EGA innovation minimises weld faults and reduces down time when cells must be replaced

Unique connection solution for cathodic flexible assemblies patented by aluminium giant

United Arab Emirates: From its inception in 1979, Emirates Global Aluminium (“EGA”) has been committed to continuous innovation in the aluminium smelting process with the aim of increasing productivity, while simultaneously reducing its operations’ impact on the environment through improved energy-efficiency and reduced emission levels. Substantial investments in ongoing research and development work have yielded advanced, high amperage reduction cell technologies that consume less energy while producing more metal; numerous innovative inventions that have improved productivity, safety, environmental performance and more; and a wealth of technology development experience that spawns new thinking and even enables effective retrofitting of modern technologies.

To protect the intellectual property associated with these advances, EGA submits applications to patent its proprietary technologies. The business has been working closely with Takamul since 2014 to develop and submit the required patent application documentation. An innovation support programme developed and operated by the Abu Dhabi Technology Development Committee (“TDC”), Takamul’s mission is to help Emirati individuals, universities and enterprises in Abu Dhabi and the wider UAE, to protect and commercialise their innovative ideas.

Among the innovations submitted for patent in March 2016 is an EGA-developed cell replacement down-time saving design for the flexible assemblies collecting the current from each cathode collector bar of the electrolytic reduction cells used to produce primary metallic aluminium from aluminium oxide. In an aluminium smelter, direct current is fed into a line of electrolytic reduction cells that are connected in series. Each cell is a large carbon-lined metal container, maintained at a temperature of about 960˚C, that forms the cathode. The cell contains an electrolytic bath of molten salt into which aluminium oxide is fed (along with aluminium fluoride, to balance the chemistry). Large carbon blocks are suspended in the solution, and serve as the anode. The electrolytic process causes the pure molten aluminium to sink to the base of the cell, creating a liquid metal pad on the cathode surface.

The current is fed to the anodes, crosses the liquid metal pad and is collected at the cathode blocks. Each cathode block has a steel collector bar, which is connected to the cathodic aluminium busbar of that cell through flexible assemblies. The cathodic aluminium busbar then supplies the current to the anodic system of the downstream cell.

Using a traditional design, EGA previously connected the flexible assemblies at one end to the cathode collector bars using a copper tab in contact and bolted to the steel collector bar. At the other end, the flexible assembly was welded to the aluminium cathodic busbar. While the bolted arrangement allowed for easy installation and removal during cell replacement after cathode failure, copper is not only very expensive but also was being used in an area of very high temperature – leading to deterioration of the connection.

An optional design, used elsewhere in the industry, uses a flexible assembly welded to the cathode collector bar through a transition joint that is also welded on the other side to the cathodic aluminium busbar. This arrangement makes the replacement of cells after cathode failure more time-consuming because of the need to cut the connection to the cathode collector bars of the old cell. It is also challenging to weld the collector bar of the new cell in high magnetic fields and very difficult working conditions (intense heat, plus limited space and access), often resulting in poor quality welds.

The development team at EGA, led by Abdalla Zarouni (Vice President, Technology Development & Transfer, Midstream) sought to overcome the challenges of either design. The team’s solution is unique – in the new EGA design, the connection between the flexible assembly and cathodic aluminium busbar is bolted; and the connection between the steel cathode collector bar and the flexible assembly is a welded steel/aluminium transition joint. “The bolted connection on the cathodic aluminium busbar side is at a lower temperature than the traditional design and continues to reduce cell replacement time when required, thus increasing operating rate and production” says Zarouni. “The welded joint at the cathode collector bar side takes place in the relining shop, far from the magnetic fields and in good working conditions – which results in excellent weld quality. This, in turn, minimises the voltage drop and optimises energy consumption throughout the lifespan of the cell.”

Importantly, the innovation has been tried and tested, confirming its reliability and advantages over the previous design. The new connection design was installed in seven D18+ Technology test cells in Potline 1 at EGA’s Jebel Ali Operations in March 2012. Since then, all 248 cells in Potline 1 have been modernised to D18+ Technology – including the new flexible assembly connector design. The retrofitment of D18+ Technology in the 272 cells Potline 3 at Jebel Ali Operations will begin in September 2016.

“The new flexible assembly connection design has also been installed on the five DX+ Ultra Technology test cells that have been operating successfully in the EGA Eagle demonstration section since March 2014,” adds Zarouni. “Based on this, the invention will also be used in the 424 DX+ Ultra Technology cells to be built in the new Potline 6 at Aluminium Bahrain BSC (“Alba”), for which the technology licence agreement was signed with EGA in February 2016 and the technology package allowing construction has been delivered.”