JPS5833019A - Method of reducing nitrogen oxides in combustion exhaust gas - Google Patents

Abstract

PURPOSE:To reduce NOx content in a waste combustion gas by a method wherein combustion waste gas and/or air is thrown in at an angle of 40 deg. or less with respect to a furnace wall so that oxygen concn. with respect to total waste gas becomes 0.5vol% or less. CONSTITUTION:A recirculated combustion waste gas introducing line 103 is provided in the middle between an additional hydrogen carbon fuel throwing line 102 and air throwing line 104 for eliminating unburnt components at a level where 0.5-1vol% of unburnt component exists. The amount of recirculated combustion waste gas to be thrown into the furnace is set so as to bring the oxygen concn. with respect to the total waste gas to 0.5vol% or less, particularly, to 0.3vol% or less. Further, the throwing angle of the gas is set to be 40 deg. or less with respect to the furnace wall. By this construction, the content of NOx can be reduced extremely.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a method for reducing nitrogen oxides (NOx) in combustion exhaust gas, and particularly to an improvement in a combustion method that can suppress the generation of NOx.

Methods for reducing ONK) x in combustion exhaust gas can be roughly divided into the following: (l) 1 reduction method by combustion modification, and (to) in-furnace high-temperature denitration (ammonia injection, etc.) method. ,(
2) Dry catalytic denitrification method and (4) Type 11 absorption treatment method and other O methods are currently under development and research, but the other methods are also lacking in terms of economic efficiency, denitrification performance, operational stability, etc. Problem 1
It cannot be said that it is +/%.

According to the above point IIK, the present invention belongs to the category of (00 combustion improvement) and provides a simple and effective NOx reduction method.

Conventionally, as a NOx reduction combustion method, 1 methane, ethane, petroleum oil, kerosene, heavy oil, alcoholic compounds, aldehyde, etc. Adding a hydrocarbon fuel such as the following, the residual oxygen in the exhaust gas is used to incompletely burn the hydrocarbon fuel to form a reducing atmosphere, converting NOx in the exhaust gas to HCN or NHstk. In addition, a method was adopted in which unburned CO, e.g., O, was removed by injecting air into the wake of the exhaust.

The inventors have conducted extensive studies on the above method, but when the method is applied to an actual large combustor, which is different from laboratory tests, the effect is not as great as expected. This is because hydrocarbon fuel is added to the exhaust gas after main combustion, and the amount of HCN and NH3 generated at the end of the main combustion is reconverted to NOx by the injection of air to eliminate unburned gas in the wake. The overall denitrification rate does not show the expected value, and the CO
This is because there was also a large amount of 0 residual dust particles. Therefore, in order to improve the above method, the present inventors first added a hydrocarbon fuel to the high temperature part of the exhaust gas after combustion of the main fuel and caused incomplete combustion with the oxygen in the exhaust gas to remove nitrogen oxides. In the nitrogen oxide reduction combustion method, which involves reducing the nitrogen oxides and adding air to its wake to burn the unburned components of the fuel, air is added to the surface sufficiently to remove the unburned components after reducing the nitrogen oxides. We proposed a combustion method for reducing nitrogen oxides, which is characterized by adding at least one of combustion exhaust gas and air so that the oxygen concentration becomes 15 volumes or less per total amount of exhaust gas before adding nitrogen oxides. .

(Refer to Japanese Patent Application No. 52-156409.) This proposed method eliminates HCN and NHs generated by incomplete combustion of hydrocarbon fuel.
In the presence of unburned matter (CO, hydrocarbon volume, etc.), if the amount of added oxygen is [15 volume or more], the following formula 0 takes priority and a large amount of N
This is based on the knowledge that Ox is regenerated and below that level, especially below a5 volume, the following formula 0 takes precedence and suppresses NOx regeneration.

NI (l, to HCN+ → No horse H, O etc. ■N
Hs, HCN + Ox →N, Ha Olk
As a result of extensive research into the operating conditions of the proposed method 11C) above, the present inventors confirmed that the input angle of combustion exhaust gas and/or air is an important factor, The invention was completed.

That is, the present invention adds a hydrocarbon fuel to the high-temperature part of the exhaust gas after the combustion of the main fuel, performs incomplete combustion with the oxygen in the exhaust gas to reduce nitrogen oxides, and adds air to the trailing stream. Nitrogen Oxide Reduction Combustion #&K> to burn the unburned matter and reduce the amount of nitrogen oxides, and before adding a sufficient amount of air to remove the unburned matter. Combustion exhaust gas characterized by injecting combustion exhaust gas and/or air into one or multiple locations at an angle of 40 degrees or less to the furnace wall so that the oxygen concentration is less than a5 volume relative to the amount of combustion exhaust gas. This paper focuses on methods for reducing nitrogen oxides.

The present invention is not only an excellent low-NOx combustion method for large-scale industrial combustors, but also has an extremely effective industrial effect as it also protects against corrosion of furnace wall tubes that are easily exposed to reducing gas. This is a certain combustion method.

Hereinafter, the present invention will be explained in detail with reference to FIGS. 1 and 2. FIG. 1 is an elevational view of a normal power generation boiler to which the method of the present invention can be applied, and FIG. 2 shows the level of addition of combustion exhaust gas. In each figure, 10
1 is a main burner, 102 is an added hydrocarbon fuel input line, 105 is a recirculation combustion exhaust gas input line, and 104 is an air input line for eliminating unburned matter. 1 and 2, the added hydrocarbon fuel input twin 102 and the recirculated flue gas input twin 103 are shown at completely different levels, but the recirculated flue gas input The line 1a3 is located between the added hydrocarbon fuel input twin 102 and the air input line 104 for eliminating unburned components, and if the unburned components are present in an amount of IIs to 1.
So 4 well 1. In the case of an extreme table, it is okay to dislike the same level,
At this time, heavy 1! The points in the table are that the input amount of recirculated combustion exhaust gas should be adjusted so that the oxygen concentration is less than a5 volume and Ktk less than KrLs volume relative to the total amount of exhaust gas, and that the input angle should be set at 40 degrees with respect to the furnace wall. I'm with Jin who tries to keep things under control.

If the input amount of recirculated flue gas is set as ζO, then 9HCN, Nus
Most of the 1d NOx K is converted into P&OK without being reconverted, and the re-generation of a large amount of ONOx can be prevented when the unburned content is completely combusted in the wake, and the injection angle can be kept below 40 degrees. Therefore, the recirculated flue gas that can be injected flows along the furnace wall, and normal pigeonhouse fluid mixing improves the poor flow near the furnace wall and tends to create a lean oxygen concentration zone <1 kb. The above reaction can be made more efficient, and at the same time, it has a film-preserving effect against corrosion of the furnace wall tubes, which are easily exposed to reducing gases.

In the above explanation, we have explained the case where recirculated flue gas is used, but it is easy to understand that the same effect can be obtained by using flue gas with air added instead of flue gas. It will probably be done.

EXAMPLE A test was conducted to confirm the usefulness of the present invention on exhaust gas from a small combustion furnace using pulverized coal as the main fuel.

A schematic diagram of the test apparatus O is shown in FIG. 20 in Figure 3
1 is the furnace body (1-OX 4 III), 202 is the pulverized coal and main combustion air O supply line, tosIi-added hydrocarbon fuel supply twin, 204 is the recirculation combustion exhaust gas input line, 205 is for eliminating unburned matter This is the air injection line.

The amount used in the main combustion is domestic coal (0 min 47%, N min tas,
The ash content is 10 g), and the 01 concentration in the exhaust gas after main combustion is 1%. After performing the denitrification operation of the present invention, the 03 concentration in the exhaust gas before and after is set to 4-4, and the amount of recirculated combustion exhaust gas used is equal to or less than the total exhaust gas. -, and the main combustion fuel 0171 @ was closed at the calorific value pace of your company's additive hydrocarbon fuel.

The exhaust gas temperature immediately after the main combustion is 1430℃, the exhaust gas temperature at the addition point of the hydrocarbon fuel on line 265 is 1350℃,
Addition point of recirculated combustion exhaust gas from twins 2 and 4 O# Gas temperature 1530°C, line 2 D,! The exhaust gas temperature at the point of addition of air for eliminating unburned gas from S shall be 1300°C. Of the amount of recirculated combustion exhaust gas (!- of the total exhaust gas) used at this time, the sleeve is used as a carrier gas for the pulverized coal in the main combustion, and the remainder - is used for inputting from the twin 104. The tests conducted to confirm the effects of the IjIO of the present invention were conducted under all of the above conditions. In addition, the NOx concentration in the exhaust gas immediately after simply burning the pulverized coal is 148 pp.
m and nine.

The test was conducted by injecting recirculated combustion exhaust gas from four locations as schematically shown in Figure 2.9. The results on the NOx meter side at the furnace outlet when the angle of the recirculated combustion exhaust gas relative to the furnace wall was varied are shown in the table below.

This is the case where it is used as a carrier gas for the pulverized coal added from 02.

Measurements of t ft NOx and 1 hour K Co emissions were less than 10 ppfl under all conditions.

If the angle (θ) is large, it will disturb the flame during combustion, which is undesirable, but if it is set to 40 degrees or less, it can be seen that the method of the present invention is effective in improving the denitrification rate.

[Brief explanation of the drawing]

Figure 1 shows a power generation boiler O to which the present invention can be applied.
FIG. 2 is a schematic plan view of the flue gas addition level shown in FIG. 1, and FIG. 5 is a schematic diagram of a small experimental reactor that was conducted for the ninth time to confirm the effects of the present invention. Sub-agents 1) Meifu agent Ryo Yabuhara -

Claims (1)

[Claims] Hydrocarbon fuel is added to the high temperature part of the exhaust gas after the combustion of the main fuel, and the oxygen in the exhaust gas causes incomplete combustion to reduce nitrogen oxides. In the nitrogen oxide reduction method, which burns the nitrogen oxides, the amount of oxygen per total exhaust gas amount is aS after reducing the nitrogen oxides and before adding sufficient air to remove the unburned
A method for reducing nitrogen oxides in flue gas, which comprises injecting flue gas and/or air at one or more locations at an angle of 40 degrees or less with respect to a furnace wall so that the volume of the flue gas is less than or equal to 100 degrees.