CN102041398B - A smelting reduction carbothermal magnesium production process and device - Google Patents

Abstract

The invention discloses a process and device for preparing magnesium by utilizing smelting reduction carbothermy. The process comprises the following steps: proportioning calcium oxide, aluminum oxide and silicon dioxide into base slag; mixing calcined magnesite, reductant coal and carbon or graphite to prepare a raw material; putting the prepared base slag into a charging crucible, and then putting the charging crucible into a vacuum reactor; heating the base slag in the vacuum reactor so that the base slag is in a complete melting state; adding the prepared raw material to the melted base slag so that MgO in the raw material is completely dissolved in the base slag; carrying out the reduction reaction of the MgO under the condition that the temperature is 1550-1650 DEG C; and collecting the magnesium steam obtained from the reduction reaction to prepare metal magnesium. The invention reduces the cost of the raw material by taking the coal with low price as a reductant, increases the reaction speed because the reaction is carried out in the slag completely melted, realizes the continuous production of the magnesium because the raw material can be continuously added to a reaction furnace, effectively reduces the labor strength and enhances the utilization rate and production efficiency of equipment.

Description

A smelting reduction carbothermal magnesium production process and device

technical field

The invention relates to a process for smelting magnesium, in particular to a process for producing magnesium by smelting reduction carbothermal method. At the same time, the invention also relates to a set of magnesium production equipment designed by using the process, which belongs to the technical field of metallurgy.

Background technique

The Pidgeon method is currently the most widely used thermal magnesium smelting process. It uses ferrosilicon alloys to reduce calcined dolomite to produce magnesium metal under vacuum. Due to the problems of environmental pollution, low production efficiency, and high energy consumption in the Pidgeon process, the development of new magnesium smelting processes has become an inevitable trend in the development of the magnesium industry. At present, there are two main development directions for thermal magnesium smelting: 1. Use cheap carbon instead of ferrosilicon alloy as a reducing agent to produce magnesium metal, that is, carbon thermal method; 2. In a semi-continuous resistance furnace, use bauxite and forging White mixed to form a slag, using ferrosilicon as a reducing agent to produce magnesium metal, that is, a semi-continuous reduction method. These two methods have some progress compared with the Pidgeon method, but there are still some shortcomings. The carbothermal method uses cheap carbon instead of ferrosilicon alloy as the reducing agent, which greatly reduces the cost of raw materials. However, the carbothermal method is still a reaction between solids, so the reduction rate is still not high, and continuous production cannot be achieved. The semi-continuous method can realize continuous production by continuously feeding slag in the semi-continuous resistance furnace, which improves the production efficiency. The cost is high, and the reaction is a solid-liquid mixture, and the proportion of the liquid phase is small, and the reaction speed is restricted by the proportion of the liquid phase, and the increase is not large.

Contents of the invention

In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a smelting reduction carbothermal magnesium production process which reduces the cost of raw materials, accelerates the reaction speed and realizes continuous production.

Another object of the present invention is a set of magnesium production equipment designed based on the above smelting reduction carbothermal magnesium production process.

The technical solution of the present invention is achieved in the following way: a smelting reduction carbothermal process for magnesium production, which uses magnesite as the main raw material, calcium oxide, aluminum oxide and silicon dioxide as slagging agents, and coal, carbon or graphite as Reducing agent; Its preparation steps are:

(1) Calcination-magnesite is calcined to obtain calcined magnesite for use;

(2) Base slag preparation - the base slag is made of calcium oxide, alumina and silicon dioxide. The range of alkalinity calcium oxide/silicon dioxide is controlled between 1 and 1.8, and alumina accounts for the total weight of the base slag. 20% ~ 40% of;

(3) Raw material preparation - mix the prepared calcined magnesite with reducing agent, the molar ratio of C in reducing agent to MgO in calcined magnesite is 1.1-1.4;

(4) Vacuuming - put the prepared base slag into the charging crucible, then put the base slag together with the charging crucible into the vacuum reactor, and the vacuum of the reactor is controlled between 10Pa and 1000Pa;

(5) Slag melting - heating the base slag in the vacuum reactor to make the base slag in a completely molten state;

(6) Feeding - Add the raw materials prepared in step (3) to the molten base slag, so that the MgO in the raw material is completely melted in the base slag to form a CaO-MgO-Al ₂ O ₃ -SiO ₂ quaternary Slag, and make MgO quality control below 20% of quaternary slag;

(7) Reduction reaction - reduce MgO at a temperature of 1550°C to 1650°C;

(8) Collection - The magnesium vapor obtained from the reduction reaction is collected by condensation to obtain metallic magnesium.

The feeding in the step (6) is continuous feeding or interval feeding, so that the reduction reaction in the (7) step continues, and the mass of MgO is always kept below 20% of the quaternary slag.

The particle size of the magnesite and carbon particles is greater than 60 mesh.

The base slag in step (4) occupies 1/3-1/2 of the volume of the crucible for charging.

The magnesium production device designed according to the above-mentioned smelting reduction carbothermal magnesium production process includes a furnace shell with an open upper end and a furnace cover that seals the upper end of the furnace shell. The furnace shell and furnace cover are vacuum; There is a refractory brick layer, and the middle of the refractory brick layer is a cavity to form a heating area. In the heating area, there is a charging crucible for containing slag, and heating elements are arranged around the charging crucible and between the refractory brick layer; Feeding mechanism, the feeding pipe of the feeding mechanism enters the charging crucible through the furnace shell and the refractory brick layer; a graphite heat insulator is arranged above the opening of the charging crucible, and the graphite heat insulator is surrounded by a refractory brick layer, and the center of the graphite heat insulator A through hole is provided; a crystallizer facing the through hole is provided above the graphite heat insulator.

Furthermore, a dust-proof cover is provided in the crystallizer, and the dust-proof cover covers the central through hole of the graphite heat insulator, and a number of ventilation holes are provided around the lower end of the dust-proof cover.

At the same time, a cooling cover with a sandwich structure is provided in the furnace cover. The cooling cover corresponds to the shape of the crystallizer and is covered on the crystallizer. The cooling cover is provided with a cooling liquid inlet and a cooling liquid outlet connected to the interlayer. The liquid outlets are respectively drawn out of the furnace cover through the cooling liquid pipes to be connected with the cooling liquid.

A refractory brick pad is arranged between the bottom of the charging crucible and the refractory brick layer.

The feeding mechanism includes a material discharge tank and a material preparation tank, and the discharge tank and the material preparation tank are connected through a pipeline, and a regulating valve is arranged on the pipeline, and the feeding pipe communicates with the material discharge tank.

In the present invention, the reduction of magnesium oxide and the collection of magnesium vapor are carried out in the same reactor. This process uses cheap coal as a reducing agent, which reduces the cost of raw materials; the reaction is carried out in completely melted slag, which speeds up the reaction speed; raw materials do not need to be pelletized, and can be continuously added to the reaction furnace, realizing the continuous production of magnesium. Effectively reduce labor intensity, and improve equipment utilization and production efficiency.

Description of drawings

Fig. 1-Schematic diagram of the structure of the magnesium production device of the present invention.

Among them, 1-furnace shell; 2-refractory brick layer; 3-refractory brick pad; 4-heating element; 5-graphite insulation; 6-dust cover; 7-crystallizer; 8-furnace cover; Vacuum system; 10-feeding mechanism; 11-charging crucible; 12-slag; 13-feeding pipe; 14-discharge tank; 15-preparation tank; 16-regulating valve; 17-through hole; 18-cooling cover; 19 - Coolant pipe.

Detailed ways

The technical solution of the present invention will be further described below in conjunction with the accompanying drawings.

The smelting reduction carbothermal magnesium production process of the present invention uses magnesite as the main raw material, calcium oxide, aluminum oxide and silicon dioxide as slagging agents, and coal, carbon or graphite as reducing agents; the preparation steps are:

(1) Calcination-magnesite is calcined to obtain calcined magnesite for use;

(2) Base slag preparation - the base slag is made of calcium oxide, alumina and silicon dioxide. The range of basicity CaO/SiO ₂ is controlled between 1 and 1.8, and Al ₂ O ₃ accounts for 10% of the total slag. 20%~40% is more appropriate;

(3) Raw material preparation - mix the prepared calcined magnesite and reducing agent carbon particles (coal or graphite). In order to increase the contact area, you can use small-sized magnesite and reducing agent particles, such as passing through a 60-mesh sieve. In order to increase the reduction speed, it is necessary to add an excessive amount of reducing agent, and the molar ratio of C/MgO in the reducing agent is 1.1~1.4; here C refers to the elemental carbon in carbon, coal or graphite that can be used for reaction.

(4) Vacuuming - put the prepared base slag into the charging crucible, the base slag should preferably occupy 1/3~1/2 of the charging crucible, and then put the base slag together with the charging crucible into the vacuum reactor ( In the reaction furnace), the lower the vacuum degree, the more favorable the reduction reaction is. At 1200°C, the solid-state carbothermal reduction can only react when the vacuum reaches 10Pa. At 1600°C, the vacuum only needs 10000Pa to occur. When the reduction is carried out in the molten state, the reaction is easier than that of the solid state. Therefore, carbon reduction below 10000Pa Liquid magnesia can be processed. When low vacuum is used, the residual oxygen in the furnace is easy to oxidize magnesia vapor, so this process controls the vacuum within 10Pa~1000Pa;

(5) Slag melting - heating the base slag in a vacuum reactor to make the base slag in a completely molten state. The reaction furnace uses silicon-molybdenum as the heating element, and the maximum heating temperature can reach 1700°C, and the CaO-Al ₂ O ₃ -SiO ₂ ternary slag can be completely molten at 1200°C~1400°C;

(6) Feeding - Add the raw materials prepared in step (3) to the molten base slag, so that the MgO in the raw material is completely melted in the base slag to form a CaO-MgO-Al ₂ O ₃ -SiO ₂ quaternary slag. In order to ensure that the slag is completely molten at the reaction temperature, the quality of MgO is controlled below 20% of the quaternary slag;

(7) Reduction reaction - reduce MgO at a temperature of 1550°C to 1650°C;

(8) Collection - The magnesium vapor obtained from the reduction reaction is collected by condensation to obtain metallic magnesium.

The feeding in the step (6) is continuous feeding or interval feeding, so that the reduction reaction in the (7) step continues, and the mass of MgO is always kept below 20% of the quaternary slag. Because the ternary base slag will not be consumed during the reaction process, it is only necessary to supplement the calcined magnesite and reducing agent consumed by the reaction in a timely manner by adding materials, so that the reduction reaction will not be interrupted, but the quality of MgO cannot exceed 20% of the quaternary slag. Can.

The magnesium production device designed according to the above smelting reduction carbothermal magnesium production process is essentially a vacuum reaction furnace, which includes a furnace shell 1 with an open upper end and a furnace cover 2 for sealing the upper end of the furnace shell, furnace shell 1 and furnace shell. The inside of the cover 2 is evacuated into a vacuum by a vacuum system 9 . The furnace shell 1 is welded with a 10mm stainless steel plate, and the thick steel plate can well prevent deformation in a vacuum state. Hollow foam ball refractory brick layer 2 is built on the bottom and surrounding of furnace shell 1, which can effectively play the role of heat preservation and heat insulation. The crucible 11 is provided with a heating element 4 between the periphery of the charging crucible 11 and the refractory brick layer 2. The heating element 4 is heated by silicon-molybdenum rods, and the upper limit of the heating temperature is as high as 1700°C. Between the bottom of the charging crucible 11 and the refractory brick layer 2, a refractory brick pad 3 for balancing the crucible is provided. A feeding mechanism 10 is arranged outside the furnace shell 1 , and a feeding pipe 13 of the charging mechanism passes through the furnace shell 1 and the refractory brick layer 2 and enters the charging crucible 11 . Above the opening of the charging crucible 11 is provided a crystallizer 7 facing it, and the crystallizer 7 is placed on the refractory brick layer 2 . The crystallizer 7 is a cylindrical structure with a small top and a large bottom.

The feeding mechanism 10 includes a discharge tank 14 and a stock tank 15, the discharge tank 14 and the stock tank 15 are connected through a pipeline, and a regulating valve 16 is arranged on the pipeline, which can effectively prevent air from entering the reaction furnace. The feed pipe 13 communicates with the discharge tank 14, and the feed pipe 13 is also provided with a regulating valve 16.

Before carrying out the reduction reaction, the charging crucible 11 containing the slag 12 is placed on the refractory brick block 3 in the heating zone. After covering the furnace cover 8, a vacuum is drawn through the vacuum system 9 and heating is started. After the slag 12 is completely melted, the raw materials mixed in proportion are added through the feeding mechanism 10 . When the raw materials in the charging crucible 11 have almost reacted, they can be fed by the feeding mechanism 10 again, so that the purpose of continuous production is achieved. Due to the use of carbothermal reduction, CO and CO ₂ will be formed during the reduction reaction, and these gases will be disposed of through the vacuum system 9 equipped with a filtering device.

Since the reduction reaction is carried out in the high-temperature slag, the heat in the heating zone is very high and will be quickly transferred to the crystallizer 7, so a graphite heat insulator 5 is placed between the charging crucible 11 and the crystallizer 7, and the graphite heat insulator 5 A central through hole 17 is provided, and the crystallizer 7 faces the through hole 17 of the graphite heat insulator. The graphite heat insulator 5 is composed of several graphite plates with a through hole in the center, supported by refractory brick layers around. The graphite insulator 5 can effectively prevent the temperature of the heating zone from being transferred upwards, and the central through hole can smoothly allow the magnesium vapor generated by reduction to pass through smoothly.

In order to prevent dust slag from polluting the crystallizer 7 through the central through hole of the graphite insulator during vacuuming and reaction, a dust cover 6 is provided in the crystallizer 7, and the dust cover 6 covers the central through hole 17 of the graphite insulator. cover up. The dust cover 6 is an inverted cylindrical structure, and the top of the dust cover 6 is closed, and some air holes are provided around the dust cover. The closed top can well prevent heat radiation and dust passing through the central through hole of the graphite insulator 5, and magnesium vapor is enriched on the crystallizer 7 through the vent holes around the dust cover.

When capturing magnesium vapor, the temperature of the crystallizer is very critical, too low or too high will affect the yield and quality of magnesium. The device is equipped with a thermocouple to monitor the temperature of the crystallizer. If the temperature is too high, it can be adjusted by the cooling mechanism. Specifically, a cooling cover 18 with a sandwich structure is provided in the furnace cover 8. The cooling cover 18 corresponds to the shape of the crystallizer and is covered on the crystallizer 7. The cooling cover is provided with a cooling liquid inlet and a cooling liquid outlet communicating with the interlayer. The cooling liquid inlet and the cooling liquid outlet are respectively drawn out of the furnace cover 8 through the cooling liquid pipe 19 to be connected with the cooling liquid. The cooling mechanism can effectively regulate the temperature of the crystallizer.

Example 1

Put the charging crucible with base slag into the heating zone of the reaction furnace, the amount of base slag added is 1/2 of the height of the crucible after melting, and the base slag composition is CaO:SiO ₂ :Al ₂ O ₃ =45% :30%:25%, the alkalinity is 1.5. Then place the graphite plate and the dust cover, then cover the furnace cover, vacuumize and heat. Vacuum pumping until the air pressure in the furnace is 1000Pa, and the reaction temperature is controlled at about 1550°C. After the temperature has stabilized for a period of time, the base slag has completely melted. At this time, the raw material is sent to the charging crucible through the feeding mechanism. The raw material is calcined magnesite and carbon particles, and the C/MgO molar ratio is 1.1. The composition of the slag formed after the addition of calcined magnesite is CaO:MgO:SiO ₂ :Al ₂ O ₃ =37%:18%:25%:20%. Carbon particles reduce the MgO in the liquid slag at high temperature. As the reaction progresses, when the raw materials are continuously consumed, the raw materials are sent to the charging crucible through the feeding mechanism again. The magnesium vapor generated by the reduction is enriched on the crystallizer. To ensure the crystallization effect, the temperature of the crystallizer is controlled at around 500°C by oil cooling. The crystallizer obtains massive metal magnesium, and after the reaction, the MgO content in the slag is 5%, and the reduction rate of magnesium oxide reaches 85%.

Example 2

The amount of base slag used is 1/3 of the height of the crucible after melting, the composition of the base slag is CaO:SiO ₂ :Al ₂ O ₃ =40%:30%:30%, and the basicity is 1.3. The vacuum is 10Pa, and the reaction temperature is controlled at about 1650°C. The raw materials are calcined magnesite and graphite powder, wherein the C/MgO molar ratio is 1.4, and the composition of the slag formed after adding calcined magnesite is CaO:MgO:SiO ₂ :Al ₂ O ₃ =35%:13%:26%: 26%. The whole process is fed three times, and finally block metal magnesium is obtained. The MgO content in the slag is 2.6%, and the reduction rate of magnesium oxide reaches 94%.

Claims (9)

1. A smelting reduction carbothermal process for magnesium production is characterized in that: the process uses magnesite as the main raw material, calcium oxide, aluminum oxide and silicon dioxide are slagging agents, and carbon is a reducing agent; its preparation steps are: (1) Calcination-magnesite is calcined to obtain calcined magnesite for use; (2) Base slag preparation - the base slag is made of calcium oxide, alumina and silicon dioxide. The range of alkalinity calcium oxide/silicon dioxide is controlled between 1 and 1.8, and alumina accounts for the total weight of the base slag. 20% ~ 40% of; (3) Raw material preparation - mix the prepared calcined magnesite with reducing agent, the molar ratio of C in reducing agent to MgO in calcined magnesite is 1.1-1.4; (4) Vacuuming - put the prepared base slag into the charging crucible, then put the base slag together with the charging crucible into the vacuum reactor, and the vacuum of the reactor is controlled between 10Pa and 1000Pa; (5) Slag melting - heating the base slag in the vacuum reactor to make the base slag in a completely molten state; (6) Feeding - Add the raw materials prepared in step (3) to the molten base slag, so that the MgO in the raw material is completely melted in the base slag to form a CaO-MgO-Al ₂ O ₃ -SiO ₂ quaternary Slag, and make MgO quality control below 20% of quaternary slag; (7) Reduction reaction - reduce MgO at a temperature of 1550°C to 1650°C; (8) Collection - The magnesium vapor obtained from the reduction reaction is collected by condensation to obtain metallic magnesium. 2. The smelting reduction carbothermal magnesium production process according to claim 1, characterized in that: the feeding in the (6) step is continuous feeding or intermittent feeding, so that the reduction reaction in the (7) step continues, And always keep the quality of MgO below 20% of the quaternary slag. 3. The smelting reduction carbothermal magnesium production process according to claim 1 or 2, characterized in that: the carbon is carbon particles, and the size of the magnesite and carbon particles is greater than 60 mesh. 4. The smelting reduction carbothermal magnesium production process according to claim 3, characterized in that: the base slag in the step (4) occupies 1/3-1/2 of the volume of the crucible for charging. 5. According to claim 1, the magnesium production device designed by the smelting reduction carbothermal magnesium production process is characterized in that it includes a furnace shell (1) with an open upper end and a furnace cover (8) for sealing the upper end of the furnace shell , the inside of the furnace shell and furnace cover is a vacuum; there is a refractory brick layer (2) at the bottom and surrounding of the furnace shell (1), the middle of the refractory brick layer is a cavity to form a heating area, and a charging crucible for containing slag is arranged in the heating area (11), a heating element (4) is provided between the surrounding of the charging crucible (11) and the refractory brick layer (2); a feeding mechanism (10) is arranged outside the furnace shell (1), and the feeding tube of the charging mechanism ( 13) Enter the charging crucible (11) through the furnace shell and refractory brick layer; a graphite heat insulator (5) is provided above the opening of the charging crucible (11), and the graphite heat insulator is surrounded by a refractory brick layer. A through hole (17) is provided in the center of the heating body (5); a crystallizer (7) facing the through hole is provided above the graphite heat insulator (5). 6. The magnesium making device according to claim 5, characterized in that: a dust cover (6) is provided in the crystallizer (7), and the dust cover (6) covers the central through hole (17) of the graphite heat insulator Cover, and be provided with some ventilation holes around the lower end of the dust cover. 7. The magnesium making device according to claim 5 or 6, characterized in that: a cooling cover (18) with a sandwich structure is provided inside the furnace cover (8), and the cooling cover (18) corresponds to the shape of the crystallizer and is covered in On the crystallizer (7), the cooling cover is provided with a cooling liquid inlet and a cooling liquid outlet communicating with the interlayer, and the cooling liquid inlet and the cooling liquid outlet are respectively drawn out of the furnace cover through the cooling liquid pipes to connect with the cooling liquid. 8. The magnesium making device according to claim 7, characterized in that: a refractory brick pad (3) is provided between the bottom of the charging crucible (11) and the refractory brick layer. 9. The magnesium making device according to claim 8, characterized in that: the feeding mechanism (10) includes a material discharge tank (14) and a material preparation tank (15), a material discharge tank (14) and a material preparation tank (15) It is communicated with the pipeline, and the pipeline is provided with a regulating valve (16), and the feed pipe (13) is communicated with the discharge tank (14).

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