Method for producing steel by melting iron ore using an electric furnace, removing oxygen in iron ore bath by blowing hydrogen onto surface of iron ore bath with high-speed hydrogen jet stream from above electric furnace or refining furnace provided separately, or introducing hydrogen into iron ore bath from hearth, or using both methods (method of introducing hydrogen from above and below) to remove oxygen in iron ore bath, and directly reducing iron ore without passing through blast furnace or steelmaking process

Abstract

To provide a new method for producing steel without discharging carbon dioxide at all in a process for producing steel from iron ore.SOLUTION: In a method, iron ore 1 is melted in an electric furnace 2 at a temperature of 1550°C or higher, and then oxygen in an iron ore bath is removed by spraying hydrogen to the iron ore bath surface using a high-speed hydrogen jet stream from above the electric furnace or a refining furnace separately provided, or by introducing hydrogen into the iron ore bath from a hearth, or by using both methods (introducing hydrogen from above and below) to remove oxygen in the iron ore bath, and the iron ore is directly reduced without passing through a blast furnace or a steelmaking process to produce steel.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention belongs to the field related to steel manufacturing that directly reduces iron ore to produce steel.

Background Art

[0002] In recent years, reduction of carbon dioxide emissions has been demanded in various countries around the world as a measure to combat global warming. Approximately 30% of the carbon dioxide emissions in our country come from power plants, and about 10% come from steel production, with the rest from the transportation and household sectors. It is expected that carbon dioxide emissions from power plants will be reduced in the future by switching from coal to LNG, ammonia power generation using ammonia as fuel, nuclear power generation, solar power generation, etc. In the transportation sector, it is expected that carbon dioxide will be reduced by shifting from internal combustion engines such as gasoline to electric vehicles using lithium batteries.

[0003] On the other hand, the largest source of carbon dioxide emissions in steel production is the process of reducing iron ore using coal (mainly coke produced by dry distillation of coal) in the blast furnace process. In the blast furnace, coal (mainly coke) is burned to generate reducing gases such as carbon monoxide to reduce iron ore. In this process, a large amount of carbon dioxide is emitted.

[0004] The hot metal produced in the blast furnace contains about 5% carbon, and in the next steelmaking process, oxygen is blown in to remove the carbon and convert it into steel. Also, in this steelmaking process, carbon monoxide is generated to remove the carbon in the molten steel, used as fuel in other steel processes, and emitted as carbon dioxide. Problems to be Solved by the Invention

[0005] In the steel industry, attempts are being made to reduce the large amount of carbon dioxide emissions from blast furnaces. For example, in order to remove carbon dioxide from the gas discharged from blast furnaces, methods such as using lithium hydroxide solution are being tried, or introducing hydrogen into the blast furnace to replace coal (mainly coke) for reducing iron ore, or reducing the amount of coal used by using hydrogen. However, these methods have the problem of being costly and difficult to put into practical use.

Summary of the Invention

Means for Solving the Problems

[0005] The present invention is characterized in that iron ore is melted in an electric furnace at a temperature of 1550 °C or higher, and hydrogen is sprayed onto the surface of the iron ore bath with a high-speed hydrogen jet airflow from above the electric furnace or a separately provided refining furnace, or hydrogen is introduced into the iron ore bath from the furnace bottom, or both methods (hydrogen introduction methods from above and below) are used to directly produce a steel bath from iron ore without going through a blast furnace or a steelmaking process.

[0006] Spraying hydrogen with a high-speed jet airflow can promote the reaction between hydrogen and oxygen in the iron ore bath by stirring the iron ore bath with the jet flow.

Effects of the Invention

[0007] By the direct reduction of the present invention, compared with the conventional blast furnace method using coal, there is no carbon dioxide emission at all. In addition, since hot metal produced in a blast furnace by the conventional method contains about 5% carbon, carbon in the hot metal is discharged as carbon monoxide or carbon dioxide by blowing oxygen in the subsequent steelmaking process. However, in the present invention, since hydrogen reduction is directly carried out from iron ore without going through a blast furnace or the subsequent steelmaking process, it is possible to produce steel without discharging any carbon monoxide or carbon dioxide.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

Examples

[0013] A method of melting iron ore using the electric furnace of the present invention will be described with reference to FIG. 1. One ton of iron ore 1 was crushed to the size of a golf ball and charged into the electric furnace 2. In this example, 250 Kg of scrap iron 3 was charged into the electric furnace 2 in order to improve the energization efficiency. Further, 40 Kg of granular aluminum (Al) was additionally charged in order to remove oxygen in the iron ore as slag. This electric furnace 2 has three graphite electrodes 4. When the iron ore 1, scrap iron 3, and aluminum are charged, the three graphite electrodes 4 descend and energization is started. In this electric furnace 2, a three-phase alternating current flows through the three graphite electrodes 4 and melting begins. The primary power source of the electric furnace 2 is adjusted by a voltage regulator 6 so that a specified voltage is always applied at 5. In this example, a voltage of 1000 V was applied to this electrode, and 1800 Kwh of electric power was required for complete melting of the iron ore 1.

[0014] The refining of Example 1 will be described with reference to FIG. 2. After completely melting the iron ore, the iron ore bath 9 is transferred from the electric furnace 2 to the refining furnace 7. The water-cooled lance 8 descends from above the refining furnace 7 and sprays a jet air flow containing hydrogen onto the iron ore bath 9 at a speed equal to or higher than the speed of sound. The water-cooled lance 8 is water-cooled in order to protect the temperature of the iron ore bath 9 from approaching 1600 °C. Also, the water-cooled lance 8 is made of copper in order to increase the cooling efficiency. The spraying time of hydrogen ejected from the water-cooled lance 8 is 1 hour, and the hydrogen used is 550 m 3To remove the slag formed on the surface of the steel bath 9, the refining furnace 7 was tilted to discharge the slag. Since the resulting steel bath 9 contained hydrogen which could cause brittle fracture, a vacuum degassing device was used to almost completely remove the hydrogen. This degassing device can also remove the oxygen remaining in the steel bath. In this example, the electric furnace 2 and the refining furnace 7 were used separately, but the refining furnace 7 can also be incorporated into the electric furnace 2.

[0015] The resulting steel was 750 Kg, and its composition was as follows. The composition of the steel was C: 0.0027, Si: 0.22, Mn: 0.35, P: 0.001, S: 0.0001, which was the same as that produced by the conventional blast furnace method of producing hot metal and then removing carbon by blowing oxygen in a converter in the steelmaking process.

Example

[0016] Until the iron ore 1 is melted in the electric furnace, it is the same as in Example 1 and will be described with reference to FIG. 1. One ton of iron ore 1 was crushed to the size of a golf ball and charged into the electric furnace 2. To improve the power supply efficiency, 330 Kg of scrap iron 3 was charged into the electric furnace 2. Further, 50 Kg of granular aluminum (Al) was additionally charged to remove the oxygen in the iron ore as slag. This electric furnace 2 has three graphite electrodes 4. When the iron ore, scrap iron, and aluminum are charged, the three graphite electrodes 4 descend and power supply is started. In this electric furnace, a three-phase alternating current flows through the three graphite electrodes 4 and melting begins. A voltage of 1000 V is applied to these electrodes, and 1980 Kwh of power was required for complete melting of the iron ore 1.

[0017] The refining in Example 2 will be described with reference to FIG. 3. After completely melting the iron ore, it is transferred to the refining furnace 10. Hydrogen is introduced into the iron ore bath 9 from the tuyere 12 installed below this refining furnace 10. Since the tuyere 12 installed at the furnace bottom 11 reaches 1600 °C, LPG is inserted around the tuyere. Since the LPG decomposes at the temperature in contact with the iron ore bath 9, the tuyere is cooled by an endothermic reaction. The inflow time of hydrogen ejected from the tuyere 12 is 1.5 hours, and the hydrogen used is 490 m 3 . In order to remove the slag generated on the surface of the iron ore steel bath 9, the refining furnace 10 is tilted to remove the slag. Since the resulting steel bath 9 contains hydrogen that causes brittle fracture, a vacuum degassing device is used to almost completely remove the hydrogen. This degassing device can also remove the oxygen remaining in the steel bath.

[0018] The resulting steel was 700 Kg, and its components were as follows. Steel components: C: 0.0025, Si: 0.21, Mn: 0.29, P: 0.001, S: 0.0001. There was no difference in the method of producing hot metal by the conventional blast furnace method and then removing carbon by blowing oxygen in a converter in the steelmaking process and the steel components.

Example

[0019] Until the iron ore is melted in the electric furnace, it is the same as in Example 1, so it will be described with reference to Figure 1. 1 ton of iron ore 1 is crushed to the size of a golf ball and put into the electric furnace 2. In order to improve the power conduction efficiency, scrap iron (150 Kg) 3 is put into the electric furnace 2. Furthermore, 60 Kg of granular aluminum (Al) is additionally put in to remove the oxygen in the iron ore as slag. There are three graphite electrodes 4 in this electric furnace 2. When the iron ore 1, scrap iron 3, and aluminum are put in, the three graphite electrodes 4 descend and power conduction starts. In this electric furnace, a three-phase alternating current flows through the three graphite electrodes 4 and melting begins. A voltage of 1000 V is applied to these electrodes, and 1950 Kwh of electric power is required for complete melting of the iron ore 1.

[0020] The refining of Example 3 will be described with reference to Figure 4. After the iron ore was completely melted, it was transferred to the refining furnace 13. The water-cooled lance 14 descended from above the refining furnace 13 and blew a jet air stream containing hydrogen onto the iron ore bath 15 at a speed above the speed of sound. At the same time, hydrogen was introduced into the iron ore bath 15 from the tuyere 16 installed on the hearth 17 under the refining furnace 13. The inflow time of hydrogen was 0.75 hours, and the hydrogen used was 450m 3 . In order to remove the slag generated on the surface of the steel bath 15, the refining furnace 13 was tilted to remove the slag. Since the resulting steel bath contained hydrogen that could cause brittle fracture, a vacuum degassing device was used to almost completely remove the hydrogen. This degassing device can also remove the oxygen remaining in the steel bath.

[0021] The resulting steel was 700 Kg, and its components were as follows. Components of the steel: C: 0.0023, Si: 0.19, Mn: 0.19, P: 0.001, S: 0.0001. There was no difference in the method of producing hot metal by the conventional blast furnace method and then removing carbon by blowing oxygen in a converter in the steelmaking process and the components of the steel. Industrial applicability

[0022] In the present invention, after melting the iron ore in an electric furnace, hydrogen was blown into a separately provided refining furnace to produce steel. However, the electric furnace can also have the function of the refining furnace.

[0023] Also, even if the iron ore previously reduced in a reduction furnace is melted in the electric furnace of the present invention and then put into a refining furnace into which hydrogen can be introduced, it is possible to produce steel having the same components as the steel produced by the blast furnace method.

Explanation of symbols

[0024] 1: Iron ore 2: Electric furnace 3: Scrap iron 4: Graphite electrode 5: Power source 6: Voltage regulator 7: Refining furnace 8: Water-cooled lance 9: Iron ore bath 10: Refining furnace 11: Hearth 12: Tuyere 13: Smelting furnace 14: Water-cooled lance 15: Iron ore bath 16: Tuyere 17: Hearth

Claims

【Claim 1】 A method for producing steel by directly reducing iron ore without passing through a blast furnace or a steelmaking process, which comprises melting iron ore in an electric furnace at a temperature of 1550 °C or higher, and then blowing hydrogen onto the surface of the iron ore bath using a high-speed hydrogen jet air stream from above the electric furnace or a separately provided refining furnace, or introducing hydrogen into the iron ore bath from the furnace bottom, or using both methods (introducing hydrogen from above and below) to remove oxygen in the iron ore bath

Images