Effect of industrial ashes with high carbon and calcium-rich on slagging characteristics of blending Zhundong coals

Influence of two kinds of industrial ashes with high carbon and calcium-rich as additives (drying ash and fly ash) on slagging characteristics for blends of high and low sodium coals was studied in detail. Experiments were performed including ash fusion temperature tests, ashing for blending coals with/without additives in a fixed bed furnace and slagging on un-cooled probe in a drop tube furnace. The results show that there is a large amount of amorphous silicon at 1000 ℃ during combustion of raw blending coals, which easily leads to low-temperature eutectic reaction at higher temperature. Adding 5% fly ash can raise soften temperature of the blended coal ashes by 100 ℃, and mass ratio of CaO to SiO₂ in ashes reaches up to 2.5. Dicalcium silicate and grossular are newly generated, which effectively reduce the slagging propensities. The main phase in slag samples collected on the probe is identified as gehlenite after adding two industrial ashes into raw blending coals. The addition of two typical ashes can transform amorphous silicon into its crystalline mineral phase, inhibit formation of low-temperature eutectics. In contrast to the case of adding 5% fly ash, impact of adding 5% drying ash into raw blending coals on slagging tendency of the ash particles on un-cooled probe is insignificant.