Method for concentrating black liquor with oxidizing followed by CO2 addition

摘要

A method and apparatus are disclosed for concentrating an alkaline waste liquor containing sulfur compounds, the so-called black liquor, which is discharged from a step of Kraft-cooking wood fibers, in order to recover the cooking chemicals from said waste liquor, characterized in that CO2 gas and/or a gas containing CO2 gas is added to said waste liquor as a boiling-point-lowering agent, viscosity-lowering agent and solidification promoter, after a step of oxidizing said waste liquor and in or prior to one or more stages during the step of concentrating said waste liquor. Also disclosed is an apparatus for concentrating an alkaline waste liquor containing substantially no sulfur compounds (i.e., an AP black liquor), comprising (1) a primary concentrator for concentrating the AP black liquor discharged from said cooking means and washing means, (2) a secondary concentrator for further concentrating the AP black liquor concentrated in said primary concentrator and (3) exhaust gas absorbing means disposed between said primary and secondary concentrators.