FIELD OF THE INVENTION
[0001] The embodiments disclosed herein relate to processes and systems for liquefying natural
gas.
DESCRIPTION OF THE RELATED ART
[0002] EP 2 336 677 A1 discloses a refrigeration system for circulating a refrigerant fluid comprising a
first compressor and a second compressor operable to compress the refrigerant fluid
in separate stages of compression.
US 3 763 658 A1 discloses a propane - precooled mixed refrigerant process, comprising a propane pre-cooling
loop comprising a two stage compressor for pressurizing the propane and at least a
cooling loop, downstream of said pre-cooling loop, where through a second refrigerant
circulates, the natural gas being adapted to be sequentially cooled in the pre-cooling
loop and in the cooling loop.
[0003] Natural gas is becoming an increasingly important source of energy. In order to allow
transportation of the natural gas from the source of supply to the place of use, the
volume of the gas must be reduced. Cryogenic liquefaction has become a routinely practiced
process for converting the natural gas into a liquid, which is more convenient, less
expensive and safer to store and transport. Transportation by pipeline or ship vessels
of liquefied natural gas (LNG) becomes possible at ambient pressure, by keeping the
chilled and liquefied gas at a temperature lower than liquefaction temperature at
ambient pressure.
[0004] In order to store and transport natural gas in the liquid state, the natural gas
is preferably cooled at around -150 to -170°C, where the gas possesses a nearly atmospheric
vapor pressure.
[0005] Several processes and systems exist in the prior art for the liquefaction of natural
gas, which provide for sequentially passing the natural gas at an elevated pressure
through a plurality of cooling stages whereupon the gas is cooled in successively
lower temperatures in sequential refrigeration cycles until the liquefaction temperature
is achieved.
[0006] Prior to passing the natural gas through the cooling stages, the natural gas is pre-treated
to remove any impurities that can interfere the processing, damage the machinery or
are undesired in the final product. Impurities include acid gases, sulfur compounds,
carbon dioxide, mercaptans, water and mercury. The pre-treated gas from which impurities
have been removed is then cooled by refrigerant streams to separate heavier hydrocarbons.
The remaining gas mainly consists of methane and usually contains less than 0.1% mol
of hydrocarbons of higher molecular weight, such as propane or heavier hydrocarbons.
The thus cleaned and purified natural gas is cooled down to the final temperature
in a cryogenic section. The resulting LNG can be stored and transported at nearly
atmospheric pressure.
[0007] Cryogenic liquefaction is usually performed by means of a multi-cycle process, i.e.
a process using different refrigeration cycles. Depending upon the kind of process,
each cycle can use a different refrigerating fluid, or else the same refrigerating
fluid can be used in two or more cycles.
[0008] Fig.1 schematically shows a diagram of a cryogenic natural gas liquefaction system
using the so-called APCI process. This known process uses two refrigeration cycles.
A first cycle uses propane as a refrigeration fluid and a second cycle uses a mixed
refrigerant, usually made of nitrogen, methane, ethane and propane. The system, labeled
1 as a whole, comprises a first cycle 2 comprising a line formed by a gas turbine
3, which drives a compressor train. The compressor train comprises a first compressor
5 and a second compressor 7 in series for compressing the mixed refrigerant. An inter-stage
cooler (inter-cooler) 9 cools the mixed refrigerant delivered by the first compressor
5 to reduce the temperature and the volume thereof before entering the second compressor
7. The compressed mixed refrigerant delivered by the second compressor 7 is condensed
against air or water in a heat exchanger 11. The mixed refrigerant is further cooled
and partly liquefied by the propane cycle 12 as disclosed here below.
[0009] The propane is processed in a second or pre-cooling cycle. The second cycle comprises
a line including a gas turbine 13, which drives a multi-stage compressor 15. The compressed
propane delivered by compressor 15 is condensed in a condenser 17 against water or
air. The condensed propane is used to pre-cool the natural gas down to -40°C and to
cool and partially liquefy the mixed refrigerant. The natural gas pre-cooling and
the mixed refrigerant partial liquefaction is performed in a multi-pressure process,
in the example shown 4-level of pressure.
[0010] The stream of condensed propane from condenser 17 is delivered to a first set of
four, serially arranged heat exchangers to cool and partly liquefy the mixed refrigerant
and to a second set of four, serially arranged, pre-cooling heat exchangers to cool
the natural gas. A first portion of the compressed propane stream from condenser 17
is delivered through pipe 19 to the first set of heat exchangers and is sequentially
expanded in serially arranged expanders 21, 23, 25 and 27 to four different, gradually
decreasing pressure levels. Downstream each expander 21, 23 and 25 a portion of the
expanded propane flow is diverted to a respective heat exchanger 29, 31, 33. The propane
flowing through the last expander 27 is delivered to a heat exchanger 35.
[0011] The compressed mixed refrigerant delivered from the heat exchanger 11 flows in a
pipe 37 towards a main cryogenic heat exchanger 38. The pipe 37 sequentially passes
through the heat exchangers 29, 31, 33 and 35, such that the mixed refrigerant is
gradually cooled and partly liquefied against the expanded propane.
[0012] A second fraction of the condensed propane flow from condenser 17 is delivered to
a second pipe 39 and expanded sequentially in four serially arranged expanders 41,
43, 45 and 47. A part of the propane expanded in each expander 41, 43 and 45 as well
as the propane flowing from the last expander 47 is diverted towards a corresponding
pre-cooling heat exchanger 49, 51, 53 and 55, respectively. A main natural gas line
61 flows sequentially through said pre-cooling heat exchangers 49, 51, 53 and 55,
such that the natural gas is pre-cooled before entering the main cryogenic heat exchanger
38. Heated propane exiting the pre-cooling heat exchangers 49, 51, 53 and 55 is collected
with the propane exiting the heat exchangers 29, 31, 33 and 35 and is fed again to
the compressor 15, which recovers the four evaporated propane side streams and compresses
the vapor to e.g. 15-25 bar to be condensed again in condenser 17.
SUMMARY OF THE INVENTION
[0013] The current invention provides a natural gas liquefaction system according to claim
1 and a natural gas liquefaction method according to claim 12.
[0014] Further embodiments are disclosed here below and are further set forth in the appended
claims, which form an integral part of the present description. The above brief description
sets forth features of the various embodiments of the present invention in order that
the detailed description that follows may be better understood and in order that the
present contributions to the art may be better appreciated. There are, of course,
other features of the invention that will be described hereinafter and which will
be set forth in the appended claims. In this respect, before explaining several embodiments
of the invention in details, it is understood that the various embodiments of the
invention are not limited in their application to the details of the construction
and to the arrangements of the components set forth in the following description or
illustrated in the drawings. The invention is capable of other embodiments and of
being practiced and carried out in various ways.
[0015] Phraeseology and terminology employed herein are for the purpose of description and
should not be regarded as limiting.
[0016] The flow rates of first refrigerant elaborated by the present system and method are
controllable acting not only to the rotational speed of compressor stages. In this
way, a more efficient and reliable LNG circuit is provided.
[0017] As such, those skilled in the art will appreciate that the conception, upon which
the disclosure is based, may readily be utilized as a basis for designing other structures,
methods, and/or systems for carrying out the several purposes of the present invention.
It is important, therefore, that the claims be regarded as including such equivalent
constructions insofar as they do not depart from the scope of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] A more complete appreciation of the disclosed embodiments of the invention and many
of the attendant advantages thereof will be readily obtained as the same becomes better
understood by reference to the following detailed description when considered in connection
with the accompanying drawings, wherein:
Fig.1 illustrates a system for liquefying natural gas according to the current art;
Fig.2 illustrates a schematic of a first embodiment of a system for the production
of LNG according to the present invention;
Fig.2A illustrates an exemplary embodiment of an integrally geared compressor used
in the arrangement of Fig.2;
Fig.3 illustrates a schematic of a system for the production of LNG according to the
present invention, in a second embodiment; and
Fig.4 illustrates section of two compressor stages of an integrally-geared turbo-compressor
for use in a LNG system according to the present invention.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0019] The following detailed description of the exemplary embodiments refers to the accompanying
drawings. The same reference numbers in different drawings identify the same or similar
elements. Additionally, the drawings are not necessarily drawn to scale. Also, the
following detailed description does not limit the invention. Instead, the scope of
the invention is defined by the appended claims.
[0020] Reference throughout the specification to "one embodiment" or "an embodiment" or
"some embodiments" means that the particular feature, structure or characteristic
described in connection with an embodiment is included in at least one embodiment
of the subject matter disclosed. Thus, the appearance of the phrase "in one embodiment"
or "in an embodiment" or "in some embodiments" in various places throughout the specification
is not necessarily referring to the same embodiment(s). Further, the particular features,
structures or characteristics may be combined in any suitable manner in one or more
embodiments.
[0021] Fig.2 schematically shows a diagram of a cryogenic natural gas liquefaction system
based on the APCI process embodying the subject matter disclosed herein. The process
uses two refrigeration cycles or loops, wherein a first refrigerant and a second refrigerant,
respectively, are processed. The first loop is a pre-cooling loop wherein the natural
gas as well as the second refrigerant, circulating in a second loop, are cooled by
exchanging heat with the first refrigerant. Herein after the first loop will be referred
to as pre-cooling loop or cycle and the second loop will be referred to as the cooling
or liquefaction loop or cycle.
[0022] In some embodiments the first refrigerant circulating in the pre-cooling loop can
include or consist of propane. The first refrigerant can have a mean molecular weight
of at least 35, for example between 35 and 41. In some embodiments the second refrigerant
circulating in the second loop can include a mixed refrigerant, for example comprising
nitrogen, methane, ethane and propane.
[0023] More specifically, in the embodiment of Fig.2 the system is labeled 101 as a whole,
the first or pre-cooling loop is labeled 103 and the second liquefaction cycle or
loop is labeled 105. Natural gas is delivered to the system 101 along a pipe 107 and
is sequentially cooled and finally liquefied by flowing through a plurality of serially
arranged heat exchangers of the pre-cooling loop 103 and of the cooling loop 105,
respectively.
[0024] The pre-cooling loop 103 comprises a multi-stage, integrally-geared turbo-compressor
109. The integrally-geared turbo-compressor can be configured as shown in more detail
in Fig. 4, and will be described in greater detail later on, reference being made
to said figure.
[0025] At least one, some, or preferably all the stages of the integrally-geared turbo-compressor
are comprised of movable inlet guide vanes, to adjust the operative conditions of
said stage(s) according to the actual operative needs of the system 101. Each set
of movable inlet guide vanes can be adjusted independently of the other, for instance
in order to take into account flow rates which differ from one stage to the other.
[0026] In some embodiments the integrally-geared turbo-compressor comprises a number of
stages comprised between two and eight. For example, the integrally-geared turbo-compressor
can comprise from three to six stages. As will be described in more detail later on,
one or more inter-coolers can be provided between one or more pairs of sequentially
arranged stages of the integrally-geared turbo-compressor. Moreover, in some embodiments,
[0027] In some embodiments the multi-stage, integrally-geared turbo-compressor 109 can be
driven by a prime mover, which can include an internal combustion motor, such as a
gas turbine, for instance an aeroderivative gas turbine. In advantageous embodiments,
the integrally-geared turbo-compressor 109 is driven by an electric motor 111.
[0028] In Fig.2 an exemplary embodiment is shown, wherein the integrally-geared turbo-compressor
109 is comprised of four stages, labeled 109A, 109B, 109C, 109D, respectively, arranged
in sequence, stage 109D being the lowest-pressure stage, and stage 109A being the
highest-pressure stage.
[0029] A flow of compressed first refrigerant is delivered by the integrally-geared turbo-compressor
109 to a condenser 115. The flow of first refrigerant delivered through the condenser
115 is cooled, e.g. against water or air, and condensed.
[0030] In some embodiments, the condensed first refrigerant is circulated in the pre-cooling
loop 103 to pre-cool the natural gas and to cool and optionally partially liquefy
the second refrigerant circulating in the cooling loop 105.
[0031] In some embodiments, the process is divided into four pressure levels. The number
of pressure levels can correspond to the number of stages of the integrally-geared
turbo-compressor 109. In preferred embodiments, the flow of first refrigerant delivered
through the condenser 115 is divided into a number of partial flows, which are then
sequentially expanded at a number of progressively reducing pressure levels. Each
partial refrigerant flow circulates in a sub-cycle and is returned as a side flow
to the integrally-geared turbo-compressor at the inlet of a corresponding one of the
plurality of compressor stages.
[0032] A delivery line 117 delivers a first part of the condensed first refrigerant flow
to a plurality of serially arranged first expansion elements 119A-119D. A second delivery
line 118 branched-off the delivery line 117 delivers a second part of the condensed
first refrigerant flow to a plurality of serially arranged second expansion elements
121A-121D.
[0033] The first part of the condensed first refrigerant from condenser 115 is sequentially
expanded in the four expansion elements 119A-119B at four different, gradually decreasing
pressure levels. Downstream each expansion element 119A-119C a portion of the flow
of partly expanded first refrigerant is diverted to a respective one of first, pre-cooling
heat exchangers 123A-123C. The remaining part of the partly expanded first refrigerant
is caused to flow through the next expansion element 119A-119C and so on. The residual
first refrigerant flowing through the most downstream one (119D) of the first expansion
elements 119A-119D is delivered to a most downstream pre-cooling heat exchanger 123D.
[0034] In each one of said first heat exchangers 123A-123D the first refrigerant exchanges
heat against the natural gas flowing in pipe 107, thus pre-cooling and optionally
partly liquefying the natural gas.
[0035] A part of the first refrigerant expanded in each second expansion elements 121A,
121B, 121C is diverted towards a corresponding one of a plurality of second heat exchangers
125A-125D. The part of refrigerant flow delivered by each one of said second expansion
elements 121A-121C and which is not caused to flow through the respective heat exchanger
125A-125C is delivered through the subsequent expansion element. The most downstream
one (125D) of said second heat exchangers receives the entire residual fraction of
first refrigerant expanding in the most downstream (121D) of said second expansion
elements 121A-121D. In each one of said second heat exchangers 125A-125D the first
refrigerant exchanges heat against the second refrigerant, circulating in the cooling
or liquefying loop 105, so that at the delivery side of the heat exchanger 125D the
second refrigerant is cooled and at least partly liquefied.
[0036] Heated first refrigerant exiting the first, pre-cooling heat exchangers 123A-123D
is collected with the heated first refrigerant exiting the second heat exchangers
125A-125D and is fed again to the integrally-geared turbo-compressor 109.
[0037] In some embodiments the heated first refrigerant exiting each second heat exchanger
125A-125D is at around the same pressure as the heated first refrigerant exiting the
corresponding first heat exchanger 123A-123D. The refrigerant collected at corresponding
pressure levels is delivered at the inlet of corresponding stages of the integrally-geared
turbo-compressor 109. A plurality of refrigerant side streams are thus returned at
gradually decreasing pressures at the inlet of the serially arranged stages of the
integrally-geared turbo-compressor 109.
[0038] In Fig.2 reference numbers 130A-130D indicate return lines, through which the side
streams of expanded and exhausted refrigerant fluid delivered from the heat exchangers
123A-123D and 125A-125D are returned to corresponding stages 109A-109D of the integrally-geared
turbo-compressor.
[0039] In some embodiments, the cooling or liquefying loop 105 comprises a compressor train.
In some embodiments the compressor train can be comprised of a first compressor 131
and a second compressor 133 arranged in series. In other embodiments a single compressor
can be provided. Each compressor can be a multi-stage compressor, for example a multi-stage
centrifugal compressor.
[0040] In some embodiments the compressor(s) of the cooling loop 105 are driven by a prime
mover, which can include an internal combustion engine. The prime mover can be a gas
turbine 135, for instance an aeroderivative gas turbine.
[0041] An inter-stage cooler (inter-cooler) 137 can be arranged between the first compressor
131 and the second compressor 133, to reduce the temperature and the volume of the
second refrigerant delivered by the first compressor 131 before entering the second
compressor 133. The compressed second refrigerant delivered by the second compressor
133 is condensed in a condenser 139. The condenser 139 can be an air condenser or
a water condenser, where the second refrigerant is condensed by exchanging heat against
air or water. The condensed second refrigerant is subsequently delivered by a delivery
line 141 through the sequentially arranged second heat exchangers 125A-125D, where
the second refrigerant is cooled and possibly liquefied by exchanging heat against
the first refrigerant circulating in the pre-cooling loop 103, as described above.
[0042] The cooled, and optionally partly liquefied second refrigerant delivered from the
heat exchangers 125A-125D flows through a pipe 143 towards a main cryogenic heat exchanger
145, where the second refrigerant removes further heat from the pre-cooled and optionally
partly liquefied natural gas, completing the liquefaction process. The entirely liquefied
natural gas exits the system at 149, and the heated second refrigerant is returned
through a line 151 to the compressor(s) or compressor train 131, 133.
[0043] In Fig.2 the integrally-geared turbo-compressor 109 is represented only schematically.
The main components of an exemplary integrally-geared turbo-compressor 109 are illustrated
in more detail in Fig.2A. Fig.4 illustrates in more detail an axial section of two
compressor stages supported on a common rotary shaft of the integrally-geared turbo-compressor
109. More specifically, Fig.4 illustrates by way of example the first and second stages
109D, 109C.
[0044] Preferably each compressor stage 109A-109D is provided with movable inlet guide vanes,
schematically shown at 110A-110D for the four stages 109A-109D. In other embodiments,
movable inlet guide vanes are provided at the inlet of only some or none of the compressor
stages. As can be appreciated from Fig.4, the inlet guide vanes can be arranged at
the axial inlet of the compressor stage. Each set of movable inlet guide vanes can
be controlled independently of the other sets for autonomously regulating flows entering
in the compressor stages. An intercooler can be provided between two sequentially
arranged compressor stages 109A-109D. As shown in Fig.2A, a first intercooler 153
can be arranged between the delivery side of the first compressor stage 109D and the
suction side of the second compressor stage 109C. A second intercooler 155 can be
arranged between the delivery side of the second compressor stage 109C and the suction
side of the third compressor stage 109B. A third intercooler 157 can be arranged between
the delivery side of the third compressor stage 109B and the suction side of the fourth
compressor stage 109A.
[0045] Each compressor stage 109A-109D comprises at least one impeller supported on a rotary
shaft. Fig.4 shows two impellers 112D, 112C of the two most upstream compressor stages
109D, 109C, respectively. Each impeller can be a radial impeller, with an axial inlet
and a radial outlet. The fluid processed through the impeller is collected in a respective
volute, such as volutes 114D, 114C of compressor stages 109D, 109C.
[0046] The impellers can be paired, each pair of impellers being supported by a common rotary
shaft. In the embodiment of Fig.2A two rotary shafts 159, 161 are provided. The impellers
of the first and second compressor stages 109D, 109C are mounted for rotation on the
first rotary shaft 159 and the impellers of the third and fourth compressor stages
109B, 109A are mounted for rotation on the second rotary shaft 161. A different number
of rotary shafts and respective compressor stages and impellers can be provided. In
some embodiments an odd number of stages can be provided, in which case one of the
rotary shafts can support a single impeller instead of paired impellers.
[0047] Each rotary shaft 159, 161 comprise a pinion 159A, 161A keyed thereon. The pinions
159A, 161A mesh with a central toothed wheel or crown 163 which is driven in rotation
by the electric motor 111 through a driving shaft 165. The two rotary shafts 159A,
161A and therefore the respective impellers mounted thereon can rotate at different
rotary speeds.
[0048] The structure of the integrally-geared turbo-compressor 109 is particularly suitable
for processing the different side streams of the first refrigerant circulating in
the pre-cooling loop 103. The position of each set of movable inlet guide vanes 110A-110D
at the inlet of the compressor stages can be adapted to the flow conditions of each
side stream, i.e. each refrigerant stream delivered to the respective suction side
of the compressor stages, so that the operative conditions of the compressor stages
can be adapted to the temperature conditions and flow rates through the different
heat exchangers 123A-123D, 125A-125D. The compressor efficiency and operability can
thus be maximized. One or more intercoolers, such as intercoolers 153, 155, 157 easily
integrated in the structure of the integrally-geared turbo-compressor 109 further
increase the efficiency of the compressor and thus of the whole LNG system.
[0049] A further embodiment of the subject matter disclosed herein is illustrated in Fig.3
and will be described here below. The LNG system 200 of Fig.3 comprises three closed
loops or cycles, labeled 201, 203 and 205 respectively. Three different refrigerants
are processed in the three loops. A first refrigerant processed in loop 201 can be
propane. The first loop 201 will be named the pre-cooling loop here below. A second
refrigerant processed in loop 203 can be ethylene and a third refrigerant circulating
in loop 205 can be methane. A natural gas line 207 flows through three sequentially
arranged heat exchangers 209, 211 and 213 of the three loops 201, 203, 205. The natural
gas enters the first heat exchanger 209 in the gaseous state and exits the last heat
exchanger 213 in the liquid state.
[0050] The system of Fig.3 is represented in a somewhat simplified manner. The first, pre-cooling
loop or cycle 201 comprises an integrally-geared turbo-compressor 229 including a
plurality of compressor stages. In some embodiments, three compressor stages 229A-229C
can be provided, as shown by way of example in the schematic representation of Fig.3.
In other embodiments a different number of compressor stages can be provided. In general,
the number of compressor stages can depend upon the number of side streams provided
in the pre-cooling loop 201, in a way similar to what has been disclosed in connection
with Figs. 2 and 2A.
[0051] Inlet guide vanes 228C, 228B, 228A can be provided at the inlet of some, and preferably
of each compressor stage. Intercoolers can be arranged between pairs of sequentially
arranged compressor stages, for example a first intercooler 230 can be arranged between
the delivery side of the first compressor stage 229C and the suction side of the second
compressor stage 229B. A further intercooler 231 can be arranged between the delivery
side of compressor stage 229B and the suction side of compressor stage 229A.
[0052] The delivery side of the last compressor stage 229A, i.e. the most downstream one
in the pressure-increasing flow direction, is connected to a condenser 233. The first
refrigerant circulating through the integrally-geared turbo-compressor 229 is condensed
in the condenser 233 and delivered through a line 235 to the first heat exchanger
209. The compressed and condensed refrigerant flow can be expanded through one or
more expansion elements, one of which is shown at 237. In a way similar to Fig.2,
the main refrigerant stream flowing in delivery line 235 can be divided into side
streams at gradually decreasing pressures and temperatures. The heat exchanger 209
can be comprised of a plurality of heat exchanger sections arranged in series and
through which a fraction of the refrigerant is caused to flow at gradually decreasing
pressures, in a way quite similar to what has been described in connection with Figs.
2 and 2A. A plurality of side streams are thus formed, each being returned at a respective
one of the compressor stages 229A, 229B, 229C.
[0053] Each compressor stage processes, therefore, a different refrigerant flow rate at
variable and gradually increasing pressures from the most upstream compressor stage
229C through the most downstream compressor stage 229A.
[0054] The integrally-geared turbo-compressor 229 can be driven by a prime mover. In some
embodiments the prime mover can be an electric motor, not shown, similarly to motor
111 described with reference to Fig.2. In other embodiments the prime mover can comprise
a gas turbine, for example an aeroderivative gas turbine.
[0055] The second loop 203 comprises compressor arrangement 241. The compressor arrangement
241 can comprise a single compressor or a plurality of sequentially arranged compressors.
One or more of the compressors of the compressor arrangement 241 can be a multi-stage
compressor, e.g. a multi-stage centrifugal compressor. The compressor arrangement
241 can be driven by a second prime mover 243. In some embodiments the second prime
mover 243 can comprise a gas turbine, for instance an aeroderivative gas turbine.
In other embodiments the prime mover can comprise an electric motor. Combinations
of different engines or motors can be envisaged as well.
[0056] The second loop 203 comprises a condenser 245 through which the compressed second
refrigerant delivered by the compressor arrangement 241 is condensed. A delivery line
247 delivers the compressed and condensed second refrigerant through the first heat
exchanger 209 and through the second exchanger 211. In the first heat exchanger 209
the condensed second refrigerant is cooled by exchanging heat against the first refrigerant
circulating in the first loop 201. In the second heat exchanger 211 the second refrigerant
is expanded in one or more sequentially arranged expansion elements, one of which
is shown at 249. In a manner known per se, said streams of second refrigerant at different
and gradually reducing pressures can thus be generated, said side streams being returned
through return lines 251, 253, 255 at decreasing pressures to the second compressor
arrangement 241. In some embodiments, each side stream is injected at the inlet of
a respective one of a plurality of serially arranged compressors forming the compressor
arrangement 241. Movable inlet guide vanes can be provided at the inlet of each such
compressors. In the second heat exchanger 211 the second refrigerant cools and/or
partly liquefies the natural gas flowing through gas line 207.
[0057] The third loop 205 comprises a further compressor arrangement 261. The compressor
arrangement 261 can be comprised of a single compressor or a plurality of sequentially
arranged compressors. The compressor(s) of the compressor arrangement 261 can be centrifugal
compressors, e.g. multi-stage centrifugal compressor. A further prime mover 263 is
provided for driving the compressor arrangement 261 into rotation. In some embodiments,
the prime mover 263 can comprise a gas turbine, for instance an aeroderivative gas
turbine. In other embodiments the prime mover 263 can comprise an electric motor.
Combinations of different motors and engines can be provided as well.
[0058] The compressed third refrigerant delivered by the compressor arrangement 261 is condensed
in a condenser 265 and delivered in the liquid state through a delivery line 267 through
the first, the second and the third heat exchangers 209, 211, 213. In the first and
second heat exchangers 209, 211 the third refrigerant flows in the liquid state and
is cooled by exchanging heat against the first refrigerant and the second refrigerant,
respectively. In the last section of the loop, the third refrigerant is expanded in
one or more sequentially arranged expansion elements 269. The vaporized third refrigerant
exchanges heat against the natural gas in the third heat exchanger 213, until the
natural gas is liquefied when delivered from the third heat exchanger 213. In some
embodiments, the third refrigerant can be subdivided into side streams at gradually
reducing pressures and each side stream is returned to the compressor arrangement
261 through respective return line 271, 273, 275. Also in this case, side streams
can be injected at the inlet of sequentially arranged compressors forming part of
the compressor arrangement, each compressor being possibly provided with movable inlet
guide vanes.
[0059] The LNG process described so far and illustrated in Fig.3 is known as a cascade process.
As noted above, differently from known cascade processes and systems, in the present
embodiment at least the first, pre-cooling loop 201 comprises a multi-stage integrally-geared
turbo-compressor.
[0060] Processing the first refrigerant in the pre-cooling loop through the integrally-geared
turbo-compressor has several advantages as already described in connection with the
embodiment of Fig.2, 2A. The integrally-geared turbo-compressor 229 of the embodiment
of Fig.3 can be conceptually similar to the integrally-geared turbo-compressor described
with respect to the embodiment of Figs.2, 2A and shown in more detail in Fig.4. Merely
by way of example the number of compressor stages of the integrally-geared turbo-compressor
229 shown in Fig.3 is different from the number of stages of the embodiment of Figs.2,
2A, this indicating that the number of stages of the integrally-geared turbo-compressor
can vary based on design considerations, for example depending upon the number of
side streams into which the main stream of the first refrigerant is divided downstream
of the condenser.
[0061] In some embodiments the integrally-geared turbo-compressor can be driven at a power
ranging from about 12 MW to about 40 MW. In some embodiments, the integrally-geared
turbo-compressor can have a rated power ranging between about 14 MW and 40 MW and
more specifically between about 25 MW and 30MW.
[0062] In some embodiments a first refrigerant flow rate ranging from about 10,000 m
3/h to about 70,000m
3/h can be processed by the integrally-geared turbo-compressor.
[0063] As disclosed above, the first refrigerant in the LNG system is usually expanded at
gradually reducing pressure values and divided into side streams, each stream being
returned to a respective one of several compressor stages of the integrally-geared
turbo-compressor. In some embodiments, the delivery pressure of the most downstream
compressor stage, i.e. the compressor stage at the highest pressure, ranges from about
45 bar absolute to about 65 bar absolute and in some embodiments said delivery pressure
can range between about 52 bar absolute and about 56 bar absolute. In some embodiments,
the respective suction pressure, i.e. the pressure at the inlet of the most upstream
compressor stage, can range between about 2.5 and about 15 bar absolute, and more
specifically e.g. between about 3 and about 10 bar absolute, for instance at around
3-3.5 bar absolute.
[0064] In other embodiments, the delivery pressure (discharge pressure) of the last stage
in the integrally-geared turbo-compressor can range between about 10 bar absolute
and 30 bar absolute, and in some specific embodiments between 15 and 25 bar absolute.
The respective suction pressure at the most upstream compressor stage can range between
about 1 and about 2.5 bar absolute, more specifically between about 1.5 and about
2 bar absolute, for instance at around 1.6-1.9 bar absolute.
[0065] The use of an integrally-geared turbo-compressor in the precooling cycle results
in enhanced efficiency of the compressor and thus reduced power consumption, and finally
in considerable cost savings when compared with a current art centrifugal multi-stage
compressor.
[0066] To fully appreciate the important advantages in terms of increased efficiency and
reduced energy consumption and the cost savings achieved thereby, the following comparative
example shall be considered.
[0067] In a system according to Fig.1, a standard configuration using a beam centrifugal
compressor, for example a 3MCL804 manufactured by GE Oil & Gas, Florence, Italy with
an efficiency of "100 %", driven by a PGT25+G4 aeroderivative gas turbine, available
from GE Oil & Gas, Florence, Italy, directly coupled to the compressor with the following
operating condition:
- inlet pressure 1.13 bar absolute
- inlet volumetric flow 56,000 m3/h
- rotary speed 6,100rpm
the compressor would absorb 21,108kW at design condition. An arrangement according
to Figs 2, 2A, comprising an integrally-geared turbo-compressor, for example an SRL804
manufactured by GE Oil & Gas, Florence, Italy driven by an equivalent gas turbine
and having an efficiency of 102.4% would absorb, under the same operative conditions,
20,493 kW, which involves a reduction of 3% of the power consumption.
[0068] The total cost saving with the integrally geared configuration is 5%.
[0069] The use of an integrally geared compressor is even more attractive considering a
configuration wherein an electric motor is used, instead of a gas turbine, due to
the removal of the gearbox. In a standard solution according to the prior art using
an electric motor as a driver, a fixed speed electric motor is drivingly connected
to the compressor through a gearbox. Conversely, if an integrally geared compressor
is used, the compressor can be designed at the optimum speed without the additional
gearbox. The compressor will reach an efficiency up to 104.1%. Under the above mentioned
operating conditions this would result in an absorbed power of 20,102kW, which results
in a reduction of power consumption of 1006 kW. In term of cost a solution with an
integrally geared compressor and an electric motor is 14% less expensive than a standard
solution with electric motor, gearbox and compressor, mainly thanks to the removal
of the gearbox.
[0070] While the disclosed embodiments of the subject matter described herein have been
shown in the drawings and fully described above with particularity and detail in connection
with several exemplary embodiments, it will be apparent to those of ordinary skill
in the art that many modifications, changes, and omissions are possible without materially
departing from the novel teachings, the principles and concepts set forth herein,
and advantages of the subject matter recited in the appended claims. Hence, the proper
scope of the disclosed innovations should be determined only by the broadest interpretation
of the appended claims so as to encompass all such modifications, changes, and omissions.
In addition, the order or sequence of any process or method steps may be varied or
re-sequenced according to alternative embodiments.
1. A natural gas liquefaction system (101) comprising:
at least a pre-cooling loop (103), through which a first refrigerant is adapted to
circulate, the pre-cooling loop comprising:
at least one compressor (109) for pressurizing the first refrigerant;
at least one prime mover (111) for driving said compressor (109);
at least one condenser (115) for removing heat from the first refrigerant;
at least a first expansion element (119A-119D) for expanding the first refrigerant;
at least a first heat exchanger (123A-123D) for transferring heat from natural gas
to the first refrigerant;
and at least a cooling loop (105), downstream of said pre-cooling loop (103), where
through a second refrigerant circulates, the natural gas being adapted to be sequentially
cooled in the pre-cooling loop (103) and in the cooling loop (105);
wherein said first refrigerant comprises a gas with a molecular weight greater than
35;
wherein the pre-cooling loop (103) further comprises:
a plurality of sequentially arranged first expansion elements (119A-119D) configured
for expanding the first refrigerant at a plurality of decreasing pressure levels;
a plurality of first heat exchangers (123A-123D) arranged and configured for receiving
respective portions of said first refrigerant expanded through said plurality of sequentially
arranged first expansion elements (119A-119D) and for transferring heat from the natural
gas to the first refrigerant; and
a plurality of return paths (130A-130D) returning side streams of the first refrigerant
from each said first heat exchangers (123A-123D) to a respective compressor stage
(109A-109D) of the compressor (109); and
characterized in that said compressor (109) is an integrally geared turbo-compressor comprising a plurality
of compressor stages (109A-109D) each one being provided with an independent set of
movable inlet guide vanes (11 OA-110D) for autonomously regulating flows entering
in the compressor stages;
and in that said compressor (109) further comprises at least one intercooler (153, 155,157) between
at least two serially arranged compressor stages arranged between the delivery side
of one of the plurality of compressor stages (109|A-109D) and the suction side of
another of the plurality of compressor stages (109A-109D).
2. The system of claim 1, wherein the pre-cooling loop (103) is configured to divide
the first refrigerant into two or more side streams returned at respective compressor
stages (109A-109D) of said integrally-geared turbo-compressor (109).
3. The system of claim 1 or 2, wherein said prime mover (111) comprises an electric motor.
4. The system of claim 1 or 2, wherein said prime mover (111) comprises a gas turbine.
5. The system of any one of the preceding claims, wherein the pre-cooling loop (103)
further comprises: at least a first auxiliary expansion element and at least a first
auxiliary heat exchanger receiving a portion of said first refrigerant expanded through
said first auxiliary expansion element and configured for transferring heat from the
second refrigerant circulating in the cooling loop (105) to the first refrigerant
circulating in the pre-cooling loop (103).
6. The system of any one of the preceding claims, wherein the pre-cooling loop (103)
further comprises: a plurality of sequentially arranged second expansion elements
(121A-121D) configured for expanding the first refrigerant at a plurality of decreasing
pressure levels; a plurality of second heat exchangers (125A-125D) arranged and configured
for receiving respective portions of said first refrigerant expanded through said
first auxiliary expansion elements (119A-119D) and for transferring heat from the
second refrigerant to the first refrigerant; a plurality of return paths returning
the portions of first refrigerant from each said second heat exchangers (125A-125D)
to a respective compressor stage of the integrally-geared turbo-compressor (109).
7. The system of any preceding claim, wherein said second refrigerant is a mixed refrigerant,
or ethylene, or methane.
8. The system of any one of the preceding claims, wherein said integrally-geared turbo-compressor
(109) comprises: a central gear (163) driven into rotation by said prime mover (111);
a plurality of driven shafts (159, 161), each driven shaft comprising a pinion (159A,
161A) meshing with the central gear (163) and driven into rotation by said central
gear (163); at least one respective compressor impeller (112C, 112D) mounted on each
shaft (159, 161).
9. The system of claim 8, wherein two respective compressor impellers (112C, 112D) are
mounted on at least one of said shafts (159).
10. The system of any one of the preceding claims, wherein the integrally-geared turbo-compressor
(109) is arranged to compress the first refrigerant so that the pressurized first
refrigerant is delivered from the last stage of the integrally-geared turbo-compressor
at a pressure ranging from about 45 to about 65 bar absolute, and preferably between
about 50 and about 60 bar absolute; and wherein the pressure of the first refrigerant
at the inlet of the first stage of the integrally-geared turbo-compressor ranges from
about 2.5 to about 10, and preferably from about 3 to about 5 bar absolute.
11. The system of any one of claims 1 to 9, wherein the integrally-geared turbo-compressor
(109) is arranged to compress the first refrigerant so that the pressurized first
refrigerant is delivered from the last stage of the integrally-geared turbo-compressor
at a pressure ranging from about 10 to about 30 bar absolute, and preferably between
about 15 and about 25 bar absolute; and wherein the pressure of the first refrigerant
at the inlet of the first stage of the integrally-geared turbo-compressor ranges from
about 1 to about 2.5, and preferably from about 1.5 to about 2 bar absolute.
12. A method of liquefying natural gas, the method comprising:
providing a pre-cooling loop (103) comprising: a turbo-compressor (109), at least
one condenser (115), at least one expansion element (119A-119D), and at least one
heat exchanger (123A-123D),
driving said turbo-compressor (109) with a prime mover (111);
circulating a first refrigerant through the turbo-compressor (109);
condensing the first refrigerant delivered by the turbo-compressor (109) in the condenser
(115);
dividing the first refrigerant in a plurality of partial flows;
expanding the condensed first refrigerant in the expansion element (119A-119D);
circulating the expanded refrigerant through the heat exchanger (123A-123D) to remove
heat from the natural gas, to pre-cool the natural gas;
providing at least one cooling loop (105);
circulating a second refrigerant in said at least one cooling loop (105);
removing heat from the pre-cooled natural gas by heat exchange against the second
refrigerant;
providing a plurality of sequentially arranged first expansion elements (119A-119D)
in the pre-cooling loop (103);
expanding the first refrigerant through the first expansion elements (119A-119D) at
a plurality of decreasing pressure levels;
receiving respective portions of the first refrigerant expanded through the plurality
of sequentially arranged first expansion elements (119A,119D) in a plurality of first
heat exchangers (123A|-123D) and transferring heat from the natural gas to the first
refrigerant; and
returning side streams of the first refrigerant from each of the first heat exchangers
(123A|-123D) through a plurality of return paths (130A|-130D) to a respective compressor
stage (109A-109D) of the turbo-compressor (109);
wherein said first refrigerant comprises a gas with a molecular weight greater than
35, characterized in that the turbo-compressor is an integrally-geared turbo-compressor (109) having a plurality
of compressor stages (109A-109D) each one being provided with independently movable
inlet guide vanes (110A-110D); controlling the independently movable inlet guide vanes
(11 0A-110D) to regulate the partial flows at the suction side of the compressor stages
(109A-109D); the integrally-geared turbo-compressor (109) comprising at least one
intercooler (153,155,157) between at least two serially arranged compressor stages;
wherein the at least one intercooler (152,155,157) is arranged between the delivery
side of one of the plurality of compressor states (109A-109D) and the suction side
of another of the plurality of compressor stages (109-109D).
1. Erdgasverflüssigungssystem (101), umfassend:
mindestens einen Vorkühlkreislauf (103), durch den zu zirkulieren ein erstes Kältemittel
ausgelegt ist, wobei der Vorkühlkreislauf umfasst:
mindestens einen Verdichter (109), um das erste Kältemittel mit Druck zu beaufschlagen;
mindestens eine Antriebseinrichtung (111) zum Antreiben des Verdichters (109);
mindestens einen Kondensator (115) zum Abführen von Wärme aus dem ersten Kältemittel;
mindestens ein erstes Expansionselement (119A-119D) zum Expandieren des ersten Kältemittels;
mindestens einen ersten Wärmetauscher (123A-123D) zum Übertragen von Wärme aus Erdgas
auf das erste Kältemittel;
und mindestens einen dem Vorkühlkreislauf (103) nachgelagerten Kühlkreislauf (105),
durch den ein zweites Kältemittel zirkuliert, wobei das Erdgas ausgelegt ist, um nacheinander
im Vorkühlkreislauf (103) und im Kühlkreislauf (105) gekühlt zu werden;
wobei das erste Kältemittel ein Gas mit einer Molekülmasse von mehr als 35 umfasst;
wobei der Vorkühlkreislauf (103) ferner umfasst:
eine Vielzahl von in Reihe angeordneten ersten Expansionselementen (119A-119D), die
eingerichtet sind, um das erste Kältemittel bei einer Vielzahl von abnehmenden Druckniveaus
zu expandieren;
eine Vielzahl von ersten Wärmetauschern (123A-123D), die angeordnet und eingerichtet
sind, um jeweilige Teile des durch die Vielzahl von in Reihe angeordneten ersten Expansionselementen
(119A-119D) expandierten ersten Kältemittels aufzunehmen und um Wärme aus dem Erdgas
auf das erste Kältemittel zu übertragen; und
eine Vielzahl von Rückleitpfaden (130A-130D), die Nebenströme des ersten Kältemittels
aus jedem der ersten Wärmetauscher (123A-123D) zu einer jeweiligen Verdichterstufe
(109A-109D) des Verdichters (109) zurückleiten; und
dadurch gekennzeichnet, dass der Verdichter (109) ein Getriebeturboverdichter ist, der eine Vielzahl von Verdichterstufen
(109A-109D) umfasst, von denen jede mit einem unabhängigen Satz beweglicher Einlassleitschaufeln
(110A-110D) zum autonomen Regulieren von Strömungen bereitgestellt ist, die in die
Verdichterstufen eintreten;
und dass der Verdichter (109) ferner mindestens einen Zwischenkühler (153, 155, 157)
zwischen mindestens zwei in Reihe angeordneten Verdichterstufen umfasst, die zwischen
der Druckseite einer der Vielzahl von Verdichterstufen (109A-109D) und der Saugseite
einer anderen der Vielzahl von Verdichterstufen (109A-109D) angeordnet sind.
2. System nach Anspruch 1, wobei der Vorkühlkreislauf (103) eingerichtet ist, um das
erste Kältemittel in zwei oder mehr Nebenströme aufzuteilen, die bei den jeweiligen
Verdichterstufen (109A-109D) des Getriebeturboverdichters (109) zurückgeleitet werden.
3. System nach Anspruch 1 oder 2, wobei die Antriebseinrichtung (111) einen Elektromotor
umfasst.
4. System nach Anspruch 1 oder 2, wobei die Antriebseinrichtung (111) eine Gasturbine
umfasst.
5. System nach einem der vorstehenden Ansprüche, wobei der Vorkühlkreislauf (103) ferner
umfasst: mindestens ein erstes zusätzliches Expansionselement und mindestens einen
ersten zusätzlichen Wärmetauscher zum Aufnehmen eines Teils des ersten Kältemittels,
das durch das erste zusätzliche Expansionselement expandiert wurde, und zum Übertragen
von Wärme aus dem zweiten Kältemittel, das im Kühlkreislauf (105) zirkuliert, auf
das erste Kältemittel, das im Vorkühlkreislauf (103) zirkuliert.
6. System nach einem der vorstehenden Ansprüche, wobei der Vorkühlkreislauf (103) ferner
umfasst: eine Vielzahl von in Reihe angeordneten zweiten Expansionselementen (121A-121D),
die eingerichtet sind, um das erste Kältemittel bei einer Vielzahl von abnehmenden
Druckniveaus zu expandieren; eine Vielzahl von zweiten Wärmetauschern (125A-125D),
die angeordnet und eingerichtet sind, um jeweilige Teile des ersten durch die ersten
zusätzlichen Expansionselemente (119A-119D) expandierten Kältemittels aufzunehmen
und um Wärme aus dem zweiten Kältemittel auf das erste Kältemittel zu übertragen;
eine Vielzahl von Rückleitpfaden, die die Teile des ersten Kältemittels aus jedem
der zweiten Wärmetauscher (125A-125D) zu einer jeweiligen Verdichterstufe des Getriebeturboverdichters
(109) zurückleiten.
7. System nach einem der vorstehenden Ansprüche, wobei das zweite Kältemittel ein gemischtes
Kältemittel oder Ethylen oder Methan ist.
8. System nach einem der vorstehenden Ansprüche, wobei der Getriebeturboverdichter (109)
umfasst: ein zentrales Zahnrad (163), das durch die Antriebseinrichtung (111) in Drehung
versetzt wird; eine Vielzahl von Abtriebswellen (159, 161), wobei jede Abtriebswelle
ein Ritzel (159A, 161A) umfasst, das mit dem zentralen Zahnrad (163) in Eingriff steht
und durch das zentrale Zahnrad (163) in Drehung versetzt wird; mindestens ein jeweiliges
Verdichterlaufrad (112C, 112D), das auf jeder Welle (159, 161) montiert ist.
9. System nach Anspruch 8, wobei zwei jeweilige Verdichterlaufräder (112C, 112D) auf
mindestens einer der Wellen (159) montiert sind.
10. System nach einem der vorstehenden Ansprüche, wobei der Getriebeturboverdichter (109)
angeordnet ist, um das erste Kältemittel zu verdichten, sodass das unter Druck stehende
erste Kältemittel aus der letzten Stufe des Getriebeturboverdichters bei einem Druck
im Bereich von ca. 45 bis ca. 65 bar absolut und vorzugsweise zwischen ca. 50 und
ca. 60 bar absolut abgegeben wird; und wobei der Druck des ersten Kältemittels am
Einlass der ersten Stufe des Getriebeturboverdichters im Bereich von ca. 2,5 bis ca.
10 bar absolut und vorzugsweise von ca. 3 bis ca. 5 bar absolut liegt.
11. System nach einem der Ansprüche 1 bis 9, wobei der Getriebeturboverdichter (109) angeordnet
ist, um das erste Kältemittel zu verdichten, sodass das unter Druck stehende erste
Kältemittel aus der letzten Stufe des Getriebeturboverdichters bei einem Druck im
Bereich von ca. 10 bis ca. 30 bar absolut und vorzugsweise zwischen ca. 15 und ca.
25 bar absolut abgegeben wird; und wobei der Druck des ersten Kältemittels am Einlass
der ersten Stufe des Getriebeturboverdichters im Bereich von ca. 1 bis ca. 2,5 bar
absolut und vorzugsweise von ca. 1,5 bis ca. 2 bar absolut liegt.
12. Verfahren zum Verflüssigen von Erdgas, wobei das Verfahren umfasst:
Bereitstellen eines Vorkühlkreislaufs (103), umfassend: einen Turboverdichter (109),
mindestens einen Kondensator (115), mindestens ein Expansionselement (119A-119D) und
mindestens einen Wärmetauscher (123A-123D),
Antreiben des Turboverdichters (109) mit einer Antriebseinrichtung (111);
Zirkulieren eines ersten Kältemittels durch den Turboverdichter (109);
Kondensieren des durch den Turboverdichter (109) abgegebenen ersten Kältemittels im
Kondensator (115);
Aufteilen des ersten Kältemittels in eine Vielzahl von Teilströmen;
Expandieren des kondensierten ersten Kältemittels im Expansionselement (119A-119D);
Zirkulieren des expandierten Kältemittels durch den Wärmetauscher (123A-123D) zum
Abführen von Wärme aus dem Erdgas, um das Erdgas vorzukühlen;
Bereitstellen mindestens eines Kühlkreislaufs (105);
Zirkulieren eines zweiten Kältemittels in dem mindestens einen Kühlkreislauf (105);
Abführen von Wärme aus dem vorgekühlten Erdgas durch Wärmeaustausch mit dem zweiten
Kältemittel;
Bereitstellen einer Vielzahl von in Reihe angeordneten ersten Expansionselementen
(119A-119D) im Vorkühlkreislauf (103);
Expandieren des ersten Kältemittels durch die ersten Expansionselemente (119A-119D)
bei einer Vielzahl von abnehmenden Druckniveaus;
Aufnehmen jeweiligen Teile des durch die Vielzahl von in Reihe angeordneten ersten
Expansionselementen (119A-119D) expandierten ersten Kältemittels in einer Vielzahl
von ersten Wärmetauschern (123A-123D) und Übertragen von Wärme aus dem Erdgas auf
das erste Kältemittel; und
Zurückleiten von Nebenströmen des ersten Kältemittels von jedem der ersten Wärmetauscher
(123A-123D) durch eine Vielzahl von Rückleitpfaden (130A-130D) zu einer jeweiligen
Verdichterstufe (109A-109D) des Turboverdichters (109);
wobei das erste Kältemittel ein Gas mit einer Molekülmasse größer als 35 umfasst,
dadurch gekennzeichnet, dass der Turboverdichter ein Getriebeturboverdichter (109) ist, der eine Vielzahl von
Verdichterstufen (109A-109D) aufweist, von denen jede mit unabhängig beweglichen Einlassleitschaufeln
(110A-110D) bereitgestellt ist; Steuern der unabhängig beweglichen Einlassleitschaufeln
(110A-110D), um die Teilströme auf der Saugseite der Verdichterstufen (109A-109D)
zu regulieren; wobei der Getriebeturboverdichter (109) mindestens einen Zwischenkühler
(153, 155, 157) zwischen mindestens zwei in Reihe angeordneten Verdichterstufen umfasst;
wobei der mindestens eine Zwischenkühler (152, 155, 157) zwischen der Druckseite einer
der Vielzahl von Verdichterstufen (109A-109D) und der Saugseite einer anderen der
Vielzahl von Verdichterstufen (109A-109D) angeordnet ist.
1. Système de liquéfaction de gaz naturel (101) comprenant :
au moins une boucle de pré-refroidissement (103), dans laquelle un premier réfrigérant
peut circuler, la boucle de pré-refroidissement comprenant :
au moins un compresseur (109) pour mettre sous pression le premier réfrigérant ;
au moins un moteur principal (111) pour entraîner ledit compresseur (109) ;
au moins un condenseur (115) pour retirer la chaleur du premier réfrigérant ;
au moins un premier élément d'expansion (119A-119D) pour dilater le premier réfrigérant
;
au moins un premier échangeur de chaleur (123A-123D) pour transférer de la chaleur
du gaz naturel vers le premier réfrigérant ;
et au moins une boucle de refroidissement (105), en aval de ladite boucle de pré-refroidissement
(103), où circule un deuxième réfrigérant, le gaz naturel étant adapté pour être refroidi
séquentiellement dans la boucle de pré-refroidissement (103) et dans la boucle de
refroidissement (105) ;
dans lequel ledit premier réfrigérant comprend un gaz ayant un poids moléculaire supérieur
à 35 ;
dans lequel la boucle de pré-refroidissement (103) comprend en outre :
une pluralité de premiers éléments d'expansion disposés séquentiellement (119A-119D)
configurés pour dilater le premier réfrigérant à une pluralité de niveaux de pression
décroissants ;
une pluralité de premiers échangeurs de chaleur (123A-123D) agencés et configurés
pour recevoir des parties respectives dudit premier réfrigérant dilaté par ladite
pluralité de premiers éléments d'expansion disposés séquentiellement (119A-119D) et
pour transférer de la chaleur du gaz naturel au premier réfrigérant ; et
une pluralité de chemins de retour (130A-130D) retournant des courants latéraux du
premier réfrigérant provenant de chacun desdits premiers échangeurs de chaleur (123A-123D)
vers un étage de compresseur respectif ( 109A-109D) du compresseur (109) ; et
caractérisé en ce que ledit compresseur (109) est un turbo-compresseur à engrenages intégrés comprenant
une pluralité d'étages de compresseur (109A-109D), chacun étant pourvu d'un ensemble
indépendant de vannes de guidage d'entrée mobiles (11 OA-110D) pour réguler de manière
autonome des flux entrant dans les étages de compresseur ;
et en ce que ledit compresseur (109) comprend en outre au moins un refroidisseur intermédiaire
(153, 155, 157) entre au moins deux étages de compresseur agencés en série, disposé
entre le côté de distribution de l'un de la pluralité d'étages de compresseur (109A
- 109D) et le côté aspiration d'un autre de la pluralités d'étages de compresseur
(109A - 109D).
2. Système selon la revendication 1, dans lequel la boucle de pré-refroidissement (103)
est configurée pour diviser le premier réfrigérant en deux ou plusieurs courants latéraux
renvoyés à des étages de compresseur respectifs (109A-109D) dudit turbo-compresseur
à engrenages intégrés (109).
3. Système selon la revendication 1 ou 2, dans lequel ledit moteur principal (111) comprend
un moteur électrique.
4. Système selon la revendication 1 ou 2, dans lequel ledit moteur principal (111) comprend
une turbine à gaz.
5. Système selon l'une quelconque des revendications précédentes, dans lequel la boucle
de pré-refroidissement (103) comprend en outre : au moins un premier élément d'expansion
auxiliaire et au moins un premier échangeur de chaleur auxiliaire recevant une partie
dudit premier réfrigérant dilaté par ledit premier élément d'expansion auxiliaire
et configuré pour transférer la chaleur du deuxième réfrigérant circulant dans la
boucle de refroidissement (105) vers le premier réfrigérant circulant dans la boucle
de pré-refroidissement (103).
6. Système selon l'une quelconque des revendications précédentes, dans lequel la boucle
de pré-refroidissement (103) comprend en outre : une pluralité de seconds éléments
d'expansion agencés séquentiellement (121A-121D) configurés pour dilater le premier
réfrigérant à une pluralité de niveaux de pression décroissants ; une pluralité de
seconds échangeurs de chaleur (125A-125D) agencés et configurés pour recevoir des
parties respectives dudit premier réfrigérant dilaté par lesdits premiers éléments
d'expansion auxiliaires (119A-119D) et pour transférer de la chaleur du deuxième réfrigérant
au premier réfrigérant ; une pluralité de chemins de retour renvoyant les parties
du premier réfrigérant provenant de chacun desdits seconds échangeurs de chaleur (125A-125D)
vers un étage de compresseur respectif du turbo-compresseur à engrenages intégrés
(109).
7. Système selon l'une quelconque des revendications précédentes, dans lequel ledit deuxième
réfrigérant est un réfrigérant mixte ou de l'éthylène ou du méthane.
8. Système selon l'une quelconque des revendications précédentes, dans lequel ledit turbo-compresseur
à engrenages intégrés (109) comprend : un engrenage central (163) entraîné en rotation
par ledit moteur principal (111) ; une pluralité d'arbres entraînés (159, 161), chaque
arbre entrainé comprenant un pignon (159A, 161A) engrenant avec l'engrenage central
(163) et entraîné en rotation par ledit engrenage central (163) ; au moins une roue
de compresseur respective (112C, 112D) montée sur chaque arbre (159, 161).
9. Système selon la revendication 8, dans lequel deux roues de compresseur (112C, 112D)
respectives sont montées sur au moins l'un desdits arbres (159).
10. Système selon l'une quelconque des revendications précédentes, dans lequel le turbo-compresseur
à engrenages intégrés (109) est agencé pour comprimer le premier réfrigérant de sorte
que le premier réfrigérant sous pression soit délivré du dernier étage du turbo-compresseur
à engrenages intégrés à une pression allant d'environ 45 à environ 65 bars absolus
et de préférence d'environ 50 à environ 60 bars absolus ; et dans lequel la pression
du premier réfrigérant à l'entrée du premier étage du turbo-compresseur à engrenages
intégrés varie d'environ 2,5 à environ 10 et de préférence d'environ 3 à environ 5
bars absolus.
11. Système selon l'une quelconque des revendications 1 à 9, dans lequel le turbo-compresseur
à engrenages intégrés (109) est agencé pour comprimer le premier réfrigérant de sorte
que le premier réfrigérant sous pression soit délivré du dernier étage du turbo-compresseur
à engrenages intégrés à une pression allant d'environ 10 à environ 30 bars absolus
et de préférence d'environ 15 à environ 25 bars absolus ; et dans lequel la pression
du premier réfrigérant à l'entrée du premier étage du turbo-compresseur à engrenages
intégrés varie d'environ 1 à environ 2,5 et de préférence d'environ 1,5 à environ
2 bars absolus.
12. Procédé de liquéfaction de gaz naturel, le procédé comprenant :
la disposition d'une boucle de pré-refroidissement (103) comprenant : un turbo-compresseur
(109), au moins un condenseur (115), au moins un élément d'expansion (119A-119D) et
au moins un échangeur de chaleur (123A-123D),
l'entrainement du turbo-compresseur (109) avec un moteur principal (111) ;
la circulation d'un premier réfrigérant à travers le turbo-compresseur (109) ;
la condensation du premier réfrigérant délivré par le turbo-compresseur (109) dans
le condenseur (115) ;
la division du premier réfrigérant en une pluralité de flux partiels ;
la dilatation du premier réfrigérant condensé dans l'élément d'expansion (119A-119D)
;
la circulation du réfrigérant dilaté dans l'échangeur de chaleur (123A-123D) pour
éliminer la chaleur du gaz naturel, pour pré-refroidir le gaz naturel ;
la disposition d'au moins une boucle de refroidissement (105) ;
la circulation d'un deuxième réfrigérant dans ladite au moins une boucle de refroidissement
(105) ;
l'élimination de la chaleur du gaz naturel pré-refroidi par échange de chaleur avec
le deuxième réfrigérant ;
la disposition d'une pluralité de premiers éléments d'expansion disposés de manière
séquentielle (119A-119D) dans la boucle de pré-refroidissement (103) ;
la dilatation du premier réfrigérant dans les premiers éléments d'expansion (119A-119D)
à une pluralité de niveaux de pression décroissants ;
la réception des parties respectives du premier réfrigérant dilaté dans la pluralité
de premiers éléments d'expansion agencés de manière séquentielle (119A, 119D) dans
une pluralité de premiers échangeurs de chaleur (123A-123D) et le transfert de la
chaleur du gaz naturel au premier réfrigérant ; et
le renvoi des courants latéraux du premier réfrigérant provenant de chacun des premiers
échangeurs de chaleur (123A/123D) par une pluralité de trajets de retour (130A-130D)
vers un étage de compresseur respectif (109A-109D) du turbo-compresseur (109) ;
dans lequel ledit premier réfrigérant comprend un gaz ayant un poids moléculaire supérieur
à 35, caractérisé en ce que le turbo-compresseur est un turbo-compresseur à engrenages intégrés (109) ayant une
pluralité d'étages de compresseur (109A-109D), chacun étant pourvu de vannes de guidage
d'entrée (110A-110D) indépendamment mobiles ; la commande des vannes de guidage d'entrée
(11 0A-110D) indépendamment mobiles pour réguler les flux partiels au niveau du côté
aspiration des étages de compresseur (109A-109D) ; le turbo-compresseur à engrenages
intégrés (109) comprenant au moins un refroidisseur intermédiaire (153, 155, 157)
entre au moins deux étages de compresseur disposés en série ; le au moins un refroidisseur
intermédiaire (152, 155, 157) étant disposé entre le côté distribution de l'un de
la pluralité d'étages de compresseur (109A-109D) et le côté aspiration d'un autre
de la pluralité d'étages de compresseur (109-109D).