Patent ID: 6468390
Filing Date: 2002-10-22
Classification: D21C

Abstract:
A method for continuous cooking of lignocellulosic fiber material, comprising:providing a vessel system having a first stage, second stage, third stage and a concurrent fourth stage, the third stage and fourth stage being separated by a screen, the vessel system having a fiber material disposed therein, the fourth stage being subsequent to the third stage, the third stage being subsequent to the second stage and the second stage being subsequent to the first stage; in the first stage, impregnating the fiber material with an impregnation liquid; in the first stage, withdrawing a hemicellulose rich spent impregnation liquid from the vessel system; in the second stage, cooking the fiber material in a first cooking liquor; in the third stage, withdrawing a first spent cooking liquor through the screen and adding the hemicellulose rich spent impregnation liquid to the fiber material at a beginning of the concurrent fourth stage; and in the concurrent fourth stage, cooking the fiber material in a second cooking liquor comprising the portion of the hemicellulose rich spent impregnation liquid added in the third stage and concurrently passing the hemicellulose rich spent impregnation liquid in the concurrent fourth stage and retaining the fiber material in the concurrent fourth stage together with the portion of the hemicellulose rich spent impregnation liquid for at least one hour and allowing the hemicellulose to precipitate onto the fiber material.