PHC bleaching systems are applied:
- For mechanical pulp for magazine grades
- For mechanical pulp for LPB liquid packaging board
- Whenever brighter board or paper contributes to market value
- Whenever dithionite bleaching does not cope with the brightness demand
Requirements for PHC bleaching
Equipment for high consistency
- ANDRITZ Twin Wire Press for highest consistencies, even at low freeness – the dewatering equipment for magazine grades
- ANDRITZ Pulp Screw Press as the most compact machine for high consistencies – the dewatering equipment for board grades
Equipment for excellent mixing
The ANDRITZ HC mixer copes with the challenge of mixing a very small amount of chemicals into a large amount of high-consistency pulp. The HC mixer fluffs the pulp to obtain a large surface area and provides optimum conditions for efficient mixing.
Equipment for even retention time
The ANDRITZ PHC bleach tower delivers uniform brightness because of the accurate and controlled retention time (first in, first out).
Post-bleach washing results in cleaner pulp to the paper machine (reduction of COD, extractives, anionic trash, turbidity) and thus improves the runability of the paper machine, reduces consumption of wet-end chemicals, and increases the intervals for cleaning of felts, wires, and roll covers. Post-bleach washing also provides an opportunity to separate the water loops of the mechanical pulping system and the paper machine. Recovery of residual peroxide and its re-use in pre-bleaching also offer economic benefits.