An expander

Abstract

The expander (3) comprises an outer casing (41) and an inner casing (51). A rotor (43) is housed in the inner casing (51) for rotation therein around a rotation axis. A plurality of generally cylindrical seats (101) are arranged around the rotation axis. Combustors (8) in a can-type arrangement project from the generally cylindrical seats (101) into an annular plenum, such that the transition pieces (113) thereof are located in the annular plenum and are supported by an annular structure (132), cantileverly mounted on the forward end of the inner casing (51).

Description

AN EXPANDERDESCRIPTIONTECHNICAL 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).

[0002] As understood herein a SCO2 expander is an expander wherein carbon dioxide in a supercritical state is present in at least a portion of the process gas flow path inside the expander.BACKGROUND ART

[0003] 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.

[0004] 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.

[0005] 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 processparticularly inefficient.

[0006] 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 or another 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.

[0007] 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.

[0008] 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.

[0009] 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.

[0010] Oxy-fuel combustion cycles, such as those described above, are particularly interesting in terms of efficiency, reduction of noxious emissions and ease of CO2 sequestration. However, they operate under CO2 supercritical conditions at the inlet of the expander and are characterized by extremely high pressure and high temperature inside the expander and specifically inside the combustor assembly. These operating conditions pose difficult constraints in the casing design.

[0011] Improvements in the design of the expanders adapted for supercritical carbon dioxide cycles, or other cycles operating in similar conditions are highly desirable.SUMMARY

[0012] The invention concerns an expander according to claim 1. Further features and embodiments are set forth in the dependent claims.

[0013] As used herein “forward” and “aft” are referred to the direction of flow of the process gas through the combustor assembly and through the expander, and therefore the forward end of a component is the end upstream of the aft end of the same component, with regard to the direction of flow of the gas stream processed through the expander or components thereof.

[0014] If not differently indicated, the terms “upstream” and “downstream” refer to the direction of flow of the process gas in the combustor assembly and in the expander.BRIEF DESCRIPTION OF THE DRAWINGS

[0015] 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 axonometric view of the expander;Fig.4 is a sectional view of a combustor of the expander;Figs. 5 and 6 are sectional axonometric views of the forward portion of the outer casing;Fig.7 is an axonometric view of a detail of the forward portion of the outer casing viewed in a forward-to-aft direction;Fig.8 is a detailed sectional view of the aft plenum and of an annular structure arranged therein;Fig.9 is an axonometric view of the annular structure;Fig.10 is an axonometric sectional view of the annular structure; andFig.11 is an axonometric sectional view of the annular structure arranged in the plenum with the combustors mounted therein.DETAILED DESCRIPTION

[0016] The schematic of Fig. 1 illustrates a simplified power system including an oxy-fuel cycle operating with supercritical carbon dioxide at the expander inlet(shortly sCCh cycle), such as an Allam cycle, or NET Power oxy -fuel cycle.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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, andpreferably at or below 1500°C.

[0022] 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.

[0023] The power rate of the expander 3 can be higher than 50MW, for instance equal to or higher than 100 MW, for instance 150 MW or higher, e.g. 200 MW or higher. In some embodiments the rated power is equal to or higher than 300 MW. In some embodiments the rated power is equal to or lower than 2000 MW, for instance equal to or lower than 1500MW, or equal to or lower than 1000 MW. For example, the rated power can be comprised between 200 MW and 650 MW.

[0024] Intermediate values of the upper limit and lower limit of each range mentioned above are also expressly disclosed herein.

[0025] 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.

[0026] 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.

[0027] The compressed combustion gas, consisting mainly of carbon dioxide anddelivered 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.

[0028] 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, which bypasses 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.

[0029] 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.

[0030] The expander 3 may include an output shaft end 31 which can be integral withthe 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.

[0031] With continuing reference to Fig.1, Fig. 2 illustrates a simplified sectional view of the expander 3 in one embodiment. The expander 3 can comprise an outer casing 41, which houses an inner casing, a rotor supported for rotation in the inner casing, and the combustor assembly 7.

[0032] 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.

[0033] 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 thereof. As understood herein, a casing or casing portion having a monolithic body structure is made of a single piece of material, which is continuous in the tangential direction around the rotation axis of the expander.

[0034] 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.

[0035] A barrel -type structure of the forward casing portion 41.1 and aft casing portion 41.2 of a vertically split outer casing 41 is particularly adapted for a supercritical carbon dioxide expander, where the pressure of the process gas in the expansion flowpath is substantially higher than in standard Bryton-cycle turbines.

[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] Reference numbers 45, 47 indicate bearing arrangements, which rotatingly support a rotor 43 of the expander 3 for rotation around the rotation axis A-A. For instance, the bearing arrangement 45 on the side opposite the combustor assembly 7 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 assembly side may include a radial bearing. A reversed arrangement is also possible, with a bearing having axial load capability arranged on the combustor assembly side.

[0038] The output shaft end 31 of the rotor 43 can be drivingly coupled to the driven machine (electric generator 33) through flanges 49. The bearing arrangements 45, 47 can be arranged in bearing housings, not shown in detail.

[0039] The rotor 43 is surrounded by an inner casing 51, which can be formed by a plurality of sections arranged in sequence in a forward-to-aft direction. 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. 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.

[0040] 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 extends in the aft casing portion 41.2 of the outer casing 41.

[0041] 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 cooling line 27, can be supplied to the annular fluid chamber 42

[0042] In some embodiments, the inner casing 51 is provided with cooling ducts, one of which is schematically shown at 51.1 in Fig.2. The cooling ducts provide a fluid coupling between the annular fluid chamber 42 and the interior of the inner casing 51. Compressed recycled combustion gas, consisting mainly of carbon dioxide, can flow from the annular fluid chamber 42 into the interior of the inner casing 51 to cool or purge annular cavities inside the inner casing 51. External cooling ducts can be provided in combination or as an alternative to cooling ducts extending through the inner casing.

[0043] The expander can be adapted to expand the combustion gas through the 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. To expand the combustion gas generated in the combustor assembly 7 a high number of expansion stages is preferred, for instance higher than three, preferably higher than five, in some examples equal to or higher than six. 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 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 extend radially from the rotor body in the expansion flow path.

[0046] In embodiments, the rotor 43 further comprises a forward shaft portion 65 and an aft shaft portion 67. In embodiments, the combustor assembly 7 extends around the forward shaft portion 65. In some embodiments, the discharge plenum 41.3 extends around the aft shaft portion 67.

[0047] 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.

[0048] 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 is housed in a respective generally cylindrical seat 101 formed in an annular body 41.4 of the forward casing portion 41.1 of the outer casing 41. The annular body has a generally toroidal shape, as shown for instance in the axonometric sectional views of Figs .5 and 6. Each generally cylindrical seat 101 is entirely contained in the toroidally shaped annular body 41.4.

[0049] Each combustor 8 comprises a tubular, i.e. can-shaped liner 103 partially housed in the respective generally cylindrical seat 101. Each liner 103 has a longitudinal axis B-B which can be coincident with, or parallel to the longitudinal axis of the of the cylindrical seat 101. The longitudinal axes B-B of the cylindrical seats 101 and of the respective liners 103 are inclined toward the rotation axis A-A of the expander and converge towards said rotation axis. In some embodiments, the axes B-B can be positioned on a conical surface, the axis whereof is coincident with the rotation axis A-A of the expander 3.

[0050] In some embodiments, the angle between the axes A-A and B-B can be between 0° and 80°, or between 0° and 60°, in some embodiments between 15° and 40°. The angle between the axes A-A and B-B is selected as a compromise between the need to reduce radial dimensions of the expander and improve the combustor design (which would be improved using smaller angles), and the overall design constraints of the expander, such as the dimension and position of the rotor shaft and bearings (which require larger angles).

[0051] Each liner 103 has a forward end 103F and an aft end 103A. Each liner 103 further includes a cylindrical or generally tubular sidewall 105 which extends from the forward end 103F to the aft end 103 A of the liner 103. The sidewall 105 has an outer surface 105A and an inner surface 105B and surrounds a combustion chamber 8.1 of the combustor 8.

[0052] Each combustor 8 comprises at least one burner 107 at the forward end 103F of the respective liner 103. In some embodiments, each combustor 8 may comprise a plurality of burners 107, i.e. a burner cluster 107.

[0053] A forward-end closure lid 106 is provided at the forward end of each generally cylindrical seat of each combustor 8, on the forward side of the burner or burner cluster 107.

[0054] The burner or burner cluster 107 is fluidly coupled with a fuel inlet 109 and with an oxidant inlet 111. The fuel inlet 109 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 I l l 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.

[0055] Each combustor 8 further comprises a transition piece 113 positioned at the aft end 103 A 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 stationary and rotary blades of the expander. 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 intermediate the annular body 41.4 of the forward casing portion 41.1 of the outer casing 41 and the expansion flow path, i.e the first annular row of stationary blades 53 of the expander 3.

[0056] Each liner 103 is surrounded by a generally cylindrical sleeve 115. The liner 103 is coaxial to the corresponding sleeve 115.

[0057] Each sleeve 115 comprises a forward end 115F and an aft end 115A. The forward end 115F of the sleeve 115 is coupled to an inner surface of the corresponding cylindrical seat 101 of the combustor 8. Each sleeve 115 divides a space between the inner surface of the cylindrical seat 101 and the liner 103 into an inner annular space 117 and an outer annular space 119. The outer annular space 119 surrounds the inner annular space 117.

[0058] In some embodiments, the sleeve 115 comprises a flange 115.1 which connects the sleeve 115 to the cylindrical seat 101 of the combustor 8. In some embodiments, the flange 115.1 can be bolted or otherwise connected to a bottom of the cylindrical seat 101, such that the sleeve 115 extends in the aft direction towards the rotation axis A-A of the expander 3 from the flange 115.1 outside of the cylindrical seat 101.

[0059] In some embodiments, the sleeve 115 can extend in a forward direction from the flange 115.1 in the cylindrical seat 101 towards the forward end 103F of the liner 103. The sleeve portion which extends from the flange 115.1 towards the forward end 103F of the liner and towards the burner 107 is labeled 115.2 and is referred to herein as the forward sleeve portion 115.1. In the illustrated embodiment, each forward sleeve portion 115.1 ends downstream of the forward end 103F of the corresponding liner 103. In other embodiments, the liner 103 and the sleeve 115 can be co-extensive in the forward direction. In yet further embodiments, the forward sleeve portion 115.1 may extend more forward than the forward end 103F of the liner 103.

[0060] Each inner annular space 117 may therefore extend parallel to the axis B-B in the forward direction towards the forward end 103F of the corresponding liner 103. In the aft direction, the inner annular space 117 can extend beyond and outside the cylindrical seat 101 of the combustor 8 to the transition piece 113.

[0061] Similarly, the outer annular space 119 can extend in the aft direction outside the cylindrical seat of the combustor 8 towards the transition piece 113.

[0062] As described above, recycled combustion gas is returned towards the combustor assembly 7 of the expander 3. More specifically, a flow of recycled combustion gas is delivered to each combustor 8 of the combustor assembly 7.

[0063] As described in connection with Fig. l, de-hydrated combustion gas is added to oxygen separated from air by the air separation unit 9. The oxidant consisting of the blend of oxygen and recycled combustion gas is delivered to the burner or burner cluster 107 of each combustor 8 through the respective oxidant inlet 111 of the combustor 8.

[0064] A further flow of de-hydrated recycled combustion gas is delivered to the expander 3 through the recycle line 25 and is fed to each combustor 8 through a firstprocess gas inlet 120 of each combustor 8. Each first process gas inlet 120 is fluidly coupled with the inner annular space 117 through a corresponding forward plenum 127 formed in the cylindrical seat 101 of the combustor 8 and surrounding the forward portion of the liner 103 and of the sleeve 115.

[0065] A yet further flow of recycled combustion gas is delivered to the expander 3 through the cooling line 27, which is fluidly coupled to one or more second process gas inlets 121. The second process gas inlet(s) 121 is(are) fluidly coupled with the outer annular space 119, preferably in a position downstream of the forward end 115F of each sleeve 115, i.e. in a position between the expansion flow path of the expander 3 and the forward end 115F of the sleeves 115.

[0066] Each first process gas inlet 120 is therefore connected to the respective combustor 8 in a position upstream of the position of the second process gas inlet(s) 121. For each combustor 8, a thermal insulation chamber is formed between the second process gas inlet(s) 121 and the forward end 115F of each sleeve 115. Each insulation chamber is formed by the outer annular space 119, or part thereof, which extends around the corresponding sleeve 115, and the corresponding liner 103. The thermal insulation chamber can be filled with stagnant process gas representing an inert, thermally insulating gas, consisting mainly of carbon dioxide at high pressure, which represents an efficient insulation material.

[0067] The forward plenum 127 is fluidly coupled with the inner annular space 117. The first process gas inlet 120 is fluidly coupled to the forward plenum 127, such that process gas, i.e. combustion gas recycled from the exhaust of the expander 3 through the recycle line 25 and the first process gas inlet 120, flows through the forward plenum 127 and therefrom into the inner annular space 117 in a forward-to-aft direction. The inner annular space 117 and / or the forward plenum 127 can be fluidly coupled with the interior of the liner 103 through holes, apertures, or ports extending through the side wall 105 of the liner 103.

[0068] Each combustor 8 can further include an igniter 129, which penetrates from the exterior of the outer casing 41 through the forward plenum and in the liner 103.

[0069] In some embodiments, the combustor assembly 7 further comprises an annular aft plenum 131 positioned at the aft end 103 A of the liners 103 of the combustors8.

[0070] In the embodiment of Fig.3, the second process gas inlet 121, or each one of a plurality of second process gas inlets 121 is positioned at the aft plenum 131, e.g. directly fluidly coupled therewith. In other embodiments, not shown, the second process gas inlet(s) 121 can be positioned in an intermediate position along the development of the outer annular space 119, between the aft end thereof and the aft plenum 131.

[0071] The aft plenum 131 can be fluidly coupled through cooling ducts (not shown) to components which face the expansion flow path, such as the stationary vanes and / or the rotary blades of the rotor.

[0072] In the embodiment of Fig.3, the inner annular space 117 of each combustor 8 is fluidly coupled at the aft end thereof with a cooling annulus 113 A of the corresponding transition piece 113. The cooling annulus can be formed between an inner duct and an outer duct of the transition piece 113, wherein the inner duct forms a hot gas path adapted to fluidly connect the combustion chamber 8.1 with the expansion flow path of an expander 3. The aft plenum 131 extends around the outer duct of the transition piece 113.

[0073] The process gas delivered through the first process gas inlet 120 flows through the inner annular space 117 and partly enters the combustion chamber 8.1 through the apertures extending through the wall of the liner 103. The remaining process gas flows from the first inner annular space 117 into the cooling annulus 113 A of the transition piece 113 in a direction of flow concordant with the direction of flow of the combustion gas generated in the combustion chamber 8.1 and which flows towards the expansion flow path. The process gas flows from the cooling annulus 113 A through cooling apertures formed in the transition piece, in the hot gas path formed b the inner duct of the transition piece 113.

[0074] Figs 8 to 11 show in more detail the aft plenum 131 and an annular structure 132 which is housed in the aft plenum and supports the transition pieces 113 in the aft plenum.

[0075] In the illustrated embodiment, the annular structure 132 comprises a ring 133,which connects the annular structure 132 to the forward end of the inner casing 51. Thus, the annular structure 132 is cantileverly supported on the inner casing 51, which is in turn supported, through a flange 51.2, at the aft end thereof (see Fig.2) to the outer casing 41, and specifically between the forward casing portion 41.1 and the aft casing portion 41.2 of the outer casing 41.

[0076] 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.

[0077] The annular structure further comprises a thrust ring 139 engaged to the cylindrical member 135. In some embodiments, the thrust ring 139 is connected to the cylindrical member through an annular ridge 139A which engages an annular groove 135 A in a radially inner surface of the cylindrical member 135.

[0078] For assembling purposes, the annular structure (including the ring 133 and the cylindrical member 135 is formed in two substantially symmetrical portions 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.

[0079] The thrust ring 139 is adapted to engage and / or support, at the radial inner end thereof, the vanes, i.e. the stationary blades 53 of the first expansion stage of the expander. 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.

[0080] 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. Each transition piece 113 can be connected to the respective strut 137 by means of a bracket 141. Alternatively, or in combination to the bracket connection, each transition piece 113 can be mechanically coupled directly to the forward end of the inner casing 51.

[0081] Thus, in some embodiments the transition pieces 113 are cantileverly supported at the forward end of the inner casing 51.

[0082] Seals, not shown, can be arranged at or around the aft end of each transition piece 113.

[0083] According to some embodiments, as best shown in Figs. 2, 3 and 4, a plurality of flanged passages are provided around the outer casing 41, said passages including the first process gas inlet 120 of each combustor 8 and the one or more second process gas inlets 121. Some of said flanged passages can be used for supplying process gas at variable temperature and / or pressure to the expander. Other of said flanged passages can be used for introducing and connecting gauges, sensors or other instruments inside the expander.

[0084] In some embodiments the first process gas inlets 120 are provided with flanges 151 which are oriented around the outer casing 41 in such way that the outer casing 51 and the components contained therein, specifically the combustors 8, can be removed for maintenance or repairing purposes, for instance, with an axial movement along axis A-A.

[0085] Particularly advantageous embodiments foresee that the flanges 151 are facing in an aft direction, such that once they have been unbolted from the piping (not shown) which supplies the process gas to the expander, the outer casing 51 and relevant devices contained therein can be removed with an axial movement in the forward direction without the need to dismantle any further equipment surrounding the expander 1.

[0086] Each flange 151 is connected to an external process gas inlet pipe 153.

[0087] In some embodiments, there can be provided a process gas inlet pipe and relevant flange 151 for each combustor 8. In other embodiment, as illustrated in particular in Figs. 3 and 7, there can be less process gas inlet pipes 153 than combustors. In this embodiment there are twelve combustors 8 and six external process gas inlet pipes 153. Each process gas inlet pipe is coupled to the outer casing 41 by welding. In other embodiments, each process gas inlet pipe 153 can be connected to the outer casing 41 by a bolted flange.

[0088] As best shown in Fig.7, each process gas inlet pipe branches inside the thickness of the outer casing 41, specifically in the monolithic toroidally shaped annularbody 41.4 thereof, to supply process gas to the first process gas inlets of two adjacent combustors 8. The sectional view of Fig.7 illustrates how one of the six process gas inlet pipes is divided into two branches 153 A, 153 A, which form the first process gas inlets for two adjacent combustors, whereof the cylindrical seat 101 is shown in Fig. 7.

[0089] In yet further embodiments, the number of process gas inlet pipes can be even less, for instance one pipe for a sub-set of combustors, each sub-set including more than two combustors 8. In some embodiments, a single process gas inlet pipe can be provided which extends outside the outer casing 41.

[0090] Whenever the number of process gas inlet pipes is smaller than the number of combustors, distribution channels for the distribution of the process gas to the combustors can be manufactured in the body of the outer casing 41.

[0091] To provide easier separation of the outer casing 41 from the piping (not shown) surrounding the expander 3 and supplying the process gas to the first process gas inlets of the combustors, the process gas inlet pipes 153 can be U-shaped (Fig.3), such that the flanges 151 can face in the aft direction.

[0092] In other embodiments, the pipes can be oriented radially outwardly.

[0093] 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.

[0094] Additionally, the present disclosure also relates to the novel features summarized in the following clauses.Clause 1 : An expander comprising a casing and a rotor adapted to rotate therein around a rotation axis; wherein the casing comprises a monolithic forward casing portion having an annular body developing around the rotation axis; the forward casing portion comprises a plurality of generally cylindrical seats formed in the annular body thereof and arranged side-by-side around therotation axis; each generally cylindrical seat houses a combustor including: a tubular liner having a forward end, an aft end, and a side wall extending from the forward end to the aft end; 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; and preferably a tubular sleeve arranged around the liner; each generally cylindrical seat is fluidly coupled with a first process gas inlet; and each liner is fluidly coupled with a transition piece at the aft end of the liner.Clause 2: An expander comprising: a casing; a rotor housed in the casing for rotation therein around a rotation axis; wherein the casing comprises an outer casing and an inner casing; the inner casing being preferably horizontally split, and / or the outer casing being preferably vertically split; 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; preferably a tubular sleeve arranged around 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; and an annular plenum between the generally cylindrical seats of the combustors and the inner casing; wherein the transition pieces are positioned in the annular aft plenum.Clause 3 : The expander of clause 2, wherein each liner projects in an aft direction from the respective generally cylindrical seat in the annular aft plenum;Clause 4 : The expander of clause 2 or 3, wherein each tubular sleeve projects in an aft direction from the respective generally cylindrical seat in the annular plenum.Clause 5: The expander of clause 2, 3 or 4, wherein the annular aft plenum is fluidly coupled with at least one second process gas inlet.Clause 6: The expander of any one of clause 2 to 5, comprising an annular structure extending around the rotation axis, in which the transition pieces are housed; wherein the annular structure is housed in the aft plenum.Clause 7: The expander of clause 6, wherein the annular structure comprises a ring coaxial to the rotation axis and connected to a forward end of the inner casing.Clause 8: The expander of clause 7, wherein the annular structure comprises a cylindrical member coaxial to the ring.Clause 9: The expander of claim 8, wherein the ring and the cylindrical member are connected to one another by a plurality of struts, preferably radially extending struts.Clause 10: The expander of clause 9, wherein a transition piece and an aft end of the respective liner and sleeve are housed between each pair of sequentially arranged struts.Clause 11 : The expander of clause 9 or 10, wherein each transition piece is supported by one of said struts.Clause 12: The expander of any one of clauses 8 to 10, further comprising a thrust ring, engaged to the cylindrical member, wherein the thrust ring is connected to, or supports stationary blades of a first expansion stage of the expander.Clause 13: The expander of any one of clauses 2 to 12, wherein each transition piece is connected directly to a forward end of the inner casing.Clause 14: An expander comprising: a casing; a rotor housed in the casing for rotation therein around a rotation axis; wherein the casing comprises an outer casing and a preferably an inner casing; the inner casing being preferably horizontally split, and / or the outer casing being preferably vertically split;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; preferably a tubular sleeve arranged around 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; and at least one, and preferably a plurality of process gas inlet pipes, fluidly coupled to the combustors; wherein each process gas inlet pipe comprises a flange adapted to connect the process gas inlet pipe to an external process gas delivery piping.Clause 15: The expander of clause 14, wherein each flange of a respective process gas inlet pipe is oriented and configured to allow an axial displacement of the outer casing of the expander with respect to the external piping, by disengaging the flanges from the external piping.Clause 16: The expander of clause 15, wherein each process gas pipe is U- shaped and the respective flange is oriented in an aft direction.

Claims

CLAIMS1. An expander comprising a vertically-split outer casing, an inner casing, and a rotor housed in the inner casing and adapted to rotate therein around a rotation axis; wherein: the outer casing comprises a monolithic forward casing portion having an annular body developing around the rotation axis; the forward casing portion comprises a plurality of generally cylindrical seats entirely formed within the annular body of the forward casing portion and arranged side-by-side around the rotation axis; each generally cylindrical seat entirely houses a respective combustor; and each generally cylindrical seat is fluidly coupled with a first process gas inlet.

2. The expander of claim 1, 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; 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.

3. The expander of claim 2, further comprising a tubular sleeve arranged around the liner.

4. The expander of any preceding claim, wherein each generally cylindrical seat has a longitudinal axis converging towards the rotation axis of the rotor.

5. The expander of claim 3, wherein each sleeve projects in an aft direction from the respective generally cylindrical seat in the annular aft plenum.

6. The expander of any preceding claim, wherein each liner projects in an aft direction from the respective generally cylindrical seat in an annular aft plenum; and wherein the transition pieces are positioned in the annular aft plenum.

7. The expander of claim 6, wherein the annular aft plenum is fluidly coupled with at least one second process gas inlet.

8. The expander of any one of claims 1 to 6, comprising at least onesecond gas inlet for each combustor, fluidly coupled with the respective generally cylindrical seat.

9. The expander of claim 7, wherein the annular aft plenum is fluidly coupled with a respective outer annular space between each generally cylindrical seat and the respective sleeve housed therein.

10. The expander of any preceding claim, comprising an annular structure extending around the rotation axis, in which the transition pieces are housed.

11. The expander of claim 10, when depending upon any one of claims 3 to 6, wherein the annular structure is housed in the annular plenum.

12. The expander of claim 10 or 11, wherein the annular structure comprises a ring coaxial to the rotation axis and connected to a forward end of the inner casing.

13. The expander of claim 12, wherein the annular structure comprises a cylindrical member coaxial to the ring.

14. The expander of claim 13, wherein the ring and the cylindrical member are connected to one another by a plurality of struts, preferably radially extending struts.

15. The expander of claim 14, wherein a transition piece and an aft end of the respective liner are housed between each pair of sequentially arranged struts.

16. The expander of claim 14 or 15, wherein each transition piece is supported by one of said struts.

17. The expander of any one of claims 13 to 16, further comprising a thrust ring, engaged to the cylindrical member, wherein the thrust ring is connected to, or supports stationary blades of a first expansion stage of the expander.

18. The expander of any one of claims 1 to 15, wherein each transition piece is connected directly to a forward end of the inner casing.

19. The expander of any preceding claim, wherein each generallycylindrical seat forms a forward plenum surrounding the liner.

20. The expander of claim 19, wherein each forward plenum is fluidly coupled with an inner annular space between the liner and the sleeve housed in the corresponding generally cylindrical seat.

21. The expander of claim 19 or 20, wherein each forward plenum is fluidly coupled with the respective first process gas inlet.

22. The expander of any preceding claim, comprising at least one, and preferably a plurality of process gas inlet pipes, fluidly coupled with the combustors; wherein each process gas inlet pipe comprises a flange adapted to connect the process gas inlet pipe to an external process gas piping.

23. The expander of claim 22, wherein each flange of a respective process gas inlet pipe is oriented and configured to allow an axial displacement of the outer casing of the expander with respect to the external process gas piping, by disengaging the flanges from the external piping.

24. The expander of claim 22, wherein each process gas pipe is U- shaped and the respective flange is oriented in an aft direction.

25. A power generating system comprising: an expander according to any preceding claim; a regenerative heat exchanger configured to cool a combustion gas exhausted from the expander to form a cooled combustion gas and to heat at least a first part of the cooled combustion gas; a recycle line fluidly coupled with expander, and adapted to feed the first part of the cooled combustion gas at a first temperature to the expander; a cooling line fluidly coupled with expander, and adapted to feed a second part of the cooled combustion gas at a second temperature to the expander, the second temperature being lower than the first temperature; an oxidant supply line adapted to feed an oxidant flow to the expander; and a fuel supply line adapted to feed a fuel to the expander.

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