Electric arc furnace direct reduction iron less-slag smelting method

Abstract

The invention provides an electric arc furnace direct reduction iron less-slag smelting method which comprises the following steps: during electric arc furnace smelting, direct reduction iron is continuously added into a molten pool, and meanwhile, slag making materials are continuously added to make slag; the slagging material comprises lime with the addition amount of 60-80 kg / ton of steel and a waste magnesia carbon refractory material with the addition amount of 15-27 kg / ton of steel; the binary alkalinity CaO / SiO2 of the slag is controlled to be 1.3-1.7, the mass percent of MgO in the slag is controlled to be 10%-12%, and the mass percent of FeO is 15%-30%. According to the direct reduction iron less-slag smelting method for the electric arc furnace, the slag generation amount is reduced, and the smelting energy consumption is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of electric arc furnace steelmaking, and in particular to an electric arc furnace direct reduction iron less-slag smelting method. Background Art

[0002] In 2023, my country's crude steel output will be about 1.02 billion tons, and the carbon emissions of the steel industry will be about 1.8 billion tons, accounting for 15% of the total carbon emissions. Therefore, reducing carbon emissions is an urgent task for the low-carbon green transformation and development of my country's steel industry. Electric arc furnace steelmaking is one of the important steelmaking methods. Due to its short process, low energy consumption and low carbon emissions, it has become a trend in the development of steelmaking technology under the background of the "dual carbon" goal.

[0003] Direct reduced iron is one of the important metal raw materials in modern electric arc furnace steelmaking. Direct reduced iron, also known as sponge iron, is solid metallic iron obtained by direct reduction of iron ore pellets / lumps by reducing gas or non-coking coal at a temperature below its soft melting temperature. Direct reduced iron has low impurity content and is particularly suitable for electric arc furnace smelting of high-quality clean steel. In particular, in the context of the "dual carbon" goal driving the steel production process to transform and develop into a "direct reduction-electric furnace" short process, the use of direct reduced iron in electric arc furnaces to replace scrap steel for steelmaking is of even greater significance.

[0004] However, unlike traditional steelmaking raw materials for electric arc furnaces such as scrap steel, the main components of direct reduced iron, in addition to metallic iron, also include almost all the original gangue impurities in the ore, which are mainly acidic gangue oxides SiO2, Al2O3 and a small amount of CaO, MgO, etc. The gangue content in direct reduced iron can usually reach more than 7%, of which the content of SiO2 is 3% to 6%. During electric arc furnace smelting, the gangue components in direct reduced iron will all enter the slag. In the current practice of using direct reduced iron for steelmaking in electric arc furnaces at home and abroad, a higher slag basicity system is usually used, and its binary basicity CaO / SiO2 is often controlled at 2.0 to 2.5. For this reason, a large amount of slag-making materials such as lime need to be added, which will lead to a sharp increase in the amount of slag, increase smelting energy consumption, and deteriorate technical and economic indicators.

[0005] If the slag basicity of electric arc furnace direct reduction iron smelting is reduced, the amount of slag-making materials such as lime can be reduced, and the amount of smelting slag can be greatly reduced. However, since the saturated content of MgO in the slag increases with the decrease of slag basicity, reducing the slag basicity will increase the solubility of MgO in the slag. The lining of the electric arc furnace is a magnesia-carbon refractory material. The low MgO content in the slag makes the MgO in the lining more soluble in the slag, accelerating the erosion of the lining. Therefore, a large amount of dolomite magnesia slag-making materials must be added under the low-basicity slag system to increase the MgO content in the slag. This is bound to increase the smelting cost and is not conducive to reducing the amount of slag.

[0006] At present, my country's huge steel industry produces a large amount of refractory materials, with an annual output of more than 9 million tons of waste refractory materials, of which 60% are magnesium carbon refractory materials, the main components of which are MgO and C. However, the current utilization rate of waste refractory materials in my country is only about 30%. Under the background of my country's "dual carbon" strategy, it is urgent to step up the recycling of waste magnesium carbon refractory materials. The early methods of dealing with waste magnesium carbon refractory materials were mostly landfilling or using them to make roadbeds, which not only brought environmental pollution, but also caused waste of high-quality magnesia and graphite resources.

[0007] If the valuable components MgO and C in waste magnesium carbon refractory can be fully utilized and waste magnesium carbon refractory can be used instead of dolomite as magnesium slag-making material for electric arc furnace direct reduced iron smelting, it can effectively solve the problems of large amount of slag in electric arc furnace direct reduced iron smelting, high energy consumption and waste of resources in the current steelmaking industry. Summary of the invention

[0008] The purpose of the present invention is to provide an electric arc furnace direct reduction iron less slag smelting method to solve the current electric arc furnace direct reduction iron smelting problems of large slag amount and high energy consumption.

[0009] In order to solve the above technical problems, the present invention provides an electric arc furnace direct reduction iron less slag smelting method, comprising the following method:

[0010] During the smelting process in an electric arc furnace, direct reduced iron is continuously added to the molten pool, and slag-making materials are continuously added to make slag;

[0011] The slag-making material includes lime added in an amount of 60-80 kg / ton of steel and waste magnesium-carbon refractory material added in an amount of 15-27 kg / ton of steel;

[0012] The binary basicity CaO / SiO2 of the slag is controlled at 1.3-1.7, the mass percentage of MgO in the slag is controlled at 10%-12%, and the mass percentage of FeO is controlled at 15%-30%.

[0013] Furthermore, during the arc furnace smelting process, oxygen is sprayed through an oxygen lance on the wall of the arc furnace, and the oxygen supply of the oxygen lance is 40-50 Nm 3 / ton of steel.

[0014] Furthermore, during the electric arc furnace smelting process, carbon powder is sprayed through a carbon gun on the wall of the electric arc furnace to carry out full-process foamed slag submerged arc smelting, and the spraying amount of carbon powder sprayed by the carbon gun is 6 to 25 kg per ton of steel.

[0015] Furthermore, when the electric arc furnace smelting is finished and steel is tapped, the steel is retained in the furnace for the next furnace smelting, and the amount of retained steel is 30% to 40% of the tapped steel mass.

[0016] Furthermore, the direct reduced iron comprises, by mass percentage, TFe≥85%, metallization rate≥92%, C of 0-5%, P≤0.1%, and gangue≤8%.

[0017] Furthermore, during the smelting process, the feeding rate of the direct reduced iron is controlled according to the input power of the arc furnace electrode, and the feeding rate of the direct reduced iron is controlled at 15 to 30 kg / (MW·min).

[0018] Furthermore, the waste magnesium-carbon refractory material is removed from the refractory material, crushed, and sieved to form granular material with a particle size of ≤10 mm.

[0019] The present invention provides an electric arc furnace direct reduction iron less slag smelting method. In the electric arc furnace direct reduction iron smelting process, by adopting a low basicity slag system with a binary basicity CaO / SiO2 of 1.3 to 1.7, not only a high dephosphorization rate of smelting is ensured, but also the slag amount and power consumption of smelting can be greatly reduced. Under the premise of controlling the dephosphorization rate of electric arc furnace direct reduction iron smelting to be ≥90%, the slag amount per ton of steel is reduced by 20% to 35%, and the power consumption is reduced by 5% to 10%.

[0020] In addition, the present invention provides an electric arc furnace direct reduction iron less slag smelting method, using waste magnesium carbon refractory materials with main components of MgO and C instead of dolomite as slag making material, and controlling the MgO in the slag to 10% to 12% under the condition of low basicity of slag binary basicity CaO / SiO2 of 1.3 to 1.7, which is conducive to providing a high content of MgO required for low basicity slag to reduce the erosion of the slag on the arc furnace lining, not only saving the use of dolomite, reducing the cost of slag making material, but also further reducing the amount of slag. On the other hand, the carbon in the waste magnesium carbon refractory materials can be fully utilized, which can increase the input of chemical energy and promote the foaming of the slag.

[0021] At the same time, the electric arc furnace direct reduction iron smelting method provided by the present invention uses waste magnesium carbon refractory materials instead of dolomite as slag-making materials, which can significantly reduce the amount of slag in the electric arc furnace direct reduction iron smelting, and also realize the resource utilization of waste magnesium carbon refractory materials, which not only improves economic benefits, but also reduces the impact on the environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A flow chart of a method for smelting low-slag iron by direct reduction in an electric arc furnace is provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0023] See also Figure 1 The embodiment of the present invention provides an electric arc furnace direct reduction iron less slag smelting method, comprising the following method:

[0024] 1) During electric arc furnace smelting, direct reduced iron is continuously added to the molten pool, and mixed slag-making materials are continuously added to make slag.

[0025] Wherein, in terms of mass percentage, the direct reduced iron includes TFe≥85%, metallization rate≥92%, C is 0-5%, P≤0.1%, and gangue≤8%.

[0026] In addition, in order to enable the direct reduced iron added to the electric arc furnace to melt quickly and avoid the added direct reduced iron not being able to melt in time, the feeding rate of the direct reduced iron is controlled according to the input power of the electric arc furnace electrode during the smelting process, and the feeding rate of the direct reduced iron is controlled at 15-30kg / (MW·min).

[0027] The mixed slag-making materials continuously added into the electric arc furnace for slag-making include lime added in an amount of 60 to 80 kg / ton of steel and waste magnesium-carbon refractory materials added in an amount of 15 to 27 kg / ton of steel.

[0028] The waste magnesium-carbon refractory material is firstly cleaned, then crushed, and finally sieved to obtain granular material with a particle size of ≤10mm.

[0029] Different from the quaternary slag system formed by scrap steel smelting in electric arc furnace, whose main components are CaO-FeO-SiO2-MgO, the quinary slag system formed by direct reduction iron smelting in electric arc furnace is mainly composed of CaO-FeO-SiO2-MgO-Al2O3. According to the thermodynamic principle of dephosphorization, when the dephosphorization rate reaches 90%, the minimum slag basicity required for the quinary slag system formed by direct reduction iron smelting in electric arc furnace is about 1.3, while the minimum slag basicity required for the quaternary slag system formed by scrap steel smelting in electric arc furnace is about 2.4. Therefore, when the binary basicity of the slag in direct reduction iron smelting in electric arc furnace is controlled at 1.3-1.7, the dephosphorization rate can reach ≥90%.

[0030] Therefore, the present invention uses waste magnesium carbon refractory materials whose main components are MgO and C to replace traditional dolomite as slag-making materials containing MgO, and controls the binary basicity CaO / SiO2 of the slag formed by smelting to be 1.3-1.7 by controlling the addition system of lime and waste magnesium carbon refractory materials to slag-making materials. Since the content of MgO in waste magnesium carbon refractory materials is significantly higher than that in dolomite, the content of MgO in the slag can be quickly increased, thereby reducing the erosion of the slag on the furnace lining.

[0031] Since the arc furnace lining is a magnesium-carbon refractory material, in order to inhibit the erosion of the lining by the slag and to allow an appropriate amount of MgO to precipitate in the slag to form a solid solution of (Fe-Mg)O to promote slag foaming, the MgO dissolved in the slag needs to reach a saturated state. The solubility of MgO in the slag increases with the decrease of the slag basicity and decreases with the increase of the FeO content in the slag. According to thermodynamic calculations, at 1550-1600°C, when the binary basicity of the slag is 1.3-1.7 and the mass percentage of FeO in the slag is 15%-30%, the solubility of MgO in the slag is 10%-12%. Therefore, when the binary basicity CaO / SiO2 is 1.3-1.7, in order to inhibit the erosion of the lining by the slag, the mass percentage of MgO in the slag is controlled to 10%-12%.

[0032] In addition, the FeO content in the slag affects the erosion of the lining by the slag and the foaming of the slag. If the FeO content is too high, the erosion of the lining by the slag will be accelerated, which is not conducive to the foaming of the slag, and it will also increase the iron loss in the slag. If the FeO content is too low, it will be not conducive to the foaming and dephosphorization of the slag. Therefore, in order to avoid the erosion of the lining and ensure the foaming performance of the slag, the mass percentage of FeO in the slag is controlled to 15% to 30%.

[0033] Therefore, the present invention controls the binary basicity CaO / SiO2 of the slag to 1.3-1.7, controls the mass percentage of MgO in the slag to 10%-12%, and controls the mass percentage of FeO to 15%-30%, which can meet the requirement of low-basicity slag for high MgO content, not only reduces the erosion of the slag on the arc furnace lining, but also saves the use of dolomite, reduces the cost of slag-making materials, and further reduces the amount of slag produced by smelting, and reduces power consumption. The present invention can reduce the amount of slag per ton of steel by 20%-35% and reduce power consumption by 5%-10% under the premise of controlling the dephosphorization rate of direct reduced iron smelting in the arc furnace to be ≥90%.

[0034] In addition, the present invention uses waste magnesium carbon refractory materials instead of dolomite as slag-making materials, which can not only make full use of a large amount of C in the waste magnesium carbon refractory materials, reduce the injection amount of carbon powder in smelting, and reduce energy consumption, but also realize the resource utilization of waste magnesium carbon refractory materials, which not only improves economic benefits but also reduces the impact on the environment.

[0035] 2) During the arc furnace smelting process, oxygen is sprayed from the arc furnace wall oxygen lance, where the oxygen supply of the oxygen lance is 40-50 Nm 3 / ton of steel. At the same time, in order to form good foam slag and provide chemical heat during the smelting process, carbon powder is sprayed from the carbon gun on the wall of the electric arc furnace to carry out the whole process of foam slag submerged arc smelting, and the spraying amount of carbon powder sprayed by the carbon gun is 6-25kg / ton of steel.

[0036] 3) When the electric arc furnace is finished and steel is tapped, in order to ensure that the direct reduced iron can be melted as soon as possible after being added to the molten pool and shorten the smelting cycle of the electric arc furnace, a large amount of molten steel is left in the flat molten pool of the electric arc furnace for the next furnace of smelting. Among them, the amount of steel left in the electric arc furnace is 30% to 40% of the tapped steel quality.

[0037] The present invention provides an electric arc furnace direct reduction iron less slag smelting method, which has the following beneficial technical effects:

[0038] (1) Compared with the high basicity slag system used in electric arc furnace direct reduction iron smelting, the present invention uses a low slag basicity system, which not only ensures a high refining and dephosphorization rate, but also greatly reduces the amount of smelting slag.

[0039] (2) Using waste magnesium-carbon refractory materials whose main components are MgO and C to replace dolomite can, on the one hand, provide the high content of MgO required for low-basicity slag to reduce lining erosion, which not only saves the use of dolomite and reduces the cost of slag making, but also further reduces the amount of slag. On the other hand, the carbon in it can be utilized to increase the chemical energy input and promote slag foaming.

[0040] (3) While significantly reducing the amount of slag from direct reduced iron smelting in electric arc furnaces, it also achieved resource utilization of a large amount of solid waste from waste magnesium-carbon refractory materials.

[0041] The following is a detailed description of the electric arc furnace direct reduction iron low-slag smelting method provided by the present invention through embodiments.

[0042] Example 1

[0043] An electric arc furnace direct reduced iron low-slag smelting method provided in an embodiment of the present invention has the following components of smelting raw materials and auxiliary materials:

[0044] The composition of the direct reduced iron used in the embodiment of the present invention is as shown in Table 1.

[0045] Table 1

[0046]

[0047] The composition of the treated waste magnesium carbon refractory powder particles used in the embodiment of the present invention is shown in Table 2.

[0048] Table 2

[0049] Element MgO C <![CDATA[Fe2O3]]> <![CDATA[SiO2]]> <![CDATA[Al2O3]]> CaO Mass percentage, % 79.8 16.4 1.6 0.92 0.28 1.0

[0050] An electric arc furnace direct reduction iron low-slag smelting method provided in an embodiment of the present invention mainly comprises the following steps:

[0051] After the previous electric arc furnace finishes tapping, 40% of the molten steel remains in the furnace.

[0052] Start the power supply and continuously add direct reduced iron from the top of the electric arc furnace. The temperature entering the furnace is 25°C and the average particle size is 12mm.

[0053] The feeding rate of direct reduced iron adopts a slow-fast-slow feeding mode, specifically: the initial rate of smelting is 10-15kg / (MW·min), the feeding rate in the middle of smelting is 25-35kg / (MW·min), and the feeding rate in the late stage of smelting is 15-25kg / (MW·min).

[0054] While continuously adding direct reduced iron, lime and waste magnesium carbon refractory materials are continuously added into the furnace. The amount of lime added is 79.4 kg / ton of steel, and the amount of waste magnesium carbon refractory added is 24.1 kg / ton of steel. The addition rate of the two is adjusted according to the feeding rate of direct reduced iron to ensure that the binary basicity CaO / SiO2 of the slag during the smelting process is controlled at 1.48, the mass percentage of MgO is controlled at 12%, and the mass percentage of FeO is 20% (the mass percentage of TFe in the slag is 13%).

[0055] The waste magnesium-carbon refractory material is crushed after impurities are removed, and then sieved after crushing, and the average particle size after sieving is 1 mm.

[0056] Use the furnace wall oxygen lance to spray oxygen, the furnace wall carbon lance to spray carbon powder, and make foam slag submerged arc operation. The oxygen supply of the furnace wall oxygen lance is 45Nm 3 / ton of steel, the amount of carbon powder sprayed by the carbon gun on the furnace wall is 6.3kg / ton of steel.

[0057] After smelting, the steel is tapped, and 40% of the steel is left for smelting in the next furnace.

[0058] The dephosphorization rate of this smelting process condition is 90%. Under the condition of achieving the same dephosphorization rate, compared with the slag system with a basicity of 2.4 used in electric arc furnace direct reduction iron smelting, the slag volume is reduced by 71kg / ton of steel (reduced by 23.3% / ton of steel) and the power consumption is reduced by 36.8kWh / ton of steel (reduced by 7.3% / ton of steel).

[0059] Example 2

[0060] The electric arc furnace direct reduction iron less slag smelting method provided in the embodiment of the present invention is different from the embodiment 1 in that:

[0061] The amount of lime added is 74.4 kg / ton of steel, and the amount of waste magnesium-carbon refractory added is 25.4 kg / ton of steel.

[0062] During the smelting process, the binary basicity of the slag is controlled at 1.4, and the mass percentage of FeO in the slag is 25%.

[0063] The oxygen supply of the furnace wall oxygen lance is 47.3Nm 3 / ton of steel, the amount of carbon powder sprayed by the carbon gun on the furnace wall is 6.1kg / ton of steel.

[0064] Under the condition of achieving the same dephosphorization rate, compared with the slag system with a basicity of 2.4 used in electric arc furnace direct reduction iron smelting, the slag volume is reduced by 85kg / ton of steel (reduced by 26% / ton of steel) and the power consumption is reduced by 38.6kWh / ton of steel (reduced by 7.7% / ton of steel).

[0065] Example 3

[0066] An electric arc furnace direct reduction iron less-slag smelting method provided in an embodiment of the present invention is different from the embodiment in that:

[0067] The amount of lime added is 71.5 kg / ton of steel, and the amount of waste magnesium-carbon refractory added is 27 kg / ton of steel.

[0068] The binary basicity of the slag during the smelting process is controlled at 1.3, and the mass percentage of FeO in the slag is 30%.

[0069] The oxygen supply of the furnace wall oxygen lance is 50Nm 3 / ton of steel, the amount of carbon powder sprayed by the furnace wall carbon gun is 6.0kg / ton of steel.

[0070] Under the condition of achieving the same dephosphorization rate, compared with the slag system with a basicity of 2.4 used in electric arc furnace direct reduction iron smelting, the slag volume is reduced by 96.7kg / ton of steel (reduced by 27.5% / ton of steel) and the power consumption is reduced by 39.2kWh / ton of steel (reduced by 8.0% / ton of steel).

[0071] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A method for smelting iron with less slag by direct reduction of iron in an electric arc furnace, characterized in that: The following methods are included: During the smelting process in an electric arc furnace, direct reduced iron is continuously added to the molten pool, and slag-making materials are continuously added to make slag; The slag-making material includes lime added in an amount of 60-80 kg / ton of steel and waste magnesium-carbon refractory material added in an amount of 15-27 kg / ton of steel; The binary basicity CaO / SiO2 of the slag is controlled at 1.3-1.7, the mass percentage of MgO in the slag is controlled at 10%-12%, and the mass percentage of FeO is controlled at 15%-30%.

2. The method for smelting low-slag electric arc furnace direct reduced iron according to claim 1, characterized in that: During the arc furnace smelting process, oxygen is sprayed by an oxygen lance on the wall of the arc furnace. The oxygen supply of the oxygen lance is 40-50 Nm 3 / ton of steel.

3. The method for smelting low-slag electric arc furnace direct reduced iron according to claim 2, characterized in that: During the electric arc furnace smelting process, carbon powder is sprayed from the electric arc furnace wall by a carbon gun to carry out the whole process of foamed slag submerged arc smelting, and the spraying amount of carbon powder sprayed by the carbon gun is 6-25kg / ton of steel.

4. The method for smelting low-slag electric arc furnace direct reduced iron according to claim 1, characterized in that: When the electric arc furnace is finished smelting and steel is tapped, the steel is retained in the furnace for the next furnace smelting, and the amount of retained steel is 30% to 40% of the tapped steel quality.

5. The method for smelting low-slag direct-reduced iron in an electric arc furnace according to claim 1, characterized in that: The direct reduced iron comprises TFe≥85%, metallization rate≥92%, C of 0-5%, P≤0.1%, and gangue≤8% by mass percentage.

6. The method for smelting low-slag direct-reduced iron in an electric arc furnace according to claim 5, characterized in that: During the smelting process, the feeding rate of the direct reduced iron is controlled according to the input power of the arc furnace electrode, and the feeding rate of the direct reduced iron is controlled at 15-30 kg / (MW·min).

7. The method for smelting low-slag direct-reduced iron in an electric arc furnace according to claim 1, characterized in that: The waste magnesium carbon refractory material is separated into granular material with a particle size of ≤10 mm through impurities removal, crushing and screening.

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