JPH04247219A - Exhaust gas treating device - Google Patents

Abstract

PURPOSE:To make the plasma reaction vessel of an exhaust gas treating device highly efficient. CONSTITUTION:A dielectric cylindrical reaction vessel 9 with the inner diameter gradually decreasing from the exhaust gas inlet side toward the outlet side, an external electrode 11 provided around the vessel 9, an internal electrode 10 furnished along the inner face of the vessel 9 with a supplied gas in-between and a power source 6 for impressing a voltage between the electrodes 11 and 10 are provided to the exhaust gas treating device. A plasma reaction is brought about between the electrodes 10 and 11, and the NOX in the exhaust gas are removed. At this time, since the flow rate is progressively increased toward the outlet side, the recombination of NOX is prevented, and the device is made highly effective.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention utilizes glow discharge plasma that can effectively and in large quantities remove NOX from exhaust gas emitted from power plant boilers, diesel engines, gas turbines, and various combustion furnaces. Related to exhaust gas treatment equipment.

0002

2. Description of the Related Art FIGS. 4 and 5 are explanatory diagrams of a conventional exhaust gas treatment apparatus using glow discharge plasma. An explanation will be given by taking as an example a case in which this device is used to treat NOX in the exhaust gas of a diesel engine.

In FIG. 4, a diesel engine 101
The exhaust gas of
It will be introduced in 2005. The plasma reaction vessel 105 is shown in FIG.
), (b), an internal electrode 110 is placed inside the cylindrical glass reaction vessel 109, and an external electrode 111 is placed outside.
The device is configured with a power supply 106 that applies voltage to internal electrodes 110 and external electrodes 111, and removes NOX in the exhaust gas by turning the exhaust gas into plasma according to the following principle. That is, when a voltage is applied between the internal electrode 110 and the external electrode 111 using the power supply 106,
The exhaust gas is turned into plasma by the atmospheric pressure glow discharge phenomenon. For example, NO2 causes the following chemical reaction.

2NO2 →2NO+O2
(1) 2NO+O2 →N2 +2O2
(2) Plasma is an ionized gas in which high-energy electrons accelerated by an external electric field collide with gas molecules, and excited molecules, atoms, free radicals, ions, and neutral particles coexist. ), (2
) formula, NO has an energy of several eV to several tens of eV.
It is thought that X becomes a chemically active species and as a result of a complex reaction, it becomes N2 and O2.

Now, as mentioned above, if engine exhaust gas is turned into plasma using the atmospheric pressure glow discharge phenomenon,
When the concentration of (NO+NO2) is about 50 to 200 ppm and the flow rate is about 30 to 60 l/min, the NOX removal rate is low when the plasma generation power, that is, the power supplied from the power supply 106 is in the range of several watts to several tens of watts. 80 to 90% can be achieved.

[0006] Therefore, it is being utilized as an exhaust gas pollution control device for various types of equipment that involve combustion, such as boilers, gas turbines, and diesel engines.

[0007]

[Problems to be Solved by the Invention] The above-mentioned conventional apparatus has the following drawbacks, which make it extremely difficult to put it into practical use.

(1) If the amount of exhaust gas is set to a certain amount, for example (3
If the flow rate is increased more than 0 to 60 l/min), glow discharge plasma will no longer be generated and NOX
It will not be possible to remove it.

(2) Furthermore, if the size of the electrode is increased in the exhaust gas flow direction, the NOX removal effect will be significantly reduced.

(3) Due to the reasons (1) and (2) above, it cannot be used as a large-capacity exhaust gas treatment device, for example, in the several 100 to several 100,000 l/min class.

[0011]

[Means for Solving the Problems] The present invention takes the following means to solve the above problems.

That is, in an exhaust gas treatment apparatus that uses glow discharge plasma to detoxify nitrogen oxides in exhaust gas, a cylinder made of a dielectric material whose inner diameter gradually decreases from the inlet side to the outlet side of the exhaust gas is used. a reaction vessel having a shape, an external electrode provided along the outer surface of the reaction vessel, an internal electrode provided along the inner surface of the reaction vessel at a predetermined interval, and a voltage between the external electrode and the internal electrode. A voltage applying means for applying the voltage is provided.

[0013]

[Operation] By the above means, exhaust gas containing NOX is introduced from the inlet of the reaction vessel between the inner surface of the vessel and the internal electrode. Further, a voltage is applied between the internal electrode and the external electrode from a voltage applying means to generate a glow discharge. Then, the above (1
) and (2) reactions occur, and NOX is removed.

In the reaction vessel, the cross-sectional area of the flow path gradually decreases from the inlet to the outlet, so the flow side increases. That is, as the NOX concentration decreases due to the plasma reaction, the contact time between the plasma and the exhaust gas (NOX) decreases. As a result, optimal power supply for NOX removal can be achieved, eliminating recombination of NOX in low concentration areas due to excessive power. Therefore, even if the reaction vessel is extended, NO
Removal rate does not decrease.

[0015] As described above, NOX can be treated with high efficiency and the throughput can be increased.

[0016]

[Embodiment] An embodiment of the present invention will be explained with reference to FIGS. 1 and 2. In FIG. 1, 1 is a general-purpose combustion furnace, which is an object for taking measures against exhaust gas pollution. 2 is a dust remover (cyclone collector, etc.) for the exhaust gas from the general-purpose combustion furnace 1 mentioned above.
This is the exhaust pipe that transfers the air to No. 3. The dust remover 3 removes particles contained in the exhaust gas. 4 is an exhaust pipe that transfers the exhaust gas from the dust remover 3 to the plasma reaction vessel 5; 6 is a power source that applies plasma generation power to the electrodes of the plasma reaction vessel 5; and 7 is an exhaust gas output connected to the plasma reaction vessel 5. It's a tube.

The plasma reaction vessel 5 will be explained in detail with reference to FIG. Conical reaction vessel 9 with open ends
is made of dielectric material (eg, glass ceramics, etc.). The reaction vessel 9 has a cylindrical shape whose diameter gradually decreases from the gas inlet side to the outlet side.

An external electrode 11 is placed in close contact with the outer surface of the reaction vessel 9. Further, a conical internal electrode 10 is coaxially provided in the interior space of the reaction vessel 9. At this time, the inner surface of the reaction container 9 and the outer surface of the internal electrode 10 are spaced apart from each other by a predetermined constant distance. The inner and outer electrodes 10 and 11 are connected to a power source 6.

The plasma reaction vessel 5 includes the above reaction vessels 9,
It has inner and outer electrodes 10 and 11.

An exhaust gas inlet pipe 18 is connected to the inlet of the plasma reaction vessel 5, and an exhaust gas outlet pipe 7 is connected to the outlet thereof.

In the above configuration, the exhaust gas containing NOx generated in the combustion furnace 1 is passed through the exhaust pipe 2 to the dust remover 3.
The dust remover 3 removes particles in the exhaust gas, and the exhaust gas is introduced into the reaction vessel 9 via the exhaust pipe 4 and the exhaust gas inlet pipe 18 of the plasma reaction vessel 5.

On the other hand, when power is supplied from the plasma generation power source 6 to the internal electrode 10 and the external electrode 11, exhaust gas plasma is generated between the dielectric of the reaction vessel 9 and the internal electrode 10. This plasma is a glow discharge plasma and NO
It excites and dissociates gas molecules such as X and N2, O2, and makes them chemically active. This causes the chemical reactions of formulas (1) and (2) above, and N
OX becomes N2 and O2 and is removed.

NOx (50-2
The removal status of 00 ppm) will be explained with reference to FIGS. 3(a) to 3(c). In this example, the flow rate is 100 l/min.

FIG. 3(a) is a graph showing the relationship between the axial position in the reaction vessel and the gas flow rate. Since the diameter of the reaction vessel 9 gradually decreases from the gas inlet side to the outlet side, the flow rate gradually increases from the gas inlet side to the outlet side (solid line in the figure). Then, as shown in FIG. 3(b) (solid line), the contact time between the plasma and the exhaust gas gradually becomes shorter from the gas inlet side to the outlet side. When the diameter of the gas inlet, the diameter of the gas outlet, and the length in the gas flow direction of the reaction vessel 9 are adjusted, the result is shown in FIG. 3(c) (solid line).
As shown in the figure, approximately 100% NO is present at the outlet of the reaction vessel 9.
X removal rate has been obtained.

[0025] In the conventional device, uniform power is supplied from the gas inlet side to the outlet side of the reaction vessel, and the contact time between the plasma and the exhaust gas is uniform, so near the gas outlet of the reaction vessel where the NOx concentration decreases, When extra power is supplied, NOX decomposed into N2 and O2 recombines and becomes N
The OX removal rate was about 50%. For these reasons, the conventional plasma method has problems in that it is not possible to extend the reaction vessel (electrode) to improve the NOX removal rate, or it is not possible to increase the exhaust gas processing rate to 60 l/min or more. Ta.

However, in this embodiment, the gas flow rate in the reaction vessel is gradually increased from the gas inlet side to the outlet side, so as the NOX concentration decreases due to the plasma reaction, the plasma and exhaust gas (NOX) contact time will be shortened. As a result, optimal power supply for NOX removal can be achieved, eliminating recombination of NOX due to excessive power. Therefore, if the reaction vessel is extended, NOx
Removal rate is improved. In addition, by connecting multiple reaction vessels in parallel, for example, a flow rate of 10,000 l/m can be achieved.
It is also possible to process in. (approximately 100 times the conventional ratio).

[0027]

As explained above, according to the apparatus of the present invention, the recombination of NOX in the downstream part of the reaction vessel is eliminated, so that the removal efficiency is greatly improved. In addition, by increasing the size or installing multiple devices in parallel, the processing capacity can be further increased significantly. Therefore, it has extremely high industrial value as a large-capacity exhaust gas NOX removal device.

[Brief explanation of the drawing]

FIG. 1 is an overall system diagram of an embodiment of the present invention.

FIG. 2 is a detailed longitudinal sectional view of the plasma reaction vessel of the same embodiment.

FIG. 3A, FIG. 3B, and FIG. 3C are explanatory views of the operation of the same embodiment.

FIG. 4 is an overall system diagram of a conventional example.

FIGS. 5(a) and 5(b) are configuration diagrams of a reaction vessel of the same conventional example.

[Explanation of symbols]

1 Combustion furnace 2 Exhaust pipe 3. Dust remover 4 Exhaust pipe 5 Plasma reaction vessel 6 Power supply 7 Exhaust gas outlet pipe 9 Reaction container 10 Internal electrode (conical) 11 External electrode (conical) 18 Exhaust gas inlet pipe

Claims (1)

[Claims] 1. An exhaust gas treatment device that uses glow discharge plasma to detoxify nitrogen oxides in exhaust gas, comprising: a cylindrical reaction vessel made of a dielectric material whose inner diameter gradually decreases from the inlet side to the outlet side of the exhaust gas; , an external electrode provided along the outer surface of the reaction container, an internal electrode provided along the inner surface of the reaction container at a predetermined interval, and voltage application for applying a voltage between the external electrode and the internal electrode. An exhaust gas treatment device comprising: means.