JPH0248803B2 - TEINO10BIFUNTANBAANA - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a NOx pulverized coal burner that pulverizes and burns coal.

Nitrogen oxides (hereinafter referred to as NOx) generated during combustion flame
) are generally combined with fuel NOx and thermal
It is classified as NOx. Fuel NOx is produced when nitrogen contained in fuel is oxidized, and thermal NOx is produced when nitrogen in the air is oxidized. Since coal contains a larger amount of nitrogen than liquid fuel, most of the NOx generated during pulverized coal combustion is fuel NOx. The low NOx combustion methods that have been developed in the past, such as the two-stage combustion method and the exhaust gas recirculation method, are aimed at reducing the combustion temperature and suppressing the oxidation reaction of nitrogen in the air. The most effective ones are the ones that are effective.

The generation path of fuel NOx generated during pulverized coal combustion is explained as follows in conjunction with the combustion mechanism. Pulverized coal combustion consists of the processes of ignition, thermal decomposition, gas combustion, and solid combustion. The initial region of combustion is a region where ignition and thermal decomposition proceed, and the nitrogen content contained in the coal here is divided into nitrogen content that evaporates and nitrogen content that remains in the solid. The combustion zone following pyrolysis is divided into a combustible gas combustion zone and a solid combustion zone. In the gaseous combustion region, a large amount of NOx is generated due to the oxidation of volatile nitrogen, while in the solid combustion region, NOx is generated due to the nitrogen remaining in the solid.

The conventional NOx suppression method by lowering the combustion temperature reduces the amount of cyanide and ammonia compounds in the volatile nitrogen content.
Since it has the property of reducing NOx to N ₂ in a low O ₂ atmosphere and at low temperatures, it can be expected to be effective in suppressing NOx. However, based on the principle of lowering the combustion temperature
When applying the NOx suppression method to pulverized coal combustion,
Solid fuel has a drawback that the combustion rate is slow, so that the amount of unburned fuel increases significantly.

Figure 1 shows a conventional pulverized coal combustion burner. The burner is composed of a fuel mixture nozzle 1 that supplies a fuel mixture consisting of pulverized coal and primary air, a secondary air nozzle 2, and a tertiary air nozzle 3. Note that 4 is an ignition burner, and 5 and 6 are swirl vanes. Low O ₂ near the burner tip due to fuel mixture and secondary air
A primary combustion zone is formed, and a secondary combustion zone is formed downstream of it by tertiary air and combustion exhaust from the primary combustion zone. In burners that use the combustion method described above, the air-fuel ratio in the primary combustion region is sensitive to the generation of NOx and unburned matter, and at the same time, the optimum air-fuel ratio for suppressing NOx depends on the type of coal. This has the disadvantage that it does not necessarily match the air-fuel ratio of the unburned content suppression limit. Furthermore, there is a limit to the amount of NOx that can be suppressed, and at the same time, this burner is designed based on the basic principle of two-stage combustion.
Furthermore, by taking measures to reduce NOx such as exhaust gas recirculation,
It has the disadvantage of increasing unburned content.

The present invention has been made to improve the above-mentioned drawbacks, and its purpose is to obtain a pulverized coal burner that can reduce NOx.

That is, the present invention is characterized by: a primary fuel nozzle that jets out a primary fuel mixture consisting of a mixture of pulverized coal and air; and an air nozzle that includes air swirling means around the outer periphery of the primary fuel nozzle. and a mixture of pulverized coal and air on the outer periphery of the air nozzle.
Next, the fuel nozzle is located in a low NOx pulverized coal burner.

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

A secondary air nozzle 13 is arranged around the outer periphery of a primary fuel mixture nozzle 12 consisting of a mixture of primary air and pulverized coal. A swirl vane 16 is attached to the secondary air nozzle 13, and the secondary air is jetted into the combustion chamber as a swirling flow. In the figure, broken line arrows and solid line arrows schematically indicate the flow of air and the flow of fuel mixture, respectively. The primary fuel mixture and secondary air form a primary combustion zone 18 in the vicinity of the burner. A secondary fuel mixture nozzle 14 for ejecting a secondary fuel mixture consisting of tertiary air and pulverized coal is disposed around the outer periphery of the secondary air nozzle 13, and a quaternary air mixture nozzle 14 having swirl vanes 17 is disposed around the outer periphery of the secondary fuel mixture nozzle 14. Nozzle 1
5 is placed. Note that 12 indicates an ignition burner.

A secondary combustion region 19 is formed at the tip of the primary combustion region by the secondary fuel mixture and the combustion exhaust from the primary combustion region 18, and the combustion exhaust from the secondary combustion region 19 and the quaternary air are further formed. Accordingly, the tertiary combustion region 20
is formed at the tip of the secondary combustion region. The air-fuel ratio of the primary combustion region 18 is such that the air-fuel ratio of the primary fuel mixture is
Below 1.0, secondary air is added to this and it is set around 1.0. In the secondary combustion region 19, the air-fuel ratio is set to 1.0 or less, and a reducing atmosphere is formed. Finally, the air-fuel ratio in the tertiary combustion area 20 is set to 1.0 or more, and the unburned matter from the primary and secondary combustion areas is combusted here.

According to this embodiment, it is possible to reduce the NOx generated in the primary combustion zone 18 by the reducing agent generated in the secondary combustion zone 19, and the NOx can be reduced to one conventional fuel supply nozzle. from the burner
Can reduce NOx. Furthermore, by making the amount of pulverized coal in the primary fuel mixture larger than the amount of pulverized coal in the secondary fuel mixture, the air-fuel ratio in the primary combustion region is higher than that in the secondary combustion region, which improves flame stability. can be improved. Furthermore, by controlling the amount of air in the tertiary combustion region,
Unburned matter can be reduced.

According to the present invention, there are two nozzles for supplying pulverized coal.
The combustion area formed at the tip of the burner is divided into 1,
Since it is possible to perform control separately in the secondary region, NOx generated in the primary combustion region can be reduced in the secondary combustion region with a reducing atmosphere. Furthermore, since the fuel ratio distribution in the primary and secondary combustion regions can be controlled individually, it is easy to control the combustion method for reducing NOx. Furthermore, flame stability can be improved by increasing the combustion load in the primary combustion region.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a conventional pulverized coal burner, and FIG. 2 is a sectional view of a pulverized coal burner showing an embodiment of the present invention. 12...Primary fuel mixture nozzle, 13...Secondary air nozzle, 14...Secondary fuel mixture nozzle, 1
5... Quaternary air nozzle, 16, 17... Swirl vane, 18... Primary combustion area, 19... Secondary combustion area, 20... Tertiary combustion area.

Claims (1)

[Scope of Claims] 1. A primary fuel nozzle for ejecting a primary fuel mixture consisting of a mixture of pulverized coal and air; an air nozzle provided with air swirling means on the outer periphery of the primary fuel nozzle; A low NOx pulverized coal burner characterized in that a secondary fuel nozzle consisting of a mixture of pulverized coal and air is provided on the outer periphery of an air nozzle. 2. The low NOx pulverized coal burner according to claim 1, characterized in that an air nozzle provided with air swirling means is disposed around the outer periphery of the secondary fuel nozzle.