Expander with preheating system and method

Description

1 / 19 EXPANDER WITH PREHEATING SYSTEM AND METHOD DESCRIPTION TECHNICAL FIELD

[0001] The present disclosure relates to expanders for generating mechanical power through a thermodynamic cycle. The embodiments disclosed herein relate specifically to oxyfuel expanders and expanders specifically designed for supercritical CO2 cycles. BACKGROUND OF THE TECHNIQUE

[0002] Expanders, sometimes called turboexpanders, are turbomachines including sequentially arranged stationary blades, also called stationary vanes, housed in a housing and rotor blades that are part of a rotor supported for rotation in the housing. The stationary blades and rotor blades define an expansion flow path for a process gas, which flows through the expander. The enthalpy drop of the process gas is converted into mechanical power available at the expander shaft.

[0003] The expander comprises at least one annular row of stationary blades and one annular row of rotor blades mounted on a rotor for co-rotation with the same in the expander compartment. More frequently, the expander includes a plurality of sequentially arranged annular rows of stationary blades and a plurality of sequentially arranged annular rows of rotor blades, the stationary blades and rotor blades being arranged in an alternating manner, one row of rotor blades following one row of stationary blades in the direction of the process gas flow. Each pair of rows of Petition 870250088288, dated 09 / 29 / 2025, page 14 / 124 2 / 19 stationary blades and a row of rotor blades form one stage of the expander.

[0004] Under all operating conditions of the expander, there must be a clearance between the stationary and rotating components along the flow path, sufficient to prevent frictional contact between them. The mutual distance must, however, be as small as possible when the expander operates in equilibrium conditions, to reduce gas leakage from the flow path, since leakage reduces the efficiency of the expander.

[0005] In some cases, for example, in oxyfuel expanders and expanders operating with supercritical carbon dioxide flow, the rotor may have a higher heat transfer coefficient compared to the stator components. This can cause accidental frictional contact between stationary and rotating components during expander start-up, since the rotor's thermal expansion is faster than the stator's thermal expansion. To prevent friction between stator and rotor components during temporary start-up conditions, a larger clearance between these components needs to be considered, which negatively affects the expander's efficiency under steady-state operating conditions.

[0006] An expander adapted to avoid or alleviate the above disadvantages of expanders of the current technique would be welcome. SUMMARY

[0007] According to one aspect, an expander is disclosed herein comprising a compartment including an outer compartment and an inner compartment. The inner compartment is disposed within the outer compartment and houses at least one set of annularly arranged stationary blades forming an annular row of stationary blades. The expander further includes at least one Petition 870250088288, dated 09 / 29 / 2025, page 15 / 124 3 / 19 first annular fluid chamber between the inner and outer compartments. The inner compartment has a perimeter wall with an outer surface facing the annular fluid chamber and an inner surface. A rotor is housed at least partially in the inner compartment and is provided with at least one set of annularly arranged rotor blades and, preferably, a plurality of sets of annularly arranged rotor blades, for example, between four and fifteen sets of rotor blades, each arranged downstream of a respective set of stationary annularly arranged blades. The expander further includes a preheating arrangement, adapted to preheat the inner compartment and cause its thermal expansion upon start-up of the expander.Preheating increases the gap or clearance between stationary and rotating components during start-up transients, preventing accidental contact between them. Once a steady-state operating condition is reached, the initially widened gap or clearance narrows again to a minimum steady-state clearance, reducing process gas leakage from the expansion flow path.

[0008] According to another aspect, a method of operating an expander at startup is disclosed here, the expander being configured as described above. The method comprises the step of preheating the internal compartment at startup of the expander and increasing a clearance between the rotor and the stationary components supported in the internal compartment by the thermal expansion of the internal compartment.

[0009] The expander can be preheated at startup so that the internal compartment expands thermally and prevents friction between the rotor components and the stationary beam components of the expander. Once an equilibrium temperature condition is reached, the expander parts, such as the rotor or parts of the Petition 870250088288, dated 09 / 29 / 2025, p. 16 / 124 4 / 19, they can be cooled to prevent overheating during steady-state operating conditions.

[0010] Other features and embodiments of the method and expander according to the present disclosure are set forth in the dependent claims and are described in the embodiment description below. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Now, brief reference is made to the attached drawings, in which: Figure 1 is a schematic diagram of an oxyfuel power circuit; Figure 2 is a cross-sectional view along an expander according to the present disclosure in an embodiment; Figure 3 is an enlargement of the expander in Figure 2. DETAILED DESCRIPTION

[0012] In the following description, reference will be made specifically to an oxy-fuel expander, that is, an expander designed specifically for an oxy-fuel combustion cycle. However, the features disclosed here can be advantageously used in different thermodynamic cycles, such as closed supercritical or transcritical carbon dioxide cycles, for example.

[0013] The schematic diagram in Figure 1 illustrates a simplified oxy-fuel cycle operating with supercritical carbon dioxide (hereinafter, SCO2 cycle), as an Aliam oxy-fuel cycle. As understood in the present invention, a supercritical cycle is a cycle in which carbon dioxide is in supercritical conditions at least at the highest pressure point along the thermodynamic cycle, i.e., at the inlet of the expanding rotor.

[0014] The power system 1 shown in Figure 1 comprises an expander 3 which includes an expansion section 5 and a combustor 7. The Petition 870250088288, dated 09 / 29 / 2025, p. 17 / 124 5 / 19 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 combustor chambers arranged around the axis of rotation of the expander 3, as shown in detail in Figure 2. In some embodiments, the combustor chambers are housed in the outer compartment of the expander, as will be described in detail below. In other embodiments, the combustor may be combined with the compartment, but arranged on or around the compartment. For example, a transition piece may be provided to fluidly connect the combustor to the expansion flow path inside the expander.

[0015] Reference number 7.1 in Figure 2 designates the combustion chamber of an annular combustor or each combustion chamber of a can or annular can type combustor.

[0016] Combustor 7 is supplied with an oxidant stream distributed by an oxidant source. The oxidant can be oxygen (O2) or a blend of oxygen and carbon dioxide (CO2). The oxidant stream can be produced by an air separation unit 9, which has an oxidant source. The air separation unit 9 can remove nitrogen or nitrogen and carbon dioxide from ambient air to produce the required oxidant stream that is supplied through an oxidant line 11 to combustor 7 from expander 3. Carbon dioxide can be added to the oxygen so that an oxygen and carbon dioxide blend is distributed to the expander, the blend containing a sufficient percentage of carbon dioxide to prevent damage to the piping.

[0017] Reference number 13 indicates a fuel supply line, for example, adapted to supply natural gas, such as methane, to combustor 7. In the embodiment shown in Figure 2, the Petition 870250088288, dated 09 / 29 / 2025, page 18 / 124 6 / 19 Fuel is supplied to each combustor chamber 7.1. The oxidizer and fuel are supplied to the combustor 7 at a high pressure, for example, around or above 50 barA, preferably at or above 100 barA, for example, at or above 150 barA, or at or above 200 barA, preferably around or above 250 barA, or higher, for example, at or above 300 barA. In some embodiments, the pressure at the expander inlet is less than 800 barA, preferably less than 650 barA. The oxidizer-fuel blend is burned in the combustor 7. The resulting pressurized hot combustion gas expands in the expansion section 5 of the expander 3.

[0018] The exhausted combustion gas is discharged on a discharge side of the expander 3 into a discharge line 15. The combustion gas in the discharge line 15 may be around 600 °C, for example, and at a pressure that may be between 10 barA and 100 barA, for example, between 20 barA and 60 barA.

[0019] The expander can be designed for a rated power value, 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 MW or lower than 800 MW. For example, the rated power can be between 200 MW and 650 MW.

[0020] The circuit further comprises a regenerative heat exchanger 17, wherein the hot combustion gas flowing through a hot side 17.1 of the regenerative heat exchanger 17 is cooled by heat exchange with a stream of chilled combustion gas flowing in a cold side 17.2 of the regenerative heat exchanger 17. The combustion gas discharged from the hot side 17.1 of the regenerative heat exchanger 17 is further chilled in a heat exchanger of Petition 870250088288, dated 09 / 29 / 2025, page 19 / 124 7 / 19 refrigeration 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.

[0021] 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 and may include one or more pumps in series.

[0022] The compressed combustion gas distributed by the combustion gas compressor 23 is partially removed from the cycle through a discharge line 25. The remaining compressed combustion gas is distributed through the cold side 17.2 of the regenerative heat exchanger 17 and is heated by heat exchange with the hot combustion gas flowing through the hot side 17.1 of the regenerative heat exchanger 17 and recycled to the expander 3 through a recycling line 25. The combustion gas recycled through the recycling line 25 is mixed with the combustion gas generated in the combustor 7 or with the oxidizer stream of the oxidizer line 11.

[0023] A side stream of chilled flue gas is distributed through a cooling line 27, which bypasses the regenerative heat exchanger 17, towards the expander components 3 that require cooling. An additional side stream of chilled and dehydrated flue gas can be distributed through a line 28 to the air separator 9 and / or to the oxidizer line 11 to blend carbon dioxide with oxygen from the air separator 9, so that a blend Petition 870250088288, dated 09 / 29 / 2025, p. 20 / 124 8 / 19 of oxygen and carbon dioxide is supplied to combustor 7. In embodiments, the oxygen and carbon dioxide blend may include 20% by volume of oxygen and 80% by volume of carbon dioxide.

[0024] The expander 3 may include an output shaft 31, in which 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 Figure 1, the output shaft 31 is drive-coupled to an electric generator 33, which is, in turn, electrically coupled to an electrical power distribution network 35. In Figures 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 may be arranged on the front side of the expander. In still other embodiments, not shown, two output shafts may be provided, one on the front side and the other on the rear side of the expander.

[0025] 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.

[0026] Figure 2 illustrates a cross-sectional view of the expander 3 in one embodiment. The expander 3 may comprise an outer compartment 41, which may house the combustor 7. In some embodiments, the outer compartment 41 includes a high-pressure compartment 41.1, in the form of a cylinder, and a low-pressure exhaust compartment 41.2. The high-pressure compartment 41.1 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 high-pressure compartment 41.1 may be manufactured by combining annular components with each other, for example, by welding. Annular, as used herein, means that the Petition 870250088288, dated 09 / 29 / 2025, page 21 / 124 9 / 19 component extends around the expander axis without separations, as a single block or piece, to provide sufficient resistance to the high pressure values ​​within the high-pressure compartment 41.1

[0027] . The low-pressure exhaust compartment 41.2 may be positioned on the discharge side, i.e., on the rear side, of the expander 3, i.e., opposite the combustor 7. The low-pressure exhaust compartment 41.2 may also be monolithic, i.e., it may consist of a single piece. In other embodiments, the low-pressure exhaust compartment 41.2 may consist of a plurality of components connected to each other. For example, the low-pressure exhaust compartment 41.2 may be divided along a plane containing the rotor's axis of rotation. The coupling of the components forming the low-pressure exhaust compartment 41.2 may be by welding or may be a reversible connection by threads or bolts.

[0028] 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 an axis of rotation AA of a rotor 43 supported for rotation in the outer compartment 41. The outer compartment 41 is therefore a so-called vertically split compartment.

[0029] 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.

[0030] Reference numbers 45, 47 indicate bearing arrangements that rotatably support rotor 43. For example, bearing arrangement 45 on the rear side, i.e., opposite the combustor 7, 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 Petition 870250088288, dated 09 / 29 / 2025, page 22 / 124 10 / 19 front side, may include a radial bearing. An inverted arrangement is also possible, with a bearing having axial load capacity disposed on the combustor side. Bearing arrangements 45, 47 may be disposed in bearing housings, not shown in detail. The rotor 43 may be actuatively coupled to a shaft 31 of a load, such as a compressor or an electric generator, by means of a joint 49.

[0031] The rotor 43 is surrounded by an inner compartment 51, housed in the outer compartment 41. The inner compartment may be formed by a plurality of sections arranged sequentially in a front-to-back direction. The inner compartment 51 may be divided horizontally, that is, it may include two portions that are coupled to each other along a plane containing the axis of rotation of the rotor 43. If the inner compartment 51 comprises a plurality of axially aligned sections, each section or some of them may be divided horizontally.

[0032] One or more annular fluid chambers 42 are formed between the inner compartment 51 and the outer compartment 41. Specifically, in the exemplary embodiment shown in Figure 2, the annular chamber 42 includes two sequentially arranged annular fluid chambers 42.1 and 42.2 separated by a septum 44, which mechanically connects the inner compartment 51 to the outer compartment 41. The fluid pressure within the two annular fluid chambers 42.1 and 42.2 may be different. For example, the front annular fluid chamber 42.1 may be at a higher pressure than the rear annular fluid chamber 42.2. In use, under steady-state conditions, the cooling or refrigerant fluid may be supplied to the rear fluid chamber 42.2 and the front fluid chamber 42.1. For example, the refrigerant or cooling fluid may include dehydrated combustion gas from cooling line 27, which may consist primarily or exclusively of carbon dioxide. Petition 870250088288, dated 09 / 29 / 2025, page 23 / 124 11 / 19

[0033] The inner compartment 51 includes a wall 51.3 (see Figure 3), which has an outer surface 51.1 facing the annular fluid chamber 42 and an inner surface 51.2 facing the rotor 43.

[0034] The pressure drop across the expander 3 can be about 200 bar or higher. 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 to 7, the expander 2 includes eight stages, each configured as an axial expansion stage. 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 less than fifteen.

[0035] Each expansion stage includes an annular row of stationary blades or stationary vanes 53 that are stationarily arranged in the inner compartment 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 a flow path extending from the combustor 7 through the expansion section 5 to the discharge volute 41.3 in a front-to-back direction.

[0036] The rotor blades 55 are part of the rotor 43, that is, they are connected to it or manufactured as a single block with it, for co-rotation with the rotor shaft. In embodiments, each annular row of rotor blades 55 is connected to a respective rotor disc, not shown in detail, or monolithically formed with it as a single body. The structure of the rotor and rotor discs is not relevant and is not shown in detail.

[0037] In some embodiments, sequentially arranged annular rows of rotor blades are separated from each other by a Petition 870250088288, dated 09 / 29 / 2025, p. 24 / 124 12 / 19 respective sealing jig 56 (see Figure 3). A respective annular row of stationary blades 53 is arranged around the sealing jig 56 radially outward from it.

[0038] In some embodiments, the rotor 43 additionally comprises a front axis portion 65 and a rear axis portion 67. In some embodiments, the combustor 7 extends around the front axis portion 65. For example, the combustor 7 comprises a plurality of combustion chambers 7.1, each of which may be housed, wholly or partially, in a seat formed in the high-pressure compartment 41.1, and the combustion chambers 7.1 may be arranged around the axis of rotation AA.

[0039] In some embodiments, the full discharge space 41.3 extends around the rear axle portion 67.

[0040] Figure 3 illustrates an enlarged detail of an expander stage 3 of Figure 2. More specifically, Figure 3 shows the flow passage through an expander stage. The stage shown in Figure 3 includes an annular row of stationary blades 53 followed by an annular row of rotor blades 55. F indicates the flow of combustion gas expanding through the expander stage.

[0041] In some embodiments, each rotor blade 55 has a shaft or foot 55.1, with which the blade is mechanically connected to the rotor, and a radially outward-facing tip 55.2. The tip 55.2 may be provided with fins or blades 55.3 arranged at a distance from a radially inward-facing surface 71.1 of a stationary casing 71, which is connected to or forms part of the inner compartment 51. The radially inward-facing surface 71.1 of the stationary casing 71 may be formed by an annular layer of abradable material 71.2. In some embodiments, the abradable material layer may be omitted.

[0042] The distance between the knives 55.3 and the surface 71.1, that is, the clearance between the rotating blades 55 and the stationary casing 71 must be Petition 870250088288, dated 09 / 29 / 2025, page 25 / 124 13 / 19 as small as possible. This distance or gap is indicated in the present invention as clearance C. In operation, clearance C must be small enough to prevent gas from flowing through it, or at least to reduce the gas flow rate through it, since gas expanding through clearance C will not contribute to the generation of mechanical power. At the same time, clearance C must be large enough to prevent mutual contact and accidental friction between the stationary casing 71 and the rotating blades 55 under all operating conditions of the expander 3, i.e., both under steady-state operating conditions and during transients, such as at start-up.

[0043] In the embodiment of Figure 3, the wall 51.3 of the inner compartment comprises a plurality of cooling ducts 73, 75, each of which has a respective duct inlet 73.1, 75.1, fluidly coupled to the annular fluid chamber 42, and a respective duct outlet 73.2, 75.2.

[0044] Cooling ducts 73 are adapted to establish a fluid connection between the annular fluid chamber 42 and an annular cooling-filled space 77 positioned radially outward from the stationary enclosure 71, opposite the abradable material 71.2. Cooling ducts 75 are arranged so as to establish a fluid connection between the annular fluid chamber 42 and an annular cooling-filled space 79 positioned radially outward from the stationary blades 53. In the cross-sectional view of Figure 3, only one cooling duct 73 and only one cooling duct 75 are visible, but it should be understood that a plurality of cooling ducts 73 may be provided, for example, one or more for each annular cooling-filled space 77, and a plurality of cooling ducts 75 may be provided, for example, one or more for each annular cooling-filled space 79. Petition 870250088288, dated 09 / 29 / 2025, page 26 / 124 14 / 19

[0045] The arrangement disclosed above provides a cooling circuit that can be fed with chilled combustion gas via cooling line 27 (Figure 1).

[0046] During steady-state operation of the expander 3, cooling carbon dioxide (or any other cooling fluid) is distributed to the annular fluid chamber 42, i.e., to each annular fluid chamber 42.1, 42.2, and flows within the inner compartment 51 to cool the stationary blades 53 and the stationary casing 71. The clearance C is designed so that, under steady-state operating conditions, the rotor and stator temperatures are maintained at values ​​such that the clearance C is minimized, but is sufficient to prevent frictional contact between the rotor blades 55 and the stationary casing 71 at each stage of the expander 3.

[0047] In some embodiments, each annular row of stationary blades 53 may be provided with an inner stationary envelope 72, facing the respective sealing jet 56. The inner stationary envelope 72 comprises a surface 72.1 facing radially inwards, that is, facing the respective sealing jet 56. The surface 72.1 may be the outer surface of a layer of abradable material 72.2. In some embodiments, the abradable material 72.2 may be omitted. The radially inward surface 72.1 of the stationary inner casing 72 is at a distance C2 (clearance C2) from the fins or blades 56.1 of the respective sealing element 56. In the same way as the clearance C, the clearance C2 should also be as small as possible, to reduce the flow of expanding gas escaping through it, instead of flowing through the flow path (F) between the stationary blades 53 and the rotor blades 55.

[0048] To cool the stationary blades 53 and control the dimension of the gap C2, the cooling fluid is distributed to the filled annular cooling space 79. Petition 870250088288, dated 09 / 29 / 2025, page 27 / 124 15 / 19

[0049] During starting, a risk of contact between the rotating components (sealing rings 56 and rotor blades 55) and the stationary components (stationary casing 71 and inner stationary casing 72) may occur due to the temperature gradient, the geometry of the mechanical components, as well as the heat transfer coefficients and the coefficients of thermal expansion of the rotor and the stationary components, respectively. This is particularly due to the rotor heating up and thermally expanding faster than the casing.

[0050] To avoid the need to maintain larger clearances under steady-state operating conditions and also to avoid mechanical friction contact between the housings 71 and the rotor blade tips 55.2 and between the housing 72 and the sealing ring 56 during transient operating conditions and specifically at startup, the expander 3 includes a preheating arrangement. The preheating arrangement is adapted to preheat the inner compartment 51 of the expander 3 at startup, i.e., when the expander is at or around ambient temperature, for example. The mechanical coupling between the inner compartment 51 and the outer compartment 41 may be such that a radial displacement of the inner compartment 51 relative to the outer compartment 41 is permitted, to allow thermal expansion of the inner compartment 51 when the outer compartment 41 is still cold, for example, at startup.

[0051] Preheating of the inner compartment 51 causes a radial thermal expansion of the same. The thermal expansion of the inner compartment 51 causes an outward radial displacement of the casings 71 and 72, and specifically of surface 71.1 and surface 72.1. Preheating of the inner compartment 51 can be performed entirely before the rotor 43 starts rotating, or when the rotor 43 has started rotating, or partially before and partially after the rotor has started rotating. In any case, the preheating is controlled by Petition 870250088288, dated 09 / 29 / 2025, page 28 / 124 16 / 19 so that the radial thermal expansion of the stationary components prevents any contact between the rotating component of the rotor 43 and the stationary components housed in the internal compartment 51. Thus, preheating expands the stationary components before frictional contact occurs between the stationary and rotating parts of the expander, due to the thermal expansion of the rotor.

[0052] Preheating the inner compartment 51 increases the clearance C between the blades 55.3 of the blade tips 55.2 and the inner surface 71.1 of the housings 71 and the clearance C2 between the blades or fins 56.1 of the sealing joints 56 and the inner surface 72.1 of the inner housings 72.

[0053] The increased clearances obtained by preheating prevent accidental friction of the rotor blades 55 against their respective housings 71 and of the housings 72 against the sealing rings 56, even if the initial (cold) and final (hot) clearances C and C2 are very small.

[0054] Preheating of the inner compartment 51 can be performed by supplying a preheating fluid to the annular fluid chamber 42, i.e., to the annular fluid chambers 42.1 and 42.2. The preheating fluid enters the inner compartment 51 through the cooling ducts 73, 75 and heats the wall 51 of the inner compartment as well as the casings 71, 72 of each expansion stage of the expander 3. Preheating causes an outward radial thermal expansion and a temporary increase in clearances C and C2. This increase will subsequently be compensated by an expansion of the rotor, i.e., clearances C, C2 will be reduced due to the gradual radial expansion of the rotor 43.

[0055] The expander 3 can thus begin to operate without a risk of frictional contact between rotating components (rotor blades 55, sealing joints 56) and stationary components (enclosures 71,72), since the radial thermal expansion of the compartment 51 is anticipated in relation to the radial thermal expansion of the rotor 43. Petition 870250088288, dated 09 / 29 / 2025, page 29 / 124 17 / 19

[0056] After starting, the hot compressed combustion gas flowing in the flow path between the stationary blades 53 and the rotor blades 55 will gradually heat the rotor, causing its thermal expansion and further heating the inner compartment, causing its additional thermal expansion. Once the inner compartment 51 has been preheated, the clearances C, C2 will be large enough to prevent frictional contact between rotating and stationary components, even though the radial expansion of the rotor 43 is faster than the radial expansion of the inner compartment 51.

[0057] The circulation of the preheating fluid will be interrupted when equilibrium temperature conditions are reached or, in any case, when the radial expansions of non-rotating and rotating components have reached such values ​​that mutual contact between them is avoided. At this stage, the cooling circuit, which was used to preheat the internal compartment 51, can be used to circulate a cooling fluid to maintain the internal compartment at the required equilibrium temperature. In fact, the same fluid that acts as a preheating fluid at startup can act as a cooling fluid under equilibrium conditions.

[0058] Figure 2 shows a schematic arrangement 80 that can be used to selectively supply preheating and cooling fluid to the annular fluid chamber 42 (chambers 42.1, 42.2) and from there to the cooling ducts 73, 75. The arrangement may include a heat exchanger 81 with a hot side 81.1 and a cold side 81.2. The hot side 81.1 may be fluidly coupled to a heat transfer fluid source 83 via a heat transfer fluid duct 84. The heat transfer fluid, circulating in the hot side 81.1 of the heat exchanger 81, may transfer heat to a recycled carbon dioxide stream fed through the cooling line 27. Petition 870250088288, dated 09 / 29 / 2025, page 30 / 124 18 / 19

[0059] A valve arrangement 85 including a valve 85.1 in parallel to the cold side 81.2 of the heat exchanger 81 and a valve 85.2 in series with the cold side 81.2 of the heat exchanger 81 can direct the flow of carbon dioxide from the cooling line 27 selectively through the heat exchanger 81 (valve 85.1 closed, valve 85.2 open) or directly to the annular fluid chamber 42 (valve 85.1 open, valve 85.2 closed). In the first condition, the carbon dioxide from the cooling line 27 will be preheated and used as a preheating fluid in the expander 3, during the temporary preheating phase. In the second condition, the heat exchanger 81 is inoperative, and the carbon dioxide enters as a cooling fluid directly into the annular cooling chamber 42.

[0060] When arrangement 80 is used, preheating of the internal compartment 51 may require the expander 3 to start operating before preheating, in order to have sufficient carbon dioxide recirculation through the cooling line 27. Timing can become a critical aspect in this embodiment, as preheating must begin before thermal expansion of the rotor causes friction between stationary and rotating components.

[0061] In some embodiments, a heat transfer fluid from an external source, for example, source 83, may be supplied directly to the annular fluid chamber 42 to initiate preheating of the internal compartment 51 before ignition of the combustor 7.

[0062] In other embodiments, the heating fluid may be supplied by the combustor 7, through a suitable fluid coupling schematically shown in 8 in Figure 2, which is selectively opened only during the preheating phase. The rotor 43 may be kept stationary, i.e., its rotation may be prevented, during an initial time interval after the ignition of the combustor 7, so that the combustion gas may preheat the internal compartment 51 and cause its thermal expansion, before the rotor begins to rotate. Petition 870250088288, dated 09 / 29 / 2025, page 31 / 124 19 / 19 The rotation of rotor 43 can begin, for example, when a suitable temperature of the inner compartment 51 is reached and the clearances C and C2 are large enough to ensure smooth, frictionless rotation of rotor 43 while the rotor expands at a faster rate than the stationary components of the expander.

[0063] 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.

[0064] For example, as mentioned above, the combustor 7 can be disposed outside the expander 3 and can be connected to it, for example, by means of a transition piece. In other embodiments, the expander 3 can be used in a closed-loop cycle, wherein the process gas can be heated, for example, by heat exchange with a heat transfer fluid in a heat exchanger. Petition 870250088288, dated 09 / 29 / 2025, page 32 / 124

Claims

1 / 6 CLAIMS 1. Expander characterized by comprising: a compartment comprising an outer compartment and an inner compartment; wherein the inner compartment is disposed within the outer compartment; and wherein the inner compartment houses at least one set of annularly arranged stationary blades; at least one first annular fluid chamber between the inner compartment and the outer compartment; and wherein the inner compartment has a perimeter wall having an outer surface facing the annular fluid chamber and an inner surface; a rotor at least partially housed within the inner compartment for rotation therein; wherein the rotor is provided with at least one set of annularly arranged rotor blades downstream of at least one set of annularly arranged stationary blades;a preheating arrangement, adapted to preheat the internal compartment and cause its thermal expansion upon starting the expander; wherein the preheating arrangement comprises a circulation system adapted to circulate a preheating fluid in heat exchange with the internal compartment; 2. Cooling system adapted to cool at least one set of annularly arranged stationary blades during the operation of the expander; wherein the cooling system comprises cooling ducts extending through the peripheral wall of the inner compartment and fluidically coupled to at least one annular fluid chamber and adapted to supply fluid from at least one annular fluid chamber towards the inner surface of the peripheral wall of the inner compartment; wherein the preheating arrangement is adapted to supply preheating fluid to at least one annular fluid chamber and through the cooling ducts at the start-up of the expander, so that the inner compartment is preheated by said heating fluid.An expander, according to claim 2, characterized by comprising at least one stationary casing housed in the inner compartment and surrounding at least one set of annularly arranged rotor blades; and wherein the cooling ducts are adapted to supply said heating fluid from the annular fluid chamber to a filled annular space between the inner surface of the peripheral wall of the inner compartment and the at least one stationary casing, upon starting of the expander.

3. Expander, according to claim 1 or 2, characterized by comprising an additional annular filled space between the inner surface of the peripheral wall of the inner compartment and at least one set of annularly arranged stationary blades; wherein the cooling ducts are adapted to supply said heating fluid from the annular fluid chamber to said additional annular filled space upon starting of the expander.

4. Expander, according to any of the preceding claims, characterized in that the stationary blades comprise respective inner and outer platforms; wherein an inner sealing casing facing a rotor sealing joint is connected to the inner platforms; and wherein the cooling ducts are adapted to supply fluid from the annular fluid chamber towards the outer platforms of at least one set of annularly arranged stationary blades.

5. Expander, according to any of the preceding claims, the expander being characterized by comprising at least one combustor housed in the external compartment.

6. Expander, according to claim 5, characterized in that the preheating arrangement comprises a fluid connection between at least one combustor and at least one annular fluid chamber; and wherein the fluid connection is adapted to be selectively opened upon starting of the expander to supply hot combustion gas from the combustor to the annular fluid chamber.

7. Expander, according to any of the preceding claims, characterized in that the heating arrangement comprises a heat exchanger with a hot side and a cold side; wherein the hot side is fluidly coupled to a heat source through a heat transfer fluid duct; and wherein the cold side is fluidly coupled to a preheating circuit adapted to supply heating fluid to the internal compartment.

8. Expander, according to claim 7, characterized in that the cold side of the heat exchanger is arranged in parallel to a cooling fluid feed duct, adapted to supply a cooling fluid to the internal compartment; and wherein a valve system is adapted to selectively divert the cooling fluid supplied by the cooling fluid feed duct through the cold side of the heat exchanger, so that the cooling fluid is heated by heat exchange with the hot side of the heat exchanger before being distributed to the internal compartment.

9. Expander, according to any of the preceding claims, the expander being characterized as an oxyfuel expander.

10. Supercritical carbon dioxide thermodynamic circuit characterized by comprising: - 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; Petition 870250088288, dated 09 / 29 / 2025, page 35 / 124 4 / 6 - 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.

11. Method of operation of an expander at startup characterized in that the expander comprises: a compartment comprising an outer compartment and an inner compartment; wherein the inner compartment is disposed within the outer compartment; and wherein the inner compartment houses at least one set of annularly arranged stationary blades; at least one first annular fluid chamber between the inner compartment and the outer compartment; and wherein the inner compartment has a perimeter wall having an outer surface facing the annular fluid chamber and an inner surface; a rotor at least partially housed within the inner compartment for rotation therein; wherein the rotor is provided with at least one set of annularly arranged rotor blades downstream of at least one set of annularly arranged stationary blades;a preheating arrangement, adapted to preheat the inner compartment and cause its thermal expansion upon start-up of the expander; wherein the preheating arrangement comprises a circulation system adapted to circulate a preheating fluid in heat exchange with the inner compartment; a cooling system adapted to cool at least one set of annularly arranged stationary blades Petition 870250088288, dated 09 / 29 / 2025, page 36 / 124 5 / 6 during the operation of the expander; wherein the cooling system comprises cooling ducts that extend through the peripheral wall of the inner compartment and are fluidically coupled to at least one annular fluid chamber and are adapted to supply fluid from at least one annular fluid chamber towards the inner surface of the peripheral wall of the inner compartment;The method comprises the step of supplying a preheating fluid to at least one annular fluid chamber and through cooling ducts towards the inner surface of the outer wall of the inner compartment, at the start-up of the expander, so that the inner compartment is preheated by said heating fluid to increase a clearance between the rotor and the stationary components supported in the inner compartment by thermal expansion of the inner compartment.

12. Method according to claim 11, characterized in that the step of preheating the internal compartment is performed at least in part while the expander rotor is held stationary.

13. Method, according to claim 11 or 12, characterized in that the step of preheating the internal compartment is performed at least in part with the rotor in a rotating condition.

14. A method according to any one of claims 11 to 13, characterized in that the expander comprises at least one combustor housed in the outer compartment; and wherein the preheating step of the inner compartment comprises the step of supplying hot combustion gas from the combustor towards the inner compartment.

15. A method according to any one of claims 11 to 14, characterized in that the heating arrangement comprises a heat exchanger with a hot side and a cold side; wherein the hot side is fluidly coupled to a heat source through a heat transfer fluid duct; wherein the cold side is fluidly coupled to a preheating circuit adapted to supply heating fluid to the inner compartment; and wherein the step of preheating the inner compartment comprises the steps of: supplying a heating fluid through the cold side of the heat exchanger; heating the heating fluid through heat exchange with the heat transfer fluid circulating in the hot side of the heat exchanger; and supplying the heated heating fluid to the inner compartment.

16. Method according to claim 15, characterized in that the heating fluid circulating on the cold side of the heat exchanger is recycled from a discharge side of the expander.

17. A method according to any one of claims 11 to 16, characterized in that, after a steady-state temperature condition of the inner compartment and rotor is reached, the heating of the inner compartment is stopped, and the circulation of a cooling fluid in heat exchange with the inner compartment is initiated.

18. Method according to claim 17, characterized in that the step of circulating a cooling fluid in heat exchange with the internal compartment comprises the step of removing heat from at least one set of annularly arranged stationary blades through said cooling fluid. Petition 870250088288, dated 09 / 29 / 2025, p. 38 / 124

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