A method for reducing secondary oxygen blowing and explosion relief after slagging in a slagging double-slag process

Abstract

A kind of regulation and control method for reducing secondary oxygen blowing and explosion relief after slagging of slag double slag process, the regulation and control method includes the following steps: scrap is mixed with molten iron, adjust the position of oxygen lance for blowing, after molten iron is ignited, the first batch of slagging material is added to control the alkalinity of 1.1~1.5, the position of oxygen lance is adjusted again, the oxygen flow is kept constant, iron ore is added, until the oxygen content in the pipeline is 0~1m 3 / h, carbon monoxide content is 0~0.1m 3 / h stop blowing, pour slag;After pouring slag, adjust the position of oxygen lance for blowing, add the second batch of slagging material to control the alkalinity of 2.8~3.0, adjust the position of oxygen lance and oxygen flow for blowing, and then tap the steel after blowing.The regulation and control method used in the present application reduces the "explosion relief" accident from 84 times per hundred furnaces before optimization to 27 times after optimization, effectively reducing the "explosion relief" accident rate.

Description

Technical Field

[0001] This invention relates to the field of metallurgical technology, and in particular to a method for controlling the secondary oxygen blowing and explosion relief after slag dumping in a slag-retaining double-slag process. Background Technology

[0002] In oxygen converter steelmaking, the common metal oxidation sequence is silicon, manganese, phosphorus, carbon, iron, and sulfur. The converter steelmaking process requires the addition of slag-forming materials to remove impurities. Slag formation allows harmful elements such as phosphorus and sulfur in the molten steel to react chemically with the slag, generating corresponding compounds that enter the slag, thereby reducing the content of harmful elements in the molten steel and improving steel quality. To improve production efficiency and reduce slag-forming costs, steel companies retain a portion of the slag from the previous heat's final stage in the converter as the starting slag for the next heat. The purpose of retaining the slag is to utilize the high basicity, high iron oxide content, and physical heat of the previous heat's final slag to accelerate the slag-forming process in the early stages of the next heat, improving dephosphorization and desulfurization efficiency and reducing the consumption of slag-forming materials such as lime. To prevent excessive slag volume from causing splashing, some slag is poured out during blowing, and then slag-forming materials are added again for repeated slag formation. This operating mode, known as "slag retention and double slag," typically involves rapid slag formation and preliminary dephosphorization in the early stages of smelting, based on the iron composition and smelting requirements. After reaching a certain stage, some slag is poured out to remove harmful elements such as phosphorus and reduce the iron oxide content. Then, lime and other slag-forming materials are added again, and smelting continues until the final stage, ensuring the steel composition and temperature meet the target requirements.

[0003] Many steelmaking enterprises use dry dust removal systems. During the smelting process, when the gas analyzer detects that the carbon monoxide concentration in the pipeline is >9% and the oxygen concentration is >6%, the converter dry dust removal system will interlock and force the converter to stop oxygen blowing (i.e., raise the lance) to ensure the safe operation of the equipment, thereby reducing the probability of system "explosion" and avoiding affecting the normal steelmaking process. At the beginning of oxygen blowing smelting, oxygen preferentially oxidizes elements such as silicon and manganese in the molten iron, releasing a large amount of heat and causing the furnace temperature to rise rapidly. As the temperature rises, carbon in the molten iron begins to react with oxygen. Because the oxygen is sufficient at this time, some carbon is completely burned to produce carbon dioxide, i.e., C + O2 = CO2. However, as the carbon-oxygen reaction proceeds, the oxygen distribution in the furnace becomes uneven. In the area where the oxygen stream is in contact with the molten metal droplets, the oxygen concentration is high, and the carbon-oxygen reaction is vigorous, mainly producing carbon dioxide. In the area inside the molten metal and far from the oxygen stream, the oxygen concentration is lower, and the temperature rises further, with the carbon-oxygen reaction mainly producing carbon monoxide, the reaction equation being 2C + O2 = 2CO. Simultaneously, carbon dioxide reacts with high-temperature carbon (CO2 + C = 2CO), which also increases the amount of carbon monoxide generated. After the slag is discharged in the "slag-retaining double-slag" operation, the oxygen lance will be lowered again for blowing. If the timing of slag discharge is not chosen properly, i.e., the reaction of elements such as silicon and manganese in the early stage has ended and the temperature is too high, the carbon-oxygen reaction is violent, generating carbon monoxide. At this time, the instantaneous gas composition in the pipeline is air, with an oxygen concentration >6% and a carbon monoxide concentration >9%, resulting in a "leakage explosion" accident.

[0004] Currently, in the slag-retaining double-slag process, oxygen is purged again after slag removal. At the moment the purging begins, some oxygen does not fully participate in the reaction and remains in the pipeline, resulting in an oxygen concentration greater than 9 mg / L. 3 / h, carbon monoxide concentration instantaneously exceeds 6m 3 The problem of high probability of "explosion leakage" accidents caused by / h is addressed by proposing a control method to reduce the risk of explosion leakage during secondary oxygen blowing after slag dumping in the slag-retaining double-slag process. Summary of the Invention

[0005] To prevent the occurrence of "explosion" accidents caused by repeated oxygen blowing after slag removal in the "slag-retaining double-slag" process, this invention provides a control method to reduce the risk of explosion during secondary oxygen blowing after slag removal in the slag-retaining double-slag process. This method involves adjusting the oxygen lance position and flow rate, improving the slag-forming mode, and optimizing the temperature regime to reduce the concentration of oxygen and carbon monoxide, thereby lowering the "explosion" accident rate. To prevent the re-oxygenation after slag removal, it is crucial to prevent residual oxygen in the pipeline from not fully participating in the reaction at the moment of starting the blowing. Additionally, since oxygen blowing stops during the slag removal process, the pipeline has already been in full contact with air, and the oxygen concentration in the pipeline is close to the oxygen concentration in the air, also remaining in the pipeline. If the oxygen concentration is greater than 9 mg / L... 3 / h, and the carbon monoxide concentration instantaneously exceeds 6m 3If the temperature is too high ( / h), it can easily lead to a leak or explosion. Furthermore, excessively high molten iron temperatures accelerate the carbon-oxygen reaction, promoting the rapid formation of carbon monoxide. Therefore, strict control of molten iron conditions before slag removal is necessary. According to one aspect of the present invention, a method for controlling the secondary oxygen blowing and explosion venting after slag removal in a slag-retaining dual-slag process is provided, the method comprising the following steps: Step 1, Pre-smelting stage: Mix scrap steel with molten iron, adjust the position of the oxygen lance and perform smelting I; Step 2, Mid-stage of smelting: After the molten iron is ignited, add the first batch of slag-forming material to control the basicity to 1.1~1.5, adjust the position of the oxygen lance, maintain a constant oxygen flow rate and carry out smelting II, add iron ore, and smelt until slag is poured off; Step 3, late stage of blowing: After slag removal, adjust the position of the oxygen lance for blowing III, add two batches of slag-forming material to control the basicity at 2.8~3.0, adjust the position of the oxygen lance and the oxygen flow rate for blowing IV, and tap the steel. Optionally, the mass mixing ratio of scrap steel to molten iron in step 1 is 1:5~7; The temperature of the molten iron in step 1 is 1250~1450℃; The mass concentrations of C, Si, Mn, P, and S in the molten iron are 3.8–4.3%, 0.3–0.5%, 0.15–0.20%, 0.07–0.12%, and 0.005–0.03%, respectively. In step 1, the oxygen lance is positioned 1.6 to 1.8 meters above the molten iron surface; In step 1, the oxygen flow rate for blowing I is 34000~36000 Nm. 3 / h; The blowing time in step 1 is 10~20s.

[0006] Optionally, the mass mixing ratio of scrap steel and molten iron in step 1 is independently selected from any value among 1:5.0, 1:5.1, 1:5.2, 1:5.3, 1:5.4, 1:5.5, 1:5.6, 1:5.7, 1:5.8, 1:5.9, 1:6.0, 1:6.1, 1:6.2, 1:6.3, 1:6.4, 1:6.5, 1:6.6, 1:6.7, 1:6.8, 1:6.9, and 1:7.0, or a range between any two of the above points.

[0007] Optionally, in step 2, the oxygen lance is positioned 1.8 to 2.2 meters above the molten iron surface; The blowing time in step 2 is 2.5~5 minutes; In step 2, the oxygen flow rate is 28,000~35,000 Nm³. 3 / h; Before the slag is dumped in step 2, the oxygen content in the pipeline is 0~1 mg / L. 3 / h; The carbon monoxide content in the pipeline is 0~0.1m. 3 / h; The temperature of the molten iron is 1400~1480℃.

[0008] Optionally, during the blowing process described in step 1, the slag-forming materials described in steps 2 and 3 are CaO and CaMg(CO3)2; In step 2, the amount of the first batch of slag-forming material added is 0-1% of the molten iron.

[0009] Optionally, the amount of iron ore added in step 2 is 0.3 to 0.7% of the molten iron.

[0010] Optionally, the tilting angle of the slag being poured in step 2 is 90°~100°; The time for pouring the slag is 0.5 to 2 minutes.

[0011] Optionally, the blowing conditions for blowing in step 3 (Blowing III) are as follows: The oxygen lance is positioned 2-2.2m above the molten iron surface; The blowing time is 10-20 seconds; The oxygen flow rate during smelting is 26,000~28,000 Nm³. 3 / h.

[0012] Optionally, the conditions for the blowing IV described in step 3 are as follows: The oxygen lance is positioned 1.8 to 2.0 meters above the molten iron surface; The blowing time is 7-10 minutes; The oxygen flow rate during smelting is 28,000~35,000 Nm³. 3 / h.

[0013] Optionally, the amount of the second batch of slag-forming material added in step 3 is 3 to 6% of the molten iron.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The technical solution provided by the present invention reduces the concentration of oxygen and carbon monoxide by adjusting the position and flow rate of the oxygen blowing gun, improving the slag forming mode, and optimizing the temperature system. The number of "explosion leakage" accidents has been reduced from 84 per 100 furnaces to 27 after optimization, effectively reducing the "explosion leakage" accident rate.

[0015] (2) Through the technical solution provided by the present invention, the oxygen lance stop blowing time after the "explosion" accident is reduced from 7.49 min to 1.82 min, the waiting time is significantly reduced, and the effective operation rate of the converter is guaranteed.

[0016] (3) With the technical solution provided by the present invention, the converter blowing time has not changed significantly, but the dephosphorization rate of the slag in the converter has increased by 0.68% compared with the previous one, ensuring the final component qualification rate of the molten steel. Attached Figure Description

[0017] Figure 1 The flowcharts are of the control methods used in embodiments 1-3 of the present invention. Detailed Implementation

[0018] The present invention will be further described below with reference to specific embodiments, but this does not limit the present invention in any way.

[0019] In the examples, the alkalinity is calculated as CaO / SiO2, where CaO originates from the decomposition of CaO and CaMg(CO3)2, and SiO2 is generated from the oxidation of Si in molten iron. Unless otherwise specified, all reagents and raw materials used in the embodiments and comparative examples of this invention were obtained through purchase. The molten iron used in this embodiment of the invention is obtained by self-production in a blast furnace.

[0020] Example 1 Pre-smelting stage: 24 tons of scrap steel were mixed with 132 tons of molten iron (the molten iron had a C concentration of 4.13%, a Si concentration of 0.37%, a Mn concentration of 0.16%, a P concentration of 0.088%, a S concentration of 0.018%, and a temperature of 1318℃) for iron mixing. Immediately after iron mixing, the oxygen lance was adjusted to be 1.8 meters above the molten iron surface, and the oxygen flow rate was 35000 Nm³. 3 / h, blow for 14 seconds.

[0021] Mid-stage of blowing: After the molten iron ignites, add 450 kg CaO and 200 kg CaMg(CO3)2 from the first batch of slag-forming materials, adjust the basicity to 1.2 and the magnesium oxide content to 6%. After blowing for 1.8 minutes, adjust the oxygen lance to 2.2 meters above the molten iron surface and maintain an oxygen flow rate of 32,000 m³ / h. 3 The blowing process lasts for 3.6 minutes per hour, with 700 kg of iron ore added and continued until slag is discharged. Before slag discharge, the oxygen content in the pipeline is 0.20 mg / L. 3 / h, carbon monoxide content is 0m 3 / h, molten iron temperature 1443℃; use a tilting angle of 96° to pour slag for 1.5 minutes until the slag is completely poured out, and bright molten iron can be seen.

[0022] Late stage of smelting: After slag removal, readjust the oxygen lance to 2.2 meters above the molten iron surface, and set the oxygen flow rate to 28000 Nm. 3After blowing for 15 seconds, add 3700 kg CaO and 1400 kg CaMg(CO3)2 in two batches of slag-forming materials, adjust the basicity to 2.8, adjust the oxygen lance to be 1.9 m above the molten iron surface, and adjust the oxygen flow rate to 34500 Nm. 3 / h, blowing for 7.4min until the steel composition is qualified (dephosphorization rate 86.61%), then stop blowing. The flow chart of the control method used in this embodiment is as follows. Figure 1 As shown in Table 1, the blowing conditions and number of explosion venting times of this method are as follows.

[0023] Example 2 Pre-smelting stage: 22 tons of scrap steel were mixed with 133 tons of molten iron (the molten iron had a C concentration of 4.08%, a Si concentration of 0.36%, a Mn concentration of 0.16%, a P concentration of 0.09%, a S concentration of 0.017%, and a temperature of 1315℃) for iron mixing. Immediately after iron mixing, the oxygen lance was adjusted to be 1.8 meters above the molten iron surface, and the oxygen flow rate was 35000 Nm³. 3 / h, blow for 13 seconds.

[0024] Mid-stage of blowing: After the molten iron ignites, add 400 kg of the first batch of slag-forming material (CaO) to adjust the basicity to 1.3 and the magnesium oxide content to 6%. After blowing for 1.9 minutes, adjust the oxygen lance to 2.2 m above the molten iron surface and maintain an oxygen flow rate of 32,000 m³ / h. 3 / h blowing process 2.9 Add 700kg iron ore and blow until slag is discharged. Before slag discharge, the oxygen content in the pipeline is 0.180m. 3 / h, carbon monoxide content is 0m 3 / h, molten iron temperature 1440℃; stop oxygen blowing, tilt at an angle of 96° for 1.2 minutes to pour slag until all slag is poured out, and bright molten iron can be seen pouring slag.

[0025] Late stage of smelting: After slag removal, readjust the oxygen lance to 2.1 meters above the molten iron surface, and set the oxygen flow rate to 27,000 Nm³. 3 After blowing for 12 seconds, add 3500 kg CaO and 1620 kg CaMg(CO3)2 in two batches of slag-forming materials, adjust the basicity to 2.8, adjust the oxygen lance to be 2.0 m above the molten iron surface, and adjust the oxygen flow rate to 33000 Nm³. 3 / h, blowing for 9 minutes until the steel composition is qualified (dephosphorization rate 85.52%), then stopping the blowing. The flow chart of the control method used in this embodiment is as follows. Figure 1 As shown in Table 1, the blowing conditions and number of explosion venting times of this method are as follows.

[0026] Example 3 Pre-smelting stage: 24 tons of scrap steel were mixed with 132 tons of molten iron (the molten iron had a C concentration of 4.09%, a Si concentration of 0.4%, a Mn concentration of 0.15%, a P concentration of 0.094%, a S concentration of 0.017%, and a temperature of 1322℃) for iron mixing. Immediately after iron mixing, the oxygen lance position was adjusted for smelting. During smelting, the oxygen lance was 1.8 meters above the molten iron surface, and the oxygen flow rate was 35,000 Nm³. 3 / h, blow for 12 seconds.

[0027] Mid-stage of smelting: After the molten iron ignites, add 200 kg of the first batch of slag-forming materials, CaO and 200 kg of CaMg(CO3)2, adjust the basicity to 1.2, and the magnesium oxide content to 7%. After blowing for 2 minutes, add 700 kg of iron ore and continue blowing until the slag is poured. Before pouring the slag, the oxygen content in the pipeline is 0.070 mg / L. 3 / h, carbon monoxide content is 0m 3 / h, molten iron temperature 1435℃; use a tilting angle of 96° to pour slag for 1.6 minutes until the slag is completely poured out, and bright molten iron can be seen.

[0028] Late stage of blowing: After slag removal, readjust the oxygen lance to 2.2 meters above the molten iron surface, and set the oxygen flow rate to 27500 Nm. 3 After blowing for 12 seconds, add two batches of slag-forming materials: 3700 kg CaO and 1200 kg CaMg(CO3)2. Adjust the basicity to 2.8, position the oxygen lance 2.0 m above the molten iron surface, and adjust the oxygen flow rate to 34000 Nm³. 3 / h, blowing for 8 minutes until the steel composition is qualified (dephosphorization rate 86.11%), then stopping blowing. The flow chart of the control method used in this embodiment is as follows. Figure 1 As shown in Table 1, the blowing conditions and number of explosion venting times of this method are as follows.

[0029] Comparative Example The difference from Example 1 lies in the fact that, during the addition of slag-forming materials (before and after slag removal), the oxygen lance position, oxygen flow rate, slag-forming mode, temperature control, and the selection of an appropriate slag removal timing (i.e., after the silicon and manganese in the molten iron have completely oxidized, but the pipeline has stopped blowing oxygen during the slag removal process, and the pipeline is already in full contact with air, with the oxygen concentration in the pipeline approaching the oxygen concentration in the air) were not adjusted. When the oxygen lance is restarted after slag removal, carbon and oxygen react, instantly generating a large amount of carbon monoxide. Therefore, explosion accidents are highly likely to occur. The blowing conditions and the number of explosions are shown in Table 1, indicating that the technical solution of this embodiment can meet the dephosphorization rate requirements in production. The number of explosions is reduced from 84 per 100 heats to 27 per 100 heats. The average shutdown time is shortened from 7.49 minutes to 1.82 minutes, which can greatly improve production efficiency.

[0030] Table 1. Blowing conditions and number of explosion venting events in Examples 1-3 and the comparative examples.

[0031] The above description is merely a few embodiments of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any modifications or alterations made by those skilled in the art without departing from the scope of the technical solution of the present invention using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for controlling the reduction of secondary oxygen blowing and explosion venting after slag removal in a slag-retaining double-slag process, characterized in that, The control method includes the following steps: Step 1, Pre-smelting stage: Mix scrap steel with molten iron, adjust the position of the oxygen lance and perform smelting I; Step 2, Mid-stage of smelting: After the molten iron is ignited, add the first batch of slag-forming material to control the basicity to 1.1~1.5, adjust the position of the oxygen lance, maintain a constant oxygen flow rate and carry out smelting II, add iron ore, and smelt until slag is poured off; Step 3, late stage of blowing: After slag removal, adjust the position of the oxygen lance for blowing III, add two batches of slag-forming material to control the basicity at 2.8~3.0, adjust the position of the oxygen lance and the oxygen flow rate for blowing IV, and tap the steel; The mass mixing ratio of scrap steel to molten iron in step 1 is 1:5~7; The temperature of the molten iron in step 1 is 1250~1450℃; The mass concentrations of C, Si, Mn, P, and S in the molten iron are 3.8–4.3%, 0.3–0.5%, 0.15–0.20%, 0.07–0.12%, and 0.005–0.03%, respectively. In step 1, the oxygen lance is positioned 1.6 to 1.8 meters above the molten iron surface; In step 1, the oxygen flow rate for blowing I is 34000~36000 Nm. 3 / h; The blowing time in step 1 is 10~20s; In step 2, the oxygen lance is positioned 1.8 to 2.2 meters above the molten iron surface; The blowing time in step 2 is 2.5~5 minutes; In step 2, the oxygen flow rate is 28,000~35,000 Nm³. 3 / h; Before the slag is dumped in step 2, the oxygen content in the pipeline is 0~1 mg / L. 3 / h; The carbon monoxide content in the pipeline is 0~0.1m. 3 / h; The temperature of the molten iron is 1400~1480℃; During the blowing process described in step 1, the slag-forming materials described in steps 2 and 3 are CaO and CaMg(CO3)2; In step 2, the amount of the first batch of slag-forming material added is 0-1% of the molten iron. The blowing conditions for blowing III in step 3 are as follows: The oxygen lance is positioned 2-2.2m above the molten iron surface; The blowing time is 10-20 seconds; The oxygen flow rate during smelting is 26,000~28,000 Nm³. 3 / h.

2. The control method according to claim 1, characterized in that, In step 2, the amount of iron ore added is 0.3 to 0.7% of the molten iron.

3. The control method according to claim 1, characterized in that, The tilting angle for dumping slag in step 2 is 90°~100°; The time for pouring the slag is 0.5 to 2 minutes.

4. The control method according to claim 1, characterized in that, The conditions for refining IV in step 3 are as follows: The oxygen lance is positioned 1.8 to 2.0 meters above the molten iron surface; The blowing time is 7-10 minutes; The oxygen flow rate during smelting is 28,000~35,000 Nm³. 3 / h.

5. The control method according to claim 1, characterized in that, In step 3, the amount of the second batch of slag-forming material added is 3-6% of the molten iron.

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