Use of Urea as an Additive in Kraft Pulping of Eucalyptus, 2008 Engineering, Pulping and Environmental Conference

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In this study, use of urea as an additive during kraft pulping of eucalyptus has been studied. Impact on unbleached pulp properties, black liquor properties, refining energy requirement and physical strength properties of unbleached and bleached pulps and bleachability of pulp, has been investigated. Using 0.2-1.0% urea during pulping, unbleached pulp yield increased to 47.6-48.2% from 47.2% (control); unbleached pulp viscosity increased to 15.4-15.5 Cp from 13.4 Cp. Black liquor properties also improved using urea; viscosity of black liquor at 52% solids reduced to 72.4-75.8 Cp from 105.2 Cp and swelling volume ratio increased to 92.1-93.2 ml/g from 86.7 ml/g. Pulps produced with urea in pulping required 17-19% less refining energy to get 500 ml CSF. Pulps produced with urea showed better physical strength properties, particularly tensile index, burst index and stiffness.