Optimization of multiple screening stages for fibre length fractionation: Two-stage case

Pressure screens are the most efficient and practical unit operation for fi bre length separation. Screens are used individually and in systems. It is not a simple task to decide which configuration to use, and what screen pla te, reject rate and dilution water flow rate are most appropriate in each s tage. Rules exist for designing systems for contaminant removal, however it is not known how well-suited these are for fractionation. The objective of this work was to propose a model and approach to optimize screening system s for fibre length fractionation. Optimization was used to compare the perf ormance of a single-stage and four two-stage systems. Limits on the maximum reject consistency, maximum total dilution and minimum aperture size were used to constrain the solutions to practical values. The proposed methodolo gy is potentially useful for fine-tuning existing screening systems, and fo r testing novel process designs.