Thermochemische Zerlegung unter superkritischen Bedingungen

This project examines the decomposition under supercritical conditions for the gasification of solid plastic waste. Gasification is currently considered one of the most important processes in solid waste recycling technology. Because polypropylene (PP) is moisture, chemical, and temperature resistant, it is widely used. Therefore, recycling PP waste is a very important problem, considered here. In the present project, supercritical water is used for recycling PP waste. PP is converted into flammable gases with a high content of H₂ and CO. The resulting CO₂ can also be further converted into CO so that the entire process does not cause any CO₂ emissions. The numerical study carried out is based on a very precise method, Direct Numerical Simulation (DNS) for reactive multiphase flows. This allows all physicochemical processes that are relevant to the gasification of PP under supercritical conditions to be examined in detail. The DNS is carried out using the in-house code called DINO. In this code, the surface of the solid PP is fully resolved using the Immersed Boundary Method (IBM). The DNS approach can be used to describe surface and gas-phase reactions as well as particle decomposition. The PP plastic waste is initially simplified as a group of C₃H₆ monomers. Thanks to this simplification, a 6-step reaction kinetics is implemented, assuming that all surface processes are first-order reactions. The results obtained from this DNS help to understand the entire decomposition and gasification processes, which are very intricate. A better understanding of these physical processes will help develop reliable models that can later be used for faster process simulations. Various operating conditions are currently being investigated (varying Reynolds number, size of PP particles, operating temperature and pressure, inflow conditions). Various parameters are used to evaluate the results, in particular drag coefficient, buoyancy coefficient, Nusselt and Sherwood numbers, surface reaction rate, and degree of decomposition of the particles.