Reagglomeration Phenomena In Fine Dry Grinding Of Coal

Investigations were performed on fine grinding of bituminous coal in a laboratory-scale pulverizer. The results indicated that the breakage behavior at relatively coarse sizes (i.e., greater than about 20 µm) is essentially "normal." However, at fine sizes (i.e., less than about 10 m), there is clear evidence of reagglomeration. A simplified population-balance model for simultaneous growth and breakage is formulated. Breakage rates and breakage distributions were assumed to follow the patterns typically observed in simple grinding systems. It is recognized, however, that solid particles and agglomerates may exhibit different breakage behaviors. Agglomeration rates are assumed to be determined by contact probability, i.e., by the relative numbers of interacting particles. Based on comparisons between model simulations and experimental data, it appears that agglomerate rebreakage rates and fragment size distributions are quite different from those for solid particles. The result is that product size passes through a minimum and then increases with time as agglomeration begins to dominate.