Patent Publication Number: US-6212218-B1

Title: Reusable lance with consumable refractory tip

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to an apparatus for melting, refining and processing metals, for example, the process of steelmaking in an electric arc furnace (EAF), and more particularly, to a reusable lance with a consumable refractory tip for the injection of an metallurgical, process gases and/or particulate materials used in such proceses. 
     2. Description of Background Art 
     The process of steelmaking in electric arc furnaces has evolved such that the application of oxidizing gases, preferably pure oxygen, or other metallurgical gases including nitrogen, methane, carbon dioxide, etc.; particulate materials such as carbon and coal powders, direct reduced iron (DRI), iron carbide, etc.; and/or combinations of these gases and or particulate materials, is now normally used in the melting, refining and other processing steps of making steel in an electric arc furnace. 
     In general, oxygen may be used for multiple purposes at different points in the melting and refining process in EAF steelmaking. For example, initially it may be used to add heat by combusting carbon and other oxidizable materials and to cut scrap during the preheating phase of a melt. Oxygen has also been used to assist in the formation of foamy slag during or at the end of the melting phase, and to decarburize the molten bath during refining. It is conventional to use oxygen for the post combustion oxidation of CO in any phase of the steelmaking process. 
     Normally, the oxygen for all of these subprocesses is introduced as a high velocity jet through a pipe generally termed, an oxygen lance. Typical lance implementations have been accomplished by one of two methods, either by one or more moveable consumable oxygen lances which may be submerged in the molten steel bath, or one or more moveable water cooled oxygen lances which are positioned above the bath. 
     In normal operation, the water cooled oxygen lance is first introduced into the EAF and then gradually moved to a position by a manipulator where the end or tip of the lance is very close to the surface of the bath. The discharge velocity and angle of the oxygen stream is carefully chosen to allow the stream of oxygen to penetrate the slag and the melt to react efficiently with the iron-carbon melt. If the angle is too shallow or the pressure too low, then the oxygen will not penetrate the molten metal bath and efficiently decarburize the melt. On the other hand, if the angle is too steep or the pressure to high, then the metal in the bath may detrimentally splash on the EAF walls and electrodes. Conventionally, the water cooled oxygen lances have used supersonic nozzles, typically of the De Laval type, to produce the high velocity gases needed to penetrate the surface of the melt. 
     The water cooled lances are gaining in popularity because they are generally less expensive than consumable lances because one can replace the lance tips by welding and reuse most of the lance body. But the water cooled lances tips are relatively complex and, even though not directly in contact with the melt, need to be replaced fairly often because of the harsh environment. Further water cooled lances are somewhat less efficient in the delivery of the oxidizing gas to the reaction zone. This is because care must be taken to not touch or submerge the lance tip in the bath, or even place it where it could be consistently splashed with hot melt. Because the lance can not be brought into the reaction zone, the result is extra oxidizing gas within the furnace. Extra oxygen in the furnace contributes to the unnecessary oxidation of the electrodes, wall panels, etc. 
     Consumable lances, while being able to be submerged directly in the molten bath to efficiently place gases and materials in a reaction zone, do not have the control of gas and particulate flow rates like water cooled lances with their nozzles. The consumable lance must always be watched by an operator to make sure its positioning and feed rate are correct as it is fed into the bath because different environments consume the lance at different rates. Additionally, the amount of injected gas or particulate material is hard to determine because the operator does not know the exact depth of the tip or the amount of gases being injected at a particular spot. These variables make gas and materials lancing with a consumable lance an art and the results difficult to repeat predictably from batch to batch. 
     Refractory materials, such as ceramics and the like, have been used in EAFs to provide oxygen and other metallurgical gases from the bottom of the melt by building tuyeres into the base of the furnace. The gases are then released through the tuyeres and bubble up through the bath to produce chemical reactions with the metal. While the refractory materials used in the tuyeres are relatively long lasting in the harsh environment of the EAF, they are hard to form and manipulate into shapes. A disadvantage of the tuyeres is that their presence requires extensive maintenance of the bottom shell, the necessity of a spare bottom shell, and the expense of changing the bottom shells every 2-3 weeks. 
     Refractory covered lances used for BOF steelmaking have been cumbersome straight lances lowered vertically through the roof or top of a steel making vessel. These lances because of their weight and size are not very useful to reach or be positioned for effective injection in an EAF. For example, they might bend or break under their own weight if mounted substantially horizontally. 
     Therefore, there is a need for a reusable injection lance for gases, particulate materials or combinations thereof which combines the advantages of both types of lances and is relatively inexpensive and easy to use. 
     There is also a need for an injection lance which is adapted to be efficiently positioned in the reaction zone for steelmaking in an EAF. 
     SUMMARY OF THE INVENTION 
     The invention solves these and other needs of the metal melting, refining and processing art by providing a reusable lance with a water cooled lance body and a consumable refractory tip. In addition, the reusable lance is used with a positioning mechanism to effectively place the lance at the most opportune areas for process control in a vessel for metal melting, refing, or processing. Preferably, the lance can be used for the injection of an oxidizing gas, preferably oxygen, other metallurgical gases, particulate materials, preferably carbonaceous particulates, and/or combinations thereof into an EAF. 
     In one embodiment, the reusable lance comprises a reusable lance body which has at least one supply conduit for the supply of a pressurized flow of a processing gas or gases, particulate materials entrained in a carrier gas, and/or combinations thereof. A consumable lance tip formed of refractory material is coupled to the lance body and includes at least one introduction conduit in fluid communication with the supply conduit of the lance body. Gases, particulate materials, and/or combinations thereof flowing through the supply conduit of the lance body are carried into the process by the introduction conduit of the lance tip. 
     The refractory lance tip allows the lance to withstand the harsh environment of a metal melting, refining or processing method for much longer times between the changes in lance tips than with water cooled tips. Advantageously, the lance has a better ability to be positioned in the bath than the stationary tuyeres, consumable or nonconsumable lances, because the refractory tip may be splashed by molten metal, touch or even be submerged in the bath without catastrophic damage or immediate failure. 
     Therefore, it is an object of the invention to provide an injection lance with a long lasting replaceable lance tip which can be reused until completely consumed. 
     It is also a object of the invention to provide an injection lance which has the flexibility of being positioned above, touching or submerged in the molten bath of an EAF during the steelmaking process. 
     Yet another object of the invention is to provide an injection lance with a movable fluid cooled body which is attached to a replaceable tip formed of refractory material. 
    
    
     These and other objects, aspects and features of the invention will be more clearly understood and better described when the following detailed description is read in conjunction with the attached drawings, wherein: 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partial cross-sectional side view of an electric arc furnace illustrating the operation of a reusable lance which is constructed in accordance with the invention; 
     FIG. 2 is a cross-sectional side view of a first embodiment of the reusable lance with a consumable refractory tip as illustrated in FIG. 1; 
     FIG. 3 is an end view of the reusable lance illustrated in FIG. 2; 
     FIG. 4 is a cross-sectional side view of a second embodiment of a reusable lance with a consumable refractory tip as illustrated in FIG. 1; 
     FIG. 5 is an end view of the lance illustrated in FIG. 4; 
     FIG. 6 is a cross-sectional side view of a third embodiment of a reusable lance with a consumable refractory tip as illustrated in FIG. 1; 
     FIG. 7 is an end view of the lance illustrated in FIG. 6; 
     FIG. 8 is a pictorial representation of the reusable portion of the lance detachably coupled to more than one lance tip; and 
     FIG. 9 is a pictorial representation of the reusable portion of the lance detachably coupled to one or more new replacement tips and a partially consumed tip. 
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
     A reusable lance  10  for metal melting, refing, and processing in an electric arc furnace (EAF)  15 , or other process furnace, is shown to advantage in FIG.  1 . The EAF  15  melts ferrous scrap, or other materials, by means of an electric arc produced from one or more electrodes  20  to produce a molten metal melt  18  at its bottom. The melt  18  is generally covered with various amounts of slag  16  which is produced during the refining process of the metal. The reusable lance  10  is preferably mounted in a side wall panel  12  of the upper shell of the EAF  15  through an aperture in the fluid cooling coils  14  of the panel of the furnace and is preferably slanted downward at an angle to direct introduced gases and particulate materials toward the metal melt  18  in the bottom of the furnace. 
     The reusable lance  10  includes a reusable lance body  13  which preferably is fluid cooled and can withstand the high temperatures of the internal area of the furnace  15  for extended periods of time and many uses and includes a consumable lance tip  17  preferably made of a refractory material which has a more limited life and number of uses. The consumable tip  17  includes at least one introduction conduit  19  and is coupled to the lance body  13  having at least one supply conduit  21  such that supplies of a gas, gases, particulate materials entrained in a carrier gas, and/or combinations thereof flowing through the body can be introduced or injected into opportune areas of the furnace  15 . 
     In operation, the consumable tip  17  is used up and can be replaced after a predetermined number or uses, duration of operation, or by inspection for deterioration. A new consumable tip  17  is then coupled on the reusable lance body  13  and the lance  10  returned to operation. The refractory protection allows the consumable lance tip  17  extended life and enhanced operation over conventional water cooled tips. Additionally, with the refractory protection and no water cooling, the consumable lance tip  17  can safely be splashed, touch or even be submerged in the slag  16  or melt  18 . The consumable lance tip  17  can also be brought closer to the center of the furnace  15  than conventional water cooled tips without a substantial loss of its useful life. These features allow the reusable lance  10  to introduce a gas, gases and/or particulate materials closer to any opportune reaction zones of the furnace  15  including above the slag  16 , in the slag  16 , in metal melt  18  or at their interface so that the reusable lance  10  is more efficient and effective in its operation. 
     In one preferred embodiment, the reusable lance  10  is alternatively supplied with two main utilities from an oxygen supply  30  and a particulate supply of carbon fines  32  to a central supply conduit  21 . Each of the supplies  30 ,  32  is coupled to the reusable lance  10  through a utility supply line which has a number of controlled valves and sensing mechanisms with which to control the flow rate of the particular utility. For example, an oxygen supply line  34  from oxygen source  30  includes a solenoid shut off valve  36 , a motorized control valve  38 , an orifice plate  40  and a manual shutoff valve  42 . A differential pressure transmitter  44  is coupled across the orifice plate  40  to measures the pressure drop produced by the restriction and a pressure transmitter  46  coupled to the supply line  34  measures the absolute pressure in the line. Additionally, the carbon or particulates supply line  48  includes a solenoid shut off valve  50 , a motorized control valve  53  and a manual shut off valve  52 . 
     The operation, timing and control of the reusable lance  10  are provided by a programmed logic controller (PLC)  54 . The PLC  54  receives electrical inputs from the pressure transmitters  44 ,  56  representative of the measured pressures and determines the actual flow of the oxidizing gas in the supply line  34  from those parameters. The PLC  54  then provides electrical signals to the motorized control valve  38  to close or open and provide regulation of the flow to a desired flow rate which has been programmed in the PLC. The PLC  54  also provides electrical signals to each of the solenoid shut off valves  36 ,  50  so that the control may selectively turn on the supplies or shut them off under programmed control. Manual valves  42 ,  52  are provided to shut off the flow of utilities when the PLC  54  is inoperative, such as when the reusable lance is being removed for maintenance, and to turn them back on before start up. The PLC  54  may further provide for the circulation of cooling fluid in the reusable lance  10  by controlling the on/off timing of a water pump  60  connected to a water source  62  which provides pressurized water to a water supply line  64 . The water is circulated through the reusable lance  10  to cool the lance body  13  and returns back to the water supply  60  via a water return line  66 . 
     The movement of the lance  10  is provided under program control of the PLC  54  by means of a lance manipulator mechanism  70 . The manipulator mechanism  70  comprises a pivotable carriage rail  71  which has a sled  76  fixed to the reusable lance  10 . An electrical signal form the PLC  54  to an electric motor  74  causes the sled to travel along the rail  71 . Another electrical signal from the PLC  54  to the solenoid  72  causes the rail  71  to pivot and thus incline the reusable lance  70 . The dual movements provided by the manipulator mechanism  70  allows the lance tip  15  to be positioned very accurately. The position can be controlled very close to the surface of the slag, touch or even be submerged in the melt and be positioned at a precise angle of attack for injection of an oxidizing gas, gases or other metallurgical gases, and/or particulate materials, and combinations thereof. 
     In FIGS. 2 and 3, a first embodiment of the reusable lance  10  with the capability of introducing a gas, gases, particulate materials entrained in a carrier gas, or combinations thereof into an EAF during the steel making process is shown to advantage. The reusable lance  10  generally comprises a reusable lance body  112  and a replaceable consumable lance tip  114 . The lance body  112  includes at least one tubular means or pipe  116  having a generally central conduit  118  for the passage of a gas, gases, particulate material entrained in a carrier gas, and/or combinations thereof from one or more pressurized sources. The central supply conduit  118  is in fluid communication with a generally central introduction conduit  120  of the lance tip  114  to permit the passage of the pressurized flow supplies from the lance body  112 . A second tubular means or pipe  122  fits over the first tubular means  116  and forms a second conduit  124  between them. A third tubular means or pipe  126  fits over the second tubular means  122  and forms a third conduit  125  between them. The conduits  124  and  125  are used for cooling the lance body  112  by circulating cooling fluid, preferably water, through the conduit  124  from the pressurized supply  64  and back to the return  66  through conduit  125 . The third tubular means  126  has connected to it a metal mounting ring  128 . The mounting ring  128  has a slope to its covex front face to provide a support surface for the tip  114 . The mounting ring  128  centers a threaded female coupling  129  between it and the first tubular means  118  for ease in coupling the tip  114  to the body  112 . 
     The lance tip  114  is generally cylindrical in shape and at least partially formed of a thermally resistive material  136 . Preferably, the thermally resistive material is a refractory material and, more preferably, the refractory material is of the type normally used in EAFs because of its chemistry and thermal resistance to the EAF environment. The refractory material can be produced from many substances, but preferably is made from a ceramic clay which has been slurried, pressed into a form and then kilned dried. 
     The thermally resistive material  136  surrounds a tubular means or pipe  120  which provides a centrally located introduction conduit  121 . One end of the pipe  120  extends past the refractory  136  and is externally threaded to form a nipple at its meeting with the lance body  112  so that it may be received in coupling  129 . The other end of the pipe  120  is recessed from the front of the refractory  136 . The back face of the thermally resistive material  136  is formed into a concave conical shape which mates with the sloping surface of the mounting ring  128 . 
     The lance body  112  can then be detachably coupled to the lance tip  114  by threading the end of pipe  120  into the coupling  129  and seating the convex conical seal of the mounting ring  128  into the concave conical seat of the refractory  136 . This first coupling means of the lance body  112 , including one of more elements of the coupling  129  and convex conical face of the mounting ring  128 , and the second coupling means of the lance tip  114 , including one or more elements of the nipple of pipe  120  and the concave face of the refractory  136 , can be used in a facile manner to connect the two portions together for forming a lance for operation or to decoupling them to change the lance tip after its useful life. The first coupling means has been shown as a female coupling means and a convex surface and the second coupling means as a male coupling means and a concave surface. It is readily evident that these roles could be reversed or any combination of the elements could be used. While coupling means as shown have been described and several alternatives disclosed, it is further evident that many other types of coupling means are available for detachably coupling the two sections together. 
     Optionally, the lance tip  114  on its front end includes another coupling means to detachably decouple one lance tip from another lance tip. Preferably, the additional coupling means are substantially identical to the coupling means of the lance body. This arrangement is shown in FIG. 2 where the refractory  136  is formed with a female coupling  138  embedded therein and the front face of the refractory  136  is formed as a convex face. Two tips are joined by the front end coupling means of one tip cooperatively coupling to the back end coupling means of the other. 
     A second preferred embodiment of the lance  10  is shown to advantage in FIGS. 4 and 5. The lance  10  is again comprised of a reusable body  200  and a consumable tip  202 , but also includes a separate passageway for the provision of a second gas or mixture of gases. In the illustrated implementation, the supplied gas or mixture of gases can be a hydrocarbon fluid fuel, preferably gaseous such as propane, natural gas, or atomized liquids such as fuel oil, etc. In the reusable body  200 , a tubular means  204  surrounding tubular means  206  provides a supply conduit  208  for the additional gas or mixture of gases. The supply conduit  208  communicates with a plurality of apertures  210  of a mounting ring  212  to allow passage of the gas or mixture of gases to the consumable tip  202 . 
     The consumable tip  202  is similar to the first embodiment in that it has a central pipe  201  which is surrounded by a thermally resistive material  203 , preferably a refractory material. The consumable tip  202  contains an annular chamber  212  which then communicate the gas or mixture of gases to a series of semicircular secondary passages  216  which travel the length of the tip and surround the pipe  201 . The secondary passages  216  carry the gas or mixture of gases to the end of consumable tip  202  where they can combine with the gas, gases, particulates entrained in a carrier gas, or combinations thereof which flow through an introduction conduit  220  in the center of the consumable tip  202 . 
     In this manner, the lance  10  may be used as a burner in one mode to introduce chemical energy by the combustion of a fuel and oxidizer and the flow of combustion products into a process. Preferably, this can be accomplished by either combusting natural gas supplied from the secondary passages  216  with oxygen supplied from the introduction conduit  220 , or vice versa, or combusting particulate carbon entrained in a carrier gas supplied from introduction conduit  220  with an oxidizer supplied from passages  216 . 
     The first, second and front end coupling means for the second embodiment are substantially the same as that described for FIGS. 2 and 3 of the first embodiment with the addition of an advantageous sealing method. The first coupling means includes the addition of a pair of circular sealing ridges  230  and  232  on the sloping face of the mounting ring  212  which mate with opposing valleys  234  and  236  of the second coupling means formed on the back face of the consumable tip  202 . Between the ridges  230  and  232 , a sealing material  233  can be compressed by the coupling of the lance body  200  to the tip  202 . The front end coupling means also includes similar ridges  238  and  240  on the sloping front face of the disposable tip  202 . 
     A third preferred embodiment of the lance  10  is shown to advantage in FIGS. 6 and 7. The lance  10  is again comprised of a reusable body  200  and a consumable tip  202 , but as with the second embodiment includes a separate passageway for the provision of a second gas or mixture of gases. In the illustrated implementation, the supplied gas or mixture of gases can be a hydrocarbon fluid fuel, preferably gaseous such as propane, natural gas, or atomized liquids such as fuel oil, etc. In the reusable body  300 , a tubular means  304  surrounding tubular means  306  provides a supply conduit  308  for the additional gas or mixture of gases. The supply conduit  308  communicates with a plurality of apertures  310  of a mounting ring  312  to allow passage of the gas or mixture of gases to the consumable tip  302 . 
     The consumable tip  302  is similar to the first and second embodiments in that it has a central pipe  301  which is surrounded by a thermally resistive material  303 , preferably a refractory material. The consumable tip  302  contains an annular chamber  312  which then communicates the gas or mixture of gases to a series of semicircular secondary passages  316  which travel the length of the tip and surround the pipe  301 . The secondary passages  316  carry the gas or mixture of gases to the end of consumable tip  302  where they can combine with the gas, gases, particulates entrained in a carrier gas, or combinations thereof which flow through an introduction conduit  320  in the center of the consumable tip  302 . 
     In this manner, the lance  10  may be used as a burner in one mode to introduce chemical energy by the combustion of a fuel and oxidizer and the flow of combustion products into a process. Preferably, this can be accomplished by either combusting natural gas supplied from the secondary passages  316  with oxygen supplied from the introduction conduit  320 , or vice versa, or combusting particulate carbon entrained in a carrier gas supplied from introduction conduit  320  with an oxidizer supplied from passages  316 . 
     The first, second and front end coupling means for the third embodiment are substantially the same as that described for FIGS. 2 and 3 of the first embodiment with the addition of an second advantageous sealing method. The first coupling means includes the addition of a plurality of circular grooves  330  on the convex face of the mounting ring  312 . A sealant mixture is applied to the grooves  330  on the convex face of the body  300  before fitting the two parts together. The convex face of the body  300  then mates with the concave face the second coupling means formed on the back face of the consumable tip  302  to press the sealant mixture into a tight seal which prevents gases from leaking between the conical surfaces. Prefereably the sealant mixture is a cement like slurry made from a refractory powder and a liquid which can be easily applied to the grooves  300  of the convex face. It is also evident that with this sealing method, simikar grooves can be placed on the concave face of the tip  302 , and used either alone or in combination with grooves  330  on the covex face. Optionally, the front end coupling means also includes similar grooves  333  on the front convex face of the disposable tip  302 . 
     The ability of all three of the embodiments to couple one lance tip to another lance tip provides several distinct advantages for the reusable lance  10 . As shown in FIG. 8, a multisegment lance can be constructed out of one reusable lance body  112  and one or more consumable lance tips or segments  114   a, b  and  c . As many segments as are needed may be coupled together to give the desired depth of penetration of a melt. Additionally, where there is a need for changing the depth of penetration from one process to the next the length of the tip is easily changed. Importantly, with this method the entirety of a segment can be used and a lance quickly returned to service. As seen in FIG. 9 when most of one lance tip has been consumed  114   e , another tip  114   d  can be coupled in back of it and to the body  112  and the lance returned to service with the new tip and the partially used one. The entire tip can then be consumed which significantly affects overall usage costs for the lance  10 . 
     While the invention has been described in connection with a preferred embodiment, this specification is not intended to limit the scope of the invention to the particular forms set forth, but, on the contrary, it is intended to cover any such alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.