AU2367599A - Method for producing briquetted iron sponge - Google Patents

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

Applicant(s): KLOCKNER INDUSTRIE-ANLAGEN GMBH and MASCHINENFABRIK KOPPERN GMBH CO KG Actual Inventor(s): Dr. Klaus Brennecke Dr. Manfred Chitil IP Australia Documents received on: (0 9 APR 1999 C3 Address for Service: PATENT ATTORNEY SIEyAS 26 Ellingworth Parade Box Hill Victoria 3128 Australia I~-T1 Title: METHOD FOR PRODUCING BRIQUETTED IRON SPONGE The following statement is a full description of this invention, including the best method of performing it known to me/us:- Method for producing briquetted iron sponge The invention relates to a method for producing briquetted iron sponge in accordance with the preamble of Claim i.

DE-B-, 119,886 has disclosed a method for producing briquetted iron sponge from iron-ore pellets which have undergone direct reduction, the reduced, i.e. iron sponge, pellets being cold-briquetted after they have been discharged from the reduction furnace and cooled after impurities have been screened out. In the cold-briquetting operation, the iron-sponge pellets are merely pressed together with a considerable force.

Nevertheless, this operation does not reduce the porosity of the iron sponge sufficiently for longdistance transportation. In this case, the use of small iron-sponge pellets or pellet fragments comprising iron sponge which are produced in normal operation serves to ensure that in this way cavities which otherwise remain between the iron-ore pellets during the coldbriquetting can be filled. To achieve this effect, it is also possible to crush whole iron-sponge pellets, although in practice this is extremely difficult owing to the toughness of the iron sponge. During coldbriquetting, the iron-sponge pellets are merely pressed together with the application of a high force.

Nevertheless, even this does not reduce the porosity of the iron sponge sufficiently to meet the demands imposed by long-distance transportation.

The tendency of the iron sponge obtained by direct reduction to reoxidize owing to the large surface-to-volume ratio manifests itself during transport and storage, since this tendency is associated with considerable evolution of heat, even up Sto smouldering fire, and an increase in weight.

Particularly when the iron sponge is being transported

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onto other plants, reoxidation presents a considerable risk, so that increased precautionary measures are required, which entail high transport and insurance costs.

Hot-briquetting reduces the high porosity of the iron sponge considerably, so that hot-briquetted iron sponge has in the meantime become a commercially available form of this product. The increase in the relative density and the good flow metering properties are regarded as further advantages of this product.

The briquettability of the hot iron sponge is dependent on numerous parameters and therefore differs from one ore type to the next. In addition to the temperature of the iron sponge when it enters the briquetting machine and the pressure applied by this machine, the shape and size of the individual ironsponge pieces also play a role.

As the temperature of the iron sponge increases, the briquettability is improved. However, since there is a maximum temperature for the directreduction process, owing to the softening of the pieces of ore and the resultant deterioration during the gas distribution, the shape and size of the pieces of ore are of particular importance.

25 It is known that the punctiform contact between iron-sponge pellets means that they have a relatively poor briquettability which is often insufficient to achieve a density of around 5 t/m 3 and a suitable durability of the briquettes in the event of numerous transhipments, as are required when transported by rail or ship.

Therefore, hitherto lump ore was admixed to the iron-sponge pellets in order to improve the briquettability. However, this lump ore has to have a high iron content and a correspondingly low gangue content, so that the quality of the briquettes for the subsequent steel-production process with regard to iron Syield and melting-energy consumption remains substantially the same. Although ore types which are suitable for this purpose are available in a few countries, theyare generally rare, so that supplying such ores at least to locations which are a long way from a port is expensive.

The object of the invention is to provide a method in accordance with the preamble of Claim 1 which makes it possible to produce hot-briquetted iron sponge, without using lump ore, which is such that its density is sufficient to ensure that it can be stored and transported substantially without reoxidation.

According to the characterizing part of Claim 1, this object is achieved by the fact that some of the iron-ore pellets produced during the pelletization are crushed into fragments with predominantly flat fracture faces and are additionally admixed, in an amount from 12 to 30% by weight, in particular from 15 to 25% by weight, to the iron-ore pellets which are to be fed to the direct reduction stage.

For this purpose, in particular the oversized iron-ore pellets produced during the pelletization are used, after they have been crushed, as an addition to the iron-ore pellets which are to be fed to the direct reduction stage.

25 The relatively coarse fragments, which are produced by the crushing, with predominantly flat fracture faces of the iron-ore pellets are accordingly having been intimately mixed in reduced together with the whole iron-ore pellets and provide larger 30 contact surfaces with the whole reduced iron-sponge pellets during hot-briquetting, which generally takes place at a temperature in the region of approximately 700*C, so that the still relatively deformable iron sponge is sintered together with surface-to-surface contact. The reduced, coarse fragments from the crushed iron-ore pellets do not fill the spaces between the **whole iron-ore pellets in the direct-reduction shaft very well, but during hot-briquetting they do successfully fill the gaps between the initially unpressed iron-sponge pellets, due to the deformation caused by the pressure, so that after hot-briquetting the iron-sponge briquettes have a sufficiently great density to ensure that they can be stored and transported substantially without reoxidation.

Small material particles produced during the pelletization, which are known as undersized material or pellet fragments and nowadays make up less than by weight, are usually screened out, comminuted and fed back to the pelletizing device, since it is undesirable in the direct reduction stage for undersized material to impede the passage of the reduction gas through the direct reduction shaft. Only pieces which are as uniform as possible give optimum direct reduction.

Consequently, particles of 4 mm, in particular 6 mm, are screened out, irrespective of whether they were formed during the pelletization or only when the oversized iron-ore pellets were crushed.

Even the relatively coarse fragments with predominantly flat fracture faces of the iron-ore pellets impair the gas distribution during the direct reduction, so that they should not make up more than approximately 30% by weight.

The iron-ore pellet diameter declared to be 25 oversized may be selected appropriately so that even after the undersized material has been screened out an appropriate quantity is available for admixing.

It is expedient if the iron-ore pellets produced during the pelletization pass continuously 30 through a crushing device in which the oversized irone* •ore pellets are crushed. For this purpose, they may, for example, pass continuously through a roll crusher, the rolls of which take hold of and crush the oversized iron-ore pellets. Alternatively, the oversized iron-ore pellets in the flow of pellets are crushed by means of a cone crusher or, semicontinuously, by means of a wedge nip crusher, the nip of which is rhythmically closed to form a parallel nip, in which case the wedge nip initially retains the oversized iron-ore pellets.

Undersized material which is not used is appropriately beneficiated and fed back to the pelletization stage.

The oversized iron-ore pellets may also be screened out, for example may be crushed in one of the abovementioned crushing devices, and then added to the iron-ore pellets of the desired particle size, after which they are uniformly distributed by mixing.

The undersized material produced during the comminution may, up to the size indicated above, be screened out of the comminuted iron-ore oversized pellet material, in a manner appropriate to the directreduction furnace charge, in order not to have an adverse effect on the gas distribution during the direct reduction.

Claims (9)

1. Method for producing briquetted iron sponge, in which method iron-ore pellets are produced from beneficiated iron ore, which pellets, after fragmentized material has been screened out, are converted into iron sponge by direct reduction and are then hot-briquetted, characterized in that some of the iron-ore pellets produced during the pelletization are crushed into fragments with predominantly flat fracture faces and are additionally admixed, in an amount from 12 to 30% by weight, to the iron-ore pellets which are to be fed to the direct reduction stage.

2. Method according to Claim 1, characterized in that the iron-ore pellets which are produced as oversized pellets during the pelletization are crushed and admixed.

3. Method according to Claim 1 or 2, characterized in that fragments are added in a quantity of from 15 to 25% by weight.

4. Method according to one of Claims 1 to 3, characterized in that particles of 4 mm, in particular 6 mm, are screened out.

5. Method according to one of Claims 1 to 4, 25 characterized in that the oversized iron-ore pellets are crushed by a roll crusher.

6. Method according to one of Claims 1 to 4, characterized in that the oversized iron-ore pellets are crushed by a cone crusher.

7. Method according to one of Claims 1 to 4, characterized in that the oversized iron-ore pellets are crushed by a wedge nip crusher.

8. Method according to one of Claims 2 to 7, characterized in that the oversized iron-ore pellets are screened out, then crushed and subsequently admixed to the iron-ore pellets for the direct reduction.

9. Method according to one of Claims 2 to 7, characterized in that all the iron-ore pellets pass *0* 0 *000 *0 0 0 0 0* 0B 00 a 0000 SOS. through the crushing device used, the oversized pellets being crushed. Dated this 6th day of April 1999 PATENT ATTORNEY SERVICES Attorneys for KLOCKNER INDUSTRIE-ANLAGEN GMBH and MASCHINENFABRIJ( KOPPERN GMBH CO. KG 0e 0 000 00 0000 0 0S 0 0000 00 00 0 0 0 00 0 0* 00 0000 00 00 0 0000 00 00 0 0 0000 0eS* 0000 0 0000 0000 0* 00 0 4**0 0 0000