JPH0549855A - Method for decreasing nitrogen oxide of combustion gas - Google Patents

Abstract

(57) [Summary] [Purpose] To reduce nitrogen oxides in exhaust gas. A nozzle 11 is arranged in a rear smoke chamber 8 into which the combustion gas 10 flows so that ammonia can be sprayed so as to face the flow of the combustion gas 10. The reaction time between the nitrogen oxide in the combustion gas 10 and the diluted ammonia water can be lengthened, and the nitrogen oxide in the combustion gas can be significantly reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reducing nitrogen oxides in combustion gas of various combustion furnaces using fuel such as gas, liquid and solid.

[0002]

2. Description of the Related Art Generally, nitrogen oxides (NO _x ) generated in a combustion furnace are mainly (a) those generated by oxidizing nitrogen components contained in various fuels, and (b) especially ,
When burning hydrocarbon raw materials such as heavy oil, kerosene, and LPG,
At an air ratio (actually supplied air amount / theoretical required air amount) of about 0.5 to 1.4, hydrocarbon reacts with nitrogen in the air, and promptly goes through some reactions. 2) (prompt NO), and (c) due to combustion, nitrogen and oxygen in the air react with each other at a high temperature (NO).

The above-mentioned nitrogen oxides pose a problem from the viewpoint of air pollution, and therefore, the following methods for suppressing the generation of various nitrogen oxides have been adopted. (I) Combustion air is divided into two stages and supplied to the combustion chamber, the first stage burns the fuel with less air than the amount required for complete combustion, and the second stage uses the remaining amount required for complete combustion. A two-stage combustion method that supplies air. (Ii) Exhaust gas recirculation method in which exhaust gas generated by combustion is circulated and mixed again with fuel. (Iii) An injection method in which steam or water is blown into the combustion chamber. (Iv) Fuel conversion method to switch to the use of low nitrogen fuel. (V) A method using an emulsion fuel. (Vi) A low oxygen combustion method for reducing oxygen in the combustion zone. Etc.

In the above method (i), it is impossible to suppress the generation of prompt NO in the range of 0.5 to 1.0 which is a general air ratio in the primary combustion region, and the air ratio is around 0.5. Even if an attempt is made to suppress the generation of prompt NO as much as possible, there is a problem that unburned matter reacts with the air in the second air supply section to generate prompt NO. As a result, soot that adheres to the inner wall of the combustion furnace and the heat transfer surface is generated,
There is also a problem of obstructing the flow of combustion air and combustion gas.

In the above method (ii), if the recirculation amount of exhaust gas is increased in order to effectively suppress the generation of nitrogen oxides, there is a problem that combustion becomes unstable.
The method (iii) has a problem that the heat loss is large, and the methods (iv) and (v) have a problem that the cost is increased.
In the method i), as in the method i), soot is attached to the inner wall of the combustion furnace and the heat transfer surface along with the smoke, and the flow of combustion air and combustion gas is obstructed. There is a point.

Therefore, in consideration of the various problems mentioned above,
The following methods for reducing nitrogen oxides by utilizing a chemical reaction with ammonia have been conceived and implemented.

(Vii) Honeycomb-shaped catalyst (material: TiO 2)
₂ , V ₂ O ₅ etc.) is installed in the flue, and ammonia water is jetted downward (in the same direction as the flow of the combustion gas) from the windward part of the catalyst installation location to cause ammonia and nitrogen oxides on the catalyst. Ammonia catalytic reduction method that reduces nitrogen oxides by promoting the reaction with.

(Viii) Combustion gas of combustion furnace (800-
A high temperature non-catalytic denitration method in which ammonia gas is directly injected into the same direction as the flow of the combustion gas into 1100 ° C.) to decompose nitrogen and water without a catalyst to reduce nitrogen oxides.

[0009]

However, the above (v
In the method (ii), there is a problem that the catalyst is expensive, and the facility cost is increased in terms of the place where the catalyst is installed and the management of the catalyst, and in the method (viii),
Since the combustion gas and the ammonia gas flow in parallel, a large amount of the ammonia gas and the unreacted combustion gas are generated. Therefore, a large amount of the ammonia gas is also injected, but nevertheless unreacted. Combustion gas and excess ammonia gas are released to the atmosphere, which is not preferable from the viewpoint of air pollution.

In view of the above situation, it is an object of the present invention to provide a method for reducing nitrogen oxides in combustion gas, which is capable of efficiently reducing nitrogen oxides in combustion gas in a combustion furnace at low cost. ..

[0011]

DISCLOSURE OF THE INVENTION The present invention is characterized by injecting ammonia diluted water at a position where the temperature of the combustion gas is approximately 900 to 1000 ° C. in opposition to the flow of the combustion gas. The present invention relates to an oxide reduction method.

[0012]

[Operation] Ammonia diluted water is injected into the combustion gas in opposition to the flow thereof to chemically react the nitrogen oxides and ammonia in the combustion gas to lower the content of nitrogen oxides in the exhaust gas and at the same time to assist the gas. Muds can also be reduced.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to FIGS. 1 and 2 by taking a flue tube boiler as an example.

As shown in FIG. 2, the furnace tube smoke tube boiler has a corrugated furnace tube 2 and first, second, and third smoke tube groups 3 in a boiler cylinder 1.
Reference numerals 4 and 5 are inner-fired boilers arranged coaxially, and a front smoke chamber 7 is provided on the burner 6 side of the corrugated furnace tube 2, and a rear smoke chamber 8 and a rear smoke chamber 8 on the side opposite to the burner 6 of the corrugated furnace tube 2. An exhaust gas discharge chamber 9 is provided, the corrugated furnace tube 2 and the rear smoke chamber 8 are formed by the first smoke pipe group 3, the rear smoke chamber 8 and the front smoke chamber 7 are formed by the second smoke pipe group 4, and the front smoke chamber 7 is formed. The exhaust gas discharge chamber 9 is connected to each other by the third smoke pipe group 5, and the combustion gas 10 is converted into the corrugated furnace tube 2 → the first smoke pipe group 3 → the rear smoke chamber 8 → the second smoke pipe group 4 → the front smoke chamber 7 → The third smoke pipe group 5 and the exhaust gas discharge chamber 9 are made to flow in this order.

A pressure spray type nozzle 11 is provided at the lower side of the rear smoke chamber 8 where the temperature of the combustion gas 10 of the furnace tube smoke tube boiler is approximately 900 to 1000 ° C. It is installed so as to face the flow of combustion gas flowing in from 3.

Further, the ammonia diluting water storage tank 12 is connected to a pump 15 via a pipe 13 incorporating a valve 14, and the other end of a flexible pipe 16 having one end connected to the nozzle 11 is connected via a pipe 17 to the pump. The pump 15 is connected to the pump 15 so that the ammonia diluted water can be pumped from the ammonia diluted water storage tank 12 to the nozzle 11.

Further, a seal pipe 18 is externally fitted to a portion of the nozzle 11 which is installed in the rear smoke chamber 8 and a portion in the vicinity thereof, and seal air 20 is supplied from a branch pipe 19 of the seal pipe 18 to the inside of the seal pipe 18 and the nozzle 11. The nozzle 11 is blown into the space with the outside and air-sealed so that the nozzle 11 can be cooled.

A method of reducing nitrogen oxides (NO _x ) will be described below.

First, by opening the valve 14 and driving the pump 15, the ammonia diluted water is supplied from the ammonia diluted water storage tank 12 to the valve 14 → the pipe 13 → the pump 15
→ Pipe 17 → Flexible pipe 16 → Nozzle 11 is pressure-fed in that order, and ammonia diluted water is sprayed from the nozzle opening of the nozzle 11 into the rear smoke chamber 8 in opposition to the flow of combustion gas.
As shown in the following formula, a reaction between ammonia and nitrogen oxides is caused to obtain nitrogen and water, the nitrogen oxides in the combustion gas are denitrified, and the nitrogen oxides in the combustion gas are reduced.

NH ₃ + 1 / 4O ₂ → NH ₂ + 1 / 2H ₂ O (I) NH ₂ + NO → N ₂ + H ₂ O (II)

In this case, since the ammonia diluting water is sprayed so as to face the combustion gas flow, the reaction time between the nitrogen oxide and ammonia in the combustion gas can be lengthened and unreacted nitrogen oxide can be greatly reduced. As a result, nitrogen oxides in the combustion gas can be significantly reduced.

Next, the case of application to a once-through boiler will be described with reference to FIG.

Combustion gas passages 24 are opened concentrically on the outside of a group of inner evaporation tubes 21 arranged in a cylindrical shape with a combustion gas distribution gap 22 formed in one side thereof in the axial direction, and the inner evaporation is carried out. An outer evaporation tube group 23 communicating with the tube group 21 is arranged in a cylindrical shape.

In the outer evaporation pipe group 23, a combustion gas discharge passage 25 is formed in the axial direction at a portion where the combustion gas flowing from the inner evaporation pipe group 21 into the combustion gas passage 24 branches and merges.
Is formed, and a gap 26 is formed in the axial direction in the portion of the outer evaporation pipe group 23 where the temperature of the combustion gas flowing in the combustion gas passage 24 corresponds to 900 to 1000 ° C. to form an insertion opening for the nozzle 11. The nozzle 1 is inserted into the combustion gas passage 24 from the opening so as to face the flow of the combustion gas so that the ammonia diluting water can be sprayed.
The root portion of 1 is fixed to the outer wall.

The system for supplying ammonia diluted water to the nozzle 11 and the air seal system are as shown in FIG.

Therefore, by spraying ammonia diluted water from the nozzle 11 so as to face the flow of the combustion gas, the reaction between ammonia and the nitrogen oxide in the combustion gas as in the above reaction formulas (I) and (II) is caused. By doing so, nitrogen and water are obtained, and nitrogen oxides in the combustion gas are made nitrogen-free, so that the nitrogen oxides in the combustion gas can be reduced.

Further, as described above, the system for supplying the ammonia diluted water to the nozzle 11 and the air seal system are independent of the combustion equipment such as the boiler, so that even if a failure occurs, the operation of the combustion equipment is affected. There is no.

The reactions of the above reaction formulas (I) and (II) depend on the temperature of the reaction atmosphere and the amount of ammonia added.

Various experiments were conducted on the relationship between the combustion gas temperature, which is the temperature of the reaction atmosphere, and the nitrogen oxide reduction value.
As shown in FIG. 4, according to FIG.
It can be seen that the nitrogen oxide reduction value sharply changes at the combustion gas temperature of about 0 ° C.

Regarding the ammonia diluted water, if the concentration of the ammonia diluted water is too high, it is difficult to adjust the spray amount of the ammonia diluted water, and in the case of a small capacity boiler, the amount of ammonia diluted water must be supplied in a large amount without being restricted. As a result, the residual ammonia in the exhaust gas is discharged together with the exhaust gas, and when the amount of sprayed ammonia diluting water becomes excessive, the amount of residual ammonia in the exhaust gas increases.

Various experiments were conducted on the relationship between the spray amount of the ammonia diluting water and the residual ammonia amount in consideration of the above-mentioned matters. As shown in FIG. 5, according to this FIG. 5, the ammonia diluting water with respect to the fuel injection amount was diluted. It can be seen that when the ratio is 10% or less, the residual ammonia amount maintains a trace amount.

If the spray angle of the nozzle for spraying the ammonia diluting water is too acute, the ammonia diluting water will not be sprayed, and the ammonia diluting water will be sprayed in a rod shape and the reaction with the nitrogen oxides in the combustion gas will be delayed, On the contrary, if the spray angle of the nozzle is wide, problems such as ammonia diluted water hitting the wall and not effectively diffusing into the combustion gas occur.

Therefore, in order to proceed the chemical reaction in the direction of erasing nitrogen oxides, the nozzle 1 should be considered in consideration of the above-mentioned matters.
The installation place of No. 1 is a place where the ammonia diluted water can be sprayed to the combustion gas of about 900 to 1000 ° C, the concentration of the ammonia diluted water is set to 1 to 5%, and the spray amount of the ammonia diluted water is the combustion amount of the raw burner. 1 to 10% of the nozzle 11
The ammonia diluting water is sprayed at an angle of 10 ° to 80 ° (60 ° to 80 ° in the case of a fire tube boiler), and the nozzle 11
Ammonia diluted water is sprayed from 7 to 10 kg /
When it was set to about cm ² , the reaction of the reaction formula (II) proceeded extremely well in various combustion furnaces, and the nitrogen oxides in the combustion gas could be reduced.

The present invention is not limited to the embodiments shown and described, and it goes without saying that various modifications can be made without departing from the gist of the present invention.

[0035]

According to the method for reducing nitrogen oxides in combustion gas of the present invention, the ammonia diluting water is sprayed against the combustion gas, so that the reaction time between ammonia and nitrogen oxides in combustion gas can be lengthened. The nitrogen oxides in the exhaust gas can be significantly reduced, and the air pollution can be prevented, which is advantageous in terms of pollution control.

[Brief description of drawings]

FIG. 1 is a partial sectional view showing an example in which a method for reducing nitrogen oxides in combustion gas according to the present invention is applied to a flue tube boiler.

2 is a perspective view showing a configuration procedure of a flue tube boiler in FIG. 1. FIG.

FIG. 3 is a diagram showing an example in which the method for reducing nitrogen oxides in combustion gas of the present invention is applied to a once-through boiler.

FIG. 4 is a graph showing the relationship between combustion gas temperature and nitrogen oxide reduction value.

FIG. 5 is a graph showing the relationship between the amount of ammonia diluted water spray and the amount of residual ammonia.

[Explanation of symbols]

 2 Corrugated furnace tube 3 First smoke tube group 4 Second smoke tube group 8 Rear smoke chamber 10 Combustion gas 11 Nozzle 12 Ammonia diluted water storage tank 15 Pump 18 Seal tube 20 Seal air

Claims (1)

[Claims] 1. The temperature of the combustion gas is approximately 900 to 1000 ° C.
A method for reducing nitrogen oxides in combustion gas, characterized in that ammonia diluted water is injected to the position of, facing the flow of combustion gas.