US 2458541 A
Description (OCR text may contain errors)
N. J. URQUHRT LOW VELQGITY'OIL BURNER Jan. l, 1949.
S Sheets-Sheet l Filed Nov. 16, 1944 INVENTOR WMH@ @www N. J. URQUHART LOW VELOCITY OIL BURNER Jam. 11, 1949.
3 Sheets-Sheet 2 Filed Nov. 16, 1944 INVENTOR V Norman l Urquhart www zi. hm
MN x mw .EN LNNNDHI Jan. l, 1949. N. J. URQUHART 2,458,541
LOW VELOCITY OI L BURNER Filed Nov. 16. 1944 s sheets-sheet s INVENTOR JVQrmaJzJ Urquh arf Parental. 11,1949
LOW VELOCITY OIL BURNER Norman J. Urquhart, Scenery Hill, Pa., aslignor to Combustion Processes Company, a corporation oi' Pennsylvania Application November 16, 1944, Serial No. 563,684
4 Claims. (Cl. 158-76) This invention relates to an oil burner and particularly to an oil burner having advantageous features when used in conjunction with furnaces of various sorts.
without producing high velocity of llame 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 burner to vary the heat output of the burner It is a primary object of my invention to pro- 5 and the atmosphere created in the furnace while vide an oil burner which is capable of furnishing retaining throughout different orders of coma low velocity luminous flame, composed of an bustion the desirable burner and furnace condiunstratifled blend of gases; in which the type tions which have been noted above. of flame and the atmosphere created by the In the accompanying drawings illustrative of burner in the enclosed space of a furnace is under my invention: l control; and in which the combined fuel and Fig. I is a longitudinal sectional view through air volume delivered to the burner may be varied a burner organization embodying the principles within wide limits, and the type of flame and of my invention. atmosphere created by the burner combustion Fig. II is a cross-sectional view through the may be varied without departing from the unil5 burner taken in the plane of the section line formly blended composition and low velocity of II-II of Fig. 1. the combustion flame and without loss of its high Fig. III is a longitudinal sectional view. taken luminosity. through the fuel-supply nozzle of the burner and In obtaining these objects I depart from the the connections thereto. usual principles of burner construction by an 20 Fig. IV is a front elevation of the nozzle ararrangement which avoids rapid flame moverangement, l l ment, and which does not utilize the principles 0f Fig. V is a cross-sectional view through the premixing the combusti@ ail' and fuel 0l' 0f burner nozzletaken in the plane oi' the section multi-stage combustion. 0n the contrary my line V--V of Fig. III. burner is so arranged that mixing takes place Fig, V1 is a, sectional functional View shgwmg within the combustion areas of the burner and is the combustion zones or area of themurner in begun in the rearward portion thereof under longitudinal section and illustrating/(he operation the heating effect of an initial supporting llame of the burner to give an unstratied gaseous -of substantial heating value. Also, the oil problend with a low lvelocity flame of high viding the fluid fuel consumed in the burner is luminosity. so introduced with relation to the supporting Fig. VII is a sectional functional view showing flame and additional air is so. supplied with the burner organization as in Fig. VI and the respect to both, that mixing in the combustion other preceding figures of the drawings but il'- areas of the burner is effected at an early stage lustrating combustion conditions when my oil under the influence of cracking conditions, and burner is operated to give an effect usual in prior conditions which produce a highrate of molecart burners. ular movement of the several gases with complete Fig. VIII is a view similar to Figs. VI and VII, and uniform mixing thereof. illustrating another condition which occurs when Thus the burner creates and supplies throughmy oil burner is so operated as to give the comout a wide operating range an unstratied blend bustion conditions obtained in other prior art of reacted and unreacted gases with such early burners.
Cracking and rapid and COmplete commlngling Considering the structural organization of the that as delivered to the furnace it gives therein a burner as shown in the accompanying drawings, highly luminous condition and an atmosphere the burner comprises an outer shell having a which is proof against oxygen slippage, and peripheral wall i and a rear closure wall 2, and which therefore does not bring substantial quanan inner shell having a peripheral wall 3 and a titles of free reactive oxygen into contact withI a rear closure Wall si. The closure wall 2 and the furnace charge. Considering a prime utility of peripheral wall i define a casing. At its forward the burner, this eect is of great value in metend the wall l of the outer shell isanged and allurgical furnaces in which the effect of the has connected to its flange 5 the flange E of an A furnace atmosphere in producing oxidation of adapter shell 1. This adapter shell 1 has a forthe furnace charge is a matter of importance. wardly presented flange 8 which is welded or Also, as indicated above, the combustion rate otherwise suitably secured to the wall 9 of a and heat output of the burner may be varied furnace .to surround aport I0 inthe furnace wall. within wide limits without causing stratification, Within shell 1 and port l0 there is a refractory lining ll which abuts rearwardly against flange :an inner supporting and heating flame.
5 of the burner shell proper and extends for.- wardly into the port I of the furnace wall, to bound a combustion tunnel I2.
In the 'inner shell of the burner there is a nozzle I3 from which oil is projected with compressed air, or steam at moderately high pressure. Surrounding nozzle I3 and the inner shell there is a flange I4 extended between wall 3 of the inner shell and wall I of the outer shell. This flange I4 is provided with a series of ports Il arranged to deliver air from chamber I8 lying between walls I and 3 of the inner and outer shells. These ports I5 desirably are, as shown, extended through the complete annular extent of flange I4 and are equi-distantly spaced therein.
4 bustion tunnel I2 immediately 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 flame of desired characteristics and such adjustment readily may be made initially by observing the primary flame itself. That is,
Air is supplied through an air-inlet duct I1,
having therein butterfly valves I8 and I8', which opens directly into air chamber I6, which may be considered an extension of the duct II. A branch air duct I9 provided with butterfly valve 20 opens into chamber 2| within the inner shell of the burner. The chamber 2I may be considered an extension of the branch air-inlet duct I9, and the air introduced by branch air-inlet duct I9 to chamber 2I may be considered primary air, inasmuch as it surrounds a lm of oil from nozzle I3 to provide primary combustion in the form of This combustion air is supplied at relatively low pressure, such as a pressure of from about .5 pound per square inch to 1.5 pounds per square inch in a suitable manner as by the action of a low pressure fan. It is to be noted that this air supply, introduced under relatively low pressure to provide low velocity burner operation, constitutes in practical effect the entire air supply depended on for combustion, no additional air being drawn or forced into the burner to support the burner flame at different stages in progressive combustion of the fuel.
Secondary air issues into tunnel I2 through ports I5 around the inner flame comprising primary air and a film of oil from the nozzle. In the primary flame the oil is carried by and surrounds the jet of compressed air or steam, and the compressed air or steam expanding as it issues from nozzle I3 carries the oil in a conical oil film, which mixes with the surrounding primary air to produce the initial supporting flame. In proper operation of the burner, primary air must be insufflcient to approximate complete combustion of the fuel, but must be suilicient to produce with the fuel a primary flame of substantial heating value. It may be explained that with the oil broken up in the nozzle and carried as a film on the expanding core of compressed air or steam there is an interior flame in which combustion is substantially complete and which is surrounded by the secondary air and by excess `fuel. The primary flame is a clear, smokeless and relatively nonluminous ame; and its central portion in which combustion is substantially complete insures against its extinguishment under the exigencies attendantv upon practical use of the burner.
It thus is to be understood, and this is yan important feature in the operation of my burner, that the primary flame above described not only serves as a pilot and combustion supporting flame, but that it has of itself sumcient heating value to raise the interior of tunnel I2 and its bounding refractory surface to a high temperature. Secondary air, which in the proper operation of my burner is supplied in volume sulcient to take part at least substantially in the combustion, is heated by radiant heat from the surface of comfuel and primary air supply may be adjusted until a clear 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 point 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 is frequently desirable to make some compensatory relative adjustment between primary air and secondary air to get the exact desired combustion conditions.
The eiect of this burner operation is illustrated in Fig. VI of the drawings. Referring to that figure of the drawings, it will be seen 'that both butterfly valve I8 in secondary air duct I'I and butterfly valve 20 in primary air duct I9 are fully open. This provides a proportioning of primary air and secondary air substantially in accordance with the cross-sectional areas of primary air duct I9 and secondary air duct I1. 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 for normal or mean burner operation with both butterfly valves fully open.
Under properly adjusted conditions the rapidly expanding conical 'film of oil, supported by the interior jet of compressed air or steam and reacting with the primary air, gives a primary flame A of substantial size. Under its heating effect, and the heating eiect of radiation from the tunnel wall there is a rapid expansion of both the primary and secondary air accompanied by vaporization and cracking of the oil and expansion of the gases produced thereby. The expansionincident to the heating and cracking, exerts an expanding pressure against the wall of the combustion tunnel which forces the secondary air inwardly as primary air and fuel expand outwardly. The secondary air being introduced under l'ow pressure, the expansion produces transverse mixing rather than accelerated forward motion. This action is the one which primarily gives the advantageous results produced by the burner.
The actual effect produced by heating the gases in this region thus is one of rapid molecular motion by which the gaseous substance of the secondary air moves inwardly and the gaseous substance of the primary flame, including the primary air and the gaseous products of vaporization and cracking of the oil, moves outwardly. In movement forwardly of the tunnel this blending progresses to such extent that the gaseous mixture, comprising both reacted and unreacted gases, is unstratified and is of approximately uniform composition throughout its entire volume. This unstratifled blending of the gases persists when the gaseous blend issues into the work chamber of a furnace.
The fundamental action in tunnel I2 is thus the production of a ine and uniform blend of air and cracked oil vapors, in which combustion has production of high luminosity in such gaseous' body moving at low velocity through the tunnel.
Apparently this fundamental effect obtains without reference to the degree to which combustion takes placein the gaseous blend. I believe that the high luminosity of the flame is due to the uniform distribution of a great number of incandescent carbon particles in the blended gases.
In many prior art burners this effect is obtainable for one combined volume of fuel and air and within a very narrow range of total fuel and air supply. It obtains throughout ail 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 by means such as the valve I8' and meanslater to be described, respectively, without destroying the function of the primary flame in heating the air and fuel in such manner as rapidly to produce an unstratiled uniform gaseous blend. There is of course a point at which it is impossible to maintain an adequate heating effect of the primary flame, but such point is low beyondv that at which anyone reasonably might desire to out 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 a 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 art that even though the furnace atmosphere may contain less than a without increasing the velocity of the flame, and without loss of luminosity therein, I amable to `provide in the furnace anoxidizing'atmosphere' ofthesort to form a fine adherent scale on the soaking pit charge. 'I'his 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 vgive agaseous blend. otherwise identical with vthat previously described, which contains an'excessof oxygen. As so use d my burner gives a scale formation of' superior sort on the furnace charge, inasmuch as the effect of the oxidizing atmosphere is unisuillciency of oxygen for complete combustion,
there is a tendency for the occurrence of what is known as oxygen slippage. That is, the oxygen of the combustion air tends to separate from the other gases of the furnace atmosphere and to gravitate to the lower regions of the furnace chamber in direct contact with the furnace charge. It is an observed fact that even when sufllcient-combustion air is provided to complete combustion the blended gases delivered by my burner are substantially proof against such 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 emphasized that uniformity in the gaseous blend and an unstratifled luminous flame is provided by the burner throughout a wide range bustion. The proportioning of fuel, primary air and secondary air having been established, the volume of fuel and total air then can be adjusted to the desired temperature conditions withoutv in any substantial degree altering the condition of the burner gases 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 llame and without disturbing the blending which prevents scale formation in the furnace.
In certain furnace operations it is desirable to provide an oxidizingl atmosphere in the furnace. One example of such condition exists in soaking pits, in -whi-ch 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 case,
form inits kcontact with the charge because of the maintenance of a blended atmosphere in the work chamber of the furnace.
It is to be understood that my burner not only may be operated to give an effect' unobtainable in prior art burners, but that if so desired it may be operated to give an effect usual in many prior art burners. If the total air be directed either wholly or excessively into chamber I6 and through ports I5 as secondary air, the effect will not be that obtained by an apportionment of primary and secondary air as Aillustrated in Fig, VI.
Thus Fig. VII of the drawings shows butterfly valve 20 in the primary air-duct completely closed, and butterfly valve I8 of the secondary air-duct completely open, so that the total air supply is delivered to the burner as secondary air. Under such conditions the primary flame B" is supported only by such air issuing from ports I5 as mingles with the expanding oil film from nozzle I3, and the major proportion of the air supplied to the burner passes forwardly through tunnel I2 to give a stratified as opposed to a blended gaseous mixture therein. Although the primary flame B is itself short and of substantially lesser heating value than the primary flame A of Fig. VI 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 a luminous flame in which approximate ultimate blending of the furnace atmosphere is obtainable. With higher and lower total air-fuel volumes, to give a greater or lesser heat output stratification always occurs. An extreme example of the effect illustrated in Fig. VII is obtained by multistage combustion in which secondary air is progressively added along the length of a central flame.
Fig. VIII of the drawings illustrates the condition in the burner if the total air supply be directed wholly or excessively as primary air. In this gure of the drawings butterfly valve I8 in secondary air inlet duct I'i is shown wholly closed, and 'butterfly valve in primary air inlet duct I9 is shown fully open. With this regulation of the air supply the primary flame C is the only flame produced by the burner. That llame begins at a point substantially forward of the jet nozzle. It is a roaring flame invwhich the air and the atomized oil are in stratified condition, there being no edective initial cracking of the oil'or blending in the composition. With a flame of this sortit is impossible to obtain complete combustion without charge or controlling oxidation in such mannerV as to effect it in desired sort and order.
Specific exemplaiy means for introducing oil in finely atomized condition and in such manner as to form an expanding conical film of oil, is shown in detail in Figs. III, IV and V of the drawings.
Such means comprise the nozzle i3, which has therein an oil chamber 22 communicating with oil inlet duct 23 having a valve 23' therein, and jet chamber 24 communicating with a duct 25 having a valve 25 therein leading to a source of compressed air or steam. The valves 23 and 25 provide means for regulating the total fuel supply. The use of valves such as 23 and 25 in conjunction with a valve such as i8' for controlling the total supply of fuel and air to av burner are old and well known in the burner art. A relatively small vacuum chamber 26 is in communication with oil chamber 22 by way of port 21 and with chamber 24 for air or steam by way of port 28. Desirably, as shown, both port 21 and port 28 are of relatively small caliber; the port 28 for compressed air or steam being of lesser caliber than port 21, and port 21 being arranged to discharge downwardly into chamber 26 at right angles to the direction in which the jet of compressed air or steam is directed.
In this nozzle, air or steam entering chamber 26 by way of constricted port 28 expands and in expanding creates at the rear of the chamber a vacuum which draws in oil through port 21. This oil is broken up and carried along by the jet of compressed air or steam. As the air or steam jety continues to expand upon issuing from the nozzle,
the effect is the formation of a thin film of o.l i
carried radially outward by the expanding air or steam. This lm is in good condition for cracking under the heat of its own combustion and the radiant heat from the wall of combustion tunnel i2. It thus contributes to the desired effect of the burner be so arranged with respect to the flow of primary air that the oil being expanded outwardly in the tunnel of the burner is surrounded by the primary air so that there is combustion susbtantially back to the .burner nozzle itself; to give in this region a flame of substantial heating value which, by its direct heat and by radiant heat from the wall of the tunnel, is capable of creating and maintaining in that region a temperature sufllciently high to produce cracking and rapid molecular motion.
It will be observed in Fig. I of the drawings that the primary air stream in chamber 2i surrounds nozzle I3, exerting a cooling effect on the nozzle and itself taking up heat as it enters the burner tunnel around the jet from the nozzle. The arrangement also is such that the primary air which supports combustion in the primary flame rapidly comes in contact with and blends with the expanding film of oil from nozzle It is desirable to avoid carbon formation against the wall 3 of the inner shell by bringing nozzle i3 out approximately to the line of flange Il in which secondary air ports I5 are placed.
I have found it impossible to give critical relative dimensions for most of my burner elements because such proportional relations vary with different sizes of burner. It can however. be said that combustion tunnel I2 should be of such bore diameter that the inner surface of its wall closely surrounds ports i5 which deliver the secondary air. This is in order that such wall may be highly heated by combustion in the tunnel, and so that secondary air is prevented from expanding outwardly and flowing along the tunnel wall to give a stratified tunnel atmosphere. In other words. the bore diameter of the tunnel should not be so great as to defeat the desired blending action which has been described above. The length of the tunnel should be adequate to provide complete blending of the gases therein before delivery of those slowly moving gases to the work chamber 4of a furnace. I have found no fixed critical relation between the diameter and length of the combustion tunnel and the ratio between the diameter and length of the tunnel will vary with burners of different size and low velocity capacity. A simple consideration of the requisites will give an appropriate length of the tunnel for any size burner, it being understood that at least the rearward portion of the tunnel wall should closely surround the secondary air ports.
Certain desirable characteristics of my oil burner may be further explained. It will have been noted that in practical entirety combustion air is introduced in the low velocity air stream which is divided into the primary and secondary air. If compressed air rather than steam be used to provide a jet for carrying the film of oil such compressed air which is of negligible volume takes no substantial part in the combustion. There are no additional streams of injected air or induced atmospheric air to support the combustion. This amongst other features brings the burner operation under direct control and permits nice regulation in the volumes of fuel and total air and in the apportionment between primary air and secondary air. The low velocity of the gases permits 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 impingement 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 of Va 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 oil 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 flame of high heating value is desirable. In all its variant uses there is great advantage in the fact that the combined volume of fuel and air utilized by the burner, and consequently the combustion rate and heating effect, may be varied within wide limits without changing the flame characteristics or composition.
Having shown and described one physical embodiment of my invention both with respect; ,to the burner and with 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.
I claim as my invention:
1. A low velocity oil 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 primary air inlet duct axially within the said casing and the said secondary air inlet duct and opening in the forward end of the casing into the said combustion tunnel, the said primary air inlet duct and secondary air inlet duct being arranged to supply an inner stream of low velocity primary air and a surrounding stream of low velocity secondary air for supporting combustion in the said tunnel, and a fluid projector structure in the said primary air inlet duct, said projector structure comprising a duct for high pressure gaseous fluid arranged to discharge a jet of gaseous fluid adjacent the forward opening of said primary air duct, means for supplying high pressure gaseous fluid to said duct therefor, an oil duct communicating with said duct for high pressure gaseous fluid to supply oil on the stream of gaseous fluid in the duct therefor adjacent the forward end thereof and supply oil to the outer surface of an expanding gaseous jet into the said combustion tunnel to give with surrounding primary air a primary core of re blending with low velocity secondary air, the said refractory wall of the combustion tunnel being in direct heat exchanging relation with air and fuel issuing from said openings.
2. A low velocity oil 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 primary air inlet duct axially within the said casing and the said secondary air inlet duct and opening in the forward end of the casing into the said combustion tunnel, the said primary air inlet duct and secondary air inlet duct being arranged to supply an inner stream of low velocity primary air and a surrounding stream of low velocity secondary air for supporting combustion in the said tunnel, and a fluid projector structure in the forward opening of said primary air inlet duct, means for supplying said fluid projector structure with high pressure gaseous fluid, said fluid projector structure including means to supply oil to the outer surface of an expanding gaseous jet into the said combustion tunnel within the stream of low velocity primary air, to give with surrounding primary air a primary core of re blending with low velocity secondary air, the said refractory wall of the combustion tunnel being in direct heat exchanging relation with air and fuel issuing from said openings.
3. The herein described method of producing a low velocity, luminous. unstratied combustion atmosphere comprising the steps of projecting a high velocity expanding gaseous jet within an expansion restraining heat-radiating refractory bounding surface, supplying oil to the outer surface of said expanding gaseous jet, substantially surrounding said expanding mixture of oil and gas with low velocity primary air sufficient to support combustion of a portion of said oil, igniting and burning a portion of the said oil, and thereby producing a primary flame of high heating value within a combustion space defined by said heatradiating refractory bounding surface, thereby highly heating said Ibounding surface by said primary llame, and substantially surrounding the said primary flame with low velocity secondary air within said combustion space, whereby the heating effect of thel primary flame and the heat radiated from said bounding surface produces cracking of the excess oil and restrained expan- Sion of the several gases including the primary air, the secondary air and the cracked oil.
4. The herein described method of producing a low velocity, luminous, unstratied combustion atmosphere comprising the steps of projecting a high velocity expanding gaseous jet within an expansion restraining heat-radiating refractory bounding surface, supplying oil to the outer surface of said gaseous jet to form an expanding slowly-moving cone of atomized oil on a gaseous carrying vehicle, substantially surrounding said expanding cone of atomized oil with low velocity primary air sufficient to support combustion of a portion of said oil, igniting and burning a portion of the said oil, and thereby producing a quiet primary core of flreof high heating value within a combustion space dened by said heat-radiating refractory bounding surface, thereby highly heating said bounding surface by said primary flame, and substantially surrounding the said primary core of fire with low velocity secondary air, whereby the heating effect of the primary core of fire and the heat radiated from said bounding surface produces cracking of the excess oil and restrained expansion of the several gases including the primary air, the secondary air and the cracked oil. NORMAN J. URQUHART.
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