Fuel spraying method in liquid fuel combustion burner, and liquid fuel combustion burner
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a fuel spraying method in a liquid fuel combustion burner used as a heat source of a boiler, a heating furnace and the like, and a liquid fuel combustion burner. More particularly, the present invention relates to a fuel spraying method in a liquid fuel combustion burner having a structure in which a liquid fuel is sprayed together with a fluid flow of air, steam or misty water droplets (hereinafter referred to as &#34;atomization-promoting fluid&#34; or &#34;division promoting fluid&#34;) which is mixed in with the liquid fuel, and a liquid fuel combustion burner. 
     2. Description of the Related Art 
     A liquid fuel combustion burner having a structure in which a liquid fuel is mixed with an atomization-promoting fluid such as steam or air and this mixed fluid is sprayed from a plurality of injection holes is known. 
     According to the fuel spraying method adopted for this liquid fuel combustion burner, the liquid fuel to be mixed with the spraying medium is atomized and diffused by the expansion energy generated when an atomization-promoting fluid such as steam or air is injected to a low-pressure side from a high-pressure side. 
     In regard to the above-mentioned spraying method, two mixing methods are known, an internal mixing method in which the injection quantity is controlled while maintaining a certain difference between the pressure of the atomization-promoting fluid and the pressure of the liquid fuel, and an intermediate mixing method in which the pressure of the liquid fuel is changed while maintaining the pressure of the atomization-promoting fluid at a certain level, whereby the injection quantity is controlled. 
     The intermediate mixing method is advantageous over the internal mixing method in that the consumption of the atomization-promoting fluid is small and a good atomizing effect is attained. 
     However, this spraying method is defective in that since the liquid fuel, which is an incompressible fluid, has no substantial dispersing force, the atomization-promoting fluid should be maintained at a high temperature and a high pressure. 
     As the means for solving this problem, there has been proposed a technique of giving a turning or swirling movement to the atomization-promoting fluid and liquid fuel. The centrifugal force generated by this turning motion promotes atomization and diffusion of the liquid fuel and improves the combustion state (see Japanese Unexamined Utility Model Publication No. 57-145116). 
     According to this conventional technique, the mixing of the liquid fuel with air and the atomization of the fluid are promoted, not only by the expansion energy generated when steam is injected to a low-pressure side from a high-pressure side, but also by the centrifugal force generated by the turning movement. The liquid fuel also becomes uniformly diffused over a broad range. 
     Recently, exhaust gas regulations for combustion apparatuses became severe, and reduction of a level of nitrogen oxides (hereinafter referred to as &#34;NO x  &#34;) produced by combustion is therefore an important problem. 
     Various experiments were done with the above-mentioned conventional liquid fuel combustion burner, and it was found that since the flame layer becomes thick and large and the heat dissipation is degraded, the flame temperature rises, the residence time in a high-temperature zone becomes long and it is difficult to reduce the level of NO x . 
     The reason it is difficult to reduce the NO x  level produced by the conventional burner is that in the conventional liquid fuel combustion burner a plurality of injection holes are arranged equidistantly or substantially equidistantly and, thus, the flame layer becomes thick and large and the heat dissipation is degraded. 
     Moreover, since both of the liquid fuel and the atomization-promoting fluid or division promoting fluid, such as steam are simultaneously turned, the frictional energy between the steam and the liquid fuel is increased. 
     Accordingly, the consumption of the atomization-promoting fluid, such as steam, increases and, thus, it becomes necessary to elevate the heating temperature of the liquid fuel, with the resultant increase of NO x  in the exhaust gas. 
     OBJECT OF THE INVENTION 
     The object of the present invention is to promote the atomization and diffusion of the liquid fuel and to reduce the level of NO x  in the exhaust gases while reducing the consumption of the spraying medium. 
     SUMMARY OF THE INVENTION 
     The present invention has been completed under this background to solve the foregoing problems of the conventional techniques. Namely, the present invention relates to a fuel spraying method in a liquid fuel combustion burner, in which a liquid fuel is sprayed together with an atomization-promoting fluid or a division promoting fluid which is mixed in with the liquid fuel, and a liquid fuel combustion burner. 
     More specifically, in accordance with the present invention there is provided a fuel spraying method in a liquid fuel combustion burner, which comprises turning or swirling a liquid fuel in a flow passage having a sectional area restricted for constraining a flow of the liquid fuel, introducing atomization-promoting fluid into the flow passage and spraying a mixed fluid of the liquid fuel and the atomization-promoting fluid from said flow passage. 
     According to this method, the liquid fuel to be mixed with the atomization-promoting fluid is atomized and uniformly diffused by the expansion energy generated when the atomization-promoting fluid is injected to a low-pressure side from a high-pressure side. Furthermore, a turning movement is given to the liquid fuel and the centrifugal force generated by this turning movement further promotes the atomization and diffusion of the liquid fuel and causes the liquid fuel to be uniformly diffused over a broad area. 
     Since only the liquid fuel is turned and the atomization-promoting fluid is not turned, the frictional energy between the atomization-promoting fluid and the liquid fuel is reduced, and hence, the consumption of the atomization-promoting fluid can be reduced. Since the consumption of the atomization-promoting fluid is reduced, the heating temperature for the liquid fuel does not need to be elevated and hence, generation of NO x  can be reduced. 
     In accordance with another aspect of the present invention, there is provided a liquid fuel combustion burner, which is attached to the top end portion of a tube for being projected into the interior of a combustion apparatus. The assembly has a structure in which a liquid fuel supplied through a fuel passage formed in the interior of the tube is sprayed into the interior of the combustion apparatus together with an atomization-promoting fluid supplied through atomization-promoting fluid passages formed in the interior of the tube and which atomization-promoting fluid is mixed with the fuel. The burner comprises a liquid fuel supply passage, a plurality of injection holes, branch passages branched from the liquid fuel supply passage, an annular passage communicating with the downstream end of the branch passages and located around the downstream end of the atomization-promoting fluid supply passages, connecting passages connecting the downstream end of the atomization-promoting fluid supply passages to the injection holes, and a burner proper having connecting passages connecting the downstream end of the liquid fuel supply passage and the annular passage to side portions of the respective injection holes. 
     In the burner having the above-mentioned structure, the liquid fuel flows into the liquid fuel supply passage and the branch passages. 
     The liquid fuel which has flowed into the liquid fuel supply passage arrives at the connecting passages through the downstream end of the liquid fuel supply passage and is injected into the interior of the injection holes from the side position of the injection hole to which the connecting passages open. 
     The liquid fuel which has flowed into the branch passages arrives at the connecting passages through the annular passage and is injected into the interior of the injection holes from the side position of the injection hole to which the connecting passage opens. 
     The atomization-promoting fluid flows into the atomization-promoting fluid supply passages from where it passes through the connecting passages and is injected into the interior of the injection holes from the downstream end of the injection holes to which the connecting passages open. 
     Since the direction of the connection of the connecting passages to the side portion of the injection holes is made in agreement with the tangential direction of the injection holes, the liquid fuel injected from the side portion of the injection holes is formed into a turning stream. 
     The plurality of injection holes are divided into a plurality of groups, each group consisting of two injection holes, and respective groups are arranged at a plurality of positions, separated from one another by predetermined angles in the circumferential direction with the central axis of the burner proper being as the center. Two injection holes of each group can be arranged so that they are brought close to each other in the circumferential direction with the central axis of the burner proper being as the center. 
     If this embodiment is adopted, the flame can be divided into a plurality of independent small flames which can be formed in the discrete state. 
     Therefore, the heat dissipation is enhanced, and the flame temperature can be reduced, and since the flame layer becomes thin, the residence time of the gas in a high-temperature zone can be shortened, with the result that formation of NO x  can be controlled. 
     It is especially preferred that the injection holes of each group be arranged contiguously to each other so that the central axes of the injection holes form a crossing angle smaller the 20° or so that they are parallel to one another. Therefore, NO x  can be effectively controlled. 
     According to the preferred embodiment, the burner proper comprises a fuel supply member and a burner tip connected to the top end of the fuel supply member, a liquid fuel supply passage, atomization-promoting fluid supply passages, branch passages, a plurality of injection holes formed in the fuel supply member, connecting passages connecting the atomization-promoting fluid supply passage to the injection holes, an annular passage, and a connecting passage connecting the downstream end of the liquid fuel supply passage and the annular passage to the injection holes of the burner tip. If this embodiment is adopted, the productivity of the burner proper can be improved, and mass production and reduction of the cost become possible. 
     Preferably, the fuel supply member is formed of a substantially columnar member having a surface of a circular cone on the top end. 
     According to this embodiment, the productivity and reduction of price become possible. 
     Furthermore, in the fuel supply member, a liquid fuel supply passage is preferably formed from the top end through to the rear end portions thereof. 
     According to this embodiment, the productivity and reduction of price become possible. 
     Moreover, it is preferred that a plurality of branch passages be formed in the fuel supply member so that the branch passages extend obliquely upward from the rear end of the liquid fuel supply passage and open to the top end face of the fuel supply member. 
     According to this embodiment, the productivity and reduction of price become possible. 
     Still further, it is preferred that in the fuel supply member, a plurality of small-diameter holes be formed such that the holes extend obliquely from positions close to the rear end of the liquid fuel supply passage on the rear end face of the fuel supply member to near the top end face of the fuel supply member. These holes are then intersected by a smaller hole orthogonal to the end face. 
     According to this embodiment, the productivity and reduction of price become possible. 
     Still in addition, it is preferred that an engaging pin be driven into the peripheral part of the top end face of the fuel supply member and that the engaging pin be positioned for engaging an engaging hole formed on the rear face of the burner tip to thus engage the fuel supply member with the burner tip. 
     According to this embodiment, the productivity and reduction of price become possible. 
     It is preferred that a recess capable of being engaged with the top end portion of the fuel supply member be formed on the rear face of the burner tip and that the burner tip be formed to have substantially a shape of a circular cone. 
     According to this embodiment, the productivity and reduction of price become possible. 
     Moreover, it is preferred that a circular recess be formed at a central part of the inner face of the burner tip, an annular passage be formed in the peripheral portion of said inner face, and a plurality of injection holes be formed from the top end face of the burner tip in a direction orthogonal to said top end face and opening to the interior of the engaging portion between said annular passage and said circular recess. 
     According to this embodiment, the productivity and reduction of price become possible. 
     Furthermore, it is preferred that between an injection hole-opening portion on the inner face of the burner tip and circular recess formed at a central part of the inner face of the burner tip, a connecting passage connecting the injection hole and the circular recess be formed, and a connecting passage connecting the injection hole to the annular passage be formed between the opening of the injection hole and the annular passage. 
     According to this embodiment, the productivity and reduction of price become possible. 
     Still further, it is preferred that between an injection hole-opening portion on the top end face of the fuel supply member and a circular recess formed at a central part of the top end face of the fuel supply member, a connecting passage connecting the injection hole to the circular recess be formed, and a connecting passage connecting the injection hole and the annular passage be formed between the opening of the injection hole and the annular passage. 
     The burner proper can comprise a fuel supply member and a burner tip to be engaged with the top end portion of the fuel supply member, which fuel supply member comprises, a liquid fuel supply passage, an atomization-promoting fluid supply passage, branch passages, a part of a plurality of injection holes, a connecting passage connecting the atomization-promoting fluid supply passage with the part of the injection holes, an annular passage and connecting passages connecting the downstream end of the liquid fuel supply passage and the annular passage to the part of the injection holes. The remainder of the plurality of injection holes are formed in the burner tip. According to this embodiment, the productivity of the burner proper is increased, and mass production and reduction of the price become possible. Since it is sufficient to form connecting passages on the top face of the fuel supply member by machining, there can be attained an advantage in that the machining operation can be performed simply and easily. 
     It is preferred that a circular recess be formed at a central part of the top end face of the fuel supply member, an annular passage be formed in the peripheral portion of the inner face of the fuel supply member, and a connecting portion of a plurality of injection holes pierced from the top end face of the burner tip in a direction orthogonal to said top end face be formed between the annular passage and the circular recess. 
     According to this embodiment, the productivity and reduction of price become possible. 
     Furthermore, it is preferred that a connecting passage be formed between the injection hole-connecting portion of the fuel supply member, the circular recess be formed at the central part of the fuel supply member to connect the injection opening- connecting portion to the circular recess, and a connecting passage be formed between the injection hole-connecting portion and the annular passage to connect the injection hole-connecting portion to the annular passage. 
     According to this embodiment, the productivity and reduction of price become possible. 
     One feature of the invention resides broadly in a fuel spraying method in a liquid fuel combustion burner, which comprises turning a liquid fuel in a flow passage having a sectional area restricted for constraining a flow of the liquid fuel, introducing atomization-promoting fluid to said flow passage and spraying a mixed fluid of the liquid fuel and the atomization-promoting fluid from said flow passage. 
     An additional feature of the invention resides broadly in a liquid fuel combustion burner, which is attached to the top end portion of a tube projected into the interior of a combustion apparatus proper and has a structure in which a liquid fuel supplied through a fuel passage formed in the interior of the tube is sprayed into the interior of the combustion apparatus proper together with an atomization-promoting fluid supplied through an atomization-promoting fluid passage formed in the interior of tube and mixed with the fuel, said burner comprising a liquid fuel supply passage, a plurality of injection holes, a branch passage branched from the liquid fuel supply passage, an annular passage communicating with the downstream end of the branch passage and located around the downstream end of the atomization-promoting fluid supply passage, a connecting passage connecting the downstream end of the atomization-promoting fluid supply passage to the injection holes, and a burner proper having a connecting passage connecting the downstream end of the liquid fuel supply passage to the annular passage and the side portions of the respective injection holes. 
     A further feature of the invention resides broadly in a method of spraying fluid fuel from a fluid fuel combustion nozzle, the method comprising the steps of: introducing the fluid fuel into a flow passage of the fluid fuel combustion nozzle, swirling the fluid fuel in the flow passage, introducing a division-promoting fluid into the flow passage to divide the fluid fuel and form a mixed fluid of the division-promoting fluid and the fluid fuel, and spraying the mixed fluid out of the flow passage. 
     A yet further feature of the invention resides broadly in a fluid fuel spray nozzle for use in a boiler, a heating furnace or the like, the fluid fuel spray nozzle comprising: at least one fluid fuel supply passage, at least one division-fluid supply passage, at least one injection passage aligned with the at least one division-fluid supply passage, at least one connecting passage connecting the at least one fuel supply passage to the at least one injection passage, the at least one connecting passage substantially tangentially connected to the at least one injection passage, at least one of: the at least one connecting passage and the at least one injection passage comprising apparatus for producing swirling of the fluid fuel upon the fluid fuel being introduced into the at least one injection passage through the at least one connecting passage from the at least one fuel supply passage. 
     The present invention will now be described in detail with reference to embodiments illustrated in the accompanying drawings, from which the present invention will be clearly understood. However, the scope of the present invention is not limited by these embodiments, but modifications can be freely made within the scope defined by the claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view illustrating the state of attachment of the liquid fuel combustion burner according to the present invention. 
     FIG. 2 is a plan view showing a fuel supply member of the burner proper shown in FIG. 1. 
     FIG. 3 is a sectional view of a burner tip of the burner proper shown in FIG. 1, which shows the section taken along the line III--III in FIG. 4. 
     FIG. 4 is a bottom view of a burner tip of the burner proper shown in FIG. 1. 
     FIG. 5 is a plan view of a burner tip of the burner proper shown in FIG. 1, which illustrates an example of the arrangement of injection holes. 
     FIG. 6 is a sectional view illustrating another embodiment of the liquid fuel combustion burner according to the present invention. 
     FIG. 7 is a plan view of a fuel supply member of the burner shown in FIG. 6. 
     FIG. 8 is a sectional view illustrating still another embodiment of the liquid fuel combustion burner according to the present invention. 
     FIG. 9 is a plan view of a fuel supply member of the burner shown in FIG. 8. 
     FIGS. 10a-10d are a plan views illustrating the arrangement of injection holes in the conventional burner. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a sectional view illustrating the attachment of the liquid fuel combustion burner according to the present invention. A liquid fuel combustion burner 1 is inserted through the peripheral wall of a furnace proper as a combustion apparatus proper not shown in the drawings and is used in the state where the top end side of the burner 1 is fixed to the top end portion of a guide pipe 2 projected into the interior of the furnace proper. An adapter 3 is inserted and fixed in the guide pipe 2, and in the adapter 3, there are formed passages 4 and 5 which are respectively connected to a fuel supply pipe and an atomization-promoting fluid supply pipe, which are extended from a fuel supply source and an atomization-promoting fluid supply source, not shown in the drawings. A cylindrical cap 6 is engaged with a proper 20 of the burner 1 in the state where the top end face of the burner proper 20 is projected, and by fitting male screw 6a formed on the peripheral face of the cap 6 to a female screw 2a formed on the inner circumferential face of the guide pipe 2, the burner proper 20 is fixed to the top end portion of the guide pipe 2. In this attachment state of the burner proper 20, the passages 4 and 5 respectively communicating with the fuel supply pipe and the atomization-promoting fluid supply pipe are connected to a fuel supply hole 23 and an atomization-promoting fluid supply hole 26, described hereinafter, of the burner proper 20. 
     The burner proper 20 comprises a fuel supply member 21 and a burner tip 22 connected to the top face of the fuel supply member 21. The fuel supply member 21 is formed of a substantially columnar body having a top end face of a circular cone. 
     The liquid fuel supply hole 23 is formed to pierce a central part of the fuel supply member 21 along the central axis thereof. 
     In the fuel supply member 21, a plurality of branch holes 25 are formed so that the branch holes 25 extend obliquely upward from a large-diameter portion formed at the rear end of the liquid fuel supply hole 23 and open to the top end face of the liquid fuel supply member 21. 
     A plurality of atomization-promoting fluid supply holes 26 are formed in the fuel supply member 21 so that the atomization-promoting fluid supply holes 26 extend obliquely from the position close to the large-diameter portion of the liquid fuel supply hole 23 while approaching the liquid fuel supply hole 23, and the holes 26 communicate with a plurality of small-diameter holes 27 pierced in the top end face of the fuel supply member 21 from a direction orthogonal to said top end face, respectively. 
     In this embodiment, as shown in the plan view of the fuel supply member in FIG. 2, the small-diameter holes 27 are arranged between the liquid fuel supply hole 23 and the branch holes 25 on the top end face of the fuel supply member 21. 
     An engaging pin 28 is driven in the peripheral portion of the top end face of the fuel supply member 21, and by engaging this engaging pin 28 with an engaging hole 36 formed on the rear face of the burner tip 22 (see FIG. 4), the fuel supply member 21 and the burner tip 22 are fixed together. 
     As shown in the sectional view of the burner tip in FIG. 3 and the bottom view of the burner tip in FIG. 4, a fitting portion 29 capable of engaging with the top end portion of the above-mentioned fuel supply member is formed as a recess on the rear face of the burner tip 22, and the burner tip 22 is formed to have substantially a shape of a circular cone as a whole. 
     A circular recess 30 is formed at a central part of the inner face of the fitting portion 29 of the burner tip 22 and an annular groove 31 is formed on the periphery of the inner face of the fitting portion 29. A plurality of injection holes 32 pierced from the top end face of the burner tip 22 in a direction orthogonal to the end face and opened to the inner face of the fitting portion 29 are formed between the annular groove 31 of the fitting portion 29 and the circular recess 30. 
     A communicating groove 33 connecting the injection holes 32 to the circular recess 30 is formed between the openings of the injection holes 32 on the inner face of the fitting portion 29 and circular recess 30. Furthermore, a communicating groove 35 connecting the injection holes 32 to the annular groove 31 is formed between the openings of the injection holes 32 on the inner face of the fitting portion 29 and the annular groove 31. 
     One side wall a of communicating grooves 33 and one side wall b of communicating groove 35 are located substantially on a line passing through the centers of the injection holes 32. The other side walls c and d of the communicating grooves 33 and 35 are parallel to the side walls a and b and are located on a line along the tangential direction of the injection holes 32. 
     In the above-mentioned structure, the connecting directions of the communicating grooves 33 and 35 to the side portions of the injection holes 32 are made in agreement with the tangential direction of the injection holes 32. 
     Referring to the plan view of the burner tip in FIG. 5, the arrangement of the injection holes 32, which is one of the characteristic features of the present invention, will now be described in detail. 
     Namely, six injection holes 32a through 32f are arranged and divided into three groups, that is, a group of injection holes 32a and 32b, a group of injection holes 32c and 32d and a group of injection holes 32e and 32f. These groups are arranged at three positions spaced by 120° from one another with the central axis of the burner tip 22 being the center. In each group, the injection holes 32a and 32b, 32c and 32d or 32e and 32f are arranged adjacently to one another so that the central axes of these injection holes cross each other at a predetermined angle α (smaller than 20°). 
     Incidentally, in each group, the injection holes 32a and 32b, 32c and 32d or 32e and 32f can be arranged adjacently to each other so that the central axes of these injection holes are parallel to one another. 
     The function of the liquid fuel combustion burner having the above-mentioned structure will now be described. A liquid fuel supplied to the fuel supply member 21 flows from the rear end of the fuel supply member 21 into the liquid fuel supply hole 23 and the branch hole 25. 
     The liquid fuel which has flowed into the liquid fuel supply hole arrives at the communicating groove 33 through the circular recess 30 of the burner tip 32 and is injected into the interior of the injection hole 32 from the position on the inner circumferential face of the injection hole 32 to which the communicating groove 33 opens. 
     The liquid fuel which has flowed into the branch hole 25 arrives at the communicating groove 35 through the annular groove 31 of the burner tip 32 and is injected into the interior of the injection hole 32 from the position of the inner circumferential face confronting to the position of the opening of the communicating groove 33 of the injection hole 32, to which the communicating groove 35 opens. 
     Steam, as the atomization-promoting fluid, flows into the atomization-promoting fluid supply hole 26 from the rear end portion of the fuel supply member 21. From the atomization-promoting fluid supply hole 26, the steam arrives at the small-diameter hole 27 and is injected into the interior of the injection hole 32 from the position on the rear end face of the injection hole 32 to which the small-diameter hole 27 opens. 
     Since side walls a and b of the communicating grooves 33 and 35 are formed to pass substantially through the center of the injection hole 32 and the other side walls c and d are formed so that they are parallel to side walls a and b and located in the tangential direction of the injection hole 32, the liquid fuel is injected from two confronting positions on the inner circumferential face of the injection hole 32, and each injected liquid fluid is formed into a turning stream. 
     Steam is injected to these turning streams of the liquid fluid, the liquid fuel is mixed with the steam, and the mixture is sprayed from the injection hole 32. At this point, the liquid fuel mixed with steam is atomized and uniformly diffused by the expansion energy generated when the steam is injected to a low-pressure side from a high-pressure side. Furthermore, a turning movement is given to the liquid fuel, and the centrifugal force generated by this turning movement further promotes atomization and diffusion of the liquid fuel and causes the liquid fuel to be uniformly diffused over a broad range. 
     Since only the liquid fuel is turned and the steam is not turned, the frictional energy between the steam and the liquid fuel is reduced, the consumption of steam can be reduced, and this reduction of the consumption of steam makes it unnecessary to elevate the temperature for heating the liquid fuel and therefore, formation of NO x  can be controlled. 
     Moreover, since the injection holes 32a through 32f are divided into three groups, the injection holes of respective groups are arranged at three positions separated from one another by 120° and in each group, the injection holes 32a and 32b, the injection holes 32c and 32d and the injection holes 32e and 32f are arranged adjacently to each other so that the central axes of the injection holes cross each other at a predetermined angle α (smaller than 20°) or they are parallel to each other, the flame can be divided into a plurality of small independent flames in the discrete state, and therefore, a good heat dissipation can be attained and the flame temperature can be lowered. Moreover, the flame layer becomes thin and the residence time of gas in a high-temperature zone can be shortened, and therefore, formation of NO x  can be effectively controlled. 
     The effects of the above-mentioned liquid fuel combustion burner of the present invention will be readily understood from the experimental results shown in Tables 1 through 4. It is obvious that the NO x  concentration and the soot quantity can be drastically reduced. 
     
                       TABLE 1                                                     
______________________________________                                    
              Conventional  Burner                                        
              Burner Invention                                            
                            of Present                                    
______________________________________                                    
capacity of boiler                                                        
              3 t/h         3 t/h                                         
spraying method                                                           
              internal      intermediate                                  
              mixing        mixing                                        
number of burners                                                         
              1             1                                             
size of injection                                                         
              .0.1.7 × 8 holes                                      
                            .0.2.6 × 6 holes                        
holes         (FIG. 10-a)   (parallel)                                    
fuel oil      kerosene      kerosene                                      
combustion oil                                                            
              280 l/h       280 l/h                                       
quantity                                                                  
spraying oil  2.7 kg/cm.sup.2                                             
                            4.7 kg/cm.sup.2                               
pressure                                                                  
spraying steam                                                            
              2.1 kg.cm.sup.2                                             
                            4.6 kg/cm.sup.2                               
pressure                                                                  
NO.sub.x concentration                                                    
              80 ppm        40 ppm                                        
exhaust gas   2.9%          3.0%                                          
O.sub.2 level                                                             
smoke concentration                                                       
              0.5-1.0       0                                             
______________________________________                                    
 
    
     
                       TABLE 2                                                     
______________________________________                                    
              Conventional  Burner                                        
              Burner Invention                                            
                            of Present                                    
______________________________________                                    
capacity of boiler                                                        
              85 t/h        85 t/h                                        
spraying method                                                           
              internal      intermediate                                  
              mixing        mixing                                        
number of burners                                                         
              4             4                                             
size of injection                                                         
              .0.3.5 × 8 holes                                      
                            .0.4.7 × 6 holes                        
holes         (FIG. 10-b)   (parallel)                                    
fuel oil      fuel oil C    fuel oil C                                    
combustion oil                                                            
              6000 l/h      6000 l/h                                      
quantity                                                                  
spraying oil  7.4 kg/cm.sup.2                                             
                            8.0 kg/cm.sup.2                               
pressure                                                                  
spraying steam                                                            
              9.0 kg.cm.sup.2                                             
                            9.4 kg/cm.sup.2                               
pressure                                                                  
NO.sub.x concentration                                                    
              223 ppm       173 ppm                                       
exhaust gas   3.9%          4.1%                                          
O.sub.2 level                                                             
smoke concentration                                                       
              5.0           3.5                                           
______________________________________                                    
 
    
     
                       TABLE 3                                                     
______________________________________                                    
              Conventional  Burner                                        
              Burner Invention                                            
                            of Present                                    
______________________________________                                    
capacity of boiler                                                        
              50 t/h        50 t/h                                        
spraying method                                                           
              internal      intermediate                                  
              mixing        mixing                                        
number of burners                                                         
              3             3                                             
size of injection                                                         
              .0.3.9 × 4 holes                                      
                            .0.4.2 × 6 holes                        
holes         (FIG. 10-c)   (α= 7.5° C.)                     
fuel oil      fuel oil C    fuel oil C                                    
combustion oil                                                            
              3774 l/h      3786 l/h                                      
quantity                                                                  
spraying oil  10.5 kg/cm.sup.2                                            
                            10.6 kg/cm.sup.2                              
pressure                                                                  
spraying steam                                                            
              10.7 kg.cm.sup.2                                            
                            10.7 kg/cm.sup.2                              
pressure                                                                  
NO.sub.x concentration                                                    
              202 ppm       182 ppm                                       
exhaust gas   1.1%          1.0%                                          
O.sub.2 level                                                             
smoke concentration                                                       
              0             0                                             
soot quantity 40-80 kg/day  20-30 kg/day                                  
______________________________________                                    
 
    
     
                       TABLE 4                                                     
______________________________________                                    
              Conventional  Burner                                        
              Burner Invention                                            
                            of Present                                    
______________________________________                                    
capacity of boiler                                                        
              120 t/h       120 t/h                                       
spraying method                                                           
              internal      intermediate                                  
              mixing        mixing                                        
number of burners                                                         
              6             6                                             
size of injection                                                         
              .0.4.9 × 5 holes                                      
                            .0.6.2 × 6 holes                        
holes         (FIG. 10-d)   (α= 15° C.)                      
fuel oil      fuel oil C    fuel oil C                                    
combustion oil                                                            
              8800 l/h      8800 l/h                                      
quantity                                                                  
spraying oil  8.2 kg/cm.sup.2                                             
                            8.4 kg/cm.sup.2                               
pressure                                                                  
spraying steam                                                            
              5.4 kg.cm.sup.2                                             
                            5.6 kg/cm.sup.2                               
pressure                                                                  
NO.sub.x concentration                                                    
              230 ppm       180 ppm                                       
exhaust gas   1.8%          1.2%                                          
O.sub.2 level                                                             
smoke concentration                                                       
              0-0.5         0-0.5                                         
______________________________________                                    
 
    
     If the crossing angle between the central axes of the injection holes is larger than 20° (for example, 25°), as shown in Table 5, the NO x  concentration and the soot quantity are larger than those attained when this angle is smaller than 20°. Accordingly, it is obvious that particular effects are attained in the present invention by arranging the injection holes adjacently to each other so that the central axes of the injection holes cross each other at an angle smaller than 20° or they are parallel to each other. 
     
                       TABLE 5                                                     
______________________________________                                    
                    Burner of Present                                     
                    Invention                                             
______________________________________                                    
capacity of boiler  120 t/h                                               
spraying method     intermediate mixing                                   
number of burners   6                                                     
size of injection   .0.6.2 × 6 holes                                
holes               (α = 25° C.)                             
fuel oil            fuel oil C                                            
combustion oil      8800 l/h                                              
quantity                                                                  
spraying oil        8.4 kg/cm.sup.2                                       
pressure                                                                  
spraying steam      5.6 kg.cm.sup.2                                       
pressure                                                                  
NO.sub.x concentration                                                    
                    210 ppm                                               
exhaust gas         1.5%                                                  
O.sub.2 level       1.5%                                                  
smoke concentration 0-0.5                                                 
______________________________________                                    
 
    
     Incidentally, in Tables 1 through 4, the conventional burners are those in which the injection holes are arranged as shown in FIGS. 10a through 10d. 
     Another of the present invention will now be described with reference to FIGS. 6 and 7. 
     In the embodiment of FIGS. 6 and 7, in the fuel supply member 21, the liquid fuel supply hole 23 and atomization-promoting fluid supply hole 26 are arranged in a positional relation reverse to that shown in FIGS. 1 through 4. 
     Namely, the atomization-promoting fluid supply hole 26 is formed at the central part of the rear end face of the fuel supply member 21, and a plurality of small-diameter holes 27 connecting the atomization-promoting fluid supply hole 26 to the injection hole 32 are formed. A plurality of liquid fuel supply holes 23 are formed in the periphery of the atomization-promoting fluid supply hole 26, and a first branch hole 37 and a second branch hole 39 branched from the liquid fuel supply hole 23 in two different directions are formed. 
     The first branch hole 37 communicates with the circular recess 30 of the burner tip 22, and the second branch hole 39 communicates with the annular groove 31 of the burner tip 22. 
     The function of the present embodiment will now be described. 
     The liquid fuel supplied to the fuel supply member 21 follows into the liquid fuel supply hole 23 from the rear end portion of the fuel supply member 21. 
     The liquid fluid which has flowed into the liquid fuel supply hole 23 is introduced into the first branch hole 37 and the second branch hole 39. The liquid fuel which has flowed into the first branch hole 37 arrives at the communicating groove 33 through the circular recess 30 and is injected into the interior of the injection hole 32 from the position on the inner circumferential face of the injection hole 32, to which the communicating groove 33 opens. 
     The liquid fuel which has flowed into the second branch hole 39 arrives at the communicating groove 35 through the annular groove 31 and is injected into the interior of the injection hole 32 from the position of the inner circumferential face confronting to the position of the opening of the communicating groove 33 of the injection hole 32, to which the communicating groove 35 opens. 
     Steam flows into the atomization-promoting fluid supply hole 26 from the rear end portion of the fuel supply member 21 and is injected into the interior of the injection hole 32 from the position on the rear end face of the injection hole 32 to which the small-diameter hole 27 opens, through the small-diameter hole 27. 
     Also in the present embodiment, the liquid fuel injected from the two confronting positions on the inner circumferential face of the injection hole 32 is formed into turning streams, while steam is not turned. 
     Still another example of the present invention will now be described with reference to FIGS. 8 and 9. 
     In the present embodiment, the communicating grooves 33 and 35, which are formed on the side of the burner tip 22 in the embodiment shown in FIGS. 1 through 4, are formed on the side of the fuel supply member 21. 
     Accordingly, in the present embodiment, it is sufficient if the communicating grooves 33 and 35 are formed on the top face of the fuel supply member 41 by matching. Therefore, the present embodiment is advantageous in that the machining operation can be performed simply and easily. 
     All, or substantially all, of the components and methods of the various embodiments may be used with at least one embodiment or all of the embodiments, if any, described herein. 
     All of the patents, patent applications and publications recited herein, if any, are hereby incorporated by reference as if set forth in their entirety herein. 
     The details in the patents, patent applications and publications may be considered to be incorporable, at applicant&#39;s option, into the claims during prosecution as further limitations in the claims to patentably distinguish any amended claims from any applied prior art. 
     The invention as described hereinabove in the context of the preferred embodiments is not to be taken as limited to all of the provided details thereof, since modifications and variations thereof may be made without departing from the spirit and scope of the invention.