Patent Application
20120087808
The subject matter disclosed herein relates to liquid ring compressors, and more particularly, to liquid ring compressors that may be employed to compress wet gases in a subsea environment.
In subsea processing, oil and/or gas may be processed using equipment located on the sea floor rather than on a fixed or floating platform. Subsea processing may be particularly useful in extreme environments where equipment on the surface may be subjected to harsh conditions. Further, subsea processing may provide increased production, as well as reducing topside equipment expenditures during development. Subsea pumping and/or boosting stations are often used to transport well streams from the sea floor to floating platforms or land based production facilities for further processing. The subsea stations may employ one or more compressors that operate in conjunction with pumps to provide the motive force for transporting the well streams to the surface.
In a first embodiment, a liquid ring compressor includes a shaft, a main body inner casing disposed about the shaft to form a chamber between the shaft and the main body inner casing, an inlet configured to remove a portion of liquid from a wet gas and to direct the wet gas into the chamber, and an impeller rotatably disposed within the chamber and configured to direct a remaining portion of the liquid in the wet gas out towards the main body inner casing to form a liquid ring within the chamber to compress the wet gas.
In a second embodiment, a liquid ring compressor includes a shaft, an inner casing disposed about the shaft to form a chamber between the shaft and the inner casing, an impeller rotatably disposed within the chamber and configured to direct a liquid out towards the inner casing to form a liquid ring within the chamber to compress a wet gas, apertures configured to remove a portion of the liquid from the liquid ring, a gas outlet coupled to the chamber to direct the compressed wet gas from the liquid ring compressor, and a liquid outlet coupled to the apertures to direct the removed portion of the liquid from the liquid ring compressor.
In a third embodiment, a subsea compression system includes a liquid ring compressor configured to remove liquid from a wet gas, and a conventional compressor disposed downstream of the liquid ring compressor to compress the wet gas from the liquid ring compressor.
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
One or more specific embodiments of the present invention will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.
When introducing elements of various embodiments of the present invention, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.
The present disclosure is directed to subsea compression systems that employ liquid ring compressors to compress wet gases that have a significant liquid volume fraction (LVF). According to certain embodiments, the LVF of the wet gases is from 0 to 5 percent, and all subranges therebetween. More specifically, the LVF of the wet gases may be at least 0.1 percent. Further, according to certain embodiments, the LVF of the wet gases may be just slightly greater than 0.1 percent. The liquid within the wet gases is used by the liquid ring compressors described herein to form a liquid ring that provides positive displacement of the wet gases within the liquid ring compressors. At least a portion of the liquid that separates from the wet gases to form the liquid ring may be removed through openings in the liquid ring compressor casing. Accordingly, the liquid ring compressors may be employed to separate liquid from the wet gases, in addition to compressing the wet gases. In certain embodiments, the liquid ring compressors may be employed upstream of conventional compressors, such as centrifugal, radial, or screw compressors, to reduce the amount of liquid that enters the conventional compressors. According to certain embodiments, the liquid ring compressors may be used upstream of conventional compressors to replace vapor-liquid separators, which have increased operational complexity and cost as compared to liquid ring compressors. Further, the liquid ring compressors may be designed to condition the flow of the wet gases that enter the conventional compressors by reducing fluctuations in the amount of liquid that enters the conventional compressors.
The compression system 10 includes a liquid ring compressor 22 located upstream from a conventional compressor 24. According to certain embodiments, the conventional compressor 24 may include a centrifugal compressor, a radial compressor, a screw compressor, or a heli-coaxial compressor, among others. In certain embodiments, the conventional compressor 24 may represent multiple stages of conventional compressors. Further, in certain embodiments, the liquid ring compressor 22 may represent multiple stages of liquid ring compressors. Moreover, in other embodiments, the conventional compressor 24 may be omitted. In these embodiments, the compression system 10 may include one or more liquid ring compressors 22 and may exclude conventional compressors 24.
The compression system 10 receives the production fluid through a flow line 26 that connects the production region 12 to the liquid ring compressor 22. The production fluid entering the liquid ring compressor 22 is a wet gas with a relatively high LVF, which, in certain embodiments may be approximately 0.1 to 5 percent, and all subranges therebetween. According to certain embodiments, it may be desirable for the LVF of the wet gas entering the compression portion of the liquid ring compressor 22 to be just slightly above 0.1 percent. For example, in certain embodiments, it may be desirable for the LVF of the wet gas entering the compression chamber to be between 0.1 and 0.2 percent, or more specifically, between 0.10 and 0.15 percent. However, in other embodiments, the target LVF for the wet gas entering the compression chamber may vary depending on factors, such as the design of the liquid ring compressor, the initial LVF of the wet gas, and operating pressures. According to certain embodiments, if the LVF of the wet gas is greater than just slightly above 0.1 percent, a portion of the liquid may be removed from the wet gas prior to the wet gas entering the compression chamber, as described further below with respect to
Within the liquid ring compressor 22, at least a portion of the liquid within the wet gas is separated from the wet gas to form a liquid ring that provides for positive displacement of the gas within the production fluid to compress the gas. According to certain embodiments, the gas may be compressed within liquid ring compressor 22. However, in other embodiments, minimal, or no compression may occur within the liquid ring compressor 22. In these embodiments, the liquid ring compressor 22 may be used to primarily separate liquid from the wet gas. The production fluid exiting the liquid ring compressor 22 may have a lower LVF than the wet gas entering the liquid ring compressor 22. According to certain embodiments, the LVF of the wet gas may be reduced by approximately 20 to 100 percent, and all subranges therebetween.
A flow line 28 is connected to the liquid ring compressor 22 to remove liquid from the liquid ring compressor 22. For example, at least a portion of the liquid from the liquid ring may be directed through the liquid flow line 28 to the production facility 16. In certain embodiments, the amount of liquid removed through the liquid flow line 28 may depend on the LVF of the wet gas entering the liquid ring compressor 22. For example, when the LVF is relatively high, more liquid may be removed than when the LVF is relatively low. Further, when the LVF is fairly low, such as approximately 0.5 to 1 percent or less, no liquid may be removed through the liquid flow line 28. In other embodiments, rather than being connected to the production facility 16, the liquid flow line 28 may be connected to a boost pump that injects the removed liquid into the discharge manifold of the boosting station 20 where the liquid may be combined with the production fluid exiting the boosting station 20.
The production fluid from the liquid ring compressor is removed through a flow line 30 that directs the production fluid, which is mostly gas, from the liquid ring compressor 22 to the conventional compressor 24. Within the conventional compressor 24, the production fluid is compressed to provide pressure to direct the production fluid from the boosting station 20 to the production facility 16. According to certain embodiments, the boosting station 20 may be designed to compensate for the loss of pressure that occurs along the flow lines 26, 28, and 32. The compressed production fluid exits the conventional compressor 24 though a flow line 32 that directs the compressed production fluid to the production facility 16.
As shown in
In certain embodiments, a bypass flow line 38 may be included within compression system 10 to direct the production fluid from the production region 12 directly to the conventional compressor 24, bypassing the liquid ring compressor 22. The bypass line 38 may be employed when there is a low amount of liquid within the production fluid. However, in other embodiments, the bypass line 38 may be omitted. Further, in certain embodiments, other equipment, such as pumps and controls, among others, may be included within the boosting station 20. The equipment may be connected to power and communication supplies by umbilical connections. For example, in certain embodiments, the boosting station 20 may receive power from an umbilical connected to an onshore or platform power supply.
The main body 40 includes an outer casing 60 disposed around an inner casing 62 that is disposed around a shaft 64. The inner casing 62 is coupled to the motor shaft 34, shown in
The inner casing 44 of the inlet section 42 may be coupled to the shaft 64 of the main body 40 to direct production fluid from the interior 52 of the inlet section 42 to an inlet chamber 74 within the shaft 64. As shown in
As the liquid flows into the chamber 72, the rotation of the impeller 66 may exert centrifugal force on the liquid, thereby directing the liquid out towards the inner casing 62 to form a liquid ring 96, as shown in
According to certain embodiments, as the production fluid is compressed within the chamber 72, liquid within the production fluid may flash to further reduce the LVF of the production fluid. Further, some liquid may become part of the liquid ring formed within the chamber 72. Openings 86, such as slots, are included within the inner casing 62 to remove excess liquid from the chamber 72. For example, excess liquid from the liquid ring may flow through the openings 86 to be collected in the chamber 70 between the inner casing 62 and the outer casing 60. From the chamber 70, the collected liquid may flow through an outlet disposed in the plate 69, as shown in
As shown, the openings 86 are depicted as slots spaced along the inner casing 62. However, in other embodiments, the size, shape, and/or spacing of the openings 86 may vary. For example, in certain embodiments, the openings 86 may be circular, rectangular, or triangular, among others. The openings 86 also may be disposed in a random or patterned configuration. Further, in certain embodiments, the openings 86 may be designed to have a cross-sectional area that is designed to extract a constant volume or mass flow of liquid from the chamber 72 under constant operating conditions. The location of the openings 86 on inner casing 62 also may be selected so that a desired amount of liquid is extracted under constant operating conditions. Moreover, in certain embodiments, the openings 86 may be strategically placed to stabilize and/or to alter the shape of the liquid ring under particular operating conditions, such as, for example, the maximum possible pressure ratio. Further, operating parameters for the liquid ring compressor 22, such as the backpres sure and/or the revolutions per minute of the impeller 66, may be varied to change the amount of liquid that is extracted.
As shown in
As shown in
As discussed above with respect to
A rear plate 110 is disposed on the opposite end of the main body 40 from the front plate 104 to allow the liquid and the compressed production fluid to exit the liquid ring compressor 22. The rear plate 110 includes an opening 112 for directing the compressed production fluid from the liquid ring compressor 22 to the flow line 30 (
As may be appreciated, the front and rear plates 104 and 110 are provided by way of example only, and are not intended to be limiting. In other embodiments, multiple plates, baffles, cones, or other fluid directing mechanisms may be employed to direct the production fluid and the liquid to and/or from the liquid ring compressor 22. Further, the locations, shapes, and/or sizes of the openings 106, 108, 112, and 94 may vary. Moreover, in other embodiments, the opening 112 for the compressed production fluid and/or the opening 94 for the liquid may be disposed on the main body 40 of the liquid ring compressor 22, rather than on the rear plate 110. Further, in certain embodiments, the opening 112 for the compressed production fluid and/or the opening 94 for the liquid may be disposed on the front plate 104.
The shape, size, and/or location of the openings 86 included on the inner casing 62 also may vary. For example,
The openings for removing liquid from the liquid ring also may be located on the front and/or rear plate, instead of, or in addition to, including openings on the inner casing 62. For example,
The openings 122 and 126 may be employed in liquid ring compressors with rotating inner casings 62 or in liquid ring compressors with rotating shafts 102. Further, the shape, size, and/or location of the openings 122 and 126 may vary. For example, in other embodiments, the openings 122 and 126 may be included on front plates. According to certain embodiments, the location of the openings 122 and 126 may be selected so that liquid is extracted when the liquid ring has reached a predetermined size. Further, in certain embodiments, the locations may be selected so that liquid is extracted under normal operating conditions of the liquid ring compressor without extracting gas from the production fluid. Moreover, in other embodiments, the openings may have another shape, such as circular, oblong, rectangular, or triangular, among others.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.
