Primary Aluminium Production

The end walls of the furnace are exposed to high temperatures, particularly during heat transfer from the fire channels and throughout the baking cycle. This zone is characterised by severe thermal stresses and a high risk of cracking resulting from temperature differences between the furnace interior and the surrounding environment. Materials used in this area should provide structural stability, high resistance to thermal shock and limited capacity for the accumulation of sodium and fluorine compounds.

Fire channels represent the most thermally loaded part of the furnace. Inside these channels, hot gases and flames flow, transferring heat to the baking chambers. Strong infiltration of reactive gases originating from the anode material occurs, leading to the formation of a glassy degradation phase. The refractory lining must ensure low porosity, resistance to the penetration of sodium vapours and fluorides, as well as long-term dimensional stability under high temperatures and fluctuating thermal loads.

The furnace floor is responsible for carrying the load of the charge and the filling material. This area is exposed to long-term thermal impact, contact with volatile organic and inorganic compounds, and the possible accumulation of condensates and contaminants. Materials used in this zone should be characterised by high creep resistance and good thermal insulation properties.

The upper lining layer provides thermal protection of the baking zone and minimises energy losses. It also plays a functional role in the furnace firing system. Due to the presence of burners, local overheating and thermal shocks may occur in this area. Materials applied in this zone should feature low thermal expansion, resistance to heating and cooling cycles, and low thermal conductivity.

Head walls are located at the ends of the baking chambers and act as structural elements closing the system. They are exposed to high temperatures, fluctuating thermal loads and mechanical stresses resulting from the thermal expansion of the entire structure. Materials applied in this zone must provide resistance to thermal shock, dimensional stability and durability under long-term high-temperature operation.

Heating flues are a key element responsible for heat transfer to the charge. Materials in this zone must exhibit good resistance to high-temperature creep and deformation, as well as high resistance to temperature fluctuations.

The furnace floor is subjected to high mechanical loads from the charge as well as the process temperature. In addition, mineral compounds and contaminants from the packing material may accumulate in this area. The refractory lining in this zone should provide high compressive strength, abrasion resistance and low water absorption, preventing long-term degradation.

Waste gas channels are responsible for the discharge of gases generated during the baking of carbon blocks. Due to contact with a mixture of exhaust gases, corrosion, condensation of aggressive components and volumetric changes of the refractory material may occur. Materials applied in this zone must exhibit resistance to aggressive process gases, chemical stability and tightness, limiting the penetration of contaminants into the furnace structure.

The barrier layer is located beneath the carbon electrodes (cathodes), and its primary function is to prevent the penetration of the electrolyte bath into the underlying insulation layers. Refractory materials used in this zone must ensure tightness as well as chemical resistance to molten aluminium and sodium- and fluorine-based compounds. Resistance to bath and molten metal penetration is particularly critical, as infiltration into deeper layers may lead to erosion, loss of insulating properties and, consequently, a reduction in the operational lifetime of the electrolytic cell.

The main function of the insulation layer is to reduce heat losses from the electrolytic cell and to maintain stable thermal conditions of the process.

The working lining is in direct contact with molten aluminium and represents the most heavily loaded part of the ladle lining. It is exposed to intense metal attack, possible contact with oxides and local overheating, particularly near the ladle walls and tapping area. A common risk is the penetration of molten aluminium into the refractory structure, leading to weakening, delamination or cracking. Materials used in this layer must exhibit high resistance to metallic corrosion, low wettability by molten aluminium and high resistance to thermal shock. Low porosity and high chemical purity are strongly recommended.

This layer separates the working lining from the external steel shell of the ladle. Its primary function is to minimise heat losses during the transport of molten metal. At the same time, it acts as a compensating layer during thermal cycling, reducing stresses within the lining structure. Lightweight refractory materials or insulating boards are typically applied in this zone. They must provide low thermal conductivity, resistance to heating cycles and sufficient mechanical strength at low bulk density.