Smelting process and apparatus

Abstract

A smelting apparatus that includes (a) a smelting vessel (4) that is adapted to contain a bath of molten metal and slag and (b) a smelt cyclone (2) for pre-treating a metalliferous feed material positioned above and communicating directly with the smelting vessel The apparatus also includes an oft-gas duct (9) extending from the smelt, cyclone for discharging an off-gas from the smelt cyclone. The off-gas duct has an inlet section (18) 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.

Claims

1. A smelting apparatus includes a smelting vessel that includes a smelting chamber adapted to contain a bath of molten metal and slag; a smelt cyclone for pre-treating a metalliferous feed material that is positioned above and communicates directly with the smelting vessel; and 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, wherein the inlet section includes: an upward extension of the smelt cyclone that defines an upstream leg of the inlet section, and 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 a first substantial change in direction as it moves through a bend that interconnects the upstream and the downstream legs; and a downstream section extending upwardly from the downstream leg of the inlet section defining a collecting area to collect solid accretions in the off-gas, the downstream section is formed to cause off-gas to undergo a second substantial change of direction as it flows through the downstream section.

2. The apparatus defined in claim 1 wherein the inlet section is in the form of a dog-leg bend that defines an included angle of at least 90 between the upstream leg of the inlet section and the downstream leg of the inlet section, with the bend causing off-gas to undergo the substantial change of direction through the angle as it flows through the inlet section into the off-gas duct.

3. The apparatus defined in claim 1 wherein the bend of the inlet section is configured to be cooled, to prevent growth of the solid accretions in the bend.

4. The apparatus defined in claim 1 wherein the downstream section includes a dog-leg bend that defines an included angle of 60-90, between an upstream leg in the direction of flow of off-gas, leg 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.

5. The apparatus defined in claim 1 wherein the smelt cyclone includes tuyeres for injecting solid feed materials and oxygen-containing gas into the cyclone chamber.

6. The apparatus defined in claim 1 wherein the smelting vessel includes lances for injecting solid feed materials and oxygen-containing gas into the smelting chamber.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

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

(2) FIG. 1 is a schematic diagram which illustrates one embodiment of as plant for smelting iron-containing metalliferous feed material to molten iron in accordance with the HIsarna smelting process in the HIsarna smelting apparatus;

(3) FIG. 2 is a schematic diagram which illustrates one embodiment of an off-gas duct of a HIsarna smelting apparatus in accordance with the present invention; and

(4) FIG. 3 is a schematic diagram which illustrates another, although not the only other, embodiment of an off-gas duct of the HIsarna smelting apparatus in accordance with the present invention.

DESCRIPTION OF EMBODIMENTS

(5) The process and the apparatus shown in FIG. 1 is an embodiment of the HIsarna process and apparatus.

(6) The process and the apparatus of the invention are not confined to HIsarna process and apparatus and also extend to any other molten bath-based smelting process and apparatus.

(7) The process and the apparatus shown in FIG. 1 are used 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.

(8) With reference to FIG. 1, a blend of metalliferous feed material in the form of magnetite-based ore (or other iron ore) with a top size of 6 Mitt and limestone is fed, via an ore dryer, into the smelt cyclone 2 using a pneumatic conveying gas 1a. 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.sub.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 H.sub.2, generated in and released from the molten bath, resulting in very hot (cyclonic) flames in the smelt cyclone 2. Typically, the oxygen 7 and 8 is technical-grade oxygen.

(9) The net effect of the above-described form of the HIsarna process is a two-step counter-current process. Metalliferous feed material is heated and partially reduced in the smelt cyclone 2 by outgoing reaction gases from the smelting vessel 4 and flows downwardly into the smelting vessel 4 and is smelted to molten iron.

(10) Molten iron 5 is discharged from smelting vessel 4 via as forehearth.

(11) Molten slag 6 produced in the process is discharged from smelting vessel 4 via a slag tap hole.

(12) The operating conditions, including but not limited to coal and ore feed rates, oxygen teed 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 a post-combustion degree that is typically at least 90%.

(13) Off-gas from the smelt cyclone 2 passes via an off-gas duct 9 to an off-gas incinerator 10, where additional oxygen 11 is injected to burn residual CO/H.sub.2 and oxide a degree of free oxygen (typically 1-2%) in the fully combusted flue gas.

(14) 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.

(15) Cool flue gas leaving the scrubber 13 is ted to a flue gas desulphurization unit 15.

(16) Clean flue gas is then vented via a stack 16 gas consists mainly of CO.sub.2 and, if appropriate, it can be compressed and geo-sequestered (with appropriate removal of residual non-condensable gas species).

(17) The smelting vessel 4 is of the type describe in International publication WO 00/01854 in the name of the applicant and comprises a hearth formed of refractory 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.

(18) The above-described apparatus may be operated as described in the above Background section of specification to produce molten metal.

(19) As is indicated above:

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

(21) (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

(22) (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.

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

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

(25) With reference to FIG. 2, the inlet section 18 of the off-gas duct 9 includes a bend, typically a dogleg bend, that defines an included angle of approximately 100-115 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. 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 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-duct 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 ate selected to be as short as possible so that the inlet section 18 is a high temperature zone.

(26) 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 section 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.

(27) 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 downstream section 24 in the form of an upward dog-leg bend that defines an included angle 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 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.

(28) With reference to FIG. 3, the inlet section 18 of the embodiment of the off-gas area 9 shown in this Figure is formed as a bend, typically a dogleg bend, that defines an included angle 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 FIG. 2 embodiment, the downstream leg 22 extends at the angle from the upstream leg 21 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 as vertical pathway in relation to the smelt cyclone 2 and the smelting vessel 4. 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 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 suffices 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.

(29) The off-gas duct 9 shown in FIG. 3 also includes a downstream section 24 in the form of a dog-leg bend that defines an included angle of 70-75 between the downstream leg 22 of the inlet section 18 and an upwardly extending downstream leg 23 of the downstream section 24. The downstream section 24 is immediately after the 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 walk 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 the horizontal.

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

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

(32) By way of example, whilst each embodiment includes two dog-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.

(33) Furthermore, 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 FIGS. 2 and 3.

(34) Furthermore, whilst the legs 21 of the inlet sections 18 of the off-gas ducts 9 of the embodiments shown in FIGS. 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 forming on the legs 21.

(35) Furthermore, whilst the bend in the inlet section 18 is defined by straight legs 21, 22, the invention is not limited to this arrangement and extends to arrangements in which one o both of the legs 21, 22 is curves or another profile.