First in Sweden: Near-infrared technology sorts out plastic and metal
First in Sweden: Near-infrared technology sorts out plastic and metal
In fact, the more accurate term is post-sorting, and it reduces CO2 emissions by 75%
The after-sorting facility located in Brista, near Stockholm (Sweden), counts with one ground-breaking technology to ensure more plastic is recycled rather than incinerated. The name of that technology – near infrared (NIT)an application technique that has been used more widely in medicine and diagnostics.
The after-sorting facility is the first of its kind in Sweden. It has been there since 2021 contribute to reducing CO2 emissions from plastic and metal combustion by 75%.
To make the planet’s resources last longer
The facility is a collaborative project between Stockholm Exergi (the capital’s energy supplier) and Sörab and is partially financed by Klimatklivet (Sweden’s national green financing program).
A sum of 11,000 tons of plastic and 2,500 tons of metal are sorted there every year. This means that the EU directive on recycling is fulfilled, which gives Stockholm a sustainable solution when it comes to extending the life cycle of materials.
The near-infrared sorting technology allows the machine to identify different types of plastic and sort those that can be recycled, such as plastic packaging.
This is how it works
There are actually two separate steps where NIT is used in the post-sorting process, once to separate organic waste from the rest and then again to separate plastic from metal.
A diagram showing the post-sorting process, Source: Stockholm Exergi
- Incoming households waste is emptied on one of four walking floors. A vibrating sieve sorts out regular garbage bags, while larger items are sent to a crusher.
- (a) Optical sorting, NIT: In a first scan, green bags with food waste are identified via Near Infrared scanning technology and sorted out from other residual waste bags using compressed air. The bags are opened in a bag opener. The bags are separated from the food waste in a drum sieve and the food waste is transported to containers. (b) Biogas plant: Food waste is sent away to become biogas, a renewable fuel and biofertilizer. Biofertilizer contains nutrients such as nitrogen, potassium and phosphorus.
- Bag opener and atomizer: All residual waste bags are opened. The large fractions returned from the drum sieve are finely divided.
- Drum sieve: The residual waste is divided according to fraction size for more efficient sorting. Larger parts are sent back to the crusher while smaller parts go on.
- Optical Sorting (NIT): Plastic is identified and sorted out. Here, no distinction is made between different types of plastic, but technically it is possible to divide it into different fractions.
- Metal separation: Magnets and eddy current separators sort out all magnetic and non-magnetic metals.
- Material recycling: Sorted plastic and metal goes to external partners for further processing before it becomes raw material for new products.
- a) Treatment of residual waste: The waste that cannot be recycled goes via a conveyor belt into Stockholm Exergi’s intermediate warehouse at the incineration plant, alternatively to containers. (b) Energy extraction from heat and electricity: Energy is extracted in the process and heat and electricity are produced.