Abstract:
A method for producing inorganic spheroidized particles according to the present invention includes a step of producing the inorganic spheroidized particles by means of a diffusion type burner ( 12 ), wherein the burner ( 12 ) comprises a first raw material supply path ( 1 A), a fuel supply path ( 4 A), a raw material diffusion chamber ( 9 ), a primary oxygen supply path ( 5 A), a second raw material supply path ( 6 A), a secondary oxygen supply path ( 7 A), and a combustion chamber ( 8 ).

Description:
TECHNICAL FIELD 
     The present invention relates to a method for producing inorganic spheroidized particles such as silica by means of an oxygen burner. 
     This application is the U.S. National Phase of international Application No. PCT/JP2009/003657, filed on Jul. 31, 2009, and claims priority on Japanese Patent Application No. 2008-201302 filed on Aug. 4, 2008, the entire contents of each which is incorporated herein by reference. 
     BACKGROUND ART 
     An inorganic spheroidized particle is obtained by melting a raw material powder produced by crushing silica rock in high-temperature flame and spheroidizing this powder by its surface tension. 
     For example, highly-pure spheroidized silica that is obtained by using silica rock as a raw material is widely used as a filler for an epoxy-sealing material of a semiconductor device, and a lot of merits such as improved fluidity of a sealing material, high filling amount, and improved abrasion resistance can be obtained by spheroidizing. 
     In the present description, an inorganic spheroidized particle may be simply described as a spheroidized particle. 
     As a prior art regarding the production of an inorganic spheroidized particle, there are the methods disclosed in Patent Literatures 1 to 4. 
     Because high-temperature flame is needed for the spheroidizing of raw material powder, a burner of an oxygen-gas combustion system is usually used. 
     Examples of the burner include a premixing type burner and a diffusion type burner. In a premixing type burner, oxygen and a fuel gas are preliminarily mixed and ejected to the combustion place. Meanwhile, in a diffusion type burner, oxygen and a fuel gas are separately ejected and mixed at the combustion place. 
     The premixing type burner is used in the method disclosed in Patent Literature 2, while the diffusion type burner is used in the methods disclosed in Patent Literatures 1, 3 and 4. 
     The diffusion type burner disclosed in Patent Literature 1 has the concentric double pipe in which a lot of small pipes are provided between the inner pipe and the outer pipe. This burner is disposed in a vertical furnace, a silicon raw material is flowed down spontaneously or flowed down with pressurization through the central pipe (inner pipe) of the burner, and the raw material powder is supplied into flame made by a fuel gas from the small pipes and an oxygen gas from the outer pipe to thereby produce a melted silica spheroidized body. 
     In the premixing type burner disclosed in Patent Literature 2, raw material powder, oxygen, and LPG are sufficiently mixed in a burner, and the raw material powder is supplied into flame made at the end of the burner. 
     The diffusion type burners disclosed in Patent Literatures 3 and 4 have the concentric quartet pipe structure in which a raw material powder is supplied into the combustion chamber from the center using oxygen or an oxygen-enriched air as a carrier gas, a fuel gas is supplied through the outer circumference thereof, the primary oxygen and the secondary oxygen are supplied through the further outer circumference thereof, and cooling water path is provided around the most outer circumference to thereby cool a burner. 
     In addition, Patent Literatures 3 and 4 disclose an apparatus that uses such a diffusion type burner to produce inorganic spheroidized particles. 
     In the production apparatus of inorganic spheroidized particles disclosed in Patent Literature 4, as shown in  FIG. 6 , a raw material powder is cut off from a raw material feeder A and carried to a burner B, together with a carrier gas that is supplied through a carrier gas supply device A′. Into the burner B, oxygen from an oxygen supply equipment C and a liquefied petroleum gas (LPG) from a LPG supply equipment D are supplied. 
     An exhaust gas containing particles spheroidized in flame in a vertical furnace E are cooled with air introduced into the bottom portion of the vertical furnace E through a path F, and then the spheroidized particles are collected by the following cyclone G and bag filter H. 
     CITATION LIST 
     Patent Literature 
     [Patent Literature 1] 
     
         
         Japanese Unexamined Patent Application, First Publication No. Sho 58-145613
 
[Patent Literature 2]
 
         Japanese Unexamined Patent Application, First Publication No. Sho 62-241543
 
[Patent Literature 3]
 
         Japanese Patent No. 3,331,491
 
[Patent Literature 4]
 
         Japanese Patent No. 3,312,228 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     The raw material powder is heated and melted in flame by forced convective heat transfer mainly due to the flame, and is spheroidized by its surface tension. 
     In the diffusion type burners having the structure disclosed in Patent Literatures 3 and 4, the combustion chamber is provided, and the aggregation state of the produced inorganic spheroidized particles is improved in comparison with the burner disclosed in Patent Literature 1. 
     However, the diffusion type burners disclosed in Patent Literatures 3 and 4 have the structure containing only one raw material supply path. 
     For this reason, in the case of treating a raw material powder with wide particle size distribution obtained by ball mill crushing using this burner, since fusion between fine particles or fusion between fine and coarse particles occurs in the flame, there could be observed a situation in which particle size distribution of the charged raw material powder is different from that of the obtained spheroidized particle product. 
     Therefore, in order to obtain the spheroidized particle product having an optimal particle size distribution, a raw material powder of fine particles and a raw material powder of coarse particles should be spheroidized by means of different burners, respectively. Then, the respective resultant spheroidized particles should be mixed so as to obtain a product. 
     Thus, an object of the present invention is to provide a production method by which spheroidized particles having the objective particle size distribution can be obtained by means of one burner without causing a variation in a mean particle diameter of a raw material powder during the process of granulation. 
     Solution to Problem 
     In order to achieve the aforementioned objects, a first aspect of the present invention is a method for producing inorganic spheroidized particles, including a step of producing the inorganic spheroidized particles by means of a diffusion type burner, wherein 
     the burner includes a first raw material supply path, a fuel supply path, a raw material diffusion chamber, a primary oxygen supply path, a second raw material supply path, a secondary oxygen supply path, and a combustion chamber, 
     a coarse powder is supplied with a carrier gas from first raw material ejection holes of the first raw material supply path provided at the center of the burner to the raw material diffusion chamber provided at the end of the first raw material supply path, 
     a fuel gas is supplied from fuel gas ejection holes of the fuel supply path provided on the outer circumference of the raw material diffusion chamber to the combustion chamber provided at the end of the raw material diffusion chamber in a direction parallel to a central axis of the burner, 
     an oxygen-containing gas is supplied from the primary oxygen supply path through primary oxygen ejection holes that are opened on the side surface of the combustion chamber so as to form rotational flow, 
     a fine powder is supplied with the carrier gas from the second raw material supply path through the second raw material ejection holes that are opened on the side surface of the combustion chamber and formed at the exit side in comparison with the primary oxygen ejection holes in a direction parallel to the central axis of the burner, and 
     an oxygen-containing gas is supplied from the secondary oxygen supply path through the secondary oxygen ejection holes that are opened on the side surface of the combustion chamber and formed at the exit side in comparison with the second raw material ejection holes. 
     In the present invention, it is preferred to further include: a step of collecting coarse particles by means of cyclone; and a step of collecting fine particles by means of a bag filter, and it is preferred that a vertical spheroidization furnace be equipped with the burner and the cyclone and the bag filter be serially disposed at the downstream side of the spheroidization furnace so as to simultaneously produce inorganic spheroidized particles having different particle size distributions. 
     In addition, in the present invention, it is preferred to further include a step of collecting the inorganic spheroidized particles in one lump by means of a bag filter, and it is preferred that a vertical spheroidization furnace be equipped with the burner and the bag filter be disposed at the downstream side of the spheroidization furnace. 
     A second aspect of the present invention is the inorganic spheroidized particles obtained by the method for producing inorganic spheroidized particles according to the first aspect of the present invention. 
     Advantageous Effects of Invention 
     According to the present invention, a diffusion type burner is used, and therefore, backfire does not occur. Moreover, a coarse powder is supplied to a first raw material supply path, and a fine powder is supplied to a second raw material supply path. Therefore, particles having a small particle diameter can be sufficiently melted in a region where the temperature of the flame outer circumference portion is low and particles having a large particle diameter can be sufficiently melted in a region where the temperature of the flame center portion is high. Also, since the particles having a small particle diameter have not satisfactory dispersibility, it is possible to eject the particles from the second raw material supply path that enables an increase in dispersion volume, and to satisfactorily disperse in the flame. 
     On the other hand, since the particles having a large particle diameter have satisfactory dispersibility, it is possible to eject the particles from the second raw material supply path that enables a decrease in dispersion volume, and to satisfactorily disperse in the flame. 
     Therefore, according to the production method of the present invention, it is possible to spheroidize both particles having a large particle diameter and particles having a small particle diameter while nearly maintaining the particle diameter. 
     Accordingly, it is possible to produce spheroidized particle having a particle diameter or particle size distribution corresponding to the raw material supplied by means one burner. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic sectional view illustrating an example of a burner used in the present invention. 
         FIG. 2  is a schematic side view illustrating an example of a burner used in the present invention. 
         FIG. 3  is a schematic configuration diagram illustrating a production apparatus of inorganic spheroidized particles used in the present invention. 
         FIG. 4  is a graph illustrating a relation between the flow rate and the vitrification ratio of primary oxygen and secondary oxygen in Example. 
         FIG. 5  is a graph illustrating a relation between the flow rate and the vitrification ratio of primary oxygen and secondary oxygen in Example. 
         FIG. 6  is a schematic configuration diagram illustrating a production apparatus of conventional inorganic spheroidized particles. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
       FIG. 1  and  FIG. 2  illustrate an example of a burner for production of inorganic spheroidized particles used in the present invention (hereinafter may be simply referred to as a burner).  FIG. 1  is a sectional view in which the burner is cut along the central axis thereof.  FIG. 2  is a side view when the burner is viewed from the end side thereof, which illustrates only the ejection holes for raw material powder, fuel, and oxygen. 
     In these figures, the reference sign  1  represents a raw material supply pipe whose inside forms the raw material supply path  1 A through which a mixture of raw material powder and a carrier gas is supplied. 
     As a carrier gas, an oxygen-containing gas having an oxygen concentration of 20 vol % or more such as oxygen, oxygen-enriched air having an oxygen concentration of 20 vol % or more, or air is used. 
     As the raw material powder, inorganic powder such as silicon oxide, aluminum oxide, or glass, the particle morphology being a nonspherical shape with a corner, is used. 
     Among the raw material powder, a coarse powder refers to a powder having a large particle diameter, whose mean particle diameter is 10 μm or more, while a fine powder refers to a powder having a small particle diameter, whose mean particle diameter is less than 10 μm. 
     This first raw material supply pipe  1  is equipped with a powder diffusion plate  2  at the exit end thereof. This powder diffusion plate  2  ejects the mixed powder of the raw material powder and the carrier gas so that it spreads radially toward a burner exit direction. A plurality of first raw material ejection hole  3 ,  3 ••, which are directed obliquely outward, are formed on a circle at regular intervals. 
     Outside the first raw material pipe  1 , a fuel supply pipe  4  is provided concentrically, and the space between the raw material supply pipe  1  and the fuel supply pipe  4  forms a fuel supply path  4 A. Through this fuel supply path, a fuel gas such as a liquefied petroleum gas (LPG) is supplied. The exit end of the fuel supply path  4 A forms a plurality of fuel gas ejection holes  4 B,  4 B••, so that the fuel is ejected in a direction parallel to the central axis of the burner. These plural fuel gas ejection holes  4 B,  4 B•• are formed on a circle at regular intervals. 
     Outside the fuel supply pipe  4 , a primary oxygen supply pipe  5  is provided concentrically, and the space between the fuel supply pipe  4  and the primary oxygen supply pipe  5  forms a primary oxygen supply path  5 A. Through the primary oxygen supply path  5 A, an oxygen-containing gas having the oxygen concentration of 20 vol % or more such as oxygen, an oxygen-enriched air having the oxygen concentration of 20 vol % or more or air is supplied. 
     The exit end of the primary supply path  5 A forms a plurality of primary oxygen ejection holes  5 B,  5 B•• and exits of these primary oxygen ejection holes  5 B,  5 B•• are opened toward a central axis of the burner, so that oxygen is ejected in a direction vertical to the central axis of the burner and a rotational flow is formed in a combustion chamber  8  described hereinafter. 
     These plural primary oxygen ejection holes  5 B,  5 B•• are formed on a circle at regular intervals, and also disposed on a circle at the position different from that of the plurality of fuel ejection holes  4 B,  4 B••, in the middle between the adjacent two fuel ejection holes  4 B,  4 B••. 
     Outside the primary oxygen supply pipe  5 , the second raw material supply pipe  6  is provided concentrically, and the space between the primary oxygen supply pipe  5  and the second raw material supply pipe  6  forms a second raw material supply path  6 A. The exit portion of the second raw material supply path  6 A forms a plurality of second raw material ejection holes  6 B,  6 B••, so that a raw material is ejected in a direction parallel to the central axis of the burner. 
     The plurality of second raw material ejection holes  6 B,  6 B•• are formed on a circle at regular intervals. 
     Outside the second raw material supply pipe  6 , the secondary oxygen supply pipe  7  is provided concentrically, and the space between the second raw material supply pipe  6  and the secondary oxygen supply pipe  7  forms a secondary oxygen supply path  7 A. This secondary oxygen supply path  7 A has a wider cross-section than the primary oxygen supply path  5 A so that a large amount of oxygen can be supplied. The exit end of the secondary oxygen supply path  7 A forms a plurality of secondary oxygen ejection holes  7 B,  7 B•• and these secondary oxygen ejection holes  7 B,  7 B•• are formed on a circle at regular intervals. These secondary oxygen ejection holes  7 B,  7 B•• are opened in parallel to a central axis of the burner, so that an oxygen-containing gas is ejected in a direction parallel to the central axis of the burner. 
     Moreover, the secondary oxygen supply pipe  7  has a thick pipe wall, and a cooling water path  71  through which cooling water flow is formed inside the pipe to cool the burner itself. 
     Furthermore, the end portion of the burner is dented in a mortar shape that broadens outward, and this part forms a combustion chamber  8 . 
     In other words, the inclined pipe wall portion of the combustion chamber  8  is constituted by obliquely forming the end portions of the secondary oxygen supply pipe  7 , the second raw material supply pipe  6  and the primary oxygen supply pipe  5 , and also the bottom portion of the combustion chamber  8  corresponds to a cylindrical raw material diffusion chamber  9 . The raw material diffusion chamber  9  is formed by extension of the exit end portion of the raw material supply pipe  1  in a thin-walled cylindrical form toward the end portion of the burner in comparison with the powder diffusion plate  2 . 
     Furthermore, on the conical wall surface of the combustion chamber  8 , fuel gas ejection holes  4 B,  4 B••, primary oxygen ejection holes  5 B,  5 B••, second raw material ejection hole  6 B,  6 B•• and secondary oxygen ejection holes  7 B,  7 B•• are respectively opened. 
     Moreover, the above second raw material ejection holes  6 B are opened at the end side of the burner in comparison with the primary oxygen ejection holes  5 B, while the above secondary oxygen ejection holes  7 B are opened at the end side of the burner in comparison with the second raw material ejection holes  6 B. 
     In the burner for production of inorganic spheroidized particles, that has such a structure, the end of the first raw material supply path  1 A is connected to the raw material diffusion chamber  9  through the powder diffusion plate  2  having a lot of holes, and the fuel gas supply path  4 A provided on the outer circumference of the first raw material supply path  1 A and the primary oxygen supply path  5 A provided on the outer circumference of the fuel gas supply path  4 A are opened toward the combustion chamber  8  whose exit side connected to the end of the respective supply paths is radially expanded, and thus dispersibility of the raw material powder in the burner flame is improved. 
     When raw material powders each having a different particle diameter are supplied to the first raw material supply path  1 A and the second raw material supply path  6 A, it is possible to treat particles having a large mean particle diameter in the region where a temperature of the flame center portion is high and to treat particles having a small mean particle diameter in the region where a temperature of the flame outer circumference portion is low, while efficiently dispersing the particles. 
     The particles having a large mean particle diameter are dispersed comparatively easily and are therefore supplied from the first raw material supply path  1 A having a small dispersion area, located at the flame center portion. The particles having a small mean particle diameter are not easily dispersed, and are therefore supplied into the flame from the second raw material supply path  6 A having a large dispersion area. Thereby, the raw material powder can be efficiently dispersed into the flame. 
     Therefore, in the present invention, it is possible to treat the particles having a large mean particle diameter and the particles having a small mean particle diameter at a time in an optimum state in one burner. 
       FIG. 3  illustrates an example of a production apparatus of inorganic spheroidized particles used in the present invention, in which the reference sign  11  denotes a spheroidization furnace. This spheroidization furnace  11  is a cylindrical vertical furnace and is equipped vertically with the above burner  12  at the ceiling portion so that the end side faces inside the furnace. 
     In the vicinity of the bottom portion of the spheroidization furnace  11 , an air intake port  13  is formed, whereby, cooling air is introduced into the furnace from the inlet thereby reducing the temperature of a combustion gas to be discharged. 
     In the vicinity of the bottom portion of the spheroidization furnace  11 , a combustion gas discharge exit  14  is formed, whereby the produced spheroidized particles are transported to a combustion gas, discharged and then transferred to the inlet of a cyclone  17  through a duct  15  and a damper  16 . 
     The duct  15  is connected to a duct  18  and branched at the upstream side of the damper  16 , and this duct  18  is connected to the inlet of a bag filter  19 . 
     In the duct  18 , an air intake port  20  is disposed on the way and, by appropriately intaking air into the duct  18  through the port  20 , the temperature of combustion gas flowing in the duct  18  can be adjusted by lowering. 
     Moreover, a duct  21  is connected to the exit of the cyclone  17  and this duct  21  is connected to an inlet of the bag filter  19  through a damper  22 . 
     The first raw material supply pipe (not shown) is connected to the first raw material supply path  1 A of a burner  2  and this first raw material supply pipe is connected to a first raw material feeder  23 . In the first raw material feeder  23 , a raw material powder in the form of coarse particles with a mean particle diameter of 10 μm or more are stored and a carrier gas from a carrier gas supply source  24  is transferred, and then a predetermined amount of a raw material powder is transported to this carrier gas and transferred to the first raw material supply path  1 A of the burner  2  through the above first raw material supply pipe. 
     The first raw material feeder  23  is equipped with a delivery system for delivering a predetermined amount of a raw material powder in response to a raw material powder supply amount control signal from a control device (not shown). 
     As the carrier gas, an oxygen-containing gas having the oxygen concentration of 20 vol % or more such as oxygen, oxygen-enriched air or air is used. 
     The carrier gas supply source  24  is also equipped with a flow regulating valve for delivering a predetermined amount of a carrier gas to a first raw material feeder  23  and a second raw material feeder  25 , respectively, in response to a carrier gas supply amount control signal from a control device (not shown). 
     A second raw material supply pipe (not shown) is connected to the second raw material supply path  6 A of the burner  2 , and this second raw material supply pipe is connected to the second raw material feeder  25 . In the second raw material feeder  25 , a raw material powder in the form of fine particles with a mean particle diameter of less than 10 μm is stored and a carrier gas from the carrier gas supply source  24  is transferred, and then a predetermined amount of the raw material powder is transported to this carrier gas and transferred to the second raw material supply path  6 A of the burner  2  through the above second raw material supply pipe. 
     The second raw material feeder  25  is also equipped with a delivery system for delivering a predetermined amount of a raw material powder in response to raw material powder supply amount control signal from a control device (not shown). 
     A fuel supply pipe (not shown) is connected to the fuel supply path  4 A of the burner  2  and this fuel supply pipe is connected to a fuel gas supply source  26 . The fuel gas supply source  26  is allowed to store a fuel gas such as a liquefied petroleum gas (LPG) or a liquefied natural gas (LNG) therein, that are to be delivered, and a predetermined amount of the fuel gas is transferred to the fuel supply path  4 A of the burner  2  through the above fuel gas supply pipe. 
     The fuel gas supply source  26  is equipped with a delivery system for delivering a predetermined amount of a fuel gas in response to a fuel gas supply amount control signal from a control device (not shown). 
     A primary oxygen supply pipe (not shown) is connected to the primary oxygen supply path  5 A of the burner  2 , and this primary oxygen supply pipe is connected to a primary oxygen supply source  27 . The primary oxygen supply source  27  is allowed to store an oxygen-containing gas therein, that are to be delivered, and a predetermined amount of the oxygen-containing gas is transferred to the primary oxygen supply path  5 A of the burner  2  through the above primary oxygen supply pipe. 
     The primary oxygen supply source  27  is equipped with a delivery system for delivering a predetermined amount of an oxygen-containing gas in response to a primary oxygen supply amount control signal from a control device (not shown). 
     A secondary oxygen supply pipe (not shown) is connected to the secondary oxygen supply path  7 A of the burner  2 , and this secondary oxygen supply pipe is connected to a secondary oxygen supply source  28 . The secondary oxygen supply source  28  is allowed to store the above oxygen-containing gas therein, that are to be delivered, and a predetermined amount of the oxygen-containing gas is transferred to the secondary oxygen supply path  7 A of the burner  2  through the above secondary oxygen supply pipe. 
     The secondary oxygen supply source  28  is also equipped with a delivery system for delivering a predetermined amount of an oxygen-containing gas in response to a secondary oxygen supply amount control signal from a control device (not shown). 
     It is also possible that the primary oxygen supply source  27  is integrated with the secondary oxygen supply source  28  and the integrated source is provided with two delivery systems, and then an oxygen-containing gas is separately delivered to a primary oxygen supply pipe and a secondary oxygen supply pipe from each delivery system and a predetermined amount of the oxygen-containing gas is respectively supplied to the primary oxygen supply path  5 A and the secondary oxygen supply path  7 A of the burner  2 . 
     Hereinafter, an example of a production method of spheroidized particles using such a production apparatus will be described. 
     From a first raw material feeder  23 , a coarse powder having a mean particle diameter of 10 μm or more is transferred to a first raw material supply path  1 A of a burner  12 , and then ejected toward a combustion chamber  8  from first raw material ejection holes  3  through a raw material diffusion chamber  9 . From a second raw material feeder  25 , a fine powder having a mean particle diameter of less than 10 μm is transferred to a second raw material supply path  6 A of a burner  12 , and then ejected toward a combustion chamber  8  from a second raw material ejection hole  6 B. 
     Herein, the reason why the supply destination of the raw material powder is divided by the mean particle diameter of 10 μm is that the raw material powder having the mean particle diameter of less than 10 μm has characteristics such as poor dispersibility. 
     A predetermined amount of an oxygen-containing gas is fed into a primary oxygen supply path  5 A and a secondary oxygen supply path  7 A of a burner  12 , respectively, from a primary oxygen supply source  27  and a secondary oxygen supply source  28 , and then ejected toward a combustion chamber  8  through primary oxygen ejection holes  5 B and secondary oxygen ejection holes  7 B. 
     A predetermined amount of a fuel gas is fed into a fuel supply path  4 A of a burner  12  from a fuel gas supply source  26 , and then ejected toward a combustion chamber  8  through fuel gas ejection holes  4 B. 
     Two kinds of raw material powders each having a different particle diameter ejected into the flame are respectively melted by heating in a central region at a high temperature and an outside region at a low temperature and then spheroidized to give spheroidized particles each having a different particle diameter. 
     These spheroidized particles are transferred to a cyclone  17  from a combustion gas discharge exit  14  of a spheroidization furnace  11  through a duct  15  and a damper  16  while floating on a gas of a combustion gas produced from a burner  2  and air to be introduced from an air intake port  13 . By mixing the combustion gas with air, the temperature of the gas to be introduced into the cyclone  17  decrease to reach the temperature suited for collection of the particles in the cyclone  17 . 
     In the cyclone  17 , among the spheroidized particles floating in the gas, only spheroidized particles in the form of coarse particles are collected. The gas discharged from the cyclone  17  is transferred to a bag filter  19  through a duct  21 , where spheroidized particles in the form of microspheres among the spheroidized particles are collected. 
     If necessary, the damper  16  of the duct  15  is closed, and a gas is allowed to flow in the duct  18  and is directly transferred to the bag filter  19 , thus making it possible to collect all spheroidized particles in the bag filter. In this case, when the temperature of the gas must be lowered, an appropriate amount of air can also be mixed in the gas from an air intake port  20 . 
     It is possible to efficiently obtain spheroidized particles having a particle diameter, which nearly agrees with that of a raw material powder, by using the above operation and one burner  12 . 
     EXAMPLES 
     Hereinafter, specific examples are described. 
     Example 1 
     Using the production apparatus of inorganic spheroidized particles shown in  FIG. 3 , spheroidized particles were produced. 
     As the entire raw material powder, a silica powder at 20 kg/h was transported with oxygen at 7.5 Nm 3 /h as a carrier gas. As a fuel gas, LPG at 5 Nm 3 /h was supplied. As the entire oxygen-containing gas, each half of oxygen at 20 Nm 3 /h was dividedly introduced into a burner  12  to produce spheroidized particles, and then a spheroidization throughput capacity that achieves a vitrification ratio of 98% or more was determined. 
     At this time, each proportion of oxygen to be supplied to the above primary oxygen ejection holes  5 B (primary oxygen) and the secondary oxygen ejection holes  7 B (secondary oxygen) was changed within a range from 0 to 100% (primary oxygen) and a range from 100 to 0% (secondary oxygen), according to the particle size of the raw material powder, and thus studying the condition that can achieve the vitrification ratio of 98% or more. 
     The results of the treatment to the raw material powder having a mean particle diameter of 30 μm and the raw material powder having a mean particle diameter of 2 μm are shown in  FIG. 4 ,  FIG. 5  and Table 1. 
     In the case of treating the raw material having a mean particle diameter of 30 μm, the raw material powder was ejected through the first raw material ejection hole  3 . In the case of treating the raw material having a mean particle diameter of 2 μm, the raw material powder was ejected through the second raw material ejection holes  6 B. 
     The raw material having a mean particle diameter of 30 μm was collected by the cyclone  17 , while the raw material having a mean particle diameter of 2 μm was collected by the bag filter  19  without through the cyclone  17 . 
     For comparison with the prior art, spheroidized particles were produced under the above condition using the same type as that of the inorganic material spheroidization apparatus described in Patent Literature 3. 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Mean particle 
                   
                   
                   
                 Mean particle diameter of 
               
               
                 diameter of raw 
                 Primary 
                 Secondary 
                 Throughput 
                 spheroidized particles [μm] 
               
             
          
           
               
                 material powder 
                 oxygen 
                 oxygen 
                 capacity 
                   
                 The present 
               
               
                 [μm] 
                 [%] 
                 [%] 
                 [kg/h] 
                 Prior art 
                 invention 
               
               
                   
               
             
          
           
               
                 30 
                 25 
                 75 
                 20 
                 36 
                 31 
               
               
                 2 
                 40 
                 60 
                 20 
                 7 
                 3 
               
               
                   
               
             
          
         
       
     
     As a result, as shown in  FIG. 4  and  FIG. 5 , the vitrification ratio of 98% or more could not be obtained under the condition of 50% or more (primary oxygen) and 50% or less (secondary oxygen) using raw materials having any particle diameter. 
     Also, in comparison with the prior art, a significant difference was not recognized with respect to an influence of primary oxygen and secondary oxygen. 
     The results shown in Table 1 revealed that inorganic spheroidized particles having a diameter more close to that of the raw material can be obtained by using a burner in the present invention. 
     Example 2 
     Using a silica powder as a raw material powder, three kinds of raw material powders, for example, a raw material powder A having a mean particle diameter of 15 μm, a raw material powder B having a mean particle diameter of 2 μm, and a raw material powder C having a mean particle diameter of 5 μm obtained by mixing 35% by weight of the raw material powder A with 65% by weight of the raw material powder B were prepared. 
     Using a burner of the prior art described in Patent Literature 3, a raw material powder C at 20 kg/h was supplied by transporting with oxygen at 7.5 Nm 3 /h as a carrier gas. As a fuel gas, LPG at 5 Nm 3 /h was supplied. Oxygen at 20 Nm 3 /h was supplied to produce spheroidized particles, and then a spheroidization throughput capacity that achieves a vitrification ratio of 98% or more was determined. 
     Using the burner in the present invention, a raw material A at 7 kg/h was transported with oxygen at 5.25 Nm 3 /h as a carrier gas to first raw material ejection holes  3 , and a raw material B at 13 kg/h was transported with oxygen at 2.25 Nm 3 /h as a carrier gas to second raw material ejection holes  6 B. As a fuel gas, LPG at 5 Nm 3 /h was supplied to fuel gas ejection holes  4 B. Each half of the entire oxygen at 20 Nm 3 /h was dividedly introduced into primary oxygen ejection holes  5 B and secondary oxygen ejection holes  7 B to produce spheroidized particles, and then a spheroidization throughput capacity that achieves a vitrification ratio of 98% or more was determined. 
     At this time, a throughput capacity of a burner was investigated by fixing the proportion of oxygen to be supplied to the primary oxygen ejection holes  5 B (primary oxygen) and the secondary oxygen ejection holes  7 B (secondary oxygen) to 30% (primary oxygen) and 70% (secondary oxygen) according to the particle size of the raw material powder thereby adjusting raw material powder supply amount. 
     The results are shown in Table 2. 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Mean particle 
                   
                 Vitrification ratio 
                 Mean particle diameter 
               
               
                   
                 diameter of raw 
                 Throughput 
                 of spheroidized 
                 of spheroidized 
               
               
                   
                 material [μm] 
                 capacity [kg/h] 
                 particle [%] 
                 particle [μm] 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Present 
                 Raw material A: 15 
                 Total: 20 
                 99 
                 7 
               
               
                 invention 
                 Raw material B: 2 
                 Raw material A: 7 
               
               
                   
                   
                 Raw material B: 13 
               
               
                 Prior art 
                 Raw material C: 5 
                 16 
                 98 
                 10 
               
               
                   
               
             
          
         
       
     
     The results shown in Table 2 revealed that inorganic spheroidized particles having a diameter more close to that of the raw material can be efficiently obtained by using a burner structure in the present invention. 
     
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 [Reference Signs List] 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                  1 
                 First raw material supply pipe 
               
               
                   
                  1A 
                 First raw material supply path 
               
               
                   
                  2  
                 Powder diffusion plate 
               
               
                   
                  3  
                 First raw material ejection hole 
               
               
                   
                  4  
                 Fuel supply pipe 
               
               
                   
                  4A 
                 Fuel supply path 
               
               
                   
                  4B  
                 Fuel gas ejection holes 
               
               
                   
                  5  
                 Primary oxygen supply pipe 
               
               
                   
                  5A 
                 Primary oxygen supply path 
               
               
                   
                  5B  
                 Primary oxygen ejection holes 
               
               
                   
                  6  
                 Second raw material supply pipe 
               
               
                   
                  6A 
                 Second raw material supply path 
               
               
                   
                  6B  
                 Second raw material ejection hole 
               
               
                   
                  7  
                 Secondary oxygen supply pipe 
               
               
                   
                  7A 
                 Secondary oxygen supply path 
               
               
                   
                  7B  
                 Secondary oxygen ejection holes 
               
               
                   
                  8 
                 Combustion chamber 
               
               
                   
                  9 
                 Raw material diffusion chamber 
               
               
                   
                 11 
                 Spheroidization furnace 
               
               
                   
                 12  
                 Burner 
               
               
                   
                 17  
                 Cyclone 
               
               
                   
                 19  
                 Bag filter 
               
               
                   
                 23  
                 First raw material feeder 
               
               
                   
                 24  
                 Carrier gas supply source 
               
               
                   
                 25  
                 Second raw material feeder 
               
               
                   
                 26  
                 Fuel supply source 
               
               
                   
                 27  
                 Primary oxygen supply source 
               
               
                   
                 28  
                 Secondary oxygen supply source