U.S. patent application number 10/505297 was filed with the patent office on 2005-06-30 for gas seal system for the shaft of an electric compressor motor.
Invention is credited to Appleford, David Eric, Lane, Brian William.
Application Number | 20050142004 10/505297 |
Document ID | / |
Family ID | 9931528 |
Filed Date | 2005-06-30 |
United States Patent
Application |
20050142004 |
Kind Code |
A1 |
Appleford, David Eric ; et
al. |
June 30, 2005 |
Gas seal system for the shaft of an electric compressor motor
Abstract
An electric motor (30) is accommodated in a first portion (42)
of a housing (40) and is arranged to drive a compressor (32)
accommodated in a second portion (44) of the housing separated from
the first housing portion (42) by a wall (46). An umbilical (48)
introduces dry motor protection gas into the first housing portion
(42) and a passage (54) between the first and second housing
portions (42,44) allows a leakage of the motor protection gas from
the first housing portion (42) into the second housing portion (44)
at a higher pressure than gas supplied to the compressor (32) via
an inlet pipe (58) thereby preventing moisture laden gas from the
compressor (32) entering the first housing portion accommodating
the electric motor (30).
Inventors: |
Appleford, David Eric;
(Essex, GB) ; Lane, Brian William; (Essex,
GB) |
Correspondence
Address: |
Summa & Allan
11610 North Community House Road
Suite 200
Charlotte
NC
28277
US
|
Family ID: |
9931528 |
Appl. No.: |
10/505297 |
Filed: |
August 20, 2004 |
PCT Filed: |
February 21, 2003 |
PCT NO: |
PCT/GB03/00779 |
Current U.S.
Class: |
417/371 ;
417/421; 417/423.9 |
Current CPC
Class: |
F04D 29/102 20130101;
H02K 5/12 20130101; F04D 25/06 20130101; F04D 25/0686 20130101 |
Class at
Publication: |
417/371 ;
417/421; 417/423.9 |
International
Class: |
F04B 017/00; F04B
035/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 21, 2002 |
GB |
0204139.0 |
Claims
1. A gas seal system assembly, comprising: a housing; an electric
motor accommodated within a first portion of the housing; rotating
machinery accommodated within a second portion of the housing and
driven by said electric motor; separation means in the housing
between said first and second portions thereof for separating fluid
acted upon by said rotating machinery from said electric motor; gas
introduction means for introducing at least substantially dry motor
protection gas into said first housing portion; wherein said gas
introduction means further comprises a restricted gas flow means
for permitting a leakage of the motor protection gas from said
first housing portion into said second housing portion; and a
circulating apparatus for diverting a portion of the fluid acted
upon by said rotating machinery to said first housing portion, said
circulating apparatus including drying means for reducing the
moisture content of the acted upon gas diverted back to said first
housing portion, said drying means having at least one outlet.
2. The assembly as claimed in claim 1, wherein said gas
introduction means includes external means for supplying the at
least substantially dry gas.
3. The assembly as claimed in claim 2, wherein said means for
supplying the at least substantially dry gas comprises a gas drying
and supply unit on a remote host facility linked to said first
housing portion by an umbilical.
4. The assembly as claimed in claim 1, wherein said drying means
separates the diverted portion of the acted upon gas into an at
least substantially moisture-free first outlet flow and said
circulating apparatus includes first routing means for routing the
first outlet flow from a first one of said at least one outlet of
said drying means to said first housing portion.
5. The assembly as claimed in claim 4, wherein said drying means
incorporates moisture extracted from the acted upon gas into a
second outlet flow from said drying means.
6. The assembly as claimed in claim 5, wherein the second outlet
flow from said drying means is transported away from the assembly
by means of the gas being acted upon by said rotating
machinery.
7. The assembly as claimed in claim 5, including second routing
means for routing the second outlet flow containing the extracted
moisture from a second outlet of said drying means and for
incorporating it into the flow of gas acted upon by said rotating
machinery.
8. The assembly as claimed in claim 7, wherein said second routing
means incorporates the second outlet flow containing the extracted
moisture into the acted upon gas at least substantially prior to
the gas being acted upon by said rotating machinery.
9. The assembly as claimed in claim 7, wherein said second routing
means incorporates the second outlet flow containing the extracted
moisture into the acted upon gas at least substantially after the
gas has been acted upon by said rotating machinery.
10. The assembly as claimed in claim 9, wherein said second routing
means includes a pressure equalizing device for incorporating the
second outlet flow containing the extracted moisture into the acted
upon gas downstream of said rotating machinery.
11. The assembly as claimed in claim 1, wherein at least one outlet
flow passes through at least one non-return valve configured to
prevent such flow or flows returning directly to said at least one
outlet of said drying means.
12. The assembly as claimed in claim 1 wherein said rotating
machinery is selected from the group consisting of compressors and
centrifugal pumps.
13. The assembly as claimed in claim 1, wherein said second housing
portion includes a compressor inlet for receiving gas at a first
pressure and a compressor outlet for delivering gas at a second
pressure higher than the first pressure and said restricted gas
flow means enables leakage of the motor protection gas into said
second housing portion.
14. The assembly as claimed in claim 13, wherein said gas flow
means is adjacent said compressor inlet.
15. The assembly as claimed in claim 1, including means for
automatically maintaining the motor protection gas at a pressure
above that of fluid in a part of said second housing portion
adjacent said restricted gas flow means.
16. A gas seal system method, comprising: operating an electric
motor accommodated in a first portion of a housing and arranged to
drive a rotating machine accommodated in a second portion of the
housing in which fluid in the second housing portion which is acted
upon by the rotating machine is separated from the first housing
portion by separation means, the method including providing gas
introduction means for introducing at least substantially dry motor
protection gas into the first housing portion, and providing
restricted gas flow means between the first and second housing
portions, wherein the method further comprises the steps of:
establishing a leakage of the motor protection gas from the first
housing portion to the second housing portion via the gas flow
means; providing circulating apparatus and diverting a portion of
the acted upon gas to the first housing portion via the circulating
apparatus; and incorporating drying means in the circulating
apparatus and reducing the moisture content of the acted upon gas
diverted back to the first housing portion by means of the drying
means.
Description
[0001] The present invention relates to the provision of a secure
environment for an electric motor of the type in which a single
housing accommodates both the motor and rotating machinery driven
by the motor.
[0002] The invention will be described with reference to a motor
used to drive a compressor. The invention is however applicable to
other sorts of rotating machinery such as centrifugal pumps. For
ease of installation and retrieval, a single housing accommodating
an electric motor and a compressor is sometimes employed. Such an
arrangement is particularly useful for sub-sea applications in
which easy installation and retrieval are important. FIG. 1 shows a
schematic representation of a typical prior art arrangement
including a motor 2 linked to a compressor unit 4 by means of a
shaft 6 mounted in bearings 8 and 10. All of these components are
mounted in a single housing 12. Inlet pipe 14 and outlet pipe 16
lead gas respectively into and out of the compressor 12. Since a
certain amount of gas being compressed will pass through the
bearing 8 into the area surrounding the motor 2, the arrangement is
only suitable for pumping dry gas because the motor will be damaged
if exposed to moisture. Such a restriction makes the arrangement
unsuitable for use in the pumping of gas from a hydrocarbon
reservoir which will generally have a high water vapour content and
contain droplets of water.
[0003] When such moisture laden gas is to be compressed, one
solution is to use a more conventional arrangement such as that
shown in FIG. 2 in which the motor 2 is accommodated within a first
housing 20 and the compressor unit 4 is accommodated within a
separate second housing 22. Particularly when used in a sub-sea
environment, it will be necessary to incorporate seals 18 where the
shaft 6 passes through the walls of the housings 20 and 22. There
is a further requirement in sub-sea applications for the apparatus
to be compact which in turn means that high operating speeds are
necessary to achieve the required volumetric throughput and
pressure increase. Such high operating speeds however lead to rapid
deterioration of the seals 18. In sub-sea applications, where
replacement is difficult and may involve stopping production from
all or part of the oil field, this is a severe disadvantage. The
object of the invention is to overcome at least some of the above
described disadvantages of existing motor/compressor
assemblies.
[0004] Thus according to the invention there is provided an
assembly comprising a housing, an electric motor accommodated
within a first portion of the housing, rotating machinery
accommodated within a second portion of the housing and driven by
the electric motor, separation means in the housing between the
first and second portions thereof for separating fluid acted upon
by the rotating machinery from the electric motor, gas introduction
means for introducing at least substantially dry motor protection
gas into the first housing portion and restricted gas flow means
for permitting a leakage of the motor protection gas from the first
housing portion into the second housing portion.
[0005] With such an arrangement, it is possible to provide a motor
and compressor in the same housing which can be operated to
compress gas regardless of its moisture content. Furthermore, seals
around a drive shaft connecting the motor and compressor are not
required.
[0006] Preferably the gas introduction means includes means for
supplying the at least substantially dry gas. This may comprise a
gas drying and supply unit on a remote host facility linked to the
first housing portion by an umbilical.
[0007] The invention is particularly applicable to the driving of
machinery for raising the pressure of fluid such as compressors or
centrifugal pumps.
[0008] When the rotating machinery comprises a compressor,
preferably the second housing portion includes a compressor inlet
for receiving gas at a first pressure and a compressor outlet for
delivering gas at a second pressure higher than the first pressure,
and the gas flow means allows leakage of the motor protection gas
into the second housing portion adjacent to the compressor inlet.
In order to accommodate variations in pressure within the second
housing portion, the assembly preferably also includes means for
automatically maintaining the motor protection gas at a pressure
above that of fluid in a part of the second housing portion
adjacent to the gas flow means.
[0009] If this pressure differential is maintained at a low value,
then the leakage of motor protection gas into the second housing
portion can be kept to a minimum which will reduce the cost of
running the assembly.
[0010] When the fluid being acted upon by the rotating machinery is
a gas, the apparatus preferably includes circulating apparatus for
diverting a portion of the acted upon gas to the first housing
portion, the circulating apparatus including drying means for
reducing the moisture content of the acted upon gas diverted back
to the first housing portion. Such an arrangement will still
further reduce the amount of motor protection gas which needs to be
supplied and will still further reduce the cost of running the
assembly. Furthermore, if the motor can tolerate wet gas for a
short start up period without damage to its components, then the
requirement for an external supply of motor protection gas can be
obviated if such circulating apparatus is provided.
[0011] Conveniently the drying means separates the extracted
portion of the acted upon gas into an at least substantially
moisture-free first outlet flow and the circulating apparatus
includes first routing means for routing the first outlet flow from
a first outlet of the drying means to the housing first
portion.
[0012] In order to facilitate removal of the extracted moisture,
preferably the drying means incorporates moisture extracted from
the first outlet flow into a second outlet flow.
[0013] The second outlet flow from the drying means can
conveniently be transported away from the assembly by means of the
gas being acted upon by the compressor. Accordingly, the
circulating apparatus preferably also includes second routing means
for routing the second outlet flow containing the extracted
moisture from a second outlet of the drying means and for
incorporating it into the flow of gas acted upon by the
compressor.
[0014] In order that the second outlet flow from the drying means
can be incorporated into a relatively low pressure gas flow,
preferably the second routing means incorporates the second outlet
flow containing the extracted moisture into the acted upon gas at
least substantially prior to it being acted upon by the
compressor.
[0015] Alternatively, in order to avoid introducing additional
moisture into gas entering the compressor, the second routing means
incorporates the second outlet flow containing the extracted
moisture into the acted upon gas at least substantially after it
has been acted upon by the compressor.
[0016] So as to avoid the necessity of raising the pressure of the
second outlet flow from the drying means to that of the gas leaving
the compressor, preferably the second routing means includes a
pressure equalising device such as an ejector for incorporating the
second outlet flow containing the extracted moisture into acted
upon gas downstream of the compressor.
[0017] Preferably one or more gas outlet flows from the drying
means pass through non-return valves configured to prevent such
flow or flows returning directly to outlets of the drying
means.
[0018] The invention also provides a method of operating an
electric motor accommodated in a first portion of a housing and
arranged to drive a rotating machine accommodated in a second
portion of the housing in which fluid in the second housing portion
which is acted upon by the rotating machine is separated from the
first housing portion by separation means, the method including the
steps of:
[0019] (i) providing gas introduction means for introducing at
least substantially dry motor protection gas into the first housing
portion;
[0020] (ii) providing restricted gas flow means between the first
and second housing portions; and
[0021] (iii) establishing a leakage of the motor protection gas
from the first housing portion to the second housing portion via
the gas flow means.
[0022] In order to reduce the amount of motor protection gas
consumed by the assembly, preferably the method involves providing
circulating apparatus and diverting a portion of the acted upon gas
to the first housing portion via the circulating apparatus,
incorporating drying means in the circulating apparatus and
reducing the moisture content of the acted upon gas diverted back
to the first housing portion by means of the drying means.
[0023] The invention will now be described by way of example only
with reference to the accompanying Figures in which:
[0024] FIG. 1 shows in schematic form a prior art arrangement;
[0025] FIG. 2 shows in schematic form a further prior art
arrangement;
[0026] FIG. 3 shows in schematic form a first embodiment of the
invention; and
[0027] FIG. 4 shows in schematic form a second embodiment of the
invention.
[0028] The prior art arrangements shown in FIGS. 1 and 2 have been
described above.
[0029] In the first embodiment of the invention shown in FIG. 3, an
electric motor 30 is linked to a compressor 32 by a shaft 34 which
is supported by a first bearing 36 and a second bearing 38. These
components are accommodated in a housing 40 having first and second
portions 42 and 44 respectively accommodating the motor 30 and the
compressor 32. Separation means, in the form of a wall 46,
separates the housing portions 42 and 44 from each other.
[0030] Gas introduction means, in the form of an umbilical 48 leads
to an inlet 50 of the first housing portion 42 for supplying at
least substantially dry, and more preferably completely dry, motor
protection gas 52 thereinto.
[0031] Gas flow means 54, comprising one or more passages between
the first and second housing portions 42 and 44, are provided to
allow a leakage of the motor protection gas 52 from the first
housing portion 42 into the second housing portion 44. This leakage
is indicated by arrows A.
[0032] The compressor 32 includes an inlet 56 connected to an inlet
pipe 58 (at pressure p1) and an outlet 60 connected to an outlet
pipe 62 (at a higher pressure p2).
[0033] The first housing portion 42 containing the motor is
maintained at a pressure p3 by the supply of motor protection gas
52. p3 is maintained higher than p1 in order that motor protection
gas 52 steadily leaks through the gas flow means 54 in the
direction of arrows A into the second housing portion. This
pressure differential prevents any of the gas supplied to the
compressor via inlet pipe 58, which may contain moisture, from
entering the first housing portion 42. Control means (not shown)
are preferably provided to maintain p3 only slightly above p1 in
order that only a low volumetric flow of motor protection gas
through the gas flow means 54 occurs. This will reduce the amount
of motor protection gas required and thereby minimise running
costs.
[0034] The so-called integrated oil-free motor compressor
manufactured by Man Turbo Maschinen AG would be the type of motor
compressor assembly to which the invention could be applied.
[0035] The second embodiment of the invention will now be described
with reference to FIG. 4 in which parts which correspond in form
and function to those shown in FIG. 3 bare indicated with like
numerals prefixed with 1 and will not be described again in
detail.
[0036] The embodiment shown in FIG. 4 includes circulating
apparatus shown generally as 170. An extraction pipe 172 is
arranged to extract a portion, for example 10%, of the gas leaving
the compressor via the outlet pipe 162 and route it to a gas drying
unit 174. The gas drying unit 174 may suitably be of the type
manufactured under the name TWISTER by Shell and its partner Stork
Product Engineering. This drying unit uses a Laval nozzle to expand
gas to supersonic velocities leading to low temperature and
pressure resulting in nucleation and condensation of water.
Droplets of water formed come into contact with a wing member and
are centrifuged onto walls of the device. A first flow 176 of at
least substantially dry gas (at pressure P3) leaves the gas drying
unit via a first gas outlet 178 and is routed by dry gas conduit
182 via a non-return valve 180 to the umbilical 148 immediately
upstream of the housing first portion 142 and downstream of a
further non-return valve 184 in the umbilical 148. The pressure P3
is arranged to be greater than the pressure P5 of gas entering the
compressor.
[0037] Since the motor 130 may be able to tolerate wet gas for a
short start up period without damage to its components, the
umbilical 148 for supplying dry gas may not be necessary in which
case the dry gas conduit 182 would lead directly into the housing
first portion 142.
[0038] A second flow 186 of wet gas (at pressure P4) containing
all, or substantially all, of the water contained in the gas
extracted from the compressor outlet pipe leaves the gas drying
unit 174 via a second outlet 188 and is routed by a wet gas conduit
190 to the inlet pipe 158 through a further non-return valve 192.
The pressure P4 is arranged to be greater than P1, the pressure of
gas approaching the compressor through the inlet pipe 158. This
flow of wet gas 186 will assist the flow of new gas entering the
compressor from the inlet pipe 158.
[0039] Alternatively, the second outlet 188 of the gas drying unit
174 may be connected by a high pressure wet gas conduit 193 which
routes the wet gas 186 through a non-return valve 194 to an ejector
196 which acts to entrain the wet gas 186 into the flow of
pressurised gas leaving the compressor via the outlet 160. The
ejector 196 is necessary because the pressure P4 of the wet gas
will be lower than the pressure P2 of the gas at the compressor
outlet 160. Downstream of the ejector 196 the pressure P6 of the
combined gas streams will be less than P2 but high enough to ensure
satisfactory conveyance of the gas to the host facility. The
alternative route for the wet gas 186 avoids reintroducing the
moisture extracted by the gas drying unit 174 back into the
compressor.
[0040] As in the first embodiment, the pressure of gas in the
housing first portion 142 will be arranged to be slightly higher
than the pressure P5 of gas entering the compressor so as to ensure
that a steady leakage (A) of at least substantially dry gas from
the first housing portion to the second is maintained and flow in
the reverse direction is prevented.
* * * * *