A gas turbine engine and a control method capable of operating at a very low part load

Abstract

The present invention relates to a gas turbine engine, comprising: a burner assembly (7) having a plurality of burners (18); a fuel supply system (9) configured to supply a fuel flow rate (M2) to the burners (18), and including a fuel supply line (17) and a main fuel valve (22) between the fuel supply line (17) and the burners (18); and a control unit (10) configured to control the fuel flow rate (M2) using the main fuel valve (22) in a first load range (LR1) from full load to a threshold partial load. The fuel supply system (9) includes a secondary fuel valve (23) fluidly connected between the fuel supply line (17) and at least one associated group of burners (18). The control unit (10) is further configured to control the fuel flow rate (M2) using the secondary fuel valve (23) in a second load range (LR2) from the threshold partial load (LTH) to the minimum load (ML).

Description

[0001] Cross-reference to related applications

[0002] This patent application claims priority to European Patent Application No. 19209834.1, filed on November 18, 2019, the entire disclosure of which is incorporated herein by reference. Technical field

[0003] The present invention relates to a gas turbine engine that can operate at very low partial loads and to a method of controlling a gas turbine engine. Background art

[0004] It is well known that controlling pollutant emissions is a primary and important objective in the design of any type of heat engine and especially gas turbines for power stations. In fact, the awareness of environmental risks has led to the enactment of regulations with increasingly stringent requirements. On the other hand, the organization of the modern electricity market and the changing demands do not allow power stations to operate under constant load conditions. Instead, the need to meet demand fluctuations (including sudden increases or decreases) and contribute to the control of the grid frequency requires very flexible operation. However, reducing pollutant emissions has become crucial due to this flexible operation.

[0005] For example, one of the problems to be solved relates to operation at very low partial loads. Reducing the number of activated burners in the burner assembly may not be sufficient to meet both the market and low requirements, and activated burners are often used in the lowest part of their power range. Since the trend is towards continuously decreasing power lower limits, key aspects relate to control and pollutant emissions. First, very fine control is required to maintain stable combustion at the lower limit of the operating range. However, the control system needs to cope with a wide range of conditions, and full-load operation is hardly compatible with fine control at very low loads. In addition, CO emissions are usually not a problem at full load, but low temperatures and instabilities at low loads may prevent complete oxidation of carbon and contribute to the formation of carbon monoxide. Summary of the invention

[0006] It is an object of the present invention to provide a gas turbine engine and a method of controlling a gas turbine engine that allow at least partially overcoming or alleviating the described limitations.

[0007] According to the present invention, there is provided a gas turbine engine comprising:

[0008] A burner assembly having a plurality of burners;

[0009] A fuel supply system configured to supply a fuel flow to the burners, and the fuel supply system includes a fuel supply line and a main fuel valve between the fuel supply line and the burners;

[0010] a control unit configured to control fuel flow using a main fuel valve in a first load range from full load to a threshold part load;

[0011] wherein the fuel supply system includes a secondary fuel valve fluidly coupled between a fuel supply line and at least one group of associated burners;

[0012] And wherein the control unit is further configured to control the fuel flow using the secondary fuel valve in a second load range from a threshold part load to a minimum load.

[0013] According to another aspect of the present invention, there is provided a method of controlling a gas turbine engine including a combustor assembly having a plurality of burners, the method comprising:

[0014] supplying fuel flow to the burner;

[0015] controlling fuel flow using a main fuel valve in a first load range from full load to a threshold part load; and

[0016] The secondary fuel valve is used to control fuel flow to at least one group of burners in a second load range from a threshold part load to a minimum load. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The invention will now be described with reference to the accompanying drawings, which show some non-limiting embodiments of the invention, in which:

[0018] - Figure 1 is a simplified block diagram of a gas turbine engine;

[0019] - Figure 2 is incorporated Figure 1 A schematic diagram of a combustor assembly and a portion of a fuel supply system in a gas turbine engine and manufactured according to one embodiment of the present invention;

[0020] - Figure 3A It is shown in Figure 1 A graph of the amount used in the gas turbine engine in the operating mode;

[0021] - Figure 3B It is shown in Figure 1 a graph of an amount used in another operating mode of a gas turbine engine;

[0022] - Figures 4 - 16 shows the corresponding different operating conditions Figure 1 Burner components;

[0023] - Figure 17 is a schematic diagram of a combustor assembly and a portion of a fuel supply system incorporated into a gas turbine engine according to another embodiment of the present invention;

[0024] - Figure 18 is a schematic view of a burner assembly and a portion of a fuel supply system incorporated into a gas turbine engine according to another embodiment of the present invention; and

[0025] - Figures 19 - 20 shows the Figure 1 burner assembly under corresponding additional different operating conditions. DETAILED DESCRIPTION

[0026] Figure 1 shows a simplified view of a gas turbine engine generally designated by the numeral 1. The gas turbine engine 1 includes a compressor 2, a first-stage burner 3, a high-pressure turbine 5, a second-stage burner 7 (also referred to as a sequential burner), and a low-pressure turbine 8.

[0027] A fuel supply system 9 delivers a fuel flow rate to operate the first-stage burner 3 and the second-stage burner 7.

[0028] A controller 10 receives status signals from system sensors 11 and operates the gas turbine via actuators to provide a controlled power output. The actuators include the orientable inlet guide vanes 12 of the compressor 2 and the first-stage fuel valve system 13 and the second-stage fuel valve system 15 of the fuel supply system 9.

[0029] The compressed air flow supplied by the compressor 2 is increased to a first fuel flow rate M1, and the resulting air / fuel mixture is burned in the first-stage burner 3. The exhaust of the first-stage burner 3 expands in the high-pressure turbine 5, and then, after a dilution air flow may be added, a second fuel flow rate M2 is mixed and burned in the second-stage burner 7. The exhaust finally expands in the low-pressure turbine 8 and is discharged to the outside or, for example, discharged to a heat recovery steam generator. The first fuel flow rate M1 and the second fuel flow rate M2 from the supply lines 16, 17 are controlled by the controller 10 using the first-stage fuel valve system 13 and the second-stage fuel valve system 15, respectively.

[0030] Figure 2 Schematically shows the second-stage fuel valve system 15 and the second-stage burner 7, the second-stage burner including a plurality of burners 18 circumferentially arranged about the machine axis A.

[0031] Fuel is supplied to the burners 18 through the supply line 17, the second-stage fuel valve system 15, the fuel plenum 20, and the corresponding supply pipes 21. More precisely, the second-stage fuel valve system 15 includes a main fuel valve 22 and a sub-fuel valve 23, both of which are controlled by the controller 10 and have corresponding inlets connected to the supply line 17 and corresponding outlets connected to the fuel plenum 20. Thus, in Figure 2In an embodiment, the main fuel valve 22 and the auxiliary fuel valve 23 are arranged in parallel. The main fuel valve 22 is sized to operate at a fuel flow rate corresponding to the load in the first load range LR1, which includes the full load LF and extends down to the threshold partial load LTH (see Figure 3A and 3B ). The auxiliary fuel valve 23 is sized to operate at a fuel flow rate corresponding to the load in the second load range LR2, which includes the threshold partial load LTH and extends down to the minimum load LM. For example, the main fuel valve 22 has a first minimum rated flow rate, while the auxiliary fuel valve 23 has a second minimum rated flow rate that is less than the first minimum rated flow rate.

[0032] The supply pipe 21 extends from the fuel gas chamber 20 to the inlets of the respective burners 18.

[0033] A shut-off valve 25 is arranged along the supply pipe 21, one shut-off valve for each burner 18 respectively. Thus, the shut-off valve 25 is arranged between the main fuel valve 22 and the fuel inlet of the respective burner 18. The shut-off valve 25 is independently controlled by the controller 10 such that the controller 10 can activate and deactivate each burner 18 independently of the other burners 18.

[0034] The controller 10 is configured to control the fuel flow rate supplied to the burners 18 using the main fuel valve 22 and / or the auxiliary fuel valve 23 according to the current load set point for the gas turbine engine 1. For load set points in the first load range LR1 from the full load down to the threshold partial load LTH, the controller 10 adjusts the main fuel valve 22, while the auxiliary control valve 23 does not participate in the flow control and can be kept closed ( Figure 3A ) or fully open ( Figure 3B ) or partially open in a fixed configuration in any case. Outside the second load range LR2, the auxiliary fuel valve 23 can be kept open, thus providing a constant contribution to the total fuel flow rate supplied to the burners 18, or can be closed depending on the design preference. The contribution of the auxiliary fuel valve 23 is in any case less than the contribution of the main fuel valve 22 that can be designed and optimized for high-load operation.

[0035] For load set points in the second load range LR2 from the threshold partial load LTH to the minimum load LM, the controller 10 adjusts the auxiliary fuel valve 23. Outside the first load range LR1, the main fuel valve 22 is closed by the controller 10 such that the control at very low partial loads is left to the auxiliary fuel valve 23 that can be specifically designed for this purpose.

[0036] In one embodiment, the first load range LR1 and the second load range LR2 can include the threshold partial load LTH ( Figure 3A and 3B) overlap within a sub-range SR. In the sub-range SR, for the purpose of controlling the flow rate, both the main fuel valve 22 and the auxiliary fuel valve 23 can be used by the controller 10.

[0037] The controller 10 is further configured to deactivate at least a threshold number of burners 18 before starting to use the auxiliary fuel valve 23. In Figure 4 the example, M = 24 is the total number of burners 18, NTH = 20 is the threshold number, and K = M - NTH = 4 is the number of burners 18 that remain active when the controller 10 starts to use the auxiliary fuel valve 23. The number of active burners 18 can be further reduced to achieve an even lower load condition.

[0038] The activation and deactivation of the burners 18 are accomplished by the controller 10 through the shut-off valves 25, which can operate individually and independently. The controller 10 is configured to activate and deactivate the burners such that, under any operating condition and independent of the number of active burners 18, the active burners 18 form a single group of adjacent active burners 18, and the non-active burners 18 form a single group of adjacent non-active burners 18. When all burners 18 are active, the controller 10 first deactivates the first of the burners 18, and then successively deactivates the active burners 18 adjacent to the non-active burners 18, as Figure 5 shown in the example of

[0039] Similarly, after at least one burner 18 has been activated from the off state of the entire second-stage burner 7, the controller 10 sequentially activates the non-active burners 18 adjacent to the active burners 18, as Figure 6 shown. The burners 18 are divided into a single group of active burners GA and a single group of non-active burners GI at all times, but the composition of each of the single group of active burners GA and the single group of non-active burners GI changes during operation.

[0040] In principle, the activation and deactivation of the burners 18 can follow any pattern, provided that at any time, all the active burners 18 in the single group of active burners GA are adjacent to each other and all the non-active burners 18 in the single group of non-active burners GI are adjacent to each other. For example, Figure 7 and 8 show another possible pattern of activation and deactivation of the burners 18. In this case, starting from the burner 18 that is deactivated first, the other burners 18 are alternately deactivated one in the clockwise direction and one in the counterclockwise direction until the Figure 8 configuration of

[0041] The controller 10 is also configured to modify the single set of active burners GA and the single set of inactive burners GI such that the active burners 18 vary not only during load transients but also at least occasionally during steady low-load operation. In particular, the controller 10 is configured to control the burners 18 such that:

[0042] - Under a first low-load condition and a second low-load condition, the same number of adjacent burners 18 remain active; and

[0043] - At least one of the burners 18 that is active under the first low-load condition is inactive under the second low-load condition, and at least one of the burners 18 that is inactive under the first low-load condition is active under the second low-load condition.

[0044] The first low-load condition and the second low-load condition may respectively include a load setpoint within a low-load range during a first time interval and a load setpoint within a low-load range during a second time interval that is different from the first time interval.

[0045] In one embodiment, the controller 10 changes the activation pattern of the burners 18 at each load cycle. For example, in one load cycle (T1, Figure 9 ), a first single set of active burners GA1 is selected, and the first single set of active burners includes burners 18 that are symmetrically arranged across a dividing line SL on the first side of the gas turbine engine 1. In a subsequent second load cycle (T2, Figure 10 ), a second single set of active burners GA2 is selected, and the second single set of active burners includes burners 18 that are symmetrically arranged across the dividing line SL on the second side of the gas turbine engine 1 opposite the first side. In fact, the burners 18 that are active in the second load cycle are symmetrically opposite to the burners 18 that are active in the first load cycle. Then, in a third load cycle (T3, Figure 11 ), a third single set of active burners GA3 is selected, and the third single set of active burners includes burners 18 that are symmetrically arranged across a plane P perpendicular to the dividing line SL at the bottom of the gas turbine engine 1. In a fourth load cycle ( Figure 12 T4 in), a fourth single set of active burners GA4 is selected, and the fourth single set of active burners includes burners 18 that are symmetrically arranged across a plane P perpendicular to the dividing line SL at the top of the gas turbine engine 1, which is opposite to the burners 18 that are active during the third load cycle.

[0046] In Figures 13 - 16 In another embodiment shown, the controller 10 changes the pattern of the active burners 18 during each load cycle. In a first time interval T1 at the start of the load cycle ( Figure 13) First, the first single - group activated burner GA1 is selected. Once the first time interval T1 has elapsed, the activated burner 18 at one end of the first single - group activated burner GA1 is deactivated, and the non - activated burner 18 adjacent to the opposite end of the first single - group activated burner GA1 is activated. Thus, the second single - group activated burner GA2 is obtained ( Figure 14 ), which rotates, for example, counter - clockwise and is maintained during the second time interval T2'. Similarly, during the subsequent third time interval T3' ( Figure 15 ), the controller 10 deactivates the activated burner 18 at one end of the second single - group activated burner GA2 and activates the non - activated burner 18 near the opposite end of the second single - group activated burner GA2. Thus, the third single - group activated burner GA3 is obtained, and the pattern of the activated burners 18 is rotated another step in the same direction (here counter - clockwise). The controller 10 iteratively repeats the process of deactivating the activated burner 18 at one end of the current single - group activated burner and activating the non - activated burner 18 near the opposite end of the current single - group activated burner, thereby obtaining a step - by - step rotation of the single - group activated burners in the same direction as the activated burner pattern. Figure 16 The I - th single - group activated burner GAI that has rotated I steps during the I - th time interval TI is shown.

[0047] In Figure 17 the illustrated embodiment, the gas turbine engine 100 includes a burner 107 and a fuel valve system 115 configured to supply fuel from a fuel supply line 117 to the burner 107. The burner 107 can be a single - stage burner system or the first - stage or second - stage burner of a two - stage (or sequential) burner system. The fuel valve system 115 includes a plurality of main fuel valves 122 and a plurality of pilot fuel valves 123. Each main fuel valve 122 and each pilot fuel valve 123 are fluidly coupled between the fuel supply line 117 and a corresponding associated group of burners 118. More precisely, each group of burners 118 is served by a corresponding main fuel valve 122 and a corresponding pilot fuel valve 123 connected in parallel between the fuel supply line 117 and the inlet of the burners 118.

[0048] Figure 18 Another embodiment of a gas turbine engine is shown, where the gas turbine engine is designated here by 200 and includes a burner 207 and a fuel valve system 215 configured to supply fuel from a fuel supply line 217 to the burner 207. The fuel valve system 215 includes a main fuel valve 222 and a pilot fuel valve 223 fluidly coupled between the fuel supply line 217 and a group G of burners 218. The inlets of the burners 218 in group G are connected to the outlet of the main fuel valve 122 through corresponding main shut - off valves 225 and to the outlet of the pilot fuel valve 223 through corresponding pilot shut - off valves 226.

[0049] According to the above exemplary embodiments, the advantages of the present invention are obvious.

[0050] Using a sub-fuel valve dedicated to fuel control at low part-loads allows for a very precise fuel supply under a wide range of operating conditions. In fact, the sub-fuel valve can be selected for the low part-load range, so that the gas turbine engine does not suffer from problems that affect known burners and stem from the need to operate a fuel supply valve at relatively opposite ends of a large range. According to the proposed solution, the main fuel valve is used for full load and high part-loads down to a threshold load, which can be conveniently selected to avoid flame instability and critical combustion conditions. Then, the main fuel valve can be closed, and fuel supply control is completed within the low-load part range below the threshold load by the sub-fuel valve. The fuel supply control is very precise because the sub-fuel valve does not need to operate over a large range. As a result, the total load range of the gas turbine engine can be advantageously extended to very low part-loads without affecting flame stability and high-quality combustion, and without exceeding the limits on pollutant emissions, especially carbon monoxide. A part-load as low as about 10% of the base load can be achieved.

[0051] The main fuel valve and the sub-fuel valve can be independently selected by a controller to optimize the performance in terms of generating the corresponding flow rate ranges for the corresponding load ranges.

[0052] Overlap in the sub-ranges allows for a smooth transition between the higher part-load range and the lower part-load range, thus preventing possible causes of instability.

[0053] The separate and independent activation and deactivation of the burners allows for a flexible selection of strategies for transitioning from full load to low part-load operating conditions, as well as a flexible selection of the mode of activating the burners at any part-load.

[0054] Tests at low part-loads have shown that the generation of carbon monoxide is affected by the number of hot / cold interfaces (i.e., the activated burners adjacent to the non-activated burners). That is, the more the number of hot / cold interfaces, the stronger the generation of carbon monoxide. The activation and deactivation of the burners are controlled such that at any operating condition, the activated burners form a single group of adjacent activated burners, while the non-activated burners form a single group of adjacent non-activated burners, thereby causing a minimization of the hot / cold interfaces (two). The generation of carbon monoxide can also be minimized thereby.

[0055] When all burners are activated, the first burner is deactivated first, and then the activated burners adjacent to the non-activated burners are successively deactivated to ensure that the number of hot / cold interfaces always remains at a minimum of two.

[0056] Alternating activation of different modes of the burners avoids the situation where certain burners are always used at low part - loads while other burners are always off. Even at part - loads, the components downstream of the activated burners are subject to thermal and mechanical stresses, which can affect the service life of the components. Due to the frequent change in the composition of the single set of activated burners, the aging is basically uniform, and premature replacement of the components in the hot zone is prevented. Therefore, the average life is increased, and compliance with pollutant emission limits (especially carbon monoxide) is not affected. The strategy for changing the alternating mode can be flexibly selected according to design preferences.

[0057] Even though keeping all activated burners adjacent to each other is beneficial for reducing carbon monoxide emissions, changing the mode of the activated burners is still advantageous in terms of extending the component life and reducing the maintenance frequency, even when the activated burners form two or more groups. For example, in Figure 19 and 20 In the embodiment of, the controller 10 keeps two separate groups of burners 18 in the activated state in two different configurations at low part - loads. In both configurations, the same number of burners 18 are in the activated state, and the same level of power output can be provided. However, the individual burners 18 forming the two groups change over time. Under the first part - load condition, the burners 18 of two first groups GA1'', GA2'' are activated. For example, the two first groups GA1'', GA2'' can include burners 18 arranged symmetrically with respect to the machine axis A across the split plane SL on opposite sides of the gas turbine engine 1. Under the second part - load condition, the controller 10 activates two second groups GA3'', GA4'' of burners 18 that are different from the two first groups GA1'', GA2''. For example, the two second groups GA3'', GA4'' can include burners 18 arranged symmetrically with respect to the machine axis A across a plane perpendicular to the split plane SL at the top and bottom of the gas turbine engine 1. Thus, the configuration of the burners 18 under the second part - load condition is rotated 90° relative to the configuration under the first part - load condition. Advantageously, the burners 18 within each of the groups GA1'', GA2'', GA3'', GA4'' are adjacent to each other.

[0058] Finally, it is obvious that the described gas turbine engine and method can be modified and varied without departing from the scope of the invention as defined by the appended claims.

[0059] Specifically, the present invention is equally applicable to gas turbine engines having a single - stage burner assembly and a two - stage or sequential burner assembly, and in the latter case, it is equally applicable to the first - stage burner and the second - stage burner. In addition, the present invention can be used for annular, can - annular, and can - type burners as needed according to design preferences. There can be high - pressure and low - pressure turbines or a single turbine.

[0060] In the example described, a group of four activated burners is shown. It should be understood that these groups can include any suitable number of burners, depending on design preferences.

Claims

1. A gas turbine engine, comprising: A burner assembly (7; 107; 207) having a plurality of burners (18; 118; 218); A fuel supply system (9) configured to supply a fuel flow rate (M2) to the burners (18; 118; 218), and including a fuel supply line (17; 117; 217) and a main fuel valve (22; 122; 222) between the fuel supply line (17; 117; 217) and the burners (18; 118; 218); A control unit (10) configured to control the fuel flow rate (M2) using the main fuel valve (22; 122; 222) in a first load range (LR1) from full load to a threshold partial load; Wherein the fuel supply system (9) includes a secondary fuel valve (23; 123; 223) fluidly connected between the fuel supply line (17; 117; 217) and at least one associated group of burners (18; 118; 218); Wherein the secondary fuel valve (23; 123; 223) is arranged in parallel with the main fuel valve (22; 122; 222); Wherein the control unit (10) is further configured to control the fuel flow rate (M2) using the secondary fuel valve (23; 123; 223) in a second load range (LR2) from the threshold partial load (LTH) to minimum load (ML); Wherein the fuel supply system (9) further includes a shut-off valve for each burner (18; 118; 218), and wherein the shut-off valve (25; 225) is arranged between the main fuel valve (22; 122; 222) and the fuel inlet of the corresponding burner (18; 118; 218); And wherein the control unit (10) is configured to control the shut-off valve (25; 225) to activate and deactivate each burner (18; 118; 218) independently of other burners (18; 118; 218), and to deactivate at least a threshold number (NTH) of burners (18; 118; 218) before starting to use the secondary fuel valve (23; 123; 223).

2. The gas turbine engine according to claim 1, characterized in that, The main fuel valve (22; 122; 222) has a first minimum rated flow rate (M2), while the secondary fuel valve (23; 123; 223) has a second minimum rated flow rate (M2) that is less than the first minimum rated flow rate (M2).

3. The gas turbine according to claim 1, characterized in that, The first load range (LR1) and the second load range (LR2) overlap in a load sub-range (SR) including the threshold partial load (LTH), and the control unit (10) is configured to close the main fuel valve (22; 122; 222) outside the first load range (LR1).

4. A gas turbine engine according to any one of the preceding claims, characterised in that The fuel supply system (9) includes a fuel gas chamber (20) and the main fuel valve (22; 122; 222), and the auxiliary fuel valve (23; 123; 223) is arranged between the fuel supply line (17; 117; 217) and the fuel gas chamber (20).

5. The gas turbine engine according to claim 1, characterized in that, The fuel supply system (9) includes a plurality of main fuel valves (22; 122; 222) and a plurality of auxiliary fuel valves (23; 123; 223), and each main fuel valve (22; 122; 222) and each auxiliary fuel valve (23; 123; 223) are fluidly coupled between the fuel supply line (17; 117; 217) and at least one corresponding associated set of burners (18; 118; 218).

6. The gas turbine engine according to claim 1, wherein, The control unit (10) is configured to activate and deactivate the burners (18; 118; 218) such that, under any operating condition, the activated burners (18; 118; 218) form a single set of adjacent activated burners (GA), and the deactivated burners (18; 118; 218) form a single set of adjacent deactivated burners (GI).

7. The gas turbine engine according to claim 1, characterized in that, The control unit (10) is configured to first deactivate the first burner (18; 118; 218) when all burners (18; 118; 218) are activated, and successively deactivate the activated burners (18; 118; 218) adjacent to the deactivated burners (18; 118; 218).

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