Mechanism of interaction of pyrite with hematite as simulation of slagging and fireside tube wastage in coal combustion

Iron-bearing minerals have been recognised as a mayor source of fire-side wall slagging in pulverised fuel boilers, which not only reduces the thermal efficiency of heat transfer of the exchangers surface, but also affects its integrity as a result of corrosion and erosion. Nevertheless, the root cause of adhesion and growing of deposits has not been clearly addressed. Our approach suggests that differential scanning calorimetry (DSC) combined with simultaneous thermogravimetry can follow the chemical reaction between pyrite and the outer layer of iron oxide on tubewalls. The changes in composition are followed by X-ray diffraction (XRD). The results indicated that the mechanism of wetting and adherence of molten pyrite over iron oxides is chemically induced: both di and mono iron sulphides interact with the oxide layer, changing the oxidation state of iron in oxide scale, from hematite to magnetite. This would imply a change in the protective ability of the scale as well as a great increment in corrosion tendency.