U.S. patent application number 09/776682 was filed with the patent office on 2001-06-28 for device and process intended for two-phase compression of a gas soluble in a solvent.
Invention is credited to Charron, Yves.
Application Number | 20010005483 09/776682 |
Document ID | / |
Family ID | 9513620 |
Filed Date | 2001-06-28 |
United States Patent
Application |
20010005483 |
Kind Code |
A1 |
Charron, Yves |
June 28, 2001 |
Device and process intended for two-phase compression of a gas
soluble in a solvent
Abstract
Device intended for two-phase compression of several fluids such
as a gas soluble in an essentially liquid solvent. The device
comprises a two-phase compression element suited to deliver energy
to each of the fluids and to mix them in order to obtain at the
outlet an essentially liquid mixture at a given pressure level
Ps.
Inventors: |
Charron, Yves; (Longpont Sur
Orge, FR) |
Correspondence
Address: |
ANTONELLI TERRY STOUT AND KRAUS
SUITE 1800
1300 NORTH SEVENTEENTH STREET
ARLINGTON
VA
22209
|
Family ID: |
9513620 |
Appl. No.: |
09/776682 |
Filed: |
February 6, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09776682 |
Feb 6, 2001 |
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09195712 |
Nov 19, 1998 |
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6210126 |
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Current U.S.
Class: |
417/244 ; 418/5;
418/9 |
Current CPC
Class: |
B01F 23/29 20220101;
F04D 31/00 20130101; B01F 25/314 20220101; B01F 23/232 20220101;
B01F 23/23 20220101; E21B 43/40 20130101; B01F 2035/98
20220101 |
Class at
Publication: |
417/244 ; 418/5;
418/9 |
International
Class: |
F04C 018/30; F01C
001/30 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 19, 1997 |
FR |
97/14.604 |
Claims
1. A two-phase compression device allowing to deliver energy to
several fluids such as an essentially liquid fluid and an
essentially gaseous fluid, at least one of the fluids being
miscible in at least one other fluid, allowing mixing of said
fluids, characterized in that it comprises at least one two-phase
compression element (CM.sub.1, CM.sub.2, 10) suited to mix the
essentially liquid and the essentially gaseous fluid and to deliver
to each one of them a given energy value, the mixture coming from
said two-phase compression element being in a liquid or essentially
liquid form and at a given pressure level Ps.
2. A two-phase compression device as claimed in claim 1,
characterized in that it comprises at least one inlet stage and/or
at least one outlet stage, each one of said stages comprising
hydraulics suited to pump an essentially liquid fluid.
3. A two-phase compression device as claimed in claim 1,
characterized in that it comprises at least two sections (50, 51),
first section (50) allowing to obtain a mixture Mi with a pressure
level Pi and second section (51) allowing to obtain, from mixture
Mi, a mixture Ms with a pressure level Ps, a line (55) for
discharging mixture Mi and a line (56) delivering a fluid Mi into
the second part, said sections (50, 51) being separated by a
sealing device (52) and the hydraulics of sections (50, 51) being
mounted "back to back" so as to minimize axial thrust stresses.
4. A two-phase compression device as claimed in any one of the
previous claims, characterized in that it comprises a fluid
processing and/or mixing unit (90, 116), said processing and/or
mixing unit (90, 116) being connected to compression device (10) by
fluid delivery and discharge lines (91, 92; 124, 125).
5. A two-phase compression device as claimed in claim 4,
characterized in that it comprises a refrigeration means (98) in
processing unit (90).
6. A compression device as claimed in claim 4, characterized in
that it comprises a circuit (93, 94, 95, 96, 97, 98, 99; 92, 93,
98, 100, 101, 102, 103) for cooling at least part of the two-phase
mixture withdrawn from the compression device and/or part of the
liquid phase coming from two-phase compression device (10).
7. A compression device as claimed in any one of the previous
claims, characterized in that it comprises means for determining
parameters related to the fluid and/or to operation of the
compression device, data computing and processing means capable of
modifying the rotating speed of the two-phase compression device
and/or to act on the refrigeration means efficiency and/or on the
flow rate of the fluid recycled to the cooling circuit.
8. A compression device as claimed in any one of the previous
claims, characterized in that it comprises a device (70) placed
between a pumping stage and a two-phase compression stage, said
device (70) being suited to introduce an essentially gaseous fluid
and to mix it with the liquid fluid coming from the pumping
stage.
9. A compression device as claimed in any one of the previous
claims, characterized in that it comprises a device (80, 81, 82)
placed at least at the level of a diffuser Ri of a compression
stage Ei(Ii, Ri) for introducing an essentially gaseous or
essentially liquid fluid in the two-phase fluid coming from
impeller Ii.
10. A process allowing to deliver energy to several fluids, at
least one of the fluids being miscible in at least one other fluid,
and to simultaneously mix said fluids, such as an essentially
gaseous fluid and an essentially liquid fluid, characterized in
that the essentially gaseous fluid and the essentially liquid fluid
at least are sent to the same two-phase compression device
(CM.sub.1, CM.sub.2, 10) suited to deliver energy to at least each
of the two fluids and to mix the fluids in order to obtain, at the
outlet, an essentially liquid fluid at a given pressure Ps.
11. A process as claimed in claim 10, characterized in that it
comprises a stage of withdrawing at least part of the mixture of
fluids after passage through a number of stages m of the two-phase
compression device, a stage of processing the withdrawn part and a
stage of sending it back, after processing, to a stage of the
compression device of higher rank than the rank of the withdrawal
stage.
12. A process as claimed in any one of claims 10 to 11,
characterized in that the fluid and/or a fluid such as part of the
two-phase mixture withdrawn and/or part of the liquid phase
extracted from the two-phase mixture withdrawn or at least part of
the liquid coming from the two-phase compression device is
refrigerated and the refrigerated fluid is recycled to the fluid
extracted from the two-phase compression device.
13. A process as claimed in any one of claims 10 to 12,
characterized in that the rotating speed of the compression device
is controlled and/or the efficiency of the refrigeration stage is
controlled and/or the flow rate of the recycled refrigerated fluid
is controlled.
14. Application of the two-phase compression device as claimed in
any one of claims 1 to 9 and of the process as claimed in any one
of claims 10 to 13 for simultaneous transfer of acid gases and of
formation water to an underground reservoir.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a process and to a system
for delivering energy to several fluids and simultaneously for
mixing them, one of the fluids being miscible in the other fluid or
fluids.
[0002] The invention is notably applicable to fluids which occur in
an essentially gaseous form and which are miscible or soluble in an
essentially liquid fluid.
[0003] The present invention notably allows, by means of a single
machine, both to compress an acid gas and a formation water from an
oil reservoir, and to mix them in an essentially liquid form, acid
gases being particularly soluble in formation water. The liquid
mixture obtained can be sent to a storage zone or reinjected in a
production well or an aquifer.
[0004] The invention is in particular applied to the processing of
a natural gas containing acid gases, carbon dioxide and/or hydrogen
sulfide, which are generally at least partly separated from the
natural gas. When present in small amounts, these separated acid
gases can be discharged into the atmosphere, directly or after
incineration. However, pollution control standards being
increasingly stringent, these discharges into the atmosphere are
less and less allowed, and it has become necessary to find other
solutions easy to implement and abiding by these new standards with
a minimum investment.
BACKGROUND OF THE INVENTION
[0005] The prior art describes various solutions for eliminating
acid gases.
[0006] One solution consists in injecting the acid gases
individually into a reservoir by using centrifugal or reciprocating
compressors.
[0007] Another procedure consists in injecting the acid gases with
another fluid, for example the formation water available in the
reservoir. This solution notably has the advantage of eliminating
simultaneously the acid gases and the formation water, considered
as two pollutants.
[0008] Pan Canadian Limited's formation water and acid gas
reinjection process, whose main stages are summed up hereafter and
described in FIG. 1, is based on this principle.
[0009] The fluid coming from production wells is split into an oil
phase which is recovered, an aqueous phase and a gas phase
circulating respectively in lines 1 and 2. The aqueous phase is
stored in atmospheric tanks 3, whereas the gas phase containing the
acid gases is processed in an amine treating plant 4 in order to
obtain a gas without acid components and a gas with a high acid
component content at a pressure close to the atmospheric pressure.
The gas fraction rich in acid gases is sent to a compressor 5 and
the formation water is sent to a single-phase pump 6. The gas and
the formation water, which have separately reached a given pressure
level, are then mixed together in a mixer 7. Mixing is performed at
a high pressure in order to facilitate dissolution of the gases in
the water, the amount of dissolved acid gases increasing with the
pressure level. This mixture occurring in the liquid form is then
reinjected for example into an underground reservoir by means of a
single-phase pump 8 suited to pump liquid single-phase fluids.
Upstream from the high-pressure pump, the gas must be entirely
dissolved in the liquid and the NPSHA (suction head available in
relation to the vapour pressure of the gas) must also be higher
than the NPSHR (suction head required at the pump inlet in relation
to the vapour pressure).
[0010] In the case of high reinjection pressure applications and
for production fluids with a high gas content, mixing of the water
and of the gas is performed in successive separate pumping,
compression and mixing stages.
[0011] This process requires an equipment which has the drawback of
being heavy and expensive, using both single-phase pumps and
compressors, as well as many heat exchangers. Furthermore, as
dissolution of the acid gases in the water is not instantaneous, it
is necessary to use static or dynamic mixers in order to obtain
perfect dissolution of the gas in the liquid upstream from the
single-phase pumps, thus increasing even further the complexity of
the materials, the cost and the overall dimensions of such a
system.
SUMMARY OF THE INVENTION
[0012] The present invention proposes to overcome the drawbacks of
the prior art by adopting a new approach allowing notably to
minimize the number of equipments commonly used.
[0013] According to the invention, one uses a two-phase compression
device capable of delivering energy to several fluids, at least one
of the fluids being soluble in at least one other fluid, and of
mixing simultaneously the fluids, so as to obtain at the outlet a
fluid in an essentially or completely liquid form.
[0014] The object of the present invention is a two-phase
compression device allowing to deliver energy to several fluids
such as an essentially liquid fluid and an essentially gaseous
fluid, at least one of the fluids being miscible in at least one
other fluid, and allowing to mix said fluids.
[0015] It is characterized in that it comprises at least one
two-phase compression element suited to mix the essentially liquid
and essentially gaseous fluids and to deliver to each one of them a
given energy value, the mixture coming from said two-phase
compression element being in a liquid or essentially liquid form
and at a given pressure level.
[0016] According to an embodiment, the two-phase compression device
can comprise at least one inlet stage and/or at least one outlet
stage, each of said stages comprising hydraulics suited to pump an
essentially liquid fluid.
[0017] The compression device can consist of at least two sections,
the first section allowing to obtain a mixture Mi with a pressure
level Pi and the second section allowing to obtain, from mixture
Mi, a mixture Ms with a pressure level Ps, a discharge line for
mixture Mi and a delivery line for fluid Mi in the second section,
said two sections being separated by a sealing device and the
hydraulics of the two sections being mounted "back to back" so as
to minimize axial thrust stresses.
[0018] The two-phase compression device can comprise a device
positioned between two compression stages and suited to mix at
least the essentially liquid fluid and the essentially gaseous
fluid, for example in cases where these two fluids are introduced
at stages of different ranks.
[0019] The compression device can also comprise a fluid processing
and/or mixing unit, said processing and/or mixing unit being
connected to the compression device by fluid delivery and discharge
lines, before and after processing.
[0020] In some instances, the processing unit comprises a
refrigeration means included in the processing unit.
[0021] The processing unit can comprise a circuit for cooling at
least part of the two-phase mixture withdrawn from the two-phase
compression device and/or part of the liquid phase coming from the
two-phase compression device.
[0022] The compression device comprises for example means for
determining parameters linked with the fluid and/or the functioning
thereof, data computing and processing means capable of changing
the rotating speed of the two-phase compression device and/or of
acting on the efficiency of the refrigeration means and/or on the
flow rate of the fluid recycled at the level of the cooling
circuit.
[0023] The object of the invention is also a process for delivering
energy to several fluids, at least one of the fluids being miscible
in at least one other fluid, and for simultaneously mixing fluids
such as an essentially gaseous fluid and an essentially liquid
fluid.
[0024] It is characterized in that the essentially gaseous fluid
and the essentially liquid fluid at least are sent to the same
two-phase compression device suited to deliver energy to at least
each one of the two fluids, and to mix the two fluids together in
order to obtain at the outlet an essentially liquid fluid at a
given pressure.
[0025] According to the process, the pressure difference between
the fluids to be mixed is for example determined prior to feeding
them into the two-phase compression device, and
[0026] if the value of this difference is less than a set value,
the two fluids are sent to the same two-phase compression stage of
the compression device,
[0027] if the value of this difference is greater than a set value,
the fluid with the lower pressure is sent to a stage of the
compression device of rank i and the fluid with the higher pressure
to a stage of higher rank i+n, number n being determined as a
function of the pressure difference.
[0028] The process can comprise a stage of withdrawing at least
part of the mixture of fluids after passing through a number m of
stages of the two-phase compression device, a stage of processing
the withdrawn part and a stage of sending the processed part back
to a stage of the compression device of a higher rank than the rank
of the withdrawal stage.
[0029] It is also possible to refrigerate the fluid and/or a fluid
such as part of the two-phase mixture withdrawn or at least part of
the liquid phase extracted from the two-phase mixture withdrawn or
at least part of the liquid coming from the two-phase compression
device, and the refrigerated fluid can possibly be recycled.
[0030] It is also possible to control the rotating speed of the
compression device and/or to control the efficiency of the
refrigeration stage and/or to control the flow rate of the recycled
fluid.
[0031] The invention is particularly well-suited for simultaneous
transfer of acid gases and of formation water to an underground
reservoir.
[0032] In relation to the prior art, the present invention thus has
the advantage of simplifying the devices required for compression
and mixing of several fluids, for example at least one essentially
gaseous fluid and at least one essentially liquid fluid miscible in
each other.
[0033] The process according to the invention can be applied to all
the fields where energy is to be delivered simultaneously to a gas
phase and to a liquid phase, the gas phase being soluble in the
liquid phase, and the pressure values of the phases can be
different.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] Other features and advantages of the invention will be clear
from reading the description hereafter, given by way of examples,
within the scope of non limitative applications to the transfer of
acid gases and of formation water to an underground reservoir or an
aquifer, with reference to the accompanying drawings wherein:
[0035] FIG. 1 diagrammatically shows Pan Canadian's process
according to the prior art,
[0036] FIG. 2 shows a two-phase compression device suited for
implementation of the process according to the invention,
[0037] FIG. 3 diagrammatically shows an example of layout of
two-phase compression stages,
[0038] FIGS. 4A and 4B show two realisation variants for the inlet
and outlet stages of the combined single-phase pumping and
two-phase compression device,
[0039] FIG. 5 shows another variant for the system of FIG. 3,
[0040] FIGS. 6, 7, 8 diagrammatically show a variant of the process
suited for fluids with different pressures and the method for
introducing them into the two-phase compression device,
[0041] FIG. 9 diagrammatically shows a realisation variant where
the mixture of the two fluids can be processed during the
compression operation,
[0042] FIGS. 10A and 10B show two devices for recycling the liquid
through the refrigeration unit,
[0043] FIG. 11 shows a generalization of the principle according to
the invention applied for several liquid and gaseous fluids having
different pressure values prior to being fed into the device,
and
[0044] FIG. 12 shows a possible control pattern for the compression
device.
DETAILED DESCRIPTION OF THE INVENTION
[0045] In order to describe the device according to the invention
more clearly, the description given hereafter by way of non
limitative example relates to the transportation of acid gases and
of a formation water, the acid gases being soluble in the formation
water.
[0046] Mixing and dissolving of the acid gases in the water are
based on physical phenomena which are reminded hereafter.
[0047] Under equilibrium conditions, dissolution of an acid gas in
water, formation water for example, varies with the pressure and
the temperature. The dissolution ratio expressed in volume unit of
gas per volume unit of liquid under standard pressure and
temperature conditions increases respectively when the pressure
increases and when the temperature decreases.
[0048] Dissolution will take place progressively owing to the
diffusion time between the phases, and approach of equilibrium
conditions can consequently be activated by increasing the surfaces
of contact between the acid gases and the formation water.
[0049] In case of two-phase compression by means of a rotodynamic
type pump, reaching equilibrium conditions is facilitated by the
formation of small-size bubbles. These bubbles appear at the
junction between the stationary parts and the rotating parts of the
pump, where strong shear forces are exerted.
[0050] This approach of equilibrium is however slowed down by the
coalescence of the bubbles which can appear in the neigbourhood of
the impellers and/or of the diffusers of the two-phase compression
device. For substantially equal performances (manometric head and
axial length), it will be advantageous to increase the number of
compression cells (impellers and/or diffusers) and to decrease the
axial length thereof so as to increase the number of times the size
of the bubbles can be reduced.
[0051] FIG. 2 diagrammatically shows an example of implementation
of the process which is suitable when the formation water and the
acid gases have similar pressure levels at the inlet of the
two-phase compression device, the difference between the pressure
levels being slight enough to allow them to be sent to the same
stage.
[0052] Pumping device 10 is connected by line 11 to device 12 which
receives the acid gases coming from a source bearing reference
number 13 through line 14 and, through line 16, the formation water
stored in a tank 15.
[0053] The acid gases can come from a processing unit as described
in the applicant's patents FR-2,605,241 and FR-2,616,087. At the
outlet of these processing units, the acid gases have a pressure
that can range between 0.5 and 1.5 MPa and a temperature ranging
between -30.degree. C. and -10.degree. C. In case of amine
processing units, the pressure is of the order of 0.1 MPa and the
temperature ranges between 10.degree. C. and 40.degree. C.
[0054] Device 12 is selected to favour at least partial dispersion
of the acid gases in the form of bubbles in the liquid or at least
partial dispersion of the liquid in the form of droplets in the
gas.
[0055] Two-phase compression or pumping device 10 is provided with
at least one discharge line 17 for the essentially liquid mixture.
The pressure level of this mixture at the outlet of the compression
device is sufficient to ensure its transfer to an aquifer or an
underground reservoir 18.
[0056] The initial pressure value of the acid gases and of the
formation water can be measured by means of pressure detectors 19a,
19b situated respectively at the outlet of processing unit 13 and
of storage tank 15.
[0057] Two-phase compression device 10 comprises at least one
pumping stage including an impeller and a diffuser denoted by Ii
and Ri in the figures hereafter. The hydraulics of the impellers
and diffusers have specific characteristics suited to deliver
energy to a two-phase fluid comprising at least one gas phase and
at least one liquid phase, the ratio of the volume flow rates of
these two phases ranging between 0 and infinity, such as
helical-axial impellers. The layout and the characteristics of
these hydraulics are the same as those described in one of the
applicant's patents FR-2,333,139, FR-2,471,501 and FR-2,665,224.
Such a device also allows to dissolve and to mix the acid gases in
the formation water in order to obtain an essentially liquid or a
liquid mixture.
[0058] The number of compression stages used depends on the
pressure level required at the outlet.
[0059] The two-phase compression device will preferably be designed
with impellers with an axial length smaller than the length of the
impellers commonly used in the claimant's aforementioned devices,
and with a larger number of impellers so as to keep the same global
performance (same outlet pressure for the same total axial length).
As explained above, the number of times the gas pockets and the
macrobubbles formed in an impeller can be reduced is thus
increased, at the interface between the rotating and the static
parts (impeller-diffuser and diffuser-impeller), in the form of
microbubbles of a diameter ranging between 1 micron and 1
millimeter.
[0060] Without departing from the scope of the invention, it is
possible for technological reasons to design the compression device
in the form of several compression or pumping machine bodies, each
one of these bodies consisting of one or more sections and each
section comprising one or more compression or pumping stages. An
example of such a device made up of several bodies is shown in FIG.
1.
[0061] FIG. 3 diagrammatically shows an example of compression
device 10 which comprises, in the present case, 4 in-line
compression stages E.sub.1 to E.sub.4.
[0062] Each stage Ei of the system comprises an impeller Ii
followed by a diffuser Ri, impeller Ii being secured to rotation
shaft 30, i denoting the rank of the two-phase compression stage,
the stages being included in a housing 31.
[0063] Two-phase compression device 10 comprises an opening 33
communicating with fluid delivery line 11 and an inlet chamber 34
placed upstream from the first impeller I1.
[0064] In the neighbourhood of its outlet, the two-phase
compression device can comprise an adapter part such as a volute 35
allowing to convert the kinetic energy into potential energy in
order to minimize energy losses at the outlet, connected to line 17
intended for discharge of the essentially liquid mixture.
[0065] The acid gases and the formation water introduced at a
pressure P0 and a temperature T0 through opening 33, then inlet 34,
are compressed in the first stage (I1, R1). At the outlet of this
stage, part of the acid gases is dissolved in the formation water
in a proportion close to that determined by the dissolution
equilibrium conditions at the outlet of stage E1, at a pressure P1
and a temperature T1. The mixture thus obtained M1 is sent to the
compression stages of higher rank in order to increase the pressure
and to intensify mixing of the acid gases in the formation water
until complete dissolution of the acid gases is reached. At the
outlet of the two-phase compression device, the mixture Ms
consisting of the acid gases dissolved in the formation water is
discharged through a line 17 in an essentially liquid or in a
liquid form, at a pressure Ps and a temperature Ts.
[0066] The last pumping stage(s) of the compression device can
advantageously comprise hydraulics suited for single-phase fluids,
such as radial impellers known to the man skilled in the art.
Examples of adaptation of the outlet and inlet stages of the
compression device are shown by way of non limitative example in
FIGS. 4A and 4B.
[0067] FIGS. 4A and 4B diagrammatically show variants of the
compression device where the characteristics of the inlet and/or
outlet pumping stages are optimized and selected according to the
nature of the fluids.
[0068] In cases where the acid gases have a markedly higher
pressure than the formation water, the acid gases are fed into
two-phase compression device 10 through a line 43 at an
intermediate compression pressure level, and device 12 is no longer
used. It is then advantageous to use, for the first compression
stages 40, hydraulics (impellers 41 and diffusers 42) suited to
pump a liquid, for example radial wheels as diagrammatically shown
in FIG. 4A.
[0069] If the acid gases are entirely dissolved in the formation
water upstream from the outlet of two-phase compression device 10,
it is advantageous to use, for the last compression stages,
hydraulics (impellers 45 and diffusers) suited to pump a liquid,
for example radial wheels, as diagrammatically shown in FIG.
4B.
[0070] In both cases, the outside diameter of the radial impellers,
Dr, can be larger than the outside diameter of the helical-axial
impellers, Dm, in order to reduce the number of single-phase stages
to the minimum.
[0071] Mechanical-hydraulic adaptation between a multiphase type
pumping stage and a single-phase type pumping stage (liquid or gas
phase) will be achieved as shown in FIG. 7 in the case of a
helical-axial impeller downstream from a radial impeller.
[0072] FIG. 5 diagrammatically shows a variant of the two-phase
compression device made up of two sections 50, 51 where the
compression stages are mounted "back to back" , the two sections
being separated by a sealing device 52, a labyrinth seal for
example. The mixture circulates in section 30 in the opposite
direction to that of section 31.
[0073] According to this variant, section 50 comprises several
compression stages EI (Ii, Ri) followed by a volute 54. The mixture
consisting of the acid gases and the formation water is sent to the
first section 50 where it reaches an intermediate pressure level Pi
and where at least partial dissolution of the acid gases is
performed. The partial mixture Mi is discharged through a line 55
downstream from volute 54.
[0074] This mixture Mi coming from first section 50 is then sent to
the second section 51 of the compression device through a line 56.
The mixture compressed through the compression stages of second
section 51 is discharged through a volute 57, then through a line
58 corresponding to the high-pressure outlet of the compression
device. While flowing through the second section of the compression
device, the pressure of mixture Mi rises to a level Ps sufficient
for almost total dissolution of the acid gases in the formation
water allowing to obtain an essentially liquid form Mj.
[0075] Such a layout notably has the advantage of minimizing the
axial thrust stresses exerted on the shaft in case of high-pressure
applications.
[0076] When the acid gases and the formation water have rather
different pressure levels at the inlet of the two-phase compression
device, it is preferable to send them to different stages of the
compression device so as to prevent energy losses. FIGS. 6, 7 and 8
show various realisation examples.
[0077] FIG. 6 shows a layout suited to the case where the formation
water is at a pressure level Pe which is lower than the pressure
level Pg of the acid gases. The formation water is introduced
through a low-pressure inlet 60 in the first pumping stage whereas
the acid gases are introduced through a line 62 connected to an
inlet 61 corresponding to a compression stage situated downstream
from the inlet stage. The gases are preferably introduced at the
level of diffuser Ri of the pumping stage of rank i at the outlet
of which the formation water has a pressure level Pe' close to the
inlet pressure level Pg of the acid gases.
[0078] FIG. 7 shows an example of an acid gas delivery device 70
placed downstream from inlet 61, whose purpose is both to
facilitate mixing of the gas and of the liquid, and to direct the
mixture towards the inlet of an impeller suited for compression of
the two-phase mixture.
[0079] Device 70 is situated between impeller Ii of the pumping
stage of rank i consisting for example of a radial wheel and
two-phase compression stage E2 consisting of a helical-axial
wheel.
[0080] Device 70, similar to a stator stage separating two radial
wheels and known to the man skilled in the art, mainly comprises a
diffuser 71 for converting the kinetic energy into potential energy
and a runback 72.
[0081] It also comprises a part 73 including a passage 74
communicating with acid gas delivery line 62 and several channels
75 of very small diameter pierced through part 73. These channels
open into runback 72 and can be evenly arranged in the radial
plane.
[0082] In case of a horizontal-joint body, part 73 is directly
supported by housing 31.
[0083] In case of a vertical-joint body, part 31 and all the
internal parts of device 70 form a cartridge mounted inside a
cylindrical housing, not shown in the figure. Such a construction
is known to the man skilled in the art.
[0084] The acid gases are fed into the two-phase compression device
successively at the level of external line 62, in internal line 74
and eventually in runback 72 through channels 75.
[0085] The device allows intimate mixing of the gas and of the
liquid, the efficiency increasing with the number of channels.
[0086] In some application instances, it may be advantageous to
introduce a fluid (gas or liquid) at the level of any two-phase
compression stage.
[0087] FIG. 8 shows in detail an example of layout of the housing
31 of compression device 10 communicating with an auxiliary line 80
delivering a single-phase fluid.
[0088] An opening 81 is provided for example at the level of
diffuser Rj of the stage of rank j of the compression device.
Downstream from opening 81, a device 82 pierced with channels 83 of
very small diameter allows to introduce the single-phase fluid and
to diffuse it in the two-phase mixture from impeller Ij. The new
mixture consisting of the two-phase mixture and the single-phase
external fluid from diffuser Rj is sent to impeller Ij+1 of the
compression stage of rank (j+1). The diameters of the impellers of
ranks Ij and Ij+1 are suited to the volume flow rate change due to
the introduction of the additional fluid through line 80.
[0089] It is also possible to use this layout to introduce
additives used in the petroleum sphere, such as anticorrosion or
antihydrate additives, or surfactants.
[0090] During two-phase compression, it may be advantageous to
process the acid gas-formation water mixture in order to activate
dissolution.
[0091] Processing will for example consist in stabilizing the
dissolution or to cool the acid gas-water mixture whose temperature
has risen during compression precisely on account of the
compression of the mixture and also of the exothermic character of
the dissolution reaction. Other processings and their associated
devices can be envisaged without departing from the scope of the
invention.
[0092] FIG. 9 diagrammatically shows a realisation example where
the compression device 10 of FIG. 5 is associated with a processing
unit 90 arranged in series.
[0093] The mixture Mi coming from medium-pressure outlet 55 is sent
through a line 91 to processing unit 90. Downstream from processing
unit 90, mixture Mi is thereafter sent through a line 92 to the
medium-pressure inlet 56 of the second part of the compression
device.
[0094] By the mere fact of the flow of the two-phase mixture and of
the residence time in lines 55, 91, 92 and 56 and in the processing
unit, it is possible to come close to the dissolution conditions
defined under equilibrium conditions. As a result, the diameters
and the lengths of the pipes situated on either side of processing
unit 90 can be calculated so as to adjust this residence time.
[0095] The residence times to be observed will possibly be defined
from preliminary tests performed under real operating conditions.
It will thus be possible to predict the dissolution differences
between transient conditions and at equilibrium, and these
differences can be expressed in lengths of time or in flow of
gas.
[0096] The processing unit can comprise a refrigeration system.
Refrigeration of the mixture has many advantages:
[0097] it will increase the capacity of the liquid to dissolve the
gas under equilibrium conditions,
[0098] it will allow to come close to equilibrium conditions
considering the time of residence in the refrigeration system,
[0099] it will allow to increase the density of the mixture, a
parameter favouring compression of a two-phase mixture,
[0100] it will allow to decrease the ratio of the volume flow rates
of gas and of liquid, a parameter which also favours compression of
a two-phase mixture.
[0101] The processing/cooling unit can be designed to cool the
two-phase mixture and/or part of the liquid phase taken from this
mixture or the liquid coming from the two-phase compression device
or part thereof. FIGS. 10A and 10B diagrammatically show two
realisation examples of the processing device comprising liquid
withdrawal and recycling means.
[0102] In FIG. 10A, processing unit 90 comprises a static or
dynamic type mixer 93 placed on line 91, a pressure drop control
valve 94, a means 95 for extracting at least part of the liquid
phase contained in the two-phase mixture circulating in line 91, a
line 96 and a pump 97 allowing to send the extracted liquid
fraction to be cooled to a cooling device such as an exchanger 98
at the outlet of which the cooled liquid fraction is recycled
through a line 99 to static mixer 93 in order to be mixed with the
fluid circulating in line 91.
[0103] When the fluid exhibits a stratified flow in line 91,
extraction means 95 are selected to withdraw at least part of the
liquid phase at a lower point of the line.
[0104] For fluids with an annular flow, extraction means 95 allow
to extract a fraction of the liquid phase on the periphery of line
91.
[0105] Pump 97 can be a single-phase pump with a low manometric
head.
[0106] FIG. 10B diagrammatically shows another realisation variant
where withdrawal of the liquid phase to be cooled is performed at
high pressure on the liquid fluid coming from the compression
device.
[0107] The processing unit comprises the static or dynamic mixer 93
placed on line 91, means 100 for extracting a fraction of liquid
from the compression device, which are connected to heat exchanger
98 by a line 101, a valve 102 allowing flow rate control of the
liquid cooled in heat exchanger 98, the cooled liquid being sent
through a line 103 to static mixer 93.
[0108] The part of the liquid phase that has not been withdrawn,
which substantially corresponds to the liquid flow circulating in
line 11, is discharged through a line 104.
[0109] Recirculation of the cooled liquid to line 91 is allowed
under normal conditions without the aid of an additional pump on
account of the positive pressure difference between line 58 and
line 55.
[0110] Such layouts (FIGS. 10A and 10B) will notably allow:
[0111] higher efficiency and volume decrease of the exchanger
operating at a high or moderately high pressure,
[0112] liquid flow increase in the recycle zone, favouring
dissolution of the gas in the liquid.
[0113] Processing unit 90 can be equipped with other lines 91b
allowing a fluid to be added to mixture Mi, the aforementioned
additives for example.
[0114] FIG. 11 diagrammatically shows an example of generalization
of the use of a two-phase compression device comprising two machine
bodies CM.sub.1 and CM.sub.2 forming the two-phase compression
device and which are connected to each other by a line 123,
suitable for example in the presence of several sources of fluids
at different pressure levels.
[0115] In this example, the second body CM.sub.2 is associated with
a processing device 116 according to a layout similar to that of
FIG. 9.
[0116] At the outlet of body CM.sub.1, the fluid occurs for example
in a multiphase form.
[0117] In FIG. 11, the compression device is fed by three acid gas
sources 110, 111 and 112 respectively, at pressures PG.sub.3,
PG.sub.2 and PG.sub.1, temperatures TG.sub.3, TG.sub.2 and
TG.sub.1, with PG.sub.1< PG.sub.2< PG.sub.3 for example.
[0118] The acid gases G.sub.1 (112) and G.sub.2 (111) are fed into
the first body CM.sub.1 through lines 113, 114 corresponding to
different compression stages of the body, whose ranks are
determined according to the values of pressures PG.sub.1 and
PG.sub.2.
[0119] Acid gases G.sub.3 (110) are sent through a line 115 to
processing device 116.
[0120] Two sources of liquid L.sub.1 and L.sub.2 at respective
pressures PL.sub.1 and PL.sub.2 and temperatures TL.sub.1 and
TL.sub.2 are also shown in this figure.
[0121] Liquid L.sub.1 (117) is sent through a line 120 to the first
body CM.sub.1. On the assumption that PL.sub.1< PG.sub.1, line
120 is directly connected to the first stage of body CM.sub.1,
whereas acid gases G.sub.1 and G.sub.2 are sent to pumping stages
of higher rank according to a pattern similar to that of FIG.
6.
[0122] The liquid contained in source L.sub.2 (118) is directly
sent to second body CM.sub.2 through a line 121, for example at the
level of the inlet stage thereof.
[0123] When following the fluid distribution given above, mixing of
the fluids and their pressure gain are for example effected as
follows:
[0124] The pressure level PL.sub.1 of liquid L.sub.1 increases
until it reaches a pressure level substantially identical to the
pressure PG.sub.1 of gas G.sub.1. In the first part of body
CM.sub.1, acid gases G.sub.1 are dissolved in liquid L.sub.1 at
least partly, the mixture M obtained being at a pressure level P.
Acid gases G.sub.2 with a pressure level PG.sub.2 are sent to the
stage at the outlet of which mixture M has a substantially
identical pressure level. These three fluids become mixed while
passing through the various compression stages of body CM.sub.1,
the resulting multiphase mixture M' being discharged through a line
122 at a pressure level P'.
[0125] Mixture M' from body CM.sub.1 is fed with liquid L.sub.2 at
a pressure PL.sub.2 into second body CM.sub.2 through a line
123.
[0126] At the outlet of the first part of the second body, mixture
Mi, which is at an intermediate pressure level Pi, is sent through
a line 124 to processing device 116 where it is mixed at least
partly with gas G.sub.3.
[0127] The mixture M'i coming from the processing device is then
sent through a line 125 to the second part of body CM.sub.2 and
flows through the various compression stages. At the outlet of body
CM.sub.2, an essentially liquid fluid Ms is discharged at a
pressure level Ps through outlet 126 for example in an aquifer.
[0128] According to another method of operation, it will be
possible to make up for differences on the operating parameters of
the two-phase compression device from various measurements on the
two-phase compression device.
[0129] FIG. 12 shows, by means of a manometric head
(ordinate)--outlet volume (abscissa) diagram, the hydraulic
performances of the two-phase compression device for various
velocities (N). This diagram includes a wanted working point C, and
two points A and B representing two dysfunctioning instances.
[0130] When the two-phase compression device is equipped with a
suitable measuring system such as pressure, temperature, flow rate,
density (or void fraction) detectors, and a control and computing
device such as a microcontroller connected to all these elements,
it is possible
[0131] to measure various parameters:
[0132] the flow rate values of the gas phase and of the liquid
phase before they are fed into the two-phase compression device Qg
and Q1, and to measure for each one the associated temperature and
pressure values Tg and T1, Pg and P1,
[0133] at the outlet of the compression device, values related to
the liquid, such as the pressure Pm, the temperature Tm, the flow
rate Qm and the density .rho.m thereof,
[0134] to store the characteristic parameters of the gaseous and
liquid fluids at the inlet of the compression device, for example
the density for the liquid fluid, .rho.1, the molar mass Mg and the
isentropic factor .gamma.g for the gaseous fluid,
[0135] from these various measurements, from the aforementioned
data and from suitable data processing, to determine the working
point of the compression device and the corresponding velocity
curve, and
[0136] by comparison with a determined value, to check whether this
working point belongs to an allowed operating range or to an
optimum operating range.
[0137] If the working point is outside the desired operating range,
it will be possible to act on the rotating speed if the device has
a variable-speed drive, and possibly on the efficiency of the
refrigeration system or on the flow rate of the recycled liquid
according to the design of the compression system.
[0138] For example, if point A represents too fast a dissolution
with a flow rate that is too low downstream and a pressure that is
too high downstream, to overcome this problem it will be possible
to intervene by reducing the rotating speed of the two-phase
compression device in order to bring working point A to the desired
working point C.
[0139] Working point B schematizes the opposite case.
[0140] The compression device will preferably be equipped with a
variable-speed drive. Speed control can be performed automatically
or manually.
COMPARATIVE EXAMPLE
[0141] The two-phase compression and mixing device has many
advantages in relation to a single-phase compression and mixing
system, including a substantial reduction in the number of
equipments, resulting in:
[0142] more safety in the presence of noxious gases such as
H.sub.2S,
[0143] a cost decrease in a corrosive environment and/or an
environment subjected to high pressures.
[0144] The reduction in the number of equipments mostly depends on
the application instances, mainly the GLR and the pressure at the
inlet of the compression device. The inlet pressure is
approximately equal to the pressure downstream from the deacidizing
unit.
[0145] A comparative study between two-phase and single-phase
(compressor and pump) compression systems has been conducted on the
following basis:
[0146] a two-phase pump comprising 13 compression stages. The
discharge pressure is determined by the two-phase compression
device. The same pressure conditions are used for both compression
types,
[0147] two single-phase manometric head values of 150 m and 300 m
per two-phase compression stage. The two-phase compression
manometric head is obtained by the product of the single-phase head
and of the two-phase efficiency, the latter depending on the GLR
and on the ratio of the phase densities,
[0148] a liquid flow rate of 200 m.sup.3/h and a gas flow rate
ranging between values corresponding to a GLR of 1 and a GLR of
15,
[0149] a pressure of 1 MPa abs at the outlet of a physical solvent
treating process and of 0.1 MPa at the outlet of a chemical solvent
treating process.
[0150] The table hereafter gives, in the conditions of the study,
the number of compression sections and consequently the number of
cooling units (also the number of drums upstream from the
compression sections) required for a single-phase compression when
one cooling unit at most is required by a two-phase
compression.
1 GLR of the fluid at the inlet of the two-phase compression device
1 4 9 15 INSTANCE I 2 2 1 1 Physical solvent treatment Manometric
head per two-phase impeller: 150 m INSTANCE II 3 3 2 2 Physical
solvent treatment Manometric head per two-phase impeller: 300 m
INSTANCE III 5 5 5 4 Chemical solvent treatment Manometric head per
two-phase impeller: 150 m
* * * * *