CA1188210A - Low pollutant domestic power burner - Google Patents
Low pollutant domestic power burnerInfo
- Publication number
- CA1188210A CA1188210A CA000372005A CA372005A CA1188210A CA 1188210 A CA1188210 A CA 1188210A CA 000372005 A CA000372005 A CA 000372005A CA 372005 A CA372005 A CA 372005A CA 1188210 A CA1188210 A CA 1188210A
- Authority
- CA
- Canada
- Prior art keywords
- swirler
- plenum
- throat
- casing
- air
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23D—BURNERS
- F23D14/00—Burners for combustion of a gas, e.g. of a gas stored under pressure as a liquid
- F23D14/34—Burners specially adapted for use with means for pressurising the gaseous fuel or the combustion air
- F23D14/36—Burners specially adapted for use with means for pressurising the gaseous fuel or the combustion air in which the compressor and burner form a single unit
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- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A gas burner apparatus is disclosed comprising a cylindrical plenum casing, having a throat of reduced diameter at one end coaxial therewith, defining a swirler plenum; a circular swirler plate mounted transversely within the swirler plenum for imparting a swirling motion to primary air passing through the said plenum to the throat; a gas outlet located substantially coaxially with the swirler plenum casing in proximity to the throat for discharge of combustible gas into the throat; an elongated cylindrical casing having a throat of reduced diameter adapted to mate with the throat of the swirler plenum casing defining a combustion chamber for receiving a mixture of swirling air and combustible gas from the swirler plenum for expansion and combustion therein; an exterior tubular casing adapted to extend from and enclose at least a portion of the swirler plenum casing coaxial with and enclosing the combustion chamber casing and spaced therefrom to define an annulus about the combustion chamber, said swirler plenum casing having a plurality of angularly spaced apertures formed therein for the discharge of air from the swirler plenum casing into the said annulus to provide a supply of secondary air for flow through the annulus for admixture with combustion products discharging from the combustion chamber for completion of combustion.
A gas burner apparatus is disclosed comprising a cylindrical plenum casing, having a throat of reduced diameter at one end coaxial therewith, defining a swirler plenum; a circular swirler plate mounted transversely within the swirler plenum for imparting a swirling motion to primary air passing through the said plenum to the throat; a gas outlet located substantially coaxially with the swirler plenum casing in proximity to the throat for discharge of combustible gas into the throat; an elongated cylindrical casing having a throat of reduced diameter adapted to mate with the throat of the swirler plenum casing defining a combustion chamber for receiving a mixture of swirling air and combustible gas from the swirler plenum for expansion and combustion therein; an exterior tubular casing adapted to extend from and enclose at least a portion of the swirler plenum casing coaxial with and enclosing the combustion chamber casing and spaced therefrom to define an annulus about the combustion chamber, said swirler plenum casing having a plurality of angularly spaced apertures formed therein for the discharge of air from the swirler plenum casing into the said annulus to provide a supply of secondary air for flow through the annulus for admixture with combustion products discharging from the combustion chamber for completion of combustion.
Description
This invention relates to a gas power burner and, more particularly, relates to a method and an apparatus for improved combustion of gaseous fuels such as natural gas and propane with reduced production of nitrogen oxides and carbon dioxide.
It has been Eound, in the use of conventional gas power burners in domestic and commercial installations which employ an integral combustion chamber, that maximum nitrogen oxide production (NO ~ NO2) varies within the range of from about 80 to 120 parts per million (ppm) depending largely on combustion temperature and on the ratio of fuel to air.
U.S. Patent 3,729,285 is directed to the ccmbustion of fuel in a plurality of stages to utilize the finding that the combustion of fuel at a fuel to air ratio either above or below stoichiometric requiremen~s results in a reduction of the production of nitrogen oxides and a lowering oF the combustion temperature range. In this patent, a method is described in which two gaseous fuel-air mixtures are combined after combustion, the primary fuel-air mixture having a ~0 surplus of air and the secondary fuel-air mixture having a surplus of fuel.
U.S. Patent 3,486,834 discloses a turndown capability for a gas burner system in which fuel gas flow is divided into two streams and a secondary air flow and gas stream is controlled to permit changes in heat production.
U.S. Patent 3,152,635 discloses an air and gas mixing apparatus for use with a gas power burner comprising gating means for controlling a secondary flow of air to stabilize combustion.
A space heater having two stages of combustion is described in Canadian Patent 1,084,~05. A gaseous fuel is fed into a swirling flow of air, provided by a two-stage impellox, at the entrance to a combustion chamber and the combustion products combined with a secondary flow of air for completion of combustion. The primary flow of air is provided by a revolving blade having predetermined characteristics for swirling the air without substantial increase in air pressure.
Conventional power gas burners normally do not have the capability of operatiny at closely controlled air/fuel ratios because of inadequate mixing of the gaseous fuel and air resulting in statification of the components of the mixture.
To avoid carbon monoxide production, the burners are delibera-tely operated with a stoichiometric excess of air to fuel with resulting low efficiency.
The production of nitrogen oxides has been found to be highest when the mixture of fuel to combustion air is slightly in excess of stoichiometric requirements and maximum combustion temperat~res have been reached. Known burners desi~ned in an effort to reduce nitrogen oxide production often suffer from low thermal efficiency or are undesirably coinplex in design and structure.
It is a principal object of the present invention to provide an improved gas power burner of modular design for facile replacement of conventional domestic and commercial burners which permits thorough mixing of fuel and air for efficient and stable combustion over a wide firing range with reduced nitrogen oxide and carbon monoxide production.
Another object of the present invention is the provision of a simple burner construction for ease of service and replacement operable with a wide variation of air supply with minimum flame impingement on surfaces to be heated.
We have found that the desired objects, including obtaining efficient combustion of gaseous fuel with attendant reduction of nitrogen oxide and carbon monoxide production, can be substantially attained by introducing a stoichiometric excess of gaseous fuel to a swirling flow of primary combustion air and igniting the resulting mixture of gaseous fuel and air in a zone of induced low pressure for primary combustion in a combustion chamber and completing the combustion of gaseous fuel by the addition of a stoichiometric excess of air to the combustion products from the primary combustion chamber by an annular air stream flowing concentric with the said combustion products.
More particularly, the gas burner apparatus of our invention comprises, in combination, a cylindrical plenum casing having a throat of reduced diameter at one end coaxial therewith defining a swirler plenum; a circular swirler plate mounted within the swirler plenum transversely of the longitudinal axis of the swirler plenum casing for imparting a swirling motion to primary air passing through the said plenum to the throat; a gas outlet located substantially coaxially with the swirler plenum casing in proximity to the throat for discharge of combustible gas into the throat; an elongated cylindrical casing having a throat of reduced diameter adapted to mate with the throat of the swirler plenum casing defining a combustion chamber for receiving a mixture of swirling air and combustible gas from the swirler plenum for expansion and combustion therein; an exterior tubular casing adapted to extend from and enclose at least a portion of the swirler plenum casing coaxial with and enclosing the combustion 21~
chamber casing and spaced therefrom to define an annulus abou~
the combustion chamber, said swirler plenum casing having a plurality oE angularly spaced apertures formed therein for the discharge of air from the swirler plenum casing into the said annulus to provide a supply of secondary air for flow through the annulus for admixture with combustion products discharging from the combustion chamber for completion of combustionO
Embodiments of the apparatus of my invention will now be described with reference to the accompanying drawings, in which:
Figure 1 is a longitudinal section of an embodiment of the burner apparatus of my invention;
Figure 2 is a longitudinal section of another embodiment of the burner apparatus of my invention;
Figure 3 is a perspective view of a deflector vane used in the embodiments of Figures 1 and 2;
and Figure 4 is a graphical illustration of the performance of the burners of the present invention compared to conventional gas burners and an oil burner.
Like reference characters refer to like parts throughout the description of the drawings.
In the em~odiment illustrated in Figure 1, the power gas burner comprises a swirler plenum 10 formed by tubular i.e. cylindrical casing 11 having a tapered throat 12 formed at one end, coaxial therewith, tapered throat 12 preferably having a generally circular cross-sectional shape 14 converging smoothly from cylindrical casing wall 16 to throat 1~. An air blowex, not shown, is in communication with the opposite end 18 of casing 11 for supplying a flow of air under a low pressure head thereto.
A vane assembly or swirler plate 20 is mounted transversely of the longitudinal axis of the swirler plenum casing in proximity to throat 12, swirler 20 having a plurality of equispaced peripheral guide vanes 22, shown more clearly in Figure 3, Eor imparting rotational spin to the longitudinal flow oE air, from right to left as viewed in Figure 1, as the air passes through ports 24.
Guide vanes 22 are employed to convert the static pressure head in plenum 10 into rotational energy by the rotational flow of alr depicted by numeral 32. This rotating mass ~f air is reduced in diameter ~rom -the diameter "D" of plenum 10 to the diameter "d" of throat 12 as the air passes through throat 12 resulting in a free vortex~
Since angular momentum is essentially conserved, the tangential velocity of the air increases linearly with the decrease in radius (r) and the resulting angular velocity increases as 1 to create a strong vortex with subatmospheric pressure and r2 reverse flow in the central region 31.
The guide vanes 22 preferably are set at an angle of about 10 from the plane of plate 20 to impart the desired rotation to the air flow.
A fuel gas conduit 2~ is centrally located within swirler plenum casing 12 coaxially therewith and terminates near throat 1~ such that nozzle 28 having end plate 29 ~ischarges the gaseous fuel laterally through apertures 30 into said throat for admixture with the vortex of swirling flow of air 32.
We have found that the plenum diameter "D" relative Z 1 ~
to throat diameter "d" bears an important relationship for providing a desired intensity of the vortex generated relative to the static pressure in plenum 10 for optimum mixing of gaseous fuel and air within throat 12 and the combustion chamber, to be described. As the D:d ratio is increased, we have found that the intensity of the vortex increases to the level that friction losses become dominant and power require-ments impractical for desired air flow. As the D:d ratio is decreased, we have found that the intensity of the vorte~x decreases to the level that inadequate mixing of the gaseous fuel and air takes place. The preferred range of D:d is about 4:1 to about 5.5:1.
The swirler plate 20 should be set back, i.e. mounted upstxeam of the initiation of the convergence of throat 12 at juncture 33, at least about one inch and not more than about two inches for a diameter "D" of five inches. A set-back in a five inch diameter of less than 1/5 D results in a substantially reduced swirl generated whereas a set-back of more than 2/5 D
provides only a marginally improved increase in swirl with an undesirable increase in length of casing 14.
A plùrality of equispaced peripheral openings 34 are - formed about wall 16 of plenum casing 11 in proximity to and upstream of swirler plate 20 for the discharge of a secondary flow of air, depicted by arrows 39, into the annulus 35 defined between exterior tubular casing 36 and wall 16. Tubular casing 16 is adapted to extend from and ~nclose at least a portion of swirler plenum casing 11 for longitudinal flow of the secondary air 39 through the annulus 38 defined between the extension 40 of casing 36 and the wall 42 of cylindrical combustion chamber 44. Sufficient wall openings 34 are provided to permit a flow of secondary air 39 equivalent to about 1/4 to about 1/3 of the 3Z~
flow of primary air at the plenum static pressure.
- The combustion chamber 44 is formed by the elongated cylindrical tube or casing 42 having an entry throat 46 adapted to mate with plenum casing throat 12 to receive the mixture of gaseous fuel and air for expansion into the combustion chamber 44 for ignition by electrical ignition device 48 centred by longitudinally extending electrodes 50,52.
The embodiment o~ gas burner illustrated in Figure 2 comprises a swirler plenum 110 formed by tubular casing 111 havin~ a throat 112 formed at one end coaxial therewith in end wall 113. The junctures 133 and 121 between cylindrical wall 116 of casing 111 and throat 112 with end wall 113 are ~ounded to streamline airflow. An air blower depicted by numeral 119 introduces air under pressure tangentially to plenum casing 111 for discharge through ports 24 of swirler plate 20 shown in Figure 3.
We have found that guide vanes 22 should be set at an angle to the plane of plate 20 of from about 15 to about 45 depending on the blower fuel input, as shown in Table 1 below.
~ . . . . .
-- -- ............. . .. . _ . _ _ .
SWIRLER VANE ANGLE
_ _. _ _ .. .
Input (xlO00 BTU/hr~ Angle () . _ ... _ .
135 to 150 45 115 to 134 25 50 to 114 _ _ _ An elongated combustion chamber casing 42 having an entry throat 46 adapted to mate with plenum casing throat 112 is axially ali~ned with plenum casing 111. A fuel conduit 126 passes through end wall 127 of plenum 110 to annulus 140 defined between two centrally disposed concentric tubes 142,144 by way of radial passage 146.
Exterior tubular casing 136 extends from end wall 113 of plenum casing 111 concentric with combustion chamber casing 142 to define annulus 138 therebetween. A plurality o angularly spaced apertures 134 formed in end wall 113 downstream of swirler plate ~0 permit the discharge of a secondary flow of air, depicted by numeral 139, into annulus 138.
Comparative tests were conducted between the embodiments of our invention illustrated in Figures 1 and 2 and between em~odiments of the present invention and conventional commercial burners~ The embodiment of Figure 1 tested had a plenum casing 11 diameter "D" of 5 inches, combustion chamber 44 dia~eter of 3.25 inches and length 13.5 inches, throat diameter 12 of 1.125 inches, outer casing 40 diameter of 3.9 inches, to produce an annulus 38 ~idth of 0.33 inch, and a swirler plate 20 set-back of about 1 inch. A ratio of D:d of about 4.4:1 was chosen for optimum swirl and completion of combustion within the combustion chamber. The combustion chamber casing was formed of 310 stainless steel and the casings 11,40 and swirler plate 20 formed of mild steel. The gas conduit 28 was closed at the discharge end by cap 29 and four e~uispaced apertures 30 formed in proximity to the end of the conduit for lateral gas discharge. Ignition electrodes 48 haviny a long reach extended into the combustion chamber.
The embodiment of Figure 2 tested had a plenum casing 111 diameter of 6 inches, throat 112 diameter of 1.5 inches and the remaining dimensions were essentially the C~ame as the Figure 1 embodiment. The plenum apertures 13~ were located in the end plate 113. The gaseous fuel conduit 126 terminated in an annulus 140 in proximity to the swirler plenum throat 112.
Ignition electrodes 1~8 were positioned within the combustion chamber throat.
A vane angle of 10 to the plane of the swirler plate for each of six vanes proved satisfactory for the full range of 50,000 to 150,000 BTU/hr input tested for the Figure 1 embodi-ment whereas the vane angle had to be adjus-ted between 15 to 45~ for the Figure 2 embodiment, as set forth in Table 1 above.
A ratio of primary to secondary air within the range of from about 2:1 to 3:1 provided optimum efficiency with minimum nitrogen oxiae emissions. For an air supply of 10% in excess of stoichiometric requirements, an increase of the ratio of primar~ to secondary air above about 3:1, i.e. more than about 80% of stoichiometric requirements, resulted-in more complete combustion and less carbon monoxide production but increased nitrogen oxide production.
Three conventional power gas burners, identified as Commercial types ~, B and C, and a conventional oil burner were subjected to performance tests for comparison with the two embodiments of the present invention, identified as C~RI type S
~Figure 1 embodiment) and CGRI type R (Figure 2 embodiment).
During each test, the nitrogen oxide (NOX) and carbon monoxide (CO) emissions were monitored as the fuel and air supplies were varied. Peak operating efficiency was chosen as being the level a~ which CO emissions reached 100 ppm, air-free, for the natural ~38~
gas burners, or a smoke number oE 1.5 on the Bacharach smoke scale for the oil burner~ A summary of the comparative per-formance date is shown in Table 2 and graphically illustrated in Figure 4.
... . ~
PERFO~M~NCE OF C.~.R.I. AND COMME~CIAL
BURNERS AT PEAK EFFICIENCY
Burner NO`} Concentration, ppm, Air free Input Btu/hr. CGRI CGRI Commercial Commercial Commercial Oil type S type R _ type A type B _ ty~C buxner 50,000 24.5 23.0 - 30.5 37.5 75,~00 33.0 29.5 ~7.0 37.5 54.~ -100,0~0 35.5 41 D 5 40.5 44.5 63.0 96.0 125,000 38.Q 50.0 ~4.5 ~4.5 ~8.0 83.0 150;,000 ~ 40 D 545 D O ~ . ~61.5: 68.0~ 113~5~.
C2 Concentrationl % ~y volume 50 t 0 0 0 . 8.95 9.50 . ~ 9.00-- ~ 8.65 ~ ~
75,000 10.30 10.40 10.00 10.40 g.30 1 0 t 000 10.45 10 D 75 10.35 9.05 9.15 7~20 125,000 lC.60 10 D 90 10.3~ 9.95 9.6Q 8.80 150,000 10.65 11.2S 9.80 - 10.25 11.05 . .
NOTE: Ultimate ~ CO2 = 11.8 for na-tural gas Ultimate % CO~ = 15.6 ~or no. 2 furnace oil The two Pmbodiments of applicant's invention, particularly the Figure 1 embodiment (CGRI Type S), provided optimum overall combustion performance over the full range of fuel input, i.e~ 50,000 to 150,000 BTU/hr, with substantially lower-NOx emissions than most of the burners, particularly the Commercial type C burner. Commercial type A burner exhibited incomplete combustion at the 50,000 BTU/hr input and high NOX
emission at higher inputs. Commerical type B burner could not be operatea beyond about 25,000 BTU/hr without incomplete combustion.
The present invention provides a number of important advantages. An improved burner of modular design can be substituted for conventional domestic and commercial burners to permit efficient and stable combustion of gaseous fuel over a wide firing range with reduced production of nitrogen oxide and carbon monoxide. Combustion air is thoroughly mixed with the fuel to produce a stable flame with minimum flame impinge-ment on combustion chamber walls.
It will be understood of course that modifications can be made in the embodiment of the invention illustrated and described herein without departing from the scope and purview of the invention as defined by the appended claims.
It has been Eound, in the use of conventional gas power burners in domestic and commercial installations which employ an integral combustion chamber, that maximum nitrogen oxide production (NO ~ NO2) varies within the range of from about 80 to 120 parts per million (ppm) depending largely on combustion temperature and on the ratio of fuel to air.
U.S. Patent 3,729,285 is directed to the ccmbustion of fuel in a plurality of stages to utilize the finding that the combustion of fuel at a fuel to air ratio either above or below stoichiometric requiremen~s results in a reduction of the production of nitrogen oxides and a lowering oF the combustion temperature range. In this patent, a method is described in which two gaseous fuel-air mixtures are combined after combustion, the primary fuel-air mixture having a ~0 surplus of air and the secondary fuel-air mixture having a surplus of fuel.
U.S. Patent 3,486,834 discloses a turndown capability for a gas burner system in which fuel gas flow is divided into two streams and a secondary air flow and gas stream is controlled to permit changes in heat production.
U.S. Patent 3,152,635 discloses an air and gas mixing apparatus for use with a gas power burner comprising gating means for controlling a secondary flow of air to stabilize combustion.
A space heater having two stages of combustion is described in Canadian Patent 1,084,~05. A gaseous fuel is fed into a swirling flow of air, provided by a two-stage impellox, at the entrance to a combustion chamber and the combustion products combined with a secondary flow of air for completion of combustion. The primary flow of air is provided by a revolving blade having predetermined characteristics for swirling the air without substantial increase in air pressure.
Conventional power gas burners normally do not have the capability of operatiny at closely controlled air/fuel ratios because of inadequate mixing of the gaseous fuel and air resulting in statification of the components of the mixture.
To avoid carbon monoxide production, the burners are delibera-tely operated with a stoichiometric excess of air to fuel with resulting low efficiency.
The production of nitrogen oxides has been found to be highest when the mixture of fuel to combustion air is slightly in excess of stoichiometric requirements and maximum combustion temperat~res have been reached. Known burners desi~ned in an effort to reduce nitrogen oxide production often suffer from low thermal efficiency or are undesirably coinplex in design and structure.
It is a principal object of the present invention to provide an improved gas power burner of modular design for facile replacement of conventional domestic and commercial burners which permits thorough mixing of fuel and air for efficient and stable combustion over a wide firing range with reduced nitrogen oxide and carbon monoxide production.
Another object of the present invention is the provision of a simple burner construction for ease of service and replacement operable with a wide variation of air supply with minimum flame impingement on surfaces to be heated.
We have found that the desired objects, including obtaining efficient combustion of gaseous fuel with attendant reduction of nitrogen oxide and carbon monoxide production, can be substantially attained by introducing a stoichiometric excess of gaseous fuel to a swirling flow of primary combustion air and igniting the resulting mixture of gaseous fuel and air in a zone of induced low pressure for primary combustion in a combustion chamber and completing the combustion of gaseous fuel by the addition of a stoichiometric excess of air to the combustion products from the primary combustion chamber by an annular air stream flowing concentric with the said combustion products.
More particularly, the gas burner apparatus of our invention comprises, in combination, a cylindrical plenum casing having a throat of reduced diameter at one end coaxial therewith defining a swirler plenum; a circular swirler plate mounted within the swirler plenum transversely of the longitudinal axis of the swirler plenum casing for imparting a swirling motion to primary air passing through the said plenum to the throat; a gas outlet located substantially coaxially with the swirler plenum casing in proximity to the throat for discharge of combustible gas into the throat; an elongated cylindrical casing having a throat of reduced diameter adapted to mate with the throat of the swirler plenum casing defining a combustion chamber for receiving a mixture of swirling air and combustible gas from the swirler plenum for expansion and combustion therein; an exterior tubular casing adapted to extend from and enclose at least a portion of the swirler plenum casing coaxial with and enclosing the combustion 21~
chamber casing and spaced therefrom to define an annulus abou~
the combustion chamber, said swirler plenum casing having a plurality oE angularly spaced apertures formed therein for the discharge of air from the swirler plenum casing into the said annulus to provide a supply of secondary air for flow through the annulus for admixture with combustion products discharging from the combustion chamber for completion of combustionO
Embodiments of the apparatus of my invention will now be described with reference to the accompanying drawings, in which:
Figure 1 is a longitudinal section of an embodiment of the burner apparatus of my invention;
Figure 2 is a longitudinal section of another embodiment of the burner apparatus of my invention;
Figure 3 is a perspective view of a deflector vane used in the embodiments of Figures 1 and 2;
and Figure 4 is a graphical illustration of the performance of the burners of the present invention compared to conventional gas burners and an oil burner.
Like reference characters refer to like parts throughout the description of the drawings.
In the em~odiment illustrated in Figure 1, the power gas burner comprises a swirler plenum 10 formed by tubular i.e. cylindrical casing 11 having a tapered throat 12 formed at one end, coaxial therewith, tapered throat 12 preferably having a generally circular cross-sectional shape 14 converging smoothly from cylindrical casing wall 16 to throat 1~. An air blowex, not shown, is in communication with the opposite end 18 of casing 11 for supplying a flow of air under a low pressure head thereto.
A vane assembly or swirler plate 20 is mounted transversely of the longitudinal axis of the swirler plenum casing in proximity to throat 12, swirler 20 having a plurality of equispaced peripheral guide vanes 22, shown more clearly in Figure 3, Eor imparting rotational spin to the longitudinal flow oE air, from right to left as viewed in Figure 1, as the air passes through ports 24.
Guide vanes 22 are employed to convert the static pressure head in plenum 10 into rotational energy by the rotational flow of alr depicted by numeral 32. This rotating mass ~f air is reduced in diameter ~rom -the diameter "D" of plenum 10 to the diameter "d" of throat 12 as the air passes through throat 12 resulting in a free vortex~
Since angular momentum is essentially conserved, the tangential velocity of the air increases linearly with the decrease in radius (r) and the resulting angular velocity increases as 1 to create a strong vortex with subatmospheric pressure and r2 reverse flow in the central region 31.
The guide vanes 22 preferably are set at an angle of about 10 from the plane of plate 20 to impart the desired rotation to the air flow.
A fuel gas conduit 2~ is centrally located within swirler plenum casing 12 coaxially therewith and terminates near throat 1~ such that nozzle 28 having end plate 29 ~ischarges the gaseous fuel laterally through apertures 30 into said throat for admixture with the vortex of swirling flow of air 32.
We have found that the plenum diameter "D" relative Z 1 ~
to throat diameter "d" bears an important relationship for providing a desired intensity of the vortex generated relative to the static pressure in plenum 10 for optimum mixing of gaseous fuel and air within throat 12 and the combustion chamber, to be described. As the D:d ratio is increased, we have found that the intensity of the vortex increases to the level that friction losses become dominant and power require-ments impractical for desired air flow. As the D:d ratio is decreased, we have found that the intensity of the vorte~x decreases to the level that inadequate mixing of the gaseous fuel and air takes place. The preferred range of D:d is about 4:1 to about 5.5:1.
The swirler plate 20 should be set back, i.e. mounted upstxeam of the initiation of the convergence of throat 12 at juncture 33, at least about one inch and not more than about two inches for a diameter "D" of five inches. A set-back in a five inch diameter of less than 1/5 D results in a substantially reduced swirl generated whereas a set-back of more than 2/5 D
provides only a marginally improved increase in swirl with an undesirable increase in length of casing 14.
A plùrality of equispaced peripheral openings 34 are - formed about wall 16 of plenum casing 11 in proximity to and upstream of swirler plate 20 for the discharge of a secondary flow of air, depicted by arrows 39, into the annulus 35 defined between exterior tubular casing 36 and wall 16. Tubular casing 16 is adapted to extend from and ~nclose at least a portion of swirler plenum casing 11 for longitudinal flow of the secondary air 39 through the annulus 38 defined between the extension 40 of casing 36 and the wall 42 of cylindrical combustion chamber 44. Sufficient wall openings 34 are provided to permit a flow of secondary air 39 equivalent to about 1/4 to about 1/3 of the 3Z~
flow of primary air at the plenum static pressure.
- The combustion chamber 44 is formed by the elongated cylindrical tube or casing 42 having an entry throat 46 adapted to mate with plenum casing throat 12 to receive the mixture of gaseous fuel and air for expansion into the combustion chamber 44 for ignition by electrical ignition device 48 centred by longitudinally extending electrodes 50,52.
The embodiment o~ gas burner illustrated in Figure 2 comprises a swirler plenum 110 formed by tubular casing 111 havin~ a throat 112 formed at one end coaxial therewith in end wall 113. The junctures 133 and 121 between cylindrical wall 116 of casing 111 and throat 112 with end wall 113 are ~ounded to streamline airflow. An air blower depicted by numeral 119 introduces air under pressure tangentially to plenum casing 111 for discharge through ports 24 of swirler plate 20 shown in Figure 3.
We have found that guide vanes 22 should be set at an angle to the plane of plate 20 of from about 15 to about 45 depending on the blower fuel input, as shown in Table 1 below.
~ . . . . .
-- -- ............. . .. . _ . _ _ .
SWIRLER VANE ANGLE
_ _. _ _ .. .
Input (xlO00 BTU/hr~ Angle () . _ ... _ .
135 to 150 45 115 to 134 25 50 to 114 _ _ _ An elongated combustion chamber casing 42 having an entry throat 46 adapted to mate with plenum casing throat 112 is axially ali~ned with plenum casing 111. A fuel conduit 126 passes through end wall 127 of plenum 110 to annulus 140 defined between two centrally disposed concentric tubes 142,144 by way of radial passage 146.
Exterior tubular casing 136 extends from end wall 113 of plenum casing 111 concentric with combustion chamber casing 142 to define annulus 138 therebetween. A plurality o angularly spaced apertures 134 formed in end wall 113 downstream of swirler plate ~0 permit the discharge of a secondary flow of air, depicted by numeral 139, into annulus 138.
Comparative tests were conducted between the embodiments of our invention illustrated in Figures 1 and 2 and between em~odiments of the present invention and conventional commercial burners~ The embodiment of Figure 1 tested had a plenum casing 11 diameter "D" of 5 inches, combustion chamber 44 dia~eter of 3.25 inches and length 13.5 inches, throat diameter 12 of 1.125 inches, outer casing 40 diameter of 3.9 inches, to produce an annulus 38 ~idth of 0.33 inch, and a swirler plate 20 set-back of about 1 inch. A ratio of D:d of about 4.4:1 was chosen for optimum swirl and completion of combustion within the combustion chamber. The combustion chamber casing was formed of 310 stainless steel and the casings 11,40 and swirler plate 20 formed of mild steel. The gas conduit 28 was closed at the discharge end by cap 29 and four e~uispaced apertures 30 formed in proximity to the end of the conduit for lateral gas discharge. Ignition electrodes 48 haviny a long reach extended into the combustion chamber.
The embodiment of Figure 2 tested had a plenum casing 111 diameter of 6 inches, throat 112 diameter of 1.5 inches and the remaining dimensions were essentially the C~ame as the Figure 1 embodiment. The plenum apertures 13~ were located in the end plate 113. The gaseous fuel conduit 126 terminated in an annulus 140 in proximity to the swirler plenum throat 112.
Ignition electrodes 1~8 were positioned within the combustion chamber throat.
A vane angle of 10 to the plane of the swirler plate for each of six vanes proved satisfactory for the full range of 50,000 to 150,000 BTU/hr input tested for the Figure 1 embodi-ment whereas the vane angle had to be adjus-ted between 15 to 45~ for the Figure 2 embodiment, as set forth in Table 1 above.
A ratio of primary to secondary air within the range of from about 2:1 to 3:1 provided optimum efficiency with minimum nitrogen oxiae emissions. For an air supply of 10% in excess of stoichiometric requirements, an increase of the ratio of primar~ to secondary air above about 3:1, i.e. more than about 80% of stoichiometric requirements, resulted-in more complete combustion and less carbon monoxide production but increased nitrogen oxide production.
Three conventional power gas burners, identified as Commercial types ~, B and C, and a conventional oil burner were subjected to performance tests for comparison with the two embodiments of the present invention, identified as C~RI type S
~Figure 1 embodiment) and CGRI type R (Figure 2 embodiment).
During each test, the nitrogen oxide (NOX) and carbon monoxide (CO) emissions were monitored as the fuel and air supplies were varied. Peak operating efficiency was chosen as being the level a~ which CO emissions reached 100 ppm, air-free, for the natural ~38~
gas burners, or a smoke number oE 1.5 on the Bacharach smoke scale for the oil burner~ A summary of the comparative per-formance date is shown in Table 2 and graphically illustrated in Figure 4.
... . ~
PERFO~M~NCE OF C.~.R.I. AND COMME~CIAL
BURNERS AT PEAK EFFICIENCY
Burner NO`} Concentration, ppm, Air free Input Btu/hr. CGRI CGRI Commercial Commercial Commercial Oil type S type R _ type A type B _ ty~C buxner 50,000 24.5 23.0 - 30.5 37.5 75,~00 33.0 29.5 ~7.0 37.5 54.~ -100,0~0 35.5 41 D 5 40.5 44.5 63.0 96.0 125,000 38.Q 50.0 ~4.5 ~4.5 ~8.0 83.0 150;,000 ~ 40 D 545 D O ~ . ~61.5: 68.0~ 113~5~.
C2 Concentrationl % ~y volume 50 t 0 0 0 . 8.95 9.50 . ~ 9.00-- ~ 8.65 ~ ~
75,000 10.30 10.40 10.00 10.40 g.30 1 0 t 000 10.45 10 D 75 10.35 9.05 9.15 7~20 125,000 lC.60 10 D 90 10.3~ 9.95 9.6Q 8.80 150,000 10.65 11.2S 9.80 - 10.25 11.05 . .
NOTE: Ultimate ~ CO2 = 11.8 for na-tural gas Ultimate % CO~ = 15.6 ~or no. 2 furnace oil The two Pmbodiments of applicant's invention, particularly the Figure 1 embodiment (CGRI Type S), provided optimum overall combustion performance over the full range of fuel input, i.e~ 50,000 to 150,000 BTU/hr, with substantially lower-NOx emissions than most of the burners, particularly the Commercial type C burner. Commercial type A burner exhibited incomplete combustion at the 50,000 BTU/hr input and high NOX
emission at higher inputs. Commerical type B burner could not be operatea beyond about 25,000 BTU/hr without incomplete combustion.
The present invention provides a number of important advantages. An improved burner of modular design can be substituted for conventional domestic and commercial burners to permit efficient and stable combustion of gaseous fuel over a wide firing range with reduced production of nitrogen oxide and carbon monoxide. Combustion air is thoroughly mixed with the fuel to produce a stable flame with minimum flame impinge-ment on combustion chamber walls.
It will be understood of course that modifications can be made in the embodiment of the invention illustrated and described herein without departing from the scope and purview of the invention as defined by the appended claims.
Claims (18)
1. A gas burner comprising, in combination, a cylindrical plenum casing having a throat of reduced diameter at one end coaxial therewith defining a swirler plenum;
a circular swirler plate mounted concentrically within the swirler plenum transversely of the longitudinal axis of the swirler plenum casing for imparting a swirling motion to primary air passing through the swirler plenum to the throat;
gas outlet means located substantially coaxially with the swirler plenum casing in proximity to the throat for discharge of combustible gas into the throat;
an elongated cylindrical casing having a throat of reduced diameter adapted to mate with the throat of the swirler plenum defining a combustion chamber for receiving a mixture of swirling air and combustible gas from the swirler plenum for expansion and combustion therein;
an exterior tubular casing, adapted to extend from and enclose at least a portion of the swirler plenum casing, concentric with and enclosing the combustion chamber and spaced therefrom to define an annulus therebetween;
said swirler plenum having a plurality of angularly spaced apertures formed therein for the discharge of air from the swirler plenum into the said annulus to provide a supply of secondary air for flow through the annulus for admixture with combustion products discharging from the combustion chamber for completion of combustion.
a circular swirler plate mounted concentrically within the swirler plenum transversely of the longitudinal axis of the swirler plenum casing for imparting a swirling motion to primary air passing through the swirler plenum to the throat;
gas outlet means located substantially coaxially with the swirler plenum casing in proximity to the throat for discharge of combustible gas into the throat;
an elongated cylindrical casing having a throat of reduced diameter adapted to mate with the throat of the swirler plenum defining a combustion chamber for receiving a mixture of swirling air and combustible gas from the swirler plenum for expansion and combustion therein;
an exterior tubular casing, adapted to extend from and enclose at least a portion of the swirler plenum casing, concentric with and enclosing the combustion chamber and spaced therefrom to define an annulus therebetween;
said swirler plenum having a plurality of angularly spaced apertures formed therein for the discharge of air from the swirler plenum into the said annulus to provide a supply of secondary air for flow through the annulus for admixture with combustion products discharging from the combustion chamber for completion of combustion.
2. A gas burner as claimed in Claim 1, in which said swirler plate has a plurality of deflector vanes defining an angle in the range of 10 to 45° from the plane of the swirler plate.
3. A gas burner as claimed in Claim 1, in which said swirler plenum casing has a diameter D, the throat has a diameter d and the ratio of D:d is within the range of from about 4:1 to 5.5:1.
4. A gas burner as claimed in Claim 3, in which the swirler plate is set back from the end of the cylindrical plenum casing adjacent the throat at least 1/5 D.
5. A gas burner as claimed in Claim 3, in which the swirler plate is set back from the end of the cylindrical plenum adjacent the throat about 1/5 D to 2/5 D.
6. A gas burner as claimed in Claim 1, in which said plenum casing throat is tapered and smoothly converging from the cylindrical plenum casing to the mating throat of the combustion chamber.
7. A gas chamber as claimed in Claim 6, in which the cylindrical swirler plenum has a plurality of angularly equi-spaced apertures formed therein for the discharge of secondary air into the said annulus to provide a ratio of primary air to secondary air within the range of from about 2:1 to 3:1.
8. A gas burner as claimed in Claim 4, 5 or 7, in which said apertures are located upstream of the swirler plate.
9. A gas burner as claimed in Claim 1, in which the cylindrical plenum casing has an end plate in which the throat is centrally located, and in which the swirler plenum casing has a diameter D, the throat has a diameter d and the ratio of D:d is within the range of from 4:1 to 5.5:1.
10. A gas burner as claimed in Claim 9, in which the swirler plate is set back from the end of the cylindrical plenum casing adjacent the throat at least about 1/5 D, and in which the plurality of angularly-spaced aperturas are formed angularly about the said end plate communicating with the annulus formed about the combustion chamber.
11. A gas burner as claimed in Claim 10, in which sufficient angularly spaced apertures are formed to discharge into the annulus to provide a ratio of primary air to secondary air within the range of from about 2:1 to 3:1.
12. A gas burner as claimed in Claim 2, 3 or 4, in which said gas outlet means comprises a closed fuel conduit having a plurality of openings formed angularly about the conduit in proximity to the end of the conduit for lateral discharge of fuel.
13. A gas burner as claimed in Claims 9 or 10, in which said gas outlet means comprise an annular conduit formed by two concentric tubes centrally located within the swirler plenum throat and a fuel conduit for supplying gaseous fuel to said annular conduit.
14. A gas burner as claimed in Claim 2, 3 or 4 in which ignition means are located within the combustion chamber adjacent the throat thereof.
15. A gas burner as claimed in Claim 10, in which the exterior tubular casing concentric with the combustion chamber abuts and extends from the plenum casing end plate.
16. A method of combusting a gaseous fuel with reduced emissions of nitrogen oxides which comprises the steps of introducing a stoichiometric excess of the gaseous fuel to a swirling flow of primary combustion air in a zone of induced low pressure and igniting the resulting mixture of gaseous fuel and air for primary combustion in an elongated combustion chamber and completing the combustion of gaseous fuel by adding a stoichiometric excess of secondary air to combustion products from the primary combustion chamber by flowing an annular stream of said secondary air concurrent with the flow of said combustion products.
17. A method as claimed in Claim 16, in which said swirling flow of primary combustion air forms a vortex in a throat of reduced diameter.
18. A method as claimed in Claim 17, in which the primary combustion air flows from a swirler plenum having a diameter D to a throat of reduced diameter d, the ratio of D to d being in the range of 4:1 to 5.5:1, said swirler plenum having means to impart a swirl to said flow of air, and the primary combustion air having a ratio to secondary combustion air within the range of from about 2:1 to 3:1.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000372005A CA1188210A (en) | 1981-02-27 | 1981-02-27 | Low pollutant domestic power burner |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000372005A CA1188210A (en) | 1981-02-27 | 1981-02-27 | Low pollutant domestic power burner |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1188210A true CA1188210A (en) | 1985-06-04 |
Family
ID=4119335
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000372005A Expired CA1188210A (en) | 1981-02-27 | 1981-02-27 | Low pollutant domestic power burner |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1188210A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6494710B2 (en) * | 2000-08-22 | 2002-12-17 | Korea Institute Of Science And Technology | Method and apparatus for increasing incineration capacity of the ground flares by using the principle of tornado |
-
1981
- 1981-02-27 CA CA000372005A patent/CA1188210A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6494710B2 (en) * | 2000-08-22 | 2002-12-17 | Korea Institute Of Science And Technology | Method and apparatus for increasing incineration capacity of the ground flares by using the principle of tornado |
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