US2487752A - Method of igniting organic fuels - Google Patents

Description

Nov. B, w49 J. G. coHN 432752 METHD OF IGNITING ORGANIC FUELS F118@ Dec. 19, 1947 www Patented Nov. 8, 1949 TE D:

METHOD OFrfIGrNITIlIG.ORGANIG.RUM-.K2

Johann Gunther Cohn, Eastorangef J;`as.:

signorto 4Baker & Cog, Incr, Newark'NJ porationl of-NeWJerseyv ApplicationDecemhen 19, 19th-Serial1 Noa-7923731' 2"'Claimsr' (Cl. 219-32) Thisinvention deals with fuel'ignitersandfis concernedin particular. withl a .method of igniting fuelsin molecular or other. stateof ne subdivision,.. such for, example` asinflammable gasesor atomized liquid fuels..

Gas igniters, as such, are, ofcourse, known. and have been.used1in,a.variety ofappliances incandescentl wire-rely on` the principle. ofin-k duced ignition by meansrof a` heating element at a temperature at least equal .tothe ignition tem-- perature; of the fuel under.v the` particular. condi-.- tionsainvolved, thexiuel-air mixture beingv heated locally,to'suchatemperature that the `heat gener atedA is fsuicientlyflarge tov propagateiiame igni` tion; inthel particular mixture.

suffer from a number of shortcomings. Pilot flames especially. are expensive inuse, unreliable` andfdangerous. Electrical sparks and incandescent Wiresare preferable to the pilot light in many; respectsbut are.quiteeexpensive--andfor this; reason unsuitable-f or ,v most frequent applications; Thus, for instance, in the case of` electrical resistance igniters, iny order to.v insure vignition independently-of .voltage fluctuations, itis necessaryl to operate such resistors at atemperature substantially irl-.excess of the minimumtemperatureat which ignition occurs.v This severely shortens the life-of such resistors since at such, temperaturethe, metal of thevvire is subject to recrystallization,.grain growth. and softening. To avoid such. an excessive temperaturey one may have to use avoltage stabilizer which makes' the appliance too expensive for most uses. Furthermore, the operation of such igniters isquiteV expensivezdue tothe very high power. consumption.

Experiments have been made to ignitegases byA means of catalyticA igniters,= i; e.- by means of'. catalysts fof. v platinum or..v the like-f, the; ignhl tion of the gas being vbased on thecatalytic combustion: of. the inflammable gas. In practice; however, suchxexperimental catalytic ig;- nitersfhave been found4 wantingydue to unreliability. of operationaand diilculties in initiating. or maintainingV4 the; catalytic reaction and, par# ticularly, iniaccelerating the vcatalytic `combustion to apoint Wherethelflameless combustionvof.v the catalytick reactiony ignites 1 the gaseous. fuel:`

incandescentA Such ,y igniters;`

amore In some cases, the;initiation'.ofithev reactionv andthe accelerationgthereof to ultimate; ignition.

is easier. than.in.othercases. Y Friinstan'ce inthe: case. of'manufactredorsc-caliedfcitygas. such. catalytic reaction is. relativelyv easydue to the' presencein such gas.of'free:hydrogen,thecata4 lytic. -combustion-of.. free. hydrogen being.A easily initiated leading to the ignition ofthe organic.

fuel. In .the case. ofA natural.;gas1.whicl1.consists mainly of.: methane; withtmnor; other; components.

and .also in.- the` case of..commer.cial., gases, such.- as,. methane, propane; ,hutane ethane. etc.,. notcontaining. free... hydrogen-,1. ignition` through.:

catalytic combustion. .of-.1 the; organic .'fuel.. is.J ex.-v

tremely diicult andthe: commercial. catalytic,

igniters doi not. operate -a-tsall. with. such... gases..

Under all conditions-1 ,cata1ytic-;igniters as here.- tofore proposed.. are: very;- erratic. andmoreover; show. a substantial:4 timeflag; .between the. start. ofthe catalytic reaction and-'the ignition,

It..is,. therefore;A onefobiect.- of"A this invention: to provide x a; simple.,V igniten' for.: 4 nelyi. divided fuels which: shall .be usedcon': mvarietw; of appli@ cations;. ltr-is anothexzt-objecta-tozprovide isuclx igniters for hydrocarbons, such as, for instance, propane, butane, etc. free:` fromu uncombin'ed hydrogen.` It is:still-fanother'objectzofthislinvenV tion to provide an: igniterrwhicli-shall'leadeto the combustion offsuchfuels.byatcombination of! electricallyas wellas'catalyticall'yIgeneratedlieat, irrespectivev of 1 Whether orf noti suchy fuel con-r tains free hydrogen. It-'isstilbanotheriobject of this invention to provide an: igniter" as VdescribedI which shallr be -simple =and`f suiiiciently'inexpensive to permit its installation-andi' reliable -usein industrialas wellas-domesticappliances: Other objects and; advantages,A ofil my invention" will" appear in the description hereinafter'.folltawing,

From the researchof 'thet-Unit'ed" States. Bureau' off'Mines. (Technical Paper.V 375fby. Pf. GL. Guest Ignition of. Naturali Gas-A'iil Mixtures-.by v-Heat'ed Surfaces), it alapearsn.that;thougha one. might have.. supposed catalyti.. action, tending o to accelerate the combnstiontoiheugases,,would result-.in.lowenignition..-temperatnres; ox-rather that ignition wouldaoccursthroulh:aoatalytically.-

heated. Vsurf ace zv maintained -at .aflower tempera.- ture, it was founda'thatsthef-temperature; of?. the catalytic; material;V mustsrbev higher# for Q. ignition of thef natural-l gasl than?,thetemperature-y ofanon.- catalytic materia1s;ez;.g;z muchaas; 3.00"?A C.` higher .forv thef-catalytcallxgactiveinlatinumzthan. for the: :catalyticallyffinwtfveinickelasthatazfor al1! practical: purnosesr` a@ noncatalytic.' material by the production of reaction products. The cat. alytic ignition starts with a reaction of relatively slow speed and which is completely confined to The slowly generated re-Y the catalytic surface. action heat raises the temperature of the catalyst surface and of the adjacentV gas layer', thusV continuously increasing the speed of the catalytic reaction and also inducing the thermal reaction in the adjacent gas layer until'e'ventually enough reactive particlesy or chain carriers are createdY to cause ignition of the gas. This process is, however, inhibited by the formation during the reaction of non-iniiai'nmable reaction products and also by the consumption of the available oxygen in the neighborhood of the catalyst. Furthermore', the ultimate ignition is interfered with in part -by rapid loss, by conduction, of the heat of the reaction by the catalyst, so that an insufficient amount of heat energy is available to ignite the gas.

In catalytic igniters as heretofore described, the results obtained are, therefore, highly irregular and contradictory due to the overheating necessary to overcome inhibiting effects. Thus there is no particular advantage in the use of a catalytic wire over an incandescent wire and, furthermore, the cost 0f a catalytic wire able to resist the overheating is such that such catalytic wire becomes entirely impractical and, since the catalytic function is not used, would in the final analysis be an incandescent resistance heater rather than a catalytic element. Thus, e. g. in the Bureau of Mines paper referred to, it is stated that, as a matter of practical fact, it is quite dinicult to ignite natural gas without fusing the catalytic platinum wire, due to the accompanying overheating.

I have found that it is nevertheless possible, notwithstanding the Vconclusions reached by earlier researchers, to provide a catalytic igniter for inflammable gases and lother fuels such as kerosene and the like in finely divided state, in a fuel-air mixture which is highly practical and which is, in fact, far superior lto any igniter heretofore developed and which is, thus, adapted to ignite not only synthetic or manufactured gas (socalled citylgas) containing free hydrogen, but also natural gas, saturated hydrocarbons such as methane, butane, propane and so forth and other finely divided fuels,v irrespective of the presence or absence of free hydrogen. l The structural features of the igniter for igniting such fuels according to my invention are illustrated in the accompanying drawings, forming part hereof, and ,in which: Figure l represents a diagram of an ignition system embodying the igniter, Y

'Figure 2 represents an elevational view of on embodiment of the igniter, and Figures 3 and 4 represent diagrammatic view o f two other embodiments of the igniter. Figure 1 illustrates a system of ignition, involving a gas burner l with hash-back port 2 and flashback tube 3 andan electrically heated igniter 4 of catalyst metal, e. g. platinum, in the form of a coil.' The igniter may' be, used in the horizontal position, as shown, or in avertical or any inclined position. The igniter coil il is more specifically shown in Figure 2 as consisting of a helically coiled wire in a circuit 5 and 5' and power supply 6. In Figure 3, the catalytic igniter il is shown in the form of a helically coiled wire with decreasing coil diameter and increasing coil pitch, and in Figure 4, the catalytic igniter is shown in the form of a plurality, in this case two, helically coiled platinum wires Il' and 4", coil ll having a larger coil diameter than coil il" and surrounding coil Il" along part thereof, ea-ch coil being adapted to be electrically heated in the circuit 5 and 5 and 5" and 5' respectively.

The igniter coil 4, as well as the coil Ll and is provided with a plurality of turns of such number as may be desired. The number of turns of the coil depends somewhat on the fuel to be ignited, the number increasing with the difficulty of igniting the fuel involved. For gases not containing free hydrogen, the number of turns should, preferably, be at least six for such gases asbutane and propane and at least twelve for a gas such as methane. The coil diameter and the spacing of the turns should be such as to provide a compact'coil unit with large catalyst surface in a relatively small space. For this reason, the coil spacing should be as close as possible, the turns being spaced apart just sufficiently to avoid shortcircuiting. The coil diameter is somewhat variable, being, however, preferably, of the order of from about 1 to 5 mm., the preferred diameter being about 2 to 4 mm.

The wire itself may consist of a single strand or a plurality of strands. The catalyst metal, of which the wire is formed, is normally platinum or an alloy thereof with other suitable metal ormetals, such as metal of the platinum group, e. g.

rhodium or iridium, or other precious metal,

divided condition refractory oxide, such as oxide of thorium, beryllium, and so forth. As far asv alloys of platinum are concerned, they will normally lcontain a major amount of platinum and a minor amount of alloying metal, e. g. in the form of such alloys as platinum with 10% rhodium or iridium, and so forth.

The critical factor in the construction of the igniter is the diameter of the wire of the coil, correlated to a small electrical power input. This diameter must not exceed a maximum of about .003 and, while not falling below about .001, should preferably be of the order of about .0015 to .0025". In the case of stranded wire, the sum total of the diameters of the individual strands must be such as to yield cross-sections within the limits stated. The power input to the catalyst wire is very small, up to the order of about 2 watts, but in anyrcase not more than that which would raise the temperature of the coil to a temperature below the recrystallization temperature of the catalyst material, i. e. the temperature at which recrystallization and grain growth occur and sagging vof the wire takes place due to serious softening, such as 600 C. for platinum.

Taking, for instance, a catalyst wire of platinum with a diameter of 0.002" in the form of a helical coil, in accordance with the embodiment of Figure 2, with six turns,'with a coil diameter of 2 mm., the wattage input is approximately`0-5 watt for the ignition of propane, compared with a customaryinput of 30 watts for ignition of the incandescent electrical resistance type. The same igniter, Figure 2, when used for ignition of city" gas containing free hydrogen requires arl-'input 4of aboutil Watt.

`The igniter may be in the 'for-m of a straight coil, ais-illustrated in Fig-ure 2,'or it maybe in the even date, I'Serial Number '792,674 dealing with such heterophase catalyst igniters, such igniters being of particular usefulness for the ignition of methane and the like.

Insofar as the use of the igniters in appliances, etc. is concerned, any suitable system may be employed. Figure l is intended to illustrate the use of the igniter of this invention in the conventional flash-back system. Any other applicable system may, of course, be employed.

The operation of the igniter according to this invention is as follows. The igniter is maintained, by way of the electrical heating, at a relatively low temperature, e. g. approximately 300 C. in the case of propane, butane and the like or approximately 450 C. in the case of methane, which is more difficult to ignite than the other gases mentioned, and is brought in contact with the gas 0r other fuel to be ignited which will customarily be by way of playing a stream of the fuel, mixed with air, on the igniter. A nameless combustion of the fuel ensues and, in the manner described above, the temperature is raised continuously until ignition occurs. time interval between the first contact of the fuel with the igniter and its actual ignition is of the order of one second or fraction thereof, so that to the observer such ignition appears to occur instantaneously. Upon completion of the ignition, the igniter is withdrawn from the fuel or the fuel is Withdrawn from the igniter, as by means of installing the igniter in a flash-back system. The withdrawal may also be accomplished by directing a horizontal stream of gas to the igniter, the flame of the ignited gas thereupon rising and thus removing itself from contact with the igniter.

The electrical heating of the catalytic igniter may be either continuous or controlled to coincide with the opening of the fuel jet, as may be desired.

The effective operation of the igniter of this invention has been quite surprising. It shows a very great advantage over the usual catalytic igniter in that the ignition occurs with such rapidity that no detrimental overheating of the wire takes place. In contrast to the resistance heaters the igniter herein described has to be heated electrically only to a very moderate temperature, far below such temperature at which recrystallization, grain growth or softening take place. This is possible because the electrically generated heat is not used to actually induce the ignition but only helps in starting the catalytic reaction. Subsequently, the catalytic process generates the heat leading to the ignition of the fuel. It is thus not necessary, in the case of igniters according to this invention, to heat the igniter to the ignition temperature or even beyond' such ignition temperature. It may be noted, also, that if a platinum coil, as used in the embodiment of the igniter of this invention, is heated by external means, rather than by elec- The 6 trical lmeans', ignition of hydrocarbons Jdoes not occur in the manner described lin the instant case, but that such coil .has to be heated close to the ignition temperature of the fuel before ignition occurs.

The small diameter wire of the igniter of the invention is adapted to heat 'up `rapidly with the progress of the catalytic reaction to the peak temperature Aprevailing upon ignition vof the fuel, but the time at which the catalyst is at vsuch Apeak temperature is only a .small fraction lof the ignition time. Recrystalliza'tion and grain growth and softening are substantially avoided during such short time interval.

The igniter may be used for the ignition of iniiammable gases, including saturated hydrocarbon gases not containing free hydrogen. It may also be used for the ignition of finely divided other fuels, such as atomized fuel oils, kerosene, etc., i. e. organic fuels in finely divided state in a fuel-air mixture, wherever the fuel in such finely divided state is capable of being oxidized in the presence of the catalyst.

The igniter may be used in domestic and industrial appliances, such as stoves, furnaces, and so forth. The source of electrical power may be the line supply, with an interposed resistor or with a suitable transformer, or a battery, as may be desired. The igniter may also be used in instruments or other devices, e. g. in cigarette lighters in conjunction with a small storage or dry battery, or in conjunction with a transformer fed by the line supply, in which case it is not necessary to use special lighter fluids but possible to use any handy organic fuel, such as gasoline.

What I claim is:

l. A method of automatically igniting an organic fuel in finely divided state capable of being catalytically oxidized in a flowing fuel-air mixture in the presence of a catalyst, comprising contacting said fuel-air mixture with an electrically heated helical closely spaced coil of catalyst metal taken from the group of metals of the platinum group and alloys thereof, the wire of said coil having a diameter of from 0.001" to about 0.003, electrically heating said coil during said contact to a temperature substantially below the ignition temperature of said fuel in said fuel-air mixture and below the recrystallization temperature of said catalyst metal, thereby oxidizing said fuel and raising the temperature in the neighborhood of said coil to the temperature at which ignition of said fuel in said fuel-air mixture occurs, and automatically terminating the contact between said coil and said ignited fuel.

2. A method of automatically igniting an organic fuel in finely divided state capable of being catalytically oxidized in a fuel-air mixture in the presence of a catalyst, comprising contacting said fuel-air mixture with an electrically heated helical closely spaced coil of platinum or alloy thereof, the wire of said coil having a diameter of from 0.001" to about 0.003", electrically heating said coil luring said contact to a temperature substantially below the ignition temperature of said fuel in said fuel-air mixture and below the recrystallization temperature of said catalyst metal, thereby oxidizing said fuel and raising the temperature in the neighborhood of said coil to the temperature at which ignition of said fuel in said fuel-air mixture occurs, and automatically -irmnating the contact between said coil and Number said ignited fuel. 712,156 JOHANN GNTHER COHN. 1,118,943 1,590,891 REFERENCES CITED 5 1,895,032

The following references are of record in the fil f this t t: J

e o Y pa en 2,360,603

UNITED STATES PATENTS Number Name Date 10 567,923 van Hoevenbergh sept. 15, 1896 Number 670,334 simonini Mar. 19, 1901 339469 Name Date Simonini Oct. 28, 1902 Lyon Dec. 1, 1914 Heany June 29, 1926 Fisher Jan. 24, 1933 Gibson Mar. 12, 1935 Schmitt Oct. 5, 1937 Kauffman et a1. Oct. 17, 1944 FOREIGN PATENTS Country Date France Nov. 17, 1904

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