The virgin pulp generally is colored, the color of pulp is mostly produced from the residual lignin, pigment of paper pulp. Pulp bleaching process is used to improve the whiteness, physical and chemical properties of pulp, purify pulp and increase the cleanness of pulp.
In general, the bleaching process uses the certain content of bleached agent to remove the lignin, and change the colored matte into colorless state. There are two main bleaching processes like reductive bleaching and oxidation bleaching.
The pulp bleaching equipment includes screw conveyor, vacuum drum washer, double roll mixer, pulp chloridizator, bleaching tower, and etc. Bleaching equipment has different classifications, by the bleaching agent and bleaching process, bleaching process includes single stage bleaching, two stages bleaching, and multiple-stages bleaching; by the operation, bleaching equipment includes batching bleaching equipment and continuous bleaching equipment.
To improve the whiteness of pulp, there are some requirements of pulp bleaching equipment as follows:
- Mix the chemicals and pulp evenly.
- Enough capacity and conditions to fully complete the chemical reaction in a short period.
- Clean the paper pulp after pulp bleaching.
- Resist the corrosion from chemicals.
