Solids, sulfur and wood extractives balances during simulated bleached mechanical pulp production

Bleached thermomechanical (TMP), dilution water sulfonation (DWS), chemithermomechanical (CTMP) and Ontario Paper Company (OPCO) pulp production processes were simulated in the pilot plant and laboratory using Pinus radiata wood, and balances constructed for total solids, sulfur-containing species and wood extractives. All aqueous effluent sources, particularly those from pulp washing and peroxide bleaching, contributed significantly to the solids contents of the overall process effluent from each simulation. Sulfonation of the fibre increased the solids loading of the effluent, with the washing losses increasing as the level of sulfonation increased. Unbleached pulp yields calculated from the balances ranged between 96 and 91%. Sulfite applied during pulping was either lost unchanged in the effluent, oxidised to sulfate, converted to fibre-bound sulfonic acids, or found as soluble lignosulfonates in the effluent. The greatest reduction in the wood extractives content of the fibre occurred on passage through the plug screw feeders and on pulp washing. The extractives content of the pulps appeared to decrease with increasing sulfur content. When sulfite was present, poor extractives balances were obtained during primary refining.