Effect of Particle Size on Residence Time and Burnout of Tunçbilek Lignite
Feyza Kazanc Burak Ozer Duarte Magalhaes
AbstractPhysical properties of coal particles have influence on combustion characteristics. Particle size is one of these physical properties that causes dramatic effect on the surface reaction rate and hence on the residence time required for complete combustion. In the present paper, the particle size influence on coal combustion is investigated for Tunçbilek lignite under two selected size cuts: 106-125 µm and 180-212 µm. Particle size effect on coal combustion is studied both experimentally and theoretically. Experiments are conducted by using a drop tube furnace (DTF). Computational Fluid Dynamics (CFD) analysis is carried out by using Fluent software. Moreover, two analytic methods namely D2 law and two- film model is used to model char combustion. The experimental tests are performed in a drop tube furnace at high temperature (1000 ºC) and high heating rate (~104 ºC s-1). CFD simulations using Fluent are performed using the Coupled algorithm, both discrete and continuum phases are solved in a 3D steady-state formulation. On the other hand, the analytical methods solve the discrete phase to obtain burnout; diffusion limited model is used in D2 calculations, while two-film model relates the surface reaction kinetics with the diffusion of the gaseous species around the particle. The burnout values from experimental and CFD analysis are similar (100 and 94%, respectively) for small particles, while for large particles values are 85 and 97%, respectively. Results obtained from analytical methods agreed on the complete combustion (100% burnout) for both particle size ranges.