One of the world’s largest plants for alumina production is located in Brazil. Situated near Belém, the capital of the state of Pará, it processes bauxite from mines in the Amazon delta to produce alumina, a raw material required for aluminium smelters. Alunorte ships the annual production of 4.4 million tons to a local aluminium smelter and customers to abroad via a nearby harbour. Operative since 1995, the plant has been kept up to date with several major modernisation steps. Between 2003 and 2006 the company invested $US 768 millions, part of which was used to update the control system.
The alumina plant extends over an area of 5km² and consists of three production areas. Alunorte lays the utmost priority on continuous efficiency improvements and thus the reliability of the automation system is a top issue. In the latest modernisation phase between 2003 and 2006 Alunorte updated the control system to ABB’s system 800xA. Through its redundancy features the system enables an undisturbed production process during at least 99% of the operation time.
The plant’s network is based on Ethernet communication in the management level and on Profibus in the field. For data transmission between the components of the distributed control system Alunorte relies on fiber optic cables. Their transmission capability is superior to copper cables and thus the long distances in the plant can easily be covered. But the main advantage achieved by using fiber optic is due to fiber optic’s immunity to electromagnetic influences.
Thus it increases the reliability of the automation system, the most important issue for Alunorte. Also for this reason the data communication on the field level is done through redundant Profibus lines, using redundant field devices and controllers from ABB. Therefore, any single failure does not interrupt the control system and does not affect the production process at all. The backbone has to meet high demands also, as it links the three areas of the plant. The high data volume on this communication level requires full duplex Gigabit Ethernet. High availability is indispensable. This means, in case of a fault, the redundancy mechanism needs to ensure a reconfiguration time of less than one second.
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