The refractory system as the decisive factor in the aluminium melting furnace

More than just a protective layer

In the aluminium industry, the refractory lining is often regarded as a pure consumable: it protects the steel shell, keeps the heat in the furnace and is replaced when it is used up. This view falls far short. The refractory system is the central factor determining energy efficiency, metal yield and product quality. A poorly designed or worn refractory system costs an aluminium plant considerably more than the lining investment alone, namely through increased energy consumption, higher melt losses and reduced furnace availability.

Energy efficiency begins at the furnace wall

The thermal insulation of the furnace is largely determined by the build-up of the refractory lining. An optimum system consists of several layers: a hot-face working layer that withstands contact with the aluminium melt, one or more insulating layers that limit the flow of heat outwards, and a safety layer to protect the steel shell. The thickness and material selection of each individual layer influences the overall heat transfer. An insulating layer a few centimetres thinner, or a material with higher thermal conductivity, can increase energy consumption by 10 to 15 per cent. Over a furnace campaign of several years, that adds up to considerable sums.

Melt losses through interaction with the refractory

An underestimated cost factor is the interaction between the aluminium melt and the refractory material. Aluminium is an extremely reactive metal that enters into chemical reactions on contact with unsuitable refractory materials. In the process, metallic aluminium is converted into aluminium oxide and lost as what is known as dross. With a poorly designed refractory system, or where wear is advanced, melt losses can rise to 3 to 5 per cent and more. In a furnace that processes several thousand tonnes of aluminium a year, even small percentages mean considerable financial losses.

• Non-wetting materials reduce the adhesion of aluminium to the furnace wall and minimise dross formation
• Dense surface structures prevent melt from penetrating the pore structure of the refractory material
• Suitable washes and coatings create an additional protective layer between melt and refractory
• Regular cleaning and slag removal extend service life and maintain thermal efficiency

A holistic view instead of isolated measures

Optimising a refractory system calls for a holistic view. Material, design, installation, drying and operating practice all have to be matched to one another. The best material is of no use if it is installed incorrectly or heated up too quickly. The highest-quality design fails if the operating parameters lie permanently outside the design limits. At SBS Refractory Service we regard the refractory system as a whole. From material selection through design and installation to support during operation, we offer an end-to-end range of services that takes account of all the factors influencing service life and cost-effectiveness.