Method for controlling FeO in slag of electric arc furnace intermittently by powder injection

Abstract

This invention relates to a method for stabilizing FeO in the slag of an electric arc furnace using intermittent pulverized carbon injection. It involves periodically opening injection valves to adjust the injection flow rate and frequency of carbon powder, thus developing an intermittent injection process. By precisely calculating the carbon content and molten pool formation time under different scrap steel ratios, the method designs the timing and initial injection process for carbon powder injection corresponding to different smelting conditions. Utilizing the imbalance between oxygen supply intensity and decarburization rate at different smelting stages, the method develops intermittent injection processes and late-stage injection processes, adjusting injection parameters in real time based on the foam slag index. This reduces the transient FeO increase in the slag without decreasing the decarburization rate, achieving an average FeO content in the slag of the entire furnace controlled between 17% and 22%, with FeO content fluctuations within 5% during the smelting process. This invention solves the problems of imbalance between oxygen supply intensity and decarburization rate at different stages, FeO generation rate exceeding consumption rate, and continuous increase in slag FeO content during the smelting process in current electric arc furnace smelting processes.

Description

Technical Field

[0001] This invention relates to a method for stabilizing and controlling FeO in slag of an electric arc furnace through intermittent powder injection, belonging to the technical field of steelmaking. Background Technology

[0002] The decarburization process in electric arc furnace (EAF) smelting is primarily an indirect reaction. O2 first reacts with [Fe] in the molten steel to form FeO. At the steel-slag interface, FeO reacts with [C] to generate [Fe] and CO bubbles. The FeO content in the slag is mainly related to its generation and consumption rates. The EAF smelting process is mainly divided into different stages, including well penetration, scrap steel melting, basic melting and clearing, decarburization and heating, and endpoint control. The amount of transient FeO generated in the slag at each stage is directly proportional to the oxygen supply intensity. Factors such as temperature, stirring intensity, and initial FeO and [C] content affect the reaction equilibrium and mass transfer rate, and the amount of transient FeO consumed in the slag varies at each stage. To ensure continuous foamy slag operation and production rhythm, EAF smelting often employs enhanced oxygen supply technology, resulting in significant fluctuations between the actual oxygen supply intensity and oxygen demand. Therefore, the FeO in the process slag continuously increases as smelting progresses, with an increase ranging from 3.0% to 25.0%.

[0003] In the early stages of electric arc furnace smelting, the slag has a high FeO content due to the addition of FeO-rich raw materials such as metallized pellets, DRI, pellets, and slag steel. When the molten pool temperature is ≥1550℃ and the C content is greater than 0.3%, the smelting enters the decarburization and heating stage. The decarburization rate gradually accelerates, and FeO in the slag is continuously consumed. The difference between FeO generation and consumption continuously decreases, and the FeO content in the slag shows a slow upward trend. When the C content in the molten pool is less than the critical C content of 0.3% in the later stages of smelting, the decarburization rate decreases rapidly due to the influence of mass transfer. The FeO generation in the slag remains unchanged, while the consumption continues to decrease, and the FeO content in the slag increases rapidly, reaching a maximum of 40-52%.

[0004] Patent CN112553401A provides a method for improving the yield of steel scrap in electric arc furnace steelmaking. This method involves adding 20-25% pig iron, 8-15 kg / ton of carbon balls, and injecting 1-2 kg / ton of carbon powder using a carbon-oxygen lance, while maintaining a slag layer thickness of ≥200 mm. This method can improve the yield of steel scrap, with the yield in the embodiment exceeding 85%. However, this invention uses a fixed and relatively low carbon powder flow rate during scrap melting and the carbon-oxygen reaction, resulting in an overall low yield of steel scrap.

[0005] Patent CN104131134A discloses a process for creating foamed slag in the molten pool of an electric arc furnace. This involves injecting graphite-like materials into the molten pool. The injection intensity is 15-18 kg / min during scrap steel melting and 20-25 kg / min after melting, ensuring a foamed slag effect throughout the process. However, this invention uses a fixed carbon powder flow rate, which cannot be adjusted in real-time according to changes in smelting conditions and the degree of carbon-oxygen reaction. Summary of the Invention

[0006] To address the aforementioned problems, this invention discloses a method for stabilizing and controlling FeO slag in an electric arc furnace using intermittent powder injection, the specific technical solution of which is as follows: A method for stabilizing and controlling FeO slag in an electric arc furnace using intermittent powder injection includes the following steps: Step 1: Determine the timing of carbon powder injection under the corresponding conditions based on the current steel material structure and smelting mode of the electric arc furnace. Step 2: Collect information on the amount of scrap steel and molten iron charged, oxygen supply intensity, blowing time and smelting power consumption in real time during the smelting process, and determine whether the corresponding process conditions have been met for the start-up. If not, do not open the carbon powder injection valve, and continue to collect information. Step 3: If the opening timing under the corresponding process conditions is reached, first open the blowing gas valve, and then open the toner spraying valve after 5 seconds. Set the opening time and intermittent cycle of the toner spraying valve according to the intermittent powder spraying process under different process conditions. Step 4: Real-time adjustment of carbon powder injection parameters during smelting: Adjust the intermittent carbon powder injection parameters in real time according to the foam slag index. If the foam slag index is greater than 95%, the carbon powder injection time is gradually reduced while the intermittent cycle remains unchanged; if the foam slag index is less than 90%, the carbon powder injection time remains unchanged while the intermittent cycle is gradually reduced; keep the foam slag index after melting and cleaning stable between 90% and 95%. Step 5: In the later stage of smelting, when the molten pool temperature is >1550℃ and the C mass content is ≤0.3%, carbon powder injection shall be carried out according to the relationship between the oxygen supply intensity and carbon powder injection parameters in the later stage of smelting. Step 6: Adjust the intermittent powder injection parameters in the later stage of smelting according to step 4; Step 7: When the temperature and composition meet the requirements of the steel grade, tap the steel and the smelting of this furnace is completed; Step 8: Repeat steps 1 to 7 for the next batch, and so on in a continuous cycle.

[0007] Furthermore, the total charge of the electric arc furnace smelting is 100~120t, the scrap steel ratio is 20%~100%, and the remainder is molten iron; When the scrap steel ratio in the ferrous material is less than or equal to 60%, the smelting mode is one batch of scrap steel, and carbon powder is injected after the molten steel is completely cleared; when the scrap steel ratio in the ferrous material is more than 60% and less than or equal to 80%, the smelting mode is either one batch of scrap steel or two batches of scrap steel according to the production process requirements and different scrap steel material sizes, carbon powder is injected after the molten steel is basically cleared for one batch of scrap steel mode, and carbon powder injection is started after the completion of material penetration for the second batch of scrap steel in the two batches of scrap steel mode.

[0008] Further, the solid C content in the carbon powder injected by the intermittent powder injection process is ≥75%, the S content is ≤0.5%, the H2O content is ≤1.0%, and the particle size is 0.5~3mm.

[0009] Further, in the intermittent powder injection process, carbon powder is injected into the oxygen impact area in the furnace through a furnace wall carbon powder gun.

[0010] Further, in the intermittent powder injection process, the auxiliary blowing gas is compressed air, the carrier gas pressure is 0.4~0.8MPa, and the pressure of the carbon powder tank is controlled between 1.8~2.5MPa.

[0011] Further, in the intermittent powder injection process, the auxiliary blowing gas is set to a normally open mode during carbon powder injection, the injection time is between 1 and 15 seconds, and the intermittent cycle is between 3 and 30 seconds.

[0012] Further, the carbon powder injection parameters are adjusted in real time during the smelting process, the foamed slag index calculated in real time in the electric arc furnace control system is used to characterize the control level of FeO in the foamed slag, when the foaming index is greater than 95%, the average injection flow rate is gradually reduced by a step length of 0.5 second of injection time, when the foaming index is less than 90%, the injection flow rate and frequency are gradually increased by a step length of 1.0 second of intermittent cycle, the adjustment of carbon powder injection parameters is triggered once every 20 seconds, the average value of the foamed slag index in 20 seconds before the adjustment node is taken as reference, until the foamed slag index is stably controlled between 90% and 95%.

[0013] Further, the step 3 is specifically: controlling the carbon powder injection process according to the scrap ratio Sc and the smelting mode, when the smelting mode is one batch of molten iron + one batch of scrap steel, when 30%<Sc≤40%, during the decarburization and temperature rising period, after the scrap steel is completely melted, carbon powder injection blowing is performed for 15min, with 1 second of injection and 13 seconds of blowing stoppage; when 40%<Sc≤50%, during the decarburization and temperature rising period, after the scrap steel is completely melted, carbon powder injection blowing is performed for 10min, with 1 second of injection and 12 seconds of blowing stoppage; when 50%<Sc≤60%, after the scrap steel is completely melted, carbon powder injection blowing is performed for 5min, with 2 seconds of injection and 7 seconds of blowing stoppage; during the decarburization and temperature rising period, the intermittent powder injection process of 1 second of injection and 8 seconds of blowing stoppage is adopted; When 60% < Sc ≤ 65% and the total power consumption reaches 11000kwh, fully open the carbon powder injection, adopt an intermittent injection process of 2 seconds injection and 7 seconds pause after molten scrap steel is completely melted, and select an intermittent injection process of 1 second injection and 7 seconds pause during decarburization and temperature rising; When 65% < Sc ≤ 70% and the total power consumption reaches 12000kwh, fully open the carbon powder injection, adopt an intermittent injection process of 2.5 seconds injection and 8 seconds pause after molten scrap steel is completely melted, and select an intermittent injection process of 1 second injection and 6 seconds pause during decarburization and temperature rising; When 70% < Sc ≤ 75% and the total power consumption reaches 14000kwh, fully open the carbon powder injection, adopt an intermittent injection process of 3 seconds injection and 8 seconds pause after molten scrap steel is completely melted, and select an intermittent injection process of 1 second injection and 6 seconds pause during decarburization and temperature rising; When the smelting mode is one ladle of molten iron plus two ladles of scrap steel, When 60% < Sc ≤ 65%, adopt an intermittent carbon powder injection process of 2 seconds injection and 5 seconds pause during the melting of the second ladle of scrap steel, an intermittent injection process of 2 seconds injection and 7 seconds pause after the scrap steel is completely melted, and select an intermittent injection process of 1 second injection and 8 seconds pause during decarburization and temperature rising; When 65% < Sc ≤ 70%, adopt an intermittent carbon powder injection process of 2 seconds injection and 5 seconds pause during the melting of the second ladle of scrap steel, an intermittent injection process of 2 seconds injection and 7 seconds pause after the scrap steel is completely melted, and select an intermittent injection process of 1 second injection and 7 seconds pause during decarburization and temperature rising; When 70% < Sc ≤ 75%, adopt an intermittent carbon powder injection process of 2 seconds injection and 5 seconds pause during the melting of the second ladle of scrap steel, an intermittent injection process of 1.5 seconds injection and 4 seconds pause after the scrap steel is completely melted, and select an intermittent injection process of 1 second injection and 6 seconds pause during decarburization and temperature rising; When 75% < Sc ≤ 80%, adopt an intermittent carbon powder injection process of 2 seconds injection and 5 seconds pause during the melting of the second ladle of scrap steel, an intermittent injection process of 1.5 seconds injection and 4 seconds pause after the scrap steel is completely melted, and select an intermittent injection process of 1.5 seconds injection and 6 seconds pause during decarburization and temperature rising; When 80% < Sc ≤ 90% and the total power consumption reaches 3000kwh, fully open the carbon powder injection, adopt an intermittent carbon powder injection process of 2.5 seconds injection and 5 seconds pause during the melting of the second ladle of scrap steel, an intermittent injection process of 1.5 seconds injection and 4 seconds pause after the scrap steel is completely melted, and select an intermittent injection process of 1.5 seconds injection and 6 seconds pause during decarburization and temperature rising; When 90% < Sc ≤ 99% and the total power consumption reaches 4000kwh, fully open the carbon powder injection, adopt an intermittent carbon powder injection process of 2.5 seconds injection and 5 seconds pause during the melting of the second ladle of scrap steel, an intermittent injection process of 2 seconds injection and 5 seconds pause after the scrap steel is completely melted, and select an intermittent injection process of 2 seconds injection and 7 seconds pause during decarburization and temperature rising; For all-scrap steelmaking, when the total power consumption reaches 5000kwh, the carbon powder injection is fully opened. During the melting of the second scrap basket, an intermittent powder injection process of injecting carbon powder for 2.5 seconds and stopping injection for 5 seconds is adopted; after the scrap is completely melted, an intermittent powder injection process of injecting for 2 seconds and stopping injection for 5 seconds is adopted; during the decarburization and temperature rising period, an intermittent powder injection process of injecting for 2 seconds and stopping injection for 7 seconds is selected.

[0014] Further, in the intermittent powder injection control process in the later stage of smelting in step 5, the carbon powder injection flow is adjusted based on the oxygen supply intensity. The electric arc furnace has three wall oxygen lances in total, LL mode represents the low-oxygen mode of the wall oxygen lance, wherein the flow rate of extra oxygen is 200m 3 / h, the flow rate of natural gas is 200m 3 / h, and the flow rate of main oxygen is 1200m 3 / h; ML mode represents the medium-oxygen mode of the wall oxygen lance, wherein the flow rate of extra oxygen is 240m 3 / h, the flow rate of natural gas is 240m 3 / h, and the flow rate of main oxygen is 2000m 3 / h; HL mode represents the high-oxygen mode of the wall oxygen lance, wherein the flow rate of extra oxygen is 300m 3 / h, the flow rate of natural gas is 300m 3 / h, and the flow rate of main oxygen is 2500m 3 / h; The blowing mode is selected according to the mass content of carbon C and the carbon-phosphorus ratio C / P in the final molten steel. When the mass content of C is the same, the smaller the C / P value is, the more difficult the dephosphorization is, and the larger the C / P value is, the less difficult the dephosphorization is: When C > 0.6%, if C / P is less than 15, the blowing mode of ML+LL+LL is selected; if C / P is 15~25, the blowing mode of HL+HL+LL is selected; if C / P is more than 25, the blowing mode of HL+HL+HL is selected; When 0.4 < C ≤ 0.6, if C / P is less than 10, the blowing mode of ML+ML+ML is selected; if C / P is 10~15, the blowing mode of ML+ML+LL is selected; if C / P is more than 15, the blowing mode of LL+LL+LL is selected; When 0.2 < C ≤ 0.4, if C / P is less than 8, the blowing mode of ML+ML+LL is selected; if C / P is 8~12, the blowing mode of ML+LL+LL is selected; if C / P is more than 12, the blowing mode of LL+LL+LL is selected; When 0.08 < C ≤ 0.2, if C / P is less than 4, the blowing mode of ML+ML+LL is selected; if C / P is 4~6, the blowing mode of ML+LL+LL is selected; if C / P is more than 6, the blowing mode of LL+LL+LL is selected; When C ≤ 0.08, if C / P is less than 2, the blowing mode of ML+LL+LL is selected; if C / P is 2~2.5, the blowing mode of LL+LL+LL is selected; if C / P is more than 2.5, the blowing mode of LL+LL is selected.

[0015] The specific intermittent blowing process corresponding to each blowing mode is as follows: When the oxygen supply mode is LL+LL, the main oxygen supply flow rate is 2400 m³ / h. 3 / h, the carbon powder spraying process adopts an intermittent spraying process with 1.5 seconds of spraying and 18.5 seconds of stop spraying, and the spraying flow rate is about 15kg / min; When the oxygen supply mode is LL+LL+LL, the main oxygen supply flow rate is 3600 m³ / h. 3 / h, the carbon powder spraying process adopts an intermittent spraying process of 2 seconds of spraying and 14 seconds of stop spraying, with a spraying flow rate of about 22kg / min; When the oxygen supply mode is ML+LL+LL, the main oxygen supply flow rate is 4400 m³ / h. 3 / h, the carbon powder spraying process adopts an intermittent spraying process with 2.5 seconds of spraying and 14.5 seconds of stop spraying, and the spraying flow rate is about 28kg / min; When the oxygen supply mode is ML+ML+LL, the main oxygen supply flow rate is 5200 m³ / h. 3 / h, the carbon powder spraying process adopts an intermittent spraying process of 2 seconds of spraying and 10 seconds of stopping, with a spraying flow rate of about 33kg / min; When the oxygen supply mode is ML+ML+ML, the main oxygen supply flow rate is 6000m³. 3 / h, the carbon powder spraying process adopts an intermittent spraying process of 2 seconds of spraying and 9 seconds of stop spraying, with a spraying flow rate of about 39kg / min; When the oxygen supply mode is HL+LL+LL, the main oxygen supply flow rate is 4700 m³ / h. 3 / h, the carbon powder spraying process adopts an intermittent spraying process of 2 seconds of spraying and 10 seconds of stopping, with a spraying flow rate of about 33kg / min; When the oxygen supply mode is HL+ML+LL, the main oxygen supply flow rate is 5500 m³ / h. 3 / h, the carbon powder spraying process adopts an intermittent spraying process of 2 seconds of spraying and 9 seconds of stop spraying, with a spraying flow rate of about 39kg / min; When the oxygen supply mode is HL+ML+ML, the main oxygen supply flow rate is 6300 m³ / h. 3 / h, the carbon powder spraying process adopts an intermittent spraying process of 1.5 seconds of spraying and 6.5 seconds of stopping, with a spraying flow rate of about 38kg / min; When the oxygen supply mode is HL+HL+LL, the main oxygen supply flow rate is 5800 m³ / h. 3 / h, the carbon powder spraying process adopts an intermittent spraying process of 1.5 seconds of spraying and 6.5 seconds of stopping, with a spraying flow rate of about 38kg / min; When the oxygen supply mode is HL+HL+ML, the main oxygen supply flow rate is 6600 m³ / h. 3 / h, the carbon powder spraying process adopts an intermittent spraying process of 1.5 seconds of spraying and 5.5 seconds of stop spraying, with a spraying flow rate of about 43kg / min; When the oxygen supply mode is HL+HL+HL, the main oxygen supply flow rate is 6900 m³ / h. 3 The carbon powder spraying process uses an intermittent spraying process with a spraying time of 1.5 seconds and a stop spraying time of 4.5 seconds, with a spraying flow rate of approximately 46 kg / min.

[0016] The working principle of this invention is: In electric arc furnace smelting, smelting conditions such as scrap ratio, carbon content, oxygen supply intensity, temperature, carbon content in steel, and decarburization rate vary significantly. Stable control of slag FeO content can only be ensured when the transient FeO generation and consumption in the slag reach equilibrium at each stage. This places high demands on the matching and adjustment capabilities of the carbon injection process. To address these requirements, real-time adjustment measures for carbon injection timing, process parameters, and parameters under different process conditions were designed. The principle of the entire process flow is as follows: (1) Taking advantage of the automatic, millisecond-level precise opening and closing control of the toner spray valve in the toner spray can, the frequency and average spray flow rate of toner are controlled by adjusting the spraying time and intermittent period of the toner spray valve. This effectively reduces the wear of the toner spray valve and improves the control accuracy of the toner spray flow rate. The blowing gas is set to normally open mode, the spraying time is controlled between 1 and 15 seconds, and the intermittent period is controlled between 3 and 30 seconds.

[0017] (2) Utilize the characteristics of electric arc furnace smelting under different scrap ratios to design different carbon powder injection timing and initial processes. The higher the scrap ratio, the longer the melting time, the slower the initial molten pool formation, and the more difficult it is to form initial slag. In order to promote early slag formation in the electric arc furnace, use high FeO raw materials and high flow rate carbon powder injection process (this is mainly reflected in the following: when the scrap ratio is >80%, after the first batch of scrap steel is added, 3000~5000kWh of electricity is supplied to form a molten pool in the furnace, and then all carbon powder is injected. If there is not a large amount of FeO in the initial slag, it is difficult to form the initial foam slag, and the significance of high flow rate carbon powder injection is not great. High flow rate carbon powder injection refers to the "full open" mode, at which time the carbon powder injection flow rate is the largest, which is 150kg / min), to form a large number of CO bubbles, promote the rapid formation of initial foam slag, and at the same time reduce the FeO content of the initial slag. Add 2000~5000kg of metallized pellets or dust removal ash cold-pressed pellets into the furnace, and set the initial carbon injection flow rate to above 150kg / min. When the scrap ratio is lower, the physical heat and chemical energy brought in by the molten iron are higher, the scrap melts faster, and the molten pool is easier to form. Therefore, the timing of starting to inject carbon powder should be extended to after the melting is cleared or in the later heating stage.

[0018] (3) Design and development of carbon powder injection process under different smelting process conditions: Based on the different oxygen supply intensity and decarburization rate of each smelting stage, the transient FeO generation and consumption of slag are also different. Different intermittent carbon powder injection processes are formulated for scrap steel ratio and smelting stage.

[0019] (4) Real-time adjustment of carbon powder injection parameters during smelting: The control level of foam slag is characterized by the inherent foam slag index in the smelting system. The carbon powder injection parameters are adjusted every 20 seconds, and the foam slag index used as the reference for adjustment is the average value of the 20 seconds before the adjustment node. When the degree of foaming is too high (greater than 95%), the average injection flow rate is gradually reduced in injection time steps of 0.5 seconds. When the degree of foaming is poor (less than 90%), the injection flow rate and frequency are gradually increased in interval period steps of 1.0 seconds until the foam slag index is stably controlled between 90% and 95%. The stable control of foam slag is a characterization of the stable control of FeO in the slag.

[0020] (5) Formulating the process for oxygen supply intensity and carbon injection parameters in the later stage of smelting: In the later stage of smelting, when the molten pool temperature is >1550℃ and the C content is ≤0.3%, the amount of transient FeO generated in the slag is directly proportional to the oxygen supply intensity. However, the consumption of transient FeO in the slag is limited by the decarburization rate, which is related to the mass transfer of carbon. Therefore, the increase in transient FeO in the slag is mainly affected by the oxygen supply intensity. Different intermittent carbon injection processes are set according to different oxygen supply intensities to stabilize and control the change in FeO content in the slag.

[0021] The beneficial effects of this invention are: Electric arc furnaces typically use carbon powder injection to reduce the FeO content in the slag, but currently the carbon powder injection flow rate is a fixed value. For different heats, the carbon powder content decreases as the scrap ratio increases, with a wide variation ranging from 0.25% to 4.5%. During smelting, oxygen is primarily used to agitate the molten pool. With a fixed oxygen supply, the total FeO formation remains constant. The lower the carbon powder content, the less FeO is consumed by the molten pool, requiring a larger amount of additional carbon powder to control the FeO content in the slag, and vice versa. For the same heat, different smelting stages correspond to different oxygen supply intensities and decarburization rates. A faster decarburization rate results in greater transient FeO consumption and a lower demand for carbon powder, while a slower rate requires more. In equilibrium, the demand for carbon powder mainly depends on the difference between the actual oxygen supply intensity and the instantaneous oxygen demand. Clearly, a fixed carbon powder injection flow rate is detrimental to the stable control of FeO in the slag during the smelting process.

[0022] This invention utilizes the automatic, millisecond-level precise opening and closing control of the carbon powder injection valve in the carbon powder injection tank. By periodically opening the valve, the injection flow rate and frequency of carbon powder are adjusted, thus developing an intermittent carbon powder injection process. The carbon powder dosage and molten pool formation time are precisely calculated using different scrap steel ratios to determine the appropriate carbon powder injection timing for different smelting processes. Furthermore, different carbon powder injection process parameters are designed based on the varying oxygen supply intensity at different stages. Moreover, adjustments are triggered every 20 seconds based on changes in the foam slag index, allowing for flexible and real-time adjustment of the intermittent carbon powder injection process parameters to achieve stable control of the slag FeO content.

[0023] This invention establishes an intermittent powder injection process for precise and real-time control of the carbon powder injection flow rate during smelting. This reduces the increase in transient FeO in the slag without reducing the decarburization rate, thereby achieving the goal of controlling the average FeO content in the slag between 17% and 22%, and controlling the FeO content fluctuation within 5% during a single furnace smelting process.

[0024] This invention solves the problems of imbalance between oxygen supply intensity and decarburization rate at different stages in the current electric arc furnace smelting process, FeO generation rate exceeding consumption rate, and continuous increase in FeO content in slag during smelting. Attached Figure Description

[0025] Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0026] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0027] Combined with appendix Figure 1 As can be seen, the control process of this invention is as follows: different intermittent powder injection processes are used under different smelting conditions to achieve precise and stable control of the transient FeO content in the slag, specifically including the following steps: Step 1: The electric arc furnace operator manually determines the steel material structure and smelting mode of the furnace, and sets the timing for starting carbon powder injection under different smelting conditions according to Table 1.

[0028] Table 1

[0029] Step 2: During the smelting process, information such as the amount of scrap steel and molten iron charged, oxygen supply intensity, blowing time, and smelting power consumption are collected in real time, and it is determined whether the corresponding process conditions have been met for the start-up. If not, the carbon powder injection valve is not opened, and information is continuously collected.

[0030] Step 3: When the starting timing corresponding to the process conditions is reached, first open the auxiliary blowing gas valve, open the carbon powder injection valve 5 seconds later, and the opening time and intermittent cycle of the carbon powder injection valve of the carbon powder tank shall be implemented according to the set process in accordance with the process carbon powder injection process under different process conditions provided in Table 2. During end point control: the carbon powder injection process with T>1550°C and C≤0.3% shall be implemented according to Table 3. No carbon powder is injected during tapping.

[0031] Table 2

[0032] Step 4: Real-time adjustment of carbon powder injection parameters during smelting: adjust intermittent powder injection parameters in real time according to the foaming slag index. If the foaming slag index is greater than 95%, the injection time is gradually reduced in steps of 0.5 seconds, and the intermittent cycle remains unchanged; if the foaming slag index is less than 90%, the injection time remains unchanged, and the intermittent cycle is gradually reduced in steps of 1.0 seconds; stably control the foaming slag index after molten clearing between 90% and 95%.

[0033] Step 5: In the later stage of smelting, when the molten bath temperature is >1550°C and the C content is ≤0.3%, the carbon powder injection process shall be implemented according to the process setting table of oxygen supply intensity and carbon powder injection parameters in the later stage of smelting provided in Table 3.

[0034] Table 3

[0035] The selection of each oxygen supply mode in Table 3 is based on Table 4.

[0036] Table 4

[0037] The blowing mode is selected according to the mass content of carbon C in the final molten steel and the carbon-phosphorus ratio C / P. When the mass content of C is the same, the smaller the C / P value is, the more difficult dephosphorization is; the larger the C / P value is, the easier dephosphorization is. Table 4 shows that when the C / P corresponding to each group of C content reaches the third group, it is determined that dephosphorization is easy.

[0038] According to Table 4: when C>0.6%, C / P is less than 15, the blowing mode is ML+LL+LL; when C / P is 15-25, the blowing mode is HL+HL+LL; when C / P is greater than 25, the blowing mode is HL+HL+HL; when 0.4<C≤0.6, C / P is less than 10, the blowing mode is ML+ML+ML; when C / P is 10-15, the blowing mode is ML+ML+LL; when C / P is greater than 15, the blowing mode is LL+LL+LL; When 0.2 < C ≤ 0.4, if C / P is less than 8, the blowing mode selected is ML+ML+LL; if C / P is between 8 and 12, the blowing mode selected is ML+LL+LL; if C / P is more than 12, the blowing mode selected is LL+LL+LL; When 0.08 < C ≤ 0.2, if C / P is less than 4, the blowing mode selected is ML+ML+LL; if C / P is between 4 and 6, the blowing mode selected is ML+LL+LL; if C / P is more than 6, the blowing mode selected is LL+LL+LL; When C ≤ 0.08, if C / P is less than 2, the blowing mode selected is ML+LL+LL; if C / P is between 2 and 2.5, the blowing mode selected is LL+LL+LL; if C / P is more than 2.5, the blowing mode selected is LL+LL.

[0039] Step 6: The parameters of the intermittent powder injection process in the later stage of smelting are adjusted according to Step 4.

[0040] Step 7: When both the temperature and composition meet the requirements of the steel grade, tap the steel, and the smelting of the current heat is completed. The operation of Steps 1 to 6 is repeated for the next heat, and the process cycles in this way.

[0041] A specific embodiment of the present invention is provided below: The smelting process utilizes a 100-ton ultra-high-power electric arc furnace with a total charge of 114 tons, including 73 tons of scrap steel and 41 tons of molten iron, resulting in a scrap steel ratio of 64.0%. A production model of "one ladle of molten iron + one ladle of scrap steel" is employed, with 3508 kg of metallized pellets added to the bottom of the ladle during scrap steel charging. No carbon powder is injected during the furnace penetration process. When the electric arc furnace power supply reaches 11000 kWh, the valves of the furnace wall carbon powder lances are opened, with the carbon powder injection parameters set to fully open. When the electric arc furnace power supply reaches 14078 kWh, the secondary system indicates that the smelting has reached the basic melting stage. At this point, the carbon powder lances are switched to intermittent carbon powder injection, with the following parameters: intermittent cycle of 7 seconds, injection time of 2 seconds, and stop time of 5 seconds. After the scrap steel is basically melted and cleared, continuous blowing begins after 3 minutes, with temperature sampling every 3-4 minutes. When the temperature reaches ≥1540℃, the operator manually initiates the decarburization and heating stage. During this stage, the carbon powder injection parameters are set as follows: intermittent cycle 7 seconds, blowing time 1 second, and stop time 6 seconds. The system displays a foam slag index of 86%. After 20 seconds, the carbon powder injection parameters are adjusted to: intermittent cycle 6 seconds, blowing time 1 second, and stop time 5 seconds. The foam slag index fluctuates around 92.0%, and blowing continues using these parameters. After 3.3 minutes of continuous blowing, the temperature sampling results show a steel C content of 0.24% and a temperature of 1570℃. At this point, the endpoint control stage is manually initiated. During the final control phase, operators adjusted the oxygen lances on furnace walls #1, #2, and #3 to LL, ML, and LL modes, respectively. The carbon powder injection parameters were adjusted to: intermittent cycle of 17 seconds, injection time of 2.5 seconds, and stop time of 14.5 seconds. After real-time adjustments based on the foam slag index, the final stable parameters were an intermittent cycle of 15 seconds, injection time of 2.5 seconds, and stop time of 12.5 seconds. At this point, the foam slag index fluctuated between 92% and 93%. Sampling and analysis were conducted from the start of slag discharge to tapping during the smelting process. The results are shown in Table 5 below. The FeO content in the slag at the smelting endpoint was 17.4%, and the FeO content fluctuation during the smelting process was 3.0%, meeting the control requirements.

[0042] Table 5

[0043] Those skilled in the art will understand that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless defined as herein.

[0044] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for stabilizing and controlling FeO slag in an electric arc furnace using intermittent powder injection, characterized in that, Includes the following steps: Step 1: Determine the timing of carbon powder injection under the corresponding conditions based on the current steel material structure and smelting mode of the electric arc furnace. Step 2: Collect information on the amount of scrap steel and molten iron charged, oxygen supply intensity, blowing time and smelting power consumption in real time during the smelting process, and determine whether the corresponding process conditions have been met for the start-up. If not, do not open the carbon powder injection valve, and continue to collect information. Step 3: If the opening timing under the corresponding process conditions is reached, first open the blowing gas valve, and then open the toner spraying valve after 5 seconds. Set the opening time and intermittent cycle of the toner spraying valve according to the intermittent powder spraying process under different process conditions. By using different scrap steel ratios, the carbon content and molten pool formation time can be accurately calculated, and the timing of carbon powder injection corresponding to different smelting processes can be determined. By taking advantage of the different oxygen supply intensities at different stages, different carbon powder injection process parameters are designed. Step 4: Real-time adjustment of carbon powder injection parameters during smelting: Adjust the intermittent carbon powder injection parameters in real time according to the foam slag index. If the foam slag index is greater than 95%, the carbon powder injection time is gradually reduced while the intermittent cycle remains unchanged; if the foam slag index is less than 90%, the carbon powder injection time remains unchanged while the intermittent cycle is gradually reduced; keep the foam slag index after melting and cleaning stable between 90% and 95%. Step 5: In the later stage of smelting, when the molten pool temperature is >1550℃ and the C mass content is ≤0.3%, carbon powder injection shall be carried out according to the relationship between the oxygen supply intensity and carbon powder injection parameters in the later stage of smelting. Step 6: Adjust the intermittent powder injection parameters in the later stage of smelting according to step 4; Step 7: When the temperature and composition meet the requirements of the steel grade, tap the steel and the smelting of this furnace is completed; Step 8: Repeat steps 1 to 7 for the next batch, and so on in a continuous cycle.

2. The method for stabilizing and controlling FeO slag in an electric arc furnace by intermittent powder injection according to claim 1, characterized in that, The total charge of the electric arc furnace smelting is 100-120t, the scrap steel ratio is 20%-100%, and the remainder is molten iron; When the scrap steel ratio in the steel material is less than or equal to 60%, the smelting mode is one bag of scrap steel, and carbon powder is injected after the material is completely dissolved. When the scrap steel ratio in the steel material is greater than 60% but less than or equal to 80%, the smelting mode is either one bag of scrap steel or two bags of scrap steel, depending on the production process requirements and the type of scrap steel. With one bag of scrap steel, carbon powder is injected after the material is basically completely dissolved. With two bags of scrap steel, carbon powder is injected after the second batch of material has been processed through the well.

3. The method for stabilizing and controlling FeO slag in an electric arc furnace by intermittent powder injection according to claim 1, characterized in that, The carbon powder sprayed by the intermittent powder spraying process has a solid C content ≥75%, S content ≤0.5%, H2O content ≤1.0%, and particle size of 0.5~3mm.

4. The method for stabilizing and controlling FeO slag in an electric arc furnace by intermittent powder injection according to claim 1, characterized in that, The intermittent powder injection process involves injecting carbon powder into the oxygen impact zone inside the furnace through a carbon powder gun on the furnace wall.

5. The method for stabilizing and controlling FeO slag in an electric arc furnace by intermittent powder injection according to claim 1, characterized in that, In the intermittent powder spraying process, the blowing gas is compressed air, the carrier gas pressure is 0.4~0.8MPa, and the toner can pressure is controlled between 1.8~2.5 MPa.

6. The method for stabilizing and controlling FeO slag in an electric arc furnace by intermittent powder injection according to claim 1, characterized in that, In the intermittent powder spraying process, the blowing gas is set to a normally open mode during the toner spraying, the spraying time is between 1 and 15 seconds, and the intermittent cycle is between 3 and 30 seconds.

7. The method for stabilizing and controlling FeO slag in an electric arc furnace by intermittent powder injection according to claim 1, characterized in that, In the said smelting process, the carbon powder injection parameters are adjusted in real time. The foamy slag index calculated in real time by the electric arc furnace control system is used to characterize the control level of FeO in the foamy slag. When the foaming index is greater than 95%, the average injection flow rate is gradually reduced with an injection time step of 0.5 seconds; when the foaming index is less than 90%, the injection flow rate and frequency are gradually increased with an intermittent cycle step of 1.0 second. The adjustment of carbon powder injection parameters is triggered once every 20 seconds, and the foamy slag index refers to the average value of 20 seconds before the adjustment node, until the foamy slag index is stably controlled between 90% and 95%.

8. The method for stabilizing and controlling FeO slag in an electric arc furnace by intermittent powder injection according to claim 1, characterized in that, Said step 3 is specifically: controlling the carbon powder injection process according to the scrap ratio Sc and the smelting mode, when the smelting mode is one heat of hot metal + one heat of scrap, when 30%<Sc≤40%, during the decarburization and temperature rising period, after the scrap is completely melted, carbon powder injection is carried out for 15min, with 1 second injection and 13 seconds pause; when 40%<Sc≤50%, during the decarburization and temperature rising period, after the scrap is completely melted, carbon powder injection is carried out for 10min, with 1 second injection and 12 seconds pause; when 50%<Sc≤60%, after the scrap is completely melted, carbon powder injection is carried out for 5min, with 2 seconds injection and 7 seconds pause; during the decarburization and temperature rising period, an intermittent injection process of 1 second injection and 8 seconds pause is adopted; when 60%<Sc≤65%, when the total power consumption reaches 11000kwh, carbon powder injection is fully turned on, after the scrap is completely melted, an intermittent injection process of 2 seconds injection and 7 seconds pause is adopted, and during the decarburization and temperature rising period, an intermittent injection process of 1 second injection and 7 seconds pause is adopted; when 65%<Sc≤70%, when the total power consumption reaches 12000kwh, carbon powder injection is fully turned on, after the scrap is completely melted, an intermittent injection process of 2.5 seconds injection and 8 seconds pause is adopted, and during the decarburization and temperature rising period, an intermittent injection process of 1 second injection and 6 seconds pause is adopted; when 70%<Sc≤75%, when the total power consumption reaches 14000kwh, carbon powder injection is fully turned on, after the scrap is completely melted, an intermittent injection process of 3 seconds injection and 8 seconds pause is adopted, and during the decarburization and temperature rising period, an intermittent injection process of 1 second injection and 6 seconds pause is adopted; when the smelting mode is one heat of hot metal + two heats of scrap, when 60%<Sc≤65%, during the melting period of the second heat of scrap, an intermittent carbon powder injection process of 2 seconds injection and 5 seconds pause is adopted, after the scrap is completely melted, an intermittent injection process of 2 seconds injection and 7 seconds pause is adopted, and during the decarburization and temperature rising period, an intermittent injection process of 1 second injection and 8 seconds pause is adopted; when 65%<Sc≤70%, during the melting period of the second heat of scrap, an intermittent carbon powder injection process of 2 seconds injection and 5 seconds pause is adopted, after the scrap is completely melted, an intermittent injection process of 2 seconds injection and 7 seconds pause is adopted, and during the decarburization and temperature rising period, an intermittent injection process of 1 second injection and 7 seconds pause is adopted; when 70%<Sc≤75%, during the melting period of the second heat of scrap, an intermittent carbon powder injection process of 2 seconds injection and 5 seconds pause is adopted, after the scrap is completely melted, an intermittent injection process of 1.5 seconds injection and 4 seconds pause is adopted, and during the decarburization and temperature rising period, an intermittent injection process of 1 second injection and 6 seconds pause is adopted; when 75%<Sc≤80%, during the melting period of the second heat of scrap, an intermittent carbon powder injection process of 2 seconds injection and 5 seconds pause is adopted, after the scrap is completely melted, an intermittent injection process of 1.5 seconds injection and 4 seconds pause is adopted, and during the decarburization and temperature rising period, an intermittent injection process of 1.5 seconds injection and 6 seconds pause is adopted; When 80%<Sc≤90%, when the total power consumption reaches 3000kwh, carbon powder injection is fully opened; an intermittent injection process of injecting carbon powder for 2.5 seconds and stopping for 5 seconds is adopted during melting of the second ladle of scrap steel, an intermittent injection process of injecting for 1.5 seconds and stopping for 4 seconds is adopted after the scrap steel is completely melted, and an intermittent injection process of injecting for 1.5 seconds and stopping for 6 seconds is selected during decarburization and temperature rise; When 90%<Sc≤99%, when the total power consumption reaches 4000kwh, carbon powder injection is fully opened; an intermittent injection process of injecting carbon powder for 2.5 seconds and stopping for 5 seconds is adopted during melting of the second ladle of scrap steel, an intermittent injection process of injecting for 2 seconds and stopping for 5 seconds is adopted after the scrap steel is completely melted, and an intermittent injection process of injecting for 2 seconds and stopping for 7 seconds is selected during decarburization and temperature rise; For all-scrap steel, when the total power consumption reaches 5000kwh, carbon powder injection is fully opened; an intermittent injection process of injecting carbon powder for 2.5 seconds and stopping for 5 seconds is adopted during melting of the second ladle of scrap steel, an intermittent injection process of injecting for 2 seconds and stopping for 5 seconds is adopted after the scrap steel is completely melted, and an intermittent injection process of injecting for 2 seconds and stopping for 7 seconds is selected during decarburization and temperature rise.

9. The method for stabilizing and controlling FeO slag in an electric arc furnace by intermittent powder injection according to claim 1, characterized in that, The intermittent powder injection control process in step 5 of the smelting stage adjusts the carbon powder injection flow rate based on the oxygen supply intensity. The electric arc furnace has three furnace wall oxygen lances. LL mode indicates the low-oxygen mode for the furnace wall oxygen lances, where epoxy: 200m 3 / h, natural gas 200m 3 / h, main oxygen 1200m 3 / h; ML mode indicates the medium oxygen mode of the furnace wall oxygen lance, where epoxy: 240m 3 / h, natural gas 240m 3 / h, main oxygen 2000m 3 / h; HL mode indicates the high oxygen mode of the furnace wall oxygen lance, where epoxy: 300m 3 / h, natural gas 300m 3 / h, main oxygen 2500m 3 / h; The blowing mode is selected according to the mass content of carbon in the final molten steel and the carbon-phosphorus ratio C / P. When the mass content of C is the same, the smaller the C / P value is, the more difficult dephosphorization is, and the larger the C / P value is, the less difficult dephosphorization is: When C>0.6%, if C / P is less than 15, ML+LL+LL is selected as the blowing mode; if C / P is 15~25, HL+HL+LL is selected as the blowing mode; if C / P is more than 25, HL+HL+HL is selected as the blowing mode; When 0.4<C≤0.6, if C / P is less than 10, ML+ML+ML is selected as the blowing mode; if C / P is 10~15, ML+ML+LL is selected as the blowing mode; if C / P is more than 15, LL+LL+LL is selected as the blowing mode; When 0.2<C≤0.4, if C / P is less than 8, ML+ML+LL is selected as the blowing mode; if C / P is 8~12, ML+LL+LL is selected as the blowing mode; if C / P is more than 12, LL+LL+LL is selected as the blowing mode; When 0.08<C≤0.2, if C / P is less than 4, ML+ML+LL is selected as the blowing mode; if C / P is 4~6, ML+LL+LL is selected as the blowing mode; if C / P is more than 6, LL+LL+LL is selected as the blowing mode; When C≤0.08, if C / P is less than 2, ML+LL+LL is selected as the blowing mode; if C / P is 2~2.5, LL+LL+LL is selected as the blowing mode; if C / P is more than 2.5, LL+LL is selected as the blowing mode.

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