Patent ID: 8808498

Claim:
A method for heating white liquor or a mixture of white liquor and another liquid for use in a pressurized vessel in a digester system of a chemical pulp mill, the method comprising: a) producing black liquor in the pressurized vessel; b) extracting black liquor from a first liquid extraction screen of the vessel, c) flashing the extracted black liquor and thereby generating flashed black liquor and flash vapor, d) directing the flash vapor to a first heat exchanger and a second heat exchanger, e) transferring heat energy from the flash vapor in the first heat exchanger to white liquor flowing through the first heat exchanger and feeding the heated white liquor from the first heat exchanger to a first white liquor inlet to the vessel, f) transferring the heat energy from the flash vapor in the second heat exchanger to white liquor flowing through the second heat exchanger and feeding the heated white liquor from the second heat exchanger to an upper inlet region of the vessel which is above the first white liquor inlet, and g) the flashed black liquor flows to at least one of a heat recovery or evaporation stage.