Influence of Reacting Conditions on Percolative Fragmentation and Ash Size Distribution

抄録

A char particle gasification model applying the discrete approach has been developed to predict the effect of the char particle structure (size, porosity and shape) and the reaction temperature on the reaction behavior. In this model, it was assumed that the shape of a char particle before the reaction was a three-dimensional cube. A large number of small lattices arranged randomly in the cube and were classified into char, ash and macropore depending on the char's proximate analysis data. In the char reaction process, one-dimensional steady state diffusion of CO₂ was considered in the cylinders. It was assumed that CO₂ diffused through a large number of the cylinders, which represented micropores inside the char particle and reacted to the wall of the cylinders. The dependence of the reaction rate on the temperature was analyzed by changing the size, porosity and shape. It is suggested that the pore diffusion behavior of CO₂ is influenced by the particle structure change. This is because the reaction rate is determined by the relationship between the chemical reaction rate and the diffusion rate. Therefore, CO₂ diffusion distance influenced by the particle size, porosity or shape, which is one of the major factors to determine the diffusion rate, remarkably contributes to control the transition temperature between chemical reaction rate controlling regime and pore diffusion rate controlling one. The uniform and peripheral reaction in the particle occurred depending on the reaction temperature. Furthermore, the reaction also occurred on the internal void surface of the particle at the high porosity, while the reaction only occurred on the external surface of the particle at the low porosity. The reaction temperature and porosity influenced the reaction position in the particle, so that the fragmentation behavior was different owing to the porosity and the reacting conditions.