Plasma Destruction of Ozone Depleting Substances

Abstract

The literature on the plasma destruction of ozone depleting substances (ODS) such as CCl2F2 and CBrF3 is reviewed, and compared with more recent work on the decomposition of CCl2F 2 and CBrClF2 in oxygen and steam. A comprehensive kinetic scheme for the decomposition of CBrClF2, which includes the decomposition of CCl2F2 and CBrF3, is presented. Simulations performed with this scheme, and experimental results, demonstrate the importance of allowing for the interconversion of ODS in the assessment of plasma destruction devices. Both experimental and modeling results show that the efficiency of operation of a practical plasma ODS destruction device can be quantified in terms of a throughput parameter, the feed to plasma power ratio (units mol (kWh)-1), or in terms of the thermochemical mixing temperature, Tm, of the plasma, ODS and oxidant. At low throughputs and high Tm, essentially complete destruction may be achieved, with below-ppm quantities of ODS remaining in the plasma exhaust gases. As throughput rises and Tm falls, a threshold is reached above which the ODS residual rises steeply towards the practical working limit set for ODS destruction by the Montreal Protocol (a destruction level of 99.99%). The assessment of this limit must include all ODS in the exhaust gases, weighted for ozone depleting potential. The use of steam, rather than oxygen, as the oxidizing gas gives superior destruction performance.