3-D Modeling of DC Transferred Arc Twin Torch for Asbestos Inertization

Summary form only given. The aim of this work is to investigate by means of a 3-D numerical model the fluid flow and temperature distribution of a plasma transferred electric arc discharge generated between two suspended metallic electrodes. This twin torch device is used inside a plasma furnace for hazardous waste incineration and asbestos inertization. Flow and energy equations are solved for an optically thin Ar plasma under conditions of LTE, while the electromagnetic field equations are solved in their scalar and vector potential form. Electrodes interfaces are taken into account using a simplified approach, imposing a current density distribution on the cathode surface. The anode and cathode regions are discretized in their detailed design, in order to better understand the effects of their geometries on the discharge behavior. Turbulence effects are taken into account into the model using a RANS approach, as well as the effect on the discharge characteristics of using different types of plasma gas (air and Ar/H₂ mixtures), for various geometric and operating conditions. Results are presented in order to characterize the fluid flow and the temperature field of this kind of device. Unsteady effects that may arise under particular operating conditions in the zone of attachment of the two plasma columns are investigated by means of a time dependent approach, in order to select operating conditions and the relative geometric configuration of the two metallic electrodes that induce a stable plasma configuration in the downstream zone of attachment of the two plasma columns. Simulations can also give important information on non-axisymmetric anode attachment under particular operating conditions. Simulations are performed using a customized CFD commercial code FLUENTcopy, parallelized over a network cluster of double processor calculators in order to use the full capabilities of the 3-D modelling code. Conclusions will be drawn concerning the possibility- of using this modelling tool to predict the plasma discharge behaviour when anode disruption occurs under critical operating conditions as an effect of gas entrainment in the anode region