MULTIPHASE PUMPING SYSTEM

Abstract

A multiphase pump system includes a pump (10) having first and second screw rotors (4) disposed within a pump body (A), and at least one inlet (3) in fluid communication with the first and second screw rotors, respectively. A discharge casing (B) is coupled to the pump body (A) for receiving fluid discharged from the first and second screw rotors (4). The discharge casing (B) is oriented orthogonally or at a non-zero angle with respect to a longitudinal axis of the pump body (A). The discharge casing (B) includes a separation chamber for separating liquid and gas components of the fluid discharged from the first and second screw rotors (4). The pump body (A) includes at least one opening (9) for directing separated liquid from the discharge casing (B) to a discharge chamber of the pump body (A).

Claims

1. A multiphase pump system, comprising: a pump having at least one set of rotors disposed within a pump body, and at least one inlet in fluid communication with the first and second screw rotors, respectively; and a discharge casing coupled to the pump body for receiving fluid discharged from the first and second screw rotors, the discharge casing further having a longitudinal axis that is oriented at a non-zero angle with respect to a longitudinal axis of the pump body; wherein the discharge casing comprises a separation chamber that facilitates separation of liquid and gas components of the fluid discharged from the first and second screw rotors, and wherein the pump body includes at least one opening for directing separated liquid from the discharge casing to a discharge chamber of the pump body.

2. The multiphase pump system of claim 1, further comprising at least one orifice in the pump body to permit liquid to recirculate from the discharge casing to the at least one inlet.

3. The multiphase pump system of claim 1, further comprising at least one orifice in a pump liner portion of the pump body to permit liquid to recirculate from the discharge casing to the at least one inlet.

4. The multiphase pump system of claim 1, wherein the discharge casing partially or fully surrounds a portion of the pump body.

5. The multiphase pump system of claim 1, wherein a central axis of the discharge casing is offset from a center of the pump body.

6. The multiphase pump system of claim 1, wherein the at least one inlet is positioned to provide inlet flow tangential to the at least one set of screw rotors.

7. The multiphase pump system of claim 1, wherein the at least one inlet comprises a plurality of inlets.

8. The multiphase pump system of claim 1, wherein the at least one set of rotors comprise a plurality of sets of rotors.

9. The multiphase pump system of claim 1, further comprising a capacity reduction line disposed between the discharge casing and the pump body, the capacity reduction line configured to provide a flow of pressurized liquid from the discharge casing to an inlet chamber of the pump.

10. The multiphase pump system of claim 9, further comprising a first isolation valve disposed in the capacity reduction line, and a second isolation valve disposed between the second pump inlet and the pump body.

11. The multiphase pump system of claim 1, further comprising a tubular separation element disposed within the discharge casing, the tubular separation element positioned to receive discharge flow from the pump body and to direct the received flow into the discharge chamber.

12. The multiphase pump system of claim 11, wherein the tubular separation element includes at least one opening along a length of the tubular separation element for directing the received flow into the discharge chamber through the opening.

13. The multiphase pump system of claim 1, further comprising at least one guide vane for initiating a spin into the fluid for enhanced liquid separation.

14. The multiphase pump system of claim 1, wherein the at least one set of rotors comprises at least one set of screw rotors.

15. The multiphase pump system of claim 1, wherein the longitudinal axis of the discharge casing is oriented at an angle so that the longitudinal axis of the discharge casing forms an angle of from 30-degrees to 90-degrees with respect to longitudinal axis of the pump body.

16. The multiphase pump system of claim 1, wherein the longitudinal axis of the discharge casing is oriented at an angle so that the longitudinal axis of the discharge casing forms an angle of about 90-degrees with respect to longitudinal axis of the pump body.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] By way of example, a specific embodiment of the disclosed device will now be described, with reference to the accompanying drawings, in which:

[0028] FIG. 1 is a schematic of a conventional coaxial pump casing design.

[0029] FIGS. 2A and 2B are side and end views of an example embodiment of a multiphase pump arrangement in accordance with the present disclosure.

[0030] FIGS. 3A and 3B are side and end views of a second example embodiment of a multiphase pump arrangement in accordance with the present disclosure.

[0031] FIGS. 4A and 4B are side views of an example of a third embodiment of a multiphase pump arrangement in accordance with the present disclosure.

[0032] FIGS. 5A and 5B are perspective and cross-section views, respectively, of a fourth example embodiment of a multiphase pump arrangement in accordance with the present disclosure.

[0033] The drawings are not necessarily to scale. The drawings are merely representations, not intended to portray specific parameters of the disclosure. The drawings are intended to depict example embodiments of the disclosure, and therefore are not to be considered as limiting in scope. In the drawings, like numbering represents like elements.

DETAILED DESCRIPTION

[0034] Numerous embodiments of an improved multiphase pumping system in accordance with the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the present disclosure are presented. The systems of the present disclosure may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will convey certain example aspects of multiphase pumping systems to those skilled in the art. In the drawings, like numbers refer to like elements throughout unless otherwise noted.

[0035] As will be described in greater detail, the disclosed pumps include discharge casings that are not coaxial with the main pump body but rather are oriented orthogonal to the pump body and its associated rotors (screws). In some embodiments the discharge casing can be oriented at an angle so that the axis of the discharge casing forms an angle of from 30-degrees to 90-degrees with respect to the axis of the pump body and screws. As arranged, the disclosed can provide sufficient liquid to the screw inlets and screw outlets. In some embodiments the preferred orientation of the discharge casing is vertical (while the orientation of the pump body and screws is horizontal), but this is not critical and the discharge casing can be oriented at an angled (e.g., 30, 45 or 60) with respect to the pump body and screws. In some embodiments the discharge casing can be oriented in the horizontal plane of the pump body and screws.

[0036] It will be appreciated that in some embodiments the discharge casing can be oriented at an angle so that the axis of the discharge casing forms an angle of from 30-degrees to 90-degrees with respect to the axis of the pump body and screws. In some embodiments the pump main body can form one end of the extended discharge casing or the pump main body can be partly of fully integrated into the discharge casing.

[0037] In general, pumps according to the present disclosure will include one or more of the following aspects: [0038] Drain/Liquid distribution hole(s) at the lowest point of the discharge casing and the pump body. [0039] External drain and/or liquid distribution piping connecting all low points in the discharge casing to a single drain port. [0040] Recirculation orifices or internal liquid recirculation paths back to suction (3% recirculation for cooling) integrated into the liner disk(s)/wall(s) which separate the suction area from the discharge area. [0041] More than one recirculation orifice, which in some embodiments includes one recirculation orifice per pump side or one recirculation orifice per screw. [0042] Flow directed from each recirculation orifice to the mechanical seal area of the pump to spray recycled liquid towards the seals. In some embodiments the tubing can be coupled to the orifice to receive and direct such flow for flushing the seal area (e.g., API 682 seal Plan 11). [0043] External recirculation piping with built in recirculation orifice(s) between pump discharge(s) to pump inlet(s). [0044] One or more inlet nozzles disposed at different positions and sides of the pump suction compartment(s). [0045] One or more outlet nozzles disposed at different positions and sides of the pump discharge casing. [0046] Inlet nozzle(s) positioned tangential to the pump suction casing. Inlet nozzle(s) oriented in any of a variety of directions with respect to the pump's suction casing. [0047] Discharge nozzle(s) positioned tangential to the discharge casing. [0048] Discharge nozzle(s) disposed inside the discharge casing with a tube and elbow. The elbow can be oriented in any direction, one example direction being upwards to collect predominantly the gas, another example direction being horizontally to the side to initiate spinning (vortex) movement of the fluid inside the discharge casing. [0049] Discharge casing of the main-pump-body includes a device to improve fluid separation inside the discharge casing, a non-limiting example of which can be an extended cylindrical tube with one or more transverse bores, another non-limiting example of which can be to install guiding plates on the top outlet of the main body to the pump discharge casing to initiate a spin of the fluid inside the pump discharge casing. It will be appreciated that any type of separation aid can also be used. [0050] Additional valves on the discharge casing (tower) for example to install the pressure limiting valve (PLV) or pressure safety valve (PSV) device. The PLV/PSV flange can be installed below the liquid level inside the tower to thereby feed the PLV/PSV with liquid and to avoid PLV/PSV instabilities when feeding the PLV/PSV with undefined liquid-gas mixtures as typical for conventional installation of the PLV/PSV on the discharge piping. [0051] Capacity reduction without efficiency impact by connecting only one inlet to pump suction and to shut off the other inlet from suction but connecting it directly to pump discharge (liquid, mixture or gas phase). Such an arrangement can efficiently reduce pump capacity by 50% without efficiency losses. As such, one set of screws still pumps 50% of the design flow rate from inlet to discharge while the second screw-pair runs idle by simply moving fluid from discharge to discharge without building up pressure and without consuming energy. [0052] To simplify the use of the capacity reduction feature the pump can be equipped with a connection from pump discharge at an optimal position on the separation tower directly to the pump inlet chamber. A valve (manual or automated) can be integrated into this capacity reduction line. [0053] In combination with pump speed control, the capacity turn down ratio can be improved to 1:20 without reduction in pump efficiency. In some embodiments internal circulation on discharge level can be provided instead of external recirculation back to suction. [0054] Capacity reduction can be achieved with low gas or pure liquid pumps using a large, small, or no separation tower. [0055] A capacity reduction line can be provided internally (i.e., integrated) or externally (as shown in the figures). [0056] The disclosed pumps can be equipped with screws of the same dimension but different pitch to allow for more accurate performance adjustment of overall pump capacity. [0057] The disclosed pumps can be equipped with screws of different dimensions and diameters, and/or the same or different pitch. [0058] For capacity reduction operations the active screw-pair at the inlet defines the pump capacity. Where the pitch is larger compared to the second screw-pair the pump reduction is less than 50%. Where the pitch is smaller the capacity reduction is more than 50%. The disclosed pumps can be equipped with two capacity reduction lines, one for each pump inlet. In such case the capacity reduction can be 100% pump capacity, x % capacity, (1x) % capacity. The difference in the screw pitch (p) can define x: x=p1/(p1+p2). [0059] The capacity reduction concept can be applied on both sides of the disclosed pumps to allow for an unloaded start of the pump before first one side, and then the second side is opened to switch over to full capacity operation. [0060] The separator tower can also act as 3-phase separator, using different outlets to pull fluid from different separation levels.

DESCRIPTION OF THE DRAWINGS

[0061] The figures illustrate the different pump components and effects in a simplistic way. The pump can include one or more sets of screws, and one or more inlet or discharge compartments. The different inlet and outlet compartments within the pump casing can be connected to each other internally-inside the pump casing, externally-by specific piping, or the inlet and outlet compartments can remain separate from each other. In cases in which the inlet and outlet compartments remain separate from each other each compartment can includes its own inlet or outlet nozzle.

[0062] The figures show embodiments having one inlet compartment, one outlet compartment and one set of screws, but this is not limiting. Moreover, certain of the figures show a design variant with 2 inlet compartments, one central discharge compartment and two sets of screws.

[0063] Referring now to FIGS. 2A, 2B, 3A and 3B, a non-limiting example of a pump 10 according to the disclosure will be described. The pump 10 includes a main pump body A that includes the pump suction chamber(s) and the screw outlet compartment(s). An integrated pump discharge casing (B) is directly mechanically and fluidly connected to the screw outlet compartment so that it receives fluid from the screw outlet compartment. The pump discharge casing (B) can be connected to the screw outlet compartment using any appropriate technique, including welding, bolting, and the like. It will also be appreciated that the pump discharge casing can be integrally formed with the pump casing and/or screw outlet compartment. The pump discharge casing (B) has a longitudinal axis B-B that is oriented orthogonal to a longitudinal axis A-A of the pump body A. In some embodiments the longitudinal axis B-B of the discharge casing can be oriented at an angle so that the longitudinal axis B-B of the discharge casing forms an angle of from 30-degrees to 90-degrees with respect to longitudinal axis A-A of the pump body A.

[0064] As shown, incoming multiphase flow (1) is directed to the screw inlet (3), and is transported to the pump outlet casing by the screws (4). The flow moves from the pump outlet casing into the pump discharge casing (B) (shown by arrow (5)). Separation of liquid and gas components of the multiphase fluid occurs within the pump discharge casing (B). Liquid storage also takes place in the discharge casing (B).

[0065] Liquid is allowed to flow from the discharge casing (B) back into the pump discharge chamber of the main pump body (A) via one or more liquid balancing hole(s) (9) (best seen in FIG. 2B) formed in an upper portion of the main pump body (A). After capturing the liquid inside the pump discharge casing (B), the remaining flow (i.e., the gas component of the multiphase flow) leaves the pump casing at the upper part of the pump casing (in the direction of arrow (2)).

[0066] As will be appreciated, the disclosed arrangement exposes the screw outlet ends to the discharge fluid which feeds the slip flow (8) along the screw gaps (i.e., the gaps between the screws and the pump liner). A portion of the liquid (typically 3 to 5%) is recirculated from the pump discharge, for example via an orifice, to the pump inlet (6). The recirculated fluid (7) is combined with the incoming multiphase flow (3) inside the pump inlet casing.

[0067] In some embodiments the orifices are integrated into the pump liner for better serviceability. Any desired number of orifices (e.g., one, two, four) can be provided for each screw to provide a desired recirculation flow. As shown in FIGS. 2A and 2B, the pump discharge casing (B) can be mounted directly on top of the pump body (A), and can extend orthogonally away from the pump body (A). As previously mentioned, in some embodiments the longitudinal axis B-B of the discharge casing can be oriented at an angle so that the longitudinal axis B-B of the discharge casing forms an angle of from 30-degrees to 90-degrees with respect to longitudinal axis A-A of the pump body (A).

[0068] FIGS. 3A and 3B illustrate an embodiment of a pump 20 including all of the features of pump 10 discussed in relation to FIGS. 2A and 2B, except that the discharge casing (B) of pump 20 can include or surround a portion of the pump body (A). In the illustrate embodiment, pump 20 includes a discharge casing (B) that is oriented orthogonal to the pump body (A) (though it will be appreciated that the discharge casing (B) can be oriented at any appropriate non-zero angle with respect to the pump body). In the illustrated embodiment the discharge casing (B) includes an upper portion (Ba) positioned above the pump body (A), a lower portion (Bb) that is disposed adjacent to, and partially encloses, a side portion of the pump body (A), and a bottom portion (Bc) that is disposed below the pump body (A). In addition, the central axis CB of the discharge casing (B) is offset from the center CA of the pump body (A) by a distance OD. This offset configuration can provide the best possible separation and liquid collection in the lower portion of the outlet casing. Also, the offset may be beneficial in that it can be required to install the inlet flange easily. Offset can be from 0 to of the pump casing diameter.

[0069] In a further embodiment, it is contemplated that two reduced-diameter outlet casings could be used in lieu of a single outlet casing where a small diameter outlet casing is beneficial.

[0070] Referring now to FIGS. 4A and 4B, a flow reduction arrangement will be described in greater detail. Because of the constant flow characteristic of twin-screw-pumps, as is typical for all positive displacement pumps, flow reduction can be difficult when a speed control device is not used. With conventional arrangements, the only way to reduce flow is to recirculate a portion of the discharge fluid back to the pump suction, which undesirably wastes energy and adds heat to the process. The unique, full double inlet design of pump 30, which includes two separate inlets, allows the user to shut off only one inlet, and to fill this inlet chamber with fluid from the discharge casing. As seen, the pump 30 of this embodiment includes a main pump body (A) with a discharge casing (B) mounted to the top of the main pump body so that the discharge casing is oriented orthogonally with respect to the main pump body (again, and as mentioned in some embodiments the discharge casing can be provided at any appropriate non-zero angle with respect to the main pump body). First and second inlets (1a), (1b) are provided to inlet regions of first and second pump screw pairs (3a), (3b). The discharge regions of the first and second pump screw pairs (3a), (3b) converge so that discharge flow (5) is routed to the discharge casing (B). A third inlet (1c) provides a flow path from the discharge casing (B) to an inlet region of the second screw pair (3b). Isolation valves V1, V2 are provided for the second and third inlets (1b), (1c) to selectively enable/prevent flow through those inlets. It will be appreciated that V1 could be a check valve, and that V1 and V2 can be manually or actuator operated.

[0071] During normal operation, shown in FIG. 4A, the first inlet (1a) is always open, while the second inlet (1b) is open only when the pump is operating at full capacity. The second isolation valve V2 is closed preventing recirculation flow from the discharge casing (B) to the inlet chamber associated with the second screw pair (3b). The inlet chamber associated with the second pump inlet (1b) is thus filled with fluid at suction pressure and flow is provided to the first and second pump screw pairs (3a), (3b) at suction pressure. The pump boosts the flow via the first and second pump screw pairs (3a), (3b) and provides the boosted flow (5) to the discharge casing (B).

[0072] During reduced capacity operation, shown in FIG. 4B, the first inlet (1a) remains open, the second inlet (1b) is closed (i.e., the first isolation valve V1 is closed), and the third inlet (1c) is open (i.e., the second isolation valve V2 is open). As can be seen, the third inlet (1c) enables fluid to recirculate from the discharge casing (B) to the inlet chamber associated with second screw (3b). Because the inlet chamber associated with the second screw (3b) is connected to the discharge casing (B) the inlet chamber is filled with fluid at discharge pressure. The flow passing through the second screw pair (3b) need not be separately pressurized, and thus no hydraulic energy is required to move flow from the inlet to the outlet of the second screw pair. Only the flow from the first (open) inlet la is boosted to discharge pressure via the first screw pair (3a). In some embodiments, one or both valves can be partially open to enable a smooth capacity change or reduced capacity operation. In one example embodiment, V2 could be partially open.

[0073] Referring now to FIGS. 5A and 5B, a multiphase pump 40 is shown with first and second inlets (1), a single discharge (2) and two sets of screws (3). The inlets (1) are positioned so that inlet flow is tangential to the screw pairs (3). As will be appreciated, it can be beneficial to use two inlet flanges per inlet compartment to feed each screw pair (3) separately.

[0074] A central discharge casing (B) extends orthogonally, vertically, from the horizontally oriented main pump body (A) so that fluid discharged by the screws (3) flows upward into the discharge casing (B) (though as mentioned, the central discharge casing (B) can be oriented at any appropriate non-zero angle with respect to the main pump body (A)). The illustrated embodiment includes an optional separation aid comprising a tubular element (C) disposed centrally within the discharge casing (B). The tubular element (C) is coupled at one end to the top of the main pump body (A) so that fluid discharged by the screws (3) enters the internal portion of the tubular element. The top end of the tubular element (C) is disposed below the top of the discharge casing (B) so that fluid flows up through the tubular element (C) and into the discharge casing. In some embodiments the tubular element (C) can include one or more openings (D) along the vertical length of the tubular element to enable fluid to pass from within the tubular element to the discharge casing (B) before the fluid reaches the top of the tubular element. In some embodiments, the tubular element (C) can include or be replaced by guide vanes to initiate a spin into the fluid for enhanced liquid separation.

[0075] In the illustrated embodiment, two liquid balancing holes (9) are disposed in an upper region of the main pump body to allow liquid to flow back from the discharge casing (B) to the discharge chamber portion of the main pump body (A) for high gas operation evolutions. The fluid which cannot be captured inside the pump discharge casing will leave the pump through the pump outlet (2). It will be appreciated that one or more liquid balancing holes can be used, and that in some embodiments more liquid balance holes (e.g., 4, 6) can be used.

[0076] The pump 40 can include a capacity reduction line, which can be the same or similar to the capacity reduction arrangement described in relation to the embodiment of FIGS. 4A and 4B. As will be appreciated, the capacity reduction line allows the user to shut off one inlet and open it to discharge so that one set of screws runs idle without adding to pump capacity.

[0077] While the present disclosure refers to certain embodiments, numerous modifications, alterations, and changes to the described embodiments are possible without departing from the sphere and scope of the present disclosure, as defined in the appended claim(s). Accordingly, it is intended that the present disclosure not be limited to the described embodiments, but that it has the full scope defined by the language of the following claims, and equivalents thereof. The discussion of any embodiment is meant only to be explanatory and is not intended to suggest that the scope of the disclosure, including the claims, is limited to these embodiments. In other words, while illustrative embodiments of the disclosure have been described in detail herein, it is to be understood that the inventive concepts may be otherwise variously embodied and employed, and that the appended claims are intended to be construed to include such variations, except as limited by the prior art.

[0078] The foregoing discussion has been presented for purposes of illustration and description and is not intended to limit the disclosure to the form or forms disclosed herein. For example, various features of the disclosure are grouped together in one or more aspects, embodiments, or configurations for the purpose of streamlining the disclosure. However, it should be understood that various features of the certain aspects, embodiments, or configurations of the disclosure may be combined in alternate aspects, embodiments, or configurations. Moreover, the following claims are hereby incorporated into this Detailed Description by this reference, with each claim standing on its own as a separate embodiment of the present disclosure.

[0079] As used herein, an element or step recited in the singular and proceeded with the word a or an should be understood as not excluding plural elements or steps, unless such exclusion is explicitly recited. Furthermore, references to one embodiment of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features.

[0080] The phrases at least one, one or more, and and/or, as used herein, are open-ended expressions that are both conjunctive and disjunctive in operation. The terms a (or an), one or more and at least one can be used interchangeably herein. All directional references (e.g., proximal, distal, upper, lower, upward, downward, left, right, lateral, longitudinal, front, back, top, bottom, above, below, vertical, horizontal, radial, axial, clockwise, and counterclockwise) are only used for identification purposes to aid the reader's understanding of the present disclosure, and do not create limitations, particularly as to the position, orientation, or use of this disclosure. Connection references (e.g., engaged, attached, coupled, connected, and joined) are to be construed broadly and may include intermediate members between a collection of elements and relative to movement between elements unless otherwise indicated. As such, connection references do not necessarily infer that two elements are directly connected and in fixed relation to each other. All rotational references describe relative movement between the various elements. Identification references (e.g., primary, secondary, first, second, third, fourth, etc.) are not intended to connote importance or priority but are used to distinguish one feature from another. The drawings are for purposes of illustration only and the dimensions, positions, order and relative to sizes reflected in the drawings attached hereto may vary.