Gas turbine with improved part load emissions behavior

Abstract

In a method for the low-CO emissions part load operation of a gas turbine with sequential combustion, the opening of the row of variable compressor inlet guide vanes is controlled depending on the temperatures of the operative burners of the second combustor and simultaneously the number of operative burners is kept at a minimum. This leads to low CO emissions at partial load of the gas turbine.

Claims

1. A method for low-CO emissions operation of a gas turbine with sequential combustion, wherein the gas turbine includes a first turbine, a second turbine, at least one compressor wherein the at least one compressor includes a row of variable compressor inlet guide vanes, a first combustor which is connected downstream to the compressor and the hot gases of which are admitted to the first turbine, and a second combustor which is connected downstream to the first turbine and the hot gases of which are admitted to the second turbine, the second combustor including operative burners each having a burner exhaust temperature, the method comprising: controlling a position of the variable compressor inlet guide vanes depending on a burner exhaust temperature of at least one the operative burners of the second combustor; in case of increasing loads, switching ON a further operative burner of the second combustor in case an average of the turbine exhaust temperature of the second turbine reaches a lower limit value; in case of decreasing loads switching OFF one of the operative burners of the second combustor in case the average of the turbine exhaust temperature of the second turbine reaches the lower limit value; and at least one of: controlling the position of the variable compressor inlet guide vanes depending on a difference between the highest burner exhaust temperature of the operative burners and a maximum turbine exhaust temperature; opening the variable compressor inlet guide vanes when the burner exhaust temperature of one of the operative burners reaches or exceeds the maximum turbine exhaust temperature; and closing the variable compressor inlet guide vanes when the highest burner exhaust temperature of the operative burners is below the maximum turbine exhaust temperature.

2. The method as claimed in claim 1, wherein the opening of the variable compressor inlet guide vanes when the burner exhaust temperature of one of the operative burners reaches or exceeds a maximum turbine exhaust temperature is performed.

3. The method as claimed in claim 2, wherein the position of the variable compressor inlet guide vanes is controlled depending on the maximum turbine exhaust temperature of the operative burners of the second combustor.

4. The method as claimed in claim 1, wherein the closing of the variable compressor inlet guide vanes when the highest burner exhaust temperature of the operative burners is below a maximum turbine exhaust temperature is performed.

5. The method as claimed in claim 4, wherein the position of the variable compressor inlet guide vanes is controlled depending on the maximum turbine exhaust temperature of the operative burners of the second combustor.

6. The method of claim 1, comprising: increasing a rate of fuel supplied to the second combustor and/or the first combustor with a load increase.

7. The method as claimed in claim 1, comprising: decreasing a rate of fuel supplied to the second combustor and/or the first combustor with a load decrease.

8. The method as claimed in claim 1, wherein both of the opening of the variable compressor inlet guide vanes when the burner exhaust temperature of one of the operative burners reaches or exceeds a maximum turbine exhaust temperature and the closing of the variable compressor inlet guide vanes when the highest burner exhaust temperature of the operative burners is below the maximum turbine exhaust temperature are performed.

9. The method as claimed in claim 1, wherein the controlling of the position of the variable compressor inlet guide vanes depending on a difference between the highest burner exhaust temperature of the operative burners and the maximum turbine exhaust temperature is performed.

10. The method as claimed in claim 1, wherein a control unit of the gas turbine performs the switching ON and performs the switching OFF.

11. The method as claimed in claim 1, wherein the gas turbine comprises at least one fuel line leading to the operative burners.

12. A method for low-CO emissions operation of a gas turbine with sequential combustion, wherein the gas turbine includes a first turbine, a second turbine, at least one compressor wherein the at least one compressor includes a row of variable compressor inlet guide vanes, a first combustor which is connected downstream to the compressor and the hot gases of which are admitted to the first turbine, and a second combustor which is connected downstream to the first turbine and the hot gases of which are admitted to the second turbine, the second combustor including operative burners each having a burner exhaust temperature, the method comprising: controlling a position of the variable compressor inlet guide vanes depending on a burner exhaust temperature of at least one the operative burners of the second combustor; in case of increasing loads, switching ON a further operative burner of the second combustor in case an average of the turbine exhaust temperature of the second turbine reaches a lower limit value; in case of decreasing loads switching OFF one of the operative burners of the second combustor in case the average of the turbine exhaust temperature of the second turbine reaches the lower limit value; and wherein in case all operative burners of the second combustor are in operation, controlling the position of the variable compressor inlet guide vanes depending on the average temperature of the turbine exhaust temperature.

13. The method as claimed claim 12, wherein the position of the variable compressor inlet guide vanes is controlled so that the average temperature of the turbine exhaust temperature is equal to an upper limit of the average turbine exhaust temperature.

14. The method as claimed in claim 12, further comprising: increasing a rate of fuel supplied to the second combustor and/or the first combustor with a load increase.

15. The method as claimed in claim 12, further comprising: decreasing a rate of fuel supplied to the second combustor and/or the first combustor with a load decrease.

16. A gas turbine comprising: a compressor with variable inlet guide vanes; a first turbine; a second turbine; a first combustor connected downstream to the compressor such that during operation hot gases from the first combustor are admitted to the first turbine; and a second combustor connected downstream to the first turbine such that hot gases from the second combustor are admitted to the second turbine wherein the second combustor comprises a plurality of operative burners; at least one fuel line leading to the plurality of operative burners of the second combustor; and an individual on/off valve or an individual control valve arranged in at least one fuel line to control individual operative burners and a control unit, the control unit executing the method of claim 12.

17. The method as recited in claim 12, comprising at least one of: opening the variable compressor inlet guide vanes when the burner exhaust temperature of one of the operative burners reaches or exceeds a maximum turbine exhaust temperature; and closing the variable compressor inlet guide vanes when the highest burner exhaust temperature of the operative burners is below the maximum turbine exhaust temperature.

18. The method as recited in claim 12, comprising both of: opening the variable compressor inlet guide vanes when the burner exhaust temperature of one of the operative burners reaches or exceeds a maximum turbine exhaust temperature; and closing the variable compressor inlet guide vanes when the highest burner exhaust temperature of the operative burners is below the maximum turbine exhaust temperature.

19. A method for low-CO emissions operation of a gas turbine with sequential combustion, wherein the gas turbine includes a first turbine, a second turbine, at least one compressor wherein the at least one compressor includes a row of variable compressor inlet guide vanes, a first combustor which is connected downstream to the compressor and the hot gases of which are admitted to the first turbine, and a second combustor which is connected downstream to the first turbine and the hot gases of which are admitted to the second turbine, the second combustor including operative burners each having a burner exhaust temperature, the method comprising: controlling a position of the variable compressor inlet guide vanes depending on a burner exhaust temperature of at least one the operative burners of the second combustor; in case of increasing loads, switching ON a further operative burner of the second combustor in case an average of the turbine exhaust temperature of the second turbine reaches a lower limit value; in case of decreasing loads switching OFF one of the operative burners of the second combustor in case the average of the turbine exhaust temperature of the second turbine reaches the lower limit value; and wherein an upper limit value of the average turbine exhaust temperature is greater than the lower limit value.

20. The method as claimed in claim 19, wherein the position of the variable compressor inlet guide vanes is controlled depending on the maximum turbine exhaust temperature of the operative burners of the second combustor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a gas turbine with sequential combustion,

(2) FIG. 2 shows a section through the second combustor of a gas turbine with sequential combustion and also the fuel distribution system with a fuel ring main and eight individual on/off valves for the restricting of eight burners,

(3) FIG. 3 shows a section through the second combustor of a gas turbine with sequential combustion and also the fuel distribution system with a fuel ring main and four individual control valves for controlling the fuel flow of four burners,

(4) FIG. 4 shows a section through the second combustor of a gas turbine with sequential combustion and also the fuel distribution system with two separately controllable sub-groups and two fuel ring mains,

(5) FIG. 5 shows a conventional method for controlling a gas turbine with sequential combustion (prior art),

(6) FIG. 6 shows a claimed method for controlling a gas turbine with sequential combustion, in which during loading-up after engaging the second combustor, the local maximum TAT limits are lowered and the TAT average temperature is kept between two lower limit,

(7) FIG. 7 shows the transient state during the claimed burner switching, e.g. during the loading procedure (when burners are switched ON).

DETAILED DESCRIPTION

(8) FIG. 1 shows a gas turbine with sequential combustion useful for implementing methods as described herein. The gas turbine includes a compressor 1, a first combustor 4, a first turbine 7, a second combustor 15, and a second turbine 12. Typically, it includes a generator 19 which, at the cold end of the gas turbine, that is to say at the compressor 1, is coupled to a shaft 18 of the gas turbine.

(9) A fuel, gas or oil, is introduced via a fuel feed 5 into the first combustor 4, mixed with air which is compressed in the compressor 1, and combusted. The hot gases 6 are partially expanded in the subsequent first turbine 7, performing work.

(10) As soon as the second combustor is in operation due to an increase of load, additional fuel, via a fuel feed 10, is added to the partially expanded gases 8 in burners 9 of the second combustor 15 and combusted in the second combustor 15. The hot gases 11 are expanded in the subsequent second turbine 12, performing work. The exhaust gases 13 can be beneficially fed to a waste heat boiler of a combined cycle power plant or to another waste heat application.

(11) For controlling the intake mass flow, the compressor 1 has at least one row of variable compressor inlet guide vanes 14.

(12) In order to be able to increase the temperature of the intake air 2, provision is made for an anti-icing line 26 through which some of the compressed air 3 can be added to the intake air 2. For control, provision is made for an anti-icing control valve 25. This is usually engaged on cold days with high relative air moisture in the ambient air in order to forestall a risk of icing of the compressor.

(13) Some of the compressed air 3 is tapped off as high-pressure cooling air 22, recooled via a high-pressure cooling air cooler 35 and fed as cooling air 22 to the first combustor 4 (cooling air line is not shown) and to the first turbine.

(14) The mass flow of the high-pressure cooling air 22, which is fed to the high-pressure turbine 7, can be controlled by a high-pressure cooling air control valve 21 in the example.

(15) Some of the high-pressure cooling air 22 is fed as so-called carrier air 24 to the burner lances of the burners 9 of the second combustor 15. The mass flow of carrier air 24 can be controlled by a carrier-air control valve 17.

(16) Some of the air is tapped off, partially compressed, from the compressor 1, recooled via a low-pressure cooling air cooler 36 and fed as cooling air 23 to the second combustor 15 and to the second turbine 12. The mass flow of cooling air 23 can be controlled by a cooling-air control valve 16 in the example.

(17) The combustors 4 and 15 are constructed as annular combustors, for example, with a large number of individual burners 9, as is shown in FIGS. 2 and 3 by way of example of the second combustor 15. Each of these burners 9 is supplied with fuel via a fuel distribution system and a fuel feed 10.

(18) FIG. 2 shows a section through the second combustor 15 with burners 9 of a gas turbine with sequential combustion, and also the fuel distribution system with a fuel ring main 30 and eight individual on/off valves 37 for deactivating eight burners 9. By closing individual on/off valves 37, the fuel feed to individual burners 9 is stopped and this is distributed to the remaining burners, wherein the overall fuel mass flow is controlled via a control valve 28. As a result, the air ratio of the burners 9 in operation is reduced.

(19) Apparently each of the operative burners 9 produces hot exhaust gases. The temperature of these hot exhaust gases are referred to as burner exhaust gases BET and may be differ between the operative burners 9.

(20) FIG. 3 shows a section through the second combustor 15 and also a fuel distribution system with a fuel ring main 30 and fuel feeds 10 to the individual burners 9. In the example, four burners 9 are provided with individual control valves 27 for controlling the fuel flow in the fuel feeds 10 to the respective burners 9. The overall fuel mass flow is controlled via a control valve 28. The separate controlling of the fuel mass flow to the four burners 9 with individual control valves 27 allows staging. The four individual control valves are fully opened at low part load so that fuel is introduced evenly into all the burners 9 of the second combustor 15, so that all the burners 9 are operated with the same air ratio for minimizing the CO emissions. With increasing relative load, particularly if, for example, above 70% relative load increased pulsations can occur, the individual control valves 27 are slightly closed in order to realize a staging and therefore to stabilize the combustion. In this case, the air ratio of the burner 9 which is supplied via the slightly closed individual control valves 27 is increased. This, however, at high load is non-critical with regard to the CO emissions.

(21) FIG. 4 shows a section through the second combustor 15 of a gas turbine with sequential combustion, and also the fuel distribution system with two separately controllable sub-groups of burners. These have in each case a fuel ring main for a first sub-group 31 and a fuel ring main for a second sub-group 32 and the associated fuel feeds 10. For the independent control of the fuel quantity of both sub-systems, provision is made for a fuel control valve for the first sub-group 33 and a fuel control valve for the second sub-group 34.

(22) The two control valves for the first and the second sub-groups 33, 34 are controlled at low part load so that the fuel mass flow per burner is the same.

(23) As a result, fuel is introduced evenly into all the burners 9 of the second combustor 15 so that all the burners 9 are operated with the same air ratio for minimizing the CO emissions. With increasing relative load, especially if, for example, above 70% relative load increased pulsations occur, the control valve of the first sub-group 33 is not opened as wide as the control valve of the second sub-group 34 in order to realize a staging and therefore to stabilize the combustion.

(24) Alternatively, the control valve of the first sub-group 33 can be connected downstream of the second control valve 34. In this case, similar to the example from FIG. 3, at part load the control valve of the first sub-group 33 is to be completely opened and at high part load is to be restricted in order to then realize a staging. The overall fuel mass flow is then controlled via the control valve 34. In the event that the fuel is a liquid fuel, such as oil, water injection becomes necessary for reducing the NOx emissions, depending upon the type of burner.

(25) This is carried out similarly to the fuel supply, for example, and provision is to be made for corresponding lines and control systems.

(26) In the case of so-called dual-fuel gas turbines, which can be operated both with a liquid fuel, such as oil, and with a combustible gas, such as natural gas, separate fuel distribution systems are to be provided for each fuel.

(27) FIG. 5 shows a conventional method for controlling a gas turbine with sequential combustion with changing loads. Starting from no-load operation, that is to say from a relative load Prel of 0%, the gas turbine is loaded up to full load, that is to say to a relative load Prel of 100%. At 0% Prel, the row of variable compressor inlet guide vanes is closed, that is to say is adjusted to a minimum opening angle.

(28) The first combustor is ignited, which leads to a turbine inlet temperature TIT1 of the first turbine 7 and to a corresponding turbine exhaust temperature TAT1. The second combustor is not yet in operation so that no heating of the gases in the second combustor takes place. The temperature TAT1 of the gases which discharge from the first turbine 7 is reduced to the turbine inlet temperature TIT2 of the second turbine 12 as a result of the combustor cooling and also in consideration of the low-pressure turbine cooling. The expanded gases discharge from the second turbine 12 with a temperature TAT2.

(29) In one phase I of the method, starting from 0% Prel, for power increase the TIT1 is first increased to a TIT1 limit. With increasing TIT1, the exhaust temperature TAT1 and the temperatures TIT2 and TAT2 of the subsequent second turbine 12 also increase.

(30) In order to further increase the power after reaching the TIT1 limit, at the start of phase II the second combustor 15 is ignited and the fuel feed 10 to the burners 9 of the second combustor is increased in proportion to the load. The TIT1 and TAT2 increase over load in phase II correspondingly with a steep gradient until a first limit of the TAT2 is reached. Conventionally, the TAT2 limit is identical to a TAT2 full-load limit.

(31) In order to further increase the power after reaching the TAT2 limit, in a phase III of the method the row of variable compressor inlet guide vanes 14 is opened in order to control the power by increasing the intake mass flow. The pressure ratio of the second turbine 12 increases in proportion to the intake mass flow, which is why at constant TAT2 the TIT2 increases further over the relative load Prel until a first TIT2 limit is reached.

(32) In order to further increase the relative load Prel after reaching the first TIT2 limit, in a phase IV of the method the row of variable compressor inlet guide vanes 14 is opened further at constant TIT2 until it reaches the maximum opened position.

(33) In the example which is shown, in a phase V of the method, with a constant position of the row of variable compressor inlet guide vanes 14, the TIT2 is increased from the first TIT2 limit to a second TIT2 limit until 100% Prel is reached.

(34) FIG. 6 shows a new and inventive method for controlling a gas turbine with sequential combustion and changing loads. Phase A of FIG. 6 is similar to phase I of FIG. 5.

(35) As can be seen in FIG. 6, the burner exhaust temperature BET of the operative burners 9 raises with increasing relative load Prel.

(36) In FIG. 6 only on burner exhaust temperature BET is shown. It is the burner exhaust temperature BET which is the highest among the operative burners 9. As mentioned before the individual burner exhaust temperature BET of each operative burner 9 is monitored by means of an appropriate temperature sensor.

(37) At a load Prel,1 some of the burners 9 of the second combustor 15 are ignited. The number of burners 9 that are ignited is as little as possible. It may be 1 or more burner 9 depending on the gas turbine. Therefore in FIG. 6 at prel,1 the number of burners 9 ignited is referred to as Nmin. The number of burners 9 of the second combustor 15 is equal to Nmax.

(38) The claimed method is executed in phase B, which may cover a load range from 20% to 70%. Phase B is also referred to as second combustor's burner grouping range.

(39) With further increasing load Prel more fuel is delivered and the opening VIGV of the row of variable compressor inlet guide vanes 14 remains constant. As a result the burner exhaust temperature BET raises.

(40) At the relative load Prel,2 the burner exhaust temperature BET of one of the operative burners 9 reaches the maximum admissible temperature TAT2 maxcontrol.

(41) To avoid overheating of this particular burner 9 the opening VIGV of the row of variable compressor inlet guide vanes 14 is increased. This results in an enlarged air flow through the turbine and consequently the burner exhaust temperature BET remains constant at the maximum admissible temperature TAT2, max, control.

(42) This means that in the load range between prel,1 and prel,2 the CO emissions of the turbine remain at a very low level, too.

(43) FIG. 6 is a more general illustration of the claimed method, whereas FIG. 7 shows the claimed method in, more detail during a typical loading procedure.

(44) As can be seen from FIG. 6 in phase B with increasing load the number of operative burners 9 increases step by step until all burners 9 at a load prel,3 are switched ON and the number of operative burners 9 is equal to Nmax.

(45) Generally spoken, in the load range between prel,2 and prel,3 the opening of the row of variable compressor inlet guide vanes 14 increases (c. f. line VIGV) and the burner exhaust temperature BET is at or at least near the maximum admissible temperature TAT2, max control. Consequently, the CO emissions of the turbine remain at a very low level also in the load range.

(46) Further it can be seen that the average exhaust temperature of the second turbine TAT2 average is saw-toothed and does not get lower than a TAT2 average, lower limit.

(47) At loads greater than prel,3 it can be seen from FIG. 6 the average exhaust temperature of the second turbine TAT2 average is no more saw-toothed and finally reaches a TAT2 average, upper limit.

(48) With regard to the burner exhaust temperature BET it can be seen that it decreases at loads above prel,3 until full load.

(49) Looking now to FIG. 7 the claimed method is explained in more detail when increasing the load.

(50) FIG. 7 shows the behavior of a gas turbine over time that is operated in accordance with the claimed method.

(51) Starting at a load prel,2 and increasing the load it can be seen from FIG. 7 that the burner exhaust temperature BET of one of the operative burners 9 reaches the maximum admissible temperature TAT2 maxcontrol at prel,2 (as illustrated in FIG. 6, too).

(52) In a load range between prel,2 and prel,4 the opening VIGV of the row of variable compressor inlet guide vanes 14 has a varying slope with a tendency to increasing opening. The slope of VIGV limits the burner exhaust temperature BET to the TAT2 maxlimit. As a result the average temperature TAT2 average decreases in this load range.

(53) At prel,4 the average temperature TAT2 average is equal to the TAT2 lowerlimit. To avoid a reduced efficiency in case of further increasing load, the average temperature TAT2 average has to be raised by igniting a further burner 9.

(54) Doing so, the burner exhaust temperature BET of the operative burners 9 is reduced significantly (c. f. FIG. 7), because the fuel is distributed to more burners 9.

(55) Consequently the VIGV may be closed slightly in the load range between prel,4 and prel,5. This leads to a rather high slope of both the burner exhaust temperature BET of the operative burners 9 and the average temperature TAT2 average.

(56) At the load prel,5 the average temperature TAT2 average again is equal to the TAT2 lowerlimit. To avoid a further increase of this temperature, the opening VIGV of the row of variable compressor inlet guide vanes 14 again has a slope greater zero. The slope of the opening VIGV in the load range between prel,5 and prel,6 is equal or at least rather similar to the slope in the load range between prel,2 and prel,3.

(57) Again this leads to a constant burner exhaust temperature BET equal to the TAT2 maxlimit. As a result the average temperature TAT2 average decreases in this load range, too.

(58) At the load prel,6 the average temperature TAT2 average is equal to the TAT2 lowerlimit. To avoid a reduced efficiency in case of further increasing load, the average temperature TAT2 average has to be raised by igniting a further burner.

(59) In the load range starting from prel,6 and ending at prel,7 (not shown) the control is similar to the control in the load range between prel,4 and prel,5.

(60) This process continues until all burners 9 are ignited at prel,3 (c. f. FIG. 6)

(61) In case the load is reduced from, for example full load to partial load, the method can be reversed.

(62) The claimed method allows to run the turbine at high efficiency and simultaneously with low emissions, especially the CO emissions, at partial load. It is easy to execute and stable and does not cause problems.