Compact turbomachine system with improved slug flow handling

A turbomachine system and method, with the system including a slug detector coupled to a main line to detect a slug flow in a multiphase fluid in the main line. The system also includes a compressor fluidly coupled to the main line and disposed downstream of the slug detector, and a bypass line fluidly coupled to the main line upstream of the compressor and downstream of the compressor. The system further includes at least an upstream control valve fluidly coupled to the main line upstream of the compressor and communicably coupled to the slug detector. The upstream control valve is configured to actuate between a normal position, in which the upstream control valve directs fluid to the compressor, and a bypass position, in which the upstream control valve directs fluid to the bypass line, according to when the slug detector detects a slug flow.

BACKGROUND

Turbomachine systems are often used to process multiphase fluids, for example, in pipeline applications, which provide a unique set of challenges to system designers. In some low flow-rate applications, the multiphase fluid may be a relatively well-mixed flow of gas and liquid. As such, a generally expected combination of gas and liquid arrives at the turbomachine, which may be separated and efficiently handled by appropriate fluid handling equipment (e.g., a compressor and a pump). However, in some higher-flow rate systems, a periodic flow may develop, in which, at some points, a disproportionately large percentage of the flow is liquid (i.e., a slug), while at other points, a disproportionately large percentage is gas. In some cases, the slugs can grow to occupy an entire cross-section of the pipeline, such that the denser liquid slugs separate pockets of gas. In severe cases, the slugs are preceded by no flow and followed by high-pressure gas flow. Further, the occurrence and position of the slugs can be relatively difficult to predict.

These slugs present a challenge, as it may be difficult to completely separate them from the gas without depriving the compressor of process fluid or flooding the separator. Accordingly, slug damping techniques and systems are often employed upstream of such processing equipment to reduce slug formation and propagation. Despite precautions taken to avoid the propagation of slugs, however, slugs often still reach the turbomachine systems.

To handle the slugs, the turbomachine systems generally include one or more slug catchers. Various types of slug catchers are known, but the general principle is that the slug catchers provide a buffer volume sufficient to store the largest slugs expected to be received from the pipeline. Accordingly, such slug catchers are typically large and heavy, substantially adding to the footprint of the system. In some applications, however, especially for offshore or subsea hydrocarbon production, space is at a premium, thus it is desirable to reduce the system footprint wherever possible. Each component is, therefore, carefully designed to occupy the least amount of space possible, while still providing for maximum operating efficiency. Slug catchers, however, remain bulky and heavy, as they must provide sufficient volume and handle sufficient pressures to accomplish their function.

What is needed is a system and method for effectively handling slug flow, while providing a reduced footprint for the turbomachine system.

SUMMARY

Embodiments of the disclosure may provide an exemplary turbomachine system. The turbomachine system includes a slug detector coupled to a main line and configured to detect a slug flow in a multiphase fluid in the main line, and a compressorfluidly coupled to the main line and disposed downstream of the slug detector. The turbomachine system also includes a bypass line fluidly coupled to the main line upstream of the compressor and downstream of the compressor. The turbomachine system further includes an upstream control valve fluidly coupled to the main line upstream of the compressor and communicably coupled to the slug detector. The upstream control valve is configured to actuate between a normal position, in which the upstream control valve directs fluid to the compressor, and a bypass position, in which the upstream control valve directs fluid to the bypass line. Further, the upstream control valve is actuated from the normal position to the bypass position when the slug detector detects the slug flow.

Embodiments of the disclosure may also provide an exemplary method for handling slugs in a turbomachine system. The method includes detecting a slug flow in a main line upstream of a compressor with a slug detector, and actuating an upstream control valve in response to a detected slug flow from a normal position, in which the upstream control valve directs fluid toward the compressor, to a bypass position, in which the upstream control valve directs fluid to a bypass line extending from a position upstream of the compressor to a position downstream of the compressor. The method also includes diverting the slug flow around the compressor via the bypass line, and returning the upstream control valve to the normal position when the slug flow has passed through the bypass line.

Embodiments of the disclosure may further provide an exemplary system for handling slugs. The system may include a slug detector disposed upstream of a compressor, the slug detector being configured to detect a slug flow in a main line fluidly coupled to a wellhead, and a bypass line coupled to the main line at a position upstream of the compressor and at a position downstream of the compressor. The system may also include a control valve communicably coupled to the slug detector and fluidly coupled to the main line, the compressor, and to the bypass line. The control valve is configured to actuate from a normal position, in which the control valve directs fluid toward in the main line to the compressor, to a bypass position, in which the control valve diverts fluid to the bypass line when the slug detector detects the slug flow.

DETAILED DESCRIPTION

FIG. 1illustrates a schematic view of a turbomachine system100, according to an embodiment, having an improved slug flow handling capability. Accordingly, the turbomachine system100may obviate any need for slug catchers, but may, in some embodiments, be used in conjunction with such traditional slug catchers. The turbomachine system100includes a turbomachine assembly102fluidly coupled to a main line104. The main line104has an upstream section104a, which is upstream of the turbomachine assembly102and coupled to an inlet106, and a downstream section104b, which is downstream of the turbomachine assembly102and coupled to an outlet103. In an embodiment, the main line104may be a natural gas pipeline and the inlet106may be a wellhead. Accordingly, in some embodiments, at least the turbomachine assembly102may be marinized or otherwise protected for location and operation in subsea environments.

The process fluid may be a multiphase fluid. As this term is used herein, “multiphase fluid” is intended to be broadly construed to include combinations of liquids and gasses (e.g., natural gas and water), immiscible liquids (e.g., hydrocarbons and water), gases of different densities, and liquids and/or gasses and solids (e.g., particulate matter such as sand).

After the process fluid reaches the outlet103, it may proceed downstream for subsequent operation, working, storage, removal, consumption, separation, etc. It will be appreciated that the turbomachine system100may be tailored to provide process fluid for any subsequent use. Moreover, the turbomachine assembly102may be any suitable machinery configured to remove and/or add energy to a process fluid. Accordingly, the turbomachine assembly102may include one or more compressors, separators, turbines, pumps, fans, blowers, combinations thereof, or the like. In at least one embodiment, the turbomachine assembly102may be or include a DATUM® C. or DATUM® I centrifugal compressor, commercially-available from Dresser-Rand Co. of Olean, N.Y., USA.

The turbomachine system100also includes a slug detector108disposed upstream of the turbomachine assembly102and fluidly coupled to the upstream section104aof the main line104. The slug detector108may include any device suitable for detecting a slug, for example, by measuring, calculating, or otherwise detecting density, pressure, mass flow rate, combinations thereof, or changes in one or more of these characteristics in the fluid flow through the main line104. As the terms are used herein, “slug” and “slug flow” generally refer to a concentrated mass of a higher density portion of the process fluid propagating through a line, e.g., the main line104. For example, in some oilfield production applications, a slug may be a mass of water moving in a natural gas pipeline.

The slug detector108may be a Coriolis tube. One example, among many, of a Coriolis tube slug detector that may be suitable for use as the slug detector108is the MIRCO MOTION ELITE®, commercially-available from Emerson Electric Co. of St. Louis, Mo., USA. Without limitation to the present disclosure, further information on Coriolis tubes that may be used in the turbomachine system100may be found, for example, in U.S. Pat. Nos. 4,127,028; 4,187,721; 4,491,025; and/or 6,513,393, the entirety of each being incorporated herein by reference to the extent consistent with the present disclosure. In another example, the slug detector108may be a sonic flow meter, as is known in the art. In still another example, the slug detector108may be coupled to the main line104in one or more locations and configured to take pressure measurements to determine when a slug flow exists. One example of such pressure measurement schemes to detect slug flow may be provided as further detailed in U.S. Pat. No. 7,239,967, the entirety of which is incorporated herein by reference to the extent consistent with the present disclosure.

The turbomachine system100may also include one or more control valves fluidly coupled to the main line104, for example, an upstream control valve110and a downstream control valve112, as shown. The upstream control valve110may be fluidly coupled to the upstream section104aof the main line104and to a bypass line113. The downstream control valve112may be fluidly coupled to the downstream section104bof the main line104and to the bypass line113. The control valves110,112may also be communicably coupled to the slug detector108via signal lines114,116, respectively. In some embodiments, the control valves110,112may be communicably coupled to the slug detector108via a controller (not shown). As such, the controller may be configured to interpret signals from the slug detector108and send signals to the control valves110,112based on the interpretation of the signals from the slug detector108. The controller and/or the slug detector108may include any suitable CPU, programmable logic controllers (PLC), memory, input connections, output connections, and the like. For example, the controller and/or the slug detector108may include a control program stored on a computer readable medium that causes the controller and/or slug detector108to receive inputs and generates outputs to cause the control valves110,112to actuate and/or may signal any other components of the system100in response to a detected slug flow and/or the completion of a slug flow.

It should be noted that the interposition of a controller between the control valves110,112(or any other component) and the slug detector108is intended to be within the scope of the term “communicably coupled” as it is used herein. Further, it will be appreciated that all “signal lines” referred to herein may be fiber optics, copper, pneumatic, hydraulic, or any other type of transmission line, or may be representative of wireless telemetry.

The control valves110,112may each include a normal position, as shown, in which fluid is directed to the turbomachine assembly102through the upstream control valve110and received from the turbomachine assembly102through the downstream control valve112. The control valves110,112may each be configured to be actuated from the normal position to a bypass position. In the bypass position, the upstream control valve110directs fluid from the upstream section104a, through an upstream section124of the bypass line113, and then to a remainder of the bypass line113, while preventing it from flowing into the turbomachine assembly102. When the downstream control valve112is in bypass position, it receives fluid from the bypass line113, directs it to the downstream section104b, and prevents it from flowing back toward the turbomachine assembly102. Accordingly, when the control valves110,112are both in the bypass position, fluid flow in the main line104bypasses the turbomachine assembly102via the bypass line113. Further, the control valves110,112may be capable of rapidly actuating between the normal and bypass positions according to signals received via the signal lines114,116, respectively.

The turbomachine system100may also include a high-pressure return line118fluidly coupled at both ends to the main line104. For example, the high-pressure return line118may extend from a point120of the downstream section104bof the main line104, for example, downstream of the downstream control valve112to a point122upstream of the upstream control valve110, for example, in the upstream section124of the bypass line113. In other embodiments, however, the point122may be in the main line104and/or within the upstream control valve110. A check valve126may also be coupled to the bypass line113, for example, upstream of the point122and/or the upstream section124of the bypass line113. The check valve126may be configured to allow fluid to flow downstream, but may generally prevent fluid from reversing flow through the main line104and travelling back toward the inlet106.

In an embodiment, an inlet scrubber125may be interposed between the turbomachine assembly102and the upstream control valve110. The inlet scrubber125may be any suitable device configured to remove contaminants, whether solid particulate matter (e.g., sand), liquid, or gas from the multiphase fluid in the main line104. A variety of inlet scrubbers (e.g., wet scrubbers, Venturi scrubbers, filtration media, etc.) are well-known and any may be used as required by a given application. In some embodiments, however, the turbomachine assembly102may have a built-in tolerance for such contaminants, or may otherwise have the capability of handling and/or separating a given range of such contaminants and thus the inlet scrubber125may be omitted.

In operation of the turbomachine system100, multiphase process fluid is received in the main line104from the inlet106. The fluid flow is monitored by the slug detector108and, during normal conditions, is sent to the upstream control valve110, which is in the normal position. The process fluid is then scrubbed by the inlet scrubber125, and then sent to the turbomachine assembly102for processing (e.g., compression). The process fluid then proceeds out of the turbomachine assembly102, through the downstream control valve112, which is also in the normal position, and is then sent to the outlet103. Prior to reaching the outlet103, a portion of process fluid may be used to pressurize the high-pressure return line118, in anticipation of a slug flow condition.

When the slug detector108detects a slug flow, it signals to the control valves110,112to actuate and move to the bypass position. In some embodiments, the slug detector108may also determine the velocity of the slug flow and may be set to delay signaling the control valves110,112to actuate until as late as is practicable, while still effectively diverting the slug flow. This may provide for a minimum duration of bypass flow and maximize flow sent through the turbomachine assembly102, thereby also maximizing production. After actuation, the upstream control valve110routes the process fluid, which should be a slug at this point, through the bypass line113thereby avoiding introducing the slug flow to the turbomachine assembly102. The slug then proceeds through the downstream control valve112and back into the downstream section104bof the main line104and then to the outlet103. Once the slug detector108registers that the slug flow is complete, the slug detector108may signal the control valves110,112to actuate back to the normal position. Again, the slug detector108may be configured to delay the signal to the control valves110,112to the optimal point to ensure full slug diversion, while avoiding normal flow bypassing the turbomachine assembly102, as far as is practicable.

While the slug flow is bypassing the turbomachine assembly102, it is urged to continue moving downstream by pressure provided via the high-pressure return line118. The check valve126prevents the pressure received from the high-pressure return line118from being transmitted, and potentially reversing flow, through the upstream section104aof the main line104. Accordingly, the pressure in the downstream section104bof the main line104is generally constant, as the slug flow is pressurized to the pressure downstream of the turbomachine assembly102during normal conditions. As such, pressure at the outlet103remains generally constant, which may facilitate subsequent, downstream processing.

When the slug flow has passed through the bypass line113, the slug flow may be considered finished. As such, the slug detector108and/or another controller (not shown) may signal to the upstream and downstream control valves110,112to actuate back to the normal position, to restart normal flow to the turbomachine assembly102.

FIG. 2illustrates a schematic view of another turbomachine system200, according to an embodiment. The turbomachine system200may be similar in structure and function to the turbomachine100and, as such, like components are given like reference numerals in both and will not be described in duplicate herein. The turbomachine system200includes a turbomachine assembly201, which includes a compressor202, as shown. The compressor202has an inlet204and an outlet206and is configured to pressurize gas therebetween. Further, the turbomachine assembly201may include an anti-surge loop, which, as shown, may include an anti-surge line207and a valve208. The valve208may be communicably coupled to the slug detector108via a signal line210. Further, the valve208may be configured to be actuated between a normal position, in which compressed gas received from the compressor outlet206proceeds therethrough to the downstream control valve112, and a bypass position, in which compressed gas received from the compressor outlet206is directed to the anti-surge line207. The anti-surge line207extends from the valve208to a position212in the main line104upstream of the compressor inlet204, but, for example, downstream of the inlet scrubber125. Although not shown, it will be appreciated that the anti-surge loop may be employed with the turbomachine system100shown in and described above with reference toFIG. 1.

The turbomachine system200may also include a secondary bypass line220, which is fluidly coupled to the inlet scrubber125and to a point downstream of the turbomachine assembly201, for example, between the turbomachine assembly201and the downstream control valve112. The turbomachine system200may further include a pump222in the secondary bypass line220, which may be controlled remotely, manually, or by the slug detector108(or a control system (not shown) associated therewith). In such an embodiment, the turbomachine assembly201may also include a check valve224to prevent backflow of fluid in the secondary bypass line220into the turbomachine assembly201.

Further, the turbomachine system200may include a fluid vessel214designed to facilitate fluid transfer. The fluid vessel214may be an accumulator and may include a pump therein. The fluid vessel214may be fluidly coupled to the upstream section124of the bypass line113, as shown. In other embodiments, the fluid vessel214may be coupled to the upstream section104aor downstream section104bof the main line104, or may be coupled to the bypass line113, downstream of the upstream control valve110. The fluid vessel214may be coupled to upstream section124of the bypass line113either directly or via one or more valves (not shown). If such valves are used, they may be actuated by a controller (not shown) and/or the slug detector108. Further, the fluid vessel214may be configured to contain a quantity of process fluid, for example, it may be configured to catch a portion of the slug flow upstream of the turbomachine assembly201.

A pump (not shown) coupled to the fluid vessel214may be communicably coupled to the slug detector108via a signal line (not shown). The fluid vessel214may be configured to increase the pressure and/or urge process fluid from the fluid vessel214, through the bypass line113, and into the downstream section104bof the main line104during slug bypass. This may ensure a relatively constant pressure in the downstream section104bof the main line104and to the outlet103, despite slug flow conditions.

In addition to the operation of the turbomachine system100discussed above with respect toFIG. 1, the turbomachine system200may avoid surge conditions in the compressor202and may maintain or otherwise stabilize pressure in the downstream section104bof the main line104during slug bypass. Before, when, or shortly after the slug detector108signals the control valves110,112to actuate to the bypass position, the slug detector108may also signal the anti-surge valve208to actuate to its bypass position. As flow is routed around the compressor202in the bypass line113, the compressor202is provided with a continuous flow of process gas via the anti-surge line207, thereby avoiding surge conditions. Further, although not shown, the anti-surge loop may include one or more pressure-reducing structures (e.g., an expander such as an expansion valve) to provide fluid to the compressor inlet204at a suitable pressure.

Further, when slug flow is detected, or intermittently during normal flow conditions, the pump222may be powered on to remove liquid from the inlet scrubber125. The liquid removed from the inlet scrubber125may be pumped to pressure by the pump222and routed via the secondary bypass line220around the compression system201for processing downstream.

FIG. 3illustrates another turbomachine system300, according to an embodiment. The turbomachine system300may be similar in structure and function to the turbomachine systems100and200and, as such, like components are given like reference numerals in both and will not be described in duplicate herein. The turbomachine system300includes a turbomachine assembly302coupled to the main line104and around which the bypass line113is configured to divert slugs, as described above with reference toFIG. 1. The illustrated turbomachine assembly302includes the compressor202and the anti-surge loop discussed above with respect toFIG. 2.

The illustrated turbomachine assembly302includes a separator304and, as such, the turbomachine system300may omit the inlet scrubber125(FIGS. 1 and 2). Some embodiments of the turbomachine systems100,200may, however, include separators. The separator304may be a dynamic separator, such as a rotary separator, a static separator, or a combination thereof. Further, the separator304may be disposed in a common casing (not shown) with the compressor202and/or may have one or more components rotatable on a common shaft (not shown) with the compressor202. One example of such a configuration may be the DATUM® I, commercially-available from Dresser-Rand Co. of Olean, N.Y., USA.

The separator304may be configured to separate a higher-density component (e.g., liquids and/or solids) from a lower-density component (e.g., gas) of the multiphase fluid. As such, the separator304may provide the turbomachine assembly302with on-board contaminant handling ability as well as some ability to handle an amount slug flow. However, large slug flow may still flood the separator304and/or components of the drainage system thereof (e.g., gas break vessels); accordingly, the slug detector108may be configured to divert larger slug flows around the turbomachine assembly302, while relying on the separator304to handle smaller slugs. This may enable the use of the bypass line113to be reduced, thereby providing longer durations of uninterrupted flow to the compressor202.

The turbomachine system300may also include a pump306fluidly coupled, for example, to the upstream section124of the bypass line113. In other embodiments, the pump306may be fluidly coupled to any section of the main line104, or may be fluidly coupled to the bypass line113, downstream from the upstream control valve110. The pump306may be controlled by the slug detector108and/or a controller (not shown) via a signal line308. Accordingly, the pump306may be off during normal conditions, but may be turned on when, or shortly after, the slug detector108detects a slug flow. When the slug reaches the pump306, the pump306may pressurize the slug flow to or to approximately the same pressure to which the compressor202normally raises the process gas. The pressurized slug flow may then be routed through the bypass line113, via the upstream control valve110, and then to the outlet103via the downstream control valve112and the downstream section104bof the main line104. Accordingly, the pressure of the fluid flow seen at the outlet103may be approximately constant, notwithstanding slug flow conditions. As such, the turbomachine system300may omit the high-pressure return line118, but in other embodiments, may include both the pump306and the high-pressure return line118.

FIG. 4illustrates another exemplary turbomachine system400, according to an embodiment. The turbomachine system400may be similar to one of the turbomachine systems100,200,300previously described; as such, like components are given like reference numerals in both and will not be described in duplicate herein. The turbomachine system400includes a separator402, which may be positioned upstream from the upstream bypass valve110. The separator402may be a gravity-base separator or sedimentation tank and may be included, for example, in lieu of the inlet scrubber125(FIGS. 1-3), but may have generally the same structural features.

The turbomachine system400may also include a second bypass line403, extending from the separator402and to the outlet103. The second bypass line403may include a pump404and a check valve405. Further, the drain from any other separation device (not shown) within the compression system102, such as, for example, the separator304(FIG. 3), may also be connected fluidly to the separator402via line406. Fluid from the turbomachine assembly302separated from the process stream may be delivered to the separator402via line406. The line406may have a check valve408to prevent liquid flow back into the turbomachine assembly302.

In operation when the slug detector108detects a slug situation, bypass valves110and112are actuated such that the bypass line113is opened, routing the slug from the separator402, around the turbomachine assembly302, and to the outlet103. The slug may thus flow in a self-pressurized manner through the bypass line113. Additionally or alternatively, the pump404may be used to pump the slug from the separator402, through the check valve405, so as to prevent back-flow, and to the outlet103. As such, the secondary bypass line403serves to provide a pump-assisted flow around the turbomachine assembly302.

FIG. 5illustrates another exemplary embodiment of the turbomachine system400. As shown, the downstream bypass valve112(FIG. 4) may be substituted with a pair of check valves450,452. As such, selection of whether the process flow proceeds into or around the turbomachine assembly302is controlled by the upstream control valve110. The check valves450,452ensure that backflow is prevented into the non-selected route, thereby obviating a need for a downstream control valve. This may simplify the turbomachine system400; however, in other embodiments, as discussed above, a downstream control valve may be beneficial to provide precision control of the system or for any other reasons as understood by one with skill in the art.

FIG. 6illustrates a flowchart of a method400for handling slug flow in a turbomachine system, such as one or more of the turbomachine systems100-400described above. In an embodiment, the method600may include detecting a slug flow in a main line upstream of a compressor with a slug detector, as at602. The method600may also include signaling an upstream control valve to actuate from a normal position to a bypass position, as at604. In the normal position, the upstream control valve directs fluid toward the compressor. In the bypass position, the upstream control valve directs fluid to a bypass line extending from a position upstream the compressor to a position downstream of the compressor. Simultaneously, before, or after signaling at604, the method600may include signaling a downstream control valve to actuate from a normal position to a bypass position, as at606. In the normal position, the downstream control valve receives a fluid flow from the compressor. In contrast, when in the bypass position, the downstream control valve receives a fluid flow (e.g., slug flow) from the bypass control line.

The method600may also include diverting the slug flow through the upstream control valve to the bypass line, as at608. The method600may also include pressurizing the slug flow in the bypass line with a high pressure line extending from the main line downstream of the compressor to the main line upstream of the upstream control valve, as at610. Further, the method400may include routing fluid through an anti-surge line extending from downstream of the compressor to upstream of the compressor, as at612. The method600may then proceed to signaling the upstream control valve to return to the normal position when the slug flow is finished, as at614, whereupon the method600may restart.

In an embodiment, detecting the slug flow at602may include using a Coriolis flow meter, a sonic flow meter, or both to detect the slug flow. Further, in at least one embodiment, the method600may include separating a multiphase fluid upstream of the compressor using a separator, an inlet scrubber, or a combination thereof. Additionally, the method600may include pumping fluid from an accumulator while the upstream control valve is in the bypass position to maintain pressure in the main line downstream of the compressor.