Relationship between the pulp yield, bleachability and cooking conditions of Loblolly pine, 2006 Engineering, Pulping, & Environmental Conference

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Selecting the optimal target kappa for bleached pulp production requires balancing yield in cooking and bleaching with recovery boiler solids load, bleaching costs, wood costs and the desired final papermaking qualities of the pulp. We designed a series of over 30 laboratory pulping and bleaching experiments to evaluate the pulping of Loblolly pine based on these criteria. The cooking conditions varied were % EA applied and temperature. The kappa numbers achieved varied between 23 and 67. As cooking conditions changed leading to higher kappa, the total yield increased. The rate of increase in screened yield with increasing kappa number levels off at between kappa numbers 35 and 40. We also measured bleach yield across the range of kappa numbers. At a given kappa target, cooking with a higher EA charge (and therefore lower temperature) has a positive effect on shive content and pulp brightness. At the same kappa target, the potential to effect pulp yield or carbohydrates seems to be rather limited. The effect of these parameters on bleachability and viscosity is also examined.