Numerical investigation of thermal gasification in enclosed screw-conveyor reactor for removal of ¹⁴C from irradiated graphite waste

Investigated numerically are the effects of the rotational speed of the screw conveyor and the reactor temperature on the changes in the diameter of graphite particles passing through a laboratory-scale enclosed screw-conveyor reactor. Also investigated experimentally are a thermal gasification of graphite particles to carbon-oxygen compounds to determine a kinetic reaction model and kinetic parameters. The non-Newtonian fluid-like flow of graphite particles in the enclosed screw-conveyor reactor is numerically simulated by solving the momentum equation using a recently developed viscoplastic model with a rotating reference frame. The numerical approach coupled with the determined kinetic model of the gasification reaction of graphite powder successfully predicted the motion of the graphite particles and changes in their diameter flowing through the reactor. For a reactor temperature of 1073 K, the size of the feed graphite particles was predicted to decrease by 2% to 30% depending on the rotational speed of the screw conveyor. The predictions of the numerical simulations can be used to optimize the operating conditions of the enclosed screw-conveyor reactor for decontaminating irradiated graphite waste by removing the radiocarbons, which are located mainly on the graphite surface. (author)