Attrition and Erosion in Powder Circulation Loops

摘要

Changes in particle size distribution play an important role in bubbling and circulating fluidised bed processes and these changes are dominated by attrition and agglomeration. Agglomeration occurs mostly with sticky particles, in moist air or at high temperatures and is not studied in this work. Particle attrition can be caused by several mechanisms including thermal stress, chemical stress and mostly kinetic stress as a result at particle collisions and impacts. Erosion of construction materials is detrimental to the lifetime of the equipment and needs to the avoided. The impact of particles on surfaces in e.g. cyclones or bends in circulation loops leads to attrition of the particles and erosion of the surfaces subject to the impact. To study attrition and erosion, an experimental circulation loop, with refractory-lined bends and cyclone was built and operated at temperatures up to approximately 500 deg C. Air velocities upto 40 m/s were wer applied and te solids loading varied from dilute (g/m~3) to very dense (> 70 kg/m~3). Several refractory lining materials were tested. Particle size distributions were measured in function of operating time. Erosion of the construction material was determined from either XRF-measurements conducted on samples of the circulating particles, or from assessment of target tracer components imbedded in the construction material.