U.S. patent application number 13/263681 was filed with the patent office on 2012-02-09 for ejector device for forming a pressurized mixture of liquid and gas, and use therefore.
This patent application is currently assigned to TOTAL SA. Invention is credited to Yves Lecoffre, Guillaume Maj, Jacques Marty.
Application Number | 20120034106 13/263681 |
Document ID | / |
Family ID | 41343301 |
Filed Date | 2012-02-09 |
United States Patent
Application |
20120034106 |
Kind Code |
A1 |
Lecoffre; Yves ; et
al. |
February 9, 2012 |
Ejector Device for Forming a Pressurized Mixture of Liquid and Gas,
and Use Therefore
Abstract
Ejector device for forming a pressurized mixture of liquid and
gas, comprising a suction chamber and a diffuser. The suction
chamber comprises an injection nozzle for producing a jet of liquid
flowing in a longitudinal direction, a gas inlet for admitting into
the suction chamber a gas to be driven by the liquid jet, and an
outlet opening for discharging the liquid jet and the driven gas
from the suction chamber. The diffuser is connected to the outlet
opening of the suction chamber and has, in the longitudinal
direction, a transversal section that increases from the outlet
opening, the diffuser being situated immediately after the outlet
opening of the suction chamber.
Inventors: |
Lecoffre; Yves; (La Tronche,
FR) ; Maj; Guillaume; (La Tronche, FR) ;
Marty; Jacques; (La Tronche, FR) |
Assignee: |
TOTAL SA
Courbevoie
FR
|
Family ID: |
41343301 |
Appl. No.: |
13/263681 |
Filed: |
April 2, 2010 |
PCT Filed: |
April 2, 2010 |
PCT NO: |
PCT/FR2010/050637 |
371 Date: |
October 7, 2011 |
Current U.S.
Class: |
417/179 |
Current CPC
Class: |
B01F 3/04985 20130101;
F04F 5/463 20130101; B01F 5/0413 20130101; B01F 5/043 20130101;
B01F 2005/0448 20130101 |
Class at
Publication: |
417/179 |
International
Class: |
F04F 5/46 20060101
F04F005/46 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 9, 2009 |
FR |
09 52369 |
Claims
1. An ejector device for forming a pressurized mixture of liquid
and gas, comprising a suction chamber and a diffuser, wherein the
suction chamber comprises: an injection nozzle for producing a jet
of liquid flowing in a longitudinal direction (X); a gas inlet for
admitting into the suction chamber a gas to be driven by the liquid
jet; and an outlet opening for discharging the liquid jet and the
driven gas from the suction chamber; wherein the diffuser is
connected to the outlet opening of the suction chamber and has, in
the longitudinal direction, a transversal section that increases
from said outlet opening, the diffuser with increasing section
being situated immediately after the outlet opening of the suction
chamber, and wherein the diffuser comprises at least one first
conical portion that has a first angle of between 0.1 and 7
degrees.
2. An ejector device according to claim 1, wherein the first angle
is between 1.5 and 4 degrees.
3. An ejector device according to claim 1, wherein the diffuser
also comprises a second conical portion continually in the
extension of the first portion in the longitudinal direction, said
first portion having a second angle greater than the first
angle.
4. An ejector device according to claim 3, wherein the second angle
is between 5 and 15 degrees, and preferably of the order of 7
degrees.
5. An ejector device according to claim 1, wherein the diffuser
also comprises a second portion continually in the extension of the
first portion in the longitudinal direction, said second portion
having a convex profile shape.
6. An ejector device according to claim 5, wherein the convex
second portion has an angle that progressively increases in the
longitudinal direction from the first angle to an angle less than
15 degrees, and preferably of the order of 10 degrees.
7. An ejector device according to claim 1, wherein the diffuser is
substantially coaxial to the injection nozzle and to the outlet
opening of the suction chamber.
8. An ejector device according to claim 1, wherein: the outlet
opening has a neck surface S.sub.c perpendicular to the
longitudinal direction, the injection nozzle has a nozzle surface
S.sub.2 inside the nozzle and perpendicular to the longitudinal
direction, and a geometrical ratio R is the ratio between the
nozzle surface S.sub.2 and the neck surface S.sub.c, said
geometrical ratio R being between 0.5 and 0.9.
9. An ejector device according to claim 1, wherein: the injection
nozzle has one end in the longitudinal direction, the outlet
opening has a circular section with a neck diameter D.sub.c, and
the end is situated a retraction distance x.sub.2 from the outlet
opening, said retraction distance x.sub.2 being between one and
five times the neck diameter D.sub.c.
10. An ejector device according to claim 1, wherein the suction
chamber comprises walls in the longitudinal direction extending
radially in said suction chamber, so that the gas flows in the
suction chamber with a flow with little turbulence, without
rotation and with substantially uniform axial speed
distribution.
11. An ejector device according to claim 1, wherein the injection
nozzle comprises liquid channelling means suitable for obtaining,
in the nozzle after such channelling means, a flow of the liquid
with little turbulence, without rotation and with substantially
uniform axial speed distribution.
12. An ejector device according to claim 11, wherein the liquid
channelling means in the nozzle are chosen from: a device that has
walls extending in the longitudinal direction, and a device that
has walls extending in the longitudinal direction, said walls
having a honeycomb shape, and a device comprising a wall in a
direction that is substantially perpendicular to the longitudinal
direction and comprising holes for distributing the liquid flow in
a substantially uniform manner in the transversal section of the
nozzle.
13. Use of an ejector device according to claim 1, wherein: the
following are measured: a gas suction pressure p.sub.1 at the gas
inlet, a liquid feed pressure p.sub.2 feeding the injection nozzle,
a discharge pressure p.sub.3 of the gas and liquid mixture
downstream of the diffuser, and at least one of said pressures is
set so that a compression parameter defined by the following
formula: .PSI. = p 3 - p 1 p 2 - p 1 , ##EQU00011## is between 0.4
and 0.6.
14. Use of an ejector device according to claim 1, wherein: the
following are measured: a gas suction pressure p.sub.1 at the gas
inlet, a liquid feed pressure p.sub.2 feeding the injection nozzle,
a discharge pressure p.sub.3 of the gas and liquid mixture
downstream of the diffuser, and said liquid feed pressure p.sub.2
is set to plus or minus twenty percent of an optimal pressure
p.sub.2,opt, such that: p.sub.2,opt=2p.sub.3-p.sub.1.
Description
[0001] The present invention relates to an ejector device for
forming a pressurized mixture of liquid and gas.
[0002] The document WO-01/34285 describes such an ejector device
comprising a suction chamber, a cylindrical tube and a
conical-shaped diffuser that widens in a longitudinal direction. A
nozzle injects a liquid at high speed into the suction chamber,
which then sucks gas through an inlet. The cylindrical tube is
situated between the suction chamber and the diffuser, so that the
liquid and the gas are mixed in this cylindrical tube before
entering into the diffuser.
[0003] Such an ejector device makes it possible to obtain
compression rates (see definition below) of the order of 4 to 8.
Thus, a gas that has a pressure of 2 atm at the inlet can be
compressed to a pressure of 16 atm. It is very difficult to go
beyond that.
[0004] The aim of the present invention is to refine an ejector
device of this type, notably to optimize its energy efficiency and
increase the compression rate.
[0005] More particularly, the invention relates to an ejector
device for forming a pressurized mixture of liquid and gas,
comprising a suction chamber and a diffuser, wherein the suction
chamber comprises: [0006] an injection nozzle for producing a jet
of liquid flowing in a longitudinal direction; [0007] a gas inlet
for admitting into the suction chamber a gas to be driven by the
liquid jet; and [0008] an outlet opening for discharging the liquid
jet and the driven gas from the suction chamber; wherein the
diffuser is connected to the outlet opening of the suction chamber
and has, in the longitudinal direction, a transversal section that
increases from said outlet opening, the diffuser with increasing
section being situated immediately after the outlet opening of the
suction chamber, and wherein the diffuser (6) comprises at least
one first conical portion that has a first angle of between 0.1 and
7 degrees.
[0009] Thanks to these arrangements, the liquid and gas mixture can
be produced at different axial positions inside the diffuser, and
the ejector device then makes it possible to operate over a wide
range of compression rates.
[0010] In various embodiments of the ejector device according to
the invention, it is possible, if necessary, to also use one and/or
other of the following arrangements: [0011] the first angle is
preferentially between 1.5 and 4 degrees; [0012] the diffuser also
comprises a second conical portion continually in extension of the
first portion in the longitudinal direction, said second portion
having a second angle greater than the first angle; [0013] the
second angle is between 5 and 15 degrees, and preferably of the
order of 7 degrees; [0014] the diffuser also comprises a second
portion continually in the extension of the first portion in the
longitudinal direction, said second portion having a convex profile
shape; [0015] the convex second portion has an angle that
progressively increases in the longitudinal direction from the
first angle to an angle less than 15 degrees, and preferably of the
order of 10 degrees; [0016] the diffuser is substantially coaxial
to the injection nozzle and to the outlet opening of the suction
chamber; [0017] the ejector device is such that: [0018] the outlet
opening, also called neck, has a neck surface S.sub.c perpendicular
to the longitudinal direction, [0019] the injection nozzle has a
nozzle surface S.sub.2 inside the nozzle and perpendicular to the
longitudinal direction, and [0020] a geometrical ratio R is the
ratio between the nozzle surface S.sub.2 and the neck surface
S.sub.c, said geometrical ratio R being between 0.5 and 0.9;
[0021] Thanks to this arrangement, the device makes it possible to
maximize the compression rate for a given injection speed, and in
particular to reach mixture compression rates that are very high,
and for example greater than 30, with a single device stage,
provided that the speed of the liquid jet is sufficiently high;
[0022] the ejector device is such that: [0023] the injection nozzle
has one end in the longitudinal direction, [0024] the outlet
opening has a circular section with a neck diameter Dc, and [0025]
the end is situated at a retraction distance x.sub.2 from the
outlet opening, said retraction distance x.sub.2 being between one
and five times the neck diameter Dc; [0026] the suction chamber
comprises walls in the longitudinal direction extending radially in
said suction chamber, so that the gas flows in the suction chamber
with a flow with little turbulence, without rotation, with fairly
uniform axial speed distribution; [0027] the injection nozzle
comprises liquid channelling means suitable for obtaining, in the
nozzle after said channelling means, a flow of the liquid with
little turbulence, without rotation and with substantially uniform
axial speed distribution; [0028] the liquid channelling means in
the nozzle are chosen from: [0029] a device that has walls
extending in the longitudinal direction, and [0030] a device that
has walls extending in the longitudinal direction, said walls
having a honeycomb shape, and [0031] a device comprising a wall in
a direction that is substantially perpendicular to the longitudinal
direction and comprising holes for distributing the liquid flow in
a substantially uniform manner in the transversal section of the
nozzle.
[0032] The invention also relates to the use of an ejector device
of the preceding type, wherein: [0033] the following are measured:
the gas suction pressure p.sub.1 at the gas inlet (3), the liquid
feed pressure p.sub.2 feeding the injection nozzle (5), the
discharge pressure p.sub.3 of the gas and liquid mixture downstream
of the diffuser (6), and [0034] at least one of said pressures is
set so that a compression parameter .PSI. by the following
formula:
[0034] .PSI. = p 3 - p 1 p 2 - p 1 , ##EQU00001##
is between 0.4 and 0.6.
[0035] The invention also relates to the use of an ejector device
of the preceding type, wherein: [0036] the following are measured:
the gas suction pressure p.sub.1 at the gas inlet (3), the liquid
feed pressure p.sub.2 feeding the injection nozzle (5), the
discharge pressure p.sub.3 of the gas and liquid mixture downstream
of the diffuser (6), and [0037] the liquid feed pressure p.sub.2 is
set to plus or minus twenty percent of an optimal pressure
p.sub.2,opt, such that:
[0037] p.sub.2,opt=2.p.sub.3-p.sub.1.
[0038] Thanks to these usage arrangements, the energy performance
levels of the ejector device are optimized.
[0039] The invention can, for example, be used in a gas compressor
comprising an ejector device fed with a gas on the one hand and a
liquid on the other hand, and a separator device suitable for
receiving a liquid and gas mixture originating from the ejector
device and extracting a gaseous component from this mixture,
wherein the ejector device comprises a suction chamber and a
diffuser, wherein the suction chamber comprises: [0040] an
injection nozzle for producing a jet of liquid flowing in a
longitudinal direction; [0041] a gas inlet for admitting a driven
gas into the suction chamber; and [0042] an outlet opening for
discharging the liquid jet and the driven gas from the suction
chamber; wherein the diffuser is connected to the outlet opening of
the suction chamber and has, in the longitudinal direction, a
transversal section that increases from said outlet opening, the
diffuser with increasing section being situated immediately after
the outlet opening of the suction chamber, and wherein the gas
separator device comprises two outlets, one for the gas and the
other for the liquid.
[0043] In various embodiments of the gas compressor, it is
possible, if necessary, to also use one or other of the following
arrangements: [0044] the diffuser comprises at least a first
conical portion that has a first angle between 0.1 and 7 degrees;
[0045] the separator device is a gravity separator; [0046] the
separator device is a cyclonic separator; [0047] the gas compressor
also comprises a pump suitable for sucking the liquid under
pressure at the level of the separator device and for feeding the
injection nozzle of the ejector device with said liquid.
[0048] Other features and benefits of the invention will become
apparent from the following description of one of its embodiments,
given by way of nonlimiting example, in light of the appended
drawings.
[0049] In the drawings:
[0050] FIG. 1 is a diagrammatic view in longitudinal cross section
of the ejector device according to the invention,
[0051] FIG. 2 is a graph, established from experimental results,
showing the driving rate .tau..sub.e (see definition below) as a
function of the compression rate .tau..sub.c (see definition below)
for different values of the gas suction pressure p.sub.1, in the
ejector device of FIG. 1,
[0052] FIG. 3 is a graph showing the theoretical efficiency of the
ejector device (see definition below) of FIG. 1, for a compression
rate of the order of 4, as a function of a geometrical ratio R for
different driving rate values,
[0053] FIG. 4 is a graph showing the efficiency of the ejector
device of FIG. 1, as a function of a compression parameter .PSI.
for different values of the motive pressure parameter .chi. (see
definition below)
[0054] FIG. 5 is a diagrammatic view of a gas compressor comprising
the ejector device of FIG. 1.
[0055] The longitudinal direction mentioned in this description
should be understood to be the direction indicated by a chain
dotted line X in FIG. 1, and corresponds to the direction of flow
in the ejector device 1 between the upstream side situated on the
left and the downstream side situated on the right in this
figure.
[0056] FIG. 1 is a diagrammatic view in longitudinal cross section
of an ejector device 1 according to the invention. This ejector
device extends along the longitudinal axis X and comprises, along
this axis: [0057] a suction chamber 2 suitable for sucking a gas by
the injection of a liquid jet at high speed into said suction
chamber 2, and [0058] a diffuser 6 suitable for mixing the liquid
and the gas and compressing this mixture, fairly abruptly, by a
phenomenon similar to a hydraulic jump, then progressively
compressing this mixture by converting the kinetic energy of the
mixture into pressure energy.
[0059] The suction chamber 2 comprises: [0060] a lateral inlet
opening 3 through which the gas is brought, [0061] an injection
nozzle 5 ending in a cylindrical tube substantially coaxial to the
longitudinal axis X and opening into said suction chamber, and
through which a liquid is injected at high speed into said suction
chamber, and [0062] an outlet opening 4 opposite the nozzle 5 in
the direction of flow, coaxial to the longitudinal axis X.
[0063] The outlet opening 4 therefore forms, at the outlet of the
suction chamber 2, a constriction which is also called neck. The
outlet opening 4 has a substantially circular section of diameter
D.sub.c. It has a neck surface S.sub.c,
S.sub.c=.pi.D.sub.c.sup.2/4, perpendicular to the longitudinal axis
X.
[0064] A first upstream duct 3a feeds the inlet opening 3 of the
suction chamber 2 with gas, at a suction pressure p.sub.1 with a
volume flow rate Q.sub.1.
[0065] A second upstream duct 5a feeds the injection nozzle 5 with
liquid, at a feed pressure p.sub.2 with a volume flow rate
Q.sub.2.
[0066] The nozzle 5 has an end 5b in the suction chamber 2, of
internal diameter D.sub.2 and having a nozzle surface S.sub.2,
S.sub.2=.pi.D.sub.2.sup.2/4, perpendicular to the longitudinal axis
X. This end 5b is placed at a retraction distance x.sub.2 from the
outlet opening 4 of the suction chamber 2. The internal diameter
D.sub.2 of the end 5b is possibly less than an internal diameter of
the nozzle 5, so that said nozzle has, at its end 5b, a contracted
section.
[0067] The injection nozzle 5 possibly includes liquid channelling
means that is suitable for obtaining, in the nozzle after said
channelling means, a flow of the liquid with little turbulence,
without rotation and with substantially uniform axial speed
distribution, that is to say, with an axial speed distribution in a
transversal section of the nozzle that is substantially constant.
The liquid jet produced by the nozzle 5 in the suction chamber then
remains substantially cylindrical as far as the outlet opening 4 of
said chamber. Thus, the liquid jet diverges little in this chamber
and does not begin to be mixed with the gas before the diffuser 6.
Usually, those skilled in the art consider that having a divergent
liquid jet helps in forming a liquid and gas mixture. As it
happens, the inventors have discovered that, on the contrary, this
arrangement makes it possible to obtain a better liquid and gas
mixture in the diffuser 6 and a better compression rate of this
mixture.
[0068] The channelling means of the liquid in the nozzle 5 can, for
example, be a device that has walls extending in the longitudinal
direction X, or a device that has walls extending in the
longitudinal direction X and said walls having a honeycomb shape,
or a device comprising a wall in a direction substantially
perpendicular to the longitudinal direction X and having holes for
distributing the liquid flow in a substantially uniform manner in
the transversal section of the nozzle, or a combination of these
devices in the nozzle 5 and arranged one after the other in the
longitudinal direction X.
[0069] The channelling means can then be placed in the nozzle at a
short distance from its end 5b, for example at a distance of
between 10 and 30 times the internal diameter D.sub.2 of the nozzle
5, and preferably equal to 20 times this diameter.
[0070] The diffuser 6 is mounted in the extension of the outlet
opening 4 of the suction chamber. This diffuser 6 has, in the
longitudinal direction X, a transversal section that increases from
said outlet opening 4. This diffuser 6 is, for example, conical in
shape, widening in the direction of flow, and is also substantially
coaxial to the longitudinal axis X. It therefore has an upstream
diameter substantially equal to the diameter D.sub.c of the outlet
opening 4 of the suction chamber 2, and a downstream diameter
D.sub.3 greater than the upstream diameter D.sub.c. The diffuser 6
forms a cone that has an angle .alpha..sub.d. The angle
.alpha..sub.d is defined as the total diffuser angle of the cone,
and has a low value, at least in a first portion of the diffuser
6.
[0071] A downstream duct 6a supplies, at the outlet, the liquid and
gas mixture at the discharge pressure p.sub.3.
[0072] Unlike the prior art devices, the inventive ejector device 1
has a diffuser 6 situated immediately at the outlet of the suction
chamber 2, that is to say without the interposition of a
cylindrical tube for mixing the liquid and the gas, so that the
mixture is produced directly in the diffuser 6.
[0073] The inventors have confirmed that such an arrangement would
enable the ejector device 1 to operate over a wide range of
compression rates .tau..sub.c.
[0074] The compression rate .tau..sub.c is defined as being the
ratio between the discharge pressure p.sub.3 and the suction
pressure p.sub.1 of the gas:
.tau. c = p 3 p 1 ##EQU00002##
[0075] The driving rate .tau..sub.c is defined as being the ratio
between the volume flow rate Q.sub.1 of the driven gas at the inlet
opening 3 and the volume flow rate Q.sub.2 of the liquid injected
through the injection nozzle 5:
.tau. e = Q 1 Q 2 ##EQU00003##
[0076] The motive pressure parameter .chi. is defined as being the
ratio between the liquid feed pressure p.sub.2 feeding the
injection nozzle 5 and the gas suction pressure p.sub.1:
.chi. = p 2 p 1 ##EQU00004##
[0077] These adimensional parameters, which can be determined by
calculation or measurement on test devices, make it possible to
establish dimensioning laws to optimize the operation of the
device.
[0078] Tests have shown that the driving rate .tau..sub.e is linked
to the compression rate .tau..sub.c. The curves of FIG. 2 show this
dependency for several gas suction pressure values p.sub.1.
[0079] The ejector device 1 operates as follows.
[0080] The liquid goes into the suction chamber 2 at the end 5b of
the nozzle 5, at a pressure equal to the gas suction pressure
p.sub.1 and at a speed U.sub.2. It forms a rectilinear and
substantially cylindrical jet inside the suction chamber 2. This
high speed jet helps to drive the gas which surrounds the jet
towards the outlet opening 4 of said suction chamber 2. We
therefore have, in the suction chamber, two substantially separate
phases: a liquid phase, the section of which is a disc, close to
the longitudinal axis X, and a gaseous phase, the section of which
is a ring in contact with said disc, at a certain distance from
this longitudinal axis and coaxial to the liquid phase.
[0081] The suction chamber 2 possibly comprises, from said distance
from the longitudinal axis X, walls that extend radially and
longitudinally, so that the liquid jet does not come into contact
with said walls and the gas contained in this suction chamber 2 is
driven with a flow with little turbulence, without rotation and
with substantially uniform axial speed distribution towards the
outlet opening 4 of the suction chamber 2.
[0082] In the diffuser 6, the flow comprises, along the axis X, a
first, a second and then a third area. In the first area of the
flow, the two coaxial phases flow in a relatively separate manner.
In the second area of flow, called mixing area, the flow changes
structure fairly abruptly and becomes an increasingly uniform
mixture of the liquid and of the gas. This change of structure of
the flow is accompanied by a fairly abrupt slowing down of the
liquid phase and an increase in pressure. In the third area of
flow, the two phases flow in the form of a finely mixed emulsion.
In this third area, the flow slows down progressively under the
effect of the increasing section of the diffuser. The kinetic
energy of the mixture is then converted into pressure energy.
[0083] These first, second and third areas of the flow are not
separated by clear and distinct transitions, the phenomena being
continuous. Also, these areas of the flow can be displaced
longitudinally in the diffuser 6, notably by the effect of
variations of the discharge pressure p.sub.3 downstream of the
diffuser 6. Despite such variations, the operation of the ejector
device is little disturbed, which shows that such a device is
stable and tolerant to the variations of the operating
parameters.
[0084] In a simplified manner, the quantity of movement of the
liquid jet at the inlet of the diffuser 6 is converted into
pressure forces that are applied either side of the mixing area. If
we draw an analogy with the compressible flows, this conversion can
be seen as a shock. If we draw an analogy with free surface flows,
this conversion can be seen as a hydraulic jump.
[0085] The conical-shaped diffuser 6 has an angle .alpha..sub.d
that is small, but not zero. A conical diffuser 6 with a greater
angle .alpha..sub.d, for example greater than 10 degrees, does not
provoke such an effective hydraulic shock and does not make it
possible to achieve such high compression rates.
[0086] The inventors have therefore confirmed that there is an
optimum angle .alpha..sub.d,opt for which the compression rate is
maximum, for a given injection speed U.sub.2. This optimum angle
lies within a range of angle values .alpha..sub.d between 0.1 and 7
degrees, and preferably between 1.5 and 4 degrees. The value of the
optimum angle .alpha..sub.d,opt is difficult to determine by prior
calculation.
[0087] In a variant of the ejector device 1, the diffuser 6
comprises, along the axis X, a first conical portion with a first
angle .alpha..sub.d, then a second conical portion with a second
angle. The second portion is continually in the extension of the
first portion. The second angle is greater than the first angle.
The second angle can be between 5 and 15 degrees, and preferably of
the order of 7 degrees. The first portion is intended to
accommodate the mixing area, which should take place under a low
divergence angle in order to maximize the compression rate. The
second portion ensures the final recovery of pressure by conversion
of the kinetic energy of the mixture. This energy conversion can
take place under a greater divergence angle, for example of the
order of 10.degree., without in any way causing a significant
pressure drop. There are therefore obtained both a high compression
rate .tau..sub.c through the first portion with low divergence
angle, and a shortened overall length of the diffuser 6.
[0088] In another variant of the ejector device 1, the diffuser 6
has a flared shape with a first portion of conical shape with a
small first angle, then, in continuity, a shape with a convex
profile. The second convex portion has an angle that increases
progressively in the longitudinal direction X from the first angle
to an angle, for example less than 15 degrees, and preferably of
the order of 10 degrees. The overall length of the diffuser 6 can
thus be further shortened without affecting the compression
rate.
[0089] In yet another variant of the ejector device 1, the diffuser
6 has a flared shape with a shape that has a convex profile, said
convex profile having an angle that increases progressively in the
longitudinal direction X from a first angle .alpha..sub.d to an
angle, for example less than 15 degrees, and preferably of the
order of 10 degrees. The overall length of the diffuser 6 can thus
be shortened further.
[0090] The first angle .alpha..sub.d of the preceding variants
advantageously has a value within the range from 0.1.degree. to
7.degree., as indicated hereinabove.
[0091] Furthermore, the efficiency .eta. of the ejector device is
the ratio between the compression power P.sub.c in the ejector
device 1 and the hydraulic power P.sub.h supplied.
[0092] If we assume that the compression is substantially
isothermic, we obtain the following compression power P.sub.c:
P c = p 1 Q 1 ln ( p 3 p 1 ) ##EQU00005##
[0093] When a pump sucks the liquid at the level of the separator
situated at the discharge of the ejector device 1, the supplied
hydraulic power P.sub.h is linked to the difference of liquid feed
pressure p.sub.2 in the injection nozzle 5 and the discharge
pressure p.sub.3 at the outlet of the diffuser 6, that is to
say:
P.sub.h=Q.sub.2(p.sub.2-p.sub.3)
hence the following efficiency .eta.:
.eta. = Q 1 Q 2 p 1 p 2 - p 3 ln ( p 3 p 1 ) ##EQU00006##
that can be expressed as a function of the adimensional parameters
defined previously:
.eta. = .tau. e ln ( .tau. c ) .chi. - .tau. c ##EQU00007##
[0094] The efficiency .eta. of an ejector device 1 can therefore be
measured on experimental devices, or be calculated by a
mathematical hydraulic flow model.
[0095] The adimensional geometrical ratio R has also been defined
as being the ratio of the nozzle surface S.sub.2 relative to the
neck surface S.sub.c:
R = S 2 S c ##EQU00008##
[0096] As shown by the theoretical curves of FIG. 3, given a fixed
driving rate, the efficiency .eta. is linked to this geometrical
ratio R of the ejector device 1. The efficiency .eta. is maximum
for a geometrical ratio R between 0.5 and 0.9, or more specifically
between 0.6 and 0.8. This trend has been confirmed by experimental
results.
[0097] Experimental tests have also shown that the optimum
retraction distance x.sub.2 for the targeted compression rates is
from one to five times the neck diameter D.sub.c of the outlet
opening 4 of the ejector device 1.
[0098] Another dimensioning criterion has been defined by
introducing a new adimensional parameter .PSI., called compression
parameter, and defined as follows:
.PSI. = p 3 - p 1 p 2 - p 1 ##EQU00009##
[0099] A first benefit of this compression parameter .PSI. is that
it can be calculated only with the pressure values, which can be
measured on an experimental ejector device.
[0100] This compression parameter .PSI. can be expressed as a
function of the other adimensionnal parameters by the following
expression:
.PSI. = .tau. c - 1 .chi. - 1 ##EQU00010##
[0101] For a given injection speed U.sub.2, the efficiency .eta. is
linked to the value of this compression parameter .PSI. of the
ejector device 1. The curves of FIG. 4 show this dependency for
several values of the motive pressure parameter .chi.. The
efficiency .eta. is then maximum for a compression parameter .PSI.
that lies within the range from 0.4 to 0.6, or preferably equal to
approximately 0.5.
[0102] A second benefit of this compression parameter .PSI. is
that, conversely, it can make it possible to determine the liquid
feed pressure p.sub.2 that is suitable for obtaining the optimum
efficiency .eta..sub.opt of the ejector device 1.
[0103] In practice, the above range for the compression parameter
.PSI. makes it possible to determine that the liquid feed pressure
p.sub.2 should be within the following range:
1.66p.sub.3-0.66p.sub.1<p.sub.2<2.5p.sub.3-1.5p.sub.1
with an optimum central liquid feed pressure value p.sub.2,opt
of:
p.sub.2,opt=2p.sub.3-p.sub.1
[0104] The ejector device 1 can then be used in a gas compressor 10
as shown in FIG. 5.
[0105] This gas compressor 10 comprises: [0106] a gas inlet 11 at
low pressure, [0107] a gas outlet 12 at high pressure, [0108] a
looped internal hydraulic circuit.
[0109] The hydraulic circuit comprises, in series: [0110] an
ejector device 1 fed on the one hand with a low pressure gas,
originating from the gas inlet 11, and on the other hand with a
high pressure liquid; said ejector device 1 supplying a mixture of
gas and liquid at intermediate pressure, [0111] a separator device
13 fed with a mixture of gas and liquid by the ejector device 1 and
supplying on the one hand a gas component to the gas outlet 12 at
intermediate pressure and a liquid, at the same intermediate
pressure, to a return circuit 14, [0112] a heat exchanger 15 in the
return circuit 14 suitable for maintaining the temperature of the
hydraulic circuit at an appropriate level, [0113] a pump 16 fed by
the liquid from the return circuit 14 and supplying a liquid at
higher pressure to a feed circuit 17.
[0114] The feed circuit 17 then feeds the ejector device 1 of the
gas compressor 10 with liquid.
[0115] The separator device 13 is either a gravity separator or a
cyclonic separator.
[0116] Furthermore, a branched circuit 14a circumvents the heat
exchanger 15 of the return circuit 14 and includes a valve 14b.
This branch circuit 14a is suitable for adjusting the temperature
of the hydraulic circuit.
[0117] The heat exchanger 15 is also fed with a cold fluid, for
example water, by a cooling circuit 15a and a pump 15b.
[0118] The gas compressor 10 operates as follows.
[0119] The ejector device 1 mixes the gas with a liquid injected at
high speed, and compresses this mixture of gas and liquid at a high
pressure. The mixture is separated in the separator device 13,
which then supplies the gas outlet 12 with a gas at high pressure,
and the return circuit 14 with a liquid that is also at high
pressure. The heat exchanger 15 makes it possible to extract heat
from the liquid. The pump 16 increases the pressure of the liquid
before feeding the feed circuit 17 and the ejector device 1. As
already explained above, the ejector device 1 comprises an
injection nozzle suitable for injecting said liquid into its
suction chamber at high speed.
[0120] Thus, the injection nozzle of the ejector device 1 produces
an expansion of the liquid (transformation of the pressure energy
of the liquid into kinetic energy). The diffuser of the injection
device 1 mixes and compresses the mixture. The pump 16 complements
the compression of the liquid to achieve the feed pressure at the
inlet of the nozzle of the ejector device.
* * * * *