US2103365A - Gas burner - Google Patents

Description

' F. HESS GAS BURNER Dec. 28, 1937.

Filed March 1 INVENTOR fififia #555 ATTORNEY Patented Dec. 23, 1937' PATENT oFF cE GAS BURNER Fred Hess, Tredyii'ryn Township, Chester County,

Pa., assignor to The Selas Company, Philadelphia, Pa., a corporation of Pennsylvania Application March 1, 1934, Serial No. 713,432

7Claims.

The present invention relates to gas burners and particularly to gas burners of relatively large unit capacity employed in burning a premixed combustible mixture of gas and air. The general object of the invention is to provide improved gas burners characterized by their mechanical simplicity and relativelylow cost of manufacture, and by their operative efiectiveness, and in particular by their capacity for the maintenance of desirable combustion conditions with a wide variation in the supply rate, and consequently in the supply pressure, of the gaseous mixture burned.

The invention is characterized by the inclusion in the burner structure of a plate like body of ceramic material, forming a burner wall interposed between an air and gas mixture supply chamber and the space in which combustion occurs, and formed with a multiplicity of burner channels or orifices leading from said chamber to said space, said channels being of an aggregate cross sectional area which is relatively large in comparison with the cross sectional area of their walls and the latter being thin enough to be cooled by the air and gas flow through them sufliciently to prevent combustion from occurring within the channels as a result of the high temperatures prevailing at the combustion space side of the body; i The various features of novelty which char- 30 acterize my invention are pointed out with particularity in the claims annexed to and forming Fig. 1 is a perspective view of refractory burner elements;

Fig. 2 is a, partial section of a burner including the elements shown in Fig. 1;

Fig. 3 is a section of a portion of a furnace wall 5 including a burner opening and burner provisions associated therewith;

Fig. 3A is a view similar to Fig. 3 but on a smaller scale and showing more of the furnace.

wall; and 50 Fig. 4 is a partial section on the line 4-4 of Fig. 3.

In the drawing and referring first to the construction shown, in Figs. 1 and 2, A represents a burner of ring form and B represents a burner 5,, element in the form of an apertured with its peripheral surface fltting within the ;wall of the axial passage A through the member A, both elements being formed of refractory ceramic material. As shown in Fig. 2, the axial passage A is enlarged adjacent one side of the member A 5 to provide a conical suriace A engaged in the assembled burner, by a conical enlargement B at one end of the peripheral portion of the disk member B. The parts A and B are held in a metallic burner portion comprising two annular 10 members 0. and D. The member 0, as shown, is

in the form of a cylinder, with an inturned flange C at its upper or combustion space end. The member A flts within the cylindrical portion 01' the member C and has a marginal portion of its 15 upper side in engagement with the end flange C being held in place by the member D which en-- gages the underside'of the member A directly or indirectly through .the member B, which is engaged at its underside and directly supported 2ov by the member D. As shown, the member D fits within the lower end of the cylindrical portion of the member C and the parts C. and D are normally held in their relative positions shown in Fig. 2

' in any suitable manner. When the burner is vertically disposed, as shown in Fig. 2, the member D may serve as a support forthe members A, B and 0, all of which may be gravitationally held in place on the member D. As shown, in Fig. 2, the member is shown as supported by a combustible mixture supply chamber member in the form of a pipe E which has its upper end received in a socket D formed in the underside of the member D.

In the burner shown in Figs. 1 and 2, the major portion of the combustible mixture supplied through the tubular element E passes upward from the latter through distributed burner orifices 38 formed in the member B, but a portion of the gas supplied passes to the combustion space side or the member A through passages between member A. The fuel mixture discharged through the groovesA ignites and forms pilot flame jets which tend to maintain the'ignition of the flame jets extending from the discharge ends of the The member A in respect to its relation to the members B and C an in respect to the form of its surface portions djacent those members, is not claimed as novel herein, but forms part of the subject matter disclosed and claimed in my Patent No. 1,995,122, granted March 19, 1935. That patent discloses and claims a burner structure differing essentially from that shown in Figs. 1 and 2 herein only in that it omits the member B disclosed herein but not disclosed in said patent. It is to be noted, however, that the internal diameter of the passage A of the burner disclosed herein may be and ordinarily. is substantially greater than the maximum permissible internal diameter of the central axial passage of the member disclosed in said patent which is like or analogous the member A disclosed herein.

While it is advantageous in some cases to employ the member A'in conjunction with the member 13, as shown in Figs. 1 and 2, it may be omitted in other forms of the present invention and is not employed in the form of the invention shown in Figs. 3, 3A and 4. The burner shownin those figures comprises a member BA of ceramic refractory material which may beidentical in form with the member B, but as shown is formed with a eripheral collar or rib B presenting a radial surface for engagement with an inturned flange portion of a member CA which may be made of ceramic material or of suitably refractory metal and has internal surfaces fitting snugly about the body of the member BA and about the peripheral surface of its ribportion B As shown, the member CA is embedded in the'refractory material comprising the wall F of a furnace chamber formed with a b er opening or throat F, the peripheral surfa e of which is in the form of a truncated throat with its smaller diameter end terminating at the upper side of the member BA. The latter is shown as held in place within the member CA by a metallic burner body DA extending about the wall F and having a peripheral flange engaging the metallic wall member I at the outer side of the wall F.

In the intended operation of the burner shown in Figs. 3, 3A and 4, all of the air and gas mixtures pass from the supply chamber DA to the combustion space formed by the throat F through the burner channels or orifices B in the member BA, and the wall surrounding the throat F becomes highly heated, and the temperature conditions within the throat are -ordi- B and BA should be kept relatively small in cross section and be closely spaced so that substantially all portions of their walls are relatively thin. To suitably approximate uniformity in thickness in the walls between'the channels and thereby minimize the maximum wall thickness,

the channelsare advantageously made polygonal in cross section and so relatively disposed that each flat side of one channel is parallel or'ap proximately parallel to the flat side of an adjacent channel. Fuithermore the flat sides of the p lygonal channel outline should be numerous enough to avoid sharp internal chan el corner which would be difllcult, if not practically impossible, to properly form with an ordinary ceramic moulding operation. In view of the practical requirements, it will thus be apparent that the hexagonal channel cross section illustrated in Figs. 1 and 4 is especially desirable.

The channels B should be small in cross section and have thin walls to prevent combustion within the channels without requiring a higher gas velocity than is practically desirable, at least, under certain conditions. Combustion within the channels B is inevitably destructive of the channel walls with those walls formed of any material practically available for the purpose. Furthermore the conditions under which combustion is initiated in the outlet ends of the channels, if maintained, will result in. a progressive movement of the combustion zones, and their destructive eifects to the inlet ends of the channels. The explanation of what has just been said is found in certain operating conditions and phenomena to which reference will now be made.

When a cold combustible mixture is passed into a channel leading from a combustible mixture supply chamber or space, to a space in which combustion should occur, the mixture stream flowing through the channel will ignite and burn as soon as it is heated to the temperature of ignition. The point along the length of the path of flow of the stream at which the ignition temperature is reached depends upon the velocity of the stream and the heating actions to. which it is subjected. The heating action to which the stream within the channel is subjected is directly due in part to the heat generatedby the portion of the stream which is burning, but -is largely due to the absorption of heat by thecombustion space and channel walls and its transfer by radiation and contact to the mixture of the heat so absorbed. The wall of the channel proper whether formed of good heat conducting material or of poor heat conducting material, would inevitably become hot enough at its combustion space side to ignite the mixture flowing through the channel, but for the wall cooling effect of the,

mixture stream.

That eflfect depends upon and'increases with the velocity of the stream. It is conceivable, for examplejthat if the burner shown in Fig. 2 were modified by the omission of the body B, with a certain high gas velocity through the axial passage A of the member A combustion would not occur within the passage A even if the latter were as large as three or four inches in diameter, but with any such diameter, combustion would inevitably occur within the passage A on some reduction in the gas velocity, and a further reduction in the gas velocity would result in ignition within the metallic supply pipe E, if the diameter of the latter were comparable with that of the passage A.

In the practical use of burners of the kind shown and described, a substantial variation in the rate of fuelconsumption and consequently in the fuel gas velocity through burner channels is essential in many cases.- In some practical uses of such burners, it is desirable to .vary the rate of gas supply to the burner from a maximum or full load rate to a rate which is not more than 5% of the full load rate. In practice, this means that the supply prasure of the combustible mixture may be varied from a maximum of 20 pounds per-square inch or so to a minimum of something like 1 pound per square inch. With the burner arrangements shown in Figs. 2 and amass! 3, and with the diameter a: the disk B or BA v as great as 12 inches or more, it has been found possible to vary the rate of combustion from the full load rate to of the full load rate by a suitable change in the pressure at which the gas is supplied, without causing combustion within the channels B in a burner in which the distance between each opposing pair of fiat sides of each channel B is about one-fourth of an inch or a little less. With the member B omitted from the burner shown in Fig. 2 and with the diameter of the axial passage A as small as one inch, ignition within the channel A would occur on a reduction in. the gas velocity through the channel to one-- third or thereabouts of what would be a maximum full load velocity through the channel. The actual permissible minimum velocity through such a channel, or through the channels 3* of the burner shown in Figs.*--2 and 3' depends somewhat, as those skilled in the art will understand, upon the character of the gaseous mixture. mixture includes as its fuel element a relatively free burning gas such as ordinary town gas or Water gas, the minimum permissible gas velocity will be higher than if the fuel element is a less freely burning gas such asnatiiral gas, or a butane gas mixture.

A reduction in the thickness of the walls of the V channels B directly reduces the heat absorption by the body B or BA, by reducing the extent of the surfaceof thebody absorbing heat by radiation and by contact with hot gases at the combustion side of the body. A decrease in the amount of heat so absorbed, decreases the amount of heat conducted to the inner surface of each channel B and which must be absorbed by the gas flowing through the channel, if the temperature of the channel wall surface is to be kept below the ignition temperature. The eifectivd channel wall cooling action of the gas-and air moving through the channels B thus requires the channel walls to be thin. In a preferred construction of the kind illustrated, the aggregate cross sectional area of the multiplicity of side by side burner channels exceeds the aggregate cross sectional area of the walls between the channels, and with the channels all similar in cross section and spaced uniformly as shown, the cross sectional area of each channel thus exceedsone half the aggregate cross sectional area of the wall between said channel and the adjacent channels.

The formation of the channelled .burner'wall members B and BA of Figs. 2 and 3 of ceramic material instead of'metal is fundamentally im-' portant because the heat conductivity of ceramic material is much less than that of available met- 7 als, and a decrease in the heat conductivity of the burner channel walls correspondingly reduces the amount'of heat which must be absorbed by the gaseous streams moving through the channels to prevent their walls from becoming hot enough to ignite the streams within the channels. The formation of the channelled wall forming members of ceramic material is practically desirable also because of the relatively low cost of manhfacturing them as compared, for example,-with the formation of such members by drilling holes through metal plate-like blocks. The channelled burner wall members of suitable ceramic material may be formed with their channels small enough and the walls between them thin enough to meet ordinary practical requirements, by following ordinary and relatively inexpensive methods of moulding ceramic bodies. If it were attempted to use a metallic body in lieu of a ceramic If that body in a burner wall member serving the purposes of the bodies B and A, by making the burner channels so small in diameter and separated by of the relatively high heat conductivity by those walls, the cost of drilling the multiplicity of fine channels would be unduly expensive. and the individual channels would be scsmall as to greatly aggravate channel clogging troubles.

Moreover, when the channels in bodies of ceramic material become clogged by deposits from the fuel or products of combustion, or by solder when the burners are used in soldering machines, or become clogged as a result of some other condition, of use, it is ordinarily possible to thoroughly clean the channels when from time to time such cleaning becomes necessary or desirable by heat ing the bodies in a suitable furnace to burn or melt out the clogging material in the clogged channels, whereas to clean out clogged channels in bodies formed of metal, would ordinarily. require an expensive re-drilling operation.

Aside from the advantages'mentioned above for dividing the burner port area into a multiplic-' ity of burner channels of relatively small individual cross sectional area, there is a further advantage in that more'eflicient combustion is obtainable when a given amount of gas is burned in a number of small streams instead of in a single large stream. This increase in emciency may be explainable in part, at least, by the greater gas turbulency in the case of the plurality of small streams than in the case of the single larger stream. In any event less excess oxygen is required for complete combustion of a given amount of gas when the latter is burned in a. plurality of small streams than when burned in one or more large streams.

In the practical use of the invention, it has been found possible to operate a burner including a burner body like the bodies B and BA with a variation in the load or burner rate substantially greater than is practically possible with any other burner heretofore known and capable of practical operation with the same full load capacity.

While in accordance with the provisions of the statutes, I have illustrated and described the best form of embodiment of my invention now known to me, it will be apparent to those skilled in the art that changes may be made in the form of the apparatus disclosed without departingfrom 7 such thin walls as to suitably minimize the effects the spirit of my invention as set forth in the appended claims and that in some cases certain features of my invention may be used to advantage without a corresponding use of other features.

Having now described my invention, what I claim as new and desire to secure by Letters Pat- I cut is:-

l. A plate-like gas burner wall member of ceramic material formed with a multiplicity of side by, side burner channels of small cross section extending through it and separated from one IrU -ceramic material formed with a multiplicity of side by side burner channels of small cross section extending through it and each of polygonal cross-section with the adjacent fiat sides of adjacent channels approximately parallel and separated from one another throughout their lengths by a wall relatively thin in respect to the crosssectional area of the channels.

3. A plate-like gas burner wall member of ceramic material formed with a multiplicity of side by side burner channels of small cross section extending through it and each of hexagonal crosssection with the adjacent fiat sides of adjacent channels approximately parallel and separated from one another throughout their lengths by a wall relatively thin in respect to the cross-sectional area of the channels.

4. A plate-like gas burner wall member of ceramic material traversed by a multiplicity of side by side burner channels of small cross section separated by walls, the average thickness of each wall being less than the average transverse dimension of a channel.

5. A burner for a combustible mixture of air.

and gas comprising a supply chamber for said mixture and a wall member separating said chamber from a combustion space and consisting of a plate-like body of ceramic material formed with a multiplicity of burner channels of small cross section leading from said chamber to said space and separated from one another by walls relatively thin in respect to the average cross sectional area of adjacent channels whereby temperatures within said channels are maintained below the ignition temperature of said mixture with a rate of mixture flow through said channels varying substantially between a permissible maximum and a minimum.

6. A burner for a combustible mixture of air and gas comprising a combustion chamber having refractory walls one portion of which is formed with a multiplicity of side by side channels for the passage ofa combustible mixture of air and gas into said chamber, and said channels being of small cross section and separated by walls relatively thin in respect to the average cross-sectional area of adjacent channels whereby there is maintained atemperature above the ignition temperature of said mixture in said chamber and temperatures within said channels below said ignition temperature with a varying rate of flow.

7. A plate-like gas burner wall member of ceramic material traversed by a multiplicity of side by side burner channels of an aggregate cross-sectional area throughout their lengths exceeding the aggregate cross-sectional area of the walls between the channels in the same plane, said channels being similar to one another in cross-sectional area and uniformly spaced in said member.

FRED HESS.

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