Efficient converter slagging process based on magnesite

Abstract

The invention discloses a magnesite-based converter high-efficiency slagging process, magnesite is decomposed at high temperature to generate MgO and CO. MgO can increase the MgO content of slag, improve the fluidity of the slag and reduce erosion to a furnace lining, and meanwhile, desulfurization and dephosphorization are facilitated, the slagging efficiency is improved, the production cost is reduced, and the environmental pollution is reduced. In the scrap steel adding and iron blending period, after scrap steel is added, a composite slag former accounting for 30-50% of the total amount is added, magnesite is pre-sintered through physical heat of molten iron in the iron blending process, and the magnesite is promoted to be decomposed to generate CO2; in the initial blowing stage, a composite slag former accounting for 30-35% of the total amount is added, decomposition of the magnesite is promoted through the initial high temperature, and part of CO participates in the decarburization reaction of C + CO2-2CO; and in the middle stage of blowing, the remaining slag former and fluorite CaF are mixed and sprayed in through a blowing system according to the mass ratio of (10-12): 1, splashing is inhibited, and the splashing rate is reduced to 5% or below.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of metallurgy, and particularly relates to a converter efficient slagging process based on magnesite. BACKGROUND

[0002] Converter steelmaking is one of the main processes of modern steel production, and its core is to remove the impurities such as carbon, silicon, phosphorus and sulfur in molten iron by oxygen blowing. In the steelmaking process, the composition and properties of the slag have an important influence on the quality of the molten steel, the service life of the furnace lining and the smelting efficiency. The traditional slagging material mainly uses lime (CaO) and dolomite (CaMg(CO3)2), and magnesite (MgCO3) as a mineral rich in magnesium oxide (MgO) has gradually attracted attention in converter steelmaking in recent years. The present application particularly relates to a slagging method in which magnesite is used to replace part of the traditional flux (such as dolomite or light burned magnesium ball) in the converter steelmaking process. Magnesite decomposes to generate MgO and CO2 at high temperatures, MgO can increase the MgO content of the slag, improve the fluidity of the slag, reduce the erosion of the furnace lining, and at the same time help to remove sulfur and phosphorus, improve the slagging efficiency, reduce the production cost and reduce environmental pollution.

[0003] Traditional converter slagging mainly relies on dolomite, lime and light burned dolomite, but there are the following problems: light burned dolomite has a high cost (market price about 600-800 yuan / ton), and the MgO content fluctuates greatly (15%-25%), which increases the smelting cost, and at the same time, the MgO content in the slag is low and unstable (usually 4%-7%), which affects the service life of the furnace lining. Although magnesite (MgCO3) is a cheap magnesium source (price about 300-500 yuan / ton, MgO content ≥45%), but direct addition to the converter can cause the melting pool temperature to drop due to the endothermic decomposition (ΔH=118 kJ / mol), and the CO2 produced by the decomposition can exacerbate spattering. SUMMARY

[0004] The present application provides a converter efficient slagging process based on magnesite, which solves the problems of temperature drop and spattering in the magnesite slagging process, improves the slagging efficiency, and at the same time, reduces the cost.

[0005] 1. Technical solution 1.1 Raw material pretreatment Crush the magnesite to 5~20mm particles (experiments show that the decomposition rate is best in this particle size range), and mix it with limestone at a mass ratio of 1:(0.3~0.6) to form a composite slagging agent.

[0006] 1.2 Staged addition method During the addition of scrap steel and iron, add 30-50% of the total amount of the composite slagging agent after the addition of scrap steel, use the physical heat of the molten iron during the iron addition process to pre-sinter the magnesite, and promote the decomposition of the magnesite to produce CO2.

[0007] Early blowing stage (5-12 minutes): Add 30-35% of the total amount of composite slagging agent, use the initial high temperature (≥1550℃) to promote the decomposition of magnesite, and CO2 participates in the decarburization reaction (C + CO2→ 2CO).

[0008] ‌Mid-stage blowing (5-12 minutes): The remaining slagging agent is mixed with fluorite (CaF2) by a mass ratio of 10-12:1 and sprayed into the furnace, and the splashing is inhibited (the splashing rate is reduced to below 5%).

[0009] 2. Process parameter optimization Control the temperature of the molten pool to be greater than or equal to 1600℃ (experimental data show that the MgO dissolution rate is greater than or equal to 95% at this temperature); dynamically adjust the oxygen supply intensity of the oxygen lance (3.5~5.0 Nm³ / min·t) to balance the CO2 release and decarburization efficiency.

[0010] 3. Supporting system 3.1 Magnesite-limestone mixing bin: equipped with a screw stirrer (rotation speed 20-30 rpm), and the uniformity of mixing is greater than or equal to 98%.

[0011] 3.2 Intelligent injection sub-system: based on sonar signal feedback to adjust the injection rate in real time (error ±2%).

[0012] The beneficial effects of the present application are: MgO can increase the basicity of the slag, promote the transfer of sulfur (S) from the molten steel to the slag, form stable MgS or CaS, at the same time, high basicity slag is beneficial to the oxidation and removal of phosphorus (P), MgO can stabilize the structure of the slag and improve the dephosphorization efficiency, through tests, the desulfurization rate of the 50-ton converter of Jiusteel is increased from 31% to 37% after using magnesite, the end point phosphorus content is reduced by 0.003% (from 0.018% to 0.015%), in addition, magnesite will decompose to produce CO2 in a high temperature environment, increase the stirring of the molten pool, improve the reaction rate of the molten pool, and reduce the oxygen consumption by 2.8 Nm³ / t. DETAILED DESCRIPTION

[0013] The present application will be further described below in conjunction with specific embodiments: 1. Technical solution 1.1 Raw material pretreatment Crush the magnesite to 5~20mm particles (experimental results show that the decomposition rate is best in this particle size range), and mix it with limestone at a mass ratio of 1:(0.3~0.6) to form a composite slagging agent.

[0014] 1.2 Staged addition method During the process of adding scrap steel to iron: After the scrap steel is added, add 30-50% of the total amount of composite slagging agent. Utilize the physical heat of the molten iron during the iron-making process to pre-sinter the magnesite and promote the decomposition of the magnesite to produce CO2.

[0015] In the initial stage of blowing (5-12 minutes): add 30% of the total amount of composite slagging agent, and use the initial high temperature (≥1550℃) to promote the decomposition of magnesite, and CO2 partially participates in the decarbonization reaction (C + CO2 → 2CO).

[0016] Mid-stage of blowing (5-12 minutes): The remaining 20% ​​of the slagging agent is mixed with fluorite (CaF2) at a mass ratio of 10:1 and injected through the blowing system to suppress splashing (the splashing rate is reduced to below 5%).

[0017] 2. Process parameter optimization Control the molten pool temperature to ≥1600℃ (experimental data show that the MgO melting rate is ≥95% at this temperature); dynamically adjust the oxygen supply intensity of the oxygen lance (3.5~5.0 Nm³ / min·t) to balance CO2 release and decarbonization efficiency.

[0018] 3. Supporting Systems 3.1 Magnesite-limestone mixing chamber: equipped with a spiral agitator (speed 20-30 rpm), with a mixing uniformity of ≥98%.

[0019] 3.2 Intelligent jetting subsystem: The jetting rate is adjusted in real time based on sonar signal feedback (error ±2%).

[0020] 4. Beneficial effects 4.1 Economic efficiency Magnesite replaces 100% lightly calcined dolomite, reducing flux cost per ton of steel by 18% (the cost of the traditional method is 39.3 yuan / ton of steel, while this invention reduces it to 31.1 yuan / ton of steel); slag consumption is reduced by 20% (from 75 kg / ton of steel to 50 kg / ton of steel).

[0021] 4.2 Environmental friendliness CO2 emissions are reduced by 10% (conventional methods emit 15 kg / ton of steel, while this invention reduces it to 13.5 kg / ton of steel); the splashing rate is reduced from 15% to 4%.

[0022] 4.3 Slag Properties The MgO content in the final slag is stable at 8.0±0.5% (compared to a fluctuation range of 5%-7% using traditional methods); the furnace lining life is extended by 14% (from 13,500 heats to 15,400 heats).

[0023] 2.1 Slag Modification Effect In converter steelmaking, the MgO content of the slag has a significant impact on its viscosity, melting point, and stability. Traditional slag-forming materials (such as lime) mainly provide CaO, while the addition of magnesite can supplement MgO, forming a MgO-CaO-SiO2-FeO system in the slag, thus improving its basicity and fluidity. Tests conducted at Jiuquan Iron & Steel's 50t converter showed (Table 1) that adding 600 kg / furnace of magnesite increased the slag MgO content from 5.2% to 8.8%, lowered the slag melting point by 30°C, and reduced the total iron (T.Fe) content in the slag by 2.9%. The cost of auxiliary materials per ton of steel decreased from 29.5 yuan / ton to 24 yuan / ton.

[0024] Table 1 - Effect of different magnesite addition amounts on slag composition Addition ratio (kg) MgO (%) CaO (%) SiO2(%) (T.Fe) (%) Slag melting point 0 5.2 48.6 15.3 18.2 1460 400 7.1 46.8 14.9 16.8 1445 500 7.8 45.2 14.5 15.9 1440 600 8.8 43.1 14.0 15.3 1430 2.2 Furnace lining protection effect Converter linings are typically made of magnesia-carbon bricks (MgO-C), but they are susceptible to erosion under high temperatures and acidic slag. MgO produced from the decomposition of magnesite can increase the MgO saturation in the slag, reducing slag penetration and dissolution of the lining, thereby reducing lining wear. Industrial tracking data from Jiuquan Iron & Steel's 50-ton converter shows that after adopting magnesite: the lining erosion rate decreased from 0.35 mm / heat to 0.22 mm / heat (a 37% reduction), the furnace life increased from an average of 13,000 heats to 15,400 heats, and the cost of refractory materials per ton of steel decreased from 9.8 yuan to 7.1 yuan.

Claims

1. A high-efficiency slag-forming process for converters based on magnesite, characterized in that... Includes the following steps: I. Raw Material Pretreatment Magnesite is crushed into 5-20mm particles and mixed with limestone at a mass ratio of 1:(0.3-0.6) to form a composite slag-forming agent; II. Phased Joining Method During the process of adding scrap steel to iron: After the scrap steel is added, add 30-50% of the total amount of composite slagging agent. Utilize the physical heat of the molten iron during the iron-making process to pre-sinter the magnesite and promote the decomposition of the magnesite to produce CO2. In the initial stage of smelting: add 30-35% of the total amount of composite slagging agent to promote the decomposition of magnesite by utilizing the initial high temperature. CO2 partially participates in the decarbonization reaction C + CO2 → 2CO. Mid-stage of blowing: The remaining slagging agent is mixed with fluorite CaF2 at a mass ratio of 10-12:1 and injected through the blowing system to suppress splashing, reducing the splashing rate to below 5%; III. Optimization of Process Parameters Control the molten pool temperature to ≥1600℃; dynamically adjust the oxygen supply intensity of the oxygen lance to 3.5~5.0 Nm³ / min·t to balance CO2 release and decarbonization efficiency.