Benign solidification of molten slag on rotary cup atomizer: slag shell formation, remelting and residue characteristics.

The rotary cup has been recently adopted to atomize the molten blast furnace slag in its waste-to-energy treatment process, forging the reputed centrifugal-granulation-assisted thermal energy recovery (CGATER) technology. The formidably high temperature (∼1500 °C) poses a great threat to the long-term running of the rotary cup regarding the possible risk of being melted by the hot slag. Indeed, it has been observed that a layer of slag shell may be formed on the atomizer because of the rapid solidification of the molten slag film caused by the strong heat dissipation at the early stage of centrifugal granulation, which can act as an insulation layer and is thus conducive to the safe operation of the atomizer. However, little is known about the formation and evolution of the slag shell on the atomizer, and some conjectures also lack direct evidence. In this work, we carry out a very important experimental observation of the slag shell formation, detachment, and residence on the atomizer. More importantly, our proposed calculation method revealed the remelting of the formed slag shell during the centrifugal granulation once the atomizer wall temperature exceeded ∼650 °C. The characteristics of the slag shell i.e., morphology, thickness, and crystal phase were specified at various initial temperatures and mass flow rates of the slag and rotary speeds. The final slag shell residue appears in finger shape with a maximum thickness of ∼3 mm. The crystalline content of the slag shell on the side wall exceeded 80 %. This work provides, so far, the first comprehensive investigation of the slag shell characteristics on the rotary cup, and is useful to envisage low-cost, CGATER-benign methods for the long-term running of the rotary cup.