Abstract:
A molten metal submergence device includes a submergence chamber, an inlet pipe, and a vortex breaker. The submergence chamber is defined by a side wall and includes an inlet in communication with an associated molten metal bath and an outlet in communication with the associated molten metal bath. The inlet is positioned in relation to the side wall such that material passing through the inlet is introduced at least substantially tangentially to the side wall. The inlet pipe is in communication with the inlet of the submergence chamber. The inlet pipe is configured to depend from a wall of the submergence chamber within the confines of the side wall. The vortex breaker is disposed in the submergence chamber between the inlet and the outlet.

Description:
This application claims the priority benefit of U.S. application Ser. No. 10/723,504, now abandoned, filed Nov. 26, 2003, which claims the priority benefit of U.S. application Ser. No. 60/429,502, filed Nov. 27, 2002, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention is directed to a submergence system. The invention can be employed in processes and apparatus for producing molten materials by electrolysis of their salts where the metal is lighter than the electrolyte. The invention can also be employed in processes and apparatus for producing molten materials not relying on electrolysis systems, one non-limiting example being a scrap submergence system. 
     Electrolytic cells for producing magnesium metal from MgCl 2  are well known and widely employed in present-day commercial practice. Typically, in such a cell, the MgCl 2  is dissolved in a molten salt electrolyte comprising a mixture of alkali metal and alkaline earth metal chlorides. Magnesium metal deposits in molten state on cell cathode(s) and chlorine gas is generated at anode(s) within a cell chamber; since both the metal and the gas are lighter than the electrolyte, both migrate upwardly. The magnesium metal is transported to a locality outside the cell chamber for collection and periodic removal, while the chlorine gas is separately collected and withdrawn above the cell chamber. 
     As more specifically described in U.S. Pat. No. 5,439,563 (“the &#39;563 patent”), which is incorporated herein by reference, an electrolytic cell can include a main chamber that holds molten salt electrolyte containing dissolved MgCl 2 . As free electrons are introduced to the molten salt electrolyte, which includes the MgCl 2 , the dissolved MgCl 2  reacts in the electrolytic cell to form molten magnesium and chlorine gas. Accordingly, to produce more molten magnesium the MgCl 2  must be replenished. A known way of replenishing the MgCl 2  is by introducing MgCl 2  particulates through a conduit that discharges the particulates into the molten salt electrolyte bath. As shown in the &#39;563 patent, a vertical screw feeder can deliver the particulate MgCl 2  through a conduit to the molten salt electrolyte bath that is below the molten magnesium layer. In another embodiment disclosed in the &#39;563 patent, the particulate MgCl 2  can be delivered onto a free surface of the molten salt electrolyte bath. 
     Each of these systems for replenishing the particulate MgCl 2  must confront the problem of submerging the particulate MgCl 2  into the molten salt electrolyte. The particulate MgCl 2  is difficult to submerge into the molten salt electrolyte because of its inherent wetting characteristics as a function of surface tension. Accordingly, it is desirable to provide an apparatus, system and method to promote the submersion of the MgCl 2  particulates into the molten salt electrolyte to replenish the system for producing molten magnesium. Furthermore, it is desirable to provide an apparatus, system and method to promote the submersion of materials, in general, into a molten liquid to replenish a system that produces molten liquid, or the like. 
     SUMMARY OF THE INVENTION 
     A molten metal submergence device includes a submergence chamber, an inlet pipe, and a vortex breaker. The submergence chamber is defined by a side wall and includes an inlet in communication with an associated molten metal bath and an outlet in communication with the associated molten metal bath. The inlet is positioned in relation to the side wall such that material passing through the inlet is introduced at least substantially tangentially to the side wall. The inlet pipe is in communication with the inlet of the submergence chamber. The inlet pipe is configured to depend from a wall of the submergence chamber within the confines of the side wall. The vortex breaker is disposed in the submergence chamber between the inlet and the outlet. 
     According to the present invention, a new method for submerging metal salts is provided. The method includes providing a chamber that is separate from while in communication with a molten salt electrolyte bath. The method also includes pumping molten salt electrolyte from the molten salt electrolyte bath through an inlet of the chamber. The method further includes creating a vortex of molten salt electrolyte inside the chamber. The method also includes introducing solid metal salt into the chamber to create a molten salt electrolyte and solid metal salt mixture. Typically, the solid metal salt will be in particulate form, such as a powder with an average particulate size of about 80 microns. The method further includes flushing the mixture inside the chamber through an outlet back into the molten salt electrolyte bath. 
     According to the present invention, a new system for submerging metal is provided. The system includes a closed top cell holding molten salt electrolyte, a molten metal layer floating on the molten salt electrolyte and a gas space interposed between the molten metal and a top of the well. A chamber is disposed inside the well. The chamber includes at least one side wall and a base wall. An inlet is disposed on one of the walls of the chamber. The inlet communicates with an inlet pipe. The inlet pipe communicates with a pump disposed in the cell. The pump delivers molten salt electrolyte to the chamber. A vortex breaker is disposed in the chamber. An outlet is disposed on one of the walls of the chamber below the inlet, which may include the bottom wall. The outlet communicates with an outlet pipe. The outlet pipe delivers the molten salt electrolyte to the cell in the molten salt electrolyte bath below the molten metal layer. 
     The advantages and benefits of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention can take physical form in certain parts and arrangements of parts, preferred embodiments of which will be described in detail in this specification and illustrated in the accompanying drawings. Since the drawings only disclose preferred embodiments, the invention must not be limited to the depictions shown herein. 
         FIG. 1  is a schematic view of a portion of an electrolytic cell including the metal submerging apparatus of the present invention. 
         FIG. 2  is top plan view of  FIG. 1  taken at line B-B. 
         FIG. 3  is a top plan view of  FIG. 1  taken at line C-C. 
         FIG. 4  is the portion of the electrolytic cell including the metal submerging apparatus of  FIG. 1  showing an example of a vortex in a chamber of the metal submerging apparatus and an alternative vortex breaker. 
         FIG. 5  is a table of test results from water modeling testing showing feed rate of polypropylene as a function of pump speed in RPM. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     It is to be understood that the specific devices, processes and systems illustrated in the attached drawings, and described in the following specification are simply exemplary embodiments of the inventive concepts. Even though the apparatus, method and system will be described in connection with submerging particulate metal salts into a molten salt electrolyte, it is understood that the invention can be used to submerge other materials, including, but not limited to, scrap, dust, and other solids, and even other liquids into a bath not limited to molten salt electrolytes. Hence, specific examples and characteristics relating to the embodiments disclosed herein are not to be considered as limiting. 
     Referring to  FIG. 1 , a portion of a cell, which can comprise a portion of an electrolytic cell, is generally designated at  8 . The cell  8  includes side walls (not shown), and a base wall (not shown). The cell also includes a top  10  that covers and optionally seals the cell when the cell is in operation. The side walls, the base wall and the top can include a refractory lining, which is well known in the art, and need not be described in greater detail. The top  10  includes an opening  12  to a charging well  13  defined by wall  15 , through which a metal submerging apparatus  20  is received. Since this invention is applicable as a component for existing electrolytic cells, the metal submerging apparatus and all of its components are sized to be received inside the charging well  13  through the top opening  12 . 
     The cell  8  holds a molten salt electrolyte bath  14 , a molten metal layer  16 , and a gas space  18 . The molten salt electrolyte bath  14 , the molten layer  16 , and the gas space  18  are well known in the art and described in U.S. Pat. No. 5,439,563. As a result of an electrolytic process that takes place in the electrolytic cell, the molten metal layer  16  is formed on top of the molten salt electrolyte bath  14  and, in the case of magnesium formed from magnesium chloride, chlorine is also formed. The chlorine is removed from the magnesium metal production system in a process that is also well known in the art. 
     In the case of producing magnesium metal from MgCl 2 , particulate MgCl 2  is introduced into the molten salt electrolyte bath  16 . Through the electrolytic process, the MgCl 2  is converted into molten magnesium and chlorine gas. The molten magnesium  16  is then removed. Accordingly, either intermittently or continuously, more particulate MgCl 2  must be introduced into the system to replenish the MgCl 2  that has been converted into molten magnesium and chlorine. The present invention is capable of either, but is particularly beneficial as a continuous process. The metal submerging apparatus  20  is disposed inside the cell  8  to facilitate submergence of the particulate MgCl 2  into the molten salt electrolyte bath  14 . 
     The metal submerging apparatus  20  generally includes a submergence chamber  22  where a vortex flow of molten salt electrolyte is created and a vortex breaker  24  to direct the vortex flow out of the chamber. In addition to the creation of a vortex, a general turbulent flow of molten salt electrolyte can also be created inside of the chamber to facilitate submersion of the particulate MgCl 2 . An inlet pipe  26  delivers molten salt electrolyte from the molten salt electrolyte bath  14  to the chamber  22 . The molten salt electrolyte is delivered to the chamber such that it intersects the chamber in a tangential direction, so that a vortex is formed. The vortex breaker  24  disrupts a vortex of the molten salt electrolyte that has been produced in the chamber  22  to direct the vortex flow of the molten salt electrolyte out of the chamber. Particulate MgCl 2  is delivered to the chamber  22 . The order of the creation of the vortex and the delivery of the particulate is not critical. The vortex that is formed in the chamber facilitates the submergence of the particulate MgCl 2 . The molten salt electrolyte and MgCl 2  mixture is then delivered back to the molten salt electrolyte bath via a discharge pipe  28 . 
     The system will now be described as molten salt electrolyte flows through the submergence system. An impeller  32  of a pump  33  is disposed in the molten salt electrolyte bath  14 . The impeller  32  is mounted to a shaft  34 . The shaft  34  is connected to a motor  36  that rotates the shaft, which rotates the impeller  32 . The impeller  32  is housed in a pump housing  40  that includes an inlet  42  to draw molten salt electrolyte into the pump housing. The housing  40  also includes an outlet  44  in communication with a discharge pipe  46 . The discharge pipe  46  communicates with the inlet pipe  24 . The inlet pipe  24  communicates with a chamber inlet  48  on a side wall  50  of the chamber  22 . Advantageously, the pump  33  and submerging apparatus  20  are both fitted within the charging well  13 . 
     The chamber inlet  48  is positioned so that molten salt electrolyte that enters the chamber enters at a generally horizontal angle. The horizontal orientation of the inlet  48  promotes formation of the molten salt electrolyte vortex inside of the chamber. The inlet  48  of the chamber is shown on a side wall  50  of the chamber; however, the inlet could also be located on a base wall  52  of the chamber. The inlet  48  could also straddle both the side wall  50  and the base wall  52  of the chamber  22 . The terms side wall and base wall are used simply to describe the figures, in that both the side wall and the base wall in combination can form the side wall of the metal submerging apparatus. As more clearly shown in  FIG. 2 , the side wall  50  is generally circular in cross-section. The circular orientation of the side wall  50  further facilitates the creation of the molten salt electrolyte vortex inside of the chamber  22 . 
     The vortex breaker  24  is situated near the chamber inlet  48 . In one embodiment of the invention, the vortex breaker  24  comprises a ramp  60 , similar to the ramp disclosed in U.S. Pat. No. 6,217,823, which is incorporated herein by reference. As seen in  FIG. 3 , the ramp  60  includes an inner edge  62  and a leading edge  64  positioned adjacent the inlet  48 . Molten salt electrolyte flows up the ramp  60  within the chamber  22  and spills over the inner edge  62  into a cavity  66  and exits through an outlet  68  positioned below the inlet  48 . While it is beneficial that the ramp  60  be sloped, this does not need to be achieved by a constant incline. For example, the ramp  60  can be sloped over a first portion, and be horizontal over a final portion. Similarly, the ramp need not encircle the entire side wall  50 . Accordingly, the invention is intended to encompass all versions of a sloped ramp. 
     In an alternate embodiment, the vortex breaker can take form in a blade  80  ( FIG. 4 ) positioned on the side wall  50 . The blade can be any shape including the device disclosed in U.S. Pat. No. 6,036,745, which is incorporated herein by reference. In this embodiment, the molten salt electrolyte enters the chamber  22  via the inlet  48  in a horizontal direction. The horizontally moving molten salt electrolyte contacts the blade resulting in a break in the vortex causing the molten salt electrolyte to move downward an out the outlet  68 . 
     In an alternate embodiment, the vortex breaker can comprise a system including a second inlet (not shown) that delivers a second molten salt electrolyte stream positioned below the horizontal chamber inlet  48  that delivers a first molten salt electrolyte stream. This system for creating a vortex is similar to that described in U.S. Pat. No. 4,286,985, incorporated herein by reference. In this embodiment, the horizontal chamber inlet  48  intersects the chamber  22  in a tangential manner while the second inlet, which also delivers molten salt electrolyte, intersects the side of the chamber  22  in a substantially radial manner. Accordingly, the second molten salt electrolyte stream breaks the vortex flow of the first molten salt electrolyte stream directing both the molten streams out of the outlet  68  of the chamber  22 . 
     In addition to the vortex systems described above, the vortex of the molten salt electrolyte can be achieved using any know apparatus, system or method that will result in a vortex. As stated above, the creation of a vortex facilitates the submergence of the particulate MgCl 2  into the molten salt electrolyte. Additionally, the vortex can be broken to direct the molten salt electrolyte stream out of the chamber in any known manner. 
     Referring back to the flow of the molten salt electrolyte through the metal submergence system, the molten salt electrolyte exits the chamber via the outlet  68 . The outlet  68  communicates with the discharge pipe  28 . The discharge pipe  28  includes an outlet  72  disposed in the molten salt electrolyte bath  14  below the molten metal  16 . The molten salt electrolyte is discharged below the molten metal layer  16  so as not to disturb the molten metal layer. Accordingly, the length of the discharge pipe  28  can be modified as a function of the depth of the molten metal layer  16 . 
     Particulate MgCl 2  is fed into the metal submergence apparatus  20  via a cell feed pipe  74 . The cell feed pipe  74  can deliver the particulate MgCl 2  via a screw feeder operator or a spinning distributor, as disclosed in U.S. Pat. No. 5,439,563. The cell feed pipe can also deliver the particulate MgCl 2  to a plurality of sprayers that will inject the particulate MgCl 2  into the chamber. In addition to those, the cell feed pipe  74  can deliver the particulate MgCl 2  via any distribution system that can deliver the particulate matter to the chamber  22 . Accordingly, the particulate matter is delivered to the chamber  22  where it submerges into the molten salt electrolyte flowing in the chamber resulting in a mixture of particulate MgCl 2  and molten salt electrolyte. 
     As has been stated above, since this invention is applicable as a component for an existing electrolytic cell, the metal submerging apparatus  20 , and all of its components, can be designed to be received inside the opening  12  in the top  10  of the cell  8 . In some known apparatus, this opening  12  can be smaller than 30 inches. Accordingly, the chamber  22  and the pump must be sized such that a vortex can be created in this limited space. Furthermore, the impeller  32  is positioned near the chamber, when measured in a direction parallel to the top  10  of the cell, due to the limited space that the metal submerging apparatus  20  is allowed to occupy when retrofitting such cells. 
     With a vertical discharge pipe  26 , the nadir of the vortex can be positioned inside of the discharge pipe  26  ( FIG. 4 ). This can be achieved through proper dimensioning of the chamber  22  in combination with adjusting the rate at which molten salt electrolyte is fed to the chamber  22  by the rotating impeller  32 . Accordingly, the metal submerging apparatus  20  can be retrofitted into an existing electrolytic cell having a short height and the metal submergence apparatus can still fit into this limited space. Moreover, the available height for the chamber  22  does not limit the submergence apparatus  20  because the rate of rotation of the vortex, which helps determine the height the molten salt electrolyte will reach on the chamber wall  50 , can be controlled by the feed rate from the pump. However, it has generally been shown that a relatively steep inclined vortex is beneficial in achieving efficient particulate submergence. 
     The following examples are provided to facilitate the explanation of the invention but are not intended to limit the invention to the specific embodiments disclosed. 
     EXAMPLES 
     Water modeling tests of the present system were conducted to evaluate the submergence performance. It is recognized that the most difficult part of the MgCl 2  melting process is particle contact with the molten metal salt. Therefore, particle contact would represent the rate controlling effect. Contact angle, as a function of surface tension, was used to judge wetting characteristics of the feed stock. 
     In the water modeling tests, polypropylene powder was used as the feed stock because of its high surface tension with water. Furthermore, polypropylene proved a difficult option as it was not melted or dissolved by the water medium. Accordingly, choosing polypropylene powder as a feed stock in the water model represented a worse case scenario as compared to the submergence of MgCl 2  in an electrolytic system. 
     In the test, the polypropylene powder had a diameter of 80 microns, which is similar to the particulate size of MgCl 2  feed stock used in present electrolytic systems. Buoyancy effects were also held constant for the water modeling tests. The ratio of specific gravity of the liquid to bulk density of the feed stock was approximately 2:1, which is approximates the ratio in an MgCl 2  system. The feed rate was demonstrated based on a constant volume calculation based on bulk density. 
     A summary of the properties of the materials used in the water modeling tests versus the equivalent properties in an actual MgCl 2  electrolytic system are provided below. 
     
       
         
               
               
               
             
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 MgCl 2   
                 Polypropylene/Water 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Bulk Density of the feed stock 
                 900 
                 g/l 
                 450 
                 g/l 
               
               
                 Specific Gravity of the liquid 
                 1700 
                 g/l 
                 1000 
                 g/l 
               
               
                 Contact Angle of the feed stock 
                 &gt;90° 
                   
                 105° 
               
               
                 Particle Size of the feed stock 
                 80 
                 microns 
                 80 
                 microns 
               
               
                   
               
             
          
         
       
     
     The design focused on maximizing the powder to liquid contact time while ensuring a high feed rate. The submergence apparatus used a Metaullics® D13 pump in conjunction with a 13″ ID chamber. The tests measure maximum wetting and submergence rate of the polypropylene powder at various pump speeds. Discharge diameter was varied to maximize the submergence and wetting rate. The results are plotted in the table at  FIG. 5 . Note that the feed rates in actual kg/hr of polypropylene submerged is about half the amount of MgCl 2  that could be submerged using the submergence apparatus due to the difference in bulk density between MgCl 2  and polypropylene. 
     The points for  FIG. 5  are as follows: 
     
       
         
               
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 4″ Outlet 
                 5″ Outlet 
               
             
          
           
               
                   
                 RPM 
                 sec/5 kg 
                 kg/hr 
                 RPM 
                 sec/5 kg 
                 kg/hr 
               
               
                   
                   
               
             
          
           
               
                   
                 1200 
                 88 
                 204.55 
                 1200 
                 54 
                 333.33 
               
               
                   
                 1400 
                 74 
                 243.24 
                 1400 
                 36 
                 500.00 
               
               
                   
                 1800 
                 22 
                 818.88 
                 1800 
                 16 
                 1125.00 
               
               
                   
                   
               
             
          
         
       
     
     The invention has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations.