A method for refining magnesium by reinforcing internal heat transfer and external heating

Abstract

This invention belongs to the field of metallurgy, specifically relating to a magnesium smelting method that enhances internal heat transfer and synergistically heats external heating. This method utilizes the heat storage and high thermal conductivity of auxiliary heated pellets to enhance heat transfer within the reduction tank, thereby significantly shortening the reduction cycle. Compared to existing technologies, this method achieves synergistic internal and external heating of cold pellets without adding any equipment. It solves the problems of poor heat transfer in traditional methods, such as long pellet heating times and inability to quickly reach the ideal reaction temperature. This effectively shortens the reduction cycle, achieving energy conservation and emission reduction, while also allowing for a larger diameter magnesium reduction tank, thus improving production efficiency.

Description

Technical Field

[0001] This invention belongs to the field of metallurgy, specifically relating to a magnesium smelting method that enhances internal heat transfer and coordinates with external heating. Background Technology

[0002] The Pidgeon process is currently the main method for producing metallic magnesium. Its raw material is dolomite, which is calcined to obtain calcined dolomite, which is then combined with fluorite and ferrosilicon to form pellets for vacuum thermal reduction to produce metallic magnesium. With the continuous development of magnesium demand and production technology, the diameter of the reduction tank has been increasing. However, magnesium pellets have poor thermal conductivity, and increasing the diameter of the reduction tank will significantly increase the reduction cycle. The large temperature gradient within the reduction tank means that, in actual production, the pellets in the central area of ​​the reduction tank still cannot reach the expected reaction temperature after the reduction is complete. Furthermore, the high-temperature magnesium slag produced is directly discharged after the reduction and sent to a slag yard for cooling, failing to effectively utilize the heat it carries.

[0003] Patent CN101706204A discloses an externally heated vertical tank magnesium smelting device, which consists of an upper and lower cover plate, a bottom support base, a central tube, a conical cap, and a crystallizer. This device has advantages such as convenient operation, low labor intensity, and high production capacity. Patent CN102776389B discloses a method for utilizing the waste heat of hot magnesium slag. It utilizes a moving bed to recover the heat from the hot magnesium slag. The moving bed is equipped with heat exchange tubes. Cold magnesium pellets inside the heat exchange tubes are heated by the hot magnesium slag outside the tubes. After being heated to above 350°C, the cold magnesium pellets are discharged and added to a magnesium reduction furnace. Magnesium slag cooled to below 200°C is then moved and discharged. Other related studies suggest using waste heat boilers to recover the heat carried by magnesium slag, converting the heat into other forms for reuse.

[0004] Patent CN1163622C discloses an internal heating process and equipment for magnesium smelting. Magnesium oxide and ferrosilicon-based magnesium pellets are added to a reactor with concentrically arranged radiant tubes. Furnace gas passes through the interior of the radiant tubes, transferring heat to the pellets filled between them. Patent CN204421605U discloses a vertical tank regenerative reduction furnace for metallic magnesium, consisting of an inner reduction tank and an outer reduction tank. Pellets are filled between the inner and outer tanks, and heating occurs simultaneously inside the inner tank and outside the outer tank.

[0005] Patent CN101020969A discloses a continuous magnesium production equipment using an internally heated sealed vacuum electric furnace. This equipment consists of a sealed vacuum electric furnace, a liquid magnesium refrigeration condenser, and a solid magnesium refrigeration condenser connected sequentially. The sealed vacuum electric furnace has a heating element inside, a feed port, an observation hole, a vacuum outlet, and a protective gas pipe at the top, and a slag discharge port at the bottom. Patents CN100557048C, CN107937735A, CN109722551A, and CN207936754U disclose methods that use electromagnetic induction to heat a pre-placed heating element within the equipment. This heating element, as part of the equipment, transfers the heat generated to the magnesium pellets, reaching the required reaction temperature. Patents CN105970004B and CN111270088A disclose methods that use electromagnetic induction to heat ferrosilicon to form a molten pool. Magnesium raw materials are added to the molten pool, and the magnesium smelting reaction is carried out using the heat provided by the molten pool. Summary of the Invention

[0006] To address the problem of long reduction cycles caused by poor heat transfer in the current magnesium smelting process, this invention provides a magnesium smelting method that enhances internal heat transfer and coordinates with external heating. By filling auxiliary heated pellets, the heat storage and thermal conductivity of the auxiliary heated pellets are utilized to enhance heat transfer within the reduction tank, forming a method that enhances internal heat transfer and coordinates with external heating, thereby significantly shortening the reduction cycle.

[0007] The technical solution of this invention is implemented through the following steps:

[0008] (1) Pellet preparation: The magnesium-containing material is mixed with reducing agent and mineralizing agent, finely ground, and pressed into pellets. These pellets are called "magnesium-containing pellets".

[0009] (2) Preparation of auxiliary hot pellets: Prepare auxiliary hot pellets with enhanced internal heat transfer function; the auxiliary hot pellets are alumina, calcium oxide, magnesium oxide, silicon oxide, titanium oxide, manganese oxide, iron oxide, copper oxide or several of them synthesized by high temperature reaction and pressed into a pellet with magnesium reducing slag, graphite, steel or iron.

[0010] (3) Loading: Add auxiliary hot pellets and magnesium-containing pellets into the reduction tank;

[0011] (4) Reduction: Cover the reduction tank with the lid, seal the reduction tank, and simultaneously heat the reduction tank externally. The heating method is either resistance heating or gas heating. The heating temperature is 900-1600℃, with a typical temperature of 1100-1300℃. The magnesium smelting process begins. The atmosphere inside the reduction tank is either vacuum, relative vacuum, or flowing inert gas. The magnesium smelting process is a continuous or semi-continuous process.

[0012] (5) Slag removal: Slag removal is performed after the reduction is completed;

[0013] (6) Recycling of auxiliary hot pellets: After the reducing residue and auxiliary hot pellets have fully exchanged heat, they are separated and the filling material is recycled.

[0014] Wherein, the magnesium-containing pellets in step (1) are pellets obtained by calcining dolomite and magnesite with one or more of the reducing agents ferrosilicon, carbon, aluminum or carbides, and adding one or more of calcium fluoride and magnesium fluoride in a stoichiometric ratio; or pellets obtained by calcining dolomite and magnesite with one or more of the reducing agents ferrosilicon, carbon, aluminum or carbides, and adding one or more of calcium fluoride and magnesium fluoride, and then pressing them at high temperature to decompose the carbonates;

[0015] The loading in step (3) is selected from one or more of the following three methods:

[0016] The first method of charging involves uniformly mixing auxiliary hot pellets with magnesium-containing pellets.

[0017] The second method involves adding magnesium-containing pellets and auxiliary heated pellets alternately, layer by layer, into the reduction tank;

[0018] The third method of charging involves inserting a packing tube into the reduction tank, adding auxiliary heated pellets into the packing tube, and adding magnesium-containing pellets into the gap between the packing tube and the reduction tank.

[0019] In step (3), the auxiliary hot pellets can be added at room temperature or heated before being added to the reduction tank. The heating temperature is 100-1600℃, and it is preferred to add them to the reduction tank after heating. The heating method of the auxiliary hot pellets is selected from one or more of the following combined heating methods: using the residual heat of the reduction slag, the residual heat of the flue gas, gas heating, resistance heating, electromagnetic induction heating, microwave heating, and electric arc heating. When the third charging method is adopted, it is preferred that the packing tube and the auxiliary hot pellets are heated together before being added to the reduction tank.

[0020] When using the first or second charging method, the volume of the auxiliary hot pellet is 0.5-2 times the volume of the magnesium-containing pellet; when using the third charging method, the size of the auxiliary hot pellet is such that it can be placed into the packing tube; the shape of the auxiliary hot pellet is preferably spherical.

[0021] When using the first or second charging method, the amount of auxiliary hot pellets added must be such that the total volume of the auxiliary hot pellets is less than or equal to 1 / 2 of the total volume of the reduction tank; when using the third charging method, the filling height of the auxiliary hot pellets must be no less than the height of the magnesium-containing pellets added, but no more than the height of the packing tube.

[0022] Among them, when the third loading method is adopted and the packing tube is open at both ends, the packing tube can be pulled out after the pellets are loaded and before the reduction tank is sealed.

[0023] When the third charging method is used, the outer diameter of the packing tube is less than 2 / 3 of the inner diameter of the reduction tank, and the material of the packing tube is selected from steel tube, graphite tube, corundum tube and mullite tube.

[0024] In step (5), the slag discharge and the separation of the reducing slag from the auxiliary hot pellets are carried out by one or more of the following methods: screening, sorting, gravity separation or magnetic separation.

[0025] The reduction tank is either horizontal or vertical.

[0026] Compared with existing technologies, this invention utilizes the method of filling auxiliary hot pellets to achieve synergistic heating of cold pellets from both inside and outside without adding any equipment. Due to the good heat storage or thermal conductivity of the auxiliary hot pellets, they rapidly transfer their own heat or the heat from outside the reduction tank to the cold pellets, causing the cold pellets to heat up quickly. This solves the problems of long pellet heating time and inability to quickly reach the ideal reaction temperature caused by poor heat transfer in traditional methods. It can effectively shorten the reduction cycle, achieve the purpose of energy saving and emission reduction, and at the same time, it can increase the diameter of the magnesium reduction tank and improve the production efficiency. Detailed Implementation

[0027] Example 1

[0028] (1) Pellet preparation: Pellet is prepared by mixing the oxides obtained from calcining dolomite and magnesite with one or more of the reducing agents ferrosilicon, carbon, aluminum, and carbides, and adding one or more of calcium fluoride and magnesium fluoride in a stoichiometric ratio; or it can be prepared by mixing and pressing dolomite and magnesite with one or more of the reducing agents ferrosilicon, carbon, aluminum, and carbides, and adding one or more of calcium fluoride and magnesium fluoride, and then calcining at high temperature to decompose the carbonates.

[0029] (2) The auxiliary hot pellets are one or more of the following: alumina, calcium oxide, magnesium oxide, silicon oxide, titanium oxide, manganese oxide, iron oxide, copper oxide, or compounds synthesized by high-temperature reaction of several of them, magnesium reducing slag, graphite, steel, or iron; the size of the auxiliary hot pellets is equal to the volume of the magnesium-containing pellets.

[0030] (3) Loading: Add auxiliary hot pellets and magnesium-containing pellets into the reduction tank, which is a vertical tank; the auxiliary hot pellets are added at room temperature, and the addition method is the first loading method, that is, the auxiliary hot pellets and magnesium-containing pellets are mixed evenly; the amount of auxiliary hot pellets added is such that the total volume of the auxiliary hot pellets is 1 / 2 of the total volume of the reduction tank.

[0031] (4) Reduction: Cover the reduction tank with the lid, seal the reduction tank, and simultaneously heat the reduction tank externally. The heating method is resistance heating, and the heating temperature is 1200℃. Start the magnesium smelting process. The atmosphere inside the reduction tank is a flowing inert gas, and the magnesium smelting process is a continuous process.

[0032] (5) Slag removal: Slag removal is performed after the reduction is completed;

[0033] (6) Recycling of auxiliary hot pellets: After the reducing residue and auxiliary hot pellets have fully exchanged heat, they are screened and separated, and the filling material is recycled.

[0034] This invention can effectively shorten the heating cycle and achieve the same reduction rate while shortening the reduction cycle by 30% compared to the method without adding auxiliary hot pellets.

[0035] Example 2

[0036] The method is basically the same as Example 1, except that: in step 2, the size of the auxiliary heated pellets is 0.5 times the volume of the magnesium-containing pellets; in step 3, the reduction tank is a horizontal tank, and the auxiliary heated pellets are heated and then loaded into the reduction tank at a heating temperature of 1200℃. The heating method includes one or more of the following combined heating methods: utilizing the residual heat of the reduction slag, the residual heat of the flue gas, gas heating, resistance heating, electromagnetic induction heating, microwave heating, and electric arc heating; the auxiliary heated pellets are added using the second loading method, that is, magnesium-containing pellets and auxiliary heated pellets are added to the reduction tank alternately, layer by layer; the amount of auxiliary heated pellets added is such that the total volume of the auxiliary heated pellets is 1 / 3 of the total volume of the reduction tank; in step 4, gas heating is used at a heating temperature of 1300℃, the atmosphere inside the reduction tank is a vacuum, and the magnesium smelting process is a semi-continuous process. This invention can effectively shorten the heating cycle and, compared with the method without adding auxiliary heated pellets, achieve the same reduction rate while shortening the reduction cycle by 20%.

[0037] Example 3

[0038] The process is basically the same as in Example 1, except that: in step 2, the size of the auxiliary heated pellets is twice the volume of the magnesium-containing pellets; in step 3, the reduction tank is a vertical tank, and the auxiliary heated pellets are heated and then loaded into the reduction tank at a heating temperature of 1600℃. The heating method includes one or more of the following combined heating methods: utilizing the residual heat of the reduction slag, the residual heat of the flue gas, gas heating, resistance heating, electromagnetic induction heating, microwave heating, and electric arc heating; the auxiliary heated pellets are added using the third loading method, i.e., a packing tube is inserted into the reduction tank, the auxiliary heated pellets are added into the packing tube, and the magnesium-containing pellets are added into the gap between the packing tube and the reduction tank; the loading height of the auxiliary heated pellets is not less than the height of the magnesium-containing pellets loaded, but not higher than the height of the packing tube; the diameter of the packing tube is equal to 2 / 3 of the diameter of the reduction tank, the material is steel pipe, and both ends are open. After loading the pellets, the packing tube is pulled out before sealing the reduction tank; in step 4, resistance heating is used at a heating temperature of 1100℃, the atmosphere inside the reduction tank is a relative vacuum, and the magnesium smelting process is continuous. This invention can effectively shorten the heating cycle. Compared with the method without adding auxiliary hot pellets, it can achieve the same reduction rate but shorten the reduction cycle by 40%.

[0039] Example 4

[0040] Similar to Example 1, except that: in step 2, the size of the auxiliary heated pellets is 0.8 times the volume of the magnesium-containing pellets; in step 3, the reduction tank is a vertical tank, and the auxiliary heated pellets are heated and then loaded into the reduction tank at a heating temperature of 100°C. The heating method includes one or more of the following combined heating methods: utilizing the residual heat of the reduction slag, the residual heat of the flue gas, gas heating, resistance heating, electromagnetic induction heating, microwave heating, and electric arc heating; the auxiliary heated pellets are added using a third loading method, i.e., inserting a packing tube into the reduction tank to load the auxiliary heated pellets. Hot pellets are added to the packing tube, and magnesium-containing pellets are added to the gap between the packing tube and the reduction tank. The loading height of the auxiliary hot pellets is not less than the height of the loaded magnesium-containing pellets, but not higher than the height of the packing tube. The diameter of the packing tube is equal to 1 / 2 of the diameter of the reduction tank, and the material is one of steel, graphite, corundum, or mullite tubes. It is open at both ends or only one end. After loading the pellets, the packing tube remains in the reduction tank. In step 4, gas heating is used at a heating temperature of 1400℃, and the atmosphere inside the reduction tank is a vacuum. The magnesium smelting process is a semi-continuous process. This invention can effectively shorten the heating cycle. Compared with the method without adding auxiliary hot pellets, it achieves the same reduction rate, but shortens the reduction cycle by 35%.

[0041] Example 5

[0042] The method is essentially the same as Example 1, except that: in step 2, the size of the auxiliary heated pellets is 1.5 times the volume of the magnesium-containing pellets; in step 3, the reduction tank is a horizontal tank, and the auxiliary heated pellets are heated and then loaded into the reduction tank at a heating temperature of 1600°C. The heating method includes one or more of the following combined heating methods: utilizing the residual heat of the reduction slag, the residual heat of the flue gas, gas heating, resistance heating, electromagnetic induction heating, microwave heating, and electric arc heating; the auxiliary heated pellets are added using the third charging method; in step 4, resistance heating is used at a heating temperature of 1300°C, the atmosphere inside the reduction tank is a vacuum, and the magnesium smelting process is continuous. This invention can effectively shorten the heating cycle, achieving the same reduction rate while reducing the reduction cycle by 35% compared to the method without adding auxiliary heated pellets.

[0043] Example 6

[0044] The method is essentially the same as Example 1, except that: in step 2, the size of the auxiliary heated pellets is 1.8 times the volume of the magnesium-containing pellets; in step 3, the reduction tank is a vertical tank, and the auxiliary heated pellets are heated and then loaded into the reduction tank at a heating temperature of 1400°C. The heating method includes one or more of the following combined heating methods: utilizing the residual heat of the reduction slag, the residual heat of the flue gas, gas heating, resistance heating, electromagnetic induction heating, microwave heating, and electric arc heating; the auxiliary heated pellets are added using the second charging method; in step 4, gas heating is used at a heating temperature of 1400°C, the atmosphere inside the reduction tank is a relative vacuum, and the magnesium smelting process is continuous. This invention can effectively shorten the heating cycle, achieving the same reduction rate while reducing the reduction cycle by 28% compared to the method without adding auxiliary heated pellets.

[0045] Example 7

[0046] The method is basically the same as Example 1, except that: in step 2, the size of the auxiliary heated pellets is equal to the volume of the magnesium-containing pellets, which is 1 times the volume of the auxiliary heated pellets; in step 3, the reduction tank is a horizontal tank, and the auxiliary heated pellets are heated and then loaded into the reduction tank at a heating temperature of 1200°C. The heating method includes one or more of the following combined heating methods: utilizing the residual heat of the reduction slag, the residual heat of the flue gas, gas heating, resistance heating, electromagnetic induction heating, microwave heating, and electric arc heating; the auxiliary heated pellets are added using the first loading method; in step 4, resistance heating is used at a heating temperature of 1200°C, the atmosphere inside the reduction tank is a vacuum, and the magnesium smelting process is a semi-continuous process. This invention can effectively shorten the heating cycle and, compared with the method without adding auxiliary heated pellets, achieve the same reduction rate while shortening the reduction cycle by 15%.

[0047] Example 8

[0048] The method is basically the same as Example 1, except that: in step 2, the size of the auxiliary heated pellets is 0.6 times the volume of the magnesium-containing pellets; in step 3, the reduction tank is a vertical tank, and the auxiliary heated pellets are heated and then loaded into the reduction tank at a heating temperature of 600°C. The heating method includes one or more of the following combined heating methods: utilizing the residual heat of the reduction slag, the residual heat of the flue gas, gas heating, resistance heating, electromagnetic induction heating, microwave heating, and electric arc heating; the auxiliary heated pellets are added using the first charging method; in step 4, gas heating is used at a heating temperature of 1100°C, the atmosphere inside the reduction tank is a flowing inert gas, and the magnesium smelting process is a semi-continuous process. This invention can effectively shorten the heating cycle, achieving the same reduction rate while reducing the reduction cycle by 20% compared to the method without adding auxiliary heated pellets.

[0049] Comparative Example 1

[0050] Without using auxiliary heated pellets, the oxides obtained from calcining dolomite and magnesite are mixed with one or more of the reducing agents ferrosilicon, carbon, aluminum, and carbides, and one or more of calcium fluoride and magnesium fluoride are added in stoichiometric ratios and pressed into pellets. The process is carried out in a horizontal tank, using a vacuum semi-continuous magnesium smelting process with a reduction temperature of 1100-1300℃. The reduction cycle is 30% longer than that in this scheme.

[0051] Comparative Example 2

[0052] Without using auxiliary heating pellets, the pellets are made by mixing and pressing dolomite, magnesite, and one or more of the reducing agents ferrosilicon, carbon, aluminum, and carbides, with the addition of one or more of calcium fluoride and magnesium fluoride. The pellets are then calcined at high temperature to decompose the carbonates. The resulting pellets are obtained through a vertical tank, relative vacuum continuous magnesium smelting process, with a reduction temperature of 1100-1300℃. The reduction cycle is 20% longer than that in this scheme.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the embodiments of the present invention have been described in detail, those skilled in the art should understand that any modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for smelting magnesium by enhancing internal heat transfer and coordinating with external heating, characterized in that, Includes the following steps: (1) Pellet preparation: The magnesium-containing material is mixed with reducing agent and mineralizing agent, finely ground, and pressed into pellets. These pellets are called "magnesium-containing pellets". (2) Preparation of auxiliary thermal pellets: Prepare auxiliary thermal pellets with enhanced internal heat transfer function. The auxiliary thermal pellets are compounds synthesized by high-temperature reaction of one or more of alumina, calcium oxide, magnesium oxide, silicon oxide, titanium oxide, manganese oxide, iron oxide or copper oxide, mixed with one or more of magnesium reducing slag, graphite, steel or iron and pressed into pellets. (3) Loading: Add auxiliary hot pellets and magnesium-containing pellets into the reduction tank; The loading method involves inserting a packing tube into the reduction tank, adding auxiliary heated pellets into the packing tube, heating the auxiliary heated pellets before loading them into the reduction tank, and adding magnesium-containing pellets into the gap between the packing tube and the reduction tank; the temperature at which the auxiliary heated pellets are added to the reduction tank is 100-1600℃. (4) Reduction: Cover the reduction vessel with the lid, seal the reduction vessel, and simultaneously heat the reduction vessel externally. (5) Slag removal: Slag removal is performed after the reduction is completed; (6) Recycling of auxiliary hot pellets: After the reducing residue and auxiliary hot pellets have fully exchanged heat, they are separated and the filling material is recycled.

2. The magnesium smelting method with enhanced internal heat transfer and synergistic external heating according to claim 1, characterized in that, The magnesium-containing pellets mentioned in step (1) are pellets obtained by calcining dolomite and magnesite and mixing the oxides and reducing agents selected from one or more of ferrosilicon, carbon, aluminum or carbides with one or more of calcium fluoride or magnesium fluoride. Alternatively, they are pellets obtained by calcining dolomite and magnesite with one or more of the reducing agents ferrosilicon, carbon, aluminum or carbides with one or more of calcium fluoride or magnesium fluoride after high-temperature calcination to decompose the carbonates.

3. The magnesium smelting method with enhanced internal heat transfer and synergistic external heating according to claim 1, characterized in that, The auxiliary hot pellets are heated by utilizing one or more of the following methods in combination: residual heat from reducing slag, residual heat from flue gas, gas heating, resistance heating, electromagnetic induction heating, microwave heating, or electric arc heating.

4. The magnesium smelting method with enhanced internal heat transfer and synergistic external heating according to claim 1, characterized in that, In the aforementioned loading method, the outer diameter of the packing tube is less than 2 / 3 of the inner diameter of the reduction tank, and the material of the packing tube is selected from one of steel tube, graphite tube, corundum tube, and mullite tube.

5. A magnesium smelting method with enhanced internal heat transfer and synergistic external heating according to claim 1, characterized in that, The heating method described in step (4) is selected from resistance heating and gas heating, with a heating temperature of 900-1600℃ and a typical temperature of 1100-1300℃; the atmosphere in the reduction tank is one of vacuum, relative vacuum, or flowing inert gas, and the magnesium smelting process is a continuous or semi-continuous process.

6. A magnesium smelting method with enhanced internal heat transfer and synergistic external heating according to claim 1, characterized in that, The slag discharge method described in step (5) is selected from one or more of the following methods: screening, sorting, gravity separation and magnetic separation.