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Waste Treatment by Thermal Plasma Systems

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Concept of waste treatment by thermal plasmas

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Plasma jet generated under atmospheric pressure

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Multi-phase AC arc for waste treatment

Thermal plasma waste treatment has attracted the most attention as a green technology for the utilization of organic waste because thermal plasmas can offer distinct advantages for waste treatment processes, such as a high enthalpy, which increases reaction rate, oxidation or reduction atmospheres in accordance with required chemical reactions, and rapid quenching (105-106 K s-1), which produces non-equilibrium chemical compositions. The decomposition of organic wastes, such as rubber, plastic, and medical wastes using thermal plasmas has been studied by many researchers.

We have developed a direct current (DC) water plasma torch for the treatment of greenhouse gases of hydrofluorocarbons (HFCs) [8], perfluorocarbons (PFCs), and other typical wastewater pollutants. In the case of decomposition of phenol solution with a high chemical oxygen demand (COD), the results of a study showed that 0.1-1 mol% phenol was drastically decomposed by the water plasma with energy efficiencies of 0.19-3.48 g kWh-1. The decomposition mechanism of phenol in water plasmas has also been reported in. Aromatic compounds can be dissociated into phenolic or simpler hydrocarbons radicals in discharge region. In addition, some active species like hydrocarbons radical produced by breaking benzene ring, O-atom, and H-atom are also considered to be beneficial to phenol conversion.

The decomposition of glycerine, methanol, ethanol, and acetone was performed using the DC water plasma torch. Moreover, under each decomposition process, the generated gas and liquid products were analyzed, and some major components such as OH, CH, C, and CH3 etc. radicals in water plasmas were identified, respectively. Furthermore, on the basis of the experimental results and information from the literature on the fundamental kinetics of hydrocarbon oxidation in the gas phase coupled with our knowledge of the reaction intermediates, the mechanisms of decomposition of organic compounds in water plasmas were proposed and the role of CH3, CH2, CH, and OH radicals were elucidated by respectively and comparatively study of the results themselves within this study with the results of other studies.

Watanabe Lab., Department of Chemical Engineering, Kyushu University
Professor Takayuki Watanabe
Assistant Professor Manabu Tanaka
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