Time-dependent layer formation on K-feldspar bed particles during fluidized bed combustion of woody fuels

Despite frequent reports on layer characteristics on quartz bed particles, few studies have focused on the layer characteristics of K-feldspar bed particles. The layer characteristics of K-feldspar bed particles were therefore investigated by collecting bed material samples of different ages from fluidized bed combustion of woody fuels in large-scale bubbling and circulating fluidized bed facilities. Scanning electron microscopy/energy-dispersive spectroscopy was used to analyze the layer morphology and elemental composition. Bed particles aged 1 day displayed a thin layer rich in Si, Ca, and Al. Inner layers had a more homogeneous composition than the outer layers, which instead were more heterogeneous and sometimes contained discernible fuel ash particles. The outer layer was thinner for K-feldspar bed particles sampled from circulating fluidized bed, as compared to particles from bubbling fluidized bed. The concentration of Ca in the inner layer increases toward the bed particle surface, the molar rati...