A power-generating turbomachine using coolant extracted from rotor cavity

Abstract

The turbomachine comprises a casing (51) and a rotor (43) housed for rotation in the casing. A high-pressure region (71) and a low-pressure region (73) are provided adjacent the rotor shaft and separated by a high-pressure package seal (75) around the rotor shaft. The high-pressure package seal separates the high-pressure region and the low-pressure region from one another; and the high-pressure region is positioned at the forward-facing side of the high-pressure package seal, and the low-pressure region is positioned at the aft-facing side of the high-pressure package seal. A first rotor cavity (77) is fluidly coupled with the high-pressure region and adapted to provide a coolant flow to an upstream section of the rotor. A second rotor cavity (83) is fluidly coupled with the low-pressure region and adapted to provide a coolant flow to a downstream section of the rotor. A sealing member (85) separates the first rotor cavity and the second rotor cavity from one another.

Description

A POWER-GENERATING TURBOMACHINE USING COOLANT EXTRACTED FROM ROTOR CAVITYDESCRIPTIONTECHNICAL FIELD

[0001] The present disclosure relates to power-generating turbomachines, such as expanders and gas turbines.BACKGROUND ART

[0002] Turbomachines are commonly used to generate mechanical power by expansion of a high-pressure and high-temperature process fluid. The process fluid flows through a flow path which extends through a plurality of turbomachine stages. Each stage includes an annular row of stationary blades, aka stationary vanes, and an annular row of rotor blades arranged downstream of annular row of the annular row of stationary blades with respect to the direction of flow of the expanding process fluid. The rotor blades are mounted around a respective rotor disk and form therewith a rotor wheel of a rotor. The rotor is housed in a casing and adapted to rotate around a rotor axis under the thrust of the expanding gas, which flows along the flow path. A wheelspace is formed between the radially inwardly oriented ends of the stationary blades of each annular row of stationary blades and the rotor wheels.

[0003] To prevent thermal damages to the rotor wheels and lengthen the useful life thereof, it is common practice to purge the wheelspaces with a flow of cooling process fluid at suitable pressure. The cooling process fluid prevents hot process fluid from escaping from the flow path into the wheelspaces. Additionally, or alternatively, cool and pressurized process fluid is used to cool the rotor blades. Cooling fluid cavities or ducts are arranged in the rotor, wherefrom the cooling process fluid is delivered to the wheelspaces and / or to blade cooling ducts through suitable holes, slots and calibrated passages.

[0004] The cooling process fluid must be at a proper pressure to reach the wheelspaces and / or blades in several positions along the turbomachine flow path, to overcome the head loss through the ducts and the pressure of the process fluid in the flowpath. The pressure of the process fluid along the flow path decreases in an upstream- to-downstream direction, i.e., in a forward-to-aft direction, following expansion in the sequentially arranged stages of the turbomachine.

[0005] Providing suitable pressure levels of the cooling fluid, especially in the most upstream stages of the flow path becomes challenging, in particular in turbomachines operating at high pressure levels, such as supercritical expanders, for instance, which are commonly used in Allam cycles and similar thermodynamic cycles.

[0006] Providing appropriate cooling and / or purging and at the same time reducing the amount of cooling fluid is important to improve the overall efficiency of the turbomachine and prevent thermal damages to the rotor components, specifically when the turbomachine operates under high temperature and pressure conditions.

[0007] In some known turbomachines, such as gas turbine engines, process fluid is extracted at different pressure levels from different stages of the air compressor of the gas turbine engine and delivered to different portions of the turbine rotor. This arrangement is not possible in turbomachines that do not include an in-line compressor, such as expanders of oxy-fuel combustion cycles and in turbomachine with a central tierod.

[0008] Therefore, a more efficient arrangement for feeding cooling process gas in wheelspaces of a power generating turbomachine would be welcome in the art.SUMMARY

[0009] According to one aspect, disclosed herein is a power-generating turbomachine, e.g., an expander, comprising a casing and a plurality of stages. Each stage comprises an annular row of stationary blades, stationarily arranged in the casing, and an annular row of rotor blades forming part of a rotor. Each annular row of rotor blades can be mounted on a respective rotor wheel or can be integral with a portion of a rotor shaft. The rotor shaft includes a forward shaft portion and an aft shaft portion. The annular rows of rotor blades are arranged between the forward shaft portion and the aft shaft portion and can be mounted on these portions directly and / or on disks stacked to one another between the forward shaft portion and the aft shaft portion.. Theturbomachine stages are arranged in sequence from a most upstream stage to a most downstream stage in a forward-to-aft direction and define an expansion flow path extending from an intake side to a discharge side of the turbomachine.

[0010] As used herein, “upstream” and “downstream” are terms that indicate a direction relative to the flow of the process fluid through the expansion flow path of the turbomachine, or a coolant through one of the turbomachine components.

[0011] As used herein “forward” and “aft” are referred to the direction of flow of the process gas through the expander 3. Specifically, “forward” indicates a position on the intake side of the turbomachine and “aft” indicates a position on the discharge side of the turbomachine. Therefore, as used herein the “forward-to-aft” direction is a direction from the intake end towards the discharge end of the turbomachine, i.e., a direction of flow of the process gas expanding through the turbomachine.

[0012] The turbomachine further comprises a high-pressure region adjacent the rotor shaft and more specifically adjacent to or around the forward shaft portion thereof. The turbomachine further comprises a low-pressure region adjacent to the rotor shaft, and more specifically adjacent to or around the forward shaft portion. The low-pressure region is arranged downstream of the high-pressure region in a forward-to-aft direction, i.e., in the direction of flow of the process fluid across the turbomachine. The high-pressure region and the low-pressure region are positioned upstream of the stationary blades and the rotor blades which form the expansion stages of the turbomachine, with respect to the direction of flow of the process fluid expanding in the turbomachine.

[0013] In some embodiments, the high-pressure region and the low-pressure region can extend around the rotor shaft, for instance in the form of a respective annular plenum.

[0014] The high-pressure region and the low-pressure region are separated from one another by a high-pressure package seal around the rotor shaft. The high-pressure region is arranged upstream of the high-pressure package seal with respect to the forward-to-aft direction, i.e., on a forward-facing side of the high-pressure package seal. The low-pressure region is arranged downstream of the high-pressure package sealwith respect to the forward-to-aft direction, i.e., on an aft-facing side of the high-pressure package seal.

[0015] A first rotor cavity is fluidly coupled with the high-pressure region and adapted to provide a coolant flow, i.e., a flow of cooling fluid, to an upstream section of the rotor.

[0016] A second rotor cavity is fluidly coupled with the low-pressure region and adapted to provide a coolant flow, i.e., a flow of cooling fluid, to a downstream section of the rotor. The coolant can be a side flow of the same process fluid, which expands through the expansion flow path. The process fluid used as a coolant flows from the high-pressure region to the first rotor cavity. Process fluid leaking through the high- pressure package seal enters the low-pressure region and is delivered therefrom to the second rotor cavity, at a pressure lower than the process fluid in the first rotor cavity. A sealing member separates the first rotor cavity and the second rotor cavity from one another.

[0017] The low-pressure region adjacent or around the rotor shaft can be fluidly coupled with a first wheelspace, arranged between the first annular row of stationary blades and the first annular row of rotor blades, i.e., the rotor blades of the first expansion stage, seen in the forward-to-aft direction along the expansion flow path. In some embodiments, the low-pressure region and the first wheelspace are at substantially the same pressure. As understood herein, “at substantially the same pressure” means that no separating seal is provided between the low-pressure region and the first wheelspace, such that the first wheelspace forms part of the low-pressure region. The first wheelspace receives a flow of coolant from the low-pressure region adjacent or around the rotor shaft.

[0018] The coolant leaking through the high-pressure package seal is thus divided into: a first flow directed to the first wheelspace and used for purging the first wheelspace, between the stationary blades and the rotor blades of the first (i.e. most upstream) stage of the turbomachine; and a second flow directed towards the second rotor cavity, and used for cooling and / or purging the downstream section of the rotor. Coolant at a higher pressure, from the high-pressure region adjacent or around the rotorshaft, is fed into the first rotor cavity and used to cool or purge the upstream section of the rotor, where a higher pressure of the coolant is required. The upstream section of the rotor comprises rotor components, such as rotor blades and wheelspaces, between the first annular row of rotor blades and the downstream rotor section.

[0019] The coolant flowrate which leaks through the high-pressure package seal can therefore be higher than the flowrate needed for purging or cooling the first wheelspace, since part of the coolant leaking through the high-pressure package seal is used for purging the downstream section of the rotor where a lower pressure of the coolant is sufficient.

[0020] A particularly efficient operation of the turbomachine is thus achieved, since the full coolant flowrate leaking past the high-pressure package seal is positively exploited for purging purposes. A highly performing seal downstream of the high-pressure region is not required, since the coolant leaking therethrough is used for purging or cooling purposes. Since the high-pressure package seal is not required to provide full seal against coolant leakages, the axial dimension thereof can be reduced, which results in a smaller total footprint of the turbomachine.BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Reference is now made briefly to the accompanying drawings, in which:Fig.l shows a cross section of an expander of the present disclosure along a plane containing the rotation axis of the rotor;Fig.2 shows an enlargement of the flow path of the expander of Fig.l;Fig.3 shows an enlargement of the flow path of the expander in a further embodiment; andFig.4 shows an oxy-fuel combustion circuit including an expander according to the present disclosure.DETAILED DESCRIPTION

[0022] To alleviate drawbacks and limitations of the current art as outlined above, according to the present disclosure cooling or purging process fluid is extracted directly from the first wheelspace, i.e., from the wheelspace between the first row ofstationary blades and the first row of rotor blades forming the first expansion stage of the turbomachine. The pressure in the first wheelspace is lower than the highest available pressure of the process fluid, at the intake of the turbomachine. Hence, the coolant at the pressure of the first wheelspace can be used to cool a downstream section of the rotor, reducing the overall coolant consumption.

[0023] In embodiments disclosed herein, around the forward shaft portion a high- pressure region and a low-pressure region are formed. In the high-pressure region, process fluid at the highest pressure available in the thermodynamic cycle is present, while the low-pressure region can be fluidly coupled with the first wheelspace of the turbomachine. A seal (here below referred to as high-pressure package seal) around the rotor shaft separates the high-pressure region from the low-pressure region. Process gas leaks through the high-pressure package seal from the high-pressure region towards the low-pressure region. The high-pressure region is fluidly coupled with a first rotor cavity and the low-pressure region is fluidly coupled with a second rotor cavity. In the first rotor cavity coolant fluid is present at a pressure higher than in the second rotor cavity and the two cavities are separated by a sealing member. Coolant from the first rotor cavity is used to cool or purge a more upstream section of the rotor, where a higher coolant pressure is needed, while coolant from the second rotor cavity is used to cool or purge a more downstream section of the rotor.

[0024] Thus, contrary to cooling and purging systems of the current art, which use coolant from different pressure sources, e.g., different compressor stages, in the turbomachine of the present disclosure high-pressure coolant and low-pressure coolant are diverted from the high-pressure region and low-pressure region, respectively, said regions being arranged around the forward shaft portion of the rotor and separated from one another by the high-pressure package seal. The low-pressure region is fluidly coupled with, or forms part of the first wheelspace. The process gas leaking through the high-pressure package seal along the forward shaft portion is therefore used to purge the first wheel space and a downstream section of the rotor, while an intermediate section of the rotor, arranged between the first wheel space and the downstream section of the rotor, is purged with coolant process gas taken from the high-pressure region upstream of the high-pressure package seal.

[0025] In the following description, reference is specifically made to an expander, and more specifically to a supercritical carbon dioxide (sCCh) expander, as a possible exemplary embodiment of a power-generating turbomachine according to the present disclosure. Those skilled it the art of turbomachinery will nevertheless understand that novel features disclosed herein can be used with advantage also in other power-generating turbomachines, such as expanders using a fluid different than carbon dioxide, or using carbon dioxide in a non-supercritical state, or such as a gas turbine, or in a gas turbine engine, including a compressor section, a combustor, and a turbine section.

[0026] Novel features disclosed herein are particularly beneficial in expanders operating at high pressure, for instance where the highest available pressure in the thermodynamic cycle is at or above 50 barA, for instance equal to or higher than 300 barA.

[0027] In some embodiments, the expander 3 comprises an outer casing 41, which houses a combustor 7, for example a can-type combustor, an annular combustor, a canannular combustor (aka cannular combustor). The combustor can include a plurality of combustion chambers 7A arranged around an axis A-A of the expander 3.

[0028] In other embodiments, not shown, the combustor can be arranged outside the expander. In yet further embodiments, the expander may not include a combustor and can be used in a closed thermodynamic cycle, wherein heat is transferred to the process fluid through a heat exchanger, for instance.

[0029] In some embodiments the outer casing 41 includes a main body 41.1, referred to herein as a high-pressure casing, and a closure 41.2, referred to herein as a low- pressure exhaust casing.

[0030] The low-pressure exhaust casing 41.2 can be positioned at the discharge side, i.e. the aft side, of the expander 3, i.e. opposite the combustor 7, which is located at the forward side of the expander 3.

[0031] The high-pressure casing 41.1 and the low-pressure exhaust casing 41.2 can be connected to one another along a plane P which is orthogonal to a rotation axis A- A of a rotor 43 supported for rotation in the outer casing 41. The expander 3 is therefore a vertically-split expander. In other embodiments, the expander can be a horizontallysplit expander, including a casing which comprises two casing portions connected to one another along a plane containing the rotation axis A-A of the rotor 43.

[0032] In some embodiments, the low-pressure exhaust casing 41.2 forms a discharge volute or discharge plenum 41.3, through which exhausted flue gas is discharged from the expander 3.

[0033] Reference numbers 45, 47 indicate bearing arrangements, which rotatingly support the rotor 43. For instance, the bearing arrangement 45 on the side opposite the combustor 7, i.e., on the aft side, may include an axial or thrust bearing in combination with a radial bearing, or a bearing having an axial-radial bearing capability. The bearing arrangement 47 on the combustor side, i.e., on the forward side, may include a radial bearing. A reversed arrangement is also possible, with a bearing having axial load capability arranged on the combustor side. The bearing arrangements 45, 47 can be housed in bearing casings, not shown in detail.

[0034] In some embodiments, the rotor 43 is housed in an inner casing 51, stationar- ily housed in the outer casing 41.

[0035] In the embodiment of Figs. 1 and 2 the expander 3 includes a plurality of stages. Just by way of example, the expander of Figs 1 and 2 includes eight stages. Those skilled in the art will, however, understand that novel features disclosed herein can be beneficial also in expanders having a different number of stages, specifically at least two stages, or three stages, or higher. Each stage comprises an annular row of stationary vanes or stationary blades 53, which are stationarily arranged in the outer casing 41. In the exemplary embodiment of Fig.1, the annular rows of stationary blades 53 are housed in the inner casings 51. Each expansion stage further includes a respective annular row of rotor blades 55, arranged downstream the respective annular row of stationary blades 53 along the expansion flow path, which extends from the combustor 7 to the discharge plenum 41.3 in a forward-to-aft direction through the plurality of expansion stages of the expander. Specifically, each annular row of stationary blades of the ithstage is labeled 53. i and each annular row of rotor blades of the ithstage is labeled 55. i, with i = 1 to 8 in this exemplary embodiment. Herein, reference number 53 is used to designate a generic annular row of stationary blades or anindividual stationary blade as such. Reference number 55 is used to designate a generic annular row of rotor blades or an individual rotor blade as such.

[0036] In some embodiments, the first, i.e., most upstream, annular row of stationary blades 53.1 can be arranged at the discharge end of the combustor 7 and forms an array of nozzles directing hot, high-pressure process fluid from the combustion chambers 7A of the combustor 7 to the first annular row of rotor blades. The first annular row of rotor blades 55.1 is arranged directly downstream of the first annular row of stationary blades 53.1. A last, i.e most downstream, annular row of stationary blades 53.8 can be positioned near the discharge plenum 41.3, upstream of the last, i.e., most downstream, annular row of rotor blades 55.8.

[0037] The rotor blades 55 form part of the rotor 43, i.e., are connected thereto for co-rotation with the rotor shaft. In embodiments, each annular row of rotor blades 55 (i.e. each row 55. i, with i=l to 8, in the exemplary embodiment shown) is mounted on a respective rotor disk. The rotor disks are labeled 57. i, with i =1 to 8. Reference number 57 indicates a generic rotor disk.

[0038] The unit comprised of a rotor disk 57 and the respective annular row of rotor blades 55 is referred to herein also as rotor wheel and is labeled 58, wherein 58.1 (Fig.2) is the most upstream, i.e., the first rotor wheel in the forward-to-aft direction; 58.8 is the most downstream, i.e., the last rotor wheel in the forward-to-aft direction.

[0039] The rotor blades 55 of each stage can be manufactured separately from the respective rotor disk 57 and mechanically mounted thereon, as schematically shown in Figs. 1 and 2. In other embodiments, the rotor blades 55 and the rotor disk 57 of each stage can be manufactured as a monolithic body, for instance by additive manufacturing. In yet further embodiments, the two design options can be combined. One or some stages may include respective monolithically manufactured components including rotor blades and disks, and one or some stages may include a rotor disk and separately manufactured rotor blades mechanically coupled to the rotor disk.

[0040] In some embodiments, the rotor disks 57 are stacked and connected to one another by tie rods. In the exemplary embodiment of Figs.1 and 2 the tie rods comprise a plurality of tie rods 61 arranged at a distance from the rotation axis A-A and a centraltie rod 63, which is coaxial with the rotor 43.

[0041] In other embodiments, a different arrangement of tie rods can be provided, for instance only a central single tie rod coaxial to the rotor 43, or only a set of tie rods arranged around the axis A-A and at a radial distance therefrom. In yet further embodiments, tie rods at different distances from the rotation axis A-A can be provided.

[0042] In some embodiments, the rotor 43 further comprises a forward shaft portion 65 and an aft shaft portion 67. Each one of said forward shaft portion 65 and aft shaft portion 67 can include one or more sections, connected to one another, e.g. by means of tie rods, as shown by way of example for the forward shaft portion 65.

[0043] While in the embodiment shown in Figs 1, 2 and 3 all rotor blades are mounted on rotor disks and the rotor disks are stacked to one another between the forward shaft portion 65 and the aft shaft portion 67, in other embodiments, not shown, one or more annular rows of rotor blades can be mounted directly on (or manufactured as one piece with) the forward shaft portion and / or one or more annular rows of rotor blades can be mounted directly on (or manufactured as one piece with) the aft shaft portion. In some embodiments, the rotor may include a forward shaft portion and an aft shaft portion, connected to one another by tie rods or the like, wherein the rotor blades of all stages are mounted on (or manufactured as one piece with) either the forward shaft portion, or the aft shaft portion, or partly on the forward shaft portion and partly on the aft shaft portion, without rotor disks in-between.

[0044] In some embodiments, the combustor 7 extends around the forward shaft portion 65. In some embodiments, the discharge plenum 41.3 extends around the aft shaft portion 67.

[0045] In some embodiments, see Fig.1, the forward shaft portion 65 and the aft shaft portion 67 are connected to the rotor disks 57 in a stacked configuration by the tie rod arrangement mentioned above.

[0046] In some embodiments, each rotor disk 57 comprises front teeth on both a forward-facing side and an aft-facing side thereof. The front teeth are provided for torsional engagement of adjacent components of the rotor 43. In the embodiment of Figs1 and 2, the forward-facing side of the most upstream rotor disk 57.1 engages the forward shaft portion 65 and the aft-facing side of the most downstream rotor disk engages the aft shaft portion 67.

[0047] In some embodiments, a respective sealing disk 68, aka distancing disk or spacer, is positioned between each pair of consecutive (i.e., adjacent) rotor disks 57. If sealing disks 68 are interspersed between pairs of rotor disks 57, front teeth are provided on the opposite sides of each sealing disk 68, and consecutively arranged rotor disks 57 are torsionally connected to one another through the interposed sealing disk 68, Hirth joints being formed between opposing sides of each rotor disk 57 and respective sealing disk 68.

[0048] As used herein, “torsionally connected” means a connection adapted to transmit a torque between the torsionally connected components, such that the torsionally connected components rotate as a single body around the rotation axis A-A of the rotor.

[0049] Each sealing disk or spacer 68 features an annular seal 68A adapted to co-act with the ends of the stationary blades 53 facing radially inwardly. In some embodiments, an annular shroud can be provided to connect the radially inwardly facing ends of the stationary blades, and in such case the annular seal 68A co-acts with the shroud, but this is not mandatory.

[0050] While in Figs. 1 and 2, sealing disks or spacers 68 extend radially inwardly between adjacent rotor discs 57, in other embodiments the rotor disks 57 can be stacked in direct mutual contact with one another, and may be provided with front teeth of respective Hirth joints, which transmit torque directly from one rotor disk 57 to the adjacent rotor disk 57. In this case, annular seals can engage between adjacent rotor wheels near the feet of the respective rotor blades 55 in co-acting arrangement with the ends of the stationary blades 53 facing radially inwardly.

[0051] In both cases, the annular seals or the sealing disks 68 provide a seal against the radially inwardly facing ends of the stationary blades, to prevent expanding process fluid from leaking from the expansion flow path defined by interspersed rows of stationary blades and rotor blades towards the rotor axis, with the risk of thermal damages to the rotor disks.

[0052] In operation, pressurized process fluid, e.g. a mixture of oxygen and carbon dioxide, if the expander 3 is operating in an oxy-fuel cycle, is delivered to the combustor 7, mixed with fuel and burned to produce hot, pressurized process fluid, i.e. hot and pressurized flue gas, which expands along the expansion flow path formed by the sequentially arranged annular rows of stationary vanes and annular rows of rotor blades, to generate mechanical power which is made available on the rotor shaft either at the aft end, at the forward end, or both at the aft end and forward end. The mechanical power can be converted into electric power by an electric generator drivingly coupled to the shaft of the rotor 43 and / or used to drive a load, such as a compressor, a pump or other rotating equipment. A gearbox can be provided along the shaft line, between the expander and the load connected thereto, such that the load can rotate at a speed different from the expander rotary speed.

[0053] If the expander does not include a combustor and is arranged in a closed thermodynamic cycle, the compressed process fluid can be heated, e.g., by heat exchange in a heat exchanger before expansion.

[0054] A flow of cooling or purging process fluid is diverted from the main cycle at the highest pressure available in the cycle, i.e., upstream of the expander, and at low temperature, i.e., upstream of the combustor 7 or of a heat exchanger. The cooling process fluid is delivered to the rotor 43 of the expander 3 and extracted from cavities provide therein, to purge the wheelspaces of the rotor and / or to cool rotor blades, especially those of the most upstream stages. The cooling process fluid prevents or limits leakages of the expanding process fluid from the expansion flow path towards the rotor disks 57, thus improving the efficiency of the expansion and preventing thermal damages to the rotor disks 57. Additionally, or alternatively cooling fluid delivered to cooling systems in the rotor blades, especially of the first stages, prevents thermal damages thereof and allows the expander 3 to operate with process fluid at higher temperatures, increasing thereby the efficiency of the thermodynamic cycle.

[0055] For effective cooling or purging of the rotor 43, according to the present disclosure a novel arrangement of cooling ducts and cavities is provided, which can reduce the consumption of process fluid for cooling or purging purposes and can increase the cooling or purging efficiency, as well as simplify the structure of the machine.

[0056] Specifically, the expander 3 comprises a high-pressure region 71 adjacent the rotor 43. In embodiments, the high-pressure region 71 develops in the form of an annulus around a portion of the rotor 43. In some embodiments, the high-pressure region 71 surrounds the forward shaft portion 65 of the rotor 43. The high-pressure region 71 can be delimited on the forward-facing side by a balance drum 72 of the turboexpander.

[0057] The high-pressure region 71 is adapted to be fluidly coupled to a process fluid path upstream of the combustor 7, in a location of the fluid path in which, in operation, the process fluid reaches the highest pressure available in the thermodynamic cycle performed by the process fluid. In use, therefore, the high-pressure region 71 contains process fluid at a high pressure. For instance, the high-pressure region 71 can be fluidly coupled with the delivery side of a process fluid compressor (not shown). The fluid pressure inside the high-pressure region 71 is usually slightly higher than the pressure inside the combustor 7, to prevent combustion gas from egressing from the combustor and entering the high-pressure region 71.

[0058] The process fluid delivered to the high-pressure region 71 is at a low temperature, i.e., close to the temperature at the delivery side of the process fluid compressor.

[0059] The expander 3 further comprises a low-pressure region 73 adjacent the rotor 43. In embodiments, the low-pressure region 73 extends around the rotor shaft forming an annulus therearound. In some embodiments, the low-pressure region 73 extends around the forward shaft portion 65.

[0060] In some embodiments, the low-pressure region 73 includes a first wheelspace 73 A, located between the first stage nozzles, i.e., the first annular row of stationary blades 53.1, and the first rotor wheel 58.1, seen in the forward-to-aft direction.

[0061] The low-pressure region 73, 73A is separated from the high-pressure region 71 by an annular seal 75, referred to herein as a high-pressure package seal 75, see Fig.2, surrounding the rotor shaft, specifically the forward shaft portion 65 of the rotor shaft. Specifically, the high-pressure region 71 is positioned on the side of the high- pressure package seal 75 facing the forward end of the expander 3, and the low-pressure region 73 is positioned on the side of the high-pressure package seal facing the aft end of the expander 3.

[0062] The pressure of the process gas leaking (arrow fL in Fig.2) through the high- pressure package seal 75, i.e., the pressure in the low-pressure region 73, is lower than the maximum available pressure of the process fluid, which is present in the high- pressure region 71. Specifically, in the embodiment shown, the pressure in the low- pressure region 73, including the first wheelspace 73 A, is set by the expansion in the first annular row of stationary blades 53.1. As will become apparent from the following description, the process fluid at lower pressure contained in the low-pressure region 73 is at a pressure sufficient for cooling or purging stages of the expander 3 which are located downstream of the first expander stage.

[0063] The rotor 43 comprises a first rotor cavity 77, which is fluidly coupled with the high-pressure region 71 through one or more high-pressure coolant ducts 79 (Fig.2). In some embodiments, the first rotor cavity 77 can be coaxial to the rotor axis A-A.

[0064] In some embodiments, a plurality of high-pressure coolant ducts 79 are provided around the rotation axis A-A of the rotor 43. Each high-pressure coolant duct 79 extends from an inlet end 79.1, which is fluidly coupled to the high-pressure region 71, to an outlet end 79.2, which is fluidly coupled with the first rotor cavity 77.

[0065] In the exemplary embodiment of Figs 1 and 2, the first rotor cavity 77 is adapted to provide a coolant flow to at least the second wheelspace between the first rotor wheel 58.1, the second rotor wheel 58.2 and the second row of stationary blades53.2. In the embodiment of Figs 1 and 2 a coolant flow pictorially represented by arrows C (Fig.2) flows from the first rotor cavity 77 through slots, holes and / or calibrated passages into a cavity 81 between the first rotor wheel 57.1, the second rotor wheel57.2. and the annular seal 68A of the sealing disk 68 therebetween.

[0066] From the cavity 81 the coolant flow C can leak between the spacer 68 and the mutually facing faces of the rotor wheels 58.1, 58.2 to prevent expanding process fluid from flowing into the wheelspace and in the cavity 81 towards the rotor disks 57.1,57.2.

[0067] To properly purge the cavity 81 and the second wheelspace between the first rotor wheel 58.1, the second rotor wheel 58.2 and the stationary blades 53.2 of thesecond stage, the coolant in the first rotor cavity 77 must be at a sufficient pressure to overcome the head losses along the coolant passages from the first rotor cavity 77 to the second wheel space. The highest available pressure of the process fluid in the high- pressure region 71 is sufficient to provide a suitable flow of purging coolant towards the second wheelspace. In some embodiments, a coolant flow Cl can be provided between the cavity 81 and a cooling system in the rotor blades 55.1 of the first rotor wheel 58.1.

[0068] The first rotor cavity 77 extends axially from the forward shaft portion 65 to an intermediate rotor disk 57. In the embodiment shown in Figs 1 and 2, the first rotor cavity 77 extends up to the second rotor disk 57.2 of the second rotor wheel 58.2. In other embodiments, the first rotor cavity 77 can have a larger axial extension and can end at the third rotor disk 57.3 or at the fourth rotor disk 57.4, for instance, as will be shown below with reference to a further embodiment.

[0069] The rotor 43 further comprises a second rotor cavity 83, which can extend along the rotation axis A-A, from the forward shaft portion 65 towards the aft shaft portion 67. The second rotor cavity 83 can be coaxial to the rotation axis A-A and can surround the tie rod 63.

[0070] The second rotor cavity 83 is fluidly separated from the first rotor cavity 77 by a sealing member 85. In some embodiments, the sealing member 85 can have an approximately cylindrical shape and can extend coaxially to the rotation axis A-A of the rotor 43 from the forward shaft portion 65 to the second rotor disk 57.2 (or another more downstream rotor disk, if the first rotor cavity 77 extends further downstream of the second rotor disk 58.2, as mentioned above).

[0071] The second rotor cavity 83 is fluidly coupled with the low-pressure region 73 and thus with the first wheelspace 73 A, which forms part of the low-pressure region 73. Low pressure coolant flows into the first wheelspace 73 A (arrow f73, Fig.2), and into the second rotor cavity 83 through one or more low-pressure coolant ducts 87 which extend from the low-pressure region 73 to the second rotor cavity 83. The low- pressure coolant ducts 87 can extend radially, as shown in Figs. 1 and 2, or can be inclined with respect to the radial direction. The low-pressure coolant flow throughducts 87 is pictorially represented by arrows f87, see Fig.2.

[0072] Thus, a coolant flow at a pressure lower than the highest available pressure in the cycle is delivered into the second rotor cavity 83, see arrows f83 and in the first wheelspace 73 A. As mentioned, pressure in the low-pressure region 73, including the first wheelspace 73 A, is set by the expansion in the first annular row of stationary blades 53.1. Depending upon the value of said pressure, the first rotor cavity 83 can extend further downstream of the second rotor wheel 58.2, as mentioned.

[0073] Specifically, each low-pressure coolant duct 87 has an inlet end 87.1 in a radially outward position, in the low-pressure region 73, and an outlet end 87.2 in a radially inward position, in the second rotor cavity 83.

[0074] In some embodiments, as best shown in Fig.2, the outlet end 87.2 of each low-pressure coolant duct 87 is positioned radially inwardly with respect to the outlet end 79.2 of each duct 79. In other words, the outlet end 87.2 of each low-pressure coolant duct 87 is at a distance from the rotor axis A-A which is smaller than a distance of the outlet end 79.2 of each high-pressure coolant duct 79. Therefore the low-pressure coolant ducts 87 and high-pressure coolant ducts 79 cross each other.

[0075] In the embodiment of Figs 1 and 2, the pressure of the coolant in the second rotor cavity 83 is sufficient for the coolant to purge at least some of the wheelspaces downstream of the second rotor wheel 58.2. In the embodiment shown in Figs. 1 and 2, coolant at the pressure of the low-pressure region 73 is extracted from the second rotor cavity 83 and used to purge the wheelspaces downstream the most downstream wheelspace cooled by coolant from the first rotor cavity 77. In the illustrated embodiment, coolant from the second rotor cavity 83 is used to purge and / or cool the wheelspaces from the second rotor wheel 58.3 to the last rotor wheel 58.8.

[0076] In general, the first rotor cavity 77 can be fluidly coupled with a first group of most upstream wheelspaces and the second rotor cavity 83 can be fluidly coupled with a second group of wheelspaces, downstream of the first group of most upstream wheelspaces. While in the embodiment of Figs. 1 and 2 the first group of most upstream wheelspaces comprises only the wheelspace between the first, i.e., the most upstream rotor wheel 58.1, and the second rotor wheel 58.2, in other embodiments,also one or more of the subsequent wheelspaces can be purged by coolant process fluid from the first rotor cavity 77.

[0077] In other words, in some embodiments, e.g., depending upon the pressure in the first wheelspace 73 A, the first rotor cavity 77 can extend further downstream and the high-pressure coolant delivered therein can be used to purge wheelspaces downstream of the second annular row of rotor blades 55.2.

[0078] The coolant from the second rotor cavity 83 can also be used for cooling the rotor blades 55 of one or more of the rotor wheels downstream of rotor wheel 58.1.

[0079] As a result of the above-described arrangement, separate high-pressure coolant flow (arow f79, Fig.2) and low-pressure coolant flow (arrow f87, Fig.2) are delivered at different pressure levels in the first rotor cavity 77 and second rotor cavity 83. Therefrom coolant is delivered for purging and / or cooling purposes at different locations along the expansion flow path of the expander. Lower coolant pressure is available in the second rotor cavity 83, and is sufficient for cooling and purging purposes of more downstream expansion stages.

[0080] In the exemplary embodiment of Figs. 1 and 2, the coolant pressure in the second rotor cavity 83 can be approximately the same as the pressure in the first wheel - space 73 A, since no sealing arrangements are provided between the first wheelspace 73A and the region immediately downstream of the high-pressure package seal 75. In other embodiments, the option is not excluded, that a further seal surrounding the rotor is positioned between the low-pressure region 73 and the first wheelspace 73 A, such that the coolant pressure in the second rotor cavity 83 is higher than the pressure in the first, i.e., most upstream wheelspace.

[0081] In some embodiments, not shown, the fluid coupling between the low-pressure region 73 and the second rotor cavity 83 can be designed such that the pressure in the second cavity 83 is smaller than in the low-pressure region 73. This may be required, for instance, in order to reduce the flowrate of the purging cooling fluid which flows from the low-pressure region 73 into the inner cavity 83. This can be obtained, for instance, by providing coolant ducts 87 which are designed to generate a head loss between the respective inlets 87.1 and outlets 87.2. For instance, the diameter of thecoolant ducts 87 can be designed sufficiently narrow to establish a desired pressure drop therethrough, such that the pressure in the second cavity 83 is smaller than (as opposed to approximately the same) the pressure in the low-pressure region 73.

[0082] In the embodiment of Figs. 1 and 2, the first rotor cavity 77 provides coolant to an upstream section of the rotor, which includes the second wheel space between the rotor wheel 58.1 and the rotor wheel 58.2, and / or to the respective rotor blades. The second rotor cavity 83 provides coolant to a downstream section of the rotor, which in the illustrated embodiment includes the remaining stages of the expander. This, however, is not the only possible arrangement.

[0083] Depending on the pressure required for the coolant in the sequentially arranged expander stages, the first rotor cavity 77 can be designed to provide a flow of coolant to more than just the second wheelspace between the first rotor wheel 58.1 and he second rotor wheel 58.2.

[0084] Fig.3 shows a cross-sectional view of an expander 3 in another embodiment, where the upstream section of the rotor comprises an additional wheelspace. The same reference numbers of Figs. 1 and 2 are used to designate the same or equivalent parts described above, and not described again in detail. In Fig.3 the first rotor cavity 77 extends from the forward shaft portion 85 to the third rotor disk 57.3 and provides a coolant or purging fluid to the second and third wheelspaces, i.e. to the wheelspaces between the first rotor wheel 58.1 and the third rotor wheel 58.3, which represent an upstream section of the rotor. The sealing member 85 sealingly separates the first rotor cavity 77 from the secondo rotor cavity 83, which provides coolant at a lower pressure, to the downstream section of the rotor.

[0085] In some embodiments the expander 3 can be a CO2 expander for an oxycombustion cycle, for instance an Allam or NET -power thermodynamic cycle.

[0086] With continuing reference to Figs 1, 2 and 3, Fig.4 illustrates an exemplary power generation system based on an oxyfuel thermodynamic cycle, where an expander 3 according to the present disclosure can be used. It shall be understood that the system of Fig.4 is shown by way of exemplary and non-limiting embodiment and that the novel features disclosed above can be embodied in expanders or other power-generating machines for different thermodynamic cycles.

[0087] The combustor 7 of expander 3 is supplied with an oxidant flow delivered by an oxidant source. The oxidant may be oxygen (O2) or a blend comprising, or mainly consisting of oxygen and carbon dioxide (CO2). The oxidant flow can be produced by an air separation unit 9, which features 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 line 11 to the combustor 7 of the expander 3. In some embodiments, for the sake of easier handling of the oxidant flow, the latter may include around 20% in volume of oxygen and 80% in volume of carbon dioxide. The CO2 and O2 percentages mentioned above are by way of example. The carbon dioxide can be added to the oxygen through a recycling line 12, as explained in more detail below.

[0088] Reference number 13 indicates a fuel supply line, for instance adapted to supply natural gas, such as methane to the combustor 7, specifically to each combustion chamber 7.1. The oxidant and the fuel are supplied at the inlet side of the expander 3 to the combustor 7 at high pressure.

[0089] The oxidant-fuel blend is burned in the combustor 7. Pressurized, hot combustion gas resulting from the combustion expands through the flow path of the expander 3 and the exhaust flue gas is discharged after expansion at a discharge side of the expander 3 in a discharge line 15.

[0090] The circuit of Fig.4 further comprises a regenerative heat exchanger 17, wherein hot flue gas flowing through a hot side 17.1 of the regenerative heat exchanger 17 is cooled in heat exchange with a flow of chilled flue gas which flows through a cold side 17.2 of the regenerative heat exchanger 17. The flue 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 steam contained in the exhausted flue gas. Condensing water is removed from the exhausted flue gas in a water / gas separator 21.

[0091] The de-hydrated exhausted and chilled flue gas, consisting mainly or exclusively of carbon dioxide, is compressed in a flue gas compressor 23 to the pressure atthe inlet side of the expander 3. The pressure at the delivery side of compressor 23 is the highest pressure of the thermodynamic cycle including the expander 3.

[0092] The compressed flue gas delivered by the flue gas compressor 23 is partly removed from the cycle through a discharge line 25. If the compressor 23 is featured by a plurality of compressing turbomachines arranged in series, the discharge line 25 can be connected between two sequentially arranged turbomachines and / or at the discharge side of the most downstream compressing turbomachine.

[0093] The remaining compressed flue gas is delivered through the cold side 17.2 of the regenerative heat exchanger 17 and is heated by heat exchange with the hot flue 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 flue gas recycled through recycle line 25 is mixed with the combustion gas generated in the combustor 7, or with the oxidant stream from oxidant line 11.

[0094] The mechanical power generated by the expansion of the combustion gas in the expander 3 is available on the output shaft end 31 for mechanical drive or power generation purposes. In the exemplary embodiment of Fig. 4 the output shaft end 31 is drivingly coupled to an electric generator 33 directly or through a gearbox, a joint or combinations thereof.

[0095] A side stream of chilled flue gas at the highest pressure of the thermodynamic cycle is delivered through a cooling line 27, which bypasses the regenerative heat exchanger 17, to the expander 3. The cooling line 27 is fluidly coupled to the high-pressure region 71 of the expander 3 and provides the flow of coolant which is distributed to the first rotor cavity 77, the low-pressure region 73 and the second rotor cavity 83 as mentioned above.

[0096] The novel features of the coolant distribution system described with reference to Figs.1 to 3 can be used also in a gas turbine engine.

[0097] 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 disclosedherein without departing from the scope of the invention as defined in the following claims.

Claims

CLAIMS1. A power-generating turbomachine, comprising: a casing (41, 51); a plurality of annular rows of stationary blades (53) arranged in the casing; a rotor (43) housed in the casing for rotation around a rotor axis (A-A); the rotor comprising: a rotor shaft with a forward shaft portion (65) and an aft shaft portion (67); and a plurality of annular rows of rotor blades (55); wherein each annular row of stationary blades (53) and the annular row of rotor blades (55) downstream thereof form a respective turbomachine stage; wherein the turbomachine stages define an expansion flow path extending in a forward-to-aft direction, from a most upstream stage to a most downstream stage; a high-pressure region (71) adjacent the forward shaft portion (65); a low-pressure region (73) adjacent the forward shaft portion (65); a high-pressure package seal (75) around the forward shaft portion, the high- pressure package seal (75) having a forward-facing side and an aft-facing side; wherein the high-pressure package seal (75) separates the high-pressure region (71) and the low-pressure region (73) from one another; and wherein the high- pressure region (71) is positioned at the forward-facing side of the high-pressure package seal (75) and the low-pressure region (73) is positioned at the aft-facing side of the high-pressure package seal (75); a first rotor cavity (77), fluidly coupled with the high-pressure region (71) and adapted to provide a high-pressure coolant flow to an upstream section of the rotor; a second rotor cavity (83), fluidly coupled with the low-pressure region (73) and adapted to provide a low-pressure coolant flow to a downstream section of the rotor; and a sealing member (85) housed in the rotor and separating the first rotor cavity (77) and the second rotor cavity (83) from one another; wherein the low-pressure region (73) comprises a first wheelspace (73A) arrangedbetween the first annular row of stationary blades (53.1) and the first annular row of rotor blades (55.1) of the most upstream stage; and wherein, in use, coolant leaking through the high-pressure package seal (75) from the high-pressure region (71) to the low-pressure region (73) flows in the low-pressure region, in the first wheelspace (73 A), and in the second rotor cavity.

2. The power-generating turbomachine of claim 1, comprising: at least one high-pressure coolant duct (79) fluidly coupling the high-pressure region (71) to the first rotor cavity (77), the at least one high-pressure coolant duct (79) having an inlet end (79.1) at the high-pressure region (71), and an outlet end (79.2) at the first rotor cavity (77), the outlet end (79.2) being at a first distance from the rotor axis (A- A); at least one low-pressure coolant duct (87) fluidly coupling the low-pressure region (73) with the second rotor cavity (83), the at least one low-pressure coolant duct (87) having an inlet end (87.1) at the low-pressure region (73), and an outlet end (87.2) at the second rotor cavity (83), the outlet end being at a second distance from the rotor axis (A-A); wherein the second distance is smaller than the first distance.

3. The power-generating turbomachine of claim 2, wherein the outlet end (79.2) of the at least one high-pressure coolant duct (79) is positioned at a distance from the rotor axis (A-A) smaller than the distance of the inlet end (87.1) of the at least one low-pressure coolant duct (87) from the rotor axis (A-A).

4. The power-generating turbomachine of any one of the preceding claims, wherein in use the coolant in the first wheelspace and in the low-pressure region is approximately at the same pressure.

5. The power-generating turbomachine of any one of the preceding claims, wherein the upstream section of the rotor comprises at least one of the first annular row of rotor blades (55); a first rotor wheel (57.1); a second wheelspace, downstream of the first wheelspace in the forward-to-aft direction.

6. The power-generating turbomachine of any one of the preceding claims, wherein the downstream section of the rotor comprises at least one of a rotorwheel (57) downstream of the upstream section of the rotor; rotor blades (55) downstream of the upstream section; a wheelspace downstream of the upstream section, in the forward-to-aft direction.

7. The power-generating turbomachine of any one of the preceding claims wherein the first rotor cavity (77) is coaxial to the second rotor cavity (83) and arranged radially outwardly thereof.

8. The power-generating turbomachine of claim 7, wherein the sealing member (85) is positioned between the first rotor cavity (77) and the second rotor cavity (83) and coaxial therewith.

9. The power-generating turbomachine of any one of the preceding claims, wherein the second rotor cavity (83) surrounds a central tie rod (63) which connects the forward shaft portion (65) and the aft shaft portion (67) to one another.

10. The power-generating turbomachine of any one of the preceding claims, wherein the sealing member (85) comprises a hollow cylindrical body coaxial to the rotor (43).

11. The power-generating turbomachine of any one of the preceding claims, further comprising a balance drum (72) torsionally coupled to the rotor shaft; and wherein the high-pressure region (71) is delimited on a forward-facing side thereof by said balance drum (72).

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