US2560078A - Combustion apparatus and method - Google Patents

Description

. J. BLOOMER COMBUSTION APPARATUS AND METHOD Filed Dec. 21

.uEy 10, 195i lill? INVENTR WWJZMf Patented July 10, `1951 COMBUSTION APPARATUS AND METHOD Ward J. Bloomer, Westfield, N. J., asslgnor to The Lummus ration of Delaware Company, New York,

N. Y., a corpo- Appllcation December 21,1950, Serial No. 202,015

s claims. (el. 11o-2s) This invention relates to combustion apparatus and methods of vortical fuel burning as generally set forth in my copending applications for Patent Serial No. 66,445, filed December 21, 1948, and Serial No. 98,976, filed June 14;' 1949. It is also a continuation-in-part of my earlier filed application Serial No. 650,284, filed February 26, 1946, and now abandoned.

In the aforementioned cases I have disclosed an apparatus and method for burning various fuels such as oil, gas and pulverized solids such as coal. A vortex or hollow column of air is established, as for example, by forcing the combustion air at a relatively high velocity between tangentially disposed blades of an open ended annular -or cylindrical tuyre. The convergence of the respective air paths creates a rotational eect which in turn, by centrifugal forces acting on the air, establishes `a substantially hollow vortical vair column. The fuel is introduced into this vortical column and becomes intimately atomized or homogenized as it follows a generally helical path through the tuyre and is then discharged into the adjacent combustion chamber as a thin hollow ca lumn or stratum of fuel-air mixture.

Such a mixing or burning is especially important with various grades of liquid fuel for as the liquid particles necessarily travel at a velocity somewhat less than the air, there is a constant shearing action as the oil particles travel through the inflnite number of layers of air, each rotating at a diierent velocity whichvaries with the distance from the central'axis. As the largest oil particles tend to be thrown outward to the blades, they are further sheared by the viscous drag of incoming air which opposes the centrifugal effect. With such a procedure, fuel particles as small as microns can` be readily made and the resulting fuel-air mixture which is discharged as a high velocity stratum or vortical column is adapted to high eilc'iency combustion in an adjacent combustion chamber.

It is essential to most eiiicient combustion that the vortical character of the air-fuel mixing be not prematurely dissipated as the mixture passes into the larger combustion chamber. In accordance with my invention, I provide for the maintenance of this intimate mixture by not only continuing the high rotational eifect but increasing it. It will be appreciated that as the initial vortex that is established by an entering air velocity of from 50 to 150 ft. per sec. and as only a part of the tuyre end opening is utilized for the gaseous discharge while the central core is a low pressure inlet zone resulting from the partial vacuum formed. the net gaseous discharge may be at a velocity several times as great` as that oi' the entering air.

It will also be appreciated that the greatly increased temperature in the combustion zone will cause such a volumetric increase in the air-fuel mixture that the combustion zone must necessarily be greater in proportionate volume, to preserve the entering gas velocity. Actually I predetermine the combustion chamber dimensions and shape to provide a unique closed or compact flame pattern which is also of a vortical character. In appearance this flame appears annular and to surround a hollow core, which is likewise a zone of reduced pressure and the flame which is thus partially heated by convection and radiation. There is actually a recycling of the fuel into the flame front which not only provides a reignition of any particles that may escape from the hottest part of the flame, but also maintains an unexpected flame stabilization and materially reduces the tendency of the unburned particles to form coke on the combustion chamber wall.

A further important advantage of the vortical combustion pattern is of course, the compactness of the ame. As the fuel-air mixture is directed substantially tangentially, and vthen limited by the annular character of the combustion chamber, fuel is not thrown out of suspension and a very intense combustion is accomplished in a relatively short total length of chamber. For many installations this is of highly critical importance, after-burning and flame impingement being generally objectionable and completely avoided herein. That the combustion is substantially complete is indicated by CO2 analysis that show as high as 15% CO2 in the products of combustion. l

The low pressure air (6" to 16" water gauge) through the-tuyre, thus performs the multiple functions of breaking the fuel into discrete particles of such size (20 microns) as are readily combustible. of entraining the aforesaid particles and suspending them uniformly therein, and :conveying the aforesaid particles in uniform suspension to the burning zone wherein they are burned with substantially only the air theoretically necessary for combustion. Secondary air may be added if desired but ordinarily it is not required in the usual commercial sense. A tuyre will cause the entrainment and atomization of nearly equal proportions of fuel and air on a pound-for-pound basis and the required amount of air for combustion may be passed through the relatively large blade openings with a nominal pressure drop. In this way the fuel is given only sufficient head as to carry it to the vortical air column.

Preferably the combustion chamber for industrial installations is refractory lined and thus becomes radiant and further maintains flame stability. It is possible however for special installations such as in gas turbines. aircraft, etc. where cost may be of less importance than other factors, to use alloy metal name tubes. It is also customary in industrial installations to make the combustion chamber cylindrical although other annular shapes may be employed and in at least one case in which low capacity is customary, I have shown a combustion chamber having a parabolic section which is truncated and closely fits over the end of the tuyre. Such a construction also has the advantage of shielding the tuyre face and permits a gradual increase in the diameter of helical path of the fuel in the burning zone. It further avoids a possible disentrainment of the fuel from the entraining air.

My present invention is thus primarily laddressed to the operation and structure of a combustion chamber into which a vortical or hollow column of an intimate air-fuel mixture is discharged at a relatively high velocity and in a helical path by any suitable fuel-air mixing device. It results in two name fronts in which the outer eddy or whirl provides primary ignition with a reduced air supply while reignition and stability are accomplished with a normal air supply. At the same time the inner eddy or whirl pulls in the flame, accomplishing a recycling of the fuel and creating intense combustion. It distinguishes from my prior applications for patent which were primarily drawn to the use of the tuyre as the most effective means for establishing such a high velocity air-fuel mixture. I am aware that other apparatus, however, will to a more or less satisfactory degree, create an intimate air-fuel mixture and its directional and velocity characteristics by which the eddies are developed for the closed flame pattern.

The following description concerns a preferred form of embodiment of my invention and is to be taken with the attached drawing illustrative thereof, and in which:

Fig. l is a substantially central vertical cross section of my burner and adjacent combustion chamber.

Fig. 2 is a transverse cross-section taken substantially along the line 2-2 of Fig. 1. J

Fig. 3 is a partial vertical cross section of a modified form of combustion chamber, and

Fig. 4 is a partial vertical cross sectional view through a still further modified form of burner and combustion chamber.

As specifically shown in Fig. l, the combustion apparatus is adapted for mounting in a furnace, boiler, or other heat absorbing unit having a wall I which in this embodiment is afioor or 4 other horizontal wall. Within the heat absorbing unit is the combustion chamber II and the burner or fuel mixer assembly I2 is mounted adjacentv the closed end of the combustion chamber.

In this preferred construction and to better describe the operation of the combustion apparatus, the `burner or mixer I2 is shown as the cylindrical tuyre which is more specifically the subject of the aforesaid applications for patent. It has the closed end Il and the side wall is formed by a plurality of generally tangential shallow vanes or blades I8 extending from the closed end Il to the open end of the tuyre. For economy, these blades may be stamped out of the tuyre wall but it will be understood that they may be separate blades and that they may overlap or be streamlined as desired. They form a plurality of elongated substantially rectangular inwardly converging air inlets or ports I1.

The tuyre l2 is generally .provided with a face plate I8 which extends to a surrounding casing 20 serving as a windbox enclosing the air inlets or slots Il, and to which air may be introduced through inlet 22. It will be understood that this air, under a suitable pressure of from 6 to 16" water gauge, and in sufiicientvolume to supply a velocity through the air paths between the blades of from 50 to 150 ft. per sec., will be supplied as by a suitable blower (not shown). 'I'he air entering the tuyre thus establishes such a rotary movement as to form a central vortex or partial vacuum zone which results from the centrifugal concentration (with a radial force in excess of times gravity) of the air along the wall as schematically represented by line X. This is a parabolic section having its theoretical vertex outside the tuyre so that the column is substantially hollow or open throughout its length. There is thus no opportunity for a central outward discharge from the tuyre.

Fuel is introduced to this vortical column from the fuel reservoir indicated at 24 which may surround the closed endv Il of the tuyre I2. In this construction, the reservoir 2l has the nature of a. shallow pan the side of which extends at 24a to partially overlap the ends of the blades I6. As the fuel in the reservoir 24 is exposed to the air passing through the air paths between the blades I6, it will be entrained and carried into the vortical air column therein. The fuel feed line to the reservoir 24 is indicated at 26.

By maintaining a velocity of air in the desired range, a continuous discharge of the airfuel mixture from the open end and adjacent the wall of the tuyre is accomplished. It is found that the rotational effect actually produces a central vortex of reduced pressure in the tuyre with the result that the discharge velocity of the air-fuel mixture is in excess of the velocity of the air through the air paths I1. This causes a discharge of the air-fuel mixture as an annular stratum at an angular relation to the wall of the combustion chamber II. No central baille is necessary to maintain the hollow column eil'ect established by the high rotational effect of the entering air.

It is found on observation that the direction of this air-fuel mixture is in the general direction of the line Y which is to say about 30 to 45 to the longitudinal axis of chamber Il. As the mass is also rapidly rotating however, and being under combustion conditions, there are generated the so called inner" eddies or whirls represented by line Z which is formed into the central low pressure core of the combustion chamber, as well as external or outer eddies or whirls represented by the line .li These are formed as a result of the change of area of the cross section of the air-fuel column in moving from the tuyre to the larger combustion zone. This is analogous to an orifice effect and is emphasized by the simultaneous rotation of the air-fuel mass in the combustion zone about an axis normal to the closed end of the combustion zone.

This closed type of flame pattern depends on a combustion zone having a relative diameter and length with respect to the diameter of the introduced stratum oi.' air-fuel mixture. I have found that in all cases utilizing all primary air as mixing air, that the inner diameter of the combustion chamber (big end) must be at least 1% times and generally not more than 4 times the tuyre or mixing device diameter. The most effective constructions have not exceeded 3 times the tuyre diameter it being understood that economy dictates as small a unit as possible. Inv

each case the length of the combustion chamber has been approximately the same as its diameter and this length varies from as low as a/m to as muchas 1.5 times the diameter. Generally the best performance on liquidv fuels has been with diameter and length approximately equal. The diameter is critical to prevent loss of vortical effect and the length must be sufliciently great to assure a chamber within which the burning is substantially completed.

The refractory curb or combustion chamber tends to stabilize sustained combustion also because of the reradiation of the flame back from the curb to the burning fuel particles or vapors and because the whirling action of the air-combustion gas mixture maintains these burning fuel particles in suspension until combustion is complete. The whirling flame serves to reignite the mixture if there is a tendency for the burning llame to be quenched with the admission of greater amounts of air.

As a practical example of commercial units utilizing low pressure air and liquid fuels, the following table sets forth approximate dimensions of units for various heat capacities.

Tuyere (70 F.'

Lgth.)

' Throat Diameter Million B. t. u.

Inches 1l 15 Starting up the burner is not a major problem asthe air is first started to establish the vortex and thereafter, the fuel being turned on, the combustion is initiated by a torch or other means applied to the center core or behind the outer eddy. With gas, ambient temperatures are appropriate for both the air and gas but with heavier fuels, some preheating will be found to` aid combustion and avoid coking. Using Bunker C fuel oil with air and oil preheat of about 250 F. is most satisfactory and asphalt may be burned when the air and asphalt are preheated to about 450 F.

With heavy duty industrial constructions, the cylindrical shape of combustion chamber is easi- ,withstanding combustion temperatures.

est to install and maintain and it provides both the internal as well as the external eddies which do so much to stabilize the flame. It is not essential that this shape be strictly followed, although the combustion chamber must be annular to most effectively take advantage ofthe introduced vortical air-fuel column. In Fig. 3 for example I have shown a paraboloidal type of combustion chamber for small furnaces with relatively low heat input and with air pressures and velocities near the minimum that will successfully operate with this type of burner and cause a substantial vortex within the tuyre.

In this case, I have provided a curb or refractory chamber generally shown at 30 which is adapted to closely embrace and be mounted upon the top plate :ilv of a tuyre 32. This top plate extends to the wall of the casing or shell 33 through which the air is directed and thence forced through the tuyre openings to form the vortical column of air as in the previous construction. The fuel, which is also introduced to this air column, is thus discharged as an open column in a thoroughly mixed condition into the burningzone formed by the refractory chamber.

The shape of the central opening in this chamber is considered to be most important to prevent a premature discharge of the fuel from the air which may occur from a sudden change of velocity as the mixture moves out of the restricted tuyre area. For this reason I consider it effective to form this opening as a surface generated by rotation of a parabola so that the increase in cross sectional area is comparatively slow as coompared with the outward movement of the air-fuel column to the llame combustion.

In this construction, the burning zone or combustion zone is spaced from the casing or shell 33 and the top plate 3| by the refractory 30 and thus relieves these parts of the necessity for By maintaining the angularity and velocity of discharge of the air-fuel column, the separate particles of fuel are burned well within the combustion chamber. The internal eddy resulting from the central low pressure zone due to the high centrifugal force normal to the central axis of the combustion chamber materially aids this combustion.

It has been my experience that the best way to produce a vortical column of air and fuel is by forcing the air between the blades and introducing the fuel into the resulting column. I have also introduced the fuel to the air column as it discharges into the combustion chamber as shown in Fig. 4. In this case the primary air passes through the tuyre 40 which is surrounded by windbox 42 which in turn is mounted in the furnace wall 44. The tuyre 40 is provided with a face plate 45 which extends to the surrounding casing 42. The` face plate may be perforated whereby a portion of the air in the enclosure passes through the face plate to keep the tuyre cool. A shield 45a may also be used above the face plate 45 to aid in this purpose as more fully described in my copending application, Serial No. 98,976, filed June 14, 1949. The

fuel may be introduced to this column as by conduit 46 having a distributing head or pressure atomizing spray nozzle 41 and to a certain degree, the advantages of the vortical fuel mixing will be obtained.

It has the advantage that fouling of the blades iby fuel which may be otheerwise thrown out is completely avoided. It also has the advantage 7 that the atomizing type of a simple nozzle or gun may be easily withdrawn and replaced if it becomes fouled or for other reasons withdrawal is necessary. It also permits the use of cold air for burning as the air is discharged into the combustion chamber 48 before the fuel is introduced to it.

The central nozzle type of fuel feed has, however, some disadvantages as compared to the tuyre mixer of Figs. 1 and 3. It requires some pressure on the fuel to cause the desired atomization and distribution. It does not provide quite the intimacy of mix of air and fuel which is accomplished by the long helical path and centrifugal forces applied by the tuyre. It also has an exposed tip which tends to become radiantly heated and will more rapidly cause coking. It is thus a somewhat less effective manner of feeding the fuel to the vortical column.

With this type of feed, and assuming a continued discharge of the vortical air column, there can still be a closed flame pattern within the combustion chamber if it has the critical dimensions characteristic of the chamber in Fig. 1. The chamber should not be less in diameter than about 11/2 times the diameter of the tuyre opening and it should be not greater than 4 times, and preferably times the diameter of the tuyre opening. In length, the combustion chamber should be nearly as long as its diameter.

In the disclosed embodiments of my invention the axial length of the side wall of the combustion chambers is from 0.8 to 1.5 times the inside diameter of the side wall at the open front end, and the circular opening in the closed rear end of said chambers is from 0.25 to 0.67 times the diameter of said open front end.

I claim:

l. The combination comprising a combustion chamber having a rear wall and a closed side wall and open at the front end, the side wall having .the shape of a surface of revolution, the axial length of said side wall being from 0.8 to 1.5

times the inside diameter of the side wall near the front end of the chamber, and said rear wall having a circular opening therein which has a diameter of from 0.25 to 0.67 times the diameter of the chamber adjacent its rear end, and means for introducing air forwardly through said opening in the form of a rotating annulus spaced from the side wall of the chamber, whereby a iiame produced in said combustion chamber will form whirls of iiame gases within the annulus for rapidly heating the rotating annulus issuing from said opening and thereby stabilizing the name against extinguishment at high rates of flow, said means including a mixing chamber open at its front end and closed at its rear end and having an annular side wall formed with a plurality of circumferentially spaced tangential air inlet slots extending to the rear end and a casing enclosing the air inlet slots of the mixing chamber, means to pass air into the casing to establish a vortex in the mixing chamber which passes as an annulus to the combustion chamber, and means for supplying fuel to the rotating air annulus.

v2. The combination as claimed in claim 1, in l 8 length of said side wall being approximately the same as the inside diameter of the chamber, and said rear wall having a circular opening therein which has a diameter of 0.33 times to 0.67 times the diameter of the chamber, and means for introducing an inflammable mixture forwardly through said rear wall opening in the form of an annulus spaced from the side wall of the chamber whereby a flame formed by'igniting said inflammable mixture will form whirls of flame gases both within the annulus and between the outside of the annulus and the chamber side wall for rapidly heating the mixture issuing from said rear wall opening and thereby stabilizing it against extinguishment at high rates of flow, said open at its front end and closed at its rear end and having an annular side wall formed with a plurality of circumferentially spaced tangential air niiet slots extending to the closed rear end and a casing enclosing the air inlet slots of the mixing chamber, means to pass air into the casing to establish a vortex in the mixing chamber which passes as an annulus to the combustion chamber, and means for supplying fuel to the rotating air annulus.

4. A method of burning fluid fuel utilizing a mixing chamber wherein the fuel and air are mixed, and an adjacent coaxial combustion chamber with a lateral wall having the shape of a Asurface of revolution in which the air-fuel mixture is burned, which lcomprises passing the air through the mixing chamber at such a rate and angular relation to the axis of the lmixing chamber that there is formed an outwardly moving rapidly rotating annular mass of airI having a centrifugal force component in excess of one hundred times gravity, intermixing fluid fuel with the rotating mass in the mixing chamber, discharging the air-fuel mixture as an annular vortical mass axially 'into the combustion chamber, initiating combustion in and burning said air-fuel mixture in said combustion chamber, and constraining the combustion to a spiral path having a diameter at least as great as the discharged annular mass and not exceeding three times the diameter of said discharged annular mass of fuel-air mixture, and a length substantially as great as its diameter whereby the vortical effect of said fuel-air mixture is substantially preserved in the combustion chamber for sufficient time to induce products of combustion into the central portion of the combustion chamberso that flame stabilization is accomplished.

5. A method of burning fluid fuel utilizing a mixing chamber wherein the fuel and air are mixed, and an adjacent coaxial combustion chamber with a lateral wall having the shape of a surface of revolution in which the air-fuel mixture is burned, which comprises passing the air through the mixing chamber at such a rate and angular relation to the axis of the mixing chamber that there is formed an outwardly moving rapidly rotating annular mass of air having a centrifugal force component in excess of one hundred times gravity, intermixing'iluid fuel with the rotating mass in the mixing chamber, discharging the airfuel mixture as an annular vortical mass axially into a sharply enlarged combustion chamber, initiating combustion in and burning said air-fuel mixture in said combustion chamber, and constraining the combustion to a spiral path having a diameter greater than that of the discharged annular mass and not exceeding three times the diameter of said discharged annular mass of assenze air-fuel mixture, and a length substantially as great as its diameter whereby the vortical effect of said air-fuel mixture is substantially preserved in the combustion chamber for suiiicient time to induce whirls of flame gases into the central portion of the combustion chamber and whirls of flame gases between the outside of said spiral path and the sidewall of the combustion chamber adjacent its inlet end so that flame stabilization is accomplished. fl

6. A method of preparing and burning liquid fuel utilizing a tuyre open at its outer end and closed at its inner end, and having an annular side wall formed with a plurality of circumferem tially spaced tangential air inlet slots extending to the closed inner end, and a casing enclosing the air inlet slots of the tuyre, said method comprising feeding air to said casing throughout the length and periphery of the slotted side wall of the tuyre and through the slots tangentially into the tuyre, said air being fed at such rate and angular relation to the axis vof the tuyre that there is formed a forwardly moving rotating column of air with a vacuum in the center thereof and having a forward velocity atleast several times the velocity of the inlet air to the casing, discharging the air as an annular vortical column into an elongated combustion zone of restricted circular cross section spaced outwardly from said tuyre, intimately mixing liquid fuel in said vortical column by entrainment therewith to form a combustible fuel-air mixture, constraining the fluel-air mixture to a rotating forwardly moving annular vortical column, and initiating combustion in and burning said fuel-air mixture in said combustion zone as a rotating mass, said burning and the resulting gas' movement forming whirls of flamegases in the combustion zone for stabilizing the name against extinction and completing combustion in a relatively short lineal distance.

7. A method of preparing and burning liquid fuel utilizing a tuyre open at its outer end and closed at its inner end, and having an annular side wall formed with a plurality of circumferentially spaced tangential air inlet slots ex, tending to the closed inner end, and a casing enclosing the air inlet slots of the tuyre, said method comprising feeding air to said casing throughout the length and periphery of the slotted side wall of the tuyre and vthrough the slots tangentially into the tuyre, said air being fed at such rate and angular relation to the axis" of the tuyre that there is .formed a forwardly moving rotating column of air with a vacuum in the center thereof and having a forward velocity at least several times the velocity of the inlet air to the casing, rapidly expanding the outwardly .moving rotating column of air with a vacuum in the center'thereof as `formed in 00- the tuyre by discharging said column of air as an annular vortical column into a sharply enlarged cylindrical combustion zone spaced outwardly from said tuyre and having an entrance diameter which is between 11/2 and 3 times 65 the diameter of the tuyre and a length approximately equal to its diameter, intimately mixing liquid fuel in said vortical air column by entrainment therewith to form a combustible fuelair mixture, constraining the fuel-air mixture 70 to a rotating forwardly moving annular vortical column, and initiating combustion in and burning said fueleair mixture in said combustion zone as a rotating mass, said burning and the resulting gas movement forming whirls of name i gases within the burning rotating mass in the combustion zone and whirls of flames between the side walls of the combustion chamber adiacent its inlet end and said burning rotating mass for stabilizing the iiame against extinction and completing combustion in a relatively short lineal distance.

8. The combination comprising a combustion .chamber having a rear Wall and an annular side wall and open at the front end, the side wall having the shape` of a surface of revolution, the axial length of said side wall being from ,0.8 to 1.5 times the inside diameter of the side wall near the rear end of the combustion chamber, and said rear wall having a circular opening therein which has a diameter of from 0.25 to 0.67 times the diameter of the vchamber adjacent its rear end, and means for introducing air forwardly through said opening in the form of a rotating annulus spaced from the side wall of the chamber, said means including a cylindrical tuyre open at the front end and closed at the rear end and having tangential ports therein, a casing enclosing the tangential ports of the cylindrical tuyre, and means for supplying fuel to the rotating annulus, whereby a flame formed by igniting the inflammable mixture of air and fuel will form whirls of name gases within the annulus for rapidly heating said mixturev adjacent said opening and stabilizing the ilame against extinction.

9. The combination comprising a cylindrical combustion chamber having a rear wall and a closed side wall and open at the front end, the axial length of said side wall being from 0.8 to 1.5 times the inside diameter of the combustion chamber, and said rear wall having a circular opening therein which has a diameter of from 0.25 to 0.67 times the diameter of the chamber, and means for introducing air forwardly through said opening in the form of a rotating annulus spaced from the side wall of the chambe'r, said means including a cylindrical tuyre open at the front end and closed at the rear end and formed with a plurality of circumferentially spaced tangential air inlet slots in the side `wall thereof, a casing enclosing the air inlet slots of the cylindrical tuyre, and means for discharging fuel under pressure into the rotating annu1us,whereby a name formed by igniting the inammable mixture of air and fuel will form whirls of flame gases within the annulus for rapidly heating said mixture adjacent said opening, and outer whirls adjacent the side wall at the rear end of the combustion chamber for stabilizing the flame against extinction.

r; ln: J. BLOOD/IER.

REFERENCES CITED The following references are of record in 'the nie of this patent: y

UNITED STATES PATENTS Great Britain ....g June 1i, 193i

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