JPH05220340A - Waste gas treating device - Google Patents

Abstract

PURPOSE:To obtain a compact and safe waste gas treating device excellent in denitrating capacity by introducing a waste gas into a plasma generation vessel, impressing a monopulse electric field on an electrode from a high-voltage pulse power source against a gas current to generate non-equilibrium plasma having a high electron temp. in the passage and further controlling the pulse repetition frequency. CONSTITUTION:An inlet pipe 2 and an outlet pipe 3 are connected to a treating vessel 1, discharge electrodes 4a and 4b are oppositely provided in the vessel, and a high-voltage pulse power source 5 contg. a trigger pulse controller 6 as the control part is connected to the discharge electrode 4. A flowmeter 7 is provided on the gas inlet side and a gas sensor 8 on the gas outlet side, and the signals are inputted to the controller 6. Gaseous NOx are introduced into the vessel 1, a monopulse high electric field is impressed to generate non- equilibrium plasma having a high electron temp. in the passage, and NOx are ionized, dissociated and removed. The high-voltage pulse string is controlled by the controller 6 to control the pulse repetition frequency proportional to the treating flow rate or NOx concn.

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 device for removing nitrogen oxides (NOx) in flue gas of an internal combustion engine, an incinerator, etc. by utilizing a short pulse glow discharge with a variable repetition frequency.

[0002]

2. Description of the Related Art NOx is generated by combustion in an internal combustion engine such as a diesel engine, a gas engine and a gas turbine engine. The NOx reduction measures are roughly classified into fuel conversion, combustion improvement, and exhaust gas denitration. Of these, there is a limit to the NOx reduction effect in fuel conversion and combustion improvement (20% to 50%), and it is difficult to comply with stricter regulations such as the Air Pollution Control Law.

As the exhaust gas denitration technology, there are a dry method and a wet method, and the selective catalytic reduction method of the wet method (hereinafter referred to as ammonia denitration method) is often used at present. The ammonia denitration method is a method in which ammonia is injected into the exhaust gas and brought into contact with a denitration catalyst installed downstream, and NOx is decomposed into harmless nitrogen and water by the following reduction reaction.
As the catalyst, V ₂ O ₅ —WO ₃ —TiO ₃ system is the mainstream.

4NO + 4NH ₃ + O ₂ → 4N ₂ + 6H ₂ O NO + NO ₂ + 2NH ₃ → 2N ₂ + 3H ₂ O The ammonia denitration method uses harmful and dangerous ammonia as a reducing agent, and other hydrocarbons and carbon monoxide. There is. Examples of catalysts used in this reaction include precious metal-based metals such as Pt and various metal oxides supported on Al ₂ O ₃ , TiO _{2 and the} like. Also, ammonia is constantly consumed, and the reduction catalyst performance by ammonia gas is further improved. Deterioration of the catalyst necessitates replacement of an expensive catalyst.

Further, as a dry method, there is an exhaust gas treatment device using discharge plasma.

[0006]

The above-mentioned ammonia denitration method has the following problems.

(1) Hazardous and dangerous ammonia gas must be used to decompose NOx.

(2) Since the reduction catalyst performance due to ammonia gas deteriorates, it is necessary to replace an expensive catalyst and the operation is troublesome.

(3) The operating temperature range of the conventional reduction method is 3
It is limited to 20 to 450 ° C. That is, at high temperatures, sintering of the catalytic component progresses, the catalytic performance deteriorates due to the phase transition of the crystal,
At 320 ° C. or lower, ammonia gas and water react with exhaust gas containing SOx to generate acidic ammonium sulfate and the like, and denitration performance is deteriorated.

(4) Since ammonia gas, which is approximately equal to the NOx amount, is injected into the exhaust gas in accordance with the denitration rate, the ammonia gas cylinder, the catalyst, etc. are large and it is difficult to downsize the entire apparatus.

Further, in the exhaust gas treatment apparatus using discharge plasma which is a dry method, it is difficult to enlarge the plasma region, and therefore, it is not suitable for large flow rate treatment, and the fluctuation of the exhaust gas flow is prevented. Therefore, it was difficult to maintain the discharge state (corona or glow discharge) and it was difficult to control the plasma with respect to the flow rate and the concentration, so that the denitration capacity could not be improved.

In view of the above problems, the present invention uses a short pulse glow discharge with a variable repetition frequency to
The purpose is to improve the denitration rate.

[0013]

In order to achieve the above object, the present invention provides a processing container in which exhaust gas circulates,
A flow meter and a gas sensor respectively disposed in the exhaust gas flow passage, at least a pair of plasma generating electrodes mounted in the processing container, and a high voltage pulse for applying a high voltage pulse to the pair of plasma generating electrodes. An exhaust gas treatment device is configured by a power supply and a pulse control unit that controls the pulse output frequency of the high-voltage pulse power supply according to the detection signal of the flow meter or the detection signal of the gas sensor.

[0014]

[Function] The exhaust gas is guided to the plasma generation container, and a short pulse electric field is applied to the electrode from the high-voltage pulse power supply to generate a non-equilibrium plasma having a high electron temperature in the flow path, thereby generating the exhaust gas. NOx after ionization or dissociation
To remove. The pulse repetition frequency is the processing flow rate or N
Control is performed according to the Ox concentration value.

[0015]

Embodiments of the present invention will be described below with reference to FIGS.

1 and 2 show an exhaust gas treatment apparatus according to an embodiment of the present invention. In FIG. 1, reference numeral 1 is a treatment container, and an introduction pipe 2 for introducing exhaust gas into the treatment container 1. And a lead-out pipe 3 for leading out the treated gas. Discharge electrodes 4a and 4b are provided inside the processing container 1 so as to face each other. A high voltage pulse power source 5 has a built-in trigger pulse controller 6 which is a pulse control unit, and is connected to the discharge electrodes 4a and 4b. Reference numeral 7 denotes a flow meter provided on the gas inflow side, which converts the flow rate detection signal into an electric signal and guides this electric signal to the trigger pulse controller 6 of the pulse power source 5. Further, 8 is a gas sensor provided on the gas outflow side, which converts a detection signal into an electric signal,
It leads to the trigger pulse controller 6.

In the exhaust gas treatment apparatus shown in FIGS. 1 and 2, NOx gas is introduced into the treatment container 1 and a short pulse (200 ns or less) high electric field is applied to the upper and lower sides or both sides of the gas flow, and the NOx gas is introduced into the passage. A non-equilibrium plasma having a high electron temperature is generated, whereby NOx is ionized or dissociated and removed. With the high voltage pulse train, the trigger pulse controller 6 controls the pulse repetition frequency proportional to the processing flow rate.

The discharge electrodes 4a, 4b are preferably arranged in a slender shape along the gas flow direction and have a small electric field strain between the electrodes. For example, a Chang type, a Rogowski type, or a parallel plate type is used. The rising edge of the pulse from the pulse power supply is assumed to be steep (100 ns or less). The control of the repetition frequency is performed by converting the reading of the flow meter 7 into an electric signal or by converting the value of the NOx concentration into an electric signal by the gas sensor 8 and making the frequency proportional to the value.

That is, as shown in the treatment system of FIG. 3, the NOx gas is introduced into the treatment container 1, treated by pulse plasma, and then discharged from the treatment container 1. N
When the Ox gas flows in, the flow rate value is detected by the flow meter 7. This detected value is input to the trigger pulse controller 6 after being converted into an electric signal. Further, the value of the NOx concentration in the processing gas derived from the processing container 1 is detected by the sensor 8, and this detection signal is input to the trigger pulse controller 6.

The trigger pulse controller 6 is a flow meter 7
A control signal is supplied to the high-voltage pulse power supply 5 in accordance with the detection signal of 1 to generate a pulse output having a frequency proportional to the flow rate and a pulse output having a frequency corresponding to the NOx concentration of the gas sensor 8. Here, the pulse repetition frequency changes in proportion to the flow rate, and the frequency is 50 Hz.
The higher the upper limit from the degree, the better. Further, the pulse power source for pulse generation or the switching element of the trigger pulse controller is preferably a discharge control switch, a field effect transistor, or the like, but any other element capable of high-speed switching may be used.

According to the embodiment shown in FIGS. 1 to 3, the following effects can be obtained.

(1) By applying a short pulse high voltage having a sharp rising edge, glow discharge plasma can be generated in a state where the voltage between electrodes is high, and the plasma region can be made wider than arc discharge.

(2) A plasma having a high electron temperature can be generated by glow discharge having a steep rise (100 ns or less),
The processing efficiency is improved.

(3) By changing the pulse repetition frequency with respect to the processing flow rate, it is possible to perform processing from a small flow rate to a large flow rate without changing the plasma processing container.

(4) Further, the processing energy efficiency is improved by controlling the frequency according to the NOx concentration of the exhaust gas.

FIGS. 4 and 5 show an exhaust gas treatment apparatus according to another embodiment of the present invention, in which the same or corresponding parts as those in FIGS. 1 to 3 are designated by the same reference numerals.

In this embodiment, both the flow meter 7 and the gas sensor 8 are provided on the gas introduction side of the processing container 1. That is, the flowmeter 7 and the gas sensor 8 are provided in the introduction pipe 2, and the detection signals of the flowmeter 7 and the gas sensor 8 are input to the trigger pulse controller 6.

As shown in the processing system of FIG. 5, the flow rate detection signal of the introduced gas by the flow meter 7 and the NOx concentration value detection signal of the introduced gas by the gas sensor 8 are input to the trigger pulse controller 6. Trigger pulse controller 6
Is for controlling the high-voltage pulse power supply 5 based on one or both of these detection signals to control the frequency of the pulse plasma generated between the discharge electrodes 4a and 4b. Similar actions and effects can be obtained.

[0029]

The present invention is as described above, in which the exhaust gas is guided to the plasma generating container, a short pulse electric field is applied to the electrode from the high voltage pulse power source with respect to the gas flow, and an electron temperature of An exhaust gas treatment system that generates a high non-equilibrium plasma and controls the pulse repetition frequency according to the treatment flow rate or the NOx concentration value. Can be obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an exhaust gas treatment device according to an embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA of the apparatus of FIG.

3 is a block diagram of the processing device of FIG. 1. FIG.

FIG. 4 is a configuration diagram of an exhaust gas treatment device according to another embodiment of the present invention.

5 is a block diagram of the processing system of FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Processing container, 2 ... Inlet pipe, 3 ... Outlet pipe, 4a, 4b ...
Discharge electrode, 5 ... High-voltage pulse power supply, 6 ... Trigger pulse controller, 7 ... Flow meter, 8 ... Gas sensor.

Claims (1)

[Claims] 1. A processing container in which exhaust gas flows,
A flow meter and a gas sensor respectively disposed in the exhaust gas flow passage, at least a pair of plasma generating electrodes mounted in the processing container, and a high voltage pulse for applying a high voltage pulse to the pair of plasma generating electrodes. An exhaust gas treatment device comprising a power supply and a pulse control unit that controls a pulse output frequency of the high-voltage pulse power supply according to a detection signal of the flow meter or a detection signal of a gas sensor.