Method for reducing TFe content in dephosphorization slag in double-slag smelting process

Abstract

The invention provides a method for reducing the content of TFe in dephosphorized slag in a double-slag-method smelting process, which comprises the following steps of: remaining slag after slag splashing furnace protection in the double-slag-method smelting process, and controlling the slag remaining amount to be 5-20kg / t steel; molten iron is added into the converter, the liquid level of the molten iron is measured after the molten iron is added, then an oxygen lance is put down for oxygen blowing for oxidation blowing, and lime and an iron-containing coolant are added in the oxidation blowing process; the proportion of iron oxide contained in the iron-containing coolant is greater than or equal to 85%; and after oxidizing blowing is carried out for 3-4.5 min, dephosphorized slag is discharged, then decarburization blowing is carried out, and tapping is carried out after decarburization blowing is finished. On the premise that the dephosphorization effect is guaranteed, the TFe content in the dephosphorization slag is remarkably reduced, a large amount of iron resources are saved, the problem of resource waste is solved, meanwhile, the smelting time in the dephosphorization period is shortened, the converter smelting efficiency is improved, the production cost is reduced, and cost reduction and efficiency improvement are achieved.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel smelting technology and relates to a method for reducing the TFe content in dephosphorized slag. Background Technology

[0002] The dual-slag process, with its excellent dephosphorization capability and low smelting cost, has become one of the main methods for steel converter smelting. Its main process is as follows: slag retention in the furnace → addition of scrap steel and molten iron → blowing for dephosphorization → discharge of dephosphorized slag → blowing for decarburization → tapping steel → slag splashing and retention. The dual-slag process uses low-basicity slag for dephosphorization and discharges the dephosphorized slag after dephosphorization, resulting in a significantly lower slag volume compared to traditional smelting processes. This significantly reduces the heat carried away by the slag during heating, leaving a large heat surplus within the converter.

[0003] In recent years, with the rising price of scrap steel, some steel companies have adopted the use of molten iron in the double-slag smelting process to reduce production costs. This has further increased the excess heat in the converter, requiring the addition of a large amount of iron ore to balance the heat. The amount of iron ore added is usually more than 30 kg / t of steel. However, since the dephosphorization period in the double-slag smelting process is usually around 4-5 minutes, it is difficult for the iron ore to be completely reduced in a short time. This results in excessively high TFe content in the dephosphorized slag. A large amount of slag with high TFe content is discharged after the dephosphorization period, causing resource waste and significantly increasing the production costs of enterprises. Summary of the Invention

[0004] To address the problem described in the background art of excessively high TFe content in dephosphorization slag caused by the use of molten iron in the dual-slag smelting process, resulting in resource waste and increased production costs for enterprises, this invention provides a method for reducing the TFe content in dephosphorization slag from the dual-slag smelting process.

[0005] The method of the present invention includes the following steps: S1. After slag splashing for furnace protection in the double-slag smelting process, the amount of slag left should be controlled at 5-20 kg / t steel. S2. Molten iron is poured into the converter. After pouring, the molten iron level is measured. Then, an oxygen lance is used for oxygen blowing to carry out oxidation smelting. During the oxidation smelting process, lime and an iron-containing coolant are added. The iron-containing coolant contains ≥85% iron oxides. S3. After oxidation blowing for 3-4.5 minutes, the dephosphorization slag is discharged, followed by decarburization blowing. After the decarburization blowing is completed, the steel is tapped.

[0006] Preferably, in step S2, the oxygen supply intensity q of the oxygen lance is controlled to be 4.0-5.0 m. 3 / (min.t); The oxygen lance position control is: hq × 0.12 + 0.3 (m), where h is the molten pool level and q is the oxygen supply intensity. The oxygen supply intensity in the oxidation blowing process of conventional dual-slag smelting is 3.0-3.2 m. 3 / (min.t); This invention further solves the problem of excessively high TFe content in dephosphorized slag caused by incomplete reduction of iron ore during full-iron smelting by optimizing oxygen supply intensity and oxygen lance position and adopting high oxygen supply intensity operation.

[0007] Preferably, in step S2, the amount of iron-containing coolant added is 30-60 kg / t of steel, added in three batches. The first batch is added at the beginning of the oxidation blowing process, with the amount controlled at 50% of the total amount. After 1.5 minutes of oxidation blowing, the amount added is controlled at 30% of the total amount, and after 2.5 minutes of oxidation blowing, the amount added is controlled at 20% of the total amount. The purpose of adding the iron-containing coolant in batches is twofold: first, to prevent adding too much at once, which would cause the molten pool temperature to be too low, which would be detrimental to the dissolution and reduction of the iron-containing coolant; and second, to prevent splashing or slag overflow caused by adding too much at once.

[0008] Preferably, in S2, the iron-containing coolant comprises the following components in parts by weight: FeO 40-85%, Fe2O3 and Fe3O4 combined 10-40%, Fe 1-5%, MgCO3 1-3%, and the remainder being unavoidable impurities. Traditional iron ore is mainly composed of Fe2O3, with a melting point of 1565℃. However, the dephosphorization temperature in a converter is generally below 1450℃. Due to the low oxygen potential within the converter, the dephosphorization reaction of traditional iron ore is primarily a stepwise reduction (Fe2O3→Fe3O4→FeO→Fe), mainly a gas-solid reaction. Furthermore, the formation of O2, a reduction product, during the reduction process creates a gas film between the iron oxides and carbon, hindering the reaction and further reducing the reduction rate of the iron ore. In the iron-containing coolant of this invention, the iron oxide is mainly FeO, with a melting point of only 1369℃, resulting in rapid melting and a fast gas-liquid reaction rate. Additionally, the iron-containing coolant contains a small amount of MgCO3, which has a low decomposition temperature. Its decomposition facilitates the fragmentation of the iron-containing coolant, increasing the reaction interface area. This further shortens the smelting time during the dephosphorization period, thereby improving the overall smelting efficiency of the converter.

[0009] Preferably, in step S2, the porosity of the iron-containing coolant is 50-100%, and the average particle size is 30-70 mm. The main purpose of controlling the porosity is to facilitate the penetration of molten iron and slag, accelerate heat conduction and chemical reaction, and to control the average particle size. If the particle size is too small, it will easily float on the surface of the slag layer, which is not conducive to melting and reduction; if the particle size is too large, the specific surface area is small, and the reaction is slow. Thus, the use of iron-containing coolants with a high proportion of iron oxides, high porosity and specific particle size can balance the excess heat in the converter and further promote its reduction in short-time oxidation blowing, thereby reducing the residual TFe in the dephosphorized slag from the source.

[0010] Compared with the prior art, the present invention has the following advantages: (1) Effectively reduce the TFe content in dephosphorization slag: By supplying oxygen with an oxygen lance and using a specially made iron-containing coolant to replace traditional iron ore, the problem of excessive TFe content in dephosphorization slag caused by incomplete reduction of iron ore during full-iron smelting is solved.

[0011] (2) Save iron resources and reduce production costs: Significantly reduce the loss of iron elements caused by the discharge of high TFe slag, directly save iron resources and reduce the steelmaking production cost of enterprises; (3) Improve smelting efficiency: Using a special iron-containing coolant to replace traditional iron ore, while achieving effective dephosphorization, the smelting time of the dephosphorization period is shortened, thereby improving the overall smelting efficiency of the converter. (4) Optimize heat balance: The use of special iron-containing coolant balances the excess heat in the converter and promotes its reduction in short-time blowing, thereby reducing TFe residue from the source.

[0012] In summary, this invention significantly reduces the TFe content in the dephosphorization slag while ensuring the dephosphorization effect, saving a large amount of iron resources and solving the problem of resource waste. At the same time, it shortens the smelting time during the dephosphorization period, improves the efficiency of converter smelting, reduces production costs, and achieves cost reduction and efficiency improvement. Detailed Implementation

[0013] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative of this application and are not intended to limit this application.

[0014] A method for reducing the TFe content in dephosphorization slag in a dual-slag smelting process is described in detail below.

[0015] S1. After slag splashing for furnace protection in the double-slag smelting process, the amount of slag left should be controlled at 5-20 kg / t steel.

[0016] S2. Add molten iron into the converter. After adding the iron, measure the molten iron level. Then, use an oxygen lance to blow oxygen for oxidation. During the oxidation process, add lime and iron-containing coolant. The iron-containing coolant contains ≥85% iron oxides.

[0017] Specifically, the oxygen supply intensity q of the oxygen lance is controlled at 4.0-5.0 m. 3 / (min.t); The oxygen lance position is controlled as: hq╳0.12+0.3(m), where h is the molten pool height and q is the oxygen supply intensity. By optimizing the oxygen supply intensity and oxygen lance position, and adopting high oxygen supply intensity operation, the problem of excessive TFe content in the dephosphorization slag caused by incomplete reduction of iron ore during full-iron smelting was further solved.

[0018] Specifically, the amount of iron-containing coolant added is 30-60 kg / t of steel, added in three batches. The first batch is added at the beginning of the oxidation blowing process, with the amount controlled at 50% of the total amount. After 1.5 minutes of oxidation blowing, the amount added is controlled at 30% of the total amount. After 2.5 minutes of oxidation blowing, the amount added is controlled at 20% of the total amount.

[0019] Specifically, the iron-containing coolant comprises the following components by weight: FeO 40-85%, Fe2O3 and Fe3O4 combined 10-40%, Fe 1-5%, MgCO3 1-3%, and the remainder being unavoidable impurities. Traditional iron ore is mainly composed of Fe2O3, with a melting point of 1565℃. However, the dephosphorization temperature in a converter is generally below 1450℃. Due to the low oxygen potential within the converter, the dephosphorization reaction of traditional iron ore is primarily a stepwise reduction (Fe2O3→Fe3O4→FeO→Fe), mainly a gas-solid reaction. Furthermore, the formation of O2, a reduction product, during the reduction process creates a gas film between the iron oxides and carbon, hindering the reaction and further reducing the reduction rate of the iron ore. In the iron-containing coolant of this invention, the iron oxide is mainly FeO, with a melting point of only 1369℃, resulting in rapid melting and a fast gas-liquid reaction rate. Additionally, the iron-containing coolant contains a small amount of MgCO3, which has a low decomposition temperature. Its decomposition facilitates the fragmentation of the iron-containing coolant, increasing the reaction interface area. This further shortens the smelting time during the dephosphorization period, thereby improving the overall smelting efficiency of the converter.

[0020] Specifically, the porosity of the iron-containing coolant is 50-100%, and the average particle size is 30-70 mm. The main purpose of controlling the porosity is to facilitate the penetration of molten iron and slag, accelerate heat conduction and chemical reactions, and to control the average particle size. If the particle size is too small, it will easily float on the slag surface, which is not conducive to melting and reduction. If the particle size is too large, the specific surface area is small, and the reaction is slow. Thus, the use of iron-containing coolants with a high proportion of iron oxides, high porosity and specific particle size can balance the excess heat in the converter and further promote its reduction in short-time oxidation blowing, thereby reducing the residual TFe in the dephosphorization slag from the source.

[0021] S3. After oxidation blowing for 3-4.5 minutes, the dephosphorization slag is discharged, followed by decarburization blowing. After the decarburization blowing is completed, the steel is tapped.

[0022] Example 1 This embodiment was carried out on a 150t converter. After slag splashing for furnace protection, slag was retained, with the retained slag amount controlled at 10kg / t steel. Then, molten iron was added to the converter. After the iron was added, the molten iron level was measured using a secondary lance, and oxygen was blown in using an oxygen lance, with the oxygen supply intensity controlled at 4.3m. 3 / (min.t), the oxygen lance position is 1.3m. Lime and iron-containing coolant are added during the oxidation blowing process. The amount of iron-containing coolant added is 45kg / t steel, added in three parts. The first batch is added at the beginning of oxygen blowing, and the amount added is controlled to be 50% of the total amount. After 1.5min of oxygen blowing, the amount added is controlled to be 30% of the total amount. After 2.5min of oxygen blowing, the amount added is controlled to be 20% of the total amount. The specific indicators of the iron-containing coolant are shown in Table 1. After blowing for 3.4min, the dephosphorization slag is discharged and the slag sample is taken for chemical analysis. The analysis results are shown in Table 1. Then decarburization blowing is carried out. After blowing is completed, the steel is tapped.

[0023] Compared with the existing dual-slag full-hot metal smelting process in the comparative example, this embodiment significantly reduces the TFe content of the slag during the dephosphorization period, while also reducing the blowing time during the dephosphorization period and improving the converter smelting efficiency. Compared with the comparative example, the TFe content of the slag during the dephosphorization period in this embodiment is 15%, a reduction of 12%, and the blowing time during the converter dephosphorization period is shortened from 4.6 min to 3.4 min.

[0024] Example 2 This experiment was conducted on a 150t converter. After slag splashing for furnace protection, slag was retained at a rate of 20kg / t steel. Molten iron was then added to the converter. After the addition was completed, the molten iron level was measured using a secondary lance, and oxygen was blown in using an oxygen lance, with the oxygen supply intensity controlled at 4.6m. 3 / (min.t), the oxygen lance position is 1.1m. Lime and iron-containing coolant are added during the oxidation blowing process. The amount of iron-containing coolant added is 42kg / t steel, added in three parts. The first batch is added at the beginning of oxygen blowing, and the amount added is controlled to be 50% of the total amount. After 1.5min of oxygen blowing, the amount added is controlled to be 30% of the total amount. After 2.5min of oxygen blowing, the amount added is controlled to be 20% of the total amount. The specific indicators of the iron-containing coolant are shown in Table 1. After blowing for 3.7min, the dephosphorization slag is discharged and the slag sample is taken for chemical analysis. The analysis results are shown in Table 1. Then decarburization blowing is carried out. After blowing is completed, the steel is tapped.

[0025] Compared with the existing double-slag full-hot metal smelting process in the comparative example, this embodiment significantly reduces the TFe content of the slag during the dephosphorization period, while also reducing the blowing time during the dephosphorization period and improving the converter smelting efficiency. Compared with the comparative example, the TFe content of the slag during the dephosphorization period in this embodiment is 18%, a reduction of 9%, and the blowing time during the converter dephosphorization period is shortened from 4.6 min to 3.7 min.

[0026] Example 3 This experiment was conducted on a 150t converter. After slag splashing for furnace protection, slag was retained at a rate of 10 kg / t of steel. Molten iron was then added to the converter. After the addition was completed, the molten iron level was measured using a secondary lance, and oxygen was blown in using an oxygen lance, with the oxygen supply intensity controlled at 5.0 m. 3 / (min.t), the oxygen lance position is 1.3m. Lime and iron-containing coolant are added during the oxidation blowing process. The amount of iron-containing coolant added is 56kg / t steel, added in three parts. The first batch is added at the beginning of oxygen blowing, and the amount added is controlled to be 50% of the total amount. After 1.5min of oxygen blowing, the amount added is controlled to be 30% of the total amount. After 2.5min of oxygen blowing, the amount added is controlled to be 20% of the total amount. The specific indicators of the iron-containing coolant are shown in Table 1. After blowing for 4.2min, the dephosphorization slag is discharged and the slag sample is taken for chemical analysis. The analysis results are shown in Table 1. Then decarburization blowing is carried out. After blowing is completed, the steel is tapped.

[0027] Compared with the existing double-slag full-hot metal smelting process in the comparative example, this embodiment significantly reduces the TFe content of the slag during the dephosphorization period, while also reducing the blowing time during the dephosphorization period and improving the converter smelting efficiency. Compared with the comparative example, the TFe content of the slag during the dephosphorization period in this embodiment is 13%, a reduction of 14%, and the blowing time during the converter dephosphorization period is shortened from 4.6 min to 4.2 min.

[0028] Example 4 This experiment was conducted on a 150t converter. After slag splashing for furnace protection, slag was retained at a rate of 12kg / t steel. Molten iron was then added to the converter. After the addition was completed, the molten iron level was measured using a secondary lance, and oxygen was blown in using an oxygen lance, with the oxygen supply intensity controlled at 4.0m. 3 / (min.t), the oxygen lance position is 1.1m. Lime and iron-containing coolant are added during the oxidation blowing process. The amount of iron-containing coolant added is 32kg / t steel, added in three parts. The first batch is added at the beginning of oxygen blowing, and the amount added is controlled to be 50% of the total amount. After 1.5min of oxygen blowing, the amount added is controlled to be 30% of the total amount. After 2.5min of oxygen blowing, the amount added is controlled to be 20% of the total amount. The specific indicators of the iron-containing coolant are shown in Table 1. After blowing for 3.3min, the dephosphorization slag is discharged and the slag sample is taken for chemical analysis. The analysis results are shown in Table 1. Then decarburization blowing is carried out. After blowing is completed, the steel is tapped.

[0029] Compared with the existing dual-slag full-hot metal smelting process in the comparative example, this embodiment significantly reduces the TFe content of the slag during the dephosphorization period, while also reducing the blowing time during the dephosphorization period and improving the converter smelting efficiency. Compared with the comparative example, the TFe content of the slag during the dephosphorization period in this embodiment is 16%, a reduction of 11%, and the blowing time during the converter dephosphorization period is shortened from 4.6 min to 3.3 min.

[0030] Comparative Example The existing double-slag full-iron smelting process was adopted, and iron ore was added during the oxidation blowing process. The specific indicators of the iron ore are shown in Table 1. Chemical analysis was performed on samples of dephosphorization slag, and the analysis results are shown in Table 1.

[0031] Table 1 Raw material information and smelting-related indicators The preferred embodiments of the present invention have been described in detail above with reference to specific examples. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

Claims

1. A method for reducing the TFe content in dephosphorization slag from a dual-slag smelting process, characterized in that, Includes the following steps: S1. After slag splashing for furnace protection in the double-slag smelting process, the amount of slag left should be controlled at 5-20 kg / t steel. S2. Molten iron is poured into the converter. After pouring, the molten iron level is measured. Then, an oxygen lance is used for oxygen blowing to carry out oxidation smelting. During the oxidation smelting process, lime and an iron-containing coolant are added. The iron-containing coolant contains ≥85% iron oxides. S3. After oxidation blowing for 3-4.5 minutes, the dephosphorization slag is discharged, followed by decarburization blowing. After the decarburization blowing is completed, the steel is tapped.

2. The method for reducing the TFe content in dephosphorization slag of a dual-slag smelting process according to claim 1, characterized in that: In S2, the oxygen supply intensity q of the oxygen lance is controlled to be 4.0-5.0 m. 3 / (min.t); The oxygen lance position control is: hq╳0.12+0.3 m, where h is the height of the molten pool and q is the oxygen supply intensity.

3. The method for reducing the TFe content in dephosphorization slag of a dual-slag smelting process according to claim 2, characterized in that: In S2, the amount of iron-containing coolant added is 30-60 kg / t of steel, added in three batches. The first batch is added at the beginning of the oxidation blowing process, with the amount controlled to be 50% of the total amount. After 1.5 minutes of oxidation blowing, the amount added is controlled to be 30% of the total amount. After 2.5 minutes of oxidation blowing, the amount added is controlled to be 20% of the total amount.

4. The method for reducing the TFe content in dephosphorization slag of a dual-slag smelting process according to claim 3, characterized in that: In S2, the iron-containing coolant comprises the following components by weight: FeO 40-85%, Fe2O3 and Fe3O4 combined 10-40%, Fe 1-5%, MgCO3 1-3%, and the remainder being unavoidable impurities.

5. The method for reducing the TFe content in dephosphorization slag of a dual-slag smelting process according to claim 4, characterized in that: In S2, the porosity of the iron-containing coolant is 50-100%, and the average particle size is 30-70 mm.

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