Understanding Ash Deposition for the Combustion of Zhundong Coal: Focusing on Different Additives Effects

The industrial application of burning Zhundong coal has been directly restricted due to severe ash deposition. To attain the wide utilization for this coal, experiments about the effects of different additives on ash deposition were conducted in a drop-tube furnace. The properties of ash deposits were characterized by ICP-OES and XRD, and mineral properties were also calculated by molecular dynamics from the perspective of elemental reactions. The results indicate that ash deposition can be divided into inner layer and outer layer. The deposited layer and the size of particles under vermiculite additive are looser and bigger than those under raw coal and kaolin additive. Additionally, ash deposition for the inner layer is thinner, and ash ratio for the outer layer is higher under vermiculite additive. The total deposited layer may be thinner under kaolin additive, but the inner layer for ash deposition is denser than that under vermiculite additive. Ash deposition for raw coal is mainly caused by the formation of hematite, magnesioferrite, anhydrite, and a littlie sodium silicate. Vermiculite additive mainly promotes the further reaction between calcium oxide with magnesium oxide, silicon dioxide, causing the formation of high melting point merwinite. Additionally, vermiculite additive also reduces the formation of magnesioferrite for the deposit layer. Kaolin additive can mainly reduce the formation of anhydrite, and accelerate the formation of anorthite. Furthermore, kaolin additive does not change the types of iron-bearing minerals for the deposit layer. On the basis of molecular dynamic simulations, alpha-Fe2O3 is more easy to combine with anhydrite, followed by merwinite, and finally anorthite based on the binding energy and the radial distribution function. This shows the formation of anhydrite is a key mineral to cause severe ash deposition for the combustion of Zhundong coal.