The Effect of Silica, Temperature, Velocity, and Particulates on Heat Transfer to Spent Bayer Liquor

Abstract

Laboratory-scale investigations were performed to determine the effect of silica, temperature, velocity, and particulates on heat transfer to spent Bayer liquor. A method for simulating continuous process conditions was developed in the 60 L heat transfer test rig at the University of Auckland. Heat transfer was measured for conditions of 0.7 to 2.1 g/L [SiO₂], 110 to 160°C surface temperature, 0.4 to 1.7 m/s flow velocity, and 0.0 to 0.3 g/L red mud concentration. A deposition model is proposed to determine the effect of silica and temperature on scaling rate. Similar to bulk desilication rate, the scaling rate was second order with respect to silica supersaturation, and had a similar Arrhenius temperature dependence. The effect of velocity on scaling rate was insignificant at heater surface temperatures below 150°C. The mild polishing effect on the heat transfer surface of the circulating red mud particulates was expected to have a beneficial etfect on scaling. For liquors with high silica supersaturations, however, the presence of small amounts of red mud dramatically decreased the heat transfer coefficient.