A method of smelting high-quality steel with low carbon emission by using an electric furnace

Abstract

The application relates to a method for smelting high-quality steel with low carbon emission in an electric furnace, and belongs to the technical field of electric furnace steelmaking. The method comprises the following steps: in the electric furnace smelting process, a first batch of low-carbon foamed slag is added into the electric furnace; a low-carbon composite foaming agent is sprayed into the electric furnace after the first batch of low-carbon foamed slag is added, the spraying position is a preset area around the electrode end portion, and the preset area is completely covered within a preset time to form a foaming agent layer with a predetermined thickness; when the amount of molten scrap steel in the furnace reaches a preset threshold, the range of spraying the low-carbon composite foaming agent is expanded to cover the whole molten pool surface; and the second batch of low-carbon foamed slag and the third batch of low-carbon foamed slag are sequentially added into the electric furnace in which the low-carbon composite foaming agent is sprayed until the smelting is completed. By using the low-carbon composite foaming agent and the low-carbon composite foamed slag in the electric furnace smelting process, high-end high-quality steel production is realized, and the environmental protection goal of extremely low carbon emission is also achieved.

Description

Technical Field

[0001] This application relates to the field of electric arc furnace steelmaking technology, and in particular to a method for smelting high-quality steel in a low-carbon emission electric arc furnace. Background Technology

[0002] In steel production, electric arc furnace (EAF) smelting technology has attracted much attention due to its relatively low carbon emissions, especially the all-scrap EAF process, which is considered an effective way to reduce carbon emissions in steel production. However, in practical applications, this process still faces many technical challenges. Among them, nitrogen control is a particularly critical issue. Excessive nitrogen content can lead to a decline in steel performance, resulting in "aging" or "senescence" phenomena. This is especially true when producing high-quality steel grades such as high-end automotive steel, where nitrogen control directly affects the final product quality. Currently, although some methods exist, such as adding molten iron or using a mixture of scrap steel and molten iron for smelting, to control nitrogen content, these methods often come with a significant increase in carbon emissions, failing to meet the market demand for low-carbon emission products.

[0003] Furthermore, foamed slag technology plays a crucial role in electric arc furnace smelting. Foamed slag effectively reduces the contact area between molten steel and air, thereby decreasing nitrogen accumulation. However, under all-scrap steel smelting conditions, the higher tapping temperature significantly increases the difficulty of controlling foamed slag, shortens its lifespan, and makes it difficult to effectively reduce nitrogen accumulation. Simultaneously, traditional foaming agents such as carbon powder not only increase carbon emissions but also result in prolonged foamed slag formation time and severe nitrogen accumulation during the process. Summary of the Invention

[0004] This application provides a method for smelting high-quality steel in a low-carbon emission electric furnace to solve the following technical problem: how to produce high-quality steel with extremely low nitrogen and extremely low carbon emissions.

[0005] This application provides a method for smelting high-quality steel in a low-carbon emission electric furnace, the method comprising:

[0006] During the electric furnace smelting process, the first batch of low-carbon foam slag is added to the electric furnace;

[0007] A low-carbon composite foaming agent is sprayed into the electric furnace after the first batch of low-carbon foam slag is added. The spraying location is a preset area around the electrode end, and the area is completely covered within a preset time to form a foaming agent layer of a predetermined thickness.

[0008] When the amount of scrap steel melted in the furnace reaches the preset threshold, the area sprayed with the low-carbon composite foaming agent is expanded to cover the entire surface of the molten pool.

[0009] The second and third batches of low-carbon foam slag are added sequentially to the electric furnace into which the low-carbon composite foaming agent is injected, until the smelting is completed.

[0010] Optionally, the low-carbon composite foam slag includes hot electric furnace steel slag and cold KR slag, and the basicity of the low-carbon composite foam slag is 1.5 to 2.5.

[0011] Optionally, the mass ratio of the hot electric furnace slag to the cold KR slag is (1-5):1.

[0012] Optionally, the particle size of the cold KR slag is 0.1 mm to 5 mm.

[0013] Optionally, the low-carbon composite foaming agent is composed of biochar and carbonaceous powder, wherein,

[0014] The biochar meets the following requirements: fixed carbon content ≥60%, calorific value ≥4800 KCal / kg, moisture ≤2%, ash content ≤3%, and particle size 0.1mm~1mm;

[0015] The carbonaceous powder meets the following requirements: fixed carbon content ≥85%, moisture ≤0.5%, ash content ≤1%, and particle size 0.5mm~3mm.

[0016] Optionally, the mass ratio of the biochar to the carbonaceous powder is (1-4):1.

[0017] Optionally, during the electric furnace smelting process, adding the first batch of low-carbon foam slag to the electric furnace includes:

[0018] Five to eight minutes after the start of electric furnace smelting, the first batch of low-carbon foam slag is added at a rate of 3 kg / t steel to 6 kg / t steel.

[0019] Optionally, the step of sequentially adding a second batch and a third batch of low-carbon foam slag to the electric furnace into which the low-carbon composite foaming agent is injected, until the smelting is completed, includes:

[0020] 10 to 12 minutes after the start of electric furnace smelting, add the second batch of low-carbon foam slag at a rate of 3 kg / t steel to 6 kg / t steel; 15 to 25 minutes after the start of electric furnace smelting, add the third batch of low-carbon foam slag at a rate of 3 kg / t steel to 4 kg / t steel, until the smelting is completed.

[0021] Optionally, the preset area is within a 50cm radius centered on the electrode, the preset time for completely covering the area is ≤1 minute, the predetermined thickness of the foaming agent layer is >1cm, and the preset threshold is the amount of scrap steel melted is >10%.

[0022] Optionally, the total consumption of the low-carbon composite foaming agent is 15 kg / t steel to 30 kg / t steel, and the total consumption of the low-carbon composite foam residue is 10 kg / t steel to 15 kg / t steel.

[0023] Optionally, the raw material for the electric furnace smelting is scrap steel, and the capacity of the electric furnace is 100t to 300t.

[0024] The technical solutions provided in this application have the following advantages compared with the prior art:

[0025] This application provides a method for smelting high-quality steel in a low-carbon emission electric arc furnace. The method includes: during the electric arc furnace smelting process, adding a first batch of low-carbon foamed slag to the electric arc furnace; spraying a low-carbon composite foaming agent into the electric arc furnace after adding the first batch of low-carbon foamed slag, the spraying location being a preset area around the electrode end, and completely covering the area within a preset time to form a foaming agent layer of predetermined thickness; when the amount of scrap steel melted in the furnace reaches a preset threshold, expanding the area of ​​the sprayed low-carbon composite foaming agent to cover the entire surface of the molten pool; and sequentially adding a second batch of low-carbon foamed slag and a third batch of low-carbon foamed slag to the electric arc furnace after spraying the low-carbon composite foaming agent, until the smelting is completed. By injecting low-carbon composite foaming agent and adding low-carbon composite foam slag during the electric arc furnace smelting process, and using a mixture of zero-carbon biochar and carbonaceous powder as the low-carbon composite foaming agent, and the low-carbon composite foam slag being a mixture of hot electric arc furnace steel slag and cold KR slag, the synergistic utilization of biochar and steel slag recycling further reduces carbon emissions. This achieves a significant reduction in carbon emissions while meeting the stringent nitrogen content requirements for high-quality steel grades, and controls the electric arc furnace smelting process to achieve near-zero emissions. Attached Figure Description

[0026] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0027] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a schematic flowchart illustrating a method for smelting high-quality steel in a low-carbon emission electric furnace, as provided in an embodiment of this application. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0030] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range; for example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range such as 1, 2, 3, 4, 5, and 6, regardless of the range; in addition, whenever a numerical range is indicated herein, it means including any referenced number (fraction or integer) within the indicated range.

[0031] In this document, terms such as “comprising” mean “including but not limited to”. Relational terms such as “first” and “second” are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. “And / or” describes the relationship between related objects, indicating that there can be three relationships, for example, A and / or B can mean: A alone, A and B simultaneously, or B alone; where A and B can be singular or plural. “At least one” means one or more, “more” means two or more; “at least one,” “at least one of the following,” or similar expressions refer to any combination of these items, including any combination of single or plural items; for example, “at least one of a, b, or c,” or “at least one of a, b, and c,” can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple. "Parts representation" such as parts by weight or parts by mass indicates the proportional relationship between components. In the proportional relationships discussed in this article, the parameters that need to be described by proportion should be understood as the first term of the proportion in the order of description, and the proportion figures should be understood as the second term of the proportion. For example, if the mass ratio of substance A, substance B, and substance C is 1:2:3, then substances A, B, and C should correspond one-to-one with the proportion figures in the proportion in the order of description, that is, the mass of substance A: the mass of substance B: the mass of substance C = 1:2:3.

[0032] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this article can be purchased from the market or prepared by existing methods.

[0033] Figure 1 This is a schematic flowchart illustrating a method for smelting high-quality steel in a low-carbon emission electric furnace, as provided in an embodiment of this application.

[0034] like Figure 1 As shown in the embodiment of this application, a method for smelting high-quality steel in a low-carbon emission electric furnace is provided, the method comprising:

[0035] S1. During the electric furnace smelting process, the first batch of low-carbon foam slag is added to the electric furnace;

[0036] In some embodiments, the low-carbon composite foam slag includes hot electric furnace steel slag and cold KR slag, and the basicity of the low-carbon composite foam slag is 1.5 to 2.5.

[0037] Hot electric arc furnace slag is hot slag collected directly during the electric arc furnace smelting process. Hot slag has a high temperature, allowing for direct utilization of its heat and reducing energy consumption during smelting. Cold KR slag is the slag produced after pretreatment of KR molten iron; it is a cold slag. KR slag contains a higher proportion of unreacted CaO and Fe. t The high oxygen content helps ensure the alkalinity control and foaming effect of the foamed slag. By preparing low-carbon composite foamed slag by mixing hot electric furnace steel slag and cold KR slag, this technical solution not only reduces carbon emissions and power consumption, but also reduces scrap steel consumption and optimizes the performance of the foamed slag.

[0038] The basicity of the low-carbon composite foam slag is calculated using the following formula: Basicity = (CaO + MgO) / (SiO2 + Al2O3). In this embodiment, the basicity of the low-carbon composite foam slag is controlled within the range of 1.5 to 2.5. A basicity below 1.5 may lead to poor melting and foaming effects of the foam slag, affecting the stability and efficiency of the smelting process. A basicity above 2.5 may increase the viscosity and density of the slag, which is detrimental to foam formation and maintenance, and also affects the heat and mass transfer efficiency during the smelting process.

[0039] In some embodiments, the mass ratio of the hot electric furnace slag to the cold KR slag is (1-5):1.

[0040] Hot electric arc furnace slag is rich in various compounds produced during the smelting process, exhibiting excellent melting and foaming properties. Cold KR slag contains unreacted CaO and Fe... t A higher oxygen content helps regulate the alkalinity and foam stability of the foam slag. By mixing the two in a mass ratio of (1-5):1, the thermal energy of the hot slag and the chemical composition of the cold slag can be fully utilized, achieving an optimal balance in terms of melting speed, foam stability, and alkalinity control.

[0041] In some embodiments, the particle size of the cold KR slag is 0.1 mm to 5 mm.

[0042] Cold KR slag with a particle size of 0.1mm to 5mm can mix better with hot electric arc furnace steel slag to form a uniform foam slag structure. At the same time, it helps the foam slag to form a good foam layer in the electric arc furnace, improves the submerged arc effect, reduces the direct contact between molten steel and air, and thus reduces the nitrogen content and oxidation loss in the steel.

[0043] In some embodiments, during the electric furnace smelting process, adding a first batch of low-carbon foam slag to the electric furnace includes:

[0044] Five to eight minutes after the start of electric furnace smelting, the first batch of low-carbon foam slag is added at a rate of 3 kg / t steel to 6 kg / t steel.

[0045] In the early stages of electric furnace smelting, 3 kg / t steel to 6 kg / t steel of the first batch of low-carbon foam slag is added to establish the basic slag layer.

[0046] In some embodiments, the raw material for smelting in the electric furnace is scrap steel, and the capacity of the electric furnace is 100t to 300t.

[0047] Using scrap steel as raw material aims to achieve extremely low carbon emissions in the electric arc furnace smelting process. The electric arc furnace capacity is selected between 100t and 300t, a range suitable for producing high-quality steel of various specifications and qualities.

[0048] S2. Inject a low-carbon composite foaming agent into the electric furnace after adding the first batch of low-carbon foam slag. The injection location is a preset area around the electrode end, and the area is completely covered within a preset time to form a foaming agent layer of a predetermined thickness.

[0049] In some embodiments, the low-carbon composite foaming agent is composed of biochar and carbonaceous powder, wherein,

[0050] The biochar meets the following requirements: fixed carbon content ≥60%, calorific value ≥4800 KCal / kg, moisture ≤2%, ash content ≤3%, and particle size 0.1mm~1mm;

[0051] Fixed carbon content refers to the percentage of carbon remaining after subtracting moisture, ash, and volatile matter from the total weight of a sample using laboratory methods. The determination principle is based on the pyrolysis process of the substance. By treating the sample at high temperatures, removable components such as moisture, volatile matter, and ash are eliminated, and the remaining substance is the fixed carbon. A fixed carbon content of ≥60% in biomass char indicates that the biomass char has a higher calorific value and better combustion stability, which is beneficial for the rapid formation of stable foam slag during electric arc furnace smelting. A calorific value of ≥4800 KCal / kg in biomass char means that it can provide heat more effectively, promoting the formation and stabilization of foam slag while reducing the energy consumption of the electric arc furnace. A moisture content of ≤2% in biomass char helps maintain its stability and combustion performance. Ash is the inorganic residue in the charcoal material; an ash content of ≤3% in biomass char helps reduce the introduction of impurities during the smelting process and improves the purity of the molten steel.

[0052] The carbonaceous powder meets the following requirements: fixed carbon content ≥85%, moisture ≤0.5%, ash content ≤1%, and particle size 0.5mm~3mm.

[0053] The fixed carbon content of the carbonaceous powder, ≥85%, ensures a stable heat source during combustion, promoting the formation and stabilization of foamy slag. The moisture content of the carbonaceous powder, ≤0.5%, maintains its dry state, facilitating uniform distribution and rapid combustion within the electric furnace. The ash content of the carbonaceous powder, ≤1%, reduces the introduction of impurities during smelting, improving the purity of the molten steel.

[0054] Low-carbon composite foaming agents combine the advantages of biochar and carbonaceous powder to achieve low-carbon, high-efficiency smelting in electric arc furnace smelting processes. The zero-carbon nature and rapid combustion performance of biochar help reduce carbon emissions and quickly form a foamy slag layer; while the high fixed carbon content and long-term foaming performance of carbonaceous powder ensure the stability and durability of the foamy slag. The combined use of these two agents not only improves smelting efficiency but also significantly reduces the nitrogen content and carbon emissions in molten steel, meeting the production requirements of high-end, high-quality steel.

[0055] In some embodiments, the mass ratio of the biochar to the carbonaceous powder is (1-4):1.

[0056] Biochar possesses zero-carbon properties, meaning it produces no additional carbon dioxide emissions during combustion, contributing to the achievement of low-carbon smelting goals. Furthermore, biochar has a low ignition point and burns rapidly, quickly generating a gas source for foamy slag in the early stages of electric arc furnace smelting, promoting rapid slag formation, achieving the arc-submerging effect earlier, and reducing nitrogen accumulation in the molten steel. Carbonaceous powder exhibits prolonged foaming properties during smelting, continuously generating foam and maintaining the arc-submerging effect, further reducing nitrogen accumulation in the molten steel. Additionally, the high fixed carbon content of carbonaceous powder provides a stable heat source, contributing to the stability and durability of the foamy slag.

[0057] When the mass ratio of biochar to carbonaceous powder is too high (above 4:1), although it can further reduce carbon emissions, it may sacrifice some foaming performance and the stability of the foam residue. When the mass ratio is too low (below 1:1), although the foaming performance and the stability of the foam residue are guaranteed, the effect of reducing carbon emissions may not be significant enough.

[0058] S3. When the amount of scrap steel melted in the furnace reaches the preset threshold, the range of the low-carbon composite foaming agent sprayed is expanded to cover the entire surface of the molten pool.

[0059] In some embodiments, the preset area is within a 50cm radius centered on the electrode, the preset time for completely covering the area is ≤1 minute, the predetermined thickness of the foaming agent layer is >1cm, and the preset threshold is the amount of scrap steel melted is >10%.

[0060] The preset area is within 50cm of the electrode. This area is where heat is concentrated in the early stages of electric furnace smelting, which is conducive to the rapid melting of the foaming agent and the formation of a foamed slag layer. The preset time is ≤1 minute. This time limit ensures that the foaming agent can quickly cover the designated area, reducing heat loss and exposure time of molten steel during the smelting process. The preset thickness of the foaming agent layer is >1cm, which can provide better submerged arc effect, reduce direct contact between molten steel and air, thereby reducing nitrogen content and oxidation loss in the molten steel.

[0061] When the amount of scrap steel melted in the furnace reaches a preset threshold (scrap steel melting amount > 10%), the area sprayed with low-carbon composite foaming agent is expanded to cover the entire surface of the molten pool. This step is to accommodate the increase in the surface area of ​​the molten pool during the scrap steel melting process and ensure that the entire surface of the molten pool is effectively covered by the foam slag layer.

[0062] S4. Add the second batch and the third batch of low-carbon foam slag to the electric furnace in which the low-carbon composite foaming agent is injected, until the smelting is completed.

[0063] In some embodiments, the step of sequentially adding a second batch and a third batch of low-carbon foam slag to the electric furnace into which the low-carbon composite foaming agent has been injected, until the smelting is completed, includes:

[0064] 10 to 12 minutes after the start of electric furnace smelting, add the second batch of low-carbon foam slag at a rate of 3 kg / t steel to 6 kg / t steel; 15 to 25 minutes after the start of electric furnace smelting, add the third batch of low-carbon foam slag at a rate of 3 kg / t steel to 4 kg / t steel, until the smelting is completed.

[0065] Ten to twelve minutes after the start of electric arc furnace smelting, as the scrap steel gradually melts and the molten steel heats up, the performance of the first batch of foamed slag may gradually decline. Adding a second batch of low-carbon foamed slag at this time can further supplement and strengthen the foamed slag layer, maintaining its good submerged arc effect and reducing the contact between the molten steel and nitrogen in the air, thereby reducing nitrogen accumulation. Fifteen to twenty-five minutes after the start of electric arc furnace smelting, as the smelting process progresses, the foamed slag layer may change due to factors such as molten steel stirring and slag surface fluctuations. Adding a third batch of low-carbon foamed slag at this time can further consolidate and stabilize the foamed slag layer, ensuring that it plays a good role in submerged arc and nitrogen control throughout the entire smelting process.

[0066] By adding low-carbon foamed slag in batches, the stability and performance of the foamed slag layer can be ensured throughout the smelting process, thereby better fulfilling its functions of submerged arc and nitrogen control. Due to the continuous stability and effectiveness of the foamed slag layer, the contact between the molten steel and nitrogen in the air is greatly reduced, thus significantly lowering the amount of nitrogen added and meeting the production requirements of high-end, high-quality steel.

[0067] In some embodiments, the total consumption of the low-carbon composite foaming agent is 15 kg / t steel to 30 kg / t steel, and the total consumption of the low-carbon composite foam residue is 10 kg / t steel to 15 kg / t steel.

[0068] By clearly defining the consumption range of low-carbon composite foaming agent and low-carbon composite foam slag (15kg / t steel to 30kg / t steel and 10kg / t steel to 15kg / t steel, respectively), the stability and efficiency of the electric arc furnace smelting process for high-quality steel can be ensured.

[0069] This application embodiment, under the condition of 100% scrap steel, adopts a control method that couples the injection of low-carbon composite foaming agent and the addition of low-carbon composite foam slag during the electric arc furnace smelting process. By using a mixture of zero-carbon biochar and carbonaceous powder as the low-carbon composite foaming agent, and by using the synergistic utilization of biochar and steel slag recycling to further reduce carbon emissions, the nitrogen increase in the electric arc furnace smelting process under 100% scrap steel conditions is ≤5ppm, and carbon emissions are reduced by more than 90%. This achieves the goal of meeting the requirements of high-end, high-quality steel production while achieving extremely low carbon emissions, and controls the electric arc furnace smelting process to achieve near-zero emissions.

[0070] The present application is further illustrated below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national / industry standards; if there is no corresponding national / industry standard, they are performed according to general international standards, conventional conditions, or conditions recommended by the manufacturer.

[0071] Example 1

[0072] An industrial experiment was conducted in an electric arc furnace at a steel plant. The furnace had a capacity of 100 tons and produced high-end automotive steel with a nitrogen content requirement of ≤30ppm. The electric arc furnace smelting methods included:

[0073] Five minutes after the start of electric furnace smelting, the first batch of low-carbon foam slag is added at a rate of 3 kg / t steel. Ten minutes after the start of electric furnace smelting, the second batch of low-carbon foam slag is added at a rate of 3 kg / t steel. Fifteen minutes after the start of electric furnace smelting, the third batch of low-carbon foam slag is added at a rate of 4 kg / t steel, until the smelting is completed. A low-carbon composite foaming agent is sprayed into the electric furnace after the first batch of low-carbon foamed slag is added. The spraying location is a predetermined area around the electrode tip, and the area is completely covered within a predetermined time to form a foaming agent layer of predetermined thickness. The predetermined area is within 50 cm centered on the electrode, and the time to completely cover the area is 1 minute. The predetermined thickness of the foaming agent layer in the electric furnace is 1 cm. When the amount of scrap steel melted in the furnace reaches 10%, the area sprayed with the low-carbon composite foaming agent is expanded to cover the entire surface of the molten pool until the smelting is completed. During the entire electric furnace smelting process, the total consumption of low-carbon composite foaming agent is 15 kg / t of steel, and the total consumption of low-carbon composite foamed slag is 10 kg / t of steel. The low-carbon composite foamed slag includes hot electric furnace steel slag and cold KR slag, and the basicity of the low-carbon composite foamed slag is 1.5. The mass ratio of hot electric furnace steel slag to cold KR slag is 1:1; the particle size of cold KR slag is 0.1 mm.

[0074] The low-carbon composite foaming agent is composed of biochar and carbonaceous powder. The biochar meets the following requirements: fixed carbon content 60%, calorific value 4800 KCal / kg, moisture 2%, ash content 3%, and particle size 0.1 mm. The carbonaceous powder meets the following requirements: fixed carbon content 85%, moisture 0.5%, ash content 1%, and particle size 0.5 mm. The mass ratio of biochar to carbonaceous powder is 1:1. By adding a new slag-forming agent during the electric arc furnace (EAF) smelting process and controlling the slag system composition and components of the slag-forming agent, the rapid generation of foamy slag in the EAF melting of scrap steel is promoted. Simultaneously, biochar is used to reduce carbon emissions. This achieves a 5 ppm increase in nitrogen content during the EAF smelting process under all-scrap steel conditions, resulting in a nitrogen content of 26 ppm in the steel. The carbon emissions per process in the EAF are reduced by 50%, representing a breakthrough in high-quality steel grades produced by large-scale EAF smelting using all-scrap steel.

[0075] Example 2

[0076] An industrial experiment was conducted in an electric arc furnace at a steel plant. The furnace had a capacity of 300 tons and produced high-end automotive steel with a nitrogen content requirement of ≤30ppm. The electric arc furnace smelting methods included:

[0077] Eight minutes after the start of electric furnace smelting, the first batch of low-carbon foam slag is added at a rate of 6 kg / t steel. Twelve minutes after the start of electric furnace smelting, the second batch of low-carbon foam slag is added at a rate of 6 kg / t steel. Twenty-five minutes after the start of electric furnace smelting, the third batch of low-carbon foam slag is added at a rate of 3 kg / t steel, until the smelting is completed. A low-carbon composite foaming agent is sprayed into the electric furnace after the first batch of low-carbon foamed slag is added. The spraying location is a predetermined area around the electrode tip, and the area is completely covered within a predetermined time to form a foaming agent layer of predetermined thickness. The predetermined area is within 50 cm centered on the electrode, and the time to completely cover the area is 0.5 minutes. The predetermined thickness of the foaming agent layer in the electric furnace is 1.5 cm. When the amount of scrap steel melted in the furnace reaches 15%, the area sprayed with the low-carbon composite foaming agent is expanded to cover the entire surface of the molten pool until the smelting is completed. During the entire electric furnace smelting process, the total consumption of low-carbon composite foaming agent is 30 kg / t of steel, and the total consumption of low-carbon composite foamed slag is 15 kg / t of steel. The low-carbon composite foamed slag includes hot electric furnace steel slag and cold KR slag, and the basicity of the low-carbon composite foamed slag is 12.5. The mass ratio of hot electric furnace steel slag to cold KR slag is 5:1; the particle size of the cold KR slag is 5 mm. The low-carbon composite foaming agent is composed of biochar and carbonaceous powder. The biochar meets the following specifications: fixed carbon content 80%, calorific value 5000 kcal / kg, moisture 1%, ash content 2%, and particle size 1 mm. The carbonaceous powder meets the following specifications: fixed carbon content 89%, moisture content 0.2%, ash content 0.5%, and particle size 3 mm. The mass ratio of biochar to carbonaceous powder is 4:1.

[0078] By adopting the above-mentioned method of adding new slag-forming agents during the electric arc furnace smelting process and controlling the slag system composition and components of the slag-forming agents, the rapid generation of foamy slag in the electric arc furnace melting of scrap steel is promoted. At the same time, biochar is used to reduce carbon emissions. Under the condition of all scrap steel, the nitrogen content in the electric arc furnace smelting process is increased by 3ppm, the nitrogen content in the steel is reduced to 20ppm, and the carbon emissions of the electric arc furnace single process are reduced by 65%. This represents a breakthrough in the high-quality steel grades required for large-scale electric arc furnace smelting of all scrap steel.

[0079] Example 3

[0080] An industrial experiment was conducted in an electric arc furnace at a steel plant. The furnace had a capacity of 150 tons and produced high-end automotive steel with a nitrogen content requirement of ≤30ppm. The electric arc furnace smelting methods included:

[0081] Six minutes after the start of electric furnace smelting, the first batch of low-carbon foam slag is added at a rate of 5 kg / t steel. Eleven minutes after the start of electric furnace smelting, the second batch of low-carbon foam slag is added at a rate of 4 kg / t steel. Twenty minutes after the start of electric furnace smelting, the third batch of low-carbon foam slag is added at a rate of 3.5 kg / t steel, until the smelting is completed. A low-carbon composite foaming agent is sprayed into the electric furnace after the first batch of low-carbon foamed slag is added. The spraying location is a predetermined area around the electrode tip, and the agent is sprayed to completely cover this area within a predetermined time to form a foaming agent layer of predetermined thickness. The predetermined area is within 50 cm centered on the electrode, and the time to completely cover this area is 0.8 minutes. The predetermined thickness of the foaming agent layer in the electric furnace is 2 cm. When the amount of scrap steel melted in the furnace reaches 18%, the area sprayed with the low-carbon composite foaming agent is expanded to cover the entire surface of the molten pool until the smelting is completed. During the entire electric furnace smelting process, the total consumption of low-carbon composite foaming agent is 25 kg / t of steel, and the total consumption of low-carbon composite foamed slag is 12.5 kg / t of steel. The low-carbon composite foamed slag includes hot electric furnace steel slag and cold KR slag, and the basicity of the low-carbon composite foamed slag is 2.0. The mass ratio of hot electric furnace steel slag to cold KR slag is 3:1; the particle size of the cold KR slag is 2 mm. The low-carbon composite foaming agent is composed of biochar and carbonaceous powder. The biochar meets the following specifications: fixed carbon content 70%, calorific value 4900 KCal / kg, moisture content 1.5%, ash content 3%, and particle size 0.8 mm. The carbonaceous powder meets the following specifications: fixed carbon content 90%, moisture content 0.3%, ash content 0.8%, and particle size 2 mm. The mass ratio of biochar to carbonaceous powder is 2:1.

[0082] By adopting a new slag-forming agent with new components during the electric arc furnace smelting process and controlling the slag system composition and components of the slag-forming agent, the rapid generation of foamy slag in the electric arc furnace melting of scrap steel is promoted. At the same time, biochar is used to reduce carbon emissions. Under the condition of all scrap steel, the nitrogen content in the electric arc furnace smelting process is increased by 4.2 ppm, and the nitrogen content in the steel is 23.5 ppm. The carbon emissions of the electric arc furnace single process are reduced by 58%, which is a breakthrough in the high-quality steel grade required by the smelting of all scrap steel in large electric arc furnaces.

[0083] Comparative Example 1

[0084] An industrial experiment was conducted in an electric arc furnace at a steel plant. The furnace had a capacity of 300 tons and produced high-end automotive steel with a nitrogen content requirement of ≤30ppm. The electric arc furnace smelting methods included:

[0085] Five minutes after the start of electric arc furnace smelting, the first batch of foamed slag is added at a rate of 6 kg / t steel. Twelve minutes after the start of smelting, the second batch of foamed slag is added at a rate of 6 kg / t steel. Twenty-five minutes after the start of smelting, the third batch of foamed slag is added at a rate of 3 kg / t steel, continuing until smelting is complete. Foaming agent is then sprayed into the electric arc furnace after the first batch of foamed slag is added. The spraying location is a predetermined area around the electrode tip, and the area is completely covered within a predetermined time to form a foaming agent layer of a predetermined thickness. The predetermined area is a 50 cm radius centered on the electrode, and the complete coverage time is 2 minutes. The predetermined thickness of the foaming agent layer in the electric arc furnace is 0.5 cm. When 5% of the scrap steel in the furnace has melted, the area sprayed with the foaming agent is expanded to cover the entire surface of the molten pool until smelting is complete. Throughout the entire electric arc furnace smelting process, the total consumption of foaming agent is 30 kg / t steel, and the total consumption of foamed slag is 15 kg / t steel. The foaming slag consists of lime and dolomite, and its alkalinity is 2.5. The foaming agent is composed of carbonaceous powder, which meets the following requirements: fixed carbon content of 90%, moisture content of 0.5%, ash content of 1%, and particle size of 3 mm.

[0086] By adding traditional slag-forming agents during the electric arc furnace smelting process and controlling the slag system composition and components of the slag-forming agents, the rapid generation of foamy slag in the electric arc furnace melting of scrap steel was promoted. Under the condition of all scrap steel, the nitrogen content in the electric arc furnace smelting process was increased by 20 ppm, achieving a nitrogen content of 45 ppm in the steel. However, this does not meet the requirements of large electric arc furnaces for smelting high-quality steel grades using all scrap steel.

[0087] As can be seen from Examples 1-3, by using low-carbon foamed slag and low-carbon composite foaming agent during the electric arc furnace smelting process, and by controlling the slag system composition and components of the slag-forming agent, the smelting process is optimized, promoting the rapid generation of foamed slag from the electric arc furnace melting scrap steel. At the same time, the recycling of biochar and steel slag is used to reduce carbon emissions, achieving a nitrogen increase of ≤5ppm in the electric arc furnace smelting process under all-scrap steel conditions. This represents a breakthrough in high-quality steel grades produced by large-scale electric arc furnace smelting using all-scrap steel.

[0088] One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

[0089] The embodiments of the present invention have four major attributes: low nitrogen increase, low carbon emissions, low power consumption, and low scrap steel consumption in the electric furnace smelting process. This enables the electric furnace smelting process to achieve near-zero emissions while meeting the requirements for high-end, high-quality steel production.

[0090] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed in this application.

Claims

1. A method for smelting high-quality steel in a low-carbon emission electric furnace, the method comprising: During the electric furnace smelting process, the first batch of low-carbon foam slag is added to the electric furnace; A low-carbon composite foaming agent is sprayed into the electric furnace after the first batch of low-carbon foam slag is added. The spraying location is a preset area around the electrode end, and the area is completely covered within a preset time to form a foaming agent layer of a predetermined thickness. When the amount of scrap steel melted in the furnace reaches the preset threshold, the area sprayed with the low-carbon composite foaming agent is expanded to cover the entire surface of the molten pool. The second and third batches of low-carbon foam slag are added sequentially to the electric furnace into which the low-carbon composite foaming agent is injected, until the smelting is completed. The low-carbon foam slag includes hot electric furnace steel slag and cold KR slag, and the basicity of the low-carbon foam slag is 1.5 to 2.

5. The low-carbon composite foaming agent is composed of biochar and carbonaceous powder, wherein, The biochar meets the following requirements: fixed carbon content ≥60%, calorific value ≥4800 KCal / kg, moisture ≤2%, ash content ≤3%, and particle size 0.1mm~1mm; The carbonaceous powder meets the following requirements: fixed carbon content ≥85%, moisture ≤0.5%, ash content ≤1%, and particle size 0.5mm~3mm; During the electric furnace smelting process, the first batch of low-carbon foam slag is added to the electric furnace, including: 5 to 8 minutes after the start of electric furnace smelting, the first batch of low-carbon foam slag is added at a rate of 3 kg / t steel to 6 kg / t steel. The process of sequentially adding a second batch and a third batch of low-carbon foam slag to the electric furnace into which the low-carbon composite foaming agent is injected, until the smelting is completed, includes: 10 to 12 minutes after the start of electric furnace smelting, add the second batch of low-carbon foam slag at a rate of 3 kg / t steel to 6 kg / t steel; 15 to 25 minutes after the start of electric furnace smelting, add the third batch of low-carbon foam slag at a rate of 3 kg / t steel to 4 kg / t steel, until the smelting is completed.

2. The method according to claim 1, characterized in that, The mass ratio of the hot electric furnace slag to the cold KR slag is (1-5):1; and / or, The particle size of the cold KR slag is 0.1 mm to 5 mm.

3. The method according to claim 2, characterized in that, The mass ratio of the biochar to the carbonaceous powder is (1-4):

1.

4. The method according to claim 1, characterized in that, The preset area is within a 50cm radius centered on the electrode, the preset time for completely covering the area is ≤1 minute, the predetermined thickness of the foaming agent layer is >1cm, and the preset threshold is the amount of scrap steel melted is >10%.

5. The method according to claim 1, characterized in that, The total consumption of the low-carbon composite foaming agent is 15 kg / t steel to 30 kg / t steel, and the total consumption of low-carbon foam slag is 10 kg / t steel to 15 kg / t steel.

6. The method according to claim 1, characterized in that, The raw material for smelting in the electric furnace is scrap steel, and the capacity of the electric furnace is 100t to 300t.

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