U.S. patent application number 14/266992 was filed with the patent office on 2014-11-06 for apparatus and method for minimizing smoke formation in a flaring stack.
This patent application is currently assigned to UOP LLC. The applicant listed for this patent is UOP LLC. Invention is credited to Jay D. Jennings, Richard R. Martin, Donnie Dee McClain.
Application Number | 20140329186 14/266992 |
Document ID | / |
Family ID | 51841576 |
Filed Date | 2014-11-06 |
United States Patent
Application |
20140329186 |
Kind Code |
A1 |
McClain; Donnie Dee ; et
al. |
November 6, 2014 |
APPARATUS AND METHOD FOR MINIMIZING SMOKE FORMATION IN A FLARING
STACK
Abstract
An apparatus and method for minimizing smoke formation in the
operation of a flaring stack. The apparatus includes a generally
annular gas deflector having an outer surface for deflecting the
waste gas therealong. A plurality of lobes extend radially from the
deflector to provide improved mixing between the waste gas and
combustion air during combustion to reduce smoke formation.
Inventors: |
McClain; Donnie Dee; (Round
Rock, TX) ; Martin; Richard R.; (Tulsa, OK) ;
Jennings; Jay D.; (Broken Arrow, OK) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
UOP LLC |
Des Plaines |
IL |
US |
|
|
Assignee: |
UOP LLC
Des Plaines
IL
|
Family ID: |
51841576 |
Appl. No.: |
14/266992 |
Filed: |
May 1, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61819192 |
May 3, 2013 |
|
|
|
Current U.S.
Class: |
431/5 |
Current CPC
Class: |
F23G 7/085 20130101 |
Class at
Publication: |
431/5 |
International
Class: |
F23G 7/08 20060101
F23G007/08 |
Claims
1. 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.
2. The method of claim 1, wherein passing the waste gas along the
outer surface includes passing the waste gas over a plurality of
circumferentially spaced generally vertical ribs extending radially
from the outer surface.
3. The method of claim 2, further comprising passing the waste gas
through channels between the vertical ribs.
4. The method of claim 3, further comprising passing the waste gas
along inclined sidewall surfaces extending from the channels to rib
top portions.
5. The method of claim 1, further comprising passing the waste gas
over a Coanda surface of the gas deflector.
6. The method of claim 5, wherein passing the waste gas over the
Coanda surface includes passing the waste gas over a plurality of
circumferentially spaced generally vertical ribs extending radially
from the Coanda surface.
7. The method of claim 5, further comprising passing the waste gas
over a lower unribbed portion of the Coanda surface and then over
an upper ribbed portion of the Coanda surface.
8. The method of claim 1, wherein passing the waste gas over the
outer surface includes 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 about 6.5 and about 20.
9. The method of claim 1, wherein passing the waste gas over the
outer surface includes 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 about 7.5 and about 16.
10. 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.
11. The method of claim 10, further comprising drawing ambient air
toward the gas deflector to mix with the waste gas and reduce smoke
formation during combustion of the waste gas.
12. The method of claim 10, wherein the gas deflector includes 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.
13. The method of claim 10, further comprising 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.
14. The method of claim 13, further comprising shifting the gas
deflector from the raised open position to the lower seated
position to close the annular opening.
15. The method of claim 14, wherein shifting the gas deflector to
the lower seated position includes 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.
16. The method of claim 14, wherein shifting the gas deflector from
the raised open position to the lowered closed position includes
biasing the gas deflector toward the lowered position with a spring
and reducing a waste gas pressure in the waste gas passageway.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Application No. 61/819,192 filed May 3, 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.
[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. Pat. No. 3,833,337 to Desty et al. and U.S. Pat.
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;
[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.
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.sub.x 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.
[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 about 5 degrees from the
vertical, less than about 3 degrees from the vertical axis in
another example, and at less than about 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 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
about 5 degrees from vertical in one example, less than about 2
degrees in another example, and less than about 1 degree from
vertical in yet another example.
[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.
[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
2.pi.r/r=2.pi.. In one example, the ratio of the perimeter to the
outer radius of the ribbed bowl described herein is greater than
2.pi.. In another example, the ratio of perimeter to outer radius
is between about 6.5 and about 20, between about 7.5 and about 16
in another example, and between about 8.5 and about 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
about a bottom 5 to 50 percent of the Coanda bowl is unribbed with
an upper portion including ribs. In another example between about 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 about 0.5 and about 5 and between about 1 and
about 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 about 0.01 and about 0.2 in one example and between
about 0.03 and about 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.
[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.
* * * * *