Magnesian stemming for submerged arc furnace by using approximately spherical Al2O3-SiO2 composite micro powder as plasticizer and preparation method of magnesian stemming

Abstract

The invention discloses magnesian stemming for a submerged arc furnace by using nearly spherical Al2O3-SiO2 composite micro powder as a plasticizer and a preparation method of the magnesian stemming. The magnesian stemming for the submerged arc furnace is prepared from aggregate A, aggregate B, powder, an additive and a carbonaceous binding agent. The aggregate A is at least one of forsterite with the particle size of 0.074 to 3 mm, medium-grade magnesia with the particle size of 0.074 to 3 mm and electric smelting leather sand with the particle size of 0.074 to 3 mm; the aggregate B is at least one of a regenerated Si3N4 combined SiC material with the size of 0.074 to 1 mm, a recarburizing agent undersize material with the size of 0.074 to 1.5 mm and a dry quenching coke undersize material with the size of 0.074 to 2 mm; the powder material is at least one of 325-mesh fused magnesite, a 325-mesh regenerated Si3N4 combined SiC material and 325-mesh medium-grade magnesite; and the additive is approximately spherical Al2O3-SiO2 composite micro powder. The additive and the aggregate are mixed and stirred, then the carbonaceous binder and the powder are added for continuous stirring, the obtained mixture is extruded and packaged after being detected to be qualified through a Marshall value, and the magnesian stemming for the submerged arc furnace is obtained. The product provided by the invention is excellent in use performance and high in cost performance, and can better protect refractory materials in a furnace eye area of a submerged arc furnace, so that the cost performance of the magnesium stemming is greatly improved.

Description

1. Technical Field:

[0001] The invention belongs to the technical field of refractory materials, and particularly relates to a magnesia taphole clay for a submerged arc furnace using nearly spherical Al2O3-SiO2 composite micropowder as a plasticizer and a preparation method thereof. 2. Background technology:

[0002] Submerged arc furnaces are primarily used for the reduction and smelting of ore, employing carbonaceous reducing agents and solvents. Magnesia refractory materials are particularly suitable for the smelting of ferromanganese, ferrochrome, and ferronickel, which require demanding temperatures. Magnesia refractory materials offer the advantages of high refractoriness and strong resistance to corrosion and erosion by these alloys, but they are susceptible to oxidation by water vapor and have poor thermal shock resistance. Every day, large quantities of high-temperature molten slag must be discharged through the furnace eye (slag and taphole). During tapping, the temperature in the furnace eye reaches approximately 1500°C, necessitating the instantaneous insertion of low-temperature plugging material (taphole mud). This frequent and drastic temperature fluctuations severely damage the magnesia refractory material in this area, making it a critical area limiting the lifespan of the submerged arc furnace. Therefore, selecting the appropriate plugging material is crucial for extending the service life of the submerged arc furnace and reducing production costs.

[0003] The slag discharged during smelting in a submerged arc furnace contains a high content of MgO (25.0-35.0%) and incompletely reduced FeO (7.0-14.0%). The high MgO content and ultra-low SiO2 content in the product of the present invention do not produce low-melting-point compounds with the alloy slag, effectively resisting corrosion from the alloy slag. Furthermore, the furnace eye area of submerged arc furnaces often uses fused magnesia bricks. The product of the present invention and fused magnesia bricks have similar compositions and contents. During the high-temperature smelting process in a submerged arc furnace, the two materials have similar thermal conductivity and thermal expansion coefficients, resulting in a higher bonding strength that better protects the refractory material in the furnace eye area and eliminates cracks caused by material mismatch. For this reason, anhydrous taphole clay (Al2O3-SiC-C) for blast furnaces and chromium oxide-containing plastics (commonly known as green mud) are not ideal for use in submerged arc furnace eyes.

[0004] Traditional magnesia taphole clay is made by mixing fused magnesia, sintered magnesia, carbonaceous raw materials, clay, and a binder. The clay in magnesia taphole clay is soft, and the SiO2 content in soft clay with good plasticity often exceeds 50%. The high SiO2 content in magnesia taphole clay can affect product performance and prevent it from effectively protecting the refractory material in the furnace eye area.

[0005] In production applications, high-quality ball clay has a high moisture content (3.0-8.0%). As a plasticizer in traditional magnesia taphole clay, the amount of carbonaceous binder added increases. After high temperatures, the escape of moisture from the ball clay and low-temperature volatiles from the carbonaceous binder causes numerous pores in the sintered magnesia taphole clay, reducing its bonding strength. Furthermore, ball clay has a high surface energy, a relatively low structural energy, and a close distance between the endothermic valleys of adsorbed and structural water. This narrows the heating temperature range for drying and dehydrating the ball clay without changing its plasticity, making the drying process difficult to control and increasing the cost of using the ball clay. 3. Summary of the invention:

[0006] The technical problem to be solved by the present invention is: in response to the current status of existing plugging materials for submerged arc furnaces and the technical problems they present, the present invention provides a magnesia taphole clay for submerged arc furnaces that utilizes nearly spherical Al2O3-SiO2 composite micropowder as a plasticizer, and a preparation method thereof. In the technical solution of the present invention, the nearly spherical Al2O3-SiO2 composite micropowder is used to completely replace clay as the plasticizer in the ingredients of the magnesia taphole clay for submerged arc furnaces, which has high economic value. The resulting magnesia taphole clay for submerged arc furnaces has excellent performance and a high cost-effectiveness, and can better protect the refractory material in the furnace eye area of the submerged arc furnace, thereby greatly improving the cost-effectiveness of the magnesia taphole clay.

[0007] In order to solve the above problems, the technical solution adopted by the present invention is:

[0008] The invention provides a magnesia taphole clay for a submerged arc furnace, which utilizes nearly spherical Al2O3-SiO2 composite micropowder as a plasticizer. The magnesia taphole clay for a submerged arc furnace comprises aggregate A, aggregate B, powder, a 3000-mesh nearly spherical Al2O3-SiO2 composite micropowder additive, and a carbonaceous binder. The mass percentages of the various raw materials are: 20-40% of aggregate A, 5-15% of aggregate B, 20-45% of powder, 5-15% of additive, and 8-15% of carbonaceous binder.

[0009] According to the above-mentioned magnesia taphole mud for submerged arc furnace using nearly spherical Al2O3-SiO2 composite micropowder as plasticizer, the aggregate A is at least one of forsterite with a diameter of 0.074 to 3 mm, mid-grade magnesia with a diameter of 0.074 to 3 mm, and fused leather sand with a diameter of 0.074 to 3 mm;

[0010] The aggregate B is at least one of 0.074-1 mm recycled Si3N4 combined with SiC material, 0.074-1.5 mm recarburizer undersize material and 0.074-2 mm dry quenched coke undersize material;

[0011] The powder material is at least one of 325-mesh fused magnesia, 325-mesh recycled Si3N4 combined with SiC material, and 325-mesh mid-grade magnesia.

[0012] According to the above-mentioned magnesia taphole clay for submerged arc furnace using nearly spherical Al2O3-SiO2 composite micropowder as plasticizer, the contents of the chemical components in the forsterite are MgO>45.0%, SiO2>40.0%, Fe2O3<9.0%, Al2O3<1.0%, CaO<1.0%, LOI<1.0% (the forsterite is obtained by mining and calcining peridotite with a forsterite phase content of more than 90%); the chemical components in the mid-range magnesia are MgO>45.0%, SiO2>40.0%, Fe2O3<9.0%, Al2O3<1.0%, CaO<1.0%, LOI<1.0%; The content of chemical components in the mid-range magnesia is MgO>95.0%, SiO2<1.5% (the mid-range magnesia is prepared by a one-step calcination process using dolomite as raw material); the content of each chemical component in the fused skin sand is MgO≥92.5%, Fe2O3≤1.0%, SiO2<2.0%, and its volume density is ≥3.40g / cm3 (the fused skin sand is a material with a fine-grained structure formed on the surface of the molten pool due to rapid cooling during the production of fused magnesia in an electric arc furnace).

[0013] According to the above-mentioned magnesia taphole mud for submerged arc furnace using nearly spherical Al2O3-SiO2 composite micropowder as plasticizer, the chemical component contents of the recycled Si3N4 combined with SiC material are SiC>70.0%, Si3N4>20.0%, K2O+Na2O<0.5%; its particle size is 0.074mm-1mm and 325 mesh;

[0014] The processing method of the regenerated Si3N4 combined SiC material is as follows:

[0015] a. Residual refractory materials produced by the steel industry and / or aluminum electrolysis industry are sorted to remove deteriorated materials, screened with a vibrating screen to remove impurities, and then crushed into 0.074-5 mm particles using a double-roll crusher. The resulting 0.074-5 mm particles are then magnetically separated by a magnetic separator to remove metal impurities;

[0016] b. The obtained 0.074-5 mm granular material and water are then stirred and preheated using kiln exhaust gas at 150-300° C., and the CO2 content in the kiln exhaust gas is 20.0-25.0%. The preheated material enters a reactor for treatment at a temperature of 120-200° C., a pressure of 0.2-0.8 MPa, and a time of 2-6 hours. The treated material is dried and processed into regenerated Si3N4-bound SiC material with particle sizes of 1-3 mm, 0.074 mm-1 mm, and 325 mesh. The contents of the chemical components in the obtained regenerated Si3N4-bound SiC material are as follows: SiC>70.0%, Si3N4>20.0%, and K2O+Na2O<0.5%.

[0017] According to the above-mentioned magnesia taphole mud for submerged arc furnace using nearly spherical Al2O3-SiO2 composite micropowder as plasticizer, the chemical components of the recarburizer undersize material are fixed carbon>90.0%, ash<7.5%, volatile matter<1.5%, and its particle size is 0.074-1.5mm;

[0018] The recarburizer undersize material is the undersize material of the graphitized recarburizer (because its fixed carbon content, ash content, nitrogen and sulfur impurity content or cold strength and other indicators do not meet the use requirements of the steel industry and the carbon product industry, the recarburizer undersize material becomes the raw material of the product of the present invention).

[0019] According to the above-mentioned magnesia taphole mud for submerged arc furnace using nearly spherical Al2O3-SiO2 composite micropowder as plasticizer, the contents of various components in the CDQ undersize material are fixed carbon>85.0%, ash<12.5%, volatile matter<1.0%, and its particle size is 0.074-2mm;

[0020] The dry quenching coke undersize is coke produced by the dry quenching process in the coking industry. It is the undersize that cannot be used in the steel smelting process. It is screened through a 2mm drum screen. Particles larger than 2mm are used in casting and ferroalloy processes. The dry quenching coke undersize smaller than 2mm is used as raw material for magnesia taphole mud for blast furnaces.

[0021] According to the above-mentioned magnesia taphole mud for submerged arc furnace using nearly spherical Al2O3-SiO2 composite micropowder as plasticizer, the content of each chemical component in the fused magnesia is MgO>97.0%, SiO2<1.5%, and CaO≤1.5% (the fused magnesia is made by melting natural dolomite in an electric arc furnace at a high temperature of more than 2750°C).

[0022] According to the above-mentioned magnesia taphole clay for submerged arc furnace using nearly spherical Al2O3-SiO2 composite micropowder as a plasticizer, the 3000-mesh nearly spherical Al2O3-SiO2 composite micropowder is formed by mixing Al2O3 micropowder and SiO2 micropowder in a weight ratio of 1:9 to 9:1.

[0023] The Al2O3 powder in the nearly spherical Al2O3-SiO2 composite powder of the present invention is selected from the aluminum oxide ultrafine powder that can no longer be used for the battery ceramic diaphragm when the aluminum oxide powder is recovered from the waste lithium battery ceramic diaphragm. The typical particle size distribution value is d (10) =0.59μm, d (50) =1.24μm, d (90) =4.36μm, BET is 2.0m 2 / g; SiO2 powder in the nearly spherical Al2O3-SiO2 composite powder is collected by condensing the dust released during the smelting process of metallic silicon. It is amorphous (non-crystalline), with SiO2>92.0% and crystalline SiO2 content less than 1.0%; its typical particle size distribution is d (10) =0.18μm, d (50) =0.33μm, d (90) =0.94μm, BET is 19.4m 2 / g.

[0024] According to the above-mentioned magnesia taphole mud for electric arc furnace using nearly spherical Al2O3-SiO2 composite micropowder as plasticizer, the carbonaceous binder has a viscosity of 250Pa·S at 50°C, moisture <1.0%, and a residual carbon value detected at 800°C×7min greater than 28wt% (the carbonaceous binder is obtained by high-temperature and high-pressure reaction of decrystallized anthracene oil produced by coal coking and coal tar resin).

[0025] In addition, a method for preparing magnesia taphole mud for a submerged arc furnace using nearly spherical Al2O3-SiO2 composite micropowder as a plasticizer is provided, the preparation method comprising the following steps:

[0026] 1) mixing Al2O3 fine powder and SiO2 fine powder in a weight ratio of 1:9 to 9:1 to obtain a 3000-mesh nearly spherical Al2O3-SiO2 composite fine powder;

[0027] 2) Weighing various raw materials according to the ratio of the magnesia taphole clay for the submerged arc furnace;

[0028] 3) Premixing the weighed nearly spherical Al2O3-SiO2 composite micropowder of the additive in a spherical mixer for 120 to 180 minutes (the composite powder after premixing has no obvious color difference, good flowability, and a chemical composition detection range value of less than 0.5%);

[0029] 4) The weighed aggregate A, aggregate B and premixed additives are placed in batching cart A, and the weighed powder is placed in batching cart B; the raw materials in batching cart A are then placed in a mixing and grinding mixer for stirring (stirring time is 5-10 minutes), followed by adding 95% of the total amount of carbonaceous binder and continuing to stir. After stirring for 3-5 minutes, the raw materials in batching cart B are added, followed by adding the remaining 5% of carbonaceous binder and continuing to stir for 15-20 minutes, and sampling is performed to test the Marshall value;

[0030] 5) After the Marshal value test is qualified, qualified clay is obtained, and the temperature of the qualified clay is controlled at 40-50℃. The qualified clay is sent into the mud extruder through a belt, and the mud is squeezed out of the mud extruder into a qualified shape and enters the packaging process to obtain the product, which is magnesia mud for electric arc furnace using nearly spherical Al2O3-SiO2 composite micropowder as the only plasticizer.

[0031] In the composition of the magnesia taphole clay for the ore-fired furnace of the present invention, although the nearly spherical Al2O3-SiO2 composite micropowder used will introduce SiO2, its content (SiO2 <0.5%) is much lower than the SiO2 content in traditional magnesia taphole clay (SiO2 about 5.0%); secondly, the amorphous SiO2 has high activation energy and can easily react with the other chemical components of the magnesia taphole clay to quickly generate highly refractory compounds under high temperature conditions in the furnace eye channel, which can not only eliminate the harm caused by crystalline SiO2 in traditional magnesia taphole clay, but also improve the bonding strength and slightly expand the volume, so that the new and old taphole clays are more firmly bonded, thereby more effectively protecting the furnace wall in the furnace eye area.

[0032] The additive (i.e., plasticizer) used in the present invention is a nearly spherical Al2O3-SiO2 composite micropowder. The diameters of the two types of micropowders, Al2O3 micropowder and SiO2 micropowder, are relatively small, resulting in an iso-spherical plasticizing effect. The additive has a large specific surface area and can accumulate carbonaceous binder at low temperatures. The magnesia mud in the mud gun before plugging is fully filled and does not deform, preventing contact with slag and iron during plugging, which could damage the gun nozzle and affect the plugging quality. During the plugging process, the carbonaceous binder is affected by temperature and flows in time to provide lubrication, ensuring smooth mud production. The ratio of the two micropowders can be adjusted according to the volume of the smelting equipment, the furnace eye environment, the furnace front equipment, and the smelting intensity.

[0033] The positive beneficial effects of the present invention are:

[0034] 1. During the preparation of the magnesia taphole clay for submerged arc furnaces produced by the present invention, the additives are thoroughly premixed, the mixing equipment and mixing time are specifically defined, the materials are added in batches with varying particle sizes, and the temperature of the qualified clay is strictly controlled (temperature range 40-50°C; insulation or heating measures are considered when the clay temperature is low, and heat dissipation and cooling measures are adopted when the temperature is high). The magnesia taphole clay for submerged arc furnaces produced using the preparation method of the present invention does not require baking before use, making it easier and faster to use and reducing worker labor intensity.

[0035] 2. In the proportioning composition of the magnesia taphole clay for the submerged arc furnace of the present invention, nearly spherical Al2O3-SiO2 composite micropowder is used as the only plasticizer, thereby eliminating the harm caused by the high content of SiO2 in refractory clay.

[0036] 3. The magnesia taphole clay produced using the present invention for submerged arc furnaces exhibits excellent plasticity, a taphole depth that meets the requirements for submerged arc furnace use, and strong taphole repairability. Applications by multiple submerged arc furnace smelters have demonstrated that the product of the present invention offers moderate taphole strength, eliminates the need for oxygen heating, is safe and environmentally friendly to operate, and does not damage the refractory materials in the furnace eye area. The taphole depth is stable and the pass rate is high. After an abnormal taphole depth, the product of the present invention can be restored to the acceptable taphole depth after two to three heats of use. The flow rate of molten iron or slag is stable and gentle, with no prolonged splashing or smoke emission during the initial tapping period, and no significant change in the furnace eye diameter before plugging. The service life of a furnace cycle is 6-15% longer than that of conventional products. Upon dismantling a furnace at the end of its service life, it was found that the refractory material in the furnace eye area remained thicker after long-term use of the product of the present invention compared to those using conventional products. The product of the present invention is not only safe and environmentally friendly, but also saves on consumables and labor. Comprehensive calculations and comparisons indicate that the product of the present invention reduces the annual costs of each submerged arc furnace smelter by over 1 million yuan. 4. Specific implementation methods:

[0037] The present invention is further described below with reference to the following examples, but the scope of protection of the technical solution of the present invention is not limited thereto.

[0038] In the following embodiments, the content of each chemical component in the forsterite used is MgO>45.0%, SiO2>40.0%, Fe2O3<9.0%, Al2O3<1.0%, CaO<1.0%, and LOI<1.0% (the forsterite is obtained by mining and calcining peridotite with a forsterite phase content of more than 90%); the content of each chemical component in the mid-range magnesia is MgO>95.0%, SiO2<1.5% (the mid-range magnesia is prepared by a one-step calcination process using magnesite as raw material); the content of each chemical component in the fused skin sand is MgO≥92.5%, Fe2O3≤1.0%, and SiO2<2.0%, and its volume density is ≥3.40g / cm3 (the fused skin sand is a material in which the surface layer of the molten pool forms a fine-grained structure due to rapid cooling during the production of fused magnesia in an electric arc furnace).

[0039] The chemical composition content of the recycled Si3N4 combined with SiC material used is SiC>70.0%, Si3N4>20.0%, K2O+Na2O<0.5%; its particle size is 0.074mm-1mm and 325 mesh;

[0040] The processing method of the regenerated Si3N4 combined SiC material is as follows:

[0041] a. Residual refractory materials produced by the steel industry and / or aluminum electrolysis industry are sorted to remove deteriorated materials, screened with a vibrating screen to remove impurities, and then crushed into 0.074-5 mm particles using a double-roll crusher. The resulting 0.074-5 mm particles are then magnetically separated by a magnetic separator to remove metal impurities;

[0042] b. The obtained 0.074-5 mm granular material and water are then stirred and preheated using kiln exhaust gas at 150-300° C., and the CO2 content in the kiln exhaust gas is 20.0-25.0%. The preheated material enters a reactor for treatment at a temperature of 120-200° C., a pressure of 0.2-0.8 MPa, and a time of 2-6 hours. The treated material is dried and processed into regenerated Si3N4-bound SiC material with particle sizes of 1-3 mm, 0.074 mm-1 mm, and 325 mesh. The contents of the chemical components in the obtained regenerated Si3N4-bound SiC material are as follows: SiC>70.0%, Si3N4>20.0%, and K2O+Na2O<0.5%.

[0043] The chemical component contents of the used recarburizer undersize material are as follows: fixed carbon>90.0%, ash<7.5%, volatile matter<1.5%, and the particle size is 0.074-1.5 mm; the recarburizer undersize material is a graphitized recarburizer undersize material (because its fixed carbon content, ash content, nitrogen and sulfur impurity content or cold strength and other indicators do not meet the use requirements of the steel industry and the carbon product industry, the recarburizer undersize material becomes the raw material of the product of the present invention).

[0044] The dry quenched coke undersize used has a fixed carbon content of more than 85.0%, an ash content of less than 12.5%, and a volatile content of less than 1.0%, and a particle size of 0.074-2 mm. The dry quenched coke undersize is coke produced by a dry quenching process in the coking industry and cannot be used in steel smelting processes. The undersize is screened through a 2 mm drum screen, and particles larger than 2 mm are used in casting and ferroalloy processes. The dry quenched coke undersize smaller than 2 mm is used as raw material (for the product of the present invention).

[0045] The chemical component contents of the adopted fused magnesia are MgO>97.0%, SiO2<1.5%, and CaO≤1.5% (the fused magnesia is formed by melting natural magnesite at a high temperature of more than 2750° C. in an electric arc furnace).

[0046] The 3000 mesh nearly spherical Al2O3-SiO2 composite micropowder used is a mixture of Al2O3 micropowder and SiO2 micropowder in a weight ratio of 1:9 to 9:1;

[0047] The Al2O3 powder in the nearly spherical Al2O3-SiO2 composite powder of the present invention is selected from the aluminum oxide ultrafine powder that can no longer be used for the battery ceramic diaphragm when the aluminum oxide powder is recovered from the waste lithium battery ceramic diaphragm. The typical particle size distribution value is d (10) =0.59μm, d (50) =1.24μm, d (90) =4.36μm, BET is 2.0m 2 / g; SiO2 powder in the nearly spherical Al2O3-SiO2 composite powder is collected by condensing the dust released during the smelting process of metallic silicon. It is amorphous (non-crystalline), with SiO2>92.0% and crystalline SiO2 content less than 1.0%; its typical particle size distribution is d (10) =0.18μm, d (50) =0.33μm, d (90) =0.94μm, BET is 19.4m 2 / g.

[0048] The carbon binder used has a viscosity of 250 Pa·S at 50°C, moisture content <1.0%, and a residual carbon value greater than 28wt% detected at 800°C×7min (the carbon binder is obtained by reacting decrystallized anthracene oil produced by coal coking and coal tar resin under high temperature and high pressure).

[0049] Example 1:

[0050] The invention discloses a magnesia taphole cement for a submerged arc furnace, which uses nearly spherical Al2O3-SiO2 composite micropowder as a plasticizer. The taphole cement comprises, expressed by mass percentage, 32% of forsterite with a size of 0.074-3 mm as an aggregate A, 6% of recycled Si3N4 combined with SiC material with a size of 0.074-1 mm as an aggregate B, 8% of recarburizer undersize material with a size of 0.074-1.5 mm, 38% of medium-grade magnesia with a size of 325 mesh as a powder, 6% of nearly spherical Al2O3-SiO2 composite micropowder with a size of 3000 mesh as an additive, and 10% of a liquid carbonaceous binder.

[0051] Example 1 of the present invention is a method for preparing magnesia taphole mud for a submerged arc furnace using nearly spherical Al2O3-SiO2 composite micropowder as a plasticizer, and the detailed steps are as follows:

[0052] 1) Al2O3 fine powder and SiO2 fine powder were mixed in a weight ratio of 6.8:3.2 to obtain a 3000 mesh nearly spherical Al2O3-SiO2 composite fine powder;

[0053] 2) Weighing various raw materials according to the ratio of the magnesia taphole clay for the submerged arc furnace;

[0054] 3) The weighed nearly spherical Al2O3-SiO2 composite powder of the additive was placed in a spherical mixer for premixing for 150 minutes. The composite powder after premixing had no obvious color difference and good flowability;

[0055] 4) The weighed aggregate A, aggregate B and premixed additives are put into batching cart A, and the weighed powder is put into batching cart B; the raw materials in batching cart A are then placed in a mixing and grinding mixer for stirring (stirring time is 8 minutes), and then 95% of the total amount of liquid carbonaceous binder is added and continued to stir. After stirring for 5 minutes, the raw materials in batching cart B are added, and then the remaining 5% of carbonaceous binder is added and continued to stir for 15 minutes. Samples are taken to test the Marshall value (after actual testing, if the Marshall value is not within the specified range, it is adjusted by adding dry materials or carbonaceous binder. After each adjustment, the sample is mixed and ground for 3 to 5 minutes and then tested again until it is qualified);

[0056] The dry material is a mixed solid material obtained by mixing aggregate A, aggregate B, powder and additives according to the proportion of magnesia taphole mud for submerged arc furnace;

[0057] 5) After the Marshal value test is qualified, qualified clay is obtained, and the temperature of the qualified clay is controlled at 40-50℃. The qualified clay is sent into the mud extruder through a belt, and the mud is squeezed out of the mud extruder into a qualified shape and enters the packaging process to obtain the product, which is magnesia mud for electric arc furnace using nearly spherical Al2O3-SiO2 composite micropowder as the only plasticizer.

[0058] The comparison of the performance test data of the magnesia taphole clay for the submerged arc furnace prepared in Example 1 and the traditional magnesia taphole clay is shown in Table 1.

[0059] Table 1 Comparison of physical and chemical properties of magnesia taphole mud prepared in this embodiment and traditional magnesia taphole mud after carbonization at 1450℃*3h

[0060] product <![CDATA[Volume density (g / cm 3 )]]> Flexural strength (MPa) Apparent porosity (%) Linear change rate (%) The product of this embodiment 2.25 4.9 17.5 0.23 Traditional magnesium taphole clay 2.05 2.5 23.4 -0.13

[0061] The product prepared in Example 1 is used for the taphole of an ore-heating furnace, and the production ratio is specially designed for the characteristics of high-temperature alloy molten iron with high specific gravity and strong iron infiltration ability. The taphole requires the following plugging material: the volume slightly expands under high temperature conditions to promote high bonding strength between new and old taphole mud, avoiding iron infiltration; the volume is dense and has low porosity after high temperature treatment, avoiding iron infiltration of the taphole and improving the anti-penetration ability of the tapping process; the high bonding strength at high temperature improves the anti-scouring ability of the molten iron. The product of the present invention forms magnesia-alumina spinel and mullite through in-situ reaction to improve the bonding strength, making the product more compatible with the refractory material of the taphole of an ore-heating furnace; while the production ratio of magnesia taphole mud for traditional tapholes only considers the selection of high-purity magnesia raw materials to improve the product grade. It can be seen from the test data related to volume density, flexural strength, apparent porosity and linear change rate in Table 1 that the relevant performance of the product of the present invention is significantly better than that of traditional products.

[0062] The actual use effect of the product of the present invention on the iron mouth of the ore-fired furnace is consistent with the experimental rules.

[0063] Example 2:

[0064] The invention discloses a magnesia taphole cement for a submerged arc furnace, which uses nearly spherical Al2O3-SiO2 composite micropowder as a plasticizer. The taphole cement comprises, expressed by weight percentage, 30% of medium-grade magnesia sand of 0.074-3mm in size as an aggregate A, 14% of dry quenched coke undersize of 0.074-2mm in size as an aggregate B, 8% of 325-mesh recycled Si3N4 combined with SiC material as a powder, 20% of 325-mesh fused magnesia sand, 14% of 3000-mesh nearly spherical Al2O3-SiO2 composite micropowder as an additive, and 14% of a liquid carbonaceous binder.

[0065] The method for preparing magnesia taphole mud for a submerged arc furnace using nearly spherical Al2O3-SiO2 composite micropowder as a plasticizer in Example 2 of the present invention is basically the same as that in Example 1, except that:

[0066] In step 1), Al2O3 micropowder and SiO2 micropowder are mixed in a weight ratio of 9:1 to obtain 3000-mesh nearly spherical Al2O3-SiO2 composite micropowder.

[0067] The magnesia taphole mud prepared in Example 2 of the present invention is mainly used for the slag mouth of an ore-fired furnace. The ore-fired furnace slag is rich in MgO and FeO, and the temperature of the alloy slag is 50 to 100°C higher than the temperature of the molten iron. Therefore, the SiO2 content of the slag taphole mud needs to be limited to reduce the content of low-melting-point compounds formed by SiO2 and the slag, thereby improving the corrosion resistance and better protecting the refractory material in the slag mouth area.

[0068] In Example 2, 5 tons of magnesia taphole mud produced in a 42MVA nickel-iron smelting submerged arc furnace were used for 11 days. The average slag hole depth was 1.65 meters, the qualified slag hole depth rate was 97.6%, and the oxygen burning rate was 3.2%. In contrast, conventional taphole mud had an average slag hole depth of 1.58 meters, a qualified slag hole depth rate of 86.7%, and an oxygen burning rate of 10.4%. This resulted in eight fewer furnaces required for the same weight of product compared to Example 2.

[0069] Example 3:

[0070] The invention discloses a magnesia taphole clay for a submerged arc furnace, which uses nearly spherical Al2O3-SiO2 composite micropowder as a plasticizer. The magnesia taphole clay comprises, expressed by mass percentage, 31% of 0.074-3mm fused sand as an aggregate A, 10% of 0.074-1.5mm recarburizer undersize as an aggregate B, 5% of 0.074-1mm recycled Si3N4 combined with SiC material, 6% of 325-mesh recycled Si3N4 combined with SiC material as a powder, 26% of 325-mesh medium-grade magnesia sand, 13% of 3000-mesh nearly spherical Al2O3-SiO2 composite micropowder as an additive, and 9% of a liquid carbonaceous binder.

[0071] The preparation method of magnesia taphole clay for submerged arc furnace using nearly spherical Al2O3-SiO2 composite micropowder as plasticizer in this embodiment 3 is basically the same as that in embodiment 1, except that:

[0072] In step 1), Al2O3 powder and SiO2 powder are mixed in a weight ratio of 9.2:0.8 to obtain 3000-mesh nearly spherical Al2O3-SiO2 composite powder.

[0073] The magnesia-based taphole clay prepared in Example 3 of the present invention is primarily used in 42MVA submerged arc furnaces. Its smelted product is high-carbon ferrochrome with a Cr content greater than 60.0% and a C content of 6.0-7.0%. The molten iron temperature is 1790-1850°C. The higher smelting temperatures place high demands on the taphole clay's refractoriness. Oxygen burnout was avoided when using the product in Example 3. Conventional taphole clay, on the other hand, requires oxygen burnout at the end of each heat to open the taphole. This phenomenon indicates that liquid-phase sintering has occurred within the furnace eye after exposure to high temperatures. The clay consumption per furnace is reduced from 150kg for conventional taphole clay to an average of 110kg per furnace for this Example 3. The taphole depth requirement is greater than 1.3 meters. Conventional products have an average taphole depth of 1.25 meters, with a taphole pass rate of 63.4%. This Example 3 product has an average taphole depth of 1.33 meters, with a taphole pass rate of 99.2%.

[0074] Example 4:

[0075] The invention discloses a magnesia taphole cement for a submerged arc furnace, which uses nearly spherical Al2O3-SiO2 composite micropowder as a plasticizer. The cement comprises, expressed by mass percentage, 18% of 0.074-3mm forsterite aggregate A and 10% of 0.074-3mm mid-grade magnesia sand, 15% of 0.074-2mm dry quenched coke undersize aggregate B, 3% of 325-mesh recycled Si3N4 combined with SiC powder and 30% of 325-mesh mid-grade magnesia sand, 10% of 3000-mesh nearly spherical Al2O3-SiO2 composite micropowder as an additive, and 14% of a liquid carbonaceous binder.

[0076] The method for preparing magnesia taphole mud for a submerged arc furnace using nearly spherical Al2O3-SiO2 composite micropowder as a plasticizer in Example 4 of the present invention is basically the same as that in Example 1, except that:

[0077] In step 1), Al2O3 powder and SiO2 powder are mixed in a weight ratio of 7.5:2.5 to obtain 3000-mesh nearly spherical Al2O3-SiO2 composite powder.

[0078] The product prepared in Example 4 of the present invention was used in a 25MVA yellow phosphate ore of a chemical company in Guizhou and a 30MVA yellow phosphate ore thermal furnace of a company in Hubei. The results of the use are shown in Table 2.

[0079] Table 2 Analysis of the use effect of the product obtained in Example 4

[0080] Yellow phosphorus furnace specifications Furnace eye material Smelting temperature Taphole depth Whether to burn oxygen Furnace eye repair capabilities Environmental protection 25MKVA carbon bricks 1450±20℃ >1.3 meters no good good 30MKVA Magnesia bricks 1480-1500℃ >1.2 meters no good good

[0081] It can be seen from the usage effect data in Table 2 that the products prepared by the embodiments of the present invention have achieved good usage effects regardless of whether carbonaceous furnace lining or magnesia furnace lining is used. 25MVA previously used homemade eye-plugging mud, which was made by mixing electrode paste, blue charcoal and refractory clay with water. Due to the poor strength of the eye-plugging mud, it frequently flowed by itself and ran into large flows, disrupting the production rhythm. Later, three furnaces of homemade eye-plugging mud and one furnace of the product of Example 4 of the present invention were used, which ensured smooth production and saved costs. This comparison proves that the magnesia gun mud of Example 4 of this embodiment can form a stable mud bag in a 25MVA yellow phosphorus ore thermal furnace, and can withstand the scouring of three furnaces and still remain intact.

[0082] The service life of a 30MVA furnace using the product of Example 4 is extended by 23 days compared with the previous one.

[0083] Example 5:

[0084] The invention discloses a magnesia taphole cement for a submerged arc furnace, which uses nearly spherical Al2O3-SiO2 composite micropowder as a plasticizer. The taphole cement comprises, expressed by mass percentage, 30% of medium-grade magnesia sand of 0.074-3mm in size as an aggregate A, 5% of recarburizer undersize of 0.074-1.5mm in size as an aggregate B, 10% of dry quenched coke undersize of 0.074-2mm in size as an aggregate B, 5% of 325-mesh recycled Si3N4 combined with SiC material as a powder, 30% of 325-mesh fused magnesia sand, 9% of nearly spherical Al2O3-SiO2 composite micropowder of 3000 mesh as an additive, and 11% of a liquid carbonaceous binder.

[0085] The method for preparing magnesia taphole mud for a submerged arc furnace using nearly spherical Al2O3-SiO2 composite micropowder as a plasticizer in Example 5 of the present invention is basically the same as that in Example 1, except that:

[0086] In step 1), Al2O3 fine powder and SiO2 fine powder are mixed in a weight ratio of 7:3 to obtain 3000-mesh nearly spherical Al2O3-SiO2 composite fine powder.

[0087] The product obtained by preparing Example 5 of the present invention achieved good results in a submerged arc furnace of a company in Suzhou, Jiangsu Province. Its smelting product is an alloy molten iron containing platinum and rhodium precious metals. This process route is the first in the world to be put into operation. The taphole depth is greater than 1.2 meters, the mud amount per furnace is 40kg, the taphole plugging and iron tapping are safe and environmentally friendly (no splashing, thick smoke, and no irritating odor), the molten iron flow rate reaches the specified value, and the platinum and rhodium precious metal recovery rate is 0.1‰ higher than that of the traditional process, providing strong support for the process design to meet the standards.

[0088] Example 6:

[0089] The invention discloses a magnesia taphole clay for a submerged arc furnace, which uses nearly spherical Al2O3-SiO2 composite micropowder as a plasticizer. The clay comprises, expressed by mass percentage, 20% of 0.074-3mm medium-grade magnesia sand as an aggregate A and 12% of 0.074-3mm fused leather sand, 5% of 0.074-1.5mm recarburizer undersize material as an aggregate B and 7% of 0.074-2mm dry quenched coke undersize material as an aggregate B, 5% of 325-mesh recycled Si3N4 combined with SiC material as a powder and 29% of 325-mesh fused magnesia sand, 10.5% of 3000-mesh nearly spherical Al2O3-SiO2 composite micropowder as an additive, and 11.5% of a liquid carbonaceous binder.

[0090] The method for preparing magnesia taphole clay for a submerged arc furnace using nearly spherical Al2O3-SiO2 composite micropowder as a plasticizer in Example 6 of the present invention is basically the same as that in Example 1, except that:

[0091] In step 1), Al2O3 fine powder and SiO2 fine powder are mixed in a weight ratio of 8:2 to obtain 3000-mesh nearly spherical Al2O3-SiO2 composite fine powder.

[0092] The magnesia taphole mud prepared in Example 6 of the present invention was successfully applied to a Zhejiang 8000KVA submerged arc furnace and a certain 5000KVA submerged arc furnace.

[0093] The Zhejiang 8000KVA mill primarily produces nickel-iron alloys by pyrometallurgically smelting stainless steel pickling sludge, pickling residues, various electroplating sludges, and other hazardous wastes containing heavy metals. Using the magnesium taphole clay from Example 6 of the present invention, the taphole depth averaged 1.1 meters (required to be greater than 1.0 meters), with a tapping time of 25 to 35 minutes and no oxygen burning at the tapping point.

[0094] A 5000KVA submerged arc furnace uses pyrometallurgical methods to smelt dust containing heavy metals such as nickel and chromium generated during stainless steel production, eliminating environmental pollution and reusing resources. This furnace uses magnesia taphole mud, which is manually formed into a conical shape, for manual taphole plugging. The taphole depth is detailed in Table 3; a taphole depth less than 400mm is considered unacceptable.

[0095] Table 3 Statistics of taphole depth

[0096]

Claims

1. A magnesia taphole clay for a submerged arc furnace using nearly spherical Al2O3-SiO2 composite micropowder as a plasticizer, characterized in that: The magnesia taphole mud for a submerged arc furnace is composed of aggregate A, aggregate B, powder, 3000-mesh nearly spherical Al2O3-SiO2 composite micropowder additive and carbonaceous binder, wherein the mass percentage of various raw materials is: aggregate A 20-40%, aggregate B 5-15%, powder 20-45%, additive 5-15% and carbonaceous binder 8-15%.

2. The magnesia taphole clay for a submerged arc furnace using nearly spherical Al2O3-SiO2 composite micropowder as a plasticizer according to claim 1, characterized in that: The aggregate A is at least one of 0.074-3mm forsterite, 0.074-3mm mid-grade magnesia and 0.074-3mm fused leather sand; The aggregate B is at least one of 0.074-1 mm recycled Si3N4 combined with SiC material, 0.074-1.5 mm recarburizer undersize material and 0.074-2 mm dry quenched coke undersize material; The powder material is at least one of 325-mesh fused magnesia, 325-mesh recycled Si3N4 combined with SiC material, and 325-mesh mid-grade magnesia.

3. The magnesia taphole clay for a submerged arc furnace using nearly spherical Al2O3-SiO2 composite micropowder as a plasticizer according to claim 1, characterized in that: The contents of the chemical components in the forsterite are MgO>45.0%, SiO2>40.0%, Fe2O3<9.0%, Al2O3<1.0%, CaO<1.0%, and LOI<1.0%; the contents of the chemical components in the mid-range magnesia are MgO>95.0%, SiO2<1.5%; the contents of the chemical components in the fused shale are MgO≥92.5%, Fe2O3≤1.0%, and SiO2<2.0%, and the bulk density is ≥3.40 g / cm 3 .

4. The magnesia taphole clay for a submerged arc furnace using nearly spherical Al2O3-SiO2 composite micropowder as a plasticizer according to claim 1, characterized in that: The chemical composition contents of the regenerated Si3N4 combined with SiC material are SiC>70.0%, Si3N4>20.0%, and K2O+Na2O<0.5%; and the particle size is 0.074mm-1mm and 325 mesh; The processing method of the regenerated Si3N4 combined SiC material is as follows: a. Residual refractory materials produced by the steel industry and / or aluminum electrolysis industry are sorted to remove deteriorated materials, screened with a vibrating screen to remove impurities, and then crushed into 0.074-5 mm particles using a double-roll crusher. The resulting 0.074-5 mm particles are then magnetically separated by a magnetic separator to remove metal impurities; b. The obtained 0.074-5 mm granular material and water are then stirred and preheated using kiln exhaust gas at 150-300° C., and the CO2 content in the kiln exhaust gas is 20.0-25.0%. The preheated material enters a reactor for treatment at a temperature of 120-200° C., a pressure of 0.2-0.8 MPa, and a time of 2-6 hours. The treated material is dried and processed into regenerated Si3N4-bound SiC material with particle sizes of 1-3 mm, 0.074 mm-1 mm, and 325 mesh. The contents of the chemical components in the obtained regenerated Si3N4-bound SiC material are as follows: SiC>70.0%, Si3N4>20.0%, and K2O+Na2O<0.5%.

5. The magnesia taphole clay for a submerged arc furnace using nearly spherical Al2O3-SiO2 composite micropowder as a plasticizer according to claim 1, characterized in that: The chemical composition content of the recarburizer undersize material is fixed carbon>90.0%, ash<7.5%, volatile matter<1.5%, and its particle size is 0.074-1.5mm; The recarburizer undersize material is a graphitized recarburizer undersize material.

6. The magnesia taphole clay for a submerged arc furnace using nearly spherical Al2O3-SiO2 composite micropowder as a plasticizer according to claim 1, characterized in that: The CDQ undersize material has a fixed carbon content of >85.0%, an ash content of <12.5%, and a volatile content of <1.0%, and a particle size of 0.074-2 mm. The dry quenching coke undersize is coke produced by the dry quenching process in the coking industry. It is the undersize that cannot be used in the steel smelting process. It is screened through a 2mm drum screen. Particles larger than 2mm are used in casting and ferroalloy processes. The dry quenching coke undersize smaller than 2mm is used as raw material for magnesia taphole mud for blast furnaces.

7. The magnesia taphole clay for a submerged arc furnace using nearly spherical Al2O3-SiO2 composite micropowder as a plasticizer according to claim 1, characterized in that: The contents of the chemical components in the fused magnesia are MgO>97.0%, SiO2<1.5%, and CaO≤1.5%.

8. The magnesia taphole clay for a submerged arc furnace using nearly spherical Al2O3-SiO2 composite micropowder as a plasticizer according to claim 1, characterized in that: The 3000-mesh nearly spherical Al2O3-SiO2 composite micropowder is prepared by mixing Al2O3 micropowder and SiO2 micropowder in a weight ratio of 1:9 to 9:1; The Al2O3 micropowder in the nearly spherical Al2O3-SiO2 composite micropowder is selected from the aluminum oxide ultrafine powder that can no longer be used for battery ceramic diaphragms when recycling aluminum oxide powder from waste lithium battery ceramic diaphragms. The typical particle size distribution value is d (10) =0.59μm, d (50) =1.24μm, d (90) =4.36μm, BET is 2.0m 2 / g; SiO2 powder in the nearly spherical Al2O3-SiO2 composite powder is selected from the dust released during the smelting process of metallic silicon and collected by condensation. It is amorphous and non-crystalline, with SiO2>92.0% and a crystalline SiO2 content of less than 1.0%; Its typical particle size distribution is d (10) =0.18μm, d (50) =0.33μm, d (90) =0.94μm, BET is 19.4m 2 / g.

9. The magnesia taphole clay for a submerged arc furnace using nearly spherical Al2O3-SiO2 composite micropowder as a plasticizer according to claim 1, characterized in that: The carbonaceous binder has a viscosity of 250 Pa·S at 50° C., a moisture content of less than 1.0%, and a carbon residue value greater than 28 wt % when tested at 800° C. for 7 minutes.

10. A method for preparing magnesia taphole clay for submerged arc furnace using nearly spherical Al2O3-SiO2 composite micropowder as a plasticizer, characterized in that: The preparation method comprises the following steps: 1) Al2O3 fine powder and SiO2 fine powder are mixed in a weight ratio of 1:9 to 9:1 to obtain a 3000-mesh nearly spherical Al2O3-SiO2 composite fine powder; 2) Weighing various raw materials according to the ratio of the magnesia taphole clay for the submerged arc furnace; 3) Premixing the weighed nearly spherical Al2O3-SiO2 composite micropowder in a spherical mixer for 120 to 180 minutes; 4) The weighed aggregate A, aggregate B and premixed additives are placed in batching cart A, and the weighed powder is placed in batching cart B; the raw materials in batching cart A are then placed in a mixing and grinding mixer for stirring (stirring time is 5-10 minutes), followed by adding 95% of the total amount of carbonaceous binder and continuing to stir. After stirring for 3-5 minutes, the raw materials in batching cart B are added, followed by adding the remaining 5% of carbonaceous binder and continuing to stir for 15-20 minutes, and sampling is performed to test the Marshall value; 5) After the Marshal value test is qualified, qualified clay is obtained, and the temperature of the qualified clay is controlled at 40-50℃. The qualified clay is sent into the mud extruder through a belt, and the mud is squeezed out of the mud extruder into a qualified shape and enters the packaging process to obtain the product, which is magnesia mud for electric arc furnace using nearly spherical Al2O3-SiO2 composite micropowder as the only plasticizer.

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