JPH0512621B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a two-stage combustor for a gas turbine, and is particularly capable of achieving a significant reduction in NOx, suppressing the generation of CO and unburned matter, and reducing the overall This article relates to a low NOx two-stage combustor that can obtain good combustion performance over the operational load range.

[Conventional technology]

Regarding gas turbines, energy saving, high temperature, and high efficiency are becoming social needs. Nitrogen oxides (NOx) contained in exhaust gas in gas turbines
There is a strict need to prevent air pollution by reducing emissions of carbon monoxide (CO) and carbon monoxide (CO), and conventional combustion technology is no longer able to deal with this problem. Japanese Patent Application Laid-Open No. 61-52523, which is an example of a known technology, satisfies regulatory values by using a two-stage combustor with two fuel systems and a low NOx combustor that combines this with air control. be. Here, NOx regulation values are applied in the entire operating load range of gas turbines, and are aimed at reducing NOx over a wide range of combustion conditions while maintaining good combustion performance and being highly reliable. Must. Generally, when operating a gas turbine under load, the air flow rate is kept approximately constant, and the load is changed by increasing or decreasing only the fuel flow rate. For example, when there is no load,
When switching the fuel for the stage, the first stage fuel flow rate is reduced, so the supply amount of the first stage fuel becomes approximately 1/4 of that at the rated time. Therefore, the combustion state becomes excessively airy, which makes it impossible to maintain good combustion.
Reliability decreases due to an increase in unburned content, increased combustion vibration, etc. On the other hand, at rated condition, NOx
In order to perform low temperature combustion for the purpose of reducing
It is necessary to introduce excess air into the combustion zone to achieve fuel-lean combustion. However, as mentioned above, if low-temperature combustion is performed at rated load to reduce NOx, there will be a tendency for excess air to occur at low load or when switching to the second stage fuel, causing unburned components to occur and combustion performance to deteriorate. It becomes a factor. For this reason, we developed a technology to reduce NOx during high loads and further suppress the unburned gas during low loads.
As shown in No. 52523, when fuel is input into the second stage, 1,
It is equipped with an air control mechanism that reduces the amount of air flowing into the second stage to prevent a decrease in combustibility during low loads and when switching to the second stage fuel. However, in the method according to the above-mentioned known technology that controls the inflow air holes in order to reduce the air flow rate flowing into the first and second stages during low load, when the second stage fuel is switched, the air flow rate in the first stage is reduced.
53→40%, second stage air flow rate is 28→
In this way, the overall air flow rate is reduced from 81% to 50%. In this way, the amount of air is reduced by approximately 30%, and the reduced air flows in through air openings other than those in the first and second stages. In this way, since the overall air opening cross-sectional area is reduced by about 30%, the inflow velocity into the combustor increases by about 1.3 times, and the pattern of air penetration distance into the combustor changes. As the combustion state changes, problems such as uneven combustion and local heating of the combustor wall occur. Furthermore, by narrowing the air opening area, the pressure difference between the inside and outside of the combustor increases by 1.7 times. As a result, compressive force is applied to the combustor due to the external pressure of air flowing into the combustor, and the compressive force acts on the locally heated parts of the combustor, causing damage such as buckling of the combustor, and burnout. However, it has shortcomings in longevity and reliability. Another drawback is that since the amount of air in the first stage is reduced, NOx generated in the first stage increases.

[Problem that the invention seeks to solve]

The above-mentioned known conventional technology has the effect of reducing the amount of air flowing into the first and second stages and suppressing unburned components such as CO and HC generated at low loads and during fuel supply to the second stage. No consideration was given to the increased pressure difference between the inside and outside of the combustor due to air control, resulting in decreased combustor reliability (life) and reduced gas turbine efficiency due to the increased pressure difference. I had a problem.

The present invention has been made in order to solve the above-mentioned problems, and it is possible to control the combustion state of the second stage combustion chamber without affecting the first stage combustion chamber or the combustion state, and to The purpose of the present invention is to provide a structure of a two-stage combustor that can suppress the amount of NOx and CO generated without the risk of giving an excessive differential pressure to the combustor.

[Means for solving problems]

The structure of the two-stage combustor for gas turbine according to the present invention created to achieve the above object is as follows: (a)
A first-stage combustion chamber provided with a first-stage fuel nozzle and an air supply path is provided on the upstream side of the combustor, and (b) a second-stage fuel nozzle and a second-stage combustion chamber are provided on the downstream side of the first-stage combustion chamber. 2
A two-stage structure including a second-stage combustion air flow path for premixing with the fuel sprayed by the second-stage fuel nozzle, and (c) a means for adjusting the supply amount of the second-stage combustion air. Applied to combustion type gas turbine combustor,
The constant flow rate of the first and second stage air 21, which is the sum of the combustion air in the first stage combustion chamber and the combustion air in the second stage combustion chamber, is defined as the combustion air 24 in the first stage combustion chamber. A flow path leading to the stage combustion chamber is provided, and the above 1 and 2 are
The first stage air 24 is calculated from the flow rate of the stage air 21.
The arbitrary flow rate within the constant flow rate after subtracting the flow rate of is 2
An air flow rate adjusting means is provided to supply the premixing section 17 as combustion air for the combustion chamber of the second stage, and the remaining air whose flow rate has been restricted by the air flow rate adjusting means is passed through the second stage by bypassing the premixing section. A bypass flow path 20 leading to the second combustion chamber is provided on the outer circumferential side of the premixing section 17, so that the flow rate of air supplied to the premixing section of the second stage combustion chamber can be adjusted while keeping the flow rate of the first stage air constant. It is configured so that it can be adjusted as desired.

[Effect]

According to the above configuration, when the second-stage combustion air (primary air for the second-stage fuel nozzle) is throttled, the remaining air passes through the bypass flow path into the second-stage combustion chamber (as secondary air). Because we can supply
Even if the second stage combustion air is throttled, the differential pressure applied to the combustor liner can be reduced. Therefore, the first stage combustion air flow rate,
By controlling the second stage combustion air flow rate, combustion control can be performed with the aim of reducing toxic exhaust components and increasing efficiency.

〔Example〕

Next, the configuration of one embodiment of the present invention will be explained with reference to FIGS. 1 and 2.

FIG. 1 is a sectional view of this embodiment, and FIG. 2 is an enlarged sectional view of the main part thereof.

The gas turbine includes a compressor 1, a turbine 2, a combustor 3, etc., and air 1a compressed by the compressor 1 is guided to the combustor through a casing 4. The combustor 3 includes outer cylinders 5a, 5b, a liner 6a,
6b and the inner cylinder 7, and the first and second stage fuels 8,
It is equipped with fuel nozzles 10, 11 that supply 9. The first stage combustion chamber 12 has a liner 6a and a cylinder 7.
It is formed by an annular space with.

The second stage combustion chamber 13 is inside the liner 6b, which has a larger diameter than the first stage combustion chamber 12. A plurality of air ports and a plurality of rows of air ports are opened in the first stage combustion chamber 12.
Additionally, air holes for wall cooling (none of these are shown)
is open. The inner cylinder 7 also has a large number of wall cooling air holes. A fuel nozzle 11 for supplying the second stage fuel 9 is installed in the air passage at the connection part between the first stage combustion chamber 12 and the second stage combustion chamber 13.
The stage injects fuel into the air. (The detailed structure of this part will be described later with reference to FIG. 2.) In this way, the air passage section 16 becomes a premixing section for the second stage air and the second stage fuel, and the premixed fuel gas 17 is transferred to the second stage. The second premixed combustion flame is guided to the second combustion chamber 13 and uses the flame formed in the first stage combustion chamber 12 as an ignition source to form a second premixed combustion flame. Although not shown, the first stage fuel is ignited by a spark type ignition plug, and the ignition is confirmed by a flame detector. When the load increases sequentially from the ignition of the gas turbine, the first stage combustion is operated only until about 20% load, and when the load becomes even higher, fuel is supplied to the second stage, and the first and second stage It causes combustion to occur. As mentioned above, the second stage combustion is a premixed combustion of the second stage fuel 9 and air, so there is a mixing ratio of fuel and air that is determined within the combustible range, and the fuel ratio is small. There is a lower limit at which combustion becomes unstable and CO is generated. Conversely, if the fuel ratio is high, there is an upper limit to the amount of NOx generated. Therefore, it is necessary to adjust the amount of air in proportion to the fuel so that the optimum mixing ratio is always maintained. In order to achieve this, a slide ring 18 that covers the second stage air inlet section 22 is installed, and by moving this in the axial direction, the effective area of the air inlet section 22 is changed, and the second stage air Try to increase or decrease the amount. This increase/decrease can be adjusted to a certain constant ratio with the second stage fuel supply amount (not shown). A bypass air passage 20 that opens into the second stage combustion chamber 13 is arranged on the outer peripheral side of the second stage air passage.

The slide ring 18 controls the air flow rate in the second stage combustion air passage 16 and also controls the air flow rate in the bypass air passage 20. Thereby, the second stage combustion air flow rate and the bypass air flow rate are controlled in conjunction.

FIG. 2 shows details of the second stage air passage 16 and the bypass section 20. Air 21 to the first and second stages is divided into air 23 that passes through the slide ring 18 and second stage air inlet 22, and air 24 that is supplied to the first stage combustion chamber 12 (see FIG. 1). While the second stage air 23 passes through the second stage air passage 16, fuel is sprayed from a plurality of fuel jet ports 25 opened at the tip of the second stage fuel nozzle 11. The fuel then passes through the fuel and air premixing section 17 and is guided to the second stage combustion chamber. When the second stage combustion is started (low flow rate), it is necessary to suppress the air flow rate 23 to a small amount, so the slide ring 18 moves inward in the figure and reduces the air flow rate by reducing the inlet area. suppress. As the slide ring 18 moves to the left, the effective area of the air inlet of the bypass 20 increases. Therefore, the effective area of the second-stage air passage inlet 22 is reduced to reduce the air flow rate, and the air 26 is transferred from the bypass passage 20 to the second stage.
It is designed to lead to a stage combustion chamber 13.

Even if the air flow rate of the bypass 20 is changed as described above, the opening area of the air hole 31 shown in FIG. 1 does not change, and the combustion state at the outlet of the second stage combustion chamber 13 does not change.

FIG. 3 is a chart showing the relationship between the stroke of the slide ring 18 and the first stage air amount _A1 and second stage air amount _A2 .

The second stage air amount _A2 draws the same curve _A2 in both the conventional example and this embodiment.

The first stage air amount A ₁ ' in the conventional example is as shown by the chain line,
The first stage air amount _A1 in this example is as shown by the broken line. Second
When switching stage fuel, the amount of A ₂ is suppressed, the second stage fuel (abbreviated as F ₂ ) is suppressed, and the excess air ratio (abbreviated as λ ₂ ) (here, excess air ratio λ ₂ is the amount of air during combustion In order to perform air control that keeps the ratio between the flow rate and the theoretical combustion air amount to 1.3 to 1.7, in this example, the slide ring is moved in the closing direction to reduce the A2 amount, and as the load increases, the _A2 amount increases. ₂ , perform an F ₂ rise.

As shown in FIG. 4, in the conventional example, the amount of cooling and dilution air A ₃ ' other than A ₁ ' and A ₂ increases by about 30%. However, in this example, it is possible to always perform constant first stage combustion regardless of changes in the amount of _A2 , and the _{amount of A1}
Since there is no decrease in the amount of cooling air for the liner 5a and the inner cylinder 7, there is no decrease in the amount of cooling air. Therefore, it is possible to compensate for the drawback that the metal temperature becomes high. moreover
Since the amount of _A3 is always constant and the effects of opening and closing the slide ring can be absorbed by changes in the amount of bypass air, stable combustion can be maintained at all times.

FIG. 5 shows how the first-stage combustion and second-stage combustion change due to load fluctuations. The upper limit of the amount of _F2 in both the first and second stage combustion is regulated by the NOx limit, and the lower limit is regulated by the CO limit. The first and second stage combustion in this example is NOx limit CO
I am satisfied with both limits. In the conventional example, the amount of _A1 decreases as seen in the first stage combustion.
NOx tends to exceed the limit value near 25% load. In this example, there is no tendency for NOx to be generated in this way, and the NOx and
It is possible to sustain combustion while suppressing the generation of CO.
As shown in Figure 6, it is possible to satisfy the NOx limit value in the entire load range and to suppress the generation of CO.

Figure 7 shows other effects of A ₂ on pressure loss.
Showing the effect of a change in quantity. In the conventional example near 25% load, the pressure loss increases rapidly due to the air opening area being reduced by approximately 30% due to the operation of reducing the amount of A ₁ A ₂ , but in this example, the pressure loss increases rapidly.
Since the decrease in the amount of _A2 air is dealt with by increasing the amount of bypass air, there is no increase in pressure loss regardless of the change in the amount of _A2 . This also means that there is no increase in the compression force applied to the outside of the combustor, and considering that the metal temperature of the combustor is heated to 500 to 700°C during combustion and the material strength decreases, it is difficult to put it into practical use. The effect is very large. On the other hand, an increase in pressure loss is directly linked to an increase in compressor output and a decrease in turbine output, and is related to turbine efficiency, so the lower the pressure loss, the higher the efficiency. From this point of view, this embodiment, which has the effect of suppressing an increase in pressure loss, has the advantage that there is no decrease in turbine efficiency and damage to the compressor and turbine can be suppressed to a small extent.

FIG. 8 shows an improved embodiment in which the influence of the outflow of bypass air on the second stage combustion is suppressed.

Since the air 26 from the bypass air passage 20 is ejected from a location close to the second stage combustion flame, there is a problem in that it cools the second stage flame 28.
In order to prevent this, the position where the bypass air is blown out may be moved to the rear side of the second stage. This exhibits the effect of further improving the combustion performance of the second stage flame. Therefore, in this embodiment, the second stage combustion chamber 13
A cylindrical partition plate 29 is provided that protrudes from the top. In this example, since the bypass air flows along the inner wall surface of the liner 5b of the second stage combustion chamber 13, it has the effect of reducing the second stage combustion chamber metal temperature, and the partition in contact with the second stage flame The plates are sufficiently cooled by heat transfer by the bypass air 26. By further applying ceramic coating or the like to this partition plate 29, it becomes more reliable.

〔Effect of the invention〕

According to the present invention, even if the second stage air is reduced, a flow rate commensurate with the change in air flow rate can be guided to the bypass passage so as not to have this effect on others.
This has the effect of eliminating the effect on stage combustion changes, and can also suppress the generation of NOx and CO over the entire load range of the gas turbine.
Furthermore, since there is no sudden change in flow rate, the gas turbine can be operated smoothly without any adverse effects on the compressor, turbine, etc. In particular, even if the second-stage combustion air flow rate is adjusted, the first-stage combustion air flow rate can be kept constant, so damage to structural members due to an increase in pressure difference can be prevented.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing one embodiment of the present invention. FIG. 2 is a partial detailed view of the above embodiment. FIG. 3 is a chart showing changes in A ₁ A ₂ due to opening and closing of the slide ring, and FIG. 4 is a chart showing changes in the amount of A ₃ as well. FIG. 5 is a chart for explaining changes in combustion conditions in the embodiment, FIG. 6 is a chart for explaining exhaust gas components, and FIG. 7 is a chart for explaining pressure loss. FIG. 8 is a sectional view of an embodiment different from the above. 12...First stage combustion chamber, 13...Second stage combustion chamber, 16...Second stage air passage, 20...Bypass air passage, 17...Slide ring, 23...Second stage air, 24...First stage Stage air.

Claims (1)

[Claims] 1. (a) A first-stage combustion chamber provided with a first-stage fuel nozzle and an air supply path is provided on the upstream side of the combustor, and (b) a first-stage combustion chamber is provided on the downstream side of the first-stage combustion chamber. a second-stage fuel nozzle and a flow path for second-stage combustion air to be premixed with the fuel sprayed by the second-stage fuel nozzle; (c) supply amount of the second-stage combustion air; In a two-stage combustion type gas turbine combustor having a structure in which a means for adjusting 21
A constant flow rate of the combustion air 24 in the first stage combustion chamber is
A flow path leading to the first stage combustion chamber is provided, and the above 1.
From the flow rate of the second stage air 21, the first stage air 2 is calculated from the flow rate of the second stage air 21.
An air flow rate adjusting means is provided for supplying an arbitrary flow rate out of the constant flow rate obtained by subtracting the flow rate of 4 to the premixing section 17 as combustion air for the second stage combustion chamber, and the air flow rate is restricted by the air flow rate adjusting means. A bypass passage 20 is provided on the outer circumferential side of the premixing section 17 to guide the remaining air to the second stage combustion chamber by bypassing the premixing section, thereby keeping the flow rate of the first stage air constant. A two-stage combustor structure characterized in that the air flow rate supplied to a premixing section of a second-stage combustion chamber can be arbitrarily adjusted. 2. The bypass flow path is provided with a bypass air flow rate adjustment means, and the bypass air flow rate adjustment means and the second stage combustion air supply amount adjustment means are interlocked with each other. A two-stage combustor structure according to claim 1. 3. The second-stage combustion air supply amount adjusting means adjusts the flow rate of the second-stage combustion air to 10 to 35% of the total air flow rate.
, and the bypass air flow rate adjusting means changes the bypass air flow rate within a range of 0 to 25% of the total air flow rate. The two-stage combustor structure according to paragraph 2. 4. The bypass air flow path is characterized in that a partition wall is provided between the bypass air flow path and a premix combustion flame formation area formed by the atomized fuel of the second stage fuel nozzle. A two-stage combustor structure according to Scope 1 or 2.