JP2002294318A - Outdoor storage method of reduced pellets - Google Patents

Abstract

(57) [Problem] To provide an outdoor storage of reduced pellets that can reliably prevent reoxidation by a simple deposition method without special processing on the reduced pellets when storing the reduced pellets outdoors. Provide storage method. SOLUTION: When depositing and storing the reduced pellets outdoors, a method for storing reduced pellets outdoors, comprising mixing a fine-grained substance with the reduced pellets to form a deposited layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for storing reduced pellets outdoors, and to prevent generation of heat due to reoxidation during storage.

[0002]

2. Description of the Related Art Reduced iron produced by a direct reduction method or the like, whether in the form of a lump or pellets or briquettes, is oxidized from the surface of the reduced iron if left in an outdoor air atmosphere for a long time. Eventually, there is a tendency to return to the state of iron oxide. This is because iron oxidizes with oxygen and moisture in the air. In addition, since this oxidation is an exothermic reaction, when the reduced pellets are deposited outdoors, the temperature of the deposited layer rises due to oxidation and becomes high. For this reason, various methods have been studied to prevent re-oxidation and heat generation.

[0003] For example, as disclosed in Japanese Patent Application Laid-Open No. 50-116343, a method of treating a surface of reduced iron with an oxygen-containing medium to form a passive film composed of a dense oxide, a so-called method. Oxidation passivation (passivation treatment) method, JP-A-50-116343, JP-A-50-116343
JP-A-5-128515, JP-B-59-17164, JP-B-60-12404, and JP-B-60-17
No. 803, etc., a method of applying an inert coating to the surface of reduced iron using a chemical solution, an oily organic rust inhibitor, a hydratable inorganic rust inhibitor such as cement, etc. Many technologies have been developed.

In the former method, the reduced pellets are treated with a weakly oxidizing gas at a temperature of 560 ° C. or lower to form a dense wustite layer having a protective action on individual particles. In the latter, the surface of the reduced iron and the air are physically blocked by a coating agent. Others aim at reducing the specific surface area and reducing the contact area with air, etc., by aggregating reduced iron by hot pressing to form a prequette. A certain effect can be expected in preventing oxidation.

[0005]

As described above, the conventional method for preventing reoxidation of reduced iron when stored outdoors is as follows.
In each case, a step of treating the surface of reduced iron in advance and an apparatus for the same are required, and a certain amount of cost is required. Therefore, it has been inevitable to implement the method from an economic viewpoint. That is, in the oxidation passivation, if the processing temperature fluctuates or the component of the processing gas fluctuates, not only a desired oxide film is not formed, but also there is a risk that re-oxidation will proceed significantly. In particular, since the oxidation reaction is an exothermic reaction, once the oxidation reaction starts suddenly, the oxidation proceeds rapidly and falls into an extremely dangerous state, so that high-precision control is required.

The method of applying an inert coating using a chemical solution, an oil-based organic rust preventive agent, paint or the like is relatively reliable if uniform coating is possible, but it is troublesome and economically difficult to achieve. In addition, there is a problem that the coating agent becomes a pollutant of steel in the steelmaking process of the next step. In addition, hot briquetting has a problem in practical use in terms of cost and reliability. As described above, at present, a highly reliable method of preventing oxidation of reduced iron and an outdoor storage method have not yet been found.

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, the present invention provides an outdoor storage method of reduced pellets that can reliably prevent reoxidation by a simple deposition method without special processing of the reduced pellets in outdoor storage. The purpose is to provide.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems in the conventional method, and its gist lies in the following means. (1) A method of storing reduced pellets outdoors by depositing the reduced pellets outdoors and storing the reduced pellets by mixing a fine-grained substance with the reduced pellets. (2) The outdoor storage method for reduced pellets according to (1), wherein the particle diameter of the fine particles mixed with the reduced pellets is 15% or less of the particle diameter of the reduced pellets. (3) The outdoor storage method for reduced pellets according to (1) or (2), wherein the weight ratio of the fine-grained substance mixed with the reduced pellets is 5 to 30% based on the reduced pellets. (4) The outdoor storage method of reduced pellets according to any one of (1) to (3), wherein the storage temperature of the reduced pellets mixed with the fine-grained substance is suppressed to 200 ° C. or less.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
According to the present invention, when the reduced pellets are deposited outdoors and stored, the reduced pellets are preliminarily mixed with a fine-grained substance, and reduced iron is deposited in an outdoor yard to form a deposited layer of reduced pellets and stored outdoors. How to In order to prevent re-oxidation and heat generation when depositing and storing the reduced pellets outdoors, it is effective to suppress the oxidation reaction, suppress the temperature rise of the deposited layer, and promote the heat radiation from the deposited layer. The present invention can achieve all of these.

[0010] Reoxidation of the reduced pellets is caused by oxygen and water in the air that have entered the voids in the deposited reduced pellet layer. Therefore, if fine particles are mixed in the reduced pellets beforehand, when the reduced pellets are deposited, the fine particles enter the voids of the deposited reduced pellet layer and are in a state of closing the gaps, thereby causing oxidation. Oxygen and water hold can be reduced.

[0011] In addition, by entering the fine-grained substance into the void,
The heat capacity of the entire deposited layer mainly composed of the reduced pellets increases, and even if oxidative heat is generated, the amount of the substance to be heated is large, so that the rising temperature is also low. Further, since the reduced pellet voids are filled with the fine-grained substance, heat conduction in the deposited layer of the reduced pellets is promoted, so that heat hardly accumulates.

Usually, the temperature rise in the deposited layer of reduced pellets is 20
When the temperature becomes 0 ° C. or more, there is a tendency to proceed rapidly. For this reason, it is important to suppress heat generation as much as possible and increase the heat dissipated to prevent the temperature from rising to 200 ° C. Non-oxidizing particles must be used as fine-grained substances. For example, sintered ore powder, fine iron ore, crushed slag powder, river sand, etc. can be easily used from a practical standpoint. It is.

If the particle size of the fine particles to be mixed is too large, the fine particles will not enter the voids of the reduced pellets and cannot enjoy the above-mentioned effects. Therefore, the particle size of the fine particles should be 15% or less of the particle size of the reduced pellets. It is desirable. In this way, when the reduced pellets are used, the fine particles and the reduced pellets can be easily separated by using a sieve, and the fine particles can be recycled, so that they can be reused.

When the weight ratio of the fine particles to be mixed to the reduced pellets is less than 5, the above-mentioned effects cannot be sufficiently achieved, and when it exceeds 30%, there is a large amount to fill the voids of the reduced pellets. Too much, reducing the storage of reduced pellets per area of the stockyard,
Not only is the storage efficiency deteriorated, but the load of sieving the fine particles when using the reduced pellets is undesirably increased.

[0015]

EXAMPLES The present invention was applied to reduced pellets having a particle diameter of 10 mm (average) obtained by reduction in a shaft furnace. Initial metallization was 93.5%. Sintered ore powder was used as the fine-grained substance. About 1000 to 1200 tons of reduced pellets were deposited in an outdoor yard in a shape of about 20 m in width, about 10 m in depth and about 4 m in height. The reduction rate of the reduced pellet and the degree of heat generation of the sedimentary layer were evaluated by changing the particle diameter and the mixing ratio of the fine-grained substance. The results are shown in Table 1 as Examples and Comparative Examples. As apparent from Table 1, by applying the present invention,
It can be seen that even if the reduced pellet is left outdoors, the progress of reoxidation and the generation of heat are prevented.

[0016]

[Table 1]

[0017]

According to the present invention, reoxidation of reduced pellets can be prevented only by mixing a fine-grained substance and forming a sedimentary layer at the time of outdoor storage of the reduced pellets without adding any special treatment to the reduced pellets. can do.

Claims (4)

[Claims] 1. A method for storing reduced pellets outdoors, comprising depositing reduced pellets outdoors and mixing fine particles with the reduced pellets to form a deposited layer. 2. The method according to claim 1, wherein the particle size of the fine particles mixed with the reduced pellets is 15% or less of the particle size of the reduced pellets. 3. The method for storing reduced pellets according to claim 1, wherein the weight ratio of the fine-grained substance mixed with the reduced pellets is 5 to 30% based on the reduced pellets. . 4. The reduced pellet according to claim 1, wherein the storage temperature of the reduced pellet mixed with the fine-grained substance is suppressed to 200 ° C. or less when the pellet is stored outdoors. Outdoor storage method.