JPH0596129A - Exhaust gas treatment and equipment therefor - Google Patents

Abstract

PURPOSE:To provide a method and a device for treating exhaust gas capable of removing NOX and SOX in large volume of exhaust gas with high efficiency. CONSTITUTION:Exhaust gas is introduced into a plasma reaction vessel 7 through a exhaust pipe 6, while, on the other hand, ammonia is fed to and mixed with the exhaust gas from an ammonia supply device 8 through a supply pipe 9 connected to an inlet pipe 10 of the plasma reaction vessel 7. A power source 11 applies plasma generating power to the electrode of the plasma reaction vessel 7 and the exhaust gas is transferred from an outlet pipe 12 connected to the plasma reaction vessel 7 to a dust collector 13 for removing and recovering ammonium nitrate and ammonium sulfate formed in the plasma reaction vessel 7. After that, the cleaned exhaust gas is discharged from an exhaust pipe 14 to the atmosphere through a chimney 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas treatment method and apparatus for treating nitrogen oxides and sulfur oxides contained in exhaust gas with a high density glow discharge plasma at a high removal rate.

[0002]

2. Description of the Related Art As an exhaust gas treatment apparatus using conventional glow discharge plasma, Japanese Patent Laid-Open Nos. 1-236924, 2-203920, and 2-227 are known.
The devices shown in FIGS. 3 to 6 are proposed in Japanese Patent Laid-Open No. 117, Japanese Patent Application Laid-Open No. 2-241519, and the like. With these, nitrogen oxides and sulfur oxides (hereinafter NO
x, SOx) will be described as an example.

In FIG. 3, the exhaust gas discharged from the combustion furnace 101 has its dust removed by a dust remover 103, and ammonia is supplied from an ammonia supply pipe 105 at a rate of several liters / minute to several tens of liters / minute to perform a plasma reaction. Bowl 108
Be introduced to. The structure of this plasma reactor 108 is, for example, a structure in which a large number of holes are provided in an exhaust gas introduction pipe as shown in FIG. 4, and a mesh-shaped electrode covered with a dielectric is arranged at a right angle in an exhaust gas passage as shown in FIG. The structure described above, the structure of a saw blade electrode whose surface is covered with a dielectric as shown in FIG. 6, and the like are used to improve the stability of discharge and the amount of gas treatment. The reaction in plasma is complicated, but it is understood as follows.

That is, the presence of ammonia as a buffer gas for promoting the chemical reaction and the first and second reaction in the reaction vessel.
The following reactions occur due to the glow discharge plasma generated by applying a voltage between the electrodes, and NOx and SOx are detoxified.

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) Buffer that promotes chemical reaction With the presence of ammonia as a gas and the devise of these electrodes, a removal rate of 80% or more for NOx and 90% or more for SOx has been obtained even with an exhaust gas amount of 1 Nm ³ / min or more.
It is being used as an exhaust gas pollution control device for various combustion-related devices such as gas turbines.

[0006]

However, the conventional device has the following problems in practical use.

(1) The amount of exhaust gas treated to obtain a NOx removal rate of 80% or more is about 1.3 Nm ³ / min per unit, for example, 100 KW, which is the most for cogeneration.
The amount of exhaust gas from a medium- or small-sized diesel engine of ~ 1000 KW class is 10 to 100 Nm ³ / min, and the amount of exhaust gas increases further in the case of a gas turbine. Therefore, the treatment amount is too small to put these into practical use.

(2) In the conventional example, since the preionization method is not adopted, the electron density of discharge plasma is small and the action of exciting atoms is small, so that plasma is formed spatially and uniformly when the exhaust gas treatment amount increases. However, the removal rate of nitrogen oxides and sulfur oxides is reduced.

(3) In the conventional example, when a large amount of high-pressure (high-density) exhaust gas is processed, glow discharge plasma is generated very locally or does not occur at all, so that it is not suitable for large-scale processing.

(4) In the case of treating a large amount of exhaust gas, for example, a structure in which a mesh-like electrode covered with a dielectric material is arranged at a right angle in the exhaust gas passage as shown in FIG. Although it is necessary to widen the space portion of the mesh-shaped electrode through which the exhaust gas flows, widening the space portion of the mesh-shaped electrode impairs the spatial uniformity of the glow discharge plasma.

(5) Therefore, if the exhaust gas treatment of the small and medium-sized diesel engine or gas turbine is to be performed,
It is necessary to connect a large number of small-capacity devices in parallel, which increases the construction cost of the device and is not suitable for cogeneration in a large city where the device scale becomes large.

An object of the present invention is to solve the above problems and to provide an exhaust gas treatment method and apparatus for removing NOx and SOx in a large amount of exhaust gas with high efficiency.

[0013]

Means for Solving the Problems The above-mentioned object is to mix high-density pulse glow discharge by mixing corona or spark discharge for preionization by mixing exhaust gas containing nitrogen oxides and / or sulfur oxides with ammonia in respective equivalent amounts or less. By fixing the nitrogen oxides, sulfur oxides as ammonium salts,
This is achieved by removing the ammonium salt from the exhaust gas.

The above-mentioned object is to introduce an ammonia injecting means connected to a duct through which exhaust gas containing nitrogen oxides and / or sulfur oxides flows and injecting ammonia, and an exhaust gas into which ammonia is injected connected to the exhaust gas duct. This is achieved by having a reaction means provided with an electrode that forms plasma by electric discharge, and a dust collection means that is connected to the reaction means and separates solid matter produced by the reaction means from the exhaust gas.

[0015]

In the above construction, the exhaust gas containing nitrogen oxides and sulfur oxides is mixed with ammonia in an equivalent amount or less and introduced into the reaction means at atmospheric pressure to several atmospheric pressure.

Main discharge composed of a plate electrode serving as an anode of the reaction means, a preionization part composed of a mesh electrode serving as a cathode, and a mesh electrode serving as a cathode, and a main electrode having a Chan-shaped semicircular cross section serving as an anode. By applying a high voltage short pulse to the field, a corona or spark discharge first occurs in the preionization part and electrons are supplied to the discharge field. Subsequently, a high-density pulse glow discharge is generated in the main discharge field with the generated electrons as nuclei, and a plasma having an electron density comparable to that of a high-pressure arc is formed. Moreover, this glow discharge is a discharge in a short time of several tens of ns, and the injected energy is mostly used for accelerating the light electrons, and the generated high energy electrons effectively excite the exhaust gas component. Although the reaction in plasma is complicated, nitrogen oxides and sulfur oxides are fixed as ammonium nitrate and ammonium sulfate by the following reactions, respectively. Ammonium salts to which nitrogen oxides and sulfur oxides are fixed are separated and removed from the exhaust gas by a dust collecting means.

1) Generation of oxidative active species N ₂ , O ₂ , H ₂ O, + e ~ → OH, H, HO ₂ (6) 2) Nitrogen oxide and sulfur oxidation Oxidation of substances NOx + (OH, H, HO ₂ ) → HNO ₃ …………………………… (7) SOx + (OH, H, HO ₂ ) → H ₂ SO ₄ ……………………… ………… (8) 3) 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) When a small amount of ammonia is added to accelerate the chemical reaction, the above-mentioned prior art (1)- It is also possible that the reaction of (5) occurs.

Pre-ionization in the reaction means enables efficient excitation of exhaust gas by high energy and high density electrons in plasma, short residence time of exhaust gas and cross flow of exhaust gas flow with discharge direction. This makes it possible to treat a large amount of exhaust gas with a high removal rate.

Glow discharge is difficult to generate under conditions other than vacuum, but since pre-ionization triggers glow discharge under pressure, the volume flow rate can be reduced by pressurization and the exhaust gas treatment device can be made compact. You can

[0020]

An embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a flow chart for explaining the structure of the exhaust gas treating apparatus of the present invention.

Exhaust gas discharged from the gas turbine 1 or the diesel engine 2, which is an object for taking measures against pollution by exhaust gas, is transferred to the exhaust heat boiler 5 for recovering heat by the exhaust pipe 3 or the exhaust pipe 4, and Exhaust gas emitted from the exhaust heat boiler 5 is introduced into the plasma reaction container 7 through the exhaust pipe 6. On the other hand, ammonia is supplied and mixed into the exhaust gas from the ammonia supply device 8 through the supply pipe 9 connected to the inlet pipe 10 of the plasma reaction vessel 7. Reference numeral 11 is a power source for applying plasma generation power to the electrodes of the plasma reaction vessel 7, and the exhaust gas from which NOx and SOx are removed is generated in the plasma reaction vessel 7 from an outlet pipe 12 connected to the plasma reaction vessel 7. It is transferred to the dust collector 13 that removes and collects ammonium nitrate and ammonium sulfate. For the dust collector 13, for example, an electric dust collector, a bag filter or the like can be used. After that, clean exhaust gas is discharged from the exhaust pipe 14 to the atmosphere through the chimney 15.

FIG. 2 is a perspective view showing the structure of the plasma reaction container 7 according to the embodiment of the present invention.

First, the electrode of the plasma reactor 7 which is a feature of the present invention will be described. An example in which a mesh electrode is used for the preionization electrode section is shown. The electrodes are a plate electrode (anode) 17 and a Chan-shaped main electrode (anode) 18 having a semicircular cross section.
Are arranged in parallel, one plate electrode 17 is covered with a dielectric 18, and a mesh electrode or a wire electrode (cathode) 19 for corona preionization is provided on one surface thereof. In the case of spark discharge preionization, spark discharge preionization electrodes are provided in parallel on both sides of the cathode electrode and the anode electrode. The electrode 18 having a semi-circular cross section and the mesh electrode (cathode) 19 for pre-ionization of corona that come into contact with exhaust gas are protected by coating an oxidation resistant ceramic such as alumina with a thickness of several microns. There is. Power supply between electrodes 1
When a high voltage pulse of 1 to several tens of ns and several tens of KV is applied, corona discharge occurs in the preionization electrode portion including the plate electrode 17 and the mesh electrode 19, and electrons are supplied to the discharge field.
Subsequently, a glow discharge is generated between the mesh electrode (cathode) 19 and the main electrode (anode) 18 by using these electrons as nuclei, and a maximum of 10
A plasma is formed with an electron density of ²¹ / m ^{3 which} is almost comparable to a high pressure arc. Quartz glass is usually used as the dielectric 18, but any dielectric such as ceramics can be used. A line flow fan 16 is provided at the reaction vessel inlet 10 as necessary in order to introduce the exhaust gas into the discharge field at a predetermined speed.

NOx and SOx using such a reaction vessel
An example of removal is shown below.

Untreated exhaust gas condition Flow rate 60 Nm ³ / min NOx concentration 1000 ppm SOx concentration 600 ppm Discharge condition Pulse energy 19 J / pulse (19 KJ / Nm 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% In another embodiment of the present invention, the discharge tube has a diameter of 30 cm and a length of about 100 cm due to the efficient excitation of the exhaust gas by the high-energy and high-density electrons in the plasma and the effect of promoting the chemical reaction by adding ammonia. A very compact treatment equipment made it possible to treat a large amount of exhaust gas of about 120 Nm ³ / min with a high removal rate (90% or more). This throughput is the output 10 that is mainly used in cogeneration.
This corresponds to the exhaust gas amount of small and medium-sized engines of 00 KW or less.

As described above, according to the present invention, the exhaust gas can be efficiently excited by the high energy and high density electrons in the plasma, the residence time of the exhaust gas in the plasma can be short, and the exhaust gas can be discharged to the electrode and the discharge. Can be introduced perpendicular to the direction. Therefore, the flow resistance can be reduced compared to the conventional method,
A large amount of exhaust gas can be made to flow between the electrodes, and the effect of promoting the chemical reaction due to the addition of ammonia is also superposed, so that a large amount of exhaust gas can be treated with a high removal rate.

[0028]

According to the present invention, exhaust gas can be efficiently excited by high-energy and high-density electrons in plasma by performing pre-ionization in the reaction means, the residence time of exhaust gas is short, and the exhaust gas flow is high. By cross-flowing with the discharge direction, a large amount of exhaust gas can be treated with a high removal rate.

Further, since glow discharge can be performed under pressure by pre-ionization, the volumetric flow rate can be reduced by pressurization and the exhaust gas treatment device can be made compact.

[Brief description of drawings]

FIG. 1 is a flowchart illustrating a configuration of an exhaust gas treatment apparatus of the present invention.

FIG. 2 is a perspective view showing a configuration of a plasma reaction container according to an embodiment of the present invention.

FIG. 3 is a block diagram showing the overall configuration of a conventional exhaust gas treatment apparatus.

FIG. 4 is a perspective view showing a structure of a conventional reactor electrode unit.

FIG. 5 is a perspective view showing a structure of a conventional electrode.

FIG. 6 is a vertical sectional view showing a structure of a conventional electrode.

[Explanation of symbols]

 1 Gas Turbine 2 Diesel Engine 3 Exhaust Pipe 4 Exhaust Pipe 5 Exhaust Heat Boiler 6 Exhaust Pipe 7 Plasma Reaction Vessel 8 Ammonia Supply Device 9 Ammonia Supply Pipe 10 Reaction Vessel Inlet 11 High Pressure Power Supply 12 Reaction Vessel Outlet Pipe 13 Dust Collector 14 Exhaust Pipe 15 Chimney 16 Line flow fan 17 Flat plate electrode (anode) 18 Main electrode (anode) 19 Corona preionization mesh electrode (cathode) 20 Dielectric 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 External electrode 109 Power source 110a Exhaust gas outlet pipe 110b Exhaust gas outlet pipe 111 Electrical insulating pipe 112 Internal electrode 113 Plasma reactor 114 Hole 115 First electrode 116 Second electrode 117 Second electrode (sawtooth shape ) 118 1st Electrode (flat) 119 dielectric

Claims (2)

[Claims] 1. Nitrogen oxides and / or sulfur oxides are mixed by mixing exhaust gas containing nitrogen oxides and / or sulfur oxides with an equivalent amount or less of ammonia, and preionizing by corona or spark discharge and high density pulse glow discharge. A method for treating exhaust gas, which comprises fixing an object as an ammonium salt and removing the ammonium salt from the exhaust gas. 2. An ammonia injecting means connected to a duct through which an exhaust gas containing nitrogen oxides and / or sulfur oxides flows to inject ammonia, and an exhaust gas into which ammonia is injected connected to the exhaust gas duct are introduced to discharge the exhaust gas. A reaction means provided with an electrode for forming plasma, a power source for applying a voltage to the electrode of the reaction means, and a dust collection means connected to the reaction means for separating solid matter generated by the reaction means from the exhaust gas. An exhaust gas treatment device comprising: