KR100365965B1 - Plasma/Catalyst System for Reduction of Nox in Diesel Engine Exhaust Gas - Google Patents

Abstract

The present invention relates to a plasma / catalyst system for reducing nitrogen oxides (Nox) in diesel exhaust gas.

In the plasma / catalyst system of the present invention, Ag / Al ₂ O connected in series to a plasma reactor and a plasma reactor supplied with a DC pulse power, wherein the metal reaction tube is an anode and the iron wire in the center of the metal reaction tube is a cathode. _It consists of a catalytic reactor in the form of a packed tower filled with _three catalysts, and the diesel engine exhaust gas to be treated is sequentially processed through a plasma reactor and a catalytic reactor operated at atmospheric pressure.

Description

Plasma / Catalyst System for Reduction of Nox in Diesel Engine Exhaust Gas}

The present invention relates to a plasma / catalyst system for reducing nitrogen oxides (Nox) in exhaust gases of internal combustion engines, in particular diesel engine exhaust gases.

As a method of reducing harmful air pollutants generated in a heat engine or a production process, selective oxidation and reduction methods using a catalyst, use of additives, post combustion or collection, etc. have been adopted.

However, the above methods have a disadvantage in that they are difficult to be applied to pollutants that move while varying combustion conditions such as automobiles due to their limited application range. In particular, since diesel engine exhaust gas is operated under conditions where the air-fuel ratio is rare, the concentration of oxygen and nitrogen oxides (NOx) is high, and the characteristics of Nox and particulate matter (PM) decrease when one side is reduced, and the other side increases. off), it is very difficult to reduce it at the same time. Soot can meet the regulations by improving the engine and using diesel particulate filters (DPF), but Nox has not yet offered a satisfactory method for post-processing.

As a method of reducing NOx, exhaust gas recirculation (EGR) method and a method using a catalyst have been proposed, but exhaust gas recirculation (EGR) has a problem of reducing the thermal efficiency and durability of the engine and increasing the smoke, and the catalyst. Using the method has a disadvantage in that Nox is not effectively reduced when the oxygen concentration is high, such as a diesel engine.

Recently, plasma-based catalysts, especially plasma / catalyst systems that simultaneously perform plasma and catalyst reactions, have been actively studied. Highly reactive intermediate products produced by plasma reactions increase the catalytic activity of the catalytic reactor and operate temperatures. It is reported that there is an effect of widening the range of. [M. Iwamoto et al., Appl. Catal. B: Environ. 5, L1-L5 (1994)]

It is an object of the present invention to provide a plasma / catalyst system that removes NOx from diesel engine exhaust gas with high efficiency.

1 is a schematic diagram of a measuring device including a plasma / catalyst system of the present invention.

2 is a schematic diagram of a plasma reactor in a system of the present invention.

** Explanation of symbols for main parts of drawings **

11: plasma reactor 12: catalytic reactor

13: DC pulse power 14: oscilloscope

15: Nox Meter 16: Gas Chromatography

17: gas 18: mass flow meter

19: preheater 111: anode

112: cathode 113: thermocouple

114: pressure gauge

Plasma / catalyst system of the present invention for achieving the above object is a plasma reactor 11 and plasma reactor is supplied with a DC pulse power, the metal reaction tube is an anode and the iron wire in the center of the metal reaction tube is a cathode It is composed of a catalytic reactor (12) of a packed tower type packed with an Ag / Al ₂ O ₃ catalyst connected in series, characterized in that the diesel engine exhaust gas to be treated is sequentially processed through a plasma reactor and a catalytic reactor. .

The form of the plasma reactor is shown in FIG. 2. The anode 111 is a steel wire passing through the center of the reaction tube and the cathode 112 is a metal reaction tube itself.

The plasma reactor supplies 10-100 J / L of energy per unit flow of exhaust gas and is operated at atmospheric pressure.

The catalytic reactor was filled with a catalyst prepared by a known method of supporting AgGa ₃ aqueous solution in γ-Al ₂ O ₃ and calcining, and the operating temperature was 200-450 ° C.

The exhaust gas to be treated causes the plasma reactor and the catalytic reactor to pass sequentially. In the plasma reactor, the Nox conversion of NO in the exhaust gas is converted to NO _2, the catalyst in the reactor takes place Nox reduction the NO ₂ is reduced to N _2. That is, in the plasma reactor is not without fundamentally Nox is removed, is reduced to N ₂ is NO ₂ harmless reaction Nox is removed, will take place in the catalytic reactor.

The construction of the present invention will become more apparent in the following examples.

<Example>

1. Experiment apparatus

In order to measure the NOx reduction performance of the plasma / catalyst system of the present invention, an experimental apparatus was configured as shown in FIG. 1.

The plasma reactor 11 (FIG. 2) was cylindrical with an inner diameter of 36 mm and a length of 300 mm, and made of stainless steel. The diameter of the electrode 111 is 1.4 mm, and the power source uses a DC pulse power 13 that has a pulse width of about 1 μsec and whose pulse repetition rate can be adjusted. The voltage and current during discharge were measured and recorded with a high voltage probe (Tektronix P6015) (not shown), current meters A6302 and A503B (not shown), and an oscilloscope (LeCroy 140) 14.

The catalytic reactor 12 was made of glass as a continuous flow fixed bed reactor having an inner diameter of 25 mm and a length of 300 mm. The catalyst was supported by installing a glass filter (glass filter) inside the reaction tube. The temperature in the reactor was measured and controlled by contacting a thermocouple to the catalyst bed.

The Nox concentration of the sample gas (exhaust gas) passed through the plasma reactor and the catalytic reactor was connected to the Nox measuring instrument (Thermo Environmental Instrument, Model 42H) (15) and gas chromatography (Youngin, 600D) (16) at the rear of each reactor. It was measured quantitatively. Porapak Q (1/8 ＂od × 2m) and Molecular Sieve 5A (1/8＂ od × 2m) were used as the column. The temperature of Porapak Q is 100 ℃ and the temperature of Molecular Sieve is It was set at 25 ° C. The temperature of the thermal conductivity detector (TCD) was set to 100 ° C.

Sample gas (17) is a reactor for a constant flow rate of pure oxygen, propylene (C ₃ H ₆ ), Nox gas diluted in He and Nox gas diluted in N ₂ through a mass flow controller (MFC) (18) It was prepared by the method of feeding.

The following is the composition of the sample gas used in the examples.

division NO NO ₂ O ₂ C ₃ H ₆ Atmosphere gas Sample gas 1 1755ppm 145 ppm 5% 1000 / 2000ppm He Sample Gas 2 1900 ppm - 5% 1000 / 2000ppm N ₂

Sample gas 2 is a man-made exhaust gas made in analogy to the composition of diesel exhaust gas, a sample gas 1 is the case of the sample gas 2 is difficult to exactly measure the amount that is, N ₂ concentration converted to N ₂ in the Nox increases the nitrogen concentration Therefore, it is a comparative gas in which atmospheric gas is He.

2. Experimental method

Since NOx reduction should be made by converting to harmless N ₂ , the reduction of Nox to N ₂ was evaluated through sample gas 1 using He as an atmospheric gas to accurately measure the change in N ₂ concentration.

The sample gas was heated up to 200 ° C. with the preliminary heater 19 and introduced into the plasma reactor at a flow rate of 1 L / min. The plasma reactor was allowed to corona discharge at 200 ° C. and the catalytic reactor was operated at 250 ° C.-550 ° C. Using a gas chromatography instrument and Nox in the steady state was measured of Nox Reduction and Nox conversion rates of the exhaust gas to N ₂ at the same time. However, since sample gas 2 has a high concentration of N _2, it is difficult to accurately measure the change in concentration, and thus only the Nox reduction amount was measured.

In the plasma reactor, the energy input amount was adjusted to the DC pulse power source so that the Nox conversion rates through the plasma reaction were similar to each other. This is because the activation energy of nitrogen and helium, which are atmospheric gases, is different. In this embodiment, the sample gas 1 has a plasma generation voltage of 3.5 kV and the sample gas 2 of 10 kV. (At this time, the energy supply per unit flow rate is 10 J / L for sample gas 1 and 37 J for sample gas 2). / L)

By comparing the experimental results of the sample gas 1 and the experimental results of the sample gas 2, the conversion rate of the reduced Nox to N ₂ in the sample gas 2 was estimated.

<Example 1>

In this example, the composition change of Nox in the sample gas was examined when the sample gas 1 and the sample gas 2 were passed through the plasma reactor. The results are summarized in the following table.

division Sample gas 1 Sample Gas 2 When C ₃ H ₆ is 1000 ppm When C ₃ H ₆ is 2000 ppm When C ₃ H ₆ is 1000 ppm When C ₃ H ₆ is 2000 ppm NO concentration 1487 1373 1500 1407 NO ₂ concentration 404 507 343 432

Through the plasma reaction, it can be seen that the total amount of Nox was not changed only when NO was oxidized to NO ₂ . In addition, it can be seen that the higher the concentration of hydrocarbon in both the sample gas 1 and the sample gas 2, the greater the amount of NO is oxidized to NO ₂ .

<Example 2>

In this example, the Nox removal rate of the plasma / catalyst system was compared with the Nox removal rate of the catalytic reactor only for the sample gas 1. Experiment at 400 ° C.

division When C ₃ H ₆ is 1000 ppm When C ₃ H ₆ is 2000 ppm Catalytic reactor Plasma / catalyst reactor Catalytic reactor Plasma / catalyst reactor Nox (NO + NO ₂ ) Conversion Rate 18 32 45 92% Nox (NO + NO ₂ ) Conversion to N ₂ 14 24 39 68%

It can be seen that the removal rate of Nox in the plasma / catalyst system using the plasma reactor is higher than the case of using only the catalytic reactor. In the same manner as in Example 1, the removal rate of Nox was high when the concentration of hydrocarbon was high. In particular, in the case of 2000 ppm of hydrocarbon concentration, the plasma / catalyst system had the highest Nox conversion rate of 92% and Nox conversion rate of N _{2 at} 68%. The higher NOx removal rate in the plasma / catalyst system using the plasma reactor than the catalyst reactor alone is attributed to the increased reaction with the catalyst due to the activation of the reactants through the plasma reaction.

<Example 3>

In this example, the Nox removal rate was investigated for sample gas 1 according to the temperature and the concentration of hydrocarbon contained in the sample gas. In the following table, C means a catalytic reactor, P / C means a plasma / catalyst system.

division Nox conversion rate or Nox → N ₂ conversion rate Temperature 250 ℃ 350 ℃ 400 ℃ 450 ℃ 550 ℃ When C ₃ H ₆ is 1000 ppm C (Nox Conversion Rate) 5 13 18 40 37 C (Nox → N ₂ conversion rate) 4 11 14 35 30 P / C (Nox Conversion Rate) 23 30 32 47 21 P / C (Nox → N ₂ conversion rate) 12 22 24 38 10 When C ₃ H ₆ is 2000 ppm C (Nox Conversion Rate) 6 26 45 84 66 C (NO ₂ → N ₂ Conversion Rate) 5 22 39 67 55 P / C (Nox Conversion Rate) 36 90 92 91 26 P / C (Nox → N ₂ conversion rate) 29 74 68 69 21

When the amount of hydrocarbon was 1000 ppm, a maximum of 47% Nox conversion was observed at 450 ° C, and the conversion of Nox to N ₂ was 38%. Increasing the hydrocarbon to 2000 ppm showed about 90% Nox conversion and about 70% Nox conversion to N ₂ at 350-450 ° C. In the case of the plasma / catalyst system, the active temperature range of the catalyst was wider than in the case of using only the catalytic reactor, and the conversion rate of Nox was also increased. However, it was also observed that at 550 ° C., the use of the plasma and the catalyst together decreased the activity rather than the use of the catalyst alone.

According to the plasma / catalyst system of the present invention, NOx can be effectively removed from diesel engine exhaust gas containing unburned hydrocarbon at atmospheric pressure and high oxygen concentration.

Claims (3)

A packed column filled with a plasma reactor supplied with a DC pulse power and an Ag / Al ₂ O ₃ catalyst connected in series with the plasma plasma reactor in which the metal reaction tube is the anode and the iron wire in the center of the metal reaction tube is the cathode. It is composed of a catalytic reactor of the type, the diesel engine exhaust gas to be treated is characterized in that the plasma reactor and the catalytic reactor is sequentially processed through the plasma / catalyst system. The plasma / catalyst system of claim 1 wherein the plasma reactor is operated at atmospheric pressure. The plasma / catalyst system of claim 1, wherein the catalytic reactor is operated at 250-450 ° C.