Producing electricity from plastic packaging20 September 1999
A new gasification plant capable of recovering aluminium and generating power from used packaging material is being built at Varkaus in Finland. It is the world's first recycled-plastic gasification plant.
The Varkaus gasification plant has been jointly developed by Corenso United Oy with Foster Wheeler and VTT for use at Corenso United's coreboard mill.
The $20 million plant, which is due for completion in autumn 2000, will process used packaging containing plastic and aluminium. Cartons containing liquid, for example, are composed of 70 per cent (dry weight) of wood fibre, and 30 per cent of plastic and aluminium foil.
The plant will convert plastic from used packaging materials into gas for energy, and at the same time recover aluminium for casting into blocks and processing back into foil at an aluminium foil factory. Foil production from blocks of recycled aluminium requires only 5 per cent of the energy used in obtaining aluminium from ore.
The aluminium foil used in cartons is very thin, about the thickness of a hair,and has been previously considered non-recoverable. A recycled fibre plant at Corenso's Varkaus mill opened at the end of 1995. In addition to domestic raw material, used liquid packagings were delivered to the mill by the shipload. The fibre component was separated for manufacture of coreboard, and the remaining plastic and aluminium mix, called reject, was incinerated in a power plant boiler. This incineration proved to be very problematic, however, with the aluminium forming layers on the walls and grate of the boiler. These layers had to be removed at regular intervals.
Solving the problem
VTT Energy, the Finnish research organization, has been studying gasification technology since the early 1980s, and has examined its suitability for processing municipal waste. VTT Energy thus investigated gasification as a possible solution to the aluminium accumulation problem. The concept was to gasify the polythene, and at the same time remove the aluminium particles from the gasifier.
Laboratory-scale experiments began in 1997, and a means of gasifying the reject was devised. Research discovered that the flue dust which gathered in a cyclone contained a considerable quantity of aluminium metal, which could be recovered and recycled. The next stage was for Foster Wheeler to build a factory-scale trial plant at Varkaus. But before this could be done, a decision had to be made between four alternative processes: high- or low-temperature gasification, and bubbling or circulating fluidized bed gasification technology. The bubbling fluidized bed technology was chosen, but the plant can operate in high- or low-temperature mode. Either a low temperature can be used, such that the aluminium does not melt, or a higher temperature where the aluminium melts and is cast into blocks.
The trial plant was built in late 1997/early 1998. Difficulties were initially encountered, most noticeably in the fuel input. Because of its lightness, the reject was difficult to feed into the gasifier evenly and reliably. New fuel input equipment had to be developed, which took a year to do.
Equipment and material procurement for the next gasifier phase has been done. The new gasification plant will be constructed within the old power plant by removal of the old boilers. The new plant's steel structure will be erected in November, and the equipment will be installed early next year.
The gasifier will have a heat output of 40 MW, and produce a total of 165 GWh of energy per year. It is estimated that this will reduce the requirement for fossil and solid fuels by the equivalent of 16 500 tonnes of oil annually.
The recovered aluminium, over 2 million kg annually, will be melted and cast into blocks, which will be sent to the Swedish company Finspong Aluminium AB, which manufactures aluminium foil.
Outline of gasification plant process
Most of the used packaging arrives in the form of bales, from which the baling wire is first removed and sent to the metal industry for recycling. The raw material is shredded and then conducted to a pulping drum, in which the wood fibre and the plastic/aluminium foil are separated from each other. The fibre is then used to produce coreboard.
The reject to be gasified comes to the power plant either directly from the recycled fibre plant, and/or via a separate feed unit into a fuel silo. The feed unit allows the use of material storage and is derived from external sources. From the fuel silo, material is fed into the gasifier, where the plastic is converted into gas. The energy that is needed for the gasification process is obtained from the plastic. Oil is only required for the start-up process. Sand removed from the gasifier due to impurities is cleaned and returned to the gasifier. The aluminium remains in solid form, allowing it to be separated mechanically from the gas phase. The aluminium is then melted and easily cast into blocks, which are sent as raw material to an aluminium foil manufacturer. The gas is conducted to a boiler, where it is burned to produce high pressure steam, which is in turn used to generate electricity. The boiler has been designed so that it can oxidize any minor quantities of aluminium that remain. The boiler is equipped with a filter, which means that dust emissions will be insignificant compared with other solid fuels. The reutilization of aluminium-oxide-containing ash, recovered by the filter, is being planned.
The plant complex that is described above allows the complete reutilization of composite packagings that were previously dumped in landfills. The metals generated by the packaging collection systems are returned to the metal industry for recycling, and the sand is used as landfill material in the area of the mill. The wood fibre contained within the packaging is utilized as raw material for coreboard and the cores made from the board are also suitable for recycling. The aluminium cast into blocks is used again in the manufacture of aluminium foil. The energy required by the board production process is obtained completely from the plastic of the recycled materials, with the surplus electricity being distributed to Varkaus' other mills.
TablesComparison of dust emissions and total ash volumes with different fuels Companies involved in the Varkaus project