Aluminium may be produced by electrolytic reactions in electrolytic smelting pots, using the Hall-Héroult process. The process produces raw gas in the form of hot, particle-laden raw gas, which is cleaned in a gas cleaning unit before being discharged to the atmosphere. A duct system is usually used for channeling the hot, particle-laden raw gas from the smelting pots to the gas cleaning unit.
A typical gas cleaning unit may comprise a dry scrubber and a dust filter, e.g. a fabric filter that may be of the bag filter type. A consideration of such systems is that energy-consuming fans are often necessary in connection with raw gas treatment systems in order to actively draw the raw gas through the gas cleaning unit. Such is the case since the raw gas collecting ducts and the raw gas cleaning unit may introduce flow resistance in flue gas collection and cleaning systems.
Still another consideration is that raw gas treatment systems may require that the raw gas is cooled before entering the raw gas cleaning system. This requirement may be dictated by, for example, the temperature sensitivity of any downstream equipment, or by the temperature dependency of the cleaning efficiency of the gas cleaning unit. It is known to cool hot raw gas produced by aluminium smelting pots by mixing cool ambient air into the raw gas ducts upstream of a gas cleaning unit. Gas/air mixing is relatively simple, but for high gas temperatures the volume of ambient air required to provide adequate cooling becomes substantial, and so does the increase in cooled raw gas volume. Hence, as the volume of raw gas is increased, there must also be a corresponding increase in the size of the gas cleaning unit, the downstream fans that pull the gas through the gas cleaning unit, and the plant energy consumption. The energy consumption of an aluminium production plant may be substantial and it is desirable to find areas where the energy consumption may be lowered.