Improving the bed movement physics of inclined grate biomass CFD simulations

Abstract

Extensive research has been performed in the field of biomass combustion, particularly in terms of numerical simulations. However, only a few studies have deepened the understanding of the dynamics of packed beds and boiler grates.This paper presents and assesses a new physical solution under a comprehensive Eulerian model that tackles the complex problem of biomass movements inside a packed boiler bed. In addition, this paper improves the precision of the obtained results, expanding the application cases of the simulation model produced by the GTE research group at the University of Vigo (Spain). The modelling algorithms are based on mechanisms that represent the crumbling of biomass particles due to gravity and the movements caused by the push generated by the feeding system. The movements’ logic affects the variables involved in the biomass thermal conversion formulation, which is integrated with other combustion models previously presented by the authors.To test the performance of the presented models, a 3D experimental grate was printed and fed with biomass pellets. The performance was compared to that of the evolution of the simulated bed. Several experiments were performed to analyse parameters, such as the bed size, slope and residence time of different fuel batches. The results of the comparison show agreement in the behaviour of the model in terms of the bed size, shape and slope for different instances of the feeding process. Otherwise, the experiments show that the internal distribution of the bed layers of different batches presents some differences with the predictions. Therefore, possible improvements, such as considering a friction factor, may be applied to the model to upgrade its performance.