Process and device for evaporating liquids, for example black liquor from cellulose cooking, which contain solid and dissolved substances
AssigneeKvaerner Pulping AB
InventorsIsmo Hirvonen, Randy Stern
Life of this patent
Estimating the term…
Abstract
The present invention relates to a process and a device for evaporating liquids, for example black liquor from cellulose cooking, which contain solid and dissolved substances which are to be concentrated, with liquid being heated to close to boiling temperature in a heat exchanger (1) of the falling-film type. The process is characterized in that the pressure on the liquid side in the falling-film heat exchanger (1) is kept so high that boiling does not take place in this heat exchanger and in that the evaporation takes place, by means of flashing, in a separate expansion tank (7) having a lower steam
Claims11
Process for evaporating liquids, for example black liquor from cellulose cooking, which contain solid and dissolved substances which are to be concentrated, with the liquid being heated in an indirect heat exchanger of the falling-film type having a heating side and a liquid side, where the heating side is entirely filled with a heating medium, preferably aqueous steam, and where the liquid on the liquid side is distributed over heating surfaces, which are heated by the heating medium, in the form of a thin film which occupies less than 40% of the volume on the liquid side, preferably less than 20% of the volume, and where the liquid side is otherwise filled with liquid vapour, characterized in that the pressure on the liquid vapour on the liquid side during established operation is maintained so high that boiling does not take place in the liquid on the liquid side and in that the evaporation of the liquid takes place by the pressure on the liquid being lowered in a separate expansion tank having a lower pressure.
Device for evaporating liquids, for example black liquor from cellulose cooking, which contain solid and dissolved substances which are to be concentrated, comprising
- an indirect heat exchanger (1) having a heating side and a liquid side,
- where the heating side is provided with an inlet (5) and an outlet (24) for heating medium (HS, CS),
- where the liquid side is provided with an element (21), which is placed at a high level on the liquid side, for distributing the liquid, which distributing element is arranged to form a falling film (LF) of liquid over heating surfaces (22) which are heated by the heating medium (HS, CS),
- such that the film (LF) which is formed occupies less than 40% of the volume on the liquid side, preferably less than 20% of the volume,
- and where the liquid side is provided with an outlet (6), which is placed at a low level, and means (10;
- 42) for keeping this outlet (6) filled with liquid,
- and where the liquid side is otherwise filled with liquid vapour,
- characterized in that means (10;
- 42;
- 30, 30a) are arranged for pressurizing the liquid vapour on the liquid side, during established operation, to a pressure which exceeds the saturation pressure for the liquid on the liquid side, with boiling of the liquid being suppressed, and in that a decompression tank (7) is connected to the outlet (6) for boiling, and thereby evaporating, the liquid by means of decompression via a throttle (10).
Dependencies are inferred from the claim text.