Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Reexamination Certificate
1998-12-04
2001-04-10
Andrews, Melvyn (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
C075S490000, C075S505000, C266S156000
Reexamination Certificate
active
06214082
ABSTRACT:
The invention relates to a process for the reduction of metal-oxide-bearing material, particularly of iron ore, in a reduction vessel, wherein the metal-oxide-bearing material is charged from a vessel for the metal-oxide-bearing material into the reduction vessel and reduced in the latter by means of a reduction gas flowing countercurrently to the metal-oxide-bearing material and wherein waste reduction gas discharged from the reduction vessel serves to preheat the metal-oxide-bearing material in the vessel for the metal-oxide-bearing material, as well as to a plant for implementing the process.
A process of this type is known, for example, from AT-B-387 403. According to this known process, iron-ore-bearing input materials are preheated and calcined in a preheating shaft separated from the direct reduction zone by means of a top gas discharged from the direct reduction zone and post-combusted in a separate combustion chamber. The hot gas formed by post-combustion has a total CO and H
2
content of at least 10 volume percent. This has the disadvantage that a gas containing CO and H
2
can escape through the preheating shaft.
Processes according to which a preheating zone is directly integrated in the reduction shaft are known from DE-C-40 41 689 and AT-B-389 124. These known processes have the disadvantage that the capacity of the reduction shaft can only be partially utilized for the direct reduction of the iron-oxide-bearing material because part of the reduction shaft is required for preheating the iron-oxide-bearing material.
A process for preheating iron-oxide-bearing material in a separate preheating chamber is known, for example, from DE-A-195 25 270. In this process, nitrogen is used for preheating, which has the disadvantage of high nitrogen consumption, and the large nitrogen quantities are moreover to be specially heated.
A separate preheating chamber for preheating iron-ore-bearing material is also known from EP-A-0 157 917. This document does not give any statements on the type of preheating.
According to DE-A-34 32 090, sulfur-bearing ore is reduced in a shaft furnace in counterflow with reduction gas. The off-gas exiting the furnace is divided into two flows, the first flow being used for preheating and desulfurization of the ore which is contained in an ore bin above the shaft furnace and the second flow being conveyed to a catalytic gas converter together with hydrocarbons for the purpose of generating reduction gas.
A container from which ore is charged into the ore bin is located above the ore bin of the arrangement described in DE-A-34 32 090. Inert gas is injected into the connection between this container and the ore bin in order to prevent sulfur-bearing off-gas from exiting the ore bin through this connection. This measure thus serves to establish a gas seal. U.S. Pat. No. 4 212 452 describes a plant in which iron oxide is reduced to sponge iron in a shaft furnace through the addition of solid carbon-bearing material which is gasified in an upper zone of the shaft furnace and also through the addition of a reduction gas containing CO and H
2
in a central part of the shaft furnace. The iron oxide is charged together with the solid carbon-bearing material from the top into the shaft furnace and flows through the shaft furnace from the top to the bottom, partly cocurrently and partly countercurrently to the reduction gases. In a lower zone of the shaft furnace, the sponge iron formed by reduction is cooled by means of cool, dry reduction gas. The shaft furnace is sealed towards the top and bottom by means of one C
0
2
-operated gas seal each in order to prevent the undesirable escape of reduction gas from the shaft furnace, C
0
2
being recovered therein from waste reduction gas through gas scrubbing. Generation of sealing gas is thus relatively expensive in the known process.
An arrangement which is used, for example, for the direct reduction of iron-oxide-bearing material by means of reduction gas in a shaft furnace is known from U.S. Pat. No. 3 850 616. The iron-oxide-bearing material flows through the shaft furnace from the top to the bottom in counterflow to the reduction gas and is cooled with cool reduction gas in the lower zone of the shaft furnace.
In order to prevent reduction gas from exiting the shaft furnace, a gas seal operated with inert gas is provided at the lower end of the shaft furnace. This known arrangement has the disadvantage of high consumption of expensive inert gas.
Processes in which iron-oxide-bearing material is reduced in a shaft furnace by means of reduction gas and melted in a melting unit structurally connected with the shaft furnace are known from U.S. Pat. No. 4 248 626 and U.S. Pat. No. 4 270 740. In the melting unit, reduction gas is generated by coal gasification. The reduction gas is withdrawn from the melting unit and cooled before it is charged into the shaft furnace in order to prevent the material reduced in the shaft furnace from agglomerating. In order to prevent the very hot reduction gas from being carried over from the melting unit directly into the shaft furnace, a gas seal is provided in the direct connection between the melting unit and the shaft furnace.
The applicant knows that gas seals operated with nitrogen, which seal shaft furnaces against the environment, are customary. These gas seals have the disadvantage that the generation of nitrogen involves high technical expenditure, which results in high costs because large amounts of nitrogen are consumed.
The technical problem of the present invention is to eliminate this disadvantage and to provide a process of the type described above where a gas seal is operated with a less expensive sealing gas.
According to the invention, at a process for the reduction of metal-oxide-bearing material, particularly of iron ore, in a reduction vessel, wherein the metal-oxide-bearing material is charged from a vessel for the metal-oxide-bearing material into the reduction vessel and reduced in the latter by means of a reduction gas flowing countercurrently to the metal-oxide-bearing material and wherein waste reduction gas discharged from the reduction vessel is used for preheating the metal-oxide-bearing material in the vessel for the metal-oxide-bearing material, the technical problem is solved by combusting the waste reduction gas discharged from the reduction vessel and by operating a gas seal located between the reduction vessel and the vessel for metal-oxide-bearing material with the combusted waste reduction gas for, whereby the reduction vessel is sealed against the vessel for metal-oxide-bearing material.
The gas seal according to the invention, which is operated with combusted waste reduction gas, prevents any reduction gas that may still contain considerable portions of reducing constituents from being carried over from the reduction vessel into the vessel for metal-oxide-bearing material. In this gas seal, a sealing gas is used which is considerably less expensive than the usual sealing gases according to prior art, such as nitrogen.
The combusted waste reduction gas is expediently compressed before it is used as sealing gas. A preferred embodiment of the process according to the invention is characterized in that the combusted waste reduction gas is set or cooled to a temperature ranging between 100° C. and 700° C.
According to another preferred embodiment, an additional gas seal is operated with inert gas apart from the gas seal operated with combusted waste reduction gas, the additional gas seal being located between the gas seal operated with combusted waste reduction gas and the reduction vessel, wherein the gas seal operated with the combusted waste reduction gas assumes the function of the main gas seal and the gas seal operated with inert gas, for example, with nitrogen, assumes the function of an auxiliary gas seal, which furthermore prevents combusted waste reduction gas form entering the reduction vessel. In this way, a considerably smaller amount of inert gas is consumed than required for gas seals known from prior art.
According to a preferr
Diehl Joerg
Rosenfellner Gerald
Andrews Melvyn
Ostrolenk Faber Gerb & Soffen, LLP
Voest-Alpine Industriean-lagenbau GmbH
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