Title of Invention

"A IMPORED SHAFT FURNACE"

Abstract

The invention relates to a shaft furnace (1), particularly to a direct reduction shaft furnace, with a packed bed (2) of lump material, particularly lump material containing iron oxide and/or sponge iron, with screw conveyors (3) dispersing the shell of the shaft furnace and serving to discharge the lump material from the shaft furnace (1), which are located above the bottom area of the shaft furnace (1) and supported in the shell of the shaft furnace.

Full Text

The present invention relates to shaft furnace. The invention relates to a shaft furnace, particularly to a direct reduction shaft furnace, with'a packed bed of lump material, particularly lump material containing iron oxide and/or sponge iron, with the screw conveyors dispersing the shell of the shaft furnace and serving to discharge the lump material from the shaft furnace, which are arranged above the bottom area of the shaft furnace and supported in the shell of the shaft furnace. Many shaft furnaces, particularly reduction shaft furnaces of the kind described above, are known from prior art. Such a shaft furnace, essentially designed as a cylindrical hollow body, generally contains a packed bed of lump material containing iron oxide and/or sponge iron, the material containing iron oxide being charged into the upper part of the shaft furnace. Reduction gas coming, for example, from a melter gasifier is injected into the shaft furnace and, thus, into the solids bed through several inlet ports arranged along the circumference of the shaft furnace in the area of the lower third of the shaft furnace. The hot, dust-laden reduction gas flows upwards through the solids bed, thereby completely or partially reducing the iron oxide of the packed bed to sponge iron. The completely or partially reduced iron oxide is discharged from the shaft furnace by means of discharging devices located between the bottom area of the shaft furnace and the area of the gas inlet ports. As a rule, these discharging devices are comprised of a radial arrangement of radially (referred to the shaft furnace) conveying screw conveyors. The zone located in the area of the shaft bottom where the discharging devices are installed is to be comprised of a maximum active discharge area in order to ensure that the bulk material descends as uniformly as possible and to achieve continuous movement of the material in the reaction zone. In a radial arrangement of screw conveyors, the demand for a maximum active discharge is only met if each screw conveyor uniformly draws off and discharges material from the packed bed over its entire length projecting into the shaft. In order to fulfill this requirement, the conveying cross section of existing screw conveyors is designed in a way that the removal of material from sections located upstream, seen in conveying direction, as well as the removal of bulk material from the area surrounding the relevant section are performed in each section of a screw conveyor. As a rule, this is achieved by continuously increasing the radius of the paddle or helix envelope in conveying direction. Additionally, the volumetric delivery of each screw section is continuously increased by a continuous increase of the spiral in conveying direction. Such a construction is claimed in US 3,704,011. Despite these measures it was established that the material at the screw head as well as at the wall of the shaft furnace is drawn off at double or triple the velocity of the central regions of the screw conveyor. As a result, the material located above the central regions of a screw conveyor features n a longer dwelling time in the shaft furnace than the material located -above regions of increased conveying capacity, which leads to the formation of increased cakings and bridges within the bulk material above the central regions, whereas channels are formed particularly frequently within the packed bed above regions of increased conveying capacity. Consequently, shaft furnaces known from prior art have the disadvantage that a uniform discharge of the bulk material located in the shaft furnace cannot even be ensured directly above the screw conveyors proper if conventional screw conveyors are used. In connection with those regions which cannot be covered anyway at radially arranged screw conveyors, i.e. the wedge-shaped regions between two adjacent screw conveyors each, as well as the space spared by the screw conveyors heads in the center of the shaft furnace, different dwelling times result for the bulk material in the shaft furnace, which, in turn, results in a nonuniform reduction course as well as variations of product quality. Therefore, the technical problem of the invention is to provide a shaft furnace, particularly a direct reduction shaft furnace, which—owing to the screw conveyors used therein—features an improved, more uniform discharge of the bulk material than shaft furnaces known from prior art where conventional screw conveyors are used. This technical problem is solved according to the invention by subdividing the discharge area of each screw conveyor, which projects into the shaft, into at least two adjacent sections in longitudinal direction, the conveying cross sections of adjacent section ends discontinuous^ increasing in conveying direction. The present invention relates to^shaft furnace, particularly direct reduction shaft furnace, with packed bed of lump material, particularly lump material containing iron oxide and/or sponge iron, with screw conveyors dispersing the shell of the shaft surface, for discharging lump material from the shaft furnace, which are located above the bottom area 'of the shaft furnace and supported in the sheU of the shaft furnace, characterized in that the discharge area of each screw conveyor, which projects into the shaft, shows two or more adjacent sections in longitudinal direction, the conveying cross sections of adjacent stction ends discontinuously increasing in conveying direction. Contrary to all other regions, the region forming the screw head has no material convey from sections connected upstream of it, which means that its entire capacity can be used for discharging material from the packed bed. In order to create such regions of increased conveying capacity also in the central part of the discharge area of the screw conveyor, which projects into the shaft, the discharge area is subdivided into sections, the conveying cross section being designed in a way that it discontinuously increases at the transition from one section to the adjacent section, seen in conveying direction. In this region of increased capacity compared with the preceding section, more material can be removed from the packed bed. Altogether, a uniform conveying capacity is achieved thereby over the entire screw length, the subdivision of the discharge area of the screw conveyor, which projects into the shaft, into two such sections already sufficing for achieving a significant improvement of the conveying behavior compared with a screw conveyor with a conveying cross section that continuously increases in conveying direction, provided the discharge areas are not too long. The discharge area projecting into the shaft is subdivided into two or more such sections depending on the length and number of spirals. The respective increase in conveying cross section is an essential criterion in selecting the number of sections. As the number of sections increases or the increase in conveying cross section decreases, respectively, the screw shape and, thus, the characteristic conveying curve approaches to those of screws of a continuously increasing conveying cross section. The discontinuous increase in conveying cross sections in the area of section ends allocated to each other is to show a mean pitch of at least 45°, preferably of at least 60°, particularly preferably of essentially 90°, referred to the longitudinal axis of the screw conveyor. In order to minimize the frictional forces between the bulk material and the face of the spiral in this area and, thus, the wear and the required driving power, it is further advantageous to design this transition to be at least partly gradually. In order to minimize the required driving power, it is further advantageous to offset the discontinuous increases on conveying cross sections in the circumferential direction of the conveying cross sections, preferably uniformly distributed, the discharge area being subdivided into at least three sections. According to a preferred embodiment, the conveying cross sections within individual sections of a screw conveyor are kept constant. This embodiment is particularly easy to implement from the manufacturing point of view. According to an alternative embodiment, the conveying cross sections within individual sections of a screw conveyor continuously increase. This variant combines the advantages of conventional screw conveyors with those of the screw conveyors according to the invention, i.e. continuously increasing screw conveyors are combined with areas of increased conveying capacity. The helicoids of the screw conveyors are preferably formed by paddles mounted to the shafts of the screw conveyors. Although the helicoids may also be continuously developed over the entire screw length, helicoids formed by paddles are easier to construct. Moreover, paddles are considerably easier to exchange in case of repair. The extent of dimensional change of the conveying cross sections of two adjacent section ends, indicated as change in radius, is in the order of double to eight times, preferably double to six times the mean grain size of the lump material to be conveyed. Tests have shown that, if the discharge area of a screw conveyors is subdivided into three sections, an increase in radius of the conveying cross section of approximately three to four times the grain size is particularly preferred. This preferred embodiment is designed in a way that, for example, if paddles are used, the second paddle of two adjacent paddles allocated to different sections is higher than the first paddle by, for example, three times the mean grain size. At a mean grain size of, for example 20 mm, the difference in height of these two paddles thus amounts to 60 mm. It was established during tests that a value of three times the mean grain as a measure of the increase in paddle height was particularly advantageous in the creation of areas of increased conveying capacity. According to another feature of the shaft furnace according to the invention, the pitch of the spiral of one screw conveyor each in conveying direction increases in an actually known way or is first kept constant in conveying direction and subsequently increases. Accordingly, the volume that can be conveyed by the screw conveyor is increased in conveying direction so that the material discharged from the packed bed to an increased extent according to the invention is indeed removed from the shaft furnace. In the following, the shaft furnace according to the invention is explained in greater detail by the drawings, Fig. 1 to Fig. 4. Fig. 1: Shaft furnace with screw conveyors Fig. 2: Schematic screw conveyor, conveying cross section of the individual sections is constant Fig. 3: Schematic screw conveyor, conveying cross section of individual sections increases Fig. 4: Comparison of the section-related conveying capacities of conventional screw conveyors and screw conveyors according to the invention Fig. 1 displays shaft furnace 1 according to the invention with packed bed 2 of lump material and screw conveyors 3 for discharging lump material from shaft furnace 1. In so-called bustle zone 4 along the shell of the shaft furnace, a number of gas inlet ports are located through which a reduction gas is injected into packed bed 2. A number (six in this case) of screw conveyors 3 radially arranged above the bottom of shaft furnace 1 serve to discharge lump material. Discharge area 5 of each screw conveyor 3, which projects into the shaft, is subdivided into three sections, the conveying cross sections of the individual sections discontinuously increasing in conveying direction, i.e. towards the wall of shaft furnace 1. Drawings Fig. 2 and Fig. 3 show two different embodiments of screw conveyors 3, Fig. 2 showing the cross section of screw conveyor 3, whose conveying part, i.e. discharge area 5 that projects into the shaft, is designed as an interrupted spiral formed by paddles 6. Discharge area 5 is subdivided into three sections 7 8, 9, the paddle height at adjacent section ends increasing by three times the grain size of the lump material to be conveyed. Within the individual sections 7, 8, 9, the paddle height and, thus, the conveying cross section are kept constant. Screw conveyor 3 represented in Fig. 3 differs from the screw conveyor represented in Fig. 2 in that the height of paddle 6 continuously increases within individual sections in conveying direction. It is only at the transition from one section to the next one that the paddle height discontinuously increases by three times the mean grain size of the lump material. Fig. 4a to Fig. 4c display a comparison of the section-related characteristic conveying curves of conventional screw conveyors and of those of a discontinuously increasing conveying cross section. The conveying capacity of a conventional screw conveyor (Fig. 4a) is essentially higher at the screw head (1st chamber) as well as near the wall of the shaft furnace (5th chamber) than in the central areas (2nd to 4th chambers). Subdividing the screw conveyors into two sections of different conveying cross sections (Fig. 4b) results in an increased conveying capacity in the area of increase in conveying cross section (3rd chamber). It is not until the screw conveyors are subdivided into three sections that a constant conveying capacity is achieved through the largest part of the discharge area. WE CLAIM: 1. Shaft furnace (1), particularly direct reduction shaft furnace, with packed bed (2) of lump material, particularly lump material containing iron oxide and/or sponge iron, with screw conygyp£S (3) dispersing the shell of the shaft surface, for discharging lump mMerial from the shaft furnace, which are located above the bottom area of the shaft furnace (1) and supported in the shell of the shaft furnace (1), characterized in that the discharge area (5) of each screw conveyor (3), which projects into the shaft, shows two or more adjacent sections in longitudinal direction, the conveying cross sections of adjacent section ends discontinuously increasing in conveying direction. 2. Shaft furnace (1) as claimed in claim 1, wherein the discontinuous increase of the conveying cross section shows a mean pitch of at least 45°, preferably at least 60°, in the area of section ends allocated to each other, referred to the longitudinal axis of the screw conveyor (3). 3. Shaft furnace (1) as claimed in claim 2, wherein the discontinuous increase of the conveying cross section shows a pitch of essentially 90° in conveying direction. 4. Shaft furnace (1) as claimed in any of claims 1 to 3, wherein the discharge area (5) of each screw conveyor (3), which projects into the shaft, shows three or more adjacent sections in longitudinal direction, the discontinuous increases of the conveying cross sections being offset against one another, preferably uniformly distributed, in the circumferential direction of the conveying cross sections. 5. Shaft furnace (1) as claimed in any of claims 1 to 4, wherein the conveying cross sections within individual sections of one screw conveyor (3) each are kept constant. 6. Shaft furnace (1) as claimed in any of claims 1 to 5, wherein the conveying cross sections within individual sections of one screw conveyor (3) each continuously increase in conveying direction. 7. Shaft furnace (1) as claimed in any of claims 1 to 6, wherein the helicoids of the screw conveyors (3) are formed by paddles (6) mounted to the shafts of the screw conveyors. 8. Shaft furnace (1) as claimed in any of claims 1 to 9, wherein the pitch of the spiral of one screw conveyor (3) each is kept constant and/or increases in conveying direction. 9. Shaft furnace substantially as herein described with reference to the accompanying drawings.

Documents:

3290-del-1998-abstract.pdf

3290-DEL-1998-Claims.pdf

3290-del-1998-correspondence-others.pdf

3290-del-1998-correspondence-po.pdf

3290-del-1998-description (complete).pdf

3290-del-1998-drawings.pdf

3290-del-1998-form-1.pdf

3290-del-1998-form-13.pdf

3290-del-1998-form-19.pdf

3290-del-1998-form-2.pdf

3290-del-1998-form-3.pdf

3290-del-1998-form-4.pdf

3290-del-1998-form-6.pdf

3290-del-1998-gpa.pdf

3290-del-1998-petition-137.pdf

3290-del-1998-petition-138.pdf