Process for the production of spongy metal

Details Process for the production of spongy metal Process for the production of spongy metal

1998-09-02

2001-07-24

Andrews, Melvyn (Department: 1742)

Specialized metallurgical processes, compositions for use therei

Processes

Producing or treating free metal

C075S446000, C075S475000, C075S492000

Reexamination Certificate

active

06264724

ABSTRACT:

The invention relates to a plant and method for producing sponge metal, in particular sponge iron, from charging materials consisting of metal ore or iron ore respectively, preferably in lumps and/or pellets, and optionally fluxes, comprising at least one first gas source dispensing a CO— and H
2
-containing feedgas, a CO
2
elimination plant and optionally a heating means for the feedgas from the first gas source and a reduction reactor which forms a further gas source for a CO— and H
2
-containing feedgas and serves for receiving the metal ore, a reducing-gas feed duct leading to this reduction reactor, an export-gas discharge duct leading out of this reduction reactor and a bringing-out means for the reduction product formed in this reduction reactor, wherein the CO
2
-eliminated feedgas from the first gas source is conducted into the reducing-gas feed duct through a discharge duct and onward into the reduction reactor, and wherein a conveying duct for at least a portion of the export gas formed in the reduction reactor and serving as a feedgas is flow-connected with the reducing-gas feed duct of the reduction reactor via a CO
2
elimination plant and optionally a heating means.
The term “sponge metal” is understood to refer to a solid end or intermediate product produced from a metal oxide by direct reduction, namely exclusively via the solid phase, i.e. without the necessity to pass via a liquid intermediate product.
An arrangement of the above-described kind is known from AT-B-396.255. AT-B-396.255 relates to a plant for producing liquid pig iron and sponge iron, from charging substances comprising iron ore and fluxes, with a first reduction reactor for iron ore, a melter gasifier, a feed duct for a reducing gas formed in the melter gasifier connecting the melter gasifier with the first reduction reactor, a conveying duct for the reduction product formed in the first reduction reactor connecting the first reduction reactor with the melter gasifier, with an export-gas discharge duct departing from the first reduction reactor, with feed ducts for oxygen-containing gases and carbon carriers opening into the melter gasifier, and with at least one additional reduction reactor for receiving metal ore, in particular further iron ore, a reducing-gas feed duct to this reduction reactor, an export-gas discharge duct leading out of this further reduction reactor and a discharging means for the reduction product formed in this further reduction reactor, wherein the export-gas discharge duct of the first reduction reactor opens into a CO
2
elimination plant from which the reducing-gas feed duct for the additional reduction reactor departs and opens into the additional reduction reactor and wherein a conveying duct for at least a portion of the export gas formed in the further reduction reactor is flow-connected with the reducing-gas feed duct for the further reduction reactor via the above-mentioned CO
2
elimination plant.
In this method therefore the portion of the reducing gas formed in the melt-down gasifying zone that incurs as a surplus gas and is supplied to the further reduction zone, after scrubbing in a scrubber is mixed with the export gas from the first reduction zone and is subjected to CO
2
removal together with the same. Admixture is thus effected prior to CO
2
elimination, so that for the two gas streams forming a gas mixture the same conditions will prevail for CO
2
elimination.
By recirculating export gas obtained from the further reduction zone, enriching of nitrogen is caused in the reducing gas supplied to this further reduction zone. Nitrogen passes i.a. into the gas cycle, as it is employed as a conveying gas for dusts of the reducing gases or export gases respectively, which are recycled to the melter gasifier or the further reduction zone respectively. This nitrogen, which is not involved in the reduction process and thus has to be conveyed along solely as ballast, increases the gas volume to be conveyed and thus causes an increase in the pressure drop inside the further reduction reactor as well as an increase in energy expenditures. Effecting a satisfactory degree of nitrogen removal from the reducing gas supplied to the further reduction zone necessitates high costs; the CO
2
elimination unit would have to be adjusted to a mode of operation sluicing out more nitrogen, which would however entail a loss in reductants, as it is feasible only with difficulty to adjust a CO
2
elimination plant in such a way that it will on the one hand yield a maximum of reductants and on the other hand sluice out a maximum of nitrogen.
A further disadvantage of the prior art, which arises due to the CO
2
elimination of the mixed gas, resides in the fact that the CO
2
elimination plant with regard to the ratio of reductants/oxidants and the CO/CO
2
ratio is also only adjustable to the chemical composition of the mixed gas. For this reason it is f.i. not feasible to have regard to the fact that one of the desired gases would have to be freed from CO
2
to only a slighter extent, which would lead to an increase in the content of reductants.
The invention aims at avoiding these disadvantages and difficulties and has as its object to provide a plant of the initially described kind and a method for producing sponge metal, in particular sponge iron, which enable improved economic efficiency and an increase in production, notably because the nitrogen content in the recirculated gas stream can be markedly lowered without losing reductants and without the need for special energy expenditures. It is a particular object of the invention to provide a particularly avid reducing gas for the further reduction zone, i.e. one that is highly reactive with respect to direct reduction. If possible, the ratio reductants/oxidants, the CO/CO
2
ratio and also the heating value are to be enhanced.
In a plant of the initially described kind this object is achieved in that at least two CO
2
elimination plants are provided which are adapted to be connectable in parallel and at least one of which is connectable with the conveying duct for the export gas that is produced in the reduction reactor forming the further gas source and that is conducted as a recycle gas, and at least one CO
2
elimination plant for the feedgas from the first gas source is provided and each of the CO
2
elimination plants is flow-connectable with the reduction reactor forming the further gas source.
A coke or coal gasification plant, such as f.i. a Lurgi gasifier, can serve as the first gas source, wherein f.i. a feedgas of the following chemical composition is formed:
TABLE
CO
15.8-24.6
H
2
20-39.8
CO
2
10-32
CH
4
3.5-16.5
CnHm
0.4-1.1
N
2
0.4-44.2
A preferred embodiment is characterized in that the first gas source is formed by a plant for producing liquid pig iron or liquid steel pre-products from iron ore, comprising at least one first reduction reactor for iron ore, a melter gasifier, a feed duct for a reducing gas formed inside the melter gasifier connecting the melter gasifier with the first reduction reactor, a conveying duct for the reduction product formed in the first reduction reactor connecting the first reduction reactor with the melter gasifier, with an export-gas discharge duct departing from the first reduction reactor, with feed ducts for oxygen-containing gases and carbon carriers opening into the melter gasifier and with a tap for pig iron and slag provided at the melter gasifier, wherein the export-gas discharge duct for the export gas formed inside the first reduction reactor is connectable with at least one of the CO
2
elimination plants.
With this process, the CO
2
elimination plant for the export gas that is conducted as a recycle gas of the further reduction reactor is operated with a view to minimizing the nitrogen contained in the recycle gas, accepting a reduction in the reductants contained in said recycle gas, whereas the CO
2
elimination plant for the export gas formed in the first reduction reactor is operated with a view to optimizing the reductants, hence aiming at an optimum CO
2

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