AN IMPROVED METHOD FOR WASHING LIGNIN PRECIPITATED FROM KRAFT BLACK LIQUOR - THE KEY TO A NEW BIOFUEL

摘要

In a previous study on the washing of lignin precipitated from kraft black liquor,problems with complete or partial plugging of the filter cake and/or filter media were encountered that resulted in uneven washing and high sodium contents in the final lignin product.This effect was ascribed to large gradients in pH and ionic strength during the washing process.Based on this understanding of the phenomenon involved,an improved method for lignin washing was developed,which gave very successful results in laboratory scale trials.In the continuing studies on lignin separation from black liquor within the FRAM (Future Resource Adapted pulp Mill) research programme,this method was evaluated in bench scale and small pilot scale trials.These trials were equally successful and it was shown that kraft lignin with low sodium content (<0.5% by weight),high dry solids content (62.5% on average) and high calorific value (LHV 25.4 MJ/kg) could be produced.There were no particular problems encountered in scaling up the new method from laboratory scale (filter area 20 cm2) to the small pilot scale (filter area 1.7 m2).The investigated separation properties concerning filtration and washing were found to be similar for bench scale and pilot scale experiments.