Abstract:
A two phase gas-liquid separation apparatus is provided that shapes the flow in a flow shaping line. Shaping the two-phase flow allows centrifugal force to send the heavier, denser liquid to the outside wall of the flow shaping line and allows the lighter, less dense vapor or gas to occupy the inner wall of the flow shaping line. With the gas positioned on the inner wall of the flow shaping line, an exit port on the inner wall will allow for the majority, if not all, of the gas, along with a low amount of liquid, to be sent to a conventional separator. A high ratio of vapor/liquid at a flow rate much lower than the total flow rate within the flow shaping line is sent to the conventional separator. This allows for efficient separation of the vapor from the liquid with the use of a smaller conventional separator.

Description:
This application is a continuation of and claims benefit to U.S. patent application Ser. No. 13/020,623, filed Feb. 3, 2011, entitled “APPARATUS AND METHOD FOR GAS LIQUID SEPARATION.” 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to the separation of gas from a gas-liquid two phase flow stream. More specifically, it relates to directionally shaping the gas-liquid two phase flow stream so that the majority of the gas is located in a certain area of the flow stream, which allows effective separation of the gas and the liquid. 
     BACKGROUND OF THE INVENTION 
     A gas-liquid two phase flow stream includes a mixture of different fluids having different phases, such as air and water, steam and water, or oil and natural gas. A gas-liquid two phase flow takes many different forms and may be classified into various types of gas distribution within the liquid. These classifications are commonly called flow regimes or flow patterns and are illustrated in  FIGS. 1A-1E . Bubble flow as illustrated in  FIG. 1A  is typically a continuous distribution of liquid with a fairly even dispersion of bubbles in the liquid. Slug or plug flow as illustrated in  FIG. 1B  is a transition from bubble flow where the bubbles have coalesced into larger bubbles with a size approaching the diameter of the tube. Churn flow as illustrated in  FIG. 1C  is a pattern where the slug flow bubbles have connected to one another. In annular flow as illustrated in  FIG. 1D , liquid flows on the wall of the tube as a film and the gas flows along the center of the tube. Finally, in wispy annular flow as illustrated in  FIG. 1E , as the liquid flow rate is increased, the concentration of drops in the gas core increases, leading to the formation of large lumps or streaks of liquid. 
     It is often desirable to separate the gas and liquid components of a fluid from one another to enable proper operation of systems, such as certain types of liquid pumps. Conventional vertical or horizontal gas-liquid separators are available to separate gas from liquid. Conventional separators typically employ mechanical structures, wherein an incoming fluid strikes a diverting baffle which initiates primary separation between the gas and liquid components. Mesh pads or demister pads are then used to further remove suspended liquid. The sizing of a separator and the particular characteristics of the separator is dependent upon many factors, which may include, the flow rate of the liquid, the liquid density, the vapor density, the vapor velocity, and inlet pressure. Vertical separators are typically selected when the vapor/liquid ratio is high or the total flow rate is low. Horizontal separators are typically preferred for low vapor/liquid ratio or for large volumes of total fluid. 
     One application of these types of separators is in oil and gas drilling operations. Specifically, a mud-gas separator is used when a kick is experienced in a wellbore during drilling operations. A kick is the flow of formation fluids into the wellbore during drilling operations. If a kick is not quickly controlled, it can lead to a blow out. As part of the process for controlling a kick, the blow-out preventors are activated to close the wellbore and wellbore fluids are slowly circulated out of the wellbore while heavier drilling fluids are pumped into the wellbore. A mud gas separator is used to separate natural gas from drilling fluid as the wellbore fluid is circulated out of the wellbore. Often times, however, prior act separators, including mud-gas separators, cannot keep up with the flow rate from the wellbore. 
     Of course, separators are also used in the production of oil and gas to separate natural gas out of the oil that is being produced. Additionally, there are many other applications that require the use of gas-liquid separators. 
     SUMMARY OF THE INVENTION 
     This invention relates to directionally shaping two-phase mixed flow in a curved path within a flow shaping line prior to introduction into a separator so as to enhance operation of the separator. Shaping the two-phase flow in a curvilinear path will allow centrifugal force to more readily force the heavier, denser liquid to the outside wall of the flow shaping line in the curved path and allow the lighter, less dense vapor or gas to occupy the inner wall of the flow shaping line. Once the gas is fairly well positioned on the inner wall of the flow shaping line, an exit port located on the inner wall will allow for the majority, if not all, of the gas, along with a low amount of liquid, to be sent to a conventional separator. A very high ratio of vapor/liquid at a flow rate much lower than the total flow rate within the flow shaping line is then sent to the conventional separator. This allows for efficient separation of the vapor from the liquid with the use of a smaller, more economical conventional separator than what would have been required for the full flow rate. 
     Additionally, a fluid guiding surface may be placed on the inner wall of the flow shaping line at the exit port to further aid in directing the gas to flow to the conventional separator. Furthermore, the liquid return from the conventional separator may be arranged in close downstream proximity to the exit port on the inner wall of the flow shaping line. The close proximity of the liquid return and the exit port allows the use of a venturi, nozzle or other restriction located adjacent the liquid return in the flow shaping line just downstream of the exit port. The venturi, nozzle or other restriction accelerates the velocity of the liquid in flow shaping line as it flows across the exit port. This acceleration of the liquid helps to pull the liquid out of the conventional gas-liquid separator. In addition, the acceleration of the liquid within the flow shaping line helps to prevent any solids that may be present in the gas-liquid flow from entering the exit port and it helps to lower the amount of liquid that enters the exit port and thus enters the conventional separator. 
     The invention therefore allows a gas-liquid fluid to be effectively separated with the use of a smaller conventional separator than was previously possible. The invention accomplishes this without using additional complex mechanical devices and thus will operate efficiently and reliably. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the present disclosure and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying figures, wherein: 
         FIGS. 1A-1E  illustrate a cross-sectional view of various flow regimes of two phase gas-liquid flow. 
         FIG. 2  illustrates a cross-sectional view of an embodiment of separation apparatus. 
         FIG. 3  illustrates a cross-sectional view of the embodiment of the separation apparatus in  FIG. 2  taken across line  3 - 3 . 
         FIG. 4  illustrates a cross-sectional view of another embodiment of a separation apparatus with two flow shaping loops. 
         FIG. 5  illustrates a cross-sectional view of another embodiment of a separation apparatus where the diameter of the flow shaping line is less than the diameter of the main line. 
         FIG. 6  illustrates a cross-sectional view of another embodiment of a separation apparatus where the flow shaping line forms a generally elliptical shape. 
         FIG. 7  illustrates a cross-sectional view of another embodiment of a separation apparatus with two exit ports. 
         FIG. 8  illustrates a cross-sectional view of another embodiment of an exit port in a separation apparatus. 
         FIG. 9  illustrates a cross-sectional view of another embodiment of an exit port with an airfoil shape located away from the inner wall in an embodiment of a separation apparatus. 
         FIG. 10  illustrates a cross-sectional view of another embodiment of a separation apparatus located near the seabed in an oil and gas drilling operation. 
     
    
    
     DETAILED DESCRIPTION 
     In the detailed description of the invention, like numerals are employed to designate like parts throughout. Various items of equipment, such as pipes, valves, pumps, fasteners, fittings, etc., may be omitted to simplify the description. However, those skilled in the art will realize that such conventional equipment can be employed as desired. 
       FIG. 2  illustrates a cross-sectional view of an embodiment of a separation apparatus  10 . In an exemplary embodiment, the separation apparatus  10  includes a gas-liquid flow  12  traveling in a vertical direction  14  in a main line  15 . The gas-liquid flow  12  could be any type of multiphase gas-liquid flow regime or flow pattern, such as, for example, bubble flow, slug or plug flow, churn flow, annular flow or wispy annular flow. The gas-liquid flow  12  within main line  15  is directed into a circular flow path  16  in a flow shaping line  17 . The circular flow path  16  of flow shaping line  17  creates an increased distribution of the gas on inner wall  24  of the flow shaping line  17 . The increased distribution of the gas on the inner wall  24  of the flow shaping line  17  results in part by the relatively heavier and denser liquid  18  of flow  12  being forced to the outer wall  20  of the flow shaping line  17  due to centrifugal force of circular flow path  16 , while the lighter gas  22  is driven to the inner wall  24 . In an embodiment with a vertical or partly vertical orientation of the flow shaping line  17 , gravitational effects may also aid in increasing the distribution of the gas on the inner wall  24  of the flow shaping line  17 . In an embodiment, a transition section  13  between the main line  15  and flow shaping line  17  may be provided with a shape as illustrated to further aid in creating the increased distribution of the gas on inner wall  24  of the flow shaping line  17 . 
     As the gas-liquid flow  12  continues to travel through the circular flow path  16  of flow shaping line  17 , the gas-liquid flow  12  forms a flow path that exhibits a high concentration of the gas  22  on the inner wall  24  of the flow shaping line  17 . In the embodiment shown in  FIG. 2 , at location  26 , which is approximately 315 degrees around shaping line  17  (or 45 degrees from the vertical), the separation of gas  22  from liquid  18  has reached a degree that gas  22  primarily occupies the space adjacent the inner wall  24  of the flow shaping line  17 . As seen in  FIG. 3 , which is a cross section  3 - 3  of the flow shaping line  17  and gas-liquid flow  12  at location  26 , the gas  22  occupies mainly the inner wall  24  of the circular flow path  16  of the flow shaping line  17 . 
     With gas-liquid flow  12  forming a more stratified flow regime, or at least the distribution or volume of gas near the inner wall  24  of the flow shaping line  17  has increased at the point of location  26 , the gas  22  may now be effectively bled off from the gas-liquid flow  12  at an outlet port  28  positioned on the inner wall  24  of the flow shaping line  17 . Although outlet port  28  may be positioned any where along flow path  16 , it is preferably selected to be at a point where substantial separation of gas from liquid has occurred. Thus, in one preferred embodiment, the outlet port  28  is downstream of location  26 . At about a location  26 , which is approximately at an angle of approximately 45 degrees from the vertical  74 , it has been found that the concentration, separation or stratification of the gas  22  from the liquid  18  is at a point that gas  22  occupies a greater volume of space adjacent the inner wall  24  of the main line  15  than liquid  18 . In other embodiments, the outlet port  28  may be located between generally 45 degrees from the vertical and generally zero degrees with the vertical. While location  26  is illustrated at approximately 315 degrees around flow shaping line  17  and has been found to be a point where a substantial volume of gas has been driven to inner wall  24 , location  26  is used for illustrative purposes only. 
     In an exemplary embodiment, a fluid guiding surface  30  is located on the inside diameter  32  of the inner wall  24  of the flow shaping line  17  upstream of the outlet port  28 . The fluid guiding surface  30  includes a downstream end  36  that curves around the corner  37  located at the junction of the outlet port  28  and the flow shaping line  17 . In one embodiment, the fluid guiding surface  30  may comprise at least a partial airfoil or hydrofoil shape. The fluid guiding surface  30  functions to guide the gas  22  into the outlet port  28 . The gas  22  follows the contour of the fluid guiding surface  30  and the gas  22  will follow the curve of the downstream end  36  into the outlet port  28 . 
     An amount of liquid  18  from the gas-liquid flow  12  will also be carried into the outlet port  28  thus forming a new gas-liquid flow  40  which includes a much lower percentage of liquid compared to the gas-liquid flow  12 . The new gas-liquid flow  40  from outlet port  28  is then directed into a conventional gas-liquid separator  38 , as shown in  FIG. 2 , for further separation of the gas and liquid. Outlet port  28  is connected to the conventional gas-liquid separator by separator inlet line  33 . The gas-liquid separator  38  contains a gas exit  39  to allow for the removal of the gas  22  separated from the new gas-liquid flow  40 . The gas-liquid separator  38  also contains a liquid exit  41  that is connected to liquid inlet port  42  in a return line  43  by a separator liquid exit line  44 . The return line  43  is formed at the end of, and is fluidicly connected to, the flow shaping line  17 . Those skilled in the art will appreciate that separation apparatus  10  is shown as integrated with gas liquid separator  38 , but can be a completely separate structure. 
     In an exemplary embodiment, the liquid inlet port  42  in the return line  43  is in close downstream proximity to outlet port  28  of the flow shaping line  17 . The close proximity of the liquid inlet port  42  and the outlet port  28  allows the use of a venturi  46  located adjacent the liquid inlet port  42  in the return line  43 . The venturi  46  accelerates the velocity of the liquid  18  in return line  43  as it flows across the liquid inlet port  42 . This acceleration of liquid  18  helps to draw the liquid out of the conventional gas-liquid separator  38 . In addition, the acceleration of the liquid  18  within return line  43  facilitates separation of gas from liquid within flow shaping line  17 , minimizes the likelihood that any solids present in the gas-liquid flow  12  will enter outlet port  28 , and minimizes the amount of liquid  18  that enters the outlet port  28 . 
     It has been observed that the liquid flow rate entering the outlet port  28  in the new gas-liquid flow  40  is approximately twenty percent of the of the flow rate of the gas-liquid flow  12  that is in the flow shaping line  17  upstream of the outlet port  28 . The new gas liquid flow  40  contains a higher percentage of the gas  22  than was in the gas-liquid flow  12 , but with much lower amount of liquid  18  in the flow. This provides a very efficient first step in the separation of the gas  22  from the liquid  18  without the use of additional pumps, valves or other mechanical equipment. 
     This efficient first step in the separation of the gas  22  from the liquid  18  is provided at least in part by one or more aspects of the invention. First, the use of the circular flow path  16  to centrifugally increase the concentration of the gas  22  on the inner wall  24  of the flow shaping line  17 . Second is the fluid guiding surface  30  used to direct the gas  22  into the outlet port  28 . Third, venturi  46  accelerates the velocity of the liquid  18  as it flows past the outlet port  28 , thereby functioning to lower the amount of liquid  18  that enters the outlet port  28  and minimize entry of solids into outlet port  28 . The venturi  46  also lowers the pressure of the liquid  18  at the liquid inlet port  42  of the return line  43 , which draws the liquid  18  out of the conventional gas-liquid separator  38 . 
     As mentioned above, the efficient first step in the separation of the gas  22  from the liquid  18  significantly decreases the amount of liquid  18  entering the conventional gas-liquid separator  38 . This allows for the use of much smaller size conventional gas-liquid separators than would have previously been possible for a given flow rate. 
     While circular flow path  16  is shown as positioned in a vertical plane, in another embodiment the circular flow path  16  could be in a horizontal plane or in a plane with an inclination between horizontal and vertical. 
     In another embodiment, illustrated in  FIG. 4 , the circular flow path  16  could be replicated in multiple loops  78  to develop the increased concentration of the gas  22  on the inner wall  24  of the flow shaping line  17 . In another embodiment as seen in  FIG. 5 , the flow shaping line  17  may be formed with a smaller cross-sectional area  72  than the cross sectional area  70  of the main line, thereby increasing the velocity of the gas-liquid flow  12  within the flow shaping line  17 . The increase in velocity of the gas-liquid flow  12  results in greater centrifugal force and increased concentration of the gas  22  on the inner wall  24  of the flow shaping line  17 . A higher velocity through the flow shaping line  17  also allows for greater turndown capability in the flow rate of the gas-liquid  12  in a system where the flow rate may be variable. 
     In other embodiments, as illustrated in  FIG. 6 , the flow pattern could be elliptical  80 , or partially circular or partially elliptical, or some other curvilinear, non-circular shape that would still provide for increased concentration of the gas  22  on the inner wall  24  of the flow shaping line  17  through the use of centrifugal force. 
     As seen in  FIG. 7 , other embodiments of the invention may employ multiple outlet ports  28 . For example, in one embodiment, an outlet port  28  may extend from the approximate bottom of a first loop, similar to the embodiment of  FIG. 2 , but the pipe may continue to make a second loop similar to the embodiment of  FIG. 4 , and have a similarly situated second outlet port  28  at the approximate bottom of the second loop. In addition, in another embodiment, one or more conventional separators may be used. 
     Other embodiments of the invention may eliminate the fluid guiding surface  30  or utilize other structures. For example, as illustrated in  FIG. 8 , in one embodiment, an outlet port  28  may have a curved entrance  82 . In another embodiment illustrated in  FIG. 9 , a fluid guiding surface  84  could be spaced away from the inner wall  24  of the flow shaping line. In addition, other embodiments of the invention may use a nozzle or other type of restriction in lieu of a venturi to accelerate the fluid flow across the outlet port  28  or across the liquid inlet port  42 , or may use no restriction at all. 
     As described above, one application for the invention is to protect against “kicks,” such as in subsea applications, by circulating out hydrocarbon gas at the seabed floor before the gas is able to rise up to a drilling rig. Referring to  FIG. 10 , in an exemplary embodiment, illustrated is a conventional sub-sea blow out preventer  50  located on the seafloor  52 . A marine riser  54  extends from the blow out preventer  50  and within the riser is a drillpipe  56 . An embodiment of the separation apparatus  10  is positioned along drillpipe  56 , preferably adjacent the blow out preventer  50 . In normal drilling operations, drilling fluid  58  is pumped down the drillpipe  56  from the drilling rig (not shown) and returns to the drilling rig via annulus  60  formed between the drillpipe  56  and the riser  54 . If a “kick” is detected, for example, by a change in the level of the mud tanks or increase in mud circulation rate, inlet annulus valve  62  is activated, diverting drilling fluid  58  from annulus  60  into the flow shaping line  17 . Natural gas  64  entrained in drilling fluid  58  from the “kick” is then separated from the drilling fluid  58  by the separation apparatus  10  as described above. The natural gas  64  exits the gas-liquid separator  38  at the gas exit  39  and may flow up riser  66  to the drilling rig where it may be safely handled, for example, sent to a flare boom of the drilling rig (not shown), or compressed and re-distributed (also not shown). 
     Following separation of natural gas  64  from the drilling fluid  58  by separation apparatus  10 , the drilling fluid  58  is re-introduced into the annulus  60  at an exit annulus valve  68 . In comparison with the usual procedure of handling a kick, the use of an embodiment of this invention allows for full flow or circulation of the drilling fluid without having to choke down the flow or operate the blow out preventer valves. 
     In another embodiment, the inlet annulus valves  62  or exit annulus valves  68  can be eliminated, bypassed or operated so that the upward flowing drilling fluid  58  continually flows through the separation apparatus  10 . Compared to the usual procedure on a drilling rig when there is a kick of choking the flow of the drilling fluid and being able to only send a portion of the flow to the mud-gas separator located on the drilling rig, an embodiment of the present invention allows the full flow of the drilling fluid to be handled by the separation apparatus  10  and the separation safely takes place near the seafloor. 
     The foregoing invention allows the use of a separation apparatus that can efficiently separate gas from a gas-liquid flow and do so at high flow rates and with the use of smaller conventional separators than would otherwise be possible at the high flow rates. 
     It is therefore evident that the particular illustrative embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the present invention. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee. 
     Although illustrative embodiments of the invention have been shown and described, a wide range of modification, changes and substitution is contemplated in the foregoing disclosure. In some instances, some features of the present invention may be employed without a corresponding use of the other features. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.