Aluminium is known as an environmentally friendly metal because it can be readily recycled and used to make lighter vehicles that consume less fuel. Still, the production of primary aluminium by electrolysis is energy intensive and a significant source of greenhouse gases, but Norsk Hydro has developed a new electrolysis cell technology that significantly reduces the amount of energy needed to produce primary aluminium and the emission of greenhouse gases.
A new concept for process-gas collection is being tested at one of the electrolysis cells in Årdal that in the future could enable capture of the CO2 from the electrolysis process. The technology is known as the HAL4e electrolysis cell concept. HAL stands for Hydro and aluminium, while “4” represents the amperage evolution above 400 kilo ampere and 4 e’s stand for environmental improvements, energy savings, emerging technology and entry to partnerships. The technology has been developed by Hydro’s research scientists in Norway and Germany.
Next Generation Cell Technology
This next generation cell technology is based on a specially designed electrolysis cell that increases the amperage used to make aluminium, while reducing energy consumption, measured in kilowatt hours of electricity per kilogram of aluminium. It also lowers the emissions of fluorocarbons, a greenhouse gas sometimes emitted during smelting, by reducing the frequency of anode effects.
On average, the electrolysis process in Hydro’s smelters worldwide in 2007 produced 2.2 tonnes of CO2 equivalents for every tonne of aluminium. The bulk of that, or 1.5 tonnes, is the CO2 produced in the electrolysis process. The remaining 0.7 comes from the fluorocarbons. The latter contribution will largely be eliminated in new production facilities based on the HAL4e.
“It’s a major step forwards, and we have already demonstrated significant reductions in energy consumption as well as greenhouse gas emissions,” said Asgeir Bardal, head of Primary Metal Technology in Hydro.
So far, Hydro has successfully implemented the technology at six pilot cells at its smelter in Årdal. The cells operated at an amperage rate of 420 kA from June 2008 -- the highest ever recorded at a Norwegian smelter -- and amperage has since been increased further. Since being in operation for one year, the company has noticed a more than 50% reduction in anode-effect frequency from earlier benchmarks, said Bardal. The next step is likely to be a larger pilot project, followed by its first smelter based on this new technology.
With HAL4e as the cell technology platform, Hydro is currently working on a suction system that can increase the concentration of the CO2 in the process gas. High CO2 concentration levels are needed for economically feasible further processing of the gas in a facility for CO2 capture. The ability of the HAL4e platform to reduce energy consumption and greenhouse gas emissions, combined with the use of hydropower at Hydro’s smelters, puts the company in the environmental forefront, in line with the company’s vision of zero-emission production.
Dow Jones Sustainability Index leader
The company’s commitment to develop new zero-emission production technologies is just one of several factors that recently made it an industry leader on the Dow Jones Sustainability Index. The company is also working on developing lighter aluminium for more fuel-efficient cars, aluminium facades for energy neutral buildings, and solar cell production. The company has a 35% stake in Ascent Solar Technologies, 18.4% in NorSun, 49% in a joint venture with Umicore of Belgium, and is an investor in Norwegian venture fund Convexa.