This disclosure relates to systems and methods for fluid processing, including but not limited to processes associated with pumping, flow conditioning, and/or separation in petroleum production in subsea, topside or land-based

applications.

BACKGROUND A continuous demand exists for improved pressure boosting and fluid

processing for various applications, for example in the petroleum industry. In that industry, technological advances continually enables exploitation of more remote and challenging fields, as well as better utilisation of existing fields. Both these aspects set increasing demands on equipment used for such fluid processing, both in terms of the external conditions under which it operates, and in terms of the fluids handled being more demanding.

Petroleum operations are expensive and equipment reliability is therefore one of the most vital selection criteria. Rotating equipment is, for example, in need of more frequent service than static equipment, and reliability and serviceability are usually given high priority in the design of such equipment. Electrical submersible pumps (ESP), for example, have limited service life compared to other pumps, in part due to the design and in part due to the very challenging environment where they normally are installed.

Documents useful for understanding the background and application include: GB 2 215 408; US 5,135,684; US 5,254,292; US 6,007,306; US 7,569,097; US 201 1 /0155385; WO 2014/019687; WO 2015/199546; US 2007/0235195; US 7,565,932; US 7,516,795; US 8,500,419; US 8,083,501 ; and US 8,083,419.

There is a continuous need for improved solutions and techniques for petroleum fluid processing, including but not limited to such processes associated with pumping, flow conditioning, and/or separation subsea or topside. The present invention has the objective to provide such improvements. SUMMARY

Embodiments disclosed herein may, for example, be used in relation to tie-in, production and pressure boosting of hydrocarbons or other fluid flows handled in the petroleum industry.

In an embodiment, there is provided a fluid separator unit comprising: an elongate body having a circular internal cross-section, an inlet configured to direct a fluid flow into the body in a rotational flow pattern around a longitudinal axis of the body, a first outlet and a second outlet, wherein the fluid separator unit has a first centrifugal separation zone and a second centrifugal separation zone within the body, wherein the second centrifugal separation zone has a smaller diameter than the first centrifugal separation zone, a fluid path from a central part of the first centrifugal separation zone to the first outlet, a fluid path from an outer periphery of the second centrifugal separation zone to the outlet, and a fluid path from the second centrifugal separation zone to the second outlet. In an embodiment, the fluid separator comprises a fluid path from an outer periphery of the first centrifugal separation zone to the outlet.

In an embodiment, the second centrifugal separation zone is defined by a cylindrical wall arranged within the body, and the fluid path from the second centrifugal separation zone to the second outlet is provided by an opening arranged in the cylindrical wall and a pipe fluidly connecting the opening to the second outlet.

In an embodiment, the fluid separator comprises a bottom plate fixed to a lower end of the cylindrical wall.

In an embodiment, the fluid path from the outer periphery of the second centrifugal separation zone to the outlet comprises a radial opening in the cylindrical wall. In an embodiment, the radial opening extends in a spiral shape along the cylindrical wall. In an embodiment, the fluid path from the second centrifugal separation zone to the second outlet extends through a third centrifugal separation zone.

In an embodiment, the fluid separator comprises an intermediate plate fixed to the cylindrical wall and extending inwardly around the inner circumference of the cylindrical wall, wherein the opening is arranged in the cylindrical wall between the intermediate plate and the bottom plate.

In an embodiment, the intermediate plate and the bottom plate define a third centrifugal separation zone therebetween.

In an embodiment, the fluid separator comprises a spin-up plate arranged between the first centrifugal separation zone and the second centrifugal separation zone. In an embodiment, the spin-up plate comprises at least one hole theretrough, the at least one hole arranged at an outer periphery of the spin-up plate.

In an embodiment, the at least one hole defines a part of the fluid path from the outer periphery of the first centrifugal separation zone to the outlet.

In an embodiment, the fluid path from the central part of the first centrifugal separation zone to the outlet is provided by a pipe having a plurality of first openings, the pipe being arranged within the body and fluidly connected to the outlet, the first openings being positioned in the first centrifugal separation zone.

In an embodiment, the pipe extends through the cylindrical wall. In an embodiment, the fluid separator comprises a second opening arranged in a lower section of the body, the second opening being fluidly connected to the outlet. In an embodiment, the fluid separator comprises a cylindrical flow channel arranged between the second opening and the outlet, a first plate arranged in the cylindrical flow channel, wherein the first plate is arranged at an angle in relation to the walls of the cylindrical flow channel which is different than 90 degrees.

In an embodiment, the fluid separator comprises an opening at a part of the first plate which is closest do the outlet.

In an embodiment, the fluid separator comprises a second plate arranged in the cylindrical flow channel, wherein the second plate is arranged at an angle in relation to the walls of the cylindrical flow channel which is different than 90 degrees.

In an embodiment, the angle of the first plate in relation to the walls of the cylindrical flow channel is identical to the angle of the second plate in relation to the walls of the cylindrical flow channel.

In an embodiment, the fluid separator comprises a third plate arranged in the cylindrical flow channel, the third plate arranged between the first plate and the second plate.

In an embodiment, the angle of the third plate in relation to the walls of the cylindrical flow channel is different from the angle of the first and second plates in relation to the walls of the cylindrical flow channel.

In an embodiment, there is provided a pump arrangement comprising a fluid separator and a pressure boosting device, the fluid separator arranged to receive a fluid stream from the pressure boosting device via a supply pipe, wherein a recycled liquid line is arranged between the second outlet and an inlet of the pressure boosting device.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative embodiments of the present invention will now be described with reference to the appended drawings, in which:

Figs 1 -9 show various aspects of a fluid separator unit, and

Fig. 10 shows a pump arrangement.

DETAILED DESCRIPTION

In an embodiment, there is provided a fluid separator unit 300. With reference to Figs 1 and 2, the fluid separator unit 300 has an elongate body 305 with a substantially circular cross-section, an inlet 304, a first outlet 306, and a second outlet 360. The fluid separator unit 300 is configured to separate a fluid received at the inlet 304 such as to provide an intermediate density fraction through the second outlet 360 and light and heavy fractions through the first outlet 306. The fluid separator unit 300 may, for example, be used to provide separated fluid to a subsea boosting system as recycled liquid for supply to a pump. The composition of such recycled liquid is of key importance for the performance and the operational life of the pump. For example, it is not desirable to recycle fluids containing sand or similar particles, as that may cause erosion or otherwise damage the pump. Further, at high pressures, gases may be absorbed into oil, thus recycling such oil may increase the gas fraction at the pump inlet, as such gas may be released when the recycled liquid is throttled down to a (comparatively) lower pressures at the pump inlet. In such a system, it may therefore be desirable to only recycle a fraction of intermediate density, which may provide mainly, or substantially only, water. The highest density fraction, which may comprise water with sand particles or other elements, and the lightest fraction, which may contain petroleum fluids (oil and/or gases), may be passed on further in the subsea processing system, and not used for recycling purposes. Other processing systems may have similar requirements, thus a fluid separator unit as described herein may have various other applications, which may include subsea, topside and land-based applications.

The inlet 304 is arranged in an upper section 301 of the body 305. The inlet 304 is configured to receive an input stream of fluid and direct the fluid, via baffles in the inlet 304, in a tangential direction along the inner circumference of the body 305, such as to create a rotational flow around the longitudinal axis 305' of the body 305. The incoming fluid will thus follow a substantially spiraling flow from the inlet 304 and downwards into the body 305, which allows for centrifugal separation of heavy and light fractions in the usual manner. The inlet 304 shown in this embodiment is an axial inlet from the top of the body 305, however the inlet 304 may, with appropriate arrangement of baffles in the inlet 304, equally well be a tangential or radial inlet arranged in the upper section 301 of the body 305.

The fluid separator 300 further comprises a pipe 307 having a plurality of first openings 3070, the pipe 307 being arranged within the body 305 and fluidly connected to the outlet 306. The openings 3070 are, in this embodiment, positioned near the upper end of the pipe 307 and in an upper section 301 of the body 305. As fluid is provided through the inlet 304 and distributes along the height of the body 305, the lightest fluids will tend towards the centre and towards the upper end of the body 305 due to gravity and the centrigufal forces of the fluid motion created by the inlet device 304. The lightest fluids can then be removed through the openings 3070, via the pipe 307 and to the outlet 306. The openings 3070 are placed at a relatively small radius, forcing the liquid exiting the body 305 via the pipe 307 to have gone through high g-fields. The fluid separator 300 further has a second opening 370 arranged in a lower section 303 of the body 305, the second opening 370 being fluidly connected to the outlet 306. As the heavier fluid, and other components such as sand, accumulate in the lower section 303 of the body 305, these can be removed from the fluid separator through the second opening 370 and the outlet 306. The fluid separator further has a cylindrical wall 381 , the cylindrical wall 381 arranged in a middle section 302 of the body 305 and concentric with the longitudinal axis 305' of the body 305. Figures 3 and 4 show the cylindrical wall 381 and associated components more clearly, in cut-out views. A bottom plate 382 is fixed to the cylindrical wall 381 , wherein a fourth opening 380 (see Fig. 3) is arranged in the cylindrical wall 381 , and a pipe 384 is provided to fluidly connect the fourth opening 380 to the second outlet 360. The pipe 307 extends concentrically inside the cylindrical wall 381 and through the bottom plate 382.

The cylindrical wall 381 and bottom plate 382 forms a cylindrical container-like structure (or "bucket") having a smaller radius than the inner radius of the body 305. As fluid flows into the bucket, the rotational speed will increase due to the conservation of momentum, creating higher g-forces on the fluid entering this bucket. One can therefore obtain an enhanced separation effect for the fluid flowing into the bucket.

The cylindrical wall 381 comprises one or more slots 385, forming a small opening in the cylindrical wall 381 . In this embodiment, the slots 385 extends in a spiral shape along the cylindrical wall 381 . The slots allows heavier

fragments, including sand, to escape the bucket, and flow downwards and out of the fluid separator through the outlet 306, while the remaining heavy fluid fractions flowing through the bucket is led out via the fourth opening 380. Illustrated in Fig. 4, the bucket may have an intermediate plate 386 fixed to the cylindrical wall 381 and extending inwardly around the inner circumference of the cylindrical wall, wherein the fourth opening 380 is arranged in the cylindrical wall 381 below the intermediate plate 386. As described in further detail below, this helps ensure that no sand or other particles reach the fourth opening 380, as the intermediate plate 386 may block the path downwards towards the fourth opening 380 along the cylindrical wall 381 . With the intermediate plate 386, the fluid flowing towards the fourth opening must flow inwardly to pass the intermediate plate, as illustrated in Fig. 4. The fluid separator 300 may further have a swirl cone ("dollar plate") 390 to stabilize the vortex. At its inner circumference, the swirl cone may have openings or a gap towards the pipe 307 to allow lighter components to escape upwards near to the pipe 307.

A spin-up plate 391 may be arranged to improve the fluid flow fields, and in particular to direct fluid flow into the bucket defined by the cylindrical wall 381 . The spin-up plate 391 thus forces liquid heading into the bucket inwardly, such as to pass through a higher g-field. The spin-up plate 391 has perforations (or other types of openings) 391 ' (see Fig. 3) on its outer rim to allow sand and heavy fractions to pass downwardly to the lower chamber on the outside of the spin-up plate 391 . Alternatively, the spin-up plate may be arranged with a gap or openings towards the body 305 for the same purpose. This forms a flow path for fluid and/or solids to the outlet 306 without passing through the bucket defined by the cylindrical wall 381 .

Figures 5 and 6 illustrate the operational principle of the fluid separator 300. The embodiments in Figs 5 and 6 differ in that the angle and configuration of the swirl cone 390 and the spin-up plate 391 are shown in two alternative arrangements; there is otherwise no difference in the principle of operation.

Figs 5 and 6 generally show the middle section 302 of the body 305 in a cut view. The arrows indicate fluid flow paths in the cut plane. (It will be understood that the fluid will also have a swirling motion in addition to the x-y velocities in the plane shown.)

The fluid enters the body near the top, and primarily along the inner

circumference of the body 305, with the flow directed in a swirling motion around this circumference by the inlet 304. The incoming fluid flows downwards along the wall of the body 305 into a first centrifugal separation zone Z1 , as indicated by the arrows. In Figs 5 and 6, the thickness of the arrows roughly indicates the density of the fluid at different positions within the body 305. As the inlet fluid proceeds downwards within zone Z1 in a swirling motion, the heavier fragments, such as water, solids (e.g. sand) and oil, will tend towards the outer circumference of the zone Z1 , while the lighter fractions, such as light oils and gases, will tend towards the central part. The lighter oils and gases will proceed to flow upwardly along the central pipe 307, into the openings 3070 (see Fig. 1 ) and out through the pipe 307 and outlet 306. The first zone Z1 thereby provides a first separation stage to separate gas and liquids.

Some heavier fragments, such as sand and some water, may flow downwardly along the inner circumference of the body 305, through the perforations 391 ' (see Fig. 2), and also out through the outlet 306. This is indicated by the thick arrows along the wall of body 305. This prevents sand build-up on the spin-up plate 391 .

Remaining intermediate to heavy fluid fragments, typically heavier oil fractions and water, will proceed into the bucket defined by the cylindrical wall 381 , and into a second centrifugal separation zone Z2. In this embodiment, the second centrifugal separation zone Z2 has a smaller diameter than the first centrifugal separation zone Z1 , and fluid proceeding into the second zone Z2 will therefore be subjected to increased spin, and thus increased centrifugal separation effect. The heaviest of these fluids will proceed downwards along the cylindrical wall 381 , as indicated by the intermediate arrows. Heavy fractions (e.g. sand) will proceed out through the slots 385 (see e.g. Fig. 4), as indicated by the thick, outwardly arrows, and to the outlet 306. Lighter fractions which are separated out by the now enhanced spin will proceed upwardly along the pipe 307 and back into the first zone Z1 (and subsequently out through the openings 3070).

The fluids flowing downwards along the inner circumference defined by the cylindrical wall 381 will proceed past the intermediate plate 386, and thus be forced further inwardly and thereby being subjected to an additional increase in spin in a third centrifugal separation zone Z3, whereby the separation effect is further enhanced. This is also illustrated in Fig. 4. Some of this fluid will then flow out through the opening 380 (see Fig. 3) which is located in the cylindrical wall 381 below the intermediate plate 386, and out through the outlet 360. The remaining lighter fluid fraction will flow along the pipe 307 and out through the opening 3070. Additional slots in the wall 381 close to the intermediate plate 386 can be included to avoid solids collection in this area.

The fluid provided through the outlet 360 has therefore been subjected to a thorough separation process when passing through zones Z1 , Z2 and Z3, and the fluid separator 300 can therefore provide such a fluid suitable, for example, for supply to a recycled liquid line to a pump. The fluid provided through outlet 360 can thereby be provided with a minimum amount of solids (e.g. sand), and also lowest possible amount of oils potentially containing dissolved gases.

Reference is now made to Figs 7-9, which show aspects of the lower section 303 of the body 305, and the outlet 306. A cylindrical channel 373 extends through the lower flange 31 1 and into the lower section 303 of the body. The pipe 307 may extend through, or end in, the cylindrical channel 373. One or more plates 371 , 372 may be arranged in the cylindrical flow channel 373 leading from the second opening 370 to the outlet 306. The plates assist to increase the local flow friction and limit flow without making the openings 374 and 375 too small and risk blocking by solids for fluid removed from the lower section 303 of the body 305.

The plates 371 , 372 may be arranged at an angle in relation to the walls of the cylindrical flow channel 373 which is different than 90 degrees. The plates 371 ,372 may preferably have the same angle as a cone 320 which is arranged in the body 305 and arranged to lead fluid towards the second opening 370. The plates 371 , 372 have one or more holes 374, 375, or a different kind of opening, at a part of the plate which is closest to the outlet 306. This improves flow conditions past the plate, and may, for example, assist in ensuring that sand cannot accumulate at any point in or around the flow path. A third plate 377 (see Fig. 8) may be arranged between the first and second plates 371 ,372, and at a different angle than the first and second plates. This creates a labyrinth-type flow field for fluid and any solids exiting the body 305. Fig. 9 illustrates a typical flow field through the flow channel 373 with this arrangement of plates 371 ,372,377. This further ensures a combination of relatively large flow openings and a considerable flow friction in the exiting fluid path, thereby reducing the risk of build-up of solids without having a very large flow rate.

Fig. 10 shows a pump arrangement having a fluid separator 300 according to any of the embodiments described above, and a pressure boosting device 100. The pressure boosting device 100 may be a subsea pump. The pump 100 receives a fluid stream 1 10, for example from a petroleum well or other subsea processing components, via an inlet pipe 101 and an inlet fluid conditioning unit /mixer 200. The pump 100 increases the pressure of the fluid and supplies it via a supply pipe 104 to the inlet 304 of the fluid separator 300. A recycled liquid line 103 is arranged between the second outlet 360 of the fluid separator 300 and the inlet mixer 200. A pressure reduction valve 102, such as a choke, is arranged in the recycled liquid line 103. By means of the recycled liquid line 103, recycled liquids can be supplied to the pump 1 00 via the inlet mixer 200, thereby improving its performance, for example when handling fluid streams with high gas content. By means of the fluid separator 300, an advantageous composition of the recycled liquid is obtained, minimising the amount of solids, which may be damaging to the pump, and also minimising the amount of light liquids and/or gaseous fluids in the recycling line, which may reduce the performance of the pump 100 and increase energy usage.

The heaviest fractions (including water and solids, e.g. sand), as well as the lightest fractions (including petroleum products) can be passed through the outlet 306 and to a process line 105, which may, for example, be a transport line to a topside plant, to shore, or to other subsea processing equipment.