Investigation on Blended Ash Fusibility Characteristics of Biomass and Coal with High Silica–Alumina

The blended ash fusibility characteristics and its variation mechanism of biomass (peanut hull (PH), bean straw (BS), and corn cob (CC)) and Changzhi coal (CZ) with high silica–alumina were investigated using an ash fusion temperature (AFT) detector, thermogravimetric differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), and FactSage software. The results showed that the AFT of CZ mixed ash decreased with the addition of PH ash, and the AFT of CZ mixed ash decreased rapidly (0–30%) and then changed slowly (30–50%) with an increasing BS ash mass ratio; however, the AFT of CZ mixed ash decreased first (0–20%) and then increased (20–50%) with an increasing CC ash mass ratio. The different AFT variations mainly depend on the ash chemical compositions and their existing form. Biomass ash with high contents of fluxing oxides promotes the transformations of high melting point (MP) mullite and quartz into low-MP minerals and their eutectics, resulting in a decrease in the AFT. At high temperature, with increasing biomass ash mass ratio, K+ replaces Ca2+ in anorthite to form the low-MP leucite, which decreases the AFT further. Some potassium element existed in the form of kaliophilite, leading to an increase in AFT. The combination of TG-DSC, XRD, and thermodynamic calculation provides a good method to explore the ash fusion mechanism from the mineral evolution.