Drainage varying

1. Need to maintain uniform stock temperature.
— increasing temperature of stock improves drainage.
— higher stock temperatures can adversely affect other properties.
2. Check system for surfactants and foaming. (See Foam control.)
— surfactants can improve water removal rate but excess will create its own stable foam.
— entrained air greatly reduces drainage rate.
— adjust surfactant or defoamer level.
3. Ash or filler content is varying. (See Filler content varying.)
— fillers do not attract water and sometimes may improve drainage rate.
— fillers lodge in pores of mat and thus can inhibit drainage.
— need to maintain uniform ash and first-pass retention.
4. Stock characteristics may be varying. (See Consistency varying.)
— freer stock drains more rapidly.
— adjust refining to maximize drainage rate if tests permit.
5. Surface charges in system varying.
— ionic environment influences retention of most chemicals in system.
— surface charges affect flocculation.
6. Flocculation effects:
— flocculating aids act to reduce effective hydration of the fibers thus improving drainage rate.
— flocculants act as drainage aids and most drainage aids act as flocculants.
7. Fines content varies: (See Retention.)
— higher fines levels (indicated by lower CSF) will retard water removal.
— good first-pass retention of fines is critical to uniform operation and efficient material (chemical additive) usage.