A smelting method for reducing electric power consumption of LF refining

Abstract

This invention relates to the field of LF refining technology, and more particularly to a smelting method for reducing LF refining power consumption. The method includes: adding refining slag to the primary furnace during tapping, without adding lime; dividing the LF smelting heating process into two stages, using different power factors, voltage levels, and currents for different time periods; adding 50% lime to the second and third time periods of the first stage; using different power factors, voltage levels, and currents to heat the molten steel in the second stage of LF heating, and calculating the time required for the molten steel to cool naturally to the required temperature at the end of the LF process and the required heating time. This invention controls the addition of slag during tapping to facilitate rapid slag formation in the early stages of LF refining, which is conducive to submerged arc heating during refining. Subsequently, by selecting the optimal power mode for rapid, low-energy heating, followed by natural cooling to the required temperature, this method reduces LF power consumption while meeting the smelting rhythm, thereby achieving cost reduction and efficiency improvement throughout the entire steelmaking process.

Description

Technical Field

[0001] This invention relates to the field of LF refining technology, and in particular to a smelting method for reducing the power consumption of LF refining. Background Technology

[0002] Most steel production processes include the LF (Lead Refining) process. LF refining is time-consuming and involves large amounts of alloys. Electricity consumption in the refining process accounts for a significant proportion of steelmaking costs. Therefore, reducing electricity consumption in LF refining can reduce energy consumption in refining and is an important part of reducing production costs. Scientific research on the electrical power characteristic curve of LF transformers and optimization of slag materials are important aspects of energy conservation and efficiency improvement in steelmaking.

[0003] The literature "Optimization of 120tLF Power Supply Curve" points out that the secondary refining of LF (ladle furnace) is a key process in the production of cold-rolled low-carbon steel in the converter-LF-CSP process. It only emphasizes how to study the most efficient heating level, but ignores the impact of the smelting rhythm and slag-making process on the LF power consumption in the actual production process. Therefore, it does not pay much attention to how to make good use of the most efficient heating level in the actual production process.

[0004] The literature "Temperature Prediction and Control of Molten Steel in LF Furnace Refining Process" points out that the entire LF heating process is divided into a heating period and a holding period. This report does not pay attention to the relationship between the slag submerged arc effect and the power supply level during the slag formation period. The slag submerged arc effect is poor during the slag formation period, requiring a low power supply level to slowly raise the temperature while waiting for slag formation and slag building to be completed before entering the heating period. On the other hand, the holding period usually uses a power supply level with higher energy consumption and lower thermal efficiency to ensure the balance between heating and cooling of molten steel, resulting in high energy consumption and low energy efficiency. Summary of the Invention

[0005] To address the shortcomings of existing methods, this invention controls the addition of slag during the steelmaking process to facilitate rapid slag formation in the early stages of LF (Leakage Fluid), which is conducive to refining and submerged arc heating. Subsequently, by selecting the optimal power supply mode, the temperature is rapidly increased with low energy consumption, followed by natural cooling to the required temperature. This approach satisfies the smelting rhythm while reducing the energy consumption of LF power supply, thereby achieving cost reduction and efficiency improvement in the entire steelmaking process.

[0006] The technical solution adopted in this invention is: a smelting method for reducing LF refining power consumption, comprising the following steps:

[0007] Step 1: When tapping steel from the primary smelting furnace, add refining slag, but do not add lime;

[0008] Furthermore, the composition requirements for refining slag are as follows: CaO: 40%–50%, MgO < 5%, Al2O3: 35%–45%, SiO2 < 5%, FeO < 1%.

[0009] Furthermore, the primary refining furnace produces 45 steel via a 120-ton converter, a 120-ton refining furnace, and a continuous casting machine.

[0010] Furthermore, the amount of lime used is 500 kg.

[0011] Step 2: Divide the LF smelting heating process into two stages. The first stage is further divided into three time periods. Different power factors, voltage levels and currents are selected for different time periods. 50% lime is added in the second and third time periods of the first stage.

[0012] Furthermore, step two specifically includes:

[0013] In the first stage of LF smelting, from 0 to 2 minutes, a power factor cosφ = 0.85 is selected, along with a voltage setting of 270V and a current of 24KA to heat the molten steel. From 2 to 4 minutes, 50% of the lime is added, and a power factor cosφ = 0.75 is selected, along with a voltage setting of 270V and a current of 30KA to continue heating the molten steel. From 4 to 8 minutes, the remaining 50% of the lime is added, and a power factor cosφ = 0.75 is selected, along with a voltage setting of 270V and a current of 30KA to continue heating the molten steel.

[0014] Step 3: The second stage of LF smelting heating involves using different power factors, different voltage levels and currents to heat the molten steel, and calculating the time required for the molten steel to cool naturally from the end of heating to the end of LF and the required heating time.

[0015] Furthermore, step three specifically includes:

[0016] After 8 minutes, the temperature T1 was measured to be 1547℃. The power factor cosφ was selected to increase the temperature by 0.75, and the voltage setting was 344V and the current setting was 37KA. The molten steel was then heated further.

[0017] Furthermore, the formula for the time required for the molten steel to cool naturally from the end of the heating process to the final LF temperature is as follows:

[0018]

[0019] Where a is the heating rate, b is the temperature drop rate, T1 is the measured temperature of the molten steel after the first stage of heating in LF smelting, T0 is the required temperature of the molten steel after the first stage of heating in LF smelting, and t′ is the heating time required for the second stage of heating.

[0020] Furthermore, the formula for the heating time required for the second stage of heating is:

[0021] t′=tt″-t0

[0022] Where t is the total LF smelting cycle, t0 is the total time of the first stage of LF smelting heating, and t″ is the time required for the molten steel to cool naturally from the end of heating to the end of LF.

[0023] The beneficial effects of this invention are:

[0024] 1. Only refining slag is added during converter tapping to achieve rapid slag formation in the initial stage of refining;

[0025] 2. By utilizing the optimal power supply curve to rapidly and efficiently heat to a certain temperature, and then naturally cool down to the temperature required to end LF, the required heating time and the time required for the molten steel to naturally cool down to the temperature required to end LF can be accurately calculated, replacing the traditional smelting method and achieving energy-saving control of LF. Attached Figure Description

[0026] Figure 1 This is a flowchart of the smelting method for reducing LF refining power consumption according to the present invention;

[0027] Figure 2 This is a power consumption comparison chart between embodiments and comparative examples of the present invention. Detailed Implementation

[0028] The present invention will be further described below with reference to the accompanying drawings and embodiments. The drawings are simplified schematic diagrams, which only illustrate the basic structure of the present invention in a schematic manner, and therefore only show the components related to the present invention.

[0029] like Figure 1 As shown, a smelting method for reducing LF refining power consumption includes the following steps:

[0030] (1) When adding slag to the primary smelting furnace, do not add lime, only add refining slag;

[0031] The composition requirements for the refined slag are: CaO: 40%–50%, MgO < 5%, Al2O3: 35%–45%, SiO2 < 5%, FeO < 1%, with the remainder being impurities. Its melting point is approximately 1500℃, which can ensure rapid melting and formation of a good slag layer in the initial stage of LF energization.

[0032] After the primary smelting furnace finishes tapping steel, the ladle is hoisted to the LF (Leakage and Refining) station. Typically, the temperature at the LF station is between 1500℃ and 1550℃. Following the conventional method of adding slag, both lime and refining slag are added. However, the high melting point of the slag leads to crusting on the slag surface, hindering the efficient conversion of electrical energy into heat when electricity is applied, resulting in low thermal efficiency. Therefore, it is necessary to add only refining slag with a melting point of approximately 1500℃, matching the LF station temperature, during primary smelting. This allows for rapid slag formation upon arrival at the LF station, enabling rapid melting upon power application. Subsequently, as the temperature of the molten steel and slag rises, lime is gradually added, achieving efficient utilization of refining electrical energy.

[0033] (2) During the LF process, the power factor cosφ = 0.85 is selected for the first 0-2 minutes of LF smelting, with a voltage level of 270V and a current of 24KA; during the second to fourth minutes of LF smelting, 50% of the lime is added, the power factor cosφ = 0.75 is selected, with a voltage level of 270V and a current of 30KA; during the fourth to eighth minutes of LF smelting, the remaining 50% of the lime is added, the power factor cosφ = 0.75 is selected, with a voltage level of 270V and a current of 30KA.

[0034] In the first 0-2 minutes of LF smelting, a power factor cosφ = 0.85 is selected. Typically, the power factor cosφ is controlled between 0.7 and 0.8, as this range corresponds to the highest heating efficiency. The purpose of controlling cosφ = 0.85 in the initial stage of LF smelting is to reduce the LF power supply current, which allows for a suitable extension of the arc length and improves slag formation before the slag is fully melted. Secondly, reducing the current minimizes direct damage to the power supply equipment caused by high current.

[0035] (3) After the first stage of LF smelting heating is 8 minutes, the temperature is measured and recorded as T1. Based on the total LF smelting cycle t, the power factor cosφ = 0.75 is selected for subsequent heating, with a voltage of 344V and a current of 37KA. The heating rate is 6℃ / min, and the cooling rate after heating is stopped is 1.8℃ / min. The temperature required for the end of LF is T0. The subsequent heating time t′ = (9t + 5T0 - 5T1 - 72) / 39 is calculated. The time for the molten steel to cool naturally to T0 after the heating is completed is t″ = tt′ - 8.

[0036] Power was applied at a power factor cosφ = 0.75, a voltage range of 344V, and a current of 37KA. The power factor, the start time of energization at this voltage, and the end time of energization were recorded to calculate the heating time; where heating time = end time of energization - start time of energization. The temperatures of the molten steel before and after energization were recorded to calculate the heating temperature rise; heating temperature rise = temperature after heating - temperature before heating. A total of 62 sets of data were tracked during the heating process, and the heating rate was obtained through fitting.

[0037] The temperatures at the end of the heating process and the temperature at the time of ladling were recorded to calculate the temperature drop difference; temperature drop difference = temperature at the end of the heating process - temperature at the time of ladling; the times at the end of the heating process and the time of ladling were recorded to calculate the temperature drop time; temperature drop time = time at the time of ladling - time at the end of the heating process; 62 sets of data on the temperatures at the end of the heating process, the temperature at the time of ladling, and the process time were tracked, and the temperature drop rate was obtained by fitting the data.

[0038] We obtain t′=(9t+5T0-5T1-72) / 39, where t0 is the total time of the first stage of LF smelting heating.

[0039] After the slag is fully smelted, it enters the heating stage. The most efficient power supply setting is used to quickly heat it to a certain temperature, and then it is naturally cooled to the temperature required for the end of LF. This process combines factors such as heating rate, temperature drop rate, LF refining cycle, and LF outlet temperature requirements to achieve efficient use of electrical energy.

[0040] The production of 45 steel using a 120-ton converter, a 120-ton refining furnace, and a continuous casting machine is used as an example and comparative example.

[0041] Example 1:

[0042] The top and bottom blowing converter adopts the conventional blowing method. When the steel is tapped from the converter, it is first alloyed, and then 400 kg of refining slag is added. The tapping temperature is 1612℃.

[0043] When the LF arrived at the station, the temperature was 1532℃. During the first 0-2 minutes of LF smelting, a power factor of cosφ = 0.85 was selected, along with a voltage of 270V and a current of 24KA, and the power consumption was recorded as 282kW·h. During the second to fourth minutes of LF smelting, 250kg of lime was added, and a power factor of cosφ = 0.75 was selected, along with a voltage of 270V and a current of 30KA, and the power consumption was recorded as 394kW·h. During the fourth to eighth minutes of LF smelting, the remaining 250kg of lime was added, and a power factor of cosφ = 0.75 was selected, along with a voltage of 270V and a current of 30KA, and the power consumption was recorded as 723kW·h.

[0044] After the total LF smelting time t0 = 8 minutes, the temperature was immediately measured and recorded as T1 = 1547℃. Based on the total LF smelting cycle of this furnace t = 32 minutes, the power factor cosφ = 0.75 was selected for subsequent heating, with a voltage setting of 344V and a current of 37KA. The heating rate was 6℃ / min, and the cooling rate after heating was stopped was 1.8℃ / min. The temperature required to end LF was T0 = 1569℃. The subsequent heating time was calculated as t′ = (9t + 5T0 - 5T1 - 72) / 39 = 8.4 minutes, and the power consumption was recorded as 2341 kWh. The time for the molten steel to cool naturally to T0 after heating was completed was t″ = tt′ - 8 = 15.6 minutes, and the power consumption was recorded as 0 kWh. The total power consumption was 3740 kWh.

[0045] Comparative Example 1:

[0046] The slag is added at the BOF tapping stage, not in batches during the LF process.

[0047] The top and bottom blowing converter adopts the conventional blowing method. When the steel is tapped from the converter, it is first alloyed, and then 500 kg of lime and 400 kg of refining slag are added. The tapping temperature is 1614℃.

[0048] When the LF arrived at the station, the temperature was 1529℃. During the first 0-2 minutes of LF smelting, a power factor of cosφ = 0.85 was selected, along with a voltage range of 270V and a current of 24KA, and the power consumption was recorded as 299kW·h. During the second to fourth minutes of LF smelting, a power factor of cosφ = 0.75 was selected, along with a voltage range of 270V and a current of 30KA, and the power consumption was recorded as 403kW·h. During the fourth to eighth minutes of LF smelting, a power factor of cosφ = 0.75 was selected, along with a voltage range of 270V and a current of 30KA, and the power consumption was recorded as 731kW·h.

[0049] Eight minutes later, the temperature was measured and recorded as T1 = 1538℃. Based on the total LF smelting cycle of this furnace, t = 33 min, the power factor cosφ = 0.75 was selected for subsequent heating, with a voltage setting of 344V and a current of 37KA. The heating rate was 6℃ / min, and the cooling rate after heating was stopped was 1.8℃ / min. The temperature required to end LF was T0 = 1569℃. The subsequent heating time was calculated as t′ = (9t + 5T0 - 5T1 - 72) / 39 = 9.7 min, and the power consumption was recorded as 2728 kW·h. The time for the molten steel to cool naturally to T0 after heating was completed was t″ = tt′ - 8 = 15.3 min, and the power consumption was recorded as 0 kW·h. The total power consumption was 4164 kW·h.

[0050] Comparative Example 2:

[0051] The top and bottom blowing converter adopts the conventional blowing method. When the steel is tapped from the converter, it is first alloyed, and then 400 kg of refining slag is added. The tapping temperature is 1613℃.

[0052] When the LF arrived at the station, the temperature was 1534℃. During the first 0-2 minutes of LF smelting, a power factor of cosφ = 0.75 was selected, along with a voltage setting of 270V and a current of 30KA, and the power consumption was recorded as 311kW·h. During the second to fourth minutes of LF smelting, 250kg of lime was added, and a power factor of cosφ = 0.75 was selected, along with a voltage setting of 270V and a current of 30KA, and the power consumption was recorded as 400kW·h. During the fourth to eighth minutes of LF smelting, the remaining 250kg of lime was added, and a power factor of cosφ = 0.75 was selected, along with a voltage setting of 270V and a current of 30KA, and the power consumption was recorded as 730kW·h.

[0053] Eight minutes later, the temperature was measured and recorded as T1 = 1540℃. Based on the total LF smelting cycle of this furnace, t = 35 min, the power factor cosφ = 0.75 was selected for subsequent heating, with a voltage setting of 344V and a current of 37KA. The heating rate was 6℃ / min, and the cooling rate after heating was stopped was 1.8℃ / min. The temperature required for the end of LF was T0 = 1569℃. The subsequent heating time was calculated as t′ = (9t + 5T0 - 5T1 - 72) / 39 = 9.9 min, and the power consumption was recorded as 2788 kW·h. The time for the molten steel to cool naturally to T0 after heating was completed was t″ = tt′ - 8 = 17.1 min, and the power consumption was recorded as 0 kW·h. The total power consumption was 4227 kW·h.

[0054] Comparative Example 3:

[0055] The top and bottom blowing converter adopts the conventional blowing method. When the steel is tapped from the converter, it is first alloyed, and then 400 kg of refining slag is added. The tapping temperature is 1611℃.

[0056] When the LF arrived at the station, the temperature was 1532℃. During the first 0-2 minutes of LF smelting, a power factor of cosφ = 0.85 was selected, along with a voltage setting of 270V and a current of 24KA, and the power consumption was recorded as 283kW·h. During the second to fourth minutes of LF smelting, 250kg of lime was added, and a power factor of cosφ = 0.75 was selected, along with a voltage setting of 270V and a current of 30KA, and the power consumption was recorded as 393kW·h. During the fourth to eighth minutes of LF smelting, the remaining 250kg of lime was added, and a power factor of cosφ = 0.75 was selected, along with a voltage setting of 270V and a current of 30KA, and the power consumption was recorded as 725kW·h.

[0057] Eight minutes later, the temperature was measured and recorded as T1 = 1546℃. Based on the total LF smelting cycle of this furnace, t = 30 min, the subsequent heating was selected with a power factor cosφ = 0.75, a voltage setting of 344V, a current of 37KA, and a heating rate of 6℃ / min. The temperature was heated for 3.8 min to T0 = 1569℃, and the power consumption was recorded as 1026 kW·h. Subsequently, the power factor for heat preservation was selected as cosφ = 0.75, with a voltage setting of 344V and a current of 37KA. Intermittent power supply was used to maintain the temperature at 1569℃ for 18.2 min, and the power consumption was recorded as 2856 kW·h. The total power consumption was 5283 kW·h.

[0058] Comparative Example 4:

[0059] The top and bottom blowing converter adopts the conventional blowing method. When the steel is tapped from the converter, it is first alloyed, and then 400 kg of refining slag is added. The tapping temperature is 1615℃.

[0060] When the LF arrived at the station, the temperature was 1534℃. During the first 0-2 minutes of LF smelting, a power factor of cosφ = 0.85 was selected, along with a voltage setting of 270V and a current of 24KA, and the power consumption was recorded as 285kW·h. During the second to fourth minutes of LF smelting, 250kg of lime was added, and a power factor of cosφ = 0.75 was selected, along with a voltage setting of 270V and a current of 30KA, and the power consumption was recorded as 389kW·h. During the fourth to eighth minutes of LF smelting, the remaining 250kg of lime was added, and a power factor of cosφ = 0.75 was selected, along with a voltage setting of 270V and a current of 30KA, and the power consumption was recorded as 731kW·h.

[0061] Eight minutes later, the temperature was measured and recorded as T1 = 1542℃. Based on the total LF smelting cycle of this furnace, t = 36 min, a power factor of cosφ = 0.75 was selected for subsequent temperature increases. Combined with intermittent power supply at 270V voltage and 30KA current, the temperature was maintained at 1569℃ for a total holding time of 28 min. The recorded power consumption was 4011 kWh. The total power consumption was 5416 kWh.

[0062] Detailed power consumption examples Figure 2 As shown.

[0063] 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 smelting method for reducing LF refining power consumption, characterized in that, Includes the following steps: Step 1: When tapping steel from the primary smelting furnace, add refining slag, but do not add lime; Step 2: Divide the LF smelting heating process into two stages. The first stage includes three time periods. Step two specifically includes: Selecting the power factor cos in the first 0-2 minutes of LF smelting =0.85, with a voltage setting of 270V and a current of 24KA, the molten steel is heated; during the 2nd to 4th minute of LF smelting, 50% lime is added, and the power factor cos =0.75, with a voltage setting of 270V and a current of 30KA, the molten steel is further heated; during the 4th to 8th minute of LF smelting, the remaining 50% of the lime is added, and the power factor cos =0.75, with a voltage setting of 270V and a current setting of 30KA, the molten steel is further heated; Step 3: The second stage of LF smelting heating, and calculate the time required for the molten steel to cool naturally from the end of heating to the end of LF, and the heating time required for the second stage of heating; Step three specifically includes: The temperature measured at the 8th minute of LF smelting was T1 = 1547℃. The power factor cos... =0.75, with a voltage setting of 344V and a current of 37KA, the molten steel is further heated.

2. The smelting method for reducing LF refining power consumption according to claim 1, characterized in that, The composition requirements for refining slag are: CaO: 40%~50%, MgO <5%, Al2O3: 35%~45%, SiO2 <5%, FeO <1%.

3. The smelting method for reducing LF refining power consumption according to claim 1, characterized in that, The primary refining furnace is a 120-ton converter, and the LF is a 120-ton refining furnace. 45 steel is produced using a continuous casting machine.

4. The smelting method for reducing LF refining power consumption according to claim 1, characterized in that, The amount of lime used is 500 kg.

5. The smelting method for reducing LF refining power consumption according to claim 1, characterized in that, The formula for the time required for molten steel to cool naturally from the end of heating to the end of LF (Full-Range) is: t´´= in, a For the heating rate, b The temperature drop rate is given by T1, which is the temperature of the molten steel measured after the first stage of LF smelting heating. The required temperature for molten steel after the first stage of LF smelting heating; The required heating time for the second stage of heating.

6. The smelting method for reducing LF refining power consumption according to claim 1, characterized in that, The formula for the heating time required for the second stage of heating is: t´=tt´´-t0 Where t is the total LF smelting cycle, t0 is the total time of the first stage of LF smelting heating, and t´´ is the time required for the molten steel to cool naturally from the end of heating to the temperature required for the LF process to end.

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