Micro-scale investigation on particle transformations of coal and biomass ashes during different heating conditions

Abstract

Changes in heating conditions might influence ash transformations during the gasification process. Ash transformations by thermal effects result in particle stickiness, which affects particle sintering and shrinkage. In this study, an optical heating stage microscope (OHSM) was used to clarify the ash particle transformations that occur during non-isothermal and isothermal heating conditions at micro-scale magnification. The value of change of surface area increased during the sintering process but then generally started to decrease during the melting process. In terms of reaction time exposed during non-isothermal heating, higher heating rate influenced the change of surface area more than lower heating rate during the sintering process. The sintering activation energy (Esin) under non-isothermal heating conditions was compared to shrinkage during the sintering process. The value of Esin increased with increasing shrinkage and decreased at high heating rates. The sintering transformation of ash under non-isothermal heating conditions was improved in comparison with that under isothermal heating condition. From scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) analysis, the morphology of particle surface was observed to change to a smooth shape and the chemical components on particle surface were replaced during sintering.