Cooling of Kraft Recovery Boiler Smelt, 2000 Engineering Conference Proceedings

Gary Tan, Masahiro Kawaji, Honghi Tran, Thomas Grace--An experimental apparatus was constructed to study the freezing and cooling of molten smelt, as part of a study of char bed cooling after an emergency shutdown. Molten smelt was collected at a smelt spout of an operating recovery boiler and poured into the apparatus. As the smelt cooled, temperatures at many fixed locations in the apparatus were recorded as a function of time. The results showed that smelt has a low thermal conductivity, and that the heat transfer rate is mainly controlled by heat conduction within the smelt interior. A transient 3-dimensional heat transfer model was developed to analyze the smelt cooling data. The best fit between numerical and experimental results was obtained using a value of 0.60 W/mºC for the thermal conductivity of frozen smelt. This is significantly lower than the value of 0.88 W/m o C found in the literature. Parametric studies were conducted on the model to evaluate the impact of other parameters such as emissivity, heat capacity, latent heat, and heat-transfer coefficient on the predicted results.