Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Reexamination Certificate
1998-10-26
2001-06-26
Andrews, Melvyn (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
C075S500000, C266S156000
Reexamination Certificate
active
06251162
ABSTRACT:
The invention relates to a method for producing liquid pig iron or liquid steel pre-products from charging substances comprising iron ore, preferably in lumps and/or pellets, and optionally fluxes, wherein the charging substances are directly reduced to sponge iron in a reduction zone, the sponge iron is melted in a melt-down gasifying zone under the supply of carbon carriers and oxygen-containing gas and a CO— and H
2
-containing reducing gas is produced which is introduced into the reduction zone, is reacted there and withdrawn as an export gas, and wherein the withdrawn export gas is conducted to a consumer, and a plant for carrying out the method.
A method of this kind is known f.i. from DE-C-40 37 977. In accordance with DE-C-40 37 977 the export gas, which incurs in considerable quantities and still has substantial contents of carbon monoxide and hydrogen, in order to minimize production costs for the sponge iron or for pig iron melted therefrom is supplied to a further reduction zone that acts as a consumer, for the reduction of additional iron-containing material, but after having been subjected to preparation.
With this known method, overheating may result in the melter gasifier if carbon carriers having a high content of C
fix
are gasified into the melter gasifier. Carbon carriers of this kind are f.i. anthracites and calcinable petroleum coke qualities. A further disadvantage of the known methods is to be seen in that the specific amount of O
2
consumed for each unit of reductants that is produced is relatively high, as carbon monoxide formation within the melter gasifier takes place exclusively through oxygen under the gasification of the carbon carriers.
The invention aims at avoiding these disadvantages and difficulties and has as its object to create a method and an arrangement for carrying out the method enabling the use of carbon carriers having a high C
fix
content. In addition, the specific amount of oxygen consumed in effecting coal gasification is to be reduced.
In accordance with the invention this object is achieved in that a highly CO
2
-containing gas having a CO
2
content far in excess of the CO
2
content of the export gas, preferably exceeding 40%, and having a CO content—if there is a CO content—that is far below the CO content of the export gas is introduced into the melt-down gasifying zone and there is reacted with carbon carriers under the formation of CO.
In accordance with AT-B-394.201, which relates to a method of a kind similar to that initially described, the CO
2
-containing export gas is cooled in a scrubber as well as purified together with a portion of the hot reducing gas having a poorer CO
2
content which is formed in the melter gasifier and subjected to a technically demanding desulfurizing operation, and is then utilized as a fuel gas for a gas turbine. With this method, process engineering expenditures for the processing of a fuel gas answering to the requirements of environmental protection are relatively high and moreover necessitate considerable investment.
From AT-B-394.201 it is known to introduce export gas from the reduction stage into the fluidized bed of the melter gasifier as an oxygen carrier under heat consumption. As the CO
2
content of the export gas, which is at roughly 25% to 35%, is only slight and the export gas in addition is dust laden, the effect achieved in this manner is slight as well. One disadvantage of this method is that along with the export gas a relatively high portion of carbon monoxide passes into the melter gasifier that must previously be cooled and then has to be re-heated in the melter gasifier. This particular portion of CO thus represents ballast that has to be sluiced through the melter gasifier, incurring all the disadvantages resulting therefrom (pressure loss, unnecessarily high-capacity compressors, increased energy consumption etc.).
One further disadvantage resides in the fact that in accordance with AT-B-394.201 a desulfurization means has to be provided for the reduction excess gas, whereas according to the invention a means of this kind is either not required at all—if the sulfur content of the reducing gas is to be transmitted to the liquid phase—or has to be provided only for the offgas exiting the CO
2
removal plant.
The advantages achieved with a method in accordance with the invention are as follows:
By the introduction in accordance with the invention of the gas having a high CO
2
content, reaction of the CO
2
takes place in accordance with the equation CO
2
+C→2 CO. Carbon monoxide is formed which increases the reducing gas stream and as a result is available for reduction. Reaction of the carbon dioxide gas under the formation of carbon monoxide takes place endothermally, whereby through a suitably dosed introduction of a gas having a high portion of CO
2
the desired temperature will adjust in the melter gasifier and overheating can be completely avoided.
Thus it is feasible in accordance with the invention to utilize carbon carriers having a high portion of C
fix
and a natural deficiency in volatile components, such as anthracites and calcinable petroleum coke qualities, in quantities which due to the overheating effect would not be permissible without simultaneously utilizing the highly CO
2
-containing gas exerting a temperature-lowering effect. Moreover, the carbon monoxide forming inside the melter gasifier from the offgas containing a high portion of CO
2
—per mol CO
2
two mol carbon monoxide are formed with one mol carbon—in a useful manner increases the reducing gas stream required for reducing iron oxides.
A further advantage of the method according to the invention lies in the fact that the specific consumption Of O
2
per unit of reductants produced decreases, since a portion of the carbon carriers in the melter gasifier is consumed in the formation of carbon monoxide not using oxygen, but using the carbon dioxide. As a result, the amount of energy required in providing the oxygen also decreases considerably. The method according to the invention thus makes it feasible to minimize the amount of CO
2
given off to the atmosphere, thus complying with the Toronto Declaration by contributing to the reduction of CO
2
emission, which is regarded as the main cause of climate shifting.
A further reduction of oxygen consumption in the melter gasifier can be achieved if the gas containing a high portion of CO
2
is subjected to preheating, because then less C
fix
from the carbon carriers charged to the melter gasifier will have to be combusted.
A further object of the invention results from the following problem:
Processing of the export gas in accordance with the prior art is generally effected by first of all cleaning it from solid particles in a scrubber, thus cooling it down considerably. Thereupon the CO
2
contained in the export gas is removed in accordance with DE-C-40 37 977, as the CO
2
impedes the further utilization of the export gas as a reducing gas; the percentage of reductants present in the export gas would be too low. A variety of methods is known for removing the CO
2
from the export gas, f.i. the pressure-swing adsorption process or a chemical CO
2
scrubbing. In accordance with DE-C-40 37 977 it is thus feasible to largely exploit the energy that is chemically bound in the export gas, yet the CO
2
-containing offgas incurring in the purification of an export gas represents a problem, as this offgas has to be disposed of in an environmentally compatible manner.
This offgas i.a. contains CO, H
2
, CH
4
and H
2
S and for reasons of environmental protection cannot be released into the environment in that state. This is also the reason why it is only conditionally suited for possible further processing. Therefore the sulfur compounds are usually removed from the offgas. Such a desulfurization is up to the present carried out by different methods, such as f.i. by what is called “Stretford scrubbing” or by catalytic oxidation on activated carbon etc. All of these methods are expensive and require additional materials, such as activa
Diehl Jorg
Eichberger Ernst
Reufer Franz
Rosenfellner Gerald
Schrey Gunter
Andrews Melvyn
Birch & Stewart Kolasch & Birch, LLP
Deutsche Voest-Alpine Industrieanlagenbau GmbH
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