US2670788A - Fuel and air mixing unit for burner assemblies - Google Patents

Description

March 2, 1954 J. L. MaCFARLANE 2,670,788

FUEL AND AIR M IXING UNIT FOR BURNER ASSEMBLIES Filed Oct. 10, 1949 3 Sheets-Sheet 1 Jahn L. Mac Farlane ATTORNEY March 2, 1954 J. M FARLANE FUEL AND AIR MIXING UNIT FOR BURNER ASSEMBLIES 3 Sheets -Sheet 2 Filed Oct. 10, 1949 INVEN TOR. L. Mac Forlone John 4 niv d=22; AI

ATTORNEY March 2, 1954 MacFARLANE I FUEL AND AIR MIXING UNIT FOR BURNER ASSEMBLIES Filed Oct. 10. 1949 3 She'ets-Sheet 3 VIII/14m v M HIN D QE H WNNNW\\\ WN INVENTOR. John L. Mac Furlone ATTQRNEY Patented Mar. 2, 1954 EU'EL' AND AIR MIXING UNITFOR BURNER ASSEMBLIES JohnLm MacFarlane;..Pueblo,- Colo., assignor. try The MacMixen-Inm, a corporatiomof Colorado.

Application Obtoberli), 1949, Serial No. 120,579

(01.; lee-11) 1% Claims.

This invention relates to a fuel and ai r'mix.=-

ingunit forburner assemblies which is useful in obtaining a controlled'heating pattern and efiii cient' combustion.

Many different types offuel and air. mixing? units orburners have previouslybeen devised in. attempts to inorease'the 'efiiciency of combustion onto-control the flame pattern. Generally most:

of the previous designs have been basedzon'th'e theory thatv turbulence is essential for the compl'ete-intermixing of" fuel and air and that a. conical flame pattern is most desirable because the hot zones of 'the'fiame-are then concentrated. Certain disadvantages-of fuel andair mixing units designed on the basis ofv the foregoing; theoryhavebecomeapparent." One disadvantage: of fiame patternshaving hot zonesis. noted'where the-capacityof original installations'has beentincreased? Such increases: in capacitynecessitatethe burning of additional fuel which causes an. elongation of the flame pattern tending to bring the hot' zone 1 of the flame into contact withiz parts? of the the box or furnace to the consequent: Accordingly burners that:

damageof said'parts. developnahot zone have-not beenusefuloverra wide range: of "flow capacities unless the furnace orr'fireboxwas' specially designed to accommo' datessucha burner;

Insofar as thesmixing ofthe -fuefl and air is" coneerned;. some of "the previous designs; have attempted by various: means to increase? the amount: ofiturbulen'ce' within thermixingnnitiand; outwardly into the fiame-Fpattern in the belief": that such" increased turbulence 'was'necessary to assure thecompletesintermixing of fuel and: air.

As a: result of." the present inventors studies, it wouldinow seemrthat: manyrprevious' devices for mixing: fuel and:' have: actually" created .too" muchturbulence in: the. flow pattern to. assure tliea'complete eintermixingof'the: combustion sup.- portingr-products;

Primarily the complete intermixture of: fuelair is desired to; increase: thes'efiiciency" of combustion. Sincemaximum efliciency'has not been: obtained previously with: prior types of."

mixing: units or burners; it: is..-evidenti that the intermixture oftfuel and air has been"; incomplete orat least not in .theproper proportions. These inefilcienciesra general-1y occur: at all levels of operation, but in most: installations an increase in the percent combustibl-es" or 'in: excess air: is

notedonv either: side of an optimum. operation condition. Any type. of: burner which? doeszenot' operate v at; near maximum. efficiency I over a; wide range--ofoperationlevelsdces not thoroughly 2: satisfy the requirements and other firebox installations.

In order to overcome the'shortcomings of prior: 7 devices, the present-inventor has devised a fuel and airmi'xing 'unit'designed to satisfy the following: objects:

To provide a fuel and'air mixing unit which efficiently combines fuel and-air in readilyad justable exactproportions-toassure efiicientcom bastion.

Tdprovide a" fuel and-air mixing unit'- in whichliquid or gaseous fuels-may be eflici'ently intermixed with air" or oxygen. without 1 creating ex=- cessive" turbulence within or at the discharge of said mixing unit.

To providea fuel and ai-r mixing unit which is adapted to give-a homogeneous flame pattern";

To provide-a fuel and air: mixing unit having a. plurality of successive expansion chambers adapted" to intermix the fuel and air products" eificientlybefore discharging said" products in a' homogeneousfiamepattern.

To provide'a fuel and air mixing unit having" diameter adapted to efficiently intermix I liquid and gaseous" fuelswith air introduced into said mixing unit by concentrically arranged conduits having flow successive chambers of increasing and: pressure controlling means associated'them with. p

're: provide a fuel burning arrangement inclusive: of a mixing unit having expansion chambers of: successively increasing diameter; conduit means for carrying fuel to said mixing" unit :at a predetermined rate of-flow together with furthenmeansfor controlling the amountof primary air" introduced? into said mixing unit and the-ramountiofrsecondary air introduced into the fire-box throughachecker preheating system;

To provide a fuel and air mixing unit which: is easily: and" economically rnanuf'actur'ed and whichin'corporates simple control features. easily I operableiby the personnel maintaining said mix ing unit;

Further: objects and advantagesof the presentinvention will be apparent from the appended de scription and drawings in'which:

Fig. 1 is anelevation'inpartial section'sh'owing the general use of themixing unit of this inven-' tion 'in'a' brick kiln' fire box 'installation inclusive-'- of a secon vlary preheating system;

Fig. Zis an el'evation in partial section showingthe features of an embodiment of this invention inexact detailxdrawn to scale;

321's an elevation in partial section. showing I the'details offaifuel and'air conduit arrangement" of modern furnace; .kiln:

together with air control means for association with said mixing unit;

Fig. 4 is an elevation in partial section showing the features of a separate embodiment of this invention in exact detail drawn to /3 scale;

Fig. 5 is an elevation in partial section showing the details of a separate embodiment of the fuel and air conduits arrangement together with the control means thereof; and

Fig. 6 is an elevation on a reduced scale taken along the lines 66 of Fig. 4.

Briefly stated the present invention provides a fuel and air mixing unit inclusive of an entrance chamber having side walls which narrow or converge to provide an opening of minimum diameter consistent with the flow capacity of the mixing unit. Downstream from the said entrance chamber and the opening therein, a plurality of expansion chambers of successively increasing diameter in the downstream direction are provided. "Each of the expansion chambers is substantially cylindrical in shape having the individual lengths thereof greater than the diameters of said chambers, but each of said chambers being of successively decreased length with respect to the next adjacent upstream chamber. The chambers themselves are separated one from another by a plurality of restrictions formed on the inner surfaces of said chambers which tend to narrow the passage therethrough to provide openings of diameter less than the diameter of the next adjacent upstream expansion chamber. Further these openings are of successively increasing diameter in the downstream direction. By means of the foregoing arrangement the inventor is able to establish a flame pattern which is homogeneous insofar as the dispersion of color is concerned. By use of separate means for controlling the amount of atmospheric air, fuel and air under pressure introduced into the mixing unit, the amount of fuel and air introduced can be controlled in exact proportion to maintain highly efiicient combustion. Separate arrangements for controlling the amount of fuel and air introduced are provided in accordance with this invention together with means for controlling the distribution of the aforementioned homogeneous flame pattern within a fire box, furnace or the like.

In Fig. 2 the details of a first embodiment of this invention are shown. In this figure it will be noted that the inventor provides a fuel and air mixing unit H having in successive downstream arrangement an entrance chamber !2, a

first expansion chamber [3, an intermediate expansion chamber 14 and a last expansion chamber I6. As shown, the entrance chamber is provided with converging side walls I! of substantially frusto-conical shape. These side walls 11 converge or narrow in the downstream direction to an opening l8 of minimum diameter consistent with the desired maximum volumetric flow for the particular installation. Beyond the opening 8 a first expansion chamber 13 having walls [9 of substantially cylindrical shape is disposed, and interconnecting the cylindrical walls B9 of the first expansion chamber 13 and the converging side walls l! of the entrance chamber I2 is a section 2| of expanding diameter to provide a transition member between the opening is and the cylindrical walls 9. The length of the first expansion chamber 13 and of the walls I9 thereof is approximately twice the inside diameter of the expansion chamber #3. At the terminal downstream end of the first expansion chamber 43, a constriction 22 disposed upon the inner surface of the walls 19 is provided. Preferably the constriction 22 narrows the passage through the first expansion chamber 3 to provide an opening 23 of diameter greater than the opening 58 and less than the diameter of the upstream expansion chamber it. An intermediate expansion chamber likewise having walls 24 of substantially cylindrical cross section is disposed downstream from the opening 23 and is interconnected to the chamber 43 by a continuation of the restriction 22 and expands in diameter from minimum size at the opening 23 to maximum size coterminous with the diameter of the chamber M. The diameter of the intermediate expansion chamber i4 is approximately 10 to 25 per cent greater than the diameter of the next adjacent upstream expansion chamber 13, and the length of the intermediate expansion chamber i4 is approximately one and one-half times the diameter.

At the downstream end 01 the intermediate expansion chambers another restriction 26 is likewise provided to narrow the passage through said intermediate chamber M to provide an opening 2? of diameter greater than the opening 23 and less than the diameter of the intermediate expansion chamber M. A third or last expansion chamber 46 having cylindrical walls 28 is provided downstream from said opening 21 and a continuation of the restriction 26 of expanding diameter interconnects the intermediate chamber I l and the walls 28 of the last chamber [6.

The diameter of the cylindrical expansion chamber it is approximately 1.2 times the diameter of the intermediate expansion chamber l4 and the length of the last chamber I6 is approximately 1.2 times the diameter. At the terminal end of the last expansion chamber It a circularly formed restriction 29 is provided which narrows the passage through said last expansion chamber to an opening 3|. The diameter of the opening 31 is greater than the diameter of the upstream opening 27 but less than the diameter of the adjacent upstream expansion chamber [6.

Besides the ratios and proportions already set forth, it should be noted that the successive openlugs 18, 23, 21 and 3! are of successively increasing diameter in the downstream direction. The expansion chambers are of successively increasing diameter in a downstream direction from the entrance chamber I2 and of successively decreasing length. In all instances however, the sizes of the openings 18, 23, 21 and 3| are of smaller diameter than the next adjacent upstream chamber. While specific ratios and proportions have been set forth, it should be apparent that modification within certain limits is possible. Accordingly it should be realized that the dimensions and proportions set forth are given only to enable others to readily practice the present invention.

As further shown in Fig. 2 a mixing unit I l is preferably used in conjunction with apparatus for delivering gaseous fuel into the mixing unit Where a plug is used, an orifice rma 3111s; dri-lledfthmuggrtheapluggfltsathanthe: gasseeouszfuelbeing carriedpwthecconduitfi2-2iss.deepliveredflhroughrthe orificeifl intosithepentrance plish suchadjustedzpositioningcyofi the-rairtcontrol: disk 39; the :inventor. in thgelnbodiments; shown.

provides threads: 4 l :of: extended :length; cutin.;the.-. outersurfaceof the pipe "32;. The air: control disk. 39 is preferably a member having a flat disk shape;- OffISiZQ larger than the entrance opening: :38 and a.boss.=42. The bossa42' and the centra1. portion: of the disk 39 is; provided withv an. opening; 4-3 having threads M thereinforzmating engagement with;.the threads 4|, on. the externaLsurface-of;

the pipe'32. It willJloenoted thatxas .th'esfiil control disk 39. is rotated With-respecttothepipe- 32 it willrbe moved: inwardly. orroutwardly with respectztothe entrance opening 38.: When the disk'is moved away-from the entrance .opening- 38: the. :openingAii of cylindrical shape betweenthes disk.39 ancLtheentrance opening: 38 .will' be;in-. creased .to.:;a1low an. increasednamount 10f; air: to" flow" into, the .2 entrance sectiomfl. of: the mixing-:. unitl l..

In. Fig. 1 a; typical .insta1latiorr: which fully:

utilizes the advantages: ofya. mixing: unit .similar. :1

to'that shownjn Fig, 2;iis shownzz. Inthisfigure itswill be seen that-the:iuelJand-air mixing-unit ll is supportedby astand 4! S0 ,tha't:thB"dOWni"' stream opening 3!. irrthe last: expansionxchame her :I 6 -.discharges through an opening-- 48 ;in the; exterior; wall .49 of:a:. fire box 51.: The conduit. 32 is interconnected .with;a:.fuel;suppl-y pip.er;52;:. and a .valve: 53 previouslymentioned isrprovide'd to control theaflow ofzffuelinto"arnhathroughtthe conduit 32.v Beyondthe .valvefifi in a downstream: direction: the. conduit 32.:is; provided;;with;.;a1tap:

determining and:. COIItIOiHIlgfthGi delivery. pres? sure: ofthe gaseous fuehbeingusedr. Asprevious-i- 1y. explained the 7 air; control .disk 39 1 is". mountert" foriadjusteol movement .alongsj the. conduitziifltita: vary "and. control the amount of primary: air

troduced into.- the mixingunit l'l-.. The firerboxz itself which. is-v inztthis.figuretshown;;as:beingrsensclosed withinraki-ln 58 isprovided:with a grate 5.9. and-a mass of broken firesbrickrfitli on other simize larmaterial .Whichseparates the firehoxrilrfromt.

a secondary ainentranceichannelA62. 'Ifhetc'ham nel 162::is connecteclrwitha: headen:63. wlnclnissinte terconnected to aconventional typesetblower (not shown) so that secondary air: willgbeainr-u troduced into thew-fire b'oxfil: through the header 63 and. channel 82- and upwardly:throughr the: broken brick 6! and gratex59- to-further control the placement of. the flame pattern: within: the? firebox 51 and to preheat-the secondary air by" means of; its passage through. the; checker-like;

system provided; by the. broken brickixfil; Bye" means of this .arrangementzwhen the5 amount of 1; fueLand air, introduced;throughntheimixinggunita:

I l:.-iseincreased',; the dilemma;patterntaemittinge frmnzv the discharge opening ,3 I 1; can be econtrollediso that.:.;it:wil1;notr impinges-upon, the flrer N with such-intensity? as to.;.destroyg; the fire waih; Sincetheefiamewpattern emitted by. the

unite Ill; issubstantially;homogeneousainichara tenandt. since r= there;;are 'no.--marked'lhot'. zones thecfla'me pattern. thiscontrolsot;.theplacemenh of-thafiame patterniis;possibleaWithoutendangera. ingany;ofrthecothenparts,.suchcasitherrooilnoirs burner: the placement: of, the: flame pattermcam be? controlled? in: .furnaces, ;ovons; open heartbeat; soaking pits .and-thehke to preventtheedestruc tiOIisIOfiQfiTtSaWit-hifiaSliCh; unitsxduemto: theascone centrationzofrheat:

The exact character: ofithe'fiamepatterntemitn tediby the. mixing. unit; H should-perhapsbemomi fully: describedr It has-been: writtenrthatnthiss' flamezpatternciszhomogeneousc. By this-termrthezz A P inventor :intendsl'to l. convey the .impressiomthatn.

there;are;-.no marked. physically; 'apparentzdemar cations ofiffiamezpatt'ern which'mightbtncmrac terizedzas oxidizing; reducing ,OI asrarhotzgzoner Insteadn-then flame remitted; from; the idisehargeii opening-113d; is: of elongated: substantia'll'ypyline dricai-ushape or slightly increasing diameterawayrfromrthe. discharge opening-:31; Thronghouttheis visible zportion of tthe. flamev patternthe intemnixeturez-oicolorsz such .asa':.the:.-.characteristic reds'r. blues greens etc;- isz'evemuor other words;.the;i-;

flame pattern iShOmOgBIIEOHSISiIICEthE5diSpe1ZSmI!5- of suc'h characteristic colorsais complete-.2;

While; theev complete. dispersion 10f: flameecolorsaz' iSiHGtCOIIClUS ive to. iprove .=that there isza compiete inten'nixture .ofi fuel" and air, such results: coupled? with flue gas analysis:results howing:a-maximum:

eifici'enoy: area. conclusive; to @show: that thee-inten mixture accomplished; by the inventor's i type--o1.:5v mixing unit is complete and may -be-regnlated inzexact 'proportion-toestablismmaximum come bustion: efli'ciency: Inc a brick kiln-z installation; thisstypeP-of mixing unit": has made-it-possible to:

obtain consistentresults showingnot over of -1 per-:cent:'excess:- oxygen with no combustibles inra the flne gas analysis. In the same installation":- mentionedj when mixing units of i the describer i type are installed, the saving inafuel was' hetter than: 48 per cent; and since a more intensee heair waszpossibles in a shorter period "of" time the-:pro-r ductiorr capacity of'the plant was-increased nnd...

the fiiel 'cost per thousand-bricks waseffective y cut-in: halt-. While it" is admittedthatthes resu'l t's are-perhaps unusual; they are -evidence ofi thepossibilitiesinherent in the ainventor s type= of-desi'gn. i

Bsidesthegaseous-flxel an d air 'installationiasz shown in-Figsz- I and 2 it has :ibcerr found that: the=present type---of mixing unit is adaptablei't'o oti'icrifuel burning applications. Actually unitsofdesign similar-to that -desc-ri-bed' have been 1 used? to interrnixgaseous; liquid and-"solidfuels air linden-pressure and-at atmospheric pressu In: all instances theresults have shown-thatthe fuel= and air intermixtureobtained is suitable fom the attainment of maximum or nearvmaximuma combustion eflicienciese arrangement for theefiicient intermixtu-re of -gaseons and liquid fuels' with air under pres-)- sureand at atmospheric pressure is=.-showrr in- Fig-2'3; In this-figurea mixing unit H is pro' vided of: f orm-.::andr shape substantiallwas 5. shownrr.

in Fig. zahayingzamentrance chamber; l ZLandQanr entrancen. opening? 335i asc previously" described? Thtzeazseparatez;concentriczconduitstaarearranged within on'adiacentztozthe entrance seetiomofzthega shown): of;-..the;:kiln-. Likewise:withithisstyype:air.

mixing unit H so that a gaseous fuel such as natural gas, a liquid fuel such as fuel oil and primary air under pressure will be conjointly introduced into the entrance section l2 on passing through a nozzle 56 having an orifice 61 therein. The actual arrangement of the conduits and associated members is fully shown in Fig. 3 where it will be noted that gas is introduced by means of a pipe 68 into a T fitting 69. A gas conveying conduit H interconnects with one opening of the T to form the outermost of the conduit members. The outer surface of this conduit H is provided with threads 72 for the reception of an air control disk 39 of shape, size and purpose corresponding to that previously described. As before, movement of the control disk 39 toward or away from the entrance opening 38 decreases or increases the amount of air introduced into the entrance chamber l2 at atmospheric pressure. A tapped plug 13 is provided in the third or remaining opening of the T fitting, and a conduit 14 having an outside diameter that is less than the inside diameter of the outer conduit ii is connected through the tapped plug 73 and disposed concentrically within the outer conduit H so as to provide a passage it through which the gas introduced into the T by the pipe 58 may be conveyed toward the orifice opening 61. One opening of a second T '11 is interconnected to the outer end of the conduit '74 and an air delivery pipe i8 is interconnected into another opening of the T ll. A tapped plug 79 is disposed in a third opening of the secondT H and an inner conduit 8! is connected through the tapped plug 19 and disposed within'the conduit 14 to convey oil to the orifice 61 and into the entrance section l2. The outside diameter of the conduit BI is substantially less than the inside diameter of the conduit 74 so that a passage 82 is provided between the conduits 8i and 74 through which air under pressure may be introduced for passage to and through the orifice 61 and into the entrance chamber 12. This particular arrangement of feed conduits is advan tageous in installations where a more intense heat is desired or where the supply of one or the other types of fuel is not thoroughly dependable. Where a more intense heat is desired both the liquid and gaseous fuel will be introduced simultaneously with air under pressure and air at atmospheric pressure to provide a homogeneous mixture having a high heating value. It is significant that the intermixture of the separate types of fuel is so complete that the resulting flame pattern is still homogeneous and the flue gas analyses show corresponding eificiencies. By the use of valve members on the separate pipes 68, i8 and illthe flow of any of the separate constituents may be closely controlled and accordingly whenever it is desired or necessary to out 01? one particular type of fuel, adjustment may be readily made to maintain the efficient combustion. In instances where the primary type of fuel is cut off, the provision of a secondary fuel which may be eihciently burned to maintain a satisfactory heat is invaluable.

In Fig. 4 a modified form of mixing unit construction is shown. In this figure the mixing unit ii is provided with an entrance chamber I2 and a plurality of expansion chambers 13', M and 15'. As in the previous arrangement the expansion chambers are successively of increasing diameter in the downstream direction. Further the side walls ll of the entrance chamber [2' narrow to provide an opening I8 at the mini mum' diameter of said entrance section. The

walls 19' of the first expansion chamber l3 are substantially cylindrical in shape and a section 2! of expanding diameter interconnects the opening 18' With the walls IQ of the first expansion chamber 13. Adjacent the downstream terminal end of the expansion chamber IS a restriction 22' is disposed to provide an opening 23' of diameter smaller than the diameter of the expansion chamber IS. The actual form of the restriction 22 is difierent than that illustrated in Fig. 2 inasmuch as the modified form of restriction 22' provides for a gradual and even reduction in diameter from a maximum size equal to the diameter of the expansion chamber E3 to a minimum size equal to the diameter of the open ing 23'. Downstream from the opening 23 the restriction 22' has an expanding or flared internal diameter adapted to provide a smooth but relatively sharp transition from the diameter of the opening 23 to the internal diameter of the walls 24' of the intermediate expansion chamber 14'.

A restriction 2G is likewise positioned adjacent the downstream terminal end of the intermediate expansion chamber Hi. The construction of the restriction 25' is similar to that of restriction inasmuch as it provides for a gradual reduction in internal diameter from the diameter of the walls 23' to the diameter of an opening 27 sepa rating the intermediate expansion chamber M from the last expansion chamber l-S. Downstream from the opening 2? the walls of the restriction have an expanding diameter to eifect a smocth but relatively sharp transition from the diameter of the opening 2? to the internal diameter of the walls 28 of the expansion chambcr jacent the downstream terminal end of the ex pansion chamber E5 to narrow the passage therethrough and to provide a discharge opening 3 l of diameter less than the inside diameter of the walls 23'. Restriction 2%)" is formed similarly to the restrictions 22 and 2 8 inasmuch as its walls are adapted to provide a gradual transition between the diameters of the external walls 28 and the discharge opening 3! As in the previous embodiment the diameter of the expansion chamber 5 3 is greater than the diameter of the opening l8. Further the expansion chambers l3, i i and it are of successively increasing diameter in the downstream direction and the diameters of the openings i8, 23', 2'! and 3E are likewise of successively increasing diameter in the downstream direction. Again each of the separate openings 18, 23, 2'! and 3| are of less inside diameter than the next adjacent upstream chamber. between the embodiments shown in 2 and Fig. 4 are concerned with providing transition shapes between the separate expansion chambers that more nearly conform to the shape of con ventional type nozzles. These change have been made inasmuch as the embodiment shown in Fig. 4 is designed for larger capacity than that shown in Fig. 2 and for the larger flow capacities the nozzle type restrictions give the proper intermixture without establishing excessive turbulence.

Figs. 5, 6 and a portion of Fig. 4. show the details and arrangement of a separate type of fuel and air feed and control. In Fig. 4 it will be noted that the entrance end 83 of the mixing unit H is provided with a flat face 3 and the side walls ll of the entrance chamber l2 are turned to provide a cylindrical face 88. These machine faces are provided so that the'y'may be 3 A further restriction 23' is disposed ad- Essentially the differences securely engaged.- in cooperative mating" surfaces fi l ofaspidermember Si}: As shown-in Fig: 6 the spider 8'8is"provided withan outer ring-8% having-the aforementioned mating surfaces 8? cut'on-the inner face thereof. Wehmembersi interconnect a central huh 9'2 I witlr'the ring" 89 so-as to provide opening'sflB communicating with the-entrance chamber 32'". set soreu are the ring 89 are adapted to"secure-thes .ormemhe'r 88 to the mixing unit '1 i andth-e hub 81? provides an opening fi l in-whicltthefuel and feed con duits are received.-

A- separate arrangement for the fuel and air feed conduits isshovrniwFi'g'. Fran-d iir-porti'on ofFig. 4 where it willaga-inhenoted that the applicant providesa plurality of concentric con duits'liii, 9'2" and steer introducing oil respectively into the entrancechamber orthe mixing unit l I. The outermost "oi "the conduits 98" is' supported in concentric positionwithin the entrance champ-swi liythe spider-8S? and its inner end is provided Winn-threads Be te-receive a reducer-member let, the outer-end of which is partially "closed-my apl'ug Ioil' hav'ingan orifice opening los therein: Anin the previous embodimerit; adjusting threads los -areprovided-"on the outer surface of the conduit- SB- for engagement by the threads -'-I ii 'of -thea-ir control-disk 39. By means of this arrangement "the air control disk 39* may b'emoved to-"adiiusted position alcng'the conduit SS' tQ'increase-or decrease the 'cross=sec-'- tional aren of flow past the air control *di-slc 3-9" and-the spider os andinto'the entrancechamber l 2 Accordingly a correspondingly accurate control of the amount oi atmospheric-air introduced into the mixin'gwunit is liltewise possible in this embodiment.

The outer end lot-"the conduit 96 is-secureei *in one opening'of-across I Mgassupply'pipe I 9 5 having a valve I It! thereon ion the control of gas through the-pipe -I fiE- is secured in a -second open in 'gof the cross l $5 in such manner -that the gas introduced-- thrOugh the-pi-pe I0 8" will now di rectl-yinto the cross 1 I Gi -and through a passage I 08' between the conduits' fi t -and 9-1 into the en trance chamber-42 Conduit-t-T whichds diep'osed concentrically within conduit e-tiis held in suchconcentric position' by a tappedplug I Se im a-third opening of the cross m5, Theairflowing through the Z1 conduit 91, however; I is: ntrocluced through .afipipe-I I I passing through p eapmg I I2 'disp'osed 1 the-fourth openingthe: cross; lE ipev I I I l is clikewise providedwith a1. valve: I I3 adapted :to control the amount of a introduced through :the pipe-I l I andithrough :amassage l I t between the ccnduits 9 1 and 982mm the entrance chamber: I2 1. In orderito malze this arrangement possible the'lpipe II I is threaded sin-to a .Ti section I I6 welded-atright angles to theconduiteil: The outerend of the conduit e1 has a reducer; i I i socured thereto, and conduit 98 .is-threaded for passage through the-smaller enclof the reducer: I IT. A valveI 1845 provided on the concluittamo control the flow of oil: through the conduit-V 9B; through-a metering. orifice I disposed in.the inner end of the conduit-Q8 and into .theentrance chamber I2'-.

By, means of. the fueliand air flowicontrol are rangemen-t last described; the. inventor is able to. control the exact proportions of fuel -and-v air introduced into the mixing unit II'-. With such control and with. theintermixing; features of: the mixing unit I I .the inventor is ableetomainta-m highly; efficient combustionhaving-gthe advantages previously described:v

The high level of efficiency possible with mixing unit's-made accordingto-the designs of the present invention-is indicated by the -following data of mixing units similar to those shown in Figs.- land 2" in a conventional silica fire brick Uakineoperation. Inone specific installation a; b'rick kiln having an inside-diameter of approximately feet: was provided with eightmixing units substantially as shown in l ies? 1 21 16 2. This==down draft periodic type ofkiln"having a capacity 'of-'approximately190,990"- nine inch fire brick was chargedto capacity andsealed. For the first n-inety-'six* hours themixingunit I -'I was provided 'with an orifice =3i having an op'ening of-an inch diameter. During-.thefirst twenty four: hours th'e m-ixing unite -were operated with a 6 ounce pressure on the natural gas feed. With the -air control 38 ad5'usted to give' eificient combustion approximately 75,000-- cubic feet of gas were used and-a temperature-of 660 was attained atthe end I of thetwenty four ho'iir l1our' period-.- For the next twenty-four hour's-12 ounces cf 'ga's -pressur'e was-used anclcorrespond ing chahg'eswere n'ia'de-in the positioning of the air control disk to 1 assure-complete combustion of tl ie greateramount of fuel. Duringthis see ond twenty=four'= hour periodapproximately 123,00'0 cubic feet of gas were usedand a tem perature of l320- F5 was obtained Duringthe =tnir-d-="twenty-rour hour period i 20 ounce's'of pressure was used'" on the-'gas -supply-"ahd the amount of primary air was increasedto giv efiicient combustion. During th-is third twentyfou-r' hour-p'eriod approximately" -163g000cubic feet of gas-was-burned-am a=tempereiture of approxi mate1y'2,000- E. was obtained; Durin'gthe fourth twenty-four hour period,-'four pounds;- four-ounces gas pressure was utilized" to burn approximately 3l7',000cu'bic=feet of gas-bringing the to-a temperature -ofapproximately-2400 F5 After ninety sh'shours "elapsedtime the orifice 31*Waschangedto provide an opening --of an inchin diameter: Withthis-"orifice"size; two pounds, four ounces of gas -pressure--was"used" for thenext twenty fourhours-toburn approXi-mateiy 4421500 cubic'feet of gas and to obtain atemp'erm ture of approximately-"265W After atotal elapsed time of hours the gas-pressure was increased-to*threepoundspersquareinch for a period of twentyfour' hours-- during" which time approximately 511E000 cubic feet of" gas was bu-rnet'l'. At the end-of this lasttwentyefourhour period =a-- temperature of-2'750' F. had been obtained'withinthekiln: As "soon as-this tempera ture was obtainedthe gas supply--was cut off and the-"bricks" were ieft inthe =withoutad'ditional neat-for fourteen days.

During tl'ie-"entire heating cycle a total of approximately 1,-63ZJJGO-"cubicfeetbf gaswa'sburned-i In connection with-these total figures it should lie-noted that-thekiln installation mentioned was located at analtitudeofaproximately Mme-feet and the heatingvalue ofthe' natural gas used wasfnecessaril'y; reduced by such" conditions:

Fromth'e foregoing figures when 'taken'to'gether with results. reviously; mentioned it should. be apparent that the; present device .fulljif satisfies the objects enumerated. Whileseparate embodi' ments .of this invention have beenshownland ide scribed, it.isrreaclilyi apparent that the invention is -adaptable-.to modifications-andchanges. All such modificationsand .changes-asarea-within. the scope of; the hereunto: appended: claimsare deemed toizbe apart of this invention:

. What is claimed is:

1. A mixing unit for burner assemblies comprising an elongated open-ended body having an entrance chamber inclusive of side walls forming a narrowing passage arranged to receive streams of air and fuel,- means for injecting streams of air and fuel into said entrance chamber at its open end, said body including a plurality of expansion chambers of successively increased crosssection downstream from said entrance chamber, and a plurality of constriction members between said chambers having surfaces arranged to narrow the passage therebetween to a cross section less than the cross sectional dimension of the next adjacent upstream chamber so as to mix said streams in their travel through said chambers.

2. A mixing unit for burner assemblies comprising an elongated open-ended body, anentrance chamber on said body inclusive of side walls forming a narrowing passage arranged to receive streams of air and fuel, means for injecting streams of air and fuel into said entrance chamber at its open end, said body including a plurality of substantially cylindrical expansion chambers of successively increased diameter downstream from said entrance chamber, and a plurality of restrictions acting as division members between said chambers having surfaces arranged to narrow the passage therebetween to a diameter less than the diameter of the next adjacent upstream chamber so as to mix said streams in their travel through said chambers.

3. A mixing unit for burner assemblies com prising an elongated open-ended body having imperforate side walls, an entrance section on said body arranged to receive streams of air and fuel, means for injecting streams of air and fuel into said entrance section at its open end, and said body including a plurality of expansion chambers disposed in open ended relation lengthwise of said body downstream from said entrance section, each of said chambers being defined by restrictions acting as division members at the ends thereof, each said expansion chamber being of shorter length than the next adjacent upstream expansion chamber so as to mix said streams in their travel through said chambers.

4. A mixing unit for burner assemblies comprising an elongated open-ended body of circular cross section, an entrance section on said body arranged to receive streams of air and fuel, means for injecting streams of air and fuel into said entrance section at its open end, and said body including a plurality of expansion chambers disposed in open ended relation lengthwise of said body downstream from said entrance section, said chambers being separated from each other by a restriction therebetween, each said expansion chamber being of greater diameter and shorter length than the next adjacent upstream expansion chamber so as to mix said streams in their travel through said chambers.

5. A fuel and air mixing unit for burner assemblies comprising an elongated open-ended body having an entrance section inclusive of side walls forming a narrowing passage, said body including a plurality of expansion chambers of successively increasing diameter and decreasing length downstream from said entrance section disposed in open ended relation lengthwise of said body, said chambers being separated by restrictions therebetween, a conduit for conveying fuel having a discharge outlet disposed within said entrance section at the open end, an

orifice member mounted at said outlet in heat conductive connection with said conduit, an air control disk mounted on said conduit at the up stream end of said entrance section for selective movement along said conduit to vary the quantity of air introduced into said entrance section, and valve means on said conduit for controlling the amount of fuel introduced through said conduit into said entrance section.

6. A fuel and air mixing unit for burner assemblies comprising an elongated open-ended body having an entrance section inclusive of side walls forming a narrowing passage, said body including a plurality of expansion chambers of successively increasing diameter downstream from said entrance section disposed in open ended relation lengthwise of said body, a first conduit having a discharge outlet disposed in the entrance section for discharging gaseous fuel into the upstream end of said mixing unit, a concentric intermediate conduit disposed within said first conduit and having its discharge outlet within said first conduit, an inner conduit disposed concentrically within said intermediate conduit having its discharge outlet within said intermediate conduit, said inner and intermediate conduits providing a passage for the introduction of air, a regulating member having an orifice opening therein for engagement with the discharge outlet of said first conduit for regulating the flow of fuel and air into said mixing unit, and valve members on each of said conduits for regulating the how and pressure of the fuel or air in the respective conduits.

7. A fuel and air mixing unit for burner assemblies comprising an elongated open-ended body, an entrance section on said body inclusive of side walls forming a narrowing passage, said body including a plurality of expansion chambers of successively increasing diameter downstream from said entrance section disposed in open ended relation lengthwise of said body, concentric external, intermediate and inner conduits of selected diameters arranged to provide a passage between said external and intermediate conduits and a second passage between said intermediate and inner conduits, with a third passage internally of said inner conduit, said conduits having their discharge ends disposed in spaced relation to the downstream end of the entrance section of the mixing unit to convey liquid fuel, gaseous fuel and air under pressure into said mixing unit, an air control member for selective positioning to vary the amount of atmospheric air introduced into said entrance section, and means for separately varying the pressure head on said liquid fuel, gaseous fuel and compressed air to maintain a regulated flow of said fuels and air as necessary to obtain efficient combustion.

8. A fuel and air mixing unit for burner assemblies comprising an elongated open-ended body, an entrance section on said body inclusive of side walls forming a narrowing passage, said body including a plurality of expansion cham bers of successively increasing diameter downstream from aid entrance section disposed in open ended relation lengthwise of said body, concentric external, intermediate and inner conduits of selected diameters arranged to provide a passage between said external and intermediate conduits for gaseous fuels and a passage between said intermediate and inner conduits for air under pressure with a third passage internally of said inner conduit for the flow of liquid fuel, said conduits having their discharge ends disposed caverns inspaced relation to the dcwnstreamrendiotfthe entrancersection; tosconvey fuels: and air into said unit, a nozzle in the end of said external condfiitdor. controlling theflow of. said feels. and air: external thread's"on"the outer'surfa'ce of. said external conduit; an air controi" disk? mounted onsaid' threads" for selectivepositioning, T011 said conduit to vary the amount of? atmospheric? air 'introducedi'into'saidentrancetsection, and means forfseparately'varyingthe' pressure headionsaid liquid: fu'ei'; gaseousfuel and compressed? air'to maintaina' regulated-flow OfISEtid fuelsand air asnecessary to obtainefiicientwombustion;

9; Affuel' and air mixin'g'nnit for burnerassemblies comprising an elongated open-cnded b'ody, an" entrance section on said*- body inci'u'siveof side walls forming: a.-narrowing:;passage and an openings of minimum diameter consistent. with the flow requirements-of -'tlfe .mixing unit; means forxinj-ecting. streams air andifueliinto said entrance chamber at=itsiopen..end, said body forming}v alplurality of "expansion.. chambers,,,including a first expansion chamber disposed downstream from said entrance section of substantially cylindrical shape, a second expansion chamber downstream from said first chamber of substantially cylindrical shape having an internal diameter greater than the internal diameter of said first expansion chamber, a third expansion chamber downstream from said second expansion chamber of substantially cylindrical shape having an internal diameter greater than the internal diameter of said second expansion chamber, constriction members between said chambers having surfaces arranged to form passages between said chambers having a diameter less than the diameter of the next adjacent upstream chamber, and a constriction at the discharge end of the last of said chambers providing a discharge opening of diameter less than the diameter of said last chamber and greater than the diameter of the passage through the next adjacent upstream constriction member.

10. A fuel and air mixing unit for burner assemblies, comprising an elongated open-ended body having an entrance chamber open to the atmosphere, said body including a plurality of expansion chambers of successively increased cross sectional area downstream from said entrance chamber, a plurality of constriction members between said chambers having surfaces arranged to form passages between said chambers having a cross section less than the cross section of the next adjacent upstream chamber, and a conduit means for delivering fuel into said entrance chamber for subsequent mixing during travel through the mixing unit.

11. A fuel and air mixing unit for burner assemblies, comprising an elongated open-ended body having an entrance chamber, said body including a plurality of expansion chambers disposed in open ended relation lengthwise of said body of successively decreasing length downstream from said entrance chamber, said chambers being separated by a constriction therebetween, and a conduit for delivering fuel and air to a point of discharge into the entrance chamber of said mixing unit.

12. A fuel and air mixing unit for burner assemblies, comprising an elongated open-ended body having an entrance chamber open to the atmosphere, said body including a plurality of expansion chambers of successively increased cross sectional area and decreased length downstream from said entrance chamber, a plurality of constrictiorf members lietweerr saidschamhers having surfaces arranged o form passages-fibe tween said chambers having a cross I sectional area less than the crossssectional area of the next adajz'tcent upstream chamber; and :a -conduitzifor delivering air an'dz fuel into. the first upstream chamber of said mixing 13. A mixing unit for burner assemblfesscoms prising an elongated'bpen body havirtgzimperferat'e sid'e walls;- anentr-ance *sectionnon' said lbody arrangedto"receivestreams of=airand fuelt means fen irrj ecting' streame= of fair and fuel: intonsaid entrance:section'at its open' end; said-bod y-formr ing a piurality of expansion chambers, including, a first expansion chamber' downstream fromasai d entrance section; a: second expansion chamber dc nst'ream-*- fr0mz1 saidifirst expansion :chamber =reater ntern'alcrosszsectitirr thantsaidifirst chamber; a this expansionchamber down stream H from saidsecondi expansiorr chamber: of greater cross section dimension than the internal cross=--'sectibn ofsaid second chamber, and restrictions acting as division members between said chambers having surfaces arranged to form passages therebetween having a cross section less than the cross section of the next adjacent upstream chamber so as to mix said streams in their travel through said chambers.

14. A mixing unit for burner assemblies comprising an elongated open-ended body of circular cross section having an entrance section inclusive of side walls forming a narrowing passage arranged to receive streams of fuel and air, means for injecting streams of air and fuel into said entrance section at its open end, said body including a plurality of expansion chambers of successively increased diameter downstream from said entrance section, and a plurality of restrictions acting as division members between said chambers having a diameter less than the diameter of the next adjacent upstream chamber, said passages being of successively increasing diameter downstream from said entrance section so as to mix said streams in their travel through said, chambers.

15. A mixing unit for burner assemblies comprising an elongated open-ended body having an entrance section inclusive of side walls forming a narrowing passage arranged to receive streams of fuel and air, means for injecting streams of air and fuel into said entrance section at its open end, said body including a plurality of expansion chambers downstream from said entrance section, and a plurality of restrictions acting as division members between said chambers having surfaces arranged to form passages between said chambers having a cross section less than the cross section of the next adjacent upstream chamber, said passages being of successively increasing cross section downstream from said entrance section so as to mix said streams in their travel through said chambers.

16. A mixing unit for burner assemblies comprising an open-ended body of circular cross section, an entranc section on said body inclusive of side walls forming a narrowing passage arranged to receive streams of fuel and air, means for injecting streams of air and fuel into said entrance section at its open end, said body in-v cluding a plurality of expansion chambers downstream from said entrance section of successively increased diameter, restrictions acting as division members between said chambers having surfaces arranged to form passages between the chambers having a diameter less than the diameter of the'next adjacent upstream chamber, and a constriction at the discharge end of the last of said chambers providing a discharge opening of diameter less than the diameter of said last chamber and greater than the diameter of the passage through the next adjacent upstream restriction so as to mix said streams in their travel through said chambers.

17. A fuel mixing unit for burner assemblies comprising an elongated open-ended body having an entrance chamber arranged to receive streams of air and fuel, mean for injecting streams of air and fuel into said entrance chamber to its open end, said body including a plurality of expansion chambers of successively increased cross section downstream from said entrance chamher, said chambers being of substantially equal volume, and a plurality of constriction members between said chambers whereby said streams are 'mixed in their travel through said chambers.

JOHN L. MHCFARLANE.

References Cited in the file of this patent UNITED STATES PATENTS Number Number Name Date Dennis May 13, 1902 Lindemann et a1. Feb. 8, 1916 Armor Feb. 27, 1917 Mastenbrook Sept. 25, 1917 Schroeder Sept. 5, 1922 Zander Dec. 4, 1923 Argo et a1. May 7, 1929 Foster June 14, 1932 Methudy May 16, 1933 Maxon, Jr Jan. 30, 1945 Focke et a1 Aug. 28, 1945 Clements Jan. 29, 1946 FOREIGN PATENTS Country Date Great Britain of 1876 Germany Sept. 24, 1900 Great Britain of 1909 France July 2, 1934

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