Separators are known in the oil and gas industry for separating the incoming mixture of liquid (oil and/or water) and gas into a stream of substantially gas and a stream of substantially liquid. Different separators are known for separating such gas/liquid mixtures.

In one type of separator a separation vessel is provided in which a number of cyclones are arranged. The separation vessel typically comprises an inlet for admitting the liquid/gas mixture, a first outlet for the discharge of a separated heavy fraction of the mixture, i. e. a fraction of the mixture mainly containing the relatively heavy liquid, and an outlet for the discharge of the light fraction of the mixture, i. e. the fraction of the liquid mainly containing the gas. Separation is achieved by forcing the liquid/gas mixture through the cyclones.

WO 00/25931 discloses a separation vessel wherein a number of so-called axial recycle cyclones are arranged in an upper compartment of the vessel. The liquid/mixture enters a lower compartment of the vessel and is forced subsequently through the cyclones. The mixture entering an axial cyclone is set into a rotating movement, whereby the heavy fraction is flung against the outer wall of the cyclone, while the light fraction remains in the centre of the cyclone. The

heavy fraction is then discharged through openings in the outer wall to a so-called downcomer leading the heavy fraction to the lower compartment of the vessel. The separated light fraction is discharged via an outlet in the upper compartment of the vessel.

The liquid/gas mixture will be subjected to a pre- treatment immediately after entering the separation vessel in order to improve the overall separation efficiency of the separator. A pre-treatment is also advisable to effect a proper separation of the mixture to the vessel at a rapid rate, since the mixture will otherwise strike the wall of the vessel situated opposite the inlet with considerable force, resulting in liquid particles being entrained to the upper compartment.

For the pre-treatment of the liquid/gas mixture inlet devices are known, in which the mixture entering the vessel is distributed so as to ensure a more uniform distribution over the cross section of the vessel. In a device known in the art as the"Evenflow"vane type inlet device a series of vanes is arranged inside the vessel in the extension of the centre line of the inlet, the vanes being arranged to catch the incoming mixture and deflect it sideways.

One of the drawbacks of the existing vane type inlet devices is that still an amount of liquid is dragged along towards the upper part of the vessel, causing a limitation of the separation efficiency of the inlet device and the separation device in general.

It is an object of the present invention to provide vane type inlet device and/or a separation device including a vane type inlet device with improved separation efficiency.

According to a first aspect of the present invention this object is achieved in a separation device for separating a liquid-gas mixture in a heavy fraction mainly containing

liquid and a light fraction mainly containing gas, comprising: - a separation vessel comprising at least one inlet, at least a first outlet for the discharge of the heavy fraction and at least a second outlet for the discharge of the light fraction, - a vane type inlet device connected to the inlet for admitting the gas-liquid mixture to the vessel en for distributing the admitted gas-liquid mixture in the vessel, the vane type inlet device comprising a support structure and a plurality of curved guiding vanes arranged one behind the other so as to intercept and deflect the admitted gas-liquid mixture, wherein one or more of the guiding vanes are provided with at least one liquid creep interrupter for interrupting liquid creeping along the surface of the guiding vane; - separating means for further separating the mixture into the heavy and light fraction.

The inventor of the present invention has surprisingly found that one of the causes of the liquid entrained by the flow and directed to the gas outlet is as follows. Liquid is collected on the curved vane blades due to the centrifugal forces exerted on the gas-liquid mixture when the liquid passes the guiding vanes of the existing inlet arrangements. The liquid creeps along the guiding vanes and is thrown into the gas space (mostly the upper compartment) of the separation vessel when leaving the guiding vanes.

Unfortunately a large part of this liquid is then being transported upwards by the gas flow and may reach the separation means. By providing liquid creep interrupters for interrupting the liquid creeping along the surface of the guiding vanes the liquid is prevented from reaching the gas space of the separator. The liquid creep interrupter enables

the liquid to be drained to a liquid chamber, whereby is prevented or at least is counteracted that liquid creeping up the guiding vanes reaches the gas compartment of the separation and as a result reduces the separation efficiency of the device.

According to a preferred embodiment the curvature of a guiding vane defines an inner vane surface and an outer vane surface, wherein the liquid creep interrupter is a protrusion, preferably a flange, arranged at the inner surface of the guiding vane. The protrusion interrupts the liquid creeping along the guiding vanes. In an at present even more preferred embodiment the liquid creep interrupter comprises a hook-like element. The hooks collect the liquid that is separated as gas is changing direction while flowing along the guiding vanes.

In another preferred embodiment the liquid creep interrupter is formed by one or more openings arranged in the guiding vane. The liquid creeping along the inner surface of the guiding vanes is discharged through the slots before it reaches the trailing end of the vanes and is taken along with the mixture flowing between the vanes. Preferably the liquid creep interrupter also includes one or more flanges arranged at the outer side of the guiding vane so as to receive the liquid crept through the openings in the vane. This prevents liquid escaping through the openings being taken along by the mixture flowing between the next pair of vanes. To reduce even more the risk that some of the liquid discharged through the openings turns up in the gas flow, the protrusion at the outer side of the guiding vane is shaped so as to form a chamber for collecting the liquid.

A further advantage of the application of openings (slots) in the guiding vanes is that the flow profile through the inlet device is improved since the degree of recycling

within the blades is reduced due to the area occupied by the flange or chamber behind the slots.

In the above mentioned embodiments the liquid creep interrupters are formed so as to guide the creeping liquid towards a liquid drain. By guiding the liquid to a liquid drain is prevented that liquid would unintentionally end up in a part of the compartments of the vessel wherein the liquid may be entrained by a gas flow. The liquid drain takes in this embodiment care of proper discharge of the liquid, for example by guiding the collected liquid to the liquid sump in the lower section of the separation vessel.

According to a preferred embodiment the separation vessel comprises a lower section and an upper section, the vane type inlet device being arranged between the upper and lower section and the liquid drain being formed so as to guide the liquid to the lower section of the vessel.

According to a preferred embodiment the liquid creep interrupters are arranged close to or at the trailing edge of the guiding vane. In this way is prevented that liquid is collected downstream of the liquid creep interrupters and would creep further along the guiding vanes, eventually ending up in the upward liquid-gas flow. However, in some cases the interrupters need to be arranged further away from the trailing edges of the guiding vanes.

According to a preferred embodiment the vane type inlet device is arranged substantially horizontally in an upright separation vessel and the guiding vanes are arranged so as to deflect the incoming mixture substantially horizontally. If diverted vertically upwards a poor gas distribution may be seen on downstream equipment in vertical vessels. For horizontal vessels liquid entrainment from liquid surface may arise since gas leaving the inlet device hits the vessel top and is diverted down towards the liquid

surface. If the gas/liquid is diverted vertically downwards in both vertical and horizontal vessels, there may be high velocities on the liquid surface with corresponding high risk of liquid entrainment from the surface.

The separation device is preferably of a type that uses one or more cyclone separators for further separating gas from the gas-liquid mixture. Particularly advantageous embodiments of the cyclone separators are known from WO 00/25931 of the present applicant, the disclosure of which is herein incorporated by reference.

According to another aspect of the invention a vane type inlet device for pre-treatment of a gas-liquid mixture to be separated in a separation vessel of the above-discusses type is provided, the separation vessel including at least an inlet for admitting the gas-liquid mixture to a bottom part of the vessel, at least one separator for separating the gas- liquid mixture in a heavy fraction mainly containing liquid and a light fraction mainly containing gas, a first outlet for discharging the heavy fraction and a second outlet for discharging the light fraction, the inlet device comprising: - an elongated support structure to be connected to the inlet, the support structure being provided with at least a partly open side; - a plurality of curved guiding vanes placed one behind the other and arranged at least partly within the support structure, the guiding vanes being arranged so as intercept and deflect the admitted gas-liquid mixture, one or more of the guiding vanes being provided with at least one liquid creep interrupter for interrupting liquid creeping along the inner surface of the guiding vane.

In the embodiments wherein the liquid creep interrupter is arranged at the inner side of the vanes, the interrupter protrudes between 1 mm and 100 mm from that inner

surface. Test have shown that the pre-defined distance between 1 and 100 mm will particularly provide good results.

The dimensions of the protrusion will depend on a plurality of factors and is determined from case to case, depending on for instance the wanted liquid removal efficiency, total liquid amount in the incoming feed to the vessel, vessel size, inlet nozzle size and allowable pressure drop through the device. For similar reasons the width of the slots will typically vary in between 1-100 mm.

According to another aspect of the present invention a method is provided for admitting gas-liquid mixture to a separation vessel and subsequently distributing the liquid and gas in the vessel, the gas-liquid mixture being passed through the above-mentioned inlet device or separation device. The method preferably comprises the steps of: - feeding the gas-liquid mixture through the inlet device, forcing a part of the heavy fraction to lower section of the vessel and guiding at least a part of the liquid creeping alongside the guiding vanes to the lower section; - guiding a part of the mixture through one or more cyclone separators in the upper part of the vessel and carrying the separated liquid part back to the lower compartment and carrying the separated gas part to the second outlet; - discharging the mixture from the lower compartment from the first outlet; - discharging the mixture from the upper compartment from the second outlet.

Further advantages, features and details of the present invention will follow from the description of preferred embodiments thereof. References is made in the description to the figures, in which:

- Figure 1 shows a partly cut-away perspective view of a separator for separating a mixture of gas and liquid; - Figure 2 shows a perspective view of a first preferred embodiment of a vane type inlet device; - Figure 3 shows a cross-section of the first embodiment of a vane type inlet device; - Figure 4 shows a cross-section of a second embodiment of the vane type inlet device; - Figure 5 shows a cross-section of a third embodiment of the vane type inlet device; - Figure 6 is a cross-section of a fourth embodiment of the vane type inlet-device; - Figure 7 is a longitudinal section, shown schematically, of a part of the separation vessel and the vane-type inlet device; and - Figures 8a to 8f show preferred embodiments of the slots provided in the guiding vanes according to the present invention.

Figure 1 shows an upright separating device 1 for separating a pressurized flow of a gas/liquid mixture, such as natural gas mixed with (salt sea-) water, into a substantially gas-containing fraction, also referred to as light fraction, and a substantially liquid-containing (water and/or oil) fraction, also referred to as heavy fraction. The separating device comprises a vessel 2 that is provided with a connecting stub 3 for in-feed of the gas/liquid mixture, a connecting stub for a liquid discharge conduit 4 for discharge of the heavy fraction and a connecting stub 5 for discharge of the light fraction.

The gas/liquid flow introduced in the vessel 1 (P1) is guided by a pre-treatment unit 6 to a lower compartment A of vessel 2. In the shown embodiment the pre-treatment unit 6 is formed by a number of curved blades or vanes which uniformly

absorb the moment of the incoming gas/liquid flow. The vanes subsequently guide the gas/liquid flow laterally (P2), a part of the flow being guided down into the lower compartment of the separating vessel. As a result of this controlled entry of the gas/liquid mixture a first portion of the liquid (F) will already be separated and accumulate at the bottom of the vessel 2 (P3). The liquid is then drained through the heavy- fraction output 4..

The separated part of the mixture which, although it contains less liquid than the mixture supplied from outside, still has a considerable liquid content, is displaced upward (Pg) The liquid, which still is present in relatively large droplets, is further separated by a number of cyclones 7. The cyclones are arranged in a plurality of boxes in the upper compartment B of the vessel 1. Provided downstream thereof is the connecting stub 5 for discharging the light fraction (mainly gas) which has been dried to a considerable extent.

The cyclones are connected to one or more downcomers 7 which are in communication with liquid F at the bottom of the vessel for draining liquid from each of the cyclones.

Preferably the cyclones are axial recycle cyclones as disclosed in the aforementioned document WO 00/25931. A general description of the separation performed by axial recycle cyclones is incorporated herein by reference.

In an embodiment (not shown) known in the art as the "schoepentoeter"inlet device and as described in GB 1 119 699, a vane type inlet device comprises two plates between which a number of partly straight partly curved left and right guiding vanes are arranged. The guiding vanes are designed so as to guide the incoming flow sideways, respectively to the left and right hand side of the vessel.

In a vane type inlet device of a different design, as is shown in present figures 2-5, also known as the"Evenflow"

inlet device, the guiding vanes are arranged between a top plate 10 and a bottom plate 11 and have a curved shape over their total length. The guiding vanes in this embodiment are maintained between the borders of the upper and lower plates.

The interspaces between the successive guiding vanes increases in the direction of the mixture flow (P,). In this embodiment the basic principle of intercepting the mixture flow and deflecting the flow towards the wall of the vessel is applied as well.

A liquid/gas flow entering the inlet device (P" figure 2) is deflected sideways by the successive guiding vanes 13,14. More specifically, the incoming liquid is intercepted by the leading edges 17 of a left guiding vane 12 and/or a right guiding vane 13 and deflected laterally (Pa) towards the trailing edges 18 of the vanes.

As a result of the centrifugal forces acting on the gas and liquid particles in the gas/liquid flow a part of the liquid is flung against the inner surface of the vanes and forms a thin layer of liquid on the vanes. The liquid moves towards the trailing edges 18 of the vanes. In existing vane type inlet arrangements the liquid thus collected on the guiding vanes is subsequently thrown into the compartment of the separator vessel. A large part of this liquid is then transported upwards (PS) by the gas flow. In the embodiment shown in figure 2, however, liquid creep interrupters in the form of a hook-like members 14 are provided at the trailing ends 18 of the guiding vanes 12,13. The liquid collected on the guiding vanes 12,13 and creeping up towards the trailing edges of the vanes is interrupted by the hook-like members 18.

The interruptors such as the hook-like members or, in another embodiment to be described hereafter, the pockets on the guiding vanes, can be open in the bottom such

that liquid collected falls directly down to the bottom liquid sump in the lower compartment A of the separation vessel 2. In an improved design, however, one or more separate drainage chambers for the collected liquid are provided. In figure 7 is shown that the he drainage chamber (s) may be located just below (lower drainage chamber 22) and/or on top the vanes (upper drainage chamber 23) of the pre-treatment unit 6. The liquid collected in the hooks or the pockets is drained downwards (Pg) or upwards (P11) respectively the liquid collection chamber 22,23 located respectively below and above the guiding vanes and then routed to the liquid compartment by one or more pipes 28,24 sticking downwards towards the bottom liquid section of the separation vessel 2. The pipes 24,28 may stick into the liquid F or end just above the liquid surface. The final location of the pipes is determined from case to case as it will depend on the pressure balances between the separate liquid chamber 22,23 of the pre-treatment unit 6 and the main liquid chamber situated at the bottom of the separation vessel 2.

In any case the interrupted liquid drains downwards to a liquid chamber located below the inlet device. From the liquid chamber the liquid is routed to the liquid sump (F) in the bottom of the separator vessel 2. In this way a part of the liquid collected on the vane blades is separated from the gas, resulting in an improved overall separation efficiency of the separator.

In another embodiment, as is shown in figure 4, the liquid creep interrupters are embodied in flanges 16 that are provided at the trailing edges 18 of the guiding vanes 12, 13. The flanges are dimensioned so as to at least partly prevent creep of liquid along the guiding vanes. The liquid creep interrupters in general and the flanges in particular

protrude a predetermined distance d from the inner surface of the guiding vane so as to on the one hand at least partly prevent creep and on the other hand keep the flow of the gas- liquid mixture substantially undisturbed. In practice distance d ranges between 1 mm and 100 mm from the inner surface of the guiding vane.

In another embodiment liquid creep interrupters 18 are provided, in addition to or instead of the liquid creep interrupters provided at the trailing edges of the vanes, on any position between the leading edges 17 and trailing edges 18 of the guiding vanes 12,13. This embodiment is elucidated in figure 4, wherein the last two guiding vanes are provided with flanges 18. For reasons of simplicity only two additional flanges 18 are depicted. In practice more guiding vanes or even each of the guiding vanes will be equipped with the elements 18. The distance the flanges 18 protrude from the respective guiding vanes generally is smaller than the above-mentioned distance.

Figure 5 shows a cross-section of a third embodiment of the vane type in the device. In this embodiment the liquid creep interruptor is formed by a number of slots 20 provided in the respective guiding vanes 12. The slots are preferably arranged in the neighbourhood of the trailing edges 18 of the vanes 12 and have a width ranging between 1 and 100 mm.

Figures 8a-8f show some preferred shapes of the slots 20 that have proven to be in particular advantageously.

Figure 8a shows that the slots can be arranged vertically.

Figure 8b shows that more than one slot, placed one behind the other, can be used. Figure 8c shows that depending on the incoming flow profile, i. e. especially where the bulk liquid is flowing, the shape of the slots can vary. For example Figure 8c shows a situation where on the upper side the slot is wider than the bottom side of the guiding vane. This

embodiment is preferred when for example the liquid flow at the bottom of the inlet device is less strong than at the upper side of the inlet device. In figure Bd the opposite situation is shown, wherein the slots are less wide at the upper side of the guiding vanes than at the lower side of the guiding vanes. Figure 8e shows that the slots may be arranged at a certain angle, the slots extending parallel to one and other. Oblique, non-parallel slots are also conceivable. In rear scenarios the slots may extent horizontally alone at the guiding vanes.

In this embodiment the liquid creeping along the inner surface of the guiding vanes eventually ends up in the neighbourhood of the slots 20 and will be discharged through the slots (Pl2) In the embodiment shown in figure 5 the interruption of the crept-up liquid is further enhanced by providing a chamber or pocket 19 behind the respective slots 20 in the guiding vanes 12. The liquid that has entered the slots 20 is accumulated in the pockets 19 and drained upwards or downwards (P1l and Pg respectively, figure 7) to one or more liquid drainage chambers.

In figure 6 a fourth embodiment is shown, wherein the pockets 19 are substituted by flanges 21. The flanges are provided at the respective trailing ends of the guiding vanes 12. The crept-up liquid is guided through the slots 20 and prevented from re-entering the flow at the back of the respective guiding vane due to the presence of the protrusion 21. Note that the exact position of the flanges 21 is preferably at the trailing end of the guiding vanes, as is shown in figure 6. However, other positions might be suitable as well, for example halfway between the trailing end and leading end of the guiding vane. In other embodiments, not shown in the figures, two or more flanges or pockets are arranged on the backside of the respective guiding vanes.

An additional advantage of the embodiments wherein one or more flanges or one or more pockets are provided at the backside of the guiding vanes is that the flow profile through the entire inlet device is improved since the degree of recycling between the guiding vanes is reduced due to the space occupied by the flange and/or chamber behind the slots.

The present invention is not limited to the above described embodiments thereof; the rights sought are defined by the following claims, within the scope of which many modifications can be envisaged. Although in the above description of preferred embodiments of the present invention an upright separating vessel is shown, it is for instance to be understood that the invention likewise applies to horizontally of obliquely arranged separating vessels.