OA20401A - Process for the smelting of a metalliferous feedstock material. - Google Patents

Abstract

The present invention relates to a process for the smelting of a metalliferous feedstock material. The process includes the steps of: (i) feeding an agglomerate comprising of a fine metalliferous feedstock material and a fine reductant to a reactor, the agglomerate forming a packed bed within the reactor; (ii) smelting the agglomerate by passing a hot reducing gas counter current through the packed bed to form a molten material comprising a partially reduced metalliferous constituent, an intermediate slag constituent and entrained unreacted reductant constituent; and (iii) channelling the molten material to flow into a vessel to form a metal product and a slag product.

Description

PROCESS FOR THE SMELTING OF A METALLIFEROUS FEEDSTOCK MATERIAL

FIELD OF THE INVENTION

The présent invention relates to a process for the smelting of a metalliferous feedstock material.

BACKGROUND TO THE INVENTION

Direct réduction processes hâve corne into increasing prominence in recent years. Direct réduction indicates a process whereby métal oxides in the ore, as the feed material, are reduced while the ore is still in the solid State. In conventional processes, reduced métal oxides are transferred from the direct réduction process to a subséquent smelting process wherein the reduced métal oxides are metallized, smelting referring to the réduction and melting ofthe feed.

It will be appreciated that the reduced métal oxides will cool down significantly whilst being transferred from the direct réduction process to the smelting process. The aforementioned cooling of the reduced métal oxides results in significant energy losses as the reduced métal oxides would hâve to be reheated during the smelting process.

A further disadvantage associated with conventional direct réduction processes and process equipment is that a directly reduced product can only be handled if same remains in the solid State.

United States of America patent number 3,033,673 entitled “Process of reducing iron oxides” discloses a direct réduction process whereby a métal iron oxide in an agglomerate is reduced in the solid State. This solid-state réduction process occurs in the shaft furnace disclosed in the patent. The patent continues to provide that the partially reduced métal oxide is smelted (i.e. melted) in an electric furnace. In other words, neitherthe agglomérâtes northe métal oxides in the agglomérâtes are melted in the shaft furnace.

Melting of the métal oxides resuit in, amongst other things, equipment blockages, reduced energy transfer and a decrease in process (i.e. réduction) efficiency.

This disadvantage is exemplified in the known commercial scale processes. The first example is direct réduction technology developed by Showa Denko for the direct réduction of chrome ore in rotary kilns at up to 1400°C. This température limitation in the process is to ensure that liquid phase build up is prevented in the kiln, otherwise the process will stop. In the Showa Denko process, the directly reduced product must be allowed to cool down to allow mechanical transfer to a final electrical smelting furnace, with the température of the product dropping down to typically 600°C during transfer.

As a further example, Kobe Steel and Midrex developed a FastSmelt process where composite agglomérâtes of iron ore can be directly reduced in a rotary hearth furnace making use of combusted pulverised coal. The agglomérâtes in the FastSmelt process again need to stay in the solid state so that they can be removed from the rotary hearth.

The next development from Kobe Steel and Midrex was the ITMK3 process whereby iron nuggets are allowed to form inside the agglomérâtes at higher operating températures, but the same limitation persist in that the agglomérâtes need to remain in solid state in order to allow removal from the rotary hearth. The nuggets are then melted in a subséquent process after cooling down and being transferred from the rotary hearth, resulting in significant energy losses. This development has not been a commercial success due to equipment challenges.

Further to the above disadvantages, it is to be appreciated that a further disadvantage in the known processes is that the température required for allowing métal oxides to be metallized cannot be effectively controlled. This is due to the fact that very high température zones need to be created in order for the processes to work. Examples of such known commercial scale processes are submerged arc furnaces and blast furnaces, and these are the only processes used to date to produce alloys such as ferromanganese and ferrochrome commercially. The lack of effective température control in these processes results in impurities being reduced to the product alloy, such as Si, Mn and S, in these high température zones, which impurities act to contaminate the final product.

United States of America patent number 3,832,158 entitled “Process for producing métal from métal oxide pellets in a cupola type vessel is known to the applicant. This patent describes a process whereby agglomérâtes containing a métal oxide are smelted (i.e. melted) using heat generated during the combustion of a coke bed. It is well-known that coke is extremely expensive and often renders the large-scale smelting of métal oxides to be less compétitive.

OBJECT OF THE INVENTION

It is accordingly an object of the présent invention to provide a novel process for the smelting of a metalliferous feedstock material which overcomes, at least partially, the abovementioned disadvantages and/or which will be a useful alternative to existing processes for the smelting of a metalliferous feedstock material while allowing for the handling of reduced products in the molten State.

SUMMARY OF THE INVENTION

According to the invention, there is provided a process for the smelting of a metalliferous feedstock material, the process including the steps of:

(i) feeding an agglomerate comprising of fine a metalliferous feedstock material and a fine reductant to a reactor, the agglomerate forming a packed bed within the reactor;

(ii) smelting the agglomerate by passing a hot reducing gas counter current through the packed bed to form a molten material comprising a partially reduced metalliferous constituent, an intermediate slag constituent and entrained unreacted reductant constituent; and (iii) channelling the molten material to flow into a vessel to form a métal product and a slag product.

In the current context, reference to fine in relation to particle size is a particle size of less than or equal to 6mm, but preferably less than 75pm.

The vessel may be separate from and in fluid flow communication with the reactor.

The process may include the additional step of adding electrical energy to the molten material in the vessel to reduce the partially reduced metalliferous constituent further to form an optimised liquid métal product and a final slag product, the entrained unreacted reductant constituent in the molten material serving as the reducing agent. In this manner, a high degree of metallization of the partially reduced metalliferous constituent can be obtained. The degree of metallization of the metalliferous feedstock material in the process may be up to 98%. The entrained unreacted reductant constituent in the slag allows for a much higher réduction of the metalliferous constituent compared to conventional smelting processes.

The addition of electrical energy to the molten material may be controlled to adjust the température of the molten material to form the optimised liquid métal product and the final slag product, the optimised liquid métal product and the final slag product being suitable for tapping from the vessel.

The entrained unreacted reductant constituent in the molten material may allow for the complété réduction of the partially reduced metalliferous constituent présent in the molten material.

The composition of the agglomérâtes may be manipulated to lower the melting température of the agglomérâtes in the packed bed to thereby increase the melting rate of the agglomérâtes and decrease the degree of réduction of the fine metalliferous feedstock material.

The composition of the agglomérâtes may be manipulated to increase the melting température of the agglomérâtes in the packed bed to thereby decrease the melting rate of the agglomérâtes and increase the degree of réduction of the fine metalliferous feedstock material.

The hot gas should be a reducing gas with a CO/CO2 ratio greater than 5 and preferably greaterthan 10 so as to avoid re-oxidation of metalliferous constituent.

The hot reducing gas may be passed through the packed bed at a température above 1200°C, preferably above 1350°C and most preferably above 1600°C, the température being dépendant on the métal product being produced.

The packed bed may include a fluid permeable interface at an operatively downstream position relative to a région where the agglomerate is fed to the reactor, the fluid permeable interface permitting the hot reducing gas to pass therethrough and through the packed bed of agglomérâtes. The fluid permeable interface may be an operatively base région of the packed bed in the reactor.

The packed bed may be suspended by side walls of the reactor at a position at which the direction of the side walls changes.

Alternatively, the packed bed may be suspended by an obstruction located in the reactor, the obstruction being at an operatively downstream position relative to the région where the agglomerate is fed to the reactor. The obstruction may be a permeable bed of refractories. Alternatively, the obstruction may be a permeable bed of coke particles.

The agglomerate may include a flux. A flux may be fed together with, but separately from, the agglomérâtes into the reactor.

The agglomerate may include a binding agent.

There is provided for the process to include the additional step of adding additional reductant to the molten material in the vessel.

There is provided for the electrical energy to be added to the molten material via électrodes in the vessel which are submerged in the molten material.

The optimised liquid métal product and the final slag product may be formed via an electrochemical reaction between the partially reduced metalliferous constituent and the unreacted entrained reductant constituent in the molten material, the intermediate slag constituent serving as an electrolyte. In this manner, a very high degree of metallization of the metalliferous feedstock material, such as métal oxides, can be achieved compared to the known prior art processes, wherein the degree of metallization achieved through the process of the présent invention may be up to 98%.

The résidence time of the metalliferous feedstock material in the packed bed of agglomérâtes may be controlled to impact the degree of réduction of the metalliferous feedstock material in the reactor.

The operating températures in the reactor and vessel may be controlled to selectively metalize a first target métal in the metalliferous feedstock material, thereby allowing the metalized first target métal to report to the optimised liquid métal product and the nontarget metals to report to the final slag product.

There is provided for the final slag product to be provided as the metalliferous feedstock material in a subséquent process, the subséquent process being a processes according to the invention, and wherein the operating températures in the reactor and vessel in the subséquent process is controlled to selectively metallize a second target métal in the metalliferous feedstock material, thereby allowing the metalized second target métal to report to the liquid métal product of the subséquent process and the remaining non-target metals to report to the final slag product of the subséquent process.

The final slag product generated may be transferred for further processing.

The température of the hot reducing gas may be set at a targeted température.

The electrical energy input may be controlled to achieve a targeted liquid métal product and final slag product température.

BRIEF DESCRIPTION OF THE DRAWING

An embodiment of the invention is described below, by way of a non-limiting example only and with reference to the accompanying drawing in which:

Figure 1 is a schematic diagram of the process of the présent invention.

DETAILED DESCRIPTION OF THE INVENTION

With reference to the accompanying drawing, in which like numerals refer to like features, a process for the smelting of a metalliferous feedstock material according to the invention is generally designated by reference number 10.

The process for the smelting of a metalliferous feedstock material 10 includes the steps of:

(i) feeding an agglomerate (not shown) comprising of a fine metalliferous feedstock material (not shown) and a fine reductant (not shown) to a reactor 12, the agglomerate forming a packed bed 14 within the reactor 12;

(ii) smelting the agglomerate (not shown) by passing a hot reducing gas counter current through the packed bed to form a molten material (not shown) comprising a partially reduced metalliferous constituent (not shown), an intermediate slag constituent (not shown) and entrained unreacted reductant constituent (not shown); and (iii) channelling the molten material to flow into a vessel 26 to form a liquid métal product 16 and a final slag product 18.

Typically, the metalliferous feedstock material is a mined métal oxide. However, the metalliferous feedstock material may be any material containing a métal oxide.

The agglomerate is fed gravitationally to the reactor 12 to form a fluid permeable packed bed 14 of agglomérâtes. The packed bed 14 of agglomérâtes is stacked between 2 and 3 métrés high in the reactor 12. Ideally, the agglomerate has a diameter of between 10 mm and 20 mm, but the process 10 can accommodate agglomérâtes with a diameter of anything between 2 mm and 80 mm and even more. It is an advantage of the process 10, owing to, amongst other things, the low height of the packed bed 14 in the reactor 12, that agglomérâtes with limited strength and therefore limited, or no binder content can be utilised. The metalliferous feedstock material is dispersed within the agglomerate and is preferably a fine material having a particle size of less than 75pm. It will be appreciated that the agglomérâtes may include a binder or binding agent, and the use or disuse of binder or binding agent would dépend on the size of the agglomerate used in the process 10 and/or the height at which the packed bed 14 of agglomérâtes is stacked in the reactor 12. Furthermore, the agglomerate may include a flux or fluxing agent.

In this example, the agglomérâtes in the packed bed 14 are smelted by passing a hot reducing gas (not shown) therethrough in a counter current fashion. The hot reducing gas is fed to the reactor 12 at an operatively downstream position 20 ofthe packed bed 14 of agglomérâtes and counter current to the direction in which agglomérâtes are fed to the reactor 12. The hot reducing gas is fed to the reactor 12 at a velocity of between 3 and 4 m/s so that the hot reducing gas permeates through the packed bed 14 of agglomérâtes. The température ofthe hot reducing gas is controlled to be above 1300°C and up to 1700°C, depending on the type of metalliferous feedstock material in the agglomerate and the extent of the réduction of the metalliferous feedstock material desired in the packed bed 14 of agglomérâtes.

By way of example, the hot reducing gas will be fed to the reactor 12 at a lower température when the metalliferous feedstock material is an iron-oxide than in an instance where the metalliferous feedstock material is a chrome-oxide. Importantly, the température ofthe hot reducing gas for smelting of iron-oxides can be set lower than the température at which silica-oxides and sulphides would be reduced, which will ensure a high purity pig iron being produced. The hot reducing gas is typically synthesis gas and preferably has a carbon monoxide to carbon dioxide (CO/CO2) ratio greater than 10, preferably 15. As the hot reducing gas pervades through the packed bed 14 of agglomérâtes, the metalliferous feedstock material is partially reduced towards its metallic form. Here, the CO/CO2 ratio of the synthesis gas is controlled to prevent reoxidation of the reduced metalliferous feedstock material in the packed bed 14 of agglomérâtes and reactor 12.

In addition to partially reducing the metalliferous feedstock material in the agglomérâtes, the hot reducing gas melts the agglomerate, thereby forming a molten material comprising of a partially reduced metalliferous constituent, an intermediate slag constituent and entrained unreacted reductant constituent; the entrained unreacted reductant constituent emanates from the agglomerate. An advantage of the process of the invention is that the melting température of the agglomerate can be controlled. Control over the melting température of the agglomerate results in control over the résidence time ofthe metalliferous feedstock material in the reactor 12; i.e. the rate at which the formed molten material flows out of the packed bed 14 is controlled. In turn, control over the résidence time ofthe metalliferous feedstock material in the reactor 12 results in control over the degree of réduction of the metalliferous feedstock material taking place in the reactor.

A further significant advantage of the présent invention is that by controlling or manipulating the composition of the agglomérâtes the melting température of the agglomérâtes can be controlled or manipulated. Thus, the rate of smelting of the agglomerate and the degree of réduction of the fine metalliferous feedstock material in the reactor 12 can be controlled. For example, by lowering the melting température of the agglomerate the rate of smelting of the agglomerate is increased and the degree of réduction ofthe metalliferous feedstock material is decreased in the reactor 12. In turn, by increasing the melting température of the agglomerate the rate of smelting of the agglomerate is decreased and the degree of réduction of the metalliferous feedstock material is increased in the reactor 12.lt will be appreciated that the afore steps will détermine the résidence time of the agglomerate and metalliferous feedstock material containing métal oxides in the reactor 12. Therefore, the degree to which the métal oxides présent in the agglomérâtes are reduced can be controlled, which is useful to optimise profitability.

The melting température of the agglomerate is controlled by a number of physical and Chemical characteristics of the agglomerate and its constituents. For example, the melting temperate of the agglomerate can be increased by adding a flux or a fluxing agent thereto. The nature or type of metalliferous feedstock material would also influence the melting température of the agglomerate; i.e. ail else being equal, an agglomerate containing iron-oxide would melt at a lower temperate than an agglomerate containing chromium-oxide.

Consequently, the résidence time of the agglomerate in the reactor and thereby the degree of réduction ofthe metalliferousfeedstock material may be controlled, depending on any one or a combination ofthe following:

- the melting température of the metalliferous feedstock material and/or agglomerate, which is controlled by:

i. the amount and nature of the flux or fluxing agent added to the agglomerate;

ii. the amount and nature of the binder or binding agent added to the agglomerate; and iii. the sélection of the ore types.

- the température at which the hot reducing gas is fed to the packed bed 14 of agglomérâtes; and

- the size of the agglomérâtes.

A fluid permeable interface is formed at an operatively lower région of the packed bed 14. The fluid permeable interface allows: (i) the hot reducing gas to pass therethrough and into the packed bed 14 of agglomérâtes and (ii) the molten material to flow out of and away from the packed bed 14 of agglomérâtes. In the embodiment shown in Figure 1, the fluid permeable interface is formed adjacent to an obstruction 22 located in the reactor 12. The obstruction 22 of Figure 1 takes the form of a porous bed of refractories. However, the obstruction 22 may also take the form of a porous bed of coke particles.

The pressure-drop of the hot reducing gas across the permeable fluid interface and packed bed 14 of agglomérâtes is minimized and typically in the order of 5 to 10 kPa. The température of the hot reducing gas, after having passed through the permeable bed 14 of agglomérâtes, is typically less than 300°C.

Having passed through the fluid permeable interface and from the packed bed 14 of agglomérâtes and to the vessel 26, electrical energy is added to the molten material. By adding electrical energy to the molten material, the partially reduced metalliferous constituent in the molten material is metallized and an optimised liquid métal product 16 and a final concentrated slag product 18 are formed. Electrical energy is added to the molten material via an electrode or électrodes 24 which is/are submerged in the molten material.

The optimised liquid métal and final slag products are, in an embodiment of the invention, formed via an electrochemical reaction between the partially reduced metalliferous constituent and the entrained unreacted reductant constituent, the intermediate slag serving as an electrolyte. This allows the métallisation to proceed to much higher levels compared to conventional smelting as known in the art.

Advantageously, the vessel 26 is in fluid flow communication with the reactor 12, thereby minimising heat loss during transfer of the molten material from the partial réduction reaction and melting to the electrochemical reaction. Furthermore, additional reductant (not shown) may be added to the molten material prior to or whilst subjecting same to the electrochemical reaction.

A major breakthrough achieved in the process 10 of the présent invention is that it allows for the processing of the ores with hot synthesis gas while further allowing the products to melt and having a process design that can transfer the molten material to a further vessel for producing a liquid métal product and final slag product. The process 10 of the présent invention thereby shows that, contrary to the perception of people skilled in the art that ores like chrome and manganèse cannot be smelted by commercially produced hot gasses, these ores can in fact be smelted through use of such gasses using the process 10 of the présent invention.

The process 10 of the présent invention further provides the major advantage that the process reaction températures can be controlled at a required température, this in turn allows a métal constituent to be reduced to be targeted at a selected température whilst avoiding réduction of impurities which are présent.

It will be appreciated by those skilled in the art that the invention is not limited to the précisé details as described herein and that many variations are possible without departing from the scope of the invention. As such, the présent invention extends to ail functionally équivalent processing equipment, structures, methods and uses that are within its scope. In particular, the steps of the process provided for need not necessarily be executed sequentially. Furthermore, it is envisaged that the steps of the process provided for need not necessarily be executed in the order listed herein.

The description is presented by way of example only in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention and/or the equipment utilised therein in more detail than is necessary for a fundamental understanding of the invention. The words which hâve been used herein are words of description and illustration, rather than words of limitation.

Claims (15)

1. A process for the smelting of a metalliferous feedstock material, the process including the steps of:

(i) feeding an agglomerate comprising of a fine metalliferous feedstock material and a fine reductant to a reactor, the agglomerate forming a , „_ht packed bed within the reactor;

(ii) smelting the agglomerate by passing a hot reducing gas counter current io through the packed bed to form a molten material comprising a partially reduced metalliferous constituent, an intermediate slag constituent and entrained unreacted reductant constituent; and (iii) channelling the molten material to flow into a vessel to form a métal product and a slag product, the vessel being separate from and in fluid flow 15 communication with the reactor.

2. The process of claim 1, wherein the process includes the additional step of adding electrical energy to the molten material in the vessel to reduce the partially reduced metalliferous constituent further to form an optimised liquid métal product and a 20 final slag product, the entrained unreacted reductant constituent in the molten material serving as the reducing agent.

3. The process of claim 2, wherein the addition of electrical energy to the molten material is controlled to adjust the température of the molten material to form the 25 optimised liquid métal product and the final slag product, the optimised liquid métal product and the final slag product being suitable for tapping from the vessel.

4. The process of claim 2 or claim 3, wherein electrical energy is added to the molten material to completely reduce the partially reduced metalliferous constituent 30 présent in the molten material.

5. The process of any one of the preceding daims, wherein the composition of the agglomérâtes is manipulated to lower the melting température of the agglomérâtes in the packed bed, to thereby increase the melting rate of the agglomérâtes and decrease the degree of réduction of the fine metalliferous feedstock material.

6. The process of any one of daims 1 to 4, wherein the composition of the agglomérâtes is manipulated to increase the melting température of the agglomérâtes to thereby decrease the melting rate of the agglomérâtes and increase the degree réduction of the fine metalliferous feedstock material.

7. The process of any one of the preceding daims, wherein the hot reducing gas has a CO/CO2 ratio of higher than 5 and preferabiy higher than 10 so as to avoid reoxidation of the partially reduced metalliferous constituent.

8. The process of any one of the preceding daims, wherein the hot reducing gas which is passed through the packed bed has a température above 1200°C, preferabiy above 1350°C and most preferabiy above 1600°C, the température being dépendent on the métal being produced.

9. The process of any one of the preceding daims, wherein the packed bed includes a fluid permeable interface at an operatively downstream position relative to a région where the agglomerate is fed to the reactor, the fluid permeable interface permitting the hot reducing gas to pass therethrough and through the packed bed of agglomérâtes.

10. The process of any one of the preceding daims, including the additional step of adding additional reductant to the molten material in the vessel.

11. The process of any one of daims 2 to 10, wherein electrical energy is added to the molten material via électrodes which are submerged in the molten material.

12. The process of any one of daims 2 to 11, wherein the optimised liquid métal product and the final slag product are formed via an electrochemical reaction between the partially reduced metalliferous constituent and the unreacted entrained reductant constituent in the molten material, the intermediate slag constituent serving as an electrolyte.

13. The process of any one of the preceding claims, wherein the résidence time of the metalliferous feedstock material in the packed bed of agglomérâtes is controlled to impact the degree of réduction of the metalliferous feedstock material in the reactor.

14. The process of any one of the preceding claims, wherein operating températures in the reactor and vessel are controlled to selectively metallize a first target métal in the metalliferous feedstock material, thereby allowing the metalized first target métal to report to the optimised Iiquid métal product and the non-target metals to 10 report to the final slag product.

15. The process of any one of claims 2 to 14, wherein the final slag product is provided as the metalliferous feedstock material in a subséquent process, the subséquent process being a processes according to any of claims 1 to 14, and wherein the 15 operating températures in the reactor and vessel in the subséquent process is controlled to selectively metallize a second target métal in the metalliferous feedstock material, thereby allowing the metalized second target métal to report to the Iiquid métal product of the subséquent process and the remaining non-target metals to report to the final slag product of the subséquent process.