Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Reexamination Certificate
1999-10-06
2001-09-25
Andrews, Melvyn (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
C075S961000, C075S766000, C075S768000, C075S771000, C075S773000
Reexamination Certificate
active
06293991
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method of producing molten pig iron or molten steel pre-products from charging substances formed of iron ore, preferably in the shape of lumps and/or pellets, and optionally of fluxes, wherein the charging substances are directly reduced to sponge iron in a reduction zone, the sponge iron is charged into a melt-down gasifying zone and, there, is melted under the supply of carbon carriers and an oxygen-containing gas, wherein a CO- and H
2
-containing reducing gas is generated, is withdrawn from the melt-down gasifying zone and introduced into the reduction zone, is reacted there and is withdrawn as a topgas, and wherein the topgas is subjected to scrubbing and the sludges thus separated are at least partially agglomerated, and a plant for carrying out the method.
2. Brief Description of the Related Art
A method of this kind is known f.i. from AT-B-376 241. Here, solid particles are separated from the reducing gas and from the topgas leaving the reduction zone in cyclones and are mixed with a binder, such as iron oxide dust, are hot-briquetted and supplied to the melt-down-gasifying zone. This solution is, however, expensive with regard to investment and operating costs. Further, the charging of iron oxides into the melt-down gasifying zone renders it necessary to do reduction work in order to reduce the iron oxide, whereby energy that would be needed for the melting operation is withdrawn from the melt-down gasifying zone.
From AT-B-400 725 it is known for the sludges formed in the scrubbing of the reducing gas that exits the melt-down gasifying zone and of the topgas that exits the reduction zone to be dewatered and granulated and finally charged back to the melt-down gasifying zone in the form of granulates. Here, too, reduction work has to be done in the melt-down gasifying zone, thus withdrawing overly great amounts of energy from the melt-down gasifying zone if very great quantities of granulates are used, which may result in a decrease in reductants and hence in process failures.
From DE-A-41 23 626 it is known to agglomerate residues from the iron and steelmaking industries and to charge the agglomerates to the upper burden area of a melting aggregate, wherein preheating and drying of the agglomerates takes place in this burden area of the melting aggregate. The burden passes through the melting aggregate in accordance with the countercurrent principle until it reaches the lower area of the melting aggregate, where it is molten. This known method involves a high energy demand inasmuch as the metallic wastes or residues are also dried and sintered in the melting aggregate and have to travel through the melting aggregate, thereby exerting a negative effect on the process taking place in the melting aggregate.
Further, a method is known from EP-A-0 623 684 in which wastes and residues containing coal dust and iron in metallic or oxidic form are collected separately in three groups, according to their chemical compositions, wherein the first group is to contain predominantly iron in oxidic form, the second group predominantly iron in metallic form and the third group predominantly carbon-containing substances. For utilization, the substances of the first group are charged into the reduction zone and those substances belonging to the second and third groups are charged directly into the melt-down gasifying zone. The dusts that have been separated from the topgas of the reduction zone with this method are recirculated only into the melt-down gasifying zone. This causes an influence on the melting-gasifying process since energy is withdrawn from the melt-down gasifying zone in order to heat and melt the residues.
SUMMARY OF THE INVENTION
The invention has as its object to further develop a method of the initially described kind in such a way as to enable the sludges developed during the process to be recirculated into the process in a simple and efficient manner while expending as little energy as possible, wherein the disadvantages associated with the charging of the sludges into the melt-down gasifying zone, i.e. the necessity of doing more reduction work in the melt-down gasifying zone as well as a heat loss from heating the charge are to be avoided.
In accordance with the invention, this object is achieved in that the agglomerate (formed from at least a partial amount of the sludges which develop during the scrubbing of the topgas of the reduction zone) is recirculated into the reduction zone, preferably only into the reduction zone.
According to a preferred embodiment, at least a partial amount of the reducing gas that exits the melt-down gasifying zone is likewise scrubbed, the sludges thus obtained are at least partially agglomerated and the agglomerate thus formed is recirculated into the reduction zone.
Advantageously, the sludges that are obtained in the scrubbing of the reducing gas from the melt-down gasifying zone and that have to be agglomerated are subjected to further treatment together with the sludges obtained in the scrubbing of the topgas from the reduction zone that have to be agglomerated. In this way, investment costs can be minimized.
Optionally, the purified topgas from the reduction zone is subjected to CO
2
elimination, after scrubbing, and as an at least largely CO
2
-free reducing gas is conducted to at least one further reduction zone serving for the direct reduction of metal ore, particularly of iron ore or pellets, after reacting with the metal ore in the further reduction zone (
32
) is withdrawn as an export gas and purified in a scrubber and the sludges obtained in the scrubbing of the export gas from the further reduction zone are at least partially agglomerated and the agglomerate thus formed is recirculated into the first reduction zone. Thus the sludges that develop during the scrubbing of the export gas of the further reduction zone can also be re-utilized in an efficient manner.
In doing so, the sludges that arise in the scrubbing of the export gas from the further reduction zone and that have to be agglomerated are advantageously subjected to further treatment together with the sludges that arise in the scrubbing of the topgas from the first reduction zone and/or together with the sludges that arise in the scrubbing of the reducing gas from the melt-down gasifying zone and that have to be agglomerated.
In accordance with a preferred embodiment of the method of this invention, the sludges that have to be agglomerated are first of all dewatered to a residual moisture content. Advantageously, oxidic dusts, optionally coal dust, and calcined lime are added to the sludges for agglomeration, preferably in a two-step continuous process.
The granulates thus formed consist of the following main components (in roughly equal proportions):
iron and iron oxides
calcium hydroxide
carbon
coal ash constituents such as Al
2
O
3
, SiO
2
, etc.
It is known that in reducing Fe
2
O
3
and FeO with CO in a reduction zone, heat is developed, and it has been found that due to a resultant temperature increase overheating may occur in the reduction zone. As a consequence, there will be caking of the reduction products—known as clustering—and hence an interruption of the reduction operation.
This can be avoided by proceeding in accordance with the invention since as the above granulates are charged to the reduction zone the following advantageous processes take place in the same:
the Boudouard reaction, C+CO
2
→2CO, which is endothermic, is promoted by the carbon contained in the granulates.
the content of calcium hydroxide, which is formed from added CaO, triggers a further endothermic reaction (re-formation of CaO).
By the two endothermic reactions it is rendered feasible to purposefully limit the temperature in the reduction zone during the reduction of the ore. As a consequence, caking of the reduction products (clustering) is prevented; also, the amount and quality of the topgas are enhanced.
From DE-A-41 23 626 it is known to recirculate into the melting aggregate
Gruenbacher Herbert
Schrey Guenter
Andrews Melvyn
Deutsche Voest-Alpine Industrieanlagenbau GmbH
Ostrolenk Faber Gerb & Soffen, LLP
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