Radiant gas burner

Abstract: A radiant gas burner which includes a refractory burner tile (12) having an elongate passageway (28) extending therethrough and a fuel-air mixture burner tube (34) disposed within the passageway. The burner tube is of a one-piece elongate construction, includes a nozzle portion (40,42) at the interior end of the passageway and is connected to a manifold block (38) by a threaded connection positioned adjacent the exterior end of the passageway. Secondary fuel is discharged from the passageway at a location (86,88) adjacent the nozzle portion of the burner tube.

Description: The present invention relates to radiant gas burners burning fuel gas and air with low NO x production. Radiant burners of the type which include central fuel gas-air mixture burner tubes surrounded by annular refractory tiles are well known and have been utilized in conjunction with reformers, cracking furnaces and the like for many years, as WO 90/04740. The refractory tiles have generally been adapted for insertion into openings in furnace walls, and the burner tubes which extend through central passageways in the burner tiles discharge fuel gas-air mixtures in directions generally parallel and adjacent to the internal faces of the burner tiles. The combustion of the fuel gas-air mixtures causes the faces of the burner tiles to radiate heat, e.g., to process tubes, and undesirable flame impingement on the process tubes is thereby avoided. Heretofore, the nozzle portions of the burner tubes of radiant burners which extend short distances past the burner tiles have been threadedly connected to the forward portions of the tubes. However, the threaded nozzle connections have been located close to the interior faces of the burner tiles which are exposed to high temperatures, i.e., temperatures in the range of from about 815°C to about 1370°C. While such threaded nozzle connections were intended to allow the nozzle portions of the burner tubes to be periodically removed and replaced, because of the high temperatures the metal forming the threads has often fused and prevented the ready removal of the nozzle portions. Consequently, the more recent radiant burners have included burner tubes with the nozzle portions welded thereto. In order to change the nozzle portions of such burner tubes when they deteriorate, it is necessary to dismantle the burner apparatus, cut off the deteriorated nozzle portions and re-weld new nozzle portions thereon. Thus, there is a need for improved radiant gas burners which include readily replaceable burner tubes. More stringent environmental emission standards are continuously being imposed by governmental authorities which limit the quantities of gaseous pollutants such as oxides of nitrogen (NO x ) and carbon monoxide which can be emitted into the atmosphere. Such standards have led to the development of various improved gas burner designs which lower the production of NO x and other polluting gases. While radiant gas burners have also been improved whereby combustion gases containing lower levels of pollutants are produced, additional improvement is necessary. Thus, there is also a need for an improved method of burning fuel gas and air using a radiant gas burner whereby combustion gases having lower pollutant levels are produced. According to the present invention we provide a radiant gas burner comprising a refractory burner tile adapted to be inserted in a wall of a furnace and including an elongate passageway extending therethrough, said passage having exterior and interior ends, a burner tube disposed within the passageway and having a nozzle positioned at the interior end of the passageway directing a fuel gas-air mixture adjacent to the refractory burner tile within the furnace space and means for introducing a fuel gas-air mixture into the burner tube, characterised in that said burner tube is of a one piece elongate construction and is connected to said means for introducing a fuel gas-air mixture thereinto by a threaded connection positioned adjacent to the exterior of said passageway, whereby said threaded connection remains relatively cool during the operation of said burner and said burner tube thereby remains selectively threadedly removable, in that said means for introducing fuel gas-air mixture into said burner tube include a manifold block having a fuel gas-air mixture passage formed therein threadedly connected to said burner tube at one end and to a device for controlling the ratio of fuel to air at an opposite end and in that means are provided for sealingly connecting said manifold block to the exterior end of the burner tile passageway, thereby to prevent the unregulated flow of air into said passageway, said sealing means being attached to said burner tile and to said manifold block. Because the burner tube is elongated and the threaded connection between it and the manifold block is positioned adjacent the exterior end of the burner tile passageway, the threaded connection remains relatively cool during the operation of the burner whereby the entire burner tube can be readily removed and replaced as required. At least one elongated secondary fuel gas discharge pipe may also be disposed in the burner tile passageway and connected to the manifold block. The discharge end of the secondary fuel gas discharge pipe may be positioned adjacent the outlet end of the burner tube for injecting secondary fuel gas into the furnace space resulting in a reduced NO x level in the combustion gases produced by the combustion of the total fuel gas input to the burner. In order that the present invention may more readily be understood, the following description is given, merely by way of example, reference being made to the accompanying drawings in which:- Figure 1 is a front view of one embodiment of radiant gas burner of the present invention; Figure 2 is a side view of the radiant gas burner of Figure 2 installed in a furnace wall; Figure 3 is a view of the radiant gas burner of Figure 2 from inside the furnace wall; Figure 4 is a partially sectional side view of the radiant burner of Figures 1, 2 and 3; Figure 5 is an enlarged sectional view of a portion of the burner illustrated in Figure 4; Figure 6 is a sectional view taken along line 6-6 of Figure 5; and Figure 7 is a sectional view taken along line 7-7 of Figure 5. The illustrated burner 10 comprises a burner tile 12 adapted to be inserted in an opening 14 of a furnace wall 16, forming one surface of an interior furnace space. As shown in Figures 2 and 4, the wall 16 comprises an external metal sheet 18 with a relatively thick liner of refractory material 20 attached thereto. The opening 14 in the furnace wall 16 can be of any suitable shape and its outer portion 22 can be enlarged to form an interior shoulder 24. The burner tile 12 is of a complementary peripheral shape to the opening 14 in the furnace wall 16 and includes a shoulder 26 co-acting with the shoulder 24 of the furnace wall 16. The burner tile 12 generally includes a central elongated passageway 28 extending therethrough, and the interior face 30 of the burner tile 12 includes a plurality of substantially radially extending ribs 32 formed thereon for directing fuel and air and the combustion gases produced therefrom radially outwardly from the passageway 28. Disposed within the passageway 28 of the burner tile 12 is a one-piece elongated burner tube 34, having an inlet end 36 (see Figure 5) threadedly connected to a manifold block 38, and an outlet nozzle end closed by a conical shaped end wall 40, and a plurality of circumferentially spaced longitudinal slots 42 are formed in the burner tube 34 adjacent the wall 40. Adjacent to the exterior face of the burner tile 12 is a mounting plate 44 having a central opening therein complementary in size to the passageway 28. A sleeve 46 having an interior size and shape corresponding to the size and shape of the passageway 28 and having a flange 48 positioned adjacent the plate 44 is attached to the plate 44 by a plurality of bolts 50. The manifold block 38 is of an external size and shape which are complementary to the internal size and shape of the sleeve 46, and the interior end portion of the manifold block 38 is positioned within the sleeve 46. The manifold block 38 includes a central passage 51 formed therein which extends between the exterior and interior ends 52 and 54 thereof (see Figures 5-7). As best shown in Figure 5, the end 36 of the burner tube 34 is threadedly connected within the passage 1 at the end 54 of the manifold block 38, and an inlet bell fitting 56 is threadedly connected to the passage 51 at the other end 52 of the manifold block 38. Referring to Figures 1, 2 and 4, the bell fitting 56 is connected to one end of an air conduit 58 by a plurality of bolts 60. In the form illustrated in the drawings, the conduit 58 includes a 90° bend therein and the other end thereof is attached to a muffler 62 of known design by a plurality of bolts 64. An air flow regulator valve 66 is connected to and disposed within the conduit 58 for manually regulating the rate of air flow conducted to the venturi comprising the fitting 56, manifold block 38 and burner tube 34. A primary fuel gas jet forming nozzle 68 is disposed within the conduit 58 or fitting 56 and is positioned to discharge a jet of primary fuel into the bell fitting 56. The nozzle 68 is connected to a fuel gas conduit 70 which sealingly passes through a wall of the conduit 58 and is connected via a tee 72 to a conduit 74, the other end of which is connected to a source of pressurized fuel gas (not shown). Tubing 78 is attached respectively by tubing fittings 76 and 82 to tee 72 and a secondary fuel gas orifice fitting 84, which is in turn connected to the manifold block 38. As can be seen in Figures 5-7, a primary fuel gas-air mixture is produced as the fuel gas jet formed by the nozzle 68 and air aspirated thereby flow through the venturi formed by the bell fitting 56, the passage 51 in the manifold block 38 and the burner tube 34, and the mixture is discharged from the burner tube 34 by way of the longitudinal slots 42 thereof. Disposed in the passageway 28 of the refractory burner tile 12, in addition to the burner tube 34, are a pair of secondary fuel gas discharge pipes 86 and 88, which are generally positioned on opposite sides of the burner tube 34, and are threadedly connected to a pair of longitudinal passages 90 and 92 formed in the end 54 of the manifold block 38. The open ends of the pipes 86 and 88 terminate at positions upstream of and closely adjacent to the slots 42 in the burner tube 34 whereby secondary fuel gas discharged from the pipes 86 and 88 flows into the interior of the furnace (see Figure 3). The passages 90 and 92 within which the discharge pipes 86 and 88 are connected are in turn connected via a passage 94 formed internally within the manifold block 38 and a longitudinal passage 96 to a lateral passage 98 within which the orifice fitting 84 is threadedly connected. Referring now to Figures 2, 6 and 7, a longitudinal air passage 100 is formed longitudinally in the manifold block 38 and an air flow closure and regulating assembly 102 is attached to the exterior end 52 of the manifold block 38 over the air passage 100. In a preferred embodiment, both the exterior portion of the manifold block 38 within the sleeve 46 and the interior of the sleeve 46 are cylindrical. In order to ensure that an unregulated flow of air does not leak into the passageway 28, the interior of the sleeve 46 includes a pair of grooves 104 formed therein, and a pair of O-rings 106 are disposed in the grooves 104 whereby a seal between the exterior of the manifold block 38 and the interior of the sleeve 46 is assured. A threaded bolt 108 is disposed in a threaded bore in the sleeve 46 for locking the manifold block 38 within the sleeve 46. In operation pressurized fuel gas from a source thereof is conducted by the conduit 74 to the tee 72. A portion of the fuel gas flows from the tee 72 into the primary fuel gas conduit 70 with the remaining portion flowing by way of the tubing 78 into the passage 98 of the manifold block 38. The orifice fitting 84 and the nozzle 68 are sized such that the pressurized fuel gas is divided between the primary fuel gas conduit 70 and the secondary fuel gas tubing 78 in a desired ratio. The secondary fuel gas flowing through the tubing 78, the fitting 82, the orifice fitting 84 and into the internal passage 98 of the manifold block 38 flows by way of the internal passages 96 and 94 to the passages 90 and 92. From the passages 90 and 92, substantially equal portions of the secondary fuel gas flow through the discharge pipes 86 and 88 to within the furnace by way of the open ends thereof. The primary fuel gas flowing through the conduit 70 is discharged in a high velocity jet by the nozzle 68 into the venturi formed by the bell fitting 56, the passage 51 in the manifold block 38 and the burner tube 34. The flow of the jet of primary fuel gas into the venturi causes air to be drawn from the atmosphere through the muffler 62 and through the conduit 58 into the bell fitting 56. The air mixes with the primary fuel gas as it and the primary fuel gas flow by way of the passage 51 in the manifold block 38 into and through the burner tube 34. The primary fuel gas-air mixture is discharged from the burner tube 34 through the longitudinal slots 42 thereof in directions generally parallel to the interior face 30 of the burner tile 12. The primary fuel gas-air mixture is ignited and combusted adjacent the face 30 of the burner tile 12 whereby the burner tile 12 is heated and radiates heat into the furnace to which the burner 10 is attached. The burner 10 can be utilized in forced draft applications where the primary pressurized fuel gas and pressurized air are mixed in a manner whereby the fuel jet and venturi apparatus described above are not required. In such applications a premixed primary fuel gas-air mixture can be introduced directly into the bell fitting 56 or into the passage 51 of the manifold block 38. A rate of air which is stoichiometric or greater than stoichiometric relative to the total rate of fuel gas (both primary and secondary fuel gas) is introduced into the furnace space by means of the burner 10. Preferably the rate of air is in the range of from about 7% to about 15% greater than the stoichiometric rate. The primary fuel-air mixture discharged by way of the longitudinal slots 42 of the burner tube 34 contains excess air which, when the fuel gas-air mixture is combusted, functions to lower the temperature of the combustion reaction and the production of NO x . The secondary fuel gas discharged into the furnace space by way of the open ends of the pipes 86 and 88 mixes with flue gases and air within the furnace space and also burns at a relatively low temperature which results in the total combustion gases produced by the burner 10 having a relatively low NO x level. The phrases "burns" or "is burned at a relatively low temperature" are used herein to mean that the combustion reaction temperature is lower than that which would occur if undiluted or stoichiometric mixtures of fuel gas and air were burned instead of the mixtures containing fuel gas described herein. Preferably about 60% to 90% of the fuel gas is primary fuel gas which is discharged by way of the burner tube 34 and the remaining 40% to 10% is discharged into the furnace by way of the pipes 86 and 88. The most preferred flow rate is about 80% primary and 20% secondary fuel gas flow. In the normal operation of the burner 10, the air passage 100 in the manifold block 38 is closed by assembly 102 whereby no air flows into the furnace space by way of the passage 28 in the burner tile 12 and all of the air is discharged into the furnace to which the burner 10 is attached by way of the burner tube 34. However, in applications where the furnace draft or fuel gas pressure are low or other similar condition is encountered, and as a result a stoichiometric rate of air or greater relative to total fuel gas rate can not be drawn into the furnace by the venturi and the primary fuel jet produced by the nozzle 68, regulated supplemental air can be allowed to enter the furnace by way of the passage 100. The burner tube 34 is most conveniently and economically cast from a metal alloy that has a high resistance to damage in furnace environments. However, when it is necessary to remove and replace the burner tube 34 as a result of corrosion or high temperature deterioration, the burner tube 34 can conveniently be threadedly removed and replaced, because the threaded connection between the exterior end 36 of the burner tube 34 and the manifold block 38 is positioned at the exterior end of the passageway 38 and remains relatively cool. As a result, the threaded connection does not fuse and become inoperable as is the case when it is positioned near the interior end of the passageway 28. Also, the arrangement whereby a portion of the manifold block 38 is disposed within the sleeve 46 and is selectively movable therein allows the position of the manifold block 38 to be adjusted whereby the interior discharge end of the burner tube 34 is positioned at a desired location with respect to the face 30 of the burner tile 12 while the pipes 86 and 88 are maintained in their desired position relative to the burner tube 34. In order to further illustrate the radiant gas burner and method of the present invention, the following example is given. EXAMPLE A burner apparatus 10 designed for a heat release of 293 kilowatts by burning natural gas having a caloric value of 45474 joules/m³ is fired into a furnace space. Pressurized fuel gas is supplied to the burner 10 at a pressure of about 2.04 bar and at a rate of 2832 litres/hour. An 80% portion of the total fuel gas (2266 litres/hour) flows into and through the assembly of the bell fitting 56, the manifold block 38 and burner tube 34 wherein it is mixed with air. The remaining portion of the fuel gas i.e., 566 litres/hour, is discharged into the furnace space by way of the pipes 86 and 88. The rate of air introduced into the assembly of the bell fitting 56, manifold block 38 and burner tube 34 is controlled by means of the valve 66 such that the total rate of air is 10% greater than the stoichiometric rate required for the total fuel. Because of the excess air in the primary fuel gas-air mixture and the flue gases mixed with the secondary fuel gas and air, such mixtures burn at relatively low temperatures whereby the flue gases formed have a low NO x content. That is, the mixture of flue gases withdrawn from the furnace space 21 has a NO x content of less than about 25 ppm. If desired, one or more orifices can be included within the passages of the manifold block 38 or other means can be utilized to proportion the fuel gas between the burner tube 34 and the pipes 86 and 88. Also, the burner tube 34 and the pipes 86 and 88 can be connected to separate flow rate regulated sources of fuel gas.

Claims: A radiant gas burner comprising a refractory burner tile (12) adapted to be inserted in a wall of a furnace and including an elongate passageway (28) extending therethrough, said passage having exterior and interior ends, a burner tube (34) disposed within the passageway (28) and having a nozzle (40,42) positioned at the interior end of the passageway directing a fuel gas-air mixture adjacent to the refractory burner tile (12) within the furnace space and means (38 to 62) for introducing a fuel gas-air mixture into the burner tube, characterised in that said burner tube (34) is of a one piece elongate construction and is connected to said means for introducing a fuel gas-air mixture thereinto by a threaded connection positioned adjacent to the exterior of said passageway, whereby said threaded connection remains relatively cool during the operation of said burner and said burner tube thereby remains selectively threadedly removable, in that said means for introducing fuel gas-air mixture into said burner tube include a manifold block (38) having a fuel gas-air mixture passage (51) formed therein threadedly connected to said burner tube (34) at one end and to a device (52 to 66) for controlling the ratio of fuel to air at an opposite end and in that means (46 to 50, 104 to 106) are provided for sealingly connecting said manifold block to the exterior end of the burner tile passageway, thereby to prevent the unregulated flow of air into said passageway, said sealing means being attached to said burner tile and to said manifold block. A burner according to claim 1, characterised in that the manifold block (38) includes a secondary fuel gas passage (86,88), said secondary fuel gas passage being connected to means (74 to 84, 90 to 94) for introducing fuel gas therein and connected to at least one secondary fuel gas discharge pipe (86,88) disposed in said burner tile passageway (28). A burner according to claim 1 or 2, characterised in that a sleeve (48) is attached to the exterior end of the burner tile passageway (28) and at least a portion of the manifold block (38), at least a portion of the manifold block and the interior of the sleeve being of complementary sizes and shapes, said portion of said manifold block which is of a complementary size and shape to the interior of the sleeve being similarly disposed within the interior of the sleeve. A burner according to claim 3, characterised in that at least one resilient sealing member (104) is disposed between the interior of the sleeve and the portion of the manifold block disposed therewithin. A burner according to claim 2, 3 or 4, characterised in that said manifold block includes an air passage (100) therein which communicates with the interior of the burner tile passageway (28) and in that means (102) are provided for regulating the air flow into said air passage. A burner according to claim 2, 3, 4 or 5, characterised in that two secondary fuel pipes are positioned on substantially opposite sides of the burner tube. A burner according to any preceding claim, characterised in that said means for introducing a primary fuel gas-air mixture to said manifold block comprise a fuel and atmospheric air venturi mixer (56,66) connected to said manifold block (38), and having an atmospheric air inlet (62) and a fuel gas nozzle (68) adapted for connection to a source (74) of pressurized fuel gas.

Inventors: SCHWARTZ ROBERT E, TRIMBLE ROBERT R, SCHWARTZ, ROBERT E., TRIMBLE, ROBERT R.
Applicants: ZINK CO JOHN, JOHN ZINK COMPANY, A DIVISION OF KOCH ENGINEERING COMPANY INC.
Application year: 1993
Main classification: F23D14
IPC codes: F23C99, F23D14