US2260166A - Fuel burner - Google Patents

Description

,tention tip which includes Patented Oct. 21, 1941 UNITED STATES PATENT OFFICE FUEL BURNER Frank '1. Cope, Salem, Ohio, assignor to The Electric Furnace Company, Salem, Ohio, a

poration of Ohio Application June 9, 1938, Serial No. 212,764

- 7 Claims. (Cl. 158--99) The invention relates to fuel burners and more particularly to a burner for discharging a premixed mixture of fuel and air into and burning the same in a heating or heat treating furnace.

In certain types of heating and heat treating furnaces, it has been found desirable if not necessary to use burners which burn a premixed mixture of gas and air supplied to all the furnace burners from a manifold or manifolds, into which manifold or manifolds the gas-air mixture in the desired proportions is introduced. This involves certain hazards because the premixed gas-air mixture delivered to the manifold or manifolds and thence to the burners, is explosive in character and the individual burners must be so constructed and operated that explosions due to "flash-back will not occur. I

On the other hand, modern heat treating furnace design requires a flexibility of operation for any given furnace installation in order that the same'may be used for either high or low temperature work during either long or short material heating cycles. This necessitates a fuel burner construction which has a high turn-down capacity for=burning say as much as twenty or central aperture, several designs of the same being available. However, these types of burners only have a turn-down ratio of about 7 to 1.

The figures given with relation to the turndown ratio ofprior art burners are, average and approximate as they are subject to variation de- I proximately 7 to 1 and are wholly inadequate-or more times as much fuel at high flow or pressure as is burned at low flow or pressure. Such a burner would be termed as having a 20 to 1 tumdown ratio or capacity.

Any given mixture of gas or fuel and air has a certain velocity of flame propagation and when the mixture is burned from a burner nozzle, if that velocity is exceeded by a certain amount, at high pressures and rates of flow, the flame leaves the nozzle and blows out. If the velocity is diminished below a certain amount, at low pressures or low rates of flow, the flame may flash back into the supply conduit.

Pre-mix burners have been used including a nozzle having a large central hole through which the fuel-air mixture is discharged into a refractory burner tunnel, but such burners have a tumdown ratio of only about 4 to 1 and will blow-off at a pressure of about 10 inches of water.

Pre-mix burners have also been used, which include a nozzle having a multiplicity of small holes therethrough parallel to the center line of the burner and which are particularly adapted for low pressures or low rates of flow, but only have a turn-down ratio of about 6 to 1.

The single hole pre-mix burner has been modified to increase'its turn-down ratio and also to raise the blow-off point by providing a flame rea plurality of small holes discharging from the unsuitable for operation where a burner having a' turn-down ratio of 20 to 25 to 1 is required.

These circumstances have accordingly necessitated materially increased installation and operating costs for providingadditional burners for high or fast heating and for providing for cut-' ting out some of the burners for low or slow heating in any given furnace installation where flexibility of operation is desiredor necessary.

Accordingly, it is a general object of the present invention to provide a pro-mix fuel-air burner which has a tum-down ratio of the order of 20 or more to 1.

It is a further object of'the present invention to provide a pre'-mix fuel-air burner which not only has a large turn-down-ratio, but which will operate satisfactorily at high pressures without blowing off, and which will operate satisfactorily at low pressures without flashing back.

Moreover, it is an object of the present invention to provide an improved pilot construction for a fuel burner, which is especially adapted for use with a burner having a high turn-down ratio.

Moreover, it is an object of the present invention to provide a pre-mix fuel-air burner construction which tends to eliminate the causes of flash-back orback firing. Likewise, it is an object of the present invention to provide a pre-mix fuel-air burner construction which tends to eliminate the causes of blowing off.

And finally, it is an obiectiof the present inventlon to generally improve the construction and operation'of pre-mix fuel-airburners and pilots,

burner around t and to generally increase the flexibility of oper ation-offuel-air fired-heating-and heat tr wall shown in-I'igJ:

' located at theleft hand of-the wall 5'.

furnaces.

I s,aeo,iaeeating; These mime objects slay be obtained by the elements, combinations, arrangements I and constructions constituting the present inven tion, a preferredembodimentof which isshown in the accompanying drawing and .is'hereinaft'er described in detail and claimed, and which may .;be-stated' in. general-terms as includingin com- .bination, a furnace wall having an. opening I thereima burner housing mounted insaid wall I opening, a preferably refractory burner tunnel e blockhavinga flaring preferably conical opening; therethrough mounted in; said wall opening and 1 burner housing, a burner nozzlemountedinsaid housing and tunnel block having a chamber '1 therein connected with a conduit for supplying a fuel-air mixture thereto and-having a plurality ofnozzle holes communicating between the chamber and saidtunnel block opening,. the axes of all: oi'isald holes being angled so asto intersect the-conical-tunnelwall and being all formed preferably asfelements of a cone, a pilot for said.

- burner releasably mounted on said burner housingincluding a tip, and a preferably curved pas sage formed in the tunnel block communicating with said pilot tip and with said tunnel-block holes intersect Inthedrawing. Figure 1 is a fragmentary sectional view taken [months line ll,f1 ig'. zrmustmti g the im-' proved fuel burner construction in the wall .of a

i heating or heat treating furnace;

2 is an elevation of certain of the parts Fig. 3 isan enlarged fragmentarysectional view of parts .of the burner nozzle and tunnel block shown inFig. 1;-'and 4 is a sectional .vlew on line burner nozzle looking jin'the direction of the refer -to similar' parts Similar numerals throughout the varicusflgui'es or the drawing.

burner 1 opening, the place .of communication of said pasl sage with said tunnel block opening; preferably being in or adjacent to the circumferential zone or region where the axes of the burner nozzle (1170181 18 tunnel wail II at 39.

' The improved burner is shown inl'ig; 1 where-- in a wall of-a heating or heat treating furnace-is indicated at .I, and the'same is providedwith apreferably' square or rectangular opening [terminating on the inside in a flaring. mouth 1,'which'0pens into the heating chamber The improved vburneris composed generally of a'housing Q, a tunnel bloclr I- and a .noazle II. The housing 8 is p eferably a casting I and includes tubular preferably rectangular side walls-ll into the furnace wall openof the-housing member tubular walls ll.

. The partition wall I!- is' provided with a central preb V erably'rjound Opening l5.

11181-811 mixture 3 Z1810.

. A central. V

including-a preferablycylindrical opening portion l9 formed in the tunnel block 9 aligned with 1 the partition wall opening-Hi5 and the opening portidn 19 extends for' a short distance from the partition wall. It to a region indicated at 29. The central opening in, the burner tunnel block 9 then begins to flare or enlarge in cross section as rees with-the center line oraxis of'the tunnel block 9, tapering from the end Zlof the cy1in-" 'drical opening portion to the the-tunnel block 9.

. The nozzle III is preferably block oylindricainpening portion is. The inner air mixture is supplied from a conduit 21 threaded into nomle ill at .29.- .Theother end of condllitllm'a? be provided Witli SAT 29L A nipple it connected to the otherend of the T 29 and the conical tunnel block p g .capped at I with 8. ight" BlflSSrPlOVidQS 101 j ready cleaningand inspection of the nozzle III.

to a manifold, from which the proper ordesired ner end wall 29 of nonle; is provided Thein with a series -ofsmall holes 31, which form theonly communication between the nozzle cham- 2t and the fiared -tunnel biockopening 2|.

The axesof holes 31 all diverge from the center or axis of the burner nozzle III ona greater taper than the taper ofthe wall 2| of the burner tunnel opening;-so that the axes of all of the holes 91, indicated by dot-dash line: at it, intersect the The axes-of holes a are preferably formed elements of a cone. preferably on about a 15 de-.

gree angle. The angle of divergence of the tunnel opening wall 2| and the angle of divergence of the axes of holes 91 may of course lvarysome- --what from the-particular figures given so long -'ence of thejtunnel opening so that the axes of the holes intersect the tapered tunnel opening j as the angle of divergence of the nozzle-holes is substantially create: than the angle of divergsurface'intermediate the ends thereof.

a pilot .40 is. flexibly removably and alignably mounted by a-spring device with its tip 42- communicating through opening 43 in burner block partition wall ll witha passage 4|. and'the pilot fill is prelerably parallel with and-b10861? The tunnel block 9 is preferably a' refractory f lblock preferably having outer rectangular or square sin-faces l9 fitting within and cemented to the walls forming. the furnace openi 0. said walls It also fitting at 11 within the tubular hous lug walls II, with the outer end of the refractory block .9 abutting at I 8 against thehousing partl scribed.

' 1 1 8 is preferable for adjacent tothe. nozzle '10. The passage as is preferably curved from opening 49 to. a place of. muliicflflon j with. diverging tunnel openerably-quite' closeto burner nozzle ill and in or adia m tothe annu ar zone 99 where the axes w l of the-nozzles intersect thewall of diverging openingIi-for reasons tobe-later detunnel Passage is shown as curved,-which smoothness of flow, but

it is understood that the same may bestraight opening is provided the block 9 furnace end-22 0f v v a casting having a v cylindrical wall 23 terminating at one end in an outturned flange 24 secured by suitable boltsill .to housing 8,"with the wall 23 cemented and sealed in the housing opening 15' and. tunnel is supplied to the burnernoz- Theplace of cornrnunicatitm ll is'pref- I from opening 43 to zone or region 45. The place of intersection 45 between passage 44 and diverging tunnel opening II should be closer to nozzle ll than to the furnace end of tunnel block 22, because it is important to reduce the length of the passage 44 as much as possible and also to bring the pilot name close to the burner nozzle.

The pilot 40 may communicate through flexible conduit 46 with any suitable source of fuel. The particular pilot construction assembly and mounting shown but not claimed herein, is

claimed in my copending application flied of even date herewith, Serial No. 212,765.

In operation, a premixed fuel-air mixture, preferably a mixture of natural or artificial gas and air, is supplied from the manifold to the burner nozzle I and this mixtureis discharged from the nozzle chamber 26 through the divergent holes 31 to impinge against the sides of the diverging tunnel opening 2|. Combustion takes place at the point where the velocity of the fuelair mixture is slow enough somewhere within the diverging tunnel opening 2!; and when the-burner tunnel block is heated up, the flame begins in the vicinity of the zone 39 where the mixture streams impinge against .the diverging tunnel opening wall 2|.

Tests performed on a burner threaded for a 1" pip having a 1 outside diameter and having ten diameter holes on a 1%" circle at the external face, each at a angle, such as shown in the accompanying drawing, indicate,

when operating with a fuel-air mixture under high presure and flow, that the burner does not blow off until a pressure of 5% inches of mercury is reached with a cold tunnel block 9,-- or 6 inches of mercury with a hot'tunnel block 9. The burner burned in an exceedingly satisfactory and efllcient manner with a pressure of 5 inches of mercury and a flow of 3240 C; F. H. of a premixed natural gas and air mixture calculated to support perfect combustion. With the same mixture, the burner was throttled down to a flow of 20 C. F. H. with a cold tunnel block 9 and 32 C. F. H. with a hot tunne. block 9 without going out or flashing back.

These conditions indicate a turn-down ratio of 3240 /20,or 162 to 1; however, if a minimum flow were taken at 40 C. F. H. the turn-down ratio would be 81 to 1.

high turn-down ratio. This principle is incorporated in the present burner by directingthe angular or divergent holes 31 against the wall2l of the expanding or diverging burner tunnel opening. Thus the velocity of the premixed gas and air streams is slowed down and the premixed gas and air streams are the tunnel wall, so that combustion takes place at and adjacent to and within the surfaces of the diverging tunnel opening 2|.

This is evidenced by a red or white hot ring around the tunnel opening after the same has become heated, generally in the region 39 of intersection of the axes of holes 31 with diverging surface 2|; and this red or white hot tunnel surface tends further to promote combustion and tokeep the burner lighted even at low pressures and flows.

As previously stated, it is desirable to locate the end of pilot passage 44 somewhere adjacent to the region which becomes red or white hot when the burner is burning so as to provide additional means for keeping th burner lighted at either low or high flows.

As has been described above, the particular pilot passage arrangement and location is especially advantageous in connection with the particular burner nozzle shown and claimed herein, yet the particular pilotpassag 'arrangement is equally useful in connection with other types and kinds of fuel burners.

Accordingly, the present improvements provide a pre mix burner construction which avoids the difliculties present in prior structures, which has a turn-down ratio of the order of 20 or more to 1, which operates satisfactorily at high pressures without blowing off and at low pressures without flashing back, which tends to eliminate the causes of flashing back and blowing off, which incorporates an improved pilot construction, and

which generally increases the flexibility of operation of fuel-air fired heating and heat treating- It is to be understood that the above tests were erating pressures or flows by only utilizing small nozzle openings extending a considerable distance through a heavy. metal wall. Thus, by breaking up the flow of premixed fuel and air into a large number of small streams and by the cooling effect of the heavy metal wall 25 through which the nozzle holes 31 pass, the improved burner does not flash-back at extremely low pressures.

While the principles of surface combustion are known, the same have never tomy knowledge been incorporated in a pre-mix burner having a furnaces. 4

Moreover, the sealed in pre-mix burner nozzle construction is especially adapted for certain types of special atmosphere furnace work and the improved construction lends further flexibility of operation to such furnaces.

Having now described the features of the invention, th construction, operation and use of a preferred embodiment thereof, and the advantageous, extraordinary and heretofore unattainable resultsattained by the improved construe tions; the new and useful parts, elements, combinations, constructions and devices, and reasonable mechanical equivalents thereof obvious to those skilled in the art, are set forth in the appended claims.

I claim:

1. In a pre-mix fuel-air burner, a burner block having walls forming a through opening having an inner tubular surface. a burner nozzle sealed in said opening closing one end thereof, said nozzle being provided with a plurality of holes forming the sole communication between the nozzle and burner block opening, and the axes of said holes being elements of a cone and intersecting said tubular burner block surface.

2. In a pre-mix fuel-air burner, a burner block having walls forming a through opening, a burnernozzle sealed in said opening closing one end thereof, the opening having a portion flaring conically from the nozzle end to the other end thereof, said nozzle being provided with a plurality of holes forming the sole communication between impinged against the nozzle and opening portion, the

dies or said. holes being elementsoi 'a-cone diverging ing cone.

otholes providingthe sole, communication beitween the nozzle andoombustion tunnel,- the axis of each hole intersectingthe flaring. tunnel wall whereby'the' points of intersection lie in an an-vnularzoheintrmediatethe endsof the tunnel, and;said burner blookbeing provided with a passage communicating-with the pilot and 3'. Ina pr'e-mix fuel-air burner} a .burnerbloclr- Y having walls formingan opening therethrough,

. a'burn'er nozzle sealed in said opening closing one -;'ing, a burner block mounted in,said housing, a burnernoz'zle mounted in said burner block and end thereof, the opening having a portion flaring from the nozzle to the other end formed as a suri'ace of a frustum 'of' a cone, said'nozzle beingprovided with a plurality 01' holes forming the sole communication between the nozzle and flarling opening portion, the axes ofhsaid holes being elements of a cone coaxial with anddive'rging in the same direction as the flaring opening conical trustum, and the angle of divergence of ,the'ihole axes cone being greater than that oi .1the flarin opening conical i'rustuin. v '4..;-1n 'a' p're-mix fuel-air burner','a refractory. burner-block provided with a through opening, av

burner nozzle member sealed in said openinghaving side andv end walls forming .a-compartmerit, a conduit connectedwith said compartr jacent-to said zone.

- communicating with the 6. In a pre-mix fuel-air burner, a burner housburner housing, and a pilot mounted on said burner housing the burner block being provided with a combustion tunnel flaring from said nozzle, said nozzle being provided with a plurality of holes providingthe sole communication between/ 1 the nozzle andcombustion tunnel, the axis oi.

' each hole intersecting the-flaring tunnel wall whereby the points of intersection lie in an an.- .nular zoneintermediate the ends of theflaring I .tunnel, and said burnerblock being-provided ment for supplying -a fuel-air mixture thereto,

.said nozzle end ;wall being. provided with 'a. plurality of holes communicating between the, compartment and burner bl'ockopening; said burner -blockopening having walls flared from -30 the noz'zleto the other end thereoLand the axes:

WIth-a-cuIvedpassage communicatingwith the .1 I pilot and"'-co'mmunicating' with the 25 tunnel adjacent to said zon'e.

7. In a pre-mix fuel-air burner, aburn'e'r bloc v having walls forming a tubular combustion tunneli extending from the outer end to the inner, I end of said block's burner nozzle at the outer end '01,, said tunnel, said nozzle being provided with a plurality of holes communicating between v the nozzle and combustion'tunnel; the axes of 'oi'gsaidholes being elements'o't a coneand'intersecting vthe flaring burner block wall.

- said holes being elements of a cone and intersect- I ding said combustion tunnel in an annular zonea 7 5. .In a pre-mix i'uel a'ir burner, a burner hous ing, a burner block mounted in said-housing, a burner-nozzle mounted in said burner block and I burner housing, and -a pilot mounted onsaid intermediate the endsthereoLsaid 'bumer block' Y being provided with a curved passage extending burner housing; the burner block beingprovided v a with a combustion -tunnelflaring from said nozzle, said nomle beingprovided with'a plurality inward from the outer end oi! the block and m tersecti'ng the combustion tunnel. adjacent to said" zone,'and apilotflring into said curved passage.

IFRANK 'T. COPE.

combustion tunnel adcombustion V

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