On the mechanical attrition and fragmentation of particles in a fast fluidized bed

Tests were performed in a batch fast fluidized bed, working at ambient cond itions, to check the influence of operational conditions, namely, superfici al gas velocity, particle diameter, test duration, and solids inventory, on the size reduction process of a friable material particle. The experimenta l system consisted of a 0.30 in i.d. vertical riser, 2.22 m high, with prim ary and secondary air injections, main and secondary cyclones, bag filters, and a solids reinjection valve. Tests were performed with calcined oil sha le particles, and the fluidization velocity. ranged from 2.89 to 4.81 m/s. Experimental observation showed the particle, size reduction rate Ito be pr oportional to the fluidization excess velocity and to mass inventory, as in bubbling fluidized beds. It was observed that a significant amount of mate rial was reduced to fines a - nd that the intermediate size intervals also exhibited some increase in their mass fractions. On this,basis, a model was proposed to simulate the process, considering the existence of two. size r eduction mechanisms, namely, abrasive attrition and mechanical fragmentatio n. The, model predicts the effects of the process conditions and changes in size distribution with time.