Melting behavior of typical ash particles in reducing atmosphere

Two coal ashes (one with high-melting temperature and one with low-melting temperature) obtained at 600 °C in air were pressed into pellets and further treated for 1 h at different temperatures from 700 to 1200 °C at the interval of 100 °C in reducing atmosphere (mole ratio CO:CO ₂ = 60:40) to investigate the melting behavior of typical ash particles. The final structures were characterized by XRD and SEM-EDX. The results showed that most Na, K, Ca, and Fe took the form of aluminosilicates. Although the low-melting particles (Na-K-enriched aluminosilicate particles and Ca-Fe-enriched aluminosilicate particles) were small in number percentage, these particles were already melted at 1000 °C. It is possible that Fe was enriched more readily in particles than Ca. The extent of fragmentation of calcite particle was closely related to the calcite type. The calcite particles with layered textures fragmented more. Gaussian distribution successfully simulated the calcite particle size distribution after calcite particle fragmentation. The detailed mechanism analysis showed that the Fe-O particle dissolution was primarily controlled by diffusion. The Fe-O crystals from pyrite and siderite showed similar patterns of crystal growth.