Patent ID: 6887345

Claim:
A process for evaporating a liquid from cellulose cooking, comprising: heating the liquid in an indirect falling-film heat exchanger, the heat exchanger having a heating side and a liquid side, the heating side being entirely filled with a heating medium; distributing the liquid on the liquid side over heating surfaces that are being heated by the heating medium; the liquid disposed on the heating surfaces forming a thin film over the heating surfaces, the thin film of liquid occupying less than 40% of a volume on the liquid side, filling a remainder of the volume on the liquid side with a vapor; maintaining the vapor with a first pressure that is sufficiently high to prevent boiling of the liquid on the liquid side; transferring the pressurized liquid to a separate expansion tank; providing the expansion tank with a second pressure that is lower than the first pressure; and permitting the liquid disposed in the expansion tank to evaporate.