CFD simulation of wood chip combustion on a grate using an Euler–Euler approach

Abstract

Due to the increase of computational power, it is nowadays common practice to use CFD calculations for various kinds of firing systems in order to understand the internal physical phenomena and to optimise the overall process. Within the last years, biomass combustion for energy purposes has gained rising popularity. On an industrial scale, mainly grate firing systems are used for this purpose. Generally, such systems consist of a dense-packed fuel bed on the grate and the freeboard region above, where in the field of numerical modelling, it is common practice to use different sub-models for both zones. To avoid this, the objective of this paper is the presentation of a numerical model including a detailed three-dimensional description of the fuel bed and the freeboard region within the same CFD code. Because of the implementation as an Eulerian multiphase model, both zones are fully coupled in terms of flow and heat transfer, and appropriate models for the treatment of turbulence, radiation, and global reactions are presented. The model results are validated against detailed measurements of temperature and gaseous species close to the bed surface and within the radiative section of a 240 kW grate firing test facility.

Keywords:

• CFD
• Euler–Euler
• grate firing
• wood combustion
• biomass

Acknowledgements

Funding of this work by Energie Baden-Württemberg (EnBW) is gratefully acknowledged. Special thanks go to Sven Unterberger and Oliver Greißl from EnBW for their cooperation, as well as our colleagues Daniel Kilgus and Kevin Brechtel for their support and for conducting the experimental measurements.