US3351048A

US3351048A - Infra-red gas burner structure

Info

Publication number: US3351048A
Application number: US395839A
Authority: US
Inventors: Jr John J Fannon
Original assignee: Fostoria-Fannon Inc
Current assignee: Fostoria-Fannon Inc
Priority date: 1964-09-11
Filing date: 1964-09-11
Publication date: 1967-11-07
Anticipated expiration: 1984-11-07
Also published as: NL6511863A; BE669503A; GB1110883A

Description

Nov. 7, 1967 J. J. FANNON, JR 3,

INFRA-RED GAS BURNER STRUCTURE Filed Sept. 11:, 1964 5 Sheets-Sheet 1 FIG. I

INVENTOR JOHN J. FANNON ,1 'JR.

BY/W MQQM ATTORNEYS Nov. 7, 1967 J. J. FANNON, JR

INFRA-RED GAS BURNER-STRUCTURE 5 Sheets-Sheet Filed Sept. 11, 1964 I NVENTOR JOHN J. FAA/MON, JR.

ATTORNEYS J. J. FANNON, JR

INFRA-RED GAS BURNER STRUCTURE 7 Nov. 7, 1967 Filed Sept; 11, 1964 5 Sheets-Sheet, 5

INVENTOR JOHN J. FAN/VON, JR.

ATTORNEYS Nov. 7, 1967 J. J. FANNON, JR

INFRA-RED GAS BURNER STRUCTURE 5 Sheets-Sheet 4 Filed Sept. 11, 1964 INVENTOR JOHN J. FAN/V0, JR.

BY MM MO M ATTORNEYS 1957 J. J. FANNON, Jr 3,351,043

INFRA-RED GAS BURNER STRUCTURE Filed Sept. 11, 1964 5 Sheets-Sheet 5 FIG. /.9

ATTORNEYS United States Patent 3,351,048 INFRA-RED GAS BURNER STRUCTURE John J. Fannon, Jr., Grosse Pointe Park, Mich., assignor,

by mesne assignments, to Fostoria-Fannon, Inc., a corporation of Ohio Filed Sept. 11, 1964, Ser. No. 395,839 6 Claims. (Cl. 126-92) This invention relates to improved line burners and to methods of producing such burners.

Application No. 370,795, now abandoned filed May 28, 1964, by Arthur C. W. Johnson discloses line type infrared generators in which a combustible fuel-air mixture flows from a plenum or distribution tube through a ribbon type orifice grid and burns on the outer surface of the grid. The heat liberated by the combustion of the fuel-air mixture is transferred by radiation and convection to a radiating and reradiating grid overlying the orifice grid, heating it to incandescence. The incandescent grid emits infrared radiation, part or" which is directed onto the articles or into the area to be heated and the remainder of which is reradiated to the distribution tube and orifice grid, raising the operating temperature of the burner. This increases the tendency of the flame to flash back into the distribution tube and ignite the combustible mixture in the tube, resulting in damage to or destruction of the burner. Also, as the rate at which the cornbustible mixture is supplied to such burners is increased to raise operating temperatures, the tendency for the flame to flash back into the distribution tube increases.

Another disadvantage of the devices disclosed in the Johnson application is that their heat output is only in the form of radiant energy except for one particular embodiment which is, however, useful only for specialized purposes. Consequently, they are unsuitable for use in numerous processes and types of heating apparatus requiring circulation of the combustion products, direct flame radiation, or flame impingement, for example.

One important object of the present invention is, therefore, the provision of novel improved line burners adapted for use in a wide variety of heat transfer devices and processes at temperatures up to 2000 F. or higher.

In conjunction with the foregoing object, another important object of the present invention is the provision of novel improved line burners adapted for use in heating devices requiring transfer of heat by direct radiation from, contact with, or circulation of the burning gases as well as those requiring heat output in the form of infrared radiation from an incandescent radiant member.

In conjunction with the foregoing, other important objects of the present invention include the provision of novel, improved line burners which:

(1) Are capable of operating at higher temperatures than prior art burners of this general type and are capable of converting a higher percentage of the heat value in the fuel employed into usable heat than has heretofore been possible;

Consist primarily of sheet metal and are easily assembled and have other characteristics which make them readily producible at low cost by mass production techniques;

(3) Are easy to install and service and have a long useful life;

(4) Are not adversely effected by the unequal expansion of their components which occurs as they heat up and cool off;

(5) Have orifice grids (or other orifice structures) that are easily removable for cleaning or replacement;

(6) Are virtually free from flashback, even when the ambient temperature is as high as 1500 F.;

i (7) In conjunction with the preceding object, have a novel combination and relative disposition of distribution tube and orifice grid and a novel arrangement for holding the foregoing components together that minimizes eating of the fuel-air distribution tube;

(8) In conjunction with object 6), have a novel, small diameter, insulated distribution tube construction which minimizes the transfer of heat to the tube, especially when the burner is operated in extremely :hot environments; and

(9) Are particularly adapted to installation in home heating plants.

Other important objects of this invention are the provision of novel, improved infrared generators which employ line burners in accord with the principles of the present invention and which:

(1) Are capable of producing emitted energy of wave lengths readily absorbed by most materials;

(2) Include novel reflector structure which efiiciently projects the radiation emitted from the radiant grid in the desired pattern and direction or directions;

(3) Are applicable to a wide variety of processes such as the heating of sheets and continuous webs, the baking or drying of many types of finishes and coatings, the heating of objects on conveyors, and the heating of rolls and platens; which may be employed in a wide variety of heating apparatus such as various types of ovens and furnaces; and which are particularly suited to applications where high concentrations of radiant energy are required;

(4) Are particularly suited for indoor and outdoor area heating; and

(5) Can use either metallic or ceramic grids.

Other important objects of the present invention reside in the provision of novel methods for manufacturing line burners and infrared generators in accord with the preceding objects.

The line burners of the present invention, by which these important objects are attained, include a sheet metal fuel-air plenum or distribution tube of novel configuration which reduces heat dissipation, thereby increasing operating efiiciency; is rigid and strong, thereby assuring long operating life; and is easily formed, thereby contributing to lower manufacturing costs. By attaching the orifice structure to the distribution system in a novel manner described in detail hereinafter, the orifice structure is made readily detachable for cleaning or replacement, so that the line burners disclosed herein are easy and inexpensive to service.

In addition, the line burners of the present invention preferably employ a novel relative disposition of distribution tube and orifice grid and a novel arrangement for holding the distribution tube and orifice grid together which, together with the distribution tube configuration just mentioned, virtually eliminate the problem of flashback. This remains true even though the burner is crowded (i.e., the combustible mixture is supplied at an abnormally high rate to obtain maximum heat output and/or temperature), is of an extremely long length, or is operated at its lowest rate facing downward.

Another important advantage of the novel line burners just described is that they are capable of operating in extremely hot environments (ambient temperatures of 1500 F. or higher). In addition, these burners have a long service life and are useful in a wide variety of heat employing processes and in many different types of ovens, furnaces, and other heating apparatuses, including those intended for home use.

A further important feature ofthe present invention is the use of a relatively small diameter, insulated distribution tube. The reduction in diameter of the tube increases the velocity at which the combustible mixture flows through the tube, increasing the rate at which heat is transferred from the tube to the mixture, and also re duces the area of the tube exposed to the ambient atmosphere, which reduces the rate at which heat is transferred from the ambient atmosphere to the tube. The tube insulation further reduces the rate at which heat is transferred from the ambient atmosphere to the tube. The net result of the foregoing factors is that the distribution tube remains cooler than it otherwise would and the possibility of flashback is even further reduced. This is extremely important in applications where overheating is most likely to occur such as where the burner is operated in an inverted orientation and in an extremely hot environ mentfor example, in an oven or furnace where the ambient temperature may be 1500 F. or higher.

The novel line burners of the present invention also represent an advance in the art in that they may be readily converted into improved infrared generators simply by the addition of a radiant grid, which may be of either the metallic or the ceramic type. In the present invention the novel mounting arrangement by which the orifice grid is attached to the distribution tube also supports the radiant grid from the distribution tube in a manner which permits the radiant grid to expand freely as the infrared generator heats up and cools off. This prevents the radiant grid from warping, which materially increases the life of the infrared generator.

The novel combination of components described briefly above has been found to result in an infrared generator of high efficiency and output and one which can readily be provided with reflectors capable of efficiently concentrating the emitted radiant energy in a beam of desired configuration and directing it in the desired direction or directions. The infrared generators of the present invention are useful in a wide variety of heat employing processes and in many different types of heating devices, especially those requiring a high concentration of radiant energy. These infrared generators are also particularly suitable for indoor and outdoor area heating. Moreover, the infrared generators of the present invention emit radiant energy in a range of wave lengths which is such that the emitted radiant energy is readily absorbed by most materials. For example, with the radiant grid at a temperature of 2000 F., 96% of the emitted radiation has a wave length in the range of 1-7 microns and is readily absorbed by most materials.

Additional advantages, other objects, and further novel features of the present invention will become apparent from the appended claims and as the ensuing detailed description and discussion proceeds in conjunction with the accompanying drawing, in which:

FIGURE 1 is a generally diagrammatic section through a line burner constructed in accordance with the principles of the present invention and the combustion chamber of a furnace in which the burner may be employed;

FIGURE 2 is a side view of the line burner of FIG- URE 1:

FIGURE 3 is a side view of an infrared generator embodying the line burner of FIGURE 1 with portions of several components being broken away to better show the construction of the infrared generator;

FIGURE 4 is a section through the infrared generator of FIGURE 3, taken substantially along line 44 of the latter figure;

FIGURE 5 is a fragmentary view of a radiant grid employed in the infrared generator of FIGURE 3, looking in the direction of arrows 55 of FIGURE 4;

FIGURE 6 is a transverse vertical section through a modified form of infrared generator;

FIGURE 7 is a fragmentary view of an orifice grid employed in the line burner of FIGURE 3, looking in the direction of arrows 7-7 of FIGURE 4;

FIGURE 8 is a view, similar to FIGURE 7, of a modified form of orifice grid;

FIGURE 9 is a perspective view of radiant grid supporting clips employed in the infrared generator of FIG- 4 URE 3 and of a portion of the grid supported by the clips;

FIGURE 10 is a side view of a modified form of line burner constructed in accord with the principles of the present invention;

FIGURE 11 is a section through the line burner generator of FIGURE 10, taken substantially along line 11-11 of the latter figure;

FIGURE 12 is a fragmentary plan view of a modified orifice structure which may be employed in the line burners of the present invention and the distribution tube to which it is attached, looking in the direction of arrows 12-12 of FIGURE 13;

FIGURE 13 is a sectional view of the distribution tube and orifice, taken substantially along line 13-13 of FIG- URE 12;

FIGURE 14 is a fragmentary perspective view of the orifice structure shown in FIGURES 12 and 13;

FIGURE 15 is a view, similar to FIGURE 13, of a further form of orifice structure and the distribution tube to which it is attached;

FIGURE 16 is a section through the orifice structure of FIGURE 15, taken substantially along line 16-16 of FIGURE 15;

FIGURE 17 is a section through an infrared generator constructed in accord with the principles of the present invention employing an insulated distribution tube which is especially resistant to overheating and a ceramic radiant grid;

FIGURE 18 is a section through a second form of insulated distribution tube; and

FIGURE 19 is a section through a third form of distribution tube.

Referring now to the drawing, in which exemplary embodiments of the present invention are shown, FIG- URE 1 depicts a conventional warm air furnace 20 having a combustion chamber 22 in which a line burner 24 constructed in accord with the principles of the present invention is mounted by brackets 26. Line burner 24 includes a fuel-air mixture distribution tube 28 and an orifice grid 30, through which the fuel-air mixture flows from the interior of distribution tube 28 to a combustion zone adjacent the outer end 32 of the grid.

Combustion air is supplied to line burner 24 by a combustion air blower 34, the outlet of which communicates through a fuel-air supply conduit 35 with the interior of distribution tube 28. Fuel is supplied through a conduit 36 terminating in an orifice 38 in conduit 35 and mixes with the blower supplied air to form a combustible mixture. Burner 24- may be operated on primary air supplied by blower 34 or secondary air can be supplied to the combustion zone in accord with conventional practice.

Furnace 29, by itself, is not part of the present invention and is shown merely to illustrate a typical application of the novel line burners disclosed herein. Typically, the furnaces combustion chamber 22 would communicate with the atmosphere through ports 40, through which secondary combustion air could enter, and a chimney or flue, through which combustion products would be discharged. The combustion chamber is conventionally surrounded by a plenum through which air is blown to heat it.

As shown in FIGURE 1, the distribution tube 28 has a generally diamond-like configuration with the two

flanges

54 and 56 lying in parallel spaced apart relationship and providing an outlet passage 64 from the interior to the exterior of the distribution tube. This flanged configuration is of substantial importance in that it materially reduces the amount of usable heat dissipated through distribution tube 28 from the combustion zone and correspondingly increases operating efiiciency.

Sheet metal end members 66 and 68 (see FIGURE 3) are fixed to the opposite ends of distribution tube 28 to prevent the escape of the combustible mixture. An aperture 7ft in end member 68 provides communication he-' tween the interior of the tube and supply conduit 35, through which the combustible fuel-air mixture flows into distribution tube 28.

"Orifice structure 30, through which the fuel-air mixture flows from distribution tube 28, is mounted in the outlet passage 64 of fuel-air distribution tube 28 between flanges 54 and S6 to prevent the flame from flashing back from the combustion zone through passage 64 into fuelair mixture distribution tube 28.

The illustrated orifice grid 30 is of the ribbon type, and consists of embossed metallic ribbons which provide a number of small passages extending between and opening onto the opposed lateral edges of the assemblage of ribbons. The particular configuration of the individual ribbon is not critical in the present invention; and the length and total area of the lateral passages may be varied as desired for particular applications of this invention. It is necessary, however, that the lateral passages be sufliciently small in diameter and sufficiently long that flame cannot flash back through the passages from the combustion zone adjacent the face 32 of the orifice structure to the interior of distribution tube 28. In addition, the total area of the openings must be sufiiciently great that the combustible mixture will flow from distribution tube 28 to the combustion zone in sufiicient quantity to maintain the desired rate of combustion.

One suitable ribbon type orifice structure, illustrated in FIGURE 7, consists of metallic ribbons 72 in which laterally extending semicircular depressions or convolutions 74 are formed at periodic intervals and are typically on the order of 0.188 inch apart. As shown in FIGURE 7, metallic ribbons 72 are arranged in two groups 76 and 78. In each group, depressions 74 extend in the same direction so that the depressions 74 of the ribbons 72 in each group are nested. The two groups 7-6 and 78 are assembled in mirror image relationship, and the individual ribbons 72 pinned or brazed together at opposite ends of orifice structure 30 to maintain them in the correct position relative to each other.

As shown in FIGURE 7, the construction just described provides an orifice structure having lateral passages 80 between adjacent depressions 74, lateral passages '82 between the adjacent planar portions of the ribbons between depressions 74, lateral passages 84 formed by the opposed depressions 74 of the two innermost ribbons 72 in groups 76 and 78, and Lateral passages 86 between the two outermost ribbons 72 and the associated

distribution tube flanges

54 and 56.

Typically, ribbons 72 will be 0.375 inch wide; and

passages

80, 82, 84, and 86 will therefore be 0.375 inch long.

Passages

80 and 82 may be on the order of 0.010 inch wide and passages 84 on the order of 0.050 inch in diameter. The passages 86 of a typical grid structure may be on the order of 0.025 inch Wide.

As this grid structure, by itself, forms no part of the present invention and as it is disclosed in detail in copending application No. 370,795, mentioned above, to which reference may be had, if desired, it is not believed necessary to describe it in more detail herein.

Orifice structure 30 is removaly retained between

distribution tube flanges

54 and 56 by studs 100 and straps 102 (see FIGURE 3). Studs 100, which extend laterally through the apertures 44 in

distribution tube flanges

54 and 56 at intervals (commonly on the order of 6") along the distribution tube, locate orifice structure 30 relative to the inner end 104 of the passage 64 between

distribution tube flanges

54 and 56. Retainers 106, threaded on the opposite ends of studs 100,

clamp flanges

54 and 56 against orifice structure 30 to removably retain it in passage 64. Straps 102 (which prevent orifice structure 30 from dropping out of passage 64) are provided at the ends of distribution tube 28. Straps 102 extend between

distribution tube flanges

54 and 56 and are fixed to the flanges as by brazing.

Orifice structure 30 can be removed from line burner 24 merely by loosening retainers 106 and sliding the orifice structure lengthwise out of the passage 64 between

distribution tube flanges

54 and 56. This is an important feature of the present invention since it facilitates the removal of orifice structure 30 for cleaning or replacement.

The novel line burners just described have a number of desirable characteristics which are not possessed by prior art burners. These burners may be used in infrared generators to heat radiation emitting members up to 2200 F. or higher and in burner lines more than ten feet long without unacceptable distortion of their components or flashback. At the same time, these burners are of light weight, are economical to manufacture, and, when used in infrared generators, are capable of maintaining uniform temperatures over the entire radiation emitting surface of the radiant member.

These heretofore unattainable operating characteristics are due, in large part, to the following features of these burners:

(A) Only extremely small areas of distribution tube 28 and orifice grid 30 are exposed to radiation from the burning gases (and the radiant member if the line burner is incorporated in an infrared generator) as the only portions of these components exposed to such radiation are the thin outer edges of

distribution tube flanges

54 and 56 and the edges of the ribbons 72 in orifice structure 30. This minimizes heating of these components, minimizing the possibility of flashback and reducing the dissipation of usable heat.

(B) The

passages

80, 82, 84, and 86 through orifice grid 30 have very small cross sectional dimensions in comparison to their length. For example, as indicated previously, these passages may typically range in width from 0.025 to 0.010 inch wide and have a length of 0.375 inch so that the minimum ratio of length to Width is 37.521. This materially reduces the possibility of flashback in comparison to prior art burners such as those shown in co pending application No. 370,795, which employ distribution tubes of pipe and in which the outlet passages are slots milled in the wall of the pipe. Even though ribbon type orifice grids are employed with such distribution tubes, the controlling factor is the ratio of slot depth (equal to the wall thickness of the pipe) to the width of the slot, a ratio much lower than the effective depth to width ratios of the present invention.

(C) The large number of ports provided by the ribbon length of the burner with minimum mixture pressure.

velocity of the gas flowing through the ports in the orifice grid, which further reduces the posslbility of flashbac (E)

Flanges

54 and 56 which separate distribution tube 28 from the combustion zone adjacent the outer face 32 of orifice grid 30 and limit the path along which heat can be conducted from the combustion zone to the

walls

50, 52, 57, and 58 of the distribution tube to one of substantial length and small cross section, minimizing, the conduction of heat to the walls of the distribution tube. This, too, reduces the possibility of flashback and the dissipation of usable heat. In addition, the flow of the combustible mixture through the passages 86 between the outermost ribbons 72 of orifice grid 30 and the flanges cools the latter, further reducing the transmission of heat to the walls of the distribution tube with the attendant beneficial results mentioned above.

(F) The cooling action of the stream of combustible mixture moving through distribution tube 28 at high velocity and entering the ports in orifice grid 30 through the narrow outlet passage 64 between

flanges

54 and 56 which removes substantial heat from the distribution tube walls. Since these passages have small cross sectional areas, the pressure drop across the orifice grid is relatively large, materially increasing the velocity of the flow through tube 28 and the elfectiveness of the action of the mixture in Wiping across the walls of the tube, both of which maxirnize its cooling effect.

By the combination of novel features described above, distribution tube 28 can be maintained at temperatures as low as 300400 F. even though line burner 24 is incorporated in an infrared generator in which the radiant member is at a temperature of 18002000 F. or higher. This virtually eliminates the possibility of flashback and results in a more efficient burner than those heretofore available.

Another line burner constructed in accord with the principles of the present invention, which may be preferable for particular applications, is shown in FIGURES and 11 and identified by reference character 108. In these figures, like reference characters have been employed to identify line burner components which are identical to those of the line burner 24 illustrated in FIGURES 1 and 2.

This embodiment of the present invention employs a fuel-air distribution tube 110 which has a circular configuration rather than the diamond configuration of fuelair distribution tube 28. As in the previously described line burner embodiment, the fuel-air distribution tube has lateral edge portions or flanges 112 bent at angles to the main body of the tube in parallel, spaced apart relation to provide a passage 114 between the interior and exterior of the tube. Orifice grid 30, which may be of any of the constructions described above or hereinafter, is mounted in passage 114 between flanges 112 in the manner previously described.

End members 116 and 118 (see FIGURE 10) are brazed or otherwise fixed to opposite ends of fuel-air distribution tube 110 to prevent the leakage of the combustible mixture. As in the previously described line burner 24, the combustible fuel-air mixture is fed into distribution tube 110 through a fuel-air supply conduit 120 extending through an aperture 122 in distribution tube end member 118.

FIGURES 12-14 and 18 and 19 illustrate modified g rid structures which, if desired, may be employed in line burners constructed in accord with the principles of the present invention. For the sake of convenience, they will be described in conjunction with line burners of the type shown in FIGURES 1 and 2. This description is not intended to be limiting, however, as these grid structures are generally applicable to line burners constructed in accord with the principles of this invention. The orifice grid structure 123 illustrated in FIGURES 12-14 is a channel having legs 124 connected by a web 126 in which narrow, laterally extending slits 128 are formed. Channel 123 is fixed in passage 64 between

flanges

54 and 56 of fuel-air distribution tube 28 in the manner described in conjunction with the embodiment of FIGURES 3 and 4; and the combustible mixture flows from the interior of the distribution tube through passage 64 and the slits 128 in channel 123 to the combustion zone adjacent the outer face 130 of the channel.

As shown in FIGURE 14, blocks 132 are fixed in the ends of channel 123 to prevent the combustible mixture from leaking through the open ends of the channel.

' This form of orifice grid does not prevent flashback as effectively as the ribbon type orifice grid described previously. However, it is substantially less expensive than the latter; and, where operating and other conditions are such that there is little tendency for flashback, the channel type of orifice grid is entirely satisfactory.

Many modifications may be made in the illustrated channel 123. For example, the size of the channel and the material from which it is formed may be varied as may the size of slits 123. Also, circular or other shapes of holes may be substituted for the narrow elongated rectangular slits shown, if desired.

The orifice structure 134 shown in FIGURES and 16 consists of two

identical channels

136 and 138 of the type just described arranged in the passage 64 between 8

flanges

54 and 56 of fuel-air distribution tube 28 in backto-back relationship with their legs 140 juxtaposed. This provides aligned

slits

142 and 144 spaced longitudinally of passage 64, an arrangement which is highly effective in preventing flashback.

Another type of orifice grid structure, which functions particularly well, is illustrated in FIGURE 8 and identified by reference character 146. Grid structure 146 is formed from metallic ribbons 148 in which laterally extending triangular convolutions 150 are formed at periodic intervals. Ribbons 148 are assembled in pairs with the two ribbons in each pair being disposed in mirror image relationship. The pairs of ribbons are assembled in side-by-side relationship with the convolutions 150 of one pair midway between the convolutions 150 of the adjacent ribbon pair. The ribbons 148 of grid structure 146, like the ribbons 72 of grid structure 30, are preferably pinned or brazed together at opposite ends of the grid structure to give the latter structural integrity.

This arrangement provides lateral passages 154 between the associated convolutions 150 of the two ribbons in each pair; lateral passages 156, which are defined by the juxtaposed convolutions 150 of ribbons in adjacent ribbon pairs and the portions of the juxtaposed ribbons in adjacent pairs intermediate the convolutions; and lateral passages 158 between the outermost ribbons 148 and

flanges

54 and 56.

The various dimensions of the orifice structure 146 illustrated in FIGURE 8 may be similar to the corresponding dimensions of orifice structure 30. However, as discussed above, the particular dimensions are not critical, it only being necessary that they be so selected as to prevent flashback and to accommodate flow of the combustion mixture at the desired rate.

Line burners constructed in accord with the principles of the present invention may be readily converted into highly efiicient infrared generators by the addition of a radiant grid. To illustrate this aspect of the present invention, reference will be made to the conversion into an infrared generator of the line burner shown in FIG- URES 1 and 2. It is to be understood, however, that the line burner of FIGURES 10 and 11 and other line burners constructed in accord with the principles of this invention may be similarly adapted to the production of infrared radiation.

Referring again to the drawing, FIGURE 3 illustrates an infrared generator 160 which includes the line burner 24 described previously and a radiant grid 162. Radiant grid 162, which is heated to incandescence by the combustible mixture flowing through orifice structure 30 and burning adjacent its outer face 32 and emits the radiant energy desired for space, article, or other heating, is preferably of the apertured construction disclosed in copending application No. 370,795. In the present invention, however, radiant grid 162 is made of a sheet of heat resistant metal such as Inconel or Hastaloy-X or a coated alloy and is bent into a horseshoe configuration providing a radiation emitting body 164 and inturned mounting flanges 166 extending toward each other from opposite sides of the radiation emitting body. In the embodiment of the present invention illustrated in FIGURES 3 and 4, the body 164 of grid 162 has a radius of 0.75 inch and a height of 1.25 inches; and legs or flanges 166 are 0 .50 inch wide. This configuration is an important feature of the present invention as it provides a grid which is uniformly heated, which is extremely rigid and resistant to distortion, and which minimizes the dissipation of usable radiation to the fuel-air distribution tube.

As best shown in FIGURES 4 and 9, the body 164 of radiant grid 162 is formed by stamping or other process into a configuration in which loops 168 are displaced from the plane of the sheet from which the grid is formed at regular intervals to form openings extending normal to the sheet through which the combustion products may pass from the combustion zone. As discussed in detail in copending application No. 370,795, this results in a grid which is a highly eflicient emitter of infrared radiation and which effectively protects the flame from air currents of sufficient strength to quench or snuff it out.

In flanges 166, loops 168 are preferably flattened back into the plane of the flanges or are omitted to provide flat flanges which can be readily clamped between the hereinafter members employed to attach grid 162 to distribution tube 28.

Referring now specifically to FIGURE 4, ears 170 are bent from grid body 164 at its ends; and grid end plates 172 are spot welded to ears 170. End plates 172 support the open ends of the grid 162 and maintain the body of the grid in the desired shape. They also prevent disturbance of the flame by air currents.

An aperture 174 may be provided in one or both of the end plates 172 to facilitate lighting the burner, to accommodate a spark plug or flame sensor, and/or to allow flame to travel from one radiant grid to the next adjacent radiant grid in an infrared generator having multiple radiants and adapted to be ignited at one end.

Grids 162 may be of any desired length. However, grids having a maximum length of 24 inches are preferred since such shorter grids are practically free of distortion due to expansion at high operating temperatures; and, if desired, longer infrared generators can readily be provided by connecting shorter ones in end to end relationship to a single longer distribution tube 28.

Referring now to FIGURES 3, 4, and 9, radiant grid 162 is removably attached to the

flanges

54 and 56 of fuel-air distribution tube 28 by cooperating pairs of inner and outer grid clamps or

clips

178 and 180. As best shown in FIGURE 9, inner clip 178 has an L-shaped configuration provided by two normally extending

integral legs

182 and 184. Outer clip 180 has a first leg 186 adapted to be fixed to leg 182 of clip 178, a second leg 188 extending at right angles to leg 186 in parallel, spaced relationship to leg 184 of clip 1'78, and a third integral leg 190. inclined at an angle to leg 188 and adapted to embrace the exterior of radiant grid 162.

A pair of

clips

178 and 180 is employed on either side of infrared generator 160 at each of the studs 100, which extend through aligned apertures 192 in

clips

178 and 194 in clips 180. In the preferred manner of assembling infrared generator 160, the

clips

178 and 180 of each pair are spot Welded together and slid onto the associated flange 166 of radiant grid 162 before end plates 172 are attached to the grid by moving them in the direction shown, the associated mounting flange 166 passing between leg 184 of clip 178 and leg 188 of clip 180 and the peripheral region of the grid body 164 passing between the edge of leg 184 of clip 178 and leg 190 of clip 180. The end plates 172 are then attached, the clip pairs assembled on studs 100, and retainers 106 threaded on the studs to retain grid 162 in place.

In the assembled infrared generator 160 the space between each pair of

clips

178 and 180 is slightly greater than the thickness of the associated flange 166. This permits longitudinal movement of flange 166 between the clips of the parts expand or contract due to temperature changes, but restrains the flange and grid against appreciable transverse movement. This permits grid 28 to expand axially as its temperature increases, which prevents it from becoming distorted as it expands and contracts longitudinally. Lateral expansion is accommodated by the horseshoe configuration of the radiant grid so that the grid is almost entirely free from expansion and contraction induced distortions.

Reflectors 198 are preferably employed in infrared generator 160 to form the infrared radiation emitted from grid 162 into a beam of the desired configuration and to project the beam in the desired direction or directions. These reflectors may be formed from sheets of aluminized steel or any other good reflector of infrared radiation. Reflectors 198 each have a main reflecting portion 200 and a mounting leg 202 connected by an integral leg 204 extending upwardly and outwardly from mounting leg 202. Mounting leg 202 is provided with apertures (not shown) through which mounting studs extend. Retainers 206, threaded on the outer ends of studs 100, secure reflectors 198 on studs 100 against retainers 106 with the reflecting portion 200 of the two reflectors inclined outwardly relative to radiant grid 162 to concentrate the infrared radiation emitted from the grid in a downwardly directed beam toward the area or onto the objects to be heated by infrared radiation (reflecting portions 200 of reflectors 198 are inclined at an angle of 45 to the horizontal in the embodiment of the invention illustrated in FIGURE 7, but this angle is not critical).

As shown in FIGURE 4, the legs 204 of reflectors 198 connecting reflecting bodies 200 and legs 202 are inclined upwardly at acute angles to mounting legs 202 with reflectors 198 assembled on studs 100. This is important in that radiant energy emitted from grid 162 and impinging on intermediate legs 204 is reflected downwardly and away from

flanges

54 and 56 of distribution tube 28. This reduces the transmission of heat to distribution tube 28 and, therefore, the dissipation of usable heat, increasing the infrared generators usable heat output and minimizing the possibility of flashback.

Like radiant grids 162, reflectors 198 are preferably made in sizes not exceeding about 24 inches by length to prevent expansion and contraction from warping them.

The particular reflector configuration just described is merely exemplary; and the angle of inclination of the reflectors main portions 200 and the shape of the reflectors can be changed as desired to provide the desired pattern of radiant energy distribution. For example, reflectors having a parabolic or elliptical cross section could be substituted for those illustrated in FIG- URE 3. As further examples, the reflector can be formed so that its main portion is normal to the axis of the burner or lies in the plane and forms a continuation of the reflectors mounting leg.

In conjunction with the foregoing, infrared generator is illustrated in an orientation in which it directs the radiant energy emitted from radiant grid 162 in a downward direction. However, the generator may equally well be disposed in other orientations to direct the beam of radiation upwardly or laterally, or at any desired angle to the horizontal.

Many modifications may be made in the embodiments of the present invention described above to adapt the present invention to particular applications. For example, certain infrared applications require that the radiant energy be confined to a narrow beam to, for example, provide a highly intense concentration of the radiant energy over a narrow area. An embodiment of the present invention, designed to produce a narrow intense beam of infrared radiation, is illustrated in FIGURE 6 and identified by reference character 208 (insofar as the components of infrared generator 208 are the same as those of infrared generator 160, they have been identified by like reference characters).

Refer-ring now to FIGURE 6, infrared generator 208 differs from infrared generator 160 primarily in the configuration of its radiant grid 210 which, in this embodiment of the present invention, has a square configuration provided by radiation emitting face 212 of the ribbed construction described above in conjunction with radiant grid 162, imperforate side walls 214 extending normally from opposite edges of the radiation emitting face, and imperforate flanges 216, extending normal to side Walls 214 from the edges thereof opposite radiant energy emitting face 212. Radiant grid 210 is preferably of one-piece construction since unitary construction provides maximum strength, simplifies manufacture, and minimizes distortion as the radiant grid is heated and cooled. To

prevent the dissipation of heat in lateral directions, insulating members of Fiberfax or metal shields identified by reference character 218 are preferably fixed to the inner surfaces of the side walls 214 of radiant grid 210.

Grid 210 is assembled to fuel-air distribution tube 28 by pairs of clips including a clip 178 and a clip 220, which is identical to the clip 180 illustrated in FIGURE 9, except that the leg 222 of clip 220 is bent at right angles to the adjacent leg 224 to match the configuration of side walls 214 of radiant grid 210.

To further prevent the dissipation of heat to the sides of infrared generator 208, reflectors 226 may be fixed, in any desired manner, to the side walls 214 of radiant grid 210 after it is assembled to distribution tube 28. Although the illustrated reflectors 226 have planar reflecting surfaces, the reflectors may as easily be formed in other configurations to alter the pattern of radiant energy emitted from radiant grid 210.

FIGURE 17 illustrates an infrared generator 228, constructed in accord with the principles of the present invention, which is particularly adapted "for use in high temperature environments; e.g., in ovens or in furnaces where the temperature of the ambient atmosphere may typically be lSOO F. or higher. To the extent that infrared generator 228 and its components are like those of previously described embodiments of the present invention, they will be identified by the same reference characters.

Infrared generator 228 differs from those previously described primarily in the construction of its combustible mixture distribution tube 230 and its radiant grid 232.

Combustible mixture distribution tube 230 is identical to the distribution tube 110 of the embodiment of the present invention illustrated in FIGURE 11 except: (1) it has a smaller internal diameter and less exposed surface area; and (2) it has an internal insulating lining 234. Lining 234 is preferably made of a material having low heat conductivity and may typically be a coat of refractory cement, enamel, or other suitable material which will adhere to the tube wall or a sheet of asbestos Fiberfax, or other insulating material cemented or otherwise secured to the tube wall.

Both the reduced internal tube diameter and exposed surface area and the insulating lining 234 are important in securing satisfactory operation in high temperature environments. Because of the smaller cross-section, combustible mixture supplied to infrared generator 228 will flow through distribution tube 230 faster than it would through a distribution tube of the type shown in FIGURE 11 having the same overall dimensions. This higher velocity effects a more rapid transfer of heat from the walls of the distribution tube to the combustible mixture; and, therefore, for a given rate of flow of combustible mixture to the burner, distribution tube 230 will remain cooler than a distribution tube of the type shown in FIGURE 11 with the same external dimensions and wall thickness.

Because of its smaller exposed surface area, less heat will be transferred to tube 230 than to a comparable tube of the type shown in FIGURE 11 in the same environment.

The insulating lining 234 further materially reduces the rate at which heat is transferred from the ambient atmosphere to the interior of distribution tube 230 and, therefore, also assists in lowering the temperature inside the tube so that, in a given environment, an insulated distribution tube of the type shown in FIGURE 17 will have a much cooler internal temperature than one of the type shown in FIGURE 11. The smaller diameter tube, the decreased exposed surface area, and the insulation, therefore, help to prevent distribution tube 230 from overheating and thereby prevent the flame adjacent the outer end 32 of orifice grid 38 from flashing back into the distribution tube.

The radiant grid 232 of infrared generator 228 has a generally horseshoe-like configuration provided by a grid 12 body 236 and integral mounting

flanges

238 and 240. Radiant grid 232 is attached to distribution tube 230 by bolts which extend through aligned apertures 242 in

flanges

238 and 240 and are retained in place by retainers 106.

Venting apertures 244 through the wall of the body 236 of radiant grid 232 permit combustion products to escape from the combustion zone adjacent the outer end 32 of orifice grid 30 to the ambient atmosphere or into a suitable exhaust system.

Radiant grid 232 may be molded from refractory clay or may be formed from a cermet, solid quartz, quartz fibers, quartz cloth, or any other refractory material meeting the requirements of a specific application.

It is to be understood that it is not necessary to employ together the specific insulated distribution tube 230 and ceramic radiant grid 232 illustrated in FIGURE 17. Specifically, radiant grid 232 may be omitted to provide a line burner in accord with the principles of the present invention where the particular application requires direct flame radiation or convection by movement of the combustion gases, for example. Also, refractory radiant grids of the type illustrated in FIGURE 17 may be employed with the types of distribution tubes described previously to provide infrared generators in accord with the principles of the present invention; and the metallic radiant grids of the type described previously may be substituted for the refractory radiant grid 232 in infrared generator 228 although, for some applications, refractory grids will prove more satisfactory.

In infrared generator 228 the combustible air mixture flows from the interior of combustible mixture distribution tube 230 through orifice grid 30 and burns adjacent the orifice grids outer face 32. The burning gases heat the body of radiant grid 232 to incandescence and escapethrough vent apertures 244. Infrared radiation is emitted from the outer surface of the radiant grids body 236. Although the infrared generator 228 shown in FIGURE 17 is shown without reflectors, it is to be understood that suitable reflectors for concentrating and directing the emitted radiant energy of any of the several forms described above can be added to infrared generator 228, if desired.

Also, the configuration of the refractory radiant grid may be varied as desired for particular applications. Examples of suitable alternate configurations are those disclosed in application No. 370,795, mentioned above.

The combustible mixture distribution tube 246 shown in FIGURE 18 is identical to the distribution tube 230 just described except that it has a layer of insulation 248 on the outer surface of its main body portion 250 rather than on its inner surface as in the embodiment of FIG- URE 17. This distribution tube embodiment may, otherwise, be identical to distribution tube 230.

FIGURE 19 illustrates a combustible mixture distribution tube 252 which is identical to the distribution tube 28 illustrated in FIGURE 1, for example, except that a first layer of insulation 254 is applied to its outer surface and a second layer of insulation 256 to its inner surface so that distribution tube 252 consists of a metal core sandwiched between inner and outer insulating layers, both of which act to reduce the transfer of heat from the ambient atmosphere to the combustible mixture within the tube.

The insulation may be added to the distributor tube 252 in the manner discussed above in conjunction with the embodiment of FIGURE 17. If desired, distribution tube 252 may be fabricated with a relatively small internal cross section to reduce the heat transfer surface in contact with the ambient atmosphere and to effect more efficient heat transferring high velocity flow of the combustible mixture through the distribution tubes.

The infrared generators of the present invention have a number of advantages over those of the prior art including those infrared generators disclosed in the above- 13 mentioned copending application No. 370,795. These include greatly improved efliciency which is due, in main part, to:. (a) the advantages discussed above resulting from the employment of line burners constructed in accord with the principles of the presentinvention; (b) the radiant grid configurations which permit higher temperatures to be attainedfor a given rate of fuel consumption;

(c) the flanged configurations of the fuel-air distribution tubes, which provide a more uniform distribution of the fuel-air mixture along the length of the infrared generators; (d) the material reduction in heat dissipated by the fuel-air distribution tubes because of the narrow necks provided by the distribution tube flanges which separate the body of the tube from the combustion zone; (e) the substantial reduction in heat dissipation because of the inturned flanges or legs at the open side of the radiant members, which isolate the fuel-air distribution tubes from hot combustion products and from radiant heat; and (f) the novel, improved reflectors, which effectively direct the radiant energy emitted from the radiant grids toward the area or objects to be heated and efliciently eliminate heat losses due to stray radiation.

. The infrared generators of the present invention are also much more durable than those mentioned above because .of: -(a) the novel arrangement for mounting the radiant grids, which permits them to move freely as they expand and contract, and thereby prevents warping and, in addition, minimizes conduction of heat from the radiant member to the fuel-air mixture distribution tube; (b) the use of comparatively short radiant grids, which keeps expansion at a minimum; the additional strength gained by the' novel radiant grid configurations; (d) the increased strength and rigidity of the novel fuel-air dis tribution tubes; and (e) the more secure method of attaching theradiatit grids to the fuel-air distribution tubes. 7

Also, in the infrared generators disclosed herein, equipment failure due to clogging of the orifice grid is eliminated as aproble'm since, because of the manner in which it is' attached, the orifice grid may readily be removed and replaced or cleaned. t

In addition, the infrared generators disclosed herein produce a high concentration of radiant energy making radiant heating applicable to processes in which it was heretofore unusable. For example, by using infrared generators as disclosed herein spaced three inches on center, heat inputs of over 80,000 b.t.u. per hour per square foot of heated area can be obtained by operating the infrared generators at radiant grid temperatures below 2,000 E, which is well below their maximum. Almost half of this heatinput is in the form of infrared radiation; and this is within a few percent of the theoretical maximum amount of infrared radiation obtainable. Moreover, a higher proportion of the emitted radiation has wave lengths in the desirable 1 to 30 micron range than prior art infrared generators.

As mentioned previously, the line burners incorporated in the infrared generator illustrated in FIGURE 17 may be employed without radiant grids where direct flame radiation or convective heating by movement of the burning gases is required. Also, combustible mixture distribution tubes as shown in FIGURES 18 and 19 may be employed in line burners used as such rather than being incorporated in infrared generators. Such burners have all the advantages of the previously described embodiments as heretofore specifically enumerated. In addition, they are even more effective than the previously described embodiments in preventing overheating of the distribution tube and the consequent flashback of the flame from the combustion zone into the tube. Therefore, line burners employing small tube diameters and insulating linings are especially useful in applications where the burner is to be located in an extremely high temperature environment. The same advantages are obtained when line burners having insulated, small diameter distribution tubes are incorporated in infrared generators in accord with the principles of the present invention.

Both the line burners and the infrared generators as disclosed herein, in addition, are simple and are easily produced by mass production techniques. In all forms of the present invention except that of FIGURE 17, they are constructed almost entirely from sheet metal and there are no castings, no machining required, no ceramic parts to handle, and a minimum of welding and other assembling steps to perform. Moreover, the sheet metal components are of simple configuration and can be readily formed.

Furthermore, the novel line burners and infrared generators disclosed herein are extremely flexible and are adapted to many diverse types of industrial applications, to area heating, both indoors and outdoors, and to incorporation in heating plants such as warm air furnaces and boilers.

Other important advantages of the present invention will be fully apparent to those skilled in the art to which it pertains from the foregoing detailed description of exemplary embodiments of the invention.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and Patent is:

1. In an infrared generator of the combustion type:

(a) a fuel-air mixture distribution tube having opposed parallel flanges forming a passage communicating with the interior of said tube;

(b) an orifice structure between said flanges and extending substantially the length thereof;

(c) a radiant grid of substantially the same length as said flanges, said grid having a flat perforate face, imperforate integral side walls normal to said perforate face, and integral, imperforate rear wall members extending at right angles to said side walls toward each other and having a slot therebetween substantially equal in width to the passage betweenthe distribution tube flanges; and

(d) means fixing said radiant grid to said distribution tube with the free edges of said flanges and thefree edges of said rear wall members juxtaposed and the perforate face of said radiant member at right-angles to said flanges and spaced from the free edges thereof.

2. The infrared generator of claim 1, together with insulating members of substantially the same length as saiti1 radiant grid fixed to the inner surfaces of said side wa s.

3. In an infrared generator of the combustion type:

(a) a fuel-air mixture distribution tube having opposed flanges forming a passage communicating with the interior of said tube;

(b) an orifice structure in said passage between said flanges;

(c) a radiant grid of sheet metal formed into a tubular configuration extending substantially the length of said distribution tube, said grid having an apertured infrared radiation emitting front wall portion, a nonapertured angular side and back wall portions, and integral flanges extending toward each other from opposite edges of said back wall and forming a slot therebetween substantially equal to the width of said passage between the distribution tube flanges; and

(c1) fastening means attaching one of said grid flanges to each of said distribution tube flanges with the grid flange free to move longitudinally of the tube flange but restrained against movement toward and desired to be secured by Letters 15 away from the latter and with the interior of said grid communicating with the passage between said distribution tube flanges.

4. A gaseous fuel line burner, comprising:

(a) a fuel-air mixture distribution tube having opposed flanges forming a passage communicating with the interior of said tube and extending substantially the length thereof, the length of said passage being substantially greater than the wall thickness of said tube;

(b) an orifice structure between said flanges;

(c) locating means preventing movement of said orifice structure laterally of said flanges but permitting movement of said orifice structure longitudinally of said flanges, said locating means comprising fastening members extending through and between said flanges and spanning the passage therebetween, said fastening members abutting the side of the orifice structure nearest the interior of said tube and thereby locating said structure relative to the interior of said tube, said locating means further including members bridging the flanges and fixed thereto on the side of the orifice structure opposite the fastening members and locating the orifice structure relative to the end of the passage between the distribution tube flanges most remote from the interior of the tube; and

- (d) clamping means including said fastening members operable to prevent all movement of said orifice structure relative to said flanges.

5. In an infrared generator of the combustion type:

(b) an orifice structure between said flanges;

(c) a radiant grid extending along substantially the length of said flanges and forming a combustion chamber around said orifice structure;

(d) reflector means including a pair of reflectors extending substantially the length of said radiant grid and located on opposite sides thereof;

(e) fastening members extending between and through said flanges and said reflectors at intervals along said flanges;

(f) clamping means associated with said fasteners for clamping said flanges against said orifice structure to retain said structure between said flanges;

(g) means supported by said fastening members for fixing said radiant grid relative to said flanges; and

(h) retainers on said fastening members for retaining said reflectors thereon.

6. In an infrared generator of the combustion type:

(a) a fuel-air mixture distribution tube having opposed 16 flanges forming a passage communicating with the interior of said tube;

(b) an orifice structure in said passage between said flanges; I

(c) a radiant grid of sheet metal formed into a horseshoe configuration extending substantially the length of said distribution tube, said grid having an apertured infrared radiation emitting body and integral flanges extending toward each other from opposite edges of said body; and

(d) fastening means fixing one of said grid flanges to each of said distribution tube flanges with the interior of said grid communicating with the passage between said distribution tube flanges, said fastening means comprising:

(e) fastening members extending between and through said flanges at intervals along said distribution tube; and

(f) inner and outer grid clips journalled on each of said fastening members adjacent each of said distribution tube flanges, said inner and outer clips having cooperating legs adapted to embrace opposite sides of the flanges of said grid and cooperating portions adapted to substantially preclude lateral movement of said grid relative to the flanges of said distribution tube.

References Cited UNITED STATES PATENTS 233,389 10/1880 Adams. 1,727,527 9/1929 Thurm 158l16 X 1,733,934 10/1929 Biers -5 126-92 1,978,177 10/1934 Sweet 158113 X 2,443,101 6/1948 Flynn et a1 158116 2,543,688 2/1951 De Coriolis et a1. 15899 2,884,998 5/1959 Taylor 1581 16 2,980,104 4/1961 Patrick et a1 158113 X 3,080,912 3/1963 Winter 158-116 X 3,169,572 2/1965 Constance et a1. 12692 X FOREIGN PATENTS 448,960 6/ 1948 Canada. 651,426 10/ 1928 France. 651,540 10/1937 Germany. 170,641 10/1921 Great Britain. 450,550 7/1936 Great Britain. 462,945 3/ 1937 Great Britain. 512,431 9/ 1939 Great Britain. 904,792 8/1962 Great Britain.

FREDERICK L. MATTESON, J R., Primary Examiner.

Claims

3. IN AN INFRARED GENERATOR OF THE COMBUSTION TYPE: (A) A FUEL-AIR MIXTURE DISTRIBUTION TUBE HAVING OPPOSED FLANGES FORMING A PASSAGE COMMUNICATING WITH THE INTERIOR OF SAID TUBE; (B) AN ORIFICE STRUCTURE IN SAID PASSAGE BETWEEN SAID FLANGES; (C) A RADIANT GRID OF SHEET METAL FORMED INTO A TUBULAR CONFIGURATION EXTENDING SUBSTANTIALLY THE LENGTH OF SAID DISTRIBUTION TUBE, SAID GRID HAVING AN APERTURED INFRARED RADIATION EMITTING FRONT WALL PORTION, A NONAPERTURED ANGULAR SIDE AND BACK WALL PORTIONS, AND INTEGRAL FLANGES EXTENDING TOWARD EACH OTHER FROM OPPOSITE EDGE OF SAID BACK WALL AND FORMING A SLOT THEREBETWEEN SUBSTANTIALLY EQUAL TO THE WIDTH OF SAID PASSAGE BETWEEN THE DISTRIBUTION TUBE FLANGES; AND (D) FASTENING MEANS ATTACHING ONE OF SAID GRID FLANGES TO EACH OF SAID DISTRIBUTION TUBE FLANGES WITH THE GRID FLANGE FREE TO MOVE LONGITUDINALLY OF THE TUBE FLANGE BUT RESTRAINED AGAINST MOVEMENT TOWARD AND AWAY FROM THE LATTER AND WITH THE INTERIOR OF SAID GRID COMMUNICATING WITH THE PASSAGE BETWEEN SAID DISTRIBUTION TUBE FLANGES.