AU636799B2

AU636799B2 - Process intended for the extraction of metals, in particular of iron, from oxidised iron ores of any grain size, at any reduction gas temperature whatsoever in a drop reduction furnace

Info

Publication number: AU636799B2
Application number: AU85818/91A
Authority: AU
Inventors: Guido Elsen
Original assignee: ELSEN TOOLING (IRELAND) Ltd
Current assignee: ELSEN TOOLING (IRELAND) Ltd
Priority date: 1991-07-12
Filing date: 1991-10-15
Publication date: 1993-05-06
Anticipated expiration: 2011-10-15
Also published as: AU8581891A; BE1006828A3; NZ240226A

Description

AUSTRALIA

Patents Act 636799 COMPLETE SPECIFICATION

(ORIGINAL)

Class Int. Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority Related Art: Name of Applicant: Elsentooling Overseas Ltd.

Actual Inventor(s): S Guido Elsen **Address for Service: Address for Service: PHILLIPS ORMONDE FITZPATRICK Patent and Trade Mark Attorneys 367 Collins Street Melbourne 3000 AUSTRALIA Invention Title: PROCESS INTENDED FOR THE EXTRACTION OF METALS, IN PARTICULAR OF IRON, FROM OXIDISED IRON ORES OF ANY GRAIN SIZE, AT ANY REDUCTION GAS TEMPERATURE WHATSOEVER IN A DROP REDUCTION FURNACE Our Ref 231746 POF Code: 1129/153899 *The following statement is a full description of this invention, including the best method of performing it known to applicant(s): 006 o -1- 6006

*,J

PROCESS INTENDED FOR THE EXTRACTION OF METALS, IN PARTICULAR OR IRON, FROM OXIDISED IRON ORES OF ANY GRAIN SIZE, AT ANY REDUCTION GAS TEMPERATURE WHATSOEVER IN A DROP REDUCTION FURNACE.

According to the present invention, there is provided a process for extracting metals, from oxidised iron ores of any grain size, at any reduction gas temperature whatsoever in a drop reduction furnace filled from the top by ore of any grain size whatsoever, which is heated up to smelting temperature and pre-reduced by unlimited hot reducing gases, rising up from the hearth at the base of the shaft, passing through a grate, heating up the bottom layers of the column of ore in which the molten fluid consisting of the pre-reduced ore and possibly molten iron and gangue passes through the grate drop by drop in counterflow to the gases, and falling down to the base of the shaft into the liquid bath where both the final reduction and the separation of the molten metal from the gangue and the undesirable elements take place, and from where the metal is passed towards appropriate use.

Preferably, high gas temperatures, up to 2000°C and beyond, assure particularly rapid pre-reduction of the iron ore to FeO/Fe and bring it to smelting temperature, 25 the drops fall through the grate without causing any damage due to the temperature or to overheating and the drops can be heated to even higher temperatures in the course of their free fall through the high temperature gases.

30 Any number of supplementary grates can be used in one reduction furnace. Furthermore, the whole process can be achieved in more than one furnace, where the off gases

CO/CO

2 from one furnace can also be applied in the next one to reach a higher percentage of CO 2 in the CO/CO 2 S 35 gases.

The high gas temperatures used in the process of the present invention allow high economically efficient outputs in the pre-reduction.

In present day metallurgy a variety of processes Ao la exist for the purpose of extracting metal from metal ores or the iron from iron ores. As regards the fundamental processes of iron, producers continually revert to the traditional process of the basic technology of a blast furnace, which predominance in this industry is due to the efficient use of reaction gases (CO gas) coming from the final reduction of FeO in the iron bath for the purpose of pre-reduction of the ore in the shaft.

Pre-reduction or indirect reduction in the shaft: CO 1/2 02 (ore) CO 2 FeO Final reduction or direct reduction in the bath: C FeO CO Fe The gaseous product resulting from the final reduction (CO gas) rises, from the place where it is generated, upwards through the porous volume of the charge of ore and coke, filled up from the top of the blast furnace. The heat of the gas is thus transferred to the charge and simultaneously the charge gives its oxygen to the gas. This oxidation reaction of gaseous CO is terminated as soon as it has been oxidised to CO 2 At the same time the oxygen content of the ore is lowered to FeO and partially to Fe and the final reduction to iron occurs in the hearth of the blast furnace by the carbon, o which by the way consumes the greatest amount of the 25 energy from the whole reaction. The two reactions, the oxidation of the gas and the reduction of the ore, take place almost over the whole of the charge column.

For economic reasons, the CO is the most important factor for the pre-reduction in the blast furnace. In 30 this case the permeability of gases is fundamental to this reaction. This permeability must exist permanently at all .I times throughout the whole of the reaction and can be assured solely by sufficient porosity of the charge. All other parameters of this reaction are not as decisive as permeability is.

In order to meet this requirement, the temperature of the gaseous CO must not exceed the maximum of 9000C to avoid compacting of the ore by sintering and thus lowering its porosity. It is also important to have -2-

M

recourse to coke which is mechanically more resistant than coal, also in order to maintain the porosity of the charge. For these reasons, one has to use also a distinct minimum grain size of ore. The use of ore fines only would result in insufficient porosity of the material mix in the shaft of the blast furnace.

Unfortunately, the reaction is also characterised by the use of stoichiometric surplus carbon. One of the reasons for this is the obligation to resort to more energy for the final reduction in the hearth than for the pre-reduction of the ore in the shaft. During the final reduction, more gaseous CO is produced than is necessary for the pre-reduction. Fortunately, the surplus CO produced can also be used externally since it burns to

CO

2 with gaseous oxygen with exothermic effects. It is, however, regrettable that this effect cannot be employed within the blast furnace. It can only take place outside the furnace, with heat transformation losses. A further reason for the stoichiometric surplus carbon is the fact that the coke and the ore pass through the furnace in the same direction. Heat reaction exchanges are fundamentally improved when the partners in the reaction move in counter-flow to each other.

To this day, however, the economic importance of the blast furnace reaction still dominates and is based on the highly efficient use of gaseous CO produced in the smelting hearth for the heating and for the pre-reduction of the ore in the shaft. This process is the standard by which all other processes should be measured. Thus 30 despite all research, to this day, only the COREX process shows an improvement as it does the same process with coal n :rather than coke. It is also a reduction and smelting process in which the hearth's own gaseous CO is also used for the pre-reduction of the ore, but also within the S. 35 temperature limitation of 900 0 C. This, however, does not take place in one furnace, but in two reactors, functioning separately, but connected to each other. The reduction gas CO produced in the lower reactor is passed to the upper reactor, which is filled with ore, with the 40 3ore pre-reduced to 95% Fe in the upper reactor being passed to the lower smelter reactor for the liquefaction and the final reduction to Fe.

Coal is fed in reduction conditions into the lower gasification and smelting hearth, where it is gasified at a temperature below 1300 0 C. The coke produced in this way moves by gravity towards the lower layer of the column where it is gasified into gaseous CO by oxygen blown in at 1600 1700°C.

This mixture of gas proceeding from coal and oxidised coke consists of approximately 75% CO and hydrogen. Before being passed to the upper pre-reduction reactor, however, cooling of the CO gas to about 9000C must take place outside these two reactors, in order to prevent the ore from baking to a compact mass. One needs for this process also gas permeability. The advantage, however, compared to the blast furnace is the use of coal rather than coke.

The pre-reduction is still slow due to the limited gas temperature of 900°C.

The pre-reduction temperature and thus the time needed for the pre-reduction determines the output of the furnace and hence the economic feasibility of the process, which is currently being used for the first time at ISCOR in South Africa. The ore, pre-reduced to 95% Fe, in the upper furnace, is fed by means of a screw extractor into •the gasification smelter reactor at the bottom where, after smelting at the temperature mentioned above, the gangue is separated from the denser iron.

A further disadvantage is the high operation pressure of up to 5 bar, with a view to achieving permeability for the gases, as only ore with a grain size above 5000 microns can be used. Since the grain size in this process has till now been limited, only a narrow 35 range of ore grain size distribution can be used. Ore in powder form or in large blocks cannot be applied. The indisputable advantage of the COREX process is the use of coal rather than coke. The indisputable disadvantage is the temperature restriction for the reducing gas to be 4 ?oo

S.

less than 1000°C.

The blast furnace remains the inspiring force behind all other new developments separating the hearth of the shaft from the charge. These may be classified into those developments in which only a solid state reaction is produced in the shaft (direct reducing process) with a final product in the solid state, and those in which the furnace contains a bath of molten iron (reduction smelting process) with a final product in the liquid state, but without pre-reduction. These processes thus present either the shaft part with pre-reduction but with no liquid final product, or a liquid final product without a pre-reduction.

The group of processes in shafts exist, in principle, since the start of the iron history.

All these shaft processes rely on the laws of permeability of gases which do not allow reduction temperatures above 900 0 C, since higher temperatures will compact the ore and lower the gas permeability. However, these direct reducing processes are applied in industry up till today.

From the second group, related to the liquid bath of the blast furnace, no process has achieved a breakthrough so far and there are good reasons that it never will happen. If one feeds an iron bath with coal and ore, one does not get pre-reduction in the bath and thus the energy demand to maintain the bath temperature and the direct reduction respectively makes the process uneconomical.

The CO gas as a result of this reaction cannot be oxidised 30 to CO within the bath. So one cannot make use neither 2 "of the chemical nor of the exothermic reaction. The reaction gas leaves the bath as CO gas. If one uses it for pre-reduction in a separate shaft then it has to follow, the laws for gas permeability. It would thus bring 35 almost no advantage when compared to the blast furnace.

If one i-tends to use it outside the furnace for the exothermic reaction CO-CO 2 then it does not help you to lower the energy demand of the inside direct reduction bath substantially.

5 In practice therefore, the blast furnace process so far is still the remarkable masterpiece with only one disadvantage: the long pre-reduction times demand big furnace dimensions which result in large outputs. These outputs are too huge to fulfil the smaller iron unit demands for cheap liquid iron of especially mini mills.

Real progress can only be achieved if one could accelerate the pre-reducing process, because the prereduction time is practically identical to the total process time. This would result in smaller furnaces having higher outputs. But there is only one chance left to accelerate the prereducing and this chance could not be used so far: To apply higher gas temperatures than 9000C unlimited temperatures if possible. This means at the same time, to give up the gas permeability the basis of all existing reduction processes. However, if the gas temperature would be as high as the melting temperature of the ore or even higher, then the smelting and simultaneously the pre-reducing would happen that fast, that gas permeability is no longer required. What takes hours up to 9000 C happens in a few seconds up to 14000 C or even higher.

The second advantage would be that grain sizes would no longer play a role in the process, as all grains would 25 be baked above 9000 C to one ore block before the smelting-prereducing process starts due to the hot gas temperatures.

The fundamental conditions for a better economical reduction process therefore are: 30 i. Resource for higher unlimited gas temperatures for the pre-reduction to accelerate the whole reduction process.

2. One should be able to use coal rather than coke.

3. The final product should be liquid.

4. Unlimited use of all ore grain sizes.

Counterflow of the gases and the prereduced product.

The Process Of High Temperature Drop Reduction In A Drop Reducing Furnace oe.e oe e i coo 6

/A

rili jj i Very high reduction gas temperatures sinter the ore to one block at the frontier with the gas and consequently the gas could only smelt and reduce the outer layers of the ore block. After liquefaction and pre-reduction of the ore, not necessarily to the final stage of FeO/Fe, the liquid ore reduction mass should leave its place by, for example, dripping downwards, into the liquid iron bath for the final reduction. One can achieve that with a grate at the bottom of the ore column, which lets the hot gases pass through upwards and the liquid drops, consisting of pre-reduced ore and gangue and possibly some iron, downwards.

During the free fall of the drops, they still can react with the gases in the shaft and eventually the prereduction can be completed before they fall into the liquid bath where the different densities of iron and gangue allow a separation of both partners.

The CO gases do their reduction job and get oxidised to CO 2 in seconds and the contact times with the ore increase with the surface area of the ore. Surplus CO gas can be even burned to CO 2 in the upper part of the shaft with the thermal effect for a better economy so that the :total energy input can be used for the process inside the reactor. One can also use the surplus CO for further 25 reaction in a second or third shaft.

The accompanying drawing illustrates schematically the above described process of high temperature drop S. reduction in a Drop Reducing Furnace.

Under the unlimited gas temperatures condition, one 30 can achieve substantially higher outputs, using coal rather than coke, and gets a liquid final product. The heat demand in the bath can also be supplemented by outside heating.

a-U IA7

INT,

Claims

2. The process of claim 1, wherein said metal is iron.
3. The process in accordance with claim 1 or claim 2, wherein high gas temperatures, up to 2000 C and beyond, assure particularly rapid pre-reduction of the iron ore to FeO/Fe and bring it to smelting temperature, the drops fall through the grate without causing any damage due to the temperature or to overheating and the drops can be heated to even higher temperatures in the course of their free fall through the high temperature gases. The process in accordance with any one of claims 1 to 3, wherein any number of supplementary grates can also be used in one reduction furnace. The process in accordance with any one of claims 1 to 4, wherein the whole process can be achieved in more than one furnace, where the off gases CO/CO 2 from one furnace can also be applied in the next one to reacha higher percentage of CO 2 in the CO/CO 2 gases.
6. The process in accordance with any one of claims 1 to 5, wherein both the indirect reduction CO 1/2 02 (ore) CO 2 FeO and the direct reduction C FeO CO Fe take place in the reactor chamber formed by the reduction 8 M chamber and the recipient of the smelting bath close to the grate and in the course of the heating during the free fall towards the smelting bath.
7. The process in accordance with any one of claims 1 to 6, wherein the energy injected in the process is mainly used fo- the purpose of reduction inside the reactor.
8. The process in accordance with any one of claims 1 to 7, wherein any surplus gaseous CO formed in the smelting bath is also used for the purpose of producing heat by reaction with pure or atmospheric oxygen in accordance with the equation CO 1/2 02 CO 2 thermal energy) in the interior or at the exterior of the reduction furnace.
9. The process in accordance with any one of claims 1 to 8, wherein the reduction gases are used directly (for example for the purpose of gasifying coal even in the bath of molten metal' or indirectly (at the exterior), and in that the heating of the smelting hearth has recourse to both secondary and primary energy. The process in accordance with any one of claims 1 to 9, wherein the gases and the materials to be reduced c* displace each other in counterflow.
11. The process in accordance with any one of claims 1 25 to 10, wherein the final product is a liquid metal. S* 12. The process in accordance with any one of claims 1 to 11, wherein high gas temperatures allow high economically efficient outputs in the pre-reduction.
13. The process in accordance with any one of claims 1 30 to 12, wherein all ore grain sizes from sand to 50cm can be used.
14. A process for extracting metals from oxidised iron ores, substantially as herein described with reference to the accompanying drawing. DATED: 4 January 1993 ELSENTOOLING OVERSEAS LTD. By their Patent Attorneys: P s. PHILLIPS ORMONDE FITZPATRICK 9766m 9 g I j ABSTRACT Process intended for the extraction of metals, in particular of iron, from oxidised iron ores of any grain size, at any reduction gas temperature whatsoever in a drop reduction furnace. The invention relates to a process for manufacturing metals, and in particular iron, from oxidised ores, and in particular iron ores, in a smelting reduction furnace filled from the top by ore of any grain size whatsoever, which is heated up to smelting .*,,'Iemperature and pre-reduced by unlimited hot reducing gases, uo'i- -ising up from the hearth at the base of the shaft, Cass i n *,',,through a grate, heating up the bottom layers of the column of .oo *ore in which the molten fluid consisting of the pre-reduced or- "and possibly molten iron and gangue passes through the grate cr by drop in counterflow to the gases, and falling down to the base of the shaft into the liquid bath where both the final reduction Sand the separation of the molten metal, preferably iron, from the oro 0 gangue and the undesirable elements take place, and from where **e..the metal, preferably iron, is passed towards appropriate use. a 0 a af o 0 e L