Patent Publication Number: US-7722800-B2

Title: Apparatus for injecting solid particulate material into a vessel

Description:
TECHNICAL FIELD 
   The present invention provides a metallurgical lance which extends into a vessel for injecting solid particulate material into a vessel. Apparatus of this kind may be used for injecting metallurgical feed material into the molten bath of a smelting vessel for producing molten metal, for example by a direct smelting process. 
   A known direct smelting process, which relies on a molten metal layer as a reaction medium, and is generally referred to as the Hismelt process, is described in International application PCT/AU/96/00197 (WO 96/31627) in the name of the applicant. 
   The Hismelt process as described in the International application comprises:
         (a) forming a bath of molten iron and slag in a vessel;   (b) injecting into the bath;
           (i) a metalliferous feed material, typically metal oxides; and   (ii) a solid carbonaceous material, typically coal, which acts as a reductant of the metal oxides and a source of energy; and   
           (c) smelting metalliferous feed material to metal in the metal layer.       

   The term “smelting” is herein understood to mean thermal processing wherein chemical reactions that reduce metal oxides take place to produce liquid metal. 
   The Hismelt process also comprises post-combusting reaction gases, such as CO and H 2 , released from the bath in the space above the bath with oxygen-containing gas and transferring the heat generated by the post-combustion to the bath to contribute to the thermal energy required to smelt the metalliferous feed materials. 
   The Hismelt process also comprises forming a transition zone above the nominal quiescent surface of the bath in which there is a favourable mass of ascending and thereafter descending droplets or splashes or streams of molten metal and/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 solid material into the metal layer in the bottom of the vessel. The lances must withstand operating temperatures of the order of 1400° C. within the smelting vessel. Each lance 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. 
   U.S. Pat. No. 6,398,842 discloses one form of lance which is able to operate effectively under these conditions. In that construction the solid particulate material is passed through a central core tube which is fitted closely within an outer annular cooling jacket, the forward end of the core tube extending through and beyond the forward end of the cooling jacket into the metallurgical vessel. 
   It has been found in operation that on plant shut down following a smelting operation the accretion of slag on the lances within the vessel and on the adjacent areas of the vessel wall can make withdrawal of the lances very difficult. In particular the slag forms a bond between the lance and the wall of the vessel and the slag accretions on the lance can be larger than the opening through it which needs to be withdrawn, making it necessary to wait for the vessel to cool sufficiently to enable slag breaking equipment to be brought into the vessel. The present invention provides a modified apparatus and a method which facilitates lance withdrawal. 
   DISCLOSURE OF THE INVENTION 
   The invention provides smelting apparatus comprising a smelting vessel having a shell enclosing an internal space of the vessel and a solids injection lance extending through an opening in the shell of the vessel into the interior space of the vessel, said solids injection lance including a central core tube through which to pass solid particulate material into the vessel and an annular cooling jacket surrounding the central core tube throughout a substantial part of its length and provided with internal water flow passages for flow of cooling water therethrough, wherein the solids injections lance further comprises an annular lance mounting part extending around the annular cooling jacket at a position spaced back from the forward end of the lance to form at that position a lance segment of increased cross sectional size compared to that part of the lance which extends forwardly from it, the vessel shell is provided with a lance mounting tube extending outwardly from the vessel about said opening, and the lance mounting part is received within the mounting tube and extends into or through the opening in the shell. 
   There may be releasable fastening means to fasten the lance to the lance mounting tube with the forward end of the lance mounting part extended through said opening in the shell. 
   The vessel shell may be internally lined with refractory material forming an internal surface of the vessel and the forward end of the lance mounting part may extend through the shell opening to a forward end generally flush with the refractory of said internal surface. 
   The internal surface of the vessel may be a surface of a water cooled refractory panel fitted to the vessel wall. 
   The lance mounting tube may extend outwardly and upwardly from an upright part of the vessel wall and the forward end of the mounting section may be inclined at an angle to a central longitudinal axis of the lance so as to be flush with an upright inner surface of the vessel. 
   The annular mounting part might have an outer diameter which is at least one and a half times the outer diameter of the annular cooling jacket of the lance. It may be of the order of twice the diameter of the cooling jacket. 
   The releasable fastening means may be such that when released the lance can be driven inwardly of the vessel for a distance by sliding of its mounting part within the mounting tube. 
   The invention further provides a method of operating a direct smelting plant which includes a metallurgical vessel and one or more solids injection lances for injecting solids material into the vessel, said method comprising locating each lance so as to extend into the vessel through an opening of a size larger than the cross section of that part of the lance within the vessel by a lance mounting of a size to fit the opening, conducting a smelting operation within the vessel such that slag adheres to the lance and the internal wall of the vessel and at the conclusion of the smelting operation removing the lance by steps which include driving the lance with its mounting inwardly of the vessel to break slag accretions in the vicinity of the opening and withdrawing the lance through the opening. 
   The lance mounting may be fitted within a lance mounting tube extending outwardly from the vessel and the lance may be driven inwardly by application of a portable hydraulic power device between the mounting of the lance and the mounting tube. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order that the invention may be more fully explained, particular embodiments will be described in some detail with reference to the accompanying drawings in which: 
       FIG. 1  is a vertical cross section through a metallurgical vessel incorporating solids injection lances constructed in accordance with the invention; 
       FIG. 2  is a longitudinal cross-section through one of the solids injection lances for injecting coal into the vessel; 
       FIG. 3  is a cross-section through a rear part of the lance shown in  FIG. 2 ; 
       FIG. 4  is a longitudinal cross-section through part of an inner core tube assembly of the lance shown in  FIG. 2 ; 
       FIG. 5  is a longitudinal cross-section through a lance for injecting hot ore material into the vessel; 
       FIG. 6  is a cross-section through a rear part of the lance shown in  FIG. 5 ; and 
       FIG. 7  illustrates a modified injection lance extended through a water cooled panel fitted to an inner face of the vessel wall. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  illustrates a direct smelting vessel suitable for operation by the Hismelt process as described in International Patent Application PCT/AU96/00197. The metallurgical vessel is denoted generally as  11  and has a hearth that includes a base  12  and sides  13  formed from refractory bricks; side walls  14  forming a generally cylindrical barrel which extends upwardly from the sides  13  of the hearth and which includes an upper barrel section  15  and a lower barrel section  16 ; a roof  17 ; an outlet  18  for off-gases; a forehearth  19  for discharging molten metal continuously; and a tap-hole  21  for discharging molten slag. 
   In use, the vessel contains a molten bath of iron and slag which includes a layer  22  of molten metal and a layer  23  of molten slag on the metal layer  22 . The arrow marked by the numeral  24  indicates the position of the nominal quiescent surface of the metal layer  22  and the arrow marked by the numeral  25  indicates the position of the nominal quiescent surface of the slag layer  23 . The term “quiescent surface” is understood to mean the surface when there is no injection of gas and solids into the vessel. 
   The vessel is fitted with a downwardly extending hot air injection lance  26  for delivering a hot air blast into an upper region of the vessel and a series of solids injection lances  27  extending downwardly and inwardly through the side walls  14  and into the slag layer  23  for injecting iron ore, solid carbonaceous material, and fluxes entrained in an oxygen deficient carrier gas into the metal layer  22 . The position of the lances  27  is selected so that their outlet ends  28  are above the surface of the metal layer  22  during operation of the process. This position of the lances reduces the risk of damage through contact with molten metal and also makes it possible to cool the lances by forced internal water cooling without significant risk of water coming into contact with the molten metal in the vessel. 
   Lances  27  may be of two kinds, a first of which is employed to inject hot ore material and the other of which is employed to inject carbonaceous material such as coal. There may for example be eight solids injection lances  27  spaced circumferentially around the vessel and consisting of a series of four hot ore injection lances and four coal injection lances spaced between the hot ore injection lances. All of the lances may fit within outer housings of a common construction but the two kinds of lance have differing interior construction because of the vastly different temperature of the hot ore and the coal being injected. 
   The construction of an injection lance for carbonaceous material, identified as  27   a , is illustrated in  FIGS. 2 to 4 . As shown in these figures lance  27   a  comprises 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. Central core tube  31  is formed of low carbon steel tubing  33  throughout most of its length but its forward end is fitted with a replaceable extension or nozzle tube  34  which projects as a nozzle from the forward end of the cooling jacket  32 . 
   Central core tube  31  is internally lined through to the forward end part  34  with a ceramic lining  37  formed by a series of cast ceramic tubes. The rear end of the central core tube  31  is connected through a coupling  38  to a coal delivery system through which particulate coal is delivered in a pressurised fluidising gas carrier, for example nitrogen. 
   Annular cooling jacket  32  comprises a long hollow annular structure  41  comprised of outer and inner tubes  42 ,  43  interconnected by a front end connector piece  44  and an elongate tubular structure  45  which is disposed within the hollow annular structure  41  so as to divide the interior of structure  41  into an inner elongate annular water flow passage  46  and an outer elongate annular water flow passage  47 . Elongate tubular structure  45  is formed by a long carbon steel tube  48  welded to a machined carbon steel forward end piece  49  which fits within the forward end connector  44  of the hollow tubular structure  41  to form an annular end flow passage  51  which interconnects the forward ends of the inner and outer water flow passages  46 ,  47 . The rear end of annular cooling jacket  32  is provided with a water inlet  52  through which a flow of cooling water can be directed into the inner annular water flow passage  46  and a water outlet  53  from which water is extracted from the outer annular passage  47  at the rear end of the lance. Accordingly in use of the lance cooling water flows forwardly down the lance through the inner annular water flow passage  46  then outwardly and back around the forward annular end passage  51  into the outer annular passage  47  through which it flows backwardly along the lance and out through outlet  53 . This ensures that the coolest water is in heat transfer relationship with the incoming solids material and enables effective cooling of both the solids material being injected through the central core of the lance as well as effective cooling on the forward end and outer surfaces of the lance. 
   The outer surfaces of the tube  42  are machined with a regular pattern of rectangular projecting bosses  54  each having an undercut or dove tail cross section so that the bosses are of outwardly diverging formation and serve as keying formations for solidification of slag on the outer surfaces of the lance. Solidification of slag onto the lance assists in minimising the temperature in the metal components of the lance. It has been found in use that slag freezing on the forward or tip end of the lance serves as a base for formation of an extended pipe of solid material serving as an extension of the lance which further protects exposure of the metal components of the lance to the severe operating conditions within the vessel. 
   The lance is mounted in the wall of the vessel  11  via a mounting structure  61  comprising a tubular part  60  extended about the cooling jacket and having a double walled construction so as to enclose an annular space  70  between these walls. The tubular part  60  fits within a tubular lance mounting bracket  62  welded to the shell of vessel  11  so as to project upwardly and outwardly from the vessel and provided at its upper end with an end flange  63 . Lance mounting structure  61  is connected to the rear end of the outer tube  42  of annular cooling jacket  32  via an annular ring  64  and it also includes an annular mounting flange  65  which can be clamped to the flange  63  at the end of mounting tube  62  via clamping bolts  66 . A split spacer ring  67  is fitted between the flanges  63 ,  65  to hold them apart when the clamping bolts  66  are tightened. The arrangement is such that the forward part of the outer sleeve  60  of structure  61  extend through to the inside of the vessel wall. As seen in  FIG. 2 , the vessel wall at this location is formed by the steel barrel shell  16   a  and an internal refractory lining  16   b  and the forward end of sleeve  60  is inclined at an angle to the central longitudinal axis of the lance so as to be flush with the inner refractory surface. 
   The tubular part  60  of mounting structure  61  is water cooled, cooling water being supplied to the interior space  70  through a water inlet  68  and return through a water outlet  69  at the rear end of the mounting sleeve. The interior space  70  may be partitioned to provide an extended cooling water flow passage within it. 
   A tubular housing  71  extending rearwardly from the mounting ring  64  of mounting structure  61  houses the rear end of the intermediate tube  48  of jacket  32  and the rear end of the core tube  31  of the lance. Housing  71  carries the cooling water inlet  52  and outlet  53  for the passage of cooling water to and from the lance cooling jacket  32 . A flexible annular connecting structure  81  connects the rear end of the intermediate tube  48  of the water jacket with the housing tube  71  so as to separate the inward and outward water flow passages within the housing and to also permit relative longitudinal movement between the inner and outer tubes and the intermediate tube of the water jacket due to differential thermal expansion and contraction in the components of the lance. 
   The rear end of tubular housing  71  provides a mounting for the rear end of the inner tube  43  of the annular cooling jacket. 
   Core tube  31  is held in spaced apart relationship within annular cooling jacket  32  by a series of spacer collars  83  projecting outwardly from the central core tube at longitudinally spaced locations along the core tube to engage the inner periphery of the inner tube of the annular cooling jacket so as to form an annular gas flow passage  84  between the central core tube and the annular cooling jacket. A purge gas inlet  85  is provided at the rear end of the lance for admission of a purge gas such as nitrogen to be admitted into the gas flow passage  84  to flow forwardly through the lance between the core tube and the annular cooling jacket to exit the lance at the forward end of the cooling jacket. 
   The central core tube is fitted with a bulbous projection  86  in the region of the forward end of the cooling jacket to provide a controlled nozzle opening between the core tube and the water jacket to control the purge gas flow rate. The spacer collars  83  are formed so as to leave circumferentially spaced gaps between the outer peripheries and the inner periphery of the cooling jacket to allow for free flow of purge gas through the annular purge gas flow passage  84 . One of the end collars  83  is located closely adjacent the bulbous projection  86  so as to provide accurate location of that projection within the forward end of the outer cooling jacket so as to create the controlled annular gap for the purge gas exit nozzle. The flow of purge gas is maintained to ensure that slag can not penetrate the forward end of the nozzle between the core tube and the outer water jacket. If slag were to penetrate the lance in this region it would immediately freeze because of the water cooled outer jacket and the cold purge gas. 
   During operation of the lances slag will accumulate on the outer surfaces of the lance and the inner surface of the vessel. On shutdown the slag will solidify tending to bond the lance to the vessel. However with the illustrated mounting arrangement this bond can readily be broken to facilitate withdrawal of the lance. This can be achieved by loosening the clamping bolts  66  sufficiently to enable withdrawal of the split spacer ring  67 . This then permits limited inward movement of the lance mounting sleeve within the mounting tube  62  so that the forward end of the mounting sleeve is moved inwardly from the wall of the vessel to break any slag accretions. This then allows the lance along with slag that has solidified on the outer tube  42  to be readily withdrawn through the enlarged opening provided for the tubular mounting  60 . 
   The hot ore injection lances may be of generally similar construction to the coal injection lances. However, as shown in  FIGS. 5 and 6 , the hot ore lance  27   b  has an inner core tube formed as a thick walled spun cast tube  31   b  with no liner. The tube  31   b  must be made in sections which are joined by split joining sleeves  91 . Adjacent tubes can be aligned and connected through the joining sleeves by stitch welding. The forward end of the core tube  31   b  is provided with a projection  86   b  to set the size of the purge gas outlet nozzle. Because of the thicker core nozzle tube in the hot ore injection lance this projection is much smaller than the more bulbous projection of the coal delivery lance. 
   In a further modification, the hot ore injection lance is provided with a water cooled flange  92  to stop overheating of the housing tube  71   b . This flange is sandwiched between the water cooled end flange of the lance housing and the flange on the end of the ore injection system which may also be water cooled. 
   The inner core tube of the hot ore injection lance is held in spaced apart relationship within the cooling jacket by a series of spacer collars projecting outwardly from the central core tube in the same fashion as in the coal lance construction. As in the coal lance, the space between the inner core tube and the water jacket provides an annular passage for flow of purge gas which exits the lace at the forward end of the cooling jacket. 
   The outer mountings for the two kinds of injection lance are identical so that both kinds of injection lances can be inserted into a common design housing. 
     FIG. 7  provides a schematic illustration of a solids injection lance  27   c  fitted into one of the tubular lance mounting brackets  62  of vessel  11 . The solids injection lance  27   c  may be of the same general construction as described in relation to  FIGS. 2 through 6  above. The vessel wall  16  is lined internally with water cooled refractory panels  100  and the lance  27   c  extends into the vessel through an aperture in the panels  100 . The lance  27   c  is modified such that the forward end of its outer annular part  60  is fitted with a covering annular disc  101  of refractory material to protect that front face against exposure to excessive temperature during start-up and lance replacement situations before there is a build up of slag within the vessel. The annular part  60  is extended within the vessel wall so that the refractory disc  101  is flush with the inner face of the water cooled panel  101  and it serves as a refractory plug in the opening through that panel.