US2873798A

US2873798A - Burner apparatus

Info

Publication number: US2873798A
Application number: US231934A
Authority: US
Inventors: Philip L Knight
Original assignee: Surface Combustion Corp
Current assignee: Surface Combustion Corp
Priority date: 1951-06-16
Filing date: 1951-06-16
Publication date: 1959-02-17
Anticipated expiration: 1976-02-17

Description

Feb. 17, 1959 Filed June 16, 1951 P. L. KNIGHT BURNER APPARATUS 2 sheets-suer. 1

P. IL. K1N IGM 1r United States Patent The present invention relates toburner apparatus and more particularly to a tiring lsystem for radiant tubesv such as are used in furnace chambers to produce radiant heat therein. This application is a continuation in part'k of my copending application Serial No.` 104,777, filed Iuly 1:4', v1949, which application is now abandoned'. In'radiant tube firing the problem is to obtain proper temperature distribution throughout the length of the tube. Combustion resulting from contiguous streams of air and fuel provides a long flame which is Well adapted for uniform temperature distribution, but this method of combustion is limited as to the quantity of fuel that canfbe properly l burned in the tube, due to the instability of the flame and to the excessively delayed combustion for relatively large quantitiesof fuel. On the other hand, fuel premixed with its full complement of air burns so rapidly a's to produce a hotspot in the wall of the tube thereby limiting the amount of fuel which can be burned without dani'- i age to the tube. The present invention has for its' general object to provide an improved tiring system for radiant tubes to the end that the maximum amount of fuel that can be burned in a radiant tube of given diameter and length need be limited only by the heat radiating capacity of the tube in a furnace rather than because of other limitations such as incomplete combustion and spotheating of the tube. Other related objects willV more fully appear hereinafter. For a consideration of what I consider to be novel and my invention, attention is directed tothe following specification and the concluding claims thereof.

In the drawings:

Figure 1 shows the improved burner applied to a radiant tube having an eductor at its exhaust end.

Figure 2 is a sectionalview of the improved burner.

Figure 3'is atransverse section on line 3 3 of Figure 2.

Figure 4 shows an alternate form of a detail'of the burner. Y

ICC

axially adjusted to compress a packing 21 interposed between the tube 10 and the mounting casting to provide a gas tight joint therebetween. The means for axially adjusting the throat casting will ordinarily comprise clamping bolts 15 carried by the mounting casting 17 and'extending through radial ears 19 on the throat casting.

The improved burner is generally indicated at 22 and comprises a head 23 from which there extends a plurality of supporting arms 24.whose outer ends are inter-connected by a ring 25. The ring 25 is adapted to lit over and to be secured' to the outer rim of the throat casting 20 to support the head 23 in front of the tube mouth 18 with an airy space therebetween so that air is free to'p'ow into said mouth under the inuence of the draft produced vThe head 23y has a central gas chamber 26'having an outlet defined' by a gas discharge nozzle 3@ in an adapter plug 27. l For reasons presently appearing and as indicated at 31 in Figure 3 the discharge orice of the nozzle 30 will ordinarily be annular. A. plurality ofpilot burners 33 (usually fourin number) are arranged in the air inlet dened by the mouth 1S in a circlev coaxial with the gas nozzle 3i) so that the advancing streamof gas from said nozzle tends to pass between said burners for ignition thereby. The pilot-burners are mounted on mixture supply tubes 34 which are mounted on the head '23 and vexftend forwardly in'a converging direction, the tubes cominunicatingA with an annular gas supply chamber 35 formed in the head- 23. Fuel gas premixed with air is delivered under appropriatefpressur'e to said chamber 35 by a. supply pipe 36. Raw fuel gas under appropriate pressure is delivered to the central gas chamber 26 by conduitmeans comprising a pipe extension 41 which` at its outer end connects' with a pipe T 42 which in turn connects with a main gas supply pipe 43. I `The stream of fuel` g'asissuing from the gas nozzle 30 is laterally unconned, hence it advances along and with the surrounding stream of air which is flowing into the tube lil because of the suction produced at the exhaust end'of. the tube by the eductor 12. Because of the cori'- tiguity of the air' and gas streams, the air` and gas thereof tend to interdiffuse to form a cone ofy combustible. mix? ture which is readily ignited bythe flame offthe pilot burnersv 33. f z

The lflame issuing from the pilot burners is not readily blown out because thebase of the flame is within'Y a chamv ber 2S intowhich a portion of the pilot gas mixture; is

Figure 5 shows a modication of the burner of Figure 2. y

Figure 6 is an end view-of the pilot circle of Figure 5 showing a relationshipVA of the igniting electrodes: to--the pilots and the central fuel discharge nozzles.

The radiant tube is indicated at 10 and is commonly of hair-pin type with its intake and exhaust ends extendtype and comprises a nozzle 13 set to discharge motive iluid into an entraining tube .14 whose intake end is coupled to the discharge end of the radiant tube. Thek wall 11 of the furnace chamber comprises the usual-re@ fractory material and an exterior metal casingld which i is apertured to receive a mounting casting;g17 vfor the pro- -jecting-endof tube 10,. A aring mouth 18 for said tube is defined by.. a throat casting 20 which` is `slideably mounted in the mounting casting :1 7 `so that it may, be

diverted by a plurality yof angled ports 29. f TheY amount of fuelv gas supplied to the pilot burners may therefore be lsubstantially increased over the minimum requiredA for pilot operation whereby a substantial portion ofthe required heat input to the radiant tube ltl'may be supplied to the pilot burners where circumstances so require.

The'annularity of the gas discharge orilce 31 of the nozzle 30r may be formed by a relativelyV slender filler member 37 extending within the bore of the nozzle 30 and held in centered position by centering pins 38 carried by the adapter plug 27.y However, orreasons presently appearing, said memberV 37 willordinarily consistofan oil conducting tube. The annularity of the orifice 31 may, however, be otherwise formedas shown in Figure 4 where the annularity of thel orice is formed by a filler plug 49 mounted on the adjacent end of the oil tube, the llatter being held in centered position by'blades 51 mount'- ed on th'e tube. v

Other things. being equal, the greater the mean diam eter` of the annular gas discharge orifice 3,1 (50),- the vgreater :is the Aamount of gas that can properly beburned inthe radiant tube 10..v By causing the gas to issue from the gas chamber 26 through anannular orifice, the issuing streamv vwi1l,fo,fY course, lbe hollow. Becausel it is hollow, there isa Alow pressure area or partial vacuumat ,the core of the gas stream which tends to produce turbulence in said stream with resultant more rapid mixing of the gas with the surrounding air than would be the case with a solid stream Vof gas. A gas stream of relatively large diameter also has more of its exterior surface exposed to the air andtherefore the cone of diusion of air and fuel will be correspondingly larger. The fuel gas will ordinarily issue from the annular orifice with such Velocity that ame will tend to blow off from the nozzle 30, hence there will ordinarily be no ame between the nozzle 30 and the pilots 33.

The oil tube 37 (52) is provided so that the oil may be burned in place of gas when the latter is in short supply as during severe winter weather. The oil is propelled through the tube 37 by a high velocity stream of air so that the oil issues from the tube in nely divided state in a carrier stream of air. The tube 37 will ordinarily be of such internal diameter that its discharge end requires to be closed by a disc 40 having a circular row of discharge orifices 41 so that the air oil mixture issues from the oil tube as a stream comprised of a plurality of individual streams. The amount of air in the air-oil mixture is only a small proportion (say one-fifth) of what is required to support combustion of the oil, hence it is primarily the air that is being drawn into the mouth 18 of the radiant tube by the eductor 12 which supports combustion of the oil. The stream of air-oil mixture issuing from the oil tube is ignited by the pilot burners 33 as it interdiifuses to form a combustible mixture with the air which is drawn into the tube by the eductor. The oil tube 37 is long enough to extend through the pipe 41 and pipe T 42 for connection with an air and oil receiving head 44 mounted on the outer end of the pipe T 42. Air under pressure is delivered to the head 44 by a supply pipe 45. The oil is sprayed into the head 44 by a spray nozzle 46 mounted thereon and oil under pressure is delivered to the spray nozzle by a supply n pipe 47.

Since it is desirable in some applications of this burner to operate the entire burner on and off subject to demand for heat as measured by a temperature control instrument, and it is often desirable to cause air to flow alone through ers there is produced a substantially uniform combustible mixture suitable for ignition. The momentary spark which simultaneously ignites all burners under the control of one instrument is produced by energizing a conventional time delay relay in the electrical circuit to the electrodes each time the instrument calls for heat and opens the fuel valve. The time delay relay will then pass current for two seconds to the electrode circuit before opening the circuit again. This will provide adequate time to ignite the pilot burners off the main fuel Astream without sufficient time for detrimental effects of the unsymmetrical ignition to accumulate.

It is seldom that the gas supply is so short that there is not even gas available for the pilot burners, but if such is the case a ring of electrodes 50 may be used to provide continuous symmetrical ignition for fuel oil. The combustion pilots are preferred for continuous ignition because of their longer life and the increased burner capacity, as well as reduced radio interference as compared with continuous electric ignition.

From the foregoing description it will now be apparent that the present invention provides a radiant tube burner that i-s relatively simple in construction and well adapted for its intended purpose.

Having disclosed my invention, I claim:

l. In a gas burner for firing into a tubular heating element through which air is free to flow under the influence of draft, in combination, a body dening a gradually converging air inlet of circular cross-section for said tube, a head member facing said air inlet in spaced relation to provide therebetween a space which lis open to the inflow of a current of said air, said head member having a rst chamber forming a plenum and an inlet for supplying a mixture of air and fuel gas thereto, an annular row of forwardly-discharging pilot burners within and coaxial with said air inlet, said pilot burners each being mounted on the discharge end of a supporting tube whose inlet end is mounted on said the tube for fast cooling thereby in special annealing cycles, electric ignition is provided for each burner. To obtain full advantage of the concentric ring of pilot burners in maintaining ignition of the burner without flame pulsations which are characteristic of non-symmetrical or weak ignition of the main fuel stream, electric i' ignition is momentarily applied to the central fuel stream next adjacent the fuel discharge nozzle whereby the llame may carry along the zone of interdilusion of fuel and air to the pilot burners, then the electric ignition'is stopped and the ame blows down to the pilot burner ring where the now ignited pilot burners maintain their characteristic uniform ignition. Spark electrodes are encased in a ceramic insulation 52 and are secured to the arms 24 of the head 23 by clips 51 and screws 53 in a manner which allows positioning of the electrodes for spark gap adjustment and alsoto move the spark downstream along the zone of interdilusion of fuel and air towards the ring` of pilot burners 33 as may be required xwith fuels such as heavy oils. With the lighter fuels such asnatural gas a single electrode will suffice to produce a spark, utilizing the main gas nozzle 30 as a ground. While such unsymmetrical'ignition of the main fuel stream as is .afforded by va single spark will produce flameV pulsations in the radiant tube, and in the case of oil as fuel will cause the fuel stream to wet theside of the tube opposite to the ignition due to expansion of burning fuel on the sparkside of the fueland air stream, a momentaryv spark ignition forv perhaps two seconds will suice tov ignite the pilot burners, and thereafter the headmember in gas receiving connection with said first chamber, said head having a second chamber forming a plenum, an inlet for supplying raw fuel gas thereto, a forwardly-discharging nozzle coaxial with said air inlet and supported by said head member in gas receiving connection with said second chamber, the discharge end of said nozzle being substantially closer to said head member than said annular row of pilot burners, and the space between said nozzle and said pilot burners being substantially unconned whereby a stream of fuel. gas on issuing from said nozzle ows substantially unconiined towards said air inlet along with said current of air.

2. In a burner according to claim 1, said nozzle having an annular discharge orifice whereby the gas issues from the nozzle as a tubular stream.

flame blows down tothe ring vof pilot burners and pulsations arel eliminated 'because in the zone of interdiifusion of airand fuel between the gas nozzle and the pilot burn lof draft, in combination, means comprising a fuel nozzle for directing a stream of fuel into said inletend of the chamber in a manner to form a cone of fuel into which surrounding air may diffuse to form combustible mixltures of fuel and air,. means comprising a concentric ring of pilot burners arranged to fire into said mixtures whereby to initiate combustion of said stream of fuel from and lafter ow thereof by said pilot burners, means Vfor supplying a preformed mixture of fuel gas and air -for combustion to said pilot burners, and means compris- 'ing an electrode for initially igniting said mixtures upstream ofrsaid pilot burners whereby to initially ignite vsaid pilot burners by ame from said mixtures.

5, In a burner for firing into a tubular heating element through which air is free to flow under the influence of draft, in combination, a body defining a converging air inlet of circular cross-section for said tube, a head member facing said inlet and supported in spaced relation thereto to provide therebetween a space which is open to the inow of a current of'said air, said head member having a rst chamber forming a plenum and an inlet for supplying a mixture of air and fuel gas thereto, an annular row of forwardly discharging pilot burners within and coaxial with said air inlet said pilot burners each being mounted on the discharge end of a supporting tube whose inlet end is mounted on said head member in gas receiving connection with said rst chamber, said head having a second chamber, an inlet thereto and a forwardly discharging nozzle coaxial with said air inlet in gas receiving connection therewith, the discharge end of said nozzle being substantially closer to said head member than said annular row of pilot burners, and the space between said nozzle and said pilot burners being substantially unconned whereby a stream of fuel on issuing from said nozzle flows towards said inlet along with said current of air to form a cone of interditfusion of fuel and air suitable for ignition by said pilot burners, and means comprising an electrode secured to said head member for initially igniting the fuel in said cone whereby to initially ignite said pilot burners.

6. In a burner for firing into a tubular heating element through which air is free to flow under the influence of draft, in combination, a body defining a gradually converging air inlet of circular cross-section for said tube, a head member facing said air inlet in spaced relation to provide therebetween a space which is open to the inow of a current of said air, said head member having a rst chamber forming a plenum andan inlet for supplying a mixture of fuel gas thereto, an annular row of forwardly discharging pilot burners within and coaxial with said air inlet, said pilot burners each being mounted on the discharge end of a supporting tube Whose inlet end is mounted on said head member in gas receiving connection with said rst chamber, said head having a second fuel chamber, an inlet for supplying fuel thereto, a forwardly-discharging nozzle coaxial with said air inlet and supported by said head member in fuel receiving connection with' said second chamber, the discharge end of said nozzle being substantially closer to said head member than said annular row of pilot burners, and the space between said nozzle and said pilot burners being substantially unconned whereby a stream of fuel on issuing from said nozzle flows substantially unconned towards said air inlet along with said current of air.

References Cited in the le of this patent UNITED STATES PATENTS 605,935 Tillman June 21, 1898 1,359,417 Musser Nov. 16, 1920 1,393,654 Wales Oct. 11, 1921 1,514,595 Assel Nov. 11, 1924 1,788,716 Hepburn Ian. 13, 1931 1,827,505 Bluhm Oct. 13, 1931 2,247,548 Forster Iuly 1, 1941 2,304,200 Plein et al. Dec. 8, 1942 2,340,734 Clark Feb. 1, 1944