Abstract:
A multiphase burner for flaring gaseous/liquid combustible mixtures is disclosed. The burner may include a hollow base with an inlet for receiving the combustible gas/liquid mixture as well as a distal end that may be coupled to or that forms a nozzle cap. The nozzle cap may form as first outlet. The base may be coupled to a central body and a hollow bushing that encircles at least part of the central body. The base may form a mouth disposed between the inlet and the central body. The mouth may be in communication with a first passage that extends from the mouth to the first outlet and between the bushing and the distal end of the base. The mouth may be in communication with a second passage that extends from the mouth to the second outlet and between the bushing and central body.

Description:
BACKGROUND 
       [0001]    Flare apparatuses in the form of a flare stack and one or more burners or ground-level flares in earthen pits are known and are used for burning combustible gases. Flare apparatuses are commonly used for disposing of flammable waste gases or other flammable gas streams in oil and gas production and refining, chemical plants, pipelines, liquefied petroleum and natural gas terminals, etc. 
         [0002]    For example, oil and gas wells are tested by burning or “flaring” well fluid at the surface. The well fluid may be comprised of hydrocarbon gases, such as natural gas, oil and formation water. The term “wet gas” is commonly used for such well fluids. One problem associated with flaring of wet gas on offshore platforms is the radiant heat produced by flaring the wet gas and the effect of the radiant heat on the personnel and equipment disposed on the platform. Other problems include smoke formation and hydrocarbon fallout. 
         [0003]    Specifically, it is generally desirable that the wet gas be flared without producing smoke and typically such smokeless or substantially smokeless flaring is mandated by regulatory agencies. Fallout of unburned hydrocarbons can occur when the wet gas being flared does not burn completely or cleanly. The resulting smoke and unburned hydrocarbon fallout may create both environmental and safety concerns as the unburned hydrocarbons may be disposed in liquid droplets that ultimately fall out of the ambient air onto the surface of the platform or the ocean. 
         [0004]    Smokeless and fallout-free flaring of wet gas can be achieved by supplying additional air (i.e., air-assisted flaring) or steam (i.e., steam-assisted flaring) to the burner, which can result in a complete oxidation of the wet gas. However, at high flow rates of the wet gas, providing the optimal supply of air or steam for premixing upstream of the burner through pumps or blowers can become impractical or impossible, especially on offshore platforms or remotely located land-based drilling rigs. In contrast, when a highly turbulent jet of combustible wet gas is created in an open-air burner that does not require premixing, most of the requisite combustion air can be obtained from the ambient atmosphere near the flame. The design of such open-air burners is based on a maximum entrainment of ambient air into a high-pressure jet emitted through the burner head. 
         [0005]    Further, the use of open-air burners for the combustion of wet gas would require spraying or atomizing of the liquid component that is carried by the input flow. The atomizing would be followed by mixing of the gas and atomized liquid with ambient air, which would create a mix suitable for clean flaring. While known atomizing nozzles are efficient if high-pressure gas and liquid flow are supplied through separate ducts, the wet gas for gas flaring at a rig site is a mixture of gas and liquid delivered to a flare apparatus together and in time-variable and unpredictable proportions. As a result, existing atomization nozzles cannot be used for oil and gas flaring without a gas/liquid separator, which is impractical for most offshore platforms and many land based well sites. Further, existing atomization nozzles are noisy, which adversely affects the safety and working environment of an offshore platform or a land-based well site. 
         [0006]    Thus, wet gas burners are required that significantly reduce heat radiation and pollutants in the form of smoke and fallout that result from incomplete combustion, that can operate under a wide range of input pressures and that can operate with a reduced noise level. 
       SUMMARY 
       [0007]    This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter. 
         [0008]    A multiphase burner is disclosed that is capable of flaring wet gas or a gas stream that includes a liquid fraction without producing smoke, particulates or hydrocarbon fallout. The disclosed multiphase burner may include a hollow base that has a central axis and a proximal end that may serve as an inlet for receiving a combustable fluid, such as wet gas. The base may further include a distal end that may be coupled to a nozzle cap. The nozzle cap may form a first outlet that is concentric with the central axis of the base. The base may also be coupled coaxially to a central body. Further, the base may also be coaxially coupled to a hollow holder that encircles at least part of the central body. The holder may be coupled to a hollow bushing that may also encircle at least part of the central body. The bushing may form a second outlet that encircles the central axis and that is disposed axially within the first outlet. The base may form a mouth disposed along the central axis in between the inlet and the central body. The mouth may be in communication with two passages for splitting the flow of wet gas through the burner. The first passage may extend from the mouth to the first outlet and between the holder and the distal end of the base. The second passage may extend from the mouth to the second outlet and between the holder and the central body. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    For a more complete understanding of the disclosed methods and apparatuses, reference should be made to the embodiment illustrated in greater detail on the accompanying drawings, wherein: 
           [0010]      FIG. 1  is a cross-sectional view of a disclosed multiphase burner with an optional liquid input that is separate from the main gas/wet gas input. 
           [0011]      FIG. 2  is a cross-sectional view showing the base and nozzle cap with the serrated outlet of the multiphase burner of  FIG. 1 . 
           [0012]      FIG. 3  is a sectional view of the central body and support of the multiphase burner of  FIG. 1 . 
           [0013]      FIG. 4  is a sectional view of the holder and nozzle cap of the multiphase burner of  FIG. 1 . 
       
    
    
       [0014]    It should be understood that the drawings are not necessarily to scale and that the disclosed embodiments are sometimes illustrated diagrammatically and in partial views. In certain instances, details which are not necessary for an understanding of the disclosed methods and apparatuses or which render other details difficult to perceive may have been omitted. It should be understood, of course, that this disclosure is not limited to the particular embodiments illustrated herein. 
       DETAILED DESCRIPTION 
       [0015]    Disclosed herein is a flaring apparatus in the form of a multiphase burner that provides clean and smokeless combustion of a waste gas effluent or a waste gas-liquid fuel mixture (i.e., “wet gas”) at high inlet pressures through fine atomization of the liquid component of the wet gas, intensive mixing with ambient air and self-sustaining ignition. The disclosed multiphase burner also may provide improved burning efficiency at decreased noise levels and improved mechanical durability and reliability. 
         [0016]    In a typical well testing operation, a gas flare is used to burn the wet gas exiting a well test separator. The wet gas typically includes a fraction of liquid that remains in the gas flow and needs to be combusted. The liquid typically includes water and oil but some formations produce wet gas with a liquid fraction that includes water without oil, oil without water, or both at the same time. As disclosed herein, smoke-free and fallout-free flaring of the wet gas is possible even with a high fraction of liquid. 
         [0017]      FIG. 1  shows a cross-sectional view of a disclosed multiphase burner  10 . The burner  10  may include a base  11  that may define an inlet  12  for wet gas flow as indicated by the arrows  13 . Also shown in  FIG. 1  is an optional liquid inlet  14  that is shown in phantom. As shown in  FIGS. 1 and 2 , the base  11  may be coupled to a nozzle cap  15  indirectly or directly. For example, the base  11  may be threadably connected to the nozzle cap  15  by equipping the base  11  with a threaded distal end  16  and by equipping the nozzle cap  15  with a threaded proximal end  17 . The base  11  and nozzle cap  15  may also form an integral structure. The nozzle cap  15  may also include an outlet  18  that may be serrated as shown in  FIG. 2  for enhancing the atomization of the liquid fraction of the waste gas as discussed below. 
         [0018]    As shown in  FIGS. 1 and 3 , the burner  10  may also include a central body  21 . The central body  21  may have a conical or tapered distal end  22  and a proximal end  23  that may be coupled to a distal end  24  of a support  25 . The support  25  may also include a tapered proximal end  26  for limiting interference with the incoming wet gas flow  13 . The support  25  may be coupled to the base  11  using a strut  27  as shown in  FIG. 1 . The proximal end  23  of the central body  21  may be connected to a frustoconical section  29  that expands radially outwardly before terminating at a circumferential bulge  31 , which may be the widest portion of the central body  21  that may be followed in the proximal direction by a series of increasingly smaller steps  32 ,  33 ,  34  disposed between increasingly smaller frustoconical sections  35 ,  36 ,  37  that extend radially inwardly before being followed by the tapered conical distal end  22 . 
         [0019]    In addition to supporting the central body  21  and support  25 , the base  11  may also support a holder  38  by way of the strut  44 . The holder  38  may be integrally connected to or coupled directly or indirectly to a bushing  41 . As shown in  FIGS. 1 and 4 , the holder  38  may include a threaded distal end  42  and the bushing  41  may include a threaded proximal end  43  for purposes of detachably connecting the holder  38  to the bushing  41 . As will be apparent to those skilled in the art, the holder  38  and the bushing  41  may also be unitary in structure. As shown in  FIG. 1 , another strut  44  may be used to couple the holder  38  and/or bushing  41  to the base  11  and/or the nozzle cap  15 . 
         [0020]    As shown in  FIGS. 1 and 4 , the bushing  41  may include a tapered outer surface  45  that follows the tapered inner surface  46  of the nozzle cap  15 . Further, the bushing  41  may also include an inner surface with a plurality of radially inwardly tapered segments  51 ,  52 ,  53  with inwardly extending ridges  71 ,  71 ,  73  disposed after each segment  51 ,  52 ,  53 . The segment  53  may be followed by a distal segment  54  that terminates at an outlet  55 . The inwardly tapered segments  51 ,  52 ,  53  of the bushing  41  may follow the contour of the frustoconical sections  35 ,  36 ,  37  of the central body  21  but in a slightly offset relationship as shown in  FIG. 1 . 
         [0021]    The base  11  may also form a mouth  57  through which the support  25  passes. The strut  27  may be used to support the central body  21  and the support  25  in the axial position shown in  FIG. 1 . The mouth  57  may be in communication with a central passage  58  as well as an outer passage  59  as the burner  10  may split the flow  13  into the dual flows  61 ,  63  as shown in  FIG. 1 . 
         [0022]    The burner  10  may operate in the following manner. The inlet wet gas flow  13  for flaring may be supplied though pipelines (not shown) to the base  11 . The inlet wet gas flow  13  may be a complex and unsteady combination different phases: gas flow (mainly methane); droplets of oil and water carried by high-velocity gas flow; liquid film on the inlet  12  (not shown), which may be transformed into liquid slugs; and, as a minor component, flow of particulates (e.g., sand from the formation and other debris from metal pipelines). This multiphase wet gas inlet flow  13  passes through the narrow mouth  57 . At the sharp edge of mouth  57 , the inlet flow  13  may be divided into two flows  61  and  63  as shown in  FIG. 1 . 
         [0023]    The flow  61  may include gas carrying liquid droplets and liquid jets, which develop as a result of detachment of liquid film from the base  11  at or near the tapered surface  64  and/or the mouth  57 . The gas, liquid droplets and liquid jets move through the central passage  58  between the central body  21  and the holder  38 /bushing  41 . Due to the converging inner surface  64  of the base  11  in the vicinity of the mouth  57  (see  FIGS. 1 and 2 ), the liquid film on the converging inner surface  64  and the mouth  57  may detach and undergo a partial dispersion into the high-velocity flow  61  before being partially captured on various outer surfaces  35 ,  36 ,  37  of the central body  21  and/or on the various inner segments  51 ,  52 ,  53  or ridges  71 ,  72 ,  73  of the bushing  41 . Specifically, the high-venolcity flow  61  through the central passage  58  may cause liquid film to be scattered onto the central body  21  and the bushing  41 , which results in additional atomizing of liquid into small droplets as the flow  61  is ejected out through the outlet  55 . 
         [0024]    In contrast, the flow  63  includes gas and liquid droplets and passes through the outer passage  59  as shown. The flow  63  exits the burner  10  through the nozzle cap outlet  18 , which as shown in  FIG. 2 , is serrated, which further enhances the atomization of any liquid droplets in the flow  63 . 
         [0025]    The design of the burner  10  and its dual passage flows  61 ,  63  may provide an improved dispersion of big liquid droplets and liquid films. Specifically, big liquid droplets and any liquid films from the flow  61  may be dispersed into smaller droplets inside the burner  10  and between the central body  21  and holder  38 /bushing  41 . Further, another atomization of the flow  61  may take places downstream the sonic transition cross-section shown in phantom at  65  in  FIG. 1 . At the sonic transition cross-section  65 , substantial gradients in the gas flow velocity upstream of the sonic transition cross-section  65  and downstream of the sonic transition cross-section  65 /outlet  55  may induce atomization of any liquid present into a smaller spray or mist. The burner  10  may also help to keep the products of atomization close to the central axis  66  of the burner  10 , which may ensure that atomized droplets will be delivered to the combustion zone and avoid fallout trajectories. 
         [0026]    For a high-pressure gas-liquid flow (when the absolute pressure at the inlet  12  of the base  11  exceeds about 0.2 MPa), transition of a flow through the narrowing central passage  58  may result in the sonic transition critical section  65  at a narrow point of the central passage  58 . The critical section  65  may be defined as a section where the gas flow at a given temperature reaches the sonic level. As an example, an expected location for critical cross-section  65  in the gas flow  61  through the central passage  58  is shown just upstream of the outlet  55  in  FIG. 1 . 
         [0027]    The smooth-shaped mouth  57  in combination with the control body  21  splits inlet gas-liquid flow  13  into two parts  61 ,  63  as shown in  FIG. 1 . One part  61  of the inlet flow  13  proceeds through the central passage  58  as described above. The other part  63  of inlet flow  13  includes gas with small droplets and undergoes a turn around the mouth  57  before being directed to the outer passage  59  defined by the base  11 /nozzle cap  15  on the outside and the holder  38 /bushing  41  on the inside. The outer passage  59  exits the burner through the annular orifice  60  ( FIG. 1 ) defined by the outlet  18  of the nozzle cap  15  and the outlet  55  of the bushing  41 . The outlet  18  may be equipped with sharp tabs or serrations as shown in  FIG. 2 . 
         [0028]    The serrations on the outlet  18  of the nozzle cap  15  may produce turbulisation of the exit flow and may improve aeration of the final mixture at the outlets  18 ,  55  of the burner  10  while suppressing jet noise while the flow  63  is ejected from the outer passage  59 . The small size of the serrations may also act to disperse the liquid film (if a film has survived up to outlet  18 ) into small droplets that continue their flight in the near the central axis  66 . 
         [0029]    The dual flows  61 ,  63  produced by the burner  10  may result in only a minor part of liquid (in the form of small droplets) that is dragged by the deviated gas flow  63  into the outer passage  59 . Therefore, the gas flow  63  passing through outer passage  59  may have much lower liquid content than the flow  61  through the central passage  58 . 
         [0030]    The smallest cross-sectional area for the central passage  58  may be at or near the outlet  55  and may also be in close proximity to the smallest cross-sectional area for the outer passage  59 , which is at the outlet  18  and which may also be small enough to generate sonic velocities for the flow  63 . Any surviving liquid droplets in the flow  63  may be dispersed into a fine mist along the central axis  66  as such droplets exit the outlet  18 . Specifically, at the outlet  18  of the nozzle cap  15 , the flow from the outer passage  59  ejects near the serrated outlet  18 . The serrations on the outlet  18  facilitate dispersion of any liquid film present in the flow  63  along the axis  66 , better mixing of gas with ambient air, and a reduction in the jet noise level. 
         [0031]    As a result of gas-liquid flow splitting into two flows  61 ,  63  and dispersion of liquid droplets inside the burner  10 , the exit flow may consist of a core flow with a high concentration of liquid droplets (spray flow) and a turbulised sheath-shaped flow with a low concentration of entrained droplets. Mixed with ambient air and entrained by a highly turbulised jet flow, the mixture of combustible gas, liquid droplets, and air becomes a mixture that may be ignited for clean and smokeless combustion of wet gas with a high amount of entrained liquid. The mass fraction of liquid in the inlet flow can be up to 30% or more. However, the described gas burner device also operates as effective burner for fluids with low liquid content (dry gas) as well. 
         [0032]    The smallest cross-sectional area for the central passage  58  is about equal to the smallest cross-sectional area for the outer passage  59 . However, the proportions between the minimal cross-sectional areas for two passages  58  and  59  can vary by 30-50% depending on the fluid composition and inlet pressure in the base  11 . The serrations on the outlet  18  may be triangular-shaped with the height in the range from about 2 to about 6 mm. However, as will be apparent to those skilled in the art, other geometries and sizes can be chosen for liquid film atomization, effective gas-air mixing, and jet noise reduction. The bushing  41  and central body  21  may have axisymmetric shapes for defining the central passage  58 . Since a minor fraction of solid particulate (sand) can be found in the burner inlet flow  13  and high-speed solid particles create an abrasive impact on target surfaces (sand-jetting), the bushing  41  and central body  21  may be fabricated from a wear-resistant alloy. 
         [0033]    In field conditions, due to high velocities of fluid flow and intensive heat radiation from the flame, the nozzle cap  15  and bushing  41  may degrade to a point of failure before other parts of burner  10 . Therefore, the nozzle cap  15  and bushing  41  may be replaced in a quick process performed on-site due to the use of threaded distal surfaces  42 ,  43 ,  16 ,  17 . Specifically, the nozzle cap  15  may be detached from the base  11  and the bushing  41  may be detached from the holder  38  without disturbing the central body  21 . Durability of the burner  10  is achieved in part by using abrasion-resistant materials for the bushing  41  and nozzle cap  15  and providing the removable design for the bushing  41  and nozzle cap  15 . 
         [0034]    In general, the disclosed high-pressure multiphase burner  10  with dual passages  58 ,  59  may be used to improve the dispersion of liquid components of wet gas and provide improved flaring over other burners known in the art. 
         [0035]    The wet gas inlet pressure may be greater than 1 barg. For input pressures above 1 barg, the critical section  65  at the outlet  55  and the critical section at the annular orifice defined by the outlet  18  and the outer surface  45  of the bushing  41  are formed inside the central passage  58  and outer passage  59  respectively, and this facilitates dispersion liquid components into a fine spray of gas-liquid fuel at the burner outlets  55 ,  18 . 
         [0036]    Although the disclosed burner  10  is described as multiphase burner, it must be appreciated that the burner  10  as described herein can be used for combustion of dry combustible gas (‘dry gas”) without any changes in design. 
         [0037]    The gas-liquid flow  13 ,  14  that is directed through the two passages  58 ,  59  within the burner  10  may pass through corresponding critical sections (shock waves) if the input pressure exceeds about 2 barg. Fluid mechanics may describe this situation as under-expanded flow. As the exit gas-liquid flow comes out from the outlets  55 ,  18  to surrounding air, shock waves may be developed, which creates zones of high and low pressure. At a stable input flow rate, the shock waves remain at certain distances from the nozzle outlets  55 ,  18 . These zones may be a place of additional atomization of liquid droplets. As the flow (gas jet with atomized fuel) keeps expanding, the axial velocity of the jet becomes close to the flame propagation speed, so self-stabilization of flare flame takes place. 
         [0038]    The disclosed multiphase burner  10  may be used in many industries, including those where a separate liquid feed  14  is required. The liquid component (or liquid component with suspended solid particles like particles of micronized coal) may be fed through the inlet  14  into the base  11  and the gas (vapour) component of the feed may be supplied through the inlet  12  as shown in  FIG. 1 . The liquid component may be carried by the gas flow and may be dispersed into smaller droplets in the central passage  58  before these liquid droplets may be dispersed into fine droplets at the outlet  55  due to the high-speed gas flow passing through the central passage  58 . The burner  10  may operate both at low pressures (&lt;1 barg) and at higher pressures (&gt;1 brag) when shock waves develop within the passages  58  and  59 . 
         [0039]    While only certain embodiments have been set forth, alternatives and modifications will be apparent from the above description to those skilled in the art. These and other alternatives are considered equivalents and within the spirit and scope of this disclosure and the appended claims.