TURBOMACHINE AND IMPELLER

Abstract

Turbomachine for increasing the pressure of a fluid or mixture of fluids, comprising an inlet and an outlet, a casing, a rotatable shaft arranged in the casing, diffusers or similar operatively arranged in the turbomachine, and a means for rotation operatively connected to the shaft. The turbomachine is distinguished in that it comprises: at least one impeller of a mixed flow type arranged on the shaft, the impeller having an inlet and an outlet, the inlet is closer to an axis of rotation than the outlet; and at least one further impeller arranged on a common or operatively connected shaft, chosen from the group consisting of axial impellers arranged upstream of the mixed flow type impeller and radial impellers arranged downstream of the mixed flow type impeller. Impeller for use in a turbomachine for increasing the pressure of a fluid or mixture of fluids, the impeller comprising at least one blade, distinguished in that it comprises at least one fluid passageway fluidly connecting the pressure side of the blade with the leeward side of the blade.

Description

FIELD OF THE INVENTION

The present invention relates to equipment for increasing the pressure of a fluid or a mixture of fluids, such as a mixture of oil, water and gas. More specifically, the invention relates to a turbomachine for increasing the pressure of a fluid or mixture of fluids and an impeller for use in a turbomachine.

BACKGROUND OF THE INVENTION AND PRIOR ART

A turbomachine is a machine that transfers energy between a rotor and a fluid, the energy is added as kinetic energy to the fluid or retrieved as kinetic energy from the fluid. Turbomachinery is a large group of machinery of which flow-machines is one type. For flowmachines having rotors, such as centrifugal pumps and compressors, the added kinetic energy is associated with an increased static pressure as the kinetic energy of the fluid is converted in means used for such purpose, such as a diffuser, a volute section or similar means. The rotors of flowmachines are usually the blades of one or more impellers. The impellers are usually arranged in series on a shaft, the number of impellers in series is determined by the required delivery pressure.

When oil, gas, condensate and inevitably also often water and possibly sand is produced from a hydrocarbon reservoir below a seabed, a turbomachine able to increase the pressure of such complex and usually variable mixture is very useful. Such turbomachines can be located on a seabed at a wellhead and even downhole in a production well. Apart from severe problems caused by possible contents of sand in the mixture, the gas contents impose problems for the turbomachine, as the efficiency tends to be severely reduced with increased gas volume fraction (GVF) in the mixture. Some such turbomachines exist and they are usually called multiphase pumps. Such multiphase pumps consist of axial flow type impellers or axial flow type impellers combined with radial flow type impellers, as described in U.S. Pat. Nos. 4,365,932, 5,375,976, 5,885,058, 5,961,282, 6,474,939, 5,562,405, 5,253,977 and 6,547,514, and in the patent publication JP 10288199. In U.S. Pat. No. 6,547,514 the first pump stage is called a helicoaxial pump, but said pump consists of helical impellers (paragraph 0021 and claim 10) for which most of the flow particles follow an axial path, for which reason the impellers or pump stage is of axial flow type but having a slightly tapered hub, which is known also for other axial impellers or pumps. From U.S. Pat. No. 5,885,058 teaching is provided (FIGS. 3, 4 and 6, col. 10 lines 4-13, col. 11 lines 14-24) in order to have a remixing action for gas having tendency to accumulate at certain places of the impeller, but only as a specific twin blade construction and a specific twin blade construction with perforations coaxial to a circle of rotation.

For further information about the turbomachines suitable for operation with multiphase fluid, reference is made to the patent publications mentioned above.

In spite of the available technology as mentioned above, there is a demand for alternative turbomachines and impellers, particularly turbomachines and impellers that can tolerate more variations with respect to the composition of fluid mixtures, particularly the contents of gas, while still reliably delivering high pressure and high throughput. The objective of the present invention is to meet said demand.

SUMMARY OF THE INVENTION

The objective is met by providing a turbomachine for increasing the pressure of a fluid or mixture of fluids, comprising an inlet and an outlet, a casing, a rotatable shaft arranged in the casing, diffusers or similar operatively arranged in the turbomachine, and a means for rotation operatively connected to the shaft. The turbomachine is distinguished in that it comprises

• • at least one impeller of a mixed flow type arranged on the shaft, the impeller having an inlet and an outlet, the inlet is closer to an axis of rotation than the outlet, and
  • at least one further impeller arranged on a common or operatively connected shaft, chosen from the group consisting of axial impellers arranged upstream of the mixed flow type impeller and radial impellers arranged downstream of the mixed flow type impeller.

The simplest version of the turbomachine of the invention comprises one impeller of a true mixed flow type on a rotatable shaft in a casing or housing, and one of the further impellers. The impeller is a true mixed flow type impeller if all flow particles or all of the fluid follow a path having both an axial and a radial component, from the inlet to the outlet, which in this context is defined by having the inlet closer to an axis of rotation than the outlet, preferably all of the inlet closer to an axis of rotation than the outlet. Accordingly, the inner part of the outlet is preferably outside the outer part of the inlet, measured from the axis of rotation. Also, the outlet is further down the axis of rotation than the inlet for a mixed flow type impeller. For axial impellers, the flow particles have only an axial component of the path of flow for at least a part of the flow or path of flow, whilst for radial impellers the flow particles have only a radial component for at least a part of the flow or path of flow.

The turbomachines or multifluid pumps of the invention comprises an impeller of true mixed flow type, in combinations not previously known with one or more of the further impellers. More specifically, in the turbomachine, following the path of fluid flow from the inlet to the outlet: one or more axial impellers are arranged, followed by one or more mixed flow type impellers, followed by one or more radial impellers, which embodiment is preferable for high to moderate gas volume fractions (GVF) and high pressure requirement. Alternatively, following the path of fluid flow from the inlet to the outlet: one or more axial impellers are arranged, followed by one or more mixed flow type impellers, which embodiment is most preferable for very high gas volume fractions. Alternatively, following the path of fluid flow from the inlet to the outlet: one or more mixed flow type impellers are arranged followed by one or more radial impellers, which embodiment is preferable for moderate gas volume fractions and high pressure requirement. The term one or more covers any integer from one to as many as required to deliver the required pressure or gas compression, such as 1 to 5, 10 or 15. Accordingly, the turbomachines of the invention are capable of subsea and/or downhole pumping and compressing a liquid/gas fluid mixture of very high GVF to very high pressure.

The turbomachine preferably includes several impellers, preferably also of the further or different types and with appropriate diffusers or similar arranged between stages or impellers in order to convert the kinetic energy into pressure. The diffusers or similar means can be a part of the casing or housing or be arranged on the shaft between stages or impellers, in the form of diffusers, stators, rectifiers, adjusters or volute chambers or other means known per se. The shaft can be divided into several releasable and thereby replaceable sections preferably coaxially connected. The casing can be divided into several parts, also inner and outer parts. The means for rotation is for example a motor of any appropriate type. The concept of having axial impellers arranged upstream of the mixed flow impeller and radial impellers arranged downstream of the mixed flow impeller has to do with the tolerance for handling gas and the capability to deliver high pressures and high throughput reliably. More specifically, the axial impellers can tolerate more gas, but deliver less pressure while the radial impellers can tolerate less gas but deliver higher pressure, relative to the mixed flow type impeller. Accordingly, high tolerance for gas can be achieved and high pressure can be achieved, since the gas can be successively compressed and the gas volume fraction can be successively reduced to a level that can be handled effectively by the next stage or impeller.

Preferably, the mixed flow type impeller is of a particular construction favorable with respect to tolerate gas, and preferably one or several features improving the tolerance for gas is included in some or all of the impellers, particularly the leading or upstream impellers operating at the highest gas volume fractions.

Accordingly, the turbomachine, comprising impellers with impeller blades, preferably comprises fluid passageways arranged so as to fluidly connect the pressure side of a blade with the leeward side of the blade, in order to have remixing of gas and liquid, said fluid passageways are preferably chosen amongst perforations arranged close to or at the inner edge of the blades, gaps between the blade or shroud and a hub or shaft, and fluid passageways arranged in the hub or shaft. Preferably one or more of the impellers, particularly the impellers of mixed flow type, comprises a hub arranged on or integral with the shaft and a shroud with blades arranged outside the hub around the periphery on and toward the inlet side of the hub and impeller, a gap is provided between the hub and the shroud, the gap is formed between the inner surface of the shroud and the outer surface of the hub, from the inlet side of the impeller, the gap preferably has the shape of a cylindrical or conical shell or helix-shaped band.

Preferably at least some impeller blades are perforated, and for impellers having several blades or pressurized volumes between blades, the perforations are not coaxial as seen parallel to the shaft. Preferably impeller blades are perforated for a number of blades, said perforations are not coaxial as seen along a circle crossing the blades, said circle being coaxial and perpendicular to the axis of rotation. Said non-coaxial arrangements will improve the remixing of gas with liquid since successive pockets of gas between blades can be avoided by arranging perforations in order to eliminate “neighbour” gas pockets. Further, at least some impellers have blades preferably having a clearance in between the blades at the portion close to the shaft, as seen parallel to the shaft, preferably said clearance, as seen along a line parallel to the shaft, in substance has the shape of a triangle having a small apex angle, and it represents a leakage passageway for fluid to remix gas and liquid.

The invention also provides an impeller for use in a turbomachine for increasing the pressure of a fluid or mixture of fluids, particularly feasible for use in a turbomachine according to the present invention. The impeller comprises at least one blade and is distinguished in that it comprises at least one fluid passageway fluidly connecting the pressure side of the blade with the leeward side of the blade, preferably across the blade or around the inner edge of the blade. Preferably the fluid passageway is chosen amongst perforations arranged close to or at the inner edge of the blade, such as within one blade width from the inner edge of the blade, gaps between the blade or shroud and a hub or shaft, and fluid passageways arranged in the hub or shaft. Preferably the impeller blades are perforated for at least a number of blades, preferably said perforations are not coaxial neither as seen along a circle crossing the blades, said circle being coaxial and perpendicular to the axis of rotation, nor as seen along an axis parallel to the shaft.

In a preferable embodiment of the invention the impeller is of a mixed flow type, distinguished in that it comprises: an inlet and an outlet, the inlet is closer to an axis of rotation than the outlet; a hub arranged on or integral with a shaft, and a shroud with blades arranged outside the hub around the periphery thereof; and a gap is provided between the hub and the shroud. Preferably the gap is formed between the inner surface of the shroud and the outer surface of the hub, from the inlet side of the impeller, the gap preferably has the shape of a cylindrical or conical shell or helix-shaped band. Said gap represents a leakage passageway for fluid to remix gas and liquid. Preferably the whole inlet is closer to an axis of rotation than the outlet. Accordingly, all flow particles or all of the flowing fluid preferably flow out from the outlet further away from an axis of rotation than the inlet. The angle of flow is preferably axial (i.e. parallel to the shaft) for the inlet and about 10° to 70° from axial for the outlet. The flow particles can be seen as a fluid molecule or particle defining a trajectory of flow as it flows through the impeller in operation. The hub is preferably conical and widest at the downstream or trailing side, allowing the shroud to be fastened easily at the downstream or trailing side of the hub by threads or by other convenient means, whilst the gap is formed between the interfaces upstream, which design is preferable also for the further impellers.

Preferably the impeller blades are having a clearance in between them at the portion close to the shaft, for a number of impellers, as seen parallel to the shaft, said clearance, as seen along a line parallel to the shaft, in substance preferably has the shape of a triangle having a small apex angle.

Any operative combination of the turbomachine of the present invention, as defined in a respective independent claim, with features mentioned or illustrated in this document, is a part of the invention. Any operative combination of the impeller of the present invention, as defined in a respective independent claim, with features mentioned or illustrated in this document, is a part of the invention.

FIGURES

The present invention is illustrated with seven figures, of which

FIG. 1 illustrates a turbomachine of the present invention,

FIG. 2 illustrates a further turbomachine of the present invention,

FIG. 3 illustrates an impeller of the present invention,

FIG. 4 illustrates comparative flow data through impellers of and not of the present invention,

FIG. 5 illustrates comparative flow data through impellers of and not of the present invention,

FIG. 6 illustrates flow through an impeller not of the present invention, and

FIG. 7 illustrates flow through an impeller of the present invention.

DETAILED DESCRIPTION

Reference is made to FIG. 1 illustrating an embodiment of a turbomachine 1 according to the present invention. More specifically the turbomachine 1 comprises an inlet 2 and an outlet 3, a casing 4 and a rotatable shaft 5 arranged in the casing, diffusers 6 or similar operatively arranged in the turbomachine, and a means 7 for rotation operatively connected to the shaft. The illustrated turbomachine comprises three impellers 8 of a mixed flow type arranged on the shaft, the impeller having an inlet and an outlet, the inlet is closer to an axis of rotation than the outlet; three axial impellers 9 arranged upstream of the mixed flow type impeller and three radial impellers 10 arranged downstream of the mixed flow type impeller.

Reference is made to FIG. 2 illustrating a further turbomachine 1 of the present invention, more specifically a longitudinal section thereof. The same reference numericals as used in FIG. 1 are used for identical or similar features also in FIG. 2. The turbomachine of FIG. 2 comprises two impellers 8 of mixed flow type, arranged on the shaft toward the inlet 2, and seven radial impellers 10. The radial impellers 10 are from left to right three impellers, then the flow is directed to the radial impeller at the very end of the shaft, from where the flow successively is directed through the remaining radial impellers back along the shaft, to the very last impeller below the outlet 3. This arrangement improves the stability of the turbomachine by balancing out axial forces. For clarity, only some of the diffusers are referenced numerically. The flow bores are not possible to follow all the way on a 2D section, however a 3D animation or a large number of successive sections would allow the flow bores to be followed through the machine. The means for rotation is not particularly relevant in this context and is known per se, and is not illustrated. The diffusers, bearings, shaft seals and other features are not particularly relevant in this context either, and are also known per se, and are therefore not discussed in further detail.

Reference is made to FIG. 3 illustrating an impeller of the present invention, more specifically a longitudinal section of a mixed flow type impeller 8. The impeller comprises an inlet 11 and an outlet 12, the inlet is closer to an axis of rotation, indicated by a dotted line, than the outlet. A hub 13 is arranged on or integral with a shaft, and a shroud 14 with blades is arranged outside the hub around the periphery and facing the inlet side of the impeller. A gap 15 or slit is provided between the hub and the shroud.

Further reference is made to FIGS. 4 and 5, illustrating head and efficiency at 100% and 120% of BEP (Best Efficiency Point), respectively, with and without a fluid passageway in the form of a gap (hub blade clearing), as a function of GVF (Gas Volume Fraction) at the pump inlet. The lines marked with “diamond” symbols represent head H and the lines marked with triangles represent efficiency Eta. The dotted lines represent data for an impeller according to the invention, with a hub gap. The solid lines are for an identical impeller outside the invention, without a hub gap. An increase in head is generated for GVF between 5 and 40% at 100% of BEP. A very significant increase in head is generated for GVF above about 5% at 120% of BEP. This illustrates a part of the technical effect of the invention.

Further reference is made to FIGS. 6 and 7, illustrating accumulated gas volume fraction in a cross section in the middle of the flow channel, with and without a gap, respectively. The gas volume fraction is illustrated by a grey scale, the darker the tone the higher GVF. In FIG. 6, without a gap and not according to the present invention, the highest GVF is in the corner between the hub and the blade. In FIG. 7, with a gap and according to the invention, it is clearly illustrated how, due to the gap, gas is redistributed or remixed, and the pressure side of the blade is practically free of accumulated gas or air, which is assumed to be crucial for good efficiency. In the figures, the blade is slightly inclined from the horizontal and almost parallel to the Y-axis, whilst the hub is on the left side at about 45° inclination from the blade.

Several other results exist able to demonstrate the technical effect of the invention, from simulations, calculations and tests, for both the turbomachine and the impeller.

For both the turbomachine and the impeller of the invention, preferably gaps are provided, and perforations and clearances, which features provide remixing of gas and liquid, thereby avoiding gas pockets blocking or disturbing the flow, the beneficial effect of remixing exceeding any reduction in pumping or compression effect due the “leakage” flow over said gaps, perforations and clearances. By following the teaching of the current document, and good engineering practice, said preferable embodiments are achievable based on calculations, modelling and testing for specific applications in order to find the correct places and sizes for gaps, perforations and clearances.

For a turbomachine of the invention, for almost any specific embodiment and application, the length of the shaft can be reduced compared to prior art equipment, which results in improved reliability, reduced size and weight and reduced power consumption, in addition to greater tolerance as to gas volume fraction or variation. Dependent on the specific embodiment, the turbomachine can operate efficiently at above 80% GVF input and deliver fluid at pressures over 200 bar. The mixed flow stage or impeller is capable of handling GVF of 50% or even higher, and is favourable for a GVF range of about 50-20%. Each impeller increases the pressure with about 20 bar, decreasing with increasing GVF. For a turbomachine required to handle higher GVF than about 50%, a pre-stage of axial impellers are preferably included. For high pressure delivery, radial impellers are preferably used downstream of the mixed flow type impellers after the GVF has been compressed to about 15% or lower.

Claims

1. A turbomachine for increasing the pressure of a fluid or mixture of fluids, comprising: an inlet and an outlet;a casing;a rotatable shaft arranged in the casing;diffusers or similar operatively arranged in the turbomachine;a means for rotation operatively connected to the shaft; andat least one impeller with at least one blade, wherein the turbomachine comprises:at least one fluid passageway connecting a pressure side of an impeller blade with a leeward side of the impeller blade, the at least one fluid passageway is arranged so as to have remixing of gas and liquid by having in substance gas flowing through the at least one fluid passageway.

2. The turbomachine according to claim 1, wherein the at least one fluid passageway is chosen amongst perforations arranged close to or at the inner edge or end of the blades, within one blade width from the inner edge or end of the blade, gaps between the blade or shroud and a hub or shaft, and fluid passageways arranged in the hub or shaft.

3. The turbomachine according to claim 1, wherein one or more of the impellers comprises a hub arranged on or integral with the shaft and a shroud with blades arranged outside and around the periphery of the hub, and a gap is provided between the hub and the blades of the shroud.

4. The turbomachine according to claim 1, wherein following the path of fluid flow from the inlet to the outlet: one or more axial impellers are arranged, followed byone or more mixed flow type impellers, followed byone or more radial impellers.

5. The turbomachine according to claim 1, wherein following the path of fluid flow from the inlet to the outlet: one or more axial impellers are arranged, followed byone or more mixed flow type impellers.

6. The turbomachine according to claim 1, wherein following the path of fluid flow from the inlet to the outlet: one or more mixed flow type impellers are arranged, followed byone or more radial impellers.

7. The turbomachine according to claim 1, wherein at least some impeller blades are perforated, and for impellers having several blades the perforations for neighbor blades are not coaxial as seen parallel to the shaft.

8. The turbomachine according to claim 1, wherein impeller blades are perforated for a number of blades, and for impellers having several blades the perforations of neighbour blades are not on the same circle of rotation around the shaft.

9. The turbomachine according to claim 1, wherein at least some impellers have blades having a clearance in between the blades at the portion close to the shaft, preferably said clearance for neighbor blades as seen along a line parallel to the shaft, in substance has shape of a triangle having a small apex angle.

10. An impeller for use in a turbomachine for increasing the pressure of a fluid or mixture of fluids, the impeller comprising: at least one blade; andwherein the turbomachine comprises at least one fluid passageway connecting the pressure side of a blade with the leeward side of the blade, the at least one fluid passageway is arranged so as to have remixing of gas and liquid by having in substance gas flowing through the fluid passageway.

11. The impeller according to claim 10, wherein the at least one fluid passageway is chosen amongst perforations arranged close to or at the inner edge or end of the blades, within one blade width from the inner edge or end of the blade, gaps between the blade or shroud and a hub or shaft, and fluid passageways arranged in the hub or shaft.

12. The impeller according to claim 10, wherein the impeller comprises: an inlet and an outlet, the inlet is closer to an axis of rotation than the outlet; anda hub arranged on or integral with a shaft, and a shroud with blades arranged outside the hub around the periphery thereof, and a gap is provided between the hub and the blades of the shroud.

13. The impeller according to claim 12, wherein the gap is formed between the inner edges of the blades of the shroud and the outer surface of the hub, from the inlet side of the impeller.

14. The impeller according to claim 10, wherein for impellers having several blades the impeller blades are perforated for at least a number of blades, preferably said perforations for neighbour blades are not coaxial as seen along an axis parallel to the shaft and preferably perforations of neighbour blades are not on the same circle of rotation around the shaft.