Metallurgical apparatus – Means for treating ores or for extracting metals – By means applying heat to work – e.g. – furnace
Reexamination Certificate
2001-04-11
2003-01-28
Kastler, Scott (Department: 1742)
Metallurgical apparatus
Means for treating ores or for extracting metals
By means applying heat to work, e.g., furnace
C266S199000, C432S095000
Reexamination Certificate
active
06511629
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a shaft furnace, in particular a direct-reduction shaft furnace, with a charge composed of particulate material, in particular particulate material containing iron oxide and/or sponge iron, the said material being capable of being fed into the shaft furnace from above, and with, arranged in one plane, a multiplicity of gas-inlet orifices for a reduction gas in the region of the lower third of the shaft furnace, the shaft furnace being surrounded externally by an annular space which is connected to the gas-inlet orifices downwards by means of gas supply ducts.
Shaft furnaces, in particular direct-reduction shaft furnaces of the type described above, are known in many forms from the prior art. Such a shaft furnace, designed essentially as a cylindrical hollow body, contains, for example, a charge composed of particulate material containing iron oxide and/or sponge iron, the material containing iron oxide being fed into the upper part of the shaft furnace. By means of a plurality of gas-inlet orifices arranged over the circumference of the shaft furnace and located in the region of the lower third of the latter, a reduction gas emanating, for example, from a melt-down gasifier is injected into the shaft furnace and consequently into the solid charge. The hot dust-laden reduction gas flows upwards through the solid charge and, at the same time, reduces the iron oxide of the charge completely or partially to sponge iron.
The completely or partially reduced iron oxide is conveyed out of the shaft furnace by means of discharge devices arranged between the bottom region of the shaft furnace and the region of the gas-inlet orifices, the charge column located in the shaft furnace sinking downwards due to gravity.
A shaft furnace must, by virtue of its design, ensure that a uniform reaction course, which is as complete as possible, and uniform sinking of the charge material can take place in it.
AT B 387,037 discloses a shaft furnace for the thermal treatment of charge materials by means of gaseous media. In this case, for the supply of reduction gas, gas-inlet orifices are provided, which are covered by an annular skirt relative to the charge materials introduced in the shaft furnace. An annular cavity is provided between the annular skirt and an annular widening of the casing of the shaft furnace, so that the reduction gas introduced can be delivered to the charge materials so as to be distributed over the circumference of the shaft furnace.
This design of the gas supply system has major disadvantages. The inner walls of shaft furnaces are conventionally lined with refractory material, for example fireclay. However, such an annular skirt cannot be produced from individual fireclay bricks, since it is connected only via its upper circumference to the casing of the shaft furnace. In principle, however, this type of gas supply system is capable of being produced monolithically, that is to say so as to be manufactured from one piece. Nevertheless, for this purpose, individual segments of the shaft-furnace casing, together with that part of the annular skirt which is suspended on the said casing, would have to be manufactured in each case from a single piece of refractory material. It is scarcely possible for this to be carried out, however, because of the size of the segments and because of their complex geometry.
Furthermore, an annular skirt produced in this way would collapse during the first loading of the shaft furnace. The lateral forces arising from charges, for example due to process-dependent increases in volume, are considerable. The annular skirt would therefore break away outwards immediately.
German Patent 34 22 185 discloses an arrangement consisting of a gasifier and of a direct-reduction shaft furnace. The direct-reduction shaft furnace has, above its bottom, screw conveyers which are arranged in a star-shaped manner and by means of which particulate material is conveyed out of the shaft furnace. The inner ends of the screw conveyers are mounted in a conical fitting in the middle of the shaft furnace. This conical fitting is connected downwards to the melt-down gasifier, so that reduction gas can flow out of the melt-down gasifier through the conical fitting into the shaft furnace. Furthermore, reduction gas is supplied to the shaft furnace via at least one gas-inlet orifice which opens into an annular space formed by an annular skirt and the shaft-furnace casing. The same applies to this annular skirt as to that in AT B 387,037, that is to say it would immediately break away laterally and/or, on account of the abrazing forces of the charge moving past it, would be ground off. This is all the more relevant as the conical fitting located at the same height as the annular skirt constitutes, from the point of view of the charge material, a reduction in the free cross section of the shaft furnace. Consequently, the laterally effective forces arising from the charge in the region of the conical fitting and of the annular skirt are also substantially higher than in other regions of the shaft furnace. Moreover, in regions of reduced cross section the charge preferentially forms baked areas, agglomerations and bridges. This prevents the charge material from sinking uniformly.
The prior art, for example U.S. Pat. Nos. 3,816,101 or 4,046,557, discloses shaft furnaces, in which a reduction gas is first introduced into a cavity which annularly surrounds the shaft furnace and from which a plurality of gas supply ducts open into a frustoconical widening of the shaft furnace casing. This annular cavity has a rectangular cross-sectional surface in vertical section, and the gas supply ducts opening into the shaft furnace lead away from the bottom and/or from the inner wall of this annular space.
This gas supply system is unsuitable when the reduction gas is to be supplied so as to be distributed uniformly over the circumference of the shaft furnace. Since the charge material rests directly against each gas-inlet orifice, the number of points for the inlet of gas into the shaft furnace and therefore into the charge is only in each case as large as the number of gas-inlet orifices.
If a dust-laden reduction gas is used, dust may settle at the mouth of the gas supply ducts into the shaft furnace and reduce the gas permeability of the charge there, with the result that further dust settles, and so on and so forth, ultimately clogging the gas supply ducts. Further dust may also be deposited on the bottom of the annular space. In an extreme situation, even particulate material from the charge may pass into the annular space. It is not possible to remove the solids which have settled in the gas supply system, without decommissioning and emptying the shaft furnace. Faults in the passage of gas through the charge, which are caused by clogged gas supply ducts, lead to an uneven reduction of the charge material and a reduction in the product quality.
SUMMARY OF THE INVENTION
The object of the invention is, therefore, to provide a shaft furnace, in particular a direct-reduction shaft furnace, the gas supply system of which is designed in such a way that the disadvantages known from the prior art are avoided.
In particular, this gas supply system is to be capable of being produced in a simple way from conventional refractory material and is to have sufficient mechanical stability relative to the laterally acting forces arising from the charge. Dust-laden reduction gas is to be capable of being distributed uniformly on the circumference of the shaft furnace and therefore, as a further consequence, also in the charge, and the clogging of gas supply channels is to be avoided.
This object is achieved, according to the invention, in that the shaft contour has a diametral widening in the region of the gas-inlet orifices and the wall of shaft furnace is designed in such a way that an annular cavity is formed between the gas-inlet orifices arranged in the region of this diametral widening and the charge.
By means of the inventive design of the gas supply sys
Kastner Rainer Walter
Kepplinger Leopold Werner
Schiffer Wilhelm
Stastny Wilhelm
Wieder Kurt
Deutsche Voest-Alpine Industrieanlagenbau GmbH
Kastler Scott
Ostrolenk Faber Gerb & Soffen, LLP
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