Patent ID: 7547374

Claim:
A method for impregnating chips in a continuous digestion system, comprising: feeding un-impregnated chips to the impregnation vessel; pre-heating, impregnating and forming the chips into a chips mixture using impregnation fluid; feeding impregnated chips mixture in a feed line from the impregnation vessel to a top separator arranged in a digester, withdrawing a hot black liquor from a withdrawal strainer in the digester and sending the withdrawn hot black liquor in a black liquor line; withdrawing fluid from the top separator and leading the withdrawn fluid in a first return line to the impregnation vessel; transferring heat from the black liquor line to the first return line in a heat exchanger arranged between the first return line and the black liquor line; more than 75% of the fluid added to the impregnation vessel being constituted by fluid withdrawn in the first return line; a principal part of a fluid contents in the impregnation vessel being constituted by chips moisture, steam condensate, added white liquor, and the fluid withdrawn from the top separator into the first return line; the impregnation fluid in the impregnation vessel not containing any black liquor from the digester; and flowing fluid and establishing an alkali content in the impregnation vessel without any influence from a fluid flow in a digester process in the digester.