Attrition and low-temperature sulfur dioxide removal of dry lime (lime) in a circulating fluidized bed absorber (CFBA)

Attrition of lime sorbent plays a very important role in utilization in fluidized bed applications for dry lime FGD processes. The experimental data of lime sorbent attrition from mechanical and thermal attrition tests in a circulating fluidized bed absorber (CFBA) are presented. An improved model is developed based upon the experimental attrition behavior in the CFBA. This model more accurately fits the attrition behavior for lime sorbent because it incorporates both mechanical and thermal attrition, while the existing models only account for mechanical attrition. The attrition rate constant is expressed in an Arrhenius form using a kinetic model which relates the attrition rate to the gas properties such as temperature and molecular weight and the geometry of the fluidized bed as well as the fluidization velocity. In addition, an unsteady state population model is employed to predict the changes in size distribution of bed materials during fluidization. The solid size distribution predicted by the population model at various time intervals during fluidization agreed well with the size distributions obtained experimentally for the corresponding time intervals. The model developed in this study is applicable for batch and continuous modes of fluidization where the particle size reduction in the bed load is predominantly a result of attrition and elutriation. This has widespread significance since mechanical attrition and elutriation is frequently seen in fast fluidized beds and in circulating fluidized beds used in other industrial applications.; Finally, the effect of water injection on the SO{dollar}sb2{dollar} removal efficiency in dry lime injection FGD processes was investigated. The experimental data obtained from circulating fluidized bed absorber (CFBA) operations with water injection through a newly designed toroidal ring nozzle were presented. The results suggest that the SO{dollar}sb2{dollar} removal efficiency is a strong function of the water injection rate.