An experimental investigation of mixing of wood pellets on a forward acting grate in discontinuous operation

The knowledge about mixing and the transport efficiency of non-spherical particles on grates is needed for the improvement of design and adaption of operational parameters in grate combustion systems. To gain insight into details of the transport of non-spherical particles experimental investigations with a scale model of a forward acting grate are performed in discontinuous operation using wood pellets as bed material. Wood pellets are an important source of biomass within an energy market increasingly relying on renewable sources. ent motion patterns, grate operational conditions and pellet types are investigated. A comparison to spherical particles is performed. The wood pellets as well as the spherical particles are dyed in different colors to distinguish between different layers applied vertically and horizontally on the grate. The particle motion and the mixing are monitored by image analysis from the top and the side of the grate through transparent walls. In addition the discharged particle mass is recorded. The particle mass, the stroke length as well as the particle shape and the motion pattern have a strong influence on the mixing. The stroke velocity only has minor effect on mixing and the amount of particles discharged from the grate. The results obtained under well established boundary conditions are suitable for use as reference data in the verification of particle based simulation approaches as, e.g. the discrete element method.