WO2001018257A1

WO2001018257A1 - Furnace for the direct reduction of iron oxides

Info

Publication number: WO2001018257A1
Application number: PCT/IB2000/001254
Authority: WO
Inventors: Milorad Pavlicevic; Alfredo Poloni; Gianni Burba
Original assignee: Danieli & C. Officine Meccaniche Spa
Priority date: 1999-09-06
Filing date: 2000-09-05
Publication date: 2001-03-15
Also published as: ITUD990159A0; AU6718300A; IT1310772B1; ITUD990159A1

Abstract

Gravitational type furnace for the direct reduction of mineral iron comprising a median reaction zone (14) in which the reactions to reduce the mineral iron occur, means (12, 13) to feed the mineral iron to said reaction zone (14), means (16, 17, 18) to introduce reducing gas into said reaction zone (14), and a discharge zone (15) to discharge the reduced metal iron, moving means (30) being provided to move said mineral iron, at least in proximity with said median reaction zone (14).

Description

"FURNACE FOR THE DIRECT REDUCTION OF IRON OXIDES"

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FIELD OF THE INVENTION This invention concerns a furnace for the production of metal iron by means of the direct reduction of mineral iron, where the iron is present in the form of oxides . The furnace is of the gravitational type and is provided with an upper container from which the mineral iron, coarse or in the form of pellets, is introduced, and a discharge zone from which the directly reduced iron (DRI) is removed. In a median reduction zone, the furnace is provided with a circumferential conduit, provided with nozzles, through which reducing gas is injected.

BACKGROUND OF THE INVENTION The state of the art includes furnaces of the gravitational type, or shaft furnaces, for direct reduction processes comprising an upper loading zone, a central part, substantially cylindrical, in which the reduction reaction occurs, a device to inject reducing gas into the central zone, and a lower discharge zone, tapered, with the taper facing downwards.

To achieve acceptable working conditions in the direct reduction of iron oxides, it is necessary, in the load column, to create conditions of uniform distribution of the reducing gas, both in the peripheral zones and also in the central zones of the load volume, possibly reducing the load of gas; it is also necessary to break up any agglomerates of sintered material in order to prevent any high temperature sticking, in the zone of transition between one zone where reduction takes place and the underlying zone where the material is discharged from the furnace.

During the reduction process, zones of different temperatures are formed in the furnace; from 300 to 500°C in the upper part and from 600 to 1000°C in the lower layers of the central cylindrical part, or in the transition zone. The maximum temperature zone is critical, because in this zone sticking can limit the overall productivity of the reduction process.

The state of the art includes a furnace in which load feeders are provided in the upper, median and lower part, consisting of rollers with fixed segments to break up the load, and in which the operating speed of the load feeders is regulated by means of hydraulic commands.

Document US-A-3 , 516 , 648 discloses a vertical retorting kiln wherein two piston-driven linear grates are positioned in horizontal planes in the lower portion thereof. In particular, one linear grate is positioned above and at right angles to the other, at a certain horizontal distance therefrom, to create a break up effect in the lower portion of the kiln.

However, the known devices have the following disadvantages : First of all, the load feeders operate continuously and only manage to break the load, instead of moving it, without improving the permeability of the load by the reducing gas, with a consequent reduction in the total efficiency of the reduction process. Moreover, load feeders do not intervene upstream of the sticking, in order to prevent it, since they do not cause the reciprocal movement of the particles of the load, but only carry out a partial action of detachment of the parts of the load which have already stuck. Additionally, these devices require the use of considerable power and complicated hydraulic systems to keep them working, due to the high density and high temperature action of the load column. Finally, in order to be exploited efficiently, their movement must be linked to the speed of descent of the material.

The present Applicant has devised, planned and embodied the furnace for the direct reduction of iron oxides according to the invention to overcome these shortcomings and to solve the as yet unresolved problems relating to the increase in permeability of the gas in the load, the uniform distribution of the reducing gas in the load volume in order to increase the interaction surface, to reduce the quantity of gas and the intensification of the heat and volume exchange.

SUMMARY OF THE INVENTION The furnace to produce metal iron by the direct reduction of iron oxides according to the invention is set out and characterized in the main claim, while the dependent claims describe other innovative characteristics of the invention.

The furnace according to the invention is of the gravitational or shaft type, wherein both the material and the gas are fed continuously, so as to create a vertical and gravitational flow of the material and so that the direct reduction of the mineral occurs.

The reduction furnace is equipped with means to feed the mineral iron and means to discharge the reduced metal iron, and is provided with at least an inlet collector, arranged laterally, to inject the reducing gas in correspondence with one or more reduction zones inside the furnace.

One purpose of the invention is to achieve a reduction furnace which will prevent as much as possible the material from sticking, especially in the transition zone, where the temperature inside the furnace is higher, so that it is possible to obtain a high productivity and a better quality of the directly reduced iron (DRI) .

In accordance with this purpose, the reduction furnace according to the invention is provided with movement means suitable to move the mineral iron introduced into the furnace, at least in proximity with its median reaction zone.

According to another characteristic feature of the invention, the movement means are arranged in the zone of transition between the median reaction zone and the discharge zone.

According to another characteristic feature of the invention, the movement means comprise at least a transverse girder element arranged below the reaction zone, orthogonal to the longitudinal axis of the latter and vibration means suitable to make the transverse girder element vibrate.

In turn, the vibration means comprise a revolving electromechanical actuator, associated with a cam. According to another characteristic feature of the invention, each transverse girder element comprises a tube, hollow inside, and provided with radial nozzles through which additional gas is suitable to be introduced into the furnace . BRIEF DESCRIPTION OF THE DRAWINGS

These and other characteristics of the invention will become clear from the following description of a preferred form of embodiment, given as a non-restrictive example, with reference to the attached drawings wherein: Fig. 1 is a sectioned side view of a furnace for the direct reduction of iron oxides according to the invention; Fig. 2 is a section along the line A-A of Fig. 1; Fig. 3 is an enlarged detail of Fig. 1; and Fig. 4 is a variant of Fig. 2. DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

With reference to the attached Figures, a furnace 10 for the direct reduction of iron oxides according to the invention comprises a container 11, substantially cylindrical in shape, an upper loading container 12 from which, through distribution tubes 13, the load of mineral (iron oxides) is suitable to be introduced, a median reaction zone, or reactor 14, wherein the reduction reaction of the iron oxides takes place, and a lower zone or discharge zone 15, shaped substantially like a truncated cone with the taper converging downwards.

In correspondence with the reactor 14, the furnace 10 comprises a pair of circumferential conduits 16, provided with nozzles 17, through which a mixture of reducing gas, arriving from corresponding conduits 18, is suitable to be introduced.

The reducing gas and the plant upstream of the conduits 18 can be of any known type, for example of the type described in the in the PCT international publication No. WO-A- 00/36156.

In the upper part of the furnace 10 an intake device 20 is provided.

In correspondence with a lower aperture 23 of the discharge zone 15 a conveyor plate 25 is provided, connected with a device 26, of a conventional type, suitable to make it vibrate.

In accordance with one characteristic of the invention, below the reactor 14, that is, in correspondence with the transition zone, where sticking is more likely to occur, there is a movement device 30 suitable to create a relative movement of the various pieces of mineral which make up the load. In this case, the movement device 30 comprises a plurality of transverse girder elements 31 constituted for example by tubes arranged on one or more transverse planes, substantially orthogonal to the longitudinal axis of the furnace 10.

The tubes 31 are connected, for example by means of a cam - _fi _

32 , to an electromechanical device 33 , consisting of a motor , which is suitable to make them vibrate in a convent ional manner . The vibrat ions caused by the electromechanical device 33 on tubes 31 may have a direction both parallel and orthogonal to the longitudinal axis of the furnace 10 , or a combination thereof .

Each tube 31 may have a square , round, elliptic , rhomboid or other shape cross sect ion , even irregular , and is provided with a central cavity 34 and with radial nozzles 35 , facing downwards , or towards the underlying discharge zone (Figs . 2-4 ) .

Supplementary reducing gas is suitable to be injected into the furnace 10 through the tubes 31; said gas expands throughout the amplitude of the cross section through the radial nozzles 35.

The furnace 10 as described heretofore functions as follows :

The mineral iron, for example in pellet form, is introduced into the furnace 10 from the upper container 12 through the distribution tubes 13, while the reducing gas is introduced by the conduits 18 and spread in the reactor 14 by the circumferential conduits 16, through the nozzles 17.

The intake device 20, carrying the reducing gas upwards, encourages the diffusion of the latter and its distribution from the periphery towards the center of the reactor 14.

Different reactions take place sequentially in the reactor 14, from the highest to the lowest iron oxides and, in the end, into metal iron, with the load flowing counter to the reducing gas . To ensure that the mineral load introduced into the furnace 10 is maintained constantly stirred, during its slow descent from the top downwards, in order to prevent sticking of the various pieces of mineral which make up the load, the - 7 - P T BOO/01254

tubes 31 are made to vibrate by means of the motor 33 and the cam 32.

Moreover, the vibrations of the tubes 31 and the additional gas introduced into the furnace 10 through the nozzles 35 encourage a uniform distribution in the load volume of the reducing gas introduced through the nozzles 17. This action also increases the heating process and the mass exchange in the furnace 10 and the overall productivity of the furnace 10 is also increased in a corresponding manner .

The fact that the tubes 31 have different shapes increases their movement of the loaded material .

Moreover, the fact that the nozzles 35 are oriented downwards means that they are not obstructed by the material above, notwithstanding the vibration of the tubes 31.

The metallized product, that is, the directly reduced iron (DRI), is then discharged through the lower aperture 23 towards the plate 25.

It is obvious that modifications and additions can be made to the furnace 10 for the direct reduction of mineral iron as described heretofore, but these shall remain within the field and scope of the invention.

For example, the movement device 30 can be controlled in such a manner that it imparts to the tubes 31 vibration impulses of a variable frequency, or different vibration impulses for each tube 31.

Moreover, the tubes 31 may be arranged offset with respect to each other on several horizontal planes, divided into blocks or layers . It is also obvious that, although this invention has been described with reference to specific examples, a person of skill in this field will certainly be able to achieve many other forms of equivalent furnaces, but these shall all come - 8 -

within the field and scope of this invention.

Claims

1 - Gravitational type furnace for the direct reduction of mineral iron comprising a median reaction zone (14) in which the reactions to reduce the mineral iron occur, means (12, 13) to feed the mineral iron to said reaction zone (14), means (16, 17, 18) to introduce reducing gas into said reaction zone (14), and a discharge zone (15) to discharge the reduced metal iron, wherein moving means (30) are provided to move said mineral iron, at least in proximity with said median reaction zone (14), characterized in that said movement means (30) comprise at least a transverse girder element (31) arranged below said reaction zone (14), orthogonal to the longitudinal axis of the latter, and vibration means (32, 33) suitable to make said transverse girder element (31) vibrate.

2 - Furnace as in Claim 1, characterized in that said movement means (30) are arranged in a zone of transition between said median reaction zone (14) and said discharge zone (15) . 3 - Furnace as in Claim 1, characterized in that said movement means (30) comprise a plurality of transverse girder elements (31) arranged below said reaction zone (14) on at least a plane orthogonal to the longitudinal axis of the latter and vibration means (32, 33) suitable to make said transverse girder elements (31) vibrate.

4 - Furnace as in Claim 1, characterized in that said vibration means comprise an electromechanical actuator (33) associated with a cam (32) .

5 - Furnace as in Claim 3 or 4 , characterized in that each of said transverse girder elements (31) comprises a tube provided with radial nozzles (35) through which additional gas is suitable to be introduced into said furnace (10) .

6 - Furnace as in Claim 5, characterized in that said radial O 01/1 57 - 10 - PCT/IBOO/01254

nozzles (35) face downwards.

7 - Furnace as in Claim 3, characterized in that said transverse girder elements (31) have a cross section of a different geometric shape: square, rhomboid, circular, elliptic or irregular.

8 - Furnace as in Claim 1, characterized in that the vibrations caused by said vibration means (32, 33) on said transverse girder element (31) may have a direction both parallel and orthogonal to the longitudinal axis of said furnace, or a combination thereof.