Note: Descriptions are shown in the official language in which they were submitted.
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APPARATUS AND METHOD FOR MINIMIZING SMOKE FORMATION IN A
FLARING STACK
STATEMENT OF PRIORITY
[0001] This application claims priority to U.S. Application Nos. 14/266,997
and
14/266,992 which were filed on May 01, 2014, which claim benefit of U.S.
Provisional
Application Nos. 61/819,189 and 61/819,192 which were filed on May 03, 2013.
FIELD OF THE INVENTION
[0002] The subject application relates to an apparatus for minimizing smoke
formation in
a flaring stack.
BACKGROUND OF THE INVENTION
[0003] Flare apparatus have traditionally been utilized for burning and
exhausting
combustible gases. Flare apparatus are commonly mounted on flare stacks and
located at
production, refining, and processing plants for disposing of flammable waste
gases or other
flammable gas streams, which are diverted for any reason, including but not
limited to venting,
shut-downs, upsets, and/or emergencies. Primarily, flare stacks are used for
venting unwanted
waste gas streams from a facility.
[0004] It is generally desirable that flammable gas be burned without
producing smoke, and
reduction in smoke production during burning may be mandated by regulatory
requirements.
[0005] One method that has been adopted for reducing smoke formation during
burning
includes mixing the waste gas stream to be burned with ambient air to maximize
oxidation of the
flammable waste gas to prevent the production of smoke. Another method that
has been used
includes supplying steam to the combustion zone, such as, for example, by an
eductor to
increase oxidation to restrict smoke formation. In some applications, ambient
air and steam
introduction are used together to further reduce smoke formation.
[0006] When sufficient ambient air or ambient air and steam is available to
contact the
combustible waste gas, the mixture can be smokelessly burned. For a typical
flare apparatus,
there is a limited quantity of air available for mixing with the waste gas and
therefore a limited
smokeless capacity.
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[0007] A wide variety of apparatus and processes have been proposed to
increase the
smokeless burning of combustible gas from a flare. For example, U.S. Patent
No. 3,833,337 to
Desty et al. and U.S. Patent No. 8,337,197 to Poe et al. propose the use of a
tulip shaped Coanda
tip. Coanda tips have been used in flares with high flow rates and pressures
to cause the
adherence of the waste gas to the surface. The negative pressure and viscous
forces caused by
the Coanda effect cause the fluid to be drawn against the surface in a
relatively thin film, which
allows proximate fluid (e.g. ambient air) to be mixed efficiently with the
fluid stream. Poe
describes that to achieve a Coanda effect, the surface of the Coanda surface
should be
substantially smooth.
[0008] While current apparatus and methods have improved the smokeless
combustion of
waste gas streams, it is desirable to further reduce the amount of smoke
formation based on
regulatory and environmental considerations.
SUMMARY OF THE INVENTION
[0009] By one aspect, an apparatus is provided minimizing the formation of
smoke in the
operation of a flaring stack. The apparatus includes a generally annular gas
deflector that has
an outer surface for deflecting waste gas therealong. The apparatus also
includes a plurality
of lobes extending radially from the gas deflector for providing improved
mixing between the
waste gas and combustion air during combustion. According to one approach, the
lobes
include circumferentially spaced, generally vertical ribs. The gas deflector
may include a
tulip-shaped bowl having a Coanda surface.
[0010] By another aspect a method is provided for combusting a waste gas to
reduce the
formation of smoke. The method includes passing the waste gas along an outer
surface of a
generally annular gas deflector including a plurality of lobes extending
radially from an outer
surface thereof The method further includes drawing ambient air toward the
outer surface
for mixing with the waste gas. The method further includes igniting the waste
gas to combust
the waste gas with decreased smoke formation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a perspective view of an apparatus including a plurality of
support arms
and a plurality of corresponding gas deflectors in accordance with various
embodiments;
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[0012] FIG. 2 is a perspective view of a support arm of the apparatus with a
gas deflector
in accordance with various embodiments;
[0013] FIG. 3 is a cross-sectional view of the support arm of FIG. 2 with the
gas deflector
supported thereon in a lowered position;
[0014] FIG. 4 is a partial cross-sectional view of the support arm of FIG 2.
with the gas
deflector in a raised position;
[0015] FIG. 5 is a top view of the gas deflector of FIG. 2;
[0016] FIG. 6 is a side cross sectional view of the gas deflector of FIG. 5
taken along line
A-A;
[0017] FIG. 7 is a side cross sectional view of the gas deflector of FIG. 6
taken along line
B-B; and
[0018] FIG. 8 is a perspective view of a support arm of the apparatus with a
gas deflector
in accordance with another approach.
[0019] Skilled artisans will appreciate that elements in the figures are
illustrated for
simplicity and clarity and have not necessarily been drawn to scale. For
example, the
dimensions and/or relative positioning of some of the elements in the figures
may be
exaggerated relative to other elements to help to improve understanding of
various
embodiments of the present invention. Also, common but well-understood
elements that are
useful or necessary in a commercially feasible embodiment are often not
depicted in order to
facilitate a less obstructed view of these various embodiments of the present
invention. It will
further be appreciated that certain actions and/or steps may be described in a
particular order
of occurrence while those skilled in the art will understand that such
specificity with respect
to sequence is not actually required. It will also be understood that the
terms and expressions
used herein have the ordinary technical meaning as is accorded to such terms
and expressions
by persons skilled in the technical field as set forth above except where
different specific
meanings have otherwise been set forth herein.
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DETAILED DESCRIPTION
[0020] The apparatus and method presented herein, in accordance with various
aspects,
relates to reducing smoke formation during combustion of a waste gas in a
flare stack. The
apparatus may be used with a flare stack, for example, at a refinery or
production facility for
flaring waste gas or other gas streams to the atmosphere. As used herein, the
term "waste
gas" refers to any combustible gas stream that is combusted by the flare
stack, including, but
not limited to undesired gas streams, product streams combusted during
shutdown or
emergency situations, and other streams.
[0021] Referring now to FIGS. 1 and 2, an apparatus 2 for the
combustion of a waste gas
stream in accordance with various aspects is provided. The apparatus 2
includes a gas
deflector 4 for deflecting waste gas along a surface 6 thereof. The apparatus
2 may also
include a support arm 8 for supporting the gas deflector 4 thereon. The waste
gas may be
passed through the support arm 8 to the gas deflector 4. In this regard, the
support arm 8 may
have a waste gas passageway 10 formed therein as illustrated in FIG. 3 for
facilitating the
flow of the waste gas therethrough. A waste gas outlet 12 is provided for
introducing the
waste gas from the waste gas passageway 10 to the gas deflector 4. As
illustrated in FIGS. 3-
4 and described further below, the outlet 12 may include an annular opening 14
between the
support arm 8 and the gas deflector 4 so that the waste gas flows through the
opening 14 and
along the gas deflector outer surface 6.
[0022] The waste gas deflector includes a plurality of lobes 16 that extend
radially
therefrom. In this regard, as waste gas flows along the outer surface of the
gas deflector 4,
the gas flows over and between the lobes 16. It has been identified that
including radially
extending lobes 16 on the gas deflector 4 improves mixing of the waste gas
stream and
ambient air during operation of the flare stack resulting in a reduction in
the amount of smoke
that is produced during combustion. It has further been identified that
including radially
extending lobes 16 as described herein provides a lower flame temperature and
reduced
emissions of unwanted by-products into the atmosphere, such as NO emissions.
By one
aspect, the lobes include a plurality of generally vertically oriented ribs 18
spaced
circumferentially about the gas deflector 4 such that the gas flows along the
ribs and through
channels 20 formed between adjacent ribs 18.
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[0023] According to various aspects, the support arm 8 is provided for
supporting the gas
deflector 4 thereon. The support arm 8 may also include a gas passageway 10
for passing the
waste gas to be combusted from a gas source to the gas deflector 4. In one
approach, as
illustrated in FIG. 1, the apparatus 2 may include a plurality of support arms
8 supporting a
plurality of gas deflectors 4. In this manner, the size of each gas deflector
4 may be
decreased as opposed to having a single large gas deflector. This may improve
the ability for
smoke free combustion by increasing the amount of air available for mixing
with the gas at
each of the plurality of gas deflectors 4 as opposed to a single larger gas
deflector.
[0024] The support arm 8 may extend from a central plenum 22 as illustrated in
FIG. 1.
As shown, one support arm 8 extends upwardly from the top of the plenum 22
while
additional support arms 8 extend at inclined angles from side portions 24 of
the plenum 22
and extend generally vertically at bent portions 26 thereof In one example,
the vertical
portions 28 of the support arms 8 extend vertically at an angle of less than 5
degrees from the
vertical, less than 3 degrees from the vertical axis in another example, and
at less than 1
degree from the vertical in yet another example. In yet another example,
vertical portions 28
of the support arms 8 extend vertically.
[0025] The support arm 8 may include the gas passageway 10 as illustrated in
FIG. 3 for
passing the waste gas through the support arm 8 toward the gas deflector 4. In
one approach,
as shown in FIG. 3, the gas passageway 10 may include a hollow passageway
through the
support arm 8. In this regard, the support arm 8 may be formed by a generally
hollow tube
providing the passageway 10. The tube may be cylindrical as illustrated in
FIG. 3 or other
suitable configurations.
[0026] According to one aspect, the support arm 8 includes an upper seating
portion 30 for
supporting the gas deflector 4 thereon. The upper seating portion 30 by one
approach
includes a rim or flange 32 for supporting the gas deflector 4. As illustrated
in FIG. 3, the
flange 32 may include a generally annular flange extending radially outwardly
from the
support arm upper seating portion 30 to provide an upper seating surface 34
that may also
serve to direct the flow of gas along the deflector 4, as described further
below.
[0027] As mentioned previously, the apparatus 2 according to various aspects
includes a
gas deflector 4. In one preferred form, the gas deflector 4 includes a gas
deflector bowl 36
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having a Coanda surface 38 as illustrated in the figures. The Coanda bowl 36
may have a
tulip-shaped configuration as illustrated in FIG. 7 having a generally
horizontal or slightly
inclined lower portion 40, a vertical or inclined upper portion 42, and a
convex portion 44
between the lower portion 40 to the upper portion 42. The remainder of the
description will
be made with reference with use of the Coanda bowl 36 as the gas deflector.
Coanda bowls
are generally known and understood by those of skill in the art, and are known
to produce a
"Coanda effect", wherein gases flowing along the outer surface thereof tend to
follow the
surface and draw in surrounding gas or air. In one approach, the Coanda bowl
has a
generally round cross-section taken along a plane orthogonal to a longitudinal
axis 46 of the
bowl, although the bowl 36 may also include other suitable cross-sectional
configurations, for
example oval or polygonal.
[0028] By one aspect, the Coanda bowl 36 includes a plurality of lobes 16
extending
radially outwardly from its outer surface 38. As illustrated in the figures,
the lobes 16 may
include a plurality of generally vertical ribs 18 spaced circumferentially
about the bowl outer
surface 38. In one approach, the ribs extend radially outwardly from the
Coanda bowl outer
surface 38 (or floors 20 of the channels). As used herein, the phrase "total
outer surface"
refers to the outer surface formed along all outer surface of the gas
deflector, including by
one example along the outer surfaces of the Coanda bowl 36, ribs 18, and
channels 20, such
that the "total outer surface" of a ribbed portion of the Coanda bowl 36 has a
larger surface
area than the outer surface of a corresponding Coanda bowl would have without
ribs.
[0029] According to one approach, the ribs 18 extend generally vertically
along the
Coanda bowl outer surface 38. It should be understood that as described
herein, the ribs 18
extend generally vertically as viewed head-on and that where the upper portion
42 of the
bowl 36 is inclined as illustrated in FIG. 6, the vertically extending ribs
may similarly be
inclined toward the longitudinal axis 46 of the bowl 36 when viewed from
profile (i.e. 90
degrees from head-on as shown by the side-cross section of FIG. 6). With this
in mind, by
one approach, the ribs have a generally vertical axis 48 when viewed head-on
as shown in
FIG. 2 that is less than 5 degrees from vertical in one example, less than 2
degrees in another
example, and less than 1 degree from vertical in yet another example.
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[0030] The ribs are circumferentially spaced so that a plurality of
corresponding channels
20 are formed between adjacent ribs 18 as illustrated in FIG. 2. The channels
20 extend
generally vertically between the ribs 18 and can have a variety of different
shapes and
configurations. The channels 20 include a channel floor 50 at a base thereof.
The channel
floor may be flush with the Coanda bowl outer surface 36, or may be raised or
indented
relative thereto.
[0031] The ribs 18 may have a generally constant radial profile (i.e. distance
the ribs
extend from the bowl outer surface 36 and/or channel floor 50). Alternatively,
the ribs 18
may have a varying radial profile as illustrated in FIG. 6. By one approach,
as seen in FIGS.
2 and 6, the ribs 18 are tapered from a lower rib portion 52 to raised rib
portion 54. In this
regard, the tapered lower portion 52 may be slightly elevated with respect to,
or flush with,
the bowl surface 36 to provide a smooth transition surface over which gas
traveling upwardly
therealong can flow. The ribs 18 may also include a tapered upper rib portion
56 to provide
for smooth flow of the waste gas and combustion air mixture as it exits the
Coanda surface.
It should be understood that the radially extending ribs may be radially
extending relative to
an outer surface of a Coanda bowl and/or relative to channels. In this regard,
the ribs may be
formed, for example by providing ribs along the outer surface of a Coanda
bowl, or by
forming channels or indentations in a Coanda bowl so that the ribs are formed
above the
channels.
[0032] The ribs 18 may have a constant circumferential width or a varying
width about the
perimeter of the Coanda bowl 36 as illustrated in FIGS. 2 and 5. Similarly,
the channels 20
may have a constant or varying circumferential width. Typically, where the
Coanda bowl
includes an inwardly tapered upper portion 42 as illustrated, at least one of
the ribs and
channels will have a varying width to account for the upwardly decreasing
circumference.
[0033] By one aspect, the ribs 18 may have inclined sidewalls 58 extending
between rib
top portions 60 and the channel floors 50 as best seen with reference to FIG.
5. The inclined
sidewalls 58 can be generally flat, or may be curved or formed in other
manners. The
inclined side walls provide a smooth surface over which the gas can flow by
reducing the
amount of sharp angles between the ribs and the channels.
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[0034] Without intending to be bound by theory, it is believed that the
addition of ribs 18
to the Coanda bowl 36 increases the total surface area of the Coanda bowl 36
to improve
waste gas/combustion air mixing without providing a corresponding increase in
outer
diameter of the bowl. In this manner, the Coanda bowl 36 can advantageously be
kept
relatively small while providing sufficient surface area for drawing in
combustion air for
mixing with the waste gas and reducing smoke formation.
[0035] To this end, by one aspect, the ribbed Coanda bowl has a relatively
high ratio of a
perimeter (as shown in FIG. 5) to an outer radius 62. As used herein, outer
radius refers to
the distance between the bowl longitudinal axis 46 and the rib top portions
60. For example,
a traditional un-ribbed Coanda bowl has a ratio of perimeter (circumference)
to outer radius
of 2nr/r = 2n. In one example, the ratio of the perimeter to the outer radius
of the ribbed bowl
described herein is greater than 2n. In another example, the ratio of
perimeter to outer radius
is between 6.5 and 20, between 7.5 and 16 in another example, and between 8.5
and 12 in yet
another example.
[0036] According to one aspect ribs 18 may be formed along the entire outer
surface 38 of
the Coanda bowl 36. In this regard, the surface area of the entire bowl 36 is
increased such
that mixing between the waste gas and the combustion air is improved along the
total outer
surface as described above.
[0037] According to another aspect, the ribs 18 may extend along one or more
portions of
the Coanda bowl 36, but less than the full outer surface 38 thereof, such that
a portion of the
gas deflector is unribbed and provides a relatively smooth surface for gas
flow. For example,
as illustrated in FIG. 7, the lower portion 40 and/or the intermediate portion
44 of the Coanda
bowl 36 may be unribbed, while an upper portion 42 includes ribs. In this
regard, gas may
better flow along the lower portion 40 of the Coanda bowl 36, along the convex
intermediate
portion 44, and to the ribbed upper portion 42 before flowing over and between
the ribs 18.
Further, having the lower portion 40 and/or the intermediate portion 44 of the
Coanda bowl
unribbed provides a lower seating portion of the Coanda bowl 36 so that when
the bowl 36 is
in a seated position, as illustrated in FIG. 3, the Coanda bowl seating
portion is in generally
close contact with the support arm upper seating portion 30 to reduce the
amount of waste gas
flowing therethrough. In one example, between a bottom 5 to 50 percent of the
Coanda bowl
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is unribbed with an upper portion including ribs. In another example between a
bottom 10 to
40 percent of the Coanda bowl is unribbed with an upper portion including
ribs. In another
example, as illustrated in FIG. 8 a bottom portion may include ribs with at
least an
intermediate portion and/or a top portion being unribbed.
[0038] As illustrated in FIGS. 2 and 8, different numbers and sizes of ribs 18
may be
included on the Coanda bowl to maximize the air/waste gas mixing. For example,
it may be
beneficial to select the number of ribs extending circumferentially about the
Coanda bowl 36
to provide increased surface area and the associated improvement in gas/air
mixing, while
still ensuring that the gas will flow smoothly over the total surface area
during operation.
FIG. 2 illustrates an example of a Coanda bowl that includes a smaller number
of relatively
wider ribs while FIG. 8 illustrates another example where a larger number of
narrower ribs 18
is used. With this in mind, in one example a ratio of a combined
circumferential width of the
one or more ribs 18 to a combined circumferential width of a plurality of
channels 12
between the ribs 18 is between 0.5 and 5 and between 1 and 3 in another
example. In another
example, a ratio of a rib radial height above the channel floor to the outer
radius of the bowl
is between 0.01 and 0.2 in one example and between 0.03 and 0.2 in another
example.
[0039] By one aspect, the gas outlet 12 is provided for introducing the waste
gas toward
the outer surface of the Coanda bowl. As illustrated in FIGS. 2-4, the gas
outlet 12 may
include a generally annular opening 14 of the waste gas passageway 10 formed
about the
outer surface 38 so that the waste gas can flow through the opening and along
the outer
surface. The annular opening 14 may include a relatively round shape, or
another shape, such
as an oval or polygon. By one approach, the annular opening includes a single
annular
opening, but may also include a plurality of openings formed about the Coanda
bowl 36. The
annular opening 14 may be formed by a gap between the support arm upper
seating portion
30 and the Coanda bowl lower portion 40, such that waste gas flowing through
the gas
passageway 10 exits through the opening 14 and flows along the outer surface
38.
[0040] In one approach, the waste gas is provided at a relatively high
pressure and
flowrate. The apparatus disclosed herein may be well suited to waste gases
flowing at high
flowrates as they will pass over the Coanda surface 38 and the ribs 18 and
draw in a large
amount of combustion air for mixing and reduced smoke formation.
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[0041] In one approach, the Coanda bowl 36 is shiftable between a seated
position as
illustrated in FIG. 3 and a raised position as illustrated in FIG. 4. In the
seated position, the
Coanda bowl seating portion contacts the support arm seating portion 30. As
mentioned
previously, in the seated position, the Coanda bowl 36 and support arm 8 are
in close contact
so that the annular opening 14 is in a closed position and the flow of gas
therethrough is
restricted. In the raised position, the Coanda bowl seating portion is raised
relative to the
support arm seating portion 30 to form a gap therebetween to provide the
annular opening 14
to allow the flow of waste gas therethrough.
[0042] By one approach, the Coanda bowl 36 is biased toward the closed
position,
however high pressure waste gas contacts the Coanda bowl 36, causing it to
lift into the
raised position shown in FIG. 4 so that the waste gas is able to pass through
the annular
opening 14. The Coanda bowl 36 may be biased toward the closed position by a
spring 64 as
illustrated in FIG. 3. A rod 66 is connected to the Coanda bowl 36 and the
spring 64, such
that the spring 64 urges the rod 66, and accordingly the Coanda bowl 36,
toward the seated
position.
[0043] According to various aspects, during operation, the waste gas to be
combusted
flows through the gas passageway and through the annular opening 14. Where the
Coanda
bowl 36 is shiftable, the waste gas may shift the Coanda bowl to the raised
position so that
the gas can exit the annular opening 14 and flow along the total outer surface
of the Coanda
bowl 36. As the waste gas flows along the outer surface, combustion air (for
example
ambient air) is drawn toward the waste gas and mixed therewith. The waste gas
passes over
the ribs 18 and through the channels 20 therebetween. The waste gas is ignited
and
combusted with reduced smoke formation.
[0044] The above description and examples are intended to be illustrative of
the invention
without limiting its scope. While there have been illustrated and described
particular
embodiments of the present invention, it will be appreciated that numerous
changes and
modifications will occur to those skilled in the art, and it is intended in
the appended claims
to cover all those changes and modifications which fall within the true spirit
and scope of the
present invention.
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[0045] One embodiment of the invention involves an apparatus for minimizing
the
formation of smoke in the operation of a flaring stack, the apparatus
comprising: a generally
annular gas deflector having an outer surface for deflecting waste gas
therealong; a plurality
of lobes extending generally radially from the deflector outer surface for
providing improved
mixing between the waste gas and combustion air during combustion. The lobes
may include
circumferentially spaced generally vertical ribs extending radially from the
outer surface of
the gas deflector. The ratio of a perimeter of a ribbed portion of the bowl to
an outer diameter
of the ribbed portion may be between 6.5 and 20. The gas deflector may include
a tulip-
shaped bowl having a Coanda surface. The ribs may extend radially from an
upper portion of
the bowl above a convex portion of the Coanda surface. The intermediate convex
portion of
the bowl may be generally smooth and free of ribs. The ribs may extend
generally vertically
from an upper portion of the bowl into at least a portion of an intermediate
convex portion of
the bowl. The ribs may be tapered radially with respect to the outer surface
from a generally
lower rib portion flush with the outer surface to a raised rib portion above
the outer surface.
The ribs may include inclined sidewalls extending from channels between the
ribs to rib top
portions. The ratio of a combined circumferential width of the one or more
ribs to a combined
circumferential width of a plurality of channels between the ribs may be
between 0.5 and 5.
The ribs may have a ratio of a rib radial height above a channel floor to an
outer radius of the
gas deflector of between 0.01 and 0.2.
[0046] Another embodiment of the invention involves an apparatus for
minimizing the
formation of smoke in the operation of a flaring stack, the apparatus
comprising: a support
arm having a generally hollow waste gas passageway for connection to a waste
gas source; a
generally annular gas deflector having an outer surface for deflecting the
waste gas
therealong; a waste gas outlet between the gas deflector and the support arm;
and a plurality
of lobes extending generally radially from the gas deflector outer surface for
providing
improved mixing between the waste gas and combustion air during combustion.
The gas
deflector may include a Coanda bowl and the outlet includes an annular opening
between an
upper seating portion of the support arm and a Coanda surface of the Coanda
bowl. The
apparatus may further comprise a shiftable connection between the Coanda bowl
and the
support arm so that the Coanda bowl is shiftable between a seated position,
wherein Coanda
bowl is supported by the upper seating portion and a raised position, wherein
the Coanda
bowl is raised from the upper seating portion to form the annular opening
between the upper
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seating portion and the Coanda surface of the Coanda bowl. The shiftable
connection may
include a spring configured to bias the Coanda bowl to the lowered seated
position. The
seating portion of the Coanda bowl may be free of ribs to form a smooth fit
between the
Coanda bowl seating portion and the support arm seating portion with the
Coanda bowl in the
seated position. The plurality of lobes may include circumferentially spaced
generally vertical
ribs extending radially from the outer surface of the Coanda bowl. The ratio
of a perimeter of
a ribbed portion of the Coanda bowl to an outer diameter of the ribbed portion
may be
between 7.5 and 16. The apparatus may further comprise comprising a plenum, a
plurality of
support arms extending from the plenum, a plurality of corresponding gas
deflectors with
annular openings between the plurality of support arms and plurality of
corresponding gas
deflectors, and a plurality of lobes extending radially from the plurality of
gas deflectors.
[0047] Another embodiment of the invention involves a method for combusting a
waste
gas to reduce the formation of smoke, the method comprising: passing the waste
gas along
an outer surface of a generally annular gas deflector including a plurality of
lobes extending
radially from an outer surface thereof; drawing ambient air toward the outer
surface for
mixing with the waste gas; and igniting the waste gas. Passing the waste gas
along the outer
surface may include passing the waste gas over a plurality of
circumferentially spaced
generally vertical ribs extending radially from the outer surface. The method
may further
comprise passing the waste gas through channels between the vertical ribs. The
method may
further comprise passing the waste gas along inclined sidewall surfaces
extending from the
channels to rib top portions. The method may further comprise passing the
waste gas over a
Coanda surface of the gas deflector. Passing the waste gas over the Coanda
surface may
include passing the waste gas over a plurality of circumferentially spaced
generally vertical
ribs extending radially from the Coanda surface. The method may further
comprise passing
the waste gas over a lower unribbed portion of the Coanda surface and then
over an upper
ribbed portion of the Coanda surface. Passing the waste gas over the outer
surface may
include passing the waste gas over an outer surface having a ratio of a
perimeter of a ribbed
portion of the gas deflector to an outer diameter of the ribbed portion of the
gas deflector of
between 6.5 and 20. Passing the waste gas over the outer surface may include
passing the
waste gas over an outer surface having a ratio of a perimeter of a ribbed
portion of the gas
deflector to an outer diameter of the ribbed portion of the gas deflector of
between 7.5 and
16.
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[0048] Another embodiment involves a method for combusting a waste gas to
reduce the
formation of smoke, the method comprising: passing a waste gas through an
inner
passageway of a support arm; passing the waste gas through an annular gas
passage between
the support arm and a generally annular gas deflector; passing the waste gas
along an outer
surface of the gas deflector and over lobes extending radially from the
annular gas deflector;
and igniting the waste gas. The method may further comprise drawing ambient
air toward the
gas deflector to mix with the waste gas and reduce smoke formation during
combustion of the
waste gas. The gas deflector may include a generally tulip-shaped Coanda bowl
and passing
the waste gas along the outer surface includes passing the waste gas over a
Coanda surface of
the Coanda bowl. The method may further comprise shifting the gas deflector
from a lower
seated position to an raised open position to provide the annular opening to
allow the waste
gas to pass through the annular opening. The method may further comprise
shifting the gas
deflector from the raised open position to the lower seated position to close
the annular
opening. Shifting the gas deflector to the lower seated position may include
contacting a
smooth un-ribbed seating portion of the gas deflector with an upper seating
portion of the
support arm to provide generally close contact therebetween. Shifting the gas
deflector from
the raised open position to the lowered closed position may include biasing
the gas deflector
toward the lowered position with a spring and reducing a waste gas pressure in
the waste gas
passageway.
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