VERTICALLY SUSPENDED CENTRIFUGAL PUMP WITH INTEGRAL SPEED REDUCER

A vertically suspended centrifugal pump including a speed reducing system disposed between a first shaft and a second shaft to allow a speed differential between the first shaft and the second shaft.

FIELD OF TECHNOLOGY

The following relates to embodiments of a vertically suspended centrifugal pump, and more specifically to embodiments of a vertically suspended centrifugal pump with an integral speed reducer.

BACKGROUND

For vertically suspended a centrifugal pump to work properly, there must be sufficient Net Positive Suction Head (NPSH) margin (NPSH available—NPSH required). NPSH available is determined by a pumping system while NPSH required is a parameter of a centrifugal pump design.

SUMMARY

An aspect relates to a vertically suspended centrifugal pump comprising: a speed reducing system disposed between a first shaft and a second shaft to allow a speed differential between the first shaft and the second shaft.

In an exemplary embodiment, the vertically suspended centrifugal pump includes a first stage operably coupled to the second shaft, a second stage operably coupled to the first shaft, and a third stage or more operably coupled to the main shaft. During an operation of the vertically suspended centrifugal pump, the first stage runs at a lower speed than the second stage as a function of the speed differential between the first shaft and the second shaft. As an example, during the operation of the vertically suspended centrifugal pump, the second stage is an impeller with a running speed at or above 3600 rpm.

Another aspect relates to a vertically suspended centrifugal pump comprising: a main shaft being driven at a first speed, a plurality of series stage impellers coupled to the main shaft, a speed reducing system comprising: a first pinion operably connected to the main shaft, configured to rotate at the first speed, a first set of gears meshed with the first pinion, configured to rotate at a second speed that is reduced from the first speed, a second set of gears meshed with a second pinion, configured to rotate at the second speed, a secondary shaft operably coupled to the second pinion of the speed reducing system, configured to rotate at the second speed, and a first stage impeller coupled to the secondary shaft.

The reduced speed is reduced by a ratio between the first pinion and the first set of gears. In an exemplary embodiment, the first set of gears are larger than the second set of gears. The vertically suspended centrifugal pump with the spur gear system minimizes a net positive suction head required of the first stage impeller by running at the second speed while the plurality of series stage impellers run at the first speed, for example, is at or above 3600 rpm.

Another aspect relates to a vertically suspended centrifugal pump comprising: a main shaft being driven at a first speed, a plurality of series stage impellers coupled to the main shaft, a speed reducing system comprising: a star gear operably connected to the main shaft, configured to rotate at the first speed, at least one planetary gear meshed with the star gear and a stationary gear, the at least one planetary gear configured to rotate at a second speed that is reduced from the first speed, and a carrier coupled to the at least one planetary gear, configured to rotate at the second speed, a secondary shaft operably coupled to the carrier, configured to rotate at the second speed, and a first stage impeller coupled to the secondary shaft.

The vertically suspended centrifugal pump with the planetary gear system also minimizes a net positive suction head required of the first stage impeller is minimized by running at the second speed while the plurality of series stage impellers run at the first speed, for example, at 3600 rpm.

Another aspect relates to a method comprising: disposing a speed reducing system between two separate shafts of a vertically suspended centrifugal pump to allow a speed differential between the two separate shafts. As a function of disposing the speed reducing system between two separate shafts, a net a net positive suction head of a first stage impeller coupled to one of the two separate shafts is minimized by running at a lower speed than a plurality of series stage impellers coupled to the other of the two separate shafts.

The foregoing and other features of construction and operation will be more readily understood and fully appreciated from the following detailed disclosure, taken in conjunction with accompanying drawings.

DETAILED DESCRIPTION

A detailed description of the hereinafter described embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the Figures. Although certain embodiments are shown and described in detail, it should be understood that various changes and modifications may be made without departing from the scope of the appended claims. The scope of the present disclosure will in no way be limited to the number of constituting components, the materials thereof, the shapes thereof, the relative arrangement thereof, etc., and are disclosed simply as an example of embodiments of the present disclosure.

In brief overview, it is desirable to minimize NPSH required of a centrifugal pump. NPSH available, usually expressed in liquid column height, is an amount of pressure that is above a vapor pressure of a pumping liquid at a pump's suction. Referencing to a certain datum point (i.e. a pump's suction nozzle), NPSH available of a pumping system can be as low as zero (i.e., the pumping liquid is at bubbling point). NPSH required is related to an impeller design, a flowrate, and a running speed. NPSH required (NPSHR) can be expressed as:

where, NPSHR is Net Positive Suction Head required in feet, Q is flowrate in gpm, Nssis suction specific speed, and n is running speed in rpm. The lowest achievable NPSH required is such that the resulting suction specific speed is in a reasonable range; a practical range is up to 13,000 in US customary units, though 18,000 or even higher is possible.

In the oil and gas industry, for applications where NPSH available is low and differential head is high, vertically suspended multi-stage pumps (e.g. API 610 VS1 or VS6 pumps) are typically used because a first stage impeller resides below grade and a pump could provide NPSH available to the first stage impeller so that sufficient NPSH margin can be obtained for the selected pumps to work properly. Conventional vertically suspended multi-stage pumps adopt one or more of the below measures to obtain needed NPSH margin: a high suction specific speed first stage impeller; an inducer before the first stage impeller; a double-suction first stage impeller; extra-long shafts (extra-long pumps) for obtaining needed NPSHA; and running the entire pump at a lower speed relative to the design speed.

Each of these measures have drawbacks. For example, high suction specific speed impellers (Nss>13,000) and inducers tend to generate “U” shaped NPSHR curves and cause internal recirculation, which narrows an operating range. Using a double suction first stage impeller, the reduction in NPSHR over with a single suction first stage impeller is limited to a factor of 22/3. Using an extra-long shaft tends to cause rotor dynamic issues and reliability issues in addition to high costs. Running the entire pump at a lower speed can reduce NPSHR by a factor of (n2n1)4/3; however, it would require a larger pump, or increase a number of stages by a factor of (η2/η1)2to meet differential head requirement, which inevitably increases costs.

Another method to reduce NPSHR is to lower the running speed when Nss and Q are kept constant. To slow down the entire pump is not desirable. If the first stage impeller and the series stage impellers can run at different speeds (i.e., the first stage impeller running at a lower speed for low NPSHR while the series stage impellers running at a higher speed for required total differential head), it would not only produce low NPSHR but also a high total differential head.

Embodiments of the present invention minimize NPSHR of a first stage (e.g. first stage impeller) by running the first stage at an optimized lower speed than the other stages of the centrifugal pump using an integral speed reducer. The integral speed reducer is a speed reducing system disposed between and connected to two separate shafts of the centrifugal pump to allow for a speed differential between the two separate shafts. For example, one or more impellers coupled to a main shaft being driven at a first speed (e.g. high-speed) can run at a higher speed than an impeller coupled to a secondary shaft, which runs at a lower speed (e.g. low-speed). The use of the speed reducing system also minimizes an overall pump length by generating low NPSHR or sufficient NPSH margin and optimizes a suction specific speed so that the pump can run in a wide range of flowrate. With a first stage impeller running at a low speed, the series stage impeller(s) can run at a speed at or above 3600 rpm for optimized efficiency, further reducing the length of the pump. In exemplary embodiments, the speed reducing system employs a spur gear system or an epicyclic gear system between the first stage and the second stage impellers of the centrifugal pump so that the first stage impeller can run at a different speed than the series stage impellers. In another exemplary embodiment, the speed reducing system uses a hydraulic coupling speed reducer between the first stage and second stage impellers of the centrifugal pump so that the first stage impeller can run at a different speed than the series stage impellers.

Referring now toFIGS.1A and1B, conventional vertically suspended centrifugal pumps include a single, main shaft5vertically extending through the pump1,1′. The pump1,1′ are multiple stage pumps, including a first stage, a second stage, a third stage, and a fourth stage. Each stage involves an impeller2a,2b,2c,2dcoupled to the main shaft5. As the main shaft5is driven, for example, caused to be rotated, each of the impellers2a,2b,2c,2dare caused to rotate at the same speed. In other words, the impeller2aof the first stage rotates at the same speed as the other series impellers2b,2c,2dwhen the main shaft5is driven by a driver (not shown).

FIG.2schematically depicts a pump100having a speed reducing system50disposed between two separate shafts10,15, in accordance with embodiments of the present invention. Pump100is a vertically suspended centrifugal pump that can be used for applications in oil and gas, petrochemical, chemical, liquid carbon dioxide, and liquid hydrogen. In an exemplary embodiment, the pump100is a vertically suspended centrifugal pump having two vertically oriented shafts10,15sharing a common longitudinally extending rotation axis3. The pump100includes a housing8that is configured to enclose or at least partially enclose the components of the pump100. The pump100includes multiple stages20a,20b,20c,20d. Stages20a,20b,20c,20dcan be an impeller, rotor, or any rotating component used for accelerating fluids through the pump100. While four stages are depicted in the illustrated embodiment, the pump100may include two, three, or more than four stages. Stage20a is coupled to secondary shaft15while the remaining stages20b,20a,20c,20dare coupled to the main shaft10. For instance, a stage20a,20b,20c,20dmay be mounted, directly or otherwise, to the shafts10,15.

Moreover, the pump100includes a speed reducing system50to allow for a speed differential between the main shaft10and the secondary shaft15so that the stage20a(e.g. first stage) can be operated at a different (e.g. lower) speed than the other stages20b,20c,20d. The speed differential between the shafts10,15minimizes net positive suction head and allows for a smaller length of the overall pump100. The speed reducing system50is disposed between the main shaft10and secondary shaft15. For example, an end of the main shaft10is attached to a component of the speed reducing system50, such as a pinion or epicyclic gear, and an end of the secondary shaft15is also attached to a component of the speed reducing system50. In some embodiment, the end of the main shaft10and/or the end of the secondary shaft15is structurally integral with components of the speed reducing system50.

FIGS.3A and3Bdepict more detailed embodiments of vertically suspended centrifugal pumps100a,100b, respectively, having a speed reducing system50a,50b, in accordance with embodiments of the present invention. Instead of a single main shaft, the pump100a,100binclude a main shaft10(e.g. first shaft) and a secondary shaft15(e.g. second shaft). The speed reducing system50a,50bis disposed between the main shaft10and the second shaft15, operably connected to both shafts10,15. The pump100a,100bincludes multiple pump stages, including a first pump stage, a second pump stage, a third pump stage, and a fourth pump stage. While four stages are depicted in the illustrated embodiment, the pump100a,100bmay include two, three, or more than four stages of impellers. The series pump stage involves impellers20a,20b,20c,20dbut the first stage impeller20ais coupled to the secondary shaft15while the series stage impellers20b,20c,20dare coupled to the main shaft10. As the main shaft10is driven, for example, caused to be rotated, the impellers associated with series pump stages after the first pump stage (e.g. impellers20b,20c,20d) are caused to rotate at the same speed. Because of the integral speed reducing system50a,50b, the secondary shaft15rotates at a reduced speed from the speed of the main shaft10. As a result, the first stage impeller20aof the first pump stage rotates at a different (e.g. lower) speed than the other series impellers20b,20c,20dwhen the main shaft1is driven by a driver (not shown). Thus, there is a speed differential between the two separate shafts10,15.

FIG.4depicts the speed reducing system50aof the pump100adepicted inFIG.3A, highlighted by section A, in accordance with embodiments of the present invention. The speed reducing system50ais a gear system used for creating a speed differential between the main shaft10and the second shaft15. In an exemplary embodiment, the speed reducing system50a is a spur gear system. The speed reducing system50a includes a first pinion51, a first set of gears52, a second set of gears53, and a second pinion54. The first pinion51, the first set of gears52, the second set of gears53, and the second pinion54each include teeth along outer, circumferential surfaces. The gear teeth may have various spacing, thickness, pitch, size, and the like. Similarly, a size of the first pinion51, the first set of gears52, the second set of gears53, and the second pinion54may vary to accomplish different desired speeds, ratios, torque transmission, and the like, of the speed reducing system50a.

The first pinion51is operably connected to the main shaft10. For example, the first pinion51may be mounted to the main shaft10so that rotation of the main shaft10translates to rotation of the first pinion51, or vice versa. In other embodiments, the first pinion51may be structurally integral with the main shaft10. The first pinion50a rotates at the speed of the main shaft10(e.g. first speed) as the main shaft10is driven. A first set of gears52mesh with the first pinion51such that rotation of the first pinion51causes rotation of the first set of gears52. The first set of gears52rotate at a reduced speed (e.g. second speed) that is reduced from the first speed. The reduced speed is reduced by a ratio between the first pinion51and the first set of gears52. A second set of gears53share pinion shafts55with the first set of gears52so that the second set of gears53rotate at the reduced rotation speed of the first set of gears52. The second set of gears53, which are smaller than the first set of gears52, mesh with a second pinion54such that rotation of the second set of gears53causes rotation of the second pinion54. The second pinion54rotates at the reduced speed. Because the secondary shaft15is operably coupled to the second pinion54, the second shaft15rotates at the reduced speed and thus at a different speed than the main shaft10. For example, the second pinion54may be mounted to the secondary shaft10so that rotation of second pinion54translates to rotation of the secondary shaft15, or vice versa. In other embodiments, the second pinion54may be structurally integral with the secondary shaft15. A first stage, such an impeller, is coupled to the secondary shaft15. The arrows depict a flow path of a fluid through the pump.

Moreover, the speed reducing system50ais housed within a diffuser70. The diffuser70, also referred to as a bowl, includes an outer diffuser portion70aand an inner diffuser portion70b. The space between the outer diffuser portion70aand the inner diffuser portion70bis a passage71that allows a fluid to flow through the pump to the next stage of the pump. A vane or blade is positioned between the outer diffuser portion70aand the inner diffuser portion70bin a spiral or helical pattern to structurally couple the outer diffuser portion70aand the inner diffuser portion70bas well as guide the flow of fluid around the inner diffuser portion70bin a spiral or helical pattern towards the next stage. Various structural configurations of the vane or blade and/or bowl configurations can be used along with the speed reducing system50a. The outer diffuser portion70ais a generally annular member having a shoulder73in which an outer diameter of the diffuser70is reduced compared with a remaining body portion of the diffuser70.

The speed reducing system50aresides within the inner diffuser portion70bproximate the longitudinal axis of the pump100. A cartridge assembly76is disposed between the inner diffuser portion70b and the speed reducing system50a. The cartridge assembly76may comprise a single structure or may be comprised of a plurality of components fastened together to form the cartridge76. Radial bearings77are disposed between the cartridge76and the speed reducing system50a to allow for rotation of the pinion shafts55with respect to the cartridge76.

The diffuser70is stationary with respect to other components of the pump100.

The diffuser70shown inFIG.4is attached to a suction bell74in which the fluid is drawn into the diffuser70. In an exemplary embodiment, the diffuser70is fixedly attached to the suction bell74via one or more fasteners, such as a bolt or similar fastener. The diffuser70is operably connected to a hub75of the impeller20a of the stage shown inFIG.4(i.e. first stage). A wear ring79is disposed between the hub75and the diffuser70. The impeller20a is mechanically coupled to the main shaft15and rotates with the secondary shaft15while the suction bell74and the diffuser70remain stationary. The rotation of the impeller20a draws the fluid through the suction bell74and into the diffuser70, specifically, the passage71between the outer diffuser portion70a and the inner diffuser portion70b.

The diffuser70is operably coupled to the second stage impeller20b proximate the shoulder73of the diffuser70. The second stage impeller20b includes a front shroud81and a back shroud82. A wear ring83is disposed between the front shroud81of the second stage impeller20band the diffuser70of the first stage. Fluid that flows through the passage71of the diffuser70is further drawn into the second stage impeller20due to the rotation of the second stage impeller20bcaused by the mechanical coupling of the second stage impeller20b to the main shaft10. The second stage impeller20brotates at a different speed than the first stage impeller20aas a result of the speed reducing system50.

FIG.5depicts the speed reducing system50bof the pump100bdepicted inFIG.3b, highlighted by section A, in accordance with embodiments of the present invention. The speed reducing system50bis a gear system used for creating a speed differential between the main shaft10and the second shaft15. In an exemplary embodiment, the speed reducing system50bis a planetary or epicyclic gear system. The speed reducing system50bincludes a star gear55, a planetary gear56, a stationary gear57and a carrier58. The star gear55, the planetary gear56, and the stationary gear57each include teeth along outer, circumferential surfaces. The gear teeth may have various spacing, thickness, pitch, size, and the like. Similarly, a size of the star gear55, the planetary gear56, and the stationary gear57may vary to accomplish different desired speeds, ratios, torque transmission, and the like, of the speed reducing system50b.

The star gear55is operably connected to the main shaft10. The star gear55rotates at the speed as the main shaft10(e.g. first speed) as the main shaft10is driven. At least one planetary gear56meshes with the star gear55and the stationary gear57; the planetary gear56rotates at a reduced speed (e.g. second speed) that is reduced from the first speed. The carrier58is coupled to the at least one planetary gear56such that rotation of the planetary gear56causes a rotation of the carrier58, which also rotates at the reduced speed. Because the secondary shaft15is operably coupled to the carrier58, the secondary shaft15rotates at the reduced speed and thus at a different speed than the main shaft10. A first stage, such an impeller, is coupled to the secondary shaft15. The arrows depict a flow path of a fluid through the pump.

Moreover, the speed reducing system50bis housed within the diffuser70. The diffuser70, also referred to as a bowl, includes the outer diffuser portion70aand the inner diffuser portion70b. The space between the outer diffuser portion70aand the inner diffuser portion70bis a passage71that allows a fluid to flow through the pump to the next stage of the pump. A vane or blade is positioned between the outer diffuser portion70aand the inner diffuser portion70bin a spiral or helical pattern to structurally couple the outer diffuser portion70aand the inner diffuser portion70b as well as guide the flow of fluid around the inner diffuser portion70bin a spiral or helical pattern towards the next stage. Various structural configurations of the vane or blade and/or bowl configurations can be used along with the speed reducing system50b. The outer diffuser portion70ais a generally annular member having a shoulder73in which the outer diameter of the diffuser70is reduced compared with a remaining body portion of the diffuser70.

The speed reducing system50bresides within the inner diffuser portion70b proximate the longitudinal axis of the pump100. A cartridge assembly76′ is disposed between the inner diffuser portion70band the speed reducing system50b. The cartridge assembly76′ may comprise a single structure or may be comprised of a plurality of components fastened together to form the cartridge76′. Bearing78is disposed between the cartridge76′ and the carrier58to allow for rotation of the carrier59with respect to the cartridge76′.

The diffuser70is stationary with respect to other components of the pump100. The diffuser70shown inFIG.6is attached to a suction bell74in which the fluid is drawn into the diffuser70. In an exemplary embodiment, the diffuser70is fixedly attached to the suction bell74via one or more fasteners, such as a bolt or similar fastener. The diffuser70is operably connected to the hub75of the impeller20aof the stage shown inFIG.5(i.e. first stage). A wear ring79is disposed between the hub75and the diffuser70. The impeller20ais mechanically coupled to the main shaft15and rotates with the secondary shaft15while the suction bell74and the diffuser70remain stationary. The rotation of the impeller20adraws the fluid through the suction bell74and into the diffuser70, specifically, the passage71between the outer diffuser portion70aand the inner diffuser portion70b.

The diffuser70is operably coupled to the second stage impeller20b proximate the shoulder73of the diffuser70. The second stage impeller20b includes a front shroud81and a back shroud82. A wear ring83is disposed between the front shroud81of the second stage impeller20b and the diffuser70of the first stage. Fluid that flows through the passage71of the diffuser70is further drawn into the second stage impeller20due to the rotation of the second stage impeller20b caused by the mechanical coupling of the second stage impeller20b to the main shaft10. The second stage impeller20brotates at a different speed than the first stage impeller20aas a result of the speed reducing system50.

FIG.6schematically depicts a pump101having a speed reducing system50disposed between two separate shafts at a different location than the pump100ofFIG.2, in accordance with embodiments of the present invention. Pump101shares the same structure and function of the pump101inFIG.2, except that the speed reducing system50is located between the second stage20band the third stage20c. For instance, stage20aand stage20bare mounted to the secondary shaft15, and stage20cand stage20dare mounted to the main shaft10. The speed reducing system50allows for a speed differential between the main shaft10and the secondary shaft15so that the stages20aand20bcan be operated at different (e.g. lower) speeds than the other stages20c,20d. The speed differential between the shafts10,15minimizes net positive suction head and allows for a smaller length of the overall pump101. The speed reducing system50is disposed between the main shaft10and secondary shaft15. For example, an end of the main shaft10is attached to a component of the speed reducing system50, such as a pinion or epicyclic gear, and an end of the secondary shaft15is also attached to a component of the speed reducing system50. In some embodiments, the end of the main shaft10and/or the end of the secondary shaft15is structurally integral with components of the speed reducing system50.

FIG.7schematically depicts a pump102having more than one speed reducing system disposed, in accordance with embodiments of the present invention. Pump102shares the same structure and function of the pump101inFIG.2, except that pump102includes two speed reducing systems50a,50b. The first speed reducing system50ais located between the first stage20aand the second stage20b, and the second speed reducing system50bis located between the second stage20band the third stage20c. For instance, stage20ais mounted to a first secondary shaft15a, stage20bis mounted to a second secondary shaft15b, and stage20cand stage20dare mounted to the main shaft10. An end of the main shaft10is attached to a component of the speed reducing system50b, such as a pinion or epicyclic gear, and an end of the second secondary shaft15bis also attached to a component of the speed reducing system50bm, such as a pinion or epicyclic gear. The opposing end of the second secondary shaft15bis attached to the speed reducing system50a, such as a pinion or epicyclic gear, and an end of the first secondary shaft15ais also attached to the speed reducing system50a, such as a pinion or epicyclic gear. In some embodiments, the ends of the main shaft10and/or the ends of the secondary shafts15a,15bare structurally integral with components of the speed reducing system50a,50b, respectively.

The speed reducing system50aallows for a speed differential between the first secondary shaft15aand the second secondary shaft15bso that the stages20acan be operated at a different (e.g. lower) speed than stage20band also at a different speed than the other stages20c,20d. The speed reducing system50ballows for a speed differential between the second secondary shaft15band the main shaft10so that the stages20bcan be operated at a different (e.g. lower) speed than stage20aand also at a different speed than the other stages20c,20d. The speed differential between the shafts10,15a,15bminimizes net positive suction head and allows for a smaller length of the overall pump102.

While this disclosure has been described in conjunction with the specific embodiments outlined above, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the preferred embodiments of the present disclosure as set forth above are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the invention, as required by the following claims. The claims provide the scope of the coverage of the invention and should not be limited to the specific examples provided herein.