High pressure integrated expander and motor-compressor unit

Abstract

The expander and motor-compressor unit (100, 200) comprises an electric motor (10) with a stator part (11) and a rotary part (12), a compressor impeller (20) mechanically coupled to a first end the rotary part (12) of the electric motor (10) through a rotating shaft (15) and configured to compress a process gas, an expander impeller (30) mechanically coupled to a second end of the rotary part (12) of the electric motor (10) through the rotating shaft (15) and configured to expand the process gas and a casing (50) comprising a first inner wall (51) and a second inner wall (52). The first and second inner walls (51, 52) form a main chamber (60) in which the electric motor (10) is located and two secondary chambers (61, 62) in which the compressor impeller (20) and the expander impeller (30) are located respectively. The expander and motor-compressor unit (100, 200) further comprise a depressurizing element (170, 270) fluidly coupled to the main chamber (60) and configured to reduce the pressure inside the main chamber (60). The depressurizing element (170, 270) is further fluidly coupled to the compressor impeller (20) and to the expander impeller (30) so that the depressurizing element (170, 270) is configured to receive process gas from the expander impeller (30), to extract process gas from the main chamber (60) to be mixed with the received process gas and to discharge the mixed process gas to the compressor impeller (20).

Description

TITLEHigh pressure integrated expander and motor-compressor unitDESCRIPTIONTECHNICAL FIELD

[0001] The subject-matter disclosed herein relates to an innovative expander and motor-compressor unit.BACKGROUND ART

[0002] In some application it is fundamental to avoid leakage of process gas to the environment, for example if the process gas is a sour gas and / or to avoid the reintegration of the process gas in a closed-loop application. There are known turbomachinery configurations in which an expander and a compressor are combined in an integral expander-compressor unit which also can include an electric machine. In an integral expander-compressor unit, the expander and the compressor are mechanically coupled through a common shaft and the electric machine is located along the common shaft between the compressor and the expander. A hermetically sealed casing is provided to contain both the compressor and the expander, as well as the electric machine, so that there is no leakage of processed gas towards the environment, in particular through the rotating shaft and the casing. Typically, the casing provides for the formation of a motor chamber, in which the electric motor is arranged, as well as two lateral chambers in which the compressor and the expander are arranged respectively; these chambers are in fluidly communication between each other.

[0003] However, when the expander and the compressor are operated over a certain pressure (i.e. they are operated at high pressure), for example with a compressor discharge pressure over 100 bar, in particular in the range 100-300bar, the integrated machine may face problems for high windage losses, which represent a loss of power of the system. Windage losses in rotary machine, in particular in electric motors, occur due to the friction between the rotor and the surrounding gas, typically air. When the windage losses become too high, the integrated machine configuration is no longer convenient and the use of standard machine becomes more appropriate. Alternatively, a sealing system with dry gas seals (=DGS) may be added in the integrated machine configuration in order to separate the motor chamber from the main flow at high pressure. Nevertheless, the use of dry gas seals would lose one of the main advantages of the integrated machine that is the absence of sealing system which typically affect the reliability of the machine.

[0004] Therefore, it would be desirable to have an integrated machine with high efficiency even when the expander and the compressor works at high pressure, i.e. an integrated machine having low windage losses even when the expander and the compressor works at high pressure.SUMMARY

[0005] According to an aspect, the subject-matter disclosed herein relates to an expander and motor-compressor unit comprising an electric motor with a stator part and a rotary part, a compressor impeller mechanically coupled to a first end of the rotary part of the electric motor through a rotating shaft and configured to compress a process gas, an expander impeller mechanically coupled to a second end of the rotary part of the electric motor through the rotating shaft and configured to expand the process gas and a casing comprising a first inner wall and a second inner wall. The first and second inner walls form a main chamber in which the electric motor is located and two secondary chambers in which the compressor impeller and the expander impeller are located respectively. The expander and motor-compressor unit further comprise a depressurizing element fluidly coupled to the main chamberand configured to reduce the pressure inside the main chamber. The depressurizing element is further fluidly coupled to the compressor impeller and to the expander impeller so that the depressurizing element is configured to receive process gas from the expander impeller, to extract process gas from the main chamber to be mixed with the received process gas and to discharge the mixed process gas to the compressor impeller.BRIEF DESCRIPTION OF THE DRAWINGS

[0006] 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 shows a schematic longitudinal section of a first embodiment of an innovative expander and motor-compressor unit with a depressurizing element,Fig. 2 shows a schematic longitudinal section of a second embodiment of an innovative expander and motor-compressor unit a depressurizing element, andFig. 3 shows a more detailed diagram of the depressurizing element of Fig. 2.DETAILED DESCRIPTION OF EMBODIMENTS

[0007] According to an aspect, the subject-matter disclosed herein relates to an innovative expander and motor-compressor unit in which a process gas is expanded in an expander and the power generated by the expansion through an electric motor is at least partly recovered as compression work by the compressor. The expander, the compressor and the electric motor are enclosed in a casing which is provided with a respective chamber for each turbomachinery and the engine. In order to reduce the pressure inside thechamber that houses the electric motor (which would increase during operation of the unit due to the leakage of the process gas and which would impact the efficiency of the electric motor), the innovative expander and motorcompressor unit is provided with an element for depressurizing the chamber in which the electric motor is located. Advantageously, the depressurizing element is an ejector or a vacuum pump impeller which sucks part of the process gas from the chamber of the electric motor and supplies it to the compressor suction.

[0008] Reference now will be made in detail to embodiments of the disclosure, examples of which are illustrated in the drawings. The examples and drawing figures are provided by way of explanation of the disclosure and should not be construed as a limitation of the disclosure. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the scope or spirit of the disclosure. In the following description, similar reference numerals are used for the illustration of figures of the embodiments to indicate elements performing the same or similar functions. Moreover, for clarity of illustration, some references may be not repeated in all the figures.

[0009] Referring now to the drawings, Fig. 1 shows, for example and without limitation, a schematic longitudinal section of a first embodiment of an innovative expander and motor-compressor unit in which the depressurizing element is an ejector (generally indicated with reference numeral 100 and referred in the following as “unit 100”). A second embodiment 200 of an innovative expander and motor-compressor unit in which the depressurizing element is a vacuum pump impeller will be described in the following with the aid of Fig. 2. It is to be noted that elements 10, 11, 12, 15, 20, 30, 40, 50, 51, 52, 60, 61 and 62 in Fig. 2 may be identical or similar respectively to elements whit the same reference in Fig. 1 and perform the same or similar functions.

[0010] With non-limiting reference to Fig. 1, the unit 100 comprises an electric motor 10, a compressor impeller 20 configured to compress a process gas and an expander impeller 30 configured to expand a process gas; advantageously, the process gas expanded by the expander impeller 30 is recirculated to the compressor impeller 20 to be compressed. Advantageously, the process gas is carbon dioxide CO2, in particular carbon dioxide CO2 in supercritical conditions.

[0011] The electric motor 10 comprises a stator part 11 and a rotary part 12, in particular the rotary part 12 is configured to be enclosed in the stator part11 and to rotate inside the stator part 11. As it will better explained in the following, the compressor impeller 20 and the expander impeller 30 are mechanically coupled to the electric motor 10, specifically to the rotary part12 of the electric motor 10 through a rotating shaft 15.

[0012] The unit 100 further comprises a casing 50 in which the compressor impeller 20, the expander impeller 30 and the rotating shaft 15 are located. The casing 50 comprises further a first inner wall 51 and a second inner wall 52, so to form a main chamber 60, in which the electric motor 10 is located, and two secondary chambers 61 and 62 in which the compressor impeller 20 and the expander impeller 30 are located respectively.

[0013] In particular, the two secondary chambers 61 and 62 are located at the two opposite ends of the main chamber 60. In fact, the compressor impeller 20 is mechanically coupled to a first end of the rotary part 12 of the electric motor 10 through the rotating shaft 15, while the expander impeller 30 is mechanically coupled to a second end of the rotary part 12 of the electric motor through the rotating shaft 15. In other words, the rotating shaft 15 is a common shaft of the compressor impeller 20, the rotary part 12 of the electric motor 10 and the expander impeller 30.

[0014] With non-limiting reference to Fig. 1, the first inner wall 51 comprisesa first through hole surrounding the rotating shaft 15. Advantageously, the first inner wall 51 comprises a contacting sealing system, in particular a labyrinth sealing system, in order to limit process gas leakage from the secondary chamber 61 to the main chamber 60. However, the leakage of process gas may not be prevented, therefore there will always be a small amount of process gas which may leakage from the secondary chamber 61 to the main chamber 60, causing an overpressure of the main chamber 60 (and the same, as it will be better explained in the following, may happen from the secondary chamber 62 to the main chamber 60).

[0015] With non-limiting reference to Fig. 1, the second inner wall 52 comprises a second through hole surrounding the rotating shaft 15. Advantageously, the second inner wall 52 comprises a contacting sealing system, in particular a labyrinth sealing system, in order to limit process gas leakage from the secondary chamber 62 to the main chamber 60. However, the leakage of process gas may not be prevented, therefore there will always be a small amount of process gas which may leakage from the secondary chamber 62 to the main chamber 60, causing an overpressure of the main chamber 60.

[0016] The unit 100 further comprises a depressurizing element 170 fluidly coupled to the main chamber 60 and configured to reduce the pressure inside the main chamber 60. As it will be described below, the depressurizing element 170 is advantageously configured to extract (i.e. suck) process gas from the main camber 60 so to reduce the pressure and limit the windage losses of the electric motor 10.

[0017] Advantageously, the depressurizing element is an ejector (see e.g. Fig. 1). The depressurizing element 170 is further fluidly coupled to the compressor impeller 20 and to expander impeller 30, in particular being located downstream the expander impeller 30 and upstream the compressor impeller 20, so that the depressurizing element 170 is configured to receive process gasfrom the expander impeller 30, to extract process gas from the main chamber 60 to be mixed with the process gas received from the expander impeller 30 and to discharge the mixed process gas to the compressor impeller 20, in particular to an inlet of the compressor impeller 20.

[0018] It is to be noted that the depressurizing element 170 is advantageously further configured to cool the electric motor 10 and possibly its electrical connection. In particular, the process gas extracted from the main chamber 60 by the depressurizing element 170 may remove heat from the electric motor 10 and possibly from its electrical connection.

[0019] With non-limiting reference to Fig. 1, the unit 100 may further comprise a cooling unit 40, for example a shell-and-tube heat exchanger or a compact cooler, configured to remove heat from the process gas, in particular to restore the process gas temperature to compressor inlet conditions. It is to be noted that Fig. 1 shows that the cooling unit 40 is located downstream the depressurizing element 170 and upstream the compressor impeller 20. However, according to another configuration, the cooling unit 40 may be located downstream the expander impeller 30 and upstream the depressurizing element 170.

[0020] According to the second embodiment shown in Fig. 2, the depressurizing element 270 is a vacuum pump impeller. Advantageously, the depressurizing element 270 is integrated with the compressor impeller 20. With non-limiting reference to Fig. 3, the vacuum pump impeller comprises a row of blades located on the back of the compressor impeller 20, so that it rotates together with the compressor impeller 20.

[0021] According to the embodiment shown in Fig. 2, the first through hole surrounds a portion of the compressor impeller 20, in particular the first through hole surrounds the rear end portion of the compressor impeller 20 so that the depressurizing element 270 is located into the main chamber 60 andthe compressor impeller 20 is located in the secondary chamber 61.

[0022] With non-limiting reference to Fig. 2, the depressurizing element 270 is further fluidly coupled to the compressor impeller 20 and to expander impeller 30, in particular being located downstream the expander impeller 30 and upstream the compressor impeller 20, so that the depressurizing element 270 is configured to receive process gas from the expander impeller 30, to extract process gas from the main chamber 60 to be mixed with the process gas received from the expander impeller 30 and to discharge the mixed process gas to the compressor impeller 20, in particular to an inlet of the compressor impeller 20.

[0023] With non-limiting reference to Fig. 2, the unit 200 may further comprise a cooling unit 40, for example a shell-and-tube heat exchanger or a compact cooler, configured to remove heat from the process gas, in particular to restore the process gas temperature to compressor inlet conditions. It is to be noted that Fig. 2 shows that the cooling unit 40 is located downstream the depressurizing element 270 and upstream the compressor impeller 20. However, according to another configuration, the cooling unit 40 may be located downstream the expander impeller 30 and upstream the depressurizing element 270.

[0024] It is to be noted that the depressurizing element 270 is advantageously further configured to cool the electric motor 10 and possibly its electrical connection. In particular, the process gas extracted from the main chamber 60 by the depressurizing element 270 may remove heat from the electric motor 10 and possibly from its electrical connection.

Claims

CLAIMS1. Expander and motor-compressor unit (100, 200) comprising:An electric motor (10) comprising a stator part (11) and a rotary part (12);A compressor impeller (20) mechanically coupled to a first end of the rotary part (12) of the electric motor (10) through a rotating shaft (15) and configured to compress a process gas;An expander impeller (30) mechanically coupled to a second end of the rotary part (12) of the electric motor (10) through the rotating shaft (15) and configured to expand the process gas;A casing (50) comprising a first inner wall (51) and a second inner wall (52); wherein the first and second inner walls (51, 52) form a main chamber (60) in which the electric motor (10) is located and two secondary chambers (61, 62) in which the compressor impeller (20) and the expander impeller (30) are located respectively; wherein the expander and motor-compressor unit (100) further comprises a depressurizing element (170, 270) fluidly coupled to the main chamber (60) and configured to reduce the pressure inside the main chamber (60), wherein the depressurizing element (170, 270) is further fluidly coupled to the compressor impeller (20) and to the expander impeller (30) so that the depressurizing element (170, 270) is configured to receive process gas from the expander impeller (30), to extract process gas from the main chamber (60) to be mixed with the received process gas and to discharge the mixed process gas to the compressor impeller (20).

2. Expander and motor-compressor unit (100, 200) of claim 1, wherein the first inner wall (51) comprises a first through hole surrounding the rotating shaft (15) or a portion of the compressor impeller (20).

3. Expander and motor-compressor unit (100, 200) of claim 2, wherein the first inner wall (51) further comprises a contacting sealing system arranged at the first through hole in order to limit the leakage of process gas from the first secondary chamber (61) to the main chamber (60).

4. Expander and motor-compressor unit (100, 200) of claim 1, wherein the second inner wall (52) comprises a second through hole surrounding the rotating shaft (15).

5. Expander and motor-compressor unit (100, 200) of claim 4, wherein the second inner wall (52) further comprises a contacting sealing system arranged at the second through hole in order to limit the leakage of process gas from the second secondary chamber (62) to the main chamber (60).

6. Expander and motor-compressor unit (100, 200) of claim 1, wherein the depressurizing element (170, 270) is located downstream the expander impeller (30) and upstream the compressor impeller (20).

7. Expander and motor-compressor unit (100, 200) of claim 1, wherein the depressurizing element (170, 270) is further configured to cool the electric motor (10) through the process gas extracted from the main chamber (60).

8. Expander and motor-compressor unit (100) of claim 1, wherein the depressurizing element (170) is an ejector.

9. Expander and motor-compressor unit (200) of claim 1, wherein the depressurizing element (270) is a vacuum pump impeller.

10. Expander and motor-compressor unit (200) of claim 9, wherein the depressurizing element (270) is integrated with the compressor impeller (20).

11. Expander and motor-compressor unit (100, 200) of claim 1, further comprising a cooling unit (40) located downstream the expander impeller (30) and upstream the depressurizing element (170, 270) or downstream the depressurizing element (170, 270) and upstream thecompressor impeller (20), wherein the cooling unit (40) is configured to remove heat from the process gas.

12. Expander and motor-compressor unit (100, 200) of claim 1, wherein the process gas is carbon dioxide (CO2), in particular carbon dioxide (CO2) in supercritical conditions.

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