Wood chip impregnation method for chemical pulping, comprises impregnating chips with liquid in different temperature zones of vessel

摘要

Chips which have not been based in steam are continuously added to and removed from an impregnation vessel (30) containing impregnation liquid zones (Z1-Z3) with different temperatures. The flow of impregnation liquid (BL1) in the upper zone is in a direction opposing the sinking direction of the chips. A method for impregnating wood chips in a chemical pulping process comprises the following steps : (a) chips which have not been based with steam are added continuously to the top of an impregnation vessel , inside which the pressure is within 0.5 bar of atmospheric pressure, and then continuously removed at the vessel base ; (b) the the chips are heated in an upper liquid zone in the vessel by adding a first impregnation liquid at a first temperature ; (c) the chips are heated in a second liquid zone (Z2) beneath the first zone by adding at least one additional impregnation liquid (BL2, BL3) at a second temperature at least 5 deg.C greater than the first temperature ; and (d) establishing a level of liquid (LIQLEV) inside the vessel by adding and removing impregnation liquid, this level lying below the maximum chip level (CHLEV) in the vessel, and the liquid is removed at a point above the first impregnation liquid supply line position (H1), so that a flow of impregnation liquid in the opposite direction to the sinking direction of the chips is established in the upper liquid zone. An Independent claim is also included for the process apparatus.