Analysis of biomass combustion ash behavior at elevated temperatures

Change in tensile strength of a biomass ash powder bed measured by a split-cell type tester at a variety of temperatures up to 900°C was discussed corresponding to the microscopic behavior of ash particles observed by a field emission scanning electron microscope (FE-SEM) with a computer-controlled stage, a heat treatment chamber and an energy dispersive X-ray spectrometer. Tensile strength of a biomass powder bed increased with temperature by two different steps. In temperatures ranging from400 to 700°C, the powder bed had liquid-phase bridging between particles, which caused the relatively large fracture distance in fracture curves. FE-SEM observation showing rounded ash particles after heat treatment at 500°C supported this phenomena. On the other hand, at temperatures higher than 700°C, powder beds showed brittle fracture, which means the absence of any liquid bridge due to evaporation. FE-SEM observation revealed successive evaporation from ash samples in this temperature region.