JPS5950889B2 - gas turbine combustor - Google Patents

Description

Detailed Description of the Invention [Field of Application of the Invention] The present invention relates to a gas turbine combustor, particularly a gas turbine combustor having a small-diameter head combustion chamber at the head and a large-diameter main combustion chamber at the rear. A gas turbine combustor that is equipped with a premixing chamber outside the combustion chamber, introduces premixed fuel gas with excess air into the head combustion chamber, and performs diluted low-temperature combustion to suppress the production of nitrogen oxides (NO). It is related to.

[Background of the invention]

Generally, during combustion, nitrogen and oxygen in the atmosphere react to produce NOx.
However, the production of NOx is suppressed by low-temperature combustion and low-oxygen combustion.

A component that causes air pollution problems in gas turbine exhaust gas is NOx, and particularly in gas turbine combustors, it is advisable to suppress the generation of NOx by lowering the combustion temperature.

In other words, in a gas turbine, excessive cooling air is introduced to lower the gas temperature (1800 to 2000°C) during the combustion reaction by about 10°C.
Although the temperature is lowered by cooling to around 00°C, this excess air is introduced into the high-temperature combustion reaction zone to perform dilution and low-temperature combustion to suppress NOx production.

However, most conventional gas turbines spray and burn liquid fuel, so even if excessive air is supplied, the NOx reduction effect may be small.

If you closely observe the process of evaporation and combustion of fuel droplets, you will see that there is a flame front at a position that is somewhat far from the droplet surface, and immediately after this flame front there is a region that burns at almost the stoichiometric air ratio.
The temperature is high and the rate of NOx generation is increasing.

Even if there is an excess of air throughout, a high temperature zone is generated during the evaporation process of the fuel droplets because there is always a portion with the stoichiometric air ratio.

Therefore, even if excessive air is introduced, effective cooling cannot be achieved, and NOx cannot be significantly reduced.

However, in the combustion of gaseous fuels, unlike droplet combustion, a flame front that performs almost theoretical combustion is not formed, and excess air is more likely to be mixed uniformly, making it possible to effectively perform lean low-temperature combustion. Gaseous fuel is effective in reducing NOx.

Therefore, a so-called evaporative premix trapezoidal combustor has been proposed in which liquid fuel is evaporated into fuel gas, premixed with air, and introduced into a combustion chamber.

As shown in Fig. 1, this combustor consists of a compressor 1, a combustor 2, and a turbine 3. Air 4 is compressed by the compressor 1 and becomes combustion air 13, which is supplied to the combustor 2. 5 is combusted to produce combustion gas 6.

After this combustion gas 6 is supplied to the turbine 3 and does work, it becomes exhaust gas 7 and is released into the atmosphere.

The combustor 2 has an outer cylinder 8. Inner cylinder 9. It consists of a transition piece 10 that rectifies the combustion gas 6 and guides it to the turbine 3, and fuel nozzles 11 and 22. The fuel nozzles 11 and 22 are attached to the lid 12 of the side closed part of the outer cylinder 8.

The inner cylinder 9 consists of a small-diameter head combustion chamber 14 and a large-diameter main combustion chamber 15 provided downstream of this combustion chamber 14. , and air flow 1
A premixing chamber 17 is provided in which the fuel spray particles 16 are heated and evaporated to produce a premixed fuel gas 25.

The premixing chamber 17 is formed in an annular space defined by the outer wall 18 and the peripheral wall 20 of the head combustion chamber 14 .

The fuel gas premixed in the premixing chamber 17 to an excess air ratio of 1.2 to 1.4 is introduced into the head combustion chamber 14 through the supply hole 21 provided in the peripheral wall 20 of the head combustion chamber 140, Since diluted low-temperature combustion is performed, less NOx is produced.

That is, an air flow is supplied by a swirler 23 from near the pilot fuel nozzle 22 used at the time of ignition and startup, and an air flow is supplied by a swirler 24 from outside thereof, and a swirling air flow 26 is generated by these swirlers 23 and 24.

The swirling air 26 and the premixed fuel gas 25 mix, and the flame is maintained by the recirculation flow 27 generated by the swirling airflow 26 to sustain combustion.

In addition, the excess air ratio in the head combustion chamber 14 is approximately 1.4 to 1.6.
The average combustion temperature is approximately 1,600 ℃.
~1400°C.

The premixing chamber 17 is configured not only to ensure complete evaporation of the atomized fuel particles and uniform mixing with the air flow 19, but also to ensure the residence time and temperature of the atomized droplets 16. .

In addition, in order to prevent backfire of the flame from the head combustion chamber 14, the outflow velocity of the fuel premixed gas from the supply hole 21 is set to approximately 100 m/s, which is considerably higher than the flame velocity of 5 m/s. It is composed of

However, if there is a high-temperature ignition source (ignition source) and a slow-flowing part in the premixing chamber 17, the air-fuel mixture in the premixing chamber 17 will be in the combustible air-fuel ratio range, so it will combust in the premixing chamber 17. happens.

When combustion occurs in the premixing chamber 17, it becomes spray diffusion combustion of droplets, which not only makes it impossible to reduce NOx, but also burns out the peripheral wall 20 of the head combustion chamber 14 because it is exposed to a high temperature of 1600°C. There is a risk of an accident.

The results of measuring the peripheral wall temperature of the inner cylinder 9 of the combustor 2 are as shown in FIG.
The peripheral wall 20 that partitions the two is at a low temperature because of the large cooling effect caused by the evaporation of the fuel and the air flow 19.

In addition, coarse spray particles from the combustion nozzle 22
There is a correlation between this and the wall sealing caused by the swirling air flow 26 from the swirler 24, and overall there is no high temperature that could become a source of ignition.

However, the connecting enlarged part 28 between the head combustion chamber 14 and the main combustion chamber 15
Due to the rapid expansion of the high-temperature combustion flame, the wall surface temperature at
Since the effect of wall sealing by the swirling air 26 from 4 is reduced, the temperature becomes high, close to 1000°C.

Furthermore, as shown in FIG.
The fluid flows into the supply hole 21 provided at 0, and generates a vortex stagnation part 31 in the part that contacts the enlarged part 28.

Since the wall surface of the enlarged part 28 in contact with this stagnation part 31 becomes high temperature, if the air-fuel ratio of the premixed gas in the stagnation part 31 falls within the flammable range, it will easily ignite and cause combustion within the premixing chamber 17. Become.

In other words, some of the fuel particles sprayed into the premixing chamber 17 adhere to the peripheral wall surface 20 of the head combustion chamber and the outer wall 18 of the premixing chamber, and when they become a liquid film, they evaporate, and some of them are absorbed into the air flow 19.
The sprayed droplets diffuse and evaporate.

In particular, the outer surface of the head combustion chamber peripheral wall 20 receives radiant heat mainly from the flame inside the combustion chamber, which becomes high temperature and promotes evaporation.
The outer wall 18 of the premixing chamber 17 is at a lower temperature than the inner circumferential wall 20 because the air discharge temperature is due to the heat of air compression by the compressor.

Therefore, because the evaporation of the fuel is delayed and the premixing time with air is short, a portion with a high fuel concentration exists on the downstream side 18a of the outer wall 18 of the premixing chamber.

Furthermore, since the stagnation portion 31 due to the vortex flow is at a high temperature, there is a risk that flames will form in the premixing chamber 17 and burn out the peripheral wall 20 of the head combustion chamber, creating a dangerous situation.

In order to prevent flame formation in the premixing chamber, the temperature of the wall forming the premixing chamber must be lower than the ignition point of the fuel, and the stagnation of the mixed gas in the premixing chamber must be eliminated. is necessary.

[Purpose of the invention]

An object of the present invention is to provide a gas turbine combustor that prevents flame generation in a premixing chamber and achieves highly safe and low NOx combustion.

[Summary of the invention]

The features of the present invention include a small-diameter head combustion chamber at the head of the combustor, a large-diameter main combustion chamber downstream of this combustion chamber, and a liquid fuel vaporized in the outer peripheral part of the head combustion chamber. In a gas turbine combustor equipped with a premixing chamber for producing premixed fuel gas, the outer wall that guides the premixed gas generated in the premixing chamber to the head combustion chamber is heated to an appropriate level to prevent stagnation. The combustion chamber is constructed with a curved surface having a radius of curvature of , and furthermore, a heat insulating space is formed between the tank surface of the connecting enlarged part of the main combustion chamber and the head combustion chamber and the outer wall.

[Embodiments of the invention]

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

In FIG. 4, 9 is an inner cylinder consisting of a small-diameter head fuel chamber 14 and a large-diameter main combustion chamber 15, 11 and 22 are fuel nozzles, and 17 is a premixing chamber provided outside the head combustion chamber 14. One side (fuel nozzle 11 side) is open to form an air intake for premixing, and also to form a wake (main combustion chamber 1 side).
5 side) is configured to communicate with the head combustion chamber 14, and the outer wall 18b of the communication portion 41 through which this premixing chamber communicates with the head combustion chamber 14 is formed into a curved surface having an appropriate radius of curvature. ing.

23 and 24 are swirlers, 28 is an enlarged part connecting the head combustion chamber 14 and the main combustion chamber 15, and 32 is a peripheral wall of the head combustion chamber 14 immediately after the communication part 41 between the premixing chamber 17 and the head combustion chamber 14. 20
This is an air inflow hole provided in the

The outer wall curved surface 18b at the downstream end of the premixing chamber 14 and the enlarged portion 2
A space S is formed between the combustion chamber 8 and the wall surface 8, and the air inflow hole 32 is provided in the head combustion chamber wall surface 20 that defines the inside of this space.

The space S has the function of a heat insulating space so that even if the wall surface of the enlarged portion 28 becomes high in temperature due to entrainment of flame, the heat is not transmitted to the curved outer wall surface 18b of the premixing chamber.

As described above, the premixing chamber 17 is converted into an enlarged section 28 extending from the head combustion chamber 14 to the main combustion chamber 15, that is, the vortex 3.
Since the premixing chamber 17 is configured to avoid contact with a high-temperature part due to the entrainment of flame by the premixing chamber 17, it is possible to eliminate the cause of fire formation within the premixing chamber 17.

In addition, the air flowing in through the air inflow hole 32 provided immediately after the communication portion 41 of the premixing chamber 17 promotes the heat shielding effect of the heat insulating space S, and promotes premixing with combustion gas and combustion in the combustion chamber. It is possible to perform low-temperature combustion.

Furthermore, by designing the premixed gas flow 33 to penetrate into the axial center of the head combustion chamber 14, it is possible to improve the cooling effect of the axial center and significantly reduce NOx. .

On the other hand, the flow in the premixing chamber 17 is determined by the curved surface 18b of the outer wall 18 with respect to the distance l between the inner surface of the outer wall 18 of the premixing chamber 17 and the peripheral wall 20 of the head combustion chamber, as shown in FIGS. It varies depending on the ratio R/l to the radius of curvature R.

That is, as shown in FIG. 5, when the radius of curvature R of the curved surface 18b is small, the gas flow separates at the curved surface 18b, and the premixed gas is observed to generate a vortex flow and stagnate at that portion.

Furthermore, if the radius of curvature R of the curved surface 18b is increased as shown in FIG. 6, the gas flow will not separate as described above, but
Since the angle θ of the gas flow 33 flowing into the head combustion chamber 14 becomes small, fuel gas is supplied from the rear of the head combustion chamber 14 to be combusted in the main combustion chamber 15.

For this reason, there is no fuel gas 33 involved in the recirculation flow 27 generated by the swirling air flow 26 caused by the swirler (not shown), so there is a drawback that the flame cannot be maintained in the head combustion chamber 14.

According to the experimental results, in order to prevent the gas flow from causing separation, it is preferable that R and l maintain a relationship of R>1/21.

If R<1721, this is not preferable because peeling as shown in FIG. 5 will occur.

Also, considering that the inflow angle l of the premixed gas into the head combustion chamber is preferably 90° or more, R and 1 are 1/2
It is desirable to maintain the relationship <1/l <1.

〔Effect of the invention〕

As explained above, according to the present invention, the outer wall of the premixing chamber is thermally shielded from the wall surface of the enlarged part from the heat insulating space, and furthermore, the stagnation of the premixed gas in the premixing chamber is reduced, so that there is no flame in the premixing chamber. can be prevented from forming.

Note that since the liquid fuel is premixed into gas and then combusted, it is possible to achieve a significant reduction in NOx.

[Brief explanation of the drawing]

Figure 1 is a sectional view of a conventional gas turbine combustor, Figure 2 is a diagram showing the temperature distribution on the peripheral wall of the combustor, Figure 3 is a sectional view of the combustion chamber in the combustor, and Figure 4 is a diagram showing the temperature distribution of the peripheral wall of the combustor. 5 and 6 are cross-sectional views of main parts (combustion chamber) showing one embodiment of the combustor of the present invention.
The figure is a diagram showing the flow state of gas flow in the premixing chamber of the combustor of the present invention. 14... Head combustion chamber, 15... Main combustion chamber, 17...
- Premixing chamber, 18... Outer wall, 18b... Outer wall curved surface, 28... Enlarged part, 32... Air inflow hole, S...
- Heat insulation space, 41... communication part.

Claims (1)

[Claims] 1 A small-diameter secondary combustion chamber, a large-diameter main combustion chamber connected to the downstream side of the head combustion chamber via an enlarged part, and a main combustion chamber provided outside the head combustion chamber to evaporate and premix liquid fuel. In a gas turbine combustor that includes a premixing chamber that generates gas and a communication section that communicates the premixing chamber and a head combustion chamber at a downstream end of the premixing chamber, the premixed gas is supplied to the communication section. In order to derive the curved surface of the outer wall of the premixing chamber, the radius of curvature R of the curved surface of the outer wall of the premixing chamber is set to a value that satisfies 1/2<R/l<1 in relation to the distance l between the outer wall and the inner wall of the premixing chamber, and further, A gas turbine combustor characterized in that a heat insulating space is formed between a curved outer wall surface and the expansion tank surface.