Computational fluid dynamic modeling of a secondary lead reverberatory furnace

Abstract

Over half of lead production worldwide comes from secondary sources. The main secondary source of lead is lead-acid batteries. Currently, over 99% of all lead based batteries in North America are recycled, amounting to 1.7 million short tons of lead annually. Secondary lead battery scrap is recycled through a combination of physical concentration, hydrometallurgical and pyrometallurgical processes. A common type of furnace used for the pyrometallurgical steps in this process is a directly fired reverberatory furnace. In the directly fired reverberatory furnace, the burden (the solid feed material) is heated through direct contact with the burner flame as well as through radiant heat transfer from the walls and combustion gases. The impingement of the flame on the burden can facilitate large amounts of heat transfer, leading to greater melting and production rates, but can also cause areas of high velocity turbulent flow and local high temperature zones within the furnace’s refractory lining. These phenomena can lead to excessive erosion and thermal stresses thereby prematurely shortening the lifetime of the refractory lining. Understanding the cause of refractory wear is critical to many operations as the rate of refractory wear will directly affect the length of refractory lifetime and the productivity of the furnace. Therefore, obtaining velocity and temperature distributions within the furnace under different conditions was the focus of this project with the goal of identifying and minimizing high wear zones while maintaining the smelting rate. A computational fluid dynamic (CFD) model has been developed to accomplish the project’s goals by calculating the temperature distribution, velocity profile and overall heat transfer within the furnace. The preliminary portion of the project focused on model development and validation. Once a base case simulation was validated using data from an operational lead reverberatory furnace, predicted areas of high refractory wear were identified through the calculation of the temperature and velocity distributions within the furnace. The average burden surface temperature was also evaluated as this parameter was used as a measure of smelting rate. The CFD model was used to assess whether the predicted areas of high refractory wear could be minimized by various operational changes to the burden geometry and burner alignment. The results showed that the amount and location of the burner flame impingement was sensitive to changes in both burden geometry and burner alignment and greatly affected the overall flow patterns and heat transfer within the furnace. The results also indicated that there could be a tradeoff between smelting rate and refractory lifetime. As a final step, a semi-empirical wear function was constructed in attempt to evaluate the combined influence of temperature and velocity on the predicted areas of high wear within the furnace refractory.