Patent Publication Number: US-2013252115-A1

Title: Power generation system using plasma gasifier

Description:
TECHNICAL FIELD 
     The present invention relates to a hydrocarbon gasification combined generation system including coal or biomass. 
     BACKGROUND ART 
     An integrated gasification combined cycle (IGCC) means generation in which coal is converted into a synthesis gas, main constituents of which are hydrogen (H 2 ) and carbon monoxide (CO), and then electricity is generated using the synthesis gas. 
     The largest advantage of using an IGCC is that generation can be performed using a coal resource that is widely spread worldwide and has rich deposits. In addition, the IGCC has high thermal efficiency and thus can reduce the generation quantities of carbon dioxide (CO 2 ), sulfur oxides, nitrogen oxides, and dust per unit generation electric power quantity and has been evaluated as technology having very excellent environmental performance. In addition, the IGCC has been spotlighted as technology of future generation that can be applied to carbon dioxide (CO 2 ) separation storage technology, hydrogen production technology, and a system associated with fuel cells. 
       FIG. 9  is a conceptual view of the IGCC. As illustrated in  FIG. 9 , in an IGCC system, first, coal is combusted to generate a synthesis gas, and the generated synthesis gas is injected into a gas turbine to produce electric power. Also, a steam turbine operates by heat of an exhaust gas discharged from the gas turbine so that electric power can be produced again. Also, the synthesis gas is not used only in generation, but liquefied fuels, such as diesel, gasoline, and dimethyl ether (DME) and chemicals, such as methanol and ethylene, can be produced from the synthesis gas using coal liquefaction technology, and hydrogen can also be produced from the synthesis gas. 
     In this way, the IGCC has advantages in relation to efficiency and environmental pollution in comparison with thermal power generation using coal according to the related art and can be combined with various fields. However, the IGCC according to the related art has the following problems. 
     First, in the IGCC according to the related art, coal is gasified by radiant heat of a high temperature furnace in a gasification process of coal, and thus preheating of 1,300° C. to 1,500° C. is required to operate a gasifier. Thus, much time and high cost for preheating the gasifier are required. 
     Also, since the IGCC according to the related art requires a high pressure of more than 25 atmospheric pressure for gasification, it is very difficult to miniaturize the gasifier and it is also difficult to control the gasifier. 
     Also, an oxygen generation facility cost required for pure oxygen gasification is 15% of the entire construction cost, and thus high cost for an oxygen generation facility is required. 
     DISCLOSURE 
     Technical Problem 
     The present invention is directed to providing a generation system in which, in a generation system for an integrated gasification combined cycle (IGCC), a synthesis gas is produced using a plasma gasifier so that, even when low-quality coal having a high ash content is used, generation can be performed and a 1 atmospheric pressure process is adopted to produce electric power at a low cost. 
     More preferably, the present invention is directed to providing coal gasification having a high ratio of H 2 /CO composition using pure steam plasma. 
     Technical Solution 
     One aspect of the present invention provides a generation system including: a plasma gasifier that combusts pulverized coal or biomass using plasma so as to generate a synthesis gas including hydrogen (H 2 ) and carbon monoxide (CO); an impurity removing device that removes an impurity included in the generated synthesis gas; a gas storage tank in which the synthesis gas, an impurity of which has been removed by the impurity removing device, is stored; and a gas engine that combusts the synthesis gas stored in the gas storage tank so as to produce electricity. 
     Another aspect of the present invention provides a generation system including: a plasma gasifier that combusts pulverized coal or biomass using plasma so as to generate a synthesis gas including hydrogen (H 2 ) and carbon monoxide (CO); an impurity removing device that removes an impurity included in the generated synthesis gas; a gas storage tank in which the synthesis gas, an impurity of which has been removed by the impurity removing device, is stored; and a solid oxide fuel cell (SOFC) that produces electricity using the synthesis gas stored in the gas storage tank. 
     Advantageous Effects 
     According to exemplary embodiments of the present invention, even when low-quality coal having high ash constituents (ash constituents of more than 45%) is used, a synthesis gas can be produced using a gasifier using plasma so that the usage range of coal for generation can be increased. 
     In addition, according to exemplary embodiments of the present invention, since the synthesis gas is produced in a 1 atmospheric pressure environment, a generation facility can be miniaturized, and the generation facility can be constructed at a low cost. Since a 1 atmospheric pressure process is used, generation can be performed using not a gas turbine but a gas engine or a solid oxide fuel cell (SOFC). 
     In addition, according to the present invention, even when not coal but biomass is used, gasification can be performed so that the present invention is advantageous in technology and device aspects in comparison with a generation method according to the related art. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  illustrates a generation system  100  using a plasma gasifier according to a first exemplary embodiment of the present invention. 
         FIG. 2  illustrates a generation system  200  using a plasma gasifier according to a second exemplary embodiment of the present invention. 
         FIG. 3  is a block diagram of a plasma generator  300  according to an exemplary embodiment of the present invention. 
         FIG. 4  is a graph showing an optical emission spectrum obtained from an electromagnetic wave plasma torch using only pure steam (H 2 O). 
         FIGS. 5A and 5B  are longitudinal cross-sectional views illustrating a portion in which a waveguide  310  and a discharge tube  312  are connected to each other, of the plasma generator  300  illustrated in  FIG. 3 . 
         FIGS. 6A through 6C  are latitudinal cross-sectional views illustrating a detailed configuration of a gas supply unit  314  of the plasma generator  300  of  FIG. 3 . 
         FIGS. 7A and 7B  are latitudinal cross-sectional views illustrating a detailed configuration of a coal supply unit  316  of the plasma generator  300  of  FIG. 3 . 
         FIGS. 8A and 8B  are views illustrating a plasma gasifier  102  including at least one plasma generator  300 , according to exemplary embodiments of the present invention. 
         FIG. 9  is a conceptual view of an integrated gasification combined cycle (IGCC) system according to the related art. 
     
    
    
     MODES OF THE INVENTION 
     Hereinafter, exemplary embodiments of the present invention will be described in detail. However, the present invention is not limited to the exemplary embodiments disclosed below, but can be implemented in various forms. 
     In the description of the present invention, if it is determined that a detailed description of a known technology related to the invention may unnecessarily obscure the subject matter of the invention, the detailed description will be omitted. In addition, the following terms are terms that are defined in consideration of functions in the present invention and may vary according to user&#39;s and operator&#39;s intentions or practices. Thus, their definitions should be based on contents throughout the present specification. 
     A technical spirit of the present invention is determined by the claims, and the following embodiments are just a means of efficiently describing the technical spirit of the present invention to one of ordinary skill in the art. 
       FIG. 1  illustrates a generation system  100  using a plasma gasifier according to a first exemplary embodiment of the present invention. 
     As illustrated in  FIG. 1 , the generation system  100  using the plasma gasifier according to the first exemplary embodiment of the present invention includes a plasma gasifier  102 , an impurity removing device  104 , a gas storage tank  106 , and a gas engine  108 . 
     The plasma gasifier  102  is a device that generates a synthesis gas including hydrogen (H 2 ) and carbon monoxide (CO) from pulverized coal or biomass using plasma. A detailed configuration of the plasma gasifier  102  will be described below. 
     The impurity removing device  104  removes an impurity included in the synthesis gas generated by the plasma gasifier  102 . The impurity removing device  104  may include a dust removing unit  110  and a sulfur compound removing unit  112 , as illustrated in  FIG. 1 . The dust removing unit  110  removes dust, such as ash included in the synthesis gas generated by the plasma gasifier  102 . Also, the sulfur compound removing unit  112  removes sulfur compounds included in the synthesis gas. Detailed configurations of the dust removing unit  110  and the sulfur compound removing unit  112  and a method of removing dust and sulfur compounds using them are well known to the present technical field, and thus detailed descriptions thereof will be omitted. Also, the impurity removing device  104  may be configured to include other units for removing the impurity included in the synthesis gas in addition to the dust removing unit  110  and the sulfur compound removing unit  112 . 
     The gas storage tank  106  is a space in which the synthesis gas, an impurity of which, such as dust or sulfur compounds, has been removed by the impurity removing device  104 , is stored. The synthesis gas with a predetermined quantity may be stored in advance in the gas storage tank  106  so as to be used in an initial operation of the generation system  100  illustrated in  FIG. 1 . Thus, the gas engine  108  produces electricity by combusting the synthesis gas that has been stored in advance in the gas storage tank  106  when the initial operation of the generation system  100  is performed, and operates the plasma gasifier  102  using part of produced electricity so that the entire generation system  100  according to the first exemplary embodiment of the present invention can operate. 
     The gas engine  108  produces electricity by combusting the synthesis gas stored in the gas storage tank  106 . An integrated gasification combined cycle (IGCC) according to the related art is configured to produce electricity using a gas turbine; however, the current embodiment of the present invention is configured to produce a synthesis gas using an 1 atmospheric pressure process and thus is configured to produce electricity by driving the gas engine  108  (not the gas turbine) using the synthesis gas. In this way, when the synthesis gas is produced using the plasma gasifier  102  and the gas engine  108  is driven using the synthesis gas, gas production and electric power production are performed under a 1 atmospheric pressure so that miniaturization can be realized in comparison with the IGCC according to the related art. 
     An operation of the generation system  100  using the plasma gasifier having the above configuration according to the first exemplary embodiment of the present invention in an energy aspect will now be described below. 
     First, when general mass constituent ratios of carbon and combustible hydrocarbon included in coal (pulverized coal) that is a raw material are 
     C:H 2 :O 2 =70%:7%:23%, 
     if the mass constituent ratios are converted into molar ratios, 
     C:H 2 :O 2 =5.83:3.5:1.44, 
     if the molar ratio of carbon is converted into 1, 
     C:H 2 :O 2 =1:0.6:0.25. 
     Meanwhile, enthalpy, H, which is required for decomposition of hydrocarbon in which oxygen and hydrogen are contained, is defined by the following equation: H=40 kJ. In this case, hydrocarbon is assumed as compounds, such as polymer hydrocarbon and methanol. 
     A reaction between carbon and hydrocarbon included in coal inside a plasma torch in the plasma gasifier  102  is as follows: 
       C+(¼)O 2 +(0.6)H 2 +(½)H 2 O→CO+(1.1)H 2  
 
     In this case, enthalpy change is defined by the following equation: ΔH=10.4 kJ. 
     Meanwhile, a combustion reaction inside the gas engine  108  is 
       CO+(1.1)H 2 +(1.05)O 2 →CO 2 +(1.1)H 2 O,
 
     and enthalpy change in this combustion reaction is defined by the following equation: ΔH=−549 kJ. 
     If an electric power production efficiency of the gas engine  108  is about 32%, electric power production quantity per 1 mole of carbon is defined by the following equation: 549 kJ×0.32=175.7 kJ. In this case, required electric energy is defined by the following equation: 40+10.4=50.4 kJ. Thus, pure electric power production quantity is defined by the following equation: 175.7−50.4=125.3 kJ. 
     Meanwhile, the generation system  100  using the plasma gasifier according to the first exemplary embodiment of the present invention may further include the plasma gasifier  102 , heat exchangers  114 ,  116 , and  118  that convert the synthesis gas produced by the plasma gasifier  102  or heat generated from the gas engine  108  into steam, and a steam turbine  120  that produces electricity using the steam generated by the heat exchangers  114 ,  116 , and  118 . In this way, heat generated in the generation system  100  is converted into electricity using the steam turbine  120  so that efficiency of the generation system  100  can be improved. 
       FIG. 2  illustrates a generation system  200  using a plasma gasifier according to a second exemplary embodiment of the present invention. 
     As illustrated in  FIG. 2 , the generation system  200  using the plasma gasifier according to the second exemplary embodiment of the present invention includes a plasma gasifier  102 , an impurity removing device  104 , a gas storage tank  106 , and a solid oxide fuel cell (SOFC)  202 . 
     Among them, the plasma gasifier  102 , the impurity removing device  104 , and the gas storage tank  106  illustrated with the same reference numerals as those of  FIG. 1  perform the same functions as those of the first embodiment and thus detailed descriptions thereof will be omitted. 
     In the present embodiment, unlike the first embodiment, electric power is produced using the SOFC  202 . The SOFC  202  is a device that converts chemical energy into electric energy using a hydrocarbon fuel, has a very high energy conversion efficiency, has high stability, and is easy to handle, because it uses a solid. In the IGCC according to the related art, a process is performed under a high pressure and thus the usage of an SOFC is not possible. However, in the present embodiment, like in the above-described first embodiment, since a process is performed under a 1 atmospheric pressure, generation using the SOFC  202  can be performed. 
     Meanwhile, the generation system  200  using the plasma gasifier according to the second exemplary embodiment of the present invention may further include the plasma gasifier  102 , heat exchangers  114  and  116  that convert heat generated from a synthesis gas produced by the plasma gasifier  102  into steam, and a steam turbine  120  that produces electricity using the steam generated by the heat exchangers  114  and  116 , like in the first embodiment. In this way, heat generated in the generation system  200  is converted into electricity using the steam turbine  120  so that efficiency of the generation system  100  can be improved. 
     Also, even in the present embodiment, like in the first embodiment, at an initial stage, the SOFC  202  is driven using the synthesis gas stored in the gas storage tank  106  to produce initial electric power, and the plasma gasifier  102  is driven using the produced electric power so that the entire system can operate. 
     Hereinafter, the plasma gasifier used in the first embodiment and the second embodiment of the present invention will be described. The plasma gasifier  102  used in the first and second embodiments of the present invention includes at least one plasma generator  300  and a gasification reactor  800  in which the synthesis gas is generated by plasma generated by the plasma generator  300 . 
       FIG. 3  is a block diagram of a plasma generator  300  according to an exemplary embodiment of the present invention. 
     As illustrated in  FIG. 3 , the plasma generator  300  includes a power unit  302 , an electromagnetic wave oscillator  304 , a circulatory system  306 , a tuner  308 , a waveguide  310 , a discharge tube  312 , a gas supply unit  314 , a coal supply unit  316 , an ignition unit  318 , and a gas discharge unit  320 . 
     The power unit  302  supplies electric power required to drive the plasma generator  300 . 
     The electromagnetic wave oscillator  304  is connected to the power unit  302  and oscillates electromagnetic waves by receiving electric power from the power unit  302 . An electromagnetic wave oscillator that oscillates electromagnetic waves having a frequency range of 902 to 928 MHz or 886 to 896 MHz is used in the present invention, and preferably, electromagnetic waves having a frequency of 915 MHz or 896 MHz are oscillated using the electromagnetic wave oscillator  304 . 
     The circulatory system  306  is connected to the electromagnetic wave oscillator  304 , outputs the electromagnetic waves oscillated by the electromagnetic wave oscillator  304  and simultaneously, dissipates electromagnetic wave energy that is reflected with impedance mismatch so as to protect the electromagnetic wave oscillator  304 . 
     The tuner  308  induces impedance matching by adjusting intensities of incident waves and reflected waves of the electromagnetic waves output from the circulatory system  306  such that an electric field induced by the electromagnetic waves is the maximum in the discharge tube  312 . 
     The waveguide  310  transmits the electromagnetic waves input from the tuner  308  to the discharge tube  312 . In the present invention, the size of the waveguide  310  has a relation with the frequency of the electromagnetic waves oscillated by the electromagnetic wave oscillator  304 . If the frequency of the electromagnetic waves oscillated by the electromagnetic wave oscillator  304  decreases, the wavelength of the electromagnetic waves increases. Thus, when electromagnetic waves having different frequencies are introduced into a waveguide having a predetermined size, electromagnetic waves having a lower frequency than a cutoff frequency of the waveguide are not introduced into the waveguide. That is, the waveguide serves as a kind of high pass filter. Thus, the size of the waveguide is determined depending on a used frequency. 
     The cutoff frequency of the waveguide is defined by the following equation 1: 
     
       
         
           
             
               
                 
                   Equation 
                    
                   
                       
                   
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                       f 
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                           c 
                           
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     where f c  is a cutoff frequency, c is the velocity of light, a is a latitudinal size of a waveguide, b is a longitudinal size of the waveguide, and m and n are electromagnetic wave mode numbers in the waveguide. 
     In the present invention, a waveguide with the latitudinal size a of 25 cm*the longitudinal size b of 12.5 cm is used. Also, in the present invention, the electromagnetic waves are oscillated in a TE 10  mode. Thus, in this case, m is 1, and n is 0. The cutoff frequency of the waveguide  310  according to the present invention is calculated by the following equation 2: 
     
       
         
           
             
               
                 
                   Equation 
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                   2 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
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                   ( 
                   2 
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     As described above, the electromagnetic wave oscillator  304  according to the present invention oscillates the electromagnetic waves having the frequency range of 902 to 928 MHz or 886 to 896 MHz. Thus, the frequency of the electromagnetic waves is higher than the cutoff frequency of the waveguide  310 . Thus, the electromagnetic waves oscillated by the electromagnetic wave oscillator  304  are not cut off but are introduced into the waveguide  310 . 
     Meanwhile, a cutoff wavelength at the waveguide  310  is defined by the following equation 3: 
     
       
         
           
             
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   3 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     λ 
                     
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                       = 
                       
                         50 
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                           cm 
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                   ( 
                   3 
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     A wavelength λ g  of the waveguide  310  when an oscillation frequency at the electromagnetic wave oscillator  304  is 915 MHz is defined by the following equation 4: 
       Equation 4 
       λ g =λ/[1−( f   c   /f ) 2 ] 1/2 =32.8/[1−(0.6/0.915) 2 ] 1/2 =43.5 cm   (4).
 
     When the discharge tube  312  is inserted spaced apart from an end of the waveguide  310  by ¼ of the wavelength λ g  in the waveguide  310 , a position in which the discharge tube  312  is inserted, is about 11 cm (≈43.5/4) from the end of the waveguide  310 . 
     As illustrated in  FIG. 3 , the above-described power unit  302 , the electromagnetic wave oscillator  304 , the circulatory system  306 , the tuner  308 , and the waveguide  310  constitute an electromagnetic wave supply unit  322  in the present invention, and the electromagnetic wave supply unit  322  generates electromagnetic waves and supplies the electromagnetic waves to the discharge tube  312 . 
     The discharge tube  312  generates plasma from the electromagnetic waves supplied by the electromagnetic wave supply unit  322  and a mixture gas including steam and oxygen, and gasifies solid coal using the generated plasma so as to generate a synthesis gas. The synthesis gas is mainly composed of carbon monoxide (CO) and hydrogen (H 2 ) and includes an impurity, such as sulfur compounds, in addition to CO and H 2 . 
     As described above, the mixture gas injected into the discharge tube  312  stabilizes the generated plasma and forms a swirl in the discharge tube  312  so as to protect inner walls of the discharge tube  312  from a high-temperature plasma flame. In general, it is very difficult to generate plasma using only pure steam in an atmospheric state, and even when plasma is generated, plasma may be easily extinguished. Thus, in the present invention, the mixture gas is composed by adding oxygen or air to pure steam that is a base so that plasma can be more stably generated in comparison with a case that pure steam is used. 
     In addition, it is also possible to control a constituent ratio of the synthesis gas generated by controlling a mixture ratio of steam (H 2 O) and oxygen (O 2 ) in the mixture gas.  FIG. 4  illustrates an optical emission spectrum obtained from an electromagnetic wave plasma torch using only pure steam (H 2 O). As illustrated in  FIG. 4 , pure steam (H 2 O) plasma generates OH, H, and O, and dominant species are OH and H. Thus, it can be predicted that, when coal is gasified from pure steam plasma, the generation quantity of hydrogen is larger than the generation quantity of carbon monoxide (CO) from a reaction of coal and steam plasma. However, when coal is gasified from the mixture gas of steam and oxygen, a mole fraction % of oxygen increases gradually from 0 to 100, in the above drawing, the generation quantity of oxygen atoms having wavelengths of 777 nm and 844.5 nm increases compared to the quantity of hydrogen atoms generated from steam. Thus, as a mixture ratio of oxygen increased, the generation quantity of carbon monoxide (CO) is larger than that of hydrogen. Thus, by controlling the mixture ratio of steam and oxygen, a composition of the synthesis gas can be changed from coal gasification. 
     The following reaction occurs in the discharge tube  312  by the plasma. 
     (1) Combustion by oxygen (oxidation reaction): C+O 2 →CO 2    
     The present reaction is a heat dissipation reaction and occurs very fast. Through this reaction, heat required for gasification can be supplied. 
     (2) Gasification by oxygen (partial oxidation reaction): C+½O 2 →CO 
     The present reaction is also a heat dissipation reaction and occurs very fast. 
     (3) Gasification by carbon dioxide (CO 2 ) (Boudouard reaction): C+CO 2 →2CO 
     The present reaction is a heat absorption reaction and is slower than the oxidation reaction. 
     (4) Gasification by steam: C+H 2 O→CO+H 2    
     The present reaction is a heat absorption reaction and is slower than the oxidation reaction. This reaction is preferred at a high temperature and under a low pressure. 
     (5) Gasification by hydrogen: C+2H 2 →CH 4    
     The present reaction is a heat dissipation reaction and is slower than the oxidation reaction. However, in case of a high pressure, exceptionally, the speed of this reaction increases. 
     (6) Water gas shift (WGS) reaction (Dussan reaction): CO+H 2 O→H 2 +CO 2    
     The present reaction is slightly a heat absorption reaction and occurs fast. A ratio of CO to H 2  of the synthesis gas is affected by the present reaction. 
     (7) Methane generation reaction: CO+3H 2 →CH 4 +H 2 O 
     The present reaction is a heat dissipation reaction and occurs very slowly. 
     Next, the gas supply unit  314  injects the mixture gas into the discharge tube  312  in the form of a swirl, and the coal supply unit  316  supplies solid coal (pulverized coal) to the plasma generated in the discharge tube  312 . Detailed configurations of the gas supply unit  314  and the coal supply unit  316  will be described below. 
     The ignition unit  318  includes a pair of electrodes disposed in the discharge tube  312  and supplies initial electrons for generating plasma through the pair of electrodes. 
     The gas discharge unit  320  is provided at an upper end of the discharge tube  312  and discharges the synthesis gas generated by the plasma to the outside. The synthesis gas discharged by the gas discharge unit  320  is purified by the impurity removing unit  104 , is stored in the gas storage tank  106 , and then is supplied to the gas engine  108 . 
       FIGS. 5A and 5B  are longitudinal cross-sectional views illustrating a portion in which a waveguide  310  and a discharge tube  312  are connected to each other, of the plasma generator  300  illustrated in  FIG. 3 . 
     First, as illustrated in  FIG. 5A , the discharge tube  312  is connected to the waveguide  310  and provides a space in which plasma is generated, by electromagnetic waves input through the waveguide  310 . The discharge tube  312  may be formed in a cylindrical shape and may be installed to pass through the waveguide  310  in a vertical direction between ⅛ and ½ of a wavelength in the waveguide  310  from an end of the waveguide  310 , preferably, in a position that corresponds to ¼ of the wavelength. The discharge tube  312  may be formed of quartz, alumina, or ceramic so that the electromagnetic waves can easily transmit the discharge tube  312 . A discharge tube holder  500  formed under the waveguide  310  supports the discharge tube  312  in such a way that the discharge tube  312  is stably inserted into the waveguide  310  and is fixed thereto. 
     The gas supply unit  314  is formed to surround the discharge tube  312  from a lower end of the discharge tube  312 , and the coal supply unit  316  is formed to surround an upper end of the gas supply unit  314 , i.e., a portion of the discharge tube  312  in which plasma is formed. 
     In  FIG. 5B , a shape in which the discharge tube  312  and the waveguide  310  are connected to each other, is the same as that of  FIG. 5A . However, there is a difference between  FIGS. 5B and 5A  in that a hanging jaw  312 - 1  that protrudes outward is additionally provided at the lower end of the discharge tube  312  so as to easily fix the discharge tube  312  and simultaneously to suppress gas effluence. The hanging jaw  312 - 1  is inserted between a first carbon block  502  and a second carbon block  504  and is supported by the first carbon block  502  and the second carbon block  504 . A case  506  is formed outside the first carbon block  502  and the second carbon block  504  so that the discharge tube  312  can be fixed by the case  506 . In the present embodiment, the gas supply unit  314  is formed at the second carbon block  504  and supplies gas to the lower end of the discharge tube  312 . 
       FIGS. 6A through 6C  are latitudinal cross-sectional views illustrating a detailed configuration of a gas supply unit  314  of the plasma generator  300  of  FIG. 3 , according to an exemplary embodiment of the present invention. 
     As illustrated in  FIGS. 6A through 6C , the gas supply unit  314  of the plasma generator  300  according to an exemplary embodiment of the present invention includes at least one steam supply tube  600  and at least one oxygen supply tube  602 . The steam supply tube  600  and the oxygen supply tube  602  are configured in such a way that one end of the steam supply tube  600  and one end of the oxygen supply tube  602  are connected to an inside of the discharge tube  312  and the steam supply tube  600  and the oxygen supply tube  602  supply steam and oxygen (or air including oxygen) into the discharge tube  312 . Steam and oxygen supplied to each of the steam supply tube  600  and the oxygen supply tube  602  are mixed in the discharge tube  312  and constitute a mixture gas of steam and oxygen. 
     The steam supply tube  600  and the oxygen supply tube  602  may be formed in the gas supply unit  314  in appropriate numbers as needed.  FIG. 6A  illustrates an embodiment in which one steam supply tube  600  and one oxygen supply tube  602  are formed, and  FIGS. 6B and 6C  illustrate an embodiment in which two or three steam supply tubes  600  and two or three oxygen supply tubes  602  are installed. As illustrated in  FIGS. 6A ,  6 B, and  6 C, the same numbers of the steam supply tube  600  and the oxygen supply tube  602  may be provided in the gas supply unit  314 . That is, when two steam supply tubes  600  are formed, two oxygen supply tubes  602  may also be formed. Also, a predetermined number of steam supply tubes  600  and a predetermined number of oxygen supply tubes  602  may be arranged in the gas supply unit  314  around the discharge tube  312  at the same intervals. As illustrated in  FIGS. 6A ,  6 B, and  6 C, the steam supply tube  600  and the oxygen supply tube  602  may be alternately arranged in the gas supply unit  314  (i.e., in the order of the steam supply tube  600 , the oxygen supply tube  602 , the steam supply tube  600 , the oxygen supply tube  602 , . . . ) 
     The steam supply tube  600  and the oxygen supply tube  602  are supplied to the discharge tube  312  so that the mixture gas of supplied steam and oxygen rotates along an inner circumferential surface of the discharge tube  312  in the form of a swirl. To this end, as illustrated in  FIGS. 6A ,  6 B, and  6 C, the steam supply tube  600  and the oxygen supply tube  602  are connected to the inside of the discharge tube  312  so that steam and oxygen discharged into the discharge tube  312  are discharged along the inner circumferential surface of the discharge tube  312 , i.e., in parallel to the inner circumferential surface of the discharge tube  312 . To this end, the steam supply tube  600  and the oxygen supply tube  602  need to be configured so that proceeding directions of the steam supply tube  600  and the oxygen supply tube  602  are parallel to the inner circumferential surface of the discharge tube  312  at an end in which the steam supply tube  600  and the oxygen supply tube  602  are connected to the discharge tube  312 . In this configuration, supplied steam and oxygen are mixed with each other in the discharge tube  312 , rotate in one direction, and have the form of a swirl. Also, rotation directions of supplied steam and oxygen are the same in the steam supply tube  600  and the oxygen supply tube  602 . 
       FIGS. 7A and 7B  are latitudinal cross-sectional views illustrating a detailed configuration of a coal supply unit  316  of the plasma generator  300  of  FIG. 3 , according to an exemplary embodiment of the present invention. 
     As illustrated in  FIGS. 7A and 7B , the coal supply unit  316  of the plasma generator  300  according to an exemplary embodiment of the present invention includes at least one coal supply tube  700  and supplies powdery coal (pulverized coal) to the plasma generated in the discharge tube  312  through the coal supply tube  700 . 
     The coal supply tube  700  may be formed in the coal supply unit  316  in an appropriate number as needed, and like in the steam supply tube  600  and the oxygen supply tube  602 , a predetermined number of coal supply tubes  700  may be arranged in the coal supply unit  316  around the discharge tube  312  at the same intervals. 
     In an embodiment of the present invention, the coal supply tube  700  may be supplied to the discharge tube  312  so that supplied powdery coal rotates along the inner circumferential surface of the discharge tube  312  in the form of a swirl. To this end, as illustrated in  FIG. 7A , the coal supply tube  700  is connected to the inside of the discharge tube  312  so that coal discharged into the discharge tube  312  is discharged along the inner circumferential surface of the discharge tube  312 , i.e., in parallel to the inner circumferential surface of the discharge tube  312 . To this end, like in the steam supply tube  600  and the oxygen supply tube  602 , the coal supply tube  700  is also configured so that a proceeding direction of the coal supply tube  700  is parallel to the inner circumferential surface of the discharge tube  312  at an end in which the coal supply tube  700  is connected to the discharge tube  312 . In this configuration, supplied coal rotates in the discharge tube  312  in one direction and has the form of a swirl. In this case, a rotation direction of the swirl may coincide with the rotation direction of the mixture gas of steam and oxygen. 
     In another embodiment of  FIG. 7B , the coal supply tube  700  may be formed to be directed to the center of plasma formed in the discharge tube  312 . In this case, pulverized coal supplied through the coal supply tube  700  is directly sprayed into the center of plasma with a high temperature so that partial combustion and gasification of coal can be more easily performed. 
     Carbon dioxide (CO 2 ) may be used as a carrier gas for supplying coal (pulverized coal) into the discharge tube  312 . The synthesis gas generated in the plasma generator  300  according to the present invention includes a considerable amount of carbon dioxide (CO 2 ) in addition to hydrogen (H 2 ) and carbon monoxide (CO). Thus, when CO 2  is separated from the synthesis gas and is reused as the carrier gas for transferring coal, coal can be efficiently transferred to plasma in the discharge tube  312  and simultaneously, environment pollution caused by emission of CO 2  in the air can also be prevented. In addition, the mixture gas of oxygen and steam may be used as the carrier gas, like in the gas supply unit  314 , and pure steam or oxygen may also be used as the carrier gas. 
       FIG. 8A  illustrates a plasma gasifier  102  including at least one plasma generator  300 , according to an exemplary embodiment of the present invention. The plasma gasifier  102  according to an exemplary embodiment of the present invention includes at least one plasma generator  300  and a gasification reactor  800  in which a synthesis gas is generated by plasma generated by the plasma generator  300 . As illustrated in  FIG. 8A , at least one plasma generator  300  is placed in the vicinity of the cylindrical gasification reactor  800 , and each plasma generator  300  is combined with the gasification reactor  800  so that the gas discharge unit  320  can be connected to an inside of the gasification reactor  800 . The synthesis gas generated by the plasma generated by each plasma generator  300  is concentrated on a synthesis gas outlet  802  at an upper end of the gasification reactor  800 , and a by-product generated in this procedure is discharged to a by-product outlet at a lower end of the gasification reactor  800 . 
       FIG. 8B  illustrates a plasma gasifier  102  including at least one plasma generator  300 , according to another exemplary embodiment of the present invention. Like in  FIG. 8A , the plasma gasifier  102  according to another exemplary embodiment of the present invention includes at least one plasma generator  300 , a gasification reactor  800 , a synthesis gas outlet  802 , and a by-product outlet  804 . All configurations of  FIG. 8B  are the same as the plasma gasifier  102  illustrated in  FIG. 8A  except that the plasma generator  300  is placed at an upper end (not a lower end) of the gasification reactor  800 . 
     While the invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit. 
     Therefore, the claim scope of the present invention should not be limited to the exemplary embodiments disclosed, and should be defined by the appended claims and equivalents thereof.