Set up of lab-scale apparatus and procedures for the characterization of attrition under circulating fluidized bed conditions.

A novel lab-scale circulating fluidized bed (CFB) apparatus has been designed and set up to routinely characterize the attrition propensity of bed materials under both ambient and high-temperature conditions. The apparatus is equipped with an L-valve for solids circulation and is characterized by simple operation and high flexibility as regards the range of possible operating conditions. In addition, each section of the circulating loop is equipped with sampling ports for pressure and temperature measurement. The solids circulation rate can also be measured online by means of a specially designed device. A preliminary fluid-dynamic characterization was carried out using beds of different particle sizes and inventories to explore the range of feasible circulating conditions and to link the solids circulation rate to the pressure drop across the L-valve. An experimental protocol was developed to study attrition of single or binary mixtures of materials based on the measurement of the elutriation rate of fines escaping from the cyclone and on the particle size distribution of the bed material before and after operation. The protocol was applied to beds of sand or sand-limestone mixtures under ambient conditions. Attrition rate results were compared to those obtained under bubbling fluidized bed conditions to highlight the influence of high-velocity solids circulation on particle breakage. Further tests are under way under high-temperature conditions to study the effect of temperature and chemical reactions (calcination, sulfation) on particle attrition.