Direct reduction ironmaking process

Abstract

This invention provides a direct reduction ironmaking method that can reduce the amount of heat supplied from an external source to maintain the temperature of the hydrogen-induced reduction reaction of iron oxide. [Solution] The direct reduction ironmaking method of the present invention is a method of reducing raw iron ore by bringing hydrogen gas into contact with the raw iron ore and heating it. Furthermore, by filling the direct reduction furnace with metal heating element particles containing a hydrogen storage alloy that absorbs and releases hydrogen to generate excess heat, along with the raw iron ore, and supplying heated hydrogen gas to the direct reduction furnace to reduce the raw iron ore, the amount of heat that needs to be supplemented from the outside during the reduction reaction of iron oxide by hydrogen can be reduced.

Description

Technical Field

[0001] The present invention relates to a direct reduction ironmaking method, and more particularly to a direct reduction ironmaking method in which hydrogen is brought into contact with raw iron ore to reduce it to pig iron particles.

Background Art

[0002] As an ironmaking method for obtaining iron (reducing iron oxide) from a raw material containing iron oxide, there is known a direct reduction ironmaking method in which iron ore is reduced while in a solid state using natural gas and then transferred to an electric furnace for melting.

[0003] Since this direct reduction ironmaking method can obtain reduced iron by reducing iron ore without using coke, it can suppress the generation of CO2 lower than that of a blast furnace.

[0004] In recent years, for the purpose of reducing carbon dioxide emissions, the development of a direct reduction ironmaking method using hydrogen as a reducing gas has been progressing.

[0005] Patent Document 1 discloses obtaining reduced iron by reducing iron oxide using a reducing gas containing hydrogen and carbon monoxide.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, since the reduction reaction of iron oxide by hydrogen is an endothermic reaction, heating is required. In Patent Document 1, since the reduction reaction of iron oxide by carbon monoxide, which is an exothermic reaction, is used as a heat source, carbon dioxide is emitted.

[0008] This invention has been made in view of the problems of the prior art, and its objective is to provide a direct reduction ironmaking method that can reduce the amount of heat supplied from the outside to maintain the temperature of the reduction reaction of iron oxide with hydrogen. [Means for solving the problem]

[0009] The inventors of this invention have conducted extensive research to achieve the above objectives and have found that these objectives can be achieved by using a hydrogen storage alloy that generates excess heat through the absorption and release of hydrogen, thereby completing the present invention.

[0010] In other words, the direct reduction ironmaking method of the present invention is a method of reducing raw iron ore by bringing it into contact with hydrogen gas and heating it. The method is characterized by filling the direct reduction furnace with metal heating element particles containing a hydrogen storage alloy that absorbs and releases hydrogen to generate excess heat, together with the raw iron ore, and then supplying heated hydrogen gas to the direct reduction furnace to reduce the raw iron ore. [Effects of the Invention]

[0011] According to the present invention, by using a hydrogen storage alloy that generates excess heat, it is possible to provide a direct reduction ironmaking method that can reduce the amount of heat that needs to be supplied from the outside during the reduction reaction of iron oxide with hydrogen. [Modes for carrying out the invention]

[0012] The direct reduction ironmaking method of the present invention will be described in detail. The present invention's direct reduction ironmaking method is an ironmaking method that uses hydrogen as a reducing agent. It involves supplying heated hydrogen gas from the bottom of a direct reduction furnace and bringing the hydrogen gas into contact with the raw iron ore at a high temperature of approximately 1000°C, thereby reducing the raw iron ore while it remains in a solid state without melting it. In this method, metal heating element particles are directly packed into the reduction furnace along with the raw iron ore to carry out the reduction.

[0013] The above-mentioned metal heating element particles include a hydrogen storage alloy that absorbs and releases hydrogen to generate excess heat. Hydrogen storage alloys absorb supplied hydrogen gas and release it when heated. While the hydrogen release reaction itself is an endothermic reaction, the hydrogen storage alloy generates pulsed heat when releasing hydrogen. This pulsed heat generation results in excess heat exceeding the amount of heat used to heat the hydrogen storage alloy.

[0014] In the hydrogen storage alloy described above, when two phases coexist within the alloy, the equilibrium points at which the energy balance between the two phases is different, resulting in different rates of hydrogen absorption and release. Therefore, one phase releases hydrogen while the other phase absorbs it. This state continues until one phase reaches its equilibrium point, at which point hydrogen release from the other phase stops.

[0015] Since the equilibrium point of one phase is offset from the equilibrium point of the other phase, the other phase then releases hydrogen and the first phase absorbs hydrogen, and the release of hydrogen from the other phase continues past the equilibrium point of the first phase until it reaches the equilibrium point of the other phase.

[0016] This cycle of hydrogen release from one phase, equilibrium point in one phase, hydrogen release from the other phase, and equilibrium point in the other phase is repeated in hydrogen gas under high-temperature conditions of 300°C to 1000°C, resulting in the continuation of the pulsed exothermic reaction described above.

[0017] The direct reduction ironmaking method of the present invention involves directly filling a reduction furnace with metal heating element particles containing the hydrogen storage alloy along with the raw iron ore, and directly supplying heated hydrogen gas from the outside into the reduction furnace to reduce the raw iron ore. As a result, excess heat can be continuously obtained, and the excess heat and hydrogen released from the metal heating element particles are directly supplied to the raw iron ore, allowing for efficient reduction of the raw iron ore and reducing the amount of heat supplied from the outside.

[0018] As the hydrogen storage alloy described above, alloy particles in which multiple solid phases coexist under desired conditions can be used. The temperature range in which multiple solid phases coexist can be determined from the equilibrium phase diagram.

[0019] Examples of the metal materials constituting the hydrogen storage alloy include Li, Be, Na, Mg, Al, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Rb, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, In, Sn, Sb, Cs, Ba, Ta, W, Re, Os, Ir, Pt, Au, Hg, Tl, Pb, Bi, Po, etc.

[0020] Among them, it is preferable to use an alloy with a large difference in the formation enthalpy between the metal hydride forming one phase and the metal hydride forming the other phase.

[0021] Examples of alloys in which two solid phases with a large difference in the formation enthalpy coexist include Ni-Zr alloys with Ni:Zr of 30:70 to 70:30 mol%, Al-Ni alloys with Al:Ni of 75:25 to 65:35 mol%, and Al-Ca alloys with Al:Ca of 80:20 to 70:3 mol%.

[0022] The metal heating element particles preferably have a core-shell structure with a porous membrane coating formed of ceramic with the hydrogen storage alloy as the core. The porous membrane coating has through-holes and allows hydrogen gas to permeate.

[0023] In the direct reduction ironmaking method of the present invention, since the metal heating element particles are filled into the direct reduction furnace together with the raw iron ore, a very large load is applied to the metal heating element particles.

[0024] Since the metal heating element particles have a porous membrane coating formed of ceramic on their surfaces, the strength of the metal heating element particles is improved, and it is possible to prevent the hydrogen storage alloy from being crushed and mixed into the reduced pig iron, resulting in a decrease in purity.

[0025] Furthermore, by containing ceramic fibers in the hydrogen storage alloy constituting the core of the metal heating element particles, the strength of the metal heating element particles can be improved.

[0026] In addition, if the metal heating element particles are spherical with a circularity of 0.8 or greater, the load will be applied isotropically, preventing the metal heating element particles from being crushed. The degree of circularity can be calculated using the following formula. Circularity = (Circumference of a circle with the same area as the projected area of ​​the particle) / (Length of the outline of the particle's projection)

[0027] It is preferable that the particle size of the metal heating element particles and the particle size of the raw iron ore satisfy the following relationship. (√2-1) × R < r < R However, R represents the average particle size (D50) of the metal heating element particles, and r represents the average particle size (D50) of the raw iron ore.

[0028] When the particle size of the metal heating element particles and the particle size of the raw iron ore satisfy the above relationship, the gaps between the metal heating element particles and between the raw iron ore particles become larger, making it easier for hydrogen gas to flow through the direct reduction furnace filled with the raw iron ore and metal heating element particles, thereby improving the reduction efficiency.

[0029] Specifically, since the average particle size of raw iron ore is generally around 10-30 mm, if the average particle size (D50) of the metal heating element particles is 10-100 mm, gaps are formed between the metal heating element particles and between the raw iron ore, making it easier for hydrogen gas to flow.

[0030] The above-mentioned raw material iron ore and metal heating element particles are directly fed into the reduction furnace through the raw material inlet at the top of the reduction furnace and filled into the furnace.

[0031] The raw iron ore and metal heating element particles packed directly into the reduction furnace may be arranged in alternating layers, forming layers of raw iron ore and metal heating element particles, or they may be uniformly dispersed.

[0032] By alternately filling the raw iron ore and metal heating element particles, it is possible to ensure air permeability within the reduction furnace while supplementing the heat necessary for the reduction reaction of the iron ore. Furthermore, by uniformly dispersing and filling the material, the distance between the raw iron ore and the metal heating element particles is reduced, allowing excess heat from the metal heating element particles to be efficiently transferred to the raw iron ore.

[0033] The above direct reduction ironmaking method includes a process for separating the pig iron obtained by reducing the raw iron ore from the metal heating element particles.

[0034] As for separation methods, if the metal heating element particles are not magnetic, one method is to separate the pig iron and the metal heating element particles using magnetic force. If the pig iron and the metal heating element particles are of different sizes, one method is to separate them by sieving.

[0035] This prevents the purity of the pig iron from decreasing due to the metal heating particles. Furthermore, the recovered metal heating particles can be reused repeatedly by regenerating them by heating them in a hydrogen atmosphere, which generates excess heat again.

Claims

1. A direct reduction ironmaking method is used, in which raw iron ore is heated by contacting it with hydrogen gas to reduce the raw iron ore, A direct reduction ironmaking method characterized by filling a direct reduction furnace with metal heating element particles containing a hydrogen storage alloy that absorbs and releases hydrogen to generate excess heat, together with the raw iron ore, and supplying heated hydrogen gas to the direct reduction furnace to reduce the raw iron ore.

2. The above metal heating element particles have a core-shell structure, The direct reduction ironmaking method according to claim 1, characterized in that the above shell has a porous membrane coating made of ceramic.

3. The direct reduction ironmaking method according to claim 1, characterized in that the metal heating element particles contain ceramic fibers inside.

4. The direct reduction ironmaking method according to claim 1, characterized in that the above-mentioned metal heating element particles are spherical and have a circularity of 0.8 or more as defined by the following formula. Circularity = (Circumference of a circle with the same area as the projected area of ​​the particle) / (Length of the outline of the particle's projection)

5. The direct reduction ironmaking method according to claim 1, characterized in that the particle size of the metal heating element particles and the particle size of the raw material iron ore satisfy the following relationship. (√2-1) × R < r < R However, R represents the average particle size (D50) of the metal heating element particles, and r represents the average particle size (D50) of the raw iron ore.

6. The direct reduction ironmaking method according to claim 5, characterized in that the average particle size (D50) of the metal heating element particles is 10 to 100 mm.

7. The direct reduction ironmaking method according to claim 1, characterized in that the above-mentioned raw iron ore and the above-mentioned metal heating element particles are alternately packed into the above-mentioned direct reduction furnace to form a raw iron ore layer and a metal heating element particle layer.

8. The direct reduction ironmaking method according to claim 1, characterized in that the above raw iron ore and the above metal heating element particles are uniformly dispersed and packed into the above direct reduction furnace.

9. Furthermore, the direct reduction ironmaking method according to claim 1 is characterized by having a process for separating the reduced pig iron and the metal heating element particles by magnetic force.

10. Furthermore, the direct reduction ironmaking method according to claim 5 is characterized by having a process of separating the reduced pig iron and the metal heating element particles by sieving.

11. Furthermore, the direct reduction ironmaking method according to claim 9 or 10 is characterized by comprising a process of regenerating the separated metal heating element particles by heating them in a hydrogen atmosphere.