Review on electrical discharge plasma technology for wastewater remediation

This paper presents a review of the literature dealing with the formation of hydrogen peroxide from plasma processes. Energy yields for hydrogen peroxide generation by plasma from water span approximately three orders of magnitude from 4 ? 10?2 to 80?g?kWh?1. A wide range of plasma processes from rf to pulsed, ac, and dc discharges directly in the liquid phase have similar energy yields and may thus be limited by radical quenching processes at the plasma?liquid interface. Reactor modification using discharges in bubbles and discharges over the liquid phase can provide modest improvements in energy yield over direct discharge in the liquid, but the interpretation is complicated by additional chemical reactions of gas phase components such as ozone and nitrogen oxides. The highest efficiency plasma process utilizes liquid water droplets that may enhance efficiency by sequestering hydrogen peroxide in the liquid and by suppressing decomposition reactions by radicals from the gas and at the interface. Kinetic simulations of water vapor reported in the literature suggest that plasma generation of hydrogen peroxide should approach 45% of the thermodynamics limit, and this fact coupled with experimental studies demonstrating improvements with the presence of the condensed liquid phase suggest that further improvements in energy yield may be possible. Plasma generation of hydrogen peroxide directly from water compares favorably with a number of other methods including electron beam, ultrasound, electrochemical and photochemical methods, and other chemical processes.

https://iopscience.iop.org/article/10.1088/0963-0252/20/3/034006/pdf

Review of the methods to form hydrogen peroxide in electrical discharge plasma with liquid water

Decomposition of toxic organic compounds is a major environmental problem. Increasingly, research is being conducted to use plasmas to decompose these wastes in water, as it is simple, effective and does not require the addition of other chemical agents. Different groups have used varied reactor designs. This study calculates and compares relative energy yields of about 27 major types of plasma reactors. The results reveal dramatic differences in the energy yields, up to five orders of magnitude. The most efficient are pulse powered reactors, in which plasma is formed in gas phase and the waste solution sprayed into it. Factors that account for this improved energy yield are discussed. This study will help narrow down efficient reactors for further studies, development and commercial uses.

Water Purification by Plasmas: Which Reactors are Most Energy Efficient?

A review of mainly the past two years is undertaken of the industrial applications of pulsed power. Repetitively operated pulsed power generators with a moderate peak power have been developed for industrial applications. These generators are reliable and have low maintenance. Development of the pulsed power generators helps promote industrial applications of pulsed power for such things as food processing, medical treatment, water treatment, exhaust gas treatment, ozone generation, engine ignition, ion implantation and others. Here, industrial applications of pulsed power are classified by application for biological effects, for pulsed streamer discharges in gases, for pulsed discharges in liquid or liquid- mixture, and for material processing.

/pdf/industrial-applications-of-pulsed-power-technology-lh58nnjdqb.pdf

Industrial Applications of Pulsed Power Technology

Lightning strike protection of composites

A technical overview of a European project on pulsed corona (PC) treatment of polluted streams is presented. Versatile high-power systems that are capable of cleaning both aqueous and gaseous streams in heterogeneous media, in either a corona above water reactor or an aerosol reactor, have been developed. Both reactors are capable of high-phenol removal yields from aqueous streams and increase the biochemical oxygen demand/chemical oxygen demand ratio for several nonbiodegradable wastewaters to such degree that further biodegradation becomes possible. The PC combined with a catalyst is capable of cleaning gaseous streams that are polluted by toluene, styrene, and malodorous constituents. Reduction rates of toluene that are higher than 99% have been achieved, and very high odor-removal efficiency has been demonstrated. The reliable operation of high-power all-solid-state compact nanosecond pulsers has also been demonstrated. For the second phase of the project, a high-power pulser was designed. One compression stage suffices for the formation of 60-kV 3-J pulses across a reactor that has a discharge impedance of approximately 100 Omega at a pulse repetition frequency of up to 500 Hz; the rise time is 15 ns, and the duration is 100 ns. The system scale-up is also analyzed. The estimated price of water treatment in systems that were scaled up to 50 m3 /h is 2 euro/m3. Incineration of aqueous organic waste streams can cost 500 euro/m3 or more, depending on the nature of the contamination, so the PC water-treatment technology may become highly competitive. It is planned in the future to investigate the cleaning efficiency of the developed processes with different industrial wastes, both at laboratory conditions and in the field

High-Power Pulsed Corona for Treatment of Pollutants in Heterogeneous Media

The system comprises an all solid-state compact nanosecond pulser and a plasma reactor. The pulser makes use of magnetic compression techniques. Owing to a fast switching at the feed of the HV transformer provided by an ABB GCT switch, one compression stage suffices for the forming of 45-kV, 100-ns pulses across a 120-/spl Omega/ resistive load at a PRF of up to 1 kHz; the risetime is 15 ns. Plasma reactor is capable of handling both gases and liquids by adding small amounts of atomized water to the gas discharge, in the case of gas, or atomizing polluted liquid itself. In both cases, the treatment is conducted in heterogeneous media. Circuit analysis of compressor and charging system accounting for nonlinear processes in magnetic switches and numerous parasitic parameters is presented. Mechanical and electrical designs are detailed. Typical voltage and current waveforms, volt-ampere characteristics, corona discharge appearance, and light emission characteristics are presented. At operation on a resistive load, the compressor efficiency was found to be approximately 80%, which allowed for air cooling. The experimental results obtained with a resistive load are in fair agreement with the circuit simulation. A novel magnetic compressor circuit improving the coupling to PC discharge is proposed and evaluated.

A high-power pulsed corona source for pollution control applications

A 1.8-kV 100-ps rise-time pulsed-power generator operating at a repetition frequency of 50 kHz is presented. The generator consists of three compression stages. In the first stage, a power MOSFET produces high voltage by breaking an inductor current. In the second stage, a 3-kV drift-step-recovery diode cuts the reverse current rapidly to create a 1-ns rise-time pulse. In the last stage, a silicon-avalanche shaper is used as a fast 100-ps closing switch. Experimental investigation showed that, by optimizing the generator operating point, the shot-to-shot jitter can be reduced to less than 13 ps. The theoretical model of the pulse-forming circuit is presented.

/pdf/a-low-jitter-1-8-kv-100-ps-rise-time-50-khz-repetition-rate-hueh1g23rt.pdf

A Low-Jitter 1.8-kV 100-ps Rise-Time 50-kHz Repetition-Rate Pulsed-Power Generator

Extinction of pool flames by means of a dc electric field

Visual appearance, electrical performance, and chemical activity of a 50-MW 100-kV 22-ns pulsed corona were studied in simulated air-SO/sub 2/ gas mixture in a coaxial reactor. Infrared and mass spectrometers and electrochemical sensors were used for gas diagnostics; solid byproducts were identified using X-ray fluorescent spectrometry. Electrochemical sensors were employed for the measurement of initial concentration, before the discharge commencement. The removal efficiency of SO/sub 2/ in dry and humid air-SO/sub 2/ mixtures was studied. The removal efficiency of SO/sub 2/ decreased at lower pollutant concentration and higher frequency, while the pulse energy was kept invariant. Removal efficiency in dry mixtures was 25 g/kWh; in humid air, it was several times greater, which is attributed to the influence of OH radicals. In dry mixtures, the removal efficiency was much higher at positive polarity. Traces of many compounds were found and identified in treated gas. Ozone was produced in large concentrations both in dry and humid mixtures. Dependence of its formation rate on the pulsed power, and on the voltage polarity was studied. The precipitation of a yellowish powder identified as sulfur was observed. It is ascribed to cleavage of bonds of the SO/sub 2/ molecule by energetic species and confirmed by experiments with dry N/sub 2/-SO/sub 2/ and Ar-SO/sub 2/ mixtures.

Alex Pokryvailo

Papers

High-Power Pulsed Corona for Treatment of Pollutants in Heterogeneous Media

A high-power pulsed corona source for pollution control applications

A Low-Jitter 1.8-kV 100-ps Rise-Time 50-kHz Repetition-Rate Pulsed-Power Generator

Extinction of pool flames by means of a dc electric field

High-power short-pulsed corona: investigation of electrical performance, SO/sub 2/ removal, and ozone generation