US 3285240 A
Abstract available in
Claims available in
Description (OCR text may contain errors)
NOV. 15, T SCHM INDUSTRIAL GAS BURNER 2 Sheets-Sheet 1 Filed July 10, 1964 INVENTORJ THEODOR SCHMIDT Nov. 15, 1966 T. SCHMIDT 3,285,240
INDUSTRIAL GAS BURNER Filed July l0, 1964 2 Sheets-Sheet 2 INVENTOR. THEODOR SCHMIDT United States Patent J 24,029 3 Claims. Cl. 126-91) The present invention relates to industrial gas burners and, more particularly, to industrial burners of the type in which a generally axial jet of fuel gas is surrounded by a combustion-sustaining gas discharged from a plurality of orifices around this jet for mixture with the fuel and subsequent combustion.
Such burners are frequently employed with radiant tubes in which the combustible fuel and air/oxygen are burned, the tube separating the combustion products from the furnace atmosphere. Industrial gas burners of this type are generally used in annealing ovens or the like wherein the radiant heat of the tube impinges directly upon the article to be heated or serves to heat an auxiliary body which, in turn, radiates heat to the workpiece. It has been proposed heretofore to provide means whereby the products of combustion are withdrawn from the radiant heater via an exhaust duct. In general, however, such burners have been relatively complex and diflicult to operate.
In the commonly assigned copending application Ser. No. 123,883, filed July 13, 1961, now US. Patent No. 3,163,202, there is disclosed and claimed an industrial burner which comprises a central fuel-inlet tube whose orifice forms a fuel-injection nozzle opening into a combustion chamber. A coaxial second tube surrounds the first and defines an annular duct for the combustion-sustaining gas which is introduced into the chamber in the form of a sheath surrounding the fuel stream or jet. Still a further tube, coaxially outwardly of that provided for delivering the combustion-sustaining gas, forms a duct for the removal of the products of combustion from the combustion chamber. Thus the sensible heat of the combustion products can be' exploited to preheat the combustion-sustaining gas, for which purpose heat-exchange means extend generally radially from the exhaust-gas duct through the air-inlet duct. To prevent excessive heating of the fuel within the innermost pipe, a protective sheath or sleeve of heat-conducted material is provided around the fuel-delivery tubes and is in heat-conducting relationship with the heat-transfer means (e.g. vanes or fins).
It is an important object of the present invention to extend the principles disclosed in the above-identified copending application to industrial gas burners using radiation tubes.
It is a Well-known problem in heating systems using industrial burners in conjunction with radiation tubes that the burner flame is concentrated locally in the region of the radiation tube at which the fuel jet and air streams emerge. To avoid this problem, in part, it has been proposed to provide the radiation tube with an inner tube in which the actual ignition and combustion occur, the hot waste gases of the combustion tube then passing into the surrounding envelope which constitutes the actual radiation element. Thus the burner nozzles introduce their streams into the respective inner or combustion tube While the outer tube serves as an extension of the duct through which the exhaust gases are withdrawn from the region of the combustion.
A significant disadvantage of earlier burner assemblies of this character has been found to be caused, in large 3,285,240 Patented Nov. 15, 1966 part, by the fact that a stable flame could not be developed at the mouth of the burner under all operating conditions. It has been suggested that the streams of com bustion-sustaining gas and the fuel jet be discharged along lines parallel to the axis of the tube. The stream lines of the fuel and air thus are parallel to the generatrices and axes of the several burner tubes and the radiant heating tube. The unstable flame resulting from this system is especially inconvenient because it causes hot spots and heat concentrations at localized areas of the radiation tube and frequently burns out the latter. It is, therefore, another object of this invention to provide an improved method of operating an industrial burner and, especially, a gas burner provided with a radiation tube.
Yet a further object of this invention is to provide an industrial gas burner in which the fuel and air streams are discharged substantially in coaxial relationship, but which constitutes a significant advance over earlier burner assemblies.
It has been found that the foregoing objects, and others which will become apparent hereinafter, can be attained, in accordance with the present invention, by a method of operating an industrial gas burner having a fuel-dispensing nozzle for discharging a jet of fuel and outlet means surrounding this nozzle and provided with a plurality of angularly spaced orifices for discharging individual streams of a combustion-sustaining gas (e.g. oxygen, air, etc.) wherein the individual streams of the combustionsustaining gas are ejected along respective straight-line generatrices of a hyperboloid of revolution whose axis coincides with that of the fuel jet. The combustion-sustaining gas thus mixes with the fuel and the mixture is then ignited. It has been found that the resulting flame is highly stable and uniform all around the axis and that this stability is a consequence of the discharge of the combustion-sustaining gas around the central fuel jet along the straight-line generatrices of the hyperboloidal surface. The advantageous results of the present invention are not obtained when the individual streams are directed toward the axis in a conical flow or when the orifices discharge the streams tangentially with respect to an imaginary cylindrical or conical surface in conventional cyclonic or vortex burners. The discovery upon which the present invention is based is particularly significant when the burner constitutes part of an assembly including a radiation tube into which the orifices for the combustion-sustaining gas and the nozzle discharge. The radiation tube can be composed of two coaxial members including an inner cylindrical envelope or sleeve surrounding the hyperboloidal surface. This tube can have an open extremity remote from the burner mouth from which the exhaust gases emerge and pass into the outer tube which defines an exhaust duct between itself and the inner tube. The inner tube can also be perforated along that portion of its length which is remote from the burner mouth to permit the combustion gases to pass into the exhaust duct.
According to a more specific feature of the present invention, each of the orifices from which emerge the streams of the combustion-sustaining gas along the straight-line generatrices is provided in a surface extending perpendicular to the respective generatrix with the orifice bored perpendicularly therethrough. A plurality of these surfaces are thus disposed about the axis of the burner with angular spacing between the surfaces. These individual surfaces may be separated from one another by nonapertured surfaces, all of the surfaces together defining a frustoconically outwardly concave burner mouth whose central passage forms a nozzle for the fuel. Since each of the orifice surfaces is generally planar and inclined to an axial plane of the burner through the junction between each orifice surface and an adjacent imperforate surface, it is an important feature of this invention that the alternating arrangement of the surfaces be constituted as an annular corrugation with angular junctions between the individual surfaces. Thus the discharge means will be formed alternatingly with generally radial ridges and troughs with an orifice surface and an imperforate surface defining each of the ridges. The ridges are geometrically congruent although, according to this invention, the orifice surface and the imperforate surface of each ridge are inclined at different angles to the respective axial plane through the junction or ridge. The surfaces can thus be sectoral in axial projection with different axial areas. The orifices are thus formed in correspondinglyoriented surfaces of each ridge and preferably are disposed along one or more circles centered upon the axis of the burner. v
The advantages of such a structure derive from the geometrical orientation of the combustion-sustaining gas stream which produce stable flames over a considerable axial length as compared with earlier burner flames. The hyperboloidal configuration of the sheath of combustion-sustaining gas markedly increases the effective length of the stable flame surrounded by this sheath. Moreover, the fact that the combustion-sustaining gas flows along generatrices of the hyperboloidal surface imparts to the sheath a rotation about its axis which ensures that the heat will be distributed uniformly over the circumference of the radiation tube. There is no noticeable instability of the flame even when the throughput of fuel and combustion-containing gas is a fraction of its maximum value. Under partial load, therefore, the burner assembly operates substantially as efliciently as under maximum through-flow condition. The burner head provided with the annular array of corrugations can be produced in a simple and inexpensive manner by casting or pressing. The head can be inserted into the inner portion of the radiation tube and can receive the air-supply duct and the heat shield of the burner assembly.
The above and other objects, features and advantages of the present invention will become more readily apparent from the following description, reference being made to the accompanying drawing in which:
FIG. 1 is an axial cross-sectional view through a burner assembly according to this invention, showing the assembly mounted in a wall of an annealing furnace;
FIG. 2 is an end view of the burner head taken in the direction of arrow II of FIG. 1;
FIG. 3 is a cross-sectional view taken along the line IIIIII of FIG. 1; and
FIG. 4 is a perspective view of the mouth of the burner assembly showing the hyperboloid of revolution along whose generatrices the combustion-sustaining gas streams are oriented.
In FIG. 1 I show a burner assembly in which the industrial gas burner is similar to that described and claimed in the copending application Ser. No. 123,883, referred to above. The burner assembly shown in FIG. 1 is mounted in the wall 30 of an annealing furnace within a radiation tube 1 consisting of an outer tubular portion 31 and an inner tubular portion defining with the tube 31 a clearance constituting an annular exhaust duct 12. The
radiation tube 1 is fitted into wall 30 and has its free.
extremity 32 provided with a pin which is loosely received within a recess 33 in the opposite wall 34 of the furnace. This arrangement permits the linearly extending radiation tube to expand and contract in its axial dimension without strain.
The burner" opening into the radiation tube 1 comprises a central fuel-supply tube 3 terminating in a nozzle 35 adapted to discharge a jet of fuel axially into the inner tube'portion 10 of the radiation tube 1. Coaxially surrounding the fuel-supply pipe 3 is a combustion-sustaining-gas duct 20 which is supplied with oxygen, air and mixtures thereof with other fluids via a connecting pipe 7, a fuel-delivery tube 8 communicating with pipe 3.
The burner head 2 is mounted upon pipes 20 and 3 while a heat shield 9 is disposed between pipe 3 and the tube 20 so as to define with the latter an annular compartment 36 through which the combustion-sustaining gas passes to the openings or orifices 6 in the burner head. The outer tube portion 31 of the radiation tube 1 can extend through wall 30 and be integral withthe outer tube 37 of the burner assembly which defines the exhaust duct 38 with tube 20. An exhaust pipe 13 removes the waste gases from the system, these gases being drawn from duct 12 through the duct 38 communicating therewith. The heat-conductive shield 9 has afiixed thereto a plurality of vanes or fins 14 extending through pipe 20 into the exhaust duct 38 and passing through the air duct 36. These vanes 14 function as heat-exchanging means deriving sensible heat from the exhaust gas and employing it to raise the temperature of the combustion-sustaining gas. Excessive heating of the fuel-supply tube 3 is prevented by terminating the vanes at the shield 9. To further insulate the fuel-supply tube from the remainder of the burner assembly, a ring of low thermal conductivity may be interposed between the nozzle 35 and the burner head 2. Any combustion heat latent in the exhaust gas can also be used for preheating the combustionsustaining gas by, for example, injecting oxygen into the exhaust duct 38 as described in the aforementioned copending application to burn combustible substances present in the waste gases. The latter can be drawn from the radiation tube 1 by the reduce-d pressure of a conventional flue system or via the Venturi technique of said copending application.
The general operation of the burner part of the assembly will be self-evident, it being noted that the orifies 6 discharge the preheated air or oxygen into the inner tube 10 wherein it combines with the fuel introduced at nozzle 35. The heat of combustion raises the temperature of tube 10 and thus of outer tube 31 by radiation and conduction (e.g. via the gases in duct 12). The inner tube 10 can be perforated as indicated in dot-dash lines at 39 to permit the flow of exhaust gases generally radially (arrows 11) into the outer tube 31. The free end of tube 10, remote from the burner mouth 2, may be open at 40 to permit the exhaust gases to flow into duct 12 as indicated by the arrows 41. In either case, the hot exhaust gases further heat the outer members 31. The radiant energy of tube 31 then heats objects within the furnace. Exhaust gases are drawn to pipe 13 from duct 12.
As best seen in FIGS. 2-4, the burner head 2 has a tapering outer periphery 43 which enables the head to be friction-fitted into tube 10 While another tapered surface 44 permits the frictional engagement of tube 20. A tapered boss 45, provided with the central aperture 5 of head 2, receives the heat shield 9 while nozzle 35 is inserted into the central bore 5. The axis 16 of the burner head is also the axis of the radiation tube 1 and the center of the flow line of the fuel jet. The orifices 6 are so oriented that they discharge their individual streams of air (represented by lines 15) along respective generatnces of a hyperboloid of revolution centered on the axis 16 as best seen in FIG. 4. The straight-line generatrices shown at 15 are skew to the axis 16 of the hyperboloid which they define according to well-known geometric principles. A comparison of FIGS. 1 and 4 shows that the geometrical center C of the hyperboloid is located within the solid portion of inner tube 10 which extends for several diameters beyond the nozzle 2. The orifices 6 are provided in the frustoconically outwardly concave mouth of the burner which is of generally corrugated configuration having alternating generally radial ridges 17 and troughs 18. As indicated by the axial projection of the flat surfaces defining these ridges and troughs (FIG. 2), each ridge 17 is defined by an imperforate surface a and an orifice surface [2 which angularly adjoin at the respective ridge 18 but are inclined to an axial plane through the burner head and that ridge at different angles. The surfaces a and b thus are sectoral with different angular extents. The ridges with their respective surfaces are, however, of similar configuration in all cases. The orifices 6 are provided in the surfaces b of similar orientation and have their axis perpendicular to the respective surfaces which thus are perpendicular to the respective generatrix of the hyperboloidal surface. The orifices 6 lie on a common circle 19 centered on this axis although additional orifices (6 in FIG. 2) can be provided along other circles '19 concentric therewith. The hyperboloidal sheath of combus- 'tion-containing gas thus emerging from the burner-head 2 provides a stable flame even when the throughput of fuel and air is a fraction of that normally required and insures that a rotary movement will be imparted both to the flame and to the exhaust gases of such nature that uniform heating of the inner tube and the outer tube 21 takes place. The hyperboloidal sheath moreover sustains an extraordinary long flame, thereby preventing localized overheating and burn-through of tube 10.
The invention as illustrated and described is believed to admit of many modifications which will be readily apparent to persons skilled in the art and are considered to fall within the spirit and scope of the invention as claimed.
What is claimed is:
1. An industrial burner comprising a radiation tube constituted by an inner tube portion and an outer tube portion, said outer tube portion coxially surrounding said inner tube portion with intervening clearance; a nozzle extending transversely across said inner tube portion; first inlet means for admitting a fuel stream to a central region of said nozzle; second inlet means for admitting a combustion-sustaining gas to an annular region of said nozzle surrounding said central region, said nozzle having a central aperture for the passage of said fuel stream and at least one circular array of orifices for the passage of said gas, the axes of said orifices being skew to the tube axis and representing straight-line generatrices of a hyperboloid of revolution centered on the tube axis, said inner tube portion extending forwardly from said nozzle for several diameters thereof and communicating with said outer tube portion at a location beyond the geometrical center of said hyperboloid whereby exhaust gases .from the combustion of a mixture of said fuel stream with said combustion-sustaining gas can reach said clearance; and an outlet for said exhaust gases connected with said outer tube portion at a point rearwardly of said nozzle whereby said exhaust gases stream past said nozzle toward said outlet.
2. A burner as defined in claim 1 wherein said annular region includes orifice surfaces separated by imperforate surfaces defining with them an annular array of corrugations with generally radial ridges and troughs defined by pairs of adjoining orifice and imperforate surfaces, said orifice surfaces being similarly oriented.
3. A burner as defined in claim 2 wherein each pair of orifice and imperforate surfaces adjoining at a respective ridge are geometrically congruent and are inclined at different angles to a respective axial plane of said tube which includes the respective ridge.
References Cited by the Examiner UNITED STATES PATENTS 2,190,190 2/1940 Peterson 158-1.5 2,391,447 12/1945 Edge 158-110 X 2,567,485 9/1951 Jenny 158-110 X 2,665,748 1/1954 Cornelius 158-76 3,022,815 2/1962 Bloom et a1. 158-109 3,163,202 12/1964 Schmidt et al. 158-75 FOREIGN PATENTS 1,074,802 2/ 1960 Germany.
FREDERICK KETTERER, Primary Examiner.