Rockwell Automation has migrated the control systems at Mozal Aluminium’s furnace assembly and ladle cleaning shop to its modern DCS based on the PlantPAx design standard. An information-rich control architecture based on the Allen-Bradley ControlLogix platform helps to ensure improved long-term plant and process performance and reliability, while also bringing all the latest diagnostic and fault-finding capabilities to these operational areas.
The migration included the rewriting of a new, optimised control philosophy. The result is a streamlined, consistent and coherent I/O architecture visualised through the latest HMIs and FactoryTalk Studio ME software, which delivers intuitive, actionable machine data and intelligence. Service teams now have far greater insight into plant processes, allowing faster, more efficient response to any point of failure through added diagnostic features.
Additionally, both plant areas were upgraded to Device Level Ring EtherNet/IP network architectures. This upgrade helped to ensure no single, localised point of failure in the network which can lead to more widespread, unnecessary downtime. The migration, for which Rockwell Automation was responsible for the engineering, product supply, integration, and commissioning, was completed in twelve months.
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 would reduce the integrity of the molten aluminium, and thus the quality of the final cast ingots.
The three upgraded ControlLogix controllers supplied for these systems deliver a rewritten I/O structure built on standards and simplified control functionality. Detailed, real-time visualisation and diagnostics of the operation floor is provided by 16 PanelView Plus 7 graphic terminals with FactoryTalk ME V8.02 software.
The drive system on the tube cleaning equipment was migrated to the Allen-Bradley PowerFlex 755 AC Drive. In addition to optimising energy efficiency, the PowerFlex 755 delivers a holistic level of actionable data that simplifies fault finding and optimises maintenance on the drive system.
“Upgrading the control systems on the ladle shop floor was also an opportunity to provide a complete inspection of the instrumentation layer,” explains Devin Whitfield, lead engineer, Rockwell Automation Sub-Saharan Africa. “Working with Mozal, defective or unreliable equipment was flagged, and related ad hoc items of code added or removed.”
In an effort to ensure minimal disruption on plant operations, each system was completed within a planned three-day commissioning period.
The casting process consists of 10 furnaces across five casting lines, which maintain the aluminium at a temperature of approximately 1000°C before feeding it into a launder for casting.
Maintaining the optimum level of aluminium in the launder during casting is critical: filling it too quickly risks molten aluminium being ejected from the launder – a significant safety hazard – while an inadequate flow results in under-cast ingots of inferior weight, size and quality.
Controlling the tilt demand, internal temperature and casting temperature of the furnaces is now achieved via PID control through the ControlLogix platform. The approximately 200 I/O control system 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 system within the casting and maintenance schedule of each furnace. “With production demand in the cast house requiring four of the five casting lines active at any one time, and only one of two furnaces casting for each line, we installed and commissioned the control of each furnace in a narrow, time-critical window,” explains Coenraad Maree, project engineer, Rockwell Automation Sub-Saharan Africa.
This required not only a high degree of efficiency and accuracy to help ensure each system migration did not extend beyond scheduled windows, but also a flexible approach in accommodating any changes to the respective schedules.
The biggest installation challenge, however, was that of working in the intense heat of the cast house environment. With ambient temperatures of over 40°C, safety of the commissioning teams was a critical consideration.
A preferred automation supplier
In addition to the migration of the casting furnaces and the ladle shop to the improved software standard, Rockwell Automation simultaneously executed a plant-wide technology migration of Mozal Aluminium’s drive network to the PowerFlex 755 platform. This project numbers over 350 drives in total, which will be complete in November 2020.
This modern, Connected Enterprise-ready distributed control system helps secure the long-term reliability of the production plant, and amplifies the level of plant and system-wide intelligence available to onsite operation and maintenance teams to improve efficiency and reduce unplanned downtime.
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