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-134 a）的过程。采用直流电弧放电的方法，在铜杆中嵌入铪作为阴极，铜杆作为阳极，产生水等离子体。水等离子体炬的优点是通过DC放电产生100%水等离子体。该系统不需要额外的水冷却，具有较高的能量利用率，并且在大气压下稳定地产生100%水直流等离子体，证明了HFC等离子体的可行性。HFC-134 a分解产生CO、CO_2。和H_2，以及可从中和容器的溶液中回收的HF。使用水而不是氧气作为等离子体辅助气体，提高了销毁性能，减少了消耗臭氧层物质的残留量，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-134 a进料速率与电弧功率之比为0.43 mmol/kJ时，可获得99.9%的分解效率，因此在1 kW的电弧功率下，最大进料速率估计为160 g/h。水等离子体系统处理危险废物的效果优于空气等离子体和传统的焚烧法。如果热等离子体作为化学反应气体得到有效利用，则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规模，减少废气中的有害物质，最终降低废物处理成本。

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.