Abstract:
A gas injection lance and an apparatus employing the lance for producing ferrous metal are provided. The lance has an elongated flow duct made of inner and outer concentric carbon steel tubes, a cooling water supply and return, and exterior surface which is designed to hold a frozen layer of slag on the duct, a gas inlet at a rear end of the duct, a tip joining the concentric tubes at the forward end of the duct, a non-metallic or refractory lining for the duct, and swirl-imparting member or members located in the duct for imparting swirl in the gas flow through the forward end of the duct.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention provides a lance for injecting preheated gas into a vessel. 
     The invention has particular, but not exclusive, application to a lance for injecting a flow of preheated gas into a metallurgical vessel under high temperature conditions. 
     The metallurgical vessel may for example be a direct smelting vessel in which molten metal is produced by a direct smelting process. 
     The present invention also provides a direct smelting apparatus which includes a lance for injecting gas into a direct smelting vessel. 
     2. Description of Related Art 
     In general, molten bath-based processes for direct smelting ferrous material into molten iron that are described in the prior art require post-combustion of reaction products such as CO and H 2  released from a molten bath in order to generate sufficient heat to maintain the temperature of the molten bath. 
     The prior art generally proposes that post combustion be achieved by injecting oxygen-containing gas via lances that extend into a top space of a direct smelting vessel. 
     For economic reasons, it is desirable that direct smelting campaigns be relatively long, typically at least one year, and therefore it is important that gas injection lances be capable of withstanding the high temperature environment, typically of the order of 2000° C., within the top space of a direct smelting vessel for the prolonged periods of campaigns. 
     One option for providing oxygen-containing gas is to use air or oxygen-enriched air that is preheated to above 800° C. 
     Stoves or pebble heaters are the only currently viable options for pre-heating air or oxygen-enriched air. One consequence of the use of stoves and pebble heaters is that the air or oxygen-enriched air will pick up hard particulate material as it passes through the stoves and pebble heaters and this material can cause considerable wear to the internal surface of a lance. 
     The use of air or oxygen-enriched air also means that considerably larger volumes of gas are required to achieve a given level of post combustion than would be required if oxygen was used as the oxygen-containing gas. Consequently, a direct smelting vessel operating with air or oxygen-enriched air must be a considerably larger structure than a direct smelting vessel operating with oxygen. 
     Consequently, a lance for injecting air or oxygen-enriched air into a direct smelting vessel must be a relatively large structure that can extend a relatively substantial distance into a direct smelting vessel and be unsupported over at least a major part of the length of the lance. By way of context, 6 meter diameter HIsmelt vessels proposed by the applicant include lances having an outer diameter of 1.2 m that are of the order of 60 tonnes and extend approximately 10 m into the vessel. 
     In addition, such a lance must be capable of delivering relatively large volume flow rates of pre-heated air or oxygen-enriched air and withstanding wear of the interior of the lance due to erosive particulate material in the air or oxygen-enriched air over prolonged smelting campaigns. 
     For economic and structural reasons, carbon steel is the preferred material for constructing a lance for injecting pre-heated air or oxygen-enriched air. 
     However, carbon steel is not a preferred material in terms of resisting wear of the interior of the lance and particularly in light of the risk of rapid oxidation (ie ignition) of steel under hot injection conditions. 
     It is evident from the above that the use of pre-heated air or oxygen-enriched air presents significant issues in terms of the construction of lances for injecting the air or oxygen-enriched air into direct smelting vessels over prolonged smelting campaigns. 
     An object of the present invention is to provide a water cooled lance that may be constructed using carbon steel as a major structural component of the lance and is capable of injecting pre-heated air or oxygen-enriched air into a direct smelting vessel during a lengthy operating campaign. 
     SUMMARY OF THE INVENTION 
     According to the present invention there is provided a lance for injecting a pre-heated oxygen-containing gas into a vessel containing a bath of molten material, the lance including: 
     (a) an elongate gas flow duct extending from a rear to a forward end of the duct from which to discharge gas from the duct, the duct including; (i) inner and outer concentric carbon steel tubes which provide major structural support for the duct, (ii) cooling water supply and return passage means extending through the duct wall from the rear end to the forward end of the duct for supply and return of cooling water to the forward end of the duct, (iii) an exterior surface that includes a mechanical means adapted to hold a layer of frozen slag on the duct; 
     (b) a gas inlet for introducing hot gas into the rear end of the duct; 
     (c) tip means joined to the concentric tubes at the forward end of the duct, 
     (d) a protective lining formed from a refractory or other material that is capable of protecting the duct from exposure to gas flow at 800-1400° C. through the duct, the lining being a non-metallic material with heat insulating properties when compared to the steel tubes; and 
     (e) a means located in the duct for imparting swirl to gas flow through the forward end of the duct. 
     Preferably the duct includes three or more concentric steel tubes extending to the forward end of the duct. 
     Preferably the gas inlet includes a refractory body defining a first tubular gas passage aligned with and extending directly to the rear end of the duct and a second tubular gas passage transverse to the first passage to receive hot gas and direct it to the first passage so that the hot gas and any particles entrained therein impinge on the refractory wall of the first passage, with the gas flow undergoing a change of direction in passing from the second passage to the first passage. 
     Preferably the mechanical means on the exterior surface of the duct includes projections that are shaped to interlock with and hold frozen slag on the duct. 
     Preferably the projections are lands with each land having an undercut or dovetail cross-section so that the lands are of outwardly diverging formation and serve as keying formations for solidification of slag. 
     Preferably the tip means is of hollow annular construction and is formed from a copper-containing material. 
     Preferably the forward end of the duct is formed as a hollow annular tip formation and the duct includes duct tip cooling water supply and return passages for supply of cooling water forwardly along the duct into the tip means and return of that cooling water back along the duct. 
     Preferably the lance includes an elongate body disposed centrally within the forward end of the duct such that gas flowing through the forward end of the duct flows over and along the elongate central body. 
     Preferably a forward end of the elongate body and the tip means co-act together and form an annular nozzle for flow of gas from the duct with swirl imparted by the swirl means. 
     Preferably the swirl means includes a plurality of flow directing vanes connected to the elongate body to impart swirl to gas flow through the forward end of the duct. 
     In one embodiment of the present invention the elongate body is an elongate central tubular structure extending within the gas flow duct from its rear end to its forward end and the vanes are disposed about the central tubular structure adjacent the forward end of the duct to impart swirl to the gas flow to the forward end of the duct. 
     Preferably the central tubular structure includes a water cooling passage for flow of cooling water forwardly to its forward end. 
     More preferably the central tubular structure includes cooling water passages for flow of cooling water forwardly through the central structure from its rear end to its forward end and to internally cool the forward end and thence to return back through the central structure to its rear end. 
     Preferably the central tubular structure defines a central water flow passage for flow of water forwardly through that structure directly to the forward end of the central structure and an annular water flow passage disposed about the central passage for return flow of water from the forward end of the central structure back to the rear end of that structure. 
     The central tubular structure may include a central tube providing the central water flow passage and a further tube disposed around the central tube to define said annular water flow passage between the tubes. 
     Preferably the central tubular structure includes a heat insulating outer shield to retard heat transfer from gas in the gas flow duct into the cooling water passages in the central structure. 
     The heat insulating shield may include a plurality of tubular segments of heat insulating material disposed end to end to form the heat shield as a substantially continuous tube extending from the rear end to the forward end of the central structure about an annular air gap disposed immediately within the heat shield. 
     The air gap may be formed between the tubular heat shield and the further tube defining the outer wall of the annular water return flow passage. 
     Preferably the tubular segments of the heat shield are supported to accommodate longitudinal expansion of each segment independently of the other such segments. 
     The forward end of the central tubular structure may include a domed nose portion provided internally with a single spiral cooling water passage to receive water from the central water flow passage in the central tubular structure at the tip of the nose and direct that water in a single flow around and backwardly along the nose to cool the nose with a single coherent stream of cooling water. 
     The central tubular structure may extend centrally through the first gas flow passage of the gas inlet means and rearwardly beyond the gas inlet. The rear end of the central structure may then be located rearwardly of the gas inlet and be provided with water couplings for the flow of cooling water to and from the central tubular structure. 
     In another, although not the only other, embodiment of the present invention the flow directing vanes are disposed between the elongate central body and the duct to impart swirl to gas flow through the forward end of the duct. 
     With this embodiment preferably the lance includes: 
     (a) internal cooling water passage means within the tip means communicating with the cooling water supply and return passage means of the duct so as to receive and return a flow of cooling water to internally cool the duct tip; and 
     (b) cooling water flow passages within the vanes and the elongate central body and communicating with the cooling water supply and return passage means in the forward end of the duct for flow of water from the supply passage means inwardly through the vanes into the cooling passages of the elongate central body and from those passages outwardly through the vanes to the water return passage means of the duct. 
     Preferably the cooling water supply and return passage means of the duct include first supply and return passages communicating with the internal cooling water passage means in the tip means and second supply and return passages communicating with the water flow passages in the vanes and the central body. 
     The tip of the duct may be formed as a hollow annular formation with the hollow formation defining an annular passage constituting the internal cooling water passage means of the tip means. 
     The carbon steel concentric tubes of the duct may define a series of annular spaces providing the water flow supply and return passage means. 
     The elongate central body may be generally of cylindrical formation with domed ends. 
     Preferably the vanes are shaped to a multi-start helical formation. The vanes may then be connected to the duct at multiple locations spaced circumferentially around the duct. Specifically, there may be four vanes arranged in a four start helical formation and connected to the duct at four locations spaced at 90 degree intervals around the duct at the forward ends of the vanes. 
     The cooling water supply and return passage means of the duct may then include an appropriate number of separated water flow passages each to supply cooling water to one of the vanes. Such separated water flow passages may be formed by dividers within an appropriate annular passage between tubes of the duct extending helically along the duct. 
     The forward ends of the concentric carbon steel tubes may be connected at their forward ends to the tip means. The rear ends of the tubes may be mounted to allow relative longitudinal movement between them so as to accommodate differential thermal expansion and contraction of the tubes. 
     The vanes may be connected to the duct and to the central body at their forward ends only so as to be free to move along the duct from those connections under thermal expansion. 
     The invention also provides an apparatus for producing ferrous metal from a ferrous feed material by a direct smelting process, which apparatus includes a vessel that can contain a bath of molten metal and molten slag and a gas continuous space above the molten bath, which vessel includes: 
     (a) a hearth formed of refractory material having a base and sides; 
     (b) side walls extending upwardly from the sides of the hearth, the side walls including water cooled panels; 
     (c) a means for supplying ferrous feed material and carbonaceous material into the vessel; 
     (d) a means for generating a gas flow in the molten bath which carries molten material upwardly above a nominal quiescent surface of the molten bath and forms a raised bath; 
     (e) at least one gas injection lance as described in the preceding paragraphs extending downwardly into the vessel for injecting oxygen-containing gas into the vessel at an angle of 20 to 90° relative to a horizontal axis at a velocity of 200-600 m/s and at a temperature of 800-1400° C., the lance being located so that: 
     (i) the lance extends into the vessel a distance that is at least the outer diameter of the forward end of the lance; and 
     (ii) the forward end of the lance is at least 3 times the outer diameter of the forward end of the lance above a quiescent surface of the molten bath; and 
     (f) a means for tapping molten metal and slag from the vessel. 
     Preferably the ferrous feed material and carbonaceous material supply means and the gas flow generating means includes a plurality of lances/tuyeres for injecting ferrous feed material and carbonaceous material with a carrier gas into the molten bath and generating the gas flow. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is more fully explained with reference to the accompanying drawings of which: 
     FIG. 1 is a vertical section through a direct smelting vessel incorporating a pair of solids injection lances and a hot air blast injection lance constructed in accordance with the invention; 
     FIG. 2 is a longitudinal cross-section through one embodiment of the hot air injection lance; 
     FIG. 3 is a longitudinal cross-section to an enlarged scale through a front part of a central structure of the lance; 
     FIG. 4 further illustrates the forward end of the central structure; 
     FIGS. 5 and 6 illustrate the construction of a forward nose end of the central structure; 
     FIG. 7 is a longitudinal cross-section through the central structure; 
     FIG. 8 shows a detail in the region  8  of FIG. 7; 
     FIG. 9 is a cross-section on the line  9 — 9  in FIG. 8; 
     FIG. 10 is a cross-section on the line  10 — 10  in FIG.  8 . 
     FIG. 11 is a longitudinal cross-section through another embodiment of the hot air injection lance; 
     FIG. 12 is a longitudinal cross-section to an enlarged scale through a forward end part of the lance shown in FIG. 11; 
     FIG. 13 is a cross-section on the line  13 — 13  in FIG. 12; 
     FIG. 14 is a cross-section on the line  14 — 14  in FIG. 12; 
     FIG. 15 is a cross-section on the line  15 — 15  in FIG. 14; 
     FIG. 16 is a cross-section on the line  16 — 16  in FIG. 15; 
     FIG. 17 illustrates water flow passages formed in a forward part of a central body disposed with the forward end of the lance shown in FIGS. 11-16; 
     FIG. 18 is a development showing the arrangement of inlet and return water galleries for the central body part and four flow swirl vanes in the forward part of the lance shown in FIGS. 11-17; and 
     FIG. 19 is an enlarged cross-section through a rear part of the lance shown in FIGS. 11-18. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description is in the context of smelting iron ore to produce molten iron and it is understood that the present invention is not limited to this application and is applicable to any suitable ferrous ores and/or concentrates—including partially reduced ferrous ores and waste revert materials. 
     The direct smelting apparatus shown in FIG. 1 includes a metallurgical vessel denoted generally as  11 . The vessel  11  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  151  formed from water cooled panels and a lower barrel section  153  formed from water cooled panels having an inner lining of refractory bricks; 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, under quiescent conditions, includes a layer  22  of molten metal and a layer  23  of molten slag on the metal layer  22 . The term “metal layer” is understood herein to mean a region of the bath that is predominantly metal. The term “slag layer” is understood herein to mean a region of the bath that is predominantly slag. 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  (ie of the molten bath). 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 at a temperature in the range of 800-1400° C. into an upper region of the vessel and post-combusting reaction gases released from the molten bath. The lance  26  has an outer diameter D at a lower end of the lance. The lance  26  is located so that: 
     (i) a central axis of the lance  26  is at an angle of 20 to 90° relative to a horizontal axis so that the angle of injection of hot air is within this range; 
     (ii) the lance  26  extends into the vessel a distance that is at least the outer diameter D of the lower end of the lance; and 
     (iii) the lower end of the lance  26  is at least 3 times the outer diameter D of the lower end of the lance above the quiescent surface  25  of the molten bath. 
     The vessel is also fitted with solids injection lances  27  (two shown) extending downwardly and inwardly through the side walls  14  and into the molten bath for injecting iron ore, solid carbonaceous material, and fluxes entrained in an oxygen-deficient carrier gas into the molten bath. The position of the lances  27  is selected so that their outlet ends  82  are above the quiescent surface of the metal layer  22 . 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. 
     By way of context, a commercial vessel being constructed by the applicant&#39;s related company has a hearth diameter of 6 m and a hot air lance  26  that weighs approximately 60 tonnes with an outer diameter of 1.2 m and will extend approximately 10 m into the vessel. 
     The construction of one embodiment the hot air injection lance  26  is illustrated in FIGS. 2-10. 
     As shown in these figures lance  26  comprises an elongate duct  31  which receives hot gas through a gas inlet structure  32  and injects it into the upper region of vessel. The lance includes an elongate central tubular structure  33  which extends within the gas flow duct  31  from its rear end to its forward end. Adjacent the forward end of the duct, central structure  33  carries a series of four swirl imparting vanes  34  for imparting swirl to the gas flow exiting the duct. The forward end of central structure  33  has a domed nose  35  which projects forwardly beyond the tip  36  of duct  31  so that the forward end of the central body and the duct tip  36  co-act together to form an annular nozzle for divergent flow of gas from the duct with swirl imparted by the vanes  34 . Vanes  34  are disposed in a four-start helical formation and are a sliding fit within the forward end of the duct. 
     The wall of the main part of duct  31  extending downstream from the gas inlet  32  is internally water cooled. This section of the duct is comprised of a series of three concentric steel tubes  37 ,  38 ,  39  extending to the forward end part of the duct where they are connected to the duct tip  36 . The duct tip  36  is of hollow annular formation and it is internally water cooled by cooling water supplied and returned through passages in the wall of duct  31 . Specifically, cooling water is supplied through an inlet  41  and annular inlet manifold  42  into an inner annular water flow passage  43  defined between the tubes  38 ,  39  of the duct through to the hollow interior of the duct tip  36  through circumferentially spaced openings in the tip. Water is returned from the tip through circumferentially spaced openings into an outer annular water return flow passage  44  defined between the tubes  37 ,  38  and backwardly to a water outlet  45  at the rear end of the water cooled section of duct  31 . 
     The outer surface of the outermost metal tube  37  of duct  31  is machined with a regular pattern of rectangular projecting lands in the form of bosses  136  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  26 . Solidification of slag on to the lance assists in minimising the temperatures of the metal components of the lance. 
     The water cooled section of duct  31  is internally lined with an internal refractory lining  46  that fits within the innermost metal tube  39  of the duct and extends through to the water cooled tip  36  of the duct. The inner periphery of duct tip  36  is generally flush with the inner surface of the refractory lining which defines the effective flow passage for gas through the duct. The forward end of the refractory lining has a slightly reduced diameter section  47  which receives the swirl vanes  34  with a snug sliding fit. Rearwardly from section  47  the refractory lining is of slightly greater diameter to enable the central structure  33  to be inserted downwardly through the duct on assembly of the lance until the swirl vanes  34  reach the forward end of the duct where they are guided into snug engagement with refractory section  47  by a tapered refractory land  48  which locates and guides the vanes into the refractory section  47 . 
     The front end of central structure  33  which carries the swirl vanes  34  is internally water cooled by cooling water supplied forwardly through the central structure from the rear end to the forward end of the lance and then returned back along the central structure to the rear end of the lance. This enables a very strong flow of cooling water directly to the forward end of the central structure and to the domed nose  35  in particular which is subjected to very high heat flux in operation of the lance. 
     Central structure  33  comprises inner and outer concentric steel tubes  50 ,  51  formed by tube segments, disposed end to end and welded together. Inner tube  50  defines a central water flow passage  52  through which water flows forwardly through the central structure from a water inlet  53  at the rear end of the lance through to the front end nose  35  of the central structure and an annular water return passage  54  defined between the two tubes through which the cooling water returns from nose  35  back through the central structure to a water outlet  55  at the rear end of the lance. 
     The nose end  35  of central structure  33  comprises an inner copper body  61  fitted within an outer domed nose shell  62  also formed of copper. The inner copper piece  61  is formed with a central water flow passage  63  to receive water from the central passage  52  of structure  33  and direct it to the tip of the nose. Nose end  35  is formed with projecting ribs  64  which fit snugly within the nose shell  62  to define a single continuous cooling water flow passage  65  between the inner section  61  and the outer nose shell  62 . As seen particularly in FIGS. 5 and 6 the ribs  64  are shaped so that the single continuous passage  65  extends as annular passage segments  66  interconnected by passage segments  67  sloping from one annular segment to the next. Thus passage  65  extends from the tip of the nose in a spiral which, although not of regular helical formation, does spiral around and back along the nose to exit at the rear end of the nose into the annular return passage formed between the tubes  51 ,  52  of central structure  33 . 
     The forced flow of cooling water in a single coherent stream through spiral passage  65  extending around and back along the nose end  35  of central structure ensures efficient heat extraction and avoids the development of “hot spots” on the nose which could occur if the cooling water is allowed to divide into separate streams at the nose. In the illustrated arrangement the cooling water is constrained in a single stream from the time that it enters the nose end  35  to the time that it exits the nose end. 
     Inner structure  33  is provided with an external heat shield  69  to shield against heat transfer from the incoming hot gas flow in the duct  31  into the cooling water flowing within the central structure  33 . If subjected to the very high temperatures and high gas flows required in a large scale smelting installation, a solid refractory shield may provide only short service. In the illustrated construction the shield  69  is formed of tubular sleeves of ceramic material marketed under the name UMCO. These sleeves are arranged end to end to form a continuous ceramic shield surrounding an air gap  70  between the shield and the outermost tube  51  of the central structure. In particular the shield may be made of tubular segments of UMCO  50  which contains by weight 0.05 to 0.12% carbon, 0.5 to 1% silicon, a maximum of 0.5% a maximum of 0.02% phosphorous, a maximum of 0.02% sulphur, 27 to 29% chromium, 48 to 52% cobalt and the balance essentially of iron. This material provides excellent heat shielding but it undergoes significant thermal expansion at high temperatures. To deal with this problem the individual tubular segments of the heat shield are formed and mounted as shown in FIGS. 7-10 to enable them to expand longitudinally independently of one another while maintaining a substantially continuous shield at all times. As illustrated in those figures the individual sleeves are mounted on location strips  71  and plate supports  72  fitted to the outer tube  51  of central structure  33 , the rear end of each shield tube being stepped at  73  to fit over the plate support with an end gap  74  to enable independent longitudinal thermal expansion of each strip. Anti-rotation strips  75  may also be fitted to each sleeve to fit about raised spline strips  76  on tube  52  to prevent rotation of the shield sleeves. 
     Hot gas is delivered to duct  31  through the gas inlet section  32 . The hot gas may be oxygen enriched air provided through heating stoves at a temperature of the order of 1200° C. This air must be delivered through refractory lined ducting and it will pick up refractory grit which can cause severe erosion problems if delivered at high speed directly into the main water cooled section of duct  31 . Gas inlet  32  is designed to enable the duct to receive high volume hot air delivery with refractory particles while minimising damage of the water cooled section of the duct. Inlet  31  comprises a T-shaped body  81  moulded as a unit in a hard wearing refractory material and located within a thin walled outer metal shell  82 . Body  81  defines a first tubular passage  83  aligned with the central passage of duct  31  and a second tubular passage  84  normal to passage  83  to receive the hot airflow delivered from stoves (not shown). Passage  83  is aligned with the gas flow passage of duct  31  and is connected to it through a central passage  85  in a refractory connecting piece  86  of inlet  32 . 
     The hot air delivered to inlet  32  passes through tubular passage  84  of body  81  and impinges on the hard wearing refractory wall of the thick refractory body  82  which is resistant to erosion. The gas flow then changes direction to flow at right angles down through passage  83  of the T-shaped body  81  and the central passage  85  of transition piece  86  and into the main part of the duct. The wall of passage  83  may be tapered in the forward flow direction so as to accelerate the flow into the duct. It may for example be tapered to an included angle of the order of 7°. The transition refractory body  86  is tapered in thickness to match the thick wall of refractory body  81  at one end and the much thinner refractory lining  46  of the main section of duct  31 . It is accordingly also water cooled through an annular cooling water jacket  87  through which cooling water is circulated through an inlet  88  and an outlet  89 . The rear end of central structure  33  extends through the tubular passage  83  of gas inlet  32 . It is located within a refractory liner plug  91  which closes the rear end of passage  83 , the rear end of central structure  33  extending back from gas inlet  32  to the water flow inlet  53  and outlet  55 . 
     The illustrated apparatus is capable of injecting high volumes of hot gas into the smelting vessel  11  at high temperature. The central structure  33  is capable of delivering large volumes of cooling water quickly and directly to the nose section of the central structure and the forced flow of that cooling water in an undivided cooling flow around the nose structure enables very efficient heat extraction from the front end of the central structure. The independent water flow to the tip of the duct also enables efficient heat extraction from the other high heat flux components of the lance. Delivery of the hot air flow into an inlet in which it impacts with a thick wall of a refractory chamber or passage before flowing downwardly into the duct enables high volumes of air contaminated with refractory grit to be handled without severe erosion of the refractory lining and heat shield in the main section of the lance. 
     The construction of another, although not the only other, embodiment of the hot air injection lance  26  is illustrated in FIGS. 11-19. 
     As shown in these figures, lance  26  comprises an elongate duct  31  through which to pass the flow of hot air, which may be oxygen enriched. Duct  31  is comprised of a series of four concentric steel tubes  32 ,  33 ,  34 ,  35  extending to a forward end part  36  of the duct where they are connected to a tip end piece  37 . An elongate body part  38  is disposed centrally within the forward end part  36  of the duct and carries a series of four swirl imparting vanes  39 . Central body part  38  is of elongate cylindrical formation with bull-nosed or domed forward and rear ends  41 ,  42 . Vanes  39  are disposed in a four-start helical formation and are connected at their forward ends by radially outwardly extending vane ends  45  to the forward part of the duct. 
     Duct  31  is internally lined throughout most of its length by an internal refractory lining  43  which fits within the innermost metal tube  35  of the duct and extends through to the forward end parts  42  of the vanes, the vanes  39  fitting neatly within the refractory lining behind these forward end parts  42 . 
     The tip end piece  37  of the duct has a hollow annular head or tip formation  44  which projects forwardly from the remainder of the duct so as to be generally flush with the inner surface of the refractory lining  43  which defines the effective flow passage for gas through the duct. The forward end of central body part  38  projects forwardly beyond this tip formation  44  so that the forward end of the body part and the tip formation co-act together to form an annular nozzle from which the hot air blast emerges in an annular diverging flow with a strong rotational or swirling motion imparted by the vanes  39 . 
     In accordance with the present invention, duct tip formation  44 , central body part  38  and vanes  39  are all internally water cooled with flows of cooling water provided by cooling water flow passage means denoted generally as  51  extending through the wall of the duct. Water flow passage means  51  comprises a water supply passage  52  defined by the annular space between the duct tubes  33 ,  34  to supply cooling water to the hollow interior  53  of duct tip formation  44  via circumferentially spaced openings  54  in tip end piece  37 . Water is returned from the tip end piece through circumferentially spaced openings  55  into an annular water return flow passage  56  defined between the duct tubes  32  and  33  and also forming part of the water flow passage means  51 . The hollow interior  53  of tip end piece  37  is thus continuously supplied with cooling water to act as an internal cooling passage. The cooling water for the lance tip is delivered into supply passage  52  through an water inlet  57  at the rear end of the lance and the returning water leaves the lance through an outlet  58  also at the rear end of the lance. 
     The annular space  59  between duct tubes  34  and  35  is divided by helically wound divider bars into eight separated helical passages  60  extending from the rear end of the duct through to the forward end part  36  of the duct. Four of these passages are supplied independently with water through four circumferentially spaced water inlets  62  to provide for independent water supplies for the cooling of vanes  39  and body part  38 . Water inlets  62  communicate with a common water supply tube  80  via an annular supply manifold  90 . The other four passages  60  serve as return flow passages which are connected to a common annular return manifold passage  63  and a single water outlet  64 . 
     Vanes  39  are of hollow formation and the interiors are divided to form water inlet and outlet flow passages through which water flows to and from the central body part  38  which is also formed with water flow passages for internal water cooling. The forward end parts  45  of vanes  39  are connected to the forward end of innermost duct tube  35  about four water inlet slots  65  through which water flows from the four separately supplied water inlet flow passages into radially inwardly directed inlet passages  66  in the forward ends of the vanes. The cooling water then flows into the forward end of central body part  38 . 
     Central body part  38  is comprised of forward and rear inner body parts  68 ,  69  housed within a casing  70  formed of a main cylindrical section  71  and domed front and rear end pieces  41 ,  42  which are hard faced to resist abrasion by refractory grit or other particulate material carried by the hot gas flow. A clearance space  74  between the inner parts  68 ,  69  and the outer casing of the central body part is sub-divided into two sets of peripheral water flow passages  75 ,  76  by means of divider ribs  77 ,  78  formed on the outer peripheral surfaces of the inner body parts  68 ,  69 . The forward set of peripheral water flow channels  75  are arranged to fan out from the front end of the central body part in the manner shown in FIG.  17  and backwardly around the body. A flow guide insert  81  is located centrally within the inner body part  68  to extend through the water flow passage  67  and to divide that passage into four circumferentially spaced water flow passages which independently receive the incoming flows of water through the water inlet passages  66  in the forward ends of the vanes, so maintaining four independent water inlet flows through to the front end of the central body part. These separate water flows communicate with the four front peripheral water flow channels  75  through which water flows back around the forward end of the central body part. 
     A baffle plate  82  divides the water inlet passages  66 ,  67  in the forward ends of the vanes and the central body part from water flow passages in the rear parts of the vanes and the central body part. The water flowing back through the forward peripheral channels  75  extends through slots  83  in this baffle located between the inlet passages  66  so as to flow back into a central passage  84  in the rear body part  69 . This passage is also divided into four separate flow channels by means of a central flow guide  85  to continue the four separate water flows through to the rear end of the central body. The rear peripheral flow channels  76  are also arranged in a set of four in similar fashion to the by-passages  75  at the front end of the central body so as to receive the four separate water flows at the rear end of the body and to take them back around the periphery of the body back to four circumferentially spaced outlet slots  86  in the casing through which the water flows into return passage  87  in the vanes. 
     The hollow vanes are divided internally by longitudinal baffles  89  so that the cooling water passages extend from the inner forward ends of the vanes back to the rear ends of the vanes then outwardly and forwardly along the outer longitudinal ends of the vanes to radially extending water outlet passages  91  in the forward ends  42  of the vanes which communicate through outlet slots  93  with the four circumferentially spaced return passages extending back through the duct wall to the common outlet  64  at the rear end of the duct. Baffle  82  divides the inlet and outlet passages  66 ,  91  within the vanes and the water inlet and outlet flow slots  65 ,  93  for each vane are formed in the forward end of the inner duct tube  35  at an angle to the longitudinal direction to suit the helix angle of the vanes as seen in FIG.  3 . 
     The forward ends of the four concentric duct tubes  32 ,  33 ,  34 ,  35  are welded to three flanges  94 ,  95 ,  96  of the tip end piece  37  so that they are firmly connected into a strong structure at the forward end of the lance. The rear ends of the duct tubes can move longitudinally with respect to one another to allow for differential thermal expansion during operation of the lance. As most clearly seen in FIG. 19, the rear end of duct tube  32  is provided with an outstanding flange  101  to which there is welded a continuous structure  102  which carries the various water inlets and outlets  57 ,  58 ,  80 ,  64 . Structure  102  includes an internal annular flange  103  fitted with an O-ring seal  104  which serves as a sliding mounting for the rear end of duct tube  33 , so allowing the duct tube  33  to expand and contract longitudinally independently of the outer duct tube  32 . A structure  105  welded to the rear end of duct tube  34  includes annular flanges  106 ,  107  fitted with O-ring seals  108 ,  109  which provide a sliding mounting for the rear end of the duct tube  34  within the outer structure  102  fixed to the rear end of duct tube  32  so that duct tube  34  can also expand and contract independently of duct tube  32 . The rear end of the inner most duct tube  35  is provided with an outstanding flange  111  fitted with an O-ring seal  112  which engages an annular ring  113  fitted to the outer structure  102  so as to also provide a sliding mounting for the innermost duct tube allowing for independent longitudinal expansion and contraction. 
     Provision is also made for thermal expansion of the flow guide vanes  39  and the inner body part  38 . The vanes  39  are connected to the duct and to the inner body part only at their forward ends and in particular at the locations where there are water inlet and outlet flows at the inner and outer parts of the forward ends of the vanes. The main parts of the vanes simply fit between the refractory lining  43  of the duct and the casing of central body part  38  and are free to expand longitudinally. The water flow divider  85  within the rear section of the inner body part has a circular front end plate which slides within a machined surface of a tubular spigot  122  on baffle  82  so as to permit the forward and rear parts of the central body part to move apart under thermal expansion while maintaining sealing between the separated water flow passages. A thermal expansion joint  133  is provided to accommodate the thermal expansion between the forward and front ends of the central body part. 
     To further allow for thermal expansion, the vanes  39  may be shaped so as they do not extend radially outwardly between the casing of the central body part and the refractory lining of the duct when viewed in cross-section but such that they are slightly offset at an angle to the truly radial direction when the lance tubes and central body are in a cold condition. Subsequent expansion of the duct tubes during operation of the lance will allow the vanes to be drawn toward truly radial positions while maintaining proper contact with the duct lining and central body part while avoiding radial stresses on the vanes due to thermal expansion. 
     In operation of the illustrated hot air injection lance, independent cooling water flows are delivered to the four swirl vanes  39  so there can be no loss of cooling efficiency due to differential flow effects. The independent cooling water flows are also provided to the forward and rear ends of the central body part  38  so as to eliminate hot spots due to lack of water flow because of possible preferential flow effects. This is particularly critical for cooling of the forward end  41  of the central body part which is exposed to extremely high temperature conditions within the smelting vessel. 
     The duct tubes can expand and contract independently in the longitudinal direction under thermal expansion and contraction effects and the vanes and central body parts are also able to expand and contract without impairing the structural integrity of the lance or maintenance of the various independent flows of cooling water. 
     The illustrated lance is capable of operating under extreme temperature conditions within a direct smelting vessel in which molten iron is produced by the high smelt process. Typically the cooling water flow rate through the four swirl vanes and the central body part will be of the order of 90 m 3 /Hr and the flow rate through the outer housing and the lance tip will be of the order of 400 m 3 /Hr. The total flow rate may therefore be of the order of 490 m 3 /Hr at a maximum operating pressure of the order of 1500 kPag. 
     Although the illustrated lances have been designed for injection of a hot air blast into a direct smelting vessel, it will be appreciated that similar lances may be used for injecting gases into any vessel in which high temperature conditions prevail, for example for the injection of oxygen, air or fuel gases into furnace vessels. 
     It is accordingly to be understood that the invention is in no way limited to the details of the illustrated construction and that many modifications and variations may be made to the invention as described.