Process control method for improving temperature rise efficiency of LF furnace electrode

Abstract

The invention discloses a process control method for improving the temperature rise efficiency of an LF furnace electrode, and belongs to the technical field of metallurgy. The method comprises the following steps: implementing a pre-slagging system in a converter tapping process, and adding an aluminum product and lime to form reductive top slag; the method comprises the following steps of: recycling hot-state refining slag pouring residue of the previous furnace, further improving the reducibility of top slag, forming high-reducibility (FeO + MnO < = 1%) top slag before the LF enters a station, cooperating with a steel ladle bottom blowing three-stage control system, controlling small gas quantity of bottom blowing in the earlier stage of the LF, forbidding adding of slagging materials and alloys, achieving a good submerged arc effect in a power transmission process, and ensuring stable output of an electric arc. By means of the measures, rapid heating in the power transmission process of the LF furnace is achieved, the electrode heating efficiency is improved by 15% or above, power consumption is remarkably reduced, the refining efficiency and the molten steel cleanliness are improved, and good industrial application prospects are achieved.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, specifically relating to a process control method for improving the electrode heating efficiency of an LF furnace. Background Technology

[0002] A ladle refining furnace is a type of metallurgical equipment that combines the functions of a steelmaking furnace for heating and refining. It is used to refine molten steel from primary furnaces (electric arc furnaces, open-hearth furnaces, converters), regulate steel temperature, buffer processes, and meet the requirements of continuous casting and rolling. It is one of the main pieces of equipment for ladle refining. The heating system mainly consists of a transformer, a high-voltage control system, water-cooled cables, conductive crossarms, electrode holders, and graphite electrodes. During the heating process, the electrical system controls the electrode current, voltage, and the distance between the graphite electrodes and the molten steel surface, generating a high-temperature electric arc between the graphite electrodes and the molten steel. The heat is then transferred between the electric arc, steel slag, and molten steel to heat the steel.

[0003] The patent with publication number "202110405981.8" discloses a method for recycling refining slag and molten steel pouring residue. The method involves recovering refining slag and molten steel pouring residue in an empty ladle and utilizing them to react with molten steel during the converter tapping process. This results in a sufficient liquid slag layer when the LF refining process is in place, shortening the time for white slag formation, saving slag-forming material consumption, reducing the heat consumption of slag melting, saving electricity, and improving electrode heating efficiency. The patent application number "202411500867.3" discloses a method for determining the voltage and current level parameters of an LF furnace to reduce power consumption. It uses database technology to obtain the economic current and the current with the fastest heating rate under each voltage level, thereby achieving a reasonable power supply system. However, it does not mention improving the electrode heating efficiency in the process path of the LF furnace. Patent application number "202311180681.X" discloses a method for controlling the temperature of molten steel by heating an LF electrode. By reasonably calculating the heating time of the LF electrode, the method can effectively improve the temperature achievement rate of the LF electrode in one heating, thereby reducing the LF processing cycle; at the same time, it can reduce the power consumption in the process without improving the electrode heating efficiency. The patent application number "202411317449.0" discloses a refining process for rapid heating of LF furnace. The LF furnace takes advantage of the rapid slag formation of fluorite to quickly form white slag, shorten the early smelting time and improve heating efficiency. However, the LF furnace has a slag formation period in the early stage, which affects the electrode heating efficiency. Electrode heating efficiency is related to the stability of the electric arc during electrode heating. The stability of the electric arc depends on the resistance of the current passing through the refining slag and the stability of the molten steel surface. The high basicity and high reducing properties of the refining white slag (characteristics of the slag) provide good arc submersion and heat insulation. The high basicity also results in high viscosity and good fluidity, allowing the slag to better cover the surface of the molten steel, forming a dense protective layer to prevent the molten steel from contacting the air and reducing heat loss. The high reducing slag (with a mass fraction of FeO+MnO of less than 1%) can absorb free electrons in the electric arc, making the arc more stable, effectively reducing arc exposure and fluctuations, and improving electrode heating efficiency. Optimizing the bottom blowing gas control system of the ladle, under the premise of uniform molten steel temperature, and controlling the bottom blowing gas volume of the ladle to a small amount improves electrode heating efficiency.

[0004] Currently, the electrode heating efficiency of the LF furnace is unstable. In the early stage, there is a dual task of heating and slag formation during the electrode power supply process, resulting in low heating efficiency. In the middle stage, slag adjustment is continued according to the refining slag condition, making it impossible to quickly and stably produce refining white slag. Therefore, how to improve the process to achieve high basicity and high reducing properties of the ladle top slag before entering the LF furnace, so as to achieve a good submerged arc effect during the power supply process, stable arc output, and improve electrode heating efficiency. Summary of the Invention

[0005] This invention provides a process control method to improve the electrode heating efficiency of an LF furnace. By implementing a reasonable pre-slag-forming system and a hot liquid refining slag recovery system during converter tapping, high-basicity, high-reducing refining slag is formed before entering the LF furnace. This eliminates the need for slag-forming materials in the early stages of the LF furnace and achieves a good submerged arc effect during the power supply process. In conjunction with the bottom blowing control system of the ladle, the molten steel level is stabilized, and a stable arc output is achieved during the power supply process, thereby improving the electrode heating efficiency of the LF furnace.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A process control method for improving the electrode heating efficiency of an LF furnace, the control method comprising the following control steps: pre-slag formation system for converter tapping, hot liquid refining slag recovery system, and LF furnace refining; The specific pre-slag formation system for converter tapping is as follows: A reasonable pre-slag formation system is implemented during the converter tapping process. Before tapping, the ladle bottom blowing flow rate is high: 700-1000 NL / min. After tapping 1 / 5-1 / 4 of the steel, aluminum products and lime are added sequentially, and the ladle bottom blowing flow rate is low: 100-400 NL / min. The heat of the molten steel and the impact and stirring of the steel flow completely melt the aluminum products and lime, and the top slag becomes reducing slag. After tapping, the ladle bottom blowing flow rate is 400-700 NL / min to promote the steel-slag interface reaction and improve the reducibility of the top slag. The specific process for recovering the hot liquid refining slag residue is as follows: hot liquid refining slag residue from the previous continuous casting is added to the ladle after tapping from the converter. The bottom blowing flow rate of the ladle is 100-400 NL / min. The slag material is homogenized to further improve the reducibility of the top slag. The FeO+MnO content in the top slag is ≤1%.

[0007] The control method of the present invention also includes a ladle bottom blowing system: the ladle bottom blowing system is designed with double permeable bricks, and the flow rate of the permeable bricks on one side is independently adjustable during ladle bottom blowing flow control, with a flow rate range of 0-1000 NL / min, implementing three-level control of ladle bottom blowing; the three-level control system of ladle bottom blowing includes: a small gas volume control stage, with a bottom blowing gas volume of 100-400 NL / min, used during pre-slag formation and the initial stage of LF furnace entry, to stabilize the molten steel surface and improve arc stability; a medium gas volume control stage, with a bottom blowing gas volume of 400-700 NL / min, used during the slag-steel reaction period, to promote inclusion flotation and slag homogenization; and a large gas volume control stage, with a bottom blowing gas volume of 700-1000 NL / min, used during molten steel desulfurization and temperature alloy homogenization, to enhance stirring desulfurization and heat conduction.

[0008] The pre-slag formation system for converter tapping described in this invention involves adding 2.2-2.3 kg / t of aluminum products, which are one or more combinations of aluminum blocks, aluminum granules, or aluminum-iron alloys, and adding 5.7-5.8 kg / t of lime.

[0009] The hydrothermal refining slag casting residue recovery system described in this invention has a temperature of 1540-1560℃ and an element weight percentage composition of the slag as follows: CaO: 50-60%, Al2O3: 25-35%, SiO2: 3-7%, MgO: 6-8%, FeO+MnO≤1%.

[0010] The hot liquid refining slag residue recovery system of the present invention involves adding 8-11 kg / t steel of hot liquid refining slag residue.

[0011] The hydrothermal refining slag recovery system described in this invention involves controlling the bottom blowing gas volume of the ladle to 100-400 NL / min during the initial power supply after the LF furnace enters the station. Before the first power supply is completed, the addition of slag-forming materials and alloys is prohibited to achieve a good submerged arc effect, form a stable resistance layer, ensure stable arc output, and improve electrode heating efficiency.

[0012] The beneficial effects of adopting the above technical solution are as follows: 1. In the process of converter tapping, the present invention implements a reasonable pre-slag-making system, which utilizes the heat of molten steel and the impact and stirring of the steel flow to completely melt the slag, realizes the deep deoxidation of molten steel, and transforms the top slag into reducing slag in advance. With the help of the bottom blowing gas volume control of the ladle, it promotes the steel-slag interface reaction and further improves the reducibility of the top slag; 2. The present invention, combined with the hot liquid refining slag casting residue recovery system, utilizes the high reducibility of the refined white slag (FeO+MnO≤1%), good arc-submerging effect, and heat preservation and insulation effect, so that the LF furnace does not need to add slag-making material in the early stage, avoids the simultaneous reduction of electrode heating efficiency during the early heating and slag-making process, and with the help of the bottom blowing gas volume control of the ladle, it realizes the stable control of the electric arc and molten steel surface during the power supply process, improves the heating efficiency of the electrodes, and at the same time realizes the rapid and stable white slag production of the LF furnace, rapid desulfurization, prolongs the holding time of refined white slag, promotes the full flotation of inclusions, improves the cleanliness of molten steel, and reduces aluminum consumption, ash consumption and energy saving. Attached Figure Description

[0013] Figure 1 This is a flowchart of the control method of the present invention. Detailed Implementation

[0014] The present invention will be further described in detail below with reference to specific embodiments.

[0015] Examples 1-5 The process control method for improving the electrode heating efficiency of the LF furnace according to the present invention includes the following control steps: converter tapping pre-slag formation system, hot liquid refining slag recovery system, and LF furnace refining; the smelting steps are as follows: Figure 1 As shown, taking a 260-ton LF ladle furnace as an example, The specific processes for each step in the embodiment are described below: Step 1: Pre-slag formation system for converter tapping: Before tapping, the bottom blowing flow rate of the ladle is 700-1000 NL / min. After tapping 1 / 5-1 / 4 of the steel, aluminum products and lime are added sequentially. The amount of aluminum products added is 2.2-2.3 kg / t steel, and the amount of lime added is 5.7-5.8 kg / t steel. The bottom blowing flow rate of the ladle is 100-400 NL / min. The heat of the molten steel and the impact and stirring of the steel flow completely melt the lime and aluminum products, and the top slag becomes reducing slag. After tapping, the bottom blowing flow rate of the ladle is 400-700 NL / min to promote the steel-slag interface reaction and improve the reducibility of the top slag. The control parameters for each embodiment are shown in Table 1. Step 2: Hot liquid refining slag residue recovery system: Add hot liquid refining slag residue from the previous continuous casting to the ladle after tapping from the converter. The bottom blowing flow rate of the ladle is 100-400 NL / min to uniformly distribute the slag and further improve the reducibility of the top slag. The temperature of the hot liquid refining slag casting residue is 1540-1560℃, and the addition amount is 8-11 kg / t steel; the weight percentage composition of elements in the slag is: CaO: 50-60%, Al2O3: 25-35%, SiO2: 3-7%, MgO: 6-8%, FeO+MnO≤1%; the control parameters of each embodiment are shown in Table 2; Step 3: After the LF furnace enters the station, take a slag sample, observe the color of the slag, and check the weight percentage composition of the elements in the slag sample. The control parameters for each embodiment are shown in Table 3. Step 4: After the LF furnace enters the station, adjust the bottom blowing gas flow rate of the ladle to 100-400 NL / min, measure the temperature, do not add slag-forming material in the early stage, start power supply, add slag material after the first power supply is completed according to the slag color entering the station, use the high temperature of molten steel to accelerate the melting of slag material, quickly produce refined white slag for desulfurization, after desulfurization, adjust the bottom blowing gas flow rate of the ladle to 100-200 NL / min (according to slight movement of the molten steel surface), measure the temperature, take process samples, and perform a second power supply according to the temperature and production rhythm. The bottom blowing gas flow rate of the ladle is shown in Table 4. Step 5: Adjust the composition according to the process sample composition and the target composition requirements of the molten steel. According to the steel grade's outlet temperature requirements, perform three power-on fine-tuning temperature adjustments. Then, perform calcium treatment and static blowing operations, and the molten steel exits the station.

[0016] Comparative Example The specific processes for each step in the comparative example are described below: Step 1: Converter tapping. Before tapping, the bottom blowing flow rate of the ladle is 700-1000 NL / min. After tapping 1 / 5-1 / 4 of the steel, aluminum products and lime are added sequentially. The amount of aluminum products added is 1.9-2.0 kg / t steel, and the amount of lime added is 3.5-4.5 kg / t steel. The bottom blowing flow rate of the ladle is small: 100-400 NL / min. The heat of the molten steel and the impact and stirring of the steel flow make the lime and aluminum products completely melt, and the top slag becomes reducing slag. After tapping, the bottom blowing flow rate of the ladle is 400-700 NL / min to promote the steel-slag interface reaction and improve the reducibility of the top slag.

[0017] Step 2: After the LF furnace enters the station, take a slag sample, observe the color of the slag, and check the weight percentage composition of the elements in the slag sample; Step 3: After the LF furnace enters the station, adjust the bottom blowing air volume of the ladle to 700-1000 NL / min, measure the temperature, add slag-forming material, and start power supply. Use the electrodes and the large volume of bottom blowing air in the ladle to stir and melt the slag-forming material. After the first power supply is completed, take a sample of the refining slag. Add slag-forming material according to the slag color to make refining white slag for desulfurization. After desulfurization, adjust the bottom blowing air volume of the ladle to 100-400 NL / min (based on slight movement of the molten steel surface), measure the temperature, take process samples, and start the second power supply according to the temperature and production rhythm. Step 4: Adjust the composition according to the process sample composition and the target composition requirements of the molten steel. According to the steel grade's outlet temperature requirements, perform three power-on fine-tuning temperature adjustments. Then, perform calcium treatment and static blowing operations, and the molten steel exits the station.

[0018] Table 1 Control parameters for the pre-slag formation system of converter tapping in Examples 1-5 and Comparative Examples

[0019] Table 2 Recovery of Thermal Liquid Refining Slag in Examples 1-5 and Comparative Examples

[0020] Table 3. Composition results of slag samples from the LF furnace inlets in Examples 1-5 and Comparative Examples.

[0021] Table 4. Variation of bottom blowing gas volume in ladle during LF furnace processes in Examples 1-5 and Comparative Examples.

[0022] Table 5. Temperature and heating rate changes in the LF furnace process of Examples 1-5 and the comparative example.

[0023] During the LF furnace smelting process, the inlet temperature, the end temperature of the first electric arc furnace, the end temperature of the second electric arc furnace, and the outlet temperature were measured. The heating rate during the smelting process was calculated. The heating rate of the first electric arc furnace increased from 4℃ / min to over 4.6℃ / min, (4.6-4) / 4×100%=15%, and the heating efficiency increased by over 15%. The heating rate of the second electric arc furnace increased from 4.5℃ / min to over 4.9℃ / min, (4.9-4.5) / 4.5×100%=8.8%, and the heating efficiency increased by over 8%. The heating rate of the third electric arc furnace increased from 4.66℃ / min to over 5℃ / min, (5-4.66) / 4.66×100%=7%, and the heating efficiency increased by over 7%. By comparing the data from Examples 1-5 with those from the comparative examples, it can be seen that the process control method for improving the electrode heating efficiency of the LF furnace of the present invention, through the synergistic effect of a reasonable pre-slag formation system, a hot liquid refining slag recovery system, and a three-stage bottom blowing control system during the converter tapping process, improves electrode utilization efficiency. The electrode heating efficiency in the early stage of the LF furnace is increased by more than 15%, and the electrode heating efficiency in the middle and late stages is increased by more than 7%, which has obvious effects and saves energy consumption such as electricity.

[0024] The above embodiments are only used to illustrate and not limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention without departing from the spirit and scope of the present invention. Any modifications or partial substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A process control method for improving the electrode heating efficiency of an LF furnace, characterized in that, The control method includes the following control steps: converter tapping pre-slag formation system, hot liquid refining slag recovery system, and LF furnace refining; The specific pre-slag formation system for converter tapping is as follows: During the converter tapping process, a reasonable pre-slag formation system is implemented. Before tapping, the ladle bottom blowing flow rate is high: 700-1000 NL / min. After tapping 1 / 5-1 / 4 of the steel, aluminum products and lime are added in sequence, and the ladle bottom blowing flow rate is low: 100-400 NL / min. The heat of the molten steel and the impact and stirring of the steel flow are used to completely melt the aluminum products and lime, and the top slag becomes reducing slag. After tapping, the ladle bottom blowing flow rate is 400-700 NL / min. The specific process for recovering the hot liquid refining slag residue is as follows: hot liquid refining slag residue from the previous continuous casting is added to the ladle after tapping from the converter. The bottom blowing flow rate of the ladle is 100-400 NL / min, and the FeO+MnO content in the top slag is ≤1%.

2. The process control method for improving the electrode heating efficiency of an LF furnace according to claim 1, characterized in that, The control method also includes a ladle bottom blowing system: the ladle bottom blowing is designed with double permeable bricks, and the flow rate of the permeable bricks on one side is independently adjusted when controlling the ladle bottom blowing flow rate. The flow rate range is 0-1000NL / min, and three-level control of ladle bottom blowing is implemented. The three-stage bottom blowing control system for the ladle includes: a small gas volume control stage with a bottom blowing gas volume of 100–400 NL / min; a medium gas volume control stage with a bottom blowing gas volume of 400–700 NL / min; and a large gas volume control stage with a bottom blowing gas volume of 700–1000 NL / min.

3. The process control method for improving the electrode heating efficiency of an LF furnace according to claim 1, characterized in that, In the pre-slag formation system for converter tapping, the amount of aluminum product added is 2.2-2.3 kg / t steel, and the aluminum product is one or more combinations of aluminum blocks, aluminum granules, or aluminum-iron alloys, and the amount of lime added is 5.7-5.8 kg / t steel.

4. The process control method for improving the electrode heating efficiency of an LF furnace according to claim 1, characterized in that, The aforementioned hydrothermal refining slag casting recovery system involves a slag casting temperature of 1540-1560℃ and a weight percentage of elements in the slag. Composition: CaO: 50-60%, Al2O3: 25-35%, SiO2: 3-7%, MgO: 6-8%, FeO+MnO≤1%.

5. A process control method for improving the electrode heating efficiency of an LF furnace according to any one of claims 1-4, characterized in that, The hot liquid refining slag residue recovery system stipulates that the amount of hot liquid refining slag residue added is 8-11 kg / t steel.

6. A process control method for improving the electrode heating efficiency of an LF furnace according to any one of claims 1-4, characterized in that, The aforementioned hot liquid refining slag recovery system involves controlling the bottom blowing gas volume of the ladle to 100-400 NL / min during the initial power supply after the LF furnace enters the station. Before the first power supply is completed, the addition of slag-forming materials and alloys is prohibited to achieve a good submerged arc effect, form a stable resistance layer, and ensure stable arc output.

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