A method of controlling the consistency of the slag of a bottom powder injection converter to prevent initial spitting

Abstract

The application discloses a method for controlling the viscosity of bottom powder injection converter slag to prevent initial splashing, wherein the change of CO2 concentration in smoke gas is monitored during the converter smelting process, when the CO2 concentration appears and reaches a peak value, lime powder is injected from the bottom, the flow of the bottom powder injection is controlled at 400-600 kg / min, and lasts for 5-8 seconds, and 2-3 tons of small particle lime is added into the furnace at the same time. The method judges the lime adding time by monitoring the change of CO2 concentration in smoke gas, and does not need to pretend other equipment, and is simple, reliable and practical. According to the change rule of the initial slag, the viscosity of the initial slag is controlled reasonably to prevent the sudden splashing of the converter in the initial stage, and the production accidents caused by the too low viscosity of the slag are avoided. The method realizes the control of the viscosity of the bottom powder injection converter slag, effectively prevents the slag splashing, improves the safety of the smelting process, and improves the smelting efficiency and product quality.

Description

Technical Field

[0001] This invention relates to a converter smelting method, and more particularly to a method for controlling the viscosity of bottom-injected powder converter slag to prevent initial splashing. Background Technology

[0002] Converter smelting is a common method for steelmaking. Its basic principle is to use oxygen jets to stir and oxidize the molten pool, causing a series of physicochemical reactions in the iron to achieve the smelting purpose. The most critical stage in converter smelting is the blowing stage, where the main reactions include silicon-manganese oxidation, decarburization, desulfurization, and dephosphorization. During the oxidation process, the reaction of CaO with Fe under the action of oxygen to form slag is a crucial step.

[0003] Converter slag is a metallurgical byproduct generated during the bottom-injection converter smelting process. The viscosity of the slag has a significant impact on the efficiency and safety of the smelting process. Currently, the main methods for controlling converter slag viscosity include adding auxiliary materials and adjusting process parameters. However, existing methods have some problems and difficulties in controlling converter slag viscosity.

[0004] Currently, there is no direct method to test the viscosity of slag. Excessive slag viscosity can lead to slag agglomeration, reducing dephosphorization rates and resulting in substandard steel with high phosphorus content. Conversely, excessively low viscosity results in high slag surface tension and severe foaming, which can cause slag to overflow from the furnace mouth and even lead to severe splashing.

[0005] In converter smelting, splashing in the early stages of smelting is a difficult-to-prevent production accident, characterized by its unpredictability and suddenness. For bottom-blown oxygen and bottom-powder-injected converters, splashing in the early stages of smelting is even more severe. In conventional converters, if splashing occurs, more serious splashing can be avoided by stopping the blowing process by raising the lance. However, because bottom-blown oxygen and bottom-powder-injected converters use simultaneous top and bottom oxygen blowing, it is impossible to prevent further reaction in the molten pool by stopping the top oxygen blowing alone. At the same time, stopping the bottom oxygen blowing will cause a more serious steel leakage accident.

[0006] Currently, regarding bottom-blown oxygen converters with bottom-injection powder, only Handan Iron and Steel Group in China possesses the equipment and technical capabilities. Therefore, there is no relevant research or report in China on how to prevent splashing in bottom-blown oxygen converters with bottom-injection powder.

[0007] Initial splashing in converter smelting differs from ordinary splashing, manifesting in characteristics such as the flame at the furnace mouth. Because various auxiliary materials are in a molten state during the initial smelting stage, the flame brightness fluctuates greatly and occurs within a short period. This initial splashing often occurs within 20% of the TSC blowing process after the oxygen lance begins blowing, resulting in a high false alarm rate for splashing predictions based on flame characteristics. Therefore, prevention of this type of splashing is not practically feasible. It is difficult to prevent splashing by observing changes in the furnace mouth flame, as described in patent applications such as CN110309973A "A Converter Splashing Prediction Method and System Based on Video Intelligent Algorithm" and CN111104856A "A Converter Smelting Splashing Monitoring Method, System, Storage Medium, and Equipment," because splashing often occurs before the flame characteristics are significant.

[0008] Patent application CN116299480A, "A Method for Calculating Slag Thickness in Converter Steelmaking," describes using slag layer thickness to determine whether splashing occurs, which is a conventional splash prevention method. However, since the initial splashing occurs in the early stage of smelting, slag is being formed when splashing does not occur, and the slag layer is still thin, coupled with the suddenness of splashing, splashing often occurs in just 2 to 3 seconds. Therefore, it is difficult to prevent splashing by changing the slag layer thickness.

[0009] Since the initial splashing occurs in the early stages of smelting, the carbon-oxygen reaction in the molten pool is not intense at this time. Therefore, the initial splashing cannot be analyzed using CO concentration curves as described in patent applications such as CN115976298A "Anti-splashing control process for high-speed iron smelting in converter based on changes in flue gas CO content" and CN113564296A "Splashing early warning method, system and industrial control equipment for steelmaking converters". This is because the CO concentration is still very low when the initial splashing occurs, which is not enough to form the characteristics of splashing. Therefore, the trend of CO concentration curve changes in the early stages of smelting is also difficult to prevent the initial splashing.

[0010] Other splash prevention schemes that adjust the oxygen supply through processes such as oxygen control are based on the core idea of ​​controlling the slag layer thickness. These schemes are suitable for conventional mid-to-late stage converter splash prevention, such as CN116356101A "A High Oxygen Supply Intensity Smelting Process". However, the types of splashes prevented are quite different from the initial splashes that occur in the early stage of smelting. Summary of the Invention

[0011] The technical problem to be solved by the present invention is to provide a method for controlling the viscosity of bottom-sprayed converter slag to prevent initial splashing.

[0012] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: during the converter smelting process, the change of CO2 concentration in the flue gas is monitored. When the CO2 concentration appears and reaches its peak, lime powder is sprayed at the bottom. The flow rate of the bottom spray powder is controlled at 400-600 kg / min and lasts for 5-8 seconds. At the same time, 2-3 tons of small-particle lime are added into the furnace.

[0013] Furthermore, 70% of the total amount of lime and 1 to 2 tons of limestone are added when the mixture is fed into the furnace.

[0014] Furthermore, when the CO2 content in the flue gas decreases to 10%, the flow rate of the bottom spray powder is reduced to 200-300 kg / min, and the bottom spray powder is stopped after 5-10 seconds, switching to normal oxygen blowing.

[0015] Furthermore, the peak value of the CO2 concentration is between 15 and 25 wt%.

[0016] The beneficial effects of adopting the above technical solution are as follows: This invention determines the timing of lime addition by monitoring changes in CO2 concentration in flue gas, eliminating the need for additional equipment; it is simple, reliable, and highly practical. Based on the changing patterns of slag in the early stages of smelting, this invention prevents sudden splashing in the early stages of converter smelting by rationally controlling the viscosity of the slag, thus avoiding production accidents caused by excessively low slag viscosity. The addition of limestone to the auxiliary materials reduces limestone costs, helping steel mills lower production costs. Furthermore, after decomposition in the molten pool, limestone forms CO2 gas, providing a monitoring indicator, and the resulting CaO aids in dephosphorization, without affecting the smelting rhythm or quality. Through this invention, the viscosity of bottom-injected converter slag is controlled, effectively preventing slag splashing, improving not only the safety of the smelting process but also smelting efficiency and product quality. Statistics show that this invention can reduce the probability of initial splashing from 14.3% to less than 0.5%. Detailed Implementation

[0017] The present invention will now be described in further detail with reference to specific embodiments.

[0018] The bottom spraying powder described in this article refers to mixing lime powder into bottom blowing oxygen, with oxygen and lime powder being sprayed together.

[0019] This method for controlling the viscosity of slag in bottom-injected converters to prevent initial splashing is applicable to bottom-injected converters with a hot metal inlet capacity of 240–270 tons, where the converter top lance flow rate is controlled between 0 and 50,000 N. 3 At a pressure of 5 MPa, six annular slit injection pipes with a diameter of 10-15 cm are located at the bottom of the converter. The annular slits are used to inject natural gas (methane), and the central pipe is used to inject oxygen. Sulfated powdered CaO is mixed into the oxygen injected through the central pipe when necessary. A laser flue gas analyzer is installed near the dust collector at the top of the converter to analyze the CO, CO2, H2, and O2 content in the flue gas using spectral analysis. The idea behind this method is to prevent sudden splashing in the early stages of smelting by rationally controlling the viscosity of the slag. The process is described below:

[0020] 1) Preparation of smelting raw materials: During the smelting process, smelting raw materials are prepared according to process requirements. These raw materials include lime (CaO), limestone (CaCO3), scrap steel, and molten iron. The amount of limestone added is 1-2 tons, molten iron 240-260 tons, scrap steel 30-60 tons, lime stock 6-10 tons, and ore stock 2-8 tons. The composition (wt) of the molten iron is: C 4.2%-4.6%, Si 0.01%-0.3%, Mn 0.05%-0.5%, P 0.08%-0.15%, S 0.01%-0.02%, with the balance being Fe and unavoidable impurities. The temperature of the molten iron is 1350-1400℃.

[0021] 2) Slag making: Calculate the total amount of lime to be added according to the basicity requirements. The amount added depends on the silicon content of the molten iron, the P content of the final product, and the actual P content of the molten iron. Add 70% of the total amount of lime into the furnace when it is fed into the furnace, along with 1 to 2.5 tons of limestone.

[0022] 3) Assessing Slag Splash Risk: During converter smelting, monitoring changes in CO2 concentration in the flue gas helps determine slag viscosity and prevent slag splashing. When CaO formed from melted limestone reacts chemically with P, Fe, and oxygen in the molten iron, excessive Fe formation and low slag viscosity can lead to slag splashing. Therefore, reading CO2 concentration changes in the flue gas analyzer indicates whether CaO has decomposed. Based on engineering experience, a peak CO2 concentration occurs after CaCO3 decomposes. When CO2 reaches its peak value (15-25 wt%), it indicates that limestone has decomposed and the added lime has dissolved. At this point, the slag viscosity is low, potentially leading to splashing and other production safety accidents.

[0023] 4) Avoiding initial splashing: After CO2 reaches its peak value in step 3), the bottom-blown oxygen is adjusted to bottom-blown powder, with the powder flow rate controlled at 400–600 kg / min for 5–8 seconds. Simultaneously, small-particle lime with a diameter ≤1 mm is added to the top hopper at a rate of 2–3 tons. This increases the viscosity of the converter slag, reduces its foaming, and prevents splashing. Extensive practical experience has shown that this method, by adjusting the powder flow rate and the amount of small-particle CaO added, effectively avoids slag splashing and improves the safety and stability of the smelting process. The sulfide lime is a special lime for bottom-blown powder converters, obtained by sulfidation of ordinary lime; the sulfide lime has extremely fine particles, ≤200 mesh.

[0024] 5) Track the oxygen content in the flue gas: After bottom injection of powder and addition of small CaO particles in step 4), the CO2 content in the flue gas decreased to 8-12 wt%, indicating that the added CaCO3 had been completely decomposed into CaO. As smelting continues, the carbon content of the molten iron in the pool will continue to decrease. Control the flow rate of bottom injection of powder at 200-300 kg / min, and stop bottom injection after 5-10 seconds, switching to normal bottom blowing oxygen.

[0025] Example 1:

[0026] The molten iron composition (wt) is: C 4.2%, Si 0.01%, Mn 0.05%, P 0.15%, S 0.001%, with a temperature of 1380°C. 250 tons of molten iron are added to the converter; 50 tons of scrap steel are also included. The pressure in the circumferential welded tube is 5 MPa, and the oxygen flow rate is stabilized at 50,000 N at the start of the blowing process. 3 / h; bottom powder spraying flow rate 300Kg / min, lime particle diameter 1mm.

[0027] At the start of the furnace charge, 70% of the total lime content (7 tons of lime CaO) and 2 tons of limestone CaCO3 were added according to the alkalinity requirements. Blowing began at 6:51 AM. At 6:53 AM, the CO2 content reached its peak at 15%, indicating that the CaCO3 had decomposed and the initially added CaO was in a molten state. The slag viscosity was low, posing a significant risk of splashing. At this point, 2 tons of small-particle lime were added to the furnace from the top hopper. Bottom blowing was then initiated with powder injection at a flow rate increased to 600 kg / min for 5 seconds. The CO2 content in the flue gas decreased to 8%, and the flow rate was adjusted to 230 kg / min. Bottom blowing was then stopped after 8 seconds, and normal bottom blowing oxygen was resumed. No abnormal splashing issues occurred during the initial smelting phase of this furnace charge.

[0028] Example 2:

[0029] The molten iron composition is: C 4.6%, Si 0.1%, Mn 0.5%, P 0.08%, S 0.01%, with a temperature of 1350°C. 240 tons of molten iron were added to the converter; 60 tons of scrap steel were also added. The pressure in the circumferential welded tube was 5 MPa, and the oxygen flow rate was stabilized at 47600 N at the start of the blowing process. 3 / h. Bottom powder spraying flow rate 300Kg / min, lime particle diameter 0.8mm.

[0030] At the start of the furnace charge, 70% of the total lime content (9 tons of lime CaO) and 1 ton of limestone CaCO3 were added according to the alkalinity requirements. Blowing began at 5:56 AM. At 5:58 AM, the CO2 content reached its peak at 18%, indicating that the CaCO3 had decomposed and the initially added CaO was in a molten state. The slag viscosity was low, posing a significant risk of splashing. At this point, 3 tons of small-particle lime were added to the furnace from the top hopper for bottom blowing, with the flow rate increased to 400 kg / min for 8 seconds. The CO2 content in the flue gas decreased to 9%, and the flow rate was adjusted to 200 kg / min. Bottom blowing was stopped after 10 seconds, and normal bottom oxygen blowing resumed. No abnormal splashing occurred during the initial smelting phase of this furnace charge.

[0031] Example 3:

[0032] The molten iron composition is: C 4.5%, Si 0.04%, Mn 0.3%, P 0.12%, S 0.008%, molten iron temperature 1400°C, 270 tons of molten iron added to the converter; 30 tons of scrap steel. The circumferential tube pressure is 5 MPa, and the oxygen flow rate is stabilized at 49800 N at the start of blowing. 3 / h. Bottom powder spraying flow rate 300Kg / min, lime particle diameter 0.75mm.

[0033] At the start of the furnace charge, 70% of the total lime content (9 tons of lime CaO) and 2.5 tons of CaCO3 were added according to the alkalinity requirements. Blowing began at 8:24 AM. At 8:28 AM, the CO2 content reached its peak at 22%, indicating that the CaCO3 had decomposed and the initially added CaO was in a molten state. Given the low viscosity of the slag, the risk of splashing was high. At this point, 2.5 tons of lime were added from the top hopper, and bottom blowing was initiated with powder injection at a flow rate increased to 500 kg / min for 6 seconds. The CO2 content in the flue gas decreased to 12%, and the flow rate was adjusted to 300 kg / min. Bottom blowing was then stopped after 8 seconds, and normal bottom blowing oxygen was resumed. No abnormal splashing occurred during the initial smelting phase of this furnace charge.

Claims

1. A method of controlling the consistency of the bottom powder injection converter slag to prevent initial spitting, characterized in that: The change of CO2 concentration in the smoke is monitored in the converter smelting process, when the CO2 concentration appears and reaches a peak, the lime powder is bottom blown, the flow of the bottom blown powder is controlled at 400-600 kg / min, lasts for 5-8 s, and 2-3 tons of small particle lime is added into the furnace at the same time; 70% of the total amount of lime added into the furnace, and 1-2 tons of limestone.

2. A method of controlling the consistency of the slag of a bottom powder injection converter to prevent initial spitting according to claim 1, characterized in that: When the CO2 content in the smoke is reduced to 10%, the flow of the bottom blown powder is reduced to 200-300 kg / min, the bottom blown powder is ended after 5-10 s, and the normal oxygen blowing is converted.

3. A method of controlling the consistency of the slag of a bottom powder injection converter to prevent initial spitting according to claim 1 or 2, characterized in that: The peak of the CO2 concentration is at 15-25 wt%.