KR20000047389A - Apparatus and method for simutaneous removal of air pollutants using non-thermal plasma technology - Google Patents

Abstract

PURPOSE: Air pollutant treatment equipment and its method by using plasma is provided for eliminating the air pollutant such as sulfur dioxide, nitrogen oxide, dioxin, etc. contained in exhaust gas generated from an iron-ore sintering plant, thermal power plant, etc. in plasma condition using pulse corona discharge. CONSTITUTION: Air pollutant treatment equipment (100) comprises a direct-current (DC) high-voltage supplier (110) for supplying the DC high-voltage; a pulse high-voltage generator (120) for outputting the DC high-voltage applied from the DC high-voltage supplier (110) by converting to the pulse high-voltage; a step-up transformer for elevating the pulse high-voltage output from the pulse high-voltage generator (120); a magnetic switch (140) for providing a pulse interval of the elevate pulse signal to a responsor after converting to a short interval by the step-up transformer (130); a plasma responsor (150) for generating corona discharge in a case of applying the pulse high-voltage from the magnetic switch (140) to a discharge pole; and a discharge circuit section (160) for discharging the full-charged high-voltage to the plasma responsor (150) after corona discharging.

Description

Apparatus and method for treating air pollutant using plasma {APPARATUS AND METHOD FOR SIMUTANEOUS REMOVAL OF AIR POLLUTANTS USING NON-THERMAL PLASMA TECHNOLOGY}

The present invention relates to an apparatus and a method for treating air pollutants, and more particularly, to plasma, which is an air pollutant contained in exhaust gases such as iron ore sintering plants and thermal power plants, nitrogen oxides, dioxins, and the like, by using a plasma corona discharge. It relates to an air pollutant treatment apparatus and method using a plasma that can be removed in a state.

In general, iron ore sintering plants and thermal power plants that burn fossil fuels contain a large amount of sulfur dioxide (SO ₂ ), nitrogen oxides (NO _x ), and dioxins that are harmful to the flue gas emitted during fuel combustion. A flue gas treatment facility for removing air pollutants is provided.

Currently, the most widely used technology for removing sulfur dioxide from flue gas is wet lime / gypsum using limestone slurry, and other dry processes using dry absorbents and activated carbon are commercially available.

On the other hand, nitrogen oxide removal methods include improvement of the combustion method during fossil fuel combustion and the denitrification method of the exhaust gas, which is a post-combustion treatment method for suppressing the generation of nitrogen oxides. Among these, the flue gas denitrification method is divided into a wet method and a dry method depending on whether or not nitrogen oxide is absorbed into the aqueous solution. The wet method is relatively inferior to the dry method because it is less economical than the dry method and requires the treatment of secondary pollutants such as water pollution. Representative commercialization of the dry process is selective catalytic reduction (SCR) (K.Kawamura and VHShui, Pilot plant experience in electron-beam treatment of iron-ore sintering flue gas and its application to coal boiler flue gas cleanup, Radiation Physical Chemical, vol. 24, no. 1, pp. 117-127,1984). The selective catalytic reduction method is a method of selectively reducing nitrogen oxide in the exhaust gas to nitrogen and water while simultaneously passing the exhaust gas and the reducing agent through the catalyst layer.

However, in the conventional air pollutant treatment method, as the pollutants are sequentially processed through two processes of desulfurization and denitrification, in which a large amount of flue gas has completely different characteristics, the initial investment and operating costs are increased, and an optimal process of desulfurization and denitrification is performed. Not only is it required to be combined, but the discharge of waste water from the wet method is pointed out as a problem.

Therefore, one way to improve this problem is to use a plasma to simultaneously remove and remove the air pollutants by dry. Referring to the conventional apparatus for treating air pollutants using plasma, the plasma reactor 10 includes a plurality of discharge electrodes 12 and ground plates 11 provided at regular intervals. It has a line-plate structure. When discharged by applying a pulsed high voltage to the discharge electrode 12 of the plasma reactor 10, the exhaust gas is in a plasma state, and a large amount of oxidative radicals and ozone such as O, OH, and HO ₂ are generated, and sulfur dioxide, nitrogen oxide, and the like. The oxidative radical and ozone are reacted and removed as in Scheme 10 through Scheme 1 below.

SO ₂ + OH-> HSO ₃

HSO ₃ + OH-> H ₂ SO ₄

SO ₂ + O-> SO ₃

SO ₃ + H ₂ O-> H ₂ SO ₄

NO + O-> NO ₂

NO + HO _2- > NO ₂ + OH

NO + OH-> HNO ₂

HNO ₂ + OH-> NO ₂ + H ₂ O

NO + O _3- > NO ₂ + O ₂

NO ₂ + OH-> HNO ₃

At this time, sulfuric acid (H ₂ SO ₄ ) and nitric acid (HNO ₃ ) produced by the reaction of sulfur dioxide and nitrogen oxides with oxidative radicals and ozone are neutralized by chemical reaction with ammonia (NH ₃ ) and converted into ammonium sulfate and ammonium nitrate. .

On the other hand, the pulse high voltage generator is provided to apply a high pulse voltage to the discharge electrode 12 of the conventional plasma reactor 10, as shown in Figure 2, the rotary spark gap switch 13 is used to convert the direct current high voltage capacitor (C _P ) and then discharge the capacitor (C _P ) instantaneously according to the switching operation of the rotary spark gap switch 13 to generate a pulsed high voltage (Civitano, L., Industrial application of plused corona processing to flue gas , in Non-Thermal Plasma Techniques for Pollution Control, Part B, BMPenetrante and SESchultheis, Ed.Springer-Verlag, 1993, pp. 103-130).

However, the rotational spark gap switch 13 has a merit of being easy to manufacture and inexpensive in implementing a pulsed high voltage generator, but a long service life due to short life due to wear of the spark gap due to repeated switching operation. There is an impossible problem. In addition, the plasma reactor 10 has both an electrical resistance component and a capacitor component, so that even if a short high voltage pulse is applied to the discharge electrode 12 of the plasma reactor 10, the pulse width of the voltage becomes considerably longer. The reason why the pulse width of the voltage is long is due to the ion space charge generated in the plasma reactor, and when the pulse width of the voltage becomes longer than 1 mV, it is difficult to apply a high voltage to the discharge electrode because it is transferred from the corona discharge to the arc discharge. .

In addition, conventionally, by designing the capacitor capacitance of the pulse high voltage generator at least 100 times larger than the capacitance of the plasma reactor, there is a problem that the electrical energy transfer efficiency from the pulse high voltage generator to the plasma reactor is about 30%. In addition, there is a problem that the reactor is enlarged because there is no design standard of the plasma reactor to effectively induce corona discharge.

The air pollutant treatment technology using the plasma reactor has a problem that the initial investment cost and the installation site are small, and the by-products are simple to be treated, but the denitrification efficiency is low compared to the desulfurization efficiency and a large operation power is required. Therefore, in order to improve the competitiveness and practical use of the plasma process, it is necessary to improve the pollutant removal efficiency and reduce the operating power.

Accordingly, the present invention has been made to solve such a conventional problem, the object of which is to prevent the corona discharge generated in applying the pulsed high voltage to the plasma reactor to the arc discharge to prevent the peak voltage applied to the reactor It is an object of the present invention to provide an apparatus and method for treating air pollutants using plasma, which can increase electrical energy introduced into a plasma reactor by increasing the amount.

Another object of the present invention is to reduce the power loss by increasing the electrical energy transfer efficiency from the pulse high voltage generator to the plasma reactor, and to reduce the size of the plasma reactor air pollution using the plasma to induce an effective corona discharge It is to provide a material processing apparatus and method thereof.

Still another object of the present invention is to provide an apparatus and method for treating air pollutants using plasma which can improve the efficiency of removing air pollutants.

1 is a view showing a schematic configuration of a conventional plasma reactor.

2 is a circuit diagram showing the electrical configuration of a conventional plasma reactor.

3 is a circuit diagram showing the configuration of the air pollutant treatment apparatus using the plasma according to the present invention.

4 is a perspective view showing an example of a plasma reactor for implementing the present invention.

5 is an arrangement structure diagram of the discharge electrode according to an embodiment of the plasma reactor for implementing the present invention.

Figure 6 shows the voltage and current waveform diagram of each circuit portion of the air pollutant treatment apparatus according to the present invention.

7 is a system diagram showing the configuration of the air pollutant treatment apparatus using the plasma according to the present invention.

Figure 8 is a graph showing the relationship between the injection amount of ammonia and propylene for explaining the air pollutant treatment method according to the present invention.

9 is a graph showing the desulfurization rate when using calcium hydroxide as a neutralizing agent in the air pollutant treatment method of the present invention.

10 is a schematic diagram of a line-plate small plasma reactor.

FIG. 11 is an electrical circuit diagram of a pulse generator manufactured to apply a pulsed high voltage to the small plasma reactor of FIG. 10.

12 is a graph showing a change in electric energy transfer efficiency when the capacitance of the pulse forming capacitor is changed.

FIG. 13 is a graph showing a relationship between removal amount of sulfur dioxide and nitrogen oxide according to a peak voltage applied to a plasma reactor.

Explanation of symbols on the main parts of the drawings

100: air pollutant treatment device, 101: ground plate,

102: half electrode, 110: DC high voltage supply,

120: pulse high voltage generator, 130: step-up transformer,

140: magnetic switch, 150: plasma reactor,

160: discharge circuit portion, 170: electrostatic precipitator.

In order to achieve the above object, the air pollutant treating apparatus using the plasma according to the present invention is an air pollutant treating apparatus for removing the air pollutants contained in the exhaust gas in a state in which the inlet exhaust gas is converted into a plasma state by corona discharge. A plasma reactor for generating a corona discharge by applying a high voltage to the discharge electrode, a DC high voltage supply for converting an input power into a DC high voltage, and outputting a DC high voltage supplied from the DC high voltage supply to a pulse high voltage of a predetermined cycle. A pulse generator for outputting the pulse generator, a boost transformer for boosting the pulse high voltage of the pulse generator to a corona discharge voltage of a predetermined level for corona discharge, and a short width of the high voltage pulse boosted by the boost transformer; Supplied to the discharge electrode The magnetic switch and the discharge circuit part which discharges the high voltage charged in the said plasma reactor immediately after the corona discharge by the said plasma reactor are provided.

In addition, the air pollutant treatment method according to the present invention is to generate a corona discharge by applying a pulsed high voltage to the plasma reactor, the atmosphere to remove the air pollutants contained in the exhaust gas in a state in which the exhaust gas is converted to a plasma state by the corona discharge. A pollutant treatment method comprising: a first step of injecting a reaction additive into the exhaust gas; and a second step of applying a pulsed high voltage to the plasma reactor after the first step to treat the exhaust gas in a plasma state.

Hereinafter, the configuration and operational effects of the air pollutant treatment apparatus and method using the plasma according to a preferred embodiment of the present invention will be described in detail.

Figure 3 is a circuit diagram showing an electrical configuration according to an embodiment of the air pollutant treatment apparatus using a plasma according to the present invention. As shown in FIG. 3, the apparatus 100 for treating air pollutants using plasma according to the present invention includes a DC high voltage supply 110 supplying a DC high voltage and a DC high voltage applied from the DC high voltage supply 110. A pulse high voltage generator 120 for converting and outputting a pulse high voltage, a boost transformer 130 for boosting the pulse high voltage output from the pulse high voltage generator 120, and a pulse signal boosted by the boost transformer 130. A magnetic switch 140 for shortening the pulse width and providing the plasma reactor, a plasma reactor 150 generating a corona discharge when a high pulse voltage is applied from the magnetic switch 140 to the discharge electrode, and after the corona discharge. And a discharge circuit unit 160 for discharging the high voltage charged in the plasma reactor 150.

In this configuration, the pulse high voltage generator 120 includes a capacitor C1 that charges the DC high voltage from the DC high voltage supply 110 according to time constants with the resistors R1 and R2, and a control unit not shown. And a switch SW1 for performing on / off switching operation by the control signal CS and discharging the voltage charged in the capacitor C1 to the boost transformer side at the on time.

The magnetic switch 140 is configured by connecting at least two or more LC circuits having the capacitor C and the inductor L in parallel.

The discharge circuit unit 160 includes a discharge resistor R _P connected in parallel to the plasma reactor 150, and includes an inductor L _P connected in series with the discharge resistor. At this time, the total impedance of the discharge resistance (for example 400 ohm) and the inductor 200μH is set to be larger than the equivalent impedance (approximately 50 ohm) of the plasma reactor 150, but preferably set to be approximately 10 times larger than the magnetic switch 140. Pulse voltage) can be provided to the plasma reactor 150 without power loss. In addition, the discharge circuit unit 160 sets the time constant by the capacitor component and the discharge resistance of the plasma reactor 150 to 1.0 to 2.0 times the pulse width required by the plasma reactor 150, preferably about 1.5 times. Set it.

The plasma reactor 150 is represented by a condenser before the start of the corona discharge and a parallel structure of the variable capacitor and the variable resistor after the start of the corona, where L _L is the stray inductance of the reactor, C _L is the variable capacitor, R _L represents a variable resistor.

In addition, the apparatus for treating air pollutants according to the present invention includes a reverse diode for preventing reverse current inflow at an output terminal of the DC high voltage supply 110 to prevent an overcurrent or reverse current from being damaged. D1).

4 is a perspective view showing the structure of a plasma reactor for implementing the present invention. As shown in FIG. 4, the plasma reactor 150 for implementing the present invention includes a discharge electrode 101 having a positive pulse voltage applied thereto, for example, having a diameter of 3 mm, and, for example, 2 m in height and length, respectively. And a ground plate 102 having a flat plate shape of 5 m and grounded. In this case, both the discharge electrode 101 and the ground plate 102 are formed of carbon steel, and the discharge electrode 101 is positioned between the two ground plates 102. The distance between the ground plate 102 which is grounded is 200 mm, for example, and therefore the distance between the discharge electrode 101 and the ground plate 102 is 100 mm. In addition, since the effective width of the plasma reactor 150 through which the exhaust gas is processed is manufactured to about 1.2 m, a total of six exhaust gas flow paths are formed in the plasma reactor.

The plasma reactor 150 is composed of a discharge electrode 101 as an anode and a ground plate 102 as a cathode, which can be regarded as a kind of capacitor. The mechanical capacitance before the corona discharge is about 4.0 kW.

Figure 5 is an embodiment showing the arrangement of the discharge electrode of the plasma reactor for implementing the present invention. As shown in FIG. 5, the discharge electrode 101 is located between two ground plates 102, and the distance between the discharge electrodes 101 is set to be at least greater than the distance between the discharge electrode 101 and the ground plate 102. One set of discharge electrodes is composed of a total of 18 discharge electrodes, the plasma reactor has a total of six discharge electrode sets, the total discharge electrode length of the plasma reactor 150 considering only the effective length that can occur corona discharge between the discharge electrode and the ground plate It is 216m (18 * 2m * 6 sets).

6A and 6B show voltage and current waveform diagrams of circuit parts of an air pollutant treatment apparatus according to the present invention. 6A and 6B, the apparatus for treating air pollutants using plasma according to the present invention receives a high DC voltage of 30 kV from the DC high voltage supply 110 and boosts the pressure to about 150 kV, which is 5 times through the boost transformer 130. The applied voltage pulse is applied to the plasma reactor 150 by the magnetic switch 140. 6A illustrates voltage waveforms measured at the measurement points VD1, VD2, and VD3, and FIG. 6B illustrates current waveforms measured at the measurement points CT1, CT2, and CT3.

The pulse voltage and current waveforms applied to the plasma reactor 150 were measured at VD3 and CT3. Finally, the voltage applied to the reactor reaches a peak value of 110 kV and the peak current reaches 2.3 kA. At this time, the width of the pulse signal applied to the plasma reactor 150 is approximately 1㎲ and arc discharge does not occur in the plasma reactor 150 even at the above voltage.

Hereinafter, with reference to the accompanying drawings, an apparatus and a method for treating air pollutants using plasma according to the present invention will be described in detail.

First, the DC high voltage supplier 110 of the air pollutant treating apparatus according to the present invention supplies a DC high voltage of up to 40 kV. In one embodiment of the present invention, a DC high voltage of about 30 kV is supplied to the pulse generator 120. .

The pulse generator 120 converts the DC high voltage supplied from the DC high voltage supply 110 into a pulse high voltage having a predetermined frequency. Specifically, the DC high voltage of 30 kV is applied to the resistors R1 and R2 and the capacitor C1. The energy stored in the capacitor C1 when the switch SW1 is charged to the capacitor C1 according to the time constant and performs the switching operation according to the control signal CS provided from the controller (not shown) is It is transmitted to the condenser C2 via the boost transformer 130 and sequentially compressed by the magnetic switch 140. The control signal CS provided from the controller is a signal in which the on control signal and the off control signal are continuously repeated, and the magnetic switch 140 continuously repeats the on / off state in response to the signal.

The boost transformer 130 has a 1 to 5 primary and secondary winding ratio, and supplies a 150 kV pulse voltage to the magnetic switch 140 by boosting the pulse voltage of the pulse generator 120 by 5 times.

The magnetic switch 140 shortens the width of the high voltage pulse boosted by the boost transformer 130 and provides the plasma reactor 150. Specifically, the magnetic switch 140 provides a circuit while the capacitor C2 is charged. A large inductance is given to the first magnetic switch L2 to close. After the first magnetic switch L2 is saturated, the energy charged in the condenser C2 flows to the condenser C3 to be charged, and the charging time at this time is approximately 1 μs. When the second magnetic switch L3 is saturated, the energy of the condenser C3 is transferred to the plasma reactor.

Further, the total impedance of the plasma of the discharge circuit 160 includes a discharge resistance (R _P) and for containing a series inductor (L _P) connected to the discharge resistor (R _P) and inductor (L _P) The pulse impedance of the magnetic switch 140 is provided to the plasma reactor 150 without power loss by being set about 10 times larger than the equivalent impedance of the reactor 150.

When a pulsed high voltage is applied to the discharge electrode 101 of the plasma reactor 150, the voltage rises rapidly to be charged in the reactor. When the voltage between the discharge electrode and the ground plate reaches the corona starting voltage due to the charging of the pulse high voltage, the corona discharge starts from the discharge electrode when a certain time, which is a statistical delay time, elapses. Due to the corona discharge, the insulation of the exhaust gas introduced between the discharge electrode and the ground plate is destroyed to form a plasma state, and thus a large amount of oxidative radicals and ozone are generated to remove sulfur dioxide or nitrogen oxide, which are air pollutants contained in the exhaust gas.

At this time, the width of the high voltage pulse signal provided to the plasma reactor is preferably about 1 kW. If the width of the high voltage pulse is kept longer than 1 kW, the arc discharge undesirably occurs. Therefore, the voltage charged in the condenser component of the plasma reactor must be quickly discharged by the discharge circuit unit 160 to maintain the width of the high voltage pulse within 1 kW. Therefore, in this embodiment of the present invention, the time constant determined by the capacitor component of the plasma reactor and the discharge resistance of the discharge circuit unit 160 is set to about 1.5 μs, which is about 1.5 times the 1 μm. After the corona discharge occurs in 150, the high voltage charged in the plasma reactor 150 may be quickly discharged through the discharge circuit unit 160.

The pulsed high voltage supplied to the plasma reactor by the configuration according to the embodiment of the present invention becomes a pulse waveform having a peak voltage of about 110 kV and a peak current of about 2.3 kV.

On the other hand, the supply energy (E) per pulse of the high-voltage pulse applied to the plasma reactor 150 is integrated over time (t) after multiplying the voltage (V) and the current (I), as shown in Equation 1 below. In this case, the power consumption P is obtained by multiplying the energy E supplied per pulse by the pulse repetition rate, that is, the frequency f.

When the energy supplied per pulse to the plasma reactor is calculated by Equation 1, the discharge power is 12 kW when the pulse repetition rate (the number of pulses applied to the discharge electrode per second, that is, the frequency) is 200 Hz. The energy supplied per pulse of 60J contains the energy consumed in the resistors connected in parallel to the plasma reactor. Therefore, if we move the current measurement position and repeat the same calculation again with only the current flowing into the plasma reactor, we can see that the energy consumed in the resistance is very small, less than about 3J per pulse, because the inductor is paralleled to the plasma reactor. This is because current is not allowed to flow through the resistor.

The change in energy supplied to the plasma reactor while changing the DC high voltage output from the DC high voltage generator of the present invention in a predetermined unit within the range of 30-40 kV is shown in Table 1 below.

DC high voltage 30 kV 35 kV 40 kV Supply energy 60J / pulse 84J / pulse 110J / pulse Supply energy per 1m of discharge electrode 0.28J / m / pulse 0.39J / m / pulse 0.51 J / m / pulse

The effective discharge electrode length of the plasma reactor is 216 m in total, and when the direct current high voltage output from the direct current high voltage generator 110 is supplied at 30 kV, the energy supplied to the reactor per pulse is 60 J, and the energy supplied to the discharge electrode 1 m per pulse is 60 J / 216 m / pulse, that is, 0.28 J / m / pulse.

In addition, when supplying a direct current high voltage at 35 kV, about 84 J of energy per pulse is supplied to a plasma reactor, and the energy supplied to 1 m of discharge electrodes per pulse is 0.39 J / m / pulse. When the DC high voltage is supplied at the maximum condition of 40 kV, the plasma reactor is supplied with energy of about 110 J per pulse, and the energy supplied to the discharge electrode 1 m per pulse is 0.51 J / m / pulse. Therefore, the reactor design conditions for supplying a large amount of power to the reactor with a low pulse repetition rate within the limit of no spark or arc in the plasma reactor 150 are about 0.5 J / m / of electrical energy supplied to the discharge electrode 1 m per pulse. It is designed to supply with pulse.

Referring to the air pollutant treatment method using a plasma according to the present invention. The composition of the exhaust gas generated in the sintering process used in the present invention is as shown in Table 2, 70% nitrogen, 15% oxygen, 5% carbon dioxide, 8% moisture, 1% carbon monoxide, 150ppm sulfur dioxide, 150ppm nitrogen oxide Consists of. In addition, the sintering process flue gas contains a small amount of toxic dioxin, a chlorine-based volatile organic compound, and its concentration is about 20ng TEQ / Nm ³ . TEQ here represents the equivalent toxicity of dioxin.

ingredient N ₂ O ₂ CO ₂ H ₂ O CO SO ₂ NO _X Furtherance 70% 15% 5% 8% One% 150 ppm 150 ppm

7 is a schematic view showing the configuration of a plasma air pollutant treating apparatus according to the present invention. As shown in FIG. 7, the apparatus for treating air pollutants using plasma according to the present invention is processing by introducing a part of exhaust gas from a sintering plant in steelworks, and a plasma reactor 150 and a product for removing the air pollutants from the exhaust gas. It is divided into an electrostatic precipitator 170 collecting the ammonium salt. The positive DC high voltage is converted into a pulse high voltage using the pulse high voltage generator 120 and applied to the discharge electrode 101 of the plasma reactor 150, and the negative pulse high voltage is applied to the electrostatic precipitator 170.

Ammonia used as a neutralizing agent and propylene, a reaction additive, are injected at the inlet of the apparatus, and sample inlets for concentration analysis of SO ₂ , NO _X , and dioxins are provided at the inlet and outlet sides of the apparatus.

In addition, the front end of the plasma reactor 150 and the rear end of the electrostatic precipitator 170, a temperature sensing unit for measuring the exhaust gas temperature is installed, the temperature of the inlet and outlet is usually 150 ℃ and 110 ℃, respectively. The exhaust gas is introduced into the plasma reactor through a pipe having a diameter of 340 mm and a porous dispersion plate. The air pollutants of the exhaust gas flowing into the plasma reactor are converted into ammonium salt in the solid state while passing through the plasma reactor 150 and then collected in the electrostatic precipitator. At this time, the electrical resistivity of ammonium sulfate and ammonium nitrate is approximately 10 ⁵ ohmcm and is easily collected in the electrostatic precipitator 170.

Injecting the neutralizing agent and the reaction additive into the flue gas is first injected with ammonia, a neutralizing agent, and then propylene is injected into the reaction additive together with the neutralizing agent to induce a large amount of oxidative radicals required to remove air pollutants.

After the neutralizing agent and the reaction additive are injected, a high voltage pulse is applied to the plasma reactor to treat the exhaust gas in the plasma state. That is, corona discharge is generated in the plasma reactor 150 by the high voltage pulse supplied from the pulse generator in the state in which propylene and ammonia are injected into the exhaust gas, so that the exhaust gas inside the plasma reactor becomes a plasma state, and thus a large amount of oxidative property is generated. Radicals and ozone are removed as they react with the harmful air pollutants contained in flue gases such as sulfur dioxide (SO ₂ ), nitrogen oxides (NO _X ), and dioxins.

At this time, the concentration of ammonia and propylene injected into the exhaust gas is determined by the following equation (3).

In determining the injection concentration of ammonia, a neutralizing agent, it is necessary to set an appropriate concentration that can suppress the emission of unreacted ammonia and propylene and at the same time increase the removal efficiency of sulfur dioxide and nitrogen oxide within the limit that the discharge of unreacted ammonia is suppressed. Preferably, in one embodiment of the present invention, the ammonia injection concentration is maintained at 0.8 as R (NH ₃ ).

Propylene, a reaction additive, is used to increase the removal efficiency of nitrogen oxides (NO _X ) and dioxins, and the propylene injection concentration is maintained at 0.5 to 0.8 of R (C ₃ H ₆ ). It demonstrates with reference to FIG.

On the other hand, Figure 8 is a graph showing the relationship between the injection amount of ammonia and propylene for explaining the air pollutant treatment method according to the present invention. As shown in FIG. 8, first, the horizontal axis of the graph represents the energy density obtained by dividing the input power P by the exhaust gas flow rate Q, where the exhaust gas flow rate Q is converted to a standard state of 0 ° C. and 1 atmosphere. will be. Ammonia used as a neutralizing agent was injected at 360 ppm corresponding to 0.8 times R (NH ₃ ), and propylene as a reaction additive was measured by injecting 0.5 and 0.8 of R (C ₃ H ₆ ).

As shown in FIG. 8, sulfur dioxide (SO ₂ ) is mostly removed regardless of the amount of propylene injected, but it can be seen that nitrogen oxide (NO _X ) is greatly improved in removal efficiency in proportion to the amount of propylene injected and energy density. For example, when propylene is not used at an energy density of 2.6 Wh / Nm ³ , about 30% of nitrogen oxides are removed, but when propylene is injected at 75 ppm and 120 ppm corresponding to 0.5 and 0.8 of R (C ₃ H ₆ ) It can be seen that the removal efficiency of nitrogen oxides is increased to 50% and 60%, respectively.

This is because oxidative (OH) radicals and ozone generated in the plasma state react with propylene to generate alkyl radicals and alkoxy radicals. The alkyl radicals and alkoxy radicals generate HO ₂ radicals when reacted with oxygen. This is because 6 can occur or be in the form of a highly oxidizing peroxy radical to promote the oxidation of nitrogen oxides (NO _X ).

That is, as shown in the graph of FIG. 8, when the amount of propylene injected is increased, the removal efficiency of nitrogen oxide is improved by increasing alkyl radicals and alkoxy radicals generated by reacting with oxidative radicals and ozone.

Therefore, the proper injection amount of propylene will vary depending on the power density input and the desired nitrogen oxide removal efficiency, but unreacted propylene is discharged when the propylene injection concentration is more than 30 ppm per 1Wh / Nm ³ of energy density, so that propylene is not emitted. The maximum amount of propylene injected in the furnace is determined to be less than 30 ppm per 1Wh / Nm ³ energy density.

Dioxin, a hydrocarbon-based trace toxic substance under these operating conditions, can be removed more than 75% by 20ng TEQ / Nm ³ or less. That is, the plasma process according to the present invention can remove not only sulfur dioxide and nitrogen oxide but also dioxin at the same time.

9 is a graph showing the desulfurization rate when calcium hydroxide is used as a neutralizing agent in the air pollutant treatment method according to the present invention. When calcium hydroxide is used instead of ammonia as the neutralizing agent, a slurry having 10 wt.% Of calcium hydroxide (Ca (OH) ₂ ) is continuously stirred in a storage tank and transferred to a nozzle using a high pressure pump. At this time, the nozzle used for spraying may be a double-fluid type injecting high pressure air and high pressure liquid to make droplets having an average particle diameter of about 30 μm. In addition, the exhaust gas temperature in the plasma reactor was 150 ° C., and the slurry flow rate set the Ca / S equivalent ratio to 1 to 10 range.

Under these conditions, the desulfurization rate increased from 68% to 75% to 85% by changing the Ca / S equivalent ratio from 1.0 to 1.5 to 2.0. Compared with the results of FIG. 8, in which the ratio of 0.8 to 95% of the desulfurization rate was obtained when ammonia was used, the results measured using calcium hydroxide in FIG. 9 may be relatively inferior, but calcium hydroxide in a process that does not require high desulfurization rate. Can also be used.

On the other hand, one important problem in the design of plasma reaction systems is to increase the electrical energy transfer efficiency, ie pulse conversion efficiency, from the pulse generator to the plasma reactor. In order to increase the electrical energy transfer efficiency, a design considering the electrical matching between the pulse generator and the plasma reactor is required. The principle of pulse generation is discharge to the reactor by charging and switching of the pulse forming capacitor by direct current high voltage.

Therefore, the capacitance of the pulse forming capacitor plays a key role in the performance of the pulse generating circuit, that is, the energy transfer efficiency. In principle, the capacitance of the pulse-forming capacitor must be equal to the capacitance of the plasma reactor so that all the electrical energy stored in the capacitor can be transferred to the reactor. In practice, however, since the capacitance of the plasma reactor changes when the corona discharge starts, the optimal pulse-forming capacitor value should be determined in consideration of the change in capacitance of the plasma reactor.

In the present invention, the capacitance of the pulse forming capacitor is changed to find the maximum electrical energy transfer condition and the electrical energy transfer efficiency to the plasma reactor is compared and examined. Dose ratios were determined.

That is, Figure 10 is a perspective view showing the configuration of a plasma reactor according to an embodiment of the present invention, Figure 11 shows a circuit configuration of a pulse generator according to the present invention. Plasma reactor according to the present invention is used in the form of a line-plate, where the thickness of the discharge electrode d, the distance between the ground plate is D, the capacitance per unit length of the discharge electrode of the reactor can be calculated by the following equation (5) .

According to Equation 5 above, the geometrical capacitance of the plasma reactor of FIG. 10 before the corona discharge occurs is 110 kW. The pulse forming capacitor C _P of FIG. 11 is charged by a DC high voltage generator. When the voltage of the capacitor reaches the dielectric breakdown voltage of the spark gap electrode, the spark gap SG is short-circuited to instantly transfer the electrical energy charged in the capacitor to the plasma reactor. In order to find the optimum condition for the electrical energy transfer efficiency, the pulse-forming capacitor (C _P ) was changed from 226 ㎋ to 5.2 ㎋ and the electrical energy transfer efficiency was compared. The electrical energy transfer efficiency was defined as the ratio of the energy delivered to the plasma reactor to the energy charged in the pulse forming condenser (C _P ). The energy charged in the pulse forming capacitor is shown in Equation 6 below.

Here, V _C represents the charging voltage of the pulse forming capacitor C _P. In the present invention, the pulse forming capacitor C _P was charged to a voltage of 18.6 kV.

12 is a graph showing the relationship between the electrical energy transfer efficiency according to the capacitance ratio of the pulse forming capacitor and the plasma reactor for the present invention. As shown in FIG. 12, the electrical energy transfer efficiency is large when the capacitance ratio (C _P / C _R ) of the plasma reactor and the pulse forming capacitor is about 2 to 5, and the capacitance ratio of the plasma reactor and the pulse forming capacitor is particularly high. When it is about 3, it can be seen that the maximum.

The reason is that if the capacitance of the pulse forming capacitor is too large compared to the reactor, only a part of the energy charged in the capacitor is transferred to the reactor and the remainder remains in the capacitor. If the capacitance of the reactor is constant, the maximum energy transfer efficiency can be obtained when the reactor capacitance and the pulse generating capacitor are equal. However, the maximum energy transfer occurs in the range where the capacitance ratio of the pulse forming capacitor and the plasma reactor is 2 to 5 because the plasma reactor capacitance is increased by corona discharge. Therefore, the capacitance of the pulsed capacitor is preferably set to the same range as the capacitance at the corona discharge of the plasma reactor, which is roughly according to the present invention when the capacitance of the pulsed capacitor is set to three times the plasma reactor capacitance. to be.

Lastly, in designing an air pollutant treatment apparatus according to the present invention, the matters to be considered are the distance relationship between the discharge electrode and the ground plate of the plasma reactor, and the distance between the discharge electrode and the ground plate is compared with the peak voltage applied to the plasma reactor. You can decide from the relationship.

13 (a) and 13 (b) are graphs showing a relationship between removal amounts of sulfur dioxide and nitrogen oxides according to peak voltages applied to the plasma reactor, respectively. As shown in FIG. 13, sulfur dioxide and nitrogen oxides do not begin to be removed until the peak voltage applied to the plasma reactor is 15 kV or more. When the peak voltage applied to the plasma reactor is 23 kV or more, spark occurs in the reactor. In this case, since the distance between the discharge electrode and the ground plate of the plasma reactor is 1.5 cm, the minimum average electric field strength (defined as the applied peak voltage divided by the distance between the discharge electrode and the ground plate) from which sulfur dioxide and nitrogen oxide are removed is 10 kV / cm. The maximum electric field strength without sparking is 15 kV / cm. This condition can be referred to as the minimum / maximum condition of the average electric field strength in the design between the discharge electrode and the ground plate of the plasma reactor. In other words, in designing the plasma reactor, if the plasma reactor is designed such that a voltage of 10-15 kV per 1 cm between the discharge electrode and the ground plate is applied, the resistance between the discharge electrode and the ground plate is reduced to arc discharge regardless of the size of the reactor. It can effectively induce corona discharge under conditions that do not transition.

Apparatus and method for treating air pollutants using plasma according to the present invention are not limited to the above-described embodiments and may be variously modified within the scope of the technical idea of the present invention.

As described above, in the apparatus and method for treating air pollutants using plasma according to the present invention, the pulse width is kept within 1 kW when the pulse high voltage is applied to the plasma reactor to prevent arc discharge for a short time in the plasma reactor. It can supply a lot of electric energy.

In addition, it is possible to reduce the power loss by increasing the electrical energy transfer efficiency from the pulse generator of the present invention to the plasma reactor, it is possible to obtain an effect that can effectively generate a corona discharge in a state of minimizing the size of the plasma reactor.

Furthermore, in the air pollutant treatment method of the present invention, by simultaneously injecting propylene, a hydrocarbon reaction additive, and ammonia, a neutralizing agent, into the exhaust gas, sulfur dioxide, nitrogen oxides, and dioxins can be simultaneously removed with low operating power, thereby improving the efficiency of removing air pollutants. have.

Claims (17)

In the air pollutant treatment apparatus for removing the air pollutants contained in the exhaust gas in a state in which the introduced exhaust gas is converted into a plasma state by a corona discharge, A plasma reactor for generating a corona discharge by applying a high voltage to the discharge electrode, DC high voltage supply for converting input power into DC high voltage and outputting A pulse generator for converting a DC high voltage supplied from the DC high voltage supply into a pulse high voltage of a predetermined period and outputting the same; A boost transformer for boosting the pulse high voltage of the pulse generator to a corona discharge voltage of a predetermined level for corona discharge; A magnetic switch for shortly converting the width of the high voltage pulse boosted by the boost transformer and supplying the discharge electrode to the plasma reactor; And a discharge circuit for discharging the high voltage charged in the plasma reactor immediately after the corona discharge by the plasma reactor. The pulse generator of claim 1, wherein the pulse generator comprises: A capacitor C1 for charging the DC high voltage from the DC high voltage supply according to the time constant with the resistors R1 and R2, And an on / off switching operation by a control signal, and a switch (SW1) for discharging the charging voltage of the capacitor (C1) to the boosting transformer side at an on time. 2. The magnetic switch of claim 1, wherein the magnetic switch comprises at least two LC circuits, and the capacitance of the capacitor C3 at the end of the circuit is set to be 2 to 5 times larger than the capacitance of the plasma reactor. Air pollutant treatment apparatus using a plasma. 4. The apparatus of claim 3, wherein the capacitance of the capacitor C3 of the magnetic switch is set to a value three times larger than the capacitance of the plasma reactor. The air pollutant treating apparatus using plasma according to claim 1, wherein the magnetic switch is formed by connecting at least two LC circuits having a capacitor and an inductor in parallel. The air pollutant treating apparatus using plasma according to claim 1, wherein the discharge circuit unit has a discharge resistance R _P connected in parallel to the plasma reactor. The method of claim 6, wherein the discharge circuit is characterized in that the time constant by the capacitor component (C _L ) and the discharge resistance (R _P ) of the plasma reactor to set 1.0 to 2.0 times the pulse width required in the plasma reactor. Air pollutant treatment device using plasma. 8. The plasma display device as claimed in claim 7, wherein the discharge circuit unit sets the time constant by the capacitor component C _L and the discharge resistance R _P of the plasma reactor to 1.5 times the pulse width required by the plasma reactor. Air pollutant treatment device used. The air pollutant treating apparatus using plasma according to any one of claims 6 to 8, wherein the discharge circuit unit further comprises an inductor L _P connected in series with the discharge resistor R _P. 10. The apparatus of claim 9, wherein the total impedance of the discharge resistance R _P and the inductor L _P of the discharge circuit unit is set to be larger than an equivalent impedance of the plasma reactor. The air pollutant using plasma according to claim 10, wherein the total impedance of the discharge resistance R _P and the inductor L _P of the discharge circuit unit is set to a value 10 times larger than the equivalent impedance of the plasma reactor. Processing unit. The air pollutant treatment apparatus using plasma according to claim 1, wherein the magnetic switch supplies the energy supplied per pulse to the plasma reactor at 0.5 J / m / pulse per 1 m effective discharge electrode length. The apparatus of claim 1, wherein the peak voltage applied to the plasma reactor is applied such that an electric field strength between the discharge electrode and the ground plate is at least 10 kV / cm and at most 15 kV / cm. In the air pollutant treatment method for applying a high voltage pulse to the plasma reactor to generate a corona discharge, to remove the air pollutants contained in the exhaust gas in a state in which the exhaust gas is converted into a plasma state by the corona discharge, A first step of injecting a reaction additive into the exhaust gas; And a second step of applying the pulsed high voltage to the plasma reactor after the first step to treat the exhaust gas in a plasma state. 15. The method of claim 14, wherein the reaction additive injected in the first step is propylene. The method for treating air pollutants using plasma according to claim 14 or 15, wherein ammonia, which is a neutralizing agent, is injected together with the reaction additive in the first step. 15. The air pollutant using plasma according to claim 14, wherein the injection amount of propylene in the first step is kept below 30 ppm per unit energy density (1 Wh / Nm ³ ) supplied to the plasma reactor in the second step. Treatment method.