Abstract:
A commingling device for combining fluid flows includes an outer fluid line for a first fluid having an inlet end and an outlet end, and an inner fluid line for a second fluid having an inlet end and an outlet end. The inner fluid line has an outlet nozzle at said outlet end, the nozzle being mounted substantially axially within the outer fluid line and configured to direct said second fluid towards the outlet end of the outer fluid line. As a result, the first and second fluids flowing through the inner and outer fluid lines are combined and flow together towards the outlet end of the outer fluid line.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority under 35 USC 119 to British application no. GB 1321916.7 filed Dec. 11, 2013, and the disclosure of said British application is hereby incorporated by reference in its entirety. 
       FIELD 
       [0002]    The present invention relates to a commingling device for combining the flow of two or more fluids. 
       BACKGROUND 
       [0003]    There are many situations where a flow of fluids from two different sources or pipelines needs to be combined so that the fluids can flow along a single pipeline. The type of fluid in each pipeline can vary and may consist of pure gas, pure liquid, or a mixture of gas and liquid (multiphase fluids). The flow rates and operating pressures of the two fluids may also be significantly different. Also the flow regimes of the fluids (represented by fluctuations in the flow rates of the fluid phases) may be different, a typical flow regime being slug flow or intermittent flow. In some applications good mixing of the fluids is also desired. 
         [0004]    A conventional method used in the oil and gas industry and other industries combines the flow of fluids from two streams using a Tee junction  1  (as shown in  FIG. 1 ) that comprises a first inlet line  2 , a second inlet line  3  at right angles to the first inlet line  2 , and an outlet line  4  that is aligned with the first inlet line  2 . A first flow of fluid enters through the first inlet line  2  and a second flow of fluid enters from the second inlet line  3  at  90  degrees to the first inlet line  2 . The first and second fluids are combined and exit the Tee junction through the outlet line  4 . However, the mixing of fluids is turbulent, leading to a loss of energy and pressure. The Tee junction  1  shown in  FIG. 1  can therefore be used as a commingler, but it is not an efficient commingler as described below. 
         [0005]    Using a Tee junction as a commingler is very inefficient, especially when the flow rates or the mass flow rates of the fluids are significantly different from one another. In addition, the pressure of the two streams of fluid in the inlet lines  2 ,  3  could also be different. 
         [0006]    A possible result of combining the flow of fluids from two pipelines with different characteristics using a Tee junction as shown in  FIG. 1  is that the fluid stream with the higher mass flow rate or velocity, or the higher momentum of flow, will impose a back pressure on the weaker inlet line, as the momentum of the stronger fluid stream will impose a resistance to flow from the weaker stream, which flows at an angle of 90 degrees into the stronger stream. In oil or gas wells or pipelines carrying flows from different sources, this may restrict production from the weaker source. 
         [0007]    An efficient commingler eliminates the shortcomings of the Tee junction arrangement and offers a number of benefits which make the commingler a superior and more efficient unit for combining fluid flow from two separate pipelines or sources. 
         [0008]    A key feature of an efficient commingler is that it enables the two fluids to commingle whilst flowing along parallel flow paths, instead of being combined at 90 degrees to one another as in a conventional Tee junction arrangement. 
         [0009]    A more efficient commingler is disclosed in EP 0717818 B1. This document describes an apparatus for mixing two fluid streams, which includes a nozzle mounted within an outlet conduit, which is arranged to introduce a stream of gas in a streamline manner into another fluid stream by directing the gas axially along the outlet conduit. 
       SUMMARY 
       [0010]    It is an object of the present invention to provide a commingling device that mitigates one or more of the problems set out above or that provides a useful alternative thereto. 
         [0011]    According to one aspect of the present invention there is provided a commingling device for combining fluid flows, comprising an outer fluid line for a first fluid having an inlet end and an outlet end, an inner fluid line for a second fluid having an inlet end and an outlet end, said inner fluid line having an outlet nozzle at said outlet end, said nozzle being mounted substantially axially within the outer fluid line and configured to direct said second fluid towards the outlet end of the outer fluid line, whereby said first and second fluids flowing through the inner and outer fluid lines are combined and flow together towards the outlet end of the outer fluid line. 
         [0012]    By combining the fluid flows so that they flow axially and in a streamlined fashion towards the outlet the efficiency of the commingler can be significantly improved, so that it is able to operate with a minimal loss of pressure and a low energy requirement. 
         [0013]    In one preferred embodiment, the outer fluid line is non-straight and the inner fluid line is substantially straight and has an outlet end that is located substantially axially within a downstream portion of the outer fluid line. Advantageously, the outer fluid line is curved. This arrangement is particularly suitable for situations where the first fluid supplied to the outer fluid line is at a relatively low pressure or has a low momentum and the second fluid supplied to the inner fluid line is at a relatively high pressure or has a high momentum, being capable of operating with high efficiency in these conditions. 
         [0014]    In another preferred embodiment, the inner fluid line is non-straight and the outer fluid line includes a substantially straight pipe section, and the inner fluid line has an outlet end that is located substantially axially within a downstream portion of the substantially straight pipe section. This arrangement is mechanically simpler and may be preferred in certain situations. 
         [0015]    Advantageously, the commingling device includes a Tee-piece pipe section comprising a substantially straight pipe section and a branch pipe section that intersects the substantially straight pipe section. The inner fluid line preferably includes an inlet end mounted within the branch pipe section and an outlet end located within the substantially straight pipe section. Advantageously, the inner fluid line is curved. This configuration is simple to implement and can be assembled using mostly conventional and readily available components. 
         [0016]    Advantageously, the inner fluid line includes an upstream portion that extends substantially perpendicular to a longitudinal axis of the substantially straight pipe section, and a downstream portion that extends substantially parallel to the longitudinal axis of the substantially straight pipe section. This configuration may be preferred where a curved inner fluid line cannot be accommodated. 
         [0017]    In another preferred embodiment the commingling device includes a Tee-piece pipe section comprising a substantially straight pipe section and a branch pipe section that intersects the substantially straight pipe section, and a removable inlet transfer pipe mounted within the Tee-piece pipe section and connected to the inlet end of either the substantially straight pipe section or the branch pipe section for guiding the flow of either the first fluid or the second fluid. In this configuration a highly efficient commingler can be assembled using largely conventional components, often without making extensive changes to existing pipework. 
         [0018]    In one embodiment, the inlet transfer pipe is connected to the inlet end of the branch pipe section and comprises an upstream portion that extends substantially perpendicular to a longitudinal axis of the substantially straight pipe section, and a downstream portion that extends substantially parallel to the longitudinal axis of the substantially straight pipe section. Again, this configuration may be useful where a curved inner fluid line cannot be accommodated. 
         [0019]    Optionally, the inlet transfer pipe may be configured to be withdrawn from the substantially straight pipe section in a direction substantially perpendicular to a longitudinal axis of the substantially straight pipe section. This allows the straight pipe section to be cleaned or inspected using a pipeline inspection gauge (or “pig”). 
         [0020]    In another embodiment, the inlet transfer pipe mounted within the Tee-piece pipe section is connected to the inlet end of the substantially straight pipe section and extends towards the outlet end of the substantially straight pipe section. This provides a useful alternative configuration, which is suitable for different fluid flow conditions. 
         [0021]    Advantageously, the commingling device includes an outlet transfer pipe mounted within the Tee-piece pipe section, wherein said outlet transfer pipe is connected to the outlet end of the substantially straight pipe section and extends upstream towards the downstream end of the inlet transfer pipe. 
         [0022]    Advantageously, the commingling device includes a spinner device mounted within the inner fluid line and configured to cause rotation of said second fluid flowing within the inner fluid line. Alternatively or additionally the commingling device may include a spinner device mounted within the outer fluid line and configured to cause rotation of said first fluid flowing within the outer fluid line. The use of spinner devices ensures that the first and second fluids are mixed thoroughly and efficiently, even when the flow characteristics of the fluids are very different. 
         [0023]    According to another aspect of the invention there is provided a commingling device for combining fluid flows, comprising a first fluid line for a first fluid having an inlet end and an outlet end, and a second fluid line for a second fluid having an inlet end and an outlet end, wherein said second fluid line intersects said first fluid line between the inlet and outlet ends thereof, and wherein said second fluid line has a longitudinal axis that extends at an acute angle to a longitudinal axis of the first fluid line, whereby said first and second fluids flowing through the first and second fluid lines are combined and flow together towards the outlet end of the first fluid line. This configuration allows the straight pipe section to be cleaned or inspected using a pipeline inspection gauge (or “pig”). 
         [0024]    Advantageously, the longitudinal axis of said second fluid line extends at least partially tangentially with respect to the first fluid line, whereby said second fluids flowing into said first fluid lines are caused to rotate about a longitudinal axis of the first fluid line. 
         [0025]    According to another aspect of the invention there is provided a commingling device for combining fluid flows, comprising a first fluid line for a first fluid having an inlet end and an outlet end, and a second fluid line for a second fluid having an inlet end and an outlet end, wherein said outlet end of said second fluid line is connected to said first fluid line through an intermediate pipe section having a plurality of apertures through which the second fluid can flow into the first fluid line. This configuration also allows the straight pipe section to be cleaned or inspected using a pipeline inspection gauge (or “pig”). 
         [0026]    Advantageously, at least one of said apertures extends at an acute angle to a longitudinal axis of the first fluid line, whereby said first and second fluids flowing through the first and second fluid lines are combined and flow together towards the outlet end of the first fluid line. 
         [0027]    Advantageously, at least one of said apertures extends at least partially tangentially with respect to the first fluid line, whereby said second fluids flowing into said first fluid lines are caused to rotate about a longitudinal axis of the first fluid line. 
         [0028]    Advantageously, said first fluid line is piggable and has no substantial obstructions between the inlet and outlet ends thereof. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0029]    Various embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, wherein: 
           [0030]      FIG. 1  is a side view of a prior art commingling device; 
           [0031]      FIG. 2  is a partially sectional side view of a commingling device according to a first embodiment of the invention; 
           [0032]      FIG. 3  is a partially sectional side view of a commingling device according to a second embodiment of the invention; 
           [0033]      FIG. 4A  is a partially sectional side view of a commingling device according to a third embodiment of the invention; 
           [0034]      FIG. 4B  is a partially sectional side view of a commingling device according to a fourth embodiment of the invention; 
           [0035]      FIG. 4C  is a partially sectional side view of a commingling device according to a fifth embodiment of the invention; 
           [0036]      FIG. 5  is a partially sectional side view of a commingling device according to a sixth embodiment of the invention; 
           [0037]      FIG. 5A  is a partially sectional side view showing part of a commingling device according to a seventh embodiment of the invention, being a first variant of the sixth embodiment; 
           [0038]      FIG. 5B  is a partially sectional side view showing part of a commingling device according to an eighth embodiment of the invention, being a second variant of the sixth embodiment; 
           [0039]      FIG. 5C  is a cross sectional end view of the commingling device shown in  FIG. 5B ; 
           [0040]      FIG. 6  is a partially sectional side view of a commingling device according to a ninth embodiment of the invention; 
           [0041]      FIG. 6A  is a cross section on line A-A of  FIG. 6 , and 
           [0042]      FIG. 7  is a partially sectional side view of a commingling device according to a tenth embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0043]    The first commingling device  100  shown in  FIG. 2  is connected to first and second inlet lines  101   a,    101   b  and outlet line  104  via radial flanges  108 ,  110 ,  111 . The commingling device  100  includes a relatively large diameter elbow pipe section  102  that bends through an angle of approximately 90° and a relatively small diameter straight pipe section  103  that passes through and is welded to the wall of the elbow pipe section  102 . The straight pipe section  103  extends axially in the direction of the downstream end of the elbow pipe section  102 , which is connected to the outlet line  104  via flange  108 . A nozzle  105  is provided on the outlet end of the straight pipe section  103 . 
         [0044]    The small diameter straight pipe section  103  is located axially within the elbow pipe section  102  providing an annular region  106  between the wall of the straight pipe section  103  and wall of the elbow pipe section  102 . A first static spinner device  107 , for example comprising fan blades or helical fins, is provided within the straight pipe section  103  towards the downstream end thereof This first static spinner device  107  may be located upstream of and/or within the nozzle  105 . A second static spinner device  109 , comprising for example fan blades or helical fins, may be provided within the annular region  106  between the elbow pipe section  102  and the straight pipe section  103 . This second static spinner device  109  may be mounted on the interior surface of the elbow pipe section  102  and/or on the exterior surface of the straight pipe section  103 . 
         [0045]    In use, first and second fluid streams flow into the commingling device  100  through the first and second inlet lines  101   a,    101   b.  The fluid stream flowing through the second inlet line  101   b  passes through the straight pipe section  103  and the nozzle  105  and is introduced in a streamlined manner into the first fluid stream that flows from the first inlet line  101   a  into the elbow pipe section  102 . The first and second spinners  107 ,  109  cause the first and second fluids flows to rotate in the same direction about the longitudinal axis of the straight pipe section  103 , which aids mixing of the first and second fluids. The mixed fluids then exit the commingling device through the outlet line  104 . Because the fluids are commingled in a streamlined manner there is very little loss of pressure or momentum and the commingling device is therefore very efficient in operation. 
         [0046]    The second commingling device  200  shown in  FIG. 3  is connected to first and second inlet lines  201   a,    201   b  and to outlet line  204  via radial flanges  208 ,  210 ,  211 . The commingling device  200  includes a relatively small diameter elbow pipe section  202  that is connected to the first inlet line  201   a  and bends through an angle of approximately 90°. The commingling device  200  also includes a relatively large diameter Tee joint  203 , which comprises a straight pipe section  203   a  and a branch pipe section  203   b  that intersects the straight pipe section  203   a  at an angle of approximately 90°. The elbow pipe section  202  extends from the inlet end of the branch pipe section  203   b  into the straight pipe section  203   a  and is configured so that the outlet end of the elbow pipe section  202  extends axially in the direction of the downstream end of the straight pipe section  203   a.  A flange  211  is provided at the upstream end of the elbow pipe section  202 , which sits within a recess at the upstream end of the branch pipe section  203   b  to support the elbow pipe section  202 . The flange  211  prevents fluids flowing from the first inlet line  201   a  directly into the branch pipe section  203   b.  Any fluids flowing through the first inlet line  201  a are therefore forced to flow through the elbow pipe section  202 . A nozzle  205  is provided at the outlet end of the elbow pipe section  202  to direct the first fluids axially into the straight pipe section  203   a.    
         [0047]    The downstream end of the small diameter elbow pipe section  202  is located approximately axially within the straight pipe section  203   a,  providing an annular region  206  between the wall of the straight pipe section  203   a  and wall of the elbow pipe section  202 . A first static spinner device  207 , for example comprising fan blades or helical fins, is provided within the downstream end of the elbow pipe section  202 . This first static spinner device  207  may be located upstream of or within the nozzle  205 . A second static spinner device  209 , comprising for example fan blades or helical fins, is provided within the annular region  206  between the elbow pipe section  202  and the straight pipe section  203   a.  This second static spinner device  209  may be mounted on the interior surface of the straight pipe section  203   a  and/or on the exterior surface of the elbow pipe section  202 . 
         [0048]      FIGS. 2 and 3  show a number of important features of the commingler. Both commingling devices  100 ,  200  serve the same function but for some operating companies the Tee shaped commingler  200  shown in  FIG. 3  will be preferred because of the simpler or superior welding details offered by the design. In the case of the elbow type commingler  100  shown in  FIG. 2  extra welding is needed where line  103  passes through the elbow  102 , which some operators may not prefer. 
         [0049]    In the first commingling device  100  shown in  FIG. 2 , a short or long radius pipe bend or elbow  102  is preferably used as the flow path for the fluids with less momentum, whilst the straight pipe section  103  is used as the flow path for the fluids with a higher momentum. Often one of the fluid streams will have a higher pressure than the other fluid stream. The difference in pressures could vary and may range from a few millibar, for example 2 millibar (200 Pa), to several bar (several times 100 kPa). In this case the fluids with the lower pressure may be called LP fluids, and the fluids with the higher pressure may be called HP fluids. 
         [0050]    The LP fluids flow through the elbow  102  and are guided to pass through the annulus  106  between the elbow  102  and the straight pipe section  103  before the two fluids are combined along the same axis in front of the nozzle  105 . 
         [0051]    The nozzle  105  attached to the downstream end of straight pipe section  103  is designed such that if the pressure of the fluids passing through the pipe section  103  is higher than the pressure of the fluids from line  101   a,  the nozzle  105  enables the pressure of the fluids from line  103  to drop to the pressure of the inlet line  101   a  and the outlet line  104  when the two fluids are combined uniaxially, so that they can flow unimpeded through downstream outlet line  104 . 
         [0052]    In the case of the Tee type commingler  200  shown in  FIG. 3 , the elbow type pipe section  202  is removably fixed into the Tee section via the flange  211 , which is fixed or bolted onto the main flange  210  of the Tee section. 
         [0053]    In both cases shown in  FIGS. 2 and 3  the commingling device  100 ,  200  is designed and sized so that the mixture velocities of the two fluids are close to one another when the two fluids are combined downstream of the nozzle  105 ,  205 . The size of each pipe section or elbow is generally selected from the standard pipe sections available in the industry and is selected so that the velocity of fluid within each stream does not exceed the limit generally recommended for that pipe section, so as to avoid excessive erosion of the pipe section. The typical pipe sections vary from ¼ inch to 48 inch (0.6 cm to 122 cm) diameter, but the invention is not limited to these sizes, which depend on the flow rate of each fluid stream. 
         [0054]    The use of a small diameter pipe section for one fluid stream is applicable mainly to cases when chemicals such as wax inhibitors or glycol are introduced in small doses into the main stream and good mixing of the flow from the two streams is desired. 
         [0055]    One preferred feature of the commingler is the use of a screw type fluid spinning static spinner device  107 ,  207  as part of the nozzle assembly  105 ,  205 . This spinner device generates spinning and rotation of the fluids passing through the nozzle assembly. Spinning the fluids helps the flow from the two streams to mix thoroughly when they are commingled beyond the nozzle  105 ,  205 . This spinner device is particularly effective when the flow passing through the nozzle is a liquid phase and the fluid passing through the annulus  106 ,  206  is a gas. If the commingling device does not include a static spinner there may be a tendency for the liquid phase to jet through the gas phase without mixing with the gas. 
         [0056]    Alternatively or additionally, a second fluid spinner device  109 ,  209  may be installed within the annulus  106 ,  206  between the elbow section and the main pipe section as shown in  FIGS. 2 and 3 . With this second static fluid spinner device flow from the first fluid stream can be subjected to spinning action. The spinning device is of fixed type and does not rotate, but its screw like fin configuration causes the fluids to spin as they pass through the spinner. When both spinners are used, they are arranged to spin both fluids in the same direction. 
         [0057]    The efficient commingler described above is generally supplied with flanges at the inlet and outlet ends, allowing it to be connected securely with existing pipe work without the need for welding work on site. 
         [0058]    Another type of commingler is the insert type, which can be introduced into an existing Tee joint. Three different commingling devices of the insert type are shown in  FIGS. 4A ,  4 B and  4 C. 
         [0059]    The commingling device  300  shown in  FIG. 4A  includes a conventional Tee joint  302 , which comprises a straight pipe section  302   a  and a branch pipe section  302   b  that intersects the straight pipe section  302   a  at an angle of approximately 90°. 
         [0060]    The commingling device  300  also includes a transfer pipe  303 , which is mounted within the straight pipe section  302   a  and extends axially from the inlet end of the straight pipe section  302   a  past the branch pipe section  302   b  and towards the downstream end of the straight pipe section  302   a.  The transfer pipe  303  includes a large diameter section  303   a  at its upstream end and a smaller diameter section  303   b  at its downstream end, which is connected to a nozzle assembly  305 . A flange  311  is provided at the upstream end of the transfer pipe section  303 , which sits within a recess at the upstream end of the straight pipe section  302   a  to support the transfer pipe  303 . The flange  311  prevents fluids flowing from the second inlet line  301   b  directly into the straight pipe section  302   a.  Instead, any fluids flowing through the second inlet line  301   b  are forced to flow through the transfer pipe  303 . A nozzle  305  is provided at the outlet end of the transfer pipe  303  to direct the fluids flowing through the transfer pipe  303  axially into the straight pipe section  302   a  with a streamlined flow. 
         [0061]    The downstream end of the transfer pipe  303  is located axially within the straight pipe section  302   a,  providing an annular region  306  between the wall of the transfer pipe  303  and wall of the straight pipe section  302   a.  A first static spinner device  307 , for example comprising fan blades or helical fins, is provided within the downstream end of the transfer pipe  303 . This first static spinner device  307  may be located upstream of and/or within the nozzle  305 . A second static spinner device  309 , comprising for example fan blades or helical fins, is provided within the annular region  306  between the transfer pipe  303  and the straight pipe section  302   a.  This second static spinner device  309  may be mounted on the interior surface of the straight pipe section  302   a  and/or on the exterior surface of the transfer pipe  303 . 
         [0062]    In use, a first fluid stream flows into the commingling device  300  through the branch pipe section  302   b  and a second fluid stream flows into the transfer pipe  302  through the second inlet line  301   b.  The fluid stream flowing through the second inlet line  301   b  passes through the transfer pipe  303  and the nozzle  305  and is introduced in a streamlined manner into the first fluid stream that flows from the branch pipe section  302   b  into the straight pipe section  302   a.  The first and second spinners  307 ,  309  cause the first and second fluid flows to rotate in the same direction about the axis of the straight pipe section  302   a,  which aids mixing of the first and second fluid streams. The mixed fluids then exit the commingling device through an outlet line connected to the downstream end of the straight pipe section  302   a.  Because the fluids are commingled in a streamlined manner there is very little loss of pressure or momentum and the commingling device is therefore very efficient in operation. 
         [0063]    The commingling device  400  shown in  FIG. 4B  includes a conventional Tee joint  402 , which comprises a straight pipe section  402   a  and a branch pipe section  402   b  that intersects the straight pipe section  402   a  at an angle of approximately 90°. 
         [0064]    The commingling device  400  includes a transfer pipe  403 , which is mounted within the branch pipe section  402   b  and extends into the straight pipe section  402   a.  At its downstream end the transfer pipe  403  has a transverse pipe section  404  that extends axially towards the downstream end of the straight pipe section  402   a.  A nozzle  405  is provided at the outlet end of the transverse pipe section  404  to direct the fluids flowing through the transfer pipe  403  axially into the straight pipe section  402   a  with a streamlined flow. An inclined plate  408  is provided at the downstream end of the transfer pipe  403  to direct the flow of fluids towards the transverse pipe section  404 . 
         [0065]    A flange  411  is provided at the upstream end of the transfer pipe  403 , which sits within a recess at the upstream end of the branch pipe section  402   b  to support the transfer pipe  403 . The flange  411  prevents fluids from flowing directly into the branch pipe section  402   b.  Instead, any fluids flowing through the first inlet line are forced to flow through the transfer pipe  403 . 
         [0066]    The transverse pipe section  404  is located axially within the straight pipe section  402   a,  providing an annular region  406  between the wall of the transverse pipe section  404  and wall of the straight pipe section  402   a.  A static spinner device  407 , for example comprising fan blades or helical fins, is provided within the downstream end of the transverse pipe section  404 . This static spinner device  407  may be located upstream of and/or within the nozzle  405 . A second static spinner device (not shown) may optionally be provided within the annular region  406  between the transverse pipe section  404  and the straight pipe section  402   a.  This second static spinner device, if provided, may be mounted on the interior surface of the straight pipe section  402   a  and/or on the exterior surface of the transverse pipe section  404 . 
         [0067]    In use, a first fluid stream flows from a first inlet line  401   a  into the transfer pipe  403  and a second fluid stream flows into the straight pipe section  402   a  from the second inlet line  401   b . The first fluid stream passes through the transfer pipe  403  and the nozzle  405  and is introduced in a streamlined manner into the second fluid stream that flows through the straight pipe section  402   a.  The spinner  407  causes the second fluid flow to rotate about axis of the straight pipe section  402   a,  which aids mixing of the first and second fluid streams. The mixed fluids then exit the commingling device  400  through an outlet line connected to the downstream end of the straight pipe section  402   a.  Because the fluids are commingled in a streamlined manner there is very little loss of pressure or momentum and the commingling device is therefore very efficient in operation. 
         [0068]    The commingling device  500  shown in  FIG. 4C  includes a conventional Tee joint  502 , which comprises a straight pipe section  502   a  and a branch pipe section  502   b  that intersects the straight pipe section  502   a  at an angle of approximately 90°. 
         [0069]    The commingling device  500  includes an inlet transfer pipe  503 , which is mounted within the straight pipe section  502   a  and extends axially from the inlet end of the straight branch pipe section past the branch pipe section  502   b  and towards the downstream end of the straight pipe section  502   a.  The downstream end of the inlet transfer pipe  503  is connected to a nozzle assembly  505 . A flange  511  is provided at the upstream end of the inlet transfer pipe  503 , which sits within a recess at the upstream end of the straight pipe section  502   a  to support the inlet transfer pipe  503 . The flange  511  prevents fluids flowing from the second inlet line  501   b  directly into the straight pipe section  502   a.  Instead, any fluids flowing through the second inlet line  501   b  are forced to flow through the inlet transfer pipe  503 . The nozzle  505  at the outlet end of the inlet transfer pipe  503  directs the fluids flowing through the inlet transfer pipe  503  axially into the straight pipe section  502   a  with a streamlined flow. 
         [0070]    The commingling device  500  also includes an outlet transfer pipe  513 , which is mounted within the straight pipe section  502   a  and extends axially from a point downstream of the nozzle  505  to the downstream end of the straight pipe section  502   a.  The downstream end of the outlet transfer pipe  503  includes a flange  514 , which sits within a recess at the downstream end of the straight pipe section  502   a  to support the outlet transfer pipe  513 . The flange  511  prevents fluids flowing from the straight pipe section  502   a  directly into the outlet pipe  504 . Instead, only fluids flowing through the outlet transfer pipe  513  are allowed to flow into the outlet pipe  504 . The upstream end of the outlet transfer pipe  513  is flared to capture the fluids flowing through the inlet transfer pipe  503  and the branch pipe section  502   b.    
         [0071]    A static spinner device  507 , for example comprising fan blades or helical fins, is provided within the outlet transfer pipe  513 . This static spinner device  507  helps to mix the fluids passing through the outlet transfer pipe  513 . 
         [0072]    In each of the commingling devices shown in  FIGS. 4A ,  4 B and  4 C each insert (the inlet and outlet transfer pipes) is designed and sized to match the operating conditions. The inserts are equipped with their own flanges, which can be bolted to the pipe work with conventional nuts and bolts (not shown). The inserts can be introduced from the three ports of the Tee joint  302 ,  402 ,  502  as dictated by the fluids in each stream. Additionally, an insert with reduced cross section area can be introduced from the discharge end of the Tee piece (as shown in  FIG. 4C ), which can also be equipped with a static spinner to enable good mixing of the fluids. 
         [0073]    Additionally each of the inserts shown in  FIGS. 4A ,  4 B and  4 C can be equipped with static fluid spinners. 
         [0074]    In cases where the size of the pipe section does not allow an elbow to be used, a straight pipe section can be used, as shown in  FIG. 4B . In this case the end of the pipe insert can be cut at an angle and blinded by welding a plate to guide the fluid flow into the transverse pipe section  404 , which is welded to the transfer pipe  403  at  90  degrees to the axis thereof. 
       Piggable Commingler 
       [0075]    There are cases where at least one of the pipelines has to be piggable: that is, it has to be possible to insert a pipeline inspection gauge (or “pig”) for the purpose of inspecting or cleaning the line whenever needed. In this case if a commingler is used to combine flow from two streams, there should be no intrusive equipment or parts within the pipeline to block the passage of the pig. 
         [0076]    To overcome this problem, the arrangement in  FIG. 5 ,  6  or  7  can be used depending on the flow conditions and the thoroughness of mixing desired. 
         [0077]      FIG. 5  shows a commingling device  600  that includes a Y-piece  602 , which comprises a straight pipe section  602   a  and a branch pipe section  602   b  that intersects the straight pipe section  602   a  at an acute angle (in this case of approximately) 45°). A spinner device  603  is mounted within the branch pipe section  602   b.  The straight pipe section  602   a  has an upstream end connected to a first inlet line  604  and a downstream end connected to an outlet line  605 . The branch pipe section  602   b  has an upstream end that is connected to a second inlet line  606 . 
         [0078]    A first fluid flows through the first inlet line  604  into the straight pipe section  602   a.  A second fluid enters through the branch pipe section  602   b  and is mixed with the first fluid within the straight pipe section  602   a.  The branch pipe section  602   b  can be equipped with a static spinner  603  to generate a spinning action of the fluids entering the commingling device  600  and achieve a good mixing of the two fluids. The straight pipe section  602  may also be equipped with guide strips  610  that extend across the entry port of the branch pipe  602   b  to prevent a pig passing through the straight pipe section  602   a  from becoming stuck in this area. 
         [0079]    In a modified version of the commingling device, the static spinner  603  may be replaced with a bundle of nozzles  607  as shown in  FIG. 5A  to generate high velocity of fluids entering straight pipe section  602   a  and achieve good mixing of the two fluids. 
         [0080]    In a further modified configuration shown in  FIG. 5B  the branch pipe section  602   b  is welded to the straight pipe section  602   a  with the axis of the branch pipe section offset from the centre line of the straight pipe section  602   a,  such that the upper part of the branch pipe section  602   b  is tangential to the upper part of the straight pipe section  602   a.  This feature enables fluids from the branch pipe section  602   b  to enter tangentially into the straight pipe section  602   a,  thus automatically creating a rotating motion of the fluids and enabling good mixing of the flow from the two lines. In this configuration the commingler  600  may also include a plate  608  that is welded at the outlet end of the branch pipe section  602   b  so that the outlet area of the branch pipe section  602   b  is further restricted to increase the velocity of fluid flow and increase the spinning action generated by the fluids flowing from the branch pipe section  602   b  into the straight pipe section  602   a.    
         [0081]      FIGS. 6 and 6A  show another type of piggable commingler  700  where a spool piece  701  which has a larger diameter than the main pipeline  705  acts as a Tee section allowing a second fluid to enter via inlet line  704  into an annular space  706  between the wall of the spool piece  701  and the pipeline  705 . A pipe section  707  housed within the spool piece  701  has the same internal diameter as the pipe line  705 . The pipe section  707  has holes drilled along its length, which act as nozzles  703 . These nozzles  703  can also be of angled or radial orientation as shown in section A-A ( FIG. 6A ) to create some rotational motion of the fluids passing through the nozzles and in this way help to improve mixing of the fluids. 
         [0082]      FIG. 7  shows another type of piggable commingler  800 , which uses a Tee section similar to that shown in  FIG. 4B , which is connected to a first inlet pipe  803 , a second inlet pipe  806  and an outlet pipe  804 . In this case a transfer pipe  810  and a transverse pipe section  811  are movable in the axial direction of a branch pipe section  805 , so that when a pigging operation is required, these pipe sections  810 ,  811  can be moved back into a housing  807  to clear the path of the pig passing through the straight pipe section  802 . The commingler includes a housing  807 , an adjusting handle  808 , a screw mechanism  813  with one or more seals to seal the moving stem  809  passing through body  807  and a retrieving stem  809 , which may have a similar construction to that of a normal gate valve housing, which allows the transfer pipe  810  and the transverse pipe section  811  to be retracted into the housing  807  during a pigging operation. A nozzle  812  is provided at the downstream end of the transverse pipe portion  811 . 
         [0083]    The commingler  800  includes a spool piece  801  which has a larger diameter than the main pipeline  803  and acts as a Tee section allowing a second fluid to enter via inlet line  806 . A pipe section  802  housed within the spool piece  801  has the same internal diameter as the inlet pipe line  803 . The pipe section  802  has holes  815  drilled along its length, which act as nozzles. The second fluid in this case can enter via line  806  into the housing  807 , and then enters the straight pipe section  802  via the retractable transfer pipe  810  and the transverse pipe section  811 . 
         [0084]    In all cases one fluid may be denser or more viscous than the other and it is for this reason that good mixing of the fluids is desired.