Abstract:
The present invention relates generally to a liquid injector for silicon production. In one embodiment, the injector includes a tube having at least one opening at a first end of said tube, a moveable sealing means disposed inside the tube for sealing the at least one opening and a heating means coupled to the tube for controlling a temperature of a liquid exiting the tube through the at least one opening.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/108,376, filed on Oct. 24, 2008, which is herein incorporated by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to an apparatus used during the production of high purity metals, and more specifically to a liquid injector for silicon production. 
       BACKGROUND OF THE INVENTION 
       [0003]    One of the processes for producing high purity metals (e.g., silicon (Si)) for the electronics and solar cell industries reacts sodium (Na) with silicon tetrafluoride (SiF 4 ) to produce Si and sodium fluoride (NaF). One example of this process is described in U.S. Pat. No. 4,753,783 assigned to SRI International, which is incorporated herein by reference. 
         [0004]    Na can be added either as a solid or as a liquid. The process can be performed in a batch mode, in which case when the reaction has run to completion, the reactant feeds to the reactor are turned off, the reactor is opened and the reaction product (e.g., pure Si and NaF) is removed. When Na is added as a liquid, it is injected into the reaction chamber from a tube in which the surface tension of the liquid sodium is used to prevent reactive gases from entering the tube. Before the reactor is opened, the liquid sodium is cooled and solidified on the nozzle tip forming a solid plug, preventing liquid Na from exiting the tube and air from entering the tube during product removal. However, the exposed surface of the sodium plug reacts with air to form sodium oxides or hydroxides. The solid oxides or hydroxides must be manually removed and the tube orifice cleaned before restarting the reactor. This leads to extended down times between reactor cycles. 
         [0005]    In addition, it is occasionally necessary to pause the liquid sodium injection to correct upset conditions elsewhere in the process. Under these circumstances, the SiF 4  gas will slowly react with the exposed liquid sodium to produce a solid plug that will prevent restart of the production without opening the reactor and cleaning the orifice. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention is directed towards a liquid injector for silicon production. In one embodiment, the liquid injector for silicon production comprises a tube having at least one opening at a first end of said tube, a moveable plunger disposed inside said tube, said moveable plunger having a tip for forming a seal with said at least one opening at said first end of said tube and a temperature control element coupled to said tube. 
         [0007]    In one embodiment, the liquid injector for silicon production comprises a tube having at least one opening at a first end of said tube and an annular volume along said first end, a moveable plunger disposed inside said tube, said moveable plunger having a tip for forming a seal with said at least one opening at said first end of said tube and a heat transfer fluid reservoir coupled to said tube for flowing a heat transfer fluid through said annular volume. 
         [0008]    In one embodiment, the liquid injector for silicon production comprises a tube having at least one opening at a first end of said tube, a moveable sealing means disposed inside said tube for sealing said at least one opening and a heating means coupled to said tube for controlling a temperature of a liquid exiting said tube through said at least one opening. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The teaching of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which: 
           [0010]      FIG. 1  illustrates a high level block diagram of the present invention; 
           [0011]      FIG. 2  illustrates a first embodiment of a liquid injector; and 
           [0012]      FIG. 3  illustrates a second embodiment of a liquid injector. 
       
    
    
       [0013]    To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. 
       DETAILED DESCRIPTION 
       [0014]    The present invention provides a liquid injector for silicon production. For example, the liquid injector can be used to inject liquid sodium into a reactor for silicon production. Although the examples discussed below are in reference to liquid sodium, the present invention is not so limited. The liquid injector may be used to deliver any liquid compound into a reactor to provide many reactor cycles with minimal operator intervention. 
         [0015]    As discussed above, before a reactor is opened during silicon production, liquid sodium that is injected into the reactor is cooled and solidifies on the nozzle tip forming a solid plug, preventing liquid sodium from exiting the tube and air from entering the tube during product removal. However, the exposed surface of the sodium plug reacts with air to form sodium oxides and hydroxides. The solid oxides or hydroxides must be manually removed and the tube orifice cleaned before restarting the reactor. This leads to extended down times between reactor cycles. However, the liquid injector discussed in the present application prevents solidification of the liquid sodium at the nozzle tip, while maintaining a required flow of the liquid and a temperature of the liquid sodium and of the reactor. 
         [0016]      FIG. 1  illustrates a high level block diagram of a liquid injector  104  within the context of a system  100  in accordance with one embodiment of the present invention. For example, the system  100  include a reactor  102  and the liquid injector  104  coupled to the reactor  102 . A valve  106  is coupled to the liquid injector  104 . The valve  106  may be actuated by a mechanical system or assembly (e.g., a mechanical ball valve or gate valve), a pneumatic system or assembly (e.g., pneumatic valves operated by air), an electric system or assembly (e.g. a solenoid valve), a hydraulic system or assembly (e.g., a hydraulic valve actuated by the flow of a fluid) or any combination thereof. For example, the valve  106  may be a mechanical valve operated by a person or the valve  106  may be a solenoid valve or pneumatic valve automatically actuated by an electrical signal or an air line. 
         [0017]    A liquid  108  may be provided to the reactor  102  using the liquid injector  104  via line  110 . In one embodiment, the liquid  108  may be liquid sodium used for the production of silicon. In one embodiment, the liquid  108  may be contained in a reservoir or a storage tank. In another embodiment, the liquid  108  may be fed from another source, for example another reactor within a process. 
         [0018]    The system  100  may also include a controller  120  coupled to the valve  106  and the liquid injector  104  via a control signal line  112 . The controller  120  may be a general-purpose computer suitable for use in performing the functions described herein. 
         [0019]    The controller  120  may comprise a processor element  122  (e.g., a CPU), a memory  124 , e.g., random access memory (RAM) and/or read only memory (ROM), a module  125  for providing a pulse rate and a temperature control algorithm, as discussed below, and various input/output devices  126  (e.g., storage devices, including but not limited to, a tape drive, a floppy drive, a hard disk drive or a compact disk drive, a receiver, a transmitter, a speaker, a display, a speech synthesizer, an output port, and a user input device (such as a keyboard, a keypad, a mouse, and the like)). 
         [0020]    It should be noted that the controller  120  can be implemented in software and/or in a combination of software and hardware, e.g., using application specific integrated circuits (ASIC), a general purpose computer or any other hardware equivalents. In one embodiment, the present module  125  for providing a pulse rate and a temperature control algorithm can be loaded into memory  124  and executed by processor  122  to implement the functions as discussed below. As such, the present module  125  for providing a pulse rate and a temperature control algorithm can be stored on a computer readable storage medium, e.g., RAM memory, magnetic or optical drive or diskette and the like. 
         [0021]    In one embodiment, the controller  120  is used to control the liquid injector  104  at a predefined pulse rate. For example, the controller  120  may automatically actuate the valve  106  by sending a control signal to the valve  106  or to an air line that actuates the valve  106  to open and close the liquid injector  104  at the predefined pulse rate. In addition, the controller  120  is communication with various sensors within the liquid injector  104  to control a temperature of the liquid exiting the liquid injector  104 , as discussed below. 
         [0022]      FIG. 2  illustrates a more detailed cross sectional view of one embodiment of the liquid injector  104 . In one embodiment, the liquid injector  104  includes a tube  206  and a moveable plunger  220  (hereinafter also referred to as a plunger  220 ) coupled to the tube  206 . The tube  206  has an interior volume. In one embodiment, the plunger  220  moves axially up and down in a direction relative to a bottom and a top of the tube  206  as indicated by line  230 . The plunger  220  is coupled to the tube  206  in the interior volume of the tube  206 . The plunger  220  is also coupled to a valve  106 . 
         [0023]    In one embodiment, the tube  206  and the plunger  220  are fabricated from metal, e.g., stainless steel. In one embodiment, the plunger  220  may be fabricated from any material that is not wetted by the liquid, e.g., liquid sodium or react with process gases. For example, when the liquid is liquid sodium and the process gases include silicon tetrafluoride (SiF 4 ), the plunger  220  may be made of a material that does not react with the liquid sodium or the SiF 4 . 
         [0024]    The tube  206  includes an inlet  208  and an outlet  210 . The outlet has a diameter that is sufficient to provide a liquid in a stream. Said another way, the outlet should not have a diameter that causes “spraying” of the liquid. 
         [0025]    In addition, the outlet  210  has a shape that is substantially similar to a shape of a tip  222  of the plunger  220 . As a result, when the tip  222  of the plunger  220  is mated with the outlet  210 , a gas tight seal is formed. In one embodiment, “gas tight” is defined as preventing any air or process gas from entering the tube  206 . Accordingly, none of the liquid within the tube  206  is reacted, thereby, preventing solidification of the liquid within the tube  206 . 
         [0026]    In addition, the outlet  210  is located on one end of the tube  206 . That is, the outlet  210  is located as close to a bottom edge or perimeter of the tube  206  and not towards the center of the tube  206  as found in valves. As a result, when the tip  222  of the plunger  220  is mated with the outlet  210 , no open volume remains in the tube  206 . In other words, a bottom of the tube  206  and a bottom of the tip  222  of the plunger  220  lie on and share a single plane. Said another way, the bottom of the tube  206  and the bottom of the tip  222  of the plunger  220  are flush. 
         [0027]    Moreover, as the tip  222  is pushed into the outlet  210 , the tip  222  is designed to discharge any residual liquid out of the tube  206 . In other words, the tip  222  is designed to “squeegee” liquid remaining in the outlet out of the tube  206 . This prevents residual liquid being left within the tube near the outlet  210  and provides another level of protection against having any liquid solidify by reacting with the air and process gases, thereby, plugging the liquid injector  104 . 
         [0028]    The liquid injector  104  also includes a temperature sensor  204 . In one embodiment, the temperature sensor  204  is located in the tip  222  of the plunger  220 . However, it should be noted that the temperature sensor  204  may be located anywhere on or within the liquid injector  104  for measuring the liquid temperature exiting the liquid injector  104 . The temperature sensor  204  may be any type of temperature sensor, for example, a thermocouple. In addition, the liquid injector  104  may include a temperature control element  202  (e.g. a coil) around the tube  206 . The temperature control element  202  may be used to heat or cool the liquid. When only heating is used, the temperature control element  202  may be heating coils that use any type of heating mechanism, e.g., radio frequency (RF) induction, resistive heating, flowing heated fluid through the temperature control element  202 , and the like. When heating and cooling is used, the temperature control element  202  may be, for example, a Peltier device or coils with a heat exchanging fluid that can heat and cool. The temperature sensor  204  and the temperature control element  202  are in communication with the controller  120  illustrated in  FIG. 1 . 
         [0029]    The combination of the temperature sensor  204  and the temperature control element  202  are used to control a temperature of the liquid exiting the liquid injector  104 . For example, the temperature of the liquid is controlled to control viscosity of the liquid to allow the liquid to flow freely. In addition, the liquid temperature is controlled to prevent the liquid from reacting immediately and self igniting. 
         [0030]    In one embodiment, the temperature sensor  204  may send temperature readings of the liquid at the outlet  210  to the controller  120 . A maximum temperature threshold and a minimum temperature threshold can be predefined. If the temperature readings of the liquid are below a minimum temperature, the controller  120  may signal the temperature control element  202  to heat the liquid. If the temperature readings of the liquid are above a maximum temperature threshold, the controller  120  may signal the temperature control element  202  to cool the liquid. 
         [0031]    It should be noted that the temperature control element  202  may be used also to maintain the liquid temperature within a predefined range, e.g., between the minimum temperature threshold and the maximum temperature threshold. For example, the controller  120  may cycle between heating and cooling to maintain the temperature within the predefined range. 
         [0032]    In  FIG. 2 , the liquid injector  104  is illustrated in an “open” position. As discussed above, the valve  106  is actuated to move the plunger  220  within the tube  206  to close the tube  206 . As discussed above, the valve  106  may be actuated by a mechanical system or assembly (e.g., a mechanical ball valve or gate valve), a pneumatic system or assembly (e.g., pneumatic valves operated by air), an electric system or assembly (e.g. a solenoid valve), a hydraulic system or assembly (e.g., a hydraulic valve actuated by the flow of a fluid) or any combination thereof. The valve  106  can be actuated periodically to move the plunger  220  up and down or pulsate the plunger  220 . The pulse rate of the plunger  220  can be used to control an average velocity of the liquid exiting the liquid injector  104  and a temperature of the reactor  102 . 
         [0033]    The rate of pulsing can be controlled manually or automatically by a controller  120 , as shown in  FIG. 1 . In one embodiment, the pulse rate is used to control the average feed rate of the liquid into the reactor. By controlling the average feed rate of the liquid, the temperature of the reactor can also be controlled. 
         [0034]    In some processes, for example injecting liquid sodium during the production of silicon, it is desirable to have the liquid sodium react with process gases towards a bottom of a reactor. This also helps to control the temperature of the reactor. Pulsing the plunger  220  at a predefined pulse rate also controls an average velocity of the liquid exiting the liquid injector  104 . 
         [0035]      FIG. 3  illustrates a more detailed cross sectional view of another embodiment of the liquid injector  104   a.  The liquid injector  104   a  illustrated in  FIG. 3  is similar to the liquid injector  104  illustrated in  FIG. 2  in many respects. For example, the liquid injector  104   a  illustrated in  FIG. 3  includes a tube  206  and a moveable plunger  220  coupled to the tube  206 . The plunger  220  moves axially up and down in a direction relative to a bottom and a top of the tube  206  as indicated by line  230 . The plunger  220  is coupled to the inside of the tube  206  and a valve  106 . 
         [0036]    In one embodiment, the tube  206  and the plunger  220  are fabricated from metal, e.g., stainless steel. In one embodiment, the plunger  220  may be fabricated from any material that does not wet the liquid, e.g., liquid sodium or react with process gases. For example, when the liquid is liquid sodium and the process gases include silicon tetrafluoride (SiF 4 ), the plunger  220  may be made of a material that does not react with the liquid sodium or the SiF 4 . 
         [0037]    The tube  206  includes an inlet  208  and an outlet  210 . The outlet has a diameter that is sufficient to provide a liquid in a stream. Said another way, the outlet should not have a diameter that causes “spraying” of the liquid. In addition, the outlet  210  has a shape that is substantially similar to a shape of a tip  222  of the plunger  220 . As a result, when the tip  222  of the plunger  220  is mated with the outlet  210 , a gas tight seal is formed. In one embodiment, “gas tight” is defined as preventing any air or process gas from entering the tube  206 . Accordingly, none of the liquid within the tube  206  is reacted, thereby, preventing solidification of the liquid within the tube  206 . 
         [0038]    In addition, the outlet  210  is located on one end of the tube  206 . That is, the outlet  210  is located as close to a bottom edge or perimeter of the tube  206  and not towards the center of the tube  206  as found in valves. As a result, when the tip  222  of the plunger  220  is mated with the outlet  210 , no open volume remains in the tube  206 . In other words, a bottom of the tube  206  and a bottom of the tip  222  of the plunger  220  lie on and share a single plane. Said another way, the bottom of the tube  206  and the bottom of the tip  222  of the plunger  220  are flush. 
         [0039]    Moreover, as the tip  222  is pushed into the outlet  210 , the tip  222  is designed to discharge any residual liquid out of the tube  206 . In other words, the tip  222  is designed to “squeegee” liquid remaining in the outlet out of the tube  206 . This prevents residual liquid being left within the tube near the outlet  210  and provides another level of protection against having any liquid solidify by reacting with the air and process gases, thereby, plugging the liquid injector  104 . 
         [0040]    The liquid injector  104  also includes a temperature sensor  204 . In one embodiment, the temperature sensor  204  is located in the tip  222  of the plunger  220 . The temperature sensor  204  may be any type of temperature sensor, for example, a thermocouple. 
         [0041]    The liquid injector  104   a  illustrated in  FIG. 3  differs from the liquid injector  104  illustrated in  FIG. 2  in the way the temperature of the liquid is controlled. The tube  206  of liquid injector  104   a  illustrated in  FIG. 3  comprises an annular volume  308  along one end of the tube  206 . In addition, a reservoir  302  of a heat transfer fluid and a pump  304  is coupled to the annular volume  308  of the tube  206 . The pump  304  is used to pump the heat transfer fluid from the reservoir  302  through the annular volume  308  of the tube  206 . The pump  304  may be any type of pump, for example, a centrifugal pump, a diaphragm pump, an impeller pump, a rotary pump, an air operated pump, and the like. The heat transfer fluid may be any hydrocarbon based or silicone based heat transfer fluid or oil that is commercially available. 
         [0042]    In addition, a temperature control element  306  is coupled to the reservoir  302 . In one embodiment, the pump  304 , the temperature control element  306  and the temperature sensor  204  are in communication with the controller  120 . 
         [0043]    Although only one reservoir  302  is illustrated, it should be noted that multiple reservoirs  302  of heat transfer fluid may be used. For example, one reservoir may be coupled to a heating element and one reservoir may be coupled to a cooling element. A switch or three way valve may be coupled to the pump  304  and both reservoirs. As a result, either heated heat transfer fluid to heat the liquid or cooled heat transfer liquid to cool the liquid may be pumped through the annular volume  308 . 
         [0044]    In one embodiment, the temperature sensor  204  may send temperature readings of the liquid at the outlet  210  to the controller  120 . A maximum temperature threshold and a minimum temperature threshold can be predefined. If the temperature readings of the liquid are below a minimum temperature, the controller  120  may signal the temperature control element  306  to heat the reservoir  302  and signal the pump  304  to begin pumping the heated heat transfer fluid through the annular volume  308 . If the temperature readings of the liquid are above a maximum temperature threshold, the controller  120  may signal the temperature control element  306  to cool the reservoir  302  and signal the pump  304  to begin pumping the cooled heat transfer fluid through the annular volume  308 . 
         [0045]    It should be noted that the heat transfer fluid may be used also to maintain the liquid temperature within a predefined range, e.g., between the minimum temperature threshold and the maximum temperature threshold. For example, the controller  120  may cycle between heating and cooling of the heat transfer fluid to maintain the temperature within the predefined range. 
         [0046]    While various embodiments have been described above, it should be understood that they have been presented by way of example only, and should not be considered limiting. Thus, the breadth and scope of a preferred embodiment should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.