Sergey Akhmetov

Studies on Background PFC Emission in Hall-Héroult Reduction Cells Using Online Anode Current Signals

It is well established that maintaining magneto hydrodynamic stability over the life of an aluminium reduction cell is important for achieving optimum performance, and this includes having balanced cell current distribution. Dubal operates at the leading edge of current density, thanks to a state of the art control algorithm which also maintains low PFC emissions. As part of a continuing performance enhancement programme, we have been investigating temporal and spatial changes in cell conditions due to routine activities such as anode set, which can impose uneven distribution of current between operating anodes. During these investigations, we have found the occasional formation of traces of background anthropogenic PFC gases, namely tetrafluoride and hexafluoroethane, commonly referred to as non-AE PFC emissions. Further insights into the causes are presented from these studies.

Update on the Development of D18 Cell Technology at Dubai

Dubai Aluminium commenced operation in 1979 with 3 potlines, each with 120 D18 technology cells. While more advanced cell technologies have since been developed and implemented at Dubal, the original D18 cell technology has continued to be updated and improved so that it remains a vital contribution to the overall smelter production.

DX+, An Optimized Version of DX Technology

Since the 1990’s, DUBAL has engaged in self-development of proprietary aluminium reduction technology. DX and DX+ technologies, both being in-house designed, modeled, tested and optimized, are the latest products of this development process. In quest to decrease capital cost per tonne, DUBAL designed DX+ technology and started up five demonstration cells between June and August 2010. DX+ cells are similar to DX cells, but larger in size: the productivity per square metre of potroom is increased by more than 17%. This paper describes the DX+ cell design evolution from DX technology. It also summarizes the on-target performance achieved by the DX+ demonstration pots during their first year of operation at 420 kA. DX+ technology has been selected for the EMAL Phase II project. The project FEED study, completed in June 2011, is based on one potline of 444 DX+ pots. The design allows for an operating amperage increase to 460 kA.

DX+ Ultra—EGA High Productivity, Low Energy Cell Technology

After successful development and industrial implementation of DX and DX+ Cell Technologies, EGA Technology Development launched several initiatives to lower CAPEX and cell energy consumption. The result is DX+ Ultra Technology, which is installed in five demonstration cells in the Eagle Section of Potline 5 Eagle at DUBAL (EGA Jebel Ali Operations), which were started up in March to May 2014 at 450 kA. The main new features of DX+ Ultra Technology are: reduced cell-to-cell distance as well as proprietary novel-design split anode risers, collector bar copper inserts and cathode flexes. More than one year of excellent performance at 455 kA with 95 % current efficiency and net specific energy consumption of 12.8 kWh/kg Al has confirmed that the technology is ready for industrial implementation. DX+ Ultra Technology has been selected for Alba’s Potline 6 expansion. Further optimization of the cells is underway to deliver best-in-class technology to the client. This includes larger busbar cross-sections for even lower energy consumption.

EGA New D20+ Technology with Reduced Energy Consumption

Following the successful design, development and industrial implementation of the low energy D18+ cell technology, Emirates Global Aluminium has initiated a new project to upgrade the CD20 and D20 cell technologies to D20+ with the aim to further reduce energy consumption and perfluorocarbon emissions. This project again demonstrates the company’s vision and commitment to lowering our environmental footprint and increasing our economic competitiveness. The work in this paper details the main retrofit changes in seven D20+ test cells with improvement in busbar design, retrofitting process, superstructure and the introduction of copper insert cathode collector bars which have resulted in lowering the cell ohmic resistance, improved the anode current density and magnetohydrodynamic stability resulting in lowering energy consumption from 14.00 to 12.99 DC kWh/kg Al. Further process optimization and feasibility analysis are in progress to fully assess the best way forward for industrial implementation of the D20+ technology.

DX+ Ultra Industrial Version: Preheat Start Up and Early Operation

Five DX+ Ultra Technology demonstration pots were started in EGA in Jebel Ali in 2014 at 450 kA and operated at increased amperages up to 460 kA until March 2017. In view of ALBA Potline 6 project, EGA decided to stop the five demonstration pots with the objectives of validating the industrial busbar design and fabrication, carrying out full autopsies to assess lining condition at an average age of 1100 days, building new industrial linings, and fine tuning the industrial operation procedures for new and restart pots. Two pots were restarted with the old lining and three pots were rebuilt and started with new industrial lining design. On these three pots, the preheat, start up and early operation procedures planned for ALBA Potline 6 were implemented with the objective of minimum energy consumption and elimination of anode effects during the start-up and early operation; the results of these three pots are presented in the paper.

Fault Detection and Diagnosis In Hall–Héroult Cells Based on Individual Anode Current Measurements Using Dynamic Kernel PCA

Individual anode current signals in aluminum reduction cells provide localized cell conditions in the vicinity of each anode, which contain more information than the conventionally measured cell voltage and line current. One common use of this measurement is to identify process faults that can cause significant changes in the anode current signals. While this method is simple and direct, it ignores the interactions between anode currents and other important process variables. This paper presents an approach that applies multivariate statistical analysis techniques to individual anode currents and other process operating data, for the detection and diagnosis of local process abnormalities in aluminum reduction cells. Specifically, since the Hall–Héroult process is time-varying with its process variables dynamically and nonlinearly correlated, dynamic kernel principal component analysis with moving windows is used. The cell is discretized into a number of subsystems, with each subsystem representing one anode and cell conditions in its vicinity. The fault associated with each subsystem is identified based on multivariate statistical control charts. The results show that the proposed approach is able to not only effectively pinpoint the problematic areas in the cell, but also assess the effect of the fault on different parts of the cell.

Implementation of D18+ Cell Technology at EGA’s Jebel Ali Smelter

In March 2012, EGA started seven test cells to validate its new D18+ cell technology. Designed with the latest technological advances to upgrade the original D18 potlines, the test cells quickly met their design targets with specific energy of 12.75 DC kWh/kg Al and AE frequency less than 0.02/cell/day. After successful validation, a project was commenced in August 2015 to upgrade the original D18 potlines to the newly developed D18+ cell technology. Unlike previous capacity expansion at EGA, the D18+ project required construction within the existing potrooms, which continued to operate while the upgrade was underway. Despite the challenges involved, full conversion of Potline 1 was successfully achieved ahead of schedule and without injury. Through increased amperage to 235 kA and higher efficiency EGA’s production capacity will be increased by 23 kt per annum. Further conversion of 272 cells to D18+ in Potline 3 will commence in September 2016.

Reduction in EGA Jebel Ali Potroom GHG Emissions

EGA’s Jebel Ali smelter hot metal production has increased above 1 million tons per annum since 2010 and produced a record 1,045,255 tons in 2015 and with forecast total production of 1,065,280 tons for 2016. Jebel Ali Potrooms has also strived to minimize its environmental impact with significant effort to reduce the three main sources of GHG emissions; power consumption, anode carbon and CO2e emissions from AE PFC’s (anode effect perflurocarbons). Specific energy has decreased from 14.82 DC kWh/kg to 14.29 DC kWh/kg, net carbon has reduced from 0.434 t/t Al to 0.423 t/t Al and AE PFC emissions have reduced from 0.263 CO2e/t Al to 0.071 t CO2e/t Al. This has resulted in reducing annual GHG emissions by 798,065 CO2e tons and was achieved despite increasing annual hot metal production by 63,266 tons since 2010. This achievement demonstrates EGA’s vision for operational excellence and continuing efforts to minimise its environmental footprint.

Studies on Anode Pre-Heating Using Individual Anode Signals in Hall-Héroult Reduction Cells

The proportional increase in modern cells’ amperage and anode size while aiming for low energy input has resulted in slowing the process of anode current pick-up rate. Changes in cell thermal and electrical balance due to anode replacement (while a thick layer of frozen electrolyte is formed under a new anode) causes a slower anode current pick-up rate which may require 4 days to reach the target current. Variations in cell conditions following anode replacement result in increasing cell magnetohydrodynamic instability and prolonged presence of low superheat zones. This increases the possibility of forming local abnormalities, such as anode spikes. As part of a continuous enhancement programme, the latest developed individual anode current monitoring system in DUBAL (EGA Jebel Ali) was used to study the benefits of preheating anodes up to 500 °C. The work includes studying the impact of anode pre-heating on current pick-up rate while conducting operations such as anode dressing.