Fluidized bed type reducing system for reducing fine iron ore

Details Fluidized bed type reducing system for reducing fine iron ore Fluidized bed type reducing system for reducing fine iron ore

1998-08-27

2001-05-01

Kastler, Scott (Department: 1742)

Metallurgical apparatus

With means treating or handling gases exhausted by treating...

C266S172000

Reexamination Certificate

active

06224819

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a fluidized bed type reducing system for reducing a fine iron ore. More specifically, the present invention relates to a fluidized bed reducing system for a fine iron ore, in which the structure of the fluidized bed reducing furnace is improved such that a fine iron ore having a wide particle size distribution can be made to undergo a fluidized bed reduction in an optimum manner.
DESCRIPTION OF THE PRIOR ART
A fluidized bed type reducing system for reducing a fine iron ore is disclosed in Japanese Patent Laid-open No. Hei-6-10021.
As shown in
FIG. 1
, this fluidized bed reducing system
10
is characterized in that a reducing gas is supplied through a lower portion of a cylindrical reducing furnace
11
so as to fluidize a fine iron ore supplied through an iron ore supplying inlet
112
. Further, the fine iron ore which is discharged while being carried by the reducing gas from an upper portion of the reducing furnace through a circulating duct
115
is separated from the reducing gas by a particle capturing device
12
so as to refeed it through an extremely fine iron ore supplying duct
121
into the reducing furnace
11
. The upper diameter of the reducing furnace is made larger than its lower diameter so that the elutriation of the fine iron ore can be reduced. Further, iron ore outlets
113
and
114
are formed on the upper and lower portions, respectively of the reducing furnace
11
. The upper iron ore outlet
113
is for discharging fine iron ore particles whereas the lower iron ore outlet
114
is for discharging coarse particles, so that the average residence time of the iron ore in the reducing furnace can be controlled for each particle size, and thus both the fine iron ore and the coarse iron ore can be simultaneously reduced with a high efficiency.
However, the iron ore has a wide particle size distribution, ranging from several scores of microns to several thousand microns. In the conventional fluidized bed type reducing system, if this iron ore is to be maintained in a fluidized state in an efficient manner, the operation should be carried out based on a superficial gas velocity of the coarse iron ore which is, otherwise distributed mostly in the lower level. In this high-gas-velocity operation with a conventional fluidized bed (cylindrical bed) in which the gas velocity is constant along the height of the bed, the coarse particles move upwardly to the upper level to be mixed with the fine iron ore particles, and therefore, these coarse iron ore particles which need more reducing time than the fines are discharged through the upper iron ore outlet without being sufficiently reduced. This insufficient reduction of coarse iron ore particles is encountered in the problem encountered in the conventional technique.
SUMMARY OF THE INVENTION
The present invention provides a fluidized bed reducing system for reducing a fine iron ore, in which the structure of the fluidized bed reducing furnace is improved such that the coarse iron ore particles are distributed in the lower portion of the fluidized bed within the furnace, whereas the fine iron ore particles are in the upper portion of the fluidized bed, so that the reducing can be done in a stable fluidized state hence, only the coarse iron ore particles are discharged through the lower iron ore outlet, and only the fine iron ore particles are discharged through the upper iron ore outlet. Thus, the average residence times of the particles in the furnace are adjusted differently for different sizes, so that the reducing efficiency can be improved, and the residence time of the reducing gas in-the furnace can be extended, thereby improving the degree of gas utilization.
The fluidized bed reducing system for reducing a fine iron ore of wide particle size distribution according to the present invention includes: an upper iron ore outlet for discharging fine iron ore particles; a lower iron ore outlet for discharging coarse iron ore particles; a gas distributor installed in a lower portion of a reducing furnace; a gas inlet formed on a lower portion of the reducing furnace for introducing a reducing gas; an iron ore inlet for supplying a fine iron ore of wide particle size distribution; a circulating duct connected to an upper portion of the fluidized bed reducing furnace for discharging extremely fine iron ore particles together with the reducing gas; a particle capturing device for separating the extremely fine iron ore particles from the reducing gas; an extremely fine iron ore recycling duct for refeeding the separated, extremely fine iron ore particles into the fluidized bed reducing furnace so as to reduce the elutriation of a fine iron ore of a wide particle size distribution.
The fluidized bed reducing furnace or the invention includes: a cylindrical upper portion and a tapered lower portion, the tapered portion being in a wide-upper-narrow-lower shape; and
the tapered portion includes: the upper iron ore outlet, the iron ore inlet and the lower iron ore outlet on a side thereof in the mentioned sequence, and the extremely fine iron ore recycling duct installed on another side of the tapered portion.


REFERENCES:
patent: 5535991 (1996-07-01), Kepplinger et al.
patent: 5785733 (1998-07-01), Lee et al.
patent: 5882579 (1999-03-01), Viramontes-Brown et al.
patent: 5897829 (1999-04-01), Kim et al.
patent: 0022098 (1981-01-01), None
patent: 6-10021 (1994-01-01), None
patent: WO8603986 (1986-07-01), None

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