Expander and thermodynamic cycle using the expander

Abstract

This specification discloses an expander for high-pressure thermodynamic cycles, such as supercritical or subsupercritical carbon dioxide cycles. The expander comprises a rotor having a shaft and a plurality of rotor discs mounted on the shaft so as to rotate with the shaft. Each rotor disc comprises a corresponding annular row of rotor blades and is shrink-fitted onto the shaft.

Description

Technical Field

[0001] The present disclosure relates to an expander specifically adapted for use in an oxy-fuel combustion power cycle operating with a high inlet pressure process gas, such as a supercritical or subcritical CO2 cycle, such as the Allam cycle, also known as the NET Power Cycle.

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, a greenhouse gas considered to be one of the main factors in global warming and climate change.

[0004] To reduce the environmental impact of power generation from the combustion of fossil fuels, options for post-combustion capture of carbon dioxide have been studied. 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 with respect to CAPEX and with respect to the energy required to operate the facilities, and reduces the overall thermodynamic efficiency of the system. The proportion of carbon dioxide in the flue gases is low. This requires large amounts of flue gases to be processed through the carbon dioxide capture facilities, making the capture process particularly inefficient.

[0005] In recent years, the oxygen combustion cycle, also known as the oxygen fuel cycle, has 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, oxidizer, and carbon dioxide is burned in the combustor of the expander to produce a pressurized flue gas consisting only of carbon dioxide and water, or almost entirely of 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 lowered to a low temperature, and condensed 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, and the working fluid supplied to the combustor consists mainly of oxygen and carbon dioxide, and does not contain 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 cycle or oxygen combustion cycle described above is particularly interesting in terms of efficiency and reduction of harmful emissions. However, they operate under supercritical or subsupercritical CO2 conditions 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 rated power of the expander increases, potentially limiting the maximum power rate of the expander.

[0010] For example, novel rotor and turbomachinery designs adapted to achieve higher power rates in oxygen fuel cycles would be welcomed in this field. [Overview of the project]

[0011] This specification discloses an expander for a supercritical carbon dioxide thermodynamic cycle. The expander comprises an outer casing, a combustor located within the outer casing, or associated with or connected to the outer casing, and a rotor having a rotating shaft, housed to rotate within the outer casing. The rotor includes an intermediate haft section to which a plurality of rotor discs are attached by shrink-fit. 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.

[0012] Additional features and embodiments of the rotor and the power-generating turbomachine including the rotor are described below with reference to the accompanying drawings and outlined in the accompanying claims. [Brief explanation of the drawing]

[0013] 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 an expander in one embodiment. [Figure 3] This is an enlarged cross-sectional view of a portion of the rotor, taken from a plane parallel to the axis of rotation. [Figure 4] This is a cross-sectional view taken along line IV-IV in Figure 3. [Figure 5] Figure 3 is a cross-sectional view taken along line VV. [Figure 6] This is a cross-sectional view taken along line VI-VI in Figure 3. [Modes for carrying out the invention]

[0014] Figure 1 shows a schematic diagram of a simplified supercritical carbon dioxide cycle (abbreviated as CO2 cycle), such as an Aram cycle or a similar oxygen-fuel combustion cycle, in which the use of an expander including a rotor according to this disclosure may be particularly beneficial.

[0015] The power system 1 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 combustor, a can annular combustor, etc. In the current preferred embodiment, the combustor is a can combustor comprising a plurality of combustion chambers arranged around the rotation axis of the expander 3, as shown in more detail in Figure 2. The combustion chambers are housed in their respective seats formed within the high-pressure casing of the expander, as will be described in more detail below. Reference numeral 7.1 in Figure 2 indicates a single combustion chamber of a can or can annular combustor. In other embodiments not shown, the combustor may be an annular combustor as described above.

[0016] The combustor 7 is supplied with an oxidizer stream provided by an oxidizer source. The oxidizer may be oxygen (O2) or a mixture of oxygen and carbon dioxide (CO2). The oxidizer stream can be generated by an air separation unit 9 having an oxidizer source. The air separation unit 9 can remove nitrogen or nitrogen and carbon dioxide from the ambient air to generate the necessary oxidizer stream supplied to the combustor 7 of the expander 3 through the oxidizer line 11. In some embodiments, for easier handling of the oxidizer stream, the oxidizer stream may contain about 20 vol% oxygen and 80 vol% carbon dioxide. The above CO2 and O2 ratios are examples. Carbon dioxide can be added to the oxygen through a recirculation line 12.

[0017] Reference numeral 13 indicates a fuel supply line adapted to supply natural gas, such as methane, to the combustor 7, specifically to each combustion chamber 7.1 of the combustor 7. The oxidizer and fuel are supplied to the combustor 7 at high pressure, for example, about 200 barA or more, preferably about 250 barA or more, or higher, for example, 300 barA or more, at the inlet side of the expander 3. Generally, the pressure may be less than 600 barA. The mixture of oxidizer and fuel is burned in the combustor 7. The pressurized, high-temperature combustion gas produced from the combustion expands in the expansion section 5 of the expander 3. The temperature at the outlet side of the fixed nozzle downstream of the combustor, i.e., at the inlet of the rotor of the expander 3, may be, for example, between 800°C and 1500°C.

[0018] The exhausted flue gas, after expansion, is discharged into the discharge line 15 on the discharge side of the expander 3. The flue gas in the discharge line 15 may have a temperature of approximately 400°C to approximately 700°C, for example, approximately 600°C, and a pressure of approximately 10 barA to approximately 100 barA, preferably approximately 20 barA to approximately 60 barA.

[0019] The circuit further includes a regenerative heat exchanger 17, where the high-temperature flue gas flowing through the high-temperature side 17.1 of the regenerative heat exchanger 17 is cooled by heat exchange with the flow of cooled flue gas flowing through the low-temperature side 17.2 of the regenerative heat exchanger 17. The flue gas discharged from the high-temperature side 17.1 of the regenerative heat exchanger 17 is further cooled in a cooling heat exchanger 19 to a temperature that causes condensation of the vapor contained in the discharged flue gas. The condensed water is removed from the exhausted flue gas in a water / gas separator 21.

[0020] The dewatered, exhausted, and cooled flue gas, consisting mainly or exclusively of carbon dioxide, is compressed in the flue gas compressor 23 to the pressure on the inlet side of the expander 3. In the schematic diagram of Figure 1, the flue gas compressor 23 is shown as a single compressor, but in some embodiments, multiple compressors may be used. For example, the flue gas compressor 23 may be a multi-stage compressor or a compressor train. In some embodiments, the main compressor may be set in series with one or more continuously arranged pumps.

[0021] 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 turbomachines arranged in series, the discharge line 25 can be connected between two consecutively arranged turbomachines.

[0022] Most of the 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 recycled to the expander 3 through the recirculation line 25. The flue gas recycled through the recirculation line 25 is mixed with the combustion gas generated in the combustor 7 or the oxidant stream from the oxidant line 11.

[0023] A sidestream of the 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.

[0024] The expander 3 can include an output shaft 31, and the mechanical power generated by the expansion of the combustion gas in the expansion section 5 of the expander 3 is available for mechanical drive or power generation purposes. In the exemplary embodiment of FIG. 1, the output shaft 31 is drivingly coupled to a generator 33, and the generator 33 is then electrically coupled to a power distribution network 35. In FIGS. 1 and 2, the output shaft is shown on the rear side of the expander 3. In other embodiments, not shown, the output shaft 31 can be arranged on the front side of the expander. In yet another embodiment, not shown, two output shafts can be provided, one on the front side and one on the rear side of the expander.

[0025] As used herein, "front" and "rear" refer to the direction of the process gas flow through the expander 3. Thus, "front" indicates the position on the side of the combustor 7, and "rear" indicates the position on the side opposite to the combustor 7, i.e., the discharge side of the expander 3.

[0026] 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 at high rated powers, such as about 50 MW or more, preferably about 100 MW or more, more preferably about 150 MW or more, for example, about 200 MW or more. The power factor may be, for example, 2000 MW or less, preferably 1500 MW or less, for example, 1000 MW or less, or 800 MW or less. In some embodiments, the power factor may fall within the range of 200 MW to 650 MW.

[0027] Continuing with reference to Figure 1, Figure 2 shows a cross-sectional view of the expander 3 in one embodiment, and Figure 3 shows an enlarged cross-sectional view of the details of the rotor of the expander.

[0028] The expander 3 comprises an outer casing 41 that houses 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. The high-pressure casing 41.1 may be barrel-shaped. The low-pressure exhaust casing 41.2 may be located on the exhaust 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 also be monolithic, i.e., it may consist of a single piece manufactured, for example, by forging, machining, casting, or a combination thereof.

[0029] 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.

[0030] 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. In some embodiments, the high-pressure casing 41.1 forms seats for individual combustion chambers 7.1, as shown in Figure 2.

[0031] Reference numerals 45 and 47 indicate bearing devices that rotatably support the rotor 43. For example, the bearing device 45 on the opposite side of 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.

[0032] The rotor 43 can be drivably coupled to the output shaft 31 via a joint 49. Bearing devices 45, 47 can be housed in bearing casings, which are not shown in detail.

[0033] 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, and form a bundle with the rotor housed inside.

[0034] The pressure drop across the expander 3 may be approximately 200 bar or more. A number of expansion stages is preferable to expand the combustion gas generated in the combustor 7. In the exemplary embodiment shown in Figure 2, 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. The expansion stages form axial passages through the expander 3 for the process gas to be expanded.

[0035] Each expansion stage includes an annular row of fixed vanes or fixed blades 53 fixedly arranged within the expander casing. In the exemplary embodiment shown in Figure 2, the annular row of fixed blades is housed within an inner casing 51. Each expansion stage further includes an annular row of rotor blades 55. Each row of rotor blades 55 is located downstream of the annular row of fixed blades along a process gas flow path that extends from the combustor 7 through the expansion section 5 to the discharge plenum 41.3 in a front-to-rear direction.

[0036] In some embodiments, a first annular row of fixed blades 53.1 may be located at the discharge end of the combustor 7 and may form an array of nozzles that guide high-temperature, high-pressure gas from the combustion chamber 7.1 of the combustor 7 to the first row of rotor blades. A first annular row of rotor blades, indicated by 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, indicated by 55.8, and near the discharge plenum 41.3. Reference numeral 55 collectively refers to any one of the annular rows of rotor blades or to the rotor blades themselves.

[0037] The rotor blades 55 form part of the rotor 43 and are connected to the rotor 43 so as to rotate together with the rotor shaft 65. In this embodiment, each annular row of rotor blades 55 (i.e., each row 55i, i=1 to 8) is connected to its respective rotor disk. The rotor disks are labeled 57.1, 57.2, 57.3, 57.4, 57.5, 57.6, 57.7, and 57.8. Reference numeral 57 indicates a general rotor disk.

[0038] The rotor blades may be manufactured separately from each rotor disk and mounted to the rotor disk. In other embodiments, each rotor disk or some thereof may be manufactured together with each rotor blade as a monolithic block, for example by additive manufacturing.

[0039] As best shown in Figure 3, the rotor disc 57 is shrink-fitted onto the shaft 65 of the rotor 43.

[0040] In this embodiment, the shaft 65 comprises a front shaft portion 65A, an intermediate shaft portion 65B, and a rear shaft portion 65C. The rotor disc 57 is preferably shrink-fitted along the intermediate shaft portion 65B.

[0041] In some embodiments, the shaft 65 and the rotor disc 57 can be made from the same metallic material. In other embodiments, for example, to more efficiently prevent loosening of the angular connection between the shaft 65 and the rotor disc 57 due to a temperature gradient, for example, during transient conditions, the shaft 65, particularly its intermediate shaft portion 65B, is made from a material having a first coefficient of thermal expansion, and the rotor disc 57 is made from a different material having a second coefficient of thermal expansion lower than the first. In embodiments, the shaft 65, specifically the intermediate shaft portion 65B, is made from a metal or metallic alloy having a higher coefficient of thermal expansion than the material from which the rotor disc 57 is made. The higher coefficient of thermal expansion of the inner portion of the rotor consisting of the intermediate shaft portion 65B results in greater thermal expansion of the shaft portion than of the rotor disc, thereby ensuring a stable connection between the rotor disc on one side and the shaft on the other side.

[0042] In this embodiment, the rotor 43 may include a balance drum. The balance drum can be formed on the front shaft portion or the rear shaft portion.

[0043] As will be described in detail below, in the embodiments shown in the drawings, the balance drum is formed by the forward shaft portion 65A of the rotor shaft. In some embodiments, the forward shaft portion 65A can be manufactured in two or more sections, as shown in Figure 2.

[0044] The intermediate shaft portion 65B and the rear shaft portion 65C are preferably manufactured monolithically as a single body, i.e., as a single block.

[0045] To support the axial force generated by the expansion of the process gas and applied to the rotor blades 55 and rotor disks 57, an annular contact portion 65D may be provided on the intermediate shaft portion 65B. The annular contact portion 65D may be located in the transition zone between the intermediate shaft portion 65B and the rear shaft portion 65C. At least the furthest downstream rotor disk 57.8 will contact the annular contact portion 65D, thereby transmitting the axial thrust applied to it to the rotor shaft.

[0046] All of the remaining shrink-fitted rotor discs 57.1–57.7 can be pressed together axially by the force generated by the expansion of the process gas, so that the contact portions 65D cooperate to support the entire axial load applied to the rotor discs 57. An annular separation ring 64 (see Figure 3) is positioned between adjacent rotor discs 57 to transmit the axial thrust applied to each rotor disc 57 from front to back to the next rotor disc.

[0047] In some embodiments, an intermediate contact ring, also called a shear ring, labeled 66, can be mounted along the intermediate shaft portion 65B between at least one pair of adjacent rotor disks 57, or preferably between multiple pairs of adjacent rotor disks 57, as schematically shown in Figures 2, 3, and 6. In Figure 2, the shear ring is positioned at even positions after each rotor disk 57, i.e., after the second, fourth, and sixth rotor disks 57.2, 57.4, and 57.6.

[0048] In some embodiments, at least one, preferably each intermediate contact ring or shear ring 66, may be manufactured from two or more ring sections or ring sectors. The ring sectors may be housed in tangential slots 70 machined into the intermediate shaft portion 65B. In some embodiments, the tangential slots 70 may include a plurality of tangential slots, each extending over an angle of less than 360° around the rotor axis. Each shear ring sector may be housed in its respective tangential slot.

[0049] For example, Figure 6 shows an enlarged cross-sectional view of a portion of the rotor, in which two tangential slots 70 are separated by a radial projection, and a cooling duct 72, which will be described in more detail below, extends through the radial projection. A separate shear ring sector 66 is housed in a separate tangential slot.

[0050] This ensures a secure mechanical connection and guarantees the transmission of axial thrust generated on each rotor disc during the operation of the expander 3 to the rotor shaft 65. More specifically, the shear rings provide structural separation between axial thrust and torque transmission to make the rotor design more effective and improve mechanical resistance.

[0051] Between adjacent rotor discs 57, there is typically an annular space 58, closed by a seal runner 68, which is adapted to receive cooling fluid and / or purge fluid. In some embodiments, the rotor 43 includes one or more cooling ducts that extend axially, i.e., parallel to the axis of rotation AA, or more generally longitudinally along the rotor 43.

[0052] Each cooling duct is adapted to supply a cooling fluid to one or more annular spaces 58. In some embodiments, at least one independent cooling duct supplies a cooling fluid to only one annular space 58. In some embodiments, for particularly efficient cooling or purging of the annular spaces 58, multiple cooling ducts, e.g., two, three, or four cooling ducts, are provided in each annular space 58, and each cooling duct supplies a cooling medium to only one of its respective annular spaces 58.

[0053] One cooling duct 72 is shown in the cross-sectional views of Figures 3 to 6. Each cooling duct 72 has an inlet end 72A which is fluidly coupled to a cooling plenum 74 (Figure 2) which can be provided in the forward region of the outer casing 41.

[0054] In the embodiment, each cooling duct 72 can be formed by a slot extending longitudinally, preferably parallel to the axis of rotation, along the rotor shaft, specifically the intermediate shaft portion 65B. Each cooling duct 72 can be manufactured by milling and initially formed as a channel that opens radially outward. A slab 72C can be welded along the slot, thus closing the slot radially outward and forming a cooling duct 72 having an inlet and an outlet at both ends.

[0055] The rotor 43 can be cooled by supplying a pressurized cooling fluid to a cooling plenum 74, from which it is supplied to a cooling duct 72 formed in the rotor 43. Specifically, in some embodiments, compressed and cooled carbon dioxide can be delivered to the cooling plenum 74.

[0056] Each cooling duct 72, or each cooling duct 72, has at least one outlet aperture 72B fluidly coupled to a single annular space 58, which delivers a cooling fluid therein. In some embodiments, the same cooling duct 72 may have multiple outlet apertures fluidly coupled to multiple annular spaces 58. In the embodiment shown in Figure 3, the cooling duct 72 has a single outlet aperture 72B fluidly coupled to a single intermediate annular space 58. Two or more cooling ducts can be fluidly coupled to each annular space 58. In the embodiment of Figure 3, the outlet apertures 72B are fluidly coupled to the annular space 58 via ports 64A formed in each of the separating rings 64.

[0057] The cooling fluid delivered to the annular space 58 between adjacent rotor disks 57 and beneath each seal runner 68 functions to purge each annular space 58, preventing process gas from flowing through it, and thus increasing the efficiency of the expander 3. Therefore, the pressure of the cooling fluid must be sufficient to balance the pressure of the process gas expanding along the flow path formed by the fixed blades 53 and rotor blades 55. The pressure of the process gas decreases along the flow path from the first expander stage to the last expander stage. The cooling fluid pressure required in the most upstream expander stage may be, for example, between 200 barA and 600 barA. The axial thrust generated on the rotor disks 57 by the cooling fluid can be balanced by the shrink-fit coupling between the rotor disks and the shaft 65, and possibly by the annular contact portion 65 and shear ring 66.

[0058] In some embodiments, the expander 3 includes a balance drum drivably coupled to the rotor 43. In the embodiment shown in Figure 2, the balance drum 75 is located at the front end of the rotor 43 between the first expander stage and the front bearing device 47, and is more specifically formed by the front shaft portion 65A.

[0059] In some embodiments, the balance drum 75 is formed integrally with the front shaft portion 65A.

[0060] In the embodiment shown in Figure 2, the balance drum 75 comprises two balance drum portions 75A and 75B connected to each other by a pair of tie rods 77 positioned around a rotating shaft AA. The tie rods 77 connect the balance drum portions 75A and 75B to each other and to a front end section 79 of a front shaft portion 65A, the front end section 79 extending through a front bearing device 47.

[0061] In addition, the tie rod 77 connects the balance drum 75 and the front end section 79 of the rotor shaft 65 to the intermediate shaft section 65B.

[0062] In some embodiments, the front shaft portion includes an inner flange 82 which can be coupled to a coaxial shank 65F of the intermediate portion 65B of the shaft 65. The balance drum 75 is coupled to the flange 82 by a tie rod 77. The flange 82 can be coupled to the shank 65F by a nut 84 which is screwed onto the threaded portion of the shank 65F.

[0063] By dividing the front shaft portion 65A into several components, specifically the balance drum portions 75.1 and 75.2, the front shaft end portion 79, and the flange 82, the manufacturing of the balance drum and the front shaft portion 65A by, for example, forging becomes easier.

[0064] 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.

[0065] For example, in the embodiments disclosed herein, the combustor is housed in the expander, but in other embodiments, the combustor may be located outside the expander.

[0066] In yet another embodiment, the expander disclosed herein can be used in a closed-loop thermodynamic cycle such as a supercritical carbon dioxide cycle, in which heat is introduced into the thermodynamic cycle via a heat exchanger rather than using a combustor.

Claims

1. An expander for supercritical or subsupercritical carbon dioxide thermodynamic cycles, - Outer casing and, - At least one combustor combined with 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, → Shaft and, →A rotor comprising a plurality of rotor discs attached to an intermediate shaft portion, each of the plurality of rotor discs having a corresponding annular row of rotor blades, - 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 duct extending along the shaft, having an inlet end adapted to be fluidly coupled to the high-pressure plenum of the turbomachinery when the rotor is mounted on the turbomachinery, and to be fluidly coupled to at least one intermediate annular space between a pair of continuously arranged rotor discs, An expander, wherein each of the plurality of rotor disks is attached to the shaft by shrink-fitting.

2. The expander according to claim 1, wherein the shaft is made at least partially of a first metal alloy, and the rotor disc is made of a second metal alloy, the first metal alloy having a higher coefficient of thermal expansion than the second metal alloy.

3. The inflator according to claim 1 or 2, wherein the shaft comprises a front shaft portion, an intermediate shaft portion, and a rear shaft portion, the rotor disc is shrink-fitted to the intermediate portion of the shaft, the intermediate shaft portion and the rear shaft portion are integrally formed as a monolithic body, the shaft has a contact portion formed monolithically with the shaft between the intermediate portion and the rear portion, and at least the most downstream side of the rotor disc abuts against the contact portion.

4. The expander according to claim 3, further comprising at least one annular contact portion attached to the intermediate shaft portion of the shaft and positioned between two consecutive rotor discs.

5. An inflator according to any one of claims 1 to 4, further comprising a balance drum.

6. The inflator according to claim 3 or 4, wherein the front shaft portion is characterized by a balance drum.

7. The inflator according to claim 5 or 6, wherein the balance drum comprises a first balance drum portion and a second balance drum portion connected to each other via at least one tie rod, preferably via a plurality of tie rods arranged circumferentially at a radial distance from the rotation axis of the rotor.

8. The expander according to claim 7, wherein the front shaft portion is provided with an inner flange coupled to the coaxial shank of the intermediate portion, and the balance drum is coupled to the flange by the tie rod.

9. An expander according to any one of claims 1 to 8, further comprising a separation ring between adjacent pairs of rotor discs.

10. The expander according to any one of claims 1 to 9, further comprising at least one shear ring interposed between two consecutive rotor discs.

11. An expander according to any one of claims 1 to 10, further comprising a plurality of cooling ducts for a plurality of rotor stages, each cooling duct having an inlet end that extends along the shaft and is adapted to be fluidly coupled to the high-pressure plenum of the turbomachinery when the rotor is mounted on the turbomachinery, and to be fluidly coupled to the respective intermediate annular spaces between a pair of continuously arranged rotor discs.

12. The expander according to any one of claims 1 to 11, wherein each cooling duct is configured as a slot extending longitudinally along the rotor and inside the outer surface of the rotor, and the slot is closed by a slab having an inner surface facing the slot and an outer surface coplanar with the outer surface of the rotor.

13. The expander according to any one of claims 1 to 12, wherein each cooling duct is fluidly coupled to its respective annular space via a port provided in a separating ring, and the separating ring is positioned between a pair of continuously arranged rotor disks, with the annular space formed between them.

14. The expander according to any one of claims 1 to 13, further comprising at least one shear ring having a plurality of ring sectors, each ring sector being housed in a respective tangential slot of the rotor, and the at least one cooling duct extending between two adjacent ring sectors and the respective tangential slots in which the ring sectors are housed.

15. The inflator according to claim 10 or 14, comprising multiple shear rings for multiple rotor disks, with at least one shear ring for each rotor disk.

16. An expander according to any one of claims 1 to 15, further comprising a high-pressure plenum adapted to receive a compressed refrigerant fluid and fluidly coupled to at least one cooling duct extending along the shaft, wherein the cooling duct is fluidly coupled to the high-pressure plenum and to at least one intermediate annular space between a pair of continuously arranged rotor discs.

17. The expander according to any one of claims 1 to 16, 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 axis of rotation.

18. The inflator according to claim 17, wherein the high-pressure casing comprises a monolithic barrel body.

19. The expander according to claim 17 or 18, wherein the low-pressure exhaust casing is configured as a monolithic body.

20. The expander according to any one of claims 1 to 19, wherein the outer casing comprises at least one seat portion, and the at least one combustor is at least partially housed in the seat portion.

21. The expander according to claim 19, wherein the low-pressure exhaust casing forms a discharge plenum.

22. An inflator according to any one of claims 1 to 21, further comprising at least one inner casing, preferably a plurality of inner casings, which are fixedly housed within the outer casing and surround the rotor, 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, and the inner casing including an annular row of fixed blades.

23. The expander according to any one of claims 1 to 22, wherein the rotor is adapted to receive a process gas at a temperature T of 800°C to 1500°C.

24. The expander according to any one of claims 1 to 23, wherein the rotor is adapted to receive process gas at a pressure higher than 50 barA, preferably higher than 100 barA, more preferably 200 barA or higher, and the rotor is adapted to receive process gas at a pressure lower than 800 barA, preferably 650 barA or lower.

25. An expander according to any one of claims 1 to 24, which is adapted to generate power higher than 50 MW, preferably 100 MW or more, and preferably lower than 2000 MW.

26. A supercritical or subsupercritical 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 to condense the moisture contained in the flue gas, The system includes a regenerative heat exchanger through which 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 25, in a supercritical or subsupercritical carbon dioxide thermodynamic circuit.

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