ATTRITION OF LIME SORBENTS DURING FLUIDIZATION IN A CIRCULATING FLUIDIZED-BED ABSORBER

The experimental data of lime sorbent attrition obtained from mechanic al and thermal attrition tests in a circulating fluidized bed absorber (CFBA) are represented. The results indicate that the predominant att rition mechanism during lime fluidization is surface abrasion due to c ollisions of the parent solids in a bed. Attrition of lime at higher t emperatures decreased due to its hardened properties with rising tempe rature, while such solids as limestone become more attritable by the c repitation resulting from the increased internal pressure. With an int roduction of the minimum weight of parent solids, the attrition rate o f lime in a CFBA has a first-order dependency with respect to time. Th e attrition rate constant is expressed in an Arrhenius form, using the kinetic model which relates the attrition rate to the gas properties such as temperature and molecular weight and the geometry of the fluid ized bed as well as the fluidization velocity. The experimental data o btained from these tests in a CFBA agree well with the attrition model , and the model indicates trends due to increased temperature consider ing thermal attrition. From the model the attrition activation energy, E(a) and k(o), can be obtained as E(a) = 3.383 x 10(-3) kJ/kg and k(o ) = 1.29 x 10(-4) s-1. Comparisons of the mechanical and thermal attri tion data obtained experimentally with the theoretical values computed with the attrition activation energy, E(a) and k(o), are in good agre ement, and thus the results may be applicable to lime attrition in a f luidized bed.