High Kappa Process for Eucalyptus Fiberline - The First Industrial Case

摘要

The increasing pressure for costs reduction within pulp mills drives the need to maximize efficiency in the use of wood, which represents the major cost in pulp production. In this context there is a demand to reevaluate kraft pulping processes, dominant for almost a century, in order to cope with the cost-effectiveness challenges mills are facing nowadays. Cooking is the process where most of the delignification of the wood occurs, with about 95% of lignin removed. Cooking to a high Kappa number has been reported as an effective alternative to overcome the overcooking risk. Trials carried out by Suzano (laboratory and industrial scale) over the past 8 years reported better results when working with higher end Kappa in the kraft process, with no increase in the reject content. The major breakthrough lays in the impregnation step, combined with a specific way of cooking; together they can provide conditions to shift the defibration point to a higher Kappa number (21 to 23) than the typical kraft process range (17 to 18). This work aims to implement the High Kappa (HK) technology at the Tres Lagoas Horizonte 2 mill (TLS H2), which was designed to fit the specifications of this technology: there is a very robust brownstock washing section with accordingly specified screenings and 85 to 90 minutes of retention time in the 2-stage oxygen delignification. During 2018 an industrial trial was conducted at TLS H2, producing more than 380 thousand tons of pulp. The main results were an increase of up to 2.3 % in lignin and HexA free yield, a decrease in effective alkali consumption, almost the same bleaching chemicals consumption, and a final pulp with better strength. The mill performed very well during the trial, and it is still able to deliver a 21 Kappa number pulp after cooking, with a better balanced mill in terms of solids generation and alkali production.