| 摘要 |
Cellulose (paper) pulp is bleached by first washing it in a first washing stage using a first wash liquid, passing the pulp from the first washing stage to a peroxide bleaching stage (either unpressurized or at superatmospheric pressure), after the peroxide bleaching stage washing the cellulose pulp in a second washing stage using a second wash liquid and producing a filtrate, and then treating the filtrate and bringing the filtrate to the first washing stage to be used as the wash liquid in it. The filtrate is treated by bringing it into intimate contact with an oxidizing gas to oxidize contaminants in it. The method typically includes an ozone bleaching stage either before or after the peroxide stage, in which ozone containing gas is used to bleach the pulp and produces an off gas containing residual amounts of ozone (typically in an oxygen carrier gas). This off gas with residual ozone (which may be supplemented by ozone from a low cost ozone generator) is preferably used as the oxidizing gas for the filtrate, and can be used to remove odors from other pulp mill fluid streams. The filtrate may be treated in a vertical tank having a gas sparger at the bottom in which case the oxidizing gas is introduced into the vertical tank through the gas sparger, and the tank is maintained at either atmospheric or superatmospheric pressure. Alternatively a gas scrubber, or other conventional gas-liquid contactor, can be used to treat the filtrate. |
