Mechanism for maintaining integrity of permanent magnets in directly driven sealless pumps and turbines

Abstract

An integral motor pump (IMP) or turbine (IMT) applicable to a low temperature process liquid, such as liquid hydrogen, includes an impeller having an annular ring of permanent magnets attached thereto passing in axial proximity to a plurality of stator coils. The magnet ring is radially bounded by inner and outer compression sleeves having coefficients of expansion (CTEs) respectively less than and greater than the CTE of the magnets. Unequal thermal contraction of the compression sleeves, when cooled by the process liquid, applies radial compression to the magnet ring, overcoming centrifugal forces and maintains the magnets in radial compression, thereby preventing fracturing or pulverizing of the magnets. The magnet ring can be a monolithic ring with alternating magnetic regions, a ring of closely abutting magnets, or a ring of discrete magnets surrounded by a barrier material having a CTE equal to the magnet CTE.

Claims

1. An integral motor pump (IMP) or integral motor turbine (IMT) configured for application to a process liquid having a liquid temperature that is below ambient temperature, the IMP or IMT comprising: a module housing configured to enable the process liquid to pass from an input thereof to an output thereof; a stator housing contained within and fixed to the module housing; a shaft extending axially and proximally from the stator housing along a longitudinal axis of the IMP or IMT; an impeller rotatable with or about the shaft; a plurality of permanent magnets fixed to a distal face of the impeller and configured to pass in proximity to a proximal face of the stator housing when the impeller rotates, the plurality of permanent magnets being arranged as an annular magnet ring that surrounds the longitudinal axis of the IMP or IMT; and a plurality of stator coils contained within an interior of the stator housing and configured to be axially proximate the permanent magnets as the permanent magnets pass in proximity to the proximal face of the stator housing, the permanent magnets and stator coils being axially separated by a rotor-stator gap; wherein: the annular magnet ring is surrounded and radially bounded by an outer compression sleeve having an outer CTE that is equal to or greater than a magnet CTE of the permanent magnets; and the annular magnet ring surrounds and is radially bounded by an inner compression sleeve having an inner CTE that is less than the magnet CTE; and the permanent magnets being radially compressed due to unequal thermal contraction of the permanent magnets and the inner and outer compression sleeves when the inner and outer compression sleeves and the permanent magnets are cooled by the process liquid.

2. The IMP or IMT of claim 1, wherein the process liquid is liquid hydrogen.

3. The IMP or IMT of claim 1, wherein the permanent magnets are ceramic magnets or rare earth magnets.

4. The IMP or IMT of claim 1, wherein, at the ambient temperature, the magnet ring is radially compressed due to an interference fit between the magnet ring and the inner and outer compression sleeves, said radial compression being increased due to the unequal thermal contraction of the permanent magnets and the inner and outer compression sleeves when the inner and outer compression sleeves and the permanent magnets are cooled to the liquid temperature of the process liquid.

5. The IMP or IMT of claim 1, wherein the magnet ring is a ring of permanent magnets that are spaced apart and surrounded by a bonding material having a bonding CTE that is equal to the magnet CTE.

6. The IMP or IMT of claim 1, wherein the magnet ring is a ring of permanent magnets that are arranged in a closely packed, mutually abutting configuration in the magnet ring.

7. The IMP or IMT of claim 1, wherein the magnet ring is a monolithic ring of magnet material comprising alternating zones of forward and reverse magnetization.

8. The IMP or IMT of claim 1, wherein the permanent magnets are mounted to an underlying magnetically conducting backing plate.

9. The IMP or IMT of claim 8, wherein the backing plate contains ferromagnetic iron.

10. The IMP or IMT of claim 1, wherein a difference between the inner CTE and the outer CTE ensures that the permanent magnets remain in a radially compressed state when the impeller is rotated at a maximum operating speed of the IMP or IMT.

11. The IMP or IMT of claim 1, wherein the magnet ring is contained within a rotor housing that is fixed to the distal face of the impeller.

12. The IMP or IMT of claim 11, further comprising a rotor housing cover plate that is sealed to the rotor housing, thereby preventing physical contact between the process liquid and the magnet ring.

13. The IMP or IMT of claim 1, wherein the shaft is fixed to the stator housing and is stationary, the impeller being configured to rotate about the shaft.

14. The IMP or IMT of claim 13, further comprising a bearing that provides a rotation interface between the impeller and the stationary shaft.

15. The IMP or IMT of claim 14, wherein the bearing is lubricated by the process liquid.

16. The IMP or IMT of claim 1, wherein the impeller is fixed to the shaft, and the shaft is suspended by at least one bearing, thereby allowing the shaft to rotate together with the impeller.

17. The IMP or IMT of claim 16, wherein the bearing is lubricated by the process liquid.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a flow diagram illustrating the use of liquid hydrogen in the prior art as a medium for transferring energy from a green energy production site to an energy consumption location;

(2) FIG. 2A is a sectional view of an IMP or IMT of the prior art, where the figure is drawn to scale except for elements 210 and 212;

(3) FIG. 2B is a close-up view drawn to scale of a portion of the IMP or IMT of FIG. 2A;

(4) FIG. 3 is a sectional view from the side, drawn to scale, of a stator housing and associated elements shown in opposition to a rotor housing containing a ring of permanent magnets, according to the prior art;

(5) FIG. 4A is a view from above of a magnet ring comprising a plurality of separate permanent magnets that are fixed within a rotor housing by a surrounding resin barrier material according to an embodiment of the present invention;

(6) FIG. 4B is a view from above, drawn to scale, of a monolithic magnet ring comprising alternating zones of forward and reverse magnetization, according to an embodiment of the present invention;

(7) FIG. 4C is a cross-sectional view from the side, drawn to scale, of a rotor housing in which the magnet ring is a monolithic magnet ring comprising alternating zones of forward and reverse magnetization, as shown in FIG. 4B, and is mounted to a common, magnetically conductive backing plate, according to an embodiment of the present invention;

(8) FIG. 4D is a perspective cross-sectional view, drawn to scale, of the embodiment of FIG. 4C; and

(9) FIG. 5 is a graph that illustrates states of radial compression of a magnet ring during successive stages of operation of the disclosed IMP or IMT, according to an embodiment of the present invention.

DETAILED DESCRIPTION

(10) The present invention is an axial direct drive IMP or IMT that maintains the integrity of its permanent magnets when operated at very low temperatures and very high rotational speeds. For simplicity, the present disclosure sometimes refers simply to IMPs, i.e. to pumps that include motors. However, it will be understood that the disclosure presented herein applies equally to turbines that include generators, and that references herein to IMPs and other pumps refer generically to both integral motor pumps (IMPs) and integral motor (generator) turbines (IMTs), while references to motors refer generically to motors and generators or alternators, unless otherwise stated or required by context.

(11) FIGS. 2A and 2B illustrate an IMP of the prior art that shares many features with embodiments of the present invention. The IMP of FIGS. 2A and 2B is configured to direct a process liquid from a module inlet 228 to a module outlet 230. The rotor, i.e. the assembly of rotating components, in the IMP 200 comprises an impeller 202 and a plurality of permanent magnets 204 that are cooperative with the impeller 202. The IMP 200 further includes a stator housing 206 containing stator coils 208 that are positioned in axial opposition to the permanent magnets 204. The stator coils 208 are energized by a power source 210 that is actuated by a controller 212, and the magnets 204 and stator coils 208 function cooperatively together as a synchronous motor that applies rotational torque directly to the impeller 202. In some embodiments, the power source 210 is an adjustable speed drive (ASD), such as a variable frequency drive (VFD), which enables the impeller rotation rate to be variable.

(12) In addition to the impeller 202 and the permanent magnets 204, the rotor in the illustrated embodiment comprises a bearing 214 that is configured to allow the impeller 202 to rotate about a fixed, non-rotating shaft 216. In the illustrated embodiment, the bearing 214 is product lubricated, and the shaft 216 is a rotor positioning stud that is firmly anchored to the stator housing 206, which is firmly attached to the IMP housing 218. In similar embodiments, the impeller 202 is fixed to the shaft 216, and the shaft 216 is suspended by one or more bearings so that it can rotate together with the impeller 202. In the illustrated embodiment, the shaft 216 is only slightly longer than the bearing 214. It can be seen in the close-up, partial view of FIG. 2B that only a very narrow axial gap 226 separates the permanent magnets 204 from the stator coils 208.

(13) FIG. 3 is a sectional view from the side, according to a similar example of the prior art, of a stator housing 206 and associated elements shown in opposition to rotor housing 306 that contains the permanent magnets 204. The rotor housing cover plate 300 and the stator cover plate 302 are also shown, as well as the laminated iron cores 304 about which the stator coils 208 are wound.

(14) With reference to FIGS. 4A and 4B, according to the present invention, the magnets 204 are arranged as an annular magnet ring 408 that is bounded by inner 404 and outer 402 compression sleeves shaped essentially as hollow cylinders or bands that have differing coefficients of thermal expansion (CTEs). The outer 402 of the two compression sleeves 402, 404 is made from a material, which can be a metal alloy, having a CTE that is equal to or greater than the CTE of the magnets 204, while the inner 404 compression sleeve is made from a different material, such as a different metal alloy, that has a CTE that is equal to or less than the CTE of the magnets 204. Accordingly, either the CTE of the outer compression sleeve 402 is greater than the CTE of the magnets 204, the CTE of the inner compression sleeve 404 is less than the CTE of the magnets 204, or both. As a result, the uneven contraction of the compression sleeves 402, 404 as the magnet ring 408 is cooled increases the radial compression of the magnets 204.

(15) In the embodiment of FIG. 4A, the magnets 204 are separate magnets that are fixed within the rotor housing 306 by a surrounding resin 400 or other bonding material. In some of these embodiments a bonding material 400 is selected having a CTE that is substantially equal to the CTE of the magnets 204.

(16) In the embodiment of FIG. 4B, the magnet ring 408 is a monolithic ring comprising alternating zones of forward and reverse magnetization. In similar embodiments, the magnet ring 408 is a continuous ring formed by separate, closely abutting magnets. In FIGS. 4A and 4B, the cross-hatching of elements 204 indicates the polarities of the segments of the magnet ring 408, which alternate between N and S.

(17) FIGS. 4C and 4D are side and perspective sectional views respectively of a rotor housing 306 in which the permanent magnets 204 are arranged in a closely packed contiguous ring 408, as shown in FIG. 4B, and mounted to a common backing plate 406, which can be a magnetically conductive plate, such as a plate that comprises ferromagnetic iron.

(18) With reference to FIG. 5, in embodiments the magnets 204 are initially compressed 500 upon installation in the rotor housing 306 between the compression sleeves 402, 404 due to an interference fit of the magnet ring between the compression sleeves 402, 404. As the rotor housing 306 is cooled 502 to the cryogenic temperature of the process liquid, the unequal contraction of the compression sleeves 402, 404 results in additional radial compression of the magnets 204. The assembly of the magnets 204 compression sleeves 402, 404, and rotor housing 306 is then allowed to stabilize and come to thermal equilibrium 504. As the rotor 202 begins to rotate, and its rotation speed increases, the resulting centrifugal forces partially offset the compressive forces applied by the compression sleeves 402, 404, and reduce the degree of magnet compression 506. However, the materials from which the compression sleeves 402, 404 are formed are selected according to their CTEs so that even during the highest anticipated operational speed of the rotor 508, the centrifugal forces will be unable to completely overcome the compression that is applied by the cryogenically cooled compression sleeves 402, 404, and the magnets 204 will remain in a compressive state. And because the magnets 204 never cross into a tensile state 510, they do not crack or pulverize.

(19) Accordingly, the present invention takes advantage of the cryogenic temperature of the process liquid as a mechanism for compressing the magnets 204, enabling the impeller to rotate at very high speeds without allowing the magnets 204 to transition to a state of tension, and thereby avoiding cracking or disintegration of the magnets 204.

(20) The foregoing description of the embodiments of the invention has been presented for the purposes of illustration and description. Each and every page of this submission, and all contents thereon, however characterized, identified, or numbered, is considered a substantive part of this application for all purposes, irrespective of form or placement within the application. This specification is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of this disclosure.

(21) Although the present application is shown in a limited number of forms, the scope of the disclosure is not limited to just these forms, but is amenable to various changes and modifications. The present application does not explicitly recite all possible combinations of features that fall within the scope of the disclosure. The features disclosed herein for the various embodiments can generally be interchanged and combined into any combinations that are not self-contradictory without departing from the scope of the disclosure. In particular, the limitations presented in dependent claims below can be combined with their corresponding independent claims in any number and in any order without departing from the scope of this disclosure, unless the dependent claims are logically incompatible with each other.