U.S. patent application number 14/780512 was filed with the patent office on 2016-02-18 for separation system using heat of compression.
The applicant listed for this patent is FMC KONGSBERG SUBSEA AS. Invention is credited to Henrik Bjartnes, Haakon Ellingsen, Sven Haagensen Hoy, Andreas Hannisdal, Jostein Kolbu.
Application Number | 20160047217 14/780512 |
Document ID | / |
Family ID | 50272594 |
Filed Date | 2016-02-18 |
United States Patent
Application |
20160047217 |
Kind Code |
A1 |
Haagensen Hoy; Sven ; et
al. |
February 18, 2016 |
SEPARATION SYSTEM USING HEAT OF COMPRESSION
Abstract
The present invention relates to a subsea system, where the
subsea system comprises a separator (1) with an inlet line (2) and
an outlet line (3), a compression unit (4) with an inlet line (5)
and an outlet line (6) and a heat transfer unit (7), where the
outlet line (6) of the compression unit (4) is guided into the heat
transfer unit (7), the heat transfer unit (7) being connected to
the inlet line (2) of the separator (1). According to the invention
the heat transfer unit (7) is used for transferring heat between at
least a part of a fluid in the inlet line (2) of the separator (1)
and at least a part of a fluid in the outlet line (6) of the
compression unit (4).
Inventors: |
Haagensen Hoy; Sven; (Asker,
NO) ; Hannisdal; Andreas; (Oslo, NO) ;
Bjartnes; Henrik; (Slependen, NO) ; Ellingsen;
Haakon; (Oslo, NO) ; Kolbu; Jostein; (Forneby,
NO) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FMC KONGSBERG SUBSEA AS |
Kongsberg |
|
NO |
|
|
Family ID: |
50272594 |
Appl. No.: |
14/780512 |
Filed: |
March 7, 2014 |
PCT Filed: |
March 7, 2014 |
PCT NO: |
PCT/EP2014/054459 |
371 Date: |
September 25, 2015 |
Current U.S.
Class: |
210/170.01 |
Current CPC
Class: |
E21B 43/385 20130101;
E21B 36/006 20130101; E21B 43/36 20130101 |
International
Class: |
E21B 43/36 20060101
E21B043/36 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 26, 2013 |
NO |
20130430 |
Claims
1. A subsea system comprising: a separator having an inlet line and
at least one outlet line; a compression unit having an inlet line
and an outlet line; and a heat transfer unit for transferring heat
between at least a part of a fluid in the inlet line of the
separator and at least a part of a fluid in the outlet line from of
the compression unit; wherein the outlet line of the compression
unit is guided into the heat transfer unit and the heat transfer
unit is connected to the inlet line of the separator.
2. The subsea system according to claim 1, wherein the compression
unit is a multiphase pump.
3. The subsea system according to claim 1, wherein the compression
unit is a compressor.
4. The subsea system according to claim 1, wherein the heat
transfer unit is a heat exchanger.
5. The subsea system according to claim 1, further comprising a
splitter which is positioned downstream of the compression unit to
split out a part of the fluid in the outlet line of the compression
unit and guide said part of the fluid into the heat transfer unit
to mix with the fluid in the inlet line upstream of the separator,
the heat transfer unit comprising a mixer.
6. The subsea system according to claim 1, wherein the inlet line
of the compression unit is connected to the outlet line of the
separator.
7. The subsea system according to claim 1, wherein the outlet line
of the compression unit is connected to a downstream wax
precipitation unit.
8. The subsea system according to claim 1, wherein the heat
transfer unit is provided with an additional heat source.
9. The subsea system according to claim 1, wherein the system
comprises at least a second compression unit arranged upstream of
the separator.
10. The subsea system according to claim 1, wherein the system
comprises at least two separation stages which each comprise a
corresponding first or second separator.
11. The subsea system according to claim 10, wherein the heat
transfer unit is a heat exchanger which is arranged downstream of
the compression unit and upstream of at least the second separator
to heat exchange a process fluid upstream of the second
separator.
12. The subsea system according to claim 11, wherein the system
comprises a second heat exchanger which is arranged upstream of the
first separator.
13. The subsea system according to claim 12, wherein the subsea
system comprises an additional separator upstream of the heat
exchanger and downstream of the compression unit, such that the
heat exchange takes place in parallel with split phases or one
phase is bypassing the heat exchanger or mixed into a process
fluid.
14. The subsea system according to claim 1, wherein the subsea
system comprises an additional separator upstream of the heat
exchanger and a bypass line for at least one phase which extends
around the heat exchanger.
Description
[0001] The present invention relates to a subsea system, and
especially to a subsea system wherein at least some of the heat in
the fluid flow resulting compression of the fluid flow is used to
heat the fluid flow before it enters a separation stage. This
subsea system is especially relevant for gas rich fluid flows or
multiphase fluid flows.
BACKGROUND OF THE INVENTION
[0002] There are several systems known to provide separation of a
well stream into different phases and thereafter transport the well
stream to shore or a platform.
[0003] The present invention provides a device and method for
providing a separation system with increased capacity in the case
of a gas rich fluid stream or a multiphase fluid stream.
SUMMARY OF THE INVENTION
[0004] The invention is defined in the independent claim, while the
dependent claims describe other embodiments of the invention.
[0005] According to the invention there is provided a subsea system
comprising a separator with a fluid inlet line and at least one
outlet line. The subsea system also comprises a compression unit
for a gas rich fluid flow with an inlet line and an outlet line.
The compression unit may be a pump, a multiphase pump, a compressor
or other kind of element for increasing the pressure in the fluid
and at the same time increasing the temperature in the fluid due to
the compression. The system is further provided with a connection
between the outlet line from the compression unit and the inlet
line of the separator to provide heat transfer from at least a part
of the fluid in the compression unit outlet line to the separator
inlet line.
[0006] This provides a separation system that uses heat from gas
compression or gas-liquid compression (also denoted multiphase
pumping or wet gas compression) to increase the temperature in the
process flow entering the separation station, so that the viscosity
of the process flow is reduced and the separation efficiency of all
involved phases therefore can be increased. The process fluids
entering the separation station which are heated by the compressed
fluids will have a reduced propensity to deposit wax or other
substances onto the internal surfaces of the separators and any
process equipment for produced water treatment.
[0007] An added benefit from this system is the reduction in
temperature of the fluid in the compression unit outlet line as
heat is transferred to the inlet line of the separator and
therefore from the fluid in the compression unit outlet line.
[0008] The temperature increase associated with the compression of
fluids will be reduced by means of heat transfer thus enabling
further downstream processing of separated or non-separated process
phases, where such processing is aided by the reduced
temperature.
[0009] According to the invention, a possible embodiment provides a
heat exchanger for heat transfer between the fluid in the
compression unit outlet line and the fluid in the separator inlet
line.
[0010] One may possibly use all the fluid in the compression outlet
line for the heat transfer. This means guiding all the fluids at
the compression outlet line through a heat exchanger. Another
possibility is to provide a separator unit at the outlet of the
compression unit to separate out a part of the fluid to be lead
through a heat exchanger with the fluid at the inlet of the
separator. There is also the possibility of having two heat
exchangers in parallel arranged downstream of the compressor, one
for each fluid phase out of the separator. Another possibility is
to have a flow splitter at the outlet line of the compressor unit,
to take only a part of the fluid through the heat exchanger. One
may guide all the fluid from the compressor outlet line through the
heat exchanger with the separator inlet line or only part of the
fluid, and then possibly let the rest of the fluid bypass the heat
exchanger. One possibility is to then combine the flows again after
the heat exchanger, or another possibility is to lead one of the
flows into another fluid line.
[0011] Another possibility is to take a part of the flow at the
outlet from the compression unit and mix this with the well stream
at the inlet of the separator. This part of the flow may be a part
of a multiphase flow or a part of a phase divided flow. The
temperature increase in the process fluid can be achieved by
recirculation of and commingling with process fluid that has been
compressed in a pump or compressor, thus avoiding the use of a heat
exchanger. In other words, a part of the compressed process fluid
can be bled off, its pressure relieved, and then it can be guided
directly into the process stream to be heated. The bleed off may
take place after or in a mixer to ensure an even distribution of
phases in the two or more flows.
[0012] The compression unit in the form of a multiphase pump or
compressor may, according to one embodiment, be placed after, or in
other words, downstream of the separation station. By using a
system according to the invention, one gets not only increased
efficiency in the separator, but also cooling of the fluid flow
after the compression unit. The separation station may comprise
several stages and sub-processes. The multiphase pump or compressor
can be placed between the separation stages or between process
parts, according to the requirements of these stages and process
parts.
[0013] Any gas in the process fluid can be separated from other
phases after the pump or compressor, according to the requirements
of the stages and process parts. By doing this, one may have a heat
exchanger at the inlet of the separator with only one phase in the
flow through the heat exchanger. Another possibility is to have one
phase through the heat exchanger and at least a part of the flow
not flowing through the heat exchanger bled down in pressure and
introduced into the process flow to increase the temperature with
mixing. Another possibility is to have this phase bypass the heat
exchanger in a bypass line and be remixed with the split phase
downstream of the heat exchanger.
[0014] Any gas in the process fluid can be intermediately separated
from the other phases upstream of the compression unit.
[0015] The pump or compressor may alternatively be placed upstream
of the separation station, thus improving separation efficiency
through a temperature increase, and/or preventing wax or other
temperature-influenced deposition on or inside the process
equipment.
[0016] Any cooler between or after the separation stages or other
process parts can be used to reduce the process fluid temperature,
according to the requirements of equipment downstream of the
cooler.
[0017] There is also the possibility of providing the system with
additional sources for heating the fluid stream at the inlet of the
separator. These may for instance be electric heating sources.
Another possibility is to heat exchange the cooling fluid of the
motor of the compression unit with the fluid at the inlet of the
separator.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The invention will now be explained with non-limiting
embodiments with reference to the attached drawings where:
[0019] FIG. 1 is a schematic representation of one embodiment the
invention;
[0020] FIG. 2 is a schematic representation of another embodiment
of the invention; and
[0021] FIG. 3 is a schematic representation of yet another
embodiment of he invention.
DETAILED DESCRIPTION OF THE INVENTION
[0022] FIG. 1 is a representation of a first embodiment of the
invention, only the elements relevant for the understanding of the
invention being shown, as many additional elements in the system
may exist. The subsea system shown in FIG. 1 comprises a separator
1 with an inlet line 2 and an outlet line 3. The inlet line 2 is
connected to an upstream source which may, e.g., be the wellhead or
another upstream subsea unit, as for instance a separator. There
would normally be an additional outlet line from the separator 1,
which is not shown in the drawings as it is not directly relevant
for the invention. The subsea system also comprises a compression
unit 4 with an inlet line 5 and an outlet line 6. The compression
unit may be a compressor or a multiphase pump. The inlet line 5 of
the compression unit may as indicated with the dotted line 10 be
connected directly with the outlet line 3 of the separator 1.
Another possibility is to have the inlet line 5 be connected to
another fluid source. The outlet line 6 is guided into a heat
transfer unit 7 which is connected to the inlet line 2 of the
separator 1. This heat transfer unit 7 may be a heat exchanger or a
mixer. In the case where the heat transfer unit is a heat exchanger
7, the fluid in the outlet line 6 of the compressor 4 may in one
embodiment be guided through the heat exchanger 7. Exiting this
heat exchanger, the fluid is cooled while heating the fluid in the
inlet line 2 of the separator 1.
[0023] Another possibility is to provide a unit 8 in the form of a
separator in the outlet line 6 downstream of the compression unit
4. This separator 8 would separate the outlet fluid in the outlet
line 6 into two streams and possibly guide one of these streams
through the heat exchanger 7 and the other stream into a bypass
line 9. These streams may be connected again downstream or lead to
different equipment subsea. Another possibility is to have the unit
8 be a splitter, splitting the fluid in the outlet line 6 into two
or more streams, whereof one or several are guided through the heat
exchanger 7.
[0024] Another possibility is to have the unit 8 split off a part
of the fluid in the outlet line 6 and then introduce this fluid
into a mixer 7 after the pressure is bled off to mix with the fluid
in the inlet line 2 of the separator 1.
[0025] Also, the inlet line 2 to the separator may be divided, with
one part leading through a heat exchanger and another part through
a bypass.
[0026] FIG. 2 shows another embodiment of the invention. In this
embodiment the separation process comprises a first separation
stage and a second separation stage, in the form of primary and
secondary separation, possibly arranged as a first separator 1 and
a second separator 1A. A compression unit 12 is arranged downstream
of the second separator 1A, and a compression unit 11 may possibly
be arranged upstream of at least one of the separators, such as
upstream of the first separator 1. The fluid exiting the second
separator 1A is pressurized in the compression unit 12 and is then
lead through a first heat exchanger 7 positioned between the first
and second separators and then possibly through a second heat
exchanger (not shown) positioned upstream of the first separator 1.
The heat exchanger upstream of the first separator is positioned
between the first separator and the optional compression unit 11.
The possibility exists of using just one heat exchanger, the
position of which being one of the above mentioned positions. The
possibility also exists of using just one compression unit in this
configuration.
[0027] Produced water from the first and second separation stages
is guided into a produced water treatment unit 20. Oily reject from
this treatment unit may be lead through a line 15 and introduced
into the flow upstream of the first or second separation stage. The
water to be re-injected into the well is lead out from the
treatment unit 20 to a water reinjection pump 13. Part of the flow
from the pump may be reintroduced through a line 16 back into the
water treatment unit. In the embodiment shown in FIG. 3, produced
water from the second separation stage is lead into a reject stream
treatment unit 22, where it is treated along with the oily reject
15 from the water treatment unit 20. If the water from the reject
stream treatment unit 22 is clean enough, it is directed to the
reinjection pump 13; otherwise, it is lead back to the produced
water treatment unit 20.
[0028] In the embodiments shown in FIGS. 2 and 3, the compression
or multiphase pumping units 11, 12 are located at different steps
in the process, in this case upstream of the first processing step
and after the secondary separation step.
[0029] The compression unit 11 increases the stream temperature so
that, e.g., the risk of wax precipitation in the oil and water
treatment parts of the process is reduced. The temperature increase
also enhances the separation efficiency, possibly allowing for a
reduction in the size and weight of the separator vessels.
Furthermore, with two-stage pumping, the size of the injection
water pump 13 can be reduced. Heated injection water also has a
lower viscosity, which may improve water permeation into the
reservoir.
[0030] The advantage of multiphase compression in one or several
stages with heat exchange is not only that the stream leaving the
subsea process for further processing or transportation is cooled.
Provided that the required injection water pressure is higher than
the upstream process pressure, water pressure is available for
recirculation back into the produced water treatment process.
Single step multiphase compression upstream of the separation
process would not facilitate this.
[0031] With the arrangement shown in FIG. 2, the temperature of the
stream 14 is maximized. Also, since water is removed from the
stream 14, the gas volume fraction into the pump or compression
unit 12 is maximized, thus increasing the temperature out of the
compression unit 12. In addition, gas is included in the hot side
of the heat exchanger, and this gas has a relatively high heat
capacity at normal processing pressures.
[0032] A further arrangement, not shown in FIG. 1 or FIG. 2, would
be to split the gas and oil stream from the pump or compression
unit 12 and lead it either as separate streams of gas and liquid,
or as split multiphase streams, to two or more heat exchangers.
[0033] Another variety of this arrangement, also not shown in FIG.
1 or FIG. 2, is to cool part of the stream from the pump or
compression unit 12 with seawater, and not heat exchange this part
with the process stream.
[0034] Another variety of this arrangement, also not shown in FIG.
1 or FIG. 2, is to provide a bypass line around each heat exchanger
in order to control the fluid flow rate entering the heat exchanger
and thus optimize the amount of heat transferred in each device.
The heat exchangers could also be arranged in parallel or in
series. In FIG. 2 the downstream processing may be a cooling unit
for precipitation of wax out of oil, so that a pipeline will not be
clogged with wax as the oil cools. The heat exchange aids a
downstream process like this. To prevent top-of-the-line corrosion,
the heat exchange could also be part of a cooling sequence to
condense water from the gas phase, to obtain controlled mixing with
a corrosion inhibited aqueous phase. In FIG. 2 the oily reject
stream 15 from the produced water treatment unit 20 may be
recombined with the process stream up- or downstream of each
separation stage.
[0035] The invention has now been explained with reference to the
attached drawings and embodiments. Alterations and modifications
may be made to these embodiments that are within the scope of the
invention as defined in the attached claims. The possibility of
combining features from the different embodiments to another
embodiment of the invention also exists.
* * * * *