Use of state-of-the-art sensors to reduce energy consumption at the TRIMET aluminium smelter

摘要

The production of aluminium with the Hall-He'roult process is even today energy intensive and prone to process disturbances. In a Hall-He'roult cell the alumina that is in solution in molten cryolite (which might be modified with other fluorides) is reduced to aluminium, which deposits on the bottom of the cell whilst simultaneously CO_2 is evolved at the carbon anode. The hostile environment and the high number of cells make it difficult to closely monitor the process with online sensors. Only line current, line voltage and cell voltage are measured continuously. These signals are used for calculations that determine pot parameters such as ACD (anode-to-cathode distance) and alumina concentration. There are many other variables in the process that are difficult to control and, therefore, prone to disturbances. Keeping the energy and mass balance constant is one of the key factors in improving process efficiency. To achieve this target the use of state-of-the-art sensors for temperature, liquidus, superheat and cathode voltage drop (CVD) measurements were introduced on full-scale production at the TRIMET ALUMINIUM AG smelter in Essen. The pots are individually controlled regarding their chemical and thermodynamic state using a newly developed 9-Box Control concept. Due to the introduction of this strategy, energy consumption was reduced and current efficiency was increased.