Attrition of bed materials in a lab-scale circulating fluidized bed

A lab-scale circulating fluidized bed (CFB) apparatus was 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. 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 fluid-dynamic characterization was first carried out using beds of sand 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 then developed to study the attrition of bed materials based on the measurement of the elutriation rate of fines escaping from the cyclone and on the comparison of the particle size distributions of the bed material before and after operation. The protocol was applied to beds of sand, limestone, lime or pumice under ambient conditions. A fragmentation index was introduced to quantitatively compare the results obtained in experiments carried out under different operating conditions.