Flare tip assembly

A high turn down ratio flare tip assembly, that allows for both low and high flowrate and pressure flows using a single flare. The flare assembly comprising a nozzle tube connected to the waste stream fuel inlet at one end. The other end of the flare tip assembly providing a seat for a conical structure with flow through orifices/ports that allow the waste stream to flow therethrough during low pressure operation. The conical structure connected to one end of a connecting rod, the connecting rod extending longitudinally downward through the nozzle tube and connected to a spring assembly. The flare tip assembly is designed to allow low flow and pressure to pass through the cone orifices, and during high flow and pressure operation, the cone is unseated from the nozzle tube, allowing the waste stream to flow therethrough. The flare tip assembly also includes a slotted/holed shroud that allows for smokeless combustion of the waste stream during high flow and pressure conditions.

Not applicable.

FIELD OF THE INVENTION

Embodiments disclosed herein relate generally to a flare tip assembly used in the combustion of gases in flare stacks for the destruction of combustible vapors in various applications, including those on oil and gas production pads, crude oil tank batteries, midstream liquified natural gas processing facilities, offshore platforms, and refining and petrochemical applications during normal and emergency operations, for efficient combustion of both low pressure vapors and high pressure vapors in a single stack, as the embodiments can safely flare both sub sonic and sonic flows.

While certain embodiments will be described in connection with the preferred illustrative embodiments shown herein, it will be understood that it is not intended to limit the invention to those embodiments. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the invention as defined by claims. In the drawing figures, which are not to scale, the same reference numerals are used throughout the description and in the drawing figures for components and elements having the same structure, purpose or function.

DETAILED DESCRIPTION

Turning now to the detailed description of the preferred arrangement or arrangements of various embodiments of the present invention, it should be understood that, although an illustrative implementation of one or more embodiments are provided below, the inventive features and concepts may be manifested in other arrangements and that the scope of the invention is not limited to the embodiments described or illustrated. The various specific embodiments may be implemented using any number of techniques known by persons of ordinary skill in the art. The disclosure should in no way be limited to the illustrative embodiments, drawings, and/or techniques illustrated below, including the exemplary designs and implementations illustrated and described herein. The scope of the invention is intended only to be limited by the scope of the claims that follow. Furthermore, the disclosure may be modified within the scope of the appended claims along with their full scope of equivalents.

While the making and using of various embodiments of the present disclosure are discussed in detail below, it should be appreciated that the present disclosure provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the disclosure and do not limit the scope of the disclosure.

As shown inFIGS.1-3, an embodiment of the present invention provides a flare tip assembly100that is capable of firing at very low rates and low pressure and firing during upset with high flow and high pressure without smoking, in order to follow federal and state regulations. The flare tip assembly100provides a high turndown ratio operation by adjusting the open area for gas flow automatically In one embodiment of the present invention, the flare tip assembly100is mounted on the top of new or existing flare stacks (not shown) and utilizes the various pressures of the waste stream to adjust the open area for proper fuel and air mixing.

As shown inFIGS.1-5, a flare tip assembly100according to an embodiment of the invention is provided for the combustion of vapors in a flare system. The flare tip assembly100is designed to safely and efficiently burn vapors, including hydrocarbon bearing waste and vent streams. The flare tip assembly100includes a nozzle tube101such as a machined pipe tapered on top to fit a machined cone104with a diameter based on flow area needed. This nozzle tube101is fitted for example with a flanged connection102(see e.g.,FIG.9D) or other suitable connection for mounting to an elevated flare stack (not shown). Opposite the flanged end102is a machined chamfered end103that is angled to allow the seating and sealing of the cone104in low pressure operations and to optimize waste and vent stream vapor flow. For example, the machined chamfered end103is can be angled between 15° and 80°, such as 30°, 45°, 60° and 75°, and other angles that can be used to optimize waste and vent stream vapor flow.

The nozzle tube101can include machined slots (not shown), spaced along the length of the nozzle tube101for attaching centering guides105. Within the nozzle tube101there is a connecting rod108that extends within the nozzle tube101along the nozzle tube101's longitudinal axis. The connecting rod108passes through the centering guides105installed in the nozzle tube101and extends into the spring assembly109. The connecting rod108also extends through an anti-rotation slotted guide119(FIGS.2,3,4and12) that is connected to a rotation stop rung120. In one embodiment the spring assembly109sets below the flanged end102of the nozzle tube101, which takes the spring assembly109below the flare's active flame, making it readily serviceable. See e.g.,FIG.9D. In another embodiment (not shown), the spring assembly109is located above the flanged end102. In another embodiment, a spring connection tube110encloses the spring assembly109. In a further aspect of this embodiment, at one end of the spring connection tube110a cap113is attached to the spring connection tube110. The type, design and material of spring assembly109can be the same or different depending on the flare tip design and gas stream properties. In one embodiment, single or multiple compression springs are used in the spring assembly109. See e.g.,FIG.5A. In another embodiment, a stack of disc springs is used to achieve the desired function. See e.g.,FIG.9D. In another embodiment (not shown), the spring assembly109, connection tube110and cap113are removed and the gravity force of the cone104and connecting rod108can still achieve the design functions.

At the end of the connecting rod108that is opposite to the spring assembly109, a cone shaped structure104is connected to the connecting rod108. In one embodiment, the cone104is attached to the connecting rod108by welding a substantially flat shaped cone104bottom to the connecting rod108, which is attached at the bottom center of the cone104. In other embodiments, the cone104is integrally formed with the connecting rod108, or the cone104is connected to the connecting rod108using a threaded connector, or the cone104is connected to the connecting rod108using a pinned connection, or the connecting rod108extends up through the cone104and is connected to the bottom of a concaved section112of the cone104body, or any combination thereof and the like. See e.g.,FIGS.3-8.

The cone104is preferably a machined cone with a concave top112having a taper with a cone angle of between 15° and 80°, such as 30°, 45°, 60°, 75° and other angles, from the top to the bottom. See e.g.,FIG.6. The cone104can be manufactured by many means such as casting, fabricated with tubes welded therein, 3-D printing or any other appropriate manufacturing methods. Sizing of the cone104is designed based on diameter of nozzle tube101and desirable flowrates at various inlet pressure. The transition from the concave top112to the taper is a rounded edge. In one embodiment of the present invention the cone has rounded smooth edges, which enhance the and help maintain a controlled frame profile. In a further aspect of any embodiment of the present invention, the cone tip diameter is sized to achieve designed flow across a wide range of capacities, and include cone diameters of 2-inch, 3-inch, 4-inch, 6-inch and 8-inch.

In one embodiment, the cone104is designed such that the tapered end sits within a seat formed by the chamfered end103of the nozzle tube101. See e.g.,FIGS.3,5A,9C,9E,13D. In one embodiment, the cone104includes tubular firing orifices111drilled from the bottom of the concaved top112through the cone104body and exiting along an outer surface of the cone104. The diameter, angle of attack, and total amount of firing orifices111are configured based on flowrate and size of the flare tip assembly100, to optimize fuel gas dispersion and air/fuel mixing. In one embodiment, the diameter of firing orifices111changes between 1/16 in and ½ in, including ⅛ in, 3/16 in, ¼ in, ⅜ in, and other sizes. In one embodiment, the total amount of firing orifices111changes between 2 and 12, including 4 (FIG.5A,7,9C),6(FIG.4,8),8,10, and other numbers. In a further aspect of an embodiment, the firing orifices111are drilled from the bottom of concaved top112through the cone104body and preferably exit at approximately half the height of the cone104. See e.g.,FIGS.3-8,9C. In another aspect of an embodiment, the orifices111are preferred to be axisymmetric and tangential to the cone104. See e.g.,FIGS.3-8,9C.

In an embodiment of the present invention, the cone104and tubular firing orifices111are configured to minimize the use of purge gas and/or velocity reduction devices in order to prevent bum back inside the nozzle tube101and flare stack (not shown). For example, in an embodiment of the present invention, no or minimum purge gas is required. In an embodiment of the present invention, the tip design minimizes and or does away with the need of purge gas and/or velocity seals used to prevent the back flow of combustible gases back into the nozzle tube101and flare stack (not shown) during low fire conditions, For example, in one embodiment this is achieved due to the cone104shape with the concave top112, with a cone104angle of between 15° and 80°, along with the multiple tangential tubular orifices111that pass through the cone104body starting in the concave face112and passing through the cone104at an angle. See e.g.,FIGS.3-8,9C. The combination of these firing orifices111and the sealing of the cone104to the chamfered end103at low flowrate, means that the flow must pass through the firing orifices111where in one embodiment, by size and position they achieve a length over diameter of greater than two, which can help prevent the propagation of the flame front back through the firing orifices111even at very low pressures.

Around the perimeter of the nozzle tube101there are gusset halves106for lower shroud107mounting. See e.g.,FIGS.1-3,9B. In one embodiment, the shroud assembly can include two parts-the upper114and lower shroud107. In one embodiment, the shrouds107,114are tubular. In another embodiment, the shrouds107,114are approximately twice or three times the diameter of the nozzle tube101. In one embodiment, the lower shroud107is positioned with mounting gussets117so that nozzle tube101is placed at the center of lower shroud107and the bottom of lower shroud107is approximately twelve to twenty-four inches below the exit of the nozzle tube101. See e.g.,FIGS.3-8,9A,9B. The mounting gussets106can be outside of lower shroud107as inFIG.1-3or inside as inFIGS.9A and9B. The lower shroud107also contains the pilot hood116extending from its side at a 45°-degree angle. The pilot hood116allows for the pilot flame to intersect the fuel exit area between the nozzle tube101and cone104. See e.g.,FIGS.13A-13D. This covered pilot design prevents excessive wear and damage of the pilot assembly. The upper shroud114is attached to the top of the lower shroud107with mating flanges118and extends upwards some distance. In one embodiment, the distance or height of the upper shroud114is based on flow rate and flare size. For example, to address the issue of the flame being affected by wind and to help induce more efficient mixing, in one embodiment of the present invention a larger/longer shroud114can be used, for example going from a 12″ shroud height to 36″ shroud height. In one embodiment of invention, using a shroud114having a larger length over diameter (LID) ratio provides better fuel and air mixing, which allows for more stable combustion before the mixture is dispersed by wind. Exemplar features of various flare tip embodiments of the present invention are shown below in Table 1.

TABLE 1ConeConeShroudNumber ofShroudOrificeOrifice Angle.TIP SizeAngleHeightOrificesL/DDiameterof AttackHTDR-Mini2″15° to 80°25′4 to 103 to 61/16″ to ½″30° to 60°HTDR-13″15° to 80°35′4 to 103 to 61/16″ to ½″30° to 60°HTDR-24″15° to 80°45′4 to 103 to 61/16″ to ½″30° to 60°HTDR-36″15° to 80°65′4 to 103 to 61/16″ to ½″30° to 60°HTDR-48″15° to 80°85′4 to 103 to 61/16″ to ½″30° to 60°

In one embodiment, there are a number of spaced openings115around the perimeter of the top of the upper shroud114. See e.g.,FIGS.1-3,10,11. In a further aspect of this embodiment, the upper shroud114includes equally spaced openings115around the perimeter of the top of the upper shroud114. The spacing and total numbers of spaced openings115varies depending on flare size. The design of the upper shroud114with spaced openings115not only enhances stability of the flame front but helps to negate some of the effects of crosswinds. In one embodiment, the upper shroud114includes multiple rows of spaced openings115. In this embodiment, during for example high fire situations, the multiple rows of spaced openings115allow more air to be induced in the mixture allowing for complete combustion, thus promoting smokeless performance.

The shape of the tapered cone104with a concave top112, and use of the tangential firing orifices111, and use of upper shroud114with openings115, aid to induce a vortex flow which creates more turbulence when mixing the fuel stream with the annular air flow between the nozzle tube101and lower shroud107, thus allow for a stable flame attachment in both low and high pressure flow conditions, providing a high turndown ratio configuration, See e.g.,FIGS.1-3,10,11. In a further aspect of an embodiment of the present invention, the cone104design directs fuel flow outward at a predetermined angle for optimized mixing and interaction with the shroud107,114, which creates a unique and efficient flow pattern that is carried throughout the flare firing range resulting in a stable, smokeless operation.

In one embodiment, during normal low-pressure operation the fuel, such as a hydrocarbon-based waste stream, is introduced to the fuel inlet on the base of an elevated flare stack (not shown) and will travel up through the stack and exit out of the nozzle tube101/cone104assembly. In one embodiment, if this is a low-pressure stream, for example less than one pound per square inch gauge (PSIG) pressure, the cone104is completely seated at the chamfered end103of nozzle tube101, with the fuel stream only passing through the firing orifices111. This low-pressure flow is ignited as it exits the firing orifices111by the pilot and the concave top112of the cone104is designed to further create a low-pressure zone of recirculation to maintain stability. Air is drawn into the bottom of the lower shroud107in a low-pressure case as the result of a draft created from heating the air inside the shroud107. In one embodiment, the spring assembly109is configured allow cone104to move upward and unseat from the chamfered end103of nozzle tube101as the pressure is increased inside the nozzle tube101. See e.g.,FIGS.1-3,9D. In this embodiment, cone104will begin move upward creating an annular orifice around the perimeter of the cone104and the exit of the nozzle tube101, while also applying some tension to the spring assembly109. Fuel gas stream now exits through both the annular orifice mentioned above and the firing orifices111. Once the pressure exceeds a predetermined value, for example approximately eight PSIG, the cone104is fully extended and the effective annular orifice open area is equal to the open area of the nozzle tube101. As the cone104begins to rise the pressure of the fuel gas will begin to create a venturi effect at the air inlet to the shroud107pulling a certain percentage of the needed combustion air into the shroud107and114, thus creating a partial premix condition. The partial premix in conjunction with the variable annular orifice between tapered surface of cone104and chamfered end103of nozzle tube101, firing orifices111and shroud107,114allow better fuel dispersion and fuel/air mixing, creating a very stable smokeless operation across a wide range of fuel gas pressure.

Referring toFIGS.13A-13D, depicted are example flow contours that depict the flow of C3H8(propane) in millions of standard cubic feet per day (MMSCFD) through a flare tip assembly embodiment of the present invention and travel of the cone104away and unseated from the nozzle tube101as the flow rate is increased. These flow contours are calculated by using advanced Computational Fluid Dynamics (CFD) simulation. As depicted the C3H8flow rate increases respectively inFIGS.13A-13D. And as the flow increase, for example, 4.05 MMSCFD inFIG.13Aand 13.36 MMSCFD inFIG.13D, the cone104is completely unseated inFIG.13Das compared to the location of the cone104within the nozzle tube101as depicted inFIGS.13A-13C. As also depicted, the flow is substantially uniform.

Above certain fuel pressure which is enough to overcome the spring tension and gravitational force of cone104, rod108and spring assembly109, the cone104tip will lift up creating more open area for the gas flow. The lifting distance of cone104is related to fuel pressure allowing for a design that adjusts the open area for various conditions while also being capable of firing variable range of fuels compositions. The flare tip assembly100is designed so that the cone104will start to lift and rise until full open within an appropriate gas pressure range, achieving better fuel/air mixing and also preventing high upstream back pressure. To create more tension in order to keep the cone104tip from becoming fully open at a low pressure stiffer springs should be used in the system. For example, in an embodiment of the present invention, six (6) polywave springs can be used for the spring assembly109. For example, during testing, using six (6) polywave springs, the system became fully open at about 4-5 PSIG. In a further aspect of an embodiment of the present invention, the configuration of the spring assembly109, and cone104design yield a larger turndown capability, keeping the fuel gas exit velocity within the design range by preventing the system from opening fully too early. The spring assembly109is designed to have a spacer (not shown) that will allow variable tension loading to add more flexibility.

In one embodiment, this apparatus, when mounted on an elevated flare stack (not shown) facilitates the mixing of fuel and air across a wide range of fuel pressures, allowing for the efficient combustion of the fuel stream, with ninety-eight percent (98%) or higher destruction efficiency and with no visible smoke. In a further aspect of an embodiment of the present invention, the flare tip assembly100including cone104, firing orifices111, spring assembly109and shroud114with openings115is designed based on the maximum flow rate that is required and the maximum available gas pressure, while maintaining acceptable gas velocity at exit of shroud114.

In one embodiment of the present invention, the flare tip assembly100provides a greater than 200 to 1 turndown ratio of the flare. In a further aspect of an embodiment of the present invention, the cone104geometry design and inclusion of firing orifices111allows for accommodating low and high-pressure vent gas eliminating the need for multiple flares (e.g., a low-pressure flare assembly and a high-pressure flare assembly). See e.g.,FIG.14. For example, as shown inFIG.14, a flare capacity curve for a flare tip assembly in accordance with an embodiment of the present invention shows that the single flare tip assembly can operate at a pressure range of 0 to 30 psig with a volumetric gas flow of 0 to approximately 24 MMSCFD, as opposed to requiring multiple flare assemblies to operate over this range. Moreover, the single flare tip assembly of an embodiment of the present invention can operate over this range while meeting emission requirements. For example, a small traditional flare would operate in the curve125region, a medium traditional flare would operate in the126region, and a large traditional flare would operate in the127region.

Further examples of flare capacity curves for various single flare tip assemblies in accordance with an embodiment of the present invention are shown inFIGS.15-19. As shown inFIGS.15-19, curve A represents a light fuel gas having a lower heating value (LHV) of 1067.87 btu/scf and a molecular weight (MW) of 20.62, curve B represents the a medium fuel gas having a lower heating v alue (LHV) of 1542.99 btu/scf and a molecular weight (MW) of 31.28, and curve C represents a heavy fuel gas having a lower heating value (LHV) of 2250.96 btu/scf and molecular weight (MW) of 43.47. For example, as shown inFIG.15, the Flare-Mini flare tip assembly in accordance with an embodiment of the present invention can operate at a pressure range of 0 to 50 psig with a volumetric gas flow of 0 to approximately 4.4 MMSCFD for a light fuel gas.

As shown inFIG.16, the FLARE-1 flare tip assembly in accordance with an embodiment of the present invention can operate at a pressure range of 0 to 40 psig with a volumetric gas flow of 0 to approximately 8.8 MMSCFD for a light fuel gas.

As shown inFIG.17, the FLARE-2 flare tip assembly in accordance with an embodiment of the present invention can operate at a pressure range of 0 to 30 psig with a volumetric gas flow of 0 to approximately 13 MMSCFD for a light fuel gas.

As shown inFIG.18, the FLARE-3 flare tip assembly in accordance with an embodiment of the present invention can operate at a pressure range of 0 to 30 psig with a volumetric gas flow of 0 to approximately 29 MMSCFD for a light fuel gas.

As shown inFIG.19, the FLARE-4 flare tip assembly in accordance with an embodiment of the present invention can operate at a pressure range of 0 to 30 psig with a volumetric gas flow of 0 to approximately 50 MMSCFD for a light fuel gas.

In a further aspect of an embodiment of the present invention, the upper shroud114length, openings115quantity, size, and placement further allow for accommodating low and high-pressure vent gas eliminating the need for multiple flares (e.g., a low-pressure flare assembly and a high pressure flare assembly).

This flare tip assembly100can be used in a wide range of applications and in certain situations negate the need for multiple flares or pieces of combustion equipment as it can safely flare both sub sonic and sonic flows. It would be suited for applications including those on oil and gas production pads, crude oil tank batteries, midstream liquified natural gas processing facilities, offshore platforms, and refining and petrochemical applications. Embodiments of the present invention can be used in conjunction with other smoke-reducing technologies, such as air-assisted flare, steam-assisted flare for handling heavier fuels and other applications that have poor air/fuel mixing. As mentioned earlier, embodiments of the present invention can be installed on flare stacks for elevated flares. Furthermore, they can also be used for ground flares, enclosed combustors and other combustion devices including thermal oxidizers, etc. Serial and/or parallel uses of multiple embodiments of the present invention can be arranged for applications such as multi-point ground and/or elevated flaring.