US3151659A

US3151659A - Radiant gas burners

Info

Publication number: US3151659A
Application number: US729153A
Authority: US
Inventors: Leonard E Ravich
Original assignee: Hupp Corp
Current assignee: SCHWANK Inc; Hupp Corp
Priority date: 1958-04-17
Filing date: 1958-04-17
Publication date: 1964-10-06
Anticipated expiration: 1981-10-06

Description

Oct. 6, 1964 E. RAVICH 3,151,659

' RADIANT GAS BURNERS Filed April 17, 1958 2 Sheets-Sheet 1 INVENTOR L EOMi/FO xawa/ BY p w w ATTORNEYS Oct. 6, 1964 L. E. RAVICH RADIANT GAS BURNERS 2 Sheets-Sheet 2 Filed April 17, 19.58

INVENTOR lzo/wwfz wm ATTORNEYS United States Patent 3,151,659 RADIANT GAS BURWERS Leonard E. Ravich, Cleveland Heights, Ohio, assignor to Hupp Corporation, Cleveland, Ohio, a corporation of Virginia Filed Apr. 17, 1958, Ser. No. 729,153 7 Claims. (El. 153-116) This invention relates to gas burners and more particularly to gas burners which have a radiation surface rendered incandescent by the combustion of fuel on or adjacent the surface.

One burner of this type is disclosed and claimed in United States Patent 2,775,294. In this burner 21 gas-air mixture is fed to a distributing chamber, one wall of which is formed by a plurality of perforated ceramic blocks through which fuel and air mixture passes. Combustion occurs on or adjacent the outer surface of the block or blocks and raises the temperature of the outer block surface to a level at which energy in the infra-red spectrum is emitted. The efficiency of burners of this type is dependent to a large extent upon the temperature to which the outer surface of the ceramic block is raised with a given gas input since, as is well known, the emission of radiant energy increases geometrically with an increase in temperature of the radiating surface.

Many expedients have been suggested in the past to increase the efficiency of such burners and specifically to raise the temperature of the radiating surface without appreciably increasing the rate at which fuel is supplied to the burner. One of these expedients involves the positioning of a screen in front of the radiant surface of the blocks. Use of the screen has produced a substantial improvement in certain performance characteristics of the burner by substantially raising the temperature of the face of the burner blocks. However, the increase in temperature efiected by this prior construction is accompanied by the production by the burner of carbon monoxide in amounts which are considerably in excess of the limits established by the American Gas Association for safe operation. The reason for the production of the excessive amount of carbon monoxide in the prior burner has not been fully known prior to the present invention. However it has now been discovered that the screen produces a slight back pressure which reduces the amount of primary air available for combustion at the surface of the tile.

Accordingly, despite the increase in overall eficiency of the burner effected by the installation of the screen and despite the other advantages which are to be derived from. the use of screens such as protection of the burner blocks against mechanical damage, nevertheless such screens can be used only when the burners are installed out-of-doors or in other areas where the ventilation is sufhcient to meet safety standards.

With the foregoing considerations in mind, it is a principal purpose and object of the present invention to provide improved screen constructions for gas-fired radiant burners which are effective to overcome the disadvantages of prior screen constructions by increasing the radiation efficiency without decreasing the combustion efficiency.

It is a further object of the present invention to provide novel gas-ired radiant burners, including novel screen constructions which effectively increase the radiant energy emitted by the burner for a given gas input, which are completely safe and produce carbon monoxide in amounts which are Well below the limits set by the American Gas Association for safe indoor operation.

It is a further and more specific object of the present invention to provide improved screen constructions for radiant gas fired burners and means for detachably supporting the screens on the burners.

3,l5l,659 Federated Get. 6, 1964 "ice There are many applications where it is desired to provide burners with a means of regulating the infra-red radiant energy emission from the ceramic surface. A reduction of gas flow into the burner venturi by a valve will cause a decrease in ceramic surface temperature with a resulting decrease in radiant energy emission. However, the decrease in gas flow will cause an accompanying decrease in air aspiration. An inefficient combustion reaction results with an increase in the carbon monoxide in the products of combustion greater than accepted limits of toxicity. In accordance with a further aspect of the present invention, screen assemblies are provided at the front face of the burner blocks along with a means for adjusting the spatial relationship of the screens and the burner face. The infra-red emissivity from the burner increases as the screen is set closer to the burner face and decreases as the screen is moved away from the burner face. All this is accomplished without a change in input gas pressure, air aspiration, or an increase in carbon monoxide in the products of combustion.

Another object of the present invention is, therefore, to provide improved gas fired radiant burners having a means for changing the position of the screen assembly at the front burner face to render the burner capable of adjustment of infra-red emission.

In certain app ications where it is desired to operate the burners with a very high surface temperature, the radiant blocks become heated to the point where flashback may occur. In accordance with another aspect of the present invention, screen assemblies are provided at the rear face of the blocks which receive heat from the rear face of the blocks and dissipate it through the burnerv housing thus maintaining the temperature of the rear face of the radiant blocks at a point below that at which flashback can occur.

It is thus a further object of the present invention to provide improved gas-fired radiant burners having novel screen constructions positioned opposite each of the faces of the burner blocks to render the burner capable of high temperature operation with an efiiciency and safety not heretofore obtainable.

Additional objects and advantages will become ap parent as the description proceeds in connection with the accompanying drawings in which:

FIGURE 1 is a front elevation of a burner constructed in accordance with the present invention; and

FIGURE 2 is an end elevation of the burner of FIG- URE l; and

FIGURE 3 is an end elevation of the burner of FIG- URE 1 provided with a means of screen adjustment; and

FIGURE 4 is a side elevation of the burner of FIG- URE 1 provided with a means for screen adjustment; and

FIGURE 5 is a front elevation of a component of burner shown in FIGURES 3 and 4 designed to provide two degrees of infra-red emissivity; and

FIGURE 6 is a front elevation of a component of burner shown in FIGURES 3 and 4 designed to provide three degrees of infra-red emissivity.

As stated above, the main burner structure may be the same as that disclosed and claimed in Patent No. 2,775,294. Accordingly, the burner will be described herein only to the extent necessary to a full understanding of the present invention, reference being had to the aforesaid Patent No, 2,775,294 for other details of construction.

The burner housing 2%) is metallic and is preferably of one-piece cast construction and comprises bottom, side and

end walls

22, 24, and 26 respectively which enclose a distributing chamber 28 of generally rectangular form. A boss 30 formed on one end of the housing carries a fuel nozzle assembly 32 which is supplied with gas through a suitable supply conduit 34. As more fully explained in Patent No. 2,775,294, the gas issuing through nozzle 32 entrains a flow of air which is delivered to the interior of the chamber 28 formed by the

walls

22, 24, and 26. The open top of the burner is closed by a plurality of burner blocks 36 which are secured to the burner housing by screws 38. a

The blocks 36, which are preferably ceramic tiles, are provided with a plurality of small straight passages 40 through which the combustible fuel-air mixture supplied to the distributing chamber passes. Combustion of the mixture occurs on or adjacent the outer surface of the blocks 36, heating the block surface rapidly to a temperature in the neighborhood of 1550 F. at which temperature the surface of the tile becomes incandescent and emits energy in the infra-red spectrum. The outer surface of the tiles in the combustion area reaches its temperature within a very short time and thereafter remains substantially at said temperature.

. It is known that the amount of infra-red energy propagated rises sharply with an increase in the temperature of the outer surface of the tile, particularly above 00 F. In accordance with the present invention, a substantial increase in the equilibrium operating temperature 'is achieved by the provision of a novel screen construction extending over only a part of the face of the burner.

In a preferred embodiment of the invention as shown in the drawings, the screen construction consists of four identical screen strips 42 which extend across the burner from side to side.- At their opposite ends the screen strips 42 extend into inwardly facing U-shaped channel frame members 44 which are mounted by machine screws 46 directly to the housing member 20. The spacing between the channel frame members 44 and the front face of the housing is determined by one or more hex-head nuts 48. The screen strips 42 are held in place by cotterpins 50 which extend through the channel frame members 44. It will be noted that the screens leave a substantial portion of the radiant blocks uncovered. In a typical case the radiant blocks are 1%" wide and the screen strips are 1" wide so that less than of the radiant blocks are covered. The screens are placed about from the burner face. a

A mechanical means for adjustment of distance between screens and burner face is shown in FIGURE 3. Screens 42 extend across burner from side to side. At their opposite ends the screens 42 extend into inwardly facing U-shaped channel frame members 44 which are attached near each corner of the burner housing 20 by springs 56 and machine screws 58. Theminimum spacing-between the screens 42 in channel frame members 44 and the front face of the housing 20 is determined by spacers 60. Well 62 in burner housing 20 permits the use of a longer spring without changing the minimum spacing between the screens and the burner block.

Spacers 64 are properly located on rod 66 so that one will rest on flange 68 of side 24 and the other will rest on the flange of side 26 of burner member20. Rod 66 is of sufiicient length to extend about one half inch beyond each spacer. The spacer and rod assembly is held in pla'ce by placing the ends of rod 66 into holes in brackets 70 which are fastened to the burner housing 20 by machine screws 72.

When sides B and B of spacers 64 are in contact with the flanges of

sides

24 and 26 and the lower surfaces of U-shaped channel frame members 44, the screen will be spaced at an optimum distance from the burner face and maximum emission for any given gas pressure will result. When sides A and A of spacer 64 are in contact with the flanges and U-shaped channels the screen will be spaced at a greater distance from the burner face and a lower surface temperature results.

The spacers may be rotated by means of knob 74 affixed to end of rod 66. Springs 56 are in a stretched condition when sides A and A of spacer 64 are used for adjusting screen height. a When spacer 64 is rotated the tension of springs 56 will pull the screen assembly down until channel frame members 44 and the flanges of burner housing 20 are in contact with sides B and B' of spacer 64.

Preferred dimensions of spacer 64 are one half inch between sides B and B and one inch between sides A and A.

For a three position setting an arrangement such as spacer 76 can be employed in the same manner as described for spacer 64. Preferred dimensions for spacer 76 are one inch between surfaces A and A, five-eighths inch between surfaces B and B and thirteen-sixteenths inch between surfaces C and C.

It has been demonstrated by actual tests that the utilization of partial screen assemblies as described above substantially raises the surface temperature of the ceramic blocks and thus improves the overall efliciency of the burner while at the same time permitting combustion to continue with such efficiency that the percentage of carbon monoxide produced is well within permissible limits. It has been found, for example, that the surface temperature of the radiant blocks can be raised to the neighborhood of 2000 F. or higher and that the limiting factor becomes the resistance of the blocks to deterioration at these relatively elevated temperatures or the tendency toward flash-back. In other cases where a very high surface temperature is not required, the normal surface temperature of about 1600 F. can be maintained with a substantially reduced supply of fuel.

The increase in the surface temperature of the radiant blocks is produced by the fact that the screen absorbs a substantial amount of heat energy from the hot products of combustion as well as from radiant energy transfer from the incandescent ceramic surface to the screen. In a short time the screen approaches the temperature of the ceramic surface. As is well known, the rate of energy transfer or propagation is proportional to the difference in temperature between the transmitter and receiver. Since the screen functions as a receiver for at least a limited portion of the radiant blocks, the rate of energy transferred away from the blocks in this area is substantially decreased and the portion of the block accordingly becomes substantially hotter. While the body of the block at normal room temperature has a very low thermal conductivity, nevertheless the surface of the block at a temperature of 1600 F. or higher has a very high thermal conductivity. The thermal conductivity is sufficiently high at the operating temperature that the creation of hot spots behind the screen is avoided and the entire surface of the tile assumes an equilibrium condition at which the temperature of the surface of the tile is substantially uniform.

While the dimensions and configuration of the screen may be varied to some extent, one screen which has worked very satisfactorily is a Nichrome screen of 5 or 6 mesh placed at a distance of approximately from the outer surface of the radiant blocks.

Alte'rnately, a one-piece variable density screen may be used having a relatively fine mesh, for example 5 or 6' mesh, over the areas roughly equivalent to the area covered by the screen strips 42 connected by areas of relatively coarse mesh. Such a screen would function in the same manner as the separate strips but would afford additional protectionto the blocks.

The substantial increase in the temperature of the outer surface of the radiant blocks which is made possible by the use of screens of the present invention also increases to some extent the tendency of the blocks to flash-back. The invention also comprises novel means for reducing the tendency toward flash-back. In accordance with the invention this is accomplished by utilization of a screen assembly indicated generally at 52 which is spaced from and parallel to the rear face of the burner blocks 10. The screen may be of relatively fine mesh and its mesh may be uniform. The screen is held in place by L-shaped strips 54 which extend around the periphery of the screen and are securely attached to the inner surfaces of the walls of the housing 29 in good heat exchange relation therewith. As indicated above, the rate of transmission or propagation of energy from one body to another is proportional to the difference in their temperatures. Since the screen 52 is maintained at a relatively low temperature which is substantially that of the body of the housing 20, energy is transmitted rapidly from the rear surface of the radiant blocks to the screen. The rate of transfer of energy is sufiiciently high so that the rear face of the burner blocks is maintained at a temperature well below the ignition point of the combustible mixture and the danger of flash-back is effectively eliminated.

From the foregoing it will be apparent that the above stated advantages of the invention have been achieved by the provision of novel screen assemblies which substantially increase the radiating efiiciency of radiant gas burners Without decreasing their combustion efficiency and in which the carbon monoxide produced by the burner is held well below permissible limits and in which the danger of flash-back is eflfectively eliminated.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is 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 desired to be secured by United States Letters Patent is:

1. A gas burner comprising a housing having a chamber therein, perforated burner plate means forming a wall of said chamber, means for introducing a fuel-air mixture into said chamber which passes through the perforations in said burner plate means and burns adjacent the outer surface thereof, frame members, means mounting said frame members in parallel spaced relation with the outer surface of said burner plate means, means resiliently urging said frame members toward said surface of said burner plate means, adjustable means acting in opposition to said resilient means to determine the spacing between said frame members and said surface of said burner plate means, and a plurality of separate wire mesh screen strips carried by said frame members in spaced relation to each other and being disposed in a single plane spaced from and substantially parallel to said burner plate means.

2. A gas burner comprising a housing having a chamber therein, perforated burner plate means forming a wall of said chamber, means for introducing a fuel-air mixture into said chamber which passes through the perforations into said burner plate means and burns adjacent the outer surface thereof, frame members, means mounting said frame members in parallel spaced relation with the outer surface of said burner plate means, means resiliently urging said frame members toward said surface of said burner plate means, a plurality of blocks interposed between said frame members and said burner housing, said blocks having pairs of opposed side surfaces spaced different distances apart, means mounting said blocks for rotation about an axis parallel to the surface of said burner plate means to selectively dispose different pairs of surfaces in engagement with said frame members and said burner housing, and wire mesh screen structure carried by said frame members and having relatively fine mesh portions opposite a portion only of said burner plate means.

3. A gas burner according to claim 2 wherein said wire mesh screen structure comprises a plurality of spaced separate screen strips.

4. A gas burner comprising a burner housing, fiat perforated burner means mounted in said housing to form a continuous wall thereof, the outer surface of said burner means becoming incandescent upon the combustion of a fuel-air mixture thereon, a plurality of fiat, separate wire mesh screen strips, and means mounting said screen strips on said burner housing to dispose said strips in a single plane adjacent said outer surface of said fiat burner means and spaced from and substantially parallel to said outer surface of said flat burner means, said screen strips extending completely across said burner means, said screen strips being effective to raise the temperature of said outer surface of said burner means, and said screen strips being spaced apart from each other sufficiently to permit the flow of combustion products away from said outer surface of said burner means and maintain eflicient combustion thereon.

5. The gas burner according to claim 4 wherein the spacing between said burner strips and said outer surface of said burner means is not more than about of an inch.

6. The gas burner according to claim 4 wherein the area of said screen strips is about 60% of the area of said burner means.

7. The gas burner according to claim 4 wherein said screen strips are each spaced not substantially more than 73 of an inch from said outer surface of said burner means and the area of said screen strips is not substantially more than 60% of the area of said burner means.

References Cited in the file of this patent UNITED STATES PATENTS 994,599 Meran June 6, 1911 1,462,643 Kreutzer July 24, 1923 2,822,285 Hayward Nov. 26, 1935 2,841,133 Schwank July 1, 1958 FOREIGN PATENTS 526,728 Belgium Mar. 15, 1954 494,087 Great Britain Oct. 17, 1938 744,980 Great Britain Feb. 15, 1956 521,503 Italy Mar. 29, 1955

Claims

4. A GAS BURNER COMPRISING A BURNER HOUSING, FLAT PERFORATED BURNER MEANS MOUNTED IN SAID HOUSING TO FORM A CONTINUOUS WALL THEREOF, THE OUTER SURFACE OF SAID BURNER MEANS BECOMING INCANDESCENT UPON THE COMBUSTION OF A FUEL-AIR MIXTURE THEREON, A PLURALITY OF FLAT, SEPARATE WIRE MESH SCREEN STRIPS, AND MEANS MOUNTING SAID SCREEN STRIPS ON SAID BURNER HOUSING TO DISPOSE SAID STRIPS IN A SINGLE PLANE ADJACENT SAID OUTER SURFACE OF SAID FLAT BURNER MEANS AND SPACED FROM AND SUBSTANTIALLY PARALLEL TO SAID OUTER SURFACE OF SAID FLAT BURNER MEANS, SAID SCREEN STRIPS EXTENDING COMPLETELY ACROSS SAID BURNER MEANS, SAID SCREEN STRIPS BEING EFFECTIVE TO RAISE THE TEMPERATURE OF SAID OUTER SURFACE OF SAID BURNER MEANS, AND SAID SCREEN STRIPS BEING SPACED APART FROM EACH OTHER SUFFICIENTLY TO PERMIT THE FLOW OF COMBUSTION PRODUCTS AWAY FROM SAID OUTER SURFACE OF SAID BURNER MEANS AND MAINTAIN EFFICIENT COMBUSTION THEREON.