AU2001265669B2

AU2001265669B2 - Device for directly reducing ore fine and installation for carrying out said method

Info

Publication number: AU2001265669B2
Application number: AU2001265669A
Authority: AU
Inventors: Martin Hiebler; Leopold Werner Kepplinger; Konstantin Milionis; Gottfried Rossmann
Original assignee: Voest Alpine Industrienlagenbau GmbH
Current assignee: Primetals Technologies Austria GmbH
Priority date: 2000-06-28
Filing date: 2001-06-27
Publication date: 2004-12-16
Anticipated expiration: 2021-06-27
Also published as: AU6566901A; AU2001265669A2; EP1294953B1; ATE265548T1; DE50102148D1; ATA11092000A; WO2002000943A1; AT408992B; MXPA02012754A; EP1294953A1

Abstract

The invention relates to a method for directly reducing, by way of a fluidized bed method, ore fine that comprises at least one ore component from the group of the magnetite, hydrated, carbonate or sulfide ores. The ore fine is heated in a heating fluidized bed zone which is operated with a heating medium, and said heating medium is combusted. The ore is then transferred to at least one reducing fluidized bed zone in which the synthesis gas is fed as the reducing gas to the ore fine in a counter-current and is removed as a top gas, the ore fine being reduced in said zone to sponge iron. In the heating fluidized bed zone the ore fine is specifically heated up by combustion of the heating medium while oxygen or an oxygen-containing gas is additionally fed to adjust oxidizing conditions, and the hydrate, carbonate and/or sulfide groups are removed and/or converted to hematite. At least a part of the top gas is used as a recycled reducing gas for the direct reduction in the reducing fluidized bed zone.

Description

Process for the Direct Reduction of Fine Ore And Plant for Carrying Out the Process The invention relates to a process for the direct reduction of fine ore containing at least one ore component from the group consisting of magnetite, hydrate, carbonate or sulfide ores by the fluidized-bed method, wherein the fine ore is heated in a fluidized-bed heating zone supplied with a heating medium under combustion of the heating medium and subsequently is passed on into at least one reduction fluidized-bed zone, into which synthesis gas is introduced as a reducing gas in counterflow to the fine ore and is drawn off as a top gas and in which a reducti6n of the fine ore to sponge iron is effected, as well as to a plant for carrying out the process.

From US-A 5,082,251 there is known a process for the direct reduction of fine ore, in which the iron-rich fine ore is reduced, by aid of reducing gas and under increased pressure, in a system of fluidized-bed reactors arranged in series and subsequently is subjected to a hot or cold briquetting, the top gas being reused as reducing gas after purification. Before being introduced into the first fluidized-bed reactor, the fine ore is dried, sieved and heated in a pre-heating reactor by burning natural gas.

Unless the fine ore already has a magnetite portion, magnetite formation takes place in the direct reduction according to US-A 5,082,251 due to the kinetics, namely in a layer growing constantly from the outside towards the inside, which layer forms on each particle or grain of the iron-oxide-containing material. In practice, it has been shown that the magnetite formation or the presence of magnetite in the fine ore impedes a direct reduction with reducing gas and that only insufficient reduction degrees can be achieved in the case of magnetite ores. Achieving a more or less complete reduction of the iron-oxide-containing material used is only feasible at an increased expenditure, by an increase in the reducing-gas consumption, given that it would be necessary to provide reducing gas having a high reduction potential also in the fluidized-bed zones arranged first.

According to AT-B 406 271, the magnetite formation, which preferably takes place at a temperature of about 580C, is avoided or reduced by bringing about the transition of the temperature of the iron-oxide-containing material within the shortest possible period of time when heating from 400 to 580C and by avoiding maintenance in this critical temperature range. One possibility of realization consists in increasing the temperature or the reduction rate in the first fluidized-bed reactor by additionally feeding fresh reducing gas or by heating up and/or partially burning the reducing gas from the subsequently arranged fluidized-bed zone. According to another possibility, the iron-oxide-containing material in the first fluidized-bed zone is heated only to a temperature below the temperature range that is critical to the magnetite formation, whereupon the reduction and further heating in the second fluidized-bed zone take place more rapidly due to the higher reduction potential and the higher temperature of the reducing gas and thus the range of the magnetite formation is passed very quickly.

However, a disadvantage connected therewith is that a magnetite portion already present in the fine ore can not be removed by these measures and that there is, for the more or less complete reduction of this portion, an increased need of reducing gas.

According to the point of origin of the fine ore, the starting material for the direct reduction may contain not only hematite and/or magnetite but also hydrate, carbonate or sulfide ore components in various percentages, either alone or as a mixture.

In case such fine ores or mixtures of the most different fine ores are used for direct reduction without pre-treatment, the reduction operation or the reduction process may be seriously impaired as a function of the amount and content of the above-named ore components. For example, in case the reduction is brought about by a reducing gas containing mostly H 2 and CO, the following reactions may take their course in the reducing atmosphere of the reduction zones besides the main reduction reaction, Fe 2 03 3 H 2 /CO 2 Fe 3

H

2 0/C0 2 Fe 3 04 CO/H 2 3 FeO C0 2

/H

2 0 (1) Fe 3 0 4 4 CO/H 2 3 Fe 4 C0 2

/H

2 0 (2) FeOOH CO/H 2 FeO C0 2

/H

2 0 H 2 (3) FeCO3 FeO C02 (4) FeS2 2 H 2 Fe 2H 2 S According to reaction a reduction of the magnetite to wilstite FeO takes place, which, however, takes its course in a kinetically impeded manner, as already mentioned. Reaction takes its course at temperatures below 570'C, reaction at temperatures above this. In the reduction of hydrate ore components, e.g. limonite separation of the hydrate group(s) gives rise to a big amount of water vapor, which influences the reduction of the iron oxide by means of hydrogen in so far as the chemical equilibrium of the reduction reaction is shifted towards the side of the hydrogen, the presence of water in the reducing gas reduces the formation of water vapor from hydrogen and the oxygen present as an oxide in the fine ore and thus the reduction rate of the iron oxides. According to reaction carbonate ore separates carbon dioxide that decreases the reduction potential of the reducing gas or increases its oxidation degree, which results in a higher gas consumption for obtaining a specific reduction degree. Sulfide ore components in turn form hydrogen sulfide which in the case of an increased proportion of sulfides in the fine ore has to be eliminated in a cumbersome manner from the reducing gas prior to its reuse.

From WO-A 97/45564 there is known a process for the treatment of EAF dust, wherein the dust is pre-heated and decontaminated under conditions where the magnetite portion of the dust is oxidized to hematite. Thereafter, the hematite in a fluidized-bed reactor is reduced in the dust by means of a reducing gas which then releases its combustion heat to heat the dust, and the iron-rich material thus obtained is recycled into the electric-arc furnace.

However, this process is not suitable for the direct reduction, by the fluidized-bed method, of a large amount of fine ore that contains, apart from magnetite and optionally hematite, also other ore components. Moreover, according to this process, the reducing gas is burnt to heat the dust and is not utilized any longer with regard to its reduction potential, whereby considerable amounts of reducing gas are necessary for the complete reduction of the ironcontaining material.

WO-A 92/02646 describes a process for the production of iron carbide, in which the ore used is pre-heated in a furnace under an oxidizing atmosphere, wherein at least a portion of the magnetite present in the ore is oxidized to hematite and subsequently is transformed into iron carbide in a fluidized-bed reactor and by means of a gas containing H 2 CO, C0 2

H

2 0,

N

2 and, mostly, CH 4 However, the disadvantage of this process is that significant amounts of gaseous hydrocarbons are required for the transformation of the iron oxides into iron carbide and that the transformation process reacts in an extremely sensitive manner to changes in the charging material and the process parameters, whereby the possibilities of use of this process are limited. Moreover, in a series of subsequent processing operations in the pig-iron and steel production, a complete replacement of sponge iron by iron carbide is possible only when effecting cumbersome adaptations.

The invention aims at avoiding the above-named disadvantages and difficulties and has as its object to provide a process for the direct reduction of fine ore, which is not limited with regard to the composition of the charging material but is applicable to all fine ores and fine-ore mixtures without disturbances in the reduction process. Furthermore, the total need of energy that is required for the direct reduction of the fine ores should be reduced if possible.

Thus, according to the invention there is provided process for the direct reduction of fine ore, including at least one ore component from the group consisting ofmagnetitic, hydratic, carbonatic or sulfidic ores, using the fluidized-bed process, in which the fine ore is heated in a heating fluidized-bed zone, ehich is acted on by a heating medium, with combudtion of the heating medium and is then transferred into at least one reduction fluidized-bed zone, into which synthesis gas is introduced as reduction gas countercurrent to the fine ore and is extracted a stop gas and in which the fine ore is reduced to form iron sponge, at least some of the top gas being used as recycle reduction gas for direct reduction in the reduction fluidized-bed zone, characterised in that the heating medium used in the heating fluidized-bed zone is an at least partially used reduction gas from the top-gas outlet line, and in that in the heating fluidized-bed zone, in addition to targeted heating of the fine ore by combustion of the heating medium, with additional supply of oxygen or an oxygen-containing gas, in order to set oxidizing conditions, a separate of the hydrate, carbonate and/or sulfide groups and/or a conversion into hematite is carried out.

It is generally known that fine ores-besides gangue-are not only composed of magnetite, hydrate, carbonate, sulfide and/or hematite iron ores but may also contain other ores, such as manganese ores, as well as traces of other elements and metals.

Magnetite is transformed into hematite according to 2 Fe304 02 3 Fe 2 0 3 In case the magnetic fine ore was reduced without such an oxidation, the reaction kinetics would be impeded because the reducing gas is prevented from diffusing by the dense magnetite layer of the ore grain and the material exchange of the reducing gas can therefore not take place as in the case of porous hematite grains.

Hydrate, carbonate and sulfide ore components react in accordance with the following equations: H,\keep\soniam\2001265669.doc.13/02/2004 4a 2 FeOOH Fe 2 0 3

H

2 0 2 FeCO 3 2 2 Fe 2 03 2 C0 2 2 FeS 2 3 V2 02 Fe 2 03 2 S0 2 In the fluidized-bed heating zone, a separation of the hydrate, carbonate and sulfide groups as water vapor, carbon dioxide and sulfur dioxide as well as a simultaneous oxidation of the mainly bivalent iron to hematite take place, which hematite considerably simplifies the subsequent direct reduction of the fine ore by the fluidizedbed method. In addition, the higher temperatures at the beginning of the reduction result in a quicker reduction progress, which allows for shorter residence times and thereby leads to a lower specific energy need.

H \keep\soniam\2001265669.doc.13/02/2004 Preferably, the heating medium is burnt completely with a high air excess, wherein the temperature of the fluidized-bed heating zone and the oxygen content of the combustion air are to be chosen as a function of the composition of the fine ore used. The minimum air excess required for the transformation into hematite results from the stoichiometric oxygen need of the ores that are respectively present, any CO 2 and H 2 0 content and also free oxygen being allowed in the gas. Practically, the need results from the desired fluidized-bed temperature, which can be set selectively by the ratio of heating medium and air, according to the exothermal combustion reaction.

The temperature range for the selective heating of the fine ore is determined on the one hand by the decomposition of the Fe hydrate and carbonate, for which minimum temperatures of 200°C-400°C are necessary, and on the other hand by the oxidation reaction of Fe 2

S

(preferably 600-800 0 FeO and/or Fe30 4 to hematite. Due to kinetic requirements, a minimum temperature of 400'C is necessary for the oxidation.

However, the technically reasonable temperature range, in which oxidation to hematite is carried out, generally is above a temperature of 600'C and extends up to the softening temperature of the ore or the ore components, i.e. about 900 to 1200 0

C.

Advantageously, the heating medium, which at least partially is formed by at least partially spent reducing gas from the subsequent reduction reactors and which is burnt at an 02 excess, is used in the unpurified state. Here, it is of advantage that the residual heat of the reducing gas can be utilized for the fluidized-bed heating zone.

According to another preferred process variant, spent reducing gas which is burnt at an 02 excess is used, in the purified and optionally compressed state, as a heating medium. The risk that duct elements, such as valves, are obstructed by dust-loaded reducing gas is eliminated by this measure.

Preferably, the fine ore is additionally dried in the fluidized-bed heating zone, also the drying being done under supply of oxygen or an oxygen-containing gas for the purpose of setting oxidizing conditions at atmospheric pressure. The sluice systems of the charging means, which are necessary for the excess-pressure operation, are liable to get obstructed when moist ore is used, so that the drying and the oxidizing pre-heating are suitable at atmospheric pressure. This measure further offers the advantage that the drying and pre-heating reactor can be on a lower level, given that it need not be connected with the subsequent reduction reactors via standpipes, the material transport from the drying and pre-heating reactor to the filling system of the reduction reactors being susceptible of being performed in a mechanical way, for example by means of a bucket conveyor. This results in a reduced overall height and therefore in substantially lower costs of the plant.

In case there are already enough reduction reactors, it is preferred that the fine ore is dried in a fluidized-bed drying zone and, after having been passed on into a fluidized-bed heating zone, in the dry state is supplied with the heating medium, wherein the fluidized-bed heating zone may be provided in the reduction reactor arranged last in the direction of the reducinggas conveyance.

According to a preferred embodiment, three further reduction fluidized-bed zones arranged in series are arranged to follow the fluidized-bed heating zone, the heated fine ore passing through these three following reduction fluidized-bed zones in a consecutive manner in counterflow to a reducing gas. Since in the fluidized-bed heating zone, an oxidation of the fine ore to hematite takes place in addition to a pre-heating, three following reduction stages are sufficient in most cases for achieving the required degree of metallization.

Suitably, the off-gas drawn off the fluidized-bed heating zone is utilized for pre-heating the air serving the purpose of burning the heating medium.

It is advantageous to utilize the top gas leaving the reduction fluidized-bed zone for preheating the air serving the purpose of burning the heating medium.

According to another embodiment of the invention, the fine ore heated in the fluidized-bed heating zone is introduced into a cooling zone and is cooled therein by means of air under pre-heating of the same, the air thus pre-heated being introduced into the fluidized-bed heating zone for the purpose of burning the heating medium.

This process variant is advantageous when there is provided a pre-heating reactor for the direct reduction, which for example has a too small capacity for the selective heating and oxidation of the fine ore. In this case, the transformation of the non-hematite fine-ore components can be done together with the drying instead of the pre-heating of the fine ore in a fluidized bed, wherein the fact that the fine ore after the selective heating under oxidizing conditions at a simultaneous drying is cooled again before being passed on into the reduction stages does not play a role because a means for pre-heating the fine ore is provided.

This embodiment further has the advantage that the calcination, oxidation and simultaneous drying can be performed in a separate system beside the fluidized-bed reduction plant. The cooling of the ore further is advantageous because it allows the charging of the ore into the subsequent fluidized-bed reactor to be done with simple equipment for low temperatures.

Preferably, the pre-heated air from the cooling zone is further heated by heat exchange with the off-gas from the fluidized-bed heating zone.

Preferably, the reducing gas leaving a reduction fluidized-bed zone arranged to follow the fluidized-bed heating zone in the conveyance direction of the fine ore in part is used as a heating medium of the fluidized-bed heating zone and in part is subjected directly to a purification, cooling and compression as well as heating together with freshly supplied reducing gas, whereupon it is, as a recycling reducing gas, again used for the direct reduction.

The invention also provides an installation for carrying out the method of the invention having a heating fluidized-bed reactor and having at least one reduction fluidized-bed reactor for direct reduction of fine ores by means of a reduction gas, having a reductiongas feed line leading to the reduction fluidized-bed reactor and a top-gas outlet line for used reduction gas from the reduction fluidized-bed reactor, an ore feed line which opens out into the heating fluidized-bed reactor and a conveying system for fine ore, which connects the heating fluidized-bed reactor to the reduction fluidized-bed reactor, the heating fluidized-bed reactor being connected to a line which carries a heating medium and a to a line which carries oxygen and/or an oxygen-containing gas, the topgas outlet line opening out into the reduction-gas feed line, characterised in that the line starts from a top-gas outlet line which carries at least partially used reduction gas, and in that there is an adjusting device for ensuring a quantity of oxygen which can be adjusted as a function of the quantity of the heating medium and is greater than the quantity required for combustion of the heating medium.

According to an embodiment, the top-gas discharge duct via a branch duct is connected with the duct conducting the heating medium.

The top-gas discharge duct is preferably equipped with means for cooling and scrubbing as well as with a compressor for compressing the top gas and, subsequent to these means or the compressor, via a branch duct is connected with the duct conducting Ht\keep\soniam\2001265669.doc.13/02/2004 7a the heating medium, whereby an obstruction of duct elements by dust-loaded top gas is avoided.

H \keep\soniarn\2001265669 .doc. 13/02/2004 Suitably, a drying means for the fine ore, such as a fluidized-bed drying reactor, is arranged to precede the fluidized-bed heating reactor.

A preferred embodiment is characterized in that three reduction fluidized-bed reactors, through which the fine ore passes in a consecutive manner, are arranged in series to follow the fluidized-bed heating reactor, the reducing-gas feed duct being connected with the reduction fluidized-bed reactor arranged last in the direction of flow of the fine ore and the top-gas discharge duct being connected with the first reduction fluidized-bed reactor.

In the duct conducting oxygen and/or the oxygen-containing gas there is preferably provided a recuperator for off-gas from the fluidized-bed heating reactor, whereby the specific consumption of heating medium for achieving a specific temperature in the fluidized-bed heating reactor may be reduced.

Furthermore, it is advantageous when a recuperator for uncooled top gas is provided in the duct conducting oxygen and/or the oxygen-containing gas.

According to another preferred embodiment of the invention, a cooler for the fine ore, which works with air as cooling medium, is provided after the fluidized-bed heating reactor and with regard to the cooling medium via a gas duct is flow-connected with the duct conducting oxygen and/or the oxygen-containing gas.

Here, suitably, a recuperator for off-gas from the fluidized-bed heating reactor is provided in the gas duct.

Preferably, a plant according to the invention is characterized in that the top-gas discharge duct via means for cooling and scrubbing, a compressor and a reduction gas furnace runs into the reducing-gas feed duct and that a reducing-gas duct conducting fresh reducing gas and running into the top-gas discharge duct before the reduction gas furnace is provided.

In the following, the invention will be explained in more detail with reference to the drawings, wherein Figs. 1 to 3 and 6 each illustrate a plant for carrying out an embodiment of the process according to the invention and Figs. 4 and 5 each illustrate in diagrammatic representation a detail of a plant for carrying out the process according to the invention.

The plant of Fig. 1 has a fluidized-bed heating reactor 1 as well as three reduction fluidizedbed reactors, 2 to 4, subsequently connected in series, wherein fine ore via an ore feed duct is fed to a dosing and/or charging means 6, from which the fine ore is charged into fluidizedbed heating reactor 1, which at the same time functions as a fluidized-bed drier for the fine ore usually being present with a specific moisture content. In fluidized-bed heating reactor 1, a drying process and, besides a selective heating under additional supply of oxygen or an oxygen-containing gas for the purpose of setting oxidizing conditions, a separation of the hydrate, carbonate and/or sulfide groups and/or a transformation into hematite take place, the temperature and oxygen content being selected according to the composition of the fine ore.

For this purpose, a duct 7, conducting an oxygen-containing gas, and a duct 8, conducting a heating medium, run into fluidized-bed heating reactor 1, in which ducts an adjusting means E for ensuring the selected amount of oxygen, which is larger than the amount required for the combustion of the heating medium, is provided. Besides the combustion gases being produced, the oxygen-containing gas, usually air, at the same time serves as a fluidizing gas for the fine-ore fluidized bed.

The hot off-gases leaving fluidized-bed heating reactor 1 via discharge duct 9 get into a cyclone 10, in which a separation of the fine-ore particles entrained by the off-gas from the gas takes place. The fine-ore particles are recycled into charging means 6 and the purified off-gas is discharged via a duct 11. The sensible heat of the off-gas may be utilized for example by means of a heat exchanger for heating the combustion air fed to fluidized-bed heating reactor 1 by duct 7.

The residence time of the fine ore in fluidized-bed heating reactor 1, the composition of the charging material, the oxygen content of the combustion gas and the temperature determine the reaction of the magnetite, hydrate, carbonate and/or sulfide ore components to hematite.

When pre-heating the combustion air, the specific amount of combustion air may be increased while the amount of heating medium remains the same, whereby the oxidation can be effected with higher 02 proportions in the smoke gas and the oxidation rate can thus be increased.

Apart from an oxidation, the fine ore, which preferably at more than 90% is reacted to hematite, in fluidized-bed heating reactor 1 is heated to a temperature of at least about 700'C. From fluidized-bed heating reactor 1, the pre-heated fine ore by aid of a conveying system 12, e.g. a bucket conveyor, is transported to reduction fluidized-bed reactor 2, arranged first in the conveyance direction of the fine ore. Since the drying, pre-heating and oxidation of the fine ore in fluidized-bed heating reactor 1 is carried out at atmospheric pressure, it is possible to arrange fluidized-bed heating reactor 1 on a lower level and not above the first reduction fluidized-bed reactor, 2, whereby the overall height of the plant is reduced.

By means of a sluice system 13, which is not represented in detail, the pre-heated fine ore is introduced into the reduction-reactor cascade, which is under pressure. From reduction fluidized-bed reactor 2, the fine ore via conveying ducts 14 is conveyed to reduction fluidized-bed reactors 3 and 4, respective fluidized-bed zones forming within fluidized-bed reactors 2 to 4. The completely reduced fine ore (sponge iron) via a duct 15 is fed to a briquetting plant 16, is hot-briquetted, is cooled in a cooling means 17 and thereafter is stored for a further use. If necessary, the reduced iron is protected from reoxidation during briquetting by an inert-gas system that is not represented.

In counterflow to the fine-ore flow, reducing gas is conducted from reduction fluidized-bed reactor 4 to reduction fluidized-bed reactors 3 and 2 via ducts 18, via a top-gas discharge duct 19 is discharged as a top gas from reduction fluidized-bed reactor 2, arranged last in the gas direction, and is cooled and scrubbed in means 20 to 22.

After the top gas has been compressed by means of a compressor 24, a reducing-gas duct 23, conducting fresh reducing gas, runs into top-gas discharge duct 19. The mixed gas thus forming is sent through a reduction gas furnace 25, is heated to a reduction gas temperature of about 800'C and is fed to reduction fluidized-bed reactor 4, arranged first in the direction of the gas flow, via a reducing-gas feed duct 26, where it reacts with the fine ores under formation of sponge iron.

A portion of the top gas is discharged from gas cycle 18, 19, 26 via a duct 27 to avoid an enrichment of inert gases, such as N 2 A portion of the mixed gas, formed of top gas and fresh reducing gas, can also be conducted past reduction gas furnace 25 via a by-pass duct 28 and can be introduced into duct 26 in the non-heated state.

A further portion of the purified top gas is branched off top-gas discharge duct 19 before compressor 24 and via duct 8 is introduced as a heating medium into fluidized-bed heating reactor 1, where it is, advantageously, completely burnt at a high air excess.

In contrast with the plant of Fig. 1, the plant represented in Fig. 2 has four fluidized-bed reactors, 1 to 4, subsequently connected in series, and a fluidized-bed reactor 29, which is intended only for the drying of the fine ore and which, for this purpose, may be designed smaller than a fluidized-bed heating reactor of Fig. 1, serving for both a drying and a heating and oxidation of the fine ore.

Via ore feed duct 5 and charging means 6, the fine ore is introduced into fluidized-bed drying reactor 29, in which the fine ore is desiccated by feeding a hot gas via duct 30. The water and dust-loaded gas is purified in a cyclone 31 and discharged via duct 32.

From fluidized-bed drying reactor 29, the dried fine ore via a conveying system 12 and a sluice system 13 gets into fluidized-bed heating reactor 1, which in the conveyance direction of the fine ore is provided as the first of fluidized-bed reactors 1 to 4, subsequently connected in series, which forms a part of the reactor cascade.

As a heating medium for the selective heating under oxidizing conditions taking place in fluidized-bed heating reactor 1, a portion of the top gas from the first reduction fluidized-bed reactor, 2, via branch duct 33 is branched off top-gas discharge duct 19 before purifying and cooling means 20 to 22 and in a combustion chamber 34, arranged below fluidized-bed heating reactor 1, is admixed to the 0 2 -containing gas fed via duct 7 and is burnt at an air excess. The amount of unpurified reducing gas fed to fluidized-bed heating zone 1 is controlled via valve 35, provided in top-gas discharge duct 19. Due to the fact that the top gas is taken from top-gas discharge duct 19 in the uncooled state, its residual heat can be utilized for the oxidation and heating process. Here, adjusting means E is designed to have two parts and is provided in both duct 33 and duct 7.

Thus, in the uppermost reactor, i.e. fluidized-bed heating reactor 1, an effective heating under oxidizing conditions takes place, and in the three reduction fluidized-bed reactors 2 to 4, a more intensive gas cycle takes place. Furthermore, the use of reducing gas instead of another heating medium in fluidized-bed heating reactor 1 results in a higher economic efficiency, as the reducing gas does its reduction work already in the three reduction fluidized-bed reactors 2 to 4.

The off-gas from the fluidized-bed heating zone leaves the process via a dedusting means that is not represented in discharge duct 9.

Alternatively, instead of a fluidized-bed reactor, the fluidized-bed heating zone could also be provided in a cyclone or cyclone cascade.

According to the embodiment represented in Fig. 3, the problem of the valve in the dustloaded top gas leaving reduction fluidized-bed reactor 2, which problem possibly arises in the process variant of Fig. 2, is avoided by branching off, after compressor 24 and via duct 36, the reducing gas in the purified and compressed state from top-gas discharge duct 19 and feeding it to combustion chamber 34 of fluidized-bed heating reactor 1. This variant is technically easier to carry out than the one in which the reducing gas is branched off as a heating medium before the purification stage.

Figs. 4 and 5 illustrate a variant of the process according to the invention, in which a drying of the fine ore takes place in addition to a transformation, under oxidizing conditions, of the ore used into hematite.

Moist fine ore 39 is charged into fluidized-bed heating zone 37 of fluidized-bed heating reactor 1, where a homogeneous fluidized bed forms. For fluidizing fine ore 39 and heating it under oxidizing conditions, a heating medium 40, preferably spent reducing gas, and an 0 2 -containing gas 41, e.g. air, are introduced into the bottom area of fluidized-bed reactor 1, in which a complete combustion of the heating medium is brought about.

Hot oxidized fine ore 42 is fed to a fluidized-bed cooler 43, which by means of air 44 cools fine ore 42, heated to about 900°C, down to about 100"C. During this, air 44 and fine ore 42 are conducted in cross-flow, whereby a smaller specific amount of cooling air is achieved.

Pre-heated drawing-off air 45 of fluidized-bed cooler 43 is used as an 0 2 -containing gas 41 for the combustion of heating medium 40 and the drying and oxidation of fine ore 39. For the separation of fine-ore particles 46, discharged by drawing-off air 45, a gas/solid separator 47, preferably a cyclone, from which air 41 is transported to fluidized-bed reactor 1 and separated fine-ore particles 46 are recycled into fluidized-bed cooler 43, is used.

Also off-gas 48 of fluidized-bed reactor 1 is purified from entrained fine-ore particles 50 in a gas/solid separator 49 and is drawn off. Separated fine-ore particles 50 are introduced into fluidized-bed cooler 43 as well. When technically required, also a recycling of fine-ore particles 50 back into fluidized-bed heating zone 37 can be performed, as is suggested by the broken arrow. Cooled, mainly hematite fine ore 51 may be either stored temporarily or charged into a reduction fluidized-bed zone immediately afterwards.

According to Fig. 5, pre-heated drawing-off air 45 from fluidized-bed cooler 43 after separation of fine-ore particles 46 in cyclone 47 is not instantly fed to fluidized-bed reactor 1 as combustion air but in a heat exchanger 52 is further heated recuperatively by hot off-gas 48 of fluidized-bed reactor 1.

Instead of fluidized-bed cooler 43, any other cooling system that is able to cool fine-grained materials may also be used.

Fig. 6 shows the process variant of Fig. 3. In contrast with Fig. 3, the combustion air fed to fluidized-bed heating reactor 1 is pre-heated in a heat exchanger 53, which is arranged in top-gas discharge duct 19 before cooling and scrubbing means 20 to 22, by the sensible heat still present in the top gas.

As synthesis gas for the reduction of the fine ore, one or several of the following gases may be used: reformed natural gas, LD off-gas, EAF off-gas, furnace gas from blast furnaces and reduction plants, coal gas, chemical gases.

Example of the simultaneous pre-heating, drying and oxidation of a moist, magnetite fine ore: The ore (moisture 0.28% bound water in the hydrate ore portion [limonite]) is to be preheated from 25°C to 700°C, natural gas being used as heating medium and energy carrier.

For the combustion of the natural gas and the oxidation of the magnetite to hematite, the oxygen portion of the air is used. The off-gases that are generated also have a temperature of 700 0

C.

For the production of a ton of dried hematite, 23 Nm 3 of oxygen or 109 Nm 3 of air are necessary. The energy need of 399 MJ/t is covered by the combustion of 16 Nm 3 of natural gas, requiring 151 Nm 3 of air for the stoichiometric combustion. Considering moreover the air excess of 260 Nm 3 -provided that there is the double excess-air coefficient-further 242 MJ/t are necessary for their heating. The energy required therefor is provided by the stoichiometric combustion of 9.5 Nm 3 of natural gas with 91 Nm 3 of air.

Thus, the result of the total balance is a need of natural gas of 25.5 Nm 3 and a need of air of 611 Nm 3 per ton of hematite produced.

In the case of a smaller air excess or when pre-heating the air required, the natural-gas consumption decreases accordingly.

-14- When using top gas instead of natural gas, approximately the double quantity of top gas is necessary, due to the lower calorific value of the top gas.

It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country.

H \keep\soniam\2001265669.doc.13/02/2004

Claims

1. Process for the direct reduction of fine ore, including at least one ore component from the group consisting of magnetitic, hydratic, carbonatic or sulfidic ores, using the fluidized-bed process, in which the fine ore is heated in a heating fluidized-bed zone, which is acted on by a heating medium, with combustion of the heating medium and is then transferred into at least one reduction fluidized-bed zone, into which synthesis gas is introduced as reduction gas countercurrent to the fine ore and is extracted as top gas and in which the fine ore is reduced to form iron sponge, at least some of the top gas being used as recycle reduction gas for direct reduction in the reduction fluidized-bed zone, characterized in that the heating medium used in the heating fluidized-bed zone is an at least partially used reduction gas from the top-gas outlet line, and in that in the heating fluidized-bed zone, in addition to targeted heating of the fine ore by combustion of the heating medium, with additional supply of oxygen or an oxygen-containing gas, in order to set oxidizing conditions, a separation of the hydrate, carbonate and/or sulfide groups and/or a conversion into hematite is carried out. -16-

2. A process according to claim 1, characterised in that the heating medium is burnt completely with a high air excess.

3. A process according to claim 1 or 2, characterised in that the heating medium, which at least partially is formed by at least partially spent reducing gas and which is burnt at an 02 excess, is used in the unpurified state.

4. A process according to claim 1 or 2, characterised in that spent reducing gas which is burnt at an 02 excess is used, in the purified and optionally compressed state, as a heating medium.

A process according to any one of claims 1 to 4, characterised in that the fine ore is additionally dried in the fluidized-bed heating zone, also the drying being done under additional supply of oxygen or an oxygen-containing gas for the purpose of setting oxidizing conditions at atmospheric pressure.

6. A process according to any one of claims 1 to 4, characterised in that the fine ore is dried in a fluidized-bed drying zone and, after having been passed on into a fluidized-bed heating zone, in the dry state is supplied with the heating medium.

7. A process according to any one of claims 1 to 6, characterised in that three further reduction fluidized-bed zones arranged in series are arranged to follow the fluidized-bed heating zone, the heated fine ore passing through these three following reduction fluidized-bed zones in a consecutive manner in counterflow to a reducing gas.

8. A process according to any one of claims 1 to 7, characterised in that off-gas drawn off the fluidized-bed heating zone is utilized for pre-heating the air serving the purpose of burning the heating medium.

9. A process according to any one of claims 1 to 7, characterised in that the top gas leaving the reduction fluidized-bed zone is utilized for pre-heating the air serving the purpose of burning the heating medium.

A process according to any one of claims 1 to 7, characterised in that the fine ore heated in the fluidized-bed heating zone is introduced into a cooling zone and is cooled therein by means of air under pre-heating of the same, the air thus pre-heated H\keep\asoniam\2001265669.doc.13/02/2004 -17- being introduced as an oxygen-containing gas into the fluidized-bed heating zone for the purpose of burning the heating medium.

11. A process according to claim 10, characterised in that the pre-heated air from the cooling zone is further heated by heat exchange with the off-gas from the fluidized- bed heating zone.

12. A process according to any one of claims 1 to 11, characterised in that the reducing gas leaving a reduction fluidized-bed zone arranged to follow the fluidized- bed heating zone in the conveyance direction of the fine ore in part is used as a heating medium of the fluidized-bed heating zone and in part is subjected directly to a purification, cooling and compression as well as heating together with freshly supplied reducing gas, whereupon it is, as a recycling reducing gas, again used for the direct reduction.

13. An installation for carrying out the process as claimed in any one of claims 1 to 12, having a heating fluidized-bed reactor and having at least one reduction fluidized- bed reactor for direct reduction of fine ores by means of a reduction gas, having a reduction-gas feed line leading to the reduction fluidized-bed reactor and a top-gas outlet line for used reduction gas from the reduction fluidized-bed reactor, an ore feed line which opens out into the heating fluidized-bed reactor and a conveying system for fine ore, which connects the heating fluidized-bed reactor to the reduction fluidized-bed reactor, the heating fluidized-bed reactor being connected to a line which carries a heating medium and a to a line which carries oxygen and/or an oxygen-containing gas, the top-gas outlet line opening out into the reduction-gas feed line, characterised in that the line starts from a top-gas outlet line which carries at least partially used reduction gas, and in that there is an adjusting device for ensuring a quantity of oxygen which can be adjusted as a function of the quantity of the heating medium and is greater than the quantity required for combustion of the heating medium.

14. A plant according to claim 13, characterised in that the top-gas discharge duct via a branch duct is connected with the duct conducting the heating medium.

A plant according to claim 14, characterised in that the top-gas discharge duct is equipped with means for cooling and scrubbing as well as with a compressor for compressing the top-gas and, subsequent to the means for cooling and scrubbing or H \keep\soniam\2001265669.doc.13/02/2004 -18- subsequent to the compressor, via a branch duct is connected with the duct conducting the heating medium.

16. A plant according to any one of claims 13 to 15, characterised in that a drying means for the fine ore is arranged to precede the fluidized-bed heating reactor.

17. A plant according to any one of claims 13 to 16, characterised in that three reduction fluidized-bed reactors, through which the fine ore passes in a consecutive manner, are arranged in series to follow the fluidized-bed heating reactor, the reducing- gas feed duct being connected with the reduction fluidized-bed reactor arranged last in the direction of flow of the fine ore and the top-gas discharge duct being connected with the first reduction fluidized-bed reactor.

18. A plant according to any one of claims 13 to 17, characterised in that the duct conducting oxygen and/or the oxygen-containing gas there is provided a recuperator for off-gas from the fluidized-bed heating reactor.

19. A plant according to any one of claims 13 to 18, characterised in that the duct conducting oxygen and/or the oxygen-containing gas there is provided a recuperator for uncooled top gas.

A plant according to any one of claims 13 to 19, characterised in that a cooler for the fine ore, which works with air as cooling medium, is provided after the fluidized-bed heating reactor and with regard to the cooling medium via a gas duct is flow-connected with the duct conducting oxygen and/or the oxygen-containing gas.

21. A plant according to claim 20, characterised in that a recuperator for off-gas from the fluidized-bed heating reactor is provided in the gas duct.

22. A plant according to any one of claims 13 to 21, characterised in that the top-gas discharge duct via means for cooling and scrubbing, a compressor and a reduction gas furnace runs into the reducing-gas feed duct and that a reducing-gas duct conducting fresh reducing gas and running into the top-gas discharge duct before the reduction gas furnace is provided. H \keep\soniam\2001265669.doc.13/02/2004 18a- Dated this 13th day of February 2004 VOEST-ALPINE Industrieanlagenbau GmbH Co By their Patent Attorneys GRIFFITH HACK Fellows Institute of Patent and Trade Mark Attorneys of Australia H. \keep\soniam\2001265669 .doc. 13/02/2004