U.S. patent application number 13/806550 was filed with the patent office on 2013-05-30 for motor and pump barrier fluids pressure regulation system in a subsea motor and pump module.
This patent application is currently assigned to VETCO GRAY SCANDINAVIA AS. The applicant listed for this patent is Ove S.ae butted.le. Invention is credited to Ove S.ae butted.le.
Application Number | 20130136634 13/806550 |
Document ID | / |
Family ID | 45370907 |
Filed Date | 2013-05-30 |
United States Patent
Application |
20130136634 |
Kind Code |
A1 |
S.ae butted.le; Ove |
May 30, 2013 |
MOTOR AND PUMP BARRIER FLUIDS PRESSURE REGULATION SYSTEM IN A
SUBSEA MOTOR AND PUMP MODULE
Abstract
A motor and pump barrier fluids pressure regulation system for a
subsea motor and pump module comprising a motor and a pump is
disclosed. The regulation system comprises a motor barrier fluid
circuit hydraulically separating the motor from the pump, and a
pump barrier fluid circuit hydraulically separating an internal
structure of the pump from a pumped medium, wherein the fluid flow
and pressure in each of the motor barrier fluid circuit and the
pump barrier fluid circuit are controlled by pressure controlled
on/off valves arranged in each circuit, the pressure controlled
on/off valves being individually controllable in response to a
detected difference in pressure between the pumped medium, on a
suction side of the pump or on a discharge side of the pump, and
the fluid in the motor barrier fluid circuit and the pump barrier
fluid circuit.
Inventors: |
S.ae butted.le; Ove;
(Billingstad, NO) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
S.ae butted.le; Ove |
Billingstad |
|
NO |
|
|
Assignee: |
VETCO GRAY SCANDINAVIA AS
Sandvika
NO
|
Family ID: |
45370907 |
Appl. No.: |
13/806550 |
Filed: |
June 22, 2010 |
PCT Filed: |
June 22, 2010 |
PCT NO: |
PCT/IB2011/001388 |
371 Date: |
February 15, 2013 |
Current U.S.
Class: |
417/423.3 |
Current CPC
Class: |
F04D 13/062 20130101;
F04D 13/086 20130101; F04D 13/10 20130101; F04C 11/008 20130101;
F04C 13/008 20130101; F04C 14/28 20130101; F04C 2/16 20130101; F04C
2270/185 20130101 |
Class at
Publication: |
417/423.3 |
International
Class: |
F04D 13/08 20060101
F04D013/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 22, 2010 |
NO |
20100904 |
Claims
1. A motor and pump barrier fluids pressure regulation system for a
subsea motor and pump module comprising a motor and a pump, the
regulation system comprising: a motor barrier fluid circuit
hydraulically separating the motor from the pump, wherein the motor
barrier fluid circuit comprises: a motor barrier fluid supply
section configured to supply motor barrier fluid to the motor from
a hydraulic fluid supply; and a motor barrier fluid relief section
configured to discharge the motor barrier fluid from the motor to a
pumped medium; a pump barrier fluid circuit hydraulically
separating an internal structure of the pump from the pumped
medium, wherein the pump barrier fluid circuit comprises: a pump
barrier fluid supply section configured to supply pump barrier
fluid to the pump from the hydraulic fluid supply; and a pump
barrier fluid relief section discharging configured to discharge
the pump barrier fluid from the pump to the pumped medium, wherein
the fluid flow and pressure in each of the motor barrier fluid
circuit and the pump barrier fluid circuit are controlled by
pressure controlled on/off valves arranged in each circuit, the
pressure controlled on/off valves being individually controllable
in response to a detected difference in pressure between the pumped
medium on a suction side of the pump or on a discharge side of the
pump, and the fluid in the motor barrier fluid circuit and the pump
barrier fluid circuit.
2. The regulation system of claim 1, wherein each of the pressure
controlled on/off valves is arranged in series with a flow
restriction of a fixed orifice diameter.
3. The regulation system of claim 1, wherein the motor barrier
fluid circuit further a first pressure control unit, wherein the
pressure controlled on/off valve in the motor barrier fluid circuit
is controllable by the first pressure control unit in response to
differential pressures received in the first pressure control unit
from a corresponding differential pressure transmitter configured
to monitor the differential pressure between the pumped medium and
the motor barrier fluid circuit, and wherein the pump barrier
fluid-circuit further comprises a second pressure control unit,
wherein the pressure controlled on/off valves in the pump barrier
fluid circuit is controllable by the associated pressure control
unit in response to differential pressures received in the second
pressure control unit from a corresponding differential pressure
transmitter configured to monitor the differential pressure between
the pumped medium and the pump barrier fluid circuit.
4. The regulation system of claim 3, wherein at least one of the
motor barrier fluid supply section, the pump barrier fluid supply
section, the motor barrier fluid relief section and the pump
barrier fluid relief section comprises a set of pressure controlled
on/off valves comprising at least a first valve and a second valve,
wherein the first valve and the second valve are arranged in
parallel to feed hydraulic fluid through the respective barrier
fluid circuit, wherein the first valve and the second valve are
each responsive to the monitored differential pressure, and wherein
the set of pressure controlled on/off valves are individually
responsive to separate ranges of differential pressure between the
respective barrier fluid circuit and the pumped medium.
5. The regulation system of claim 4, wherein the first valve is a
first motor barrier fluid supply valve configured to open for
hydraulic fluid flow in response to a differential pressure at or
below about 10 bar, and wherein the second valve is a second motor
barrier fluid supply valve configured to open for hydraulic fluid
flow in response to a differential pressure at or below about 9.5
bar.
6. The regulation system of claim 4, wherein the first valve is a
first pump barrier fluid supply valve configured to open for
hydraulic fluid flow in response to a differential pressure at or
below about 5 bar, and wherein the second valve is a second pump
barrier fluid supply valve configured to open for hydraulic fluid
flow in response to a differential pressure at or below about 4.5
bar.
7. The regulation system of claim 4, wherein the first valve is a
first motor barrier fluid relief valve configured to open for
hydraulic fluid flow in response to a differential pressure above
about 10.5 bar, and the second valve is a second motor barrier
fluid relief valve configured to open for hydraulic fluid flow in
response to a differential pressure at or above about 11 bar.
8. The regulation system of claim 4, wherein the first valve is a
first pump barrier fluid relief valve configured to open for
hydraulic fluid flow in response to a differential pressure above
about 5.5 bar, and the second valve is a second pump barrier fluid
relief valve configured to open for hydraulic fluid flow in
response to a differential pressure at or above about 6 bar.
9. The regulation system of claim 5, wherein the first valve is
configured for lower flow rates ranging down to about 0.3 l/min,
and wherein the second valve is configured for higher flow rates
ranging up to about 100 l/min.
10. The regulation system of claim 9, further comprising a first
restriction orifice downstream of the first valve configured for
lower flow rates ranging down to about 0.3 l/min, and a second
restriction orifice downstream of the second valve configured for
higher flow rates ranging up to about 100 l/min
11. The regulation system of claim 1, further comprising a
differential pressure transmitter configured to monitor the
pressure difference between the motor barrier fluid circuit and the
pump barrier fluid circuit, and to transmit readings to a pressure
control unit of the motor barrier fluid circuit.
12. The regulation system of claim 11, wherein the motor barrier
fluid circuit is controlled by a first set of pressure controlled
on/off valves being individually controllable in response to the
monitored difference in pressure between the motor barrier fluid
and the pump barrier fluid.
13. The regulation system of claim 12, wherein the pump barrier
fluid circuit is controlled by a second set of pressure controlled
on/off valves, and wherein the pressure differential set points of
the first set of pressure controlled on/off valves are equal to the
pressure differential set points of the second set of pressure
controlled on/off.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This is a national stage application under 35 U.S.C.
.sctn.371(c) prior-filed, co-pending PCT patent application serial
number PCT/IB2011/001388, filed on Jun. 20, 2011, which claims
priority to Norwegian Patent Application No. 20100904, filed on
Jun. 22, 2010, the entire contents of which are incorporated herein
by reference.
BACKGROUND OF THE INVENTION
[0002] Embodiments of the present invention relate generally to
subsea equipment involved in the transport of process fluids
generated in subsea hydrocarbon production. More specifically,
embodiments of the present invention relate to a system that is
designed for the management of barrier and lubrication fluid
pressures in a subsea motor and pump module.
[0003] 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, for example, the 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.
[0004] Screw rotor pumps are often used for the purpose of pumping
a multiphase fluid in subsea production. 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 is hydraulically separated
from the pump 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.
[0005] For purposes of lubrication and cooling, as well as for
preventing intrusion of sea water and pumped medium into the
structures of a subsea motor and pump module, hydraulic fluid needs
to be supplied to the motor/pump module. In this connection,
barrier fluid and lubrication fluid are basically different
definitions of the same type of fluid applied to protect the
internals of the motor/pump module.
[0006] Accordingly, a motor housing that protects the motor from
the ambient sea and from the medium in the pump is to be maintained
at a pressure above the internal pressure of the pump, this way
acting also as a barrier which prevents intrusion of process fluid
and particles into the motor housing via the seal and bearing
arrangement. As a 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.
[0007] Likewise, hydraulic fluid is typically supplied also to the
pump for lubrication of its internal structure, such as pump rotor
bearings, seals and timing gears. The pressure in the pump's
lubrication fluid circuit is thus to be maintained above the
pressure of the medium that is displaced through 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 the external
supply of hydraulic fluid.
[0008] 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 to
connect them in a driving relationship. 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 pumped medium, respectively.
[0009] Conventionally, motor barrier and pump barrier fluids are
supplied via an umbilical, and leakage compensation as well as
pressure control is managed from the host facility. As subsea
hydrocarbon production sites are increasingly installed and
operated at increasing depths and step-out distances, the response
times in lubrication and cooling systems increase correspondingly.
As a consequence, there is a rising need for a motor and pump
barrier fluids pressure regulation system that operates with
instant response to a change in pressures in the motor and pump
module and which provides increased reliability in operation.
BRIEF SUMMARY OF THE INVENTION
[0010] Embodiments of the present invention provide a motor and
pump barrier 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.
[0011] Embodiments of the present invention provide a motor and
pump barrier fluids pressure regulation system in a subsea motor
and pump module, the system having an inherent capability to adapt
to pressure changes in the pumped medium. Embodiments of the
present invention further provide a motor and pump barrier 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. Embodiments of the
present invention provide a motor and pump barrier fluids pressure
regulation system wherein a preset pressure differential between a
motor barrier fluid circuit and a pump barrier fluid circuit is
automatically maintained at all times, and balanced towards the
medium pressure.
[0012] The motor and pump barrier fluids pressure regulation system
according to embodiments of the present invention may 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 via a seal
arrangement and is configured to displace a fluid medium from the
pump inlet for discharge via the pump outlet.
[0013] According to an embodiment of the present invention, there
is provided a motor and pump barrier fluids pressure regulation
system for a subsea motor and pump module. The regulation system
comprising a motor barrier fluid circuit hydraulically separating
the motor from the pump, wherein the motor barrier fluid circuit
comprises a motor barrier fluid supply section configured to supply
motor barrier fluid to the motor from a hydraulic fluid supply
motor barrier fluid relief section configured to discharge the
motor barrier fluid from the motor to a pumped medium. The
regulation system further comprises a pump barrier fluid circuit
hydraulically separating an internal structure of the pump from the
pumped medium wherein the pump barrier fluid circuit comprises a
pump barrier fluid supply section configured to supply pump barrier
fluid to the pump from the hydraulic fluid supply, and a pump
barrier fluid relief section configured to discharge the pump
barrier fluid from the pump to the pumped medium. The fluid flow
and pressure in each of the motor barrier fluid circuit and the
pump barrier fluid circuit are controlled by pressure controlled
on/off valves arranged in each circuit, the pressure controlled
on/off valves being individually controllable in response to a
detected difference in pressure between the medium on a suction
side of the pump or on a discharge side of the pump, and the fluid
in the motor barrier fluid circuit and pump barrier fluid
circuit.
[0014] A system according to an embodiment of the present 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 motor and pump barrier fluid circuits, and which at all times
keeps the circuit pressures in balance with the pressure of the
pumped medium.
[0015] Because the valves can be located close to the consumer,
i.e. the motor/pump assembly, and without delay in operation, the
pressure regulation system can be used without modification
regardless of pump tie-back distance and water depth.
[0016] The pressure regulation system according to an embodiment
enables the operator to maintain a steady supply pressure through
an umbilical.
[0017] Embodiments of the present invention can be applied to a
pressure regulation system wherein the motor barrier fluid is at
all times maintained at a higher pressure than the pump barrier
fluid, and the pump barrier fluid is at all times maintained at a
higher pressure than the process medium in the pump. The pressure
regulation system according to an embodiment of the present
invention is operative either for raising the pressure in the motor
barrier fluid circuit or for lowering the pressure in the pump
barrier fluid circuit. The pressure regulation system according to
an embodiment of the present invention can also be extended to
multiple pressure levels, i.e. by adding an intermediate pressure
level between the motor barrier fluid and the pump barrier
fluid.
[0018] In an embodiment, each pressure controlled on/off valve is
arranged in series with a flow restriction of fixed orifice
diameter which may be realized, alternatively, through a manually
controllable valve whose opening position is preset before
installation.
[0019] The pressure regulation system is based on subsea on/off
valves for supply and relief of barrier fluids. Suitable types of
valves may be, but are not limited to, solenoid valves or
directional control valves. Flow orifice downstream or upstream
valve determines flow capacity when valve is open.
[0020] According to an embodiment, each of the motor and pump
barrier fluid circuits comprises a respective pressure control
unit, and the on/off valves in each barrier fluid circuit are
individually controllable from the associated pressure control unit
in response to differential pressures received in the pressure
control unit from a corresponding differential pressure transmitter
monitoring the differential pressure between the pumped medium and
the respective one of the motor barrier fluid circuit or the pump
barrier fluid circuit.
[0021] The embodiment provides valve position indication and
operator control of each valve. The valves are operated based on
differential pressure between barrier fluid and process medium.
This can either be with reference to suction side or discharge side
of pump--whichever side of the pump and motor to which the barrier
fluid is connected. Valves are operated from the control system
based on readings by differential pressure transmitters. The
differential pressure set point can either be a single value, for
example, 10 bar, or it can be an exemplary range, such as 5 to 15
bar. The latter is achieved by closing the supply valve(s) when
differential pressure has reached 15 bar, and opening supply
valve(s) when pressure differential has again reached 5 bar.
[0022] The pressure regulation system according to an embodiment of
the present invention enables the operator full control of valves
and valve position, and the pressure set-point can be varied by the
operator at the push of a button.
[0023] Leakage through seals in the motor and pump module can vary
and may be low or high. Low in the sense that an on/off valve in
the supply circuit is required to open only rarely, such as once or
twice a day, or high in the sense that a supply valve of low
capacity in combination with a flow restriction of fixed orifice
diameter will be in open position most of the time.
[0024] Also, pumps can experience transient conditions where the
differential pressure between the pump's reference side and the
barrier fluid pressure varies independent of the leakage rate.
[0025] Accumulators can be incorporated in the circuits to prevent
the valves from operating frequently, and can provide added time
between valve operations. However, the pressure regulation system
can be designed to operate sufficiently without accumulators.
[0026] To this purpose, at least one of the barrier fluid supply
and barrier fluid relief sections, according to an embodiment,
comprises a set of pressure controlled on/off valves, including at
least a first and a second valve, which are arranged in parallel to
feed hydraulic fluid through the barrier fluid circuit, and which
are each responsive to the differential pressure, and further
wherein said at least two pressure controlled on/off valves are
individually responsive to separate ranges of differential pressure
between the barrier fluid circuit and the pumped medium.
[0027] In an embodiment, in a set of first and second pressure
controlled on/off supply valves the first motor barrier fluid
supply valve may be set to open for hydraulic fluid flow in result
of a differential pressure at or below 10 bar, and the second motor
barrier fluid supply valve be set to open for hydraulic fluid flow
in result of a differential pressure at or below 9.5 bar.
[0028] Correspondingly, in a set of first and second pressure
controlled on/off supply valves the first pump barrier fluid supply
valve may be set to open for hydraulic fluid flow in result of a
differential pressure at or below 5 bar, and the second pump
barrier fluid supply valve be set to open for hydraulic fluid flow
in result of a differential pressure at or below 4.5 bar.
[0029] Likewise in a set of first and second pressure controlled
on/off relief valves, the first motor barrier fluid relief valve
may be set to open for hydraulic fluid flow in result of a
differential pressure above 10.5 bar, and the second motor barrier
fluid relief valve be set to open for hydraulic fluid flow in
result of a differential pressure at or above 11 bar.
[0030] Also in a set of first and second pressure controlled on/off
relief valves, the first pump barrier fluid relief valve may be set
to open for hydraulic fluid flow in result of a differential
pressure above 5.5 bar, and the second pump barrier fluid relief
valve be set to open for hydraulic fluid flow in result of a
differential pressure at or above 6 bar.
[0031] In some embodiments, the first valve in a parallel set of
first and second on/off valves is sized for lower flow rates
ranging down to about 0.3 1/min, and the second valve is sized for
higher flow rates ranging up to about 100 l/min.
[0032] Specifically, the restriction orifice arranged downstream of
the first valve may be sized for lower flow rates ranging down to
about 0.3 l/min, and the restriction orifice downstream the second
valve may be sized for higher flow rates ranging up to about 100
l/min.
[0033] A differential pressure transmitter may alternatively be
arranged to monitor the pressure difference between the motor
barrier fluid circuit and the pump barrier fluid circuit, and to
transmit its readings to the pressure control unit of the motor
barrier fluid circuit. In such embodiment, the motor barrier fluid
circuit is controlled by pressure controlled on/off valves that are
individually controllable in response to monitored difference in
pressure between the motor barrier fluid and the pump barrier
fluid. The pressure differential set points of the motor barrier
fluid valves are then typically equal to the pressure differential
set points of the pump barrier fluid valves.
[0034] Without being limited to any specific type or model of motor
or pump, the motor and pump barrier fluids pressure regulating
system according to an embodiment of the present invention is
applied in a subsea motor and pump module comprising an electric
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 drive-connected to the motor and configured to
displace a fluid medium from the pump inlet for discharge via the
pump outlet.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] The accompanying drawings illustrate exemplary embodiments,
wherein:
[0036] FIG. 1 is a schematic drawing of a system according to an
embodiment of the present invention; and
[0037] FIG. 2 is a schematic drawing of a system according to an
embodiment of the present invention.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION
[0038] In the following, embodiments of the present invention will
be described in more detail with reference made to the accompanying
diagrammatic drawings, FIGS. 1 and 2. In the drawings, a subsea
motor and pump module comprises a motor/pump assembly 1 to which
motor barrier fluid and pump barrier fluid are supplied from an
external hydraulic fluid supply.
[0039] Since the present invention is not limited to any specific
type or model of motor/pump assembly, but indeed can be applied to
various motor/pump configurations involved in the transport of a
process fluid from subsea hydrocarbon production, and which are
familiar to the skilled person, the internals of the motor/pump
assembly 1 need not be discussed in detail. In general, the
motor/pump assembly comprises a motor M that is encased in a
pressurized water tight enclosure or motor housing 2, as well as a
pump rotor assembly P 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 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
liquid-filled) motor housing by means of a seal and bearing
arrangement 6 which seals against the outside of a rotary shaft
(indicated at 7) by which the pump rotor is drive-connected to the
motor. The pump rotor is journalled in seal and bearing
arrangements 6 and 8 in the pump housing 3. Internally of the pump,
pump barrier fluid is typically circulated as indicated through the
dash dotted lines connecting the seal/bearing arrangements 6 and 8,
for lubrication of internal structures in the pump, such as
bearings, seals, timing gears if appropriate, etc.
[0041] Motor barrier fluid and pump barrier fluid is supplied to
the subsea motor and pump module from an external supply of
hydraulic fluid via feed line 9. The motor barrier fluid is
supplied to the motor housing via an on/off valve 10 connected in
series with a flow restriction 11 of fixed orifice diameter. The
on/off valve 10 is pressure controlled and operated in response to
the difference in pressure between the motor barrier fluid circuit
and the pumped medium. The pressures in the pumped medium are
continuously monitored and detected and returned to a pressure
control unit 12 that operates the on/off valve 10 between open and
closed states. The pressures are monitored and detected by means of
a pressure differential transmitter 13 inserted between the motor
barrier fluid circuit and the pumped medium on the suction side or
on the discharge side of the pump. The choice of side is determined
by flow direction through the pump and location of motor/pump
seals, as illustrated in FIG. 2.
[0042] Likewise, pump barrier fluid is supplied to the pump housing
via an on/off valve 14 connected in series with a flow restriction
15 of fixed orifice diameter. The on/off valve 14 is pressure
controlled and operated in response to the difference in pressure
between the pump barrier fluid circuit and the pumped medium. The
pressures in the pumped medium are continuously monitored and
detected and returned to a pressure control unit 16 that operates
the on/off valve 14 between open and closed states. The pressures
are monitored and detected by means of a pressure differential
transmitter 17 inserted between the pump barrier fluid circuit and
the pumped medium on the suction side or on the discharge side of
the pump.
[0043] The control logic in pressure control units 12 and 16 is set
to provide valve operation in immediate response to any change in
pressure of the pumped medium, and maintains a predetermined
pressure difference between them by refilling the barrier fluid
circuits via the pressure controlled on/off valves 10 and 14. The
illustrated embodiment provides immediate response to pressure
variations in the pumped medium on the suction side of the pump,
keeping the circuit pressures in balance with the pressure of the
pumped medium, this way effectively avoiding intrusion of process
fluids, sea water and particulate matter into the barrier fluid
circuits.
[0044] In an embodiment, as previously stated, the pressure
differential transmitters 13 and 17 may instead be connected to the
discharge side of the pump in dependence on, for example, flow
direction through the pump and the location of motor/pump seal
arrangements.
[0045] Sufficient supply of fluid to the barrier fluid circuits can
be accomplished by a corresponding setting of the control logic. As
an alternative to a more frequent valve operation in case of sudden
peaks in fluid leakage or pressure variation, additional barrier
fluid can be instantly supplied through a parallel arrangement of
pressure controlled on/off valves. To this purpose, a second
pressure controlled on/off valve 18 connected in series with a flow
restriction 19 of fixed orifice diameter is arranged in parallel
with on/off valve 10 and flow restriction 11 included in the motor
barrier fluid circuit. Correspondingly, a second pressure
controlled on/off valve 20 connected in series with a flow
restriction 21 of fixed orifice diameter is arranged in parallel
with on/off valve 14 and flow restriction 15 included in the pump
barrier fluid circuit.
[0046] Both first and second on/off valves arranged in parallel are
individually operated by the pressure control units 12 and 16,
respectively. Flow capacity through the valves in open state is
determined by the orifice diameter. According to an embodiment, the
first and second on/off valves in parallel arrangement are designed
for different flow capacities and pressure ranges. However,
embodiments of the present invention are not strictly limited to
the pressures/pressure ranges and flow rates stated above, and
those values are merely to be seen as examples.
[0047] Transient conditions in operation of the subsea motor and
pump module may also require the barrier fluid pressures to be
reduced in order to maintain a steady differential pressure. In
that case, a similar valve and orifice arrangement can be installed
to open for relief of barrier fluids to the pumped medium on the
suction side or on the discharge side of the pump.
[0048] To this purpose, the motor barrier fluid circuit comprises a
barrier fluid relief section 22, 23 in addition to the barrier
fluid supply section 10, 11 as described above. At least a first
pressure controlled on/off valve 22 is connected in series with a
flow restriction 23 of fixed orifice diameter, and operated by the
pressure control unit 12 for feeding barrier fluid into the pumped
medium in response to the readings of pressure differential
transmitter 13, which returns the pressure difference between the
motor barrier fluid and the pumped medium to the pressure control
unit 12. A second pressure controlled on/off valve 24 connected in
series with a flow restriction 25 of fixed orifice diameter can be
arranged in parallel with the first on/off valve 22 in the motor
barrier fluid relief section for increased flow capacity.
[0049] Correspondingly, the pump barrier fluid circuit comprises a
barrier fluid relief section 26, 27 in addition to the barrier
fluid supply section 14, 15 as described above. At least a first
pressure controlled on/off valve 26 is connected in series with a
flow restriction 27 of fixed orifice diameter, and operated by the
pressure control unit 16 for feeding barrier fluid into the pumped
medium in response to the readings of pressure differential
transmitter 17, which returns the pressure difference between the
pump barrier fluid and the pumped medium to the pressure control
unit 16. A second pressure controlled on/off valve 28 connected in
series with a flow restriction 29 of fixed orifice diameter can be
arranged in parallel with the first on/off valve 26 in the pump
barrier fluid relief section for increased flow capacity.
[0050] Likewise in correspondence with the barrier fluid supply
sections, valves in parallel arrangement in the barrier fluid
relief sections may be designed for different flow capacities and
pressure ranges.
[0051] Alternatively, a third pressure differential transmitter 30
may optionally be inserted between the motor and pump barrier fluid
circuits, to read the pressures therein and to return its readings
to the motor barrier pressure control unit 12. In this embodiment,
the pressure differential set points of the motor barrier fluid
valves 10, 22, 18, and 24 are typically equal to the pressure
differential set points of the pump barrier fluid valves 14, 20, 26
and 28.
[0052] Basically, the components which are incorporated in the
barrier fluids pressure regulation system are familiar to the
skilled person and need no further presentation. On/off valves
suitable for the purpose are for example solenoid operated
directional control valves (DCVs) which are normally used in subsea
hydraulic systems. The DCVs are electrically activated and can
either be of a mono-stable or bi-stable type, and of 2-port or
3-port configuration. The return/relief connection of the DCV can
be coupled to the suction side of the pump if the suction side
pressure is the reference for the differential pressure set points
in the barrier fluid system. Alternatively, the return/relief
connection can be coupled to the discharge side of the pump if the
discharge side pressure is the reference for the differential
pressure set points. In an embodiment, the valve includes
hydraulically activated valves which are controlled by bi-stable
DCVs. The on/off valves can be arranged in an oil-filled chamber in
the subsea control unit 12, 16, or be situated in a separate
oil-filled chamber which is mountable on the motor/pump assembly.
In another embodiment, the valve comprises hydraulically operated
half inch gate or needle valves or similar, which are controlled by
bi-stable DCVs located inside the subsea control module (SCM). The
same system control set-up can still be employed.
[0053] As for the necessary instrumentation and control system,
single pressure sensors or differential pressure sensors can be
employed and connected to a subsea electronics module (SEM) that is
situated in the SCM. The signals can be processed either subsea in
the SEM, or topside. If processing is situated topside, the topside
communication with the SEM can be effected via optical modem. Local
communication, i.e. sensor signal communication, can be performed
through conventional copper based electric leaders.
[0054] The present invention is 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
present invention such as defined in the appended claims.
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