Method for preparing aluminum oxide hollow sphere thermal insulation material by using waste residues generated in chromium production

Abstract

A method for preparing an alumina hollow sphere thermal insulation material by using waste residues generated in chromium production relates to a comprehensive utilization method of smelting waste residues, and adopts a mode of replacing a furnace shell, chromium oxide is reduced into metal chromium liquid which is remained at the lower part of the furnace shell, and the upper layer is covered with alumina melt, so that the possibility that the metal chromium is oxidized due to contact with air is avoided; and the efficiency of refining the metal chromium from the aluminum-chromium slag is improved. According to the invention, the slag generated during the production of metal chromium by an aluminothermic method is converted into two products, namely an aluminum oxide hollow ball and a high-grade thermal insulation material; and the other is metal chromium. The two products are high in price, so that high-value utilization in comprehensive resource utilization of the waste aluminum-chromium slag is realized.

Description

Technical Field

[0001] The invention relates to a method for comprehensive utilization of smelting waste residue, in particular to a method for preparing alumina hollow ball thermal insulation material by using waste residue generated in chromium production. Background Art

[0002] The aluminothermic process is a major method for producing metallic chromium. It uses metallic aluminum to react with chromium oxide to reduce chromium oxide to metallic chromium, and metallic aluminum is oxidized to aluminum oxide. Aluminum oxide is the slag of this reaction, floating on the upper layer; metallic chromium sinks to the lower layer. Due to the incompleteness of the reaction, some chromium oxide will be mixed in the aluminum oxide melt. After the slag solidifies, a co-solvent of aluminum oxide and chromium oxide is formed. This is the slag produced in the aluminothermic process. Generally, the aluminum oxide content in this slag is about 80% to 90%, and the chromium oxide content is about 10% to 20%. At present, this slag is only used as a raw material for primary refractory materials. There is no further deep processing of this by-product, and the added value is not high.

[0003] At present, this slag is used to separate alumina from chromium oxide in order to obtain metallic chromium. The alumina obtained after separation is only used as sub-white corundum, which is a primary refractory raw material with low added value. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing alumina hollow ball insulation material using waste slag generated in the production of chromium. The present invention melts the slag generated in the process of producing metallic chromium in a plasma electric melting furnace, purifies the alumina melt, and blows it into alumina hollow balls, so that the slag generated in the process of producing metallic chromium by the aluminothermic method is transformed into alumina hollow ball high-end insulation material with higher added value, thereby realizing high-value utilization of waste slag resources.

[0005] The objective of the present invention is achieved through the following technical solutions: A method for preparing alumina hollow sphere thermal insulation material using waste slag generated in the production of chromium, the method comprising the following preparation steps: (1) firstly, the aluminum-chromium slag is mixed with a carbon reducing agent in a ratio of 100 / 4 to 100 / 8 by weight of the slag to the carbon reducing agent; (2) The mixture of aluminum-chromium slag and carbon reducing agent is melted in a plasma electric melting furnace. During the melting process, the chromium oxide in the slag is reduced to metallic chromium and deposited at the bottom of the furnace, while the aluminum oxide melt is on the upper layer, thus achieving the separation of aluminum oxide and metallic chromium. (3) After a furnace melting cycle is completed, the alumina melt is blown into hollow balls to be taken out of the furnace; the furnace body is tilted to allow the alumina melt to flow out from the furnace nozzle, and compressed air is used to blow this stream to disperse the alumina melt into small droplets to form hollow balls; (4) During the process of blowing the hollow balls, the oxygen in the air burns off the residual carbon in the alumina melt, thereby purifying the alumina; the alumina hollow balls are thermal insulation material products; (5) By adjusting the pressure and air volume of compressed air and the viscosity of the alumina melt, different particle sizes of hollow balls can be further achieved; (6) This process produces three furnaces in a row, that is, after the third furnace is finished blowing, the furnace shell is replaced; the removed furnace shell has already achieved the enrichment of metallic chromium, that is, the accumulated metallic chromium after melting, reduction and separation in the three furnaces is accumulated in the lower part of the furnace shell, covered with a molten alumina, which prevents the air from contacting the liquid metallic chromium and prevents the separated metallic chromium from being oxidized; (7) Install an empty furnace shell on the plasma electric melting furnace and restart production; (8) After the furnace shell with material is cooled, the solidified material inside is dug out. The lower part is metallic chromium and the upper part is alumina melt. The metallic chromium is sold directly as a product, and the alumina melt returns to the previous process cycle to participate in the blowing of alumina hollow balls. The waste slag prepared is converted into two products: alumina hollow balls and metallic chromium.

[0006] The method for preparing alumina hollow sphere thermal insulation material using waste slag generated by chromium production, wherein the carbon reducing agent in step (1) is petroleum coke, semi-coke, charcoal, graphite block, or metallic aluminum, or carbon is used as the reducing agent.

[0007] In the method for preparing alumina hollow sphere thermal insulation material using waste slag generated in the production of chromium, in the step (2) of melting in an ion electric melting furnace, the melting cycle of one furnace is 4 to 5 hours.

[0008] The method for preparing alumina hollow ball thermal insulation material using waste slag generated in the production of chromium, wherein the particle size of the hollow ball is achieved by adjusting the pressure and air volume of compressed air and the viscosity of the alumina melt.

[0009] The advantages and effects of the present invention are: 1. The present invention adopts a method of replacing the furnace shell, so that the liquid reduced from chromium oxide to metallic chromium remains in the lower part of the furnace shell, and the upper layer is covered with molten aluminum oxide, thereby avoiding the possibility of metallic chromium being oxidized by contact with air and improving the efficiency of refining metallic chromium from aluminum-chromium slag.

[0010] 2. The slag produced when producing metallic chromium in the present invention is converted into two products, one is hollow alumina balls, a high-grade thermal insulation material; the other is metallic chromium. Both products are relatively expensive products, achieving high-value utilization of waste slag such as aluminum-chromium slag in the comprehensive utilization of resources. DETAILED DESCRIPTION

[0011] The present invention is described in detail below with reference to the embodiments.

[0012] The present invention adopts a plasma electric melting furnace, adds aluminum-chromium slag into the electric melting furnace, flattens it on the bottom of the furnace, and has a thickness of about 300 mm. Carbon blocks are laid on the slag materials, and the carbon blocks can be petroleum coke blocks or graphite blocks, and the size of the blocks is 30 to 50 mm. After the electrode is energized, the descending electrode approaches the carbon block, so that a plasma arc is generated between the electrode and the carbon block. The heat of the arc melts the aluminum-chromium slag. When these slag materials form a molten pool, the current of the electric melting furnace is stable, and a batch material mixed with aluminum-chromium slag and a carbon reducing agent is added to the electric melting furnace. The weight ratio of the aluminum-chromium slag to the carbon reducing agent is in the range of 100 / 4 to 100 / 8. The reducing agent can be petroleum coke, blue charcoal, charcoal, graphite block, etc., or metal aluminum, etc., and carbon is generally used as the reducing agent. The function of the carbon reducing agent is to reduce the chromium oxide in the aluminum-chromium slag into metal and settle it at the bottom of the furnace to achieve the purification of aluminum oxide. The electric melting furnace is powered on during the charging process, and the material is added while melting until the liquid level in the electric melting furnace reaches a level close to the furnace nozzle, and no more material is added. Continue melting for 3 hours, and the melting cycle of a furnace is over. The upper layer of the molten liquid in the furnace is molten alumina, and the lower layer is molten metal chromium. The melting cycle of a furnace is 4 to 5 hours. About 40 minutes before the end of the melting cycle of a furnace, the reaction degree of the molten liquid is tested by the dip solder method. If the reaction degree is found to be insufficient, carbon should be added to the furnace. Out of the furnace: After the melting cycle of a furnace is over, the furnace body is tilted, and the upper layer of molten alumina in the electric melting furnace flows out of the furnace nozzle. At the same time, compressed air is used to blow the stream of molten alumina, so that the molten alumina is dispersed into small droplets to form hollow balls; at the same time, the residual carbon in the molten alumina is oxidized by oxygen in the air, and the purification of alumina is achieved. When there is still a small amount of alumina melt in the electric melting furnace, stop tilting the furnace and let the furnace body return to its normal position, that is, the state where the furnace body is not tilted. Under the action of compressed air, the hollow alumina balls fly in the air, which is also the process of cooling down. Finally, the balls fall into a hopper. Then, through screening, balls of different particle sizes are obtained, which are the products. By controlling the flow rate of the stream and the pressure of the compressed air, the blowing of hollow balls of different particle sizes can be achieved. After repeating the same process twice, after blowing the balls in the third furnace, the furnace shell of the electric melting furnace is removed and moved to the designated place. After the material in the furnace shell is cooled, the remaining material in the furnace is dug out. The upper layer of the remaining material is alumina and the lower layer is metallic chromium. The upper layer of the material goes back to repeat the above process, and the metallic chromium on the lower layer is the product. After the previous furnace shell is removed, the next empty furnace shell is moved over and connected to the furnace body, and the aforementioned process is repeated. Embodiment 1

[0013] A 1800KVA plasma electric melting furnace is used, and aluminum-chromium slag is added into the electric melting furnace and flattened on the bottom of the furnace to a thickness of about 300mm. Carbon blocks are laid on the slag, which can be petroleum coke blocks or graphite blocks, with a size of 30 to 50mm.

[0014] When the plasma melting furnace is powered on and the electrode is lowered, an arc is generated between the electrode and the carbon blocks on the slag, which heats the slag to melt it. At this time, the voltage is 170V and the current is 5000A. This stage lasts for 20 to 30 minutes. At the beginning, the current may fluctuate, and the current will be stable for about 20 to 30 minutes.

[0015] Add the mixture of slag and blue carbon reducing agent into the electric furnace. The proportion of the mixture: the weight ratio of slag to blue carbon reducing agent is 100 / 5. The size of the blue carbon block is 30-40mm. Add materials while melting until the liquid level approaches the level of the furnace nozzle, then stop adding materials. The voltage of this process is 170V, and the current is 6000A. The melting time of this stage is 2 hours. In this stage, the metal chromium is reduced and deposited at the bottom of the furnace shell, and the upper layer is alumina melt.

[0016] One hour before taking the furnace out of the furnace, use the dip soldering method to test the reaction degree of the molten metal. If the reaction degree is found to be insufficient, add carbon to the furnace.

[0017] After carbon replenishment, the melting is continued for 30 minutes, and then the voltage is adjusted to 190V, the current is 4500A, and the melting is continued for 30 minutes, and the melting of this furnace is completed.

[0018] After the melting cycle of a furnace is completed, the furnace body is tilted, and the upper layer of alumina melt in the furnace flows out from the furnace nozzle. At the same time, compressed air is used to blow the stream of alumina melt, so that the alumina melt is dispersed into small droplets to form hollow balls; at the same time, the residual carbon in the alumina melt is oxidized by the oxygen in the air, and the alumina is purified. Under the action of compressed air, the hollow alumina balls fly in the air, which is also the process of cooling. Finally, the balls fall into a hopper.

[0019] When there is still a small amount of molten alumina in the furnace, stop tilting the furnace and let the furnace body return to its normal position, that is, the state where the furnace body is not tilted.

[0020] When blowing the balls, the flow rate of the stream and the pressure of the compressed air are controlled to achieve the blowing of hollow balls of different particle sizes.

[0021] The hollow balls are sieved through a sieving machine to obtain balls of different particle sizes, and the hollow balls are the products.

[0022] After repeating the same process twice, the furnace shell is replaced after the third furnace is finished blowing. The furnace shell of the electric melting furnace is removed and moved to a designated place. After the material in the furnace shell is cooled, the remaining material in the furnace is dug out. The upper layer of these remaining materials is alumina, and the lower layer is metal chromium. The upper layer of the material is returned to repeat the above process, and the metal chromium in the lower layer is the product.

[0023] After the previous furnace shell is removed, the next empty furnace shell is moved over and connected to the furnace body, and the aforementioned process is repeated. Example

[0024] A 3600KVA plasma electric melting furnace is used, and aluminum-chromium slag is added into the electric melting furnace and flattened on the bottom of the furnace with a thickness of about 400mm. Carbon blocks are laid on the slag, and the carbon blocks are made of graphite blocks with a size of 30 to 50mm.

[0025] When the plasma electric melting furnace is powered on and the electrode is lowered, an arc is generated between the electrode and the carbon blocks on the slag, which heats the slag to melt it. At this time, the voltage is 170V and the current is 8000A. This stage lasts for 30 minutes. The current may fluctuate at the beginning, and the current will be stable for about 30 minutes.

[0026] Add a mixture of aluminum-chromium slag and graphite blocks into the electric melting furnace. The proportion of the mixture is: the total weight of the aluminum-chromium slag and the weight of the graphite blocks is 100 / 5, and the size of the graphite blocks is 20 to 30 mm.

[0027] Add materials while melting until the liquid level is close to the level of the furnace nozzle, then stop adding materials. The voltage of this process is 180V, the current is 10000A, and the time is 3 hours. This process allows the reduced metal chromium to deposit on the bottom of the furnace, and the upper layer is alumina melt.

[0028] One hour before taking the furnace out of the furnace, use the dip soldering method to test the reaction degree of the molten metal. If the reaction degree is found to be insufficient, add carbon to the furnace.

[0029] After carbon replenishment, the melting is continued for 30 minutes, and then the voltage is adjusted to 190V, the current is 7500A, and the melting is continued for 30 minutes, and the melting of this furnace is completed.

[0030] After the melting cycle of a furnace is completed, the furnace body is tilted, and the upper layer of alumina melt in the furnace flows out from the furnace nozzle. At the same time, compressed air is used to blow the stream of alumina melt, so that the alumina melt is dispersed into small droplets to form hollow balls; at the same time, the residual carbon in the alumina melt is oxidized by the oxygen in the air, and the alumina is purified. Under the action of compressed air, the hollow alumina balls fly in the air, which is also the process of cooling. Finally, the balls fall into a hopper.

[0031] When there is still a small amount of molten alumina in the furnace, stop tilting the furnace and let the furnace body return to its normal position, that is, the state where the furnace body is not tilted.

[0032] By controlling the flow rate of the stream and the pressure of the compressed air, the blowing of hollow balls of different particle sizes can be achieved.

[0033] The hollow balls are sieved through a sieving machine to obtain balls of different particle sizes. The hollow balls are the products.

[0034] After repeating the same process twice, after the third furnace is blown, the furnace shell is removed and moved to a designated place. After the material in the furnace shell is cooled, the remaining material in the furnace is dug out. The upper layer of these remaining materials is alumina and the lower layer is metal chromium. The upper layer of the material is returned to repeat the above process, and the metal chromium in the lower layer is sold as a product.

[0035] After the previous furnace shell is removed, the next empty furnace shell is moved over and connected to the furnace body, and the aforementioned process is repeated.

[0036] The furnace shell of the plasma electric melting furnace used in the present invention can be removed, and the furnace body remains unchanged, so that the furnace shell can be replaced.

[0037] 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 the present invention. Although the present invention is described in detail with reference to preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for preparing alumina hollow sphere insulation material using waste slag generated in the production of chromium, characterized in that: The method comprises the following preparation steps: (1) firstly, the aluminum-chromium slag is mixed with a carbon reducing agent in a ratio of 100 / 4 to 100 / 8 by weight of the slag to the carbon reducing agent; (2) The mixture of aluminum-chromium slag and carbon reducing agent is melted in a plasma electric melting furnace. During the melting process, the chromium oxide in the slag is reduced to metallic chromium and deposited at the bottom of the furnace, while the aluminum oxide melt is on the upper layer, thus achieving the separation of aluminum oxide and metallic chromium. (3) After a furnace melting cycle is completed, the alumina melt is blown into hollow balls to be taken out of the furnace; the furnace body is tilted to allow the alumina melt to flow out from the furnace nozzle, and compressed air is used to blow this stream to disperse the alumina melt into small droplets to form hollow balls; (4) During the process of blowing the hollow balls, the oxygen in the air burns off the residual carbon in the alumina melt, thereby purifying the alumina; the alumina hollow balls are thermal insulation material products; (5) By adjusting the pressure and air volume of compressed air and the viscosity of the alumina melt, different particle sizes of hollow balls can be further achieved; (6) This process produces three furnaces in a row, that is, after the third furnace is finished blowing, the furnace shell is replaced; the removed furnace shell has already achieved the enrichment of metallic chromium, that is, the accumulated metallic chromium after melting, reduction and separation in the three furnaces is accumulated in the lower part of the furnace shell, covered with a molten alumina, which prevents the air from contacting the liquid metallic chromium and prevents the separated metallic chromium from being oxidized; (7) Install an empty furnace shell on the plasma electric melting furnace and restart production; (8) After the furnace shell with material is cooled, the solidified material inside is dug out. The lower part is metallic chromium and the upper part is alumina melt. The metallic chromium is sold directly as a product, and the alumina melt returns to the previous process cycle to participate in the blowing of alumina hollow balls. The waste slag prepared is converted into two products: alumina hollow balls and metallic chromium.

2. The method for preparing alumina hollow sphere thermal insulation material using waste residue generated in chromium production according to claim 1, characterized in that: The carbon reducing agent in step (1) is petroleum coke, blue coke, charcoal, graphite block, or metal aluminum, or carbon is used as the reducing agent.

3. The method for preparing alumina hollow sphere thermal insulation material using waste residue generated in chromium production according to claim 1, characterized in that: In the step (2) of melting in the ion electric melting furnace, the melting cycle of one furnace is 4 to 5 hours.

4. The method for preparing alumina hollow sphere thermal insulation material using waste residue generated in chromium production according to claim 1, characterized in that: The hollow ball particle size is achieved by adjusting the pressure and air volume of compressed air and the viscosity of alumina melt.