PLC upgrade of smelter substation under way

Industrial automation and information solutions provider Rockwell Automation South Africa is upgrading the programmable logic controller (PLC) of mining major BHP Billiton’s joint venture (JV) Mozal aluminium smelter’s 22 kV substation, in Maputo, Mozambique.

The PLC upgrade, which is scheduled for completion in August, follows the R7.5-million upgrade of the smelter’s controller hardware and compressor house, which was undertaken by Rockwell Automation in September 2013 and completed in October 2014.

Rockwell Automation lead engineer Jonathan Armstrong notes that the PLC upgrade is being conducted while the plant, which produces 580 000 t/y of aluminium, is fully functional, which presents several challenges.

“Since this is a live plant, with very little downtime permitted, it is of the utmost importance that everything is planned meticulously beforehand. “Every detail is discussed with Mozal’s project manager and engineers, and acceptance of the strategy for the implementation of the changes is discussed extensively and ultimately approved by Mozal’s team,” he details.

Armstrong tells Mining Weekly that the success of this project will highlight the company’s capabilities in the automation field across Africa. He says it will also serve as a valuable reference for future projects of this nature, as Rockwell Automation’s team has gained valuable experience.

“Ageing infrastructure is a reality and customers need to accept that it is a natural cycle in a plant’s existence. By undertaking and successfully implementing projects of this size and nature, Rockwell Automation is proving itself as a reliable and competent partner for these projects,” he elaborates.

Armstrong says the company’s record includes work on large, difficult and high-risk plants, where “we turn them into successful solutions, helping our customers to make a smooth transition to new technology, which ultimately benefits their plant from an operational and maintenance point of view”.

Foundation Phase
The Mozal controller migration project undertaken by Rockwell Automation was part of Phase 1 of a ten-phase migration strategy scheduled to take place over the next ten years at Mozal aluminium smelter.

This phase entailed upgrading the Allen Bradley ControlLogix programmable controllers, which are also Rockwell Automation’s flagship controllers, in the compressor house to reduce downtime and modernise essential equipment and processes.

Armstrong explains that the project’s scope included the design, installation and commissioning of all hardware and software, as well as interfacing ControlLogix with a competitor’s supervisory control and data acquisition system. The project also incorporated operator and maintenance personnel training using simulation software initially developed for factory acceptance testing.

Hardware installation was done in four phases to mitigate risk and comprised ten ControlLogix controllers and one redundant controller. Rockwell Automation also installed 11 PanelView Plus 6 HMI terminals to monitor, control and display application status information graphically, and a FactoryTalk View Site Edition workstation.

Rockwell Automation’s software, Mining Solution (MS), was also implemented, along with compressor anti-surge software.

Armstrong adds that MS was included to standardise the upgraded compressor plant control systems and to enable on-site personnel full capability using the transparent ControlLogix solutions.

The project provides additional value-adds for the Mozal smelter, such as the automatic start-up of backup diesel compressors and spare compressor capacity, which were previously unavailable at the plant. Automatic compressor start-up was achieved by installing the Rockwell Automation Master Control for networked compressors. Additional compressor capacity was achieved by optimising the guide vane control and dynamically changing the producer pressure set points to meet consumer demand.

The Mozal smelter is responsible for 30% of Mozambique’s official exports and uses about 45% of the electricity generated in the country. The JV comprises BHP Billiton, with 47.1%; Japan-founded trading company Mitsubishi Corporation, with 25%; South Africa’s Industrial Development Corporation, with 24%; and the Mozambique government, with 3.9%.