Grantee Research Project Results

Final Report: Sensor Fusion for Contaminant Detection and Removal From Plastics Recycle Streams

EPA Contract Number: 68D01065
Title: Sensor Fusion for Contaminant Detection and Removal From Plastics Recycle Streams
Investigators: Sommer, Edward J.
Small Business: National Recovery Technologies Inc.
EPA Contact: Richards, April
Phase: II
Project Period: September 1, 2001 through September 1, 2003
Project Amount: $225,000
RFA: Small Business Innovation Research (SBIR) - Phase II (2001) Recipients Lists
Research Category: Hazardous Waste/Remediation , SBIR - Waste , Small Business Innovation Research (SBIR)

Description:

The objective of this research project was to develop an automated sorting system for the removal of non-ferrous metal contaminants from a stream of recycled plastic in the flake form. The increased value of the product improves the economics for recovery and recycling of plastics.

Summary/Accomplishments (Outputs/Outcomes):

Based on a market analysis, National Recovery Technologies, Inc. (NRT) identified removal of non-ferrous contaminants from the recycled plastics stream as important for increasing the value of the recycled material. Ferrous metals can be removed with a magnet, but materials such as stainless steel, aluminum, and copper require more sophisticated methods. The removal of other materials, such as wood and stone, as well as off-colored flake, also is a desirable trait.

NRT investigated three primary sorting technologies for the removal of non-ferrous contaminants from the recycled plastics stream. Two of these technologies were based on innovative techniques for detecting metal presence within the flake stream based on the disturbance of a magnetic field due to eddy currents. These methods are based upon advanced magnetic sensing technologies and are suitable for non-ferrous identification for particles down to approximately 1 mm². Realistic spacing of these sensors at 25.4 mm (1 in) or more may result in significant product loss compared with the machine vision approach discussed below.

The third method investigated utilized a machine vision approach. Until recently, machine vision was not a viable alternative due to the required speed of data acquisition and processing necessary to identify material of the required size at feed rates suitable for industrial applications. The advent of high-speed color line scan camera technology coupled with new high-speed digital signal processor technology makes this approach attractive for the identification of contaminants within the recycled plastic flake stream. This approach has the advantage over the others, in that wood, stone, and other contaminants can be removed from the stream as well as metal contaminants. This approach also affords the opportunity to remove off-color flake from the material stream.

With this approach, a detection resolution of 0.5 mm (0.02 in) with material moving at a rate of 3 m/s (9.84 ft/s) on a 40 inch (101.6 cm) wide belt is achieved. Ejection stations can be spaced at 6.35 mm (0.25 in) intervals to provide a sorting resolution, which is significantly smaller than with the magnetic approaches discussed earlier.

Conclusions:

This research project has led to the development of three distinct technologies suitable for identification and sorting of non-ferrous metal contaminant within a stream of recycled plastic flake. A machine vision approach has been developed as the most versatile of these technologies. This technology is expected to have significant impact within the plastics recycling industry because it will increase the value of the recycled resin.

Supplemental Keywords:

sensor fusion, contaminant detection, contaminant removal, plastics recycle streams, metal removal, mass sortation, color sorting, machine vision, contaminant sorting, non-ferrous contaminants, flake, off-color flake, sorting technology, recycled resin, small business, SBIR., Sustainable Industry/Business, RFA, Scientific Discipline, Waste, Hazardous, Technology for Sustainable Environment, Chemical Engineering, Sustainable Environment, Municipal, Environmental Chemistry, Chemistry and Materials Science, Hazardous Waste, cleaner production/pollution prevention, Environmental Engineering, municipal waste, municipal waste plastics, polymeric waste, recycling, hazardous waste disposal, plastics, new end products, complex waste plastics particle mixtures, waste recycling, small metals detection