Expander and manufacturing method

Description

1 / 19 EXPANDER AND MANUFACTURING METHOD TECHNICAL FIELD

[0001] The present disclosure relates to gas expanders particularly adapted for use in oxy-fuel power cycles operating with process gas at high pressures, for example, CO2 cycles, such as Aliam cycles, also called NET power cycles. The present disclosure further relates to methods for mounting rotors for supercritical carbon dioxide expanders. BACKGROUND OF THE TECHNIQUE

[0002] Fossil fuels are an important source of chemical energy used for the generation of mechanical power. Fossil fuels are mixed with air and burned to generate a high-pressure, high-temperature combustion gas, which expands in a turbine or expander. The expander converts the enthalpy of the combustion gas into mechanical power available at the expander's output shaft and used to drive a load, such as a compressor or compressor train, or to turn an electric generator and convert mechanical power into electrical energy.

[0003] One of the main concerns regarding the combustion of fossil fuels relates to the production of carbon dioxide, a greenhouse gas considered one of the main contributors to global warming and climate change.

[0004] To reduce the environmental impact of power generation through the combustion of fossil fuels, the option of post-combustion carbon dioxide capture has been investigated. Carbon dioxide capture facilities have been developed to process exhaust flue gases from gas turbines and remove carbon dioxide from them before discharging the flue gases into the environment. The costs of a carbon dioxide capture facility are high, both Petition 870250085842, dated 09 / 23 / 2025, page 54 / 139 2 / 19 in terms of CAPEX, as well as in terms of energy required to operate the facility, which reduces the overall thermodynamic efficiency of the system, since the percentage of carbon dioxide in the flue gas is low. This requires large volumes of flue gas to be processed through the carbon dioxide capture facility and makes the capture process particularly inefficient.

[0005] In recent years, oxy-combustion cycles, also known as oxy-fuel cycles, have been developed, in which the fuel, such as natural gas or another fossil fuel, is blended into a mixture of an oxidant consisting mainly of oxygen (O2) and carbon dioxide (CO2) at high pressure. The blend of fuel, oxygen, and carbon dioxide burns in a combustor of an expander, producing a pressurized combustion gas consisting exclusively or almost exclusively of carbon dioxide and water.

[0006] The combustion gas is expanded in the expander to generate mechanical power. The exhausted combustion gas discharged on the discharge side of the expander is cooled in a regenerative heat exchanger and further chilled to condense water which can thus be removed from the chilled combustion gas. The low-temperature combustion gas, consisting mainly or exclusively of carbon dioxide, is pressurized and recycled through the regenerative heat exchanger towards the expander combustor.

[0007] The oxygen supplied to the expander combustor can be obtained by separating the ambient air, removing nitrogen from it, so that the working fluid supplied to the combustor consists mainly of oxygen and carbon dioxide and does not include nitrogen. The resulting combustion gas consists mainly of water and carbon dioxide. The water is removed from the combustion gas by condensation, and the portion of the water-free combustion gas that is not recycled to the combustor, Petition 870250085842, dated 09 / 23 / 2025, page 55 / 139 3 / 19 can be efficiently processed in a carbon dioxide capture unit.

[0008] The oxy-fuel cycle summarized above is a semi-closed cycle, in which only a fraction of the combustion gas exits the cycle after the water has been removed from it.

[0009] Oxy-fuel or oxy-combustion cycles, such as those described above, are particularly interesting in terms of efficiency and reduction of harmful emissions. However, they operate under supercritical CO2 conditions at the expander inlet and are characterized by a high pressure drop across the expander and a high torque applied to the expander rotor. These factors become critical and raise serious challenges in the expander rotor design when the expander's rated power increases, and may represent limitations to the expander's maximum power rate.

[0010] An innovative expander adapted to achieve higher power rates, for example, in an oxy-fuel cycle or other supercritical carbon dioxide cycle, would be welcome in the art. SUMMARY

[0011] An expander for a supercritical carbon dioxide thermodynamic cycle is disclosed herein. As understood in the present invention, a supercritical carbon dioxide thermodynamic cycle is a cycle in which the carbon dioxide is in a supercritical condition at least at the inlet of the expander.

[0012] The expander comprises an outer compartment, a combustor combined with the outer compartment, and a rotor with a rotating shaft, housed for rotation in the outer compartment. The rotor comprises a rear shaft portion and a front shaft portion. Between the rear shaft portion and the front shaft portion, a plurality of rotor discs are arranged. Each rotor disc comprises a Petition 870250085842, dated 09 / 23 / 2025, page 56 / 139 4 / 19 respective annular row of rotor blades. Upstream of each annular row of rotor blades, a respective annular row of stationary blades is provided. Each annular row of stationary blades and the respective annular row of rotor blades form an expander stage.

[0013] The plurality of rotor discs between the rear shaft portion and the front shaft portion are connected to each other by welding - at least one section of the rear shaft portion is welded to a rotor disc further aft among the plurality of rotor discs, that is, to the rotor disc adjacent to the rear shaft portion. Finally, at least one portion of the front shaft portion is welded to a rotor disc further forward among the plurality of rotor discs, that is, to the rotor disc adjacent to the front shaft portion.

[0014] The resulting rotor is thus formed by a plurality of components, each of which can be manufactured separately and can be made of a temperature-resistant metal alloy. As the individual components are small compared to the entire rotor, manufacturing with high-temperature metal alloys, such as a nickel-based alloy, is simple. Welding the individual components results in a large rotor, which can include a large number of annular rows of rotor blades, corresponding to a large number of expansion stages. Welding results in a strong structure adapted to withstand the high pressures and high torques that typically develop in a supercritical carbon dioxide expander.

[0015] The suggested design can be used to achieve high power ratings, preferably higher than 50 MW, for example, in the order of 100 MW or higher, for example, 150 MW or higher, for example, 200 MW or higher, or 300 MW or higher. In embodiments, the rated power can be lower than 2000 MW, preferably lower than 1500 MW, for example, lower than 1000 or lower than 800 MW. For example, the rated power can be comprised Petition 870250085842, dated 09 / 23 / 2025, page 57 / 139 5 / 19 between 200 MW and 650 MW. Intermediate values ​​of the upper and lower limits of each range mentioned above are also expressly revealed here.

[0016] Additional features and modalities are described below and presented in the attached claims.

[0017] The present disclosure also relates to a method of manufacturing a rotor for a supercritical carbon dioxide expander and a thermodynamic cycle that uses said expander. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Now, brief reference is made to the attached drawings, in which: Figure 1 is a schematic of an oxyfuel power circuit; Figure 2 is a cross-sectional view along an expander according to the present disclosure in a first embodiment; Figure 3 is a cross-sectional view of a rotor for the expander of Figure 2 in an additional embodiment, from which the rotating blades have been removed; Figure 4 is an enlargement of a welded area after machining to remove the annular notch. DETAILED DESCRIPTION

[0019] The scheme in Figure 1 illustrates a simplified supercritical carbon dioxide cycle (in short, SCO2 cycle), such as an Aliam cycle or a similar oxy-fuel combustion cycle, in which the use of an expander according to the present disclosure can be particularly beneficial. In general terms, a supercritical carbon dioxide cycle as understood in the present invention is a cycle in which the carbon dioxide is in a supercritical condition at least at the inlet of the expansion flow path in the expander. Petition 870250085842, dated 09 / 23 / 2025, p. 58 / 139 6 / 19

[0020] The power system 1 shown in Figure 1 comprises an expander (also called a turbo-expander) 3 which includes an expansion section 5 and a combustor 7. The combustor 7 may be an annular combustor, a can-type combustor, a can-type annular combustor or similar, for example. In currently preferred embodiments, the combustor is a can-type combustor comprising a plurality of combustion chambers arranged around the axis of rotation of the expander 3, as shown in detail in Figure 2. In some embodiments, as shown schematically in Figure 2, the combustion chambers are housed in a high-pressure compartment of the expander, as will be described in detail below. In some embodiments, each combustion chamber is housed in a respective seat formed in a high-pressure compartment of the expander, as will be described in detail below.

[0021] Reference number 7.1 in Figure 2 designates single combustor chambers of a can or annular can type combustor. In other embodiments, not shown, the combustor may be an annular combustor, as mentioned.

[0022] Combustor 7 is supplied with an oxidant stream distributed by an oxidant source. The oxidant may be oxygen (O2) or a blend comprising or consisting primarily of oxygen and carbon dioxide (CO2). The oxidant stream may be produced by an air separation unit 9, which features an oxidant source. The air separation unit 9 may remove nitrogen or nitrogen and carbon dioxide from ambient air to produce the required oxidant stream which is supplied via an oxidant line 11 to combustor 7 of expander 3. In some embodiments, to facilitate handling of the oxidant stream, the latter may include approximately 20% by volume of oxygen and 80% by volume of carbon dioxide. The percentages of CO2 and O2 mentioned above are examples. The carbon dioxide Petition 870250085842, dated 09 / 23 / 2025, page 59 / 139 7 / 19 carbon can be added to oxygen via a recycling line 12, as explained in detail below.

[0023] Reference number 13 indicates a fuel supply line, for example, adapted to supply natural gas, such as methane, to the combustor 7, specifically to each combustion chamber 7.1. The oxidizer and fuel are supplied on the inlet side of the expander 3 to the combustor 7 at a high pressure. The upper pressure of the thermodynamic cycle may be, for example, 50 barA or higher, preferably 100 barA or higher, for example, around or above 200 barA, preferably around or above 250 barA, or higher, for example, higher than or equal to 300 barA. In general, the pressure may be lower than 800 barA or lower than 600 barA. In some configurations, the upper pressure of the thermodynamic cycle, that is, the pressure in the combustor and in the first expansion stage, can be 100, 150, 200, 250, 300 or 350 barA.

[0024] The oxidizer-fuel mixture is burned in the combustor 7. The resulting pressurized hot combustion gas expands in the expansion section 5 of the expander 3. The temperature on the outlet side of the stationary nozzles downstream of the combustor may be between 800 °C and 1500 °C, for example.

[0025] The exhausted combustion gas is discharged after expansion on a discharge side of the expander 3 into a discharge line 15. The combustion gas in the discharge line 15 may be at a temperature between about 400 °C and about 700 °C, for example, about 600 °C, and at a pressure that may be in the range between about 10 barA and about 100 barA, preferably between about 20 barA and about 60 barA.

[0026] The circuit further comprises a regenerative heat exchanger 17, with the hot combustion gas flowing through a hot side 17.1 of the regenerative heat exchanger 17 being cooled in Petition 870250085842, dated 09 / 23 / 2025, page 60 / 139 8 / 19 heat exchange with a chilled flue gas stream flowing through a cold side 17.2 of the regenerative heat exchanger 17. The flue gas discharged from the hot side 17.1 of the regenerative heat exchanger 17 is further chilled in a cooling heat exchanger 19 to a temperature that causes condensation of water vapor contained in the exhausted flue gas. The condensation water is removed from the exhausted flue gas in a water / gas separator 21.

[0027] The exhausted and dehydrated chilled combustion gas, consisting mainly or exclusively of carbon dioxide, is compressed in a combustion gas compressor 23 to the pressure on the inlet side of the expander 3. Although in the diagram of Figure 1 the combustion gas compressor 23 is pictorially represented as a single compressor, in some embodiments, multiple compressors may be used. For example, the combustion gas compressor 23 may be a multi-stage compressor or a compressor train. In some embodiments, the compressor may be an intercooled compressor. In some embodiments, a main compressor may be arranged in series with two sequentially arranged pumps.

[0028] The compressed combustion gas supplied by the combustion gas compressor 23 is partially removed from the cycle through a discharge line 25. If the compressor 23 is characterized by a plurality of compression turbomachines arranged in series, the discharge line 25 may be connected between two sequentially arranged turbomachines and / or on the discharge side of the most downstream compression turbomachine.

[0029] The remaining compressed flue gas is distributed through the cold side 17.2 of the regenerative heat exchanger 17 and is heated by heat exchange with the hot flue gas flowing through the hot side 17.1 of the regenerative heat exchanger 17 and recycled to the expander 3 via a recycling line 25. The flue gas Petition 870250085842, dated 09 / 23 / 2025, page 61 / 139 9 / 19 recycled through recycling line 25 is mixed with the combustion gas generated in combustor 7 or with the oxidant stream from oxidant line 11.

[0030] A side stream of chilled combustion gas is distributed through a cooling line 27, which bypasses the regenerative heat exchanger 17, towards the expander components 3 that require cooling.

[0031] The expander 3 may include an output shaft end 31 which may be integral with the central portion of the rotor or may be mounted to the central portion of the rotor by bolting, welding, Hirth or groove connections, or similar, or a combination thereof. The mechanical power generated by the expansion of the combustion gas in the expansion section 5 of the expander 3 is available at the output shaft end 31 for mechanical drive or power generation purposes. In the exemplary embodiment of Figure 1, the output shaft end 31 is drive-coupled to an electric generator 33 directly or through a gearbox, a joint or combinations thereof. A flange connection between the output shaft end 31 and the electric generator 33 is shown at 49 in Figure 2. The electric generator 33 is in turn electrically coupled to an electrical power distribution network 35.In Figures 1 and 2, the end of the output shaft 31 is shown on the rear side of the expander 3. In other embodiments, not shown, the end of the output shaft 31 may be arranged on the front side of the expander. In still other embodiments, not shown, two output shaft ends may be provided, one on the front side and the other on the rear side of the expander.

[0032] As used herein, front and rear refer to the direction of process gas flow through the expander 3. Therefore, front indicates a position on the side of the combustor 7, and rear indicates a position on the opposite side of the combustor 7, i.e., the discharge side of the expander 3. Petition 870250085842, dated 09 / 23 / 2025, page 62 / 139 10 / 19

[0033] The high pressure drop across the expander 3, the high absolute pressure in the combustor 7 and in the expander cooling ducts, as well as the high torque applied to the expander shaft, represent serious challenges in the design of expander 3, particularly for high power ratings, for example, at or around 100 MW or higher, such as between 100 MW and 2000 MW, preferably at or above 150 MW and below 2000 MW. The expander, and specifically the rotor design disclosed herein, can be used to achieve high power ratings, preferably higher than 50 MW, for example, on the order of 100 MW or higher, for example, 150 MW or higher, for example, 200 MW or higher, or 300 MW or higher. In these configurations, the nominal power can be lower than 2000 MW, preferably lower than 1500 MW, for example, lower than 1000 MW or lower than 800 MW. For example, the nominal power can be between 200 MW and 650 MW.Intermediate values ​​for the upper and lower limits of each range mentioned above are also expressly revealed here.

[0034] Still referring to Figure 1, Figure 2 illustrates a cross-sectional view of expander 3 in one embodiment. As an example, the expander in Figure 2 includes a rotor in one embodiment. An additional embodiment of an alternative rotor for expander 3 in Figure 2 is shown separately in Figure 3, which is shown separately in Figure 3.

[0035] In some embodiments, the expander 3 comprises an external compartment 41, which houses the combustor 7. In some embodiments, the external compartment 41 includes a main body 41.1, referred to in the present invention as the high-pressure compartment, and a closing system 41.2, referred to in the present invention as the low-pressure exhaust compartment. The high-pressure compartment 41.1 may include a main body that may be monolithic, that is, it may consist of a single piece, for example, manufactured by forging, machining, casting, or combinations thereof. In some embodiments, the Petition 870250085842, dated 09 / 23 / 2025, page 63 / 139 11 / 19 high-pressure compartment 41.1 can be manufactured by welding together a plurality of components, preferably interfaced along a plane orthogonal to the axis of rotation.

[0036] The low-pressure exhaust compartment 41.2 can be positioned on the discharge side, i.e., on the rear side, of the expander 3, i.e., on the opposite side to the combustor 7. The low-pressure exhaust compartment 41.2 can be monolithic, i.e., it can consist of a single piece, for example, manufactured by forging, machining, casting, or combinations thereof. In some embodiments, the low-pressure exhaust compartment 41.2 can be manufactured in two or more components that can be irreversibly connected to each other, for example, by welding, or that can be coupled to each other in a reversible manner, for example, by means of screws or similar. For example, the low-pressure exhaust compartment 41.2 can be divided into two portions along a plane containing the axis of rotation of the expander.

[0037] The high-pressure compartment 41.1 and the low-pressure exhaust compartment 41.2 can be connected to each other along a plane P that is orthogonal to a rotation axis AA of a rotor 43 supported for rotation in the outer compartment 41.

[0038] In some embodiments, the low-pressure exhaust compartment 41.2 forms a discharge volute or a discharge-filled space 41.3, through which the exhausted combustion gas is discharged from the expander 3.

[0039] Reference numbers 45, 47 indicate bearing arrangements that rotatably support rotor 43. For example, bearing arrangement 45 on the opposite side to the combustor 7, i.e., on the rear side, may include an axial or thrust bearing in combination with a radial bearing or a bearing with an axial-radial bearing capacity. Bearing arrangement 47 on the combustor side, i.e., on the Petition 870250085842, dated 09 / 23 / 2025, page 64 / 139 12 / 19 front side, may include a radial bearing. An inverted arrangement is also possible, with a bearing having axial load capacity arranged on the combustor side. Bearing arrangements 45, 47 may be arranged in bearing compartments, not shown in detail.

[0040] In some embodiments, the rotor 43 is surrounded by one or more inner compartments 51, stationarily housed in the outer compartment 41. Each inner compartment 51 may be divided into two portions along a plane parallel to the axis of rotation AA of the rotor 43, for example, a plane containing the axis of rotation AA. The arrangement of the inner compartments 51 and the outer compartment 41 is particularly beneficial when the combustion gas reaches high pressures, around 200 to 300 barA or higher. The monolithic high-pressure compartment 41.1 can withstand the loads generated by the high pressure within the outer compartment, while the inner compartments 51 facilitate the mounting of the stationary blades or stationary vanes, described below.

[0041] The pressure drop across the expander 3 can be about 150 bar or higher, preferably about 200 bar or higher, for example, between 250 and 400 bar. To expand the combustion gas generated in the combustor 7, a high number of expansion stages is preferred. In the exemplary embodiment of Figures 2 and 3, the expander 3 includes eight stages. In other embodiments, a different number of expansion stages may be provided, preferably higher than or equal to four, more preferably higher than or equal to five. In some embodiments, the number of expansion stages may be higher than eight, for example, nine, ten, eleven or more, and preferably lower than fifteen. The expansion stages form an axial expansion flow path for the process gas being expanded in the expander 3. Petition 870250085842, dated 09 / 23 / 2025, page 65 / 139 13 / 19

[0042] Each expansion stage includes an annular row of stationary blades or stationary blades 53 that are stationarily arranged in the outer compartment. In the exemplary embodiment of Figure 2, the annular rows of stationary blades are housed in the inner compartments 51. Each expansion stage further includes a respective annular row of rotor blades 55, arranged downstream of the respective annular row of stationary blades 53 along the expansion flow path extending from the combustor to the discharge-filled space 41.3 in a front-to-back direction, through the expansion section 5.

[0043] In some embodiments, a first annular row of stationary blades 53.1 may be arranged at the discharge end of the combustor 7 and form an array of nozzles directing high-pressure hot gas from the combustion chambers of the combustor to the first row of rotor blades. A first annular row of rotor blades identified as 55.1 may be arranged directly downstream of the first annular row of stationary blades 53.1 in a position adjacent to the combustor 7. A last annular row of stationary blades 53.8 may be positioned near the discharge-filled space 41.3, upstream of the last annular row of rotor blades shown in 55.8. The reference number 55 generally refers to any of the annular rows of rotor blades or to a rotor blade as such.

[0044] Rotor blades 55 are part of rotor 43, that is, they are connected to it for co-rotation with the rotor shaft. In embodiments, each annular row of rotor blades 55 (that is, each row 55.i, with i=1 to 8) is connected to a respective rotor disc. Rotor discs are identified as 57.i, with i =1 to 8. Reference number 57 indicates a generic rotor disc.

[0045] Rotor 43 additionally includes a front shaft portion 65 and a rear shaft portion 67. Each shaft portion 65, 67 can, by Petition 870250085842, dated 09 / 23 / 2025, p. 66 / 139 14 / 19 in turn, comprise a single monolithic structure, that is, it may be formed by a single body or may comprise a plurality of sections that may be connected to each other by tie rods or similar. In Figure 2, the rear portion of shaft 67 is monolithic, while the front portion of shaft 65 comprises four sections 65A, 65B, 65C and 65D, which are mutually stacked and connected to each other by tie rods 66.

[0046] In the embodiment of Figure 2, the first rotor disc 57.1 is formed monolithically as a single piece or body with the front portion of shaft 65 and, more specifically, with section 65D thereof. Similarly, the last rotor disc 55.8 is formed monolithically as a single piece with the rear shaft portion 67. The intermediate rotor discs 57.2, 57.3, 57.4, 57.5, 57.6 and 57.7 form a plurality of rotor discs that are manufactured as separate components and mounted between the front rotor disc 57.1 and the rear rotor disc 57.8 by welding, as described in detail below. The rearmost of the plurality of rotor discs, that is, rotor disc 57.7, is welded to the rear portion of the shaft, and the forwardest of the plurality of rotor discs, that is, rotor disc 57.2, is welded to the front portion of shaft 65.

[0047] In the embodiment of Figure 3, the rotor again comprises eight rotor discs 57.1 to 57.8 which, however, are all manufactured as separate bodies, either by forging or other suitable means, and connected to each other and to the front portion of shaft 65 and to the rear portion of shaft 67 by welding. In Figure 3, the rotor blades are omitted for clarity. In this embodiment, the most forward rotor disc 57.1 is welded to the front portion of shaft 65, and the most rear rotor disc 57.8 is welded to the rear portion of shaft 67.

[0048] The rotor blades of each stage can be manufactured separately from the respective rotor disc and mechanically assembled onto it. In other embodiments, the rotor blades and the rotor disc of each stage can be manufactured as a monolithic body, by Petition 870250085842, dated 09 / 23 / 2025, page 67 / 139 15 / 19 example, by additive manufacturing. In still other embodiments, the two design options can be combined. One or more stages may include respective components manufactured monolithically, including rotor blades and discs, and one or more stages may include a rotor disc and rotor blades separately manufactured mechanically coupled to the rotor disc.

[0049] As mentioned above, the front portion of shaft 65 and section 65D thereof, rotor discs 57 and the rear portion of shaft 67 are connected to each other by welding. In some embodiments, the welding is an autogenous weld and, specifically, a weld without the use of additional filler material. The welding is achieved by melting a portion of the base material that forms the two components to be connected to each other, supplying energy to it and subsequently solidifying the molten base material.

[0050] In some embodiments, the welding is electron beam welding. This welding technique is an autogenous welding process in which a high-speed electron beam is applied to two materials to be joined. The workpieces fuse and flow together as the kinetic energy of the electrons is transformed into heat upon impact. Electron beam welding can be beneficial for welding rotor discs and the front portion of shaft 65 and the rear portion of shaft 67 together, since the molten volume can be narrow in the axial direction and thick in the radial direction. For example, the volume of molten material can have an extension in the axial direction of around or above 0.1 mm, preferably around or above 2 mm, or higher, for example, around or above 10 mm and preferably less than 15 mm.The molten material can have a thickness in the radial direction, for example, around or above 10 mm, preferably around or above 60 mm, or higher, for example, at or above 200 mm. This results in strong welding due to the extension in the radial direction, but... Petition 870250085842, dated 09 / 23 / 2025, page 68 / 139 16 / 19 reduces thermal distortions of welded parts due to the limited weld size in the axial direction. Furthermore, thermally induced changes in the physical and chemical properties of the base material forming the various components of rotor 43 are reduced.

[0051] In some embodiments, the welding process to manufacture rotor 43 may start from the front portion of shaft 65. In the embodiment of Figure 2, the second rotor disc 57.2 is stacked on top of the first rotor disc 57.1 which is manufactured as a single body part that also forms section 65D of the front portion of shaft 65.

[0052] Rotor disc 57.2 is welded to rotor disc 57.1. The next step will be welding the third rotor disc 57.3 to the second rotor disc 57.2. The welding steps are repeated until the second-to-last rotor disc 57.7 is welded to rotor disc 57.6. The assembly process is completed by welding the rear shaft portion 67 and the last rotor disc 57.8, formed monolithically with it, to the second-to-last rotor disc 57.7.

[0053] In the embodiment of Figure 3, a similar sequence of manufacturing steps is performed, with the difference that each of the eight rotor discs 57.1 to 57.8 is manufactured as a separate component, and the discs are then welded one after the other from rotor disc 57.1 welded to section 65D of the front portion of shaft 67.

[0054] In other embodiments, the welding process can be reversed, starting with welding the rotor disc 57.8 to the rear portion of shaft 67 (in Figure 3) or the rotor disc 57.7 to the rear portion of shaft 67 formed integrally with the rotor disc 57.8 (in Figure 2), followed by sequential welding of the other rotor discs 57.7 (Figure 3) or 57.6 (Figure 2) up to rotor disc 57.1 (Figure 3) or 57.2 (Figure 2) and finally welding the front portion of shaft 65, that is, section 65D thereof. Petition 870250085842, dated 09 / 23 / 2025, page 69 / 139 17 / 19

[0055] In some embodiments, to facilitate the mutual positioning of the rotor discs 57 and the front shaft portion 65 and the rear shaft portion 67, the rotor discs 57 and the last shaft portion to be welded (in the embodiment shown in Figure 3, the rear shaft portion 67) may be provided with internal annular notches 71. Each internal annular notch 71 is used to center the respective component (57 or 67) to the one in the adjacent position before welding. Thus, for example, in the embodiment of Figure 3, the internal annular notch 71 of the first rotor disc 57.1 is introduced into a circular seat of the front portion of shaft 65 to center the first rotor disc 57.1 in relation to the front portion of shaft 65. After welding the first rotor disc 57.1 to the front portion of shaft 65 and, more specifically, to section 65D thereof, the next rotor disc 57.2 is mounted on the first rotor disc 57.1 and centered on it using the respective internal annular notch which is inserted into a hole in the first rotor disc 57.1, so that the first rotor disc 57.1 surrounds the internal annular notch 71 of the next rotor disc 57.2. The welding of rotor disc 57.2 to rotor disc 57.1 is then performed. The process is repeated until the rear portion of shaft 67 is centered in relation to the last rotor disc 57.8 using the internal annular notch 71 of the rear portion of shaft which is inserted into the central hole of rotor disc 57.8. The final welding is then performed.

[0056] In some embodiments, at least one or all except an annular notch 71 are removed after welding. Figure 4 illustrates an enlargement of a pair of rotor discs, generally identified as 57.a and 57.b. The inner annular notch 71 of rotor disc 57.b has been removed by machining to create a smooth transition zone between rotor disc 57.a and rotor disc 57.b on the inward-facing surface thereof, in the weld area. The volume of molten and solidified base material that forms the weld connection is shown. Petition 870250085842, dated 09 / 23 / 2025, page 70 / 139 18 / 19 schematically in W. Removing the internal annular notch 71 reduces the risk of failure due to crack initiation.

[0057] Once the last component to be welded (e.g., the rear portion of shaft 67) closes the empty volume inside the rotor, an annular notch 71, for example, the notch of the rear portion of shaft, will not be accessible for machining and will not be removed after welding.

[0058] The volume of metallic material forming the welded seam between adjacent rotor discs 57a, 57b has a dimension Wa in the axial direction and a dimension Wr in the radial direction. Preferably, the dimension Wa is between 0.1 and 15 mm, or between 0.1 and 10 mm. The dimension Wr is preferably between 10 and 200 mm. A small dimension in the axial direction is beneficial in terms of rotor dimensional stability. Welding can preferably be electron beam welding, which is particularly useful in generating deep welds (large radial dimension Wr) with reduced extension in the axial direction (small axial dimension Wa).

[0059] After welding the rotor discs 57 and the front shaft portion 65 and the rear shaft portion 67, a cooling chamber 73 is obtained in the rotor. The cooling chamber 73 can be fluidly coupled through one or more ducts 75 (Figure 2) with a cooling-filled space 77 adapted to receive a cooling fluid, for example, chilled combustion gas, consisting mainly of carbon dioxide, from the cooling line 27. The cooling chamber 73 can be fluidly coupled to the annular spaces 79 provided between adjacent rotor discs 57 and between the first and last rotor discs and the front and rear shaft portions, respectively. Each annular space 79 can be radially closed outwards by an annular seal or a sealing nozzle 81. Pressurized cooling fluid from the cooling chamber 73 thus flows into each annular space 79 at a pressure sufficient to purge the annular space.A decrease in fluid pressure. Petition 870250085842, dated 09 / 23 / 2025, page 71 / 139 19 / 19 cooling in the annular spaces 79 can be achieved by using connecting ducts with decreasing cross-section, so that the correct flow rate of the cooling fluid is obtained in the various annular spaces 79.

[0060] In some embodiments, the rotor 43 of the expander 3 may include a balancing drum, adapted to balance the axial force generated by the expanding process gas flowing through the flow path. The balancing drum may be provided on the rear portion of shaft 67, on the front portion of shaft 65, or on both the rear portion of shaft 67 and the front portion of shaft 65.

[0061] In the embodiments of Figures 2 and 3, a balance drum 83 is provided in the front portion of shaft 65, as best shown in Figure 2. In some embodiments, the balance drum 83 comprises two drum portions 83A and 83B. The two drum portions 83A and 83B can be formed monolithically as a single body with a respective one of the various sections forming the respective front portion of shaft 65 or rear portion of shaft 67. In Figure 2, the balance drum 83 includes two drum portions 83A, 83B formed integrally with sections 65B and 65C of the front portion of shaft. Dividing the balance drum into individual drum portions makes its manufacture easier.

[0062] The exemplary embodiments have been disclosed above and illustrated in the accompanying drawings. It will be understood by those skilled in the art that various changes, omissions, and additions may be made to what is specifically disclosed in the present invention without departing from the scope of the invention as defined in the following claims. Petition 870250085842, dated 09 / 23 / 2025, p. 72 / 139

Claims

1 / 6 CLAIMS 1. Expander for a supercritical or transcritical carbon dioxide thermodynamic cycle, the expander being characterized by comprising: - an outer compartment; - a combustor in the outer compartment, the combustor being adapted to receive a flow of compressed oxidant and fuel; - a rotor with a rotating shaft, housed for rotation in the outer compartment; the rotor comprising: > a rear shaft portion; > a front shaft portion; and > a plurality of rotor discs disposed between the rear shaft portion and the front shaft portion; each rotor disc among said plurality of rotor discs comprising a respective annular row of rotor blades; and - upstream of each annular row of rotor blades, a respective annular row of stationary blades; each annular row of stationary blades and the respective annular row of rotor blades forming an expander stage;- a cooling chamber inside the rotor; wherein the cooling chamber is fluidly coupled to a high-pressure filled space adapted to receive compressed cooling fluid; and wherein the cooling chamber is fluidly coupled to at least some of said expander stages, wherein: the plurality of rotor discs between the rear shaft portion and the front shaft portion are connected to each other by welding; at least one section of the rear shaft portion is welded to a rotor disc further aft among the plurality of rotor discs; and at least one portion of the front shaft portion is welded to a rotor disc further forward among the plurality of rotor discs.

2. Expander, according to claim 1, characterized in that the rotor discs, the rear portion of the shaft and the front portion of the shaft are welded together by electron beam welding.

3. Expander, according to claim 1 or 2, characterized in that, between adjacent rotor discs, between the front portion of the shaft and a rotor disc connected thereto, and between the rear portion of the shaft and a rotor disc connected thereto, a weld volume is provided, which has an extension in a direction parallel to the axis of rotation of the rotor between 0.1 and 15 mm, preferably between 0.1 and 10 mm, and a radial thickness in a direction orthogonal to the axis of rotation of the rotor between 10 and 200 mm.

4. Expander, according to any of the preceding claims, characterized in that the cooling chamber is circumferentially surrounded by rotor discs and closed at a rear axial end by the rear portion of the shaft and at a front axial end by the front portion of the shaft.

5. Expander, according to any of the preceding claims, characterized in that the cooling chamber is fluidly coupled through cooling ducts with annular spaces between pairs of sequentially arranged rotor discs.

6. Expander, according to claim 5, characterized in that the annular seals or sealing rings are disposed between said sequentially arranged rotor discs, wherein the cooling ducts are adapted to supply pressurized cooling fluid from the cooling chamber to an annular space formed between the annular seal or sealing ring and the respective two sequentially arranged rotor discs. Petition 870250085842, dated 09 / 23 / 2025, p. 74 / 139 3 / 6 7. Expander, according to any of the preceding claims, characterized in that the rotor additionally comprises a balancing drum.

8. Expander, according to claim 7, characterized in that the balance drum is integrally formed from at least one section of the rear portion of the axle or the front portion of the axle.

9. Expander, according to any of the preceding claims, characterized in that the outer compartment comprises a high-pressure compartment and a low-pressure exhaust compartment, wherein the high-pressure compartment and the low-pressure exhaust compartment are coupled along a plane orthogonal to the axis of rotation of the rotor.

10. Expander, according to claim 9, characterized in that the low-pressure exhaust compartment is disposed at a rear end of the expander, opposite the combustor; and the low-pressure exhaust compartment forms a full discharge space.

11. Expander, according to claim 9 or 10, characterized by further comprising at least one inner compartment, housed stationarily in the outer compartment and surrounding the rotor discs; wherein the at least one inner compartment is divided into a first compartment portion and a second compartment portion along a plane parallel to or containing the axis of rotation of the rotor; and wherein the annular rows of stationary blades are supported in the inner compartment.

12. Expander, according to claim 9 or 10, characterized by further comprising a plurality of internal compartments, housed stationarily in the external compartment and surrounding the rotor discs; wherein each internal compartment is divided into a first compartment portion and a second compartment portion along a plane parallel to or containing the axis of rotation of the rotor; and wherein the annular rows of stationary blades are supported in the internal compartments.

13. Expander, according to any of the preceding claims, characterized in that at least one of said rotor discs comprises an internal annular notch, surrounded by an adjacent rotor disc.

14. Expander, according to any of the preceding claims, characterized in that the rotor is adapted to receive process gas at a temperature between 800 °C and 1500 °C.

15. Expander, according to any of the preceding claims, characterized in that the rotor is adapted to receive process gas at a pressure higher than 50 barA, preferably higher than 100 barA, more preferably higher than or equal to 200 barA and preferably lower than 800 barA, more preferably lower than 650 barA.

16. Expander, according to any of the preceding claims, characterized by being adapted to generate a power higher than 50 MW, preferably higher than or equal to 100 MW, preferably lower than 2000 MW, most preferably lower than 1500 MW.

17. Expander, according to any of the preceding claims, characterized in that at least one of said front axle portion and said rear axle portion comprises two axle sections connected to each other by tie rods.

18. Expander, according to claim 17, when dependent at least on claim 8 or 9, characterized in that the balancing drum comprises two drum portions, each integrally formed from one of said two shaft sections.

19. Supercritical carbon dioxide thermodynamic circuit characterized by comprising: Petition 870250085842, dated 09 / 23 / 2025, page 76 / 139 5 / 6 - an oxidant source; - an expander with an inlet side and a discharge side, the inlet side being fluidly coupled to the oxidant source; - a combustion gas recycling line, adapted to recycle combustion gas from the discharge side of the expander to a combustor of the expander; - in the combustion gas recycling line, a cooler adapted to cool the combustion gas from the discharge side of the expander and condense the water contained in the combustion gas; - a regenerative heat exchanger, the combustion gas from the expander flowing in heat exchange with chilled combustion gas from the cooler; the expander being an expander as defined in any of the preceding claims.

20. A method characterized by being intended for the manufacture of a rotor for an expander, wherein the rotor has a rotation axis and comprises: - a plurality of rotor discs, each rotor disc comprising a respective annular row of rotor blades; - a front shaft portion; and - a rear shaft portion; wherein the front shaft portion, the rear shaft portion and the rotor discs are aligned along the rotor's rotation axis, with the rotor discs disposed between the front shaft portion and the rear shaft portion; wherein the method comprises the step of connecting the front shaft portion, the rotor discs and the rear shaft portion by welding;wherein at least one of said rotor discs has an internal annular notch adapted to be coupled to an adjacent rotor disc, such that the adjacent rotor disc encircles the internal annular notch, wherein said at least one rotor disc and said adjacent rotor disc are connected by welding; and wherein the method further comprises the step of removing the internal annular notch after welding said at least one rotor disc and said adjacent rotor disc to each other.

21. Method according to claim 20, characterized in that the front portion of the shaft, the rotor discs and the rear portion of the shaft are connected by electron beam welding.

22. A method according to claim 20 or 21, characterized in that, between adjacent rotor discs, between the front portion of a shaft and a rotor disc connected thereto, and between the rear portion of a shaft and a rotor disc connected thereto, a weld volume is provided, having an extension in a direction parallel to the axis of rotation of the rotor between 0.1 and 10 mm, and a radial thickness in a direction orthogonal to the axis of rotation of the rotor between 10 and 200 mm. Petition 870250085842, dated 23 / 09 / 2025, p. 78 / 139

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