U.S. patent application number 16/470980 was filed with the patent office on 2020-01-02 for device and method for liquefying a natural gas and ship comprising such a device.
The applicant listed for this patent is ENGIE. Invention is credited to Hicham GUEDACHA.
Application Number | 20200003488 16/470980 |
Document ID | / |
Family ID | 58707661 |
Filed Date | 2020-01-02 |
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United States Patent
Application |
20200003488 |
Kind Code |
A1 |
GUEDACHA; Hicham |
January 2, 2020 |
DEVICE AND METHOD FOR LIQUEFYING A NATURAL GAS AND SHIP COMPRISING
SUCH A DEVICE
Abstract
The device (600) for liquefying a natural gas comprises: --a
first centrifugal compressor (605), --a fractionating means (110),
--a second centrifugal compressor (610), --a first heat exchange
body (115), --a second heat exchange body (120) and --a return
conduit (125) leading to the first compressor, --upstream of an
inlet (116) in the first exchange body, a third heat exchange body
(420), --a third centrifugal compressor (620), the first and third
centrifugal compressors being actuated by a single common turbine
(630), --a casing (635) common to the first compressor and the
third compressor, --a cooling means (430) and --a transfer conduit
(435) leading to the third exchange body.
Inventors: |
GUEDACHA; Hicham;
(Courbevoie, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ENGIE |
Courbevoie |
|
FR |
|
|
Family ID: |
58707661 |
Appl. No.: |
16/470980 |
Filed: |
December 15, 2017 |
PCT Filed: |
December 15, 2017 |
PCT NO: |
PCT/FR2017/053612 |
371 Date: |
June 19, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F25J 1/0283 20130101;
F25J 1/029 20130101; F25J 1/0277 20130101; F25J 1/0072 20130101;
F25J 1/0216 20130101; F25J 1/0218 20130101; F25J 2210/04 20130101;
F25J 1/0055 20130101; F25J 1/0057 20130101; F25J 2230/08 20130101;
F25J 2230/60 20130101; F25J 1/0052 20130101; F25J 1/0292 20130101;
F25J 2220/64 20130101; F25J 1/0278 20130101; F25J 1/0279 20130101;
F25J 1/0215 20130101; F25J 2245/02 20130101; F25J 1/0022 20130101;
F25J 2270/90 20130101 |
International
Class: |
F25J 1/00 20060101
F25J001/00; F25J 1/02 20060101 F25J001/02 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 22, 2016 |
FR |
1663213 |
Claims
1. A device for liquefying a natural gas, comprising: a first
centrifugal compressor of a first vaporized coolant chemical
mixture, a means for fractionating the compressed mixture into a
heavy fraction and a light fraction, a first body for exchanging
heat between the heavy fraction of the first mixture and the
natural gas in order to cool at least the natural gas, a second
body for exchanging heat between the compressed light fraction of
the first mixture and the natural gas cooled in the first exchange
body in order to liquefy the natural gas, and a conduit for
returning the first coolant mixture vaporized in the heat exchange
bodies to the first compressor, characterized in that it comprises:
upstream of an inlet for the natural gas in the first exchange
body, a third body for exchanging heat between the natural gas and
a second coolant chemical compound, a third centrifugal compressor
of the second vaporized compound, the first and third centrifugal
compressor being actuated by a single common turbine, a casing
common to the first compressor and the third compressor, a means
for cooling the second compressed compound, a conduit for
transferring the second cooled compound towards the third exchange
body, between the second compressor and the second exchange body, a
fourth centrifugal compressor of the light fraction of the first
mixture, the second and fourth centrifugal compressor being
actuated by a single common turbine, and a casing common to the
second compressor and the fourth compressor.
2. A device according to claim 1, wherein the turbine actuating the
first and third compressors are coupled mechanically.
3. A device according to claim 2, wherein the turbines are
combined.
4. A device according to claim 1, which comprises: a separator of a
gas fraction and a liquid fraction of the compressed light phase,
the fourth compressor compressing the separated gas fraction, a
regulator for the liquid fraction of the light phase heated in the
second exchange body, the turbine of the fourth compressor being
actuated by the expansion energy.
5. A device according to claim 1, wherein the second chemical
compound comprises a pure substance comprising nitrogen, propane
and/or ammonia.
6. A device according to claim 1, wherein the first cooling mixture
comprises nitrogen and methane and at least one compound amongst:
ethylene; ethane; propane; and/or butane.
7. A device according to claim 1, which comprises: a regulator for
the liquefied natural gas, a collector for the evaporation gas
produced during the expansion of the gas in the regulator, and a
conduit for injecting the evaporation gas at the inlet of the
second exchange body.
8. A device according to claim 1, wherein the means for cooling the
second compound comprises an outlet for the second compound, the
device comprising, between said outlet and the third exchange body,
a circuit for cooling the second compound with the heavy fraction
of the first mixture inside the first exchange body.
9. A device according to claim 1, wherein the first exchange body
and/or the second exchange body is a coil exchanger.
10. A device according to claim 1, wherein the means for cooling
the second compound is an exchanger of heat between the second
compound and water.
11. A method for liquefying a natural gas, comprising: a first step
of centrifugal compression of a first vaporized coolant chemical
mixture, a step of fractionating the compressed mixture into a
heavy fraction and a light fraction, a second step of centrifugal
compression of the light fraction, a first step of exchanging heat
between the heavy fraction of the first mixture and the natural gas
in order to cool at least the natural gas, a second step of
exchanging heat between the light fraction of the first mixture and
the cooled natural gas in the first exchange body in order to
liquefy the natural gas, and a step of returning the first coolant
mixture vaporized during the heat exchange steps to the first
compression step, characterized in that it comprises: upstream of a
step of inputting the natural gas into the first exchange step, a
third step of exchanging heat between the natural gas and a second
coolant chemical compound, a third step of centrifugal compression
of the second vaporized compound, the first and third centrifugal
compression step being actuated by a single common turbine, the
first and third compression step being carried out in a common
casing, a step of cooling the second compound compressed during the
third exchange step, a step of transferring the second cooled
compound towards the third exchange step, between the second
compression step and the second exchange step, a fourth step of
centrifugal compression of the light fraction of the first mixture,
the second and fourth centrifugal compression step being actuated
by a single common turbine, and the first and third compression
step being carried out in a common casing.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] The present invention relates to a device for liquefying a
natural gas, a method for liquefying a natural gas, and a ship
comprising such a device. It applies, in particular, to the
offshore or onshore liquefaction of natural gas.
STATE OF THE ART
[0002] Liquefying the gas allows natural gas to be transported in a
smaller volume compared to transporting non-liquefied natural
gas.
[0003] Over the last few decades, liquefaction technologies have
focused on large gas capacities for reasons of economy of
scale.
[0004] Implementation of the technologies thus used requires very
substantial investments and has very high transportation costs
(marine liquefaction and reception facilities). As a result,
firstly the trend for liquefaction capacities has been to increase
the volume of natural gas transported in order to obtain economies
of scale and to make these projects economically more attractive.
Secondly, the investments made to implement these technologies
focused on this sizing, and the construction of liquefaction
methods had to be the most efficient possible in order to minimize
the subsequent operating costs.
[0005] Today, the number of large-scale projects has decreased
significantly, and there is renewed interest in the production of a
small capacity of liquefied natural gas from natural gas or
biogas.
[0006] In effect, the upcycling of small gas sources, by-product
gases and biogas are new opportunities encouraged in particular by
a growing environmental awareness among populations and
governments, or a wish to reach isolated consumers in areas with no
gas transportation and/or distribution infrastructure. However,
these opportunities are too small to justify the use of
technologies intended for large-scale production (the transposition
of conventional technologies is not appropriate, as they are too
complex and cannot be used to support the economic viability of
these technologies), hence the need to propose new technologies
that can meet the two main challenges relating to liquefaction on a
small scale: [0007] reducing investment costs as much as possible
while keeping efficiency as high as possible in order to minimize
operating costs; and [0008] increasing the efficiency of the method
so as to minimize product loss: the gas volumes to be upcycled are
small, which makes every molecule important.
[0009] Today, offshore and near-shore gas resources are booming,
leading to technical solutions adapted to the marine environment,
known as "FLNG" (for "Floating Liquefied Natural Gas"), being
used.
[0010] In particular, several types of liquefaction cycles are
known: [0011] cascade cycles; [0012] mixed coolant cycles; and
[0013] expansion cycles.
[0014] The liquefaction cycles are based on these cycles or on a
combination of these cycles. This is notably the case of the
"Integral Incorporated Cascade" process, aka CII (short for
"cascade integrale incorporee").
[0015] In the CII system: [0016] a mixture of coolants is
compressed and then fractionated into a heavy fraction and a light
fraction; [0017] the heavy fraction is utilized in a first plate
heat exchanger to exchange heat between this heavy fraction and the
natural gas in order to cool it; [0018] the light fraction is
compressed; [0019] the light fraction is utilized in a second plate
heat exchanger to exchange heat between this heavy fraction and the
cooled natural gas to liquefy this natural gas; and [0020] the two
reheated fractions of the mixture are then collected and supplied
once more compressed.
[0021] This system has several drawbacks: [0022] plate heat
exchangers are very sensitive to the distribution of fluids, which
poses a problem of marine adaptation for the marine applications;
[0023] the coolant mixture has a significant number of components,
especially heavy compounds, and these compounds crystallize in the
heat exchangers under particular pressure and temperature
conditions whose arrival is difficult to forecast; and [0024] the
method has limited flexibility, especially in terms of operating
flow rate, and a limited production capacity per compression
means.
[0025] In the CII method, the coolant mixture is a mixture of
nitrogen and hydrocarbons (methane, ethane, ibutane, nbutane,
ipentane and npentane). The partial vaporization of this mixture at
low pressure makes it possible to cool and liquefy the natural gas,
and super-cool the LNG produced: [0026] vaporization at low
pressure of the heavy fraction of the coolant mixture (gas at the
top of the fractionating column) makes it possible to contribute
the negative heat necessary for cooling the natural gas; and [0027]
the light fraction will make it possible to liquefy the natural gas
and super-cool the LNG.
[0028] On output from the exchange line, the coolant mixture is
completely vaporized.
[0029] For the CII system the main drawbacks are that: [0030] the
CII method had been developed for large-scale LNG production on
land; [0031] the method is not very flexible: efficiency drops
significantly with any deviation from the operating/design point;
[0032] the coolant mixture contains too many constituents
(hydrocarbons), making the logistics and operational aspect more
complex; [0033] storage increases the weight of the facilities,
critical for offshore facilities; [0034] the method has
difficulties concerning the ethane supply, which poses significant
difficulties for offshore facilities; [0035] the method presents
risks of alteration to the equipment (exchangers) due to the risk
of crystallization of the pentane (iC5 and nC5) contained in the
coolant mixture; [0036] the efficiency of the method is limited by
the dimensions of the exchanger and by manufacturing constraints;
and [0037] the method presents problems concerning the installation
of equipment at sea (significant drop in the performance of the
plate exchanger if the distribution is not right).
[0038] The CII method is based on a single compression line using
centrifugal compressors.
[0039] A centrifugal compressor is used to compress a gas and as a
result increase its pressure. Centrifugal compressors are fitted
with wheels rotating around a shaft driven by a turbine or by an
electric motor. These rotating wheels allow the kinetic energy
contained in the gas to be transformed into potential energy in
order to increase its pressure.
[0040] As the possible pressure increase that can be achieved by a
wheel is limited, it is necessary to increase their number in order
to achieve the desired discharge pressure.
[0041] The set of wheels is contained in a body called the
"casing". A casing can contain from eight to a maximum of ten
wheels; the greater the number, the more the compressor is likely
to present stability problems.
[0042] Compression is central to a liquefaction method. In effect,
each additional point of efficiency gained at the compressor allows
the production of liquefied natural gas to be increased.
[0043] In addition, the compression train is the capital-intensive
component in a liquefaction unit.
[0044] Increasing the efficiency of a centrifugal compressor leads
to an increased investment. Conversely, reducing the investment
leads to solutions that are less efficient and/or significantly
less flexible.
[0045] The financial value of a compressor is directly linked to
the number of casings. In effect, the higher the number of casings,
the higher the investment to be made but the greater the
operational flexibility. Conversely, a reduction in the number of
casings results in a loss of operational flexibility, sometimes
accompanied by a loss of efficiency.
[0046] The challenge for the present invention therefore consists
of providing a better compromise between efficiency and investment
so as to keep satisfactory performance levels in as broad an
operating range as possible.
[0047] The compression trains of the CII method comprise a low- and
medium-pressure section and a high-pressure compression section.
The compression steps are grouped together in one, two or three
casings.
[0048] The low- and medium-pressure section makes it possible to
compress the coolant mixture at low pressure on output from the
cryogenic exchange line.
[0049] The high-pressure section makes it possible to compress the
light fraction of the coolant mixture, which will make it possible
to contribute the negative heat necessary for liquefaction and the
super-cooling of the liquefied natural gas.
[0050] The actuation of low- and high-pressure sections in the
compression train by the same shaft results in a single speed of
rotation between the turbines of these sections. This speed of
rotation can be differentiated by using multiplication mechanisms
between the speed of rotation of the turbines relative to the
single shaft. However, with or without a multiplication mechanism,
the rotation speeds must be proportional or identical, depending on
the case, which makes the compression train inflexible when the
flow rates entering each section are not identical or proportional.
This can pose problems of mechanical stability.
[0051] In addition, a large drop in efficiency is observed in the
high-pressure section, even more significant when one wishes to
include both sections in a single casing.
[0052] Lastly, this configuration is not very flexible, which
limits the field of opportunities that can be addressed: a drop in
efficiency, which can be significant, can be observed if one
deviates from the operating point for which the equipment was sized
(natural gas, and precise production conditions) and mechanical
stability problems can occur leading to more frequent
maintenance.
[0053] The current CII systems present the following drawbacks:
[0054] a variation in the flow rate between the low-pressure and
high-pressure sections of the compression train leading to an
imbalance between these two sections, which can lead to mechanical
instability problems during the shutdown and start-up phases;
[0055] a significant drop in efficiency is observed between the
low-pressure section and high-pressure section; and [0056] limited
flexibility for the compression train in terms of flow-rate range
and composition.
[0057] For example, the description in documents U.S. Pat. No.
6,347,532, US 2015/152884, US 2011/259045, U.S. Pat. Nos. 6,023,942
and 4,755,200 is known. However, none of these documents enable the
device to be made compact, and their combination could lead to
mechanical stability problems for the shaft compressing the coolant
mixture.
SUBJECT OF THE INVENTION
[0058] The present invention aims to remedy all or part of these
drawbacks.
[0059] To this end, according to a first aspect, the present
invention relates to a device for liquefying a natural gas,
comprising: [0060] a first centrifugal compressor of a first
vaporized coolant chemical mixture, [0061] a means for
fractionating the compressed mixture into a heavy fraction and a
light fraction, [0062] a second centrifugal compressor of the light
fraction, [0063] a first body for exchanging heat between the heavy
fraction of the first mixture and the natural gas in order to cool
at least the natural gas, [0064] a second body for exchanging heat
between the compressed light fraction of the first mixture and the
natural gas cooled in the first exchange body in order to liquefy
the natural gas, and [0065] a conduit for returning the first
coolant mixture vaporized in the heat exchange bodies to the first
compressor, which comprises: [0066] upstream of an inlet for the
natural gas in the first exchange body, a third body for exchanging
heat between the natural gas and a second coolant chemical
compound, [0067] a third centrifugal compressor of the second
vaporized compound, the first and third centrifugal compressor
being actuated by a single common turbine, [0068] a casing common
to the first compressor and the third compressor, [0069] a means
for cooling the second compressed compound, [0070] a conduit for
transferring the second cooled compound towards the third exchange
body, [0071] between the second compressor and the second exchange
body, a fourth centrifugal compressor of the light fraction of the
first mixture, the second and fourth centrifugal compressor being
actuated by a single common turbine, and [0072] a casing common to
the second compressor and the fourth compressor.
[0073] These provisions enable: [0074] the manufacturing cost of
the device to be reduced significantly; [0075] the device to have a
more extended operating range in terms of composition and flow
rate; [0076] the device to have a better balance between the
compression sections; and [0077] the method performed by the device
to be more robust, allowing more frequent shutdowns and
start-ups.
[0078] In addition, the use of two separate exchange bodies enables
the heat exchanges that occur in each said exchange body to be
controlled better. Lastly, the use of four compressors allow the
compression to be better balanced throughout the heat exchange line
to maximize the efficiency of each compression section.
[0079] In some embodiments, the turbine actuating the first and
third compressors and the turbine actuating the second and fourth
compressors are coupled mechanically.
[0080] In some embodiments, the turbines are combined.
[0081] These embodiments make it possible to reduce the size of the
device.
[0082] In some embodiments, the device that is the subject of the
present invention comprises: [0083] a separator of a gas fraction
and a liquid fraction of the compressed light phase, the fourth
compressor compressing the separated gas fraction, [0084] a
regulator for the liquid fraction of the light phase heated in the
second exchange body, [0085] the turbine of the fourth compressor
being actuated by the expansion energy.
[0086] In some embodiments, the second chemical compound comprises
a pure substance comprising nitrogen, propane and/or ammonia.
[0087] The use of such a composition to form the second compound
allows the natural gas to be cooled before this natural gas enters
into the exchange line formed of the first and second exchange
body. This pre-cooling makes it possible to simplify/limit the
number of constituents in the first cooling mixture used, which
also makes it possible to reduce the dimensions of the exchange
surfaces between the natural gas and the first cooling mixture.
[0088] In some embodiments, the first cooling mixture comprises
nitrogen and methane and at least one compound amongst: [0089]
ethylene; [0090] ethane; [0091] propane; and/or [0092] butane.
[0093] Use of such a mixture makes it possible to minimize the
energy supply to the system for liquefying the natural gas.
[0094] In effect, in the CII system as currently implemented, heavy
compounds are used in the first coolant mixture, these compounds
having the advantage of ensuring the vaporization of the first
mixture before it enters the first compressor.
[0095] However, these heavy compounds have the drawback of
crystallizing in the coldest portion of the exchanger as a function
of the content of these compounds and of the specified operating
conditions possibly being exceeded temporarily. To date, no clear
universal limit is known that makes it possible to determine when
the crystallization occurs, which leads to uncertainty and risks of
damage. However, the person skilled in the art, who currently
favors the gaseous state on input to the first compressor, uses
this type of compounds despite this drawback.
[0096] In some embodiments, the device that is the subject of the
present invention comprises: [0097] a regulator for the liquefied
natural gas, [0098] a collector for the evaporation gas produced
during the expansion of the gas in the regulator, and [0099] a
conduit for injecting the evaporation gas at the inlet of the
second exchange body.
[0100] In some embodiments, the means for cooling the second
compound comprises an outlet for the second compound, the device
comprising, between said outlet and the third exchange body, a
circuit for cooling the second compound with the heavy fraction of
the first mixture inside the first exchange body.
[0101] These embodiments make it possible to cool the second
compound in the cascade of exchangers formed of the first and
second exchangers.
[0102] In some embodiments, the first exchange body and/or the
second exchange body is a coil exchanger.
[0103] In some embodiments, the means for cooling the second
compound is an exchanger of heat between the second compound and
water.
[0104] According to a second aspect, the present invention relates
to a method for liquefying a natural gas, comprising: [0105] a
first step of centrifugal compression of a first vaporized coolant
chemical mixture, [0106] a step of fractionating the compressed
mixture into a heavy fraction and a light fraction, [0107] a second
step of centrifugal compression of the light fraction, [0108] a
first step of exchanging heat between the heavy fraction of the
first mixture and the natural gas in order to cool at least the
natural gas, [0109] a second step of exchanging heat between the
light fraction of the first mixture and the cooled natural gas in
the first exchange body in order to liquefy the natural gas, and
[0110] a step of returning the first coolant mixture vaporized
during the heat exchange steps to the first compression step, which
comprises: [0111] upstream of a step of inputting the natural gas
into the first exchange step, a third step of exchanging heat
between the natural gas and a second coolant chemical compound,
[0112] a third step of centrifugal compression of the second
vaporized compound, the first and third centrifugal compression
step being actuated by a single common turbine, [0113] the first
and third compression step being carried out in a common casing,
[0114] a step of cooling the second compound compressed during the
third exchange step, [0115] a step of transferring the second
cooled compound towards the third exchange step, [0116] between the
second compression step and the second exchange step, a fourth step
of centrifugal compression of the light fraction of the first
mixture, the second and fourth centrifugal compression step being
actuated by a single common turbine, and [0117] the first and third
compression step being carried out in a common casing.
[0118] As the particular aims, advantages and features of the
method that is the subject of the present invention are similar to
those of the device that is the subject of the present invention,
they are not repeated here.
BRIEF DESCRIPTION OF THE FIGURES
[0119] Other advantages, aims and particular features of the
invention will become apparent from the non-limiting description
that follows of at least one particular embodiment of the device,
ship and method that are the subjects of the present invention,
with reference to drawings included in an appendix, wherein:
[0120] FIG. 1 represents, schematically, a first particular
embodiment of the device that is the subject of the present
invention;
[0121] FIG. 2 represents, schematically, a particular embodiment of
the ship that is the subject of the present invention;
[0122] FIG. 3 represents, schematically and in the form of a
logical diagram, a first particular series of steps of the method
that is the subject of the present invention;
[0123] FIG. 4 represents, schematically, a second particular
embodiment of the device that is the subject of the present
invention;
[0124] FIG. 5 represents, schematically and in the form of a
logical diagram, a second particular series of steps of the method
that is the subject of the present invention;
[0125] FIG. 6 represents, schematically, a third particular
embodiment of the device that is the subject of the present
invention;
[0126] FIG. 7 represents, schematically, a particular embodiment of
the compressors of the device that is the subject of the present
invention; and
[0127] FIG. 8 represents, schematically and in the form of a
logical diagram, a third particular series of steps of the method
that is the subject of the present invention.
DESCRIPTION OF EXAMPLES OF REALIZATION OF THE INVENTION
[0128] The present description is given in a non-limiting way, each
characteristic of an embodiment being able to be combined with any
other characteristic of any other embodiment in an advantageous
way.
[0129] It is now noted that the figures are not to scale.
[0130] FIG. 1, which is not to scale, shows a schematic view of an
embodiment of the device 100 that is the subject of the present
invention. This device 100 for liquefying a natural gas,
comprising: [0131] a compressor 105 of a first vaporized coolant
chemical mixture, [0132] a means 110 for fractionating the
compressed mixture into a heavy fraction and a light fraction,
[0133] a first body 115 for exchanging heat between the heavy
fraction of the first mixture and the natural gas in order to cool
at least the natural gas, [0134] a second body 120 for exchanging
heat between the light fraction of the first mixture and the
natural gas cooled in the first exchange body in order to liquefy
the natural gas, and [0135] a conduit 125 for returning the first
coolant mixture vaporized in the heat exchange bodies to the
compressor 105, which comprises: [0136] upstream from an inlet 116
for the natural gas in the first exchange body 115 or downstream
from an outlet 121 of liquefied natural gas from the second
exchange body 120, a third body, 130 or 135, for exchanging heat
between the natural gas and a second coolant chemical compound, and
[0137] a means, 140 or 145, for compressing the second vaporized
compound.
[0138] The compressor 105 is, for example, a centrifugal compressor
fitted with a wheel rotating around a shaft driven by a turbine or
by an electric motor. This rotating wheel allows the kinetic energy
contained in the gas to be transformed into potential energy in
order to increase the pressure of said gas. In order to increase
the compression carried out, the number of wheels is increased in
order to achieve a defined discharge pressure.
[0139] The pressure of the compressor 105 on input is, for example,
a minimum of around 2 bars absolute. The compression ratio produced
in the compressor 105 is, for example, between 2 and 6.
[0140] This compressor 105 is, for example, configured to compress
a first coolant mixture that comprises nitrogen and methane and at
least one compound amongst: [0141] ethylene; [0142] ethane; [0143]
propane; and/or [0144] butane.
[0145] The composition of the first compound is adjusted as a
function of the composition of the natural gas to be liquefied in
the device. This adjustment is carried out as a function of the
vapor characteristics curve, i.e. the pressure/temperature balance,
of the composition of the gas along the exchange line formed of the
first exchange body 112 and the second exchange body 120.
[0146] The use of propane is aimed at balancing out volatility
differences between the heavy compounds and light compounds of the
first mixture.
[0147] This compressor 105 comprises an inlet (unnumbered) for
vaporized coolant mixture and an outlet (unnumbered) for compressed
coolant mixture.
[0148] The compressed coolant mixture is preferably cooled in a
fifth heat exchanger 106. This heat exchanger 106 is, for example,
a tubular exchanger in which the cold source is air or water. The
colder the source, the more efficient the method. Preferably, the
maximum cooling temperature is equal to the temperature of the air
or water plus fifteen degrees Celsius.
[0149] The coolant mixture, preferably cooled in the fifth
exchanger 106, is supplied to the fractionating means 110. This
fractionating means 110 is, for example, a fractionating
column.
[0150] The flow input to the fractionating column is diphasic, one
portion being gaseous and one portion being liquid. The gaseous
fraction flows in the column to emerge from the top and the liquid
fraction from the bottom.
[0151] This fractionating means 110 comprises: [0152] an inlet
(unnumbered) for compressed coolant mixture, [0153] an outlet
(unnumbered) for a light fraction of the coolant mixture positioned
in a bottom portion of the fractionating means 110, and [0154] an
outlet (unnumbered) for a heavy fraction of the coolant mixture in
a top portion, relative to the outlet for the light fraction, of
the fractionating means 110.
[0155] Preferably, the light fraction leaving the fractionating
means 110 enters the first exchange body 115 and is cooled by the
heavy fraction traversing the first exchange body 115. Depending on
the operating conditions, this light fraction can also act as cold
source in the heat exchange occurring with the natural gas entering
by the inlet 116 of the first exchange body 115.
[0156] In some preferred variants, the fractionating means 110 also
comprises an inlet for the reflux of a portion of the light
fraction and this portion of the light fraction is collected, for
example, in a reflux drum 111.
[0157] The fractionating means 110 therefore preferably comprises
packing, making it possible to improve the mass transfer between
the gaseous flow and the liquid fraction coming from the reflux
drum 111, which absorbs the heaviest compounds of the gaseous
fraction making it possible to obtain a flow rich in nitrogen and
methane at the head.
[0158] The fractionating means 110 is preferably fitted with
meshing to limit the carry-over of droplets in the gaseous
fraction.
[0159] This reflux drum 111 is connected to the outlet for the
light fraction of the fractionating means 110, with or without
intermediate exchange in the first body 115, and operates in a
similar way in separating the light fraction from heavy fraction
residues transported unexpectedly by the light fraction away from
the fractionating means 110.
[0160] The drum 111 is preferably fitted with meshing to limit the
carry-over of droplets in the gaseous fraction.
[0161] The light fraction leaving the fractionating means 110, or
the reflux drum 111 when such a drum 111 is present, is preferably
compressed by a second compressor 112.
[0162] The second compressor 112 is, for example, a centrifugal
compressor. This centrifugal compressor is preferably actuated by
the turbine utilized at the location of the compressor 105 when
this compressor 105 is a centrifugal compressor.
[0163] The pressure on output from the second compressor 112 is,
for example, around 40 bars absolute and the compression ratio is
preferably between 2 and 4.
[0164] The light fraction, with or without compression in the
second compressor 112, is preferably cooled in a sixth heat
exchanger 113.
[0165] This heat exchanger 113 is, for example, a tubular exchanger
in which the cold source is air or water. The colder the source,
the more efficient the cooling. Preferably, the maximum cooling
temperature is equal to the temperature of the air or water plus
fifteen degrees Celsius. The resulting flow contributes the cold or
negative heat necessary for cooling the natural gas.
[0166] The light fraction, compressed or not in the second
compressor 112, cooled or not in the sixth exchanger 113, is
transmitted to the first heat exchanger 115.
[0167] The first heat exchanger 115 is, for example, a coil
exchanger in which the light fraction acts as cold source and the
natural gas acts as hot source. Preferably, the first exchanger 115
and the second exchanger 120 are formed from a single coil
exchanger.
[0168] The natural gas enters the first exchanger 115 by the inlet
116.
[0169] The light fraction vaporized during the exchange with the
natural gas in the first exchange body 115 is preferably directed
towards a drum 114 configured to separate the light fraction into
two portions, one being heavier than the other.
[0170] The device 100 preferably comprises a valve 136 upstream of
the drum 114. This valve creates, for example, an expansion of the
gaseous portion of the first mixture of around 20 to 25 bars.
[0171] The two portions of the light fraction are transmitted to
the second exchange body 120, the light fraction acting as cold
source in the heat exchange carried out with the natural gas cooled
beforehand in the first exchange body 115.
[0172] When the device 100 utilizes a drum 114, the heavy portion
of the light fraction, after traversing the second exchange body
120, is expanded in an expander 118, then is transmitted to the
compressor 105 via the return conduit 125.
[0173] This expander 118 is positioned in place of a valve 123 or
in parallel to this valve 123.
[0174] In some variants, between the expander 118 and the
compressor 105, the heavy portion of the light fraction,
compressed, is reinjected into the second exchange body 120.
[0175] The light portion of the light fraction is transmitted to
the compressor 105 via the return conduit 125.
[0176] In some variants, the light portion of the light fraction,
upon leaving the second exchange body 120, is expanded in a valve
122, and is reinjected into this second exchange body 120 before
being directed to the compressor 105.
[0177] The valve 122 creates an expansion to reach a pressure of
about 4 to 5 bars as a function of the pressure drop of the
downstream circuit, for example.
[0178] The heavy fraction of the coolant mixture leaving the
fractionating means 110 is transmitted to the first exchange body
115 and acts as cold source in the exchange occurring with the
natural gas.
[0179] In some variants, the device 100 comprises an expander 127
in parallel to the valve 122.
[0180] Preferably, the device 100 comprises the expander 127 and
does not comprise a valve 122.
[0181] In some variants, the heavy fraction leaves the first
exchange body 115 and is reinjected into this first exchange body
115, after being expanded in a regulator 119, before being directed
to the compressor 105.
[0182] The regulator 119 creates an expansion to reach a pressure
of about 4 to 5 bars as a function of the pressure drop of the
first exchange body 115, for example.
[0183] In some variants, the return conduit 125 comprises a drum
126 between the first exchange body 115 and the compressor 105.
[0184] This drum 126 makes it possible to ensure that, on input to
the first compressor 105, the first coolant mixture is exclusively
gaseous.
[0185] The drum 126 is preferably fitted with meshing to limit the
carry-over of droplets in the gaseous fraction.
[0186] Preferably, the device 100 comprises a conduit connecting
one portion of the drum 126, intended to receive the liquid portion
of the first mixture, to the fractionating means 110. Preferably,
this conduit is fitted with a pump. Preferably, this pump is
actuated as a function of a level of liquid captured, by a sensor,
in the portion of the drum 126 intended to receive the liquid
portion of the first mixture.
[0187] In this way, as can be understood, the natural gas is
liquefied thanks to two successive cooling steps. The first step
takes place in the first exchange body 115 and the second step
takes place in the second exchange body 120.
[0188] The natural gas circulates, in the first body 115 and in the
second body 120, preferably in counter-current to the first coolant
mixture.
[0189] The cooled natural gas preferably leaves the first body 115
at a temperature of about -30.degree. C. This cooled natural gas is
then preferably directed to a fractionation section (not shown) to
separate any condensates from the gaseous fraction. The gaseous
fraction is transmitted to the second body 120 to be liquefied.
[0190] In addition to these two steps, the present invention
proposes adding a third cooling step positioned either before or
after the first two steps.
[0191] In the first case, a third exchange body 130 is positioned
upstream of the inlet 116 for the natural gas in the first exchange
body 115. This third exchange body 130 is, for example, a tubular
exchanger using, as cold source, a second coolant compound, and as
hot source the natural gas entering the device 100 so as to be
liquefied.
[0192] The second chemical compound is, for example, a pure
substance composed of nitrogen, propane and/or ammonia or a mixture
of nitrogen and propane.
[0193] Preferably, when ammonia is used, this ammonia is used
alone.
[0194] In the second case, a third exchange body 135 is positioned
downstream of the outlet 121 for liquefied natural gas from the
second exchange body 120. This third exchange body 135 is, for
example, a tubular exchanger using, as cold source, a second
coolant compound, and as hot source the liquefied natural gas
exiting from the device 100 to be stored or used. The natural gas
liquefied in this way can be expanded to atmospheric pressure by a
regulator (not shown) before storage. The evaporation gas, called
"BOG" (for "Boil-off gas"), collected in the storage of the
liquefied natural gas can be reinjected into the device 100 at the
location of the gaseous fraction leaving the fractionation section
between the first exchange body 115 and the second exchange body
120.
[0195] The second coolant compound is here, for example, liquid
nitrogen.
[0196] Downstream of this third body, 130 or 135, the device 100
comprises a means, 140 or 145, for compressing the second
compound.
[0197] This compressor, 140 or 145, is for example a centrifugal
compressor.
[0198] In some preferred embodiments, the device 100 comprises both
the upstream cooling step and the downstream cooling step.
[0199] In these embodiments, the third exchange body 130 is
designated the exchange body positioned upstream of the first
exchange body 115, and the fourth exchange body 135 is designated
the exchange body positioned downstream of the second exchange body
120. The second coolant compound is designated the coolant mixture
utilized in the third body 130, and the third coolant mixture is
designated the coolant mixture utilized in the fourth exchange
body.
[0200] In some embodiments, the device 100 comprises: [0201] a
means 150 for cooling the second compound compressed in the
compression means 140, and [0202] a conduit 155 for transferring
the second compressed compound towards the third exchange body
130.
[0203] The cooling means 150 is, for example, an exchanger of heat
between the second compound vaporized during the heat exchange with
the natural gas in the third exchange body 130 and the air or
water.
[0204] In some embodiments, such as that shown in FIG. 1, the
device 100 comprises, between an outlet 131 for the second compound
of the means 150 for cooling the second compound and the third
exchange body 130, a circuit 170 for cooling the second compound
with the heavy fraction of the first mixture inside the first
exchange body 115.
[0205] This cooling circuit 170 is achieved, for example, by
inputting the second cooled compound into the first exchange body
115, the second cooled compound acting as hot source relative to
the heavy fraction and any light fraction traversing this first
exchange body 115. This second vaporized compound can
simultaneously act as cold source relative to the natural gas input
into the first body 115 by the inlet 116 for natural gas.
[0206] In some variants, the second vaporized compound leaves the
first body 115, is expanded in a regulator 124 then reinjected into
the first body 115 or into the second body 120.
[0207] The second compound is expanded, for example, to a pressure
between 3 and 4 bars as a function of the pressure drop in the
upstream conduits.
[0208] The purpose of this cooling circuit 170 is to facilitate the
cooling occurring in the cooling means 150.
[0209] In some embodiments, such as that shown in FIG. 1, one
portion of the cooling circuit 170 is configured to cool the second
compound by exchanging heat with the light fraction of the first
mixture in the second exchange body 120.
[0210] In these embodiments, the second compound, cooled by heat
exchange in the first exchange body 115, is injected into the
second exchange body 120. The second vaporized compound then acts
as hot source relative to the light fraction of the first coolant
mixture traversing this second exchange body 120. At the same time,
this second vaporized compound can act as cold source relative to
the natural gas input into the second exchange body 120.
[0211] In some embodiments, the device 100 comprises: [0212] a
means 160 for cooling the compressed nitrogen, and [0213] a conduit
165 for transporting the cooled nitrogen to the fourth exchange
body 135.
[0214] The cooling means 160 is, for example, an exchanger of heat
between the compressed third mixture and the air or water.
[0215] The natural gas can undergo pre-treatment prior to the third
exchange body 130.
[0216] The compressors and compression means, 105, 112 and 140,
utilized in this embodiment can be replaced by the compressors,
605, 610 and 620, described with reference to FIG. 6 and whose
functions are similar.
[0217] FIG. 2, which is not to scale, shows a schematic view of an
embodiment of the ship 200 that is the subject of the present
invention. This ship 200 comprises: [0218] a device 100 for
liquefying a natural gas as described with regard to FIG. 1, [0219]
a device 400 for liquefying a natural gas as described with regard
to FIG. 4, or [0220] a device 600 for liquefying a natural gas as
described with regard to FIG. 6.
[0221] FIG. 3 shows, schematically and in the form of a logical
diagram, a particular series of steps of the method 300 that is the
subject of the present invention. This method 300 for liquefying a
natural gas, comprising: [0222] a step 305 of compressing a first
vaporized coolant chemical mixture, [0223] a step 310 of
fractionating the compressed mixture into a heavy fraction and a
light fraction, [0224] a first step 315 of exchanging heat between
the heavy fraction of the first mixture and the natural gas in
order to cool at least the natural gas, [0225] a second step 320 of
exchanging heat between the light fraction of the first mixture and
the natural gas cooled during the first exchange step to liquefy
the natural gas, and [0226] a step 325 of returning the first
coolant mixture vaporized in the heat exchange bodies to the
compressor step, which comprises: [0227] before an input of the
natural gas of the first exchange step or after an output of
liquefied natural gas from the second exchange step, a third step
330 of exchanging heat between the natural gas and a second coolant
chemical compound, and [0228] a step 335 of compressing the second
vaporized compound.
[0229] This method 300 is performed, for example, by utilizing the
device 100 as described with regard to FIG. 1. As can be
understood, all the variants, all the examples and all the
embodiments of the device 100 can also be transposed as steps
within method 300.
[0230] FIG. 4, which is not to scale, shows a schematic view of an
embodiment of the device 400 that is the subject of the present
invention. This device 400 for liquefying a natural gas,
comprising: [0231] a compressor 105 of a first vaporized coolant
chemical mixture, [0232] a means 110 for fractionating the
compressed mixture into a heavy fraction and a light fraction,
[0233] a first body 115 for exchanging heat between the heavy
fraction of the first mixture and the natural gas in order to cool
at least the natural gas, [0234] a second body 120 for exchanging
heat between the light fraction of the first mixture and the
natural gas cooled in the first exchange body in order to liquefy
the natural gas, and [0235] a conduit 125 for returning the first
coolant mixture vaporized in the heat exchange bodies to the
compressor, comprises: [0236] a regulator 405 for the liquefied
natural gas, [0237] a collector 410 for the evaporation gas
produced during the expansion of the gas in the regulator 405, and
[0238] a conduit 415 for injecting the evaporation gas at the inlet
of the second exchange body.
[0239] In this FIG. 4, the various means relative to the first
coolant mixture are identical to the means described with reference
to FIG. 1 or 6, including the particular variants and embodiments
described with reference to these FIGS. 1 and 6. These means are:
[0240] the compressor 105, [0241] the exchanger 106, [0242] the
fractionating means 110, [0243] the reflux drum 111, [0244] the
compressor 112, [0245] the exchanger 113, [0246] the drum 114,
[0247] the first exchange body 115, [0248] the inlet 116 for
natural gas, [0249] the expander 118, [0250] the regulator 119,
[0251] the second exchange body 120, [0252] the outlet 121 for
liquefied natural gas from the second exchange body 120, [0253] the
regulator 122, [0254] the expander 126, [0255] the return conduit
125, [0256] the drum 126, and [0257] the valve 136.
[0258] In this way, as can be understood, the natural gas is
liquefied thanks to two successive cooling steps. The first step
takes place in the first exchange body 115 and the second step
takes place in the second exchange body 120.
[0259] Between these two steps, i.e. between an outlet (unnumbered)
for cooled natural gas from the first body 115 and an inlet
(unnumbered) for cooled natural gas into the second body 120, the
device 400 preferably comprises a fractionation section configured
for removing condensates from the gas flow.
[0260] The liquefied natural gas leaving the second body 120 by the
outlet 121 traverses a regulator 405 configured to expand the
liquefied natural gas to atmospheric pressure.
[0261] The regulator 405 is, for example, a valve utilizing the
Joule-Thomson effect.
[0262] This expansion leads to the appearance of evaporation gas,
aka BOG.
[0263] The BOG generated in this way is collected in a collector
410 and injected, via a conduit 415, at the inlet of the second
exchange body 120. This injection can take place upstream of, in or
downstream of the fractionation section, if such a section is
present.
[0264] The collector is, for example, a gas/liquid separator drum
410 fitted with meshing to limit the carry-over of droplets in the
gaseous fraction.
[0265] Preferably, the conduit 415 is equipped with a compressor
416 compressing the gaseous fraction leaving the collector 410.
[0266] In some embodiments, such as that shown in FIG. 4, a third
exchange body 420 is positioned upstream of the inlet 116 for the
natural gas in the first exchange body 115. This third exchange
body 420 is, for example, a tubular exchanger using, as cold
source, a second coolant compound, and as hot source the natural
gas entering the device 400 so as to be liquefied.
[0267] The device 400 therefore comprises a compressor 425 of the
second vaporized compound downstream from the third exchange body
420. This compressor 425 is, for example, a centrifugal
compressor.
[0268] The second chemical compound is, for example, a pure
substance composed of nitrogen, propane and/or ammonia or a mixture
of nitrogen and propane.
[0269] In some embodiments, the device 400 comprises: [0270] a
means 430 for cooling the second compressed compound, and [0271] a
conduit 435 for transferring the second cooled compound towards the
third exchange body 420.
[0272] The cooling means 430 is, for example, an exchanger of heat
between the second compressed compound and the water or glycol
water.
[0273] In some embodiments, such as that shown in FIG. 4, the
device 400 comprises, between an outlet 421 for the second compound
of the means 430 for cooling the second compound and the third
exchange body 420, a circuit 440 for cooling the second compound
with the heavy fraction of the first mixture inside the first
exchange body 115.
[0274] This cooling circuit 440 is achieved, for example, by
inputting the second cooled compound into the first exchange body
115, the second cooled compound acting as hot source relative to
the heavy fraction and any light fraction traversing this first
exchange body 115. At the same time, this second cooled compound
can act as cold source relative to the natural gas entered into the
first body 115 by the inlet 116 for natural gas.
[0275] In some variants, the second vaporized compound leaves the
first body 115, is expanded in a regulator 424 then reinjected into
the first body 115 or into the second body 120.
[0276] The second compound is expanded, for example, to a pressure
of 3 to 4 bars on output from the regulator 424.
[0277] The purpose of this cooling circuit 440 is to facilitate the
cooling that occurs in the cooling means 430.
[0278] This circuit 440 can also comprise a second portion, in the
second exchange body 120, as described with regard to FIG. 1.
[0279] In some particular embodiments, the first cooling mixture
comprises nitrogen and methane and at least one compound amongst:
[0280] ethylene; [0281] ethane; [0282] propane; and/or [0283]
butane.
[0284] FIG. 5 shows, schematically, a particular embodiment of the
method 500 that is the subject of the present invention. This
method 500 for liquefying a natural gas, comprising: [0285] a step
505 of compressing a first vaporized coolant chemical mixture,
[0286] a step 510 of fractionating the compressed mixture into a
heavy fraction and a light fraction, [0287] a first step 515 of
exchanging heat between the heavy fraction of the first mixture and
the natural gas in order to cool at least the natural gas, [0288] a
second step 520 of exchanging heat between the light fraction of
the first mixture and the natural gas cooled during the first
exchange step to liquefy the natural gas, and [0289] a step 525 of
returning the first coolant mixture vaporized in the heat exchange
bodies to the compressor step, comprises: [0290] a step 530 of
expanding the liquefied natural gas, [0291] a step 535 of
collecting evaporation gas produced during the expansion step, and
[0292] a step 540 of injecting the evaporation gas on input to the
second exchange body.
[0293] This method 500 is performed, for example, by utilizing the
device 400 as described with regard to FIG. 4. As can be
understood, all the variants, all the examples and all the
embodiments of the device 400 can also be transposed as steps
within method 500.
[0294] FIGS. 6 and 7 show, schematically, a particular embodiment
of the device 600 that is the subject of the present invention.
This device 600 for liquefying a natural gas, comprising: [0295] a
first centrifugal compressor 605 of a first vaporized coolant
chemical mixture, [0296] a means 110 for fractionating the
compressed mixture into a heavy fraction and a light fraction,
[0297] a second centrifugal compressor 610 of the light fraction,
[0298] a first body 115 for exchanging heat between the heavy
fraction of the first mixture and the natural gas in order to cool
at least the natural gas, [0299] a second body 120 for exchanging
heat between the compressed light fraction of the first mixture and
the natural gas cooled in the first exchange body in order to
liquefy the natural gas, and [0300] a conduit 125 for returning the
first coolant mixture vaporized in the heat exchange bodies to the
first compressor, comprises: [0301] upstream from an inlet 116 for
the natural gas in the first exchange body, a third body 420 for
exchanging heat between the natural gas and a second coolant
chemical compound, [0302] a third centrifugal compressor 620 of the
second vaporized compound, the first and third centrifugal
compressor being actuated by a single common turbine 630, [0303] a
casing 635 common to the first compressor and the third compressor,
[0304] a means 430 for cooling the second compressed compound, and
[0305] a conduit 435 for transferring the second cooled compound
towards the third exchange body 420.
[0306] The term "casing" refers to a housing that comprises at
least one compressor. Each compressor comprises one or more
wheels.
[0307] In this FIG. 6: [0308] the exchanger 106, [0309] the
fractionating means 110, [0310] the reflux drum 111, [0311] the
exchanger 113, [0312] the first exchange body 115, [0313] the inlet
116 for natural gas, [0314] the regulator 119, [0315] the second
exchange body 120, [0316] the outlet 121 for liquefied natural gas
from the second exchange body 120, [0317] the regulator 122, [0318]
the expander 127, [0319] the return conduit 125, [0320] the drum
126, [0321] the valve 136, [0322] the third exchange body 420,
[0323] the transfer conduit 435, [0324] the fourth exchange body
430, [0325] the outlet 421 for the second coolant compound, [0326]
the cooling circuit 400, [0327] the regulator 424, [0328] the
regulator 405, [0329] the collector 410, and [0330] the injection
conduit 415, are identical to the corresponding means described
with reference to FIG. 1 or 4, including the particular variants
and embodiments described with reference to these FIGS. 1 and
4.
[0331] The third compressor 620 corresponds to the third compressor
140 as described with reference to FIG. 1. However, this third
compressor 620 is actuated by the utilization of a single turbine
shared with the turbine actuating the first compressor 605. The
first compressor corresponds to the first compressor 105 as
described with reference to FIG. 1.
[0332] The fourth compressor 615 is configured to increase the
pressure of the light portion of the light fraction of the first
coolant mixture. This fourth compressor shares a single common
turbine with the second compressor 610, this second compressor 610
corresponding to the second compressor 112 as described with
reference to FIG. 1.
[0333] In some preferred embodiments, such as that shown in FIGS. 6
and 7, the turbine actuating 630 the first and third compressors,
605 and 620, and the turbine 640 actuating the second and fourth
compressors, 610 and 615, are coupled mechanically.
[0334] This coupling is achieved, for example, by any type of
coupling for rotating shafts known to the person skilled in the
art.
[0335] In some preferred embodiments, such as that shown in FIGS. 6
and 7, the turbines, 630 and 640, are combined.
[0336] In some preferred embodiments, such as that shown in FIGS. 6
and 7, the device 600 that is the subject of the present invention
comprises: [0337] between the second compressor 610 and the second
exchange body 120, a fourth centrifugal compressor 615 of the light
fraction of the first mixture, the second and fourth centrifugal
compressor being actuated by a single common turbine 640, and
[0338] a casing 645 common to the second compressor and the fourth
compressor.
[0339] In some preferred embodiments, such as that shown in FIG. 6,
the device 600 that is the subject of the present invention
comprises: [0340] a separator 650 of a gas fraction and a liquid
fraction of the compressed light phase, the fourth compressor 615
compressing the separated gas fraction, [0341] a regulator 625 for
the liquid fraction of the light phase heated in the second
exchange body, [0342] the turbine 640 of the fourth compressor
being actuated by the expansion energy.
[0343] The separator 650 is, for example, similar to the reflux
drum 114 as described with regard to FIG. 1. The regulator 625 is,
for example, similar to the expander 118 as described with regard
to FIG. 1.
[0344] In some preferred embodiments, such as that shown in FIG. 6,
the second chemical compound comprises nitrogen, propane and/or
ammonia.
[0345] In some preferred embodiments, such as that shown in FIG. 6,
the first cooling mixture comprises nitrogen and methane and at
least one compound amongst: [0346] ethylene; [0347] ethane; [0348]
propane; and/or [0349] butane.
[0350] In some preferred embodiments, such as that shown in FIG. 6,
the device 600 comprises: [0351] a regulator 405 for the liquefied
natural gas, [0352] a collector 410 for the evaporation gas
produced during the expansion of the gas in the regulator, and
[0353] a conduit 415 for injecting the evaporation gas at the inlet
of the second exchange body.
[0354] In some preferred embodiments, such as that shown in FIG. 6,
the device 600 comprises, between an outlet 421 for the second
compound of the cooling means 430 and the third exchange body 420,
a circuit 440 for cooling the second compound by the heavy fraction
of the first mixture inside the first exchange body 115.
[0355] In some preferred embodiments, such as that shown in FIG. 6,
the first exchange body 115 and/or the second exchange body 120 is
a coil exchanger.
[0356] In some preferred embodiments, such as that shown in FIG. 6,
the means 430 for cooling the second compound is an exchanger of
heat between the second compound and water.
[0357] FIG. 8 shows, schematically, a particular embodiment of the
method 700 that is the subject of the present invention. This
method 700 for liquefying a natural gas, comprising: [0358] a step
705 of centrifugal compression of a first vaporized coolant
chemical mixture, [0359] a step 710 of fractionating the compressed
mixture into a heavy fraction and a light fraction, [0360] a second
step 715 of centrifugal compression of the light fraction, [0361] a
first step 720 of exchanging heat between the heavy fraction of the
first mixture and the natural gas in order to cool at least the
natural gas, [0362] a second step 725 of exchanging heat between
the light fraction of the first mixture and the cooled natural gas
in the first exchange body in order to liquefy the natural gas, and
[0363] a step 730 of returning the first coolant mixture vaporized
during the heat exchange steps to the first compression step,
comprises: [0364] upstream of a step 735 of inputting the natural
gas into the first exchange step, a third step 740 of exchanging
heat between the natural gas and a second coolant chemical
compound, [0365] a third step 745 of centrifugal compression of the
second vaporized compound, the first and third centrifugal
compression step being actuated by a single common turbine, [0366]
the first and third compression step being carried out in a common
casing, [0367] a step 750 of cooling the second compound compressed
during the third exchange step, [0368] a step 755 of transferring
the second cooled compound towards the third exchange step, [0369]
between the second compression step and the second exchange step, a
fourth step 760 of centrifugal compression of the light fraction of
the first mixture, the second and fourth centrifugal compression
step being actuated by a single common turbine, and [0370] the
first and third compression step being carried out in a common
casing.
[0371] This method 700 is performed, for example, by utilizing the
device 600 as described with regard to FIGS. 6 and 7. As can be
understood, all the variants, all the examples and all the
embodiments of the device 600 can also be transposed as steps
within method 700.
* * * * *