A method of controlling the operation of a large, closed, submerged arc furnace process

Abstract

The present application belongs to the technical field of ferroalloy smelting process in an electric arc furnace. A method for controlling the process operation of an electric arc furnace by a model is provided to solve the problem of judging and adjusting the furnace condition for smelting high-carbon ferrochrome in a totally-enclosed electric arc furnace. Through heat transfer analysis, theoretical calculation and statistical analysis of a large amount of production data, a process model for judging and adjusting the furnace condition is provided, the operation ideas and methods of the workers are unified, the problem of long-term stable operation of the electric arc furnace is solved, and the technical and economic indexes such as power consumption and ore consumption reach the world advanced level.

Description

Technical Field

[0001] This invention belongs to the field of ferroalloy submerged arc furnace smelting technology, and relates to a method for controlling the process operation of a large-scale closed submerged arc furnace. Background Technology

[0002] With increasingly stringent national environmental protection policies, fully enclosed submerged arc furnaces have become the main equipment for ferroalloy smelting. Because of their completely different capacity and structure compared to open and semi-enclosed submerged arc furnaces, a new process control and operation method is urgently needed for efficient production.

[0003] Traditional ferroalloy smelting enterprises using submerged arc furnaces generally employ a process operation method that relies on visual observation of the furnace condition and adjustment of electrode positions based on electrode current. This involves judging whether the reaction inside the furnace is normal and whether the electrode length needs to be adjusted by visually observing the material surface and the current. However, with the adoption of fully enclosed submerged arc furnaces, it is no longer possible to visually observe the material surface inside the furnace. Furthermore, the large electrode size makes frequent electrode movement unsuitable. The electrode current fluctuates greatly due to the characteristics of the furnace charge, the temperature field inside the furnace, and the electrode insertion depth. Therefore, the operation method of stabilizing production by adjusting the electrode position is no longer suitable. Consequently, there is an urgent need for a more effective process control operation method.

[0004] Based on long-term production practice, a suitable resistance control range for fully enclosed submerged arc furnaces was summarized. According to factors such as changes in furnace bottom and body temperature, changes in electrode resistance, slag composition, and cumulative electrode pressure release, coefficients were set according to their different degrees of importance to the stability of the submerged arc furnace. Finally, a furnace condition adjustment and control model based on electrode resistance, furnace bottom and body temperature, and iron flow rate was developed for fully enclosed submerged arc furnaces, ultimately achieving stable furnace conditions and reaching the optimal economic and technical indicators. Summary of the Invention

[0005] The purpose of this invention is to address the above-mentioned problems by providing a method for controlling the process operation of a large-scale closed submerged arc furnace.

[0006] The objective of this invention is achieved as follows: a method for controlling the process operation of a large-scale closed submerged arc furnace, comprising the following steps: Step 1: The composition standards of slag and molten iron must be stable within the control range; Step 2: The normal temperature ranges for the slag layer, molten iron layer, and furnace bottom refractory are: hot spot temperature range of the slag layer (°C): 50-450°C, hot spot temperature range of the molten iron layer (°C): 50-350°C, hot spot temperature range of the furnace bottom refractory (°C): 150-930°C; If the temperatures of the slag layer, molten iron layer, and furnace bottom refractory are within the standard range and the daily fluctuation is less than 20°C, the furnace condition is considered normal. If the temperature exceeds the above range and continues to rise or fall, it indicates that the electrode position is too long or too short. In this case, the furnace bottom refractory temperature parameter becomes a basis for process adjustment: if the furnace bottom temperature at the corresponding electrode end rises rapidly, and the electrode resistance of that phase is low, reduce the number of electrode press-outs to 0-2 times / shift; conversely, increase the number of electrode press-outs to 3-9 times / shift. Step 3: Control the electrode resistance: 1.5-3.5. mΩ; Step 4: Power consumption: When the preheating temperature of the furnace charge is 300℃ or above, the power consumption index of a single furnace is 2800-3000 kWh / t. When the preheating temperature of the furnace charge is 200℃ or below, the power consumption index of a single furnace should be increased by 200-300 kWh / t; Step 5: Slag and molten iron discharge: Slag should be discharged first, followed by molten chromium. The total discharge time for slag and molten chromium is 25-45 minutes / furnace; Step 6: Adjustment parameters: Si: The average value of 3 consecutive furnaces should be increased or decreased by 0.5 percentage points compared to the standard, and the reducing agent in the batch should be reduced or increased by 15 kg; SiO2: The average value of 3 consecutive furnaces should be increased or decreased by 0.5 percentage points compared to the standard, and the silica in the batch should be reduced or increased by 28 kg; Al2O3, R((MgO+CaO) / SiO2), and M / A should be controlled according to the raw material composition by adding slag-forming agents such as serpentine and dolomite, respectively: Al2O 3：28-31%, R((MgO+CaO) / SiO2): 0.9-1.1, M / A: 0.75-0.95, Furnace bottom temperature: If the temperature exceeds the upper limit, reduce the electrode pressure release frequency by 0-4 times per shift; conversely, increase the electrode pressure release frequency by 0-4 times per shift. Ferrochrome molten layer temperature: If the temperature exceeds the upper limit, reduce the power consumption per furnace by 5-30 MWh; conversely, increase the power consumption per furnace by 5-30 MWh. Slag layer temperature: If the temperature exceeds the upper limit, it indicates that the slag temperature is high or the slag discharge is not smooth. The slag melting point needs to be lowered to 1780±20℃ or the power consumption per furnace needs to be reduced by 5-30 MWh to remove the slag that has not been discharged smoothly from the furnace. Resistance: If it exceeds the upper limit, increase the electrode pressure release frequency by 0-4 times per shift to reduce the resistance of this phase. Control the galvanic flow rate to within 4mΩ; if it is below the lower limit, it indicates that the furnace temperature is low or the electrode length is too long. Reduce electrode pressure release by 0-4 times per shift or increase the power consumption of a single furnace by 5-30MWh; Power consumption: If the power consumption is 100kwh / t or more higher than normal for two consecutive days, adjust the furnace condition by increasing electrode pressure release by 2-5 times per day for every 100kwh / t increase in power consumption; Iron tapping and slag removal: If there is no slag removal, adjust the silica ratio by increasing the silica ratio by 5℃ for every 30kg increase in the batch; If there is no iron tapping, if it is determined to be due to low furnace temperature, quickly raise the molten iron temperature to 1580-1630℃ by adjusting the slag melting point to 1780±20℃, increasing the power consumption of a single furnace to 200-280MWh, or increasing electrode pressure release by 3-6 times per shift.

[0007] The standard composition of slag and molten iron in step one is as follows: molten iron composition: Si: 5±0.5%, slag composition: SiO2: 28.5-31.5%, Al2O3: 28.5-32.5%, R((MgO+CaO) / SiO2): 0.9-1.1, M / A: 0.75-0.95.

[0008] The beneficial effects of this invention are as follows: Through nearly six months of production practice, using the above-mentioned model to predict and adjust the furnace condition of the submerged arc furnace, the furnace condition has not deteriorated significantly. The average furnace output and technical and economic indicators have all reached the design values. Compared with before the model was used for control, the monthly ferrochrome production has increased by about 5%, and technical and economic indicators such as power consumption and ore consumption have reached the advanced level in the industry. Through the application of this model, the thinking and methods of employees in judging the furnace condition and adjusting the process of the submerged arc furnace have been unified, realizing the long-term stability and smooth operation of the submerged arc furnace for smelting high-carbon ferrochrome, and the technical and economic indicators have reached the international advanced level. Implementation

[0009] The basic concept of this invention is to utilize the electrode resistance parameters in the imported Outotec 75MW fully enclosed submerged arc furnace monitoring system, combined with the distribution of thermocouples in the furnace bottom and furnace body, and the composition of ferrochrome and slag, to design a process control model suitable for smelting high-carbon ferrochrome in a submerged arc furnace using big data statistical analysis. This model will be continuously optimized in actual operation to unify and standardize the process operation of personnel, stabilize the furnace condition, and achieve the best economic and technical indicators for smelting in the submerged arc furnace.

[0010] The operating method of this invention involves analyzing the resistance data of the three electrodes in a submerged arc furnace, combined with process parameters such as furnace bottom and body temperature changes, slag and iron discharge rate, and slag and iron composition, to determine the position of the three-phase electrodes and the reaction status within the furnace. If the resistance difference between the three electrodes is large and the furnace bottom temperature deviates from the normal value, it indicates that the ends of the three electrodes are not on the same horizontal plane. Poor communication between the three phase electrodes leads to high power consumption and unstable furnace conditions. By constructing a model to analyze and judge the furnace conditions, the main influencing factors are identified. Accordingly, corresponding control measures such as electrode pressure release, power consumption adjustment, and feed adjustment are taken to ensure that the ends of the three electrodes reach the same horizontal plane as soon as possible and expand the molten pool, thereby improving the smelting conditions within the furnace, enhancing technical and economic indicators, and achieving stable and high production of the submerged arc furnace.

[0011] The resistance parameters of this invention are derived from theoretical calculations, i.e., the phase voltage divided by the electrode current of each phase. The resistance can be directly read from the computer screen. The temperature of the furnace bottom and furnace body is measured by judging the material structure and temperature field inside the furnace. Thirteen points are arranged at the furnace bottom, ten points in the metal layer area of ​​the furnace body, and twelve points in the slag layer area. Two thermocouples of different lengths are inserted at each point. The size of the molten pool and the position of the electrodes inside the furnace are judged by the temperature and temperature difference at each point. Combined with parameters such as slag composition, slag-iron temperature, and flow rate, an effective method for judging the furnace condition is formed. Based on this, the electrode pressure release, power consumption, and material composition are finely adjusted to achieve stable and efficient production of the submerged arc furnace.

[0012] (I) Main parameter control standards for this operation method: 1. Slag and iron composition standards: molten iron composition: [Si]: 5±0.5%, slag composition: (SiO2): 28.5-31.5%; (Al2O3): 28.5-32.5%; R((MgO+CaO) / SiO2): 0.9-1.1; M / A: ≥0.75.

[0013] 2. The normal temperature ranges for the slag layer, metal layer, and furnace bottom refractory are as follows.

[0014]

[0015] Note: The above temperature standards are based on the distribution of thermocouples in the furnace, combined with heat transfer calculations and big data statistical analysis.

[0016] 3. Resistance standard: R: 1.5-3.5 mΩ.

[0017] 4. Power consumption: When the preheating temperature of the furnace charge is stable at 300℃ or above, the power consumption of a single furnace (48-53 tons of iron produced / furnace) is 2800-3000 kWh / t; when the preheating temperature of the furnace charge is 200℃ or below, the power consumption will increase by 200-300 kWh / t.

[0018] 5. Iron discharge: Slag is discharged first, followed by iron. Slag and iron discharge is vigorous and short in time (25-45 minutes / furnace), which is normal furnace condition.

[0019] (II) Establishment of the control model: 1. The standard of slag and iron composition is the basis for controlling the stability of the furnace condition. Based on the structure and composition of the purchased ore, the structure and quantity of each batch of material are determined through theoretical calculations. The proportion of raw materials is finely adjusted by actual detection of slag and iron composition to keep the slag and iron composition stable within the above control range for a long time. On this basis, the normality of the furnace condition is judged based on other parameters and corresponding measures are taken to achieve long-term and efficient production of the electric arc furnace.

[0020] 2. If the slag layer, iron layer, and furnace bottom temperatures are within the above-mentioned standard range and the daily fluctuation is less than 20℃, the furnace condition is considered normal, and this parameter is not used as a basis for furnace condition adjustment. However, if the temperature exceeds the above range and continues to rise or fall, it indicates that the electrode position is too long or too wide, and this parameter becomes a basis for process adjustment.

[0021] 3. If the electrode resistance is consistently high (≥4 mΩ), it indicates that the electrode is too short or the furnace temperature is too high. In conjunction with parameters such as slag and iron discharge and furnace cover temperature, determine the direction and extent of process parameter adjustments. If the electrode resistance is consistently low (≤1.2 mΩ), it indicates that the electrode is too long or the furnace temperature is too low. In conjunction with other parameters, determine the direction and extent of adjustments.

[0022] 4. High power consumption indicates that the furnace temperature is too low, and measures such as increasing power consumption and strengthening electrode pressure release need to be taken.

[0023] 5. If the slag and iron discharge takes a long time or if there is a phenomenon of complete slag or complete iron discharge, it indicates that the furnace condition has deteriorated, and specific process measures need to be taken in combination with the changing trends of other parameters.

[0024] 6. Based on the above basic judgments, the following furnace condition judgments and adjustment parameters are determined.

[0025]

[0026] The implementation was carried out in two 75MW closed submerged arc furnaces at Shanxi Taigang Wanbang Furnace Materials Co., Ltd., and the implementation method is shown in Table 4.

[0027] Case 1: On April 12, 2022, Taiyuan Iron & Steel Group Wanbang No. 1 furnace experienced a prolonged period of low phase A resistance (≤1.2mΩ) and power loss. Statistics revealed that on April 11, the maximum temperature drop (22H) of the refractory material at the bottom of the No. 1 submerged arc furnace reached 32℃, and temperatures at other points also showed a significant downward trend. The smelting power consumption that day reached 3300 kWh / t, approximately 200 kWh / t higher than normal. Slag and iron discharge was poor throughout the day, with some furnace tapping times exceeding one hour, and the slag and iron flow was weak and lacked momentum. Preliminary assessment indicated a risk of the No. 1 furnace condition cooling down and deteriorating.

[0028] Analysis suggests that the cause of this situation is that the electrodes are too short and the three-phase communication is poor. Based on this judgment, it is believed that raising the furnace temperature and transferring heat from the furnace charge layer to the molten pool area is the main way to reverse the deterioration of the furnace condition.

[0029] Specific measures: 1. Increase electrode pressure release: Increase the number of three-phase electrode pressure releases from 0.5-2 times / shift last week to 6-8 times / shift, and extend the total length of electrodes in the furnace by 0.5-0.7 meters; 2. Increase furnace temperature: Raise the slag temperature to 1780-1800℃, and increase the power consumption of a single furnace to 180-220MWh to ensure sufficient heat in the furnace; 3. After the furnace temperature reaches a certain level, adjust it back in time to restore electrode pressure release, slag temperature, and power consumption of a single furnace to the normal range to prevent the refractory material temperature from becoming too high due to excessive furnace temperature.

[0030] Results: After two consecutive days (i.e., six shifts of adjustment), on the day shift of April 14, 2022, the furnace condition of No. 1 furnace basically returned to normal, the process operation was restored from the adjustment stage to normal operation, and the furnace condition once again entered the stable operation stage.

[0031] The above description is only a specific embodiment of the present invention, but the structural features protected by the present invention are not limited thereto. Any changes or modifications made by those skilled in the art within the scope of the present invention are covered by the patent scope of the present invention.

Claims

1. A method for controlling the process operation of a large-scale closed submerged arc furnace, characterized in that: Includes the following steps: Step 1: The composition standards of slag and molten ferrochrome must be kept within the control range; Step Two: Normal Temperature Ranges for Slag Layer, Molten Iron Layer, and Furnace Bottom Refractory Material: Hot spot temperature range for slag layer: 50-450°C; hot spot temperature range for molten iron layer: 50-350°C; hot spot temperature range for furnace bottom refractory material: 150-930°C. If the temperatures of the slag layer, molten iron layer, and furnace bottom refractory material are within the standard range and the daily fluctuation is less than 20°C, the furnace condition is considered normal. If the temperatures exceed the above ranges and the temperature continues to rise or fall, it indicates that the electrode position is too long or too short. In this case, the furnace bottom refractory material temperature parameter becomes a basis for process adjustment: if the furnace bottom temperature at the corresponding electrode end rises rapidly and the electrode resistance is low, reduce the electrode pressing and releasing frequency to 0-2 times / shift; conversely, increase the electrode pressing and releasing frequency to 3-9 times / shift. Step 3: Control the electrode resistance: 1.5–3.5 mΩ; Step 4: Power consumption: When the preheating temperature of the furnace charge is 300℃ or above, the power consumption index of a single furnace is 2800-3000 kWh / t. When the preheating temperature of the furnace charge is 200℃ or below, the power consumption index of a single furnace should be increased by 200-300 kWh / t. Step 5: Slag and molten iron discharge: First discharge the slag, then discharge the molten chrome. The total discharge time for slag and molten chrome is 25-45 minutes per furnace. Step Six: Adjust parameters: Si: The average value of the SiO2 in three consecutive furnaces should be increased or decreased by 0.5 percentage points compared to the standard, and the reducing agent in the batch should be decreased or increased by 15 kg; SiO2: The average value of the SiO2 in three consecutive furnaces should be increased or decreased by 0.5 percentage points compared to the standard, and the silica in the batch should be decreased or increased by 28 kg; Al2O3, R((MgO+CaO) / SiO2), and M / A should be controlled according to the raw material composition by adding slag-forming agents such as serpentine and dolomite, respectively, at the following ratios: Al2O3, R((MgO+CaO) / SiO2), M / A, and M / A. 3： 28-31%, R((MgO+CaO) / SiO2): 0.9-1.1, M / A: 0.75-0.95, Furnace bottom temperature: If the temperature exceeds the upper limit, reduce the electrode pressing and releasing frequency by 0-4 times per shift; otherwise, increase the electrode pressing and releasing frequency by 0-4 times per shift; Ferrochrome molten layer temperature: If the temperature exceeds the upper limit, reduce the power consumption of a single furnace by 5-30 MWh; otherwise, increase the power consumption of a single furnace by 5-30 MWh; Slag layer temperature: If the temperature exceeds the upper limit, it indicates that the slag temperature is high or the slag discharge is not smooth. The slag melting point needs to be lowered to 1780±20℃ or the power consumption of a single furnace needs to be reduced by 5-30 MWh to remove the slag that has not been discharged smoothly from the furnace. Resistance: If it exceeds the upper limit, increase electrode pressure discharge 0-4 times / shift to control the resistance within 4mΩ; if it is below the lower limit, it indicates that the furnace temperature is low or the electrode is too long. Reduce electrode pressure discharge 0-4 times / shift or increase the power consumption of a single furnace by 5-30MWh. Power consumption: If power consumption is 100 kWh / t or more higher than normal for two consecutive days, adjust the furnace condition by increasing electrode pressure release 2-5 times / day for every 100 kWh / t increase in power consumption; Iron tapping and slag removal: If slag is not being discharged, adjust the silica ratio by increasing the silica ratio by 5°C for every 30 kg increase in the batch; If no iron is being tapped, and it is determined that the furnace temperature is low, raise the iron temperature to 1580-1630°C by adjusting the slag melting point to 1780±20°C, increasing the power consumption per furnace to 200-280 MWh, or increasing electrode pressure release 3-6 times per shift.

2. The method for controlling the process operation of a large-scale closed submerged arc furnace according to claim 1, characterized in that: The standard composition of slag and molten iron in step one is as follows: molten iron composition: Si: 5±0.5%, slag composition: SiO2: 28.5-31.5%, Al2O3: 28.5-32.5%, R((MgO+CaO) / SiO2): 0.9-1.1, M / A: 0.75-0.95.

Images