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Publication numberUS20090004032 A1
Publication typeApplication
Application numberUS 12/012,541
Publication dateJan 1, 2009
Filing dateFeb 2, 2008
Priority dateMar 29, 2007
Publication number012541, 12012541, US 2009/0004032 A1, US 2009/004032 A1, US 20090004032 A1, US 20090004032A1, US 2009004032 A1, US 2009004032A1, US-A1-20090004032, US-A1-2009004032, US2009/0004032A1, US2009/004032A1, US20090004032 A1, US20090004032A1, US2009004032 A1, US2009004032A1
InventorsKevin A. Kaupert
Original AssigneeEbara International Corporation
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Deswirl mechanisms and roller bearings in an axial thrust equalization mechanism for liquid cryogenic turbomachinery
US 20090004032 A1
Abstract
Vane, fin, and hole arrangements establish a predetermined reduced swirl at the inlet of mechanical seals and the inlet of a variable axial orifice gap which act in harmony as an axial thrust equalizing system for use in liquid cryogenic turbines and pumps. In said establishment the stiffness, damping, and inertia in said seal in conjunction with said variable orifice gap is manipulated, including the destabilizing cross-coupled stiffness which is reduced. Said seal is of either labyrinth annular type formed by a plurality of teeth, annular smooth, or a plurality diamond annular surface pattern. Said variable orifice gap is smooth. Liquid for the axial thrust equalizing seal is initially bled from the main to pass through a preset deswirl mechanism. The deswirl mechanism consists of either a plurality of vanes, fins, grooves, or circular holes that guide liquid radial inward before passing through said mechanical seal. After exiting the seal said liquid passes through a second deswirl mechanism consisting of a plurality of vanes, fins, or grooves before entering a variable axial orifice gap. The variable orifice moves in axial position to variably restrict balancing liquid and generate backpressure in the pressure chamber to balance the axial thrust caused by a plurality of impellers on the same single shaft. After passing through the variable orifice the bleed liquid can pass past a sealed lubricated roller bearing for heat exchange to cool said bearing with the cryogenic liquid along grooves in a bearing liner. Alternatively the liquid can also pass directly through an open unsealed bearing for cooling.
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Claims(28)
1. A pump with thrust equalizing mechanism for liquid cryogenic materials capable of operating at cryogenic liquid temperatures, the pump comprising, in part, a housing, a low pressure annular chamber in said housing to contain a low pressure liquid, a high pressure annular chamber in said housing to contain high pressure liquid, a rotating shaft concentric in said housing, said rotatable shaft constituting a rotatable element with a plurality of pump impellers mounted and rotating on a shaft connected to a submerged electric motor or generator, a liquid flow driven through a mechanical seal by a pressure difference from said high pressure chamber to said low pressure chamber, a first deswirl mechanism located inside said high pressure chamber arranged upstream of said mechanical seal to preset the preswirl of the liquid thrust equalizing flow that enters said seal to a predetermined predominantly radial inward direction, said first deswirl mechanism having largest radius inlet exposed to said high pressure chamber inlet, said first deswirl mechanism having outlet exposed to said mechanical seal inlet, such that said first deswirl mechanism deswirls said liquid thrust balancing flow swirl which was imparted by said rotating impeller to provide said seal with a preset inlet liquid flow swirl which may be zero in radial inward direction only, said mechanical seal exits liquid to said low pressure chamber, and a second deswirl mechanism positioned concentric with the rotatable shaft, said second deswirl mechanism arranged in a radial orientation upstream of an variable axial clearance to permit impeller rotation about said shaft center.
2. The pump of claim 1, wherein the first deswirl mechanism comprises a plurality of vanes arranged about the circumference along the said rotatable shaft center, the plurality of vanes lying oriented in predetermined flow directions relative the location of the rotatable shaft center.
3. The pump of claim 2, wherein the plurality of vanes are pivotable and can be locked into place in a predetermined position.
4. The pump of claim 3, further comprising a controller and associated actuator, wherein the associated actuator can be used to control the direction of the plurality of pivotable vanes.
5. The pump of claim 1, wherein the first deswirl mechanism comprises a plurality of fins arranged about the circumference along the said rotatable shaft center, the plurality of fins lying oriented in predetermined flow directions relative the location of the rotatable shaft center.
6. The pump of claim 5, wherein the plurality of fins are pivotable and can be locked into place in a predetermined position.
7. The pump of claim 6, further comprising a controller and associated actuator, wherein the associated actuator can be used to control the direction of the plurality of pivotable fins.
8. The pump of claim 1, wherein the first deswirl mechanism comprises a plurality of grooves arranged about the circumference along the said rotatable shaft center, the plurality of grooves lying oriented in predetermined flow directions relative the location of the rotatable shaft center.
9. The pump of claim 1, further comprising a primary plurality of liquid flow bypass passageway holes exiting said high pressure chamber, each of said liquid flow bypass passageway holes extending downstream to said seal with injection of deswirled liquid into the seal near said seal inlet at some intermediate pressure between that in said low high chamber and said low pressure chamber, said primary plurality of bypass holes having a predetermined radius.
10. The pump of claim 9, further comprising a second plurality of liquid flow bypass passageway holes exiting said high pressure chamber, each of said liquid flow bypass passageway holes extending downstream to said seal with injection of deswirled liquid into the seal near said seal inlet at some intermediate pressure between that in said low high chamber and said low pressure chamber, said second plurality of bypass holes having a second predetermined radius.
11. The pump of claim 1, wherein the mechanical seal is an annular mechanical seal to achieve pressure drop from said high pressure chamber to said low pressure chamber across said seal with rotating and stationary portions which is dependant on liquid flow rate through said seal, said seal rotating portion is a rotating labyrinth annulus positioned concentric with said rotatable shaft mounted on the highest pressure impeller stage, said labyrinth annulus consists of a plurality of circumferential grooved teeth with land and valley lengths, said seal stationary portion is smooth, distance between the rotating and stationary seal is the wear ring clearance wherein said liquid pressure drop results.
12. The pump of claim 1, wherein the mechanical seal is an annular mechanical seal to achieve pressure drop from said high pressure chamber to said low pressure chamber across said mechanical seal with rotating and stationary portions which is dependant on liquid flow rate through said seal, said seal rotating portion is a smooth annulus positioned concentric with said rotatable shaft mounted on the highest pressure impeller stage, said seal stationary portion is a diamond surface pattern to act as a circumferential liquid flow deswirl mechanism, the distance between the rotating and diamond surface pattern stationary seal is the wear ring clearance wherein said liquid pressure drop results.
13. The pump of claim 9, wherein the mechanical seal is an annular mechanical seal to achieve pressure drop from said high pressure chamber to said low pressure chamber across said seal with rotating and stationary portions which is dependant on liquid flow rate through said seal, said seal rotating portion is a rotating labyrinth annulus positioned concentric with said rotatable shaft mounted on the highest pressure impeller stage, said labyrinth annulus consists of a plurality of circumferential grooved teeth with land and valley lengths, said seal stationary portion is smooth, distance between the rotating and stationary seal is the wear ring clearance wherein said liquid pressure drop results.
14. The pump of claim 10, wherein the mechanical seal is an annular mechanical seal to achieve pressure drop from said high pressure chamber to said low pressure chamber across said seal with rotating and stationary portions which is dependant on liquid flow rate through said seal, said seal rotating portion is a rotating labyrinth annulus positioned concentric with said rotatable shaft mounted on the highest pressure impeller stage, said labyrinth annulus consists of a plurality of circumferential grooved teeth with land and valley lengths, said seal stationary portion is smooth, distance between the rotating and stationary seal is the wear ring clearance wherein said liquid pressure drop results.
15. The pump of claim 11 further comprising a second deswirl mechanism downstream of said liquid pressure drop apparatus comprising a plurality of fins to preset and adjust rotational swirl of said thrust equalizing liquid which exits said upstream seal and enters said low pressure chamber, itself upstream of a variable axial orifice gap.
16. The pump of claim 12 further comprising a second deswirl mechanism downstream of said liquid pressure drop apparatus comprising a plurality of fins to preset and adjust rotational swirl of said thrust equalizing liquid which exits said upstream seal and enters said low pressure chamber, itself upstream of a variable axial orifice gap.
17. The pump of claim 11 further comprising a second deswirl mechanism downstream of said liquid pressure drop apparatus comprising a plurality of vanes to preset and adjust rotational swirl of said thrust equalizing liquid which exits said upstream seal and enters said low pressure chamber, itself upstream of a variable axial orifice gap.
18. The pump of claim 12 further comprising a second deswirl mechanism downstream of said liquid pressure drop apparatus comprising a plurality of vanes to preset and adjust rotational swirl of said thrust equalizing liquid which exits said upstream seal and enters said low pressure chamber, itself upstream of a variable axial orifice gap.
19. The pump of claim 11 further comprising a second deswirl mechanism downstream of said liquid pressure drop apparatus comprising a plurality of grooves to preset and adjust rotational swirl of said thrust equalizing liquid which exits said upstream seal and enters said low pressure chamber, itself upstream of a variable axial orifice gap.
20. The pump of claim 12 further comprising a second deswirl mechanism downstream of said liquid pressure drop apparatus comprising a plurality of grooves to preset and adjust rotational swirl of said thrust equalizing liquid which exits said upstream seal and enters said low pressure chamber, itself upstream of a variable axial orifice gap.
21. The pump of claim 20 wherein the liquid cryogenic apparatus further comprises an axial gap of variable axial gap size capable of axial movement acting as a variable orifice to constitute a variable liquid flow restriction based on the axial location of said rotating shaft, the axial gap comprising a rotating and stationary smooth surface with a variable axial orifice gap, said rotating surface coupled to the neighboring highest pressure impeller, said rotating surface able to move axially acting as the variable side of a variable orifice, said rotating surface making up one side of a radially orientated axial gap, said stationary surface as the other side of a radially orientated variable axial orifice gap.
22. The pump of claim 21 further comprising a variable pressure chamber controlled with said variable axial orifice gap, the variable pressure chamber further comprising the second deswirl mechanism.
23. The pump of claim 22 further comprising a liquid cryogenic roller bearing assembly functioning in tandem and conjunction with said first and second liquid deswirl mechanisms and said variable axial orifice gap, the roller bearing assembly comprising an unsealed roller bearing cooled with thrust equalizing liquid flow flushing through, said unsealed bearing lubricated with a dry impregnated lubricant bearing cage, said unsealed bearing accepting a fraction of the thrust equalizing liquid from said variable orifice mechanism with remaining unwanted liquid flow bypassing, said unsealed bearing located concentric with outer race inside a bearing liner with a small radial clearance of between about 10 μm and about 60 μm to permit said unsealed bearing to move axially with said variable orifice gap, said bearing liner is fixed in a stationary housing.
24. The pump of claim 22 further comprising a liquid cryogenic roller bearing assembly functioning in tandem and conjunction with said first and second deswirl mechanisms and said variable axial orifice gap, the roller bearing assembly comprising a sealed roller bearing packed permanently with low temperature lubricant, said sealed bearing located with outer race concentric inside a bearing liner with a small radial clearance of between about 10 μm and about 60 μm to permit said sealed bearing to move axially with said variable orifice mechanism, said sealed bearing accepting no through liquid flow, said bearing liner fixed in a stationary housing, said bearing liner further having a plurality of grooved axial slots about the circumference to pass a fraction of liquid flow from said variable orifice mechanism for cooling, said sealed roller bearing apparatus with a bearing start-up heater located near said bearing liner, bearing temperature sensor mounted circumferentially about 180 degrees or more or less from said bearing heater, the pump further comprising a start-up delay control system whereby said bearing heater is activated to preheat said roller bearing lubricant to a predetermined temperature before start-up is permitted.
25. The pump of claim 22, wherein the cryogenic liquid mechanical seal assembly comprises a plurality of impeller eye wear rings functioning in conjunction and harmony with the first and second deswirl mechanisms as part of the thrust equalizing mechanism, the thrust equalizing mechanism comprising a rotating labyrinth seal with a plurality of circumferential grooved teeth on the rotating impeller wear ring, the thrust equalizing mechanism further comprising a stationary smooth surface which together with said rotating wear ring forms a radial clearance gap to seal impeller shroud leakage fluid, the thrust equalizing mechanism further comprising a plurality of tertiary deswirl mechanisms upstream of the seal.
26. The pump of claim 22, wherein the cryogenic liquid mechanical seal assembly comprises a plurality of impeller eye wear rings functioning in conjunction and harmony with the first and second deswirl mechanisms as part of the thrust equalizing mechanism in cryogenic liquids comprising a rotating annular smooth seal on the rotating impeller or rotating impeller wear ring, a stationary diamond pattern mesh surface which together with said rotating wear ring forms a radial clearance gap to seal impeller shroud leakage liquid and deswirl liquid in the clearance gap, the thrust equalizing mechanism further comprising a plurality of deswirl mechanisms upstream of the seal.
27. The pump of claim 1 further comprising a cryogenic liquid mechanical seal assembly on the plurality of impeller interstage bushings and wear rings functioning in conjunction and harmony with first and second deswirl mechanisms as part of the thrust equalizing mechanism, the mechanical seal assembly comprising a stationary smooth surface annular wear ring mounted in a fixed housing, a rotating labyrinth seal with a plurality of circumferential grooved teeth on a rotating impeller or rotating impeller annular wear ring which together with said stationary wear ring forms a radial clearance gap to seal interstage return liquid, the thrust equalizing mechanism further comprising a plurality of tertiary deswirl upstream of the seal.
28. A pump of claim 1 further comprising a cryogenic liquid mechanical seal assembly on the plurality of impeller interstage bushings and wear rings functioning in conjunction and harmony with first and second deswirl mechanisms as part of the thrust equalizing mechanism, the mechanical seal assembly comprising a stationary diamond pattern mesh surface on an annular surface seal, a rotating smooth surface on the impeller or impeller wear ring which together with said stationary wear ring forms a radial clearance gap to seal interstage return liquid, a plurality of tertiary deswirl mechanisms upstream of the seal.
Description
RELATED APPLICATIONS

This Application is related to U.S. Provisional Patent Application Ser. No. 60/920,618 filed Mar. 29, 2007 entitled DESWIRL MECHANICS AND ROLLER BEARINGS IN AN AXIAL THRUST EQUALIZATION MECHANISM FOR LIQUID CRYOGENIC TURBOMACHINERY, which is incorporated herein by reference in its entirety, and claims any and all benefits to which it is entitled therefrom.

FIELD OF THE INVENTION

The present invention relates to liquid cryogenic centrifugal pumps and turbines of the submerged motor or generator type.

BACKGROUND OF THE INVENTION

Vertical cryogenic submerged motor pumps and submerged generator turbines operate in the liquefied cryogenic gases industry. They are most prominent in the liquid hydrocarbon industry for liquefied natural gas, liquefied ethane gas, and liquefied propane gas. U.S. Pat. No. 5,659,205 to Weisser, which is hereby incorporated by reference in its entirety herein, teaches that due to the low cryogenic temperatures this style of pump and turbine operates with the axial thrust of the rotating assembly totally equalized to zero. U.S. Pat. No. 6,441,508 to Hylton is also hereby incorporated by reference in its entirety herein.

To achieve this, a conventional axial thrust equalizing mechanism such as shown in FIG. 1 is applied that uses pressurized bleed liquid which is passed through a seal restriction at the back of the highest pressure impeller. Afterwards this bleed liquid passes into a pressure chamber whose pressure is controlled by a downstream variable area orifice. This orifice is variable in the axial direction along the pump and turbine shaft and comes from the rotating assembly which is designed to float axially a small distance. In a condition of up axial thrust on the rotating assembly, the variable orifice is pushed smaller. As such, the bleed liquid flow rate is reduced and the pressure drop across the bleed wear ring is reduced. The pressure in the downstream pressure chamber rises which increases the force on the impeller and rotating assembly so that a reaction force is established to push the variable orifice larger and equalize the thrust. Contrarily, in a condition of down axial thrust on the rotating assembly, the variable orifice is pulled larger. As such, the bleed liquid flow rate is increased and the pressure drop across the bleed wear ring is increased. The pressure in the downstream pressure chamber decreases which decreases the force on the impeller and rotating assembly so that a reaction force is established to push the variable orifice smaller and equalize the thrust. So a net zero axial thrust is always established by the thrust equalization mechanism.

SUMMARY AND ADVANTAGES OF THE PRESENT INVENTION

The power rating of liquid cryogenic pumps and turbines in high pressure applications continues to grow as motivated by customer demands. This translates to higher power concentration machinery. So the axial thrust mechanism must balance larger thrust levels. Greater radial thrust levels are also experienced which the seals must react to avoid overly larger shaft deflections and overly large shaft diameters to compensate. Thus, means are sought to increase the stiffness of impeller flow induced reaction forces to stiffen the shaft. Increasing the shaft damping is also beneficial. Benckert, H., et al. teach in “Flow Induced Spring Coefficients of Labyrinth Seals for Application in Rotor Dynamics” published 1980, which is hereby incorporated by reference in its entirety, that means are also sought to reduce the well documented destabilizing cross-coupled stiffness in the mechanical seals. Overall increasing the stiffness and damping while decreasing the cross-coupled stiffness will reduce rotordynamic whirl and vibrations. This can be seen from first principles with the equation of motion applied to a rotating assembly experiencing small displacements δ in the x and y direction written as follows:

- [ F x ( t ) F y ( t ) ] = [ k xx ( δ ) k xy ( δ ) k yx ( δ ) k yy ( δ ) ] [ x y ] + [ c xx ( δ ) c xy ( δ ) c yx ( δ ) c yy ( δ ) ] [ x t y t ] + [ m xx ( δ ) m xy ( δ ) m yx ( δ ) m yy ( δ ) ] [ 2 x t 2 2 y t 2 ]

Note: Both the direct coupled and cross coupled terms are represented in the stiffness (k), damping (c), and inertia mass (m) matrix. For small displacements, the coefficients in these equations are taken as linear. Separating the forcing contributions in the absolute reference frame results in the following:

[ F x ( t ) F y ( t ) ] = [ F xa F ya ] + [ F x ( t ) F y ( t ) ] whirl + [ F x ( t ) F y ( t ) ] nonwhirl

The force contributions are dividing into steady and unsteady. The unsteady force contribution is further subdivided into whirl and none whirl portions. The whirl contribution will be taken as a circular orbit that experiences small periodic displacements of δ in x and y so δ=δo+iy and δ=δo exp(iωwt). In this relation, ωw is the impeller whirl frequency. Now, expanding the previous equation for the whirl terms gives the following:

[ F x ( t ) F y ( t ) ] whirl = [ ( m xx ω w 2 - c xy ω w - k xx ) ( m xy ω w 2 + c xx ω w - k xy ) ( m yx ω w 2 - c yy ω w - k yx ) ( m yy ω w 2 + c yx ω w - k yy ) ] [ δ o cos ω w t δ o sin ω w t ]

It is now more convenient and intuitive to write this equation in dimensionless form as follows:

[ F x * ( t ) F y * ( t ) ] = [ ( m xx * ω w 2 ω 2 - c xy * ω w ω - k xx * ) ( m xy * ω w 2 ω 2 + c xx * ω w ω - k xy * ) ( m yx * ω w 2 ω 2 - c yy * ω w ω - k yx * ) ( m yy * ω w 2 ω 2 + c yx * ω w ω - k yy * ) ] [ δ o cos ω w t / R 2 δ o sin ω w t / R 2 ]

The * designates use of the dimensionless quantities with F*=F/πρR2 3B2ω2, x*=x/R2, dx*/dt=(dx/dt)/R2ω, and dx2*/dt=(d2x/dt2)/R2ω2. The dimensionless stiffness, damping and added mass coefficients used are k*ij=kij/πρR2 2B2ω2, c*ij=cij/πρR2 2B2ω, m*ij=mij/πρR2 2B2. This expression gives the x, y component of the forces but the greater interest for turbomachinery vibrations lies in the tangential and radial forces from the rotating assembly center. So we convert to polar coordinates with F*r+iF*θ=(F*x+iF*y)exp(−iωwt) and get the following equation:

[ F θ * F r * ] whirl = [ - m xy * ( ω w ω ) 2 - c xx * ( ω w ω ) + k xy * + m yz * ( ω w ω ) 2 - c yy * ( ω w ω ) - k yx * m xx * ( ω w ω ) 2 - c xy * ( ω w ω ) - k xx * + m yy * ( ω w ω ) 2 + c yx * ( ω w ω ) - k yy * ]

Now the rotation of the coefficients about the x, y axis is taken with isometry, which most whirl related test data supports, meaning the terms with subscript xx equal the yy terms and the subscript xy terms equal the negative yx terms. This then gives the following equation:

[ F θ * F r * ] whirl = 2 [ - m xy * ( ω w ω ) 2 - c xx * ( ω w ω ) + k xy * + m xx * ( ω w ω ) 2 - c xy * ( ω w ω ) - k xx * ]

For the circumferential force if F*θ is negative, in the reverse direction of the impeller whirl rotation, an impeller whirl stabilizing force is experienced. If F*θ is positive, in the direction of whirl, this destabilizes the impeller by eliciting greater whirl. The stability boundary is found by taking the value of F*θ=0 and mxy as negligible in the previous equation to give ωw/ω=k*xy/c*xx as the whirl ratio limit. Taking mxy as negligible with respect to the stiffness and damping is reasonable for most but not all rotordynamic problems, although it does illustrate the origins of the whirl ratio limit. In dimensional form, this tangential whirl ratio limit as a stability condition then simplifies to the following:

( ω w ω ) θ limit = k xy c xx ω

Therefore, the tangential stability whirl ratio limit is a balance between cross coupled stiffness forces kxy that drive the whirl and damping forces cxxω that oppose the whirl. For a constant angular frequency with a whirl larger than (ωw/ω)θ limit, the tangential force acts in a stabilizing manner. For a constant angular frequency with a whirl smaller than (ωw/ω)θ limit the tangential force acts in a destabilizing manner, unless the whirl orbit is backwards in which case this is stabilizing. Hence the desire to decrease the cross-coupled stiffness kxy (and increase the direct damping) is beneficial for improved whirl stability and reduced rotordynamic vibrations. Applying this finding, several research institutions and patents such as U.S. Pat. No. 5,190,440 to Maier have applied swirl brakes to labyrinth seals in high temperature gas compressors.

It is this premise applied in conjunction with a thrust equalization mechanism that is unique for liquid cryogenic pumps and turbines. In so doing the benefit of a reduced destabilizing cross-coupled stiffness in the seal and balance mechanism is gained. Further, the direct coupled stiffness kxx is increased in the seal along with an increase in the direct coupled cxx damping. The reduced swirl in the variable orifice of the balance mechanism also provides an improved equalization of the axial thrust with unwanted flow separation regions avoided in the orifice gap. So several advancements in thrust balancing devices for liquid cryogenic pumps and turbines are addressed with the claims of this patent.

Accordingly, there are provided herein several unique improvements to the axial thrust equalizing mechanism which address the deficiencies of preswirl in the prior art of submerged motor liquid cryogenic pumps and turbines. The invention reduces the destabilizing cross-coupled stiffness while concurrently increasing the direct coupled stiffness and direct coupled damping in the mechanical seals. This is achieved within the framework of an improved axial thrust equalization. The seals themselves consist of either labyrinth type, smooth type, or surface pattern type such as diamond surface mesh. Holes are also claimed to locally inject fluid with zero swirl and stop any residual swirling liquid seal flow.

Another embodiment provides deswirl fins, vanes or grooves upstream of the variable orifice used for the thrust equalization. These ensure the variable orifice receives liquid with adjusted prespecified preswirl which may be zero with the flow directed primarily radially. This avoids fluid instabilities including separation near the orifice which can suddenly collapse or form giving the thrust balance system a rapid change in balance position. The predominately radial flow liquid direction also improves the capacity of balancing higher thrust levels needed for more powerful pumps and turbines.

A further embodiment provides both a sealed and unsealed roller bearing operating in conjunction with the axial thrust equalizing mechanism and the deswirl devices. Currently unsealed roller bearings are the prior art. Sealed bearings packed with lubricants are not used in cryogenic applications for fear of freezing. Recent advances in synthetic grease now make available unfrozen grease down to temperatures of −60° C. This is applicable to liquid propane and butane pumps and turbines, particularly in situations where the fluid is dirty and can cause reduced bearing life for an unsealed bearing. For situations where the fluid temperature is lower, a bearing heater and sensor are embodied which briefly preheat the frozen grease before start-up. After start-up, the bearing heater may no longer be needed as the bearing itself may generate sufficient heat.

A last embodiment provides deswirl vanes, fins, or holes on the seals on the plurality of impeller eyes and interstages. These are also useful to reduce the cross-coupled stiffness while concurrently increasing the direct coupled stiffness and direct coupled damping. Surface patterns such as diamond mesh are also utilized with a smooth rotating surface and a inlet deswirl mechanism for the same rotordynamic benefit.

Numerous other advantages and features of the present invention will become readily apparent from the following detailed description of the invention and the embodiments thereof, from the claims and from the accompanying drawings.

Benefits and features of the invention are made more apparent with the following detailed description of a presently preferred embodiment thereof in connection with the accompanying drawings, wherein like reference numerals are applied to like elements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial, cross-sectional overall view of a multistage cryogenic pump at the axial thrust equalizing mechanism highest pressure impeller including seal deswirl mechanisms and lubricated sealed roller bearing which are constructed in accordance with the invention.

FIG. 2 is a partial, cross-sectional view of four embodiments of the vaned or grooved or finned deswirl mechanism upstream of an impeller backside labyrinth seal and the variable axial orifice gap constructed in accordance with the invention.

FIG. 3 is a partial, cross-sectional view of one embodiment of the deswirl mechanism incorporating holes upstream of an impeller backside labyrinth seal with local injection into the seal constructed in accordance with the invention.

FIG. 4 is a partial, cross-sectional view of one embodiment of the deswirl mechanism incorporating a diamond surface pattern on the seal stator and smooth surface on the impeller backside constructed in accordance with the invention.

FIG. 5 is a partial, cross-sectional view of four embodiments of the deswirl mechanism operating in conjunction with the variable axial orifice gap using a cooled lubricated scaled roller bearing constructed in accordance with the invention.

FIG. 6 is a partial, axial view of two embodiments of the sealed roller bearing liner with a bearing heater and temperature sensor for cold liquid applications constructed in accordance with the invention.

FIG. 7 is a partial, cross-sectional view of two embodiments of the deswirl mechanism operating in conjunction with the variable axial orifice gap using a cooled dry lubricated unsealed roller bearing constructed in accordance with the invention.

FIG. 8 is a partial, cross-sectional view of three embodiments with fins or vanes or grooves upstream of the impeller eye seal as a deswirl mechanism constructed in accordance with the invention.

FIG. 9 is a partial, cross-sectional view of one embodiment with a diamond surface pattern on the stator seal upstream of the impeller eye seal as a deswirl mechanism constructed in accordance with the invention.

FIG. 10 is a partial, cross-sectional view of three embodiments with fins or vanes or grooves upstream of the impeller interstage seal as a deswirl mechanism constructed in accordance with the invention.

FIG. 11 is a partial, cross-sectional view of one embodiment with a diamond surface pattern on die seal stator upstream of the impeller interstage seal as a deswirl mechanism constructed in accordance with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The description that follows is presented to enable one skilled in the art to make and use the present invention, and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be apparent to those skilled in the art, and the general principals discussed below may be applied to other embodiments and applications without departing from the scope and spirit of the invention. Therefore, the invention is not intended to be limited to the embodiments disclosed, but the invention is to be given the largest possible scope which is consistent with the principals and features described herein.

It will be understood that while numerous preferred embodiments of the present invention are presented herein, numerous of the individual elements and functional aspects of the embodiments are similar. Therefore, it will be understood that structural elements of the numerous apparatus disclosed herein having similar or identical function may have like reference numerals associated therewith.

Referring to FIG. 1 in particular, shown therein is a centrifugal impeller apparatus of a centrifugal pump or turbine used for handling cryogenic liquids. The apparatus incorporates annular labyrinth seal elements that are constructed in accordance with the invention. For clarity, the various components of the centrifugal pump or turbine impeller apparatus, as well as the annular labyrinth seal elements, are shown with sectional views of an upward portion thereof, it being realized that such elements are symmetrically oriented entirely around the rotatable shaft center.

The case of a centrifugal pump is described realizing the reverse flow equivalent nature of a centrifugal turbine for which the claims also hold. It will be understood that for purposes of the current application, an LNG pump may be used to increase the pressure of the liquid LNG, while a turbine may act to lower the pressure of the liquid LNG. While the terms “pump” and “turbine” may be used interchangeably in certain portions of the current application, in general the primary differences between the two are described as follows: In the case of an LNG pump used to increase the pressure of the liquid LNG, flow of the main stream of liquid LNG will be into the pump at fluid inlet 25, across impeller portion 2 located toward the radial periphery of the assembly, across return vane 5, down and up through diffuser housing 3 and out the exhaust 4 at a higher pressure than at the fluid inlet 25. Flow is from LEFT to RIGHT through the pump. Conversely, in the case of a turbine which lowers the overall pressure of the liquid LNG, flow is from RIGHT to LEFT through the turbine.

The centrifugal pump comprises a rotatable shaft 1 rotating a plurality of impellers 2 with fluid leaving the impeller to be diffused in the diffuser 3 and then passed to exhaust lines 4 which surround a submerged motor housing 10. Fluid enters the impeller eye from a return-vane 5 enclosed in a diffuser housing 6 all of which are encompassed in a pump housing 7. The preceding impeller hub leakage is contained with an annular mechanical hub seal 8 which consists of a labyrinth and a smooth seal arrangement. The impeller eye is sealed with a mechanical shroud seal 9 using a shroud labyrinth or smooth seal arrangement. The impeller is circumferentially locked to the rotatable shaft with a key 14 and axially a locknut 12. Behind the highest pressure impeller is the axial thrust equalizing mechanism consisting of a high pressure chamber 150 and mechanical seal 100 through which pressurized fluid passes to the low pressure chamber 204 and thrust plate 200. After passing through this low pressure chamber an axial variable orifice gap 203 is traverse by the thrust equalizing liquid and passes into the thrust plate pocket 16 from where it exits the pocket through motor housing holes 19 or through the roller bearing 17 or through the bearing liner cooling holes 300. The roller bearing is axially limited in travel with a locknut 15 and washer 22 and spacer 23. Liquid which passes through the roller bearing or bearing linear then passes through a motor housing bushing 21 before entering the submerged cryogenic motor or generator cavity 20.

The destabilizing cross-coupled stiffness is a large influence on the forces that arise in mechanical seals and if too large can lead to excessive synchronous and subsynchronous vibrations in centrifugal pump and turbines.

The deswirl mechanisms claim in this invention serve two purposes. Firstly they act to deswirl liquid at the inlet of the mechanical seals which make up part of the thrust equalizing mechanism. Secondly the deswirl mechanisms at the inlet of the variable axial orifice gap, also part of the axial thrust equalizing mechanism, removes unwanted circumferential liquid velocity to avoid flow separation pockets which gives a more stable axial thrust equalization than conventional liquid cryogenic systems. Together the mechanical seals and variable axial orifice gap act in harmony to equalize the axial thrust on the rotating shaft. The present invention provides means for achieving the desirable inlet swirl reduction at two key locations in the axial thrust equalizing mechanism of cryogenic pumps and turbines.

Referring to the drawing and FIG. 2 in particular, shown therein is a cross section zoom of the region near 100. High pressure axial thrust equalizing liquid leaves the main core flow and travels inward along the back of the impeller in the annular high pressure chamber. Here substantial swirl is imparted on the liquid. The deswirl mechanisms 101 in the high pressure chamber reduce and preset the circumferential rotation of the liquid before it enters the clearance seal between the stationary wear ring 102 and the rotating labyrinth 103 mounted on the impeller 2. The deswirl mechanisms are either vanes, fins, or grooves cut into the material of the motor housing 10. Each of these deswirl mechanisms may be radial or inclined at an angle shown as α. In the case of vanes or fins they are fastened to the motor housing 10 with bolts 104 and are set to give a preswirl in the range 45°<α<135° with α=90° as predominant. Testing and computational fluid dynamics with regard to rotordynamic stability and in particular the stiffness and damping in the seal optimizes the angle setting. After the thrust equalizing liquid leaves the seal and has undergone a substantial pressure drop in enters the low pressure balance chamber 204. Since at the seal outlet the liquid will again have circumferential swirl a set of deswirl mechanisms 201 are installed on the thrust plate 200. This deswirl mechanisms can be fins, vanes, grooves or a combination thereof. The deswirl vanes or fins can be pivoted and locked into place with the bolts 202. The thrust equalizing liquid is then directed radially towards the variable axial orifice gap 203 where due to the lack of swirl it is more stable and avoids separation pockets. This serves for a more stable and improved thrust equalizing mechanism. The impeller 2 is permitted to move axially in the range of 500 μm-3000 μm so that the axial orifice gap 203 is variable. If an axial thrust is not equalized such that the axial orifice gap 203 begins to close the pressure in low pressure balance chamber 204 rises since the flow is restricted and there is less pressure drop across the seal 102 and 103 from the high pressure chamber. This causes an increase in the axial opening force on the back of the impeller which counteracts and equalizes the closing axial thrust imbalance. If the axial thrust is not equalized in the reversed situation such that the axial orifice gap 203 begins to open the pressure in low pressure balance chamber 204 decreases since the flow is less restricted and there is more pressure drop across the seal 102 and 103 from the high pressure chamber. This causes a decrease in the opening force on the back of the impeller which counteracts and equalizes the opening axial thrust imbalance. After the axial thrust equalizing liquid leaves the axial orifice gap 203 it moves to toward the roller bear 17 and the thrust plate pocket 16.

Referring to the drawing and FIG. 3 in particular, shown therein is a cross section zoom of the region near 100. High pressure axial thrust equalizing liquid leaves the main core flow and travels inward along the back of the impeller in the annular high pressure chamber. Here substantial swirl is imparted on the liquid. A plurality of holes at a larger radius 301 and smaller radius 302 are drilled into the motor housing 10 where liquid by passes the wear ring gap inlet. The plurality of holes are located about the circumference and radially staggered. The holes and bypass liquid enter the clearance gap shortly downstream of the stationary wear ring 102 inlet and before the labyrinth rotating wear ring 103. The holes are radially oriented so that liquid in the holes is of zero preswirl. After the axial thrust equalizing liquid leaves the seal and has undergone a substantial pressure drop it enters the low pressure balance chamber 204 where it operates in harmony with the variable axial orifice gap 203 as in the previous paragraphs described manner.

Referring to the drawing and FIG. 4 in particular, shown therein is a cross section zoom of the region near 100. High pressure axial thrust equalizing liquid leaves the main core flow and travels inward along the back of the impeller in the annular high pressure chamber. Here substantial swirl is imparted on the liquid. The surface of the rotating wear ring 103 is made smooth as mounted on the impeller 2. The surface of the stationary wear ring 102 is made up of a plurality of ridges arranged in a diamond like pattern 400. These ridges 401 can be 1 mm to 5 mm tall. They serve to brake the liquid swirl in the seal gap. The diamond pattern is fixed annular type mounted inside the stationary wear ring 102 which in turn is mounted into the motor housing 10. After the axial thrust equalizing liquid leaves the seal and has undergone a substantial pressure drop in enters the low pressure balance chamber 204 where it operates in harmony with the variable axial orifice gap 203 as in the previous paragraphs described manner.

Referring to the drawing and FIG. 5 in particular, shown therein is a cross section zoom of the region near 300 for the situation after the thrust equalizing liquid leaves the low pressure chamber and variable orifice gap and enters the thrust plate chamber 16 of the thrust plate 200. The liquid is blocked from entering the roller bearing 17 by a bearing seal 502 that keeps low temperature lubricant 503 encapsulated in the roller bearing. The roller bearing 17 is permitted to move axially approximately 500 μm-3000 μm in total to give the impeller axial travel and vary the axial gap 203 depending on the axial thrust to be equalized. The roller bearing 17 is locked onto the shaft with the locknut 15 washer 22 and spacer 23. The thrust equalizing liquid passes around the roller bearing either passing though the bearing liner 501 cooling slots 504 or the motor housing holes 19. If the liquid passes through the bearing liner cooling slots it then travels to the back of the roller bearing where it passes through the motor housing bushing 21 and then to cool the submerged motor or generator. In this manner the roller bearing is completely lubricated with the low temperature lubricant while the cryogenic liquid cools the bearing and lubricant.

Referring to the drawing and FIG. 6 in particular, shown therein is a axial section zoom of the bearing liner 501. A plurality of axial groove cooling slots 504 and lands on the bearing liner 501 are used to pass cooling liquid past the bearing. During start-up the cryogenic liquid may be sufficiently cold to freeze the roller bearing lubricant. A bearing heater 505 is then need at start-up until the lubricant reaches near −60° C. A temperature sensor 506 on the opposite side of the heater is applied to verify the start-up permission. The heater is applied for a few minutes before start-up of the pump or turbine. Afterward the heat from rotation in the roller bearing will keep the bearing lubricant warm and the heater can be shut-off.

Referring to the drawing and FIG. 7 in particular, shown therein is a cross section zoom of the region near 300 for the situation after the thrust equalizing liquid leaves the low pressure chamber and variable orifice gap and enters the thrust plate chamber 16 of the thrust plate 200. The liquid is freely permitted to enter the roller bearing 17 where it cools the bearing along the ball 705, inner race 704, and outer race 702 as contact is made during rotation. The bearing cage material 703 is impregnated with a dry lubricant that wipes and partially lubricates the bearing. The entire roller bearing 17 is permitted to move axially approximately 500 μm-3000 μm in the bearing liner 701 to give the impeller axial travel and vary the axial orifice gap 203 depending on the axial thrust to be equalized. The roller bearing 17 is locked onto the shaft with the locknut 15 washer 22 and spacer 23. The axial thrust equalizing liquid passes either through the roller bearing 17 or through the motor housing holes 19. If the liquid passes through the roller bearing it then travels to the back of the roller bearing where it passes through the motor housing bushing 21 and then to cool the submerged motor or generator. In this manner the roller bearing is completely cooled by flushing with low temperature thrust equalizing liquid.

Referring to the drawing and FIG. 8 in particular, shown therein is a cross section zoom of the impeller 2 and impeller eye seal region 9. The impeller shroud clearance leakage liquid passes through the mechanical labyrinth seal with a plurality of teeth to the impeller eye. Normally it enters the gap between the stationary smooth wear ring 801 embedded in the diffuser housing 6 and the impeller eye wear ring 802 with substantial circumferential swirl. This swirl increases the destabilizing cross-coupled stiffness. To eliminate this effect the cross-coupled stiffness is reduced using seal inlet deswirl mechanisms 803. These are fins, vanes, or grooves. This operates to seal the impeller and stabilize the rotordynamics in conjunction with the axial thrust equalizing mechanism.

Referring to the drawing and FIG. 9 in particular, shown therein is a cross section zoom of the impeller eye stationary seal wear rings 902 and the smooth impeller eye wear ring 903, the operation of which is described in the previous paragraph. On the stationary wear ring a diamond like surface pattern 901 like that shown previously in FIG. 4 deswirls liquid in the clearance gap and reduces the cross-coupled stiffness. This seal operates to seal the impeller and stabilize the rotordynamics in conjunction with the axial thrust equalizing mechanism.

Referring to the drawing and FIG. 10 in particular, shown therein is a cross section zoom of the impeller 2 and hub wear ring of region 8. The impeller hub clearance leakage liquid passes through the mechanical labyrinth seal with a plurality of teeth to the impeller hub. Normally it enters the gap between the stationary smooth wear ring 951 embedded in the return-vane 5 and the impeller hub wear ring 952 with substantial circumferential swirl. This swirl increases in the destabilizing cross-coupled stiffness. To eliminate this the cross-coupled stiffness is reduced using inlet deswirl mechanisms 953. These are fins, vanes, or grooves. This functions to seal the impeller hub clearance and stabilize the rotordynamics in conjunction with the axial thrust equalizing mechanism.

Referring to the drawing and FIG. 11 in particular, shown therein is a cross section zoom of the return-vane stationary seal wear ring 975 and the smooth impeller hub wear ring 977, the operation of which is described in the previous paragraph. On the stationary wear ring a diamond like surface pattern 976 like that shown previously in FIG. 4 is made to deswirl liquid in the clearance gap and reduce the cross-coupled stiffness. This seal operates to seal the impeller and stabilize the rotordynamics in conjunction with the axial thrust equalizing mechanism.

The foregoing description is intended to illustrate the present invention. Those of ordinary skill will be able to envisage certain additions, deletions or modifications to the described embodiments which do not depart from the spirit or scope of the invention as defined by the claims herein.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. Although any methods and materials similar or equivalent to those described can be used in the practice or testing of the present invention, the preferred methods and materials are now described. All publications and patent documents referenced in the present invention are incorporated herein by reference.

While the principles of the invention have been made clear in illustrative embodiments, there will be immediately obvious to those skilled in the art many modifications of structure, arrangement, proportions, the elements, materials, and components used in the practice of the invention, and otherwise, which are particularly adapted to specific environments and operative requirements without departing from those principles. The appended claims are intended to cover and embrace any and all such modifications, with the limits only of the true purview, spirit and scope of the invention.

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Classifications
U.S. Classification417/365, 415/163, 415/144, 417/423.3
International ClassificationF04B17/03, F04D27/00, F04D29/56, F01D3/00
Cooperative ClassificationF04D29/0416, F01D15/005, F01D25/22, F01D11/001
European ClassificationF01D15/00B, F01D25/22, F01D11/00B
Legal Events
DateCodeEventDescription
Mar 31, 2008ASAssignment
Owner name: EBARA INTERNATIONAL CORPORATION, NEVADA
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:KAUPERT, KEVIN A.;REEL/FRAME:020728/0539
Effective date: 20080128