Effect of the Brownstock Kappa Number on Fiber Line Bleached Yield, 1995 Pulping Conference Proceedings

J. L. Colodette, J. L. Gomide and D. V. Salles

Federal University of Viçosa

A. C. H. de Brito

White Martins Gases Inds. S/A

Conventional eucalyptus kraft pulps of kappa 17-27 were produced in the laboratory. Several extended oxygen delignification (EOD) methods for these pulps are discussed. EOD results for industrial conventional and MCC kraft pulps are also presented. The highest EOD delignification rates and brightnesses were obtained by the OQEop and OAEop processes. Alkali charge and retention time were significant variables in the O-stage of the EOD processes. A washing step between the O and Eop stages negatively affected the delignification rate but positively affected viscosity. The delignification rates during the EOD were superior for pulps of higher initial kappa, with rejects of these pulps being virtually eliminated during the process. Kraft pulps of kappa 27 and 17 presented similar bleachabilities by ECF and TCF sequences, requiring equal amounts of bleaching chemicals to reach full brightness, if previously treated by an EOD sequence. The bleached pulps provided similar strength properties and OX, and similar bleaching effluent load. Terminating the kraft cook at a kappa of c.a. 19 and continuing delignification by an EOD process resulted in a gain of approximately 2.5% fiber line yield and c.a. 5% reduction in wood consumption as compared to cook to kappa c.a. 17, followed by conventional oxygen delignification. As a consequence, a 12% reduction in the dissolved solids load to recovery was obtained.