Optimizing Boron Sources and Hydroxides for Cold-Top Furnaces to Prevent Hot Spots and Volcano Effect

Abstract

Cold-top electric furnaces (CTEF) are increasingly used in glass production as electrification reduces carbon emissions. This shift requires a deeper understanding of raw material selection and its impact on melting efficiency. While 100% anhydrous borax has shown energy and carbon reduction benefits in gas-fired and oxy-fuel borosilicate glass melting, its use in CTEF causes sudden temperature spikes ("volcano effect") on the batch blanket, leading to energy loss. This study investigates a borate mixture suitable for insulation fibreglass melting in CTEF and evaluates hydroxide additives as means to prevent the volcano effect. A laboratory-scale CTEF set up equipped with a high temperature melting observation system (HTMOS) was used to evaluate different ratios of anhydrous borax and borax pentahydrate, as well as anhydrous borax with hydroxides. The results indicate that incorporating 20% borax pentahydrate effectively mitigates the volcano effect, enabling a gradual and controlled batch heating, thereby reducing energy loss. The introduction of hydroxide raw materials showed similar benefit in controlling the volcano effect. Additionally, a long-term stability testing in an environmental chamber confirmed that the optimized borates mixture exhibits the same storage stability as 100% anhydrous borax. These findings offer a viable pathway for improving borate use in full-electric glass melting processes.