Ies Pulsed Power

NOx Treatment Using Inductive-Energy-Storage Pulsed Power Generator Fumito Endo, Non-member (Nagaoka University of Technology, [email protected]) Weihua Jiang, Member (Nagaoka University of Technology, [email protected]) Kiyoshi Yatsui, Member (Nagaoka University of Technology, [email protected]) Naohiro Shimizu, Member (NGK Insulators, Ltd., [email protected]) Keywords : pulsed corona discharge, SI-thyristor, NOx, inductive energy storage

wall. The total volume of the reactor is 0.05 l, giving the average gas residual time of ~ 1.5 s at a flow rate of 2 l/min. Figure 2 shows NO removal rate as a function of input voltage, with different inductively stored energy as a parameter.

50

5.8 [mJ] 4.7 [mJ]

ε [%]

Nitrogen oxides (NOx) by diesel combustion engines have caused serious environmental problems. However, the amount of NOx can hardly be reduced only by improving the combustion system, because NOx can be easily formed by oxygen and nitrogen at high temperature. A process of after treatment is required to remove NOx from the exhaust gas before it is released into the atmosphere. NOx removal can be achieved through chemical reactions. Active radicals leading to various chemical reactions were obtained by a non-equilibrium thermal plasma method. The non-equilibrium thermal plasma method is considered to be promising for NOx treatment of diesel exhaust gas. In this paper, we report our experimental results obtained by using a very compact pulsed-power generator. The objective of this research is to develop a portable flue-gas system that can be used on diesel vehicles. Figure 1 shows the circuit diagram of compact pulsed-power system, the inductive-energy-storage (IES) generator.

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3.7 [mJ]

30

20

50

150 100 Input Voltage (E) [V]

Fig. 2 NO removal rate as a function of input voltage, in nitrogen atmosphere. Initical NO concentration 500ppm, repetition rate of 500Hz. Here, NO removal rate (ε) is defined by the following equation.

ε=

Fig.1 Circuit diagram of IES generator by SI-thyristor The IES generator produces pulsed high voltage by cutting off an inductive current using a SI-Thyristor. Since the circuit operation is controlled by an FET, the IES generator is made to be very compact. A discharge reactor is a coaxial corona discharge cell consisting of a tungsten wire at the center and a stainless-steel cylinder as the

[NOx] – [NOx]’ [NOx]

×100 [%]

(1)

where [NOx] and [NOx’] are the initial and final NO concentrations [ppm], respectively. As seen from Fig. 2 the NO removal rate increases as the input voltage is increased. The experiments of NOx treatment by using an IES pulsed-power generator and a coaxial corona discharge reactor have given the following conclusions. 1. NO and NO2 can be decomposed in nitrogen atmosphere. 2. In N2/O2 atmosphere, the total concentration of NOx does not change on the repetition rate. 3. Under a constant inductor-stored energy, the NO removal rate in N2 atmosphere increases as the input voltage is increased. 4. The maximum NO removal efficiency obtained is ~ 50 g/kWh.