JPH04247218A - Method for treating exhaust gas and device therefor - Google Patents

Abstract

PURPOSE:To effectively decompose and remove remaining NOx by passing an exhaust gas in a sprayed atmosphere of a hydrogen azide soln. to reduce and remove the NOx, then passing the exhaust gas in a discharge plasma atmosphere at the time of removing the NOx from the exhaust gas. CONSTITUTION:This device consists of a wet process denitrificationtreating section 1 and a plasma denitrification treating section 2. The wet process denitrification-treating section 1 is constituted by providing a spraying nozzle 8, to which a soln. mixture composed of sodium azide and hydrochloric acid in a tank 6 is fed by a pump 7, in a wet process denitrification--treating container 3 connected with exhaust gas flow pipes 4, 5 and reduces and removes the NOx by passing the exhaust gas into the sprayed atmosphere of the hydrogen azide soln. The plasma denitrification-treating section 2 is constituted by providing a cylindrical electrode 11 and a needle electrode 12 in a plasma denitrification treating container 9 connected to exhaust gas flow pipes 5, 10 and decomposes and removes the NOx remaining in the exhaust gas by passing the exhaust gas in the discharge plasma atmosphere.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention uses discharge plasma to remove nitrogen oxides (
The present invention relates to an exhaust gas treatment method and device for removing NOx).

0002

2. Description of the Related Art NOx is generated by combustion in internal combustion engines such as diesel engines, gas engines, and gas turbine engines. Measures to reduce NOx can be roughly divided into fuel conversion, combustion improvement, and exhaust gas denitrification. Among these, fuel conversion and combustion improvement have a limited NOx reduction effect (20% to 50%), making it difficult to respond to stricter regulations such as the Air Pollution Control Act.

[0003] There are two types of denitrification technology: dry method and wet method.
Currently, the wet selective catalytic reduction method (
(hereinafter referred to as the ammonia denitrification method). In the ammonia denitrification method, ammonia is injected into exhaust gas and brought into contact with a denitrification catalyst installed downstream, and NOx is decomposed into harmless nitrogen and water through the following reduction reaction. V as a catalyst
The 2O5-WO3-TiO3 system is the mainstream.

4NO+4NH3+O2→4N2+6H2O
...(1) NO+NO2+2NH
3→2N2+3H2O…(2
) Furthermore, as a dry method, there is an exhaust gas treatment device that uses discharge plasma.

[0005]

[Problems to be Solved by the Invention] The exhaust gas treatment apparatus using the ammonia denitration method described above has the following problems.

(1) Ammonia is required to decompose NOx. This ammonia is a harmful and dangerous gas, so it must be handled with great care, and is also subject to legal regulations such as the Poisonous and Deleterious Substances Control Act, the High Pressure Gas Control Act, the Offensive Odor Control Act, the Air Pollution Control Act, and the Industrial Safety and Health Act. It is regulated by laws such as the Dangerous Goods Ship Transportation and Storage Regulations, the Port Regulations Law, and the Aviation Law.

(2) The operating temperature is limited to 320 to 400°C. If the temperature is below 320°C, the denitrification rate will decrease and the catalyst will deteriorate, and if it is above 450°C, the catalyst function will deteriorate.

(3) Miniaturization is difficult. As can be seen from the above-mentioned reaction equation, since the NOx displacement reaction is equimolar, it is necessary to inject into the exhaust gas approximately the same amount of ammonia as the amount of NOx to be denitrified, which increases the size of the ammonia storage equipment, catalyst, etc.

(4) There is a limit to the denitrification rate of 50 to 80%.

(5) The catalyst deteriorates. Lifespan approximately 2 years (80
00 hours) Deterioration progresses due to exhaust gas components (soot dust, SOx, etc.). Since the catalyst is based on precious metals and is expensive, it is economically disadvantageous.

[0011] As described above, the wet ammonia denitrification method has various problems.

In addition, exhaust gas treatment equipment that uses discharge plasma, which is a dry method, is inefficient due to the fact that discharge occurs at atmospheric pressure, which tends to cause fireworks discharge, and it takes a long time to obtain a high denitrification rate. Electricity is required. In order to reduce the discharge current and expand the discharge area using corona discharge,
This leads to complicated electrodes. Due to these problems, it is difficult to apply an exhaust gas treatment device using discharge plasma to a diesel engine or the like that has a large amount of NOx emissions.

[0013] This invention solves these problems,
The purpose is to provide a simple exhaust gas treatment technology with a high denitrification rate.

[0014]

The invention as set forth in claim 1 is a method for removing NOx from exhaust gas containing NOx, in which the following steps are sequentially performed.

(1) A step of reducing and removing NOx by circulating exhaust gas in an atmosphere in which a hydrogen azide solution is sprayed.

(2) A step of decomposing and removing remaining NOx by circulating exhaust gas in a discharge plasma atmosphere.

[0017] Furthermore, the invention stated in claim 2
In an apparatus for removing NOx from exhaust gas containing x, the following means (1) and (2) are provided.

(1) A wet denitration treatment section that performs a first denitration treatment on exhaust gas. This wet denitrification processing section uses the following means (
It is equipped with a) to (d).

(a) Tank for storing hydrogen azide solution.

(b) A transport device for transporting the solution from the tank of (a).

(c) A wet processing container through which exhaust gas flows.

(d) A spraying device for spraying the solution conveyed from the tank in (a) into the wet processing container.

(2) A plasma denitrification processing section that performs a second denitrification process using discharge plasma on the gas after the first denitrification process. This plasma denitrification processing section includes the following means (e) to (
g).

(e) A plasma processing vessel through which exhaust gas flowing out from the wet processing vessel flows.

(f) A plasma generation electrode installed inside the plasma processing container.

(g) A plasma generation power source that applies voltage to the plasma generation electrode.

[0027]

According to the present invention, the exhaust gas first flows into the wet treatment section and is subjected to the first denitration treatment. That is, the hydrogen azide solution is transported to the spray device by the transport device, and the solution is sprayed by the spray device. As a result, a spray atmosphere of hydrogen azide solution is generated inside the wet processing container. As the exhaust gas flows through this atmosphere, NOx in the exhaust gas reacts with hydrogen azide to be reduced and removed. In this wet denitrification treatment, even if the exhaust gas has a high NOX concentration, the NOX concentration can be easily reduced to a certain degree.

After this, the exhaust gas flows into the plasma denitrification processing section, and a second denitration processing (plasma denitration processing) is performed. That is, by driving the plasma generation power source and applying a voltage to the plasma generation electrode, discharge plasma is generated inside the plasma processing container. By flowing the exhaust gas through this discharge plasma atmosphere, NOx remaining in the exhaust gas is decomposed and removed. Since the NOX concentration of the exhaust gas has been reduced in advance by wet denitrification treatment, effective denitrification treatment is performed by this plasma denitrification treatment, and a high denitrification rate can be achieved.

[0029]

Embodiments Hereinafter, embodiments of the present invention will be described based on the drawings.

FIG. 1 shows an outline of an exhaust gas treatment apparatus according to an embodiment of the present invention. In the figure, arrows indicate the flow of exhaust gas. This apparatus consists of a wet denitrification processing section 1 and a plasma denitration processing section 2.

In the wet denitration processing section 1, 3 is a wet denitration processing container. This processing container 3 has an exhaust gas distribution pipe 4.
, 5 are connected, and the exhaust gas is passed from the pipe 4 to the processing vessel 3.
The water flows into the interior of the pipe 5 and flows out through the pipe 5.

Tank 6 is for storing a mixed solution of sodium azide and hydrochloric acid. Pump 7 transports this mixed solution to spray nozzle 8. The spray nozzle 8 is installed inside the processing container 3 and sprays the mixed solution toward the opening of the tube 4 .

Further, in the plasma denitrification processing section 2, 9
is a plasma denitrification treatment vessel. Exhaust gas distribution pipes 5 and 10 are connected to this plasma denitrification processing container 9,
Exhaust gas treated in the wet denitrification processing section 1 flows into a processing container 9 through a pipe 5, and flows out through a pipe 10 to the outside.

A cylindrical electrode 11 and a needle electrode 12 are provided inside the processing container 9. The cylindrical electrode 11 is provided at the opening of the tube 5 so that exhaust gas flowing from the tube 5 flows through the cylindrical electrode 11. The needle electrode 6 is fixed at a position on the axis of the cylindrical electrode 11. The plasma generation electrode 13 applies a high voltage (direct current, alternating current, high frequency, or pulse) to the electrodes 11 and 12 to generate plasma. Electrode 11
, 12 can be arbitrarily selected to be used as the positive electrode or the negative electrode.

In the above structure, exhaust gas discharged from a diesel engine or the like passes through the pipe 4 and first reaches the wet denitrification section 1. At this time, by driving the pump 7, the mixed solution in the tank 6 is sprayed from the spray nozzle 8, and a spray atmosphere 14 of the mixed solution is formed near the opening of the pipe 4. During the process in which the exhaust gas that has flowed into the processing container 3 from the pipe 4 flows through this spray atmosphere 14, N in the exhaust gas is
Ox is reduced and removed. This main reaction is as follows (3) ~
It is expressed by equation (5).

NO+NO2+H2O→2HNO2
...(3) 6NaN3+6H
Cl→6N3H+6NaCl…(4)
2HNO2+6N3H→10N2+4H2O
(5) Since the mixed solution is sprayed toward the opening of the tube 4, the exhaust gas flowing out from the tube 4 flows through the spray atmosphere, and the reaction of equation (3) occurs effectively. Furthermore, as shown in equation (4), N3+ is liberated by adding acid (HCl) to the mixed solution, so the reaction in equation (5) proceeds. It was confirmed that in addition to hydrochloric acid, sulfuric acid, nitric acid, acetic acid, etc. can be used as acids to be added to the mixed solution. In this wet denitration treatment, the treatment may be performed to such an extent that the NOx concentration is reduced to 100 to 150 ppm. Therefore, the consumption of reagents (such as NaN3) can be reduced.

After this, the exhaust gas passes through the tube 5 and is led to the tube 10 through the cylindrical electrode 11. Here, by driving the plasma generation power source 13, corona discharge is generated between the electrodes 11 and 12. When the exhaust gas flowing out from the cylindrical electrode 11 passes through the discharge plasma atmosphere 15, NOx remaining in the exhaust gas that could not be removed by the wet denitration process is decomposed and removed, as shown in the following equation (6). be done.

2NO→N2+O2
...(6) The discharge path of the corona discharge is formed in the shape of a cap at the opening of the cylindrical electrode 11, and the inflowing exhaust gas always passes through the plasma atmosphere, so that the decomposition processing efficiency is improved. Furthermore, in the plasma denitrification process, the denitration rate is low when the NOx concentration is high, but the denitration rate is high when the NOx concentration is low. When the NOx concentration is 100 to 150 ppm or less, a denitrification rate of 80% or more can be obtained. As mentioned above, wet denitrification treatment reduces NO
Since the NOx concentration is treated to about 100 to 150 ppm, it is possible to reduce the NOx concentration to 20 ppm or less by plasma denitrification treatment.

This exhaust gas treatment device is applicable to the treatment of all types of exhaust gas containing NOx, and is particularly suitable for treating exhaust gas from diesel engines and the like with a high concentration of NOx.

[0040]

[Effects of the Invention] As explained above, according to the present invention,
A first denitrification process is performed by circulating exhaust gas in a spray atmosphere of a hydrogen azide solution, and then a second denitration process is performed by circulating exhaust gas in a discharge plasma atmosphere.
Since the denitrification process is carried out, it has the following effects.

(1) The remaining NOx that was not completely reduced and removed by the first denitrification process is decomposed and removed by the second denitrification process.
Since NOx is removed, a high denitrification rate is possible even for exhaust gas with a particularly high concentration of NOx.

(2) Ammonia, which is troublesome to handle, is not required, and the treatment can be carried out using a liquid agent (for example, an azide compound aqueous solution and an acid solution), so handling is easy and the equipment can be made smaller. Become. Furthermore, since the first denitrification treatment does not necessarily require a high denitrification rate,
The amount of liquid used can be reduced.

(3) The usable temperature range is wider than that of the ammonia denitrification method.

(4) Since no catalyst is used, there is no need to replace the catalyst, which is economically advantageous.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an exhaust gas treatment device according to an embodiment of the present invention.

[Explanation of symbols]

1...Wet denitrification processing section 2...Plasma denitrification processing section 3,9...processing container 6...Tank 7...Pump 8...Spray nozzle 11, 12...electrode 13...Power supply for plasma generation

Claims (2)

[Claims] Claim 1: In a method for removing NOx from NOx-containing exhaust gas, NOx is reduced and removed by flowing the exhaust gas in a hydrogen azide solution spray atmosphere, and then in a discharge plasma atmosphere. An exhaust gas treatment method characterized in that residual NOx is decomposed and removed by circulating exhaust gas. 2. An apparatus for removing NOx from NOx-containing exhaust gas, comprising: a wet denitration treatment section that performs a first denitration treatment on the exhaust gas; and a discharge plasma treatment unit that performs a first denitration treatment on the exhaust gas; a plasma denitrification processing section that performs a second denitration processing using The plasma denitrification processing section includes a wet processing container that carries out a process, and a spraying device that sprays a solution conveyed from the tank into the wet processing container, and the plasma denitrification processing unit is configured to perform plasma processing in which exhaust gas flowing out from the wet processing container circulates inside the wet processing container. An exhaust gas treatment device comprising: a container; a plasma generation electrode installed inside the plasma processing container; and a plasma generation power source that applies voltage to the plasma generation electrode.