Pulp and Paper
Black liquor evaporation and chemical recovery
In a pulp mill, black liquor, a by-product of the raw material digesting process, contains inorganic spent cooking materials which are typically recovered by evaporation and incineration. Concentration of black liquor is typically achieved by the use of multi-effect evaporators (either rising or falling film type).
This is possible by condensing water vapor generated in one effect, in the shell side of the following effect’s heating element. Saturated steam at 20 to 100 psig in the first effect heating element’s shell side boils liquor in the tube side. This boiling liquor/vapor enters the vapor head where vapor is separated and channeled to the shell side of the second effect heating element.
ENSEPATEC provides vane type separators retaining black liquor droplets within the evaporator and allowing only the dry steam to pass to the subsequent effect. The vane type separator avoids an inefficient heat transfer caused by the carry-over of black liquor into the subsequent effect.
Typical applications for liquid/gas separators in a pulp plant are
- Retention of black liquor in black liquor evaporators and concentrators
- Removal of condensed liquids in offgas systems
