EFFECT OF ENTRAINED BLACK LIQUOR CARRY-OVER ON MEDIUM-CONSISTENCY OXYGEN DELIGNIFICATION

How is a medium-consistency oxygen reactor affected by total dissolved solids carry-over? The effects were studied in an attempt to find the best way to remove lignin using oxygen delignification with pulp washing. Using two computer models, the authors predicted the amounts of solids carry-over. These solids were broken down into proportions of raw black liquor solids (dissolved solids carried forward from the digester) and oxidized solids (the dissolved solids discharged from the reactor and washed back through the system). The amount and type of dissolved solids carried over to the medium-consistency reactor affect the extent of delignification. Specific findings are given as to the amount of dissolved solids (in kilograms), dilution factors, pH, viscosity, sodium hydroxide levels, and reductions in kappa number. In a closed oxygen delignification system, the effect of adding more sodium hydroxide is to negate the higher dissolved solids carry-over to the reactor. The authors recommend a configuration consisting of three stages of preoxygen washing and two stages of postoxygen washing.