VARIABLE FLOW NOZZLE FOR A BURNER ASSEMBLY

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 63/685,878, filed Aug. 22, 2024, which is hereby incorporated herein by reference in its entirety.

BACKGROUND

The Environmental Protection Agency (EPA) identifies and regulates emissions that may harm humans or the environment in the United States. Volatile organic compounds (VOCs) and methane are included in the list of regulated emissions established by the EPA. Oil and gas production, processing, storage, and transmission generate off-gases that contain VOCs and methane, which escape into the atmosphere.

Disposal methods have included flares and flare stacks to burn the off-gases, reducing them to combustion byproducts that can more safely be released into the atmosphere. Problems remain, however, for such flares and flare stacks. For example, rates of off-gas removal from natural gas may vary over time as natural gas of varying composition is removed from a well. These variations can result in unpredictable and inconsistent performance of a flare or flare stack, especially those with burners or burner assemblies having valves with fixed flow rates.

Current combustion devices typically have low turndown ratios of only 4:1 or 5:1. Outside this flow range, the combustor does not perform efficiently, as it can either exhibit low hydrocarbon destruction efficiency or produce visible emissions, such as smoke or soot. Burners typically operate at a rich stoichiometry since the gas flowing through the nozzle is 100% fuel, and it must mix with air outside the nozzle before it can burn. Low pressures yield low fuel velocities out of the nozzle, poor mixing, and poor combustion, which limits the turndown ratio of a fixed orifice nozzle.

The most common method to increase the turndown ratio of combustors is to add forced air with a device, such as a fan or blower. Air assist leans the fuel-air mixture by providing better mixing through increased energy from the forced air supply, resulting in higher destruction efficiency and no visible smoke. Due to the addition of components and complexity, air-assisted combustors are more expensive than their naturally aspirated counterparts. They require significant electrical power to operate the blower, neither of which is desirable

To solve these problems, a method and apparatus are needed to increase the combustor's turndown ratio, thus providing efficient destruction without increasing the system's cost or complexity. It is to such an apparatus and method that the inventive concepts disclosed herein are directed.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

To assist those of ordinary skill in the relevant art in making and using the subject matter hereof, reference is made to the appended drawings, which are not intended to be drawn to scale and in which, like reference numerals, are intended to refer to similar elements for consistency. For clarity, not every component may be labeled in every drawing.

FIG. 1 is a diagrammatic view of a burner assembly.

FIG. 2 is a sectional, perspective view of the burner assembly.

FIG. 3 is a perspective view of a nozzle constructed in accordance with the inventive concepts disclosed herein.

FIG. 4 is a cross-sectional view of the nozzle of FIG. 3.

FIG. 5 is a partial cutaway, perspective view of the nozzle of FIG. 3.

FIG. 6 is a cross-sectional view of the nozzle shown in an open condition.

FIG. 7 is a perspective view of a flexure spring.

FIG. 8 is a graph comparing the linear shear length of fixed-area and variable-area flow orifices for a given flow area.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Before explaining at least one embodiment of the inventive concepts disclosed herein in detail, it is to be understood that the inventive concepts are not limited in their application to the details of construction and the arrangement of the components or steps or methodologies set forth in the following description or illustrated in the drawings. The inventive concepts disclosed herein are capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting the inventive concepts disclosed and claimed herein in any way.

In the following detailed description of embodiments of the inventive concepts, numerous specific details are set forth in order to provide a more thorough understanding of the inventive concepts. However, it will be apparent to one of ordinary skill in the art that the inventive concepts within the instant disclosure may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid unnecessarily complicating the instant disclosure.

As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having,” and any variations thereof are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements and may include other elements not expressly listed or inherently present therein.

Unless expressly stated to the contrary, “or” refers to an inclusive or and not to an exclusive or. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B is true (or present).

In addition, the use of the “a” or “an” is employed to describe elements and components of the embodiments disclosed herein. This is done merely for convenience and to give a general sense of the inventive concepts. This description should be read to include one or at least one, and the singular also includes the plural unless it is obvious that it is meant otherwise.

As used herein, qualifiers like “substantially,” “about,” “approximately,” and combinations and variations thereof, are intended to include not only the exact amount or value they qualify but also some slight deviations therefrom, which may be due to manufacturing tolerances, measurement error, wear and tear, stresses exerted on various parts, and combinations thereof, for example.

Finally, as used herein, any reference to “one embodiment” or “an embodiment” means that a particular element, feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. The appearances of the phrase “in one embodiment” in various places in the specification do not necessarily all refer to the same embodiment.

Referring now to FIGS. 1 and 2, an exemplary burner assembly 100 constructed in accordance with one embodiment of the present disclosure, is illustrated. The burner assembly 100 has a burner 108 in the form of a tube 112, an ignitor 120, and a nozzle 200. The burner assembly 100 is further illustrated with the fuel supply 220 connected to the burner assembly 100 and, more specifically, to the nozzle 200 via fuel supply line 132. Fuel supply line 132 is equipped with shutoff valve 222, which is controlled by the electronic control module 122. The fuel source 220 may be any source of fuel, but it will generally include off-gases, such as combustible VOCs and BTEX, produced from various hydrocarbon processes, including natural gas dehydration.

Referring now to FIGS. FIGS. 3-5 illustrate one implementation of the nozzle 200, which may be a fuel nozzle that provides a variable area for fuel flow based on fuel pressure, as described further herein. The nozzle 200 has a nozzle body 302 having an inlet 304, an outlet 306, an outer surface 308, and an inner surface 310 that forms a passageway 312 through the nozzle body 302 from the inlet 304 to the outlet 306. The nozzle 200 has a valve member 314 with an upper portion 316 and a lower portion 318. The upper portion 316 may be sized and shaped to provide an annular gap between the valve member 314 and the outlet 306 when the valve member 304 is in its resting or closed position, thereby providing a minimum flow rate through the outlet 306. Alternatively, the upper portion 316 of the valve member 314 is sized and shaped to close or seal the outlet 306 when the valve member 314 is in the closed position.

The upper portion 316 is shown to be generally disk-shaped and has an annular seal surface 319. The lower portion 318 may be a stem for axially guiding the upper portion 316.

The nozzle 200 may further be provided with a guide 320, a bushing 322, a return spring 324, a spring retainer 326, a snap ring 328 that holds the spring retainer326 in place, a flexure spring 330, and a flexure spring retainer 332 that may be secured in place by a cap screw 334, for instance. Optionally, the nozzle 200 may include spring shims 336 as needed to set a spring force of the return spring 324 and damping devices 338a and 338b as necessary to prevent oscillation of the valve member 314.

The flexure spring 330 (best illustrated in FIG. 7) may be positioned near the outlet 306 to maintain annular alignment of the valve member 314 within the body 302 and the valve seat 350, which is also annular. Maintaining a uniform annular flow area around the circumference of the valve member 314 is critical for uniform combustion.

Optionally, the nozzle 200 may include spring shims 336 as needed to set a spring force of the return spring 324 and damping devices 338a and 338b as necessary to prevent oscillation of the lower portion 318 of the valve member 314. Damping might be required if pressure pulsations in the fuel stream cause unwanted oscillations in the nozzle. Damping can be achieved by hydraulic means, such as a shock absorber, or by a simple friction device, such as properly cleared O-rings, as illustrated in FIGS. 4-6.

Referring to FIGS. 1 and 2, in operation of the nozzle 200, fuel enters the nozzle body 302 through the inlet 304 and fills the passageway 312 of the nozzle body 302. The fuel enters the nozzle body 302, having a pressure that acts on a bottom side of the valve member 314, resulting in an upward force (force=pressure×area) on the valve member 314. This upward force is resisted by the weight of the valve member 314 and the spring force of the return spring 324. When the pressure force is sufficient to overcome the resisting force, the valve member 314 is moved between the closed position and the open position, allowing fuel to flow through the outlet 306 of the nozzle 200, where it is mixed with air in the burner 108 and ignited by the ignitor 120. In some applications, fuel may be supplied at varying pressures. The nozzle 200 automatically adjusts to these varying pressures, as will be described in further detail below

The return spring 324 has a spring constant (Ibf/inch) that increases the resisting force with displacement or movement of the valve member 314 between the closed position (FIGS. 3-5) and the fully open position (FIGS. 2 and 6). The result is that each fuel pressure gives a unique and repeatable position (lift) of the valve member 314 relative to the outlet 306. The outlet 306 is provided with a valve seat 350 configured to receive the valve member 314. The valve seat 350 and the valve member 314 are profiled or shaped such that the resulting flow area, as a function of lift, is precisely defined to give the desired lift versus flow area relationship.

In Simplified Terms, the Flow Through an Orifice Such as the Outlet 306 of the Nozzle Body 302 is Proportional to:

Q ∝(orifice flow area)×√(pressure differential across the orifice)

By defining the valve geometry (outlet 306 of the nozzle body 302) in relation to lift when designing the nozzle 200, the flow area can be precisely defined as a function of fuel pressure. This also allows the fuel flow curve through the nozzle 200 to be precisely defined.

The valve member 314 can either provide positive shut-off and seal or not. If the valve member 314 does not shut off completely, then a minimum defined flow rate of the nozzle 200 will be proportional to a minimum flow area (when the valve member 314 is seated) times the square root of the minimum pressure differential.

In an example in Table 1 below, a flow turndown ratio for a nozzle, such as the valve member 314 of the nozzle 200 that has an area increase from ‘x’ to ‘4×’ and a pressure range from ‘y’ to ‘9y’ is defined as:

Compare this flow turndown ratio (12:1) to that of a standard fixed orifice nozzle under the same conditions, which would have only a 3:1 turndown ratio.

A good mixing of fuel and air is a fundamental requirement for effective combustion. To this end, two (2) parameters define the performance of a fuel nozzle as it pertains to open-chamber combustion:

• • 1. sufficient exit velocity for good mixing; and
  • 2. sufficient (surface area)/(flow area) ratio for mixing.

Velocity is defined as the volume flow rate (Q) divided by the flow area of the orifice (V=Q/(Flow Area)). The fuel exiting the nozzle 200 must have sufficient velocity to penetrate and entrain the air required for combustion. If the velocity is too low, the fuel does not mix with sufficient air to support the complete combustion of the fuel, and smoke and soot can result. If the velocity is too high, the fuel is moving much faster than a flame speed can support, and the flame is extinguished, resulting in incomplete combustion of the fuel. Upper and lower limits exist for fuel exit velocity to support complete combustion best. The back pressure provided by the spring-loaded valve member 314 and the variable area of the nozzle 200 provide the correct velocity to support efficient mixing and complete combustion.

On a conventional flare, if a fixed nozzle orifice is sized for maximum flow rate at maximum fuel pressure, then the minimum flow with the fixed orifice would be limited to the velocity necessary to produce good mixing and combustion. The variable-area nozzle 200, on the other hand, provides significantly lower flow rates due to its reduced orifice area compared to the fixed orifice, while maintaining a velocity above the minimum allowed.

The second parameter to consider when designing a burner nozzle for optimal performance is the shear area-to-flow area ratio of a fuel jet exiting the nozzle. The more surface area the fuel has as it exits the orifice, the more air it will entrain, and the better the mixing will be. FIG. 8 illustrates the shear area for both fixed and variable area orifices. For a given total flow area, the smaller the orifice, the larger the number of orifices required to achieve the desired flow, and the greater the shear length it offers. This promotes better mixing. The variable-area orifice of the nozzle 200 offers an improvement in shear length, even over a large number of small orifices, 30 vs. 18, respectively, as shown in the graph in FIG. 8.

From the above description, it is clear that the inventive concepts disclosed herein are well adapted to carry out the objects and to attain the advantages mentioned herein, as well as those inherent in the inventive concepts disclosed herein. While presently preferred embodiments of the inventive concepts disclosed herein have been described for purposes of this disclosure, it will be understood that numerous changes may be made that will readily suggest themselves to those skilled in the art and which are accomplished within the scope and coverage of the inventive concepts disclosed herein.