Effect of Blending Ratio on the Sodium Release Behaviors, Ash Slagging Characteristics and Char Gasification Performances during Co-gasification of Zhundong Coal with Wuhai Coal

Some ash related problems, such as slagging at furnace bottom and fouling at the air pre-heater surface, are frequently encountered during circulating fluidized bed gasification (CFBG) of Zhundong coal. Low ash fusion temperatures (AFTs) and intense sodium release should be responsible for those problems. In industry, coal blending is deemed to be a feasible method to both improve AFTs and control sodium release. In this work, Wuhai coal was selected as blending coal. The ratio is varied from 0% to 40% by mass with 10% interval. The mixed samples were gasified by steam at 950 & DEG;C in a lab-scale furnace. Some key indices, such as sodium release behaviors, ash slagging characteristics and char gasification performances, were investigated by ICP-OES, AFTs, XRD and TG analyzers, respectively. The results indicated that coal blending could significantly decrease sodium release behaviors. For ash slagging characteristics, it is surprised to find that three out of four AFTs (deformation temperature, softening temperature, hemispherical temperature) show an U-shaped correlation with blending ratio, indicating that a low ratio possibly causes more severe ash slagging problem. It is ascribed to the formation of substantial percentage of fusible Na-containing silicates and aluminosilicates. In addition, coal blending greatly increases ST-DT, implying that the ability of resistance to bed temperature fluctuation is markedly enhanced. Due to the high level of alkali and alkaline species, the synergistic effect is clearly observed during co-gasification. Taking all key indices into consideration, 30% blending ratio of Wuhai coal is recommended.