Ash melting behaviors of high-sodium coal and its co-combustion with coal gangue to inhibit slagging

Abstract

Fouling and slagging are major challenges that impede the clean and efficient use of high-sodium coals (HC) for power generation. To address these persistent issues, this study examined the impact of sodium (Na) on ash-melting behaviors and assessed the feasibility of mitigating fouling and slagging through the co-combustion of HC with coal gangue (CG). The mineral transformation mechanisms were analyzed through experimental and thermodynamic calculations using the FactSage software. The potential for inhibiting slagging through the co-firing of HC with CG rich in silica (SiO2) and alumina (Al2O3) was also investigated. The presence of Na-containing species led to the formation of more flexible minerals and lowered the ash fusion temperatures (AFTs). Na not only decreased the initial temperature required for the formation of the liquid phase but also increased the proportion of the liquid phase during high-temperature ash-melting processes. Co-firing with CG rich in silica and alumina significantly improved the AFTs of HC. Furthermore, this approach effectively reduced the propensity for fouling and slagging. In practice, it is recommended to control the co-firing ratios of CG within 10–30% to inhibit slagging and fouling issues while maintaining a smooth boiler operation.