JPH0116892Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an improvement of a pulverized coal combustion burner, and particularly to a burner suitable for reducing nitrogen oxides generated during combustion of pulverized coal.

[Prior Art] Most of the NOx generated during the combustion of pulverized coal is fuel NOx generated by oxidation of nitrogen contained in the coal. Fuel NOx is generated due to thermal oxidation of nitrogen in the air.
Lower flame temperature dependence than NOx. Therefore, the two-stage combustion method, exhaust gas recirculation method, etc., which are aimed at lowering the flame temperature and which have been conventionally developed as low NOx combustion methods, have little effect on low NOx combustion of pulverized coal. Therefore, the inventors developed a new-bottom NOx combustion burner that swirls and blows out the mixture of pulverized coal and this conveying air, and then swirls and blows out the outer periphery of this fuel flow in the same manner as the pulverized coal. A burner surrounded by secondary air was proposed. The principle of NOx reduction using this burner is to give swirling momentum to the mixed air flow of pulverized coal and air, and disperse the pulverized coal using centrifugal force, thereby making the pulverized coal concentration distribution within the flame uneven. be. This creates a complete combustion region with an air ratio of 1 or more in the flame and an air ratio of 1 or more.
The following incomplete combustion regions are formed; in the former region, NOx is generated, and in the latter region, reducing substances are generated. In the flame wake, the combustion products from both regions mix and the NOx is reduced to nitrogen by the reducing agent. The performance of this burner is greatly influenced by the method of dispersing the pulverized coal within the flame, and for this reason, the strength of the swirling effect on the mixed airflow of primary air and pulverized coal is one of the important factors in operation. As a result of repeated experimental studies, the inventors have found that the amount of NOx generated can also be controlled by the distance of the fuel nozzle ejection hole from the burner reference plane. This optimum position differs depending on the type of coal, swirling strength, etc., and must be adjusted as necessary as the type of coal changes during burner operation.

[Purpose of invention]

The purpose of this invention is to
An object of the present invention is to provide a burner structure for burning pulverized coal that can suppress the amount of NOx generated.

[Summary of the idea]

The key point of the present invention is that a means for swirling the mixture is installed in the fuel nozzle that spouts a mixture of finely powdered fuel stones placed at the center of the burner and primary air for transporting it. In a burner, the axial position of the fuel nozzle is adjustable, and the tip of the fuel nozzle is arranged so that the air-fuel mixture spreads before being mixed with the secondary air. The pulverized coal combustion burner is provided with a lapper-shaped nozzle, and an ignition burner for igniting the air-fuel mixture is provided at the axial center of the fuel nozzle so as to be concentric with the fuel nozzle.

[Example of idea]

An example of a burner structure according to the present invention is shown in FIG. The burner of this embodiment has a propane nozzle 1
1, a fuel nozzle 12, and a secondary air nozzle 13. The propane nozzle 11 is installed at the center of the burner and is used for preheating the combustion furnace and igniting pulverized coal. A fuel nozzle 12 for ejecting pulverized coal and primary air for transporting the pulverized coal is installed concentrically around the outer periphery of the propane nozzle 11, and a swirling vane 17 is arranged inside the nozzle. The secondary air nozzle 13 is installed on the outer periphery of the fuel nozzle 12, and the nozzle ejection hole is oriented in the tangential direction of the concentric circle of the fuel nozzle 12 so that the secondary air is ejected as a swirling flow surrounding the pulverized coal and the primary air. It will be done.

The fuel nozzle 12 is arranged within the nozzle installation pipe 14 and fixed with a nozzle fixing flange 15. The fuel nozzle 12 is movable within the nozzle installation pipe 14 by loosening the flange 15, and its position is adjusted at any time depending on combustion conditions.
The position of the fuel nozzle 12 from the burner reference plane is adjusted by a tightening fitting 16.

The air-fuel mixture coming out of the swirling vane 17 becomes a swirling flow and further spreads radially before being mixed with secondary air by a flap-like nozzle provided at the tip of the fuel nozzle. When ejected as a swirling flow, the way it spreads varies depending on the particle size, with large particles gathering on the outer periphery and small particles gathering on the inner periphery. Therefore, large particles with low flammability will have a high air ratio, and small particles with high flammability will have a low air ratio.
By mixing these combustion flames, NOx can be reduced. Furthermore, large particles with low combustibility can be combusted at a high air ratio, and the combustion rate can be improved because they are well mixed with the secondary air flow.

FIG. 3 shows experimental results when pulverized coal was burned using the burner shown in FIG. The burned coal is Pacific coal that has been crushed so that more than 80wt% passes through a 200-mesh sieve. The combustion furnace is rectangular with an internal cross section of 600 mm x 600 mm and a length of 2 m. The amount of coal supplied to the combustion furnace is 20 kg/h.
The angle of the swirl vanes installed in the fuel nozzle is 45° with respect to the flow direction. The flow rate of the primary air that conveys the pulverized coal is 40 m ³ per hour, and the mixed air flow of the primary air and the pulverized coal swirls and blows out.

FIG. 3 shows the results of an experiment conducted under these experimental conditions while changing the position of the fuel nozzle. The distance l between the burner reference plane and the fuel nozzle shown in Fig. 1 is 0 mm,
That is, the white circle in Fig. 3 is the result when the burner reference plane and the position of the fuel nozzle ejection hole are aligned, and the black circle is the result when the burner reference plane is aligned with the position of the fuel nozzle jet hole, and the result when the position is set to 10 mm is the black circle. The horizontal axis in Figure 3 is the air ratio (ratio between the supply air flow rate and the theoretical air flow rate),
The vertical axis is the amount of fuel gas measured at the combustion furnace outlet.
This is the value obtained by converting the NOx concentration into 6% O ₂ . From Figure 3, NOx generated depending on the position of the fuel nozzle
It can be seen that the position of the fuel nozzle needs to be adjusted in order to reduce NOx. This is because the state of dispersion of pulverized coal within the flame changes depending on the position of the fuel nozzle. The dispersion of pulverized coal varies depending on the centrifugal force applied to the particles and the weight of the particles. Therefore, when burning coals with different crushability, the optimum nozzle position will naturally differ depending on the type of coal because the particle size distribution will differ depending on the type of coal, and even if the coal is of the same type, the crushing conditions will vary. The optimum position of the nozzle changes because the particle size distribution differs depending on the material.
When considering the practical aspects of burners, it is difficult to replace the burners depending on the type of coal being burned and the pulverization conditions. It is very beneficial.

[Effect of idea]

According to the present invention, it is easy to adjust the position of the fuel nozzle, and the burner that swirls and blows out the pulverized coal.
The NOx reduction effect can be maximized.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a burner according to an embodiment of the present invention.
FIG. 2 is a view of the burner shown in FIG. 1 in the - arrow direction, and FIG. 3 is a graph showing the results of a combustion experiment of the burner shown in FIG. 11... Propane nozzle, 12... Fuel nozzle, 13... Secondary air nozzle, 14... Nozzle installation pipe, 15... Nozzle fixing flange, 16...
...Tightening metal fitting, 17...Swivel vane.

Claims (1)

[Scope of utility model registration request] A burner in which a fuel nozzle for ejecting a mixture of pulverized coal and primary air is provided with means for swirling the mixture, and secondary air for ejecting secondary air as a swirling flow is arranged around the outer periphery of the fuel nozzle, The means for swirling the air-fuel mixture can be adjusted in the axial direction of the fuel nozzle, and a flange-like nozzle is provided at the tip of the fuel nozzle so that the air-fuel mixture spreads before being mixed with the secondary air, A pulverized coal combustion burner, characterized in that an ignition burner for igniting an air-fuel mixture is provided at the axial center of the fuel nozzle so as to be concentric with the fuel nozzle.