The excess black liquor is concentrated in a multiple effect evaporator to 60% or even 80% solids ("heavy black liquor") and burned in the recovery boiler to recover the inorganic chemicals for reuse in the pulping process.
The excess black liquor is concentrated in a multiple effect evaporator to 60% or even 80% solids ("heavy black liquor"). The excess black liquor is burned in the recovery boiler. This was to recover the inorganic chemicals for reuse in the pulping process.