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  • Random forest classifier an...
    Fischer, J.; Wirtz, S.; Scherer, V.

    Fuel (Guildford), 06/2023, Volume: 341
    Journal Article

    •Refuse-derived fuels (RDF) made from waste are co-fired in cement production plants.•Composition of RDF determines cement quality, but is unknown.•A database of individual RDF images was built.•Random forrest classifier and neural network tested to identify RDF fractions.•The neural network was tested in a conveyor belt setup and reached 71 % accuracy. The current paper aims at the evaluation of computer vision methods to identify RDF (Refuse-derived fuels) fractions based on images of the RDF particles. For this purpose, images of 1345 single RDF particles, with a typical size in the cm-range, were taken in bird’s eye view and assigned manually to one of six predefined material fractions. Two possible methods were tested for fraction identification: First, a classical machine learning approach consisting of feature extraction of color histograms and Haralick-textures as input for a random forest classifier and, second, a neural network approach with transfer learning. In the machine learning approach, the random forest classifier with feature extraction based on image color distribution (histograms of colors in images) and Haralick-textures (matrix of gray-value co-occurrences) achieved an accuracy of 49 %. The neural network approach is based on the Xception network, a state-of-the-art convolutional neural network with depthwise separable convolutions. The accuracy of the Xception network for recognizing RDF fractions with transfer learning is 69%, thus considerably better than with the machine learning approach and a good starting point for identifying the very inhomogeneous appearance of RDF fractions. The Xception approach was then used in a more realistic setup where the RDF particles are transported by a conveyor belt which allowed for simplified image acquisition. Here, some additional measures are needed for image recognition like edge detection performed by the Canny algorithm. The accuracy for a test data set could be increased to 71 % after using images from this setup to improve the neural network.