Abstract:
A system and method of separating metal powder from a slurry of liquid metal and metal powder and salt is disclosed in which the slurry is introduced into a first vessel operated in an inert environment when liquid metal is separated from the metal powder and salt leaving principally salt and metal powder substantially free of liquid metal. The salt and metal powder is transferred to a second vessel operated in an inert enviroment with both enviroments being protected from contamination. Then the salt and metal powder substantially free of salt and liquid metal. The method is particularly applicable for use in the production of Ti and its alloys.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates to a separation system and process as illustrated in  FIG. 1  useful for the product produced by Armstrong method as disclosed and claimed in U.S. Pat. Nos. 5,779,761; 5,958,106 and 6,409,797, the disclosures of each and every one of the above-captioned patents are incorporated by reference.  
       SUMMARY OF THE INVENTION  
       [0002]     A principal object of the invention is to provide a separation system for the Armstrong process disclosed in the &#39;761, &#39;106 and &#39;797 patents;  
         [0003]     Another object of the invention is to provide a continuous separation system.  
         [0004]     The invention consists of certain novel features and a combination of parts hereinafter fully described, illustrated in the accompanying drawings, it being understood that various changes in the details may be made without departing from the spirit, or sacrificing any of the advantages of the present invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]      FIG. 1  is a schematic illustration of the separation system of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0006]     The system  10  of the present invention deals with the separation of a metal, alloy or ceramic product, such as titanium, for example only, from the reaction products in the Armstrong process. Although the Armstrong process is applicable to a wide variety of exothermic reactions, it is principally applicable to metals, mixtures, alloys and ceramics disclosed in the above-mentioned patents. The product of Armstrong process is a slurry of excess reductant metal, product metal and alloy or ceramic and salt produced from the reaction. This slurry has to be separated so that various parts of it can be recycled and the produced metal, alloy or ceramic separated and passivated if necessary.  
         [0007]     Turning now to the schematic illustration of the system and process of the present invention illustrated in  FIG. 1 , there is disclosed in the system  10  a source of, for illustration purposes only, titanium tetrachloride  12  which is introduced into a reactor  15  of the type hereinbefore disclosed in the Armstrong process. A supply tank or reservoir  17  with a supply of sodium (or other reductant)  18  is transferred by a pump  19  to the reactor  15  wherein a slurry product  20  of excess reductant and metal, alloy or ceramic, and salt is produced at an elevated temperature, all as previously described in the incorporated patents.  
         [0008]     The slurry product  20  is transferred to a vessel  25  which is in the illustration dome-shaped, but not necessarily of that configuration, the vessel  25  having an interior  26  into which the slurry product  20  is introduced. A filter  27 , preferably but not necessarily cylindrical, is positioned within the interior  26  and defines an annulus  28 , the slurry product  20  being received inside the cylindrical filter  27 . An annular heat exchanger  29  is positioned around the vessel  25 , all for a purpose hereinafter disclosed.  
         [0009]     The vessel  25  further includes a moveable bottom closure  30 . Heat exchange plates  32  are connected as will hereinafter be described to an isolated heating system  50 . A collection vessel  35  is positioned below the vessel  25  and is sealed therefrom by the moveable bottom closure  30 . The collection vessel  35  has an inwardly sloping bottom surface  36  which leads to a crusher  38  and a valve  39  in the outlet  40  of the collection vessel  35 .  
         [0010]     Finally, a vapor conduit  42  interconnects the top of the vessel  25  and particularly the interior  26  thereof with a condenser vessel  45 , the condenser vessel having a heat exchange plate  46  connected, as hereinafter described, to an isolated cooling system  60 . The condenser  45  is connected to a condenser reservoir  49 , the condensate collected therein being routed to the sodium supply tank or reservoir  17 .  
         [0011]     The isolated heating system  50  includes a head tank  52  for the heating fluid which is moved by pump  53  to the heater  55  as will be hereinafter described, connected to both the heat exchanger  29  surrounding the vessel  25  and the heat exchange plates  32  interior of the vessel  25 . The isolating cooling system  60  also is provided with a head tank  62 , a pump  63  and a cooler  65  which serves to cool the cooling fluid circulated in an isolated loop to the cooling plates  46  as will be hereinafter set forth.  
         [0012]     Below the valve  39  and the collection vessel  35  is a product conveyor  70  having a baffle or cake spreader  71  extending downwardly toward the conveyor  70 . The conveyor  70  onto which the produced metal, alloy or ceramic and salt are introduced from the collection vessel  35 , after removal of the excess reductant metal, is contacted with a counter current flow of gas, preferably but not necessarily oxygen and argon,  77  from a blower  75  in communication with a supply  76  of oxygen and the supply of inert gas such as argon. The heat exchanger  79  is in communication with the blower  75  so as to cool the oxygen/argon mixture  77  as it flows in counter current relationship with the produced metal, alloy or ceramic on the conveyor  70 , thereby to contact the product particulates with oxygen to inertthe produced metal, alloy or ceramic when required but not so much as to contaminate the produced material.  
         [0013]     As indicated in the flow sheet of  FIG. 1 , there are a plurality of flow meters  81  distributed throughout the system, as required and as well known in the engineering art. There are pressure transducers  86  and pressure control valves  89  where required, all within the engineering skill of the art. A back filter valve  91  is provided in order to flush the filter  27  if necessary. Additionally, a variety of standard shut-off valves  93  are positioned within the loop, hereinafter to be explained and as required. A vacuum pump  95  is used to draw a vacuum in the vessel  25 , as will be explained, and the symbol indicated by reference numeral  100  indicates that a plurality of the same or similar systems may be operating at any one time, it being remembered that the enclosed figure is for a single reactor  15  and one separation vessel  25 , wherein as in a commercial production plant, a plurality of reactors  15  may be operating simultaneously each reactor  15  may have more than one separation vessel  25 , all depending on engineering economics and ordinary scale up issues.  
         [0014]     Product  20  from the reactor  15  exits through line  110  and enters vessel  25  at the top thereof. Although line  110  is shown entering above the filter  27 , preferably the line  110  and filter  27  are positioned so that slurry  20  is introduced below the top of filter  27  or in the center of the filter or both. As described in the previously incorporated patents, the slurry product  20  consists of excess reductant metal, salt formed by the reaction and the product of the reaction which in this specific example is titanium existing as solid particles. The product  20  in slurry form from the reactor  15  is at an elevated temperature depending on the amount of excess reductant metal present, the heat capacity thereof and other factors in the reactor  15  during operation of the Armstrong process. In the vessel  25  is a filter  27  which occupies a portion of the interior  26  of the vessel  25 , the interior optionally being heated with the annular heat exchanger  29 . The slurry product  20  is directed to the interior of the filter  27  where the slurry contacts the heat exchange plates  32 .  
         [0015]     In the heating system  50 , the heat exchange fluid in the plates  32  pass with the heat exchange fluid from the annular heat exchanger  29  through line  111  to the line  112  which connects the heat exchange medium supply in the head tank  52  to the heat exchanger  55 . Fluid moves from the heater  55  through the heat exchange plates  32  by means of the pump  53  as the heated heat exchange fluid flows out of the heat exchanger  55  through line  113  and back into the heat exchange plates  32  and/or the annular heat exchanger  29 . Because the heating system  50  is a closed loop, the heat exchange fluid may or may not be the same as the reductant metal used in the reactor  15 . NaK is shown as an example because of the low melting point thereof, but any other suitable heat exchange fluid may be used. Suitable valves  93  control the flow of heat exchange fluid from the heater  55  to either or both of the heat exchanger  29  and plates  32 . Preferably, the plates  32  are relatively close together, on the order of a few inches, to provide more heat to the cake which forms as excess reductant metal vaporizes. Moreover, closer plates  32  reduce the path length the heat has to travel and the path length the excess reductant metal vapor travels through the forming cake, thereby to reduce the time required to distill and remove excess reductant metal from the vessel  25 . Exact spacing of the plates  32  depends on a number of factors, including but not limited to, the total surface area of the plates, the heat transfer coefficient of the plates, the amount of reductant metal to be vaporized and the temperature differential between the inside and the outside of the plates.  
         [0016]     When the slurry product  20  comes out of the reactor  15 , it is at a pressure at which the reactor  15  is operated, usually up to about two atmospheres. The product slurry  20  enters the inside of filter  27  under elevated pressure and gravity results in the liquid reductant metal being expressed through the filter  27  into the annular space  28  and fed by the line  120  into the reservoir  17 . The driving force for this portion of the separation is gravity and the pressure differential between the reactor  15  and the inlet pressure of pump  19 . If required the annulus  28  may be operated under vacuum to assist removal of liquid reductant metal, or the pressure in vessel  25  may be increased during the deliquoring of the reductant metal. After sufficient liquid metal has drained through the filter  27  by the aforementioned process, the PCV valve  89  is closed and other valves  93  are closed to isolate vessel  25  and then the valve  93  to the vacuum pump  95  is opened, whereupon a vacuum is established in the interior  26  of vessel  25 . Heating fluid (liquid or vapor, for instance Na vapor) is directed into the heat exchanger plates  32  to boil the remaining reductant metal  18  producing a filter cake. The temperature in vessel  25  is elevated sufficiently to vaporize remaining liquid metal reductant  18  therein which is drawn off through conduit  42  to the condenser  45 . The conduit  42  is required to be relatively large in diameter to permit rapid evacuation of the interior  26  of the vessel  25 . Because the pressure drop between the vessel  25  and the condenser  45 , during vaporization of the reductant metal  18  is low, the specific volume is high and the mass transfer low, requiring a large diameter conduit  42 . Boiling the reductant metal on the shell side is accomplished by heat exchange with a heated fluid on the tube side.  
         [0017]     The annular heat exchanger  29  is optionally operated to maintain the expressed liquid in the annulus  28  at a sufficient temperature to flow easily and/or to provide additional heat to the vessel  25  to assist in vaporization of excess reductant metal from the interior  26  thereof. After liquid metal reductant vapor has been removed from the interior  26  of the vessel  25 , a filter cake remains from the slurry  20 . The appropriate valves  93  are closed and the vacuum pump  95  is isolated from the system.  
         [0018]     In the condenser  45 , heat exchange plates  46  are positioned in order to cool the reductant metal vapor introduced thereinto. The cooling system  60  is operated in a closed loop and maintained at a temperature sufficiently low that reductant metal vapor introduced into the condenser  45  condenses and flows out of the condenser, as will be disclosed. The cooling system  60  includes a cooler  65  as previously described and the pump  62 . The coolant exits from the cooler  65  through line  114  which enters the heat exchange plates  46  and leaves through a line  115  which joins the line  116  to interconnect the head tank  62  and the cooler  65 . As seen in the schematic of  FIG. 1 , the heat exchange fluid used in the heating system  50  and the cooling system  60  may be the same or may be different, as the systems  50  and  60  can be maintained separately or intermixed.  
         [0019]     Both the vessel  25  and the condenser  45  are operated at least part of the time under a protective atmosphere of argon or other suitable inert gas from the argon supply  85 , the pressure of which is monitored by the transducer  86 , the (argon) supply inert gas  85  being connected to the condenser  45  by a line  117 , the condenser  45  also being in communication with the vessel  25  by means of the oversized conduit  42 . Further, as may be seen, each of the heating system  50  and the cooling system  60  is provided with its own pump, respectively  53  and  63 . As suggested in the schematic of  FIG. 1 , the heating and cooling fluid may, preferably be NaK due to its lower melting point, but not necessarily, and as an alternative could be the same as the reductant metal in either liquid or vapor phase, as disclosed.  
         [0020]     After sufficient reductant metal  18  has been removed from the slurry  20 , via the filter  27  and the conduit  42 , remaining therein is a combination of the titanium product in powder form and salt made during the exothermic reaction in reactor  15 . Because the resultant dried cake has a smaller volume than the slurry product  20  introduced, when the movable bottom closure  30  is opened, the dry cake falls from the filter  27  into the collection vessel  35  whereupon the combination of salt and titanium fall into the crusher  38  due to the sloped bottom walls  36 . In the event the cake does not readily fall of its own accord, various standard vibration inducing mechanism or a cake breaking mechanism may be used to assist transfer of the cake to the collection vessel  35 . The collection vessel  35  as indicated is maintained under an inert atmosphere at about atmospheric pressure, and after the cake passes through the crusher  38  into the exit or outlet  40 , the cake passes downwardly through valve  39  onto the conveyor  70 . There is a cake spreader or baffle  71  downstream of the valve  39  which spreads the cake so that as it is contacted by a mixture  77  of inert gas, preferably argon, and oxygen flowing counter-current to the direction of the product, the titanium powder is passivated and cooled. Although the conveyor  70  is positioned in  FIG. 1  horizontally, it may be advantageous to have the conveyor move upwardly at a slant as a safety measure in the event that closure  30  fails, then excess reductant metal would not flow toward a water wash. In addition, there may be cost advantages in having the product wash equipment on the same level as the separation equipment.  
         [0021]     Cooling and passivating is accomplished in the cooler  79  with blower  75  which blows a cooled argon and oxygen mixture through a conduit  121  to the product, it being seen from the schematic that the counter-current flow of argon and oxygen with the product has the highest concentration of oxygen encountering already passivated and cooled titanium so as to minimize the amount of oxygen used in the passivation process. Oxygen is conducted to the system from a supply thereof  76  through a valve  93  and line  122  and is generally maintained at a concentration of about 0.1 to about 3% by weight. The mixture of passivated titanium and salt is thereafter fed to a wash system not shown. Various flow meters  81  are positioned throughout the system as required, as are pressure control valves  89  and pressure transducers  86 . A filter backwash valve  91  is positioned so that the filter  27  can be backwashed when required if it becomes clogged or otherwise requires backwashing. Standard engineering items such as valves  93 , vacuum pump  95  and pressure transducers  86  are situated as required. Symbol  100  is used to denote that parallel systems identical or similar to all or a portion of the system  10  illustrated may be operated simultaneously or in sequence.  
         [0022]     In the Armstrong process, the production of the metal, alloy or ceramic is continuous as long as the reactants are fed to the reactor. The present invention provides a separation system, apparatus and method which permits the separation to be either continuous or in sequential batches so rapidly switched by appropriate valving as to be as continuous as required. The object of the invention is to provide a separation apparatus, system and method which allows the reactor(s)  15  in a commercial plant to operate continuously or in economic batches. Reduction of the distillation time in vessel  25  is important in order to operate a plant economically, and economics dictate the exact size, number and configuration of separation systems and production systems employed. Although described with respect to Ti powder, the invention applies to the separation of any metal, alloy thereof or ceramic produced by the Armstrong process or other industrial processes.  
         [0023]     The heating mechanism shown is by fluid heat exchange, but heaters could also be electric or other equivalent means, all of which are incorporated herein. The bottom closure  30  is shown as hinged and is available commercially. The closure  30  may be clamped when shut and hydraulically moved to the open position; however, sliding closures such as gate valves are available and incorporated herein. Although the reactor  20  is shown separate from the vessel  25 , the invention includes engineering changes within the skill of the art, such as but not limited to incorporating reactor  20  into vessel  25 . Although vessel  35  is illustrated in one embodiment, the vessel  35  could easily be designed as a pipe. Also, the crusher  38  could be located in vessel  25  or intermediate vessel  25  and vessel  35 . Moreover, the cake forming on the filter  27  may be broken up prior to or during or subsequent to removal of the liquid metal therefrom. Similarly, when referring to an inert environment, the invention includes a vacuum as well as an inert gas. An important feature of the invention is the separation of vessels  25  and  35  so the environments of each remain separate. That way, no oxygen can contaminate either vessel.  
         [0024]     In one specific example, a reactor  15  producing 2 million pounds per year of titanium powder or alloy powder requires two vessels  25 , each roughly 14′ high and 7′ in diameterwith appropriate valving, so that the reactor  15  would operate continuously and when one vessel  25  was filled, the slurry product from the reactor would switch automatically to the second vessel  25 . The fill time for each vessel  25  is the same or somewhat longer than the deliquor, distill and evacuation time for vessel  25 .  
         [0025]     Changing production rates of reactor  15  simply requires engineering calculations for the size and number of vessels  25  and the related equipment and separation systems. The invention as disclosed permits continuous production and separation of metal or ceramic powder, while the specific example disclosed permits continuous separation with two or at most three vessels  25  available for each reactor  15 . With multiple reactors  15 , the number of vessels  25  and related equipment would probably be between 2 and 3 times the number of reactors.  
         [0026]     While there has been disclosed what is considered to be the preferred embodiment of the present intention, it is understood that various changes in the details may be made without departing from the spirit, or sacrificing any of the advantages of the present invention.