The present invention relates to a device and method for controlling the exhaust temperature of a gas turbine of a power plant.

Plants for producing electricity are known, comprising a compressor, a combustion chamber, a gas turbine and a device for controlling the exhaust temperature of the gas turbine.

The compressor is provided with an inlet stage defined by a plurality of adjustable inlet guide vanes, the position of which regulates the air flow at the compressor inlet.

The device for controlling the temperature at the gas turbine exhaust comprises a module for regulating the position of the plurality of inlet guide vanes of the compressor so that the gas turbine exhaust temperature is equal to a fixed reference value, calculated a priori, and a module for regulating the supply of fuel into the combustion chamber.

However, the devices for controlling the gas turbine exhaust temperature thus configured are not able to optimize plant performance according to the variation of the different environmental conditions and of the type of plant in which they are installed, while keeping the pollutant emission levels under the limits of law.

It is therefore an object of the present invention to provide a method for controlling the exhaust temperature of a gas turbine of a plant for producing electricity, which is free from the prior art drawbacks identified herein; in particular, it is an object of the invention to provide a method for controlling the exhaust temperature of a gas turbine which is capable of optimizing plant performance.

In accordance with these objects, the present invention relates to a method for controlling the exhaust temperature of a gas turbine of a power plant comprising the step of regulating the position of a plurality of inlet guide vanes of a compressor of the plant in such a way that the exhaust temperature of the gas turbine is equal to a reference value; the method being characterized in that it comprises the step of calculating the reference value on the basis of actual environmental conditions, on the basis of an actual power delivered by the plant and on the basis of a first reference base power in standard environmental conditions.

It is a further object of the invention to provide a device for controlling the exhaust temperature of a gas turbine in a plant for producing electricity which is simple, cost-effective and capable of optimizing plant performance.

In accordance with these objects, the present invention relates to a device for controlling the exhaust temperature of a gas turbine of a power plant comprising regulating means for regulating the position of a plurality of inlet guide vanes of a compressor of the plant in such a way that the exhaust temperature of the gas turbine is equal to a reference value; the device being characterized in that it comprises calculation means for calculating the reference value on the basis of actual environmental conditions, on the basis of an actual power delivered by the plant and on the basis of a first reference base power in standard environmental conditions.

Further features and advantages of the present invention will be apparent from the following description of a non-limitative embodiment thereof, with reference to the figures in the accompanying drawings, in which:

• figure 1 diagrammatically shows a power plant for producing electricity;
• figure 2 diagrammatically shows the device for controlling the exhaust temperature of a gas turbine according to the present invention;
• figure 3 diagrammatically shows the exhaust temperature trend of the gas turbine according to the variation of the ratio between the actual power delivered by the plant and a base reference power in the actual environmental conditions.

In figure 1, reference numeral 1 indicates a power plant for producing electricity comprising a compressor 3, a combustion chamber 4, a gas turbine 5, a generator 7 which is connected to the same shaft as the turbine 5 and transforms the mechanical power supplied by the turbine 5 into electrical power W_ACT, a device 9 for controlling the exhaust temperature of turbine 5, a detection module 10, and an actuator 12.

A variant (not shown) includes plant 1 being of the combined cycle type, also comprising a steam turbo assembly, in addition to gas turbine 5 and generator 7.

Compressor 3 is provided with an inlet stage 13 having a variable geometry. The inlet stage 13 comprises a plurality of inlet guide vanes (not shown for simplicity in the accompanying figures), commonly known as IGV, the inclination of which may be modified to regulate the air flow aspirated by the compressor 3 itself.

In particular, the inclination of the plurality of inlet guide vanes is regulated by the actuator 12, which is controlled by the device 9 for regulating the exhaust temperature of the turbine 5, as shown in detail below.

The detection module 10 comprises a plurality of sensors (not shown for simplicity in the appended figures), which detect a plurality of parameters related to plant 1 to be fed to the device 9 for controlling the exhaust temperature of turbine 5; in particular, the detection module 10 detects the following parameters:

• actual environmental temperature T_ACT detected at the inlet of compressor 3;
• actual environmental pressure p_ACT detected at the inlet of compressor 3;

• actual exhaust temperature TETC_ACT of turbine 5;
• actual power W_ACT delivered by plant 1, preferably detected at the terminals of the generator 7 by means of a wattmeter.

The device 9 for controlling the exhaust temperature of turbine 5 comprises a FUEL regulating module 14a for regulating the supply of fuel into the combustion chamber 4 and an IGV regulation module 14b for regulating the position of the plurality of inlet guide vanes of the compressor 3.

The FUEL regulation module 14a is configured to provide position signals to a plurality of actuators 15 (diagrammatically shown in figure 1 with one block) of respective valves (not shown) for feeding fuel to the combustion chamber 4.

With reference to figure 2, the IGV regulation module 14b (diagrammatically indicated in figure 2 by a dash-and-dotted line) is configured to regulate the position of the plurality of inlet guide vanes of compressor 3 and comprises a first calculation module 16 (diagrammatically indicated in figure 2 by a dashed line) to calculate a reference base power in the actual environmental conditions on the basis of a reference base power value in standard environmental conditions W_{BASE_ISO}, and on the basis of the values of actual environmental temperature T_ACT and actual environmental pressure p_ACT, a second calculating module 17

(diagrammatically indicated in figure 2 by a dashed line) to calculate a reference value NEWSET_TETC of the exhaust temperature of the gas turbine 5 on the basis of the reference base power in the actual environmental conditions W_{BASE_ACT} and on the basis of an actual delivered power W_ACT, a control module 18 configured to send a position signal S_IGV to the actuator 12 on the basis of the actual exhaust temperature TETC_ACT of the turbine 5 and on the basis of the reference temperature value NEWSET_TETC calculated by the second calculation module 17, and a parameter definition module 19.

The first calculation module 16 comprises a first calculating block 20 for calculating a temperature correction factor α on the basis of the actual environmental temperature T_ACT according to a function F1, a second calculating block 21 configured for calculating a pressure correction factors β on the basis of the actual environmental pressure p_ACT according to a function F2, and a multiplier node 23 for multiplying the temperature correction factor α, the pressure corrector factor β, and the reference base power value W_{BASE_ISO} in standard environmental conditions so as to obtain the reference base power W_{BASE_ACT} in the actual environmental conditions.

The reference base power W_{BASE_ISO} in standard environmental conditions is a parameter determined by the parameter definition module 19 and is the maximum power, commonly named "base load", which may be delivered by the plant 1 in standard environmental conditions, i.e. at 15° C and 1013 mbars.

The reference base power W_{BASE_ACT} in actual environmental conditions is calculated by the multiplier node 23 and is the maximum power which may be delivered by the plant 1 in the actual environmental conditions, i.e. at temperature T_ACT and pressure p_ACT.

The functions F1 and F2 are preferably tables obtained by means of calculations based on the characteristic curve of the gas turbine 5.

In the example described and illustrated herein, function F1 is defined by the following table:

ACTUAL ENVIRONMENTAL TEMPERATURE T_ACT

TEMPERATURE CORRECTION FACTOR α

-10

1.087

-5

1.068

5

1.033

15

1

30

0.91

40

0.837

The second calculation module 16 comprises a divider node 24 for calculating a power ratio R_P between the actual power W_ACT delivered by the plant 1 and the reference base power W_{BASE_ACT} in the actual environmental conditions, a third calculation module 26 for calculating a temperature correction C_TETC and a fourth calculating module 27 for calculating the reference value NEWSET_TETC in accordance with the following formula: $${\mathrm{NEWSET}}_{\mathrm{TETC}}\mathrm{=}{\mathrm{SET}}_{\mathrm{TETC}}\mathrm{-}\mathrm{\Delta T}\mathrm{+}{\mathrm{C}}_{\mathrm{TETC}}$$

where

C_TETC is the temperature correction calculated by the third calculating module 26;

SET_TETC is the reference base value of the exhaust temperature of turbine 5 at the maximum power which may be delivered by the plant 1 determined by the parameter definition module 19 on the basis of requirements which are to be ensured, such as for example requirements related to power, efficiency, exhaust temperature of turbine 5 and combustion stability;

Δ T is a temperature offset adapted to avoid the onset of instability phenomena within the combustion chamber 4, normally indicated by the term "humming", and is determined by the parameter definition module 19.

The actual power W_ACT is preferably filtered by a filter 25 before being fed to the divider node 24 for suppressing signal interference and oscillations.

The power ratio R_P substantially expresses the actual productivity level of plant 1. If the power ratio R_P is of 1, plant 1 is running at the top of its potentials, i.e. the actual delivered power W_ACT is equal to the reference base power W_{BASE_ACT} in the actual environmental conditions, which coincides with the maximum deliverable power, while if the power ratio R_P is lower than 1, plant 1 is not running at the top of its potentials.

The third calculating module 26 is configured so as to calculate the temperature correction C_TETC to be added to the reference base value SET_TETC of the exhaust temperature of turbine 5 on the basis of the power ratio R_P. In particular, the third calculating module 26 is configured to calculate the temperature correction C_TETC on the basis of the power ratio R_P according to an experimentally determined function F3.

In the example described and illustrated herein, function F3 is defined by the following table:

POWER RATIO R_P

CORRECTION TEMPERATURE C_TETC [°C]

0.45

5

0.55

5

0.65

2

0.8

0

1

0

The control module 18 is configured to send the position signal S_IGV to the actuator 12 on the basis of the difference between the actual exhaust temperature TETC_ACT of turbine 5 detected by the detection module 10 and the reference value of the exhaust temperature NEWSET_TETC calculated by the second calculation module 16. In particular, the control module 18 is configured to generate a position signal S_IGV such as to determine a variation of the position of the inlet guide vanes which is sufficient to cancel the difference between the actual exhaust temperature TETC_ACT of the turbine 5 and the exhaust temperature reference value NEWSET_TETC of the gas turbine 5.

Figure 3 shows the exhaust temperature trend of the gas turbine 5 controlled by the device 9 for controlling the exhaust temperature according to the power ratio R_P.

In particular, the exhaust temperature trend TETC of the gas turbine 5 is characterized by a rising, as compared to a constant reference value of the known solutions (not shown), to the low power ratio values R_P (approximately about 0.5) so as to decrease the carbon monoxide emissions (CO), and by a lowering at a high power ratio R_P (approximately about 0.9) so as to contain nitrogen oxide emissions (NOx) and prevent the onset of combustion instability phenomena. Therefore, due to the control action of the device 9, the efficiency of plant 1 is higher, especially at low power values W_ACT. This results in apparent advantages especially when plant 1 is running at night, i.e. when the plant is running at minimum power.

In detail, the exhaust temperature trend TETC of the gas turbine 5 is mainly regulated by the IGV regulation module 14b for power ratio values R_P between about 0.55, which corresponds to the maximum closing position of the inlet guide vanes, and about 0.95/0.98, which corresponds to the maximum opening position of the inlet guide vanes.

It is finally apparent that changes and variations may be made to the method and device described herein, without departing from the scope of the appended claims.