Heating – Work chamber having heating means – Having means by which work is progressed or moved mechanically
Reexamination Certificate
2000-02-22
2001-07-10
Wilson, Gregory (Department: 3749)
Heating
Work chamber having heating means
Having means by which work is progressed or moved mechanically
C432S126000, C414S284000
Reexamination Certificate
active
06257879
ABSTRACT:
FIELD OF INVENTION
This invention relates to equipment for the reduction of metal oxides with carbonaceous reductants.
BACKGROUND OF THE INVENTION
Rotary hearth furnaces (RHF) are used for reduction of iron oxides in agglomerates containing iron ore or waste oxides with carbonaceous reductant in steel plants. The largest one RHF currently under construction for ironmaking from iron ores in Thailand represents the best available technology for comparison with the present invention. The RHF of Nakornthai Strip Mill Company Ltd. (NSM), in Thailand is of 45 meters (O.D.) with a hearth width of 6.5 meters to given an annual capacity in the range of 300,000 to 500,000 totals of direct reduced iron (DRI) on the total hearth area of 800 m
2
, depending on the degree of metallization of products. It is designed to have one or two layers of pellets containing carbonaceous reductant on the rotating hearth with heat provided by a flame. Near the end of one revolution, DRI is discharged with a screw discharger.
Use of an RHF for reduction of metal oxides at the present time has the following shortcomings:
(A) Less efficient use of land because the space inside the rotary hearth is of essentially the same area as that of the hearth.
(B) High speed of the rolling stock. The linear speed of the rotating hearth increases with the increase of the diameter of the RHF, and limits the size of each unit.
(C) The discharging operation: Higher linear speed of hearth movement and wider width of the hearth will lead to increasingly demanding operation of the screw discharger.
(D) Servicing of any part of the hearth of an RHF necessitates shutdown of the whole unit and cooling to a low temperature. This lowers production per unit and shortens the service life of the furnace lining due to temperature changes.
SUMMARY OF THE INVENTION
According to the invention, equipment for the reduction of metal oxides with carbonaceous reductants including a pair of straight moving hearth furnaces each having a charging end and a discharging end, each furnace comprising a train of detachable hearth sections to enable each hearth section to be removed at the discharging end of one furnace and attached to the charging end of the other furnace.
The pair of straight hearth moving furnaces may be in side-by-side parallel relationship with the charging end of each furnace adjacent the discharging end of the other furnace.
The detachable hearth sections of each furnace may be lined with refractory material so as to be impermeable to gas flow therethrough. Also, each detachable hearth section may have retaining walls on opposite sides thereof which extend parallel to the direction of movement of the furnace hearth, retaining walls having a height at least as high as the height of the agglomerate bed on the hearth.
The equipment may also include means to direct the generated gas from a region adjacent the charging end of each furnace to a region adjacent the discharging end of the other furnace for flow through at least a portion of the other furnace counter-current to the metal oxides and carbonaceous reductants.
Each straight moving hearth furnace may have firewalls adjacent the ends thereof which separate the charging and discharging ends from the high temperature processing zone therebetween.
Each furnace may have a chimney of predetermined height and location to maintain hot gas flow countercurrent to the solid flow in the furnace and maintain a negative pressure.
The equipment may also include means to control the temperature and reducing potential of the flame in each furnace such that the solids are exposed to an atmosphere with increased reducing power with increase of processing time and the gas is fully oxidized before leaving the furnace.
REFERENCES:
patent: 1738039 (1929-12-01), Cope et al.
patent: 4205935 (1980-06-01), Edler et al.
patent: 5350295 (1994-09-01), Kenji
patent: 5890890 (1999-04-01), Groom
Huang Dianbing
Lu Wei-Kao
Delbridge Robert F.
Wilson Gregory
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