Method for operating a power plant and power plant

Abstract

The present invention is entitled "Method for operating a power plant and a power plant". The present invention discloses a method for operating a power plant (1) comprising at least one gas turbine engine (10, 20) and at least one fuel gas compressor (53, 54, 55). The method comprises supplying a fuel gas (5) through a common supply line (51), compressing the fuel gas to a power plant supply pressure in at least one operating fuel gas compressor, and supplying the compressed fuel gas to a power plant supply line (52). The at least one gas turbine engine is operated at a set power output according to a power demand signal. If a failure of the operating fuel gas compressor is detected, the power output of the at least one gas turbine engine is reduced to an emergency power output below the set power output, and the power output of the at least one gas turbine engine is limited to the emergency power output. The reduction in power output is performed in a single step and is controlled by at least one feedforward control signal.

Description

Technical Field

[0001] The present disclosure relates to a method for operating a power plant and to a power plant configured to operate according to the method as claimed. Background Art

[0002] A gas turbine or combined cycle power plant comprises one or more gas turbine engines and, if the gas turbine engines are intended to operate using fuel gas, a fuel gas supply system. The fuel gas supply system typically comprises at least one fuel gas compressor or reduction equipment, or a combination of both. The fuel gas compressor may be dedicated to a single gas turbine engine, or may be configured to operate using a common header connected to multiple gas turbine engines.

[0003] In order to provide a stable gas supply pressure during steady-state operation of the gas turbine, the fuel gas supply system includes a pressure controller that usually operates slowly in order to avoid steep pressure gradients and significant oscillations in the supply pressure of the fuel gas supplied to the gas turbine engine. The load control of the power plant also operates relatively slowly in order to take into account the delay time of the feedback signal inherent in the power plant.

[0004] While these systems produce stable operation of the gas turbine engines and other rotating equipment of a power plant, these control mechanisms may be too slow if unexpected transients occur.

[0005] For power plant economics (including saving power plant and auxiliary agent self-consumption) and investment costs, fuel gas compressors are usually designed and operated so that the fuel mass flow and pressure are just enough to operate one or more gas turbine engines at rated load in a steady state. Therefore, when one or more gas turbine engines are operating at a set power output, the failure of the fuel gas compressor may result in a rapid drop in the equipment fuel gas supply pressure to which the control system may not be able to react. Therefore, the gas turbine engine may be shut down suddenly due to the lack of ability of the control system to adjust the fuel control valve or simply the lack of sufficient fuel gas mass flow at the minimum required power plant fuel gas supply pressure. In a combined cycle power plant, the shutdown of one or more gas turbine engines also results in a rapid steam turbine shutdown. The sudden shutdown of the main rotating equipment (also known as TRIP) causes greater stress in the heat load part of the gas turbine and steam turbine, and therefore leads to high life consumption, and may require a delay until the power plant supplies power to the grid again.

[0006] Overview of the Disclosed Subject Matter

[0007] The object of the subject matter disclosed in the present invention is to provide a method for operating a power plant of the initially mentioned type and a power plant adapted to be operated according to said method. In a more specific aspect, a method will be provided which allows avoiding a sudden shutdown of the main rotating equipment of the power plant in the event of a failure of a fuel gas compressor. In a more specific aspect, it can be found that it is desirable to be able to return to a normal, e.g. unrestricted, load control operating mode in order to provide a predetermined or required power output to the grid.

[0008] This is achieved by the subject matter of the independent claims.

[0009] Whether or not explicitly mentioned, further effects and advantages of the disclosed subject matter will become apparent from the disclosure provided below.

[0010] It should be noted that within the framework of the present disclosure, the use of the indefinite article "a" or "an" in no way specifies singularity, nor does it exclude the presence of a plurality of the named components or features. Therefore, it should be read in the sense of "at least one" or "one or more".

[0011] Therefore, the present invention discloses a method for operating a power plant, wherein the power plant includes at least one gas turbine engine and at least one fuel gas compressor. The method includes supplying fuel gas through a common supply pipeline, wherein the fuel gas in the common supply pipeline is at a pipeline supply pressure. The fuel gas supplied through the common supply pipeline and at the pipeline supply pressure is then compressed to the power plant supply pressure in at least one fuel gas compressor, and the compressed fuel gas at the equipment supply pressure is supplied to the power plant supply pipeline. The technician will readily understand that the compressed fuel gas is supplied to at least one gas turbine engine from the power plant supply pipeline through at least one fuel gas control valve of each gas turbine engine. The technician will also understand that at least one fuel control valve may include a control valve for controlling the total fuel gas mass flow to the corresponding gas turbine engine, but in addition or alternatively, also includes a control valve or stop valve for distributing the fuel gas mass flow to, for example, but not limited to, different fuel lances, flamers, fuel discharge openings of the flamers, or combustion zones within the gas turbine engine. The method initially includes operating the gas turbine engine at a set power output according to a power demand signal. That is, in other words, the operation of the gas turbine engine is controlled by the load controller and is controlled according to an external predetermined demand signal with a power output matched to the control input. The method also includes detecting whether the operating fuel gas compressor experiences a fault. This function may be included in the fuel gas pressure controller, for example but not limited to. According to the method disclosed herein, if a fault of the operating fuel gas compressor is detected, which means that the fuel gas compressor may no longer be running, the power output of at least one gas turbine engine is reduced to an emergency power output below the set power output. In this regard, the term "emergency power output" is interpreted broadly, and in an embodiment, the method may include the step of downloading at least one gas turbine engine to "full speed-no load"; that is, the power output to the grid is zero, but at least one gas turbine engine remains running at a speed at least substantially synchronized with the grid frequency. However, as outlined in more detail below, if the fuel gas from the at least one gas turbine engine is used to generate steam in a combined cycle power plant, this may require shutting down the steam turbine because the mass flow and temperature of the fuel gas at "full speed-no load" may not be sufficient to maintain the minimum required real-time steam temperature and / or mass flow. The power output of the at least one gas turbine engine is then limited to the emergency power output. The reduction in power output is performed in a single step, and in particular may be a sudden load reduction in a substantially discontinuous step-like manner, and is controlled by at least one feed-forward signal. That is, one or more control signals are set directly by the control system and fed to specific hardware control components without involving a closed-loop controller. The at least one feed-forward control signal does not rely on a control loop, and therefore provides significantly faster dynamic characteristics than a closed-loop control signal.In an embodiment, the method includes providing a feedforward control signal to at least one fuel flow control valve of at least one gas turbine engine, and changing the valve position to a predefined emergency position, and then operating the at least one gas turbine engine in a load control mode at an emergency power output. The technician will readily appreciate that the feedforward signal may also be sent to other hardware components (e.g., variable inlet guide vane rows) of the at least one gas turbine engine, and the feedforward signal may be used to adjust other operating parameters of the emergency power output. In a specific embodiment, the predefined emergency position of the at least one fuel flow control valve may be determined, for example, during a test run, as a valve position suitable for safely operating the at least one gas turbine engine at approximately the emergency power output. In other words, the predetermined emergency valve position is a valve position corresponding to the position of the fuel flow control valve at the emergency power output when it is operated under closed-loop control. When the feedforward control signal is provided, the gas turbine engine is very quickly deloaded to approximately the emergency power output, wherein fine adjustment of the actual power output of the emergency power output can then be achieved by closed-loop load control. Thus, the fuel gas consumption of the at least one gas turbine engine is reduced very quickly so that the fuel gas buffered in the buffer volume provided by and / or in communication with the power plant supply line can maintain the supply of fuel gas to the at least one gas turbine engine at a sufficiently high power plant supply pressure for a longer time. As described above, the at least one fuel control valve may include a control valve for controlling the fuel gas mass flow to the respective gas turbine engine, but in addition or alternatively also includes a control valve or stop valve for distributing the fuel gas mass flow to, for example but not limited to, different fuel lances, flamers, fuel discharge openings of a flamer or combustion zones within the gas turbine engine.

[0012] It will generally be understood that the fuel gas compressor operates according to a characteristic diagram of pressure ratio versus inlet mass flow, or, in the case of providing a constant pressure in the common supply line, according to a characteristic diagram of power plant supply pressure versus mass flow. In addition, at least one gas turbine engine has a characteristic pair of fuel mass flow and required minimum fuel gas pressure at each power output. Steady-state operation can be achieved if the mass flow required by at least one gas turbine engine at a specific power output is lower than the mass flow that can be delivered by the minimum fuel gas pressure required by at least one fuel gas compressor at said specific power output. Therefore, if, in the event of a failure of the fuel gas compressor, the power output of at least one gas turbine engine is reduced to an emergency power output at which the fuel mass flow consumed is lower than the mass flow that can be delivered by the minimum fuel gas pressure required by the at least one fuel gas compressor that remains in operation at said power output, the operation of the at least one gas turbine engine at the emergency power output can continue for a substantially unlimited time. In other cases, as described below, there may be a situation where the pipeline supply pressure is sufficient to maintain the operation of at least one gas turbine engine at the emergency power output. However, if there is no fuel gas compressor that remains in operation, at least one fuel gas compressor that remains in operation at the required fuel gas pressure cannot supply the required fuel mass flow, then it can be considered that at least the power plant supply pipeline provides a buffer volume, which is initially filled with buffer fuel gas at an initial pressure when the fuel gas compressor fails. If any of the one or more fuel gas compressors remains in operation, the buffer fuel gas can be used to make up for the difference between the fuel mass flow demand and the supply capacity of at least one gas turbine engine. In this case, as the net extraction of fuel gas occurs, the power plant supply pressure in the power plant supply pipeline steadily decreases. In this way, the operation of at least one gas turbine engine can continue for a limited time. Ideally, the time is sufficient to restore full fuel gas supply capacity, or at least for a normal shutdown of at least one gas turbine engine, where the life consumption is significantly lower than a sudden unscheduled flameout. Thus, reducing the power output of at least one gas turbine engine to an emergency power output serves at least one of the following purposes: (a) reducing the fuel mass flow consumed by the at least one gas turbine engine and the required minimum fuel pressure to values ​​that can be maintained by the fuel gas supply system with reduced capacity or without additional fuel gas compression, and / or (b) reducing the fuel mass flow consumed by the at least one gas turbine engine and the required minimum fuel pressure so as to extend the time until the pressure in the power plant supply pipeline drops below the required minimum fuel pressure at the emergency power output.

[0013] It will be appreciated that the emergency power output is preferably high enough to keep the generator of the gas turbine engine connected to the grid.

[0014] In another non-limiting embodiment, the method includes determining a sustainable critical gas turbine engine power output based on the fuel gas mass flow / output pressure characteristics of one or more fuel gas compressors maintained in operation, and determining that the emergency power output is less than or at most equal to the critical power output, thereby avoiding shutdown of at least one gas turbine engine.

[0015] In a further non-limiting embodiment, the method comprises directing an exhaust mass flow of at least one gas turbine engine through at least one heat recovery steam generator, generating steam, and supplying the generated steam to a steam turbine to drive the steam turbine, wherein the emergency power output is higher than or at least equal to the minimum gas turbine engine power output required to generate steam at a minimum mass flow, pressure and temperature to drive the steam turbine. Shutdown of the steam turbine engine can thus be avoided.

[0016] Both measures produce significant economic and technical advantages, since the main rotating equipment, namely the gas and optionally steam turbine engines, remain running and avoid being stationary, life consumption is greatly reduced and the delay time of a complete start-up from stationary is avoided.

[0017] In frequently used embodiments, the power plant includes redundant fuel gas compression capabilities, which means that, for example, only two of the three fuel gas compressors are required to operate the power plant at rated power output. In this regard, in the event of a fuel gas compressor failure, at least one fuel gas compressor of the power plant is not operational. In these cases, the method disclosed herein may include starting a previously inoperative fuel gas compressor and causing it to begin operation.

[0018] The method may then further comprise: determining a minimum required power plant supply pressure for the at least one gas turbine engine to operate at the emergency power output, determining a start-up time for a previously non-operating fuel gas compressor, and providing a buffer volume suitable for buffering fuel gas and fluidly arranged between the at least one fuel gas compressor and the at least one gas turbine engine, wherein the buffer volume is sufficiently large to supply fuel gas to the at least one gas turbine engine operating at the emergency power output after a fuel gas compressor failure and before the previously non-operating fuel gas compressor is fully operational without the pressure in the buffer volume dropping below the minimum required power plant supply pressure. In an embodiment, the buffer volume is in and provided by a power plant supply line, i.e., a fuel supply line extending from downstream of the at least one fuel gas compressor to the at least one gas turbine engine. The method may be implemented in particular in a non-limiting embodiment, comprising providing a fuel supply line having a sufficiently large cross-section or more particularly a diameter so as to provide a sufficient buffer volume.

[0019] Once the previously inoperative fuel gas compressor is fully operational, limiting the power output to the emergency power output may be terminated and the power output of the at least one gas turbine engine may be controlled by the power demand signal to return to normal operation of the power plant.

[0020] In a particular power plant, a bypass line is installed to connect a utility supply line and a power plant supply line and bypass at least one fuel gas compressor, and wherein a check valve is installed in the bypass line to prevent fuel gas from flowing back from the power plant supply line into the utility supply line while enabling fuel gas to flow from the utility supply line to the power plant supply line. Specifically, it may be the case that a pipeline supply pressure provided by a utility in the utility supply line is high enough that at least one gas turbine engine can operate with the pipeline supply pressure from the utility supply line. In this case, the method may include determining a critical gas turbine power output that is sustainable with the pipeline supply pressure, and determining that an emergency power output is less than or at most equal to the critical power output. If at least one fuel gas compressor remains in operation after a fuel gas compressor failure, the method may also include determining the power output of at least one gas turbine engine sustainable with the supply pipeline pressure, the power output of at least one gas turbine engine sustainable with the at least one fuel gas compressor that remains in operation, and, if the power output of the at least one gas turbine engine sustainable with the supply pipeline pressure is greater than the power output of the at least one gas turbine engine sustainable with the at least one fuel gas compressor that remains in operation, isolating the at least one fuel gas compressor that remains in operation from the power plant supply pipeline fluid.

[0021] On the other hand, wherein at least one fuel gas compressor remains in operation after a fuel gas compressor failure, in an embodiment, the method may include: determining a critical gas turbine power output that is sustainable with a maximum pressure of the power plant supply pressure that can be maintained by the at least one fuel gas compressor that remains in operation and the pipeline supply pressure, and determining an emergency power output that is less than or at most equal to the critical power output.

[0022] In another aspect, the present invention discloses a power plant, which includes at least one gas turbine engine, at least one fuel gas compressor, and a power plant supply pipeline connecting the downstream end of the at least one fuel gas compressor and the at least one gas turbine engine, wherein the upstream end of the at least one fuel gas compressor is connected to a common supply pipeline. The power plant also includes a fuel gas pressure control system and a gas turbine engine control system. A control line is provided from the fuel gas pressure control system to the gas turbine control system, and is adapted and configured to forward a fuel gas compressor fault signal from the fuel gas pressure control system to the gas turbine engine control system. In response to the fuel gas compressor fault signal, the gas turbine engine control system is adapted and configured to forward a preset feedforward emergency control signal to at least one fuel flow control valve of at least one gas turbine engine. In a non-limiting more specific embodiment, the power plant also includes a buffer volume suitable for buffering fuel gas and arranging the fuel gas fluid between at least one fuel gas compressor and at least one gas turbine engine, wherein the buffer volume is large enough to supply fuel gas to at least one gas turbine engine operating at an emergency power output during the time required to start the fuel gas compressor from standstill without the pressure in the buffer volume dropping below the minimum required power plant supply pressure required to operate the at least one gas turbine engine at an emergency power output.

[0023] It should be understood that the features and embodiments disclosed above can be combined with each other. It should also be understood that other embodiments can be conceived within the scope of the present disclosure and claimed subject matter, which embodiments are obvious to the skilled person. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The subject matter of the present disclosure will now be explained in more detail by means of selected exemplary embodiments shown in the accompanying drawings.

[0025] Figure 1 An exemplary embodiment of a power plant; and

[0026] Figure 2 Flowchart of an exemplary embodiment of the above method.

[0027] It should be understood that the drawings are highly schematic and that details not necessary for illustrative purposes may be omitted for ease of understanding and depiction. It should also be understood that the drawings only illustrate selected exemplary embodiments and that embodiments not shown may still be fully within the scope of the subject matter disclosed and / or claimed herein.

[0028] Exemplary Modes of Carrying Out the Teachings of the Present Disclosure

[0029] Figure 1An exemplary combined cycle power plant 1 is depicted. The combined cycle power plant 1 includes two gas turbine engines 10 and 20. In a manner familiar to the skilled person, each gas turbine engine 10 and 20 includes a respective compressor 11 and 21, a respective combustion chamber 12 and 22, a respective expansion turbine 13 and 23, and a respective generator 15 and 25. The respective expansion turbine, compressor, and generator of each gas turbine engine are mechanically coupled by a shaft so that the mechanical power from the expansion turbine drives the compressor and the generator. During operation, the compressors 11 and 21 compress ambient air. The compressed ambient air flows to the respective combustion chamber 12, 22, where it is mixed with fuel. The fuel is burned in the compressed air in the combustion chamber, and the resulting high-pressure fuel gas is directed to the respective expansion turbine 13, 23 and expanded therein, whereby the turbine generates useful shaft power and drives the compressor and the generator, thereby generating the electrical output of the respective gas turbine engine. In a manner familiar to the skilled person, the gas turbine engine also includes a control system, which controls, among other things, the electrical output. The control system is not shown in the current illustration; however, the skilled person is fully familiar with the control systems in the gas turbine engine and the power plant, respectively. The control system of each gas turbine engine receives the power demand signal, compares it with the actual electrical power output from the corresponding generator, and sends an actuation signal to the corresponding fuel control valves 16 and 26, thereby controlling the mass flow of fuel provided to the combustion chamber so that the actual electrical output matches the set power output corresponding to the power demand signal. As will be readily understood, the fuel control valve of each gas turbine engine is therefore operated in a closed-loop control. In addition, the technician will understand that the control parameters are set so that the control loop works relatively slowly in order to avoid instability and oscillation of the control signal. The technician also knows that the gas turbine engines of the prior art are usually provided with a plurality of fuel control valves in order to control the total fuel mass flow on the one hand and distribute the total fuel mass flow to different flamethrowers, combustion zones, fuel discharge orifices, burners, etc. on the other hand. The technician is also familiar with the fact that the gas turbine engine may include a plurality of burners, turbines and compressors. However, this is irrelevant to the understanding of the subject matter of the present disclosure, and therefore a rather basic non-limiting example has been selected to outline the subject matter of the present disclosure, in which the fuel control system of the gas turbine engine is represented by a single fuel gas control valve.

[0030] The exemplary power plant 1 also includes a heat recovery steam generator 40 and a steam turbine engine 30. The expanded exhaust gas from the gas turbine engine expansion turbines 13 and 23 is directed through the heat recovery steam generator 40, thereby exchanging heat with the feed water fed to the heat recovery steam generator and generating steam in a manner known to the skilled person. The steam is directed to the expansion steam turbine 33 and expanded therein, thereby generating useful shaft power for driving the steam turbine engine generator 35 and generating additional electrical power output.

[0031] Fuel gas 5 is provided to a utility supply line 51 at a pipeline supply pressure by a utility. When operating in all operating states, the supply line pressure may be insufficient to supply the gas turbine engine. Therefore, fuel gas compressors 53, 54 and 55 are provided for compressing the fuel gas from the pipeline supply pressure to the power plant supply pressure. The fuel gas is fed to the combustion chambers 12 and 22 through the power plant supply line 52 at the power plant supply pressure, whereby the fuel mass flow is controlled by the fuel control valves 16 and 26. The combustion system of the gas turbine engine includes a nozzle through which the fuel gas is injected into the compressed air in the combustion chamber. Therefore, when the fuel gas is provided to the combustion chamber, the fuel gas must be supplied at a minimum required fuel gas pressure, as will be understood, generally as a rule of thumb, the higher the minimum required fuel gas pressure, the higher the fuel mass flow or the power output of the gas turbine engine. In other words, if the power plant supply pressure drops below a certain threshold, this limits the power output that can be generated by the gas turbine engine. Generally speaking, in order to increase the reliability of the power plant, the redundant fuel gas compressors here, that is, the cumulative pressure / mass flow of all fuel gas compressors is higher than the demand of the gas turbine running at the rated power output. For example, in the exemplary embodiment shown, each fuel gas compressor is capable of providing 50% of the maximum fuel gas mass flow required for the gas turbine engine running at the maximum power output, or slightly more than 50%. Therefore, in order to avoid excessive power plant auxiliary power loss, only two of the three fuel gas compressors can be operated. For example, fuel gas compressors 53 and 54 can be operated, while fuel gas compressor 55 is not operated. It should be understood that in this regard, at least one of the pipelines connecting each fuel gas compressor to the common supply pipeline 51 and the power plant supply pipeline 52 is equipped with a check valve or a stop valve to prevent the fuel gas from flowing back from the power plant supply pipeline to the common supply pipeline through the compressor that is not running. It should also be understood that each fuel gas compressor can be equipped with a pipeline and a valve system to allow another compressor in the fuel gas compressor to be started while the compressor is running. For the sake of clarity, the auxiliary systems of the fuel gas compressors which are not immediately required for understanding the subject matter disclosed herein, but which are familiar to those skilled in the art, are omitted from the drawings. These fuel gas compressors are controlled by a pressure control system which is not shown but is well known to those skilled in the art.

[0032] Figure 2 An exemplary embodiment of a method 200 as described herein is summarized. Figure 2 With the help of Figure 1Overview of the method disclosed herein, as indicated above, now assumes that initially the fuel gas compressors 53 and 54 are operating, while the fuel gas compressor 55 is not operating. As described above, the gas turbine engine is operated in a closed-loop load control mode, wherein the fuel mass flow to the gas turbine engine is controlled by a fuel control valve so as to operate the gas turbine engine at a set power output and in accordance with an externally provided load demand signal. This initial operating state is indicated at 210. At step 220, it is determined whether the operating fuel gas compressor has failed. If this is not the case, at 210, the gas turbine engine continues to operate in the load control mode at the set power output in accordance with the power demand signal. However, if a failure of the operating fuel gas compressor (e.g., the fuel gas compressor 53) is detected, then at 230, a fault signal 100 is generated, and at 240, a start signal 103 is sent to the non-operating fuel gas compressor 55. However, this requires a certain start-up time until the previously non-operating fuel gas compressor 55 can completely replace the compression and fuel mass flow previously provided by the failed compressor 53. If the gas turbine engine is operated at a power output above a certain threshold, the remaining fuel gas compressor 54 may not be able to maintain the required fuel mass flow at the required minimum power plant supply pressure in order to operate the gas turbine engine at the power output according to the power demand signal. Therefore, if the pressure in the power plant supply pipeline drops below the required minimum pressure corresponding to the power output of the gas turbine engine, the gas turbine engine will likely be shut down suddenly. That is, the combustion in the combustion chamber is suddenly extinguished from a high power level, thereby causing a high temperature gradient in the gas turbine engine, which in turn causes high heat-induced stress and life consumption. It should be understood that the shutdown of the gas turbine engine will also result in the shutdown of the steam turbine engine. In addition to the high life consumption of the engine, the power plant completely stops generating electricity. It may take an extended delay time to restart the power plant. It can therefore be found that avoiding the complete shutdown of the main rotating equipment (i.e., mainly the gas turbine engine, but also the steam turbine engine) is of the utmost concern. In the event of a failure of the fuel gas compressor, the power plant supply pipeline 52 is filled with fuel gas at the power plant supply pressure and thus serves as a compressed fuel buffer volume. The gas turbine engine can be operated using fuel from this buffer volume as long as the pressure in the buffer volume does not drop below the minimum pressure required to operate the gas turbine engine at a specific power output. It should be understood that for a given buffer volume and initial pressure, the slower a certain pressure drop occurs, the less fuel is consumed per time unit, that is, the lower the power output of the gas turbine engine operation. In addition, it is generally and reasonably assumed that the lower the critical minimum power plant supply pressure required to maintain the operation of the gas turbine engine, the lower the power output of the gas turbine engine. Therefore, at 250, a rapid feed-forward load reduction of the gas turbine engines 10 and 20 is initiated.In this regard, in the exemplary embodiment shown herein, feedforward control signals 101, 102 are generated in response to the fuel gas compressor failure signal and forwarded to the fuel control system of the gas turbine engine, as simply represented by the fuel flow control valves 16 and 26. As described above, the fuel control system can be significantly more complex and include multiple fuel flow control valves that control the distribution of the total fuel mass flow to the gas turbine engine and / or the portion of the total fuel mass flow within the combustion system of the gas turbine engine. The feedforward control signal can also act on the position of one or more rows of variable inlet guide vanes to reduce the air mass flow through the gas turbine engine. The feedforward control signals 101, 102 are transmitted very quickly and are predetermined fixed signals that are not subject to closed-loop control. The feedforward control signals 101 and 102 are predetermined so that the total fuel mass flow provided to each of the gas turbine engines corresponds to the fuel mass flow required to operate the gas turbine engine at approximately the emergency power output. The fuel flow control valve and other operating parameters are controlled to predetermined values ​​by the feedforward control signals 101, 102, which ensures the safe operation of the gas turbine engine at the emergency power output. The quantitative values ​​of the feedforward control signals 101 and 102 may depend on the actual initial power plant supply pressure in the power plant supply pipeline 52, the type of fuel, and other parameters familiar to those skilled in the art, such as environmental conditions or power plant operating conditions. It should be easily understood that the order of method steps 240 and 250 can be reversed, or they can be implemented at least substantially simultaneously. The technician will understand that the fuel gas compressor start signal 103 and the feedforward control signals 101, 102 should be generated and provided to the corresponding components within a few seconds. After the power output has been reduced in a substantially discontinuous step-like manner to reduce the total fuel mass flow, at 260, the gas turbine engine can be operated at the emergency power output in a closed-loop load control mode. In step 270, it is verified whether the previously non-operating fuel gas compressor 55 is fully operational. As long as this is not the case, the gas turbine engine continues to be operated at the emergency power output in step 260. However, if the fuel gas compressor 55 is fully operational and is capable of completely replacing the failed fuel gas compressor 53, limiting the gas turbine power output to the emergency power output is terminated and the power output of the gas turbine engine is ramped up so that in step 210, the gas turbine engine can operate again at the set power output according to the power demand signal.

[0033] During method step 260, the fuel mass flow consumed by the gas turbine engine is reduced by the remaining fuel mass flow provided by the fuel gas compressor 54 that remains in operation plus the mass flow of the fuel mass buffered in the buffer volume provided by the power plant supply line 52. If the mass flow that can be maintained by the fuel gas compressor 54 is lower than the fuel mass flow consumed by the gas turbine engine at the emergency power output, the pressure in the power plant supply line 52 decreases over time. Once the actual pressure in the power plant supply line 52 drops below the critical required minimum pressure to operate the gas turbine engine at the emergency power output, the gas turbine engine must be shut down. Therefore, the emergency power output can be selected so that the fuel mass flow provided by the fuel gas compressor 54 plus the fuel mass buffered in the power plant supply line 52 is sufficient to operate the gas turbine engine at the emergency power output during the time required for the fuel gas compressor 55 to operate. The technician will understand that the emergency power output of the gas turbine engine should preferably be the power output of the generator of the gas turbine engine to remain connected to the grid, that is, the relevant grid switch should not be disconnected, although in an embodiment, the gas turbine engine can be gradually downloaded to "full speed-no load", that is, running at a speed at least substantially synchronized with the grid frequency, but the grid switch is disconnected, as described above. This at least provides a lower limit on the allowable emergency power output. Other operating considerations can provide further restrictions on the lower allowable emergency power output. In an embodiment, the design and size of the fuel supply pipeline 52 is set to provide a sufficiently large buffer volume to operate the gas turbine engine at the minimum allowable emergency power output during the full operation of the fuel gas compressor that was previously not in operation. For example, this can be achieved when designing a power plant supply pipeline with a sufficiently large cross-section. In other cases where a power plant supply pipeline already exists, an external buffer container in fluid communication with the power plant supply pipeline 52 can be provided.

[0034] It should be understood that the power output of the gas turbine engine has a direct impact on the mass flow and temperature of the gas turbine fuel gas used to generate steam for the steam turbine engine 30 in the heat recovery steam generator 40. On the one hand, this means that the power output of the steam turbine engine is also reduced, whereby this reduction in power output is delayed due to the thermal inertia of the heat recovery steam generator. If the temperature of the fuel gas from the gas turbine engine drops below a certain threshold, the steam generated in the heat recovery steam generator may no longer be at a temperature and pressure sufficient to maintain the operation of the steam turbine engine. Therefore, it may be necessary to shut down the steam turbine engine. In this regard, the emergency power output of the gas turbine engine can be defined so that a minimum temperature and pressure can be provided in the heat recovery steam generator 40 to maintain the operation of the steam turbine engine while the steam turbine engine generator 35 remains connected to the grid. The buffer volume provided by the power plant supply line 52 can be designed so that the pressure in the power plant supply line, starting from the nominal power plant supply pressure, does not drop below the fuel pressure required to operate the gas turbine engine at the emergency power output when the gas turbine engine is operated at the emergency power output, and the reduced mass flow provided by the fuel gas compressor remains in operation.

[0035] The above method may be performed in slightly different ways depending on the pipeline supply pressure. If the pipeline supply pressure is sufficient to operate the gas turbine engine at an emergency power output, the fuel gas compressor may be completely isolated from the power plant supply line during the operation of the previously non-operating fuel gas compressor, and fuel may be supplied to the power plant supply line via a bypass line 57 and a check valve 56, which provide a bypass connection between the utility supply line 51 and the power plant supply line 52, bypassing the fuel gas compressor. The check valve 56 is provided to prevent fuel from flowing back from the power plant line 52 into the utility line 51, but to allow fuel to flow from the utility line 51 to the power plant line 52. In another variation, the compressor 53 that remains in operation may be operated and compressed fuel gas may be supplied from the utility supply line 51 to the power plant supply line 52 as long as the actual power plant supply pressure in the power plant supply line 52 is higher than the pipeline supply pressure in the utility supply line 51, that is, as long as the check valve 56 is closed. However, if it is detected that the check valve 56 disconnects the fluid communication between the utility supply line 51 and the power plant supply line 52 via the bypass line 57, the fuel gas compressor is fluidly isolated from the power plant supply line 52, and the gas turbine engine is supplied with fuel gas from the utility supply line 51 via the bypass line 57 at the pipeline supply pressure. In these operating modes, the pressure in the power plant supply line 52 (i.e., the fuel pressure available to the gas turbine engine) will not substantially drop below the pipeline supply pressure. Therefore, the emergency power output of the gas turbine engine can be selected based on the pipeline supply pressure, and the associated minimum required fuel gas pressure is lower than or at most equal to the pipeline supply pressure.

[0036] Although the subject matter of the present disclosure has been explained by exemplary embodiments, it should be understood that these are in no way intended to limit the scope of the invention claimed. It should be understood that the claims cover embodiments not explicitly shown or disclosed herein, and embodiments that deviate from those embodiments disclosed in the exemplary mode of carrying out the teachings of the present disclosure will still be covered by the claims.

Claims

1. A method (200) for operating a power plant (1), the power plant comprising at least one gas turbine engine (10, 20) and at least one fuel gas compressor (53, 54, 55), the method comprising: supplying a fuel gas (5) via a common supply line (51), wherein the fuel gas in the common supply line is at a line supply pressure; compressing the fuel gas to a power plant supply pressure in at least one operating fuel gas compressor and supplying the compressed fuel gas to a power plant supply line (52); operating (210) the at least one gas turbine engine at a set power output in response to the power demand signal, detecting (220) whether an operating fuel gas compressor has a fault; as well as generating at least one feedforward control signal to reduce the power output of the at least one gas turbine engine to an emergency power output below the set power output and to limit the power output of the at least one gas turbine engine to the emergency power output, and generating a start signal to start the previously inoperative fuel gas compressor and place it into operation, in response to detecting a failure of the operating fuel gas compressor (240); Therein, the reduction in power output is performed in a single step.

2. The method according to claim 1, comprising: A feedforward control signal is provided (250) to at least one fuel flow control valve (16, 26) of the at least one gas turbine engine and the valve position is changed to a predefined emergency position and the at least one gas turbine engine is subsequently operated (260) in a load control mode at the emergency power output. 3 . The method of claim 2 , wherein the predetermined emergency valve position is a valve position corresponding to a desired position of the fuel flow control valve at the emergency power output.

4. The method according to any one of claims 1 to 3, wherein the method comprises: A sustainable critical gas turbine engine power output is determined based on fuel gas mass flow / output pressure characteristics of one or more fuel gas compressors (53, 54, 55) that remain in operation, and the emergency power output is determined to be lower than or at most equal to the critical gas turbine engine power output.

5. The method according to any one of claims 1 to 3, wherein the method comprises: Directing an exhaust mass flow of the at least one gas turbine engine (10, 20) through at least one heat recovery steam generator (40), generating steam, and supplying the generated steam to a steam turbine (32) to drive the steam turbine, wherein the emergency power output is higher than or at least equal to a minimum gas turbine engine power output required to generate steam at a minimum mass flow, pressure and temperature to drive the steam turbine.

6. The method according to any one of claims 1 to 3, comprising: Determining a minimum required power plant supply pressure for the at least one gas turbine engine (10, 20) to operate at the emergency power output, determining a start-up time for the previously inoperative fuel gas compressor, and providing a buffer volume suitable for buffering fuel gas and fluidly arranged between the at least one fuel gas compressor (53, 54, 55) and the at least one gas turbine engine (10, 20), wherein the buffer volume is large enough to supply fuel gas to the at least one gas turbine engine operating at the emergency power output after a fuel gas compressor failure and prior to full operation of the previously inoperative fuel gas compressor without the pressure in the buffer volume dropping below the minimum required power plant supply pressure.

7. The method according to any one of claims 1 to 3, comprising: After the previously inoperative fuel gas compressor is fully operational, limiting the power output to the emergency power output is terminated, and the power output of the gas turbine engine is controlled by the power demand signal.

8. The method according to any one of claims 1 to 3, wherein a bypass line (57) is installed to connect the common supply line (51) and the power plant supply line (52) and bypass the at least one fuel gas compressor (53, 54, 55), and wherein a check valve (56) is installed in the bypass line to prevent the fuel gas from flowing back from the power plant supply line (52) into the common supply line (51) while enabling the fuel gas to flow from the common supply line (51) to the power plant supply line (52), wherein the method comprises: A critical gas turbine power output sustainable with the pipeline supply pressure is determined, and the emergency power output is determined to be less than or at most equal to the critical gas turbine power output.

9. The method according to any one of claims 1 to 3, wherein a bypass line (57) is installed to connect the common supply line (51) and the power plant supply line (52) and bypass the at least one fuel gas compressor (53, 54, 55), and wherein a check valve (56) is installed in the bypass line (57) to avoid the backflow of fuel gas from the power plant supply line (52) into the common supply line (51) while enabling the fuel gas to flow from the common supply line to the power plant supply line, and wherein at least one fuel gas compressor remains in operation after a fuel gas compressor failure, the method comprising: Determining the power output of at least one gas turbine engine (10, 20) sustainable with the supply line pressure, the power output of at least one gas turbine engine sustainable with at least one fuel gas compressor maintained in operation, and isolating the at least one fuel gas compressor maintained in operation from the power plant supply line fluid if the power output of the at least one gas turbine engine sustainable with the supply line pressure is greater than the power output of the at least one gas turbine engine sustainable with the at least one fuel gas compressor maintained in operation.

10. The method according to any one of claims 1 to 3, wherein the at least one fuel gas compressor (53, 54, 55) comprises two or more fuel gas compressors, and at least one of the two or more fuel gas compressors remains in operation after a fuel gas compressor failure, the method further comprising: determining a critical power output of the at least one gas turbine engine of the two or more fuel gas compressors, the critical power output being sustainable with a maximum pressure of the power plant supply pressure that can be maintained by the at least one fuel gas compressor remaining operational and the pipeline supply pressure, and The emergency power output is determined to be lower than or at most equal to the critical power output.

11. A power plant (1) comprising at least one gas turbine engine (10, 20) operating at a set power output, at least one fuel gas compressor (53, 54, 55) and a power plant supply line (52) connecting a downstream end of the at least one fuel gas compressor and the at least one gas turbine engine, in, The upstream end of the at least one fuel gas compressor is connected to a common supply line (51), The power plant further comprises a fuel gas pressure control system and a gas turbine engine control system. wherein a control line is provided from the fuel gas pressure control system to the gas turbine control system and is adapted and configured to forward a fuel gas compressor fault signal (100) from the fuel gas pressure control system to the gas turbine engine control system, and Wherein, in response to a fuel gas compressor fault signal, the gas turbine engine control system is adapted and configured to: forward a preset feedforward emergency control signal (101, 102) to at least at least one fuel flow control valve of the at least one gas turbine engine to reduce the power output of the at least one gas turbine engine to an emergency power output lower than the set power output; and send a start signal to a previously non-operating fuel gas compressor to cause it to start operating.

12. A power plant according to claim 11, comprising a buffer volume, which is suitable for buffering fuel gas and is fluidly arranged between the at least one fuel gas compressor (53, 54, 55) and the at least one gas turbine engine (10, 20), wherein the buffer volume is large enough to supply fuel gas to the at least one gas turbine engine operating at an emergency power output during the time required to start the fuel gas compressor from standstill without the pressure in the buffer volume dropping below the minimum required power plant supply pressure required to operate the at least one gas turbine engine at the emergency power output.

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