Expander and method with preheating system

Abstract

The expander comprises a casing including an outer casing and an inner casing. The inner casing is located within the outer casing and houses at least one pair of annularly arranged stator vanes. The expander further includes at least a first annular fluid chamber between the inner and outer casings. The inner casing has a peripheral wall having an outer surface and an inner surface facing the annular fluid chamber. The rotor is at least partially housed within the inner casing and comprises at least one pair of annularly arranged rotor vanes, preferably multiple pairs of annularly arranged rotor vanes, e.g., 4 to 12 pairs, each pair positioned downstream of each pair of annularly arranged stator vanes. The expander further includes a preheating device adapted to preheat and thermally expand the inner casing when the expander is started.

Description

Technical Field

[0001] The present disclosure relates to an expander for generating mechanical power through a thermodynamic cycle. Embodiments disclosed herein relate particularly to oxygen fuel expanders and expanders specifically intended for supercritical CO2 cycles.

Background Art

[0002] An expander, sometimes called a turboexpander, is a turbomachine that includes stationary blades, also known as fixed vanes, disposed continuously within a casing, and moving blades that form part of a rotor supported to rotate within the casing. The stationary and moving blades define an expansion flow path for a process gas flowing through the expander. The enthalpy drop of the process gas is converted into mechanical power available on the expander shaft.

[0003] An expander includes at least one annular row of stationary blades and one annular row of moving blades attached to the rotor to rotate with the rotor within the expander casing. More often, an expander includes a plurality of continuously arranged annular rows of stationary blades and a plurality of continuously arranged annular rows of moving blades, with the stationary and moving blades arranged alternately, and the rows of moving blades following the rows of stationary blades in the flow direction of the process gas. Each pair of a row of stationary blades and a row of moving blades forms a stage of the expander.

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

[0005] In some cases, such as in oxygen-fueled expanders and expanders operating with supercritical carbon dioxide flow, the rotor may have a higher heat transfer coefficient compared to the stator components. This is because the thermal expansion of the rotor is faster than that of the stator, which can cause accidental frictional contact between the stationary and rotating components during expander startup. To prevent friction between the stator and rotor components during the transient state of startup, a larger clearance between these components must be considered, which negatively impacts the efficiency of the expander under steady-state operating conditions.

[0006] An inflator adapted to avoid or mitigate the aforementioned shortcomings of current inflators would be welcome. [Overview of the project]

[0007] In one embodiment, this specification discloses an inflator comprising a casing including an outer casing and an inner casing. The inner casing is located within the outer casing and houses at least one pair of annularly arranged stator vanes forming an annular row of vanes. The inflator further includes at least a first annular fluid chamber between the inner and outer casings. The inner casing has a peripheral wall having an outer surface and an inner surface facing the annular fluid chamber. The rotor is at least partially housed within the inner casing and comprises at least one pair of annularly arranged rotor vanes, preferably multiple pairs of annularly arranged rotor vanes, e.g., 4 to 15 pairs, each pair positioned downstream of each pair of annularly arranged stator vanes. The inflator further includes a preheating device adapted to preheat and thermally expand the inner casing when the inflator is started. Preheating increases the gap or clearance between stationary and rotating components during the starting transient to prevent accidental contact between them. Once steady-state operating conditions are met, the initially enlarged gap or clearance narrows again to the minimum steady-state clearance, reducing the leakage of process gas from the expansion channel.

[0008] In another embodiment, this specification discloses a method for operating an expander at startup, the expander being configured as outlined above. This method includes preheating the inner casing at startup of the expander, thereby increasing the clearance between the rotor and components fixedly supported within the inner casing by thermal expansion of the inner casing.

[0009] The expander can be preheated at startup, and the inner casing expands due to heat, preventing rotor components from rubbing against components of the expander's fixed bundle. Once steady-state temperature conditions are achieved, the expander components, such as the rotor or its parts, can be cooled to prevent overheating of the components during steady-state operation.

[0010] Further features and embodiments of the methods and inflators described herein are described in the dependent claims and in the following description of embodiments. [Brief explanation of the drawing]

[0011] 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 an embodiment. [Figure 3] Figure 2 is an enlarged view of the expander. [Modes for carrying out the invention]

[0012] In the following description, we will particularly refer to oxygen fuel expanders, i.e., expanders specifically designed for oxygen fuel combustion cycles. However, the features disclosed herein can be advantageously used in different thermodynamic cycles, such as closed supercritical or transcritical carbon dioxide cycles.

[0013] The schematic diagram in Figure 1 shows a simplified oxygen-fueled cycle (abbreviated as the sCO2 cycle), such as the Allam oxygen-fueled cycle, operating using supercritical carbon dioxide. As understood herein, a supercritical cycle is a cycle in which carbon dioxide is in a supercritical state at least at the highest pressure point along the thermodynamic cycle, i.e., at the inlet of the expander rotor.

[0014] The power system 1 shown in Figure 1 comprises an 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 comprising a plurality of combustor chambers arranged around the rotation axis of the expander 3, as shown in more detail in Figure 2. In some embodiments, the combustor chambers are housed within an outer casing of the expander, as will be described in more detail below. In other embodiments, the combustor is combined with the casing, but can be arranged on or around the casing. For example, a transition piece can be provided to fluidly connect the combustor to the expansion passage inside the expander.

[0015] Reference numeral 7.1 in Figure 2 indicates the combustion chamber of an annular combustor, or the individual combustion chambers of a can-type or can-annular combustor.

[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. Carbon dioxide can be added to the oxygen so that a mixture of oxygen and carbon dioxide is sent to the expander, and this mixture contains a sufficient proportion of carbon dioxide to prevent damage to the piping.

[0017] Reference numeral 13 indicates a fuel supply line adapted to supply natural gas, such as methane, to the combustor 7. In the embodiment shown in Figure 2, fuel is supplied to each combustor chamber 7.1. The oxidizer and fuel are supplied to the combustor 7 at high pressure, for example, about 50 barA or higher, preferably 100 barA or higher, for example 150 bar or higher, or 200 barA or higher, preferably about 250 barA or higher, or higher, for example 300 barA or higher. In some embodiments, the pressure at the inlet of the expander is lower than 800 barA, preferably lower than 650 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.

[0018] The exhausted flue gas is discharged into the discharge line 15 on the discharge side of the expander 3. The flue gas in the discharge line 15 is, for example, about 600°C and can have a pressure ranging from 10 barA to 100 barA, for example, from 20 barA to 60 barA.

[0019] The expander may be designed for rated power values ​​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 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 may fall between 200 MW and 650 MW.

[0020] 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.

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

[0022] The compressed flue gas supplied by the flue gas compressor 23 is partially removed from the cycle through the discharge line 25. 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 produced in the combustor 7 or with the oxidizer stream from the oxidizer line 11.

[0023] A sidestream of cooled flue gas is sent through a cooling line 27 that bypasses the regenerative heat exchanger 17 to components of the expander 3 that require cooling. A further sidestream of cooled and dehydrated flue gas is sent through line 28 to the air separator 9 and / or oxidizer line 11, which can supply a mixture of oxygen and carbon dioxide to the combustor 7. In this embodiment, the mixture of oxygen and carbon dioxide may contain 20% by volume of oxygen and 80% by volume of carbon dioxide.

[0024] The expander 3 can include an output shaft 31, and the mechanical power generated by the expansion of combustion gas within the expansion section 5 of the expander 3 can be utilized 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, although not shown, the output shaft 31 can be disposed on the front side of the expander. In yet another embodiment, although not shown, two output shafts can be provided, one on the front side of the expander and one on the rear side.

[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] FIG. 2 shows a cross-sectional view of the expander 3 in one embodiment. The expander 3 can include an outer casing 41 that houses the combustor 7. In some embodiments, the outer casing 41 includes a high-pressure casing 41.1 having a cylindrical shape and a low-pressure exhaust casing 41.2. The high-pressure casing 41.1 can be monolithic, i.e., it can consist of a single part manufactured, for example, by forging, machining, casting, or a combination thereof. In some embodiments, the high-pressure casing 41.1 can be manufactured by combining annular components with each other, for example, by welding. As used herein, "annular" means that the component extends around the axis of the expander without separation as a single block or part and provides sufficient resistance to the high-pressure value within the high-pressure casing 41.1.

[0027] 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 also be monolithic, i.e., it may consist of a single part. In other embodiments, the low-pressure exhaust casing 41.2 may consist of multiple components connected to one another. For example, the low-pressure exhaust casing 41.2 may be divided along a plane containing the rotor's axis of rotation. The connections of the components forming the low-pressure exhaust casing 41.2 may be by welding, or by reversible connections with screws or bolts.

[0028] 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. Thus, the outer casing 41 is a so-called "vertically split" casing.

[0029] 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.

[0030] Reference numerals 45 and 47 indicate bearing devices that rotatably support the rotor 43. For example, the bearing device 45 on the rear side, i.e., opposite the combustor 7, may include an axial bearing or thrust bearing in combination 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 housings not shown in detail. The rotor 43 can be drivably coupled via a joint 49 to a load shaft 31, such as a compressor or generator.

[0031] The rotor 43 is surrounded by an inner casing 51 housed within an outer casing 41. The inner casing can be formed by a plurality of sections arranged sequentially from front to rear. The inner casing 51 can be divided horizontally, that is, it can include two parts joined together along a plane containing the axis of rotation of the rotor 43. If the inner casing 51 includes a plurality of axially aligned sections, each section or some of them can be divided horizontally.

[0032] One or more annular fluid chambers 42 are formed between the inner casing 51 and the outer casing 41. Specifically, in the exemplary embodiment shown in Figure 2, the annular chambers 42 include two continuously arranged annular fluid chambers 42.1 and 42.2 separated by a partition wall 44, which mechanically connects the inner casing 51 to the outer casing 41. The fluid pressures inside the two annular fluid chambers 42.1 and 42.2 may differ. For example, the front annular fluid chamber 42.1 may have a higher pressure than the rear annular fluid chamber 42.2. During use, under steady-state conditions, a cooling or defrosting fluid can be supplied to the rear fluid chamber 42.2 and the front fluid chamber 42.1. For example, the cooling or defrosting fluid may include dehydrated flue gas from a cooling line 27, which may consist mainly or exclusively of carbon dioxide.

[0033] The inner casing 51 includes a wall 51.3 (see Figure 3) having 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 before and after the expander 3 may be about 200 bar or more. 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 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 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.

[0035] Each expansion stage includes an annular row of stationary vanes or fixed vanes 53 fixedly positioned within the inner casing 51. Each expansion stage further includes an annular row of rotor vanes 55 positioned downstream of each annular row of stationary vanes 53 along an expansion flow path extending from front to rear from the combustor 7 through the expansion section 5 to the discharge volute 41.3.

[0036] The rotor blades 55 form part of the rotor 43, i.e., they are connected to the rotor 43 so as to rotate with the rotor shaft, or they are manufactured as a single block with the rotor 43. In some embodiments, each annular row of rotor blades 55 is connected to a respective rotor disk, which is not shown in detail, or they are formed monolithically with the rotor disk as a single part. The structure of the rotor and rotor disk is not important and is not shown in detail.

[0037] In some embodiments, the continuously arranged annular rows of rotor blades are separated from each other by their respective seal runners 56 (see Figure 3). Each annular row of stator blades 53 is positioned radially outward around the seal runner 56.

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

[0039] In some embodiments, the discharge plenum 41.3 extends around the rear shaft portion 67.

[0040] Figure 3 shows a magnified detail view of one stage of the expander 3 in Figure 2. More specifically, Figure 3 shows the flow path through one expander stage. The stage shown in Figure 3 includes an annular row of stationary vanes 53 followed by an annular row of rotor vanes 55. F represents the flow of combustion gases expanding through the expander stage.

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

[0042] The distance between the knife 55.3 and the surface 71.1, i.e., the gap between the rotor blade 55 and the fixed shroud 71, must be as small as possible. This distance or gap is referred to herein as clearance C. During operation, clearance C must be small in order to prevent gas from flowing through it, or at least to reduce the flow rate of gas through it, since the gas expanding through clearance C does 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 fixed shroud 71 and the rotor blade 55 under all operating conditions of the expander 3, i.e., under steady-state operating conditions and during transient conditions such as startup.

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

[0044] Cooling duct 73 is adapted to establish a fluid connection between the annular fluid chamber 42 and the annular cooling plenum 77, which is located radially outward of the fixed shroud 71 on the opposite side of the abradable material 71.2. Cooling duct 75 is arranged to establish a fluid connection between the annular fluid chamber 42 and the annular cooling plenum 79, which is located radially outward of the stator vanes 53. Although only one cooling duct 73 and one cooling duct 75 are visible in the cross-sectional view of Figure 3, it should be understood that multiple cooling ducts 73 can be provided, for example, one or more cooling ducts 73 can be provided for each annular cooling plenum 77, and multiple cooling ducts 75 can be provided, for example, one or more cooling ducts 75 can be provided for each annular cooling plenum 79.

[0045] The configuration disclosed above provides a cooling circuit that can supply cooled flue gas through a cooling line 27 (Figure 1).

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

[0047] In some embodiments, each annular row of stator vanes 53 may be provided with an inner fixed shroud 72 facing its respective seal runner 56. The inner fixed shroud 72 has a radially inward-facing surface 72.1, i.e., facing its respective seal runner 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-facing surface 72.1 of the inner fixed shroud 72 is at a distance C2 (clearance C2) from the fins or vanes 56.1 of the respective seal runner 56. Just like clearance C, clearance C2 should also be as small as possible to reduce the flow rate of expansion gas escaping through clearance C2 rather than flowing through the passage (F) between the fixed vanes 53 and the rotor vanes 55.

[0048] To cool the stator vanes 53 and control the clearance C2 dimension, a cooling fluid is delivered to the annular cooling plenum 79.

[0049] During startup, there is a risk of contact between the rotating components (seal runner 56 and rotor blades 55) and the stationary components (fixed shroud 71 and inner fixed shroud 72) due to the temperature gradient, the shape of the mechanical parts, and the respective heat transfer coefficients and thermal expansion coefficients of the rotor and stationary components. This is particularly because the rotor heats up and expands more quickly than the casing.

[0050] To avoid the need to maintain a larger clearance under steady-state operating conditions, and to avoid mechanical friction contact between the shroud 71 and the tip 55.2 of the rotor blades 55, and between the shroud 72 and the seal runner 56, during transient operating conditions, particularly at startup, the expander 3 includes a preheating device. The preheating device is adapted to preheat the inner casing 51 of the expander 3 when the expander is started, i.e., when the expander is at or near ambient temperature. The mechanical coupling between the inner casing 51 and the outer casing 41 can be configured to allow radial displacement of the inner casing 51 relative to the outer casing 41 in order to allow thermal expansion of the inner casing 51 when the outer casing 41 is still cold, for example, when the expander is started.

[0051] Preheating the inner casing 51 causes its thermal expansion in the radial direction. This thermal expansion of the inner casing 51 causes radially outward displacement of the shrouds 71 ​​and 72, specifically surfaces 71.1 and 72.1. Preheating of the inner casing 51 can be performed completely before the rotor 43 begins to rotate, or when the rotor 43 begins to rotate, or partially before the rotor begins to rotate, and partially after the rotor begins to rotate. In any case, preheating is controlled so that the radial thermal expansion of the stationary components prevents any contact between the rotating components of the rotor 43 and the stationary components housed within the inner casing 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 casing 51 increases the clearance C between the knife 55.3 of the wingtip 55.2 and the inner surface 71.1 of the shroud 71, and the clearance C2 between the knife or fin 56.1 of the seal runner 56 and the inner surface 72.1 of the inner shroud 72.

[0053] The increase in clearance obtained by preheating prevents accidental friction of the rotor blades 55 against the shrouds 71 ​​and accidental friction of the shrouds 72 against the seal runners 56, even when the initial (low temperature) and final (high temperature) clearances C and C2 are very small.

[0054] Preheating of the inner casing 51 can be performed by supplying preheating fluid to the annular fluid chambers 42, i.e., annular fluid chambers 42.1 and 42.2. The preheating fluid enters the inner casing 51 through cooling ducts 73 and 75, heating the inner casing walls 51 and the shrouds 71 ​​and 72 of each expansion stage of the expander 3. Preheating causes radially outward thermal expansion and a temporary increase in clearances C and C2. This increase is then compensated for by the expansion of the rotor, i.e., clearances C and C2 decrease due to the gradual radial expansion of the rotor 43.

[0055] Therefore, since the thermal radial expansion of the casing 51 is expected relative to the thermal radial expansion of the rotor 43, the expander 3 can start operating without the risk of frictional contact between the rotating components (moving blades 55, seal runner 56) and the stationary components (shrouds 71, 72).

[0056] After startup, the compressed, high-temperature combustion gas flowing through the passage between the stationary blades 53 and the rotor blades 55 gradually heats the rotor, causing its thermal expansion, and further heats the inner casing, causing its further thermal expansion. Since the inner casing 51 is preheated, the clearances C, C2 are large enough to prevent frictional contact between the rotating and stationary components, even if the radial expansion of the rotor 43 is faster than the radial expansion of the inner casing 51.

[0057] The circulation of the preheating fluid is stopped when the steady-state temperature conditions are achieved, or in any case when the radial expansion of the non-rotating and rotating components reaches a value that avoids contact between them. At this stage, the cooling circuit used to preheat the inner casing 51 can be used to circulate the cooling fluid and maintain the inner casing at the required steady-state temperature. In fact, the same fluid that acts as the preheating fluid at startup can act as the cooling fluid under steady-state conditions.

[0058] Figure 2 shows a schematic configuration 80 that can be used to selectively supply preheating fluid and cooling fluid into annular fluid chambers 42 (chambers 42.1, 42.2) and from there into cooling ducts 73, 75. The configuration may include a heat exchanger 81 having a high-temperature side 81.1 and a low-temperature side 81.2. The high-temperature side 81.1 can be fluidly coupled to a heat transfer fluid source 83 via a heat transfer fluid duct 84. The heat transfer fluid circulating on the high-temperature side 81.1 of the heat exchanger 81 can transfer heat to a flow of recirculated carbon dioxide supplied through a cooling line 27.

[0059] A valve device 85, including a valve 85.1 in parallel with the low-temperature side 81.2 of the heat exchanger 81 and a valve 85.2 in series with the low-temperature side 81.2 of the heat exchanger 81, can selectively direct the flow of carbon dioxide from the cooling line 27 through the heat exchanger 81 (valve 85.1 closed, valve 85.2 open) or directly into the annular fluid chamber 42 (valve 85.1 open, valve 85.2 closed). In the first state, the carbon dioxide from the cooling line 27 is preheated and used as a preheating fluid in the expander 3 during a transient preheating phase. In the second state, the heat exchanger 81 is not operating, and the carbon dioxide enters the annular cooling chamber 42 directly as a cooling fluid.

[0060] When the device 80 is used, preheating of the inner casing 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 be a critical aspect in this embodiment, as preheating begins before the thermal expansion of the rotor causes friction between the stationary and rotating components.

[0061] In some embodiments, a heat transfer fluid from an external source, such as a source 83, can be supplied directly to the annular fluid chamber 42 to initiate preheating of the inner casing 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 Figure 28, the fluid coupling being selectively opened only during the preheating phase. The rotor 43 can be kept stationary for a first time interval following combustor ignition 7, i.e., its rotation can be prevented, so that the combustion gases preheat the inner casing 51 and cause its thermal expansion before the rotor begins to rotate. The rotation of the rotor 43 can be started, for example, when a suitable temperature of the inner casing 51 is achieved and clearances C and C2 are large enough to ensure smooth rotation of the rotor 43 without friction while the rotor expands at a faster rate than the stationary components of the expander.

[0063] 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.

[0064] For example, as described above, the combustor 7 may be located outside the expander 3, or it may be connected to the expander 3 by, for example, a transition piece. In other embodiments, the expander 3 can be used in a closed-loop cycle, and the process gas may be heated, for example, by heat exchange with a heat transfer fluid in a heat exchanger.

Claims

1. It is an inflator, A casing comprising an outer casing and an inner casing, wherein the inner casing is disposed within the outer casing, and the inner casing accommodates at least one pair of annularly arranged stator vanes; At least a first annular fluid chamber between the inner casing and the outer casing, wherein the inner casing has a peripheral wall having an outer surface and an inner surface facing the annular fluid chamber, A rotor, at least partially housed within the inner casing so as to rotate internally, wherein the rotor includes at least one pair of annularly arranged rotor blades downstream of at least one pair of annularly arranged stator blades, A preheating device adapted to preheat the inner casing to cause thermal expansion when the expander is started, the preheating device includes a circulation system adapted to circulate a preheating fluid that exchanges heat with the inner casing, An expander comprising a cooling system adapted to cool the at least one pair of annularly arranged stator vanes during the operation of the expander, the cooling system including a cooling duct that extends through the circumferential wall of the inner casing and is fluidly coupled to the at least one annular fluid chamber and adapted to supply fluid from the at least one annular fluid chamber toward the inner surface of the circumferential wall of the inner casing, wherein the preheating device is adapted to supply preheating fluid into the at least one annular fluid chamber through the cooling duct when the expander is started, thereby preheating the inner casing with the heating fluid.

2. The expander according to claim 2, comprising at least one fixed shroud housed within the inner casing and surrounding the at least one pair of annularly arranged rotor blades, wherein the cooling duct is adapted to supply the heating fluid from the annular fluid chamber into an annular plenum between the inner surface of the peripheral wall of the inner casing and the at least one fixed shroud when the expander is started.

3. The expander according to claim 1 or 2, further comprising an annular plenum between the inner surface of the peripheral wall of the inner casing and the at least one pair of annularly arranged stator vanes, wherein the cooling duct is adapted to supply the heating fluid from the annular fluid chamber to the further annular plenum when the expander is started.

4. The expander according to any one of claims 1 to 3, wherein the stator vanes include an inner platform and an outer platform, an inner sealing shroud facing the seal runner of the rotor is connected to the inner platform, and the cooling duct is adapted to supply fluid from the annular fluid chamber toward the outer platform of the at least one pair of annularly arranged stator vanes.

5. The expander according to any one of claims 1 to 4, comprising at least one combustor housed within the outer casing.

6. The expander according to claim 5, wherein the preheating device comprises a fluid connection between the at least one combustor and the at least one annular fluid chamber, the fluid connection being adapted to selectively open when the expander is started in order to supply high-temperature combustion gas from the combustor to the annular fluid chamber.

7. The expander according to any one of claims 1 to 6, wherein the heating device includes a heat exchanger having a high-temperature side and a low-temperature side, the high-temperature side being fluidly coupled to a heat source via a heat transfer fluid duct, and the low-temperature side being fluidly coupled to a preheating circuit adapted to supply a heating fluid to the inner casing.

8. The expander according to claim 7, wherein the low-temperature side of the heat exchanger is arranged in parallel with a cooling fluid supply duct adapted to supply a cooling fluid to the inner casing, and a valve system adapted to selectively divert the cooling fluid supplied by the cooling fluid supply duct through the low-temperature side of the heat exchanger, thereby heating the cooling fluid by heat exchange with the high-temperature side of the heat exchanger before it is sent to the inner casing.

9. The expander according to any one of claims 1 to 8, wherein the expander is an oxygen-fuel expander.

10. 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 in 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 exchanges heat with the cooled flue gas from the cooler, A supercritical carbon dioxide thermodynamic circuit, wherein the expander is the expander described in any one of claims 1 to 9.

11. A method for operating an expander at startup, wherein the expander is A casing comprising an outer casing and an inner casing, wherein the inner casing is disposed within the outer casing, and the inner casing accommodates at least one pair of annularly arranged stator vanes; At least a first annular fluid chamber between the inner casing and the outer casing, wherein the inner casing has a peripheral wall having an outer surface and an inner surface facing the annular fluid chamber, A rotor, at least partially housed within the inner casing so as to rotate internally, wherein the rotor includes at least one pair of annularly arranged rotor blades downstream of at least one pair of annularly arranged stator blades, A preheating device adapted to preheat the inner casing to cause thermal expansion when the expander is started, the preheating device includes a circulation system adapted to circulate a preheating fluid that exchanges heat with the inner casing, A cooling system adapted to cool the at least one pair of annularly arranged stator vanes during the operation of the expander, the cooling system comprising a cooling duct extending through the circumferential wall of the inner casing, fluid-coupled to the at least one annular fluid chamber, and adapted to supply fluid from the at least one annular fluid chamber toward the inner surface of the circumferential wall of the inner casing, The method comprises the step of supplying a preheating fluid to the at least one annular fluid chamber through the cooling duct toward the inner surface of the peripheral wall of the inner casing when the expander is started, thereby preheating the inner casing with the heating fluid and increasing the clearance between the rotor and components fixedly supported within the inner casing due to the thermal expansion of the inner casing.

12. The method according to claim 11, wherein the step of preheating the inner casing is performed at least partially while the rotor of the expander is kept stationary.

13. The method according to claim 11 or 12, wherein the step of preheating the inner casing is performed at least partially on the rotor while it is rotating.

14. The method according to any one of claims 11 to 13, wherein the expander comprises at least one combustor housed within the outer casing, and the step of preheating the inner casing includes supplying a hot combustion gas from the combustor to the inner casing.

15. The heating device includes a heat exchanger having a high-temperature side and a low-temperature side, the high-temperature side being fluidly coupled to a heat source via a heat transfer fluid duct, the low-temperature side being fluidly coupled to a preheating circuit adapted to supply a heating fluid to the inner casing, and the step of preheating the inner casing includes the steps of supplying a heating fluid through the low-temperature side of the heat exchanger, heating the heating fluid through heat exchange with the heat transfer fluid circulating through the high-temperature side of the heat exchanger, and supplying the heated heating fluid to the inner casing, the method according to any one of claims 11 to 14.

16. The method according to claim 15, wherein the heating fluid circulating on the low-temperature side of the heat exchanger is recirculated from the discharge side of the expander.

17. The method according to any one of claims 11 to 16, wherein after steady-state temperature conditions for the inner casing and the rotor are achieved, heating of the inner casing is interrupted and circulation of a cooling fluid that exchanges heat with the inner casing is started.

18. The method according to claim 17, wherein the step of circulating a cooling fluid to exchange heat with the inner casing includes the step of removing heat from the at least one pair of annularly arranged stator vanes via the cooling fluid.

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