U.S. patent application number 11/438078 was filed with the patent office on 2007-12-06 for flare stack.
Invention is credited to Robert C. Rajewski.
Application Number | 20070281266 11/438078 |
Document ID | / |
Family ID | 38790670 |
Filed Date | 2007-12-06 |
United States Patent
Application |
20070281266 |
Kind Code |
A1 |
Rajewski; Robert C. |
December 6, 2007 |
Flare stack
Abstract
A Coanda flare is described that provides improved operation of
a flare stack. A Coanda flare comprises a gas flue having a flare
end, a Coanda body disposed adjacent the flare end to form an
annular gap between the Coanda body and the flare end of the gas
flue, such that gas emitted from the flare end passes through the
annular gap and around the Coanda body, and a gas flow adjustor for
adjusting pressure on gas flowing through the annular gap. The gas
flow adjustor may be provided by a dual acting piston, which may
for example be sensitive on one side to waste gas pressure, and on
the other side to a control pressure.
Inventors: |
Rajewski; Robert C.;
(Stettler, CA) |
Correspondence
Address: |
CHRISTENSEN, O'CONNOR, JOHNSON, KINDNESS, PLLC
1420 FIFTH AVENUE, SUITE 2800
SEATTLE
WA
98101-2347
US
|
Family ID: |
38790670 |
Appl. No.: |
11/438078 |
Filed: |
May 18, 2006 |
Current U.S.
Class: |
431/202 |
Current CPC
Class: |
F23G 7/08 20130101 |
Class at
Publication: |
431/202 |
International
Class: |
F23G 7/08 20060101
F23G007/08 |
Claims
1. A gas flare, comprising: a gas flue having a flare end; the gas
flue being connected to a source of waste gas; a body disposed
adjacent the flare end to form a gap between the body and the flare
end of the gas flue, such that gas emitted from the flare end
passes through the gap and around the body; and a gas flow adjustor
connected to the gas flue and to the body to adjust the gap and
control gas flow through the gap.
2. The gas flare of claim 1 in which the gap is annular.
3. The gas flare of claim 2 in which the gas flow adjustor is
responsive to waste gas pressure and to a control pressure from a
pressure source.
4. The gas flare of claim 3 in which the gas flow adjustor
comprises: a dual acting piston connected to the body for adjusting
the annular gap, the dual acting piston being responsive on a first
side of the dual acting piston to waste gas pressure and on a
second side of the dual acting piston to the control pressure.
5. The gas flare of claim 1 in which the pressure source has an
operating pressure range that includes 2 psig and 15 psig.
6. The gas flare of claim 3 in which the pressure source is a
source of LPG.
7. The gas flare of claim 6 further comprising a gas pilot
connected to the pressure source.
8. The gas flare of claim 2 in which the annular gap has an
adjustment range that includes gaps of about 0.05 inches and about
0.5 inches.
9. The gas flare of claim 2 in which the body is a Coanda body.
10. The gas flare of claim 3 in which the body is a Coanda
body.
11. The gas flare of claim 4 in which the body is a Coanda
body.
12. A method of controlling a gas flare connected to a waste gas
source, comprising: providing a gas flare with an adjustable gap
between a body and a flare end of a gas flue; supplying the gas
flue with waste gas from the waste gas source; and controlling the
pressure of gas flowing through the adjustable gap by controlling
the gap size.
13. The method of claim 12 in which the body is an adjustable
Coanda body.
14. The method of claim 13 in which controlling the pressure of the
gas flow comprises providing a control pressure from a gas source
to a first side of a pressure responsive control device.
15. The method of claim 14 in which the pressure responsive control
device is a piston or diaphragm linked to the adjustable Coanda
body.
16. The method of claim 15 in which: the pressure responsive
control device has a second side; and waste gas pressure is
provided to the second side of the pressure responsive control
device.
17. The method of claim 16 in which the gap is adjusted to provide
a desired flame characteristic.
18. The method of claim 17 in which the desired flare
characteristic is selected from a group consisting of flame speed,
flame pattern, flame length, Coanda body stability, and noise
level.
19. The method of claim 12 in which the gap is adjusted to provide
a desired flame characteristic.
20. The method of claim 19 in which the desired flare
characteristic is selected from a group consisting of flame speed,
flame pattern, flame length, adjustable body stability, and noise
level.
Description
BACKGROUND
[0001] U.S. Pat. No. 6,960,075 describes a flare stack operating on
the Coanda principle with an adjustable gap for flare gas to pass
through. This was done to allow the gap to be closed off by the
Coanda body at low pressures to avoid having to purge the gas flue.
While this product has served its purpose, the device was designed
to provide constant back pressure on gas in the flue. This meant
that with different gas compositions, the resulting flame had
different, and sometimes deleterious, characteristics. For example,
with heavy ends and constant pressure, the flame may shorten and
become more turbulent. Turbulent flow close to the flare tip can
cause premature erosion of the flare tip. The spring also caused a
risk of chatter at the gap, and hence increased noise.
SUMMARY
[0002] A gas flare is described that provides improved operation of
a flare stack. A gas flare comprises a gas flue having a flare end,
a body disposed adjacent the flare end to form a gap between the
body and the flare end of the gas flue, such that gas emitted from
the flare end passes through the gap and around the body, and a gas
flow adjustor for adjusting the gap, hence the pressure on gas
flowing through the gap. In one embodiment, the body is adjustable
and connected to the gas flow adjustor. Pressure or flow adjustment
allows adjustment for gas composition and therefore tailored flame
characteristics. The gas flow adjustor may be provided by a dual
acting piston, which may for example be sensitive on one side to
waste gas pressure, and on the other side to a control pressure.
The body may be a Coanda body, and gap may be annular.
[0003] There is also provided a method for operating a gas flare in
which gas pressure of gas flowing through the gap of a gas flare is
adjusted to provide desired flame characteristics. Thus, for
example, in the case of a heavier mix of gas, the gap size may be
decreased to increase flow rate and extend the flame beyond the
metal of the flare tip
[0004] These and other aspects are set out in the claims, which are
incorporated here by reference.
BRIEF DESCRIPTION OF THE FIGURES
[0005] Embodiments of a gas flare stack will now be described with
reference to the figures, in which like reference characters denote
like elements, by way of example, and in which:
[0006] FIG. 1 is a section through a Coanda flare; and
[0007] FIG. 2 is a schematic of a gas flow adjustor for a Coanda
flare, in which a solid line with arrows indicates a primary flow
line, a line with repeated hash marks indicates instrument tubing
and a wavy line indicates flex hose.
DETAILED DESCRIPTION
[0008] In the claims, the word "comprising" is used in its
inclusive sense and does not exclude other elements being present.
The indefinite article "a" before a claim feature does not exclude
more than one of the feature being present.
[0009] Referring to FIG. 1, there is shown an embodiment of a flare
stack 100 of the Coanda type, which has a Coanda body 10 disposed
adjacent the flare end 11 of a gas flue 12. Gas flue 12 receives
gas from a waste gas source 17 (FIG. 2), for example, an oil-gas
separator, through pipe connection 13. Pipe connection 13 and the
gas flue 12 are secured to one side of a frame 15 that is secured
on its other side to a gas flow adjustor, which in the embodiment
shown includes a dual acting cylinder 20. The double acting
cylinder 20 incorporates a dual acting piston 19 having a lower
piston face 22 that responds to pressure in a lower chamber 23 of
the dual acting cylinder 20 and an upper piston face 24 that
responds to pressure in an upper chamber 25 of the dual acting
cylinder 25. The dual acting piston 19 is connected to the Coanda
body 10 through shaft 21. The Coanda flare stack 100 is mounted in
conventional fashion on a support structure.
[0010] The Coanda body 10 responds to gas pressure in the gas flue
12 by lifting off the flare end 11 to form an adjustable annular
gap 18 between the Coanda body 10 and the flare end 11 of the gas
flue 12. Gas emitted from the flare end 11 passes through the
adjustable annular gap 18 and around the Coanda body 10. The
annular gap 18 is controlled by the gas flow adjustor, which in the
embodiment of FIG. 2 is provided by controlled pressure on either
side of the dual acting piston 19. The weight of the Coanda body
tends to close the gap, but the device can be set with a minimum
gap such as 0.100 inches by providing an uneven shape to the mating
surfaces of the Coanda body and flare tip. The uneven shape may be
provided by any suitable means such as small bumps on the end of
the gas flue.
[0011] FIG. 2 shows a gas flow adjustor for two Coanda flare stacks
100. The description of the gas flow control system will be
described for just one of the two Coanda flare stacks 100. In any
flare facility, there may be one, two or more Coanda flare stacks
100, such as six or eight. As shown in FIG. 2, waste gas to be
flared is provided through line 26 and connection 13 to the gas
flue 12. The waste gas is also provided to the dual acting cylinder
20 so that the lower face 22 of the dual acting piston 19 is acted
upon by the gas pressure of the gas to be flared. The flare gas
line 26 is connected to the cylinder 20 by gas line 28. Gas line 28
ends with flex hose connected into lower chamber 23 of the dual
acting cylinder 20. The upper face 24 of the dual acting piston 19
of the flare stack 100 is acted upon by gas from a separate
pressure source 30 connected to piston 20 by gas lines 31 and 32.
Gas line 32 terminates in flex hose 33 that connects to the upper
chamber 25 of the dual acting cylinder 20. The pressure in the
upper chamber 25 of each dual acting cylinder 20, hence on the
upper faces 23, is adjustable by a pinch valve 34, although other
means of adjusting the pressure could be used. In this embodiment,
the pressure source 30 used is LPG (liquid petroleum gas), which
may also used to supply pilot burners 35 with fuel through line 37.
Pressure in the line 37 may be controlled by a pinch valve 39. The
pilot burner 35 is any suitable burner known in the art. It will be
understood that other pressure sources 30 could be substituted,
depending on the desired configuration.
[0012] Increasing pressure from the waste gas source 17 acting
against the lower face 22 of the dual acting piston 19 acts to
increase the gap 18, while increasing pressure against the upper
face 24 of the dual acting piston 19 acts to reduce the gap 18. In
one embodiment, there is a deadband where pressure in the gas flue
from the waste gas does not increase the gap. The device thus has a
deadband from 0 lb up to some set pressure where lift off of the
Coanda body occurs. As the pressure of gas to be flared increases
beyond the set point, for example 1 lb to 5 lb of pressure, the
force against the lower face 22 causes the gap 18 to increase, in
order to accommodate the higher rate of flow. As pressure in the
gas flue increases, without control pressure, the gap tends to
increase until the gap is at a maximum. A gap range of 0.51-0.550
inches may be used in some embodiments. The pressure at which the
gap reaches a maximum can be set by the designer, as for example 10
lb. FIG. 2 also shows a flame arrestor 36 on the waste gas line 26,
and various ball valves 38 for controlling flow of gas in the gas
lines.
[0013] In the embodiment of FIG. 2, the control pressure against
the upper face 24 tends to close the gap, and thus increase gas
flow. The control pressure is thus chosen to maintain a desired
rate of flow of the gas to be flared to achieve certain flare
characteristics, such as flame speed, flame pattern, and flame
length. The control pressure may be adjusted by operation of valve
34 manually or by an automatic system. With higher flow rates, the
flame will lengthen. By increasing the flame length, for example,
the heat released will not be concentrated on the Coanda body 10,
which helps reduce the damage caused by heat exposure, and a
relatively flat orifice velocity is obtained, which reduces noise
levels. Thus, a mix of flare gas with larger amounts of propane,
and relatively less methane, tends to burn with a shorter flame and
more turbulence, which results in more damage to the flare tip, as
compared with a lighter gas having more methane, at a given gap
size. In the case of propane, therefore, the gap size may be
decreased to increase flow velocity and extend the burn beyond the
Coanda body.
[0014] The control pressure may also chosen to achieve a certain
level of stability for the Coanda body 10, and the noise level
emitted by the flare stack 100. The noise level can be reduced
significantly by choosing a control pressure that allows gas to
escape from the gap 18 at sub-sonic speeds. In addition, by having
a regulated pressure acting against one side of the dual acting
piston 19, ball flutter due to high frequency vibration of the
Coanda body 10 is reduced. Not only does this increase the
efficiency of the flare stack 100, it also reduces the noise as
these vibrations would otherwise be transferred to the flame front
since the flow of gas would be disrupted by a changing gap 18.
Favorable results have been obtained by using a control pressure
between 2 and 15 psig, and with the gap 18 adjustable between about
0.05 inches and 0.5 inches, where 0.05 is the minimum width of the
gap 18. The control pressure that may be used to close the gap may
be important in some applications such as emergency shutdown or
blow down situations.
[0015] In an array of gas flares, some gas flares may be isolated
by turning off gas flow to the gas flue while providing additional
flow to the remaining gas flares.
[0016] Immaterial modifications may be made to the embodiments
described above without departing from what is claimed. For
example, the gas flow adjustor may be provided by a dual acting
diaphragm, or an electronic device responsive to a pressure or flow
sensor on the waste gas flow line, flow sensors, noise sensors,
flame sensors and/or other sensors. While in some embodiments a
Coanda body is used for its desirable gas flow characteristics, the
gas flare control may also be used with a plate or other mechanism
that provides an adjustable gap. While the Coanda body is shown as
adjustable, it is possible in some embodiments to fix the Coanda
body or other body and adjust the gap through other means such as
movement of the upper end of the gas flue. Gas from the gas source
may also be provided to both sides of the actuating cylinder 20 for
added control.
* * * * *