JPH05237337A - Exhaust gas treatment method and exhaust gas treatment device - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To provide an exhaust gas treatment method and apparatus for highly efficiently removing nitrogen oxides NOx and sulfur oxides SOx in a large amount of exhaust gas. In a plasma reactor, a trigger electrode 34 surrounded by a dielectric material 32b having a photocatalytic action and a main electrode 36 having a Chan-shaped semicircular cross section are installed in parallel, and the main electrode 36 side of the trigger electrode 34 is provided. A corona preionization mesh electrode 38 is installed. Photocatalyst layers 32a and 32c having a plate-like structure supporting a photocatalyst are provided so as to surround the electrodes 34 and 36 at the inlet and outlet of the exhaust gas. [Effect] NOx and SOx are immobilized as ammonium nitrate and ammonium sulfate at a high removal rate by the plasma excitation and the action of the photocatalyst, and are detoxified.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a power plant boiler, a diesel engine, a gas turbine, various combustion furnaces,
Further, an exhaust gas treatment method and an exhaust gas treatment apparatus for treating nitrogen oxide NOx and sulfur oxide SOx contained in gases discharged from various combustion engines such as automobiles with discharge plasma such as glow discharge, pulse glow discharge, pulse corona discharge In particular, the present invention relates to an exhaust gas treatment method and an exhaust gas treatment apparatus for treating nitrogen oxides NOx and sulfur oxides SOx contained in exhaust gas with discharge plasma and a photocatalyst in a large amount and at a high removal rate.

[0002]

2. Description of the Related Art A conventional exhaust gas treating apparatus using glow discharge plasma is disclosed in Japanese Patent Laid-Open Nos. 1-236924 and 2-20.
3920, JP-A-2-227117, JP-A-2-241519
It is proposed in the Japanese publication. An outline of a method for treating nitrogen oxides NOx and sulfur oxides SOx in exhaust gas by a conventional device will be described with reference to FIGS. 4 to 7.

In FIG. 4, the exhaust gas from the combustion furnace 101 has its dust removed by a dust remover 103, and ammonia is supplied from an ammonia supply pipe 105 in the range of several liters / minute to several tens of liters / minute. 108. As shown in FIG. 5, the plasma reactor 108 has a large number of holes 1 in the exhaust gas introducing pipe, that is, the internal electrode 112.
14 is adopted, or, as shown in FIG. 6, a structure in which a mesh-shaped electrode 116 covered with a dielectric is arranged substantially at right angles to the exhaust gas flow path, or, as shown in FIG. 7, A structure in which a saw-toothed electrode 117 whose surface is covered with a dielectric is arranged is adopted to improve the stability of discharge and increase the amount of gas treatment.

Although the reactions that take place in the plasma are complex,
It is understood as follows. Plasma reactor 10
In 8, the presence of ammonia as a buffer gas that promotes the chemical reaction, when a voltage is applied between the first electrode and the second electrode to generate glow discharge plasma, the following reaction occurs and NH ₃ → NH ₂ ＋ H ………………………………………………………… (1) 2NO ₂ → 2NO + O ₂ ………………………………………………… ( 2) 2NO + O ₂ → N ₂ + 2O ₂ ……………………………………………… (3) NH ₂ + NO → N ₂ + H ₂ O ……………………………… …………… (4) 2NH ₂ + SO ₂ → S + N ₂ + 2H ₂ O ………………………………… (5) Nitrogen oxide NOx and sulfur oxide SOx are detoxified. It

When ammonia is present as a buffer gas for promoting the chemical reaction and the structure of the electrode is properly adjusted, 1
Even with an exhaust gas amount of Nm ³ / min or more, a removal rate of 80% or more for nitrogen oxide NOx and a removal rate of 90% or more for sulfur oxide SOx will be obtained. It is being used as an exhaust gas pollution control device for various devices associated with combustion such as a gas turbine.

[0006]

However, in the above-mentioned conventional apparatus, the amount of exhaust gas treated to obtain the NOx removal rate of 80% or more is about 1.3 Nm ³ / min per apparatus. On the other hand, for example, the most common one for cogeneration
The amount of exhaust gas from a medium- or small-sized diesel engine of 00 kW to 1000 kW class is about 10 to 100 Nm ³ / min, and the amount of exhaust gas further increases in a gas turbine.
In order to put these various combustion devices into practical use as an exhaust gas pollution control device, the above conventional device has a too small throughput.

Further, since there is no preionization system, the electron density of the discharge plasma is small and the action of exciting atoms is small. Therefore, when the exhaust gas treatment amount increases, spatially uniform plasma is not formed, and the removal rate of nitrogen oxides NOx and sulfur oxides SOx decreases.

Further, when a large amount of high-pressure / high-density exhaust gas is processed, glow discharge plasma is very locally generated or not generated at all, which is not suitable for large-scale processing.

When a large amount of exhaust gas is treated, for example, even in the electrode structure shown in FIG. 6 which is considered to be most suitable for the large amount treatment, it is necessary to widen the space portion of the mesh electrode 116 through which the exhaust gas flows. On the other hand, if the space of the mesh electrode 116 is widened, the spatial uniformity of the glow discharge plasma is impaired.

As a result, even in the case of treating exhaust gas of a medium- or small-sized diesel engine or a gas turbine, it is necessary to connect a large number of small-capacity devices in parallel, which increases the construction cost of the device, resulting in a considerably large device scale. Not suitable for cogeneration in big cities.

When high-energy electrons in discharge plasma excite exhaust gas components, various oxidizing active species are generated.
The oxidizing active species are nitrogen oxide NOx and sulfur oxide S.
Collide with Ox and oxidize them. However, if the treatment progresses and the concentrations of nitrogen oxides NOx and sulfur oxides SOx decrease, the probability of collision between the oxidizing active species and the nitrogen oxides NOx and sulfur oxides SOx decreases, and the removal efficiency per energy decreases. To do. Therefore, there is a drawback that the amount of energy required to obtain a high removal rate increases.

In order to suppress energy loss and obtain a high removal rate, it is necessary to effectively use plasma energy and generate as many oxidizing active species as possible. The discharge plasma has energy loss such as bremsstrahlung, cyclotron radiation, and radiation due to excitation / recombination mainly caused by deceleration of electrons. However, until now, the emission energy from the discharge plasma has hardly been used for treating exhaust gas.

An object of the present invention is to provide an exhaust gas treatment method and an exhaust gas treatment apparatus for effectively utilizing emission energy from discharge plasma to remove nitrogen oxides NOx and sulfur oxides SOx in a large amount of exhaust gas with high efficiency. Is to provide.

[0014]

The above object is to dispose a photocatalyst which is excited by light emission from the discharge plasma and has an activity at a position surrounding the discharge plasma such as the inner surface of the discharge tube, the surface of the discharge electrode, and the front and rear of the discharge electrode. In addition to the energy of the plasma itself, the emission energy of the plasma can be achieved by effectively using it for exhaust gas treatment.

That is, according to the present invention, in order to achieve the above object, nitrogen oxides NOx and / or sulfur oxides S.
In a method of treating exhaust gas containing Ox by introducing it into discharge plasma, the exhaust gas is mixed with ammonia in an amount equal to or less than the equivalent of nitrogen oxide NOx and / or sulfur oxide SOx,
Nitrogen oxide NOx and / or sulfur oxide SOx is fixed as an ammonium salt in the presence of a discharge plasma and a photocatalyst which is pre-ionized by a corona or spark discharge and becomes active in response to light from the discharge plasma. It proposes an exhaust gas treatment method for removing carbon dioxide from exhaust gas.

In order to achieve the above object, the present invention also provides nitrogen oxide NOx and / or sulfur oxide SOx.
In an exhaust gas treatment apparatus for introducing exhaust gas containing plasma into plasma reaction means and detoxifying the discharge plasma, means for injecting ammonia into the exhaust gas and at least the inside of the discharge tube for generating discharge plasma, the surface of the discharge electrode, and at least before and after the discharge electrode. Exhaust gas consisting of a plasma reaction means for reacting the exhaust gas and ammonia with a photocatalyst that is partially activated by light from the discharge plasma and has an activity, and a dust collection means for separating the substance immobilized by the plasma reaction means from the exhaust gas A processing device is proposed.

The emission energy from the discharge plasma is distributed over a wide range from the infrared region to the X-ray region, but the wavelength in the ultraviolet region is particularly large. Therefore, TiO ₂ , ZnO, SrTiO ₂ and Zn whose band gap is in the ultraviolet region are
A substance such as S can be used as a photocatalyst. In particular, TiO ₂ which can be used in the presence of oxygen and has SOx resistance is most desirable.

[0018]

The inventors previously mentioned in Japanese Patent Application No. 3-260664 that nitrogen oxides NOx and SOx contained in a large amount of exhaust gas.
As an exhaust gas treatment device for removing the exhaust gas, an ammonia injecting means that is connected to an exhaust gas duct through which exhaust gas containing nitrogen oxides NOx and sulfur oxides SOx flows and injects ammonia, and an exhaust gas into which the ammonia is injected are introduced to discharge an ammonium salt by discharge plasma. As a result, an apparatus having a reaction means for producing solid matter as described above and a dust collecting means for separating solid matter produced by the reaction means from exhaust gas was proposed.

In this apparatus, the exhaust gas containing the nitrogen oxides NOx and the sulfur oxides SOx is mixed with ammonia in an equivalent amount or less and introduced into the reaction means at atmospheric pressure to several atmospheric pressures. When a high-voltage short pulse is applied to each of the preionization unit composed of the anode plate electrode and the cathode mesh electrode of the reaction means and the main discharge field composed of the cathode mesh electrode and the anode main electrode having the Chan-shaped semicircular cross section, first, , Corona or spark discharge occurs in the preionization part, and electrons are supplied to the main discharge field. Subsequently, a high-density pulse glow discharge is generated in the main discharge field using the generated electrons as nuclei, and plasma having an electron density comparable to that of a high-pressure arc is formed. This glow discharge is a short-time discharge of several tens of ns, and most of the injection energy is used for accelerating light electrons. Therefore, the generated high-energy electrons effectively excite the exhaust gas component.

Although the reaction in plasma is complicated, nitrogen oxides NOx and sulfur oxides SO are generated by the following reactions.
x is fixed as ammonium nitrate and ammonium sulfate, respectively. a. Generation of oxidative active species N ₂ , O ₂ , H ₂ O, + e ~ → OH, H, HO ₂ (6) b. Oxidation of nitrogen oxide NOx and sulfur oxide SOx NOx + (OH, H, HO ₂ ) → HNO ₃ ………………………… (7) SOx + (OH, H, HO ₂ ) → H ₂ SO ₄ …………………………………… (8) c. Formation of ammonium nitrate and ammonium sulfate HNO ₃ + NH ₃ → NH ₄ NO ₃ ………………………………………… (9) H ₂ SO ₄ + 2NH ₃ → (NH ₄ ) ₂ SO ₄ ………… (10) Nitrogen oxide NOx and sulfur oxide SOx fixed ammonium salts are separated and removed from the exhaust gas by the dust collecting means.

When a very small amount of ammonia is added to the extent that the chemical reaction is promoted, (1)-
It is also possible that the reaction of (5) occurs.

Pre-ionization in the reaction means makes it possible to efficiently excite the exhaust gas by high energy / high density electrons in the plasma, and when the exhaust gas flow cross-flows with the discharge direction, the residence time of the exhaust gas becomes short. Because it will
A large amount of exhaust gas can be detoxified with a high removal rate.

Glow discharge is difficult to generate under conditions other than vacuum, but when pre-ionization is used as a trigger, glow discharge under pressure becomes possible. Therefore, the volumetric flow rate can be reduced by pressurization, and the exhaust gas treatment device can be made compact.

Thus, when the exhaust gas containing nitrogen oxide NOx and sulfur oxide SOx is introduced into the discharge plasma of pulse glow discharge, glow discharge, pulse corona discharge, etc., high-energy electrons in the plasma excite exhaust gas components. To produce various oxidatively active species. The generated oxidizing active species oxidize nitrogen oxides NOx and sulfur oxides SOx, and solidify as ammonium nitrate and ammonium sulfate by ammonia added to the exhaust gas. If this solid matter is removed, the exhaust gas can be detoxified. In the case where a small amount of ammonia is added to the extent that it promotes a chemical reaction, detoxification treatment can be performed by the excitation action of ammonia by plasma and the reduction action of nitrogen oxide NOx and sulfur oxide SOx by the excited ammonia. There is also.

However, in this apparatus, as already described, when the high-energy electrons in the discharge plasma excite the exhaust gas component, various oxidizing active species are generated. The oxidizing active species are nitrogen oxide NOx and sulfur oxide SOx.
And oxidize them. However, if the treatment progresses and the concentrations of nitrogen oxides NOx and sulfur oxides SOx decrease, the probability of collision between the oxidizing active species and the nitrogen oxides NOx and sulfur oxides SOx decreases, and the removal efficiency per energy decreases. To do. Therefore, there is a drawback that the amount of energy required to obtain a high removal rate increases.

In order to suppress the energy loss and obtain a high removal rate, it is necessary to effectively use the plasma energy and generate as many oxidizing active species as possible. The discharge plasma has energy loss such as bremsstrahlung, cyclotron radiation, and radiation due to excitation / recombination mainly caused by deceleration of electrons. These energy losses are about 20% of the total plasma energy, of which the emission energy in the ultraviolet region accounts for 60% to 80%. Therefore,
The energy available for photocatalytic excitation in the ultraviolet region is about 10% to 15% of the total plasma energy. But,
Until now, the emission energy from the discharge plasma has hardly been used for treating exhaust gas.

Therefore, in the present invention, the photocatalyst is arranged at a position surrounding the plasma such as the inner surface of the discharge tube of the discharge plasma reactor, the surface of the discharge electrode, the front and rear of the discharge electrode, and the like. By generating ultraviolet rays having a wavelength of 400 nm or less, which occupies 10% to 15% of the total amount of electrons, on the photocatalyst surface, electrons and holes are formed, and active species of oxygen captured by the electrons and holes are generated.
Nitrogen oxide NOx such as N ₂ O and sulfur oxide SOx such as SO and SO ₂ are rendered harmless to N ₂ , S and O ₂ . That is, in addition to the conventional detoxification process using discharge plasma, a detoxification process using a photocatalyst excited by light emission from plasma can be performed in parallel, and the removal efficiency of nitrogen oxides NOx and sulfur oxides SOx is increased. That is, the energy for removing the same amount of exhaust gas and the same concentration of nitrogen oxides NOx and sulfur oxides SOx is more than that of the conventional one.
It can be reduced by about 0% to 15%.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of an exhaust gas treating apparatus according to the present invention will be described with reference to FIGS. FIG. 1 is a block diagram for explaining the overall configuration common to the embodiments of the exhaust gas treating apparatus according to the present invention. Exhaust gas discharged from the gas turbine 2 or the diesel engine 4, which is the target of the exhaust gas countermeasure, is transferred to the waste heat boiler 10 for heat recovery through the exhaust pipe 6 or the exhaust pipe 8. The exhaust gas that has passed through the waste heat boiler 10 is introduced into the plasma reactor 14 which is a feature of the present invention through the exhaust pipe 12. On the other hand, ammonia is
It is supplied from the supply pipe 18 of the ammonia supply device 16 to the reactor inlet pipe 20 of the plasma reactor 14 and mixed with the exhaust gas. Electric power for generating plasma is supplied from the power supply 22 to the electrodes of the plasma reactor 14. The plasma reactor 14 solidifies nitrogen oxides NOx and sulfur oxides SOx in the exhaust gas as ammonium nitrate and ammonium sulfate, and sends them to the dust collector 26 together with the exhaust gas through the reactor outlet pipe 24. The dust collector 26 removes and collects ammonium nitrate and ammonium sulfate solidified in the plasma reactor 14. This dust collector 26
An electrostatic precipitator, a bag filter, or the like can be used for the. The clean exhaust gas obtained by removing the nitrogen oxides NOx and the sulfur oxides SOx in the form of ammonium nitrate and ammonium sulfate is discharged from the exhaust pipe 28 to the stack 3
It is released into the atmosphere through 0.

FIG. 2 is a perspective view showing the structure around the electrodes of the plasma generating portion of the high density discharge plasma reactor 14 used in one embodiment of the exhaust gas treatment apparatus according to the present invention. In this embodiment, a flat plate electrode (anode) 34 which is surrounded by a dielectric 32b made of a ceramic having a photocatalytic action such as TiO ₂ and serves as a trigger electrode and a main electrode (anode) 36 having a Chan-shaped semicircular cross section are parallel to each other. It is installed in. The plate electrode 34 is surrounded by a dielectric 40, and a corona preionization mesh electrode (cathode) 38 is installed on the side of the main electrode 36. Chang-shaped semi-circular cross-section electrode 3 that contacts exhaust gas
6 and the corona preionization mesh electrode 38 are covered with and protected by a ceramic having a thickness of several microns, which is resistant to oxidation, such as alumina. Further, at the inlet and outlet of the exhaust gas flowing so as to traverse between the electrodes 34 and 36, a honeycomb structure carrying a photocatalyst such as TiO ₂ so as to surround the electrodes 34 and 36, or slightly open in the electrode direction. The photocatalyst layers 32a and 32c having the plate-like structure are installed.

When a high voltage pulse of several tens of ns and several tens of kV is applied from the high voltage power source 22 to the electrodes 34, 36 and 38, corona discharge occurs in the preionization electrode portion composed of the flat plate electrode 34 and the mesh electrode 38, Electrons are supplied to the main discharge field. A glow discharge is generated between the mesh electrode (cathode) 38 and the main electrode (anode) 36 using these electrons as nuclei, and a plasma having an electron density of 10 ²¹ / m ^{3 at} maximum, which is almost equal to that of a high-voltage arc, is formed. .. Quartz glass is usually used for the dielectric 36, but a dielectric such as ceramic can also be used. Although not shown here, in order to introduce the exhaust gas into the main discharge field at a predetermined speed, a line flow fan may be provided in the reactor inlet pipe 20 as needed.

When nitrogen oxides NOx and sulfur oxides SOx are removed by using such a high-density pulse glow discharge plasma reactor 14, untreated exhaust gas condition flow rate 60 Nm ³ / min NOx concentration 1000 ppm SOx concentration 600 ppm discharge condition pulse Energy 17J / pulse / l (17KJ / N
m ³ ) Number of repetitions 1000 Hz Exhaust gas condition after treatment NOx concentration 100 ppm SOx concentration 30 ppm Removal efficiency NOx 90% SOx 95% The results were obtained. That is, according to the present invention, the pulse energy required to obtain the same processing efficiency can be reduced by about 10% as compared with the conventional discharge plasma processing.

FIG. 3 shows a high-density discharge cylindrical plasma reactor 14 used in another embodiment of the exhaust gas treating apparatus according to the present invention.
FIG. 3 is a perspective view showing a structure around an electrode of a plasma generating portion of FIG. In this embodiment, the linear electrode 42 is arranged at the center of the cylindrical plasma reactor 14, while Ti is provided on the inner wall.
A photocatalyst layer 32d such as O ₂ is formed, and pulse glow discharge, glow discharge,
Causes a pulsed corona discharge. The exhaust gas is introduced in the axial direction of the cylindrical plasma reactor 14 and is treated to be harmless with a high removal rate by the synergistic effect of plasma and photocatalyst.

In this embodiment, the discharge tube has a diameter of 30 cm and a length of 100 cm due to the multiple effects of efficient excitation of exhaust gas by high energy / high density electrons in plasma and photocatalyst and promotion of chemical reaction by addition of ammonia.
Using a very compact cylindrical plasma reactor of the order of magnitude, a large amount of exhaust gas of about 120 Nm ³ / min can be treated with a high removal rate of 90% or more. This processing amount corresponds to the exhaust gas amount of a small or medium-sized engine having an output of 1000 kW or less which is mainly used in cogeneration.

According to the above embodiments, the high energy / high density electrons in the plasma and the action of the photocatalyst efficiently excite the exhaust gas, shorten the time during which the exhaust gas stays in the plasma, and discharge the exhaust gas into the electrode. And it can be introduced at high speed perpendicular to the discharge direction. Therefore, compared with the conventional method, the flow resistance can be reduced, a large amount of exhaust gas can be flown between the electrodes, a large amount of exhaust gas can be treated with a high removal rate, and the energy efficiency can be increased by about 10%.

[0035]

According to the present invention, when the exhaust gas is excited by the high energy / high density electrons in the plasma, the photocatalyst excited by the light emission from the plasma is also used.
Efficient excitation is possible, the residence time of exhaust gas can be shortened, a large amount of exhaust gas can be treated with a high removal rate, and energy consumption can be reduced by about 10%.

Further, the pre-ionization enables glow discharge under pressure, the volumetric flow rate can be reduced, and the exhaust gas treating apparatus can be made compact.

Furthermore, in the case of processing only the plasma, but our it also there was the a greenhouse gas that is generated in the plasma N ₂ O is discharged untreated, in the photocatalyst N ₂
O can be effectively detoxified into N ₂ , O _2, etc., and especially N ₂ O
The amount can be significantly reduced.

[Brief description of drawings]

FIG. 1 is a block diagram illustrating an overall configuration common to an embodiment of an exhaust gas treating apparatus according to the present invention.

FIG. 2 is a perspective view showing a structure around electrodes of a plasma generating portion of a high-density discharge plasma reactor used in an embodiment of an exhaust gas treating apparatus according to the present invention.

FIG. 3 is a perspective view showing a structure around electrodes of a plasma generating portion of a high-density discharge cylindrical plasma reactor used in another embodiment of the exhaust gas treating apparatus of the present invention.

FIG. 4 is a block diagram showing an overall configuration of an exhaust gas treatment apparatus according to a conventional technique.

FIG. 5 is a perspective view showing an example of a structure of a reactor electrode portion in a conventional technique.

FIG. 6 is a perspective view showing another example of the structure of the reactor electrode section in the prior art.

FIG. 7 is a vertical cross-sectional view showing another example of the structure of the reactor electrode section in the prior art.

[Explanation of symbols]

 2 Gas turbine 4 Diesel engine 6 Exhaust pipe 8 Exhaust pipe 10 Waste heat boiler 12 Exhaust pipe 14 Plasma reactor 16 Ammonia supply device 18 Ammonia supply pipe 20 Reactor inlet pipe 22 High pressure power supply 22 Reactor outlet pipe 23 Dust collector 28 Exhaust Tube 30 Chimney 32 Photocatalyst layer 34 Flat plate electrode (anode) 36 Main electrode (anode) 38 Corona preionization mesh electrode (cathode) 40 Dielectric 42 Internal electrode 44 External electrode 101 Combustion furnace 102 Exhaust pipe 103 Dust remover 104 Exhaust pipe 105 Ammonia supply pipe 106 Ammonia supply device 107 Exhaust gas inlet pipe 108 Plasma reactor 109 Power supply 110 Exhaust gas outlet pipe 111 Electrical insulating pipe 112 Internal electrode 113 External electrode 114 Hole 115 First electrode 116 Second electrode 117 Sawtooth second electrode 118 Flat plate No. 1 electrode 1 9 dielectric

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location B01J 35/02 J 7821-4G

Claims (4)

[Claims] 1. A method of introducing exhaust gas containing nitrogen oxide NOx and / or sulfur oxide SOx into discharge plasma for treatment, wherein the exhaust gas has an equivalent amount of the nitrogen oxide NOx and / or sulfur oxide SOx or less. Ammonia is mixed, preionized by corona or spark discharge, and the nitrogen oxide NOx and / or the sulfur oxide SOx is ammonium salt in the presence of a discharge plasma and a photocatalyst which becomes active in response to light from the discharge plasma. And the ammonium salt is removed from the exhaust gas. 2. An exhaust gas treatment apparatus for introducing an exhaust gas containing nitrogen oxides NOx and / or sulfur oxides SOx into a plasma reaction means and detoxifying it by discharge plasma, a means for injecting ammonia into the exhaust gas, and the discharge. An inner surface of a discharge tube for generating plasma, a surface of a discharge electrode, and a plasma reaction means for reacting the exhaust gas with ammonia, which is provided with a photocatalyst activated by light from the discharge plasma on at least a part of the discharge electrode, An exhaust gas treating apparatus comprising: a dust collecting unit that separates an object fixed by the plasma reaction unit from the exhaust gas. 3. The exhaust gas treating apparatus according to claim 2, wherein the plasma reaction means includes a trigger electrode surrounded by a photocatalyst, and a main electrode having a Zhang-shaped semicircular cross section and arranged in parallel with the trigger electrode. A corona preionization mesh electrode installed on the main electrode side of the trigger electrode, and a photocatalyst layer having a plate-like structure that is provided at the inlet and outlet of exhaust gas so as to surround the trigger electrode and the main electrode and carries a photocatalyst. An exhaust gas treatment device comprising: 4. The exhaust gas treatment apparatus according to claim 2, wherein the plasma reaction means has a cylindrical plasma reaction container having an external electrode, an electrode arranged in a central portion of the cylindrical plasma reaction container, and An exhaust gas treatment apparatus comprising: a photocatalyst layer disposed on an inner wall of a cylindrical plasma reactor.