Simulation and performances of main processes for waste and biomass gasification

In order to define practical application conditions for thermal treatment of mixed solid wastes, the presented study has been conducted in order to describe the fundamental processes that occur during a gasification process, with the aim to construct a specific model for the gasification reactor. The model has been realized by using the tools of energy and mass balances and by considering a chemical gas phase homogeneous equilibrium; the governing equations under steady condition have been defined. In order to completely establish the set of the required equations, some assumption were made: the main concern solid residue composition formed only by inert material, no tar formation, very fast reaction kinetics, adiabatic conditions. Subsequently, on the basis of the above mentioned model, numerical simulations have been performed, and in particular we evaluated: • the change in the operating temperature and the performance parameters, syngas volume, Lower Heating Value (LHV), gasification yield (η), consequent to variation of the inlet air volume; • the change of the operative parameters as a consequence of the choice of a specific gasifying agent (air, dioxide carbon, oxygen and steam); • the change, with reference to pressure variation, of the parameters: air volume, flue gases volume, LHV and gasification yield (η). By considering gasification fundamental processes the above mentioned numerical simulation led to a comparison between the thermal gasification treatment and the usual direct combustion (incineration) operation. The first comparison aspect has been the environmental performance (quantity and quality of the generated flue gas in the two different systems, upstream and downstream of the flue gas treatment system), and it was conducted both on local (pollutant emission) and global scale (GHG formation). Subsequently the aspect of energetic production have been considered, both for electric production or co-generation. The obtained results can be useful to identify possibilities of use, advantages and limits for gasification technology.