Process for producing sponge iron by direct reduction of iron-ox

Details Process for producing sponge iron by direct reduction of iron-ox Process for producing sponge iron by direct reduction of iron-ox

1998-09-30

2000-11-07

Andrews, Melvyn

Specialized metallurgical processes, compositions for use therei

Processes

Producing or treating free metal

75450, 423439, C21B 1300

Patent

active

061430536

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention relates to a process for producing sponge iron by direct reduction of iron-oxide-containing material, wherein synthesis gas, preferably reformed natural gas, is mixed with top gas forming in the direct reduction of the iron-oxide-containing material and is utilized as a CO- and H.sub.2 -containing reducing gas for direct reduction and for heating the iron-oxide-containing material to a reduction temperature.


PRIOR ART

A process of this type is known, for instance, from U.S. Pat. No. 2,752,234, U.S. Pat. No. 5,082,251 and EP-A-0 571 358, WO 96/00304 and DE-B-24 05 898.
From EP-A-0 571 358 it is known to carry out the reduction of fine ore not exclusively via the strongly endothermic reaction with H.sub.2 according t o lower the operational costs, in particular the energy costs, involved.
The sponge iron produced by directly reducing iron-oxide-containing material according to this prior art as a rule has a carbon content amounting to between 1 and 1.5%. 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 2 and 4%, particularly in excess of 2.5%. However, this is to be enabled by only a slightly--if at all--elevated expenditure in terms of energy, so that compared to conventional processes for producing sponge iron only slight additional costs will incur and the savings in energy arising in the refining process will not be compensated but will have the most complete effect possible on the economic efficiency of the steel or steel prematerial production process.
In accordance with the invention, this object is achieved by the combination of the following characteristic features: gas, or a gas having higher hydrocarbons is utilized for reduction exceeding the period necessary for complete reduction is exposed to the reducing gas and to the additionally supplied carbon-containing gas, and of 2.5, and in particular a ratio in ecxess of 3, is adjusted in the reducing gas.
From WO 96/00304 it is known to reduce or prevent "metal dusting" by adjusting a specific CO/CO.sub.2 ratio, namely in a range between 1 and 3, but aiming at a range between 1.5 and 2, which per se does not contribute towards achieving the object of the invention.
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 sensitiv nature of the iron carbide formation process, a higher residence time is aimed at for the conversion. The mere increase in the residence time of the iron-oxide-containing material in direct reduction causes a considerable decrease 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 operati

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