U.S. patent application number 12/012541 was filed with the patent office on 2009-01-01 for deswirl mechanisms and roller bearings in an axial thrust equalization mechanism for liquid cryogenic turbomachinery.
This patent application is currently assigned to Ebara International Corporation. Invention is credited to Kevin A. Kaupert.
Application Number | 20090004032 12/012541 |
Document ID | / |
Family ID | 40160759 |
Filed Date | 2009-01-01 |
United States Patent
Application |
20090004032 |
Kind Code |
A1 |
Kaupert; Kevin A. |
January 1, 2009 |
Deswirl mechanisms and roller bearings in an axial thrust
equalization mechanism for liquid cryogenic turbomachinery
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.
Inventors: |
Kaupert; Kevin A.; (Reno,
NV) |
Correspondence
Address: |
RAY K. SHAHANI, ESQ., ATTORNEY AT LAW
TWIN OAKS OFFICE PLAZA, 477 NORTH NINTH AVENUE, SUITE 112
SAN MATEO
CA
94402-1858
US
|
Assignee: |
Ebara International
Corporation
Sparks
NV
|
Family ID: |
40160759 |
Appl. No.: |
12/012541 |
Filed: |
February 2, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60920618 |
Mar 29, 2007 |
|
|
|
Current U.S.
Class: |
417/365 ;
415/144; 415/163; 417/423.3 |
Current CPC
Class: |
F01D 15/005 20130101;
F01D 25/22 20130101; F01D 11/001 20130101; F04D 29/0416
20130101 |
Class at
Publication: |
417/365 ;
417/423.3; 415/163; 415/144 |
International
Class: |
F01D 3/00 20060101
F01D003/00; F04B 17/03 20060101 F04B017/03; F04D 29/56 20060101
F04D029/56; F04D 27/00 20060101 F04D027/00 |
Claims
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
.mu.m and about 60 .mu.m 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 .mu.m and
about 60 .mu.m 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
[0001] 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
[0002] The present invention relates to liquid cryogenic
centrifugal pumps and turbines of the submerged motor or generator
type.
BACKGROUND OF THE INVENTION
[0003] 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.
[0004] 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
[0005] 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 .delta. in the x and y direction written as
follows:
- [ F x ( t ) F y ( t ) ] = [ k xx ( .delta. ) k xy ( .delta. ) k
yx ( .delta. ) k yy ( .delta. ) ] [ x y ] + [ c xx ( .delta. ) c xy
( .delta. ) c yx ( .delta. ) c yy ( .delta. ) ] [ x t y t ] + [ m
xx ( .delta. ) m xy ( .delta. ) m yx ( .delta. ) m yy ( .delta. ) ]
[ 2 x t 2 2 y t 2 ] ##EQU00001##
[0006] 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 ##EQU00002##
[0007] 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 .delta. in x and y so .delta.=.delta..sub.o+iy and
.delta.=.delta..sub.o exp(i.omega..sub.wt). In this relation,
.omega..sub.w 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 .omega. w 2 - c xy .omega.
w - k xx ) ( m xy .omega. w 2 + c xx .omega. w - k xy ) ( m yx
.omega. w 2 - c yy .omega. w - k yx ) ( m yy .omega. w 2 + c yx
.omega. w - k yy ) ] [ .delta. o cos .omega. w t .delta. o sin
.omega. w t ] ##EQU00003##
[0008] It is now more convenient and intuitive to write this
equation in dimensionless form as follows:
[ F x * ( t ) F y * ( t ) ] = [ ( m xx * .omega. w 2 .omega. 2 - c
xy * .omega. w .omega. - k xx * ) ( m xy * .omega. w 2 .omega. 2 +
c xx * .omega. w .omega. - k xy * ) ( m yx * .omega. w 2 .omega. 2
- c yy * .omega. w .omega. - k yx * ) ( m yy * .omega. w 2 .omega.
2 + c yx * .omega. w .omega. - k yy * ) ] [ .delta. o cos .omega. w
t / R 2 .delta. o sin .omega. w t / R 2 ] ##EQU00004##
[0009] The * designates use of the dimensionless quantities with
F*=F/.pi..rho.R.sub.2.sup.3B.sub.2.omega..sup.2, x*=x/R2,
dx*/dt=(dx/dt)/R.sub.2.omega., and
dx.sup.2*/dt=(d.sup.2x/dt.sup.2)/R.sub.2.omega..sup.2. The
dimensionless stiffness, damping and added mass coefficients used
are k*.sub.ij=k.sub.ij/.pi..rho.R.sub.2.sup.2B.sub.2.omega..sup.2,
c*.sub.ij=c.sub.ij/.pi..rho.R.sub.2.sup.2B.sub.2.omega.,
m*.sub.ij=m.sub.ij/.pi..rho.R.sub.2.sup.2B.sub.2. 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*.sub.r+iF*.sub..theta.=(F*.sub.x+iF*.sub.y)exp(-i.omega..sub.wt)
and get the following equation:
[ F .theta. * F r * ] whirl = [ - m xy * ( .omega. w .omega. ) 2 -
c xx * ( .omega. w .omega. ) + k xy * + m yz * ( .omega. w .omega.
) 2 - c yy * ( .omega. w .omega. ) - k yx * m xx * ( .omega. w
.omega. ) 2 - c xy * ( .omega. w .omega. ) - k xx * + m yy * (
.omega. w .omega. ) 2 + c yx * ( .omega. w .omega. ) - k yy * ]
##EQU00005##
[0010] 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 .theta. * F r * ] whirl = 2 [ - m xy * ( .omega. w .omega. ) 2
- c xx * ( .omega. w .omega. ) + k xy * + m xx * ( .omega. w
.omega. ) 2 - c xy * ( .omega. w .omega. ) - k xx * ]
##EQU00006##
[0011] For the circumferential force if F*.sub..theta. is negative,
in the reverse direction of the impeller whirl rotation, an
impeller whirl stabilizing force is experienced. If F*.sub..theta.
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*.sub..theta.=0 and m.sub.xy as
negligible in the previous equation to give
.omega..sub.w/.omega.=k*.sub.xy/c*.sub.xx as the whirl ratio limit.
Taking m.sub.xy 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:
( .omega. w .omega. ) .theta. limit = k xy c xx .omega.
##EQU00007##
[0012] Therefore, the tangential stability whirl ratio limit is a
balance between cross coupled stiffness forces k.sub.xy that drive
the whirl and damping forces c.sub.xx.omega. that oppose the whirl.
For a constant angular frequency with a whirl larger than
(.omega..sub.w/.omega.).sub..theta. limit, the tangential force
acts in a stabilizing manner. For a constant angular frequency with
a whirl smaller than (.omega..sub.w/.omega.).sub..theta. 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 k.sub.xy (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.
[0013] 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 k.sub.xx is increased
in the seal along with an increase in the direct coupled c.sub.xx
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.
[0014] 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.
[0015] 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.
[0016] 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.degree. 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.
[0017] 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.
[0018] 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.
[0019] 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
[0020] 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.
[0021] 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.
[0022] 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.
[0023] 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.
[0024] 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.
[0025] 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.
[0026] 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.
[0027] 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.
[0028] 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.
[0029] 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.
[0030] 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
[0031] 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.
[0032] 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.
[0033] 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.
[0034] 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.
[0035] 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.
[0036] 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.
[0037] 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.
[0038] 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 .alpha.. 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.degree.<.alpha.<135.degree. with .alpha.=90.degree. 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 .mu.m-3000 .mu.m 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.
[0039] 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.
[0040] 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.
[0041] 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 .mu.m-3000 .mu.m 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.
[0042] 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.degree. 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.
[0043] 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 .mu.m-3000 .mu.m 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.
[0044] 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.
[0045] 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.
[0046] 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.
[0047] 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.
[0048] 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.
[0049] 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.
[0050] 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.
* * * * *