Hybrid Flare Apparatus

Abstract

A hybrid flare assembly for waste gas combustion includes a shell having an exhaust portion extending from an offset portion, and an ignitor for igniting the waste gas. The ignitor and support shaft longitudinal moves within the exhaust portion which is attached to the offset portion at an acute angle. Pluralities of risers are arrayed about the ignitor shaft for conducting gas from first and second high pressure inlets to a combustion chamber. A second shell partially defines a first chamber through which low pressure gas conducts and a second chamber separated from the first chamber by a perforated support plate through which high pressure gas conducts into the first plurality of risers. A method of combusting waste gas includes the steps of conducting a first high pressure gas flow to the first plurality of risers and conducting a second high pressure gas flow to the second plurality of risers.

Description

TECHNICAL FIELD

This document relates generally to the field of waste gas flares for disposing of flammable gas streams released due to venting requirements, start-ups, shut-downs, upsets, and/or emergencies at facilities such as production facilities, refineries, processing plants, and others. In particular, this disclosure is directed to a hybrid flare apparatus having a flare designed around an ignitor and pilot.

BACKGROUND

Flares are safety devices used in various facilities such as production facilities, refineries, processing plants, and others. The purpose of the flare is to safely burn excess hydrocarbon gases which are not susceptible to recovery or recycling. In use, excess hydrocarbon gases are safely combusted in/by the flare apparatus, providing an environmentally sound alternative to simply releasing the gases into the atmosphere. During the flaring process, excess waste gases are combined with steam and/or air to increase gas flow turbulence and/or air intake to achieve complete combustion and smokeless flaring to the extent possible. The waste gas/steam/air mixture is combusted to produce water vapour and carbon dioxide. Use of flare systems or “flaring” is minimized to the extent possible, but may be required during processes such as start-ups, shut-downs, upsets, and/or emergencies at such facilities.

Conventional flares may have one or more flare pilots depending on the size of the flare. As a general rule, the larger the flare assembly, the more pilots are recommended. The positioning of the flare pilot(s), depending on prevailing wind direction, may range from upwind, leeward, or downwind relative to the flare. High cross-wind speeds and direction may negatively impact destruction and removal efficiency (DRE) of a flare. A pilot located at the downwind position of a conventional flare is most likely to ignite the flare, compared to a pilot disposed upwind or leeward of the flare. In particular, smaller flares having a single pilot are at the mercy of winds which may approach from any direction. Depending on wind direction relative to the flare, pilot positioning can potentially interfere with ignition of the flare.

To address these and other issues, the present disclosure provides a hybrid flare apparatus having a pilot supported centrally within a combustion chamber disposed about exit nozzles of the flare gas. This advantageously provides a protected space for flare ignition/combustion to initiate and become established with a reduced risk of stress on the combustion process caused by cross-winds or the like. At lower waste gas flow rates (whether high pressure (HP) gas or low pressure (LP) gas), the hybrid flare assembly operates in a combustor mode whereby the flame and waste gas combustion can occur completely, or at least predominately, inside the combustion chamber. At higher waste gas flow rates, combustion may necessarily occur at least partially outside the defined combustion chamber. Another functionality is provided by the disclosed hybrid flare apparatus and described herein, which is allowing staging of the HP gas combustion according to pressure thresholds.

SUMMARY

In accordance with the purposes and benefits described herein, a hybrid flare assembly for waste gas combustion is provided. The hybrid flare assembly includes a shell defining a duct, the shell including an exhaust portion extending from an offset portion, and an ignitor for igniting the waste gas. The ignitor is mounted to a shaft for longitudinal movement within the exhaust portion and an angle between longitudinally extending lines of the exhaust portion and the offset portion is acute.

In another embodiment, the shell further includes an input portion extending from the offset portion.

In still another embodiment, the hybrid flare assembly includes a flare stack attached to the shell and the flare stack and the exhaust portion are substantially parallel.

In yet another possible embodiment, the hybrid flare assembly includes a first plurality of risers at least partially arrayed about the ignitor shaft for conducting high pressure gas from a first high pressure inlet to a combustion chamber partially defined by the exhaust portion of the shell.

In one other possible embodiment, the hybrid flare assembly includes a second shell partially defining a first chamber through which low pressure gas conducts and a second chamber separated from the first chamber by a support plate having a plurality of holes formed therein through which high pressure gas conducts into the first plurality of risers.

In still yet another possible embodiment, the hybrid flare assembly includes a guide tube within which the ignitor and the ignitor shaft move, wherein the guide tube extends longitudinally within and through the second chamber of the second shell.

In still on other possible embodiment, the hybrid flare assembly includes a shield attached to the shell and partially defining the combustion chamber.

In another possible embodiment, an upper edge of the shield extends above an upper edge of the exhaust portion.

In yet another possible embodiment, the hybrid flare assembly includes a second plurality of risers at least partially arrayed about the first plurality of risers for conducting high pressure gas from a second high pressure inlet to the combustion chamber.

In still another possible embodiment, the hybrid flare assembly includes a manifold for conducting high pressure gas from the second high pressure inlet to each of the second plurality of risers.

In one other possible embodiment, the hybrid flare assembly includes a shield attached to the shell and partially defining the combustion chamber.

In yet another possible embodiment, an upper edge of the shield extends above an upper edge of the exhaust portion.

In accordance with another aspect of the invention, a hybrid flare assembly for waste gas combustion is provided. The hybrid flare assembly includes a shell defining a duct, the shell including an exhaust portion extending from an offset portion, an ignitor for igniting the waste gas, the ignitor mounted to a shaft for longitudinal movement within the exhaust portion, and a first plurality of risers at least partially arrayed about the ignitor shaft for conducting high pressure gas from a first high pressure inlet to a combustion chamber.

In another possible embodiment, the hybrid flare assembly includes a flare stack attached to the shell.

In still another possible embodiment, the hybrid flare assembly includes a guide tube within which the ignitor and the ignitor shaft move.

In yet another possible embodiment, the hybrid flare assembly includes a shield attached to the shell and partially defining the combustion chamber. In still another possible embodiment, the hybrid flare assembly includes a first plurality of risers at least partially arrayed about the ignitor shaft for conducting high pressure gas from a first high pressure inlet to a combustion chamber.

In one other possible embodiment, the hybrid flare assembly includes a second shell partially defining a first chamber through which low pressure gas conducts and a second chamber separated from the first chamber by a support plate having a plurality of holes formed therein through which high pressure gas conducts into the first plurality of risers.

In another possible embodiment, the hybrid flare assembly includes a manifold for conducting high pressure gas from a second high pressure inlet through a second plurality of risers to the combustion chamber.

In accordance with another aspect of the invention, a hybrid flare assembly for waste gas combustion is provided. The hybrid flare assembly includes a flare stack, a shell attached to and extending from the flare stack, defining a duct, and including an offset portion and an exhaust portion, an ignitor for igniting the waste gas, the ignitor mounted to a shaft for longitudinal movement within the exhaust portion of the shell, and a first plurality of risers at least partially arrayed about the ignitor shaft for conducting a first gas flow from a first inlet to a combustion chamber.

In another possible embodiment, the hybrid flare assembly includes a manifold for conducting a second gas flow from a second inlet through a second plurality of risers at least partially arrayed about the ignitor shaft to the combustion chamber.

In one other possible embodiment, the hybrid flare assembly includes a common manifold for receiving a common waste gas stream, and first and second valves for controllably releasing the first gas flow to the first inlet and the second gas flow to the second inlet.

In yet another possible embodiment, the flare stack and the exhaust portion are substantially parallel and the intermediate portion is angled relative to the exhaust portion.

In still another possible embodiment, the hybrid flare assembly includes a second shell partially defining a first chamber through which a third gas flow conducts and a second chamber separated from the first chamber by a perforated support plate through which the second gas flow conducts into the first plurality of risers.

In still yet one other embodiment, the exhaust portion of the shell partially defines the combustion chamber and the ignitor is centrally supported within the combustion chamber.

In one other possible embodiment, the hybrid flare assembly includes a shield attached to the shell and partially defining the combustion chamber.

In another aspect of the invention, a method of combusting waste gas by a flare includes the steps of conducting a low pressure gas flow from a low pressure gas inlet to a combustion chamber, conducting a first high pressure gas flow from a first high pressure gas inlet to a first plurality of risers at least partially arrayed about an ignitor shaft, conducting a second high pressure gas flow from a second high pressure gas inlet to a second plurality of risers at least partially arrayed about the first plurality of risers and the ignitor shaft to the combustion chamber, mixing the low pressure gas flow, and the first and second high pressure gas flows with an air flow, and combusting the mixed low pressure gas flow, the first and second high pressure gas flows, and the air flow within the combustion chamber.

In another possible embodiment, the step of conducting a second high pressure gas flow is performed only when a measured gas flow rate or pressure exceeds a first pressure threshold.

In still another possible embodiment, the step of conducting a second high pressure gas flow is discontinued when a measured gas flow rate or pressure falls below a second pressure threshold.

In yet another possible embodiment, the step of conducting a low pressure gas flow from a low pressure gas inlet to a combustion chamber includes the step of conducting the low pressure gas from the low pressure gas inlet, through a shell defining a duct, and to the combustion chamber.

In one other possible embodiment, the shell includes an exhaust portion extending from an offset portion, and the first and second plurality of risers are at least partially contained within the exhaust portion of the shell.

In still yet another possible embodiment, the shell includes an exhaust portion attached to an offset portion at an angle sufficient to allow a retractable ignitor to move longitudinally within an interior of the exhaust portion.

In one other possible embodiment, the method further includes the step of controllably releasing the first high pressure gas flow and the second high pressure gas flow from a common manifold receiving a common waste gas stream dependent upon a pressure or flow rate.

In the following description, there are shown and described several embodiments of hybrid flare apparatus and related methods of combusting waste gas by a flare. As it should be realized, the hybrid flare apparatus and related methods of combusting waste gas by a flare are capable of other, different embodiments and their several details are capable of modification in various, obvious aspects all without departing from the hybrid flare apparatus as set forth and described in the following claims. Accordingly, the drawings and descriptions should be regarded as illustrative in nature and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, incorporated herein and forming a part of the specification, illustrate several aspects of the invention and together with the description serve to explain certain principles thereof. In the drawings:

FIG. 1A shows a perspective view of a hybrid flare assembly according to the present disclosure;

FIG. 1B is a front elevational view of the hybrid flare assembly;

FIG. 2 is a schematic illustration of waste gas flows from their respective sources to the hybrid flare;

FIG. 3A is a front perspective view of an inner tip assembly for the hybrid flare assembly;

FIG. 3B is a front elevational view of the inner tip assembly;

FIG. 4 is a top view of a plate for use in the inner tip assembly;

FIG. 5 is a front sectional view of the inner tip assembly;

FIG. 6 is a side sectional view of the hybrid flare assembly and the inner tip assembly;

FIG. 7 is a perspective view of an HP waste gas manifold and concentrically arrayed waste gas risers for use in the hybrid flare assembly;

FIG. 8 is another perspective view of the hybrid flare assembly having an outer shell removed to expose the HP waste gas manifold, waste gas risers, and inner tip assembly; and

FIG. 9 is a front perspective view of the portion of the outer shell that was removed from FIG. 8.

Reference will now be made in detail to the present embodiments of the hybrid flare assembly and related methods of use, examples of which are illustrated in the accompanying drawing figures.

DETAILED DESCRIPTION

Reference is now made to FIGS. 1A and 1B, generally illustrating a hybrid flare assembly 10. The hybrid flare assembly 10 may be a standalone construct or may be adapted for affixation as a tip end of a flare riser (not shown). As depicted, the hybrid flare assembly 10 includes an outer shell 12 defining an air duct. The outer shell 12 includes an input end portion 14a for receiving air from a controllable blower 13 or like air motivating device, an offset portion 14b, and an exhaust end portion 14c. Tabs or ears 18a-18f extend radially from exhaust end portion 14c for supporting a shield 82 which is removed in these figures to allow other components to be seen. The shield 82 is shown in FIG. 9 and partially defines a combustion chamber 64 for flare ignition/combustion to initiate and become established without the detrimental effects of cross winds and the like.

The input end portion 14a includes a flange 16 for attachment to a flare stack (not shown) or like structure depending on its use as is known in the art. In other embodiments, input end portion 14a may be eliminated and the offset portion 14b may include a flange for attachment to the flare stack. The input end portion 14a and the exhaust end portion 14c are substantially vertically oriented and the offset portion 14b angularly connects the two. In other words, the offset portion 14b laterally shifts the exhaust end portion 14c in order to accommodate an ignitor 28 and retractable support shaft 30 which are centrally located in the described embodiment and described further below. In addition to allowing for the ignitor 28 to be centrally located within the outer shell 12, the offset feature facilitates removal of the ignitor for service, replacement, etc. During such service or replacement, one or more secondary external pilots (not shown) may be provided in order to maintain proper operation of the hybrid flare assembly 10.

As further shown in FIGS. 1A-B, the hybrid flare assembly 10 includes a low pressure (LP) gas inlet 22, a first high pressure (HP) gas inlet 24, and a second HP gas inlet 26. It should be noted that the second HP gas inlet 26 provides an optional improvement to overall flare performance and may be removed from certain embodiments of the invention.

As noted and shown in FIG. 2, waste gas inlet 22 receives a low pressure (LP) waste gas flow 84 or an LP waste gas. LP waste gas is typically a vapor that forms above a liquid crude oil storage tank 86. Such storage tanks are typically fabricated of thin gauge sheet metal that is not designed to withstand high internal vapor or high vacuum pressures. When the storage tank pressure exceeds a predetermined internal value, for example 0.5 psig, a pressure relief valve 88 is manually or automatically opened to release LP waste gas from the storage tank. The released LP waste gas 84 is conducted to and through LP waste gas inlet 22 and to the flare assembly 10 for disposal.

As amplified in FIGS. 3A and 3B, the ignitor 28 is mounted to a retractable shaft 30 which is positioned at least partially within a guide tube 32. The retractable shaft 30 and mounted ignitor 28 may be inserted or retracted within the guide tube 32, as shown by action arrow A, or completely removed through the tube for maintenance or repair. While a pulley system is contemplated to insert or retract the retractable shaft 30, retractable shafts/ignitors are generally known in the flare art. Any such known arrangement may be utilized to provide retraction of the shaft/ignitor, including manual or automated arrangements.

As best shown in FIG. 3A, the guide tube 32 also supports a support plate 34. The support plate 34 is perforated, i.e., it includes a plurality of through-bores 36a-36h, as illustrated in FIG. 4. The support plate 34 in turn supports a plurality of waste gas risers 38a-h arrayed around the guide tube 32, the ignitor 28, and the retractable shaft 30 which together form an inner tip assembly 40. Although the described embodiment includes eight waste gas risers, more or fewer may be utilized in other embodiments. As described in more detail below, the waste gas risers 38a-h conduct a high pressure (HP) waste gas flow 90, or an HP waste gas, that entered the flare assembly 10 via HP waste gas inlet 24, to a pilot flame created by the ignitor 28 for combustion.

As shown in FIGS. 5 and 6, the guide tube 32 and the inner tip assembly 40 are at least partially enclosed by a shell 42. The support plate 34 divides the shell 42 into first and second portions 44 and 46. The first shell portion 44 extends above the support plate 34 and partially defines a first chamber 48. The first chamber 48 is further defined by an upper portion of the guide tube 32 which it encompasses along with the inner tip assembly 40. The second shell portion 46, on the other hand, extends below the support plate 34 and partially defines a second chamber 50. The second chamber 50 acts as a reservoir for HP waste gas 90 received via HP waste gas inlet 24 through aperture 52. HP waste gas is typically the associated gas, i.e., the gas that comes up with oil when drilling for oil, whether intended or not. The HP waste gas 90 is conducted from the second chamber 50 through the support plate bore holes 36a-36h and gas risers 38a-38n and exhausted near an upper end 54 of shell 42. Similarly, the first chamber 48 acts as a reservoir for LP waste gas 84 received via LP waste gas inlet 22 through aperture 55 as shown in FIGS. 1A and 5. The LP waste gas 84 is conducted through the first chamber 48 and exhausted near the upper end 54 of shell 42 where the LP waste gas is mixed with the HP waste gas for combustion.

With further reference to FIG. 6, it is important to note that the input end portion 14a and the exhaust end portion 14c extend along substantially parallel longitudinal axes (e.g., axes 60 and 58 respectively). In the described embodiment, the longitudinal axes are generally vertical which coincides with a flare stack extending from the ground. Meanwhile, the offset portion 14b extends angularly to connect the input end portion 14a and the exhaust end portion 14c in an offset manner. Neither the particular angle (B) of the offset portion 14b nor the distance (D) between central axes 60, 58 of the input end portion 14a and the exhaust end portion 14c matter so long as the distance between the central axes is sufficient to accommodate movement of the central ignitor 28 and retractable shaft 30 within the guide tube 32 as exemplified by action arrow A in FIG. 3B. It should be noted, however, that angle (B) between the offset portion 14b and the exhaust end portion 14c is an acute angle.

As generally referenced above, the flare assembly 10 includes a second HP gas inlet 26. As shown in FIG. 7, the second HP waste gas inlet 26 is in fluid communication with a manifold 60 and a waste gas conduit (not shown) connected to flange 62. The manifold 60 is an HP waste gas manifold which conducts and distributes a second HP waste gas flow 92, or a second HP waste gas, to a combustion chamber (generally designated reference numeral 64) via a plurality of waste gas risers 66a-k. Although the described embodiment includes eleven waste gas risers 66, more or fewer may be utilized in other embodiments. The plurality of waste gas risers 66a-k are supported by the manifold 60 and arrayed about the ignitor 28. The second HP waste gas 92 is conducted through the waste gas risers 66a-k and exhausted near the upper end 54 of shell 42 where the LP waste gas 84 and the first HP waste gas 90 are mixed with the second HP waste gas for combustion.

Turning to FIG. 8, the manifold 60 and plurality of waste gas risers 66a-k are shown supported by tabs 68 (only partially visible) extending from the outer shell 12 such that the manifold/waste gas risers are concentrically arrayed about the shell 42 and inner tip assembly 40. In this position, the waste gas risers 66a-k are further supported by exhaust end portion 14c of the outer shell 12. More specifically and as best shown in FIG. 1A, the waste gas risers 66a-n are supported by a first plurality of semi-circular cutouts 70 formed along an upper edge 72 of a lower portion 74 of the exhaust end portion 14c. The plurality of cutouts 70 are dimensioned and adapted to nestingly receive a lower portion of each of the waste gas risers 66a-k such that each waste gas riser traverses outer shell 12. An upper portion 76 of the exhaust end portion 14c includes a second plurality of semi-circular cutouts 78 formed along a lower edge 80 for receiving an upper portion of the waste gas risers 66a-k. The waste gas risers 66a-k may engage the first and second plurality of cutouts 70, 78 in a sealed manner to minimize or eliminate the escape of any motive gas from the shell 12.

Returning to FIG. 9, shield 82 is attached to ears 18a-f and supported by the upper end 76 of the exhaust end portion 14c of the shell 12. As best shown in FIG. 6, an upper edge 84 of shield 82 extends beyond an upper edge 86 of the exhaust end portion 14c. While there is no particular distance the shield 82 needs to extend beyond the upper edge 86, the purpose of the extension is to minimize, if not eliminate, the detrimental effects of cross winds on initiation of combustion within the combustion chamber 64. As perhaps best shown in FIG. 7, the shield 82 partially defines the combustion chamber 64 for flare ignition/combustion to initiate and become established without the detrimental effects of cross winds.

As will be appreciated by the skilled artisan, a variety of additional devices and mechanisms may be involved in the flare operation process, including, without intending any limitation, sensors, valves, automated and manually operated controls, and others for, among other functions, controlling waste gas flows, waste gas sources, waste gas flow rates, etc. For example, one or more phase separators (e.g., water-oil-gas or gas-liquid) are commonly used and positioned upstream of the flare 10 between the drilling rig 98 and manifold 94. These additional devices and mechanisms are known in the art and exceed the scope of this disclosure, and are not discussed in detail herein.

In operation, when a flare operation is required, LP waste gas 84 passes through LP waste gas inlet 22 via aperture 58 into the first or upper chamber 48 and exits near ignitor 28 as schematically illustrated in FIG. 2. Similarly, HP waste gas 90 passes through HP waste gas inlet 24 via aperture 52 into the second or lower chamber 46. From there, the HP waste gas 90 is conducted through perforated riser plate 36 and waste gas risers 38a-k and, again, exits near ignitor 28. Also, a motivated air flow 106 passes through air duct 12 and exits near ignitor 28 to assist combustion of the LP and HP gases. Because the air flow 106 and HP and LP gases exit near the ignitor 28, the combustion chamber 64 provides a protected space for waste gas combustion to initiate and establish itself without external influence from cross-winds or the like. This is the case whether the waste gas is HP or LP.

At low flow rates, whether the waste case is HP or LP, combustion occurs predominately, if not completely, within the combustion chamber 64. In this situation, the hybrid flare 10 is operating in a combustor mode and the flame is predominately, if not entirely, maintained within the combustion chamber 64. When the flow rate of the waste gas increases beyond a certain threshold, the flame can no longer be fully maintained within the combustion chamber 64 and the flame will be partially visible from observation points around the hybrid flare 10. As the flow rate continues to increase, the flame will become longer and more visible, more and more resembling the flame of a traditional flare. This may be termed a combustor mode of operation. At waste gas flow rates exceeding a threshold, combustion/flame may be visible from an exterior of the hybrid flare assembly 10 more akin to the operation of a conventional flare. This may be termed a flare mode of operation. In such situations, the hybrid flare 10 is operating in a flare mode.

Although not required in all embodiments of the invention, the above-described hybrid flare assembly 10 includes a second HP gas inlet 26. This second HP gas inlet 26 allows the flare 10 to operate in first and second HP operating stages which are intended to improve overall flare performance. A common HP waste gas manifold 94 receives an HP waste gas flow 96 from a drilling rig or like upstream source. A pressure sensor 100 is associated with the common manifold 94 in order to determine a pressure of the HP waste gas in the manifold. Outputs from the pressure sensor 100 may be provided indirectly through a controller (not shown) or directly to first and second shut-off valves 102, 104 associated with the above-described first HP waste gas flow 90 and second HP waste gas flow 92 as shown in FIG. 2. Alternatively, the outputs may be wirelessly transmitted to the controller or valves, or otherwise as is known in the art depending upon relevant placement of the manifold, sensor, and valves, or merely design choice.

In operation, the second HP operating stage is engaged/disengaged dependent on the manifold pressure. Alternatively, the second HP operating stage may be engaged/disengaged when a measured gas flow rate and/or pressure of the HP waste gas 90, for example, at the first HP gas inlet 24, exceeds a threshold where the first HP stage of operation has reached capacity. The gas flow rate may be measured, downstream of the valve 102, by a flow meter (not shown) described herein and generally known in the art, or the pressure may be measured by a downstream pressure sensor and output to a controller.

Typically, the hybrid flare assembly 10 is operating at generally low flow rates wherein the first HP operating stage and an LP operating stage (LP waste gas disposal) are operating with the second HP operating stage disengaged. In this scenario, valves 88 and 102 are open and valve 104 is closed and HP waste gas 90 exits from waste gas risers 38a-h which, as noted above, are arrayed about and positioned closest to the ignitor 28. This arrangement achieves a high destruction and removal efficiency (DRE) even when flare gas flow rate (whether HP or LP) is low. In this first HP operating stage, HP waste gas is typically flowing at a normal pressure threshold.

When HP waste gas flow exceeds a certain pressure threshold, for example 25 psig or more, the second HP operating stage is also engaged opening valve 104 and conducting HP waste gas 92 through the second HP waste gas inlet 26, manifold 60, and waste gas risers 66a-k. Again, the HP waste gas 92 exits in an arrayed manner about the waste gas risers 38a-h and still near ignitor 28 as best shown in FIG. 8. This approach maintains satisfactory DRE even at the higher waste gas flow rates. When the HP waste gas pressure decreases, for example to 0.5 psig or below, the second HP operating stage may be discontinued by closing valve 104 with the hybrid flare assembly 10 operating with only the first HP operating stage enabled. Of course, the noted 25 psig and 0.5 psig thresholds may vary depending on many factors and the present invention and first and second HP operating stages are not intended to be limited to these thresholds.

The foregoing has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the embodiments to the precise form disclosed. Obvious modifications and variations are possible in light of the above teachings. All such modifications and variations are within the scope of the appended claims when interpreted in accordance with the breadth to which they are fairly, legally and equitably entitled.

Claims

1. A hybrid flare assembly for waste gas combustion, comprising: a shell defining a duct, the shell including an exhaust portion extending from an offset portion; andan ignitor for igniting the waste gas, the ignitor mounted to a shaft for longitudinal movement within the exhaust portion, wherein an angle between longitudinally extending lines of the exhaust portion and the offset portion is acute.

2. The hybrid flare assembly of claim 1, wherein the longitudinal movement of the ignitor and shaft occurs at least partially within a guide tube extending substantially along a centerline of the exhaust portion.

3. The hybrid flare assembly of claim 1, wherein the exhaust portion of the shell partially defines a combustion chamber and the ignitor is supported within the combustion chamber.

4. The hybrid flare assembly of claim 1, wherein the shell further includes an input portion extending from the offset portion.

5. The hybrid flare assembly of claim 1, further comprising a flare stack attached to the shell, wherein the flare stack and the exhaust portion are substantially parallel.

6. The hybrid flare assembly of claim 1, further comprising a first plurality of risers at least partially arrayed about the ignitor shaft for conducting high pressure gas from a first high pressure inlet to a combustion chamber partially defined by the exhaust portion of the shell.

7. The hybrid flare assembly of claim 6, further comprising a second shell partially defining a first chamber through which low pressure gas conducts and a second chamber separated from the first chamber by a support plate having a plurality of holes formed therein through which high pressure gas conducts into the first plurality of risers.

8. The hybrid flare assembly of claim 7, further comprising a guide tube within which the ignitor and the ignitor shaft move, wherein the guide tube extends longitudinally within and through the second chamber of the second shell.

9. The hybrid flare assembly of claim 3, further comprising a shield attached to the shell and partially defining the combustion chamber.

10. The hybrid flare assembly of claim 9, wherein an upper edge of the shield extends above an upper edge of the exhaust portion.

11. The hybrid flare assembly of claim 6, further comprising a second plurality of risers at least partially arrayed about the first plurality of risers for conducting high pressure gas from a second high pressure inlet to the combustion chamber.

12. The hybrid flare assembly of claim 11, further comprising a manifold for conducting high pressure gas from the second high pressure inlet to each of the second plurality of risers.

13. The hybrid flare assembly of claim 11, further comprising a shield attached to the shell and partially defining the combustion chamber.

14. The hybrid flare assembly of claim 13, wherein an upper edge of the shield extends above an upper edge of the exhaust portion.

15. A hybrid flare assembly for waste gas combustion, comprising: a shell defining a duct, the shell including an exhaust portion extending from an offset portion;an ignitor for igniting the waste gas, the ignitor mounted to a shaft for longitudinal movement within the exhaust portion; anda first plurality of risers at least partially arrayed about the ignitor shaft for conducting high pressure gas from a first high pressure inlet to a combustion chamber.

16. The hybrid flare assembly of claim 15, wherein the exhaust portion of the shell partially defines the combustion chamber and the ignitor is supported within the combustion chamber.

17. The hybrid flare assembly of claim 15, further comprising a flare stack attached to the shell.

18. The hybrid flare assembly of claim 15, further comprising a guide tube within which the ignitor and the ignitor shaft move.

19. The hybrid flare assembly of claim 15, further comprising a shield attached to the shell and partially defining the combustion chamber.

20. The hybrid flare assembly of claim 15, further comprising a first plurality of risers at least partially arrayed about the ignitor shaft for conducting high pressure gas from a first high pressure inlet to a combustion chamber.

21. The hybrid flare assembly of claim 20, further comprising a second shell partially defining a first chamber through which low pressure gas conducts and a second chamber separated from the first chamber by a support plate having a plurality of holes formed therein through which high pressure gas conducts into the first plurality of risers.

22. The hybrid flare assembly of claim 20, further comprising a manifold for conducting high pressure gas from a second high pressure inlet through a second plurality of risers to the combustion chamber.

23. A hybrid flare assembly for waste gas combustion, comprising: a flare stack;a shell attached to and extending from the flare stack, defining a duct, and including an offset portion and an exhaust portion;an ignitor for igniting the waste gas, the ignitor mounted to a shaft for longitudinal movement within the exhaust portion of the shell; anda first plurality of risers at least partially arrayed about the ignitor shaft for conducting a first gas flow from a first inlet to a combustion chamber.

24. The hybrid flare assembly of claim 23, further comprising a manifold for conducting a second gas flow from a second inlet through a second plurality of risers at least partially arrayed about the ignitor shaft to the combustion chamber.

25. The hybrid flare assembly of claim 24, further comprising a common manifold for receiving a common waste gas stream, and first and second valves for controllably releasing the first gas flow to the first inlet and the second gas flow to the second inlet.

26. The hybrid flare assembly of claim 23, wherein the flare stack and the exhaust portion are substantially parallel and the intermediate portion is angled relative to the exhaust portion.

27. The hybrid flare assembly of claim 23, further comprising a second shell partially defining a first chamber through which a third gas flow conducts and a second chamber separated from the first chamber by a perforated support plate through which the second gas flow conducts into the first plurality of risers.

28. The hybrid flare assembly of claim 23, wherein the exhaust portion of the shell partially defines the combustion chamber and the ignitor is centrally supported within the combustion chamber.

29. The hybrid flare assembly of claim 27, further comprising a shield attached to the shell and partially defining the combustion chamber.

30. A method of combusting waste gas by a flare, comprising the steps of: conducting a low pressure gas flow from a low pressure gas inlet to a combustion chamber;conducting a first high pressure gas flow from a first high pressure gas inlet to a first plurality of risers at least partially arrayed about an ignitor shaft;conducting a second high pressure gas flow from a second high pressure gas inlet to a second plurality of risers at least partially arrayed about the first plurality of risers and the ignitor shaft to the combustion chamber;mixing the low pressure gas flow, and the first and second high pressure gas flows with an air flow; andcombusting the mixed low pressure gas flow, the first and second high pressure gas flows, and the air flow within the combustion chamber.

31. The method of combusting waste gas by a flare of claim 30, wherein the step of conducting a second high pressure gas flow is performed only when a measured gas flow rate or pressure exceeds a first threshold.

32. The method of combusting waste gas by a flare of claim 30, wherein the step of conducting a second high pressure gas flow is discontinued when a measured gas flow rate or pressure falls below a second threshold.

33. The method of combusting waste gas by a flare of claim 30, wherein the step of conducting a low pressure gas flow from a low pressure gas inlet to a combustion chamber includes the step of conducting the low pressure gas from the low pressure gas inlet, through a shell defining a duct, and to the combustion chamber.

34. The method of combusting waste gas by a flare of claim 33, wherein the shell includes an exhaust portion extending from an offset portion, and the first and second plurality of risers are at least partially contained within the exhaust portion of the shell.

35. The method of combusting waste gas by a flare of claim 33, wherein the shell includes an exhaust portion attached to an offset portion at an angle sufficient to allow a retractable ignitor to move longitudinally within an interior of the exhaust portion.

36. The method of combusting waste gas by a flare of claim 30, further including the step of controllably releasing the first high pressure gas flow and the second high pressure gas flow from a common manifold receiving a common waste gas stream dependent upon a pressure or flow rate.