Implications of water cooling of green anodes during anode baking – a thermodynamic study

Abstract

Water can be present in significant amounts in green anodes due to cooling with water after the forming process. The chemical environment in the pit can potentially be affected by the presence of water and may cause degradation mechanisms of the refractory lining so far not considered. A thermodynamic assessment of the role of water on formation of HF(g) due to traces of cryolite bath in the green anodes is presented. It is shown that water results in the formation of HF, and subsequently, it is predicted that HF will react with the refractory materials forming a solid oxyfluoride phase at moderate temperatures. The oxyfluoride is however not thermally stable during the whole baking cycle and SiF4 will evaporate upon further heating. Finally, the effect of water on carbon gasification and CO and H2 production during anode baking is also addressed. The findings are discussed in relation to previous studies of the degradation of refractory linings in anode baking furnace