Improved Monolithic Materials for Lining Aluminium Holding and Melting Furnaces – Roof, Upper Walls and Flue

Abstract

Monolithic refractories are now well established as linings for a range of holding and melting applications for the processing of aluminium. The refractory lining in an aluminium furnace has to withstand a wide variety of physical and chemical environments. Each of the different furnace zones presents a different set of operating conditions, in terms of peak temperature, temperature fluctuation, metal contact, flux contact, impact from ingot loading, etc. Therefore, in order for a monolithic material to successfully perform in a particular area of the furnace, it needs to be able to cope with the specific environmental conditions in that region of the furnace. Aluminium producers continue to increase productivity through their Melt-Hold furnaces to maintain competitiveness. The use of more powerful burners to increase heat input to the furnace is therefore becoming increasingly common practice. But faster melting leads to increased metal losses from surface oxidation and to segregation from large heat gradients. These effects are countered by increased use of fluxes and increased stirring. Given the increasingly challenging environment within which the refractory lining has to work, traditional lining solutions can no longer be relied upon to provide the service lives that were previously achieved. Therefore, a new generation of furnace lining materials is required to cope with today’s aluminium furnace. This paper describes one such newly developed monolithic material, designed specifically to improve performance in the superstructure zone of Aluminium furnaces. The non-metal contact, superstructure regions of aluminium furnaces present their own unique set of challenges for the refractory lining. Refractories in these regions – roof, upper walls and flue – have to cope with excessively high levels of alkali vapour and thermal shock. This paper reviews the operating conditions found in the superstructure areas of a typical melting and holding furnace and the implications these have on monolithic lining material design and performance. The improved behaviour of the newly developed monolithic material against the critical performance criteria in these furnace regions is demonstrated in the laboratory, compared to existing industry leading materials, using industry standard test methods.