Rotary kinetic fluid motors or pumps – Smooth runner surface for working fluid frictional contact
Reexamination Certificate
1999-08-06
2001-05-08
Lopez, F. Daniel (Department: 3745)
Rotary kinetic fluid motors or pumps
Smooth runner surface for working fluid frictional contact
C415S073000, C415S199100, C416S004000, C416S19800R, C416S20100A, C416S22300B
Reexamination Certificate
active
06227796
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to improvements to a pumping apparatus for handling viscous liquids, such as heavy oil which is extracted from underground oil bearing stratum.
BACKGROUND OF THE INVENTION
The extraction of heavy oil bitumen from an underground “reservoir” presents significant handling problems, by reason of the high viscosity of bitumen, and the presence of other liquids, gases and even solid particles in fluid admixture with the bitumen. Conventionally, pumping action is carried out using bladed impellers or vane-type pumps which pump the fluid to surface installations where subsequent separation of the fluid into its constituent parts takes place. High viscosity of bitumen, use of steam injection to lower the bitumen viscosity and abrasive materials result in many difficulties including solids impingement wear, and cavitation leading to pumping inefficiencies and incipient pump failures.
In a co-pending Canadian Patent Application No. 2,185,176, published on Mar. 11, 1998, the inventor previously disclosed a prior pump for handling viscous liquids, such as heavy oil bituminous fluid mixtures, and which overcomes some of the limitations of conventional vaned pumps. The inventor's prior pump utilizes a composite impeller “the prior impeller” having a stack of thin disks positioned concentrically over a cylindrical core. The disks are parallel and are spaced axially along the core. The core is formed with a plurality of upwardly spiraling vanes. The radial periphery of the core between vanes is open for fluid communication to the spaces between the disks. The core has a fluid inlet at one end of the vanes and fluid discharges at the periphery of the disks. The prior impeller is located concentrically within a cylindrical housing, forming an annular flow chamber therebetween. This stack of disks and the housing each have a cylindrical profile. In pumping operation, the core and disks are rotated. Boundary layer drag between pumped fluid and the rotating disks and centripetal force drives the fluid radially outwards to discharge at the disks' periphery and into the annular flow chamber. Fluid exiting the disks inducts fluid from the core's spiral vanes and from the previous impeller stage or pump intake.
A multiplicity of vortices are formed in the annular flow chamber. Like a centrifuge or cyclone, the fluid can separate into at least some of its separate component parts or phases, more dense fluid, such as contained solids, being driven outwardly. The vortices result in very unfavorable intake conditions should the fluid in the flow chamber be routed into the intake of a successive pumping stage. A stationary vane diffuser is applied between pumping stages. The prior impeller, while improving pumping capacity and performing primary separation, results in two phenomenon which are disadvantageous; high wear of the pump housing, particularly at the exit of the annular flow chamber, and high back-pressure at the impeller discharge which limits flow capacity.
At each downstream increment of the annular flow chamber, greater and greater accumulated flow is experienced. The accumulated flow results from each incremental increase in fluid exiting from each successive planer disk of the impeller. The linear increment in fluid discharge results in the development of back-pressure which affects the accumulating flow. Additionally, the combination of the incremental linear fluid discharge, the concentration of solids at the periphery of the flow chamber and turbulence results in high wear at the discharge of the flow chamber. The turbulence, the formation of discharge back-pressure and the housing wear result in reduced pump performance and increasing pumping inefficiencies.
This prior impeller is an improvement over other conventional impellers, and produces higher throughput and capability for handing mixtures including solids. However side effects, such as high housing wear, is an undesirable characteristic and, further, because multistage pumping can incorporate several hundred stages, the losses and back-pressure associated with each stage can be significant.
SUMMARY OF THE INVENTION
An improved impeller is provided for a viscous fluid pump, said impeller providing several advantages over even the inventor's own prior art. In a preferred form, the improved impeller comprises a plurality of radially extending and axially spaced conical stack of ever diminishing diameter disks for providing ever diminishing incremental flow therefrom. Surprisingly, when compared to the prior art cylindrical stack of disks, all of which have the same diameter, the improved impeller produces greater flow despite its reduced ability to induce flow. Instead, in one implementation, a conical impeller having 16% reduced flow induction capability but much reduce head losses can actually provide about 30% more throughput over the prior stacked-disk impeller design without an increase in power requirements. Additionally, high impeller housing wear is markedly reduced. The observed improvements are hypothesized to be due to the manipulation of the flow patterns at the radial periphery of the impeller so as to significantly reduce head losses in the annular flow chamber, particularly by the minimizing of flow turbulence and back-pressure for each successive disk and at the discharge of the annular flow chamber.
Accordingly, in a broad aspect of the invention, an improved pump impeller for viscous fluids is provided, the impeller having a rotational axis, an upstream end, a downstream end and a plurality of parallel flow passages spiraling axially about the rotational axis, the axial flow passages being open at the upstream end and blocked at the downstream end, the impeller being concentrically and rotationally supported within a housing for forming an annular flow passage between the radial extent of the impeller and the radial extent of the housing, the improvement comprising:
a stack of circular disks wherein each disk extends radially and concentrically from the spiral flow passages and is spaced axially from each other disk for forming a plurality of radial flow passages which communicate with the spiral flow passages so that fluid flows from the impeller's upstream end, through the spiral flow passages and is distributed into the radial flow passages; and
the disks at the downstream end have a lesser radial extent than do the upstream disks so that incrementally less fluid issues from the radial flow passages between disks at the impeller's downstream end is less than that which issues from the radial flow passages at the upstream end and thereby minimizing head losses in the resulting flow.
Preferably, the radial extent of successive disk is linearly diminishing for forming a frusto-conical profile of disks between the upstream and downstream ends.
The improved impeller is particularly suited for providing an improved viscous fluid pump comprising:
a rotatable impeller having a plurality of parallel flow passages spirally axially about its rotational axis and a stack of circular disks mounted concentrically therearound, each disk extending radially and concentrically from the axial flow passages and being spaced axially from one another for forming a plurality of radial flow passages therebetween, each downstream disk having a smaller outside diameter than the preceding upstream disk, the radial flow passages being in communication with the axial flow passages so that fluid flows from the impeller's upstream end, through the axial flow passages and is issued into the radial flow passages, the incremental flow of fluid issuing from the radial flow passages at the downstream end being is less than that issuing from the upstream end; and
a housing which rotationally supports the impeller therein for forming an annular flow passage therebetween, the annular flow passage receiving and conducting the flow of fluid incrementally issuing from the radial flow passages.
Preferably, the stack of diminishing diameter disks has frusto-conical profile and
Gowling Lafleur Henderson LLP
Lopez F. Daniel
Nguyen Ninh
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