Towards complete impregnation of wood chips – new research enables effective processes.


The important role of impregnation prior to chemical pulping has been long recognized qualitatively but not fully realized quantitatively. Cost effective production of uniform, high quality pulp can only be achieved by efficient mass transfer of pulping chemicals that must start with complete impregnation of wood chips. The present paper describes the main results of an in-depth research project dealing with the process of liquid penetration into softwood chips and it’s modelling. Pre-steaming and impregnation experiments were carried out in an impregnation reactor incorporating continuous measurement of the chip sample weight. The obtained data were used to illustrate the effects of various factors on the one hand and to develop and validate a new mathematical model on the other hand. The new model provides quantitative information on the course and end-point of chip steaming and liquor penetration under varying process conditions. The impact of impregnation conditions on the result of pulping was studied by carrying out displacement batch cooks with four different front-end scenarios. Cooking performance, delignification uniformity, bleachability and papermaking potential of the experimental pulps were studied.