FLAME TRANSFORMATIONS AND BURNER SLAGGING IN A 2.5-MW FURNACE FIRING PULVERIZED COAL .1. FLAME TRANSFORMATIONS

This is the first study in which the mechanism of burner slagging in a furnace firing pulverized coal has been investigated. The objective w as to relate the in-flame transformations of the coal minerals to the nature of the slags formed on deposition probes designed to simulate a burner quarl and a superheater tube. The experiments were performed i n the 2.5 MW refractory-lined IFRF furnace No. 1, using a swirl-stabil ized pulverized coal burner, firing a pyrite-rich coal. In-flame sampl es and slag deposits were extracted and analysed for pyrite and pyrite decomposition products by electron probe microanalysis and X-ray diff raction. Immediately after injection into the flame, pyrite (FeS2) dec omposed to pyrrhotite (FeS), molten droplets of which were oxidized to solid iron oxide (Fe3O4 and Fe2O3) particles in both the internal and external recirculation zones in the furnace. Owing to the complex flo w pattern in the furnace, the kinetics of the pyrite conversion steps could not be directly determined but were indirectly derived from a co mparison with the coal devolatilization and char oxidation steps. It i s concluded that the decomposition of pyrite proceeds as fast as the c oal devolatilization step and that the oxidation of pyrrhotite to iron oxide is as fast as the oxidation of the coal/char.