| A birch Kraft pulp grade at Irving Pulp and Paper was experiencing poor environmental operation and pulp selectivity. Optimization of the pulping process was used to find potential strategies to minimize the loss of pulp viscosity.;It was determined that the second oxygen delignification stage had a decrease in viscosity of up to five cp for only a two unit decrease in kappa number. Therefore, it was suggested that this stage be removed and replaced with a new treatment to remove uronic acids.;Hardwoods such as birch contain large amounts of uronic acids, which can contribute three to six units to the kappa number because they consume permanganate during this test. Therefore, by removing the uronic acids with an acid stage, the viscosity may be able to be preserved.;Both a hot chlorine dioxide stage and a hot acid treatment were used to accomplish this removal of uronic acids. It was found that the hot chlorine dioxide stage was able to achieve the desired kappa number but was unable to improve the pulp viscosity. Alternatively, the acid treatment produced a pulp with about five units higher viscosity at the same kappa number. Less chlorine dioxide would be required in the D0 stage to meet the target kappa number, which would introduce some cost savings. However, the high temperature stage and cost of acid would need to be taken into account when determining the economics of a new acid stage. |
