Patent Application
20220356885
The present disclosure relates to inducers for submersible pumps; in particular, the present disclosure relates to inducers for submersible pumps for pumping a slurry containing solids and viscous fluids, and a method of designing such inducers.
An inducer is a rotating component on a centrifugal pump that lies outside of the volute casing and immediately upstream of the impeller. The purpose of inducers is primarily to reduce the required Net Positive Suction Head (“NPSHR”), and thus reduce or prevent cavitation in the pump. There are two NPSH measures. The available NPSH (“NPSHA”) is a measure of the difference between the suction pressure (pressure at the inlet of the pump) and the vapour pressure of a fluid. Fluids have a vapour pressure at which point some of the fluid will evaporate, forming small air bubbles which will soon condense and implode back to liquid. This phenomenon is generally referred to as cavitation. It is desirable to reduce or eliminate cavitation, as it may worsen the performance of pumps when it occurs, as well as significantly wear out and damage the pump components where cavitation occurs. NPSHR is used to identify at what NPSHA or inlet suction pressure enough cavitation is present in the pump such that the performance of the pump is measurably affected. For example, by some standards, when the head produced by a pump drops by 3%, the NPSHA at that point is considered the NPSHR. The 3% lower head will be compared to the head at higher NPSHA. Typically, the head will remain constant at NPSHA higher than that point. It thus is important to ensure that the NPSHA in any application is equal to or above the NPSHR. That is, the pressure of the fluid that will be pumped must be at least as high as the NPSHR at the suction inlet of the pump. NPSHR is based on the pump, whereas the NPSHA is based on the system that the pump will be placed in.
The purpose of an impeller in a centrifugal pump is to increase the pressure of the fluid from the inlet to outlet. However, the pressure typically drops sharply at the leading edge of the impeller blades before increasing. This is usually where cavitation occurs, but it can occur elsewhere in the impeller where a pressure drop occurs. Inducers reduce NPSHR by increasing the pressure upstream of the impeller. Inducers do this by accelerating the flow of the slurry more gently at the leading edges of the impeller blades, which reduces the possibility of cavitation occurring there. Throughout the inducer, the pressure rises gradually so that the pressure at the outlet of the inducer and inlet of the impeller is higher than it would otherwise have been without the inducer. The pressure drop at the impeller blades' leading edges will still occur, but since the pressure is already higher to begin with, there is less chance of cavitation occurring.
The inducers shown in
A typical inducer for a submersible centrifugal pump, in the applicant's experience, cannot pump high-viscosity slurries, including but not limited to slurries comprising abrasive solids and/or relatively large solids, without experiencing performance degradation. An example of a highly viscous slurry, without intending to be limiting, includes mature fine tailings settled at the bottom of a tailings pond from an oil sands mining operation. Such slurry may comprise of water, bitumen, fine particulates, sand, rocks and other debris, such as trees and tree parts, which may enter the tailings pond from the surrounding area. The viscosity of the slurry may be in the range of 15 centi-poise (cP) and solids content in the range of 37% solids by weight. Relatively large and abrasive solids, for example having a diameter in the range of 33 mm to 130 mm, tend to damage the inducer blades, especially when the blades are thin. With the abrasiveness and size of the solids in a viscous slurry of the type found in a mature fine tailings pond, the inducer blades of a typical inducer will break from impact or wear away at an accelerated rate, reducing the useful life of the inducer. Furthermore, typical inducer designs do not allow large solids to pass easily through the inducer, thereby clogging the pump inlet. Additionally, high acceleration of the viscous slurry fluid during pumping may cause flow separation of the highly viscous fluid, so that the fluid then separates and falls away from the pump impeller, in which case the highly viscous slurry fluid may not begin to flow at all. As such, there is a need for an inducer which may be utilized on a submersible pump for pumping highly viscous slurries which slurries may additionally contain large solids.
The inducer according to one aspect of the present disclosure is designed to assist pumping of a viscous slurry, such as slurries, containing large solids. With a fast acceleration, a slurry comprising viscous fluids may not begin flowing at all, or the flow may separate from the impeller blades. The applicant realized that reducing acceleration at the impeller blades by smoothing out the velocity profile of the slurry from the leading edge of the inducer to the leading edge of the corresponding impeller, results in reducing the acceleration of the fluid at the leading edge of the impeller blades as the flow transitions between the closely adjacent inducer and impeller blades. As such, selecting inducer parameters that result in a smooth velocity profile of the slurry as it travels through the inducer and transitions to and through the impeller leads to an optimized inducer design capable of moving a highly viscous fluid, for example, mature fine tailings and/or heavy bitumen, through the pump.
Design limitations impacting the design of the inducer, dictated by the presence of large solids in a highly viscous slurry, may be taken into consideration during the inducer design and optimization process. For example, the space between the blades of the inducer, which form a plurality of channels through which the slurry flows through the inducer to the impeller, may be dimensioned so as to receive and allow the passage of the large solids. As used herein, the phrase “large solids” is defined relative to the size of the pump. For example, “large solids” may be considered to be solids that have a maximum diameter in the range of 50% to 150% larger than a calculated blade height for the impeller of a standard, non-slurry pump; such standard, non-slurry pumps being known to persons skilled in the art. As would be known to one skilled in the art, the height of an impeller blade is the distance between the hub side and shroud side of the blade at the trailing edge of the impeller, such as the impeller blade height H shown in
Because the slurry pump is designed around a defined maximum solid size which is considered large for the pump, based on the flow rate, head and rotational speed of the pump, the inducer designed for that slurry pump must be capable of passing a large solid with a diameter corresponding to the blade height of the slurry pump's impeller. In some cases, the phrase “a large solid with a diameter corresponding to the blade height of the slurry pump's impeller” means that the correspondence between the maximum diameter of the solid and the blade height of the slurry pump's impeller is 1:1, although in other cases, the maximum diameter of the solid size may be slightly less than the impeller blade height of the slurry pump (such as, without intending to be limiting, a 99:100 or a 98:100 correspondence between the maximum solid size diameter and the impeller blade height of the slurry pump).
An illustrative example of an inducer designed in accordance with the present disclosure, referred to herein as the Prototype Model 7 or “PM7” inducer, was designed for pumping a viscous slurry containing solids having a maximum diameter of 130 mm. In this particular example, the impeller blade height is also 130 mm. However, it will be appreciated by a person skilled in the art that a solid having a maximum diameter of 130 mm is meant as an illustrative example only of what is meant by a “large solid” and is not intended to be limiting, and that the combination of a pump and inducer may be designed for passing solids having diameters of less than or greater than 130 mm.
In some embodiments of the present disclosure, matching the number of inducer blades to a corresponding number of impeller blades and aligning the trailing edge of each inducer blade with a leading edge of a corresponding impeller blade may enable or facilitate large solids to flow from the inducer to the impeller without being blocked by the leading edge of the impeller blades. Whereas, with conventional centrifugal pump configurations that include an inducer, the impeller may typically have a greater number of blades than the inducer. For example, radial impellers for centrifugal pumps may typically have five to seven blades, and sometimes as few as three blades or as many as nine blades; whereas, an inducer may typically have two to four blades.
In what follows, the term “axial direction” is intended to refer to a direction that is parallel to the axis of rotation of the drive shaft of the pump, and the term “radial direction” is intended to refer to a direction that extends radially outwardly from the axis of rotation and perpendicular to the axial direction.
The axial length of the inducer, defined below as length L and measured between the leading and trailing edges of the inducer blades, is preferably relatively short in highly viscous slurry applications, so as to reduce drive shaft deflection and limit the increased power draw of the pump. For some pump configurations, the axial length may also need to be limited to provide sufficient space for additional pump elements upstream of the inducer inlet, such as a cutting mechanism for reducing the size of the solids entering the inlet.
Furthermore, when integrating the inducer into a submersible pump for optimizing the inducer and impeller combination, the applicant discovered that reducing the gap or distance between the inducer blades and the corresponding impeller blades tends to reduce the acceleration of the slurry that may otherwise occur at the leading edges of the impeller blades, thereby assisting in maintaining a relatively smooth velocity profile as the slurry passes from the inducer to the impeller. Whereas conventional inducers, such as shown in
Other aspects of the inducer of the present disclosure may also depart from the theory for designing typical inducers for submersible fluid pumps. For example, in some embodiments of the present disclosure, the inlet angle of the leading edge of the inducer blade is larger than is theoretically called for in an ideal inducer, so as to enlarge the resulting fluid channels of the inducer to accommodate large solids and/or to accommodate the diameter of the inducer. As well, conventional inducers, to applicant's knowledge, include inducer blades having a backwards sweep, as defined below, at the leading edge; for example, in the range of 65° to 90°. In some embodiments of the present disclosure, the inducer blades sweep back at a smaller angle, such as in the range of 25°, to provide sufficient clearance to pass the required maximum solid size specified for the pump.
In one aspect of the present disclosure, an inducer for a submersible slurry pump is configured to pump a slurry containing large solids and viscous fluids. The pump includes an impeller having an impeller blade height, and the solids have a maximum diameter equal to the impeller blade height of the pump. The inducer is configured to be positioned within the pump's casing and mountable to a drive shaft of the pump, so that the inducer is adjacent to and immediately upstream of the impeller mounted on the drive shaft, and the inducer and the impeller are rotated on the drive shaft in a direction of rotation. The inducer comprises: a hub; at least two and no more than four inducer blades mounted to and extending axially along the hub, wherein the inducer blades extend outwardly from and wrap helically around the hub, the hub and the inducer blades thereby defining a plurality of channels. Each channel of the plurality of channels is bounded by the hub, the inducer blades, a plurality of impeller blades and an inner surface of the casing. A trailing edge of each blade of the inducer blades is configured so as to be positioned snugly adjacent to and in fluidical alignment with a leading edge of each corresponding blade of a plurality of impeller blades of the impeller when the inducer is mounted on the drive shaft of the pump, such that a velocity curve of the slurry is substantially smooth as the slurry travels from a leading edge of the inducer blades to the leading edge of the plurality of impeller blades.
In another aspect of the present disclosure, a submersible slurry pump is configured to pump a slurry containing solids and viscous fluids. The pump comprises: the inducer described in the paragraph above, which inducer is mounted on a drive shaft of the pump; an impeller mounted on the drive shaft downstream of and snugly adjacent to the inducer, the impeller having an impeller blade height; and a casing of the pump, the casing housing the inducer and the impeller. A trailing edge of each blade of the inducer blades is positioned snugly adjacent to and in fluidical alignment with a leading edge of a corresponding impeller blade of a plurality of impeller blades of the impeller when the inducer is mounted on the drive shaft, thereby defining a radial gap between the two, radial relative to the drive shaft, such that a velocity curve of the slurry is substantially smooth as the slurry travels from a leading edge of the inducer blades to and over the leading edge of the plurality of impeller blades. A maximum diameter of the solids is equal to the impeller blade height.
Additionally, a method for designing an inducer for a submersible slurry pump is provided. The submersible slurry pump is designed to pump a slurry containing solids in the range of 50% to 150% larger than a typical blade height for an impeller of a standard, non-slurry pump. The method includes the steps of:
A resulting inducer, designed according to the initial groups of primary and secondary parameters, produces a smooth velocity curve of the slurry from the leading edge of the inducer to the corresponding leading edge of the impeller. In some embodiments, the resulting inducer also produces a substantially flat velocity curve of the slurry as the slurry travels from the leading edge of the inducer to the corresponding leading edge of the impeller of the pump.
In another aspect of the present disclosure, a plurality of preliminary inducer designs obtained by following the steps of the method described above may each be simulated, and at least one preliminary inducer of the plurality of preliminary inducers which produces a substantially smooth (and, in some cases, also substantially flat) velocity curve, as the slurry moves from the leading edge of the inducer to the leading edge of the impeller, is selected for further optimization.
The optimization steps may include:
Optimization may also involve modifying one or more parameters of the initial group of primary parameters, in the optimization step (a) described above.
The initial group of primary parameters may include: a hub diameter of the inducer; an outer diameter of an inducer blade of the inducer; an inlet angle of the inducer blade; an outlet angle of the inducer blade. The initial group of primary parameters may further include a range for a blade chord length of the inducer blade at the shroud side. The initial group of secondary parameters may include: a number of blades of the inducer; a wrap angle of the inducer blade from a leading edge to a trailing edge of the inducer blade; a progression of a blade angle of the inducer blade from the leading edge to the trailing edge of the inducer blade; a chord length of the inducer blade; a sweep angle of the inducer blade; an axial tapering of the leading edge or the trailing edge of the inducer blade; a trim of the leading edge or the trailing edge of the inducer blade towards a shroud side of the inducer blade. The secondary parameter of the number of inducer blades may be determined so as to equal the number of impeller blades of the pump's impeller.
In one aspect of the present disclosure, and by way of example and without intending to be limiting, an inducer, referred to herein as the “PM7 inducer”, is described for a 600 horsepower (hp) slurry pump with a semi-open impeller, for pumping high viscosity slurries with solids up to 130 mm in diameter. For example, without intending to be limiting, such high viscosity slurries may be found at the bottom of a tailings pond of an oil sands production site, wherein the high viscosity slurry comprises water, bitumen, sand, silt, rocks and other debris, such as trees and tree parts, that may enter the tailings pond from the surrounding area. The viscosity of such a slurry may be in the range of 15 cP and may have a solids content in the range of 37% solids by weight. However, it will be appreciated by a person skilled in the art that the PM7 inducer is provided herein as an illustrative example only, and is not intended to be limiting. A further example of an inducer 100, referred to herein as the Prototype Model 1 or “PM1” inducer, illustrated in
Although the specific examples of the PM7 and PM1 inducers are described herein to illustrate different aspects of the present disclosure, it will be appreciated by a person skilled in the art that the disclosure is not intended to be limited to the characteristics of the PM7 or PM1 inducers or to the operating requirements for which the PM7 or PM1 inducers were designed. Inducers for other submersible slurry pumps, designed to pump slurries of different viscosities and containing large solids having a range of maximum diameters, are within the scope of the present disclosure.
As such, one of the design goals for the present inducers disclosed herein was to assist with getting the highly viscous slurry fluid to flow effectively and efficiently through the slurry pump, inhibiting separation of the slurry fluid flow from the inducer and impeller blades of the pump. With a fast acceleration, fluids with high viscosity may not begin flowing at all, or may separate and fall away from the blades; for this reason, inducing a slower, gentler acceleration of the slurry fluid upstream of the impeller is preferable. In the absence of an inducer, high acceleration of the viscous slurry will occur on the impeller blades. Another design goal of the inducer disclosed herein was to reduce the NPSHR, since there may be low pressures at the suction end of the inducer, and large slurry pumps will tend to cavitate more readily in such conditions.
The pumping environment and nature of the slurry thereby necessitates implementing certain design limitations that are, in applicant's opinion, counterintuitive when taking into consideration the theoretical design parameters of a typical or ideal inducer. For example, the inducer blades had to be much thicker on the present inducers than on a typical inducer in order to handle the abrasive solids being passed. With the abrasiveness and size of the solid material, thin blades would break from impact and/or wear away quickly. An embodiment of the inducer, the PM7 inducer discussed herein, is designed to receive and pass through large solids to the impeller, the solids having a diameter of up to 130 mm, without clogging the inducer or suction of the pump. With reference to
Other design limitations for the inducer may include a limited or shortened axial length of the inducer L, as seen in
Additional considerations for limiting the axial length L of the inducer include limiting the increased resistance or drag acting on the inducer blades for an inducer having a longer axial length as compared to an inducer having a shorter axial length, as well as limiting the weight the inducer added to the system, thereby reducing the additional power draw that may be required by adding the inducer to the drive shaft and reducing the potential for bending or deflection of the drive shaft to occur. Without intending to be limiting, in the example of the PM7 inducer as shown in
As previously mentioned, positioning the inducer near the impeller so as to reduce the gap between, and fluidically align, the inducer and the impeller, applicant has been found, plays a significant role in maintaining the pressure and velocity of the slurry as it flows from the outlet of the inducer to the inlet of the impeller across the gap between the inducer and the impeller. The term “gap” as used herein is defined as the location of, and the distance between, an inducer blade and a corresponding impeller blade where that distance is the smallest. Ideally, the gap between the inducer and impeller blades is reduced as much as reasonably possible while taking into account the spacing between the inducer and impeller required to allow for machining tolerances. For example, without intending to be limiting, the distance of the radial gap G, best viewed in
In a conventional pump having an inducer, the number of blades of the inducer and the number of blades of the corresponding impeller may be different. For example, a typical impeller may have five to seven blades, while a typical inducer may have two to four blades. However, a pump configuration where the number of impeller blades differs from the number of inducer blades results in the trailing edge of at least some of the inducer blades not aligning with the leading edge of at least some of the inducer blades. For applications in which the slurry includes solids, the mismatch in the number of impeller blades and inducer blades may result in some solids becoming blocked as the slurry flows from the inducer to the impeller. Advantageously, matching the number of inducer blades to the number of impeller blades on an impeller and inducer mounted closely adjacent to one another on a common drive shaft may provide for nearly continuous channels between the inducer and impeller blades through which the slurry flows, thereby reducing the blockage of solids that may otherwise occur as the slurry flows through the inducer and impeller. For example, not intended to be limiting, in some embodiments the plurality of inducer blades consists of three blades 16 and three corresponding blades 26 on the impeller 20. However, it will be appreciated by a person skilled in the art that the same advantage may be realized, in other pump configurations, by matching the number of inducer blades to the number of corresponding impeller blades on the impeller of a given pump configuration, so long as the channels remain large enough to handle the anticipated solids. In another example, an impeller may have four blades and the corresponding inducer may have two blades, which configuration may still enable for alignment between the trailing edge of the inducer blades and the leading edge of two of the four blades of the corresponding impeller. It will further be appreciated that for slurry which does not include large solids, it may not be required to match the number of inducer blades to the number of impeller blades when designing the inducer.
In one aspect of the present disclosure, a number of design parameters for a new inducer designed to pump a slurry containing viscous fluids and large solids are determined, including the thickness of the blades, the length-to-diameter ratio and the size (diameter) of the hub of the inducer were defined. Then, one or more initial inducer designs featuring these design parameters were modelled utilizing software so as to obtain a performance baseline. An example of such modelling software, without intending to be limiting, includes the ANSYS™ Computational Fluid Dynamics software package (such modelling software referred to herein as the “CFD Software”). One or more of the initial inducers were modified and then modelled so as to assess the modified inducers' performance against the performance baseline. Performance of each of the modified inducers was assessed by plotting the average velocity of the fluid, from the inlet of the pump to the outlet of the impeller. Reductions in the velocity gradient or curve, so as to smooth and lessen or flatten the velocity gradient of the fluid flowing between the pump inlet and the outlet of the impeller, were observed by the applicant as an improvement over the baseline performance measurement, thereby identifying one or more of the modified inducers as an optimized new inducer design.
Furthermore, to determine the existence of, or an amount of, cavitation occurring in the pump, one or two methods may be utilized during the modelling process. Firstly, a standard method for determining cavitation in physical tests is to measure the head or pressure increase over a pump component at a specific inlet fluid pressure. That pressure of the fluid, as measured at the inlet, is then lowered until the head or pressure produced drops 3% from its baseline value. These tests may be replicated in the CFD Software to determine the inlet fluid pressure that would produce a 3% head drop. Once this inlet fluid pressure is determined, analysis of the amount of cavitation present involved running simulations on inducers at that inlet fluid pressure where cavitation occurs, then measuring the volume of air present. If the volume of air present was reduced in the presence of the inducer, NPSHR was improved. Another method that may be used for measuring cavitation is to maximize the head at the inlet fluid pressure previously determined to produce a 3% head drop. If the resulting head or pressure was found to be higher, one may deduce that less cavitation was occurring.
Simulations utilizing the CFD Software may be initially run with only the impeller and the pump casing to plot the velocity and assess the resulting velocity gradients (or in other words, the acceleration of the pumped fluid). The NPSHR may also be determined. With these baseline results, simulations were subsequently run with different versions of the inducer to determine whether the inducer produced a smooth, relatively flat velocity curve and/or reduced cavitation. If cavitation was reduced but not eliminated, the cavitation preferably occurs around the inducer and not in the impeller area, as the inducer is considered a sacrificial, or in other words, expendable, component of the pump, similar to the concept of a sacrificial anode, whereby cavitation, to the extent that it occurs, causes damage to the inducer that would otherwise occur at the impeller. Advantageously, to the extent that cavitation occurs and damages the inducer, in addition to damage to the inducer caused by impacts of the solids in the slurry, the inducer is generally smaller and less expensive to manufacture compared to the impeller, and also may be less labour intensive to replace as compared to the impeller. Thus, an inducer may extend the life of the impeller, and an inducer is also simpler and less expensive to replace as compared to replacement of the impeller.
In response to the results obtained from the initial simulations, modifications may be made to one or more parameters of the inducer and then further simulations may be run to determine whether the modifications produced improved results, such as a smoother, flatter velocity curve and/or reduced cavitation. A number of further design parameters, in addition to those mentioned above, may be used to define and modify the shape and design of the inducer. Such parameters, defined below, may include in particular: the inlet and outlet angles of the inducer blades, measured at the inducer hub and at the outer diameter of the inducer blades; the wrap angle of the inducer blades at the hub and at the outer diameter of the inducer blades; the sweep of the leading edge of the blades; and the shape of the leading and trailing edges of the blades when viewed from the side profile of the inducer.
The shape of the leading and trailing edges of the inducer blades may be defined radially, such as having a straight edge, or having a convex or concave shape relative to the direction of rotation X (as seen in the PM7 inducer illustrated in
The wrap angle defines the radial angle between the leading edge and trailing edge of a blade at a specific layer, such as the hub or shroud layers of the inducer blade. The term “hub layer”, as used herein, refers to dimensions or characteristics of a blade as measured at the interface between the blade and the hub, while the term “shroud layer”, as used herein, refers to dimensions or characteristics of a blade as measured at a free edge of the blade, distal from the hub, where the blade is adjacent the shroud or casing. It will be appreciated by a person skilled in the art that the term “shroud layer” may be used regardless of whether the inducer or the impeller actually has a shroud or not.
Typical inducers may have large wrap angles measured at the shroud layer, for example exceeding in the range of 180° to 400°. A wrap angle of 360°, measured at the shroud layer, for example, means that a single inducer blade wraps entirely around the hub of the inducer once. In contrast, examples of inducers designed in accordance with the present disclosure have comparatively small wrap angles. For example, the PM7 inducer has a wrap angle WS of 65° measured at the shroud layer, as shown in
An illustrative example of an inducer of the present disclosure, referred to herein as the PM7 inducer 10, is illustrated in
As may be seen in
Additionally, the velocity gradient does not increase greatly prior to entering the inducer, where the viscous fluid will flow better because it is in contact with the inducer blades. In comparison, the solid line velocity plot NI for the pump without an inducer, illustrates a significant increase in velocity approaching (ie: upstream of) the leading edge of the impeller (line B). Whereas, in the pump incorporating the inducer, the velocity of the pumped fluid remains relatively constant as it flows between the leading edges of the inducer and the impeller, with only a slight increase in velocity as the fluid moves past the leading edges of each of the inducer and the impeller. It may also be seen that the velocity of the fluid increases gradually between entering the inlet of the pump (line AA) and before it reaches the leading edge of the inducer (line A), for the pump including the inducer, whereas the velocity of the fluid remains constant before sharply increasing as it approaches the leading edge of the impeller (line B), in the pump without an inducer. Further, in the pump without an inducer, the velocity profile spikes, at the trailing edge of the impeller (line C), and to a higher velocity as compared to the pump with the inducer.
Similar features are illustrated in
The velocity of the fluid observed during simulations may also be viewed in
Advantageously, the applicant observed during simulations that the power draw of the pump configured with the illustrative PM7 inducer disclosed herein was approximately 1.9% lower than the power draw of the same pump without the inducer. Although the addition of the inducer to the drive shaft adds weight and drag loading to the drive shaft, thereby increasing the power draw required, the inducer also assists the impeller with achieving the head or pressure rise required and improves the overall fluid flow, thereby resulting in a net decrease in the power draw of the pump. In other inducers designed in accordance with the present disclosure, the Applicant has observed a power draw reduction of up to 4.4% lower with the addition of the inducer to the pump system.
The NPSHR of the pump was deduced to either remain the same or improve with the addition of the inducer disclosed herein, based on the velocity profiles obtained from simulations of earlier proposed inducer designs and comparing those prior results to the velocity profiles obtained for the present inducers, and compared to the velocity profiles obtained for the same pump without the inducer. Specifically, the deduction that adding the inducer disclosed herein to the pump system likely caused the NPSHR of the pump to either remain the same or improve, was accomplished by comparing the measured head obtained at one inlet pressure or NPSHA value as between a pump with the inducer and the same pump without the inducer, as the applicant has observed during simulations, with the result that the pump configured with the inducer reduced regions of low pressure. Furthermore, as illustrated in
A detailed description of the illustrative example of the PM7 inducer disclosed herein follows, with reference to
The hub 13 of the inducer includes a slight, gradual increase in diameter from the leading to trailing edges 12, 14 of the inducer blades, and then the diameter of the hub 13 increases dramatically between the trailing edges 14 of the inducer blades and the outlet end 13c of the inducer hub. An increasing diameter from the inlet end to the outlet end of the hub 13 has been found to be advantageous as the increase in diameter, it has been found, helps the fluid pressure to increase more gradually and reduces the potential for flow separation. The higher increase in diameter of the hub, downstream of the trailing edges 14, advantageously provide a smoother flow pathway from the nearly vertical inducer hub to the nearly horizontal impeller hub.
The thickness of the blades, for example in the illustrative example of the PM7 inducer 10, may vary throughout the blade, depending on which point on the blade the thickness is measured. In general, the inducer blade 16 is thicker at the hub and thinner at the free edge of the blade. For example, without intending to be limiting, at the hub layer the thickness T1 of the blade may be 40 mm at the leading edge 12, as shown in
In the prior art, such as in the Gulich textbook mentioned above, it is conventional for an inducer blade to have a sweep back angle of approximately 65° to 90°. In another aspect of the present disclosure, as seen in
The profile of the leading edge 12 of the example PM7 inducer, as viewed for example in
During simulation testing of various configurations of inducers and impellers coupled to the drive shaft, the applicant observed that the positioning of the inducer relative to the impeller plays a role in achieving the smooth, relatively flat velocity profile of the slurry as it flows through the inducer and the impeller. Configurations of inducers having a substantially horizontal trailing edge profile and which were therefore positioned farther away from the impeller along the drive shaft were observed by the applicant, during simulation testing, to result in a significant velocity decrease as the slurry flowed between the inducer and the impeller. In other simulation tests in which the same inducer, having a substantially horizontal trailing edge when viewed in side profile of the inducer, wherein the inducer was positioned as close to the impeller as possible, the applicant observed the velocity decrease remained relatively significant, due to the lack of extending the trailing edge 14 of blade 16 in axial direction Y along the hub 13.
Achieving the close positioning between the trailing edges 14 of the inducer blades and the leading edges 22 of the impeller blades also resulted in significant nesting of the inducer within the impeller. In applicant's experience, conventionally the inducer is positioned upstream, outside of and adjacent to the inlet eye 11 of the impeller blades, as seen in
In
It will be appreciated by a person skilled in the art that certain characteristics of the inducers disclosed herein may be modified so as to optimize the inducer for pumping a slurry containing larger solids, for example having a diameter exceeding 130 mm; or conversely, a slurry containing smaller solids, for example solids having a diameter less than 130 mm.
Referring to
On the other hand, for an inducer designed to pump a viscous slurry which does not contain large solids, but which may include, for example, small and abrasive solids such as rocks or pebbles, certain design limitations of the inducer would not need to be as restricted when optimizing the inducer design. For example, such an inducer for pumping a viscous slurry may include larger wrap angles WH and WS, smaller inlet angles β and larger reverse sweep angles S at the leading edge 12 of inducer blades 16, for example such sweep angles may be in the range of up to 60° to 90°.
In many cases, the inducer designs disclosed herein are very unlike a theoretical inducer design, which inducers are typically designed for improving NPSHR rather than for improving the velocity profile of a viscous slurry flowing through the inducer and between the inducer and the impeller and then through the impeller. Velocity plots such as seen in
In one aspect of the present disclosure, an example of the methodology is provided for designing inducers configured to work with a submersible slurry pump designed to pass large solids, as defined elsewhere herein.
When designing a new inducer in accordance with the present disclosure, the inducer constraints are defined as follows:
Once the constraints of the inducer are identified, the primary design parameters of the inducer are calculated, based on theoretical calculations. The primary parameters include: the inducer hub diameter, inducer blade outer diameter, blade inlet angles and blade outlet angles. Optionally, a recommended range for the inducer blade chord length at the shroud side may also be included in the primary design parameters. The chord length is the length of the blade from leading edge tip to trailing edge tip if the inducer blade was “unrolled” and “flattened”. The chord length is based on the diameter of the blade, the wrap angle, and the axial length of the inducer from the leading edge to the trailing edge.
Applicant believes that conventional design theory for ideal inducers requires a suction specific speed of 400-700 in order to perform well regarding NPSHR. However, with the constraints required for submersible slurry pump inducers designed to pass large solids, it may not be possible or needed to achieve a suction specific speed in this range. However, the goal is to achieve a suction specific speed that approaches the ideal range, by modifying the primary parameters. For example, the hub diameter may be minimized, and be designed to have an increasing diameter from leading edge to trailing edge. The Applicant observes this helps pressure to build up slowly as area decreases with increasing hub diameter, and this modification can also help avoid flow separation. Furthermore, the inlet blade angles may be selected to achieve the best suction specific speed.
Other primary design parameters, such as the inducer blade outer diameter and the blade inlet and outlet angles, may be modified so as to approach the parameters of an ideal non-slurry pump inducer according to theory. Although the applicant found it is often not possible to select these primary parameters to fall within the recommended theoretical ranges for an ideal inducer, given the constraints, the applicant would select primary design parameters to approach the theoretical recommendations for those parameters. Several of these parameters may be well outside the recommended ranges, which illustrates the uniqueness of the inducers disclosed herein. For example, the applicant has found the outer diameter of the inducer is typically much smaller than the theoretically recommended diameter, due to the limitations imposed by the suction diameter of the pump. Due to the outer diameter constraint, the blade angles were larger than what is theoretically common. Based on calculations, the blade angles may be defined as small as possible given the existing constraints.
The next step is to utilize design software to input the primary parameters calculated above to generate the secondary parameters for the possible inducer designs. The secondary parameters, which may be identified with the assistance of design software, include:
To the extent possible, given the constraints, the secondary parameters may be selected in accordance with theory for an ideal inducer designed for a non-slurry submersible liquid pump, and then modified for pumping slurries containing viscous fluids and large solids. The conventional ranges for each of the secondary parameters include the following:
The next step involves adapting the primary and secondary parameters for the design constraints identified in the earlier steps. Usually, the most limiting constraint is the maximum solid size that the inducer must pass. Each of the primary and secondary parameters may be modified to allow for larger solids to pass, than would otherwise be possible in a conventional submersible liquid pump of the prior art.
As described herein, when the number of inducer blades matches the number of impeller blades (such as, three impeller blades and three inducer blades), or if the number of impeller blades is a multiple of the number of inducer blades (such as, four impeller blades and two inducer blades), such a configuration would advantageously enable the alignment of the trailing edge of each inducer blade with a leading edge of an impeller blade, thereby providing sufficient room for a large solid to pass from the inducer to the impeller, a reduced radial gap between the trailing edge of the inducer blades and the leading edge of the impeller blades, and enables fluidical alignment between the channels created by the inducer blades and the channels created by the impeller blades, all of which, the applicant has found, assists with smoothing the velocity curve of the fluid as it passes from the inducer to the impeller.
Other secondary parameters which may be modified includes the reduction of the sweep angle. In the example of the PM7 inducer, the sweep angle was reduced to 25 degrees, which provides more clearance for passage of the large solids. Tapering the leading edge axially and trimming the leading edge/shroud corner may also provide more clearance at the leading edge of the inducer blades. From the leading edge to the trailing edge, the space between the blades should enable the maximum size large solids to pass. In some designs, it was possible to maintain a consistent blade angle over the first 25% of the blade length starting at the leading edge of the blade, and then allow the blade angle to gradually change to the selected outlet angle. Taking the PM1 inducer as an illustrative example, the inlet blade angle was 50.5 degrees at the hub and 31.7 degrees at the shroud. The blade angle was maintained at these values for approximately the first 25% portion of the blade length, measured from the leading edge of the inducer blade. Then, the angle begins to vary along the blade length, increasing to become 80.5 degrees at the trailing edge at the hub layer and 67 degrees at the trailing edge of the shroud layer. To provide another illustrative example, the PM7 inducer did not allow for the inlet blade angle to be maintained at a constant value over the first 25% of the blade length, measured from the leading edge of the blade. In that example, the inlet blade angle varied substantially throughout the entire length of the inducer blade, from the leading edge to the trailing edge of the blade.
The wrap angle, chord length and sweep angle from leading edge to trailing edge were the other secondary parameters adjusted to ensure solids could pass through the blades of the inducer. In extreme cases for inducers designed to pass very large solids, the wrap angle may need to be very small (such as, less than 100 degrees), and the chord length may need to be relatively small (as compared to the recommended chord length for submersible liquid pumps, according to theory) so as to accommodate the large solid sizes. While a low wrap angle and high chord length would be possible, the blades would be nearly axial, would draw excessive power, and would increase the velocity of the slurry too high, such that the velocity would then decrease before entering into the impeller and then increase again through the impeller. That said, a shorter chord length combined with the small wrap angle allowed for a more ideal and helical shaped inducer. Finally, the sweep back of the blade past the leading edge may also need to be limited to ensure sufficient spacing within the inducer for passage of large solids.
The trailing edge design of the inducer blade may be based upon the impeller leading edge dimensions as well as the maximum solid size constraint. The Applicant has observed that the blade trailing edge/shroud corner is trimmed axially and radially to provide sufficient clearance between the inducer and impeller blades. This trim also helps achieve the required maximum solid size. The trailing edge is often tapered axially such that the hub side is further back axially than the shroud side with respect to a line extending radially outward from the hub. This helps bring the inducer trailing edge closer to the impeller leading edge, thus providing a smoother flow transition between the inducer and impeller. Such parameter also assists with achieving sufficient clearance through the inducer for the maximum solid size constraint.
The next step in the method includes simulating one or more simulation inducers, the simulation inducers designed in accordance with the constraints and primary and secondary parameters discussed above. For example, the one or more simulation inducers may be simulated using CFD software, and the results analyzed to observe whether or not the intended outcome of a smoother and flatter velocity curve of the pumped media as it moves through the inducer to the impeller is achieved, wherein the desired outcome is that the velocity gradient is smoother and increases gradually as the pumped media travels into the impeller. The secondary desired outcomes include that the NPSHR is as good or better with the inducer, as compared to simulations run on the pump without the inducer, and that the head and efficiency are not negatively impacted when the inducer is included.
In some embodiments, the steps above may be performed multiple times to obtain an optimized inducer. The secondary parameters listed above may be modified first, to optimize performance while still achieving the identified constraints. Then, the primary parameters determined above may also be modified in order to analyze their effects on the velocity curve of the fluid travelling through the inducer and impeller of the pump.
| Number | Date | Country | Kind |
|---|---|---|---|
| 3048275 | Jun 2019 | CA | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CA2020/050902 | 6/29/2020 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 62868093 | Jun 2019 | US |
