An expander with a sealing and damping structure

Abstract

The expander comprises a casing and a rotor supported for rotation in the casing around a rotation axis and provided with a plurality of rotor disks with dovetail slots formed around the perimeter of the rotor disks. An annular row of rotor blades is mounted around each rotor disk. Each rotor disks further comprises a plurality of seal bodies, a respective one of said plurality of seal bodies positioned between each pair of adjacent rotor blades. Each seal body comprises: an enlarged seal plate at a forward end of the seal body, the seal plate having a forward surface and an aft surface; and a longitudinal structure cantileverly extending in a forward-to-aft direction from the aft surface of the enlarged seal plate in a cavity between the shanks of the pair of adjacent rotor blades.

Description

AN EXPANDER WITH A SEALING AND DAMPING STRUCTUREDESCRIPTIONTECHNICAL FIELD

[0001] The present disclosure relates generally to expanders and to sealing structures for an expander. More particularly, embodiments disclosed herein relate to oxy-fuel combustion expanders and related sealing structures.BACKGROUND ART

[0002] Oxy-fuel combustion cycles have recently been investigated as a promising way to generate mechanical power through combustion of fossil fuels, with reduced emissions of environmentally harmful gases, particularly carbon dioxide.

[0003] Oxy-fuel combustion cycles operate under high temperature and high pressure conditions, compared to standard Bryton cycles. This poses serious challenges with respect to seals in the expansion flow path.

[0004] US7097429 discloses a gas turbine for a Brayton cycle, including a plurality of seal bodies. Each seal bodies is positioned between a respective pair of adjacent rotor blades. Each seal body comprises an enlarged seal plate at a forward end of the seal body, and a longitudinal structure cantileverly and symmetrically extending in a forward-to-aft direction from an aft surface of the enlarged seal plate in a cavity between the shanks of the pair of adjacent rotor blades. The seal body is retained in the sealing position by the centrifugal force which is generated by rotation of the gas turbine rotor.

[0005] An object of embodiments disclosed herein is to provide efficient sealing of gaps between rotor blades, to increase efficiency of the expanders, in particular oxy- fuel combustion expanders.SUMMARY

[0006] According to one aspect, disclosed herein is an expander comprising a casing and a rotor supported for rotation in the casing around a rotation axis. The rotor comprises at least one rotor disk with a plurality of dovetail slots formed around a perimeterof the rotor disk. The latter comprises a forward disk face and an aft disc face. An annular row of rotor blades is mounted around the rotor disk. Each rotor blade comprises: an airfoil with a suction side and a pressure side extending from a leading edge to a trailing edge; a platform; a shank extending radially inwardly from the platform and including: a forward surface corresponding with the leading edge of the airfoil; an aft surface corresponding with the trailing edge of the airfoil; a first side corresponding with the pressure side of the airfoil; and an opposite, second side corresponding with the suction side of the airfoil; and a dovetail extending radially inwardly from the shank and engaging a corresponding one of said dovetail slots. The rotor disk further comprises a plurality of seal bodies, a respective one of said plurality of seal bodies positioned between each pair of adjacent rotor blades. Each seal body comprises: an enlarged seal plate at a forward end of the seal body, the seal plate having a forward surface and an aft surface, i.e. a forward-facing surface and an aft-facing surface; and a longitudinal structure cantileverly extending in a forward-to-aft direction from the aft surface of the enlarged seal plate in a cavity between the shanks of the pair of adjacent rotor blades.

[0007] In certain embodiments, when the expander is in operation, and the process gas flows through a flow path extending through the stationary and rotary blades, a pressure difference established between the forward surface and the cavity ensures sealing between a forward chamber upstream of the rotor disk and an aft chamber downstream of the rotor disk. The pressure difference between the forward disk side or forward disk face, and the aft disk side or aft disk face may be at least between 3 and 15 bars. It has been surprisingly discovered, that this pressure difference, which may be present in an oxyfuel combustion expander, such as a supercritical carbon dioxide expander, ensures a reliable retention of the seal body against in sealing contact with the forward facing side, i.e. the forward facing surface, of the rotor disk,

[0008] In contrast to known sealing systems, wherein the seal body is retained by centrifugal force, retention through pressure differential ensures a more efficient sealing effect and more reliable retention, independent of the rotation speed of the turbomachine. The retention and sealing effect is reliably reached also at low rotational speeds.

[0009] In certain embodiments, the longitudinal structure of each seal platecomprises: a foot at a first, proximal end, i.e. adjacent the enlarged seal plate, and a head at a second, distal end. In certain embodiments, wherein the foot is directly coupled to the enlarged seal plate. In certain embodiments, a extends from the foot to the head, along the longitudinal extension of the longitudinal structure. The stem may have a cross-sectional area that is smaller than a cross-sectional area of the foot and a cross- sectional area of the head. As will be described in greater detail with reference to certain exemplary embodiments, the configuration outlined above may advantageously facilitate effective sealing by leveraging differential pressure across the sealing interface.

[0010] In certain embodiments, each longitudinal structure extends non-symmetri- cally from the respective enlarged seal plate. For instance, the longitudinal structure of each seal plate is skewed with respect to the rotation axis.

[0011] An improved sealing is thus achieved, since the longitudinal structure may have an inclination which at least approximately matches an inclination of the platforms and of the dovetails of the blades.

[0012] In embodiments disclosed herein, the longitudinal structure of each seal plate comprises: a foot at a first, proximal end, directly coupled to the enlarged seal plate; and a head at a second, distal end. The foot and the head may be staggered with respect to each other in a tangential direction. Specifically, the head may be set back from the foot in the direction of rotation of the rotor.

[0013] In some embodiments, the longitudinal structure can be inclined towards the rotation axis, starting from the head towards the foot. I.e. the foot and the head of each longitudinal structure can be staggered with respect to each other in a radial direction, with the head being nearer to the rotation axis than the foot. In some embodiments, the center of the head can be nearer to the rotation axis than the center of the foot.

[0014] Further features and embodiments of the expander according to the present disclosure are described below with reference to the attached drawings, and are set forth in the appended claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Reference is now made briefly to the accompanying drawings, in which:Fig.1 illustrates a sectional view of an expander according to the present disclosure;Figs.2 and 3 illustrate axonometric views of a portion of a rotor disk with two blades mounted thereon;Figs. 4 and 5 illustrate a sectional view of an annular row of blades according to a plane containing the rotation axis of the rotor;Figs 6 and 7 illustrate axonometric views of a portion of the rotor disk with one blade mounted thereon;Figs.8 and 9 illustrate axonometric views of a seal body;Fig.10 illustrates a top view of the seal body of Figs. 8 and 9;Fig. 11 illustrates a side view according to XI-XI of Fig.10;Fig.12 illustrates a side view according to XII-XII of Fig.11;Figs. 13 and 14 illustrate end views according to XIII-XIII and XIV-XIV of Fig. H;Figs. 15, 16 and 17 illustrate axonometric views of a single rotor blade separate from the rotor disk and with the seal bodies mounted thereon; andFig.18 illustrate a view according to a radial inward direction of two rotor blades and relevant rotor disk.DETAILED DESCRIPTION

[0016] Fig.l shows a sectional view of an expander 1 according to one embodiment of the present disclosure, for instance an oxy-fuel combustion expander, specifically a supercritical expander. The section is taken along a plane containing a rotation axis A- A of the expander. The sectional view shows only half expander, which is axial-symmetrical.

[0017] The expander 1 can be a supercritical carbon dioxide (sCCh) expander. As understood herein, a supercritical carbon dioxide expander is an expander wherein the process gas consists mainly of carbon dioxide, or carbon dioxide and steam, such as typically foreseen in an oxyfuel cycle, and wherein in at least one section of the expansion flow path the carbon dioxide is in a supercritical state.

[0018] In this embodiment, the expander 1 includes an outer casing 3 and an inner casing 5. The outer casing 3 can include a main body 3 A and a closure 3B on the aftside of the expander. In this embodiment the outer casing 3 is a so-called vertically split casing, wherein the main body 3A and the closure 3B are coupled, through respective flanges, along a plane orthogonal to the rotation axis A-A of the expander. In the embodiment disclosed herein, the inner casing 5 is a horizontally split casing, comprising two casing portions coupled to one another along a plane containing the rotation axis A-A.

[0019] This combination of inner horizontally split casing 5 and outer vertically split casing 3 is particularly beneficial in case of a supercritical carbon dioxide expander, or another expander which processes a gas under similar thermodynamic conditions involving high temperature gradients and elevated pressure drops across some at least of the expansion stages. Nevertheless, in other embodiments, the novel features disclosed herein can be used in a different expander or turbine structure, for instance including a single casing, or a vertically split inner casing and a horizontally split outer casing, for instance.

[0020] A combustor, such as a can combustor including a plurality of combustion chambers 7, or a cannular combustor, is positioned at the forward side of the expander. An annular chamber 6 is positioned between the outer casing 3 and the inner casing 5.

[0021] As used herein “forward” and “aft” are referred to the direction of flow of the process gas through the expander 1. Therefore, “forward” indicates a position on the side of the combustor chambers 7 and “aft” indicates a position on the side opposite the combustor chambers 7, i.e., the discharge side of the expander 1.

[0022] The expander 1 further comprises a rotor 11 housed in the inner casing 5 and adapted to rotate about the rotation axis A-A. The rotor 11 comprises a rotor shaft 13 and a plurality of annular rows of rotor blades 15. Each annular row of rotor blades comprises a plurality of rotor blades circumferentially arranged around the rotation axis A-A of the rotor 11 and mounted on a respective rotor disk 16. The rotor disks 16 can be connected to one another by a tie-rod arrangement 14. References 16.1 and 16.2 indicate a forward side and an aft side of each rotor disk 16.

[0023] An annular row of stationary blades 17 is positioned upstream of each annular row of rotor blades 15, i.e. on the forward side of the annular row of rotor blades 15. The blades 17 of the annular rows of stationary blades are circumferentially arrangedaround the rotation axis A-A. Pairs of adjacent stationary blades or vanes define respective nozzles which direct the expanding gas in the correct orientation with respect to the downstream annular row of rotor blades 15. Each annular row of stationary blades 17 and respective annular row of rotor blades 15 form together a stage of the expander 1. Each annular row of rotor blades 15 is surrounded by a respective shroud 19.

[0024] In a supercritical carbon dioxide expander, such as an expander for an oxyfuel cycle, the pressure drop across each rotor disk can range between 3 bar and 15 bar, for instance between 5 bar and 15 bar, which is higher than the pressure drop across a stage of a gas turbine typically used in a traditional Brayton cycle.

[0025] Figs. 2 to 7 illustrate a plurality of views of portions of one of the rotor disks 16 with respective rotor blades 15 mounted thereon. Each rotor disk 16 comprises a plurality of peripherally arranged dovetail slots 41, adapted to engage each a dovetail of a corresponding one of the rotor blades 15 mounted on the rotor disk 16, to be described.

[0026] Each rotor blade 15 comprises an airfoil 43 with a suction side 43 S and a pressure side 43P extending from a leading edge 45 to a trailing edge 47. The airfoil 43 extends radially outwardly from a platform 49. Each rotor blade 15 further comprises a shank 51 extending radially inwardly from the platform 49, opposite to the airfoil 43. The shank 51 comprises a forward surface 53 corresponding with the leading edge 45 of the airfoil 43 and an aft surface 55 corresponding with the trailing edge 47 of the airfoil 43. Each shank 51 further comprises a first side 57 corresponding with the pressure side 43P of the airfoil 43, and an opposite, second side 59 corresponding with the suction side 43 S of the airfoil 43.

[0027] A dovetail 61 extends radially inwardly from the shank 51 of each rotor blade 15. Each dovetail 61 engages with a corresponding dovetail slot 41 formed in the periphery of the rotor disk 16.

[0028] In the exemplary embodiment shown in the drawings, the shank of each rotor blade 15 comprises a first forward lug 63 and a first aft lug 65 on the first side 57 of the shank 51. The first forward lug 63 is positioned adjacent the forward surface 53 of the shank 51. The first aft lug 65 is positioned adjacent the aft surface 55 of the shank51. A second forward lug 67 is provided on the second side 59 of the shank 51 and adjacent the forward surface 53 of the shank 51. A second aft lug 69 is provided on the second side 59 of the shank 51 and adjacent the aft surface 55 of the shank 51.

[0029] A seal body 71 is positioned between each pair of adjacent rotor blades 15 that are part of the same annular row of rotor blades. A seal body is shown in isolation in Figs. 8 to 14. Each seal body 71 comprises an enlarged seal plate 73 at a forward end of the seal body 71. Each enlarged seal plate 73 has a forward surface 73F facing in the forward direction, i.e. opposite the direction of flow of the process gas expanding through the expander. Each enlarged seal plate 73 further comprises an aft surface 73 A, facing in the direction of flow.

[0030] A longitudinal structure 75 extends in a cantilever fashion in a forward to aft direction from the aft surface 73 A of the enlarged seal plate 73. Each seal body 71 is mounted on the annular row of rotor blades 15 such that the aft surface 73 A of the enlarged seal plate 73 is in sealing contact with the forward surfaces 53 of the respective two adjacent rotor blades 15 and with the forward surface 16.1 of the rotor disk 16. In the mounted state, the longitudinal structure 75 extends in a corresponding cavity, or pocket, between the shanks 51 of the pair of adjacent rotor blades 15.

[0031] In some embodiments, as best shown in Figs. 8 to 14, the longitudinal structure 75 of each seal body 71 comprises a foot 91 at a first, proximal end thereof, and a head 93 at a second, distal end thereof. The proximal end may be directly attached to the enlarged seal plate 73. In certain embodiments, a stem 92 extends from the foot 91 to the head 93, along the longitudinal extension of the longitudinal structure 75. In certain embodiments, the stem has a cross-sectional area that is smaller than a cross- sectional area of the foot and a cross-sectional area of the head.

[0032] In some embodiments, the longitudinal structure 75 is non- symmetrical with respect to the enlarged seal plate 73. Specifically, the longitudinal structure 75 extends from the enlarged seal plate 73 in an inclined fashion, i.e. non-parallel to the rotation axis A- A of the rotor.

[0033] As best shown in Figs. 3, 10, 12, 17 and 18, the longitudinal structure 75 is inclined such that the foot 91 and the head 93 thereof are staggered with respect to each other in a tangential direction, i.e. in the direction of the rotational speed whenthe seal body is mounted in the rotor disk. In Fig. 18 the direction of the rotational speed is indicated by arrow fR. As clearly shown in Fig.18, the head 93 of the longitudinal structure is behind the foot in the direction of the peripheral velocity fR of the rotor disk 16, i.e. the head is set back from the foot in the direction of rotation of the rotor 11. In some embodiments, each the platform 49 can have a parallelogram shape with two long sides 49X, 49B, extending generally in the forward to aft direction and inclined at an angle A to the direction of the rotation axis A-A. In the radial view of Fig. 18 the longitudinal structure 75 has approximately the same inclination A with respect to the axial direction represented by rotation axis A-A.

[0034] In addition, the foot 91 and the head 93 of each longitudinal structure 75 can be staggered with respect to each other in a radial direction, as best shown in Figs. 4 and 11. The reference Rs in Figs. 4 and 11 indicates the radial distance, i.e. the distance in the radial direction between the center of the head 93 and the center of the foot 91.

[0035] The foot 91 of each seal body 71 is retained between the first forward lug 63 of one of the two adjacent blades, between which the seal body 71 is positioned, and the second forward lug 67 of the other of said two adjacent blades. Similarly, the head of each seal body 71 is retained between the first aft lug 65 of one of the two adjacent blades and the second aft lug 69 of the other of the adjacent blades. Each head 93 and foot 91 are positioned radially inwardly of the respective lugs, such that, when the expander 1 is in operation, the centrifugal force acting on each seal body forces the respective foot 91 and head 93 radially outwardly against the lugs 63, 65, 67 and 69. In certain embodiments, where the longitudinal stem 92 connecting the head 93 and the foot 91 has a smaller cross-sectional area than the head 93 and the foot 91, only these latter are in contact with the lugs 63, 65, 67 and 69, such that the frictional force between the seal body 71 and the lugs generated by the centrifugal force is limited, as the contact area between seal body 71 and lugs is limited. This configuration facilitates axial displacement of the seal body 71 in response to the pressure differential between the forward and aft sides of the rotor disk 16, thereby promoting enhanced sealing engagement of the aft-facing surfaces of the enlarged seal plates 73 with the forwardfacing surfaces 53 of the adjacent rotor blades 15 and the forward surface 16.1 of the rotor disk 16.

[0036] In use, i.e. when the expander 1 is operating, a flow of process gas flowsthrough the expansion flow path formed by the sequentially arranged annular rows of stationary blades 17 and rotor blades 15. Enthalpy of the process gas is converted into mechanical power, which rotates the rotor 11. The pressure of the process gas decreases along the expansion flow path. A pressure drop is therefore created between the forward side and the aft side of each rotor disk 16. Specifically, a higher pressure will be present in a forward chamber 81 upstream of the rotor disk 15 and a lower pressure will be present in an aft chamber 83, downstream of the rotor disk 15. An intermediate process gas pressure is established in the cavity or pocket between adjacent rotor blades 15. This creates a pressure differential between the forward surface 73F and the aft surface 73A of the enlarged seal plate 73 is generated. The pressure difference urges each seal body 71 against the forward surfaces 53 of the shanks 51 of the rotor disk 16, to seal the gap between adjacent shanks 51 and thus provide a sealing action between the forward chamber 81 and the aft chamber 83. The gas leakage between the forward chamber and the aft chamber 83, through the cavities between adjacent rotor blades 1, is thus reduced.

[0037] The arrangement is particularly useful in an oxyfuel expander, such as a supercritical carbon dioxide expander, where the pressure difference across each row of rotor blades, i.e. the pressure difference between the forward side (forward chamber 81) and the aft side (aft chamber 83) of the rotor disk, ranges between 3 bar and 15 bar.

[0038] In some embodiments, each enlarged seal plate 73 may include an orifice 96 extending from the forward surface 73F to the aft surface 73A of the enlarged seal plate 73 and providing a fluid coupling between the forward chamber 81 and the cavity or pocket between the shanks of adjacent rotor blades 15. Each orifice 96 provides a calibrated leakage of process gas from the forward chamber 81 at a higher pressure to the aft chamber 83 at a lower pressure, such that the gas pressure in the cavity between adjacent shanks the gas pressure is at a value intermediate between the pressure upstream and downstream of the respective annular row of rotor blades 15.

[0039] By providing a controlled leakage between the forward chamber 81 and the cavity between shanks of the rotor blades 15 the pressure difference across the enlarged seal plate is reduced compared to the pressure difference in the absence of such controlled leakage. The pressure in the cavity between the shanks will approach thepressure upstream of the rotor disk. The pressure inside the cavity can thus be controlled based on the size of the orifice.

[0040] According to some embodiments, an additional sealing and damping member 101 may be provided between each pair of adj acent rotor blades 15. Each damping and sealing member 101 is positioned between the seal body 71 and the platforms 49 of the relevant pair of adjacent rotor blades 15. In some embodiments, a recess 103 is formed on the first side 57 or the second side 59 of each shank 51 for receiving the respective sealing and damping member 101. Figs 3, 4 and 17 illustrate the recess 103 without the sealing and damping member 101 therein, while Figs. 5 and 7 illustrate the sealing and damping member 101 mounted in the respective recess 103.

[0041] In the embodiment illustrated in the drawings, the recess 103 is formed on the first side 57 of the shank, i.e. on the side corresponding with the pressure side 43P of the airfoil 43. When mounted, each sealing and damping member 101 can slightly protrude outside the recess 103 in the tangential direction, to provide a full contact with the opposite second side 59 of the adjacent shank. In this way the opposing first side 57 and second side 59 of each pair of adjacent shanks do not contact each other directly, but are spaced apart with the sealing and damping member 101 interposed therebetween. The sealing and damping member 101 can thus provide a damping action, aimed at suppressing or reducing vibration of the rotor blades during use and seal the gap between the platforms 49 of adjacent rotor blades 15.

[0042] In some embodiments, each sealing and damping member 101 may include a main or intermediate body 101C (see Figs. 5 and 7) extending in a forward to aft direction between the shanks 51 of each pair of adjacent rotor blades 15. Each sealing and damping member 101 may further include a forward appendage 10 IF projecting radially inwardly from a forward end of the main or intermediate body 101C towards the seal body 71. Each sealing and damping member 10 may further include an aft appendage 101 A projecting radially inwardly from an aft end of the main or intermediate body 101C towards the seal body 71. In other embodiments, not shown, only one of the forward appendage 101F and the aft appendage 101 A can be provided.

[0043] In some embodiments, each recess 103 can be radially inwardly partly closed by the first forward lug 63 and the first aft lug 65. Thus, the forward appendage 10 IFcan rest on the first forward lug 63 of the respective shank 51 and the aft appendage 101 A can rest on the first aft lug 65 of the respective shank 51.

[0044] The forward appendage 101F and the aft appendage 101A, if provided, improve the seal between adjacent rotor blades 15, since the appendages provide a seal between adjacent shanks 51 in the area above the feet 91 and the heads 93 of the seal bodies 71.

[0045] 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.

[0046] Further aspects are provided by the subject matter of the following clauses:Clause (a) An expander comprising: a casing; a rotor supported for rotation in the casing around a rotation axis, the rotor comprising at least one rotor disk with a plurality of dovetail slots formed around a perimeter of the rotor disk; the rotor disk having a forward disk face and an aft disc face; an annular row of rotor blades mounted around the rotor disk; wherein each rotor blade comprises:- an airfoil with a suction side and a pressure side extending from a leading edge to a trailing edge,- a platform,- a shank extending radially inwardly from the platform and including: a forward surface corresponding with the leading edge of the airfoil; an aft surface corresponding with the trailing edge of the airfoil; a first side corresponding with the pressure side of the airfoil; and an opposite, second side corresponding with the suction side of the airfoil, and- a dovetail extending radially inwardly from the shank and engaging a corresponding one of said dovetail slots; and a plurality of seal bodies, a respective one of said plurality of seal bodiespositioned between each pair of adj acent rotor blades; wherein each seal body comprises:- an enlarged seal plate at a forward end of the seal body, the seal plate having a forward surface and an aft surface, and- a longitudinal structure cantileverly extending in a forward-to-aft direction from the aft surface of the enlarged seal plate in a cavity between the shanks of the pair of adjacent rotor blades; wherein each longitudinal structure extends non-symmetrically from the respective enlarged seal plate.Clause (b) The expander of clause (a), wherein the longitudinal structure of each seal plate is skewed with respect to the rotation axis.Clause (c) The expander of clause (a) or (b), wherein the longitudinal structure of each seal plate comprises: a foot at a first, proximal end, preferably directly coupled to the enlarged seal plate; and a head at a second, distal end.Clause (d) The expander of clause (c), wherein the foot and the head are staggered with respect to each other in a tangential direction.Clause (e) The expander of clause (d), wherein the head is set back from the foot in the direction of rotation of the rotor.Clause (f) The expander of any one of clauses (c) to (e), wherein the foot and the head of each longitudinal structure are staggered with respect to each other in a radial direction.Clause (g) The expander of any one of clauses (c) to (f), wherein a stem extends from the foot to the head, along the longitudinal extension of the longitudinal structure.Clause (h) The expander of clause (i), wherein the stem has a cross- sectional area that is smaller than a cross-sectional area of the foot and a cross- sectional area of the head.

Claims

AN EXPANDER WITH A SEALING AND DAMPING STRUCTURECLAIMS1. An expander comprising: a casing a rotor supported for rotation in the casing around a rotation axis, the rotor comprising at least one rotor disk with a plurality of dovetail slots formed around a perimeter of the rotor disk; the rotor disk having a forward disk face and an aft disc face; an annular row of rotor blades mounted around the rotor disk; wherein each rotor blade comprises:- an airfoil with a suction side and a pressure side extending from a leading edge to a trailing edge,- a platform,- a shank extending radially inwardly from the platform and including: a forward surface corresponding with the leading edge of the airfoil; an aft surface corresponding with the trailing edge of the airfoil; a first side corresponding with the pressure side of the airfoil; and an opposite, second side corresponding with the suction side of the airfoil, and- a dovetail extending radially inwardly from the shank and engaging a corresponding one of said dovetail slots; a plurality of seal bodies, a respective one of said plurality of seal bodies positioned between each pair of adjacent rotor blades; wherein each seal body comprises:- an enlarged seal plate at a forward end of the seal body, the seal plate having a forward surface and an aft surface, and- a longitudinal structure cantileverly extending in a forward-to-aft direction from the aft surface of the enlarged seal plate in a cavity between the shanks of the pair of adjacent rotor blades; wherein, in operation, a pressure difference established between the forward surface and the cavity ensures sealing between a forward chamber upstream of the rotor disk and an aft chamber downstream of the rotor disk; wherein when the expander is in operation, a pressure difference between a forward side and an aft side of the rotor diskis comprised between 3 bar and 15 bar.

2. The expander of claim 1, wherein each enlarged seal plate comprises an orifice between the forward surface and the aft surface of each enlarged seal plate.

3. The expander of claim 1 or 2, wherein each longitudinal structure extends non-symmetrically from the respective enlarged seal plate.

4. The expander of claim 3, wherein the longitudinal structure of each seal plate is skewed with respect to the rotation axis.

5. The expander of any one of the preceding claims, wherein the longitudinal structure of each seal plate comprises: a foot at a first, proximal end, and a head at a second, distal end.

6. The expander of claim 5, wherein the foot is directly coupled to the enlarged seal plate.

7. The expander of claim 5 or 6, wherein a stem extends from the foot to the head, along the longitudinal extension of the longitudinal structure.

8. The expander of claim 7, wherein the stem has a cross-sectional area that is smaller than a cross-sectional area of the foot and a cross-sectional area of the head.

9. The expander of claim 5, wherein the foot and the head are staggered with respect to each other in a tangential direction.

10. The expander of any one of claims 5 to 9, wherein the head is set back from the foot in the direction of rotation of the rotor.

11. The expander of any one of claims 5 to 10, wherein the foot and the head of each longitudinal structure are staggered with respect to each other in a radial direction.

12. The expander of any one of the preceding claims, wherein the shank of each rotor blade comprises: a first forward lug on the first side of the shank and adjacent the forward surface of the shank; a second forward lug on the second side ofthe shank and adjacent the forward surface of the shank; a first aft lug on the first side of the shank and adjacent the aft surface of the shank; a second aft lug on the second side of the shank and adjacent the aft surface of the shank; and wherein each seal body is retained between the first forward lug and the second forward lug of the respective two adjacent rotor blades, and between the first aft lug and the second aft lug of the respective two adjacent rotor blades.

13. The expander of any one of the preceding claims, further comprising a sealing and damping member positioned between the shanks of each pair of adjacent rotor blades.

14. The expander of claim 13 wherein each sealing and damping member is positioned between the seal body and the platforms of the relevant pair of rotor blades.

15. The expander of claim 13 or 14, wherein each sealing and damping member is housed in a recess formed in one of the first side and second side of the shank of each blade.

16. The expander of claim 15, wherein each sealing and damping member projects from the recess of the respective rotor blade and contacts the other of said first side and second side of the adjacent rotor blade.

17. The expander of any one of claims 13 to 16, wherein each sealing and damping member comprises: a main body extending in a forward to aft direction between the shanks of each pair of adjacent rotor blades; a forward appendage projecting radially inwardly from a forward end of the main body towards the seal body; and an aft appendage projecting radially inwardly from an aft end of the main body towards the seal body.

18. The expander of any one of claims 13 to 17, when dependent upon claim 9, wherein the recess of each sealing and damping member is formed on the first side of the shank of the respective rotor blade; and wherein the recess is radially inwardly partly closed by the first forward lug and the first aft lug.

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

20. The expander of any one of the preceding claims, wherein when the expander is in operation, the pressure difference between the forward side and the aft side of the rotor disk is comprised between 5 bar and 15 bar.

Images