Design Optimisation of Grate Firings for Biomass Combustion by Coupling CFD and DEM Simulation Tools – European Transfer of Results

Project Number 382

The aim of research project no. 294 was the experimental and numerical study of the mixing and transport processes of granular media in grate firing systems in order to understand the involved mechanisms and the influence of material and system parameters. To realize this, the Discrete Element Method (DEM) was used as a modelling tool. The method tracks every single particle in a system to determine position as well as translational and rotational velocity of each single particle.

Based on this, research project no. 328 investigated the influence of mechanical agitation on heat transfer and thermo chemical processes within particle assemblies through experiments and numerical simulation. Therefore the DEM code was coupled to a commercial CFD code for the surrounding combustion air enabling a detailed analysis of heat transfer and thermo chemical processes within particle assemblies on grate firing systems.

The running research project no. 377 is investigating the impact of mechanical agitation and local cooling on the thermal conversion of non-spherical fuel particles. The aim is to implement the influence of operational parameters (stoking rate, heat extraction, air flow) and physical fuel properties (particle geometry, local bulk porosity) on the combustion of non-spherical fuels in grate firing systems into the CFD/DEM simulation tool.

Overall these three projects are resulting in a modern and economic engineering tool for simulation and validation of grate firing systems, relevant especially for the combustion of biomass and municipal solid waste in a small to medium scale range. It enhances the possibility to optimize operation and design, while avoiding time-consuming and cost-intensive empirical approaches.

As all projects were, respectively are financed by the German Ministry of Economics (via AiF), the reporting language is German, although results are relevant for all VGB members.

Supervised by the Department of Energy Plant Technology of the Ruhr University of Bochum, being the research institution responsible for all three projects, the final reports will be translated by an external translation agency. Essential results of the projects will be presented to the VGB-European Working Group Biomass thus allowing to technically supervising the ongoing research project 377 and enabling a European exchange of information about advanced technology for biomass utilisation in grate fired boilers.