A combustor for an expander, an expander including the combustor, and a power generating system comprising the expander

Abstract

The combustor (7) comprises a casing (101), in which there are housed a burner (107), a liner (103), and a transition piece (113). A sleeve (115) is arranged around the liner (103), between the liner (103) and the casing (101). The sleeve (115) divides a space between the casing (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).

Description

A COMBUSTOR FOR AN EXPANDER, AN EXPANDER INCLUDING THE COMBUSTOR, AND A POWER GENERATING SYSTEM COMPRISING THE EXPANDERDESCRIPTIONTECHNICAL FIELD

[0001] The present disclosure pertains to combustors for turbomachines and parts thereof. Embodiments disclosed herein specifically refer to combustors adapted for use in oxyfuel combustion expanders, such as supercritical carbon dioxide expanders (sCO2expanders).

[0002] As understood herein a sCCh 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 process particularly 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 burns in a combustor 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 of the expander.

[0008] Oxygen supplied to the combustor of the expander can be obtained by separation from ambient air, removing nitrogen therefrom, such that the working fluid supplied to the combustor 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, 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 high pressure and temperature values inside the expander and specifically inside the combustor. These operating conditions pose difficult constraints in the casing design.

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

[0012] The present disclosure relates to improvements to the combustor layout which are particularly aimed at improving the operating conditions of the combustor. The present disclosure also pertains to an expander, such as a supercritical carbon dioxide expander, comprising an improved combustor layout, as well as to a power generation system including the improved expander.SUMMARY

[0013] According to a first aspect, disclosed herein is a combustor for an expander, such as, but not limited to, a supercritical carbon dioxide expander. As used herein, the term expander includes any power-generating turbomachine, wherein a hot and compressed gas, generated by combustion, is expanded and mechanical power is generated by expansion of the combustion gas. Thus, the term expander specifically includes turbines which process a combustion gas.

[0014] The combustor includes a casing and, inside said casing, a liner having a forward end, an aft end, and a side wall between the forward end and the aft end. The side wall has an outer surface and an inner surface and may have cooling holes extending from the outer surface to the inner surface.

[0015] The combustor further comprises a burner at the forward end of the liner. The burner is fluidly coupled with a fuel inlet and an oxidant inlet.

[0016] The combustor further includes a transition piece at the aft end of the liner, as well as a sleeve arranged around the liner. The sleeve is positioned between the liner and the casing. The sleeve divides a space between the casing and the liner into an inner annular space and an outer annular space. The outer annular space surrounds the inner annular space. The sleeve comprises a forward end and an aft end. The forward end of the sleeve is coupled to an inner surface of the casing.

[0017] A first process gas inlet is fluidly coupled with the inner annular space, and a second process gas inlet is fluidly coupled with the outer annular space in a position downstream of the forward end of the sleeve, and preferably downstream of the aftend of the liner.

[0018] A thermal insulation chamber adapted to be filled with process gas is formed between the second process gas inlet and the forward end of the sleeve, the insulation chamber extending around the sleeve and the liner and being adapted to be filled with process gas delivered by the second process gas inlet. The thermal insulation chamber can be closed upstream of the second process gas inlet, such that the process gas filling the thermal insulation chamber is stagnant in said thermal insulation chamber. In other embodiments, the thermal insulation chamber may be fluidly coupled with a forward plenum, which surrounds the liner, such that a coolant stream can be established through the thermal insulation chamber in an aft to forward direction.

[0019] As an alternative, or in combination with the above outlined thermal insulation chamber, the forward end of the sleeve is positioned in an intermediate position between the forward end of the liner and the aft end of the liner.

[0020] By distancing the second process gas inlet from the first process gas inlet, and specifically from the forward end of the liner where the burner is positioned, more space is provided in the area surrounding the forward end of the liner, where several instrumentalities must be installed, such as ducts and measurement instruments. The process gas insulation chamber provides an efficient thermal insulation between the liner and the casing which houses the combustor, even if the second process gas inlet, which typically receives cooled process gas, is positioned at a distance from the forward end of the liner.

[0021] By arranging the forward end of the sleeve, which divides the space surrounding the liner into an inner and an outer annular space, in an intermediate position between the forward end of the liner and the aft end of the liner, additional space is gained around the critical area surrounding the forward end of the liner.

[0022] As will be described in detail herein, in some embodiments the combustor can be integrated in an expander for a supercritical carbon dioxide cycle, such as an Allam cycle. The process gas delivered at the first process gas inlet and at the second process gas inlet can be recycled combustion gas, consisting mainly of carbon dioxide. The process gas at the first process gas inlet can be at a temperature higher than the process gas at the second process gas inlet.

[0023] Further features and advantageous embodiments of the combustor according to the present disclosure are outlined in the dependent claims.

[0024] The present disclosure further pertains to an expander, which may include a gas turbine, and adapted to expand a combustion gas, including at least one combustor as outlined above.

[0025] As will be clarified below, the combustor can be an annular combustor with a single liner extending around the rotation axis of the expander and fluidly coupled with a single transition piece.

[0026] In other embodiments, the combustor can include a plurality of combustor units in a can-type or in a cannular configuration, or in a combined can-type and can- nular configuration.

[0027] For instance, the combustor can include a casing comprising a plurality of annularly arranged seats. Each seat can entirely or partly house a tubular, i.e. can-type liner. Each liner has a forward end, an aft end, and a side wall between the forward end and the aft end. At least one burner is provided at the forward end of each liner of said plurality of liners. Each burner is fluidly coupled with a fuel inlet and an oxidant inlet. Each liner is connected to a transition piece at the aft end of the liner. Each combustor unit includes a sleeve, specifically a tubular sleeve, arranged around the liner, between the liner and the casing, i.e. the inner surface of the respective seat housing the sleeve. In this way the sleeve divides a space between the casing, i.e. the inner surface of the seat housing the liner, and the liner itself, into an inner annular space and an outer annular space. The inner and outer annular spaces of each combustor unit surround the respective tubular liner, and the outer annular space surrounds the inner annular space. Each sleeve comprises a forward end and an aft end. The forward end of the sleeve is coupled to an inner surface of the respective seat formed in the casing. A first process gas inlet is fluidly coupled with the inner annular space of each combustor unit. A second process gas inlet is fluidly coupled with the outer annular space in a position downstream of the forward end of the sleeve.

[0028] In such multiple combustor unit arrangement, in some embodiments, a respective thermal insulation chamber, adapted to be filled with stagnant process gas can thus be formed between the second process gas inlet and the forward end of eachsleeve, the insulation chamber extending around the sleeve and the liner. If the thermal insulation chamber is fluidly coupled with a forward plenum surrounding the forward end of the liner, a coolant flow can be established in an aft-to-forward direction through the thermal insulation chamber.

[0029] In some embodiments, the forward end of each sleeve of each combustor unit can be positioned in an intermediate position between the forward end of the respective liner and the aft end of said liner.

[0030] According to yet another aspect, disclosed herein is a power generating system comprising an expander including a combustor as outlined above. In embodiments disclosed herein, the power generating system comprises 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 is fluidly coupled with the first process gas inlet of the combustor, and is adapted to feed the first part of the cooled combustion gas at a first temperature to the expander. A cooling line fluidly is coupled with the second process gas inlet of the combustor, and is 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. The system further includes an oxidant supply line fluidly coupled with the oxidant inlet of the combustor and adapted to deliver an oxidant to a burner of the combustor in the expander. A fuel supply line is fluidly coupled with the fuel inlet of the combustor.As used herein “forward” and “aft” are referred to the direction of flow of the process gas through the combustor 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.

[0031] If not differently indicated, the terms “upstream” and “downstream” refer to the direction of flow of the process gas in the combustor and in the expander.BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Reference is now made briefly to the accompanying drawings, in which:Fig.1 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 enlarged and more detailed sectional view of the combustor of the expander of Fig.2;Fig.4 is a front view of the burner in one embodiment;Fig.4A is an enlargement of a central area of Fig.4;Figs. 5 is a cross-sectional view according to line V-V of Fig.4;Fig.5 is a sectional view of the burner of Fig.4;Fig.6 is a side view of the liner in an embodiment;Fig.7 is a sectional view of the liner of Fig.6 along a plane containing the longitudinal axis thereof;Fig.7A is an enlargement of Fig.7;Fig.8 is an axonometric view of the transition piece in one embodiment;Fig.9 is an axonometric sectional view of the transition piece of Fig.8;Fig.10 is an axonometric sectional view of a first component of the transition piece in another embodiment;Fig.11 is an axonometric view of the first component of FiglO;Fig.12 is an axonometric sectional view of a second component of the transition piece of Fig.10;Fig. 13 is an axonometric view of the second component of Fig.12; andFigs. 14, 15 and 16 are schematics of different combustion chamber layouts.DETAILED DESCRIPTION

[0033] 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 SCO2 cycle), such as an Allam cycle or NET Power oxy-fuel cycle.

[0034] The power generating system 1 shown in Fig. l comprises a turbine or expander 3 that includes an expansion section 5 and a combustor 7. The combustor 7 can be an annular combustor, a can-type combustor, a can-annular combustor (aka cannu- lar combustor), or the like, for instance. In the embodiments disclosed herein, the combustor is a can-type combustor or a combined can-type and cannular combustor, as will be described in more detail below.

[0035] When in the form of a can-type or cannular-type, the combustor comprises a plurality of combustor chambers arranged around the rotation axis of the expander 3, as shown in more detail in the subsequent figures and described in detail later on. The combustor chambers are housed in an outer casing of the expander, as will described in more detail below. Each combustion chamber is surrounded by a tubular liner, to be described.

[0036] Reference number 7.1 in Fig.2 designates one combustion chamber of a cantype, cannular or combined can-type and cannular combustor. In some embodiments, each combustion chamber 7.1 is housed in a respective seat formed in a casing, as will be described in greater detail below with reference to Fig.3. The combustion chambers 7.1 are arranged circumferentially around a rotation axis A-A of the expander 3.

[0037] The combustor 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 (Fig.1) 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 7 of the expander 3.

[0038] 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 combustor chamber 7.1. The oxidant and the fuel are supplied at a forward side of the expander 3 to the combustor 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 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 7. Pressurized, hot combustion gas resulting from the combustion expands in the expansion section 5 of the expander 3.

[0039] 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.

[0040] 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.

[0041] 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 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 instance, the rated power can be comprised between 200 MW and 650 MW.

[0042] Intermediate values of the upper and lower limit of each range mentioned above are also expressly disclosed herein.

[0043] 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.

[0044] 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.

[0045] 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 7 and mixed with combustion gas generated therein as will be described in more detail later.

[0046] 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 7. The oxidant flow delivered to the combustor 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, and helps to tune the reactivity of the mixture within the combustor. The percentages outlined above are by example only and shall not be understood as limiting the scope of the present disclosure.

[0047] 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 7.

[0048] The expander 3 may include an output shaft end 31 which can be integral with the central portion of the rotor, or can be assembled with the central portion of the rotorby 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 Figs 1 and 2 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.

[0049] 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 the combustor 7. In embodiments, the outer casing 41 includes a high-pressure casing 41.1 and a low-pressure exhaust casing 41.2. The high-pressure casing 41.1 can be in the form of a barrel including a monolithic body, for example manufactured by forging, casting, or combination thereof. I.e. the outer casing can be a vertically split casing. The monolithic body extends around the longitudinal axis of the expander, i.e., around the rotation axis.

[0050] The low-pressure exhaust casing 41.2 can be positioned on the discharge side, i.e. the aft side, of the expander 3, i.e., on the side opposite the combustor 7.

[0051] In some embodiments, the low-pressure exhaust casing 41.2 forms a discharge plenum 41.3, through which exhausted combustion gas is discharged from the expander 3.

[0052] Reference numbers 45, 47 indicate bearing arrangements, which rotatingly support a rotor 43 of the expander 3. For instance, the bearing arrangement 45 on the side opposite the combustor 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 side may include a radial bearing. A reversed arrangement is also possible, with a bearing having axial load capability arranged on the combustor side.

[0053] 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.

[0054] The rotor 43 is surrounded by an inner casing 51, which can be formed by plurality of sections arranged in sequence in a forward-to-aft direction. In Fig.2 the inner casing 1 comprises two casing sections sequentially arranged in the forward-to- aft direction, i.e., parallel to the rotation axis. The inner casing 51 can be horizontally split, i.e. can include 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 casing sections arranged in sequence in the axial direction, each section can in turn be split into two portions along a plan containing the rotation axis of the rotor 43.

[0055] The inner casing 51 is fully or partly housed in the high-pressure casing 41.1. In some embodiments, as shown in Fig.2, the inner casing 51 projects in the low-pressure exhaust casing 41.2.

[0056] One or more annular fluid chambers 42 are formed between the inner casing 51 and the outer casing 41. Specifically, in the exemplar embodiment shown in Fig.2 the annular chamber 42 includes two sequentially arranged annular fluid chambers 42.1 and 42.2 separated by a septum 44. The fluid pressure inside the two annular fluid chambers 42.1 and 42.2 can be different. For instance, the forward annular fluid chamber 42.1 can be at a higher pressure than the aft annular fluid chamber 42.2. In use, at steady state conditions, the aft fluid chamber 42.2 and the forward fluid chamber 42.1 can be fed with chilling or cooling fluid, e.g. with chilled, dehydrated combustion gas from cooling line 27.

[0057] 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 one or each of several annular fluid chambers 42.1, 42.2 with the interior of the inner casing 51. Compressed recycled combustion gas, consisting mainly of carbon dioxide, can flow from the annular fluid chambers 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.

[0058] 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 7 a high number of expansion stages is preferred. In the exemplary embodiment of Fig.2, the expander 3 includes eight stages, each configured as an axial expansion stage. In other embodiments, a different number of expansion stages can be foreseen, preferably equal to or higher than four, more preferably equal to or higher than five. In some embodiments, the number of expansion stages can be higher than eight, for instance nine, ten, eleven or more.

[0059] Each expansion stage includes an annular row of stationary blades 53, aka vanes 53, which are stationarily arranged in the inner casing 51 and form nozzles at the inlet of the expansion flow path.

[0060] Each expansion stage further includes a respective annular row of rotor blades 55, arranged downstream the respective annular row of stationary blades 53 along an expansion flow path which extends from the combustor 7 through the expansion section 5 to the discharge plenum 41.3 in a forward-to-aft direction.

[0061] The rotor blades 55 form part of the rotor 43, i.e., they are connected thereto for co-rotation with the rotor shaft. In some embodiments, each annular row of rotor blades 55 is connected to a respective rotor disk, not shown in detail. The structure of the rotor and of the rotor disks is not relevant and is not shown in detail.

[0062] In embodiments, the rotor 43 further comprises a forward shaft portion 65 and an aft shaft portion 67. In 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.

[0063] 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.

[0064] With continuing reference to Figs. 1 and 2, a general layout of the combustor 7 in one embodiment is shown in Fig.3. The embodiment of Fig.3 is based on a can-type combustor architecture, wherein the expander comprises a plurality of can-shaped liners, i.e. tubular liners, wherein each liner contains one or more burners, and wherein each tubular or can-shaped liner is surrounded by its own can-shaped casing, which forms a substantially cylindrical seat for the liner. In other embodiments, as mentioned above, the combustor can be a cannular (aka tubo-annular or can-annular) combustor, or else an annular combustor.

[0065] Turning now to Fig.3, in the illustrated embodiment the expander comprises a can-type combustor, which includes a plurality of combustor units. The units are arranged around the rotation axis A- A of the expander. One combustor unit is shown in a longitudinal sectional view in Fig.3. Each combustor unit will be referred herein simply as “combustor” and comprises a combustor casing 101 forming a seat 101A which houses a tubular, i.e. can-shaped liner 103. Each liner 103 has a longitudinal axis B-B. Since the combustor units form part of a can-type combustor, the liners 103 are positioned with their longitudinal axes B-B on a conical surface, the axis whereof is coincident with the rotation axis A-A of the expander. 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).

[0066] In some embodiments, the combustor units can be housed in a combustor casing, which can be manufactured separately from the main outer casing of the expander. The two casings can be connected to one another with a flanged coupling. This may improve casing manufacturability. In the enclosed drawings, a single casing is shown for the sake of simplicity.

[0067] In some embodiments, wherein the combustor is a can-type combustor, the combustor units can be housed in a monolithic toroidal body formed by the outer casing or by a separate combustion casing, connected to the outer casing. In this case, the toroidal body can comprise a plurality of seats 101 A arranged around the rotation axis A-A of the expander 3. Each tubular, i.e. can-shaped liner 103 is housed in a respective one of said plurality of seats 101 A. In such embodiment, the combustor casings 101together form the toroidal body.

[0068] In other embodiments, the combustor can be an annular combustor or a can- nular combustor. The general layouts of can-type combustors, cannular combustors and annular combustors are known per se and are summarized in the schematics of Figs. 14, 15 and 16, respectively. As shown in Fig.14, the can-type combustor includes individual liners 103, arranged around the axis A- A of the turbomachine and coupled to one another by crossfire tubes 104. A cannular type combustor, as schematically shown in Fig.15, includes an annular pressure shell 106, housing the liners 103 and crossfire tubes 104. A schematic representation of an annular combustor is shown in Fig.16 In such case, the combustor comprises a single liner 103 developing symmetrically around the rotation axis A-A of the expander and having an inner, generally conical liner wall and an outer, generally conical liner wall, coaxial to one another. Burners are arranged annularly around the machine axis A-A and are housed in the liner, as schematically shown in Fig.16.

[0069] The liner 103 will be described in detail later with reference to the next figures. As mentioned, the liner 103 extends along a longitudinal axis B-B and has a forward end 103F, and an aft end 103 A. A, generally cylindrical side wall 105 of the liner 103 extends between the forward end 103F and the aft end 103 A. The side wall 105 has an outer surface 105 A and an inner surface 105B and surrounds the combustion chamber 7.1 of the combustor or combustor unit 7.

[0070] The combustor 7 comprises at least one burner 107 at the forward end 103F of the liner 103. In some embodiments, the burner 107 is coupled with a forward end closure or lid 102 of the liner 103. In some embodiments, the forward end closure 105 of the liner 103 comprises a plurality of apertures wherethrough recycled combustion gas, mainly consisting of carbon dioxide, can enter the combustion chamber 7.1.

[0071] As will be described in detail below, the burner 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 fuel, for instance gaseous fuel, such as natural gas, therefrom. The oxidant inlet 111 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.

[0072] The combustor 7 further comprises a transition piece 113 positioned at the aft end 103A of the liner 103. The transition piece 113 forms an extension of the duct formed by the liner 103 towards the array of stationary nozzles 53 and guides the combustion gas generated in the combustion chamber 7.1 toward the expansion flow path formed by the stationary and rotary blades of the expander.

[0073] In the embodiment of Fig.3, since the combustor is based on a can-type combustor architecture, each combustion chamber 7.1 extending along the longitudinal axis B-B of the respective liner 103 merges in a respective one of a plurality of transition pieces 113 positioned circumferentially around the rotation axis A-A. In other embodiments, the combustor can be an annular combustor including a conically shaped liner. In such embodiment, not shown, the conical liner merges with a single, generally conical transition piece. In both cases, the transition piece(s) fluidly cou- ple(s) the liner(s) with the row of stationary vanes 53 of the first expansion stage of the expander, positioned at the inlet of the expansion flow path.

[0074] The combustor 7 further comprises a sleeve 115, which is arranged around the liner 103 and substantially coaxial therewith. Specifically, the sleeve 115 is positioned between the liner 103, i.e. between the side wall 105 thereof, and the combustor casing 101. The sleeve 115 comprises a forward end 115F and an aft end 115A.

[0075] In some embodiments, the forward end 115F of the sleeve 115 is in the form of a flange which is coupled to an inner surface of the combustor casing 101.

[0076] In other embodiments, the sleeve 115 extends in a forward direction towards the forward end 103F of the liner 103 beyond the flange 115F, which connects the sleeve 115 to the combustor casing 101, This option is shown in dashed lines in Fig.3. In such case the forward end of the sleeve 115 will be located at 115FX. In the present disclosure whenever reference is made to the forward end of the sleeve, such end can be either the flange 115F or the end 115FX, depending on whether the sleeve projects fowardly from the flange 115F towards the forward end 103F of the liner, or ends at the flange 115F.

[0077] The sleeve 115 divides a space between the combustor casing 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. The inner annular space 117and the outer annular space 119 are substantially co-axial.

[0078] As in the embodiment of Fig.3 the combustor is a can-type combustor, each generally cylindrical liner is surrounded by a generally cylindrical sleeve 115. The inner annular space and the outer annular space surrounding each liner 103 extend coaxial to the liner 103, i.e. in the direction of the longitudinal axis B-B and have a cylindrical cross-section. In other embodiments, not shown, where the combustor is an annular combustor, the sleeve is generally conical and coaxial to the rotation axis A- A of the expander. The inner and outer annular spaces are conical and co-axial to the rotation axis A-A.

[0079] As described above, recycled combustion gas is returned towards the combustor 7 of the expander 3. As described regarding Fig. l, 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 combustor 7 through the oxidant inlet 111.

[0080] A further flow of recycled combustion gas, wherefrom condensed water has been removed is delivered to the expander through recycle line 25 and is fed to the combustor 7 through a first process gas inlet 120, which is fluidly coupled with the inner annular space 117 as described below. A yet further flow of recycled combustion gas is delivered to the expander 3 through the cooling line 27, which is fluidly coupled to a second process gas inlet 121. The second process gas inlet 121 is fluidly coupled with the outer annular space 119 in a position downstream of the forward end 115F of the sleeve 115, i.e. in a position between the expansion flow path of the expander and the forward end 115F of the sleeve 115. The first process gas inlet 120 is therefore connected to the combustor 7 in a position upstream of the position of the second process gas inlet 121. A thermal insulation chamber is formed between the second process gas inlet 121 and the forward end 115F of the sleeve 115. The insulation chamber is formed by the outer annular space 119, or part thereof, which extends around the sleeve 115 and the 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.

[0081] In the embodiment of Fig.3 the forward end 115F of the sleeve 115 ispositioned in a position intermediate the forward end 103F of the liner 103 and the aft end 103A of the liner, i.e. between the two ends 103F and 103A of the liner 103.

[0082] Thus, the liner 103 projects in a forward direction beyond the sleeve 115 which surrounds the liner 103. In this embodiment the combustor further comprises a forward plenum 127, which is positioned at the forward end 103F of the liner 103. Specifically, in Fig.3, the forward plenum 127 surrounds the forward end 103F of the liner 103, which projects inside the forward plenum 127. In the illustrated embodiment, which is based on a can-type combustor architecture, each liner 103 is tubular, i.e. can-shaped, and is surrounded by a tubular sleeve 115. Each tubular liner 103 and coaxial tubular sleeve 115 are surrounded by a respective forward plenum 127 which is shaped in the form of a substantially cylindrical cavity. The plurality of cylindrical cavities which form the forward plenums 127 of the several can-type combustors can be formed in a monolithic body of the outer casing 41, which can have a toroidal shape.

[0083] In other embodiments, the forward end 103F of the liner and the forward end 115F of the sleeve 115 can be substantially aligned along the axis B-B. Therefore, the sleeve 115 will be flush with the liner 103 at the aft ends thereof.

[0084] In some embodiments, the the thermal insulation chamber represented by the outer annular space 119, may be fluidly coupled with the forward plenum 127, instead of being closed. If a fluid coupling between the outer annular space 119 and the forward plenum 127 is established, for instance under or around the flange at the forward end 115F of the sleeve 115, a coolant flow in the aft-to-forward direction can establish in the thermal insulation chamber 119. Typically, only a small fraction of the coolant entering through the second process gas inlet 121 flows in the aft-to-forward direction, while most of the coolant flow flows towards the expansion flow path of the expander.

[0085] In Fig.3, the forward plenum 127 extends parallel to an axis of the liner 103 from the forward end 115F of the sleeve 115 in a forward direction towards a lid or closure 129, which closes the forward side of the combustor casing 101. The fuel inlet 119 and the oxidant inlet 111 extend through the closure 129. The closure 129 closes the forward plenum 127 at the forward side thereof.

[0086] 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 thatprocess 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 combustion chamber 7.1 through holes, apertures, or ports extending through the side wall 105 of the liner. A description of the holes, apertures, or ports which extend through the side wall 105 of the liner will be given later herein. The ports, holes or apertures provided in the side wall 105 of the liner allow process gas, consisting mainly of carbon dioxide, which flow through the inner annular space 117, to flow into the combustion chamber 7.1 as a cooling fluid or dilution fluid.

[0087] In some embodiments, the combustor 7 further comprises an aft plenum 131 positioned at the aft end 103A of the liner 103. For instance, the aft plenum 131 can surround the aft end 103 A of the liner 103. In some embodiments, the aft plenum 131 also surrounds the transition piece 113, i.e. the transition piece is at least partly housed in the aft plenum 131.

[0088] In some embodiments, the aft plenum can be annular and develop around the rotation axis A-A. Each one of a plurality of tubular liners 103 and corresponding sleeves 115 can protrude from the respective seat 101 A into the annular aft plenum 131, which also encloses the transition pieces 113. In this case the combustor 7 will be a combined can-type and cannular combustor.

[0089] In Fig.3 the aft plenum 131 is fluidly coupled with the outer annular space 119, which surrounds the liner 103 and the sleeve 115. The outer annular space 119 can extend from the aft plenum 131 toward the forward end 103F of the liner 103.

[0090] In the embodiment of Fig.3, the second process gas inlet 121 is positioned at the aft plenum, i.e. directly coupled therewith. In other embodiments, not shown, the second process gas inlet 121 can be positioned in an intermediate position along the development of the outer annular spaec 119 between the aft end thereof and the aft plenum 131.

[0091] 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.

[0092] In the embodiment of Fig.3, the inner annular space 117 is fluidly coupled at the aft end thereof with a cooling annulus 113 A of the transition piece 113. As will be explained in more detail below, 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 7.1 with the expansion flow path of an expander 3. The aft plenum 131 extends around the outer duct of the transition piece 113.

[0093] The process fluid delivered through the first process gas inlet 120 flows through the inner annular space 117 and partly enters the combustion chamber 7.1 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 in a direction of flow concordant with the direction of flow of the combustion gas generated in the combustion chamber 7.1 and which flows towards the expansion flow path. The process fluid flows from the cooling annulus 113 A through cooling apertures formed in the transition piece, which will be described in more detail below and cools the inner surface of the transition piece 113 by effusion or film cooling.

[0094] In the cross-sectional view of Fig.3, an igniter 118 is also shown. In a cantype combustor, one igniter can be provided for each combustor, i.e. for each combustion chamber 7.1. The igniter 118 can extend from an outer flange 122 through the casing 7y . The igniter extends through the casing where the combustor is housed and through the forward plenum 127. The distal end of the igniter 118 reaches the interior of the liner 103, to provide an appropriate ignition source inside the liner. The igniter can be oriented orthogonal to the axis B-B of the combustor, as schematically shown in Fig.3. In other embodiments, the igniter can be inclined over the radial direction of the liner, i.e. the direction orthogonal to axis B-B, with an angle comprised between - 60° and 60°, for instance, preferably between -30° and 30°. The igniter can include a laser system, a hot spot glow plug, a high energy spark plug, or other suitable devices. Cross fire tubes can be provided, which fluidly couple adjacent liners to one another, to ensure proper ignition in all liners, even in case the igniter is present in only some of them.

[0095] An embodiment of the at least one burner 107 positioned at the forward end of the combustion chamber 7.1 is illustrated in Figs. 4, 4A and 5.

[0096] The burner 107 comprises a concentrical arrangement of ducts, wherethrough oxidant from the oxidant inlet 111 and fuel from the fuel inlet 109 are delivered into the combustion chamber 7.1, where they are intimately mixed and burned to generate the flow of compressed and hot combustion gas which then expands through the expansion flow path of the expander.

[0097] In the embodiment of Figs 4, 4A and 5 the burner 107 comprises a centerbody 135, which extends in a longitudinal direction parallel to the longitudinal axis B- B of the liner 103. If a single burner faces the combustion chamber 7.1, the centerbody 135, and therefore the burner 107 can be coaxial with the liner 103 and the combustion chamber 7.1, as shown in Fig.3.

[0098] The center-body 135 is surrounded by an intermediate annular wall 137, which extends coaxially around the center-body. The center-body 135 and the intermediate annular wall 137 form a first annular oxidant flow path 139 therebetween. More specifically, the first annular oxidant flow path 139 is formed between an outer wall of the center-body 135 and an inner wall of the intermediate annular wall 137. In some embodiments, the outer surface of the center-body 135 and the inner wall of the intermediate annular wall 137 are cylindrical, at least in the most downstream portion thereof, such that the first annular oxidant flow path 139 has a constant cross-section in the shape of a circular annulus.

[0099] The intermediate annular wall 137 forms a fuel passage 141 therein. The fuel passage 141 is fluidly coupled with at least one fuel port 143. In the embodiment of Figs. 4, 4A, and 5, the fuel passage 141 comprises a plurality of fuel ports 143. In some embodiments, the fuel port 143 or the plurality of fuel ports 143 are positioned on a front surface 137A of the intermediate annular wall 137. The fuel ports 143 are positioned at or near the distal end, i.e. the aft end of the intermediate annular wall 137. In the embodiment of Figs. 4, 4A, and 5, the fuel ports 143 are formed in a front end surface of the intermediate annular wall 137. The front end surface can be planar.

[0100] If a plurality of fuel ports 143 are foreseen, they can be arranged with a constant pitch around the axis B-B of the burner, as shown in Fig.4.

[0101] In the embodiment of Figs. 4, 4A and 5, the burner 107 further comprises an outer annular wall 145, which surrounds the intermediate annular wall 137. Theintermediate annular wall 137 and the outer annular wall 145 form a second annular oxidant flow path 149 therebetween. In some embodiments, the cross-sectional area of the first annular oxidant flow path 139 is smaller than the cross-sectional area of the second annular oxidant flow path 149. For instance, the cross-sectional area of the first annular oxidant flow path 139 can be comprised between 50% and 70%, preferably between 60% and 65% of the cross-sectional area of the second oxidant flow path 149.

[0102] More specifically, the second oxidant flow path 149 is formed between an outer surface of the intermediate annular wall 137 and an inner surface of the outer annular wall 145. In some embodiments, the outer surface of the intermediate annular wall 137 and the inner surface of the outer annular wall 147 are cylindrical, at least in the most downstream portion thereof, such that the second annular oxidant flow path 149 has a constant cross-section in the shape of a circular annulus.

[0103] To impart a tangential or swirling motion to the oxidant which flows in the first annular oxidant flow path 139, a first swirling flow generator 151 can be positioned in the first annular oxidant flow path 139. This swirling motion is beneficial for enhancing mixing, improving combustion efficiency, and controlling flow pattern within the combustion chamber 7.1. In the embodiment of Figs 3 and 4, the first swirling flow generator 151 comprises a plurality of inclined first blades, which span between the outer surface of the center-body 135 and the inner surface of the intermediate the intermediate annular wall 137, and configured to impart a tangential motion to an oxidant flow in the first annular oxidant flow path.

[0104] In some embodiments, the burner 107 further comprises a second swirling flow generator positioned in the second annular oxidant flow path. In the embodiment of Figs 4, 4A and 5, the second swirling flow generator 153 comprises a plurality of inclined first blades 153.1, which span between the outer surface of the intermediate annular wall 137 and the inner surface of the outer annular wall 145, and configured to impart a tangential motion to an oxidant flow in the second annular oxidant flow path.

[0105] In other embodiments, not shown, the first swirling flow generator, or the second swirling generator, or both the first swirling generator and second swirling generator can comprise inclined oxidant inlet ports, which are configured to feed oxidantflow having a tangential speed component in the respective annular oxidant flow paths.

[0106] In the embodiment of Figs. 4, 4A and 5, the first swirling flow generator and the second swirling flow generator are adapted to induce a tangential motion in the same direction in both the first annular oxidant flow path and the second annular oxidant flow path, respectively.

[0107] In the embodiment of Figs. 4, 4A and 5, at least one fuel feed duct 155 extends through at least one of the inclined second blades 153.1 from the outer annular wall 145 to the intermediate annular wall 137. Each fuel feed duct 155 comprises an inlet end 155.1 which is fluidly coupled with a fuel inlet plenum 157, and an outlet end 155.2 fluidly coupled with the fuel passage 141 extending along the intermediate annular wall 137.

[0108] In some embodiments, in addition to the first annular oxidant flow path 139 and the second annular oxidant flow path 149, the burner 107 can feature a third oxidant flow path inside the center-body 135. The third oxidant flow path can comprise an oxidant flow duct 159 in the center-body 135, which is fluidly coupled with one or more oxidant outlet ports 161, which are positioned at or adjacent the front distal end of the center-body 135. In Figs. 4 and 5 the oxidant outlet ports 161 are positioned at a front distal end surface of the center-body. The third oxidant flow path as well as the first annular oxidant flow path 139 second annular oxidant flow path 149 are fluidly coupled with the oxidant inlet 111 (Fig.3). An embodiment of the liner 103 is shown in detail in Figs. 6, 7 and 7A. The side wall 105 of the liner 103 comprises a plurality of cooling holes 171. Each cooling hole 171 extends through the side wall 105 from the outer surface 105 A to the inner surface 105B of the side wall 105.

[0109] The liner 103, and in particular the side wall 105 thereof, can be manufactured as a single monolithic component by additive manufacturing, for instance starting from the forward end 103F to the aft end 103 A of the liner 103. Using additive manufacturing for the production of the liner 103 the thickness of the side wall 105 can be made larger than with standard manufacturing technologies.

[0110] In some embodiments, the inner diameter of the liner, i.e the cross-sectional diameter of the inner surface 105B of the wall 105, can be equal to or less than 300 mm, or equal to or less than 250 mm, for instance equal to or less than 200 mm. Theratio between the thickness of the side wall 105 and the inner cross-sectional diameter can be equal to or higher than 0.015, preferably equal to or higher than 0.02. For instance, the ratio between the wall thickness and the inner diameter can be comprised between 0.02 and 0.05, or 0.2 and 0.04, or 0.02 and 0.03.[oni] If the liner has a non-circular inner cross section, the above-mentioned ratio can be referred to the equivalent diameter defined as follows:where S is the area of the cross section of the hot gas path in the liner.

[0112] In some embodiments, specifically for liners of large dimensions, which may be difficult to produce in a single additive manufacturing step due to the dimension of available additive manufacturing machines, the liner 103, and specifically the side wall 105 thereof, can be manufactured in individual ring-shaped portions or sections which are then welded to one another. Specifically, the liner can be formed by producing individual ring-shaped portions by additive manufacturing and subsequently welding the portions together. For instance, the ring-shaped portions can be bonded or coupled to one another by electron-beam welding.

[0113] Each ring-shaped portion represents a part of the axial development of the liner and extends circularly around the B-B axis of the liner. Each part can be delimited by planes orthogonal to the axis B-B of the liner. Once the individual ring-shaped portions of the liner have been manufactured by additive manufacturing, they are aligned with each other in the axial direction and welded peripherally along the annular edges of two consecutive portions abutting each other.

[0114] In some embodiments, the perforated intermediate section of the side wall 105 can be manufactured as a single piece by additive manufacturing, and only nonperforated end sections of the wall 105, which form the forward end 103F and the aft end 103 A, can be manufactured in separate additive manufacturing steps and welded to the perforated central or intermediate portion of the wall 105.

[0115] In some embodiments, the cooling holes are generated by additive manufacturing. This renders the manufacturing process faster. However, in other embodiments, some or all the cooling holes can be formed by drilling once the liner 103 has beenmanufactured by additive manufacturing. If the liner is formed by a plurality of ringshaped portions welded to one another, cooling holes can be machined in each portion prior to welding, or after welding the portions to one another. The cooling holes can be machined by electrical discharge machining (EDM).

[0116] In the embodiment of Figs 6, 7, 7A the cooling holes 171 are distributed according to annular arrays of cooling holes 171, sequentially spaced from one another from the forward end 103F to the aft end 103 A of the liner 103. Each annular array of cooling holes is positioned at a bridge 173, which connects two consecutively arranged ring panels 175 of the side wall 105 of the liner 103.

[0117] In some embodiments, each array of cooling holes 171 is associated with one or more lips or projections 177, which project from the inner surface of the side wall 105 and extend in a forward-to-aft direction inside the wall 105 of the liner 103. In the embodiment shown in Figs. 7, 7A, each lip 177 is ring-shaped and extends around the entire circumference of the inner surface of the side wall 105. Each lip 177 forms a respective annular slot which forms a guide for a cooling fluid which enters the combustion chamber 7.1 through the cooling holes 171. The lips 177 are oriented such as to impart to the cooling fluid a velocity component which is tangent to the inner surface of the side wall, i.e. oriented in a forward-to-aft direction inside the combustion chamber 7.1. Each lip 177 forms a ring-shaped gap 179 in front of the respective annular array of cooling holes 171.

[0118] In preferred embodiments, the lips 177 are generated by additive manufacturing while forming the side wall 105 and form, therefore, a monolithic body therewith. If the side wall 105 is manufactured by producing individual ring-shaped portions which are subsequently welded to one another, each portion is manufactured by additive manufacturing with the respective lips 177 forming a monolithic integral body with the ring-shaped portion of the wall 105.

[0119] The liner can further comprise dilution holes 181, which extend from the outer surface to the inner surface of the side wall 105. The dilution holes 181 can be distributed in various ways along the length of the wall 105 of the liner 103, to optimize the fuel combustion and the flow of combustion gas along the liner 103. The distribution of dilution holes illustrated in the drawing is merely illustrative.

[0120] In some embodiments the dilution holes 181 can be generated in the wall 105 of the liner by additive manufacturing, i.e. during the additive manufacturing process which generates the liner 103 or part thereof. In other embodiments, the dilution holes 181 can be added once the liner 103, or a ring-shaped portion thereof has been generated by additive manufacturing. For instance, the dilution holes 181 can be machined by electrical discharge machining (EDM).

[0121] The liner shown in Figs. 6, 7, 7A can be manufactured as a single piece by additive manufacturing starting from the forward end 103F and ending with the aft end 103 A. The cooling holes 171 and the dilution 181 are formed during the additive manufacturing process, along with the lips 177.

[0122] The liner 103 can also comprise one or more additional holes in the side wall 105 thereof, for connection of cross fire tubes and / or sensors, transducers, and other instruments useful for the control of the combustion process. These additional holes are not shown.

[0123] At the end of the additive manufacturing process, the liner 103 is completely formed.

[0124] In other embodiments, the cooling holes 171 and / or the dilution holes 181 can be machined in the wall 105 after the latter has been formed.

[0125] If the dimension of the liner so requires, the wall 105 can be manufactured by separately forming by additive manufacturing two or more ring-shaped portions of the wall 105 in separate processes. The ring-shaped portions can then be welded together to form the liner 103. Each ring-shaped portion is manufactured monolithically with the respective lips 177. The cooling holes 171 and / or the diffusion ports 181 can be formed by additive manufacturing in each ring-shaped portion of the side wall 105, or can be machined therein after manufacturing of the ring-shaped portion, before or after welding the ring-shaped portions together.

[0126] Figs. 8 and 9 illustrate an embodiment of the transition piece 113. In this embodiment, the transition piece 113 comprises an inner duct 201 which extends in a forward-to-aft direction from an upstream end, or forward end, labeled 20 IF to a downstream end, or aft end 201 A. The inner duct 201 forms a hot gas path 207 whichextends from the liner 103 to the stationary nozzles 53, where the expansion flow path of the expander 3 starts. The inner duct 201 has an inner surface 20 IB facing the hot gas path, and an outer surface 201C.

[0127] The outer surface 201C of the inner duct 201 faces an outer duct 205, which extends from an upstream end, or aft end 205F, to a downstream end, or aft end 205 A. The outer duct 205 surrounds the inner duct 201 and has an inner surface 205B which faces the inner duct 201, and an outer surface 205C which faces the aft plenum 131.

[0128] The cooling annulus 113A is formed between the inner surface 205B of the outer duct 205 and the outer surface 201C of the inner duct 201.

[0129] The cooling annulus 113 A can be fluidly coupled with the hot gas path 207 through one or more effusion cooling holes 209. Each effusion cooling hole 209 extends through the thickness of the inner duct 201 from the outer surface to the inner surface thereof.

[0130] In some embodiments, the inner duct 201 and the outer duct 205 are manufactured by additive manufacturing as a single monolithic block, in the same 3D-print- ing process. The effusion cooling holes can be manufactured by additive manufacturing during the process of generating the inner duct 201 and outer duct 205.

[0131] The downstream, i.e. aft end 201 A of the inner duct 201 and the downstream, or aft end 205 A of the outer duct 205 can be coupled to one another by a flange 211 surrounding the hot gas path and closing a downstream end of the cooling annulus 113 A. If the outer duct 205 and the inner duct 201 are manufactured by additive manufacturing in the same process, with the inner and outer ducts growing simultaneously from one end toward the other end thereof, the additive manufacturing process can start from the flange 2011 and proceed further from the aft end 201 A and 205 A of the inner duct 201 and of the outer duct 205 towards the forward end 20 IF and 205F of the inner duct 201 and of the outer duct 205 respectively. During the additive manufacturing process, the effusion cooling holes 209 are also generated in the inner duct 201.

[0132] Thus, the inner duct 201, the outer duct 205 and the flange 211 form in this embodiment a monolithic structure manufactured by additive manufacturing in thesame additive manufacturing sequence.

[0133] According to a different embodiment, the outer duct is 205 formed by a first shell and a second shell, which are manufactured separately from one another and separately from the inner duct 201, and connected to one another by welding, and further connected by welding to the inner duct 201.

[0134] In this embodiment, the inner duct 201 can be manufactured in one additive manufacturing sequence. The flange 211 can be manufactured during this first additive manufacturing sequence monolithically with the inner duct. The resulting transition piece component generated in this additive manufacturing sequence is shown in a sectional axonometric view in Fig.10, while Fig.11 shows a full axonometric view of the entire transition piece component.

[0135] In a modified embodiment, the flange 211 can be manufactured separately from the inner duct 201 and welded thereto afterwards, for instance by electron-beam welding.

[0136] The effusion cooling holes 209 can be produced by additive manufacturing during this manufacturing step.

[0137] The outer duct 205 is produced by additive manufacturing in two separate steps, each step producing a portion of the outer duct 205 in form of an outer shell. Fig.12 illustrates one of said shells, the other being substantially symmetrical. In Fig.13 the two shells, labeled 205X and 205 Y are welded to one another along a welding line 206. While in Fig. 13 the outer duct 205 produced by welding together the two shells 205X and 205Y is shown in isolation, it shall be understood that the two shells 205X and 205 Y are actually welded to one another after placing them around the inner duct 201. The aft end of each shell 205X, 205Y is welded to the flange 211.

[0138] If the transition piece 113 is produced by assembling three separate pieces 201, 205X, 205 Y which are manufactured separately, the effusion cooling holes 209 can be machined in the inner duct 201 before welding the two shells 205X, 205 Y therearound.

[0139] Producing the transition piece 113 by additive manufacturing as described above, the inner duct 201 and / or the outer duct 205 can have a thickness which ishigher than usually achievable the manufacturing technique of the current art. Specifically, a higher ratio between the thickness of the duct 201, 205, and equivalent diameter of the hot gas path can be achieved. In some embodiments the ratio between the thickness of the inner duct 201 and / or of the outer duct 205 and the equivalent diameter of the hot gas path can be equal to or higher than 0.020, preferably equal to or higher than 0.025 along the entire extension of the transition piece. The equivalent diameter of the transition piece can be defined aswhere S is the area of the cross section of the hot gas path.

[0140] 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.

Claims

CLAIMS1. A combustor for an expander, the combustor comprising:- a casing;- in said casing, a liner having a forward end, an aft end, and a side wall between the forward end and the aft end; wherein the side wall has an outer surface and an inner surface;- a burner at the forward end of the liner; wherein the burner is fluidly coupled with a fuel inlet and an oxidant inlet;- a transition piece at the aft end of the liner;- a sleeve arranged around the liner, between the liner and the casing; wherein the sleeve divides a space between the casing and the liner into an inner annular space and an outer annular space; wherein the outer annular space surrounds the inner annular space; wherein the sleeve comprises a forward end and an aft end; and wherein the forward end of the sleeve is coupled to an inner surface of the casing;- a first process gas inlet, fluidly coupled with the inner annular space;- a second process gas inlet, fluidly coupled with the outer annular space in a position downstream of the forward end of the sleeve and downstream of the aft end of the liner; wherein a thermal insulation chamber adapted to be filled with process gas is formed between the second process gas inlet and the forward end of the sleeve, the insulation chamber extending around the sleeve and the liner.

2. The combustor of claim 1, wherein the thermal insulation chamber is closed upstream of the second process gas inlet, such that the process gas filling the thermal insulation chamber is stagnant in said thermal insulation chamber.

3. The combustor of claim 1, wherein the forward end of the sleeve is positioned in an intermediate position between the forward end of the liner and the aft end of the liner.

4. The combustor of any one of the preceding claims, further comprising a forward plenum positioned at the forward end of the liner and fluidly coupled with the inner annular space.

5. The combustor of claim 4, wherein the forward plenum surrounds the forward end of the liner and extends upstream thereof.

6. The combustor of claim 4 or 5, wherein the sleeve fluidly separates the forward plenum and the outer annular space from one another.

7. The combustor of any one of claims 4 to 6, wherein the forward end of the liner extends upwards beyond the forward end of the sleeve in the forward plenum.

8. The combustor of any one of claims 4 to 7, wherein the first process gas inlet is positioned at the forward plenum.

9. The combustor of any one of claims 4 to 8, wherein the thermal insulation chamber is fluidly coupled with the forward plenum, to generate a coolant flow in an aft to forward direction through the thermal insulation chamber.

10. The combustor of any one of the preceding claims, further comprising an aft plenum at the aft end of the liner; wherein the aft plenum is fluidly coupled with the outer annular space; and wherein the outer annular space extends from the aft plenum toward the forward end of the liner.

11. The combustor of claim 10, wherein the second process gas inlet is positioned at the aft plenum.

12. The combustor of claim 10 or 11, wherein the aft plenum surrounds the transition piece.

13. The combustor of any one of the preceding claims, wherein the liner comprises a plurality of cooling holes extending through the side wall of the liner, from the outer surface to the inner surface thereof; wherein the cooling holes are fluidly coupled with the forward plenum and with the inner annular space.

14. The combustor of any one of the preceding claims, wherein the liner comprises a plurality of dilution holes, extending through the side wall of the liner,from the outer surface to the inner surface thereof; wherein the dilution holes are fluidly coupled with the forward plenum and with the inner annular space.

15. The combustor of any one of the preceding claims, wherein the inner annular space is fluidly coupled at the aft end thereof with a cooling annulus of the transition piece, the cooling annulus being formed between an inner duct and an outer duct of the transition piece, the inner duct forming hot gas path being adapted to fluidly couple the liner with an expansion flow path of an expander.

16. The combustor of claim 15, wherein the transition piece comprises a plurality of cooling holes which extend from the cooling annulus to the hot gas path.

17. The combustor of 15 or 16, when dependent on at least claim 4, wherein the aft plenum extends around the outer duct of the transition piece.

18. The combustor of any one of the preceding claims, wherein the burner is coupled with a forward end closure of the liner.

19. The combustor of claim 18, when depending on at least on claim 3, wherein the forward end closure of the liner comprises a plurality of apertures, fluidly coupled with the forward plenum.

20. The combustor of any one of the preceding claims, wherein the combustor is a can-type combustor comprising a plurality of combustor units arranged around an axis.

21. The combustor of any one of claims 1 to 19, wherein the combustor comprises a cylindrical seat surrounding the liner and the sleeve; wherein the liner and the sleeve project from the cylindrical seat into an annular plenum; and wherein the transition piece is positioned in the annular plenum22. The combustor of any one of claims 1 to 19, wherein the combustor is an annular combustor or a cannular combustor.

23. The combustor of any one of the preceding claims, comprising anigniter.

24. The combustor of claim 23, wherein the igniter is selected from the group comprising: a laser system, a hot spot glow plug, a high energy spark plug, or combinations thereof.

25. An expander comprising: an expander casing; a rotor adapted to rotate in the expander casing; and a combustor according to any one of the preceding claims.

26. The expander of claim 25, wherein the combustor comprises at least one liner having a longitudinal axis, and wherein the longitudinal axis of the expander forms with a rotation axis of the rotor an angle between 0° and 80°, or between 0° and 60°, or between 15° and 40°.

27. A power generating system comprising: an expander comprising: an expander casing, a rotor adapted to rotate in the expander casing; an expansion flow path; a combustor according to any one of claims 1 to 24; 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 the first process gas inlet of the combustor, 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 the second process gas inlet of the combustor, 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 fluidly coupled with the oxidant inlet of the combustor; and a fuel supply line fluidly coupled with the fuel inlet of the combustor.

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