MechChem Africa January 2019

Modern Rockwell DCS for Mozal Aluminium

pleted within a planned three-day commis- sioning period. With respect to the furnace assembly, the casting process consists of 10 furnaces across five casting lines, which maintain the aluminiumat a temperatureof approximately 1 000 °C before feeding it into a launder for casting. Maintaining the optimum level of alu- miniuminthelaunderduringcastingiscritical: filling it too quickly risks molten aluminium being ejected from the launder – a significant safety hazard – while an inadequate flow re- sults in under-cast ingots of inferior weight, size and quality. Controlling the tilt demand, internal tem- perature and casting temperature of the fur- naces is nowachievedviaPIDcontrol through the ControlLogix platform. A control system with approximately 200 IOs automates both the position and speed of the furnace tilt and integrates with existing third-party furnace sub-systems, including the burner management systems, tightness control and hardwired safety systems. In order to execute the migration without affecting production, Rockwell Automation installed the control systemwithin the casting and maintenance schedule of each furnace. “With production demand in the cast house requiring four of the five casting lines to be active at any one time, and only one of two furnaces casting for each line, we installed andcommissioned the control of each furnace in a narrow, time-critical window,” explains Rockwell Automation project engineer, Coenraad Maree. This required a high degree of efficiency and accuracy to help to ensure each system migration did not extend beyond scheduled windows, and a flexible approach in accom- modating any changes to the respective schedules. The biggest installation challenge, how- ever, was that of working in the intense heat of the cast house environment.With ambient temperatures of over 40 °C, safetyof the com- missioning teamswas a critical consideration. In addition to the migration of the casting furnaces and the ladle shop to the improved software standard, Rockwell Automation is simultaneously executing a plant-wide tech- nology migration of Mozal Aluminium’s drive network to the PowerFlex 755 platform. This project numbers over 350 drives in total and ismooted for completionbyNovember 2020. “Themodern,ConnectedEnterprise-ready distributed control system helps secure the long-term reliability of the production plant, and amplifies the level of plant- and system- wide intelligence,” Whitfield concludes. q

Rockwell Automation has migrated the control systems at Mozal Aluminium’s furnace assembly and ladle cleaning shop to its modern distributed control system based on the PlantPAx design standard.

A modern, information-rich control architecture, based on the Allen- Bradley ControlLogix platform, ensures improved long-term plant andprocess performanceand reliability, while alsobringingall the latest diagnosticand fault- finding capabilities to theseoperational areas. The migration includes the rewriting of a new, optimised control philosophy. The result is a streamlined, consistent and coherent IO architecture, visualised through the latest Rockwell Automation HMIs and FactoryTalk Studio ME software that delivers intuitive, actionable machine data and intelligence. Service teams now have far greater insight into plant processes, allowing faster, more ef- ficientresponsetoanypointoffailurethrough added diagnostic features. Additionally, both plant areas were up- graded to Device Level Ring EtherNet/IP network architectures. This upgrade helped to ensure no single, localised point of failure in the network, which would lead to more widespread, unnecessary downtime. The migration, for which Rockwell Automationwas responsible for theengineer- ing, product supply, integration, and commis- sioning, was completed in twelvemonthswith both systems integrated into live production environments. The ladle shop comprises three systems – pre-heating, tube cleaning and ladle cleaning equipment –which deliver rapid and efficient

automated cleaning and heating of the ladles and the distribution tubes that fill them. These systems help to ensure that no bath material and aluminium products can collect in the ladles, which reduce the integrity of the molten aluminium and thus the quality of the final cast ingots. The three upgraded ControlLogix con- trollers supplied for these systems deliver a rewritten IO structure built on standard and simplified control functionality. Detailed, real-time visualisation and diagnostics of the operationfloor areprovidedby16PanelView Plus 7 graphic terminals with FactoryTalk ME V8.02 software. The drive system on the tube cleaning equipmentwasmigrated to theAllen-Bradley PowerFlex 755 AC Drive. In addition to opti- mising energy efficiency, the PowerFlex 755 delivers a holistic level of actionable data that simplifies faultfinding and optimises mainte- nance on the drive system. “Upgrading the control systems on the ladle shop floor was also an opportunity to provide a complete inspection of the instru- mentation layer,” explains Devin Whitfield, lead engineer for Rockwell Automation sub-Saharan Africa. “Working with Mozal, defectiveorunreliableequipmentwasflagged and related ad hoc items of code added or removed.” In an effort to ensure minimal disruption on plant operations, each system was com-

Rockwell Automation installed pre-heating, tube cleaning and ladle cleaning systems into the ladle shop.

24 ¦ MechChem Africa • January 2019