Editing Kraft process (section)

===Impregnation===
Common [[wood chips]] used in pulp production are {{convert|12|-|25|mm|in}} long and {{convert|2|-|10|mm|in}} thick. The chips are first wetted and preheated with [[steam]]. Cavities inside fresh wood chips are partly filled with liquid and partly with air. The steam treatment causes the air to expand and about 25% of the air to be expelled from the chips. The next step is to saturate the chips with [[Black liquor|black]] and [[white liquor]]. Air remaining in chips at the beginning of liquor impregnation is trapped within the chips. The impregnation can be done before or after the chips enter the digester and is normally done below {{convert|100|°C|°F}}. During impregnation, cooking liquors penetrate into the capillary structure of the chips and low temperature chemical reactions with the wood begin. A good impregnation is important to get a homogeneous cook and low rejects. About 40–60% of all alkali consumption, in the continuous process, occurs in the impregnation zone.