TECHNICAL FIE LD The present invention relates to a process and an apparatus for smelling a metalliferous material

hi particular, although by no means exclusively, the present invention relates to a smelting process and apparatus for smelting an. iron-containing material, such as an iron ore, and producing iron.

BACKGROUND

A known molten bath-based smelting process is referred to hereinafter as the "B isarmr" process,

The term "smelting" is herein understood to mean thermal processing wherein chemical reactions that reduce metal oxides take place to produce molten metal.

The Hlsarna process and apparatus are described in International application PCT/AU99/00884 (WO 00/022176) in the name of the applicant.

The Hisarna process is associated particularly with producing molten iron from iron ore or another iron-containing material.

The Hisarna process is carried out in a smelting apparatus that includes (a) a smelting vessel that defines a smelting chamber and includes lances for injecting solid feed materials and oxygen-containing gas into the smelting chamber and is adapted to contain a bath of molten metal and slag and (b) a smelt cyclone for pre-treating a metalliferous feed material that defines a cyclone chamber and includes tuyeres for injecting solid feed materials and. oxygen-containing gas into the cyclone chamber and is positioned above and communicates directly with the smelting vessel

The term "smelt cyclone" is understood herein to mean a vessel that typically defines a vertical cylindrical chamber and includes tuyeres for injecting solid feed materials and oxygen-containing gas into the chamber and is constructed, so that feed materials supplied to the chamber move in a path around a vertical centra! axis of the chamber and can withstand high operating temperatures sufficient to at least partially .roe it metalliferous feed materials.

The smelting vessel includes refractory-lined sections in a lower hearth and water cooled panels in a side wall and a roof of the vessel, and water is circulated continuously through the panels in a continuous circuit.

The smelting vessel also includes a forehearth connected to the smelting chamber via a forehearth connection thai allows continuous metal product outflow from the vessel. A forehearth operates as a molten metal-filled siphon seal, naturally

"spilling" excess molten metal from the smelting vessel as it is produced. This allows the molten metal level in the smelting chamber of the- melting vessel to be known and controlled to within a small tolerance ··· ^■ this is essential, for plant safety.

In one form of the HIsaraa process, carbonaceous feed material (typically coal) and optionally flux (typically calcined limestone) are injected into a molten bath in the smelting chamber of the smelting vessel The carbonaceous material is provided as a source of a reductant and a source of energy. Metalliferous feed material, such as iron ore, optionally blended with flux, is injected, into and heated and partially melted and partially reduced in the smelt cyclone. This molten, partly reduced, metalliferous material flows downwardly from the smelt cyclone into the molten bath in the smelting vessel and is smelted to molten metal, in the bath.

Hot reaction gas (typically CO, CO?, ¾, and ¾Q) produced in the molten bath is partially combusted by oxygen-containing gas (typically technical-grade oxygen) in an. upper part of the smelting chamber. Heat generated by the post- combustion is transferred to molten droplets in the upper section that fall back into the molten bath to maintain the temperature of the hath.

The hot partially-combusted reaction gas flows upwardly fr m the smelting chamber and enters the bottom of the smelt cyclone. Oxygen-containing gas (typically technical- grade oxygen) is injected into the smelt, cyclone via tuyeres that are arranged in such a way as to generate a cyclonic swirl pattern in a horizontal plane, i.e. about a vertical, central axis of the chamber of the smelt cyclone. This injection of oxygen- con taming gas leads to further combustion of smel ting vessel gases, resulting in very hot (cyclonic) flames. Incoming metalliferous feed material to the smelt cyclone, typically in the form, of fines, is injected pneumatically into these flames via tuyeres in the smelt cyclone, resulting in rapid heating and partial melting accompanied by partial reduction (roughly 10-20% reduction). The redaction is due to both thermal decomposition of hematite and the reducing action of CO/Ha in the reaction gases from the smelting chamber. The hot, partially melted metalliferous feed material is thrown outwards onto the walls of the smelt cyclone by cyclonic swirl action and, as described above, .flows downwardly into the smelting vessel below for smelting in the smelting chamber of thai vessel .

Off-gas resulting from the further post-combustion, of reaction gases in the smelt cyclone is taken away from an upper region, ofthe smelt cyclone through an off- gas, duct.

The net effect ofthe above-described form ofthe HIsarna process is a two-step counter-current, process. Metalliferous feed material is heated and partially reduced in the smelt cyclone by outgoing reaction, gases from the smelting vessel (w th oxygen - containing gas addition) and flows downwardly irom the smelt cyclone into the smelting vessel and is smelted to molten iron in the smelting chamber of the smelting vessel. In a. general sense, this counter-current arrangement increases productivity and energy efficiency.

The above description is not to be taken as an admission of the common general knowledge, in Australia or elsewhere . SUMMARY OF THE DISCLOSURE

The present invention is based on a realisation that undesirable slag foaming events in smelting chamber of a smelting vessel of an H l saraa smelting apparatus may be caused by large solid or near solid iron oxide-rich accretions (hereinafter referred to as "accretions") breaking off from, an off-gas duct above a smel t cyclone of the apparatus and falling into the molten bath in the smelting vessel, where they can cause a rapid carbon boil and very rapid foaming which is extremely difficult to contain. The applicant believes that these more or less regular falling solid lumps cause undesirable "mini carbo boil" events, each one increasing the CO released from the molten bath for a short time period.

In broad, terms, the present invention, provides a smelting apparatus that includes (a) a smelting vessel that defines a smelting chamber and is adapted to contain a bath of molten .metal and slag and (b) a smelt cyclone for pre-treating a metalliferous feed material that defines a cyclone chamber and is positioned above and communicates directly with the smelting vessel, and (c) an off-gas duct extending from, the smelt cyclone for discharging an off-gas from the smelt cyclone, with the off-gas duct having an inlet section that extends upwardly from the smelt cyclone and is formed to cause off-gas to undergo a substantial change of direction as it flows through the inlet section of the off-gas duct.

The inlet section includes (a) an upward, typically vertical, extension of the cyclone chamber thai defines an upstream leg of the inlet section and (b) a downstream leg of the inlet section, with the downstream leg extending at. an angle to the upstream, leg so that, the off-gas undergoes the substantial change in direction as it moves through, a bend that interconnects the upstream and the downstream legs. The purpose of the substantial change in direction in the inlet section is to move off-gas quickly away from the upward, typical ly vertical, extension of the cyclone chamber. This encourages (a) liquid material to de-entrain in a high temperature section of the off-gas duct that is downstream of and displaced laterally from the upward extension (in the direction of flow of off-gas ) and run back continuously into the molten bath in. the smelting chamber and (b) accretions formed on. walls in an upper part of the off-gas duct that is downstream of the high temperature downstream section to fell down in the high temperature downstream section and be melted there, with the resulting liquid falling directl into the molten bath in the smelting chamber.

It is noted that the accretions may be due to (a ) molten material entrained in the off-gas solidifying on. the walls that form the off-gas duct and (¾} solid material entrained in the off-¾as being deposited on the wails that form the off-gas duct.

The upstream leg of the inlet section of the inlet section may extend vertically upwardly from the smelt cyclone.

The bend of the nlet section may be in the form of a dog-leg bend that defines an included angle of at least 90° , typically 90-120" . between the upstream (in the direction of flow of off-gas) leg of the inlet section and the downstream leg of the inlet section. m use, the bend causes off-gas to undergo the substantial change of direction, with the gas angle change being an angle of at least 60% typically 60-90°, as it flows through the inlet section into the downstream sections of the off-gas duct. The bend of the inlet section may be cooled and constructed in such a way as to prevent growth of large solid aecretions in this location.

The bend of the inlet section may include cooling elements, such as water- cooled staves.

The cooling elements may b any suitable elements.

As described above, the off-gas duct may include a downstream (in the direction of flow of off-gas) section that is a high, temperature section, i.e. at a temperature that is above the solidification temperature range of slag.

The downstream section may be formed to cause off-gas to undergo another substantial change of direction as it flows through the downstream section. As with the first direction change described above, this second change of direction, facilitates separating solid and liquid material from, the off-gas. Moreover, as is described above, the downstream section is also a collection are for aecretions that form on walls of the off-gas duct downstream of the downstream section and subsequently melt or fall off the walls. Over time, these accretions melt and the molten material flows back into the smelting chamber.

The downstream section may include a bend, typically a dog-leg bend, that defines an included angle of less than.90°, typically 60-90°, between an upstream leg in the direction of flow of off-gas and a downstream leg of the downstream section, with the bend causing off-gas to undergo the substantial change of direction through the angle as it flows through the downstream section.

The smelt cyclone may include tuyeres tor injecting solid feed materials and oxygen-containing gas into the cyclone chamber.

The smelting vessel may include lances for injecting solid feed, materials and oxygen-containing gas into the smelting chamber.

According to the present invention there is provided a process for smelting a metalliferous feed. material including smelting the metalliferous feed material is the molten bath of the smelting vessel in the above-described, smelting apparatus.

The process may include (a) at least partially reducing and partially melting the metalliferous feed material in the smelt cyclone in the above-described smelting apparatus and (b) completely smelting the at least partially reduced/melted material in the molten bath of the smelting vessel of the apparatus. The process ma include maintaining an. oxygen potential in the smelt cyclone that is sufficient so that the off-gas from the smelt cyclone has a post, combustion degree of at least 80%.

The metalliferous feed material may be any material that contains metal oxides.

The metalliferous feed material may be ores, partly reduced ores and metal containing waste streams.

The metalliferous feed material may be an iron-containing feed, material, such as an iron, ore. In thai event, the process may be characterised by maintaining a temperature of at least 1100°C, typically at. least 1200°C in the smelt cyclone.

The metalliferous feed material ma he a iitania slag.

The metalliferous feed material ma be an other suitable material.

BRIEF DESCRIPTION OF THE DRAWINGS

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

Figure 1 is a schematic diagram which illustrates one embodiment of a plant for smelting iron-containing metalliferous feed material to molten iron in accordance with the Hlsarna smelting process in the Hlsarna smelting apparatus;

Figure 2 is a schematic diagram which illustrates one embodiment of an off-gas duet of a Hlsarna smelting apparatus in accordance with the present invention; and

Figure 3 is a schematic diagram which illustrates another, although not. the only other, embodiment of an off-gas duet of the Hlsarn smelting apparatus in accordance with the present invention.

DESCRIPTION OF EMBODIMENTS

The process and the apparatus shown in Figure 1 is an embodiment of the Hlsarn process and apparatus. The process and the apparatus of the invention are not confined to the Hlsaraa process and apparatus and also extend to any other molten bath-based smelting process and apparatus.

The process and the apparatus shown in Figure 1 are based on the use of an apparatus that includes a smelt cyclone .2 and a molten bath-based smelting vessel 4 located directly beneath the smelt cyclone 2, with direct communication between the chambers of the smelt cyclone 2 and the smelting vessel 4.

With reference to Figure 1 , a blend of metalliferous feed material in the form of magnetite-based ore (or other iron ore) with a top size of 6 mm and limestone 1 is fed, via an ore dryer, into the smelt cyclone 2 using a pneumatic conveying gas l a.

Limestone represents roughly 8-10 wt% of the combined stream of ore and limestone.

Coal 3 is fed. via a separate dryer, to the smelting vessel 4 where it is injected into a molten bath of metal and slag using conveying gas 2a. Oxygen 7 is injected into the smelting vessel 4 to post-combust gas, typically CO and H ₂ , generated in and released from the molten bath and provide the necessary heat for the smelting process in the bath before the gases flow upwardly from the smelting vessel 4 into the smelt cyclone 2.

Oxygen 8 is injected into the smelt cyclone 2 to preheat and partly melt the ore.

Specifically, the oxygen 8 further post-combusts gas, typically CO and ¾, generated in and released from the molten bath, resulting in ver hot (cyclonic) flames in the smelt cyclone 2. Typically, the oxygen 7 and 8 is technical-grade oxygen.

The net effect, of the above-described form of the Hlsarna process is a two-step counter-current process. Metalliferous feed material is heated and partially reduced in the smelt cyclone 2 b outgoing reaction gases from the smelting vessel.4 and flows do wnwardly into the smelting vessel 4 and is smelted to molten iron.

Molten iron 5 is discharged from smelting vessel 4 via a forehearth.

Molten slag 6 produced in the process is discharged from sme ting vessel 4 via a slag tap hole.

The operating conditions, including but not limited to, coal and ore feed rates, oxygen feed rates to the direct smelting vessel 4 and the smelt cyclone 2 and heat losses from the smelting vessel 4, are selected so that off-gas leaving the smelt cyclone 2 via an off-gas outlet duct 9 has post-combustion degree that is typically at least 90%. Off-gas from the smelt cyclone 2 passes via an off-gas duc 9 to an off-gas incinerator 10, where additional oxygen 1 1 is injected to burn residual CO/¾ and provide a degree of free oxygen (typically 1-2%) in the fully combusted fine gas.

Fully combusted gas then passes through a waste heat recovery section 12 where the gas is cooled and steam, is generated. Flue gas then passes through a wet scrubber 13 where cooling and dust removal are achieved. The resulting sludge 14 is available for recycle to the smelter via the ore feed, stream 1.

Cool flue gas leaving the scrubber 13 is fed to a flue gas desulphurisation unit

1.5,

Clean flue gas is the vented via a stack 16. Tins gas consists mainly of€(¾ and, if appropriate, it can be compressed and. geo-sequestered (with appropriate removal of residual non-condensable gas species).

The smelting vessel 4 is of the type described in International publication WO

00/01854 in the name of the applicant and comprises a hearth formed of refractor material and side walls extending upwardly from the sides of the hearth , with the side wall including water cooled panels. The disclosure in the international publication is incorporated herein by cross-reference.

The above-described apparatus may be operated as described in the above

Background, section of the specification to produce molten metal.

As is indicated above:

(a) undesirable slag foaming in the smelting chamber of the smelting vessel 4 may be caused by large solid (or near solid) iron oxide-rich accretions breaking off from the off-gas duct above the smelt cyclone and felling into the molten bath in the smelting vessel, where they can cause a rapid carbon boil and foaming on the time-scale of a minute or so;

(b) pilot plant trials indicate that the "product" falling into the smelting vessel from the smelt cyclone largely comprises liquid or slurry droplets and from time to time also comprises the solid accretions; and

(c) the applicant believes that these more or less regular falling solid accretions cause undesirable "mini carbon boil" events, each one increasing CO for a short period.

Figure 2 and Figure 3 each show an embodiment of the off-gas duct 9 in accordance with the present invention.

With reference- to Figures 2 and 3, the present invention addresses the above- described undesirable slag foaming events caused by accretions from, the off-gas duct 9 failing into the molten bath in the smelting vessel by providing an inlet section 18 (see the circled parts of Figures 2 and 3) of the off-gas duct 9 that extends upwardly

(vertically in the embodiments shown in Figures 2 and 3 ) from a roof of the smelt cyclone 2 and is formed to cause off-gas to undergo a substantial change of direction a it flows through the inlet section.. The substantial change in direction in the inlet section moves off-gas quickly away from the upward (in these embodiments vertical) extension of the smelting chamber and the cyclone chamber so that any accretions that form in the duct 9 are more likely to form downstream, (in the direction of movement of off-gas) of and are laterally displaced from the inlet section and therefore cannot fall directly into the molten bath in the smoking chamber.

With reference to Figure 2, the inlet section 18 of the off-gas duct. 9 includes a. bend, typically a. dogleg bend, that defines .an included angle a of approximately 100- 1 15° between an upstream (in the direction of flow of off-gas) vertically extending leg 21 of the inlet section. 18 and a downstream !eg 22 of the inlet section 18. In other words, the inlet section includes the upstream leg 21 and the downstream leg 22, with the downstream, leg 22 extending at the angle o. from the upstream leg 21 and defining the bend of the inlet section 18. The inlet section 18 is positioned so that the upstream leg 21 extends vertically upwardly from a roof of the smelt cyclone 2, The inlet section 18 is centrally positioned in the roof of the smelt cyclone 2. This arrangement channels the upwardly flowing off-gas from the smelt cyclone 2 into the inlet section 18. Almost immediately, the off-gas is caused to flow around the bend, i .e. with a substantial, change of direction through the bend angle of 100- 115° between the legs 21, 22 of the inlet section 18, and moves away from a vertical pathway in relation to the smelt cyclone 2 and the smelting vessel 4, The gas angle change through the bend is 65-80°, This arrangement minimizes, the surface area of the wall of the off- gas duct 9 on which solid accretions can form and subsequently separate from the off-duet 9 and drop directly into the molten bath in the smelting vessel 4 and cause slag, foaming events. The upstream leg 21 and the downstream leg 22 may be any suitable length. Typically, the legs 21 are selected to be as short as possible so that the inlet section 1.8 is a high temperature zone.

In order to minimize accretion growth, the inlet section 18 is cooled by means of cooling elements in the form of water-cooled copper staves 1 in the sections of the walls of the inlet section 18 that are the main contact surfaces for off-gas flowing through the inlet, section 18, such as on the upper surface of the bend between the upstream leg 21 and the downstream leg 22 of the inlet section 18.

The off-gas duct 9 further includes a straight section 23 that is an extension of the downstream leg 22 that extends upwardly away from the inlet section 18 at an angle of 10- 15° to the horizontal. The straight, section 23 may be at. any suitable angle to the horizontal and may be any suitable length. The straight section 23 ends in a

do wnstream section 24 in the form of an upward dog-leg bend that de fi nes an. incl uded angle β of at least 75 ° and typically 75-80", between the straight section 23 and a vertically extending downstream leg 25 of the downstream section 24. The bend causes off-gas to undergo another substantial change of direction (through a gas angle change of 75-80"') as it flows through the downstream section 24. This second change of direction facilitates separating accretions from the off-gas. The downstream section, is also a collection area for accretions that form on the walls of the off-gas- duct downstream of the downstream section 24 and subsequently melt or tail off di wal ls. Over time, these accretions melt and the molten material flows back into the smelting cyclone 2 and the smelting vessel 4.

With reference to Fi gure 3, the inlet, section 18 of the embodiment of the off-gas duct 9 shown in this Figure is formed as a bend, typically a dogleg bend, that defines an included, angle a of approximately 90° between an upstream (in the direction of flow of off-gas) vertically extending leg 21 of the inlet section 18 and a downstream leg 22 of the inlet section 18. As described in relation to the Figure 2 embodiment, the downstream leg 22 extends at the angle a from the upstream leg 2.1 and defines the bend of the inlet section 18. The inlet section .18 is positioned so that the upstream leg 21 extends vertically upwardly from a roof of the smelt cyclone 2. The inlet section 18 is centrally positioned in the roof of the smelt cyclone 2. This arrangement channels the upwardly flowing off-gas from the smelt cyclone 2 into the inlet section .18. Almost immediately, the off-gas is caused to flow around the bend, i.e. with a substantial change of direction, namely a gas angle change of 90", and moves away from a vertical pathway in relation to the smelt cyclone 2 and the smelting vessel 4, This arrangement minimizes the surface area of the wail of the off-gas duct 9 on which solid accretions can form, and subsequently separate from, the duct and drop directly into the molten bath in the smelting vessel 4 and cause slag foaming events. In order to minimize accretion growth, the inlet section 18 is cooled by means of cooling elements in the form of water-cooled copper staves 19 in the sections of the walls of the inlet section 18 that are the main contact surfaces for off-gas flowing through the inlet section S, such as on the upper surface of the bend between the upstream leg 21 and the downstream leg 22 of the inlet section 18.

The off-gas duct 9 shown in Figure 3 also includes a downstream section 24 in the form of a dog-leg bend that, defines an included angle β of 70-75° between the do wnstream leg 22 of the inlet section 18 and an upwardly extending do wnstream leg 23 of the downstream section 24. The downstream section 24 is immediately after the inlet section 18. The bend causes off-gas to undergo another substantial change of direction (through a. gas angle change of 105-110°) as it flows through the downstream section 24. This second change of direction facilitates separating accretions from the off-gas. The downstream section is also a collection area for accretions that form on the walls of the off-gas duct 9 downstream of the downstream section 24 and subsequently melt or fall off the walls. Over time, these accretions melt and. the molten material flows back into the smelting cyclone 2 and the smelting vessel 4. The downstream leg 23 is a straight section that extends upwardly at an angle of 60-70° to the horizontal.

The embodiments of the off-gas duct 9 of the present invention shown in Figures 2 and 3 are effective options for minimising accretions in the off-gas duct 9 dropping directly into the molten bath in the smelting vessel 4 and causing slag foaming events.

Many modifications may be made to the embodiments of the present invention described above without departing from the spirit and scope of the invention.

By way of example, whilst each embodiment includes two log-leg bends in the inlet section 18 and the downstream section 24, the present invention is not so limited and the broadest embodiments of the invention include a single dog-leg bend in the inlet section 18. The invention also extends to arrangements in which there are more than two bends,

urthermore* the present invention is not limited to the particular relative dimensions of the legs and other parts of the off-gas ducts 9 in the embodiments shown in Figures 2 and 3.

Furthermore, whilst the legs 21 of the inlet sections 18 of the off-gas ducts 9 of the embodiments shown in Figures 2 and 3 are. vertical legs 21 , the present invention is not so limited and includes arrangements in which the legs 21 extend upwardly but not necessarily vertically. The selection of the angle for the legs 21 is governed by an. objective of wanting to minimise the possibility of accretions torming on the legs 21.

Furthermore, whilst the bend in. the inlet, section. 1.8 is defined by straight legs 21 , 22, the invention is not limited to this arrangement and extends to arrangements .in which one or both of the legs 21, 22 is curves or another profile.