Expansion machine and method for manufacturing the same

Abstract

This specification discloses an expander for a supercritical carbon dioxide thermodynamic cycle. The expander comprises an outer casing, a combustor within the outer casing, and a rotor having a rotational axis, housed to rotate within the outer casing. The rotor comprises a rear shaft portion and a front shaft portion. A plurality of rotor discs are arranged between the rear shaft portion and the front shaft portion. Each rotor disc comprises an annular row of rotor blades. Upstream of each annular row of rotor blades is an annular row of fixed vanes. Each annular row of fixed vanes and each annular row of rotor blades forms an expander stage.

Description

Technical Field

[0001] The present disclosure relates to a gas expander specifically adapted for use in an oxy-fuel power cycle operating with a high-pressure process gas, such as a CO2 cycle, such as the Allam cycle, also known as the NET Power cycle. The present disclosure further relates to a method of assembling a rotor for a supercritical carbon dioxide expander.

Background Art

[0002] Fossil fuels are the main source of chemical energy used for the generation of mechanical power. Fossil fuels are mixed with air, burned to produce high-pressure and high-temperature combustion gases, and expanded in a turbine or expander. The expander converts the enthalpy of the combustion gases into mechanical power available at the output shaft of the expander, and is used to drive loads such as compressors or compressor trains, or to rotate a generator to convert mechanical power into electrical power.

[0003] One of the main concerns regarding the combustion of fossil fuels relates to the production of carbon dioxide, which is considered to be one of the main factors contributing to global warming and climate change.

[0004] In order to reduce the environmental impact of power generation from the combustion of fossil fuels, options for post-combustion capture of carbon dioxide have been investigated. Carbon dioxide capture facilities have been developed to treat flue gases discharged from gas turbines and remove carbon dioxide from the flue gases before discharging the flue gases to the environment. The cost of carbon dioxide capture facilities is high both in terms of CAPEX and in terms of the energy required to operate the facilities, and due to the low proportion of carbon dioxide in the flue gases, it reduces the overall thermodynamic efficiency of the system. This requires a large amount of flue gas to be processed through the carbon dioxide capture facility, making the capture process particularly inefficient.

[0005] In recent years, oxygen-combustion cycles, also known as oxy-fuel cycles, have been developed in which a fuel, such as natural gas or another fossil fuel, is mixed under high pressure with an oxidizer mixture consisting mainly of oxygen (O2) and carbon dioxide (CO2). The mixture of fuel, oxygen, and carbon dioxide is burned in the combustor of an expander to produce a pressurized flue gas consisting of only carbon dioxide and water, or almost entirely carbon dioxide and water.

[0006] The flue gas is expanded in the expander to generate mechanical power. The exhaust flue gas discharged from the expander's outlet is cooled in a regenerative heat exchanger, further reduced to a low temperature, and condenses into water, which can be removed from the cooled flue gas. The low-temperature flue gas, consisting mainly or exclusively of carbon dioxide, is pressurized and recirculated through the regenerative heat exchanger towards the combustor of the expander.

[0007] The oxygen supplied to the combustor of the expander can be obtained by separating it from the ambient air and removing nitrogen, so that the working fluid supplied to the combustor consists mainly of oxygen and carbon dioxide, and no nitrogen. The resulting flue gas consists mainly of water and carbon dioxide. Water is removed from the flue gas by condensation, and a portion of the water-free flue gas that is not recirculated to the combustor can be efficiently processed in a carbon dioxide capture unit.

[0008] The oxygen-fueled cycle summarized above is a semi-closed cycle in that only a portion of the flue gas leaves the cycle after the water has been removed from it.

[0009] The oxygen-fuel (oxy-combustion) cycles 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 high torque applied to the expander rotor. These factors become important and significant challenges in expander rotor design as the expander's rated power increases, potentially limiting the expander's maximum power output.

[0010] Novel expanders adapted to achieve higher power rates in, for example, oxygen fuel cycles or other supercritical carbon dioxide cycles would be welcomed in the art. [Overview of the project]

[0011] This specification discloses an expander for a supercritical carbon dioxide thermodynamic cycle. As understood herein, a “supercritical carbon dioxide thermodynamic cycle” is a cycle in which carbon dioxide is in a supercritical state, at least at the inlet of the expander.

[0012] The expander comprises an outer casing, a combustor combined with the outer casing, and a rotor having a rotational axis, housed within the outer casing to rotate. The rotor comprises a rear shaft portion and a front shaft portion. Multiple rotor discs are arranged between the rear shaft portion and the front shaft portion. Each rotor disc comprises an annular row of rotor blades. Upstream of each annular row of rotor blades is an annular row of fixed vanes. Each annular row of fixed vanes and each annular row of rotor blades forms an expander stage.

[0013] Multiple rotor discs between the rear shaft section and the front shaft section are connected to each other by welding. At least one section of the rear shaft section is welded to the rearmost rotor disc of the multiple rotor discs, i.e., the rotor disc adjacent to the rear shaft section. Finally, at least one portion of the front shaft section is welded to the frontmost rotor disc of the multiple rotor discs, i.e., the rotor disc adjacent to the front shaft section.

[0014] Therefore, the resulting rotor is formed from multiple components, each of which can be manufactured separately and made from a heat-resistant metal alloy. Since the individual components are small compared to the entire rotor, manufacturing them from high-temperature metal alloys such as nickel-based alloys is also straightforward. Welding the individual components results in a rotor of large dimensions, which can contain numerous annular rows of rotor blades corresponding to numerous expansion stages. The welding typically results in a robust structure adapted to withstand the high pressures and high torques generated in supercritical carbon dioxide expanders.

[0015] The proposed design can be used to achieve high power outputs, preferably higher than 50 MW, for example, on the order of 100 MW or more, for example, 150 MW or more, for example, 200 MW or more, or 300 MW or more. In embodiments, the rated output may be less than 2000 MW, preferably less than 1500 MW, for example, less than 1000 MW, or less than 800 MW. For example, the rated output may fall within the range of 200 MW to 650 MW. The intermediate values ​​between the upper and lower limits of each of the above ranges are also expressly disclosed herein.

[0016] Further features and embodiments are described below and outlined in the attached claims.

[0017] This disclosure also relates to a method for manufacturing a rotor for a supercritical carbon dioxide expander, and a thermodynamic cycle using said expander. [Brief explanation of the drawing]

[0018] Here, we will briefly refer to the attached diagram. [Figure 1] This is a schematic diagram of an oxygen fuel power circuit. [Figure 2] This is a cross-sectional view of the inflator according to the present disclosure in the first embodiment. [Figure 3] This is a cross-sectional view of the rotor for the expander in Figure 2 in a further embodiment, with the rotating blades removed. [Figure 4] This is a magnified view of the welded area after machining to remove the annular ravet. [Modes for carrying out the invention]

[0019] The schematic diagram in Figure 1 shows a simplified supercritical carbon dioxide cycle (abbreviated as sCO2 cycle), such as the Aram cycle or a similar oxygen-fuel combustion cycle, in which the use of the expander according to this disclosure may be particularly beneficial. Generally, a supercritical carbon dioxide cycle as understood herein is a cycle in which carbon dioxide is in a supercritical state at least at the inlet of the expansion channel in the expander.

[0020] The power system 1 shown in Figure 1 comprises an expander (also known as a turbo expander) 3 including an expansion section 5, and a combustor 7. The combustor 7 can be, for example, an annular combustor, a can-type combustor, a can-annular combustor, etc. In the current preferred embodiment, the combustor is a can-type combustor having a plurality of combustion chambers arranged around the rotation axis of the expander 3, as shown in more detail in Figure 2. In some embodiments, the combustion chambers are housed within the high-pressure casing of the expander, as schematically shown in Figure 2, as will be described in more detail below. In some embodiments, each combustion chamber is housed in its respective seat formed within the high-pressure casing of the expander, as will be described in more detail below.

[0021] Reference numeral 7.1 in Figure 2 indicates a single combustor chamber of a can-type or can-annular combustor. In other embodiments not shown, the combustor may be an annular combustor as described above.

[0022] The combustor 7 is supplied with an oxidant stream supplied by an oxidant source. The oxidant may be oxygen (O2), or a mixture containing or consisting mainly of oxygen and carbon dioxide (CO2). The oxidant stream can be generated by an air separation unit 9 characterized by an oxidant source. The air separation unit 9 can remove nitrogen or nitrogen and carbon dioxide from ambient air to generate the necessary oxidant stream supplied to the combustor 7 of the expander 3 through the oxidant line 11. In some embodiments, for easier handling of the oxidant stream, the oxidant stream can contain about 20% by volume of oxygen and 80% by volume of carbon dioxide. The above ratio of CO2 to O2 is an example. Carbon dioxide can be added to oxygen through the recirculation line 12 as will be described in detail below.

[0023] Reference numeral 13 indicates a fuel supply line adapted to supply natural gas such as methane, for example, to the combustor 7, specifically to each combustion chamber 7.1. The oxidant and fuel are supplied to the combustor 7 at high pressure from the inlet side of the expander 3. The upper limit pressure of the thermodynamic cycle can be, for example, 50 barA or more, preferably 100 barA or more, for example about 200 barA or more, preferably about 250 barA or more, or higher, for example 300 barA or more. Generally, the pressure can be less than 800 barA, or less than 600 barA. In some embodiments, the upper limit 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 mixture of oxidant and fuel is combusted in the combustor 7. The pressurized high-temperature combustion gas resulting from the combustion expands in the expansion section 5 of the expander 3. The temperature on the outlet side of the fixed nozzle downstream of the combustor can be included, for example, in the range of 800°C to 1500°C.

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

[0026] The circuit further comprises a regenerative heat exchanger 17, and the hot flue gas flowing through the hot side 17.1 of the regenerative heat exchanger 17 is cooled by heat exchange with the flow of the cooled flue gas flowing through the 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 cooled in the cooling heat exchanger 19 to a temperature that causes condensation of the steam contained in the discharged flue gas. The condensed water is removed from the discharged flue gas in the water / gas separator 21.

[0027] The dehydrated, exhausted, and cooled flue gas mainly or exclusively consists of carbon dioxide and is compressed in the flue gas compressor 23 to the pressure on the inlet side of the expander 3. In the schematic diagram of FIG. 1, the flue gas compressor 23 is illustrated as a single compressor, but in some embodiments, a plurality of compressors can be used. For example, the flue gas compressor 23 can be a multi-stage compressor or a compressor train. In some embodiments, the compressor can be an intercooled compressor. In some embodiments, the main compressor can be arranged in series with two continuously arranged pumps.

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

[0029] The remaining compressed flue gas is sent through the low-temperature side 17.2 of the regenerative heat exchanger 17, heated by heat exchange with the high-temperature flue gas flowing through the high-temperature side 17.1 of the regenerative heat exchanger 17, and recirculated to the expander 3 through the recirculation line 25. The flue gas recirculated through the recirculation line 25 is mixed with the combustion gas generated in the combustor 7 or with the oxidizer stream from the oxidizer line 11.

[0030] The sidestream of cooled flue gas is sent through a cooling line 27 that bypasses the regenerative heat exchanger 17 towards the components of the expander 3 that require cooling.

[0031] The expander 3 may include an output shaft end 31 that can be integrated with the central portion of the rotor, or that can be assembled to the central portion of the rotor by bolting, welding, hearth or spline connection, or a combination thereof. The mechanical power generated by the expansion of the combustion gases 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 driven and coupled to the generator 33 directly, or via a gearbox, joint, or a combination thereof. A flange connection between the output shaft end 31 and the generator 33 is shown at 49 in Figure 2. The generator 33 is then electrically coupled to the power distribution network 35. In Figures 1 and 2, the output shaft end 31 is shown on the rear side of the expander 3. In other embodiments, not shown, the output shaft end 31 may be located on the front side of the expander. In yet another embodiment, not shown, two output shaft ends may be provided, one on the front side of the expander and the other on the rear side.

[0032] As used herein, “forward” and “rear” refer to the direction of the process gas flow through the expander 3. Thus, “forward” refers to the position on the combustor 7 side, and “rear” refers to the position on the opposite side of the combustor 7, i.e., the discharge side of the expander 3.

[0033] The high pressure drop across the expander 3, the high absolute pressure in the combustor 7 and the expander cooling duct, and the high torque applied to the expander shaft present significant challenges to the design of the expander 3, especially in the case of high rated powers of 100 MW or more, preferably 150 MW or more and less than 2000 MW, such as 100 MW to 2000 MW. The expander, and in particular the rotor designs disclosed herein, can be used to achieve high power rates, preferably higher than 50 MW, for example, on the order of 100 MW or more, for example 150 MW or more, for example 200 MW or more, or 300 MW or more. In embodiments, the rated power may be less than 2000 MW, preferably less than 1500 MW, for example less than 1000 MW, or less than 800 MW. For example, the rated power may fall within the range of 200 MW to 650 MW. The intermediate values ​​between the upper and lower limits of each of the above ranges are also expressly disclosed herein.

[0034] Referring again to Figure 1, Figure 2 shows a cross-sectional view of the expander 3 in one embodiment. For example, the expander in Figure 2 includes a rotor in one embodiment. A further embodiment of an alternative rotor for the expander 3 of Figure 2, shown separately in Figure 3, is shown separately in Figure 3.

[0035] In some embodiments, the expander 3 comprises an outer casing 41 housing the combustor 7. In some embodiments, the outer casing 41 includes a body 41.1, referred herein as the high-pressure casing, and a closure 41.2, referred herein as the low-pressure exhaust casing. The high-pressure casing 41.1 may be monolithic, i.e., it may include a body consisting of a single piece manufactured, for example, by forging, machining, casting, or a combination thereof. In some embodiments, the high-pressure casing 41.1 may be manufactured by welding together a plurality of components joined along a plane perpendicular to the axis of rotation.

[0036] The low-pressure exhaust casing 41.2 can be located on the discharge side of the expander 3, i.e., the rear side, i.e., opposite to the combustor 7. The low-pressure exhaust casing 41.2 may be monolithic, i.e., it may consist of a single piece manufactured by, for example, forging, machining, casting, or a combination thereof. In some embodiments, the low-pressure exhaust casing 41.2 can be manufactured from two or more components that can be irreversibly connected to each other, for example by welding, or reversibly joined to each other, for example by bolts. For example, the low-pressure exhaust casing 41.2 can be divided into two parts along a plane containing the rotation axis of the expander.

[0037] The high-pressure casing 41.1 and the low-pressure exhaust casing 41.2 can be connected to each other along a plane P perpendicular to the axis of rotation AA of the rotor 43, which is supported to rotate within the outer casing 41.

[0038] In some embodiments, the low-pressure exhaust casing 41.2 forms an exhaust volute or exhaust plenum 41.3 through which the exhausted flue gas is discharged from the expander 3.

[0039] Reference numerals 45 and 47 indicate bearing devices that rotatably support the rotor 43. For example, the bearing device 45 on the opposite side from the combustor 7, i.e., the rear side, may include an axial bearing or thrust bearing combined with a radial bearing, or a bearing having axial-radial bearing capability. The bearing device 47 on the combustor side, i.e., the front side, may include a radial bearing. The reverse arrangement is also possible, with a bearing having axial load capacity located on the combustor side. The bearing devices 45 and 47 may be housed in bearing casings not shown in detail.

[0040] In some embodiments, the rotor 43 is surrounded by one or more inner casings 51 fixedly housed within an outer casing 41. Each inner casing 51 can be divided into two parts along a plane parallel to the rotation axis AA of the rotor 43, for example, the plane containing the rotation axis AA. This arrangement of the inner casings 51 and outer casings 41 is particularly beneficial when the combustion gases reach high pressures of about 200–300 barA or higher. The monolithic high-pressure casing 41.1 can withstand the load generated by the high pressure inside the outer casing, while the inner casings 51 facilitate the mounting of fixed vanes or fixed blades, as described below.

[0041] The pressure drop before and after the expander 3 may be about 150 bar or more, preferably about 200 bar or more, for example, 250 to 400 bar. A number of expansion stages is preferable to expand the combustion gas generated in the combustor 7. In the exemplary embodiments shown in Figures 2 and 3, the expander 3 includes eight stages. In other embodiments, a different number of expansion stages may be assumed, preferably four or more, more preferably five or more. In some embodiments, the number of expansion stages may be more than eight, for example, nine, ten, eleven, or more, and preferably less than fifteen. The expansion stages form axial expansion passages for the process gas to be expanded in the expander 3.

[0042] Each expansion stage includes an annular row of fixed vanes or fixed blades 53 fixedly arranged within the outer casing. In the exemplary embodiment shown in Figure 2, the annular row of fixed blades is housed within the inner casing 51. Each expansion stage further includes an annular row of rotor blades 55 positioned downstream of each annular row of fixed blades 53 along an expansion flow path that extends from front to rear through the expansion section 5 from the combustor to the exhaust plenum 41.3.

[0043] In some embodiments, a first annular row of fixed blades 53.1 may be located at the exhaust end of the combustor 7 and may form an array of nozzles that guide high-temperature, high-pressure gas from the combustion chamber of the combustor to the first row of rotor blades. A first annular row of rotor blades, designated 55.1, may be located immediately downstream of the first annular row of fixed blades 53.1 adjacent to the combustor 7. A last annular row of fixed blades 53.8 may be located upstream of the last annular row of rotor blades, designated 55.8, and near the exhaust plenum 41.3. Reference numeral 55 refers collectively to any one of the annular rows of rotor blades or to the rotor blades themselves.

[0044] The rotor blades 55 form part of the rotor 43 and are connected to the rotor 43 so as to rotate with the rotor shaft. In this embodiment, each annular row of rotor blades 55 (i.e., each row 55i, i=1 to 8) is connected to a respective rotor disk. The rotor disks are denoted 57i, i=1 to 8. Reference numeral 57 indicates a typical rotor disk.

[0045] The rotor 43 further includes a front shaft portion 65 and a rear shaft portion 67. Each shaft portion 65, 67 can then comprise a single monolithic structure, i.e., be formed from a single body, or it can comprise multiple sections that can be connected to each other by tie rods or the like. In Figure 2, the rear shaft portion 67 is monolithic, and the front shaft portion 65 comprises four sections 65A, 65B, 65C, and 65D, which are stacked on top of each other and connected to each other by tie rods 66.

[0046] In the embodiment shown in Figure 2, the first rotor disc 57.1 is monolithically formed as a single part or body with the front shaft portion 65, and more specifically with its section 65D. Similarly, the last rotor disc 55.8 is monolithically formed as a single part 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, which are manufactured as separate components and assembled between the front rotor disc 57.1 and the rear rotor disc 57.8 by welding, as will be described in more detail below. The rearmost rotor disc of the plurality, i.e., rotor disc 57.7, is welded to the rear shaft portion, and the frontmost rotor disc of the plurality, i.e., rotor disc 57.2, is welded to the front shaft portion 65.

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

[0048] Each rotor blade can be manufactured separately from its respective rotor disk and mechanically mounted thereon. In other embodiments, each rotor blade and rotor disk can be manufactured as a monolithic body, for example, by additive manufacturing. In yet another embodiment, two design options can be combined. One or more stages may include each monolithically manufactured component, including the rotor blades and disks, while one or more stages may include a rotor disk and separately manufactured rotor blades mechanically coupled to the rotor disk.

[0049] As described above, the front shaft portion 65, its section 65D, the rotor disc 57, and the rear shaft portion 67 are connected to each other by welding. In some embodiments, the welding is a self-sharpening weld, specifically a weld that does not use additional filler material. The welding is achieved by supplying energy to melt a portion of the base material that forms two components to be connected to each other, and then allowing the molten base material to solidify.

[0050] In some embodiments, the welding is electron beam welding. This welding technique is a self-sharpening welding method in which a high-speed electron beam is irradiated onto two materials to be joined. When the kinetic energy of the electrons is converted into heat upon impact, the workpieces melt and flow together. Electron beam welding can be beneficial for welding the rotor disk to the front shaft portion 65 and the rear shaft portion 67 because the molten volume can be narrow in the axial direction and thick in the radial direction. For example, the volume of the molten material may have an axial extension of about 0.1 mm or more, preferably about 2 mm or more, or greater, for example, about 10 mm or more, and preferably less than 15 mm. The volume of the molten material may have a radial thickness of, for example, about 10 mm or more, preferably about 60 mm or more, or greater, for example, 200 mm or more. This results in a strong weld thanks to the radial extension, while reducing thermal distortion of the welded workpiece thanks to the limited dimensions of the axial weld. Furthermore, thermally induced changes in the physical and chemical properties of the base materials forming the various components of the rotor 43 are reduced.

[0051] In some embodiments, the welding process for manufacturing the rotor 43 can begin with the front shaft portion 65. In the embodiment shown in Figure 2, the second rotor disc 57.2 is stacked on top of the first rotor disc 57.1, which is manufactured as part of a single body that also forms section 65D of the front shaft portion 65.

[0052] Rotor disc 57.2 is welded to rotor disc 57.1. The next step is to weld the third rotor disc 57.3 to the second rotor disc 57.2. The welding step is 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, which is monolithically formed with it, to the second-to-last rotor disc 57.7.

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

[0054] In other embodiments, the welding process can be reversed, starting with welding rotor disc 57.8 to the rear shaft portion 67 (Figure 3), or rotor disc 57.7 to the rear shaft portion 67 (Figure 2) which is integrally formed with rotor disc 57.8, followed by sequentially welding the other rotor discs from 57.7 (Figure 3) or 57.6 (Figure 2) to rotor disc 57.1 (Figure 3) or 57.2 (Figure 2), and finally welding the front shaft portion 65, i.e., its section 65D.

[0055] In some embodiments, to facilitate the relative positioning of the rotor disc 57 with the front shaft portion 65 and the rear shaft portion 67, the rotor disc 57 and the last shaft portion to be welded (the rear shaft portion 67 in the embodiment shown in Figure 3) may be provided with inner annular ravets 71. Each inner annular ravet 71 is used to center each component (57 or 67) relative to an adjacent component before welding. Thus, for example, in the embodiment of Figure 3, the inner annular ravet 71 of the first rotor disc 57.1 is introduced into the circular seat of the front shaft portion 65 to center the first rotor disc 57.1 with respect to the front shaft portion 65. After the first rotor disc 57.1 is welded to the front shaft portion 65, more specifically to its section 65D, the next rotor disc 57.2 is mounted on the first rotor disc 57.1 and centered with the first rotor disc 57.1 using the inner annular ravets introduced into the holes of the first rotor disc 57.1 so that the first rotor disc 57.1 surrounds the inner annular ravets 71 of the next rotor disc 57.2. Next, the rotor disc 57.2 and rotor disc 57.1 are welded together. This process is repeated until the rear shaft portion 67 is centered with respect to the last rotor disc 57.8 using the inner annular ravets 71 of the rear shaft portion introduced into the central hole of the rotor disc 57.8. The final welding is then performed.

[0056] In some embodiments, at least one or all but one of the annular ravets 71 are removed after welding. Figure 4 shows an enlarged view of a pair of rotor discs collectively shown as 57.a and 57.b. The inner annular ravet 71 of rotor disc 57.b is removed by machining in the weld area to create a smooth transition zone between rotor discs 57.a and 57.b on its inward-facing surface. The volume of molten and solidified material forming the weld joint is schematically shown by W. Removal of the inner annular ravet 71 reduces the risk of failure due to cracking.

[0057] Since the last component to be welded (e.g., the rear shaft portion 67) closes off the empty volume inside the rotor, one annular ravet 71, for example, the ravet on the rear shaft portion, is not accessible for machining and is not removed after welding.

[0058] The volume of metal material forming the weld seam between adjacent rotor discs 57a and 57b has an axial dimension Wa and a radial dimension Wr. Preferably, the dimension Wa is in the range of 0.1 to 15 mm, or 0.1 to 10 mm. The dimension Wr is preferably in the range of 10 to 200 mm. A smaller axial dimension is beneficial in terms of the dimensional stability of the rotor. The welding may preferably be electron beam welding, which is particularly useful for producing a deep weld (large radial dimension Wr) with reduced axial elongation (small axial dimension Wa).

[0059] After welding the rotor disc 57 and the front and rear sections 65 and rear shaft section 67, a cooling chamber 73 is obtained within the rotor. The cooling chamber 73 can be fluidically coupled to a cooling plenum 77 adapted to receive a cooling fluid, such as cooled flue gas consisting mainly of carbon dioxide, from a cooling line 27 via one or more ducts 75 (Figure 2). The cooling chamber 73 can be fluidly coupled to annular spaces 79 provided between adjacent rotor discs 57, and between the first and last rotor discs and the front and rear shaft sections, respectively. Each annular space 79 can be closed radially outward by an annular seal or seal runner 81. Thus, pressurized cooling fluid from the cooling chamber 73 flows into each annular space 79 with sufficient pressure to purge the annular space. Pressure reduction of the cooling fluid within the annular spaces 79 can be achieved by using connecting ducts with reduced cross-section, resulting in precise flow rates of the cooling fluid within several annular spaces 79.

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

[0061] In the embodiments shown in Figures 2 and 3, the balance drum 83 is mounted on the front shaft portion 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 monolithically formed as a single body, with one of several sections each forming the respective front shaft portion 65 or rear shaft portion 67. In Figure 2, the balance drum 83 includes two drum portions 83A and 83B formed integrally with sections 65B and 65C of the front shaft portion. Dividing the balance drum into individual drum portions facilitates its manufacture.

[0062] Exemplary embodiments are disclosed above and shown in the accompanying drawings. Those skilled in the art will understand that various modifications, omissions, and additions may be made to those specifically disclosed herein without departing from the scope of the invention as defined in the following claims.

Claims

1. An expander for supercritical or transcritical carbon dioxide thermodynamic cycles, - Outer casing and, - A combustor within the outer casing, which is adapted to receive a flow of compressed oxidizer and fuel, - A rotor having a rotating shaft, housed to rotate within the outer casing, →Rear shaft section, →Front shaft section, →A plurality of rotor discs disposed between the rear shaft portion and the front shaft portion, each of the plurality of rotor discs comprising a plurality of rotor discs, each having an annular row of rotor blades, and a rotor comprising: - Each annular row of fixed vanes located upstream of each annular row of rotor blades, wherein each annular row of fixed vanes and each annular row of rotor blades form an expansion stage, - A cooling chamber inside the rotor, which is fluidly coupled to a high-pressure plenum adapted to receive a compressed cooling fluid, and is fluidly coupled to at least some of the expansion stages, An expander in which 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 the rearmost rotor disc of the plurality of rotor discs, and at least one portion of the front shaft portion is welded to the frontmost rotor disc of the plurality of rotor discs.

2. The expander according to claim 1, wherein the rotor disc, the rear shaft portion, and the front shaft portion are welded to each other by electron beam welding.

3. An expander according to claim 1 or 2, wherein welding volumes are provided between adjacent rotor discs, between the front shaft portion and the rotor disc connected thereto, and between the rear shaft portion and the rotor disc connected thereto, having extensions of the rotor in a direction parallel to the rotation axis, which are 0.1 to 15 mm, preferably 0.1 to 10 mm, and radial thicknesses of the rotor in a direction perpendicular to the rotation axis, which are 10 to 200 mm.

4. The expansion machine according to any one of claims 1 to 3, wherein the cooling chamber is surrounded in the circumferential direction by the rotor disk and closed at the rear axial end by the rear shaft portion and at the front axial end by the front shaft portion.

5. The expander according to any one of claims 1 to 4, wherein the cooling chamber is fluidly coupled to an annular space between a pair of continuously arranged rotor disks via a cooling duct.

6. The expander according to claim 5, wherein an annular seal or seal runner is positioned between the continuously arranged rotor disks, and the cooling duct is adapted to supply a pressurized cooling fluid from the cooling chamber to the annular space formed between the annular seal or seal runner and each of the two continuously arranged rotor disks.

7. The expander according to any one of claims 1 to 6, wherein the rotor further comprises a ballast drum.

8. The inflator according to claim 7, wherein the balance drum is integrally formed with at least one section of the rear shaft portion or the front shaft portion.

9. The expander according to any one of claims 1 to 8, wherein the outer casing includes a high-pressure casing and a low-pressure exhaust casing, and the high-pressure casing and the low-pressure exhaust casing are coupled along a plane perpendicular to the rotation axis of the rotor.

10. The expander according to claim 9, wherein the low-pressure exhaust casing is located at the rear end of the expander opposite to the combustor, and the low-pressure exhaust casing forms a discharge plenum.

11. The inflator according to claim 9 or 10, further comprising at least one inner casing fixedly housed within the outer casing and surrounding the rotor disk, wherein the at least one inner casing is divided into a first casing portion and a second casing portion along a plane parallel to the rotation axis of the rotor or a plane including the rotation axis, and the annular row of fixed vanes is supported within the inner casing.

12. The inflator according to claim 9 or 10, further comprising a plurality of inner casings fixedly housed within the outer casing and surrounding the rotor disk, each inner casing being divided into a first casing portion and a second casing portion along a plane parallel to the rotation axis of the rotor or a plane including the rotation axis, and the annular row of fixed vanes being supported within the inner casings.

13. The inflator according to any one of claims 1 to 12, wherein at least one of the rotor disks is provided with an inner annular ravet surrounded by adjacent rotor disks.

14. The expander according to any one of claims 1 to 13, wherein the rotor is adapted to receive process gases having temperatures in the range of 800°C to 1500°C.

15. The expander according to any one of claims 1 to 14, wherein the rotor is adapted to receive process gas at a pressure of 50 barA or more, preferably 100 barA or more, more preferably 200 barA or more, preferably less than 800 barA, and more preferably less than 650 barA.

16. An expander according to any one of claims 1 to 15, which is adapted to generate power of more than 50 MW, preferably 100 MW or more, preferably less than 2000 MW, and more preferably less than 1500 MW.

17. The inflator according to any one of claims 1 to 16, wherein at least one of the front shaft portion and the rear shaft portion comprises two shaft sections connected to each other by a tie rod.

18. The inflator according to claim 17, wherein, as dependent on at least claim 8 or 9, the balance drum comprises two drum portions, each integrally formed with one of the two shaft sections.

19. This is a supercritical carbon dioxide thermodynamic circuit, - Oxidizing agent source, - An expander having an inlet side and a discharge side, wherein the inlet side is fluidly coupled to the oxidizing agent source, - A flue gas recirculation line adapted to recirculate flue gas from the discharge side of the expander to the combustor of the expander, - A cooler located within the flue gas recirculation line, which is adapted to cool the flue gas from the discharge side of the expander and condense the moisture contained in the flue gas, - A regenerative heat exchanger is provided, in which the flue gas from the expander flows while exchanging heat with the cooled flue gas from the cooler, The aforementioned expander is the expander described in any one of claims 1 to 19, in a supercritical carbon dioxide thermodynamic circuit.

20. A method for manufacturing a rotor for an inflator, wherein the rotor has a rotating shaft and, - A plurality of rotor disks, each rotor disk having a corresponding annular row of rotor blades, - Front shaft section, - comprising a rear shaft portion, wherein the front shaft portion, the rear shaft portion, and the rotor disc are aligned along the rotation axis of the rotor, and the rotor disc is positioned between the front shaft portion and the rear shaft portion. The method comprises the step of joining the front shaft portion, the rotor disc, and the rear shaft portion by welding, wherein at least one of the rotor discs has an inner annular ravet adapted to be coupled to an adjacent rotor disc, so that the adjacent rotor disc surrounds the inner annular ravet, and the at least one rotor disc and the adjacent rotor disc are joined by welding, and the method further comprises the step of removing the inner annular ravet after welding the at least one rotor disc and the adjacent rotor disc to each other.

21. The method according to claim 20, wherein the front shaft portion, the rotor disk, and the rear shaft portion are connected by electron beam welding.

22. The method according to claim 20 or 21, wherein a weld volume is provided between adjacent rotor discs, between the front shaft portion and the rotor disc connected thereto, and between the rear shaft portion and the rotor disc connected thereto, having an extension portion of the rotor parallel to the rotation axis, which is 0.1 to 10 mm in length, and a radial thickness of the rotor perpendicular to the rotation axis, which is 10 to 200 mm in length.

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