High-intensity mechanical pretreatment and high-compression screw pressing for deresination of aspen kraft pulps

A 12-in. disc refiner and a bench-scale screw press were used in a pilot pulp-washing study to evaluate the effects of process variables on the removal efficiency of wood resin [dichloromethane (DCM) extractives] from aspen kraft pulps. The combined effects of multiple-stage high-compression screw pressing, high-intensity mechanical pretreatment, and chip seasoning removed more than 93% of the original pulp resin and lowered the final content to less than 0.05% on brownstock pulp. Pulp bleaching in a C/DEoD sequence strongly inhibited screw-press deresination, but feedstock consistency and filtrate recycle had no significant effect. These results demonstrate that a mill brownstock washing system consisting of screw-press washing, medium-consistency refiner pretreatment, and drum postwashing could easily remove more than 80% ofthe resin and lower the final resin content to far below 0.30%.