New ways to sort old rubbish

Citation

(1999), "New ways to sort old rubbish", Sensor Review, Vol. 19 No. 2. https://doi.org/10.1108/sr.1999.08719baf.004

New ways to sort old rubbish

New ways to sort old rubbish

Keyword Recycling

French companies have come up with a variety of new techniques for sorting waste. Traditionally it has been difficult for machines to sort waste ready for recycling as there are too many variables (different types and colours of plastics for example), but new machines are coming onto the market from France which can resolve this problem.

It is difficult to sort waste without making mistakes. Plastic packaging is the most tricky category, as each different type of plastic must be separated before recycling. However, French company Sydel has developed and patented an original machine called Dibop, which sorts bottles by type of plastic. It has already sold machines to Ateliers Fouesnantais, a Brittany-based environmental company, to Tecmed in Madrid and to Sumitomo in Osaka.

Dibop places the bottles in line with a patented centrifugal feeder. The bottles are each illuminated by three halogen lamps then examined by a factorial filter spectrometer. The sensor replaces the human eye and, by means of 50 to 250 measurements per bottle, it distinguishes between five different types of plastic: PVC, PET, HDPE (high-density polyethylene), PP (polypropylene) and PS (polystyrene).

The installation is equipped with a programmable controller which controls the bottle movements and the ejection devices. It has a sorting capacity of 12,000 bottles per hour and sorting purity exceeds 98 per cent, crushed bottles included.

One of the Dibop models is able to recognise coloured bottles: transparent, azure blue and coloured. "PVC used to be recycled to make pipes, so we didn't worry about the colour," notes François Tuloup, sales engineer with Sydel. "Now, PET is used for packaging and is recycled into consumer products where colour is important."

Vauché, one of the leading French manufacturers of sorting equipment, has built a machine called Neuroplast, which sorts packaging items as they travel continuously along a conveyor belt. It identifies individual items by means of three optical sensors and sends them to the appropriate bins.

The key innovation of this system is the neural network which identifies each waste item by comparing it with memorised data stored during an initial learning phase. During this phase, which covers the first thousand items, the system is assisted by a technician who validates or corrects the machine's diagnosis. Only then is it capable of operating alone. During normal operation, the machine analyses three items per second. The system costs around 1.3 million francs.

Walco, the company which manages the waste produced by the city of Bruges in Belgium, has ordered two Neuroplast machines that will work simultaneously, as well as automatic bag openers, an overband machine to extract ferrous metals, and three eddy current machines to remove non-ferrous metals. With a capacity of 4.5 metric tonnes per hour, it is operated by eight people who are responsible for input, monitoring and removal of non-recyclable waste.

Any metals must be removed before recycling can begin. French company Andrin has developed an automatic machine to extract aluminium and non-ferrous metal packaging from recyclable plastic waste. A polarised wheel next to the waste-carrying conveyor belt rotates at a speed of 2,600rpm, and emits eddy currents which temporarily magnetise the non-ferrous metals, pushing them off the conveyor belt. Depending on their weight, items either slide or jump off the conveyor belt. A second eddy current machine is used for finer sorting of milk cartons. Sorting centres in Lille and Montpellier are already equipped with these systems.

French manufacturer Pellenc's machine uses a grab arm for more effective sorting. "We have developed a fully automatic sorting line called Planeco," explains Roger Pellenc, CEO of the company. Planeco first removes all ferrous items by magnetisation. Items measuring less than 40mm are then removed by screening. This leaves behind the packaging items made of plastic, complex materials and aluminium. They are located by a colour video camera and then picked up by the grab arm. Plastic objects are placed in front of an infrared sensor which determines the plastic type. After identification of the material, each object is sent down the appropriate chute.

Automatic sorting of recyclable waste is not financially viable in small centres, although it is possible to improve the working conditions of manual sorters. For example, Vauche has recently patented an individual sequential sorting system which enables operators to work at their own pace. Each workstation comprises of a circular plateau divided into three segments and measuring around 1.2 meters in diameter. The plateau turns and stops in front of the operator long enough for him to sort the waste contained in one segment. When he has finished, he sets the plateau in motion again and sorts the next segment. In the meantime, the plateau is reloaded from a conveyor belt.

Akros, based in the Alps, has patented a new circular sorting concept, called Astrid ­ a turn-table equipped with specific emptying devices. The table rotates continuously, enabling sorters to check the same pile of waste several times for more thorough sorting. The table has a steel plateau which is stronger than linear conveyor belts, generally made of rubber. It has a diameter of four to ten meters and between one and ten sorters can be placed around it. It costs between 250,000 and 400,000 francs.

For more information, please contact Dan Ray at French Technology Press Bureau, 21-24 Grosvenor Place, London SWIX 7TB. Tel: +44 (0)171 235 5330; Fax: +44 (0)171 235 2773; E-mail: info@ftpb.u-net.com