research results or patents have been found to solve the problem of "glaze adhesion to the smelting pot" in magnesium smelting. In response, the inventors of this invention first conducted a systematic study on the mechanism of "glaze adhesion to the smelting pot." The silicothermic process for magnesium smelting uses calcined dolomite (calcined dolomite, effective component MgO·CaO) as raw material and ferrosilicon (effective component Si) as a reducing agent. A reduction reaction occurs under high temperature and low vacuum (1200℃, 10Pa): 2(MgO·CaO) (s) +Si (s) →2Mg (g) +2CaO·SiO 2(s) The main substances in the reducing slag are CaO, SiO2, MgO, Fe2O3, Al2O3 and their composite oxides, as well as the active agent CaF2 and elements Fe and Si. Phase diagram analysis and experimental investigation revealed that during the silicothermic magnesium reduction process, when the raw materials are within the normal composition range, the binary and ternary systems of the four oxides CaO, MgO, SiO2, and Al2O3 do not form a liquid phase (low-melting-point substance) below 1200℃, thus preventing molten agglomeration. Figure 1 As shown, the lowest temperature at which the CaO-Al2O3-MgO ternary system forms a liquid phase is around 1500℃, and a liquid phase will not form under magnesium smelting conditions.

[0004] When FeO or Fe2O3 (collectively known as iron oxides) are present, they will form liquid-phase composite oxides with calcium oxide or magnesium oxide at a temperature of 1200℃, such as calcium ferrite or magnesium ferrite.

[0005]

[0006] Furthermore, in the presence of SiO2, FeO, SiO2, and CaO or MgO can also form low-melting-point composite oxides, such as... Figure 2 As shown in the ternary phase diagram of CaO-SiO2-FeO, melting below 1200℃ can occur within the range of CaO < 40 wt%, SiO2 < 50 wt%, and FeO > 20 wt%. Therefore, ferrite compounds are the core factor causing the melt-bonding problem.

[0007] However, in actual production, the content of ferrooxides is relatively low, and their source is controllable. Therefore, controlling ferrooxides can prevent can sticking. There are three main sources of ferrooxides in magnesium smelting: ① introduction by raw material impurities; ② reaction between air entering during feeding and slag removal and ferrosilicon to generate ferrooxides; ③ reaction between air entering during feeding and slag removal and heat-resistant steel to generate ferrooxides. The ferrooxides generated in the first and second situations account for a small proportion and are mainly distributed within the feed pellets, having limited impact on the melting and adhesion of the pipe wall. Therefore, the ferrooxides generated on the inside of the heat-resistant steel due to the third situation are the main factor causing "can sticking and glazing." Therefore, if contact between the raw material and the heat-resistant steel can be avoided, i.e., the raw material should not come into contact with the ferrooxides on the inside of the heat-resistant steel, the problem of "can sticking and glazing" can be effectively solved.

[0008] The inventors discovered that some patents propose using non-metallic reduction vessels to replace metallic ones, thus avoiding direct contact between the raw materials and heat-resistant steel. For example, Chinese patent document CN101182219A discloses a silicon carbide reduction vessel and its preparation method. This patent uses a silicon carbide reduction vessel to replace the existing chromium-nickel heat-resistant steel reduction vessel, aiming to reduce manufacturing costs while extending the vessel's service life. However, the porosity of SiC ceramic products prepared under conventional production conditions is typically above 10%, lacking the ability to maintain a high vacuum. Therefore, reduction vessels made of silicon carbide cannot be used alone in magnesium smelting. Chinese patent document CN102212692A discloses a high-temperature resistant non-metallic vertical reduction vessel. The reduction vessel designed in this invention is made by extruding carbonaceous refractory materials (such as silicon carbide or graphite clay) and then sintering them at high temperature. However, the reduction vessel made of this ceramic material not only cannot meet the requirements for maintaining a high vacuum, but the graphite material is also prone to oxidation at high temperatures and cannot be used for a long time at 1200℃. In addition, the ceramic products made of graphite clay have low toughness and poor thermal shock resistance, which is not suitable for the working environment of periodic feeding and slag discharge in magnesium smelting. Therefore, this invention cannot be applied to magnesium smelting, and no practical application of this type of patent has been seen to date.

[0009] Furthermore, some patents have been found to combine ceramics with metals to address the issue of ceramic materials not being able to maintain a high vacuum, thus also preventing direct contact between raw materials and heat-resistant steel. For example, Chinese patent document CN2310075Y discloses a structure for refractory materials lining the inside and outside of a magnesium reduction tank; Chinese patent document CN106591597A discloses a ceramic composite reduction tank; and Chinese patent document CN203976894U discloses a magnesium reduction tank. These patents aim to provide support to the metal tank by bonding refractory materials to it or using ceramic materials as an inner lining, thereby reducing the corrosive effects of the working environment and extending the tank's lifespan. However, these patents do not fully consider the chemical interactions between the metal and the refractory materials, as well as the physical effects such as the coefficient of thermal expansion, making them unusable in actual production. The coefficients of thermal expansion of heat-resistant steel and refractory materials differ significantly (as shown in Table 1). The coefficient of thermal expansion of austenitic steel at high temperatures (1000℃) is approximately 20 × 10⁻⁶. -6 / ℃, the coefficient of thermal expansion of general refractory materials at high temperatures does not exceed 8×10 -6 / ℃, the difference in their expansion coefficients is more than double.

[0010] Table 1. Linear expansion coefficients of common substances at room temperature

[0011]

[0012] Therefore, the contact surface will inevitably crack or break under high temperatures due to uneven expansion, eventually causing the mounting material to fail and fall off, resulting in irreversible damage to the reduction vessel. Thus, the designs of these patents lack basic rationality, and reduction vessels manufactured based on these designs will inevitably have extremely short lifespans or be completely unusable. To date, none of these patents have been applied in actual production. Summary of the Invention

[0013] In view of the above-mentioned deficiencies of the prior art, the present invention provides a magnesium smelting double-layer composite reduction device, including a reduction reaction unit, a slag discharge unit and a crystallization unit, wherein the slag discharge unit is disposed at the bottom of the reduction reaction unit and the crystallization unit is disposed at the top of the reduction reaction unit;

[0014] The reduction reaction unit includes a heat-resistant steel outer tank, a ceramic inner tank, and a central cylinder.

[0015] The lower inner side of the heat-resistant steel outer tank is equipped with a support device to support the ceramic inner tank. The outer diameter of the ceramic inner tank is smaller than the inner diameter of the heat-resistant steel outer tank, and there is a gap between the ceramic inner tank and the heat-resistant steel outer tank.

[0016] The central cylinder is located inside the ceramic inner tank, and the space between the outer side of the central cylinder and the inner side of the ceramic inner tank forms a metallurgical furnace charge receiving space; in addition, a pressure adjustment device is provided above the ceramic inner tank to adjust the pressure applied to the ceramic inner tank.

[0017] The magnesium smelting double-layer composite reduction device provided by this invention, by installing a ceramic inner tank inside the heat-resistant steel vertical tank, avoids direct contact between the magnesium smelting raw materials and reducing slag and the heat-resistant steel, effectively preventing the formation of molten and agglomerated substances. It also avoids physical friction between the furnace charge and the inner wall of the heat-resistant steel during charging and slag removal. The outer diameter of the ceramic inner tank is smaller than the inner diameter of the heat-resistant steel outer tank, with a gap between them. This prevents direct contact between the ceramic inner tank and the heat-resistant steel outer tank, preventing chemical reactions at high temperatures and avoiding cracking or damage at high temperatures due to the significant difference in thermal expansion coefficients between metal and ceramic. Since the magnesium smelting temperature is around 1200℃, the heat-resistant steel outer tank undergoes severe high-temperature deformation at this temperature, far exceeding the deformation of the ceramic inner tank. A pressure regulating device is installed above the ceramic inner tank. After heating, pressure is applied to the ceramic inner tank to stabilize it and prevent movement, misalignment, or tilting during operation. Conversely, during cooling, the heat-resistant steel outer tank shrinks significantly more than the ceramic inner tank. Adjusting the pressure regulating device reduces pressure on the ceramic inner tank to prevent crushing of the inner tank due to the outer tank's greater shrinkage. Furthermore, the pressure regulating device can also prevent insecure installation, movement, misalignment, or tilting of the ceramic inner tank during the slag discharge stage of the magnesium smelting vertical tank, or during the lifting or jacking of the central cylinder. Such instability could disrupt continuous magnesium smelting operations, damage the reduction tank, or cause serious economic losses.

[0018] In one embodiment, the clamping adjustment device includes a limiting plate, a pressure rod fixing plate, an adjusting screw, a fixing nut, and a pressure rod;

[0019] Among them, the limiting plate and the pressure rod fixing plate are fixed on the inner wall of the double-layer composite reduction device, with the limiting plate located above the pressure rod fixing plate;

[0020] The adjusting screw passes through the limiting plate, and the fixing nut is fitted on the adjusting screw. The fixing nut is located below the limiting plate. The adjusting screw can be fixed or moved up and down by adjusting the fixing nut.

[0021] There are at least two pressure bar fixing plates with holes on them. The pressure bar passes through the holes to maintain stability. The pressure bar is in direct or indirect contact with the top of the ceramic inner tank.

[0022] The clamping adjustment device adjusts the pressure on the pressure rod by adjusting the up and down movement of the adjusting screw, thereby adjusting the pressure applied to the ceramic inner tank.

[0023] In one embodiment, the clamping adjustment device includes a limiting plate, a pressure rod fixing plate, an adjusting screw, and a pressure rod;

[0024] Among them, the limiting plate and the pressure rod fixing plate are fixed on the inner wall of the double-layer composite reduction device, with the limiting plate located above the pressure rod fixing plate;

[0025] The adjusting screw passes through the limiting plate, which has a tapping structure that engages with the thread of the adjusting screw, thus allowing the adjusting screw to be fixed and move up and down.

[0026] There are at least two pressure bar fixing plates with holes on them. The pressure bar passes through the holes to maintain stability. The pressure bar is in direct or indirect contact with the top of the ceramic inner tank.

[0027] The clamping adjustment device regulates the pressure applied to the pressure rod by adjusting the up-and-down movement of the adjusting screw, thereby regulating the pressure exerted on the ceramic inner tank. Removing the fixing nut simplifies the device, making installation and adjustment more convenient.

[0028] In one embodiment, a rigid sleeve is provided outside the pressure bar to prevent the pressure bar from deforming or bending.

[0029] In one embodiment, the limiting plate and the pressure rod fixing plate are disposed within the crystallization unit to facilitate control of the adjusting screw during operation.

[0030] In one embodiment, a high-temperature resistant insulating gasket is provided between the pressure rod and the ceramic inner tank to prevent a chemical reaction between the pressure rod and the ceramic inner tank at high temperatures.

[0031] In one embodiment, the number of clamping adjustment devices is greater than or equal to two, and they are evenly distributed around the inner wall of the double-layer composite reduction device to better stabilize the ceramic inner tank.

[0032] In one embodiment, the ceramic inner tank is made of SiC to ensure that it can be used for a long time in a high-temperature vacuum environment.

[0033] In one embodiment, the support device is made of steel, and an isolation layer is provided between the ceramic inner tank and the support device to prevent the ceramic inner tank from undergoing a physicochemical reaction with the steel at high temperatures, thereby corroding the heat-resistant steel and causing the melting point of the heat-resistant steel to drop below 1200°C, causing the metal tank to melt and become unstable.

[0034] In one embodiment, the material of the insulating layer is a high-temperature resistant material that does not undergo physicochemical reactions with SiC or steel, preferably alumina, magnesium oxide, calcium oxide, or any mixture thereof.

[0035] In one embodiment, the material of the isolation layer is in the form of powder, sheet, or plate.

[0036] In one embodiment, the thickness of the isolation layer is not less than 1 mm.

[0037] In one embodiment, the material of the high-temperature resistant insulating gasket is a high-temperature resistant material that does not undergo physical and chemical reactions with SiC or steel, preferably alumina, magnesium oxide, calcium oxide, or any mixture thereof.

[0038] In one embodiment, the ceramic inner tank consists of one or more ceramic tank sections. These sections are detachably connected to form the inner tank, thereby facilitating its transportation, installation, and replacement.

[0039] In one embodiment, the multi-section ceramic jar is connected by a snap-fit ​​or socket joint.

[0040] In one embodiment, the support device is a support ring.

[0041] In one embodiment, a mounting groove is provided inside the support ring, and the ceramic inner tank is placed in the mounting groove.

[0042] In one embodiment, the edge of the mounting groove is spaced from the heat-resistant steel outer tank to prevent direct contact between the heat-resistant steel outer tank and the ceramic inner tank.

[0043] In one embodiment, the support device is welded to the inside of the heat-resistant steel outer tank.

[0044] This invention has at least the following technical effects:

[0045] 1) By installing a ceramic inner tank inside the heat-resistant steel vertical tank, direct contact between magnesium smelting raw materials and reducing slag and heat-resistant steel is avoided, effectively preventing the formation of molten and agglomerated substances, as well as physical friction between the furnace charge and the inner wall of the heat-resistant steel during the feeding and slag discharge process. This helps to achieve automated slag discharge, improves production efficiency, and thus achieves the goal of smooth slag discharge and long-term stable operation.

[0046] 2) By setting a gap between the ceramic inner tank and the heat-resistant steel outer tank, direct contact between the high-temperature ceramic and the heat-resistant steel is avoided, preventing chemical reactions at high temperatures and preventing cracking or damage at the contact surface due to inconsistent expansion caused by the large difference between the thermal expansion coefficients of metal and ceramic at high temperatures.

[0047] 3) Pressure is applied to the ceramic inner tank through the clamping and adjusting device to fix the ceramic inner tank and maintain the stability of the ceramic tank body. This prevents the ceramic inner tank from shifting or tilting during the slag discharge process, i.e., the lifting or jacking of the central cylinder, so that the magnesium smelting process can be carried out continuously. At the same time, the clamping and adjusting device can flexibly adjust the pressure on the ceramic inner tank, which can effectively avoid damage to the ceramic inner tank caused by the shrinkage of the heat-resistant steel outer tank during the cooling process and extend the service life of the ceramic inner tank.

[0048] 4) By using a rigid sleeve to prevent the pressure bar from deforming or bending, pressure can be applied more effectively to the ceramic inner tank;

[0049] 5) By setting an isolation layer between the pressure bar and the ceramic inner tank, as well as between the support device and the ceramic inner tank, the ceramic inner tank is completely separated from the steel pressure bar and support device, thus avoiding physical and chemical reactions between the two and extending the service life of the device.

[0050] 6) Due to limitations in ceramic product manufacturing conditions, integral ceramic inner tanks are not only difficult to manufacture and have high production and transportation costs, but are also prone to damage and difficult to install and replace. By designing multi-segment ceramic inner tanks, manufacturing becomes easier, and transportation, installation, and replacement of ceramic inner tanks are also facilitated, greatly reducing production costs.

[0051] The following will further explain the concept, specific structure, and technical effects of the present invention in conjunction with the accompanying drawings, so as to fully understand the purpose, features, and effects of the present invention. Attached Figure Description

[0052] Figure 1 It is a ternary phase diagram of CaO-Al2O3-MgO;

[0053] Figure 2 It is a ternary phase diagram of CaO-SiO2-FeO;

[0054] Figure 3 This is a schematic diagram of a preferred embodiment of the magnesium smelting double-layer composite reduction device of the present invention;

[0055] Figure 4 This is a top view of a preferred embodiment of the magnesium smelting double-layer composite reduction apparatus of the present invention;

[0056] Figure 5 This is a partial enlarged view of the clamping adjustment device under the clamping state according to a preferred embodiment of the present invention;

[0057] Figure 6 This is a partial enlarged view of the clamping adjustment device under the clamping state according to another preferred embodiment of the present invention;

[0058] Figure 7 This is the TG-DTA diagram of heat-resistant steel;

[0059] Figure 8 This is a morphological diagram of the ceramic material and heat-resistant steel after calcination at 1200°C, which is a preferred embodiment of the present invention.

[0060] Among them, 1-slag discharge unit, 2-support ring, 3-isolation layer, 4-central cylinder, 5-heat resistant steel outer tank, 6-ceramic inner tank, 7-isolation gasket, 8-pressure rod, 9-crystallization unit, 10-pressure rod fixing plate, 11-limiting plate, 12-adjusting screw, 13-fixing nut. Detailed Implementation

[0061] The following description, with reference to the accompanying drawings, illustrates several preferred embodiments of the present invention to make its technical content clearer and easier to understand. The present invention can be embodied in many different forms, and the scope of protection of the present invention is not limited to the embodiments mentioned herein.

[0062] In the accompanying drawings, components with the same structure are indicated by the same numerical designation, and components with similar structures or functions are indicated by similar numerical designations. The dimensions and thicknesses of each component shown in the drawings are arbitrary, and the present invention does not limit the dimensions and thicknesses of each component. To make the illustrations clearer, the thickness of some components has been appropriately exaggerated in the drawings.

[0063] This invention provides a double-layer composite reduction device for magnesium smelting, comprising a reduction reaction unit, a slag discharge unit, and a crystallization unit. The slag discharge unit is located at the bottom of the reduction reaction unit, and the crystallization unit is located at the top of the reduction reaction unit. The reduction reaction unit includes a heat-resistant steel outer tank, a ceramic inner tank, and a central cylinder. A support device is provided on the lower inner side of the heat-resistant steel outer tank to support the ceramic inner tank. The outer diameter of the ceramic inner tank is smaller than the inner diameter of the heat-resistant steel outer tank, and there is a gap between the ceramic inner tank and the heat-resistant steel outer tank. The central cylinder is located inside the ceramic inner tank, and the space between the outer side of the central cylinder and the inner side of the ceramic inner tank forms a metallurgical furnace charge receiving space. Furthermore, a pressure adjustment device is provided above the ceramic inner tank to adjust the pressure applied to the ceramic inner tank.

[0064] The magnesium smelting double-layer composite reduction device provided by this invention, by installing a ceramic inner tank inside the heat-resistant steel vertical tank, avoids direct contact between the magnesium smelting raw materials and reducing slag and the heat-resistant steel, effectively preventing the formation of molten and agglomerated substances. It also avoids physical friction between the furnace charge and the inner wall of the heat-resistant steel during charging and slag removal. The outer diameter of the ceramic inner tank is smaller than the inner diameter of the heat-resistant steel outer tank, with a gap between them. This prevents direct contact between the ceramic inner tank and the heat-resistant steel outer tank, preventing chemical reactions at high temperatures and avoiding cracking or damage at high temperatures due to the significant difference in thermal expansion coefficients between metal and ceramic. Since the magnesium smelting temperature is around 1200℃, the heat-resistant steel outer tank undergoes severe high-temperature deformation at this temperature, far exceeding the deformation of the ceramic inner tank. A pressure regulating device is installed above the ceramic inner tank. After heating, pressure is applied to the ceramic inner tank to stabilize it and prevent movement, misalignment, or tilting during operation. Conversely, during cooling, the heat-resistant steel outer tank shrinks significantly more than the ceramic inner tank. Adjusting the pressure regulating device reduces pressure on the ceramic inner tank to prevent crushing of the inner tank due to the outer tank's greater shrinkage. Furthermore, the pressure regulating device can also prevent insecure installation, movement, misalignment, or tilting of the ceramic inner tank during the slag discharge stage of the magnesium smelting vertical tank, or during the lifting or jacking of the central cylinder. Such instability could disrupt continuous magnesium smelting operations, damage the reduction tank, or cause serious economic losses.

[0065] In one embodiment, the clamping adjustment device includes a limiting plate, a pressure rod fixing plate, an adjusting screw, a fixing nut, and a pressure rod; wherein, the limiting plate and the pressure rod fixing plate are fixed to the inner wall of the double-layer composite reduction device, with the limiting plate located above the pressure rod fixing plate; the adjusting screw passes through the limiting plate, and the fixing nut is fitted onto the adjusting screw, located below the limiting plate, allowing the adjusting screw to be fixed or moved up and down by adjusting the fixing nut; there are at least two pressure rod fixing plates, each with holes through which the pressure rod passes to maintain stability, and the pressure rod is in direct or indirect contact with the top of the ceramic inner tank; the clamping adjustment device adjusts the pressure applied to the pressure rod by adjusting the up and down movement of the adjusting screw, thereby adjusting the pressure applied to the ceramic inner tank.

[0066] In one embodiment, the clamping adjustment device includes a limiting plate, a pressure rod fixing plate, an adjusting screw, and a pressure rod. The limiting plate and the pressure rod fixing plate are fixed to the inner wall of the double-layer composite reduction device, with the limiting plate positioned above the pressure rod fixing plate. The adjusting screw passes through the limiting plate, which has a tapping structure that engages with the thread of the adjusting screw, allowing the adjusting screw to be fixed and move up and down. There are at least two pressure rod fixing plates, each with holes through which the pressure rod passes for stability. The pressure rod is in direct or indirect contact with the top of the ceramic inner tank. The clamping adjustment device adjusts the pressure applied to the pressure rod by adjusting the up and down movement of the adjusting screw, thereby adjusting the pressure applied to the ceramic inner tank. Removing the fixing nut simplifies the device and makes installation and adjustment more convenient.

[0067] In one embodiment, a rigid sleeve is provided outside the pressure bar to prevent the pressure bar from deforming or bending.

[0068] In one embodiment, the limiting plate and the pressure bar fixing plate are disposed within the crystallization unit.

[0069] In one embodiment, a high-temperature resistant insulating gasket is provided between the pressure rod and the ceramic inner tank to prevent a chemical reaction between the pressure rod and the ceramic inner tank at high temperatures.

[0070] In one embodiment, the number of clamping adjustment devices is greater than or equal to two, and they are evenly distributed around the inner wall of the double-layer composite reduction device to better stabilize the ceramic inner tank.

[0071] In one embodiment, the ceramic inner tank is made of SiC to ensure that the ceramic inner tank can be used for a long time in the environment of external flame heating in magnesium smelting.

[0072] In one embodiment, the support device is made of steel, and an isolation layer is provided between the ceramic inner tank and the support device to prevent the ceramic inner tank from undergoing a physicochemical reaction with the steel at high temperatures, thereby corroding the heat-resistant steel and causing the melting point of the heat-resistant steel to drop below 1200°C, causing the metal tank to melt and become unstable.

[0073] In one embodiment, the materials of the high-temperature resistant insulating gasket and the insulating layer are high-temperature resistant materials that do not undergo physicochemical reactions with SiC or steel, preferably alumina, magnesium oxide, calcium oxide, or any mixture thereof.

[0074] In one embodiment, the material of the isolation layer is in the form of powder, sheet, or plate.

[0075] In one embodiment, the thickness of the isolation layer is not less than 1 mm.

[0076] In one embodiment, the ceramic inner tank consists of one or more ceramic tank sections. These sections are detachably connected to form the inner tank, thereby facilitating its transportation, installation, and replacement.

[0077] In one embodiment, the multi-section ceramic jar is connected by a snap-fit ​​or socket joint.

[0078] In one embodiment, the support device is a support ring.

[0079] In one embodiment, a mounting groove is provided inside the support ring, and the ceramic inner tank is placed in the mounting groove.

[0080] In one embodiment, the edge of the mounting groove is spaced from the heat-resistant steel outer tank to prevent direct contact between the heat-resistant steel outer tank and the ceramic inner tank.

[0081] In one embodiment, the support device is welded to the inside of the heat-resistant steel outer tank.

[0082] Example 1

[0083] Figure 3-5 A double-layer composite reduction device for magnesium smelting is shown, comprising a slag discharge unit 1, a support ring 2, an isolation layer 3, a central cylinder 4, a heat-resistant steel outer tank 5, a ceramic inner tank 6, an isolation gasket 7, a crystallization unit 9, and a pressing and adjusting device.

[0084] The slag discharge unit 1, the heat-resistant steel outer tank 5, and the crystallization unit 9 are connected by flanges or welding to form a sealable cavity.

[0085] The space between the central cylinder 4 and the ceramic inner tank 6 forms a metallurgical furnace charge receiving space, in which solid furnace charge is contained during operation. Multiple vent holes connected to the metallurgical furnace charge receiving space are provided on the side wall of the central cylinder 4. Under high-temperature vacuum working conditions, the solid furnace charge generates metal vapor through a chemical reaction. The metal vapor enters the interior of the central cylinder through the vent holes and then rises into the crystallization unit 9 for crystallization.

[0086] The ceramic inner tank 6 is placed on a support ring 2 located on the lower inner side of the heat-resistant steel outer tank 5. The support ring 2 is made of metal, preferably steel. To prevent chemical corrosion between the ceramic inner tank 6 and the support ring 2 due to direct contact, an isolation layer 3 with a thickness of 1 mm is added between them to separate them. The isolation layer 3 is made of alumina (Al2O3).

[0087] A mounting groove is provided inside the support ring 2, and the ceramic inner tank 6 is placed in the mounting groove. The edge of the mounting groove maintains a certain distance from the heat-resistant steel outer tank 5 to ensure that the ceramic inner tank 6 does not directly contact the heat-resistant steel outer tank 5.

[0088] The inner ceramic can 6 is made of silicon carbide and is assembled from 5 ceramic sections from bottom to top. Each ceramic section is connected by a socket or interlocking joint.

[0089] The clamping adjustment device includes a pressure rod 8, a pressure rod fixing plate 10, a limiting plate 11, an adjusting screw 12, and a fixing nut 13. The adjusting screw 12 is moved up and down or fixed by adjusting the fixing nut 13 located below the limiting plate 12. The adjusting screw 12 and the limiting plate 11 are made of metal, such as steel. The pressure rod 8 passes through two holes in the pressure rod fixing plate 10 to maintain its stability. The pressure rod 8 can only move up and down through the holes in the pressure rod fixing plate 10. There are four clamping adjustment devices, evenly distributed around the double-layer composite reduction device.

[0090] The pressure applied to the ceramic inner tank 6 is controlled by the adjusting screw 12 located at the upper end. By controlling the up-and-down movement of the adjusting screw 12, the pressure rod 8 is tightened or loosened, thereby changing the pressure applied to the ceramic inner tank 6 by the pressure rod 8 to maintain the stability of the ceramic inner tank 6. The pressure rod 8 is preferably made of heat-resistant steel. An isolation gasket 7 is provided between the pressure rod 8 and the ceramic inner tank 6. When the temperature of the contact area between the ceramic inner tank 6 and the pressure rod 8 is high, the isolation gasket 7 can prevent the pressure rod 8 from reacting chemically with the ceramic inner tank 6. The material of the isolation gasket 7 is Al2O3.

[0091] During operation, solid furnace charge is added to the metallurgical furnace charge containment space and heated to 1200℃. For the magnesium reduction unit, the operating temperature is 1200±50℃, and the tank material is heat-resistant steel with a coefficient of thermal expansion of approximately 18×10⁻⁶. -6 ℃ -1 Approximately (measured value). However, apart from specially fired magnesia bricks, silica bricks, and other refractory bricks, the coefficient of thermal expansion of various refractory materials is only about 4 to 7 × 10⁻⁶. -6 ℃ -1 Therefore, the coefficients of thermal expansion of heat-resistant steel and refractory materials differ by approximately 11 to 14 × 10⁻⁶. -6 ℃ -1 Furthermore, refractory materials are brittle and their strength at high temperatures is lower than that of heat-resistant steel. Taking a commonly used reduction device with a height of 2700mm as an example, after heating from room temperature to 1200℃, the height expansion of the heat-resistant steel reduction device is 2700×1200×18×10. -6 =58.32mm, but the coefficient of thermal expansion of silicon carbide ceramic products is approximately 4×10. -6 ℃ -1 The refractory material, when used as an inner tank, expands by 2700×1200×4×10 at 1200℃. -6=12.96mm, the difference between the two is 45.36mm. Therefore, even if the silicon carbide ceramic inner tank 6 is fixed at room temperature, the two will inevitably separate or be damaged at high temperature due to the difference in expansion. Therefore, it is necessary to re-fix the ceramic inner tank 6 at high temperature. So after heating to 1200℃, the pressure rod 8 will separate from the adjusting screw 12 and will not be able to fix the ceramic inner tank 6. It is necessary to move the adjusting screw 12 downward to push against the pressure rod 8 to press and fix the ceramic inner tank 6, so as to prevent the ceramic inner tank 6 from moving, misaligning or tilting during use and affecting the continuous operation of magnesium smelting. The reduction device is sealed, vacuumed, and the reaction is maintained at high temperature for 8-10 hours. When cooling down after the reaction, since the shrinkage of the heat-resistant steel outer tank 5 is significantly greater than that of the ceramic inner tank 6, it is necessary to move the adjusting screw 12 upward to reduce the pressure applied by the adjusting screw 12 to the pressure rod 8, thereby reducing the pressure applied to the ceramic inner tank 6 and preventing the ceramic inner tank 6 from being crushed due to excessive shrinkage of the heat-resistant steel outer tank 5 during the cooling process. During slag discharge, the slag discharge port located in the discharge unit 1 is opened, and the adjusting screw 12 is moved downward to press against the pressure rod 8 to tighten and fix the ceramic inner tank 6. During the slag discharge process as the central cylinder 4 moves up and down, the ceramic inner tank 6 can remain stable and will not move, misalign or tilt.

[0092] The device operated continuously for 6 months without any issues such as glaze buildup or dead pots, and the lifespan of the reduction device was extended from the original 3 months to more than 6 months.

[0093] Example 2

[0094] A double-layer composite reduction device for magnesium smelting is provided, comprising a slag discharge unit 1, a support ring 2, an isolation layer 3, a central cylinder 4, a heat-resistant steel outer tank 5, a ceramic inner tank 6, an isolation gasket 7, a crystallization unit 9, and a pressing and adjusting device.

[0095] The slag discharge unit 1, the heat-resistant steel outer tank 5, and the crystallization unit 9 are connected by flanges or welding to form a sealable cavity.

[0096] The space between the central cylinder 4 and the ceramic inner tank 6 forms a metallurgical furnace charge receiving space, in which solid furnace charge is contained during operation. Multiple vent holes connected to the metallurgical furnace charge receiving space are provided on the side wall of the central cylinder 4. Under high-temperature vacuum working conditions, the solid furnace charge generates metal vapor through a chemical reaction. The metal vapor enters the interior of the central cylinder through the vent holes and then rises into the crystallization unit 9 for crystallization.

[0097] The ceramic inner tank 6 is placed on a support ring 2 located on the lower inner side of the heat-resistant steel outer tank 5. The support ring 2 is made of metal, preferably steel. To prevent chemical corrosion between the ceramic inner tank 6 and the support ring 2 due to direct contact, an isolation layer 3 with a thickness of 2 mm is added between them to separate them. The isolation layer 3 is made of magnesium oxide (MgO).

[0098] A mounting groove is provided inside the support ring 2, and the ceramic inner tank 6 is placed in the mounting groove. The edge of the mounting groove maintains a certain distance from the heat-resistant steel outer tank 5 to ensure that the ceramic inner tank 6 does not directly contact the heat-resistant steel outer tank 5.

[0099] The inner ceramic can 6 is made of silicon carbide and is assembled from four ceramic sections from bottom to top. The ceramic sections are connected by sockets or interlocking joints.

[0100] like Figure 6 As shown, the clamping adjustment device includes a pressure rod 8, a pressure rod fixing plate 10, a limiting plate 11, and an adjusting screw 12. The limiting plate 11 has a tapping structure that engages with the threads on the adjusting screw 12, allowing the adjusting screw 12 to be fixed and move up and down. The adjusting screw 12 and the limiting plate 11 are made of metal, such as steel. The pressure rod 8 passes through two holes in the pressure rod fixing plate 10 to maintain its stability; the pressure rod 8 can only move up and down through the holes in the pressure rod fixing plate 10. There are four clamping adjustment devices, evenly distributed around the double-layer composite reduction device.

[0101] The pressure applied to the ceramic inner tank 6 is controlled by the adjusting screw 12 located at the upper end. By controlling the up-and-down movement of the adjusting screw 12, the pressure rod 8 is tightened or loosened, thereby changing the pressure applied to the ceramic inner tank 6 by the pressure rod 8 to maintain the stability of the ceramic inner tank 6. The pressure rod 8 is preferably made of heat-resistant steel. An isolation gasket 7 is provided between the pressure rod 8 and the ceramic inner tank 6. When the temperature of the contact area between the ceramic inner tank 6 and the pressure rod 8 is high, the isolation gasket 7 can prevent the pressure rod 8 from reacting chemically with the ceramic inner tank 6. The material of the isolation gasket 7 is calcium oxide (CaO).

[0102] During operation, solid furnace charge is added to the metallurgical furnace charge containment space and heated to 1200℃. The adjusting screw 12 is moved downwards to press against the pressure rod 8, thereby securing the ceramic inner tank 6 and preventing it from moving, shifting, or tilting during use, which would affect the continuous operation of magnesium smelting. The reduction unit is sealed, a vacuum is drawn, and the reaction is maintained at high temperature for 8-10 hours. After the reaction is completed and the temperature is lowered, the pressure applied by the adjusting screw 12 to the pressure rod 8 is reduced, thereby reducing the pressure applied to the ceramic inner tank 6 and preventing the ceramic inner tank 6 from being crushed due to excessive shrinkage of the heat-resistant steel outer tank 5 during the cooling process. During slag discharge, the slag discharge port located in the discharge unit 1 is opened, and the adjusting screw 12 is moved downwards to press against the pressure rod 8, thereby securing the ceramic inner tank 6. During the slag discharge process as the central cylinder 4 moves up and down, the ceramic inner tank 6 remains stable and will not move, shift, or tilt.

[0103] The device operated continuously for 6 months without any issues such as glaze buildup or dead pots, and the lifespan of the reduction device was extended from the original 3 months to more than 6 months.

[0104] Example 3: Selection of Ceramic Inner Tank Material and Isolation Layer Material

[0105] The inventors of this invention studied the operating temperatures of some common ceramics. Table 2 shows the highest operating temperatures of common ceramics in air. However, the inventors found that Si3N4, BN, etc., undergo rapid oxidation in oxygen-rich environments above 1000℃. Although high-temperature resistant ceramics prepared from Al2O3 are relatively stable under high-temperature conditions, their thermal shock resistance is extremely poor. At temperatures above 1000℃, cracking may occur if the cooling rate exceeds 3℃ / min. Therefore, these ceramic products are not suitable for use in the external flame heating environment of magnesium smelting, and the ceramic inner tank needs to be replaced frequently during the actual smelting process, increasing production costs. SiC does not have these problems. Therefore, after research, it was determined that SiC is the most suitable material for ceramic inner tanks in magnesium smelting.

[0106] Table 2. Maximum operating temperature of common ceramics in air.

[0107]

[0108] Magnesium smelting is generally carried out under conditions below 1200℃ and 10 Pa. The inventors discovered that under these conditions, silicon carbide can corrode heat-resistant steel, causing its melting point to drop below 1200℃, leading to instability due to melting. For example... Figure 7 As shown, compared with the original heat-resistant steel material, the melting point of the corroded heat-resistant steel material is significantly reduced, and it begins to melt at 1139.8℃, showing a strong endothermic peak.

[0109] This invention includes a support device for supporting the ceramic inner tank, preferably made of heat-resistant steel. Therefore, to prevent the heat-resistant steel from being corroded by the SiC ceramic inner tank, an isolation layer is provided on the support device to avoid direct contact between the SiC ceramic inner tank and the heat-resistant steel. The thickness of the isolation layer is not less than 1 mm.

[0110] The inventors of this invention also conducted experimental research on the selection of materials for the isolation layer. The materials selected must have a melting point above 1200℃, be resistant to oxidation, and not easily decompose under vacuum conditions. Commonly used easily oxidized materials such as graphite cannot be used, nor can some silicon-containing materials with strong reducing properties that react with heat-resistant steel. Considering cost factors, usable materials include high-temperature oxides such as Al2O3, CaO, and MgO, or mixtures of these substances. Figure 8 It refers to the morphology of heat-resistant steel and different materials such as Al2O3, CaO, and MgO after calcination at 1200℃ and 10Pa. Among them, the morphology of Al2O3, CaO, and MgO is basically unchanged after calcination with the heat-resistant steel section. Therefore, Al2O3, CaO, or MgO can be used as isolation materials.

[0111] The isolation layer can be aluminum oxide, magnesium oxide, or calcium oxide in powder, sheet, or plate form.

[0112] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A double-layer composite reduction device for magnesium smelting, characterized in that, It includes a reduction reaction unit, a slag discharge unit, and a crystallization unit, wherein the slag discharge unit is located at the bottom of the reduction reaction unit and the crystallization unit is located at the top of the reduction reaction unit; The reduction reaction unit includes a heat-resistant steel outer tank, a ceramic inner tank, and a central cylinder; The lower inner side of the heat-resistant steel outer tank is provided with a support device to support the ceramic inner tank. The outer diameter of the ceramic inner tank is smaller than the inner diameter of the heat-resistant steel outer tank, and there is a gap between the ceramic inner tank and the heat-resistant steel outer tank. The central cylinder is disposed inside the ceramic inner tank, and the space between the outer side of the central cylinder and the inner side of the ceramic inner tank forms a metallurgical furnace charge receiving space; and... The ceramic inner tank is also provided with a pressure adjustment device above it, which is used to adjust the pressure applied to the ceramic inner tank; The clamping adjustment device includes a limiting plate, a pressure rod fixing plate, an adjusting screw, a fixing nut, and a pressure rod; The limiting plate and the pressure rod fixing plate are fixed on the inner wall of the double-layer composite reduction device, and the limiting plate is located above the pressure rod fixing plate; The adjusting screw passes through the limiting plate, and the fixing nut is fitted on the adjusting screw. The fixing nut is located below the limiting plate. The adjusting screw can be fixed or moved up and down by adjusting the fixing nut. There are at least two pressure rod fixing plates, each with a hole. The pressure rod passes through the hole to maintain stability, and the pressure rod is in direct or indirect contact with the top of the ceramic inner tank. The clamping adjustment device adjusts the pressure applied to the pressure rod by adjusting the up-and-down movement of the adjusting screw, thereby adjusting the pressure applied to the ceramic inner tank; or The clamping adjustment device includes a limiting plate, a pressure rod fixing plate, an adjusting screw, and a pressure rod; The limiting plate and the pressure rod fixing plate are fixed on the inner wall of the double-layer composite reduction device, and the limiting plate is located on the pressure rod fixing plate. The adjusting screw passes through the limiting plate, which has a tapping structure that engages with the thread of the adjusting screw, thereby fixing or moving the adjusting screw up and down. There are at least two pressure rod fixing plates, each with a hole. The pressure rod passes through the hole to maintain stability, and the pressure rod is in direct or indirect contact with the top of the ceramic inner tank. The clamping adjustment device adjusts the pressure applied to the pressure rod by adjusting the up and down movement of the adjusting screw, thereby adjusting the pressure applied to the ceramic inner tank.

2. The magnesium smelting double-layer composite reduction device as described in claim 1, characterized in that, The pressure rod is provided with a rigid sleeve.

3. The magnesium smelting double-layer composite reduction device as described in claim 1, characterized in that, A high-temperature resistant insulating gasket is provided between the pressure rod and the ceramic inner tank.

4. The magnesium smelting double-layer composite reduction device as described in claim 1, characterized in that, The number of the compression adjustment devices is greater than or equal to two, and they are evenly distributed around the inner wall of the double-layer composite reduction device.

5. The magnesium smelting double-layer composite reduction device as described in claim 1, characterized in that, The ceramic inner can is made of SiC.

6. The magnesium smelting double-layer composite reduction device as described in claim 1, characterized in that, The support device is made of steel, and an isolation layer is provided between the ceramic inner tank and the support device.

7. The magnesium smelting double-layer composite reduction device as described in claim 6, characterized in that, The material of the isolation layer is aluminum oxide, magnesium oxide, calcium oxide, or any mixture thereof.

8. The magnesium smelting double-layer composite reduction device as described in claim 6, characterized in that, The material of the isolation layer is in the form of powder, flakes, or plates.

9. The magnesium smelting double-layer composite reduction device as described in claim 6, characterized in that, The thickness of the isolation layer is not less than 1 mm.

10. The magnesium smelting double-layer composite reduction device as described in claim 3, characterized in that, The material of the high-temperature resistant insulating pad is aluminum oxide, magnesium oxide, calcium oxide, or any mixture thereof.

11. The magnesium smelting double-layer composite reduction device as described in claim 1, characterized in that, The ceramic inner tank is composed of one or more ceramic tank sections.

12. The magnesium smelting double-layer composite reduction device as described in claim 11, characterized in that, The multi-section ceramic jar can be detachably connected.

13. The magnesium smelting double-layer composite reduction device as described in claim 11, characterized in that, The multi-section ceramic jar is connected by a seam or a socket joint.

14. The magnesium smelting double-layer composite reduction device as described in claim 1, characterized in that, The supporting device is a support ring.

15. The magnesium smelting double-layer composite reduction device as described in claim 14, characterized in that, The support ring has an installation groove, and the ceramic inner tank is placed in the installation groove.

16. The magnesium smelting double-layer composite reduction device as described in claim 15, characterized in that, The edge of the mounting groove maintains a distance from the heat-resistant steel outer tank.

17. The magnesium smelting double-layer composite reduction device as described in claim 1, characterized in that, The support device is welded inside the heat-resistant steel outer tank.

18. The magnesium smelting double-layer composite reduction device as described in claim 1, characterized in that, The limiting plate and the pressure rod fixing plate are disposed within the crystallization unit.

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