Effect of hydrocyclone classification on the filtration characteristics of green liquor dregs

M. Golmaei*, T. Kinnarinen, E. Jernström, A. Häkkinen, Lappeenranta University of Technology, Finland

Green liquor dregs have the largest share among the inorganic solid residues of kraft pulp mills. These solid residues are generated in the chemical recovery cycle in the stage where the smelt from the chemical recovery boiler is dissolved in weak white liquor to produce green liquor. Green liquor dregs are separated from the green liquor and disposed of in the landfill after washing and deliquoring. One of the most typically applied separation methods at the green liquor purification stage is cake filtration. The formation of a highly resistant dregs cake in the filter is a major challenge in the industrial scale. As a common technique for improving the filterability of green liquor sludge, a fraction of lime mud generated in the chemical recovery cycle is utilized as a filter aid in precoat filters. However, this technique also increases the amount of contaminated solid residue, which has to be transported to the landfill. In this study, classification with a narrow-angle hydrocyclone was used as a pretreatment method for the pressure filtration of green liquor sludge without lime mud precoat. The hydrocyclone was utilized to split dregs into overflow and underflow fractions according to their size and density. In the hydrocyclone classification stage, the effects of variables such as the overflow/underflow diameter ratio and the feed pressure on the classification of dregs were studied. Then the filtration properties of the obtained overflow and underflow samples were compared with the original green liquor sludge by using a laboratory-scale pressure filter. The results show that...

Session: L14 - Slurry Pretreatment by Shearing, Classification, pH-shift
Day: 15 March 2018
Time: 13:00 - 14:15 h

Learn more at FILTECH 2018 - Register Now!