U.S. patent application number 13/806552 was filed with the patent office on 2013-06-13 for combined barrier and lubrication fluids pressure regulation system and unit for a subsea motor and pump module.
This patent application is currently assigned to VETCO GRAY SCANDINAVIA AS. The applicant listed for this patent is Ole Peter Tomter. Invention is credited to Ole Peter Tomter.
Application Number | 20130146299 13/806552 |
Document ID | / |
Family ID | 45370909 |
Filed Date | 2013-06-13 |
United States Patent
Application |
20130146299 |
Kind Code |
A1 |
Tomter; Ole Peter |
June 13, 2013 |
Combined Barrier and Lubrication Fluids Pressure Regulation System
and Unit for a Subsea Motor and Pump Module
Abstract
A barrier and lubrication fluids pressure regulation system for
a subsea motor and pump module is disclosed, comprising a
lubrication fluid circuit in flow communication with a hydraulic
fluid supply via a first pressure reducing regulator (15); and a
barrier fluid circuit in flow communication with the hydraulic
fluid supply via a second pressure reducing regulator (14). The
first pressure reducing regulator (15) is configured to reduce the
supply fluid pressure in response to the pumped medium pressure at
the suction side (4) or at the discharge side (5) of the pump, and
the second pressure reducing regulator (14) is configured to reduce
the supply fluid pressure in response to the output pressure of the
first pressure reducing regulator (15). A pressure regulation unit
is likewise disclosed, and arranged for housing the components of
the barrier and lubrication fluids pressure regulation system in a
pressurized vessel.
Inventors: |
Tomter; Ole Peter; (Nesoya,
NO) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Tomter; Ole Peter |
Nesoya |
|
NO |
|
|
Assignee: |
VETCO GRAY SCANDINAVIA AS
Sandvika
NO
|
Family ID: |
45370909 |
Appl. No.: |
13/806552 |
Filed: |
June 20, 2011 |
PCT Filed: |
June 20, 2011 |
PCT NO: |
PCT/IB2011/001399 |
371 Date: |
March 1, 2013 |
Current U.S.
Class: |
166/340 ;
166/335 |
Current CPC
Class: |
E21B 33/035 20130101;
F04B 53/18 20130101; F16J 15/406 20130101; F04B 47/06 20130101;
F04B 49/08 20130101 |
Class at
Publication: |
166/340 ;
166/335 |
International
Class: |
E21B 33/035 20060101
E21B033/035 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 22, 2010 |
NO |
20100905 |
Claims
1. A barrier and lubrication fluids pressure regulation system for
a subsea motor and pump module operable for displacement of a
pumped medium from a pump suction side to a pump discharge side,
the pressure regulation system comprising: a lubrication fluid
circuit (12, 22, 23, 24, 27, 30, 31) in flow communication with a
hydraulic fluid supply via a first pressure reducing regulator
(15); a barrier fluid circuit (11, 16, 17, 20) in flow
communication with the hydraulic fluid supply via a second pressure
reducing regulator (14), wherein the first pressure reducing
regulator (15) reduces of the hydraulic fluid supply in response to
pressure of the pumped medium at the pump suction side (4) or at
the pump discharge side (5), and the second pressure reducing
regulator (14) reduces pressure of the hydraulic fluid supply in
response to an output pressure of the first pressure reducing
regulator (15).
2. The system of claim 1, wherein each of the first and second
pressure reducing regulators (15; 14) are dome-loading regulators
with adjustable bias set to deliver an output pressure exceeding a
dome loading pressure by an amount comprising a value selected from
the group consisting of a range of about 2-10 bar and about 5
bar.
3. The system of claim 2, wherein the pumped medium pressure is
applied to the dome of the first pressure reducing regulator (15)
via a diaphragm (29), or via a pressure compensator, arranged to
separate the fluids in a pilot circuit (27, 28, 30) connecting the
first pressure reducing regulator (15) with the pumped medium.
4. The system of claim 1, wherein pressure of the pumped medium
communicates via a pilot circuit (28, 30) to a dome of a third
pressure reducing regulator (35) arranged in the hydraulic fluid
supply upstream of the first and second pressure reducing
regulators, wherein the third pressure reducing regulator delivers
an output pressure exceeding a loading pressure of the dome of the
third pressure reducing regulator (35) by an amount comprising a
value selected from the group consisting of a range of about 20-50
bar and about 30 bar.
5. The system of claim 1, wherein each of the barrier fluid circuit
and the lubrication fluid circuit communicate with the pump inlet
or the pump outlet via respective pressure controlled pressure
relief regulator valves (19; 26) opening into a pilot line
(28).
6. The system of claim 5, wherein the pressure relief regulator
valve in the lubrication fluid circuit is a dome-loading back
pressure regulator (26) responsive to the pumped medium pressure at
the suction side or at the discharge side of the pump.
7. The system of claim 5, wherein the pressure relief regulator
valve in the barrier fluid circuit is a dome-loading back pressure
regulator (19) responsive to the output pressure of the first
pressure reducing regulator (15).
8. The system of claim 1, wherein the pressure reducing regulators
(14, 15) and the back pressure regulators (19, 26) are each
associated with a motor drive for selectively setting a bias of the
regulators.
9. A barrier and lubrication fluids pressure regulation unit
comprising: a pressure vessel (36) selectively exposed to seawater,
housing a volume of hydraulic fluid, and selectively in being
hydraulic communication with a lubrication fluid circuit in a
subsea motor and pump module; a first pressure reducing regulator
(15) arranged in the pressure vessel, and for regulating a fluid
flow from an external hydraulic fluid supply into the pressure
vessel interior; a second pressure reducing regulator (14) arranged
in the pressure vessel, and for regulating a fluid flow between the
external hydraulic fluid supply and a barrier fluid circuit in the
subsea motor and pump module, wherein an output flow of the first
pressure reducing regulator (15) controls the internal pressure of
the pressure vessel, and an output flow of the second pressure
reducing regulator (14) is responsive to the internal pressure of
the pressure vessel.
10. The pressure regulation unit of claim 9, wherein the first
pressure reducing regulator (15) controls the internal pressure in
the vessel (36) by reducing the pressure of supplied hydraulic
fluid in response to the pumped medium pressure at a suction side
of the pump or at a discharge side of the pump via a pilot line
(30) extended into the pressure vessel (36).
11. The pressure regulation unit of claim 10, wherein the pressure
vessel (36) comprises: a flow line connection that carries
hydraulic fluid flow from a hydraulic fluid supply (10); a flow
line connection via which pumped medium pressure is communicated
from the suction side of the pump or from the discharge side of the
pump to the first pressure reducing regulator (15); a flow line
connection via which barrier fluid is supplied to the motor from
the second pressure reducing regulator (14); a flow line connection
via which lubrication fluid is supplied to the pump from the
pressure vessel interior, and a flow line connection via which
hydraulic fluid can be dumped into the pumped medium at the suction
side of the pump or at the discharge side of the pump.
12. (canceled)
13. The pressure regulation unit of claim 9, wherein the pressure
vessel comprises a base plate with hydraulic couplings allowing the
unit to be installed onto a mounting base allowing for
disconnection by an Remotely Operated Vehicle (ROV) and retrieved
to surface for replacement and/or repair.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] The present invention relates generally to subsea equipment
involved in the transport of hydrocarbon production fluids from a
production site at the sea floor to a sea surface or land based
host facility. More specifically, the present invention is
concerned with a system that is designed for management of barrier
and lubrication fluid pressures in a subsea motor and pump module.
In another aspect the present invention relates also to a pressure
regulation unit for a subsea motor and pump module.
BACKGROUND AND PRIOR ART
[0002] A process fluid in subsea hydrocarbon production is
typically a multiphase fluid comprising oil and gas and eventually
solid matter, which is extracted from an underground reservoir. A
motor/pump module is arranged on the sea floor and configured for
transport of the process fluid from the reservoir to a surface or
land based host facility. The motor/pump module is frequently
subjected to substantial variations in pressure in the pumped
medium, as well as substantial transitional loads during pump start
and stop sequences. The pumped medium pressure at the suction side
of the pump may be in the order of hundreds of bar, requiring
corresponding measures in the motor/pump module to prevent process
fluid and particulate matter from immigration from the pump
interior into a motor housing via bearings and seals in the
motor/pump module.
[0003] For the purpose of pumping a multiphase fluid in subsea
production, screw rotor pumps are advantageously used. The screw
rotor pump is a positive displacement type of pump having two screw
shafts that are driven in rotation with intermeshing gears, between
which a specific volume of fluid is displaced in the axial
direction of the screws from a suction side of the pump to be
discharged on the pressure side of the pump. The screws are
journalled in bearings in a pump housing, and are drive-connected
to a motor arranged in a motor housing. In case of a twin rotor
screw pump, intermeshing timing gears carried on the screw shafts
provide synchronization of the rotary motion. The motor housing
interior is hydraulically separated from the pump housing interior
by a seal arrangement, where the drive shaft is journalled to
extend for connection with the pump rotor shaft. The pump bearings
are separated from the pump medium by seal arrangements at both
ends of the pump.
[0004] A hydraulic fluid in the motor housing is to be maintained
at a pressure above the internal pressure of the pump, acting as a
barrier which prevents intrusion of process fluid and particles
into the motor housing via the seal and bearing arrangement. In
result of the pressure difference, a leak flow of hydraulic fluid
along the drive shaft is unavoidable. The leakage rate is dependent
on fluid properties, differential pressure, the transient operating
conditions of the pump, and the tightness of the seal(s). The
leakage is compensated by refilling the motor housing from an
external supply of hydraulic fluid. Likewise, hydraulic fluid is
used for lubrication of pump bearings and timing gears. The
pressure in the pump lubrication fluid is to be maintained above
the pumped medium pressure internally of the pump, in order to
prevent intrusion of process fluid and particles into pump
bearings, seals and timing gears. Leakage via the pump seals into
the pumped medium is compensated by refilling from an external
supply of hydraulic fluid.
[0005] The motor and pump can be drive-connected inside the motor
housing, or outside the motor housing. For instance, the motor and
pump can share one and the same shaft with no separate coupling
that connects them in a driving relation. In other designs the pump
shaft can be coupled to the motor shaft inside the motor housing.
In still other designs, the motor and pump is drive-connected by
means of a coupling located in a coupling chamber defined between
the motor housing and the pump. However, in all alternatives it is
desirable to maintain at all times a pressure difference over the
interfaces, i.e. between the motor housing, the coupling chamber
when present, and the pump lubrication system and the pumped
medium, respectively.
[0006] Conventionally, a motor barrier fluid and a pump lubrication
fluid are each supplied from a host facility, and leakage
compensation as well as pressure control are managed from the host
facility, usually via an umbilical. As subsea hydrocarbon
production sites are increasingly installed and operated at
increasing depths and step-out distances, the response times and
control requirements in lubrication and cooling systems increase
correspondingly. As a consequence, there is a rising need for a
barrier fluid and lubrication system that operates with improved
control requirements and which provides increased reliability in
operation.
SUMMARY OF THE INVENTION
[0007] The present invention thus aims at providing a barrier and
lubrication fluids pressure regulation system for a subsea motor
and pump module which avoids the problems of prior art systems, and
specifically those problems which are associated with long step-out
distances and great water depths.
[0008] The present invention specifically aims at providing a
barrier and lubrication fluids pressure regulation system for a
subsea motor and pump module, the system having an inherent
capability to adapt to pressure changes in the pumped medium. The
present invention further aims at providing a barrier and
lubrication fluids pressure regulation system having an inherent
capability to compensate for loss of hydraulic fluid caused by
leakage via seals and bearings in the motor and pump module. Still
another object of the present invention is to provide a barrier and
lubrication fluids pressure regulation system wherein a preset
pressure differential between a barrier fluid circuit and a
lubrication fluid circuit is automatically maintained at all times,
and balanced towards the pumped medium pressure.
[0009] The barrier and lubrication fluids pressure regulation
system of the present invention may advantageously be applied to a
subsea motor and pump module which comprises a pump motor disposed
in a motor housing; a pump disposed in a pump housing having a pump
inlet at a suction side and a pump outlet at a discharge side of
the pump, and a pump-rotor assembly arranged there between and
journalled in bearings in the pump housing. The pump-rotor assembly
is drive-connected to the motor through a drive-shaft that reaches
between the motor and pump housings via a seal and bearing
arrangement and is configured to displace a fluid medium from the
pump inlet for discharge via the pump outlet.
[0010] Briefly, the object of the present invention is achieved in
a barrier and lubrication fluids pressure regulation system for a
subsea motor and pump module that is operable for displacement of a
pumped medium from a pump suction side to a pump discharge side,
the pressure regulation system comprising: [0011] a lubrication
fluid circuit in flow communication with a hydraulic fluid supply
via a first pressure reducing regulator [0012] a barrier fluid
circuit in flow communication with the hydraulic fluid supply via a
second pressure reducing regulator, wherein [0013] the first
pressure reducing regulator is configured to reduce the supply
fluid pressure in response to the pumped medium pressure at the
suction side or at the discharge side of the pump, and [0014] the
second pressure reducing regulator is configured to reduce the
supply fluid pressure in response to the output pressure of the
first pressure reducing regulator.
[0015] A system according to the invention provides immediate
response to any change in the pumped medium pressure, as well as a
simple and robust solution which continuously maintains a
predetermined pressure difference between the barrier and
lubrication fluid circuits and which at all times keeps the circuit
pressures in balance with the pressure of the pumped medium.
[0016] Preferably, each of the first and second pressure reducing
regulators are dome-loading regulators with adjustable bias set to
deliver an output pressure exceeding the dome loading pressure
within a range of 2-10 bar. The output pressure of these regulators
may typically be set to exceed the dome loading pressure with about
5 bar.
[0017] The pumped medium pressure is preferably applied to the dome
of the first pressure reducing regulator via a diaphragm, or via a
pressure compensator, arranged to separate the fluids in a pilot
circuit connecting the first pressure reducing regulator with the
pumped medium at the suction side or at the discharge side of the
pump.
[0018] The embodiment provides immediate response to pressure
variations in the pumped medium on the suction side or on the
discharge side of the pump, while avoiding intrusion of process
fluids, sea water and particulate matter into the pump lubrication
circuit.
[0019] Optionally, the pumped medium pressure may also be applied
via a pilot circuit to the dome of a third pressure reducing
regulator arranged in the hydraulic fluid supply upstream of the
first and second pressure reducing regulators. This optional third
pressure reducing regulator can be set to deliver an output
pressure exceeding its dome loading pressure within the order of
20-50 bar. The output pressure of this regulator may typically be
set to exceed the dome loading pressure with about 30 bar.
[0020] The embodiment improves reliability and service life of the
first and second pressure reducing regulators by reducing the load
applied from the supply fluid pressure, which may range to an order
of about 500 bar, e.g. The optional pressure reducing regulator
constitutes a stepwise reduction from the supply fluid pressure to
a pressure level that exceeds the pumped medium pressure
sufficiently for an adequate response to changes in the medium
pressure.
[0021] However, in order to avoid interruption of operation caused
by excessive pressure peaks or pressure build-up in the circuits,
each of the barrier fluid circuit and the lubrication fluid circuit
will be arranged to communicate with the pumped medium flow at the
pump inlet or outlet via respective pressure controlled pressure
relief regulators opening into the pilot circuit. These pressure
relief regulators can be realized as dome-loaded back pressure
regulators that are normally effective to reduce and vent the
pressure in the barrier and lubrication fluid circuits typically
during system start-up. A secondary function of the pressure
controlled pressure relief regulators is to serve as safety relief
valves.
[0022] More specifically, the pressure relief regulator in the
lubrication fluid circuit can be a dome-loading back pressure
regulator responsive to the pumped medium pressure at the suction
side or at the discharge side of the pump. The pressure relief
regulator in the barrier fluid circuit can be a dome-loading back
pressure regulator responsive to the output pressure of the first
pressure reducing regulator. Each of the back pressure regulators
is set to open for dumping hydraulic fluid into the pilot circuit
if the pressure in the lubrication fluid circuit or in the barrier
fluid circuit, respectively, exceeds the dome loading pressure for
the subject regulator by a preset amount of pressure which is
higher than the output pressures of the first and second pressure
reducing regulators. The output pressure of these regulators may
typically be set to exceed the dome loading pressure with about 8
bar. As indicated above, the pressure relief regulators can also be
seen as ultimate safety relief valves for the circuitry.
[0023] The pressure reducing regulators, as well as the back
pressure regulators, may each be associated with a motor drive
which is operable for setting the bias and thereby the pressure
level of the subject regulator. The embodiment permits remote
control and adjustment of flows and pressures from a topside
facility.
[0024] In another aspect the present invention relates to a
pressure regulation unit comprising: [0025] a pressure vessel
arranged to be exposed to surrounding seawater, the pressure vessel
housing a volume of hydraulic fluid and being hydraulically
connectable to a lubrication fluid circuit in a subsea motor and
pump module; [0026] a first pressure reducing regulator arranged in
the pressure vessel, and configured to regulate a fluid flow from
an external hydraulic fluid supply into the pressure vessel
interior; [0027] a second pressure reducing regulator arranged in
the pressure vessel, and configured to regulate a fluid flow
between the external hydraulic fluid supply and a barrier fluid
circuit in the subsea motor and pump module, [0028] wherein the
output flow of the first pressure reducing regulator controls the
internal pressure of the pressure vessel, and the output flow of
the second pressure reducing regulator is responsive to the
internal pressure of the pressure vessel.
[0029] Preferably, the first pressure reducing regulator is
configured to control the internal pressure in the pressure vessel
by reducing the pressure of supplied hydraulic fluid in response to
the pumped medium pressure at a suction side or at a discharge side
of the pump, which is communicated to the first pressure reducing
regulator via a pilot line extended into the pressure vessel.
[0030] The pressure vessel may further comprise: [0031] a flow line
connection that provides hydraulic fluid flow from a topside
(offshore or onshore) hydraulic fluid supply; [0032] a flow line
connection via which pumped medium pressure is communicated from
the suction side or the discharge side of the pump to the first
pressure reducing regulator; [0033] a flow line connection via
which barrier fluid is supplied to the motor from the second
pressure reducing regulator; [0034] a flow line connection via
which lubrication fluid is supplied to the pump from the pressure
vessel interior, and a flow line connection via which hydraulic
fluid can be dumped into the pumped medium at the suction side or
at the discharge side of the pump.
[0035] Without being limited to any specific type or model of motor
and pump module, the barrier fluid and lubrication system and
pressure regulating unit of the present invention is advantageously
applied to a pump equipped with a twin-screw rotor, and the
lubrication circuit is arranged to supply oil to pump bearings, as
well as to timing gears that are installed in the pump for
synchronizing the rotation of the rotors.
SHORT DESCRIPTION OF THE DRAWINGS
[0036] In the following, preferred embodiments of the invention
will be described in more detail with reference made to the
accompanying, schematic drawings, of which
[0037] FIG. 1 is a diagram of the barrier and lubrication fluids
pressure regulation system for a subsea motor and pump module,
and
[0038] FIG. 2 is a schematic view of a pressure regulation unit for
a subsea motor and pump module.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0039] In the drawing of FIG. 1, reference number 1 refers to a
subsea motor and pump module comprising a motor that is encased in
a pressurized, water tight enclosure or motor housing 2, as well as
a pump rotor assembly encased in a pump housing 3. The motor
driving the pump is typically an electric motor, although other
drive units such as hydraulic motors or turbines may alternatively
be employed.
[0040] The pump rotor is configured for displacement of a pumped
medium, typically a multi-phase production fluid from a reservoir
below the sea floor, which enters the pump via a pump inlet 4 to be
discharged via a pump outlet 5, as illustrated by an arrow F. The
pump rotor is drive-connected to the motor, and the pump interior
is hydraulically separated from the pressurized (typically
oil-filled) motor housing by means of a seal arrangement 6 which
seals against the outside of a rotary shaft (indicated by reference
number 7) by which the pump rotor is drive-connected to the motor.
The pump bearings are separated from the pump medium by seal
arrangements 8 and 9 at both ends of the pump. The pump rotor is
journalled in bearing arrangements (not shown) in the pump housing
3.
[0041] Since the invention is not limited to any specific type or
model of motor and pump assembly, but indeed can be applied to
various motor and pump configurations which are involved in the
transport of a hydrocarbon production fluid and operated by the
skilled person, the internals of the motor and pump module 1 need
not be discussed in detail.
[0042] Hydraulic fluid is supplied to the motor and pump module 1
via lines 10, 11, 12 from a hydraulic fluid supply (indicated by
reference n umber 13), which may be located topside on a surface
platform, or on a land based host facility, e.g. All other
components of the barrier and lubrication fluids pressure
regulation system are advantageously installed subsea.
[0043] A pressure accumulator may be arranged in the fluid line 10
to deliver hydraulic fluid at an operating pressure, which may be
in the order of about 500 bar, e.g. The hydraulic fluid is supplied
via pressure reducing regulators 14 and 15, the output flow of
which is automatically adjusted concurrently with a change in fluid
pressure in the barrier fluid and lubrication system. The pressure
changes are caused by varying pressure in the pumped medium, and by
leakage of hydraulic fluid through the sealing arrangements as
illustrated by arrows L in FIG. 1.
[0044] The regulators 14 and 15, as well as any other pressure
reducing regulator discussed below, may be any available type of
dome loading pressure regulator designed for use at full sea depth,
and which operates at the subject system pressures. The regulators
are additionally equipped with an adjustable spring bias by which a
regulator set point can be varied above the dome loading pressure.
The regulators may advantageously be equipped with an electric (or
hydraulic) motor drive (not illustrated) for remote adjustment of
the regulator set point.
[0045] More precisely, the regulator 14 serves for refilling and
pressurizing a motor barrier fluid circuit acting as a barrier at
the interface between the motor and pump housings 2 and 3, and
typically also providing lubrication and cooling fluid for the
motor. In FIG. 1, line 11 connects the barrier fluid circuit with
the hydraulic fluid supply via the regulator 14. Line 16 opens for
hydraulic fluid from the regulator 14 into the motor housing
interior. The barrier fluid circuit is indirectly connectable for
flow communication with the pump inlet 4 via lines 17 and 18 which
serve for dumping hydraulic fluid from the motor barrier fluid
circuit via a pressure relief regulator valve 19, in case of a rise
of the fluid pressure to a too high level. The fluid pressure in
lines 16 and 17 of, the motor barrier fluid circuit is controlled
by the output pressure of the regulator 14, which is responsive to
the fluid pressure in a line 20 that is applied to the dome of the
pressure reducing regulator 14. The pressure reducing regulator 14
is arranged to open when downstream pressure in the barrier fluid
circuit falls below the pressure in line 20, which is the
lubrication fluid pressure as will be understood from below, by a
preset amount.
[0046] Similarly, the regulator 15 serves for refilling and
pressurizing a pump lubrication fluid circuit providing lubrication
fluid to pump rotor bearings and, if appropriate, to timing gears
which effect rotor synchronization in a twin-screw rotor pump. Line
12 connects the lubrication fluid circuit with the hydraulic fluid
supply via the regulator 15. Lines 22 and 23 open for hydraulic
fluid from the regulator 15 into the pump housing. The lubrication
fluid circuit is indirectly connectable for flow communication with
the pump inlet via lines 24 and 25 which serve for dumping
hydraulic fluid from the motor barrier fluid circuit via a pressure
relief regulator valve 26, in case of a rise of the fluid pressure
to a too high level. The fluid pressure in lines 20, 22, 23 and 24
of the lubrication fluid circuit is controlled by the output
pressure of the regulator 15, which is responsive to the fluid
pressure in a line 27 that is applied to the dome of the pressure
reducing regulator 15. The pressure reducing regulator 15 is
arranged to open when downstream pressure in the lubrication fluid
circuit falls below the pressure in line 27 by a preset amount.
[0047] More precisely, the dome loading pressure applied to the
regulator 15 via line 27 is the pressure of the pumped medium,
which is communicated from the suction side of the pump to the
regulator 15 via a pilot line 28. A separating diaphragm 29 is
preferably incorporated in the pilot line to effect isolation of
the pumped medium from a hydraulic fluid that is included in a
pilot circuit comprising lines 27, 30 and 31. In this connection it
should be clarified, that the pumped medium pressure communicated
to the system can either be the pumped medium pressure at the
suction side or at the discharge side of the pump. The choice of
side is determined by flow direction through the pump and location
of motor/pump seals.
[0048] In result, the fluid pressure in the barrier fluid circuit
is in this way balanced relative to the pressure in the lubrication
fluid circuit, and a constant pressure difference between the two
circuits is maintained at varying actual pressures in the
lubrication fluid circuit. The pressure differential is determined
by the bias of the pressure reducing regulator 14 which may be
adjustable. A pressure differential of typically about 5 bar (72.5
psi) is in most cases considered appropriate.
[0049] In addition, the fluid pressures in the barrier and
lubrication fluid circuits are together balanced relative to the
pressure of the pumped medium. The pressure level is set by the
medium pressure at the pump inlet which is added to the preset bias
of the second pressure reducing regulator 15 and applied to the
fluid in the lubrication fluid circuit. The pressure difference
between the pumped medium and circuit pressures is determined by
the bias of the regulator 15, which may be adjustable. A pressure
differential of typically about 5 bar (72.5 psi) is in most cases
considered appropriate.
[0050] With respect to the sequence of pressure regulation effected
by the regulators 14 and 15 arranged in a series, the regulator 15
can be regarded as a first pressure reducing regulator and the
regulator 14 can be regarded as a second pressure reducing
regulator.
[0051] In order to manage a rise of pressure in any of the barrier
and lubrication fluid circuits to a too high level, hydraulic fluid
can be dumped from the circuits into the pilot line 28 via the
pressure relief regulator valves 19 and 26. The pressure relief
regulator valves are advantageously realized in the form of dome
loading back pressure regulators. The regulator 19 is responsive to
the lubrication fluid circuit pressure in line 20 which is
communicated to the dome of the regulator 19, which is set to open
when upstream pressure in the barrier fluid circuit 17 exceeds the
lubrication fluid pressure in line 20 by a preset amount.
Similarly, the regulator 26 is responsive to the pumped medium
pressure which is communicated to the dome of the regulator 26 via
line 31, and the regulator 26 is set to open when upstream pressure
in the lubrication fluid circuit 24 exceeds the pumped medium
pressure by a preset amount. In both cases, the regulators may be
set to open at a pressure difference of about 8 bar.
[0052] Likewise in order to manage a sudden critical situation,
such as hydrocarbon detection external to the pump e.g., an
isolation valve 32 is preferably arranged to cut pressure
communication between the pumped medium and the barrier and
lubrication fluid circuits.
[0053] In order to avoid gas accumulation in the pilot line 28 or
in the housing of the diaphragm 29, which could cause misreading of
the actual pumped medium pressure due to compression or hydrate
formation, a pipe loop 33 can be included in the pilot line to
effect capture of a gas phase portion of a multi-phase production
fluid.
[0054] Further, in order to avoid hydrate formation and
solidification of gaseous and liquid components of a multi-phase
production fluid in the pilot line 28, the pilot line as well as
the fluid dumping lines 18 and 25 may be associated with a heating
trace 34 which is effective for maintaining fluid temperature in
these lines above a solidification temperature for the fluid
components.
[0055] A dome loading pressure reducing regulator 35 may optionally
be arranged in the hydraulic fluid supply 10 upstream of the first
and second pressure reducing regulators 14 and 15. The regulator 35
is responsive to the pumped medium pressure which is communicated
to the dome of the regulator 35 via the pilot circuit line 30. The
regulator 35 reduces downstream pressure in the hydraulic fluid
supply lines 11 and 12, and includes an adjustable spring bias by
which the regulator 35 can be preset to deliver an output pressure
exceeding its dome loading pressure within the order of 20-50 bar,
preferably exceeding its dome loading pressure with about 30
bar.
[0056] In order to complete the description of the set up of FIG. 1
it should also be mentioned that an external cooler 21 may be
incorporated in the motor barrier fluid circuit.
[0057] With reference to FIG. 2 a pressure regulation unit for the
subsea motor and pump module 1 will now be explained. In FIG. 2,
the system components already discussed with reference to FIG. 1
are referenced by the same reference numbers as those used in FIG.
1. Since the operation and interaction between the system
components are also the same as previously discussed, these need no
further explanation with reference to FIG. 2.
[0058] In the embodiment of FIG. 2, however, the pressure
regulating components and associated fluid circuitry are housed in
hydraulic fluid inside a pressure vessel 36. The pressure vessel 36
is configured to be located subsea and can be arranged for standing
on the sea floor or arranged to be coupled to, or integrated with,
the motor and pump module.
[0059] The pressure in pressure vessel 36 is controlled by the
pressure reducing regulator 15 which provides flow communication
between an external hydraulic fluid supply 10 and the interior of
pressure vessel 36. The volume of hydraulic fluid in pressure
vessel 36 is in flow communication with the pump seals and bearings
via fluid flow lines 22 or 23 of the lubrication fluid circuit, in
which the pressure is determined by the internal pressure of
pressure vessel 36. The same pressure is applied to the dome of the
pressure reducing regulator 14 which supplies hydraulic fluid from
the external fluid supply to the motor via lines 11, 16 and 17 of
the barrier fluid circuit. Pumped medium pressure is communicated
to the regulator 15 via a pilot pressure line 30 that is introduced
through the wall of the pressure vessel, connecting to the pilot
pressure circuit 27, 30 and 31 inside the pressure vessel. A supply
fluid pressure reducing regulator 35 as previously discussed may
additionally be arranged inside the pressure vessel 36. Pressure
relief regulator valves in the form of back pressure reducing
regulators 19 and 26 may be arranged as illustrated to dump
hydraulic fluid via a common flow line 18 or 25.
[0060] A coupling interface to the motor and pump module can be
reduced to a low number of flow line connections such as: a flow
line connection via which pumped medium pressure is communicated
from the suction side of the pump to a first pressure reducing
regulator 15; a flow line connection via which barrier fluid is
supplied to the motor from a second pressure reducing regulator 14;
a flow line connection via which lubrication fluid is supplied to
the pump from the pressure vessel interior, and a flow line
connection via which hydraulic fluid can be dumped into the pumped
medium at the suction side of the pump. Naturally, one connection
that provides fluid flow from a topside hydraulic fluid supply is
additionally required. An electrical interface may also be included
in the pressure regulator unit, through which electrical power can
be supplied to regulator motor drives, if appropriate, and via
which the regulator settings and/or fluid circuit pressures can be
returned to a control logic that is monitored and operated from a
topside location.
[0061] The pressure vessel 36 provides a compact unit configured
for controlling the barrier and lubrication fluid pressures in a
subsea motor and pump module. Except for the necessary connections,
the pressure regulating unit may be given a non-complicated,
box-like design, which is easy to handle and easy to install at a
subsea production site. In order to allow for disconnection by a
Remotely Operated Vehicle (ROV) so as to be retrieved to surface
for replacement and/or repair, the pressure vessel advantageously
comprises a base plate with automatic hydraulic couplings allowing
the unit to be installed onto a mounting base arranged on the
motor/pump module.
[0062] The invention is of course not in any way restricted to the
embodiments described above. On the contrary, many possibilities to
modifications thereof will be apparent to a person with ordinary
skill in the art without departing from the basic idea of the
invention such as defined in the appended claims.
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