U.S. patent application number 11/988238 was filed with the patent office on 2009-02-26 for device and method for cleaning a compressor.
This patent application is currently assigned to Aker Kvaerner Subsea AS. Invention is credited to Audun Grynning.
Application Number | 20090050326 11/988238 |
Document ID | / |
Family ID | 35295144 |
Filed Date | 2009-02-26 |
United States Patent
Application |
20090050326 |
Kind Code |
A1 |
Grynning; Audun |
February 26, 2009 |
Device and Method for Cleaning a Compressor
Abstract
A system for cleaning compressors (1) that are situated at a
difficultly accessible location, e.g., on or near the seabed or
downhole in a well bore, comprises a cleaning liquid line (8)
extending between a readily accessible liquid source and the
compressor. The liquid source may be a line (7) for supplying
hydrate inhibitor, anti foam chemicals, barrier liquid, demulsifier
or other types of chemicals to a subsea production or processing
activity. Alteratively, the liquid source can be an accumulator
tank (13) situated in the vicinity of the compressor.
Inventors: |
Grynning; Audun; (Stabekk,
NO) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Assignee: |
Aker Kvaerner Subsea AS
Lysaker
NO
|
Family ID: |
35295144 |
Appl. No.: |
11/988238 |
Filed: |
June 8, 2006 |
PCT Filed: |
June 8, 2006 |
PCT NO: |
PCT/NO2006/000219 |
371 Date: |
March 13, 2008 |
Current U.S.
Class: |
166/312 ;
166/72 |
Current CPC
Class: |
F04D 29/705 20130101;
E21B 37/06 20130101; F04D 25/0686 20130101; E21B 43/36 20130101;
B08B 9/00 20130101 |
Class at
Publication: |
166/312 ;
166/72 |
International
Class: |
E21B 37/00 20060101
E21B037/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 5, 2005 |
NO |
20053296 |
Claims
1. System for cleaning compressors that are situated at a
difficultly accessible location, characterized in that it comprises
a cleaning liquid line extending between a readily accessible
liquid source and the compressor.
2. System for inhibiting hydrate formation in compressors that are
situated at a difficultly accessible location, characterized in
that it comprises a hydrate inhibitor line extending between a
readily accessible hydrate inhibitor source and the compressor.
3. System according to claim 1 or 2, characterized in that the
compressor is situated on or near the seabed or downhole in a well
bore.
4. System according to claim 1, 2 or 3, characterized in that the
liquid source is a line for supplying hydrate inhibitor, anti foam
chemicals, barrier liquid, demulsifier or other types of chemicals
to a subsea production or processing activity.
5. System according to claim 1, 2 or 3, characterized in that the
liquid source is an accumulator tank situated in the vicinity of
the compressor.
6. System according to claim 5, characterized in that the
accumulator tank is in communication with a supply line for hydrate
inhibitor, anti foam chemicals, barrier liquid, demulsifier or
other types of chemicals to a subsea production or processing
activity.
7. System according to claim 5, characterized in that the
accumulator tank is in communication with the liquid outlet of a
gas/liquid separator.
8. System according to any of the claims 5-7, characterized in that
the accumulator tank is in communication with a high pressure line
diverting high pressurized gas from the compressor to boost the
pressure of the cleaning liquid in the accumulator tank and
evacuate the cleaning liquid.
9. Method for cleaning compressors that are situated at a
difficultly accessible location, characterized in that a cleaning
liquid is diverted from a readily accessible liquid source to the
compressor.
10. Method for inhibiting hydrate formation in compressors that are
situated at a difficultly accessible location, characterized in
that a hydrate inhibitor is diverted from a readily accessible
liquid source to the compressor.
11. Method according to claim 9 or 10, characterized b y installing
the compressor on or near the seabed or downhole in a well
bore.
12. Method according to claim 9, 10 or 11, characterized in that
the liquid is diverted from a line for supplying hydrate inhibitor,
anti foam chemicals, barrier liquid, demulsifier or other types of
chemicals to a subsea production or processing activity.
13. Method according to claims 9, 10, 11 or 12, characterized in
that the liquid is stored in an accumulator tank before injection
into the compressor.
14. Method according to claim 13, characterized in that the liquid
in the accumulator tank is boosted by pressurized gas from the
compressor before injection into the compressor.
15. Method according to claims 10, 11, 12, 13 or 14, characterized
in that the inhibitor is injected during shutdown of the
compressor.
Description
[0001] The present invention relates a device and a method for
cleaning of compressors that are situated at a difficultly
accessible location, e.g. subsea, according to the preamble of the
subsequent independent claims 1 and 8.
[0002] In general all compressors will during the operating life
experience degradation and fouling from different types of
particles and contaminants in the compressed fluid. Particles stick
to both static and rotating parts of the compressor flow path,
adversely affecting the aerodynamic form leading to a decrease in
mass flow, efficiency, pressure ratio and surge margin. This
implies an increase in the required electrical power in order to
maintain a constant production/delivery rate.
[0003] In recent years it has become desirable to place
compressors, especially compressors for compressing natural gas
exploited from an offshore hydrocarbon well, at or close to the
seabed, or even downhole. Compressing the gas as far upstream in
the production line as possible will reduce the required dimensions
of risers and flowlines. Especially in deep waters a reduction of
required diameter of risers has a great impact and will reduce
weight substantially and hence the need for use of sophisticated
materials, flotation devices and specially designed installation
equipment. All of which have significant cost impact.
[0004] However, maintenance of a compressor placed at such a
location has been an obstacle to putting this idea into practice.
The maintenance would involve retrieving the compressor at regular
intervals. The consequence of this would be not only the costs of
retrieving the compressor and replacing it with another, but also a
substantial down time in the production.
[0005] The present invention has as its main objective to maintain
compressor capacity as high as possible and hence power consumption
as low as possible during its entire operating life. As maintenance
of subsea compressors is extremely expensive, a further objective
is to avoid having to retrieve the compressor due to potentially
severe compressor fouling.
[0006] Subsea compressors would typically be located a long
distance from the host and the supply of electrical power and
utilities would be performed via service lines from the host,
offshore platform or onshore facility, at a typical distance of 40
to 180 km. The maintenance and cleaning of the subsea compressors
would typically be performed by retrieving the subsea compressor to
the surface (topside) in order to be cleaned manually. This is a
costly operation that will require compressor system shutdown and
an offshore vessels to perform the operation. The operation would
not be performed as frequently as it should have been due to the
high cost and possible loss of production during intervention. The
compressor will therefore experience degradation and reduction of
efficiency in the period between the intervention intervals.
[0007] Remotely located and difficultly accessible subsea
compressors have a limited power supply system due to high costs
involved in building the power supply line. A relatively small
reduction in efficiency for a large compressor will significantly
increase the required compressor power consumption in order to
maintain constant production rate. Fouling by different kinds of
substances, e.g., particles, sticking to the parts of the
compressor in the flow path would therefore relatively quickly lead
to an unacceptable reduction of efficiency that cannot be
compensated by increasing the power supply to the compressor. An
additional object of the invention is therefore to remove these
substances adhering to the compressor flow path while the
compressor is still in place at the difficultly accessible
location.
[0008] It is today common practice for compressors located topside
or onshore to utilize specialized cleaning liquids to perform
"online" or "offline" washing. However, the topside or onshore
located compressors are easily accessible and the system for supply
of cleaning liquids is located nearby.
[0009] A system for on-line washing of subsea compressors is not
existent today. It is important that the subsea compressor stations
system solutions that can show low risk, simplicity, robustness,
good efficiency and a minimum of auxiliary systems.
[0010] These objectives are obtained by a method wherein a readily
accessible liquid is supplied as a cleaning liquid to the
compressor while the compressor is still in place. According to the
invention this is realized by a cleaning liquid line extending
between a readily accessible liquid source and the compressor.
[0011] In particular the invention is suitable for a compressor
that is situated on or near the seabed or downhole in a well bore,
since this positioning of a compressor is highly desirable but
would involve substantial problems in cleaning the compressor with
the existing technology.
[0012] In a preferred embodiment the liquid source is a line for
supplying hydrate inhibitor, anti foam chemicals, barrier liquid,
demulsifier or other types of chemicals to a subsea production or
processing activity. This embodiment would involve reasonable
design measures to be taken and could be achieved by well proven
technology, per se.
[0013] Alternatively, the liquid source is an accumulator tank
situated in the vicinity of the compressor. This would ensure
sufficient liquid at a sufficient pressure at the time of
performing the cleaning of the compressor.
[0014] If the accumulator tank is in communication with a supply
line for hydrate inhibitor, anti foam chemicals, barrier liquid,
demulsifier or other types of chemicals to a subsea production or
processing activity, the accumulator tank can easily be filled with
cleaning liquid from this line.
[0015] If the accumulator tank is in communication with the liquid
outlet of a gas/liquid separator the accumulator tank can be filled
with liquid from the well flow, functioning as cleaning fluid.
[0016] The accumulator tank is in communication with a high
pressure line diverting high pressurized gas from the compressor to
boost the pressure of the cleaning liquid in the accumulator tank
and evacuate the cleaning liquid.
[0017] Thoroughly tested and reliable systems for supply of
inhibitors and chemical fluids in pipeline/tubing to subsea
production systems exist today, but are not utilized for other
purposes than flow assurance.
[0018] Design of subsea processing and boosting systems also
includes supply of inhibitors, barrier fluids and other chemical
fluids in pipelines/tubing and is based on the existing
technology.
[0019] The compressor cleaning liquid can be one of several liquids
that are readily available at the location. High pressure oil/gas
wells and subsea production systems have some sort of hydrate
prevention/control system in order to avoid hydrate formation,
especially in flowlines. Hydrates will form when the hydrocarbon
wellstream contains water in combination with high pressures and
low temperatures. To avoid formation of hydrates, a liquid hydrate
inhibitor is normally injected at the wellheads and is a part of
the oil production infrastructure. Subsea processing and boosting
systems will have means of injecting hydrate inhibitor or other
chemical inhibitor supply.
[0020] Using the liquid inhibitor for injection at the compressor
inlet (suction) will result in cleaning the fouling on compressor
parts that are in direct contact with the compressed medium and
re-establish (at least to a certain extent) the original
geometry.
[0021] Also, by injection of a cold liquid (seawater temperature)
into the compressor, the compressor performance will improve due to
reduced actual volumetric flow rate and increased density of the
compressed medium through the compressor.
[0022] The injection of a readily available liquid into the
compressor will contribute to [0023] Maintaining compressor
efficiency at a high level during operation without shut down of
gas production [0024] Reduce complexity of the overall system (no
need for extra tubing in umbilical and specialized auxiliary
systems topside) [0025] Increase reliability/availability [0026]
Minimize cost (CAPEX and OPEX) for a compressor cleaning
system/infrastructure
[0027] The invention will be explained in more detail, referring to
the enclosed drawings illustrating exemplary embodiments of the
invention, in which:
[0028] FIG. 1 illustrates schematically a first and preferred
embodiment of the invention, with cleaning liquid injected from an
inhibitor supply line which also includes an optional interstage
injection of cleaning liquid in the compressor,
[0029] FIG. 2 illustrates a second embodiment of the present
invention, with cleaning liquid supplied from an ROV and stored in
an accumulator tank, or alternatively supply of cleaning liquid
directly from an ROV,
[0030] FIG. 3 illustrates a third embodiment of the present
invention with cleaning liquid supplied from an inhibitor supply
line via an accumulator tank with alternative accumulator
evacuation systems,
[0031] FIG. 4 illustrates a fourth embodiment of the present
invention with injection of process liquid as cleaning liquid,
[0032] Referring first to FIG. 1, a compressor 1 is shown. The
compressor can be of any type that is capable of compressing dry or
wet natural gas, as the types of compressors currently used for
this purpose onshore or topside.
[0033] Well fluid is supplied from a wellbore via a well fluid line
2. Unless the well fluid consists entirely of dry, or to a certain
extent, wet gas, the well fluid is separated in a subsea or
downhole separator 3. The liquid portion (water, condensate and
oil) of the well fluid is led from the separator 3 to a liquid line
4. The gas is routed through a gas line 5 to the compressor 1. From
the compressor the compressed gas is discharged into line 6 which
is extended to a riser or flowline (single phase or
multiphase).
[0034] In the vicinity of the compressor is a supply line 7 for
supplying hydrate inhibitor to the wellhead, or other available and
suitable liquid (e.g. MEG, methanol, barrier liquid, demulsifier,
anti foam chemicals or different combinations of chemical
components required for operation of a subsea production/processing
system or to ensure reliable production). From this line extends a
branch line 8. The branch line 8 is connected to the gas line at an
injection and dosage valve 9. In the branch line 8 is an isolation
valve 10.
[0035] When there is a need for cleaning of the compressor a small
portion of the inhibitor liquid is tapped from the supply line 7 to
the branch line 8 by opening the isolation valve 10. The liquid is
fed to the injection nozzle and dosage valve 9. Typically there
will be a number of nozzles distributed at optimal locations over
the flow area, which is well known from current applications
onshore.
[0036] The compressor often comprises more than one compressor
stage. The liquid is injected in front of the first compressor
stage. The washing liquid will flow trough the compressor at high
pressure and knock loose particles that have adhered internally in
the flow path. The compressor condition monitoring system may make
the decision of when to perform washing, based on gas flow
measurements, power input measurements or other parameters
indicating reduced performance. Alternatively, the cleaning can
occur periodically in order to prevent fouling before it degrades
the compressor performance significantly and the power supply
increase or production is reduced.
[0037] The washing liquid leaves the compressor via the compressed
gas line 6 and can be carried with the gas to a subsequent station
for separating the washing liquid from the gas.
[0038] FIG. 1 also shows a solution for interstage injection of
washing liquid. This is represented by a second branch line 11
extending from the first branch line 8 downstream of the isolation
valve 10. The second branch line 11 includes a second dosage valve
12.
[0039] The advantage of interstage injection of washing liquid is
more efficient cleaning, since fresh cleaning liquid can be
introduced at optimal locations into the flow path of the
compressor. It is also feasible to have more than one interstage
injection, e.g. one for each compressor stage.
[0040] FIG. 2 shows an alternative embodiment of the invention
where an accumulator tank 13 is supplying the cleaning liquid
instead of extracting it from a supply line 7. The cleaning liquid
accumulator tank 13 can be filled onshore or topside before
installation of the tank 13 and/or it can be filled by an ROV
during compressor station operation. The ROV can either access the
compressor injection system via a connection line 25 (I which case
the accumulator 13 can be omitted) or by filling up the accumulator
13 via a connection system 33. Alternatively, a specialized tube in
the umbilical from topside may be utilized. However, this is not
preferred, due to the very high costs involved in manufacturing
umbilicals. However, the umbilical tubing used for supply of
compressor cleaning liquid does not necessarily have to be sized to
be able to supply full cleaning liquid flow rate at the time of
injection if a properly sized accumulator tank is installed
subsea.
[0041] The advantage of an accumulator tank 13 as illustrated in
FIG. 2 is that it can be filled with specialized cleaning liquids
instead of hydrate inhibitors or other available liquids. This is
especially advantageously if heavy degradation and compressor
fouling is expected and the basic mechanical effect of compressor
cleaning by liquid injection has little or no effect. Specialized
compressor cleaning liquids may increase the washing effectiveness
if the fouling is especially resistant or tough. The special
cleaning liquid can be a concentrate mixed with other available
subsea liquids (for example barrier liquid) or pre-mixed onshore
and delivered to the subsea compression system by an ROV.
[0042] In all other basic features the embodiment of FIG. 2 is
similar to the embodiment of FIG. 1. Interstage injection may of
course also be applicable for the embodiment in FIG. 2 or all other
embodiments described.
[0043] FIG. 3 shows another embodiment of the present invention.
This embodiment is similar to the embodiment of FIG. 1, the
difference being that an accumulator tank 20 and an additional
isolation valve 21 is present in the branch line 8 between the
isolation valve 10 and the injection nozzle and dosage valve 9. In
order not to disturb other processes requiring this liquid, the
accumulator tank 20 may be slowly filled to ensure that the
required compressor cleaning liquid flow rate and correct amount
can be provided so that cleaning can be performed without
disturbing other processes requiring the same liquid at other
locations in the subsea production system. In order to evacuate the
cleaning liquid from the accumulator tank 20, two options exist
where the first mentioned is preferred. A bleed line 22 is routed
from the compressor to the accumulator tank 20. The bleed line 22
will extract a small amount of pressurized gas from the compressor
1 and make it possible to evacuate the contents of the accumulator
tank 20 by opening the valve 23 while the compressor 1 is running.
As a second alternative, it is possible to route a bleed line 33
from upstream of the separator 3 to the accumulator tank 20. Due to
the fact that the separator and pipeline between the separator 3
and the compressor 1 will cause a pressure drop, the accumulator
pressure will be higher than the compressor 1 suction if valve 26
is open, and hence liquid will be pushed out of the accumulator
tank 20 to the injection nozzles 9 in front of the compressor
1.
[0044] The line similar to the bleed line 22 can also be used for
boosting the pressure of the accumulator tank 13 and evacuate its
content according to the embodiment of FIG. 2.
[0045] FIG. 4 shows a further alternative embodiment that is
feasible if a separation unit 3 is present. The figure shows a
liquid booster pump 14 that normally is present to boost the
pressure of oil, condensate and/or water after separation and
before transporting. A branch line 15 is extending from the liquid
line 31 after the booster pump 14. The branch line 15 includes an
isolation valve 16, which is opened to let fluid into an
accumulator and settling tank 17. From the accumulator and settling
tank 17 a washing liquid line 8, having an isolation valve 27,
extends to the injection nozzles and dosage valve 9, which is
generally of the same type as in FIG. 1.
[0046] In order to fill the accumulator tank 17 with liquid from
the pump 14 through the line 15, it may be necessary to bleed off
fluid already present in the tank 17 (which can be a mixture of
gas, liquid and settled particles). Preferably this fluid should be
routed to a location upstream of the separator 3. This can be done
from the settling vessel 17 via a return line 18, having an
isolation valve 19, and a flowline 30 to an upstream location of
the separator 3, or a flowline 29 into the pipeline 4 upstream of
the pump 14. The particles will be transported through line 18 and
line 29 or 30. Line 18 is therefore connected to the bottom of the
accumulator 17 in order to ensure evacuation of any settled
particles and route them through the liquid pump 14.
[0047] Any gas in the accumulator tank 17 can be evacuated through
a line 28, having an isolation valve 32, extending from the top of
the accumulator tank 17 to a location upstream of the separator 3.
The line 28 can also serve as a means for evacuating the liquid in
the settling tank 17 when the valves 19 and 16 are closed (valve 27
and 32 open). This can be done during operation due to the fact
that there is a dynamic pressure drop over the separator 3. By
opening valve 32, the pressure in tank 17 will be higher than at
the compressor suction side so that injection of the liquid in the
settling tank 17 is possible. An additional pressure increase in
the liquid line 8 can be obtained by placing the settling tank 17
at a physically higher location than the compressor.
[0048] In the accumulator and settling tank 17 the liquid coming
from the branch line 15, which often will contain particles of sand
etc, can settle for some time before it is injected as a cleaning
liquid into the compressor on one or more locations as described in
connection with FIG. 1. After injection in the compressor the
remaining fluid (and particles) in the settling vessel 17 can be
re-injected into the suction side of the pump 14 or separator 3 and
boosted back through the pump and to the receiving facility through
line 31. This evacuation of particles and remaining liquid from the
settling tank 17 can be done using the return line 18 to either
upstream of the separator (through line 29) or upstream of the
separator 3 (through line 30). The line 18 contains an isolation
valve 19, to selectively return liquid and particles to a chosen
one of these locations.
[0049] The injected inhibitor liquid must be injected in front of
the first compressor impeller but the injection nozzle and dosage
valve does not have to be a part of the compressor casing. The
injected liquid should as far as practically possible be
distributed evenly over the flow area in order to be carried with
the gas flow and gain momentum and increase washing
effectiveness.
[0050] In general, the injection device 9 may also be used as an
injection point for hydrate inhibitor during planned or unplanned
shutdown of the compressor.
* * * * *