Abstract:
A lance for injecting gas into a furnace vessel. The lance imparts a spiral or swirling flow to gas discharged by the lance. The lance includes a plurality of internally water-cooled flow vanes in fluid communication with a fluid-cooled structure that is discrete from the fluid-cooled outer wall of the lance. The result is a lance that effectively discharges gas with a desired swirling motion, that is comparatively simple in design and construction, and whose flow vanes are capable of withstanding the extreme thermal stresses encountered in a metallurgical or other high temperature furnace vessel.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention provides an apparatus for injecting gas into a vessel. It has particular, but not exclusive, application to apparatus for injecting a flow of gas into a metallurgical vessel under high temperature conditions. Such metallurgical vessel may, for example, be a smelting vessel in which molten metal is produced by a direct smelting process. 
       BACKGROUND OF THE INVENTION 
       [0002]    The term “smelting” is herein understood to mean thermal processing wherein chemical reactions take place that reduce metal oxides to produce liquid metal. 
         [0003]    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 U.S. Pat. Nos. 6,398,842; 6,440,356; 6,773,659 and 6,939,391 and published U.S. Patent Application No. 2006/0108722, the disclosures of which are incorporated herein in their entireties by reference thereto. 
         [0004]    The HIsmelt process generally 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. 
         [0005]    The HIsmelt process also comprises post-combusting reaction gases released from the bath, such as CO and H 2 , 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. 
         [0006]    The HIsmelt process also comprises forming a transition zone above the nominal quiescent surface of the bath in which there is a favorable mass of ascending and thereafter descending droplets or splashes or streams of molten metal and/or slag which provide an effective medium to transfer to the bath the thermal energy generated by post-combusting reaction gases above the bath. 
         [0007]    In the HIsmelt process the metalliferous feed material and solid carbonaceous material are 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 solids material into the metal layer in the bottom of the vessel. To promote post-combustion of reaction gases in the upper part of the vessel, a blast of hot air, which may be oxygen enriched, is injected into the upper region of the vessel through a downwardly extending hot air injection lance. To promote effective post-combustion of the gases in the upper part of the vessel, it is desirable that the incoming hot air blast exit the lance with a swirling motion. To achieve this, the outlet end of the lance may be fitted with internal flow guides to impart an appropriate swirling motion. The upper regions of the vessel may reach temperatures of the order of 2000° C. and the hot air may be delivered into the lance at temperatures of the order of 1100-1400° C. The lance must therefore be capable of withstanding extremely high temperatures both internally and on the external walls, particularly at the delivery end of the lance which projects into the combustion zone of the vessel. 
         [0008]    U.S. Pat. No. 6,673,305 and published U.S. Patent Application No. 2006/0108722 disclose gas injection lance constructions for use in a direct smelting process such as the HIsmelt process. In those constructions, spiral flow guide vanes are mounted on a central tubular structure extending throughout the length of the gas flow duct. The central structure includes water flow passages which provide for the flow of cooling water to the front part of the central structure which is located generally within the tip of the gas flow duct. The flow guide vanes are disposed near the tip of the duct within a refractory lined wall section of the duct. Although the central structure on which they are carried is water-cooled, the vanes themselves are not. Consequently, they are exposed, essentially uncooled, to the extreme thermal stresses caused by the high temperature conditions within the furnace vessel which may cause warping, erosion or other thermally-related damage to the vanes. 
         [0009]    U.S. Pat. Nos. 6,440,356; 6,773,659 and 6,939,391 disclose alternative lance constructions in which the flow guides are in the form of spiral vanes mounted on a central body at the forward end of a gas flow duct. The vanes are physically connected to the wall of the gas flow duct and are internally water cooled by cooling water which flows through supply and return passages within the wall of the duct. While the gas flow vanes of these lances are water-cooled to enhance their resistance to thermal damage, their direct physical connection with the coolant flow passages of the lance results in a construction which is highly complex in design and manufacture. First, the direct fluid connection between the vanes and the wall of the duct requires considerable modification to the simple lance coolant flow passageway system employed in conventional water-cooled lances. Second, the designs of the vanes&#39; own internal coolant flow passages as well as those of the central body, with which they are also in fluid communication, are quite complicated. 
         [0010]    An advantage exists, therefore, for a lance for injecting a flow of gas into a metallurgical vessel under high temperature conditions, which lance has internally-cooled gas flow directing vanes of simple design and construction that impart a spiral flow to gas discharged from the lance. 
       SUMMARY OF THE INVENTION 
       [0011]    The present invention provides a lance for injecting gas into a furnace vessel. The lance imparts a spiral or swirling flow to gas discharged by the lance. In this regard, the lance includes a plurality of internally water-cooled flow vanes in fluid communication with a coolant fluid-cooled structure that is discrete from the water cooled outer wall of the lance. The result is a lance that effectively discharges gas with a desired swirling motion, that is comparatively simple in design and construction, and whose flow vanes are capable of withstanding the extreme thermal stresses encountered in a metallurgical or other high temperature furnace vessel. 
         [0012]    Other details, objects and advantages of the present invention will become apparent as the following description of the presently preferred embodiments and presently preferred methods of practicing the invention proceeds. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The invention will become more readily apparent from the following description of preferred embodiments thereof shown, by way of example only, in the accompanying drawings wherein: 
           [0014]      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 present invention; 
           [0015]      FIG. 2  is a longitudinal cross-section through a hot air injection lance according to the present invention; 
           [0016]      FIG. 3  is a top plan view of a water-cooled gas flow guide assembly according to the present invention that may be attached to a central structure of a hot air injection lance; 
           [0017]      FIG. 4  is a cross section of the water-cooled gas flow guide assembly taken along line IV-IV of  FIG. 3 ; and 
           [0018]      FIG. 5  is enlarged view of encircled portion V of  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]    Referring to the drawings wherein like or similar references indicate like or similar elements throughout the several views, there is shown in  FIG. 1  a direct smelting vessel suitable for operation by the HIsmelt process as described above. A 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  form a generally cylindrical barrel extending upwardly from the sides  13  of the hearth. Vessel  11  further includes an upper barrel section  15 , 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. It will be understood that vessel  11  is an example of but one of many possible furnace vessels with which the hot air injection lance of the present invention, described below, may find beneficial application. 
         [0020]    In use, vessel  11  contains a molten bath of iron and slag which includes a layer  22  of molten metal and a layer  23  of molten slag above 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 herein to mean the surface when there is no injection of gas and solids into the vessel. 
         [0021]    Vessel  11  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 two 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 preferably 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. 
         [0022]    A representative, although not limitative, construction of hot air injection lance  26  according to the present invention is illustrated in  FIGS. 2-5 . 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  11 . Lance  26  includes an elongate tubular central structure  33  which extends within the gas flow duct  31  from its rear end to its forward or distal end. Adjacent the forward end of the duct, central structure  33  carries a plurality of helical vanes  34  for imparting swirl to the gas flow exiting the duct. In the exemplary construction, four gas flow vanes  34  are shown although it is contemplated that a greater or fewer number of vanes may be provided depending on the requirements of the materials processing operation in which lance  26  is utilized. The forward end of central structure  33  has a domed nose  35  which may project forwardly beyond the tip  36  of duct  31 . The forward end of central structure  33  and the duct tip  36  cooperate to form an annular nozzle for divergent flow of gas from the duct with swirl being imparted to the gas flow by vanes  34 . Vanes  34  are desirably slidably received within the forward end of duct  31 . 
         [0023]    Downstream from the gas inlet  32  duct  31  is internally water cooled. This section of the duct is desirably comprised of a series of three concentric steel tubes  37 ,  38  and  39  extending to the forward end 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  defined by tubes  37 ,  38  and  39 . 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  and  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  and  38  and upwardly to a water outlet  45  at the rear or upper end of the water cooled section of duct  31 . 
         [0024]    The water cooled section of duct  31  is preferably internally lined with a 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 preferably 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 desirably 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 . Reduced diameter refractory section  47  is not necessary, however it does provide radial stability to central structure  33  during lance operation. 
         [0025]    The front end of central structure  33  which carries 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. 
         [0026]    Central structure  33  preferably comprises inner and outer concentric steel tubes  50  and  51  formed by tube segments disposed end-to-end and welded together. Inner tube  50  defines a central water supply passage  52  through which water flows forwardly through the central structure from a water inlet  53  at the rear end of lance  26  to the front end or nose  35  of the central structure and an annular water return passage  54  defined between tubes  50  and  51  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. 
         [0027]    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 body  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 preferably formed with projecting ribs (not illustrated) which fit snugly within the nose shell  62  to define and maintain a continuous cooling water flow passage  65  between the inner section  61  and the outer nose shell  62 . 
         [0028]    The forced flow of cooling water in a single coherent stream through passage  65  extending around and back along the nose end  35  of central structure  33  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. The specific structure which defines the manner by which water flows through the forward end of central structure  33 , including vanes  34  is described in greater detail hereinafter. 
         [0029]    Central structure  33  is preferably surrounded by 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. The sleeves are arranged end-to-end to form an essentially 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 to 1% manganese, 0.02% phosphorous, 0.02% sulfur, 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 to enable them to expand longitudinally independently of one another while maintaining a substantially continuous shield at all times. It will be understood, however, that any suitable refractory or ceramic material that is capable of thermally shielding tube  51  would be acceptable for use as shield  69 . 
         [0030]    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 minimizing damage of the water cooled section of the duct. In this regard, the duct gas inlet  32  preferably comprises a T-shaped body  81  molded as a unit of 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 . 
         [0031]    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  70 . 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  48  of the main section of duct  31 . It is accordingly also preferably 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 . 
         [0032]    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 is preferably formed with projecting ribs (not shown) which fit snugly within the nose shell  62  to define a continuous cooling water flow passage  65  between the inner section  61  and the outer nose shell  62 . If present, the ribs are desirably generally helical such that passage  65  extends from the tip of the nose in a spiral whereby 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. 
         [0033]    As most clearly shown in  FIG. 4 , prior to passing from central passage  52  of central structure  33  into central water flow passage  63  of nose end  35 , a substantial portion of coolant water from the central passage  52  is diverted into coolant fluid passage means that internally cool the helical gas flow guide vanes  34 . The coolant fluid passage means comprise one or more coolant passageways  100  that lie within vanes  34  and follow the helical contours thereof. Each coolant passageway  100  includes an inlet  102  provided in an upper region of its associated vane and an outlet  104  provided in a lower region its associated vane. According to a presently preferred embodiment, each of vanes  34  includes a plurality of coolant passageways  100  that are arranged in an axially and radially nested array within the vanes to provide consistent cooling throughout the vanes. Alternatively, however, it will be understood that a single slot-like passageway spanning a substantial portion of the axial and radial dimensions of the vanes could be used to achieve the desired cooling effect. Regardless of their number, coolant passageway(s)  100  are preferably formed by copper or steel conduit  106  that is bendable to assume the desired ultimate helical shape of vanes  34 . A casting block assembly having the appropriate number and shape of vane cavities is then enclosed around the conduit and molten copper is poured in the casting block assembly. As seen in  FIG. 4 , the resultant casting is a monolithic gas flow guide member  108  including masses of cast copper  110  with conduit  106  embedded therein to define vanes  34  and a cast copper central sleeve  110  which is adapted to closely surround the outer wall of tube  51 . So constructed, the mass of the vanes renders gas flow guide member  108  highly structurally rigid as well providing the vanes with excellent thermal conductivity characteristics that enhance their effective cooling by the internal water flow through coolant passageway(s)  100  during operation of lance  26 . 
         [0034]    Water restriction means, exemplified in the form of a plate  114 , is affixed such as by welding or the like to the inner wall of a distal segment of inner tube  50  at a location between the coolant passageway inlet(s)  102  and outlet(s)  104 . Plate  114  preferably has one or more appropriately sized apertures  116  to assure a high water flow rate through central structure  33  so that the entire central structure and the gas flow vanes  34  carried thereby are effectively cooled, as described in greater detail below. 
         [0035]    As previously noted, during operation of the lance  26  water is supplied to lance in order to cool its outer wall. According to the present invention, a separate flow of water is directed downwardly through central passage  52  of central structure  33 . When water passing through central passage strikes  52  strikes plate  114 , back pressure is generated which forces a substantial portion of the water flow to enter the vane coolant passageway inlet(s)  102 , pass through coolant passageway(s)  100  and exit vane coolant passageway outlet(s)  104  to thereby cool vanes  34 . As mentioned above, it is preferred that plate  114  include one or apertures  116  Such aperture(s) are provided to permit passage of the balance of the water that flows through central passage  52  but that does not enter the vane coolant passageway(s) to pass directly to the central water flow passage  63  of inner copper body  61 . It is conceivable that in certain situations the absence of aperture(s)  116  in plate  114  could constrict water flow through central structure  33  to an extent that thermally related damage could result in the central structure and/or vanes  34 . A further advantage of apertures(s)  116  is that it/they produce one or more downwardly flowing columns of water beneath plate  114  that intersect and mix with the water discharged from outlet(s)  104 . Consequently, the kinetic energy and potentially erosive effects of high-velocity water exiting the outlet(s)  104  and aperture(s)  116  are substantially reduced. 
         [0036]    Assembly of the lower portion of the central structure  33  of the present invention, hereinafter generally referred to as gas flow guide assembly  118 , may be as follows, although variations in the manufacturing steps are possible. Plate  114  is initially affixed to a distal segment of pipe  50  between inlets  102  and outlets  104 . A weld sleeve  51   a  is welded to the upper end of the distal segment of pipe  51 . The distal segment of pipe  51  is then inserted into and welded to gas flow guide member  108  at upper and lower continuous fluid-tight welds. 
         [0037]    Referring to  FIG. 5 , there is shown an enlarged view of threaded orifices  120  that form the openings for inlets  102  Orifices  120  are adapted for threaded engagement with pipe  50 . During assembly, the orifices  120  are first partially threaded into pipe  50  and then pipe  50  is inserted in pipe  51 . The orifices are then brought into alignment with the openings of conduits  106 . Thereafter, the orifices are threaded into pipe  50  causing reduced diameter portions  122  of the orifices to be received in the openings of conduits  106 . Threading of the orifices is continued until leading ends of tapered surfaces  124  of the orifices come into firm contact with the openings of conduits  106  whereby a metal-to-metal fluid seal is created between central passage  52  and return water flow passage  54 . In the alternative, the fluid seal between orifices  120  and the openings of conduits  106  may be achieved by O-rings or similar sealing means. To facilitate threading of orifices  120  into pipe  50  the orifices may be provided with tool-engageable internal or, as shown, external surfaces  130  that are configured to receive a suitable tool such as a wrench or the like. Optionally, but preferably, the outer surface of pipe  50  is provided with spacers  132  to maintain substantially uniform spacing between pipes  50  and  51  to define a substantially uniform return water flow passage  54  in gas flow guide assembly  118 . 
         [0038]    Upon installation of orifices  120 , an annular sleeve  126  is then welded by a continuous fluid-tight weld to the bottoms of both of pipe  51  and gas flow guide member  108 . An O-ring  134  is placed in a corresponding groove in an upper neck portion of inner copper body  61  and the upper neck portion of the inner copper body is inserted into the lower end of the distal pipe section of pipe  50 . The frictional yet sealing fit thus produced between inner copper body  61  and pipe  50  provides a fluid seal between central water flow passage  63  of the inner copper body and return water flow passage  54 . It also permits limited movement of the inner copper body  61  that may be useful to avoid possible hydraulic and/or thermal shock that could damage a rigid connection between pipe  50  and the inner copper body when the lance  26  is in operation. Lastly, the outer domed nose shell  62  is welded by a continuous fluid-tight weld to annular sleeve  126 . The resultant gas flow guide assembly  118  may then be connected to the reminder of central structure  30  by welding the upper ends of pipe  50  and weld sleeve  51   a  of  FIG. 4  to the next corresponding segments of pipes  50  and  51  in the central structure. 
         [0039]    As noted above, the water supply used for cooling the gas flow guide assembly  118  is separate from the coolant supply for the outer wall of lance  26 . And, gas flow guide assembly  118  also lacks many of the internal components and flow channels that reside in the water-cooled central body parts of the lances disclosed in U.S. Pat. Nos. 6,440,356; 6,773,659 and 6,939,391. As a result, a gas flow guide assembly constructed in accordance with the present invention simplifies construction and maintenance of a hot air injection lance to which it is connected in comparison to the lances described in those patents. 
         [0040]    Although the invention has been described in detail for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention as claimed herein.