AU715697B2

AU715697B2 - Arrangemente for discharging and mixing lumpy material

Info

Publication number: AU715697B2
Application number: AU48559/97A
Authority: AU
Inventors: Leopold Werner Kepplinger; Gerald Rosenfellner; Felix Wallner
Original assignee: Voest Alpine Industrienlagenbau GmbH
Current assignee: Primetals Technologies Austria GmbH
Priority date: 1996-11-12
Filing date: 1997-11-07
Publication date: 2000-02-10
Anticipated expiration: 2017-11-07
Also published as: JP2001503477A; SK58499A3; CA2271435A1; DE19750773A1; ATA197796A; TW428029B; ZA9710200B; WO1998021537A1; EP0946849A1; DE19750773C2; ID21347A; KR20000053194A; AU4855997A; TR199901020T2; BR9713015A; AT406299B; CN1244911A

Description

Arrangement for Discharging and Mixing Lumpy Material The invention relates to an arrangement for discharging and mixing lumpy material, in particular partially and/or completely reduced iron ore in and from a shaft furnace, preferably a direct reduction shaft furnace, comprised of a hollow body opening downwards and/or to at least one side for discharging the reaction material, in which hollow body screws are radially arranged.

EP-B 166 679 describes screws of equal lengths and cylindrical cross sections for moving solid particles in a shaft furnace and discharging solid particles from such shaft furnace, which are radially arranged and cantilevered. Dead comers are minimized by installing wedge-shaped baffles between the screws. This arrangement has the disadvantage that the area of dead comers, which is also referred to as "dead man", is reduced by the baffles, but at the same time the active volume is maintained.

EP-B 85 290 describes arrangements of short conical screws, which are mounted in a tapered baffle located in the center, which at the same time serves as angle of repose, as well as along the circumference. As quoted in patent EP-B 166 679, the arrangement is radially and diagonally opposed and offset by the same angle.

CH-A 376 134 describes a process for reducing iron ore to iron, wherein the bulk material is conveyed by superimposed diametrical screws. The screws show a constant pitch and height and are seated on cylindrical shafts which are supported on both sides.

GB-A 15 02 090 describes screw conveyors arranged in parallel, with a tapered screw shape, which serve for discharging iron ores. The shafts are connected to one another by means of V-belts and are synchronously driven.

In the reduction of ores by reactive gases, it is an economical necessity to bring only a specific gas volume leaner than stoichiometric in contact with the ore. However, this requires a homogeneous gas distribution as well as a uniform subsiding movement of the solids bed in the shaft furnace.

%%VA ALLahw ~mrm-ArawktgMOD31SWo TA1977m df In a shaft furnace, according to the COREX® process, the solids are moved and discharged by radially arranged screws at the lower shaft end. To ensure that the bulk material subsides as uniformly as possible, the zone located at the shaft bottom has to be comprised of a maximum of active discharge area, and furthermore, a continuous movement and thorough mixing of the reaction zone has to be ensured. Non-moving zones featuring very steep inner angles of repose are formed above non-active areas.

These zones, which are referred to as "dead man", have the essential disadvantage that the volume percent of the reaction space becomes partially inactive. As a result, cakings and agglomerates may form in these regions owing to the long dwelling times of the ores as well as of already reduced ores which impair the material flow and consequently reduce the material reaction and thus also productivity.

In this state-of-the-art arrangement, wherein the screws are cantilevered and have equal lengths, almost no movement occurs in the central region of the shaft. Owing to the fact that the gas flow concentrates in the shaft center if dust-laden gases are fed through nozzles mounted along the circumference, the gas is not homogeneously distributed.

The technical problem of the invention is to avoid those regions where no movement occurs, to minimize regions of reduced movement and at the same time to maximize the active volume of the moving shaft material. Active volume means the region of a shaft furnace where the desired gas-solids reactions continue to take place.

The invention is characterized in that screws arranged in one level have different lengths.

A preferred development is characterized in that opposed screws have equal lengths and/or one screw is designed as through screw.

The arrangement of screws of different lengths ensures that also those regions of the discharge zone can be activated which are close to the center. This arrangement provides for a largely exhaustive continuous mixing and subsiding of the bulk material in particular in the upper part of the shaft in the area of the reaction space where the reduction processes ,occur.

This invention for the first time allows to achieve a uniform mixing and continuous discharge of the solids in the reaction area of a direct reduction shaft furnace. The invention adjusts the arrangement and design of the screws optimally to the fluid dynamic conditions of the reaction partners, solids and gas.

For example, by using through screws combined with short screws, the "dead man" areas can be extremely reduced in size, especially because inactive solids beds will hardly build up at relatively close distances from active screws. By placing, 4 long screws and 4 short screws, the active area can be extended up to the peripheral edge zones. By installing one adjacent long and short screw each the product discharge can be combined via one downpipe each. Owing to this measure, the arrangement of the downpipes can moreover be better adjusted to the geometry of the melter gasifier coupled therewith. When combining short and long screws, the behavior can be adjusted both to the movement and to the discharge of the solids through the screw design in such a way that both the discharge performance and the mixing characteristics can be influenced. Primarily, however, the discharge behavior of the solids bed can be influenced.

According to a feature of the invention, the screws are arranged in two or more levels, so the bed in the bottom part of the fumrnace can be better moved.

According to another feature of the invention, the opposed long screws are of selfcentering and/or catching design. If screws are installed in an existing bed, it has to be ensured that the screw halves meet one another and are centered.

According to a feature of the invention, the helicoidal surfaces of the screws start from their free ends. As a result, the core zone is optimally mixed and the reaction product constantly discharged.

According to another feature of the invention, the screws are tapered towards the center, so the active cross section of those regions of the reaction zone which are moved by the screws is maximized.

C ~4 IVATPALODCl AVCOIWkrVMMISNWMTAIOImac According to another feature of the invention, the helicoidal surfaces of the screws show a constant pitch. This development provides for a uniform feeding behavior above the cross section of the screw.

According to another feature of the invention, the helicoidal surfaces of the screws show different pitches related to the process. Due to the nonlinear pitch of the helicoidal surfaces of the screws, the reaction behavior of the melter gasifier as well as the fluid behavior of the reaction material can be taken into account. Because of the mathematically simulated development of the feeding characteristics, the reaction material in the shaft as well as the reaction behavior of the reaction gas can be taken into account.

According to another development of the invention, coupled motors are provided for driving the screws. If the screws are driven by motors, the screws can flexibly adjust themselves to the process and can move by their own drive during installation and dismantling.

According to a feature of the invention, the short and long shafts have the same speed.

If a plant involving minimum investment expenditure is demanded, preferably noncontrolled operation of the motors is suggested. As a result, the screws have approximately the same speed but do not involve any control expenditure.

According to another feature of the invention, the speeds of the individual screws are controlled in accordance with the feeding characteristics of the process. Owing to the controlled operation of the screws, the energy-related as well as process-related requirements of the reaction zone of the melter gasifier can be taken into account.

According to another feature of the invention, the screws are axially movable. During inspection or in case of failure, the screws can be more easily installed and dismantled.

In case of irregularities in the reaction zone, the fluid behavior can be decisively influenced by changing the depth of immersion of the screws.

I M XATA According to one embodiment, the blades forming the helicoidal surfaces have a shape corresponding to the feeding characteristics of the process. Because of this modelled shape, the caking behavior of the solids bed and the formation of the reaction zone can be taken into account.

According to a last feature of the invention, the helicoidal surfaces of the screw bodies have a shape corresponding to the feeding characteristics of the process. This adjustment ensures an optimized relationship between the reactivity of the charging materials and the geometrical conditions of the reduction shaft.

The invention is described in greater detail by means of embodiments, with Fig. 1 showing eight screws of different lengths in a shaft furnace, Fig. 2 six screws of different lengths in a shaft furnace, Fig. 3 the combination of screws of two different lengths, Fig.

4 the arrangement of two through screws in a shaft furnace, Fig. 5 the top view of an arrangement of two through screws in a shaft furnace, Fig. 6 the combination of one through screw with six cantilevered screws, Fig. 7 the same with four cantilevered screws, Fig. 8 the self-centering and catching version of a through screw, Fig. 9 the cross section of this connection, Fig. 10 a self-centering version of a through screw, and Fig. 11 the section through the connection.

Fig. 1 displays an example where cantilevered screws 2 of three different lengths are combined, which are arranged radially to form an octagon in shaft furnace 1. The "dead man" area, the inactive space in the center of the shaft furnace, is extremely reduced by this combination.

Fig. 2 displays an example where cantilevered screws 2 of two different lengths are combined, which are arranged radially to form a hexagon in shaft furnace 1. In this combination, the near-edge regions of the furnace are less thoroughly mixed, and the material to be discharged is not discharged as uniformly as shown in Fig. 1.

Fig. 3 displays an example of an embodiment where cantilevered screws 2 of two different lengths are also combined, which, however, are radially arranged to form an :octagon. Movement in the near-edge region of shaft furnace 1 is better than is the case in Fig. 2.

TP&OCVXVNIKhkO"ftnP"IlmmlvWMSWItAT l97 rW I I 6 Fig. 4 shows the spatial arrangement of the combination of two through screws 3 in shaft furnace 1.

Fig. 5 shows the plan view of the arrangement according to Fig. 4, wherein four cantilevered screws 2 of the same short length ensure an optimum movement of the material in the first level of through screw 3.

Fig. 6 displays the combination of through screw 3 with six cantilevered screws 2 in shaft furnace 1.

Fig. 7 displays six cantilevered screws 3 in one level with a through screw.

Fig. 8 shows the fit of the two screw halves of through screw 3, wherein this fit is toothed for the purpose of centering and meshing. The screw half has the advantage that it meets the screw half boring on the opposite side in a centrical and toothed manner during boring into the bed of a shaft furnace not yet drained off.

Fig. 9 displays the section through this toothed, self-centering connection of the screw halves of a through screw.

Fig. 10 displays the cut cross section of the longitudinal view of a centering connection of screw halves of through screws 3.

Fig. 11 displays a section through the centering fit of the screw halves of through screw 3. Controlling the speed of the drive motors of the shaft halves ensures an exact fit and exact characteristics of the screw halves.

Claims

1. Arrangement for discharging and mixing of lumpy material, in particular partially and/or completely reduced iron ore from a shaft furnace, preferably a direct reduction shaft furnace, comprised of a hollow body opening downwards and/or to at least one side for discharging the reaction material, in which hollow body screws are radially arranged, characterized in that the screws arranged in one level have different lengths.

2. Arrangement according to claim 1, characterized in that opposed screws have equal lengths and/or one screw is designed as through screw.

3. Arrangement according to claim 1 or 2, characterized in that the screws are arranged in two or more levels.

4. Arrangement as claimed in any of claims 1 to 4, characterized in that the opposed long screws are of self-centering and/or catching design.

Arrangement as claimed in any of claims 1 to 4, characterized in that the helicoidal surfaces of the screws start from their free ends.

6. Arrangement as claimed in any of claims 1 to 5, characterized in that the shafts of the screws are tapered towards the center.

7. Arrangement as claimed in any of claims 1 to 6, characterized in that the helicoidal surfaces of the screws show a constant pitch.

8. Arrangement as claimed in any of claims 1 to 7, characterized in that the helicoidal surfaces of the screws have different pitches related to the process.

9. Arrangement as claimed in any of claims 1 to 8, characterized in that coupled motors are provided for driving the screws.

AVATPALW- Vpooj&WfMD&%Nftndwt~mo~r4%4=1%W&ATTgll d Arrangement as claimed in any of claims 1 to 9, characterized in that the short screws and the long screws have the same speed.

11. Arrangement as claimed in any of claims 1 to 10, characterized in that a control of the speeds of the individual screws in accordance with the feeding characteristics of the process is provided.

12. Arrangement as claimed in any of claims 1 to 11, characterized in that the screws are axially movable.

13. Arrangement as claimed in any of claims 1 to 12, characterized in that the helicoidal surfaces of the screw bodies have a shape corresponding to the feeding characteristics of the process.

14. Arrangement as claimed in any of claims 1 to 13, characterized in that the blades forming the helicoidal surfaces have a shape corresponding to the characteristics of the feed.