Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02694415 2010-03-03
1 "NATURAL DRAFT BURNER"
2
3 FIELD OF THE INVENTION
4 The present invention relates to the field of burners and particularly
to gas burners used in industrial heaters.
6
7 BACKGROUND OF THE INVENTION
8 It is well known in a variety of industries to use heaters having
9 burner assemblies for a number of different applications, including kilns,
drying
apparatus, furnaces and for preventing freezing of tanks and pipelines. In the
oil
11 and gas industry, heaters are particularly used in regions where low
ambient
12 temperatures may result in freezing of storage tanks or in production and
process
13 pipelines. Further process heaters are used which may be used when knocking
14 water out of oil and when heating salt baths and the like. Gas burner
assemblies
are typically arranged in a housing or firetube which extends into a storage
or
16 holding tank to be heated.
17 In prior art natural draft or "non-forced draft" situations, primary
18 combustion air is drawn into a mixing chamber or mixer head of the gas
burner
19 assembly as a result of the velocity of the flammable gas entering the
mixing
chamber or venturi. The premixed gas/air fuel mixture exits the venturi at a
21 burner nozzle, typically a rosebud nozzle, where the mixture is ignited.
22 Secondary combustion air is drawn into the housing and around the burner
23 assembly as a result of draft. The secondary air, intended to aid in
combustion,
24 may adversely affect the operation of the burner assembly. Large volumes of
secondary air creating a large turbulent draft at the burner head may result
in the
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CA 02694415 2010-03-03
1 flame being lifted from the burner nozzle or may blow out a flame at the
nozzle.
2 Attempts to reduce or dampen the amount of secondary air entering the bumer
3 can substantially shutoff the flow of secondary air which compromises the
4 efficiency of the burner.
Further, variability in operation can adversely affect the consistency
6 of ignition and flame sensing. Typically, burners may be operated in high-
fire and
7 low-fire situations. In a low-fire situation, the pressure of fuel entering
the burner
8 is relatively low compared to a high-fire situation. Conventional burners
which
9 are set to operate under low-fire conditions can experience lifting of the
flame
from the burner nozzle should they be used in a high-fire situation. Thus, in
11 conventional burners, ignition and flame sensing, which are optimized for
one
12 flame characteristic, become problematic as the position of the flame
alters. Use
13 of a pilot has provided a consistent flame source and ignition sensing. In
variable
14 firing conditions, should the fuel/air ratio and secondary air flow be
sufficiently
unstable at the burner nozzle, remote lighting of the burner becomes
difficult. As
16 a result, the industry has typically relied on manual lighting of such
burners which
17 has resulted in significant hazard to personnel performing the task.
18 Additionally, freezing is a common problem with natural draft burner
19 assemblies. Typically, areas of low pressure adjacent the orifice of the
burner
may result in freezing at the orifice or in the gas lines which feed the
orifice. Low
21 flow of fuel at pilot assemblies are even more prone to freezing
22 Clearly, there is interest in the industry to provide a reliable burner
23 which remains lit under ambient conditions, is safe to ignite and operate
and
24 permits flame-sensing in both low fire and high fire situations, does not
freeze in
low ambient temperature and is efficient.
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1 SUMMARY OF THE INVENTION
2 A natural draft burner assembly according to one embodiment of
3 the invention comprises a pilotless ignition and flame sensing system and a
4 burner head having a nozzle tip situated in a secondary air housing and
which is
equally operable at low and high fire. The nozzle tip discharges a mixture of
6 primary air and gaseous fuel which is separated from the secondary air
flowing
7 therearound for stabilizing flame at the nozzle tip. A flame ionization
sensor
8 senses flame at the nozzle tip throughout low and high fire operation,
obviating
9 the need for a pilot. Secondary air is separated from the nozzle tip by
directing
the secondary air away from the tip such as through a conical ring situated on
the
11 burner head or by an air deflector ring which also serves to swirl the
secondary
12 air circumferentially in the housing or in a preferred embodiment, by a
13 combination of both the low pressure ring and the deflector plate
manufactured
14 as a unitary structure with the nozzle head. More preferably, the burner
assembly comprises a tubular barrel having a mixing chamber at the gas inlet
16 end and a nozzle tip having a plurality of orifices at the burner head end.
The
17 mixing chamber can received aspirated primary combustion air, preferably
18 through a plurality of air orifices, or through a forced air inlet.
19 In a broad aspect of the invention, a natural draft burner assembly
is provided for mounting in a housing and forming an annular space
21 therebetween, the burner assembly having a nozzle tip mounted in a burner
head
22 at a first distal end of a tubular barrel, the tubular barrel having a
primary
23 combustion air inlet and a fuel inlet at a second proximal end for
providing a flow
24 of primary combustion air and fuel in the tubular barrel directed toward
the nozzle
tip and a flow of secondary combustion air in the annular space directed
towards
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1 the nozzle tip, the burner assembly comprising: a deflector for deflecting
the flow
2 of secondary combustion air in the annular space away from at least the
nozzle
3 tip for stabilizing at least a position of a flame thereon. Preferably, a
conical low
4 pressure ring is positioned circumferentially about the nozzle tip and
extends
radially outwardly from the burner head for substantially separating the flow
of
6 primary combustion air and fuel from the flow of secondary combustion air at
the
7 nozzle tip creating an area of low pressure at the nozzle tip relative to a
pressure
8 of the secondary air in the annulus whereby lifting of the flame from the
nozzle tip
9 is reduced.
In another embodiment, a pilotless burner assembly comprises the
11 burner assembly as described above and further comprises an igniter
supported
12 in the air deflector for remotely igniting the burner assembly which is
positioned
13 adjacent the burner tip and therefore separated from the secondary air.
14 Preferably the igniter further comprises flame sensor.
In another embodiment, a mixer provided primary air and fuel to the
16 tubular barrel comprising a mixing chamber for combining the primary
17 combustion air and fuel therein, the mixing chamber being fluidly connected
to
18 the tubular barrel for supplying the primary air and fuel mixture thereto;
a fuel
19 orifice for admitting a flow of fuel therethrough to the mixing chamber;
and
plurality of air orifices through which primary combustion air is directed
into the
21 mixing chamber.
22
23 BRIEF DESCRIPTION OF THE DRAWINGS
24 Figure 1 is a schematic side view of a burner according to an
embodiment of the invention and positioned for operation in a firetube or
housing;
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1 Figure 2a is a side view of the burner assembly removed from the
2 housing for clarity;
3 Figure 2b is a plan view of a deflector plate positioned at a nozzle of
4 the burner according to Fig. 1, the housing being removed for clarity;
Figure 3 is a bottom perspective view of a burner according to Fig.
6 1 positioned in the housing, an igniter and heat return tube removed for
clarity;
7 Figure 4 is a side view of a nozzle portion of the burner according to
8 Fig. 1, the housing removed for clarity and illustrating a heat return tube
for
9 preventing freezing of the burner by heat tracing;
Figure 5 is a schematic side view of a mixer head according to Fig.
11 1;
12 Figure 6 is a plan view of the mixer head according to Fig. 5 shown
13 along section lines A-A;
14 Figure 7 is a sectional view of the mixer head according to Fig. 5
shown along section lines B-B; and
16 Figure 8 is a sectional view of the mixer head according to Fig. 5
17 shown along section lines C-C.
18
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1 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
2 Having reference to Figs. 1-8, a burner assembly 1 according to an
3 embodiment of the invention is shown.
4 As shown in Fig. 1, the burner assembly 1 comprises a tubular
barrel 2 which is mounted in the bore of a firetube or other such housing 3,
6 forming an annulus 5 therebetween. The tubular barrel 2 conducts primary
fuel
7 gas G from a gas inlet 6 at a base or proximal end 8 of the tubular barrel 2
to a
8 burner head 12 at a distal end 11 of the tubular barrel 2. The barrel 2 is
typically
9 of conventional configuration. The gas at the gas inlet 6 is fed at a first
pressure
P, through an orifice 50 to a mixer head 7 (Figs. 5, 7 and 8) at the proximal
end
11 8. Primary combustion air Ap is drawn into the mixer head 7 via natural
draft and
12 the combined air Ap and gas G are mixed therein and flow through the
tubular
13 barrel 2 at a second pressure P2 to an orifice or plurality of orifices 10
in the
14 burner head 12. The air and gas discharge from the burner head 12 at a
nozzle
tip 13 and, when ignited, form a flame 15.
16 Secondary combustion air As is aspirated or drawn into the annulus
17 5 and flows therein toward the nozzle tip 13 at a third pressure P3, to mix
with the
18 primary air Ap and fuel G and enhance combustion of the primary air Ap and
fuel
19 G in a combustion zone C at the nozzle tip 13 and in the housing 3
extending
outwardly therefrom. Depending upon the draft created by a pressure
differential
21 along the burner assembly 1, the velocity of the secondary air As is
altered. A
22 chimney effect in an exhaust stack for the heated system (not shown), aids
in
23 creating a draft.
24 In low pressure fuel or low-fire conditions, the velocity of secondary
air As is relatively low compared to a high-fire condition. If unrestricted,
the flow
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1 of secondary air As up the annulus 5 and past the nozzle tip 13 can
adversely
2 affect the flame 15.
3 In order to stabilize at least a position of the flame 15 relative to the
4 nozzle tip 13, means are provided to deflect the flow of secondary air AS
away
from at least the nozzle tip 13.
6 In a preferred embodiment, best seen in Fig. 4, the means for
7 deflecting the flow of secondary air As is a radially outwardly extending
low
8 pressure ring 14 extending from the burner head 12. The low pressure ring 14
is
9 shaped such as an inverted, truncated frustum of a cone and is positioned
circumferentially about the nozzle tip 13 of the burner head 12. A diameter of
the
11 low pressure ring 14 increases as it extends downstream and away from the
12 nozzle tip 13.
13 The secondary combustion air As flowing through the annulus 5
14 from the proximal end 8 of the burner assembly 1 to the distal end 11 of
the
burner assembly 1 and approaching the nozzle tip 13 is deflected outwardly by
16 the low pressure ring 14, typically creating a turbulence pattern in the
flow of the
17 secondary air As which aids in establishing a local area of low pressure P4
at the
18 nozzle tip 13 and particularly at the plurality of orifices 10. The low
pressure P4 at
19 the tip 13 is low relative to the pressure P3 of the secondary air As.
Further, the
low pressure ring 14 separates the flow of secondary air As from the flow of
21 primary air AP and fuel G exiting the orifices 10 at the nozzle tip 13
which further
22 aids in maintaining the area of low pressure P4. The area of low pressure
P4 acts
23 to minimize lifting of the flame 15 from the nozzle tip 13, resulting in
increased
24 stability and reliability of the flame 15 regardless the pressure P2 and
velocity of
the primary combustion air Ap and fuel G in the burner assembly I and the
draft
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1 in the housing 3. Further, the low pressure ring 14 aids in preventing the
flame
2 from being extinguished by the secondary combustion air A.
3 Preferably, the nozzle head 12 and the low pressure ring 14 are
4 formed as a unitary structure.
Alternately, as shown in Figs. 1-4, , the means for deflecting the
6 flow of secondary air As in the annulus 5 away from at least the nozzle tip
13 is
7 included as part of an air deflector plate 20 which extends radially
outwardly from
8 the burner head 12. The deflector plate 20 extends from the burner head 12,
9 such as from an underside 21, and extends radially from the burner head 12
across the annulus 5. The deflector plate has an inner mounting ring 29
adjacent
11 the burner head and extending circumferentially therearound. Preferably,
the
12 inner ring 29 can act to restrict and deflect the flow of secondary
combustion air
13 As away from and around the nozzle tip 13.
14 As shown in Figs. 2a, 2b and 3, the air deflector plate 20 comprises
a plate base 22, preferably extending radially from the burner head 12 and
across
16 a diameter of the housing 3. The burner head 12 can be conveniently
supported
17 concentrically in the housing 3 by the air deflector plate 20.
18 A plurality of angled deflectors or vanes 23 are formed about the
19 plate base 22, each vane 23 being formed adjacent one of a plurality of
radially
extending openings 24 formed in the plate base 22. The plate base 22 and the
21 openings 24 act to dampen or reduce the pressure P3 the secondary
combustion
22 air As reaching the burner head 12 and nozzle tip 13. Further, the angled
vanes
23 23 act to direct the secondary combustion air As outward and
circumferentially to
24 the walls of the housing 3, creating a turbulence pattern therein which
substantially fills the housing 3 at the combustion zone C for improved mixing
of
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1 the primary air Ap and fuel G therein. Preferably, angled vanes 23 also act
to
2 restrict and deflect the flow of secondary combustion air AS away from and
3 around the nozzle tip 13.
4 Thus, higher efficiency combustion is achieved as a greater amount
of the available fuel G is burned in the housing 3. Further, the deflection of
at
6 least a portion of the gas/air mixture to the outer walls of the housing 3
caused by
7 the turbulence patterns as described establishes a flame pattern which
extends
8 to about the diameter of the housing 3 aiding in a more complete combustion
of
9 the gas/air mixture therein.
An angle of the vanes 23 of the deflector plate 20 may be
11 adjustable so as to control the amount of secondary air As reaching the
housing
12 3 and the combustion zone C therein and thus the combustion efficiency of
the
13 burner assembly 1. Controlling the rate of secondary combustion As air
further
14 acts to control the draft of the burner assembly 1 which increases the
retention
time in the housing 3 and permits more efficient heat transfer therein.
16 Most preferably, as shown in Figs 1, 3 and 4, the means for
17 deflecting the flow of secondary air AS in the annulus 5 away from at least
the
18 nozzle tip 13 comprises both the low pressure ring 14 and the deflector
plate 20.
19 In this embodiment, the nozzle head 12, low pressure ring 14 and deflector
plate
20 are preferably manufactured as a unitary nozzle structure.
21 As shown in Figs. 1 and 2a, a venturi sleeve 25 may be positioned
22 within the tubular barrel 2 to accelerate the flow of primary combustion
air Ap and
23 fuel G therein causing turbulence which results in enhanced mixing of the
primary
24 combustion air Ap and fuel G prior to reaching the orifices 10.
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1 In an embodiment shown in Fig. 4, at least a first port 30 is formed
2 in the air deflector plate 20 to accommodate and support an ignition system,
3 preferably a pilotless ignition system such as an igniter/flame rod 31 for
igniting
4 the primary fuel/air mixture exiting the plurality of orifices 10 in the
burner head
12. The flame/igniter rod 31 preferably incorporates flame sensing using flame
6 ionization technology. Due to the isolation of the nozzle tip 13 from the
direct
7 flow of secondary air As, a consistent flame 15 is maintained at the nozzle
tip 13
8 and will be detected by the flame sensor regardless whether the burner
assembly
9 1 is operated at low-fire or high-fire conditions. Thus, the burner assembly
1 can
be reliably and remotely lit using the igniter/flame rod 31. Incorporation of
the
11 igniter/flame rod 31 eliminates the need for a conventional pilot and
additional
12 troublesome components associated therewith which are conventionally
subject
13 to freezing.
14 Preferably, the igniter/flame rod 31 is arranged to pass along the
housing 3 from the proximal end 8 of the tubular barrel 2, through the air
deflector
16 plate 20 and to be positioned with a sparking tip 32 oriented at an optimal
17 sparking distance (such as about 1/8") from the nozzle tip 13.
18 Also with reference to Fig. 4, in another embodiment, at least one
19 additional port 32 is formed in the air deflector plate 20 to support a
heat return
tube 40. The heat return tube 40, typically a flexible metal tube, extends
from and
21 is in communication with the mixer head 7 at the base 8 of the burner
assembly
22 1. An intermediate length of the heat return tube 40 extends along at least
the
23 fuel feed line 6, along the gas inlet orifice 50 to the tubular barrel 2
and along the
24 tubular barrel 2 to extend outward through the additional port 32 into the
housing
3 adjacent the burner tip 13, positioning a first intake end 41 adjacent or
within
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1 the combustion zone C. The heat return tube 40 draws heated combustion
2 gases from the housing 3 into the first intake end 41 of the heat return
tube 40
3 and the heated combustion gases are communicated therealong to a second end
4 42 at the mixer head 7 to conduct heat and prevent freezing of the
components of
the burner assembly 1 which are adjacent the heat return tube 40. A pressure
6 differential between the mixer head 7 and housing 3 at the combustion zone C
7 acts to draw the combustion gases into and along the heat return tube 40.
8 As shown in Figs. 5-8, the mixer head 7 preferably comprises a
9 tubular housing 60 having a solid base 61 through which a plurality of
orifices 62
are formed. Primary combustion air is aspirated through the air orifices 62.
The
11 air orifices 62 extend into a mixing chamber 63 formed in the tubular
housing 60.
12 The mixing chamber 63 is positioned intermediate the air orifices 62 and
the
13 tubular barrel 2 which is connected thereto. The gas inlet orifice 50 is
formed at a
14 center of the base 61 through which fuel G is introduced to the mixing
chamber
63 from the gas inlet 6. Fuel/primary combustion air G/Ap combined in the
mixing
16 chamber 63 are discharged into the tubular barrel 2. The plurality of
orifices 62
17 act to minimize or prevent gusts of primary combustion air AP from entering
the
18 mixer 7 which is particularly advantageous in low velocity fuel conditions.
19 An air shutter 26 is provided at the base 61 of the mixer head 7 for
controlling the amount of primary combustion air AP entering the air orifices
62.
21 Preferably the air shutter 26 is threaded onto a gas inlet nipple 64
extending
22 outward from the mixer base 61. The air shutter 26 can be moved along the
23 nipple 64 away from and toward the base 61 of the mixer 7 to permit more or
less
24 air to pass thereby into the air orifices 62.
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1 Preferably, the fuel orifice 50 is provided in a fuel orifice insert 65
2 which is threadably connected into the mixer base 61. The size of the fuel
orifice
3 50 can be altered by swapping the insert 65 for an insert 65 having a
different
4 size fuel orifice 50.
Alternatively, in another embodiment of the invention as shown in
6 Figs 5, 6 and 8, the burner assembly 1 further comprises an auxiliary air
inlet 51
7 in the mixer head 7 through which primary combustion air Ap may be forced
into
8 the flow of fuel G in the mixer head 7 prior to entering the tubular barrel
2. In this
9 situation, the air shutter 26 at the base 8 of the burner assembly 1 can be
closed
completely and the flow of primary combustion air Ap is controlled through the
11 forcible addition of air through the auxiliary air inlet 51. The flow of
fuel gas G is
12 controlled by adjusting the size of the fuel orifice 50 in the mixer head
7. In this
13 embodiment, the burner assembly 1 can operate as a forced draft burner
14 assembly, which may be preferable in cases where a more precise control of
the
primary combustion air /fuel ratio Ap/G is required. Secondary air As
continues to
16 be aspirated as in the natural draft embodiment.
17 Applicant has found this unique burner assembly operates at
18 efficiencies in the order of 7-10% more efficient than other natural draft
burners
19 and can operate efficiently at pressures ranging from about 0.25 psig to
about 15
psig. Burners employing this unique design can be manufactured to range in
size
21 from about 1" X 6" to about 2" X 24". Those skilled in the art would
appreciate
22 these specifications are guidelines only and the burner of the present
invention is
23 not limited to these dimensions or pressure ranges.
12
