Method of operating a combustion system, combustion system, and gas turbine engine including a combustion system - Patents.com

Abstract

A method is disclosed for enabling operation of a combustion system having at least two combustion zones arranged in series, typically for fuels with varying flame speeds. First, operating parameters of a gas turbine engine are determined (110). Control parameters of a control means configured to distribute a total fuel mass flow rate to the individual combustion zones are determined (120) depending on the operating parameters of the gas turbine engine. Information regarding the fuel composition is determined, particularly quantifying the relative proportion of at least one combustible species having a higher flame speed than a first combustible species (130). Depending on the information regarding the fuel composition, the control parameters of the control means 23 can be adjusted (140). The control parameters are transferred to the control means as control signals (150).

Description

[Technical Field]

[0001] The present disclosure relates to the subject matter set forth in the claims. [Background technology]

[0002] Combustion of hydrogen and synthesis gas containing hydrogen and / or hydrocarbon species with two or more carbon atoms in the fuel molecule, so-called C2+ hydrocarbons, is increasingly being discussed in the context of reducing net carbon dioxide emissions in power generation. In certain aspects, co-combustion of natural gas with hydrogen and / or combustibles containing C2+ species in various proportions is desirable. One advantage of such co-combustion is increased operational flexibility to accommodate the availability of each fuel. Preferably, the combustion system, which may be a gas turbine engine combustion system in some embodiments, can operate on a fuel composition containing natural gas and, in some embodiments, various fractions of either hydrogen or C2+ species, or, in other embodiments, a mixture of hydrogen and C2+ species. In further embodiments, operation on 100% natural gas, 100% hydrogen, 100% C2+ species, or a mixture of 100% hydrogen and C2+ species is understood to be within the above operating range.

[0003] Natural gas is generally understood as a gaseous combustible found on Earth as a fossil fuel, containing primarily methane, along with smaller proportions of other hydrocarbons and various non-hydrocarbon gases (which may include nitrogen, carbon dioxide, carbon monoxide, etc.). Generally, the methane content is 85% or greater by volume at 1013.25 hectopascals and 15°C. In other examples, the methane content in natural gas may be 90% or greater by volume, or 95% or greater by volume. In still other examples, methane may comprise 85% or greater by volume, 90% or greater by volume, or 95% or greater by volume of the total hydrocarbon content, all of which volume fractions are referenced to 1013.25 hectopascals and 15°C.

[0004] Hydrogen and / or C2+ species result in higher flame speeds and ignition potential than natural gas. Therefore, one issue when burning hydrogen and / or C2+ species in a combustion zone designed to operate with natural gas is potential combustion flashback. Conversely, an issue with burning natural gas in a combustion zone designed for the combustion of hydrogen and / or C2+ species can be flame blowout.

[0005] The problem of burning fuel compositions comprising natural gas and, in embodiments, either hydrogen or C2+ species in varying proportions, or in other embodiments, mixtures of hydrogen and C2+ species, in one and the same combustion system can be broadly considered to be a problem of burning fuels with different flame speeds, while avoiding flame blowout when burning a fuel with a relatively high proportion of combustible species with low flame speeds, and avoiding flashback when burning a fuel with a relatively high proportion of combustible species with relatively high flame speeds.

[0006] Flashback is a problem that becomes more severe as the temperature of the combustion fluid in which the fuel is combusted increases. Therefore, flashback, when burning fuels containing components with relatively high flame temperatures, must be addressed, for example, in staged combustion systems in which a downstream combustion zone is supplied with a hot, still-oxygen-rich fluid containing combustion products from an upstream combustion zone. Such combustion systems are typically known from gas turbine engines, where the fluid exiting the upstream combustion stage may or may not be partially expanded before being supplied to the downstream combustion zone.

[0007] US 7,216,486 B2 discloses several proposals to address this issue when burning natural gas, which may be mixed with various proportions of C2+ species. One proposed method is to shift the fuel mass flow distribution so that the relative fuel flow fraction in the upstream combustion stage increases and the relative fuel flow fraction in the downstream combustion stage decreases. It is assumed that a leaner mixture in the downstream combustion zone reduces the risk of flashback. However, if the total fuel mass flow rate is maintained constant, it is clear that the temperature of the combustion fluid supplied to the downstream combustion zone may increase, making flashback more likely. For this reason, US 7,216,486 B2 also proposes reducing the total fuel mass flow rate to lower the load on the gas turbine engine or shutting down the system completely if the C2+ fraction exceeds a certain threshold. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] U.S. Patent Application No. 2017-0059164A1 Summary of the Invention

[0009] The present disclosure aims to provide the subject matter mentioned at the outset. More specifically, a method for operating a combustion system is provided. The method, in one aspect, avoids the drawbacks of the art, more specifically the above-cited art. In a further aspect, the method is suitable for enabling operation of a combustion system with a fuel containing various proportions of combustible species having different flame speeds. In a more specific aspect, the method should be suitable for enabling operation of a combustion system with a fuel in which the combustible species consist of either 100% combustible species having a relatively low flame speed, 100% combustible species having a relatively high flame speed, or any mixture of combustible species having a relatively low and a relatively high flame speed. Said operation with a fuel having a varying composition of combustible species should be achieved without having to reduce the thermal output of the combustion system or the useful power of a gas turbine engine equipped with a combustion system operated in the proposed manner based on the change in the composition of combustibles.

[0010] In another aspect, a combustion system configured to perform the methods proposed herein is disclosed. In yet another aspect, a gas turbine engine to which the methods proposed herein may be applied is disclosed.

[0011] This is achieved by the subject matter set forth in claim 1 and the further independent claims. Further advantages and benefits of the disclosed subject matter, whether explicitly mentioned or not, will become apparent in view of the disclosure provided below.

[0012] Accordingly, a method of operating a combustion system is disclosed. The method includes supplying a flow of combustion fluid to the combustion system, flowing the flow of combustion fluid through the combustion system in an upstream-to-downstream direction, discharging a flow of fuel into the combustion system, and combusting the fuel flow with at least a portion of the flow of combustion fluid. To this extent, the method includes generating a flow of combustion gas and discharging the flow of combustion gas at a downstream end of the combustion system. Discharging the fuel flow into the combustion system includes allocating a first fuel mass flow fraction of the total fuel mass flow to a first combustion zone located relatively upstream of the combustion system and supplying at least a second fuel mass flow fraction of the total fuel mass flow to at least one second combustion zone located relatively downstream from the first combustion zone. The fuel stream includes a fuel having a fuel composition including a first relative fraction of a fuel composition consisting of a first combustible species having a first flame speed when combusted in a combustion fluid and at least one second relative fraction of a fuel composition consisting of at least one second combustible species having a second flame speed when combusted in a combustion fluid, the second flame speed being greater than the first flame speed. It is understood that the relative fraction of species may refer to one of a mass fraction and a volume fraction of the species as a fraction of the total fuel composition, among others. The method further includes quantifying at least one of the first relative fraction of the fuel composition and the second relative fraction of the fuel composition. It is understood that the second relative fraction can be determined directly, but in embodiments can also be derived indirectly from a measured relative fraction of another species, such as, for example, the first relative fraction of the fuel composition, i.e., the relative fraction of the first combustible species. It shall be understood hereinafter that a change in the second relative fraction of the fuel composition may similarly be expressed as a change in the first relative fraction of the fuel composition with an opposite algebraic sign.The method further includes controlling the allocation of fuel to a first fuel mass flow fraction of the total fuel mass flow such that, in a range between at least two values ​​of the first relative fraction of the fuel composition and the at least one second relative fraction of the fuel composition, the first fuel mass flow fraction of the total fuel mass flow, i.e., the fraction allocated to the relatively upstream first combustion zone, decreases with increasing second relative fraction of the fuel composition, and said first fuel mass flow fraction of the total fuel mass flow increases with decreasing second relative fraction of the fuel composition. Those skilled in the art will appreciate that the allocation may also be controlled depending on other operating parameters, such as, but not limited to, the total fuel mass flow rate supplied to the combustion system and the useful power output of a gas turbine engine into which the combustion system is integrated. The control of the fuel allocation to the first fuel mass flow fraction is controlled depending on the fuel composition, e.g., at least one combustible species fraction, and is controlled independently of and in addition to the control depending on other operating parameters. The control actions described herein may be performed when other operating parameters, such as the thermal power output of the combustion system or the useful power output of the gas turbine engine, do not change or are each held constant.

[0013] The terms "first" and "second" should not be construed as limiting the presence of exactly two of each feature. For example, the first and second combustion zones need not be the most upstream and most downstream combustion zones in a combustion system, and additional combustion zones intervening between the named first and second combustion zones are not excluded.

[0014] The combustion fluid may be any fluid in which a fuel may be combusted, or a mixture of any fluids in which a fuel may be combusted. Typically, but not exclusively, the combustion fluid may include or consist of air or other oxygen-containing gaseous fluids, and / or mixtures of air or other oxygen-containing gaseous fluids with steam and / or combustion products from a relatively upstream combustion zone.

[0015] Shifting a portion of the total fuel mass flow from a relatively upstream combustion zone to a relatively downstream combustion zone reduces the temperature of the fluid entering the relatively downstream combustion zone, thereby reducing the risk of flashback in the relatively downstream combustion zone. In particular, when the temperature of the combustion fluid entering the relatively upstream combustion zone is significantly lower than the temperature at the inlet of the relatively downstream combustion zone, as is typically the case, the overall risk of flashback in the combustion system can be significantly reduced, if not avoided. In a particular example, the relatively upstream combustion zone receives air from a fan or compressor, such as the compressor of a gas turbine engine, and the relatively downstream combustion zone receives a mixture of combustion products from the upstream combustion zone and residual air.

[0016] It should be noted that within the framework of this disclosure, the use of the indefinite article "a" or "an" does not in any way define singularity or exclude the presence of multiple named items or features. Thus, the indefinite article is used in the sense of "at least one" or "one or multiple."

[0017] The flame speed of a combustible species is defined as the speed at which the flame front moves relative to the unburned gas mixture. In combustion systems of the type disclosed herein, the velocity of the unburned mixture of combustion fluid and fuel is designed so that the flame front remains stationary and within an acceptable distance to the upstream combustor wall and / or internal fixtures. If the flame speed increases relative to the mixed convection velocity of the unburned combustion fluid and fuel, the flame front may move too close to the upstream combustor wall and / or internal fixtures, resulting in overheating and damage to the combustion system components. The flame speed of a combustible species is determined by methods known to those skilled in the art. For purposes of comparing species flame speeds used herein, the flame speeds are understood to be flame speeds determined at equal reference conditions for both combustible species, i.e., at the same temperature, pressure, and equivalence ratio. The reference conditions to which the flame speed refers can be selected to be representative of conditions within the combustion system. In the following, specific examples of first and second combustible species are provided, by way of non-limiting example, where methane is the first combustible species having a relatively low flame speed, and hydrogen or at least one C2+ hydrocarbon or C2+ alkane, or a mixture thereof, is at least one combustible species having a relatively high flame speed.

[0018] In some embodiments, the method includes online monitoring of the fuel composition, including at least quantifying the second fraction of the fuel composition and / or the ratio of the second relative fraction of the fuel composition to the first relative fraction of the fuel composition. An example of a method for determining fuel composition online and in real time, which may be applied in this context, is disclosed in DE 103 02 487 A1. This disclosed embodiment provides for accurate and dynamic adjustment of fuel distribution to a relatively upstream and at least one relatively downstream combustion zone. In other embodiments, two fuel streams containing different proportions of a first combustible species and at least one second combustible species may be mixed together via separate supply lines before being discharged into the combustion system, each of the supply lines having a control valve for controlling the respective fuel streams. In such cases, the relative first and second fractions of the resulting fuel composition may be determined through the respective valve strokes and may be compensated for, for example, by the temperature and pressure of the respective fuel streams upstream of the respective control valves.

[0019] Natural gas can have a variety of compositions, as described above. Accordingly, in embodiments, the fuel composition may be characterized by the proportion of methane and the proportion of a second combustible species in the fuel. That is, in embodiments, the first combustible species is methane. In other embodiments, the natural gas may be characterized before being mixed with the second combustible species, as non-limiting examples, for additional hydrogen and / or C species, and further characterization of the mixed fuel allows for quantification of the proportion of natural gas and the proportion of the added second combustible species. "Characterization" of a fluid in this context is broadly understood as the determination of species contained in the fluid.

[0020] The at least one second combustible species may, in more specific embodiments, be composed of at least one of hydrogen and / or at least one C2+ hydrocarbon, or a mixture thereof. That is, characterization of the fuel composition will include determining the proportion of hydrogen and / or C2+ species. This proportion may be determined by direct measurement resulting from quantification of other species, as described above.

[0021] In a further, more specific, but non-limiting example, it may be provided that the flow of combustion fluid and combustion products exiting the first combustion zone is at least partially expanded before entering the second combustion zone. The expansion may be performed, for example, in a high-pressure expansion turbine including at least one expansion turbine stage fluidly interposed between the first and second combustion zones. Gas turbine engines having a high-pressure expansion turbine fluidly interposed between the first and second combustion zones are disclosed, for example, in EP 620 362 and EP 740 057. In these references, the flow of combustion fluid and combustion products exiting the first combustion zone is only partially expanded before entering the second combustion zone, and further expanded downstream of the second combustion zone in a low-pressure expansion turbine. Therefore, the at least one high-pressure expansion turbine may be referred to as a pre-expansion turbine. As indicated above, the flow of gas exiting the second combustion zone is discharged to an expansion turbine, or at least one expansion turbine stage, respectively, located downstream of the second combustion zone. The expansion turbine may be a low-pressure expansion turbine, for example as defined in EP 620 362 and EP 740 057. Both the high-pressure expansion turbine and the low-pressure expansion turbine located downstream of the second combustion zone may, in embodiments, be powered by a common shaft.

[0022] To the extent that the combustion system is provided in a gas turbine engine, the gas turbine engine may include at least one row of variable inlet guide vanes at the upstream end of the compressor, the vanes having a variable angle or pitch relative to the direction of flow, in embodiments relative to the axial direction of the compressor, and serving to regulate, or selectively increase or decrease, the volumetric flow rate of fluid entering the compressor, and thus, in terms of the present disclosure, the volumetric flow rate of combustion fluid. The method may then include controlling the vane angle of the at least one row of variable inlet guide vanes to increase the mass flow rate of the combustion fluid as the second relative fraction of the fuel composition increases and to decrease the mass flow rate of the combustion fluid as the second relative fraction of the fuel composition decreases, within a second range between at least two values ​​of the first relative fraction of the fuel composition and the at least one second relative fraction of the fuel composition. The second range between at least two values ​​of the first relative fraction of the fuel composition and at least one second relative fraction of the fuel composition may be within, overlap, or be completely different from the range defined between the first relative fraction of the fuel composition and at least one second relative fraction of the fuel composition. In an embodiment, the control of the at least one variable inlet guide vane row may be enabled when the second relative fraction of the second combustible species having a relatively high flame speed is equal to or greater than a threshold value. The threshold value may be defined depending on operating parameters of the combustion system or the gas turbine engine on which the combustion system is operated, such as an initial position of the at least one variable inlet guide vane row, total fuel mass flow rate, heat load, or relative load of the gas turbine engine. The parameters may be used alone or in combination with other parameters. Increasing the flow rate of the combustion fluid while maintaining or only slightly changing the total mass flow rate of the fuel can reduce the equivalence ratio of the combustion zones and the temperature of the combustion fluid received by the second combustion zone, while simultaneously increasing the convection velocity within the combustion zones and therefore reducing the risk of flashback in both combustion zones.

[0023] Also disclosed is a combustion system configured to perform the above-described method. The combustion system includes at least one combustion flow path for flowing a combustion fluid therethrough and a fuel supply system. The combustion flow path has an upstream end and a downstream end. The at least one combustion flow path further includes a first combustion zone located relatively upstream within the at least one combustion flow path and at least one second combustion zone located relatively downstream within the at least one combustion flow path. The at least one second combustion zone is located downstream of the first combustion zone and configured to receive a fluid flow emanating from an upstream combustion zone, such as from the first combustion zone. The first combustion zone is provided with a first fuel discharge means for discharging fuel from the fuel supply system into the combustion flow path and to the first combustion zone, and the at least one second combustion zone is provided with a second fuel discharge means for discharging fuel from the fuel supply system into the combustion flow path and to the second combustion zone. That is, for clarity, each second combustion zone may be provided with its own second fuel discharge means. The fuel supply system is configured to supply fuel from a fuel source to the first combustion zone via a first fuel outlet means and to supply fuel to at least one second combustion zone via respective second fuel outlet means. The fuel supply source may be a fuel source common to both combustion zones. The fuel supply system includes control means for allocating a first fuel mass flow rate fraction of the total fuel mass flow rate to the first combustion zone. In certain embodiments, the control means includes at least one valve or multiple valves configured to perform a specified function. The configuration of such valves is essentially known to those skilled in the art. The system further includes a control system adapted and configured to receive information regarding the fuel composition, including quantitative information regarding the relative proportion of at least one combustible species. As mentioned above, this may be quantitative information regarding the relative proportion of at least one second combustible species, but it may also be or include information regarding the relative proportions of other species in the fuel from which the relative proportion of the at least one second combustible species can be derived. The information regarding the fuel composition may be provided intermittently, for example, as a result of repeated offline analysis of the fuel.In other embodiments, the information regarding the fuel composition may be provided from an online measurement system, as defined in more detail below. In yet other embodiments, the information may be derived from valve strokes of valves for metering different fuel components to be mixed to form the fuel mixture supplied through the fuel supply system. As described above, the relative fraction values ​​derived from said valve stroke information may be further corrected by, inter alia, pressure and temperature measurements from respective sensors that may be located in the fuel line and upstream of the valves for metering the different fuel components. The control device is further adapted and configured to control the control means to allocate a first fuel mass flow fraction of the total fuel mass flow to the first combustion zone in a range between two values ​​of the first relative fraction of the fuel composition and at least one second relative fraction of the fuel composition, such that the first fuel mass flow fraction of the total fuel mass flow allocated to the first combustion zone decreases as the second relative fraction of the fuel composition increases and the first fuel mass flow fraction of the total fuel mass flow allocated to the first combustion zone increases as the second relative fraction of the fuel composition decreases.

[0024] As alluded to above, in embodiments of the combustion system, a measurement device suitable for online characterization of the composition of fuel supplied to at least one combustion flow channel can be operably coupled to the fuel supply system and configured to quantify the proportion of at least one species, and in certain embodiments, the proportion of at least one combustible species, in the fuel composition supplied through the fuel supply system. The measurement device is operably linked to the controller to provide quantitative information regarding the proportion of the at least one combustible species in the fuel composition to the controller. In embodiments, the measurement device can be configured to directly quantify at least one relative proportion of at least one second combustible species. In other embodiments, the at least one relative proportion of the at least one second combustible species can be subtracted from the relative proportions of other species.

[0025] The suggested combustion system may be further configured with a high-pressure expansion turbine having at least one expansion turbine stage fluidly interposed between the first combustion zone and the second combustion zone.

[0026] The first and second combustion zones may be arranged in a common combustion space, also called a combustion chamber or combustor. Such an arrangement is known, for example, from the so-called delayed lean burn technique.

[0027] Also disclosed is a gas turbine engine comprising a compressor, an expansion turbine, and a combustion system of the kind suggested above, the combustion system being arranged and configured to receive combustion fluid from the compressor and discharge fluid from the combustion system to the expansion turbine, in which embodiment at least one high-pressure expansion turbine including at least one expansion turbine stage may be fluidly interposed between a first combustion zone and a second combustion zone, while at least one low-pressure combustion turbine is provided downstream of the second combustion zone, as generally proposed, for example, in EP 620 362 and EP 740 057.

[0028] It is understood that the above-disclosed features and embodiments can be combined with one another. It is further understood that further embodiments are possible within the scope of this disclosure and claimed subject matter that will be obvious and apparent to those skilled in the art from this disclosure. [Brief explanation of the drawings]

[0029] The subject matter of the present disclosure will now be explained in more detail by means of selected exemplary embodiments illustrated in the accompanying drawings. [Figure 1] 1 illustrates a first exemplary embodiment of a gas turbine engine including a combustion system according to the present teachings and suitable for carrying out methods according to the present teachings; [Figure 2] 1 is a block diagram illustrating an overview of one embodiment of a method according to the present teachings. [Figure 3]FIG. 2 illustrates a second exemplary embodiment of a gas turbine engine including a combustion system according to the present teachings and suitable for carrying out a method according to the present teachings. [Figure 4] FIG. 10 illustrates a third exemplary embodiment of a gas turbine engine including a combustion system according to the present teachings and suitable for carrying out a method according to the present teachings.

[0030] It is understood that the drawings are highly schematic and, for ease of understanding and depiction, may omit details not necessary for purposes of explanation. Furthermore, it is understood that the drawings depict only selected exemplary embodiments, and that embodiments not shown may still fall well within the scope of the subject matter disclosed and / or claimed herein. DETAILED DESCRIPTION OF THE INVENTION

[0031] FIG. 1 shows an overview of a first exemplary embodiment of an arrangement for implementing the teachings of the present disclosure. The gas turbine engine 1 includes a compressor 11 and an expansion turbine 12 arranged on a common shaft 13. In a manner known to those skilled in the art, the expansion turbine 12 drives the compressor 11 to provide useful power to a generator 14, which is drivingly connected to the shaft 13, for example, to be driven by the gas turbine engine. The compressor 11 includes at least one row of adjustable inlet guide vanes 111, also known as variable inlet guide vanes or VIGVs. The gas turbine engine 1 further includes a combustion system including two combustion zones 15 and 16. The combustion zones 15 and 16 may or may not be located in a common combustion chamber. Combustion chambers including two combustion zones in fluid series are known, for example, from the so-called delayed lean combustion technique. Both combustion zones can be supplied independently of each other with fuel, which is burned as a combustion fluid in the combustion zone. In a manner known per se, the compressor 11 compresses ambient air and supplies the compressed ambient air to the combustion system as a combustion fluid. A first portion of the total fuel mass flow is discharged into the combustion system in relatively upstream combustion zone 15 and combusted therein. The resulting mixture of combustion products and residual air enters relatively downstream second combustion zone 16, where a second proportion of the total fuel mass flow is discharged into the combustion system. This second portion of the total fuel mass flow is ignited and combusted in the hot mixture of combustion gases and residual air exiting the first relatively upstream combustion zone 15. The flow of combustion products and residual air exiting the relatively downstream second combustion zone 16 is expanded in expansion turbine 12, thereby producing mechanical power for driving compressor 11 and providing further useful power.

[0032] Combustion systems including multiple combustion zones arranged in series in the direction of combustion fluid flow are known in the art and serve, for example, to reduce the production of unwanted pollutants.

[0033] In certain examples, a first fuel supply stream 203 having a first fuel composition and a second fuel supply stream 204 having a second fuel composition are supplied to a gas turbine engine fuel supply system to form a mixed fuel or mixture 205. The fuel supplied as the first fuel supply stream 203 may comprise, by way of example, natural gas, and the fuel supplied as the second fuel supply stream 204 may be, or include, hydrogen and / or C species, and may provide a higher flame speed than the fuel supplied as the first fuel supply stream 203. Generally speaking, the mixed fuel 205 may include at least two combustible species having different flame speeds, and such composition may vary depending on the relative mass flow rates of the fuel supplied as the first fuel supply stream 203 and the fuel supplied as the second fuel supply stream 204, and / or the composition of the fuels supplied thereto. Accordingly, the flame speed of the mixed fuel 205 may vary. Thus, the fuel mixture 205 may include a first combustible species having a first, relatively low flame speed. The first combustible species may be methane, which is typically a major component of natural gas provided as the first feed stream of fuel 203. The fuel mixture 205 may further include a second combustible species having a second, relatively high flame speed. The second combustible species includes at least one of hydrogen and / or C2+ hydrocarbons or alkanes. The relative fractions of the first and second combustible species in the total combustible fraction of the fuel mixture 205 may vary, in some cases, from 0% to 100%. The main control valve 21 is configured to control the total fuel mass flow rate 206 provided to the combustion system so that a useful output, which may be represented by, for example, power output from the generator 14, meets a set value. The control valves 22 and 23 control the allocation of fuel to a first fuel mass flow fraction 201 that is combusted in a first relatively upstream combustion zone 15 and a second fuel mass flow fraction 202 that is combusted in a second relatively downstream combustion zone 16. In this embodiment, one of the control valves 22 and 23 or the main regulating valve 21 can be omitted, in which case the control valves 22 and 23 must be configured to jointly control the total fuel mass flow supplied to the combustion system so that the useful power meets the set value.In a manner known to those skilled in the art, fuel distribution to the combustion zones is controlled depending on the specific operating parameters of the gas turbine engine 1. However, as the relative fractions of combustible species in the fuel mixture change, the flame speed of the fuel being burned in the combustion zone changes. Furthermore, the combustion temperature also changes. The increased flame speed of the fuel mixture, combined with potentially increased temperatures of the fluids emanating from the first, relatively upstream combustion zone 15 and flowing as combustion fluids to the second, relatively downstream combustion zone 16, can significantly increase the susceptibility of flashback in the second combustion zone 16. It has been discovered that reducing the first relative fuel mass flow fraction 201 delivered to the upstream combustion zone 15 relative to the total fuel mass flow 206 can mitigate the risk of flashback associated with increased fuel flame speed, even when the operating parameters of the gas turbine engine remain unchanged. It will be appreciated that in this embodiment having two combustion zones, an increase in the second fuel mass flow proportion 202 relative to the total fuel mass flow 206 is accompanied by a decrease in the first relative fuel mass flow proportion 201 relative to the total fuel mass flow 206.

[0034] The above-described method requires some quantitative information regarding the composition of combustibles in the fuel mixture 205. Therefore, in the illustrated embodiment, a measurement device 31 suitable for online characterization of the fuel's composition is provided in the fuel supply line through which the fuel mixture 205 flows. The measurement device is configured to quantify the relative proportion of at least one combustible species in the fuel mixture 205. Useful information regarding the fuel composition, enabling at least a qualitative conclusion regarding the flame speed, is provided to a controller 32. The controller 32 may, in particular, be part of a control system for a gas turbine engine or a power plant. The information includes, for example, the total fuel composition or the relative proportion of a second combustible species relative to the content of a first combustible species. The controller 32 then provides control signals to the control valves 22 and 23 to vary the allocation of fuel to the different combustion zones. The controller 32 may further provide control signals to the variable inlet guide vanes 111 to control the variable inlet guide vanes 111 depending on the relative fractions of the different combustible species, as outlined above.

[0035] The described method is shown schematically in the block diagram of FIG. 2. In block 110, operating parameters of the gas turbine engine are determined. In block 120, control parameters of the control valves 22 and 23 are determined depending on the operating parameters of the gas turbine engine. In block 130, information about the fuel composition is determined, such as quantifying the relative proportion of at least one combustible species having a higher flame speed than a first combustible species. The relative proportion of the at least one combustible species having a higher flame speed may be quantified, for example, as a percentage of the total fuel composition, as a percentage of the total combustible content, or in relation to the relative proportion of the first combustible species. As described above, the first combustible species may be methane. The at least one combustible species having a higher flame speed compared to the first combustible species may consist of or include hydrogen and / or C2+ species. Depending on the information about the fuel composition, the control parameters of the control valves 22 and 23 may be adjusted in block 140. In block 150, the control parameters are transferred as control signals to the control valves 22 and 23.

[0036] The embodiment shown in Figure 3 differs from the embodiment shown in Figure 1 in that a high-pressure expansion turbine 121 is fluidly interposed between the upstream combustion zone 15 and the downstream combustion zone 16, and a low-pressure expansion turbine 122 is provided downstream of the downstream combustion zone 16, as suggested, for example, in EP 620 362 and EP 740 057. It will be understood that each of the high-pressure expansion turbine 121 and the low-pressure expansion turbine 122 constitutes at least one expansion turbine stage. Otherwise, the fuel supply and control systems for allocating fuel to the upstream and downstream combustion zones are the same as those outlined in connection with Figure 1.

[0037] FIG. 4 illustrates an embodiment of the gas turbine engine shown in FIG. 1 equipped with a slightly modified fuel supply and control system. The measurement device 31 shown in FIGS. 1 and 3 has been omitted. The supply lines for the first and second fuel supply streams include control valves 25 and 26, respectively. As with the embodiment of FIG. 1, the first and second combustion zones 15 and 16 may or may not be located within a common combustion space or chamber, combustor 17. The travels or strokes of the control valves 25 and 26 are used as control inputs for the controller 32. These travels or strokes are considered representative of the relative fractions of the first and second fuels in the fuel mixture 205. Assumptions must be made about the composition of the first and second fuels provided as the first and second fuel supply streams. For example, periodic offline fuel analysis can be performed to determine the composition of the first and second fuels provided as the first and second fuel supply streams. The valve stroke can thus provide quantitative information about the relative proportion of at least one combustible species. To more accurately determine the mass flow rate through valves 25 and 26, the valve opening or stroke can be supplemented by temperature and pressure measurements upstream of valves 25 and 26. Controller 32 can then generate control parameters for control valves 22 and 23, and thus for the distribution of total fuel mass flow 206, according to the valve opening or stroke of valves 25 and 26, information about the fuel composition, particularly the combustible species composition, in supply fuel streams 203 and 204, and, optionally, pressure and temperature values ​​upstream of valves 25 and 26. It will be appreciated that the fuel supply and control system shown in FIG. 4 can also be applied in connection with a gas turbine engine in which at least one expansion turbine stage is fluidly interposed between a relatively upstream combustion zone and a relatively downstream combustion zone, such as the gas turbine engine shown in FIG. 3.

[0038] Those skilled in the art can readily apply the teachings of the present disclosure to multi-shaft gas turbine arrangements such as those used in, but not limited to, propulsion of land vehicles, ships, and aircraft.

[0039] While the subject matter of the present disclosure has been described in terms of exemplary embodiments, it will be understood that these are in no way intended to limit the scope of the claimed invention. It will be understood that the claims cover embodiments not expressly shown or disclosed herein, and that embodiments that deviate from the disclosed embodiments in exemplary modes of carrying out the teachings of the present disclosure will still be covered by the claims. [Explanation of symbols]

[0040] 15 First Combustion Zone 130 blocks 140 blocks 150 blocks 201 First fuel mass flow fraction 202 Second fuel mass flow fraction 203 First Flammable Species 204 Secondary Combustible Species 205 Mixed fuel 206 Fuel

Claims

1. 1. A method for operating a combustion system, the method comprising: supplying a flow of combustion fluid to the combustion system; flowing the flow of combustion fluid in an upstream-to-downstream direction through the combustion system; discharging a flow of fuel (205) into the combustion system; and combusting the flow of fuel with at least a portion of the flow of combustion fluid, discharging the flow of fuel into the combustion system includes allocating a first fuel mass flow fraction (201) of the total mass flow of fuel (206) to a first combustion zone (15) located relatively upstream of the combustion system, and supplying at least a second fuel mass flow fraction (202) of the total fuel mass flow to at least one second combustion zone (16) located relatively downstream from the first combustion zone; the flow of fuel (205) comprises a fuel having a fuel composition comprising a first relative fraction of a fuel composition consisting of a first combustible species (203) having a first flame speed when combusted in the combustion fluid and at least one second relative fraction of a fuel composition consisting of at least one second combustible species (204) having a second flame speed when combusted in the combustion fluid, the second flame speed being greater than the first flame speed; the method further comprising quantifying (130) at least one of the first relative fraction (203) of the fuel composition and the second relative fraction (204) of the fuel composition (205); The method further comprises controlling (140, 150) fuel allocation to the first fuel mass flow fraction (201) of the total fuel mass flow such that, at least in a range between at least two values ​​of the first relative fraction of the fuel composition and the at least one second relative fraction of the fuel composition, the first fuel mass flow fraction (201) of the total fuel mass flow decreases as the second relative fraction of the fuel composition increases and the first fuel mass flow fraction (201) of the total fuel mass flow increases as the second relative fraction of the fuel composition decreases. The method.

2. 10. The method of any preceding claim, wherein the method comprises online monitoring of the fuel composition, the monitoring comprising at least quantifying a second fraction of the fuel composition and / or a ratio of the second relative fraction of the fuel composition to the first relative fraction of the fuel composition.

3. 10. The method of any of the preceding claims, wherein the first combustible species (203) is methane.

4. 10. The method of any preceding claim, wherein the at least one second combustible species (204) comprises at least one of hydrogen and / or at least one C2+ hydrocarbon or mixtures thereof.

5. 10. The method of any preceding claim, wherein the stream of combustion fluids and combustion products exiting the first combustion zone is at least partially expanded before entering a second combustion zone.

6. 10. The method of any preceding claim, wherein the expansion is at least partially performed in a high pressure expansion turbine including at least one expansion turbine stage (121).

7. 10. A method according to any preceding claim, wherein the gas stream exiting the second combustion zone is discharged to an expansion turbine (12, 122).

8. A method combining claims 6 and 7, wherein the high pressure expansion turbine (121) and a low pressure expansion turbine (122) downstream from the second combustion zone (16) power a common shaft (13).

9. 10. The method of claim 9, comprising controlling a vane angle of at least one row of variable inlet guide vanes (111) to increase the mass flow rate of combustion fluid as the second relative fraction of the fuel composition increases and to decrease the mass flow rate of combustion fluid as the second relative fraction of the fuel composition decreases, at least in a second range between at least one of two values ​​of the first relative fraction of the fuel composition and the at least one second relative fraction of the fuel composition.

10. 1. A combustion system configured to carry out a method according to any preceding claim, said system comprising: at least one combustion flow path for flowing a combustion fluid; and a fuel supply system; the combustion flow path has an upstream end and a downstream end, and includes a first combustion zone (15) located relatively upstream within the at least one combustion flow path and at least one second combustion zone (16) located relatively downstream within the at least one combustion flow path; the at least one second combustion zone is located downstream of the first combustion zone and configured to receive a fluid flow emanating from the upstream combustion zone, the first combustion zone (15) comprising first fuel discharge means for discharging fuel from the fuel supply system into the combustion flow path and into the first combustion zone, and the at least one second combustion zone (16) comprising second fuel discharge means for discharging fuel from the fuel supply system into the combustion flow path and into at least one second combustion zone; the fuel supply system is configured to supply fuel from a fuel source (205) to the first combustion zone (15) via the first fuel discharge means and to supply fuel to the at least one second combustion zone (16) via the respective second fuel discharge means, the fuel supply system including control means (22) for allocating a first fuel mass flow fraction (201) of a total fuel mass flow (206) to the first combustion zone (15); the system further comprises a control system (32) adapted and configured to receive information about the fuel composition, including quantitative information about the relative proportion of the at least one combustible species, and adapted and configured to control the control means (22) for allocating the first fuel mass flow fraction of the total fuel mass flow to the first combustion zone (15) at least such that, in a range between at least two values ​​of the first relative fraction of the fuel composition and the at least one second relative fraction of the fuel composition, the first fuel mass flow fraction of the total fuel mass flow allocated to the first combustion zone decreases as the second relative fraction of the fuel composition increases and the first fuel mass flow fraction of the total fuel mass flow allocated to the first combustion zone increases as the second relative fraction of the fuel composition decreases. The system.

11. 10. The combustion system of claim 9, wherein a measurement device (31) suitable for online characterization of the composition of the fuel supplied to the at least one combustion flow channel is operably coupled to the fuel supply system and configured to quantify the proportion of at least one species in the fuel composition supplied through the fuel supply system, the measurement device being further operably coupled to the controller (32) such that the measurement device provides the controller with the quantitative information regarding the proportion of at least one combustible species in the fuel composition.

12. 10. The combustion system of claim 9, wherein the combustion system is configured with a high-pressure expansion turbine including at least one expansion turbine stage fluidly interposed between the first combustion zone and the second combustion zone.

13. 12. A combustion system according to claim 10 or 11, wherein the first combustion zone and the second combustion zone are arranged in a common combustion space (17).

14. 12. A gas turbine engine including a compressor (11), an expansion turbine (12, 121, 122), and a combustion system according to any one of claims 9 to 11, wherein the combustion system is arranged and configured to receive combustion fluid from the compressor and to discharge fluid from the combustion system to the expansion turbine.

15. 10. The gas turbine engine of claim 9, wherein at least one high-pressure expansion turbine including at least one expansion turbine stage (121) is fluidly interposed between the first combustion zone (15) and the second combustion zone (16), and at least one low-pressure combustion turbine (122) is provided downstream of the second combustion zone.

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