Modelling and validation of biomass combustion in a screw burner

Authors: Barroso G, Hediger L, Nussbaumer T.

A combined 1D-fuel-bed and 3D-CFD model for the simulation of an innovative 35 kW screw burner has been developed and validated with experiments. The 1D-fuel-bed model is a further development of a previously presented walking column approach and accounts for the special transport conditions in a screw burner. A new reduced chemical mechanism combined with the Eddy Dissipation Concept (EDC) combustion model is used in the subsequent 3D-CFD simulation. Detailed and reduced mechanisms are first compared in an opposed jet burner and then an improved reduced chemistry model is used in CFD calculations to investigate the influence of different primary and secondary air settings and to be validated with experimental data from a 35 kW prototype burner. The model enables a reasonable prediction of the trends of variations of the excess air ratio in the primary zone (primary λ) and of the global excess air on the emissions and the heat output and is therefore suitable for the design of biomass combustion systems with a moving fuel bed.

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