Wireless Instrumentation for Control of Greenhouse Gas Emissions by the Aluminum Industry; Measurement and Monitoring of Current Distribution in Aluminum Reduction Cells

There are 315 to 458 million metric tons of CO2 (or equivalents) emissions per year due to primary aluminum production, of which 21 to 31 million metric tons are estimated to be produced in the United States. In part, this is due to the enormous electrical energy consumption entailed: 548,350 gigawatt hours worldwide (more than the electricity consumed by the whole of Germany), and the energy inefficiency of primary aluminum production (only 40-45% energy efficiency). It also is due to the emission of polyfluorinated hydrocarbons (PFCs). PFCs are more pernicious than CO2 in their impact on global warming with a global warming potential of 6,500 – 9,200 that of CO2. These PFCs are emitted by the large electrolytic cells in aluminum smelters at a level equivalent to 0.7 tons of CO2 equivalents per ton of aluminum produced. PFCs are emitted mainly during an upset condition of the cells known as an “anode effect”. These anode effects are marked by a large increase in cell voltage; methods are available for their quenching, but only after the excursion of cell voltage is detected, and typical effects last around 2 minutes. A typical aluminum plant, with a few hundred cells, would experience on the order of 100 anode effects per day. An alternative method of detecting anode effects has been investigated in prior work at Wireless Industrial Technologies (WIT). Hall effect sensors, connected to wireless transceivers, were used to tract the currents passing through individual anodes. Preliminary results indicated that the “signature” on an incipient anode effect was discernible in the anode currents approximately 1 minute before the cell voltage increase, providing an opportunity for earlier quenching of the effect or, perhaps, avoidance of the anode effect. In addition, measurement of individual anode currents has been shown by WIT to provide a means of detecting cells, which otherwise are performing below par (“noisy” cells or shorted cells) and thereby provides a further opportunity for reduction of greenhouse gas (GHG) emissions by reduction in electrical energy consumed per ton of aluminum produced. This project will allow WTI to carry the technology to the next stage: demonstration of technical viability and potential benefits on all anodes of one cell of a primary aluminum plant. Potential commercial applications are in the world aluminum industry. Projected gross revenues for WIT at Year 5 are $24 million with deployment completed at 21 of the world’s 200 primary aluminum plants.