Process for producing sponge iron

Details Process for producing sponge iron Process for producing sponge iron

1998-08-04

2000-11-21

Andrews, Melvyn

Specialized metallurgical processes, compositions for use therei

Processes

Producing or treating free metal

75450, C21B 1314

Patent

active

061497088

DESCRIPTION:

BRIEF SUMMARY
The invention relates to a process for producing sponge iron by directly reducing particulate, iron-oxide-containing material, wherein reducing gas that is formed from carbon carriers and an oxygen-containing gas in a melt-down gasifying zone is introduced into a reduction zone that contains the iron-oxide-containing material.
From EP-A -0 594 557, a process is known for producing molten pig iron from charging substances formed of iron ores and fluxes and at least partially comprising fines, wherein the charging substances are directly reduced to sponge iron in at least one reduction zone, the sponge iron is melted in a melting-gasifying zone under supply of carbon carriers and oxygen-containing gas, and a reducing gas is produced which is injected into the reduction zone, is reacted there and is withdrawn as an export gas. With this process it is feasible to use fine ore in an economic manner in that primarily hematite and/or magnetite fine ores and/or ore dusts are subjected to preheating by the fluidized bed method in a preheating zone and the thus preheated charging substances are completely reduced to a major extent in at least one consecutively arranged reduction zone by the fluidized bed method, whereupon the charging substances are charged into the fluidized bed of the melting-gasifying zone by forced conveyance, and are melted there.
A process of the kind initially mentioned is known from EP-A-0 217 331. In that process, a gas is employed for directly reducing fine ore, which gas essentially comprises CO and H.sub.2 and has been dedustified in a cyclone.
The sponge iron produced by directly reducing iron-oxide-containing material according to this prior art as a rule has a low carbon content in the amount of about 1%. Yet, for further processing the sponge iron, an elevated carbon content is advantageous, so as to be able to save energy when melting the sponge iron and in the subsequent refining process, without the need for a separate addition of carbon (carburization).
The invention therefore has as its object to modify a process in accordance with the initially described kind in such a manner that the sponge iron will exhibit an elevated carbon content, preferably of a dimension between 1 and 4%, particularly in excess of 2.5%.
According to the invention, this object is achieved by the combination of the following characteristic features: 100 g per Nm.sup.3 of a dust having a carbon content of between 30 and 70 mass %, and time period that exceeds the period required for complete reduction.
The production of sponge iron having a carbon content of between 0.5 and 2.5% is already known from WO-A-93/14228; more specifically, with this known process, small amounts of natural gas are employed for adjusting the carbon, wherein the natural gas is charged directly into a fluidized bed reactor. But this measure alone is not very efficient, since complete decomposition of the natural gas is not assured at the reduction temperatures envisaged for direct reduction.
From U.S. Pat. No. 5,137,566 it is known to produce highly concentrated iron carbide from iron ore by means of reducing gas and carburizing gas, wherein on account of the time sensitive nature of the iron carbide formation process, a higher residence time is aimed at for the conversion. Just by increasing the residence time of the iron-oxide-containing material in direct reduction a considerable decrease is caused in terms of production, i.e. a substantially reduced output of reduced material per time unit. This method therefore involves fairly great expenditures and, accordingly, the iron carbide thus produced is utilized in steelmaking processes only by way of an addition, whereas the object to be achieved in accordance with the invention is that all of the sponge iron utilized for making steel is to have an elevated carbon content, i.e. the sponge iron of elevated carbon content that is thus produced is not just used as an addition in a steelmaking operation but itself constitutes the base material for it.
From U.S. Pat. No. Re-32,247 it is k

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patent: 5514203 (1996-05-01), Grunbacher et al.
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