US2560074A - Method and apparatus for burning fuel - Google Patents

Description

July 1951 w. J. BLOOMER 7 2,560,074

METHOD AND APPARATUS FOR BURNING FUEL- Filed Dec. 21, 1948 2 Sheets-Sheet 1 K 121 1 Y 65 14a I N VEN TOR. fiard .lfi m2" July 10, 1951 w. J. BLOOMER METHOD AND APPARATUS FOR BURNING FUEL 2 Sheets-Sheet 2 Filed Dec. 21, 1948 INVENTOR- W W'M' Patented July 10, 1951 UNITED STATES PATENT OFFICE METHOD AND APPARATUS FOR BURNING Ward J. Bloomer, Westlield, N. J assignor to The Lnmmus Company, New York, N. Y., a corporation of Delaware Application December 21, 1948, Serial no. 66,445

1 24 Claims. This invention relates to improvements in a method and apparatus for burning fuel and is a continuation in part of and improvement on my copending applications Serial No. 550,933, filed August 24, 1944; Serial No. 650,284, filed February 26, 1946; and Serial No. 22,982, filed April 24, 1948; each forementioned application is now abandoned.

In my copending application, Serial No.

" 550,933, I have described a new and improved method of burning fuel wherein an extremely 'high degree of efllciency and completeness of ize it into a mist or suspension comprising small air-home fuel particles is utilized also as combustion air, 1. e., wherein a volume of low pressure air is made to perform the multiple functions of breaking the fuel into discrete particles of such size as are readily combustible, of entraining the aforesaid particles and suspending them therein, and conveying the aforesaid particles in suspension to a burning zone, separated or spaced from the zone or zones wherein they are mixed and entrained, while supplying the air necessary for combustion.

The physical apparatus-which aids to carry out the aforesaid methods is preferably a fixed type of tuyere having shallow tangential blades between which low pressure air passes, thus creating a centrifugal effectv and forming a hollow envelope or hollow column in the nature of a vortex with a relatively small axial component inward of the center of the tuyre. This gives a most intimate mixing of the fuel and air during the movement of the rapidly swirling mass in a relatively long helical path through which it moves before discharging from the tuyre.

In my copending application Serial No. 650,284, I have further provided for maintaining this intimate suspension of the air with entrained fuel after the mass passes out of the tuyere by providing a restricted cross section combustion chamber which will maintain the high efliciency of mixing resulting fromthe creation of the hollow rotating envelope or column of fuel and air. I have found that this combustion chamber materially improves the efilciency of combustion and also prevents periodic fluctuations of combustion which otherwise intermittently or periodically result frbm incomplete combustion.

As described in my copending applications the type of fuel may be a liquid or gas or comminuted solids so long as it may be entrained or picked-up by the low pressure air and carried into the whirling vortex so that an intimate fuel-air mixture results. In my copending application Serial No. 22,982 I have also shown a modified form of apparatus of the horizontal or end fired type which may likewise be fed with a fluid or fluidized fuel in a manner such that a horizontal axis of the vortex of the fuel-air mixture can be directly provided for those installations requiring a wall burner rather than a floor type burner. Y 1 v The principal object of this invention is to more clearly set forth the importance of the factors entering into the design and construction of a continuous fuel burner for industrial purposes, to set forth the range of the separate elements, to coordinate the disclosures of the prior applications, and to establish 'the preferred form of embodiment of the invention.

A more specific object of the invention is to provide an improved method and apparatus for burning fuels hitherto considered of low grade in industrial furnaces by establishing a vortex or a commercial burner assembly including associated wind box, primary and secondary air controls, fixed. cylindrical tuyere and mounting plate whereby the entire assembly can be readily attached to a furnace.

Further objects and advantages of my invention will appear from the following description of preferred forms of embodiment thereof, taken in conjunction with the attached drawings in which:

Fig. 1 is a partial diagrammatic vertical central section through a burner and combustion chamber.

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

Fig. 2a is a partial vertical section of a modified form of burner.

Fig. 3 is a substantially central vertical section through a part of a furnace setting showing a modified arrangement of burner. 1

Fig. 4 is a partial vertical cross section from the inside of the tuyere, taken on the line l-l of Fig. 3.

Fig. 5 is an enlarged vertical section of the feed end of the tuyere taken on the line 5'-5 of Fig. 4.

Referring to the drawing in detail and as parparticularly shown in Figures 1 and 2, the burner comprises a tuyere generally designated 10, sur-- rounded by a shell or casing generally designated H, through which a column or stream of low pressure air passes between the vanes or blades of the tuyere w, as hereinafter described. A fuel pan or container l2 having a continuous annular side wall l3 surrounds the lower end portion of the tuyere Ill. The bottom of the container l2 has an orifice for the fuel feed pipe or inlet 14 which is connected to a suitable source of fuel 15. While diagrammatically shown, this fuel source may include a gravity feed tank for liquid fuel, or a powdered fuel hopper, or in case of gas, it may include a gas blower. Liquid fuel may of course, also be fed by a liquid fuel pump. The tuverev i0, is of generally cylindrical form,

being open at one end and closed at the other by a solid wall It, the side thereof being formed by a plurality of generally tangential shallow vanes or blades I8 extending throughout substantially the entire length of the tuyere proper. These blades form a plurality of elongated substantially rectangular air inlets 20 disposed between adjacent blades l8.

The tuyere l0 may be provided with an annuiar, substantially frusto-conical plate 2| provided with a central orifice the full diameter of column of air in the tuyere [0 for the purpose hereinafter described in detail.

As the fuel in the pan l2 flows through the blade openings, it is then entrained in the vortex inside the blades to form a fuel-air suspension in the form of a swirling hollow column designated 23. This hollow column 23 is open throughout its length to establish a linear velocity component of the fuel particles which thus travel in a spiral or helix through the tuyere, becoming thoroughly mixed with or in suspension in air, from the entrainment and mixing zone to the burningzone.

The liquid pick-up and entrainment zone is designated 24 and comprises an annular zone inside the tuyre i0 adjacent the lower end of the blades l8 and the fuel surface in the fuel pan I2; The mixing zone is designated '25, and is inside the tuyere Ill, and is in the form of a gen erally cylindrical hollow column which is open at the bottom of the tuyere as shown in Fig. 2.

Perhaps the fuel air column 23 might more accurately or mathematically, be described as truncated paraboloidal with its theoretical vertex lying outside the closed end wall [6 of the tuyere III, or in other words, a hollow column having its inner surface defined by a parabola of revolution wherein the theoretical vertex of the parabola is spaced outside the tuyere Ill,

whereby the lower end of the column is maintained open. However, this envelope 23 shall be described herein as generally cylindrical, as hollow and open throughout, since I hare-found these are the properties necessary in such a fuelair column to achieve the objects and advantages of this invention.

The burning zone or combustion zone is generally designated at 26 and as described above, is so spaced from the casing or shell H and other parts of the burner, as to relieve these parts of the necessity for withstanding combustion temperatures. This spacing of the zone of combustion 26 from the mixing zone 25 and entrainment zone 24 is achieved through the avoidance of-forces acting in opposition to the vertical or linear velocity component of the swirling hollow generally cylindricalfuel air column 23. The separate particles of fuel pass, generally speaking, in spiral or helical paths in fully dispersed air-surrounding condition into the zone of combustion, whereby complete combustion thereof,

i. e., an extremely high degree of combustion efliciency is achieved in the combustion zone.

If the above described forces in opposition to the vertical or linear velocity of the fuel envelope did exist, there would be a tendency for these separate or discrete fuel particles to fall out of suspension, which would materially impair the efliciency of combustion since the uniformity of the fuel-air suspension supplied to the combustion zone 26 would be impaired or destroyed, resulting in periodic fluctuations intermittently or periodically producing incomplete combustion. The closing of the column 23 at the bottom of the tuyere Ill due to an insufficient initial air velocity imposed on the tuyre would result in production of such above described deleterious forces in opposition to the aforesaid vertical or linear velocity component of the swirling fuel-air column and consequent impairment of the uniformity of the suspension and the uniformity of the vertical component of this velocity which are the factors upon which uniformity of combustion is dependent.

, The distance of the aforesaid spacing of the combustion zone from'the entrainment and mixing zones is controllable by varying the air pressure in the casing II. It is also dependent upon the ratio of the diameter of the tuyre III to the length of the blades I8. For example, doubling the tuyere diameter and halving the blade length, with the same air inlet area, pressure drop and air capacity in the burner provides four times the cross sectional area in the orifice defined by the upper end of the tuyere III. For this reason, the net axial discharge velocity would be reduced. and the pattern of the combustion zone would thus be varied accordingly by variation of the diameter-height ratio. Ordinarily I find that a ratio of greater height than diameter is the most advantageous construction in giving more eflicient atomization.

I find that it is not. only necessary to provide the previously described envelope of helical moving air-fuel mixture, but that great care must be usedto 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 tuyere area. As one most effective manner of accomplishing this, I provide a curb or'refractory chamber adjacent the end of the tuyere. This is generally shown at 23 and is adapted to embrace and be mounted upon the top plate 2| of the tuyre.

- In small furnaces with relatively low heat input, and with air pressures and velocities near the minimum that will successfully operate with increasein cross sectional area is comparatively slow. In such a construction unusually good combustion results, with a brilliant toms of flame.

The refractory curb or combustion chamber permits a stable sustained combustion in part because of the re-radiation of the heat back from the curb to the burning fuel particles or vapors and becausethe whirling action of the air-combustion gas'mixture maintains these burning fuel particles in suspension until combustion is complete. The whirling flame will serve to re-ignite the mixture if the tendency were for the burning flame to be quenched with the admission of greater amounts of air.

The vortical movement of the fuel and air within the tuyere causes a low pressure central region in which the pressure is so low as to induce into the central path a body which is held over the center of the tuyere. This 'vortical movement thus tends to induce some of the hot gases from the combustion chamber as well as a portion of the flame itself into the tuyre so that the heat from the combustion chamber thus heats the mixture of the fuel and air within the burner for some preheating. This results in highly eflicient combustion.

The angle of the blades and their relative length and the effective opening will vary for different results, but in general I find it desirable to keep the blades about 0.39 inch in width, with an opening of Generally a blade angular-ity of about 13 55' on a 7" diameter tuyere is appropriate. The essential element, however, is the relatively high velocity ofair required to pick up the fuel. While I have operated at as low as 30 feet per second, usually I find a minimum of 50 feet per second to be necessary for safety and the top range may be 100 feet per second or more. Higher ranges of 150 feet per second have been used but the pressure drop is excessive and if such a large fuel capacity is required, then a larger tuyre should be used. For practical purposes the range of my burner is about 70% of r designcapacity to 140% of design capacity. The pressure drop in such case will vary from about 3" of water to about 12" of water. With one pound per square inch gauge which is equal to 27.7" of water, I'obtained 216% of designed working range.

The following table gives the approximate size of burners heretofore constructed and tested:

Diameter of fuel panm:

Air pressure in casing 11. 0.58 lb. per sq. in. Air feed rate cu. ft. per minute Fuel gas heating value 550 B. t. u. per cu. ft. Fuel rs 44.6 cu. ft. per minute Combined feed 244 cu. ft. per minute Volumetric ratio of air to .5 to l Combined feed velocit 8,640 ft. per minute Combined vertical f velocity. 5,000 ft. per minute Premure drop throu h tuyeres 10 inches of water Minimum pressure up for satisfactory 3 inches of water operation. Heat release 1,408,000 B. t. u. per hour In the above case, the ratio of inlet area to cross sectional area of 58% will result in a low 6 forward component of the fuel-air vortex. My experience has been that with ratios of from 120% to 130%, a much greater forward velocity could be obtained which in certain cases, provides a better flame pattern.

The same burner, under the same conditions using 41.3 A. P. I. kerosene weighing 6.818 lb. per gal. and having a heat value of 19,810 B. t. u. per 1b., burned 8.8 gal. per hour equal to a heat release of 1,128,600 B. t. u. per hour.

The same burner, when charged with powdered coal of 12,000 B. t. u. per 1b., supplied at the rate of 64.5 lb. per hour, the other conditions being the same, gave a heat release of 769,000 B. t. u. per hour.

A further example of capacity is illustrated by a somewhat larger tuyere. In this case a tuyere of 5 /4 inches in height and 5 in diameter mounted in an 8 inch casing was supplied with a gas of 550 B. t. u. per cu. ft. heat value at the rate of 181.! cu. ft. per minute to release 6,000,000 B. t. u.

, per hour.

While, as above described, the low pressure air which entrains the fuel becomes combustion air, i. e., all of it takes part in fuel combustion, other, secondary air may be added to this low pressure air where the combustion air requirements are greater than this low pressure air. Such additional or secondary air may be supplied by a booster or other means as in Fig. 3. The fuel feed may also be increased, if desired, by increased pressure on the air passing through the tuyere blades.

The application of the foregoing general principles to a horizontal type of burner is disclosed in my copending application Serial No. 22,982 above referred to. It was found that while it could be expected that a fluid fuel would normally tend to drain away from the high point of the tuyere. with a non-uniform flame, this was not a fact if the feed pan closely flt the end of the 1 tuyere. In such a case the feed of fuel is suitably accomplished at only sufficient head to maintain the feed pan full and by starting the air first, the flame is uniform.

The advantage of this discovery is of major importance for many furnace installations require a wall burner, not only for accessibility but also for uniformity of heating. A commercial burner mounting of this type which is adaptable to a furnace side wall is shown in Figures 3 to 5. The burner mounting 30 in this case includes the tuyere 32, its feed pan 33, the primary air duct 34, the wind box and the controls all in an integral unit. In this manner, the entire burner mounting 30 may be bolted to the furnace plate 31 as by bolts 38 and the entire unit is in place.

It is only necessary to connect the fuel line at 39 and the. air intake at 40 and the unit can be placed in operation at once. I A fixed position of the burner from the combustion chamber 42 is assured and operating variables are reduced to a minimum.

More specifically referring to Figure 3, it will be noted that the forward end of the primary air casing 34 in'which the tuyere 32 is mounted, ex-

tends to the outer edge of the combustion chamfractory at 46 which may have a plurality of rows of secondary air ports 46a and 4% connecting the wind box 35 with the combustion chamber.

The secondary air may be brought into the windbox through port 48 and I prefer to use a louvred portion 50 with a movable louvred valve plate 5! to vary the air. This plate 5i may have a handle 52 to permit adjustment during operation if necessary bringing more or less of the fixed louvre openings 50a into coincidence with the movable openings 51a.

Thetuyere 32 may have two sets of blades 32a and 32b and be provided with a generally cylindrical skirt 54 which closely embraces the blades near their center line and is secured in position by the clip 55. The skirt has an effective diameter such that approximately equal amounts of air passing through the main air duct 34 go through the respective blade banks. In large type units, operating under high air velocity, there might otherwise be a tendency to channel the air which may easily be corrected by this device.

As in the prior case the blades may be struck out of a suitable metal which need not be completely heat resistant itself. I find that although temperatures of several thousand degrees Fahrenheit are generated in front of the burner, the rapid passage of air tends to keep the blades relatively cool. Long life of blades has been attained by using the various alloy steels such as 18% nickel, 8% chrome, and others. Preferably the blades are straight throughout their length to simplify their fabrication.

The fuel pan 33, is conveniently spaced from the closed end 320 of the tuyre as by the blocks 51. The feed pan side wall 33a as previously mentioned, is mounted tight against the tuyre blades thereby forming small openings generally indicated at 58 with the end of the tuyre blades all around the periphery as shown in Figures 4 and 5. The wall 330 of the pan extends approximately one-half inch to one inch beyond the end of the blades and thereby forms the uniformly spaced restricted orifices which are directly in the air path. As a result, each particle of fuel is promptly entrained in a substantial quantity of air and due to the high velocity of the air entering the tuyere a very rapid vortical movement of air and fuel is accomplished.

Although this very intimate mix carries the fuel particles in a number of turns in a helical path through the tuyere, the path itself is substantially smooth and uniform with a minimum of pressure drop. The air undoubtedly moves faster than the fuel particles however, so that there is a complete dispersion of the fuel-particles in a highly atomized or mixed form.

After the desired amount of mixing, the airfuel mix is thrown out into the combustion chamber 42 in whirling fashion where it is initially ignited by suitable means, as for example, a pilot flame in tube 58. Combustion takes place substantially entirely within the range of the length of the combustion chamber. The shortness of flame and completeness of combustion without the presence of smoke indicates the substantially.

holes on the 7% inch circle. The tuyre opening was 7 inch inside diameter. The amount of air that passes through these openings is relatively small but it tends to aid the flame pattern and to avoid coke formation either in the combustion chamber or on .the tuyere face itself.

In general, I have found that combustion is so complete and effective that secondary air as generally understood is not necessary. However, I find it desirable to use a small amount of secondary air, as for example, from 10% to 20% to avoid overheating cf the refractory throat of combustion chamber 42. The small amount of air is sumcient for this purpose and it does not detract from the general efficiency of the furnace.

I have heretofore suggested the flexibility of the burner in using various fluid or fluidized fuels. In one installation that was particularly successful, I introduced gas through line 60 and oil through line GI to the single fuel line 39. In starting up, it was most convenient to use the gas and when the combustion chamber 42 was hot, the oil could be ignited without difficulty. As both fuels can be burned at once as well as either fuel burned alone, it makes possible a single installation which is adaptable to various market conditions of fuel oil and gas, using whichever is in plentiful supply and most economical.

I have also successfully burned powdered coal as previously mentioned by adapting the burner for such fuel as shown in Fig. 2a. The feed pan I2a was provided with a continuousv annular wall l3a extending above the lower ends of the tuyre blades as in Fig. 1 but the lower wall was flared downwardly and made generally frusto-conical or funnel-like to accommodate the powdered or comminuted fuel. A hearing H5 is suitably secured to the bottom or lower wall Ilia of the tuyere H, which bearing supports the upper end of a conveyor screw or worm memlcer 65 which fits c'osely in the modified feed pipe or inlet Ma. The lower end of the feed screw will of course, be driven by any suitable means, not shown, and the fuel which may be coal or coke or other material may be fed to the feed pipe by any means, such as by gravity from a hopper, not shown, but otherwise well under stood in this art.

Altematively, the powdered fuel may be fluidized with air and conveyed direct to the fuel pan as is the caseof the gas or other fluid fuel.

Some fuel, to be fluid, must be partially heated, and it will be understood that preliminary heating can be accomplished in any well known manner. In the case of asphalt of 96 penetration, which I have burned most effectively, the temperature of the fuel was raised to 400 F. and in such case, it could be pumped or gravity fed without difficulty. The use of preheated air is advantageous with this high melting point asphalt to avoid any premature chilling of the asphait as it passes through the blade openings. It is also usually desirable to completely scavenge the end of a run as with normally liquid fuel such as kerosene. It will be appreciated that combustion of asphalt is a valuable advance in thisfield and of substantial economic value as fuel is normally bought on a liquid basis but its heat value is on the weight basis which gives heavy residues and asphalts an advantage.

My burner is also particularly adapted to household or domestic type merely by reducing the diameter and height to an appropriate size and providing a pilot to permit repeated starting. A unit burning 1.5 gals. per hour of furnace oil will be of approximately 1 /2 inch diameter and about 1 to 2 inches in height. Provision may be made for adjustment of the fuel pan with respect to the bottomof the tuyere to expose or cover more or less of the blades, if desired.

Summon! The principle of operation of my burner as I now understand it is based on the high velocity entraining fuel and mixing it with the air of said tangential flow of combustion supporting gases I preheat the envelope or column of fuel and air therein. The resulting combustion is thus completed within a few feet of the tuyere and yet the tuyre itself is comparatively cool even though the flame and furnace gas are recycled to the whirling combustion zone. Secondary air may be used to avoid furnace decomposition but is not essential for completion of combustion. The application to fluid or fluidized fuels is accomplished in a common unit by the mere change of valves.

The range of burner sizes for various duties is generally found in the following table, it being understood that by varying the air velocity, a range of operation of from 70 to 140% may be obtained in any burner.

Capacity 1 MM 4.8 MM 1 7.2 MM 1 12MM Tuytre Diame r 7% l0 Tuyere Length. 3 6 9 Curb Diameter 20 22% Curb Length 20 27' Fuels, Gals. per

hour-Bunker MM is equal to 1,000,000 British thermal units.

It will be appreciated that modifications may be made to my invention and I therefore desire such an interpretation thereof as will come within the scope and spirit of the description herein and of the claims appended hereinafter.

I claim:

.1. In a fuel burner, a hollow tuyre having a closed end wall, and a side-wall provided with a plurality of blades forming inwardly convergent air paths, the end of the tuyere opposite the closed end being open, a fuel container having a sidewall surrounding a portion of said tuyre side wall, means for continuously feeding fuel to said fuel container and means for supplying an air current adjacent thesurface of the fuel in said container and through said air paths between said blades for entraining fuel and mixing it with the air of said current; and discharging the mixture through the open end of the tuyre.

2. In a fuel burner, a tuyre having a solid bottom wall and a side wall provided with a plurality of blades forming inwardly convergent air paths, a fuel container surrounding the lower end of said tuyre side wall, means forming an enclosure surrounding said tuyre and said fuel container and capable of guiding air currents upwardly over fuel in said fuel container and through said air paths formed by said blades for currents, means for supplying air to said enclosure forming means for producing said currents, and inlet means for receiving fuel to said fuel container for entrainment by said air w rents outside said tuyere and passage through said convergent air paths to be mixed with the air of said currents to form a swirling fuel-air column in said tuyere, said column conveying said fuel in suspension to a combustion zone spaced from said tuyere.

3. In a fuel burner, a casing connected with a source of air, a tuyre supported in said casing and providing communication between the interior of said casing and the exterior thereof, said tuyre being open at the outer end and having a continuousvside wall formed by a plurality of blades and having a solid inner end wall closing the inner end of the tuyere side wall formed by said blades, and fuel supply means forming a fuel supply surrounding the inner tuyre end wall and the inner ends of said blades, said tuyere being adapted to receive air and entrained fuel from said casing, to form therein a hollow swirling fuel-air column and deliver the fuel-air mixture of said column to a combustion zone spaced from said tuyere.

4. The combination of a. fuel ,burner. comprising a tuyre having a solid bottom wall and a side wall provided with a plurality of blades forming inwardly convergent air paths, said tuyre having an outlet opposite the solid wall, a fuel container having a side wall surrounding a portion of said tuyre side wall, means for continuously feeding fuel to said fuel container and means for supply-ing an air current upwardly over the surface of the fuel in said container and through said air paths between said blades for entraining fuel and mixing it with the air of said current, and a truncated paraboloidal cumbustion chamber of refractory material superposed on said tuyere, said chamber registering with the outlet of said tuyere.

5. The combination of a fuel burner, comprising a tuyre having a solid bottom wall and a side wall provided with a plurality of blades forming inwardly convergent air paths, said tuyere having an outlet opposite the solid wall, a fuel container having a side wall surrounding the lower end of said tuyere side wall,-means for continuously feeding fuel tosaid fuel container and means forming a shell spaced from said tuyre for supplying an air current upwardly over the surface of the fuel in said container and through said air paths between said blades for entraining fuel and mixing itwith the air of said current, and a truncated paraboloidal combustion chamber of refractory material superposed on said tuyre, said combustion chamber having an opening greater than the diameter of the tuyre outlet and registering therewith.

6. The combination of a fuel burner, comprising a tuyere having an end wall and a plurality 11 the air of said current and a truncated paraboloidal combustion chamber of a refractory material superposed on said tuyre and registering with the tuyere outlet and restricting the path of the fuel-air mixture in the combustion zone.

7. The combination of a fuel burner, comprising a tuyere having' an end wall and a plurality of blades forming a side wall, said tuyere having an outlet opposite the end wall, said blades being angularly spaced to form inwardly convergent air paths, a liquid fuel container adjacent said end wall and in communication with the inside of said tuyere surrounding the side wall, means for continuously feeding fuel to said fuel container whereby said fuel enters said tuyere adjacent the outer edge thereof, means for supplying an air current through said air paths between said blades for forming a vortex therein and for entraining fuel and mixing it with the air of said current and acombustion chamber having an internal surface of revolution of a refractory material having an outlet diameter of between 2 and 3 times the diameter of the tuyre and having a length approximately the same as its diameter, said combustion chamber being contiguous to said tuyere and registering with the tuyere outlet and laterally restricting the path of the liquid fuel-air mixture in the combustion zone.

8. In a fuel burner, a tuyere open at its upper end and having a solid bottom wall and a side wall provided with a plurality of blades forming inwardly convergent air paths therebetween, a fuel pan enclosing the lower end of said tuyere side wall, a casing closed at its upper end and surrounding said tuyere and said fuel pan and terminating at the upper open end of said tuyre, said casing guiding an air current upwardly over fuel in said fuel pan and through said air paths between said blades for entraining fuel and suspending it in the air of said current, means for supplying air to said casing for producing said current, and fuel supply means for maintaining a predetermined fuel level in said fuel pan for entrainment of said fuel by said air current outside said tuyere and passage through said convergent air paths for suspension in the air of 11. The structure defined in claim 8 wherein said fuel supply means comprises a powdered fuelhopper and a power operated screw conveyor connected between said hopper and said feed pan.

12. In a method of burning fuel in an open tuyre having an open end, a closed end and plural generally tangential blades forming its wall, which comprises providing a uniform supply of fuel outside said tuyre, providing a low pressure column offlowing air outside said tuyre, and directing said low pressure air over said fuel for entrainment of fuel particles thereby, thence through said blades to impart a rotary component to said column and form within said tuyere a hollow generaly cylindrical mixing and atomizing zone for suspending said fuel particles uniformly in said air, while applying sufllcient linear componnet in said column in an axial direction outward 0f the tuyre adjacent the wall thereof 'to maintain the fuel-air column in said mixing zone unclosed throughout its length and form a combustion zone spaced from said tuyere and maintained so spaced by said axial linear component.

13. In a method of burning fuel with an upright tuyere having an open top, a closed bottom and plural generally tangential blades forming its side which comprises maintaining a supply of fuel adjacent the lower ends of said blades outside said tuyere, directing a low pressure column of upward flowing air outside said tuyere, and directing said low pressure air over said fuel for entrainment of said fuel thereby, thence through said blades to impart a rotary component to said column and form a hollow generally cylindrical mixing zone in said' tuyere for suspending said fuel particles in said air, while regulating the linear component of air in said column in an upward direction adjacent the inner wall of the tuyere and the linear component of air in a downward direction adjacent the center of the tuyere to maintain the--fuel-air column in said mixing zone hollow and unclosed throughout its length and discharging the fuel-air mixture to form a combustion zonespaced from said mixing zone.

14. The method defined in claim 13 wherein said fuel comprises a finely divided combustible solid material.

15. The method defined in claim 13 wherein said fuel comprises a combustible gas.

16. A method of burning a fluid fuel, which comprises introducing air under low pressure through the tangential sides of a cylindrical tuyere whereby a rotating truncated-parabolic column of air is created with a relatively small axial component inward of the center of the tuyre and a linear component out of th tuyere adjacent the wall thereof, with every fluid particle taking a helical path, restraining the radially outward movement of the column by the continuous tangential feed of low pressure air to the column substantially throughout its length, the inner wall of the column being formed by the centrifugal force of rotation, maintaining a body of fluid fuel adjacent the outside of the tuyere at one end of the column, and-entraining the fluid fuel into said hollow column adjacent the outer wall thereof at a zone opposite the discharge end substantially entirely by the low pressure air, whereby the fuel particles will be introduced into said rotating air column and carried through a plurality of complete turns so that said fuel is intimately mixed with said air.

17. A method of burning a fluid fuel, which comprises introducing air under low pressure through the tangential sides of a cylindrical tuyere whereby a truncated-parabolic column of air is created with a relatively small axial component inward of the center of the tuyere and a linear component out of the tuyere adjacent the wa'l thereof, withevery fluid particle taking a helical path, restraining the radially outward movement of the column by the continuous tangential feed of the low pressure air to the column substantially throughout its length, the inner wad of the column being formed by the centrifugal force of rotation, maintaining a body of fluid fuel adjacent the outside of the tuyere at one-end of the column. entraining the fluid fuel into said hollow column adjacent the outer wall thereof a a zone opposite the discharge end substantially entirely by the low pressure air, whereby the fuel particles will be'introduced into said rotating air column and carried through a plurality of complete turns to mix said fuel intimately with saidair, discharging the intimately mixed air-fuel column longitudinally and laterally into a chamber of greater cross-sectional area than the column, and preheating the inner wall of the column by the products of combustion which radiate heat into the center thereof.

18. A method of burning a fluid fuel, which comprises introducing air under low pressure through the tangential sides of a cyl ndrical tuyere whereby a semi-parabolic column of air is created with a relatively fixed radius and a relatively small axial component, with every component taking a helical path, restraining the outer wall of the column by the continuous tarrgential feed of low pressure air to the column substantially throughout its length, the inner wall of the column being formed by the centrifugal force of rotation, maintaining a body of fluid fuel adjacent the outside of the tuyre at one end of the column, entraining the fluid fuel into said hollow column adjacent the outer wall thereof aoaopn cylindrical chamber having a side wall closely embracing the outer edges of the tuyere blades and forming a plurality of small apertures therewith, means for supplying fuel through said fuel feeding means to said apertures adjacent the edges of said air inlets at the end of the blades air inlets between said blades over said fuel for 19. A burner as claimed in c aim 3 in which the tuyre is provided with a face plate extending from the outer end to said casing, said face plate having a series of openings around the periphery communicating with the casing whereby a small amount of the air will purge the face plate of the tuyere.

20. In a horizontal fuel burner, a tuyre having a closed end wall and a side wall provided with a plurality of blades forming inwardly convergent air paths, 9. fuel container having a portion closely surrounding a portion of said tuyere side wall, means for continuously feeding fuel to said fuel container, and means for supplying an air current through said air paths between said blades for entraining fuel and mixing it with the air of said current. 21. In a fuel burner, a tuyere having a solid end wall and a substantially cylindrical side wall provided with a plurality of angularly opened bades forming inwardly convergent air paths. said tuyre having a horizontal axis, a fuel container tuyere, said blades and said embracing container sidewall forming a plurality of peripherally spaced fuel feed openings between the blades, means for continuously feeding fuel to said fuel container and meansfor supplying an air current through said air paths between said blades for entraining fuel and mixing it with the air of said current.

22. In a fluid fuel burner, a substantially cylindrically tuyre on a horizontal axis having its side wall formed by a plurality of spaced blades extending substantially throughout the length of the tuyre and forming inwardly directed air inlets therebetween, said tuyere being open at one end and closed at the other end. fuel feeding means adjacent the closed end, said fuel feeding means comprising a substantially entralning said fuel and forming a swirling outwardly moving column adjacent the inner wall of said tuyre, said column having a-central low pressure area, said column comprising a combustible fuel-air mixture.

23. In a fuel burner, a substantially cylindrical hollow horizontal tuyre having a closed fuel feeding end, an open fuel discharging end, and a side wall including a plurality of projecting tangential blades forming air openings therebetween, means to apply air to said tuyere to establish a whirling column within the tuyere,

'said column having a low pressure central portion and being confined by the inflow of air through the tuyere blades, and means to uniformly distribute fuel tothe column adjacent the closed end of the tuyere whereby the fuel is entrained in and moves outwardly with the air column to the fuelidischarging end, said fuel distributing means including a. fixed container having a wall portion surrounding. the closed end of the tuyre and closely embracing the blades, said container wall portion forming with the tangential blades ofthe tuyere, a series of uniformly spaced external openings adjacent the closed fuel feeding end of the tuyere whereby the fuel is presented to the slowest axially moving part of the air column.

24. In a method of burning fuel with a horizontal tuyre having an open end, a closed end. and a plurality of generally tangential blades forming its side, which comprises maintaining a supply of fuel to the portion of said blades adjacent said closed end and between a. portion of the blades, direcitng a, low pressure column of flowing air outside said tuyere, directing said low pressure air through said blades and over said fuel for entrainment of said fuel thereby, and to impart a rotary component to said column and form a hollow generally cylindrical mixing zone in said tuyere for suspending said fuel particles in said air, and regulating the linear component of the air in said column adjacent the inner wall of the tuyere in a direction away from said closed end and with a suflicient linear component of air in the opposite direction adjacent the center of the tuyere to maintain the fuel-air column in said mixing zone hollow and unclosed throughout its length, and discharging the fuel-air mixture to form a combustion zone spaced from said mixing zone.

WARD. J. BLOOMER.

REFERENCES crrEn The following references are of record in the file of this patent:

- UNITED STATES PATENTS Number Name Date 120,680 Smith Nov. 7, 1871 1,297,138 Gardner Mar. 11, 1919 1,468,008 Dyson Sept. 18, 1923 1,591,679 Hawley July 6, 1926 (Other references on following page) Number 15 UNITED STATES PATENTS Name Date Burg Feb. 22, 1927 Bansen Jan. 24, 1928 Schutz Jan. 31, 1928 Schutz Jan. 31, 1928 Fletcher June 19, 1928 Molz Jan. 8, 1929 Trent Sept. 3, 1929 Van Brunt Mar. 10, 1931 Sherwood Sept. 15, 1931 Rosencrants Aug. 2, 1932 Heaton Dec. 27, 1932 v Burg Jan. 16, 1934 Frisch Mar. 13, 1934 Foltz June 19, 1934 Kennedy July 24, 1934 Number Number Name Date Hawley Aug. 7, 1934 Avery Jan. 8, 1935 Boland Mar, 19, 1935 Hardgrove June 16, 1936 Saha Oct. 26., 1937 Saba Oct, 26, 1937 Sharp Aug. 9, 1938 Sorg Nov. 9, 1938 Kerrie]: June 2, 1942 Don Howe Nqv. 24, 1942 FOREIGN PATENTS Country Date Denmark May' 27, 1931 Great Britain Apr. 18, .1929 Great Britain July 15, 1929 Germany Feb, 18, 1933

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