Taichi Sugai

The Effect of Spraying of Water Droplets and Location of Water Droplets on the Water Treatment by Pulsed Discharge in Air

In this paper, some characteristics of a method for decomposing organic compounds by spraying a water solution of organic compounds as droplets into pulsed streamer discharges in air are presented. For the characteristics, the effect of spraying the water droplets compared with water film flowing in a chamber wall, and locations of water droplets into the discharge area on water treatment by the pulsed discharge in air was investigated. In the experiments, a coaxial electrode was used. A solution of organic dye, indigo carmine, was used for a sample. Experimental methods of the effect of spraying the water droplets were to sample each solution gotten through the discharge area as water droplets and water film. Experimental methods of the effect of locations of the water droplets were to spray the water droplets near the wire electrode or the cylindrical electrode. The time spent for decolorizing the water droplets, including indigo carmine, was 0.57 times shorter than that flowing along the inner wall of a reactor into the discharge. This result shows that spraying as water droplets into the discharge in air is effective for faster treatment of water. The time spent for decolorizing the water droplets, including indigo carmine, at the location near the cylindrical electrode of the reactor was 1.5 times faster than that at the location near the wire electrode of the reactor. This result shows that the location near the cylindrical electrode of the reactor has many radicals that are effective for degradation of organic compounds.

Influence of a Circuit Parameter for Plasma Water Treatment by an Inductive Energy Storage Circuit Using Semiconductor Opening Switch

In this paper, we investigate a water treatment method that sprays waste water droplets into a pulsed discharge space. For this method, it is important to apply pulsed voltages with a short pulse width and a fast rise to the electrode to realize high energy efficiency. An inductive energy storage (IES) circuit using a semiconductor opening switch (SOS) outputs pulsed voltages similar to the above-mentioned voltage. We report the characteristics of the water treatment using the IES circuit. The capacitance and inductance in the IES circuit are varied. An increase in the inductance in the secondary circuit of the pulse transformer, results in the formation of pulsed voltages with a longer pulse width; thus, the ratio of the thermal loss to the discharge energy becomes high. However, the energy transfer efficiency improves. Additionally, we vary the maximum current of the SOS, keeping the pulse width constant, by adjusting the capacitance and the inductance. As a result, when the current in the SOS increased, pulsed voltages with a higher peak and a shaper rise are obtained. Further, the pulse width of the voltage and the energy transfer efficiency are not affected by the current in the SOS. Hence, the energy density of the discharge is higher. The increase in the secondary inductance and the forward current increased the energy efficiency of the water treatment system owing to the increase in the energy transfer efficiency and the discharge energy density.

Investigation for Optimization of an Inductive Energy Storage Circuit for Electrical Discharge Water Treatment

In this paper, we investigated a water treatment method that sprays waste water droplets into a pulsed discharge space. To increase energy efficiency of this method, a pulsed power generator should output a pulsed power of a high peak and a short pulse width and be low circuit loss, high repetition rate, high power, and high stability. An inductive energy storage circuit using a semiconductor opening switch was studied to satisfy the above-mentioned requirement. Initially, effect of turn ratio of a pulse transformer (PT) in the circuit was investigated. Energy transfer efficiency and the pulsewidth of the output voltage increased with the PT turn ratio, resulting in an increase of the efficiency of the water treatment system. Then, the effect of the load impedance was investigated. The result showed that an optimum resistance to maximize the efficiency exists. From these results and a previous experimental report, we concluded that the optimization conditions are summarized below. The turn ratio and the inductance in the secondary circuit should be as high as possible under the condition, which does not output the very long pulse. The impedance of the discharge at an electrode for the water treatment should be a value that maximizes the energy transfer efficiency. Capacitance of capacitors in the circuit should be adjusted to obtain optimal peak voltage for the generation of active species.

Influence of Rise Rate of Applied Voltage for Water Treatment by Pulsed Streamer Discharge in Air-Sprayed Droplets

This paper investigates a water treatment method of spraying droplets of wastewater into a pulse discharge space. Water treatment is performed by applying a pulsed voltage with different rise rates to investigate the influence of rise rate. The rise rates of the applied voltage are 1300, 830, and 240 V/ns, and the discharge current in the faster rise rates is higher. The plasma diameter of the streamer discharge is believed to increase with an increase in the rise rate. The treatment is applied to an aqueous solution of indigo carmine. Active species, e.g., ozone and OH radicals, generated by the discharge increase owing to the effect of a higher rise rate. Therefore, the chromogenic bond of the indigo carmine is decomposed more rapidly with a higher rise rate. The decomposition speed of the benzene ring of the indigo carmine is, however, similar because the more OH radicals there are, the shorter their lifetime is. The energy efficiency for the decomposition of the indigo carmine depends on the discharge power and the discharge duration, which varies owing to the difference of the rise rate.

Investigation of optimum pulse width of appled voltage for water treatment by pulsed streamer discharge in air spraying water droplets

We have studied the water treatment method of spraying the droplets of waste water into a pulse discharge space. In this method, we have been developing the pulse generator which realizes higher treatment efficiency. For that, the investigation of an optimum applied voltage from the pulse generator for the treatment is needed. In this paper, investigation of an optimum pulse width has been carried out by applying the voltage of different pulse widths. As sample water for the investigation, indigo carmine solution was used. The pulse widths of applied voltage was 40, 60 and 80 ns, and Those rIse time was 12, 19 and 32 ns, respectively. By the water treatment of the pulse width of 40 ns, indigo carmine was decomposed at lower energy than that of the other pulse width. From the result, generating of active species is considered to increase in early time of the discharge and to decrease with development of the discharge. Therefore it is expected that shorter pulse width realize higher treatment efficiency.

Improvement of efficiency for decomposition of organic compound in water using pulsed streamer discharge in air with water droplets by increasing of residence time

Water treatment using pulsed streamer discharge in water is studied currently, because the pulsed streamer discharge in water generates active species that decompose organic compounds in water. However, the system for generating streamer discharge in water needs big pulsed voltage supply for applying high voltage and high power, because the breakdown electric field of water is high. To solve this problem, we have studied the method spraying water droplets into discharge space in air whose breakdown electric field is lower than that in water, and have demonstrated that the method can decompose organic compounds faster in low energy consumption. In this paper, to obtain higher decomposition rate by increasing of residence time of water in the discharge space has been investigated. Two types of reactors were designed for increasing the residence time of water in discharge space in air. One of the reactors has pellets packed into a cylindrical electrode, and another has fluorocarbon wires weaving like many cobwebs into the cylindrical electrode. For 60 minutes treatment, the treatment rate of the reactor with packed bed of the pellets was 40 % lower than that without the pellets because the discharge space was narrow by the pellets. In contrast, for the 10∼60 minutes treatment, the treatment rate of the reactor weaving the fluorocarbon wire was 2∼10 % higher than that without the fluorocarbon wire. This is because the treated water was exposed to more streamer discharges by increasing of the residence time of water droplets and maintaining the discharge space size without the fluorocarbon wire.

Waveform Control of Pulsed-Power Generator Based on Solid-State LTD

Pulsed-power generator based on linear transformer driver (LTD) technology has been used to demonstrate waveform control for pulsed atmospheric discharge. This kind of discharge load is known for its time-varying impedance where constant voltage usually does not result in constant current. In this paper, an LTD system has been combined with a field-programmable gate array in order to generate a flexible voltage waveform which, in turn, dictates the discharge current. The experimental results have proved that the current of a discharge load can be arbitrarily controlled, to a certain extent, by properly adjusting the applied voltage. This kind of current waveform control should have significant implications for various applications of discharge-generated plasmas.

Study of Pulsed Atmospheric Discharge Using Solid-State LTD

Pulsed atmospheric discharge has been studied by using a pulsed high-voltage generator based on linear transformer driver (LTD) scheme. Taking advantage of the output flexibility of the LTD, we have studied gas discharge behavior by applying two consecutive pulses to a coaxial discharge load consisting of a wire and a pipe. The experimental results have shown that the discharge current of the second pulse is always lower than that of the first pulse for the same voltage amplitude, when the two pulses are too close to each other (<100

The Effect of Scale-Up of Pulsed Corona Discharge for Treatment of Pollution Water Sprayed in Discharge Gap

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The Effect of Flow Rate and Size of Water Droplets on the Water Treatment by Pulsed Discharge in Air

). An explanation for this phenomenon has been explored by using a model that considers the effect of residual charge left by the first pulse. The findings obtained by this paper will help us understand the fundamental characteristics of pulsed atmospheric discharge.