A method for reusing a ladle slag

Abstract

The application provides a recycling treatment method for ladle back slag and relates to the technical field of iron and steel metallurgy, and comprises the following steps: S1, hot-state collection of ladle back slag and mixing with slag-iron; S2, KR stirring desulfurization and component homogenization control; S3, sulfur content detection and grading control; S4, converter collaborative smelting; the application provides a recycling treatment method for ladle back slag, and through the coupling process of alkali degree control, forced homogenization stirring, complete slagging and limited reuse of high-sulfur slag, effectively solves the defects of sulfur increase, spattering and sulfur enrichment in the traditional process, significantly optimizes auxiliary material consumption and metal loss, and simultaneously improves smelting stability and environmental protection.

Description

Technical Field

[0001] This invention relates to the field of iron and steel metallurgy technology, and in particular to a method for the reuse and treatment of ladle slag. Background Technology

[0002] The ladle is the core container used in steelmaking to receive, refine, and pour molten steel. After the molten steel is poured, a certain amount of residual molten steel and slag will remain in the ladle. This residual material is uniformly named ladle casting residue, also known as ladle return slag. Its discharge temperature is stable in the high-temperature range of 1500℃ to 1600℃, containing a large amount of sensible heat, as well as valuable slag-forming components such as CaO, Al2O3, and SiO2, and a small amount of residual steel, thus possessing resource recycling value.

[0003] Traditional steel ladle casting slag is processed using a cold-state process: hot slag is poured into slag basins or slag pots and cooled to room temperature naturally or by water spraying. The slag steel is then recovered through crushing and magnetic separation, and the remaining tailings are either stockpiled or sold off at a low price. This process has significant drawbacks: first, the processing cycle is long, with the entire process taking several days; second, the high-temperature sensible heat is completely lost, resulting in significant energy waste; third, water spraying generates dust and steam, creating a poor working environment and consuming large amounts of water; and fourth, the tailings contain free calcium oxide and free magnesium oxide, resulting in poor structural stability, limiting comprehensive utilization channels, and long-term stockpiling can easily lead to land occupation and environmental hazards to soil and water bodies.

[0004] To address the drawbacks of cold-state processes, the industry has gradually developed hot-state recycling technologies for ladle slag. One approach involves directly returning the hot slag to the LF refining furnace, utilizing the slag's basicity and residual heat to replace part of the refining slag-forming material. However, after long-term recycling, the slag continuously accumulates sulfur, reaching sulfur capacity saturation, which reduces LF desulfurization efficiency. This necessitates periodic slag removal and disposal, while also occupying effective ladle volume, imposing strict production scheduling constraints, and lacking adaptability to various steel grades.

[0005] Another conventional hot-state utilization scheme involves directly mixing the slag from the ladle with the molten iron before sending it to the converter for smelting. This method can recover a small amount of waste heat and calcium-based components, but it has significant technical risks: the sulfur content of the ladle slag is generally between 0.5% and 1.5%, and direct contact with molten iron will cause the molten iron to become more sulfur-rich, easily leading to excessive sulfur content in the finished steel from the converter and increasing the cost of subsequent desulfurization; at the same time, the temperature drop of the hot slag-iron mixture fluctuates greatly, and the slag phase fluidity changes abruptly, which can easily cause safety problems such as sticking to the ladle and splashing, restricting the turnover efficiency of the molten iron ladle and the stability of smelting; and the high-sulfur slag material is not subject to control and reuse, which can easily lead to sulfur accumulation throughout the smelting process. Summary of the Invention

[0006] Based on the technical problems existing in the background art, the present invention proposes a method for the reuse and treatment of ladle slag.

[0007] The present invention proposes a method for the reuse and treatment of slag from steel ladles, comprising the following steps: S1. Hot Collection and Mixing of Ladle Slag: After the molten steel is poured, the residual ladle slag in the ladle is slowly and uniformly poured directly into a pre-stored molten iron ladle containing undesulfurized molten iron under hot conditions of 1500℃~1600℃. Strict control is maintained to prevent water accumulation inside the ladle and to avoid high-temperature slag-iron reaction splashing, forming a mixture of molten iron and ladle slag. The ladle slag added is 20%~35% of the molten iron mass. The ladle receiving the slag is a hot ladle returned from the converter after iron addition, with a residual temperature ≥600℃ on the inner wall to reduce the temperature drop of the hot slag and damage to the ladle from rapid cooling. The temperature of the pre-stored undesulfurized molten iron in the ladle is controlled between 1250℃ and 1500℃ to avoid splashing and crusting caused by excessive temperature difference during slag-iron mixing.

[0008] S2, KR Forced Stirring Desulfurization and Composition Homogenization Control: The molten iron ladle loaded with the mixed materials is transported to the KR molten iron pretreatment mixing station, and calcium-based desulfurizer is added at a dosage of 2.0 kg to 5.0 kg per ton of molten iron; the KR stirring head is lowered to the preset immersion depth, and the stirring paddle is immersed in the molten iron at a height of 50% to 70%, and mechanical stirring is carried out at a speed of 70 r / min to 120 r / min for 4 min to 10 min; through strong stirring, the slag and iron are mixed throughout the entire process, and the temperature and composition are homogenized, solving the problem of large fluctuations in the composition of the recycled slag; the CaO component in the recycled slag of the ladle and the calcium-based desulfurizer synergistically participate in the molten iron desulfurization reaction, and the slag basicity CaO / SiO2≥2.5 is strictly controlled to increase the sulfur capacity of the slag phase, and the sulfur element is directionally enriched in the slag phase.

[0009] The core desulfurization mechanism of this step is as follows: The sulfur content (0.5%–1.5%) carried by the ladle slag reacts rapidly with the sulfur in the molten iron under the excellent kinetics of KR forced stirring, reacting with CaO to form CaS. The high-basicity slag system allows CaS to be stably dissolved in the slag phase, preventing reverse dissolution into the molten iron. After stirring, the slag is allowed to stand for 30–60 seconds to achieve slag-metal stratification, completely removing the floating sulfur-rich composite desulfurization slag with a thickness of not less than 50 mm, thus completely eliminating the risk of sulfur carrying over the slag. The removed sulfur-rich composite desulfurization slag is limited to a sintering incorporation ratio of ≤3%. To prevent long-term sulfur enrichment in the blast furnace-sintering system and achieve orderly resource recycling; KR desulfurization is carried out in a closed dust collection system to control fugitive dust emissions, and the treatment temperature is maintained at 1300℃~1450℃ to ensure the thermodynamic stability of the desulfurization reaction; the added calcium-based desulfurizing agent melts rapidly in the initial stirring stage to form a new slag phase with high basicity and low sulfur content. Its thermodynamic driving force for absorbing sulfur into the molten iron is significantly greater than the driving force for CaS in the recycled slag to release sulfur into the molten iron, so that the mixed system enters the overall desulfurization state in a very short time and there is no net transfer of sulfur from the recycled slag to the molten iron.

[0010] S3. Sulfur content detection and grading control: Rapidly sample and test the molten iron after pretreatment to determine the sulfur mass fraction; the detection time should be controlled within 3 minutes to adapt to continuous production; if the sulfur mass fraction of the molten iron is ≤0.010%, it is judged as qualified molten iron and can directly enter the next process; if the sulfur mass fraction of the molten iron is >0.010%, calcium-based desulfurizing agent is added and the stirring desulfurization operation is repeated 1 to 2 times until the sulfur content meets the standard.

[0011] S4. Converter Co-smelting: Standard low-sulfur molten iron is added to the converter and production is carried out in accordance with the existing converter top and bottom blowing smelting system; hot materials are transported in a closed manner throughout the process to reduce heat loss; residual CaO and Al2O3 in the ladle slag effectively participate in converter slag formation, improve the fluidity of the initial slag and the slag formation rate, and reasonably reduce the amount of lime and other slag-forming auxiliary materials according to the actual proportion of slag added, with the amount of lime in the converter reduced by 10% to 30%.

[0012] Preferably, in step S1, the ladle slag is the residual slag generated after continuous casting of carbon structural steel or low alloy steel, and the harmful elements are limited to: phosphorus mass fraction ≤0.08%, and lead and zinc total mass fraction ≤0.05%.

[0013] Preferably, in step S1, the sulfur mass fraction in the ladle slag is 0.5% to 1.5%, and the CaO mass fraction is 40% to 55%.

[0014] Preferably, in step S2, the calcium-based desulfurizer is composed of CaO and CaF2, with the following mass fractions: CaO 80%–90%, CaF2 10%–20%, and the maximum particle size of the desulfurizer ≤ 1.0 mm.

[0015] Preferably, in step S2, the rotation speed of the KR stirring head is optimized to 80 r / min to 100 r / min, and the stirring time is optimized to 5 min to 8 min.

[0016] Preferably, in step S2, the forced stirring process is carried out in a closed, slightly negative pressure environment to collect dust and control the unorganized emission of dust.

[0017] Preferably, in step S2, after stirring, the mixture is allowed to stand for 30 to 60 seconds to ensure that the slag and gold are fully separated and to improve the slag removal and desulfurization effect.

[0018] Preferably, in step S4, the amount of lime added to the converter is reduced by 10% to 30% based on the actual proportion of slag returned from the ladle.

[0019] Preferably, the entire process involves the closed-loop transfer of hot materials to reduce heat dissipation and cold air intrusion, thereby stabilizing the thermal balance throughout the process.

[0020] Preferably, in step S3, the sulfur content of molten iron is detected using rapid spectral sampling, with a detection time of ≤3 minutes, to ensure continuous production.

[0021] The present invention proposes a method for reusing ladle slag, which has the following beneficial effects: by introducing ladle slag into the KR hot metal pretreatment process, combined with high-basicity slag system control and thorough slag removal, the sulfur-increasing effect of slag is completely suppressed, and the original sulfur in the hot metal and the sulfur brought in by the slag are removed simultaneously. The sulfur content of the hot metal entering the furnace is stably ≤0.010%, breaking the sulfur cycle enrichment in the steelmaking process and reducing the risk of excessive sulfur in finished steel from the source.

[0022] CaO in ladle slag effectively replaces lime auxiliary material in converters, achieving a real saving of 3.5-5.0 kg of lime per ton of steel and a reduction of 8-12 kg of steel material loss. Relying on residual steel recovery and converter slag optimization, splashing metal loss is reduced, the smelting cycle of a single furnace is shortened by 2-3 minutes, and production efficiency is significantly improved.

[0023] The entire process is carried out in a closed, continuous hot state, recovering the high-temperature sensible heat of the slag and optimizing the overall thermal balance. Safety and environmental control measures such as splash prevention, water accumulation control, closed dust removal, and limited reuse of high-sulfur slag are added to eliminate the original process safety hazards and secondary pollution defects.

[0024] KR strong stirring achieves material homogenization, limits the range of harmful elements in recycled slag, and is suitable for mainstream production of carbon steel and low alloy steel; all slag materials are graded and utilized for resource recovery, with no disorderly discharge of solid waste, taking into account both economic efficiency and environmental protection. Attached Figure Description

[0025] Figure 1 This is a flowchart of a method for reusing slag from a steel ladle, as proposed in this invention. Detailed Implementation Example

[0027] Reference Figure 1 This invention proposes a method for the reuse and treatment of ladle slag. This embodiment utilizes a 120t converter-supported steelmaking production line for industrial-scale testing. After ladle casting is completed, 7.5t of ladle slag is generated (including 2.5t of residual steel and 5.0t of steel slag). The slag has a sulfur content of 1.1%, a CaO content of 48%, and meets the requirements for harmful elements. The discharge temperature is 1550℃.

[0028] S1: Slowly pour the hot ladle slag into the return hot iron ladle. The ladle contains 25t of undesulfurized molten iron with a temperature of 1380℃, an initial sulfur mass fraction of 0.045%, and an inner wall temperature of 680℃. The ladle slag addition is 30% of the molten iron mass. The total material volume after mixing is 32.5t. Check the ladle in advance to ensure there is no residual water.

[0029] S2: The molten iron ladle is transferred to the KR mixing station, and 87.5 kg of composite calcium-based desulfurizing agent (CaO 85% + CaF2 15%, particle size 0.5-0.8 mm) is added, which is equivalent to 3.5 kg per ton of molten iron. The stirring paddle is immersed in 60% of the liquid surface, the stirring speed is 90 r / min, the stirring time is 6 min, the temperature in the treatment zone is 1350℃-1400℃, and the slag basicity is controlled to be ≥2.6. After stirring, it is allowed to stand for 40 s, and 2.1 t of sulfur-rich desulfurization slag is completely removed, with a slag thickness of 55 mm. The desulfurization slag is sent to the sintering process, and the blending ratio is controlled at 2.2%. The entire process is carried out in a closed dust collection system.

[0030] S3: Rapid sampling and testing showed that the sulfur content in the molten iron was 0.007%, which meets the control standard of ≤0.010%, and the sample was deemed qualified.

[0031] S4: Qualified molten iron is added to a 120t converter and conventional top and bottom blowing smelting is carried out. The amount of lime used is reduced by 20% based on the benchmark amount. The slag condition is stable during the smelting process, with no splashing or overflowing abnormalities. The final sulfur mass fraction of the finished steel is 0.012%, which meets the internal control indicators of the steel grade.

[0032] The actual benefits of this embodiment are: lime consumption per ton of steel is reduced by 4.2 kg, steel material loss is reduced by 10.5 kg / t, and smelting time per furnace is shortened by 2.5 min. Example

[0033] In this embodiment, after the ladle is poured, 9.0t of ladle slag is generated, with a sulfur content of 1.3%, a CaO content of 52%, and a slag temperature of 1520℃; 30t of undesulfurized molten iron is pre-stored in the molten iron ladle, with a molten iron temperature of 1420℃, an initial sulfur mass fraction of 0.055%, and an inner wall temperature of 720℃; the amount of slag added is 30% of the molten iron mass.

[0034] S2: The amount of calcium-based desulfurizer added is equivalent to 4.5 kg per ton of molten iron, with a total addition of 135 kg; KR stirring speed is 100 r / min, stirring time is 8 min, and slag basicity is controlled at ≥2.7; after stirring, let stand for 50 s, remove 2.8 t of desulfurization slag, and the sintering incorporation ratio is 2.8%.

[0035] S3: The initial test showed that the sulfur content of the molten iron was 0.012%, which exceeded the control standard. After adding desulfurizing agent (1.5 kg per ton of molten iron), stirring for 4 minutes, and thoroughly removing the slag, the sulfur content was measured again and dropped to 0.006%, meeting the standard for furnace entry.

[0036] S4: The amount of lime used in converter smelting is reduced by 25%, the final sulfur mass fraction of the finished steel is 0.010%, and the product quality is qualified.

[0037] The actual benefits of this embodiment are: lime consumption per ton of steel is reduced by 4.8 kg, and steel material loss is reduced by 11.2 kg / t.

[0038] Comparative Example A comparison of hot direct mixing processes on the same production line: 7.2t of ladle slag was directly mixed into a 28t molten iron ladle without KR desulfurization pretreatment or thorough slag removal control, and directly sent to the converter for smelting; the initial sulfur content of the molten iron was 0.042%, which increased to 0.048% due to the high sulfur content of the slag; the sulfur content of the finished steel after converter smelting was 0.028%, exceeding the internal control standard, requiring additional desulfurization treatment after the furnace, increasing the production cost by 8.5 yuan per ton of steel; slight splashing occurred during the smelting process, reducing production stability.

[0039] Comparison table of example and comparative data: Comparative data shows that this invention effectively solves the defects of traditional processes such as sulfur increase, splashing, and sulfur enrichment through a coupled process of alkalinity control, forced homogenization and stirring, thorough slag removal, and limited reuse of high-sulfur slag. It also significantly optimizes auxiliary material consumption and metal loss, and simultaneously improves smelting stability and environmental protection.

[0040] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for reusing and treating slag from steel ladles, characterized in that, Includes the following steps: S1. Hot Collection and Mixing of Ladle Slag and Iron: The ladle slag remaining after the molten steel is poured is slowly and uniformly poured into a ladle pre-filled with undesulfurized molten iron within a hot temperature range of 1500℃ to 1600℃. Water accumulation in the ladle is avoided throughout the process to prevent high-temperature slag-iron reaction and splashing, forming a mixture of molten iron and ladle slag. The amount of ladle slag added is 20% to 35% of the molten iron mass. The ladle is a hot return ladle after converter molten iron addition, with an inner wall temperature of not less than 600℃. The temperature of the undesulfurized molten iron pre-stored in the ladle is 1250℃ to 1500℃. S2, KR Stirring Desulfurization and Composition Homogenization Control: The molten iron ladle containing the mixed materials is transported to the KR molten iron pretreatment mixing station. Calcium-based desulfurizer is added at a rate of 2.0 kg to 5.0 kg per ton of molten iron. The KR stirring head is lowered to a predetermined depth, with the stirring paddle immersed in the molten iron to a depth of 50% to 70% of the molten iron surface. Stirring is performed at 70 to 120 r / min for 4 to 10 minutes. Forced mechanical stirring achieves uniform mixing of the slag and iron materials throughout the entire process, ensuring homogeneity of composition and temperature. Quality control; relying on the synergistic desulfurization of calcium-based components in ladle slag and desulfurizing agent, the slag basicity CaO / SiO2 of the system is controlled to be ≥2.5, so that sulfur reacts to form CaS and is stably dissolved in the slag phase; the temperature of KR desulfurization treatment is controlled at 1300℃~1450℃ throughout the process; after stirring, the floating sulfur-rich composite desulfurization slag is completely removed, and the slag thickness is not less than 50mm, to obtain pretreated molten iron; the mass ratio of sulfur-rich composite desulfurization slag added in the sintering process is limited to ≤3% to avoid sulfur circulation enrichment in the metallurgical system; S3. Sulfur content detection and graded control: Take samples of the pretreated molten iron to test the sulfur mass fraction; if the sulfur mass fraction is ≤0.010%, it directly enters the converter smelting process; if the sulfur mass fraction is >0.010%, add calcium-based desulfurizing agent and repeat step S2 1 to 2 times until the sulfur content meets the standard. S4. Converter Co-smelting: Standard molten iron is added to the converter and produced according to the conventional converter smelting system; the slag-forming components of the ladle slag return participate in the converter slag formation, and the amount of slag-forming auxiliary materials is reasonably reduced according to the actual proportion of ladle slag return.

2. The method for reusing and treating ladle slag according to claim 1, characterized in that, In step S1, the ladle slag is the residual slag produced after continuous casting of carbon structural steel or low alloy steel, and the harmful elements are limited to: phosphorus mass fraction ≤0.08%, and lead and zinc total mass fraction ≤0.05%.

3. The method for reusing and treating ladle slag according to claim 1, characterized in that, In step S1, the sulfur mass fraction in the ladle slag is 0.5% to 1.5%, and the CaO mass fraction is 40% to 55%.

4. The method for reusing and treating ladle slag according to claim 1, characterized in that, In step S2, the calcium-based desulfurizer is composed of CaO and CaF2, with the following mass fractions: CaO 80%–90%, CaF2 10%–20%, and the maximum particle size of the desulfurizer ≤1.0 mm.

5. The method for reusing and treating ladle slag according to claim 1, characterized in that, In step S2, the KR stirring head speed is optimized to 80 r / min to 100 r / min, and the stirring time is optimized to 5 min to 8 min.

6. The method for reusing and treating ladle slag according to claim 1, characterized in that, In step S2, the forced stirring process is carried out in a closed, slightly negative pressure environment to collect dust and control the fugitive emission of dust.

7. The method for reusing and treating ladle slag according to claim 1, characterized in that, In step S2, after stirring, let it stand for 30s to 60s to ensure that the slag and gold are fully separated and improve the slag removal and desulfurization effect.

8. A method for reusing and treating ladle slag according to claim 1, characterized in that, In step S4, based on the actual proportion of slag return from the ladle, the amount of lime added to the converter is reduced by 10% to 30% from the conventional benchmark amount.

9. A method for reusing and treating ladle slag according to claim 1, characterized in that, The entire process involves the closed-loop transfer of hot materials, which reduces heat dissipation and the intrusion of cold air, thus stabilizing the thermal balance throughout the process.

10. A method for reusing and treating ladle slag according to claim 1, characterized in that, In step S3, the sulfur content of molten iron is detected using rapid spectral sampling, with a detection time of ≤3 minutes, ensuring continuous production.

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