Patent Publication Number: US-8530780-B2

Title: Direct current steam plasma torch and method for reducing the erosion of electrodes thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional of U.S. application Ser. No. 12/149,085, filed on Apr. 25, 2008 and currently pending, to which priority is claimed and the contents of which are incorporated by reference in their entirety. 
    
    
     BACKGROUND OF INVENTION 
     1. Field of Invention 
     The present invention relates to a direct current (“DC”) steam plasma torch and a method for reducing the erosion of electrodes thereof. 
     2. Related Prior Art 
     Plasma torches have been widely used in the metallurgy of special metal, the making of extremely fine particles and the changing of superficial properties. In the protection of the environment, plasma torches have been used to melt, pyrolyze or gasify flammable or non-flammable toxic waste, lowly radioactive waste, ash from incinerators or perfluorocompounds for de-toxication, volume reduction, solidification or conversion into resources. 
     As disclosed in U.S. Pat. Nos. 4,587,397 and 4,625,092 issued on 6 May 1986, working gas is only introduced into a DC plasma torch between front and rear electrodes of the DC plasma torch, and the rear electrode is a closed-loop gas supply system. A magnetic field may or may not be provided in the DC plasma torch. Where no magnetic field is provided, an arc does not move in a large area. Therefore, the area for the radiation of heat is small, and the thermal load on the front and rear electrodes are heavy so that the front and rear electrodes can easily be melted. The working gas is dry gas such as air, nitrogen, argon or helium. Where air and nitrogen are used, there may be hazardous byproducts such as NO X . 
     The present invention is therefore intended to obviate or at least alleviate the problems encountered in prior art. 
     SUMMARY OF INVENTION 
     It is an objective of the present invention to provide a durable DC steam plasma torch. 
     To achieve the foregoing objective, a DC steam plasma torch includes front, middle and rear sections. The front section includes a first amount and a first electrode attached to the first amount, thus defining co-axial first internal and external coolant channels. The middle section includes a second mount and a second electrode co-axially connected to the second mount, thus defining co-axial second internal and external coolant channels. The rear section includes an insulating transient element connected to the second electrode, a window frame connected to the insulating transient element and a window provided in the window frame. A first swirl generator is provided between the first and second sections to receive primary working gas and generating a swirl in the same. A second swirl generator is provided between the middle and rear sections to receive auxiliary working gas and generating a swirl in the same. 
     It is another objective of the present invention to provide a method for reducing the erosion of first and second electrodes of a DC steam plasma torch. 
     To achieve the foregoing objective, a negative high-voltage terminal of a DC power supply is connected to a helical coil via a conducting element. Another terminal of the DC power supply is connected to the first electrode. There is provided first coaxial thermostatic piping including a first swirl generator to introduce primary working gas into the first and second electrodes. There is provided a trigger generator to generate a discharge arc between the first and second electrodes. The current and the flow rate of the primary working gas are gradually increased to cause an arc root to enter the internal side of the first and second electrodes to generate a high-speed swirl on the internal side of the first and second electrodes. There is provided second thermostatic piping including a second swirl generator to introduce auxiliary working gas into the second electrode periodically to regulate the pressure in the rear electrode to move the arc root to and fro axially. There is provided an inlet conduit to introduce pulsed and pressurized air into the second electrode to clean the internal side of the second electrode of residual powder to retain the normal distribution of a current filed in the second electrode to stabilize the properties of the operation of the DC steam plasma torch. 
     Other objectives, advantages and features of the present invention will become apparent from the following description referring to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The present invention will be described via detailed illustration of the two embodiments referring to the drawings. 
         FIG. 1  is a cross-sectional view of a DC steam plasma torch according to the preferred embodiment of the present invention. 
         FIG. 2  is a perspective view of a helical coil of the DC steam plasma torch shown in  FIG. 1 . 
         FIG. 3  is a flow chart of a method for reducing the erosion of electrodes of the DC steam plasma torch shown in  FIG. 1 . 
         FIG. 4  is another cross-sectional view of the DC steam plasma torch shown in  FIG. 1  for illustrating the operation. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
     Referring to  FIG. 1 , a DC steam plasma torch  1  includes a front section, a middle section and a rear section according to the preferred embodiment of the present invention. There is a first swirl (or “vortex”) generator  13  between the front and middle sections. There is a second swirl generator  14  between the middle and rear sections. 
     The front section of the DC steam plasma torch  1  includes a first electrode  11  and a first mount  21 . Both of the first electrode  11  and the first mount  21  are tubular. With a threaded bolt  3   a , the first electrode  11  is co-axially connected to the first mount  21 , thus defining a first internal channel  31  and a first external channel  32 . Coolant can travel in the first internal channel  31  and the first external channel  32 . 
     The middle section of the DC steam plasma torch  1  includes a second electrode  12  and a second mount  22 . Both of the second electrode  12  and the second mount  22  are tubular. The second electrode  12  is co-axially connected to the second mount  22 , thus defining a second internal channel  33  and a second external channel  34 . A conductive transient element  41  is provided between an annular portion of the second electrode  12  and a front end of the second mount  22 . A helical coil  42  ( FIG. 2 ) is provided around the second electrode  12  and connected to the conductive transient element  41 . The helical coil  42  is used to generate a magnetic field. A jacket  23  is provided around the helical coil  42 . An insolating ring  24  is connected to the jacket  23  and the helical coil  42  with a threaded bolt  3   b . An insulating alignment element  25  is connected to the insolating ring  24 . The second electrode  12  is aligned with the first electrode  11  by the insulating alignment element  25 . A third mount  26  is connected to the insulating alignment element  25 . The third mount  26  is provided around the insulating alignment element  25  and the isolating ring  24 . 
     The rear section of the DC steam plasma torch  1  includes an inlet conduit  15 , an insulating transient element  16 , a window frame  27  and a window  28 . The insulating transient element  16  is connected to the rear electrode  12  with threaded bolts. The window  28  is made of quartz glass. The window  28  is located at the rear end of the DC steam plasma torch  1  so that the discharge of plasma and the erosion of the first electrode  11  and the second electrode  12  are visible. 
     Primary working gas is provided into the DC steam plasma torch  1  through the first swirl generator  13 . The primary working gas is steam. A swirl is generated in the first swirl generator  13 . The first swirl generator  13  includes a nozzle made of tool steel subjected to thermal processing. The nozzle of the first swirl generator  13  is about 5 to 10 degrees biased towards the axis of the first swirl generator  13 . 
     Auxiliary working gas is provided into the DC steam plasma torch  1  through the second swirl generator  14 . The auxiliary working gas is steam. A swirl is generated in the second swirl generator  14 . The auxiliary working gas is periodically added to the primary working gas to adjust the pressure. The second swirl generator  14  includes a nozzle made of tool steel subjected to thermal processing. The nozzle of the second swirl generator  14  is about 5 to 10 degrees biased towards the axis of the second swirl generator  14 . 
     Periodically, pulsed and pressurized air travels into the second electrode  12  through the inlet conduit  15 . The pulsed and pressurized air cleans the interior of the second electrode  12 . 
     Refractory insulating elements  5   a  and  5   b  and a refractory ultraviolet-resisting insulating element  6  are provided around the first swirl generator  13 . The center of the nozzle of the first swirl generator  13  is aligned to the middle point of a gap between the first electrode  11  and the second electrode  12 . The refractory insulating elements  5   a  and  5   b  are made of quartz glass and polytetrafluoroethylene (“PTFE”). 
     An insulating sleeve  7  is connected to the first mount  21  with a threaded bolt  3   c  and connected to the second mount  22  with another threaded bolt  3   d.    
     Referring to  FIGS. 3 and 4 , there is shown a method for reducing the erosion of the first electrode  11  and the second electrode  12  of the DC steam plasma torch  1 . An interface  29  of the DC steam plasma torch  1  is connected to a reactor  30  by a threaded bolt  3   e . A front portion of the interface  29  is exposed to the interior of the reactor  30  and operated in a non-transmitting mode. 
     At  81 , a steam generator  91  is activated. As the coolant, hot water of 80 to 90 degrees Celsius travels into the DC steam plasma torch  1  through an inlet  211  in the first mount  21  and an inlet  222  in the second mount  22 . The coolant travels through the first external channel  32  and the second external channel  34 . Finally, the coolant returns to the steam generator  91  through an outlet  212  in the front mount  21  and an outlet  222  in the second mount  22 . Thus, a closed circulation system is formed. A negative high voltage terminal of a DC power supply  92  is connected to the helical coil  42  via a conducting element  43 . Another terminal of the DC power supply  92  is connected to the first electrode  11 . The conducting element  43 , the helical coil  42  and the conductive transient element  41  together form a magnetic field module. 
     At  82 , under the control of a programmable flow controller  93   a , the primary working gas travels into the first swirl generator  13  through the first internal channel  31 . The direction of the movement of an arc root is consistent with the direction of the swirl in the first swirl generator  13  so that the swirl enters the first electrode  11  and the second electrode  12 . A pulsed or radio-frequency high voltage trigger generator causes the first electrode  11  and the second electrode  12  to provide arc ignition. The current and the flow rate of the primary working gas are gradually increased. An arc root  10  is directed to an internal side  36  of the first electrode  11  and the second electrode  12 . Not only the arc resistance is increased to increase the power, but also low-voltage zones are generated in the first electrode  11  and the second electrode  12 . Thus, a high-speed swirl is generated on the internal side  36  of the first electrode  11  and the second electrode  12  to stabilize the arc and cool the internal side  36  of the first electrode  11  and the second electrode  12 . 
     At  83 , under the control of a programmable flow controller  93   b , from time to time, at different flow rates, the auxiliary working gas travels into the second swirl generator  14  through the second internal channel  33  of a thermostatic piping  35   b . The auxiliary working gas periodically travels into the second electrode  12  from the second swirl generator  14 . The pressure in the second electrode  12  is regulated. The arc root  10  travels to and fro axially in the second electrode  12 . Thus, the area of the scanning by the arc root  10  is increased while the thermal load on the second electrode  12  is reduced so that the effective mass of the second electrode  12  available for erosion is increased. 
     At  84 , under the control of a programmable flow controller  93   c , in regular short intervals, pulsed and pressurized gas travels into the second electrode  12  through the inlet conduit  15 . The pulsed and pressurized gas cleans the internal side  36  of the second electrode  12  of residual copper compound or oxide. Thus, the normal distribution of air current field in the second electrode  12  is retained. The properties of the operation of the DC steam plasma torch  1  is stabilized. 
     As the steam is used as the working gases, the production of the nitrogen oxide produced by the DC steam plasma torch  1  is very limited. The DC steam plasma torch  1  is a highly chemically active clean heat source that provides plasma at a high temperature of 4000 to 10000 degrees Celsius, a high plasma density of 10 16  #/cm 3  and a high energy density 5 to 20 MJ/kg. The plasma contains a lot of hydrogen atoms, oxide atoms and OH −  radicals. The DC steam plasma torch  1  effectively turns toxic waste into organic substances, produces synthetic gas and stabilizes lava that can be turned into resources, thus completely turning the toxic waste into resources. The DC steam plasma torch  1  is reliable and durable. The time interval between two activities of maintenance is long so that the cost in the operation of the DC steam plasma torch  1  is low. Hence, the reliability and workability of the DC steam plasma torch  1  are increased. 
     Moreover, the problems addressed in the RELATED PRIOR ART are overcome by the method according to the present invention because the arc root  10  periodically moves in a large area of the internal side  36  of the electrodes  11  and  12 . Thus, the effective mass of the electrodes  11  and  12  available for erosion is large. Therefore, the lives of the electrodes  11  and  12  are long. 
     The present invention has been described via the detailed illustration of the preferred embodiment. Those skilled in the art can derive variations from the preferred embodiment without departing from the scope of the present invention. Therefore, the preferred embodiment shall not limit the scope of the present invention defined in the claims.