APPARATUS AND METHOD FOR MINIMIZING SMOKE FORMATION IN A FLARING STACK
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, steam, and combustion air during combustion to reduce smoke formation.
Latest UOP LLC Patents:
- Process for removing cobalt, lead, cadmium and chromium ions from bodily fluids using metallate ion exchange compositions
- Integrated process for the conversion of crude to olefins
- Method to improved redox flow battery performance
- Process for hydrotreating a feed stream comprising a biorenewable feedstock with treatment of an off-gas stream
- Process for the hydrogenation of olefins
This application claims the benefit of U.S. Provisional Application No. 61/819,173 filed May 3, 2013.
FIELD OF THE INVENTIONThe subject application relates to an apparatus for minimizing smoke formation in a flaring stack.
BACKGROUND OF THE INVENTIONFlare 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.
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.
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.
When sufficient ambient air and/or steam is available to contact the combustible waste gas, the mixture may be smokelessly burned. In typical flare apparatus, only a portion of the desired amount of air and/or steam is present for mixing with the waste gas.
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.
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 INVENTIONBy one aspect, an apparatus is provided minimizing the formation of smoke in the operation of a flaring stack. The apparatus includes a support arm having a generally hollow waste gas passageway for connection to a waste gas source. The apparatus further includes a generally annular gas deflector having an outer surface for deflecting waste gas and steam therealong. A waste gas outlet is provided between the gas deflector and the support arm. The apparatus further includes a steam distributor for distributing steam with an outlet configured to direct the steam along the outer surface of the gas deflector. The gas deflector includes a plurality of lobes extending generally radially from the gas deflector outer surface for providing improved mixing between the steam, waste gas, and combustion air during combustion.
By another aspect, a method is provided for combusting a waste gas to reduce the formation of smoke. The method includes passing steam along an outer surface of a generally annular gas deflector including a plurality of lobes extending radially outwardly therefrom. The method includes passing the waste gas along the outer surface of the gas deflector, including over the plurality of lobes. The method further includes drawing ambient air toward the outer surface for mixing with the waste gas and steam and igniting the waste gas mixture.
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 DESCRIPTIONThe 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.
Referring now to
The waste gas deflector includes a plurality of lobes 16 that extend radially therefrom. In this regard, as steam and waste gas flow along the outer surface of the gas deflector 4, the steam and gas flow 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 the steam, and also combustion air where present 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 NOX. By one aspect, the lobes 16 include a plurality of generally vertically oriented ribs 18 spaced circumferentially about the gas deflector 4 such that the steam and gas flow along the ribs and through channels 20 formed between adjacent ribs 18.
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. The support arm may also include a steam passageway 11 for passing steam from a steam source to the gas deflector. In one approach, as illustrated in
The support arm 8 may extend from a central plenum 22 as illustrated in
The support arm 8 may include the gas passageway 10 as illustrated in
The support arm 8 may also include the steam passageway as illustrated in
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
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 without ribs.
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
The ribs are circumferentially spaced so that a plurality of corresponding channels 20 are formed between adjacent ribs 18 as illustrated in
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
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.
The ribs may have a constant circumferential width or a varying width about the perimeter of the Coanda bowl 36 as illustrated in
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
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 mixing of the steam and waste gas, and also combustion air when it is present, 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 mixing of the steam, gas and combustion air reducing smoke formation.
To this end, by one aspect, the ribbed Coanda bowl has a relatively high ratio of a perimeter (as shown in
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 steam, waste gas and the combustion air is improved along the total outer surface as described above.
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
As illustrated in
As mentioned previously, by one aspect, a steam outlet 13 is provided for introducing the steam toward the outer surface of the Coanda bowl. With reference to
As illustrated in
By one aspect, the openings 78 may be aligned with the ribs 18 to provide for increased flow of steam over the ribs 18. By another approach, the openings 78 may be aligned with the channels 20. By yet another approach, openings may be aligned with both the ribs and the channels or may be offset relative to one or both.
As mentioned, 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
According to one aspect, the gas outlet 12 is provided radially outwardly of the steam outlet 13 as illustrated in
According to various aspects, during operation, the steam flows through the steam passageway 11 and through the annular opening 15 along the Coanda bowl outer surface 38. The waste gas to be combusted flows through the gas passageway 10 and through the annular opening 14. As the steam and waste gas flow along the outer surface 38, they mix together and may further mix with combustion air (for example surrounding ambient air) that is drawn toward the waste gas and steam and mixed therewith. The steam and waste gas pass over the ribs 18 and through the channels 20 therebetween. The mixture is ignited and combusted with reduced smoke formation.
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.
Claims
1. 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 waste gas;
- a waste gas outlet between the gas deflector and the support arm;
- a steam distributor for distributing steam;
- an outlet of the steam distributor configured to direct steam along the outer surface of the gas deflector; and
- a plurality of lobes extending generally radially from the gas deflector outer surface for providing improved mixing between the steam, waste gas, and combustion air during combustion.
2. The apparatus of claim 1, wherein the gas deflector includes a tulip-shaped Coanda bowl.
3. The apparatus of claim 1, wherein the lobes include circumferentially spaced generally vertical ribs extending radially from the outer surface of the gas deflector.
4. The apparatus of claim 3, wherein the steam distributor includes an annular outlet positioned about the annular gas deflector for directing steam therealong.
5. The apparatus of claim 4, wherein the steam distributor annular outlet includes a plurality of circumferentially spaced openings positioned about the annular gas deflector.
6. The apparatus of claim 5, wherein the openings are generally aligned with the ribs.
7. The apparatus of claim 5, wherein the openings are generally aligned with channels formed between the ribs.
8. The apparatus of claim 4, wherein the waste gas outlet includes a generally annular outlet positioned radially outwardly of the steam distributor.
9. The apparatus of claim 3, wherein a ratio of a perimeter of a ribbed portion of the bowl to an outer diameter of the ribbed portion is between about 6.5 and about 20.
10. The apparatus of claim 3, wherein the ribs are 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.
11. The apparatus of claim 3, wherein the ribs include inclined sidewalls extending from channels between the ribs to upper raised rib portions.
12. 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 waste gas;
- a waste gas outlet between the gas deflector and the support arm;
- a steam distributor for distributing steam;
- a plurality of circumferentially spaced generally vertical ribs extending radially from the gas deflector outer surface for providing improved mixing between the steam, waste gas, and combustion air during combustion; and
- a generally annular outlet of the steam distributor configured to direct steam along the outer surface of the gas deflector.
13. The apparatus of claim 12, wherein the support arm includes a steam passageway positioned within the waste gas passageway.
14. The apparatus of claim 12, wherein the steam distributor includes a steam chamber and the steam chamber outlet includes plurality of upper openings.
15. The apparatus of claim 14, wherein the steam chamber includes an inverted generally hollow frustoconical member with the upper openings about an upper portion thereof
16. The apparatus of claim 14, wherein the steam chamber upper openings include a notched upper rim adjacent to a bottom portion of the steam distributor.
17. The apparatus of claim 14, wherein the steam chamber upper openings include a plurality of apertures about the upper portion of the steam chamber.
18. The apparatus of claim 14, wherein the upper openings are generally aligned with the ribs.
19. The apparatus of claim 14, wherein the upper openings are generally aligned with channels between the ribs.
20. The apparatus of claim 12, wherein the waste gas outlet is generally annular and positioned radially outwardly of the steam distributor outlet to provide steam along the outer surface of the gas deflector.
Type: Application
Filed: May 1, 2014
Publication Date: Nov 6, 2014
Applicant: UOP LLC (Des Plaines, IL)
Inventors: Donnie Dee McClain (Round Rock, TX), Richard R. Martin (Tulsa, OK), Jay D. Jennings (Broken Arrow, OK)
Application Number: 14/266,972
International Classification: F23G 7/08 (20060101);