The impact of lignin removal on the dimensioning of eucalyptus pulp mills

Lignin removal decreases the quantity of organics in pulp mill black liquor, while the inorganics remain essentially unchanged. Balances have been performed to show how lignin removal affects the sizing of different pulp mill departments and the operation of equipment. A modern South American eucalyptus pulp mill served as the base case model. This work shows that the energy balance and the recovery boiler operation are important factors that limit the removal rate of lignin. At 30% lignin removal, steam generation from the recovery boiler decreases 22%, the black liquor heating value decreases about 9% and the required recovery boiler capacity (in terms of dry solids flow, tDS/d) decreases by about 10%. A key calculation result shows that if the heat load into the recovery furnace is fixed, an increase of 23% in pulp production can be achieved if 30% of lignin is removed. The simulation results show that removing lignin should be considered as one alternative for new pulp mill projects.