Secondary fragmentation of a char in a circulating fluidized bed combustor

Secondary fragmentation of Kentucky No. 9 chars, obtained with two different procedures of devolatilization, has been studied in a laboratory scale circulating fluidized bed combustor. The apparatus essentially consists of a 41 mm ID, 1.92 m high riser, a solids collecting system, a 41 mm ID recirculation column. Gas velocity and size of inert material have been varied in ranges of practical interest. An appropriate experimental technique has been developed to isolate secondary fragmentation effects from those related to other comminution phenomena taking place during fluidized bed combustion of chars. Particle multiplication factor, i.e. the number of particles generated per one char particle by secondary fragmentation, has been determined for each set of experimental conditions. The probability that a shrinking particle of a given size breaks into fragments and the fragments size distribution under similarity hypothesis have also been determined. These fragmentation functions are embodied into carbon particle population balances which are the basis of circulating fluidized bed combustion modelling. © 1992 Combustion Institute.