PNNL

Abstract

Increasing the efficiency of all-electric melters is a hot topic not only in the waste glass melting industry, where the melting rate directly influences the life cycle of the cleanup process, but also in the commercial glass industry, where increasingly stringent environmental regulations and rapid development of renewable energy sources ask for transformation of traditional fossil fuel technology. Batch-to-glass conversion in an all-electric melter proceeds in the cold cap—a layer of reacting and melting material floating on molten glass. The heat transfer into the cold cap is controlled by convection and conduction in the thermal boundary layer on the melt side, and by the properties of the foam layer at the cold cap/melt boundary. An overview of factors affecting heat transfer is presented and assessed using data from laboratory and pilot-scale experiments. The heat flux can be improved by (i) decreasing glass melt viscosity, (ii) decreasing the temperature at which the foam starts to collapse at the cold cap bottom, and (iii) increasing melt convection by bubbling gas into the glass melt under the cold cap. Detailed understanding of the conversion process can guide the formulation of feeds that melt easily and quickly.