ITUA20164168A1 - COMPRESSION TRAIN WITH TWO CENTRIFUGAL COMPRESSORS AND LNG PLANT WITH TWO CENTRIFUGAL COMPRESSORS - Google Patents

Description

COMPRESSION TRAIN WITH TWO CENTRIFUGAL COMPRESSORS AND LNG SYSTEM WITH TWO CENTRIFUGAL COMPRESSORS

DESCRIPTION

TECHNICAL FIELD

Embodiments of the object disclosed in this document correspond to compression trains including two centrifugal compressors and LNG plants [= liquefied natural gas] including two centrifugal compressors.

STATE OF THE ART

Figure 1 shows a schematic diagram of an LNG 100 plant according to the prior art, in particular a plant that implements an APCI process, i.e. a well-known liquefaction technique with a first cycle that uses a pure refrigerant and a second cycle that uses a mixed refrigerant.

The plant 100 consists of a first compression train with a centrifugal compressor 130 and a centrifugal compressor 160, having a common first shaft, and a second compression train with a centrifugal compressor 140 and a centrifugal compressor 150, having a second shaft common. Compressor 130 is used to compress propane; an inlet 131 of the compressor 130 is in fluid connection with a propane line; an output 132 of the compressor 130 supplies compressed propane. Compressors 140, 150 and 160 are used to compress a mixed refrigerant gas; an inlet 141 of the compressor 140 is in fluid connection with a mixed refrigerant line; an outlet 142 of the compressor 140 is in fluid connection with an inlet 151 of the compressor 150; an outlet 152 of the compressor 150 is in fluid connection with an inlet 161 of the compressor 160; an output 162 of the compressor 160 supplies compressed mixed refrigerant.

The first compression train is driven by a first engine 110, and the second compression train is driven by a second engine 120. The first engine 110 and the second engine 120 are low-speed engines and may, for example, be an engine electric which rotates at a speed of for example 1500 RPM or a gas turbine which rotates at a speed of for example 3000 or 3600 RPM.

Each of the compressors 130, 140, 150 and 160 is housed inside a separate case.

SUMMARY

It would be desirable to provide an LNG system with a reduced number of compressor cases compared to the solutions of the prior art; this is also advantageous from the point of view of space.

In general, it is advantageous to increase the yield, availability and modularity of LNG plants as well as reduce the initial investment costs for LNG plants.

The aforementioned purposes and benefits apply in particular to LNG plants implementing an APCI process.

First embodiments of the object disclosed herein concern compression trains.

According to such first embodiments, the compression train comprises an engine, a first engine driven centrifugal compressor and a second engine driven centrifugal compressor; the first centrifugal compressor is housed inside a box; the second centrifugal compressor is housed inside a box; the first centrifugal compressor has a first inlet in fluid connection with a high molecular weight gas line, in particular higher than 40; the second centrifugal compressor has a second inlet in fluid connection with a low molecular weight gas line, in particular between 20 and 30; the second centrifugal compressor is able to provide a compression ratio higher than 10: 1, preferably higher than 15: 1.

Second embodiments of the object disclosed herein concern LNG plants.

In accordance with these second embodiments, the LNG plant includes a compression train; the compression train comprises an engine, a first engine driven centrifugal compressor and a second engine driven centrifugal compressor; the first centrifugal compressor is housed inside a box; the second centrifugal compressor is housed inside a box; the first centrifugal compressor has a first inlet in fluid connection with a high molecular weight gas line, in particular higher than 40; the second centrifugal compressor has a second inlet in fluid connection with a low molecular weight gas line, in particular between 20 and 30; the second centrifugal compressor is able to provide a compression ratio higher than 10: 1, preferably higher than 15: 1.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and form an integral part of the present patent description, illustrate exemplary embodiments of the present invention and, together with the detailed description, explain these embodiments. In the drawings:

Figure 1 shows a schematic diagram of an LNG plant according to the prior art;

Figure 2 shows a schematic diagram of embodiments of a compression train;

Figure 3 shows a schematic diagram of an embodiment of a compressor which may be a component of the compression train of Figure 2; and Figure 4 shows a schematic diagram of an embodiment of an LNG plant.

DETAILED DESCRIPTION

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

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

The reference throughout the patent description to "an embodiment" means that a specific function, structure or characteristic described in relation to an embodiment is included in at least one embodiment of the disclosed object. Therefore, the presence of the expression "in an embodiment" at various points throughout the patent description does not necessarily refer to the same embodiment. Furthermore, the specific functions, structures or features can be combined in any appropriate manner in one or more embodiments.

In what follows (and in accordance with its mathematical meaning), the term “series” indicates a group of two or more elements.

The compression train 200 of Figure 2 comprises an engine 210, a first centrifugal (i.e. centrifugal flow) compressor 220 driven by the motor 210 and a second centrifugal (i.e. centrifugal flow) compressor 230 driven by the engine 210. The first centrifugal compressor 220 it is housed inside a box; the second centrifugal compressor 230 is housed inside a box. The first centrifugal compressor 220 has a first inlet in fluid connection with a high molecular weight gas line, in particular higher than 40; the second centrifugal compressor 230 has a second inlet in fluid connection with a low molecular weight gas line, in particular between 20 and 30. Therefore, the gas treated by the compressor 220 and then supplied at a first outlet 222 is different from gas treated by the compressor 230 and then supplied at a second outlet 232.

The second centrifugal compressor 230 is a high compression ratio compressor; in particular, it is arranged so as to provide a compression ratio higher than 10: 1, preferably higher than 15: 1.

A train identical or similar to that shown in Figure 2 is particularly advantageous when arranged to provide both compressed propane and compressed mixed refrigerant to implement an APCI process. In this case,

the high molecular weight gas mentioned above is propane, e

the low molecular weight gas mentioned above is a mixed refrigerant gas, in particular a mixture of propane, ethylene or ethane, and methane.

The train of Figure 2 includes only two centrifugal compressors.

Figure 2 shows two sets of embodiments. According to a first series, there is a single shaft and the second compressor 230 is directly mechanically connected to the first compressor 220. According to a second series, there are two shafts and the second compressor 230 is indirectly mechanically connected to the first compressor 220 via a Gearcase 250. In Figure 2, the gearcase is shown with dashed lines as it is optional.

The following applies to the first set of embodiments.

The compression train has a single shaft.

The engine 210 may be an electric motor or a steam turbine or a gas turbine, in particular an aeroderivative gas turbine.

Motor 210 is a high-speed motor preferably having a maximum rotation speed in the range of 5000-9000 RPM, more preferably a maximum rotation speed in the range of 6000-9000 RPM.

The following applies to the second set of embodiments.

The compression train has two shafts.

The second centrifugal compressor 230 is mechanically connected to the first centrifugal compressor 220 via a gearbox 250 having a transmission ratio preferably higher than 2: 1.

The engine 210 is an electric motor or a steam turbine or a gas turbine, in particular an aeroderivative gas turbine.

Motor 210 is a low speed motor preferably having a maximum rotation speed in the range of 1500-5000 RPM, more preferably a maximum rotation speed in the range of 1500-4000 RPM.

The following applies to both sets of embodiments.

The train may further comprise an auxiliary motor, preferably an electric motor, such as the motor 240 in Figure 2. In Figure 2, the motor 240 is directly connected, for example, to the second compressor 230.

Note that the auxiliary engine can be used when starting the train and / or to assist the main engine when the power absorbed by the compressor or compressors exceeds certain thresholds; this auxiliary engine is sometimes called "assistant".

According to the embodiment of Figure 3, the high compression ratio compressor 230 is a high compression ratio centrifugal (i.e. centrifugal flow) compressor and comprises a first set of impellers (i.e. one or more impellers) and a second set of impellers (i.e. one or more impellers) arranged downstream or upstream (preferably downstream) of the first series of impellers.

As shown in Figure 3, the first series includes two impellers 311 and 312, but any number of impellers from 1 to, for example, 20 is adequate. According to this embodiment, the second series includes three impellers 321 and 322 and 323 , but any number of impellers from 1 to, for example, 20 is adequate. The impellers 311 and 312 of the first series are centrifugal and without cover. As shown in Figure 3, the impellers 321 and 322 and 323 of the second series are centrifugal and covered. At least the impellers 311 and 312 and 321 and 322 and 323 of the first series and of the second series are housed inside a single case 300. The impellers 311 and 312 and 321 and 322 and 323 of the first and second series are coupled to each other by mechanical connections.

According to an alternative embodiment, all impellers are centrifugal and covered.

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

There may be one or more auxiliary inputs.

There can be one or more auxiliary outputs.

Advantageously, as in the embodiment of Figure 3, at least some of the impellers of said high compression ratio centrifugal compressor are stacked on top of each other and mechanically coupled by means of Hirth joints. The stacked and coupled impellers are tightened together by means of a tie rod, in this way a very stable and reliable mechanical connection is obtained. Each impeller has for example a through hole at its rotational axis and is configured in such a way that the tie rod can pass through it. A rotor is obtained when the impellers are stacked and tightened to each other.

In the embodiment of Figure 3, all impellers 311, 312, 321, 322, 323 of the two series are stacked, coupled by Hirth joints 340A, 340B, 340C, 340D, and tightened to each other by means of a tie rod 330.

The compressor 230 has a main inlet 301 (denoted 231 in Figure 2), a main outlet 302 (denoted by 232 in Figure 2), and at least one auxiliary inlet and / or at least one auxiliary outlet in an intermediate position along the flow path from main entrance 301 to main exit 302; Figure 3 shows the generic case of an intermediate plug 303, which in some embodiments is an auxiliary inlet (see upward arrow) and which in some embodiments is an auxiliary outlet (see down arrow).

Advantageously, as in the embodiment of Figure 3, the second series of impellers (321 and 322 and 323) is downstream of the first series of impellers (311 and 312), and the impellers (321 and 322 and 323) of the second series they may have a larger diameter than the impellers (311 and 312) of the first series.

According to the embodiment of Figure 3, the impellers of the first set of impellers (311 and 312) are uncovered and with a larger diameter than those of the second set of impellers (321 and 322 and 323).

The impellers without cover are able to rotate more quickly than impellers with cover, due to the absence of the cover; in fact, when the impeller rotates, the cover is drawn outwards by the centrifugal force acting on it and, above a certain rotation speed, the cover risks pulling away the impeller.

Thanks to the rotor configuration of the high compression ratio centrifugal compressor defined above, the compressor is able to rotate faster than traditional centrifugal compressors, resulting in a higher compression ratio.

Note that uncovered impellers and covered impellers can alternate with each other; this happens in particular when there are one or more auxiliary inputs and / or outputs.

Centrifugal compressors identical or similar to the one shown in Figure 3 can rotate very quickly, therefore they can achieve a very high compression ratio. Therefore, a single innovative centrifugal compressor in a single (and small) box can replace two or three or more traditional centrifugal compressors in separate boxes.

Furthermore, thanks to the high rotation speeds of the impellers, high flow coefficients can be obtained.

By using a train identical or similar to that shown in Figure 2 (particularly with a compressor identical or similar to that shown in Figure 3), high LNG production can be achieved in a smaller space and / or with a smaller footprint. small and with fewer machines.

Note that having only one crate instead of two or more crates is advantageous from many points of view:

- simplifies installation and maintenance,

- reduces maintenance time,

- increases reliability (fewer components and lower probability of failures),

- reduces the size and weight of the machines,

- reduces gas loss,

- reduces the complexity and size of the lubricating oil system.

A train identical or similar to the one shown in Figure 2 is primarily configured for use in an LNG plant.

Figure 4 shows a schematic diagram of an embodiment of an LNG plant comprising two such trains; gearboxes are not shown but may be present.

In this embodiment, both trains are advantageously identical.

In such an embodiment, both trains implement an APCI process.

In such an embodiment, both trains comprise a compressor identical or similar to that shown in Figure 3.

A plant such as the one shown in Figure 4 can have a power substantially equal to the plant in Figure 1. In any case, one of the advantages of the plant in Figure 4 compared to the plant in Figure 1 is that, if a component of the plant breaks down, the plant in Figure 1 will not be able to produce any LNG, while the plant in Figure 4 will be able to produce 50% of the nominal production.

Claims (13)

CLAIMS A compression train (200) comprising an engine (210), a first centrifugal compressor (220) driven by the engine (210) and a second centrifugal compressor (230) driven by the engine (210); in which the first centrifugal compressor (220) is housed inside a box; in which the second centrifugal compressor (230) is housed inside a box; wherein the first centrifugal compressor (220) has a first inlet in fluid connection with a high molecular weight gas line, in particular higher than 40; wherein the second centrifugal compressor (230) has a second inlet in fluid connection with a low molecular weight gas line, in particular between 20 and 30; Wherein the second centrifugal compressor (230) is adapted to provide a compression ratio higher than 10: 1, preferably higher than 15: 1. 2. The compression train of claim 1, where the high molecular weight gas is propane, wherein the low molecular weight gas is a mixed refrigerant gas, in particular a mixture of propane, ethylene or ethane, and methane. The compressor train of claim 1 or 2, wherein the engine (210) is an electric motor or a steam turbine or a gas turbine, in particular an aeroderivative gas turbine. The compression train of claim 3, wherein the engine (210) is a high-speed engine. The compression train of claim 1 or 2, wherein the second centrifugal compressor (230) is mechanically connected to the first centrifugal compressor (220) via a gearbox (250) having a gear ratio preferably greater than 2: 1. The compressor train of claim 5, wherein the engine (210) is an electric motor or a steam turbine or a gas turbine, in particular an aeroderivative gas turbine. The compression train of claim 5 or 6, wherein the engine (210) is a low speed engine. The compression train of any of the preceding claims, further comprising an auxiliary engine (240). The compression train of any of the preceding claims 1 to 8, wherein the second centrifugal compressor (230) comprises a first set of impellers (411, 412) and a second set of impellers (421, 422, 423); the impellers (411, 412) of the first series being centrifugal and without cover; the impellers (421, 422, 423) of the second series being centrifugal and equipped with a cover. The compression train of any of the preceding claims 1 to 8, wherein the second centrifugal compressor (230) comprises a first set of impellers and a second set of impellers; the impellers of the first series being centrifugal and equipped with a cover; the impellers of the second series being centrifugal and equipped with a cover. An LNG plant (100) comprising a compression train (200) according to any of the preceding claims 1 to 10. 12. The LNG plant (100) of claim 10, comprising two compression trains (200, 300) according to any of the previous claims 1 to 10. The LNG plant (100) of claim 11 or 12, wherein the or each first centrifugal compressor (220, 320) is adapted to compress a high molecular weight gas, wherein the or each second centrifugal compressor (230, 330) is adapted to compress a low molecular weight gas; the or each first centrifugal compressor (220, 320) and the or each second centrifugal compressor (230, 330) cooperating to liquefy a flow of natural gas.