Abstract:
A dual outlet injector is disclosed for use in a dual lance or dual port desulfurization station, whereby reagent from a given injector vessel may be injected into two separate supply pipes respectively corresponding to the dual lances or dual ports. The dual outlet injector enables a desulfurization station to be configured comprising only one supply vessel for powdered magnesium reagent and only one supply vessel for a carrier reagent such as powdered lime.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority of U.S. provisional application No. 61/078,076 filed Jul. 3, 2008, which provisional application is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to metal making equipment and processes, and more particularly to an apparatus, system, and method applicable to desulfurization stations for injecting desulfurization reagents into transfer ladles of molten metal. 
     BACKGROUND OF THE INVENTION 
     It is common when making steel to take molten iron from a blast furnace, subject it to desulfurization, introduce it into a basic oxygen furnace to remove carbon, and to then continuously cast the resultant liquid product. In desulfurization pretreatment, a lance is lowered into the molten iron in the transfer ladle and a controlled amount of powdered reagents consisting typically of magnesium, lime and calcium carbide is injected through the lance into the molten iron. Sulfur impurities are thereby reacted into insoluble sulfides that collect in the slag which can then be raked off. As a practical matter, it is desired to complete the desulfurization process without undue delay, in order not to interrupt downstream processing. If there is an interruption in flow or plugging of materials and the ribbon of continuous cast material becomes broken, significant costs are involved to restart the ribbon. Therefore, it is essential that desulfurization continue without significant interruption. To help ensure uninterrupted desulfurization, dual port lances such as that described in U.S. Pat. No. 5,188,661 were introduced, followed by dual lance desulfurization stations, as described for example in U.S. Pat. No. 6,010,658. In state of the art desulfurization stations, a mixture of powdered magnesium and a carrier reagent, like for example powdered lime and/or calcium carbide, is injected through each of a pair of lances of a dual lance station, or through each port of a dual port lance, into the molten iron. 
     The powdered reagents are initially stored in separate “injectors” each including a pressurized storage vessel and a single outlet orifice (co-injection). Alternatively, depending on the metallurgical treatment requirements of some applications, it is not required to use separate “injectors” but instead a single injector (mono-injection) is used that injects a suitable reagent containing the components required for that particular treatment application. For yet other metallurgical treatment requirements of some applications, it is required to use a combination of separate “injectors” and single injectors (multiple-injection) to be able to inject the desired combination of reagents for the given application. 
     For the sake of clarity the following disclosures do concentrate on the co-injection process of lime reagent and magnesium reagent but it shall be understood that the same principles shall apply to the other injection processes and suitable reagents as well. Flow of powdered reagent through the injector outlet orifice may be governed by a variable orifice valve of the type disclosed in U.S. Pat. No. 5,108,075, or by a fixed orifice valve. If a fixed orifice valve is used, flow rates may be varied by varying the pressure in the vessel, or by changing the orifice. A shut-off valve is also provided upstream of the orifice valve for selectively stopping flow through the orifice valve, thereby allowing for maintenance of the orifice valve. 
     Initially, an inert gas under pressure, which is typically referred to as transport gas, will be introduced into a tube below the outlet orifice of the lime injector to initiate flow of the lime reagent. The transport gas will then flow to a location below the outlet orifice of the magnesium injector, so the powdered lime can pick up the magnesium reagent and transport it to a lance. 
       FIG. 1  is a schematic diagram of a dual-lance desulfurization station  10  of the prior art. Station  10  includes a first magnesium injector  2  having a magnesium supply vessel  12  and a first lime injector  4  having a lime supply vessel  14 , each injector  2 ,  4  feeding material into a first supply pipe  16  through respective outlet orifices  18  and  20 . First supply pipe  16  carries material, with the help of an inert pressurized transport gas, to a first lance  22  for injection into molten metal contained within ladle  24 . Station  10  also includes a second magnesium injector  3  having a magnesium supply vessel  13  and a second lime injector  5  having a lime supply vessel  15 , each injector  3 ,  5  feeding material into a second supply pipe  17  through respective outlet orifices  19  and  21 . Material from second magnesium injector  3  and second lime injector  5  flows with the aid of pressurized transport gas through second supply pipe  17  to a second lance  23  for injection into the molten metal within ladle  24 . 
     As may be understood, dual lance system  10  requires a pair of magnesium injectors  2 ,  3  and a pair of lime injectors  4 ,  5  in order to supply each of the dual injection lances  22 ,  23  with a controlled amount of a suitably proportioned mixture of magnesium and lime. A similar duplication of reagent injectors is necessary in the case of a single immersion lance having independent, dual exit ports injecting magnesium-lime mixture though each port. 
     SUMMARY OF THE INVENTION 
     Therefore, it is an object of the present invention to eliminate the need for a duplicate set of reagent injectors in a dual lance or dual port desulfurization station. 
     In order to achieve this object, a dual outlet injector is provided in a desulfurization station, whereby reagent from the dual outlet injector may be fed simultaneously to two independent supply pipes respectively corresponding to a pair of lances or pair of lance ports of the desulfurization station. The dual outlet injector may comprise an outlet splitter adapted for attachment to the injector&#39;s reagent supply vessel. The outlet splitter may include an attachment flange and a pair of conduit branches extending from the flange, whereby powdered reagent may be simultaneously received into each conduit branch of the splitter from a common outlet of the reagent supply vessel. The splitter may further include a pair of orifice valves, one in each conduit branch, for regulating output flow from the injector to the associated supply pipe carrying reagent to a lance. The splitter may also include a gate or shut-off valve in each conduit branch at a location upstream from the orifice valve for selectively allowing and stopping flow through the associated conduit branch. 
     The invention extends to a dual lance or dual port desulfurization station comprising a first dual outlet injector having a magnesium supply vessel and a second dual outlet injector having another reagent supply vessel, such as a lime supply vessel. Each injector simultaneously feeds powdered reagent to two different supply pipes, whereby a suitable reagent mixture can be carried to each lance or lance port without the need for a duplicate pair of reagent injectors. 
     A programmable logic controller may be used to automatically operate the orifice valves of the injectors based on information from sensors and detectors installed in the desulfurization station. In one embodiment, weigh cells associated with the reagent supply vessels and flow sensors associated with the lance supply pipes send signal information to the programmable logic controller for feedback control to achieve and maintain a target mixing ratio and flow rate of reagent mixture to a pair of lances. It is also possible to install pressure sensors in the lance supply pipes and/or the reagent supply vessels for feedback control purposes. Manual operation is also possible. 
     A diverter system may be installed between the lance supply pipes for diverting all flow to one lance or lance port when the other lance or lance port is malfunctioning or being serviced. The diverter system may be manually operated, and it may be connected to the programmable logic controller for automatic diversion of flow if a problem is sensed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       The nature and mode of operation of the present invention will now be more fully described in the following detailed description of the invention taken with the accompanying drawing figures, in which: 
         FIG. 1  is a schematic diagram of a desulfurization station having a dual lance injection system in accordance with prior art; 
         FIG. 2  is a schematic diagram of a desulfurization station having a dual lance injection system operating with a single magnesium injector and a single lime injector, wherein each injector is a dual outlet injector in accordance with an embodiment of the present invention; 
         FIG. 3  shows an outlet splitter attached to the respective reagent supply vessel of each dual outlet injector in the system of  FIG. 2 ; and 
         FIG. 4  is a schematic diagram of a desulfurization station having a dual lance injection system in accordance with another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference is now made to  FIG. 2  of the drawings, wherein a desulfurization station formed in accordance with an embodiment of the present invention is identified by reference numeral  110 . Desulfurization station  110  comprises a single magnesium injector  102  having a magnesium supply vessel  112  feeding powdered magnesium into a first supply pipe  116  and also into a second supply pipe  117  by way of an outlet splitter  40  attached to magnesium supply vessel  112  to receive powdered magnesium exiting the supply vessel through an outlet orifice  118  at a bottom portion of the vessel. Outlet splitter  40 , described in greater detail below, includes a first branch  42  connected to first supply pipe  116  and a second branch  43  connected to second supply pipe  117 , and is operable to inject powdered magnesium from vessel  112  into both supply pipes  116  and  117 . Supply pipes may be, for example, ¾ inch pipe (0.75 inch ID, 1.05 inch OD), 1 inch pipe (1.0 inch ID, 1.31 inch OD), or other size pipe suitable for flow communication with lances  122 ,  123 . 
     Likewise, desulfurization station  110  further comprises a single lime injector  104  having a lime supply vessel  114  feeding powdered lime into first supply pipe  116  and into second supply pipe  117  by way of another outlet splitter  40  attached to lime supply vessel  114  in association with an outlet orifice  120  of lime supply vessel  114 . As will be understood, lime is a carrier reagent in the example embodiments described herein, and another carrier reagent may be substituted for lime without straying from the invention. 
     Powdered magnesium from injector  102  and powdered lime from injector  104  flows through first supply pipe  116  to a first lance  122  for injection into molten metal contained within a transfer ladle (not shown). In similar fashion, powdered magnesium from injector  102  and powdered lime from injector  104  flows through second supply pipe  117  to a second lance  123  for injection into molten metal contained within the transfer ladle (not shown). 
     Outlet splitter  40 , shown in greater detail in  FIG. 3 , is designed for attachment to a reagent supply vessel, such as magnesium supply vessel  112  or lime supply vessel  114 . Splitter  40  may include a flange  44  adapted for attachment to the outlet portion of the supply vessel, for example by providing a bolt-hole circle about the flange or by configuring the flange to cooperate with other attachment devices. Splitter  40  may be removably attached to the supply vessel, for example by threaded fasteners or other suitable means, or permanently attached to the supply vessel, for example by welding. For typical applications, a six-inch diameter ANSI standard-class 300# flange may be used. As mentioned above, splitter  40  includes first branch  42  and second branch  43 . Branches  42  and  43  are each in communication with the vessel outlet orifice and may diverge slightly from one another as they extend downward from flange  44 . Each branch  42 ,  43  defines a passageway for carrying powdered reagent out of the vessel to a different associated supply pipe  116 ,  117 . By way of example, branches  42 ,  43  may comprise 1½ inch pipe (1.5 inch ID, 1.9 inch OD). In the embodiment shown in  FIG. 3 , each branch  42 ,  43  includes a gate valve  46  operable to shut-off or open flow from the vessel to the branch, and an orifice valve  48  located downstream from gate valve  46 . Gate valve may be a suitable commercially available valve, such as a 1½ inch Worcester ball valve, product #1 ½-4446TSE. Orifice valve  48  may be a fixed orifice valve, in which case flow rates may be varied by varying the pressure in the vessel, or by changing the orifice. Alternatively, orifice valve  48  may be a variable orifice valve having an adjustable orifice, for example a variable orifice valve of the type disclosed in U.S. Pat. No. 5,108,075. 
     In the context of providing an outlet splitter  40  on each of the magnesium and lime supply vessels, several alternative orifice valve configurations are contemplated. These include four fixed orifice valves (two on the branches of the lime injector&#39;s splitter and two on the branches of the magnesium injector&#39;s splitter); four variable orifice valves (two on the branches of the lime injector&#39;s splitter and two on the branches of the magnesium injector&#39;s splitter); two fixed orifice valves on the branches of the lime injector&#39;s splitter and two variable orifice valves on the branches of the magnesium injector&#39;s splitter; or two fixed orifice valves on the branches of the magnesium injector&#39;s splitter and two variable orifice valves on the branches of the lime injector&#39;s splitter. 
     As may be appreciated, dual outlet injectors  102  and  104  enable desulfurization station  110  to operate with exactly one magnesium injector and exactly one lime injector. Consequently, a second magnesium injector and a second lime injector required in desulfurization stations of the prior art may be eliminated or used to provide another independent desulfurization station. 
     In another aspect of the present invention, desulfurization station  110  may comprise a programmable logic controller (PLC)  50  that sends control signals to orifice valves  48  (in this case variable orifice valves) via lines  51  to automatically achieve and maintain desired flow rates of the respective reagents and a desired mixing ratio thereof. PLC  50  receives a plurality of input signals as feedback. The input signals may include respective weight signals from weigh cells  52  associated with supply vessels  112  and  114  communicated to PLC  50  by way of lines  53 , wherein the weight signals indicate the weight of reagent remaining in each vessel. The input signals may include respective flow rate signals from flow sensors  54  positioned along supply pipes  116  and  117  communicated to PLC  50  via lines  55 . In the embodiment shown in  FIG. 2 , flow sensors  54  are located along each supply pipe  116 ,  117  between the injection point of lime from injector  104  and the injection point of magnesium from injector  102  and also after (downstream from) the injection point of magnesium from injector  102 . PLC  50  may be programmed to send control signals to orifice valves  48  based on the input signals the PLC receives from weigh cells  52  and flow sensors  54  to continually adjust injection of reagent into supply lines  116  and  117  to achieve and maintain targeted reagent flow rates and a targeted mixing ratio for the reagent mixture delivered to lances  122  and  123 . As mentioned above, pressure sensors may be installed to provide additional feedback signals to PLC  50 . Of course, desulfurization station  110  may be manually controlled by overriding or omitting PLC  50 . 
       FIG. 4  shows a desulfurization station  210  formed in accordance with another embodiment of the present invention. Station  210  is generally similar to station  110  of  FIG. 2 , however a lance diverter system  60  is provided between supply pipes  116  and  117  for diverting some or all of the reagent flow from one supply pipe to the other, whereby only one of the dual lances  122 ,  123  injects to ladle  24  while the other lance is serviced. Lance diverter system  60  includes a crossover pipe  62  from supply pipe  116  to supply pipe  117 , and another crossover pipe  64  from supply pipe  117  to supply pipe  116 . Flow through crossover pipe  62  is restricted by an associated valve  63 , and flow through crossover pipe  64  is restricted by an associated valve  65 . A shut-off valve  66  is located downstream from crossover pipe  62  along supply pipe  116  for selectively stopping flow to lance  122 , in which case flow from supply pipe  116  may be diverted to supply pipe  117  for injection by lance  123 . Similarly, a shut-off valve  68  is located downstream from crossover pipe  64  along supply pipe  117  for selectively stopping flow to lance  123 , in which case flow from supply pipe  117  may be diverted to supply pipe  116  for injection by lance  122 . Valves  63 ,  65 ,  66 , and  68  may be connected to PLC  50  by lines  69  for automatic diversion of flow to one of the lances if a flow problem is detected with respect to the other lance. Of course, the valves of lance diverter system  60  may be manually operated to divert flow if a problem is observed or detected. 
     While a preferred form of this invention has been described above and shown in the accompanying drawings, it should be understood that applicant does not intend to be limited to the particular details described above and illustrated in the accompanying drawings. Thus, it is the desire of the inventors of the present invention that it be clearly understood that the embodiments of the invention, while preferred, can be readily changed and altered by one skilled in the art and that these embodiments are not to be limiting or constraining on the form or benefits of the invention.