SULFUR MANAGEMENT IN A SMELTING PROCESS

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 63/721,055 filed on Nov. 15, 2024, the entirety of which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a process and an apparatus for smelting of a metalliferous material with control of sulfur introduction for the reduction of slag foaming and/or process instability.

BACKGROUND

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. The HIsmelt process utilizes an SRV, while the HIsarna process utilizes an SRV in conjunction with a CCF. Although this present disclosure relates primarily to the HIsarna process, it may also be applied to the HIsmelt process.

The HIsmelt process relates to direct smelting of metalliferous material in the form of iron and its oxides (which may be unreduced, partly reduced or highly pre-reduced) and producing molten carbon-containing iron. The process includes forming a bath of molten iron and slag in a vessel (SRV). Solid carbonaceous material (e.g., coal, or the like) is injected into the bath. Metalliferous material may be injected into the bath and/or fed into the slag layer by dropping from above. Solid carbonaceous material acts as a reductant of iron oxides and a source of energy for forming the molten metal bath within the SRV.

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 to satisfy the thermal energy required to heat and smelt the metalliferous materials.

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 (at relatively high oxygen potential) to the bath where it is used for smelting purposes (at relatively low oxygen potential). As such, the plume effectively acts as a heat pump.

In the HIsmelt process, solid carbonaceous material and optionally metalliferous material are injected into the molten bath through a number of solids injection lances. These lances may be inclined to the vertical so as to extend downwardly and inwardly through a side wall of the vessel and into a lower region 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. Offgas 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 closed cooling circuit.

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).

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 key difference between the two is that in the HIsarna process incoming metalliferous feed (typically iron ore) is not injected or dropped directly into the bath but is rather heated, partially pre-reduced, and substantially melted in a smelt cyclone (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 final smelting proceeds. Principally, carbon-rich metal reacts with iron(II)oxide (FeO) in slag to produce additional carbon-containing iron metal. 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.

SUMMARY

In examples, a direct smelting process for production of molten metal and slag is provided, the process comprising: introducing to a smelt reduction vessel (SRV) comprising molten metal, independently, a first solids amount and a second solids amount, the first solids amount comprising a first sulfur level and the second solids amount comprising a second sulfur level different from the first sulfur level; controlling a metal sulfur range in the molten metal by independently manipulating the first solids amount and the second solids amount introduced to the SRV; and reducing slag foaming and/or instability during metal smelting operation of the SRV.

In aspects, the process further comprises determining a metal sulfur value and/or a metal carbon value by analysis of the slag and/or determining a FeO in slag value, or combinations thereof. In aspects, alone or in combination with any of the previous aspects, the determining the metal sulfur value, the carbon value, and/or the FeO in slag value is performed continuously, semi-continuously, periodically, or randomly within a repeated time interval.

In aspects, alone or in combination with any of the previous aspects, the process further comprises adjusting at least one of the first sulfur level and the second sulfur level introduced into the SRV based on the metal sulfur value. In aspects, alone or in combination with any of the previous aspects, the process further comprises maintaining the metal sulfur value in the molten metal within a range of at least 0.07 weight percent and below 0.15 weight percent. In aspects, alone or in combination with any of the previous aspects, the process further comprises adjusting at least one of the first sulfur level and the second sulfur level introduced into the SRV to maintain the metal carbon value in the molten metal within a range of 3.0 to 4.5 weight percent. In aspects, alone or in combination with any of the previous aspects, the process further comprises adjusting at least one of the first sulfur level and the second sulfur level introduced into the SRV to maintain the FeO in slag value within a range of greater than 3 weight percent and less than 8 weight percent. In aspects, alone or in combination with any of the previous aspects, the process further comprises maintaining the metal carbon value in the molten metal in a range of about 3 weight percent.

In aspects, alone or in combination with any of the previous aspects, the process further comprises, during startup of the SRV, controlling introduction of the first and the second solids feed so that a metal sulfur level is maintained above 0.07 wt. %. In aspects, alone or in combination with any of the previous aspects, the process further comprises, during an operation of at least 50% of maximum productivity of the SRV, a ratio of the first sulfur level and the second sulfur level is controlled such that FeO in the slag is less than 8 wt. %.

In aspects, alone or in combination with any of the previous aspects, the first sulfur level is greater than or less than the second sulfur level. In aspects, alone or in combination with any of the previous aspects, the first solids feed is fed continuously to the SRV and the second solids feed is fed intermittently on an as-needed basis. In aspects, alone or in combination with any of the previous aspects, the first sulfur level is less than or equal to 0.5 wt. % sulfur. In aspects, alone or in combination with any of the previous aspects, the second sulfur level is greater than 0.5 wt. % sulfur.

In aspects, alone or in combination with any of the previous aspects, the at least one of the two or more solids feeds comprises at least one carboniferous material. In aspects, alone or in combination with any of the previous aspects, the at least one carboniferous material comprises biochar. In aspects, alone or in combination with any of the previous aspects, the at least one carboniferous material comprises natural gas pyrolysis char. In aspects, alone or in combination with any of the previous aspects, the at least one carboniferous material comprises a combination of biochar and natural gas pyrolysis char.

In aspects, alone or in combination with any of the previous aspects, the at least one of the first or second solids feed comprises a sulfur additive. In aspects, alone or in combination with any of the previous aspects, the sulfur additive is slag with at least 2 wt. % sulfur content (“sulfur slag”). In aspects, alone or in combination with any of the previous aspects, the sulfur additive is gypsum. In aspects, alone or in combination with any of the previous aspects, the sulfur additive is one or more of iron-sulfur compounds, for example, iron sulfate or iron sulfide. In aspects, alone or in combination with any of the previous aspects, the sulfur additive is two or more of iron sulfide, iron sulfate, gypsum, and sulfur slag.

In aspects, alone or in combination with any of the previous aspects, the at least one carboniferous material comprises a first carboniferous material and a second carboniferous material. In aspects, alone or in combination with any of the previous aspects, the first carboniferous material comprises coal containing the first sulfur level and the second carbonaceous feed is biochar and/or natural gas pyrolysis carbon with the second sulfur level, the second sulfur level being less than 0.1 wt. %.

In aspects, alone or in combination with any of the previous aspects, the method further comprises, during startup of the SRV, controlling introduction of the first and the second solids feed so that a metal sulfur level is maintained above 0.07 wt. %. In aspects, alone or in combination with any of the previous aspects, the method further comprises, during an operation of at least 50 percent of maximum productivity of the SRV, a ratio of the first sulfur level and the second sulfur level is controlled such that FeO in the slag is less than 8 wt. %.

In aspects, alone or in combination with any of the previous aspects, the first sulfur level and the second sulfur level is controlled such that metal sulfur content is greater than 0.07 wt. % independent of a metal ore introduction rate.

In aspects, alone or in combination with any of the previous aspects, the SRV further comprises a cyclone converter furnace (CCF).

In aspects, alone or in combination with any of the previous aspects, SRV sulfur input is controlled such that metal sulfur content does not fall below 0.07 wt. % at any time, regardless of ore injection rate.

In other examples, a method of controlling slag foaming and process instability in an smelt reduction vessel (SRV) is provided, the method comprising: (i) introducing, to the SRV comprising molten metal, an amount of a first solids comprising a first sulfur content and a second solids feed comprising a second sulfur content; (ii) determining a metal sulfur content of the molten metal; (iii) adjusting at least one of the first sulfur content or the second sulfur content based on the metal sulfur content of the molten metal; (iv) maintaining, within a target zone, the metal sulfur content in the molten metal by repeating steps (ii) and (iii); and (v) continuously reducing foaming and slag instability of the SRV during operation thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is described further by way of examples with reference to the accompanying drawings, of which:

FIG. 1 is a diagram of carbon wt. % in metal vs FeO wt. % in slag and a superimposed target zone of metal sulfur content for reducing foaming and instability during SRV operation.

FIG. 2 is an example of a direct smelting process according to the current present disclosure involving an SRV, a CCF and a coal injection system using two different coal types.

FIG. 3 is an example of the process according to the current present disclosure using only one coal type, supplemented by intermittent use of a sulfur additive feed.

FIG. 4 is an example of the process according to the current present disclosure using (i) one coal type, (ii) a carbonaceous material with very low sulfur and (iii) intermittent use of a high sulfur feed.

DETAILED DESCRIPTION

The present disclosure is directed to an improved direct smelting process. In examples, the current present disclosure is directed to optimizing the rate of FeO reduction at the metal-slag interface. In examples, manipulation of carboniferous sulfur in feed materials is used. In examples, a level of metal sulfur is provided that balances iron oxide (FeO) reduction in the smelting process. In examples, controlling a level of sulfur so as to balance FeO reduction achieves increased productivity and efficiency. In examples, controlling a level of sulfur so as to balance FeO reduction avoiding problems associated with “over-activation” and “under-activation,” among other problems, which reduces or eliminates process disturbances, e.g., slag foaming.

In examples, the presently disclosed process comprises a smelt reduction vessel (SRV) optionally connected to a cyclone converter furnace (CCF). The present disclosure further comprises carboniferous feed material (such as coal) introduction into the bath, with controlled manipulation of total sulfur input such that the process can run without disturbance at both low and high iron ore introduction rates.

In examples, two different carboniferous feeds, one with low sulfur content and the other with higher sulfur content are used. When the process is in startup or otherwise operated at low rates, the higher sulfur carboniferous feed is used in excess or without the low sulfur feed. This keeps metal sulfur at a reasonably high level, for example, about 0.07-0.15 wt. % metal sulfur so as to provide metal carbon below over-saturated levels, for example, below about 4.5 wt. % metal carbon. Metal sulfur interferes with carbon dissolution, so higher metal sulfur generally means lower metal carbon. If the metal becomes over-saturated with carbon (for example, because sulfur is too low), potential for slag foaming and/or unstable metal-slag interfaces increases.

When the SRV process is operated at high rate, e.g., more than 50% of maximum capacity, in examples, carboniferous feed is gradually transitioned to a lower sulfur total bath feed, causing metal carbon to drop and FeO in slag to increase. If this is allowed to go unchecked for too long, slag FeO could increase beyond about 10 wt. % and there is an increasing risk that it could become “oxygen conducting” (as in BOF or EAF slag), leading to breakdown of the smelting process and undesirable slag foaming. As the presently disclosed method provides for deliberately lowering metal sulfur under these conditions, the FeO smelting rate at the metal-slag interface increases, leading to higher metal carbon and lower FeO in slag. This improves efficiency and moves the process away from the high FeO area of slag foaming instability.

To the accomplishment of the foregoing and the related ends, one or more examples of the present disclosure 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 one or more examples. These features are indicative, however, of but a few of the various ways in which the principles of various examples may be employed, and this description is intended to include all such examples and their equivalents.

Examples of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all, examples of the present disclosure are shown. Indeed, the present disclosure may be embodied in many different forms and should not be construed as limited to the examples set forth herein; rather, these examples are provided so that this disclosure will satisfy applicable legal requirements.

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 (i) at high temperatures, (ii) only at sufficiently low oxygen potential and (iii) are highly endothermic, requiring a large heat supply to maintain constant process conditions.

The term “biochar” as used herein is a broad term, and is to be given its ordinary and customary meaning to a person of ordinary skill in the art (and is not to be limited to a special or customized meaning), and refers without limitation to any material obtained from the thermochemical conversion of biomass in an oxygen-limited environment, for example, carbon and ashes remaining after the pyrolysis of biomass. An example of biochar includes charcoal.

The phrases “carboniferous feeds” and “carbonaceous material” are used interchangeably, and are broad phrases, and are to be given their ordinary and customary meaning to a person of ordinary skill in the art (and is not to be limited to a special or customized meaning), and refers without limitation to coal and other carbon-based material derived from plant and animal life from the Paleozoic period.

The phrase “metalliferous material” as used herein is a broad phrase, and is to be given its ordinary and customary meaning to a person of ordinary skill in the art (and is not to be limited to a special or customized meaning), and refers without limitation to a metal-containing material, deposit, or ore typically used in metal making. In examples, “metalliferous material” refers to iron ore and/or partly pre-reduced or partly metallized iron ore.

The phrases “metal sulfur” and “metal carbon” as used herein are broad phrases, and are to be given their ordinary and customary meaning to a person of ordinary skill in the art (and are not to be limited to a special or customized meaning), and refers without limitation to an amount (e.g., weight percent) of sulfur and carbon, respectively, present in the molten metal of the SRV during operation thereof. “Metal sulfur” and “metal carbon” are synonymous with “sulfur in metal” and “carbon in metal,” respectively.

In examples, SRV productivity is correlated to the rate of FeO reduction by dissolved metal carbon at the metal-slag interface. At normal SRV conditions, two factors are known to effect SRV productivity:

• • (i) A total metal-slag interfacial area that is generated by gas and solids injection. Injected coal, for example, releases contained volatiles “explosively” upon heating, thus creating a strong upward plume in or near the center of the bath. This plume drags metal and slag upwardly, generating a transient fresh metal-slag interfacial area. The total amount of area is a function of injection fluid mechanics and the chemical nature of the solids injectants. While not to be held to any theory, this total area, although impossible to measure with precision, is believed to be many times greater than that of a quiescent bath metal-slag interface (without material injection); and
  • (ii) A reaction rate of FeO, on a per unit interfacial area basis, with dissolved metal carbon of the bath. While not to be held to any theory, this rate is considered to be controlled by liquid-phase mass transfer in the boundary layer on the slag side (FeO diffusing through an FeO-depleted slag film at the interface). However, it is also known to be influenced by how much sulfur is present in metal.

Sulfur is known to be surface active in a molten metal bath, and while not to be held to any theory, implies high sulfur levels interfere with and may slow down the smelting reaction. Sulfur is also known to inhibit the dissolution of carbon (eg from coal) into metal, implying high sulfur is naturally associated with lower metal carbon (hence a lower driving force for FeO reduction from slag).

Foaming in a smelting process negatively impacts SRV fluid mechanics and leads to unwanted process disturbances. Thus, in examples of the presently disclosed method, avoidance of slag foaming in the SRV is provided. Although there can be various foaming triggers including lumps of solid FeO-rich material dropping into the bath, two in-bath foam generation mechanisms are addressed by the present disclosure:

• • (i) Normally, char particles are non-wetting to slag in the SRV and the presence of such char particles acts as a natural foam-breaker. However, if FeO is above about 10 wt. % in the slag, then it becomes possible to deposit a thin layer of metal on the surface of these char particles. This makes them mutually wetting to metal and slag and removes their ability to break “beer foam” bubbles arising from ore smelting at the interface. The slag itself also gains a significantly higher proportion of Fe³⁺ ions (relative to Fe²⁺). This allows slag to effectively “conduct” oxygen via the Fe³⁺ to Fe²⁺ oxidative shift. This in turn means top-injected oxygen in the SRV can find its way down to the metal interface below the slag, thereby consuming carbon (e.g., a “short-circuit” reaction mechanism). Thus, in the presently disclosed method, SRV slag is maintained below about 10 wt. % FeO to avoid the short-circuit foaming mechanism and loss of process integrity; and
  • (ii) If metal sulfur is too low and metal carbon is too high, there is another competing foaming mechanism. This type of foaming has been observed by the applicant on both HIsmelt and HIsarna plants and is believed associated with uncharacteristically low sulfur content coal. As a result of the introduction of such low sulfur content coal, what is observed is super-saturated carbon of around 4.5 wt. % or above, together with slag FeO content of around 3 wt. % or less and resultant undesirable, persistent, slag foaming. While not to be held to any theory, the low sulfur coal introduction resulting in persistent slag foaming is thought to be related to insufficient sulfur moderation of the smelting rate. While not to be held to any theory, with very low metal sulfur, reaction rates at the metal-slag interface become so high that the interface becomes unstable.

It is also believed that metal carbon that is super-saturated under super-saturated carbon of around 4.5 wt. % or above, together with slag FeO content of around 3% or less conditions, can result in fine graphite flakes being expelled when metal is cooled incrementally (for example, at the walls of the SRV just below the bulk metal-slag interface). The physical presence of such flakes could also affect the interface instability described above.

Thus, the presently disclosed method is directed to avoiding a metal sulfur decrease in concentration during SRV operation so that metal carbon is maintained below about 4.5 wt. %, below about 4.0 wt. %, below about 3.5 wt. %, or above about 3 wt. %, and FeO in slag maintained above about 3 wt. %, above about 4 wt. %, above about 5 wt. %, above about 6 wt. %, above about 7 wt. %, or less than 8 wt. % in the slag of the SRV process. In examples, the presently disclosed method maintains metal carbon below about 4.5 wt. %, below about 4.0 wt. %, below about 3.5 wt. %, or above about 3 wt. %, and simultaneously maintains FeO in slag above about 3 wt. %, above about 4 wt. %, above about 5 wt. %, above about 6 wt. %, above about 7 wt. %, or less than 8 wt. % in the slag continuously or semi-continuously during the SRV process.

To avoiding a metal sulfur decrease in concentration during SRV operation so that metal carbon and FeO in slag are maintained as described above, sulfur-containing material introduction to the SRV molten metal is controlled so as to achieve or target a metal sulfur of greater than 0.07% independent of a metal ore introduction rate. In examples, introduction to the SRV molten metal of at least two feeds of sulfur-containing material are controlled. In examples, introduction to the SRV molten metal of at least two feeds of sulfur-containing material are controlled based on an analysis of metal carbon and/or FeO in slag. In examples, the at least two feeds of sulfur-containing material introduced to the SRV molten metal comprise different sulfur contents.

The applicant has discovered, from various SRV observations and calculations over an extended period, that slag FeO is essentially a balance between how much ore is fed into the system (directly or via a smelt cyclone) and how fast the FeO smelt-reduction reaction proceeds at the metal-slag interface.

Ore feed is thought to be introduced mostly to slag, thus, high feed rates tends to push slag FeO higher. FeO removal from slag is a function of both metal-slag interfacial area and the rate of FeO reduction at the metal-slag interface as described above. More ore (and coal) injection is consistent with greater bath mixing and splash generation, hence higher metal-slag interfacial area. While not to be held to any theory, if the intrinsic reaction rate at the interface (per unit interfacial area) remains constant, then the observed increase in slag FeO would result in increased interfacial area generation that does not quite keep up (after an ore addition rate increase) and steady-state slag FeO must increase to restore the balance between iron ore feed and FeO smelting rates. This non-equilibrium is usually also accompanied by a drop in the percentage of dissolved metal carbon.

The overall result is that, as ore feed rates increase from low to high, slag FeO naturally increases and metal carbon naturally decreases. The level of metal sulfur affects this relationship, with more sulfur leading to a higher slag FeO and lower metal carbon “path” as ore feed increases.

FIG. 1 shows a plot of slag FeO vs metal carbon. In examples, if, during operation of the SRV, metal sulfur is determined to be high, then line 105 is followed. In examples, at low iron ore injection rate the presently disclosed process runs at Point A, and as ore injection increases it moves progressively upwards and to the left. In the extreme (too much ore injection) it could move all the way to Point B, where FeO exceeds 10% and high FeO foaming occurs as described earlier.

If metal sulfur is determined to be low, line 110 is followed. In this case high injection rates (Point C) are much less likely to result in excessive (troublesome) slag FeO levels, but at low injection rates the second of the foaming mechanisms (related to interface instability) (Point C) may occur and cause instability of the process.

In examples, the SRV process is started at low ore injection rates. Higher metal sulfur is helpful under these conditions, and the reverse is true at high ore injection rates. Thus, the current present disclosure provides for dynamically targeting higher metal sulfur during startup and low ore injection rate operation, then deliberately shifting to lower sulfur in feed materials at a later time interval, when ore injection rates increase. In this manner it is possible to keep the SRV in a target zone 103 of a FeO in slag range and metal carbon range as indicated in FIG. 1.

Deviation from target zone 103 during SRV operation is possible using the determined metal sulfur values of lines 105, 110 within the ranges indicated by arrows 107, 109 that represent, in examples, an upper boundary of metal sulfur of about 0.15 wt. % (at arrow 107) and a lower boundary of metal sulfur of about 0.07 wt. % (at arrow 109). In examples, target zone 103 is defined by a target zone operational range comprising a FeO in slag range of >3 wt. % and a metal carbon range of >3% wt. % during ore introduction. In examples, target zone 103 target zone operational range comprises a FeO in slag range of <3 wt. % and less than 6 wt. %, and a metal carbon range of >3% wt. and less than about 4.5 wt. %.

During operation of the SRV, a FeO in slag range of <3 wt. % and less than 8 wt. % and a metal carbon range of >3% wt. and less than about 5 wt. % is acceptable and is subsequently controllable by adjustment of at least one of the sulfur-containing feeds until target zone 103 operational ranges are achieved.

In examples, the SRV is operated at a FeO in slag range of <3 wt. % and less than 8 wt. % and a metal carbon range of >3% wt. and less than about 5 wt. % such that the metal sulfur is controlled/maintained within a range not exceeding an amount indicated by arrow 107, which is below the amount indicated by Point B of line 105 and above Point D of line 110.

In examples, the SRV is operated at a FeO in slag range of <3 wt. % and less than 8 wt. %, and a metal carbon range of >3% wt. and less than about 5 wt. % such that the metal sulfur is controlled/maintained within a range not falling below about 0.07 wt. % sulfur, which is above the amount indicated at line 109 and above Point D of line 110, and below the amount indicated by Point B of line 105.

In examples, the SRV is operated at a FeO in slag range of <3 wt. % and less than 8 wt. %, and a metal carbon range of >3% wt. and less than about 5 wt. % such that the metal sulfur is controlled/maintained within a range of about 0.07 to about 0.15 wt. % metal sulfur.

An exemplary process 200 of the present disclosure is shown in FIG. 2, where at least two coal feed types are used, one high in sulfur and the other low in sulfur. In examples, “high in sulfur” means greater than 0.5 wt. % sulfur (ultimate analysis, dry basis) and “low in sulfur” means less than or equal to 0.5 wt. % sulfur on the same basis. Coal with a sulfur content of between 0.4-0.7 wt. % can be blended with the high/low coals described above, or can be combined with one or more sulfur additives, e.g., during startup of the SRV unit or during normal operation.

In the early part of startup of SRV 201 with optional CCF 203 and upper injection lances 213, coupled to gas-solid stream junction 212 providing for combining and/or mixing, when sulfur rates are low in the ore, the process is operated by introducing high in sulfur coal via lower injection lance 215. As ore injection increases to about 70 % of a full injection rate, coal type is gradually switched over to low in sulfur coal by changing the blend ratio between the coal sources via feed controller. Exemplary feed controllers include feed hoppers connected to mechanical feeding devices, such as screw feeders, rotary feeders, and the like. Feedback in terms of a blend ratio control is achieved via metal and slag sample analysis, so that the SRV 201 remains within the target zone as indicated in FIG. 1.

A second exemplary process 300 is shown in FIG. 3. In this case there is one coal type 305 (low sulfur content) is used. A sulfur additive 310 is also fed intermittently and selectively, as needed. This additive may be any suitable organic or inorganic sulfur-bearing feed, for example, iron sulfide, gypsum or slag comprising greater than 2 wt. % sulfur.

When the process depicted in FIG. 3 uses low sulfur coal feed 305, sulfur additive 310 may be admitted into the SRV 210 via lance 215, coupled to gas-solid stream junction 212, by feed hopper etc., to buffer the metal and ensure that “unstable interface” foaming is avoided. In examples, as ore injection rates increase, sulfur additive 310 introduction is attenuated with a feed controller, but otherwise available for subsequent low-rate conditions and adjusted as needed based on slag analysis and/or metal analysis during operation.

A third exemplary process 400 is shown in FIG. 4 using one coal type 406 of medium sulfur content and a second carboniferous material 407 that are fed, controlled by one or more feed controllers, coupled to gas-solid stream junctions 412, 413, into SRV 201. In examples, second carboniferous material 407 is biochar and/or natural gas pyrolysis char. This second carboniferous material 407 has low sulfur (<0.1 wt. % sulfur ultimate analysis, dry basis). A sulfur additive (for example, a compound of >5 wt. % sulfur content) 414 in combination with coal type 406, and carboniferous material 407 is also configured to be controllably and selectively introduced as needed to SRV 201 based on slag analysis. Sulfur additive 414 may be any suitable sulfur-bearing feed such as iron sulfide, gypsum or sulfur slag. Feed controllers can be manually or computer controlled and/or or programmed to introduce coal and/or sulfur additive at any desired rate, e.g., weight/time.

When the process is at low ore injection rates, coal feed is used and sulfur additive 414 may be introduced into the SRV 201 to buffer the metal and ensure “unstable interface” foaming is avoided. As ore injection rates increase, carboniferous material 407 (and/or pyrolysis carbon) is added. In examples, sulfur additive 414 may still be used if metal sulfur drifts too low (depending on the ratio of the two carboniferous feeds) based on slag and/or metal analysis.

In examples, the present disclosure comprises controlling the sulfur input at any time during a smelt reduction to control/maintain the metal sulfur content in a range that avoids slag foaming or slag instability. In examples, continuously or intermittently evaluating a last metal and slag analysis from the SRV is performed and subsequent sulfur input is adjusted up or down based on the analysis so as to maintain the target sulfur range of the metal sulfur content. In examples, calculations and assumptions based on previous knowledge, experience, and/or other process conditions are used in the adjustment of sulfur input.

In other examples, the direct smelting process for production of molten metal and slag comprises: controlling, independently, introduction of a first solids feed and a second solids feed into a smelt reduction vessel (SRV), the first solids feed with a first sulfur level and the second solids feed with a second sulfur level different from the first sulfur level. Adjusting the amount of the first solids feed relative to that of the second solids feed to achieve a target sulfur content in molten metal is performed based on a slag/metal analysis during operation. The analysis can be performed during a predetermined fixed time interval or randomly performed within a time interval, for example, depending on the delay of obtaining a slag/molten metal sample and performing an analysis thereof. Maintaining metal sulfur within the target range that reduces slag foaming and/or instability during metal smelting operation of the SRV is achieved.

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