Method for operating a power plant, and power plant

Abstract

To provide a method for operating a power plant, and a power plant configured to be operated according to the method.SOLUTION: For operating a power plant 1 comprising a gas turbine engine 10, 20 and a fuel gas compressor 53, 54, 55, the method comprises supplying fuel gas 5 through a utility supply line 51, compressing the fuel gas to a plant supply pressure in an operating fuel gas compressor, and supplying the compressed fuel gas to a plant supply line 52. The gas turbine engine is operated at a set power output according to a power demand signal. If a failure of an operating fuel gas compressor is detected, the power output of the at least one gas turbine engine is reduced to an emergency power output which is lower than the set power output, and the power output of the at least one gas turbine engine is restricted to the emergency power output. The reduction of the power output is performed in one single step, and controlled by at least one feedforward signal.SELECTED DRAWING: Figure 1

Description

Field of Technology

[0001] The present disclosure relates to a method for operating a power generation plant and a power generation plant configured to be operated in accordance with the method, as recited in the claims.

Background Art

[0002] A gas turbine or a combined cycle power generation plant includes one or more gas turbine engines and, if the gas turbine engines are intended to be operated with fuel gas, a fuel gas supply system. The fuel gas supply system typically includes either at least one fuel gas compressor or a reducing device, or a combination of both. The fuel gas compressor can be dedicated to a single gas turbine engine or configured to operate with a common header connected to multiple gas turbine engines.

[0003] To provide a stable gas supply pressure during steady-state operation of the gas turbine, the fuel gas supply system typically includes a pressure controller that operates at a relatively low speed to avoid sudden pressure gradients and significant fluctuations in the supply pressure of the fuel gas supplied to the gas turbine engine. The load control of the power generation plant also operates at a relatively low speed, taking into account the delay time of the feedback signal specific to the power generation plant.

[0004] These systems result in stable operation of the gas turbine engine and other rotating equipment of the power generation plant, but these control mechanisms may be too slow when unexpected transient phenomena occur.

[0005] For plant and auxiliary equipment self-consumption savings, as well as plant economics including investment costs, fuel gas compressors are generally designed and operated near full load with just enough fuel mass flow rate and pressure to operate one or more gas turbine engines at steady state at rated load. Therefore, a failure of a fuel gas compressor can result in a rapid drop in plant fuel gas supply pressure, which the control system may not be able to react to, due to one or more gas turbine engines operating at set power. Thus, gas turbine engines may experience abrupt shutdowns due to either a failure of the control system to adjust the fuel control valves, or a simple lack of sufficient mass flow rate of fuel gas at the minimum required plant fuel gas supply pressure. In combined cycle power plants, the shutdown of one or more gas turbine engines also causes the steam turbines to shut down rapidly. Abrupt shutdowns of major rotating equipment (also known as trips) place significant stress on the thermal load parts of the gas and steam turbines, leading to increased lifetime consumption and potentially requiring a delay before the power plant can resume supplying power to the grid. [Overview of the project]

[0006] The subject matter of this disclosure is to provide a method for operating a power plant of the type initially described, and a power plant suitable for being operated according to said method. In a more specific embodiment, a method must be provided to enable avoidance of a sudden shutdown of the main rotating equipment of the power plant in the event of a fuel gas compressor failure. In a more specific embodiment, it may be desirable to be able to return to a normal, for example, unrestricted load-controlled operating mode to provide scheduled or requested output to the grid.

[0007] This is achieved by the subject matter described in the independent claim.

[0008] Further effects and benefits of the disclosed subject matter, whether explicitly mentioned or not, will become apparent upon consideration of the disclosures provided below.

[0009] Within the framework of this disclosure, it should be noted that the use of the indefinite article "a" or "an" never specifies a singularity and does not preclude the presence of multiple specified members or features. Therefore, it should be read as meaning "at least one" or "one or more."

[0010] Accordingly, a method for operating a power plant is disclosed, the power plant comprising at least one gas turbine engine and at least one fuel gas compressor. The method comprises supplying fuel gas through a utility supply line, the fuel gas in the utility supply line being at line supply pressure. The fuel gas supplied through the utility supply line at line supply pressure is then compressed to plant supply pressure by at least one fuel gas compressor, and the fuel gas compressed at plant supply pressure is supplied to the plant supply line. Those skilled in the art will readily understand that from the plant supply line, the compressed fuel gas is supplied to at least one gas turbine engine through at least one fuel gas control valve in each gas turbine engine. Those skilled in the art will further understand that at least one fuel control valve may comprise a control valve for controlling the total fuel gas mass flow rate to each gas turbine engine, but may also comprise, or otherwise, a control valve or stop valve for distributing the fuel gas mass flow rate to, for example, different fuel lances, burners, fuel outlets of burners, or combustion zones within the gas turbine engines, for example, but not limited to. The method first includes operating a gas turbine engine at an output set according to a power request signal. In other words, the operation of the gas turbine engine is controlled by a load controller and at an output matching the control input according to an externally scheduled request signal. The method further includes detecting whether a fuel gas compressor has failed during operation. This functionality can be included in, for example, a fuel gas pressure controller, but is not limited to this. According to the method disclosed herein, if a failure of a fuel gas compressor is detected during operation, this means that the fuel gas compressor may no longer be operating, and the output of at least one gas turbine engine is reduced to an emergency output lower than the set output.The term “emergency output” should be interpreted broadly in this regard, and the method may, in embodiments, include step-downloading at least one gas turbine engine to “full speed-no load,” i.e., zero output to the grid, but at least one gas turbine engine continues to operate at a speed at least essentially synchronized with the grid frequency. However, as outlined in more detail below, if flue gas from at least one gas turbine engine is used to generate steam in a combined cycle power plant, the mass flow rate and temperature of the flue gas at “full speed-no load” may be insufficient to maintain the minimum required raw steam temperature and / or mass flow rate, which may necessitate the shutdown of the steam turbine. The output of at least one gas turbine engine is then limited to emergency output. The output reduction is carried out in a single step, which in particular may be an abrupt unloading in an essentially discontinuous, stepwise manner, controlled by at least one feedforward signal; i.e., one or more control signals are set directly by the control system and supplied to specific hardware control members without the use of a closed-loop controller. Since at least one feedforward control signal is independent of the control loop, it provides significantly faster dynamics than a closed-loop control signal. In embodiments, the method includes providing a feedforward control signal to at least one fuel flow control valve of at least one gas turbine engine, changing the valve position to a predefined emergency position, and subsequently operating at least one gas turbine engine in load-controlled mode at emergency output. Those skilled in the art will readily understand that the feedforward signal may also be transmitted to other hardware components of at least one gas turbine engine, such as a row of variable inlet guide vanes, and that the feedforward signal may be used to adjust further operating parameters for emergency output. The predefined emergency position of at least one fuel flow control valve may, in certain embodiments, be determined as a valve position suitable for safely operating at at least one gas turbine engine at near emergency output, for example, during a test run.In other words, a predetermined emergency valve position is the valve position corresponding to the position of the fuel flow control valve expected at emergency output when operated with closed-loop control. When providing a feedforward control signal, the gas turbine engine is unloaded very quickly to near emergency output, and then the actual output can be fine-tuned to emergency output by closed-loop load control. Thus, the fuel gas consumption of at least one gas turbine engine is reduced very quickly, and as a result, the fuel gas supplied by the plant supply line and / or buffered by a buffer volume communicating with the plant supply line can sustain the supply of fuel gas to at least one gas turbine engine at a sufficiently high plant supply pressure for a longer period. As described above, at least one fuel control valve may comprise a control valve for controlling the fuel gas mass flow rate to each gas turbine engine, but may also comprise, or alternatively, a control valve or stop valve for distributing the fuel gas mass flow rate to, for example, different fuel lances, burners, fuel outlets of burners, or combustion zones within the gas turbine engine, without limiting them.

[0011] It is generally understood that fuel gas compressors operate according to a pressure ratio versus inlet mass flow rate characteristic map, or, if a constant pressure is applied to the utility supply line, according to a plant supply pressure versus mass flow rate. Furthermore, at least one gas turbine engine at each output has a pair of characteristics of fuel mass flow rate and the minimum required fuel gas pressure. Steady-state operation is achievable when the mass flow rate required by at least one gas turbine engine at a particular output is lower than the mass flow rate that at least one fuel gas compressor can deliver at the minimum required fuel gas pressure at that particular output. Therefore, in the event of a fuel gas compressor failure, if the output of at least one gas turbine engine is reduced to an emergency output where the consumed fuel mass flow rate is lower than the mass flow rate that at least one operating fuel gas compressor can deliver at the minimum required fuel gas pressure at that output, operation of at least one gas turbine engine at the emergency output can be sustained for essentially unlimited time. In other examples, as outlined below, the line supply pressure may be sufficient to sustain operation of at least one gas turbine engine at the emergency output. However, if there are no operating fuel gas compressors and at least one operating fuel gas compressor is unable to supply the required fuel mass flow rate at the required fuel gas pressure, at least the plant supply line may first provide a buffer volume filled with buffered fuel gas at an initial pressure in the event of a fuel gas compressor failure. This buffered fuel gas can be used to compensate for the difference between the fuel mass flow rate requirements of at least one gas turbine engine and the supply capacity of one or more operating fuel gas compressors, if present. In such a case, the plant supply pressure in the plant supply line steadily decreases as the net extraction of fuel gas occurs. Thus, the operation of at least one gas turbine engine can be sustained for a limited time. This time is ideally sufficient to restore full fuel gas supply performance, or at least sufficient for a normal shutdown of at least one gas turbine engine at a significantly lower lifetime consumption than a sudden, unscheduled misfire.Therefore, reducing the output of at least one gas turbine engine to emergency output served at least one of the following purposes: (a) reducing the fuel mass flow rate and required minimum fuel pressure consumed by at least one gas turbine engine to a value that can be sustained by the fuel gas supply system without reduced capacity or additional fuel gas compression, and / or (b) reducing the fuel mass flow rate and required minimum fuel pressure consumed by at least one gas turbine engine to extend the time until the pressure in the plant supply line falls below the required minimum fuel pressure at emergency output.

[0012] Preferably, the emergency power is understood to be high enough to maintain the generators of a grid-connected gas turbine engine.

[0013] Furthermore, in a non-limiting embodiment, the method includes determining a sustainable critical gas turbine engine output based on the fuel gas mass flow rate / power pressure characteristics of one or more fuel gas compressors in operation, and determining that the emergency output is lower than or equal to the critical output at most. Thus, the shutdown of at least one gas turbine engine can be avoided.

[0014] Furthermore, in a non-limiting embodiment, the method includes guiding the exhaust gas mass flow rate of at least one gas turbine engine through at least one waste heat recovery boiler, generating steam, and supplying the generated steam to a steam turbine to drive the steam turbine, wherein the emergency power is higher than or at least equal to the minimum gas turbine engine power required to generate steam of the minimum mass flow rate, pressure, and temperature to drive the steam turbine. Thus, the shutdown of the steam turbine engine can be avoided.

[0015] Both measures offer significant economic and technical advantages, as they greatly reduce the life consumption of major rotating machinery, namely gas turbine engines, and optionally steam turbine engines, by allowing them to continue operating and avoiding downtime, and by eliminating the delay time required to fully restart from idle.

[0016] In frequently applied embodiments, a power plant has redundant fuel gas compression capabilities, for example, in the sense that only two of three fuel gas compressors are needed to operate the power plant at rated output. In this regard, in the event of a fuel gas compressor failure, at least one of the power plant's fuel gas compressors is not operating. Methods disclosed herein may in these cases include starting and operating the previously inactive fuel gas compressor.

[0017] Next, the method may further include determining the minimum plant supply pressure required to operate at least one gas turbine engine at emergency power, determining the start-up time for a previously inactive fuel gas compressor, and providing a buffer volume suitable for buffering fuel gas and fluidly positioned between the at least one fuel gas compressor and the at least one gas turbine engine, the buffer volume being large enough to supply fuel gas to the at least one gas turbine engine operating at emergency power after a failure of the fuel gas compressor and before the previously inactive fuel gas compressor is fully operational without the pressure in the buffer volume falling below the minimum required plant supply pressure. In embodiments, the buffer volume is provided in and by the 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. In particular, in non-limiting embodiments, the method may include providing the fuel supply line with a sufficiently large cross-sectional area, or more specifically, a diameter such that it provides a sufficient buffer volume.

[0018] Once the fuel gas compressor, which was previously not operating, is fully operational, the limiting of output to emergency power may be terminated, and the output of at least one gas turbine engine may be controlled by a power request signal to return the power plant to normal operation.

[0019] In certain power plants, a bypass line is installed connecting the utility supply line and the plant supply line, bypassing at least one fuel gas compressor, and a check valve is installed in the bypass line to prevent backflow of fuel gas from the plant supply line to the utility supply line while allowing fuel gas to flow from the utility supply line to the plant supply line. In particular, the line supply pressure provided by the utility in the utility supply line may be sufficiently high, and as a result, at least one gas turbine engine may be operated at the line supply pressure from the utility supply line. In this case, the method may include determining a critical gas turbine output that is sustainable at the line supply pressure and determining that the emergency output is lower than or equal to the critical output at most. If at least one fuel gas compressor continues to operate after a fuel gas compressor failure, the method may further include determining the output of at least one gas turbine engine that is sustainable at the supply line pressure, the output of at least one gas turbine engine that is sustainable with at least one operating fuel gas compressor, and, if the output of at least one gas turbine engine that is sustainable at the supply line pressure is greater than the output of at least one gas turbine engine that is sustainable with at least one operating fuel gas compressor, fluidically isolating at least one operating fuel gas compressor from the plant supply line.

[0020] In a further embodiment in which at least one fuel gas compressor continues to operate after a fuel gas compressor failure, the method may, in embodiments, include determining a critical gas turbine output that is sustainable at the maximum plant supply pressure given the operating at least one fuel gas compressor and line supply pressure, and determining an emergency output that is lower than or equal to the critical output at most.

[0021] In a further embodiment, a power plant is disclosed comprising at least one gas turbine engine, at least one fuel gas compressor, and a plant supply line connecting the downstream end of at least one fuel gas compressor to at least one gas turbine engine, the upstream end of at least one fuel gas compressor being connected to a utility supply line. The power plant further comprises 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 transfer a fault signal of the fuel gas compressor from the fuel gas pressure control system to the gas turbine engine control system. The gas turbine engine control system is adapted and configured to transfer a pre-configured feedforward emergency control signal to at least one fuel flow control valve of at least one gas turbine engine in response to a fault signal of the fuel gas compressor. In a less limiting, more specific embodiment, the power plant is suitable for buffering fuel gas and may further comprise a fluidly positioned buffer volume between at least one fuel gas compressor and at least one gas turbine engine, the buffer volume being large enough to supply fuel gas to at least one gas turbine engine operating at emergency power for the time required to start the fuel gas compressor from idle without the pressure within the buffer volume falling below the minimum required plant supply pressure necessary to operate at least one gas turbine engine at emergency power.

[0022] It will be understood that the features and embodiments described above can be combined with each other. Furthermore, it will be understood that further embodiments are conceivable within the scope of the present disclosure and the subject matter claimed, although these will be obvious and clear to those skilled in the art.

[0023] The subject matter of this disclosure is described in more detail hereby by selected exemplary embodiments shown in the accompanying drawings. The drawings are as follows: [Brief explanation of the drawing]

[0024] [Figure 1] This figure shows an exemplary embodiment of a power plant. [Figure 2] This is a flowchart illustrating an exemplary embodiment of the method described above. [Modes for carrying out the invention]

[0025] It should be understood that the drawings are highly schematic, and details not necessary for explanation have been omitted to facilitate understanding and depiction. The drawings show only selected exemplary embodiments, and it should be further understood that embodiments not shown are within the scope disclosed herein and / or the subject matter claimed.

[0026] Figure 1 illustrates an exemplary combined-cycle power plant 1. The combined-cycle power plant 1 comprises two gas turbine engines 10 and 20. In a manner well known to those skilled in the art, each gas turbine engine 10 and 20 comprises its respective compressors 11 and 21, its respective combustion chambers 12 and 22, its respective expansion turbines 13 and 23, and its respective generators 15 and 25. The respective expansion turbines, compressors, and generators of each gas turbine engine are mechanically coupled by shafts such that mechanical power from the expansion turbines drives the compressors and generators. During operation, the compressors 11 and 21 compress ambient air. The compressed ambient air flows into the respective combustion chambers 12 and 22, where it is mixed with fuel. The fuel is burned in the compressed air within the combustion chambers, and the resulting high-pressure flue gas is led to the respective expansion turbines 13 and 23, where the flue gas is expanded, thereby generating useful shaft power that drives the compressors and generators, and thereby producing the power output of each gas turbine engine. As is well known to those skilled in the art, a gas turbine engine further comprises a control system, among other things, for controlling the power output. While the control system is not shown in this description, those skilled in the art are fully familiar with the respective control systems of gas turbine engines and power plants. The control system of each gas turbine engine receives a power request signal, compares it to the actual power output from the respective generator, and transmits an operating signal to the respective fuel control valves 16 and 26, thereby controlling the mass flow rate of fuel supplied to the combustion chamber so that the actual power output matches the set power output corresponding to the power request signal. Thus, as is easily understood, the fuel control valves of each gas turbine engine are operated in closed-loop control. Furthermore, those skilled in the art will understand that the control parameters are set so that the control loop operates at a relatively low speed to avoid instability and fluctuation of the control signals. It is further known to those skilled in the art that state-of-the-art gas turbine engines generally comprise a number of fuel control valves to control the total fuel mass flow rate on the one hand, and to distribute the total fuel mass flow rate to different burners, combustion zones, fuel discharge orifices, combustors, etc.Those skilled in the art are further familiar with the fact that a gas turbine engine may include a plurality of combustors, turbines, and compressors. However, this is not relevant to the understanding of the subject matter of the present disclosure, and therefore, a very basic non-limiting example has been selected to outline the subject matter of the present disclosure, and the fuel control system of a gas turbine engine is represented by a single fuel gas control valve.

[0027] Exemplary power generation plant 1 further includes an exhaust heat recovery boiler 40 and a steam turbine engine 30. The expansion exhaust gas from the expansion turbines 13 and 23 of the gas turbine engine is led through the exhaust heat recovery boiler 40, thereby exchanging heat with the feed water supplied to the exhaust heat recovery boiler in a manner known to those skilled in the art to generate steam. The steam is led to the expansion steam turbine 33, where the steam is expanded, thereby driving the steam turbine engine generator 35 to generate useful shaft power for generating additional power output.

[0028] Fuel gas 5 is supplied by the utility to the utility supply line 51 at the line supply pressure. The supply line pressure may not be sufficient to supply the gas turbine engine when operating under all operating conditions. Therefore, fuel gas compressors 53, 54, and 55 are provided to compress the fuel gas from the line supply pressure to the plant supply pressure. The fuel gas at the plant supply pressure is supplied to the combustion chambers 12 and 22 through the plant supply line 52, thereby controlling the fuel mass flow rate by fuel control valves 16 and 26. The combustion system of the gas turbine engine is equipped with nozzles from which the fuel gas is injected into the compressed air in the combustion chamber. Therefore, when the fuel gas is supplied to the combustion chamber, it must be supplied at the minimum required fuel gas pressure, which will generally be understood, as an empirical rule, to be higher as the fuel mass flow rate, or power, of the gas turbine engine increases. In other words, if the plant supply pressure falls below a certain threshold, the power that can be generated by the gas turbine engine is limited. Generally, to enhance plant reliability, fuel gas compressors are designed with redundancy, meaning the cumulative pressure / mass flow capacity of all fuel gas compressors exceeds the requirements of a gas turbine operating at rated power. For example, in the exemplary embodiment shown, each fuel gas compressor may be capable of providing 50% or slightly more than 50% of the maximum fuel gas mass flow rate cumulatively required by the gas turbine engine operating at maximum power and associated required fuel gas pressure. Therefore, to avoid excessive auxiliary power consumption of the plant, only two of the three fuel gas compressors may be operated. For example, fuel gas compressors 53 and 54 may be operating while fuel gas compressor 55 is not. In this regard, it will be understood that at least one of the lines connecting each fuel gas compressor to the utility supply line 51 and the plant supply line 52, respectively, is equipped with a check valve or shut-off valve to prevent backflow of fuel gas from the plant supply line to the utility supply line through a non-operating compressor.It will be further understood that each fuel gas compressor may be equipped with a line and valve system that allows the compressor to be started while another fuel gas compressor is operating. The auxiliary systems of the fuel gas compressors that are not immediately necessary for understanding the subject matter disclosed herein are omitted from the drawings for clarity but are well known to those skilled in the art. The fuel gas compressors are controlled by a pressure control system, which is not shown but is well known to those skilled in the art.

[0029] Figure 2 outlines an exemplary embodiment of method 200 as described herein. In relation to Figure 2, to outline the method disclosed herein by Figure 1, we hereby assume that, as described above, fuel gas compressors 53 and 54 are initially operating while fuel gas compressor 55 is not operating. The gas turbine engine is operating in closed-loop load control mode, as described above, and the fuel mass flow rate to the gas turbine engine is controlled by a fuel control valve to operate the gas turbine engine at a set output according to an externally provided load request signal. This initial operating state is shown at 210. In step 220, it is determined whether the operating fuel gas compressor has failed. If not, the gas turbine engine continues to operate in load control mode at the set output according to the power request signal at 210. However, if a failure is detected in the operating fuel gas compressor, for example fuel gas compressor 53, a failure signal 100 is generated at 230, and a start signal 103 is sent at 240 to the non-operating fuel gas compressor 55. However, a certain start-up time is required before the previously inactive fuel gas compressor 55 can fully replace the compression and fuel mass flow capacity previously provided by the failed compressor 53. If the gas turbine engine is operating at an output exceeding a certain threshold, the remaining fuel gas compressor 54 may not be able to sustain the required fuel mass flow at the minimum plant supply pressure necessary to operate the gas turbine engine at the output according to the power request signal. Therefore, if the pressure in the plant supply line falls below the minimum required pressure corresponding to the output of the gas turbine engine, the gas turbine engine may be abruptly switched off. That is, combustion in the combustion chamber suddenly ceases from a high power level, causing a high temperature gradient within the gas turbine engine, and consequently, high thermal induction stress and lifetime consumption. As is understood, the shutdown of the gas turbine engine also causes the shutdown of the steam turbine engine. In addition to the high lifetime consumption of the engine, the power plant completely stops generating electricity. Restarting the power plant may result in a long delay time.Therefore, it is sometimes of paramount importance to avoid the complete shutdown of the main rotating equipment, i.e., not only the gas turbine engines but also the steam turbine engines. In the event of a fuel gas compressor failure, the plant supply line 52 is filled with fuel gas at the plant supply pressure, and as a result, it functions as a compressed fuel buffer volume. The gas turbine engines can operate on fuel from this buffer volume as long as the pressure in the buffer volume does not fall below the minimum pressure required to operate the gas turbine engines at a particular output. For a given buffer volume and initial pressure, it is understood that the occurrence of a particular pressure drop will be slower as less fuel is consumed per unit of time, i.e., as the output on which the gas turbine engines are operated decreases. Furthermore, it can be generally and reasonably assumed that the critical minimum plant supply pressure required to sustain the operation of the gas turbine engines is lower as the output of the gas turbine engines decreases. Therefore, at 250, rapid feedforward unloading of the gas turbine engines 10 and 20 is initiated. To that extent, in the exemplary embodiments shown herein, feedforward control signals 101, 102 are generated in response to a fuel gas compressor failure signal and transmitted to the fuel control system of the gas turbine engine, as simply represented by fuel flow control valves 16 and 26. As outlined above, the fuel control system is considerably more complex and may comprise a number of fuel flow control valves that control the distribution of the total fuel mass flow to the gas turbine engine and / or a portion of the total fuel mass flow within the combustion system of the gas turbine engine. The feedforward control signals may also act on the position of one or more rows of variable inlet guide vanes to reduce the mass flow of air through the gas turbine engine. The feedforward control signals 101, 102 are transmitted at very high speeds 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 supplied to each of the gas turbine engines corresponds to the fuel mass flow required to operate the gas turbine engine at approximately emergency power.The fuel flow control valve and other operating parameters are controlled by the feed-forward control signals 101, 102 to a predetermined value that ensures the safe operation of the gas turbine engine at emergency output. The quantitative values of the feed-forward control signals 101 and 102 may depend on the actual initial plant supply pressure in the plant supply line 52, the type of fuel, and other parameters such as ambient conditions or the operating state of the power plant, which are well known to those skilled in the art. It will be readily understood that the order of method steps 240 and 250 can be reversed or that they can be executed at least essentially simultaneously. Those skilled in the art will understand that the start signal 103 for the fuel gas compressor and the feed-forward control signals 101, 102 should be generated and provided to their respective components within a few seconds. After the output is reduced in an essentially discontinuous stepwise manner when reducing the total fuel mass flow rate, the gas turbine engine can operate at emergency output in a closed-loop load control mode at 260. At step 270, it is verified whether the previously non-operating fuel gas compressor 55 has fully operated. Unless this is the case, the gas turbine engine continues to operate at emergency output at step 260. However, if the fuel gas compressor 55 is fully operating and it is possible to completely replace the failed fuel gas compressor 53, the limitation of the gas turbine output to emergency output ends, the output of the gas turbine engine increases, and as a result, the gas turbine engine can operate again at the output set according to the power demand signal of step 210.

[0030] During step 260 of the method, the fuel mass flow rate consumed by the gas turbine engine consists of the remaining fuel mass flow rate provided by the operating fuel gas compressor 54 plus the reduced fuel mass buffered by the buffer volume provided by the plant supply line 52. If the mass flow rate that can be sustained by the fuel gas compressor 54 is lower than the fuel mass flow rate consumed by the gas turbine engine at emergency power, the pressure in the plant supply line 52 will decrease over time. As soon as the actual pressure in the plant supply line 52 falls below the minimum critical pressure required to operate the gas turbine engine at emergency power, the gas turbine engine must be shut down. Thus, the emergency power can be selected such that the fuel mass buffered in the plant supply line 52, in addition to the fuel mass flow rate provided by the fuel gas compressor 54, is sufficient to operate the gas turbine engine at emergency power for the time required to operate the fuel gas compressor 55. Those skilled in the art will understand that the emergency power of a gas turbine engine should preferably be the power at which the gas turbine engine's generator remains connected to the grid, i.e., the associated grid switch should not be opened, and in embodiments, it is possible to step-down the gas turbine engine to "full speed-no load", i.e., operating at a speed at which it is at least essentially synchronized with the grid frequency, but with the grid switch open as described above. This provides at least a lower limit on the allowable emergency power. Other operational considerations may impose further limitations on the reduction of the allowable emergency power. In embodiments, the fuel supply line 52 is designed and dimensionally defined to provide a buffer volume large enough to operate the gas turbine engine at the minimum allowable emergency power during the time until the fuel gas compressor, which was previously not operating, becomes fully operational. This can be achieved, in one example, by designing a plant supply line with a sufficiently large cross-sectional area. In other examples, if a plant supply line already exists, an external buffer vessel may be provided in fluid communication with the plant supply line 52.

[0031] It will be understood that the output of the gas turbine engine directly affects the mass flow rate and temperature of the gas turbine flue gas used to generate steam for the steam turbine engine 30 in the heat recovery boiler 40. This means that the output of the steam turbine engine will also be reduced, and this reduction in output will be delayed due to the thermal inertia of the heat recovery boiler. If the temperature of the flue gas from the gas turbine engine falls below a certain threshold, the steam generated in the heat recovery boiler may not be at a temperature and pressure sufficient to sustain the operation of the steam turbine engine. As a result, the steam turbine engine may need to be shut down. In this regard, the emergency output of the gas turbine engine can be defined to provide the heat recovery boiler 40 with a minimum temperature and pressure so that the steam turbine engine generator 35 can continue operating while remaining connected to the grid. The buffer volume provided by the plant supply line 52 may be designed so that the pressure in the plant supply line, starting at the nominal plant supply pressure, does not fall below the fuel pressure required to operate the gas turbine engine at emergency power when the gas turbine engine is operated with emergency power output and the mass flow rate provided by the operating fuel gas compressor is reduced.

[0032] Depending on the line supply pressure, the above method may be implemented in a slightly different manner. If the line supply pressure is sufficient to operate the gas turbine engine at emergency power, the fuel gas compressor may be completely isolated from the plant supply line during the period when the fuel gas compressor, which was not previously operating, is in operation, and fuel may be supplied to the plant supply line through a bypass line 57 and a check valve 56, which bypass the fuel gas compressor and provide a bypass connection between the utility supply line 51 and the plant supply line 52. The check valve 56 is provided to prevent backflow of fuel from the plant supply line 52 to the utility supply line 51, but to allow the flow of fuel from the utility supply line 51 to the plant supply line 52. In another modification, the operating compressor 53 may be operated to supply compressed fuel gas from the utility supply line 51 to the plant supply line 52, as long as the actual plant supply pressure in the plant supply line 52 is higher than the line supply pressure in the utility supply line 51, i.e., as long as the check valve 56 is closed. However, if the check valve 56 detects that the fluid communication between the utility supply line 51 and the plant supply line 52 is opened through the bypass line 57, the fuel gas compressor is fluidly isolated from the plant supply line 52, and the gas turbine engine is supplied with fuel gas from the utility supply line 51 through the bypass line 57 at the line supply pressure. In these operating modes, the pressure in the plant supply line 52, i.e., the fuel pressure available to the gas turbine engine, will not fall below the line supply pressure in any way. Therefore, the emergency power of the gas turbine engine can be selected according to the line supply pressure, and as a result, the relevant minimum required fuel gas pressure is either less than or equal to the line supply pressure.

[0033] While the subject matter of this disclosure is illustrated by exemplary embodiments, it will be understood that these are not intended in any way to limit the scope of the claimed invention. The claims cover embodiments not expressly illustrated or disclosed herein, and embodiments that deviate from the embodiments disclosed in exemplary embodiments for carrying out the teachings of this disclosure will still be encompassed by the claims. [Explanation of Symbols]

[0034] 1. Combined cycle power plant 5 Fuel gas 10 Gas turbine engines 11 Compressor 12 Combustion chamber 13 Expansion Turbine 15 Generators 16 Fuel flow control valve 20 Gas turbine engines 21 Compressor 22 Combustion chamber 23 Expansion Turbine 25 Generators 26 Fuel flow control valve 30 Steam turbine engine 33 Expansion Steam Turbine 35 Steam Turbine Engine Generator 40. Waste heat recovery boiler 51 Utility supply lines 52 Plant supply lines / fuel supply lines 53 Fuel gas compressor 54 Fuel gas compressor 55 Fuel gas compressor 56 Check valve 57 Bypass Line 100 Fault signal 101 Feedforward control signal 102 Feedforward control signal 103 Start signal 200 ways 210 steps 220 steps 230 steps 240 Method Steps 250 steps 260 Method Steps 270 steps

Claims

1. A method (200) for operating a power plant (1), the power plant (1) comprising at least one gas turbine engine (10, 20) and at least one fuel gas compressor (53, 54, 55), the method (200) comprising: supplying fuel gas (5) through a utility supply line (51), the fuel gas (5) in the utility supply line (51) being at line supply pressure; compressing the fuel gas (5) to a plant supply pressure with at least one operating fuel gas compressor (53, 54, 55) and supplying the compressed fuel gas (5) to a plant supply line (52); operating (210) the at least one gas turbine engine (10, 20) at a power output set in accordance with a power demand signal; Detecting (220) whether an operating fuel gas compressor (53, 54, 55) has failed; When a failure of an operating fuel gas compressor (53, 54, 55) is detected, the output of the at least one gas turbine engine (10, 20) is reduced to an emergency output lower than the set output, and the output of the at least one gas turbine engine (10, 20) is limited to the emergency output. Including, said reduction of said power output being performed in a single step and being controlled by at least one feedforward signal (101, 102); Method(200).

2. 2. The method of claim 1, comprising: providing a feedforward control signal to at least one fuel flow control valve of the at least one gas turbine engine; and changing a valve position to a predefined emergency position, and subsequently operating the at least one gas turbine engine in a load control mode at the emergency power output.

3. 3. The method (200) of claim 2, wherein the predetermined emergency valve position is a valve position corresponding to the position of the fuel flow control valve (16, 26) expected at the emergency power output.

4. 4. The method (200) of claim 1, comprising determining a critical sustainable gas turbine engine power output based on a fuel gas mass flow rate / output pressure characteristic of one or more fuel gas compressors (53, 54, 55) in operation, and determining the emergency power output to be lower than or at most equal to the critical power output.

5. 5. The method of claim 1, wherein the method includes directing an exhaust gas mass flow rate of the 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, and wherein the emergency power output is greater than or at least equal to a minimum gas turbine engine power output required to generate steam of a minimum mass flow rate, pressure, and temperature to drive the steam turbine.

6. 6. The method (200) of any one of claims 1 to 5, comprising starting up and operating (240) a previously inoperable fuel gas compressor (53, 54, 55).

7. 10. The method of claim 6, further comprising: determining a minimum required plant supply pressure to operate the at least one gas turbine engine 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 disposed between the at least one fuel gas compressor and the at least one gas turbine engine, the buffer volume being sufficiently large to supply fuel gas to the at least one gas turbine engine operating at the emergency power output after a failure of a fuel gas compressor and before the previously inoperative fuel gas compressor becomes fully operational without the pressure in the buffer volume dropping below the minimum required plant supply pressure.

8. and controlling the output of the gas turbine engine (10, 20) according to the power demand signal after terminating the limiting of the output to the emergency output and after the previously inoperative fuel gas compressor (53, 54, 55) is fully operational.

9. 9. The method (200) of claim 1, wherein a bypass line (57) is provided connecting the utility supply line (51) and the plant supply line (52) and bypassing the at least one fuel gas compressor (53, 54, 55), and a check valve (56) is provided in the bypass line (57) to prevent a backflow of the fuel gas (5) from the plant supply line (52) to the utility supply line (51) while allowing a flow of the fuel gas (5) from the utility supply line (51) to the plant supply line (52), the method (200) comprising: determining a critical gas turbine power output that is sustainable at the line supply pressure; and determining the emergency power output to be lower than or at most equal to the critical power output.

10. a bypass line (57) is provided connecting the utility supply line (51) and the plant supply line (52) and bypassing the at least one fuel gas compressor (53, 54, 55); a check valve (56) is provided in the bypass line (57) to prevent a backflow of the fuel gas (5) from the plant supply line (52) to the utility supply line (51) while allowing a flow of the fuel gas (5) from the utility supply line (51) to the plant supply line (52); after a failure of a fuel gas compressor (53, 54, 55), at least one fuel gas compressor (53, 54, 55) continues to operate; and the method (200) further comprises:

10. The method (200) of claim 1, comprising: determining a power output of one gas turbine engine (10, 20), a power output of the at least one gas turbine engine (10, 20) sustainable by the at least one fuel gas compressor (53, 54, 55) in operation; and fluidly isolating the at least one fuel gas compressor (53, 54, 55) in operation from the plant supply line (52) if the power output of the at least one gas turbine engine (10, 20) sustainable at the supply line pressure is greater than the power output of the at least one gas turbine engine (10, 20) sustainable by the at least one fuel gas compressor (53, 54, 55) in operation.

11. 11. The method (200) of claim 1, comprising determining a critical power output of the at least one gas turbine engine (10, 20) that is sustainable at a maximum pressure of the plant supply pressure that is sustainable by at least one fuel gas compressor (53, 54, 55) continuing to operate after a failure of a fuel gas compressor (53, 54, 55) and the at least one fuel gas compressor (53, 54, 55) that is operating and the line supply pressure, and determining the emergency power output to be lower than or at most equal to the critical power output.

12. The present invention relates to a gas turbine engine (10, 20) and a plant (52) that includes at least one gas turbine engine (10, 20), at least one fuel gas compressor (53, 54, 55), and a plant supply line (52) that connects a downstream end of the at least one fuel gas compressor (53, 54, 55) with the at least one gas turbine engine (10, 20), and an upstream end of the at least one fuel gas compressor (53, 54, 55) is connected to a utility supply line (51). The present invention also relates to a gas turbine engine (10, 20), and a plant (52) that connects a downstream end of the at least one fuel gas compressor (53, 54, 55) with the at least one gas turbine engine (10, 20), and a fuel gas pressure control system and a gas turbine engine control system, and a control line is connected from the fuel gas pressure control system to the gas turbine. a control system adapted and configured to transfer a failure signal (100) of a fuel gas compressor (53, 54, 55) from the fuel gas pressure control system to the gas turbine engine control system, the gas turbine engine control system adapted and configured to at least transfer a preset feedforward emergency control signal (101, 102) to at least one fuel flow control valve (16, 26) of the at least one gas turbine engine (10, 20) in response to the failure signal (100) of the fuel gas compressor (53, 54, 55);

13. 13. The power plant (1) of claim 12, further comprising a buffer volume suitable for buffering fuel gas (5) and fluidly disposed between the at least one fuel gas compressor (53, 54, 55) and the at least one gas turbine engine (10, 20), the buffer volume being sufficiently large to supply fuel gas (5) to the at least one gas turbine engine (10, 20) operating at emergency power output for a time required to start the fuel gas compressor (53, 54, 55) from shutdown without the pressure in the buffer volume falling below a minimum required plant supply pressure required to operate the at least one gas turbine engine (10, 20) at emergency power output.

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