TECHNICAL FIELD

The present invention relates to metallurgical lances for injecting solid particulate materials into vessels. Apparatus of this kind may be used for injecting metallurgical feed material into the molten bath of a smelting vessel for producing molten metal, for example by a direct smelting process.

A known direct smelting process, which relies on a molten metal layer as a reaction medium, and is generally referred to as the Hismelt process, is described in International application PCT/AU/96/00197 (WO 96/31627) in the name of the applicant.

The Hismelt process as described in the International application comprises:

(a) forming a bath of molten iron and slag in a vessel;

(b) injecting into the bath;

(i) a metalliferous feed material, typically metal oxides; and

(ii) a solid carbonaceous material, typically coal, which acts as a reductant of the metal oxides and a source of energy; and

(c) smelting metalliferous feed material to metal in the metal layer.

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

The Hismelt process also comprises post- combusting reaction gases, such as CO and H ₂ , released from

the bath in the space above the bath with oxygen- containing gas and transferring the heat generated by the post-combustion to the bath to contribute to the thermal energy required to smelt the metalliferous feed materials.

The Hismelt process also comprises forming a transition zone above the nominal quiescent surface of the bath in which there is a favourable mass of ascending and thereafter descending droplets or splashes or streams of molten metal and/ir slag which provide an effective medium to transfer to the bath the thermal energy generated by post-combusting reaction gases above the bath.

In the Hismelt process the metalliferous feed material and solid carbonaceous material is injected into the metal layer through a number of lances/tuyeres which are inclined to the vertical so as to extend downwardly and inwardly through the side wall of the smelting vessel and into the lower region of the vessel so as to deliver the solid material into the metal layer in the bottom of the vessel. The lances must withstand operating temperatures of the order of 1400 ⁰ C within the smelting vessel. The lances must accordingly has an internal forced cooling system to operate successfully in this harsh environment and must be capable of withstanding substantial local temperature variations.

US Patent 6,398,842 discloses one form of lance which is able to operate effectively under these conditions. In that construction the solid particulate material is passed through a central core tube which is fitted closely within an outer annular cooling jacket, the forward end of the core tube extending through and beyond the forward end of the cooling jacket into the metallurgical vessel. It has been found in the operation of such lances that the injection of hot ore presents particular difficulties and in particular, the core tube

is prone to very rapid wear. The present invention enables the provision of a core tube made from wear resistant tube components which will be replaceable when the plant is shut down for a reline or other maintenance and which can therefore be supplied as consumable items.

DISCLOSURE OF THE INVENTION

According to the invention there is provided a metallurgical lance to extend into a vessel for injecting solid particulate material into molten material held within the vessel, comprising a central conveyor tube through which to pass the solid particulate material and a lance housing surrounding the central core tube throughout a substantial part of its length and provided with internal water flow passages for flow of cooling water therethrough, wherein the conveyor tube comprises a series of wear resistant tubes disposed end to end , joining sleeves fitted externally about ends of adjacent tubes and connected to them to join the adjacent tubes together, and a series of collars spaced along the tube and each encircling the tube to serve as spacers to centre the tube within the lance housing.

The term "wear resistant" as used in this specification means that the tubes are made of a metal having a Brunell hardness number of 200 or above. It has been found that the tubes must have a hardness of this magnitude to provide adequate service when conveying hot ore. Tubes of this hardness may be cast from high chrome white iron.

The invention further provides a solids conveyor tube for installation within a housing of a hot ore injection lance comprising a series of wear resistant tubes disposed end to end ;

joining sleeves fitted externally about ends of adjacent segments and connected to those tube ends to join the adjacent tubes together; and a series of collars spaced along the tube and each encircling the tube for, in use, centering the tube within the lance housing.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be more fully explained, particular embodiments will be described in some detail with reference to the accompanying drawings in which:

Figure 1 is a vertical cross section through a metallurgical vessel incorporating solids injection lances constructed in accordance with the invention;

Figure 2 is a longitudinal cross-section through one of the solids injection lances for injecting hot ore into the vessel;

Figure 3 is a cross-section through a forward part of the lance shown in Figure 2;

Figure 4 is a longitudinal cross-section through a rear part of the lance shown in Figure 2;

Figure 5 is a perspective view of a solids conveyor tube of the lance shown in Figure 2;

Figure 6 is a cross-section through a rear part of the conveyor tube shown in Figure 5; and

Figures 7 and 8 provide further details of the rear part of the conveyor tube.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Figure 1 illustrates a direct smelting vessel suitable for operation by the Hismelt process as described in International Patent Application PCT/AU96/00197. The metallurgical vessel is denoted generally as 11 and has a hearth that includes a base 12 and sides 13 formed from refractory bricks; side walls 14 which form a generally cylindrical barrel extending upwardly from the sides 13 of the hearth and which includes an upper barrel section 15 ' and a lower barrel section 16; a roof 17; an outlet 18 for off-gases; a forehearth 19 for discharging molten metal continuously; and a tap-hole 21 for discharging molten slag.

In use, the vessel contains a molten bath of iron and slag which includes a layer 22 of molten metal and a layer 23 of molten slag on the metal layer 22. The arrow marked by the numeral 24 indicates the position of the nominal quiescent surface of the metal layer 22 and the arrow marked by the numeral .25 indicates the position of the nominal quiescent surface of the slag layer 23. The term "quiescent surface" is understood to mean the surface when there is no injection of gas and solids into the vessel.

The vessel is fitted with a downwardly extending hot air injection lance 26 for delivering a hot air blast into an upper region of the vessel and a series of solids injection lances 27 extending downwardly and inwardly through the side walls 14 and into the slag layer 23 for injecting iron ore, solid carbonaceous material, and fluxes entrained in an oxygen deficient carrier gas into the metal layer 22. The position of the lances 27 is selected so that their outlet ends 28 are above the surface of the metal layer 22 during operation of the process. This position of the lances reduces the risk of

damage through contact with molten metal and also makes it possible to cool the lances by forced internal water cooling without significant risk of water coming into contact with the molten metal in the vessel.

Lances 27 may be of two kinds, a first of which is employed to inject hot ore material and the other of which is employed to inject carbonaceous material such as coal. There may for example be eight solids injection lances 27 spaced circumferentially around the vessel and consisting of a series of four hot ore injection lances and four coal injection lances spaced between the hot ore injection lances. All of the lances may fit within outer housings of a common conveyor but the two kinds of lance have differing interior construction tubes because of the vastly different temperature of the hot ore and the coal being injected.

The construction of an injection lance for hot ore, identified as 27a, is illustrated in Figures 2 to 8. As shown in these figures lance 27a comprises a central solids conveyor tube 31 through which to deliver the hot ore and a lance housing 30 including an annular cooling jacket 32 surrounding the conveyor tube 31 throughout a substantial part of its length.

Annular cooling jacket 32 comprises a long hollow annular structure 41 comprised of outer and inner tubes 42, 43 interconnected by a front end connector piece 44 and an elongate tubular structure 45 which is disposed within the hollow annular structure 41 so as to divide the interior of structure 41 into an inner elongate annular water flow passage 46 and an outer elongate annular water flow passage 47. Elongate tubular structure 45 is formed by a long carbon steel tube 48 welded to a machined carbon steel forward end piece 49 which fits within the forward end connector 44 of the hollow tubular

structure 41 to form an annular end flow passage 51 which interconnects the forward ends of the inner and outer water flow passages 46, 47. The rear end of annular cooling jacket 32 is provided with a water inlet 52 through which a flow of cooling water can be directed into the inner annular water flow passage 46 and a water outlet 53 from which water is extracted from the outer annular passage 47 at the rear end of the lance. Accordingly in use of the lance cooling water flows forwardly down the lance through the inner annular water flow passage 46 then outwardly and back around the forward annular end passage 51 into the outer annular passage 47 through which it flows backwardly along the lance and out through outlet 53. This ensures that the coolest water is in heat transfer relationship with the incoming solids material and enables effective cooling of both the solids material being injected through the central core of the lance as well as effective cooling on the forward end and outer surfaces of the lance.

The outer surfaces of the tube 42 are machined with a regular pattern of rectangular projecting bosses each having an undercut or dove tail cross section so that the bosses are of outwardly diverging formation and serve as keying formations for solidification of slag on the outer surfaces of the lance. Solidification of slag onto the lance assists in minimising the temperature in the metal components of the lance. It has been found in use that slag freezing on the forward or tip end of the lance serves as a base for formation of an extended pipe of solid material serving as an extension of the lance which further protects exposure of the metal components of the lance to the severe operating conditions within the vessel.

The lance is mounted in the wall of the vessel 11 via a mounting structure 61 comprising a tubular part 60

extended about the cooling jacket and having a double walled construction so as to enclose an annular space 70 between these walls. The tubular part 60 fits within a tubular lance mounting bracket 62 welded to the shell of vessel 11 so as to project upwardly and outwardly from the vessel and provided at its upper end with an end flange 63. Lance mounting structure 61 is connected to the rear end of the outer tube 42 of annular cooling jacket 32 via an annular ring 64 and it also includes an annular mounting flange 65 which can be clamped to the flange 63 at the end of mounting tube 62 via clamping bolts 66. A split spacer ring 67 is fitted between the flanges 63, 65 to hold them apart when the clamping bolts 66 are tightened. The arrangement is such that the forward part of the outer sleeve 60 of structure 61 extend through to the inside of the vessel wall.

The tubular part 60 of mounting structure 61 is water cooled, cooling water being supplied to the interior space 70 through a water inlet 68 and return through a water outlet 69 at the rear end of the mounting sleeve. The interior space 70 may be partitioned to provide an extended cooling water flow passage within it.

A tubular housing 71 extending rearwardly from the mounting ring 64 of mounting structure 61 houses the rear end of the intermediate tube 48 of jacket 32 and the rear end of the conveyor tube 31 of the lance. Housing 71 carries the cooling water inlet 52 and outlet 52 for the passage of cooling water to and from the lance cooling jacket 32. A flexible annular connecting structure 81 connects the rear end of the intermediate tube 48 of the water jacket with the housing tube 71 so as to separate the inward and outward water flow passages within the housing and to also permit relative longitudinal movement between the inner and outer tubes and the intermediate

tube of the water jacket due to differential thermal expansion and contraction in the components of the lance.

The rear end of tubular housing 71 provides a mounting for the rear end of the inner tube 43 of the annular cooling jacket.

Conveyor tube 31 is comprised of a series of wear resistant tubes 81 disposed end to end and joined together by joining sleeves 82 fitted externally about ends of adjacent tubes and stitch welded to them to connect the adjacent tubes together. Tubes 81 are cast from metal having a Brunell hardness of 200 or more, for example a high chrome white iron. Tube 31 is centered within the annular cooling jacket 32 of the lance housing by a series of spacer collars 83 projecting outwardly from the conveyor tube at longitudinally spaced locations along that tube to engage the inner periphery of the inner tube of the annular cooling jacket. An annular gas flow passage 84 is thus formed between the central core tube and the annular cooling jacket. A purge gas inlet 85 is provided at the rear end of the lance to allow a purge gas such as nitrogen to be admitted into the gas flow passage 84 and to flow forwardly through the lance between the core tube and the annular cooling jacket to exit the lance at the forward end of the cooling jacket.

One of the tube joining sleeves 82 at the front end of conveyor tube 31 is formed with a raised projection 86 in the region of the forward end of the cooling jacket to define an outlet nozzle 87 at the forward end of gas flow passage 84. Projection 86 is sized so as to leave an annular gap between that projection and the inner periphery of the cooling jacket 32, gap 88 constituting a controlled exit opening for the nozzle 87.

The spacer collars 84 are formed so as to leave σircumferentially spaced gaps between their outer

peripheries and the inner periphery of the cooling jacket to allow for free flow of purge gas through the annular purge gas flow passage 83. More particularly, each collar 83 has six circumferentially spaced lobes leaving six low regions between the lobes creating the gaps for free flow of purge gas. The flow of purge gas is maintained to ensure that slag can not penetrate the forward end of the nozzle between the core tube and the outer water jacket. If slag were to penetrate the lance in this region it would immediately freeze because of the water cooled outer jacket and the cold purge gas.

The rear end of conveyor tube 31 is provided with an outwardly projecting flange 92 by which it is mounted to the rear end of the lance housing tube 71. More specifically, the flange 92 is sandwiched between the water cooled end flange of the lance housing and the flange on the end of the ore injection system which may also be water cooled. Flange 92 is shrink fitted onto a sleeve 93 stitch welded to the rear end tube 81 of the central conveyor tube 31. It is formed with an internal circumferential water flow passage 94 through which cooling water can be circulated from inlet and outlet flow connectors 95, 96.

The joining sleeves 82 and spacer collars 83 are all interconnected by sets of connector straps 97 to form a cage structure denoted generally as 98 which surrounds the cast tubes 81. This cage structure 98 is connected to the end flange 92 of the conveyor tube 31 through a set of three end connector straps 99 and the sleeve 93, the three end connector straps 99 being circumferentially spaced around the end tube and welded to the rear end spacer collar 83 and the sleeve 93. Each set of connector straps 97 consists of three straps spaced circumferentially around the tube 31 with the straps of adjacent sets being circumferentially offset relative to one another. Some of

- li ¬ the sets of connector straps connect directly between adjacent spacer collars whereas others connect between spacer collars and adjacent tube jointing sleeves 82. The connector straps are positioned so as to connect with the respective collars 83 at the low regions of the collars between the lobes.

The resulting cage structure 98 formed by the interconnected joining sleeves 82, spacer collars 83 and connector straps 97, being attached to the water cooled flange through the end straps 99, can serve as a load bearing structure that will contain the hard cast metal tubes 81 in the event of a tensile failure of one or more of the tubes either during installation or during operation of the lance.

The cage structure also results in a conveyor tube construction which enables the cast tubes 81 to be replaced readily during any plant shut down for a vessel reline or for routine maintenance and the tubes can be supplied as consumable replacement components.

During operation of the lances slag will accumulate on the outer surfaces of the lance and the inner surface of the vessel. On shutdown the slag will solidify tending to bond the lance to the vessel. However with the illustrated mounting arrangement this bond can readily be broken to facilitate withdrawal of the lance. This can be achieved by loosening the clamping bolts 66 sufficiently to enable withdrawal of the split spacer ring 67. This then permits limited inward movement of the lance mounting sleeve within the mounting tube 62 so that the forward end of the mounting sleeve is moved inwardly from the wall of the vessel to break any slag accretions. This then allows the lance along with the slag that has solidified on the outer tube 42 to be readily withdrawn

through the enlarged opening provided for the tubular mounting 60.

The coal injection lances may have outer housings of the same construction as the hot ore injection lances. However, the service requirements for injection of the coal are less severe than for injection of hot ore and those lances may have central core tubes of a different construction not employing the present invention, for example a single continuous tube fitted with a ceramic lining.