Determination of the contribution of penetration, diffusion and alkali consumption in the impregnation of Eucalyptus grandis chips

The influence of impregnation conditions on the phenomena involved in the impregnation of Eucalyptus grandis chips was studied with the aid of a new impregnation method. When pre-steaming was used, 30 minutes of penetration time was sufficient to achieve the final degree of penetration (over 95%) with white and black liquor. An impregnation time of 15 minutes was found to be sufficient to transfer the required amount of alkali into the wood for kraft cooking, provided that a high-concentrate white liquor was used.

Only part of the alkali required was transferred into chips during 60 minutes of impregnation using black liquor with an effective alkali concentration of 20g NaOH/L. In addition, almost all of the alkali was consumed as it entered into the wood. This risks running out of alkali if the temperature is raised quickly to cooking temperature