Semi-steel desulfurization method

Abstract

The invention discloses a semi-steel desulfurization method, and belongs to the field of steel smelting. The method comprises the following steps: S1, extracting vanadium from vanadium-containing molten iron to obtain semisteel; the semi-steel and a first desulfurizing agent are mixed and then subjected to pre-desulfurization, and the first desulfurizing agent is fly ash of an electrolytic aluminum factory, active lime, aluminum particles and silicon iron; s2, mixing the pre-desulfurized semi-steel with a second desulfurizer, and stirring for desulfurization to obtain desulfurized semi-steel; the second desulfurizing agent is lime, the stirring desulfurization is carried out while whole-course gas blowing stirring is carried out, and the gas for gas blowing stirring is mixed gas of inert gas and reducing gas. The problem of poor desulfurization effect of vanadium extraction semisteel can be effectively avoided, the desulfurization effect is improved, the problem that the pretreatment desulfurization cost is increased after the sulfur content of the molten iron is increased is reduced, and a technical support is provided for producing low-sulfur steel by adopting the vanadium-containing molten iron.

Description

Technical Field

[0001] The present invention belongs to the field of steel smelting, and in particular relates to a method for desulfurizing semi-steel, which can be called a method for improving the desulfurization efficiency of semi-steel. Background Art

[0002] To optimize steelmaking production processes, pre-desulfurization of hot metal is often performed. Conventional hot metal desulfurization processes primarily include the KR desulfurization method and the injection method. The KR method typically uses lime and fluorite as desulfurizers. A stirrer rotates the hot metal, creating a vortex and drawing the added desulfurizer into the molten iron for a full reaction, ultimately achieving desulfurization. The injection method includes injecting magnesium powder and lime, as well as pure magnesium powder.

[0003] For companies using vanadium-titanium iron ore as raw material for smelting, controlling sulfur content during the process is quite challenging. Specifically, hot metal produced in blast furnaces using vanadium-titanium magnetite differs from conventional hot metal in several ways, including lower furnace temperatures and poor blast furnace desulfurization capacity. The resulting hot metal sulfur content is, on average, 0.030-0.040 percentage points higher than that of other domestic steel mills that do not use vanadium-titanium magnetite, and the temperature is 40-50°C lower. Consequently, hot metal desulfurization results in a significant temperature drop, poor slag quality, and high iron losses. This is particularly true for desulfurization of vanadium-containing hot metal. Due to the unique characteristics of vanadium-containing hot metal, desulfurizer consumption and iron losses increase significantly, leading to a decrease in desulfurization capacity. Furthermore, after desulfurization, hot metal undergoes vanadium extraction in a converter. The addition of coolant and / or pig iron during this extraction process results in significant resulfurization of the semi-smelted steel, hindering sulfur control during steelmaking. Therefore, optimization of pretreatment desulfurization of vanadium-titanium hot metal is necessary. Summary of the Invention

[0004] In view of this, the object of the present invention is to provide a method for desulfurization of semi-steel, which can improve the desulfurization efficiency of semi-steel, thereby improving the desulfurization effect and providing technical support for the production of low-sulfur steel.

[0005] The present invention provides a method for desulfurization of semi-steel, comprising the following steps:

[0006] S1. Extracting vanadium from vanadium-containing molten iron to obtain semi-steel; and pre-desulfurizing the semi-steel after mixing it with a first desulfurizer, wherein the first desulfurizer comprises dust from an aluminum smelter, activated lime, aluminum granules, and ferrosilicon;

[0007] S2. Mixing the pre-dewurized semi-steel with a second desulphurizing agent and performing stirring desulphurization to obtain desulphurized semi-steel; the second desulphurizing agent is lime; and the stirring desulphurization is performed simultaneously with blowing and stirring throughout the process, wherein the gas used for blowing and stirring is a mixture of an inert gas and a reducing gas.

[0008] Preferably, in step S1, the temperature of the semi-steel obtained by vanadium extraction is controlled between 1360 and 1390° C.; and the first desulfurizing agent is added to the semi-steel for mixing when the tapping amount reaches 1 / 4 to 1 / 3.

[0009] Preferably, in step S1, the first desulfurizer is prepared by mixing dust from an aluminum electrolytic plant, active lime, aluminum particles and ferrosilicon, and the mass ratio of the dust from the aluminum electrolytic plant, active lime, aluminum particles and ferrosilicon is 40% to 50%: 45% to 62%: 5% to 10%: 5% to 10%.

[0010] Preferably, in step S1, the particle sizes of the electrolytic aluminum plant dust, active lime, aluminum particles and ferrosilicon of the first desulfurizer are all less than 2 mm.

[0011] Preferably, in step S1, the dosage of the first desulfurizer is controlled to be 10-25 kg / t semi-steel.

[0012] Preferably, in step S2, the stirring desulfurization is performed using a stirring head, the stirring head is inserted 200 to 1000 mm below the liquid surface, and the stirring speed is 30 to 120 r / min.

[0013] Preferably, in step S2, the dosage of the second desulfurizer is 5-10 kg / t semi-steel, and the stirring time of the stirring desulfurization is 10-15 min.

[0014] Preferably, in step S2, the gas for blowing and stirring is a mixture of nitrogen and hydrogen.

[0015] Preferably, in step S2, the volume ratio of hydrogen to nitrogen is 1 to 3:5, and the gas flow rate of the mixed gas is 100 to 150 m 3 / min.

[0016] Preferably, the sulfur content of the desulfurized semi-steel is less than 0.005 wt%.

[0017] To address the increased desulfurization burden of vanadium-extracted semi-steel after the sulfur content of vanadium-containing hot metal increases, the present invention provides a method for desulfurizing semi-steel. The method involves first subjecting vanadium-containing hot metal to converter vanadium extraction, then adding a first desulfurizer to the semi-steel for pre-desulfurization. The first desulfurizer comprises aluminum smelter dust, activated lime, aluminum granules, and ferrosilicon. The pre-desulfurized semi-steel is then mixed with a second desulfurizer, lime, and then subjected to agitation desulfurization. Air agitation is performed throughout the process, utilizing a reducing gas to create favorable thermodynamic conditions for desulfurization, thereby producing desulfurized semi-steel. The method first utilizes activated lime, metallic aluminum, aluminum smelter dust, and ferrosilicon as precursor desulfurizers for the semi-steel, forming a slag with sulfur-binding properties. Lime is then further used as a desulfurizer for agitation desulfurization, effectively ensuring the mass production of low-sulfur steel. Therefore, the present invention effectively avoids the problem of poor desulfurization efficiency in vanadium-extracted semi-steel, improves desulfurization efficiency, and reduces the increased pre-treatment desulfurization costs associated with elevated sulfur content in the hot metal. This provides technical support for the production of low-sulfur steel using vanadium-containing hot metal. DETAILED DESCRIPTION

[0018] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, the technical solutions of the present invention are described in detail below in conjunction with specific embodiments. The described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0019] The present invention provides a method for desulfurization of semi-steel, comprising the following steps:

[0020] S1. Extracting vanadium from vanadium-containing molten iron to obtain semi-steel; and pre-desulfurizing the semi-steel after mixing it with a first desulfurizer, wherein the first desulfurizer comprises dust from an aluminum smelter, activated lime, aluminum granules, and ferrosilicon;

[0021] S2. Mixing the pre-dewurized semi-steel with a second desulphurizing agent and performing stirring desulphurization to obtain desulphurized semi-steel; the second desulphurizing agent is lime; and the stirring desulphurization is performed simultaneously with blowing and stirring throughout the process, wherein the gas used for blowing and stirring is a mixture of an inert gas and a reducing gas.

[0022] The semi-steel desulfurization method provided by the present invention has high desulfurization efficiency and improved desulfurization effect, thereby ensuring the batch production of low-sulfur steel.

[0023] In this embodiment of the present invention, vanadium-containing molten iron enters a steel mill and undergoes vanadium extraction in a converter. At a certain vanadium extraction endpoint temperature, semi-steel is tapped. Tapping is the process of releasing the molten steel when its temperature and composition meet the specified requirements for the desired steel grade. Care must be taken to prevent slag from flowing into the ladle during tapping.

[0024] In some embodiments of the present invention, the temperature of the vanadium-containing hot metal before the vanadium extraction process may be 1250-1350°C, preferably 1270-1330°C, and more preferably 1290-1310°C. The main components of the vanadium-containing hot metal include iron (Fe), carbon (C), vanadium (V), and titanium (Ti), silicon (Si), sulfur (S), etc. The carbon content of the vanadium-containing hot metal is preferably greater than or equal to 4.0% by mass, more preferably greater than or equal to 4.2%, and even more preferably greater than or equal to 4.5%, for example, 4.0-4.3%. The vanadium content of the vanadium-containing hot metal is preferably greater than or equal to 0.25% by mass, more preferably greater than or equal to 0.5%, for example, 0.25-0.35%. The sulfur content of the vanadium-containing hot metal is generally 0.01%-0.2%, for example, 0.07%-0.13%.

[0025] The embodiment of the present invention has no specific limitation on the vanadium extraction process, and vanadium extraction can be performed by blowing oxygen into a converter, etc. Preferably, the semi-steel temperature obtained by vanadium extraction, i.e., the terminal temperature of vanadium extraction, is controlled between 1360 and 1390°C, which is beneficial for subsequent desulfurization, etc.

[0026] Moreover, in the embodiment of the present invention, it is preferred to add the first desulfurizer to the semi-steel tank when the steel output reaches 1 / 4 to 1 / 3, and utilize the impact force of the semi-steel to fully mix the first desulfurizer with the semi-steel to ensure that the sulfur in the semi-steel can be effectively removed. In the embodiment of the present invention, the first desulfurizer can be called a semi-steel precursor desulfurizer, etc., which is prepared by mixing dust from the electrolytic aluminum plant, active lime, aluminum particles and ferrosilicon; the main functions of the first desulfurizer include: utilizing the efficient deoxidation function of aluminum and silicon to remove oxygen in the semi-steel in advance and form oxides; at the same time, aluminum, silicon and lime (the main component is calcium oxide CaO) cooperate to partially remove sulfur in the semi-steel in advance; the oxides of aluminum and silicon and CaO can form low-melting-point calcium aluminate and calcium silicate, which improve the subsequent slag-metal reaction ability, thereby improving the desulfurization efficiency, and promoting slag-metal separation, reducing iron loss in the desulfurization process.

[0027] In the first desulfurizer, the mass ratio of electrolytic aluminum plant dust ash, active lime, aluminum particles and ferrosilicon is preferably 40% to 50%: 45% to 62%: 5% to 10%: 5% to 10%, and can further be 40%: 45%: 10: 5%, or 45%: 45%: 5%: 5%, or 40%: 50%: 5%: 5%.

[0028] The electrolytic aluminum plant dust removal ash primarily contains metallic aluminum (~2%), aluminum oxide (70%-85%), carbide (~3%), and MgO (~3%). The active lime (or soft-burned lime) is typically quicklime calcined at 920°C to 1200°C and has a relatively small particle size. The aluminum particles are granular metallic aluminum. Ferrosilicon is an iron-silicon alloy composed primarily of iron and silicon, with a silicon content of 50-70% by weight. Furthermore, the particle size of each raw material for the first desulfurizer is <2 mm. The consumption of the first desulfurizer is preferably controlled at 10-25 kg / t semi-steel, for example, 25 kg / t semi-steel, 20 kg / t semi-steel, or 10 kg / t semi-steel.

[0029] After the pre-desulfurized semi-steel is tapped, the embodiment of the present invention continues to transport it to the pre-treatment desulfurization station for stirring desulfurization (usually using a stirring head). Preferably, the stirring head for stirring desulfurization is inserted 200 to 1000 mm below the liquid surface, the stirring speed is 30 to 120 r / min, and 5 to 10 kg / (t semi-steel) of lime is added as the second desulfurizer. The stirring time can be 10 to 15 minutes to ensure a good desulfurization effect.

[0030] During the stirring desulfurization process described in the embodiment of the present invention, the bottom of the semi-steel tank is blown with air for stirring throughout the process. The gas is a mixture of inert gas and reducing gas, preferably a mixture of nitrogen and hydrogen, and the reducing properties of hydrogen are used to create good thermodynamic conditions for desulfurization. In a preferred embodiment of the present invention, the volume ratio of hydrogen to nitrogen is 1 to 3:5, that is, H2:N2=1 to 3:5; the gas flow rate of the mixed gas is preferably 100 to 150m 3 / min.

[0031] After the stirring desulfurization is completed, the sulfur content of the desulfurized semi-steel in the embodiment of the present invention is less than 0.005wt%, with high desulfurization efficiency. The semi-steel desulfurization method in the embodiment of the present invention is simple, has good desulfurization effect, and is low in cost, providing technical support for the production of low-sulfur steel using vanadium-containing molten iron.

[0032] To further illustrate the present invention, the following examples are described in detail. In the examples, all raw reagents and materials are commercially available. Experimental methods without specific experimental conditions are conventional methods and conditions well known in the art. The dust from the electrolytic aluminum plant primarily contains metallic aluminum (~2%), aluminum oxide (70%-85%), carbide (~3%), and MgO (~3%); the silicon content in ferrosilicon is 50%-75%. Unless otherwise specified, all values are expressed by mass.

[0033] Example 1

[0034] After entering the steel mill, vanadium-containing molten iron (temperature 1310°C, [C] 4.12%, [V] 0.31%, [Ti] 0.15%, [Si] 0.16%, [S] 0.095%) undergoes vanadium extraction in a converter (oxygen blowing in the converter, the same as in the following examples), with the final vanadium extraction temperature at 1385°C. When the semi-steel is 1 / 4 of the way through, a first desulfurizer is added to the semi-steel tank. The first desulfurizer is made from a mixture of 40% electrolytic aluminum plant dust (all with a particle size of less than 2mm), 45% active lime, 10% aluminum granules, and 5% ferrosilicon. Consumption of the first desulfurizer is controlled at 25kg / (t of semi-steel).

[0035] After the pre-desulfurized semi-steel is tapped, it is transported to the pre-treatment desulfurization station for stirring desulfurization. The stirring head is inserted 1000mm below the liquid level, the stirring speed is 120r / min, and 10kg / (t semi-steel) of lime is added as the second desulfurizer. The stirring time is 15min. During the stirring desulfurization, the bottom of the semi-steel tank is blown with air for stirring. The gas is a mixture of nitrogen and hydrogen, H2:N2=3:5, and the gas flow rate is 150m 3 After stirring desulfurization, the sulfur content of semi-steel was reduced from 0.121% to 0.003%, and the desulfurization rate reached 97.52%.

[0036] Example 2

[0037] After entering the steel mill, vanadium-containing molten iron (temperature 1310°C, [C] 4.12%, [V] 0.31%, [Ti] 0.15%, [Si] 0.16%, [S] 0.095%) undergoes vanadium extraction in a converter, with the final vanadium extraction temperature reaching 1390°C. When one-third of the semi-steel is discharged, a first desulfurizer is added to the semi-steel tank. The first desulfurizer is made from a mixture of 45% aluminum smelter dust (all with a particle size of less than 2mm), 45% active lime, 5% aluminum granules, and 5% ferrosilicon. Consumption of the first desulfurizer is controlled at 20kg / t of semi-steel.

[0038] After the pre-desulfurized semi-steel is tapped, it is transported to the pre-treatment desulfurization station for stirring desulfurization. The stirring head is inserted 800mm below the liquid surface, the stirring speed is 90r / min, and 5kg / (t semi-steel) of lime is added as the second desulfurizer. The stirring time is 12min. During the stirring desulfurization, the bottom of the semi-steel tank is blown with air for stirring. The gas is a mixture of nitrogen and hydrogen, H2:N2=2:5, and the gas flow rate is 120m 3 After stirring desulfurization, the sulfur content of semi-steel was reduced from 0.082% to 0.002%, and the desulfurization rate reached 97.56%.

[0039] Example 3

[0040] After entering the steel mill, vanadium-containing molten iron (temperature 1297°C, [C] 4.23%, [V] 0.29%, [Ti] 0.11%, [Si] 0.18%, [S] 0.091%) undergoes vanadium extraction in a converter, with the final vanadium extraction temperature reaching 1390°C. When one-third of the semi-steel is discharged, a first desulfurizer is added to the semi-steel tank. The first desulfurizer is made from a mixture of 40% electrolytic aluminum plant dust (with a particle size of less than 2mm), 50% active lime, 5% aluminum granules, and 5% ferrosilicon. Consumption of the first desulfurizer is controlled at 10kg / t of Fe.

[0041] After the pre-desulfurized semi-steel is tapped, it is transported to the pre-treatment desulfurization station for stirring desulfurization. The stirring head is inserted 200mm below the liquid surface, the stirring speed is 30r / min, and 8kg / (t semi-steel) of lime is added as a desulfurizer. The stirring time is 10min. During the stirring desulfurization period, the bottom of the semi-steel tank is blown with air for stirring. The gas is a mixture of nitrogen and hydrogen, H2:N2=1:5, and the gas flow rate is 130m 3 After stirring desulfurization, the sulfur content of semi-steel was reduced from 0.075% to 0.004%, and the desulfurization rate reached 94.2%.

[0042] Comparative Example 1

[0043] After entering the steel mill, vanadium-containing molten iron (temperature 1306°C, [C] 4.21%, [V] 0.32%, [Ti] 0.17%, [Si] 0.19%, [S] 0.105%) undergoes vanadium extraction in a converter, with the final vanadium extraction temperature reaching 1390°C. When two-fifths of the semi-steel is tapped, a first desulfurizer is added to the semi-steel tank. This first desulfurizer is made from a mixture of 60% passivated lime, 20% sodium carbonate, 5% passivated magnesium, 8% calcium fluoride, and 7% silicon dioxide, all with a particle size less than 2mm. Consumption of the first desulfurizer is controlled at 10kg / t of semi-steel. After tapping, the semi-steel is transported to the pretreatment desulfurization station for desulfurization by injection. Desulfurization is carried out using magnesium powder and lime, with a mass ratio of 1:4, for a total consumption of 5.5kg / t.

[0044] After desulfurization during the steel-making process, the sulfur content of the semi-steel was reduced from 0.125% to 0.092%, and the desulfurization rate reached 26.40%; the sulfur content after injection desulfurization was 0.008%, and the total desulfurization rate was 93.6%.

[0045] As can be seen from the above examples, the present invention first uses activated lime, metallic aluminum, aluminum electrolytic plant dust, and ferrosilicon as semi-steel precursor desulfurizers, which synergistically form a slag with sulfur-binding capacity. Lime is then used as a desulfurizer for stirring and desulfurization, effectively ensuring the mass production of low-sulfur steel. This invention effectively improves desulfurization efficiency and reduces costs, providing technical support for the production of low-sulfur steel using vanadium-containing molten iron.

[0046] The foregoing descriptions of specific exemplary embodiments of the present invention are for purposes of illustration and description. These descriptions are not intended to limit the invention to the precise forms disclosed, and it is apparent that many variations and modifications are possible in light of the foregoing teachings. The exemplary embodiments have been selected and described for the purpose of explaining the specific principles of the invention and their practical application, thereby enabling those skilled in the art to realize and utilize a variety of exemplary embodiments of the invention and various options and modifications. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A method for desulfurization of semi-steel, characterized in that: The following steps are involved: S1. Extracting vanadium from vanadium-containing molten iron to obtain semi-steel; and pre-desulfurizing the semi-steel after mixing it with a first desulfurizer, wherein the first desulfurizer comprises dust from an aluminum smelter, activated lime, aluminum granules, and ferrosilicon; S2. Mixing the pre-dewurized semi-steel with a second desulphurizing agent and performing stirring desulphurization to obtain desulphurized semi-steel; the second desulphurizing agent is lime; and the stirring desulphurization is performed simultaneously with blowing and stirring throughout the process, wherein the gas used for blowing and stirring is a mixture of an inert gas and a reducing gas.

2. The method for desulfurization of semi-steel according to claim 1, characterized in that: In step S1, the temperature of the semi-steel obtained by vanadium extraction is controlled between 1360 and 1390° C.; and the first desulfurizing agent is added to the semi-steel for mixing when the tapping amount reaches 1 / 4 to 1 / 3.

3. The method for desulfurization of semi-steel according to claim 1, characterized in that: In step S1, the first desulfurizer is prepared by mixing dust from an aluminum electrolytic plant, active lime, aluminum particles and ferrosilicon, and the mass ratio of the dust from the aluminum electrolytic plant, active lime, aluminum particles and ferrosilicon is 40% to 50%: 45% to 62%: 5% to 10%: 5% to 10%.

4. The method for desulfurization of semi-steel according to any one of claims 1 to 3, characterized in that: In step S1, the particle sizes of the electrolytic aluminum plant dust, active lime, aluminum particles and ferrosilicon of the first desulfurizer are all less than 2 mm.

5. The method for desulfurization of semi-steel according to claim 4, characterized in that: In step S1, the dosage of the first desulfurizer is controlled to be 10-25 kg / t semi-steel.

6. The method for desulfurization of semi-steel according to any one of claims 1 to 3, characterized in that: In step S2, the stirring desulfurization is performed using a stirring head, the stirring head is inserted 200 to 1000 mm below the liquid surface, and the stirring speed is 30 to 120 r / min.

7. The method for desulfurization of semi-steel according to claim 6, characterized in that: In step S2, the dosage of the second desulfurizer is 5-10 kg / t semi-steel, and the stirring time of the stirring desulfurization is 10-15 minutes.

8. The method for desulfurization of semi-steel according to any one of claims 1 to 3, characterized in that: In step S2, the gas for blowing and stirring is a mixture of nitrogen and hydrogen.

9. The method for desulfurization of semi-steel according to claim 8, characterized in that: In step S2, the volume ratio of hydrogen to nitrogen is 1 to 3:5, and the gas flow rate of the mixed gas is 100 to 150 m 3 / min.

10. The method for desulfurization of semi-steel according to any one of claims 1 to 3, characterized in that: The sulfur content of the desulfurized semi-steel is less than 0.005 wt%.