Specialized metallurgical processes – compositions for use therei – Processes – Electrothermic processes
Reexamination Certificate
2002-05-21
2004-05-25
Andrews, Melvyn (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Electrothermic processes
Reexamination Certificate
active
06740138
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a molten steel producing method and particularly to a method of storing a high-carbon molten bath in a reservoir furnace and using the stored molten bath to produce a molten steel in a steel producing furnace.
2. Discussion of Related Art
There are two molten-steel producing methods that are widely practiced; one is so-called blast-furnace-converter process in which iron ore and coke are put in a blast furnace so as to be molten and reduced at high temperature and the thus obtained hot metal whose C content is high is transferred to a converter in which oxygen is blown into the hot metal to decarbonize the metal and produce a molten steel; and the other is electric-furnace process in which scrap is molten in an electric furnace so as to produce a molten steel.
In the latter, electric-furnace process, scrap obtained from, e.g., waste cars, and a slag-producing material such as calcium oxide are put in an electric furnace such as an arc furnace, and electric power is applied to the electric furnace to melt the scrap.
Subsequently, usually, oxygen is blown into the molten steel to remove phosphorus and other impurities, and the concentration of carbon of the molten steel is adjusted.
Then, the molten steel is further heated, and the electric furnace is tilted to output a core portion of the molten steel and remove the slag on the molten steel.
In the former, blast-furnace-converter process, since iron ore is used as the starting material (the iron material), a lot of energy is needed to reduce the iron ore in producing hot metal. In addition, a large equipment is needed. Thus, the equipment cost, the maintenance cost, and the running cost are high.
Moreover, in the former process, the operation of the blast furnace is a continuous operation in which hot metal is continuously outputted from the furnace. Thus, it is substantially impossible to produce only a needed amount of hot metal, i.e., molten steel, at only a timing when the hot metal is needed.
In contrast, in the latter, electric-furnace process, since, usually, scrap is used as the iron material, the energy needed to melt the scrap is less than the energy needed when iron ore is used, by an amount needed to reduce the iron ore. In addition, an equipment needed to perform the latter process is simpler. Thus, the equipment cost, the maintenance cost, and the running cost are lower. Moreover, since the latter process is carried out on a batch basis, it is possible to produce, depending upon the economical circumstances, only a needed amount of molten steel, at only a timing when the steel is needed.
Furthermore, the latter process can be carried out in the nighttime when electric power costs low.
Since the cost of the molten-metal producing process using the electric furnace largely depends on the electric-power cost, the cost of the process can be reduced by operating the electric furnace in the nighttime.
However, it is practically difficult to carry out the process using the electric furnace, all in the nighttime, and at least a portion of the process is carried out also in the daytime when the electric power costs high.
In addition, the molten-steel producing method using the electric furnace cannot help using scrap having a certain quality, for the purpose of producing a final product having a certain quality. This is why the cost of production of molten steel according to this method is high.
That is, it is practically impossible to use, as the iron material, lower scrap that contain much impurities or whose impurities may largely change, or use the lower scrap in a much amount in combination with other sorts of scrap.
Moreover, in the molten-steel producing method using the electric furnace, it is desirable to use scale that has been disposed off, because the scale discarded can be utilized and the cost of production of molten steel can be lowered. However, in the conventional molten-steel producing method, the scale cannot be used as the iron material.
The scale essentially consists of iron oxides such as wustite, magnetite, hematite, etc. that are produced on the surfaces of iron or steel, e.g., when iron or steel is subjected to hot rolling or cast iron is subjected to soaking. Usually, the scale is removed from the iron or steel by acid cleaning, cutting, etc., and then it is discarded.
The Fe content of the scale is about 70 to 80 wt %. Therefore, if the scale can be used as an iron material for producing a molten steel, the cost of production of molten steel can be lowered. However, the scale essentially consists of the iron oxides, and the electric furnace that can melt the scale cannot reduce the scale or recover the Fe component. Thus, in the conventional molten-steel producing method using the electric furnace, the scale cannot be used.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a molten-steel producing method that is free of the above-indicated problem.
According to a first feature of the present invention, there is provided a method of producing a molten steel, comprising the steps of putting, in an electric furnace, an iron material and a carbon material, to melt the iron material and the carbon material and thereby produce a high-carbon molten iron whose carbon content is not lower than 1%, storing, in a reservoir furnace whose capacity is larger than a capacity of the electric furnace, an amount of the high-carbon molten iron that corresponds to a plurality of charges of the electric furnace, and using a portion of the high-carbon molten iron stored in the reservoir furnace, to produce the molten steel in a steel producing furnace.
According to the present invention, an iron material and a carbon material such as breeze or coal are put in an electric furnace, and a high-carbon molten iron whose carbon content is not lower than 1% is produced in the electric furnace. The high-carbon molten iron produced is temporarily stored in a reservoir furnace, and a portion of the high-carbon molten iron stored in the reservoir furnace is taken and used to produce a molten steel in a steel producing furnace.
Thus, according to the present invention, the high-carbon molten iron can be produced in the electric furnace in the nighttime when electric power costs low, so that the molten iron produced may be stored in the reservoir furnace. The high-carbon molten iron stored in the reservoir furnace can be used to produce the molten steel in the steel producing furnace, in the daytime when the electric power costs high.
According to a second feature of the present invention that includes the first feature, the step of using the high-carbon molten iron to produce the molten steel, comprises putting the high-carbon molten iron, and scrap, in the steel producing furnace to produce the molten steel.
According to this feature, when the high-carbon molten iron is used to produce the molten steel in the steel producing furnace, the high-carbon molten iron and another sort of iron material, i.e., scrap are put in the steel producing furnace, and are molten in mixture. In this case, since the latent heat of the high-carbon molten iron, that is, the thermal energy of the molten iron, and the heat of reaction produced when the molten iron is decarbonized and CO and CO
2
gases are produced, are effectively utilized, the molten steel can be produced, with reduced energy, in the steel producing furnace.
Since the high-carbon molten iron can be produced in the nighttime when the electric power costs low, the total energy needed to produce the molten steel can be reduced, which contributes to reducing the cost of the electric power needed to produce the molten steel.
The above-indicated advantage results from the present molten-steel producing method including the steps in which the high-carbon molten iron is produced using the electric furnace, is stored in the reservoir furnace, and is used to produce the molten steel in the steel producing furnace.
The reason why the C content of the high-carbon molten ir
Amano Hajime
Hattori Atushi
Nagatani Akihiro
Andrews Melvyn
Daido Tokushukou Kabushikikaisha
Parkhurst & Wendel L.L.P.
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