US3237680A - Gas burner with radially aspirated air - Google Patents

Description

March 1, 1966 H. LEVIN GAS BURNER WITH RADIALLY ASPIRATED AIR Filed Aug. 20, 1962 IN VEN TOR.

HERMAN LEV/H ATTOIZNEV United States Patent 3,237,680 GAS BURNER WITH RADIALLY ASPIRATED AIR Herman Levin, Los Angeles, Calil:'., assignor, by mesne assignments, to Electronic Specialty Co., Los Angeles, Calif., a corporation of California Filed Aug. 20, 1962, Ser. No. 217,947 2 Claims. (Cl. 158116) This invention relates to a combustion apparatus.

It is an object of my invention to generate a quiescent flame at a relatively high fuel rate and flame velocity, and at a relatively high burning rate.

In designing fuel burners and combustion chambers which generate heat at a high rate and thus require relatively high mass rates of fuel and air flow, flames and combustion gases are generated at a condition of turbulent flow. Such flames generate considerable acoustic energy and are noisy. This is aggravated by the added masses of secondary air which are added to the flaming mixture of the combustible gases and thus increase the mass velocity of the flame and burning gases.

In uses where noise is objectionable, this puts a severe limitation on the burning rate which is permissible. I have solved the problem by producing a flame and combustion gas stream of such low turbulence that the flame roar is substantially reduced and, ideally, eliminated. This I accomplished by constructing the combustion chamber so that, at the linear velocity of the movement of the flame and combustion gases, the Reynolds number which determines this turbulence of the gas streams is below the critical range at which turbulence occurs. As is well known, in circular pipes, the Reynolds number above about 2100 results in turbulent flow.

In order to develop a given B.t.u. output, the rate of gas and air flow must be sufficiently high for this purpose. The linear velocity of the gasesentering and passing through the combustion zone depends on the port areas of the burner and secondary ports and the geometry of the combustion space and flue. Thus, for required linear velocity of the gases, I restrict the relevant geometry of the ports and combustion space so that the Reynolds numbers are below the critical range, below about 2100 and, for example, in the range of 1000 or less. In addition, I design the port openings of the burner and secondary air admission ports so that the momentum of the gases passing through the ports and during their ascendency into the combustion space is sufficiently small so that the flame will not roll into a doughnut shape.

These considerations introduce however, severe restrictions on the permissible horizontal dimensions of the combustion space. This is particularly true if the combustion walls are kept below the ignition temperature of the gases as by loss due to convection, radiation, or conduction. In such case, if the transverse dimensions of the combustion space is kept sufficiently low to give the desired Reynolds number for the required linear velocity of the gases, the burning gases may contact the walls and thus be quenched. This will result in a relatively large amount of unburned gases and produce a combustion gas mixture of undesirably high carbon monoxide.

I have solved the above problem as well as others, as will more fully appear below, by introducing the combustion gases in a stream and introducing secondary air through ports positioned adjacent to the burner port inlets for the combustible gas and primary air, and in directions, through secondary air inlets of geometry described herein, to constrain the flame to flow in a stream separated from the combustion space walls.

While I do not wish to be bound by any theory of the operation of my apparatus, I believe that in my apparatus,

r6 Ce the radial momentum of the secondary air, directed towards the column of combustion gases, is greater than the radial momentum of the combustible gas stream directed towards the wall of the combustion zone. The effect of this method of introduction is to contain the flaming gases into a rising column which is less in diameter than the lateral dimensions of the combustion zone. The mixture of secondary air is produced by introducing the air in discrete ribbon jets by passing the secondary air through spaced ports positioned in opposed walls, circumambiently positioned adjacent to the burner ports and on both sides of the axial column of ascending combustion gases. The radial momentum of the secondary air through the opposed jets are in opposite directions. By proper spacing of the ports and their geometry related to the width of the gas annulus, the secondary air is made to pass as discrete jets into the stream of combustible gases with a radial momentum described above. The ribbon jets interrupt the stream of combustible gases into coarse discrete streams in the zone of the secondary air injection. These form a heterogeneous mixture of secondary air and primary air-gas mixture.

A further mixture occurs by diffusion from the jets as the heterogeneous mixture enters the combustion zone, rather than by fluid turbulent disintegration of the combustible gas stream by the jets of secondary air, to form a homogeneous mixture prior to entry into the main combustion zone. This also reduces the turbulence of the gas flame and reduces the acoustic energy released by the gas flame.

In the following specification, I will illustrate my invention applied to an atmospheric system, but it may also be applied to pressure systems as the terms are understood by those skilled in the art, and as defined by the American Gas Association. (See Perrys Chemical Engineering Handbook, 1950 edition, page 1592.) These and other objects of my invention will be clear to those skilled in the art by reference to the herein specification and drawings, of which:

FIGURE 1 is a vertical section through the combustion apparatus;

FIGURE 2 is a section taken on line 2-2 of FIG- URE 1;

FIGURE 3 is a fragmentary section taken on line 33 of FIGURE 2; and

FIGURE 4 is a fragmentary plan view enlarged on line 44 of FIGURE 3.

The combustion apparatus includes a burner formed with a fuel injection nozzle 1, positioned axially in the venturi 2, with an open end 3, communicating with the atmosphere. The venturi is formed integrally with the injection tube 4, which terminates in an annular plenum 5, closed by top 6, in which is positioned an annular slot 7.

Placed in the annular slot 7 is plurality of spirally arranged rows of ports openings 9, formed by spirally winding in parallel a corrugated metallic ribbon strip 8, together with a flat metallic ribbon strip, which is positioned in the annular slot 7. The corrugated ribbon 8 is placed against a flat ribbon 8' of the same width and the two wound spirally so that the flat ribbon lies between the turns of the corrugated ribbon. The openings 9 are positioned between that corrugated ribbon and the flat ribbon. The ports are thus positioned between the parallel and spirally wound corrugated and flat ribbon to form two interwound spirally corrugated ports -9 and 9" on each side of the corrugated and flat ribbon. The width of the ribbon and, therefore, the depth of the ports 9, is substantially equal to the thickness of the top 6.

The central bore 10 through the plenum 5 communicates with the atmosphere at one end and with a a bore 12 of smaller diameter. Bore 12 is provided with an internal shoulder 11. Spaced about slot '7 is a plurality, for example, four narrow fingers '7 uniformly spaced and extending across the annulus to support the ribbons.

The burner head carries an exterior circumferential shoulder 13 and a projection 14a for mounting on any desired structure. Positioned on the shoulder 11 is a central secondary air admission cap, formed with a circumambient wall 18 and the closed top 20. The wall 18 is slotted, with uniformly spaced slots 19 positioned in the circumambient wall 18 and spaced from each other by fingers 18. As shown in the drawing it is positioned interiorly of the annular slot 7,

Positioned concentrically with the cap on shoulder 13 is a secondary air admission ring 14, whose circumambient wall =14 carries a horizontal flange 15 and is slotted by a plurality of uniformly spaced slots 16, separated by fingers 17. As shown in the drawing it is positioned exteriorly of the annular slot 7.

The combustion chamber 21 extends above and below the flange 15 and makes contact therewith. "It is carried by flange I27 on any desired structure 23. The depending skirt 24 of the chamber 21 forms a plenum 26 for the admission of secondary air to ring 114.

The length of slots '16 and 19 is substantially greater than their width. For purposes of illustration only and not as a limitation of my invention as claimed in the appended claims, the slots 16 and 119 may be in length about 12 times their width, and the fingers may be in width about twice the width of the slots. The number of slots in the wall 18 is less, for example, about half the number of slots in the ring 14. The slots are designated to have a low Reynolds number, so that the air stream is substantially non-turbulent passing through the slots.

The annulus width between the ring 14 and the cap is made from about 2 to about 16 times the width of the individual slots, preferably in the range of about 6 to times the width of the slots '16 and 19.

In operation the primary air-gas stream enters the plenum 5 and the restricted annulus 7 provides for a uniform distribution of gas pressure and velocity across the downstream side of the gas ports 9. It will also be observed that the vertical approach to the downstream side of the gas ports 9 is made- -very small. The annularly positioned ports 9 also act as straightening vanes. The result of this construction is to aid materially in providing a non-turbulent emission of gas and primary air from downstream openings of the gas ports 9. The primary air-combustible gas mixture exits the ports 9 in a plurality of annularly positioned jets. The

secondary air is introduced by the draft in the combustion zone 21 and enters as a plurality of radially directed sheet jets through the elongated slots. The dimensions of the slots are such that their Reynolds number is below the critical, so that the secondary air passes into the annular space between the walls 14' and 18 in a plurality of substantially non-turbulent radial, elongated ribbons, spaced uniformly and circum'ferentially about the combustion flame.

It is to be noted that, as the gases issue from burner ports 9 in a plurality of streams closely spaced about the annulus across the cross-section of the flame, they coalesce into an annular ribbon of combustible gases and primary air. The flame is thus propagated as an annular stream into the annulus between the walls 14' and 18. This stream is cut in a plurality of zones circumferentially spaced about the annulus by the jet ribbons of the air that enter through the slots adjacent to and downstream from the point of entry of the streams from the burner ports 9. The burning gases are thus sliced into ribbons by the secondary air ribbons. One set of ribbons are propagated from slots 19 radially outwardly from the interior of the annular burner ports 9 and cut outwardly across the gas stream. The other set of ribbons are propagated from slots 16 radially inwardly above the exterior of the annular burner ports 9'and cut inwardly across the gas stream.

The momentum of the secondary air provided by the much greater port area for the secondary air than the port area for the ports 9, and entering under substantially the same pressure drop as the primary air-gas stream, develops a radial momentum for the secondary air through slots 19 and 16 substantially greater than the radial momentum of the combustible gases. The result is to constrain the flame into a constricted annular cone, schematically illustrated by the dotted lines on FIGURE 1. The cone then develops into a column of flame, as shown schematically by the dotted lines. Due to the relatively low Reynolds number of the gas stream in the combustion zone 21, the flame is propagated as a stream of relatively low turbulence. Because of the columnar nature of the flame, the gas velocities near the center of the chamber 21 are the highest. This forms a down-draft along the wall 21 and an air updraft along the flame and at the center of the chamber 21. This causes a recirculation of combustion gases from an upper section downward along the wall of the chamber 21, as is illustrated by the dotted arrows on FIGURE 1. This recirculation, taken together with the stream of combustion gases in a zone of low Reynolds number results in a columnar flameof relatively low turbulence. This flame geometry is of such character that the dimensions of its cross section is less than the dimensions of the cross section of the combustion space between the confining walls 21 of the combustion space. This assures that the flame will not contact the wall 21 to be quenched thereby until substantially complete combustion has taken place.

While I have described particular embodiments of my invention for purposes of illustration, it should be understood that various modifications and adaptations thereof may be made within the spirit of the invention, as set forth in the appended claims.

I claim:

1. A burner comprising a primary air and combustible gas plenum, a primary air and combustible gas supply inlet to said plenum, said plenum having a top, bottom, and side walls, a plurality of burner ports in said top, said burner ports comprising an annular slot in said plenum top and a spirally interwound corrugated ribbon strip and adjacent flat ribbon strip positioned in said annular slot, said flat strip being positioned between corrugated turns to produce a plurality of interspiral wound ports, between said flat ribbon and corrugated ribbon, in communication with said plenum, said burner also including a cap positioned interiorly of said annular slot, said cap having a circumambient wall, a plurality of elongated slots spaced about said wall and extending longitudinally of said wall, a closed top for said cap, means to admit secondary air to the interior of said cap, a ring positioned exteriorly of said annular slot and spaced from said' wall, said ring having a circumambient wall, a plurality of elongated slots extending longitudinally of said wall of said ring and positioned opposite to the slots in saidwall of said cap, a major portion of the slots in said wall of said ring and said slots in said wall of said cap being positioned substantially at the same distance above said annular slot, means to admit secondary air to said slots in saidwall of said ring whereby the stream of combustible gas and primary air entering through said ports are cut into a plurality of zones spaced circumferentially about the space between the wall of said cap and the wall of said ring by opposed jets of secondary air entering in opposite directions at substantially the same distance above said annular slot.

2. A burner comprising a primary air and combustible gas plenum, a primary air and combustible gas supply inlet to said plenum, said plenum having a top, bottom, and side walls, a plurality of burner ports in said top, said burner ports comprising an annular slot in said plenum top and a spirally interwound corrugated ribbon strip and adjacent flat ribbon strip positioned in said annular slot, said flat strip being positioned between corrugated turns to produce a plurality of interspiral Wound ports, between said flat ribbon and corrugated ribbon, in communication with said plenum, said burner also including a cap positioned interiorly of said annular slot, said cap having a circumambient Wall, a plurality of elongated slots spaced 5 about said Wall and extending longitudinally of said wall, a closed top for said cap, means to admit secondary air to the interior of said cap, a ring positioned exteriorly of said annular slot and spaced from said wall, said ring having a circumambient wall, a plurality of elongated slots eX- 10 tending longitudinally of said wall of said ring and positioned opposite to the slots in said wall of said cap, the slots in said wall of said ring and said slots in said Wall of said cap being positioned substantially at the same distance above said annular slot, means to admit secondary 15 air to said slots in said wall of said ring whereby the stream of combustible gas and primary air entering through said ports are cut into a plurality of zones spaced circumferentially about the space between the Wall of said cap and the wall of said ring by opposed jets of secondary air entering in opposite directions at substantially the same distance above said annular slot,

References Cited by the Examiner UNITED STATES PATENTS JAMES W. WESTHAVER, Primary Examiner.

MEYER PERLIN, Examiner.

Claims (1)

1. A BURNER COMPRISING A PRIMARY AIR AND COMBUSTIBLE GASE PLENUM, A PRIMARY AIR AND COMBUSTIBLE GAS SUPPLY INLET TO SAID PLENUM, SAID PLENUM HAVING A TOP, BOTTOM, AND SIDE WALLS, A PLURALITY OF BURNER PORTS IN SAID TOP, SAID BURNER PORTS COMPRISING AN ANNULAR SLOT IN SAID PLENUM TOP AND A SPIRALLY INTERWOUND CORRUGATED RIBBON STRIP AND ADJACENT FLAT RIBBON STRIP POSITIONED IN SAID ANNULAR SLOT, SAID FLAT STTIP BEING POSITIONED BETWEEN CORRUGATED TURNS TO PRODUCE A PLURALITY OF INTERSPIRAL WOUND PORTS, BETWEEN SAID FLAT RIBBON AND CORRUGATED RIBBON, IN COMMUNICATION WITH SAID PLENUM, SAID BURNER ALSO INCLUDING A CAP POSITIONED INTERIORLY OF SAID ANNULAR SLOT, SAID CAP HAVING A CIRCUMAMBIENT WALL A PLURALITY OF ELONGATED SLOTS SPACED ABOUT SAID WALL AND EXTENDING LONGITUDINALLY OF SAID WALL, A CLOSED TOP FOR SAID CAP, MEANS TO ADMIT SECONDARY AIR TO THE INTERIOR OF SAID CAP, A RING POSITIONED EXTERIORLY OF SAID ANNULAR SLOT AND SPACED FROM SAID WALL, SAID RING HAVING A CIRCUMAMBIENT WALL, A PLURALITY OF ELONGATED SLOTS EXTENDING LONGITUDINALLY OF SAID WALL OF SAID RING AND POSITIONED OPPOSITE TO THE SLOTS IN SAID WALL OF SAID CAP, A MAJOR PORTION OF THE SLOTS IN SAID WALL OF SAID RING AND SAID SLOTS IN SAID WALL OF SAID CAP BEING POSITIONED SUBSTANTIALLY AT THE SAME DISTANCE ABOVE SAID ANNULAR SLOT, MEANS TO ADMIT SECONDARY AIR TO SAID SLOTS IN SAID WALL OF SAID RING WHEREBY THE STREAM OF COMBUSTIBLE GAS AND PRIMARY AIR ENTERING THROUGH SAID PORTS ARE CUT INTO A PLURALITY OF ZONES WALL OF SAID CAP AND THE WALL OF SAID RING BY OPPOSED THE WALL OF SAID CAP AND THE WALL OF SAID RING BY OPPOSED JETS OF SECONDARY AIR ENTERING IN OPPOSITE DIRECTIONS AT SUBSTANTIALLY THE SAME DISTANCE ABOVE SAID ANNULAR SLOT.

Images