UNDERSTANDING AND MITIGATING HEAT-EXCHANGER FOULING IN BAUXITE REFINERIES

Laboratory and plant measurements have been performed to evaluate poss ibilities of reducing the formation of desilication product (DSP) scal e in the heat exchangers of the low-temperature Bayer process. It was found that the rate of scale formation is independent of the flow velo city, proportional to the square of the silica supersaturation, and it increases exponentially with heat-transfer surface temperature. Becau se of the restricted operation conditions, variation of operating cond itions may not reduce DSP formation sufficiently. Installation of turb ulence promoters in the heat exchanger pipes had no beneficial aspects . Laboratory and plant measurements with a fluidized bed test heater i ndicated a strong potential of this technology to increase the operati on times between chemical washes. Deposition of DSP could almost be el iminated if the process was modified such that developed subcooled boi ling occurred at the heat-transfer surface.