JPS60133205A - Low nox burning method - Google Patents

Abstract

PURPOSE:To perform the bearing of a thermal load and the gaseous phase reduction of NOx effectively by one burner, by separating the flame, which undertakes the thermal load, and the flame, which forms an intermediate reducing product on the upstream side of the flames, and mixing both flames on the downstream side of the flames. CONSTITUTION:The amounts of the primary air, the secondary air and an inactive gas are adjusted, respectively. Adjustment is performed so that the partial pressure of O2 becomes the low value of about 1-7% at the base part of a high temperature flame formed by the flow of powdered coal 3. As a result, in the vicinity of a primary jetting port 5, only the primary air is burned. Owing to the burning of the flow of powdered coal 3, a low O2 region and a high temperature region are formed. The nitrogent component in the coal is converted into N. Thereafter, burning is accelerated by the secondary air 8. Then, from the jetting port 15, a flow of powdered coal 13, which is transported by an air stream of an inactive gas as an exhausted gas, is jetted. The flow of the powdered coal 13 is diffused to the outside by a baffle plate 16. During the diffusion, an intermediate reducing product is formed by the heat in a furnace. The intermediate product is mixed at the downstream side of the flame. NOx in the flame is reduced in the gaseous phase by the intermediate product.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a combustion method that reduces nitrogen oxide emissions.

Nitrogen oxides (hereinafter abbreviated as "NO-J") are one of the air pollutants, and various combustion methods and combustion devices have been proposed and put into practical use to reduce their emissions. First, (1) those generated when the N content in the fuel is oxidized at relatively low temperatures (fuel NOX), and (2) the OH radicals generated by thermal decomposition of the fuel after the combustion reaction has progressed to some extent. N2 in the air acts on HON, and 0□ acts on it to generate HON (prong).
(3) It is thought that there is some (thermal NOX) that is generated locally as combustion progresses, and stable N in the combustion air is oxidized in the high temperature range.

The NOx reduction combustion methods that have been used in the past include the exhaust gas recirculation method, which mixes a portion of the exhaust gas with combustion air to lower the oxygen partial pressure and lower the combustion temperature.

(b) A two-stage combustion method in which combustion air is divided into two or more stages, the air supply amount in the first stage is less than the theoretical air amount, and the insufficient amount of air is supplied in the second and subsequent stages.

(c) Proprietary methods have been proposed for lowering the combustion temperature by lowering the temperature of the combustion air, but all of them have problems such as a significant decrease in thermal efficiency and unstable combustion. ,
The reality is that it is difficult to further significantly increase the NOx reduction rate using only these methods.

Recently, an in-furnace denitrification method, which reduces and removes NOx during the combustion stage using reducing intermediate products generated in a burner with an extremely low air-fuel ratio, has been developed as a type of combustion method. has been done.

This in-furnace denitrification method is usually carried out by installing a reduction burner whose main purpose is to generate reducing intermediate products and a main burner whose purpose is to bear the heat load of the combustion equipment. . However, the following points have been pointed out as problems with this method.

Flames that contain large amounts of reducing intermediate products (reducing flames) have little chance of contacting oxygen in the center of the flame.
There is a tendency for a large amount of the intermediate products to be contained in the center side, but as a result, when mixed with the main burner flame, the mixing of NOx and the reducing properties is poor, resulting in a high efficiency (NOx cannot be reduced). .

Further, since the reduction burner performs combustion at a considerably low air ratio (for example, about 0.6), the fuel becomes excessively excessive and the flame becomes unstable.

Furthermore, in a reduction burner, it takes a long time to achieve complete combustion, and the furnace has to be made larger.

The object of the present invention is to provide a combustion method that eliminates the above-mentioned problems and allows a single burner to bear the heat load and effectively perform in-furnace denitration, that is, gas phase reduction of NOx.

In short, this invention is a method for carrying out both the burden of heat load and the gas phase reduction of NOx in a burner based on 5.
This is a combustion method that effectively separates the flame that bears the heat load and the flame that produces reducing intermediate products on the upstream side of the flame, and promotes the mixing of both flames on the downstream side of the flame.

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

In Figures 1 and 2, when starting the burner, a starting burner 1 burns a starting fuel such as oil or gas, which is conveyed from the surrounding area by conveying air (-secondary air), and is Pulverized coal rectified at 4 (e.g. 2
00 mesh passing amount (approximately 70%) is injected to form a -order flame. In this case, if an annular member 12 called a frame holder is attached to the outer periphery of the nozzle 5, the flame will not be blown downstream by the vortex formed by the frame holder, which is effective for flame retention. This secondary flame burns with an air ratio of about 1 or slightly less, forming a high temperature flame. Inert gas 6 is injected from around this flame through a primary gas nozzle formed in an annular shape. This inert gas is, for example, combustion exhaust gas extracted from the downstream side of the combustion device. Inert gas 6
Secondary air 8, which has been given a swirling force in the air register 9, is injected from the surrounding area through an annular secondary air nozzle 10.

In the above case, although the supply amounts of secondary air, secondary air and inert gas are adjusted respectively, the 01 partial pressure at the base of the high temperature flame formed by the pulverized coal flow 3 is a low value of about 1 to 7%. Adjust so that .

As a result, in the vicinity of the secondary nozzle 5, only the primary air is combusted, and the pulverized coal flow 3 is combusted, resulting in a low 0□ region and high temperature region, and the nitrogen content in the coal is converted to N. After that, combustion is promoted by the above-mentioned secondary air 8.

Next, from the nozzle 15, a pulverized coal flow 13 that is air-transported by an inert gas such as the exhaust gas is injected.

Immediately after injection, this pulverized coal releases volatile matter due to the heat of the high-temperature flame, but as mentioned above, at the base of the high-temperature flame, O2
The partial pressure is low so no combustion takes place. The pulverized coal flow 13 is diffused outward by a funnel-shaped deflection plate 16, and during this diffusion, the heat in the furnace produces reducing intermediate products.

As a result of various experiments conducted by the inventors regarding the production of intermediate products, it was confirmed that this intermediate product is produced by the above-mentioned thermal decomposition reaction of volatile matter, and the solid content (char) is It was confirmed that they were not directly involved in the production. Therefore, the production of reducing intermediate products occurs in addition to pulverized coal.
A high denitrification rate can be obtained using gas fuel that does not contain char such as methane.

The intermediate products of the high temperature flame and the reduction flame mix on the downstream side of the flame, and NOx in the flame is reduced in the gas phase by the intermediate products. In this case, air may be further supplied from around the pulverized coal flow 13 to achieve complete combustion of unburned matter.

When injecting the pulverized coal flow 13, the supply passage 20 for the pulverized coal flow is formed into a single line, and if it cannot be formed to have an annular cross section like the passage for the pulverized coal flow 3, the supply passage 20 as shown in FIG. Gotaku spout 15
A mixing chamber 14 is formed on the upstream side of the mixing chamber, and a lower wall surface 14a of the mixing chamber is formed to be located on an extension of the side wall of the nozzle 15 to prevent pulverized coal from staying in the lower portion.

Next, FIG. 4 shows an example of a method of supplying the pulverized coal stream 13. A part of the exhaust gas G discharged from the furnace 11 is introduced into the crusher 19 via the fan 17, and is used for drying the coal 18 that has been input and for airflow transporting the produced pulverized coal.
3 to the burner.

By carrying out this invention, it is possible to effectively bear the heat load and reduce NOx in the gas phase with a single burner.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a burner for carrying out the method according to the present invention, FIG. 2 is a perspective view taken along line A-A in FIG.
The figure is a sectional view taken along the line B--B in FIG. 2, and FIG. 4 is a system diagram showing the supply of exhaust gas as an inert gas.

Claims (1)

[Claims] 1. In a method of forming a reducing flame containing a reducing intermediate product around a high-temperature flame and reducing nitrogen oxides in a gas phase with the intermediate product, the partial pressure of oxygen at the base of the high-temperature flame is reduced. A low NOx combustion method, characterized in that the reduction flame is mixed with the reducing flame on the downstream side of the flame. 2. The oxygen partial pressure near the base of the high temperature flame is approximately 1.
% to about 7%.
Combustion method. 3. Claim 1 or 2, characterized in that the fuel for the flame for producing the reducing intermediate product is gas fuel.
Low NOx combustion method described in section.