JP2019502046A - LNG plant including axial and centrifugal compressors - Google Patents

Abstract

The LNG plant includes a compression train (100) and a further compression train (200), for example, advantageously implementing a three-cycle pure refrigerant liquefaction technique or a multi-cycle pure refrigerant and mixed refrigerant liquefaction technique. it can. The compression train (100) includes first and second sets of axial compression stages (321, 322, 323), one main inlet (301), one main outlet (302), and one auxiliary inlet. (303) and / or one auxiliary outlet, fluid entering the compressor (130) through the auxiliary inlet (303) is redirected from a substantially radial direction to a substantially axial direction, and / or Or, fluid exiting the compressor (130) through the auxiliary outlet is diverted from substantially axial to substantially radial. The further compression train (200) is centrifugal and has a first set of impellers (411, 412) without a shroud and a second set of impellers (421, 412) with a shroud. 422, 423).
[Selection] Figure 3

Description

  Embodiments of the presently-disclosed subject matter correspond to LNG [= liquefied natural gas] plants that include axial and centrifugal compressors.

  In the field of “oil and gas”, ie machines and plants for exploration, production, storage, refining and distribution of oil and / or gas, there is always a need for improved solutions.

  The improvement may be derived from, for example, the structure and / or operation of the machine, the connection of the machine, or a combination of machines (eg, a machine train).

  Improvements may include, for example, increased efficiency and / or loss, increased production and / or reduced waste, increased functionality, reduced cost, reduced size and / or footprint.

  In the field of “oil and gas”, two main LNG processes are known.

  -Air Products & Chemicals Inc. Designed C3-MR process (hence sometimes simply referred to as “APCI”); this process is pure refrigerant (“C3”), ie propane, as well as mixed refrigerant (“MR”), ie typically A mixture of propane, ethylene and methane is used; this process is a two-cycle (one) pure refrigerant and (one) mixed refrigerant liquefaction technique.

  A cascade process designed by Conoco Phillips (hence sometimes simply referred to as “CPOC”); this process uses three pure refrigerants, typically propane, ethylene or ethane, and methane; Is a three-cycle (three) pure refrigerant liquefaction technology.

  A further LNG process is known as “AP-X” in the field of “oil and gas”; this process consists of two pure refrigerants, ie propane and nitrogen, and a mixed refrigerant, ie typically propane, ethylene. This process is a three-cycle (two) pure refrigerant and (one) mixed refrigerant liquefaction technology; this process is an evolution of the “APCI” process.

  Note that the expression “pure refrigerant” actually means that one substance in the refrigerant is predominant (eg, at least 90% or 95% or 98%); (For example, propane, ethane, ethylene, methane) or a chemical element (for example, nitrogen).

  These known processes have already been optimized in terms of process, but improvements are sought in particular in terms of the number of machines used in the LNG plant and / or the machine footprint.

International Publication No. 2013/182492

  Embodiments of the presently disclosed subject matter relate to LNG plants.

  According to such an embodiment, the LNG plant includes a compression train and a further compression train. The compression train includes an engine and a compressor driven by the engine, wherein the compressor is an axial compressor, and includes a first set of axial compression stages and a first set of axial compression stages. A second set of axial compression stages disposed downstream, wherein at least the first set and the second set of axial compression stages are housed in one case, the compressor comprising: One main inlet disposed upstream of the set axial compression stage, one main outlet disposed downstream of the second set of axial compression stages, and downstream of the first set of axial compression stages And at least one auxiliary inlet and / or at least one outlet disposed upstream of the second set of axial compression stages, the compressor substantially allowing fluid to enter the compressor through the auxiliary inlet. Redirected from radial to substantially axial Sea urchin, and / or configured so that fluid exiting through the auxiliary outlet compressor is substantially diverted radially from substantially axially. The further compression train includes a further engine and a further compressor driven by the further engine, the further compressor being a centrifugal compressor, downstream of the first set of impellers or the first set of impellers or A second set of impellers disposed upstream, the first set of impellers being centrifugal and without a shroud, and the second set of impellers being centrifugal and having a shroud At least a first set and a second set of impellers are housed in one case, and the first set and the second set of impellers are coupled together by a mechanical connection.

  This type of axial compressor is a high flow compressor and is hereinafter also referred to as a “large flow axial compressor”.

  The “substantially axial direction” is a direction parallel to the direction of the compressor shaft or substantially in contact with the compression flow path, and the compression flow path is a path defined by the fluid flow during compression. is there.

  Such an LNG plant can advantageously implement, for example, a three-cycle pure refrigerant liquefaction technique or a multi-cycle pure refrigerant and mixed refrigerant liquefaction technique.

  The accompanying drawings, which are incorporated in and constitute an integral part of the specification, illustrate exemplary embodiments of the invention and, together with the detailed description, explain the embodiments. The description of the drawings is as follows.

1 is a schematic view of a first embodiment of a compression train. FIG. 3 is a schematic diagram of a second embodiment of a compression train. FIG. 2 is a schematic diagram of a first embodiment of a compressor that may be a component of the compression train of FIG. 1. FIG. 3 is a schematic diagram of a second embodiment of a compressor that may be a component of the compression train of FIG. 2. 1 is a schematic view of a first embodiment of an LNG plant. It is the schematic of 2nd Embodiment of an LNG plant.

  The following description of exemplary embodiments refers to the accompanying drawings.

  The following description does not limit the invention. Instead, the scope of the invention is defined by the appended claims.

  Reference throughout the specification to “one embodiment” or “an embodiment” refers to a particular feature, structure, or characteristic described in connection with the embodiment, at least one embodiment of the disclosed subject matter. Means it is included. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification do not necessarily refer to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

  In the following (and according to its mathematical meaning), the term “set” means a group of one or more items.

FIG. 1 shows a compression train 100 that includes an engine 110 and a compressor 130 driven by the engine 110. The compressor 130 is an axial flow (ie, axial flow) compressor and includes at least a first set of axial compression stages (ie, one or more stages) and a first set of axial compression stages. And at least a second set of axial compression stages (ie, one or more stages) disposed downstream. According to the embodiment of FIG. 3, the first set includes two stages 311 and 312, but any number from 1 to, for example, 20 is suitable. According to the embodiment of FIG. 3, the second set includes three stages 321 and 322 and 323, although any number from 1 to, for example, 20 is suitable. At least the first set and the second set of axial compression stages are housed in one case 300 and typically all sets of stages are housed in this case. The compressor 130 is
To receive the fluid to be compressed (shown at 131 in FIG. 1) disposed upstream of the first set of axial compression stages, which may be disposed directly upstream of these stages (ie, nothing in between). One main entrance 301 of
Provides a compressed fluid (denoted 132 in FIG. 1) disposed downstream of the second set of axial compression stages that may be disposed directly downstream of these stages (ie, nothing in between). One main outlet 302 for
3 comprising at least one auxiliary inlet and / or at least one outlet arranged downstream of the first set of axial compression stages and upstream of the second set of axial compression stages, according to the embodiment of FIG. For example, there is only one auxiliary inlet 303 arranged directly downstream of the stages 311 and 312 and directly upstream of the stages 321 and 322 and 323.

  The first set and the second set of axial compression stages may be arranged to compress the same type of working fluid or different types of working fluid.

  For example, if the working fluid types are the same, the first set of axial compression stages processes the first flow of working fluid (see, eg, arrow 301 in FIG. 3) and the second set of shafts. The directional compression stage enters the first flow of working fluid (eg, see arrow 304 in FIG. 3) and the auxiliary inlet (eg, see arrow 303 in FIG. 3) after being processed by the first set of stages. A second flow of working fluid (eg, see arrow 303C in FIG. 3) is processed.

  For example, if the types of working fluid are different, the first working fluid enters the main inlet (eg, inlet 301 in FIG. 3), exits from the auxiliary outlet (FIG. 3 does not show the auxiliary outlet), and the second The working fluid enters the auxiliary inlet (eg, inlet 303 of FIG. 3) and exits from the main outlet (eg, outlet 302 of FIG. 3).

  In the embodiment of FIG. 3, the main inlet 301 is used to receive a first fluid flow to be compressed and the auxiliary inlet 303 is used to receive a second fluid flow to be compressed. The auxiliary inlet 303 is jetted of a fluid flow that is oriented substantially radially (or completely) on the outer side 303A and substantially (or completely) axially oriented on the inner side 303C, and the stage 311 The first fluid flow that has already been partially compressed by 3 and 312 and flows axially (304) and the second fluid flow that has not yet been compressed and flows axially (303C) are stages 321 and 322. And the second fluid flow is diverted from radial to axial along the intermediate path 303B from the outer 303A to the inner 303C, ie, bent. It is.

  The set of axial compression stages may be more than two, for example three or four.

  One or more auxiliary inlets may be present.

  One or more auxiliary outlets may be present.

  With the axial compressor configuration defined above, the machine is very compact and only one casing is needed to handle more than one fluid flow.

  Further, axial injection of one or more sidestreams of working fluid in the mainstream of working fluid processed by the compressor can increase the overall efficiency of the compressor.

  An axial compressor is a type of compressor that can handle higher flow rates than other types of compressors under the same conditions.

  In general, axial compressors are more efficient than centrifugal compressors, so they can compress more fluid, ie more fluid flow, at the same output. Therefore, it is advantageous to use an axial compressor for propane because the amount of liquefied natural gas produced is directly proportional to the flow rate of propane.

  In general, axial compressors are smaller than centrifugal compressors at the same output. It is therefore advantageous to use an axial compressor for propane, since the size and / or number of compressors in the plant, in particular the LNG plant, is reduced.

  The auxiliary inlet and / or auxiliary outlet can be made more flexible by the compressor, and the operating conditions of the machine can be adapted to the process in which the compressor is used. For example, the auxiliary inlet and auxiliary outlet may be used to extract the working fluid from the compressor and cool it before reinjecting it.

  The engine 110 may be an electric motor or a steam or gas turbine, in particular an aeroderivative gas turbine. In addition to the main engine, there may be an auxiliary engine connected to the shaft of the compression train (especially in the LNG plant) that helps the main engine when the power absorbed by the compressor exceeds a certain threshold. Please keep in mind. Such auxiliary engines are sometimes referred to as “helpers”.

  The engine 110 and the compressor 130 can be connected directly or by a gear train 120 (usually part of the gearbox) as shown in FIG.

  A train identical or similar to that shown in FIG. 1 (and FIG. 3) is particularly advantageous when arranged to obtain compressed propane. For example, this is an LNG plant that implements a liquefaction technique with three cycles of three pure refrigerants (eg, “CPOC”), a liquefaction technique with two cycles of one pure refrigerant and one mixed refrigerant (eg, “APCI”). This is a case of an LNG plant to be implemented, and an LNG plant to implement a liquefaction technique (for example, “AP-X”) by three cycles of two pure refrigerants and one mixed refrigerant.

  FIG. 2 shows a compression train 200 that includes an engine 210 and a high compression ratio compressor 230 driven by the engine 210. The high compression ratio compressor 230 is a centrifugal (ie, centrifugal flow) compressor and is located downstream or upstream of the first set of impellers (ie, one or more impellers) and the first set of impellers. And a second set of impellers (ie, one or more impellers). According to the embodiment of FIG. 4, the first set includes two impellers 411 and 412, but any number of impellers from 1 to 20, for example, is suitable. According to the embodiment of FIG. 4, the second set includes three impellers 421 and 422 and 423, but any number from 1 to, for example, 20 impellers is suitable. The first set of impellers 411 and 412 is centrifugal and does not have a shroud. The second set of impellers 421 and 422 and 423 is centrifugal and has a shroud. At least the impellers 411 and 412 and 421 and 422 and 423 of the first set and the second set are accommodated in one case 400. The first and second sets of impellers 411 and 412 and 421 and 422 and 423 are coupled to each other by a mechanical connection.

  The set of axial compression stages may be more than two, for example three or four.

  One or more auxiliary inlets may be present.

  One or more auxiliary outlets may be present.

  Advantageously, as in the embodiment of FIG. 4, at least some of the impellers of the high compression ratio centrifugal compressor are stacked on top of each other and mechanically joined by a Hight joint. The stacked and joined impellers are clamped together by tie rods, thus achieving a very stable and reliable mechanical connection. Each impeller has, for example, a through hole in its rotating shaft, and is configured so that the tie rod can pass through the through hole. The rotor is achieved when the impellers are stacked and clamped together.

  In the embodiment of FIG. 4, all two sets of impellers 411, 412, 421, 422, 423 are stacked, joined together by Hirth joints 440 A, 440 B, 440 C, 440 D and clamped together by tie rods 430.

  The compressor 230 has at least one intermediate position along the flow path from the main inlet 401 (indicated by 231 in FIG. 2), the main outlet 402 (indicated by 232 in FIG. 2), and the main inlet 401 to the main outlet 402. FIG. 4 is an auxiliary inlet (see up arrow) in some embodiments, and an auxiliary outlet (see down arrow in some embodiments), with four auxiliary inlets and / or at least one auxiliary outlet. ) Is a general case of one intermediate tap 403.

  Advantageously, as in the embodiment of FIG. 4, the second set of impellers (421 and 422 and 423) is downstream of the first set of impellers (411 and 412) and the second set of impellers (421 and 422 and 423) have a smaller diameter than the first set of impellers (411 and 412).

  According to the embodiment of FIG. 4, the impellers of the first set of impellers (411 and 412) are not shrouded and have a larger diameter than the second set of impellers (421 and 422 and 423).

  An impeller without a shroud can rotate faster than an impeller with a shroud because it does not have a shroud. In fact, when the impeller rotates, the shroud is pulled outward by the acting centrifugal force and is constant. There is a risk that the shroud pulls out the impeller at the rotational speed.

  The rotor configuration of the high compression ratio centrifugal compressor defined above allows the compressor to rotate faster than a conventional centrifugal compressor and thus achieve a higher compression ratio.

  Note that impellers without shrouds and impellers with shrouds may be interleaved with each other. This occurs especially when one or more auxiliary inlets and / or outlets are present.

  The engine 210 may be an electric motor or a steam or gas turbine, in particular an aeroderivative gas turbine. In addition to the main engine, there may be an auxiliary engine connected to the shaft of the compression train (especially in the LNG plant) that helps the main engine when the power absorbed by the compressor exceeds a certain threshold. Please keep in mind. Such auxiliary engines are sometimes referred to as “helpers”.

  The engine 210 and the compressor 230 can be connected directly or by a gear train 120 (usually part of the gearbox), as shown in FIG.

  A centrifugal compressor identical or similar to that shown in FIG. 2 (and FIG. 4) can rotate very fast and therefore can reach very high compression ratios. Thus, two or more conventional centrifugal compressors in separate cases can be replaced by a single (and small) case single innovative centrifugal compressor.

  Furthermore, a high flow coefficient can be obtained due to the high rotational speed of the impeller.

  A train identical or similar to that shown in FIG. 2 (and FIG. 4) is particularly advantageous when arranged to obtain compressed methane. For example, this is the case for an LNG plant that implements a liquefaction technique with three cycles of three pure refrigerants (eg, “CPOC”).

  A train identical or similar to that shown in FIG. 2 (and FIG. 4) is particularly advantageous when arranged to obtain a compressed mixed refrigerant. For example, this is an LNG plant that implements a two-cycle liquefaction technique (eg, “APCI”) of one pure refrigerant and one mixed refrigerant, and a three-cycle liquefaction technique (eg, two pure refrigerants and one mixed refrigerant) , “AP-X”).

  A train identical or similar to that shown in FIG. 2 (and FIG. 4) is particularly advantageous when arranged to obtain compressed nitrogen. For example, this is the case for an LNG plant that implements a three-cycle liquefaction technique (eg, “AP-X”) of two pure refrigerants and one mixed refrigerant.

  One or more trains identical or similar to those shown in FIG. 1 (and FIG. 3) and / or one or more trains identical or similar to those shown in FIG. 2 (and FIG. 4) May be included in the LNG plant.

  By using such a train with such a compressor, higher LNG production can be obtained with fewer machines in less space and / or less footprint.

Having only one case instead of two or more cases
Simplify installation and maintenance,
Reduce maintenance time,
Increase reliability (reduced components and potential failure),
Reduce the machine footprint and weight,
Reduce gas leakage,
It should be noted that it is advantageous from many viewpoints of reducing the complexity and size of the lubricating oil system.

  5 and 6 show embodiments of LNG liquefaction lines 500 and 600 of the LNG plant. Reference numerals 501 and 601 indicate gaseous natural gas inlets, and reference numerals 502 and 602 indicate liquefied natural gas outlets. Reference numerals 540 and 640 denote lines of equipment that process natural gas and cool and liquefy it. Other components in the line supply pressurized refrigerant gas to such equipment.

  For example, device 540 implements a two-cycle pure refrigerant and mixed refrigerant liquefaction technique (eg, “APCI”) and thus uses pressurized propane and pressurized mixed refrigerant.

  For example, the instrument 640 implements a three-cycle pure refrigerant liquefaction technique (eg, “CPOC”) and thus uses pressurized propane, pressurized methane, and pressurized ethane or ethylene.

  The LNG liquefaction line of FIG. 5 includes at least one high flow axial flow compression (driven by an engine not shown) in a single case for compressing propane from at least two different low pressures to high pressures. There is a machine 510. The low pressure propane inlet can typically be two or three or four.

  The LNG liquefaction line of FIG. 5 includes at least one high (driven by an engine not shown) in a single case to compress the mixed refrigerant from at least two different low pressures to at least two high pressures. There is a compression ratio centrifugal compressor 520. The compressor 520 is fluidly connected to the intercooler 550 by a corresponding auxiliary inlet and a corresponding auxiliary outlet of the compressor 520 to perform an intermediate cooling step. In such an LNG liquefaction line there may be, for example, two or three, two or more intercooling steps.

  The LNG liquefaction line of FIG. 5 has at least one compressor (not shown) (driven by an engine not shown) in a single case for compressing nitrogen from low pressure to high pressure. Can do.

  The LNG liquefaction line of FIG. 6 includes at least one high flow axial flow compression (driven by an engine not shown) in a single case for compressing propane from at least two different low pressures to high pressures. There is a machine 610. The low pressure propane inlet can typically be two or three or four.

  The LNG liquefaction line of FIG. 6 includes at least one high compression ratio centrifugal compression (driven by an engine not shown) in a single case for compressing methane from at least two different low pressures to high pressures. There is a machine 620. The low pressure methane inlet can typically be two or three or four.

  The LNG liquefaction line of FIG. 6 includes at least one compressor 630 (driven by an engine not shown) in a single case for compressing ethane or ethylene from at least two different low pressures to high pressures. Exists. The low pressure ethane or ethylene inlet can typically be two or three or four.

  Note that a single engine can drive one or more compressors, depending on the engine power used and the compressor power used.

  If a single engine drives, for example, two compressors, a gear train (usually part of the gearbox) can be used to rotate the two compressors at two different speeds.

DESCRIPTION OF SYMBOLS 100 Compression train 110 Engine 120 Gear train 130 Compressor 131 Fluid to be compressed 132 Compressed fluid 200 Further compression train 210 Further engine 230 Further compressor, high compression ratio compressor 231 Main inlet 232 Main outlet 300 Case 301 Main inlet 302 Main outlet 303 Auxiliary inlet 303A Outer 303B Intermediate path 303C Second flow of working fluid, inner 304 First flow of working fluid, axial 311 First set of axial compression stages 312 First set of axial compression Stage 321 Second set of axial compression stages 322 Second set of axial compression stages 323 Second set of axial compression stages 400 Case 401 Main inlet 402 Main outlet 403 Intermediate tap 411 First set of impellers 412 The first set of impellers 421 The second set of impellers 421 Impeller 422 Second set of impellers 423 Second set of impellers 430 Tie rod, mechanical connection 440A High joint, mechanical connection 440B High joint, mechanical connection 440C High joint, mechanical connection 440D High joint, mechanical connection 500 LNG liquefaction line 501 gas natural gas inlet 502 liquefied natural gas outlet 510 large flow axial compressor, first compression train 520 high compression ratio centrifugal compressor, second compression train 540 equipment 550 intercooler 600 LNG liquefaction line 601 gas natural Gas inlet 602 Liquefied natural gas outlet 610 High flow axial compressor, first compression train 620 High compression ratio centrifugal compressor, second compression train 630 Compressor, third compression train 640 Equipment

Claims (12)

An LNG plant including a compression train (100),
The compression train (100) includes an engine (110) and a compressor (130) driven by the engine (110), the compressor (130) being an axial compressor, A set of axial compression stages (311, 312) and a second set of axial compression stages (321, 322, 323) disposed downstream of the first set of axial compression stages (311, 312) Including
At least the first set and the second set of axial compression stages (311, 312, 321, 322, 323) are housed in one case (300);
The compressor (130)
One main inlet (301) disposed upstream of the first set of axial compression stages (311, 312);
One main outlet (302) disposed downstream of the second set of axial compression stages (321, 322, 323);
At least one auxiliary inlet (303) disposed downstream of the first set of axial compression stages (311, 312) and upstream of the second set of axial compression stages (321, 322, 323); And / or at least one auxiliary outlet,
The compressor (130) may be configured such that fluid entering the compressor (130) through the auxiliary inlet (303) is redirected from a substantially radial direction to a substantially axial direction and / or the The fluid exiting the compressor (130) through the auxiliary outlet is configured to be diverted from a substantially axial direction to a substantially radial direction;
The LNG plant further includes an additional compression train (200), the additional compression train (200) including an additional engine (210) and an additional compressor (230) driven by the additional engine (210). The further compressor (230) is a centrifugal compressor, and a first set of impellers (411, 412) and a first compressor disposed downstream or upstream of the first set of impellers (411, 412). Two sets of impellers (421, 422, 423),
The first set of impellers (411, 412) is centrifugal and has no shroud;
The second set of impellers (421, 422, 423) is centrifugal and has a shroud;
At least the first set and the second set of impellers (411, 412, 421, 422, 423) are housed in one case (400);
The LNG plant, wherein the first set and the second set of impellers (411, 412, 421, 422, 423) are coupled together by mechanical connections (430, 440).   The said fluid is redirected by an intermediate path (303B) extending from the auxiliary inlet (303) / outside of the outlet (303A) to the auxiliary inlet (303) / inside of the outlet (303C). LNG plant.   LNG plant according to claim 1 or 2, wherein the engine (110) is an electric motor or a steam or gas turbine, in particular an aeroderivative gas turbine.   The LNG plant according to claim 1 or 2 or 3, wherein the engine (110) and the compressor (130) are connected directly or by a gear train 120.   The compression train (100) is a first compression train (610) and is arranged to compress propane, the further compression train (200) is a second compression train (620) and methane A third compression train (630) arranged to compress and arranged to compress ethylene or ethane, the first compression train (610), the second compression train (620) and The third compression train (630) according to any of the preceding claims, wherein the third compression train (630) cooperates to liquefy the gaseous natural gas stream (601) into a liquid natural gas stream (602). LNG plant (600).   The compression train (100) is a first compression train (610) and is arranged to compress propane, and the further compression train (200) is a second compression train (620), ethylene or A third compression train (630) arranged to compress ethane and arranged to compress methane, the first compression train (610), the second compression train (620) and The third compression train (630) according to any of the preceding claims, wherein the third compression train (630) cooperates to liquefy the gaseous natural gas stream (601) into a liquid natural gas stream (602). LNG plant.   The LNG plant according to claim 5 or 6, wherein the third compression train (630) comprises at least one centrifugal compressor (630). The at least one centrifugal compressor (630) of the third train (630) is downstream or upstream of a first set of impellers (411, 412) and the first set of impellers (411, 412). A second set of impellers (421, 422, 423) disposed in the
The first set of impellers (411, 412) is centrifugal and has no shroud;
The second set of impellers (421, 422, 423) is centrifugal and has a shroud;
At least the first set and the second set of impellers (411, 412, 421, 422, 423) are housed in one case (400);
The LNG plant of claim 7, wherein the first set and the second set of impellers (411, 412, 421, 422, 423) are coupled to each other by mechanical connections (430, 440).   The compression train (100) is a first compression train (510) and is arranged to compress propane, the further compression train (200) is a second compression train (520), and a mixed refrigerant And the first compression train (510) and the second compression train (520) liquefy the gaseous natural gas stream (501) into a liquid natural gas stream (502). The LNG plant (500) according to any one of claims 1 to 4, which cooperates with   The compression train (100) is a first compression train (510) and is arranged to compress propane, the further compression train (200) is a second compression train (520), and a mixed refrigerant And a fourth compression train arranged to compress nitrogen, the first compression train (510), the second compression train (520) and the fourth compression train. The LNG plant according to any one of the preceding claims, wherein the compression train cooperates to liquefy the natural gas stream (501).   The LNG plant of claim 10, wherein the fourth compression train includes at least one centrifugal compressor. The at least one centrifugal compressor of the fourth train is disposed in a first set of impellers (411, 412) and a second set of downstream or upstream of the first set of impellers (411, 412). A set of impellers (421, 422, 423),
The first set of impellers (411, 412) is centrifugal and has no shroud;
The second set of impellers (421, 422, 423) is centrifugal and has a shroud;
At least the first set and the second set of impellers (411, 412, 421, 422, 423) are housed in one case (400);
12. The LNG plant of claim 11, wherein the first set and the second set of impellers (411, 412, 421, 422, 423) are coupled to each other by mechanical connections (430, 440).