Distribution Modelling of Stock Preparation Systems for Recycled Fibers

Stock preparation systems for recycled papers need to be designed to produce a high quality, uniform product from a source that has significantly varying properties. Process models are a useful tool for analyzing and optimizing stock preparation systems. However, many models only account for the bulk flows of the components in the form of the fraction of fibers, contaminants, and ash. This report extends some of these modelling ideas to include component distributions. For example, the fiber fraction can be treated as a distribution based on fiber length and possibly fiber coarseness and composition. The contaminant concentration is expressed as a function of both particle size and density of the contaminant. Finally, the separation efficiency of the processing steps also becomes a function of fiber and contaminant distributions. Ultimately, these models are used to determine the efficiency of various stock preparation systems with differing configurations of the cleaners, screens, washing, and other operations. Such models allow the performance of existing and new systems to be compared and optimized, especially in the light of the changing composition of the feedstock.