Method for impregnating chips in a continuous digestion system

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• withdrawing a hot black liquor from a withdrawal strainer in the digester and sending the withdrawn hot black liquor in a black liquor line;
• withdrawing fluid from the top separator and leading the withdrawn fluid in a first return line to the impregnation vessel;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• more than 75% of the fluid added to the impregnation vessel being constituted by fluid withdrawn in the first return line;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in the impregnation vessel being constituted by chips moisture, steam condensate, added white liquor, and the fluid withdrawn from the top separator into the first return line;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.