JPH09228853A - Gas turbine combustor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a NOx value within a specified limit of NOx even when load is fluctuated by providing the difference in time for a change starting point between the quantity of air feed and the quantity of fuel feed when the gas turbine is controlled in operation. SOLUTION: In a gas turbine employing a thermal power generation device, fuel is fed from a fuel tank 244, it is gasified by a carbureter 248, and it is fed to a combustor 200 by way of each flow rate control valve 252 thereafter. Meanwhile, air is controlled in flow rate by an air flow rate control valve 259 by way of a humidity measurement equipment 286 and an air flow rate measurement equipment 284, and it is fed to the combustor 200 thereafter. Thus as mentioned above, when the gas turbine is controlled in operation, based on selected information where let respective control commands for the quantity of air feed and the quantity of fuel feed cope with time for starting the change of both the quantity of air feed and the quantity of fuel feed which are measured by a plurality of measuring means disposed within the combustor, and let the result be stored therein, time for starting the change of the quantity of fuel feed is to be determined in such a way that the quantity of fuel feed is started so as to be changed while being delayed from the start of a change in the quantity of air feed when load is fluctuated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas turbine combustor using a gas such as air or natural gas, and NOx
The present invention relates to an operating method for realizing combustion and a gas turbine combustor.

[0002]

2. Description of the Related Art In order to protect the global environment, low NOx combustion is required as part of exhaust gas regulation. For this reason,
Instead of diffusion combustion in which fuel and air are supplied from different ejection ports and mixed and burned in a combustion chamber, premixed combustion in which fuel and air are mixed in advance and then burned is being used.

In this premixed combustion, the reaction region of combustion can be reduced, so that high load combustion can be performed. Also,
When the ratio of the fuel amount to the air amount is called the fuel-air ratio, by using the lean premixed combustion method in which the fuel is burned in a state where the fuel is less than the theoretical fuel-air ratio required for complete combustion,
The NOx emission amount can be reduced. This lean premixed combustion method is being adopted in gas turbine combustors and the like.

By the way, it has been known that the stability of the premixed flame and the NOx emission amount are influenced by the humidity and temperature in the atmosphere, the temperature of the combustion air, the property of the fuel, the calorific value and the like. For example, when the humidity in the atmosphere is high, the NOx emission amount is small, but the flame stability is low and the misfire tends to occur.

As a means for dealing with such a decrease in flame stability due to changes in the atmospheric temperature and humidity, the properties of the fuel, the heat generation amount, etc., for example, in Japanese Patent Laid-Open No. 187271/1993, the atmospheric humidity and humidity and the fuel A method of detecting a change in the amount of heat generation and controlling the amount of air and the amount of fuel supplied to the premix combustion burner by a detection signal of this change is disclosed.

Further, in Japanese Unexamined Patent Publication No. 4-318233, a limit line of exhausted NOx according to the state of atmospheric humidity is stored in advance, and if the measured value of NOx exceeds the limit value, NOx It is disclosed that the amount of air and the amount of fuel supplied to the combustor are controlled so that the ratio is below the limit value.

Further, Japanese Patent Application Laid-Open No. 62-111135 discloses controlling the fuel-air ratio in response to changes in atmospheric conditions (atmospheric temperature) and fuel conditions (calorific value).

[0008]

However, the above-mentioned Japanese Patent Laid-Open No. 5-187271 discloses that the air amount and the fuel are changed by using the changes in the atmospheric temperature and the humidity and the heat generation amount of the fuel in order to maintain the stability of the flame. The amount of air was controlled, and the amount of air and the amount of fuel were not controlled so that the NOx value maintained the desired limit value.

Further, in the prior art described in the above-mentioned Japanese Patent Laid-Open No. 4-318233, since the NOx emission amount changes due to the change in atmospheric humidity, the ratio of fuel and air in the premixed flame (hereinafter , Which is referred to as the fuel-air ratio), has been known as described above. However, it is necessary to control the combustion conditions of gas turbine combustion control elements such as atmospheric temperature and humidity and the calorific value of fuel. For that reason, no specific control method is proposed, and therefore,
Satisfactory NOx limits could not be achieved throughout operation.

As the most significant factor, in the above-mentioned publication, the fuel amount and the air amount are controlled by the command value based on the design value, and the actual flow rate has not been grasped. Some flowmeters were located away from the combustor, and the flow rate of each part of the combustor was not accurately grasped.

It has been found that there is a difference in responsiveness between the fuel flow rate and the air flow rate with respect to the load control command value depending on the flow path length. However, in the known example, such a point has not been sufficiently taken into consideration.

According to the present invention, even when the load changes, the predetermined NOx
An object of the present invention is to provide a combustion apparatus and method for a gas turbine that is kept within a limit value.

[0013]

A first feature of the present invention is as follows.
A method of operating a gas turbine combustor is characterized in that when the load changes, the fuel supply amount starts to be changed after the start of changing the air supply amount.

A plurality of sensing units are provided in the combustion chamber equipped with a hot-wire anemometer to store the flow rate flow with respect to the load control command value and store it. When the combustion condition is changed, the fuel supply amount is delayed after the air supply amount is changed. You can make changes.

For example, since the flow rate control command and the actual signal in the combustor are compared and stored as relational information, and the relational information is searched for the load request and the flowrate control command is applied, the flowrate control command is once If the actual signal in the combustor is compared and stored as relational information, it is possible to retrieve the relational information and apply the flow rate control command to the load request without providing a flowmeter.

In the method for operating the gas turbine combustor of the first feature, a plurality of fuels arranged in the combustion chamber corresponding to the air supply amount control command, the fuel supply amount control command, the fuel and the air supply amount control means, and The signal from the measuring instrument of the air amount is compared to store the relationship information in which the command time and the change time of the fuel and air supply amount are associated with each other, and the change start time of the fuel supply amount is the relationship information. Based on the above, it is determined for each fuel supply means so as to suppress the variation in the change start time of the air in the combustion chamber or the fuel supply amount.

It is possible to create and store relational information comparing the flow rate control command and the actual signal of the flow rate in the combustor, and retrieve the relational information at the time of load request to give the flow rate control command.

In addition, the load command value, the air supply amount, the fuel supply amount command value, the measured values of the air supply flow rate and the fuel supply flow rate by a plurality of flow rate measuring means arranged in the combustor, and the NOx amount of the combustion gas are associated with each other. Stored as relational information and comparing the load command value with the relational information at the time of load change, NOx of the combustion gas within the range in which stable combustion can be performed from the stored condition.
It is also possible to control the fuel and air flow rates by selecting a fuel and air amount control command value that reduces the amount.

Further, as a condition to be stored as the relational information and a condition to be compared, any one of the load command value, the temperature and pressure of the air supplied to the combustion chamber, the humidity of the air introduced into the compressor, and each fuel supply means. It is also possible to control with higher accuracy by using necessary conditions from the fuel calorific value of the supplied combustion gas or the mixing ratio of fuel and air.

For example, a sensor for measuring the flow rate in the combustor is provided, and relation information that compares the load request, the flow rate command value, the sensor output, the NOx value, and the combustion condition with each other is prepared at any time,
The relevant information is searched for the load request, and a flow rate control command value for low NOx combustion is given in the stable combustion range.

In addition, (a) flow rate detecting means for detecting the amount of fuel and the amount of air supplied to the combustor of the gas turbine,
(B) fuel amount control means for controlling the amount of fuel supplied to the combustor of the gas turbine; (c) air flow rate control means for controlling the amount of air supplied to the combustor; and (d) the fuel. In the relation of the mixture ratio with air (the fuel-air ratio is not general, the mixture ratio is the whole sentence), at least the heat generation amount of the fuel and the temperature and humidity of the air are classified and set. Storage means for storing relational information representing a limit value of NOx concentration in the exhaust gas, which is predetermined corresponding to the zone, and (e) the relation corresponding to the calorific value of fuel and the measured values of air temperature and humidity. Combustion control means for retrieving information and applying a control signal to the fuel amount control means and / or the air flow rate control means according to the mixture ratio in the retrieved relational information based on the load command value. Rukoto can.

Thus, (a) the temporal flow rate detection values of the amount of fuel and the amount of air supplied to the combustor of the gas turbine,
(B) a fuel amount control command value for controlling the fuel amount supplied to the combustor of the gas turbine, and (c) an air flow rate control command value for controlling the air flow amount supplied to the combustor. The correlation becomes clear, and (d) the NOx concentration in the exhaust gas can be stored corresponding to the calorific value of the fuel including the mixing ratio of the fuel and air and the temperature and humidity of the air.
For easy understanding, the memory that stores the combustion conditions, the control conditions, and the combustion results as relational information by comparing them is referred to as a map as necessary. This map determines these combustion conditions and combustion results by factors such as NOx and stable combustion in order to correspond to the variety of combustion conditions such as the gas turbine combustion control elements described above, such as atmospheric temperature and humidity and the calorific value of fuel. , Divide into each area as long as there is no significant difference. This divided area will be called a zone. The NOx concentration corresponding to the set zone is stored and the flow rate command value for the load request is determined.

Although a map will be described below as appropriate, the present invention can be applied to any map as long as similar related information can be stored and output without storing the map.

That is, the above-mentioned combustion conditions exist in a wide variety depending on the climate and the operating state of the gas turbine, and if all of them are to be stored, not only a huge storage capacity is required, but also the search time becomes long. Since the controllability is also deteriorated, the combustion conditions are divided into respective states, and when the NOx concentration in the set zone, for example, the atmospheric temperature 10 ° C to 30 ° C is substantially the same, the range is regarded as the same condition. The information is set and the relationship information of the NOx concentration limit value corresponding to the range is stored, and not only the NOx concentration can be suppressed below the limit value in the zones set as the same condition, but also contributes to the reduction of the storage capacity. To do.

Therefore, even if the number of control elements for performing the combustion control increases, the low NOx combustion control can be performed correspondingly.

In the actual combustor, (e) the calorific value of the fuel, the temperature and the humidity of the air are measured, and the low NOx condition is searched from the relation information with respect to the load command value from the host computer, and the fuel control is performed. Output the air flow rate control amount.

Further, the flow rate control command and the actual signal in the combustor can be compared and stored in a map, and the map can be searched for the load request and the flow rate control command can be applied. In the conventional real-time feedback control of the combustion state, there is a response delay from the control valve to the combustor, so it is necessary to perform feedforward control of the appropriate fuel and air flow rate values for similar past combustion conditions and load demands. You can
The amount of fuel and air supplied to the combustor of the gas turbine,
The temporal correlation between the fuel amount control command value and the air flow rate control command value becomes clear. Further, the NOx concentration in the exhaust gas is stored in correspondence with the heat generation amount of the fuel including the mixing ratio of the fuel and air and the combustion conditions of the temperature and humidity of the air.
Also, the delays of the air flow rate and the fuel flow rate in the combustion field are stored with respect to the flow rate control command value. Then, the map is searched for the load request and the flow rate control command is applied. The conventional feedback control of the combustion state in real time is not practical because the response delay from the control valve to the combustor is large. The present invention selects low NOx and stable combustion conditions for similar fuel conditions and load demands in the past, and
And feed-forward control of the value of the air flow rate.

A second feature is that a combustion chamber for burning fuel and the air, a plurality of means for supplying air to the combustion chamber,
In a gas turbine combustor having a plurality of fuel supply means for supplying fuel to the combustion chamber, a control unit that gives a predetermined time difference to start changing the fuel supply amount after the start of changing the air supply amount when changing the load. It was equipped with.

For example, a hot-wire anemometer is provided, the delay of the flow rate with respect to the flow rate control command is stored, and when changing the combustion condition,
The control unit generates a flow rate control command that compensates for the delay.

As a result, even in the transitional state in which the combustion conditions are switched, an appropriate fuel-air ratio can be maintained, so that stable combustion and low exhaust gas can be maintained. Unstable elements such as the distance from the control valve to the combustor and flow loss can be eliminated.

In the second gas turbine combustor, the flow rate is measured by a hot wire anemometer equipped with a sensing unit and a temperature compensating unit, and a sensor circuit for performing signal processing from the sensing unit and the temperature compensating unit. A plurality of sensing units are arranged in parallel in the combustion chamber, the flow velocity is measured by one of the sensing units, and a switching unit that switches wiring so that any one of the sensing units serves as a temperature compensation unit is provided. To have.

For example, a plurality of sensing units and a switching unit for selecting the sensing units are provided, and the switching unit reads the detection values of each of the sensing units to determine the fuel flow rate and the air flow rate. A map associated with the NOx value can be created.

A plurality of sensing units and a switching unit for selecting the sensing units are provided, and the sensing unit for temperature compensation and flow velocity can select the sensing units in the vicinity by the switching unit.

It is also possible to combine a plurality of sensitive portions and detect the average value of the respective sensitive portions.

For example, the hot-wire anemometer according to the present invention is provided with a plurality of sensing units and a switching unit, one of the sensing units is used for temperature compensation by the switching unit, and the rest is used for flow velocity measurement. , It is configured to operate, and all the plurality of sensing units can be used for flow velocity measurement.

The minimum constitution is such that two sensing units are provided, and both of them are operated by the switching unit for measuring the flow velocity, and either one or each detected value can be read.

In this way, one end of the sensing section is electrically joined, one signal line is taken out from the joined section, these are selectively operated, and it is operated as a hot-wire anemometer with a small number of lead wires. Since it is possible to reduce the number of lead wires in the combustor, it is possible to measure the flow rate without obstructing the flow, and it is possible to realize a low NOx combustor which has never been achieved.

By the way, the hot-wire anemometer is based on the principle of detecting the flow velocity by the action of making the resistance values of the flow velocity and temperature compensating parts substantially equal. Even when measured below, there is a difference in the detected value, that is, the sensitivity. This is the same as the conventional one. When the measurement is performed by changing the combination as in the present invention, the sensitivity can be easily corrected by a control device or a computer that issues the combination. Specifically, it is characterized in that the detection value by each combination is obtained under a constant flow rate, and a so-called calibration value is stored and converted.

The hot-wire anemometer is provided with a switching unit for selectively operating the temperature compensation sensing unit in the vicinity of the operating velocity sensing unit, so that the flow rate control condition based on the load command and the actual fuel flow rate can be obtained. The control means, the air flow rate control means and the flow path loss, the flow rate imbalance due to the length, etc. can be measured with a hot-wire anemometer, so the relationship between the fuel amount and the air amount becomes clear, including the time delay. Further, since the temperature compensation sensing unit in the vicinity is used, temperature compensation with less error can be performed.

[0040]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing embodiments of the present invention,
The matters investigated by the present inventors will be described.

The inventors of the present invention have particularly preferred premixed combustion with excess air, particularly preferably a fuel-air ratio of 1.0 or less and 0.5 or more (theoretical fuel-air ratio of 1 or more).
In the premixed combustion of a value (normalized as
Correlation of Ox concentration, CO concentration, flame blowout limit, oscillatory combustion occurrence limit, flame flashback limit, etc. is memorized and the conditions of less NOx and CO concentration are learned, and these are respectively learned. The present invention has been found to be applicable to the fuel-air ratio control of the above. The stable combustion range of premixed combustion shows a good correlation between the fuel-air ratio and the load ratio.

The matters investigated by the present inventors are shown below.

[I] The NOx emission amount is substantially the same as long as the fuel composition (fuel heat generation amount), the fuel-air ratio, the mixture temperature before combustion, and the water concentration in the mixture are the same.

[Ii] Since the NOx emission amount shows a relatively good correlation with the fuel component at the same fuel air ratio, a physical quantity of fuel, for example, a specific gravity sensor is provided to increase or decrease the fuel air ratio with respect to the fuel which changes for a while. .

[Iii] The jetting speed of the mixed gas when the flame blows out is almost the same even if the fuel composition, the partial concentration in the mixed gas, and the mixed gas temperature before combustion change.

[Iv] The jetting speed of the mixed gas when oscillating combustion occurs is almost the same even if the fuel composition, the water content in the mixed gas, and the mixed gas temperature before combustion change.

[V] Further, as a result of measuring the flow rate, there is a steady flow rate imbalance in each combustor (can) and in the can.

[Vi] There is a response delay in the fuel flow rate and the air flow rate that increase / decrease according to the change in the load command, and the fuel-air ratio transiently changes.

[Vii] The above [v] and [vi] differ depending on the combustor and the system.

[Viii] Relationship between combustion conditions (air temperature, humidity, fuel calorific value, flow rate, fuel-air ratio) and NOx.

[Ix] There is a flow velocity distribution and a temperature distribution in the flow path.

Based on the above, atmospheric humidity, temperature,
Combustion conditions such as fuel composition and air amount, fuel amount and exhaust gas sensor or change of combustion state by flame image etc. are measured,
Remember. When the ratio of the fuel amount to the air amount is called the fuel-air ratio, the fuel-air ratio and the combustion state are measured in contrast and stored. Then, optimization of the fuel-air ratio of low NOx in a stable combustion state is learned by an actual combustor (can) and mapped. Depending on the combustion condition being measured and the load request from the host computer, the pointer moves on the map to refer to,
Recognize the amount of air. Among the combustion conditions, the atmospheric humidity and the temperature are slow changes as described above. Therefore, if only changes in the fuel composition can be predicted, the fuel-air ratio required to keep the combustion state optimum can be known in advance. Here, the change of the fuel composition is a slow change and a fast change when the safety valve of the fuel tank operates. Slow changes can be accommodated by some means of observing combustion conditions. In the case of a rapid change, the air amount in the combustor may be adjusted with a time delay from the safety valve operation detection signal.

Therefore, as a concrete method of controlling the combustion state, for example, NO for the fuel-air ratio is set in accordance with the load.
x Emission concentration and flame stability are measured and stored. The NOx emission concentration and flame stability with respect to the fuel-air ratio when the humidity, temperature, and fuel composition of the combustion air are changed are measured and stored as a map. Based on this map, the amount of fuel and / or the amount of air supplied to the burner is controlled so that a flame with low NOx emission concentration and good stability is formed.

Further, in the present invention, it is preferable that the operation command has a pattern suitable for low NOx operation, high efficiency operation, load fluctuation operation and the like. In addition, learning is performed as an indirect value of NOx and fuel amount / air amount with any value such as command value, command voltage, command current, control target, control voltage, control current, displacement of control mechanism, measured value by flow meter. You can also

By the way, the premixed combustion in which the fuel and air are mixed and ejected from the nozzle in advance is a combustion system which can reduce NOx compared to the diffusion combustion, but our research results show that it is unstable at low load. It became clear that it would be in a burning state. In addition, premixed combustion has NOx in the fuel-air ratio.
The values depend on each other and the fuel-air ratio is low, that is, the NOx value is lower in lean combustion.

On the other hand, even if the above-mentioned control with a constant fuel-air ratio is carried out, a delay occurs with respect to the flow rate control command value described later due to the difference in the flow path length to the combustor, so that the fuel-air ratio becomes excessive. It was found that there was a dynamic fluctuation. Therefore, it is a feature that fluctuations in the fuel-air ratio do not occur by giving a delay to the command values of the fuel flow rate and the air flow rate in consideration of this response delay in advance.

In the present invention, the fuel amount and / or air amount can be controlled for each of a plurality of cans of the combustor, and the combustion conditions and the combustion conditions (results) are stored in comparison with each other, and the stability and stability are improved. The feature is that the optimum values of the fuel amount and the air amount are learned so as to satisfy the low NOx combustion condition.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is an explanatory view of the entire thermal power plant, which represents one of the gas turbine combustors (cans) suitable for using the velocity meter of the present invention.

100 is a compressor, 200 is a combustor, and 300
Is a turbine, 400 is a generator, 500 is another turbine, 5
Reference numeral 02 represents an exhaust heat recovery boiler, 506 represents exhaust gas, and 508 represents a condenser.

The fuel is supplied from the fuel tank 244, vaporized by the vaporizer 248, and sent to the fuel supply pipe 256. The fuel is measured by the fuel calorific value sensor 254, the flow rate is controlled by the fuel flow rate control valve 252, and the combustor 200 of the gas turbine is used.
Sent to On the other hand, the flow rate of the air 270 is controlled by the air flow rate control valve 259 after passing through the humidity measuring instrument 286 and the air flow measuring instrument 284, and the pressure measuring instrument 278 and the air temperature sensor 28 are controlled.
2 to the combustor 200 of the gas turbine.

The gas turbine combustor has an outer cylinder 261 and an inner cylinder 2.
67, the high pressure air 271 flows between the outer cylinder 261 and the inner cylinder 267, and the F2 premix combustor is used as combustion air.
Supplied to 260. A part of the high pressure air 271 is supplied to the combustion chamber as inner cylinder cooling air. A dilution air amount control device is provided on the downstream side of the combustion chamber. When the load on the gas turbine is small, a part of the combustion air is discharged to the downstream side of the combustor as diluted air. Fuel is supplied from the fuel nozzle, mixed with combustion air and then combusted in the premix combustor 260. Due to the action of the flame stabilizer 273 provided in the premix combustion combustor 260, a circulating flow of high-temperature gas is formed downstream of the flame stabilizer, and the heat from this circulating flow stabilizes the premix flame. The gas generated from the premixed flame is mixed with the inner cylinder cooling air and the diluted air to become the high temperature combustion gas 274,
It is guided to the gas turbine 300 via the transition piece. The high temperature combustion gas 274 that drives the gas turbine, the air compressor 100 connected to the gas turbine, and the generator 400 becomes low temperature combustion exhaust gas 274 and is guided to the flue gas denitration device. Nitrogen oxides in low-temperature flue gas react with ammonia in the flue gas denitration device and are converted to nitrogen,
It is guided to the waste heat recovery boiler 502. Waste heat recovery boiler 50
The steam turbine 500 is driven by the steam 504 generated in 2. This steam turbine is also connected to the generator 400. The steam that has driven the steam turbine 500 becomes water in the condenser 508 and is supplied again to the waste heat recovery boiler 502. Here, the positions of the waste heat recovery boiler and the flue gas denitration device may be reversed. A denitration device may be incorporated in the waste heat recovery boiler. Combustion exhaust gases are mixed with exhaust gases from other gas turbines at the chimney and released into the atmosphere.

As will be described later, even in thermal power generation, regulations are strengthened so that exhaust gas does not pollute the global environment. In the gas turbine, it is required to reduce NOx in the combustor, and in order to realize this, it is effective to reduce the ratio of fuel to air during combustion and the fuel-air ratio. However, if the fuel-air ratio is lowered, the combustion stability will deteriorate, so
Understanding the values of the air and fuel in the combustor is an important issue. We have already examined the use of a hot-wire anemometer that has already been put to practical use for detecting the engine air amount for automobiles, but to use it in a high-temperature, high-pressure combustor, the anemometer of the heat resistance and pressure resistance structure of the present invention is used. Must be used.

In the present invention, as will be described later, it has been found that there is a delay difference in the response of the fuel flow rate and the air amount flow rate to the flow rate control command value, and the fuel-air ratio fluctuates excessively. By doing so, the transient fluctuation of the fuel-air ratio can be suppressed.

By the way, one of several factors that make stable combustion in the combustor difficult as the NOx is reduced will be described. In the figure, when the fuel used is a fuel having a low boiling point such as LNG, a part of the fuel is vaporized in the fuel tank 244 and the pressure in the fuel tank 244 rises. At this time, in order to prevent the destruction of the fuel tank 244, the pressure in the tank is measured by the fuel tank pressure gauge value 246, and when the pressure in the tank exceeds the limit value, the fuel tank pressure adjustment valve 2
50 is opened, and a part of the gas in the tank is supplied to the fuel supply pipe 256.
To release. The gas vaporized in the tank has many components with a low boiling point and differs from the composition of the fuel that is normally supplied. Therefore, when the fuel tank pressure adjustment valve 250 is opened, the fuel composition and the calorific value change. Therefore, the calorific value measuring device 254 is provided after the pressure adjusting valve 250.

FIG. 13 shows the response of the fuel flow rate and the air flow rate to the generated flow rate control command value based on the load request. Here, a pattern corresponding to the time of the flow rate control command value is shown for both fuel and air. Actually, the product of this pattern and the coefficients α and β is given as the fuel flow rate command value and the air flow rate command value. Time t
At 0, the flow rate control command value rises, the fuel flow rate rises at time t1 after Δt1, and the air flow rate rises at time t2 after Δt2. Due to the time delay Δt2 between the fuel flow rate and the air flow rate, the fuel-air ratio increases from t1 when the fuel precedes to t2 when the air rises. From t2 to t4 after Δt1 of t3 when the flow control command value becomes constant, there is a lot of fuel due to the fuel leading, and the fuel-air ratio is a little higher than that when the flow control command value is constant. It will be constant. Command value is t3
The air flow rate is (Δt1 + Δt
2) At t5 after that, it becomes a constant value, and the fuel flow rate becomes constant, and the fuel flow rate and the air flow rate match at a high flow rate command value, so the fuel air ratio returns to a predetermined air fuel ratio and becomes constant. Further, at time t6, the flow rate control command value starts to decrease and then decreases to t8. The fuel flow rate and the air flow rate respond to this command value with the same delay time as when they increased. Therefore, the fuel-air ratio starts decreasing at time t7, becomes constant at t8, shows a substantially constant value until t9, and returns to constant at t10.
As described above, in the conventional distribution of the fuel flow rate and the air flow rate without considering the delay, it was revealed that the fuel-air ratio excessively fluctuates when the load command value is changed for the generator.
This change in the fuel-air ratio not only changes the NOx value,
It leads to combustion instability. That is, as a result of pursuing a reduction in NOx, there is less margin in combustibility, so that the conditions become close to a flashback when the fuel-air ratio becomes high and a misfire when the fuel-air ratio becomes low. Therefore, the time difference until the air flow rate and the fuel flow rate reach the combustor with respect to the flow rate command value, Δ in FIG.
It is desirable to delay the fuel flow rate command value so that t2 becomes small.

This can be given by software as described in FIG. 11 or by hardware. Thus, if there is no difference in response time between the fuel and air with respect to the flow rate command value, even if the command value increases or decreases, the fuel-air ratio will remain constant and the flow rate will increase or decrease. Therefore, low NOx combustion can be realized.

Here, the case where the fuel flow rate responds prior to the air flow rate is shown. This is because the fuel flow rate control valve 252 is closer to the combustor than the air flow rate control valve 259. In some cases, the opposite may occur depending on the condition of the piping.

Air humidity sensor 286, flow rate measuring device 28
4, signals from the air temperature sensor 282, the pressure measuring device 278, and the fuel calorific value sensor 254 are supplied to the control device (MPU-1,
700, MPU-2, 701, host computer 70
0) and store it. On the other hand, when the load changes, the conditions are selected from the stored settings and the air flow control valve 259 and the fuel flow control valve 252 are controlled based on the load demand so that the NOx amount is low in the stable combustion range. Order to

For example, the air supply amount control command and the fuel supply amount control command are compared with the measured values of the fuel and air amounts from the plurality of measuring means arranged in the combustion chamber corresponding to the fuel and air supply amount control means. A map associating the command time with the fuel and air supply amount changes is created and stored. The change start time of the fuel supply amount can be set for each fuel supply means based on the map so as to suppress the variation of the change start time of the air in the combustion chamber or the fuel supply amount.

Further, the load command value, the air supply amount, the fuel supply amount command value, the measured values of the air supply flow rate and the fuel supply flow rate by a plurality of flow rate measuring means arranged in the combustor, and the NOx amount of the combustion gas are associated with each other. Remember and map. When the load changes, the load command value is compared with the above map, and the N of the combustion gas within the range in which stable combustion can be performed from the stored conditions is performed.
A fuel and air amount control command value that reduces the Ox amount is selected to control the fuel and air flow rates. These allow control according to the characteristics of the actual machine.

FIG. 2 is a schematic view showing an embodiment of a hot-wire anemometer having a plurality of sensing parts according to the present invention. Sensing unit 611
To sensing unit 617 are sensing units installed in the fluid. This sensing unit is the relay 6 of the sensor switching circuit 640.
The relay 646 is switched from 42 to selectively connect to the sensor circuit 602. In FIG. 2, the sensing unit 611 and the sensing unit 612, which are shown by thick lines, are the sensor circuits 602.
1 of the hot wire type flow meter described in FIGS.
Make up the composition. The sensor switching circuit 640 selectively connects the sensing unit 612 to the sensing unit 616 to the sensor circuit 602, and the flow velocity according to the position of each sensing unit is detected. Here, the sensing unit 611 is the sensing unit 6 in FIG.
21 is for compensating the error of the detection signal due to the temperature change of the fluid. Generally, there is little change in the temperature distribution of the fluid in the flow path, and thus the sensing unit 611 for compensation is not switched, and there is no practical problem even if only the sensing unit is switched.

FIG. 3 shows a block diagram of a comparative hot-wire anemometer. The sensing unit 620 and the sensing unit 621 are sensing units, and are made of, for example, stainless steel, which have good heat resistance and conductivity, such as a sensor terminal C660, a sensor terminal D662, a sensor terminal E664, and a sensor terminal F.
It is supported by 666. This sensor terminal C660
Serves also as a power source and a lead wire for the sensor sensing unit 620, and is connected to the sensor circuit 602.

FIG. 4 shows an outline of the hot wire type circuit, which shows a part of the circuit of the sensor circuit 602, in which a current is supplied to the bridge circuit by an amplifier 603. In this case, the temperature of the sensing unit 620 is set higher than the temperature of the sensing unit 621 by a constant temperature, for example, about 200 ° C. This bridge circuit increases or decreases the current so that the resistance value does not change due to the cooling effect due to the heat transfer diffused by the sensing unit 620 according to the flow velocity.
This current increase / decrease is automatically performed according to the well-known resistance unbalance of the bridge circuit. In order to set the temperature of the sensing unit 620 to be higher by a constant temperature, it is sufficient to set a constant value at which the resistances of the bridge are balanced while the temperature of the sensing unit 620 is increased by a constant temperature.

FIG. 5 is a schematic diagram showing the structure of a hot-wire anemometer having a plurality of sensitive parts. The sensing parts 611 to 619 have a diameter of 0.2.
20 for ceramic pipes of ~ 0.6mm, length 1-3mm
It is constructed by winding a platinum wire having a diameter of ˜50 μm. The sensing units 611 to 619 are supported by the sensor holder A624 and the sensor holder B626 via the insulating stator 628 and the insulating stator 630. For the insulating stator 628 and the insulating stator 630, for example, a ceramic material having low electric conductivity and thermal conductivity is suitable. The sensitive portions 611 to 619 are electrically and mechanically joined to the sensor terminals A632 and B634 by spot welding or the like. Here, the sensor terminal A 632 and the sensor terminal B 634 preferably have a diameter of about 0.5 to 2.0 mm in order to prevent the sensitive portions 611 to 619 from being vibrated by the pressure of the fluid. A thicker one is more suitable for preventing vibration, but the sensing units 611 to 61
The heat from 9 is transmitted to the sensor terminal 632 and the sensor terminal B634, the amount of the heat escaped increases, and the measurement accuracy deteriorates. Here, the insulating stator 628 needs to be electrically insulated, but the insulating stator 630 does not need to be electrically insulated in some cases. Sensing unit 61 of FIG.
This is for electrically connecting as shown in 2-617.
In this case, the sensor holder B626 having a high electric conductivity is used. When the insulating stator 630 is an insulator, the sensor terminal B634 is electrically connected.

A hot-wire anemometer having a plurality of sensitive parts as shown in this figure has a sensor switching circuit 640 as shown in FIG.
The flow velocities at the positions of the sensing units 611 to 619 can be measured by switching and selecting at any time.

FIG. 6 shows an example of the flow velocity distribution obtained by measuring the air flow velocity in the combustor with reference to FIG. FIG. 6A is a measurement result, FIG. 6B is a predicted value of the flow direction and flow velocity distribution of the high-pressure air 271, and FIG. 6C is a schematic diagram showing the measured combustor locations. 671 is a swirler outlet of the premixing section, 672 is a flow path formed around the fuel section, 673 is an upstream section of the swirler, 67
Reference numerals 4 are respectively provided in the premixed combustion air supply section around the diffusion combustion section and between the premixed combustion section.

FIG. 6A shows the sensing units 611 to 619 of FIG.
Is a measurement result corresponding to. Since the cross sections of the flow paths having different flow velocities can be measured in this manner, the air flow rate can be accurately obtained from the average value of these.

FIG. 7 is a schematic diagram showing the switching of the sensitive portion which is actually measured using FIG.

The sensing section 610 is connected to the sensor circuit 602 by connectors A606, B607 and C608. A sensor switching circuit 640 is provided between the connector B607 and the connector C608, and the sensing unit of the sensing unit 610 selectively selects the sensor circuit 60.
2 is connected. Here, relay 1 641 to relay 6
646 has a power supply of 15 V and has a relay 7 647 and a relay 8
Switched when turned off by 648. This drawing shows this switching by an automatic / manual switch 68.
6 shows a circuit that can be selected automatically / manually.
When manual is selected, the sensor switching circuit 640 is switched at any time by pressing the relay switching push button 688. When automatic is selected, it is sequentially switched by an external control signal. This control signal is given from the I / F board from the personal computer, and at the same time, the detection signal from the sensor circuit 602 is taken in, so that the sensing unit can be automatically switched at high speed and read.

FIG. 8 is a schematic diagram showing a time sequence of the switching circuit of FIG. Relay switch push button 688
The relay 7647 is turned on while the button is being pushed, and is turned off with a time constant of about 2 seconds for a certain period of time.
Any one Ry (n) of the sensor switching circuit 640 is turned off when the relay switching push button 688 is turned back on, and Ry (n) is turned off.
y (n + 1) is turned on. That is, the relays 1641 to 6646 of the sensor switching circuit 640 are configured to switch when the relay 7647 is off. This is to prevent the sensing section of the sensing section 610 from being damaged by the current during the transition by switching the power source + 15V when the relay 7647 is off.

FIG. 9 is a schematic diagram showing an example of an averaging circuit when a plurality of sensing units are used. The sensing unit 690 is a temperature compensating sensing unit and is fixedly connected to the sensor circuit 602. Sensing units 691 to 694 are flow-sensing units and correspond to Rw1 to Rw4 shown in (b). Since these have the configuration as shown in FIG. 9C, the average value of the signal corresponding to the flow velocity at these positions is shown. Here, a configuration has been shown in which the four sensing units are used to obtain the average value of the flow without changing other resistors or the sensor circuit 602.

FIG. 10 shows an embodiment of the structure for controlling the flow rate of the gas turbine combustor (can) and measuring the NOx value according to the present invention. Reference numerals not described indicate the same or the same functions as those described above. The combustor (can) is composed of a plurality of cans as described above, and in this figure, the combustor (can) 202, the combustor (can) 204, the combustor (can) 20.
Only five combustors (combustor (can) 208 and combustor (can) 210) are shown. 254 is a calorific value measuring device, 259 is an air flow rate control valve, 252 is a fuel flow rate control valve, 280 is an exhaust gas sensor, 276 is a combustion exhaust gas, and 268 is a fuel gas outlet.

An air flow rate control valve and a fuel flow rate control valve are provided in each of these cans so that the flow rate can be controlled individually. Although not shown in the figure, a measuring device of an air temperature / humidity sensor for combustion conditions is provided for each combustor, and is connected to a control device such as 700, 701, 702.
NOx from the heat value of fuel and exhaust gas sensor
Value is obtained. Further, the flow rate sensor of the present invention is provided, and the combustion conditions by the above-described sensor, the measured air flow rate when the fuel amount and the air amount are increased and decreased for each of these cans, and the NOx value for the fuel flow rate are measured and stored. . With this configuration, even if there is a flow rate loss to each can or variations in flow rate control characteristics, the control amount, air flow rate, and fuel flow rate based on actual measurements are stored, so refer to the stored data for stable combustion. Equalization can be achieved by appropriately giving a flow rate control command for each can so as to reduce the amount of NOx within a possible range. Also, the fuel change command can be issued after the air flow rate command.

Even when the air flow rate control valve and the fuel flow rate control valve are not provided in each can, the flow rate sensor of the present invention is provided and NO for the measured air flow rate and fuel flow rate is provided.
When the x value is measured, the apparatus can be improved to reduce the flow loss to each can and the variation in the characteristics of the flow control.

The system of FIG. 11 is arranged, and after the air flow rate sensor 296 measures the air flow rate and the air humidity sensor 286 measures the humidity, the air is sucked into the air compressor 100 and becomes high pressure air. If necessary, the high pressure air is provided with an air pressure measuring device to measure the pressure and the gas turbine combustor inlet temperature measuring device to measure the temperature. Then, it is sent to the gas turbine combustor 200. If the amount of air taken into the air compressor 100 can be calculated from the atmospheric temperature and humidity and the characteristics of the air compressor 100, the air compressor 1
If a control device is provided so that the amount of air sucked into 00 is constant, the air flow rate sensor 296 is not always necessary.

FIG. 11 is a schematic diagram showing an embodiment of the system configuration of the thermal power generation system for carrying out the fuel-air ratio control of the present invention.

The memory area 707 stores the combustion conditions, the load command value, the fuel amount, and the NOx value indicating the combustion result with respect to the air amount. As will be described later, these conditions have a complicated causal relationship, and until now, the amount of fuel and the amount of air have been appropriately adjusted based on experiments. In the present invention, the fuel amount, the air amount and the NOx value with respect to the load are actually measured for each condition, and these conditions are zoned within a range where there is no significant difference and stored for comparison.

What is referred to as zone division here is that, as described above, the exhausted NOx value is influenced by changes in atmospheric temperature, humidity and fuel calorific value, and there are countless combinations of these.
If all of these combustion conditions and exhausted NOx values are to be stored, not only a large-capacity storage device is required, but also the control response becomes slow, which is a practical problem. Therefore, the combustion conditions are zoned within a range where there is no significant difference, that is, a range where they can be regarded as the same condition, and the fuel amount, the air amount, and the NOx value corresponding to the load are stored and corresponded for each condition.

These values are close to the amounts of fuel and air that have been experimentally obtained in the past, but especially the configuration of the present invention continues the operation when the conditions determined during the trial run deviate from the optimum values. The optimum value is learned over time, and the accuracy error and design error of the combustor can be corrected for a while. Furthermore, as described below, a plurality of combustors of the thermal power generation device,
Specifically, it is composed of a dozen or more cans of combustor, and each can has an unbalanced amount of fuel and / or air. The present invention has a configuration in which the flow rate of fuel and / or air can be controlled for each can, and each can be controlled to a fuel-air ratio with a small NOx.

The air temperature of the combustion condition is measured by the air temperature sensor 28.
2. The air pressure is measured by the air pressure sensor 278, the air humidity is measured by the air humidity sensor 286, and the fuel calorific value is measured by the fuel calorific value sensor 254, and is taken into each can map 708 as a combustion condition. Further, the air amount and the fuel amount are measured by 296 and 294, and are fetched in comparison with the air flow rate control signal 716 and the fuel flow rate control signal 718. The combustion conditions of the combustor with respect to these combustion conditions, the amount of air, and the amount of fuel are measured by the exhaust gas sensor 280 or the fuel-air ratio sensor 281, and are captured in comparison with each can map 708. When controlling the flow rate of each conventional can as a whole, there are variations in the flow rate due to the difference in the flow path resistance to each can and the shape accuracy inside each can. It could not be burned at the fuel-air ratio. On the other hand, in the present invention, not only can the flow rate be controlled for each can, but it can also be controlled to an optimum fuel-air ratio given or learned in advance.

Combustion control unit MPU-2 (control of each can) 70
3 is an air temperature sensor 282, an air humidity sensor 286,
From the output signals representing the respective states of the fuel heat generation amount sensor 254, a map corresponding to the state, that is, the combustion condition at that time is searched from each can map 708 which is a storage unit. Each can map 708 stores a map showing a NOx value equal to or less than the limit value corresponding to the combustion condition in the relationship of the fuel-air ratio as shown in FIGS. 4, 5 or 7 to 10 described later. . Then, the air flow rate control signal 716 and the fuel flow rate control signal 718 are created based on the searched map and the load command value, and the combustion control of the combustor 200 is performed. Furthermore, MPU-2 (controlling each can) 703
Is equipped with learning means for learning the optimum fuel-air ratio described above.

In this way, the optimum fuel amount and air amount command values peculiar to the combustor with respect to the combustion conditions and load demands are stored in each can map. As described above, since the combustion conditions are innumerable depending on the combination of the respective conditions, the ranges having no significant difference in the combustion conditions are regarded as the same conditions and handled.

The MPU-1 (overall control) 701 outputs an operation command and a load command for each can based on a load request to the host computer 700 and a basic control plan input in advance. The MPU-2 (can control for each can) 703 receives the operation command and the load command for each can, determines the fuel flow rate and the air flow rate for each can, and outputs the flow rate command value. Here, the air temperature, the humidity, etc. of the combustion conditions are appropriately measured by each sensor and serve as a pointer for map reference. When there is a change in the combustion condition, the pointer immediately refers to the map corresponding to the combustion condition and changes it to a flow rate control signal to appropriately change the fuel amount and the air amount. In the present embodiment, the sampling times of the combustion conditions are made different in consideration of the changing speed of the combustion conditions. That is, the change in temperature and humidity is gradual, so the sampling is slowed down and the sampling is speeded up in response to the load demand. Although the fuel calorific value usually changes slowly, the fuel calorific value becomes high when the safety valve 250 of the fuel tank operates. The NOx value occurs when nitrogen in the air is exposed to a high temperature. Therefore, in the case of a fuel gas having a high heating value, it is generally preferable to set the fuel-air ratio low. This change in the amount of heat generation reaches the combustor with a time constant that depends on the length of the pipe from the safety valve to the combustor. Since this time constant is unique to each device, the operation of the safety valve can be detected and interrupt control can be performed. When the operation of the safety valve 250 returns, it returns to the normal command value of the fuel-air ratio with a constant time constant. here,
Although not shown, an interrupt can be generated based on the operation signal of the safety valve to output the fuel flow rate control signal 718 with the time constant adjusted.

As means for not using the operation signal of the safety valve,
It is also possible to deal with this by increasing the heating value sampling time.

Here, the control for increasing / decreasing the fuel amount with respect to the operation of the safety valve has been described, but the air amount may be controlled. It is also an effective means to let the gas from the safety valve escape to another pipe. Actually, it is sufficient to prepare a table or map of about 2 to 5 representative changes in the fuel calorific value when the safety valve operates or including a difference in liquefied natural gas (LNG) composition. As a result, the fuel-air ratio corresponding to the heat value of the fuel can be output.

By the way, the control of the flow rate at the rated rotation has been described so far. However, since the rotation speed of the compressor 100 fed into the combustor changes when the generator starts, the air pressure of the compressor changes. For this reason, the flow rate control at the time of startup needs to have a pattern different from that at the time of rating. Therefore, a startup pattern 710 is separately provided at the time of startup to control the flow rate at startup. This start-up pattern also holds differences in combustion conditions and start-up conditions such as air temperature, humidity, pressure, and fuel calorific value.

Next, each can default value 712 in the memory area
Is an area for inputting design values for each can map 708 to be learned at the time of test operation. This is an area for inputting the optimum values of the same type combustor from the past combustor database before the test run. This area is R for backup
If OM is used or RAM is used, it is preferable to protect it so that it cannot be easily rewritten. At the beginning of the operation of the new combustor, this command value is used to control the flow rate according to the combustion conditions and load demand.

Here, for example, it is possible to feed back the value of NOx in real time to control to the optimum fuel-air ratio, but in the present invention, it is preferable to install it at the outlet of the turbine because of the heat resistance of the NOx sensor. , Because it is practical,
There is a time lag between the measured values of the fuel-air ratio and NOx, and feedback control is difficult, so past data is used offline.

By adopting the gas turbine power generator and control method of the present invention, changes in NOx emissions due to seasonal changes, fuel composition changes, installation areas, etc. are minimized, and low N
It is Ox and can maintain good flame stability. Generally, in order to eliminate the need for a denitration device, the NOx concentration discharged from the gas turbine combustor is 1% in terms of 16% O ₂ conversion.
It is said that it should be 0 ppm or less.

FIG. 12 shows N for the air flow rate and the fuel flow rate.
The stability of Ox value and combustion condition was shown. In order to reduce it to 10 ppm or less, it is necessary to reduce the fuel-air ratio, and the combustion stability becomes poor. Therefore, the absolute values of the air flow rate and the fuel flow rate can be grasped by using a hot-wire anemometer with multiple sensitive parts that provides higher measurement accuracy than the conventional single-sensitivity hot-wire anemometer. It can handle severe combustion conditions. The figure shows the amount of fuel,
Alternatively, the relationship with the actual flow rate measurement value is shown instead of the air volume control command value. As a matter of course, the relationship between the command value and the actual measurement value and the delay can be found. Therefore, if these are learned, stable combustion, low N based on the flow rate control signal can be achieved even if the actual measurement value is not always measured.
Ox combustion can be realized.

The range of the NOx value is not always 10 pp.
It is not necessary to set m or less, and if it is difficult to set this value, set it to 20 to 30 ppm,
An exhaust gas purification device may be provided.

[0103]

The present invention has a sensing unit for measuring the flow rate of fuel and air in a combustor for thermal power generation, measures the response of fuel flow rate and air flow rate to a flow rate control command signal, and measures the fuel flow rate to a load command. The optimum flow rate of air can be provided. Further, by the means for removing the response delay, the mixture ratio (fuel air ratio) of the fuel and the air which changes transiently can be reduced, and low NOx and stable combustion can be realized.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a gas turbine combustor of the present invention.

FIG. 2 is a conceptual diagram of a hot-wire anemometer having a plurality of sensing units according to the present invention.

FIG. 3 is an explanatory diagram of a hot-wire anemometer.

FIG. 4 is a schematic diagram of a hot-wire circuit.

FIG. 5 is a configuration diagram of a hot-wire anemometer having a plurality of sensing units according to the present invention.

FIG. 6 is a diagram showing an example of measuring the flow velocity distribution of the present invention.

FIG. 7 is a schematic diagram showing switching of the sensing unit of the present invention.

FIG. 8 is a schematic diagram showing a switching time sequence of the present invention.

FIG. 9 is a schematic diagram showing an example of an averaging circuit of the present invention.

FIG. 10 is a schematic diagram showing a configuration for controlling gas turbine flow rate and measuring a NOx value.

FIG. 11 is an overall configuration diagram of a thermal power generation system that implements fuel-air ratio control of the present invention.

FIG. 12 is a diagram showing a fuel amount / air amount and a combustion state of the present invention.

FIG. 13 is a response diagram of a flow rate control command value, a fuel flow rate, and an air flow rate.

[Explanation of symbols]

200 ... Combustor (can), 244 ... Fuel tank, 252 ... Fuel flow rate control valve, 254 ... Fuel calorific value sensor, 259 ... Air flow rate control valve, 280 ... Exhaust gas sensor, 282 ... Air temperature sensor, 286 ... Air humidity Sensor, 610 ... Sensing unit, 640 ... Sensor switching circuit, 702 ... Load command,
703 ... Combustion control device, 708 ... Can maps.

Claims (6)

[Claims] 1. A method of operating a gas turbine combustor having a combustion chamber for combusting fuel and air, air supply means for supplying air to the combustion chamber, and fuel supply means for supplying fuel to the combustion chamber. In the method of operating the gas turbine combustor, the change of the air supply amount and the fuel supply amount is provided at the starting point. 2. A method of operating a gas turbine combustor according to claim 1, wherein a plurality of measuring means are provided in the combustion chamber in correspondence with the air supply amount control command, the fuel supply amount control command, and the fuel and air supply amount control means. The relational information in which the command time and the change time of the fuel and air supply amount are associated with each other is stored by comparing the measured values of the fuel and air amount, and the change start time of the fuel supply amount is the relational information. Based on the above, a method for operating a gas turbine combustor, characterized in that it is determined for each fuel supply means so as to suppress variations in change start time of air or fuel supply amount in the combustion chamber. 3. The method for operating a gas turbine combustor according to claim 1, wherein a load command value, an air supply amount, a fuel supply amount command value, and an air supply flow rate and a fuel supply flow rate by a plurality of flow rate measuring means arranged in the combustor. The relationship information in which the measured value of NOx and the NOx amount of the combustion gas are associated is stored, and when the load changes, the load command value and the relationship information are compared,
A method for operating a gas turbine combustor, characterized in that a fuel and air flow rate control command value that results in a low NOx amount of combustion gas is selected from a stored condition in a stable combustion range, and the fuel and air flow rates are controlled. 4. The method of operating a gas turbine combustor according to claim 3, wherein the map is created for each load change. 5. A gas turbine combustion system having a combustion chamber for burning fuel and air, a plurality of air supply means for supplying air to the combustion chamber, and a plurality of fuel supply means for supplying fuel to the combustion chamber. A gas turbine combustor, wherein the gas turbine combustor is provided with a control unit that gives a predetermined time lag so as to start changing the fuel supply amount after the start of changing the air supply amount when the load is changed. 6. The gas turbine combustor according to claim 5,
The flow rate is measured by a hot-wire anemometer equipped with a sensor circuit that performs signal processing from the sensing unit and temperature compensating unit, and a plurality of sensing units are arranged in parallel in the combustion chamber. A gas turbine combustor having a switching unit that switches the wiring so that the flow velocity is measured by one of the sensing units and the other sensing unit is used as the temperature compensation unit.