Methods for start-up operations of gas turbines with highly-reactive fuels

Abstract

The innovative method serves for safe start-up operation of a gas turbine (100) and is aimed at reducing, or even eliminating, risks deriving from uncombusted fuel, particularly if the fuel is a highly reactive fuel, in a gas turbine during its "start-up" period, particularly in case of "hot-restart". As known, a gas turbine (100) comprises a compressor section (110) and a combustor section (120) and an expander section (130) and an exhaust section (140). According to the innovative method, during a start-up period of the gas turbine (100) a purging gas is flowed in at least a portion of the combustor section (120) and / or in at least a portion of the expander section (130) and / or in at least a portion of the exhaust section (140). In particular, the purging gas is flown during the ignition phase.

Description

TITLEMethods for Start-Up Operations of Gas Turbines with Highly-Reactive FuelsDESCRIPTIONTECHNICAL FIELD

[0001] The subject matter disclosed herein relates to methods for start-up operation of gas turbines, in particular if a highly reactive fuel is used, and gas turbines implementing such methods during start-up, in particular during so- called “hot-restart”, i.e. when a gas turbine is started a short time after being stopped.BACKGROUND ART

[0002] As known, a gas turbine includes essentially a compressor section, a combustor section, an expander section, and an exhaust section; these sections are fluidly coupled. In particular the expander section may be divided into expander portions; for example, there may be a high-pressure portion and a low-pressure portion fluidly coupled between each other. The high-pressure portion may have a first shaft and the low-pressure portion may have a second shaft; the first shaft and the second shaft are typically separate and mechanically uncoupled or unconnected; the shaft of the high-pressure portion of the compressor is typically mechanically coupled or connected to the shaft of the compressor section.

[0003] A “start-up” period of a gas turbine is a period of time that goes from when the gas turbine is stationary, i.e. its compressor and expander are not rotating, to when the gas turbine is rotating thanks to combustion of fuel in thecombustor. The “start-up” period may be considered successfully finished when ignition occurs; typically, at the end of the “start-up” period the gas turbine rotates at a reduced speed, for example 25% of full speed.

[0004] At the beginning of the “start-up” period, a device accelerates the compressor and the expander from zero rotation speed to a certain rotation speed. This device, that may be called “starter device” or “helper device”, is typically a motor, for example an electric motor or a diesel engine. Such rotation may be maintained for a short period of time, for example a couple of minutes.

[0005] Thereafter, the so-called “ignition” phase starts: the fuel is injected in the combustor chamber so that it mixes with the oxidizer (often compressed air from the compressor) and sparks are generated so that combustion of the fuel may start in the combustor chamber. The “ignition” phase lasts for a short time, for example 60 seconds. During the “ignition” phase one or more flames establish in the combustion chamber; in this case, the “ignition” phase ends successfully; otherwise, it ends unsuccessfully. Depending on if establish late or do not establish, some or all of the fuel injected during the “ignition” phase may be left uncombusted and flow downstream the combustor section; it may flow along the flow path and reach the outlet of the expander section.

[0006] The “ignition” phase is typically followed by a so-called “warm-up” phase and a so-called “initial acceleration” phase and a “final acceleration” phase. During the “warm-up” phase, the gas turbine rotates relatively low, for example 25% of full speed; at the beginning of the “warm-up” phase, the quantity of fuel is often reduced, e.g. 20% with respect to the “ignition” phase. During the “initial acceleration” phase, the gas turbine is accelerated to e.g. 60% of full speed. During the “final acceleration” phase, the gas turbine is accelerated to 90-100% of full speed. Typically, the “starter device” or “helper device” is deactivated after the “initial acceleration” phase and before the“final acceleration” phase.

[0007] From the above, it is evident that during the “start-up” period there may be some uncombusted fuel in the gas turbine, especially downstream the combustor section, for example in the expander section or in the exhaust section, due to the injection of fuel during the “ignition” phase.

[0008] The uncombusted fuel may cause problems of unwanted combustion outside the combustion chamber and / or of explosions in the gas turbine.

[0009] Such problems are particularly serious in the regions of the main flow path of the gas turbine where the flow speed is low (for example at the outlet of the expander or at the exhaust section).

[0010] Such problems are particularly serious in the regions of the main flow path of the gas turbine where the temperature of the parts is high (for example at the outlet of the combustor, at the inlet of the expander, in the transition piece connecting the outlet of the combustor to the inlet of the expander). In fact, if the temperature of parts in contact with the main flow is sufficiently high and if the gas mixture in the main flow is sufficiently rich in uncombusted fuel, combustion may be triggered.

[0011] It is to be noted that at the beginning of a “start-up” phase (for example during the “ignition” phase and the “warm-up” phase), the rotation speed of the gas turbine is relatively low and thus also the flow speed of the gasses flowing in the main flow path of the gas turbine is relatively low.

[0012] It is also to be noted that during a “hot-restart”, i.e. when a gas turbine is started a short time after being stopped, many parts of the gas turbine are already quite hot at the beginning of the “ignition phase”.SUMMARY

[0013] Therefore, it would be desirable to reduce, or even eliminate, risks deriving from uncombusted fuel, in particular highly reactive fuel, in a gas turbine during its “start-up” period, in particular in case of “hot-restart”.

[0014] According to a first aspect, the subject matter disclosed herein relates to innovative methods. The methods serve for safe start-up operation of a gas turbine comprising a compressor section and a combustor section and an expander section and an exhaust section. During a start-up period of a gas turbine, in particular during its ignition phase, a purging gas is flowed in at least a portion of the combustor section and / or in at least a portion of the expander section and / or in at least a portion of the exhaust section.

[0015] According to a second aspect, the subject matter disclosed herein relates to innovative gas turbines. The gas turbines are configured to carry out an innovative method, i.e. to flow a purging gas in at least a portion of the combustor section and / or in at least a portion of the expander section and / or in at least a portion of the exhaust section during a start-up period, in particular during an ignition phase.BRIEF DESCRIPTION OF THE DRAWINGS.

[0016] A more complete appreciation of the disclosed embodiments of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:Fig. 1 shows a simplified exemplary block diagram of a first embodiment of an innovative gas turbine provided with a combustor section,Fig. 2 shows a simplified exemplary block diagram of a second embodiment of an innovative gas turbine provided with the combustor section,Fig. 3A shows a cross-section view of a first example of a first portion of an embodiment of an innovative gas turbine provided with a spring -loaded device in a first position.Fig. 3B shows a cross-section view of a first example of a first portion of an embodiment of an innovative gas turbine provided with the spring -loaded device in a second position.Fig. 3 shows a cross-section view of a first example of a first portion of an embodiment of an innovative gas turbine.Fig. 4A shows a cross-section view of a second example of a first portion of an embodiment of an innovative gas turbine for purging gas in a wheel space cavity.Fig. 4 shows a cross-section view of a second example of a first portion of an embodiment of an innovative gas turbine.Fig. 5A shows a cross-section view of third example of a first portion of an embodiment of an innovative gas turbine for purging gas in a wheel space cavity.Fig. 5 shows a cross-section view of a third example of a first portion of an embodiment of an innovative gas turbine.Fig. 6A shows a cross-section view of an example of a double shaft gas turbine.Fig. 6 shows a cross-section view of an example of a second portion of an embodiment of an innovative gas turbine.Fig. 7A shows a cross-section view of an example of a third portion of an embodiment of an innovative gas turbine, provided with a blowerFig. 7 shows a cross-section view of an example of a third portion of an embodiment of an innovative gas turbine, andFig. 8 shows an exemplary flow chart of an embodiment of an innovative method.DETAILED DESCRIPTION OF EMBODIMENTS

[0017] The innovative methods serve for safe start-up operation of gas turbines and are aimed at reducing, or even eliminating, risks deriving from uncombusted fuel in a gas turbine during a “start-up” period, in particular during an “ignition” phase. The idea is to add a purging gas to the gas mixture flowing through the gas flow of the gas turbine during the “start-up” period, in particular during the “ignition” phase. In this way, if such gas mixture contains uncombusted fuel, the percentage of fuel in the gas mixture is reduced (i.e. fuel gas is diluted) and so the risk of combustion and explosion is reduced.

[0018] Features of the innovative methods will be described in the following with not limiting reference to the embodiment of the gas turbine 100 of Fig. 1. Also the embodiment of the gas turbine 200 of Fig. 2 incorporates features of the innovative methods. Other gas turbines alternative to the ones of Fig. 1 and Fig. 2 may incorporate features of the innovative methods.

[0019] Gas turbine 100 comprises a compressor section 110 and a combustor section 120 and an expander section 130 and an exhaust section 140. The expander section 130 is mechanically coupled to the compressor section 110 through a shaft 190. The combustor section 120 is fluidly coupled to the compressor section 110. The expander section 130 is fluidly coupled to the combustor section 120. The exhaust section 140 is fluidly coupled to the expander section 140 As it is apparent, Fig. 1 is a very simplified schematic diagram of a gas turbine; each of these four sections includes several components. On the right of the expander section 130 there is shown a shaft180 configured to drive a load, for example an electric generator.

[0020] Gas turbine 100 comprises also a control unit 150 and several injectors 160A, 160B, 160C, 160D, 160E, 160F configured to inject purging gas at distinct points A, B, C, D, E, F of the gas turbines 100. The injectors 160A, 160B, 160C, 160D, 160E, 160F are controlled by the control unit 150; it is to be expected that the control unit 150 may perform other controls for other purposes; however, it is not to be excluded that control unit 150 performs only the functions according to the subject matter described herein. In the embodiment of Fig. 1, the purging gas is contained for example in one tank 170 and all the injectors 160A, 160B, 160C, 160D, 160E, 160F are fluidly to the tank 170.

[0021] The main difference between the embodiments of Fig. 1 and Fig. 2 is that the expander section of Fig. 1 includes a single expansion portion while the expander section of Fig. 2 includes two expansion portions fluidly coupled; each of such expansion portions includes typically several expansion stages. Both embodiments of the innovative gas turbine will be better described later on.

[0022] As already anticipated, according to the subject matter described herein, during a start-up period of the gas turbine 100 a purging gas is flowed in at least a portion (or even the whole) of the combustor section 120 and / or in at least a portion (or even the whole) of the expander section 130 and / or in at least a portion of the exhaust section 140. In this way, the purging gas will add to the flowing gas mixture and will provide the mentioned advantageous effect. One or more distinct injection points are possible as clarified in following; however, injection in the compressor section 110 is excluded as useless.

[0023] The “purging gas” may be an inert gas or air or steam or any mixture thereof; water in the form of very small droplets may be considered equivalentsteam and may act as a “purging fluid”. According to some advantageous embodiments, the purging gas is a mixture of an inert gas and air. Advantageous inert gasses are N2 or CO2.

[0024] Typically, during the "start-up” period (specifically during the “ignition” phase), a fuel gas is fed to the combustor section through a primary fuel line. According to some embodiments (like e.g. the one of Fig. 1), the fuel gas is a highly reactive fuel, in particular hydrogen or acetylene or propane or butane or pentane or a blend thereof.

[0025] According to some embodiments (like e.g. the one of Fig. 1), the purging gas is flowed (A) in the combustion chamber of the combustor section 120; this is schematically represented by point A in Fig. 1 and injector 160A.

[0026] According to some embodiments (like e.g. the one of Fig. 1), the purging gas is flowed downstream of the combustor section 120 and upstream of the expander section 130; this is schematically represented by point B in Fig. 1 and injector 160B.

[0027] According to some embodiments (like e.g. the one of Fig. 1), the purging gas is flowed in a flow path of the expander section 130; this is schematically represented by points C, D, E in Fig. 1 and injectors 160C, 160D, 160E. Depending on the specific embodiment, injection may occur at one or more of these injectors.

[0028] According to some embodiments (like e.g. the one of Fig. 1), the purging gas is flowed in an initial part of the flow path of the expander section 130; this is schematically represented by point C in Fig. 1 and injector 160C.

[0029] According to some embodiments (like e.g. the one of Fig. 1), the purging gas is flowed in an intermediate part of the flow path of the expander section 130; this is schematically represented by point D in Fig. 1 and injector160D. In particular, it may be flowed between a high-pressure portion and a low-pressure portion of the expander section; this is schematically represented in Fig. 6 and will be better described later on.

[0030] According to some embodiments (like e.g. the one of Fig. 1), the purging gas is flowed in a final part of the flow path of the expander section 130; this is schematically represented by point E in Fig. 1 and injector 160E.

[0031] According to some embodiments (like e.g. the one of Fig. 1), the purging gas is flowed in the plenum cavity of the combustor section 140; this is schematically represented by point F in Fig. 1 and injector 160F.

[0032] According to some embodiments, the purging gas is flowed so to reach secondary flow zones of the expander section; this is schematically represented in Fig. 5 and Fig. 6 and will be better described later on.

[0033] According to some embodiments (like e.g. the one of Fig. 1), the purging gas is injected at a plurality of distinct points of the gas turbine. For example, in the gas turbine 100 of Fig. 1, there are six points schematically shown and labelled A, B, C, D, E, F and six corresponding injectors 160A, 160B, 160C, 160D, 160E, 160F.

[0034] According to some embodiments, one or more specific injectors are provided configured to inject only the purging gas; in this case, the one or more injectors are used only during the “start-up” period. According to alternative embodiments, the purging gas is injected through one or more injectors used for a different purpose before the “start-up” period or after the “start-up” period.

[0035] In general, purging gas may be flowed in the gas turbine during the whole “start-up” period. However, in order to deal with the risks described above at least during an “ignition” phase of the gas turbine 100 the purging gasis flowed in at least a portion of the combustor section 120 and / or in at least a portion of the expander section 130.

[0036] According to some embodiments, purging gas flow is started exactly when the “ignition” phase starts.

[0037] According to some embodiments, purging gas flow is stopped exactly when the “ignition” phase ends.

[0038] According to some embodiments, during at least an initial part of a “warm-up” phase of the gas turbine, i.e. sometime after the “ignition” phase, the purging gas is flowed in at least a portion of the combustor section and / or in at least a portion of the expander section. This may be done in order to ensure an enhanced safety level. In this case, after the “warm-up” phase of the gas turbine the purging gas flow is typically stopped.

[0039] According to some embodiments, some time before the “ignition” phase, the purging gas is flowed in at least a portion of the combustor section and / or in at least a portion of the expander section. This may be done in order to ensure an enhanced safety level.

[0040] As it is apparent from the above explanation, it is particularly useful to flow the purging gas in case of “hot restart” of the gas turbine. In fact, in this case, risks of unwanted combustions and / or explosions are higher. However, the practice of flowing purging gas, especially during the “ignition” phase, is useful in any case of “start-up”.

[0041] The purging gas flow rate may be specifically regulated so to avoid explosions and / or to avoid combustions in the expander section 130 or the exhaust section 140 of the gas turbine 100. It is to be understood that, according to simple solutions, the flow rate of the purging gas may be fixed and predetermined.

[0042] It is not to be excluded that during the “start-up” period, even before the “ignition” phase, a purging gas is flowed in a combustion chamber of the combustor section and downstream of a combustion chamber of the combustor section, in particular all along the flow path of the expander section and of the exhaust section. For example, purging gas flow may start exactly when the “start-up” period starts.

[0043] The flow chart 800 of Fig. 8 corresponds to a specific embodiment of innovative method; however, many other alternatives are possible. Block 810 is the begin of the method and corresponds to the begin of a “start-up” period of a gas turbine. Block 860 is the end of the method a corresponds to the end of the “start-up” period of the gas turbine. At block 820, the control unit waits till the begin of the “injection” phase of the gas turbine. At block 830, the control unit controls the one or more injectors so to start purging gas injection in the gas turbine. At block 840, the control unit waits till the end of the “injection” phase of the gas turbine; during this time injection of the purging gas continues. At block 850, the control unit controls the one or more injectors so to stop purging gas injection in the gas turbine. According to this embodiment, purging gas flow is started and stopped exactly in coincidence with the begin and end of the “injection” phase.

[0044] Any of the embodiments of the innovative method as just described may be incorporated into a gas turbine. In this way, an innovative gas turbine configured to carry out an innovative method is obtained. As it is apparent, an innovate gas turbine, such as e.g. gas turbine 100 in Fig. 1 or gas turbine 200 in Fig. 2, comprises a compressor section, such as e.g. section 110 in Fig. 1 or section 210 in Fig. 2, a combustor section, such as e.g. section 120 in Fig. 1 or section 220 in Fig. 2, an expander section, such as e.g. section 130 in Fig. 1 or section 230 in Fig. 2, and an exhaust section, such as e.g. section 140 in Fig. 1 and section 240 in Fig. 2.

[0045] According to the embodiment of Fig. 1, the expander section 130 is mechanically coupled to the compressor section 110 through a shaft 190. The combustor section 120 is fluidly coupled to the compressor section 110. The expander section 130 is fluidly coupled to the combustor section 120. The exhaust section 140 is fluidly coupled to the expander section 130. As it is apparent, Fig. 1 is a very simplified schematic diagram of a gas turbine; each of these four sections includes several components. On the right of the expander section 130 there is shown a shaft 180 configured to drive a load, for example an electric generator.

[0046] Gas turbine 100 comprises also a control unit 150 and several injectors 160A, 160B, 160C, 160D, 160E, 160F configured to inject purging gas at distinct points A, B, C, D, E, F of the gas turbines 100. The injectors 160A, 160B, 160C, 160D, 160E, 160F are controlled by the control unit 150; it is to be expected that the control unit 150 may perform other controls for other purposes; however, it is not to be excluded that control unit 150 performs only the functions according to the subject matter described herein. In the embodiment of Fig. 1, the purging gas is contained for example in one tank 170 and all the injectors 160A, 160B, 160C, 160D, 160E, 160F are fluidly to the tank 170.

[0047] According to the embodiment of Fig. 2, the expander section includes a first expansion portion 230 A and a second expansion portion 230B. The first expansion portion is mechanically coupled to the compressor section 210 through a shaft 290. The combustor section 220 is fluidly coupled to the compressor section 210. The first expansion portion 230A is fluidly coupled to the combustor section 220. The second expansion portion 230B is fluidly coupled to the first expansion portion 230A, but not mechanically coupled to the first expansion portion 230A. The exhaust section 240 is fluidly coupled to the second expansion portion 230B. As it is apparent, Fig. 2 is a very simplifiedschematic diagram of a gas turbine; each of these four sections includes several components. On the right of the expansion portion 230B there is shown a shaft 280 configured to drive a load, for example an electric generator. It is to be noted that shaft 290 and shaft 280 are separate as well as not coupled or connected between each other.

[0048] Gas turbine 200 comprises also a control unit 250 and several injectors 260A, 260B, 260C, 260D, 260E, 260F configured to inject purging gas at distinct points A, B, C, D, E, F of the gas turbines 200. The injectors 260A, 260B, 260C, 260D, 260E, 260F are controlled by the control unit 250; it is to be expected that the control unit 250 may perform other controls for other purposes; however, it is not to be excluded that control unit 250 performs only the functions according to the subject matter described herein. In the embodiment of Fig. 2, the purging gas is contained for example in one tank 270 and all the injectors 260A, 260B, 260C, 260D, 260E, 260F are fluidly to the tank 270. It is to be noted that injector 260D is configured to inject purging gas in the middle between the first expansion portion 230A and the second expansion portion 230B, i.e. to add purging gas to the gas mixture exiting the first expansion portion 230A (a high-pressure expansion portion) before entering the second expansion portion 230B (a low-pressure expansion portion).

[0049] Injection of purging gas in a gas turbine will be better explained with non-limiting help of figures from 3 to 7.

[0050] These figures refer to the same gas turbine, that is a two-shafts turbine. Each of these solutions may be used and incorporated in the gas turbine independently from each other or combined in any possible way.

[0051] With non limiting reference to Figs. 3 A, and 3B the gas turbine 100 is provided with at least the spring-loaded device 121. Advantageously thespring-loaded device 121 purging in a combustor transition piece preferably cold side through at least a hole 122, preferably a dilution hole.

[0052] Considering Figs. 3 A and 3B the spring-loaded device 121 comprises: a pipe 123 disposed vertically with respect to the combustor section 120 along the axis A of the pipe 123; a spring pull 124 able to move the spring-loaded device 121 up and down along the axis A of the pipe 123.

[0053] It is be noted that the pipe 123 of the spring-loaded device 121 is positioned with one end closest to at least the hole during at the beginning of the start-up period before the ignition phase, facilitating the feeding of purging gas into the combustor section 120, and moved away from at least the hole 122 by the action of the spring pull 124 after the start-up period, facilitating the compressor discharge air flow through at least the hole 122. In particular at the beginning of the start-up period, the spring-loaded pipe 121 connected to dilution holes 122 of the combustor, purged with high pressure inert gas or air or steam. After successful start-up period, the spring-loaded pipe 121 should move away from at least the hole 122 of the combustor, so that the normal sequence of the CDC (Compressor Discharge Casing) air purging through the dilution holes 122 could resume.

[0054] Advantageously "spring pull" or "pull type gas spring" is a type of gas spring that uses compressed gas to generate a pulling force. Unlike standard gas springs that push, these springs pull the piston inward into the cylinder. In this case after successful startup the spring pull 124 back the pipe 123 to move outward, so that the compressed discharge air flows through the hole 122.

[0055] In Fig. 3, an injector 310 (schematically represented) is located on a wall upstream of the combustor, in particular a wall upstream of the combustor fuel nozzles and the combustor liner. Fig. 3 does not show the combustor bit does show the transition piece 320 between the combustor liner and theexpander. The injector 310 is configured to inject purge gas at high pressure. Injection may occur in the plenum between the compressor and the combustor and the purge gas enters the combustion chamber together with compressed air.

[0056] Fig. 4A shows that the gas turbine comprises at least an injector 411 for purging gas in a forward portion and / or aft portion, of a wheel space cavity 412.

[0057] In particular the wheel space cavity is the area between the rotating turbine disc and the stationary diaphragm. This zone is critical for cooling and temperature management within the gas turbine. The injector for nitrogen injection into the wheel space cavity ensures that nitrogen is evenly distributed both in the forward and aft portions of the cavity. Preferably, nitrogen purging occurs on the cold side of the turbine, which is the part of the turbine not directly exposed to high-temperature combustion gases.

[0058] At the beginning of the “start-up” period, the injector 411 connected to wheel space cavity 412 of the high-pressure rotor, purged with high pressure inert gas, or air, or team. It’s an injection to cold section of the gas turbine parts, in particular of the wheel space cavity.

[0059] In Fig. 4, an injector 410 (schematically represented) is located in the transition piece 420, i.e. a member fluidly coupling the combustor chamber with the expander. The injector 410 is configured to inject purging gas at high pressure; a dedicated pipe may connect the injector 410 to a source of purging gas. Injection may occur just before the first stage nozzle of the high-pressure portion of the expander section. Furthermore, Fig. 4 schematically represents another injector 430 for injecting purging gas into secondary flow zones of the gas turbine; in this case, the injector 430 is configured to inject purging gas at high pressure in the rotor-stator wheel space region; a dedicated pipe mayconnect the injector 430 to a source of purging gas. Alternatively, a same pipe may be used for both the injector 410 and the injector 430.

[0060] Fig 5A shows a injector 531 connected to a wheel space cavity 551, and to a nozzle-inner casing cavity 521 introducing purging gas like high pressure inert gas, air, or steam into the wheel space cavity 551 and the nozzle-inner casing cavity 521. Therefore, the injection 531 is able to purge the purging gas on the cold section of an injection location like the wheel space cavity 551.

[0061] In Fig. 5, an injector 510 (schematically represented) is configured to inject purging gas at the first stage nozzles 520 of the high-pressure portion of the expander section. A dedicated pipe may connect the injector 510 to a source of purging gas. The purging gas may be ejected from the cooling holes of these nozzles.

[0062] In Fig. 5, an injector 530 (schematically represented) is configured to inject purging gas at the second stage nozzles 540 of the high-pressure portion of the expander section. A dedicated pipe may connect the injector 530 to a source of purging gas. The purging gas may be ejected from the cooling holes of these nozzles. Furthermore, Fig. 5 schematically represents another injector 550 for injecting purging gas into secondary flow zones of the gas turbine; in this case, the injector 550 is configured to inject purging gas at the wheel space region between the buckets and the nozzles; a dedicated pipe may connect the injector 550 to a source of purging gas. Alternatively, and more typically, a same pipe may be used for both the injector 530 and the injector 550. Preferably Fig. 6A shows a double shaft gas turbine, wherein the high-pressure HP and low pressure LP rotors are separated by a transition duct assembly 610 and define a wheel space cavity 613. In this embodiment the gas turbine 100, comprises at least an injector 612 able to introduce purging gas like high pressure inert gas or air or steam between the high- and the low-pressure rotorsin the wheel space cavity 613, preferably on the cold side of wheel space cavity 613.

[0063] The injector 612 is connected to the wheel space cavity 613, physically passing through the transition duct assembly 610 and the casing cavity 614, purging the gas in the wheel space cavity 613

[0064] The injector 612 can be a separate pipe or the extraction pipes from compressor to the turbine section in particular this injector involves a specific set of pipes designed to carry purging gas for purging purposes. These pipes are strategically placed to ensure effective distribution of purging gas within the designated areas. Purging on the cold side means that nitrogen is introduced into the wheel space cavity, like the space between the rotating parts (wheels) of the turbines, when the turbines are not in operation or are at a lower temperature.

[0065] In Fig. 6, an injector 610 (schematically represented) is located in the transition piece 620, i.e. a member fluidly coupling the high-pressure portion of the expander section to the low-pressure portion of the expander section. A dedicated pipe may connect the injector 610 to a source of purging gas. Furthermore, Fig. 6 schematically represents another injector 630 for injecting purging gas into secondary flow zones of the gas turbine; in this case, the injector 630 is configured to inject purging gas at the wheel space region; a dedicated pipe may connect the injector 630 to a source of purging gas. Alternatively, and more typically, a same pipe may be used for both the injector 610 and the injector 630.

[0066] According to Fig 7. A the gas turbine 100 comprises at least a blower 711 , a plurality of pipes 720, and an exhaust fame assembly 730.

[0067] At the beginning of the start-up period the blower 711 pumps purging gas like inert gas or air or steam in the exhaust fame assembly 730 through theplurality of pipes 720. The inert gas is injected to the cold section of the exhaust assembly 730 like an inner exhaust struct gap 714, an outer exhaust strut to casing gap 713 and a last wheel space cavity 712.

[0068] After the successful start-up period, the blower 711 pumps only air for cooling the exhaust frame assembly 730, maintaining the exhaust frame at the optimal temperature by following standard cooling procedures.

[0069] In Fig. 7, an injector 710 (schematically represented) is configured to inject purging gas between the last stage buckets 720 and the exhaust frame 730 of the low-pressure portion of the expander section. A dedicated pipe may connect the injector 710 to a source of purging gas.

[0070] In Fig. 7, an injector 740 (schematically represented) is configured to inject purging gas at the plenum cavity of the exhaust section of the gas turbine. A dedicated pipe may connect the injector 740 to a source of purging gas.

Claims

CLAIMS1. A method for start-up operation of a gas turbine (100), the gas turbine (100) comprising a compressor section (110) and a combustor section (120) and an expander section (130) and an exhaust section (140), wherein during a startup period before the ignition phase of the gas turbine a purging gas is flowed in a combustion chamber of the combustor section (120) and downstream of a combustion chamber of the combustor section (120).

2. The method of claim 1, wherein during a start-up of the gas turbine the purging gas is flowed in at least a portion of the combustor section (120) and / or in at least a portion of the expander section (130), through at least a spring loaded device (121).

3. The method of claim 1, wherein the purging gas is an inert gas or air or steam or a mixture thereof, in particular a mixture of an inert gas and air, the inert gas being in particular N2 or CO2.

4. The method of claim 1, wherein during the start-up period a fuel gas is fed to the combustor section (120) through a primary fuel line, the fuel gas being a highly reactive fuel, in particular hydrogen or acetylene or propane or butane or pentane or a blend thereof.

5. Then method of claim 1, wherein the gas turbine (100) comprising also the exhaust section (140), during a start-up period of the gas turbine a purging gas is flowed in at least a portion of the exhaust section (140).

6. The method of claim 1, wherein the purging gas is flowed (A) in the combustion chamber of the combustor section (120).

7. The method of claim 1, wherein the purging gas is flowed (B) downstream of the combustor section and upstream of the expander section.

8. The method of claim 1, wherein the purging gas is flowed (C, D, E) in a flow path of the expander section.

9. The method of claim 6, wherein the purging gas is flowed (C) in an initial part of the flow path of the expander section.

10. The method of claim 6, wherein the purging gas is flowed (D) in an intermediate part of the flow path of the expander section, in particular between a high-pressure portion of the expander section and a low-pressure portion of the expander section.

11. The method of claim 6, wherein the purging gas is flowed (E) in a final part of the flow path of the expander section.

12. The method of claim 1, wherein the purging gas is flowed (F) in the plenum cavity of the combustor section (140).

13. The method of claim 1, wherein the purging gas is flowed so to reach secondary flow zones of the expander section.

14. The method of claim 1, wherein the purging gas is injected at a plurality of distinct points (A, B, C, D, E, F) of the gas turbine (100).

15. The method of claim 1, wherein the purging gas is injected through an injector, the injector being used for a different purpose before the start-up period or after the start-up period.

16. The method of claim 1, wherein at least during the ignition phase of the gas turbine the purging gas is flowed in at least a portion of the combustor section (120) and / or in at least a portion of the expander section (130) and / or in at least a portion of the exhaust section (140).

17. The method of claim 14, wherein after the ignition phase of the gas turbine the purging gas flow is stopped.

18. The method of claim 14, wherein at least during at least an initial part of a warm-up phase of the gas turbine the purging gas is flowed in at least a portion of the combustor section (120) and / or in at least a portion of the expander section (130).

19. The method of claim 16, wherein after the warm-up phase of the gas turbine the purging gas flow is stopped.

20. The method of claim 1, wherein the purging gas flow is regulated so to avoid explosions and / or to avoid combustions in the expander section.

21. A gas turbine (100) comprising a compressor section (110) and acombustor section (120) and an expander section (130) and an exhaust section (140), the gas turbine (100) being configured to carry out the method of any preceding claims wherein the gas turbine (100) provided with at least the spring- loaded device (121).

22. The gas turbine (100) of claim 21, wherein the spring-loaded device (121) purging in a combustor transition piece preferably cold side through at least a hole (122).

23. The gas turbine (100) of claim 21, wherein the spring-loaded device(121) comprises: a pipe (123) disposed vertically with respect to the combustor section (120) along the axis (A) of the pipe (123); a spring pull (124) able to move the spring-loaded device (121) up and down along the axis (A) of the pipe (123).

24. The gas turbine (100) of claims 22 and 23, wherein the pipe (123) of the spring-loaded device (121) is connected with one end closest to at least the hole at the beginning of the start-up period, facilitating the feeding of purging gas into the combustor section (120).

25. The gas turbine (100) of claim 24, wherein the pipe (123) of the spring- loaded device (121) after the start-up period moves away from at least the hole(122) by the action of the spring pull (124), facilitating the compressor discharge air flow through at least the hole (122).

26. The gas turbine (100) of claim 21, comprising at least an injector (411) for purging gas in a forward portion and / or aft portion, of a wheel space cavity (412).

27. The gas turbine (100) of claim 26, wherein the injector (411) allows an injection of purging gas to cold section of the wheel space cavity.

28. The gas turbine (100) of claim 21, comprising at least an injector (531) connected to a wheel space cavity (551), and to a nozzle-inner casing cavity (521), wherein at least the injector (531) introduces purging gas into the wheel space cavity (551) and the nozzle-inner casing cavity (521).

29. The gas turbine (100) of claim 21, comprising at least an injector (612) able to introduce purging gas in a wheel space cavity (613) located between- pressure a high- and a low-pressure rotors,30. The gas turbine (100) of claim 29, wherein the injector (612) is connected to the wheel space cavity (613), physically passing through a transition duct assembly (610) and a casing cavity (614).

31. The gas turbine (100) of claim 21, comprising at least a blower (711) able to feed purging gas to an exhaust frame (730) through a plurality of pipes (720), preferably to the cold section of the exhaust assembly (730) 32. The gas turbine (100) of claim 21, comprising at least one injector (160A, 160B, 160C, 160D, 160E, 160F) and a control unit (150), wherein the at least one injector (160A, 160B, 160C, 160D, 160E, 160F) is fluidly coupled to a source (170) of a purging gas and is configured to inject (A, B, C, D, E, F) the purging gas into the gas turbine (100), wherein the control unit (150) is configured to control the at least one injector (160A, 160B, 160C, 160D, 160E, 160F).- l-

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