The technology called pyrolysis is a way of extending the recycling of the drink carton beyond paperboard to the other 27 per cent of the pack.
The pyrolysis process begins with the polylaminate (plastic-aluminium mixture) that has been separated from the beverage carton paper in a pulping chamber that works much like a washing machine.
This residue is dried and broken down into small pieces before being put through the pyrolysis process that involves exposing the material to 400oC of heat in an oxygen free chamber.
The heat causes the plastic to evaporate while the aluminum stays where it is. The evaporated gas can be used to generate electricity and steam and the aluminum can be used to again to make new aluminum products.
Pyrolysis benefits
At a press conference held at the Stora Enso paper mill in Barcelona, Spain, where the pyrolysis process has been put into action, plant manager Juan Vila explained the benefits of the system.
Vila told this publication that there are two main distinguishing features of the new system. Unlike a previous technology used at a plant in Finland that failed for economic reasons, the new pyrolysis operates at a lower temperature (400oC versus nearly 800oC) and operates in a zero oxygen chamber.
He said: “The other chamber had 10-15 per cent oxygen and this created aluminum oxide which is worth much less than aluminum.”
The managing director of Stora Enso Barcelona explained to journalists that the newly installed facilities should increase the profitability of recycling beverage cartons.
The process generates valuable aluminium and enough power, via the evaporated plastic, to provide for 10 per cent of the energy requirements at the Barcelona paper mill. And lower temperatures mean this can be achieved with a lower energy bill.
With the help and technical assistance of Tetra Pak, Stora Enso began operating the pyrolysis process this summer after having already run a pilot with an annual capacity of 1,000 tons of beverage carton. The newly installed machinery will allow Stora Enso to move up to industrial scale production next year, with a capacity to process 30,000 tons of used beverage cartons annually.