Evaluation of aluminum ash in alleviating the ash deposition of high-sodium and high-iron coal

Abstract

The high sodium and high iron contents induce severe ash deposition in pulverized coal boiler. Additive injection technology is deemed as an effective solution to solve these problems. This work is to evaluate the effect of aluminum ash on alleviating the ash deposition of high-sodium and high-iron coal. Results show that sodium vapor volatilizes, condenses and forms a viscous bottom layer, then the co-melting behavior of sodium-containing mineral and calcium aluminosilicate causes the ash deposition of high-sodium coal, and the co-melting behavior of Fe2O3 and calcium aluminosilicate causes the ash deposition of high-iron coal. When the addition ratio of aluminum ash reaches 4%, ST (softening temperature) and FT (flowing temperature) of mixed ash sample are close to and exceed 1773 K, meanwhile, slag types of ash deposit are transformed from molten slag and viscous slag to attached ash. Al2O3 and MgAl2O4 in aluminum ash can inhibit the interaction between sodium, iron and calcium aluminosilicate, making the particles less sticky. The optimum temperature of aluminum ash for sodium capture is 823 K. Aluminum ash has a better sodium capture ability for high-sodium coal than high-iron coal. Based on the above analysis, this work also provides the blending strategies of additives due to the different ash deposition mechanisms of coal.