HIGH-KAPPA PULPING AND EXTENDED OXYGEN DELIGNIFICATION DECREASES RECOVERY CYCLE LOAD

It is well established that the removal of lignin by an oxygen/alkali treatment is more selective than by conventional pulping. The aim of t his study was to evaluate the feasibility of pulping to kappa numbers ranging from 30 to 60, followed by one or two oxygen stages to lower t he lignin content of the pulps entering the bleach plant and at the sa me time to minimize the load to the boiler. Computer-aided process sim ulation of the mill, using GEMS, was carried out for all the cases. By pulping to a kappa number of 40, followed by two-stage oxygen treatme nt [40(OO)] to kappa 13, the load to the recovery boiler is lower than in the base case-pulping to kappa 30. In addition, operating costs an d pollution potential of the fully bleached pulps by a conventional se quence (DEopD) were lower when compared to the base case. Even lower l oading to the boiler could be achieved if the pulping is terminated at kappa number 50 and followed by two-stage oxygen delignification [50( OO)].