JPH0743136B2 - Turbulent premixed burner that reduces nitrogen oxides by reducing combustion - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a turbulent premixing burner for reducing nitrogen oxides by reducing combustion, and particularly to a premixing unit installed in a combustor of a gas turbine. It is used as a combustion type burner.

[Prior Art] Conventionally, in a combustor of a gas turbine, the combustion temperature reaches a high temperature of 1000 ° C or higher, nitrogen in the air is oxidized, and nitrogen oxides are generated. Several methods have been proposed. That is, such nitrogen oxides originating from nitrogen in the air are called thermal nitrogen oxides, and it is known that the amount produced is proportional to the flame temperature. The combustion technology based on the basic idea of reducing the flame temperature is being studied. Examples of conventional techniques for reducing the flame temperature include a technique of injecting water or steam into the flame and a technique of lean combustion. Although the generation of nitrogen oxides has been greatly improved by these techniques, it has been required in recent years to raise the temperature of the combustion gas in order to improve the efficiency of the gas turbine. This requires a new combustion technique that can suppress the emission of nitrogen oxides even if the temperature of the combustion gas is increased, and various new combustion methods have been studied.

Then, for example, as described in JP-A-61-41810, in the reduction of nitrogen oxides generated, nitrogen oxides generated in a high temperature flame are formed into a low air ratio flame lacking oxygen. As a result, a technique for detoxifying the reducing chemical species generated from the low air ratio flame is known.

[Problems to be Solved by the Invention] The technique described in the above-mentioned JP-A-61-41810 is
Even if it is attempted to use it for a high temperature combustion gas turbine that has been required in recent years, the residence time of the gas in the combustor of the gas turbine is extremely short, so the reaction time is short, and the reduction reaction of reducing species and nitrogen oxides There is a problem that it does not progress sufficiently. The present invention is intended to solve such a problem. That is, the present invention provides a turbulent flow predictor capable of sufficiently mixing nitrogen oxides and reducing chemical species in a gas turbine combustor or the like and effectively promoting a reduction reaction between the two. The purpose is to provide a mixed burner.

[Means for Solving Problems] Premixing having a space necessary for sufficiently mixing fuel and air in advance and forming a high air ratio combustion flame and a reducing combustion flame as the same flame In the die burner, the tip of the nozzle that forms the reducing combustion flame can be moved toward the center of the combustion flame. In addition, a turbulent flow grid was provided at a position upstream from the tip of the nozzle so as to have a space required to form a turbulent flame from the nozzle.

[Operation] The tip of the nozzle that forms the reducing combustion flame installed in the turbulent premixing burner can freely change its position in the direction of the premixing combustion flame in the combustor. Therefore, by positioning the position of the reducing flame where the reducing chemical species are generated in the region where the nitrogen oxides are generated most in the combustor, the reduction reaction of the generated nitrogen oxides can be effectively advanced. In addition, by providing a turbulent flow grid upstream of the tip of the nozzle that forms the reducing combustion flame, it is possible to form a turbulent flame in the turbulent premixing burner and to generate nitrogen oxides from the premixing flame. And the reducing species generated from the reducing flame are rapidly and uniformly mixed, and the reduction reaction of the generated nitrogen oxides can be effectively progressed.

[Embodiment] FIG. 1 shows a first embodiment of the present invention. In FIG. 1, reference numeral 1 is a nozzle for forming a reducing flame, which is provided so as to be movable in the left-right direction in FIG. 1 and is made of a heat-resistant ceramic or the like. This nozzle is
A reducing flame is formed by ejecting fuel only or a fuel-air mixture with a low air ratio. By positioning the tip of the nozzle 1 in a region where most nitrogen oxides are generated in the fuel device of the gas turbine, the nitrogen oxides generated by the premixed combustion can be effectively rendered harmless by the reducing chemical species. it can. 2 is a turbulent flow grid, which is installed to form a premixed turbulent flame. 3 is a fuel nozzle for premixed combustion, 4 is an air supply port for premixed combustion, 5 is a fuel supply chamber for premixed combustion, 6 is a premixing chamber of fuel and air for reducing flame formation, and 7 and 8 Is a fuel supply pipe, 9 is an air supply pipe, and 10 and 11
Is a packing provided so as not to hinder the movement of the nozzle 1.

In the turbulent premixed burner configured as shown in FIG. 1, nitrogen oxides generated from the premixed flame are formed by supplying a low air ratio fuel-air mixture to the nozzle 1. CH radicals generated from the reducing flame
By reacting with C ₂ radicals it is reduced to harmless nitrogen. Since the nozzle 1 is movably provided,
By positioning the tip of the nozzle 1 in a region where most nitrogen oxides are generated in the premixed flame, the generated nitrogen oxides can be effectively reduced.

FIG. 2 shows an example of the structure of the turbulent flow grid 2 installed in the turbulent premixed burner shown in FIG. That is, a disc having a thickness of 1 mm has a large number of holes, each hole has a diameter of 2 mm, and the centers of the holes are arranged so as to be located at the vertices of an equilateral triangle having a side of 3 mm.

Then, as shown in FIG. 3, the fuel-air mixture is radially ejected from each hole of the turbulent flow grid 2 as if a large number of nozzles were arranged, and the oblique line in FIG. A region where fluids having different streamlines collide with each other is generated as shown in FIG. Therefore, in this region, turbulence occurs in the streamline of the fluid, and turbulent flow occurs as shown in FIG. 3 (b).

FIG. 4 shows the outline of the premixed flame combustion experimental apparatus.
The gas mixing section of the premixed flame burner 12 is composed of a perforated plate 13 and a turbulent flow grid 14, which are installed in this order from the upstream side of the gas flow to the perforated plate 13 and the turbulent flow grid 14. Perforated plate 13
Has holes with a diameter of 6 mm arranged at the vertices of an equilateral triangle with a side of 7.4 mm. These holes cause a pressure difference between the inlet and the outlet of the perforated plate 13 so that the methane-air mixed gas flows from the upstream side to the downstream side of the burner. The turbulent flow grating 14 has the same structure as the turbulent flow grating 2 shown in FIG. 2 and is installed for the purpose of forming a turbulent flame. The sampling probe 15 is made of quartz, and the inner diameter of the tip is 180 μm. When the inside of the probe 15 is evacuated, combustion gas is sucked into the probe at a high speed of the Mach 1. Then, the sucked combustion gas is adiabatically expanded, and as a result, the high temperature combustion gas is rapidly cooled, and the oxidation reaction and the like can be stopped. In order to control the mixing ratio of the fuel-air mixture gas used for combustion, a flow rate control device 16 capable of controlling the flow rates of fuel and air under a constant pressure is installed. Surround the four sides of the flame with a quartz combustion tube 18,
It prevents the diffusion of air from the outside. The collected combustion gas was analyzed by a nitrogen oxide meter and a gas chromatograph (TCD
Type). The air ratio was calculated from the analysis value by the gas chromatograph. In addition, P _t
A −R _h thermocouple was used. In FIG. 4, 17 is methane and a vacuum cylinder, 19 is packing, 20 is a trap, 21 is a vacuum pump, 22 is a diaphragm pump, and 23 is a sampling bag.

FIG. 5 shows a nitrogen oxide concentration distribution and a temperature distribution obtained by using the premixed flame combustion experimental apparatus shown in FIG. The air ratio of the premixed combustion flame in this experiment is 0.98. According to the sampling lobes used in this experiment,
Since the amount of suction is small, sampling can be performed without disturbing the flow state of combustion gas.

The nitrogen oxide concentration distribution shown by the black circle 24 in Fig. 5 is 10 ppm or less around the primary flame, and the nitrogen oxide concentration increases as it goes downstream from the primary flame, and around 1.0 cm on the downstream side of the primary flame. Is the highest nitrogen oxide concentration of 30 ppm. On the further downstream side, the nitrogen oxide concentration tends to gradually decrease.

In the temperature distribution indicated by the white circle 25 in FIG. 5, the temperature is higher in the range of ± 1.0 cm in the x direction in which the primary flame is formed, compared to the surrounding area. Within this range, the temperature is higher near the primary flame, and the ambient temperature of the primary flame is the highest at 1200 ° C. The area 1 cm downstream of the primary flame is 1100 ° C. Further downstream, the temperature drops to 1000 and 900 degrees Celsius. Generally, it is known that the amount of thermal nitrogen oxides generated is proportional to the temperature, but comparing the nitrogen oxide distribution and the temperature distribution obtained in this experiment, the primary flame ambient temperature is 1200 ° C, which is the highest. Nevertheless, it can be seen that the distribution of nitrogen oxides is the smallest at 10 ppm or less. In this way, the highest nitrogen oxide concentration distribution from the primary flame, where the combustion temperature is highest, to the downstream is because the thermal nitrogen oxides generated around the primary flame have moved downstream due to the combustion gas flow. it is conceivable that. It is considered that the nitrogen oxide concentration is low due to diffusion on the downstream side.

As described above, the nitrogen oxide concentration distribution in the combustor depends on the flow state of the combustion gas, and it is considered that the nitrogen oxide concentration distribution also changes if the jet speed of the fuel-air mixed gas changes. Therefore, a reducing flame that generates reducing chemical species,
If formed at the position where the nitrogen oxide concentration is the highest, the generated nitrogen oxide can be effectively reduced.

FIG. 6 shows the relative emission intensities of the reducing radicals CH radicals and C ₂ radicals generated when the air ratio (λ) is changed in the premixed flame combustion experimental apparatus of FIG. 4 in the vicinity of the burner nozzle.

As shown in FIG. 6, CH radical emission intensity 26 is
At around 0.5, the C ₂ radical emission intensity 27 shows the highest value at around the air ratio of 0.6. As described above, it is understood that reducing species such as CH radicals and C ₂ radicals are most often generated at a certain point in the low air ratio region where the air ratio (λ) is 1 or less. From the above results, if the air ratio of the fuel-air mixture gas for forming the reducing flame ejected from the central nozzle 1 provided in the turbulent premixing burner of FIG. 1 is set to about 0.5 to 0.6, CH
A large amount of reducing chemical species such as radicals and C ₂ radicals are generated, and the reduction reaction of nitrogen oxides can be effectively advanced.

FIG. 7 shows a second embodiment of the present invention. The position of the fuel nozzle for forming the reducing flame in this embodiment can be selected as shown in FIGS. 7 (a) and 7 (b). That is, in FIG. 7A, when the premixing burner nozzle 28 and the reducing flame forming fuel nozzle 29 are located at the same position in the Z-axis direction, FIG. 7B shows the reducing flame forming fuel. This is when the nozzle 29 is located 2.5 cm downstream of the premix burner nozzle 28.

First, the fuel nozzle 29 for reducing flame formation is positioned at the position shown in FIG. 7 (a), and the turbulent flow grid is installed in the premix burner, and when the turbulent flow grid is not installed. FIG. 8 compares the nitrogen oxide concentrations of the gas discharged from the combustion cylinder 18.

The solid curve 32 in FIG. 8 is the nitrogen oxide concentration in the gas discharged when the turbulent flow grid is not installed in the premixed burner, and the dotted curve 33 is the nitrogen in the gas discharged when the turbulent flow grid is installed. It is the oxide concentration. As shown in FIG. 8, both curves 32,3
In both cases, the lower the reduction flame, the lower the air ratio flame, and the more the nitrogen oxides are reduced. In addition, curve 33 shows that the nitrogen oxide concentration is lower in the low air ratio region than curve 32, so the mixing of the reducing species generated from the low air ratio flame and the generated nitrogen oxides is sufficiently promoted by the effect of the turbulent flow lattice, and the reduction reaction You can see that is progressing well.

Next, a turbulent flow grid is installed in the premixed burner, and the reducing flame forming fuel nozzle 29 is positioned at the position shown in FIG. 7 (a) and the position shown in FIG. 7 (b). FIG. 9 compares the nitrogen oxide concentrations in the exhaust gas with.

The dotted curve 34 in FIG. 9 is the nitrogen oxide concentration in the gas discharged when the reducing flame forming fuel nozzle 29 is located at the position in FIG. 7 (a), and the chain curve 35 is in FIG. 7 (b). ) Is the concentration of nitrogen oxides in the gas discharged when the fuel nozzle 29 for reducing flame formation is located at position (a). As shown in FIG.
Since the curve 35 shows that the nitrogen oxide concentration is smaller than that of the curve 34 in the low air ratio region, by forming the reducing flame that generates the reducing species in the region where the nitrogen oxide is most generated, the generated nitrogen oxide It is considered that the reduction reaction could be effectively advanced.

[Effects of the Invention] The first aspect of the present invention is a premixed burner, wherein a tip of a nozzle that forms a reducing combustion flame is provided so as to be movable toward the center of the high air ratio combustion flame. Therefore, the tip of the nozzle can be moved so as to be positioned in the region where most nitrogen oxides are generated in the combustor, and therefore, the generated nitrogen oxidation can be reduced by the reducing species from the reducing flame. Therefore, there is an effect that the amount of nitrogen oxides generated during combustion can be reduced.

A second aspect of the invention is provided with the configuration of the first aspect of the invention, and is provided at a position upstream from the tip of the nozzle so as to have a space required to form a turbulent flame from the nozzle. Since it has a turbulent flow grid provided,
In addition to the effect of the second invention, a turbulent premixed flame is formed to prolong the residence time of nitrogen oxides generated by premixed combustion in the combustor and sufficiently mix with reducing species generated from the reducing flame. Therefore, the reduction reaction between them can be promoted, and the amount of nitrogen oxides generated during combustion can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view showing a first embodiment of the present invention, FIG. 2 is an explanatory view of a turbulent flow lattice of FIG. 1, and FIGS. 3 (a) and 3 (b) are the same. Fig. 4 is an explanatory view of the action, Fig. 4 is an explanatory view showing the outline of the experimental apparatus, Fig. 5 is an explanatory view of nitrogen oxide concentration distribution and temperature distribution
FIG. 6 is an explanatory view of the relative emission intensity of reducing species, FIGS. 7 (a) and 7 (b) are sectional views showing a second embodiment of the present invention, and FIG. 8 is an air ratio of reducing flame and nitrogen oxidation. FIG. 9 is another explanatory diagram of the relationship of the substance concentration, and FIG. 1 ... Nozzle for reducing flame formation 2 ... Turbulent flow grid 3 ... Fuel nozzle for premixed combustion 4 ... Air supply port for premixed combustion 5 ... Fuel supply for premixed combustion 6 ... Reduction Fuel and air premixing chamber for flame formation 7,8 …… Fuel supply pipe 9 …… Air supply pipe 10, 11 …… Packing 28 …… Premixing burner nozzle 29 …… Fuel nozzle for reducing flame formation

Front Page Continuation (72) Inventor ▲ Nara To Kiyoshi 4026 Kuji Town, Hitachi City, Hitachi, Ibaraki Prefecture Hitachi Research Laboratory, Ltd. (72) Keinobu Kobayashi 4026 Kuji Town, Hitachi City, Ibaraki Prefecture Hitachi, Ltd. Hitachi, Ltd. (72) Inventor Toru Inada 4026 Kujimachi, Hitachi City, Hitachi, Ibaraki Prefecture Hitachi Research Institute, Ltd. (72) Norio Arashi 4026, Kujicho, Hitachi City, Ibaraki Hitachi, Ltd. Hitachi Institute, Ltd.

Claims (2)

[Claims] 1. A premix burner which has a space necessary for sufficiently mixing combustion and air in advance and which forms a high air ratio combustion flame and a reducing combustion flame as the same flame. A turbulent premixing burner for reducing nitrogen oxides by reducing combustion, wherein a tip of a nozzle that forms a reducing combustion flame is provided so as to be movable toward the center of the combustion flame. 2. A premix burner having a space necessary for sufficiently mixing fuel and air in advance, and forming a high air ratio combustion flame and a reducing combustion flame as the same flame. The tip of the nozzle that forms the reducing combustion flame is movably provided toward the center of the combustion flame, and the tip of the nozzle has a space necessary to form a turbulent flame from the nozzle. A turbulent premixed burner for reducing nitrogen oxides by reducing combustion, characterized by comprising a turbulent flow grid provided at a more upstream position.