Garry R. Kenny, Felix A. Hottenstein, Arthur Doak
IMPC 2000, July 23-28, 2000, Rome, Italy

Recovered glass from household waste processing Material Recovery Facilities (MRF‘s) contains high amounts of contamination: ceramics, metal, dirt, etc. and can only be used in low grade applications or needs to be landfilled generating high, unnecessary costs. The so-called "Dirty-Three-Mix" consists of an extremely dirty mixture of flint, green, and brown glass. Up to now, no sufficient sorting technology was available to recover each of the color fractions for a re-use in a glass processing plant.

This paper presents a newly developed, digital signal processing based technology allowing to separate and recover all three color fractions from the Dirty-Three-Mix with very high accuracy and product purity. It is based on LED technology operating at multiple visible and near infrared wavelengths. All data is completely digitally processed. The combined use of different wavelengths with controlled bandwidth and selected center frequencies (as opposed to standard video camera filters) allows the specifically developed software to ignore contamination (dirt, labels) on glass cullets and therefore is able to classify color with high accuracy. A more than welcome side effect of the new technology is the no need of any automated sensor cleaning mechanism because the software is also able to ignore dirt being built up on the sensor protection wear cover.

Beside the color separation, the sensor is also able to identify and separate ceramic particles from the incoming glass stream. The separation module can therefore also additionally be used as a final cleanup unit for the CSP separation.

More than 9 separation modules with capacities of 5 tons per hour have been successfully installed over the last six months in the United States. Sensor removal effiency has been reported to be up to 99%, minimal product purity of flint glass after one sensor pass is 95%, averaging at 97-98%.

Not only the production of the furnace-ready cullet quality convinced plant operators but significantly lower landfill costs and very short payback periods of down to 4 months per sorting module have proven the technical and economic feasibility of the presented technology.