U.S. patent application number 13/806572 was filed with the patent office on 2013-06-27 for differential pressure controlled motor and pump barrier fluids pressure regulation system.
This patent application is currently assigned to VETCO GRAY SCANDINAVIA AS. The applicant listed for this patent is Tom Kjonigsen. Invention is credited to Tom Kjonigsen.
Application Number | 20130164152 13/806572 |
Document ID | / |
Family ID | 45370908 |
Filed Date | 2013-06-27 |
United States Patent
Application |
20130164152 |
Kind Code |
A1 |
Kjonigsen; Tom |
June 27, 2013 |
DIFFERENTIAL PRESSURE CONTROLLED MOTOR AND PUMP BARRIER FLUIDS
PRESSURE REGULATION SYSTEM
Abstract
A motor and a pump barrier fluids pressure regulation system for
a subsea motor and pump module is disclosed. The pressure
regulation system comprises--a barrier fluid circuit (10) providing
fluid flow communication from a hydraulic fluid supply (8) to a
first cavity in the motor and pump module,--a pressure controlled
flow control valve (9) controlling the supply of hydraulic fluid to
the barrier fluid circuit (10);--a second cavity arranged to
receive hydraulic fluid from the hydraulic fluid supply via the
first cavity, and--a pilot pressure circuit (11) comprising means
for detecting and returning to the pressure controlled flow control
valve (9) a differential pressure over a flow restriction (7; 13)
connecting the first and second cavities.
Inventors: |
Kjonigsen; Tom; (Sande,
NO) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kjonigsen; Tom |
Sande |
|
NO |
|
|
Assignee: |
VETCO GRAY SCANDINAVIA AS
Sandvika
NO
|
Family ID: |
45370908 |
Appl. No.: |
13/806572 |
Filed: |
June 20, 2011 |
PCT Filed: |
June 20, 2011 |
PCT NO: |
PCT/IB11/01391 |
371 Date: |
March 1, 2013 |
Current U.S.
Class: |
417/279 |
Current CPC
Class: |
F04D 25/0686 20130101;
F16J 15/406 20130101; F04D 29/063 20130101; F04B 47/06 20130101;
F04B 53/16 20130101; F04D 13/062 20130101; F04C 15/0003 20130101;
F04D 13/086 20130101; F04D 29/122 20130101; F04C 13/008 20130101;
F04C 2/16 20130101; F04B 7/02 20130101 |
Class at
Publication: |
417/279 |
International
Class: |
F04B 7/02 20060101
F04B007/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 22, 2010 |
NO |
20100903 |
Jun 10, 2011 |
IB |
PCT/IB2011/001391 |
Claims
1. A motor and a pump barrier fluids pressure regulation system for
a subsea motor and pump module (1), the pressure regulation system
comprising: a barrier fluid circuit (10) providing fluid flow
communication from a hydraulic fluid supply (8) to a first cavity
in the motor and pump module, a pressure controlled flow control
valve (9) controlling a flow of hydraulic fluid from the hydraulic
fluid supply to the barrier fluid circuit (10); a second cavity in
selective fluid communication with the hydraulic fluid supply via
the first cavity, and a pilot pressure circuit (11) comprising
means for detecting and returning to the pressure controlled flow
control valve (9) a differential pressure over a flow restriction
(7; 13) connecting the first and second cavities.
2. The regulation system of claim 1, wherein a pump barrier fluid
circuit (12) receives hydraulic fluid from a motor barrier fluid
circuit (10) via a flow restriction (13) of fixed orifice diameter
arranged externally of the motor and pump module (1), and over
which the differential pressure is detected and returned to the
pressure controlled flow control valve (9) that feeds hydraulic
fluid into the motor and pump barrier fluid circuits in response to
deviations from a predefined, desired pressure difference.
3. The regulation system of claim 1, wherein said pressure
controlled flow control valve (9) is one of a set of valves,
including at least first and second valves (9, 14), which are
arranged in parallel to feed hydraulic fluid into the motor barrier
fluid circuit (10), and which are each responsive to the
differential pressure over the flow restriction (7; 13), and
further wherein said at least two pressure controlled flow control
valves are individually responsive to separate ranges of the
differential pressure over the flow restriction.
4. The regulation system of claim 3, wherein in a set of first and
second pressure controlled flow control valves the first valve (9)
is set to open for hydraulic fluid flow into the motor barrier
fluid circuit (10) in result of a differential pressure at or below
a first predefined differential pressure at the flow restriction
(7; 13), and the, second valve (14) is set to open for hydraulic
fluid flow into the motor barrier fluid circuit (10) in result of a
differential pressure at or below a second predefined differential
pressure lower than the first predefined differential pressure.
5. The regulation system of claim 4, wherein the first predefined
differential pressure is about 5 bar, and the second predefined
differential pressure is about 4.5 bar.
6. The regulation system of claim 2, wherein in a set of first and
second pressure controlled flow control valves the first valve (9)
is sized for lower flow rates and the second valve (14) is sized
for higher flow rates.
7. The regulation system of claim 6, wherein the first valve (9) is
sized for flow rates ranging down to about 0.3 l/min, and the
second valve (14) is sized for flow rates ranging up to about 100
l/min or above.
8. The regulation system of claim 3, wherein an ON/OFF valve is
connected in series with the second pressure controlled flow
control valve (14) of higher flow rate.
9. The regulation system of claim 1, wherein a pressure controlled
pressure relief valve (15) is arranged in parallel with the flow
restriction (7; 13) to dump hydraulic fluid from the motor barrier
fluid circuit (10) into the pump.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] The present invention relates generally to subsea equipment
involved in the transport of process fluids generated in subsea
hydrocarbon production. 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.
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, e.g. 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.
[0003] 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 screws 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.
[0004] 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.
[0005] 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. 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.
[0006] 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 lubrication
fluid circuit of the pump is 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 an external supply of hydraulic
fluid.
[0007] 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 the two 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 pump
lubrication system and the pumped medium, respectively.
[0008] Conventionally, motor barrier fluid and pump barrier fluid
is supplied via the umbilical, and leakage compensation and
pressure control is managed through directional control valves
located at the topside facility. 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 fluid 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.
SUMMARY OF THE INVENTION
[0009] The present invention thus aims at providing 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.
[0010] The present invention specifically aims to provide a motor
and pump barrier fluids pressure regulation system in a subsea
motor and pump module, the 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 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.
[0011] As used in this context, the motor barrier fluid circuit
shall be understood to include the fluid volumes in the motor
housing cavity and its associated components and flow lines which
are involved for controlling the fluid pressure in the motor
housing cavity. Correspondingly, the pump barrier fluid circuit
shall be understood at least to include the fluid volumes in the
connection chamber cavity and its associated components and flow
lines which are involved for controlling the fluid pressure in the
connection chamber cavity. In a more general meaning, the pump
barrier fluid circuit may also include fluid volumes in other
cavities or passages in the pump.
[0012] The object of the present invention is achieved through the
provision of a motor and a pump barrier fluids pressure regulation
system for a subsea motor and pump module as defined in the
accompanying claims.
[0013] Briefly, a pressure regulation system for the management of
motor and pump barrier fluids in a subsea motor/pump application
comprises: [0014] a barrier fluid circuit providing fluid flow
communication from a hydraulic fluid supply to a first cavity in
the motor and pump module, [0015] a pressure controlled flow
control valve controlling the supply of hydraulic fluid to the
barrier fluid circuit, [0016] a second cavity arranged to receive
hydraulic fluid from the hydraulic fluid supply via the first
cavity, and [0017] a pilot pressure circuit comprising means for
detecting and returning to the pressure controlled flow control
valve a differential pressure over a flow restriction connecting
the first and second cavities.
[0018] An automatic pressure control system is in this way provided
locally at the subsea motor and pump module, and characterized by a
fast response and high reliability.
[0019] The system may be multiplied to maintain, independently,
constant differential pressures between fluids in: [0020] a motor
housing cavity (first cavity) and a cavity/passage (second cavity)
in a pump structure; [0021] a motor housing cavity (first cavity)
and a cavity (second cavity) in a connection chamber; [0022] a
cavity (first cavity) in a connection chamber and a cavity/passage
(second cavity) in the pump structure; or [0023] a cavity/passage
(first cavity) in the pump structure and the cavity (second cavity)
in the pump through which the pumped medium is displaced in
operation.
[0024] In other words, with respect to the first recited
implementation, a flow control valve is used to supply fluid to the
motor housing in order to maintain a constant differential pressure
across a restriction, this way maintaining a constant over-pressure
in the motor barrier circuit relative to the pump barrier circuit,
and thus across the motor shaft seal. The flow rate through the
flow control valve is controlled by the differential pressure over
a restriction. In result, the supply fluid flow rate is always
identical to the leakage rate at the defined differential pressure,
regardless of system pressure variations. If the seal leakage rate
should increase due to wear, e.g., the valve will automatically
increase the flow rate as required to maintain the differential
pressure across the seal. When the pump pressure increases during
normal operations, the valve will automatically adjust the flow
rate to maintain a constant differential pressure across the seal.
When the pump pressure is reduced during normal operations, the
valve will automatically adjust the flow rate as required to
maintain a constant differential pressure across the seal.
[0025] One alternative and advantageous embodiment foresees, that
pump barrier fluid is received from the motor barrier fluid circuit
via a flow restriction of fixed orifice diameter arranged
externally of the motor and pump module, and over which the
differential pressure is detected and returned to the pressure
controlled on/off valve that feeds hydraulic fluid into the motor
and pump barrier fluid circuits in response to detected deviations
from a predefined, desired pressure difference.
[0026] In some applications very accurate control of the fluid flow
rate is required in a lower flow rate range, while high maximum
flow rates will be required at certain operating conditions. Both
requirements are met in an embodiment wherein two or more valves
having different flow rate ranges are connected in parallel in the
fluid supply to the motor barrier circuit. More precisely, this
embodiment comprises a set of valves, including at least first and
second valves, which are arranged in parallel to feed hydraulic
fluid into the motor barrier fluid circuit, and which are each
responsive to the differential pressure over the flow restriction,
and further wherein said at least two pressure controlled flow
control valves are individually responsive to separate ranges of
the differential pressure over the flow restriction.
[0027] In a set of first and second pressure controlled flow
control valves the first valve is preferably set to open for
hydraulic fluid flow into the motor barrier fluid circuit in result
of a differential pressure at or below a first predefined
differential pressure at the flow restriction, and the second valve
is preferably set to open for hydraulic fluid flow into the motor
barrier fluid circuit in result of a differential pressure at or
below a second predefined differential pressure lower than the
first predefined differential pressure.
[0028] In many applications for subsea hydrocarbon production the
first predefined differential pressure may be set to about 5 bar,
and the second predefined differential pressure can be set to about
4.5 bar.
[0029] In the set of first and second pressure controlled flow
control valves arranged in parallel to feed hydraulic fluid into
the motor barrier fluid circuit, the first valve can be sized for
lower flow rates and the second valve be sized for higher flow
rates. For example, the first valve may be sized for flow rates
ranging down to about 0.3 l/min, and the second valve may be sized
for flow rates ranging up to about 100 l/min or above.
[0030] If required, an ON/OFF valve may be connected in series with
the second pressure controlled flow control valve of higher flow
rate in order to control eventual internal leakage in this
valve.
[0031] For security, a pressure controlled safety relief valve may
be arranged in parallel with the flow restriction to dump hydraulic
fluid from the motor barrier fluid circuit into the pump.
[0032] The motor and pump barrier 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 twin-screw 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.
SHORT DESCRIPTION OF THE DRAWINGS
[0033] Embodiments of the invention will be more closely described
below with reference made to the drawings. In the drawings,
[0034] FIG. 1 is a diagram illustrating the motor and a pump
barrier fluids pressure regulation system in a first embodiment,
and
[0035] FIG. 2 is a corresponding diagram illustrating a second
embodiment of the pressure regulations system.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0036] In the drawings, a subsea motor and pump module comprises a
motor/pump assembly generally denoted 1 to which motor barrier
fluid and pump barrier fluid is supplied from an external hydraulic
fluid supply.
[0037] Since the 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 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.
[0038] 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 in a connection chamber 6, the
interior of which is hydraulically separated from the pressurized
(typically oil-filled) motor housing by means of a seal arrangement
7 which seals against the outside of a rotary shaft by which the
pump rotor is drive-connected to the motor. The pump rotor is
further journalled in bearing arrangements in the pump housing 3.
Internally of the pump, pump barrier fluid is typically circulated
for lubrication of internal structures in the pump, such as
bearings, seals, timing gears if appropriate, etc., providing also
a barrier towards the medium which passes through the pump.
[0039] Motor barrier fluid and pump barrier fluid is supplied to
the subsea motor and pump module from an external supply (topside
offshore or onshore) of hydraulic fluid via hydraulic fluid supply
line 8. All other components of the system are installed subsea.
Motor barrier fluid is supplied to the motor housing via a flow
control valve 9 which controls the flow of hydraulic fluid into a
motor barrier fluid circuit 10 that opens into the motor
housing.
[0040] Pump barrier fluid is received in the connection chamber 6
from the motor housing 2 which communicates with the connection
chamber via the seal arrangement 7. This flow communication over
the seal arrangement 7 is a leakage of hydraulic fluid through the
seal, the seal arrangement 7 in this context representing a
restriction of fixed orifice diameter, disregarding wear of seal
surfaces over time.
[0041] In order to compensate for leak flow via the restriction 7,
the flow control valve 9 is pressure controlled and operated in
response to the difference in pressure between the motor barrier
fluid on the upstream side of flow restriction 7 and the pump
barrier fluid on the downstream side thereof, i.e. the pressure
difference between the motor housing and the connection chamber.
The differential pressure over the flow restriction 7 is
continuously detected and returned to the flow control valve 9 by
means of a pilot pressure circuit 11. In the drawings, the pilot
pressure circuit 11 is illustrated by thin and/or broken lines.
[0042] In the alternative embodiment illustrated in FIG. 2, pump
barrier fluid is supplied to the pump/connection chamber 6 from the
motor barrier fluid circuit 10 via pump barrier fluid circuit 12. A
flow restriction 13 of fixed orifice diameter is arranged in the
pump barrier fluid circuit externally of the motor/pump module and
restricts the flow of hydraulic fluid from the motor barrier fluid
circuit 10 into the pump barrier fluid circuit 12.
[0043] Accordingly, the valve 9 is a pilot controlled flow control
valve which cooperates with an internal (7) or an external (13)
restriction to maintain a constant pressure difference between the
motor barrier and pump barrier fluid circuits by adjusting the flow
through the flow control valve. The flow through the restriction is
only a small flow going into the pump via pump barrier fluid
circuit, whereas the main flow is supplied to the motor via the
motor barrier circuit.
[0044] In ordinary practise and scale it is considered sufficient
to cover flow rates in the order of 0-100 l/min of supplied
hydraulic fluid. However, in order to manage a wider range of flow
rates than a singular valve 9 can provide, at least one additional
pressure controlled flow control valve 14 may optionally be
arranged in parallel with the first flow control valve 9 to supply
fluid into the motor barrier fluid circuit 10. The flow control
valves 9 and 14 are each responsive to the pressure in the pilot
pressure circuit 11. As previously discussed, the flow control
valves 9 and 14 may be individually responsive to separate ranges
of the differential pressure over the flow restriction, and they
may also be sized for different flow rates. If required, a set of
more than two flow control valves may be connected in parallel to
supply hydraulic fluid into the motor barrier fluid circuit.
[0045] With further reference to the drawing, reference number 15
refers to a pressure relief valve arranged to permit motor barrier
fluid into the pump barrier fluid circuit via a by-pass line 16
which opens into the pump barrier fluid circuit downstream of the
flow restriction 7 or 13. The pressure relief valve 15 manages and
controls higher differential pressure during start-up and resulting
from thermal expansion of the liquid volumes in the motor and pump.
The pressure relief valve 15 also operates as a safety valve in
case of an unexpected rise of the fluid pressure to a too high
level. A one-way valve 17 is preferably arranged to prevent
back-flow from the pump into the motor barrier circuit 10. A
pressurized accumulator 18 may be arranged in the supply fluid line
to provide adequate supply fluid pressure to the pressure
controlled flow control valve(s) 9, 14.
[0046] The illustrated embodiment meets the purpose of the
invention, namely to maintain a constant differential pressure
between two fluid-filled cavities which are hydraulically
interconnected in the motor and pump module. Fluid is supplied at a
controlled flow rate to the cavity having the highest pressure such
that the differential pressure is maintained constant independent
of leakage rate between the cavities. The invention is also
effective for compensation of flow rates caused by compression and
thermal expansion of the fluids in the cavities.
[0047] Although the invention is disclosed with reference to a
system for controlling barrier fluid pressures over an interface
between a motor housing and a connection chamber, it will be
realized that a similar setup can be used for controlling barrier
fluid pressures at other interfaces in a motor and pump module at
subsea level, requiring fluid barriers for separation or for
preventing intrusion from surrounding media. It will be realized
that in addition to the interfaces listed in the summary, the
invention may be applied at any separating interface in the motor
or pump, such as seals and bearings forming parts of a pump
lubrication system, or seals and bearings forming parts of a motor
lubrication or cooling system, e.g.
[0048] 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.
* * * * *