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.