A method for controlling the sulfur content of molten iron during tapping of a blast furnace

Abstract

This invention discloses a method for controlling the sulfur content of molten iron during blast furnace tapping, belonging to the field of ironmaking technology. This invention achieves efficient desulfurization by optimizing slag composition, adjusting tuyere parameters, controlling the smelting process, and improving the quality of raw materials and fuels. Controlling the MgO mass fraction in the slag to 8%-12% lowers the melting temperature and viscosity, improving fluidity and promoting the desulfurization reaction; strictly controlling FeO in the slag to ≤1.0% reduces heat consumption and sulfur transfer to the molten iron. Reducing the size of the tuyere above the taphole and changing the straight tuyere to an angled tuyere of 5°-7° optimizes airflow distribution and extends the residence time of the molten iron. Appropriately reducing the air inlet area ensures an actual wind speed ≥280m / s and a blast kinetic energy ≥14500Kg·m / s, strengthening the central airflow. At the same time, reduce the pressure difference by 5-10 kPa and the smelting strength by 0.5%-1.0%, select high-quality coke with a post-reaction strength of ≥67%, thermal reactivity of ≤22%, and sulfur content of ≤0.75%, reduce the slow air intake and quickly restore the air volume, stabilize the hearth activity, and improve desulfurization efficiency, thereby ensuring the efficient operation of the blast furnace and the economical smelting of subsequent steelmaking processes.

Description

Technical Field

[0001] This invention belongs to the field of ironmaking technology, specifically relating to a method for controlling the sulfur content of molten iron during the tapping process of a blast furnace. Background Technology

[0002] The sulfur content in blast furnace hot metal has a significant impact on blast furnace operation, hot metal quality, and subsequent steelmaking processes. Controlling the sulfur content in blast furnace hot metal is key to ensuring efficient blast furnace operation, hot metal quality, and the economic efficiency of subsequent steelmaking processes.

[0003] Sulfur reduces the viscosity and surface tension of molten iron, enhancing the wettability of molten iron and carbon bricks, accelerating the interfacial reaction rate, and increasing the mass transfer coefficient of carbon in molten iron. This leads to accelerated carburizing reaction in carbon bricks, causing them to be eroded and embrittled, thus affecting the lifespan of the blast furnace hearth. Excessive sulfur content may cause uneven temperature distribution in the hearth, leading to localized overheating or undercooling, affecting hearth activity, and even causing problems such as hearth accumulation and slag shedding, reducing the smooth operation of the blast furnace. The higher the sulfur content in molten iron, the more desulfurizing agents (such as magnesium powder and lime) need to be added in the steelmaking process, increasing steelmaking costs and potentially affecting the quality of molten steel, such as forming sulfide inclusions and reducing the toughness, ductility, and other properties of the steel.

[0004] Therefore, controlling the sulfur content in blast furnace molten iron has become an important issue that urgently needs to be addressed. Summary of the Invention

[0005] Therefore, the purpose of this invention is to provide a method for controlling the sulfur content of molten iron during the tapping process of a blast furnace, so as to solve the problem of high sulfur content in molten iron in the prior art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for controlling the sulfur content of molten iron during the tapping process in a blast furnace, comprising the following steps: S1: Reduce the size of the air vent above the iron tap, and change the straight air vent above the iron tap to an angled vent of 5°-7°; S2: After smelting, the molten iron from the blast furnace is discharged from the taphole, passes through the main ditch, and is then separated by the slag skimmer. The molten iron flows into the iron ditch, and the slag flows into the slag ditch. S3: Detect the mass fraction of MgO and FeO in the slag. By increasing the proportion of sintered magnesite powder and controlling the slag temperature to ≥1530℃, the mass fraction of MgO in the slag can be controlled to be 8%-12% and the mass fraction of FeO ≤1.0%.

[0007] Specifically, appropriately reducing the size of the tuyeres above the taphole, from 120mm to 110mm, can effectively suppress edge gas in this area while ensuring sufficient taphole depth, allowing the material feeding speed and slag / iron dripping speed above the taphole to synchronize with other areas. Reducing the air inlet area and increasing the wind speed and blast energy (specifically, wind speed ≥ 280m / s, blast energy ≥ 14500Kg.m / s) promotes the development of central airflow, which is beneficial for improving and balancing desulfurization conditions in the hearth.

[0008] Specifically, appropriately increasing the taphole angle and replacing the straight tuyeres above the taphole with tuyeres at a 5°-7° angle increases the safe iron capacity of the hearth, optimizes airflow distribution, and ensures the residence time of molten iron in the hearth, thus meeting desulfurization requirements. A 5°-7° angle refers to the angle between the airflow direction and the plane where the taphole is located being 5°-7°.

[0009] Controlling the MgO mass fraction in the slag to 8%-12% lowers the melting temperature and viscosity, improving fluidity and promoting the desulfurization reaction. Within this range, the slag has a lower melting temperature and better thermal and chemical stability. A suitable MgO mass fraction in the slag can reduce its melting temperature and viscosity, improve its fluidity and stability, accelerate the diffusion of the reaction product CaS, speed up the desulfurization reaction, and reduce the sulfur content in the molten iron.

[0010] Among these measures, the FeO content in the slag must be strictly controlled to be ≤1.0% to reduce heat consumption and sulfur transfer to the molten iron. Increased FeO in the slag not only increases the consumption of direct reduction heat in the hearth, but also promotes more S— to combine with Fe++ into the molten iron. At the same time, the high viscosity and poor fluidity of the slag also affect the diffusion rate of sulfur from the molten iron to the slag.

[0011] Based on the above technical solution, further, in S1, the difference between the hot air pressure and the furnace top pressure is controlled to be 5-10 kPa lower than the normal difference.

[0012] Based on the above technical solution, the smelting intensity is further reduced by 0.5%-1.0% compared to the normal smelting intensity.

[0013] The smelting intensity value refers to the amount of coke burned per cubic meter of blast furnace per day and night, with a normal smelting intensity of 1.0-1.5.

[0014] Based on the above technical solution, the intake air velocity is ≥280m / s and the blower kinetic energy is ≥14500Kg.m / s.

[0015] Based on the above technical solution, further, the coke post-reaction strength is ≥67%, the coke thermal reactivity is ≤22%, and the coke sulfur content is ≤0.75%.

[0016] Based on the above technical solution, further, during the blast furnace tapping process, the period from the blast furnace shutdown to the blast volume recovering to the full blast level is ≤4 hours.

[0017] Among them, the period from blast furnace shutdown to the return of air volume to full air level should be ≤4 hours to reduce blast furnace shutdown and slow air operation; if the recovery time is too long, the hearth will be in an inactive state for a long time, the working performance of the hearth will deteriorate, the desulfurization efficiency will be greatly reduced, and the sulfur content of molten iron will increase.

[0018] Compared with the prior art, the present invention has the following beneficial effects: This invention achieves efficient desulfurization by optimizing slag composition, adjusting tuyer parameters, controlling the smelting process, and improving the quality of raw materials and fuels. The MgO mass fraction in the slag is controlled at 8%-12%, reducing melting temperature and viscosity, improving fluidity, and promoting the desulfurization reaction. FeO in the slag is strictly controlled to ≤1.0%, reducing heat consumption and sulfur transfer to the molten iron. The tuyeres above the taphole are reduced in size, and the straight tuyeres are changed to angled tuyeres at 5°-7°, optimizing airflow distribution and extending the residence time of the molten iron. The air inlet area is appropriately reduced to ensure an actual wind speed ≥280m / s and a blast kinetic energy ≥14500Kg·m / s, strengthening the central airflow. Simultaneously, the pressure difference is reduced by 5-10KPa, the smelting strength by 0.5%-1.0%, and high-quality coke with a post-reaction strength ≥67%, thermal reactivity ≤22%, and sulfur content ≤0.75% is selected. This reduces slow-moving airflow and quickly restores air volume, stabilizing hearth activity and improving desulfurization efficiency, thereby ensuring efficient blast furnace operation and economical smelting in subsequent steelmaking processes. Detailed Implementation

[0019] The present invention will be described in detail below with reference to the embodiments. However, the implementation of the present invention is not limited thereto. Obviously, the embodiments described below are only some embodiments of the present invention. For those skilled in the art, other similar embodiments can be obtained without creative effort and all fall within the protection scope of the present invention.

[0020] Example 1 This embodiment 1 uses a method to control the sulfur content of molten iron during the blast furnace tapping process. A large blast furnace is used, and the specific process is as follows: Using sintered ore and pelletized ore as raw materials, with sintered ore accounting for 70%-80% and pelletized ore accounting for 20%-30%, iron ore is smelted. During the smelting process, coke with a sulfur content of ≤0.75% is used, and the strength of the coke after reaction is ≥67%, and the thermal reactivity of the coke is ≤22%. Reduce the size of the tuyeres above the taphole, ensuring an inlet air velocity ≥280 m / s and a blower kinetic energy ≥14500 kg·m / s. Change the straight tuyeres above the taphole to a 5° angled tuyeres. Control the difference between the hot blast pressure and the furnace top pressure to be 5 kPa lower than the normal difference, specifically 475 kPa (normal is 480 kPa). Reduce the smelting intensity by 0.5% compared to the normal smelting intensity, specifically 0.95 (normal is 1).

[0021] After smelting, the molten iron from the blast furnace is discharged from the taphole, passes through the main ditch, and is then separated by a skimmer. The molten iron flows into the iron ditch, and the slag flows into the slag ditch. The mass fractions of MgO and FeO in the slag were measured. By increasing the proportion of sintered magnesite powder and controlling the slag temperature to ≥1530℃, the mass fractions of MgO and FeO in the slag were controlled to be 8% and ≤1.0%, respectively, before continuing blast furnace tapping. The sulfur content of the obtained molten iron was ≤0.030%.

[0022] Example 2 The difference between this embodiment and Embodiment 1 is as follows: the straight tuyeres above the taphole are changed to a 7° angle, and the difference between the hot blast pressure and the furnace top pressure is controlled to be 10 kPa lower than the normal difference, specifically 470 kPa (normal is 480 kPa). The smelting intensity is reduced by 1.0% compared to the normal smelting intensity, specifically 0.9 (normal is 1). The MgO mass fraction in the slag is controlled to be 12%.

[0023] The sulfur content of the molten iron obtained was ≤0.030%.

[0024] Example 3 The difference between this embodiment and embodiment 1 is that: during the blast furnace tapping process, the blast is stopped, and the blast volume is restored to the full blast level within 4 hours after the blast furnace stops.

[0025] The sulfur content of the molten iron obtained was ≤0.030%.

[0026] Comparative Example 1 The difference between this comparative example and Example 1 is that the method of controlling the sulfur content of molten iron during the blast furnace tapping process was not used.

[0027] The sulfur content of the molten iron obtained was ≤0.055%.

[0028] Comparative Example 2 The difference between this comparative example and Example 3 is that the air volume was not restored to full air volume within a 4-hour period.

[0029] The sulfur content of the molten iron obtained was ≤0.055%.

[0030] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for controlling the sulfur content of molten iron during blast furnace tapping, characterized in that, Includes the following steps: S1: Reduce the size of the air vent above the iron tap, and change the straight air vent above the iron tap to an angled vent of 5°-7°; S2: After smelting, the molten iron from the blast furnace is discharged from the taphole, passes through the main ditch, and is then separated by the slag skimmer. The molten iron flows into the iron ditch, and the slag flows into the slag ditch. S3: Detect the mass fraction of MgO and FeO in the slag. By increasing the proportion of sintered magnesite powder and controlling the slag temperature to ≥1530℃, the mass fraction of MgO in the slag can be controlled to be 8%-12% and the mass fraction of FeO ≤1.0%.

2. The method for controlling the sulfur content of molten iron during blast furnace tapping according to claim 1, characterized in that, In S1, the difference between the hot air pressure and the furnace top pressure is controlled to be 5-10 kPa lower than the normal difference.

3. The method for controlling the sulfur content of molten iron during blast furnace tapping according to claim 1, characterized in that, The smelting intensity is reduced by 0.5%-1.0% compared to the normal smelting intensity.

4. The method for controlling the sulfur content of molten iron during blast furnace tapping according to claim 1, characterized in that, Inlet air velocity ≥280m / s, blower kinetic energy ≥14500Kg.m / s.

5. The method for controlling the sulfur content of molten iron during blast furnace tapping according to claim 1, characterized in that, The coke produced during smelting has a post-reaction strength of ≥67%, a thermal reactivity of ≤22%, and a sulfur content of ≤0.75%.

6. The method for controlling the sulfur content of molten iron during blast furnace tapping according to claim 1, characterized in that, During the blast furnace tapping process, the period from the blast furnace shutdown to the blast volume recovering to the full blast level is ≤4 hours.