Halogenated Hydrocarbon Decomposition by Water DC Plasmas under Atmospheric Pressure

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The purpose of this paper is to investigate decomposition process of hydrofluoroethylene (HFC-134a) by water plasmas. The water plasma was generated by DC arc discharge with a cathode of hafnium embedded into a copper rod and a nozzle-type copper anode. The advantage of the water plasma torch is generation of 100%-water plasma by DC discharge. The distinctive steam generation leads to the portable light-weight plasma generation system that does not require the gas supply unit, as well as the high energy efficiency owing to the nonnecessity of the additional water-cooling.A feasibility of HFC destruction was demonstrated by stable DC 100%-water plasma generation under atmospheric pressure. Decomposition of HFC-134a produces CO, CO_2. and H_2 in the off-gas, and HF which can be recovered in the solution of the neutralization vessel. The use of water as plasma supporting gas, rather than oxygen, improves the destruction performance, reducing the ODS residual level with eliminating CF_4 production. The TOC as the by-products after the decomposition can be negligible in the solution. The decomposition efficiency of 99.9% can be obtained up to 0.43 mmol/kJ of the ratio of HFC-134a feed rate to the arc power, hence the maximum feed rate was estimated to be 160 g/h at 1 kW of the arc power. Water plasma system for hazardous waste treatments is more effective than air plasma process and the conventional incineration process.Thermal plasmas such as steam would provide more capability for waste treatments, if thermal plasmas are utilized effectively as chemically reactive gas. Application of plasma systems for waste treatments is expected to downsize the system, reduce hazardous substances in the off-gas, finally low cost of waste treatments.