Downsizing and numbering-up of a fiber fractionator

Abstract

A length-based hydrodynamic fiber fractionation process has been developed as an energy efficient alternative to existing technologies (e.g., pressure screens) in order to separate short fibers from long fibers of cellulose pulp. Potential limitations to relatively low channel Reynolds numbers were resolved by a radical downsizing of the fractionation device to a channel diameter-to-fiber length ratio of D/L1 ≤ 7. Results of a four-step single-channel fractionator show, that placing of fractionation steps in series is the method of choice to increase fractionator capacity without affecting fractionation selectivity. For the numbering-up of fractionation channels, a novel multi-scale bifurcation distributer was designed, which was capable of (i) sufficiently splitting the feed suspension flow rate, as well as (ii) homogeneously distributing the fiber phase of the suspension. Experiments with a multi-channel fractionator prototype with eight parallel fractionation channels demonstrate the feasibility of our numbering-up strategy.