WO2023244479A1

WO2023244479A1 - A direct bath smelting process with management of peripheral cold zones at the metal-slag interface

Info

Publication number: WO2023244479A1
Application number: PCT/US2023/024715
Authority: WO
Inventors: Rodney James Dry
Original assignee: Nucor Corporation
Priority date: 2022-06-15
Filing date: 2023-06-07
Publication date: 2023-12-21

Abstract

An improved direct smelting vessel comprising a smelt reduction vessel (SRV) and optionally a cyclone converter furnace (CCF). The SRV provides means for promoting metal mixing at a zone below a slag layer adjacent to a vessel wall of the direct smelting vessel. The means for promoting metal mixing may include a split-level refractory hearth with two refractory floor levels, a refractory hearth with one or more gas bubbling devices, and/or at least one pair of solids injection lances that provide alternating solids injection at any given time (or other means). The means for promoting the metal mixing reduces a stagnant region capable of supporting a semi-solid slag layer that restricts metal-slag heat transfer. The means for promoting the metal mixing maintains an effective temperature delta between tapped metal at a forehearth and metal at the vessel wall of no greater than 40 °C.

Description

A DIRECT BATH SMELTING PROCESS WITH MANAGEMENT OF PERIPHERAL COLD ZONES AT THE METAL-SLAG INTERFACE

PRIORITY CLAIM UNDER 35 U.S.C. §119

[0001] This application claims priority to U.S. Provisional Application No. 63/352,492 entitled "A Direct Bath Smelting Process with Management of Peripheral Cold Zones at the Metal- Slag Interface" filed on June 15, 2022, and U.S. Non-Provisional Patent Application No. 18/204, 683 entitled "A Direct Bath Smelting Process with Management of Peripheral Cold Zones at the Metal-Slag Interface" filed on June 1, 2023, both of which are assigned to the assignee hereof and hereby expressly incorporated by reference herein.

Field of the Invention

[0002] The present invention relates to a process and an apparatus for direct smelting a metalliferous material.

Background

[0003] Two known direct smelting processes for a metalliferous material, which rely principally on a molten bath as the smelting medium, are generally referred to as HIsmelt and HIsarna .

Summary of the Invention

[0004] The present invention is directed to an improved direct smelting vessel comprising a smelt reduction vessel (SRV) and optionally a cyclone converter furnace (CCF) . In particular, the direct smelting vessel may be an enclosed vessel with a roof, a refractory hearth region in a base of the vessel for containing the molten bath, and a gaseous region between the molten bath and the roof. Means are provided for promoting metal mixing (e.g., passive mixing and/or active mixing) at a zone adjacent the outer periphery of the vessel at the metal slag interface (e.g., cold shoulder zone) . For example, providing improved metal mixing in this zone reduces a stagnant region capable of supporting a semi-solid slag layer that restricts metal-slag heat transfer. In particular, the means for providing metal mixing maintains an effective temperature delta between tapped metal at a forehearth and metal at the vessel wall of no greater than 40 °C (72 °F) .

[0005] In some embodiments of the invention, the means for promoting metal mixing may comprise a split-level refractory hearth with two refractory floor levels, a refractory hearth that utilizes one or more gas bubbling devices, and/or at least one pair of solids injection lances in which a first opposing lance of the pair provides all the injected feed solids for the pair at any given time before switching to the second opposing lance of the pair (e.g., immediately or after some period of time) .

[0006] With respect to the split-level refractory hearth, this means provides a main level having a depth that improves the molten metal mixing, which plays a key role in relation to metal-slag heat transfer. Moreover, the SRV provides a secondary level having a different depth (e.g., deeper than the main level depth) that provides safety features related to preventing slag from being blown out of the forehearth. The depths of the split-level refractory hearth will be described in further detail herein.

[0007] With respect to the refractory hearth that utilizes one or more gas bubbler devices, the gas bubblers promote metal convention by injecting gas (e.g., argon, or the like) into the zone below the slag layer adjacent to a vessel wall of the direct smelting vessel.

[0008] With respect to the at least one pair of solids injection lances, the injection lances provide injection plumes strong enough to promote metal convection at the opposite wall of the vessel. Alternating between the opposing lances (e.g., with respect to a given pair of lances) on a regular cycle based on the time it takes for the hot metal adjacent the wall of the vessel to cool may be used to promote metal convection that restricts establishment of a semi-solid slag layer at the metalslag interface.

[0009] It should be understood that other means for promoting metal mixing adjacent the metal wall, either passively or actively, may be utilized to reduce the semi-solid slag layer described herein.

[0010] One embodiment of the present disclosure comprises a method for direct smelting of metalliferous material and producing molten metal in a direct smelting vessel. The method comprises injecting solid carbonaceous material through at least one injection lance extending into the direct smelting vessel such that solids penetrate at least partially into a molten metal layer in the direct smelting vessel, wherein a slag layer is floating on the molten metal layer. The method further comprises promoting metal mixing at a zone immediately below the slag layer adjacent to a vessel wall of the direct smelting vessel .

[0011] In further accord with embodiments, the metal mixing reduces a volume occupied by a stagnant region cold enough to be capable of supporting a semi-solid slag layer that restricts metal-slag heat transfer.

[0012] In other embodiments, the metal mixing maintains an effective temperature delta between tapped metal at a forehearth and metal at the vessel wall of no greater than 40 °C. [0013] In still other embodiments, the metal mixing is promoted using the direct smelting vessel comprising a splitlevel refractory floor with two refractory floor levels comprising a first level having a first depth that supports a first metal depth and a second level having a second depth that supports a second metal depth. The second metal depth is greater than the first metal depth. The first depth that supports the first metal depth promotes the metal mixing by metal convection into and out of the zone below the slag layer adjacent to the vessel wall.

[0014] In yet other embodiments, the first level comprises at least 70% of a cross-sectional area of the split-level refractory floor.

[0015] In other embodiments, the first depth supports the first metal depth that is not greater than 900mm.

[0016] In further according with embodiments, the first depth supports the first metal depth that is not greater than 700mm. [0017] In other embodiments, the first depth supports the first metal depth that is not greater than 600mm.

[0018] In still other embodiments, the second depth supports the second metal depth that is at least 300mm greater than the first metal depth.

[0019] In yet other embodiments, the metal mixing is promoted by injecting gas in the direct smelting vessel using one or more gas bubbling devices for promotion of metal convection to the zone below the slag layer adjacent to the vessel wall.

[0020] In other embodiments, the gas comprises argon gas or nitrogen gas.

[0021] In further accord with embodiments, the metal mixing is promoted by using one or more pairs of solids injection lances in the direct smelting vessel, wherein one branch of a pair of solids injection lances provides at least a majority of the injected feed solids for the pair of solids injection lances at any given time.

[0022] In other embodiments, injection of the feed solids through the one branch of the pair of solids injection lances is reversed to an opposing branch of the pair of solids injection lances, either immediately following injection through the one branch or a period of time later.

[0023] Another embodiments of the present disclosure comprises an apparatus for direct smelting metalliferous material and producing molten metal and molten slag. The apparatus comprises a direct smelting vessel comprising at least one of a split-level refractory hearth, a refractory hearth with one or more gas bubbling devices, or one or more pairs of solids injection lances. The split-level refractory hearth with two refractory floor levels comprises a first level having a first depth that supports a first metal depth and a second level having a second depth that support a second metal depth. The second metal depth is greater than the first metal depth. The one or more pairs of solids injection lances utilize one branch of a pair of solids injection lances that provides at least a majority of the injected feed solids for the pair of solids injection lances at any given time. The split-level refractory hearth, the one or more gas bubbling devices, or the one or more pairs of solids injection lances promotes metal mixing at a zone below a slag layer adjacent to a vessel wall of the direct smelting vessel .

[0024] In further accord with embodiments, the metal mixing reduces a stagnant region capable of supporting a semi-solid slag layer that restricts metal-slag heat transfer between the molten metal and the molten slag.

[0025] In other embodiments, the metal mixing maintains an effective temperature delta between tapped metal at a forehearth and metal at the vessel wall of no greater than 40 °C. [ 0026 ] In still other embodiments , the direct smelting vessel comprises the split-level refractory hearth .

[ 0027 ] In yet other embodiments , the first level compri ses at least 70% of the cross-sectional area of the refractory floor, wherein the first depth supports the first metal depth that is not greater than 900mm, and wherein the second depth supports the second metal depth that is at least 300mm greater than the first metal depth .

[ 0028 ] In other embodiments , the direct smelting vessel comprises the refractory hearth with the one or more gas bubbling devices .

[ 0029 ] In still other embodiments , the direct smelting vessel comprises the one or more pairs of solids inj ection lances .

[ 0030 ] To the accomplishment of the foregoing and the related ends , the one or more embodiments of the invention comprise the features hereinafter fully described and particularly pointed out in the claims . The following description and the annexed drawings set forth certain illustrative features of the one or more embodiments . These features are indicative, however, of but a few of the various ways in which the principles of various embodiments may be employed, and this description is intended to include all such embodiments and their equivalents .

Brief Description of the Drawings

[ 0031 ] The present invention is described further by way of examples with reference to the accompanying drawings , of which : [ 0032 ] Figure 1A is a cross-sectional side view of a direct smelting vessel having an SRV that uses the shallow-bath concept to achieve metal mixing in the cold shoulder region, in accordance with embodiments of the present disclosure . [ 0033 ] Figure IB is a is a cross-sectional top view of the direct smelting vessel of Figure 1A, in accordance with embodiments of the present disclosure .

[ 0034 ] Figure 2A is cross-sectional side view of a direct smelting vessel having an SRV which uses stirring gas inj ection to achieve metal mixing in the cold shoulder region, in accordance with embodiments of the present disclosure .

[ 0035 ] Figure 2B is a cross-sectional top view of the direct smelting vessel of Figure 2A, in accordance with embodiments of the present disclosure .

[ 0036 ] Figure 3 is a process flow for direct smelting utili zing a direct smelting vessel having an SRV that uses a means for providing metal mixing in the cold shoulder zone , in accordance with embodiments of the present disclosure .

Detailed Description

[ 0037 ] Embodiments of the present invention will now be described more fully hereinafter with reference to the accompanying drawings , in which some , but not all , embodiments of the invention are shown . Indeed, the invention may be embodied in many di f ferent forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satis fy applicable legal requirements . Like numbers refer to like elements throughout .

[ 0038 ] The term " smelting" is herein understood to mean thermo-chemical processing wherein chemical reactions that reduce metal oxides occur to produce carbon-containing molten metal . These smelting reactions take place only at suf ficiently low oxygen potential and are highly endothermic, requiring a large heat supply to maintain constant process temperature . [0039] Two direct smelting processes for a metalliferous material which rely principally on a molten bath as the smelting medium are generally referred to as the HIsmelt process and the HIsarna process. As will be discussed in further detail herein, the HIsmelt process utilizes an SRV, while the HIsarna process utilizes an SRV with a CCF located above the SRV.

[0040] The HIsmelt process relates to direct smelting metalliferous material in the form of iron oxides and producing molten iron. The process includes forming a bath of molten iron and slag in a vessel (e.g., SRV) . Material is injected into the bath, including metalliferous material (e.g., iron oxides, or the like) and solid carbonaceous material (e.g., coal, or the like) that acts as a reductant of the iron oxides and a source of energy for forming the molten metal bath within the vessel. [0041] The HIsmelt process also includes post-combusting reaction gases, such as CO and H2 released from the bath, in the generally gas-continuous space above the bath (e.g., referred to as the topspace) with oxygen-containing gas, typically hot oxygen-enriched air or technically pure cold oxygen. Heat generated by post-combustion reactions is transferred to the bath in order to satisfy the thermal energy required to smelt the metalliferous materials.

[0042] The HIsmelt process also includes forming a transition zone above the nominal quiescent surface of the bath. In this zone, there is a mass of ascending and descending droplets and splashes or streams of molten metal and/or slag, which provides an effective medium to transfer to the bath a significant portion of the thermal energy generated by post-combusting reaction gases above the bath. This plume moves heat from the topspace where it is generated (e.g., at relatively high oxygen potential) to the bath where it is used for smelting purposes (e.g., at relatively low oxygen potential) . As such, the plume effectively acts as a heat pump. [0043] In the HIsmelt process, metalliferous material and solid carbonaceous material are injected into the molten bath through a number of solids injection lances. The lances may be inclined to the vertical so as to extend downwardly and inwardly through a side wall of a direct smelting vessel and into a lower region of the vessel so as to deliver at least part of the solids material into a molten metal layer in the bottom of the vessel. To promote the post-combustion of reaction gases in an upper part of the vessel, cold oxygen or a blast of hot air, which may be oxygen-enriched, is injected into an upper region of the vessel through one or more downwardly extending gas injection lances. Off gases resulting from post-combustion of reaction gases in the vessel are taken away from the upper region of the vessel through an offgas duct. The vessel also includes slag- coated water-cooled panels in the side walls and the roof of the vessel, through which water is circulated in a continuous circuit .

[0044] Molten metal product is removed from the smelt reduction vessel (SRV) via a forehearth. The forehearth is a siphon overflow device connected to the bath via an opening ("forehearth connection") near the bottom of the metal bath in the SRV. The forehearth allows for extraction of molten metal from the SRV in a continuous manner during operation, while maintaining a metal level in the SRV that allows safe operation (e.g., keeping bulk metal well away from water-cooled elements) . [0045] The HIsarna process, as far as the SRV is concerned, has the same or similar physical components and layout as the HIsmelt process, and operates in the same or similar way. A difference between the two is that in the HIsarna process incoming iron ore is not injected into the bath but is rather heated, partially pre-reduced, and substantially melted in a smelt cyclone (e.g., within a CCF) which is directly coupled to the top gas outlet of the SRV. Substantially molten, partly reduced iron ore droplets fall from the smelt cyclone into the SRV slag, and from there smelting proceeds (e.g., principally carbon-rich metal reacting with FeO in slag) . Carbonaceous material is still injected into the bath as previously described to carburize metal and generate the splash, fountain plume, and mixing within the SRV.

[0046] In both the HIsmelt and HIsarna processes, the heat transfer process from the topspace combustion region to the bath effectively occurs in two steps. The first step is heat transfer from the gas space to slag in the upper region of the SRV, and the second is heat transfer from slag to metal in the lower region. There are effectively two fountains in the SRV, that is first, a predominately slag fountain which splashes into the topspace to gain heat from hot combustion gases, and second, a metal fountain which splashes into the slag layer in order to gain heat from hot slag and bring it to the metal bath.

[0047] A previously unrecognized mechanism which restricts metal-slag heat transfer is referred to herein as the "cold shoulder". When slag splashes against a water-cooled panel, an intermediate semi-solid layer is formed between the solidified slag freeze-layer and bulk molten slag. This semi-solid layer can move downwards under gravity until it encounters the metalslag interface near the vessel wall. If the temperature of molten metal at this location is low enough, semi-solid slag can float inwards from the wall towards the center of the vessel. A layer of semi-solid slag can thus occupy a portion of the bath crosssection, thereby inhibiting free movement of both metal and slag across this horizontal interface. This restricts metal-slag heat transfer which in turn compromises SRV productivity. The term "cold shoulder" refers to metal temperature at the outer periphery of the bath - the colder it is, the more it allows semi-solid slag to float inwards (leading to more restricted metal-slag heat transfer) . [0048] Ideally, metal and slag temperatures will be reasonably close with slag slightly hotter than the metal. Typical metal forehearth temperatures targets are 1400-1450 °C (2252-2642 °F) . With a nominal 20 °C (36 °F) temperature drop across the forehearth, this implies actual metal temperatures in the main splash region around 1420-1470 °C (2588-2678 °F) . Slag temperatures in the main splash region will be slightly higher than this, ideally 1430-1500 °C (2606-2732 °F) , for example, as measured during slag tapping through the slag notch. The stronger the cold shoulder effect, the greater the temperature difference between metal and slag. A suitable (practical) target for efficient SRV process operation is a temperature difference between slag tap temperature and forehearth metal temperature of no more than about 70 °C (126 °F) . This is equivalent to a metal-slag temperature difference of about 50 °C (90 °F) inside the SRV.

[0049] The present invention relates to improvements in the metal-slag heat transfer based on a means for improving the metal mixing (e.g., passive or active) at a zone (e.g., cold shoulder zone) below the slag layer adjacent to a vessel wall of the direct smelting vessel. For example, providing improved metal mixing in this zone reduces a stagnant region capable of supporting a semi-solid slag layer that restricts metal-slag heat transfer. In particular, the means for providing metal mixing maintains an effective temperature delta between tapped metal at a forehearth and metal at the vessel wall of no greater than 40 °C (72 °F) (or in some embodiments no greater than 30 °C, i.e., 54 °F, or no greater than any value between 30-40 °C) . [0050] In some embodiments of the invention, the means for promoting metal convection may comprise a split-level refractory hearth with two refractory floor levels. The effective depth of the metal bath in the first level provides for passive metal convection in the cold shoulder zone of the SRV, while maintaining safety features around the forehearth using a second deeper level, as will be described in further detail herein.

[0051] In other embodiments of the invention, the means for promoting metal convection may comprises a refractory hearth that utilizes one or more gas bubbling devices.

[0052] Other means may comprise at least one pair of solids injection lances in which a first opposing lance of the pair provides the injected feed solids (e.g., all, a majority of, or the like) for the pair at any given time before switching to the second opposing lance of the pair (e.g., immediately or after some period of time) . These means will be described in further detail herein.

[0053] In a HIsmelt pilot plant, the vertical SRV operated with a metal bath depth of around 250-400 mm (around 10-16 inches) in a hearth with an internal diameter of 2.7m (about 8.9 feet) . Metallurgical performance in this HIsmelt processes was such that high rates of heat transfer between metal and slag were achieved, allowing up to about 30 MW of useful heat to be transferred to the metal bath. The net result was a process wherein 15 t/h of wet ore (at an iron content of 62.8%) was converted into 8.5 t/h of hot metal (containing 4% carbon) . Operationally, the pilot plant SRV was judged to be highly responsive to coal and ore injection rate changes. The temperature difference between tapped metal and tapped slag was modest, typically between about zero °C and about 40°C (72 °F) . However, it is difficult to measure the temperature differences within the SRV with high precision. During testing, it was identified that increased coal and ore injection led to increased splash (e.g., both slag-in-gas and metal-in-slag) , which in turn led to increased heat transfer to the bath. As such, the pilot plant SRV was judged to operate in a process "sweet spot" that was subsequently used as justification for building a commercial-scale demonstration plant, that is, a 6m (about 19.7 ft) SRV.

[0054] One of the practical concerns related to the pilot plant SRV (2.7m) was that because the metal bath was relatively shallow, the height of liquid metal providing a liquid seal over the top of the forehearth connection was small (typically 150- 250 mm / 6-10 inches) . Should back-pressure control valves malfunction, the pilot plant SRV pressure could increase momentarily, and thus, slag could be blown out of the forehearth. This creates potential dangers and forces the process to stop. [0055] A practical response was that all subsequent SRVs (e.g., the 6m SRV, or the like) were designed to run with a deeper metal bath in order to minimize the potential for slag to blow out. Subsequent designs used a metal bath around 1200- 1500 mm (around 47 to 59 inches) deep in a 6m SRV and around 850-1000 mm (around 34-39 inches) deep in the 2.7m pilot plant SRV. Whilst this metal depth increase was highly effective in terms of reducing the probability of blowing slag through the forehearth connection, it is thought to have had unintended potential negative consequences. That is, during commissioning of the 6m SRV, the heat transfer from gas to slag was highly effective (e.g., slag was heated to 1500-1550 °C / 2732-2822 °F) , but heat transfer from slag to the metal bath was not as effective (e.g., metal was only around 1400 °C / 2552 °F) . Moreover, improving the heat transfer from slag to the metal bath was difficult to remedy. The temperature delta between tapped metal and tapped slag was typically around 100-150 °C (around 180-270 °F) , and in some cases 200 °C (360 °F) or higher. Heat-to-bath was limited as a result, and this imposed significant productivity and efficiency penalties. A potential cause was believed to be a function of solids injection lance configuration, but changes in the lance arrangements (e.g., shifting from 8 lances to 2 "mega-lances") only minimally eased the issues, which essentially remained unresolved.

[0056] A slag drain test was performed on the 6m SRV, which involved opening a taphole through the side wall at the metalslag interface whilst the SRV was running normally, then measuring temperature and sampling tapped metal and slag. Results indicated that the metal/slag temperature at the location of the slag drain taphole was around 150 °C (around 270 °F) colder than that of slag tapped normally (e.g., at the slag notch higher up) , and also about 50 °C (about 90 °F) colder than that of metal tapped at the forehearth. Snap-quenched slag samples were taken from both the slag notch and the slag drain for morphological analysis. Samples taken from the slag notch (higher up, hotter) showed uniform (fully molten) morphology, whereas samples taken from the slag drain showed the presence of crystalline phases indicating that the material at this location had a temperature significantly below its liquidus temperature. The analysis confirmed the presence of unexpectedly cold metal and slag at the outer periphery of the 6m SRV just below the slag layer.

[0057] Slag that is thrown against water-cooled elements in the SRV forms a freeze layer that is typically 20-30 mm (0.79- 1.18 inches) in thickness. As described above, there is a transition region between solid slag in the freeze layer and hot, fully liquid slag further away from the freeze layer. The transition region is expected to contain semi-solid slag (e.g., mixture of solid slag and viscous slag) of high viscosity, containing crystalline phases consistent with precipitates from bulk slag. It is further expected that this type of semi-solid slag could migrate slowly downwards along the walls under gravity, eventually finding its way to the metal-slag interface. At this location, it may effectively float on the molten metal. It is believed that the material sampled in the slag drain trial was taken from semi-solid slag located at the metal-slag interface .

[0058] The presence of the semi-solid slag at the metal-slag interface indicates a more significant potential issue in that the temperature of metal immediately adjacent to the semi-solid slag is also below the desired temperatures. Bulk metal temperature in the bath (e.g., as measured at the forehearth plus an estimated heat loss of about 20 °C (36 °F) across the forehearth itself) was thus estimated to be about 70 °C (126 °F) hotter than metal adjacent to the semi-solid slag at the location of the slag drain taphole. This implies that the uppermost part of the metal bath, at the outer periphery near the vessel wall, was about 70 °C (126 °F) colder than bulk metal (e.g., molten mixed metal) in the center of the SRV (e.g., center zone) .

[0059] Analysis of metal-bath fluid mechanics suggests metal depth and mixing in the cold shoulder zone appear to be connected. Injection of solids results in a more or less central metal upwelling into the central fountain zone, with an associated zone of turbulence around the central injection active area. For continuity, whatever metal has been displaced upwards in the central zone of the SRV is replaced locally by metal flowing in from elsewhere. If the metal bath is deep, this metal replacement flow can come from the sides and from below, which is consistent with normal liquid flow in a large body of liquid. Under such conditions the upper outer periphery, that is the cold shoulder zone, is not necessarily engaged in mixing, and thus, may become a stagnant "dead spot" (e.g., little or no mixing) . With little metal movement into and out of this cold shoulder zone, natural heat losses from the refractory wall can lead to a degree of local metal cooling, hence the potential cause of the observed results of the slag drain test.

[0060] In a shallow metal bath, such as that in the pilot plant SRV (i.e., 2.7m SRV) , metal replacement cannot come as much from below (e.g., because the floor is in the way) , and instead is obliged to flow in more strongly from the sides. As such, in the pilot plant SRV, the zone of liquid turbulence associated with the injection plume is "squashed" from below, and thus, naturally the metal turbulence region likely expands in a lateral direction towards the vessel walls. As a result, there is significantly stronger metal convection into and out of the cold shoulder zone, with a consequential increase in metal temperature in this zone. High viscosity cold semi-solid slag (e.g., having the solid slag and viscous slag) in the transition area moving down the wall will therefore encounter a significantly hotter metal layer relative to the slag liquidus temperature .

[0061] As described earlier, semi-solid slag (e.g., viscous slag having solid-containing slag) arriving at the metal-slag interface can, if it remains cold enough, form a scum layer that floats on the molten metal and penetrates as far as possible towards the center of the SRV. At some point along a radial line from the wall to the center, metal mixing and temperature increases sufficiently such that the scum layer having the semisolid slag will be broken up, melted, and moved away (e.g., convected or mixed) . The scum layer therefore would have a dynamic equilibrium, with a given average size, in the form of a doughnut-shaped ring (in a plan view) . The outer diameter of the ring is defined by the SRV wall, and inner diameter of the ring is defined by local metal mixing and temperatures across the metal-slag interface.

[0062] This scum layer (e.g., doughnut-shaped, or the like) can provide a barrier that effectively reduces the metal-slag heat transfer. Within the "scum radius" in the outer regions, the barrier effectively limits free liquid metal and slag movement in both upward and downward directions. The smaller the scum radius, that is, the smaller the distance from the outer wall to the radial point where scum is broken, melted, and moved away, the more readily bulk metal and bulk slag layers in the SRV will be able to interact and exchange heat. This is believed to be the reason why the pilot plant SRV (i.e., 2.7m) performed better than the 6m SRV with respect to slag-metal heat transfer .

[0063] A key issue identified is that stagnant metal in the cold shoulder zone leads to local cooling, and this in turn allows the scum layer to grow more than it otherwise would. To improve the metal-slag heat transfer efficiency in larger SRVs (e.g., deep metal SRVs) , metal mixing (e.g., passive and/or active) should be promoted in the cold shoulder zone. As described herein, the mixing in the cold shoulder zone may be improved in a number of ways through different means. However, the core objective is to bring a sufficient amount of hot bulk molten metal into the cold shoulder zones to break, mix, and melt the scum layer and widen the central "active core" zone for free metal-slag mixing and heat transfer.

[0064] As described herein, the means for promoting metal mixing (e.g., passive mixing and/or active mixing) at the cold shoulder zone may comprise (i) a split-level refractory hearth with two refractory floor levels, (ii) a refractory hearth that utilizes one or more gas bubbling devices, and/or (iii) at least one pair of solids injection lances in which a first opposing lance of the pair provides the injected feed solids for the pair at any given time before switching to the second opposing lance of the pair.

[0065] With respect to the split-level refractory hearth, by making a majority of the SRV metal bath shallow enough, passive radial metal mixing is promoted (as per the pilot plant 2.7m SRV) , whilst retaining a deep-bath zone adjacent to the forehearth connection and the end-drain taphole for safety purposes . [0066] Alternatively, or additionally, deliberate injection of additional stirring gas into the bath by appropriate means may be used, such that metal mixing near the walls is enhanced and the required heat transfer outcome is achieved.

[0067] Moreover, alternatively or additionally, the process may comprise deliberate use of paired one-sided solids injection lances with injection plumes strong enough to promote the necessary level of convection in the metal layer at the opposite wall. A strategy of alternating between opposite lances (in a given pair) on a regular cycle could thus be used to control the scum layer, using the relatively long time-constant associated with hot metal in the wall region cooling sufficiently before the scum layer can re-establish itself in a meaningful way.

[0068] Referring to the figures, Figure 1A illustrates a side cross-sectional view of a direct smelting vessel 101 that forms a part of a plant that is suitable particularly to be used to carry out the HIsarna process as described herein. Moreover, Figure IB illustrates a top cross-sectional view of the direct smelting vessel 101 of Figure 1A. As illustrated in Figure 1A, a layer of molten slag 102 is located above a layer of molten metal 103, supported by a refractory-lined hearth 104 within the SRV 120.

[0069] The direct smelting vessel 101 utilizes two solids injection lances 105 for injecting coal and additives into the molten metal bath to penetrate the molten metal layer 103 and form a turbulent injection zone 106. The bottom of the injection zone 106 is determined by conditions at the exit of the injection lances 105 and is typically located around 200-300 mm (around 7.9-11.8 inches) below the quiescent metal level in the SRV 120. [0070] The hearth bottom illustrated in Figure 1A includes two different levels. For example, a main level (otherwise described as a first level) , comprising 60, 65, 70, 75, 80, 85, 90, 95, or a range of percentages (e.g., which fall within, outside, or overlap these values) of the plan area (cross- sectional area) of the refractory heath, may have a higher floor level. In particular embodiments, the area of the main level having the higher floor level is preferably at least 70%. In other embodiments, the area of the main level having the higher floor level ranges between about 75-85%, and in some embodiments is preferably about 80%. The remaining percentage of the area of the hearth floor is a secondary level (otherwise described as a second level) adjacent to the forehearth connection 109 that is deeper than the main level. In particular embodiments, the percentage of the secondary level ranges between 15-25% of the area of the floor of refractory hearth, and in some embodiments is preferably about 20%. Floor height in the main level may be selected such that the working metal depth 107 is no more than about 2x the calculated metal injection depth from the lance injection plumes. In practice this translates to a metal bath depth around 400-600 mm (around 15.7-23.6 inches) in a commercial-scale SRV (e.g., a 6m SRV, or the like) . It should be understood that the bath depth may change based on the diameter of the refractory hearth (e.g., scaled as the diameter changes) . As such, the ratios of the depths described herein may be used to scale the depths for different SRVs with different diameters .

[0071] The height of the floor in the secondary level may be set to meet safety requirements around maintaining a forehearth seal (e.g., 1200-1500 mm, or 47.2 to 59.1 inches, for a commercial scale 6m SRV) . The secondary level may be sized to act as a metal sump accommodating both the forehearth connection 109 and one or more end-drain tapholes 110. In this type of refractory arrangement, strong lateral metal mixing into the cold shoulder zone will occur naturally (e.g., passively from the perspective of a plant operator) . This will provide the necessary "melt-back" to keep the scum layer small and allow free metal-slag interaction for heat transfer. In turn, this leads to lower FeO in slag, higher productivity, higher efficiency and lower cost. For slag formulations where bulk foaming is a potential issue (e.g., iron ores containing 2-6% titania) , this also leads to reduced foaming potential and more reliable operation of the SRV.

[0072] Figures 2A and 2B illustrate an SRV 201 with the refractory floor being configured in the conventional manner having a metal bath depth around 1200-1500 mm (around 47.2 to 59.1 inches) across the full diameter of a 6m SRV.

[0073] As illustrated in Figures 2A and 2B, in some embodiments of the present invention, in order to mix the molten metal in SRVs, and in particular, promote mixing at the cold shoulder zone, a series of downwardly angled bubbling lances 202 may be utilized. The bubbling lances 202 direct bubbling stirring gas (e.g., argon gas, or the like) into the metal bath, which promotes gas stirring in the molten metal (e.g., similar to the use of gas bubbling to promote mixing in steel ladles) . [0074] Gas bubblers 202 (e.g., argon bubblers, or the like) are typically heavy-wall stainless steel tubes with an internal diameter (ID) of about 5 mm (about 0.20 inches) , lined with an outer alumina layer around 5-15 mm (around 0.20-0.59 inches) thick. The design of these bubblers is such that, if backpressure is lost for any reason, molten metal will attempt to push back up into the bubbler but will be frozen there (e.g., by virtue of the thermal mass of the tube wall relative to that of liquid metal) . In this manner, an inherently fail-safe design is possible, which does not compromise the rest of refractory lining in the event of a bubbler failure.

[0075] These bubblers provide an active metal mixing impulse into the otherwise stagnant cold shoulder zone, thereby achieving similar benefits to those described with respect to the main and secondary levels of the split-level refractory hearth .

[0076] In some embodiments, paired one-sided solids injection lances with injection plumes strong enough to promote convection in the metal layer at the opposite wall are used. A strategy of alternating between opposite lances (in a given pair) on a regular cycle could thus be used to control the scum layer, using the relatively long time-constant associated with hot metal in the wall region cooling sufficiently before the scum layer can re-establish itself in a meaningful way. As such, at least one pair of opposing solids injection lances may be utilized, for which substantially all the bath-injected feed solids assigned to each pair are fed via one branch of that pair at any given time (e.g., for at least 50% of the total time in normal operation) . Feed via one branch of each lance pair is then followed by reversal to the other branch, either immediately following the previous one-branch period or at some later time. As such, this asymmetric lance injection together with metal thermal inertia may be used to achieve similar benefits to those described with respect to the main and secondary levels of the split-level refractory hearth and/or the gas bubblers described above. It should be understood that providing substantially all of the feed solids may include all or all with a negligible amount of feed solids coming from the opposing lance. Moreover, in some embodiments, a substantial majority of the feed solids may be assigned to one of a pair opposing lances. As such, in some embodiments the feed solids being provided by one branch of a pair of opposing lances may include 99, 98, 97, 96, 95, 94, 93, 92, 91, 90, 85, 80, 75, or the like percentage of feed solids for that pair of opposing lances .

[0077] In some embodiments, different means for promoting metal mixing in the cold shoulder zone may be used in combination. For example, the means may include one or more of the SRV having the main and secondary levels described with respect to Figures 1A and IB, using the bubblers 202 to provide improved melting in the cold shoulder zones, using at least one pair of opposing solids injection lances and alternating solids feeds between each lance in the pair, and/or using other like means not specifically described herein.

[0078] Figure 3 provides a molten bath-based method for direct smelting metalliferous material, such as iron oxides, and producing molten metal in a direct smelting vessel. As illustrated in block 310 of Figure 3, metalliferous material (e.g., ore, such as iron ore fines, or the like) is injected into the SRV 120 using solids lances 105 and/or into a smelt cyclone 130 from which it then enters the SRV 120.

[0079] In some embodiments, an ore pre-treatment unit, such as an ore dryer or an ore pre-heater, may be utilized for drying and/or heating the solid metalliferous material before it is injected through the injection lance 105 into the SRV 120 or before it is injected into the smelt cyclone 130. Moreover, a metalliferous material dispensing/metering unit may be utilized for the pre-treated metalliferous material to control the timing and amount of metalliferous material used.

[0080] Block 320 of Figure 3 illustrates that solid carbonaceous material (e.g., coal, or the like) is injected through at least one injection lance (e.g., extending downwardly and inwardly, or the like) into a molten bath in the SRV 120, such that injected solids at least partially penetrate the molten metal layer. Moreover, a carbonaceous material dispensing/metering unit may be utilized for the carbonaceous material to control the timing and amount of carbonaceous material used.

[0081] Figure 3 further illustrates in block 330, that a means of promoting metal mixing in the cold shoulder zone adjacent the wall and below the slag layer is utilized to control the scum layer described herein. The means for promoting metal mixing is used to maintain the metal at the cold shoulder zone at a temperature of no more than 40 °C (72 °F) , or other temperatures described herein, below that of the metal in the forehearth of the SRV.

[0082] As illustrated in block 330, the means includes promoting passive radial metal mixing, whilst retaining a deepbath zone adjacent to the forehearth connection using the splitlevel refractory hearth described herein.

[0083] Alternatively, or additionally, the means includes deliberate injection of additional stirring gas into the bath, such as by gas bubblers, which enhance metal mixing near the walls of the SRV to achieve slag-metal heat transfer.

[0084] Alternatively, or additionally, the means includes deliberate use of paired one-sided solids injection lances with injection plumes strong enough to promote the convection in the metal layer at the opposite wall. Alternating between opposite lances of a given pair on a regular cycle can control the formation of the scum layer by using the relatively long timeconstant associated with hot metal in the wall region cooling sufficiently before the scum layer can re-establish itself in a meaningful way.

[0085] To supplement the present disclosure, this application further incorporates entirely by reference the following references :

1. US Patent 6989042 "Direct Smelting Process and

Apparatus", Priority 17 April 2000

2. US Patent 8221675 "Direct Smelting Vessel and Cooler

Therefor", Priority 18 May 2006 3. US Patent 9175907 "Direct Smelting Process and

Apparatus", Priority 9 Feb 2010

4. Australian Patent 2011301784 (WO2012/034184 ) "Direct Smelting Process", Priority 15 Sept 2011

5. US Patent 9359656 "Direct Smelting Process", Priority 9 Feb 2012

6. PCT/AU2012/000293 ( WO2012 / 126055 ) "Direct Smelting Process for High Sulphur Feed", Priority 21 March 2012

7. PCT/AU2012/001486 ( WO2013/ 082658 ) "Starting a Smelting Process", Priority 6 Dec 2011

8. PCT/AU2012/001481 ( WO2013/ 082653 ) "Starting a Smelting Process", Priority 6 Dec 2011

9. PCT/AU2012/001487 ( WO2013/ 082659 ) "Starting a Smelting Process", Priority 6 Dec 2011

10. CT/AU2014/001098 (WO2015/081376) "Smelting Process and Apparatus", Priority 4 Dec 2014

11. PCT/AU2014 / 001146 ( WO2015/ 089563 ) "Smelting Process and Apparatus", Priority 19 Dec 2014

[0086] Specific embodiments of the invention are described herein. Many modifications and other embodiments of the invention set forth herein will come to mind to one skilled in the art to which the invention pertains, having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the speci fic embodiments disclosed and that modi fications and other embodiments and combinations of embodiments are intended to be included within the scope of the appended claims . Although speci fic terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation .

Claims

What is Claimed Is :

1 . A method for direct smelting of metalli ferous material and producing molten metal in a direct smelting vessel , the method comprising : inj ecting solid carbonaceous material through at least one inj ection lance extending into the direct smelting vessel such that solids penetrate at least partially into a molten metal layer in the direct smelting vessel , wherein a slag layer is floating on the molten metal layer ; and promoting metal mixing at a zone immediately below the slag layer adj acent to a vessel wall of the direct smelting vessel .

2 . The method of claim 1 , wherein the metal mixing reduces a volume occupied by a stagnant region cold enough to be capable of supporting a semi-solid slag layer that restricts metalslag heat trans fer .

3 . The method of claim 1 , wherein the metal mixing maintains an ef fective temperature delta between tapped metal at a forehearth and metal at the vessel wall of no greater than 40 ° C .

4 . The method of claim 1 , wherein the metal mixing is promoted using the direct smelting vessel comprising : a split-level refractory floor with two refractory floor levels comprising a first level having a first depth that supports a first metal depth and a second level having a second depth that supports a second metal depth; wherein the second metal depth is greater than the first metal depth; and wherein the first depth that supports the first metal depth promotes the metal mixing by metal convection into and out of the zone below the slag layer adjacent to the vessel wall .

5. The method of claim 4, wherein the first level comprises at least 70% of a cross-sectional area of the split-level refractory floor.

6. The method of claim 4, wherein the first depth supports the first metal depth that is not greater than 900mm.

7. The method of claim 4, wherein the first depth supports the first metal depth that is not greater than 700mm.

8. The method of claim 4, wherein the first depth supports the first metal depth that is not greater than 600mm.

9. The method of claim 4, wherein the second depth supports the second metal depth that is at least 300mm greater than the first metal depth.

10. The method of claim 1, wherein the metal mixing is promoted by injecting gas in the direct smelting vessel using one or more gas bubbling devices for promotion of metal convection to the zone below the slag layer adjacent to the vessel wall.

11. The method of claim 10, wherein the gas comprises argon gas or nitrogen gas.

12. The method of claim 1, wherein the metal mixing is promoted by using one or more pairs of solids injection lances in the direct smelting vessel, wherein one branch of a pair of solids injection lances provides at least a majority of the injected feed solids for the pair of solids injection lances at any given time.

13. The method of claim 12, wherein injection of the feed solids through the one branch of the pair of solids injection lances is reversed to an opposing branch of the pair of solids injection lances, either immediately following injection through the one branch or a period of time later.

14. An apparatus for direct smelting metalliferous material and producing molten metal and molten slag, the apparatus comprising : a direct smelting vessel comprising at least one of:

(a) a split-level refractory hearth with two refractory floor levels comprising: a first level having a first depth that supports a first metal depth; and a second level having a second depth that support a second metal depth, wherein the second metal depth is greater than the first metal depth;

(b) a refractory hearth with one or more gas bubbling devices; or

(c) one or more pairs of solids injection lances, wherein one branch of a pair of solids injection lances provides at least a majority of the injected feed solids for the pair of solids injection lances at any given time ; wherein the split-level refractory hearth, the one or more gas bubbling devices, or the one or more pairs of solids injection lances promotes metal mixing at a zone below a slag layer adjacent to a vessel wall of the direct smelting vessel.

15 . The apparatus of claim 14 , wherein the metal mixing reduces a stagnant region capable of supporting a semi-solid slag layer that restricts metal-slag heat trans fer between the molten metal and the molten slag .

16 . The apparatus of claim 14 , wherein the metal mixing maintains an ef fective temperature delta between tapped metal at a forehearth and metal at the vessel wall of no greater than 40 ° C .

17 . The apparatus of claim 14 , wherein the direct smelting vessel comprises the split-level refractory hearth .

18 . The apparatus of claim 17 , wherein the first level comprises at least 70% of the cross-sectional area of the refractory floor, wherein the first depth supports the first metal depth that is not greater than 900mm, and wherein the second depth supports the second metal depth that is at least 300mm greater than the first metal depth .

19 . The apparatus of claim 14 , wherein the direct smelting vessel comprises the refractory hearth with the one or more gas bubbling devices .

20 . The apparatus of claim 14 , wherein the direct smelting vessel comprises the one or more pairs of solids inj ection lances .