It all starts at the Calciner Plant, as we buy Green Petroleum Coke (GPC) to produce carbon anodes for the aluminium smelting process. Having a dedicated Calciner Plant helped Alba in controlling the quality of the CPC by producing it in-house and, thus control the quality of the aluminium we produce.
The aluminium metal is made of alumina which is composed of aluminium and oxygen. During the smelting process, electrical energy is used to separate the aluminium metal from the oxygen to produce molten aluminium. To produce one tonne of aluminium, about two tonnes of alumina are required.
The smelting process is done in large steel, carbon-lined furnaces called reduction cells. When alumina is fed into these cells, it gets dissolved in molten cryolite, a liquid which can dissolve alumina and conduct electricity at 970°C. Electricity is introduced into each cell via carbon blocks, called anodes, that we manufacture in-house. All reduction cells in the smelter are connected in a series by an aluminium busbar, which carries electrical current to the cells.
The process is continuous with an electrical current of 100,000 to 320,000 amp flowing from the anode through the alumina and cryolite mixture, to the carbon cell lining, to the anode of the next cell, and so on. The electrical current causes the alumina in this mixture to react with the carbon anode, forming aluminium and carbon dioxide. In its molten form, the aluminium sinks to the bottom of the reduction cell, while the carbon dioxide and other gaseous by-products form at the top of the cell.
In our efforts to optimise natural gas which we use to generate electricity, we use the waste heat generated in the smelting process to produce steam for generating additional electricity in what is known as the combined cycle effect. The generated heat from this cycle is delivered to the reduction pots. Molten aluminium is siphoned from the bottom of the cell by a process called tapping. From the reduction lines, liquid metal is transported to the casthouses where it is poured into mixing furnaces where elements such as silicon, magnesium, copper, iron, titanium or boron are added to meet the customer required alloy specifications.
The prepared aluminium is then cast to create many forms of our final products, including Standard Ingots, Sows and T-ingots which are used for remelting by other industries, Extrusion Billets for the manufacture of extruded products such as window frames and structural supports, Rolling Slabs that are used in the production of aluminium sheets and foil and Foundry alloy ingots that are used as wheel alloys. Finally, the remainder is supplied in molten form to local industries located in the immediate vicinity of the Alba smelter.