Reference Manual

11−4
Figure 11-2. Falling Film Concentrator
E0895
Foul condensates are formed in both the
evaporators and digesters. The primary reason for
stripping foul condensate is pollution control. A
common method of treatment involves feeding the
condensate to a stripping column or tower, which
is supplied with fresh steam. The steam tends to
remove most of the contaminants and leaves
clean condensate suitable for pulp washing. The
contaminants are usually carried in a gaseous
form to an incinerator.
Concentrators
Concentrators are an extension of the evaporation
of water from black liquor. As mentioned earlier,
evaporators are typically limited to 50 - 60% solids
concentration due to scale build-up of sodium salts
on heating surfaces. Concentrators accept the 50
- 60% solids from the evaporators and further
concentrate it to 65 - 80% solids. A typical falling
film concentrator is shown on figure 11-2.
D Direct Contact Concentrators
The first type of concentrator used in the pulp and
paper industry was a direct heated type. Even
though it served the same basic purpose as