Patent applications submitted for in-house developed innovations.
United Arab Emirates: Emirates Global Aluminium (“EGA”), the largest industrial company in the UAE outside the oil and gas industry, has filed another four new patents that increase productivity and operating efficiencies.
The patent applications result from EGA’s technology development programme, which has focused on continual improvement for the past 25 years
EGA’s latest reduction technology, DX+ Ultra, has more than double the pot productivity of the company’s original D18 technology. Last year EGA licensed DX+ Ultra to Aluminium Bahrain for Alba’s potline 6 expansion, making EGA the first UAE industrial company to license its own large scale industrial technology internationally.
EGA began filing patents several years ago when it began to consider licensing its technology to others. EGA had filed 19 patents by the end of 2016, including nine in that year alone.
The four most recent patent applications target improvements in the electrolytic Hall-Héroult[i] process, used to produce metallic aluminium from aluminium oxide, and are detailed below.
Bi-metallic insert in the cathode collector bar
Bernard Jonqua (Manager, Technology Potlining, Technology Development & Transfer) and Abdalla Alzarouni (Vice President, Technology Development & Transfer) have devised an innovative cathode block assembly, incorporating a novel bi-metallic insert (copper and aluminium) that serves to optimise the current collection of the traditional steel cathode collector bar, decreasing voltage drop in the cell and reducing energy consumption. The voltage gained can be used to reduce the production cost of the aluminium, or to increase the production of the pot by increasing the current at constant power.
The invention also ensures even distribution of the collected cathode current, increasing the lifespan of the pot lining and enabling better stability in the operating cell.Reducing the horizontal currents inside the molten metal pad caused by non-uniform currents improves the stability of the pot. The anode-cathode distance of the pot can therefore be reduced without perturbing the current efficiency of the electrolytic cell, leading to a further decrease in the total voltage drop of the electrolytic cell.
The EGA-developed cathode assemblies may be incorporated into existing aluminium production cells with standard carbon cathode blocks.
Jonqua and Alzarouni have also developed a cathode assembly in which rectangular copper inserts are placed on top of the steel cathode collector bars. The copper inserts extend to the end of the collector bar and carry most of the current between the cathode and the busbar. The copper inserts decrease the total voltage drop of the cathode, improving energy consumption.
The cathode assembly includes a non-contact zone between the copper insert and cathode bar at the end wall of the cathode bar – an innovation previously patented by EGA which decreases the energy consumption of a cell by lengthening the path taken by the current to reach the collector bars, resulting in more even distribution of current and thus a more stable pot. The electrical contact between the cathode collector bar (with the copper insert) and the carbon cathode block is ensured by filling the gaps between the facing peripheral walls in the groove with cast iron (and/or with a carbonaceous intermediate material), which also absorbs the higher thermal expansion of metallic connection bar versus that of the cathode material.
The pot insulation is increased to compensate for the heat loss arising from the copper inserts extending beyond the pot and for the heat generated by the pot being lower than the usual pot.
A layer of insulating paint at the extremity end of the cathode block grooves decreases the current density at the end of the cathode blocks, reducing cathode wearing and consequently lengthening pot life.
Another advantage of placing the rectangular copper inserts on top of the collector bars is that it eases the recovery of copper metal before selling used steel bars. This addresses the requirement of steel factories for aluminium producers using copper inserts to separate the steel from the copper beforehand (steel cannot be recycled with a content of 10% to 20% copper).
Five pots at EGA’s Jebel Ali smelter operation have been operating with this copper insert design for over three years. This simple-to-manufacture cathode assembly is designed for use in a Hall-Héroult electrolysis cell, but could also be used in other electrolytic processes.
Split anode riser busbar system
Vinko Potocnik (Senior Manager, Technology Transfer, Technology Development & Transfer) and Marwan Bastaki (formerly Engineer: R&D, Technology Development & Transfer) have developed a unique cathode busbar system that balances the electrical current distribution in the cathode collector bars. The resulting optimal electrical equilibrium within the reduction cell effectively minimises magnetohydrodynamic (“MHD”) instabilities and allows the appropriate anode-to-cathode distance to be maintained. In turn, this lowers the electrical resistance and associated voltage drop of the cell, reducing energy consumption. And by simultaneously maintaining the desired magnetic equilibrium, the overall cell operation is improved.
The solution is particularly pertinent in the primary aluminium industry’s quest for energy optimisation and the trend to increase the pot-size and the current of operating pots, especially that the vertical component of the magnetic field tends to increase with the size of reduction cells and higher cell current. The EGA inventors discovered that placing a straight cathode busbar along the end of a cell and using a novel anode riser design significantly reduces the vertical magnetic field in the upstream corners of a cell.
Each anode riser is split into two along the whole length from the cathode busbars to a common point on the anode beam. The upstream risers are connected to and feed their current into the upstream anode beam; while the downstream risers are connected to and feed their current into the upstream or downstream anode beam of the adjacent downstream cell. At the base of the risers, the downstream riser is connected to the downstream cathode busbar of the cell and the upstream riser is connected to the upstream cathode busbar of the cell. This arrangement provides a much longer straight path from the downstream side to the anode beam than previous designs. It also requires busbars of reduced mass, such that the need for zig-zag busbars on the downstream side of the cell is therefore eliminated and pot-to-pot distance can be reduced by 300 mm to 400 mm – together offering a key space-saving advantage as well as decreasing capital costs.
Novel potline energising procedure
Nadia Ahli (Associate Manager, Technology Development & Transfer)and Sajid Hussain (Supervisor, Technology Transfer, Technology Development & Transfer) have designed a unique busbar system that facilitates the start-up of an electrolysis potline, as well as the total or partial shut-down of the potline. The system described in the patent application features a specific, step-by-step implementation procedure for these scenarios.
The system employs temporarily used crossover busbars (“TUCBs”), which are capable of creating and disconnecting an electrical connection in a reversible manner. The TUCBs are conductors located between two adjacent sectors in a potline and connect the conductors of the lines in the two potrooms comprising a potline, thereby forming a low resistance electrical conduction path between the current output of the first half of cells in the one potroom and the current input of the second half of cells in the second potroom.
The TUCBs, which are of similar construction to the permanent crossover busbars connecting the potrooms, comprise a temporarily used switch busbar that is either bolted between two sections of the TUCB to establish the electrical connection; or taken out of the TUCB to disconnect the circuit. Welded connectors (flexible or otherwise) can be used.
The innovation makes it possible to cut-out one or more sections of pots, starting at the section adjacent to the permanent crossover busbar. This may serve to temporarily decrease the capacity of the plant (most frequently for commercial reasons or in case of power shortage or raw material shortage or labour conflicts) by cutting out one or more section; allow maintenance or refurbishment of the cells or their busbar system in the cut-out section(s); or shut down the whole plant (for instance prior to its demolition) section by section while continuing to produce metal in the sections that are still connected.
The innovation also facilitates potline (or individual pot) start-up, section by section – starting with the section adjacent to the rectifier substation. This allows the plant to start operating the first sector(s) while the subsequent ones are being built or completed.
Since 2014, EGA has developed and submitted patent applications to protect its inventions, working simultaneously with Takamul – an innovation support programme developed and operated by the Abu Dhabi Technology Development Committee. 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. To date, seven of EGA’s 19 patent applications have been accepted for implementation funding by Takamul. A further two have been filed with Takamul.
[i]The Hall-Héroult process is the only continuous industrial process for producing metallic aluminium form aluminium oxide. Aluminium oxide (Al2O3) is dissolved in molten cryolite (Na3AlF6), and the resulting mixture (typically at a temperature comprised between 940°C and 970°C) acts as a liquid electrolyte in an electrolytic cell. An electrolytic cell (also called “pot”) used for the Hall-Héroult process typically comprises a steel shell, a lining usually made from refractory bricks, a cathode usually covering the whole bottom of the pot (and which is usually made from graphite, anthracite or a mixture of both), and multiple anodes (usually made from carbon) that plunge into the liquid electrolyte. Anodes and cathodes are connected to external bus bars. An electrical current is passed through the cell (typically at a voltage between 3.8 V to 5 V), which splits the aluminium oxide into aluminium ions and oxygen ions. The oxide ions are reduced to oxygen at the anode, which reacts with the carbon of the anode to form carbon dioxide (which is emitted). The aluminium ions move to the cathode where they accept electrons supplied by the cathode. The resulting metallic aluminium is not miscible with the liquid electrolyte, has a higher density than the liquid electrolyte and will thus accumulate as a liquid metal pad on the cathode surface from where it needs to be removed from time to time, usually by suction.