Heating – Shaft type
Reexamination Certificate
2000-08-16
2001-08-28
Wilson, Gregory (Department: 3749)
Heating
Shaft type
C432S098000, C266S197000
Reexamination Certificate
active
06280181
ABSTRACT:
The invention relates to a shaft furnace, in particular a direct-reduction shaft furnace, having a bed of lumpy material, in particular lumpy material containing iron oxide and/or iron sponge, having worm conveyors which penetrate through the shell of the shaft furnace for discharging the lumpy material from the shaft furnace, which conveyors are arranged above the base area of the shaft furnace and are mounted in the shell of the shaft furnace.
Numerous shaft furnaces, in particular reduction shaft furnaces, of the type described above are known from the prior art. Such a shaft furnace, which is substantially designed as a cylindrical hollow body, generally contains a bed of lumpy material containing iron oxide and/or iron sponge, the material containing iron oxide being introduced into the top part of the shaft furnace. A reduction gas which is derived, for example, from a melter gasifier is blown into the shaft furnace and thus into the solids bed through a plurality of inlet openings which are arranged over the circumference of the shaft furnace in the region of the bottom third of the shaft furnace. The hot dust-laden reduction gas flows up through the solids bed and, in the process, reduces some or all of the iron oxide in the bed to iron sponge.
The fully or partially reduced iron oxide is conveyed out of the shaft furnace by discharge devices which are arranged between the base region of the shaft furnace and the region of the gas inlet openings. These discharge devices are generally designed as worm conveyors which are arranged in the form of a star and convey in the radial direction (with respect to the shaft furnace).
The zone which lies in the region of the shaft base and in which the discharge devices are located is to have a maximum active discharge surface area, in order, on the one hand, to lower the level of the bed material as evenly as possible and, furthermore, to ensure continuous movement of the material in the reaction zone.
With a star-shaped arrangement of worm conveyors, the requirement for a maximum active discharge surface area is only satisfied if each of the worm conveyors takes material out of the bed and conveys it away uniformly over its entire length projecting into the shaft.
To achieve this, the conveying cross section of existing worm conveyors is designed in such a way that, in each section of a worm conveyor, both the removal of material from sections which are arranged at the front, as seen in the direction of conveying, and the removal of bed material from the region surrounding this section, would have to be ensured. This is generally achieved by means of a radius of the paddle or spiral envelope which increases continuously in the direction of conveying. In addition, the conveying volume of each worm section is continuously increased by means of an increasing pitch of the worm spiral in the direction of conveying.
Despite these measures, it has been established that the material at the end of the worm and at the wall of the shaft furnace is taken off at two to three times the rate as that in the central regions of the worm conveyor.
Consequently, the material which is located above the central regions of a worm conveyor has a longer residence time in the shaft furnace than the material above regions which have a high conveying capacity. This increases caking and bridging within the lumpy material above the central areas, while the formation of tunnels within the bed occurs particularly frequently above the regions with a high conveying capacity.
Shaft furnaces which are known from the prior art therefore have the drawback that, when conventional worm conveyors are used, it is impossible to ensure uniform discharge of the bed material situated in the shaft furnace by means of the worm conveyors alone. In conjunction with the regions which can in any case not be touched using worm conveyors arranged in a star shape, i.e. the wedge-shaped regions between two adjacent worm conveyors, and the space which is cleared by the worm conveyor ends in the centre of the shaft furnace, varying residence times of the bed material in the shaft furnace result, leading in turn to a non-uniform reduction process and fluctuating product qualities.
The object of the present invention is therefore to provide a shaft furnace, in particular a direct-reduction shaft furnace, which, by dint of the worm conveyors used therein, provides improved, more uniform discharge of the bed material than shaft furnaces which are known from the prior art and use conventional worm conveyors.
According to the invention, this object is achieved by the fact that the take-off region of each worm conveyor, which projects into the shaft, in the longitudinal direction is divided into at least two adjacent sections, the conveying cross sections of adjacent ends of these sections increasing suddenly in the direction of conveying.
In contrast to all the other regions, the region forming the end of the worm does not have to convey any material out of sections which precede it. Consequently, its entire capacity is free to take material out of the bed. In order to provide regions with such a high conveying capacity in the middle part of the take-off region of the worm conveyor, which projects into the shaft, as well, the take-off region is divided into sections, the conveying cross section being designed in such a way that it increases suddenly at the transition from one section to the next section, as seen in the direction of conveying. In this region having an increased capacity compared to that of the preceding section, it is again possible to remove more material from the bed.
Consequently, in total, a conveying capacity which is more even over the entire length of the worm is achieved, and dividing the take-off region of the worm conveyor, which projects into the shaft, into two such sections alone, if the take-off regions are not excessively long, is sufficient to achieve a significant improvement in the conveying performance compared to a worm conveyor with a conveying cross section which increases continuously in the direction of conveying.
Depending on the length and number of screw turns, the take-off region which projects into the shaft is divided into two or more such sections. An essential criterion when selecting the number of sections is the particular increase in the conveying cross section. With an increasing number of sections or a reduced increase in the conveying cross sections, the shape of the screw and therefore the conveying characteristic more closely approximates that of screws with a continuously increasing conveying cross section.
The sudden increase in the conveying cross section in the region of associated section ends is to have—with respect to the longitudinal axis of the worm conveyor—a mean increase of at least 45°, preferably of at least 60°, particularly preferably of substantially 90°. To keep the frictional forces between the bed material and the end face of the worm spiral in this region and therefore the wear and the drive capacity required as low as possible, it is furthermore advantageous to make this transition at least partially a running transition.
To keep the drive capacity required at a low level, it is furthermore advantageous if the sudden increases in the conveying cross sections are offset with respect to one another, preferably with an even distribution, in the circumferential direction of the conveying cross sections, the take-off region being divided into at least three sections.
According to a preferred embodiment, the conveying cross sections are kept constant within individual sections of a worm conveyor. This embodiment is particularly simple to achieve in terms of manufacturing technology.
According to an embodiment which constitutes an alternative to that described above, the conveying cross sections are designed to increase continuously within individual sections of a worm conveyor. This variant combines the advantages of conventional worm conveyors with those of the worm conveyors according to the invention, i.e. continuously
Aichinger Georg
Lassnig Herbert
Schmidt Martin
Wieder Kurt
Wurm Johann
Deutsche Voest-Alpine Industrieanlagenbau GmbH
Ostrolenk Faber Gerb & Soffen, LLP
Wilson Gregory
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