Transient Overheating of Floor Tubes, 1998 International Chemical Recovery Conference Proceedings

This paper considers the transient overheating that can occur in water- cooled floor tubes as a result of sudden debonding of the frozen smelt layer from the tube. A detailed transient one-dimensional heat transfer model is developed that includes conduction through frozen smelt, conduction through a flat steel plate cooled from below, and a contact resistance between the frozen smelt and the plate. Starting from a steady state temperature profile, a step change is made in the contact resistance and the transient temperature profiles in the smelt and plate as well as the transient heat flux followed. The time required to melt through a frozen smelt layer is calculated. The effects of expanding the analysis to a two- dimensional situation that takes into account tube geometry are also examined. The results of this analysis are used to determine the temperature- ime profiles that a floor tube crown thermocouple or a smelt thermocouple might see. The focus is on the rate of temperature rise, the potential size range of the thermal disturbance, and the duration of the event. Calculated profiles will be compared to available data from floor tube temperature transient events. Based on this comparison, the significance of smelt debonding as a mechanism leading to floor tube overheating will be determined.