Simulation and experimental study on the degradation of the greenhouse gas SF6 by thermal plasma

SF6 gas is widely used on many occasions especially in the power equipment, but it has been restricted since Kyoto Protocol as the strongest greenhouse gas. To reduce the SF6 emission, several methods are now used such the recycling & purification and the SF6 degradation. Considering the huge market of SF6 and the recent demand in the field of power equipment, it is necessary to explore new ways to thoroughly destroy SF6. This work brought out the idea to degrade retired SF6 by thermal plasma. A simplified kinetic model was established to predict the feasibility of this idea as well as the degradation products of SF6, and then the prototype of SF6 degradation by thermal plasma was built and tested. In thermal plasma, SF6 gradually decomposed into atoms, and then H2 was added to capture the released F atoms to generate HF and also prevent the association reactions of SF6. In order to achieve the desired degradation effect, the reaction temperature and the mixing ratio of H2 should be sufficiently high. However, excessive H2 could generate the H2S, and excessive discharge power could decrease the energy yield. When the flow rate of SF6/H2 was set as 8/30 L/min and the discharge current was set as 100A, the destruction removal efficiency (DRE) of SF6 was 99.0% and the energy yield was 206 g/kWh. This work also discusses how to further treat the by-products such as HF and S from this prototype effectively.