OptoSort GmbH, a company specializing in sorting rock, offers its developments as new solutions for sorting construction waste and other waste materials like plastics and glass. Sorting is performed, unlike in competitor installations, in freefall with material detection from two sides. In addition, thanks to a specific configuration, several sensors, like near-infrared (NIR) and colour sensors, can be combined in order to detect and remove different materials and composites. With this system, high-quality waste-derived resources can be recovered.
Up to now, only few cases are known in which sensor-assisted sorting installations are used in the recycling of waste materials. Examples can be found in Germany, Switzerland or Spain. Either colour line cameras are used to recover, for example, clay bricks from mineral-based construction and demolition waste or NIR cameras are operated for the removal of foreign materials and impurities as well as for sorting. With neither of these two variants on their own is it possible to recover unmixed construction material fractions.
On account of the increasingly complex composition of building structures, new technologies are needed with which unmixed and impurity-free products can be recovered. In particular, gypsum particles can only be detected with a NIR camera and removed from the product flow. Detection of gypsum in a composite building material, e.g. gypsum plaster on a wall building material, is only possible if all sides of the particles are scanned.
Development of a robust freefall sorting installation for stationary application
Working in cooperation with the IAB-Institut für Angewandte Bauforschung Weimar gGmbH, Optosort set itself the task of developing a robust freefall sorting installation for the separation of mineral construction and demolition waste and the removal of impurities (gypsum, bitumen, tar, plastics, etc.). With a combination of hyperspectral near-infrared technology and colour detection as well as simultaneous “observation” of all particle surfaces, current and/or expected recyclables and/or impurities can be detected and sorted with a high recovery rate. Sorting of the construction and demolition waste is the precondition for closed material cycles in the construction industry.
To date, a freefall sorting installation with a combination of detection systems and arrangement of the detectors on two sides of the falling construction rubble particles has not been available worldwide. But with such an installation, the disadvantages of the two individual technologies can be balanced out (Fig. 1).
The freefall sorting installation is equipped with coupled RGB line cameras and hyperspectral NIR line cameras, arranged on two sides of the material stream. Focus is on the following key functions:
Detection of dry and wet mineral particles
Scanning of all particle surfaces
Reliable ejection of the detected impurities
Robustness and low-wear when exposed to abrasion by mineral particles
Flexibility, for mobile operation, too
Suitable for particles between 10 mm and 100 mm
Low-maintenance and automatic white balance in continuous operation
Low energy consumption, selective control of the particle discharge with compressed air pulses
Integration in local networks (LAN) or modem
In the NIR range, fewer misdetections occur although some special materials sometimes deliver unsatisfactory spectra. Not identified are glass (amorphous) and very absorbent materials, like roofing felt or bituminous materials. The highest detection rates are achieved for wood, gypsum and aerated concrete. The latter make up the impurity fractions that most urgently need to be removed from the product.
With a stationary freefall sorting installation, up to 20 tonnes construction rubble per hour with particle sizes larger than 10 mm can be sorted. Fig. 6 shows the freefall sorting installation, with its very robust design, which can also be used for the separation of plastic mixes and waste glass.
In November 2019, at the IAB Recycling Testing Centre, the freefall sorting machine was commissioned and successfully trialled (