| 摘要 |
A medium consistency mechanical pulp (e.g. RMP, CMP, TMP, CTMP or stone groundwood) is treated to effect efficient reductive bleaching. The pulp, at about 8-15% consistency is simultaneously pumped and degassed utilizing a fluidizing pump (13), and by controlling the pump head to maximize deaeration. The pulp may be immediately passed -- without air introduction -- to a fluidizing mixer (28), where it is mixed with hydrosulfite (dithionite) bleaching chemical. Alternatively, the hydrosulfite may be added directly to the discharge (25) or suction (14) of the pump, and the mixer eliminated. After chemical addition, the pulp is retained at predetermined pH and temperature conditions for a predetermined period of time to effect the desired bleaching, as in an upflow tower (31). |
