An expander with an annular structure which supports the first stage stationary blades

Abstract

The expander (3) comprises a casing (40), which in turn includes an outer casing (41), and an inner casing (51) housed in the outer casing (41). The expander (3) further includes a rotor (43) housed in the casing (40) for rotation therein around a rotation axis. Several combustors are positioned around the rotation axis. Each combustor (8) includes a tubular liner (103) and a transition piece (113) at the aft end of the of the liner and at least one burner (107) at the forward end of the liner. The transition pieces (113) are positioned in an annular plenum (1431), which further houses an annular structure that is cantilevered from a forward end of the inner casing (51) and extends around the rotation axis.

Description

AN EXPANDER WITH AN ANNULAR STRUCTURE WHICH SUPPORTS THE FIRST STAGE STATIONARY BLADESDESCRIPTIONTECHNICAL FIELD

[0001] The present disclosure pertains to turbomachines and parts thereof. Embodiments disclosed herein specifically refer to oxyfuel combustion expanders, such as supercritical carbon dioxide expanders (sCO2 expanders).BACKGROUND ART

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

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

[0004] To reduce the environmental impact of power generation through combustion of fossil fuels, the option of post combustion capture of carbon dioxide has been investigated. Carbon dioxide capture facilities have been developed, to process flue gas exhausted from gas turbines and remove carbon dioxide therefrom, prior to discharging the flue gas in the environment. The cost of a carbon dioxide capturing facility are high, both in term CAPEX, as well as in terms of energy required to run the facility, which reduces the overall thermodynamic efficiency of the system. The percentage of carbon dioxide in flue gas is low. This requires large volumes of flue gas to be processed through the carbon dioxide capturing facility and renders the capturing process particularly inefficient.

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

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

[0007] Oxygen supplied to the combustor assembly of the expander can be obtained by separation from ambient air, removing nitrogen therefrom, such that the working fluid supplied to the combustor assembly mainly consists of oxygen and carbon dioxide and does not include nitrogen. The resulting flue gas mainly consists of water and carbon dioxide. Water is removed from the flue gas by condensation and the part of water-free flue gas, which is not recycled to the combustor assembly, can be efficiently processed in a carbon dioxide capturing unit.

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

[0009] The design of oxy-fuel expanders is challenging, particularly in view of the thermodynamical (pressure and temperature) conditions therein and of the chemical composition of the process gas, which consists mainly of carbon dioxide.SUMMARY

[0010] According to embodiments disclosed herein, an expander comprises a casing, which in turn includes an outer casing, and an inner casing housed in the outer casing. The expander further includes a rotor housed in the casing for rotation therein around a rotation axis. Several combustors are positioned around the rotation axis. Each combustor is at least partially housed in a generally cylindrical seat and includes a tubular liner having a forward end, an aft end, and a side wall extending from the forward end to the aft end. Each combustor further includes a transition piece at the aft end of the liner and at least one burner at the forward end of the liner. The burner is fluidlycoupled with a fuel inlet and an oxidant inlet. A first process gas inlet is fluidly coupled with each combustor. In some embodiments, a first process gas inlet is fluidly coupled a respective one of the generally cylindrical seats where the combustors are housed. An annular plenum is provided between the generally cylindrical seats of the combustors and the inner casing. The transition pieces are positioned in the annular plenum. An annular structure is cantilevered from a forward end of the inner casing, extends around the rotation axis and is housed in the annular plenum and the transition pieces are housed in the annular structure.

[0011] In some embodiments, the annular structure comprises a ring coaxial to the rotation axis and connected to the forward end of the inner casing. The annular structure can include a cylindrical member coaxial to the ring and connected thereto by a plurality of struts, for example. Each transition piece and an aft end of the respective liner can be housed between each pair of sequentially arranged struts.

[0012] In some embodiments, the cylindrical member supports an annular row of stationary blades of a first expansion stage of the expander. Thus, the first annular row of stationary blades of the expander are cantilevered from the forward end of the inner casing, in contrast to the configuration of gas turbines of the current art, where the annular row of stationary blades of the first expansion stage is supported at the aft end of the compressor casing. The annular structure cantilevered from the forward end of the inner casing of the expander provides an efficient way of supporting the first annular row of stationary blades in turbines, i.e. expanders, where no compressor casing is positioned upstream of the expander casing.

[0013] Thus, the annular structure disclosed herein is particularly useful in expansion turbomachines, i.e., expanders for oxy-fuel cycles. Notwithstanding the foregoing, a similar annular structure may also be used in other types of turbomachinery where appropriate under the circumstances.

[0014] In some embodiments, the annular row of stationary blades of the first expansion stage can be mounted on a thrust ring, which is in turn engaged to the cylindrical member. The thrust ring enables a fine tuning of the position of the stationary vanes.

[0015] The annular structure and the thrust ring can be each formed by two substantially symmetrical halves along a plane containing the rotation axis of the rotor, i.e., can be formed by two semi-annular parts. This facilitates assembling the annularstructure.

[0016] The cylindrical member of the annular structure can comprise an inner surface surrounding a shaft portion of the rotor. A high-pressure seal that interacts with the shaft portion, to provide a sealing action therearound, can be mounted on said inner surface of the cylindrical member. In particular, the high-pressure seal can be positioned upstream of the thrust ring.

[0017] The expander can include a balance drum constrained to the rotor for co-ro- tation therewith. The balance drum can be surrounded by a seal ring, stationarily mounted in the casing and supporting a balance drum seal, the balance drum seal interacts with a peripheral surface of the balance drum. For example, the seal ring engages a forward end of the annular structure, projecting cantilevered from the inner casing. An annular seal can be positioned between the forward end of the annular structure and the seal ring, so that annular seal closes an annular gap between the ring seal and the annular structure.

[0018] Additional features and embodiments of the expander according to the present disclosure are described below with reference to the accompanying drawings and are further set forth in the appended claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Reference is now made briefly to the accompanying drawings, in which:Fig.l illustrates a schematic of an expander system according to the present disclosure;Fig.2 is a sectional view of an expander in a simplified representation;Fig.3 is an enlargement of a portion of the expander of Fig.2;Fig.4 is an axonometric view, from the aft side, of the annular structure of the expander shown in Figs. 2 and 3;Fig.5 is an axonometric view, from the forward side, of the annular structure of the expander shown in Figs. 2 and 3; andFig.6 is an axonometric sectional view of the annular structure.DETAILED DESCRIPTION

[0020] The schematic of Fig. 1 illustrates a simplified power system including an oxy-fuel cycle operating with supercritical carbon dioxide (shortly SCO2 cycle), suchas an Allam cycle, or NET Power oxy-fuel cycle.

[0021] The power generating system 1 shown in Fig. l comprises a gas turbine, i.e. an expander 3, that includes an expansion section 5 and a combustor assembly 7. The combustor assembly 7 comprises a plurality of combustors 8, each provided with a combustion chamber 8.1, as will be described in more detail below.

[0022] The combustors 8 are arranged circumferentially around a rotation axis A-A (Fig.2) of the expander 3, as shown in more detail in the subsequent figures, and each combustor 8 is housed in a respective cylindrical seat as will be described in more detail below.

[0023] The combustor assembly 7 is supplied with an oxidant flow delivered by an oxidant source. The oxidant may be oxygen (O2). In some embodiments, the oxidant is a blend of oxygen and carbon dioxide (CO2). The oxidant flow, or the oxygen forming part of the oxidant blend, can be produced by an air separation unit 9 which represents an oxidant source. The air separation unit 9 may remove nitrogen or nitrogen and carbon dioxide from ambient air to produce the required oxidant stream, which is supplied through an oxidant supply line 11 to the combustor assembly 7 of the expander 3.

[0024] Reference number 13 indicates a fuel supply line, for instance adapted to supply natural gas, such as methane, to the combustor assembly 7, specifically to each combustor 8. The oxidant and the fuel are supplied at a forward side of the expander 3 to the combustor assembly 7 at high pressure, for instance at 50 barA or higher, preferably a pressure equal to or higher than 100 barA, more preferably equal to or higher than 150 barA, even more preferably equal to or higher than 200 barA. In some embodiments, the upper pressure of the cycle performed in the thermodynamic system depicted in Fig. 1 can be equal to or above 250 barA, or higher, for example equal to or lower than 1000 barA, or equal to or lower than 800 barA, or equal to or lower than 600 barA. The oxidant-fuel blend is burned in the combustor assembly 7. Pressurized, hot combustion gas resulting from the combustion expands in the expansion section 5 of the expander 3.

[0025] In some embodiments, the temperature at the inlet of the gas expansion flow path, i.e., at the inlet of the rotor of the expander can be at or above 800°C, and preferably at or below 1500°C.

[0026] After expansion, the exhausted combustion gas is discharged at a discharge side of the expander 3 in a discharge line 15. The combustion gas in the discharge line 15 can be at around 600°C, for instance, and at a pressure which may range between 10 barA and 100 barA, for instance between 20 barA and 60 barA.

[0027] The power system 1 further comprises a regenerative heat exchanger 17, wherein hot exhausted combustion gas flowing through a hot side 17.1 of the regenerative heat exchanger 17 is cooled in heat exchange with a flow of chilled exhausted combustion gas, which flows through 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 chilling heat exchanger 19 to a temperature which causes condensation of water vapor contained in the exhausted combustion gas. Condensed water is removed from the exhausted combustion gas in a water / gas separator 21.

[0028] The de-hydrated exhausted and chilled combustion gas, consisting mainly (e.g. up to 90% by weight) or exclusively of carbon dioxide, is compressed in a combustion gas compressor 23 to the pressure at the inlet side of the expander 3. While in the schematic of Fig.1 the combustion gas compressor 23 is pictorially represented as a single compressor, in some embodiments a multiple compressor can be used. For instance, the combustion gas compressor 23 can be a multi-stage compressor, or a compressor train and can include one or more intercoolers.

[0029] The compressed combustion gas, consisting mainly of carbon dioxide and delivered by the combustion gas compressor 23, is partly removed from the cycle through a discharge line 24. The major part of the compressed combustion gas is divided into a first part of recycled combustion gas and a second part of recycled combustion gas. The first part of recycled combustion gas is delivered 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 recycle line 25. The combustion gas recycled through recycle line 25 is fed to the combustor assembly 7 and mixed with combustion gas generated therein as will be described in more detail later.

[0030] A side stream of chilled and dehydrated combustion gas, consisting of the second part of recycled combustion gas, is delivered through a cooling line 27, whichbypasses the regenerative heat exchanger 17, towards components of the expander 3 which require cooling. A further side stream of chilled, dehydrated combustion gas can be delivered through a line 28 to the air separator 9 and / or to the oxidant supply line 11 to add carbon dioxide to the oxygen from the air separation unit 9. The combustion gas from line 28 and the oxygen from the air separation unit are blended to form the oxidant flow which is delivered to the combustor assembly 7. The oxidant flow delivered to the combustor assembly 7 can contain for instance approximately 20% by volume of oxygen and 80% by volume of carbon dioxide. The addition of carbon dioxide to the oxidant stream prevents corrosive damages to the piping and expander components, which may be caused if pure oxygen were used as an oxidant. Moreover, carbon dioxide blended with oxygen in the oxidant stream mitigates safety issues related to the delivery of pure oxygen to the combustor assembly 7, and helps to tune the reactivity of the mixture within the combustor assembly 7. The percentages outlined above are by example only and shall not be understood as limiting the scope of the present disclosure.

[0031] To recover further heat from the regenerative heat exchanger 17, the oxidant supply line 11 can include a heating section 11.1 which extends through the regenerative heat exchanger 17, such that the oxidant is heated by heat exchange against the hot combustion gas flowing in the hot side 17.1 of the regenerative heat exchanger 17 prior to be fed to the combustor assembly 7.

[0032] The expander 3 may include an output shaft end 31 which can be integral with the central portion of the rotor, or can be assembled with the central portion of the rotor by bolting, welding, Hirth or spline connections, or the like, or a combination thereof. The mechanical power generated by the expansion of the combustion gas in the expansion section 5 of the expander 3 is available on the output shaft end 31 for mechanical drive or power generation purposes. In the exemplary embodiment of Fig. 1 the output shaft end 31 is drivingly coupled to an electric generator 33 directly or through a gearbox, a joint, or combinations thereof. The electric generator 33 is in turn electrically coupled to an electric power distribution grid 35. In the illustrated embodiment, the output shaft end 31 is shown at the aft side of the expander 3. In other embodiments, not shown, the output shaft end 31 can be arranged at the forward side of the expander. In yet further embodiments, not shown, two output shafts ends can be provided, one at the forward side and one at the aft side of the expander.

[0033] With continuing reference to Fig.1, Fig. 2 illustrates a simplified sectional view of the expander 3 in one embodiment. Since the expander is substantially axial symmetrical, in Fig.2 only the upper half of the expander is shown.

[0034] The expander 3 comprises a casing 40 which can comprise an outer casing 41 and an inner casing 51, the outer casing 41 housing the inner casing 41. The casing 40 houses combustor assembly 7 and a rotor 43 supported for rotation in the inner casing 51.

[0035] In some embodiments, the outer casing 41 includes a forward casing portion 41.1 and an aft casing portion 41.2. The forward casing portion 41.1 of the outer casing 41 can be in the form of a barrel, i.e. can be monolithic, and can include a monolithic annular body, for example manufactured by forging, casting, additive manufacturing, or combination thereof. The monolithic body forming the forward casing portion 41.1 of the outer casing 41 extends around the longitudinal axis of the expander, i.e., around the rotation axis A-A of the rotor 43. Similarly, the aft casing portion 41.2 of the outer casing 41 can be in the form of a barrel. I.e. the outer casing 41 can be a vertically split casing. The forward casing portion 41.1 and the aft casing portion 41.2 are coupled to one another along a plane P-P, which can be orthogonal to the rotation axis A-A of the expander 3.

[0036] In some embodiments, the aft casing portion 41.2 of the outer casing 41 forms a discharge plenum 41.3, through which exhausted combustion gas is discharged from the expander 3.

[0037] The inner casing 51 comprises a forward end 5 IF and an aft end 51 A. The aft end 51 A is mechanically coupled to the outer casing 41. More in detail, in some embodiments the aft end 51 A of the inner casing 51 is constrained to the outer casing 41 adjacent or near the discharge plenum 41.3. The aft end 51 A of the inner casing 51 can be provided with a discharge diffuser 5 ID projecting towards or in the discharge plenum 41.3.

[0038] Reference numbers 45 and 47 indicate an aft bearing arrangement and a forward bearing arrangement, respectively, which rotatingly support the rotor 43 of the expander 3 for rotation around the rotation axis A-A. For instance, the aft bearing arrangement 45 may include an axial or thrust bearing in combination with a radial bearing, or a bearing having an axial-radial bearing capability. The forward bearingarrangement 47 may include a radial bearing. A reversed arrangement is also possible, with a bearing having axial load capability arranged on the combustor assembly side.

[0039] The bearing arrangements 45, 47 can be positioned outside the casing 40, as shown in the exemplary embodiment of Fig.2 and the rotor can be supported by the bearing arrangements 45, 47 through a forward shaft portion 65 and an aft shaft portion 67 which project outside the casing 40. Seals 46 and 48 are positioned inboard of the bearing arrangements 45 and 47, respectively, to seal the casing 40.

[0040] The rotor 43 is surrounded by the inner casing 51. In some embodiments, the inner casing 51 can be horizontally split, i.e. can be comprised of two portions which are coupled to one another along a plane containing the rotation axis of the rotor 43. If the inner casing comprises two or more casing sections arranged in sequence in the axial direction (i.e. along the forward-to-aft direction), each section can in turn be horizontally split, i.e. comprised of two portions coupled along a plane containing the rotation axis of the rotor 43.

[0041] The inner casing 51 is fully or partly housed in the forward casing portion 41.1 of the outer casing 41. In some embodiments, as shown in Fig.2, the inner casing 51 protrudes in the aft casing portion 41.2 of the outer casing 41.

[0042] One or more annular fluid chambers 42 are formed between the inner casing 51 and the outer casing 41. In use, at steady state conditions, chilling or cooling fluid, e.g. chilled, dehydrated combustion gas from the cooling line 27, can be supplied to the annular fluid chamber 42.

[0043] The expander can be adapted to expand the combustion gas through a gas expansion flow path with a pressure drop of at least 150 bar, preferably of at least 250 bar, more preferably between 250 and 400 bar. In order to expand the combustion gas generated in the combustor assembly 7, at least one expansion stage, or preferably a plurality of expansion stages, is arranged along the expansion flow path. For instance, three or more, expansion stages are provided. In some examples there are five, six or more expansion stages. In some embodiments, the number of stages can be equal to or less than fifteen, in other embodiments, equal to or less than ten.

[0044] Each expansion stage includes an annular row of stationary blades 53, aka vanes, which are stationarily arranged in the inner casing 51. In some embodiments,intermediate supporting rings 52 can be housed in the inner casing 51, between the inner surface of the inner casing 51 and the stationary blades 53. The stationary blades 53 and stationary shroud segments can be connected to the inner casing through said rings. The first expansion stage includes an annular row of stationary blades which form nozzles between the combustion assembly 8 and the inlet of the expansion flow path.

[0045] The stationary blades 53 extend radially from the inner casing 51 in the expansion flow path. Each expansion stage further includes an annular row of rotor blades 55, arranged downstream the respective annular row of stationary blades 53 along the expansion flow path. The rotor blades 55 are supported by the rotor 43 for co-rotation therewith and extend radially from the rotor body in the expansion flow path.

[0046] A balance drum 69 can be constrained to the rotor 43 for co-rotation therewith. In the embodiment of Fig.2 the balance drum 69 includes a first balance drum portion 69A and a second balance drum portion 69B connected to one another by tie rods 70. The balance drum 69 is surrounded by a seal ring 72, which is stationarily housed in the outer casing 41. The seal ring 72 supports a balance drum seal 74 which surrounds a peripheral surface of the balance drum 69 and co-acts therewith, to prevent process gas from flowing in an upstream-to-downstream direction along the outer periphery of the balance drum 69.

[0047] The combustor assembly 7 includes a plurality of combustors 8. The combustors 8 are arranged around the rotation axis A-A of the expander. Each combustor 8 can be housed in a respective generally cylindrical seat 101 which can be at least partly or entirely formed in the forward casing portion 41.1 of the outer casing 41.

[0048] Each combustor 8 can comprise a tubular liner 103, i.e. a can-shaped liner 103. The liner is partially housed in the respective generally cylindrical seat 101.

[0049] Each combustor 8 comprises at least one burner 107 at the forward end of the respective liner 103. In some embodiments, each combustor 8 may comprise a plurality of burners 107, i.e. a burner cluster 107.

[0050] The burner or burner cluster 107 is fluidly coupled with a fuel inlet and an oxidant inlet. The fuel inlet is in turn fluidly coupled with the fuel supply line 13(Fig.1 ) and receives a fuel, for instance a gaseous fuel, such as natural gas, therefrom. The oxidant inlet is fluidly coupled with the oxidant supply line 11 and receives oxidant therefrom, the oxidant mainly consisting of oxygen and carbon dioxide, as mentioned above.

[0051] Each combustor 8 further comprises a transition piece 113 positioned at the aft end of the liner 103 and extending therefrom. Each transition piece 113 forms an extension of the respective liner 103 towards the first annular row of stationary blades 53 and guides the combustion gas generated in the combustion chamber 8.1 toward the expansion flow path formed by the annular rows of stationary blades 53 and rotor blades 55 of the expander 3. As will be explained in more detail below, the transition pieces and an aft portion of each liner 103 are positioned outside the cylindrical seat 101 of the relevant combustor 8, in an annular structure positioned in the outer casing 41, upstream of the inner casing 51.

[0052] The expander, and specifically the combustor assembly 7, further comprises an annular plenum 131 positioned at the aft end of the liners 103 of the combustors 8. The annular plenum houses an annular structure 132, which houses the transition pieces 113. In some embodiments, the annular structure 132 supports the transition pieces 113, such that each transition piece 113 is entirely supported by the annular structure 132. In other embodiments, each transition piece 113 can be supported partly by the annular structure 132 and partly by the respective liner 107. In yet further embodiments, each transition piece 113 may be directly coupled to the forward end 5 IF of the inner casing 51 and be supported at least in part by the inner casing 51, possibly in combination with the annular structure 132 and / or the liner 107.

[0053] The annular structure 132 further supports the first annular row of stationary blades 51 of the expansion flow path, positioned downstream of an aft end of the transition pieces 113.

[0054] Figs 4 to 6 show in more detail the annular structure 132 housed in the annular plenum 131. In Fig.4 the annular structure 132 is shown separate from the other components of the expander but with the transition pieces 113 housed therein. Fig. 5 illustrates the annular structure 132 in isolation with all components removed therefrom.

[0055] In the illustrated embodiment, the annular structure 132 comprises a ring 133 connecting the annular structure 132 to the forward end 5 IF of the inner casing 51. Forinstance, the ring 133 can be connected to the forward end 5 IF of the inner casing by means of tie rods 134 which extend through holes 133A of the ring 133 and holes 136 provided in a forward flange of the inner casing 51. Thus, the annular structure 132 is cantileverly supported on the inner casing 51, i.e. cantilevered from the inner casing 51, which is in turn supported, at the aft end thereof (see Fig.2) to the outer casing 41.

[0056] The annular structure 132 further comprises a cylindrical member 135 coaxial to the rotation axis A-A. The ring 133 and the cylindrical member 135 are coaxial to one another and are connected to one another by a plurality of radially extending struts 137 arranged around the rotation axis A-A.

[0057] The annular structure further comprises a thrust ring 139 (see in particular Fig.6) engaged to the cylindrical member 135. In some embodiments, the thrust ring 139 is connected to the cylindrical member by mutually engaging annular grooves and ridges. For example, the thrust ring 139 can comprise an annular ridge 139A which engages an annular groove 135 A in a radially inner surface of the cylindrical member 135.

[0058] For assembling purposes, the annular structure (including the ring 133 and the cylindrical member 135 is comprised of two substantially symmetrical portions 132A, 132B which are coupled to one another along a plane containing the rotation axis A-A of the expander 3. For the same purpose, the thrust ring 139 is split into two symmetrical parts along a plane containing the rotation axis A-A.

[0059] The thrust ring 139 is adapted to engage and / or support, the vanes, i.e. the stationary blades 53 of the first expansion stage of the expander, as shown in Fig.3. The stationary blades 53 are connected to the thrust ring 139 at the radial inner end of the blades. One or more annular slots 140 are provided along the radially outer surface of the thrust ring 139 for mounting the stationary blades 53. The thrust ring 139 can ensure a fine tuning of the position of the stationary blades 53 of the first expansion stage, e.g. in the axial and / or tangential direction.

[0060] The struts 137 are also adapted to connect the transition pieces 113 thereto. Therefore, in some embodiments the number of struts 137 is equal to the number of transition pieces 113. Each transition piece 113 can be connected to the respective strut 137 by means of a bracket (not shown), integral with the transition piece 113 and coupled to the strut 137 by connection plates or the like, not shown. As mentioned,alternatively, or in combination to the bracket connection to the annular structure 132, each transition piece 113 can be mechanically coupled directly to the forward end 5 IF of the inner casing 51.

[0061] Thus, in some embodiments the transition pieces 113 are cantilevered at the forward end of the inner casing 51.

[0062] Seals, not shown, can be arranged at or around the aft end of each transition piece 113.

[0063] As best shown in Figs.3 and 5, the cylindrical member 135 of the annular structure 132 comprises an inner surface surrounding the shaft portion 67 of the rotor 43. A high-pressure seal 151 is mounted on the inner surface of the cylindrical member 135 upstream of the thrust ring, with respect to the direction of flow of the expanding process fluid flowing through the expander. The high-pressure seal 151 surrounds the shaft portion 67 to provide a sealing therearound.

[0064] In some embodiments, the forward end of the annular structure 132 co-acts with the seal ring 72 stationarily mounted in the outer casing 41. In some embodiments, an annular gap between the seal ring 72 and the forward end of the annular structure 132 can be sealingly closed by an annular seal 153. In some embodiments, the annular seal 153 can be constrained to the forward end of the annular structure 132. In other embodiments, the annular seal 153 can be constrained to the seal ring 72.

[0065] In some embodiments, the seal ring 72 engages the forward end of the annular structure 132 such that axial and / or angular displacements of the seal ring 72 are restricted. Preferably, these displacements are not entirely prevented, so that differential thermal expansions of the annular structure 132 and of the seal ring 72 are possible. For example, the seal ring 72 can engage the forward end of the annular structure 132 with protrusions 72 A projecting in an aft direction from the seal ring 72 and engaging in cavities 155 (see Fig.5) formed in a forward-facing surface of the annular structure 132, or vice-versa. The protrusion and cavity configuration formed by cavities 155 and protrusions 72A is adapted to allow an axial and / or radial mutual displacement between the seal ring 72 and the annular structure 132.

[0066] In some embodiments, one or more ducts 152 extend radially through the annular structure 132. In some embodiments, the ducts 152 extend through one or morestruts 137 of said annular structure 132. The ducts 152 provide a fluid connection to a radially inner portion 131 A of the annular plenum 131, whereto a cooling flow of process gas can be delivered through the ducts 152. The cooling flow can be supplied through the cooling line 27 (Fig.l).

[0067] At least one, or some, or each strut 137 may house one or more auxiliary passages or ducts. In some embodiments, one or more of the auxiliary passages are adapted to feed a cooling fluid (such as ducts 152) and / or a lubricant. Said auxiliary passages can be particularly advantageous to feed lubricant oil to bearings arranged coaxial to the combustion chamber and surrounded thereby.

[0068]

[0069] 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 that which is specifically disclosed herein without departing from the scope of the invention as defined in the following claims.

[0070] The following examples also form part of the present disclosure:Example 1. An expander comprising: a casing, comprising an outer casing and an inner casing housed in the outer casing; a rotor housed in the casing for rotation therein around a rotation axis; a plurality of combustors, wherein each combustor comprises: a tubular liner; a transition piece at an aft end of the liner; and at least one burner at the forward end of the liner; an annular plenum between the generally cylindrical seats of the combustors and the inner casing; wherein the transition pieces are positioned in the annular plenum; and an annular structure cantilevered from a forward end of the inner casing and extending around the rotation axis; wherein the annular structure is housed in the annular plenum; wherein the transition pieces are positioned in the annular structure; and wherein the annular structure supports an annular row of stationary blades of a first expansion stage of the expander, such that the annular row of stationary blades are supported in a cantilevered fashion by the annular structure from the inner casing.Example 2. The expander of example 1, wherein the annular structure comprises a ring coaxial to the rotation axis and connected to the forward end of the inner casing.Example 3. The expander of example 2, wherein the annular structure comprises a cylindrical member coaxial to the ring.Example 4. The expander of example 3, wherein the ring and the cylindrical member are connected to one another by a plurality of struts.Example 5. The expander of example 4, wherein a transition piece and an aft end of the respective liner are housed between each pair of sequentially arranged struts.Example 6. The expander of one or more of the preceding examples, further comprising a thrust ring engaged to the cylindrical member, wherein the thrust ring is connected to, or supports said annular row of stationary blades of the first expansion stage of the expander.Example 7. The expander of example 6, wherein: the thrust ring is divided into two semi-annular portions; / or the annular structure is divided into two semi-annular portions; or both the thrust ring and the annular structure are both divided into two semi-annular portions.Example 8. The expander of one or more of examples 2 to 7, wherein the cylindrical member comprises an inner surface surrounding a shaft portion of the rotor; wherein a high-pressure seal co-acting with the shaft portion is mounted on said inner surface of the cylindrical member.Example 9. The expander of example 8, when depending upon at least example 7, wherein the high-pressure seal is positioned upstream of the thrust ring.Example 10. The expander of one or more of the preceding examples, comprising a balance drum constrained to the rotor for co-rotation therewith; wherein the balance drum is surrounded by a seal ring, stationarily mounted in the casing and supporting a balance drum seal; and wherein the balance drum seal co-acts with a peripheral surface of the balance drum.Example 11. The expander of example 10, wherein the seal ring engagesa forward end of the annular structure, projecting cantilevered from the inner casing; and wherein an annular seal is positioned between the forward end of the annular structure and the seal ring; the annular seal closing an annular gap between the ring seal and the annular structure.Example 12. The expander of example 11, wherein the annular seal is constrained to the forward end of the annular structure, or to the seal ring.Example 13. The expander of example 11 or example 12, wherein the seal ring engages the forward end of the annular structure with a projection and cavity configuration, adapted to prevent or limit mutual angular displacements between the annular structure and the seal ring.Example 14. The expander of example 13, wherein the projection and cavity configuration is adapted to allow an axial and / or radial mutual displacement between the seal ring and the annular structure.Example 15. The expander of one or more of the preceding examples, wherein the inner casing is supported through a flange at an aft end thereof to the outer casing.Example 16. The expander of one or more of the preceding examples, wherein the inner casing is horizontally split, and the outer casing is vertically split.Example 17. The expander of example 16, wherein the outer casing includes a forward casing portion and an aft casing portion; wherein the aft casing portion forms a discharge plenum; wherein the inner casing is housed in the outer casing and extends from and aft end of the inner casing, which engages the outer casing, to the forward end of the inner casing; and wherein the annular structure projects cantilevered from the forward end of the inner casing towards a forward end of the outer casing.Example 18. The expander of one or more of the preceding examples, wherein opposing ends of a rotor shaft project outside the casing and are engaged in respective bearings positioned outside the casing.Example 19. The expander of one or more of the preceding examples, wherein the expander is a supercritical carbon dioxide expander.

Claims

CLAIMS1. An expander comprising: a casing, comprising an outer casing and an inner casing housed in the outer casing; a rotor housed in the casing for rotation therein around a rotation axis; a plurality of combustors, wherein each combustor is at least partially housed in a generally cylindrical seat; wherein each combustor comprises: a tubular liner having a forward end, an aft end, and a side wall extending from the forward end to the aft end, a transition piece at the aft end of the liner, and at least one burner at the forward end of the liner, the at least one burner being fluidly coupled with a fuel inlet and an oxidant inlet; a first process gas inlet for each combustor; wherein each generally cylindrical seat is fluidly coupled with said first process gas inlet; an annular plenum between the generally cylindrical seats of the combustors and the inner casing; wherein the transition pieces are positioned in the annular plenum; and an annular structure cantilevered from a forward end of the inner casing and extending around the rotation axis; wherein the annular structure is housed in the annular plenum; and wherein the transition pieces are housed in the annular structure.

2. The expander of claim 1, wherein the annular structure comprises a ring coaxial to the rotation axis and connected to the forward end of the inner casing.

3. The expander of claim 2, wherein the annular structure comprises a cylindrical member coaxial to the ring.

4. The expander of claim 3, wherein the ring and the cylindrical member are connected to one another by a plurality of struts.

5. The expander of claim 4, wherein a transition piece and an aft end of the respective liner are housed between each pair of sequentially arranged struts.

6. The expander of any one of claims 3 to 5, wherein the cylindricalmember supports an annular row of stationary blades of a first expansion stage of the expander.

7. The expander of claim 6, further comprising a thrust ring engaged to the cylindrical member, wherein the thrust ring is connected to, or supports said annular row of stationary blades of the first expansion stage of the expander.

8. The expander of claim 7, wherein the thrust ring and the annular structure are each divided into two semi-annular portions.

9. The expander of claim 7 or 8, wherein the thrust ring and the cylindrical member are coupled to one another by mutually engaging annular grooves and ridges.

10. The expander of claim 7, 8 or 9, wherein the thrust ring comprises an annular slot engaging the annular row of stationary blades of the first stage of the expander.

11. The expander of any one of claims 2 to 10, wherein the cylindrical member comprises an inner surface surrounding a shaft portion of the rotor; wherein a high-pressure seal co-acting with the shaft portion is mounted on said inner surface of the cylindrical member.

12. The expander of claim 11, when depending upon at least claim 7, wherein the high-pressure seal is positioned upstream of the thrust ring.

13. The expander of any one of the preceding claims, comprising a balance drum constrained to the rotor for co-rotation therewith; wherein the balance drum is surrounded by a seal ring, stationarily mounted in the casing and supporting a balance drum seal; and wherein the balance drum seal co-acts with a peripheral surface of the balance drum.

14. The expander of claim 13, wherein the seal ring engages a forward end of the annular structure, projecting cantilevered from the inner casing; and wherein an annular seal is positioned between the forward end of the annular structure and the seal ring; the annular seal closing an annular gap between the ring seal and the annularstructure.

15. The expander of claim 14, wherein the annular seal is constrained to the forward end of the annular structure, or to the seal ring.

16. The expander of claim 14 or claim 15, wherein the seal ring engages the forward end of the annular structure with a projection and cavity configuration, adapted to prevent or limit mutual angular displacements between the annular structure and the seal ring.

17. The expander of claim 16, wherein the projection and cavity configuration is adapted to allow an axial and / or radial mutual displacement between the seal ring and the annular structure.

18. The expander of anyone of the preceding claims, wherein the inner casing is supported through a flange at an aft end thereof to the outer casing.

19. The expander of any one of the preceding claims, wherein the inner casing is horizontally split, and the outer casing is vertically split.

20. The expander of claim 19, wherein the outer casing includes a forward casing portion and an aft casing portion; wherein the aft casing portion forms a discharge plenum; wherein the inner casing is housed in the outer casing and extends from and aft end of the inner casing, which engages the outer casing, to the forward end of the inner casing; and wherein the annular structure projects cantilevered from the forward end of the inner casing towards a forward end of the outer casing.

21. The expander of any one of the preceding claims, wherein opposing ends of a rotor shaft project outside the casing and are engaged in respective bearings positioned outside the casing.

22. The expander of any one of the preceding claims, wherein the expander is a supercritical carbon dioxide expander.

23. The expander of claim 3 or 4, wherein at least one strut houses at least one auxiliary passage adapted to allow the passage of a cooling fluid or alubricant.

24. An expander comprising: a casing, comprising an outer casing and an inner casing housed in the outer casing; a rotor housed in the casing for rotation therein around a rotation axis; a plurality of combustors, wherein each combustor comprises: a tubular liner; a transition piece at an aft end of the liner; and at least one burner at the forward end of the liner; an annular plenum between the generally cylindrical seats of the combustors and the inner casing; wherein the transition pieces are positioned in the annular plenum; and an annular structure cantilevered from a forward end of the inner casing and extending around the rotation axis; wherein the annular structure is housed in the annular plenum; wherein the transition pieces are positioned in the annular structure; and wherein the annular structure supports an annular row of stationary blades of a first expansion stage of the expander, such that the annular row of stationary blades are supported in a cantilevered fashion by the annular structure from the inner casing.

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