Modeling the devolatilization and fragmentation of biomass pellets with the bonded particle method for fluidized bed applications

Abstract

By extending the bonded particle method, the major structural changes during the devolatilization of a wood pellet in a fluidized bed and the resulting mechanical behavior have been successfully reproduced. A comparison with experiments from the literature showed that the implemented particle-based pyrolysis model enables predicting the entire pellet’s kinetics with a high agreement. The developed shrinkage model for the particles and bonds further allowed to emulate the reported formation of a large-scale pore network inside the pellet. The simulation of a radial compression test with the predicted structure showed good agreement with experimental data and could confirm the importance of the pores for the mechanical behavior. The results demonstrated that the large pores cause the fragmentation of agglomerates already at low mechanical loads which could promote attrition. In general, the results have shown that the developed extension of the bonded particle method allows studying and predicting the behavior of a single pellet during conversion inside a fluidized bed gasification reactor in more detail.