Method for efficiently smelting molten iron through electric furnace melting separation of medium-low-grade iron ore direct reduction iron

Abstract

The invention discloses a method for efficiently smelting molten iron through electric furnace melting separation of medium-low-grade iron ore direct reduction iron, which comprises the following steps: (1) uniformly mixing and blending different kinds of medium-low-grade iron ore to prepare oxidized pellets; (2) adopting a hydrogen-based shaft furnace to carry out hydrogen-based reduction, so as to prepare medium-low-grade DRI; and (3) the medium-low-grade DRI is subjected to hot charging and hot conveying to a melt separation electric furnace, carbon and a tempering agent are added for melt separation, and after melt separation is completed, high-purity molten iron and molten slag are obtained through slag-iron separation. According to the method, a small amount of carbon is adopted for reducing the medium-low-grade DRI, the melting temperature is reduced by adding the tempering agent, the high-purity molten iron is obtained, and the problems that the low-grade DRI is fed into an electric furnace for steelmaking, too many impurities exist, and power consumption is too large are remarkably solved.

Description

Technical Field

[0001] The invention belongs to the technical field of comprehensive utilization of metallurgical resources, and specifically relates to a method for efficiently smelting molten iron by directly reducing medium and low-quality iron ore with electric furnace smelting. Background Art

[0002] The steel industry is a typical high-energy consumption and high-carbon emission industry. Carbon emissions from my country's steel industry account for about 15% of total carbon emissions, and carbon emissions from the smelting process account for more than 95% of the entire steel process. Therefore, carbon reduction in the steel smelting process is a top priority. Using a hydrogen-based vertical furnace direct reduction-electric furnace short process instead of a blast furnace-converter long process can reduce carbon emissions per ton of steel from 1.8-2.0t to 0.4-0.6t.

[0003] However, unlike blast furnace ironmaking, in the direct reduction process of hydrogen metallurgy, iron ore is neither melted nor refined. The main chemical change is to remove oxygen from the compound, and most impurities and gangue remain in the DRI product. When the DRI product enters the electric furnace for smelting, the excessively high acidic gangue content will significantly increase power consumption and wear refractory materials. Therefore, the existing hydrogen metallurgical process requires the impurity content in the ore to be as low as possible and the iron ore grade to be higher than 67%. In addition, although the grade of some iron ores is high, their physical properties are difficult to meet the needs of hydrogen metallurgy. The proportion of small and medium-sized powders in the obtained DRI is relatively high, which is difficult to melt during electric arc furnace smelting, wasting iron resources and increasing power consumption. Therefore, the supply of iron ore (DR pellets) for hydrogen metallurgy is stretched globally.

[0004] Solving the problem of iron ore grade required for hydrogen metallurgy is a research hotspot in the hydrogen metallurgy industry. The patent application with publication number CN117535464A discloses a low-carbon steelmaking method and system using low-grade direct reduced iron as raw material, but the metallization rate of the direct reduced iron used is as high as 93%, the total iron content is close to 80%, and the iron ore grade is still around 65%, which belongs to medium-high grade iron ore in my country, and does not involve the problem of pellet strength. In actual production, the DRI powder ratio is too high, which has an adverse effect on the electric furnace. The patent application with publication number N118048496A discloses a method for preparing copper tailings oxidized pellets and its application, using copper tailings and high-grade iron ore to produce oxidized pellets for use in hydrogen-based vertical furnaces, but its iron grade requirements for copper tailings and high-grade iron ore are 65% and 69% respectively, and it still has not gotten rid of the dependence of hydrogen-based vertical furnaces on high-grade iron ore. Patent application with publication number CN117737335 A discloses a method for recovering iron and titanium from vanadium extraction slag by hydrogen-based reduction-electric furnace smelting. However, it uses wet leaching to remove impurities in the vanadium slag, which is time-consuming, produces a lot of pollutants such as wastewater, and cannot be used to treat ordinary ore DRI. Summary of the invention

[0005] The present invention aims to provide a method for smelting molten iron efficiently by directly reducing medium and low-grade iron ore through electric furnace smelting, which can effectively solve the problem that hydrogen-based vertical furnaces have too high requirements for the grade of iron ore.

[0006] To achieve the above object, the present invention adopts the following technical solutions: A method for efficiently smelting molten iron by directly reducing medium and low-quality iron ore with an electric furnace, comprising the following steps: (1) Mix different types of medium and low-grade iron ores to make oxidized pellets; (2) Using a hydrogen-based vertical furnace for hydrogen-based reduction to produce medium and low-quality DRI; (3) The medium and low-quality DRI is hot-charged and sent to the melting furnace, where carbon and tempering agent are added in proportion for melting. After the melting is completed, high-purity molten iron and slag are obtained by slag-iron separation.

[0007] Furthermore, the sources of the medium- and low-grade iron ore in step (1) of the present invention include China, Brazil, Australia, South Africa, etc., and the iron grade thereof is 58% to 65%.

[0008] Furthermore, the low-grade iron ore in step (1) of the present invention needs to be finely ground to a particle size of D [4,3] 50~100 μm.

[0009] Furthermore, the compressive strength of the oxidized pellets in step (1) of the present invention is greater than 2000N, the bonding index is ≤20%, LTD+6.3 is greater than 80%, and LTDup is greater than 60%.

[0010] Furthermore, the gas used for the hydrogen-based vertical furnace reduction in step (2) of the present invention includes natural gas and reformed coke oven gas, the hydrogen-based reduction temperature is 900-1050° C., the duration is 30-60 min, the obtained DRI metallization rate is greater than 85%, and the proportion of particles with a particle size less than 6.3 mm is less than 5%.

[0011] Furthermore, the DRI in step (3) of the present invention is delivered to a melting furnace by hot charging at a temperature of 500-800°C, preferably 600°C.

[0012] Furthermore, the smelting furnace in step (3) of the present invention is a closed furnace to reduce pollution and save heat, but no protective gas is required.

[0013] Furthermore, in step (3) of the present invention, the carbon ratio is 4% to 8%; the conditioning agent comprises dolomite and limestone, and the mass ratios of the dolomite and limestone to DRI are 1% to 10% and 1% to 10%, respectively.

[0014] Furthermore, in step (3) of the present invention, the melting temperature is 1200-1400° C., and the melting time is 30-55 min.

[0015] Furthermore, the slag-iron separation in step (3) of the present invention adopts slag-iron separation, with the upper part being the slag outlet and the lower part being the iron outlet.

[0016] Furthermore, the high-purity molten iron in step (3) of the present invention has an Fe content of 95% to 98%, a C content of 2% to 4.5%, a Si content of 0.05% to 0.25%, a P content of 0.005% to 0.014%, a S content of 0.02% to 0.08%, and a Mn content of 0.03% to 0.07%.

[0017] Furthermore, the slag discharge ratio of the slag in step (3) of the present invention is 150-250 kg / t, the FeO content in the slag is less than 2%, the SiO2 content is 30%-45%, the Al2O3 content is 2%-10%, the MgO content is 5%-30%, the CaO content is 10%-50%, and the TiO2 content is 0.03%-0.3%.

[0018] The present invention has the following advantages and positive effects: (1) A small amount of carbon is used to reduce low-quality DRI, and the melting temperature is lowered by adding a tempering agent to obtain high-purity molten iron, which is then put into the furnace for steelmaking. This significantly improves the problem of excessive impurities and excessive power consumption when low-quality DRI is directly put into the electric furnace for steelmaking. Compared with the traditional blast furnace-converter process, the method of the present invention significantly reduces carbon emissions, and the difficulty of adding CCUS process is extremely low.

[0019] (2) The method of the present invention solves the inherent shortcomings of the hydrogen metallurgy-electric furnace steelmaking process and can produce steel grades that are difficult to produce using the DRI-EAF route (such as low-nitrogen steel). The method can also pre-treat the molten iron before steelmaking, such as dephosphorization and carburizing, thereby reducing the burden of the steelmaking process and producing more advanced special steel grades.

[0020] (3) Unlike the hydrogen metallurgy-electric furnace steelmaking process, which requires the construction of a new electric arc furnace, the method of the present invention can be smoothly connected to the existing converter of the steel plant, and the production cycle is easier to match.

[0021] (4) The slag obtained by the method of the present invention has physical and chemical properties similar to those of blast furnace slag. The process for producing cement and other building materials is very mature, which reduces the cost of solid waste resource treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic diagram of a method for efficiently smelting molten iron by directly reducing medium and low-quality iron ore in an electric furnace. DETAILED DESCRIPTION

[0023] For the convenience of understanding the present invention, the present invention lists the following embodiments. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention. Example 1

[0024] A method for high-efficiency smelting of molten iron by directly reducing medium and low-quality iron ore with electric furnace smelting, such as Figure 1 As shown, the specific steps include: (1) The low- and medium-grade iron ores used in this example come from Liaoning, Hebei and Australia, with iron grades of 63%, 61% and 62% respectively. The three types of iron ores are crushed and ground to a particle size of D [4,3] 70 μm, with 1% bentonite and 0.8% organic binder, the continuous crystal strength of the three iron ores was 812, 613 and 439N respectively. The compressive strength of the oxidized pellets was 2642N, the bonding index was 17.3%, and the LTD was +6.3 is 87.55, and LTDup is 61.0%; (2) Using reformed coke oven gas from a steel plant in Hebei Province, the DRI was reduced at 950°C for 45 min. The metallization rate was 86%, and the proportion of particles with a particle size less than 6.3 mm was 3.5%.

[0025] (3) DRI at 600 °C was mixed with 4% coke, 5% limestone and 3.5% dolomite. The proportions of CaO and MgO in the charge were 14% and 16%, respectively. The mixture was placed in a smelting furnace and heated to 1350 °C for 40 min. After the smelting was completed, molten iron and slag were obtained by separation of slag and iron.

[0026] After testing, the iron content of the molten iron obtained was 97.5%, the carbon content was 2.4%, the Si content was 0.05%, the S content was 0.03%, and the P content was 0.007%, which fully met the standards for entering an electric furnace; 210 kg of slag was produced per ton of iron, and the slag contained 1.7% FeO, 39.6% SiO2, 4.7% Al2O3, 27.8% MgO, 25.8% CaO, and 0.3% TiO2, which can be used as a cement raw material after water cooling.

[0027] In comparison, the DRI obtained under the same conditions, with only 4% coke added and no limestone and dolomite added, had a melting point of 1570°C and significantly increased energy consumption. Example 2

[0028] A method for high-efficiency smelting of molten iron by directly reducing medium and low-quality iron ore with electric furnace smelting, such as Figure 1 As shown, the specific steps include: (1) The low- and medium-grade iron ores used in this example come from Australia, Liaoning and Hebei, with iron grades of 62%, 59% and 60% respectively. The three types of iron ores are crushed and ground to a particle size of D [4,3] 50 μm, with 1.2% bentonite and 0.5% organic binder, the continuous crystal strength of the three iron ores are 431, 856 and 630N respectively. The balls are matched in a ratio of 3.5:5:1.5, and the compressive strength of the obtained oxidized pellets is 2438N, the bonding index is 18.6%, and the LTD +6.3 is 95.64, and LTDup is 66.0%; (2) Using natural gas and a hydrogen-based vertical furnace for reduction at 1050°C for 30 min, the resulting DRI metallization rate was 87%, and the proportion of particles with a particle size less than 6.3 mm was 4.5%; (3) DRI at 600 °C was mixed with 8% coke, 1% limestone and 10% dolomite. The proportions of CaO and MgO in the charge were 12% and 17% respectively. The mixture was placed in a smelting furnace and heated to 1200 °C for smelting. The smelting time was 55 min. After the smelting was completed, molten iron and slag were obtained by separation of slag and iron.

[0029] After testing, the iron content of the molten iron obtained was 96.3%, the carbon content was 3.1%, the Si content was 0.20%, the S content was 0.05%, and the P content was 0.008%, which fully met the standards for entering an electric furnace; 270 kg of slag was produced per ton of iron, and the slag contained 1.2% FeO, 37.7% SiO2, 4.4% Al2O3, 29.8% MgO, 24.3% CaO, and 0.17% TiO2, which can be used as a cement raw material after water cooling.

[0030] In comparison, the DRI obtained under the same conditions, with only 3.5% coke added, without limestone and dolomite, had a melting temperature of 1600°C, and the energy consumption was significantly increased. Example 3

[0031] A method for high-efficiency smelting of molten iron by directly reducing medium and low-quality iron ore with electric furnace smelting, such as Figure 1 As shown, the specific steps include: (1) The low- and medium-grade iron ores used in this example come from Brazil, Hebei and South Africa, with iron grades of 62%, 59% and 62% respectively. The three types of iron ores are crushed and ground to a particle size of D [4,3] 100 μm, with 1.2% bentonite and 0.5% organic binder, the continuous crystal strength of the three iron ores are 387, 762 and 524N respectively. The balls are matched in a ratio of 3:5:2, and the compressive strength of the obtained oxidized pellets is 2105N, the bonding index is 19.4%, and the LTD +6.3 is 96.43, and LTDup is 64.2%; (2) Using reformed coke oven gas from a steel plant in Hebei, a hydrogen-based vertical furnace was used for reduction at 900°C for 50 min. The resulting DRI metallization rate was 86%, and the proportion of particles with a particle size less than 6.3 mm was 3.5%; (3) DRI at 600 °C was mixed with 6% coke, 10% limestone and 1% dolomite. The proportions of CaO and MgO in the charge were 18% and 12% respectively. The mixture was placed in a smelting furnace and heated to 1400 °C for 30 min. After the smelting was completed, molten iron and slag were obtained by separation of slag and iron.

[0032] After testing, the iron content of the molten iron obtained was 96.9%, the carbon content was 2.8%, the Si content was 0.13%, the S content was 0.04%, and the P content was 0.09%, which fully met the standards for entering an electric furnace; 250 kg of slag was produced per ton of iron, and the slag contained 1.5% FeO, 40.4% SiO2, 3.5%, 19.5% Al2O3, 33.3% MgO, and 0.08% TiO2, which can be used as a cement raw material after water cooling.

[0033] In comparison, the DRI obtained under the same conditions, with only 3.5% coke added and no limestone and dolomite added, had a melting temperature of 1620°C and significantly increased energy consumption.

Claims

1. A method for efficiently smelting molten iron by directly reducing medium and low-quality iron ore with electric furnace smelting, characterized in that: The following steps are involved: (1) Mix different types of medium and low-grade iron ores to prepare oxidized pellets; (2) Using a hydrogen-based vertical furnace for hydrogen-based reduction to produce medium and low-quality DRI; (3) The medium and low-quality DRI is hot-charged and sent to the melting furnace, where carbon and tempering agents are added for melting. After the melting is completed, high-purity molten iron and slag are obtained by slag-iron separation.

2. The method for efficiently smelting molten iron by directly reducing medium and low-quality iron ore in an electric furnace according to claim 1, characterized in that: The iron grade of the medium and low-grade iron ore is 58% to 65%.

3. The method for efficiently smelting molten iron by directly reducing medium and low-quality iron ore in an electric furnace according to claim 1, characterized in that: The particle size of the medium and low-quality iron ore in step (1) is D [4,3] 50~100 μm.

4. The method for efficiently smelting molten iron by directly reducing medium and low-quality iron ore by electric furnace smelting according to claim 1, characterized in that: The compressive strength of the oxidized pellets in step (1) is greater than 2000N, the bonding index is ≤20%, LTD+6.3 is greater than 80%, and LTDup is greater than 60%.

5. The method for efficiently smelting molten iron by directly reducing medium and low-quality iron ore by electric furnace smelting according to claim 1, characterized in that: In step (2), the hydrogen-based vertical furnace reduction temperature is 900-1050° C., the duration is 30-50 min, the obtained DRI metallization rate is greater than 85%, and the proportion of particles with a particle size less than 6.3 mm is less than 5%.

6. The method for efficiently smelting molten iron by directly reducing medium and low-quality iron ore in an electric furnace according to claim 1, characterized in that: The mass ratio of carbon to DRI in step (3) is 4% to 8%.

7. The method for efficiently smelting molten iron by directly reducing medium and low-quality iron ore in an electric furnace according to claim 1, characterized in that: The conditioning agent in step (3) comprises dolomite and limestone, and the mass ratios of dolomite and limestone to DRI are 1% to 10% and 1% to 10%, respectively.

8. The method for efficiently smelting molten iron by directly reducing medium and low-quality iron ore in an electric furnace according to claim 1, characterized in that: The melting temperature in step (3) is 1200-1400° C., and the melting time is 30-55 min.

9. The method for efficiently smelting molten iron by directly reducing medium and low-quality iron ore with an electric furnace according to claim 1, characterized in that: The high-purity molten iron in step (3) has an Fe content of 95% to 98%, a C content of 2% to 4.5%, a Si content of 0.05% to 0.25%, a P content of 0.005% to 0.014%, a S content of 0.02% to 0.08%, and a Mn content of 0.03% to 0.07%.

10. The method for high-efficiency smelting of molten iron by direct reduction of medium and low-quality iron ore in an electric furnace according to claim 1, characterized in that: The slag in step (3) has a FeO content of less than 2%, a SiO2 content of 30% to 45%, an Al2O3 content of 2% to 10%, a MgO content of 5% to 30%, a CaO content of 10% to 50%, and a TiO2 content of 0.03% to 0.3%.

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