Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Patent
1997-11-17
2000-02-29
Willis, Prince
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
75414, 266144, 266157, 266172, C21B 1100, C22B 110
Patent
active
060304324
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for the reduction of fine ore by reducing gas in the fluidized bed method and an arrangement for carrying out the process.
In the reduction of ores it is often necessary to employ fine ores having a wide range of grain sizes, for example grain sizes ranging from dust particle size up to 8 mm. Here, difficulties occur due to the superfines, as these are often discharged along with the spent, respectively partially spent reducing gas and, to avoid losses, have then to be separated from the same and recycled to the reduction process.
To overcome these difficulties it is known to separate the fine ore by means of the reducing gas by gas classification into two fractions having different grain size distributions each and to substantially completely reduce these two fractions separately (AT-B-390622). It is of advantage, as already disclosed in JP-A-6-10021, if both fluidized beds are maintained directly above each other, which results in short gas and material flows. According to JP-A-6-10021, in a first reactor vessel, in which a first fluidized bed has been formed, entrainment of the fine particles of the charged ore by the reducing gas occurs. The reducing gas emerging from the first reactor vessel is introduced into a second reactor vessel arranged directly on top of the first reactor vessel and, there, pressure is released under formation of a further fluidized bed, by this second reactor vessel being provided with a larger cross section than the first reactor vessel. From each of the two fluidized beds completely, respectively substantially completely reduced ore is discharged directly. Supply of ore and of reducing gas is only effected into the first lower reactor vessel.
One disadvantage involved here is that optimum reduction can only be adjusted for one of the fluidized beds each by supplying a specific amount of reducing gas having a specific chemical composition. The reduction resulting for the further upper fluidized bed will be a function of the reduction of the ore and thus of the change in the chemical composition of the reducing gas in the lower fluidized bed. In addition, optimum separation of the ore into fractions containing different grain size distributions each is difficult to accomplish here, as the amount of reducing gas that is introduced has to be adjusted predominantly as a function of the coarse-grain fraction provided in the lower reduction vessel and the degree of metallization desired for the same, which, in turn, results in a very specific quantitative discharge of fine-grain fraction, wherein it is impossible to influence or optimize the reduction of the fine-grain fraction as such.
In this connection, a further difficulty results, namely that backflowing of the fine-grain fraction separated from the reducing gas may occur, as the gas velocity at the walls of the upper and lower reactor vessel vanishes toward zero and, there, a downward movement of ore particles, i.e. toward the fluidized bed containing coarser ore particles, takes place.
To avoid the latter disadvantage it is known from U.S. Pat. No. 4,975,116 to provide a narrow between two reactor vessels disposed one above the other, where the reducing gas is accelerated. Thereby it becomes feasible to prevent backmixing of the ore particles present in the superposed fluidized beds. However, according to U.S. Pat. No. 4,975,116 the entire ore passes through both reactor vessels, as discharge of solids and gas is only provided for at the upper end of the upper reactor vessel. Hence, gas classification of the ore into fractions having different grain size distributions is not provided for. This constitutes a disadvantage in that, as a consequence, different retention times result for ore having different grain sizes and, accordingly, different degrees of metallization ensue. This process is therefore not suited for ore having a wide grain size range.
From KR-Patent applications 92-24265, 91-19779, 92-27502 and 92-24266 it is known to separate ore by gas classification by aid of the reducing
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Gennari Udo
Kepplinger Werner Leopold
Kim Yong-Ha
Lee Il-Ock
Park Gyu-Dae
McGuthry-Banks Tima
Pohang Iron & Steel Co. Ltd.
Research Institute of Industrial Science & Technology Incorporat
Voest-Alpine Industriean-lagenbau GmbH
Willis Prince
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