The characteristics of mineralogy, morphology and sintering during co-combustion of Zhundong coal and oil shale

Abstract

The high-sodium coal from Zhundong region induces severe ash-related problems during combustion. Oil shale rich in silicon and aluminum has been adopted as an additive of Zhundong coal during co-combustion to investigate the characteristics of mineralogy, morphology and sintering at various temperatures and blending ratios in this study. The size distributions of the ash depositions have also been determined. The study results reveal that the fluxing minerals, such as sodium-based compounds, with sizes less than 10 μm are dominant in Zhundong coal. These fine particles may present in a molten or sintering state at high temperature. Some refractory minerals with size exceeding 10 μm, such as nepheline or anorthite, form during co-combustion. These irregular particles retain their shapes during combustion resulting from their high melting temperatures. The blending of oil shale can change the migration path of the sodium during combustion, indicating that sodium gradually migrates from the water-soluble phase to the aluminosilicate phase. The amount of ash particles less than 10 μm decreases from 84.31% to 40.29% with an increase in temperature. Furthermore, the refractory minerals with high melting point and high viscosity can result in high sintering temperature. The sintering temperature increases from 700 °C to 1055 °C when the blending ratio of oil shale reaches 20% and combustion temperature reaches 1050 °C. In addition, 30-50% sodium-based compounds volatilize to the gaseous phase during combustion of Zhundong coal. When the proportion of oil shale reaches 10%, and combustion temperature is 850 °C, sodium volatility will decrease to the lowest point of 14.49%, which can suppress ash sintering to a large extent.