Modelling grate combustion of biomass and low rank fuels with CFD application.

A reactor cascade model is used for the numerical simulation of the fixed bed combustion of biomass, municipal solid waste and other low rank fuels. Non-spherical particle geometries are accounted for via their plain specific surface. The model is able to reproduce key quantities like ignition delay time, ignition rate, reaction front velocity and mass conversion rate in close agreement with experimental data. This provides a basis to transfer the fixed bed results to the situation of continuous combustion on forward acting grates. A simplified numerical procedure is presented for this purpose. It allows to estimate the structure of a fuel bed moving on the grate as well as the overbed gas temperature and composition. These data serve as input for separate CFD applications which simulate the gas flow in small scale and in industrial scale power plants together with the associated heat transfer processes. Validation of the modelling is presented for lab scale and bench scale experiments as well as for an industrial municipal solid waste incinerator.