JPH04363115A - Exhaust gas treating equipment - Google Patents

Abstract

PURPOSE:To make exhaust gas treating equipment by glow discharge plasma having a large capacity. CONSTITUTION:A reaction tank 60 through which nitrogen oxide and sulfur oxide containing exhaust gas passes, plural plate type electrodes 61-1 to 61-n which are installed along gas flow in the tank and whose surface is covered with a dielectric, plural saw-shaped electrodes 62-1 to 62-n which are respectively installed opposite to the plate type electrodes and whose surface is covered with a dielectric, and a power source 70 which is connected to the plate type electrode and the saw-shaped electrode in-between and applies composite wave of high-frequency wave and low-frequency wave, are provided in the objective equipment.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is aimed at reducing NOX, N2 O, and S in exhaust gas emitted from boilers for power plants, diesel engines, gas turbines, various combustion furnaces, etc.
The present invention relates to an exhaust gas treatment device using glow discharge that can effectively remove OX in a large amount.

0002

2. Description of the Related Art A conventional exhaust gas treatment apparatus using glow discharge plasma will be described with reference to FIGS. 4 to 6.

In FIG. 4, reference numeral 1 indicates an object for taking measures against exhaust gas pollution in a general-purpose combustion furnace. 3 is a dust remover, 2 is an exhaust pipe that transfers the exhaust gas from the general-purpose combustion furnace 1 to the dust remover (cyclone collector, etc.) 3, 6 is a plasma reaction vessel, 4 is a plasma reactor for the exhaust gas from the dust remover 3. an exhaust pipe for transferring to the reaction vessel 6; 7 a power source for applying a plasma generation voltage to the electrodes of the plasma reaction vessel 6; 8 an exhaust gas output pipe connected to the plasma reaction vessel 6;
1 is an ammonia supply device that supplies ammonia at a predetermined setting value in the range of several liters/min to several tens of liters/min;
4 is an ammonia supply pipe connected to the discharge pipe 4.

5 and 6 below, the plasma reaction vessel 6
I will explain about it. A sawtooth electrode 110 and a plate electrode 11 are placed in a cylindrical plasma reaction vessel 6 that is open at both ends.
1 is provided with its surface parallel to the gas flow. Further, the sawtooth electrode 110 and the plate electrode 111 are covered with dielectrics 112 and 113 so that they do not come into direct contact with exhaust gas.

In the above configuration, ammonia is supplied from the ammonia supply device 16 at a rate of several liters/min to several tens of liters/min.
It is introduced into the plasma reaction vessel 6 together with the exhaust gas at a flow rate of n. From a power source 7 for plasma generation, a sawtooth electrode 1
10 and the plate electrode 111, the dielectric 11
Between 2 and 113, plasma of ammonia-containing exhaust gas is generated.

[0006] This plasma is a glow discharge plasma, which excites and dissociates gas molecules such as ammonia, NOX, SOX, etc., and makes them chemically active. This causes the chemical reaction described below.

NH3 + electron energy approximately 6.4 eV → NH2
+H...(1) 2NO2 + electron energy approximately 9.5eV → 2NO+O2...(2
) NH2 +NO→N2 +H2 O
…(3
) 2NH2 +SO2 →S+N2 +2H2 O
...(4) Above (
Equations 1) to (4) indicate that NO, NO2 and SO2 in the exhaust gas of the combustion furnace 1 introduced into the plasma reaction vessel 6 are
2, S and H2O. In this case, as described above, the exhaust gas containing ammonia does not directly contact the sawtooth electrode 110 or the plate electrode 111, and instead
It only touches 3. Since there is no contact with exhaust gas (especially ammonia), there is no corrosion or wear of the electrodes, and stable glow discharge plasma can be generated for a long time.

[0008] 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.

[0009]

SUMMARY OF THE INVENTION The conventional apparatus described above has the following drawbacks, making it difficult to put it into practical use. (1) Exhaust gas processing amount per electrode set is 100l/mi
n, 100 sets of electrodes are required to obtain a processing capacity of 10,000 l/min. Although alternating current power is used to generate plasma, if there are variations in the capacitance of the electrodes (caused by the temperature distribution of the gas, differences in electrode spacing, etc.), the plasma power of each electrode will become non-uniform. Therefore, with 100 pairs of electrodes, the flow rate is 10,000 l/m.
When it becomes in, NOX, N2 due to plasma non-uniformity
The reduction rate of O and SOX decreases, making it impossible to obtain a satisfactory throughput. (2) In the case of one set of electrodes, increasing the power by increasing the voltage or frequency of the plasma power source improves the reduction rate of NOX, N2O, and SOX, and increases the throughput. However, in the case of 100 pairs of electrodes, when the plasma of each electrode is non-uniform as described in (1) above, increasing the voltage and frequency will further exacerbate the non-uniformity of the power of each electrode. Ru. Therefore, even if an attempt is made to increase the throughput by connecting a plurality of electrodes in parallel, the reduction rate decreases, making it impossible to obtain a satisfactory throughput.

0010

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

That is, the exhaust gas treatment device includes a reaction vessel through which exhaust gas containing nitrogen oxides and sulfur oxides passes;
A plurality of flat electrodes whose surfaces are covered with a dielectric material are installed along the gas flow inside the reaction vessel, and a plurality of sawtooth electrodes whose surfaces are covered with a dielectric material are provided facing each of the flat electrodes. An electrode, and a power supply means connected between the flat plate electrode and the sawtooth electrode and applying a composite wave of high frequency and low frequency.

0012

[Operation] By the above means, glow discharge plasma is generated between the flat plate electrode and the sawtooth electrode, and NOX, N in the exhaust gas is removed.
2 O and SOX are activated and rendered harmless. At this time, the plasma power increases with the high frequency component of the applied composite wave voltage, and the removal rate of NOX, N2O, and SOX improves. Further, the low frequency component suppresses power non-uniformity due to capacitance variation between pairs of opposing flat plate electrodes and sawtooth electrodes. As a result, the electric power between each group becomes uniform, and a large amount of exhaust gas can be treated.

Furthermore, since the electrodes are covered with a dielectric and do not come into direct contact with exhaust gas, durability is improved.

[0014]

Embodiment One embodiment of the present invention will be explained with reference to FIGS. 1, 2 and 3.

In FIG. 1, reference numeral 1 indicates an object for taking measures against exhaust gas pollution in a general-purpose combustion furnace. Reference numeral 2 denotes an exhaust pipe that transfers the exhaust gas from the general-purpose combustion furnace 1 to a dust remover (such as a cyclone collector) 3, and 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 exhaust gas inlet pipe 5; 5 is an exhaust pipe that transfers the exhaust gas from the exhaust pipe 4 to the plasma reaction vessel 60; and 60 is an exhaust pipe that generates glow discharge plasma to remove the exhaust gas. A reaction vessel to be rendered harmless, 70 is the plasma reaction vessel 6 described above.
0 is a power source for supplying plasma generation power, and 8 is an exhaust gas outlet pipe which is a device for discharging the exhaust gas treated by the reaction vessel 60.

The plasma reaction vessel 60 will be explained in detail with reference to FIG. A flat electrode 61-1 whose surface is covered with a dielectric material a is provided in contact with one wall of a cylindrical reaction vessel 60 made of glass or ceramics and open at both ends. A flat sawtooth electrode 62-1 having a sawtooth surface and covered with a dielectric material a is provided opposite to the electrode 61-1. One set of these will be referred to as a first set. Furthermore, this one set is reversed around the axis along the gas flow, and the adjacent electrodes, that is, the flat electrode 61-2 and the sawtooth electrode 62-2 are used as a second set. Thereafter, an nth set (100 sets) of flat plate electrodes 61-n and sawtooth electrodes 62-n are provided in the same manner. At this time, the flat electrode 61-n is in contact with the other wall of the reaction vessel 60.

The flat electrodes 61-1 to 61-n are connected to one terminal of the power source 70, and the sawtooth electrodes 62-1 to 62-n
is connected to the other terminal. The exhaust gas enters the reaction vessel 60 from the inlet pipe 5, passes between the flat plate electrode and the sawtooth electrode, and is discharged from the outlet pipe 8. Further, an ammonia supply pipe 14 is connected to the inlet pipe 5, and ammonia is supplied from an ammonia supply device 15 at a predetermined setting value in the range of several l/min to several tens of l/min, and mixed with the exhaust gas.

In the plasma reaction vessel 60 having such a structure, the exhaust gas from the combustion furnace 1 is supplied to the exhaust gas inlet pipe 5 from the exhaust pipe 4, and at the same time, ammonia from the ammonia supply device is supplied from the ammonia supply pipe 14. These gases are mixed to become an exhaust gas containing ammonia and the flat electrode 61-
1 to 61-n and sawtooth electrodes 62-1 to 62-n, and a voltage is applied between each electrode from a power source 70. Then, the exhaust gas between the electrodes is turned into plasma, and NOX, N2 O, and SOX in the exhaust gas are rendered harmless by a chemical reaction and are discharged from the exhaust gas outlet pipe 8. This plasma is a glow discharge plasma, with NOX and N
Excite and dissociate gas molecules such as 2 and make them chemically active. This causes the chemical reaction described below.

NH3 + electron energy approximately 6.4 eV → NH2
+H...(1) 2NO2 + electron energy approximately 9.5eV → 2NO+O2...(2
) NH2 +NO→N2 +H2 O
…(3
) 2NH2 +SO2 →S+N2 +2H2 O
…(4) 2
N2 O→2N2 +O2
...(5) Equations (3) to (5) above indicate that NO, NO2, and N2O in the exhaust gas of the combustion furnace 1 introduced into the plasma reaction vessel 60 are
2 and O2, SO2 becomes S and O2 and becomes harmless.

At this time, a voltage having a composite waveform shown in FIG. 3(c) is applied from the power source 70 to each electrode. The voltage of the composite waveform is the low frequency voltage waveform shown in Fig. 3(a) (for example, f=5
0 Hz) and the high frequency voltage waveform (for example, f=500 Hz) shown in FIG. 3(b).

Since a plurality of electrodes are connected in parallel, the lower the frequency of the applied voltage, the less the influence of variations in capacitance of each electrode, and uniform plasma power is supplied to each electrode. In this respect, it is sufficient to set the applied voltage so that the electron energy of the plasma becomes 9.5 eV with a low frequency voltage. However, at lower frequencies the power is lower;
In particular, the N2O removal effect decreases. On the other hand, if the frequency is increased to improve the N2O removal effect, non-uniformity in plasma power due to variations in the capacitance of each electrode will be promoted, and the throughput across multiple electrode sets will be reduced. . Therefore, as shown in Figure 3(c), by combining high-frequency voltage and low-frequency voltage, that is, by using an AC voltage in which high frequency is modulated by low frequency, the low frequency component suppresses the non-uniformity of plasma power at each electrode. , high frequency can be supplied to each electrode with uniform power.

Therefore, even in this embodiment in which 100 pairs of electrodes are connected in parallel, sufficient power can be uniformly applied to each electrode, and exhaust gas treatment with large capacity (about 10,000 l/min) and high treatment rate is possible. It is.

Furthermore, since it is easy to increase the throughput by connecting a large number of the apparatuses of this embodiment in parallel, the range of application is wide and the industrial value as an exhaust gas treatment apparatus is extremely high.

[0024]

Effects of the Invention As explained above, according to the device of the present invention, power distribution to a plurality of electrodes becomes uniform, and a large volume of exhaust gas containing NOX, N2O, and SOX can be generated, which was impossible with conventional devices. can be processed efficiently and easily.

[Brief explanation of drawings]

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

FIG. 2 is a cross-sectional view of the structure of the reaction container section of the same embodiment.

FIG. 3 is an explanatory diagram of the operation of the same embodiment.

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

FIG. 5 is a perspective view of the structure of the reaction container section of the conventional example.

FIG. 6 is a sectional view of the reaction vessel of the conventional example.

[Explanation of symbols]

Claims (1)

[Claims] Claim 1: A reaction vessel through which exhaust gas containing nitrogen oxides and sulfur oxides passes; a plurality of flat electrodes provided along the gas flow within the reaction vessel and having surfaces covered with a dielectric; a plurality of sawtooth electrodes each facing the flat electrode and having a surface covered with a dielectric; a power source connected between the flat electrode and the sawtooth electrode for applying a composite wave of high and low frequencies; An exhaust gas treatment device comprising: