PROJECT DESCRIPTION
BACKGROUND
Aluminium is the second most available metal in the world, being lighter of weight and possessing non-corrosive properties. In comparison to iron, there will be a strong and growing demand for aluminium in the future. The application of aluminium in the packaging industry has already been a longstanding practice, due to its low weight, good formability, good heat conductivity, strength and non-corrosiveness. These properties have also led to its application in areas such as automation, construction, the airline and car industries and ship building. Because of its wide applicability, alluminium production has doubled in the last 20 years and this trend is continuing. In Western Europe the consumption of primary aluminium grew at an average rate of 2%, to 4.7 million tons per year. This is approximately 20% of worldwide consumption. But one of the most important and economic attractive properties of aluminium is the fact that it can be used and reused without loosing any of its properties. Whilst the energy consumption of new ("primary") alluminium production from bauxite requires 148 MJ per kg aluminium, the remelting followed by reuse requires only 7.4 MJ per kg aluminium. Production of secondary aluminium thus only requires 5% of the energy of primary aluminium. With an annual production capacity of 240,000 tons, Hoogovens Aluminium in Duffel is one of Europe's largest producers of aluminium semi-finished products, where high value aluminium alloys are transformed for very diverse applications. In the site casthouse the scrap created during production, (external) clean scrap and primary metal are re-melted and alloyed to the specification of the client. The so called Greenmelt installation is a new addition to the casthouse at Duffel. Construction began in 1996 and the system went into operation in august 1997. The installation is designed specifically for remelting aluminium scraps containing organic contaminants, such as lacquers, oil and plastic coatings, in an environmentally friendly way. The loss of quality of the aluminium is negligable. The regional and international environmental criteria regarding flue gas emissions are easily met and metal recovery is very good. A special feature of the Greenmelt concept is that the furnace has to be able to remelt a large variety of alloys and make them available to the existing casthouse in liquid form. In this way, Greenmelt coontributes significantly to the internal casting capacity. The need for additional remelting capacity for external, more contaminated scrap is continuously growing. If a suitable processsing installation is available this can be economically feasible. However, a new environmental law has been introduced which limites the processing of scrap in the existing casthouse (could not meet the imposed emission limits). This was very influential in the decision to develop Greenmelt.
OBJECTIVES
The aim of the project was to optimise the use of "secondary" aluminium in an environmentally friendly way. A new concept was developed for the remelting of aluminium. The novelties were a new form of the oven in combination with recently developed techniques and mathematical optimisation of the aluminium flow during the production process. The aim of the "Greenmelt" project was to create a melting capacity of secondary aluminium of 30 000 tonnes per year (previously this way 18 000 tonnes per year). In this way aluminium residuals of the automobile and packaging industry could be recycled and reused in the same processes. The necessity of primary metal would decrease 12 000 tonnes per year. Additionally the need for electricity would be reduced (about 10 million Kwh per year). The oven concept would also reduce the quantity of residual aluminium-oxides and emissions into the air. Another important objective was to be able to process a large spectrum of scrap types.
RESULTS
Two years after the start-up of Greenmelt the following results were obtained: - The Greenmelt emissions were far below the maximum levels imposed by the authorities. The dioxine content in the flue gases was 10 times lower than the norm of 0.1 ng/Nm3 Teq. - The production level (remelt capacity) was on average, above 85 ton/day, with a maximum of 90 ton/day. - The consumption of primary aluminium was low (<4% of capacity), which meant the furnace was effectively used to remelt. - The average metal yield varied from 90% - 92%, but this was strongly dependent on the type of scrap processed and the type and amount of contamination. - More than 98% of the liquid metal produced by Greenmelt was used in the casthouse in liquid form, demonstrating that the production scheduling system was functioning well. In the coming years work will continue on optimising the plant and the results are expected to improve even further. Overall however, the production capacity levels obtained are a clear proof of the economic potential of the Greenmelt installation. The installation has proven its capacity to provide a safe, environmentally friendly and economically sound way of remelting organically contaminated aluminium scrap. Two years after the start-up of Greenmelt the following results were obtained: - The Greenmelt emissions were far below the maximum levels imposed by the authorities. The dioxine content in the flue gases was 10 times lower than the norm of 0.1 ng/Nm3 Teq. - The production level (remelt capacity) was on average, above 85 ton/day, with a maximum of 90 ton/day. - The consumption of primary aluminium was low (<4% of capacity), which meant the furnace was effectively used to remelt. - The average metal yield varied from 90% - 92%, but this was strongly dependent on the type of scrap processed and the type and amount of contamination. - More than 98% of the liquid metal produced by Greenmelt was used in the casthouse in liquid form, demonstrating that the production scheduling system was functioning well. In the coming years work will continue on optimising the plant and the results are expected to improve even further. Overall however, the production capacity levels obtained are a clear proof of the economic potential of the Greenmelt installation. The installation has proven its capacity to provide a safe, environmentally friendly and economically sound way of remelting organically contaminated aluminium scrap.
