U.S. patent application number 12/997675 was filed with the patent office on 2011-05-05 for subsea heat exchanger.
Invention is credited to Bastiaen Van Der Rest.
Application Number | 20110100589 12/997675 |
Document ID | / |
Family ID | 41466163 |
Filed Date | 2011-05-05 |
United States Patent
Application |
20110100589 |
Kind Code |
A1 |
Van Der Rest; Bastiaen |
May 5, 2011 |
SUBSEA HEAT EXCHANGER
Abstract
Subsea convection heat exchanger (1) for cooling or heating a
hydrocarbon-containing fluid in subsea environment. The heat
exchanger (1) comprises a convection section with a fluid carrying
pipe (7) adapted for heat transfer between the carried fluid on one
side of the pipe wall and the surrounding water on the opposite
side of the pipe wall. The convection section is enclosed by an
enclosure (9) with sea water inlet (11) and a sea water outlet
(13). The heat exchanger (1) is furthermore provided with means
(15) for controlled through-flow of surrounding sea water from the
sea water inlet (11) to the sea water outlet (13).
Inventors: |
Van Der Rest; Bastiaen;
(Slependen, NO) |
Family ID: |
41466163 |
Appl. No.: |
12/997675 |
Filed: |
July 2, 2009 |
PCT Filed: |
July 2, 2009 |
PCT NO: |
PCT/NO2009/000248 |
371 Date: |
January 20, 2011 |
Current U.S.
Class: |
165/45 |
Current CPC
Class: |
F28D 1/022 20130101;
F28F 27/02 20130101; F28F 2250/08 20130101; F28D 1/05316
20130101 |
Class at
Publication: |
165/45 |
International
Class: |
F28F 99/00 20060101
F28F099/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 3, 2008 |
NO |
2008 2957 |
Claims
1. A subsea convection heat exchanger for cooling or heating a
hydrocarbon-containing fluid in a subsea environment, said heat
exchanger comprising: a convection section comprising a fluid
carrying pipe for heat transfer between carried fluid on one side
of a pipe wall and surrounding water on an opposite side of the
pipe wall; wherein said convection section is enclosed by an
enclosure comprising a sea water inlet and a sea water outlet; and
wherein the subsea convection heat exchanger comprises a pump for
controlled through-flow of surrounding sea water from the sea water
inlet to the sea water outlet.
2. A subsea convection heat exchanger according to claim 1, wherein
the subsea convection heat exchanger is hydrostatically balanced as
there is fluid connection between an exterior and interior of the
enclosure through at least one of said sea water inlet and said sea
water outlet.
3. (canceled)
4. A subsea convection heat exchanger according to claim 1, wherein
said pump is arranged in connection with the sea water outlet of
the enclosure creating a pressure drop from the exterior of the
enclosure to the interior of the enclosure.
5. A subsea convection heat exchanger according to claim 4,
wherein: said pump is arranged in a pump unit with a pump motor
arranged in a motor chamber which is isolated from the surroundings
and adapted to be hydrostatically balanced with surrounding sea
water; wherein the pump motor is adapted to operate the pump via a
shaft running through a mechanical seat; and wherein the
arrangement of the pump unit creates a pressure drop over said
mechanical seal from the motor chamber to the pump when the pump is
running, as the pump is adapted to create a pressure drop from its
outlet to its inlet.
6. A subsea convection heat exchanger according to claim 1,
wherein: the subsea convection heat exchanger exhibits a fluid
inlet and a fluid outlet for the fluid to be cooled or heated; and
wherein said pump for through-flow of water is controlled by a
controller, wherein the controller is at least partially controlled
on a basis of a temperature of the fluid flowing in at least one of
the fluid outlet and the fluid inlet, as measured by temperature
sensor(s).
Description
[0001] The present invention relates to subsea processing of
hydrocarbon-containing fluids. In particular the invention relates
to a convection heat exchanger adapted to operate in a body of
surrounding water, using said water as cooling or heating
medium.
BACKGROUND
[0002] In subsea fluid processing it is known to use the
surrounding seawater to cool or heat fluid flowing in a pipe.
Common practice is to arrange said pipe with a plurality of bends
or combining a plurality of such pipes in a parallel configuration
in order to achieve large contact area between the pipe and the
water, and thus a high heat transfer rate between the fluid in the
pipe(s) and the surrounding water. If there is a current present in
the seawater, the heat transfer rate will rise. But even with no
current, the pipe and its interior fluid will be cooled or heated
in dependence of the temperature difference between the fluid and
the surrounding seawater.
[0003] In processes where the flow-rate, the temperature, or
characteristics of the fluid flowing through the pipe varies, the
above described arrangement can involve challenges for the
operator, since he cannot control the exact cooling or heating
rate. Varying temperatures of the surrounding seawater can also
imply corresponding challenges.
[0004] Possible remedies for such challenges can be to control the
flow rate of the fluid in the pipe(s) or to flow the fluid through
longer or shorter lengths of the pipe by the control of
appropriately arranged valves. For instance, the convection section
can consist of a plurality of parallel branches. If a higher heat
transfer rate is needed, more branches can be connected.
Correspondingly, if less heat transfer rate is needed, the operator
can disconnect one or more branches.
[0005] However, each of the above solutions exhibits a
disadvantage. Depending on the specific process in question,
controlling the flow rate of the fluid can in many cases not be
done because it increases complexity, costs, and lowers
reliability. Dividing the flow into a specific number of branches
by the use of valves will limit the heat transfer rate into a
limited number of possible heat transfer rate values, depending on
the number and the design/size of each branch.
[0006] Thus, there is a need for a subsea convection heat exchanger
that overcomes the above-mentioned disadvantages. Such a heat
exchanger is provided with the subsea convection heat exchanger
according the present invention, as given in the characteristic
part of the independent claim 1.
[0007] The Invention
[0008] According to the invention, there is provided a subsea
convection heat exchanger for cooling or heating a
hydrocarbon-containing fluid in a subsea environment. The heat
exchanger comprises a convection section with a fluid carrying pipe
adapted for heat transfer between the carried fluid on one side of
the pipe wall and the surrounding water on the opposite side of the
pipe wall. The convection section is enclosed by an enclosure
comprising a sea water inlet and a sea water outlet. Furthermore,
the heat exchanger is provided with means for controlled
through-flow of surrounding sea water from the sea water inlet to
the sea water outlet. With such a subsea convection heat exchanger,
an operator is able to control the heat transfer rate between the
fluid flowing through the convection section and the sea water.
This can be performed for instance by varying the pump speed or by
controlling a throttling valve to control the through-flow of sea
water.
[0009] Preferably, the heat exchanger according to the invention is
hydrostatically balanced, as there is fluid connection between the
exterior and interior of the enclosure, preferably through said
inlet and/or outlet. Thus, it can operate in any depth as desired
without having to dimension the enclosure according to hydrostatic
pressure in the surrounding sea water.
[0010] The means for through-flow of sea water is advantageously a
pump. The pump can be arranged in connection with the sea water
outlet of the enclosure, thereby creating a pressure drop from the
exterior of the enclosure to its interior.
[0011] In a particularly preferred embodiment, a pump is arranged
in a pump unit with a pump motor arranged in a motor chamber (23)
which is isolated from the surroundings and adapted to be
hydrostatically balanced with surrounding sea water. The motor is
then preferably adapted to operate the pump with a shaft running
through a mechanical seal, and in such way that the arrangement of
the pump unit creates a pressure drop over said mechanical seal
from the motor chamber to the pump when the pump is running, as the
pump is adapted to create a pressure drop from its outlet to its
inlet. This advantageous set-up results in that sea water does not
penetrate into the motor chamber through the seal, thereby
contributing to a longer operating time of the pump motor.
[0012] In an advantageous embodiment, the heat exchanger according
to the invention preferably exhibits a fluid inlet and a fluid
outlet for the fluid to be cooled or heated, wherein the means for
through-flow of water is controlled by a controller which at least
partially is controlled on the basis of the temperature of the
fluid flowing in the fluid outlet and/or inlet, as measured by
temperature sensor(s). The control of the means for through-flow of
sea water can then be automatically controlled.
EXAMPLE OF EMBODIMENT
[0013] In the following, an example of an embodiment of the subsea
convection heat exchanger according to the present invention will
be given with reference to the drawings, in which
[0014] FIG. 1 is a diagrammatic view of a subsea convection heat
exchanger; and
[0015] FIG. 2 is a diagrammatic view of a preferred arrangement of
the pump and pump motor.
[0016] FIG. 1 illustrates a subsea convection heat exchanger 1
according to the present invention. It is arranged on the seabed in
connection with a subsea processing facility. The purpose of the
heat exchanger 1 is to obtain exact control of process outlet
temperature of a hydrocarbon-containing gas in order to avoid
condensation or the formation of hydrates.
[0017] The heat exchanger 1 exhibits a high pressure inlet 3 for
process fluid, and a high pressure process outlet 5. The heat
exchanger 1 further exhibits a convection section comprising a
plurality of heat transfer pipes 7. The heat transfer pipes 7 are
in direct contact with the sea water.
[0018] The convection section of the heat exchanger 1 is
encapsulated with an enclosure 9. The enclosure has a sea water
inlet 11 and a sea water outlet 13. In connection with the sea
water outlet 13, there is arranged a remotely controllable pump
unit 15.
[0019] The pump unit 15 is described in more detail below with
reference to FIG. 2. Still referring to FIG. 1, the pump unit 15 is
adapted to pump ambient sea water into the enclosure 9 through the
sea water inlet 11 and out of the enclosure 9 through the sea water
outlet 13. As described in more detail below, the pump unit 15 is
advantageously arranged on the downstream side of the sea water
flow, in connection with the sea water outlet 13.
[0020] The assembly of the pump unit 15 and enclosure 9 which
encapsulates the convection section, results in an exact process
control of the temperature of the process fluid flowing out of the
heat exchanger 1 through the process fluid outlet 5. As the
controllable pump unit 15 flows surrounding sea water through the
heat exchanger 1, the controlling of the pump unit 15 will directly
control the heat transfer rate of the heat exchanger. In addition,
if no convection or heat transfer is desired, the pump unit 15 can
be halted, and as the sea water inside the enclosure 9 approaches
the temperature of the process fluid, practically no heat transfer
will take place. In order to reduce heat transfer through the
enclosure 9 between the sea water inside and outside of the
enclosure 9, one can arrange additional enclosures or isolated
enclosures (not shown).
[0021] Advantageously, the pressure difference between the
enclosure interior and the surrounding sea water needs not be much
in order to flow a desired amount of sea water through the heat
exchanger 1. Thus, only a small pump unit 15 is needed.
[0022] Preferably, a temperature sensor (not illustrated) is
arranged to measure the fluid temperature of the process fluid
flowing out of process fluid outlet 5. To monitor the operation of
the heat exchanger 1, one can preferably also arrange a temperature
sensor (not illustrated) in connection with the process fluid inlet
3.
[0023] FIG. 2 illustrates the pump unit 15 in more detail. The pump
unit 15 comprises a pump motor 17 and a pump 19 arranged in a pump
unit housing 21. The pump motor 17 is arranged in a motor chamber
23 which is isolated from the surroundings, but which is
hydrostatically balanced with the pressure of the surrounding sea
water (preferably with a membrane solution). The motor 17 operates
the pump 21 with a shaft running through a mechanical seal 25. As
mentioned above, the pump unit 15 is advantageously arranged on the
downstream side of the sea water flow. Such an arrangement results
in a pressure drop over the mechanical seal 25 from the motor side
to the pump side. Thus, no sea water will penetrate into the motor
chamber 23 along the mechanical seal 25.
[0024] In another embodiment of the present invention, the means to
provide for the flow of sea water through the heat exchanger is not
a regular pump. Instead, the heat exchanger is arranged in such
manner that the sea water will flow through it in a vertically
direction. Due to the heat transfer in the convection section, the
temperature difference between the sea water inside and outside the
enclosure will result in different specific gravity of the water.
This difference will effect the vertical flow of sea water. The
flow can for instance be controlled by a valve at the inlet of
outlet of sea water.
* * * * *