Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~;13S5
This invention lies in the field of the smokeless
burning of waste gases by means of flares.
Still more particularly, this invention relates to
the construction of flares for the burning of very large
flows of waste gas, of size 200,000 pounds per hour or
greater.
Still more particularly, it concerns an improved
; type of construction for flares to burn large quantities
of gas smokelessly with reduced expenditure of energy
for pressurization of the primary combustion air.
In the prior art large high-powered flares for the
srQokeles~ burning of waste gas have been built, up to
the size o ab~ut 100,000 pounds per hour, using the
power o pressurized air for smokeless combustion. Such
prior art devices were constructed in such a form that
the primary combustion air was pre-pressured and pre-
mixed with the waste gas in such a way that the total
flow was in the form of a solid vertical cylinder of
rapid upflowing gas and air, such that there was a
large induction of secondary air around the outer
periphery of this column of flame and gas.
; Because of the surface area limitation to the flow
of induced secondary air into the outer wall of the
rising column of gas, and the necessity for the secondary
air to penetrate to the center of the column in order
to avoid incomplete and smoky com~ustion, there was a
practical limit of the order of 100,000 pounds per hour
for such flares. Such applications that had larger
flows than this would require a duplication of two or
, more such flares to handle a total flow capacity,
;i3SS
By the present invention it is now possible to
provide combustion of 200,000 pounds per hour in a
single flare, or less with reduced expenditure of
electrical energy for pressurizing the primary combustion
air.
However, there is another serious problem in the
smokeless combustion of hydrocarbons where the hydrogen
to carbon ratio ~H/C-R) is low. Venting~ from an ethylene
facility (principally olefinic, or unsaturated compounds)
provides gases for smokeless flare burning where the H/C
weight ratio can be as low as 0.166, and difficulty with
smoky burning increases as the H/C ratio decreases. For
example, consider methane (H/C = .3331 makes no smoke as
it burns at the flare; ethane (H/C = .25) makes fa~nt
trailing smoke, and propane (H/C =.222) smokes relatively
heavily. Smoke density increases as the H/C falls below
.222, and difficulty in smoke suppression wi~l vary as
the potential smoke density increases. Thus, as the
H/C-R decreases, means must be provided to increase the
rate of induction of secondary air to provide smokeless
combustion. With this invention it is possible to
1are burn without smoke, large flows of waste gases,
which are combustible, and which have H/C-~ in the
range of 0.333 down to 0.083 (acetylene).
It is the primary object of this invention to
provide a smokeless combustion of flare-vented gases
for the burning of large flows of waste gases with a
minimum expenditure of electrical power for pressurizing
the primary combustion air.
116~3SS
It is a further object of this invention to provide a flare for
the smokeless combustion of waste gases where total flows of combustible
gases can be handled which are considerably greater than the maximum flow
possible with prior art equipment, and with reduced expenditure of energy
for air pressurization.
It is a still further object to provide a flare for the burning
of hydrocarbons having hydrogen to carbon ratios less than about 0.2, with-
out smoking.
These and other objects are realized and the limitations of the
prior art are overcome in this invention by providing a flare for smokeless
combùstion of vented waste gases, comprising:
(a) an inner vertical conduit of diameter Dl, for the upward flow of
waste gases for burning;
(b~ an outer vertical conduit of diameter D2 larger than Dl, substan-
tially coaxial with said first conduit, forming a substantially enclosed
chamber thereabout open at the top and having a first annular passage bétween
the two conduits, and connected at the bottom with an air mover means through
which primary combustion air is forced at greater than atmospheric pressure
by said air mover means;
(c) closed cylindrical obstacle means having an upwardly curved
bottom, said obstacle of diameter D3A greater than Dl, but less than D2,
supported axially above the top of said inner cylinder by a selected dis-
tance, and forming a second annular passage between said obstacle means
and said outer conduit;
whereby said waste gas is deflected by said curved bottom radial-
ly upwardly and outwardly to intersect and mix with the rising column of
primary combustion air flowing in said second annular passage;
(d) means to flow said primary air into said first annular passage
sufficient to cause velocity flow of said air in said second annular
.30 passage of at least 50 feet per second; and
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355
(e) means to ignite said mixture of gas and air at the top of said
second passage.
A better understanding of the principles and details of the in-
vention will be obtained from the following description taken in conjunc-
tion with the appended drawings in which:
FIGURE 1 is a vertical section of one embodiment of this invention.
FIGURES 2 and 3 are cross-sectional views taken respectively
across the planes 2-2 and 3-3 of FIGURE 1.
FIGURES 4 and 5 show plan and cross-sectional views of a modi-
fication of FIGURE 1.
FIGURES 6 and 7 show details of the modification of FIGURES 4
and 5
Referring now to the drawings and, in particular, to PIGURE 1,
ther~ is shown one embodimcnt of this invention illustrated in cross-section,
indicated generally by the numeral 10
The waste gases flow from their source, through the conduit 11
and up to the conduit 12 in accordance with arrows 14. Conduit 12 is of
diameter Dl.
There is a second larger, outer conduit 16 of diameter D2, which
is closed at the bottom around the inner conduit 12, into which primary
combustion air is flowed under selected pressure by means of blower 17, in
accordance with arrow 19. The air flow from the blower flows into the bottom
of the annular space 18, between the inner and outer conduits. The annular
space 18 between the inner 12, and outer 16, conduits is designated as the
first annular space
The air flow 19 from the blower 17 may enter the space 18, axially
or radially, in which case it will flow vertically in the first annular
space in accordance with arrows 20. Alternatively, the blower can be mount-
ed tangentially to the conduit 16, in which case the air will flow upwardly
in the form of a helix in accordance with arrow l9A The helical flow adds
turbulence, which assists in the mixing of air and gas.
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355
The second conduit 16 may be reduced in diameter above the point
23 to the diameter of 24, for the purpose of increasing the velocity of the
upward flow of air in the space 25. The diameter of this reduced conduit 24
is designated D2A.
Above the top of the inner conduit 12 there is a closed cylindrical
object or obstacle 34, which has a curved bottom surface and a curved top
surface. It is supported by pipe 38, which is supported by spacers 40, in-
: side of, and coaxial with the inner conduit 12. There is a vertical gap
between the top of the conduit 12 and the obstacle 34 for the outflow of
gases in accordance with arrows lS. The obstacle is of outer diameter D3A.
It is preferred that the top 36 of the obstacle 34 be above the top of the
conduit Z4.
A shroud 26 of outer ~iameter D3 substantially, not necessarilydimensionally, eq~al to D3A of the obstacle 34 is fastened to the outer
surface of the conduit 12 and the space between the conduit 12 and
i 35S
the shroud 26 is filled with a refractory material 30.
This may be a castable material, not necessarily
refractory, since the temperature at this point does
not warrant refractory material. The top surface of
the refractory material defines a conical passage 32
leading from the inside of the conduit 12, out into
the second annular space 25 at a point substantially
at the vena contracta of the air flow between the
obstacle 34 and the top portion of the outer conduit
16. The approximate vena contracta is shown by dotted
line. This second annular space is of selected inner
and outer diameter, such that under the rapid flow of
the primary combustion air 20, mixing with the out-
wardly flowing gases 15, there will be a rising
annular column 44 of gas and air substantially vertically
from the second annular space in accordance with arrows
42. Means such as 48 are provided for igniting the
gas. Therefore, there will be flame and hot air and
gas rising above the top of the flare.
The purpose of the shroud 26 is to decrease the
radial width of the second annular space 25 to in-
crease the flow velocity of primary air 42 prior to
- mixing with the gas flow 15.
The preferred value of the ratio D2/Dl is
approximately 1-7. It can be larger or smaller depend-
ing on the desired flow velocity of the gas-air mixture
in the second annular passage. The preferred value
of flow velocity is 75 ft./sec., but can be as high
as 200 ft./sec. or more, or as low as 50 ft./sec.,
depending on the composition of the waste gas and its
hydrogen to carbon ratio.
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3SS
Because of the high velocity of the rising air/
gas mixture 44, secondary combustion air will be
induced radially inwardly and outwardly, in accordance
with arrows 46 into the outer surface 50 of this
annular column 44. Also, there will be a reduced
pressure directly above the obstacle 34, which will
cause a downflow of atmospheric air 54, which will
then be deflected outwardly into the inner surface
52 of this annular wall of gas. Because of the
relatively large diameter of the obstacle 34 and the
outer conduit 24 there will be a very large surface
area for contact and mixing between the induced
secondary air 46 and the rising column 44. Also,
there will be a large contact area of the inner sur-
face 5Z, which will likewise be receiving and mixing
with the induced secondary air 54.
Because of the relatively narrow radial dimension
of the annular column the penetration depth required
of the atmospheric air in order to contact the entire
volume of gas in the annular wall will be very much
less than that required when the rising column of
gas is in the form of a solid cylinder. Consequently,
the efficiency of induction and contact of secondary
air with the rising column of gas and primary air,
: will make this embodiment very efficient in the smoke-
less combustion of very large flows of waste gases,
without substantial increase in the amount of
electrical energy required to provide the pressurized
primary air.
Because of this greater efficiency of mixing of
the primary air with the waste gases and the more
efficient induction and mixing of secondary air, the
embodiment shown in FIGURE 1 is more efficient than
the prior art devices and, therefore, can handle
much larger flows of gas with the same amount of
energy required for pressurizing the primary air.
Experience shows that primary air flow in the quantity
of about eight to ten percent of the total stoichiometric
flow is adequate to provide smokeless combustion of
very large flows of gas.
Referring now to PIGURES 2 and 3, there are shown
two views in cross-section taken acro~s the planes
2-2 and 3-3, respectively, of FIGURE 1. The drawings
are self-explanatory and identical numerals are used
to identify identical parts.
An improvement in the first embodiment shown in
FIGURE 1 is illustrated in FIGU~ES 4-7. The improve-
ment lies in the use of a plurality of circumferentially
spaced radial baffles 60 across the second annular
- passage 25. While four such baffles are shown, there
can be any desired number. The baffles are flat bars
which extend from the outer conduit 24 transverse to
the air-gas flow, up to the wall of the obstacle 34.
They can be attached, as by welding 68 to outer
conduit 24, or to both 24 and 34. Air-gas flow in
passage 25, which is not covered by baffles is unimpeded,
but the gas-air flow velocity is increased by the
reduction of cross-section.
3S5
The purpose of the baffles is to cause accelerated
indraft or induction of secondary air 70, FIGURES 4 and
7, to the area above the obstacle for enhancing burning.
The air 70 moving inwardly over the baffles adds to
the flow of secondary air 54.
This induction effect exists because when a
baffle such as those shown in FIGURES 3-7 is transverse
to (or blocks) flow, as in passage 25, where the flow
42 is at significant velocity, the pressure above the
baffle is reduced according to V2/2g flow energy of
42. If the pressure of air immediately adjacent to
the top of 24 is atmospheric, the low-pressure at
the upper suxface of the bafle causes air flow 70,
and since the pressure above obstacle 36 is equally
low, the air thus induced flows to the area above 36
to add to 54.
The baffles may be either solid, or may be per-
forated with closely adjacent ports 66, which are sub-
stantially aligned as in FIGURE 6 for continuous
ignition across the baffle because of air travel to
~; their vicinity. The ba~fles may be perpendicular to
-~ the wall of the outer conduit or at a selected angle
upwardly or downwardly to the horizontal
The length of the reduced diameter D2A portion
24 above point 23 is very short as compared to the
length of conduit 16 in order to minimize the distance
traveled by the high velocity air flow 42 and thus
minimize linear pressure drop within the annular
space 25. This reduces the energy demand that would
otherwise be necessary to overcome excessive pressure
drop. In a typical field service situation the
length of portion 24 is about three feet while the
length of conduit 16 can be upwards of 200 feet. The
flow velocity of air in space 18 is but a fraction
of the velocity as the air passes the orifice 23
(75 feet per second preferred) into space 25, the
ratio being a function of D2A to D2.
While the invention has been described with a
certain degree of particularity, it is manifest that
many changes may be made in the details of construction
and the arrangement o components without departing
from the spirit and scope of this disclosure. It is
undexstood that the invention is not limited to the
embodiments set forth herein for purposes of exemplifica-
tion but is to be limited only by the scope of the
attached claims, including the full range of equivalency
to which each element or step thereof is entitled.
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