An ignition device including a hot spot, and expander including the ignition device

Abstract

The ignition device comprises a longitudinal support structure and an ignition rod housed in the support structure. The ignition rod extends parallel to the support structure, and terminates with an electrical heater tip projecting from a distal end of the support structure. The ignition device also comprises a heat dissipator in conductive heat exchange with the support structure and positioned at the proximal end of the support structure.

Description

An ignition device including a hot spot, and expander including the ignition deviceDESCRIPTIONTECHNICAL FIELD

[0001] The present disclosure pertains to igniters, i.e. ignition devices, for power generating turbomachines. Embodiments disclosed herein specifically refer to igniters adapted for use in oxyfuel combustion expanders or turbines, such as supercritical carbon dioxide expanders (sCO? expanders), and to expanders including such igniters.

[0002] As understood herein a SCO2 expander is an expander or turbine in which 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 specifically to improvements to the igniters, i.e. ignition devices, for igniting a mixture of process gas and fuel in an expander, in particularan expander or turbine for a supercritical carbon dioxide expander.SUMMARY

[0013] According to embodiments disclosed herein, an ignition device for a combustion engine, in particular an expander, is disclosed, comprising a longitudinal support structure including an outer tubular member having a proximal end and a distal end. The proximal end of the outer tubular member is integral with a head that is mechanically and thermally coupled with a heat dissipator in conductive heat exchange with the support structure, at the proximal end of the support structure. An ignition rod is housed in the support structure and extends parallel to the support structure and coaxial with the outer tubular member. The ignition rod ends with an electrical heater tip projecting from the distal end of the outer tubular member. A mechanical connector mechanically and thermally couples the head of the of the outer tubular member to the heat dissipator. The heat dissipator is thus attached at an end thereof to the longitudinal support structure and specifically to the outer tubular member thereof.

[0014] In some embodiments, the heat dissipator is in conducting heat exchange with the ignition rod.

[0015] Further features and embodiments are set forth in the attached claims and are described below and illustrated in the attached drawings.

[0016] According to another aspect, the subject matter disclosed herein concerns an internal combustion engine, comprising: a casing, a combustion chamber located within the casing, and an ignition device as outlined above. The supporting structure of the ignition device projects through a combustion chamber access port and the ignition rod projects into the combustion chamber, while the dissipator is located outside the casing of the internal combustion engine.

[0017] In some embodiments, the internal combustion engine is a turbine or expander, for instance a supercritical carbon dioxide including a combustor.BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Reference is now made briefly to the accompanying drawings, in which:Fig.1 illustrates a schematic of a power generation system including a supercriticalcarbon dioxide expander;Fig.2 is a sectional view of an expander, i.e. a turbine, in a simplified representation;Fig.3 is an enlarged and more detailed sectional view of a portion of the expander of Fig. 2, including an ignition device according to the present disclosure;Fig.4 is a side view of an ignition device;Fig.5 is a sectional view according to line V-V of Fig.4;Fig.6 is an enlargement of Fig.5;Fig.7 is an axonometric view of a clamping system adapted to connect the ignition device to the casing of the expander;Fig.8 is a schematic of the control circuit of the ignition device; andFigs.9 and 10 are schematics of a further embodimentDETAILED DESCRIPTION

[0019] The schematic of Fig. 1 illustrates a simplified power system including an oxyfuel cycle operating with supercritical carbon dioxide at the expander inlet (shortly SCO2 cycle), such as an Allam cycle, or NET Power oxy-fuel cycle.

[0020] 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. In some embodiments, the combustor assembly 7 comprises a plurality of combustors 8 (Fig.2), each provided with a combustion chamber 8.1, as will be described in more detail below.

[0021] In some embodiments, 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.

[0022] 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.

[0023] 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.

[0024] In some embodiments, the temperature at the inlet of the gas expansion flow path, i.e., at the inlet of the rotor of the expander can be at or above 800°C, and preferably at or below 1500°C.

[0025] 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.

[0026] 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.

[0027] Intermediate values of the upper limit and lower limit of each range mentioned above are also expressly disclosed herein.

[0028] 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 furtherchilled 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.

[0029] 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.

[0030] The compressed combustion gas, consisting mainly of carbon dioxide and delivered by the combustion gas compressor 23, is partly removed from the cycle through a discharge line 24. The major part of the compressed combustion gas is divided into a first part of recycled combustion gas and a second part of recycled combustion gas. The first part of recycled combustion gas is delivered through the cold side 17.2 of the regenerative heat exchanger 17 and is heated by heat exchange with the hot combustion gas flowing through the hot side 17.1 of the regenerative heat exchanger 17 and recycled to the expander 3 through a recycle line 25. The combustion gas recycled through recycle line 25 is fed to the combustor assembly 7 and mixed with combustion gas generated therein as will be described in more detail later.

[0031] 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 theoxidant 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.

[0032] 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.

[0033] The expander 3 may include an output shaft end 31 which can be integral with the central portion of the rotor, or can be assembled with the central portion of the rotor by bolting, welding, Hirth or spline connections, or the like, or a combination thereof. The mechanical power generated by 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.

[0034] 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.

[0035] In some embodiments, the outer casing 41 includes a forward casing portion 41.1 and an aft casing portion 41.2. The forward casing portion 41.1 of the outer casing 41 can be in the form of a barrel, i.e. can be monolithic, and can include a monolithic annular body, for example manufactured by forging, casting, additive manufacturing, or combination thereof.

[0036] 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.

[0037] 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.

[0038] A barrel -type structure the forward casing portion 41.1 and aft casing portion 41.2 of a vertically split outer of casing 41 is particularly adapted for a supercritical carbon dioxide expander, where the pressure of the process gas in the expansion flow path is substantially higher than in standard Bryton-cycle turbines.

[0039] 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.

[0040] 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. The bearing arrangements 45, 47 can be arranged in bearing housings, not shown in detail The output shaft end 31 of the rotor 43 can be drivingly coupled to the driven machine (electric generator 33 in the exemplary embodiment of Fig.1) through a joint schematically shown at 49.

[0041] 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.

[0042] 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.

[0043] 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

[0044] 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.

[0045] 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.

[0046] Each expansion stage includes an annular row of stationary blades 53, 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 combustor assembly 7 and the inlet of the expansion flow path.

[0047] 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.

[0048] In embodiments, the rotor 43 further comprises a forward shaft portion 65 andan 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.

[0049] 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.

[0050] With continuing reference to Figs 1 and 2, details of an embodiment of the combustor assembly 7 are described below with reference to Fig.3.

[0051] In the illustrated embodiment, the combustor assembly 7 includes a plurality of can-shaped 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 (Fig.3) formed in the forward casing portion 41.1 of the outer casing 41.

[0052] Each combustor 8 comprises a tubular 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.

[0053] 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).

[0054] Each liner 103 has a forward end 103F and an aft end 103 A. Each liner 103 further includes a generally cylindrical or 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] In some embodiments, the liner 103 of each combustor 8 can be surrounded by a generally tubular or cylindrical sleeve 115, which can be coaxial with the liner 103.

[0060] Each sleeve 115 comprises a forward end 115F and an aft end 115A. In some embodiments, 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.

[0061] 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 an annular abutment formed inside the cylindrical seat 101 and the sleeve 115 extends in the aft direction from the flange 115.1 towards the rotation axis A- A of the expander 3 from the flange 115.1 projectingoutside of the cylindrical seat 101.

[0062] In the embodiment of Fig.3 the forward end 115F of the sleeve 115 is positioned between the forward end 103F of the liner 103 and the flange 115.1. In other embodiments, the sleeve 115 can terminate at the flange 115.1, and the forward end 115F thereof will therefore be coincident with the flange 115.1. In yet further embodiments, the sleeve 115 can extend forward till the forward end 103F of the liner or even beyond the forward end 103F of the liner 103.

[0063] Each inner annular space 117 may 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.

[0064] Similarly, the outer annular space 119 can extend in the aft direction outside the cylindrical seat 101 of the combustor 8 towards the transition piece 113.

[0065] 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.

[0066] 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.

[0067] 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 first process 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.

[0068] 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 eachsleeve 115, i.e. in a position between the expansion flow path of the expander 3 and the forward end 115F of the sleeves 115.

[0069] 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, thermal insulating gas, consisting mainly of carbon dioxide at high pressure, which represents an efficient insulation material.

[0070] 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.

[0071] Each combustor 8 can further include an ignition device 129, which penetrates from the exterior of the outer casing 41 through the forward plenum and faces the combustion chamber 8.1. The ignition device 129 will be described in detail below with reference to Figs 4 to 6.

[0072] 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 combustors 8.

[0073] 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 inlets) 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.

[0074] 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.

[0075] 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.

[0076] 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 by the inner duct of the transition piece 113.

[0077] An embodiment of the above-mentioned ignition device 129 is shown in Figs 4, 5 and 6 and is described in detail below.

[0078] The ignition device 129 comprises a longitudinal support structure 201 along an axis X-X. The longitudinal support structure houses an ignition rod 203, which extends parallel to the support structure 201 and ends with an electrical heater tip 205, which from a distal end 201.1 of the support structure 201. The ignition device further includes a heat dissipator 209, at a proximal end of the longitudinal support structure 201, and in conductive heat exchange with the support structure 201.

[0079] When mounted on the expander, the position of the ignition device 129 is such that the electrical heater tip 205 projects at least partially inside the liner 103, such that a fuel-oxidant mixture present inside the liner 103 reaches an ignition temperature when the ignition device is turned on, to start combustion.

[0080] The position of the electrical heater tip 205, and therefore of the entire ignition device 129, can be selected based on the following considerations. The most appropriate position to rapidly reach an ignition temperature would be at or around the burner 107 facing the interior of the liner 103. This position, however, is the worst one from the perspective of the thermal load on the ignition device. The most peripheral position, i.e. near the wall of the liner 103 would be the most appropriate position to prevent thermal damages to the ignition device, and specifically to the electrical heater tip 205, since in this position the electrical heater tip 205 would be cooled by the cooling oxidant flow during normal operation of the expander, i.e. after ignition. However, the peripheral position is the less appropriate to reach an effective ignition of the fuel-oxidant mixture.

[0081] The actual position of the electrical heater tip 205 can be selected between these two end positions. If needed, the electrical heater tip 205 can be retractable. In such case, the electrical heater tip 205 can be moved toward the center of the liner during ignition and retracted at or outside the liner wall once the combustion of the fuel-oxidant mixture has commenced.

[0082] In some embodiments, the support structure 201 comprises an outer tubular member 211, which is coaxial with the ignition rod 203. The outer tubular member 211 has a distal end 211.1 and a proximal end 211.2. The proximal end 211.2 of the outer tubular member 211.1 is integral with a head 213 of the support structure 201. The head 213 and the outer tubular member 211 can be manufactured as a single, monolithic body, i.e. formed as a single block for instance by machining. The ignition rod 203 projects with the electrical heater tip 205 thereof from the distal end 211.1 of the outer tubular member 211.

[0083] In some embodiments, the head 213 can comprise an outer flange 213.1 adapted to provide a clamping feature to clamp the ignition device 129 to the outer casing of the expander, for instance to a corresponding flange affixed to the outer casing of the expander. Fig.7 illustrates a clamping arrangement adapted to connect the ignition device 129 to a combustion chamber access port 301. In this embodiment, the combustion chamber access port 301 includes a terminal flange 301.1, which can have a conical shape and which can be coupled with the flange 213.1 of the head. A pair of clamps 303 surround the flanges 301.1 213.1 therearound by means of bolts or tie rods 195.

[0084] In some embodiments, the head 213 is mechanically and thermally coupled with the heat dissipator 209. For example, a cup-shaped mechanical connector 215 connects the head 213 to the dissipator 209.

[0085] The dissipator 209 may comprise a cylindrical body 209.1 with an inner cavity 209.2, which can be coaxial to the cylindrical body 209.1. Circular dissipation fins 209.3 can extend around the cylindrical body 209.1 of the dissipator 209. The cavity 209.2 houses electrical connectors, as will be described in more detail below. The inner cavity 209.2 of the cylindrical body 209.1 can be closed at an upper end by a lid 209.10 and the lower end by a bottom wall 209.11, wherefrom an annular collar 209.12 projects and forms a seat for the mechanical connector 215.

[0086] The outer tubular member 211 houses a tubular electrical conductor 217, extending coaxially with and between the outer tubular member 211 and the ignition rod 203.

[0087] In some embodiments, a first gap 221 is formed between the outer tubular member 211 and the tubular electrical conductor 217. The first gap 221 is coaxial the support structure 201 and extends axially therein. Between the tubular electrical conductor 217 and the ignition rod 203 a second gap 219 is formed, which extends coaxially along the support structure 201 and inside the first gap 211.

[0088] In some embodiments, at least one of the first gap 221 and second gap 219 is filled with an electrically insulating material, which is preferably a good heat conductor. For instance, the electrically insulating material can be a ceramic material. The ceramic material can be poured in liquid form in the outer gap.

[0089] In some embodiments, both the first gap 221 and the second gap 219 are filled with an electrically insulating material having a good thermal conductivity. The same insulating material, for instance a ceramic material may be used to fill both gaps 221 and 219. To facilitate filling of the two gaps 221, 219, the tubular electrical conductor 217 can have one or a plurality of ports 217.1 along the axial extent which place the first gap 221 and the second gap 219 in communication with each other, to allow a pourable electrically insulating material to flow from one of said gaps into the other when the insulating material is in a liquid form, prior to curing or setting.

[0090] In some embodiments, the heat dissipator 209, in addition to being in heat-exchange contact with the head 213, is also in conductive heat exchange with the tubular electrical conductor 217 and, through the electrically insulating and thermally conducting material which fills the gaps 219, with the ignition rod 203. To provide a good heat conduction between the tubular electrical conductor 217 and the dissipator 209, the tubular electrical conductor 217 can include a flange 217.2, which can form an integral part of the tubular electrical conductor 217, as shown in Fig.6, or affixed thereto. The flange 217.2 is clamped between the head 213 and the mechanical connector 215. In some embodiments, washers 233 made of thermally conducting and electrically insulating material (such as aluminum oxide - AI2O3) can be positioned between each surface of the flange213.1 and the mechanical connector 215 on one side and the head 213 on the other side.

[0091] The ignition rod 203 may be electrically connected to a control circuit and to a source of electrical energy through a cable 235, which extends through the axial cavity209.2 of the dissipator 209. A further cable 237, which extends through the axial cavity 209.2, connects electrically the source of electric energy and the control circuit to the tubular electric conductor 217.

[0092] From a circuit perspective, the ignition rod may include an electrical heating resistor positioned at the electrical heater tip 205 and extending partially in the tubular member 211. The electrical heating resistor is coupled to a control circuit, adapted to power the electrical heating resistor, to measure a current flowing through the electrical heating resistor and to perform ancillary functions which are described below.

[0093] A schematic of the control circuit is illustrated in Fig.8. The control circuit is labeled 241. An electric power source 243, for instance an AC source at 110 V or 220 V is electrically coupled to the control circuit 241 through a circuit breaker 245. Through the circuit breaker 245, electric power is fed to a first AC / DC supplier 247, which is electrically couped to a switch 249 through a fuse 251. A further AC / DC supplier 259 provides DC electrical current to a controller 253 a and a start circuit 255, connected to a selector 257. The controller 253 controls opening and closing of the switch 249. Electric power is supplied through the switch 249, when the latter is closed, to a shunt resistor 265 and a series of resistors 261, 263. The two resistors 261 and 263 are housed in the ignition rod 203 and are in series with the shunt resistor 265. One of the two resistors 261, 263 is the actual heating resistor while the other of said resistors 261, 263 is a control resistor. Preferably, the actual heating resistor, for instance resistor 261, is located at the distal endof the ignition rod, which projects outside of the support structure, and specifically outside of the distal end 211.1 of the tubular member 211. The heating resistor can protrude fully or partly from the tubular member 211. The control resistor 263 is preferably surrounded by the tubular member 211 and is protected thereby.

[0094] The control resistor 263 can be a PTC resistor (aka PTC thermistor), i.e. a positive temperature coefficient resistor, i.e. a resistor the electrical resistance whereof increases with the temperature.

[0095] The control circuit 241 can operate in several modes, for instance in an ignition mode and in a stand-by or testing mode. The operation modes are selected through the selector 257. In the ignition mode, electric power flows, in an intermittent or continuous way, through the switch 249, the shunt resistor 265, the control resistor 265 and the electrical heating resistor 261. By Joule effect the temperature of the electrical heating resistor 261 is heated till an ignition temperature of the fuel-oxidant mixture in the combustor chamber is recached, to ignite the mixture and start operation of the expander.

[0096] The intensity of the electric current through the electrical heating resistor 261 is controlled by the PTC resistor 263, to prevent overcurrent and damages to the ignition device 129.

[0097] Ignition can be obtained using a duty-cycle operative mode of the control circuit. The duty-cycle operative mode can be controlled by controller 253, such that electric power is supplied initially with a low duty cycle, i.e. with a sequence of on and off time intervals of the switch 249, to achieve the desired ignition temperature in a more gradual manner. After pre-heating, an ignition step with a 100% duty cycle (switch 249 fixedly in a closed state) is performed until ignition of the fuel-oxidant mixture. Afterwards, the ignition circuit is turned off.

[0098] During normal operation of the expander, when burning of the fuel-oxidant mixture is self-sustained by the continuous feed of oxidant and fuel, the ignition device can remain in a non-operative condition. Heat is dissipated from the ignition device 129 through the dissipator 209, to maintain the components thereof at a suitable temperature preventing damages of the ignition device. The control circuit 241 can be switched in an

[0099] When the ignition device 129 is in a non-operative mode, i.e. is not in anignition phase, the control circuit 241 can be programmed to put the ignition device in a testing mode. The testing mode is a stand-by mode wherein the integrity of the ignition device can be periodically tested. This can be done by powering the circuit at regular intervals, and checking through the shunt resistor 265 whether electric current flows through the resistors 265, 261, 263.

[0100] The shunt resistor can be used also in the ignition mode, to check the intensity of current flowing through the resistors 265, 261, 263. Based on the features of the shunt resistor, the from the value of the electric current flowing through the shunt resistor and through the PTC an information on the temperature of the PTC resistor, and thus of the electrical heater tip 205 can be obtained.

[0101] In the above-described embodiment, the heat dissipator 209 and the longitudinal support structure 201 are arranged in a coaxial fashion, with the support structure 201 extending from an end of the heat dissipator 209. The mechanical connector 215 mechanically and thermally couples the body of the heat dissipator 209 and the support structure 201 to one another and is positioned at the end of the heat dissipator 209.

[0102] In other embodiments, the body of the heat dissipator 209 may project sideways at an angle, or include a portion of the heat dissipator 209 projecting sideways and including the heat dissipation fins 209.3. Figs. 9 and 10 illustrate a schematic of an embodiment wherein the heat dissipator is arranged with a set of dissipation fins extending sideways and at an angle with respect to the axis of the support structure 201. The same reference numbers designate the same or equivalent components in Figs. 9, 10 and in Figs. 5, 6. These components will not be described again.

[0103] Specifically, Fig.9 illustrates a sectional view similar to Fig. 5, according to line IX-IX of Fig.10. Fig.10 illustrates a top view according to line X-X of Fig.9.

[0104] In Figs. 9 and 10 the heat dissipator 209 comprises two main portions, namely: a coupler 209.20 adapted to mechanically and thermally connect the heat dissipator 209 to the support structure 201 through the mechanical connector 215; and a finned dissipating structure 209.21 projecting sideways at an angle a greater than zero, and possibly comprised between zero and 90°, to the axis of the support structure 201. The angle a is shown by way of example only and it shall be understood that the mutual inclination between the portions 209.20 and 209.21 may be different from the one shown. In someembodiments, the coupler 209.20 may be connected to or integrally formed with the mechanical connector 215. In some embodiments, the finned dissipating structure 209.21 may have a core 209.22 supporting the dissipation fins 209.3. The core 209.22 can have a rectangular cross-section as shown in Figs. 9 and 10. In other embodiments the core 209.22 may have a different shape, e.g. circular.

[0105] 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 which is specifically disclosed herein without departing from the scope of the invention as defined in the following claims.

Claims

CLAIMS1. An ignition device (129) for a combustion engine, in particular an expander, the ignition device comprising: a longitudinal support structure (201) comprising an outer tubular member (211) having a proximal end (211.2) and a distal end (211.1); wherein the proximal end (211.2) of the outer tubular member (211) is integral with a head (213) that is mechanically and thermally coupled with a heat dissipator (209) in conductive heat exchange with the support structure (201); an ignition rod (203) housed in the support structure (201), extending parallel to the support structure and coaxial with the outer tubular member (211), and ending with an electrical heater tip (205) projecting from the distal end (211.1) of the outer tubular member (211); wherein a mechanical connector (215) mechanically and thermally couples the head (213) of the of the outer tubular member (211) to the heat dissipator (209).

2. The ignition device (129) of claim 1, wherein the heat dissipator (209) is in conducting heat exchange with the ignition rod (203).

3. The ignition device (129) of claim 1 or 2, wherein the heat dissipator (209) comprises a hollow body (209.1) comprising a plurality of outer dissipation fins (209.3).

4. The ignition device (129) of claim 3, wherein electric cables (235, 237) connected to the ignition rod (203) extend through an inner cavity (209.2) of the hollow body (209.1).

5. The ignition device (129) of claim 3 or 4, wherein the hollow body (209.1) of the heat dissipator (209) is closed at a first end by a lid (209.10) and at a second end by a bottom wall (209.11), wherefrom an annular collar (209.12) projects and forms a seat for the connector (215). .

6. The ignition device (129) of any preceding claim, wherein the outer tubular member (211) houses a tubular electrical conductor (217), extending coaxially with and between the outer tubular member (211) and the ignition rod (203).

7. The ignition device (129) of claim 6, wherein the heat dissipator (209)is in conductive heat exchange with the tubular electrical conductor (217).

8. The ignition device (129) of claim 7, wherein the tubular electrical conductor (217) comprises a flange (217.2) clamped between the head (213) and the mechanical connector (215).

9. The ignition device (129) of claim 8, wherein a first thermally conducting and electrically insulating washer (233) is positioned between a first surface of the flange (217.2) of the tubular electrical conductor (217) and the mechanical connector (215); and wherein a second thermally conducting and electrically insulating washer (233) is positioned between a second surface of the flange (217.2) and the head (213) of the outer tubular member (211).

10. The ignition device (129) of any one of claims 6 to 9, wherein the tubular electrical conductor (217) is in conductive heat exchange with the heat dissipator (209).

11. The ignition device (129) of any preceding claim, wherein the outer tubular member (211) is at least partially filled with an electrical insulating material.

12. The ignition device (129) of any one of claims 6 to 10, wherein a first gap (221) between the outer tubular member (211) and the tubular electrical conductor (217) is filled with an electrical insulating material.

13. The ignition device (129) of any one of claims 6 - 10 and 12, wherein a second gap (219) between the tubular electrical conductor (217) and the ignition rod (203) is filled with an electrical insulating material.

14. The ignition device of any one of claims 11 to 13, wherein the electrical insulating material comprises a ceramic material.

15. The ignition device of any preceding claim, wherein the head (213) comprises a first flange (213.1) coaxial to the tubular member (211) and adapted to be mechanically clamped to a second flange (301.1) integral with a casing of the expander.

16. The ignition device (129) of any preceding claim, wherein the ignition rod (203) comprises an electrical heating resistor (261) positioned at the electrical heatertip (205), the electrical heating resistor (261) being coupled to a control circuit (241), adapted to measure a current flowing through the electrical heating resistor (261).

17. The ignition device (129) of claim 16, wherein the control circuit (241) comprises a shunt resistor (265) in series with the electrical heating resistor (261).

18. The ignition device (129) of claim 16 or 17, wherein the electrical heating resistor (261) is coupled in series with a control resistor (263), adapted to modify a current flowing through the electrical heating resistor (261) as a function of temperature.

19. The ignition device (129) of claim 18, wherein the control resistor is housed inside the outer tubular member (211), while the electrical heating resistor (261) at least partially projects from the distal end (211.1) of the outer tubular member (211).

20. The ignition device (129) of any one of claims 16 to 19, wherein the control circuit is adapted to measure a temperature of the electrical heating resistor (261) as a function of the current flowing through the electrical heating resistor (261).

21. The ignition device (129) of any one of claims 16 to 20, wherein the control circuit (241) is adapted to be switched between an ignition mode and a testing mode; wherein in the ignition mode the control circuit (241) performs an ignition cycle; and wherein in the testing mode the control circuit (241) performs a repetitive testing cycle to check integrity of the electrical heating resistor (261).

22. The ignition device (129) of any one of claims 16 to 21, wherein the control circuit (241) is adapted to adjust a powering duty cycle of the electrical heating resistor (261).

23. The ignition device (129) of any preceding claim, wherein the ignition rod (203) is retractable.

24. The ignition device (129) of any preceding claim, wherein the longitudinal support (201) extends from an axial end of the heat dissipator (209).

25. The ignition device (129) of claim 24, wherein the longitudinal support (201) and the heat dissipator (209) are coaxial.

26. The ignition device (129) of any one of claims 1 to 23, wherein the heatdissipator comprises a finned dissipating structure (209.21) mechanically and thermally coupled to the mechanical connector (215) and angled with respect to the support structure (201).

27. An internal combustion engine (3), comprising: a casing (41), a com- bustion chamber (8.1) located within the casing (41), and an ignition device (129) according to any one of the preceding claims; wherein: the supporting structure (201) of the ignition device (129) projects through a combustion chamber access port (301); the ignition rod (203) projects into the combustion chamber (8.1); and the heat dissipator (209) is located outside the casing (41).

28. The internal combustion engine (3) of claim 27, wherein the internal combustion engine is an expander comprising a combustor (8) and an expansion flow path.

29. The internal combustion engine (3) of claim 27, wherein the internal combustion engine is a supercritical carbon dioxide expander comprising a combustor and an expansion flow path.

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