A better understanding of biomass co-firing by developing an advanced non-spherical particle tracking model

Co-firing biomass with coal or gas in the existing units has gained increasing interest in the recent past to increase the production of environmentally friendly, renewable green power. In this paper, co-firing biomass with natural gas in a 10m long wall-fired burner model is studied numerically. To better understand biomass co-firing and therefore improve the design for co-firing biomass in wall-fired burners, the most commonly used spherical particle shape assumption is not used here, which may deviate a lot from reality for big biomass particles. A sphere gives a minimum in terms of the surface-area-to-volume ratio and thus experiences a totally different motion and reaction as a non-spherical particle. Therefore, an advanced non-spherical particle-tracking model is developed to calculate the motion and reaction of nonspherical biomass particles. The biomass particles are assumed as solid or hollow cylinders. In the particle force balance, the forces that could be important are all considered, which includes a drag proposed for non-spherical particles, an additional lift due to particle non-sphericity, and a ?virtual-mass? force due to relatively light biomass particles, as well as gravity and a pressure-gradient force. Since the drag and lift forces are both shape factor- and orientation-dependent, coupled particle rotation equations are resolved to update particle orientation. In the reaction of biomass particles, the actual particle surface area available and the average oxygen mass flux at particle surface are considered, both of which are shape factor-dependent.