JPS6287707A - Nox control combustion method - Google Patents

Abstract

PURPOSE:To complete combustion in a complete combustion range and to decrease an unburnt content in exhaust gas, by a method wherein combustion exhaust gas after reduction of NOx and before a complete combustion range is heated by an auxiliary burner. CONSTITUTION:In a vertical furnace 1, secondary fuel 5 is fed in combustion exhaust gas present after primary fuel 3 has been burnt by a primary air 2, and is incompletely burnt by means of low concentration oxygen remaining in the exhaust gas to reduce Nox. Subsequent exhaust gas is heated by an auxiliary burner 9 to which auxiliary air 7 and auxiliary fuel 8 are fed. Further, secondary air 10 is fed in the heated exhaust gas for complete combustion. As noted above, exhaust gas after reduction of NOx and before complete combustion is heated to a given temperature, and through an agitating effect produced by means of jet through the auxiliary burner, a combustion speed of an unburnt content in a final stage or a complete combustion range is promoted, and an unburnt content in the exhaust gas is sharply decreased.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a NOx suppression combustion method.

BACKGROUND OF THE INVENTION Conventionally, a three-stage combustion method has been proposed as a NOx suppression combustion method. This three-stage combustion method is shown in Figure 5 (in the case of a vertical furnace).
And as shown in Figure 6 (for horizontal furnace), the primary fuel 2
1 is combusted by the primary air 22, only the secondary fuel 23 is supplied to the combustion exhaust gas, and NOx is reduced by incomplete combustion with the low H degree oxygen remaining in the primary combustion exhaust gas. ,
Then, only the 21st air 24 is supplied into the subsequent exhaust gas to completely burn the unburned components.

Problems to be Solved by the Invention When the above-mentioned three-stage combustion method is applied to a furnace, such as a boiler, where the heat receiving surface is relatively low temperature, has a large area, and absorbs a large amount of heat, it is possible to keep the NOx emission to an extremely low level. However, due to the large amount of heat absorbed in the furnace, the temperature of the exhaust gas drops slowly and combustion is not completed in the final stage, resulting in the problem that the exhaust gas tends to contain a large amount of unburned matter. Ta.

Therefore, the present invention aims at reducing NOx, l, which can solve the above problem.
The purpose is to provide a combustion method.

Step 1 to Solve the Problem In order to solve the above problem, the NOx suppression combustion method of the present invention supplies secondary fuel into the combustion exhaust gas of the primary fuel to reduce the oxygen remaining in the exhaust gas. to cause incomplete combustion and NO
In the NOx suppression combustion method, which reduces x and supplies secondary air to its downstream side to burn unburned matter, an auxiliary burner is installed after reducing NOx and before supplying the secondary air to lower the temperature of the exhaust gas. This is a method to prevent I):'Tj.

Action-Fl′i[! According to the NOx suppression combustion method, the combustion exhaust gas after reducing NOx but before the complete combustion range is heated by an auxiliary burner, so that unburned gas can be combusted in the complete combustion range.

EXAMPLE Hereinafter, an example of the present invention will be described based on the drawings. 1st
In the figure, 1 is a vertical furnace, and on its side wall 1a, from the bottom to the top, there are main barbs 4, which burn the primary fuel 3 with the primary air 2, and a secondary fuel supply for supplying the secondary fuel 5. A nozzle 6 , an auxiliary burner 9 for burning auxiliary fuel 8 with auxiliary air 7 , and a secondary air supply nozzle 11 for supplying secondary air 10 are provided.

In the vertical furnace 1, the secondary fuel 5 is supplied into the combustion exhaust gas after the primary fuel 3 is combusted by the primary air 2, and the low concentration of oxygen remaining in the exhaust gas causes incomplete combustion. to reduce NOx. The subsequent exhaust gas is then heated by an auxiliary burner 9 to which auxiliary air 7 and auxiliary fuel 8 are supplied. Secondary air 10 is supplied into this heated exhaust gas to achieve complete combustion.

In this way, the city exhaust gas, which is completely combusted after NOx reduction, is heated to a predetermined temperature, and the agitation effect by the jet of the auxiliary burner allows the combustion of unburned gas in the final stage, that is, the complete combustion zone. The speed is increased and the amount of unburned matter in the exhaust gas is significantly reduced. At this time, when coal is used as the fuel, if the air ratio of the auxiliary burner is set to 1.0 or less, the thermal decomposition of the dia in the reducing gas is promoted by the high-temperature hot air, which has the effect of reducing NOx.

In Fig. 1, (A> is the main combustion area (primary combustion area), (
8) is the reducing combustion area (secondary combustion area), (C) is the heating area, (
D) is a complete combustion region (tertiary combustion region).

Next, the experimental results are shown in FIGS. 2 and 3.

From this, it was found that the most effective range was when the amount of auxiliary fuel in the auxiliary burner was 5 to 20% of the total fuel consumption and the air ratio was 0.85 to 1.1. Furthermore, the temperature of the reducing gas after reheating is 1
The temperature is preferably 100°C to 1350°C. If it is lower than 1100°C, there will be little improvement, and if it is higher than 1350°C, the amount of NOx generated in the complete combustion area will increase.

The combustion conditions in Figure 2 are as follows: bituminous coal (ash content 11%, nitrogen content 1.8%) is used as fuel, the overall air ratio is 1.20, and the primary combustion area is The air ratio is 1.05 and the primary fuel ratio is 70%. In the case of FIG. 3, the same fuel as above is used and the overall air ratio is 1.20.

By the way, in the embodiment described above, the case where the present invention is applied to the vertical furnace 1 is shown, but as shown in FIG. 4, it can also be applied to the horizontal furnace 12. In FIG. 4, the same parts as in FIG. 1 are given the same numbers.

Effects of the Invention According to the above combustion method of the present invention, the combustion exhaust gas after NOx reduction and before the complete combustion zone is heated by the auxiliary burner, so combustion in the complete combustion zone is completed, and therefore, the unused gas contained in the exhaust gas is Fuel consumption can be significantly reduced.

[Brief explanation of drawings]

1 to 3 show an embodiment of the present invention. Therefore, Figure 1 shows the schematic configuration of the device, Figure 2 is a graph showing the influence of temperature in the complete combustion region, Figure 3 is a graph showing the effect of the auxiliary burner, and Figure 4. Figures 5 and 6 are cross-sectional views showing a schematic configuration when applied to other devices. ...Primary fuel, 4...Main burner, 5...Secondary fuel, 6...Secondary fuel supply nozzle,
7... Auxiliary air, 8... Auxiliary fuel, 9... Auxiliary barb, 10... Secondary air, 11... Secondary air supply nozzle agent Yoshihiro Morimoto Figure 1 1σ-2 Paku 3); wide; *) or -2 shi 1

Claims (1)

[Claims] 1. A secondary fuel is supplied into the combustion exhaust gas after the combustion of the primary fuel, and the oxygen remaining in the exhaust gas is used to cause incomplete combustion.
In the NOx suppression combustion method, which reduces Ox and supplies secondary air to its wake to combust unburned matter, an auxiliary burner is installed after reducing NOx and before supplying the secondary air to lower the temperature of the exhaust gas. A NOx suppression combustion method characterized by preventing. 2. The amount of fuel supplied to the auxiliary burner is 5 to 5 of the total amount of fuel supplied.
The NOx suppression combustion method according to claim 1, wherein the NOx suppression combustion method is within the range of 20%. 3. The NOx suppression combustion method according to claim 1 or 2, characterized in that the air ratio in the auxiliary burner is in the range of 0.85 to 1.1.