Abstract:
The present invention relates to an apparatus for generating flames and more particularly to the microwave plasma burner for generation of high-temperature plasma flame by injecting gaseous, liquid or solid-powder hydrocarbon-fuels into plasma generated by microwaves. The invention provides a compact and portable apparatus for generating plasma flame. The apparatus includes a magnetron, an electrical power supplier, a waveguide system, a microwave power monitering system, stub tuners, a discharge tube, a gas supply system, a plasma ignitor and a fuel supply system. The method and apparatus is described for generation of a large volume of high-temperature plasma by injecting gaseous, liquid or solid-powder hydrocarbon-fuels into the microwave plasma torch to decompose the hydrogen and carbon containing fuels, and to mix the resultant gaseous hydrogen and carbon compounds with air or oxygen gas, instantaneously generating a large volume of high-temperature flames.

Description:
REFERENCE CITED  
       [0001]     U.S. Patent Documents  
                                                           5,505,909   04/1996   Dummersdorf et al           5,830,328   11/1998   Uhm           6,620,394 B2   09/2003   Uhm et al           6,620,439 B2   10/2004   Uhm et al                      
 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates generally to the apparatus for generating flames, and particularly to the microwave plasma burner for generating a large volume of high-temperature plasma flames by injecting gaseous, liquid or solid-powder hydrocarbon-fuels into an atmospheric microwave plasma torch and by near perfect combustion of the fuels with air or oxygen gas through the high-temperature plasma torch.  
       BACKGROUND OF THE INVENTION  
       [0003]     The plasma torch in general is a device of arc plasma column generated between two electrodes. There are several kind of plasma torch including DC arc torch, induction torch and high-frequency capacitive torch. The DC arc torch is operated by the DC electric field between two electrodes, which must be replaced often due to their limited lifetime. The DC arc torch is also operated at a high arc current in the range of 50-10,000 A, which requires an expensive high electrical-power supplier. The induction torch and high-frequency capacitive torch are inefficient devices with typical thermal efficiency in the range of 40-50%. These conventional torches have a small volume of plasma, have high operational cost and require many expensive additional systems for operation.  
         [0004]     In order to overcome difficulties of the conventional torches, a microwave plasma torch was proposed in U.S. Pat. No. 6,620,394 B2 issued to Uhm et. al., present inventors, on Sep. 16, 2003. The microwave plasma torch provides high density and high temperature plasmas in inexpensive ways, but the plasma volume and temperature of the microwave plasma torch decrease drastically outside the discharge tube, thereby limiting its capability of bulk treatment of waste. In this context, the purpose of the present invention is providing an apparatus for generating an enlarged plasma flames by injecting gaseous, liquid or solid-powder hydrocarbon-fuels into the microwave plasma torch.  
       SUMMARY OF THE INVENTION  
       [0005]     In order to generate a high-temperature large-volume plasma flames, the present invention includes a magnetron that generates microwaves;  
         [0006]     a power supply system that provides an electrical power to the magnetron;  
         [0007]     a microwave circulator that forwards the microwaves from the magnetron to a discharge tube and absorbs the reflected microwaves;  
         [0008]     a directional monitoring system that monitors forward and backward microwave powers;  
         [0009]     stub tuners that control the forward and backward microwave power;  
         [0010]     a tapered waveguide system that delivers effectively the microwave power to the discharge tube;  
         [0011]     a discharge tube wherein an oncoming microwave power is converted into a plasma column in a swirl gas injected from outside;  
         [0012]     a gas supplier that provides the swirl gas to the discharge tube;  
         [0013]     an ignitor that provides initial electrons to ignite plasma inside the discharge tube; and  
         [0014]     a fuel supply system that injects hydrocarbon fuels into the plasma in the discharge tube and maintains the plasma flames in the flame exit.  
         [0015]     The purpose of this invention is to modify the microwave plasma torch design such that the improved apparatus produces enlarged size plasma better suited for such industrial applications as burning toxic gases, purifying contaminated gases and liquids. The key features of this invention is directed to adding fuel injective nozzles to a microwave plasma torch whereby enlarging size of the plasma.  
         [0016]     It is therefore an important object of the present invention to generate a large-volume of plasma flames with high temperature from hydrocarbon fuel and swirl gas so that this plasma flame serves as a high temperature source in waste incineration facilities where hazardous materials like dioxins may not be formed because of controlled incineration temperature due to the high temperature source of the present invention.  
         [0017]     Other object of the present invention is generation of a high-temperature large-volume plasma flame for elimination of volatile organic compounds (VOCs) in air, elimination of dioxins from incinerators, elimination of hydrogen sulfide from factories and elimination of ammonia compounds from waste of livestock farms.  
         [0018]     Another object of the present invention is generation of a high-temperature large-volume plasma flame for quick elimination of poisonous gas in air sprayed by terrorists, thereby deterring terror actions and protecting the public against any terrorist attack.  
         [0019]     Additional objects, and advantages and novel features of the invention will be explained in the description which follows, and in part will be apparent from the description, and will be learned by practice of the invention. The objectives and other advantages of the invention will be realized and obtained by the process and apparatus, particularly pointed out in the written description and claims hereof, as well as the appended drawings. 
     
    
     BRIEF DESCRIPTION OF DRAWING FIGURES  
       [0020]     A more complete appreciation of the invention and many of its attendant advantages will be aided by reference to the following detailed description in connection with the accompanying drawings:  
         [0021]      FIG. 1  is a block diagram illustrating the apparatus related to the microwave plasma burner of the present invention:  
         [0022]      FIG. 2  is a side cross-sectional view of a microwave plasma burner in one of desirable examples of the present invention;  
         [0023]      FIG. 3  is a side cross-sectional view of multiple-nozzle fuel-supply system;  
         [0024]      FIG. 4  is a frontal projection view of two-nozzle fuel-supply system;  
         [0025]      FIG. 5  is a side cross-sectional view of one-nozzle fuel-supply system with additional gas supply tube;  
         [0026]      FIG. 6  is a side cross-sectional view of two-nozzle fuel-supply system with additional gas supply tube;  
         [0027]      FIG. 7  is a frontal projection view of two-nozzle fuel-supply system with additional gas supply tube;  
         [0028]      FIG. 8  is a side cross-sectional view of one-nozzle fuel-supply system with different angle of nozzle direction;  
         [0029]      FIG. 9  is a side cross-sectional view of one-nozzle fuel-supply system with additional gas supply tube and with different angle of nozzle direction;  
         [0030]      FIG. 10  is a side cross-sectional view of an application example of the microwave plasma burner; 
     
    
     DETAILED DESCRIPTION  
       [0031]     The present invention is about an apparatus for generation of high temperature flame, and particularly to the microwave plasma burner for generating a large volume of high-temperature plasma flame by injecting gaseous, liquid or solid-powder hydrocarbon-fuels into an atmospheric microwave plasma torch. The present invention provides a near perfect combustion of a hydrocarbon fuels with air or oxygen gas through the high-temperature plasma torch.  
         [0032]     Referring now to the drawing in details,  FIG. 1  is diagram of the microwave plasma burner system. The basic portion of the present invention is the discharge tube  100  and other adjacent devices  300 , where air or oxygen gas enters the discharge tube  100  made of dielectric materials like quartz or alumina through the gas supplier  60 , making a swirl gas inside the discharge tube  100 . The power supplier  20  made of AC transformers or DC power suppliers provides the electrical power into the magnetron  10 , which generates microwaves. The circulator  30  sends the microwaves from the magnetron  10  into the directional coupler  40  and protects the magnetron  20  from reflected waves caused by impedance mismatching, which can be corrected by the 3-stub tuner  50 , reducing the reflected wave intensity less than 1%. The reflected wave intensity is less than 10% of the incoming wave intensity even without tuner adjustment, once the plasma torch is ignited.  
         [0033]     The electrode tips of the ignitor  90  inside the discharge tube  100  provide initiation electrons of the plasma column in the discharge tube  100 . The swirl gas from the gas supplier  60  inside the discharge tube  100  stabilizes plasma column and protects inner wall of the discharge tube  100  from plasma heat. The plasma column length depends on the amount of swirl gas. For example, the plasma column length is about 20-30 cm for 1 kW microwave power with 2.45 GHz, for a quartz discharge tube with 27 mm inner diameter and for 20 liters per minute (lpm) of air swirl gas. The plasma column length reduces to 10 cm if the swirl gas increases from 20 to 80 lpm. The hydrocarbon fuel from the fuel injector system  70  enters the discharge tube  100  sideways and the plasma flame generated from fuel with air or oxygen exits through the flame exit  80 . For example, the liquid hydrocarbon fuel evaporates instantaneously by the plasma column with its center temperature of 5000-6000 degree Celsius and burns immediately with air. The aforementioned hydrocarbon fuel is methane, ethane, propane, butane in gaseous state, gasoline, diesel, kerosene, bunker oil, waste oil in liquid state and coal powders in solid state, etc.  
         [0034]      FIG. 2  is a side cross-sectional view of the apparatus designated by the dashed box  300  in  FIG. 1  and represents a drawing of the microwave plasma torch and fuel injector. The microwaves  12  from the 3-stub tuner  50  in  FIG. 1  passes through the tapered waveguide  52  and enter the discharge tube  100  installed at the location a quarter wavelength away from the end  54  of the waveguide  52 . Height of the tapered waveguide  52  attached to a standard rectangular waveguide (86 mm width and 43 mm height) is gradually reduced to induce the maximum energy density at the discharge tube  100  location. The swirl gas suppliers  62  and  64  in  FIG. 2  are attached to the upstream housing  98  made of metal such as stainless steel and is configured to form a vortex flow inside the discharge tube  100 . The swirl gas supplier can have one gas injector or multiple gas injectors to ensure a uniform vortex flow inside the discharge tube  100 . The swirl gas can be air, oxygen or a mixture of air and oxygen. The ignitor  90  provides initiation electrons of the plasma column from the microwaves and the swirl gas, and its electrode tip must be located inside the discharge tube  100 . The ignitor  90  consisted of the tungsten electrode  94  and dielectric tube is wrapped by a dielectric material such as ceramic, in order to prevent arcing between the ignitor  90  and the upstream housing  98 . The downstream housing  96  made of metal has the same inner size as the discharge tube and is installed on the tapered waveguide to sustain a steady vortex flow of the swirl gas. The fuel injector  78  is installed in the downstream housing  96  to provide fuel for plasma flame. The fuel injector  78  consists of nozzle head  72 , nozzle body  76  and fuel supply tube  74 . The fuel injector  78  is located at a certain distance from the tapered waveguide  52 , and there can be one fuel injector or multiple fuel injectors. The hydrocarbon fuel  82  injected into plasma mixes with the swirl gas (air or oxygen) and extends plasma flame  110  into the flame exit  80 .  
         [0035]      FIG. 3  is a side cross-sectional view of the double fuel injectors installed at the downstream housing  96  with different distances relative to the tapered waveguide  52 . In order to have a large and extended plasma flame  110 , multiple fuel injectors  78   a  and  78   b  are installed at the downstream housing  96  in  FIG. 3 . Each fuel injector in the multiple fuel injector system injects fuel into different part of the plasma column, extending the burner size and enlarging the plasma-flame volume.  FIG. 4  is a frontal projection view of multiple fuel injector system. The fuel injectors  78   a  and  78   b  installed in the downstream housing  96  in  FIG. 4  are arranged to have 180 degree angular separation between them. There may have more fuel injectors with an equal angular separation between them and located at different distances relative to the tapered waveguide  52 , if needed for further enlargement of the plasma flame.  
         [0036]      FIG. 5  is a side cross-sectional view of the fuel injector with additional gas supplier. The fuel injector system  144  with additional oxidation-gas supply consists of nozzle head  72 , nozzle body  76 , fuel supply tube  74 , additional gas-supply input  140  and additional gas injector  142 . The additional oxygen gas can be supplied through the gas-supply input  140 , supplying oxygen gas and fuel deep into the plasma column.  
         [0037]      FIG. 6  is a side cross-sectional view of the double fuel injectors with additional gas supplier, which are installed at the downstream housing  96  with different distances relative to the tapered waveguide  52 . In order to have a large and extended plasma flame  110 , multiple fuel injectors  144   a  and  144   b  are installed at the downstream housing  96 . Each fuel injector in the multiple fuel injector system with additional oxygen gas injects fuel and additional oxygen gas into different part of the plasma column, extending the burner size and enlarging the plasma-flame volume.  FIG. 7  is a frontal projection view of multiple fuel injector system with additional oxygen supplier. The fuel injectors  144   a  and  144   b  with additional oxygen supplier installed in the downstream housing in  FIG. 6  are arranged to have 180 degree angular separation between them. There may have more fuel injectors with additional oxygen supplier, with an equal angular separation between them and located at different distances relative to the tapered waveguide  52 , if needed for further enlargement of the plasma flame.  
         [0038]      FIG. 8  is a side cross-sectional view of a fuel injector  78  which has a certain injection angle in the range of from 0 degree to 180 degree against the axial direction of the burner. Multiple injectors can be installed around the downstream housing  96  with an equal angular separation between them and located at different distances relative to the tapered waveguide  52 , similar to  FIG. 4 , if needed for further enlargement of the plasma flame.  FIG. 9  is a side cross-sectional view of the fuel injector  144  with additional oxygen supplier installed at the downstream housing  96 . The fuel injector  144  has a certain injection angle in the range of 0 degree to 180 degree against the axial direction of the burner.  
         [0039]      FIG. 10  is a side cross-sectional view of an application example of the microwave plasma burner shown in  FIG. 2 . A contaminated gas  150  enters the microwave plasma flame  110  through the untreated-gas supply tube  200  located further downstream from the fuel injector  78  and the contaminant materials in the contaminated gas  150  are dissociated by the high-temperature plasma flame  110 . The contaminant materials are chemical and biological warfare agents, waste-gas from the cleaning process in semiconductor industries, volatile organic compounds, and bad smelling gases from factories.  
       EXAMPLE  
       [0040]     The microwaves  12  with 2.45 GHz and 1 kW power generated from the magnetron  10  enter the discharge tube  100  with its inner diameter of 27 mm. The air swirl gas of 50 liters per minute (lpm) from the gas supply  60  creates a vortex flow inside the discharge tube  100 . Kerosene injected from the fuel injector system  78  in  FIG. 2  into the discharge tube  100  is 1500 cc per hour. The length of the downstream housing  96  in  FIG. 2  is about 10 cm. The plasma flame is shooting out through the flame exit  80  in  FIG. 2 . The plasma flame diameter and length from the flame exit  80  are about 10 cm and 40 cm, respectively. The flame temperature at the center of the flame exit measured by a thermo-coupler is about 1400 degree Celsius. 20 lpm oxygen gas is added to the swirl gas and it was observed that the plasma flame color changes from yellowish white to bluish white. The flame temperature at the flame exit with additional oxygen gas is measured to be 1700 degree Celsius.  
         [0041]     Although this embodiment is the microwave plasma burner for the generation of high-temperature plasma flame by injecting gaseous, liquid or solid-powder hydrocarbon-fuels into plasma generated by microwaves, the invention is not limited to the use of the microwave plasma burner. Without departing from the spirit of the invention, numerous other rearrangements, modifications and variations of the present invention are possible in light of the foregoing teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.