METHOD FOR OPERATING A GAS TURBINE

Abstract

 The invention relates to a method for operating a gas turbine (2) comprising a compressor section (4); a combustion section (6) in which combustion gases are produced, the combustion section (6) having a plurality of burners (22), and a turbine section (8), wherein the combustion gases generated in the combustion section (6) flow through the turbine section (8) and exit the turbine section (8) as exhaust gases. In order to provide a reliable and accurate technique for calculating the swirl angle (α) of the combustion gases in a gas turbine (2), the method comprises the steps of:
- S1: measuring a first reference temperature (T₁) of the combustion gases at a plurality of peripheral measuring positions arranged downstream of the turbine section (8) at a first point of time (t₁);
- S2: changing the fuel air ratio of one predetermined burner (22a) ;
- S4: measuring a second reference temperature (T₂) of the combustion gases at the plurality of measuring positions at a second point of time (t₂);
- S5: comparing the first reference temperature (T₁) with the second reference temperature (T₂) for each of the plurality of measuring positions;
- S6: identifying the measuring position with the highest deviation between the first reference temperature (T₁) and the second reference temperature (T₂);
- S7: calculating a swirl angle (α) between the predetermined burner (22) and the measuring position with the highest deviation between the first reference temperature (T₁) and the second reference temperature (T₂).

Description

[0001] The present invention relates to a method for operating a gas turbine comprising a compressor section; a combustion section, in which combustion gases are produced, the combustion section having a plurality of burners; and a turbine section, wherein the combustion gases generated in the combustion section flow through the turbine section and exit the turbine section as exhaust gases. Furthermore, the invention relates to a gas turbine as described above.

[0002] In a gas turbine air is sucked in and passes through the compressor section, where it is compressed. High pressure air from the compressor section enters the combustion section where it is mixed with fuel and burned using a plurality of burners. The hot combustion gases exit the combustion section to power the turbine section which, in turn, drives the compressor section and an output power shaft. The combustion gases exit the turbine through the exhaust duct. The combustion gases swirl partially around the axial centerline of the gas turbine, as the gases move axially through the turbine. This swirl of the combustion gases is due to the rotation of the turbine blades and of the compressor blades. The amount of swirl between the combustion section and the exhaust ducts depends on the operating condition of the gas turbine, such as its load, duty cycle, ambient temperature and other factors. When the combustion gases exit the exhaust duct as exhaust gases, the gases have swirled about the axis of the gas turbine and are not axially aligned with the burners that have generated the gases. This makes it difficult to identify malfunctioning burners.

[0003] A method and a system for identifying malfunctioning combustion chambers in a gas turbine are disclosed in US 2002/183916 A1. A combustion chamber graphic analyzer (CCGA) computer software application is used to identify combustion chambers that are sustaining abnormally hot or cold combustion temperatures. The identification of hot or cold combustion chambers is graphically displayed by the CCGA on a computer display, printed report or other computer output. Whether a combustion chamber is operating hot or cold is determined based on a circumferential profile of the temperatures of the combustion gases from the gas turbine. This circumferential temperature profile is rotated using a swirl angle to correlate the combustion gases temperature profile with the circular array of combustion chambers. A big disadvantage of this method is that with respect to the swirl angle different equations are applied for different gas turbine loads as well as for different gas turbines (i.e. combined cycle and simple cycle). This makes the calculation very complicated and the applied equations are not specific for each gas turbine.

[0004] It is therefore an object of the present invention to provide a reliable and accurate technique for calculating the swirl angle of the combustion gases in a gas turbine.

[0005] The object of the invention is achieved by the independent claims. The dependent claims describe advantageous developments and modifications of the invention.

[0006] In accordance with the invention there is provided a method for operating of a gas turbine comprising a compressor section, a combustion section in which combustion gases are produced, the combustion section having a plurality of burners, and a turbine section, wherein the combustion gases generated in the combustion section flow through the turbine section and exit the turbine section as exhaust gases, the method comprising the steps of:

• S1: measuring a first reference temperature of the combustion gases at a plurality of peripheral measuring positions arranged downstream of the turbine section at a first point of time;
• S2: changing the fuel air ratio of one predetermined burner;
• S4: measuring a second reference temperature of the combustion gases at the plurality of measuring positions at a second point of time; S5: comparing the first reference temperature with the second reference temperature for each of the plurality of measuring positions;
• S6: identifying the measuring position with the highest deviation between the first reference temperature and the second reference temperature;
• S7: calculating a swirl angle between the predetermined burner and the measuring position with the highest deviation between the first reference temperature and the second reference temperature.

[0007] In accordance with the invention there is provided also a gas turbine comprising a compressor section; a combustion section in which combustion gases are produced, the combustion section having a plurality of burners, and a turbine section, wherein the combustion gases generated in the combustion section flow through the turbine section and exit the turbine section as exhaust gases;
the gas turbine further comprising:

• a control unit designed for changing the fuel air ratio of at least one predetermined burner,
• a plurality of temperature sensors arranged peripherally downstream of the turbine section, wherein the plurality of temperature sensors is designed for providing the control unit with a first reference temperature at a first point of time and a second reference temperature at a second point of time,

wherein the control unit is designed for calculating a swirl angle between the predetermined burner and the temperature sensor in the measuring position with the highest deviation between the first reference temperature and the second reference temperature.

[0008] The expression "a plurality of peripheral measuring positions" should mean that a plurality of temperature sensors is provided, which are arranged at the same axial position but different circumferential locations. In particular, there are more than ten temperature sensors, e.g. thermocouples, arranged equidistant around the combustion gases path.

[0009] The essential idea of the present invention is to determine the swirl angle of the combustion gases by manipulating the combustion temperature of one of the burners and establishing a special correlation between this particular burner and the temperature sensor that detects the temperature change. In the first step the temperature of the combustion gases is measured by all temperature sensors at all different circumferential positions. When the first reference temperature value is recorded, a step response is applied to the predetermined burner, i.e. the fuel air ratio to the predetermined burner is either increased or decreased, so that the combustion temperature rises or falls. This manipulated combustion temperature is detected at the second point of time by at least some of the temperature sensors downstream the turbine and stored as a second reference temperature. The control unit then compares the first reference temperature with the second reference temperature for each of the plurality of measuring positions and identifies the measuring position with the highest deviation between the first and the second reference temperatures. In this measuring position the temperature sensor is located, which was most affected by the change of the fuel or ratio of the predetermined burner. In order to estimate the swirl angle, it is only necessary to determine the angle position between this temperature sensor and the predetermined burner. The same swirl angle applies for all combustion gases produced by the other burners under the same operating conditions.

[0010] The greatest advantage of the approach described in the previous paragraph is that the determination of the swirl angle can be done fully automated during operation of the gas turbine. The approach requires only minor changes to the operating mode of only one burner, thus the influence on the combustion process is neglectable. Also, the operation method is anytime reproducible for different operating or ambient conditions. No manual intervention is necessary, which saves times and costs.

[0011] In accordance with a preferred embodiment, the result of the swirl angle calculation is used to adjust the amount of fuel supplied to at least one of the plurality of burners. Knowing the exact swirl angle helps to interpret the measuring values of the individual temperature sensors and whenever deviations or abnormalities are detected, the burners producing them may be traced back by means of the swirl angle.

[0012] In accordance with another preferred embodiment, in step S2 the fuel air ratio is changed by adjusting the amount of fuel supplied to the predetermined burner. In all gas turbines technical means in form of different type of valves are provided for adjusting the fuel supply to the single burners, these valves may be used to change the amount of fuel provided to each single burner and thus changing the fuel air ratio of the respective burner.

[0013] In yet another preferred embodiment, stabilization time is introduced between the first point of time and the second point of time. This means that the second reference temperature is not measured immediately after the fuel air ratio of the predetermined burner is changed, but some stabilization time is provided, so that the change of the combustion temperature may take effect. Preferably, the stabilization time spans in the range between 10 sec to 60 sec. Still preferably, during the stabilization time the turbine operation conditions are kept constant, otherwise the swirl angle may change in the period between the first point of time and the second point of time. In particular, the turbine load remains unchanged during the stabilization time.

[0014] Preferably, the adjustment of the fuel amount supplied to the at least one of the plurality of burners is done multiple times. In particular, the fuel supply adjustment if done every time when the operating or ambient conditions are changed. This results in a real-time fine tuning of the fuel supply. Alternatively, the adjustment of the fuel supply is performed at predetermined points of time or continuously.

[0015] In a preferred embodiment, the swirl angle is calculated for different loads of the gas turbine. This data may be stored and used during operation of the gas turbine, wherein no new calculations are necessary.

[0016] In another preferred embodiment, the compressor section comprises adjustable inlet guide vanes and the swirl angle is calculated for different positions of the adjustable inlet guide vanes. In order to change dynamically the gas flow properties of the gas inlet of the compressor section, it is known to use inlet guide vanes. Such inlet guide vanes are described e.g. in US 7,269,953 B2. Due to the adjustment of the inlet guide vanes the flow angle of fluid passing through the compressor is selectively controlled so as to maximize the operating efficiency of the compressor. When the angle of the inlet guide vanes is changed, the swirl angle of the combustion gases is calculated again.

[0017] In yet another preferred embodiment, the swirl angle is calculated for different ambient conditions, since these may influence the performance of the gas turbine. Such ambient conditions could be e.g. ambient air temperature, humidity, etc.

[0018] Embodiments of the invention are now described, by way of example only, with reference to the accompanying drawings, of which:

Figure 1

shows a gas turbine comprising a control unit designed for calculating a swirl angle;

Figure 2

shows the swirl angle between a burner and a temperature sensor in a gas turbine according to FIG 1; and

Figure 3

shows a block diagram displaying the procedure for calculating a swirl angle in a gas turbine.

[0019] The illustration in the drawings is in schematic form. It is noted that in different figures, similar or identical elements may be provided with the same reference signs.

[0020] FIG 1 shows a gas turbine 2 which rotates around an axis A. The gas turbine 2 comprises a compressor section 4 and a turbine section 8. High pressure air from the compressor section 4 in fed into the combustion section 6, where it is burned in a plurality of burners, which are not shown in detail. In a fuel supply line 10 to one of the plurality of burners a valve 12 for adjusting the amount of fuel is integrated. Each burner or burner fuel supply has a valve, in particular designed as an active orifice, also a main fuel control valve is provided, which is not shown in the figure. In the combustion section 6 combustion gases 26 are produced due the combustion of a fuel-air-mixture. These combustion gases 26 drive the turbine section 8 which, in turn, drives the compressor section 4 and an output power shaft 14. The combustion gases 26 exit the turbine section 8 as exhaust gases 26.

[0021] In FIG 1 a single shaft gas turbine 2 is shown, yet the method for operating a gas turbine described below may also be applied to a two-shaft or multiple-shaft gas turbine.

[0022] A plurality of temperature sensors, e.g. thermocouples, is arranged peripherally downstream of the turbine section 8. In FIG 1 only one of the temperature sensors 16 is shown. The plurality of temperature sensors 16 measure the temperature of the combustion gases 26 and provide the measuring data to a control unit 18 via data line 20. The control unit 18 is designed for analyzing the measuring data as well as for regulating the valves 12 of the fuel supply lines 10 to all burners.

[0023] The arrangement of the plurality of burners 22 and temperature sensors 16 round the periphery of the gas turbine 2 is shown FIG 2 presenting a view in the axial direction the gas turbine 2. When the combustion gases 26 exit the exhaust duct, they have swirled about the axis A of the gas turbine 2 and are not axially aligned with the burners 22 that have generated the combustion gases 26. A swirl angle α between a predetermined burner 22a and one of the temperature sensors 16a is also shown in FIG 2.

[0024] FIG 3 shows the steps for the estimation of the swirl angle α shown in FIG 2.

[0025] In a first step S1, a first reference temperature T₁ of the combustion gases is measured by the temperature sensors 16 at a first point of time t₁.

[0026] In a second step S2, the fuel air ratio of one predetermined burner 22a is either increased or decreased by setting a new fuel throughput through the valve 12 by means of the control unit 18.

[0027] In a third step S3, a stabilization time Δt_s is provided so that the change of the combustion temperature of the predetermined burner 22a can take effect. The stabilization time Δt_s takes in particular 10 sec to 60 sec and depends on the type of the gas turbine 2 and / or the operating condition. During the stabilization time Δt_s the gas turbine 2 is kept in a steady state.

[0028] Next, in step S4 at a second point of time t₂ a second reference temperature T₂ of the combustion gases 26 is measured by the temperature sensors 16.

[0029] The second reference temperature T₂ measured by each temperature sensor 16 is evaluated by comparing it with the first reference temperature T₁ measured by the same temperature sensor 16 in step S5. By doing this, the measuring position with the highest deviation between the first reference temperature T₁ and the second reference temperature T₂ is identified in step S6.

[0030] Finally, the swirl angle α between the predetermined burner 22a and the temperature sensor 16a in the measuring position with the highest deviation between the first reference temperature T₁ and the second reference temperature T₂ is calculated in step S7.

[0031] The results for the actual swirl angle α may be used to trace back abnormalities of the combustion gases temperature, detected by a temperature sensor 16, to a specific burner 16. Optionally, this information is used in step S8 to adjust the fuel supply to a burner 22 producing the temperature abnormalities. When the combustion temperature of this burner 22 is higher than it should be, then the amount of fuel to this burner 22 is reduced by the control unit 18 and vice versa. The calculated swirl angle α may be stored and used during operation of the gas turbine 2 under the same conditions, so that no new calculations are necessary. This case is expressed by the arrow 24 in FIG 3. The information about the actual swirl angle is used to perform fine adjustment of the fuel supply continuously, at predetermined points of time or upon request. Normally, a new swirl angle has to be calculated when the turbine load of the operating or ambient conditions change.

[0032] Although the present invention has been described in detail with reference to the preferred embodiment, it is to be understood that the present invention is not limited by the disclosed examples, and that numerous additional modifications and variations could be made thereto by a person skilled in the art without departing from the scope of the invention.

Claims

1. Method for operating a gas turbine (2) comprising a compressor section (4); a combustion section (6) in which combustion gases (26) are produced, the combustion section (6) having a plurality of burners (22), and a turbine section (8), wherein the combustion gases (26) generated in the combustion section (6) flow through the turbine section (8) and exit the turbine section (8) as exhaust gases,
the method comprising the steps of:

- S1: measuring a first reference temperature (T₁) of the combustion gases (26) at a plurality of peripheral measuring positions arranged downstream of the turbine section at a first point of time (t₁);

- S2: changing the fuel air ratio of one predetermined burner (22a) ;

- S4: measuring a second reference temperature (T₂) of the combustion gases (26) at the plurality of measuring positions at a second point of time (t₂);

- S5: comparing the first reference temperature (T₁) with the second reference temperature (T₂) for each of the plurality of measuring positions;

- S6: identifying the measuring position with the highest deviation between the first reference temperature (T₁) and the second reference temperature (T₂);

- S7: calculating a swirl angle (α) between the predetermined burner (22a) and the measuring position (16a) with the highest deviation between the first reference temperature (T₁) and the second reference temperature (T₂) .

2. Method according to claim 1,
wherein the result amount of the swirl angle (α) calculation is used to adjust the amount of fuel supplied to at least one of the plurality of burners (22).

3. Method according to any of the preceding claims,
wherein in step S2 the fuel air ratio of the predetermined burner (22a) is changed by adjusting the amount of fuel supplied to the predetermined burner (22a).

4. Method according to any of the preceding claims,
wherein stabilization time (Δt_s) is introduced between the first point of time (t₁) and the second point of time (t₂).

5. Method according to claim 4,
wherein the stabilization time (Δt_s) spans in the range between 10 sec to 60 sec.

6. Method according to claim 5 or 6,
wherein during the stabilization time (Δt_s) the turbine operation conditions are kept constant.

7. Method according to claim 2 to 6,
wherein the adjustment of the amount of fuel supplied to the at least one of the plurality of burners (22) is done multiple times.

8. Method according to any of the preceding claims,
wherein the swirl angle (α) is calculated for different loads of the gas turbine (2).

9. Method according to any of the preceding claims,
wherein the compressor section (4) comprises adjustable inlet guide vanes and the swirl angle (α) is calculated for different positions of the adjustable inlet guide vanes.

10. Method according to any of the preceding claims,
wherein the swirl angle (α) is calculated for different ambient conditions.

11. A gas turbine (2) comprising a compressor section (4); a combustion section (6), in which combustion gases (26) are produced, the combustion section (6) having a plurality of burners (22); and a turbine section (8), wherein the combustion gases (26) generated in the combustion section (6) flow through the turbine section (8) and exit the turbine section (8) as exhaust gases, the gas turbine (2) further comprising:

- a control unit (18) designed for changing the fuel air ratio of at least one predetermined burner (22a),

- a plurality of temperature sensors (16) arranged peripherally downstream of the turbine section (8), wherein the plurality of temperature sensors (16) are designed for providing the control unit (18) with a first reference temperature (T₁) of the combustion gases (26) at a first point of time (t₁) and a second reference temperature (T₂) at a second point of time (t₂),

wherein the control unit (18) is designed for calculating a swirl angle (α) between the predetermined burner (22a) and the temperature sensor (16a) in the measuring position with the highest deviation between the first reference temperature (T₁) and the second reference temperature (T₂).

12. A gas turbine (2) according to claim 11,
wherein the control unit (18) is designed for adjusting the fuel supply (10) to at least one of the plurality of burners (22) based on the result of the swirl angle (α) calculation.

13. A gas turbine (2) according to claim 11 or 12,
wherein the control unit (18) is designed for changing the fuel air ratio of the predetermined burner (22a) in step S2 by adjusting the amount of fuel supplied to the predetermined burner (22a).

14. Method according to any of the claims 11 to 13,
wherein the control unit (18) is designed for introducing stabilization time (Δt_s) between the first point of time (t₁) and the second point of time (t₂).

15. Method according to claim 11 to 14,
wherein during the stabilization time (Δt_s) the turbine operation conditions are kept constant.

16. Method according to claim 2 to 6,
wherein the control unit (18) is designed for adjusting the amount of fuel supplied to the at least one of the plurality of burners (22) multiple times.

17. Method according to any of the preceding claims,
wherein the control unit (18) is designed for calculating the swirl angle (α) for different loads of the gas turbine (2).

18. Method according to any of the preceding claims,
wherein the compressor section (4) comprises adjustable inlet guide vanes and control unit (18) is designed for calculating the swirl angle (α) for different positions of the adjustable inlet guide vanes.

19. Method according to any of the preceding claims,
wherein the control unit (18) is designed for calculating the swirl angle (α) for different ambient conditions.

Drawing