# Patent

## Title
Temperature measuring device and regulation of the temperature of hot gas of a gas turbine

## Abstract

The invention relates to a regulation of the temperature of a hot gas of a gas turbine, particularly of a stationary gas turbine used for generating electricity, which comprises an injecting device for injecting a liquid into an airflow, which can be drawn into a compressor and with the aid of which a fuel inside a combustion chamber, which is situated downstream, combusts while producing the hot gas that is subsequently expanded when flowing through the turbine part located downstream. A temperature measuring device is provided that measures the temperature of the airflow before the compressor, whereby the temperature of the hot gas is regulated by the quantity of fuel. The aim of the invention is to provide a regulation with which, during wet compression operation, the serviceable life of the components subjected to the action of hot gas is lengthened. To this end, the invention provides that the temperature measuring device is mounted before the injecting device, and that the temperature of the airflow is calculated at the entry of the compressor by using the measured temperature.

## Background
CROSS REFERENCE TO RELATED APPLICATION
This application is the U.S. National Stage of International Application No. PCT/EP2004/003184, filed Mar. 25, 2004 and claims the benefit thereof The International Application claims the benefits of German Patent application No. 10314389.0 DE filed Mar. 28, 2003, and European Patent application No. 03022209.5 EP filed Sep. 30, 2003, all of the applications are incorporated by reference herein in their entirety.
FIELD OF THE INVENTION
The invention relates to a gas turbine, in particular a stationary gas turbine for power generation, in accordance with the preamble of the claims, and to a temperature-measuring device for recording the temperature of the air stream of a gas turbine in accordance with the preamble of the claims. The invention also relates to a control arrangement for controlling the hot-gas temperature of a gas turbine in accordance with the preamble of the claims.
BACKGROUND OF THE INVENTION
It is known that stationary gas turbines are used to generate mechanical energy, which a generator generally converts into electrical energy. For this purpose, a fossil fuel is burnt in the gas turbine with an air stream that has been compressed by the compressor, to form a hot gas which then expands so as to perform work at the rotor in a turbine. The gas turbine is operated in such a way that sufficient energy is output at the rotor shaft to generate the electrical energy, while a maximum temperature of the hot gas at the turbine inlet should not be exceeded.
The turbine inlet temperature cannot be measured directly, on account of its high values. Therefore, the temperature of the exhaust gas which is present at the turbine outlet is recorded, and the turbine inlet temperature can then be determined by calculation from this turbine outlet temperature. The turbine outlet temperature and therefore indirectly also the turbine inlet temperature can be controlled by means of the quantity of fuel introduced into the combustion chamber, while these temperatures are also dependent on the temperature of the air at the compressor inlet. To simplify control of the gas turbine, an auxiliary variable is calculated by means of a mathematical model, eliminating the dependency of the turbine outlet temperature on the compressor inlet temperature.
This auxiliary variable is used as a corrected turbine outlet temperature. It is dependent only on the quantity of fuel consumed, resulting in simple control of the gas turbine. Although the control is also dependent on the mains frequency of the power generated by the generator, this influence is not taken into account here.
To increase the performance of the gas turbine, it is also possible for water to be fed to the air stream sucked in by the compressor even before it has been compressed, in order to increase the mass flow through the gas turbine. This is generally known as wet compression mode.
The temperature of the air which is sucked in generally differs from the temperature of the liquid which is injected. Since the temperature-measuring devices arranged at the inlet of the compressor for measuring the air temperatures are wetted by the liquid that has been introduced, the temperature-measuring devices are not recording the temperature of the air, but rather that of the liquid.
If, on account of a compressor inlet temperature which is clearly higher following the measurement, a lower turbine outlet temperature is determined than the turbine outlet temperature which is actually present, the controller of the gas turbine increases the supply of fuel into the combustion chamber in order to compensate for the presumed difference. However, this leads to overfiring of the gas turbine, i.e. the actual turbine inlet temperature may become higher than the maximum permissible turbine inlet temperature. The gas turbine is underfired if the compressor inlet temperature measured is lower than the actual turbine inlet temperature.
Overfiring of the gas turbine can lead to overheating of the components exposed to hot gas and therefore to a reduction in their service life, or even to defects. On the other hand underfiring of the gas turbine leads to loss of performance.
SUMMARY OF THE INVENTION
The object of the invention is to provide a gas turbine in which the service life of the components exposed to hot gas is increased in wet compression mode yet nevertheless the maximum power output is achieved. A further object of the invention is to provide a control arrangement which implements operation of this type. A further object of the invention is to provide a corresponding temperature-measuring device.
The object relating to the gas turbine is achieved by the features of the claims. Advantageous configurations are given in the subclaims.
The solution provides for the temperature-measuring device to be arranged upstream of the injection apparatus, as seen in the direction of flow of the air, and for the temperature of the air stream at the compressor inlet to be calculated by means of the measured air temperature. Therefore, the liquid which is introduced cannot wet the temperature-measuring devices, which means that it is always the temperature of the air stream that is sucked in which is measured. Simply protecting the temperature-measuring devices by means of protective tubes does not eliminate the problem, since in this case the temperature-measuring devices would measure the temperature of the protective tubes, and these tubes would in turn be wetted with the liquid.
In an advantageous refinement, the humidity of the air stream can be determined by means of air-humidity-measuring devices upstream of the injection apparatus. If the air humidity and air temperature of the air stream that is sucked in are known, it is possible to determine the evaporation of the liquid which is introduced on its way to the compressor inlet. By taking the air humidity into account, it is possible for the temperature at the inlet of the compressor to be calculated particularly accurately.
If the temperature of the air stream at the compressor inlet is calculated by means of a function based on air temperature and humidity distributions, this calculation is particularly simple.
In an advantageous refinement, the air temperature and humidity distributions can be predetermined in the form of diagrams, so that it is particularly simple to portray the dependency of the evaporation of the injected liquid in the air stream. This contributes to simple calculation.
The object relating to the temperature-measuring device is achieved by the features of the claims. The advantages of the temperature-measuring device suitably correspond to those of the gas turbine.
The object relating to the control arrangement is achieved by the features of the claims. Advantageous configurations are given in the subclaims.
The solution provides for the temperature-measuring device to be arranged upstream of the injection apparatus and for the air temperature of the air stream at the inlet of the compressor to be calculated by means of the measured temperature. The advantages of the control arrangement suitably correspond to those of the gas turbine.
In an advantageous configuration of the control arrangement, with 100% evaporation a minimum possible temperature is determined and used as replacement for the temperature at the inlet of the compressor. In this context, it is assumed that the liquid introduced by the injection apparatus evaporates sufficiently for a relative air humidity of 100% to be established at the compressor inlet. Working on the basis of this assumption, it is possible, in conjunction with the measured air humidity and air temperature, to determine the minimum feasible (lowest possible) temperature at the compressor inlet. If the minimum possible temperature is now used as the temperature for the air stream at the compressor inlet, the temperature which actually prevails at the compressor inlet is always greater than the minimum possible temperature, since an air humidity of 100% is never achieved without external action. In this situation, the gas turbine is always underfired. Overheating of the components exposed to hot gas is therefore avoided, so that the service life of the components is not reduced.
An improved control arrangement for the gas turbine ensues if the temperature of the air stream at the inlet of the compressor is calculated taking account of the actual evaporation of the injected liquid in the air stream. The efficiency of the evaporation is determined by calculations and/or tests, and this efficiency, with the aid of the minimum possible temperature, is used to determine the air temperature which is present at the compressor inlet. With this control arrangement, it is possible to reproduce the true conditions with regard to evaporation of the introduced liquid on the way to the compressor inlet, and thereby to bring about reliable and more high-performance operation of the gas turbine, avoiding both overfiring and underfiring of the gas turbine.
In a preferred configuration of the control arrangement, the quantity of liquid injected into the air stream is altered as a function of the evaporation. The compressors of gas turbines are usually dimensioned for a predetermined quantity of liquid which evaporates during the compression. However, the evaporation causes a small proportion of the injected liquid to evaporate even before the compression, which means that the compressor is not operated in the optimum range. This drawback can be avoided by adapting the quantity of liquid injected.
The efficiency of the evaporation, which is substantially dependent on the droplet characteristics and the geometry, i.e. the spatial arrangement of the components of a compressor, can be estimated from tests and/or determined from calculations, which are then stored in the form of models or formulae in the controller. The avoidance of underfiring increases the power output of the gas turbine, and the prevention of overfiring of the gas turbine means that the service life of the components which guide hot gas is not adversely affected.
The advantages of the control arrangement suitably correspond to the advantages of the gas turbine.



BRIEF DESCRIPTION OF THE DRAWINGS
The invention is explained with reference to a drawing, in which:
FIG. 1 shows a gas turbine installation, and
FIG. 2 shows an intake housing of a gas turbine as shown in FIG. 1.



DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 diagrammatically depicts a gas turbine installation for converting fossil energy into electrical energy by means of a gas turbine 1 and a generator 2 coupled to it. The stationary gas turbine 1 substantially comprises a compressor 3, a combustion chamber 5 and a turbine part 7. The compressor 3 is connected to the turbine part 7 and the generator 2 via a common rotor shaft 10.
When the gas turbine 1 is operating, the compressor 3 sucks in air through an intake housing 11 and compresses it. The compressed air is mixed with a fuel B, which can be supplied through a shut-off member 8, in a burner and fed to the combustion chamber 5. In operation, the mixture burns to form a hot gas H which then flows into the turbine part 7, where the hot gas H expands and in so doing drives the rotor shaft 10. Then, the hot gas H leaves the gas turbine 1 as exhaust gas A, passing into an exhaust conduit (not shown in more detail). The rotor shaft 10 drives the compressor 3 and the generator 2.
To control operation of the gas turbine 1, the temperature TAT of the hot gas H at the outlet 6 of the turbine part 7 is monitored by means of a temperature-measuring device MAT, since the Temperature TT1 of the hot gas H which is present at the inlet 14 of the turbine part 7 cannot be measured. Both the power of the gas turbine 1 and the turbine outlet temperature TAT, and therefore indirectly also the turbine inlet temperature TT1, can be controlled by the quantity of fuel B introduced into the combustion chamber 5. An increase in the volumetric flow of the fuel B into the gas turbine 1 leads to a higher temperature of the hot gas H and to an increase in the power of the gas turbine 1. For this purpose, the controller 13 controls the shut-off member 8, which it actuates via its outlet.
Since the turbine inlet temperature TT1 is also dependent on the temperature Tv1 of the air stream L which is sucked in upstream of the compressor 3, this temperature is likewise recorded or determined constantly, i.e. at recurring intervals throughout the entire duration of operation.
The controller 13 eliminates the dependency of the turbine outlet temperature TAT on the air temperature TV1 by determining a corrected turbine outlet temperature TATK as auxiliary variable in accordance with the followings equation

TATK=TAK−k1·TV1  (1).

Accordingly, the corrected turbine outlet temperature TATK is dependent only on the fuel B which is introduced, so that the gas turbine 1 can be controlled more easily by controlling the corrected turbine outlet temperature TATK as a control variable and setting the volumetric flow of the fuel B as manipulated variable. The corrected turbine outlet temperature TATK could also be determined on the basis of a quadratic equation or on the basis of other functions.
The controller 13 has an input, at which the desired value TSo11 of the corrected turbine outlet temperature can be set. In the controller 13, the desired value TSo11 is compared with the determined corrected turbine outlet temperature TATK. If the actual value, the corrected turbine outlet temperature TATK is lower—higher—than the desired value TSo11, the controller 13 uses the, shut-off member 8 to increase—reduce—the supply of fuel.
If the gas turbine 1 is operated without a liquid being introduced into the air stream L, the temperature-measuring device MLU arranged upstream of the intake housing 11 can measure the temperature TV1 of the air stream at the compressor inlet 12 directly.
FIG. 2 shows the intake housing 11 of the gas turbine 1. The temperature-measuring devices MTU are arranged above an injection apparatus 9, so that the liquid W which is introduced does not wet the temperature-measuring devices MTU and the air-humidity-measuring devices MFU.
In wet compression mode, a liquid W, in particular water, is injected into the air stream L sucked in the intake housing 11 via the injection apparatus 9.
The temperature TU of the air which is sucked in is determined upstream of the intake housing 11 by means of the temperature-measuring devices MLU, and the air humidity FU of this air is determined upstream of the intake housing 11 by means of the air-humidity-measuring devices MFU. The outputs of these measuring devices are connected to the inputs of the controller 13.
The temperature TV1 which is present at the inlet 12 of the compressor 3 and is required for control is determined as a function of the measured values and on the basis of models in the controller 13. Therefore, the gas turbine 1 can be controlled by controlling the turbine outlet temperature TATK by means of the quantity of fuel B injected using equation (1).
If it is intended for the gas turbine 1 to be operated with injection of a liquid W into the air stream L sucked in by the compressor 3, two different control arrangements are possible: control with a theoretical evaporation which leads to an assumed air humidity of 100%, and adapted control with variable evaporation.
In the case of the control with the theoretical evaporation, it is assumed that enough of the injected liquid has evaporated for the air humidity in the intake air stream L at the compressor inlet 12 to be 100%. On this assumption, a minimum feasible temperature TWetBulb, which replaces the temperature TV1 at the compressor inlet 12, is determined on the basis of the measured temperature TU and air humidity FU of the air stream L. The compressor inlet temperature TV1 determined in this way can be ascertained by calculation or also from diagrams which are reproduced in electronic form in measurement technology, or also by means of mathematical formulae. The equation for the controller 13 for determining the corrected turbine outlet temperature TATK is then as follows:

TATK=TAK−k1·TWetBulb  (2).

Since an air humidity of 100% is never achieved in real operation, the actual temperature TV1 at the inlet 12 of the compressor 3 is always greater than the assumed minimum feasible temperature. The use of the minimum feasible compressor inlet temperature TWetBulb in each case determines an excessively high corrected turbine outlet temperature TATK, so that the controller 13 always provides an insufficient quantity of fuel B to the burner. This prevents overfiring of the gas turbine 1. Accordingly, the components of the gas turbine 1 which are exposed to hot gas, such as turbine blades and vanes, guide rings, platforms and combustion chamber heat shields, are exposed to the appropriate temperatures and premature fatigue is prevented in these components.
In the case of the adapted control of the gas turbine 1, an air humidity which is present at the inlet 12 of the compressor 3 is determined, although this air humidity is lower than 100% and can be determined as a function of the measured air humidity Fu, the measured temperature TU of the air stream L and the quantity of liquid W introduced by the injection apparatus 9. The efficiency η of the evaporation of the liquid W in the intake air stream L is also taken into account in this calculation in order to determine the temperature TV1 at the inlet 12 of the compressor 3.
The efficiency of saturation of the air stream L with a liquid W can be calculated according to




  
    
      
        η
        =
        
          
            
              
                T
                U
              
              -
              
                T
                
                  V
                  ⁢
                  
                    
                  
                  ⁢
                  1
                
              
            
            
              
                T
                U
              
              -
              
                T
                WetBulb
              
            
          
          .
        
      
    
    
      
        (
        3
        )
      
    
  




Resolving equation (3) with respect to TV1 and then inserting it into equation (1) gives:

TATK=TAT−k1·[TU−η·(TU−TWetBulb)]  (4).

The efficiency η of the evaporation, which is dependent on the droplet characteristics of the injected water and on the geometry, i.e. the spatial arrangement of the components of the compressor 3, can be determined by calculation and/or by tests and is then stored on the basis of a model or a diagram in electronic form in the controller 13.
Evaporation of the liquid W which leads to an air humidity at the inlet 12 of the compressor 3 which is lower than 100% gives a better description of the real conditions, resulting in improved control of the gas turbine 1.
A corrected turbine outlet temperature (TATK) determined in accordance with equation (4) is lower than a corrected turbine outlet temperature TATK determined on the basis of equation (2), so that power losses resulting from the turbine inlet temperature TT1 being assumed to be too low are avoided.
Furthermore, it is possible to determine the quantity of liquid W which evaporates before it reaches the inlet 12 into the compressor 3, and this quantity is then additionally injected by the injection apparatus 1. This leads to a further increase in the power of the gas turbine 1, since only the proportion of the liquid (W) which evaporates during the compression—i.e. in the compressor 3—contributes to increasing the power of the gas turbine 1 by wet compression.

## Claims

1. A stationary gas turbine for power generation, comprising:
an injection apparatus for injecting a liquid into an air stream that is sucked in by a compressor;
a fuel mixed with the air stream and combusted in a combustion chamber to form a hot gas which expands as it flows through a downstream turbine; and
a humidity-measuring device for recording the humidity of the air stream upstream of the injection apparatus; and
a first temperature-measuring device for recording a temperature of the air stream upstream of the injection apparatus; and
a second temperature-measuring device for recording a turbine outlet temperature of an exhaust present at an outlet of the turbine; and
a controller unit controlling flow of the fuel into the gas turbine comprising;
inputs receiving the recorded humidity from the humidity-measuring device and the temperatures from the first and second temperature-measuring devices;
an output connected to a shut-off member for controlling the flow of fuel;
wherein the controller unit is configured to produce the output by;
determining a temperature of the air stream at an inlet of the compressor,
determining a corrected turbine outlet temperature as a function of the temperature of the air stream at the inlet of the compressor,
comparing the determined corrected turbine outlet temperature to an inputted desired value of corrected turbine outlet temperature, and
producing the output effective to control the shut-off member as a function of the compared corrected turbine outlet temperatures.

2. The gas turbine as claimed in claim 1, wherein the temperature and humidity of the air stream can be predetermined in the form of diagrams.

3. The controller unit as claimed in claim 1, wherein the controller unit is adapted to determine the temperature of the air stream at the inlet of the compressor as a function based on the temperature and humidity of the airstream upstream of the injection apparatus.

4. The controller unit as claimed in claim 1, wherein the controller unit is adapted to calculate the temperature of the air stream at the inlet of the compressor according to the function:


Tu−η·(TU−TWetBulb)


wherein TU is the measured air temperature of the air stream upstream of the injection apparatus, η is an efficiency of evaporation of the liquid in the intake airstream, and TWetBulb is a minimum feasible temperature at which 100% of the liquid has evaporated at the compressor inlet.

5. The controller unit as claimed in claim 1, wherein the controller unit is adapted to calculate the corrected turbine outlet temperature according to:


TAT−k1·TWeyBulb 


wherein TAT is the exhaust gas temperature at the turbine outlet, k1 is a constant, and TWetBulb is the minimum feasible temperature at which 100% of the liquid has evaporated at the compressor inlet

6. The controller unit as claimed in claim 1, wherein the controller unit is adapted to calculate the corrected turbine outlet temperature according to:


TAT−k1·[Tu−η·(TU−TWetBulb)]


wherein TU is the air stream temperature upstream of the injection apparatus, TAT is the exhaust temperature at the turbine outlet, and TWetBulb is a minimum feasible temperature at which 100% of the liquid has evaporated at the compressor inlet, and η is an efficiency of evaporation of the liquid at the compressor inlet.