Patent Application
20110223039
This invention relates generally to pump assemblies and methods for pumping fluids. More particularly, this invention relates to pump assemblies employing centrifugal pumps and methods for pumping multiphase fluids.
Multiphase fluids, such as gaseous and liquid two-phase fluids exist in many areas of technology, such as oil production. Centrifugal pumps are often preferred when pumping multiphase process fluids, due to their lower cost, smaller size, and simplicity of operation and construction relative to other types of pumps, for example twin screw pumps.
One drawback to the use of centrifugal pumps in the operations involving multiphase process fluids, for example petroleum-gas mixtures from a subsurface reservoir, is the unintended segregation of the multiphase process fluid into its liquid and gaseous components as a result of shear forces applied to the multiphase process fluid by the rotating impellers of the centrifugal pump. In some instances, a liquid phase separates from the multiphase process fluid and moves to the periphery of the pump impellers while the gaseous components of the multiphase process fluid accumulate near the eyes of the impellers. As a result, the performance of the centrifugal pump may decrease and eventually it may no longer be possible to pump the multiphase process fluid effectively. This behavior may become particularly acute for multiphase process fluids characterized by a high gas volume fraction.
Therefore, there is a need for new and improved pump assemblies employing centrifugal pumps and methods for pumping multiphase fluids.
A pump assembly for pumping a multiphase fluid is provided in accordance with one embodiment of the invention. The pump assembly comprises a centrifugal pump configured to pump a multiphase fluid, a suction conduit in fluid communication with the centrifugal pump, and a discharge conduit in fluid communication with the centrifugal pump. The pump further comprises an eductor comprising one or more motive nozzles disposed within the suction conduit. Wherein the one or more motive nozzle are configured to introduce a motive fluid into the suction conduit and toward the centrifugal pump along a suction direction roughly co-directional with the suction conduit toward the centrifugal pump.
A method for pumping a multiphase fluid is provided in accordance with another embodiment of the invention. The method comprises introducing a multiphase fluid into a centrifugal pump via a suction conduit, receiving a discharge fluid from the centrifugal pump via a discharge conduit, and introducing a motive fluid into the multiphase fluid such that from initial contact of the multiphase fluid and the motive fluid, both fluids move unidirectionally along a flow path leading to the centrifugal pump.
Another aspect of the invention further provides a pump assembly for pumping a multiphase fluid. The pump assembly comprises a plurality of centrifugal pumps configured to pump a multiphase fluid, a suction conduit in fluid communication with the plurality of the centrifugal pumps, and a discharge conduit in fluid communication with the plurality of the centrifugal pumps. The pump assembly further comprises an eductor comprising one or more motive nozzles. The one or more motive nozzles are disposed within the suction conduit and configured to extend along a suction direction of the multiphase fluid so as to introduce a motive fluid into the suction conduit and toward the centrifugal pump.
These and other aspects, features, and advantages of the present disclosure will become more apparent in light of the subsequent detailed description when taken in conjunction with the accompanying drawings in which:
Embodiments of the present disclosure are described herein with reference to the accompanying drawings. In the subsequent description, well-known functions or constructions are not described in detail to avoid obscuring the disclosure in unnecessary detail.
As illustrated in
It should be noted that the arrangements in
In some applications, the discharge fluid may also be multiphase and have a higher or same total pressure than that of the multiphase fluid. In non-limiting examples, the discharge fluid may be discharged from any stage of the centrifugal pump when the centrifugal pump has a multistage configuration. Additionally, since the multiphase fluid 11 passes through the centrifugal pump 12, the discharge fluid may have a lower gas volume fraction (GVF) than that of the multiphase fluid.
For certain arrangements, the suction conduit 13 and/or the discharge conduit 14 may be detachably assembled onto the centrifugal pump 12 for delivering the multiphase fluid into and the discharge fluid away from the centrifugal pump 12, respectively. In other applications, the suction conduit 13 and/or the discharge conduit 14 may be unitary with the centrifugal pump 12, for example, to function as a suction nozzle 24 (shown in
In the example illustrated in
In non-limiting examples, the recirculation apparatus 15 may comprise a container 17 and a separator (not shown) disposed within the container 17 for gas and liquid separation of the discharge fluid. Non-limiting examples of the separator include a cyclone separator and a static separator with enhanced gravity. In some applications, the separator may not be employed and the discharge fluid may be separated by gravity separation.
Thus, when the discharge fluid is delivered into the container 17, the separator performs the gas and liquid separation of at least a portion of the discharge fluid in the container 17, so that a motive fluid 22 (shown in
In some examples, due to the higher total pressure of the discharge fluid and the presence of the separator, the motive fluid may also have a higher total pressure and a lower GVF than those of the multiphase fluid. Additionally, in some applications, since the discharge fluid may have a lower GVF than that of the suction fluid 11, the separator may not be employed and at least a portion of the discharge fluid may act as the motive fluid to pass through the container 17 for delivery into the eductor 16.
In the illustrated example in
The eductor 16 is assembled onto the suction conduit 13 and is configured to receive and eject the motive fluid from the recirculation apparatus 15 into the suction conduit 13 to improve flow conditions of the suction fluid, for example reducing the GVF of the multiphase fluid. In some applications, the eductor 16 may be detachable disposed on or be unitary with the suction conduit 13.
For the arrangement illustrated in
In some applications, the motive nozzle 21 may introduce the motive fluid into the suction conduit 13 and toward the centrifugal pump 12 along a suction direction 23 or a flow direction roughly co-directional with the flow of the multiphase fluid through the suction conduit 13 toward the centrifugal pump 12, which may indicate that, in some examples, the motive nozzle 21 may extend along an axis (not shown) parallel to an axis of the suction conduit 13, as depicted in
Thus, the motive fluid is introduced into the multiphase fluid such that from initial contact of the multiphase fluid and the motive fluid, both fluids move unidirectionally along a flow path leading to the centrifugal pump. In some example, the motive nozzle 21 may be coaxial with the suction conduit 13. In one example, the suction direction indicates a substantially horizontal flow direction.
It should be noted that the arrangements in
For some arrangements, the motive fluid may have a higher total pressure and a lower GVF than those of the multiphase fluid 11. Thus, during the motive fluid is ejected into the suction conduit 13 and mixes with the multiphase fluid 11, a static pressure and a flow velocity of a mixture fluid, which may also act as a suction fluid, of the motive fluid and the multiphase fluid 11 are increased. Meanwhile, the increased pressure of the multiphase fluid and compressibility of the gaseous liquids therein result in that the multiphase fluid may have a lower GVF for suction into the centrifugal pump 12.
Accordingly, in non-limiting examples, the mixture fluid may have a higher pressure and a lower GVF due to the higher pressure of the motive fluid, so that the flow conditions of the mixture fluid may be enhanced to ensure stable operation of the centrifugal pump 12 without loss of prime even though the multiphase fluid 11 has a higher GVF before suction into the centrifugal pump 12.
Additionally, for the arrangement illustrated in
Thus, during operation, the centrifugal pump 12 is actuated, for example using an electrical motor (not shown) to pump the multiphase fluid 11 via the suction conduit 13. The detector 25 detects the GVF of the multiphase fluid 11 while the multiphase fluid 11 enters into the centrifugal pump 12 and at least a portion of the discharge fluid enters into the recirculation apparatus 15. Then, when the GVF of the multiphase fluid 11 exceeds a threshold value, the detector 25 triggers the control valve 26 to open the conduit 18, so that the motive fluid is ejected into the suction conduit 13 to mix with the multiphase fluid 11 via the eductor 16 so as to decrease the GVF of the mixture fluid (suction fluid) to ensure stable operation of the centrifugal pump 12. Next, when the GVF of the mixture fluid drops below the threshold value, the detector 25 triggers the control valve 26 to close the conduit 18 and conserve the motive fluid in the recirculation apparatus 15.
In some examples, the detector 25 may not be employed. For example, before delivery of the motive fluid into the suction conduit 13, when the GVF of the multiphase fluid 11 exceeds the threshold value, the centrifugal pump 12 may vibrate due to the accumulation of the gaseous fluid and imbalance flow in the pump 12. Thus, one may turn on the control valve manually to make the motive fluid enters into the eductor 16 via the conduit 25.
It should be noted that the arrangements in
For other arrangements, a motive fluid source (not shown) separated from the discharge conduit 14 may be provided to be in fluid communication with and provide a motive fluid with a higher pressure to the eductor 16. In certain applications, the motive fluid from the separated fluid source may have a lower GVF than that of the multiphase fluid 11. Alternatively, the motive fluid may have the same GVF as or a higher GVF than that of the multiphase fluid 11.
While the disclosure has been illustrated and described in typical embodiments, it is not intended to be limited to the details shown, since various modifications and substitutions can be made without departing in any way from the spirit of the present disclosure. As such, further modifications and equivalents of the disclosure herein disclosed may occur to persons skilled in the art using no more than routine experimentation, and all such modifications and equivalents are believed to fall within the spirit and scope of the disclosure as defined by the claims presented herein.
