Use of Digester Additives and Oxygen Delignification to Gain Bleached Pulp Tield and Achieve Environmental Objectives, 1998 Breaking the Pulp Yield Barrier Symposium Proceedings

Polysulfide (PS), anthraquinone (AQ) and surfactant based chip penetrants (SURF) can be used to gain bleached pulp yields of as much as 4 to 6 percentage points when pulping is ceased at Kappa number 40 or 50. For a 1000 TPD bleach mill, this would result in daily wood savings of almost 9 to 12%. Incremental pulp tonnage gained from high Kappa Pulping would be as high as 131 TPD. Pulping to high Kappa numbers also makes it easier to quantify pulp yield in mill. High kappa pulping with digester additives can downsize significant amount of organic and heat load to the recovery boiler. By using oxygen delignification, kappa number can be decreased by as much as 50% with only a small shrinkage of yield. Material and heat balances can be maintained even with oxygen delignification and the recirculation of oxygen stage filtrate to recovery boiler. Digester additives aided high kappa pulping and extended oxygen delignification would help mills to increase bleached pulp yield per unit consumption of wood, decrease pulp manufacturing cost and reduce environmental impact of bleaching. This shift in pulping and bleaching requires capital investment and would add to operating cost and to establish the benefits to mills, detailed cost benefit and return on investment analysis is provided.