Patent Description:
<CIT> discloses a combined pump and motor structure including a vibrationstabilizing bearing, anti-friction bearings, a stator of a squirrel cage motor and a motor rotor electrically associated with the stator. <CIT> discloses an electrical pump including a floodable motor which might be of the inside-out motor type. Neither one of these documents discloses independently controllable stator sections and a fluid recirculation system in which the production fluid emerging from the stator cooling channels encounters and lubricates the plurality of bearings.

Electric pump assemblies are used in a wide variety of industrial practices including the transport of fluids over long distances in pipelines, in wellbore applications for pumping production fluids, such as water or petroleum; and in chemical synthesis and processing applications. Electric pump assemblies used in industrial practice typically include, among other components, a pumping section that provides for the pumping of high volumes of fluid. A typical electric pump utilizes a combination of diffusers and impellers, together referred to as pump stages, for pumping fluids. During operation, the impellers are configured to rotate adjacent to fixed diffusers. Typically, the pumping section is coupled to an electric motor which provides mechanical energy to the pumping section by means of a rotary shaft coupled to the motor. A typical electric motor configured to drive the pumping section comprises an outer stator disposed around a torque-producing complement of an inner rotor. This necessarily limits both the size of the rotor and options for its mechanical coupling to the pumping section.

There remains a need to increase the utility of electric pump assemblies by making them more compact and more powerful. Accordingly, it is desired to provide electric pump assemblies which provide greater flexibility by being more compact and powerful relative to conventional electric pump assemblies.

Among other features, the present invention provides an electric pump comprising: (a) a hollow rotor defining a rotor inner surface, a rotor outer surface and a rotor cavity; (b) a stator comprising a plurality of independently controllable stator sections disposed within the rotor cavity; and (c) a plurality of bearings configured to allow rotation of the rotor; wherein the hollow rotor comprises (i) one or more impellers fixed to the rotor outer surface, and (ii) one or more torque-producing complements to the independently controllable stator sections.

In one embodiment, the electric pump comprises: (d) one or more diffusers extending into a fluid flow path defined by the pump; wherein (i) one or more impellers extend into the fluid flow path defined by the pump, and (ii) a plurality of torque-producing complements to the independently controllable stator sections.

In another embodiment, the electric pump comprises: (d) one or more diffusers extending into a fluid flow path defined by the pump; (f) a pump housing; wherein (i) one or more impellers extend into the fluid flow path defined by the pump, and (ii) a plurality of torque-producing complements to the independently controllable stator sections.

Various features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters may represent like parts throughout the drawings. Unless otherwise indicated, the drawings provided herein are meant to illustrate key features of the invention. These key features are believed to be applicable in a wide variety of systems which comprising one or more embodiments of the invention. As such, the drawings are not meant to include all conventional features known by those of ordinary skill in the art to be required for the practice of the invention.

In the following specification and the claims, which follow, reference will be made to a number of terms, which shall be defined to have the following meanings.

The singular forms "a", "an", and "the" include plural referents unless the context clearly dictates otherwise.

Accordingly, a value modified by a term or terms, such as "about" and "substantially", are not to be limited to the precise value specified.

As noted, the present invention provides a novel electric pump in which the pumping component is powered by an electric motor having a stator disposed within a hollow rotor. In one or more embodiments, the stator and the hollow rotor are essentially coextensive and occupy the same bearing span. In an alternate set of embodiments, the stator and hollow rotor are not coextensive with respect to the bearing span. By disposing the stator within a hollow rotor the present invention solves a number of problems of long standing. First, in one or more embodiments, motor windage losses are reduced, relative to conventional motors in which the rotor is disposed within the stator, owing to a reduction in the diameter of the air gap between the stator and the rotor. Second, the peripheral speed of the pump is increased owing to an increase in the rotor diameter. Third, the pump can be made more compact since the pumping and motor sections may be integrated into essentially the same bearing span.

According to the invention, a production fluid being processed by the electric pump is used to cool the stator and lubricate bearings common to both the stator and the rotor. A portion of a production fluid being processed by the pump at the outer surface of the hollow rotor is introduced into the rotor cavity and encounters bearings supported between the inner surface of the hollow rotor and the outer surface of the stator.

The outer surface of the hollow rotor is equipped with one or more impellers configured as a pump stage. Pump stages are discussed in detail with respect to <FIG> herein. In one or more embodiments, the one or more impellers are configured as a single pump stage. In an alternate embodiment, the one or more impellers are configured as a plurality of pump stages. In one or more embodiments, the electric pump comprises a plurality of pump stages and at least two of the pump stages are arranged back to back and configured for parallel pumping of a production fluid. In an alternate set of embodiments, at least two of the pump stages are arranged back to back and configured for series pumping of a production fluid. Parallel and series pumping principles are discussed in greater detail with respect to <FIG> and <FIG>.

The electric pump provided by the present invention may in one or more embodiments comprise one or more stator sections comprising stator windings arranged in a distributed winding configuration. In an alternate set of embodiments, one or more stator sections may comprise stator windings arranged in a concentrated (tooth) winding configuration.

In one or more embodiments, the hollow rotor and the stator are configured as a squirrel cage induction motor. In a first alternate set of embodiments, the hollow rotor and the stator are configured as an interior permanent magnet motor. In a second alternate set of embodiments, the hollow rotor and the stator are configured as surface permanent magnet motor. In a third alternate set of embodiments, the hollow rotor and the stator are configured as an inset permanent magnet motor. In a fourth alternate set of embodiments, the hollow rotor and the stator are configured as a synchronous reluctance motor. In yet another alternate set of embodiments, the hollow rotor and the stator are configured as a combination of two or more of the foregoing rotor-stator configurations.

Turning now to the figures, <FIG> illustrates an electric pump <NUM> shown as a cross-section of the top half of the electric pump. The electric pump comprises a housing <NUM>, defining a pair of fluid inlets <NUM> and a single fluid outlet <NUM>. The electric pump comprises a hollow rotor <NUM> having an inner surface <NUM> and an outer surface <NUM>. Inner surface <NUM> defines a rotor cavity <NUM>. Stator <NUM> is disposed within the rotor cavity. In the embodiment shown, the rotor is supported relative to the stator by three bearings <NUM> constituting a bearing span <NUM> (See <FIG>). In the embodiment shown, independently controllable stator sections <NUM> and their torque-producing complements <NUM>, impellers <NUM> and diffusers <NUM> are shown as falling within the same portions of the bearing span defined by bearings <NUM>. This condition may be at times herein referred to as the motor and pump being contained within the same bearing span. In the embodiment shown, independently controllable stator sections <NUM> and their torque-producing rotor section counterparts <NUM> are regarded as the motor, while pump stages <NUM> comprising impellers <NUM> and diffusers <NUM> are regarded as the pump.

As noted, stator sections <NUM> are independently controllable, meaning that each stator section is independently powered and controlled. This feature allows for a high level of control over the performance characteristics of the pump by controlling power supply to individual stator sections <NUM> during operation. The need for less or more power to be delivered to individual stator sections may vary rapidly, as when the production fluid to be processed by the pump is a multiphase fluid comprising varying amounts of gas. For example, the gas volume fraction (GVF) of a multiphase production fluid may vary significantly over a short period of time in a hydrocarbon producing well. In one or more embodiments, stator sections are independently controlled by variable frequency drives. In one or more embodiments, stator sections may be controlled by a combination of one or more variable frequency drives together with sensorless control techniques such as are disclosed in <CIT>.

Still referring to <FIG>, the figure represents an electric pump <NUM> in operation. An unprocessed production fluid <NUM> is introduced at each of inlets <NUM> and into fluid flow path <NUM> defined by the outer surface <NUM> of the hollow rotor and pump stages <NUM>, and exits the pump as processed production fluid <NUM> at common outlet <NUM>. In the embodiment shown, a portion of the production fluid is introduced into rotor cavity <NUM> via rotor perforations <NUM>. Driven by the action of pump stages <NUM>, the portion of the production fluid introduced into the rotor cavity encounters and lubricates bearings <NUM> before being reintroduced into fluid flow path <NUM>. The direction of fluid flow through the rotor cavity is indicated by numbered elements <NUM>. Those of ordinary skill in the art will appreciate that the production fluid is shown as being processed in two parallel pump stages before being combined at outlet <NUM>. Pump stages <NUM> are arranged back to back along the outer surface of the rotor in the sense that the portions of each pump stage from which the processed production fluid <NUM> exits the pump stage are arranged opposite one another, or back to back, at pump outlet <NUM>.

Referring to <FIG>, the figure illustrates an electric pump <NUM> provided by the present invention shown as a cross-section of the top half of the electric pump as in <FIG>. A portion of the production fluid is used as a coolant fluid for independently controllable stator sections <NUM>. The pumping action of parallel, back to back pump stages <NUM> drives a portion of processed production fluid <NUM> through rotor perforations <NUM> and stator cooling channels <NUM> in directions of flow indicated by numbered elements <NUM>. Bearings <NUM> are contacted by at least a portion of the production fluid emerging from the stator cooling channels <NUM> prior to returning to the main flow of the production fluid in fluid flow path <NUM>. Rotor perforations <NUM>, stator cooling channels <NUM>, the action of pump stages <NUM> and the portion of the production fluid circulated through the stator sections prior to being returned to fluid flow path <NUM> constitute a coolant fluid recirculation system <NUM> in which the production fluid serves as the coolant fluid. Such an arrangement may be most useful when the fluid being processed by the electric pump is relatively benign and relatively cool, for example when the fluid being processed by the pump is a fluid such as cold ethylene glycol.

Referring to <FIG>, the figure illustrates an electric pump <NUM> shown as a cross-section of the top half of the electric pump as in <FIG>. In the embodiment shown, the electric pump is provided with a dedicated coolant fluid circuit <NUM> configured to cool stator sections <NUM>. Coolant fluid circuit comprises a coolant fluid cooler <NUM> and fluid pump <NUM>. Driven by pump <NUM>, coolant fluid is introduced into stator cooling channels <NUM> where the coolant fluid absorbs heat from the stator section before returning to fluid cooler <NUM>. Again, numbered elements <NUM> indicate the direction of flow of coolant fluid. In the embodiment shown, bearings <NUM> are shown as being lubricated by production fluid as in <FIG>. In one or more embodiments, bearings <NUM> are not lubricated by production fluid. In one or more embodiments, the bearings are lubricated by an exogenous fluid, such as the coolant fluid from a dedicated coolant fluid circuit. In another set of embodiments, bearings <NUM> are selflubricating.

Referring to <FIG>, the figure represents an electric pump <NUM> configured as in <FIG> and further comprising a separator <NUM> configured to receive processed production fluid <NUM> and to separate from it a liquid-only fraction <NUM>. This liquid-only fraction may be used to lubricate and/or cool bearings <NUM>. In the embodiment shown, the pump is configured to lubricate bearings 40E representing the two ends of the bearing span using liquid only fraction <NUM>. The separator <NUM> may be equipped with a pump (not shown) to circulate the liquid-only fraction <NUM> through conduits <NUM> and into contact with end bearings 40E. The action of pump stages <NUM> causes the liquid-only fraction <NUM> to flow in the direction indicated by numbered elements <NUM> and subsequently enter pump flow path <NUM>. The flow of the liquid-only fraction <NUM> to end bearings 40E may be regulated by pressure drop control valve <NUM>. Perforations <NUM> allow a portion of the fluid being processed by the pump to enter the rotor cavity and contact all of the bearings present. In certain applications, the production fluid entering the electric pump is hot, for example a production fluid from a deep hydrocarbon producing well. Where the pump is located in a cold environment, for example on the sea floor, both the cooler <NUM> and separator <NUM> may rely on the cold ambient environment to serve as a heat sink for heat contained in the production fluid and heat generated in the bearings, in the stator sections <NUM>, and in torque-producing complements <NUM>. In an alternate embodiment related to that illustrated in <FIG>, separator <NUM> is located upstream of pump inlets <NUM> and feeds the pump with a liquid only fraction <NUM> derived from a multiphase production fluid, in addition to circulating a portion of liquid only fraction <NUM> through bearings 40E.

Referring to <FIG>, the figure represents an electric pump <NUM> in which the pump stages <NUM> act in series. Thus, unprocessed fluid <NUM> enters the electric pump at inlet 14A and is impelled through first pump stage 26A and emerges at outlet chamber 16A as processed fluid 72A. Processed fluid 72A is then driven by the action of the pump stages through conduit 78A and enters the second pump stage 26B at inlet 14B. Processed fluid 72A is impelled through pump stage 26B and emerges at outlet chamber 16B as further processed fluid 72B which is conducted further downstream by conduit 78B. In the embodiment shown, outlet chambers 16A and 16B are separated by dividing wall <NUM> comprising seal <NUM> at its base. Seal <NUM> allows free rotation of the hollow rotor while inhibiting processed fluid 72A from passing from outlet chamber 16A to the adjacent outlet chamber 16B without first passing through pump stage 26B. Similarly, seal <NUM> inhibits further processed fluid 72B in outlet chamber 16B from entering outlet chamber 16A. In one or more embodiments, such inhibition enhances the efficiency of the electric pump. In one or more embodiments, seal <NUM> is a brush seal comprising metallic seal bristles. In an alternate set of embodiments, seal <NUM> is a brush seal comprising seal bristles comprising an organic polymer. In one such embodiment, the seal bristles comprise the engineering plastic, PEEK.

Referring to <FIG>, the figure represents an electric pump configured as in <FIG> for "in series" processing of a production fluid <NUM>, but further comprising a dedicated coolant fluid circuit <NUM>. In the embodiment shown, the dedicated coolant fluid circuit <NUM> constitutes an additional coolant fluid recirculation system, which supplements coolant fluid recirculation system <NUM>. Coolant fluid recirculation system <NUM> causes a portion of the production fluid being processed by the pump to contact all three bearings <NUM> disposed within rotor cavity <NUM>, thereby cooling and lubricating them.

Referring to <FIG>, the figure represents a hollow rotor - stator subassembly <NUM> provided by the present invention. Subassembly <NUM> may at times herein be referred to as an electric motor, or simply a motor. Motor <NUM> is suitable for use in one or more embodiments of an electric pump <NUM> provided by the present invention, and as configured, constitutes a squirrel cage induction motor. In the embodiment shown, motor <NUM> comprises a hollow rotor <NUM> defining an inner cavity <NUM> and a stator <NUM> disposed within rotor cavity <NUM>. The motor is shown in cross-section and illustrates a portion of a single independently controllable stator section <NUM> (See <FIG>) and a corresponding torque-producing complement <NUM>. Stator slots <NUM> are configured to accommodate the stator windings (not shown) in a distributed winding configuration. Stator <NUM> and hollow rotor <NUM> are supported relative to one another by bearings <NUM> (not shown) which contact an inner surface <NUM> of the hollow rotor and a suitable outer surface <NUM> (See <FIG>) of the stator. As will be appreciated by those of ordinary skill in the art, bearings <NUM> (See <FIG>) allow the hollow rotor to rotate relative to the fixed stator. In the embodiment shown in <FIG>, the torque-producing rotor sections <NUM> may be in the form of conductive rotor bars disposed within the body of the hollow rotor <NUM>. In one or more embodiments, such rotor bars comprise a conductive metallic material such as aluminum or copper. The outer surface <NUM> of rotor <NUM> is configured to be joined to one or more impellers which may, for example be joined to the rotor outer surface in one or more shrink fitting steps in which an impeller is inserted into one or more appropriately sized and spaced grooves of a hot outer surface. In one or more embodiments, the impellers may be welded to the outer surface of the hollow rotor. The stator defines a plurality of stator cooling channels <NUM> through which a coolant fluid may be passed in order to maintain the motor within an acceptable temperature range.

Referring to <FIG>, the figure represents a hollow rotor - stator subassembly <NUM> configured as an interior permanent magnet motor. The subassembly is configured essentially as in <FIG> with the exception that the torque-producing complements <NUM> to stator sections <NUM> are permanent magnets disposed within the body of the hollow rotor <NUM>. In order to be applicable in the present invention, the subassembly shown in <FIG> (and any of <FIG>) should be equipped with stator cooling channels <NUM> (See for example <FIG>) configured to be fluidly coupled to a coolant fluid recirculation system <NUM>. The stator <NUM> comprises stator slots <NUM> configured to accommodate the stator windings (not shown) in a distributed winding configuration.

Referring to <FIG>, the figure represents a hollow rotor - stator subassembly <NUM> configured as a surface permanent magnet motor. In the embodiment shown, permanent magnets indicated as torque-producing complements <NUM> are attached to the inner surface <NUM> of the hollow rotor <NUM> and project into rotor cavity <NUM>. The surface permanent magnets may be attached to the inner surface <NUM> by techniques known to those of ordinary skill in the art, such as welding and/or shrink fitting. The stator <NUM> comprises stator slots <NUM> configured to accommodate the stator windings (not shown) in a distributed winding configuration.

Referring to <FIG>, the figure represents a hollow rotor - stator subassembly <NUM> configured as a surface permanent magnet motor as in <FIG>, with the exception that the stator <NUM> comprises stator slots <NUM> configured to accommodate the stator windings <NUM> in a concentrated (tooth) winding configuration.

Referring to <FIG>, the figure represents a hollow rotor - stator subassembly <NUM> configured as an inset permanent magnet motor. In the embodiment shown, permanent magnets indicated as torque-producing complements <NUM> to independently controllable stator sections <NUM> (not shown) are accommodated by grooves on the inner surface <NUM> of the hollow rotor <NUM> and do not project into rotor cavity <NUM>. The permanent magnets may be attached to the hollow rotor by techniques known to those of ordinary skill in the art, such as welding and/or shrink fitting. The stator <NUM> comprises stator slots <NUM> configured to accommodate the stator windings (not shown) in a distributed winding configuration.

Referring to <FIG>, the figure represents a hollow rotor - stator subassembly <NUM> configured as a synchronous reluctance motor. In the embodiment shown, the body of the hollow rotor comprises a torque-producing complement <NUM>, which may be, for example, a ferromagnetic material such as iron, nickel, cobalt, and aluminum-nickel-cobalt alloys such as alnico. In one or more embodiments, the hollow rotor is comprised of a ferromagnetic material and contains a single torque-producing complement <NUM> along its entire length. Air slots <NUM> within the hollow rotor body provide for magnetic reluctance. The stator <NUM> comprises stator slots <NUM> configured to accommodate the stator windings (not shown) in a distributed winding configuration. Stator sections <NUM> may be controlled by microcontrollers.

Claim 1:
An electric pump (<NUM>) comprising:
(a) a hollow rotor (<NUM>) defining a rotor inner surface (<NUM>), a rotor outer surface (<NUM>) and a rotor cavity (<NUM>);
(b) a stator (<NUM>) comprising a plurality of independently controllable stator sections (<NUM>) disposed within the rotor cavity (<NUM>),
wherein the hollow rotor (<NUM>) comprises (i) one or more impellers (<NUM>) fixed to the rotor outer surface (<NUM>) , and (ii) one or more torque-producing complements (<NUM>) to the independently controllable stator sections (<NUM>) which together define an electric motor;
(c) a plurality of bearings (<NUM>) configured to allow rotation of the hollow rotor (<NUM>), the bearings (<NUM>) being supported between the inner surface of the hollow rotor (<NUM>) and an outer surface of the stator (<NUM>),
wherein the electric pump is configured such that, driven by the action of the one or more impellers (<NUM>), a production fluid (<NUM>) is introduced in each one of one or more inlets (<NUM>) of the electric pump into a fluid flow path (<NUM>) defined by the rotor outer surface (<NUM>) and the production fluid exits the electric pump at each one of one or more outlets (<NUM>); and
(d) a fluid recirculation system (<NUM>) comprising :
rotor perforations (<NUM>) located proximate the one or more fluid outlets (<NUM>) to introduce fluid radially into the rotor cavity (<NUM>), and
stator cooling channels (<NUM>) through which a fluid may be passed in order to maintain the motor within an acceptable temperature range,
wherein the electric pump is configured such that, driven by the action of the one or more impellers (<NUM>), a portion of the production fluid (<NUM>) flows through the rotor perforations (<NUM>) and through the stator cooling channels (<NUM>), and, prior to returning to the fluid flow path (<NUM>), the production fluid emerging from the stator cooling channels (<NUM>) encounters and lubricates the plurality of bearings (<NUM>).