Patent Publication Number: US-2016223194-A1

Title: Burner and coal upgrading plant

Description:
TECHNICAL FIELD 
     The present invention relates to a burner and a coal upgrading plant. 
     Priority is claimed on Japanese Patent Applications No. 2013-199699, filed on Sep. 26, 2013, the contents of which are incorporated herein by reference. 
     BACKGROUND ART 
     In coal upgrading plants that upgrade low-grade coal to high-grade coal, pyrolytic treatment is performed in some cases to remove impurities such as mercury contained in the low-grade coal. When this pyrolytic treatment is performed, a combustible gas is separated from the low-grade coal. In some cases, this combustible gas is burnt in a combustion furnace and is reused as a high-temperature gas. This high-temperature gas is sent to a jacket such as a rotary kiln as, for instance, a heat source for pyrolyzing the low-grade coal, and then is discharged to the outside via, for instance, an exhaust gas purifier. 
     The combustible gas obtained from the low-grade coal is generally a low-calorie gas. For this reason, if the combustible gas cannot be stably burnt due to lack of a calorific value when burnt in the combustion furnace, a high-calorie gas such as natural gas is partly input into the combustion furnace, and the low-grade coal and the high-calorie gas are sometimes burnt at the same time. In the above coal upgrading plant, a burner for the high-calorie gas which is an auxiliary burner is disposed in the vicinity of a burner for the low-calorie gas in order to improve transfer of flames from the high-calorie gas to the low-calorie gas. Further, an ignition torch is disposed in the vicinity of the burner for the high-calorie gas. 
     However, since it is necessary to individually feed air to each of the burners, for instance, the burner for the low-calorie gas and the burner for the high-calorie gas, pipes are complicated. Further, since each of the burners is individually mounted on a wall surface of the combustion furnace via dedicated pipe stands, the number of pipe stands is increased and it is hard to reduce the size of the plant. 
     A combustor equipped with a nozzle for a low-calorie gas and a nozzle for a high-calorie gas is set forth in Patent Literature 1. The nozzle for the low-calorie gas feeds the low-calorie gas. The nozzle for the high-calorie gas feeds the high-calorie gas to an inner center of the nozzle for the low-calorie gas. This combustor burns the low-calorie gas and the high-calorie gas at the same time. 
     A mixed combustion type burner that burns a high-calorie fuel such as natural gas using an auxiliary burner to assist with combustion of an exhaust gas using flames of the high-calorie fuel is set forth in Patent Literature 2. 
     CITATION LIST 
     Patent Literature 
     [Patent Literature 1] 
     U.S. Pat. No. 8,220,272 
     [Patent Literature 2] 
     U.S. Pat. No. 4,154,567 
     SUMMARY OF INVENTION 
     Problem to be Solved by the Invention 
     Meanwhile, in the coal upgrading plant, the high-calorie gas is ignited for the purpose of raising a temperature during plant start-up. However, an inert gas (e.g., nitrogen) is used to purge the kiln that pyrolyzes the low-grade coal during the plant start-up. In that case, the inert gas is sometimes fed in the vicinity of the nozzle for the high-calorie gas via the nozzle for the low-calorie gas. As a result, flames of the nozzle for the high-calorie gas disposed in the vicinity of the nozzle for the low-calorie gas are accidentally misfired in some cases. 
     An object of the present invention is to provide a burner and a coal upgrading plant that are capable of reducing accidental misfire of flames of a high-calorie gas due to an inert gas ejected from a nozzle for a low-calorie gas when a nozzle for the high-calorie gas is disposed in the vicinity of the nozzle for the low-calorie gas. 
     Means for Solving the Problem 
     According to a first aspect of the present invention, a burner is a burner that simultaneously burns a first gas and a second gas having a higher calorific value than the first gas. This burner includes: a tubular first outer cylinder having an opening through which primary air is fed in a first direction; and a diffuser disposed inside the first outer cylinder and having an inner circumferential surface, a diameter of which gradually increases in the first direction. This burner further includes: a first gas nozzle disposed inside the first outer cylinder and configured to feed the first gas to a radial outer region of the diffuser in the first direction; and a second gas nozzle disposed adjacent to the first gas nozzle in a circumferential direction of the first outer cylinder and configured to feed the second gas to the radial outer region of the diffuser in the first direction. This burner further includes an ignition torch disposed inside the first outer cylinder and configured to ignite at least one of the second gas and the first gas. 
     According to a second aspect of the present invention, in the burner of the first aspect, an opening end of the first gas nozzle in the first direction may include a contact portion configured to abut along an outermost circumferential portion of the diffuser. 
     According to a third aspect of the present invention, the burner of the second aspect may include a plurality of first gas nozzles, and a sum of circumferential angle ranges within which the each contact portion of the first gas nozzles come into contact with the diffuser may range from 90 degrees to 200 degrees. 
     According to a fourth aspect of the present invention, in the burner of any one of the first to third aspects, the second gas nozzle may include a flame holding pad that generates a vortex of the second gas at an opening end thereof in the first direction. 
     According to a fifth aspect of the present invention, the burner of any one of the first to fourth aspects may include a second outer cylinder disposed outside the first outer cylinder and configured to form a flow channel through which secondary air flows between the first outer cylinder and the second outer cylinder. 
     According to a sixth aspect of the present invention, the burner of the fifth aspect may include swirlers disposed between the first outer cylinder and the second outer cylinder and configured to swirl the second air in a circumferential direction.  
     According to a seventh aspect of the present invention, the burner of any one of the first to sixth aspects may include a temperature drop reducing part configured to cover at least a part of an outer circumferential surface of the first gas nozzle and to prevent a drop in temperature of the first gas. 
     According to an eighth aspect of the present invention, a coal upgrading plant includes a combustion furnace provided with the burner according to any one of the first to seventh aspects. 
     Effects of the Invention 
     According to the burner and the coal upgrading plant, it is possible to reduce accidental misfire of flames of a high-calorie gas due to an inert gas ejected from a nozzle for a low-calorie gas when a nozzle for the high-calorie gas is disposed in the vicinity of the nozzle for the low-calorie gas. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic constitutional view of a coal upgrading plant ( 1 ) in this embodiment. 
         FIG. 2  is a sectional view illustrating a schematic constitution around a burner of a combustion furnace of this invention. 
         FIG. 3  is a front view of the burner ( 10 ) when viewed in a direction III of  FIG. 2 . 
         FIG. 4  is a sectional view taken along line VI-VI of  FIG. 3 . 
         FIG. 5  is a perspective view illustrating a state in which a temperature drop reducing part is mounted on a first gas nozzle of the burner. 
         FIG. 6  is a map illustrating primary air ratios at which stable combustion is possible with respect to an input heat rate (%) of a second gas nozzle ( 23 ). 
         FIG. 7  is a map illustrating primary air mixed oxygen concentrations (vol %) at which stable combustion is possible with respect to a primary air ratio. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, a coal upgrading plant according to an embodiment of the present invention will be described. 
       FIG. 1  is a schematic constitutional view of the coal upgrading plant  1  in this embodiment. 
     The coal upgrading plant  1  in this embodiment is a plant that removes moisture, impurities, etc. contained in low-grade coal to mold the low-grade coal, and thereby converts the low-grade coal to high-grade coal. 
     As illustrated in  FIG. 1 , the coal upgrading plant  1  is mainly equipped with a crusher  2 , a drier  3 , a pyrolyzer  4 , a combustion furnace  5 , a quencher  6 , a finisher  7 , a kneader  8 , and a briquetting device  9 . 
     The crusher  2  crushes raw coal L, and thereby adjusts a size of the raw coal L to a size at which the raw coal L is easily processed in a subsequent process. The raw coal L, the size of which is adjusted by the crusher  2 , is sent to the drier  3 . 
     The drier  3  dries the raw coal L, the size of which is adjusted by the crusher  2 . As this drier  3 , for example, a steam tube drier indirectly heating the raw coal L using steam may be used. The coal dried by the drier  3  is sent to the pyrolyzer  4 . 
     The pyrolyzer  4  is a device that slightly pyrolyzes the coal dried by the drier  3 . To be more specific, the pyrolyzer  4  gasifies and extracts volatile components and various impurities such as mercury contained in the coal. A gas separated by this pyrolyzer  4  is sent to the combustion furnace  5  as a low-calorie gas (first gas). The upgraded coal that has been pyrolyzed by the pyrolyzer  4  is sent to the quencher  6 . 
     The combustion furnace  5  burns the low-calorie gas separated by the pyrolyzer  4  along with, for instance, primary air to generate a high-temperature gas. This high-temperature gas is fed to a jacket  4   a  of the pyrolyzer  4 , and is used as a heat source of the pyrolyzer  4 . The high-temperature gas used to heat the raw coal L by this pyrolyzer  4  is purged by, for instance, an exhaust clean system (AQCS) Cs, and then is discharged to the atmosphere. In  FIG. 1 , a reference sign “F” indicates an air volume adjusting fan, and a reference sign “B” indicates a blower. The air volume adjusting fan F and the blower B, which are installed on a pipe between the jacket  4   a  and the exhaust clean system Cs, deliver the spent high-temperature gas to the exhaust clean system Cs together. 
     The quencher  6  cools the upgraded coal that has been subjected to the pyrolytic treatment by the pyrolyzer  4 . A temperature of the upgraded coal which was about 400° C. is cooled to 70° C. or so by this quencher  6 . The upgraded coal cooled by the quencher  6  is sent to the finisher  7 . 
     The finisher  7  moderately adjusts the temperature of the upgraded coal that is cooled to some extent by the quencher  6  using, for instance, the atmosphere again. The finisher  7  adjusts the temperature of the upgraded coal, for instance, to be equal to or less than 50° C. The upgraded coal, the temperature of which is adjusted by the finisher  7 , is sent to the kneader  8 . 
     The kneader  8  pulverizes the upgraded coal, the temperature of which is adjusted by the finisher  7 , and forms it into a finer particle shape. When an additive such as a binder for molding the upgraded coal along with the pulverization is needed, the kneader  8  inputs the binder into the upgraded coal, and agitates the upgraded coal. The upgraded coal pulverized and agitated by the kneader  8  is sent to the briquetting device  9 . 
     The briquetting device  9  molds the upgraded coal into a predetermined briquette shape. The briquetting device  9  molds the upgraded coal into the briquette shape by, for instance, compression molding. Briquettes Br of the upgraded coal molded by this briquetting device  9  are transported to a destination by a transporting means such as a vehicle, a ship, or the like. 
     Next, a burner  10  of the aforementioned combustion furnace  5  will be described on the basis of the drawings. 
       FIG. 2  is a sectional view illustrating a schematic constitution around the burner  10  of the combustion furnace  5 . 
     As illustrated in  FIG. 2 , the combustion furnace  5  is equipped with a container  11  that forms a space K for combustion. The burner  10  is mounted in this container  11  via one pipe stand  11  a. The burner  10  burns two types of gases having different calorific values. An end  10   a  of the burner  10  which is adjacent to the space K has the same position as an inner surface  11   b  of the container  11  in a direction of an axis O of the burner  10 . Pipes  12   a  to  12   d  for feeding a low-calorie fuel, a high-calorie fuel, an ignition torch fuel, and air are connected to the burner  10 . Flow regulating valves  13   a  to  13   d  are mounted on the respective pipes  12   a  to  12   d.  In an example of this embodiment, the low-calorie gas that is generated by the pyrolyzer  4  and acts as the low-calorie fuel is fed to the burner  10 . Further, in an example of this embodiment, a high-calorie gas (second gas) such as natural gas that has a higher calorific value than the low-calorie gas and acts as the high-calorie fuel is fed to the burner  10 . The air fed to the burner  10  is used as primary and secondary air to be described below. 
       FIG. 3  is a front view of the burner  10  when viewed in a direction III of  FIG. 2 .  FIG. 4  is a sectional view taken along line VI-VI of  FIG. 3 . 
     As illustrated in  FIGS. 3 and 4 , the burner  10  is equipped with a first outer cylinder  20 , a diffuser  21 , first gas nozzles  22 , second gas nozzles  23 , ignition torches  24 , and a second outer cylinder  25 . 
     The first outer cylinder  20  forms a flow channel that feeds the primary air toward the internal space K. The first outer cylinder  20  is formed in a tubular shape, and more particularly in a cylindrical shape. The first outer cylinder  20  has an opening  27  at a side of the internal space K (hereinafter referred to simply as “first direction”) in a direction of an axis O thereof. 
     The diffuser  21  has an inner circumferential surface  28  that is disposed inside the first outer cylinder  20  and is gradually increased in diameter in the first direction. A conical space is radially formed inside this diffuser  21 . When viewed from the side of the internal space K, the diffuser  21  is formed in a circular shape having the same center as the first outer cylinder  20 . A position of an outermost circumferential portion  29  that is a first-direction end of the diffuser  21  is disposed at the same position as a first-direction end  30  of the first outer cylinder  20  in the direction of the axis O. Here, an angle θ 0  between the inner circumferential surface  28  of the diffuser  21  and the axis O is preferably set to 50 to 70 degrees. 
     The first gas nozzles  22  are disposed radially inside the first outer cylinder  20 . The first gas nozzles  22  feed the low-calorie gas to a radial outer region of the diffuser  21  in the first direction. The burner  10  in this embodiment is provided with a plurality of first gas nozzles  22 , and more particularly two first gas nozzles  22 . Openings  31  of the first gas nozzles  22  are disposed across the axis O at symmetrical positions. 
     Opening ends  32  of the first gas nozzles  22  in the first direction have contact portions  33  coming into contact with the diffuser  21 . The contact portions  33  are formed along the outermost circumferential portion  29  in a sectional circular arc shape. Each contact portion  33  is in contact with the outermost circumferential portion  29  of the diffuser  21  over an entire circumferential region thereof. Thereby, the primary air flowing inside the first outer cylinder  20  is configured not to flow between the contact portions  33  of the first gas nozzles  22  and the outermost circumferential portion  29  of the diffuser  21  in the first direction. If circumferential angle ranges within which the two contact portions  33  come into contact with the outermost circumferential portion  29  of the diffuser  21  are set to θ 1  and θ 2 , the sum of these angle ranges θ 1  and θ 2  ranges from 90 degrees to 200 degrees. 
     The opening end  32  of each of the first gas nozzles  22  is provided with two sidewall portions  34  that extend in parallel from circumferential opposite sides of the contact portion  33  toward the first outer cylinder  20 . The opening end  32  is provided with an outer wall portion  34   a  that connects ends of the parallel sidewall portions  34  which are adjacent to the first outer cylinder  20 . The outer wall portion  34   a  is formed in a sectional circular arc shape in which it protrudes toward the first outer cylinder  20  to extend along the inner surface of the first outer cylinder  20 . 
     The second gas nozzles  23  feed the high-calorie gas to the radial outer region of the diffuser  21  in the first direction. The burner  10  in this embodiment is provided with a plurality of second gas nozzles  23 , and more particularly two second gas nozzles  23 . The second gas nozzles  23  are disposed adjacent to the first gas nozzles  22  in the circumferential direction of the first outer cylinder  20 . Further, the two second gas nozzles  23  are disposed across the axis O at symmetrical positions. 
     Opening ends  35  of the second gas nozzles  23  in the first direction are disposed upstream from the outermost circumferential portion  29  of the diffuser  21  in the first direction. That is, when viewed from the side of the internal space K, the opening ends  35  of the second gas nozzle  23  are disposed behind the diffuser  21 . A distance d between the outermost circumferential portion  29  of the diffuser  21  and the opening end  35  of each of the second gas nozzles  23  in the direction of the axis O may be set to 0 to 30 mm. Also, the distance d is more preferably set to 0 mm. 
     The opening end  35  of each of the second gas nozzles  23  is provided with a flame holding pad  36 . When the high-calorie gas fed from each of the second gas nozzles  23  is ignited, the flame holding pad  36  functions to hold flames of the high-calorie gas. To be specific, each of the flame holding pads  36  has a plane  37  that extends in a direction perpendicular to the first direction to block the opening end  35  in the first direction. The flame holding pad  36  has a plurality of through-holes  38 , each of which has a smaller cross section than the flow channel of the second gas nozzle  23  at the opening end  35 . These through-holes  38  communicate between the internal space of the second gas nozzle  23  and the radial outer region of the outermost circumferential portion  29  of the diffuser  21 . When the high-calorie gas flowing through the second gas nozzle  23  goes through the through-holes  38  to run out of the second gas nozzle  23 , a small vortex (not illustrated) is formed around the through-holes  38 . Accidental misfire of the flames of the high-calorie gas is reduced by this small vortex. 
     Here, the flame holding pads  36  in this embodiment can efficiently hold the flames when widths w directed from the second gas nozzles  23  toward the diffuser  21  are set to 5 to 20 mm in order to hold the flames of the second gas nozzles  23 . Further, each of the widths w is more preferably set to 10 mm. That is, the primary air sometimes flows between the flame holding pads  36  and the diffuser  21 . 
     The ignition torches  24  form a source that ignites at least one of the aforementioned high- and low-calorie gases. The aforementioned ignition torch fuel is fed to the ignition torches  24 . The ignition torches  24  are disposed between the first gas nozzles  22  and the second gas nozzles  23  inside the first outer cylinder  20 . In this embodiment, an example in which the two ignition torches  24  are provided is given, but one ignition torch  24  may be provided. 
     The second outer cylinder  25  forms a flow channel through which secondary air flows between the first outer cylinder  20  and the second outer cylinder  25 . The second outer cylinder  25  is disposed to cover the outside of the first outer cylinder  20  at a predetermined interval. The second outer cylinder  25  overlaps the first outer cylinder  20  at the axis O, and is formed in a cylindrical shape having a larger diameter than the first outer cylinder  20 . That is, the flow channel through which the secondary air flows is formed such that a radial dimension thereof is the same throughout the circumference of the first outer cylinder  20 . 
     A plurality of swirlers  39  are disposed between the first outer cylinder  20  and the second outer cylinder  25 . These swirlers  39  are disposed at predetermined regular intervals in a circumferential direction. The swirlers  39  function as deflection plates that swirl the secondary air around the axis O. That is, a flow of the secondary air that flows from the flow channel between the first outer cylinder  20  and the second outer cylinder  25  to the internal space K becomes a swirl flow having a cylindrical shape and a spiral shape. Due to this swirl flow of the secondary air, a region adjacent to the opening  27  at a radial inner side thereof becomes a negative pressure. Thus, due to this negative pressure, as the secondary air is separated from the opening  27  in the direction of the axis O, its diameter is gradually reduced. Thereby, since the primary air, the low-calorie gas, and the high-calorie gas that flow out to the inside of the secondary air are collected toward the axis O, the accidental misfire of the flames can be further reduced. Here, a blade angle for swirling the secondary air is set to 0 to 45 degrees, and thereby the swirlers  39  in this embodiment can effectively reduce the accidental misfire of the flames. Further, the blade angle is more preferably set to 30 degrees. 
       FIG. 5  is a perspective view illustrating a state in which a temperature drop reducing part  40  is mounted on the first gas nozzle  22 . 
     As illustrated in  FIG. 5 , the burner  10  is equipped with the temperature drop reducing part  40  that reduces a drop in temperature of the first gas nozzle  22 . This temperature drop reducing part  40  covers at least a part of an outer circumferential surface  41  of the first gas nozzle  22 . The temperature drop reducing part  40  is provided with at least one of a heater that can heat the first gas nozzle  22  and an insulator that can insulate the first gas nozzle  22 . Thereby, it is possible to reduce a drop to a temperature that is equal to or lower than a condensation temperature of tar, etc. contained in the high-temperature low-calorie gas sent from the pyrolyzer  4 , and the resultant condensation. 
     The burner  10  in this embodiment has the aforementioned constitution. 
       FIG. 6  is a map illustrating primary air ratios at which stable combustion, i.e., stabilized ignition and stabilized flame retention, is possible with respect to an input heat rate (%) of the second gas nozzle  23 . Here, the primary air ratio is defined as a theoretical air quantity ratio between a total flow rate of the primary air and a total flow rate of the high-calorie gas. Also, the input heat rate of the second gas nozzle  23  is a value indicating how much of the high-calorie gas is contained in a total flow rate of the low- and high-calorie gases, and is defined as “the input heat of the high-calorie gas/(the input heat of the low-calorie gas+the input heat of the high-calorie gas)×100 (%).” 
     The burner  10  is adjusted according to the input heat rate of the second gas nozzle  23  to have the primary air ratio greater than a lower limit indicated by a solid line of  FIG. 6 . In  FIG. 6 , “o” indicates the primary air ratio at which the stable combustion (including the stable ignition and the stable flame retention) was verified by a test, over the input heat rate of the second gas nozzle  23 . Also, in  FIG. 6 , “x” indicates the primary air ratio at which unstable combustion was verified by a test, over the input heat rate of the second gas nozzle  23 . 
     As illustrated in  FIG. 6 , as the input heat rate of the second gas nozzle  23  decreases, a rising rate of the lower limit the primary air ratio drastically increases, and it is difficult to carry out flow rate adjustment as well as stable combustion of the primary air. For this reason, the flow rate of the high-calorie gas is preferably adjusted such that the input heat rate is greater than 10%. However, from the viewpoint of energy saving, the flow rate of the high-calorie gas is adjusted to be as small as possible. 
       FIG. 7  is a map illustrating primary air mixed oxygen concentrations (vol %) at which stable combustion, i.e., stabilized ignition and stabilized flame retention, is possible with respect to a primary air ratio. Here, the primary air mixed oxygen concentration is a value indicating how much oxygen in primary air is contained in a total flow rate of the primary air and an inert gas (e.g., nitrogen), and is defined as “the flow rate of the oxygen deposited in the primary air/(the flow rate of the primary air+the flow rate of the inert gas)×100 (%).” 
     When the inert gas is used to purge the pyrolyzer  4 , the inert gas flows out of the first gas nozzles  22 . In this case, the burner  10  is set to have a primary air mixed oxygen concentration that is greater than a lower limit indicated by a solid line of  FIG. 7  according to a primary air ratio, and thereby stable combustion, i.e., stabilized ignition and stabilized flame retention, is possible. In  FIG. 7 , “o” indicates the primary air mixed oxygen concentration at which the stable combustion (including the stable ignition and the stable flame retention) was verified by a test, over the primary air ratio. Also, in  FIG. 4 , “x” indicates the primary air mixed oxygen concentration at which unstable combustion was verified by a test, over the primary air ratio. 
     As illustrated in  FIG. 7 , the lower limit of the primary air mixed oxygen concentration is lowest when the primary air ratio is about “2.” Thus, as the primary air ratio increases from a value at which the primary air mixed oxygen concentration is lowest, the lower limit of the primary air mixed oxygen concentration smoothly increases. On the other hand, as the primary air ratio decreases from the value at which the primary air mixed oxygen concentration is lowest, the lower limit of the primary air mixed oxygen concentration drastically increases. For this reason, the flow rate of the primary air is preferably adjusted such that the primary air ratio is greater than “1.” 
     The adjustment of the primary air ratio and the adjustment of the primary air mixed oxygen concentration may be designed to be automatically performed by executing a pre-stored program on a computer. 
     When the primary air ratio and the primary air mixed oxygen concentration are automatically adjusted, for example, actuators (not illustrated) that individually drive the flow regulating valves  13   a  to  13   c  and flow meters (not illustrated) that measure the flow rate of the high-calorie gas, the flow rate of the low-calorie gas, and the flow rate of the primary air are provided. The computer calculates the input heat rate of the second gas nozzle  23  on the basis of a measured result of each of the flow meters, and finds the primary air ratio and the primary air mixed oxygen concentration at which the stable combustion is obtained with reference to the map. Further, the computer controls the flow rate of the primary air to have the found primary air ratio. Here, the adjustment of the primary air ratio is not limited to automatically controlling it. Instead of the control process based on the computer, for example, the measured results of the flow meters and the maps illustrated in  FIGS. 6 and 7  may be displayed by a display, and thereby a worker may appropriately perform the control of the flow rates. 
     Therefore, according to the burner  10  of the above embodiment, as illustrated in  FIG. 4 , the primary air flowing outside the diffuser  21  in the first direction is suctioned to form a swirl at an inner circumferential surface side of the diffuser  21 . Further, the high-calorie gas fed from the second gas nozzles  23  is suctioned to this swirl, and thereby a small ball of fire can be produced in the diffuser  21 . For this reason, it is possible to ensure mixing the primary air and the high-calorie gas to reduce an influence of the inert gas fed from the first gas nozzles  22 . Also, when the low-calorie gas is fed from the first gas nozzles  22 , it is possible to suction the low-calorie gas to the diffuser  21  and reliably bum the low-calorie gas. 
     As a result, when the nozzle for the high-calorie gas is disposed in the vicinity of the nozzle for the low-calorie gas, the accidental misfire of the flames of the high-calorie gas by the inert gas ejected from the nozzle for the low-calorie gas can be reduced. 
     Also, as the opening ends  32  of the first gas nozzle  22  have the contact portions  33 , the low-calorie gas fed from the first gas nozzles  22  can be smoothly suctioned to the diffuser  21  via the contact portions  33 . 
     Further, as the sum of the circumferential angle ranges within which the contact portions  33  come into contact with the diffuser  21  is set to 90 to 200 degrees, a range within which the low-calorie gas is drawn into the diffuser  21  can be set to an optimal range for the combustion of the low-calorie gas. 
     On the other hand, when the sum of the circumferential angle ranges within which the contact portions  33  come into contact with the diffuser  21  falls below 90 degrees, there is a possibility of the low-calorie gas being unable to be properly fed into the diffuser  21  and to be subjected to the stable combustion. Also, when the sum of the circumferential angle ranges within which the contact portions  33  come into contact with the diffuser  21  falls above 200 degrees, there is a possibility of the range within which the low-calorie gas is drawn into the diffuser  21  being excessively widened, and the high-calorie gas and the primary air being inhibited from being suctioned to the diffuser  21 . 
     Further, when the opening ends  35  of the second gas nozzles  23  in the first direction are disposed upstream from the outermost circumferential portion  29  of the diffuser  21  in the direction of the axis O, even if the inert gas is ejected from the first gas nozzles  22 , the inert gas does not flow toward the opening ends  35  of the second gas nozzles  23  disposed upstream from the opening ends  32  of the first gas nozzles  22 . For this reason, the accidental misfire of the flames of the second gas nozzles  23  can be reduced by the inert gas. 
     Also, as the flame holding pads  36  are provided, the vortex caused by the high-calorie gas can be formed around the opening ends  35  of the second gas nozzles  23 . For this reason, by igniting the vortex, the flames generated at the second gas nozzles  23  are held, and the accidental misfire of the flames inside the diffuser  21  can be further reduced. 
     Further, as the second outer cylinder  25  is provided, a downstream space of the first outer cylinder  20  can be surrounded from the outside by the secondary air. For this reason, the primary air, the low-calorie gas, and the high-calorie gas can be more reliably introduced into the diffuser in a greater quantity. 
     Also, as the swirlers  39  are provided, the space inside the secondary air has the negative pressure due to the swirl of the secondary air, and thus the primary air, the low-calorie gas, and the high-calorie gas can be efficiently introduced into the diffuser  21 . 
     Also, according to the coal upgrading plant  1  in the above embodiment, since the accidental misfire of the flames of the burner  10  can be reduced, the pyrolytic treatment can be stably performed in a coal upgrading process. 
     The present invention is not limited to the aforementioned embodiment, and includes various upgrades of the aforementioned embodiment without departing from the spirit and scope of the present invention. That is, the specific shapes and constitutions represented in the embodiment are merely examples and can be appropriately upgraded. 
     For example, in the aforementioned embodiment, the example in which the two first gas nozzles  22 , the two second gas nozzles  23 , and the two ignition torches  24  are provided has been described. However, the number of first gas nozzles  22 , the number of second gas nozzles  23 , and the number of ignition torches  24  may be one or more. 
     Further, the example in which the internal space of the diffuser  21  of the aforementioned embodiment is formed in the conical shape has been described. However, a mounting through-hole passing through the diffuser in the direction of the axis O and a slit extending in a radial direction when viewed from the side of the space K in order to prevent cracks caused by thermal deformation may be provided in the diffuser  21 . 
     Also, in the aforementioned embodiment, the burner  10  provided for the combustion furnace  5  of the coal upgrading plant  1  has been described by way of example, but it may be applied to combustion furnaces other than the coal upgrading plant  1 . 
     INDUSTRIAL APPLICABILITY 
     The present invention relates to the burner in which the nozzle for the high-calorie gas is disposed in the vicinity of the nozzle for the low-calorie gas, and the coal upgrading plant equipped with this burner. According to the burner and the coal upgrading plant of the present invention, the accidental misfire of the flames of the high-calorie gas by the inert gas ejected from the nozzle for the low-calorie gas can be reduced. 
     REFERENCE SIGNS LIST 
       1  Coal upgrading plant 
       2  Crusher 
       3  Drier 
       4  Pyrolyzer 
       4   a  Jacket 
       5  Combustion furnace 
       6  Quencher 
       7  Finisher 
       8  Kneader 
       9  Briquetting device 
       10  Burner 
       10   a  End 
       11  Container 
       11   a  Pipe stand 
       11   b  Inner surface 
       12   a  to  12   d  Pipe 
       13   a  to  13   d  Flow regulating valve 
       20  First outer cylinder 
       21  Diffuser 
       22  First gas nozzle 
       23  Second gas nozzle 
       24  Ignition torch 
       25  Second outer cylinder 
       26  Flow channel 
       27  Opening 
       28  Inner circumferential surface 
       29  Outermost circumferential portion 
       30  End 
       31  Opening 
       32  Opening end 
       33  Contact portion 
       34  Wall portion 
       34   a  Outer sidewall portion 
       35  Opening end 
       36  Flame holding pad 
       37  Plane 
       38  Through-hole 
       39  Swirler 
       40  Temperature drop reducing part 
       41  Outer circumferential surface 
     B Blower 
     Br Briquette 
     Cs exhaust clean system 
     F Air volume adjusting fan 
     K Space 
     L Raw coal