Abstract:
An elongate metallurgical lance ( 27 ) for injecting solid particulate material into molten material held within a vessel ( 11 ) is disclosed. The lance includes a central core tube ( 31 ) through which to pass solid particulate material, an annular cooling jacket ( 32 ) surrounding the central core tube throughout a substantial part of its length, a coolant inlet means ( 52 ), and a coolant outlet means ( 53 ). An outer wall of a forward end section of the jacket is formed from a first material which has high heat transfer properties and can withstand external temperatures above 1100° C. for prolonged periods when the jacket is cooled by coolant flow. An outer wall of a body section of the jacket is formed from a second material that maintains its structural properties when exposed to external temperatures above 1100° C. for prolonged periods when the jacket is cooled by coolant flow, whereby the outer wall acts as a structural member that contributes to supporting the lance at these temperatures. The outer wall of the forward end section and the outer wall of the body section are welded together.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention provides a metallurgical lance for injecting solid particulate material into a vessel. 
     One application of the lance is as a means for injecting metallurgical feed material into the molten bath of a vessel in a process (such as a direct smelting process) for producing molten metal. 
     2. Description of Related Art 
     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/AU96/00197 (WO 96/31627) in the name of the applicant. 
     The HIsmelt process as described in the International application is a molten bath-based direct smelting process which has particular application for producing molten ferrous metal from ferrous feed material (such as ores, partly reduced ores, and metal containing waste streams). The HIsmelt process includes: 
     (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 includes 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 includes 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/or 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 solids material into the metal layer in the bottom of the vessel. In a commercially operating process the lances must withstand hostile conditions, including operating temperatures of the order of 1400° C., within the smelting vessel for prolonged periods, typically at least several months. The lances must accordingly have an internal forced cooling system to operate successfully in this harsh environment and must be capable of withstanding substantial local temperature variations. The present invention enables the construction of lances that are able to operate effectively under these conditions. 
     SUMMARY OF THE INVENTION 
     According to the invention, there is provided an elongate metallurgical lance to extend into a vessel for injecting solid particulate material into molten material held within the vessel, which lance includes: 
     (a) a central core tube through which to pass the solid particulate material; 
     (b) an annular cooling jacket surrounding the central core tube throughout a substantial part of its length, which jacket defines an inner elongate annular coolant flow passage disposed about the core tube, an outer elongate annular coolant flow passage disposed about the inner coolant flow passage, and an annular end flow passage interconnecting the inner and outer annular coolant flow passages at a forward end of the jacket; 
     (c) coolant inlet means for inlet of coolant into the inner annular coolant flow passage of the jacket at a rear end region of the jacket; and 
     (d) coolant outlet means for outlet of coolant from the outer annular coolant flow passage at the rear end region of the jacket, whereby to provide for flow of coolant forwardly along the inner annular coolant flow passage to the forward end of the jacket then through the annular end flow passage and backwardly through the outer annular coolant flow passage, 
     and wherein: 
     (i) an outer wall of a forward end section of the jacket is formed from a first material which has high heat transfer properties and can withstand external temperatures above 1100° C. for prolonged periods when the jacket is cooled by coolant flow; 
     (ii) an outer wall of a body section of the jacket is formed from a second material that maintains its structural properties when exposed to external temperatures above 1100° C. for prolonged periods when the jacket is cooled by coolant flow, whereby the outer wall acts as a structural member that contributes to supporting the lance at these temperatures; and 
     (iii) the outer wall of the forward end section and the outer wall of the body section are welded together. 
     The above-described combination of high heat transfer and structural sections of the lance makes it possible to make the lance relatively long so that; 
     (a) the entry position of the lance into a vessel that contains a molten bath of metal and slag can be in a side wall of the vessel above the quiescent slag layer, and necessarily above the very hostile hearth region of the vessel; and 
     (b) the lance extends downwardly and inwardly a sufficient distance to deliver feed material into a central portion of the hearth region. 
     Locating the entry point of the lance in this position, ie above the quiescent slag layer, also makes it possible for the lance to be changed-over if necessary while the vessel still holds molten metal and slag. Thus, lance change-over does not necessitate a major shut-down of the vessel involving draining the vessel. 
     Preferably the jacket includes a transition section positioned between the outer wall of the forward end section and the outer wall of the body section and the transition section is welded to both outer walls. 
     Preferably the wall thickness of the outer wall of the body section is less than that of the outer wall of the forward end section. 
     Preferably the wall thickness at one end of the transition section is substantially the same as that of the outer wall of the forward end section and the wall thickness at the other end of the transition section is substantially the same as that of the body section. 
     Preferably the temperatures are above 1200° C. 
     More preferably the temperatures are above 1300° C. 
     Preferably the first material is copper or a copper alloy. 
     Preferably the second material is steel. 
     Preferably the transition section is formed from steel. 
     Preferably the weld between the forward end section and the transition section is buttered with nickel or a nickel alloy. 
     Preferably the outer wall of the jacket includes keying formations for solidification of slag onto the outer wall. 
     Preferably the keying formations have an undercut or dove-tail cross-section. 
     Preferably the length of the lance that, in use, is self-supporting, is at least 1.5 meters. 
     Preferably the inner and outer annular coolant flow passages and the annular end flow passage of the jacket are defined by: 
     (a) an inner tube and an outer tube interconnected at a forward end of the jacket by an annular bullnose end connector to form a single hollow annular structure which is closed at the forward end of the jacket by the annular bullnose end connector; and 
     (b) an elongate tubular structure disposed within the hollow annular structure and having (i) a tube part which extends within it to divide the interior of the hollow annular structure into said inner and outer elongate annular flow passages and (ii) a forward end part disposed adjacent the annular bullnose end connector of said hollow annular structure such that the annular end flow passage is defined between said forward end part of the tubular structure and the annular bullnose end connector of said hollow annular structure. 
     Preferably the outer tube includes a forward part and a rearward part welded together. 
     More preferably the forward part of the outer tube defines the outer wall of the forward end section of the jacket that is formed from the first material. 
     More preferably also the rearward part of the outer tube defines the outer wall of the body section of the jacket that is formed from the second material. 
     More preferably the outer tube includes the transition section positioned between and welded to the forward and rearward parts. 
     More preferably the bullnose end connector is formed from the first material. 
     Preferably the forward end part and the tube part of the elongate tubular structure are welded together. 
     Preferably the bullnose end connector is welded to each of the inner tube and the outer tube. 
     Preferably the weld connections between the following components of the jacket are axially spaced to facilitate assembly of the jacket: 
     (i) the bullnose end connector and the inner tube; 
     (ii) the bullnose end connector and the outer tube; and 
     (iii) the forward end part and the tube part. 
     Preferably the core tube includes a nozzle that has one part that is located partially within and is shielded by the cooling jacket and another part that extends beyond the cooling jacket, and the nozzle has a threaded rear end that engages a complementary threaded section of the core tube so that the nozzle can be readily attached and detached from the core tube. 
     Preferably the annular end flow passage curves smoothly outwardly and backwardly from the inner annular coolant flow passage to the outer annular coolant flow passage and the effective cross-sectional area for water flow through the annular end flow passage is less than the cross-sectional flow areas of both the inner and outer annular coolant flow passages. 
     Preferably further the single hollow annular structure is mounted so as to permit relative longitudinal movement between the inner and outer tubes thereof due to differential thermal expansion or contraction thereof and the elongate tubular structure is mounted to accommodate that movement. 
     Preferably the coolant is water. 
     According to the present invention there is also provided a vessel for operating a molten bath-based process for smelting ferrous feed material to produce molten ferrous metal which includes a hearth, a side wall extending upwardly from the hearth, and at least one of the above-described metallurgical lance extending through the side wall and into the vessel. 
     Preferably the dimensions of the lance are selected such that the lance extends at least 1.5 meters into the vessel and is self-supporting over that length. 
     Preferably the self-supporting length of the lance is at least 2.5 meters. 
     Preferably the lance extends downwardly through the side wall of the vessel into a hearth region of the vessel at an angle of 30 to 60° to the horizontal. 
     Preferably the side wall includes a section formed from water-cooled panels and the lance extends through that section. 
    
    
     In order that the invention may be more fully explained, one particular embodiment will be described with reference to the accompanying drawings in which: 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a vertical section through a metallurgical vessel incorporating a pair of solids injection lances constructed in accordance with the invention; 
     FIGS. 2A and 2B join on the line A—A to form a longitudinal cross-section through one of the solids injection lances; 
     FIG. 3 is an enlarged longitudinal cross-section through a rear end of the lance; 
     FIG. 4 is an enlarged cross-section through the forward end of the lance; 
     FIG. 5 is an enlarged cross-section of a part of the forward end of the lance which illustrates the transition section of the jacket; and 
     FIG. 6 is an enlarged transverse cross-section on the line  6 — 6  in FIG.  2 B. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates a direct smelting vessel suitable for operating the HIsmelt process as described in International Patent Application PCT/AU96/00197 and the disclosure in the International application is incorporated herein by cross-reference. The following description is in the context of smelting iron ore to produce molten iron. 
     With reference to the Figures, 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  151  formed from water cooled panels and a lower barrel section  153  formed from water cooled panels and 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 into an upper region of the vessel. 
     The vessel is also fitted with solids injection lances  27  (two shown) 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 molten bath. The position of the lances  27  is selected so that their entry points are above the quiescent surface  25  of the slag layer  23  and 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. The lances  27  extend at least 1.5 meters into the vessel at an angle of 30° to 60° to the horizontal and are self-supporting over that length. The construction of the solids injection lances is illustrated in detail in FIGS. 2 to  6 . 
     In use of the vessel to operate the HIsmelt process, iron ore, solid carbonaceous material (typically coal), and fluxes (typically lime and magnesia) entrained in a carrier gas (typically N 2 ) are injected into the molten bath via the lances  27 . The momentum of the solid material/carrier gas causes the solid material and gas to penetrate to a lower region of the molten bath. The injection of the solid material and the carrier gas causes buoyancy uplift of molten metal, solid carbon and slag which in turn causes substantial agitation in the molten bath, with the result that the molten bath expands in volume and has a surface indicated by the arrow  30 . The extent of agitation is such that there is reasonably uniform temperature throughout the molten bath—typically, 1450°-1550° C. In addition, upward movement of splashes, droplets and streams of molten material caused by the buoyancy uplift of molten metal, solid carbon, and slag extends into the top space  31  above the molten bath in the vessel and: 
     (a) forms a transition zone  28 ; and 
     (b) projects some molten material (predominantly slag) beyond the transition zone  28  and onto the part of the upper barrel section  151  of the side walls  14  that is above the transition zone  28  and onto the roof  17 . 
     The expanded molten bath and the transition zone  28  define a raised bath. 
     In addition to the above, a hot air blast at a temperature of 800-1400° C. via the lance  26  post-combusts reaction gases CO and H 2  in the transition zone  28  and generates high temperatures of the order of 2000° C. or higher in the gas space. The heat is transferred to the ascending and descending splashes droplets, and streams, of molten material in the region of gas injection and the heat is then partially transferred throughout the molten bath. 
     With reference to FIGS. 2 to  6 , each solids injection lance  27  includes a central core tube  31  through which to deliver the solids material and an annular cooling jacket  32  surrounding the central core tube  31  throughout a substantial part of its length. 
     With particular reference to FIG. 4, central core tube  31  is formed of steel tubing  33  throughout most of its length. Central core tube  31  also includes a stainless steel section  34  at its forward end that forms a nozzle that projects beyond the forward end of cooling jacket  32 . The forward end part  34  of core tube  31  includes a forward section  93  and an adaptor section  35  which are welded together at weld  101 . The forward end part  34  is connected to the tubing  33  through a screw thread  36  formed on both the adaptor section  35  and the tubing  33 . This arrangement makes it possible to readily replace the forward end section  34 . 
     Central core tube  31  is internally lined through to the forward end part  34  with a thin ceramic lining  37  formed by a series of cast ceramic tubes. As can best be seen in FIG. 3, the rear end of the central core tube  31  is connected through a coupling  38  to a T-piece  39  through which particulate solids material is delivered in a pressurised fluidising gas carrier, for example nitrogen. 
     With reference initially to FIG. 2A, annular cooling jacket  32  includes a long hollow annular structure  41  comprised of outer and inner tubes  42 ,  43  interconnected by a bullnose 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 . 
     With particular reference to FIG. 4, front end connector  44  of jacket  32  is hand machined from a solid hot forged copper billet. The materials selection for the connector  44  is based on providing high heat transfer at operating temperatures above 1300° C. 
     Outer and inner tubes  42 ,  43  are typically at least 2 meters long. Inner tube  43  is formed from steel and is welded at a forward end to front end connector  44  at weld  83 . Outer tube  42  is in two main parts, a forward part  50  and a rearward part  48 , and includes a transition part  51  positioned between and welded to the two main parts at welds  95 ,  97 . The forward part  50  is formed from copper, the rearward part  48  and the transition part  51  are formed from steel. The weld  95  between the forward part  50  and the transition part  51  is buttered with nickel or a nickel alloy. The buttering step includes preheating the parts to be welded to 600° C. The forward part  50  is welded to the front end connector  44  at weld  79 . The section of the lance that is forward of the transition part  51  is a forward end section of the lance and the transition section  51  and the section of the lance that is rearward of the transition piece  51  is a body section of the lance. The materials selection for the inner tube  43  and the rearward part  48  of the outer tube  42  is based on maintaining structural integrity of the lance when exposed to temperatures above 1300° C. in the vessel. Accordingly, the main consideration for the materials selection for these components is performance of the components as structural members. The materials selection for the forward part  50  of the outer tube  42  is based on providing high heat transfer at operating temperatures above 1300° C. In order to meet performance requirements the wall thickness of the forward part  50  is greater than that of the rearward part  48 . Transition section  51  is formed with a wall thickness that decreases from the end that is welded to forward part  50  to the other end that is welded to rearward part  48 . 
     Elongate tubular structure  45  is formed by a long steel tube  60  welded at weld  85  to a machined steel forward end piece  49  which fits within the front end connector  44  of the hollow tubular structure  41  to form an annular end flow passage  53  which interconnects the forward ends of the inner and outer water flow passages  46 ,  47 . 
     As can best be seen in FIG. 4, welds  79 ,  83  and  85  are axially offset to facilitate construction of jacket  32 . The arrangement is such that the components of jacket  32  are assembled together by first welding together front end connector  44  and inner tube  43  and forming weld  83 . The next steps are to connect forward end piece  49  to front end connector  44  via a series of circumferentially spaced dowels  70  and then to weld tube  60  to forward end piece  49 . Locating resultant weld  85  axially forward of weld  83  minimises heat effects on the already-formed weld  83  when forming weld  85 . The final step is to weld outer tube  42  (which has previously been assembled by welding together forward part  50 , transition part  51 , and rearward part  48 ) to front end connector  44 . Again, locating resultant weld  79  axially forward of weld  85  minimises heat effects on the already-formed weld  85  when forming weld  79 . 
     The rear end of annular cooling jacket  32  is provided with a water inlet  52  through which the 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 the outlet  53 . This ensures that the coolest water is in heat transfer relationship with the incoming solids material to ensure that this material does not melt or burn before it discharges from the forward end of the lance and enables effective cooling of both the solids material being injected through the central core of the lance as well as effective cooling of the forward end and outer surfaces of the lance. 
     The outer surfaces of the tube  42  and front end piece  44  of the hollow annular structure  41  are machined with a regular pattern of rectangular projecting bosses  54  each having an undercut or dove tail cross-section so that the bosses serve as keying formations for solidification of slag on the outer surfaces of the lance. Solidification of slag on to the lance assists in minimising the temperatures 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. 
     It has been found that it is important to cooling of the tip end of the lance to maintain a high water flow velocity around the annular end flow passage  51 . In particular it is most desirable to maintain a water flow velocity in this region of the order of 10 meters per second to obtain maximum heat transfer. In order to maximise the water flow rate in this region, the effective cross-section for water flow through passage  51  is significantly reduced below the effective cross-section of both the inner annular water flow passage  46  and the outer water flow passage  47 . Forward end piece  49  of the inner tubular structure  45  is shaped and positioned so that water flowing from the forward end of inner annular passage  46  passes through an inwardly reducing or tapered nozzle flow passage section  61  to minimise eddies and losses before passing into the end flow passage  53 . The end flow passage  53  also reduces in effective flow area in the direction of water flow so as to maintain the increased water flow velocity around the bend in the passage and back to the outer annular water flow passage  47 . In this manner, it is possible to achieve the necessary high water flow rates in the tip region of the cooling jacket without excessive pressure drops and the risk of blockages in other parts of the lance. 
     In order to maintain the appropriate cooling water velocity around the tip end passage  51  and to minimise heat transfer fluctuations, it is important to maintain a constant controlled spacing between the front end piece  49 , tubular structure  45  and the end piece  44  of the hollow annular structure  41 . This presents a problem due to differential thermal expansion and contraction in the components of the lance. In particular, the outer tube  42  of hollow annular structure  41  is exposed to much higher temperatures than the inner tube  43  of that structure and the forward end of that structure therefore tends to roll forwardly in the manner indicated by the dotted line  62  in FIG.  4 . This produces a tendency for the gap between components  44 ,  49  defining the passage  53  to open when the lance is exposed to the operating conditions within the smelting vessel. Conversely, the passage can tend to close if there is a drop in temperature during operation. In order to overcome this problem the rear end of the inner tube  43  of hollow annular structure  41  is supported in a sliding mounting  63  so that it can move axially relative to the outer tube  42  of that structure, the rear end of inner tubular structure  45  is also mounted in a sliding mounting  64  and is connected to the inner tube  43  of structure  41  by a series of circumferentially spaced connector cleats  65  so that the tubes  43  and  45  can move axially together. In addition, the end pieces  44 ,  49  of the hollow annular structure  41  and tubular structure  45  are positively interconnected by circumferentially spaced dowels  70  to maintain the appropriate spacing under both thermal expansion and contraction movements of the lance jacket. 
     The sliding mounting  64  for the inner end of tubular structure  45  is provided by a ring  66  attached to a water flow manifold structure  68  which defines the water inlet  52  and outlet  53  and is sealed by an O-ring seal  69 . The sliding mounting  63  for the rear end of the inner tube  43  of structure  41  is similarly provided by a ring flange  71  fastened to the water manifold structure  68  and is sealed by an O-ring seal  72 . An annular piston  73  is located within ring flange  71  and connected by a screw thread connection  80  to the back end of the inner tube  43  of structure  41  so as to close a water inlet manifold chamber  74  which receives the incoming flow of cooling from inlet  52 . Piston  73  slides within hardened surfaces on ring flange  71  and is fitted with O-rings  81 ,  82 . The sliding seal provided by piston  73  not only allows movements of the inner tube  43  due to differential thermal expansion of structure  41  but it also allows movement of tube  43  to accommodate any movement of structure  41  generated by excessive water pressure in the cooling jacket. If for any reason the pressure of the cooling water flow becomes excessive, the outer tube of structure  41  will be forced outwardly and piston  73  allows the inner tube to move accordingly to relieve the pressure build up. An interior space  75  between the piston  73  and the ring flange  71  is vented through a vent hole  76  to allow movement of the piston and escape of water leaking past the piston. 
     The rear part of annular cooling jacket  32  is provided with an outer stiffening pipe  83  part way down the lance and defining an annular cooling water passage  84  through which a separate flow of cooling water is passed via a water inlet  85  and water outlet  86 . 
     Typically cooling water will be passed through the cooling jacket at a flow rate of 100 m 3 /Hr at a maximum operating pressure of 800 kPa to produce water flow velocities of 10 meters/minute in the tip region of the jacket. The inner and outer parts of the cooling jacket can be subjected to temperature differentials of the order of 200° C. and the movement of tubes  42  and  45  within the sliding mountings  63 ,  64  can be considerable during operation of the lance, but the effective cross-sectional flow area of the end passage  51  is maintained substantially constant throughout all operating conditions. 
     Although the illustrated lance has been designed for injection of solids into a direct reduction smelting vessel, it will be appreciated that similar lances may be used for introducing solid particulate material into any metallurgical vessel or induced any vessel in which high temperature conditions prevail. It is accordingly to be understood that this invention is in no way limited to the details of the illustrated construction and that many modifications and variations will fall within the spirit and scope of the invention.