JPH0674892B2 - Combustion control method and apparatus for multi-stage combustor - Google Patents

Description

The present invention relates to a combustor for an industrial gas turbine, and more particularly to a combustion control method for a multi-stage combustor having a low nitrogen oxide (NOx) concentration in exhaust gas, and a method thereof. It relates to the device.

[Conventional technology]

Prior art relating to the present invention includes, as
E-paper 85-GT-50 (1985) (ASME paper 85
-GT-50 (1985)) operates a normal combustor with NOx and CO values within the limits, so water is injected into the combustor and the amount is empirically determined by the atmospheric temperature. There is an example where it is uniquely determined.

[Problems to be solved by the invention]

In the above-mentioned conventional technique, the combustion gas temperature of the combustor is lowered to reduce NO.
Water is sprayed to reduce x.

In this system, the fuel injection nozzle is provided only at the head of the combustion chamber, which is so-called single-stage combustion.Therefore, the amount of water injection is simply determined as an empirical value as a function of only the atmospheric temperature, and low NOx is set. I'm driving.

Such a wet NOx reduction method does not perform water injection because the efficiency of the gas turbine plant as a whole decreases.
Various so-called dry NOx reduction methods are being developed. The dry NOx reduction technology is different from the wet method shown in the related art, and naturally, different measures are required to meet the demand for changes in atmospheric temperature and the like.

An object of the present invention is to provide a two-stage combustor, that is, a combustor in which the first stage is diffusion combustion and the second stage is premixed combustion, and changes in NOx value due to changes in atmospheric temperature, humidity and other ambient conditions,
(EN) A combustion control method for a multi-stage combustor that absorbs by controlling the distribution of the fuel-air ratio and operates so as to keep the NOx value within a limit value under any condition, and an apparatus for carrying out the method. .

[Means for solving problems]

The above object is to maintain the total fuel supply amount of the first and second stages of the two-stage combustor at a value determined by the load while
This is achieved by changing the ratio of the second stage fuel flow rate to the second stage fuel flow rate according to the NOx concentration in the combustion gas.

As a specific method, while maintaining the total fuel flow rate of the first-stage and second-stage fuel supply means at a value determined by the load,
The fuel distribution ratio to the first-stage and second-stage fuel supply means is
Normally, it is set to a constant value, and when the NOx concentration in the combustion gas exceeds the allowable value, the ratio of the fuel flow rate to the second stage fuel supply means is adjusted to be high. .

Also, the device for carrying out the above method is
According to a signal from the NOx concentration detecting means for detecting NOx, a means for changing the diversion ratio to both nozzles while maintaining the total fuel flow rate of the first and second stage nozzles at a value determined by the load is provided. It is characterized by being provided.

Further, the first stage nozzle is provided so as to project into the combustion chamber, the second stage nozzle is provided in the air supply passage, and the diffusion flame due to the fuel from the first stage nozzle and the second stage nozzle are provided in the combustion chamber. The premixed flame may be formed by the fuel from the stage nozzle.

Furthermore, the means for determining the total fuel amount according to the load includes a converter that outputs a total fuel flow signal from a load request signal, and a divider that divides the total fuel flow signal into a predetermined ratio. The means for changing the diversion ratio is an adder for adding a predetermined value to one of the signals divided by the divider according to the detection signal from the NOx concentration detection means, and adding a correction so as to reduce the predetermined value from the other. It is also possible to include a regulating valve that controls the amount of fuel to the first-stage nozzle and the second-stage nozzle according to the corrected signal.

[Action]

As an example of the multi-stage combustor, the principle of the operation of the present invention will be described by using a two-stage multi-combustor that performs diffusion combustion in the first stage and premix combustion in the second stage.

Combustion phenomena are roughly classified into diffusion combustion and premixed combustion. The amount of NOx generated when these combustions occur is generally as shown in FIG. As can be seen from this figure, lean combustion is extremely effective in reducing the amount of NOx produced. In addition, when the degree of premixing is increased, that is, when complete premixing is performed, NOx rapidly decreases as the fuel-air ratio decreases and N
It can be seen that there is a large possibility of Ox reduction.

However, from the viewpoint of stability of combustion, the characteristic of the premixed combustion is that the range of stable fuel-air ratio is narrower than that of diffusion combustion.

On the other hand, one of the features of the gas turbine combustor is that the change range of the fuel-air ratio from the start to the rated load is extremely wide. In order to perform stable operation in the full load zone of operation, use diffusion combustion with a wide range of stable combustion in the start-up and low load zones where the fuel-air ratio changes greatly, and use premixed combustion at high load when NOx reduction is required. It becomes effective to do.

FIG. 3 shows the operating range of the _first and second stage nozzles (F ₁ , F ₂ ). A comparison is made between a combustion method using only diffusion combustion and a method combining diffusion combustion using lean combustion and premixed combustion. Compared to the conventional diffusion combustion method only, a lean combustion diffusion combustion nozzle is used in the first stage and a premixed combustion nozzle is used in the second stage to achieve comprehensive NOx reduction. Here is an example. For details of this combustor, see
No. 61-22127.

The above is the outline of the operation of the two-stage combustor from the viewpoint of NOx, but there is a problem of carbon monoxide CO from the viewpoint of the combustion performance of the actual combustor. CO is one of the unburned components, and its amount increases when the combustion performance deteriorates. FIG. 4 shows the relationship between the fuel-air ratios of the first and second stages and CO and NOx. In the case of this combustor, first attach it to the first stage nozzle,
Next, a method of igniting the second stage with the flame of the first stage is adopted. FIG. 4 will be described by taking the case where the first-stage air-fuel ratio F ₁ / A _{1 is a} constant value of 0.02 as an example. The combustion of the first stage is performed with F ₁ / A ₁ = 0.02, and after reaching a certain load, the fuel-air ratio is increased to ignite the second stage, so that F ₂ / A ₂ = 0.02
Ignition of F ₂ occurs in the shaded area in the vicinity. However, sufficient combustion does not occur and a large amount of CO is generated. This CO also decreases in combustion as F ₂ / A ₂ becomes larger. This also shows that the combustion gas temperature gradually rises, and as the CO decreases, the NO
x increases. The shaded area is about 150 ppm, and NOx will increase as F ₂ / A ₂ increases. In case of F ₁ / A ₁ = 0.02 for actual combustor C
The operating point is selected when F ₂ / A _2, which is a low range for both O and NOx, is between 0.03 and 0.04.

That is, there is a contradictory tendency that when one of NOx and CO is reduced, the other increases, it is important to select a region that satisfies both as the operating region.

Moreover, although it must be considered as an important factor that influences the NOx value of the actual combustor, there are changes in shape due to atmospheric conditions and aging. NOx is generally
It is known that it can change greatly depending on the humidity.
Although the experimental coefficient differs depending on the structure of the combustor,
If the temperature changes by 10 ° C, the NOx value changes by about 4%, and if the humidity changes by 30%, the NOx value changes by about 6%. Furthermore, if the atmospheric temperature changes, the pressure at the compressor outlet changes, and then the pressure inside the combustor changes, and if the shape of the combustor changes over time, the fuel-air ratio of the combustion part changes. In some cases, the value of NOx changes depending on the circumstances.

The method of estimating these changes is usually performed by an empirical formula containing experimental coefficients, and the estimation is performed by using the formula defined by the structure of the combustor. When operating an actual machine, such characteristics must be taken into consideration.

As described above, when one combustor shape is manufactured and operated, the amount of NOx and CO depends on the ambient conditions such as the atmosphere, the first stage,
It is determined by the fuel distribution ratio to the second stage nozzle, etc., and is not uniquely determined. FIG. 5 shows the NOx characteristics of the first stage diffusion combustion and the second stage premixed combustion. When the equivalence ratio is the same, NOx in diffusion combustion is large, but combustion in a wide equivalence ratio range is possible. On the contrary, premixed combustion has low NOx but narrow combustion range. From this figure, even when burning the same amount of fuel as a whole, in other words, even when the load is constant, the first
It can be estimated that if the fuel distributions of the second stage and the second stage are changed, the distribution of the fuel-air ratio changes under the condition that the air distribution is constant, and the total NOx value can be changed.

FIG. 6 shows how to control the values of NOx and CO in response to the above-mentioned various changes in the surrounding environment under the condition that the air distribution is constant. The values of NOx and CO and the gas turbine load are taken as the coordinate axes. The gas turbine load is a value proportional to the total value (F ₁ + F ₂ ) of the fuel amount F ₁ of the first stage and the fuel amount F ₂ of the second stage, and takes (F ₁ + F ₂ ). It can also be said. Now, the operating load range and L _A ~L _B. NOx
Is a curve on the upper surface of (NOx-L), and takes F ₁ / (F ₁ + F ₂ ) as a parameter.
Ox becomes high. If the limit value of NOx is N _A , it is sufficient if the value of NOx is below the straight line connecting the points 1 _N and 2 _N when the loads are L _A and L _B.

However, if NOx falls too low, CO will generally increase. CO
Is a curve on the (NOx-CO) plane. For example, when looking at the curve of CO at load L _A , the value of CO at NOx1 _N is 1c, NOx
The value of CO at 3 _N is 3 _C , and when the value of NOx decreases, CO rapidly increases. If the limit value of CO is C _A , CO at load L _A
The point of the limit value of is 3c, and the value of NOx for this is 3 _N. Therefore, considering NOx and CO, when the load is L _A
It is necessary to drive between 1 _N and 3 _N , and NOx during this period
The value of can be changed by selecting the parameter F ₁ / (F ₁ + F ₂ ). Similarly, when the load is L _B , there is an operable area between 2 _N and 4 _N.

For the reasons described above, in the operating range of L _A ~L _B,
1 _{N −} 2 _{N −} 4 _N − 3 _N so that NOx enters the quadrangle F ₁ / (F ₁
If + F ₂ ) is selected, operation that satisfies the CO limit value is possible.

For example, when the load is L _B , it is possible that NOx does not fall within the limit range such as point Z due to changes in ambient conditions such as atmospheric temperature. In this case, NOx, to keep the CO within limits, (F ₁ + F ₂₎ a constant, i.e., the load L _B remains constant, F _1, Yotsute to changing the ratio of F ₂ F ₁ / (F ₁ + F ₂ ) can be made small and NOx can be kept below 2 _N.

The operating point when NOx is suppressed to the limit value is on the 1 _{N −} 2 _N line, and the 3 _{N −} 4 _N line is the line that realizes the lowest NOx value that satisfies the CO limit value, which can be seen from NOx. If it is the driving line with the optimum value. Also, by selecting F ₁ / (F ₁ + F ₂ ), the driver can get NOx.
It is also possible to set and drive.

As described above, the change in NOx caused by the change in the ambient conditions in the multi-stage combustor can be suppressed within the limit value by changing the fuel distribution of each stage.

[Embodiment] An embodiment of the present invention will be described below with reference to FIG. This figure shows the case applied to the case of two-stage combustion.

First, the outline of the system configuration will be described. Although this is an example of a combined plant, air is introduced into the compressor 1 and is made to have a high pressure, then guided to the combustor 2 to become high-temperature combustion gas, enter the turbine 3, and drive the generator 4. And generate electricity. Exhaust gas from turbine 3 is exhaust heat recovery boiler 5
After the exhaust heat is recovered as steam in the
Is further reduced and released from the chimney into the atmosphere.

The combustor 2 will be described in more detail. This combustor has 2
It is a stage combustor, and the fuel is divided into a first stage fuel (F ₁ ) 7 and a second stage fuel (F ₂ ) 8, which are a first stage nozzle 9 and a second stage fuel, respectively.
It is ejected from the step nozzle 10. The first stage nozzle 9 has a first stage header 11 so that the fuel is evenly distributed to the plurality of first stage nozzles 9. The fuel injected from the first-stage nozzle 9 is burned in the sub chamber 14 surrounded by the inner cylinder 12 and the outer cylinder 13.

On the other hand, the second-stage fuel 8 is injected from the second-stage nozzle 10, premixed with combustion air while passing through the swirler 15, and then introduced into the main chamber 16 to cause premixed combustion. This combustor first ignites the first-stage fuel, increases the fuel flow rate until it reaches a certain load, then inputs the second-stage fuel, and uses the first-stage combustion gas to produce the second-stage fuel. The fuel is being ignited and the fuel is being increased to the rated load.

The hot gas generated here is guided to the turbine 3 by the transition piece 17.

In the example of the present system, an exhaust gas characteristic acquisition device 18 that obtains concentration information by directly measuring combustion gas of the gas turbine 3, specifically, components of the gas turbine exhaust gas, particularly NOx and CO, or estimating from other measured values, Atmospheric conditions, especially temperature and humidity, NO
x For controlling the system, an atmospheric condition measuring device 19 that measures the amount that greatly affects the generated amount and a compressor outlet condition (pressure, temperature) calculating device 20 that estimates the state of the compressor outlet air based on this are used. Of the first-stage fuel 7 and the second-stage fuel 8 and determines the distribution of the first-stage fuel 7 and the second-stage fuel 8. This controls the first-stage fuel valve 22 and the second-stage fuel valve 23.

In FIG. 7, the fuel system and control system of the gas turbine will be described in more detail. The fuel 32 supplied to the combustor 2 is split into the first stage fuel and the second stage fuel 8. The first stage fuel 7 is measured by the first stage flow meter 33 and
The flow rate is controlled by the stage fuel valve 22. The second stage fuel 23 similarly passes through the second stage flow meter 34 and the second stage fuel valve 23.

The first-stage fuel valve 22 and the second-stage fuel valve 23 receive signals 35 and 36 from the fuel flow rate distribution setting device 21 (signal divider),
The 23 and the flow meters 33 and 34 each independently form a minor loop and perform feedback control.

When a deviation occurs between the load request signal 37 of the gas turbine and the measured load signal 38, the signal divider 21 works to make the deviation zero, and also divides the signal as a function of the load request signal 37 to obtain the respective fuels. It is given to valves 22 and 23.

The divided signals 35 and 36 are respectively the NOx bias signal 39 and
Receive CO bias signal 40. For the maximum set value 41 of NOx concentration, for example, compared with the average value 42 of the measured NOx concentration by sampling of 10 points, if there is a difference, and the measured NOx concentration is high, through the low barrier gate 43. , And the open (+) signal 45 is supplied to the second fuel valve 23 to adjust the ratio of F ₁ / F ₂ . Actual N
When the Ox concentration is low, the signal 39 output from the low-vari gate 43 is zero, and the opening degrees of the fuel valves 22 and 23 are maintained as they are. Similarly, when the CO concentration 46 becomes higher than the set value 47, on the contrary, the (+) signal 48 is given to the first fuel valve 22 and the second fuel valve 22 is supplied.
A (-) signal 49 is supplied to the fuel valve 23. Both the former and the latter
The total sum of the fuels 7 and 8 passing through the 1 and 2 fuel valves 22 and 23 is always a value determined by the load signal.

FIG. 8 shows the flowmeters 33 and 34 in FIG. 7 replaced with fuel valve stroke potentiometers 50 and 51. The valve stroke feedback control system is used in the fuel system of a conventional combustor that does not reduce NOx.
This method is excellent in that the accuracy of division of the fuel flow rate is low, but it is not easily affected by the fuel pressure fluctuation, and the vibration phenomenon of the valve stroke, that is, so-called hunting is hard to occur.

The signal divider 21 is a function of the load demand signal 37 and divides it as shown in FIG. From no load to 25% load of the gas turbine, a signal is given only to the first fuel valve 22, and the second fuel valve 23 is
It is fully closed. The second fuel valve 22 is opened at 25% load,
The flow rates of the second fuels 7 and 8 are the same (F ₁ / F ₂ = 1). This is the standard fuel split, and the measured NOx 42 or CO concentration 46
However, when the set values 41 and 47 are exceeded, the bias signals 39 and 40 are received and F ₁ / F ₂ becomes a value other than ₁ as described above.

By the way, the maximum load of the gas turbine is the atmospheric temperature,
The fuel switching point load (25% of maximum load) changes significantly,
It is necessary to correct by atmospheric conditions 19 (temperature, pressure, humidity), and this correction method is well known to gas turbine manufacturers and users.

For example, when the atmospheric temperature rises from 15 ° C to 5 ° C, the air flow rate increases by 3.6%. Therefore, the fuel switching load with an atmospheric temperature of 5 ° C is 3.6% less than the fuel switching load with an atmospheric temperature of 15 ° C.
If it increases by%, the combustion conditions are the same.

Further, the maximum load of the gas turbine changes over time, particularly when the compressor efficiency is lowered due to the dirt of the compressor blades, and this influence appears in the compressor discharge condition 20 (pressure, temperature). Therefore, the fuel switching point load needs to be corrected by the discharge condition 20, and this correction method is well known to gas turbine manufacturers and users.

For example, if the temperature difference between the inlet and outlet of the compressor rises 5 ° C. over the years, the fuel flow rate will decrease by 1% under the rated conditions. Therefore, if the fuel switching load is also reduced by 1%, the combustion condition becomes the same as the original condition.

As described above, the fuels 7 and 8 of the two-stage combustor 2 are controlled, but it can be said in any equipment, but it is necessary to clarify how to deal with equipment abnormality or control abnormality. There will be a clarification below.

The exhaust gas characteristic acquisition device 6 includes an exhaust duct 52 of a gas turbine.
From 10 locations, gas sampling was performed, and NO
x and (0 concentration is analyzed. If combustion condition is normal,
The deviation from the average NOx concentration at each location is
It is very small as shown in Figure 0. However, for example,
When the fuel flows too low in one of the ten combustors 2, the NOx concentration becomes extremely low and the CO concentration also increases in the downstream of the combustor 2. If the NOx concentration is lower than 90% of the average value even at one location, the operational comparator 55 discriminates and issues an alarm (buzzer 58, lamp 57 lighting). Further, the NOx and CO concentrations have the correlation shown in FIG. 11 in the case of normal combustion. As in the above example, when the comparator 56 deviates from this width, it is judged to be abnormal and an alarm (buzzer 58, lamp 57 lighting) is issued.

The conventional combustor uses diffusion combustion without the risk of flashback, but the combustor 2 of the present invention aims to reduce NOx,
A two-stage combustion system is used. Diffusion combustion is used at startup and low load, and premixed combustion is used at high load. Premixed combustion is effective in reducing NOx as shown in Fig. 3, but it may backfire. Due to the flashback, the combustion shifts from premixing to diffusion combustion, and as a result, the NOx concentration becomes high, and the combustor 2 may be burned out.

This phenomenon can be determined by performing gas sampling at 10 locations from the exhaust duct 52 and determining whether or not the NOx concentration is locally high.

In this embodiment, the NOx concentration is 1 of the average value even at one place.
When it becomes 15% or more, it is judged that the flashback occurs and the second fuel valve 23 is fully closed. In this case, the bell rings at the same time, and the red lamp of the gas turbine serious failure lights up.

〔The invention's effect〕

According to the present invention, in the multi-stage combustor, the distribution of the fuel-air ratio is changed to meet the NOx limit value with respect to the NOx value change that occurs as a result of atmospheric condition changes, aging changes, and deformation of the combustor structure. It is possible to perform operation, and it is possible to perform highly reliable operation that environmentally satisfies the limit value against such changes in the surrounding conditions.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of the present invention, FIG. 2 is a relationship diagram between a combustion system and NOx generation amount, FIG. 3 is a characteristic diagram showing combustion conditions of two-stage combustion, and FIG. 4 is a fuel-air ratio. Showing NOx and CO generation by the distribution of NOx, Fig. 5 is an example of NOx measurement in each combustion part of the two-stage combustor, and Fig. 6 is a diagram of the operating region when NOx and CO are taken into consideration.
FIG. 7 is a detailed view of an embodiment of the present invention, FIG. 8 is a view showing another embodiment of the present invention, FIG. 9 is a characteristic view showing a fuel split ratio,
Figure 10 shows the measurement results of NOx concentration distribution in the exhaust duct,
FIG. 11 is a characteristic diagram showing the correlation between NOx and CO concentration. 1 ... Compressor, 2 ... Combustor, 3 ... Turbine, 4 ...
Generator, 5 ... Exhaust heat recovery boiler, 6 ... Denitration device, 7 ...
… First stage fuel (F ₁ ), 8 …… Second stage fuel (F ₂ ), 9 ……
1st stage nozzle, 10 ... 2nd stage nozzle, 11 ... 1st stage header, 12 ... inner cylinder, 13 ... outer cylinder, 14 ... sub chamber, 15 ... swirler, 16 ... main chamber, 17 ... Tail tube, 18 ... Exhaust gas characteristic acquisition device, 19 ... Atmospheric condition measuring device, 20 ... Compressor outlet condition measuring device, 21 ... Fuel flow distribution setting device, 22 ... First stage fuel valve , 23 …… Second stage fuel valve, 53 …… NOx gas sampling tube, 54 …… CO gas sampling tube.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Seiichi Kirikami 3-1-1, Saiwaicho, Hitachi, Ibaraki Hitachi Ltd. Hitachi factory (72) Inventor Nobuyuki Iizuka 3 Saiwaicho, Hitachi, Ibaraki 1-1-1, Hitachi Ltd., Hitachi Works (72) Inventor, Yoji Ishibashi, 502 Jintamachi, Tsuchiura-shi, Ibaraki Prefecture, Ritsuji Seisakusho Co., Ltd. (72) Takashi Omori, 502, Kamimachi-cho, Tsuchiura, Ibaraki Prefecture Address: In the Institute of Mechanical Research, Hiritsu Seisakusho Co., Ltd. (56) Reference JP-A-58-80422 (JP, A) JP-A-57-187531 (JP, A) JP-A-59-183202 (JP, A)

Claims (4)

[Claims] 1. A first-stage fuel supply means is provided near the head of a cylindrical combustion chamber, and a second-stage fuel supply means is provided downstream of the flow of combustion gas. In the combustion control method for a multi-stage combustor, wherein the fuel supplied from the supply means is diffusion combustion, and the fuel supplied from the second-stage fuel supply means is premixed combustion, the first stage and the second stage While maintaining the total fuel flow rate of the fuel supply means at a value determined by the load, the fuel distribution ratio to the first-stage and second-stage fuel supply means is usually set to a constant value, and NOx in the combustion gas is set. If the concentration exceeds the allowable value, the fuel flow rate to the second-stage fuel supply means is adjusted to be high, and the combustion control method for a multi-stage combustor is characterized. 2. A cylindrical combustion chamber, a first stage nozzle located near the head of the combustion chamber for supplying fuel, and a downstream side of the first stage nozzle with respect to the flow of combustion gas. A second stage nozzle for supplying fuel to the combustion chamber, means for supplying combustion air to the combustion chamber, and means for determining the total fuel amount of the first and second stage nozzles according to the load And a means for detecting NOx concentration in the combustion gas, wherein the fuel supplied from the first stage nozzle is diffusion combustion and the fuel supplied from the second stage nozzle is premixed combustion. In a combustion control device for a multi-stage combustor configured, in accordance with a signal from the NOx concentration detection means, while maintaining the total fuel flow rate of the first-stage and second-stage nozzles at a value determined by the load, both nozzles -Stage combustion characterized by having means for changing the diversion ratio to the Combustion control device. 3. The first-stage nozzle is provided so as to project into a combustion chamber, the second-stage nozzle is provided in an air supply passage, and a diffusion flame due to fuel from the first-stage nozzle is provided in the combustion chamber. A combustion control device for a multi-stage combustor according to claim 2, wherein a premixed flame is formed by the fuel from the second stage nozzle. 4. The means for determining the total fuel amount according to the load includes a converter for outputting a total fuel flow rate signal from a load request signal and a divider for dividing the total fuel flow rate signal into a predetermined ratio. In addition, the means for changing the diversion ratio adds a predetermined value to one of the signals divided by the divider according to the detection signal from the NOx concentration detection means, and adds a correction to reduce the predetermined value from the other addition And a regulating valve for controlling the amount of fuel to the first-stage nozzle and the second-stage nozzle according to the corrected signal. A combustion control device for a multistage combustor according to item 2.