Halogenated Hydrocarbon Decomposition by Water DC Plasmas under Atmospheric Pressure

研究了水等离子体分解氢氟乙烯（HFC-134a）的过程。在铜棒内嵌铪阴极和喷嘴型铜阳极，采用直流电弧放电产生水等离子体。水等离子炬的优点是通过直流放电产生100%的水等离子体。独特的蒸汽产生导致便携式轻型等离子体产生系统，不需要燃气供应单元，以及由于不需要额外的水冷却而具有高能效。通过常压下稳定的直流100%水等离子体生成，证明了氢氟烃破坏的可行性。HFC-134a分解产生CO、CO_2。废气中的H_2和中和容器溶液中可回收的HF。使用水作为等离子体的支持气体，而不是氧气，提高了破坏性能，降低了ODS残留水平，同时消除了CF_4的产生。分解后的副产物TOC在溶液中可以忽略不计。当HFC-134a进给量与电弧功率之比为0.43 mmol/kJ时，分解效率可达99.9%，因此在1 kW电弧功率下，最大进给量可达160 g/h。水等离子体处理危险废物比空气等离子体处理和传统焚烧处理更有效。如果热等离子体作为化学反应气体得到有效利用，那么蒸汽等热等离子体将为废物处理提供更大的能力。等离子体系统应用于废物处理有望缩小系统的体积，减少废气中的有害物质，最终降低废物处理的成本。

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.