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Title:
LOW STEAM CONSUMPTION HIGH SMOKELESS CAPACITY WASTE GAS FLARE
Document Type and Number:
WIPO Patent Application WO/2019/055335
Kind Code:
A1
Abstract:
A steam flare is provided that injects steam, unmixed with air into a waste gas stream at locations where the resulting accelerated steam and waste gas mixture upon exposure to the surrounding air induces a mixture of steam, waste gas and air with improved combustion and effectively complete destruction of the waste gas, and where under low-flow conditions, reduced steam and/or assist gas are required to maintain smokeless operation.

Inventors:
MARTIN, Matthew A (UOP LLC, 25 East Algonquin RoadP. O. Box 501, Des Plaines Illinois, 60017-5017, US)
MARTIN, Richard R (UOP LLC, 25 East Algonquin RoadP. O. Box 501, Des Plaines Illinois, 60017-5017, US)
KRAUS, Kurt E (UOP LLC, 25 East Algonquin RoadP. O. Box 501, Des Plaines Illinois, 60017-5017, US)
JENNINGS, Jay D (UOP LLC, 25 East Algonquin RoadP. O. Box 501, Des Plaines Illinois, 60017-5017, US)
Application Number:
US2018/050171
Publication Date:
March 21, 2019
Filing Date:
September 10, 2018
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
UOP LLC (UOP LLC, 25 East Algonquin RoadP. O. Box 501, Des Plaines Illinois, 60017-5017, US)
International Classes:
F23G7/08; F23D14/46; F23J15/00
Foreign References:
US7967600B22011-06-28
US20160138805A12016-05-19
RU2203450C12003-04-27
EP2256409A22010-12-01
Attorney, Agent or Firm:
ROMANO, Ashley E (UOP LLC, 25 East Algonquin RoadP. O. Box 501, Des Plaines Illinois, 60017-5017, US)
Download PDF:
Claims:
CLAIMS:

1. A steam flare comprising a waste gas cylinder connected at an upper portion of said waste gas cylinder to a plurality of extensions that extend away from a center of said waste gas cylinder, wherein each of said extensions contain a plurality of flare gas conduits, and wherein a steam tube is located in each of said flare gas conduits.

2. The steam flare of claim 1 wherein said flare gas conduit is a tube having a cylindrical, square, rectangular, oval or complex configuration.

3. The steam flare of claim 1 further comprising a multiplicity of flow-reducing cones in said flare gas conduit and below a top portion of said steam tube.

4. The steam flare of claim 1 with a curved, straight or sloped transition piece from said waste gas cylinder to said flare gas conduits.

5. The steam flare of claim 1 with a cone and/or a flat plate capping the waste gas

cylinder.

6. The steam flare of claim 1 wherein said steam tube has two to twenty orifices pointing at an angle between zero and fifty degrees from vertical.

7. A process of operating a steam flare comprising sending a waste gas stream through a waste gas cylinder to a plurality of flare gas conduits while sending a stream of steam through a tube wherein said tube extends into said flare gas conduit, mixing said waste gas stream and said steam and then causing a flame to burn as a resulting mixture of said waste gas stream, said steam and oxygen in outside ambient air.

8. The process of claim 7 wherein a ring at the upper portion of the waste gas tip of said flare gas conduit comprises perforation or other surface features properly sized in proportion to the waste gas stream and thereby values approaching or less than 0.05 kg (0.10 lbs) steam is used per pound of propane waste gas.

9. The process of claim 7 wherein all of said steam is injected internally to said waste gas before exposure to surrounding atmospheric air.

10. The process of claim 7 wherein curved transition pieces between flare gas cylinder and said waste gas conduits improve flow distribution exiting said waste gas conduits and reduce pressure drop through flare gas system.

Description:
LOW STEAM CONSUMPTION HIGH SMOKELESS CAPACITY WASTE GAS FLARE

STATEMENT FO PRIORITY

[0001] This application claims priority from U.S. Provisional Application No. 62/559,318 filed September 15, 2017, the contents of which cited application are hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to an improved flare apparatus and more specifically to an efficient steam-assisted flare apparatus.

[0003] Steam assisted flares are used in refinery and petrochemical plants for the combustion of high volume releases of waste gases during interruptions of normal plant operation. The "smokeless" capacity is an extremely important operating parameter. High quantities of high pressure steam is used to entrain atmospheric air and force the mixing of the air with the waste gases. The greater the quantity of air mixed per pound of steam injected with the waste gases the higher the achievable smokeless capacity.

[0004] Flare apparatus for burning and disposing of combustible gases are well known. Flare apparatus are commonly mounted on flare stacks and are located at production, refining, processing plants and the like 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. Flare apparatus are extremely important in the event of plant emergencies such as fire or power failure and a properly operating flare system is a critical component to prevent plant disruption in any of the above-mentioned or other circumstances.

[0005] In one example of an illustration of "traditional" prior art high capacity steam assisted flare design, the waste gas flow enters at the bottom of the flare tip through a 60 inch diameter waste gas connection (conduit). The flare tip is 9 to 10 feet in diameter. There are numerous 8 inch diameter nozzles that extend through the wall of the flare tip near the base then vertically to the discharge end of the tip. Attached to the inlet of the nozzle is a "venturi mixer". Steam injection nozzles are located at the inlet end of the venturi mixer. The high pressure steam injection entrains atmospheric air that travels through the nozzle and is injected into the waste gas that travels from the waste gas inlet at the bottom of the tip through the space around air nozzles to the discharge the end of the tip. Only a small portion of the required combustion air flows through the nozzles. The remainder of the required combustion air flows up around the outside of the flare tip. At the discharge end of the flare tip there is the second set of steam nozzles that are used to force the air into the waste gas stream.

[0006] There are several shortcomings for this design. First, the relatively small 8 inch diameter nozzles severely limit the quantity of the air that can be entrained by the steam. Secondly, the steam flow and waste gas flow are essentially parallel which reduces the mixing efficiency. And finally, the waste gas has a tendency to flow up through the center of the tip instead of spreading uniformly across the tip diameter. This causes higher

concentrations of waste gas in the center of the tip resulting in incomplete combustion that produces smoke.

[0007] It is generally desirable that the flammable gas be burned without producing smoke and typically such smokeless or substantially smokeless burning is mandatory. One method for accomplishing smokeless burning is by supplying combustion air with a steam jet pump, which is sometimes referred to as an eductor. Combustion air insures the flammable gas is fully oxidized to prevent the production of smoke. Thus, steam is commonly used as a motive force to move air in a flare apparatus. When a sufficient amount of combustion air is supplied, and the supplied air mixes well with combustible gas, the steam/air mixture and flammable gas can be smokelessly burned. In a typical flare apparatus, only a fraction of the required combustion air is supplied using motive force such as blower, a jet pump using steam, compressed air or other gas. Most of the required combustion air is obtained from the ambient atmosphere along the length of the flame.

[0008] One type of known steam-assisted flare apparatus comprises a generally cylindrical gas tube into which flammable gas is communicated. Lower steam is

communicated through a plurality of steam tubes at an inlet and is forced to negotiate a bend in the steam tube, which causes a pressure drop. At the bend, the steam tubes are redirected so that they are parallel with the outer cylinder. Center steam is injected into the center of the gas tube so that flammable gas and steam pass upwardly through the outer tube and is mixed with steam that exits the lower steam tubes. At the upper end or exit of the gas tube, steam injectors direct steam radially inwardly to control the periphery of the mixture exiting the gas tube, and the steam/air and gas mixture is ignited. The center steam is provided to ensure burning does not occur internally in the gas tube. Internal burning is typically seen at low gas flow rates such as purge rates, and is aggravated by cross wind, capping effects caused by the upper steam, and if the purge gas has a lower molecular weight than air. A purge rate is typically the minimum gas flow rate continuously flowing to the flare to prevent explosion in the flare stack.

[0009] Another type of steam-assisted flare uses only center and upper steam injectors, and works in a similar fashion. The steam-assisted flares described herein may accomplish smokeless flaring. However, such flare apparatus may require more steam per waste gas than other steam-assisted flare types, especially at larger sizes; additionally, they may create an excessive amount of noise. The noise from the lower steam can be muffled, while the noise from the upper steam is difficult or impractical to muffle due to its vicinity to the flare flame. A muffler for the lower steam not only adds to the costs, but also increases the wind load of the flare stack, resulting in increased flare stack costs. Due to the high cost of steam and the piping and flare stack structure associated with delivering the steam, it is desirable that less steam be utilized to achieve smokeless burning. Thus, there is a need for an improved flare apparatus and methods for smokelessly burning combustible gases with air to lessen the noise and to increase the efficiency whereby more fuel may be burned without added steam.

[0010] Under low-flow operating conditions, steam is often added to maintain smokeless combustion, more with higher-wind conditions; however, due to regulatory requirements that the combined steam and waste gas mixture remain above 270 Btu/SCF, extra assist gas, commonly methane, must additionally be added to maintain smokeless combustion. With many steam-assisted flares, the steam and steam/air mixtures are introduced to the waste gas fairly uniformly, whereas the waste gas can exit the flare non-uniformly with higher wind, requiring higher steam and/or assist gas utilities to maintain smokeless combustion. Thus, there is a need for an improved flare apparatus to consume reduced steam and/or assist gas utilities under low-flow conditions, regardless of the wind conditions.

SUMMARY OF THE INVENTION

[0011] In one embodiment, the invention provides a steam flare comprising a waste gas cylinder connected at an upper portion of said waste gas cylinder to a plurality of extensions that extend away from a center of said waste gas cylinder, wherein each of the extensions contain a plurality of flare gas conduits, and a steam tube is located in each of the flare gas conduits. The steam flare may have a ring at a top portion of said flare gas conduit and above a top portion of said steam tube. The steam flare may additionally have a singular or plurality of flow-restricting cones in some section of the flare gas conduit below the conduit exit. The flare gas conduit may be a tube having a cylindrical configuration or other configuration such as a square, rectangular, oval or complex configuration. The steam tube may be a single tube having branches that extend into each of said flare gas conduits. The steam exit may be a singular orifice or plurality of orifices directly vertical or at an angle. The ring may contain perforations or other surface features. The transition from the waste gas cylinder to the waste gas equipment may be completely horizontal, at a certain slope, curved in some direction, or a combination of two or more of these features. The cap of the waste gas cylinder may involve a flat plate, a cone, a smaller concentric cylinder, or a combination of two or more of these features.

[0012] In another embodiment, the invention is a process of operating a steam flare comprising sending a waste gas stream through a waste gas cylinder to a plurality of flare gas conduits while sending a stream of steam through a tube wherein said tube extends into said flare gas conduit, mixing said waste gas stream and said steam and then causing a flame to burn as a resulting mixture of said waste gas stream, said steam and oxygen in outside ambient air. There may be a ring at an upper portion on a waste gas tip of the flare gas conduit that comprises perforations or other surface features to direct mixture of said steam and said waste gas. The steam flare may have a singular or plurality of velocity seals or flow- restricting cones in some section of said flare gas conduit below the conduit exit to reduce atmospheric air backflow into the flare gas extensions, additionally reducing the level of assist gas and/or steam required to maintain smokeless combustion under low-flow operating conditions. The steam exit may involve an orifice directly vertical or multiple orifices at an angle to increase mixing of the steam, surrounding atmospheric air, and waste gas and additionally increase the velocity of the waste gas stream while reducing the level of atmospheric air backflow at low flow rates through partial steam-capping of the flare gas conduit, reducing the level of assist gas and/or steam required to maintain smokeless combustion under low-flow operating conditions. The flare gas conduit may have a configuration selected from the group consisting of cylindrical, square, rectangular, oval and complex shapes. The transition from the waste gas cylinder to the waste gas extension may be completely horizontal, at a certain slope, curved in some direction, or a combination of these features to reduce the pressure drop through the tip so as to not require increased nominal tip size with higher structural requirements; in addition, this improves structural integrity of tip by reducing stress from thermal growth due to combustion within tip. The cap of the waste gas cylinder may involve a flat plate, a cone, a smaller concentric cylinder, or a combination of these features, to reduce the stresses from thermal growth, increasing the structural integrity of the apparatus, and result in better flow distribution within the flare apparatus, resulting in acceptable pressure drop. The invention also addresses the situation where atmospheric air ingress into the tip mixes with waste gas and assist gas and combusts within the tip, thereby heating the tip and reducing equipment life; therefore, reducing level of air ingress is important to maximizing equipment life at low-flow operating conditions. In addition, the invention provides advantages in the low amount of steam that is needed with less than 0.20 lbs steam used per pound of propane waste gas. All of the steam that is injected internally to the waste gas before exposure to surrounding atmospheric air. The steam imparts mixing and momentum transfer to said waste gas and said surrounding atmospheric air. The invention also provides advantages under low-flow conditions, requiring reduced steam and/or assist gas to maintain smokeless combustion and increase equipment life.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Fig. 1 is an isometric perspective of a top portion of a steam flare.

[0014] Fig. 2 is a view of the steam flare including a waste gas cylinder and tube for steam.

[0015] Fig. 3 is a cutaway upper portion of the steam flare.

[0016] Fig. 4 shows an isometric view of two flare enclosure conduits.

DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention delivers smokeless combustion while utilizing less than 0.20 lbs steam per lb of propane waste gas stream while requiring no steam for cooling and minimal steam for warming (less than 0.0006 lbs steam per maximum vent gas flow).

[0018] The invention relies solely on completely internal steam, steam injected completely internally to the flare vent gas ducting with no exposure to surrounding atmospheric air while imparting a significant mixing and momentum transfer effect on the surrounding ambient air environment. Other flares rely on stream that is injected into the air near and immediately surrounding the periphery of the flare tip and aimed so that they drive steam and air near and immediately surrounding the periphery of the flare tip and aimed so that they drive stream and air into the waste gas or effluent stream of the waste gas. Such flares are referred to as "External Steam Flares". There are other flares that may be termed "Internal Steam Flares" that rely on injecting steam through conduits, passageways, or a venturi from a surrounding air atmosphere thereby injecting air and steam through the containing wall or shell of the waste gas stream and into the central core of the waste gas stream.

[0019] In the present invention, as shown in FIG. 1, a waste gas stream passes up through a cylinder 12. Steam 2 is injected into the waste gas stream 1 at one or more locations 4 whereupon the resulting accelerated stream and waste gas mixture, upon exposure to the surrounding air induces the surrounding air into the waste gas (fuel) and steam mixture. There is no mixture of the surrounding air 3 with the waste gas stream 1 before exiting the top of the flare enclosure conduits. The steam and waste gas 5 are partially mixed prior to mixing with the surrounding ambient air 6 but emit from the confines of the flare enclosure or waste gas conduit with sufficient combined velocity and momentum to induce effective mixing of fuel and steam with the surrounding air to affect improved combustion and effectively complete destroying combustible waste gas. Relatively high velocity steam 2 transfers momentum to the relatively low velocity waste gas 1 and induces some mixing of steam and waste gas 5 before exiting into surrounding air 3. The resulting partially mixed steam and waste gas stream then imparts momentum, drawing in and mixing with, the surrounding ambient air 6 as the steam and waste gas emit from the flare enclosure conduits 7. In Figure 1 are shown four sets of four enclosure conduits 7, conduit steam injection nozzles 8, rings 9, velocity seals 10, and hub steam injection nozzles 16. Also shown are transition plates 11, curved to allow for sufficient flow distribution into cans with minimal wind area and a hub expansion cylinder and plate 13 to mitigate growth from thermal stresses.

[0020] Fig. 2 is a view that includes the lower portion of the flare assembly with the cylinder 12 into which waste gas 1 passes and the pipe in which steam 2 is sent to the upper portion that contains the explained above. Hub steam injection nozzles 16 are shown, which result in steam separating the combusting waste gas stream mixture from the center hub metal. [0021] Fig. 3 illustrates detail of several flare enclosure conduits. Steam 2 passes into flare conduits 7 and then into surrounding air 3 to be burned effectively. Rings 9 and velocity seals or flow-restricting cones 10 are shown in each enclosure conduit 7.

[0022] Fig. 4 is a view that shows more detail of two individual flare enclosure conduits 7 with steam 8 entering through a tube 14 that extends to near the top of the flare enclosure conduit while waste gas passes up to mix with the outside ambient air to then burn efficiently.

[0023] In other embodiments of the invention, there is a reliance on internally injected steam to keep the steam warm. This steam is injected wholly within the flare tip conduit enclosure and is sufficiently away from, upstream of, the exit to atmosphere opening of the flare tip that this steam completely mixes with the waste gas and imparts a small but largely insignificant momentum component to the waste gas stream and is sufficiently upstream of the flare exit as to impart no significant effect on enabling or enhancing the mixing of the resulting waste gas and steam mixture with the surrounding atmospheric air. This design relies on internal steam as injected through a conduit or venture drawing in surrounding air as described above. External steam is used in drawing in surrounding air from the periphery of the exiting waste gas stream and steam to keep warm is injected wholly within the flare waste stream conduit. The present invention relies on a new, separate and different mixing method of partially mixing steam with waste gas at a location where it can then mix with and impart momentum upon the surrounding atmospheric air.

[0024] The depicted embodiment shows twenty-four waste gas conduits 7, four on each of six transition sections, for a twenty-four inch riser cylinder 12. In another embodiment, the number and size of waste gas conduits and number and size of transition sections could vary more or less.

[0025] In one embodiment (pictured), the steam injection nozzle in located upstream of the plane at the exit of the waste gas conduit. In another embodiment (not pictured) the steam injection tip extends through and beyond the plane of at the exit of the waste gas conduit while remaining completely enveloped in the waste gas stream.

[0026] In the depicted embodiment, the waste gas tip has a ring 9 located near, but slightly upstream of the waste gas exit. This ring is not necessary, but can serve to 1) enhance the mixing of waste gas, steam and air, 2) stabilize or create as stable bluff body for flame stabilization and 3) serve as a fine tuning location whereby adjusting the size of the passage(s) in the ring the flow capacity of the flare can be adjusted to specifically meet the flow capacity requirements of a particular flaring application or operation. The benefits of adjusting the capacity of the flare to correctly match the flow and capacity requirements of a particular flaring application or operation include fuller utilization of the available pressure loss in the waste stream system thereby enhancing the mixing of the waste gas, steam and air. Improved or enhance mixing of waste gas, steam and air not only improves the combustion, thereby increasing the smokeless capacity of the flare burner but also further reduces the steam utilization of the flaring system to values of much less than 0.20 lbs steam is used per pound of propane waste gas approaching or less than 0.10 lbs steam used per pound of propane waste gas. This ring or rings can be located as depicted, upstream of the exit, at the exit or suspended on a structure and held downstream of the exit. These rings may also reside singularly or in plurality on the outside of the outside of the waste gas conduit. The depicted waste gas conduit 7 is cylindrical but in practice may be of various shapes including square, rectangular, oval or complex. Given the multiplicity of possible shapes, the "ring(s)" may be of various shapes and dimensions and may contain perforations or other surface features the may disrupt, guide or channel the flow of steam, waste gas or air to affect the mixing of the three component streams.

[0027] In the depicted embodiment, the waste gas tip 9 has three velocity seals or flow- restricting cones 10 per waste stream conduit 7. These cones are not necessary but serve to 1) restrict air from flowing upstream into the flare transition or entry cylinder 12 under low-flow operating conditions, 2) maintain combustion in waste stream conduits 7, and 3) reduce combustion within the waste stream entry cylinder 12. Additionally, these cones can be increased or decreased in count per waste stream conduit or flow diverted from them as required.

[0028] Curved transition plate 11 is shown in the depicted embodiment, but this plate can be flat, sloped, or curved in a direction opposite to that depicted in the figure. The curved shape is utilized to optimize flow distribution while minimizing pressure drop. Hub cylinder and flat plate 13 are not required but as depicted are used to maximize equipment life. Other embodiments not depicted involve cone with flat plate or simple flat plate.

[0029] The entrance of steam 2 into mixing zone with waste gas stream 5 is depicted with nine orifices 15 at a forty degree angle from vertical. Other embodiments include more or less orifices down to a single orifice, ranging from an angle up to fifty degrees from vertical to directly vertical. [0030] The depicted embodiment displays hub steam injection nozzles which are not required but which lengthen the life of the equipment by separating the center hub metal from the combustion with cooling steam.

SPECIFIC EMBODIMENTS [0031] While the following is described in conjunction with specific embodiments, it will be understood that this description is intended to illustrate and not limit the scope of the preceding description and the appended claims.

[0032] A first embodiment of the invention is a steam flare comprising a waste gas cylinder connected at an upper portion of the waste as cylinder to a plurality of extensions that extend away from a center of the waste gas cylinder, wherein each of the extensions contain a plurality of flare gas conduits, and wherein a steam tube is located in each of the flare gas conduits. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the steam flare further comprises a ring at a top portion of the flare gas conduit and above a top portion of the steam tube. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the flare gas conduit is a tube having a cylindrical configuration. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the flare gas conduit is a tube having a square, rectangular, oval or complex configuration. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the steam tube comprises a single tube having branches that extend into each of the flare gas conduits. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the ring contains perforations or other surface features. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the steam flare further comprises a multiplicity of flow-reducing cones in the flare gas conduit and below a top portion of the steam tube. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the steam flare further comprises a singular flow-reducing cone in each of the flare gas conduits and below a top portion of the steam tube. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the stream flare comprises a curved transition piece from waste gas cylinder to flare gas conduits. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the steam flare comprises a straight transition piece from waste gas cylinder to flare gas conduits. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the steam flare has a sloped transition piece from waste gas cylinder to flare gas conduits. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein there is a flat plate capping the waste gas cylinder. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein there is a cone and a flat plate capping the waste gas cylinder. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the steam flare has a cylinder and a flat plate capping the larger concentric waste gas cylinder. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the steam flare has a steam tube with a singular orifice pointing vertical. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the steam flare has a team tube with two to twenty orifices, pointing at an angle between zero and fifty degrees from vertical. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the steam flare has external steam tubes injecting steam between hub metal and combusting stream.

[0033] A second embodiment of the invention is a process of operating a steam flare comprising sending a waste gas stream through a waste gas cylinder to a plurality of flare gas conduits while sending a stream of steam through a tube wherein the tube extends into the flare gas conduit, mixing the waste gas stream and the steam and then causing a flame to burn as a resulting mixture of the waste gas stream, the steam and oxygen in outside ambient air. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein a ring at an upper portion on a waste gas tip of the flare gas conduit comprises perforations or other surface features to direct mixture of the steam and the waste gas. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the flare gas conduit has a configuration selected from the group consisting of cylindrical, square, rectangular, oval and complex shapes. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein less than 0.09 kg (0.20 lbs) steam is used per pound of propane waste gas. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein a ring at the upper portion of the waste gas tip of the flare gas conduit comprises perforation or other surface features properly sized in proportion to the waste gas stream and thereby values approaching or less than 0.05 kg (0.10 lbs) steam is used per pound of propane waste gas. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein all of the steam is injected internally to the waste gas before exposure to surrounding atmospheric air. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein most of the steam is injected internally to waste gas before exposure to surrounding atmospheric air and some of the steam is injected externally to separate combusting stream from hub metal. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the steam imparts mixing and momentum transfer to the waste gas and the surrounding atmospheric air. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein a singularity or multiplicity of flow- reducing cones in the flare gas conduit reduce the amount of air flowing upstream into the flare gas conduit. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein reduced steam and/or assist gas is required to maintain smokeless operation under low-flow operating conditions. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein curved transition pieces between flare gas cylinder and the waste gas conduits improve flow distribution exiting the waste gas conduits and reduce pressure drop through flare gas system. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein a singular vertical orifice or multiple orifices at an angle are utilized to increase mixing of the steam, surrounding atmospheric air, and waste gas. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the orifices increase the velocity of the waste gas stream while reducing the level of atmospheric air backflow at low flow rates through partial steam-capping of the flare gas conduit.