Heat Transfer From a Molten Phase to an Immersed Coal Particle During Devolatilization

In several developmental and commercial processes, coal particles come into direct contact with a high-temperature molten phase. These processes include molten carbonate coal gasification and bath smelting for the production of iron. Recently, real-time X-ray fluoroscopic images have been published that show volatile matter evolving rapidly from coal particles immersed in molten phases, displacing the surrounding melt and producing a periodic cycle of formation, rise, and detachment of gas cavities. The present work makes use of these observations to develop a model of heat transfer from the melt to particles undergoing gas evolution. The model is developed for the general case and applied to predict melt-particle heat transfer coefficients under conditions relevant to bath smelting processes. The model shows that the presence of the gas film can actually increase the overall heat transfer rate under certain conditions.