Penetration of water into industrial softwood chips – influence of physical properties.


In earlier studies, the fundamentals of the liquor penetration process in the case of hand made, homogenous, identically shaped wooden blocks have been studied. However, the efficiency of liquor penetration into real industrial chips may differ from the efficiency of penetration into ideal handmade chips. In this paper, impregnation experiments with three industrial softwood chip grades including sawmill chips, juvenile chips from 1st thinning and normal pulpwood chips from 3rd thinning (final felling) were carried out using a new impregnation vessel concept. The effects of chips’ physical properties and differing penetration conditions on the penetration process were investigated. The highest degree of penetration was achieved with sawmill chips. The lowest degree of penetration was achieved with 3rd thinning chips, because of the high heart-wood and initial air content. A lower initial degree of penetration resulted in higher liquor uptake at the same process conditions. The influences of both penetration conditions and wood permeability on the penetration process were pronounced with 3rd thinning chips. The experiments showed, also, that the final degree of penetration and liquor uptake can be predicted for different process conditions based on the initial penetration degree calculated from the moisture and basic density properties of the wood chips used.