JPH0487623A - Treatment of nox gas and its device - Google Patents

Abstract

PURPOSE:To obtain a high treatment efficiency of NOx gas even in a neutral region by spraying an aq. soln. of azide compd. from at least two nozzles selected from plural nozzles on NOx gas. CONSTITUTION:An aq. soln. of azide compd. is supplied to plural nozzles 4, 5 with using a pump 7 in order to treat NOx gas. This azide compd. aq. soln. is sprayed from at least two nozzles selected from nozzles 4, 5 on the NOx gas so as to allow NOx gas to react with the azide compd. and to reduce the NOx gas. The reduced NOx gas is discharged through a discharge port 3.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a method and apparatus for treating NOx gas, and more particularly to a method and apparatus for treating NOx gas in exhaust gas from diesel engines and gas turbine motors.

B9 Summary of the Invention The present invention provides a method and apparatus for treating NOx gas, comprising: spraying NOx gas with an aqueous solution containing an azide compound dissolved therein, which is supplied to at least two freely selected from a plurality of nozzles; The equipment used directly in this method contains harmful and dangerous ammonia (hereinafter referred to as NH3).
and without using strong acids (allowing reduction of NOx).

C8 Prior Art Conventionally, NOx gas treatment has been put to practical use as a flue gas denitrification technology. Flue gas denitrification methods are broadly divided into dry methods and wet methods, and the most advanced dry method is the selective catalytic reduction method. This method has the following three advantages.

(1) The system is simple.

(2) High denitrification rate is possible.

(3) NOx is decomposed into harmless N2, H, and O, eliminating the need for exhaust treatment.

In this selective catalytic reduction method, ammonia, hydrocarbons, and carbon oxides are used as reducing agents. Among these, ammonia selectively reacts with NOx even in the presence of oxygen, while other reducing agents react with oxygen. For this reason, particularly in the case of diesel and gas turbine engines, ammonia gas is used, which selectively reacts with NOx even if oxygen is present.

In addition, the catalyst used for this reaction is a noble metal type such as PT, or A1□03. Examples include various metal oxides supported on Tj02 and the like. Most of the components of NOx generated during combustion in diesel and gas turbine prime movers are N.
o, and NO2 is about 5%. For this reason, No is mixed with ammonia gas, and this mixed gas is catalytically reduced on a catalyst to be decomposed into N2 and N20. This reaction formula is shown next.

However, the selective catalytic reduction method shown in the above reaction formula has the following problems.

(1) Harmful and dangerous ammonia gas must be used to decompose NOx.

(2) The performance of the reduction catalyst caused by ammonia gas deteriorates.

In particular, the reduction catalyst deteriorates due to the exhaust gas components, and therefore requires replacement, which is cumbersome to operate.

(3) The operating temperature range is limited.

That is, at high temperatures (approximately 1000° C.), sintering of catalyst components progresses, and catalyst performance deteriorates due to crystal phase transition. Also,
At temperatures below 320° C., ammonia gas and moisture react with exhaust gas containing SOx to produce compounds such as acidic ammonium sulfate, resulting in a decrease in denitrification performance.

For these reasons, the operating temperature range for the conventional reduction method is 3.
The temperature was 20-450°C. Therefore, the temperature range in which it can be used is limited, and it is difficult to use it at room temperature.

(4) It is difficult to downsize the entire processing device.

This means that from the above reaction equation, the reduction reaction of NOx is equimolar, so ammonia gas that is approximately equal to the amount of NOx must be injected into the exhaust gas to match the denitrification rate, and therefore the ammonia gas cylinder, catalyst, etc. This is because the size of the device makes it difficult to downsize the entire device.

Therefore, as a result of intensive research to solve the above problems, the present inventors found that by using sodium azide instead of harmful and dangerous ammonia gas, and by using at least one selected from oxygen and plasma treatment, N
We discovered that Ox could be reduced, and completed a method and apparatus for treating NOx gas (Japanese Patent Application No. 1-30236, Japanese Patent Application No. 2-29255).

D0 Problems to be Solved by the Invention However, the above application proposed a method of dissociating sodium azide in an aqueous solution under acidic conditions using an acid, particularly hydrochloric acid, but if the acidity (pH value) is too high, There was a risk that acid would be released into the atmosphere, causing secondary pollution.

Therefore, the present invention was devised to solve this problem, and by changing the sodium azide spraying method for treating NOx gas to a multistage nozzle type, a high NOx gas treatment rate can be achieved even in conditions with low acidity. This aims to prevent the release of acids into the atmosphere.

E5 Means and Action for Solving the Problems The present inventors have conducted extensive research to solve the above problems, and have found that the sodium azide spraying method for treating NOx gas is of a multi-stage nozzle type, resulting in low acidity. It was discovered that a high NOx gas treatment rate can be achieved even near neutrality, and the N
Completed a method and device for treating Ox gas.

(1) That is, the NOx gas treatment method according to the present invention
Spraying an aqueous solution containing an azide compound dissolved in the azide compound supplied to at least two freely selected from a plurality of nozzles to the Ox gas, causing the NOx gas and the azide compound to react, and reducing the NOx gas. The solution is to remove it.

(2) Furthermore, the NOx gas treatment device according to the present invention
A reaction tube provided with an inlet for introducing Ox gas, a plurality of nozzles inserted into the reaction tube, a pump connected to the nozzles to supply an aqueous solution in which an azide compound is dissolved, and a pump provided in the reaction tube. The solution is to include an exhaust port for removing the reduced NOx gas.

The present invention will be explained in more detail below.

The above applications (Japanese Patent Application No. 1-30236, Japanese Patent Application No. 2-2
The method for treating NOx gas according to No. 9255 is not particular about theory, but sodium azide is dissolved in water, and this aqueous solution reacts with NOx gas to convert NOx to N2+.
The principle was to chemically change it to H20.

That is, this reaction can be explained by the following three equations.

N O+ N O2+ H20' → 2 HNO2・
・・・・・・・・・ (1) 6NaN3+6HC1-'
6N3H+6NaC1--(2)2 HN 02+
6 N5H-1-10N2 + 4 N20...
(3) Normally, it is very inefficient to absorb gas into liquid. Equation (1) above is a reaction in which No and No2 are absorbed into water to form HNO2, and this reaction is the so-called rate-determining step that governs the overall reaction rate. Therefore, if the reaction at this stage can be carried out efficiently, the reaction of the above formula (3) will proceed easily. This was the central problem that conventional methods attempted to solve.

That is, in the conventional method, the reaction of the above formula (2) was carried out separately in advance, thereby converting NaN3 into N3H. At this time, in order to allow the reaction to proceed completely, it is necessary to use acidic conditions, and this condition preferably has a pH of 3 or less, and therefore it is necessary to add a strong acid such as hydrochloric acid.

On the other hand, the method according to the present invention is characterized in that the method of directly spraying an aqueous sodium azide solution onto NOx gas such as NO, No2, etc. is carried out using a multi-stage nozzle method.

By the way, as shown in the reaction of equation (2) above, sodium azide exhibits alkalinity (pH 9,0) when dissolved in water, but when an acid is added to it, it becomes acidic and dissociates with the production of hydrogen azide. state. This dissociation rate is determined by the acidity (p
H) decreases as it increases, and the NOx gas treatment rate also decreases accordingly. However, even at a pH of 5.0, a NOx gas treatment rate of nearly 30% can be obtained. This shows that it is possible to treat NOx gas even in a relatively neutral state.

In the method according to the present invention, it is possible to treat NOx gas even near neutrality, so a high NOx gas treatment rate can be achieved by applying sodium azide to NOx gas using a multi-stage nozzle method.

That is, when the NOx gas treatment method and treatment device according to the present invention spray sodium azide, by using a multi-stage spray method, the effect of each spray goes beyond the mere total effect compared to the one-stage spray blade method. The combination of these methods produces a synergistic effect, which can significantly improve the NOx gas treatment rate. This means that the number of nozzles can be increased or decreased depending on the concentration of NOx gas, and thereby a NOx gas treatment rate of nearly 100% can be achieved under any circumstances.

Next, NOx according to the present invention that can suitably implement this method
The gas processing device will be explained.

The NOx gas treatment described above proceeds in a reaction column provided within this apparatus. That is, a plurality of nozzles are provided in this reaction cylinder, and sodium azide is sprayed from at least two of these nozzles, and the introduced NO
Reacts with x gas.

This spraying is performed by a pump installed in the device, and the N
At least two of a plurality of nozzles freely selected depending on the concentration of Ox gas may be used simultaneously or in stages. In addition, in the apparatus according to the present invention, a recirculation system may be used in which the atomized sodium azide can be used again via the pump. The NOx gas treated in this way is discharged as N2 gas.

F. Examples Hereinafter, a detailed explanation of the NOx gas processing method and its apparatus according to the present invention will be explained based on Examples and Reference Examples along with drawings.

Here, FIG. 1 is a schematic configuration diagram of a two-stage nozzle spraying device showing an embodiment of the NOx gas processing device according to the present invention.

(1) In this configuration diagram, ■ is a reaction cylinder, 2 is a NOx gas inlet, 3 is an exhaust port, 4 and 5 are spray nozzles, 6 is a sealing material, 7 is a pump, 8 is a tank, 9.10 and 12 indicates a pipe, and 11 indicates a discharge port.

(2) Next, N in the two-stage nozzle spray device with the above configuration
The process of treating Ox gas will be explained.

The reaction tube 1 is made of a metal such as stainless steel in consideration of charging an aqueous solution containing sodium azide when performing NOx gas treatment, and is preferably cylindrical in view of reaction efficiency.

Further, this reaction tube 1 is provided with an inlet 2 at its upper part for introducing NOx gas, and has a flange section at its lower part,
An exhaust port 3 is provided to which other equipment, such as a NOx concentration analyzer, can be connected.

Furthermore, this reaction column 1 has spray nozzles 4 and 5 on its side. These spray nozzles 4 and 5 are each sealed with a heat-resistant sealing material 6 to prevent the NOx gas introduced from the inlet 2 from leaking. A sodium azide aqueous solution adjusted to pH 6 is supplied to the spray nozzles 4 and 5 through a pump 7 from a tank 8 to a pipe 9.
and introduced through 10. The introduced sodium azide is first sprayed by the pump 7 from the spray nozzle 4 and then from the spray nozzle 5 into the reaction column 1 to treat the NOx gas introduced from the inlet 2.

This two-stage atomization method significantly reduces the concentration of NOx gas.

Further, in the NOx gas treatment method according to the present invention, the number of nozzles can be increased according to the concentration of NOx gas, thereby further enhancing the synergistic effect.

Note that the NOx gas processing apparatus according to the present invention may employ a so-called recirculation method in which the atomized sodium azide is sent from the aqueous solution outlet 11 via the pump 7 and back into the tank 8 through the pipe 12.

The NOx gas thus treated becomes N2 gas and is discharged from the exhaust port 3 to the outside of the reaction tube 1.

(3) Next, a detailed explanation of a method for treating NOx gas using an apparatus having the above-described function will be explained based on reference examples and examples.

Reference example: Relationship between pH and NOx treatment rate■ A 30KVA diesel generator (manufactured by Meidensha, product number ZX-30, PBS) is used as a NOx gas generator.
) was used to inject exhaust gas containing 50 oppm of NoX gas into reaction tube 1 from NOx gas inlet 2 at 50 DI/min.
introduced within.

■Next, 25g of sodium azide was dissolved in 500cc of water, and then hydrochloric acid was added to adjust the pH to 9.0°7.0.6.
．． Aqueous solutions prepared at 0.5, 0.4.0, and 2.0 were put into tank 8, respectively.

(2) Furthermore, each aqueous solution was sprayed from the spray nozzle 2 by the pump 6 at a rate of 20 mA' per minute to react with the NOx gas.

■ In addition, the gas generated by this reaction is measured using a NOx concentration analyzer 6 (Shimadzu Corporation: Shimadzu Portable NOx Analyzer N0).
A-305 type).

■ The measurement results are shown in Table 1. pH as shown in Table 1
It can be seen that when the value becomes 5 or less, the NOx gas treatment rate decreases significantly.

Table 1 Relationship between pH value and NOx gas treatment rate■ Spray nozzle 2 (one-stage nozzle spray method) was replaced with spray nozzles 2 and 3 (two-stage nozzle spray method), and a sodium azide aqueous solution adjusted to pH 6.0 was first used. NOx gas treatment was performed in the same manner as in the reference example except that the spray nozzle 2 was used for spraying and then the spray nozzle 3 was used for spraying.

■ The results are shown in Table 2. As shown in Table 2, by replacing the two-stage nozzle spraying method, 500 ppm of NOx gas can be reduced to 9
It can be seen that it was reduced to oppm. Note that this value is significantly lower than the nitrogen oxide emission standard set by the Air Pollution Control Act.

Table 2 NOx gas treatment method G1 using two-stage nozzle spraying method
Effects of the Invention (1) The present invention makes it possible to achieve a high NOx gas treatment rate even near neutrality by using a multi-stage nozzle type sodium azide spraying method for treating NOx gas.

Therefore, according to the method of the present invention, NOx gas can be treated without using a strong acid, so that acid can be prevented from being released into the atmosphere, thereby preventing the risk of secondary pollution.

(2) Furthermore, according to the apparatus according to the present invention, a recirculation method can be adopted in which the atomized sodium azide can be reused, leading to cost reduction and ease of handling.

(3) Since the present invention is configured as described above, the following effects are also achieved at the same time.

■ According to the method of the present invention, since an azide compound is used, there is no need to use harmful and dangerous ammonia (NO
x can be reduced.

(2) According to the method according to the present invention, NOx can be significantly reduced compared to the nitrogen oxide emission standard value.

(2) According to the method according to the present invention, since a reduction catalyst is not required, the entire apparatus can be downsized and its operation can be simplified.

(2) According to the method according to the present invention, the reduction reaction of NOx gas can be carried out at room temperature, and the treatment of NOx gas can be easily performed.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing an example of a NOx gas processing apparatus according to the present invention. 1... Reaction cylinder, 2... NOx gas inlet, 3...
Exhaust port, 4 and 5... spray nozzle, 6... sealing material, 7... pump, 8... tank, 9 10 and 12... pipe, 11... discharge port.

Claims (2)

[Claims] (1) An aqueous solution containing an azide compound dissolved in the NO_x gas is sprayed from at least two freely selected from a plurality of nozzles, the NO_x gas and the azide compound are reacted, and the NO_x gas is reduced. A method for treating NO_x gas, the method comprising: removing NO_x gas. (2) A reaction cylinder provided with an inlet for introducing NO_x gas, a plurality of nozzles inserted into the reaction cylinder, a pump connected to the nozzles and supplying an aqueous solution in which an azide compound is dissolved, and the reaction cylinder an exhaust port provided in the cylinder to remove the reduced NO_x gas;
x gas processing equipment.