JP4472638B2 - Exhaust gas treatment method and apparatus - Google Patents

Description

TECHNICAL FIELD The present invention relates to an exhaust gas treatment method and an apparatus for treating the same, and suppresses reaction by-products (eg, N ₂ O, HNO ₂ , HNO ₃ , NO ₃ ⁻ , CO) in the exhaust gas, and efficiently converts nitrogen oxides. The present invention relates to a method and a purification device.

In general, nitrogen oxides such as nitrogen monoxide (NO) and nitrogen dioxide (NO ₂ ) are discharged with the supply of energy represented by power plants and diesel engines and the consumption of such energy. . Nitrogen oxides discharged into the environment cause photochemical smog and the like, and countermeasures are being considered as an important issue for environmental problems in large cities. Further, dinitrogen monoxide (N ₂ O) has attracted attention as a cause of global warming gas, which has become a problem in recent years.

  As a method for reducing nitrogen oxides, a combustion method, a catalyst method, a selective catalytic reduction method (SCR), an ammonia injection method, and, in recent years, technologies such as the catalyst method, non-thermal plasma, and electron beam There are known methods for reducing nitrogen oxides by combining them, and other methods for reducing nitrogen oxides by combining the above methods with methods using chemical substances or catalysts such as ammonia, hydrogen peroxide, and calcium chloride. It has been.

Among them, the plasma-chemical hybrid method is attracting attention. Regarding the direct non-thermal plasma method based on this principle, the following Patent Documents 1 to 3 have been proposed.
Japanese Patent Application Laid-Open No. 2000-117049 JP 2000-51653 A Japanese Patent Laid-Open No. 2001-300257

However, the conventional method using a catalyst such as the SCR method has a problem that it takes a great deal of cost to increase the removal efficiency of nitrogen oxides. In addition, in the conventional method using low temperature non-equilibrium plasma, in order to decompose and remove nitrogen oxides in the environment, in the reaction process, dinitrogen monoxide (N ₂ O), nitrate ions (NO ₃ ⁻ ), There was a problem that by-products such as nitrous acid (HNO ₂ ) and nitric acid (HNO ₃ ) were produced in large quantities, and these by-products were not removed. In order to purify these by-products by oxidation / reduction, there is a problem that the cost increases further. In the method using plasma, exhaust gas to be treated is directly flowed into a reactor, oxidized from NO to NO ₂ using non-thermal plasma, and treated with a chemical scrubber (Patent Documents 1 and 2), that is, non-thermal. A direct plasma method has been proposed, but the energy efficiency is relatively low. Since high temperature gas is allowed to flow through the plasma reactor, the processing efficiency is reduced. Further, since corrosive exhaust gas is caused to flow through the plasma reactor, there are problems such as corrosion of electrodes and the like.

  In the method of Patent Document 3, the exhaust gas is once cooled, the harmful gas contained in the exhaust gas is adsorbed on the adsorbent and directly decomposed into plasma, but the corrosive exhaust gas flows directly into the plasma reactor. There remains a problem that the electrodes and the like are corroded, and that a gas byproduct after plasma decomposition is not removed.

In order to solve the above-mentioned conventional problems, the present invention suppresses reaction by-products (for example, N ₂ O, HNO ₂ , HNO ₃ , NO ₃ ⁻ , CO) in exhaust gas and efficiently emits exhaust gas. An apparatus and method capable of processing are provided.

The exhaust gas treatment method of the present invention is a method for purifying exhaust gas containing nitrogen oxides, supplying air to an atmospheric pressure low temperature non-equilibrium discharge plasma reactor to generate radical gas, Supplying the exhaust gas to the oxidation reaction region and supplying the exhaust gas from a line separate from the radical gas generation line to the oxidation reaction region, thereby oxidizing nitrogen oxide in the exhaust gas with NO ₂ by the radical gas oxidized to the gas, then the oxidizing gas _{Na 2 SO 3, Na 2 S} , and by contacting at least the reduction reaction area with the reducing agent aqueous solution containing one compound selected from Na ₂ S ₂ O ₃ , by reduction reaction NO ₂ to nitrogen gas (N ₂₎ Runisaishi, wherein the reduction reaction region and the oxidation reaction zone is present on one wet reactor, the lower said oxidation reaction zone of the wet reactor There is a top the reduction reaction area of the wet reactor, and is characterized by circulating the aqueous solution of the reducing agent.

The exhaust gas treatment apparatus of the present invention is an apparatus for purifying exhaust gas containing nitrogen oxides, which is an atmospheric pressure low temperature non-equilibrium discharge plasma reactor for converting air into radical gas, and oxidation reaction of the radical gas. A line supplying the region, a line supplying the exhaust gas to the oxidation reaction region from a line separate from the radical gas generation line, and oxidizing the nitrogen oxide in the exhaust gas with NO ₂ by the radical gas and said oxidation reaction zone for oxidizing the gas, the oxidizing gas _{Na 2 SO 3, Na 2 S} , and Na ₂ S ₂ O ₃ at least one reducing reaction area with the reducing agent aqueous solution containing a compound selected from by contacting the NO ₂ comprises a reduction reaction region for reduction in nitrogen gas (N _2), present in the oxidation reaction zone and the reducing reaction zone one wet reactor, before A lower said oxidation reaction zone of the wet reactor, wherein a top the reduction reaction area of the wet reactor and the reducing agent aqueous solution is characterized in that it is a circulating.

The method and apparatus of the present invention supplies air radicalized by atmospheric pressure low-temperature non-equilibrium plasma and separately supplies exhaust gas to the oxidation reaction region, and oxidizes nitrogen oxide in the exhaust gas with NO ₂ by radical gas. NO ₂ is reduced to nitrogen gas (N ₂ ) by oxidizing to gas and then contacting the oxidizing gas with a reducing agent solution. Thereby, reaction by-products (for example, N ₂ O, HNO ₂ , HNO ₃ , NO ₃ ⁻ , CO) in the exhaust gas can be suppressed and efficiently removed.

In the present invention, air is treated with atmospheric low-temperature non-equilibrium plasma (hereinafter referred to as “low-temperature non-equilibrium plasma”) to generate radical gas, which is supplied to the oxidation reaction region and reacted with separately supplied exhaust gas. Thus, the nitrogen oxide in the exhaust gas is oxidized to an oxidizing gas containing NO ₂ by the radical gas, and then the oxidizing gas is brought into contact with the reducing agent solution to reduce NO ₂ to nitrogen gas (N ₂ ). In the above, the oxidation reaction region and the reduction reaction region are preferably present in one wet reactor.

The present invention introduces air into a plasma reactor, mixes radical gas of air component excited by low temperature non-equilibrium plasma with exhaust gas at the bottom of the wet reactor, oxidizes NO to NO ₂ , and then chemical scrubber ( Reduction with a wet reactor). Hereinafter, the method of the present invention is also referred to as “non-thermal remote plasma / chemical hybrid method”.

  The low temperature non-equilibrium plasma used in the present invention means an ionized plasma whose gas temperature is considerably lower than a normal gas combustion temperature (about 700 to 1000 ° C.), and usually means a plasma of 300 ° C. or lower. Even if the lower limit temperature is −200 ° C., it can be used. More preferable conditions are temperature: 100 ° C. or less, particularly preferably normal temperature (0 to 40 ° C.). Other preferable conditions are pressure: atmospheric pressure, relative humidity: 60% or less, applied voltage: 10 to 100 kV, peak current 1 to 100 A, frequency: 250 Hz to 1000 Hz.

  In the present invention, it is preferable that the oxidation reaction region and the reduction reaction region exist in one wet reactor. In particular, it is preferable that the wet reactor is a tower type or column type reactor, the oxidation reaction region is present in the lower part of the wet reactor, and the reduction reaction region is present in the upper part of the wet reactor. In this way, the device can be downsized.

The reducing agent solution is preferably an aqueous solution containing at least one compound selected from Na ₂ SO ₃ , Na ₂ S, NaOH, Na ₂ S ₂ O ₃ and Ca (OH) ₂ . An aqueous solution containing these compounds has a high reducing action and can be recycled.

The exhaust gas that can be treated in the present invention is combustion exhaust gas, and the components to be treated are NO, NO ₂ , N ₂ O, N ₂ O ₅ , SO ₂ , SO ₃ , volatile organic compounds (VOCs), dioxins. At least one selected from environmental pollutants, hydrocarbons, CO, CO _2, and water vapor (H ₂ O), which are typified by a class, is preferable. For example, nitrogen oxides (NO _x ) such as NO, NO ₂ , N ₂ O, and N ₂ O ₅ are reduced to nitrogen gas (N ₂ ), sulfur oxides (SO _x ) such as SO ₂ and SO ₃ , and carbonization. Volatile organic compounds (VOCs) such as hydrogen, CO, CO ₂ , toluene, benzene, xylene, and environmental pollutants such as dioxins, halogenated aromatic substances, and highly condensed aromatic hydrocarbons are harmless substances or the environment. It can be decomposed or converted into a low-load substance.

The advantages of the low temperature non-equilibrium plasma in the present invention are shown below.
(1) Since the gas to be plasma-treated is smaller and lower in temperature than the exhaust gas, the residence time in the reactor is increased, and activated radicals are efficiently formed.
(2) Plasma consumption energy per unit flow rate can be reduced.
(3) By optimizing with a small amount of radicals, it is possible to oxidize tens of times more NO. Therefore, the reactor can be miniaturized.
(4) Adaptable to high temperature exhaust gas. For example, high temperature exhaust gas of 300 ° C. or higher can be efficiently oxidized to NO ₂ by low temperature remote plasma of about room temperature (27 ° C.).

An embodiment of the present invention relates to an exhaust gas processing method and an apparatus for processing the same, and relates to a wet chemical using a reducing agent solution from a radical gas formed by low-temperature non-equilibrium plasma at atmospheric pressure installed separately from an exhaust gas line. Provided are an apparatus and a method capable of suppressing and efficiently treating reaction by-products (N ₂ O, HNO ₂ , HNO ₃ , NO ₃ ⁻ , CO, etc.) in exhaust gas by remote treatment injected into a scrubber.

In one embodiment of the present invention, a low-temperature non-thermal plasma reactor installed outside an exhaust gas flow channel and a wet chemical scrubber (wet reactor) into which radicals activated thereby are directly connected. Thus, the low-temperature non-thermal plasma reactor so supplying only air, it is possible to steady operation. That is, even if the exhaust gas flow rate fluctuates, it is not necessary to fluctuate the operating conditions of the low-temperature non-thermal plasma reactor if the plasma gas generation amount is set to the maximum required amount or more. In addition, energy efficiency is high and processing efficiency is also high. In addition, since only air flows in the plasma reactor, the problem of corrosion of electrodes and the like is also improved.

  Although the kind of low-temperature non-thermal plasma reactor and the kind of generated plasma are not particularly limited, the non-equilibrium plasma reactor described in the following examples can be given as a suitable example. Other methods of applying plasma are pulse discharge method by AC or DC voltage, silent discharge method, corona discharge method, creeping discharge method, barrier discharge method, honeycomb discharge method, pellet packed bed discharge method, arc discharge method, inductive coupling Type discharge method, capacitively coupled discharge method, microwave excitation discharge method, laser induced discharge method, electron beam induced discharge method, particle beam induced discharge method, or a combination method thereof can be used. That is, the plasma reactor used in the present invention can adopt various conceivable methods suitable for each method of applying plasma. In particular, it is convenient to use the non-equilibrium plasma as a non-equilibrium plasma generated by pulse corona discharge.

  The type of wet chemical scrubber is not particularly limited, and various types of wet chemical scrubbers can be used, but a Raschig ring-filled general chemical scrubber described in Example 1 below can be cited as a preferred example. In addition, a bubble scrubbing chemical scrubber can be cited as a suitable example.

(1) Explanation of reaction In this embodiment, removal of air pollutants such as nitrogen oxides NOx discharged from diesel engines, thermal power plants, etc. by a hybrid process combining a non-equilibrium plasma process and a wet chemical reaction process. It is an object. The chemical reaction of this process is a combination of the following two reactions.

Plasma process: NO + O ^* (oxygen radical) + M (third body object) → NO ₂ + M (1)
Wet chemical reaction process: 2NO ₂ + 4Na ₂ SO ₃ → N ₂ + 4Na ₂ SO ₄ (2)
NO which occupies most of the exhaust gas by the reaction (1) is oxidized to NO ₂ at a low cost, and NO ₂ is reduced to harmless water-soluble Na ₂ SO ₄ and N ₂ by the reaction (2). An agent different from Na ₂ SO ₃ (for example, Na ₂ S, NaOH, Na ₂ S ₂ O ₃ , Ca (OH) _2, etc.) may be used.

In this example, in a non-equilibrium plasma process (the above reaction (1)), an experiment was performed using a non-thermal remote (indirect) plasma method compared with a conventional direct plasma method, and the performances of the two were compared. Here, the method of flowing the exhaust gas to be treated directly into the reactor and oxidizing NO to NO ₂ is named the direct plasma method. On the other hand, a method of flowing air or a small amount of additives (hydrocarbon, ammonia, etc.) into the plasma reactor, injecting excited radical gas into the exhaust gas flow path, and oxidizing NO to NO ₂ is a non-thermal remote ( Indirect) Plasma method.
(2) Experimental apparatus of the present embodiment An outline of an experimental apparatus 50 using the non-thermal remote plasma method of the present invention is shown in FIG.

Compressed air is supplied from the compressor 32 to a dryer 33 equipped with an air filter to produce dry air, and this dry air is supplied to the nonthermal plasma reactor 1 by the mass flow controller 35 at a predetermined flow rate. A fast rising short pulse high voltage generated by an IGBT pulse power source (manufactured by Masuda Laboratories, PPCP Pulsar SMC (30/1000) 21) is applied to the non-thermal plasma reactor 1. Thereby, O ₃ , O ^* , An activated gas containing radicals such as OH and N was generated, and applied voltage, current, and power consumption of the nonthermal plasma reactor 1 were an oscilloscope (DL 1740 manufactured by Yokogawa Electric Corporation) 37, a high voltage probe, and a current probe (Sony Tektronix). The power consumption was determined from the integral value of the instantaneous power, and the activated gas thus obtained is directly injected into the chemical scrubber 11 of the wet reactor.

On the other hand, NO gas, which is an exhaust gas model gas, is supplied from the 2% NO cylinder 31 at a predetermined flow rate by the mass flow controller 34, supplied from the air supply line 51 at a predetermined flow rate by the mass flow controller 52, and mixed with NO. Then, the simulated exhaust gas (air diluted NOx, concentration 300 ppm) in which NO is adjusted to a predetermined concentration is directly injected into the chemical scrubber 11. The reaction (1) occurs in the oxidation reaction region 10 below the chemical scrubber 11, and the reaction (2) occurs in a portion above the bottom of the chemical scrubber 11. In this way, the reactions (1) and (2) are continuously caused in the chemical scrubber 11. Product gas passed through the ozone removing heater 38 was measured _{NO, NO X, CO, N} 2 O, the concentration of CO _2, O ₂ by a gas analyzer (Horiba PG-235 and VIA-510) 39. Reference numeral 40 denotes a gas discharge port, and reference numeral 41 denotes a Na ₂ SO ₃ aqueous solution tank.
(3) Plasma reactor of this example A schematic cross-sectional view of a non-thermal plasma reactor is shown in FIG. The non-thermal plasma reactor 1 has a cylindrical reaction by passing a stainless steel discharge wire electrode 3 having a diameter of 1.5 mm through an internal space of a cylinder 2 made of Pyrex (registered trademark) glass (quartz glass) having an inner diameter of 20 mm and an outer diameter of 24 mm. A copper mesh (effective length 260 mm) was wound around the outer wall of the tube 2 to form the ground electrode 4. A pulse high voltage power source 21 was connected between the discharge line electrode 3 and the ground electrode 4. The hollow portions below and above the cylinder 2 were sealed with silicone rubber stoppers 5 and 6. 7 is a perforated plate made of polytetrafluoroethylene, 8 is a gas supply port, 9 is a gas discharge port, and a and b are gas flows. The reaction (1) is realized by this plasma reactor.
(4) Wet reactor of the present example FIG. 3 shows a schematic cross-sectional view of a chemical scrubber (packed tower) 11 which is a wet reactor. A gas to be treated is caused to flow from the lower part to the upper part of the stainless steel tube 12 having an inner diameter of 55.5 mm and an outer diameter of 60.5 mm, and the Na ₂ SO ₃ aqueous solution 14 is sprayed from the upper part by a liquid spraying (spraying) nozzle 13. Wet chemical reaction (2) is performed. A Raschig ring (made of cylindrical glass, inner diameter 5 mm, outer diameter 7 mm, width 7.2 mm) 15 is filled in the interior to promote the reaction. 15a is an enlarged shape of the Raschig ring. The filling height of the Raschig ring 15 is 160 mm, the height of the liquid spray nozzle 13 is 340 mm from the gas inlet 16, and the difference in height from the gas inlet 16 to the Raschig ring start point is 100 mm. Reference numeral 17 denotes a gas outlet, and c and d denote gas flows. 18 is a manometer for measuring the height of the liquid, 19 is a valve, 20 is a liquid (drain) discharge port, and e is a discharged liquid flow.
(5) Experimental apparatus for direct plasma method used in comparative example FIG. 4 shows an outline of an experimental apparatus 30 for direct plasma method. NO gas is supplied from the 2% NO gas cylinder 31 by the mass flow controller 34 at a predetermined flow rate. On the other hand, compressed air is supplied from the compressor 32 to a dryer 33 equipped with an air filter to produce dry air, and this dry air is supplied by the mass flow controller 35 at a predetermined flow rate. Thereafter, mixed with NO and supplied to the plasma reactor 1 is a simulated exhaust gas (air diluted NOx, concentration 300 ppm) in which NO is adjusted to a predetermined concentration. A fast rising short pulse high voltage generated by an IGBT pulse power source (manufactured by Masuda Laboratories, PPCP Pulsar SMC (30/1000) 21) is applied to the plasma reactor 1. This causes the reaction (1) to occur. Next, the reduction treatment reaction (2) is carried out in the chemical scrubber 11. Next, the ozone analyzer 38 is passed through the ozone removal heater 38, and NO, NO _x , CO are analyzed by a gas analyzer (PG-235 and VIA-510 manufactured by Horiba, Ltd.) 39. , N ₂ O, CO ₂ , and O ₂ concentrations were measured, and the applied voltage, current, and power consumption of the non-thermal plasma reactor 1 were measured using an oscilloscope (DL 1740 manufactured by Yokogawa Electric Corporation) 37, a high-voltage probe, and a current probe (Sony). Measured with Tektronix, P6015A and P6021), the power consumption was determined from the integrated value of the instantaneous power. Scan outlet 41 is aqueous solution of Na ₂ SO ₃ tank.

(Example 1, Comparative Examples 1-3)
Example 1 uses the apparatus shown in FIG. 1, Comparative Example 1 is only the direct plasma processing apparatus 30 shown in FIG. 4, and Comparative Example 2 is a process in which the direct plasma apparatus 30 and wet reactor 11 shown in FIG. 3 is only the non-thermal remote plasma apparatus 50 shown in FIG. 1, and an NO _x removal experiment was conducted when the flow rate of the simulated gas was 5.0 L / min.

The simulated exhaust gas flow rate was 5.0 L / min, the remote radical gas flow rate was 0.5 L / min, and the initial NO concentration was 300 ppm. When the wet reactor 11 was used, the flow rate of the reducing agent aqueous solution flowing through the packed tower was 0.20 L / min, and the concentration of Na ₂ SO ₃ was 2.0 g / L. The frequency of the IGBT pulse power supply was set to 420 Hz. The residence time in the plasma reactor at this time was 0.84 s for the direct method and 8.4 s for the remote method.

  The above results are shown in FIGS. 5A-B and 6A-B. 5A shows only the direct plasma method (Comparative Example 1), FIG. 5B shows a process in which the direct plasma method and a wet reactor are directly connected (Comparative Example 2), FIG. 6A shows only the non-thermal remote plasma method (Comparative Example 3), and FIG. These are the data of the process (Example 1) which connected the non-thermal remote plasma method and the wet reactor directly.

Comparing FIGS. 5A-B and 6A-B, the non-thermal remote plasma method (FIGS. 6A-B) consumes less reactor power and the NO and NOx decrease compared to the direct plasma method (FIGS. 5A-B). It can be seen that the amount is large. Also, comparing FIGS. 6A-B, it can be seen that FIG. 6B has lower reactor power consumption and a greater reduction in NO and NOx. Although there were concerns about the generation of N ₂ O and CO as harmful by-products when plasma was applied, FIG. 6B, which is an example of the present invention, had N ₂ O of around 10 ppm and CO of 7 ppm or less. The CO ₂ concentration was around 360 ppm, and a decrease of several ppm was observed.

(Example 2, Comparative Examples 4 to 6)
Example 2 uses the apparatus shown in FIG. 1, Comparative Example 4 is only the direct plasma processing apparatus 30 of FIG. 4, and Comparative Example 5 is a process in which the direct plasma apparatus 30 and wet reactor 11 shown in FIG. 6 is only the non-thermal remote plasma apparatus 50 shown in FIG. 1, and an NO _x removal experiment was performed when the flow rate of the simulated gas was 7.0 L / min.

Next, the flow rate of simulated exhaust gas was 7.0 L / min, the remote radical gas was 0.7 L / min, and the initial concentration of NO was 300 ppm. When the wet reactor 11 was used, the flow rate of the reducing agent aqueous solution flowing through the packed tower was 0.20 L / min, and the concentration of Na ₂ SO ₃ was 2.0 g / L. The frequency of the IGBT pulse power supply was set to 420 Hz. The residence time in the plasma reactor at this time was 0.6 s for the direct method and 6.0 s for the remote method.

  The results are shown in FIGS. 7A-B and FIGS. 8A-B. 7A shows only the direct plasma method (Comparative Example 4), FIG. 7B shows a process in which the direct plasma method and a wet reactor are directly connected (Comparative Example 5), FIG. 8A shows only the non-thermal remote plasma method (Comparative Example 6), and FIG. These are the data of the process (Example 2) which connected the non-thermal remote plasma method and the wet reactor directly.

7A-B and 8A-B are compared, the non-thermal remote plasma method (FIGS. 8A-B) consumes less reactor power as in FIGS. 5A-B and 6A-B. Also, comparing FIGS. 8A-B, it can be seen that FIG. 8B has lower reactor power consumption and a greater reduction in NO and NOx. In FIG. 8B which is an example of the present invention, N ₂ O was around 10 ppm and CO was 7 ppm or less. The concentration of CO ₂ was around 370 ppm, and a decrease of several ppm was observed.

  9A-B show examples of voltage and current waveforms corresponding to FIGS. 8A-B, respectively.

(Example 3, Comparative Example 7)
Unit processing gas volume for the non-thermal remote plasma method and the wet reactor shown in FIG. 1 (Example 3) and the direct plasma method and the wet reactor shown in FIG. 4 (Comparative Example 7) The relation between the plasma consumption energy (SED) and the removal efficiency was investigated. That is, SED (plasma consumption energy per unit processing gas volume) was calculated from the reactor power consumption, and the relationship between SED, NO, and NOx removal efficiency was examined.

The result is shown in FIG. This is a result of performing plasma treatment and wet chemical treatment simultaneously at a flow rate of 7 L / min. From FIG. 10, when using the non-thermal remote plasma method (remote), about 30% SED = 35 J / L = 10 Wh / m ³ when using the direct plasma method (direct), about 80% NO, It can be seen that NOx is reduced and removed.

  From the above experiments, in the plasma-chemical hybrid process using the non-thermal remote plasma method of this example, the energy efficiency is greatly improved, and the unit flow rate is about 30% as compared with the case using the direct plasma method. It was confirmed that NOx was reduced and removed with the hit energy.

The advantages of the non-thermal remote plasma method found from the above experiments are shown below.
(A) Since the amount of gas to be plasma-treated is smaller than that of exhaust gas, when a plasma reactor of the same size is used, the residence time is increased, and the size can be reduced.
(B) The plasma energy consumption per unit flow rate can be reduced, and the energy efficiency can be further improved.
(C) If optimization is performed by injection with a small flow rate, it is possible to oxidize tens of times more NO.

Example 4
In Example 4, a pilot test using an actual boiler was conducted to verify the remote non-thermal plasma-chemical hybrid process technology of the present invention.

An experimental apparatus diagram is shown in FIG. The same reference numerals are given to the devices common to FIG. 1, and the description thereof is omitted. The boiler used was a smoke tube type small boiler 60 using A heavy oil as fuel. The exhaust gas from the boiler 60 was supplied from the exhaust gas supply line 23 to the oxidation reaction region 10 below the chemical scrubber 11. A pulse discharge reactor was used as the non-thermal plasma reactor 1. 21 High voltage power supply. The chemical scrubber 11 is filled with a filler as shown in FIG. 3 in order to promote the gas-liquid contact reaction. The aqueous solution of Na ₂ SO ₃ was supplied from the tank 41 to the spray 42 from the top of the chemical scrubber 11 and sprayed, recovered at the bottom, and returned to the top again using a pump.

The radical gas sucked in outside air and generated in the non-thermal plasma reactor 1 was carried by a fan 61 rotated by a motor, injected into an exhaust gas flue, and supplied to the oxidation reaction region 10 below the chemical scrubber 11. NO in the exhaust gas is oxidized to NO ₂ by radicals such as ozone, NO ₂ is reduced and removed to N ₂ by Na ₂ SO ₃ in the chemical scrubber 11, and exhaust gas from the boiler 60 exhausted from the top of the chemical scrubber 11 FIG. 12 shows the relationship between the plasma consumption energy per unit processing gas volume and the NO and NOx removal efficiency when the flow rate Q _g = 450 to 1170 Nm ³ / h and the radical gas flow rate Q _r = 50 to 180 Nm ³ / h. Show. From FIG. 12, it was confirmed that NO and NOx can be efficiently removed even with high-temperature exhaust gas.

  As a result, it was shown that the remote non-thermal plasma / chemical hybrid process technology of the present invention is also effective for actual boiler exhaust gas.

  The exhaust gas treatment method and apparatus of the present invention can be applied to a combustion system such as a diesel engine, a boiler, a gas turbine, or an incinerator.

BRIEF DESCRIPTION OF THE DRAWINGS Schematic of the apparatus which directly connected the reactor and wet reactor which perform the non-thermal remote plasma processing of this invention in one Example of this invention. The schematic sectional drawing of a non-thermal plasma reactor. The schematic sectional drawing of a chemical scrubber (packing tower). The schematic of the experimental apparatus of the direct plasma method of a comparative example. AB is a graph which shows the density | concentration change in the direct plasma processing method of a comparative example. A is a graph showing a concentration change of a comparative example, and B is a graph showing a concentration change in a treatment method in which a reactor for performing non-thermal remote plasma and a wet reactor are directly connected in one embodiment of the present invention. AB is a graph which shows the density | concentration change in the direct plasma processing method of a comparative example. A is a graph showing a concentration change in a comparative example, and B is a graph showing a concentration change in a treatment method in which a non-thermal remote plasma method and a wet reactor are directly connected in one example of the present invention. AB is a graph showing voltage and current waveforms. The graph which shows the removal efficiency of the plasma consumption energy per unit process gas volume, and nitrogen oxide. The schematic of the apparatus which processed the waste gas of the boiler in Example 4 of this invention using the non-thermal remote plasma method and wet reactor of this invention. The graph of the experimental data which investigated the relationship of NO and NOx removal efficiency of Example 4 and the plasma consumption energy per unit process gas volume .

Claims (16)

A method for purifying exhaust gas containing nitrogen oxides,
Supplying air to an atmospheric pressure low temperature non-equilibrium discharge plasma reactor to generate radical gas, supplying the radical gas to the oxidation reaction region,
By supplying the exhaust gas to the oxidation reaction region from a line separate from the radical gas generation line, nitrogen oxides in the exhaust gas are oxidized into an oxidizing gas containing NO ₂ by the radical gas,
Next, the oxidizing gas is brought into contact with an aqueous reducing agent solution containing at least one compound selected from Na ₂ SO ₃ , Na ₂ S, and Na ₂ S ₂ O _{3 in a} reduction reaction region, whereby NO ₂ is nitrogen gas. Runisaishi by reduction reaction (N _2),
The oxidation reaction region and the reduction reaction region are present in one wet reactor;
The lower part of the wet reactor is the oxidation reaction region, the upper part of the wet reactor is the reduction reaction region,
And the exhaust gas treatment method, wherein the reducing agent aqueous solution is circulated . Method of processing an exhaust gas according to claim 1 wherein the wet reactor is tower or column reactor. The exhaust gas treatment method according to claim 1, wherein a reaction temperature in the low-temperature non-equilibrium discharge plasma reactor is 300 ° C. or lower. The exhaust gas treatment method according to claim 3 , wherein a reaction temperature in the low-temperature nonequilibrium discharge plasma reactor is 100 ° C. or lower.   The plasma generating means is a pulse discharge method by AC or DC voltage, silent discharge method, corona discharge method, creeping discharge method, barrier discharge method, honeycomb discharge method, pellet packed bed discharge method, arc discharge method, inductively coupled discharge method. The exhaust gas processing method according to claim 1, which is a capacitively coupled discharge method, a microwave excitation discharge method, a laser induced discharge method, an electron beam induced discharge method, a particle beam induced discharge method, or a combination thereof. 2. The exhaust gas processing method according to claim 1, wherein the non-equilibrium discharge plasma generation conditions in the non-equilibrium discharge plasma reactor for radicalizing air are applied voltage: 10 to 100 kV and frequency: 250 Hz to 1000 Hz. The non-equilibrium discharge plasma treatment method of exhaust gas according to claim 1, wherein the non-equilibrium discharge plasma generated by pulse corona discharge. The exhaust gas processing method according to claim 1, wherein the atmospheric pressure low-temperature nonequilibrium discharge plasma reactor for supplying the air is operated in a steady state. An apparatus for purifying exhaust gas containing nitrogen oxides,
An atmospheric low temperature non-equilibrium discharge plasma reactor to turn air into a radical gas;
A line for supplying the radical gas to the oxidation reaction region;
A line for supplying the exhaust gas to the oxidation reaction region from a line separate from the radical gas generation line;
The oxidation reaction region for oxidizing nitrogen oxide in the exhaust gas to an oxidizing gas containing NO ₂ by the radical gas;
By contacting the oxidizing gas with a reducing agent aqueous solution containing at least one compound selected from Na ₂ SO ₃ , Na ₂ S, and Na ₂ S ₂ O _{3 in a} reduction reaction region , NO ₂ is nitrogen gas (N ₂ Including a reduction reaction region for reduction reaction,
The oxidation reaction region and the reduction reaction region are present in one wet reactor;
The lower part of the wet reactor is the oxidation reaction region, the upper part of the wet reactor is the reduction reaction region,
The exhaust gas treatment apparatus is characterized in that the reducing agent aqueous solution is a circulation type . The exhaust gas processing apparatus according to claim 9 , wherein the wet reactor is a tower-type or column-type reactor, and a supply port for the radical gas and the exhaust gas is present in a lower part. The exhaust gas treatment apparatus according to claim 9 , wherein a reaction temperature in the low-temperature nonequilibrium discharge plasma reactor is 300 ° C. or less. The exhaust gas treatment apparatus according to claim 11 , wherein a reaction temperature in the low-temperature nonequilibrium discharge plasma reactor is 100 ° C or lower. The plasma generating means is a pulse discharge method using AC or DC voltage, silent discharge method, corona discharge method, creeping discharge method, barrier discharge method, honeycomb discharge method, pellet packed bed discharge method, arc discharge method, inductively coupled discharge method. The exhaust gas processing apparatus according to claim 9 , which is a capacitively coupled discharge method, a microwave excitation discharge method, a laser induced discharge method, an electron beam induced discharge method, a particle beam induced discharge method, or a combination thereof. The exhaust gas processing apparatus according to claim 9 , wherein the non-equilibrium discharge plasma generation conditions in the non-equilibrium discharge plasma reactor for radicalizing air are applied voltage: 10 to 100 kV and frequency: 250 Hz to 1000 Hz. The exhaust gas processing apparatus according to claim 9 , wherein the non-equilibrium discharge plasma is a non-equilibrium plasma generated by pulse corona discharge. The exhaust gas processing apparatus according to claim 9, wherein the atmospheric pressure low temperature non-equilibrium discharge plasma reactor supplying the air is operated in a steady state.

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