Method for desulfurizing molten iron by using calcium aluminate

Abstract

The invention discloses a method for desulfurizing molten iron by adopting calcium aluminate. The method comprises the steps of preparation of a desulfurizing agent, pretreatment of the molten iron, stepped desulfurization and treatment and recovery of desulfurization residues. The preparation method comprises the following steps: mixing the following raw materials in percentage by mass: 70-85% of active calcium aluminate, 5-15% of calcium oxide, 3-8% of calcium fluoride and 1-5% of metal aluminum powder, and crushing the mixed raw materials in a jet mill to obtain a calcium aluminate desulfurizer; the temperature of the molten iron is 1250-1350 DEG C, the initial sulfur content is controlled to be 0.02%-0.08%, the silicon content of the molten iron is smaller than or equal to 0.8%, and a calcium aluminate desulfurizer is blown through a top spray gun of a ladle blowing desulfurization device; the method comprises the following steps: adding molten iron into a desulfurization furnace, introducing nitrogen or argon, adding limestone into the molten iron until the sulfur content of the molten iron is less than or equal to 0.005%, stopping blowing and stirring, and slagging off, grinding and recycling after the desulfurization reaction is ended, and the method has the advantages that the consumption of a desulfurizer is reduced, the desulfurization efficiency is improved, and the environmental protection performance is improved.

Description

Technical Field

[0001] This invention belongs to the field of molten iron pretreatment technology in iron and steel metallurgy, specifically involving a method for desulfurizing molten iron using calcium aluminate. Background Technology

[0002] Sulfur in molten iron is one of the key harmful elements affecting steel quality, causing hot brittleness and significantly reducing the mechanical and processing properties of steel. Therefore, molten iron desulfurization is a crucial step in steel production, and its effectiveness directly impacts subsequent steelmaking processes and the quality of the final product. Currently, commonly used industrial molten iron desulfurization methods include the calcium carbide method (CaC2), magnesium-based desulfurization (metallic Mg or Mg alloy), and lime method (CaO). However, these methods have significant drawbacks: 1) The calcium carbide method has a high desulfurization efficiency of 80%-90%, but it generates a large amount of acetylene gas (C2H2) during the process, posing an explosion risk. Furthermore, waste gas treatment costs are high, and the resulting calcium carbide slag has a high phosphorus content, making it difficult to recycle and increasing environmental pressure. 2) The magnesium-based desulfurization method has a fast reaction speed and high desulfurization efficiency of over 90%, but the high price of metallic magnesium (approximately 20,000 RMB / ton) leads to high desulfurization costs. Additionally, the reaction between magnesium vapor and molten iron is violent, easily causing splashing, requiring strict control of reaction conditions. 1) The operation is difficult; 2) The lime method is low in cost and has a wide range of raw material sources, but the desulfurization efficiency is low, only 50%-60%, the reaction speed is slow, and a large amount of lime is required (the desulfurizing agent consumption reaches 10-15 kg / t), the slag volume is too large, and the subsequent treatment burden is heavy; 3) The lime method is low in cost and has a wide range of raw material sources, but the desulfurization efficiency is only 60%-70%, and a high reaction temperature (≥1350℃) is required, resulting in high energy consumption and limiting its large-scale application.

[0003] Chinese Patent CN 108048615 A ​​discloses a desulfurizing agent for molten iron pretreatment and its preparation method. The desulfurizing agent is formulated from quicklime, limestone, calcium aluminate, and metallic calcium granules as raw materials, with the following weight percentages: quicklime 50-70 parts; limestone 10-30 parts; calcium aluminate 10-20 parts; metallic calcium 1-10 parts. The quicklime contains ≥80% CaO and <2.0% SiO2; the limestone contains ≥92% CaCO3 and <1.0% SiO2; the calcium aluminate contains 45-55% CaO, 35-45% Al2O3, and <5.0% SiO2; and the metallic calcium contains ≥95% Ca. However, the amount of metallic calcium added to this desulfurizing agent is only 1-10 parts, and its purity is required to be ≥95%. As a strong reducing alkali metal, metallic calcium requires complex processes such as electrolytic molten calcium chloride for industrial preparation, resulting in production costs far exceeding those of traditional desulfurizing agents (such as magnesium and CaF2). Compared to conventional desulfurizers, the high proportion of metallic calcium significantly increases the overall production cost of desulfurizers. Furthermore, metallic calcium is chemically reactive, readily reacting with oxygen and water vapor in the air to form calcium oxide and calcium hydroxide. This not only reduces the content of effective components in the desulfurizer but also poses a risk of spontaneous combustion due to the exothermic reaction, further increasing logistics costs and management complexity, which is detrimental to large-scale industrial applications.

[0004] Chinese patent CN 104531951 B discloses a desulfurizing agent for molten iron. The components and their mass fractions of the desulfurizing agent are as follows: CaO: 80-85 parts; C: 5-10 parts; Mg: 5-10 parts; Zn: 5-10 parts; cyclic dimethyl silicone oil: 5-10 parts; hydraulic oil: 5-10 parts; soybean oil: 5-10 parts; calcium aluminate: 5-8 parts; soda ash: 5-10 parts. The patent adds cyclic dimethyl silicone oil, hydraulic oil, and soybean oil (5-10 parts each), claiming that their function is to form a protective film on the surface of CaO and improve desulfurization efficiency through volatilization. However, the pretreatment temperature of molten iron is 1300-1450℃, which far exceeds the boiling point of soybean oil (230℃), hydraulic oil (usually 200-300℃), and cyclic dimethyl silicone oil (about 150-200℃). At high temperatures, these organic components volatilize rapidly and violently. On the one hand, this may cause the protective film to rupture prematurely, failing to achieve the expected effect of "extending the storage period to 3-4 months" (in Example 1, powdering occurred after 90 days of storage). On the other hand, the contact between a large amount of organic vapor and high-temperature molten iron may trigger local deflagration or produce harmful gases containing carbon and hydrogen (such as methane and carbon monoxide), which not only pollutes the environment but may also interfere with the desulfurization reaction. Zinc has a boiling point of 907℃, which is far lower than the pretreatment temperature of molten iron. It will volatilize rapidly during the desulfurization process and will not be able to effectively participate in the desulfurization reaction (the patent does not clearly define the reaction mechanism between Zn and S, and in existing theories, the affinity of Zn for S is much lower than that for Mg and Ca).

[0005] The two patents both involve calcium aluminate, but their roles differ. In (CN104531951B), although the specific mechanism of action is not explicitly explained, it is analyzed that calcium aluminate participates in the reaction as one of the components of the molten iron desulfurizing agent, but at a low content of only 5-8 parts. In patent CN 108048615 A, calcium aluminate mainly replaces CaF2 to achieve environmentally friendly fluxing and improve desulfurization kinetics. This patent provides a method for molten iron desulfurization using activated calcium aluminate. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a method for desulfurizing molten iron using calcium aluminate. This method aims to overcome the shortcomings of existing calcium-based, magnesium-based, and original calcium aluminate-based desulfurizers, such as low desulfurization efficiency, slow reaction rate, requirement for high-temperature conditions, and large consumption of desulfurizers. By optimizing the composition and particle size of the calcium aluminate desulfurizer, designing a stepped reaction process, and combining stirring enhancement measures, this invention can achieve efficient desulfurization under medium and low temperature conditions, while reducing costs and environmental impact.

[0007] The core idea of ​​this invention is to improve the reactivity and mass transfer efficiency of calcium aluminate with sulfur in iron by using a four-step synergistic strategy: precise formulation of desulfurizing agent (the composition ratio should be close to the liquid phase or low melting point region in the calcium aluminate phase diagram), widening the pretreatment temperature range of molten iron, using a blowing process to achieve a suitable stirring intensity of molten iron, adding an appropriate amount of limestone to decompose CO2 at high temperature to enhance stirring and improve reaction kinetics, and assisting calcium aluminate in desulfurization.

[0008] According to one aspect of the present invention, a method for desulfurizing molten iron using calcium aluminate is provided, the method comprising the following steps: (1) Preparation of desulfurizing agent: Mix the raw materials in the following mass ratio: 70%-85% active calcium aluminate, 5%-15% calcium oxide, 3%-8% calcium fluoride, and 1%-5% metallic aluminum powder (purity ≥95%, particle size ≤100μm). Then, send the mixed raw materials into an air jet mill for pulverization to obtain calcium aluminate desulfurizing agent. (2) Pretreatment of molten iron: The temperature of molten iron is 1250-1350℃, the initial sulfur content is controlled at 0.02%-0.08%, and the silicon content of molten iron is ≤0.8%; (3) Step-by-step desulfurization: The calcium aluminate desulfurizer prepared in step (1) is sprayed into the molten iron in step (2) through the top spray gun of the molten iron ladle desulfurization device. In the first stage, the calcium aluminate desulfurizer prepared in step (1) is sprayed in, and nitrogen or argon is introduced to control the sulfur content to 0.01%-0.02%. In the second stage, the calcium aluminate desulfurizer prepared in step (1) is sprayed in again, and nitrogen or argon is introduced. Then limestone is added to the molten iron until the sulfur content of the molten iron is ≤0.005%. Spraying and stirring are stopped, and the mixture is left to stand. (4) Treatment and recycling of desulfurization residue.

[0009] Based on the above technical solution, the average particle size of the calcium aluminate desulfurizing agent in step (1) is 30-50 μm, and the specific surface area is ≥1.5 m². 2 / g.

[0010] Based on the above technical solution, the active calcium aluminate in step (1) contains 50%-60% CaO and 35%-45% Al2O3, and the main phase is 12CaO•7Al2O3. The purity of calcium oxide in step (1) is ≥90%.

[0011] Based on the above technical solution, the first stage of step (3) specifically involves: injecting 60%-70% of the calcium aluminate desulfurizer prepared in step (1) at a blowing rate of 0.8-1.5 kg / (t•min) for 0-5 min; and introducing nitrogen or argon gas through the bottom permeable brick, controlling the gas flow rate of nitrogen or argon to be 0.05-0.15 m³ / min. 3 / (t•min), stirring power density ≥50W / m 3 The desulfurization temperature is 1250-1350℃, which reduces the sulfur content to 0.01%-0.02%.

[0012] Based on the above technical solution, the second stage of step (3) specifically involves: a spraying rate of 0.3-0.8 kg / (t•min), spraying 30%-40% of the calcium aluminate desulfurizer prepared in step (1) for 5-15 min; and a gas flow rate of 0.02-0.08 m³ / min. 3 / (t•min), stirring power density 30-50W / m³ 3 Add 0.1-0.6 kg / t of limestone powder (CaO content ≥ 53%) to the molten iron until the sulfur content of the molten iron is ≤ 0.005%. Then stop blowing and stirring, and let it stand for 2-3 minutes to allow the desulfurization slag to float and separate fully.

[0013] Based on the above technical solution, the desulfurization slag treatment and recycling in step (4) is as follows: after the desulfurization reaction is completed, the desulfurization slag on the surface of the molten iron is removed by a slag remover, and the desulfurization slag is sent to a ball mill to be ground to a particle size ≤100μm. It is recycled at a ratio of 10%-20% for the preparation of the desulfurizing agent in step (1).

[0014] Based on the above technical solution, the desulfurization efficiency of the method is 85%-95%; the final sulfur content of molten iron is ≤0.005%; the total desulfurizing agent dosage is 6-9 kg / t; and the desulfurization slag recovery rate is 10-20%. Attached Figure Description

[0015] Figure 1 The process flow diagrams for calcium aluminate molten iron desulfurization in Examples 1-3 of this invention are shown below. Figure 2The image shows the SEM and elemental analysis results of the calcium aluminate product described in Example 1 of this invention.

[0016] Beneficial effects The technical solution adopted in this invention significantly improves desulfurization efficiency. By optimizing the desulfurizing agent composition and reaction process, the desulfurization efficiency is increased from 60%-70% in the existing calcium aluminate method to 85%-95%, and the final sulfur content of molten iron can be stably controlled below 0.005%, meeting the production requirements of low-sulfur steel (such as pipeline steel and bearing steel). The reaction temperature is reduced from the traditional ≥1350℃ to 1250-1350℃, expanding the desulfurization efficiency of low-temperature molten iron. The consumption of desulfurizing agent is reduced, with the total desulfurizing agent usage being only 6-9 kg / t (compared to 1 kg / t in the traditional calcium aluminate method). The desulfurization process yields 0-12 kg / t, with a desulfurization slag recovery rate of 10%-20%, further reducing raw material costs by approximately 15%-20%. Environmental performance is optimized, avoiding acetylene gas pollution from the calcium carbide method and metal vapor hazards from the magnesium-based method. No toxic gas emissions are emitted during the desulfurization process, and the desulfurization slag is recyclable, reducing solid waste emissions by over 30%. Operational stability is improved; the stepped injection and stirring intensity control effectively prevent molten iron splashing, ensuring a stable reaction process, reducing equipment failure rate by 25%, and shortening processing time from 15-20 minutes to 10-15 minutes, thus improving production efficiency. Detailed Implementation

[0017] The present invention will now be described in detail with reference to specific embodiments.

[0018] Unless otherwise specified, the raw materials and reagents used in the embodiments and comparative examples of this invention are obtained through self-production, recycling, and purchase.

[0019] The present invention provides a method for desulfurizing molten iron using calcium aluminate in the specific embodiments section, the method comprising the following steps: (1) Preparation of desulfurizing agent: The raw materials are mixed in the following mass ratios: 70%-85% active calcium aluminate (CaO content 50%-60%, Al2O3 content 35%-45%, main phase 12CaO•7Al2O3), 5%-15% calcium oxide (purity ≥90%), 3%-8% calcium fluoride, and 1%-5% metallic aluminum powder (purity ≥95%, particle size ≤100μm). The mixed raw materials are then fed into an air jet mill for pulverization. The average particle size of the desulfurizing agent is controlled to be 30-50μm, and the specific surface area is ≥1.5m². 2 / g, yielding calcium aluminate desulfurizing agent; (2) Pretreatment of molten iron: The temperature of molten iron is 1250-1350℃, the initial sulfur content is controlled at 0.02%-0.08%, the silicon content of molten iron is ≤0.8%, and the calcium aluminate desulfurizer prepared in step (1) is sprayed through the top spray gun of the molten iron ladle desulfurization device (the bottom of the molten iron ladle is equipped with permeable bricks, and nitrogen or argon is blown in to strengthen the stirring of molten iron); (3) Step-by-step desulfurization: The desulfurization reaction temperature range is 1250-1350℃.

[0020] Phase 1 (Rapid Response Period, 0-5 min): A. Injection rate: Inject calcium aluminate desulfurizer at a rate of 0.8-1.5 kg / (t•min) (60%-70% of the total dosage); Stirring intensity: Introduce nitrogen or argon gas through the bottom permeable brick, controlling the gas flow rate to 0.05-0.15 m³ / min. 3 / (t•min), causing the molten iron to form a violent circulation (stirring power density ≥50W / m). 3 This promotes the rapid dispersion of the desulfurizing agent; B. Reaction objective: To reduce the sulfur content to 0.01%-0.02% by utilizing the rapid reaction between highly active calcium aluminate and sulfur.

[0021] Second stage (deep reaction period, 5-15 min): A. Injection rate: Reduce the injection rate to 0.3-0.8 kg / (t•min) and inject the remaining 30%-40% of the desulfurizer; B. Stirring intensity: Bottom-blown gas flow rate reduced to 0.02-0.08 m³ / h. 3 / (t•min)(stirring power density 30-50W / m 3 This reduces molten iron splashing and promotes the polymerization and flotation of desulfurized products. C. Auxiliary measures: Add 0.1-0.6 kg / t of limestone (CaO content ≥53%) powder to the molten iron. The CaCO3 in the limestone decomposes at high temperature to generate CO2 bubbles, which carry the desulfurization products to the surface.

[0022] Reaction termination judgment: When the online sulfur content detector shows that the sulfur content of molten iron is ≤0.005% (target value), stop blowing and stirring, let stand for 2-3 minutes, and allow the desulfurization slag to float and separate fully.

[0023] (4) Desulfurization slag treatment and recycling: After the desulfurization reaction is completed, the desulfurization slag (mainly CaS, Al2O3 and unreacted calcium aluminate) on the surface of the molten iron is removed by a slag remover. The desulfurization slag is then fed into a ball mill and ground to a particle size of ≤100μm. 10%-20% of the slag is recycled for the preparation of new desulfurizing agent (to replace part of the calcium aluminate) to achieve resource recycling.

[0024] Example 1 Processing 170 tons of molten iron (initial sulfur content 0.05%) (1) Preparation of desulfurizing agent: The raw materials are mixed in the following mass ratio: 80% active calcium aluminate (CaO 55%, Al2O3 40%, 12CaO•7Al2O3 phase ratio 75%), 10% CaO, 5% CaF2, and 5% metallic aluminum powder. After pulverization, the average particle size is controlled to be 40μm and the specific surface area is 1.6m². 2 / g, i.e., calcium aluminate desulfurizer, the SEM and elemental analysis results of the calcium aluminate desulfurizer are as follows: Figure 2 As shown.

[0025] (2) Pretreatment of molten iron: The temperature of molten iron is 1280℃, the silicon content is 0.25%, and 170t of molten iron is poured into the ladle. The bottom permeable brick and the top spray gun are started.

[0026] (3) Step-by-step desulfurization: The desulfurization reaction temperature is 1280℃. In the first stage, calcium aluminate desulfurizing agent is injected at a rate of 1.1 kg / (t•min) for 5 min, and the injection amount is 66% (935 kg) of the total amount of desulfurizing agent in molten iron. The argon flow rate is 0.10 m³ / min. 3 / (t•min), stirring power density 55W / m³ 3 After 5 minutes, the sulfur content was measured to have decreased to 0.012%. In the second stage, the remaining 34% of the desulfurizing agent (476 kg) was injected at a rate of 0.4 kg / (t•min) for 7 minutes, with an argon flow rate of 0.06 m³ / min. 3 / (t•min), stirring power density 35W / m³ 3 At the 8th minute, 0.2 kg / t of limestone powder (34 kg) was added. After 15 minutes, the sulfur content was measured to be 0.003%, which met the target.

[0027] (4) Slag treatment and recycling: Approximately 1.2 tons of desulfurization slag were removed, ground, and recycled at a rate of 15% for use in the preparation of the next desulfurization agent. This slag can replace 180 kg of calcium aluminate. The specific flow chart of the desulfurization process is shown below. Figure 1 As shown.

[0028] Effect verification: The desulfurization efficiency was (0.05%-0.003%) / 0.05%×100%=94%, the total consumption of desulfurizing agent was (935+476) / 170=8.3kg / t, the processing time was 12min, the desulfurization slag recovery rate was 15%, the raw material cost was 996 yuan, the solid waste discharge was 1020kg, and there was no splashing phenomenon.

[0029] Example 2 Processing 170 tons of molten iron (initial sulfur content 0.07%) (1) Preparation of desulfurizing agent: 75% active calcium aluminate (CaO 58%, Al2O3 38%), 12% CaO, 8% CaF2, and 5% metallic aluminum powder were mixed in the following mass ratio, with an average particle size of 35 μm and a specific surface area of ​​1.8 m². 2 / g, which refers to calcium aluminate desulfurizer.

[0030] (2) Pretreatment of molten iron: molten iron temperature 1300℃, silicon content 0.20%, initial sulfur content 0.07%, 170t molten iron ladle, start bottom permeable brick and top spray gun.

[0031] (3) Step-by-step desulfurization: The desulfurization reaction temperature is 1330℃. In the first stage, the injection rate is 1.4 kg / (t•min), and the total injection volume is 70% (170×1.4×5=1190 kg); the argon flow rate is 0.12 m³ / min. 3 / (t•min), stirring power density 60W / m³ 3 After 5 minutes, the sulfur content dropped to 0.015%.

[0032] Second stage (5-10 min): Injection rate 0.4 kg / (t•min), injecting the remaining 30% (170 × 0.4 × 5 = 340 kg); argon flow rate 0.07 m³ / min. 3 / (t•min); 0.3 kg / t limestone (51 kg) was added at the 8th minute. After 10 minutes, the sulfur content was 0.005%. The rest of the process was the same as in Example 1. The specific flow chart of the desulfurization process is as follows. Figure 1 As shown.

[0033] Effect verification: The desulfurization efficiency was (0.07%-0.005%) / 0.07%×100%=92.9%, the desulfurizing agent consumption was (1190+340) / 170=9kg / t, the processing time was 10min, the desulfurization slag recovery rate was 18%, the raw material cost was 1080 yuan, the solid waste discharge was 980kg, and there was no splashing phenomenon.

[0034] Example 3 The top slag after desulfurization in Example 1 was recovered. The composition of the recovered calcium aluminate desulfurizer was as follows: CaO 55%, Al2O3 35%, 5% CaF2, 5% Al. Desulfurization was carried out by spraying the molten iron with a spray gun. After the desulfurization reaction was completed, the top slag floating on the surface of the molten iron (still containing a large amount of active substances) was collected by a mechanical slag remover and temporarily stored in a slag bin as raw material. The composition of the recovered top slag was analyzed and found to be CaO 45%, Al2O3 30%, CaS 12% (previous desulfurization product), FeO 6%, SiO 25%, and metallic iron 2%. Because the top slag contains a small amount of iron beads (affecting desulfurization activity and slag-iron separation), the recovered slag is pretreated first: magnetic separation to remove iron, using a drum magnetic separator (magnetic field strength 12000Gs) to remove metallic iron, with an iron recovery rate of 95%; crushing and screening, using a jaw crusher to coarsely crush to <10mm, then sending the desulfurization slag to a ball mill for grinding, and screening with a vibrating screen, requiring particle size ≤100μm (to increase the contact area between slag and iron); drying and stabilization, drying in a 120℃ forced-air drying oven for 4 hours to remove adsorbed water, avoiding splashing when adding molten iron, and sealing for later use, i.e., the pretreated desulfurization slag; the pretreated slag is then used again in the preparation of desulfurizing agent, and the remaining processes are consistent with Example 1.

[0035] Comparative Example The difference from Example 1 is that lime powder desulfurizer is used, the desulfurization efficiency is 65%, the final sulfur content of molten iron is 0.005%, the desulfurization reaction temperature is 1430℃, the total desulfurizer dosage is 12kg / t, the desulfurization slag recovery rate is 0%, the raw material cost is 2040 yuan, the solid emission is 2600kg, and the treatment time is 20min. As can be seen from the comparative data, the method disclosed in this embodiment is significantly better than the technical solution used in the comparative example in terms of desulfurization efficiency, cost, and energy consumption.

Claims

1. A method for desulfurizing molten iron using calcium aluminate, characterized in that, The method includes the following steps: (1) Preparation of desulfurizing agent: Mix the raw materials in a mass ratio of 70%-85% active calcium aluminate, 5%-15% calcium oxide, 3%-8% calcium fluoride and 1%-5% metallic aluminum powder, and then send the mixed raw materials into an air jet mill to pulverize them to obtain calcium aluminate desulfurizing agent. (2) Pretreatment of molten iron: The temperature of molten iron is 1250-1350℃, the initial sulfur content is controlled at 0.02%-0.08%, and the silicon content of molten iron is ≤0.8%; (3) Step-by-step desulfurization: The calcium aluminate desulfurizer prepared in step (1) is sprayed into the molten iron in step (2) through the top spray gun of the molten iron ladle desulfurization device. In the first stage, the calcium aluminate desulfurizer prepared in step (1) is sprayed in, and nitrogen or argon is introduced to control the sulfur content to 0.01%-0.02%. In the second stage, the calcium aluminate desulfurizer prepared in step (1) is sprayed in again, and nitrogen or argon is introduced. Then limestone is added to the molten iron until the sulfur content of the molten iron is ≤0.005%. Spraying and stirring are stopped, and the mixture is left to stand. (4) Treatment and recycling of desulfurization residue.

2. The method according to claim 1, characterized in that, The calcium aluminate desulfurizer in step (1) has an average particle size of 30-50 μm and a specific surface area ≥1.5 m². 2 / g.

3. The method according to claim 1, characterized in that, The active calcium aluminate described in step (1) contains 50%-60% CaO and 35%-45% Al2O3, with the main phase being 12CaO•7Al2O3; The purity of calcium oxide in step (1) is ≥90%.

4. The method according to claim 1, characterized in that, Step (3) The first stage specifically involves: injecting 60%-70% of the calcium aluminate desulfurizer prepared in step (1) at a blowing rate of 0.8-1.5 kg / (t•min) for 0-5 min; and introducing nitrogen or argon gas through the bottom permeable brick, controlling the gas flow rate of nitrogen or argon to be 0.05-0.15 m³ / min. 3 / (t•min), stirring power density ≥50W / m 3 The desulfurization temperature is 1250-1350℃, which reduces the sulfur content to 0.01%-0.02%.

5. The method according to claim 1, characterized in that, Step (3) The second stage specifically involves: a spraying rate of 0.3-0.8 kg / (t•min), spraying 30%-40% of the calcium aluminate desulfurizer prepared in step (1) for 5-15 min; and a gas flow rate of 0.02-0.08 m³ / min. 3 / (t•min), stirring power density 30-50W / m³ 3 Add 0.1-0.6 kg / t of limestone powder (CaO content ≥ 53%) to the molten iron until the sulfur content of the molten iron is ≤ 0.005%. Then stop blowing and stirring, and let it stand for 2-3 minutes to allow the desulfurization slag to float and separate fully.

6. The method according to claim 1, characterized in that, The desulfurization slag treatment and recycling in step (4) specifically involves: after the desulfurization reaction is completed, a slag remover is used to remove the desulfurization slag from the surface of the molten iron, and the desulfurization slag is fed into a ball mill to be ground to a particle size ≤100μm, and recycled at a ratio of 10%-20% for the preparation of the desulfurizing agent in step (1).

7. The method according to claim 1, characterized in that, The desulfurization efficiency of the method is 85%-95%; the final sulfur content of molten iron is ≤0.005%; the total desulfurizing agent dosage is 6-9 kg / t; and the desulfurization slag recovery rate is 10-20%.

Images