Multistage turboexpander

Abstract

Turboexpander (100, 200, 300) for expanding high-pressure ratio gas, comprising: a plurality of hollow impellers (EXP (1); EXP (2);....EXP(J)) configured in multiple stages; and a tie rod to pass through each of the plurality of hollow impellers (EXP (1); EXP (2);.... EXP(J)), wherein the plurality of hollow impellers (EXP (1); EXP (2);.... EXP(J)) are stacked together and tightened through the tie rod disposed in a rotor (120, 220, 320); wherein the turboexpander (100, 200, 300) comprises a first radial bearing (130, 230, 330), and a second radial bearing (140, 240, 340).

Description

TITLEMULTISTAGE TURBOEXPANDERDESCRIPTIONTECHNICAL FIELD

[0001] The subject matter disclosed herein relates to a turboexpander relevant to high-pressure ratio gas expansion, in particular to a multistage turboexpander. The subject matter disclosed herein relates also to a corresponding method. A particularly advantageous field of application for the turboexpander is in applications with low molecular weight gas, such as hydrogen or hydrogen mixtures, and high rotational speed.BACKGROUND ART

[0002] In general, a turboexpander, also known as a turbo-expander or an expansion turbine, is a centrifugal or axial-flow turbine, through which a high- pressure gas is expanded to produce work that is often used to drive a compressor or generator.

[0003] Typically, turboexpanders have few impellers and integrally geared mechanical configurations for several reasons: each additional stage introduces additional losses due to friction, turbulence, and other aerodynamic inefficiencies. These losses can outweigh the energy gains from additional gas expansion. Integrally geared configurations are needed to interface with electrical generators, but with additional complexity for multiple pinions design, resulting in more components that can fail, increased difficulty in design and manufacturing, and heightened maintenance complexity.

[0004] Moreover, more impellers decrease the compactness of the solution andrequire connecting piping between each expansion stage.

[0005] Each additional impeller also increases production, installation, and maintenance costs, making the turboexpander less economically feasible. Managing and controlling a system with numerous impellers can be complex, necessitating advanced and costly control systems.

[0006] For these reasons, turboexpander design typically limits the number of impellers to balance efficiency, complexity, costs, and operational stability.

[0007] Therefore, a turboexpander with multiple impellers could enhance gas expansion efficiency, enabling improved pressure and temperature reduction, and potentially extracting more energy from the expanding gas to increase mechanical or electrical power output.

[0008] Furthermore, multi -impeller turboexpanders may operate across a wider range of conditions, enhancing versatility for various industrial applications.

[0009] Patent ITMI20100684 Al describes a stacked rotor with tie rods and bolted flanges; this invention involves a compressor comprising a first full hub, a second full hub and a plurality of impellers., wherein the plurality of impellers are inserted on a tie rod.

[0010] Patent US8985945 describes a uniaxial multi-stage radial gas expander designed to provide a single-shaft (uniaxial) multistage radial gas expander capable of withstanding high-pressure, high-pressure ratio conditions. In one embodiment of this invention an even number of sections are arranged in a back-to-back, or front to front configuration, with an equivalent number of impellers for each section to compensate for the axial thrust, assisting axial load balancing.

[0011] Several patent documents disclose multistage turboexpandertechnologies, reflecting the industry's strong interest in systems capable of handling high pressures and rotational speeds. For instance, US 2024 / 026895 Al introduces advanced configurations for high-pressure gas expansion, while WO 2022 / 228727 Al and US10809000B2, both filed by Nuovo Pignone Tecnologie Sri, focus on enhancing the mechanical efficiency and robustness of turboexpanders. CN 111042921 A targets automotive applications, and EP 2009286 Bl (Siemens AG) along with WO2012145486A2 (Dresser-Rand) describe well-established architectures for radial and axial expanders.

[0012] Despite these developments, existing solutions still face limitations. Integrally geared designs often introduce mechanical complexity, making systems harder to manufacture and maintain. Additionally, managing multiple expansion stages can be challenging, particularly when axial thrust balancing relies on symmetrical impeller arrangements or complex mechanical layouts.

[0013] It would be desirable to adopt a high-speed rotation turboexpander, particularly a multistage turboexpander with stacked multiple impellers, able to achieve high rotational speeds in a compact design without limiting the number of expansion sections and the relevant impeller number, with the introduction of an axial bearing to guarantee the required design flexibility.SUMMARY

[0014] According to a first aspect a turboexpander for expanding high- pressure ratio gas, comprises: a plurality of hollow impellers configured in multiple stages; and a tie rod to pass through each of the plurality of hollow impellers, wherein the plurality of hollow impellers is stacked together and tightened through the tie rod disposed in a rotor.

[0015] According to a second aspect a rotor of the turboexpander for expanding high-pressure ratio gas, wherein the rotor comprises: two tie rods disposed in the rotor and mutually connected through an intermediate hub; andat least an intermediate bearing disposed in correspondence with the intermediate hub.BRIEF DESCRIPTION OF THE DRAWINGS.

[0016] A more complete appreciation of the disclosed embodiments of the subject matter 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 view of a first embodiment of an innovative multistage turboexpander;Fig. 2 shows a schematic view of the first embodiment with an intermediate bearing of the innovative turboexpander of Fig. 1;Fig. 3 shows a schematic view of a second embodiment of an innovative turboexpander;Fig. 4 shows a schematic view of the second embodiment with an intermediate bearing of the innovative turboexpander of Fig. 3;Fig. 5 shows a schematic view of a third embodiment of an innovative turboexpander;Fig. 6 shows a schematic view of the third embodiment with an intermediate bearing of the innovative multistage turboexpander of Fig. 4;Fig. 7 shows a schematic view of a rotor of the innovative turboexpander.DETAILED DESCRIPTION OF EMBODIMENTS

[0017] The subject -matter disclosed herein relates to an innovative turboexpander, for expanding high-pressure ratio gas i.e. a turboexpander morecompact and with a relevant number of impellers compared to known turboexpanders thanks to a plurality of hollow impellers arranged in multiple stages, stacked together, and tightened through a tie rod disposed in a rotor.

[0018] The subject -matter disclosed is able to achieve high rotational speeds in a compact design without limiting the number of expansion sections and the relevant impeller number, with the introduction of an axial bearing to provide better control and stability of the rotating components, reducing vibrations and wear. In particular an axial bearing is used to balance the thrust forces generated by the plurality of impellers in the turboexpander.

[0019] In other word the innovative turboexpander is a multistage turboexpander for expanding high-pressure ratio gas provided with a plurality of hollow impellers, wherein these impellers are arranged in multiple stages. A tie rod is incorporated into the design. This rod passes through each of the hollow impellers, which are stacked together and tightened through the tie rod. This assembly is then positioned within a stator, ensuring the efficient operation of the turboexpander.

[0020] Advantageously, the innovative turboexpander has a plurality of embodiments that allow for achieving high rotational speeds with relevant impeller number:

[0021] A first embodiment with a plurality impellers arranges in multiple stages; preferably with intermediate bearing, provides better control over the expansion process, leading to more stable and reliable process.;

[0022] A second embodiment with a plurality impeller arranges in multiple stages back-to-back, preferably with intermediate bearing, offers high compatibility with the process gas and better supports the high number of impellers.

[0023] A third embodiment with a plurality impellers arranges in multiple stages multistage back to back with overhung wheel, preferably with intermediate bearing, reduces the load on bearings and enhances the overall stability of the system turboexpander. The overhung wheel design can lead to a more compact and lightweight turboexpander. In this case the back-to-back configuration can be applied to both axial and radial stages.

[0024] Also the subject -matter disclosed herein relates to a rotor of the turboexpander for expanding high-pressure ratio gas, wherein the rotor comprises: two tie rods disposed in the rotor and mutually connected through an intermediate hub; and at least an intermediate bearing disposed in correspondence with the intermediate hub.

[0025] Reference now will be made in detail to embodiments of the disclosure, an example of which is illustrated in the drawings. Each example is provided by way of explanation of the disclosure, not 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 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 figures.

[0026] In Figures 1-6 are schematically shown a plurality of embodiments of an innovative turboexpander. The innovative turboexpander is generally indicated with reference numeral 100 in Figures 1 and 2, with reference numeral 200 in Figures 3 and 4, and with reference numeral 300 in Figures 5 and 6.

[0027] Typically, with non-limiting reference to Figures 1-6 theturboexpander 100, 200, 300 for expanding high-pressure ratio gas, , comprises: a plurality of hollow impellers (EXP (1); EXP (2);.... EXP(J)) configured in multiple stages; and a tie rod to pass through each of the plurality of hollow impellers (EXP (1); EXP (2); .... EXP(J)), wherein the plurality of hollow impellers (EXP (1); EXP (2);.... EXP(J)) are stacked together and tightened through the tie rod disposed in a rotor 120, 220, 320.

[0028] Preferably the hollow impellers consist of bladed disks, and the cavity refers to a concentric bore that allows the passage of the tie rod, in particular, the impellers are stacked and clamped together by the tie rod to form a rotor.

[0029] Advantageously the turboexpander (100, 200, 300) comprises a first radial bearing (130, 230, 330), and a second radial bearing 140, 240, 340 which provide enhanced rotor stability and minimize vibration during highspeed operation.

[0030] Preferably the turboexpander 100, 200, 300 comprises moreover at least an intermediate radial bearing 150, 250, 350, the use of three or more radial bearings in a turboexpander represents a particularly advantageous design choice, especially in high-speed applications involving light gases such as hydrogen. Unlike the traditional configuration — which typically includes two radial bearings and one thrust bearing to manage axial loads — the three- radial-bearing solution allows for a more balanced distribution of loads along the rotor axis, improving the system’s dynamic stability. This is especially beneficial for long or flexible rotors that are more susceptible to vibration and deflection.

[0031] Advantageously the innovative turboexpander, is a hydrogen or hydrogen mixture expander, for expanding high-pressure ratio gas with a rangefrom 50 to 300 bar.

[0032] Advantageously each of the plurality of hollow impellers (EXP (1); EXP (2);... . EXP(J)) have a hirth mechanism coupling them to each other, the hirth mechanism can help achieve better balance of the plurality of hollow impellers in the turboexpander, reducing vibrations and enhancing the lifespan of the machine.

[0033] Considering Fig. l, Fig.3 and Fig 5, the turboexpander 100, 200, 300 of claim 1, comprising first bearing 130, 230, 330 provided at first end of the rotor 120, 220, 320.

[0034] According to first and second embodiment show in Fig. 1 and in Fig. 3 the turbo expander 100, 200 comprises a second bearing 140, 240, disposed at second end of the rotor 120, 220 and, according to Fig. 2 and Fig.4 the turbo expander 100, 200 comprises at least the intermediate radial bearing bearing 150, 250 disposed on the rotor 120, 220.

[0035] Advantageously the turboexpander 100, 200, 300 comprising magnetic bearings, in particular the first, the second and at least the intermediate radial bearing may be magnetic bearing. The magnetic bearing, in the turboexpander, eliminates the need for oil lubrication, thereby reducing maintenance requirements and potential contamination risks. Furthermore, it can be directly incorporated into the process gas stream, eliminating the need for a dry gas seal, reducing potential points of failure.

[0036] With non-limiting reference to Fig. 2, at least the intermediate radialbearing 150 of the turboexpander 100 is disposed on the intermediate section of the rotor 120.

[0037] The term “intermediate section of the rotor” refers to the portion of the rotor where the two tie rods are mutually connected via an intermediatehub. This hub houses at least the intermediate radial bearing, which provides additional radial support to the rotor shaft.

[0038] Advantageously, the turboexpander 100 is a radial turboexpander, and according to first embodiment shown in Fig. 1 the gas enters through a radial inlet 180 at the first impeller of the plurality impeller (EXP (1), EXP (2,) .. EXP(J)) and after expansion the gas exits through a radial outlet 190 at the last impeller of the plurality impeller EXP (1), EXP (2,) ...EXP(J)).

[0039] According to second and third embodiments shown in Fig. 3 and in Fig. 5, the turboexpander 200, 300 comprises also first and second sections 260, 360; 270, 370 with a back-to-back connection, wherein the output of the first section 260, 360 is the input of the second section 270, 370.

[0040] Advantageously the turboexpander 200, 300 further comprises the plurality of hollow impellers (EXP(l), EXP(2), EXP (j)) disposed in the second section 270, 370, and a plurality of hollow impellers (EXP(l), EXP(2), EXP (k)) are disposed in the first section 260, 360, wherein j ^k

[0041] In other words, the turboexpander comprises two sections, and each section contains a variable number of hollow impellers with a back-to- back connection. In fact, in this invention, the balance is not provided by the equal number of hollow impellers present in each of two sections, but by the presence of at least one axial bearing.

[0042] Advantageously the axial bearing, physically connected to the rotor of the turboexpander, is able to balance the thrust forces generated by the plurality of impellers in the turboexpander. In particular the turboexpander might include a combined axial and radial bearing.

[0043] A combined axial and radial bearing in a turboexpander withmultiple impellers is able to handle both axial and radial loads, ensuring operational stability and efficiency. These bearings are crucial in high-speed and high-precision applications like turboexpanders, where the forces generated by the impellers can be significant. In particular, as shown in Fig. 4, third bearing 250 is disposed in the first section 260, or in the second section 270 on the rotor 220, in an intermediate position.

[0044] Advantageously the turboexpander 200 as shown in Fig. 3 and Fig. 4, is a radial turboexpander, wherein the gas enters through a radial inlet 280 in a first section 260, and after expansion the gas exits through a radial outlet 290 in a second section 270.

[0045] According to third embodiment shown in the Fig. 5 and Fig. 6 the turboexpander 300 comprising a radial inlet 380 in a first section 360 and an axial outlet 391 in a second section 370, wherein the gas enters through a radial inlet 380 in the first section 360, and after expansion, the gas exits through an axial outlet 391 parallel to the rotor 320.

[0046] Advantageously the turboexpander 300, as shown in Fig. 5, comprises a second bearing 340, wherein the second bearing 340 is disposed on the rotor 320 in the second section 370 before the last impeller of the plurality of hollow impellers.

[0047] Considering Fig. 6 the turboexpander 300, comprising the second bearing 340 and a third bearing 350, wherein bearing 350 is disposed on the rotor 320 in an intermediate position.

[0048] Fig. 7 shows a rotor 420 of the turboexpander for expanding high-pressure ratio gas, wherein the rotor 420 comprises: two tie rods 421, 422 disposed in the rotor 420 and mutually connected through a intermediate hub 410; and at least an intermediate bearing 450 disposed in correspondence with the intermediate hub 410. It is to be noted that the rotor, comprising further: afirst hub 411 disposed at the end of a first of the two tie rods 421, 422; a second hub disposed at the end of a second of the two tie rods 421, 422, a first and a second bearings 440, 430 respectively disposed in correspondence with the first and second hub 411, 412.

[0049] According to first embodiment of Fig. 1, to second embodiment of Fig. 3, and to third embodiment of Fig. 5 the intermediate hub 410 facilitates the mutual connection between two tie rods 421, 422 of the rotor 420.

Claims

CLAIMS1. A turboexpander (100, 200, 300) for expanding high-pressure ratio gas, comprises: a plurality of hollow impellers (EXP (1); EXP (2); .... EXP(J)) configured in multiple stages; and a tie rod to pass through each of the plurality of hollow impellers (EXP (1); EXP (2);.... EXP(J)), wherein the plurality of hollow impellers (EXP (1); EXP (2);.... EXP(J)) are stacked together and tightened through the tie rod disposed in a rotor (120, 220, 320);wherein the turboexpander (100, 200, 300) comprises a first radial bearing (130, 230, 330), and a second radial bearing (140, 240, 340)2. The turboexpander (100, 200, 300) of claim 1, wherein the turboexpander (100, 200, 300) comprises at least an intermediate radial bearing (150, 250, 350).

3. The turboexpander (100, 200, 300) of claim 1, wherein each of the plurality of hollow impellers (EXP (1); EXP (2);.... EXP(J)) have a hirth mechanism coupling them to each other.

4. The turboexpander (100, 200, 300) of claim 1, wherein the first bearing (130, 230, 330) provided at first end of the rotor (120, 220, 320).

5. The turbo expander (100, 200) of claim 1, wherein the second bearing (140, 240,) disposed at second end of the rotor (120, 220) and at least the intermediate radial bearing (150, 250) disposed on the rotor (120, 220).

6. The turboexpander (100) of claim 4, wherein at least the intermediate radial bearing (150) is disposed on the intermediate section of the rotor (120).

7. The turboexpander (100) of claim 1, wherein the turboexpander (100) is a radial turboexpander, the gas enters through a radial inlet (180) at the first impeller of the plurality impeller (EXP (1), EXP (2,) ...EXP(J)) and after expansion the gas exits through a radial outlet (190) at the last impeller of theplurality impeller EXP (1), EXP (2,) ...EXP(J)).

8. The turboexpander (200, 300) of claim 1, further comprising : first and second sections (260, 360; 270, 370) with a back-to-back connection, wherein the output of the first section (260, 360) is the input of the second section (270, 370);- the plurality of hollow impellers (EXP(l), EXP(2), EXP (j)) are disposed in the second section (270, 370), and a plurality of hollow impellers (EXP(l), EXP(2), EXP (k)) are disposed in the first section (260, 360), wherein j fk .

9. The turboexpander (200, 300) of claim 7, comprising an axial bearing physically connected to the rotor (220, 320).

10. The turboexpander (200) of claims 4 and 7, wherein at least the intermediate radial bearing (250) is disposed in the first section (260), or in the second section (270) on the rotor (220), in an intermediate position.

11. The turboexpander (200) of claim 7, wherein the turboexpander (200) is a radial turboexpander, the gas enters through a radial inlet (280) in the first section (260), and after expansion the gas exits through a radial outlet (290) in the second section (270).

12. The turboexpander (300) of claim 7, comprising a radial inlet (380) in a first section (360) and an axial outlet (391) in the second section (370), wherein the gas enters through a radial inlet (380) in the first section (360), and after expansion, the gas exits through an axial outlet (391) parallel to the rotor (320).

13. The turboexpander (300) of claim 7, comprising the second bearing (340), wherein the second bearing (340) is disposed on the rotor (320) in the second section (370) upstream of the last impeller of the plurality of hollowimpellers.

14. The turboexpander (300) of claim 12, comprising the second bearing (340) and at least the intermediate radial bearing (350), wherein at least the intermediate radial bearing (350) is disposed on the rotor (320) in an intermediate position.

15. The turboexpander (100, 200, 300) of claim 2, wherein at least the intermediate radialbearing (150, 250, 350) is a magnetic bearing.

16. The turboexpander (100, 200, 300) of claim 1, comprising magnetic bearings.

17. The turboexpander (100, 200, 300) of claim 1, wherein the turboexpander (100, 200, 300) is a hydrogen or hydrogen mixture expander.

18. The turboexpander (100, 200, 300) of any precedent claims , comprising a rotor (420) for expanding high-pressure ratio gas, wherein the rotor (420) comprises: two tie rods (421, 422) disposed in the rotor (420) and mutually connected through an intermediate hub (410); and at least an intermediate bearing (450) disposed in correspondence with the intermediate hub (410).

19. The turboexpander (100, 200, 300) of claim 18, wherein the rotor (420) comprises: a first hub (411) disposed at the end of a first of the two tie rods (421, 422); a second hub (412) disposed at the end of a second of the two tie rods (421, 422), a first and a second bearings (440, 430) respectively disposed in correspondence with the first and second hub (411, 412).

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