U.S. patent application number 14/768783 was filed with the patent office on 2016-01-07 for station for reducing gas pressure and liquefying gas.
The applicant listed for this patent is CRYOSTAR SAS. Invention is credited to Frederic Marcuccilli, Guillaume Pages.
Application Number | 20160003528 14/768783 |
Document ID | / |
Family ID | 48170651 |
Filed Date | 2016-01-07 |
United States Patent
Application |
20160003528 |
Kind Code |
A1 |
Pages; Guillaume ; et
al. |
January 7, 2016 |
STATION FOR REDUCING GAS PRESSURE AND LIQUEFYING GAS
Abstract
The invention relates to a station comprising an expansion
turbine 12; means for recovering mechanical work (G) produced
during the gas pressure reduction in the expansion turbine; a
cooling system (6) comprising compression means (C1, C2, C3),
condensation means (14) for liquefying gas (G11) using the cold
provided by the cooling system, means for recovering heat produced
by the compression means (C1, C2, C3) of the cooling system and
means (10) for heating the gas upstream of the expansion turbine
that are associated with the heat-recovery means.
Inventors: |
Pages; Guillaume; (Huningue,
FR) ; Marcuccilli; Frederic; (Colmar, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CRYOSTAR SAS |
Hesingue |
|
FR |
|
|
Family ID: |
48170651 |
Appl. No.: |
14/768783 |
Filed: |
February 20, 2014 |
PCT Filed: |
February 20, 2014 |
PCT NO: |
PCT/FR2014/050349 |
371 Date: |
August 19, 2015 |
Current U.S.
Class: |
62/613 |
Current CPC
Class: |
F25J 1/0052 20130101;
F25J 2210/06 20130101; F25J 1/0296 20130101; F25J 2230/20 20130101;
F25J 1/0212 20130101; F25J 1/0265 20130101; F25J 1/005 20130101;
F25J 2240/90 20130101; F25J 1/0022 20130101; F25J 1/0232 20130101;
F25J 1/0284 20130101; F25J 1/0281 20130101; F25J 1/0288 20130101;
F25J 1/0204 20130101; F25J 1/0035 20130101; F25J 1/0072 20130101;
F25J 1/0285 20130101; F25J 1/0242 20130101 |
International
Class: |
F25J 1/00 20060101
F25J001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 20, 2013 |
FR |
13 00380 |
Claims
1-11. (canceled)
12. A station for reducing the pressure (PLD) of a gas and for
liquefying the gas, comprising: an expansion turbine (12); means
for recovering mechanical work (WM) produced during reduction of
pressure of the gas; a refrigeration system comprising compression
means (C1, C2, C3); condensation means (14) for liquefying the gas;
and means for recovering heat (Q) produced by the compression means
(C1, C2, C3; C) of the refrigeration system; the compression means
associated with means (10; 110) for heating the gas upstream of the
expansion turbine (12).
13. The station according to claim 1, further comprising a branch
pipeline (G9) downstream of the expansion turbine (12) for
supplying the condensation means (14).
14. The station according to claim 1, wherein said station
comprises a closed loop between the condensation means (14), the
compression means (C1, C2, C3; C) and the heating means (10) for
the gas.
15. The station according to claim 1, wherein said station
comprises a first closed loop between the compression means (C1,
C2, C3), the condensation means (14) and at least one intermediate
heat exchanger (10); and a second closed loop, between the at least
one intermediate heat exchanger (10) and the heating means (110)
for the gas.
16. The station according to claim 15, wherein the first closed
loop comprises a first heat transfer fluid, and the second closed
loop comprises a second heat transfer fluid different from said
first heat transfer fluid.
17. The station according to claim 1, further comprising means for
converting (G) mechanical work into electrical energy, said
converting means associated with the means for recovering
mechanical work (WM) produced during the reduction of the pressure
of the gas.
18. The station according to claim 17, wherein the converting means
(G) comprises an electrical generator mechanically coupled to the
means for recovering mechanical work (WM), and further comprising a
motor (M) supplied with electrical energy by the electric generator
for driving the compression means (C1, C2, C3).
19. The station according to claim 1, wherein the means for
recovering mechanical work (WM) produced during the reduction of
the pressure of the gas is mechanically connected to the
compression means (C1, C2, C3; C).
20. The station according to claim 19, further comprising an
auxiliary motor (M) for driving the compression means (C1, C2,
C3).
21. The station according to claim 1, wherein the refrigeration
system comprises a refrigerant selected from the group consisting
of nitrogen, a mixture of hydrocarbons, and nitrogen and a mixture
of hydrocarbons.
22. The station according to claim 1, further comprising
compressors and/or radial flow expanders.
23. The station according to claim 1, further comprising means for
treatment (8, 36) of the gas by at least one of adsorption,
adsorption arranged upstream of the condensation means (14), and
adsorption and absorption arranged upstream of the condensation
means.
24. The station according to claim 1, wherein the gas comprises
natural gas.
Description
[0001] The present invention relates to a station for reducing the
pressure of a gas and for liquefying the gas, particularly natural
gas.
[0002] Thus, the field of the present invention is that of
treatment of gases, particularly of natural gases, for the
production of liquefied natural gas.
[0003] Liquefied natural gas is used in different applications, It
is mainly used as fuel for vehicles, particularly transport trucks.
The fuel oil generally used for such vehicles can indeed be
replaced by pressurized gas or liquefied natural gas, In comparison
with the use of bottles of pressurized gas, the use of liquefied
gas offers an advantage in terms of volume and weight inasmuch as,
on one hand, natural gas liquefied by cooling occupies much less
volume than the same quantity of gaseous natural gas, and on the
other hand, the thermal insulation of the cryogenic tanks is much
less heavy than the jacket of the gas bottles. The vehicles
therefore have much more autonomy. Liquefied natural gas is
moreover a clean energy source, which limits the discharge of fine
particles such as soot, etc.
[0004] Liquefied natural gas can also be used for supplying small
gas power plants or for supplying small networks in villages.
[0005] Gas pipelines, or pipelines, are pipelines intended for
transporting gaseous materials under pressure. The majority of gas
pipelines convey natural gas between extraction zones and
consumption or exportation zones. From treatment sites of the gas
fields or storage sites, the gas is transported at high pressure
(from 16 to more than 100 bars) to delivery sites where it must be
brought to a much lower pressure so that it can be used.
[0006] For this purpose, the gas passes through pressure reduction
stations in which the pressure of the gas is reduced by expansion
through a valve or a turbine. The pressure reduction thus achieved
produces energy which, in the case of a valve, is lost.
[0007] There are known gas expansion systems that use the natural
gas entering the pressure reduction stations as refrigerant in a
system that can be described as open loop (Linde, Solvay or Claude
cycles). In these systems, one uses the fact that the natural gas
is present under high pressure. The natural gas is expanded in a
valve, and during this expansion a small portion of the gas is
liquefied. The liquid obtained is collected, and the cold low
pressure natural gas coming out of the valve is conveyed to the low
pressure pipe of the reduction station. These systems have the
advantage of being relatively simple, but since the temperature
obtained coming out of the valve depends on the composition of the
gas and since the composition of natural gas is variable, the gases
liquefied with these systems are mainly heavy gases such as butane
or propane but not methane. This gas liquefaction method is also
known as flashing.
[0008] All of the gas entering the pressure reduction station and
passing through the valve or the turbine is cooled during the
pressure drop that occurs. The gas still contains water and carbon
dioxide at contents on the order of around one hundred ppm or one
percent. A condensation phenomenon can then occur during this
expansion step, which is capable of causing the formation of ice
(hydrates) that can block the pipes. It is therefore necessary to
treat the gas flow in order to prevent the water and carbon dioxide
contained in the natural gas from being transformed into ice in the
pipes and thus causing problems in conveying the natural gas during
its treatment in the pressure reduction stations.
[0009] The present invention aims in particular to provide means
making it possible, at the site of a pressure reduction station, to
liquefy gas, particularly natural gas, by controlling the
composition of the liquefied gas obtained. Advantageously, a device
according to the invention will make it possible. to recover energy
of expansion resulting from the difference in pressure of the gas
between the inlet and the outlet of the pressure reduction station
in order to produce a liquefied natural gas fraction while avoiding
the formation of ice inside the pipes of these stations. The device
will also preferably be easy to use and have a simple design.
[0010] For this purpose, the present invention proposes a station
for reducing the pressure of a gas and for liquefying gas,
particularly natural gas, comprising: [0011] an expansion turbine,
[0012] means for recovering mechanical work produced during the
reduction of the pressure of the gas, [0013] a refrigeration system
comprising compression means, and [0014] condensation means for
liquefying gas.
[0015] According to the invention, this station moreover comprises
means for recovering heat produced by the compression means of the
refrigeration system, which are associated with means for heating
the gas upstream of the expansion turbine.
[0016] Such a station thus provides for integrating the heating of
the natural gas before its expansion and the cooling of the
refrigerant while saving a significant amount of energy and/or gas
for the manufacture of the liquefied (natural) gas.
[0017] A flow of (natural) gas in gaseous form is always maintained
between a high pressure pipe and a low pressure pipe which are
associated with a pressure reduction station. Based on a volume of
100 m.sup.3 of natural gas, 5 to 15 m.sup.3, for example, are
transformed into liquefied natural gas. Work can here be recovered
during the expansion between the two pressure levels in order to be
used later for transformation of a small portion (5 to 15%) of the
(natural) gas into liquefied (natural) gas.
[0018] The heating of the gas occurs, for example, at the inlet of
the pressure reduction station (that is to say upstream of the
expansion turbine) by recovery of the heat emitted by the
compression means used for liquefying the gas. The gas going from
the high pressure pipe to the low pressure pipe is thus heated
before entering the pressure reduction station so that it is
present at the outlet of said station with a temperature higher
than the solidification point of the water.
[0019] In order to optimize the station described here and to
recover a maximum amount of energy, it is provided that the gas
under high pressure is first of all run into the expansion turbine
and that subsequently, downstream of this turbine, a portion of the
expanded gas is removed in order to be sent to the condensation
means. it is thus provided that these condensation means are
supplied by a branch pipeline downstream of the expansion
turbine.
[0020] According to a first embodiment, the station comprises a
closed loop between the condensation means, the compression means
and the means for heating the natural gas. This closed loop makes
it possible to combine a refrigeration system (compressor and
condenser) for the liquefaction of the gas with a heat exchanger,
bringing about the thermal integration between the reduction of the
pressure of the gas and the production of liquefied gas.
[0021] According to a second embodiment, the station comprises a
first closed loop between the compression means, the condensation
means and at least one intermediate heat exchanger, as well as a
second closed loop, possibly using a different heat transfer fluid
from a heat transfer fluid used in the first loop, between at least
one intermediate heat exchanger and the means for heating the
gas.
[0022] Proposed here, with these two embodiments, is a station with
an intermediate system that can be likened to a closed loop,
possibly double, making it possible to cool a fraction of the gas
until its liquefaction. The advantage of an independent closed loop
system is that it allows one to reach significantly lower
temperatures inasmuch as it is not connected with the lowering of
pressure achieved within the pressure reduction station. Thanks to
this system, the composition of the liquefied gas hardly varies
with respect to the entering gas, given that the change in state is
obtained by direct cooling inside of a heat exchanger reserved for
this operation, instead of the conventional flashing system.
[0023] In a particular embodiment of a pressure reduction and
liquefaction station, the means for recovering mechanical work
produced during the reduction of the pressure of the gas are
associated with means for converting mechanical work into
electrical energy. In this embodiment, the means for recovering
mechanical work produced during the reduction of the pressure of
the gas can be mechanically coupled to an electric generator, and
the compression means are advantageously driven by a motor supplied
with electrical energy by the electric generator.
[0024] In another embodiment of a pressure reduction and.
liquefaction station, the means for recovering mechanical work
produced during the reduction of the pressure of the gas are
mechanically associated with the compression means. An auxiliary
motor can optionally be provided for driving the compression
means.
[0025] Within such a station, one therefore has the integration of
a refrigeration loop for liquefying gas and of preheating of the
inlet of the expansion turbine.
[0026] The liquefied natural gas can be produced within a station
according to the invention from a refrigeration unit involving a
refrigerant system using interchangeably nitrogen and/or a mixture
of hydrocarbons.
[0027] A refrigeration system used in a station according to the
invention can for example comprise a heat exchanger and/or a
condenser of the aluminum PFHE type.
[0028] In a particular embodiment, the refrigeration system
comprises compressors and/or radial flow expanders.
[0029] In another embodiment, the station according to the
invention comprises means for treatment of the water and carbon
dioxide of the low pressure natural gas by adsorption and/or
absorption arranged upstream of the means for condensation of the
gas.
[0030] Details and advantages of the present invention will appear
more clearly from the description that follows given in reference
to the appended diagrammatic drawing in which:
[0031] FIG. 1 is a very diagrammatic overview illustrating a
station according to the present invention,
[0032] FIG. 2 is a more detailed diagrammatic view showing a first
embodiment of the present invention,
[0033] FIG. 3 is a view similar to the view of FIG. 2, illustrating
a second embodiment of the invention,
[0034] FIG. 4 is a view similar to that of FIGS. 2 and 3, in the
case of a third embodiment of the present invention, and
[0035] FIG. 5 is a view similar to that of FIGS. 2 to 4, in the
case of a fourth embodiment of the present invention.
[0036] FIG. 1 diagrammatically represents a gas pipeline 2
conveying a gas, for example, natural gas composed of mostly
methane, under high pressure, for example, on the order of 60 to
100 bars (generally in the present application, the examples and
the numerical values are illustrative and non-limiting). A gas
pressure reduction station, called PLD (English acronym for
Pressure Let Down, or in French "baisse de pression" [lowering of
pressure]) in FIG. 1, makes it possible to supply a pipe 4 intended
for supplying a domestic network or the like with gas (natural gas,
to re-use the preceding example) under low pressure, generally on
the order of a few bars.
[0037] A liquefied gas production unit 6 is associated with the
pressure reduction station PLD. It is supplied with gas from the
gas pipeline 2, downstream of the pressure reduction station PLD,
goes through a treatment unit 8 that performs a treatment of the
gas before it enters the production unit 6 in order rid the gas of
the impurities that are generally found in "raw" gas. Leaving the
production unit 6, a liquefied natural gas LNG is obtained which,
for example, is stored in a storage unit (not illustrated in FIG.
1).
[0038] When gas is expanded in the pressure reduction station PLD,
the gas gives up mechanical work WM. Proposed here is the recovery
of all or part of this work in some form, mechanical or electrical,
for example, in order to supply the production unit 6 which
requires energy in order to switch the gas from its gaseous state
to a liquid state. Inasmuch as the energy recovered is not
sufficient for the production of liquefied gas, it is possible to
supply the production unit with a supplementary source of energy,
for example, electrical energy diagrammatically represented by "WE"
in FIG. 1. Finally, in the production unit 6, one generally has a
compressor (not represented in FIG. 1) or another device that
releases heat, represented simply by Q in FIG. 1. Proposed in an
original manner is the recovery of this quantity of heat Q in order
to heat the gas entering the pressure reduction station PLD.
Indeed, in the course of expansion, the expanded gas is cooled. It
risks falling below the temperature of solidification of the water
and thus leading to formation of ice which can lead to partial or
complete obstruction of the corresponding pipeline. By heating the
gas before the expansion, it is thus possible to limit the risks of
icing and obstruction.
[0039] FIG. 2 shows in more detail a first embodiment of the
invention implementing the overall scheme of FIG. 1.
[0040] In FIG. 2, as well as in the following figures, the
references of FIG. 1 are used again to designate similar
elements.
[0041] One thus finds again in FIG. 2 a gas pipeline 2 which
supplies a pressure reduction station PLD in order to provide gas
under lower pressure in a pipe 4. Furthermore, a production unit 6
provides liquefied gas LNG.
[0042] In the pressure reduction station PLD, gas coming from the
gas pipeline 2 passes through pipes G2 and G3. It is heated in each
of these pipes by a preheating device 10. Leaving these preheating
devices, pipes G4 and G5 are collected in a pipe G6 which supplies
an expansion turbine 12. Leaving the turbine, the gas is expanded
and can rejoin the pipe 4 directly through a pipe G7.
[0043] The production unit 6 essentially comprises a condenser 14.
The gas supplying the production unit 6 is supplied from a branch
G9 of the pipe G7 before coming to a valve 16 where an additional
pressure reduction is achieved. The gas is conveyed through a pipe
G10 to the treatment unit 8 which performs a purification of the
gas, for example, by absorption or preferably by adsorption. The
purified gas is conveyed through G11 to the desuperheater 18 before
being introduced through G12 into the condenser 14. Leaving the
latter, liquefied gas is obtained, which passes through a pipe L1
to a control valve 20 and then through L2 in order to arrive at a
storage device for liquefied natural gas LNG.
[0044] An interaction between the expansion turbine 12 of the
pressure reduction station PLD and the production unit 6 is
achieved here. In this embodiment of FIG. 2, the energy recovered
during the expansion in the station PLD is used in the form of
electrical energy in the production unit 6, and the heat produced
in the production unit 6 is used for heating the gas entering the
station PLD, that is to say upstream of the expansion turbine
12.
[0045] It is noted in FIG. 2 first that the turbine 12 is coupled
to a generator G. Thus, mechanical energy is recovered at the
turbine 12 in order to be converted into electrical energy. The
electricity thus recovered then supplies a motor M which drives
three compressors C1, C2 and C3 each forming a stage of a
compression unit. In this way, an electrical coupling is produced
between the pressure reduction station and the production unit.
[0046] In order to optimize the quantity of mechanical energy
recovered at the turbine 12, both the gas intended for supplying
the low pressure pipe 4 and the gas intended for supplying the
production unit 6, that is to say the gas to be liquefied, are run
into this turbine 12.
[0047] The thermal integration is achieved by a closed loop circuit
which is described hereafter. For this description, we propose then
to follow the refrigerant fluid moving in this circuit. As a
non-limiting example, the fluid used can be nitrogen or else a
mixture of hydrocarbons.
[0048] The refrigerant fluid arrives in the compressor C1 through a
pipe R1 and leaves it through a pipe R2. It then arrives in a first
preheating device 10 in order to heat gas that comes from the gas
pipeline 2 and that is intended for supplying the turbine 12 of the
pressure reduction station PLD. The fluid is then led through a
pipe R3 to a cooler 22 in order to achieve a control of the
temperature of the refrigerant fluid before being sent to the
compression unit through a pipe R4. The fluid is then compressed by
the second compressor C2 and is then led through R5 to the second
preheating device 10 before being conveyed through R6 to a second
cooler 22 and reaching, through R7, a third compression stage of
the compression unit. A third cooler 22, connected to the third
compressor C3 through a pipe R8, makes it possible to control the
temperature of the fluid leaving the compression unit.
[0049] A pipe R9 brings the refrigerant fluid to a counterflow heat
exchanger 24, and is then led through R10 to an expander 26. The
latter is mechanically connected to the motor M and to the
compression unit. Leaving the expander 26, the fluid is then led
(R11) to the condenser 14 of the production unit 6 where it absorbs
calories from the natural gas portion that one wishes to liquefy in
order to obtain liquefied natural gas (LNG). Leaving the condenser
14, the fluid is conveyed (R12) to the desuperheater 18 before
reaching, through R13, the counterflow heat exchanger 24 which is
connected downstream to the first compressor C1 of the compression
unit.
[0050] As emerges from this description, the refrigerant fluid is
used to achieve a thermal integration between the production unit
and the pressure reduction station by recovering in particular the
calories released during the compression of the fluid in order to
use them for heating the natural gas entering the pressure
reduction station PLD.
[0051] Accessory elements of the refrigerant circuit are not
described in detail here. One thus finds, for example, a tank 28
which is used in a conventional manner as expansion vessel for the
refrigerant fluid.
[0052] FIG. 3 illustrates an embodiment variant which re-uses
certain references of the preceding figures in order to designate
similar elements. Compared to the embodiment of FIG. 2, another
form of thermal integration is achieved. It is proposed to have a
closed loop of pressurized water (or of another heat transfer fluid
such as, for example, a thermal oil) in order to recover the heat
of compression and to transfer it upstream of the expansion
turbine. An air cooler, for example, can be placed on this line in
order to adjust the cooling capacity to the demand of the
compression loop. A volumetric pump is used in order to allow the
circulation of the heat transfer fluid (pressurized water), and an
expansion vessel can in a conventional manner be integrated in this
circuit.
[0053] One thus recognizes in FIG. 3 a refrigerant circuit between
the compression unit and its three compressors C1, C2 and C3 and
the production unit 6 with its condenser 14. This circuit is
simplified. It passes successively through the three stages of the
compression unit, and after each stage, passes through a preheating
device 10. The refrigerant circuit then passes through the
counterflow heat exchanger 24 before going into the expander 26 and
then into the condenser 14, again passing through the counterflow
heat exchanger 24 and coming back to the first compression stage
and its compressor C1.
[0054] The main difference from the first embodiment of FIG. 2 is
that the preheating devices 10 do not directly transfer the
calories extracted from the compression stages to the natural gas
but rather they transfer them to another heat transfer fluid such
as, for example, pressurized water. A second refrigerant circuit is
thus produced, which passes in parallel through the three
preheating devices 10 in order to supply a preheating device 110
which transfers the calories coming from the compression stages to
the natural gas entering the station PLD. These preheating devices
10 thus form intermediate heat exchangers. Between the preheating
devices 10 and the preheating device 110, one notes the presence of
a volumetric pump 142 making it possible to circulate the heat
transfer fluid in the corresponding circuit, as well as a cooler
122 for controlling the temperature of the heat transfer fluid in
this circuit. In a conventional manner for the person skilled in
the art, an expansion vessel 144 is advantageously integrated in
this refrigerant circuit.
[0055] As for FIG. 4, it illustrates a simplified version of the
first embodiment illustrated in FIG. 2. Here also, as is generally
the case in the present application, the references already used
are re-used for designating similar elements in order to simplify
reading comprehension.
[0056] In this simplified embodiment, one notes that the
compression unit only has a single stage with a single compressor
C. The natural gas is then heated within a single preheating device
10 which allows a direct exchange of the calories coming from the
compressor with the natural gas entering the station PLD, upstream
of the expansion turbine 12.
[0057] In this embodiment, the refrigerant circuit uses, for
example, a mixture of hydrocarbons and nitrogen as heat transfer
fluid. The latter is compressed by the compressor C driven by the
electric motor M (electrically coupled to the generator G of the
turbine 12 of the station PLD. The fluid then cooled in contact
with the natural gas in the preheating device 10 at the entrance of
the turbine 12 (it is appropriate to note that one could here also
provide another refrigerant circuit between the preheating device
10 and the natural gas as in the preceding figure).
[0058] A cooler 22 or (air cooler) can be introduced into the
circuit in order to adjust the cooling capacity to the demand of
the compression loop. The heat transfer fluid is then sent through
a heat exchanger 214, for example, of type PHFE (English acronym
for Plate Fin Heat Exchanger or in French "echangeur de chaleur a
plaques et ailettes" [plate and fin heat exchanger]), where it is
cooled and condensed during a first pass. It is then expanded
through a valve 246 where, by Joule-Thompson effect, it partially
vaporizes, again causing a lowering of its temperature. It again
passes (2.sup.nd pass) through the heat exchanger 214 and vaporizes
and is heated in contact with the natural gas to be liquefied and
with the refrigerant mixture to be condensed. After this second
pass, leaving the heat exchanger 214, the heat transfer fluid
(mixture of hydrocarbons and nitrogen, for example) returns to the
compressor C.
[0059] In the embodiment of FIG. 5, compared to the embodiments of
the preceding figures, between the pressure reduction station and
the production unit, a mechanical integration (FIG. 5) is achieved
instead of an electrical integration (FIGS. 2 to 4).
[0060] Indeed, whereas in the embodiment of FIG. 2, the turbine 12
drives a generator G which produces electricity which is consumed
in a motor M, it is proposed in FIG. 5 to mechanically connect the
turbine 12 with the compressors C1, C2 and C3 of the compression
unit of the production unit 6.
[0061] It seems unnecessary to describe here the different elements
of the pressure reduction station that are similar to those
represented in FIG. 2. Likewise, one finds again a similar
refrigerant circuit for producing both the liquefied gas production
unit and the thermal integration of this production unit with the
pressure reduction station.
[0062] Also represented in this FIG. 5 is a motor M which is used
here as additional energy source (corresponds to WE in FIG. 1) in
order to adjust the power necessary for the liquefied gas
production unit with the power delivered at the site of the
pressure reduction station.
[0063] As a purely illustrative example, it is possible to provide,
for example, in the various embodiments described, that the
quantity (weight) of gas passing through the liquefied gas
production unit 6 is on the order of 5 to 20% of the quantity
(weight) of gas passing through the pressure reduction station PLD,
the rest of the gas (80 to 95%) supplying the pipe 4.
[0064] The systems described above allow complete control of the
production of liquefied natural gas. The composition of this gas
can be controlled. It does not depend on the difference in pressure
within the pressure reduction station.
[0065] Furthermore, the preheating of the gas entering the pressure
reduction station makes it possible to prevent problems of icing
and obstruction of the pipeline.
[0066] Energy recovery takes place at the pressure reduction
station, and more precisely at its expansion turbine. This recovery
is optimized by having the whole gas flow pass through this
turbine, that is to say the gas which is intended for being
expanded in gaseous form as well as the gas intended for being
liquefied.
[0067] The present invention is not limited to the preferred
embodiments described above as non-limiting examples. It also
relates to the embodiment variants accessible to the person skilled
in the art within the scope of the claims hereafter.
* * * * *