JPH08239708A - Fluidized reduction method of powder iron ore - Google Patents

Abstract

PURPOSE: To greatly improve reduction ratio by oxidizing the iron whose oxidation number is 2 in the powder iron ore into the iron whose oxidation number is 3 prior to the reduction to improve the reducibility of the ore. CONSTITUTION: A raw material ore in which the ratio of the iron whose oxidation number is 2 in the total iron ratio is >=10wt.% is charged in an iron ore oxidizing furnace 1 from an oxidized raw material feeding port 2, and an oxidizing gas 4 is introduced from a gas diffusing plate 3 for blowing the oxidizing gas at the bottom part of the oxidizing furnace to form a fluidized layer to oxidize the powder ore through the solid-gas reaction. The oxidized ore 5 is discharged from a discharge tube 6 and the exhaust gas 7 from an oxidizing furnace is discharged from the top of the oxidizing furnace. The oxidized ore 5 is charged from a reducing raw material feeding port 19 of a fluidized reducing equipment 10 into a riser 11 through a relay hopper 20, the reducing gas 13 is introduced from a reducing gas blowing nozzle 12 at the bottom part of the riser to form a fluidized layer, and the powder ore is reduced through the solid-gas reaction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reducing powdered iron ore containing iron having an oxidation number of 2 in a fluidized bed.

[0002]

2. Description of the Related Art Iron ore is Fe ₂ composed of iron with an oxidation number of 3.
Hematite-based ores containing O ₃ as a main component are generally used. There are also magnetite or maghemite series ores having a relatively high FeO or Fe ₃ O ₄ content of iron having an oxidation number of 2. Although there is no clear standard, if the proportion of iron with an oxidation number of 2 in the total iron content is less than a few percent, hematite ore, if about 10 to 20%, maghemite ore, it If it is above, it is said to be magnetite ore. Techniques for performing reduction operations on ores of these various properties have been devised.

A fluidized bed for reducing powdered iron ore is used as a preliminary reduction device for powdered ore in the production of pig iron by smelting reduction, as disclosed in, for example, JP-A-1-111807. This fluidized bed is of a type called a circulating fluidized bed, and comprises a riser having a powdery ore charging section at the top and a reducing gas introducing section at the bottom, a cyclone provided outside the riser, and a powdery ore collected by the cyclone. It consists of a downcomer for returning to the riser.
Further, JP-A-62-228889 discloses a technique of improving the efficiency of the process by preheating the iron ore before reducing it in the fluidized bed preliminary reduction furnace. Further, Japanese Patent Publication No. 6-37653 discloses a technique for appropriately maintaining the particle volume fraction in a fluidized-bed reduction reactor by adjusting the gas flow rate and the circulation flow rate of the ore aiming at reducing iron ore with high efficiency. Is disclosed.

[0004]

In the field of fluidized reduction of iron ore, various efforts have been made to devise an apparatus and a reduction method for obtaining high efficiency and high productivity. However, among the ores that are naturally produced, ores that contain a large amount of iron with an oxidation number of 2 have poor reducibility, and even if they are inexpensive, they require a lot of time and a reducing agent for reduction, and as a result, It has been said that cost competitiveness is low. That is, even if an attempt is made to fluidize and reduce magnetite or maghemite ore with conventional technology, the reaction rate is significantly smaller than that of hematite ore, so the production amount per fluidized bed is low, As the gas consumption rate increases, good results cannot be achieved industrially.

Further, even if some improvement can be achieved by the prior art,
As for hematite-based ores, since similar measures can be used to improve them, the relative differences do not change and the evaluation as an ore raw material remains low. The present invention has been made in view of these points, by performing a reduction in a fluidized bed after the magnetite, maghemite ore is treated in advance to improve the reducibility, as a result of the conventional Also aims to greatly improve the reduction efficiency.

[0006]

According to the present invention, in a fluidized reduction method of reducing powdered iron ore in a fluidized bed to obtain reduced ore, the ratio of iron having an oxidation number of 2 to the total iron content in the powdered iron ore is 10% by weight. The iron ore powder described above is oxidized into iron having an oxidation number of 3 in an oxidizing atmosphere, and then fluidized and reduced in a fluidized bed. Further, the present invention is characterized by oxidizing 10 to 50% of iron having an oxidation number of 2 contained in the fine iron ore.

[0007]

The present invention will be described below with reference to FIG. From the oxidizing raw material supply port 2 of the iron ore oxidizing furnace 1, to the iron ore oxidizing furnace 1, the raw ore in which the proportion of iron having an oxidation number of 2 in the total iron content is 10% by weight or less is charged, and the oxidizing gas at the bottom of the oxidizing furnace is introduced. The oxidizing gas 4 is introduced from the blowing gas dispersion plate 3 to form a fluidized bed, and the powdery ore is oxidized by a solid-gas reaction. The oxidized ore 5, which is an intermediate product, is discharged from the oxide ore discharge pipe 6, and the oxidizing furnace exhaust gas 7 is discharged from the upper part of the iron ore oxidizing furnace 1.

Oxide ore 5 oxidized in the iron ore oxidation furnace 1
Is charged into the riser 11 from the reducing raw material supply port 19 of the fluidized reduction apparatus 10 via the relay hopper 20, and the reducing gas 13 is introduced from the reducing gas blowing nozzle 12 at the bottom of the riser to form a fluidized bed. , Reduce powdery ore by solid-gas reaction.

The thus-reduced ore is sent from the top of the riser to the primary cyclone 14 together with the exhaust gas, and the ore collected there from the primary downcomer 15 to the riser 1
Cycle to 1. A part thereof is extracted as a final product through the reduced ore extracting pipe 16. Further, the exhaust gas discharged from the primary cyclone 14 is guided to the secondary cyclone 17 to remove dust again, and then the collected powder 18 is returned to the primary downcomer 15.

The present invention is intended to efficiently reduce iron ore. When magnetite or maghemite-type powdered ore is used as a raw material, it is intentionally oxidized and then charged into a reduction furnace. There is a feature of the present invention. Originally, magnetite or maghemite-based ores are somewhat reduced compared to hematite-type ores, and it is considered that the reduction operation is advantageous accordingly. However, according to the study by the present inventors, once the iron having the oxidation number 2 is oxidized to the iron having the oxidation number 3, the reducibility is improved.

That is, it is effective to shorten the reduction time by oxidizing iron having an oxidation number of 2 and changing it to iron having an oxidation number of 3 which has a good reducibility. Therefore, although the present invention requires two steps of oxidation and reduction, the total required time is shortened compared with the case where the present invention is not applied, and the total basic unit of gas required for reduction is also reduced. However, although the time required for reduction is shortened by performing the oxidation treatment, the time required for oxidation is required. Therefore, if the overall productivity is to be improved, all irons with an oxidation number of 2 are required. Need not be oxidized to iron with an oxidation number of 3.

[0012] Even if only partially oxidized, the effect of shortening the reduction time occurs, and if the ratio of iron having an oxidation number of 2 to the total iron content in the oxidized iron ore is 10 to 50% of the value in the raw ore. The effect of shortening the reduction time becomes extremely remarkable. Here, the oxidation time is too long to oxidize iron having an oxidation number of 2 to less than 10%, and 50% of iron having an oxidation number of 2 is not preferable.
In the case of superoxidation, the effect of reducing the reduction time by oxidation is small.

Since the oxidation furnace used in the present invention only oxidizes iron having an oxidation number of 2, it is obvious that a rotary kiln can be used instead of the fluidized bed. From the viewpoint of effectively utilizing sensible heat, it is desirable to load the oxide ore into the reduction furnace at a high temperature, but in consideration of the difficulty of transfer technology and the complexity of operation control, once stored outside the system, Even if the cooled one is charged into the reduction furnace, the effect of improving the reducibility in the reduction furnace is not affected at all.

Further, the oxidizing atmosphere can be easily created by, for example, a gas obtained by completely burning a gaseous fuel or a liquid fuel. The gas composition of the oxidizing atmosphere is CO
Any one of ₂ , H ₂ O and O ₂ must be contained. Although an inert gas such as nitrogen lowers the partial pressure of the oxidizing gas and lowers the oxidation rate, its inclusion is acceptable. Considering the cost, the time required for oxidation, the combustion temperature, etc., it may be determined whether to burn the fuel with air or oxygen or oxygen-enriched air.

Further, the incorporation of CO and H ₂ is not desirable because it acts on the reduction, and should be minimized. However,
Normally, if the theoretical oxygen ratio is set to 1 or more and fuel is burned, C
Since the existence of O and H ₂ can be almost ignored, the theoretical oxygen amount with respect to the fuel may be set to 1 or more when producing the oxidizing gas. Further, the higher the temperature of the oxidation furnace is, the faster the oxidation reaction is. Therefore, a temperature of 400 ° C. or higher, preferably 600 ° C. or higher is suitable in order to shorten the time required for the oxidation.

[0016]

EXAMPLE In a fluidized bed reduction apparatus, the reduction temperature is 80
The iron ore was reduced under the conditions of 0 ° C to 910 ° C and a gas flow rate in the riser of 5 m / s. The components of the reducing gas used are shown in Table 1.

[Table 1]

In Example 1, a magnetite-based powdered iron ore in which the ratio of iron having an oxidation number of 2 to the total iron content in the raw material was about 40% by weight was subjected to an oxidation treatment and then charged into a reduction furnace. The average particle size was 180 μm and the weight percentage of −2 mm was 98%. The operating temperature of the iron ore oxidation furnace was 850 ° C. The oxidizing gas was produced by burning pulverized coal with oxygen-enriched air. The oxidizing gas composition is shown in Table 2.

[Table 2]

In Example 1-1, the residence time of the ore in the iron ore oxidation furnace was set to 15 minutes. In Example 1-2, the residence time in the oxidation furnace was set to 8 minutes. It was used for reduction without doing anything. Table 3 shows the ore compositions of Example 1-1 and Example 1-2 before oxidation (oxidation raw material) and after oxidation.

[Table 3]

A comparison of the total time required for reduction and oxidation of Example 1-1 and Example 1-2 and Comparative Example 1 is shown in FIG. In this case, the final product reduction rate is 85%. The total time of oxidation and reduction required to obtain a product with this reduction rate was 36 minutes in the case of Example 1-1, which was the shortest, and 41 minutes and 45 minutes in Example 1-2 and Comparative Example 1 respectively. Became. Also, comparing only the time required for reduction,
In Example 1-1, it is less than half of Comparative Example 1 in which no oxidation treatment is performed, and the effect of shortening is also recognized in Example 1-2.

In Example 2, a maghemite-type pulverized iron ore in which the ratio of iron having an oxidation number of 2 to the total iron content in the raw material was approximately 10% by weight was subjected to an oxidation treatment and then charged into a reduction furnace. . The average particle size was 360 μm and the weight percentage of −2 mm was 87%. The operating temperature of the oxidation furnace was 650 ° C. Oxidizing gas is L
It was produced by burning PG with air. Table 4 shows the oxidizing gas composition.

[Table 4]

In Example 2-1, the residence time in the iron ore oxidizing furnace was 20 minutes, and in Example 2-2, the residence time in the oxidizing furnace was 12 minutes. In Comparative Example 2, reduction was carried out without any oxidation treatment. Example 2 before oxidation (oxidation raw material) and after oxidation
-1, and the ore composition of Example 2-2 is shown in Table 5.

[Table 5]

A comparison of the final product reduction rates of Example 2-1, Example 2-2, and Comparative Example 2 is shown in FIG. In this case, the total time required for reduction and oxidation was 60 minutes. The product reduction rate reached in the same time was the case of Example 2-1 in which the proportion of iron having an oxidation number of 2 in the total iron content in the ore before the reduction operation was 45% of that in the raw ore. It was the highest, followed by Example 2-2 and Comparative Example 2.

[0023]

According to the present invention, it is possible to greatly improve the reduction rate of a powdered iron ore containing iron having an oxidation number of 2, which is originally poor in reducibility, and to improve the productivity of the reduced ore and the reduction gas basic unit. Therefore, its industrial contribution is great.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a fluidized reduction system based on the method of the present invention.

FIG. 2 is a comparison chart of an example of time required to obtain a product with a reduction rate of 85% and a comparative example.

FIG. 3 is a comparison chart of the reduction ratios reached within a certain processing time between an example and a proportional ratio.

[Explanation of symbols]

 1: Iron ore oxidation furnace 2: Oxidizing raw material supply port 3: Oxidizing gas blowing gas dispersion plate 4: Oxidizing gas 5: Oxide ore 6: Oxide ore discharge pipe 7: Oxidation furnace exhaust gas 10: Fluidization reduction device 11: Riser 12: Reducing gas blowing nozzle 13: Reducing gas 14: Primary cyclone 15: Primary downcomer 16: Reduction ore extraction pipe 17: Secondary cyclone 18: Collecting powder 19: Reduction raw material supply port 20: Relay hopper

Claims (2)

[Claims] 1. A fluidized reduction method of reducing iron ore in a fluidized bed to obtain reduced ore, wherein the iron ore having an oxidation number of 2 with respect to the total iron content in the iron ore is 10% by weight or more, A fluidized reduction method for fine iron ore, comprising fluidizing in a fluidized bed after being oxidized to iron having an oxidation number of 3 in an oxidizing atmosphere. 2. One of irons having an oxidation number of 2 contained in fine iron ore.
The fluidized reduction method according to claim 1, wherein 0 to 50% is oxidized.