Specialized metallurgical processes – compositions for use therei – Processes – Process control responsive to sensed condition
Patent
1997-09-23
2000-10-10
Kastler, Scott
Specialized metallurgical processes, compositions for use therei
Processes
Process control responsive to sensed condition
C21C 104
Patent
active
061297763
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a raw fuel charging method to a vertical furnace which can continuously melt a pig iron with high heat efficiency and at a low material and fuel rate irrespective of properties of a solid fuel by using an iron-containing dust and/or iron scraps and/or a reduced iron having a small impurity content as an iron source, and also to an operation method of the vertical furnace.
BACKGROUND ART
Various methods of producing a pig iron from an unreduced ore have been developed to this date, and a blast furnace method has been mainly employed at present. According to this blast furnace method, a raw material charged from the furnace top is sufficiently pre-heated by a high temperature gas flowing from below to above while the raw material falls, and iron oxide is indirectly reduced by a carbon monoxide (CO) at a ratio of at least 60%. To secure such an indirect reduction ratio in the blast furnace method, a raceway space is disposed in front of a tuyere, and a reducing gas of .eta.co (=CO.sub.2 /(CO+CO.sub.2))=0 is produced. To raise the temperature of the combustion gas serving as the high temperature gas described above, a blast temperature is set to a temperature of not less than 1,000.degree. C.
In a melting furnace using the iron source such as the iron-containing dust and/or the iron scrap as the principal material, however, the necessity for producing the reducing gas at the tuyere portion becomes lower. It is therefore believed efficient to utilize the combustion of a coke in front of the tuyere as means for securing the heat source for heating the changing material melting iron source.
In the case of the cupola method, for example, which is mainly directed to melt the iron source such as the iron scrap, the casting scrap, the pig iron, etc, but does not require the reducing function, the raw material and fuels are generally charged in mixture and melting of the iron source is generally carried out under the condition of .eta.co (gas utilization ratio)=40 to 50%. To accomplish such a gas composition, the cupola method uses a casting-coke which has a particle size of 100 to 150 mm, and prevents the solution loss reaction after the combustion of the coke. Because the large diameter coke for casting is expensive, however, it is believed effective to use a coke having a smaller particle diameter so as to reduce the fuel cost. In this case, however, the solution loss reaction rate as the endothermic reaction becomes greater and gas utilization ratio .eta.co of the coke drops, so that the melting calory drops and a stable operation becomes difficult to practice.
On the other hand, there are not many operation examples of a vertical furnace which use a self-reducible lump ore and the iron scrap as the main raw materials and requires the reducing function up to melting. Unlike the blast furnace, the raceway is not disposed in such a vertical furnace, and the operation is carried out by setting the blast temperature to not higher than 600.degree. C.
Goksel et al (Transactions of the American Foundrymen's Society, Vol. 85, AFS Des Plaines, III, (1977), pp. 327-332) report the experiment of a hot blast cupola using 5 wt % of a C-containing pellet at a blast temperature of 450.degree. C., but no prior art references have been found which deal with the operation of the normal temperature blast cupola or the operation of the vertical furnace when a large quantity of the C-containing pellet is used.
Japanese Unexamined Patent Publication (Kokai) No. 1-501401 discloses a pig iron producing apparatus comprising a blast furnace having a secondary tuyere and a hearth having a diameter more than that of the blast furnace and having a primary tuyere. According to this furnace, only the iron source is charged from the furnace top, and the fuel is directly added to the fuel bed existing at the junction between the blast furnace and the hearth. Therefore, because the inside of the blast furnace is an ore layer in which the fuel does not exist, the solution loss reaction due to the solid
REFERENCES:
patent: 4857106 (1989-08-01), Wakimoto et al.
Patent Abstracts of Japan, vol. 005, No. 195 (C-083), Dec. 11, 1981 & JP 56 119710 A (Kawasaki Steel Corp), Sep. 19, 1981.
Patent Abstracts of Japan, vol. 011, No. 185 (C-428), Jun. 13, 1987 & JP 62 010203 A (Kawasaki Steel Corp), Jan. 19, 1987.
Patent Abstract of Japan, vol. 013, No. 399 (C-632), Sep. 5, 1989 & JP 01 142006 A (NKK Corp), Jun. 2, 1989.
Oeters F et al: "Entwicklungslinien der Schmelzreduktion" Stahl und Eisen, No. 16, Aug. 14, 1989, pp. 728-742.
Transactions of the American Foundarymen's Society, vol. 85, pp. 327-332, Dec. 1997.
Araki Kyoichi
Fujiwara Yasuhiko
Kokubun Teruhiko
Konno Norimitsu
Naito Masaaki
Kastler Scott
Nippon Steel Corporation
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