The Sequential Liquid-Lignin Recovery and Purification process: Analysis of integration aspects for a kraft pulp mill

At present, acid precipitation is the most developed and implemented kraft lignin removal process. This study investigates the possibility of the implementation of a novel, partly-pressurized, lignin precipitation process called Sequential Liquid Lignin Recovery and Purification (SLRP) in a Swedish kraft pulp mill. The process simulation tool WinGEMS has been used to analyze such an implementation. It is found that the effects of the lignin process integration are predominant on three process areas, the evaporation plant, the recovery boiler and the causticization. The consumption of sodium-makeup chemicals, steam requirement for the evaporation plant, and steam generation in the recovery boiler are the key performance indicators examined. In order to maintain constant composition of the white liquor, sodium carbonate needs to be added as sodium makeup. Comparison with similar processes seems to indicate that the SLRP-process has certain advantages with regard to the energy balance of the pulp mill. The steam consumption in the evaporation plant stays constant (or is slightly reduced), despite the integration of the SLRP-process during lignin removal, while alternative processes consume more steam.