Role of surface morphology in bed particle layer formation on quartz bed particles in fluidized bed combustion of woody biomass.

• Bed particle layer growth on quartz is faster at convex regions of the particle. • Convexes show thick inner and outer layer, concaves mainly show a thin inner layer. • Smooth areas of bed particles have the thickest Ca-rich inner and outer layers. • Crack layers form in concaves with cracks in the inner and a missing outer layer. • Ca-rich protective layers on smooth particles may reduce operational problems. The influence of quartz bed particle surface morphology on the bed particle layer and crack layer formation process in fluidized bed combustion of woody biomass was investigated in this work. Bed material samples were collected at different sampling times from the startup with a fresh bed in industrial scale bubbling fluidized bed (BFB) and circulating fluidized bed (CFB) boilers, both utilizing woody biomass. X-ray microtomography (XMT) and scanning electron microscopy coupled with energy dispersive spectroscopy (SEM/EDS) were employed to characterize bed particle layers and crack layers in the samples. Results showed that there is a noticeable difference between the bed layer characteristics over the so-called "concave" and "convex"-shaped morphologies on the bed particle surface with respect to layer formation. The concave areas are mainly covered with a thin inner layer, whilst the convex display a comparably thick inner layer and an outer layer. In addition, 3D images of the particles revealed that the crack layers mainly originate from concave areas where the particle is less protected by an outer bed particle layer in conjunction with cracks in the inner layer. [ABSTRACT FROM AUTHOR]