Discrete element analysis of experiments on mixing and bulk transport of wood pellets on a forward acting grate in discontinuous operation

Abstract

Grate systems are of significant importance in many energy technology applications, where heterogeneous fuel like biomass which is composed of non-spherical particles of varying sizes is processed. Particulate solid mixing and transport on a grate have direct influence on the thermal conversion process. Therefore, a detailed understanding of the mixing and transport of the particulate solid is essential for the further development of biomass and waste incineration plants. The discrete element method (DEM), in which all particles and their interactions are tracked over time, allows obtaining in-depth information on mixing and bulk transport on grate systems and provides an easy way to avoid extensive experimental investigations. Up to now, grate systems have mainly been addressed by the discrete element method for particles of spherical shape. In the current paper simulations with the discrete element method of a scale model of a forward acting grate are performed neglecting particle/gas interaction, heat and mass transfer as well as chemical reactions. The grate is operated discontinuously with cylindrical shaped wood pellets applied as bed material. Different motion patterns and grate operational conditions are investigated. The particle motion and the mixing are monitored through image analysis and the discharged particle mass is analyzed. The obtained results indicate a reasonable agreement of simulations and experiments, and show that the discrete element method is capable of predicting mixing and bulk transport on grate systems.