US2458543A - Low velocity gas burner - Google Patents

Description

Jan. ll, 1949. N. J. 'uQuHART Low VELOCITY GAS URNER 4 Sheets-Sheet 2 Filed Apri; 24, -1945 I INI/ENTOR MrmcwJUr-quamf B Y I l .1' TTORN E Y Jan. 11, 1949. N. J. URQUHART 2,458,543

LOW VELOCITY GAS BURNER Filed April 24, 1945A 4shee't`s-sneets Jan. l1, 1949. N. J. URQUHART LOW VELOCITY GAS BURNER 4 sheets-sheet 4 Filed Aplil 24, 1945 IN1/wrok l Norman d Urquiza/'t JTTORNE Y Patented Jan. 11, 1949 LOW VELOCITY GAS BURNER Norman J. Urquhart, Scenery Hill, Pa., ssignor to Combustion Processes Company, a corporation of Pennsylvania Application April 24,1945, serial No. 590.034

1o claims. (ci. 15s- 110) This invention relates to a gas burner having advantageous features when used in conjunction with furnaces of various sorts. The application herein is a continuation-impart of my copending applications Serial No. 499,814, filed August 24, 1943, now abandoned, and Serial No. 563,685, filed November 16, 1944.

Primary objects of my invention are to provide a gas burner which is capable of furnishing a low yvelocity luminous flame composed of an unstratiiled blend of gases; in which the type of llame and the atmosphere created by the burner in the enclosed space of a furnace is under con* trol; and in which the combined fuel and air volume delivered to the burner may be varied within wide limits and the type of llame and atmosphere created by the burner combustion may be varied without departing from the low velocity of the combustion flame and without loss of its high luminosity.

Another object of my invention is to provide Vmeans for producing by operation of tht,` burner an extremely high furnace temperature, which means is so formed and is so associated in the burner organization that its operation does not impair the effectiveness of the burner as a whole in attaining the primary objects of the invention noted above.

Other advantages, incidental to my invention are inherent in the structure of my burner or in the. method of combustion which may be performed in it, and will in part be explained or readily understood from the following description of the burner and its operation.

In attaining these objects I depart from the usual principles of lburner construction by an arrangement which avoids rapid flame movement and which does not utilize the principles of premixing thev combustion air and fuel or of multistage combustion. On the contrary my burner is so arranged that mixing takes place within the combustion areas of the burner and is begun in the rearward portion thereof under the heating effect of an initial supporting llame of substantial heating value. Also, the fuel gas consumed in the burner is so introduced with relation to the supporting flame and additional air is so supplied with respect to both that mixing in the combustion areas of the burner is effected at an early stage under the influence of cracking conditions and conditions which produce a reacted and unreacted gases,.with such early cracking and rapid and complete commingling that as delivered to the furnace it gives therein a highly luminous condition and an atmosphere which is proof against oxygen slippage, and which therefore does not bring substantial quantities of free reactive oxygen into contact with the furnace charge. Considering a prime utility of the burner, this effect is of great value in metallurgical furnaces in which the effect of the furnace atmosphere in producing oxidation of the furnace charge is a matter of primary importance.

Also, as indicated above, the combustion rate and heat output of the burner may be varied within wid limits without causing stratification, `without producing high velocity of flame movement and without loss of luminosity. Thus it is possible to control combustion by regulating the volume of the fuel and total air supply to the buiner to vary the heat output of the burner and the atmosphere created in the furnace, while retaining throughout different orders of combustion the desirable burner and furnaceconditions which have been noted above.

In the accompanying drawings illustrative of my invention:

Fig. I is a longitudinal sectional view through a gas burner organization embodying the principles of my invention;

Fig. II is an elevationalfront view of the burner structure lying rearwardly of the furnace `wall in which the burner is associated;

Fig. III is a cross-sectional rear view of the burner taken-in theplane of the section line III-III of Fig. I;

Fig. IV is a longitudinal sectional view through a modified form of the burner constructed and arranged to include an additional structural feature and to give an additional operative eil'ect high rate of molecular movement ol' the several gases with complete and uniform mixing thereof. 'I'hus the burnerlcreates and supplies throughout a wide operating range an runstratiiled blend of to the structure and operation of the vburner as shown in Figs. I to III inclusive;

Fig. V is a cross-sectional view through the modified burner taken in the plane of the section line V -V of Fig. IV.

Fig. VI is a cross-,sectional view through the modified burner taken in the plane of the section line VI-VI of Fig. IV.

The structural organization of the burner comprises an outer shell having a peripheral wall i, a rear closure wall 2, an inner shell having a vperipheral wall 3 and a gas ignition tube 4. At

its forward end'the wall i of -the outer shell .carries a flange 5 welded or otherwise suitably secured to the wall 6 of a furnace to surround a port in the furnace wall. Within the outer shell i of the burner there is a refractory heat radiating lining 1 which abuts rearwardly against a circular flange or wall 8 standing normal to the axis of the burner between ignition tube 4 and the inner surface of outer shell I. The refractory lining 'I extends forwardly to the port in the furnace wall, and cooperates with a refractory lining 1' within the port in the furnace wall to bound a combustion tunnel or chamber 9 lying partially within the outer shell of the burner and partially within the wall of the furnace. The closure wall 2, and that portion of heat of the combustion sumciently to impart to the primary flame and the combustion gas a definite forward propulsion. i

Mixing of the gas entering chamber 22 Iof the ignition tube and the air entering at the same end of the chamber and substantial combustion in the chamber arc promoted by preheating the gas in annular entry chamber I8 by contact with the the peripheral wall I that extends between the y walls 2 and 8, define a rearwardly closed casing.

A primary air tube I proiects forwardly through rear closure 2 to adjacent the rearward end of gas ignition tube 4 and receives low pressure air through a valved primary air duct II branching from an air conduit I2 having a valve I2' therein. Another valved branch duct I8 from air conduit I2.opens into a chamber I4 lying between inner and outer walls I and 3 and rearwardly of circular flange l. Flange 8 has therein a series of ports Il extending around it to place chamber I4 in communication with the combustion tunnel or chamber 9, which includes the chamber within refractory lining 1 and the port through the furnace wall. A gas duct I6 having a valve I8' therein terminates in gas inlet tube I1 which passes through peripheral walls I and 3 to open into an annular. chamber I8, lying b`etween inner wall 3 and the wall of ignition tube 4 and primary air tube I0.

In operation of the burner, air which in the form of the burner shown in Figs. I to III inclusive is the total combustion air, is supplied-to the burner by air conduit I2 and branch conduits II and I3 at relatively low pressure, such as a pressure of from about .5 pound per square inch to 1.5 pounds per square inch in some suitable manner as by the action of a low pressure fan. The air passing by way of branch air duct IIv to air tube Iii is to be considered primary air inasmuch as it supports combustion of gaseous fuel in the primary combustion chamber lying within ignition tube 4. The air introduced by way of branch air duct I3 enters secondary air chamber I4 and issues from it through ports I in wall 8, as secondary air which supports combustion in combustion tunnel 9. Valve I9 in branch air duct I I and valve 20 in branch air duct Il serve to aPPortion the low velocity combustion air into primary air and secondary air.

Gas is supplied to the burner by way of gas duct I6 terminating in gas inlet tube I1. 'I'he gas likewise is supplied under moderate pressure such as a pressure of from .5 pound per square inch to 1.5 pounds per square inch. The gas entering annular gas chamber IB receives heat from the wall of ignition tube 4 and enters the interior of that tube at the rear thereof. The forward edge I0' of primary air supply tube I0 and the rearward edge 4' of gas ignition tube 4 are oppositely chamfered to provide an annular. gas inlet passage 2| directed obliquely inwardly and forwardly of the primary combustion chamber 22 in the ignition' tube.

In -chamber 22 of gas ignition tube 4 the gas mixes sufficiently with primary air entering the chamber from air supply tube I0 to give combustion within the chamber. A proportion of the gas does. however, pass forwardly along the interior surface of tube 4 to issue as a relatively thin layer surrounding the inner flame. In operation, the primary air and the fuel gas are expanded by the heated outerwall of the ignition tube. This preheating should not be of an order sufficient to produce cracking of the gas and the deposit of carbon on the walls bounding the chamber I8. It is, therefore, possible to make ignition tube 4 relatively so short that there is no tendency for the flame to be smothered. It is merely necessary that the length of the tube be sufficient so to preheat the gas in chamber I8 as to expand it, thus facilitating mixing with the primary air and placing the gas in a condition favorable to combustion.

The size oi' the burners and their component parts naturally will differ for different uses to which the burner is to be put in service. I have found that the optimum proportion'of the length of the combustion tube to its diameter varies with the size of the burner, but that there is no relative propcrtioning of length to diameter strict adherence to which must be had. In general the primary combustion chamber within ignition tube 4 must be sufilciently long for partial combustion of the combustion gases introduced at the rear of the chamber to form, a core fire therein; and must not be so long as to smother the flame or to require for its sustension a cracking of the gaseous fuel in chamber I8. The burners first made and operated in accordance with my invention were of relatively smally size, having a primary air tube one inch in diameter and an ignition tube about one and one-half inches in diameter. With a burner of this size which may be considered an advantageous size for quantity production and sale, I have found it desirable to provide an ignition tube the length of which is approximately twice its diameter. In constructing burners of larger size I have found it desirable to decrease the length of the ignition tube with respect to its diameter down to an approximate equality and in the larger sizes even to make the diameter of the tube somewhat greater than its length. In all sizes of burner the gas inlet passage 2i around the air tube at the rear of the primary combustion chamber is kept relatively narrow.

Upon issuance of gases from ignition tube 4 into the rearward region of combustion tunnel 9 lying within refractory lining 1 the expansion begun in the rearward portion of the burner continues. It is, therefore, necessary that the dimensions of the combustion tunnel be greater than those of the primary combustion chamber in order to accommodate continued expansion of the gases. There is advantage in having the rearward portion of the combustion tunnel within refractory lining 'I of somewhat lesser diameter than the forward portion of the combustion tunnel continued through the wall of the furnace. because such arrangement while providing space for the outward expansion of the gases brings the tunnel wall forward of the ignition tube into close proximity to secondary air entering through ports I5 and to the primary flame initiating in ignition tube 4.

In proper operation of the burner, primary air lmust be insufficient to approximate complete stantial heating value. It may be explained that with the described preheating of the gas and mixing of the preheated gas and air lin the primary combustion chamber of the ignition tube, there is in the combustion tunnel an interior flame in which combustion is substantially coin-4 plete and which is surrounded by unconsumed fuel in preheated and cracked condition from the primary combustion chamber; and by secondaryl air. The primary flame is a clear. smokeless and relatively non-luminous flame: and its central portion' inl which combustion is substantially complete insures against its extinguishment under 4the exigencies attendant upon practical use of the burnerL It thus is to be understood, and this is anim.. portant feature in the operation of my burner. that the primary flame above described not only serves as a combustion supporting flame, but that it has of itself suiilcient heating value to raise the interior of the combustion tunnel I and its bounding refractory surface to a high temperature. Secondary air, which in the proper operation of my burner is supplied in volume sufllcient to take part at least substantially in the combustion. is heated by radiant heat from the surface of the combustion tunnel immedi' ately upon its entry into the tunnel, as well as by heat directly received from the primary flame.

In operating my burner the supply of primary air, fuel and secondary air are all adjusted to give a primary flameof desired characteristics and such adjustment readily may be made initially by observing the primary flame itself. That is. fuel and primary air supply may be adjusted until a lclear flame of substantial size and obviously high heating value has been obtained. Desirably this primary flame is. allowed to burn with a relatively small supply of secondary air until the wall of the combustion tunnel has been brought to a relatively high temperature, and at such stage the supply of secondary air is gradually increased until a very bright luminous flame moving forwardly at low velocity is seen to be entering the furnace from the tunnel. At this point it isI frequently desirable to make some compensatory` relative adjustment between primary airand secondary air to get the exact desired combustion conditions.

Let it be assumed that the burner is operating with both valve 2 0 in secondary air duct i3 and valve i8 in primary air duct il fully open. This provides a proportioning of primary air and secondary air substantially in accordance with the cross-sectional areas of primary duct il and secondary duct i3. Desirably, though not necessarily. the ratio between the cross-sectional areas of these ducts is such as of itself to approximate optimum proportioning of primary air and secondary air with both valves fully open.

Under the described conditions the rapidly" expanding conical layer of 'gas reacting with the primary air, gives a primary flame of substantial size. Under its heating effect, and the heating effect of radiation from the tunnel wall there is a rapid expansion of both the primary flame and secondary air. The expansion, incident to the heating and cracking, exerts an expanding pressure against the wall of the combustion tunnel which forces the secondary air inwardly as the primary name and fuel expand outwardly. The secondary air being introduced under low pressure, the expansion produces transverse mixing rather than accelerated forward motion.

The actual effect produced by heating the of the combustionair tain an adequate heating effect of gases in this 'region thus is one of rapid molecularmotion by which the gaseous substance of the secondary air moves inwardly and the gaseous substance of the primary flame moves outwardly. In movement forwardly of the eombustion tunnel this blending progresses to such extent that the gaseous mixture, comprising both reacted and unreacted of approximately uniform composition throughout its entire volume. This unstratined blending of the'gases persists when the gaseous blend issues into the work chamber of a furnace.

The fundamental action in tunnel 9 is thus the production of a fine and uniform blend of air and cracked fuel. gas, in 'which combustion has in some measure taken place; together with the production of high luminosity in such gaseous body movingfat low velocity through the tunnel.

I believe that the high luminosity of the name.

is due tol the uniform distribution of a great number of incandescent carbon particles in the blended gases.

In many prior art burners this eect is ob tainable for one' proportioning of fuel and air volumes and within a verynarrow range of total fuel and air supply. t obtains throughout a very wide range of total air and fuel supply in operating my burner, as above described. That is, the total air and fuel supply may be cut to a very low point without destroying theA function of the primary flame in heating the air and fuel in such manner as rapidly to produce an unstratifled uniform gaseous blend. There is of course a point at which it is impossible to mainthe primary flame, but such point is low beyond that at which any one reasonably might desire to cut down the heat output of the burner.

This effect of the burner in providing a uniform and apparently molecular blending of the gases is of great advantage when the burner is used with metallurgical furnaces. In most such furnace operations, such as those conducted in heating, heat treating. melting and bath furnaces for iron and steel. it usually is desirable to avoid oxidation of the furnace charge. It has been the experience of the artl that even though the furnace atmosphere may contain less than a suillciency of oxygen for complete combustion, there is a tendency for the occurrence of what is known as oxygen slippage. That is, the oxygen tends to separate from the other gases of the furnace atmosphere and to r gravitate to the lower regions of the furnace chamber in direct contact with the furnace charge. It is an observed fact that even when sufficient combustion air is vprovided to complete combustion, the blended gases delivered by lmy burner are substantially proof against sucil oxygen slippage, so that there may be high heat delivery in the furnace and the furnace charge may be brought to a desired high temperature with minimum scale formation.

It should be emphasizedthat uniformity 'in the gaseous blend and anvunstratified luminous flame is provided by the burner' throughout a wide range in the combined volume of air and fuel and thus throughout wide variation in the rate of combustion. The proportioning lof fuel, primary air and secondary air having been established, the volume of fuel and total air then can be adjusted by means such as the valves i8' and l2', respectively, to the desired temperature conditions without in any substantial degree altering the condition of the burner gases gases, is unstratifled and is many prior art burners.

and the furnace atmosphere. Thus the furnace temperature may be raised. lowered. or maintained, regardless of heat absorption by the charge, without disturbing the luminosity of the flame and without disturbing the blending which prevents scale formation in the furnace. This overall regulation is suitably obtained by use of ratio control apparatus, and most desirably by use of the organization disclosed in my cepending application Serial No. 549,396, filed August 14, 1944, new Patent No. 2,408,114, granted September 24, 1946.

In certain furnace loperations it is desirable to provide an oxidizing atmosphere in the furnace. One example of such condition may exist in soaking pits, in which a close adherent scale on the ingots, or other soaking pit charge, tends toward heat insulation and improvement in the desired effect of the soaking operation. In such ease, without increasing the velocity of the flame, and without loss of luminosity therein, I am able to provide in the furnace an oxidizing atmosphere of the sort to form a fine adherent scale on the soaking pit charge. This I do merely by increasing the volume of total air supplied to the burner; without disturbing the ratio between primary air and secondary air. to give a gaseous blend, otherwise identical with that previously described, which contains an excess of oxygen.- As so used my burner gives a scale formation of superior sort on the furnace charge, inasmuch as the effect ofthe oxidizing atmosphere is uniform in its contact with the charge because of the maintenance of a blended atmosphere in the work chamber of the furnace.

It is to be understood, as is specifically illustrated in my copending application Serial No.

l 563,684, nied November 16, 1944, that my burner not only may be operated to give an effect unobtainable in prior art burners, but if so desired it may be operated to give an effect usual in If the total air be directed either wholly or excessively into chamber Il and through ports i as secondary air, the effect will not be that above described as attendant upon a proportioning of the primary and secondary air supplies. f

Thus if valve I9 in the primary air duct Ii be completely closed, and valve of the secondary air duct I3 be completely open the total air supply is delivered to the burner as secondary air.

Under such conditions the primary flame is supported only by such air issuing from ports i! as mingles with expanding gases from ignition tube I. and the major proportion of the air supply of the burner passes forwardly through tunnel 8 to give a stratified as opposed to a blended gaseous mixture therein. Although the primary flame is itself short' and of substantially lesser heating value than the flame which is obtained if primary air be supplied, this condition produces a long secondary flame burning within and progressively mixing with an outer envelope of secondary air. The tendency thus is to introduce into the work chamber of a furnace a; stratified atmosphere which is not controllable as is the blended atmosphere obtained in the optimum operation of my burner, and is an atmosphere in which oxygen slippage occurs. With combustion of this sort there is only one specific combined volume of fuel and air which produces aluminous flame and in which approximate ultimate blending in the furnace atmosphere is obtainable. With higher and lower total air-fuel volumes to give a greater or lesser Iheat output,

means stratification always occurs. An extreme example of this effect is obtained by multi-stage combustion in which secondary air is progressively added along the length 'of a central flame.

Another operation of Ithe burner simulatini that of prior art burners, and which condition is illustrated in my above-identified application. (takes place if the total air supply to the burner be directed wholly or excessively as primary air. In such case'valve 20 in secondary air inlet Il may be assumed to be wholly closed and valve i9 in primary air inlet duct Il may be assumed to be fully open. With this apportionment of the air supply the primary flame is the only flame produced in the burner. That flame begins at a point substantially forward of the ignition tube. It is a roaring flame in which the air and gas are in stratified condition, there being no effeo tive cracking of the gas or blending in the composition. With a flame of this sort it is impossible to obtain complete combustion without subjecting a furnace charge to the effect of uncontrolled free oxygen. It is, therefore, a fact that in burners capable of operating only in this manner. it is impossible to obtain a high heating effect while avoiding oxidation of a rmetallurgical charge. or to control oxidation in such manner as *f to effect it in desired sort and order.

Figs. IV, V and VI of the drawings show the burner of my invention modified by the addition of specialized cooperative structure. The burner shown in these figures of the drawings does not differ in principle, or fundamentally in structure from the burner shown in Figs. I to III inclusive, except for the addition to which reference lhas been made. The figures of the drawings do show the burner in greater structural detail and in accordance with more finished engineering than do Figs. I, II and III. Referring now to these figures of the drawings, similarly to the showing of Figs. I, II and III the burner comprises an outer shell having a peripheral wall 23 and a rear closure wall 24, an inner shell having a peripheral wall 25, and a gas ignition tube 2B providing the l primary combustion and expansion chamber of the burner. Y

At its forward end the wall 23 of the outer shell -is flanged, and has connected to its flange 21 the flange 28 of an adapter shell 29. This adapter shell 28 has a forwardly presented flange 30 which is welded or otherwise suitably secured to the wall 3i of a furnace to surround a port 22 through the furnace wall. Within shell 28 there is a refractory lining 33 which abuts rearwardly against flange 21 Aoi' the burner shell proper and extends forwardly into the port l2 through'the furnace wall to bound the combustion tunnel 34 throughout its length.

Surrounding ignition tube 28 and extending to wall 25 of the inner shell there is a flange 3B provided with an annularly arranged series of ports 38 arranged to deliver secondary air from chamber 31 lying between walls 23 and 25 of the outer and inner shells. These ports 3B desirably are. as shown, extended through the complete ambit vof flange 25 and equidistantly spaced therein.

Secondary air is supplied through an air inlet duct 38 having therein a valve 89 shown as a butterfly valve in accordance with desirable specific construction. Valved secondary air inlet duct 38 opens directly into secondary air chamber 21. A branch air duct 40 provided with a butterfly valve il opens into a rearwardly closed primary air supply tube 42 passing through rear closure wall 24 and arranged ccaxially within the 9 inner shell of the burner. The air introduced by,

branch air inlet duct 40 to the primary air supgas line 43 opens into annular gas supply chamv ber 44 defined by peripheral wall 25 `of the inner shell, and the walls of ignition tube 26 and air l supply tube 42. The rearward edges of primary 10 air tube 42 and ignition tube 26 are oppositely beveled, to give an oblique gas entry passage, 45 directing the gas angularly inward to primary combustion chamber 46. The peripheral wall 23 and the rear wall 24 de ne a rearwardly closed casing. y

It will be seen that the above structure exactly parallels that shown in Figs. I, II and III of the drawings and it readily will be understood that the functioning of the burner and the desirable regulation attendant thereto is identical with that above described specilcallywith reference to Figs. I, II and III of the drawings.

The structure which is not comprised in the form of the burner shown in Figs. I to III consists of means for providing a fine pressure jet of gaseous iiuid interiorly of the core flame formed in'the ignition tube. Such means comprises a duct 41 extended centrally through rear closure wall 24 into ignition tube 2G. At the forward end of duct 4l there is mounted a jet nozzle 48 constructed to provide a ne jet of gaseous fluid under pressure.l With the burner operating in accordancelwith what may be considered normal optimum conditions to produce an unstratified low velocity flame of high luminosity, the jet from nozzle 48 functions as a mixing jet accelerating the blending of primary gases and secondary air into an unstratified blend of cracked fuel gas, products of combustion, and combustion air. The jet expandsv as it issues from nozzle 46 under pressure substantially higher than the normal burner pressure, and in expanding expands the primary flame. It thus increases turbulence, intensifybeen noted that in practical entirety combustion air is introduced in the low velocity vair stream which is divided into the primary and secondary air. The low velocity of the combustion gases per- 5 mits combustion of the sort which has been above described and avoids stratification in a furnace with which the burner is associated as well as in the burner itself. It is to be noted that the burner does not use the impingem'ent principle to obtain cracking and blending. That is, the burner does not direct a rapidly moving gaseous body against a refractory surface, such as the wall y of a furnace, so to utilize the heat thereof as to crack the fuel. It thus avoids the uncertainties of operation, erosive effect and other undesirable effects of impingement burners.

Although my burner has been specifically described as used in metallurgical furnaces its utility is not limited to furnaces of that sort. Its

various advantageous properties give it definite utility in furnaces of various sorts and for general heating use in which a low velocity iiame of high heating value is desirable. In all its variant uses there is great advantage in the fact that the 25 combined volume of fuel and air utilized by the burner, and consequently the combustion rate and heating effect, may be varied within wide limits withoutchanging the fiame characteristics or composition.

Having shown and described one physical embodiment of my invention both with respect to the burner and with a respect to a method of combustion appropriate to'its use, I wish it to be understood that my invention is not limited to the specific physical and operational details given herein, but that the scope of my invention is to be limited only by the statement of the claims appended hereto.

An example of such obvious modification is 40 found in the formation of the gas inlet passage by way of which fuel gas is introduced at the rear of the primary combustion chamber, and which promotes the mixing oi' some fuel gas with the ing the effect of forming the desired homogeneousf` 15 primary air' other angula'rly directed annular gaseous mixture in the rearward region of the" combustion tunnel and intensifying combustion in that region.

The volume of gaseous iiuid passed through the jetnozzle may be very small with respect to the volumes of fuel gas and combustion air. A

f function of the jet being to accelerate mixing and thus to serve as a, primer for the normal functions of the burner, any gaseous fluid which suitably may be used for the purpose of mixing in the burner may be employed. Thus itis possible to use superheated steam, carbon. dioxide, or the like gas in the jet. Air is preferred, however, both for reasons of convenience andbecause it contributes to the combustion in the primary flame. The use of the high velocity mixing jet is desirable when operating at extremely high temperatures,

and its use particularly is indicated with fuels of certain combustion characteristics, such for example Vas coke oven gas. When jet nozzle 48 is placed at, or a short distance forwardly or rearwardly of the forward end of ignition tube 26, the `iet is able to expand immediately upon its issuance from the nozzle, and I have found that in such position it does not interfere with the propagation of the primary flame in the ignition tubek As shown, it is placed to deliver its jet immediately at the forward end of the tube.,

Certain desirable characteristics; of my gas burner may be further'explained. It will have 75 port arrangements are substantially equivalent to the one shown for increasing the proportion of the fuel gas initially mixed with the air.

I claim as my invention:

1. A low velocity gas burner comprising a rearwardly closed casing, a valved primary air inlet duct projected forwardly from the rear of the said casing, a tubular member forming a primary combustion and expansion chamber of greater diameter than said air inlet duct and extended forwardly from adjacent the forward end of the said duct, means forming a gas chamber in said casing around the wall of the said primary combustion and expansion chamber in communication with the said chamber at the rear thereof,

ha valved gas inlet duct in communication with said gas chamber in position to subject incoming gas to heat from the wall of the said primary combustion chamber, the said primary combustion chamber being dimensioned for incomplete l1 opening within the said casing and arranged to deliver` secondary air to the said secondary combustior1 chamber around the expanding gases from t e said primary combustion chamber.

2. A low velocity/gas burner comprising a rearwarcily closed casing, a valved primary air inlet duct projected forwardly from the rear of the said casing, a tubular member forming a primary combustion and expansion chamber of greater diam-eter than said air inlet duct and extended forwardly from adjacent the forward end of the said duct, means forming a gas chamber in said casing around the wall of the said primary combustion and expansion chamber in communication with the said chamber at the rear thereof, a valved gas inlet duct in communication with said gas chamber in position to subject incoming gas to heatl from the wall of the said primary combustion chamber, the said primary combustion chamber being dimensioned for incomplete combustion therein of the combustible mixture composed of the said primary air and preheated gas introduced at the rear thereof, means forming a secondary combustion chamber having a rear ward region having av heat-radiating refractory wall arranged to receive expanding gases from the said primary combustion chamber and of suflcient cross-sectional area and length to accommodate expansin thereof and a forward region of increased dimensionsr and a valved air duct arranged to introduce secondary air into the rearward region of the said secondary combustion chamber around the gases issuing from said primary combustion chamber to support combustion in said gases and to be heated thereby.

3. A low velocity gas burner comprising a casing, a valved primary air inlet duct projected forwardly from the rear of the said casing, a tubular member forming a primary combustion chamber extended forwardly from adjacent the forward end of the said primary air duct, means forming a gas chamber in said casing around the wall of the said primary combustion chamber, means forming a gas inlet passage from the said gas chamber to the rearward end of the said primary combustion chamber arranged to introduce gas at an angle to the axis of the said primary combustion chamber, a valved gas inlet duct in communication with said gas chamber in position to subject incoming gas to heat from the wall -of the said primary combustion chamber, the said primary combustion chamber being dimensioned for incomplete combustion therein of the combustible mixture composed of the said primary air and preheated gas introduced at the rear thereof, means forming a combustion tunnel having a heat-radiating refractory wall arranged to receive expanding gases from the said primary combustion chamber and of;crosssectional area and length greater than that of the said primary combustion chamber to accomodate expansion of said gases, and a valved secondary air duct opening within the said casing and arranged to deliver secondary air to the said combustion tunnel around the expanding gases from the said primary combustion chamber.

4. A low velocity gas burner comprising a casing, a valved primary air inlet duct projected forwardly from the rear of the said casing, a tubular member forming a primary combustion chamber extended forwardly from adjacent the forward end of the said primary 'air duct, means forming a gas chamber in said casing around the wall of the said primary combustion chamber and communicating with said primary combustion chamber by means forming a gas inlet passage arranged to introduce gas at an angle to the axis of the said primary combustion chamber, a valved gas inlet duct in communication with said gas chamber in position to subject incoming gas to heat from the Wall of the said primary combustion chamber, the said primary combustion chamber being dimensioned for incomplete combustion therein of the combustible mixture composed of the said primary air and preheated gas introduced at the rear thereof, a nozzle arranged to deliver a fine jet of gaseous fluid adjacent tne forward end of said primary combustion chamber, means forming a combustion tunnel having a heat-radiating refractory wall arranged to receive expanding gases from the said primary combustion chamber and of cross-sectional area and length greater than that of the said primary combustion chamber to accommodate expansion of said gases, and a valved secondary air duct opening within the said casing and arranged to deliver secondary air to the said combustion tunnel around the expanding gases from the said primary combustion chamber.

5. A low velocity gas burner comprising a casing, a primary air inlet duct projected forwardly from the rear of the said casing, a tubular member forming a primary combustion chamber extended forwardly from adjacent the forward end of the said primary air duct, means forming a gas chamber in said casing around the wall of the said primary combustion chamber, means forming a gas inlet passage from the said gas chamber to the rearward end of the said primary combustion chamber arranged to introduce gas at an angle to the axis of said primary combustion chamber, a gas inlet duct in communication with said gas chamber in position to subject incoming gas to heat from the wall of the said primary combustion chamber, the said primary combustion chamber being dimensioned for incomplete combustion therein of the combustible mixture composed of the said primary air and preheated gas introduced at the rear thereof, means forming a combustion tunnel having a heat-radiating refractory wall arranged to receive expanding gases from the said primary combustion chamber and of cross-sectional area and length greater than that of the said primary combustion chamber to accommodate expansion of said gases, and a secondary air inlet duct opening within the said casing and arranged to deliver secondary air to the said combustion tunnel around the expanding gases from the said primary combustion chamber.

6. The herein described method of producing a low velocity, unstratied, luminous combustion atmospherevcomprising the steps 0f passing a stream of low velocity primary air through a restricted primary combustion space, substantially surrounding said primary air with low velocity fuel gas, said primary air being suflicient to support combustion of a portion of said gas,'igniting and burning a portion of the said gas, and thereby producing a primary flame composed of combustible gas on an expanding core of burning gases, directing the said gas and primary air to issuance from the said restricted space into a more extended combustion spa'ce bounded by a heat radiating surface thereby highly heating said bounding surface by said primary flame, and substantially surrounding the said primary flame as it enters the more extended combustion space with low velocity secondary air, whereby the heating eiect of the primary flame and the heat radiated from said bounding surface produces cracking of saidv combustible gas and rapid expansion of said secondary air and uniform admixture thereof Withpthe gases of said primary flame.

7. 'I'he Vherein described method of producing a low velocity, luminous, unstratified combustion atmosphere comprising the steps of projecting an expanding gaseous jet within an expansion restraining heat-radiating bounding surface, substantially surrounding said expanding gaseous jet with low velocity primary airsubstantially surrounding said primary air 'with low velocity fuel gas, said primary air being sufficient to support combustion of a portion of said gas, igniting and burning a portion of the said gas and thereby producing a primary ame composed of combustible gas on an expanding core of burning gases thereby highly heating said bounding surface by said primary ame, andV substantially surrounding the said primary flame with low velocity secondary air, whereby the heating effect of the primary iiame and the heat radiated from said bounding surface produces cracking of said com bustible gas and rapid expansion of said secondary air and uniform admixture thereof with the gases of said primary ame.-

8. A low velocity gas burner comprising a chambered forwardly opening casing,a secondary air inlet duct including a chamber of said casing and having a forwardly directed opening therefrom, a combustion tunnel comprising a refractory wall surrounding the forward opening of said secondary air inlet duct and extending forwardly of the casing, a gas ignition tube axially within the said casing and opening in the forward end thereof, a, primary air inlet duct to deliver primary air at the rear of said ignition tube, and a gas inlet duct and a. connection therefrom for introducing fuel gas between said primary air inlet duct and said gas ignition tube, means for directing said gas in an annular stream around the primary air in the ignition tube to issue into the said combustion tunnel as combustible gas on an expanding core of primary dame of substantial heating value, the said gas ignition tube being relatively short, Kand the said refractory wall of the combustion tunnel being in direct heat exchanging relation with gases issuing from the said openings.

9. A low velocity gas burner comprising a chambered forwardly opening casing, a secondary air inlet duct including a chamber of said casing and having a forwardly directed opening therefrom, a combustion tunnel comprising a refractory wall surrounding the forward opening of said secondary air inlet duct and extending forwardly of the casing. a gas ignition tube axially within the said casing and opening in the forward end thereof, a primary air inlet duct to deliver primary airattherearofsaidignitiontube,agasinlet 14 duct and a connection therefrom for introducing fuel gas between said primary air inlet duct and said gas ignition tube, means for directing said gas in an annular stream around the primary air in the ignition tube to issue into the said combastion tunnel as combustible gas on an expanding core of primary flame of substantial heating value, a nozzle within the said ignition tubeadjacent the forward opening thereof and including means to deliver a line jet of gaseous fluid forwardly from the said ignition tube into the said combustion chamber within the primary air and the combustible gas surrounding the same, the said refractory wall of the combustion tunnel being in direct heat exchanging relation with gases issuing from the said openings. 10. A low velocity gas burner comprising a chambered forwardly opening casing, a secondary air inlet duct including a chamber of said casing and having a forwardly directed opening therefrom, a combustion tunnel comprising a refractory wall surrounding the forwardopening of said secondary air inlet duct and extending forwardly of the casing, a primary air inlet duct to deliver primary air to said casing rearwardly of the forward open end thereof, primary air directing means axially within the said casing and to direct primary air therein tothe forward open end of the casing, a gas inlet duct and a connection therefrom for introducing fuel gas between said primary air inlet duct and said gas ignition tube, means for directing said gas around primary air in said primary air" directing means, .a nozzle within the said air directing means adjacent the forward opening from the casingand including means to deliver a ne jet of gaseous fluid forwardly from the casing and within the forwardly directed primary air and the gaseous fuel surrounding the same, the said refractory wall of the combustion tunnel being in direct heat exchanging relation. with gases issuing from the said openings.

NORMAN J. URQUHART.

i REFERENCES lCITED The following references are of record in'the ffile of this patent:`

UNITED STATES PATENTS

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